publicationDate,title,abstract,id
2021-12-15,Effect of magnetocrystalline anisotropy on magnetocaloric properties of AlFe$_{2}$B$_{2}$ compound,"It is well known that the temperature dependence of the effective
magnetocrystalline anisotropy energy obeys the $l(l+1)/2$ power law of
magnetization in the Callen-Callen theory. Therefore, according to the
Callen-Callen theory, the magnetocrystalline anisotropy energy is assumed to be
zero at the critical temperature where the magnetization is approximately zero.
This study estimates the temperature dependence of the magnetocrystalline
anisotropy energy by integrating the magnetization versus magnetic field
($M$--$H$) curves, and found that the magnetocrystalline anisotropy is still
finite even above the Curie temperature in the uniaxial anisotropy, whereas
this does not appear in the cubic anisotropy case. The origin is the fast
reduction of the anisotropy field, which is the magnetic field required to
saturate the magnetization along the hard axis, in the case of cubic
anisotropy. Therefore, the magnetization anisotropy and anisotropic magnetic
susceptibility, those are the key factors of magnetic anisotropy, could not be
established in the case of cubic anisotropy. In addition, the effect of
magnetocrystalline anisotropy on magnetocaloric properties, as the difference
between the entropy change curves of AlFe$_{2}$B$_{2}$ appears above the Curie
temperature, which is in good agreement with a previous experimental study.
This is proof of magnetic anisotropy at slightly above Curie temperature.",2112.08154v1
2013-07-23,Mechanism of uniaxial magnetocrystalline anisotropy in transition metal alloys,"Magnetocrystalline anisotropy in transition metal alloys (FePt, CoPt, FePd,
MnAl, MnGa, and FeCo) was studied using first-principles calculations to
elucidate its specific mechanism. The tight-binding linear muffin-tin orbital
method in the local spin-density approximation was employed to calculate the
electronic structure of each compound, and the anisotropy energy was evaluated
using the magnetic force theorem and the second-order perturbation theory in
terms of spin-orbit interactions. We systematically describe the mechanism of
uniaxial magnetocrystalline anisotropy in real materials and present the
conditions under which the anisotropy energy can be increased. The large
magnetocrystalline anisotropy energy in FePt and CoPt arises from the strong
spin-orbit interaction of Pt. In contrast, even though the spin-orbit
interaction in MnAl, MnGa, and FeCo is weak, the anisotropy energies of these
compounds are comparable to that of FePd. We found that MnAl, MnGa, and FeCo
have an electronic structure that is efficient in inducing the
magnetocrystalline anisotropy in terms of the selection rule of spin-orbit
interaction.",1307.5961v2
2016-03-16,Illustrative view on the magnetocrystalline anisotropy of adatoms and monolayers,"Even though it has been known for decades that the magnetocrystalline
anisotropy is linked to the spin-orbit coupling (SOC), the mechanism how it
arises for specific systems is still subject of debate. We focused on finding
markers of SOC in the density of states (DOS) and on employing them for
understanding the source of magnetocrystalline anisotropy for the case of
adatoms and monolayers. Fully relativistic ab-initio KKR-Green function
calculations were performed for Fe, Co, and Ni adatoms and monolayers on
Au(111) to investigate changes in the orbital-resolved DOS due to a rotation of
magnetization. In this way one can see that a significant contribution to the
magnetocrystalline anisotropy for adatoms comes from pushing of the SOC-split
states above or below the Fermi level. As a result of this, the
magnetocrystalline anisotropy energy crucially depends on the position of the
energy bands of the adatom with respect to the Fermi level of the substrate.
This view is supported by model crystal field Hamiltonian calculations.",1603.05053v2
2018-09-29,Micromagnetic Simulations Study of Skyrmions in Magnetic FePt Nanoelements,"The magnetization reversal in 330 nm triangular prismatic magnetic
nanoelements with variable magnetocrystalline anisotropy similar to that of
partially chemically ordered FePt is studied using micromagnetic simulations
employing Finite Element discretizations. Several magnetic properties including
the evaluation of the magnetic skyrmion number $S$ are computed in order to
characterize magnetic configurations exhibiting vortex-like formations.
Magnetic vortices and skyrmions are revealed in different systems generated by
the variation of the magnitude and relative orientation of the
magnetocrystalline anisotropy direction, with respect to the normal to the
triangular prism base. Micromagnetic configurations with skyrmion number
greater than one have been detected for the case where magnetocrystalline
anisotropy was normal to nanoelement's base. For particular magnetocrystalline
anisotropy values three distinct skyrmions are formed and persist for a range
of external fields. The simulation-based calculations of the skyrmion number S
revealed that skyrmions can be created for magnetic nanoparticle systems
lacking of chiral interactions such as Dzyaloshinsky-Moriya, but by only
varying the magnetocrystalline anisotropy.",1810.00253v1
2024-02-26,Efficient calculation of magnetocrystalline anisotropy energy using symmetry-adapted Wannier functions,"Magnetocrystalline anisotropy, a crucial factor in magnetic properties and
applications like magnetoresistive random-access memory, often requires
extensive $k$-point mesh in first-principles calculations. In this study, we
develop a Wannier orbital tight-binding model incorporating crystal and spin
symmetries and utilize time-reversal symmetry to divide magnetization
components. This model enables efficient computation of magnetocrystalline
anisotropy. Applying this method to $\mathrm{L1_0}$ $\mathrm{FePt}$ and
$\mathrm{FeNi}$, we calculate the dependence of the anisotropic energy on
$k$-point mesh size, chemical potential, spin-orbit interaction, and
magnetization direction. The results validate the practicality of the models to
the energy order of $10~[\mathrm{\mu eV}/f.u.]$.",2402.16331v1
2017-08-04,Tunable dimensional crossover and magnetocrystalline anisotropy in Fe$_2$P-based alloys,"Electronic structure calculations are used to examine the magnetic properties
of Fe$_2$P-based alloys and the mechanisms through which the Curie temperature
and magnetocrystalline anisotropy can be optimized for specific applications.
It is found that at elevated temperatures the magnetic interaction in pure
Fe$_2$P develops a pronounced two-dimensional character due to the suppression
of the magnetization in one of the sublattices, but the interlayer coupling is
very sensitive to band filling and structural distortions. This feature
suggests a natural explanation of the observed sharp enhancement of the Curie
temperature by alloying with multiple elements, such as Co, Ni, Si, and B. The
magnetocrystalline anisotropy is also tunable by electron doping, reaching a
maximum near the electron count of pure Fe$_2$P. These findings enable the
optimization of the alloy content, suggesting co-alloying of Fe$_2$P with Co
(or Ni) and Si as a strategy for maximizing the magnetocrystalline anisotropy
at and above room temperature.",1708.01683v2
2020-06-07,Magnetocrystalline anisotropy of the easy-plane metallic antiferromagnet Fe$_2$As,"Magnetocrystalline anisotropy is a fundamental property of magnetic materials
that determines the dynamics of magnetic precession, the frequency of spin
waves, the thermal stability of magnetic domains, and the efficiency of
spintronic devices. We combine torque magnetometry and density functional
theory calculations to determine the magnetocrystalline anisotropy of the
metallic antiferromagnet Fe$_2$As. Fe$_2$As has a tetragonal crystal structure
with the N\'eel vector lying in the (001) plane. We report that the four-fold
magnetocrystalline anisotropy in the (001)-plane of Fe$_2$As is extremely
small, ${K_{22}} = - 150~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$ at T = 4 K, much
smaller than perpendicular magnetic anisotropy of ferromagnetic structure
widely used in spintronics device. ${K_{22}}$ is strongly temperature dependent
and close to zero at T > 150 K. The anisotropy ${K_1}$ in the (010) plane is
too large to be measured by torque magnetometry and we determine ${K_1} =
-830~{\rm{ kJ/}}{{\rm{m}}^{\rm{3}}}$ using first-principles density functional
theory. Our simulations show that the contribution to the anisotropy from
classical magnetic dipole-dipole interactions is comparable to the contribution
from spin-orbit coupling. The calculated four-fold anisotropy in the (001)
plane ${K_{22}}$ ranges from $- 292~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$ to
$280~{\rm{ J/}}{{\rm{m}}^{\rm{3}}}$, the same order of magnitude as the
measured value. We use ${K_1}$ from theory to predict the frequency and
polarization of the lowest frequency antiferromagnetic resonance mode and find
that the mode is linearly polarized in the (001)-plane with $f = $ 670 GHz.",2006.04192v1
1995-02-27,Magnetocrystalline Anisotropy Energy of a Transition Metal Monolayer: A Non-perturbative Theory,"The magnetocrystalline anisotropy energy $E_{anis}$ for a monolayer of Fe and
Ni is determined using a fully convergent tight-binding calculation including
$s$-$d$ hybridization. The spin-orbit interaction $\lambda_{so}$ is treated
non-perturbatively. Remarkably, we find $E_{anis}\propto\lambda_{so}^2$ and
important contributions to $E_{anis}$ due to the lifting of degeneracies near
the Fermi-level. This is supported by the calculated decrease of the anisotropy
energy with increasing temperature on a scale of several hundred K. Our results
clarify the present debate on the origin of $E_{anis}$.",9502112v1
2013-11-01,Strain-Tunable Magnetocrystalline Anisotropy in Epitaxial Y3Fe5O12 Thin Films,"We demonstrate strain-tuning of magnetocrystalline anisotropy over a range of
more than one thousand Gauss in epitaxial Y3Fe5O12 films of excellent
crystalline quality grown on lattice-mismatched Y3Al5O12 substrates.
Ferromagnetic resonance (FMR) measurements reveal a linear dependence of both
out-of-plane and in-plane uniaxial anisotropy on the strain-induced tetragonal
distortion of Y3Fe5O12. Importantly, we find the spin mixing conductance G_r
determined from inverse spin Hall effect and FMR linewidth broadening remains
large: G_r = 3.33 x 10^14 Ohm^-1m^-2 in Pt/Y3Fe5O12/Y3Al5O12 heterostructures,
quite comparable to the value found in Pt/Y3Fe5O12 grown on lattice-matched
Gd3Ga5O12 substrates.",1311.0238v1
2016-02-05,Skyrmions in thin films with easy-plane magnetocrystalline anisotropy,"We demonstrate that chiral skyrmionic magnetization configurations can be
found as the minimum energy state in B20 thin film materials with easy-plane
magnetocrystalline anisotropy with an applied magnetic field perpendicular to
the film plane. Our observations contradict results from prior analytical work,
but are compatible with recent experimental investigations. The size of the
observed skyrmions increases with the easy-plane magnetocrystalline anisotropy.
We use a full micromagnetic model including demagnetization and a
three-dimensional geometry to find local energy minimum (metastable)
magnetization configurations using numerical damped time integration. We
explore the phase space of the system and start simulations from a variety of
initial magnetization configurations to present a systematic overview of
anisotropy and magnetic field parameters for which skyrmions are metastable and
global energy minimum (stable) states.",1602.02064v2
2003-10-10,Magnetocrystalline anisotropy and orbital polarization in ferromagnetic transition metals,"The magnetocrystalline anisotropy energies (MAEs) of the ferromagnetic metals
bcc Fe, fcc and hcp Co, and fcc Ni have been calculated by using the {\it ab
initio} tight-binding method. Disentangling the strong correlation among the
$d$ orbitals with the Hamiltonian in the local spin-density approximation, we
have investigated the orbital polarizations induced by the Hubbard $U$ and
Racah $B$. The experimental MAE of fcc Ni is found with the value of $U$ close
to that determined from experiments and used in other theories. With the
optimized values of $U$ and $J$, both the MAEs and the orbital moments for Fe
and Co are in close agreement with experiment.",0310249v1
2005-08-31,Uniaxial magnetocrystalline anisotropy in ${\rm CaRuO_3}$,"${\rm CaRuO_3}$ is a paramagnetic metal and since its low temperature
resistivity is described by $\rho=\rho_0+AT^\gamma $ with $\gamma \sim 1.5$, it
is also considered a non-Fermi liquid (NFL) metal. We have performed extensive
magnetoresistance and Hall effect measurements of untwinned epitaxial films of
${\rm CaRuO_3}$. These measurements reveal that ${\rm CaRuO_3}$ exhibits
uniaxial magnetocrystalline anisotropy. In addition, the low-temperature NFL
behavior is most effectively suppressed when a magnetic field is applied along
the easy axis, suggesting that critical spin fluctuations, possibly due to
proximity of a quantum critical phase transition, are related to the NFL
behavior.",0508038v1
2011-09-30,An ultrafast image recovery and recognition system implemented with nanomagnets possessing biaxial magnetocrystalline anisotropy,"A circular magnetic disk with biaxial magnetocrystalline anisotropy has four
stable magnetization states which can be used to encode a pixel's shade in a
black/gray/white image. By solving the Landau-Lifshitz- Gilbert equation, we
show that if moderate noise deflects the magnetization slightly from a stable
state, it always returns to the original state, thereby automatically
de-noising the corrupted image. The same system can compare a noisy input image
with a stored image and make a matching decision using magneto-tunneling
junctions. These tasks are executed at ultrahigh speeds (~2 ns for a
512\times512 pixel image).",1109.6932v1
2012-10-16,Degree of order dependence on magnetocrystalline anisotropy in bct FeCo alloys,"We investigate the magnetocrystalline anisotropy (MCA) energy of tetragonal
distorted FeCo alloys depending on the degree of order by first-principles
electronic structure calculation combined with the coherent potential
approximation. The obtained results indicate that the MCA energy of FeCo alloys
strongly depends on the degree of order under optimal conditions, where the
axial ratio of the bct structure is 1.25 and the composition is Fe0.5Co0.5. We
find that the modification of the electronic structure resulting from electron
scattering by chemical disorder has a considerable influence on the MCA under
these conditions.",1210.4386v1
2016-02-26,Tuning the magnetocrystalline anisotropy in $R$CoPO by means of $R$ substitution: a ferromagnetic resonance study,"We report on broad-band electron spin resonance measurements performed within
the itinerant ferromagnetic phase of $R$CoPO ($R$ = La, Pr, Nd and Sm). We
reveal that the $R$ substitution is highly effective in gradually introducing a
sizeable easy-plane magnetocrystalline anisotropy within the Co sublattice. We
explain our results in terms of a subtle interplay of structural effects and of
indirect interactions between the $f$ and $d$ orbitals from $R$ and Co,
respectively.",1602.08377v1
2016-12-27,Giant atomic magnetocrystalline anisotropy from degenerate orbitals around Fermi level,"Nano-structures with giant magnetocrystalline anisotropy energies (MAE) are
desired in designing miniaturized magnetic storage and quantum computing
devices. Through ab initio and model calculations, we propose that special
p-element dimers and single-adatom on symmetry-matched substrates possess giant
atomic MAE of 72-200 meV with room temperature structural stability. The huge
MAE originates from degenerate orbitals around Fermi level. More importantly,
we developed a simplified quantum mechanical model to understand the principle
on how to obtain giant MAE for supported magnetic structures. These discoveries
and mechanisms provide a paradigm to design giant atomic MAE in nanostructures.",1612.08679v1
2022-01-27,Temperature Dependence of Magnetocrystalline Anisotropy in Itinerant Ferromagnets,"We theoretically investigated magnetocrystalline anisotropy (MA) at a finite
temperature $T$ in ferromagnetic metals. Assuming a Rashba-type ferromagnet
with uniaxial MA, we defined the MA constants $K_\mathrm{u}(T)$ derived from
several different concepts. Our purpose was to examine the equality between
them and to confirm a power law between $K_\mathrm{u}(T)$ and magnetization
$M(T)$ in the form of $K_\mathrm{u}(T)/K_\mathrm{u}(0)=[M(T)/M(0)]^\alpha$. We
demonstrate that $\alpha$ equals 2 in the itinerant-electron limit and
increases with the localized feature of electrons passing through $\alpha=3$,
predicted for the single-ion MA in spin models.",2201.11269v1
2000-01-19,Fermi surface origin of the interrelationship between magnetocrystalline anisotropy and compositional order in transitional metal alloys,"Recently, we outlined a scheme to investigate the effects of compositional
order on the magnetocrystalline anisotropy of alloys from a first-principles
electronic structure point of view \{Phys. Rev. Lett. {\bf 83}, 5369 (1999)\}
and showed that compositional order enhances the magnitude of
magnetocrystalline anisotropy energy (MAE) of Co$_{0.5}$Pt$_{0.5}$ alloy by
some two orders of magnitude as well as affecting the equilibrium magnetization
direction. Here we describe our scheme in detail and present an in-depth study
of the effect by demonstrating its Fermi surface origin. In
Co$_{0.25}$Pt$_{0.75}$ alloy we find that the perfect $ L1_2 $ structure has a
very small MAE whereas imposition of directional order enhances the MAE by two
orders of magnitude. We also present the effect of lattice distortion
(tetragonalization) on the MAE on the same footing and find that in the
Co$_{0.5}$Pt$_{0.5}$ alloy it accounts for only about 20% of the observed MAE,
thus confirming that compositional order is the major player in the enhancement
of MAE. We also examine the directional chemical order that can be produced by
magnetic annealing within the same framework. We extract a Fermi surface
mechanism for the effect in an explicit study of permalloy. Finally, we propose
that the Fermi surface plays a major role in the strong coupling between
magnetocrystalline anisotropy and compositional order in many magnetic alloys.",0001271v1
2005-04-20,Aligning spins in antiferromagnetic films using antiferromagnets,"We have explored the possibility to orient spins in antiferromagnetic thin
films with low magnetocrystalline anisotropy via the exchange coupling to
adjacent antiferromagnetic films with high magnetocrystalline anisotropy. We
have used MnO as a prototype for a system with negligible single-ion
anisotropy. We were able to control its spin direction very effectively by
growing it as a film on antiferromagnetic CoO films with different
predetermined spin orientations. This result may pave the way for tailoring
antiferromagnets with low magnetocrystalline anistropy for applications in
exchange bias systems. Very detailed information concerning the exchange
coupling and strain effects was obtained from the Mn $L_{2,3}$ soft x-ray
absorption spectroscopy.",0504520v2
2010-03-30,Electric Field Effect on Magnetization and Magnetocrystalline Anisotropy at the Fe/MgO(001) Interface,"Density-functional calculations are performed to explore magnetoelectric
effects originating from the influence of an external electric field on
magnetic properties of the Fe/MgO(001) interface. It is shown that the effect
on the interface magnetization and magnetocrystalline anisotropy can be
substantially enhanced if the electric field is applied across a dielectric
material with a large dielectric constant. In particular, we predict an
enhancement of the interface magnetoelectric susceptibility by a factor of the
dielectric constant of MgO over that of the free standing Fe (001) surface. We
also predict a significant effect of electric field on the interface
magnetocrystalline anisotropy due to the change in the relative occupancy of
the 3d-orbitals of Fe atoms at the Fe/MgO interface. These results may be
interesting for technological applications such as electrically controlled
magnetic data storage.",1003.5870v1
2014-09-17,Increased magnetocrystalline anisotropy in epitaxial Fe-Co-C thin films with spontaneous strain,"Rare earth free alloys are in focus of permanent magnet research since the
accessibility of the elements needed for nowadays conventional magnets is
limited. Tetragonally strained iron-cobalt (Fe-Co) has attracted large interest
as promising candidate due to theoretical calculations. In experiments,
however, the applied strain quickly relaxes with increasing film thickness and
hampers stabilization of a strong magnetocrystalline anisotropy. In our study
we show that already 2 at% of carbon substantially reduce the lattice
relaxation leading to the formation of a spontaneously strained phase with 3 %
tetragonal distortion. In these strained
(Fe$_{0.4}$Co$_{0.6}$)$_{0.98}$C$_{0.02}$ films, a magnetocrystalline
anisotropy above 0.4 MJ/m$^3$ is observed while the large polarization of 2.1 T
is maintained. Compared to binary Fe-Co this is a remarkable improvement of the
intrinsic magnetic properties. In this paper, we relate our experimental work
to theoretical studies of strained Fe-Co-C and find a very good agreement.",1409.4952v1
2017-06-12,Voltage-Controllable Colossal Magnetocrystalline Anisotropy in Single Layer Transition Metal Dichalcogenides,"Materials with large magnetocrystalline anisotropy and strong electric field
effects are highly needed to develop new types of memory devices based on
electric field control of spin orientations. Instead of using modified
transition metal films, we propose that certain monolayer transition metal
dichalcogenides are the ideal candidate materials for this purpose. Using
density functional calculations, we show that they exhibit not only a large
magnetocrystalline anisotropy (MCA), but also colossal voltage modulation under
external field. Notably, in some materials like CrSe_2 and FeSe_2, where spins
show a strong preference for in-plane orientation, they can be switched to
out-of-plane direction. This effect is attributed to the large band character
alteration that the transition metal d-states undergo around the Fermi energy
due to the electric field. We further demonstrate that strain can also greatly
change MCA, and can help to improve the modulation efficiency while combined
with an electric field.",1706.03521v1
2018-01-20,Magnetic Behaviour of Assemblies of Interacting Cobalt-Carbide Nanoparticles,"Recent work [1] demonstrated high coercivity and magnetic moment in cobalt
carbide nanoparticle assemblies and explained the high coercivity from first
principles in terms of the high magnetocrystalline anisotropy of the cobalt
carbide nanoparticles. In this work, we comprehensively model the interaction
between the nanoparticles comprising the assembly and systematically understand
the effect of particle size, distribution of the orientations of the
nanoparticles' magnetocrystalline anisotropy axis with respect to the applied
magnetic field, and dipole coupling between nanoparticles on the temperature
dependent magnetic behavior of the nanoparticle assembly. We show that
magnetocrystalline anisotropy alone is not enough to explain the large
hysteresis over the 50K-400K temperature range and suggest that defects and
inhomogeneties that pin the magnetization could also play a significant role on
this temperature dependent magnetic behavior.",1801.06672v1
2018-02-22,Power law analysis for temperature dependence of magnetocrystalline anisotropy constants of Nd$_2$Fe$_{14}$B magnets,"Phenomenological analysis for the temperature dependence of the
magnetocrystalline anisotropy (MA) in rare earth magnets is presented. We
define phenomenological power laws applicable to compound magnets using the
Zener theory, apply these laws to the magnetocrystalline anisotropy constants
(MACs) of Nd$_2$Fe$_{14}$B magnets. The results indicate that the MACs obey the
power law well, and a general understanding for the temperature-dependent MA in
rare earth magnets is obtained through the analysis. Furthermore, to examine
the validity of the power law, we discuss the temperature dependence of the
MACs in Dy$_2$Fe$_{14}$B and Y$_2$Fe$_{14}$B magnets as examples wherein it is
difficult to interpret the MA using the power law.",1802.07959v2
2018-03-22,Large Perpendicular Magnetocrystalline Anisotropy at Fe/Pb(001) interface,"Search for ultrathin magnetic film with large perpendicular
magnetocrystalline anisotropy (PMA) has been inspired for years by the
continuous miniaturization of magnetic units in spintronics devices. The common
magnetic materials used in research and applications are based on Fe because
the pure Fe metal is the best yet simple magnetic material from nature. Through
systematic first-principles calculations, we explored the possibility to
produce large PMA with ultrathin Fe on non-noble and non-magnetic Pb(001)
substrate. Interestingly, huge magnetocrystalline anisotropy energy (MAE) of
7.6 meV was found in Pb/Fe/Pb(001) sandwich structure with only half monolayer
Fe. Analysis of electronic structures reveals that the magnetic proximity
effect at the interface is responsible for this significant enhancement of MAE.
The MAE further increases to 13.6 meV with triply repeated capping Pb and
intermediate Fe layers. Furthermore, the MAE can be tuned conveniently by
charge injection.",1803.08219v1
2020-09-01,Lattice dynamics effects on the magnetocrystalline anisotropy energy: application to MnBi,"Using a first-principles fully relativistic scheme based on ultrasoft
pseudopotentials and density functional perturbation theory, we study the
magnetocrystalline anisotropy free energy of the ferromagnetic binary compound
MnBi. We find that differences in the phonon dispersions due to the different
orientations of the magnetization (in-plane and perpendicular to the plane)
give a difference between the vibrational free energies of the high-temperature
and low-temperature phases. This vibrational contribution to the
magnetocrystalline anisotropy energy (MAE) constant, $K_u$, is non-negligible.
When the energy contribution to the MAE is calculated by the PBEsol exchange
and correlation functional, the addition of the phonon contribution allows to
get a $T = 0$ K $K_u$ and a spin-reorientation transition temperature in
reasonable agreement with experiments.",2009.00410v1
2014-04-22,First principles investigation of magnetocrystalline anisotropy at the L2$_1$ Full Heusler|MgO interfaces and tunnel junctions,"Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been
studied using first principles calculations. It is found that Co terminated
Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31
mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic
anisotropy. Atomic layer resolved analysis indicates that the origin of
perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be
attributed to the out-of-plane orbital contributions of interfacial Co atoms.
At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to
favor in-plane magnetic anisotropy for all terminations.",1404.5646v2
2018-05-29,Electronic structure and magnetic anisotropies of antiferromagnetic transition-metal difluorides,"We compare GGA+U calculations with available experimental data and analyze
the origin of magnetic anisotropies in MnF$_2$, FeF$_2$, CoF$_2$, and NiF$_2$.
We confirm that the magnetic anisotropy of MnF$_2$ stems almost completely from
the dipolar interaction, while magnetocrystalline anisotropy energy plays a
dominant role in the other three compounds, and discuss how it depends on the
details of band structure. The latter is critically compared to available
optical measurements. The case of CoF$_2$, where magnetocrystalline anisotropy
energy strongly depends on $U$, is put into contrast with FeF$_2$ where
theoretical predictions of magnetic anisotropies are nearly quantitative.",1805.11339v3
2023-05-18,Giant coercivity induced by perpendicular anisotropy in Mn2.42Fe0.58Sn single crystals,"We report the discovery of a giant out-of-plane coercivity in the Fe-doped
Mn3Sn single crystals. The compound of Mn2.42Fe0.58Sn exhibits a series of
magnetic transitions accompanying with large magnetic anisotropy and electric
transport properties. Compared with the ab-plane easy axis in Mn3Sn, it
switches to the c-axis in Mn2.42Fe0.58Sn, producing a sufficiently large
uniaxial anisotropy. At 2 K, a giant out-of-plane coercivity (Hc) up to 3 T was
observed, which originates from the large uniaxial magnetocrystalline
anisotropy. The modified Sucksmith-Thompson method was used to determine the
values of the second-order and the fourth-order magnetocrystalline anisotropy
constants K1 and K2, resulting in values of 6.0 * 104 J/m3 and 4.1 * 105 J/m3
at 2 K, respectively. Even though the Curie temperature (TC) of 200 K for
Mn2.42Fe0.58Sn is not high enough for direct application, our research presents
a valuable case study of a typical uniaxial anisotropy material.",2305.10876v2
1996-09-03,Magnetocrystalline Anisotropy Energy of Transition Metal Thin Films: A Non-perturbative Theory,"The magnetocrystalline anisotropy energy E(anis) of free-standing monolayers
and thin films of Fe and Ni is determined using two different semi-empirical
schemes. Within a tight-binding calculation for the 3d bands alone, we analyze
in detail the relation between bandstructure and E(anis), treating spin-orbit
coupling non-pertubatively. We find important contributions to E(anis) due to
the lifting of band degeneracies near the Fermi level by SOC. The important
role of degeneracies is supported by the calculation of the electron
temperature dependence of the magnetocrystalline anisotropy energy, which
decreases with the temperature increasing on a scale of several hundred K. In
general, E(anis) scales with the square of the SOC constant. Including 4s bands
and s-d hybridization, the combined interpolation scheme yields anisotropy
energies that quantitatively agree well with experiments for Fe and Ni
monolayers on Cu(001). Finally, the anisotropy energy is calculated for systems
of up to 14 layers. Even after including s-bands and for multilayers, the
importance of degeneracies persists. Considering a fixed fct-Fe structure, we
find a reorientation of the magnetization from perpendicular to in-plane at
about 4 layers. For Ni, we find the correct in-plane easy-axis for the
monolayer. However, since the anisotropy energy remains nearly constant, we do
not find the experimentally observed reorientation.",9609028v1
2020-07-02,Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study,"We study the tunnel magnetoresistance (TMR) effect and magnetocrystalline
anisotropy in a series of magnetic tunnel junctions (MTJs) with $L1_1$-ordered
fcc ferromagnetic alloys and MgO barrier along the [111] direction. Considering
the (111)-oriented MTJs with different $L1_1$ alloys, we calculate their TMR
ratios and magnetocrystalline anisotropies on the basis of the first-principles
calculations. The analysis shows that the MTJs with Co-based alloys (CoNi,
CoPt, and CoPd) have high TMR ratios over 2000$\%$. These MTJs have
energetically favored Co-O interfaces where interfacial antibonding between Co
$d$ and O $p$ states is formed around the Fermi level. We find that the
resonant tunneling of the antibonding states, called the interface resonant
tunneling, is the origin of the obtained high TMR ratios. Our calculation of
the magnetocrystalline anisotropy shows that many $L1_1$ alloys have large
perpendicular magnetic anisotropy (PMA). In particular, CoPt has the largest
value of anisotropy energy $K_{\rm u} \approx 10\,{\rm MJ/m^3}$. We further
conduct a perturbation analysis of the PMA with respect to the spin-orbit
interaction and reveal that the large PMA in CoPt and CoNi mainly originates
from spin-conserving perturbation processes around the Fermi level.",2007.01068v2
2019-04-27,Critical Behavior and Anisotropy in Single Crystal SrRuO$_3$,"The magnetization of single crystal SrRuO3 is studied as a function of
temperature along different crystallographic directions. The magnetocrystalline
anisotropy and behavior near the critical transition temperature are analyzed
in detail. The magnetization vs temperature is found to vary more like $T^2$
rather than $T^{3/2}$ expected for spin waves.",1904.12193v1
2019-06-21,Strain and thickness effects on magnetocrystalline anisotropy of CoFe(011) films,"We investigate MCA of CoFe(011) thin films as a function of strength of
strain and film thickness has been studied. It is elucidated that perpendicular
magnetocystalline anisotropy (MCA) energy (EMCA) is getting stronger with
compressed xy-plane lattice constant while in-plane MCA is become an easy-axis
by tensile strain on xy-plane. The reason of the EMCA behaviors can be
explained by features of electronic structures.",1906.09153v1
2009-11-15,Field induced resistivity anisotropy in SrRuO3 films,"SrRuO3 is an itinerant ferromagnet with orthorhombic structure and uniaxial
magnetocrystalline anisotropy - features expected to yield resistivity
anisotropy. Here we explore changes in the resistivity anisotropy of epitaxial
SrRuO3 films due to induced magnetization in the paramagnetic state by using
the planar Hall effect. We find that the effect of the induced magnetization on
the in-plane anisotropy is strongly angular dependent, and we provide a full
description of this behavior at 160 K for induced magnetization in the (001)
plane.",0911.2879v1
2019-01-14,First-principles calculations of the magnetocrystalline anisotropy of the prototype 2:17 cell boundary phase Y(Co$_{1-x-y}$Fe$_x$Cu$_y$)$_5$,"We present a computational study of the compound
Y(Co$_{1-x-y}$Fe$_x$Cu$_y$)$_5$ for 0 $\leq x,y \leq 0.2$. This compound was
chosen as a prototype for investigating the cell boundary phase believed to
play a key role in establishing the high coercivity of commercial Sm-Co 2:17
magnets. Using density-functional theory, we have calculated the magnetization
and magnetocrystalline anisotropy at zero temperature for a range of
compositions, modeling the doped compounds within the coherent potential
approximation. We have also performed finite temperature calculations for
YCo$_5$, Y(Co$_{0.838}$Cu$_{0.162}$)$_5$ and
Y(Co$_{0.838}$Fe$_{0.081}$Cu$_{0.081}$)$_5$ within the disordered local moment
picture. Our calculations find that substituting Co with small amounts of
either Fe or Cu boosts the magnetocrystalline anisotropy $K$, but the change in
$K$ depends strongly on the location of the dopants. Furthermore, the
calculations do not show a particularly large difference between the magnetic
properties of Cu-rich Y(Co$_{0.838}$Cu$_{0.162}$)$_5$ and equal Fe-Cu
Y(Co$_{0.838}$Fe$_{0.081}$Cu$_{0.081}$)$_5$, despite these two compositions
showing different coercivity behavior when found in the cell boundary phase of
2:17 magnets. Our study lays the groundwork for studying the rare earth
contribution to the anisotropy of Sm(Co$_{1-x-y}$Fe$_x$Cu$_y$)$_5$, and also
shows how a small amount of transition metal substitution can boost the
anisotropy field of YCo$_5$.",1901.04185v1
2010-07-16,"Strain control of magnetic anisotropy in (Ga,Mn)As microbars","We present an experimental and theoretical study of magnetocrystalline
anisotropies in arrays of bars patterned lithographically into (Ga,Mn)As
epilayers grown under compressive lattice strain. Structural properties of the
(Ga,Mn)As microbars are investigated by high-resolution X-ray diffraction
measurements. The experimental data, showing strong strain relaxation effects,
are in good agreement with finite element simulations. SQUID magnetization
measurements are performed to study the control of magnetic anisotropy in
(Ga,Mn)As by the lithographically induced strain relaxation of the microbars.
Microscopic theoretical modeling of the anisotropy is performed based on the
mean-field kinetic-exchange model of the ferromagnetic spin-orbit coupled band
structure of (Ga,Mn)As. Based on the overall agreement between experimental
data and theoretical modeling we conclude that the micropatterning induced
anisotropies are of the magnetocrystalline, spin-orbit coupling origin.",1007.2766v1
2022-04-29,"Controlled Curie temperature, magnetocrystalline anisotropy, and valley polarization in 2D ferromagnetic Janus 2H-VSeS monolayer","Inspired by the successful synthesis of two-dimensional (2D) V-based Janus
dichloride monolayers with intrinsic ferromagnetism and high Curie temperature
(T$_{c}$), the electronic structure, spin-valley splitting and magnetic
anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using
first-principles calculations. The results show that the Janus 2H-VSeS
monolayer exhibits a large valley splitting of 105meV, high T$_{c}$ of 278K and
good magnetocrystalline anisotropy (0.31meV) contributed by the in-plane
d$_{x^{2}-y^{2}}$/d$_{xy}$ orbitals of V atoms. The biaxial strain
($-$8%<$\varepsilon$<8%) can effectively tune the magnetic moments of V atom,
valley splitting $\Delta$E, T$_{c}$ and MAE of Janus 2H-VSeS monolayer. The
corresponding $\Delta$E and T$_{c}$ are adjusted from 72meV to 106.8meV and
from 180K to 340K, respectively. The electronic phase transition from bipolar
magnetic semiconductor (BMS) to half-semiconductor (HSC), spin gapless
semiconductor (SGS), and half-metal (HM) is also observed due to the change of
V 3d-orbital occupation. Due to the broken space- and time-reversal symmetry,
the opposite valley charge carriers carry opposite Berry curvature, which leads
to prominent anomalous Hall conductivity at the K and K$^{\prime}$ valleys. The
maximum modulation of Berry curvature can reach to 45% and 9.5% by applying the
biaxial strain and charge carrier doping, respectively. The stable in-plane
magnetocrystalline anisotropy and large spontaneous valley polarization make
the ferromagnetic Janus 2H-VSeS monolayer a promising material for achieving
the spintronics and valleytronics devices.",2205.00106v2
2011-08-30,"Spin-orbit coupling effect in (Ga,Mn)As films: anisotropic exchange interactions and magnetocrystalline anisotropy","The magneto-crystalline anisotropy (MCA) of (Ga,Mn)As films has been studied
on the basis of ab-initio electronic structure theory by performing magnetic
torque calculations. An appreciable contribution to the in-plane uniaxial
anisotropy can be attributed to an extended region adjacent to the surface.
Calculations of the exchange tensor allow to ascribe a significant part to the
MCA to the exchange anisotropy, caused either by a tetragonal distortion of the
lattice or by the presence of the surface or interface.",1108.5870v1
2012-02-14,Magnetic anisotropies of quantum dots,"Magnetic anisotropies in quantum dots (QDs) doped with magnetic ions are
discussed in terms of two frameworks: anisotropic $g$-factors and
magnetocrystalline anisotropy energy. It is shown that even a simple model of
zinc-blende p-doped QDs displays a rich diagram of magnetic anisotropies in the
QD parameter space. Tuning the confinement allows to control magnetic easy axes
in QDs in ways not available for the better-studied bulk.",1202.3145v1
2001-06-03,Magnetization reversal by uniform rotation (Stoner-Wohlfarth model) in f.c.c. cobalt nanoparticles,"The combination of high sensitive superconducting quantum interference device
(SQUID) with high quality nanoparticles allowed to check the simplest classical
model describing the magnetisation reversal by uniform rotation which were
proposed more than 50 years ago by Neel, Stoner and Wohlfarth. The micrometer
sized SQUIDs were elaborated by electron beam lithography and the nanoparticles
were synthesised by arc-discharge. The measured angular dependence of switching
fields of nearly all f.c.c. Co nanoparticles revealed a dominating uniaxial
magnetic anisotropy. This result suggests that twin boundaries and stacking
faults strongly alter the cubic magnetocrystalline anisotropy leading to
dominating uniaxial anisotropy. However, few particles were sufficiently
""perfect"" in order to show a more complex switching field surface and a field
path dependence of the switching field which is the important signature of the
cubic magnetocrystalline anisotropy.",0106035v1
2007-07-23,"Magnetocrystalline anisotropy controlled local magnetic configurations in (Ga,Mn)As spin-transfer-torque microdevices","The large saturation magnetization in conventional dense moment ferromagnets
offers flexible means of manipulating the ordered state through demagnetizing
shape anisotropy fields but these dipolar fields, in turn, limit the
integrability of magnetic elements in information storage devices. We show that
in a (Ga,Mn)As dilute moment ferromagnet, with comparatively weaker magnetic
dipole interactions, locally tunable magnetocrystalline anisotropy can take the
role of the internal field which determines the magnetic configuration.
Experiments and theoretical modeling are presented for lithographically
patterned microchannels and the phenomenon is attributed to lattice relaxations
across the channels. The utility of locally controlled magnetic anisotropies is
demonstrated in current induced switching experiments. We report structure
sensitive, current induced in-plane magnetization switchings well below the
Curie temperature at critical current densities 10^5 Acm^-2. The observed
phenomenology shows signatures of a contribution from domain-wall
spin-transfer-torque effects.",0707.3329v1
2011-03-19,Magnetic dynamics of single domain Ni nanoparticles,"The dynamic magnetic properties of Ni nanoparticles diluted in an amorphous
SiO2 matrix prepared from a modified sol-gel method have been studied by the
frequency f dependence of the ac magnetic susceptibility \c{hi}(T). For samples
with similar average radii ~ 3-4 nm, an increase of the blocking temperature
from TB ~ 20 to ~ 40 K was observed for Ni concentrations of ~ 1.5 and 5 wt.%,
respectively, assigned to the effects of dipolar interactions. Both the
in-phase \c{hi}'(T) and the out-of-phase \c{hi}""(T) maxima follow the
predictions of the thermally activated N\'eel-Arrhenius model. The effective
magnetic anisotropy constant Keff inferred from \c{hi}""(T) versus f data for
the 1.5 wt.% Ni sample is close to the value of the magnetocrystalline
anisotropy of bulk Ni, suggesting that surface effects are negligible in the
present samples. In addition, the contribution from dipolar interactions to the
total anisotropy energy Ea in specimens with 5 wt.% Ni was found to be
comparable to the intrinsic magnetocrystalline anisotropy barrier.",1103.3783v1
2013-09-18,"Magnetocrystalline anisotropy energy of Fe$(001)$, Fe$(110)$ slabs and nanoclusters: a detailed local analysis within a tight-binding model","We report tight-binding (TB) calculations of magnetocrystalline anisotropy
energy (MAE) of Iron slabs and nanoclusters with a particuler focus on local
analysis. After clarifying various concepts and formulations for the
determination of MAE, we apply our realistic TB model to the analysis of the
magnetic anisotropy of Fe$(001)$, Fe$(110)$ slabs and of two large Fe clusters
with $(001)$ and $(110)$ facets only: a truncated pyramid and a truncated
bipyramid containg 620 and 1096 atoms, respectively. It is shown that the MAE
of slabs originates mainly from outer layers, a small contribution from the
bulk gives rise, however, to an oscillatory behavior for large thicknesses.
Interestingly, the MAE of the nanoclusters considered is almost solely due to
$(001)$ facets and the base perimeter of the pyramid. We believe that this fact
could be used to efficiently control the anisotropy of Iron nanoparticles and
could also have consequences on their spin dynamics.",1309.4578v1
2018-03-01,Calculating the Magnetic Anisotropy of Rare-Earth-Transition-Metal Ferrimagnets,"Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism,
is often explained in terms of ferromagnets. However, the best performing
permanent magnets based on rare earths and transition metals (RE-TM) are in
fact ferrimagnets, consisting of a number of magnetic sublattices. Here we show
how a naive calculation of the magnetocrystalline anisotropy of the classic
RE-TM ferrimagnet GdCo$_5$ gives numbers which are too large at 0 K and exhibit
the wrong temperature dependence. We solve this problem by introducing a
first-principles approach to calculate temperature-dependent magnetization vs.
field (FPMVB) curves, mirroring the experiments actually used to determine the
anisotropy. We pair our calculations with measurements on a recently-grown
single crystal of GdCo$_5$, and find excellent agreement. The FPMVB approach
demonstrates a new level of sophistication in the use of first-principles
calculations to understand RE-TM magnets.",1803.00235v1
2019-04-09,Ferromagnetic Resonance Studies of Strain tuned Bi:YIG Films,"Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large
Magneto-optical activity with low losses still needs to get probed for its
magnetization dynamics. We demonstrate a controlled tuning of
magnetocrystalline anisotropy in Bi-doped Y_3 Fe_5 O_12 (Bi:YIG) films of high
crystalline quality using growth induced epitaxial strain on [111]-oriented
Gd_3 Ga_5 O_12 (GGG) substrate. We optimize a growth protocol to get thick
highly-strained epitaxial films showing large magneto-crystalline anisotropy,
compare to thin films prepared using a different protocol. Ferromagnetic
resonance measurements establish a linear dependence of the out-of-plane
uniaxial anisotropy on the strain induced rhombohedral distortion of Bi:YIG
lattice. Interestingly, the enhancement in the magnetoelastic constant due to
an optimum substitution of Bi^(3+) ions with strong spin orbit coupling does
not strongly affect the precessional damping (~2x10^(-3) ). Large
magneto-optical activity, reasonably low damping, large magnetocrystalline
anisotropy and large magnetoelastic coupling in BiYIG are the properties that
may help BiYIG emerge as a possible material for photo-magnonics and other
spintronics applications.",1904.04800v2
2021-06-22,Quantum-confined charge transfer that enhances magnetic anisotropy in lanthanum M-type hexaferrites,"Iron-based hexaferrites are critical-element-free permanent magnet components
of magnetic devices. Of particular interest is electron-doped M-type
hexaferrite i.e., LaFe$_{12}$O$_{19}$ (LaM) in which extra electrons introduced
by lanthanum substitution of barium/strontium play a key role in uplifting the
magnetocrystalline anisotropy. We investigate the electronic structure of
lanthanum hexaferrite using a \textit{localized} density functional theory
which reproduces semiconducting behavior and identifies the origin of the very
large magnetocrystalline anisotropy. Localized charge transfer from lanthanum
to the iron at the crystal's $2a$ site produces a narrow $3d_{z^2}$ valence
band strongly locking the magnetization along the $c$ axis. The calculated
uniaxial magnetic anisotropy energies from fully self-consistent calculations
are nearly double the single-shot values, and agree well with available
experiments. The chemical similarity of lanthanum to other rare earths suggests
that LaM can host for other rare earths possessing non-trivial $4f$ electronic
states for, \textit{e.g.,} microwave-optical quantum transduction.",2106.11947v1
2021-04-05,Transverse Rashba Effect and Unconventional Magnetocrystalline Anisotropy in Double-Gd-adsorbed Zigzag Graphene Nanoribbon,"The transverse Rashba effect is proposed and investigated by the
first-principle calculations based on density functional theory in a
quasi-one-dimensional antiferromagnet with a strong perpendicular
magnetocrystalline anisotropy, which is materialized by the Gd-adsorbed
graphene nanoribbon with a centric symmetry. The Rashba effect in this system
is associated with the local dipole field transverse to and in the plane of the
nanoribbon. That dipole field is induced by the off-center adsorption of the Gd
adatom above the hex-carbon ring near the nanoribbon edges. The transverse
Rashba effect at the two Gd adatoms enhances each other in the
antiferromagnetic (AFM) ground state and cancels each other in the
ferromagnetic (FM) meta-stable state, because of the centrosymmetric atomic
structure. The transverse Rashba parameter is 1.51 eV A. This system shows a
strong perpendicular magnetocrystalline anisotropy (MCA), which is 1.4 meV per
Gd atom in the AFM state or 2.2 meV per Gd atom in the FM state. The origin of
the perpendicular MCA is analyzed in k-space by filtering out the contribution
of the transverse Rashba effect from the band structures perturbed by the
spin-orbit coupling interactions. The first-order perturbation of the orbit and
spin angular momentum coupling is the major source of the MCA, which is
associated with the one-dimensionality of the system. The transverse Rashba
effect and the strong perpendicular magnetization hosted simultaneously by the
proposed AFM Gd-adsorbed graphene nanoribbon lock the up- (or down-) spin
quantization direction to the forward (or backward) movement. This finding
offers a magnetic approach to a high coherency spin propagation in
one-dimensionality, and open a new door to manipulating spin transportation in
graphene-based spintronics.",2104.01922v1
2022-04-11,DFT calculation of intrinsic properties of magnetically hard phase L1$\mathrm{_0}$ FePt,"Due to its strong magnetocrystalline anisotropy, FePt L1$\mathrm{_0}$ phase
is considered as a promising magnetic recording media material. Although the
magnetic properties of this phase have already been analyzed many times using
density functional theory (DFT), we decided to study it again, emphasizing on
full potential methods, including spin-polarized relativistic
Korringa-Kohn-Rostoker (SPR-KKR) and full-potential local-orbital (FPLO)
scheme. In addition to the determination of exact values of the
magnetocrystalline anisotropy constants K$\mathrm{_1}$ and K$\mathrm{_2}$, the
magnetic moments (m), the Curie temperature, and the magnetostriction
coefficient, we focused on the investigation of the magnetocrystalline
anisotropy energy (MAE) dependence on the magnetic moment values using the
fully relativistic fixed spin moment (FSM) method with various
exchange-correlation potentials. We present nearly identical MAE(m) curves near
the equilibrium point, along with different equilibrium values of MAE and
magnetic moments. For a magnetic moment reduced by about 10%, we determined a
theoretical MAE maximum in the ground state (0 K) equal to about 20.3 MJ
m$\mathrm{^{-3}}$ and independent of the choice of the exchange-correlation
potential form. These calculations allow us to understand the discrepancies
between the previous MAE results for different exchange-correlation potentials.",2204.05073v1
2007-03-23,Magnetocrystalline anisotropy and magnetization reversal in GaMnP synthesized by ion implantation and pulsed-laser melting,"We report the observation of ferromagnetic resonance (FMR) and the
determination of the magnetocrystalline anisotropy in (100)-oriented
single-crystalline thin film samples of GaMnP with x=0.042. The contributions
to the magnetic anisotropy were determined by measuring the angular- and the
temperature-dependencies of the FMR resonance fields and by superconducting
quantum interference device magnetometry. The largest contribution to the
anisotropy is a uniaxial component perpendicular to the film plane; however, a
negative contribution from cubic anisotropy is also found. Additional in-plane
uniaxial components are observed at low temperatures, which lift the degeneracy
between the in-plane [011] and [01-1] directions as well as between the
in-plane [010] and [001] directions. Near T=5K, the easy magnetization axis is
close to the in-plane [01-1] direction. All anisotropy parameters decrease with
increasing temperature and disappear above the Curie temperature T_C. A
consistent picture of the magnetic anisotropy of ferromagnetic GaMnP emerges
from the FMR and magnetometry data. The latter can be successfully modeled when
both coherent magnetization rotation and magnetic domain nucleation are
considered.",0703625v1
2011-06-09,Quantitative model for anisotropy and reorientation thickness of the magnetic moment in thin epitaxially strained metal films,"A quantitative mathematical model for the critical thickness of strained
epitaxial metal films is presented, at which the magnetic moment experiences a
reorientation from in-plane to perpendicular magnetic anisotropy. The model is
based on the minimum of the magnetic anisotropy energy with respect to the
orientation of the magnetic moment of the film. Magnetic anisotropy energies
are taken as the sum of shape anisotropy, magnetocrystalline anisotropy and
magnetoelastic anisotropy, the two latter ones being present as constant
surface and variable volume contributions. Other than anisotropy materials
constants, readily available from literature, only information about the strain
in the films for the determination of the magnetoelastic anisotropy energy is
required. Application of the epitaxial Bain path allows to express the strain
in the film in terms of substrate lattice constant and film lattice parameter,
and thus to obtain an approximate closed expression for the reorientation
thickness in terms of lattice mismatch. The model can predict the critical spin
reorientation transition thickness with surprising accuracy.",1106.1917v1
2015-02-20,Magnetic properties of (Fe$_{1-x}$Co$_x$)$_2$B alloys and the effect of doping by 5$d$ elements,"We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing Co$_2$B, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between $x=0.1$ and $x=0.5$. A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5$d$ transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(Fe$_{0.7}$Co$_{0.3}$)$_2$B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.",1502.05916v3
2000-05-02,Magnetoelastic coupling in epitaxial magnetic films: An ab-initio study,"A method is developed which allows to determine the first-order and the
second-order magnetoelastic coefficients of a magnetic bulk material from the
ab-initio calculation of the magnetocrystalline anisotropy energy as function
of a prestrain. Excplicit results are given for bcc Fe, and they agree well
with experimental data obtained from the magnetostrictive stress measurements
for epitaxial Fe films.",0005053v1
2002-10-31,Superradiant Operation of Spin Masers,"The theory of spin superradiance, developed earlier for nuclear magnets, is
generalized to a wider class of spin systems, such as granular magnets and
molecular magnets. The latter may possess strong single-site magnetocrystalline
anisotropy, whose role in nonlinear spin dynamics is analysed. Transient as
well as pulsing superradiant regimes are described. These coherent regimes may
be employed in the operation of spin masers.",0210698v1
2004-04-08,Stoner-Wohlfart model applied to bicrystal magnetoresistance hysteresis,"We calculate numerically the magnetization direction as function of magnetic
field in the Stoner-Wohlfart theory and are able to reproduce the shape of the
low-field magnetoresistance hysteresis observed in manganite grain boundary
junctions. Moreover, we show that it is necessary to include biaxial
magnetocrystalline anisotropy to fully describe the grain boundary
magnetoresistance in La$_{0.7}$Sr$_{0.3}$MnO$_3$/SrTiO$_3$ bicrystal tunnel
junctions.",0404193v1
2014-02-22,LDA+DMFT Approach to Magnetocrystalline Anisotropy of Strong Magnets,"The new challenges posed by the need of finding strong rare-earth free
magnets demand methods that can predict magnetization and magnetocrystalline
anisotropy energy (MAE). We argue that correlated electron effects, which are
normally underestimated in band structure calculations, play a crucial role in
the development of the orbital component of the magnetic moments. Because
magnetic anisotropy arises from this orbital component, the ability to include
correlation effects has profound consequences on our predictive power of the
MAE of strong magnets. Here we show that incorporating the local effects of
electronic correlations with dynamical mean-field theory provides reliable
estimates of the orbital moment, the mass enhancement and the MAE of YCo5.",1402.5543v2
2015-01-14,Origin of the spin reorientation transitions in (Fe$_{1-x}$Co$_{x}$)$_{2}$B alloys,"Low-temperature measurements of the magnetocrystalline anisotropy energy $K$
in (Fe$_{1-x}$Co$_{x}$)$_{2}$B alloys are reported, and the origin of this
anisotropy is elucidated using a first-principles electronic structure
analysis. The calculated concentration dependence $K(x)$ with a maximum near
$x=0.3$ and a minimum near $x=0.8$ is in excellent agreement with experiment.
This dependence is traced down to spin-orbital selection rules and the filling
of electronic bands with increasing electronic concentration. At the optimal Co
concentration, $K$ depends strongly on the tetragonality and doubles under a
modest 3% increase of the $c/a$ ratio, suggesting that the magnetocrystalline
anisotropy can be further enhanced using epitaxial or chemical strain.",1501.03483v2
2015-03-16,Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets,"The origins of the anomalous temperature dependence of magnetocrystalline
anisotropy in (Fe$_{1-x}$Co$_{x}$)$_{2}$B alloys are elucidated using
first-principles calculations within the disordered local moment model.
Excellent agreement with experimental data is obtained. The anomalies are
associated with the changes in band occupations due to Stoner-like band shifts
and with the selective suppression of spin-orbit ""hot spots"" by thermal spin
fluctuations. Under certain conditions, the anisotropy can increase, rather
than decrease, with decreasing magnetization due to these peculiar electronic
mechanisms, which contrast starkly with those assumed in existing models.",1503.04790v2
2015-04-21,Tailoring the magnetodynamic properties of nanomagnets using magnetocrystalline and shape anisotropies,"Magnetodynamical properties of nanomagnets are affected by the demagnetizing
fields created by the same nanoelements. In addition, magnetocrystalline
anisotropy produces an effective field that also contributes to the spin
dynamics. In this article we show how the dimensions of magnetic elements can
be used to balance crystalline and shape anisotropies, and that this can be
used to tailor the magnetodynamic properties. We study ferromagnetic ellipses
patterned from a 10 nm thick epitaxial Fe film with dimensions ranging from 50
x 150 nm to 150 x 450 nm. The study combines ferromagnetic resonance (FMR)
spectroscopy with analytical calculations and micromagnetic simulations, and
proves that the dynamical properties can be effectively controlled by changing
the size of the nanomagnets. We also show how edge defects in the samples
influence the magnetization dynamics. Dynamical edge modes localized along the
sample edges are strongly influenced by edge defects, and this needs to be
taken into account in understanding the full FMR spectrum",1504.05404v2
2017-03-04,Impact of Anisotropy on Antiferromagnet Rotation in Heusler-type Ferromagnet/Antiferromagnet Epitaxial Bilayers,"We report the magnetotransport properties of ferromagnet (FM)/antiferromagnet
(AFM) Fe$_2$CrSi/Ru$_2$MnGe epitaxial bilayers using current-in-plane
configurations. Above the critical thickness of the Ru$_2$MnGe layer to induce
exchange bias, symmetric and asymmetric curves were observed in response to the
direction of FM magnetocrystalline anisotropy. Because each magnetoresistance
curve showed full and partial AFM rotation, the magnetoresistance curves imply
the impact of the Fe$_2$CrSi magnetocrystalline anisotropy to govern the AFM
rotation. The maximum magnitude of the angular-dependent resistance-change
ratio of the bilayers is more than an order of magnitude larger than that of
single-layer Fe$_2$CrSi films, resulting from the reorientation of AFM spins
via the FM rotation. These results highlight the essential role of controlling
the AFM rotation and reveal a facile approach to detect the AFM moment even in
current-in-plane configurations in FM/AFM bilayers.",1703.01406v2
2017-05-09,"Ab initio study of magnetocrystalline anisotropy, magnetostriction, and Fermi surface of L10 FeNi (tetrataenite)","The ordered L1$_0$ FeNi phase (tetrataenite) is recently considered as a
promising candidate for the rare-earth free permanent magnets applications. In
this work we calculate several characteristics of the L1$_0$ FeNi, where most
of the results come form the fully relativistic full potential FPLO method with
the generalized gradient approximation (GGA). A special attention deserves the
summary of the magnetocrystalline anisotropy energies (MAE's), the full
potential calculations of the anisotropy constant $K_3$, and the combined
analysis of the Fermi surface and three-dimensional $\mathbf{k}$-resolved MAE.
Other calculated parameters presented in this article are the magnetic moments
$m_{s}$ and $m_{l}$, magnetostrictive coefficient $\lambda_{001}$, bulk modulus
B$_0$, and lattice parameters. The MAE's summary shows rather big discrepancies
between the experimental MAE's from literature and also between the calculated
MAE's.",1705.03371v2
2017-06-22,Magnetocrystalline anisotropy in YCo5 and LaCo5: A choice of correlation parameters and the relativistic effects,"The dependence of the magnetocrystalline anisotropy energy (MAE) of MCo5 (M =
Y, La) on the Coulomb correlations and strength of spin orbit (SO) interaction
within the GGA + U scheme is investigated. A range of parameters suitable for
the satisfactory description of key magnetic properties is determined. The
origin of MAE in these materials is mostly related to the large orbital moment
anisotropy of Co atoms on the 2c crystallographic site. Dependence of
relativistic effects on Coulomb correlations, applicability of the second order
perturbation theory for the description of MAE and effective screening of the
SO interaction in these systems are discussed using a generalized virial
theorem.",1706.07368v1
2017-08-30,Micrometer thick soft magnetic films with magnetic moments restricted strictly in plane by negative magnetocrystalline anisotropy,"Stripe domains or any other type domain structures with part of their
magnetic moments deviating from the film plane, which usually occur above a
certain film thickness, are known problems that limit their potential
applications for soft magnetic thin films (SMTFs). In this work, we report the
growth of micrometer thick c-axis oriented hcp-Co84Ir16 SMTFs with their
magnetic moments restricted strictly in plane by negative magnetocrystalline
anisotropy. Extensive characterizations have been performed on these films,
which show that they exhibit very good soft magnetic properties even for our
micrometer thick films. Moreover, the anisotropy properties and high-frequency
properties were thoroughly investigated and our results show very promising
properties of these SMTFs for future applications.",1708.09179v1
2017-12-06,First-principles investigation of magnetocrystalline anisotropy oscillations in Co$_{2}$FeAl/Ta heterostructures,"We report first-principles investigations of magnetocrystalline anisotropy
energy (MCAE) oscillations as a function of capping layer thickness in Heusler
alloy Co\textsubscript{2}FeAl/Ta heterostructures. Substantial oscillation is
observed in FeAl-interface structure. According to $k$-space and
band-decomposed charge density analyses, this oscillation is mainly attributed
to the Fermi-energy-vicinal quantum well states (QWS) which are confined
between Co\textsubscript{2}FeAl/Ta interface and Ta/vacuum surface. The smaller
oscillation magnitude in the Co-interface structure can be explained by the
smooth potential transition at the interface. These findings clarify that MCAE
in Co\textsubscript{2}FeAl/Ta is not a local property of the interface and that
the quantum well effect plays a dominant role in MCAE oscillations of the
heterostructures. This work presents the possibility of tuning MCAE by QWS in
capping layers, and paves the way for artificially controlling magnetic
anisotropy energy in magnetic tunnel junctions.",1712.02139v2
2018-08-02,Exchange interactions and Curie temperature of Ce-substituted SmCo5,"A partial substitution of Sm by Ce can have drastic effects on the magnetic
performance, because it will introduce strain in the structure and breaks the
lattice symmetry in a way that enhances the contribution of the Co atoms to
magnetocrystalline anisotropy. However, Ce substitutions, which are benefit to
improve the magnetocrystalline anisotropy, are detrimental to enhance the Curie
temperature (TC). With the requirements of wide operating temperature range of
magnetic devices, it is important to quantitatively explore the relationship
between the TC and ferromagnetic exchange energy. In this paper we show, based
on mean-field approximation, that Ce substitution-induced tensile strain in
SmCo5 leads to enhanced effective ferromagnetic exchange energy and TC while Ce
atom itself reduces TC.",1808.00988v1
2019-02-03,Design of Face Centered Cubic Co81.8Si9.1B9.1 with High Magnetocrystalline Anisotropy,"Despite the composition close to glassy forming alloys, face centered cubic
(FCC) Co81.8Si9.1B9.1, designed based on Co9B atomic cluster (polyhedral), are
synthesized as singlephase ribbons successfully. These ribbons, with grain
sizes of ca. 92 nm, show supreme ductility and strong orientation along (111),
which couples with shape anisotropy leading to high magnetocrystalline
anisotropy comparable to Co rich Co-Pt nanoscale thin films, with a coercivity
of 430 Oe and squareness of 0.82 at room temperature. The stability and
magnetic behaviors of the phase are discussed based on experimental electronic
structure. This work not only develops low cost Co-based materials for hard
magnetic applications, but also extends the atomic cluster model developed for
amorphous alloys into the design of new crystalline materials.",1902.05120v1
2019-10-16,"Temperature-dependent magnetocrystalline anisotropy of rare earth/transition metal permanent magnets from first principles: The light RCo$_5$ (R=Y, La-Gd) intermetallics","Computational design of more efficient rare earth/transition metal (RE-TM)
permanent magnets requires accurately calculating the magnetocrystalline
anisotropy (MCA) at finite temperature, since this property places an upper
bound on the coercivity. Here, we present a first-principles methodology to
calculate the MCA of RE-TM magnets which fully accounts for the effects of
temperature on the underlying electrons. The itinerant electron TM magnetism is
described within the disordered local moment picture, and the localized RE-4f
magnetism is described within crystal field theory. We use our model, which is
free of adjustable parameters, to calculate the MCA of the RCo$_5$ (R=Y, La-Gd)
magnet family for temperatures 0--600 K. We correctly find a huge uniaxial
anisotropy for SmCo$_5$ (21.3 MJm$^{-3}$ at 300 K) and two finite temperature
spin reorientation transitions for NdCo$_5$. The calculations also demonstrate
dramatic valency effects in CeCo$_5$ and PrCo$_5$. Our calculations provide
quantitative, first-principles insight into several decades of RE-TM
experimental studies.",1910.07436v1
2019-11-04,DFT+U Investigation of magnetocrystalline anisotropy of Mn-doped transition-metal dichalcogenides monolayers,"Doped transition-metal dichalcogenides monolayers exhibit exciting magnetic
properties for the benefit of two-dimensional spintronic devices. Using density
functional theory (DFT) incorporating Hubbard-type of correction (DFT$+U$) to
account for the electronic correlation, we study the magnetocrystalline
anisotropy energy (MAE) characterizing Mn-doped MS$_2$ (M=Mo, W) monolayers. A
single isolated Mn dopant exhibits a large perpendicular magnetic anisotropy of
35 meV (8 meV) in the case of Mn-doped WS$_2$ (MoS$_2$) monolayer. This value
originates from the Mn in-plane orbitals degeneracy lifting due to the
spin-orbit coupling. In pairwise doping, the magnetization easy axis changes to
the in-plane direction with a weak MAE compared to single Mn doping. Our
results suggest that diluted Mn-doped MS$_2$ monolayers, where the Mn dopants
are well separated, could potentially be a candidate for the realization of
ultimate nanomagnet units.",1911.01173v2
2019-12-06,Understanding the origin of magnetocrystalline anisotropy in pure and Fe/Si substituted SmCo5,"We report magnetocrystalline anisotropy of pure and Fe/Si substituted SmCo5.
The calculations were performed using the advanced density functional theory
(DFT) including onsite electron-electron correlation and spin orbit coupling.
Si substitution substantially reduces both uniaxial magnetic anisotropy and
magnetic moment. Fe substitution with the selective site, on the other hand,
enhances the magnetic moment with limited chemical stability. The magnetic
hardness of SmCo5 is governed by Sm 4f localized orbital contributions, which
get flatten and split with the substitution of Co (2c) with Si/Fe atoms, except
the Fe substitution at 3g site. It is also confirmed that Si substitutions
favor the thermodynamic stability on the contrary to diminishing the magnetic
and anisotropic effect in SmCo5 at either site.",1912.03368v1
2020-09-02,"Phase transition in the magnetocrystalline anisotropy of tetragonal Heusler alloys: Rh$_2T$Sb, $T=$ Fe, Co","This work reports on first principles calculations of the electronic and
magnetic structure of tetragonal Heusler compounds with the composition
Rh$_2$Fe$_{x}$Co$_{1-x}$Sb ($0\leq x\leq1$). It is found that the magnetic
moments increase from 2 to 3.4~$\mu_B$ and the Curie temperature decreases from
500 to 464~K with increasing Fe content $x$. The $3d$ transition metals make
the main contribution to the magnetic moments, whereas Rh contributes only
approximately 0.2~$\mu_B$ per atom, independent of the composition. The paper
focuses on the magnetocrystalline anisotropy of the borderline compounds
Rh$_2$FeSb, Rh$_2$Fe$_{0.5}$Co$_{0.5}$Sb, and Rh$_2$CoSb. A transition from
easy-axis to easy-plane anisotropy is observed when the composition changes
from Rh$_2$CoSb to Rh$_2$FeSb. The transition occurs at an iron concentration
of approximately 40\%.",2009.00920v1
2021-06-16,Towards hexagonal $C_{2v}$ systems with anisotropic DMI: Characterization of epitaxial Co$(10\bar{1}0)$/Pt$(110)$ multilayer films,"Ferromagnet/heavy metal (FM/HM) multilayer thin films with $C_{2v}$ symmetry
have the potential to host antiskyrmions and other chiral spin textures via an
anisotropic Dzyaloshinkii-Moriya interaction (DMI). Here, we present a
candidate material system that also has a strong uniaxial magnetocrystalline
anisotropy aligned in the plane of the film. This system is based on a new
Co/Pt epitaxial relationship, which is the central focus of this work:
hexagonal closed-packed Co$(10\bar{1}0)[0001]$ $\parallel$ face-centered cubic
Pt$(110)[001]$. We characterized the crystal structure and magnetic properties
of our films using X-ray diffraction techniques and magnetometry respectively,
including q-scans to determine stacking fault densities and their correlation
with the measured magnetocrystalline anisotropy constant and thickness of Co.
In future ultrathin multilayer films, we expect this epitaxial relationship to
further enable an anisotropic DMI while supporting interfacial perpendicular
magnetic anisotropy. The anticipated confluence of these properties, along with
the tunability of multilayer films, make this material system a promising
testbed for unveiling new spin configurations in FM/HM films.",2106.10249v2
2021-07-23,Reduced magnetocrystalline anisotropy of CoFe$_2$O$_4$ thin films studied by angle-dependent x-ray magnetic circular dichroism,"Spinel-type CoFe$_2$O$_4$ is a ferrimagnetic insulator with the N\'eel
temperature exceeding 790 K, and shows a strong cubic magnetocrystalline
anisotropy (MCA) in bulk materials. However, when a CoFe$_2$O$_4$ film is grown
on other materials, its magnetic properties are degraded so that so-called
magnetically dead layers are expected to be formed in the interfacial region.
We investigate how the magnetic anisotropy of CoFe$_2$O$_4$ is modified at the
interface of CoFe$_2$O$_4$/Al$_2$O$_3$ bilayers grown on Si(111) using x-ray
magnetic circular dichroism (XMCD). We find that the thinner CoFe$_2$O$_4$
films have significantly smaller MCA values than bulk materials. The reduction
of MCA is explained by the reduced number of Co$^{2+}$ ions at the $O_h$ site
reported by a previous study [Y. K. Wakabayashi $\textit{et al.}$, Phys. Rev. B
$\textbf{96}$, 104410 (2017)].",2107.11204v1
2023-02-28,Bistable electric field control of single-atom magnetocrystalline anisotropy,"We reversibly switch the polar environment of an individual magnetic atom
with an electric field to control the energy barrier for reversal of
magnetization. By applying an electric field in the gap between the tip and
sample of a scanning tunneling microscope, we induce bistable changes in the
polarization of the region surrounding a chlorine vacancy in a monolayer of
sodium chloride on copper terminated by a monolayer of copper nitride. The
displacement of the sodium chloride ions alters the local electric polarization
and modifies the magnetocrystalline anisotropy experienced by a single cobalt
atom. When a cobalt atom is near a chlorine vacancy, spin-sensitive inelastic
electron tunneling spectroscopy measurements can reveal the change in
anisotropy. The demonstration of atomic-scale control of magnetic properties
with electric fields opens new possibilities for probing the origins of
magnetoelectric coupling and will stimulate the development of model artificial
mutliferroic systems.",2302.14667v1
2015-05-21,General Formalism for Magnetic Anisotropy Constants,"Direct expressions for the magnetic anisotropy constants are given at a
finite temperature from microscopic viewpoints. In the present derivation, it
is assumed that the Hamiltonian is a linear function with respect to the
magnetization direction. We discuss in detail the first-order constant $K_1$
and show that the results reproduce previous results. We also apply our method
to Nd$_2$Fe$_{14}$B compounds and demonstrate that the temperature dependencies
of the magnetocrystalline anisotropy constants $K_1$, $K_2$, and $K_3$ are
successfully computed.",1505.05686v1
2016-05-23,Large magnetic anisotropy in Fe_{0.25}TaS_2,"We present a first-principles study of the large magneto-crystalline
anisotropy in the intercalated di-chalcogenide material \ce{Fe_{0.25}TaS_2},
investigated with the DFT+U approach. We verify a uniaxial magnetocrystalline
anisotropy energy(MAE) of 15meV/Fe. in the material. We further analyze the
dependence of MAE on the constituent elements and the effect of spin-orbit
coupling. Contrary to conventional intuition, we find a small contribution to
MAE due to strong spin-orbit coupling in the heavier element, Ta. We show that
the electronic configuration, crystal field environment and correlational
effects of the magnetic ion are more important.",1605.07141v1
2018-07-24,Pushing the limits of magnetic anisotropy in the Sm-Co system,"Materials based on the Sm-Co system exhibit remarkable magnetic performance
due to their high Curie temperature, large saturation magnetization, and strong
magnetic anisotropy, which are the result of the electronic structure in Co and
Sm and their arrangement in the hexagonal lattice. In this paper we show, using
first-principles calculations, mean-field theory, and atomistic Monte Carlo
simulations that slight modifications of the SmCo5 crystal structure, induced
by strain or partial substitution of Sm by Ce, change the exchange interaction
energy and increase the magnetocrystalline anisotropy energy drastically. This
finding shows how small changes in local-structure environments lead to
substantial changes in macroscopic properties and enables the optimization of
high-performance materials at the atomic level.",1807.09257v1
2023-07-07,Anomalous Nernst effect in perpendicularly magnetised τ-MnAl thin films,"$\tau$-MnAl is interesting for spintronic applications as a ferromagnet with
perpendicular magnetic anisotropy due to its high uniaxial magnetocrystalline
anisotropy. Here we report on the anomalous Nernst effect of sputter deposited
$\tau$-MnAl thin films. We demonstrate a robust anomalous Nernst effect at
temperatures of 200 K and 300 K with a hysteresis similar to the anomalous Hall
effect and the magnetisation of the material. The anomalous Nernst coefficient
of (0.6$\pm$0.24) $\mu$V/K at 300 K is comparable to other perpendicular
magnetic anisotropy thin films. Therefore $\tau$-MnAl is a promising candidate
for spin-caloritronic research.",2307.03458v1
2016-11-20,The effect of dynamical compressive and shear strain on magnetic anisotropy in low symmetry ferromagnetic film,"Dynamical strain generated upon excitation of a metallic film by a
femtosecond laser pulse may become a versatile tool enabling control of
magnetic state of thin films and nanostructures via inverse magnetostriction on
a picosecond time scale. Here we explore two alternative approaches to
manipulate magnetocrystalline anisotropy and excite magnetization precession in
a low-symmetry film of a magnetic metallic alloy galfenol (Fe,Ga) either by
injecting picosecond strain pulse into it from a substrate or by generating
dynamical strain of complex temporal profile in the film directly. In the
former case we realize ultrafast excitation of magnetization dynamics solely by
strain pulses. In the latter case optically-generated strain emerged abruptly
in the film modifies its magnetocrystalline anisotropy, competing with
heat-induced change of anisotropy parameters. We demonstrate that the
optically-generated strain remains efficient for launching magnetization
precession, when the heat-induced changes of anisotropy parameters do not
trigger the precession anymore. We emphasize that in both approaches the
ultrafast change of magnetic anisotropy mediating the precession excitation
relies on mixed, compressive and shear, character of the dynamical strain,
which emerges due to low-symmetry of the metallic film under study.",1611.06599v3
2017-07-10,Giant interfacial perpendicular magnetic anisotropy in Fe/CuIn$_{1-x}$Ga$_x$Se$_2$ beyond Fe/MgO,"We study interfacial magnetocrystalline anisotropies in various
Fe/semiconductor heterostructures by means of first-principles calculations. We
find that many of those systems show perpendicular magnetic anisotropy (PMA)
with a positive value of the interfacial anisotropy constant $K_{\rm i}$. In
particular, the Fe/CuInSe$_2$ interface has a large $K_{\rm i}$ of $\sim
2.3\,{\rm mJ/m^2}$, which is about 1.6 times larger than that of Fe/MgO known
as a typical system with relatively large PMA. We also find that the values of
$K_{\rm i}$ in almost all the systems studied in this work follow the
well-known Bruno's relation, which indicates that minority-spin states around
the Fermi level provide dominant contributions to the interfacial
magnetocrystalline anisotropies. Detailed analyses of the local density of
states and wave-vector-resolved anisotropy energy clarify that the large
$K_{\rm i}$ in Fe/CuInSe$_2$ is attributed to the preferable $3d$-orbital
configurations around the Fermi level in the minority-spin states of the
interfacial Fe atoms. Moreover, we have shown that the locations of interfacial
Se atoms are the key for such orbital configurations of the interfacial Fe
atoms.",1707.02694v3
2021-11-03,Anisotropic magnetocaloric effect of CrI$_{3}$: A theoretical study,"CrI$_{3}$ is considered to be a promising candidate for spintronic devices
and data storage. We derived the Heisenberg Hamiltonian for CrI$_{3}$ from
density functional calculations using the Liechtenstein formula. Moreover, the
Monte--Carlo simulations with the Sucksmith--Thompson method were performed to
analyze the effect of magnetic anisotropy energy on the thermodynamic
properties. Our method successfully reproduced the negative sign of isothermal
magnetic entropy changes when a magnetic field was applied along the hard
plane. We found that the temperature dependence of the magnetocrystalline
anisotropy energy is not negligible at temperatures slightly above the Curie
temperature. We clarified that the origin of this phenomenon is attributed to
anisotropic magnetic susceptibility and magnetization anisotropy. The
difference between the entropy change of the easy axis and the hard plane is
proportional to the temperature dependence of the magnetic anisotropy energy,
implying that the anisotropic entropy term is the main source of the
temperature dependence of the free energy difference when magnetizing in a
specific direction other than the easy axis. We also investigated the magnetic
susceptibility that can be used for the characterization of the negative sign
of the entropy change in the case of a hard plane. The competition of
magnetocrystalline anisotropy energy and external magnetic field at low
temperature and low magnetic field region causes a high magnetic susceptibility
as the fluctuation of magnetization. Meanwhile, the anisotropy energy is
suppressed at a sufficient magnetic field applied along the hard axis, the
magnetization is fully rotated to the direction of the external magnetic field.",2111.02063v1
2016-05-18,Interfacial magnetic anisotropy from a 3-dimensional Rashba substrate,"We study the magnetic anisotropy which arises at the interface between a thin
film ferromagnet and a 3-d Rashba material. The 3-d Rashba material is
characterized by the spin-orbit strength $\alpha$ and the direction of broken
bulk inversion symmetry $\hat n$. We find an in-plane uniaxial anisotropy in
the $\hat{z}\times\hat{n}$ direction, where $\hat z$ is the interface normal.
For realistic values of $\alpha$, the uniaxial anisotropy is of a similar order
of magnitude as the bulk magnetocrystalline anisotropy. Evaluating the uniaxial
anisotropy for a simplified model in 1-d shows that for small band filling, the
in-plane easy axis anisotropy scales as $\alpha^4$ and results from a twisted
exchange interaction between the spins in the 3-d Rashba material and the
ferromagnet. For a ferroelectric 3-d Rashba material, $\hat n$ can be
controlled with an electric field, and we propose that the interfacial magnetic
anisotropy could provide a mechanism for electrical control of the magnetic
orientation.",1605.05739v1
2016-07-21,Perpendicular magnetic anisotropy of two-dimensional Rashba ferromagnets,"We compute the magnetocrystalline anisotropy energy within two-dimensional
Rashba models. For a ferromagnetic free-electron Rashba model, the magnetic
anisotropy is exactly zero regardless of the strength of the Rashba coupling,
unless only the lowest band is occupied. For this latter case, the model
predicts in-plane anisotropy. For a more realistic Rashba model with finite
band width, the magnetic anisotropy evolves from in-plane to perpendicular and
back to in-plane as bands are progressively filled. This evolution agrees with
first-principles calculations on the interfacial anisotropy, suggesting that
the Rashba model captures energetics leading to anisotropy originating from the
interface provided that the model takes account of the finite Brillouin zone.
The results show that the electron density modulation by doping or an external
voltage is more important for voltage-controlled magnetic anisotropy than the
modulation of the Rashba parameter.",1607.06470v2
2020-02-10,On the anisotropies of magnetization and electronic transport of magnetic Weyl semimetal Co3Sn2S2,"Co3Sn2S2, a quasi-two-dimensional system with kagome lattice, has been found
as a magnetic Weyl semimetal recently. In this work, the anisotropies of
magnetization and transport properties of Co3Sn2S2 were investigated. The high
field measurements reveal a giant magnetocrystalline anisotropy with an
out-of-plane saturation field of 0.9 kOe and an in-plane saturation field of
230 kOe at 2 K, showing a magnetocrystalline anisotropy coefficient Ku up to
8.3 * 10^5 J m-3, which indicates that it is extremely difficult to align the
small moment of 0.29 {\mu}B/Co on the kagome lattice from c axis to ab plane.
The out-of-plane angular dependences of Hall conductivity further reveal strong
anisotropies in Berry curvature and ferromagnetism, and the vector directions
of both are always parallel with each other. For in-plane situation, the
longitudinal and transverse measurements for both I parallel a and I
perpendicular a cases show that the transport on the kagome lattice is
isotropic. These results provide essential understanding on the magnetization
and transport behaviors for the magnetic Weyl semimetal Co3Sn2S2.",2002.03940v1
2006-01-26,"Magnetic anisotropy switching in (Ga,Mn)As with increasing hole concentration","We study a possible mechanism of the switching of the magnetic easy axis as a
function of hole concentration in (Ga,Mn)As epilayers. In-plane uniaxial
magnetic anisotropy along [110] is found to exceed intrinsic cubic
magnetocrystalline anisotropy above a hole concentration of p = 1.5 * 10^21
cm^-3 at 4 K. This anisotropy switching can also be realized by post-growth
annealing, and the temperature-dependent ac susceptibility is significantly
changed with increasing annealing time. On the basis of our recent scenario
[Phys. Rev. Lett. 94, 147203 (2005); Phys. Rev. B 73, 155204 (2006).], we
deduce that the growth of highly hole-concentrated cluster regions with [110]
uniaxial anisotropy is likely the predominant cause of the enhancement in [110]
uniaxial anisotropy at the high hole concentration regime. We can clearly rule
out anisotropic lattice strain as a possible origin of the switching of the
magnetic anisotropy.",0601603v2
1996-05-22,Theory of Magnetocrystalline Anisotropy Energy for Wires and Corrals of Fe adatoms: A Non-Perturbative Theory,"The magnetocrystalline anisotropy energy $E_{anis}$ for free-standing chains
(quantum wires) and rings (quantum corrals) of Fe-adatoms $N=$(2...48) is
determined using an electronic tight-binding theory. Treating spin-orbit
coupling non-perturbatively, we analyze the relationship between the electronic
structure of the Fe $d$-electrons and $E_{anis}(n_{d})$, for both the chain and
ring conformations. We find that $E_{anis}(N)$ is larger for wires than for
rings or infinite monolayers. Generally $E_{anis}(n_{d})$ decreases in chains
upon increasing $N$, while for rings $E_{anis}(n_{d})$ is essentially
independent of $N$. For increasing $N$, $E_{anis}(n_{d})$ in corrals approaches
the results for freestanding monolayers. Small rings exhibit clear odd-even
oscillations of $E_{anis}(N)$. Within our theoretical framework we are able to
explain the experimentally observed oscillations of $E_{anis}(n_{d})$ during
film growth with a period of one monolayer. Finally, a generalization of Hund's
third rule on spin-orbit coupling to itinerant ferromagnets is proposed.",9605137v1
2000-01-13,Ab-initio Theoretical Description of the Interrelation between Magnetocrystalline Anisotropy and Atomic Short-Range Order,"The cubic lattice symmetry of ferromagnetic homogeneously disordered alloys
is when a compositional modulation is imposed. This can have a profound
influence on the magnetocrystalline anisotropy energy (MAE). We describe our
ab-initio theory of this effect and use the framework of concentration waves
with the electronic structure described within the spin-polarised relativistic
Korringa-Kohn-Rostoker coherent-potential approximation. We find that ordering
produces a 2 order of magnitude increase in the MAE as well as altering the
equilibrium direction of magnetisation. Using the same theoretical framework we
also examine directional compositional order produced by magnetic annealing
with an explicit study of permalloy.",0001181v1
2010-01-09,Correlation induced half-metallicity in a ferromagnetic single-layered compound: Sr$_2$CoO$_4$,"The electronic and magnetic properties of Sr$_2$CoO$_4$ compound have been
studied using $\emph{ab initio}$ electronic structure calculations. As opposed
to GGA calculation, which gives ferromagnetic metallic solution, GGA+$U$
calculations provide two kind of ferromagnetic solutions: (i) half-metallic and
(ii) metallic. The half-metallic solution is a ground state of the system and
the metallic one is a metastable state. The strong hybridization between Co
3$d$ and O 2$p$ orbitals decides the electronic and magnetic properties of the
compound. The total magnetic moment per formula unit is found to be $\sim$ 3
$\mu_B$ ($S$ = 3/2). Our calculations give the magnetocrystalline anisotropy
energy of $\sim$ 2.7 meV, which provides a good description of experimentally
observed large magnetocrystalline anisotropy. The Heisenberg exchange
parameters up to fourth nearest neighbours are also calculated. The mean-field
theory gives the $T_C$ = 887 K. The possible physical implications of the
ferromagnetic half-metallic ground state are also discussed.",1001.1405v1
2010-03-11,High-temperature multiferroicity and strong magnetocrystalline anisotropy in 3d-5d double perovskites,"Using density functional calculations we explore the properties of
as-yet-unsynthesized $3d - 5d$ ordered double perovskites ($A_2BB'$O$_6$) with
highly polarizable Bi$^{3+}$ ions on the $A$ site. We find that the
Bi$_2$NiReO$_6$ and Bi$_2$MnReO$_6$ compounds are insulating and exhibit a
robust net magnetization that persists above room temperature. When the
in-plane lattice vectors of the pseudocubic unit cell are constrained to be
orthogonal (for example, by coherent heteroepitaxy), the ground states are
ferroelectric with large polarization and a very large uniaxial
magnetocrystalline anisotropy with easy axis along the ferroelectric
polarization direction. Our results suggest a route to multiferroism and
electrically controlled magnetization orientation at room temperature.",1003.2449v2
2011-11-17,"Theory of magnetization precession induced by a picosecond strain pulse in ferromagnetic semiconductor (Ga,Mn)As","A theoretical model of the coherent precession of magnetization excited by a
picosecond acoustic pulse in a ferromagnetic semiconductor layer of (Ga,Mn)As
is developed. The short strain pulse injected into the ferromagnetic layer
modifies the magnetocrystalline anisotropy resulting in a tilt of the
equilibrium orientation of magnetization and subsequent magnetization
precession. We derive a quantitative model of this effect using the
Landau-Lifshitz equation for the magnetization that is precessing in the
time-dependent effective magnetic field. After developing the general
formalism, we then provide a numerical analysis for a certain structure and two
typical experimental geometries in which an external magnetic field is applied
either along the hard or the easy magnetization axis. As a result we identify
three main factors, which determine the precession amplitude: the
magnetocrystalline anisotropy of the ferromagnetic layer, its thickness, and
the strain pulse parameters.",1111.4043v1
2012-06-27,Effect of Pt impurities on the magnetocrystalline anisotropy of hcp Co: a first-principles study,"In terms of the fully relativistic screened Korringa-Kohn-Rostoker method we
investigate the variation in the magnetocrystalline anisotropy energy (MAE) of
hexagonal close-packed cobalt with the addition of platinum impurities. In
particular, we perform calculations on a bulk cobalt system in which one of the
atomic layers contains a fractional, substitutional platinum impurity. Our
calculations show that at small concentrations of platinum the MAE is reduced,
while at larger concentrations the MAE is enhanced. This change of the MAE can
be attributed to an interplay between on-site Pt MAE contributions and induced
MAE contributions on the Co sites. The latter ones are subject to pronounced,
long-ranged Friedel-oscillations that can lead to significant size effects in
the experimental determination of the MAE of nano-sized samples.",1206.6200v1
2013-04-04,Effect of stacking faults on the magnetocrystalline anisotropy of hcp Co: a first-principles study,"In terms of the fully relativistic screened Korringa-Kohn-Rostoker method we
investigate the effect of stacking faults on the magnetic properties of
hexagonal close-packed cobalt. In particular, we consider the formation energy
and the effect on the magnetocrystalline anisotropy energy (MAE) of four
different stacking faults in hcp cobalt -- an intrinsic growth fault, an
intrinsic deformation fault, an extrinsic fault and a twin-like fault. We find
that the intrinsic growth fault has the lowest formation energy, in good
agreement with previous first-principles calculations. With the exception of
the intrinsic deformation fault which has a positive impact on the MAE, we find
that the presence of a stacking fault generally reduces the MAE of bulk Co.
Finally, we consider a pair of intrinsic growth faults and find that their
effect on the MAE is not additive, but synergic.",1304.1353v1
2013-04-19,Effects of composition and chemical disorder on the magnetocrystalline anisotropy of Fe_{x}Pt_{1-x} alloys,"We perform first principles calculations of the magnetocrystalline anisotropy
energy (MAE) of the L1_{0}-like Fe_{x}Pt_{1-x} samples studied experimentally
by Barmak and co-workers in [J. Appl. Phys. 98 (2005) 033904]. The variation of
composition and long-range chemical order in the samples was studied in terms
of the coherent potential approximation. In accordance with experimental
observations, we find that, in the presence of long-range chemical disorder,
Fe-rich samples exhibit a larger MAE than stoichiometric FePt. By considering
the site- and species-resolved contributions to the MAE, we infer that the MAE
is primarily a function of the degree of completeness of the nominal Fe layers
in the L1_{0} FePt structure.",1304.5323v1
2014-04-28,Electronic structure and magnetic properties of L1_0 binary alloys,"We present a systematic study of the magnetic properties of L1$_0$ binary
alloys FeNi, CoNi, MnAl and MnGa via two different density functional theory
approaches. Our calculations show large magnetocrystalline anisotropies in the
order $1~\text{MJ/m}^3$ or higher for CoNi, MnAl and MnGa while FeNi shows a
somewhat lower value in the range $0.48 - 0.77 ~\text{MJ/m}^3$. Saturation
magnetization values of $1.3~\text{MA/m}$, $1.0~\text{MA/m}$, $0.8~\text{MA/m}$
and $0.9~\text{MA/m}$ are obtained for FeNi, CoNi, MnAl and MnGa respectively.
Curie temperatures are evaluated via Monte Carlo simulations and show
$T_\text{C}=916~\text{K}$ and $T_\text{C}=1130~\text{K}$ for FeNi and CoNi
respectively. For Mn-based compounds Mn-rich off-stoichiometric compositions
are found to be important for the stability of a ferro or ferrimagnetic ground
state with $T_\text{C}$ greater than $600~\text{K}$. The effect of
substitutional disorder is studied and found to decrease both
magnetocrystalline anisotropies and Curie temperatures in FeNi and CoNi.",1404.7097v2
2014-05-02,Jahn-Teller driven perpendicular magnetocrystalline anisotropy in metastable Ruthenium,"A new metastable phase of the body-centered-tetragonal ruthenium ({\em
bct}--Ru) is identified to exhibit a large perpendicular magnetocrystalline
anisotropy (PMCA), whose energy, $E_{MCA}$, is as large as 150 $\mu$eV/atom,
two orders of magnitude greater than those of 3$d$ magnetic metals. Further
investigation over the range of tetragonal distortion suggests that the
appearance of the magnetism in the {\em bct}--Ru is governed by the Jahn-Teller
spit $e_g$ orbitals. Moreover, from band analysis, MCA is mainly determined by
an interplay between two $e_g$ states, $d_{x^2-y^2}$ and $d_{z^2}$ states, as a
result of level reversal associated with tetragonal distortion.",1405.0499v3
2017-12-27,Effective reduction of the coercivity for Co$_{72}$Pt$_{28}$ thin film by exchange coupled Co$_{81}$Ir$_{19}$ soft layer with negative magnetocrystalline anisotropy,"We report on the investigation of coercivity changes of the
Co$_{72}$Pt$_{28}$/Co$_{81}$Ir$_{19}$ exchange-coupled composite (ECC) media
with negative soft-layer (SL) magnetocrystalline anisotropy (MA) . Our results
show that the hard-layer (HL) of our sample exhibits a columnar type
microstructure with well isolated grains and the SL with hcp-structure grows on
top of the HL with the same texture. Therefore, strong coupling of the two
layers have been realized as evidenced by the magnetic characterization.
Importantly, we observe a more effective reduction of the coercivity of the ECC
media by using SLs with negative MA when compared to the use of SLs with
positive or negligible MA. The experimental results are corroborated by
theoretical calculations.",1712.09504v1
2018-01-25,Heusler compounds -- how to tune the magnetocrystalline anisotropy,"Tailoring and controlling magnetic properties is an important factor for
materials design. Here, we present a case study for Ni-based Heusler compounds
of the type Ni$_2$YZ with Y = Mn, Fe, Co and Z = B, Al, Ga, In, Si, Ge, Sn
based on first principles electronic structure calculations. These compounds
are interesting since the materials properties can be quite easily tuned by
composition and many of them possess a non-cubic ground state being a
prerequisite for a finite magnetocrystalline anisotropy (MAE). We discuss
systematically the influence of doping at the Y and Z sublattice as well of
lattice deformation on the MAE. We show that in case of Ni$_2$CoZ the phase
stability and the MAE can be improved using quaternary systems with elements
from group 13 and 14 on the Z sublattice whereas changing the Y sublattice
occupation by adding Fe does not lead to an increase of the MAE. Furthermore,
we studied the influence of the lattice ratio on the MAE. Showing that small
deviations can lead to a doubling of the MAE as in case of Ni$_2$FeGe. Even
though we demonstrate this for a limited set of systems the findings may carry
over to other related systems.",1801.08511v1
2018-06-05,Efficient technique for ab-initio calculation of magnetocrystalline anisotropy energy,"Ab-initio calculation of magnetocrystalline anisotropy energy (MCAE) often
requires a strict convergence criterion and a dense k-point mesh to sample the
Brillouin zone, making its convergence problematic and time-consuming. The
force theorem for MCAE states that MCAE can be calculated by the band energy
difference between two magnetization directions at a fixed potential. The
maximally localized Wannier function can be utilized to construct a compact
Hilbert space of low-lying electron states and interpolate band eigenvalues
with high precession. We combine the force theorem and the Wannier
interpolation of eigenvalues together to improve the efficiency of MCAE
calculations with no loss of accuracy. We use a Fe chain, a Fe monolayer and a
FeNi alloy as examples and demonstrate that the Wannier interpolation method
for MCAE is able to reduce the computational cost significantly and remain
accurate simultaneously, compared with a direct ab-initio calculation on a very
dense k-point mesh. This efficient Wannier interpolation approach makes it
possible for large-scale and high-throughput MCAE calculations, which could
benefit the design of spintronics devices.",1806.01536v2
2018-07-19,Magnetocrystalline anisotropy in the Kondo lattice compound CeAgAs$_2$,"We report on the single crystal growth and anisotropic physical properties of
CeAgAs$_2$. The compound crystallizes as on ordered variant of the
HfCuSi$_2$-type crystal structure and adopts the orthorhombic space group
$Pmca$~(\#57) with two symmetry inequivalent cerium atomic positions in the
unit cell. The orthorhombic crystal structure of our single crystal was
confirmed from the powder x-ray diffraction and from electron diffraction
patterns obtained from the transmission electron microscope. The anisotropic
physical properties have been investigated on a good quality single crystal by
measuring the magnetic susceptibility, isothermal magnetization, electrical
transport and heat capacity. The magnetic susceptibility and magnetization
measurements revealed that this compound orders antiferromagnetically with two
closely spaced magnetic transitions at $T_{\rm N1} = 6$~K and $T_{\rm N2} =
4.9$~K. Magnetization studies have revealed a large magnetocrystalline
anisotropy due to the crystalline electric field (CEF) with an easy axis of
magnetization along the [010] direction. The magnetic susceptibility measured
along the [001] direction exhibited a broad hump in the temperature range 50 to
250~K, while typical Curie-Weiss behaviour was observed along the other two
orthogonal directions. The electrical resistivity and the heat capacity
measurements revealed that CeAgAs$_2$ is a Kondo lattice system with a magnetic
ground state.",1807.07265v1
2018-11-29,Response of the skyrmion lattice in MnSi to cubic magnetocrystalline anisotropies,"We report high-precision small angle neutron scattering of the orientation of
the skyrmion lattice in a spherical sample of MnSi under systematic changes of
the magnetic field direction. For all field directions the skyrmion lattice may
be accurately described as a triple-$\vec{Q}$ state, where the modulus $\vert
\vec{Q} \vert$ is constant and the wave vectors enclose rigid angles of
$120^{\circ}$. Along a great circle across $\langle 100\rangle$, $\langle
110\rangle$, and $\langle 111\rangle$ the normal to the skyrmion-lattice plane
varies systematically by $\pm3^{\circ}$ with respect to the field direction,
while the in-plane alignment displays a reorientation by $15^{\circ}$ for
magnetic field along $\langle 100\rangle$. Our observations are qualitatively
and quantitatively in excellent agreement with an effective potential, that is
determined by the symmetries of the tetrahedral point group $T$ and includes
contributions up to sixth-order in spin-orbit coupling, providing a full
account of the effect of cubic magnetocrystalline anisotropies on the skyrmion
lattice in MnSi.",1811.12439v1
2019-02-05,Intersublattice magnetocrystalline anisotropy using a realistic tight-binding method based on maximally localized Wannier functions,"Using a realistic tight-binding Hamiltonian based on maximally localized
Wannier functions, we investigate the two-ion magnetocrystalline anisotropy
energy (MAE) in $L1_0$ transition metal compounds. MAE contributions from
throughout the Brillouin zone are obtained using magnetic force theorem
calculations with and without perturbation theory. The results from either
method agree with one another, and both reflect features of the Fermi surface.
The intra-sublattice and inter-sublattice contributions to MAE are evaluated
using a Green's function method. We find that the sign of the inter-sublattice
contribution varies among compounds, and that its amplitude may be significant,
suggesting MAE can not be resolved accurately in a single-ion manner. The
results are further validated by scaling spin-orbit-coupling strength in
density functional theory. Overall, this realistic tight-binding method provide
an effective approach to evaluate and analyze MAE while retaining the accuracy
of corresponding first-principles methods.",1902.01561v2
2019-08-06,Strain controllable magnetocrystalline anisotropy in FeRh/MgO bilayers,"Ultra-thin film of FeRh on insulator MgO substrate has been investigated
usingab-initio electronic structure calculations. From this calculation, we
have found the interesting effect of epitaxial strain on the magnetocrystalline
anisotropy (MCA). Analysis of the energy and k-resolved distribution of the
orbital character of the band structure reveals that MCA largely arises from
the spin-orbit coupling (SOC) between dx2-y2 andd xz,yz orbitals of Fe atoms at
the FeRh/MgO interface. We demonstrate that the strain has significant effects
on the MCA: It not only affects the value of the MCA but also induces a
switching of the magnetic easy axis from perpendicular to in-plane direction.
The mechanism is the strain-induced shifts of the SOC d-states. Our work
demonstrates that strain engineering can open a viable pathway towards
tailoring magnetic properties for antiferromagetic spintronic applications.",1908.04761v1
2019-08-06,Prediction magnetocrystalline anisotripy Fe-Rh thin films via machine leaning,"Least absolute shrinkage and selection operator (Lasso) was originally
formulated for least squares models and this simple case reveals a substantial
amount about the behavior of the estimator. It also shows that the coefficient
estimates need not be unique if covariates are collinear. Using this Lasso
technique, we analyze a magnetocrystalline anisotropy energy which is a
long-standing issue in transition-metal thin films, expectially for Fe-Rh thin
film systems on a MgO substrate. Our LASSO regression took advantage of the
data obtained from first principles calculations for single slabs with seven
atomic-layers of binary Fe-Rh films on MgO(001). In the case of Fe-Rh thin
films, we have successfully found a linear behavior between the MCA energy and
the anisotropy of orbital moments.",1908.04762v1
2019-11-26,Mapping Skyrmion Stability in Uniaxial Lacunar Spinel Magnets from First-Principles,"The identification of general principles for stabilizing magnetic skyrmion
phases in bulk materials over wide ranges of temperatures is a prerequisite to
the development of skyrmion-based spintronic devices. Lacunar spinels with the
formula GaM4X8 with M=V, Mo; X=S, Se are a convenient case study towards this
goal as they are some of the first bulk systems suggested to host equilibrium
chiral skyrmions far from the paramagnetic transition. We derive the magnetic
phase diagrams likely to be observed in these materials, accounting for all
possible magnetic interactions, and prove that skyrmion stability in the
lacunar spinels is a general consequence of their crystal symmetry rather than
the details of the material chemistry. Our results are consistent with all
experimental reports in this space and demonstrate that the differences in the
phase diagrams of particular spinel chemistries are determined by
magnetocrystalline anisotropy, up to a normalization factor. We conclude that
skyrmion formation over wide ranges of temperatures can be expected in all
lacunar spinels, as well as in a wide range of uniaxial systems with low
magnetocrystalline anisotropy.",1911.11297v2
2020-12-09,Spin-lattice model for cubic crystals,"We present a methodology based on the N\'{e}el model to build a classical
spin-lattice Hamiltonian for cubic crystals capable of describing magnetic
properties induced by the spin-orbit coupling like magnetocrystalline
anisotropy and anisotropic magnetostriction, as well as exchange
magnetostriction. Taking advantage of the analytical solutions of the N\'{e}el
model, we derive theoretical expressions for the parameterization of the
exchange integrals and N\'{e}el dipole and quadrupole terms that link them to
the magnetic properties of the material. This approach allows to build accurate
spin-lattice models with the desire magnetoelastic properties. We also explore
a possible way to model the volume dependence of magnetic moment based on the
Landau energy. This new feature can allow to consider the effects of
hydrostatic pressure on the saturation magnetization. We apply this method to
develop a spin-lattice model for BCC Fe and FCC Ni, and we show that it
accurately reproduces the experimental elastic tensor, magnetocrystalline
anisotropy under pressure, anisotropic magnetostrictive coefficients, volume
magnetostriction and saturation magnetization under pressure at
zero-temperature. This work could constitute a step towards large-scale
modeling of magnetoelastic phenomena.",2012.05076v3
2021-09-24,Impact of local arrangement of Fe and Ni on the phase stability and magnetocrystalline anisotropy in Fe-Ni-Al Heusler alloys,"On the basis of density functional calculations, we report on a comprehensive
study of the influences of atomic arrangement and Ni substitution for Al on the
ground state structural and magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$
Heusler alloys. We discuss systematically the competition between five
Heusler-type structures formed by shuffles of Fe and Ni atoms and their
thermodynamic stability. All~Ni-rich Fe$_2$Ni$_{1+x}$Al$_{1-x}$ tend to
decompose into a dual-phase mixture consisting of Fe$_2$NiAl and~FeNi.
The~successive replacement of Ni by Al leads to a change of ground state
structure and eventually an increase in magnetocrystalline anisotropy
energy~(MAE). We predict for stoichiometric Fe$_2$NiAl a ground state structure
with nearly cubic lattice parameters but alternating layers of Fe and Ni
possessing an uniaxial MAE which is even larger than tetragonal L1$_0$-FeNi.
This opens an alternative route for improving the phase stability and magnetic
properties in FeNi-based permanent magnets.",2109.12005v2
2022-03-22,A strategic high throughput search for identifying stable Li based half Heusler alloys for spintronics applications,"In this work, high throughput DFT calculations are performed on the alkali
metal-based half Heusler alloys; LiY$_p$Y$^\prime_{1-p}$S (Y, Y$^\prime$ = V,
Cr, Mn, Fe, Co, Ni and $\mathit{p}$ = 0, 0.25, 0.5, 0.75, 1). Starting with 243
structural replica, systematic filters are designed to select the energetically
and vibrationally favorable compositions by considering the contributions
stemming from the magnetic alignments of the ions. Thereby, 26 dynamically
stable magnetic compositions are identified, of which 10 are found to be
ferromagnetic (FM), 4 antiferromagnetic (AFM) and 12 ferrimagnetic (FiM). 4 FM
and 8 FiM ones are found to show 100 $\%$ spin polarization. Further,
tetragonal distortion is found to be present in 4 FM, 3 FiM and 4 AFM
compositions, which indicates the possibility of easy-axis magnetocrystalline
anisotropy. The ferromagnetic LiFe$_{0.5}$Mn$_{0.5}$S and antiferromagnetic
LiFeS are found to have the most prominent easy-axis magnetocrystalline
anisotropy.",2203.11794v1
2022-09-18,Magnetocrystalline Anisotropy and Magnetocaloric Effect Studies on the Room-temperature 2D Ferromagnetic Cr$_4$Te$_5$,"We present a thorough study on the magnetoanisotropic properties and
magnetocaloric effect in the layered ferromagnetic Cr$_4$Te$_5$ single crystals
by performing the critical behaviour analysis of magnetization isotherms. The
critical exponents $\beta$=0.485(3), $\gamma$=1.202(5), and $\delta$=3.52(3)
with a Curie temperature of $T_C \approx 340.73(4)$ K are determined by the
modified Arrott plots. We observe a large magnetocrystalline anisotropy
K$_u$=330 kJ/$m^3$ at 3 K which gradually decreases with increasing
temperature. Maximum entropy change -$\Delta S_{M}^{max}$ and the relative
cooling power (RCP) are found to be 2.77 $J/kg-K$ and 88.29 $J/kg$,
respectively near $T_C$ when the magnetic field applied parallel to
$\it{ab}$-plane. Rescaled -$\Delta S_M (T, H)$ data measured at various
temperatures and fields collapse into a single universal curve, confirming the
second order magnetic transition in this system. Following the renormalization
group theory analysis, we find that the spin-coupling is of 3D Heisenberg-type,
$\{d:n\}=\{3:3\}$, with long-range exchange interactions decaying as $J (r) =
r^{-(d+\sigma)}= r^{-4.71}$.",2209.08477v1
2023-06-09,Finite-temperature second-order perturbation analysis of magnetocrystalline anisotropy energy of L10-type ordered alloys,"We present a novel finite-temperature second-order perturbation method
incorporating spin-orbit coupling to investigate the temperature-dependent
site-resolved contributions to the magnetocrystalline anisotropy energy (MAE),
specifically K1(T), in FePt, MnAl, and FeNi alloys. Our developed method
successfully reproduces the results obtained using the force theorem from our
previous work. By employing this method, we identify the key sites responsible
for the distinctive behaviors of MAE in these alloys, shedding light on the
inadequacy of the spin model in capturing the temperature dependence of MAE in
itinerant magnets. Moreover, we explore the lattice expansion effect on the
temperature dependence of on-site contributions to K1(T) in FeNi. Our results
not only provide insights into the limitations of the spin model in explaining
the temperature dependence of MAE in itinerant ferromagnets but also highlight
the need for further investigations. These findings contribute to a deeper
understanding of the complex nature of MAE in itinerant magnetic systems.",2306.05681v1
2023-09-12,Predicting synthesizable manganese nitride with unprecedentedly giant magnetocrystalline anisotropy energy,"Using modern crystal structure prediction program (CALYPSO), we searched many
experimentally synthesizable low-energy structures with perfect or nearly
perfect easy-axis magnetocrystalline anisotropy energy (MAE) in manganese
nitride, including MnN, Mn2N, Mn3N2, Mn5N2, Mn4N, respectively, which are the
more frequently studied stoichiometries by experimental researchers. MnN (
I-42d) shows giant MAE with values of E001=1006, E010=0, E100=920 ueV/atom
(same hereinafter), respectively. One perfect easy-axis MAE in Mn3N2 (P42/mmc)
with correspondent values of E010=E100=12 is observed, the other nearly perfect
easy-axis MAE one (Ibam) with respective values of E001=324 and E010=345 is
observed. Four almost totally perfect easy-axis MAE structures are obtained in
Mn2N, including P4/mmm with individual E001=249 and E100=250, Pccm with
E001=E100=62, P4/nmm with E001=58 and E100=60, Imma with E001=108 and E100=109,
respectively. Three structures including one perfect candidates are found in
Mn4N, including Fmmm with individual E001=126 and E010=121, I4/mmm with
E010=127 and E100=133, I4/mmm with E001= E100=169, respectively. Too many
valuable structures are deserved to be further studied by both theoretical and
experimental scientists. The present study might attract close attention to
these several compounds.",2309.06110v1
2023-09-16,Investigation of the Anomalous and Topological Hall Effects in Layered Monoclinic Ferromagnet Cr$_{2.76}$Te$_4$,"We studied the electrical transport, Hall effect, and magnetic properties of
monoclinic layered ferromagnet Cr$_{2.76}$Te$_4$. Our studies demonstrate
Cr$_{2.76}$Te$_4$ to be a soft ferromagnet with strong magnetocrystalline
anisotropy. Below 50 K, the system shows an antiferromagnetic-like transition.
Interestingly, between 50 and 150 K, we observe fluctuating magnetic moments
between in-plane and out-of-plane orientations, leading to non-coplanar spin
structure. On the other hand, the electrical resistivity data suggest it to be
metallic throughout the measured temperature range, except a $kink$ at around
50 K due to AFM ordering. The Rhodes-Wohlfarth ratio
$\frac{\mu_{eff}}{\mu_{s}}=1.89 (>1)$ calculated from our magnetic studies
confirms that Cr$_{2.76}$Te$_4$ is an itinerant ferromagnet. Large anomalous
Hall effect has been observed due to the skew-scattering of impurities and the
topological Hall effect has been observed due to non-coplanar spin-structure in
the presence of strong magnetocrystalline anisotropy. We examined the mechanism
of anomalous Hall effect by employing the first principles calculations.",2309.08898v1
2024-03-21,Magnetocrystalline anisotropy in metallic systems: fast and stable estimation in Green`s functions formalism,"In this work we suggest a theoretical approach, that allows to study the
effects of magnetocrystalline anisotropy (MCA) in metallic systems using the
Green`s functions formalism. We demonstrate that employment of the reciprocal
space resolution instead of its reduction in the inter-site variant essentially
improves the numerical stability of MCA energy by means of Monkhorst-Pack grid
density and spatial convergence. The latter problem is able to be completely
removed due to rigorous analytical replacement of pairwise atomic summation by
simple composition of sublattices contributions, calculated as a whole. The
approach is validated on the effective model of single atom, which nevertheless
inherits the qualitative MCA picture of Co monolayer and Au/Co/Au sandwiched
material. The numerical convergence is confirmed using the model of atomic
chain in the strong metallic regime. For cobalt monoxide, described by ab
initio calculations using GGA+U, the MCA energy angular profile reveals the
prevailing role of ferromagnetically aligned Co sublattices in forming of the
easy axis.",2403.14241v1
2003-11-14,Large anisotropy in the paramagnetic susceptibility of SrRuO3 films,"By using the extraordinary Hall effect in SrRuO3 films we performed sensitive
measurements of the paramagnetic susceptibility in this itinerant ferromagnet,
from Tc (~ 150 K) to 300 K. These measurements, combined with measurements of
magnetoresistance, reveal that the susceptibility, which is almost isotropic at
300 K, becomes highly anisotropic as the temperature is lowered, diverging
along a single crystallographic direction in the vicinity of Tc. The results
provide a striking manifestation of the effect of exceptionally large
magnetocrystalline anisotropy in the paramagnetic state of a 4d itinerant
ferromagnet.",0311341v1
2011-08-12,Magnetic anisotropy of FePt: effect of lattice distortion and chemical disorder,"We perform first principles calculations of the magnetocrystalline anisotropy
energy in the five L10 FePt samples studied experimentally by Ding et al. [J.
App. Phys. 97, 10H303 (2005)]. The effect of temperature-induced spin
fluctuations is estimated by scaling the MAE down according to previous
Langevin dynamics simulations. Including chemical disorder as given in
experiment, the experimental correlation between MAE and lattice mismatch is
qualitatively well reproduced. Moreover we determine the chemical order
parameters that reproduce exactly the experimental MAE of each sample. We
conclude that the MAE is determined by the chemical disorder rather than by
lattice distortion.",1108.2572v1
2013-01-17,Imaging the antiferromagnetic to ferromagnetic first order phase transition of FeRh,"The antiferromagnetic (AFM) to ferromagnetic (FM) first order phase
transition of an epitaxial FeRh thin-film has been studied with x-ray magnetic
circular dichroism using photoemission electron microscopy. The FM phase is
magnetized in-plane due to shape anisotropy, but the magnetocrystalline
anisotropy is negligible and there is no preferred in-plane magnetization
direction. When heating through the AFM to FM phase transition the nucleation
of the FM phase occurs at many independent nucleation sites with random domain
orientation. The domains subsequently align to form the final FM domain
structure. We observe no pinning of the FM domain structure.",1301.4164v1
2013-04-19,First Principles Calculation of Magnetocrystalline Anisotropy Energy of MnBi and MnB_{1-x}Sn_x,"We calculated the magnetic anisotropy constant Ku of MnBi using a first
principles approach, and obtained a negative Ku in agreeable with experimental
results. Furthermore, we also found a band filling dependence indicating that a
slight decrease in the valence electron number will change Ku from negative to
positive. When some of the Bi is replaced with Sn to decrease the valence
electron number, the Ku value of MnBi1-xSnx drastically changes to a positive
value, Ku~2 MJ/m3, for x > 0.05.",1304.5307v1
2013-07-10,Magnetocrystalline Anisotropy and the Magnetocaloric Effect in Fe2P,"Magnetic and magnetocaloric properties of high-purity, giant magnetocaloric
polycrystalline and single-crystalline Fe2P are investigated. Fe2P displays a
moderate magnetic entropy change which spans over 70 K and the presence of
strong magnetization anisotropy proves this system is not fully itinerant but
displays a mix of itinerant and localized magnetism. The properties of pure
Fe2P are compared to those of giant magnetocaloric (Fe,Mn)2(P,A) compounds
helping understand the exceptional characteristics shown by the latter which
are so promising for heat pump and energy conversion applications.",1307.2784v1
2014-05-22,Improvement of magnetic hardness at finite temperatures: ab initio disordered local moment approach for YCo$_5$,"Temperature dependence of the magnetocrystalline anisotropy energy and
magnetization of the prototypical rare-earth magnet YCo$_5$ is calculated from
first principles, utilizing the relativistic disordered local moment approach.
We discuss a strategy to enhance the finite-temperature anisotropy field by
hole doping, paving the way for an improvement of the coercivity near room
temperature or higher.",1405.5673v2
2007-05-20,Anisotropy and magnetization reversal with chains of submicron-sized Co hollow spheres,"Magnetic properties with chains of hcp Co hollow spheres have been studied.
The diameter of the spheres ranges from 500 to 800 nm, with a typical shell
thickness of about 60 nm. The shell is polycrystalline with an average
crystallite size of 20 to 35 nm. The blocking temperature determined by the
zero-field-cooling MZFC(T) measurement at H = 90 Oe is about 325 K. The
corresponding effective anisotropy is determined as, Keff = 4.6*10^4 J/m^3. In
addition, the blocking temperature and the effective anisotropy determined by
the analysis on HC(T) are 395 K and 5.7*10^4 J/m^3, respectively. The
experimentally determined anisotropy is smaller by one order of magnitude than
the magnetocrystalline anisotropy of the bulk hcp Co, which is about 3 to
5*10^5 J/m^3. A further analysis on HC(T) shows that the magnetization reversal
follows a nucleation rotational mode with an effective switching volume, V* =
2.3*10^3 nm^3. The corresponding effective diameter is calculated as 16.4 nm.
It is slightly larger than the coherence length of Co, about 15 nm. The
possible reason for the much reduced magnetic anisotropy is discussed briefly.",0705.2870v1
2010-09-04,Uniaxial contribution to the magnetic anisotropy of La0.67Sr0.33MnO3 thin films induced by orthorhombic crystal structure,"La0.67Sr0.33MnO3 (LSMO) thin films under compressive strain have an
orthorhombic symmetry with (1-10)o and (001)o in-plane orientations. (The
subscript o denotes the orthorhombic symmetry.) Here, we grew LSMO on cubic
(LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrates and observed a uniaxial
contribution to the magnetic anisotropy which is related to the orthorhombic
crystal structure. Since the lattice mismatch is equal in the two directions,
the general understanding of anisotropy in LSMO, which relates the uniaxial
anisotropy to differences in strain, cannot explain the results. These findings
suggest that the oxygen octahedra rotations associated with the orthorhombic
structure, possibly resulting in different Mn-O-Mn bond angles and therefore a
change in magnetic coupling between the [1-10]o and [001]o directions,
determine the anisotropy. We expect these findings to lead to a better
understanding of the microscopic origin of the magnetocrystalline anisotropy in
LSMO.",1009.0815v1
2017-02-17,Magnetic anisotropy in Permalloy: hidden quantum mechanical features,"By means of relativistic, first principles calculations, we investigate the
microscopic origin of the vanishingly low magnetic anisotropy of Permalloy,
here proposed to be intrinsically related to the local symmetries of the alloy.
It is shown that the local magnetic anisotropy of individual atoms in Permalloy
can be several orders of magnitude larger than that of the bulk sample, and
5-10 times larger than that of elemental Fe or Ni. We, furthermore, show that
locally there are several easy axis directions that are favored, depending on
local composition. The results are discussed in the context of perturbation
theory, applying the relation between magnetic anisotropy and orbital moment.
Permalloy keeps its strong ferromagnetic nature due to the exchange energy to
be larger than the magnetocrystalline anisotropy. Our results shine light on
the magnetic anisotropy of permalloy and of magnetic materials in general, and
in addition enhance the understanding of pump-probe measurements and ultrafast
magnetization dynamics.",1702.05414v1
2018-10-12,Room temperature biaxial magnetic anisotropy in La0.67Sr0.33MnO3 thin films on SrTiO3 buffered MgO (001) substrates for spintronic applications,"Spintronics exploits the magnetoresistance effects to store or sense the
magnetic information. Since the magnetoresistance strictly depends on the
magnetic anisotropy of the system, it is fundamental to set a defined
anisotropy to the system. Here, we investigate by means of vectorial
Magneto-Optical Kerr Magnetometry (v-MOKE), half-metallic La0.67Sr0.33MnO3
(LSMO) thin films that exhibit at room temperature pure biaxial magnetic
anisotropy if grown onto MgO (001) substrate with a thin SrTiO3 (STO) buffer.
In this way, we can avoid unwanted uniaxial magnetic anisotropy contributions
that may be detrimental for specific applications. The detailed study of the
angular evolution of the magnetization reversal pathways, critical fields
(coercivity and switching) allows for disclosing the origin of the magnetic
anisotropy, which is magnetocrystalline in nature and shows four-fold symmetry
at any temperature.",1810.05435v1
2019-08-30,"Magnetization reversal, damping properties and magnetic anisotropy of L10-ordered FeNi thin films","L10 ordered magnetic alloys such as FePt, FePd, CoPt and FeNi are well known
for their large magnetocrystalline anisotropy. Among these, L10-FeNi alloy is
economically viable material for magnetic recording media because it does not
contain rare earth and noble elements. In this work, L10-FeNi films with three
different strengths of anisotropy were fabricated by varying the deposition
process in molecular beam epitaxy system. We have investigated the
magnetization reversal along with domain imaging via magneto optic Kerr effect
based microscope. It is found that in all three samples, the magnetization
reversal is happening via domain wall motion. Further ferromagnetic resonance
(FMR) spectroscopy was performed to evaluate the damping constant and magnetic
anisotropy. It was observed that the FeNi sample with moderate strength of
anisotropy exhibits low value of damping constant ~ 4.9X10^-3. In addition to
this, it was found that the films possess a mixture of cubic and uniaxial
anisotropies.",1908.11761v1
2009-11-20,Magnetisation dynamics in exchange coupled spring systems with perpendicular anisotropy,"Magnetisation dynamics in exchange spring magnets have been studied using
simulations of the FePt/Fe bilayer system. The FePt hard layer exhibits strong
perpendicular magnetocrystalline anisotropy, while the soft (Fe) layer has
negligible magnetocrystalline anisotropy. The variation of the local spin
orientation in the Fe layer is determined by the competition of the exchange
coupling interaction with the hard layer and the magnetostatic energy which
favours in-plane magnetisation. Dynamics were studied by monitoring the
response of the Fe layer magnetisation after the abrupt application of a
magnetic field which causes the systems to realign via precessional motion.
This precessional motion allows us to obtain the frequency spectrum and hence
examine the dynamical magnetisation motion. Since the rotation of the spins in
the soft layer does not have a well defined magnetic anisotropy, the system
does not present the usual frequency field characteristics for a thin film.
Additionally we obtain multi-peaked resonance spectra for the application of
magnetic fields perpendicular to the film plane, though we discount the
existence of spin wave modes and propose that this arises due to variations in
the local effective field across the Fe layer. The dynamic response is only
considered in the Fe layer, with the FePt layer held fixed in the perpendicular
orientation.",0911.4137v2
2012-08-21,High temperature structural and magnetic properties of cobalt nanowires,"We present in this paper the structural and magnetic properties of high
aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in
situ X ray diffraction (XRD) and SQUID characterizations. We show that the
anisotropic shapes, the structural and texture properties are preserved up to
500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the
magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant
and Ms the saturation magnetization. Hc decreases linearly when the temperature
is increased due to the loss of the Co magnetocrystalline anisotropy
contribution. At 500K, 50% of the room temperature coercivity is preserved
corresponding to the shape anisotropy contribution only. We show that the
coercivity drop is reversible in the range 300 - 500 K in good agreement with
the absence of particle alteration. Above 525 K, the magnetic properties are
irreversibly altered either by sintering or by oxidation.",1208.4403v2
2014-07-06,Control of single-spin magnetic anisotropy by exchange coupling,"The properties of quantum systems interacting with their environment,
commonly called open quantum systems, can be strongly affected by this
interaction. While this can lead to unwanted consequences, such as causing
decoherence in qubits used for quantum computation, it can also be exploited as
a probe of the environment. For example, magnetic resonance imaging is based on
the dependence of the spin relaxation times of protons in water molecules in a
host's tissue. Here we show that the excitation energy of a single spin, which
is determined by magnetocrystalline anisotropy and controls its stability and
suitability for use in magnetic data storage devices, can be modified by
varying the exchange coupling of the spin to a nearby conductive electrode.
Using scanning tunnelling microscopy and spectroscopy, we observe variations up
to a factor of two of the spin excitation energies of individual atoms as the
strength of the spin's coupling to the surrounding electronic bath changes.
These observations, combined with calculations, show that exchange coupling can
strongly modify the magnetic anisotropy. This system is thus one of the few
open quantum systems in which the energy levels, and not just the excited-state
lifetimes, can be controllably renormalized. Furthermore, we demonstrate that
the magnetocrystalline anisotropy, a property normally determined by the local
structure around a spin, can be electronically tuned. These effects may play a
significant role in the development of spintronic devices5 in which an
individual magnetic atom or molecule is coupled to conducting leads.",1407.1542v1
2018-09-04,Enhanced perpendicular magnetocrystalline anisotropy energy in an artificial magnetic material with bulk spin-momentum coupling,"We systematically investigate the perpendicular magnetocrystalline anisotropy
(MCA) in Co$-$Pt/Pd-based multilayers. Our magnetic measurement data shows that
the asymmetric Co/Pd/Pt multilayer has a significantly larger perpendicular
magnetic anisotropy (PMA) energy compared to the symmetric Co/Pt and Co/Pd
multilayer samples. We further support this experiment by first principles
calculations on the CoPt$_2$, CoPd$_2$, and CoPtPd, which are composite bulk
materials that consist of three atomic layers in a unit cell, Pt/Co/Pt,
Pd/Co/Pd, Pt/Co/Pd, respectively. By estimating the contribution of bulk
spin-momentum coupling to the MCA energy, we show that the CoPtPd multilayer
with the symmetry breaking has a significantly larger perpendicular magnetic
anisotropy (PMA) energy than the other multilayers that are otherwise similar
but lack the symmetry breaking. This observation thus provides an evidence of
the PMA enhancement due to the structural inversion symmetry breaking and
highlights the asymmetric CoPtPd as the first artificial magnetic material with
bulk spin-momentum coupling, which opens a new pathway toward the design of
materials with strong PMA.",1809.00801v3
2022-09-09,Understanding magnetocrystalline anisotropy based on orbital and quadrupole moments,"Understanding magnetocrystalline anisotropy (MCA) is fundamentally important
for developing novel magnetic materials. Therefore, clarifying the relationship
between MCA and local physical quantities observed by spectroscopic
measurements, such as the orbital and quadrupole moments, is necessary. In this
review, we discuss MCA and the distortion effects in magnetic materials with
transition metals (TMs) based on the orbital and quadrupole moments, which are
related to the spin-conserving and spin-flip terms in the second-order
perturbation calculations, respectively. We revealed that orbital moment
stabilized the spin moment in the direction of the larger orbital moment, while
the quadrupole moment stabilized the spin moment along the longitudinal
direction of the spin-density distribution. The MCA of the magnetic materials
with TMs and their interfaces can be determined from the competition between
these two contributions. We showed that the perpendicular MCA of the
face-centered cubic (fcc) Ni with tensile tetragonal distortion arose from the
orbital moment anisotropy, whereas that of Mn-Ga alloys originated from the
quadrupole moment of spin density. In contrast, in the Co/Pd(111) multilayer
and Fe/MgO(001), both the orbital moment anisotropy and quadrupole moment of
spin density at the interfaces contributed to the perpendicular MCA.
Understanding the MCA of magnetic materials and interfaces based on orbital and
quadrupole moments is essential to design MCA of novel magnetic applications.",2209.04070v1
2023-07-28,Revisiting Néel 60 years on: the magnetic anisotropy of $\mathrm{L}1_0$ FeNi (tetrataenite),"The magnetocrystalline anisotropy energy of atomically ordered
$\mathrm{L}1_0$ FeNi (the meteoritic mineral tetrataenite) is studied within a
first-principles electronic structure framework. Two compositions are examined:
equiatomic Fe$_{0.5}$Ni$_{0.5}$ and an Fe-rich composition,
Fe$_{0.56}$Ni$_{0.44}$. It is confirmed that, for the single crystals modelled
in this work, the leading-order anisotropy coefficient $K_1$ dominates the
higher-order coefficients $K_2$ and $K_3$. To enable comparison with
experiment, the effects of both imperfect atomic long-range order and finite
temperature are included. While our computational results initially appear to
undershoot the measured experimental values for this system, careful scrutiny
of the original analysis due to N\'{e}el et al. [J. Appl. Phys. 35, 873 (1964)]
suggests that our computed value of $K_1$ is, in fact, consistent with
experimental values, and that the noted discrepancy has its origins in the
nanoscale polycrystalline, multivariant nature of experimental samples, that
yields much larger values of $K_2$ and $K_3$ than expected a priori. These
results provide fresh insight into the existing discrepancies in the literature
regarding the value of tetrataenite's uniaxial magnetocrystalline anisotropy in
both natural and synthetic samples.",2307.15470v2
2009-10-22,Interplay between the magnetic anisotropy contributions of Cobalt nanowires,"We report on the magnetic properties and the crystallographic structure of
the cobalt nanowire arrays as a function of their nanoscale dimensions. X-ray
diffraction measurements show the appearance of an in-plane HCP-Co phase for
nanowires with 50 nm diameter, suggesting a partial reorientation of the
magnetocrystalline anisotropy axis along the membrane plane with increasing
pore diameter. No significant changes in the magnetic behavior of the nanowire
system are observed with decreasing temperature, indicating that the effective
magnetoelastic anisotropy does not play a dominant role in the remagnetization
processes of individual nanowires. An enhancement of the total magnetic
anisotropy is found at room temperature with a decreasing nanowire
diameter-to-length ratio (d/L), a result that is quantitatively analyzed on the
basis of a simplified shape anisotropy model.",0910.4285v1
2010-09-08,Controllable modification of the anisotropy energy in Laves phase YFe2 by Ar+ ion implantation,"Implanted 3.25 keV Ar+ ions have been used to modify the in-plane bulk
anisotropy in thin films of epitaxially grown Laves phase YFe2. The magneto
optical Kerr effect, vibrating sample magnetometry and computational modeling
have been used to show that the dominant source of anisotropy changes from
magnetoelastic in as-grown samples to magnetocrystalline in ion implanted
samples. This change occurs at a critical fluence of order 1017 Ar+ ions cm-2.
The change in source of the anisotropy is attributed to a relaxation of the
strain inherent in the epitaxially grown thin-films. Atomic force microscopy
shows that the samples' topography remains unchanged after ion implantation.
The ability to control the dominant source of magnetic anisotropy without
affecting the sample surface could have important consequences in the
fabrication of patterned media for high use in density magnetic data storage
devices.",1009.1520v1
2014-11-10,Temperature evolution of the effective magnetic anisotropy in the MnCr$_2$O$_4$ spinel,"In this work we present a study of the low temperature magnetic phases of
polycrystalline MnCr$_2$O$_4$ spinel through dc magnetization and ferromagnetic
resonance spectroscopy (FMR). Through these experiments we determined the main
characteristic temperatures: T$_C$ $\sim$41 K and T$_H$ $\sim$18 K
corresponding, respectively, to the ferrimagnetic order and to the low
temperature helicoidal transitions. The temperature evolution of the system is
described by a phenomenological approach that considers the different terms
that contribute to the free energy density. Below the Curie temperature the FMR
spectra were modeled by a cubic magnetocrystalline anisotropy to the second
order, with $K_1$ and $K_2$ anisotropy constants that define the easy
magnetization axis along the <110> direction. At lower temperatures, the
formation of a helicoidal phase was considered by including uniaxial anisotropy
axis along the [1-10] propagation direction of the spiral arrange, with a $K_u$
anisotropy constant. The values obtained from the fittings at 5 K are
$K_1$=-2.3x10$^4$ erg/cm$^3$, $K^2$=6.4x10$^4$ erg/cm$^3$ and $K_u$=7.5x10$^4$
erg/cm$^3$.",1411.2461v1
2014-12-23,Tuning the magnetic anisotropy of single molecules,"The magnetism of single atoms and molecules is governed by the atomic scale
environment. In general, the reduced symmetry of the surrounding splits the $d$
states and aligns the magnetic moment along certain favorable directions. Here,
we show that we can reversibly modify the magnetocrystalline anisotropy by
manipulating the environment of single iron(II) porphyrin molecules adsorbed on
Pb(111) with the tip of a scanning tunneling microscope. When we decrease the
tip--molecule distance, we first observe a small increase followed by an
exponential decrease of the axial anisotropy on the molecules. This is in
contrast to the monotonous increase observed earlier for the same molecule with
an additional axial Cl ligand. We ascribe the changes in the anisotropy of both
species to a deformation of the molecules in the presence of the attractive
force of the tip, which leads to a change in the $d$ level alignment. These
experiments demonstrate the feasibility of a precise tuning of the magnetic
anisotropy of an individual molecule by mechanical control.",1412.7454v2
2015-11-24,Ferromagnetic Resonance of a YIG film in the Low Frequency Regime,"An improved method for characterizing the magnetic anisotropy of films with
cubic symmetry is described and is applied to an yttrium iron garnet (111)
film. Analysis of the FMR spectra performed both in-plane and out-of-plane from
0.7 to 8 GHz yielded the magnetic anisotropy constants as well as the
saturation magnetization. The field at which FMR is observed turns out to be
quite sensitive to anisotropy constants (by more than a factor ten) in the low
frequency (< 2 GHz) regime and when the orientation of the magnetic field is
nearly normal to the sample plane; the restoring force on the magnetization
arising from the magnetocrystalline anisotropy fields is then comparable to
that from the external field, thereby allowing the anisotropy constants to be
determined with greater accuracy. In this region, unusual dynamical behaviors
are observed such as multiple resonances and a switching of FMR resonance with
only a 1 degree change in field orientation at 0.7 GHz.",1511.07892v1
2016-10-10,Origin of magnetic anisotropy in doped Ce$_2$Co$_{17}$ alloys,"Magnetocrystalline anisotropy (MCA) in doped Ce$_{2}$Co$_{17}$ and other
competing structures was investigated using density functional theory. We
confirmed that the MCA contribution from dumbbell Co sites is very negative.
Replacing Co dumbbell atoms with a pair of Fe or Mn atoms greatly enhance the
uniaxial anisotropy, which agrees quantitatively with experiment, and this
enhancement arises from electronic-structure features near the Fermi level,
mostly associated with dumbbell sites. With Co dumbbell atoms replaced by other
elements, the variation of anisotropy is generally a collective effect and
contributions from other sublattices may change significantly. Moreover, we
found that Zr doping promotes the formation of 1-5 structure that exhibits a
large uniaxial anisotropy, such that Zr is the most effective element to
enhance MCA in this system.",1610.02767v2
2018-07-18,Controlled anisotropic dynamics of tightly bound skyrmions in a synthetic ferrimagnet due to skyrmion-deformation mediated by induced uniaxial in-plane anisotropy,"We study speed and skew deflection-angle dependence on skyrmion deformations
of a tightly bound two-skyrmion state in a synthetic ferrimagnet. We condsider
here, an in-plane uniaxial magnetocrystalline anisotropy-term in order to
induce lateral shape distortions and an overall size modulation of the
skyrmions due to a reduction of the effective out-of-plane anisotropy, thus
affecting the skyrmion speed, skew-deflection and inducing anisotropy in these
quantities with respect to the driving current-angle. Because of frustrated
dipolar interactions in a synthetic ferrimagnet, sizeable skyrmion deformations
can be induced with relatively small induced anisotropy constants and thus a
wide range of tuneability can be achieved. We also show analytically, that a
consequence of the skyrmion deformation can, under certain conditions cause a
skyrmion deflection with respect to driving-current angles, unrelated to the
topological charge. Results are analyzed by a combination of micromagnetic
simulations and a compound particle description within the Thiele-formalism
from which an over-all mobility tensor is constructed. This work offers an
additional path towards in-situ tuning of skyrmion dynamics.",1807.06884v2
2018-07-24,Impact of magnetic moment and anisotropy of Co$_\textrm{1-x}$Fe$_\textrm{x}$ thin films on the magnetic proximity effect of Pt,"We present a systematic study of the magnetic proximity effect in Pt,
depending on the magnetic moment and anisotropy of adjacent metallic
ferromagnets. Element-selective x-ray resonant magnetic reflectivity
measurements at the Pt absorption edge (11565$\,$eV) are carried out to
investigate the spin polarization of Pt in Pt/Co$_\textrm{1-x}$Fe$_\textrm{x}$
bilayers. We observe the largest magnetic moment of (0.72$\,\pm\,$0.03)$\,
\mu_\textrm{B}$ per spin polarized Pt atom in
Pt/Co$_\textrm{33}$Fe$_\textrm{67}$, following the Slater-Pauling curve of
magnetic moments in Co-Fe alloys. In general, a clear linear dependence is
observed between the Pt moment and the moment of the adjacent ferromagnet.
Further, we study the magnetic anisotropy of the magnetized Pt which clearly
adopts the magnetic anisotropy of the ferromagnet below. This is depicted for
Pt on Fe(001) and on Co$_\textrm{50}$Fe$_\textrm{50}$(001), which have a
45$^{\circ}$ relative rotation of the fourfold magnetocrystalline anisotropy.",1807.09032v2
2004-07-14,An ab-initio theoretical investigation of the soft-magnetic properties of permalloys,"We study Ni80Fe20-based permalloys with the relativistic spin-polarized
Korringa-Kohn-Rostoker electronic structure method. Treating the compositional
disorder with the coherent potential approximation, we investigate how the
magnetocrystalline anisotropy, K, and magnetostriction, lambda, of Ni-rich
Ni-Fe alloys vary with the addition of small amounts of non-magnetic transition
metals, Cu and Mo. From our calculations we follow the trends in K and lambda
and find the compositions of Ni-Fe-Cu and Ni-Fe-Mo where both are near zero.
These high permeability compositions of Ni-Fe-Cu and Ni-Fe-Mo match well with
those discovered experimentally. We monitor the connection of the magnetic
anisotropy with the number of minority spin electrons, Nmin. By raising Nmin
via artificially increasing the band-filling of Ni80Fe20, we are able to
reproduce the key features that underpin the magnetic softening we find in the
ternary alloys. The effect of band-filling on the dependence of
magnetocrystalline anisotropy on atomic short-range order in Ni80Fe20 is also
studied. Our calculations, based on a static concentration wave theory,
indicate that the susceptibility of the high permeability of the Ni-Fe-Cu and
Ni-Fe-Mo alloys to their annealing conditions is also strongly dependent on the
alloys' compositions. An ideal soft magnet appears from these calculations.",0407355v1
2013-12-30,"Ground state search, hysteretic behaviour, and reversal mechanism of skyrmionic textures in confined helimagnetic nanostructures","Magnetic skyrmions have the potential to provide solutions for low-power,
high-density data storage and processing. One of the major challenges in
developing skyrmion-based devices is the skyrmions' magnetic stability in
confined helimagnetic nanostructures. Through a systematic study of equilibrium
states, using a full three-dimensional micromagnetic model including
demagnetisation effects, we demonstrate that skyrmionic textures are the lowest
energy states in helimagnetic thin film nanostructures at zero external
magnetic field and in absence of magnetocrystalline anisotropy. We also report
the regions of metastability for non-ground state equilibrium configurations.
We show that bistable skyrmionic textures undergo hysteretic behaviour between
two energetically equivalent skyrmionic states with different core orientation,
even in absence of both magnetocrystalline and demagnetisation-based shape
anisotropies, suggesting the existence of Dzyaloshinskii-Moriya-based shape
anisotropy. Finally, we show that the skyrmionic texture core reversal dynamics
is facilitated by the Bloch point occurrence and propagation.",1312.7665v3
2014-03-17,Second-order Perturbation Formula for Magnetocrystalline Anisotropy using Orbital Angular Momentum Matrix,"We derive a second-order perturbation formula for an electronic system
subject to spin-orbit interactions (SOI). The energy correction originates in
the spin-conserving and the spin-flip transitions. The former are represented
by the orbital angular momentum (OAM) acquired via the SOI. The latter come
from the quantum fluctuation effect. By using our formula, we examine the
relativistic electronic structures of a d orbital chain and L1_0 alloys. The
appearance of OAM in the chain is understood by using a parabolic-bands model
and the exact expressions of the single-particle states. The total energy is
found to be accurately reproduced by the formula. The self-consistent fully
relativistic first-principles calculations based on the density functional
theory are performed for five L1_0 alloys. It is found that the formula
reproduces qualitatively the behavior of their exact magnetocrystalline
anisotropy (MCA) energies. While the MCA of FePt, CoPt, and FePd originates in
the spin-conserving transitions, that in MnAl and MnGa originates in the
spin-flip contributions. For FePt, CoPt, and FePd, the tendency of the MCA
energy with the variation in the lattice constant obeys basically that of the
spin-flip contributions. These results indicate that not only the anisotropy of
OAM, but also that of spin-flip contributions must be taken into account for
the understanding of the MCA of the L1_0 alloys.",1403.3987v1
2016-11-22,Uranium ferromagnet with negligible magnetocrystalline anisotropy - $\mathrm{U_{4}Ru_{7}Ge_{6}}$,"Strong magnetocrystalline anisotropy is a well-known property of uranium
compounds. The almost isotropic ferromagnetism in $\mathrm{U_{4}Ru_{7}Ge_{6}}$
reported in this paper represents a striking exception. We present results of
magnetization, AC susceptibility, thermal expansion, specific heat and
electrical resistivity measurements performed on a $\mathrm{U_{4}Ru_{7}Ge_{6}}$
single crystal at various temperatures and magnetic fields and discuss them in
conjunction with results of first-principles electronic-structure calculations.
$\mathrm{U_{4}Ru_{7}Ge_{6}}$ behaves as an itinerant 5$f$-electron ferromagnet
($T_{\mathrm{C}}= 10.7 K$, $\mu_{\mathrm{S}}= 0.85 \mu_{\mathrm{B}}/f.u.$ at
1.9 K. The ground-state easy-magnetization direction is along the [111] axis of
the cubic lattice. The anisotropy field $\mu_{0}H_{\mathrm{a}}$ along the [001]
direction is only of $\sim0.3 T$, which is at least 3 orders of magnitude
smaller value than in other U ferromagnets. At $T_{r}=5.9 K$ the easy
magnetization direction changes for [001] which holds at temperatures up to
$T_{\mathrm{C}}$. The magnetoelastic interaction induces a rhombohedral
(tetragonal) distortion of the paramagnetic cubic crystal lattice in case of
the [111]([001]) easy-magnetization direction. The rhombohedral distortion is
connected with two crystallographically inequivalent U sites. The ab initio
calculated ground-state magnetic moment of $1.01 \mu_{\mathrm{B}}/f.u.$ is
oriented along [111]. The two crystallographically inequivalent U sites are a
consequence of spin-orbit coupling of the U 5$f$-electrons. In the excited
state which is only 0.9 meV above the ground state the moment points to the
[001] direction in agreement with experiment.",1611.07335v1
2016-12-20,Magnetocrystalline anisotropy of Laves phase Fe$_2$Ta$_{1-x}$W$_x$ from first principles - the effect of 3d-5d hybridisation,"The magnetic properties of Fe$_2$Ta and Fe$_2$W in the hexagonal Laves phase
are computed using density functional theory in the generalised gradient
approximation, with the full potential linearised augmented plane wave method.
The alloy Fe$_2$Ta$_{1-x}$W$_x$ is studied using the virtual crystal
approximation to treat disorder. Fe$_2$Ta is found to be ferromagnetic with a
saturation magnetization of $\mu_0 M_\text{s} = 0.66~\mathrm{T}$ while, in
contrast to earlier computational work, Fe$_2$W is found to be ferrimagnetic
with $\mu_0 M_\text{s} = 0.35~\mathrm{T}$. The transition from the ferri- to
the ferromagnetic state occurs for $x \leq 0.1$. The magnetocrystalline
anisotropy energy (MAE) is calculated to $1.25~\mathrm{MJ/m^3}$ for Fe$_2$Ta
and $0.87~\mathrm{MJ/m^3}$ for Fe$_2$W. The MAE is found to be smaller for all
values $x$ in Fe$_2$Ta$_{1-x}$W$_x$ than for the end compounds and it is
negative (in-plane anisotropy) for $0.1 \leq x \leq 0.9$. The MAE is carefully
analysed in terms of the electronic structure. Even though there are weak 5d
contributions to the density of states at the Fermi energy in both end
compounds, a reciprocal space analysis, using the magnetic force theorem,
reveals that the MAE originates mainly from regions of the Brillouin zone with
strong 3d-5d hybridisation near the Fermi energy. Perturbation theory and its
applicability in relation to the MAE is discussed.",1612.06802v1
2019-04-10,Optical excitation of propagating magnetostatic waves in an epitaxial Galfenol film by an ultrafast magnetic anisotropy change,"Using a time-resolved optically-pumped scanning optical microscopy technique
we demonstrate the laser-driven excitation and propagation of spin waves in a
20-nm film of a ferromagnetic metallic alloy Galfenol epitaxially grown on a
GaAs substrate. In contrast to previous all-optical studies of spin waves we
employ laser-induced thermal changes of magnetocrystalline anisotropy as an
excitation mechanism. A tightly focused 70-fs laser pulse excites packets of
magnetostatic surface waves with a $e^{-1}$ propagation length of 3.4 $\mu$m,
which is comparable with that of permalloy. As a result, laser-driven
magnetostatic spin waves are clearly detectable at distances up to 10 $\mu$m,
which promotes epitaxial Galfenol films to the limited family of materials
suitable for magnonic devices. A pronounced in-plane magnetocrystalline
anisotropy of the Galfenol film offers an additional degree of freedom for
manipulating the spin waves' parameters. Reorientation of an in-plane external
magnetic field relative to the crystallographic axes of the sample tunes the
frequency, amplitude and propagation length of the excited waves.",1904.05171v2
2021-01-10,Magnetic anisotropy in van-der-Waals ferromagnet VI3,"A comprehensive study of magnetocrystalline anisotropy of a layered
van-der-Waals ferromagnet VI3 was performed. We measured angular dependences of
the torque and magnetization with respect to the direction of the applied
magnetic field within the ""ac"" plane perpendicular to and within the basal ab
plane, respectively. A two-fold butterfly-like signal was detected by
magnetization in the perpendicular ""ac"" plane. This signal symmetry remains
conserved throughout all magnetic regimes as well as through the known
structural transition down to the lowest temperatures. The maximum of the
magnetization signal and the resulting magnetization easy axis is significantly
tilted from the principal c axis by ~40{\deg}. The close relation of the
magnetocrystalline anisotropy to the crystal structure was documented. In
contrast, a two-fold-like angular signal was detected in the paramagnetic
region within the ab plane in the monoclinic phase, which transforms into a
six-fold-like signal below the Curie temperature TC. With further cooling,
another six-fold-like signal with an angular shift of ~30{\deg} grows
approaching TFM. Below TFM, in the triclinic phase, the original six-fold-like
signal vanishes, being replaced by a secondary six-fold-like signal with an
angular shift of ~30{\deg}.",2101.03542v1
2022-04-15,"First-principles Calculation of Magnetocrystalline Anisotropy of Y(Co,Fe,Ni,Cu)$_5$ Based on Full-potential KKR Green's Function Method","The performance of permanent magnets YCo$_5$ can be improved by replacing
cobalt with other elements, such as iron, copper, and nickel. In order to
determine its optimum composition, it is necessary to perform systematic
theoretical calculations in a consistent framework. In this study, we
calculated the magnetocrystalline anisotropy constant $K_{\rm u}$ of
Y(Co$_{1-x-y}$Fe$_{x}$Cu$_{y}$)$_3$(Co$_{1-z}$Ni$_{z}$)$_2$ on the basis of the
full-potential Korringa-Kohn-Rostoker Green's function method in conjunction
with the coherent potential approximation. The calculated $K_{\rm u}$ of
YCo$_5$ was smaller than the experimental value because of a missing
enhancement due to orbital polarization. Although the value of $K_{\rm u}$ of
Y(Co$_{1-x-y}$Fe$_{x}$Cu$_{y}$)$_3$(Co$_{1-z}$Ni$_{z}$)$_2$ was systematically
underestimated compared to their experimental counterparts, the doping effect
can be analyzed within a consistent framework. The results have shown that
YFe$_3$Co$_2$ has much higher $K_{\rm u}=5.00$ MJ/m$^3$ than pristine YCo$_5$
($K_{\rm u}=1.82$ MJ/m$^3$), and that nickel as a stabilization element
decreases $K_{\rm u}$ and magnetization in YFe$_3$(Co$_{1-z}$Ni$_z$)$_2$.
However, the anisotropy field of $z\sim0.5$ can compete with the value of
YCo$_5$.",2204.07384v1
2006-01-04,Prospect for room temperature tunneling anisotropic magnetoresistance effect: density of states anisotropies in CoPt systems,"Tunneling anisotropic magnetoresistance (TAMR) effect, discovered recently in
(Ga,Mn)As ferromagnetic semiconductors, arises from spin-orbit coupling and
reflects the dependence of the tunneling density of states in a ferromagnetic
layer on orientation of the magnetic moment. Based on ab initio relativistic
calculations of the anisotropy in the density of states we predict sizable TAMR
effects in room-temperature metallic ferromagnets. This opens prospect for new
spintronic devices with a simpler geometry as these do not require
antiferromagnetically coupled contacts on either side of the tunnel junction.
We focus on several model systems ranging from simple hcp-Co to more complex
ferromagnetic structures with enhanced spin-orbit coupling, namely bulk and
thin film L1$_0$-CoPt ordered alloys and a monatomic-Co chain at a Pt surface
step edge. Reliability of the predicted density of states anisotropies is
confirmed by comparing quantitatively our ab initio results for the
magnetocrystalline anisotropies in these systems with experimental data.",0601071v1
2009-04-06,"Magneto crystalline anisotropies in (Ga,Mn)As: A systematic theoretical study and comparison with experiment","We present a theoretical survey of magnetocrystalline anisotropies in
(Ga,Mn)As epilayers and compare the calculations to available experimental
data. Our model is based on an envelope function description of the valence
band holes and a spin representation for their kinetic-exchange interaction
with localised electrons on Mn ions, treated in the mean-field approximation.
For epilayers with growth induced lattice-matching strains we study in-plane to
out-of-plane easy-axis reorientations as a function of Mn local-moment
concentration, hole concentration, and temperature. Next we focus on the
competition of in-plane cubic and uniaxial anisotropies. We add an in-plane
shear strain to the effective Hamiltonian in order to capture measured data in
bare, unpatterned epilayers, and we provide microscopic justification for this
approach. The model is then extended by an in-plane uniaxial strain and used to
directly describe experiments with strains controlled by postgrowth lithography
or attaching a piezo stressor. The calculated easy-axis directions and
anisotropy fields are in semiquantitative agreement with experiment in a wide
parameter range.",0904.0993v1
2015-09-14,From soft to hard magnetic Fe-Co-B by spontaneous strain: A combined first principle and thin film study,"In order to convert the well-known Fe-Co-B alloy from a soft to a hard
magnet, we propose tetragonal strain by interstitial boron. Density functional
theory reveals that when B atoms occupy octahedral interstitial sites, the bcc
Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is
predicted to reach a strong magnetocrystalline anisotropy which may compete
with shape anisotropy. Probing this theoretical suggestion experimentally,
epitaxial films are examined. A spontaneous strain up to 5 % lattice distortion
is obtained for B contents up to 4 at%, which leads to uniaxial anisotropy
constants exceeding 0.5 MJ/m^3. However, a further addition of B results in a
partial amorphization, which degrades both anisotropy and magnetization.",1509.04126v1
2015-10-19,Minimum Anisotropy of a Magnetic Nanoparticle out of Equilibrium,"In this article we study magnetotransport in single nanoparticles of Ni,
Py=Ni$_{0.8}$Fe$_{0.2}$, Co, and Fe, with volumes $15\pm 6$nm$^3$, using
sequential electron tunneling at 4.2K temperature. We measure current versus
magnetic field in the ensembles of nominally the same samples, and obtain the
abundances of magnetic hysteresis. The hysteresis abundance varies among the
metals as Ni:Py:Co:Fe=4\,:50\,:100\,:100(\%), in good correlation with the
magnetostatic and magnetocrystalline anisotropy. The abrupt change in the
hysteresis abundance among these metals suggests a concept of minimum magnetic
anisotropy required for magnetic hysteresis, which is found to be $\approx
13$meV. The minimum anisotropy is explained in terms of the residual
magnetization noise arising from the spin-orbit torques generated by sequential
electron tunneling. The magnetic hysteresis abundances are weakly dependent on
the tunneling current through the nanoparticle, which we attribute to current
dependent damping.",1510.05325v1
2016-03-11,Atomic-scale control of magnetic anisotropy via novel spin-orbit coupling effect in La2/3Sr1/3MnO3/SrIrO3 superlattices,"Magnetic anisotropy (MA) is one of the most important material properties for
modern spintronic devices. Conventional manipulation of the intrinsic MA, i.e.
magnetocrystalline anisotropy (MCA), typically depends upon crystal symmetry.
Extrinsic control over the MA is usually achieved by introducing shape
anisotropy or exchange bias from another magnetically ordered material. Here we
demonstrate a pathway to manipulate MA of 3d transition metal oxides (TMOs) by
digitally inserting non-magnetic 5d TMOs with pronounced spin-orbit coupling
(SOC). High quality superlattices comprised of ferromagnetic La2/3Sr1/3MnO3
(LSMO) and paramagnetic SrIrO3 (SIO) are synthesized with the precise control
of thickness at atomic scale. Magnetic easy axis reorientation is observed by
controlling the dimensionality of SIO, mediated through the emergence of a
novel spin-orbit state within the nominally paramagnetic SIO.",1603.03794v2
2018-08-03,Ferromagnetic resonance in thin films - cross-validation analysis of numerical solutions of Smit-Beljers equation. Application to GaMnAs,"(Dated: August 3, 2018) The new method of numerical analysis of experimental
ferromagnetic resonance (FMR) spectra in thin films is developed and applied to
(Ga,Mn)As thin films. Specifically, it starts with the finding of numerical
solutions of Smit-Beljers (SB) equation and continues with their subsequent
statistical analysis within the cross-validation (CV) approach taken from
machine learning techniques. As a result of this treatment, we are able to
reinterpret the available FMR experimental results in diluted ferromagnetic
semiconductor (Ga,Mn)As thin films with the resulting determination of
magnetocrystalline anisotropy constants. The outcome of CV analysis points out
that it is necessary to take into account terms describing the bulk cubic
anisotropy up to the fourth order to reproduce FMR experimental results for
(Ga,Mn)As correctly. This finding contradicts the wide-spread conviction in the
literature that only first order cubic anisotropy term is important in this
material. We also provide numerical values of these higher order cubic
anisotropy constants for (Ga,Mn)As thin films resulting from SB-CV approach.",1808.01347v1
2019-02-14,Vectorial observation of the spin Seebeck effect in epitaxial NiFe$_2$O$_4$ thin films with various magnetic anisotropy contributions,"We have developed a vectorial type of measurement for the spin Seebeck effect
(SSE) in epitaxial NiFe$_2$O$_4$ thin films which have been grown by pulsed
laser deposition on MgGa$_2$O$_4$ (MGO) with (001) and (011) orientation as
well as CoGa$_2$O$_4$ (011) (CGO), thus varying the lattice mismatch and
crystal orientation. We confirm that a large lattice mismatch leads to strain
anisotropy in addition to the magnetocrystalline anisotropy in the thin films
using vibrating sample magnetometry and ferromagnetic resonance measurements.
Moreover, we show that the existence of a magnetic strain anisotropy in
NiFe$_2$O$_4$ thin films significantly impacts the shape and magnitude of the
magnetic-field-dependent SSE voltage loops. We further demonstrate that
bidirectional field-dependent SSE voltage curves can be utilized to reveal the
complete magnetization reversal process, which establishes a vectorial
magnetometry technique based on a spin caloric effect.",1902.05384v2
2019-05-30,Predicting New Iron Garnet Thin Films with Perpendicular Magnetic Anisotropy,"Perpendicular magnetic anisotropy (PMA) is a necessary condition for many
spintronic applications like spin-orbit torques switching, logic and memory
devices. An important class of magnetic insulators with low Gilbert damping at
room temperature are iron garnets, which only have a few PMA types such as
terbium and samarium iron garnet. More and stable PMA garnet options are
necessary for researchers to be able to investigate new spintronic phenomena.
In this study, we predict 20 new substrate/magnetic iron garnet film pairs with
stable PMA at room temperature. The effective anisotropy energies of 10
different garnet films that are lattice-matched to 5 different commercially
available garnet substrates have been calculated using shape, magnetoelastic
and magnetocrystalline anisotropy terms. Strain type, tensile or compressive
depending on substrate choice, as well as the sign and the magnitude of the
magnetostriction constants of garnets determine if a garnet film may possess
PMA. We show the conditions in which Samarium, Gadolinium, Terbium, Holmium,
Dysprosium and Thulium garnets may possess PMA on the investigated garnet
substrate types. Guidelines for obtaining garnet films with low damping are
presented. New PMA garnet films with tunable saturation moment and field may
improve spin-orbit torque memory and compensated magnonic thin film devices.",1905.13042v1
2019-08-21,"Two-dimensional Ferromagnetic van der Waals CrX3 (X=Cl, Br, I) Monolayers with Enhanced Anisotropy and Curie Temperature","Among the recently widely studied van der Waals layered magnets CrX3 (X=Cl,
Br, I), CrCl3 monolayer (ML) is particularly puzzling as it is solely shown by
experiments to have an in-plane magnetic easy axis and, furthermore, all of
previous first-principles calculation results contradict this. Through
systematical first-principles calculations,we unveil that its in-plane shape
anisotropy that dominates over its weak perpendicular magnetocrystalline
anisotropy is responsible for the in-plane magnetic easy axis of CrCl3 ML. To
tune the in-plane ferromagnetism of CrCl3 ML into the desirable perpendicular
one, we propose substituting Cr with isovalent tungsten (W). We find that
CrWCl6 has a strong perpendicular magnetic anisotropy and a high Curie
temperature up to 76 K. Our work not only gives insight into understanding the
two-dimensional ferromagnetism of van der Waals MLs but also sheds new light on
engineering their performances for nanodevices.",1908.07710v2
2022-05-16,Magnetic neutron scattering from spherical nanoparticles with Neel surface anisotropy: Analytical treatment,"The magnetization profile and the related magnetic small-angle neutron
scattering cross section of a single spherical nanoparticle with Neel surface
anisotropy is analytically investigated. We employ a Hamiltonian that comprises
the isotropic exchange interaction, an external magnetic field, a uniaxial
magnetocrystalline anisotropy in the core of the particle, and the Neel
anisotropy at the surface. Using a perturbation approach, the determination of
the magnetization profile can be reduced to a Helmholtz equation with Neumann
boundary condition, whose solution is represented by an infinite series in
terms of spherical harmonics and spherical Bessel functions. From the resulting
infinite series expansion, we analytically calculate the Fourier transform,
which is algebraically related to the magnetic small-angle neutron scattering
cross section. The approximate analytical solution is compared to the numerical
solution using the Landau-Lifshitz equation, which accounts for the full
nonlinearity of the problem.",2205.07549v1
2022-06-02,Anisotropic Gigahertz Antiferromagnetic Resonances of the Easy-Axis van der Waals Antiferromagnet CrSBr,"We report measurements of antiferromagnetic resonances in the van der Waals
easy-axis antiferromagnet CrSBr. The interlayer exchange field and
magnetocrystalline anisotropy fields are comparable to laboratory magnetic
fields, allowing a rich variety of gigahertz-frequency dynamical modes to be
accessed. By mapping the resonance frequencies as a function of the magnitude
and angle of applied magnetic field we identify the different regimes of
antiferromagnetic dynamics. The spectra show good agreement with a
Landau-Lifshitz model for two antiferromagnetically-coupled sublattices,
accounting for inter-layer exchange and triaxial magnetic anisotropy. Fits
allow us to quantify the parameters governing the magnetic dynamics: at 5 K,
the interlayer exchange field is $\mu_0 H_E =$ 0.395(2) T, and the hard and
intermediate-axis anisotropy parameters are $\mu_0 H_c =$ 1.30(2) T and $\mu_0
H_a =$ 0.383(7) T. The existence of within-plane anisotropy makes it possible
to control the degree of hybridization between the antiferromagnetic resonances
using an in-plane magnetic field.",2206.01286v2
2022-08-04,Electric-field induced magnetic-anisotropy transformation to achieve spontaneous valley polarization,"Valleytronics has been widely investigated for providing new degrees of
freedom to future information coding and processing. Here, it is proposed that
valley polarization can be achieved by electric field induced magnetic
anisotropy (MA) transformation. Through the first-principle calculations, our
idea is illustrated by a concrete example of $\mathrm{VSi_2P_4}$ monolayer. The
increasing electric field can induce a transition of MA from in-plane to
out-of-plane by changing magnetic anisotropy energy (MAE) from negative to
positive value, which is mainly due to increasing magnetocrystalline anisotropy
(MCA) energy. The out-of-plane magnetization is in favour of spontaneous valley
polarization in $\mathrm{VSi_2P_4}$. Within considered electric field range,
$\mathrm{VSi_2P_4}$ is always ferromagnetic (FM) ground state. In a certain
range of electric field, the coexistence of semiconductor and out-of-plane
magnetization makes $\mathrm{VSi_2P_4}$ become a true ferrovalley (FV)
material. The anomalous valley Hall effect (AVHE) can be observed under
in-plane and out-of-plane electrical field in $\mathrm{VSi_2P_4}$. Our works
pave the way to design the ferrovalley material by electric field.",2208.02425v1
1995-08-25,Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets,"The spin-lattice relaxation time $\tau_{SL}$ is a key quantity both for the
dynamical response of ferromagnets excited by laser pulses and as the speed
limit of magneto-optical recording. Extending the theory for the electron
paramagnetic resonance of magnetic impurities to spin-lattice relaxation in
ferromagnetic rare earths we calculate $\tau_{SL}$ for Gd and find a value of
48 ps in very good agreement with time-resolved spin-polarized photoemission
experiments. We argue that the time scale for $\tau_{SL}$ in metals is
essentially given by the spin-orbit induced magnetocrystalline anisotropy
energy.",9508120v1
1998-08-21,Spin Reorientations Induced by Morphology Changes in Fe/Ag(001),"By means of magneto-optical Kerr effect we observe spin reorientations from
in-plane to out-of-plane and vice versa upon annealing thin Fe films on Ag(001)
at increasing temperatures. Scanning tunneling microscopy images of the
different Fe films are used to quantify the surface roughness. The observed
spin reorientations can be explained with the experimentally acquired roughness
parameters by taking into account the effect of roughness on both the magnetic
dipolar and the magnetocrystalline anisotropy.",9808236v1
1999-12-22,Observation of domain wall resistivity in $\rm SrRuO_3$,"$\rm SrRuO_3$ is an itinerant ferromagnet with $T_c \sim 150 \rm K$. When
$\rm SrRuO_3$ is cooled through $T_c$ in zero applied magnetic field, a stripe
domain structure appears whose orientation is uniquely determined by the large
uniaxial magnetocrystalline anisotropy. We find that the ferromagnetic domain
walls clearly enhance the resisitivity of $\rm SrRuO_3$ and that the
enhancement has different temperature dependence for currents parallel and
perpendicular to the domain walls. We discuss possible interpretations of our
results.",9912404v1
2006-05-31,"Spin injection from perpendicular magnetized ferromagnetic $δ$-MnGa into (Al,Ga)As heterostructures","Electrical spin injection from ferromagnetic $\delta$-MnGa into an (Al,Ga)As
p-i-n light emitting diode (LED) is demonstrated. The $\delta$-MnGa layers show
strong perpendicular magnetocrystalline anisotropy, enabling detection of spin
injection at remanence without an applied magnetic field. The bias and
temperature dependence of the spin injection are found to be qualitatively
similar to Fe-based spin LED devices. A Hanle effect is observed and
demonstrates complete depolarization of spins in the semiconductor in a
transverse magnetic field.",0606013v1
2006-07-17,Magnetic transition and magnetic structure of Sr4Ru3O10,"We have investigated the magnetic transition and magnetic structure of
triple-layered ruthenate Sr4Ru3O10 directly using neutron scattering
techniques. Only one ferromagnetic phase is observed, and previously proposed
antiferromagnetic phase transitions are ruled out. The complex anisotropic
magnetotransport, magnetization and in-plane metamagnetic behaviors of this
quasi two-dimensional (2D) material are most likely due to magnetic domain
processes with strong magnetocrystalline anisotropy and a strongly anisotropic
demagnetization factor.",0607428v1
2008-04-26,Spin-torque oscillator based on tilted magnetization of the fixed layer,"The spin torque oscillator (STO), where the magnetization of the fixed layer
is tilted out of the film plane, is capable of strong microwave signal
generation in zero magnetic field. Through numerical simulations of the
Landau-Lifshitz-Gilbert-Slonczewski equations, within a macro-spin
approximation, we study the microwave signal generation as a function of drive
current for two realistic tilt angles. The tilt magnetization of the fixed
layer can be achieved by using a material with high out-of-plane
magnetocrystalline anisotropy, such as L10 FePt.",0804.4213v1
2008-08-06,Surface Magnetoelectric Effect in Ferromagnetic Metal Films,"A surface magnetoelectric effect is revealed by density-functional
calculations that are applied to ferromagnetic Fe(001), Ni(001) and Co(0001)
films in the presence of external electric field. The effect originates from
spin-dependent screening of the electric field which leads to notable changes
in the surface magnetization and the surface magnetocrystalline anisotropy.
These results are of considerable interest in the area of
electrically-controlled magnetism and magnetoelectric phenomena.",0808.0841v1
2008-10-26,The magnetoresistance tensor of La(0.8)Sr(0.2)MnO(3),"We measure the temperature dependence of the anisotropic magnetoresistance
(AMR) and the planar Hall effect (PHE) in c-axis oriented epitaxial thin films
of La(0.8)Sr(0.2)MnO(3), for different current directions relative to the
crystal axes, and show that both AMR and PHE depend strongly on current
orientation. We determine a magnetoresistance tensor, extracted to 4th order,
which reflects the crystal symmetry and provides a comprehensive description of
the data. We extend the applicability of the extracted tensor by determining
the bi-axial magnetocrystalline anisotropy in our samples.",0810.4679v1
2011-01-05,Four-state nanomagnetic logic using multiferroics,"The authors show how to implement a 4-state universal logic gate (NOR) using
three strain-coupled magnetostrictive-piezoelectric multiferroic nanomagnets
(e.g. Ni/PZT) with biaxial magnetocrystalline anisotropy. Two of the
nanomagnets encode the 2-state input bits in their magnetization orientations
and the third nanomagnet produces the output bit via dipole interaction with
the input nanomagnets. A voltage pulse alternating between -0.2 V and +0.2 V is
applied to the PZT layer of the third nanomagnet and generates alternating
tensile and compressive stress in its Ni layer to produce the output bit, while
dissipating ~ 57,000 kT (0.24 fJ) of energy per gate operation.",1101.0980v1
2011-03-25,Temperature dependence of spin resonance in cobalt substituted NiZnCu ferrites,"Cobalt substitutions were investigated in Ni0.4Zn0.4Cu0.2Fe2O4 ferrites,
initial complex permeability was then measured from 1 MHz to 1 GHz. It appears
that cobalt substitution led to a decrease in the permeability and an increase
in the \mus\timesfr factor. As well, it gave to the permeability spectrum a
sharp resonance character. We also observed a spin reorientation occurring at a
temperature depending on the cobalt content. Study of the complex permeability
versus temperature highlighted that the most resonant character was obtained at
this temperature. This shows that cobalt contribution to second order
magnetocrystalline anisotropy plays a leading role at this temperature.",1103.5024v1
2011-11-27,Large Coercivity in Nanostructured Rare-earth-free MnxGa Films,"The magnetic hysteresis of MnxGa films exhibit remarkably large coercive
fields as high as 2.5 T when fabricated with nanoscale particles of a suitable
size and orientation. This coercivity is an order of magnitude larger than in
well-ordered epitaxial film counterparts and bulk materials. The enhanced
coercivity is attributed to the combination of large magnetocrystalline
anisotropy and ~ 50 nm size nanoparticles. The large coercivity is also
replicated in the electrical properties through the anomalous Hall effect. The
magnitude of the coercivity approaches that found in rare-earth magnets, making
them attractive for rare-earth-free magnet applications.",1111.6267v1
2013-07-09,Giant magnetostriction in Tb-doped Fe83Ga17 melt-spun ribbons,"Giant magnetostriction is achieved in the slightly Tb-doped Fe83Ga17
melt-spun ribbons. The tested average perpendicular magnetostriction is -886
ppm along the melt-spun ribbon direction in the Fe82.89Ga16.88Tb0.23 alloy. The
calculated parallel magnetostriction is 1772 ppm, more than 4 times as large as
that of binary Fe83Ga17 alloy. The enhanced magnetostriction should be
attributed to a small amount of Tb solution into the A2 matrix phase during
rapid solidification. The localized strong magnetocrystalline anisotropy of Tb
element is suggested to cause the giant magnetostriction.",1307.2385v1
2016-11-01,Spin-Mechanical Inertia in Antiferromagnet,"Angular momentum conservation has served as a guiding principle in the
interplay between spin dynamics and mechanical rotations. However, in an
antiferromagnet with vanishing magnetization, new fundamental rules are
required to properly describe spin-mechanical phenomena. Here we show that the
N\'eel order dynamics affects the mechanical motion of a rigid body by
modifying its inertia tensor in the presence of strong magnetocrystalline
anisotropy. This effect depends on temperature when magnon excitations are
considered. Such a spin-mechanical inertia can produce measurable consequences
at small scales.",1611.00100v3
2017-07-29,Thermodynamics of the SmCo5 compound doped with Fe and Ni: an ab initio study,"SmCo5 permanent magnets exhibit enormous uniaxial magnetocrystalline
anisotropy energy and have a high Curie temperature. However, a low energy
product presents a significant drawback in the performance of SmCo5 permanent
magnets. In order to increase the energy product in SmCo5, we propose
substituting fixed amount of cobalt with iron in a new magnet, SmFe3CoNi, where
inclusion of nickel metal makes this magnet thermodynamically stable. We
further discuss some basic theoretical magnetic properties of the SmCo5
compound.",1707.09447v1
2018-08-01,Long range dynamical coupling between magnetic adatoms mediated by a 2D topological insulator,"We study the spin excitation spectra and the dynamical exchange coupling
between iron adatoms on a Bi bilayer nanoribbon. We show that the topological
character of the edge states is preserved in the presence of the magnetic
adatoms. Nevertheless, they couple significantly to the edge spin currents, as
witnessed by the large and long-ranged dynamical coupling we obtain in our
calcula- tions. The large effective magnetocrystalline anisotropy of the
magnetic adatoms combined with the transport properties of the topologically
protected edge states make this system a strong candidate for implementation of
spintronics devices and quantum information and/or computation protocols.",1808.00347v1
2019-03-05,Electronic structure and magnetism of transition metal dihalides: bulk to monolayer,"Based on first-principles calculations, the evolution of the electronic and
magnetic properties of transition metal dihalides MX$_2$ (M= V, Mn, Fe, Co, Ni;
X = Cl, Br, I) is analyzed from the bulk to the monolayer limit. A variety of
magnetic ground states is obtained as a result of the competition between
direct exchange and superexchange. The results predict that FeX$_2$, NiX$_2$,
CoCl$_2$ and CoBr$_2$ monolayers are ferromagnetic insulators with sizable
magnetocrystalline anisotropies. This makes them ideal candidates for robust
ferromagnetism at the single layer level. Our results also highlight the
importance of spin-orbit coupling to obtain the correct ground state.",1903.01789v1
2019-11-08,Magnetic i-MXene: a new class of multifunctional two-dimensional materials,"Based on density functional theory calculations, we investigated the
two-dimensional in-plane ordered MXene (i-MXenes), focusing particularly on the
magnetic properties. It is observed that robust two-dimensional magnetism can
be achieved by alloying nonmagnetic MXene with magnetic transition metal atoms.
Moreover, both the magnetic ground states and the magnetocrystalline anisotropy
energy of the i-MXenes can be effectively manipulated by strain, indicating
strong piezomagnetic effect. Further studies on the transport properties reveal
that i-MXenes provide an interesting playground to realize large thermoelectric
response, antiferromagnetic topological insulator, and spin-gapless
semiconductors. Thus, i-MXenes are a new class of multifunctional
two-dimensional magnetic materials which are promising for future spintronic
applications.",1911.03470v1
2021-06-09,Unraveling the role of the magnetic anisotropy on thermoelectric response: a theoretical and experimental approach,"Magnetic anisotropies have key role to taylor magnetic behavior in
ferromagnetic systems. Further, they are also essential elements to manipulate
the thermoelectric response in Anomalous Nernst (ANE) and Longitudinal Spin
Seebeck systems (LSSE). We propose here a theoretical approach and explore the
role of magnetic anisotropies on the magnetization and thermoelectric response
of noninteracting multidomain ferromagnetic systems. The magnetic behavior and
the thermoelectric curves are calculated from a modified Stoner Wohlfarth model
for an isotropic system, a uniaxial magnetic one, as well as for a system
having a mixture of uniaxial and cubic magnetocrystalline magnetic
anisotropies. It is verified remarkable modifications of the magnetic behavior
with the anisotropy and it is shown that the thermoelectric response is
strongly affected by these changes. Further, the fingerprints of the energy
contributions to the thermoelectric response are disclosed. To test the
robustness of our theoretical approach, we engineer films having the specific
magnetic properties and compare directly experimental data with theoretical
results. Thus, experimental evidence is provided to confirm the validity of our
theoretical approach. The results go beyond the traditional reports focusing on
magnetically saturated films and show how the thermoelectric effect behaves
during the whole magnetization curve. Our findings reveal a promising way to
explore the ANE and LSSE effects as a powerful tool to study magnetic
anisotropies, as well as to employ systems with magnetic anisotropy as sensing
or elements in technological applications.",2106.05063v1
1999-03-19,Field dependence of the temperature at the peak of the ZFC magnetization,"The effect of an applied magnetic field on the temperature at the maximum of
the ZFC magnetization, $M_{ZFC}$, is studied using the recently obtained
analytic results of Coffey et al. (Phys. Rev. Lett. {\bf 80}(1998) 5655) for
the prefactor of the N\'{e}el relaxation time which allow one to precisely
calculate the prefactor in the N\'{e}el-Brown model and thus the blocking
temperature as a function of the coefficients of the Taylor series expansion of
the magnetocrystalline anisotropy. The present calculations indicate that even
a precise determination of the prefactor in the N\'{e}el-Brown theory, which
always predicts a monotonic decrease of the relaxation time with increasing
field, is insufficient to explain the effect of an applied magnetic field on
the temperature at the maximum of the ZFC magnetization. On the other hand, we
find that the non linear field-dependence of the magnetization along with the
magnetocrystalline anisotropy appears to be of crucial importance to the
existence of this maximum.",9903302v3
2007-03-29,Easy-plane magnetocrystalline anisotropy in the multi-step metamagnet CeIr3Si2,"Highly anisotropic properties of CeIr$_3$Si$_2$ have been observed by the
magnetization $M$($B$), electrical resistivity $\rho$, and specific heat
measurements on a single-crystalline sample. This compound with an orthorhombic
structure having zigzag chains of Ce ions along the a-axis undergos magnetic
transitions at 3.9 K and 3.1 K. At 0.3 K, metamagnetic transitions occur at
0.68 T and 1.3 T for $B$$//$$b$ and 0.75 T for $B$$//$$c$. Easy-plane
magnetocrystalline anisotropy is manifested as $M$($B//b$) $\cong$ $M$($B//c$)
$\cong$ 11$M$($B//a$) at $B$ = 5 T. Electrical resistivity is also anisotropic;
$\rho_{b}$ $\cong$ $\rho_{c}$ $\ge$ 2$\rho_{a}$. The magnetic part of $\rho$
exhibits a double-peak structure with maxima at 15 K and 250 K. The magnetic
entropy at $T$$\rm_{N1}$ = 3.9 K is a half of $R$ln2. These observations are
ascribable to the combination of the Kondo effect with $T$$\rm_{K}$ $\sim$ 20 K
and a strong crystal field effect. The analysis of $M$($B$) and paramagnetic
susceptibility revealed unusually large energy splitting of 500 K and 1600 K
for the two excited doublets, respectively.",0703776v1
2012-03-28,"Multifunctional L10-Mn1.5Ga films with ultrahigh coercivity, giant perpendicular magnetocrystalline anisotropy and large magnetic energy product","We present the fascinating magnetic properties in homogenous noble-metal-free
and rare-earth-free L10-Mn1.5Ga epitaxial films on GaAs (001), including
ultrahigh perpendicular coercivity remarkably tunable from 8.1 to 42.8 kOe,
giant perpendicular magnetocrystalline anisotropy with a maximum of 22.9
Merg/cc, easily controllable magnetization from 27.3 to 270.5 emu/cc, excellent
squareness exceeding 0.94 and large magnetic energy product up to 2.6 MGOe.
These magnificent room-temperature magnetic characteristics make our
L10-Mn1.5Ga films multifunctional as outstanding and cost-effective alternative
for not only perpendicular magnetic recording bits with areal density over 30
Tb inch-2 and thermal stability over 60 years, but variety of novel devices
with high magnetic-noise immunity and thermal stability like spin-torque MRAMs
and oscillators pillars below 5 nm in dimension, and giant magnetoresistance
sensors able to measure high fileds up to 42 kOe . Moreover, this kind of
materials can also be expected as permanent magnets for replacing the expensive
rare-earth magnets widely used today.",1203.6176v5
2012-05-24,Enhancing magnetocrystalline anisotropy of the Fe70Pd30 magnetic shape memory alloy by adding Cu,"Strained epitaxial growth provides the opportunity to understand the
dependence of intrinsic and extrinsic properties of functional materials at
frozen intermediate stages of a phase transformation. In this study, a
combination of thin film experiments and first-principles calculations yields
the binding energy and magnetic properties of tetragonal Fe70Pd30-xCux
ferromagnetic shape memory thin films with x = 0, 3, 7 and structures ranging
from bcc to beyond fcc (1.07<c/a_bct<1.57). We find that Cu enhances the
quality of epitaxial growth, while spontaneous polarisation and Curie
temperature are only moderately lowered as expected from our calculations.
Beyond c/a_bct>1.41 the samples undergo structural relaxations through adaptive
nanotwinning. For all tetragonal structures, we observe a significant increase
of the magnetocrystalline anisotropy constant K1, which reaches a maximum of
K1=-2.4*10^5 Jm^-3 at room temperature around c/a_bct=1.33 and is thus even
larger than for binary Fe70Pd30 and the prototype Ni-Mn-Ga magnetic shape
memory system. Since K1 represents the driving force for variant reorientation
in magnetic shape memory systems, we conclude that Fe-Pd-Cu alloys offer a
promising route towards microactuators applications with significantly improved
work output.",1205.5422v1
2017-02-27,Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: a systematic study,"With a view to the design of hard magnets without rare earths we explore the
possibility of large magnetocrystalline anisotropy energies in Heusler
compounds that are unstable with respect to a tetragonal distortion. We
consider the Heusler compounds Fe$_2$YZ with Y = (Ni, Co, Pt), and Co$_2$YZ
with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find
that for the Co$_2$NiZ, Co$_2$PtZ, and Fe$_2$PtZ families the cubic phase is
always, at $T=0$, unstable with respect to a tetragonal distortion, while, in
contrast, for the Fe$_2$NiZ and Fe$_2$CoZ families this is the case for only 2
compounds -- Fe$_2$CoGe and Fe$_2$CoSn. For all compounds in which a tetragonal
distortion occurs we calculate the MAE finding remarkably large values for the
Pt containing Heuslers, but also large values for a number of the other
compounds (e.g. Co$_2$NiGa has an MAE of -2.11~MJ/m$^3$). The tendency to a
tetragonal distortion we find to be strongly correlated with a high density of
states at the Fermi level in the cubic phase. As a corollary to this fact we
observe that upon doping compounds for which the cubic structure is stable such
that the Fermi level enters a region of high DOS, a tetragonal distortion is
induced and a correspondingly large value of the MAE is then observed.",1702.08150v1
2018-04-16,Strong orientation dependent spin-orbit torque in antiferromagnet Mn2Au,"Antiferromagnets with zero net magnetic moment, strong anti-interference and
ultrafast switching speed have potential competitiveness in high-density
information storage. Body centered tetragonal antiferromagnet Mn2Au with
opposite spin sub-lattices is a unique metallic material for N\'eel-order
spin-orbit torque (SOT) switching. Here we investigate the SOT switching in
quasi-epitaxial (103), (101) and (204) Mn2Au films prepared by a simple
magnetron sputtering method. We demonstrate current induced antiferromagnetic
moment switching in all the prepared Mn2Au films by a short current pulse at
room temperature, whereas different orientated films exhibit distinguished
switching characters. A direction-independent reversible switching is attained
in Mn2Au (103) films due to negligible magnetocrystalline anisotropy energy,
while for Mn2Au (101) and (204) films, the switching is invertible with the
current applied along the in-plane easy axis and its vertical axis, but becomes
attenuated seriously during initially switching circles when the current is
applied along hard axis, because of the existence of magnetocrystalline
anisotropy energy. Besides the fundamental significance, the strong orientation
dependent SOT switching, which was not realized irrespective of ferromagnet and
antiferromagnet, provides versatility for spintronics.",1804.05465v1
2018-11-29,Magnetocrystalline Anisotropy of Fe-based $L1_0$ Alloys: Validity of Approximate Methods to Treat the Spin-Orbit Interaction,"First-principles calculations are used to gauge different levels of
approximation to calculate the magnetocrystalline anisotropy energies (MAE) of
five $L1_0$ FeMe alloys (Me=Co, Cu, Pd, Pt, Au). We find that a second-order
perturbation (2PT) treatment of the spin-orbit interaction (SOI) breaks down
for the alloys containing heavier ions, while it provides a very accurate
description of the MAE behaviour of FeCo, FeCu, and FePd. Moreover, the
robustness of the 2PT approximation is such that in these cases it accounts for
the MAE of highly-non-neutral alloys and, thus, it can be used to predict their
performance when dopants are present or when they are subject to applied gate
bias, which are typical conditions in working magnetoelectric devices. We also
observe that switching of the easy axis direction can be induced in some of
these alloys by addition or removal of, at least, one electron per cell. In all
cases, the details of the bandstructure are responsible for the finally
observed MAE value and, therefore, suggest a limited predicting power of models
based on the expected orbital moment values and bandwidths. Finally, we have
confirmed the importance of various calculation parameters to obtain converged
MAE values, in particular, those related to the accuracy of the Fermi level
determination.",1811.12100v1
2018-12-10,Noncollinearity effects on magnetocrystalline anisotropy for $R_2$Fe$_{14}$B magnets,"We present a theoretical investigation of the magnetocrystalline anisotropy
(MA) in $R_2$Fe$_{14}$B ($R$ is a rare-earth element) magnets in consideration
of the non-collinearity effect (NCE) between the $R$ and Fe magnetization
directions. In particular, the temperature dependence of the MA of
Dy$_2$Fe$_{14}$B magnets is detailed in terms of the $n$th-order MA constant
(MAC) $K_n(T)$ at a temperature $T$. The features of this constant are as
follows: $K_1(T)$ has a broad plateau in the low-temperature range and $K_2(T)$
persistently survives in the high-temperature range. The present theory
explains these features in terms of the NCE on the MA by using numerical
calculations for the entire temperature range, and further, by using a
high-temperature expansion. The high-temperature expansion for $K_n(T)$ is
expressed in the form of
$K_n(T)=\kappa_1(T)\left[1+\delta(T)\right][-\delta(T)]^{n-1}$, where
$\kappa_1(T)$ is the part without the NCE and $\delta(T)$ is a correction
factor for the NCE introduced in this study. We also provide a convenient
expression to evaluate $K_n(T)$, which can be determined only by a second-order
crystalline electric field coefficient and an effective exchange field.",1812.03611v2
2019-02-14,Database of novel magnetic materials for high-performance permanent magnet development,"This paper describes the open Novamag database that has been developed for
the design of novel Rare-Earth free/lean permanent magnets. The database
software technologies, its friendly graphical user interface, advanced search
tools and available data are explained in detail. Following the philosophy and
standards of Materials Genome Initiative, it contains significant results of
novel magnetic phases with high magnetocrystalline anisotropy obtained by three
computational high-throughput screening approaches based on a crystal structure
prediction method using an Adaptive Genetic Algorithm, tetragonally distortion
of cubic phases and tuning known phases by doping. Additionally, it also
includes theoretical and experimental data about fundamental magnetic material
properties such as magnetic moments, magnetocrystalline anisotropy energy,
exchange parameters, Curie temperature, domain wall width, exchange stiffness,
coercivity and maximum energy product, that can be used in the study and design
of new promising high-performance Rare-Earth free/lean permanent magnets. The
results therein contained might provide some insights into the ongoing debate
about the theoretical performance limits beyond Rare-Earth based magnets.
Finally, some general strategies are discussed to design possible experimental
routes for exploring most promising theoretical novel materials found in the
database.",1902.05241v1
2019-03-02,"A spin dynamics study in layered van der Waals single crystal, Cr$_2$Ge$_2$Te$_6$","We study the magnetisation dynamics of a bulk single crystal
Cr$_2$Ge$_2$Te$_6$ (CGT), by means of broadband ferromagnetic resonance (FMR),
for temperatures from 60 K down to 2 K. We determine the Kittel relations of
the fundamental FMR mode as a function of frequency and static magnetic field
for the magnetocrystalline easy - and hard - axis. The uniaxial
magnetocrystalline anisotropy constant is extracted and compared with the
saturation magnetisation, when normalised with their low temperature values.
The ratios show a clear temperature dependence when plotted in the logarithmic
scale, which departs from the predicted Callen-Callen power law fit of a
straight line, where the scaling exponent \textit{n}, $K_{u}(T) \propto
[M_s(T)/M_s(2$ K$)]^n$, contradicts the expected value of 3 for uniaxial
anisotropy. Additionally, the spectroscopic g-factor for both the magnetic easy
- and hard - axis exhibits a temperature dependence, with an inversion between
20 K and 30 K, suggesting an influence by orbital angular momentum. Finally, we
qualitatively discuss the observation of multi-domain resonance phenomena in
the FMR spectras, at magnetic fields below the saturation magnetisation.",1903.00584v2
2021-07-08,"Magnetic properties of 3d, 4d, and 5d transition-metal atomic monolayers in Fe/TM/Fe sandwiches: Systematic first-principles study","Previous studies have accurately determined the effect of transition metal
point defects on the properties of bcc iron. The magnetic properties of
transition metal monolayers on the iron surfaces have been studied equally
intensively. In this work, we investigated the magnetic properties of the 3d,
4d, and 5d transition-metal (TM) atomic monolayers in Fe/TM/Fe sandwiches using
the full-potential local-orbital (FPLO) scheme of density functional theory. We
prepared models of Fe/TM/Fe structures using the supercell method. We selected
the total thickness of our system so that the Fe atomic layers furthest from
the TM layer exhibit bulk iron-bcc properties. Along the direction
perpendicular to the TM layer, we observe oscillations of spin and charge
density. For Pt and W we obtained the largest values of perpendicular
magnetocrystalline anisotropy and for Lu and Ir the largest values of in-plane
magnetocrystalline anisotropy. All TM layers, except Co and Ni, reduce the
total spin magnetic moment in the generated models, which is in good agreement
with the Slater-Pauling curve. Density of states calculations showed that for
Ag, Pd, Ir, and Au monolayers, a distinct van Hove singularity associated with
TM/Fe interface can be observed at the Fermi level.",2107.03768v1
2021-07-19,Impact of local arrangement of Fe and Ni in Fe-Ni-Al Heusler alloys on the phase stability and magnetocrystalline anisotropy,"On the basis of the density functional calculations in combination with the
supercell approach, we report on a complete study of the influences of atomic
arrangement and Ni substitution for Al on the ground state structural and
magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss
systematically the competition between five cubic Heusler-type structures
formed by shuffles of Fe and Ni atoms to reveal routes for improving the phase
stability and magnetic properties, in particular magnetocrystalline
anisotropy~(MAE). We predict that in case of Fe$_2$NiAl the ground state cubic
structure with alternated layers of Fe and Ni possesses the highest uniaxial
MAE which twice larger than that for the tetragonal L1$_0$ FeNi. The successive
Ni doping at Al sublattice leads to a change of ground state structure and to
reduce of the MAE. In addition, the phase stability against the decomposition
into the stable systems at finite-temperatures is discussed. All~Ni-rich
Fe$_2$Ni$_{1+x}$Al$_{1-x}$ are turned to be decomposed into a dual-phase
consisting of Fe$_2$NiAl and FeNi.",2107.08804v2
2021-12-08,Lattice dynamics and its effects on magnetocrystalline anisotropy energy of pristine and hole-doped YCo$_5$ from first principles,"We study the lattice dynamics effects on the phase stability and
magnetocrystalline anisotropy (MCA) energy of CaCu$_5$-type YCo$_5$ at finite
temperatures using first-principles calculations based on density functional
theory (DFT). Harmonic lattice dynamics (HLD) calculations indicate that
YCo$_5$ with 56 full valance electrons is dynamically unstable and this
instability can be cured by reducing the number of electrons ($N_e$). Crystal
orbital Hamilton population analysis reveals that the observed phonon
instability originates from the large population of antibonding states near the
Fermi level, which is dominated by the Co atoms in the honeycomb layer. The
antibonding state depopulates with decreasing $N_e$, resulting in stable
phonons for hole-doped YCo$_5$ with $N_e$ $\leq$ 55. We then evaluate the
temperature-dependent MCA energy using both HLD and $ab$ $initio$ molecular
dynamics (AIMD) methods. For the pristine YCo$_5$, we observe a very weak
temperature decay of the MCA energy, indicating little effect of lattice
dynamics. Also, the MCA energies evaluated with AIMD at all target temperatures
are larger than that of the static hexagonal lattice at 0 K, which is mainly
attributed to the structural distortion driven by soft phonon modes. In the
hole-doped YCo$_5$, where the distortion is suppressed, a considerable
temperature decay in MCA energy is obtained both in HLD and AIMD methods,
showing that lattice dynamics effects on MCA energy are non-negligible.",2112.04124v1
2023-02-14,A theoretical perspective on the modification of the magnetocrystalline anisotropy at molecule-cobalt interfaces,"We study the modification of the magnetocrystalline anisotropy (MCA) of Co
slabs induced by several different conjugated molecular overlayers, i.e.,
benzene, cyclooctatetraene, naphthalene, pyrene and coronene. We perform
first-principles calculations based on Density Functional Theory and the
magnetic force theorem. Our results indicate that molecular adsorption tends to
favour a perpendicular MCA at surfaces. A detailed analysis of various
atom-resolved quantities, accompanied by an elementary model, demonstrates that
the underlying physical mechanism is related to the metal-molecule interfacial
hybridization and, in particular, to the chemical bonding between the molecular
C $p_z$ and the out-of-plane Co $d_{z^2}$ orbitals. This effect can be
estimated from the orbital magnetic moment of the surface Co atoms, a
microscopic observable accessible to both theory and experiments. As such, we
suggest a way to directly assess the MCA modifications at molecule-decorated
surfaces, overcoming the limitations of experimental studies that rely on fits
of magnetization hysteresis loops. Finally, we also study the interface between
Co and both C$_{60}$ and Alq$_3$, two molecules that find widespread use in
organic spintronics. We show that the modification of the surface Co MCA is
similar upon adsorption of these two molecules, thereby confirming the results
of recent experiments.",2302.07330v1
2013-12-13,Micromagnetics of shape anisotropy based permanent magnets,"In the search for rare-earth free permanent magnets, various ideas related to
shape anisotropy are being pursued. In this work we assess the limits of shape
contributions to the reversal stability using micromagnetic simulations. In a
first series of tests we altered the aspect ratio of single phase prolate
spheroids from 1 to 16. Starting with a sphere of radius $4.3$ times the
exchange length $ L_{\mathrm{ex}}$ we kept the total magnetic volume constant
as the aspect ratio was modified. For a ferromagnet with zero
magnetocrystalline anisotropy the maximum coercive field reached up to $0.5$
times the magnetization $M_{\mathrm{s}}$. Therefore, in materials with moderate
uniaxial magnetocrystalline anisotropy, the addition of shape anisotropy could
even double the coercive field. Interestingly due to non-uniform magnetization
reversal there is no significant increase of the coercive field for an aspect
ratio greater than 5. A similar limit of the maximum aspect ratio was observed
in cylinders. The coercive field depends on the wire diameter. By decreasing
the wire diameter from $8.7 L_{\mathrm{ex}}$ to $2.2 L_{\mathrm{ex}}$ the
coercive field increased by 40%. In the cylinders nucleation of a reversed
domain starts at the corners at the end. Smoothing the edges can improve the
coercive field by about 10%.
  In further simulations we compacted soft magnetic cylinders into a bulk-like
arrangement. Misalignment and magnetostatic interactions cause a spread of $0.1
M_{\mathrm{s}}$ in the switching fields of the rods. Comparing the volume
averaged hysteresis loops computed for isolated rods and the hysteresis loop
computed for interacting rods, we conclude that magnetostatic interactions
reduce the coercive field by up to 20%.",1312.3791v3
2008-09-24,The role of magnetic anisotropy in the Kondo effect,"In the Kondo effect, a localized magnetic moment is screened by forming a
correlated electron system with the surrounding conduction electrons of a
non-magnetic host. Spin S=1/2 Kondo systems have been investigated extensively
in theory and experiments, but magnetic atoms often have a larger spin. Larger
spins are subject to the influence of magnetocrystalline anisotropy, which
describes the dependence of the magnetic moment's energy on the orientation of
the spin relative to its surrounding atomic environment. Here we demonstrate
the decisive role of magnetic anisotropy in the physics of Kondo screening. A
scanning tunnelling microscope is used to simultaneously determine the
magnitude of the spin, the magnetic anisotropy and the Kondo properties of
individual magnetic atoms on a surface. We find that a Kondo resonance emerges
for large-spin atoms only when the magnetic anisotropy creates degenerate
ground-state levels that are connected by the spin flip of a screening
electron. The magnetic anisotropy also determines how the Kondo resonance
evolves in a magnetic field: the resonance peak splits at rates that are
strongly direction dependent. These rates are well described by the energies of
the underlying unscreened spin states.",0809.4289v1
2019-02-28,Effect of atomic ordering on the magnetic anisotropy of single crystal Ni80Fe20,"We investigate the effect of atomic ordering on the magnetic anisotropy of
Ni80Fe20 at.% (Py). To this end, Py films were grown epitaxially on MgO (001)
using dc magnetron sputtering (dcMS) and high power impulse magnetron
sputtering (HiPIMS). Aside from twin boundaries observed in the latter case,
both methods present high quality single crystals with cube-on-cube epitaxial
relationship as verified by the polar mapping of important crystal planes.
However, X-ray diffraction results indicate higher order for the dcMS deposited
film towards L12 Ni3Fe superlattice. This difference can be understood by the
very high deposition rate of HiPIMS during each pulse which suppresses adatom
mobility and ordering. We show that the dcMS deposited film presents biaxial
anisotropy while HiPIMS deposition gives well defined uniaxial anisotropy.
Thus, higher order achieved in the dcMS deposition behaves as predicted by
magnetocrystalline anisotropy i.e. easy axis along the [111] direction that
forced in the plane along the [110] direction due to shape anisotropy. The
uniaxial behaviour in HiPIMS deposited film then can be explained by pair
ordering or more recent localized composition non-uniformity theories. Further,
we studied magnetoresistance of the films along the [100] directions using an
extended van der Pauw method. We find that the electrical resistivities of the
dcMS deposited film are lower than in their HiPIMS counterparts verifying the
higher order in the dcMS case.",1903.00105v1
2021-08-24,Shape anisotropy effect on magnetization reversal induced by linear down chirp pulse,"We investigate the influence of shape anisotropy on the magnetization
reversal of a single-domain magnetic nanoparticle driven by a circularly
polarized linear down-chirp microwave field pulse (DCMP). Based on the
Landau-Lifshitz-Gilbert equation, numerical results show that the three
controlling parameters of DCMP, namely, microwave amplitude, initial frequency
and chirp rate, decrease with the increase of shape anisotropy. For certain
shape anisotropy, the reversal time significantly reduces. These findings are
related to the competition of shape anisotropy and uniaxial magnetocrystalline
anisotropy and thus to the height of energy barrier which separates the two
stable states. The result of damping dependence of magnetization reversal
indicates that for a certain sample shape, there exists an optimal damping
situation at which magnetization is fastest. Moreover, it is also shown that
the required microwave field amplitude can be lowered by applying the
spin-polarized current simultaneously. The usage of an optimum combination of
both microwave field pulse and current is suggested to achieve cost efficiency
and faster switching. So these findings may provide the knowledge to fabricate
the shape of a single domain nanoparticle for the fast and power-efficient
magnetic data storage device.",2108.10965v2
2023-08-25,Thermal effect on microwave pulse driven magnetization switching of Stoner particle,"Recently it has been demonstrated that the cosine chirp microwave pulse
(CCMP) is capable of achieving fast and energy-efficient magnetization-reversal
of a nanoparticle with zero-Temperature. However, we investigate the finite
temperature, $T$ effect on the CCMP-driven magnetization reversal using the
framework of the stochastic Landau Lifshitz Gilbert equation. At finite
Temperature, we obtain the CCMP-driven fast and energy-efficient reversal and
hence estimate the maximal temperature, $T_{max}$ at which the magnetization
reversal is valid. $T_{max}$ increases with increasing the nanoparticle
cross-sectional area/shape anisotropy up to a certain value, and afterward
$T_{max}$ decreases with the further increment of nanoparticle cross-sectional
area/shape anisotropy. This is because of demagnetization/shape anisotropy
field opposes the magnetocrystalline anisotropy, i.e., reduces the energy
barrier which separates the two stable states. For smaller cross-sectional
area/shape anisotropy, the controlling parameters of CCMP show decreasing trend
with temperature. We also find that with the increment easy-plane
shape-anisotropy, the required initial frequency of CCMP significantly reduces.
For the larger volume of nanoparticles, the parameters of CCMP remains constant
for a wide range of temperature which are desired for the device application.
Therefore, The above findings might be useful to realize the CCMP-driven fast
and energy-efficient magnetization reversal in realistic conditions.",2308.13124v1
2007-02-23,"Evolution of the magnetic anisotropy with carrier density in hydrogenated (Ga,Mn)As","The magnetic properties of (Ga,Mn)As thin films depend on both the Mn doping
level and the carrier concentration. Using a post growth hydrogenation process
we show that it is possible to decrease the hole density from 1.1021 cm-3 to
<1017 cm-3 while maintaining the manganese concentration constant. For such a
series of films we have investigated the variation of the magnetization, the
easy and hard axes of magnetization, the critical temperatures, the coercive
fields and the magnetocrystalline anisotropy constants as a function of
temperature using magnetometry, ferromagnetic resonance and magneto-transport
measurements. In particular, we evidenced that magnetic easy axes flipped from
out-of-plane [001] to in-plane [100] axis, followed by the <110> axes, with
increasing hole density and temperature. Our study concluded on a general
agreement with mean-field theory predictions of the expected easy axis
reversals, and of the weight of uniaxial and cubic anisotropies in this
material.",0702548v1
2008-12-19,Domain structure of epitaxial Co films with perpendicular anisotropy,"Epitaxial hcp Cobalt films with pronounced c-axis texture have been prepared
by pulsed lased deposition (PLD) either directly onto Al2O3 (0001) single
crystal substrates or with an intermediate Ruthenium buffer layer. The crystal
structure and epitaxial growth relation was studied by XRD, pole figure
measurements and reciprocal space mapping. Detailed VSM analysis shows that the
perpendicular anisotropy of these highly textured Co films reaches the
magnetocrystalline anisotropy of hcp-Co single crystal material. Films were
prepared with thickness t of 20 nm < t < 100 nm to study the crossover from
in-plane magnetization to out-of-plane magnetization in detail. The analysis of
the periodic domain pattern observed by magnetic force microscopy allows to
determine the critical minimum thickness below which the domains adopt a pure
in-plane orientation. Above the critical thickness the width of the stripe
domains is evaluated as a function of the film thickness and compared with
domain theory. Especially the discrepancies at smallest film thicknesses show
that the system is in an intermediate state between in-plane and out-of-plane
domains, which is not described by existing analytical domain models.",0812.3797v1
2011-03-28,The effect of chemical disorder on the magnetic anisotropy of strained Fe-Co films,"Strained Fe-Co films have recently been demonstrated to exhibit a large
magnetocrystalline anisotropy (MCA) and thus to be of potential interest as
magnetic storage material. Here, we show by means of density-functional (DF)
calculations, that chemical order can remarkably enhance the MCA. We also
investigate the effect of relaxation perpendicular to the applied strain and
evaluate the strain energy as a function of Co concentration and substrate
lattice parameter. On this basis, favourable preparation routes for films with
a large perpendicular anisotropy are suggested.",1103.5303v1
2013-03-21,"Co monolayers and adatoms on Pd(100), Pd(111) and Pd(110): Anisotropy of magnetic properties","We investigate to what extent the magnetic properties of deposited
nanostructures can be influenced by selecting as a support different surfaces
of the same substrate material. Fully relativistic ab initio calculations were
performed for Co monolayers and adatoms on Pd(100), Pd(111), and Pd(110)
surfaces. Changing the crystallographic orientation of the surface has a
moderate effect on the spin magnetic moment and on the number of holes in the d
band, a larger effect on the orbital magnetic moment but sometimes a dramatic
effect on the magnetocrystalline anisotropy energy (MAE) and on the magnetic
dipole term T_alpha. The dependence of T_alpha on the magnetization direction
alpha can lead to a strong apparent anisotropy of the spin magnetic moment as
deduced from the X-ray magnetic circular dichroism (XMCD) sum rules. For
systems in which the spin-orbit coupling is not very strong, the T_alpha term
can be understood as arising from the differences between components of the
spin magnetic moment associated with different magnetic quantum numbers m.",1303.5262v1
2014-03-20,Magnetization of densely packed interacting magnetic nanoparticles with cubic and uniaxial anisotropies: A Monte Carlo study,"The magnetization curves of densely packed single domain magnetic
nanoparticles (MNP) are investigated by Monte Carlo simulations in the
framework of an effective one spin model. The particles whose size
polydispersity is taken into account are arranged in spherical clusters and
both dipole dipole interactions (DDI) and magnetic anisotropy energy (MAE) are
included in the total energy. Having in mind the special case of spinel
ferrites of intrinsic cubic symmetry, combined cubic and uniaxial
magnetocrystalline anisotropies are considered with different configurations
for the orientations of the cubic and uniaxial axes. It is found that the DDI,
together with a marked reduction of the linear susceptibility are responsible
for a damping of the peculiarities due to the MAE cubic component on the
magnetization. As an application, we show that the simulated magnetization
curves compare well to experimental results for $\gamma$--Fe$_2$O$_3$ MNP for
small to moderate values of the field.",1403.5157v1
2014-07-22,Out- versus in-plane magnetic anisotropy of free Fe and Co nanocrystals: tight-binding and first-principles studies,"We report tight-binding (TB) and Density Function Theory (DFT) calculations
of magnetocrystalline anisotropy energy (MAE) of free Fe (body centerd cubic)
and Co (face centered cubic) slabs and nanocrystals. The nanocrystals are
truncated square pyramids which can be obtained experimentally by deposition of
metal on a SrTiO$_3$(001) substrate. For both elements our local analysis shows
that the total MAE of the nanocrystals is largely dominated by the contribution
of (001) facets. However, while the easy axis of Fe(001) is out-of-plane, it is
in-plane for Co(001). This has direct consequences on the magnetic reversal
mechanism of the nanocrystals. Indeed, the very high uniaxial anisotropy of Fe
nanocrystals makes them a much better potential candidate for magnetic storage
devices.",1407.5830v1
2014-09-19,"Magnetic anisotropy of Fe_1-yX_yPt-L10 [X=Cr,Mn,Co,Ni,Cu] bulk alloys","We demonstrate by means of fully relativistic first principles calculations
that, by substitution of Fe by Cr, Mn, Co, Ni or Cu in FePt-L10 bulk alloys,
with fixed Pt content, it is possible to tune the magnetocrystalline anisotropy
energy by adjusting the content of the non-magnetic species in the material.
The changes in the geometry due to the inclusion of each element induces
different values of the tetragonality and hence changes in the magnetic
anisotropy and in the net magnetic moment. The site resolved magnetic moments
of Fe increase with the X content whilst those of Pt and X are simultaneously
reduced. The calculations are in good quantitative agreement with experimental
data and demonstrate that models with fixed band structure but varying numbers
of electrons per unit cell are insufficient to describe the experimental data
for doped FePt-L10 alloys.",1409.5806v1
2015-04-21,Anisotropic interactions opposing magnetocrystalline anisotropy in Sr$_3$NiIrO$_6$,"We report our investigation of the electronic and magnetic excitations of
Sr$_3$NiIrO$_6$ by resonant inelastic x-ray scattering at the Ir L$_3$ edge.
The intra-$t_{2g}$ electronic transitions are analyzed using an atomic model,
including spin-orbit coupling and trigonal distortion of the IrO$_6$
octahedron, confronted to {\it ab initio} quantum chemistry calculations. The
Ir spin-orbital entanglement is quantified and its implication on the magnetic
properties, in particular in inducing highly anisotropic magnetic interactions,
is highlighted. These are included in the spin-wave model proposed to account
for the dispersionless magnetic excitation that we observe at 90 meV. By
counterbalancing the strong Ni$^{2+}$ easy-plane anisotropy that manifests
itself at high temperature, the anisotropy of the interactions finally leads to
the remarkable easy-axis magnetism reported in this material at low
temperature.",1504.05420v2
2016-10-11,Large magnetic anisotropy predicted for rare-earth free Fe16-xCoxN2 alloys,"Structures and magnetic properties of Fe16-xCoxN2 are studied using adaptive
genetic algorithm and first-principles calculations. We show that substituting
Fe by Co in Fe16N2 with Co/Fe ratio smaller than 1 can greatly improve the
magnetic anisotropy of the material. The magnetocrystalline anisotropy energy
from first-principles calculations reaches 3.18 MJ/m3 (245.6 {\mu}eV per metal
atom) for Fe12Co4N2, much larger than that of Fe16N2 and is one of the largest
among the reported rare-earth free magnets. From our systematic crystal
structure searches, we show that there is a structure transition from
tetragonal Fe16N2 to cubic Co16N2 in Fe16-xCoxN2 as the Co concentration
increases, which can be well explained by electron counting analysis. Different
magnetic properties between the Fe-rich (x < 8) and Co-rich (x > 8) Fe16-xCoxN2
is closely related to the structural transition.",1610.03544v1
2017-10-04,Ferromagnetic order in dipolar systems with anisotropy: application to magnetic nanoparticle supracrystals,"Single domain magnetic nanoparticles (MNP) interacting through dipolar
interactions (DDI) in addition to the magnetocrystalline energy may present a
low temperature ferromagnetic (SFM) or spin glass (SSG) phase according to the
underlying structure and the degree of order of the assembly. We study, from
Monte Carlo simulations in the framework of the effective one-spin or macrospin
models, the case of a monodisperse assembly of single domain MNP fixed on the
sites of a perfect lattice with fcc symmetry and randomly distributed easy
axes. We limit ourselves to the case of a low anisotropy, namely the onset of
the disappearance of the dipolar long-range ferromagnetic (FM) phase obtained
in the absence of anisotropy due to the disorder introduced by the latter.",1710.01532v2
2018-02-26,Multiferroic Micro-Motors with Deterministic Single Input Control,"This paper describes a method for achieving continuous deterministic
360$^{\circ} $ magnetic moment rotations in single domain magnetoelastic discs,
and examines the performance bounds for a mechanically lossless multiferroic
bead-on-a-disc motor based on dipole coupling these discs to small magnetic
nanobeads. The continuous magnetic rotations are attained by controlling the
relative orientation of a four-fold anisotropy (e.g., cubic magnetocrystalline
anisotropy) with respect to the two-fold magnetoelastic anisotropy. This
approach produces continuous rotations from the quasi-static regime up through
operational frequencies of several GHz. Driving strains of only $\approx$90 to
180 ppm are required for operation of motors using existing materials. The
large operational frequencies and small sizes, with lateral dimensions of
$\approx$100s of nanometers, produce large power densities for the rotary
bead-on-a-disc motor, and a newly proposed linear variant, in a size range
where power dense alternative technologies do not currently exist.",1802.09420v1
2018-10-02,Magnetocrystalline anisotropy and exchange probed by high-field anomalous Hall effect in fully-compensated half-metallic Mn2RuxGa thin films,"Magnetotransport is investigated in thin films of the half-metallic
ferrimagnet Mn$_2$Ru$_x$Ga in pulsed magnetic fields of up to 58 T. A
non-vanishing Hall signal is observed over a broad temperature range, spanning
the compensation temperature 155 K, where the net magnetic moment is strictly
zero, the anomalous Hall conductivity is 6673 $\Omega^{-1}.m^{-1}$ and the
coercivity exceeds 9 T. Molecular field modelling is used to determine the
intra- and inter-sublattice exchange constants and from the spin-flop
transition we infer the anisotropy of the electrically active sublattice to be
216 kJ/m$^3$ and predict the magnetic resonances frequencies. Exchange and
anisotropy are comparable and hard-axis applied magnetic fields result in a
tilting of the magnetic moments from their collinear ground state. Our analysis
is applicable to collinear ferrimagnetic half-metal systems.",1810.01158v1
2019-04-08,Magnetic anisotropy and entropy change in trigonal Cr$_{0.62}$Te,"We present a comprehensive investigation on anisotropic magnetic and
magnetocaloric properties of the quasi-two-dimensional weak itinerant
ferromagnet trigonal Cr$_{0.62}$Te single crystals. Magnetic-anisotropy-induced
satellite transition $T^*$ is observed at low fields applied parallel to the
$ab$ plane below $T_c$. The $T^*$ is featured by an anomalous magnetization
downturn, similar to that in structurally related CrI$_3$, and shows a
monotonous shift towards lower temperature with increasing field.
Magnetocrystalline anisotropy is also reflected in magnetic entropy change
$\Delta S_M(T,H)$ and relative cooling power RCP. Given the high $T_c$,
Cr$_{0.62}$Te crystals are materials of interest for nanofabrication in basic
science and applied technology.",1904.04247v3
2019-06-26,Concentration tuned tetragonal strain in alloys: application to magnetic anisotropy of FeNi$_{1-x}$Co$_x$,"We explore an opportunity to induce and control tetragonal distortion in
materials. The idea involves formation of a binary alloy from parent compounds
having body-centered and face-centered symmetries. The concept is illustrated
in the case of FeNi$_{1-x}$Co$_x$ magnetic alloy formed by substitutional
doping of the L1$_0$ FeNi magnet with Co. Using electronic structure
calculations we demonstrate that the tetragonal strain in this system can be
controlled by concentration and it reaches maximum for $x=0.5$. This finding is
then applied to create a large magnetocrystalline anisotropy (MAE) in
FeNi$_{1-x}$Co$_x$ system by considering an interplay of the tetragonal
distortion with electronic concentration and chemical anisotropy. In
particular, we identify a new ordered FeNi$_{0.5}$Co$_{0.5}$ system with MAE
larger by a factor 4.5 from the L1$_0$ FeNi magnet.",1906.11329v1
2020-06-03,Superconductivity-induced change in magnetic anisotropy in epitaxial ferromagnet-superconductor hybrids with spin-orbit interaction,"The interaction between superconductivity and ferromagnetism in thin film
superconductor/ferromagnet heterostructures is usually reflected by a change in
superconductivity of the S layer set by the magnetic state of the F layers.
Here we report the converse effect: transformation of the magnetocrystalline
anisotropy of a single Fe(001) layer, and thus its preferred magnetization
orientation, driven by the superconductivity of an underlying V layer through a
spin-orbit coupled MgO interface. We attribute this to an additional
contribution to the free energy of the ferromagnet arising from the controlled
generation of triplet Cooper pairs, which depends on the relative angle between
the exchange field of the ferromagnet and the spin-orbit field. This is
fundamentally different from the commonly observed magnetic domain modification
by Meissner screening or domain wall-vortex interaction and offers the ability
to fundamentally tune magnetic anisotropies using superconductivity - a key
step in designing future cryogenic magnetic memories.",2006.02118v2
2020-11-11,Characterization of room-temperature in-plane magnetization in thin flakes of CrTe$_2$ with a single spin magnetometer,"We demonstrate room-temperature ferromagnetism with in-plane magnetic
anisotropy in thin flakes of the CrTe$_2$ van der Waals ferromagnet. Using
quantitative magnetic imaging with a single spin magnetometer based on a
nitrogen-vacancy defect in diamond, we infer a room-temperature in-plane
magnetization in the range of $M\sim 27$ kA/m for flakes with thicknesses down
to $20$ nm. In addition, our measurements indicate that the orientation of the
magnetization is not determined solely by shape anisotropy in micron-sized
CrTe$_2$ flakes, which suggest the existence of a non-negligible
magnetocrystalline anisotropy. These results make CrTe$_2$ a unique system in
the growing family of van der Waals ferromagnets, as it is the only material
platform known to date which offers an intrinsic in-plane magnetization and a
Curie temperature above $300$ K in thin flakes.",2011.05722v2
2021-09-14,Valence state determines the band magnetocrystalline anisotropy in 2D rare-earth/noble-metal compounds,"In intermetallic compounds with zero-orbital momentum ($L=0$) the magnetic
anisotropy and the electronic band structure are interconnected. Here, we
investigate this connection on divalent Eu and trivalent Gd intermetallic
compounds. We find by X-ray magnetic circular dichroism an out-of-plane easy
magetization axis in 2D atom-thick EuAu$_2$. Angle-resolved photoemission and
density-functional theory prove that this is due to strong $f-d$ band
hybridization and Eu$^{2+}$ valence. In contrast, the easy in-plane
magnetization of the structurally-equivalent GdAu$_2$ is ruled by
spin-orbit-split $d$-bands, notably Weyl nodal lines, occupied in the Gd$^{3+}$
state. Regardless of the $L$ value, we predict a similar itinerant electron
contribution to the anisotropy of analogous compounds.",2109.06769v2
2022-10-21,A possible electronic state quasi-half-valley-metal in $\mathrm{VGe_2P_4}$ monolayer,"One of the key problems in valleytronics is to realize valley polarization.
Ferrovalley (FV) semiconductor and half-valley-metal (HVM) have been proposed,
which possess intrinsic spontaneous valley polarization. Here, we propose the
concept of quasi-half-valley-metal (QHVM), including electron and hole carriers
with only a type of carriers being valley polarized. The QHVM may realize
separation function of electron and hole. A concrete example of
$\mathrm{VGe_2P_4}$ monolayer is used to illustrate our proposal through the
first-principle calculations. To better realize QHVM, the electric field is
applied to tune related valley properties of $\mathrm{VGe_2P_4}$. Within
considered electric field range, $\mathrm{VGe_2P_4}$ is always ferromagnetic
(FM) ground state, which possesses out-of-plane magnetization by calculating
magnetic anisotropy energy (MAE) including magnetic shape anisotropy (MSA) and
magnetocrystalline anisotropy (MCA) energies. These out-of-plane FM properties
guarantee intrinsic spontaneous valley polarization in $\mathrm{VGe_2P_4}$.
Within a certain range of electric field, the QHVM can be maintained, and the
related polarization properties can be effectively tuned. Our works pave the
way toward two-dimensional (2D) functional materials design of valleytronics.",2210.11827v1
2023-07-24,In-plane magnetocrystalline anisotropy in the van der Waals antiferromagnet FePSe$_3$ probed by magneto-Raman scattering,"Magnon gap excitations selectively coupled to phonon modes have been studied
in FePSe$_3$ layered antiferromagnet with magneto-Raman scattering experiments
performed at different temperatures. The bare magnon excitation in this
material has been found to be split (by $\approx~1.2$ cm$^{-1}$) into two
components each being selectively coupled to one of the two degenerated, nearby
phonon modes. Lifting the degeneracy of the fundamental magnon mode points out
toward the biaxial character of the FePS$_3$ antiferromagnet, with an
additional in-plane anisotropy complementing much stronger, out-of-plane
anisotropy. Moreover, the tunability, with temperature, of the phonon- versus
the magnon-like character of the observed coupled modes has been demonstrated.",2307.12692v1
2023-12-05,Iron and gold thin films: first-principles study,"Using density functional theory, we carried out systematic calculations for a
series of ultrathin iron layers with thicknesses ranging from one atomic
monolayer to eleven monolayers (up to about 1.5 nm). We considered three cases:
(1) iron layers both on a gold substrate and coated with gold, (2) iron layers
on a gold substrate but without coverage, and (3) freestanding iron layers
adjacent to a vacuum. For our models, we chose initial bcc Fe(001) surfaces and
fcc Au(001) substrates. Based on the calculations, we determined the details of
the geometry and magnetic properties of the systems. We calculate lattice
parameters, magnetic moments, Curie temperatures and magnetocrystalline
anisotropy energies. From the thickness dependence, we determined the volume
and surface contributions to the magnetic anisotropy constant. The further
analysis allowed us to determine the thickness ranges of the occurrence of
perpendicular magnetic anisotropy, as well as the effect of thickness and the
presence of a substrate and cap layer on the direction of the magnetization
easy axis.",2312.02701v1
2020-12-09,Pressure control of the magnetic anisotropy of the quasi-two-dimensional van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$,"We report the results of the pressure-dependent measurements of the static
magnetization and of the ferromagnetic resonance (FMR) of Cr$_2$Ge$_2$Te$_6$ to
address the properties of the ferromagnetic phase of this quasi-two-dimensional
van der Waals magnet. The static magnetic data at hydrostatic pressures up to
3.4 GPa reveal a gradual suppression of ferromagnetism in terms of a reduction
of the critical transition temperature, a broadening of the transition width
and an increase of the field necessary to fully saturate the magnetization
$M_{\rm s}$. The value of $M_{\rm s} \simeq 3\mu_{\rm B}$/Cr remains constant
within the error bars up to a pressure of 2.8 GPa. The anisotropy of the FMR
signal continuously diminishes in the studied hydrostatic pressure range up to
2.39 GPa suggesting a reduction of the easy-axis type magnetocrystalline
anisotropy energy (MAE). A quantitative analysis of the FMR data gives evidence
that up to this pressure the MAE constant $K_{\rm U}$, although getting
significantly smaller, still remains finite and positive, i.e. of the easy-axis
type. Therefore, a recently discussed possibility of switching the sign of the
magnetocrystalline anisotropy in Cr$_2$Ge$_2$Te$_6$ could only be expected at
still higher pressures, if possible at all due to the observed weakening of the
ferromagnetism under pressure. This circumstance may be of relevance for the
design of strain-engineered functional heterostructures containing layers of
Cr$_2$Ge$_2$Te$_6$.",2012.05193v2
2021-02-02,"On the relationship between orbital moment anisotropy, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya interaction in W/Co/Pt trilayers","We have studied the Co layer thickness dependences of magnetocrystalline
anisotropy (MCA), Dzyaloshinskii-Moriya interaction (DMI), and orbital moment
anisotropy (OMA) in W/Co/Pt trilayers, in order to clarify their correlations
with each other. We find that the MCA favors magnetization along the film
normal and monotonically increases with decreasing effective magnetic layer
thickness ($t_\mathrm{eff}$). The magnitude of the Dzyaloshinskii-Moriya
exchange constant ($|D|$) increases with decreasing $t_\mathrm{eff}$ until
$t_\mathrm{eff} \sim$1 nm, below which $|D|$ decreases. The MCA and $|D|$ scale
with $1/t_\mathrm{eff}$ for $t_\mathrm{eff}$ larger than $\sim$1 nm, indicating
an interfacial origin. The increase of MCA with decreasing $t_\mathrm{eff}$
continues below $t_\mathrm{eff}$ $\sim$ 1 nm, but with a slower rate. To
clarify the cause of the $t_\mathrm{eff}$ dependences of MCA and DMI, the OMA
of Co in W/Co/Pt trilayers is studied using x-ray magnetic circular dichroism
(XMCD). We find non-zero OMA when $t_\mathrm{eff}$ is smaller than $\sim$0.8
nm. The OMA increases with decreasing $t_\mathrm{eff}$ more rapidly than what
is expected from the MCA, indicating that factors other than OMA contribute to
the MCA at small $t_\mathrm{eff}$. The $t_\mathrm{eff}$ dependence of the OMA
also suggests that $|D|$ at $t_\mathrm{eff}$ smaller than $\sim$1 nm is not
related to the OMA at the interface. We propose that the growth of Co on W
results in a strain and/or texture that reduces the interfacial DMI, and, to
some extent, MCA at small $t_\mathrm{eff}$.",2102.01283v2
2021-08-26,Magnetoelastic anisotropy in Heusler-type Mn$_{2-δ}$CoGa$_{1+δ}$ films,"Perpendicular magnetization is essential for high-density memory application
using magnetic materials. High-spin polarization of conduction electrons is
also required for realizing large electric signals from spin-dependent
transport phenomena. Heusler alloy is a well-known material class showing the
half-metallic electronic structure. However, its cubic lattice nature favors
in-plane magnetization and thus minimizes the perpendicular magnetic anisotropy
(PMA), in general. This study focuses on an inverse-type Heusler alloy,
Mn$_{2-\delta}$CoGa$_{1+\delta}$ (MCG) with a small off-stoichiometry
($\delta$) , which is expected to be a half-metallic material. We observed
relatively large uniaxial magnetocrystalline anisotropy constant
($K_\mathrm{u}$) of the order of 10$^5$ J/m$^3$ at room temperature in MCG
films with a small tetragonal distortion of a few percent. A positive
correlation was confirmed between the $c/a$ ratio of lattice constants and
$K_\mathrm{u}$. Imaging of magnetic domains using Kerr microscopy clearly
demonstrated a change in the domain patterns along with $K_\mathrm{u}$. X-ray
magnetic circular dichroism (XMCD) was employed using synchrotron radiation
soft x-ray beam to get insight into the origin for PMA. Negligible angular
variation of orbital magnetic moment ($\Delta m_\mathrm{orb}$) evaluated using
the XMCD spectra suggested a minor role of the so-called Bruno's term to
$K_\mathrm{u}$. Our first principles calculation reasonably explained the small
$\Delta m_\mathrm{orb}$ and the positive correlation between the $c/a$ ratio
and $K_\mathrm{u}$. The origin of the magnetocrystalline anisotropy was
discussed based on the second-order perturbation theory in terms of the
spin--orbit coupling, claiming that the mixing of the occupied $\uparrow$- and
the unoccupied $\downarrow$-spin states is responsible for the PMA of the MCG
films.",2108.11547v2
2013-10-23,Magnetoelastic coupling induced magnetic anisotropy in Co$_2$(Fe/Mn)Si thin films,"The influence of epitaxial strain on uniaxial magnetic anisotropy of
Co$_{2}$FeSi (CFS) and Co$_{2}$MnSi (CMS) Heusler alloy thin films grown on
(001) SrTiO$_3$ (STO) and MgO is reported. The in-plane biaxial strain is
susceptible to tune by varying the thickness of the films on STO, while on MgO
the films show in-plane easy axis for magnetization (\overrightarrow{M})
irrespective of their thickness. A variational analysis of magnetic free energy
functional within the Stoner-Wohlfarth coherent rotation model with
out-of-plane uniaxial anisotropy for the films on STO showed the presence of
magnetoelastic anisotropy with magnetostriction constant $\approx$
(12.22$\pm$0.07)$\times 10^{-6}$ and (2.02$\pm$0.06)$\times 10^{-6}$, in
addition to intrinsic magnetocrystalline anisotropy $\approx$ -1.72$\times
10^{6}$ erg/cm$^{3}$ and -3.94$\times 10^{6}$ erg/cm$^{3}$ for CFS and CMS,
respectively. The single-domain phase diagram reveals a gradual transition from
in-plane to out-of-plane orientation of magnetization with the decreasing film
thickness. A maximum canting angle of 41.5$^{\circ}$ with respect to film plane
is predicted for the magnetization of the thinnest (12 nm) CFS film on STO. The
distinct behaviour of \overrightarrow{M} in the films with lower thickness on
STO is attributed to strain-induced tetragonal distortion.",1310.6204v1
2016-10-02,"Intrinsic magnetic properties of {$R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$} ($R$ = Y and Ce; $Z$ = H, C, and N)","To guide improved properties coincident with reduction of critical materials
in permanent magnets, we investigate via density functional theory (DFT) the
intrinsic magnetic properties of a promising system,
$R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$ with $R$=Y, Ce and interstitial doping
($Z$=H, C, N). The magnetization $M$, Curie temperature $T_\text{C}$, and
magnetocrystalline anisotropy energy $K$ calculated in local density
approximation to DFT agree well with measurements. Site-resolved contributions
to $K$ reveal that all three Fe sublattices promote uniaxial anisotropy in
YFe$_{11}$Ti, while competing anisotropy contributions exist in YCo$_{11}$Ti.
As observed in experiments on $R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti, we find a
complex nonmonotonic dependence of $K$ on Co content, and show that anisotropy
variations are a collective effect of MAE contributions from all sites and
cannot be solely explained by preferential site occupancy. With interstitial
doping, calculated $T_\text{C}$ enhancements are in the sequence of N$>$C$>$H,
with volume and chemical effects contributing to the enhancement. The uniaxial
anisotropy of $R$(Fe$_{1-x}$Co$_{x}$)$_{11}$Ti$Z$ generally decreases with C
and N; although, for $R$=Ce, C doping is found to greatly enhance it for a
small range of 0.7$<$$x$$<$0.9.",1610.00365v1
2020-05-29,Electron spin resonance and ferromagnetic resonance spectroscopy in the high-field phase of the van der Waals magnet CrCl$_3$,"We report a comprehensive high-field/high-frequency electron spin resonance
(ESR) study on single crystals of the van der Waals magnet CrCl$_3$. This
material, although being known for quite a while, has received recent
significant attention in a context of the use of van der Waals magnets in novel
spintronic devices. Temperature-dependent measurements of the resonance fields
were performed between 4 and 175 K and with the external magnetic field applied
parallel and perpendicular to the honeycomb planes of the crystal structure.
These investigations reveal that the resonance line shifts from the
paramagnetic resonance position already at temperatures well above the
transition into a magnetically ordered state. Thereby the existence of
ferromagnetic short-range correlations above the transition is established and
the intrinsically two-dimensional nature of the magnetism in the title compound
is proven. To study details of the magnetic anisotropies in the field-induced
effectively ferromagnetic state at low temperatures, frequency-dependent
ferromagnetic resonance (FMR) measurements were conducted at 4 K. The observed
anisotropy between the two magnetic-field orientations is analyzed by means of
numerical simulations based on a phenomenological theory of FMR. These
simulations are in excellent agreement with measured data if the shape
anisotropy of the studied crystal is taken into account, while the
magnetocrystalline anisotropy is found to be negligible in CrCl$_3$. The
absence of a significant intrinsic anisotropy thus renders this material as a
practically ideal isotropic Heisenberg magnet.",2005.14559v1
2022-07-27,Importance of magnetic shape anisotropy in determining magnetic and electronic properties of monolayer $\mathrm{VSi_2P_4}$,"Two-dimensional (2D) ferromagnets have been a fascinating subject of
research, and magnetic anisotropy (MA) is indispensable for stabilizing the 2D
magnetic order. Here, we investigate magnetic anisotropy energy (MAE), magnetic
and electronic properties of $\mathrm{VSi_2P_4}$ by using the generalized
gradient approximation plus $U$ (GGA+$U$) approach. For large $U$, the magnetic
shape anisotropy (MSA) energy has a more pronounced contribution to the MAE,
which can overcome the magnetocrystalline anisotropy (MCA) energy to evince an
easy-plane. For fixed out-of-plane MA, monolayer $\mathrm{VSi_2P_4}$ undergoes
ferrovalley (FV), half-valley-metal (HVM), valley-polarized quantum anomalous
Hall insulator (VQAHI), HVM and FV states with increasing $U$. However, for
assumptive in-plane MA, there is no special quantum anomalous Hall (QAH) state
and spontaneous valley polarization within considered $U$ range. According to
the MAE and electronic structure with fixed out-of-plane or in-plane MA, the
intrinsic phase diagram shows common magnetic semiconductor (CMS), FV and VQAHI
in monolayer $\mathrm{VSi_2P_4}$. At representative $U$$=$3 eV widely used in
references, $\mathrm{VSi_2P_4}$ can be regarded as a 2D-$XY$ magnet, not
Ising-like 2D long-range order magnets predicted in previous works with only
considering MCA energy. Our findings shed light on importance of MSA in
determining magnetic and electronic properties of monolayer
$\mathrm{VSi_2P_4}$.",2207.13420v1
2022-12-15,Exploration of all-3d Heusler alloys for permanent magnets: an ab initio based high-throughput study,"Heusler alloys have attracted interest in various fields of functional
materials since their properties can quite easily be tuned by composition.
Here, we have investigated the relatively new class of all-3d Heusler alloys in
view of its potential as permanent magnets. To identify suitable candidates, we
performed a high-throughput study using an electronic structure database to
search for X$_2$YZ-type Heusler systems with tetragonal symmetry and high
magnetization. For the alloys which passed our selection filters, we have used
a combination of density functional theory calculations and spin dynamics
modelling to investigate their magnetic properties including the
magnetocrystalline anisotropy energy and exchange interactions. The candidates
which fulfilled all the search criteria served as input for the investigation
of the temperature dependence of the magnetization and determination of Curie
temperature. Based on our results, we suggest that Fe$_2$NiZn, Fe$_2$NiTi and
Ni$_2$CoFe are potential candidates for permanent magnets with large
out-of-plane magnetic anisotropy (1.23, 0.97 and 0.82 MJ/m$^3$ respectively)
and high Curie temperatures lying more than 200 K above the room temperature.
We further show that the magnitude and direction of anisotropy is very
sensitive to the strain by calculating the values of anisotropy energy for
several tetragonal phases. Thus, application of strain can be used to tune the
anisotropy in these compounds.",2212.07845v3
2023-02-06,Large ordered moment with strong easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe$_3$Sn,"We report the structural and magnetic properties of high-quality bulk single
crystals of the kagome ferromagnet Fe$_3$Sn. The dependence of magnetisation on
the magnitude and orientation of the external field reveals strong easy-plane
type uniaxial magnetic anisotropy, which shows a monotonous increase from
$K_1=-0.99\times 10^6 J/m^3$ at 300\,K to $-1.23\times10^6 J/m^3$ at 2\,K. Our
\textit{ab initio} electronic structure calculations yield the value of total
magnetic moment of about 6.9 $\mu_B$/f.u. and a magnetocrystalline anisotropy
energy density of 0.406\,meV/f.u. ($1.16\times10^6 J/m^3$) both being in good
agreement with the experimental values. The self-consistent DFT computations
for the components of the spin/orbital moments indicate that the small
difference between the saturation magnetisations measured along and
perpendicular to the kagome layers results from the subtle balance between the
Fe and Sn spin/orbital moments on the different sites. In zero field, magnetic
force microscopy reveals micrometer-scale magnetic vortices with weakly pinned
cores that vanish at $\sim$3\,T applied perpendicular to the kagome plane. Our
micromagnetic simulations, using the experimentally determined value of
anisotropy, well reproduce the observed vortex-domain structure. The present
study, in comparison with the easy-axis ferromagnet Fe$_3$Sn$_2$, shows that
varying the stacking of kagome layers provides an efficient control over
magnetic anisotropy in this family of Fe-based kagome magnets.",2302.13810v1
2024-01-04,Anisotropy of the anomalous Hall effect in the altermagnet candidate Mn$_5$Si$_3$ films,"Altermagnets are compensated magnets belonging to spin symmetry groups that
allow alternating spin polarizations both in the coordinate space of the
crystal and in the momentum space of the electronic structure. In these
materials the anisotropic local crystal environment of the different
sublattices lowers the symmetry of the system so that the opposite-spin
sublattices are connected only by rotations, which results in an unconventional
spin-polarized band structure in the momentum space. This low symmetry of the
crystal structure is expected to be reflected in the anisotropy of the
anomalous Hall effect. In this work, we study the anisotropy of the anomalous
Hall effect in epitaxial thin films of Mn$_5$Si$_3$, an altermagnetic candidate
material. We first demonstrate a change in the relative N\'eel vector
orientation when rotating the external field orientation through systematic
changes in both the anomalous Hall effect and the anisotropic longitudinal
magnetoresistance. We then show that the anomalous Hall effect in this material
is anisotropic with the N\'eel vector orientation relative to the crystal
structure and that this anisotropy requires high crystal quality and unlikely
correlates with the magnetocrystalline anisotropy. Our results provide further
systematic support to the case for considering epitaxial thin films of
Mn$_5$Si$_3$ as an altermagnetic candidate material.",2401.02275v1
2015-02-18,"Magnetocrystalline anisotropic effect in GdCo$_{1-x}$Fe$_x$AsO ($x = 0, 0.05$)","From a systematic study of the electrical resistivity $\rho(T,H)$, magnetic
susceptibility $\chi(T,H)$, isothermal magnetization $M(H)$ and the specific
heat $C(T,H)$, a temperature-magnetic field ($T$-$H$) phase diagram has been
established for GdCo$_{1-x}$Fe$_x$AsO ($x = 0$ and $0.05$) polycrystalline
compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic
(FM) transition of Co $3d$ electrons ($T_\textup{C}^\textup{Co}$) and
antiferromagnetic (AFM) transition of Gd $4f$ electrons
($T_\textup{N}^\textup{Gd}$). For the Fe-doped sample ($x=0.05$), an extra
magnetic reorientation transition takes place below $T_\textup{N}^\textup{Gd}$,
which is likely associated with Co moments. The two magnetic species of Gd and
Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM)
behavior in the magnetic susceptibility. Upon decreasing the temperature ($T <
T_\textup{C}^\textup{Co}$), the magnetocrystalline anisotropy breaks up the FM
order of Co by aligning the moments with the local easy axes of the various
grains, leading to a spin reorientation transition at
$T_\textup{R}^\textup{Co}$. By applying a magnetic field,
$T_\textup{R}^\textup{Co}$ monotonically decreases to lower temperatures, while
the $T_\textup{N}^\textup{Gd}$ is relatively robust against the external field.
On the other hand, the applied magnetic field pulls the magnetization of grains
from the local easy direction to the field direction via a first-order
reorientation transition, with the transition field ($H_\textup{M}$) increasing
upon cooling the temperature.",1502.05139v1
2010-12-21,Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films,"We present an investigation of the magnetic behavior of epitaxial MnAs films
grown on GaAs(100). We address the dependence of the magnetic moment,
ferromagnetic transition temperature ($T_c$) and magnetocrystalline anisotropy
constants on epitaxial conditions. From thorough structural and magnetic
investigations, our findings indicate a more complex relationship between
strain and magnetic properties in MnAs films than a simple stretch/compression
of the unit cell axes. While a small increase is seen in the anisotropy
constants the enhancement of the magnetic moment at saturation is significant.
X-ray magnetic circular dichroism results show a behavior of the spin- and
orbital-moment which is consistent with a structural transition at $T_c$. In
particular, we find that the ratio of the orbital to spin moment shows a marked
increase in the coexistence region of the ferromagnetic $\alpha$- and
paramagnetic $\beta$-phases, a result that is well in accord with the observed
increase of the $c/a$-ratio in the same temperature region. The \textit{ab
initio} density functional calculations reveal that the magnetic properties are
more sensitive towards change in in-plane axis as compared to a change of the
out-of-plane axis, which is explained by the analysis of band structures. The
effects of electron correlation in MnAs using \textit{ab initio} dynamical mean
field theory are also presented.",1012.4717v1
2018-03-22,Tuning magnetocrystalline anisotropy of Fe$_{3}$Sn by alloying,"The electronic structure, magnetic properties and phase formation of
hexagonal ferromagnetic Fe$_{3}$Sn-based alloys have been studied from first
principles and by experiment. The pristine Fe$_{3}$Sn compound is known to
fulfill all the requirements for a good permanent magnet, except for the
magnetocrystalline anisotropy energy (MAE). The latter is large, but planar,
i.e. the easy magnetization axis is not along the hexagonal c direction,
whereas a good permanent magnet requires the MAE to be uniaxial. Here we
consider Fe$_{3}$Sn$_{0.75}$M$_{0.25}$, where M= Si, P, Ga, Ge, As, Se, In, Sb,
Te and Bi, and show how different dopants on the Sn sublattice affect the MAE
and can alter it from planar to uniaxial. The stability of the doped Fe$_{3}$Sn
phases is elucidated theoretically via the calculations of their formation
enthalpies. A micromagnetic model is developed in order to estimate the energy
density product (BH)max and coercive field $\mu_{0}$H$_{c}$ of a potential
magnet made of Fe$_{3}$Sn$_{0.75}$Sb$_{0.25}$, the most promising candidate
from theoretical studies. The phase stability and magnetic properties of the
Fe$_{3}$Sn compound doped with Sb and Mn has been checked experimentally on the
samples synthesised using the reactive crucible melting technique as well as by
solid state reaction. The Fe$_{3}$Sn-Sb compound is found to be stable when
alloyed with Mn. It is shown that even small structural changes, such as a
change of the c/a ratio or volume, that can be induced by, e.g., alloying with
Mn, can influence anisotropy and reverse it from planar to uniaxial and back.",1803.08292v1
2018-07-27,Magnetocrystalline anisotropy of Fe5PB2 and its alloys with Co and 5d elements: a combined first-principles and experimental study,"The Fe$_5$PB$_2$ compound offers tunable magnetic properties via the
possibility of various combinations of substitutions on the Fe and P-sites.
Here, we present a combined computational and experimental study of the
magnetic properties of (Fe$_{1-x}$Co$_{x}$)$_5$PB$_2$. Computationally, we are
able to explore the full concentration range, while the real samples were only
obtained for 0 <= x <= 0.7. The calculated magnetic moments, Curie
temperatures, and magnetocrystalline anisotropy energies (MAEs) are found to
decrease with increasing Co concentration. Co substitution allows for tuning
the Curie temperature in a wide range of values, from about six hundred to zero
kelvins. As the MAE depends on the electronic structure in the vicinity of
Fermi energy, the geometry of the Fermi surface of Fe$_5$PB$_2$ and the
k-resolved contributions to the MAE are discussed. Low temperature measurements
of an effective anisotropy constant for a series of
(Fe$_{1-x}$Co$_{x}$)$_5$PB$_2$ samples determined the highest value of 0.94 MJ
m$^{-3}$ for the terminal Fe$_5$PB$_2$ composition, which then decreases with
increasing Co concentration, thus confirming the computational result that Co
alloying of Fe$_5$PB$_2$ is not a good strategy to increase the MAE of the
system. However, the relativistic version of the fixed spin moment method
reveals that a reduction in the magnetic moment of Fe$_5$PB$_2$, by about 25%,
produces a fourfold increase of the MAE. Furthermore, calculations for
(Fe$_{0.95}$X$_{0.05}$)$_5$PB$_2$ (X = 5$d$ element) indicate that 5% doping of
Fe$_5$PB$_2$ with W or Re should double the MAE. These are results of high
interest for, e.g., permanent magnet applications, where a large MAE is
crucial.",1807.10649v3
2021-08-06,"Strong magneto-optical and anomalous transport manifestations in two-dimensional van der Waals magnets Fe$_n$GeTe$_2$ ($n$ = 3, 4, 5)","Utilizing the first-principles calculations together with the group theory
analysis, we systematically investigate the magnetocrystalline anisotropy
energy, magneto-optical effect, and anomalous transport properties (including
anomalous Hall, Nernst, and thermal Hall effects) of monolayer and bilayer
Fe$_n$GeTe$_2$ ($n$ = 3, 4, 5). The monolayer Fe$_n$GeTe$_2$ ($n$ = 3, 4, 5)
exhibits the out-of-plane, in-plane, and in-plane ferromagnetic orders with
considerable magnetocrystalline anisotropy energies of -3.17, 4.42, and 0.58
meV/f.u., respectively. Ferromagnetic order is predicted in bilayer
Fe$_4$GeTe$_2$ while antiferromagnetic order prefers in bilayer Fe$_3$GeTe$_2$
and Fe$_5$GeTe$_2$. The group theory analysis reveals that in addition to
monolayer ferromagnetic Fe$_n$GeTe$_2$ ($n$ = 3, 4, 5), the magneto-optical and
anomalous transport phenomena surprisingly exist in bilayer antiferromagnetic
Fe$_5$GeTe$_2$, which is much rare in realistic collinear antiferromagnets. If
spin magnetic moments of monolayer and bilayer Fe$_n$GeTe$_2$ are reoriented
from the in-plane to out-of-plane direction, the magneto-optical and anomalous
transport properties enhance significantly, presenting strong magnetic
anisotropy. We also demonstrate that the anomalous Hall effect decreases with
the temperature increases. The gigantic anomalous Nernst and thermal Hall
effects are found in monolayer and bilayer ferromagnetic Fe$_n$GeTe$_2$, and
the largest anomalous Nernst and thermal Hall conductivities, respectively, of
-3.31 A/Km and 0.22 W/Km at 130 K are observed in bilayer ferromagnetic
Fe$_4$GeTe$_2$. Especially, bilayer antiferromagnetic Fe$_5$GeTe$_2$ exhibits
large zero-temperature anomalous Hall conductivity of 2.63 e$^2$/h as well as
anomalous Nernst and thermal Hall conductivities of 2.76 A/Km and 0.10 W/Km at
130 K, respectively.",2108.02926v2
2000-05-24,Crystal-field interactions in PrRu2Si2,"Ferromagnetic compound PrRu2Si2 exhibits a giant magnetocrystalline
anisotropy of about 400 T. Its ordered moment below Tc=14K reaches 2.7 mB and
is parallel to [0 0 1] crystalline direction. We have attributed the magnetism
of PrRu2S2 to the Pr ions and performed calculations of the fine electronic
structure of the Pr ion in the tetragonal symmetry, relevant to PrRu2Si2 taking
into account crystal-field and inter-site, spin-dependent exchange
interactions. Spin-dependent interactions have been taken into account by means
of molecular-field approximation. The derived energy level scheme is associated
with the removal of the degeneracy of the lowest multiplet given by Hund's
rules, 3H4. Magnetic and electronic properties resulting from this fine
structure are compared with all known experimental results. Our calculations
reproduce well the zero-temperature moment, temperature dependence of the
magnetic susceptibility, single-crystalline magnetization curves with the
anisotropy field of 400T, the specific heat with the sharp peak at Tc as well
as inelastic-neutron-scattering data.",0005406v1
2000-06-26,Wess-Zumino-Berry phase interference in spin tunneling at excited levels with a magnetic field,"Macroscopic quantum coherence and spin-phase interference are studied between
excited levels in single-domain ferromagnetic particles in a magnetic field
along the hard anisotropy axis. The system has the general structure of
magnetocrystalline anisotropy, such as biaxial, trigonal, tetragonal, and
hexagonal symmetry. This study not only just yields the previous spin-phase
interference results for the ground state tunneling, but also provide a
generalization of the Kramers degeneracy to coherently spin tunneling at
low-lying excited states. These analytical results are found to be in good
agreement with the numerical diagonalization. We also discuss the transition
from quantum to classical behavior and the possible relevance to experiment.",0006392v2
2002-06-19,Magnetic structure of antiferromagnetic NdRhIn5,"The magnetic structure of antiferromagnetic NdRhIn5 has been determined using
neutron diffraction. It has a commensurate antiferromagnetic structure with a
magnetic wave vector (1/2,0,1/2) below T_N = 11K. The staggered Nd moment at
1.6K is 2.6mu_B aligned along the c-axis. We find the magnetic structure to be
closely related to that of its cubic parent compound NdIn3 below 4.6K. The
enhanced T_N and the absence of additional transitions below T_N for NdRhIn5
are interpreted in terms of an improved matching of the
crystalline-electric-field (CEF), magnetocrystalline, and exchange interaction
anisotropies. In comparison, the role of these competing anisotropies on the
magnetic properties of the structurally related compound CeRhIn5 is discussed.",0206381v1
2004-07-02,Large LFMR observed in twinned La2/3Ca1/3MnO3 thin films epitaxially grown on YSZ-buffered SOI substrates,"La2/3Ca1/3MnO3 thin films have been grown on yttria-stabilized zirconia (YSZ)
buffered silicon-on-insulator (SOI) substrate by the pulsed laser deposition
technique. While full cube-on-cube epitaxy was achieved for the YSZ layer, the
top manganite layer was multi-domain-oriented, with a coexistence of
cube-on-cube and cube-on-diagonal epitaxy. Due to a combined influence from the
magnetocrystalline anisotropy and the magnetoelastic anisotropy, in zero field
the local spin orientation varies across the twin boundaries. As a result, a
quite large low-field magnetoresistance (LFMR) based on spin-dependent
tunnelling was observed. The film shows a resistance change of ~20% in a
magnetic field <1000 Oe at 50 K, which is promising for real applications.",0407053v1
2006-03-22,"Out-of-plane magnetization reversal processes of (Ga,Mn)As with two different hole concentrations","We study magnetization reversal processes of in-plane magnetized (Ga,Mn)As
epilayers with different hole concentrations in out-of-plane magnetic fields
using magnetotransport measurements. A clear difference in the magnetization
process is found in two separate samples with hole concentrations of 10^20
cm^-3 and 10^21 cm^-3 as the magnetization rotates from the out-of-plane
saturation to the in-plane remanence. Magnetization switching process from the
in-plane remanence to the out-of-plane direction, on the other hand, shows no
hole concentration dependence, where the switching process occurs via domain
wall propagation. We show that the balance of <100> cubic magnetocrystalline
anisotropy and uniaxial [110] anisotropy gives an understanding of the
difference in the out-of-plane magnetization processes of (Ga,Mn)As epilayers.",0603568v1
2006-03-28,Ferromagnetic one dimensional Ti atomic chain,"Using the full potential linearized augmented plane wave (FLAPW) method, we
have explored the magnetic properties of one dimensional (1D) Ti atomic chain.
Astonishingly, we for the first time observed that the 1D Ti atomic chain has
ferromagnetic ground state even on NiAl(110) surface although the Ti has no
magnetic moment in bulk or macroscopic state. It was found that the physical
property of direct exchange interaction among Ti atoms occurred in free
standing state is well preserved on NiAl(110) surface and this feature has an
essential role in ferromagnetism of 1D Ti atomic chain. It was shown that the
m=$|2|$ state has the largest contribution to the magnetic moment of Ti atom
grown on NiAl(110) surface. In addition, we found that the magnetic dipole
interaction is a key factor in the study of magnetic anisotropy, not the
magnetocrystalline anisotropy arising from spin-orbit interaction.",0603740v1
2007-05-03,"Domain imaging and domain wall propagation in (Ga,Mn)As thin films with tensile strain","We have performed spatially resolved Polar Magneto-Optical Kerr Effect
Microscopy measurements on as-grown and annealed Ga0.95Mn0.05As thin films with
tensile strain. We find that the films exhibit very strong perpendicular
magnetic anisotropy which is increased upon annealing. During magnetic
reversal, the domain walls propagate along the direction of surface ripples for
the as-grown sample at low temperatures and along the [110] direction for the
annealed sample. This indicates that the magnetic domain pattern during
reversal is determined by a combination of magnetocrystalline anisotropy and a
distribution of pinning sites along the surface ripples that can be altered by
annealing. These mechanisms could lead to an effective method of controlling
domain wall propagation.",0705.0474v1
2008-01-06,Voltage control of magnetocrystalline anisotropy in ferromagnetic - semiconductor/piezoelectric hybrid structures,"We demonstrate dynamic voltage control of the magnetic anisotropy of a
(Ga,Mn)As device bonded to a piezoelectric transducer. The application of a
uniaxial strain leads to a large reorientation of the magnetic easy axis which
is detected by measuring longitudinal and transverse anisotropic
magnetoresistance coefficients. Calculations based on the mean-field
kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the
measured effect. Electrically induced magnetization switching and detection of
unconventional crystalline components of the anisotropic magnetoresistance are
presented, illustrating the generic utility of the piezo voltage control to
provide new device functionalities and in the research of micromagnetic and
magnetotransport phenomena in diluted magnetic semiconductors.",0801.0886v2
2009-08-27,Magnetocrystalline anisotropy and antiferromagnetic phase transition in PrRh$_{2}$Si$_{2}$,"We present magnetic and transport properties of PrRh$_{2}$Si$_{2}$ single
crystals which exhibit antiferromagnetic order below T$_{N}$ = 68 K. Well
defined anomalies due to magnetic phase transition are observed in magnetic
susceptibility, resistivity, and specific heat data. The T$_{N}$ of 68 K for
PrRh$_{2}$Si$_{2}$ is much higher than 5.4 K expected on the basis of de-Gennes
scaling. The magnetic susceptibility data reveal strong uniaxial anisotropy in
this compound similar to that of PrCo$_{2}$Si$_{2}$. With increasing pressure
T$_{N}$ increases monotonically up to T$_N$ = 71.5 K at 22.5 kbar.",0908.4017v1
2010-01-26,Competing magnetic anisotropies in atomic-scale junctions,"Using first-principles calculations, we study the magnetism of 5d
transition-metal atomic junctions including structural relaxations and
spin-orbit coupling. Upon stretching monatomic chains of W, Ir, and Pt
suspended between two leads, we find the development of strong magnetism and
large values of the magnetocrystalline anisotropy energy (MAE) of up to 30 meV
per chain atom. We predict that switches of the easy magnetization axis of the
nanocontacts upon elongation should be observable by ballistic anisotropic
magnetoresistance measurements. Due to the different local symmetry, the
contributions to the MAE of the central chain atoms and chain atoms in the
vicinity of the leads can have opposite signs which reduces the total MAE. We
demonstrate that this effect occurs independent of the chain length or geometry
of the electrodes.",1001.4618v1
2010-08-12,Rotational Doppler Effect in Magnetic Resonance,"We compute the shift in the frequency of the spin resonance in a solid that
rotates in the field of a circularly polarized electromagnetic wave. Electron
spin resonance, nuclear magnetic resonance, and ferromagnetic resonance are
considered. We show that contrary to the case of the rotating LC circuit, the
shift in the frequency of the spin resonance has strong dependence on the
symmetry of the receiver. The shift due to rotation occurs only when rotational
symmetry is broken by the anisotropy of the gyromagnetic tensor, by the shape
of the body, or by magnetocrystalline anisotropy. General expressions for the
resonance frequency and power absorption are derived and implications for
experiment are discussed.",1008.2142v1
2010-10-25,High-temperature magnetic properties of noninteracting single-domain Fe3O4 nanoparticles,"Magnetic measurements have been performed on 40-nm sphere-like Fe3O4
nanoparticles using a Quantum Design vibrating sample magnetometer. Coating
Fe3O4 nanoparticles with SiO2 effectively eliminates magnetic interparticle
interactions so that the coercive field HC in the hightemperature range between
300 K and the Curie temperature (855 K) can be well fitted by an expression for
noninteracting randomly oriented single-domain particles. From the fitting
parameters, the effective anisotropy constant K is found to be (1.68 \pm 0.17)
\times 105 erg/cm3, which is slightly larger than the bulk magnetocrystalline
anisotropy constant of 1.35 \times 105 erg/cm3. Moreover, the inferred mean
particle diameter from the fitting parameters is in quantitative agreement with
that determined from transmission electron microscope. Such a quantitative
agreement between data and theory suggests that the assemble of our SiO2-coated
sphere-like Fe3O4 nanopartles represents a good system of noninteracting
randomly-oriented single-domain particles.",1010.5264v2
2010-12-21,"Detection of stacking faults breaking the [110]/[1-10] symmetry in ferromagnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P)","We report high resolution x-ray diffraction measurements of (Ga,Mn)As and
(Ga,Mn)(As,P) epilayers. We observe a structural anisotropy in the form of
stacking faults which are present in the (111) and (11-1) planes and absent in
the (-111) and (1-11) planes. The stacking faults produce no macroscopic
strain. They occupy 0.01 - 0.1 per cent of the epilayer volume. Full-potential
density functional calculations evidence an attraction of Mn_Ga impurities to
the stacking faults. We argue that the enhanced Mn density along the common
[1-10] direction of the stacking fault planes produces sufficiently strong
[110]/[1-10] symmetry breaking mechanism to account for the in-plane uniaxial
magnetocrystalline anisotropy of these ferromagnetic semiconductors.",1012.4690v1
2011-03-19,Magnetic properties and energy absorption of CoFe2O4 nanoparticles for magnetic hyperthermia,"We have studied the magnetic and power absorption properties of three samples
of CoFe2O4 nanoparticles with sizes from 5 to 12 nm prepared by thermal
decomposition of Fe (acac)3 and Co(acac)2 at high temperatures. The blocking
temperatures TB estimated from magnetization M(T) curves spanned the range 180
< TB < 320 K, reflecting the large magnetocrystalline anisotropy of these
nanoparticles. Accordingly, high coercive fields HC \approx 1.4 - 1.7 T were
observed at low temperatures. Specific Power Absorption (SPA) experiments
carried out in ac magnetic fields indicated that, besides particle volume, the
effective magnetic anisotropy is a key parameter determining the absorption
efficiency. SPA values as high as 98 W/g were obtained for nanoparticles with
average size of \approx12 nm.",1103.3786v1
2011-11-23,Magnetic and structural characterization of nanosized BaCo_xZn_{2-x}Fe_{16}O_{27} hexaferrite in the vicinity of spin reorientation transition,"Numerous applications of hexagonal ferrites are related to their easy axis or
easy plane magnetocrystalline anisotropy configurations. Certain W-type
ferrites undergo spin reorientation transitions (SRT) between different
anisotropy states on magnetic field or temperature variation. The transition
point can be tuned by modifying the chemical composition, which suggests a
potential application of hexaferrites in room temperature magnetic
refrigeration. Here we present the results of structural and magnetic
characterization of BaCo_xZn_{2-x}Fe_{16}O_{27} (0.7 \leq x \leq 2) doped
barium ferrites. Fine powders were prepared using a sol-gel citrate precursor
method. Crystal structures and particle size distributions were examined by
X-ray diffraction and transmission electron microscopy. The optimal synthesis
temperature ensuring complete formation of single W-phase with limited grain
growth has been determined. Spin reorientation transitions were revealed by
thermomagnetic analysis and AC susceptibility measurements.",1111.5453v1
2012-01-17,Spin-orbit field switching of magnetization in ferromagnetic films with perpendicular anisotropy,"As an alternative to conventional magnetic field, the effective spin-orbit
field in transition metals, derived from the Rashba field experienced by
itinerant electrons confined in a spatial inversion asymmetric plane through
the s-d exchange interaction, is proposed for the manipulation of
magnetization. Magnetization switching in ferromagnetic thin films with
perpendicular magnetocrystalline anisotropy can be achieved by current induced
spin-orbit field, with small in-plane applied magnetic field. Spin-orbit field
induced by current pulses as short as 10 ps can initiate ultrafast
magnetization switching effectively, with experimentally achievable current
densities. The whole switching process completes in about 100 ps.",1201.3505v4
2012-09-12,Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements,"We determine experimentally the spin structure of half-metallic
Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following
magnetic saturation, the dominant magnetic states consist of quasi-uniform
configurations, where a strong influence from the magnetocrystalline anisotropy
is visible. Heating experiments show the stability of the spin configuration of
domain walls in confined geometries up to 800 K. The switching temperature for
the transition from transverse to vortex walls in ring elements is found to
increase with ring width, an effect attributed to structural changes and
consequent changes in magnetic anisotropy, which start to occur in the narrower
elements at lower temperatures.",1209.2702v1
2013-08-07,Magnetocrystalline anisotropy energy for adatoms and monolayers on non-magnetic substrates: where does it comes from?,"The substrate contribution to the magnetic anisotropy energy (MAE) of
supported nanostructures can be quantified by a site-selective manipulation of
the spin-orbit coupling (SOC) and the effective exchange field B_ex. A
systematic study of Co adatoms and Co monolayers on the (111) surfaces of Cu,
Ag, Au, Pd and Pt is performed to study common trends in this class of
materials. It is found that for adatoms, the substrate contribution is
relatively small (10-30% of the MAE) while for monolayers, the substrate
contribution can be substantial. The contribution from the SOC is much more
important than the contribution from the exchange field B_ex, except for highly
polarizable substrates with a strong SOC (such as Pt). The substrate always
promotes the tendency to an out-of-plane orientation of the easy magnetic axis
for all the investigated systems.",1308.1597v3
2014-10-23,Surface aligned magnetic moments and hysteresis of an endohedral single-molecule magnet on a metal,"The interaction between the endohedral unit in the single-molecule magnet
Dy$_2$ScN@C$_{80}$ and a rhodium (111) substrate leads to alignment of the Dy
4$f$ orbitals. The resulting orientation of the Dy$_2$ScN plane parallel to the
surface is inferred from comparison of the angular anisotropy of x-ray
absorption spectra and multiplet calculations in the corresponding ligand
field. The x-ray magnetic circular dichroism (XMCD) is also angle dependent and
signals strong magnetocrystalline anisotropy. This directly relates geometric
and magnetic structure. Element specific magnetization curves from different
coverages exhibit hysteresis at a sample temperature of $\sim4$ K. From the
measured hysteresis curves we estimate the zero field remanence life-time
during x-ray exposure of a sub-monolayer to be about 30 seconds.",1410.6272v2
2015-02-28,Band-filling effect on magnetic anisotropy using a Green's function method,"We use an analytical model to describe the magnetocrystalline anisotropy
energy (MAE) in solids as a function of band filling. The MAE is evaluated in
second-order perturbation theory, which makes it possible to decompose the MAE
into a sum of transitions between occupied and unoccupied pairs. The model
enables us to characterize the MAE as a sum of contributions from different,
often competing terms. The nitridometalates Li$_{2}$[(Li$_{1-x}$T$_{x}$)N],
with $T$=Mn, Fe, Co, Ni, provide a system where the model is very effective
because atomic like orbital characters are preserved and the decomposition is
fairly clean. Model results are also compared against MAE evaluated directly
from first-principles calculations for this system. Good qualitative agreement
is found.",1503.00063v2
2015-06-01,Evaluation of (BH)max and magnetic anisotropy of cobalt ferrite nanoparticles synthesized in gelatin,"CoFe2O4 nanoparticles were synthesized using gelatin as a polymerizing agent.
Structural, morphological and magnetic properties of samples treated at
different temperatures were investigated by X-ray diffraction, scanning
electron microscopy, Mossbauer spectroscopy and magnetization measurements. Our
results revealed that the samples annealed at 623 K and temperatures above 973
K have a cation distributions given by (Co0.19Fe0.81)[Co0.81Fe1.19]O4 and
(Co0.06Fe0.94)[Co0.94Fe1.06]O4, respectively. The particle sizes varied from 73
to 296 nm and the magnetocrystalline anisotropy, K1, has values ranging from
2.60x10^6 to 2.71x10^6 J/m3, as determined from the law of approach to
saturation applied to the MxH data at high field. At 5 K, the saturation
magnetization, coercive field and (BH)max varied from 76 to 95 Am2/kg, 479.9 to
278.5 kA/m and 9.7 to 20.9 kJ/m3, respectively. The reported values are in good
agreement with near-stoichiometric cobalt ferrite samples.",1506.00505v1
2015-07-24,Theory of perpendicular magnetocrystalline anisotropy in Fe/MgO (001),"The origin of large perpendicular magneto-crystalline anisotropy (PMCA) in
Fe/MgO (001) is revealed by comparing Fe layers with and without the MgO.
Although Fe-O $p$-$d$ hybridization is weakly present, it cannot be the main
origin of the large PMCA as claimed in previous study. Instead, perfect epitaxy
of Fe on the MgO is more important to achieve such large PMCA. As an evidence,
we show that the surface layer in a clean free-standing Fe (001) dominantly
contributes to $E_{MCA}$, while in the Fe/MgO, those by the surface and the
interface Fe layers contribute almost equally. The presence of MgO does not
change positive contribution from $\langle xz|\ell_Z|yz\rangle$, whereas it
reduces negative contribution from $\langle z^2|\ell_X|yz\rangle$ and $\langle
xy|\ell_X|xz,yz\rangle$.",1507.06799v1
2015-09-30,Magnetic anisotropy in Shiba bound states across a quantum phase transition,"The exchange coupling between magnetic adsorbates and a superconducting
substrate leads to Shiba states inside the superconducting energy gap and a
Kondo resonance outside the gap. The exchange coupling strength determines
whether the quantum many-body ground state is a Kondo singlet or a singlet of
the paired superconducting quasiparticles. Here, we use scanning tunneling
spectroscopy to identify the different quantum ground states of Manganese
phthalocyanine on Pb(111). We observe Shiba states, which are split into
triplets by magnetocrystalline anisotropy. Their characteristic spectral weight
yields an unambiguous proof of the nature of the quantum ground state.",1509.09108v1
2016-02-09,Magnetocrystalline anisotropy of Fe and Co slabs and clusters on SrTiO$\_3$ by first-principles,"In this work, we present a detailed theoretical investigation of the
electronic and magnetic properties of ferromagnetic slabs and clusters
deposited on SrTiO$\_3$ via first-principles, with a particular emphasis on the
magneto-crystalline anisotropy (MCA). We found that in the case of Fe films
deposited on SrTiO$\_3$ the effect of the interface is to quench the MCA
whereas for Cobalt we observe a change of sign of the MCA from in-plane to
out-of-plane as compared to the free surface. We also find a strong enhancement
of MCA for small clusters upon deposition on a SrTiO$\_3$ substrate. The
hybridization between the substrate and the $d$-orbitals of the cluster
extending in-plane for Fe and out-of-plane for Co is at the origin of this
enhancement of MCA. As a consequence, we predict that the Fe nanocrystals (even
rather small) should be magnetically stable and are thus good potential
candidates for magnetic storage devices.",1602.03141v1
2016-04-01,Magnetocrystalline anisotropy of FePt: a detailed view,"To get a reliable ab-initio value for the magneto-crystalline anisotropy
(MCA) energy of FePt, we employ the full-potential linearized augmented plane
wave (FLAPW) method and the full-potential Korringa-Kohn-Rostoker (KKR) Green
function method. The MCA energies calculated by both methods are in a good
agreement with each other. As the calculated MCA energy significantly differs
from experiment, it is clear that many-body effects beyond the local density
approximation are essential. It is not really important whether relativistic
effects for FePt are accounted for by solving the full Dirac equation or
whether the spin-orbit coupling (SOC) is treated as a correction to the
scalar-relativistic Hamiltonian. From the analysis of the dependence of the MCA
energy on the magnetization angle and on the SOC strength it follows that the
main mechanism of MCA in FePt can be described within second order perturbation
theory. However, a distinct contribution not accountable for by second order
perturbation theory is present as well.",1604.00176v3
2016-07-07,Giant perpendicular magnetic anisotropy energies in CoPt thin films: Impact of reduced dimensionality and imperfections,"The impact of reduced dimensionality on the magnetic properties of the
tetragonal L1$_{0}$ CoPt alloy is investigated from ab-initio considering
several kinds of surface defects. By exploring the dependence of the
magnetocrystalline anisotropy energy (MAE) on the thickness of CoPt thin films,
we demonstrate the crucial role of the chemical nature of the surface. For
instance, Pt-terminated thin films exhibit huge MAEs which can be 1000% larger
than those of Co-terminated films. Besides the perfect thin films, we
scrutinize the effect of defective surfaces such as stacking faults or
anti-sites on the surface layers. Both types of defects reduce considerably the
MAE with respect to the one obtained for Pt-terminated thin films. A detailed
analysis of the electronic structure of the thin films is provided with a
careful comparison to the CoPt bulk case. The behavior of the MAEs is then
related to the location of the different virtual bound states utilising second
order perturbation theory.",1607.01919v2
2016-11-26,Specific Heat of Spin Excitations Measured by FerromagneticResonance,"Using ferromagnetic-resonance spectroscopy (FMR), we investigate the
anisotropic properties of epitaxial 3 nmPt/2 nmAg/10 nmFe/10 nmAg/GaAs(001)
films in fully saturated meta-stable states at temperatures ranging from 70 K
to 280 K. By comparison to spin-wave theory calculations, we identify the role
of thermal fluctuation of magnons in overcoming the energy barrier associated
with these meta-stable states. We show that the energy associated with the size
of the barrier that bounds the meta-stable regime is proportional to the heat
stored in the magnonic bath. Our findings offer the possibility to measure the
magnonic contribution to the heat capacity by FMR, independent of other
contributions at temperatures ranging from 0 K to ambient temperature and
above. The only requirement being that the selected sample exhibits magnetic
anisotropy, here, magnetocrystalline anisotropy.",1611.08713v2
2017-02-22,Missing magnetism in Sr$_{4}$Ru$_{3}$O$_{10}$: Indication for Antisymmetric Exchange Interaction,"We report a detailed study of the magnetization modulus as a function of
temperature and applied magnetic field under varying angle in
Sr$_{4}$Ru$_{3}$O$_{10}$ close to the metamagnetic transition at
$H_{c}\backsimeq 2.5\,$T for $H \perp c$. We confirm that the double-feature at
$H_{c}$ is robust without further splitting for temperatures below 1.8 K down
to 0.48 K. The metamagnetism in Sr$_{4}$Ru$_{3}$O$_{10}$ is accompanied by a
reduction of the magnetic moment in the plane of rotation and large
field-hysteretic behavior. The double anomaly shifts to higher fields by
rotating the field from $H\,\perp \,c$ to $H\,\parallel\,c$. We compare our
experimental findings with numerical simulations based on spin reorientation
models caused by intrinsic magnetocrystalline anisotropy and Zeeman effect.
Crystal anisotropy is able to explain a metamagnetic transition in the
ferromagnetic ordered system Sr$_{4}$Ru$_{3}$O$_{10}$, but a
Dzyaloshinskii-Moriya term is crucial to account for a reduction of the
magnetic moment as discovered in the experiments.",1702.06882v1
2017-08-28,Electric-field-induced changes of magnetic moments and magnetocrystalline anisotropy in ultrathin cobalt films,"In this study, the microscopic origins of the voltage-controlled magnetic
anisotropy (VCMA) in 3d-ferromagnetic metals are revealed. Using in-situ X-ray
fluorescence spectroscopy that provides a high quantum efficiency,
electric-field-induced changes in orbital magnetic moment and magnetic dipole
Tz terms in ultrathin Co films are demonstrated. An orbital magnetic moment
difference of 0.013{\mu}B. was generated in the presence of electric fields of
+(-)0.2 V/nm. The VCMA of Co was properly estimated by the induced change in
orbital magnetic moment, according to the perturbation theory model. The
induced change in magnetic dipole Tz term only slightly contributed to the VCMA
in 3d-ferromagnetic metals.",1708.08549v2
2018-02-15,Origin of spin reorientation transitions in antiferromagnetic MnPt-based alloys,"Antiferromagnetic MnPt exhibits a spin reorientation transition (SRT) as a
function of temperature, and off-stoichiometric Mn-Pt alloys also display SRTs
as a function of concentration. The magnetocrystalline anisotropy in these
alloys is studied using first-principles calculations based on the coherent
potential approximation and the disordered local moment method. The anisotropy
is fairly small and sensitive to the variations in composition and temperature
due to the cancellation of large contributions from different parts of the
Brillouin zone. Concentration and temperature-driven SRTs are found in
reasonable agreement with experimental data. Contributions from specific
band-structure features are identified and used to explain the origin of the
SRTs.",1802.05685v2
2018-05-16,Magnetic properties of single crystalline itinerant ferromagnet AlFe2B2,"Single crystals of AlFe$_{2}$B$_{2}$ have been grown using the self flux
growth method and then measured the structural properties, temperature and
field dependent magnetization, and temperature dependent electrical resistivity
at ambient as well as high pressure. The Curie temperature of AlFe$_{2}$B$_{2}$
is determined to be $274$~K. The measured saturation magnetization and the
effective moment for paramagnetic Fe-ion indicate the itinerant nature of the
magnetism with a Rhode-Wohlfarth ratio $ \frac{M_{C}}{M_{sat}}\approx 1.14$.
Temperature dependent resistivity measurements under hydrostatic pressure shows
that transition temperature \textit{T$_C$} is suppressed down to 255 K for $p =
2.24$~GPa pressure with a suppression rate of $\sim -8.9$~K/GPa. The anisotropy
fields and magnetocrystalline anisotropy constants are in reasonable agreement
with density functional theory calculations.",1805.06373v1
2019-02-10,Spin dynamics of anisotropic azimuthal modes in heterogeneous magnetic nanodisks,"It is well known that azimuthal spin wave modes of magnetic vortex state in
permalloy nanodisks have circular symmetry. Intuitively, magnetic materials
having magnetocrystalline anisotropy is not compatible with the circular
symmetry of the azimuthal modes. In this article, however, we report cubic
azimuthal modes in heterogeneous nanodisks consisting of a permalloy core and a
Fe shell. The fourfold symmetry of azimuthal modes is due to the exchange, and
magneto-static, interactions between the permalloy core and the Fe shell. In
comparison to results of circular azimuthal mode, the vortex switching occurs
considerably faster under the excitation of cubic azimuthal mode. The gyration
path of vortex core turns into square under the influence of induced cubic
anisotropy in the Py region. We find out periodic oscillation of the vortex
core size and the gyration speed as well. Our findings may offer a new route
for spintronic applications using heterogeneous magnetic nanostructures.",1902.03536v1
2019-06-28,Zero-field propagation of spin waves in waveguides prepared by focused ion beam direct writing,"Metastable face-centered-cubic Fe78Ni22 thin films grown on Cu(001)
substrates are excellent candidates for focused ion beam direct writing of
magnonic structures due to their favorable magnetic properties after
ion-beam-induced transformation. The focused ion beam transforms the originally
nonmagnetic fcc phase into the ferromagnetic bcc phase with additional control
over the direction of uniaxial magnetic in-plane anisotropy. The
magnetocrystalline anisotropy in transformed areas is strong enough to
stabilize the magnetization in transverse direction to the long axis of narrow
waveguides. Therefore, it is possible to propagate spin waves in these
waveguides without the presence of an external magnetic field in the favorable
Demon-Eshbach geometry. Phase-resolved micro-focused Brillouin light scattering
yields the dispersion relation of these waveguides in zero as well as in
nonzero external magnetic fields.",1906.12254v2
2019-10-23,Computational screening of Fe-Ta hard magnetic phases,"In this work we perform a systematic calculation of the Fe-Ta phase diagram
to discover novel hard magnetic phases. By using structure prediction methods
based on evolutionary algorithms, we identify two new energetically stable
magnetic structures: a tetragonal Fe$_3$Ta (space group 122) and cubic Fe$_5$Ta
(space group 216) binary phases. The tetragonal structure is estimated to have
both high saturation magnetization ($\mu_0$M$_s$=1.14 T) and magnetocrystalline
anisotropy (K$_1$=2.17 MJ/m$^3$) suitable for permanent magnet applications.
The high-throughput screening of magneto-crystalline anisotropy also reveals
two low energy metastable hard magnetic phases: Fe$_5$Ta$_2$ (space group 156)
and Fe$_{6}$Ta (space group 194), that may exhibit intrinsic magnetic
properties comparable to SmCo$_5$ and Nd$_2$Fe$_{14}$B, respectively.",1910.10531v1
2019-11-02,Tuning Non-Gilbert-type damping in FeGa films on MgO(001) via oblique deposition,"The ability to tailor the damping factor is essential for spintronic and
spin-torque applications. Here, we report an approach to manipulate the damping
factor of FeGa/MgO(001) films by oblique deposition. Owing to the defects at
the surface or interface in thin films, two-magnon scattering (TMS) acts as a
non-Gilbert damping mechanism in magnetization relaxation. In this work, the
contribution of TMS was characterized by in-plane angular dependent
ferromagnetic resonance (FMR). It is demonstrated that the intrinsic Gilbert
damping is isotropic and invariant, while the extrinsic mechanism related to
TMS is anisotropic and can be tuned by oblique deposition. Furthermore, the two
and fourfold TMS related to the uniaxial magnetic anisotropy (UMA) and
magnetocrystalline anisotropy were discussed. Our results open an avenue to
manipulate magnetization relaxation in spintronic devices.",1911.00728v1
2020-02-26,Extreme narrow magnetic domain walls in U ferromagnets: The UCoGa case,"Surface magnetic domains of a UCoGa single crystal during
magnetization/demagnetization processes in increasing/decreasing magnetic
fields were investigated by means of magnetic-force-microscopy (MFM) images at
low temperatures. The observed domain structure is typical for a ferromagnet
with strong uniaxial anisotropy. The evolution of magnetic domains during
cooling of the crystal below TC has also been manifested by MFM images.
Analysis of the available data reveals that the high uniaxial
magnetocrystalline energy in combination with the relatively small
ferromagnetic exchange interaction in UCoGa gives rise to the formation of very
narrow domain walls formed by the pairs of the nearest U neighbor ions with
antiparallel magnetic moments within the basal plane. Since the very high
anisotropy energy is a common feature of the majority of the uniaxial U
ferromagnets, analogous domain-wall properties are expected for all these
materials.",2002.11517v1
2020-05-02,Lorentz microscopy and small-angle electron diffraction study of magnetic textures in La$_{1-x}$Sr$_x$MnO$_3$ (0.15 $< x <$ 0.30): the role of magnetic anisotropy,"Magnetic textures in the ferromagnetic phases of La$_{1-x}$Sr$_x$MnO$_3$ for
0.15 $< x <$ 0.30 have been investigated by Lorentz microscopy combined with
small-angle electron diffraction experiments. Various types of magnetic
textures characterized by stripe, plate-shaped, and cylindrical (magnetic
bubble) domains were found. Two distinct types of magnetic stripe domains
appeared in the orthorhombic structure with an inversion symmetry of
La$_{0.825}$Sr$_{0.175}$MnO$_3$, depending significantly on magnetocrystalline
anisotropy. Based on in-situ observations as functions of temperature and the
strength of the external magnetic field, a magnetic field-temperature phase
diagram was constructed, showing the stabilization of magnetic bubbles in the
ferromagnetic phase of La$_{0.825}$Sr$_{0.175}$MnO$_3$.",2005.00720v1
2020-05-10,Anisotropic Magnetocaloric Properties of The Ludwigite Single Crystal Cu2MnBO5,"We present the results of a thorough study of the specific heat and
magnetocaloric properties of a ludwigite crystal Cu2MnBO5 over a temperature
range of 60 - 350 K and in magnetic fields up to 18 kOe. It is found that at
temperatures below the Curie temperature (92 K), capacity possesses a linear
temperature-dependent behavior, which is associated with the predominance of
two-dimensional antiferromagnetic interactions of magnons. The temperature
independence of capacity is observed in the temperature range of 95 - 160 K,
which can be attributed to the excitation of the Wigner glass phase. The
magnetocaloric effect (i.e. the adiabatic temperature change) was assessed
through a direct measurement or an indirect method using the capacity data.
Owing to its strong magnetocrystalline anisotropy, an anisotropic MCE or the
rotating MCE is observed in Cu2MnBO5. A deep minimum in the rotating MCE near
the TC is observed and may be associated with the anisotropy of the
paramagnetic susceptibility.",2005.04572v1
2020-11-10,Spin-waves in the collinear antiferromagnetic phase of Mn$_\bf{5}$Si$_\bf{3}$,"By combining two independent approaches, inelastic neutron scattering
measurements and density functional theory calculations, we study the
spin-waves in the high-temperature collinear antiferromagnetic phase (AFM2) of
Mn$_5$Si$_3$. We obtain its magnetic ground-state properties and electronic
structure. This study allowed us to determine the dominant magnetic exchange
interactions and magnetocrystalline anisotropy in the AFM2 phase of
Mn$_5$Si$_3$. Moreover, the evolution of the spin excitation spectrum is
investigated under the influence of an external magnetic field perpendicular to
the anisotropy easy-axis. The low energy magnon modes show a different magnetic
field dependence which is a direct consequence of their different precessional
nature. Finally, possible effects related to the Dzyaloshinskii-Moriya
interaction are also considered.",2011.05455v3
2021-04-03,"Predicting synthesizable cobalt and manganese silicides, germanide with desirable magnetic anisotropy energy","The nanoparticle Co3Si (P63/mmc) displays remarkable magnetism [Appl. Phys.
Lett. 108, 152406 (2016)], we thus searched cobalt silicides and several phases
are searched including a Cmcm with 60 meV/atom lower than that of P63/mmc. A
lower-energy Co R3m (-7.03 eV/atom) is predicted, whose energy is higher than
that of known P63/mmc (-7.04 eV/atom) but is lower than that of Fm3m (-7.02
eV/atom). Three small-magnetism low-energy Fe5Si3 structures are searched with
energies 30 meV/atom lower than that of experimental P63/mcm. The strong
lattice shape dependence of magnetocrystalline anisotropy energy (MAE) is
studied through X5Si3 (X=Mn, Fe, Co). The building-block shape and energy order
of cobalt silicide is dominated by Co P63/mmc, Fm3m , R3m , respectively. The
Co3C and Co3Sn have positive formation of energy, thus only Co3Ge has similar
structures with those of counterparts of Co3Si. Several low-energy perfect or
nearly-perfect easy-axis/plane MAE Mn3Si, Mn5Si2, and Mn5Si3 structures are
searched and present important application, as is also the case in
Ge-containing counterparts. A structure I4122 with energy 300 meV/atom lower
than that of experimental Mn5Si3 P63/mcm is searched",2104.01333v2
2021-05-19,Experimental Evidence of a change of Exchange Anisotropy Sign with Temperature in Zn-Substituted Cu2OSeO3,"We report small-angle neutron scattering from the conical state in a single
crystal of Zn-substituted Cu2OSeO3. Using a 3D vector-field magnet to reorient
the conical wavevector, our measurements show that the magnitude of the conical
wavevector changes as a function of crystallographic direction. These changes
are caused by the anisotropic exchange interaction (AEI), whose magnitude
transitions from a maxima to a minima along the <111> and <100>
crystallographic directions respectively. We further find that the AEI constant
undergoes a change of sign from positive to negative with decreasing
temperature. Unlike in the related compound FeGe, where similar behaviour of
the AEI induces a reorientation of the helical wavevector, we show that the
zero field helical wavevector in (Cu0.98Zn0.02)2OSeO3 remains along the <100>
directions at all temperatures due to the competing fourth-order
magnetocrystalline anisotropy becoming dominant at lower temperatures.",2105.09273v1
2021-06-17,Computational Optimization of MnBi to Enhance Energy Product,"High energy density magnets are preferred over induction magnets for many
applications, including electric motors used in flying rovers, electric
vehicles, and wind turbines. However, several issues related to cost and supply
with state-of-the-art rare-earth-based magnet necessities development of
high-flux magnets containing low cost, earth-abundant materials. Here, we
demonstrate the possibility of tuning magnetization and magnetocrystalline
anisotropy of one of the candidate materials, MnBi, by alloying it with foreign
elements. By using the density functional theory in the high-throughput
fashion, we consider the possibility of alloying MnBi with all possible metal
and non-metal elements in the periodic table and found that MnBi-based alloys
with Pd, Pt, Rh, Li, and O are stable against decomposition to constituent
elements and have larger magnetization, energy product compared and magnetic
anisotropy compared to MnBi We consider the possibility of these elements
occupying half and all of the available empty sites. Combined with other
favorable properties of MnBi, such as high Curie temperature and earth
abundancy of constituents elements, we envision the possibility of MnBi-based
high-energy-density magnets.",2106.09631v1
2021-08-25,$\textit{Ab initio}$ theory of magnetism in two-dimensional $1T$-TaS$_2$,"We investigate, using a first-principles density-functional methodology, the
nature of magnetism in monolayer $1T$-phase of tantalum disulfide ($1T$-TaS$_2$
). Magnetism in the insulating phase of TaS$_2$ is a longstanding puzzle and
has led to a variety of theoretical proposals including notably the realization
of a two-dimensional quantum-spin-liquid phase. By means of non-collinear spin
calculations, we derive $\textit{ab initio}$ spin Hamiltonians including
two-spin bilinear Heisenberg exchange, as well as biquadratic and four-spin
ring-exchange couplings. We find that both quadratic and quartic interactions
are consistently ferromagnetic, for all the functionals considered.
Relativistic calculations predict substantial magnetocrystalline anisotropy.
Altogether, our results suggest that this material may realize an easy-plane
XXZ quantum ferromagnet with large anisotropy.",2108.11277v1
2021-08-31,Antiferromagnetic Hysteresis above the Spin Flop Field,"Magnetocrystalline anisotropy is essential in the physics of antiferromagnets
and commonly treated as a constant, not depending on an external magnetic
field. However, we demonstrate that in CoO the anisotropy should necessarily
depend on the magnetic field, which is shown by the spin Hall magnetoresistance
of the CoO $|$ Pt device. Below the N\'eel temperature CoO reveals a spin-flop
transition at 240 K at 7.0 T, above which a hysteresis in the angular
dependence of magnetoresistance unexpectedly persists up to 30 T. This behavior
is shown to agree with the presence of the unquenched orbital momentum, which
can play an important role in antiferromagnetic spintronics.",2109.00093v2
2021-09-23,The free energy of twisting spins in Mn$_3$Sn,"The magnetic free energy is usually quadratic in magnetic field and depends
on the mutual orientation of the magnetic field and the crystalline axes. Tiny
in magnitude, this magnetocrystalline anisotropy energy (MAE) is nevertheless
indispensable for the existence of permanent magnets. Here, we show that in
Mn$_3$Sn, a non-collinear antiferromagnet attracting much attention following
the discovery of its large anomalous Hall effect, the free energy of spins has
superquadratic components, which drive the MAE. We experimentally demonstrate
that the thermodynamic free energy includes terms odd in magnetic field
($\mathcal{O}(H^3)+\mathcal{O}(H^5)$) and generating sixfold and twelve-fold
angular oscillations in the torque response. We show that they are
quantitatively explained by theory, which can be used to quantify relevant
energy scales (Heisenberg, Dzyaloshinskii-Moriya, Zeeman and single-ion
anisotropy) of the system. Based on the theory, we conclude that, in contrast
with common magnets, what drives the MAE in Mn$_3$Sn is the field-induced
deformation of the spin texture.",2109.11122v1
2022-03-02,Polaronic Conductivity in Cr$_2$Ge$_2$Te$_6$ Single Crystals,"Intrinsic, two-dimensional (2D) ferromagnetic semiconductors are an important
class of materials for spin-charge conversion applications. Cr$_2$Ge$_2$Te$_6$
retains long-range magnetic order in bilayer at cryogenic temperatures and
shows complex magnetic interactions with considerable magnetic anisotropy.
Here, we performed a series of structural, magnetic, X-ray scattering,
electronic, thermal transport and first-principles calculation studies which
reveal that localized electronic charge carriers in Cr$_2$Ge$_2$Te$_6$ are
dressed by surrounding lattice and are involved in polaronic transport via
hopping that is sensitive on details of magnetocrystalline anisotropy. This
opens possibility for manipulation of charge transport in Cr$_2$Ge$_2$Te$_6$ -
based devices by electron-phonon- and spin-orbit coupling-based tailoring of
polaron properties.",2203.00817v1
2022-05-06,Strain-induced Shape Anisotropy in Antiferromagnetic Structures,"We demonstrate how shape-induced strain can be used to control
antiferromagnetic order in NiO/Pt thin films. For rectangular elements
patterned along the easy and hard magnetocrystalline anisotropy axes of our
film, we observe different domain structures and we identify magnetoelastic
interactions that are distinct for different domain configurations. We
reproduce the experimental observations by modeling the magnetoelastic
interactions, considering spontaneous strain induced by the domain
configuration, as well as elastic strain due to the substrate and the shape of
the patterns. This allows us to demonstrate and explain how the variation of
the aspect ratio of rectangular elements can be used to control the
antiferromagnetic ground state domain configuration. Shape-dependent strain
does not only need to be considered in the design of antiferromagnetic devices,
but can potentially be used to tailor their properties, providing an additional
handle to control antiferromagnets.",2205.02983v2
2022-11-03,Magnetism in Two-Dimensional Ilmenenes: Intrinsic Order and Strong Anisotropy,"Iron ilmenene is a new two-dimensional material that has recently been
exfoliated from the naturally-occurring iron titanate found in ilmenite ore, a
material that is abundant on earth surface. In this work, we theoretically
investigate the structural, electronic and magnetic properties of 2D
transition-metal-based ilmenene-like titanates. The study of magnetic order
reveals that these ilmenenes usually present intrinsic antiferromagnetic
coupling between the 3d magnetic metals decorating both sides of the Ti-O
layer. Furthermore, the ilmenenes based on late 3d brass metals, such as
CuTiO$_3$ and ZnTiO$_3$, become ferromagnetic and spin compensated,
respectively. Our calculations including spin-orbit coupling reveal that the
magnetic ilmenenes have large magnetocrystalline anisotropy energies when the
3d shell departs from being either filled or half-filled, with their spin
orientation being out-of-plane for elements below half-filling of 3d states and
in-plane above. These interesting magnetic properties of ilmenenes make them
useful for future spintronic applications because they could be synthesized as
already realized in the iron case.",2211.01732v1
2022-11-20,Spin-wave spectra in antidot lattice with inhomogeneous perpendicular magnetocrystalline anisotropy,"Magnonic crystals are structures with periodically varied magnetic properties
that are used to control collective spin-wave excitations. With micromagnetic
simulations, we study spin-wave spectra in a 2D antidot lattice based on a
multilayered thin film with perpendicular magnetic anisotropy (PMA). We show
that the modification of the PMA near the antidot edges introduces interesting
modifications to the spin-wave spectra, even in a fully saturated state. In
particular, the spectra split in two types of excitations, bulk modes with
amplitude concentrated in a homogeneous part of antidot lattice, and edge modes
with an amplitude localized in the rims of reduced PMA at the antidot edges.
Their dependence on the geometrical or material parameters is distinct but at
resonance conditions fulfilled, we found strong hybridization between bulk and
radial edge modes. Interestingly, the hybridization between the fundamental
modes in bulk and rim is of magnetostatic origin but the exchange interactions
determine the coupling between higher-order radial rim modes and the
fundamental bulk mode of the antidot lattice.",2211.11002v1
2023-06-30,Achiral dipoles on a ferromagnet can affect its magnetization direction,"We demonstrate the possibility of a coupling between the magnetization
direction of a ferromagnet and the tilting angle of adsorbed achiral molecules.
To illustrate the mechanism of the coupling, we analyze a minimal Stoner model
that includes Rashba spin-orbit coupling due to the electric field on the
surface of the ferromagnet. The proposed mechanism allows us to study magnetic
anisotropy of the system with an extended Stoner-Wohlfarth model, and argue
that adsorbed achiral molecules can change magnetocrystalline anisotropy of the
substrate. Our research's aim is to motivate further experimental studies of
the current-free chirality induced spin selectivity effect involving both
enantiomers.",2306.17592v2
2023-07-21,First-principles prediction of phase transition of YCo$_5$ from self-consistent phonon calculations,"Recent theoretical study has shown that the hexagonal YCo$_5$ is dynamically
unstable and distorts into a stable orthorhombic structure. In this study, we
show theoretically that the orthorhombic phase is energetically more stable
than the hexagonal phase in the low-temperature region, while the phonon
entropy stabilizes the hexagonal phase thermodynamically in the
high-temperature region. The orthorhombic-to-hexagonal phase transition
temperature is $\sim$165 K, which is determined using the self-consistent
phonon calculations. We investigate the magnetocrystalline anisotropy energy
(MAE) using the self-consistent and non-self-consistent (force theorem)
calculations with the spin-orbit interaction (SOI) along with the Hubbard $U$
correction. Then, we find that the orthorhombic phase has similar MAE, orbital
moment, and its anisotropy to the hexagonal phase when the self-consistent
calculation with the SOI is performed. Since the orthorhombic phase still gives
magnetic properties comparable to the experiments, the orthorhombic distortion
is potentially realized in the low-temperature region, which awaits
experimental exploration.",2307.11304v1
2023-10-20,Exchange-driven spin Hall effect in anisotropic ferromagnets,"Crystallographic anisotropy of the spin-dependent conductivity tensor can be
exploited to generate transverse spin-polarized current in a ferromagnetic
film. This ferromagnetic spin Hall effect is analogous to the spin-splitting
effect in altermagnets and does not require spin-orbit coupling.
First-principles screening of 41 non-cubic ferromagnets revealed that many of
them, when grown as a single crystal with tilted crystallographic axes, can
exhibit large spin Hall angles comparable with the best available
spin-orbit-driven spin Hall sources. Macroscopic spin Hall effect is possible
for uniformly magnetized ferromagnetic films grown on some low-symmetry
substrates with epitaxial relations that prevent cancellation of contributions
from different orientation domains. Macroscopic response is also possible for
any substrate if magnetocrystalline anisotropy is strong enough to lock the
magnetization to the crystallographic axes in different orientation domains.",2310.13688v2
2024-01-05,Integrated ab initio modelling of atomic order and magnetic anisotropy for rare-earth-free magnet design: effects of alloying additions in $\mathrm{L}1_0$ FeNi,"We describe an integrated modelling approach to accelerate the search for
novel, single-phase, multicomponent materials with high magnetocrystalline
anisotropy (MCA). For a given system we predict the nature of atomic ordering,
its dependence on the magnetic state, and then proceed to describe the
consequent MCA. Crucially, within our modelling framework, the same ab initio
description of the material's electronic structure determines both aspects. We
demonstrate this holistic method by studying the effects of alloying additions
in FeNi, examining systems with the general stoichiometry Fe$_4$Ni$_3X$,
including $X = $ Pt, Pd, Al, and Co. The atomic ordering behaviour predicted on
adding these elements, fundamental for determining a material's MCA, is rich
and varied. Equiatomic FeNi has been reported to require ferromagnetic order to
establish the tetragonal $\mathrm{L}1_0$ order suited for significant MCA. Our
results show that when alloying additions are included in this material,
annealing in an applied magnetic field and/or below a material's Curie
temperature may also promote tetragonal order, along with an appreciable effect
on the predicted MCA.",2401.02809v1
2024-02-14,Manipulation of magnetic anisotropy of 2D magnetized graphene by ferroelectric In$_2$Se$_3$,"The capacity to externally manipulate magnetic properties is highly desired
from both fundamental and technological perspectives, particularly in the
development of magnetoelectronics and spintronics devices. Here, using
first-principles calculations, we have demonstrated the ability of controlling
the magnetism of magnetized graphene monolayers by interfacing them with a
two-dimensional ferroelectric material. When the 3$d$ transition metal (TM) is
adsorbed on the graphene monolayer, its magnetization easy axis can be flipped
from in-plane to out-of-plane by the ferroelectric polarization reversal of
In$_2$Se$_3$, and the magnetocrystalline anisotropy energy (MAE) can be high to
-0.692 meV/atom when adopting the Fe atom at bridge site with downward
polarization. This may be a universal method since the 3$d$ TM-adsorbed
graphene has a very small MAE, which can be easily manipulated by the
ferroelectric polarization. As a result, the inherent mechanism is analyzed by
second variation method.",2402.09153v1
2002-09-26,Magnetization orientation dependence of the quasiparticle spectrum and hysteresis in ferromagnetic metal nanoparticles,"We use a microscopic Slater-Koster tight-binding model with short-range
exchange and atomic spin-orbit interactions that realistically captures generic
features of ferromagnetic metal nanoparticles to address the mesoscopic physics
of magnetocrystalline anisotropy and hysteresis in nanoparticle quasiparticle
excitation spectra. Our analysis is based on qualitative arguments supported by
self-consistent Hartree-Fock calculations for nanoparticles containing up to
260 atoms. Calculations of the total energy as a function of magnetization
direction demonstrate that the magnetic anisotropy per atom fluctuates by
several percents when the number of electrons in the particle changes by one,
even for the largest particles we consider. Contributions of individual
orbitals to the magnetic anisotropy are characterized by a broad distribution
with a mean more than two orders of magnitude smaller than its variance and
with no detectable correlations between anisotropy contribution and
quasiparticle energy. We find that the discrete quasiparticle excitation
spectrum of a nanoparticle displays a complex non-monotonic dependence on an
external magnetic field, with abrupt jumps when the magnetization direction is
reversed by the field, explaining recent spectroscopic studies of magnetic
nanoparticles. Our results suggests the existence of a broad cross-over from a
weak spin-orbit coupling to a strong spin-orbit coupling regime, occurring over
the range from approximately 200- to 1000-atom nanoparticles.",0209608v2
2016-06-10,"Spin-orbit coupling control of anisotropy, ground state and frustration in 5d2 Sr2MgOsO6","The influence of spin-orbit coupling (SOC) on the physical properties of the
5d2 system Sr2MgOsO6 is probed via a combination of magnetometry, specific heat
measurements, elastic and inelastic neutron scattering, and density functional
theory calculations. Although a significant degree of frustration is expected,
we find that Sr2MgOsO6 orders in a type I antiferromagnetic structure at the
remarkably high temperature of 108 K. The measurements presented allow for the
first accurate quantification of the size of the magnetic moment in a 5d2
system of 0.60(2) muB - a significantly reduced moment from the expected value
for such a system. Furthermore, significant anisotropy is identified via a spin
excitation gap, and we confirm by first principles calculations that SOC not
only provides the magnetocrystalline anisotropy, but also plays a crucial role
in determining both the ground state magnetic order and the size of the local
moment in this compound. Through comparison to Sr2ScOsO6, it is demonstrated
that SOC-induced anisotropy has the ability to relieve frustration in 5d2
systems relative to their 5d3 counterparts, providing an explanation of the
high TN found in Sr2MgOsO6.",1606.03231v1
2016-09-09,Effect of lithographically-induced strain relaxation on the magnetic domain configuration in microfabricated epitaxially grown Fe81Ga19,"We investigate the role of lithographically-induced strain relaxation in a
micron-scaled device fabricated from epitaxial thin films of the
magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic
patterning induces a magnetic anisotropy that competes with the
magnetocrystalline and shape induced anisotropies to play a crucial role in
stabilising a flux-closing domain pattern. We use magnetic imaging,
micromagnetic calculations and linear elastic modelling to investigate a region
close to the edges of an etched structure. This highly-strained edge region has
a significant influence on the magnetic domain configuration due to an induced
magnetic anisotropy resulting from the inverse magnetostriction effect. We
investigate the competition between the strain-induced and shape-induced
anisotropy energies, and the resultant stable domain configurations, as the
width of the bar is reduced to the nanoscale range. Understanding this
behaviour will be important when designing hybrid magneto-electric spintronic
devices based on highly magnetostrictive materials.",1609.02930v2
2017-09-28,Magnetization and Anisotropy of Cobalt Ferrite Thin Films,"The magnetization of thin films of cobalt ferrite frequently falls far below
the bulk value of 455 kAm-1, which corresponds to an inverse cation
distribution in the spinel structure with a significant orbital moment of about
0.6 muB that is associated with the octahedrally-coordinated Co2+ ions. The
orbital moment is responsible for the magnetostriction and magnetocrystalline
anisotropy, and its sensitivity to imposed strain. We have systematically
investigated the structure and magnetism of films produced by pulsed-laser
deposition on different substrates (TiO2, MgO, MgAl2O4, SrTiO3, LSAT, LaAlO3)
and as a function of temperature (500-700 C) and oxygen pressure (10-4 - 10
Pa). Magnetization at room-temperature ranges from 60 to 440 kAm-1, and
uniaxial substrate-induced anisotropy ranges from +220 kJm-3 for films on
deposited on MgO (100) to -2100 kJm-3 for films deposited on MgAl2O4 (100),
where the room-temperature anisotropy field reaches 14 T. No rearrangement of
high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce
the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+
and low-spin Co3+ on octahedral sites will reduce the low-temperature
magnetization to 120 kAm-1, and a consequent reduction of Curie temperature can
bring the room-temperature value to near zero. Possible reasons for the
appearance of low-spin cobalt in the thin films are discussed.
  Keywords; Cobalt ferrite, thin films, pulsed-laser deposition, low-spin Co3+,
strain engineering of magnetization.",1709.09965v1
2018-03-28,Perpendicular magnetic anisotropy at the Fe/MgAl$_2$O$_4$ interface: Comparative first-principles study with Fe/MgO,"We present a theoretical study on interfacial magnetocrystalline anisotropy
for Fe/MgAl$_2$O$_4$. This system has a very small lattice mismatch at the
interface and therefore is suitable for realizing a fully coherent
ferromagnet/oxide interface for magnetic tunnel junctions. On the basis of
density functional theory, we calculate the interfacial anisotropy constant
$K_{\rm i}$ and show that this system has interfacial perpendicular magnetic
anisotropy (PMA) with $K_{\rm i} \approx 1.2\,{\rm mJ/m^2}$, which is a little
bit smaller than that of Fe/MgO ($K_{\rm i} \approx$ 1.5--1.7$\,{\rm mJ/m^2}$).
Second-order perturbation analysis with respect to the spin-orbit interaction
clarifies that the difference in $K_{\rm i}$ between Fe/MgAl$_2$O$_4$ and
Fe/MgO originates from the difference in contributions from spin-flip
scattering terms at the interface. We propose that the insertion of tungsten
layers into the interface of Fe/MgAl$_2$O$_4$ is a promising way to obtain huge
interfacial PMA with $K_{\rm i} \gtrsim 3\,{\rm mJ/m^2}$.",1803.10428v5
2018-06-06,High performance magnetic material with Ce and La: an alternative to Nd-Fe-B magnet,"A systematic study of magnetocrystalline anisotropy is performed for
R(La/Ce/Nd)2Fe14B tetragonal compound with the site substitution mechanism.
Theoretical calculation suggests the 50% doping with Ce at 4f-site can lead to
competitive magnetic anisotropy to that of the champion magnet Nd2Fe14B.
Electronic structure calculations are performed using the full-potential
linearized augmented plane wave method by inclusion of the spin-orbit coupling
and Hubbard (U) interaction in the calculation for the rare-earth elements to
get the correct influence of the localized 4f orbitals. Detailed analysis of
the magnetic moment and magnetic anisotropy change has been studied by
individually inserting the La and Ce atoms at the two inequivalent sites (4g
and 4f sites) of the 2-14-B tetragonal structure. Accurate prediction of the
total magnetic moment with the orbital contribution in the 2-14-B structure
shows the maximum moment for Ce2Fe14B (3.86 {\mu}B/f.u less) compared to
Nd2Fe14B. Theoretical analysis confirms that regardless of the anti-parallel
spin moment emerging in the Ce atom the complex structure of the Ce substituted
compound at 4f-site gives the maximum anisotropy of 2.27 meV/cell with lowering
the magnetic moment by 1.26 {\mu}B/f.u. compared to the Nd2Fe14B compound.",1806.01990v1
2019-07-05,Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy,"Materials suitable for magnonic crystals demand low magnetic damping and long
spin wave (SW) propagation distance. In this context Co based Heusler compounds
are ideal candidates for magnonic based applications. In this work, antidot
arrays (with different shapes) of epitaxial
$\mathrm{Co}_2\mathrm{Fe}_{0.4}\mathrm{Mn}_{0.6}\mathrm{Si}$ (CFMS) Heusler
alloy thin films have been prepared using e-beam lithography and sputtering
technique. Magneto-optic Kerr effect and ferromagnetic resonance analysis have
confirmed the presence of dominant cubic and moderate uniaxial magnetic
anisotropies in the thin films. Domain imaging via x-ray photoemission electron
microscopy on the antidot arrays reveals chain like switching or correlated
bigger domains for different shape of the antidots. Time-resolved MOKE
microscopy has been performed to study the precessional dynamics and magnonic
modes of the antidots with different shapes. We show that the optically induced
spin-wave spectra in such antidot arrays can be tuned by changing the shape of
the holes. The variation in internal field profiles, pinning energy barrier,
and anisotropy modifies the spin-wave spectra dramatically within the antidot
arrays with different shapes. We further show that by combining the
magnetocrystalline anisotropy with the shape anisotropy, an extra degree of
freedom can be achieved to control the magnonic modes in such antidot lattices.",1907.02746v1
2021-07-28,Field tunable three-dimensional magnetic nanotextures in cobalt-nickel nanowires,"Cylindrical magnetic nanowires with large transversal magnetocrystalline
anisotropy have been shown to sustain non-trivial magnetic configurations
resulting from the interplay of spatial confinement, exchange, and
anisotropies. Exploiting these peculiar 3D spin configurations and their
solitonic inhomogeneities are prospected to improve magnetization switching in
future spintronics, such as power-saving magnetic memory and logic
applications. Here we employ holographic vector field electron tomography to
reconstruct the remanent magnetic states in CoNi nanowires with 10 nm
resolution in 3D, with a particular focus on domain walls between remanent
states and ubiquitous real-structure effects stemming from irregular morphology
and anisotropy variations. By tuning the applied magnetic field direction, both
longitudinal and transverse multi-vortex states of different chiralities and
peculiar 3D features such as shifted vortex cores are stabilized. The chiral
domain wall between the longitudinal vortices of opposite chiralities exhibits
a complex 3D shape characterized by a push out of the central vortex line and a
gain in exchange and anisotropy energy. A similar complex 3D texture, including
bent vortex lines, forms at the domain boundary between transverse-vortex
states and longitudinal configurations. Micromagnetic simulations allow an
understanding of the origin of the observed complex magnetic states.",2107.13201v1
2021-11-13,Sensitive electronic correlation effects on electronic properties in ferrovalley material Janus FeClF monolayer,"The electronic correlation may have essential influence on electronic
structures in some materials with special structure and localized orbital
distribution. In this work, taking Janus monolayer FeClF as a concrete example,
the correlation effects on its electronic structures are investigated by using
generalized gradient approximation plus $U$ (GGA+$U$) approach. For
perpendicular magnetic anisotropy (PMA), the increasing electron correlation
effect can induce the ferrovalley (FV) to half-valley-metal (HVM) to quantum
anomalous Hall (QAH) to HVM to FV transitions. For QAH state, there are a unit
Chern number and a chiral edge state connecting the conduction and valence
bands. The HVM state is at the boundary of the QAH phase, whose carriers are
intrinsically 100\% valley polarized. With the in-plane magnetic anisotropy, no
special QAH states and prominent valley polarization are observed. However, for
both out-of-plane and in-plane magnetic anisotropy, sign-reversible Berry
curvature can be observed with increasing $U$. It is found that these
phenomenons are related with the change of $d_{xy}$/$d_{x^2-y^2}$ and $d_{z^2}$
orbital distributions and different magnetocrystalline directions. It is also
found that the magnetic anisotropy energy (MAE) and Curie temperature strongly
depend on the $U$. With PMA, taking typical $U=$2.5 eV, the electron valley
polarization can be observed with valley splitting of 109 meV, which can be
switched by reversing the magnetization direction. The analysis and results can
be readily extended to other nine members of monolayer FeXY (X/Y=F, Cl, Br and
I) due to sharing the same Fe-dominated low-energy states and electronic
correlations with FeClF monolayer.",2111.07110v1
2019-09-10,Contributions of magnetic structure and nitrogen to perpendicular magnetocrystalline anisotropy in antiperovskite $ε$-Mn$_4$N,"To study how nitrogen contributes to perpendicular magnetocrystalline
anisotropy (PMA) in the ferrimagnetic antiperovskite Mn$_4$N, we examined both
the fabrication of epitaxial Mn$_4$N films with various nitrogen contents and
first-principles density-functional calculations. Saturation magnetization
($M_{\rm s}$) peaks of 110 mT and uniaxial PMA energy densities ($K_{\rm u}$)
of 0.1 MJ/m$^3$ were obtained for a N$_2$ gas flow ratio ($Q$) of $\sim 10 \%$
during sputtering deposition, suggesting nearly single-phase crystalline
$\epsilon$-Mn$_4$N. Segregation of $\alpha$-Mn and nitrogen-deficient Mn$_4$N
grains was observed for $Q \approx 6\%$, which was responsible for a decrease
in the $M_{\rm s}$ and $K_{\rm u}$. The first-principles calculations revealed
that the magnetic structure of Mn$_4$N showing PMA was ""type-B"" having a
collinear structure, whose magnetic moments couple parallel within the c-plane
and alternating along the c-direction. In addition, the $K_{\rm u}$ calculated
using Mn$_{32}$N$_x$ supercells showed a strong dependence on nitrogen
deficiency, in qualitative agreement with the experimental results. The
second-order perturbation analysis of $K_{\rm u}$ with respect to the
spin-orbit interaction revealed that not only spin-conserving but also
spin-flip processes contribute significantly to the PMA in Mn$_4$N. We also
found that both contributions decreased with increasing nitrogen deficiency,
resulting in the reduction of $K_{\rm u}$. It was noted that the decrease in
the spin-flip contribution occurred at the Mn atoms in face-centered sites.
This is one of the specific PMA characteristics we found for
antiperovskite-type Mn$_4$N.",1909.04308v3
2021-01-26,Data-driven design of a new class of rare-earth free permanent magnets,"A new class of rare-earth-free permanent magnets is proposed. The parent
compound of this class is Co$_3$Mn$_2$Ge, and its discovery is the result of
first principles theory combined with experimental synthesis and
characterisation. The theory is based on a high-throughput/data-mining search
among materials listed in the ICSD database. From ab-initio theory of the
defect free material it is predicted that the saturation magnetization is 1.71
T, the uniaxial magnetocrystalline anisotropy is 1.44 MJ/m$^3$, and the Curie
temperature is 700 K. Co$_3$Mn$_2$Ge samples were then synthesized and
characterised with respect to structure and magnetism. The crystal structure
was found to be the MgZn$_2$-type, with partial disorder of Co and Ge on the
crystallographic lattice sites. From magnetization measurements a saturation
polarization of 0.86 T at 10 K was detected, together with a uniaxial
magnetocrystalline anisotropy constant of 1.18 MJ/m$^3$, and the Curie
temperature of $T_{\rm C}$ = 359 K. These magnetic properties make
Co$_3$Mn$_2$Ge a very promising material as a rare-earth free permanent magnet,
and since we can demonstrate that magnetism depends critically on the amount of
disorder of the Co and Ge atoms, a further improvement of the magnetism is
possible. From the theoretical works, a substitution of Ge by neighboring
elements suggest two other promising materials - Co$_3$Mn$_2$Al and
Co$_3$Mn$_2$Ga. We demonstrate here that the class of compounds based on
$T_3$Mn$_2$X (T = Co or alloys between Fe and Ni; X=Ge, Al or Ga) in the
MgZn$_2$ structure type, form a new class of rare-earth free permanent magnets
with very promising performance.",2101.10773v1
2022-04-20,"The first- and second-order magneto-optical effects and intrinsically anomalous transport in 2D van der Waals layered magnets CrXY (X = S, Se, Te; Y = Cl, Br, I)","Recently, the two-dimensional magnetic semiconductor CrSBr has attracted
considerable attention due to its excellent air-stable property and high
magnetic critical temperature. Here, we systematically investigate the
electronic structure, magnetocrystalline anisotropy energy, first-order
magneto-optical effects (Kerr and Faraday effects) and second-order
magneto-optical effects (Schafer-Hubert and Voigt effects) as well as
intrinsically anomalous transport properties (anomalous Hall, anomalous Nernst,
and anomalous thermal Hall effects) of two-dimensional van der Waals layered
magnets CrXY (X = S, Se, Te; Y = Cl, Br, I) by using the first-principles
calculations. Our results show that monolayer and bilayer CrXY (X = S, Se) are
narrow band gap semiconductors, whereas monolayer and bilayer CrTeY are
multi-band metals. The magnetic ground states of bilayer CrXY and the easy
magnetization axis of monolayer and bilayer CrXY are confirmed by the
magnetocrystalline anisotropy energy calculations. Utilizing magnetic group
theory analysis, the first-order magneto-optical effects as well as anomalous
Hall, anomalous Nernst, and anomalous thermal Hall effects are identified to
exist in ferromagnetic state with out-of-plane magnetization. The second-order
magneto-optical effects are not restricted by the above symmetry requirements,
and therefore can arise in ferromagnetic and antiferromagnetic states with
in-plane magnetization. The calculated results are compared with the available
theoretical and experimental data of other two-dimensional magnets and some
conventional ferromagnets. The present work reveals that monolayer and bilayer
CrXY with superior magneto-optical responses and anomalous transport properties
provide an excellent material platform for the promising applications of
magneto-optical devices, spintronics, and spin caloritronics.",2204.09223v2
2015-04-09,Site occupancy and magnetic properties of Al-substituted M-type strontium hexaferrite,"We use first-principles total-energy calculations based on density functional
theory to study the site occupancy and magnetic properties of Al-substituted
$M$-type strontium hexaferrite SrFe$_{12-x}$Al$_{x}$O$_{19}$ with $x=0.5$ and
$x=1.0$. We find that the non-magnetic Al$^{3+}$ ions preferentially replace
Fe$^{3+}$ ions at two of the majority spin sites, $2a$ and $12k$, eliminating
their positive contribution to the total magnetization causing the saturation
magnetization $M_s$ to be reduced as Al concentration $x$ is increased. Our
formation probability analysis further provides the explanation for increased
magnetic anisotropy field when the fraction of Al is increased. Although
Al$^{3+}$ ions preferentially occupy the $2a$ sites at a low temperature, the
occupation probability of the $12k$ site increases with the rise of the
temperature. At a typical annealing temperature ($> 700\,^{\circ}{\rm C}$)
Al$^{3+}$ ions are much more likely to occupy the $12k$ site than the $2a$
site. Although this causes the magnetocrystalline anisotropy $K_1$ to be
reduced slightly, the reduction in $M_s$ is much more significant. Their
combined effect causes the anisotropy field $H_a$ to increase as the fraction
of Al is increased, consistent with recent experimental measurements.",1504.02320v2
2015-07-09,Validity of the Néel-Arrhenius model for highly anisotropic Co_xFe_{3-x}O_4 nanoparticles,"We report a systematic study on the structural and magnetic properties of
Co_{x}Fe_{3-x}O_{4} magnetic nanoparticles with sizes between $5$ to $25$ nm,
prepared by thermal decomposition of Fe(acac)_{3} and Co(acac)_{2}. The large
magneto-crystalline anisotropy of the synthesized particles resulted in high
blocking temperatures ($42$ K \leqq $T_B$ $\leqq 345$ K for $5 \leqq$ d $\leqq
13$ nm ) and large coercive fields ($H_C \approxeq 1600$ kA/m for $T = 5$ K).
The smallest particles ($<d>=5$ nm) revealed the existence of a magnetically
hard, spin-disordered surface. The thermal dependence of static and dynamic
magnetic properties of the whole series of samples could be explained within
the N\'{e}el-Arrhenius relaxation framework without the need of ad-hoc
corrections, by including the thermal dependence of the magnetocrystalline
anisotropy constant $K_1(T)$ through the empirical Br\""{u}khatov-Kirensky
relation. This approach provided $K_1(0)$ values very similar to the bulk
material from either static or dynamic magnetic measurements, as well as
realistic values for the response times ($\tau_0 \simeq 10^{-10}$ s).
Deviations from the bulk anisotropy values found for the smallest particles
could be qualitatively explained based on Zener\'{}s relation between $K_1(T)$
and M(T).",1507.02711v1
2016-12-08,Elucidating the Voltage Controlled Magnetic Anisotropy,"Voltage controlled magnetic anisotropy (VCMA) is an efficient way to
manipulate the magnetization states in nanomagnets, promising for low-power
spintronic applications. The underlying physical mechanism for VCMA is known to
involve a change in the d-orbital occupation on the transition metal interface
atoms with an applied electric field. However, a simple qualitative picture of
how this occupation controls the magnetocrystalline anisotropy (MCA) and even
why in certain cases the MCA has opposite sign still remains elusive. In this
paper, we exploit a simple model of orbital populations to elucidate a number
of features typical for the interface MCA and the effect of electric field on
it, for 3d transition metal thin films used in magnetic tunnel junctions. We
find that in all considered cases including the Fe (001) surface, clean
Fe1-xCox(001)/MgO interface and oxidized Fe(001)/MgO interface, the effects of
alloying and electric field enhance the MCA energy with electron depletion
which is largely explained by the occupancy of the minority-spin dxz,yz
orbitals. On the other hand, the hole doped Fe(001) exhibits an inverse VCMA,
where the MCA enhancement is achieved when electrons are accumulated at the Fe
(001)/MgO interface with applied electric field. In this regime we predict a
significantly enhanced VCMA which exceeds 1pJ/Vm. Realizing this regime
experimentally may be favorable for a practical purpose of voltage driven
magnetization reversal.",1612.02724v1
2018-04-27,Intrinsic permanent magnetic characteristics beyond Ce2Co17 with Ce/Co substitutions,"By understanding the small easy axis magnetocrystalline anisotropy energy
(MAE) of hexagonal Ce2Co17, an attempt has been made to improve anisotropy and
consequently to obtain better characteristics for a high energy permanent
magnet via site selective substitutional doping of Ce/Co with suitable
elements. The present calculations of the electronic and magnetic properties of
Ce2Co17 and related substituted compounds have been performed using the full
potential linear augmented plane wave (FPLAPW) method within the generalized
gradient approximation (GGA). Sm-substituted compounds were simulated using
Coulomb corrected GGA (GGA+U) to provide a better representation of energy
bands due to the strongly correlated Sm-f electrons. The formation energies for
all substituted compounds are found to be negative which indicate their
structural stability. Of the substitutions, Zr substitution at the Co-dumbbell
site enhances uniaxial anisotropy of Ce2Co17. Furthermore, Sm-substitution at
Ce-2c sites favors incremental MAE whereas a La-substitution at both 2b- and
2c-sites depletes the tiny MAE in Ce2Co17. These observed trends in the MAE
have been examined in terms of contributions from various electronic states.
Finally, Ce2Zr2Co15 and SmCeCo17 are foreseen as suitable materials for
designing permanent magnets derived from the crystal lattice structure of
hexagonal Ce2Co17.",1804.10310v2
2018-08-17,Temperature Dependence of Magnetic Properties of an 18-nm-thick YIG Film Grown by Liquid Phase Epitaxy: Effect of a Pt Overlayer,"Liquid phase epitaxy of an 18 nm thick Yttrium Iron garnet (YIG) film is
achieved. Its magnetic properties are investigated in the 100 -- 400 K
temperature range, as well as the influence of a 3 nm thick Pt overlayer on
them. The saturation magnetization and the magnetocrystalline cubic anisotropy
of the bare YIG film behave similarly to bulk YIG. A damping parameter of only
a few $10^{-4}$ is measured, together with a low inhomogeneous contribution to
the ferromagnetic resonance linewidth. The magnetic relaxation increases upon
decreasing temperature, which can be partly ascribed to impurity relaxation
mechanisms. While it does not change its cubic anisotropy, the Pt capping
strongly affects the uniaxial perpendicular anisotropy of the YIG film, in
particular at low temperatures. The interfacial coupling in the YIG/Pt
heterostructure is also revealed by an increase of the linewidth, which
substantially grows by lowering the temperature.",1808.05785v2
2019-05-16,Ultralow-loss domain wall motion driven by magnetocrystalline anisotropy gradient in antiferromagnetic nanowire,"Searching for new methods controlling antiferromagnetic (AFM) domain wall is
one of the most important issues for AFM spintronic device operation. In this
work, we study theoretically the domain wall motion of an AFM nanowire, driven
by the axial anisotropy gradient generated by external electric field, allowing
the electro control of AFM domain wall motion in the merit of ultra-low energy
loss. The domain wall velocity depending on the anisotropy gradient magnitude
and intrinsic material properties is simulated based on the
Landau-Lifshitz-Gilbert equation and also deduced using the energy dissipation
theorem. It is found that the domain wall moves at a nearly constant velocity
for small gradient, and accelerates for large gradient due to the enlarged
domain wall width. The domain wall mobility is independent of lattice dimension
and types of domain wall, while it is enhanced by the Dzyaloshinskii-Moriya
interaction. In addition, the physical mechanism for much faster AFM wall
dynamics than ferromagnetic wall dynamics is qualitatively explained. This work
unveils a promising strategy for controlling the AFM domain walls, benefiting
to future AFM spintronic applications.",1905.06695v2
2022-05-20,A feasibility analysis towards the simulation of hysteresis with spin-lattice dynamics,"We use spin-lattice dynamics simulations to study the possibility of modeling
the magnetic hysteresis behavior of a ferromagnetic material. The temporal
evolution of the magnetic and mechanical degrees of freedom is obtained through
a set of two coupled Langevin equations. Hysteresis loops are calculated for
different angles between the external field and the magnetocrystalline
anisotropy axes. The influence of several relevant parameters is studied,
including the field frequency, magnetic damping, magnetic anisotropy (magnitude
and type), magnetic exchange, and system size. The role played by a moving
lattice is also discussed. For a perfect bulk ferromagnetic system we find
that, at low temperatures, the exchange and lattice dynamics barely affect the
loops, while the field frequency and magnetic damping have a large effect on
it. The influence of the anisotropy magnitude and symmetry are found to follow
the expected behavior. We show that a careful choice of simulation parameters
allows for an excellent agreement between the spin-lattice dynamics
measurements and the paradigmatic Stoner-Wohlfarth model. Furthermore, we
extend this analysis to intermediate and high temperatures for the perfect bulk
system and for spherical nanoparticles, with and without defects, reaching
values close to the Curie temperature. In this temperature range, we find that
lattice dynamics has a greater role on the magnetic behavior, especially in the
evolution of the defective samples. The present study opens the possibility for
more accurate inclusion of lattice defects and thermal effects in hysteresis
simulations",2205.10418v3
2022-08-13,"2D-XY ferromagnetism with high transition temperature in Janus monolayer V$_{2}$XN (X = P, As)","Two-dimensional (2D) XY magnets with easy magnetization planes support the
nontrivial topological spin textures whose dissipationless transport is highly
desirable for 2D spintronic devices. Here, we predicted that Janus monolayer
V$_{2}$XN (X = P, As) with a square lattice are 2D-XY ferromagnets by
first-principles calculations. Both the magnetocrystalline anisotropy and
magnetic shape anisotropy favor an in-plane magnetization, leading to an easy
magnetization $xy$-plane in Janus monolayer V$_{2}$XN. Resting on the Monte
Carlo simulations, we observed the Berezinskii-Kosterlitz-Thouless (BKT) phase
transition in monolayer V$_{2}$XN with transition temperature $T_{\rm BKT}$
being above the room temperature. Especially, monolayer V$_{2}$AsN has a
magnetic anisotropy energy (MAE) of 292.0 $\mu$eV per V atom and a $T_{\rm
BKT}$ of 434 K, which is larger than that of monolayer V$_{2}$PN. Moreover, a
tensile strain of 5\% can further improve the $T_{\rm BKT}$ of monolayer
V$_{2}$XN to be above 500 K. Our results indicated that Janus monolayer
V$_{2}$XN (X = P, As) were candidate materials to realize high-temperature
2D-XY ferromagnetism for spintronics applications.",2208.06745v2
2023-08-08,Giant magnetic and optical anisotropy in cerium-substituted M-type strontium hexaferrite driven by 4$f$ electrons,"By performing density functional calculations, we find a giant
magnetocrystalline anisotropy (MCA) constant in abundant element cerium (Ce)
substituted M-type hexaferrite, in the energetically favorable strontium site,
assisted by a quantum confined electron transfer from Ce to specific iron (2a)
site. Remarkably, the calculated electronic structure shows that the electron
transfer leads to the formation of Ce$^{3+}$ and Fe$^{2+}$ at the $2a$ site
producing an occupied Ce($4f^1$) state below the Fermi level that adds a
significant contribution to MCA and magnetic moment. A half Ce-substitution
forms a metallic state, while a full substitution retains the semiconducting
state of the strontium-hexaferrite (host). In the latter, the band gap is
reduced due to the formation of charge transferred states in the gap region of
the host. The optical absorption coefficient shows an enhanced anisotropy
between light polarization in parallel and perpendicular directions. Calculated
formation energies, including the analysis of probable competing phases, and
elastic constants confirm that both compositions are chemically and
mechanically stable. With successful synthesis, the Ce-hexaferrite can be a new
high-performing critical-element-free permanent magnet material adapted for use
in devices such as automotive traction drive motors.",2308.04594v2
2024-02-15,Dimension-Dependent Critical Scaling Analysis and Emergent Competing Interaction Scales in a 2D Van der Waals magnet Cr$_{2}$Ge$_{2}$Te$_{6}$,"We investigate thickness-dependent transformation from a paramagnetic to
ferromagnetic phase in Cr$_{2}$Ge$_{2}$Te$_{6}$ (CGT) in bulk and few-layer
flake forms. 2D Ising-like critical transition in bulk CGT occurs at $T_{c}$ =
67 K with out-of-plane magnetic anisotropy. Few-layer CGT on hBN/SiO$_{2}$/Si
substrate displays the same $T_{c}$ but also exhibits a new critical transition
at $T^{\prime}_c$ = 14.2 K. Here, critical scaling analysis reveals the
critical exponents differ significantly from those in bulk and do not align
with the known universality classes. Our Density Functional Theory (DFT) and
classical calculations indicate competition between magnetocrystalline and
dipolar anisotropy emerges with reduced dimensions. The observed behavior is
due to minor structural distortions in low dimensional CGT, which modify the
balance between spin-orbit coupling, exchange interactions and dipolar
anisotropy. This triggers a critical crossover at $T^{\prime}_c$. Our study
shows the emergence of a complex interplay of short- and long-range
interactions below $T^{\prime}_c$ as CGT approaches the 2D limit.",2402.09741v1
1995-08-26,Magnetic Properties of Epitaxial and Polycrystalline Fe/Si Multilayers,"Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown
via ion-beam sputtering on both glass and single-crystal substrates. High-angle
x-ray diffraction measurements show that both sets of films have narrow Fe
peaks, implying a large crystallite size and crystalline iron silicide spacer
layers. Low-angle x-ray diffraction measurements show that films grown on glass
have rougher interfaces than those grown on single-crystal substrates. The
multilayers grown on glass have a larger remanent magnetization than the
multilayers grown on single-crystal substrates. The observation of
magnetocrystalline anisotropy in hysteresis loops and $(hkl)$ peaks in x-ray
diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The
smaller remanent magnetization in Fe/Si multilayers with better layering
suggests that the remanence is not an intrinsic property.",9508117v1
1997-01-07,Magnetic Field Dependence of Macroscopic Quantum Tunneling and Coherence of Ferromagnetic Particle,"We calculate the quantum tunneling rate of a ferromagnetic particle of $\sim
100 \AA$ diameter in a magnetic field of arbitrary angle. We consider the
magnetocrystalline anisotropy with the biaxial symmetry and that with the
tetragonal symmetry. Using the spin-coherent-state path integral, we obtain
approximate analytic formulas of the tunneling rates in the small $\epsilon
(=1- H/H_c)$-limit for the magnetic field normal to the easy axis ($\theta_H =
\pi/2$), for the field opposite to the initial easy axis ($\theta_H = \pi$),
and for the field at an angle between these two orientations ($\pi/2 <<
\theta_H << \pi$). In addition, we obtain numerically the tunneling rates for
the biaxial symmetry in the full range of the angle $\theta_H$ of the magnetic
field ($\pi/2 < \theta_H \leq \pi$), for the values of \epsilon =0.01 and
0.001.",9701030v1
2000-05-23,Spin tunneling of trigonal and hexagonal ferromagnets in an arbitrarily directed magnetic field,"The quantum tunneling of the magnetization vector are studied theoretically
in single-domain ferromagnetic nanoparticles placed in an external magnetic
field at an arbitrarily directed angle in the $ZX$ plane. We consider the
magnetocrystalline anisotropy with trigonal and hexagonal crystal symmetry,
respectively. By applying the instanton technique in the spin-coherent-state
path-integral representation, we calculate the tunnel splittings, the tunneling
rates and the crossover temperatures in the low barrier limit for different
angle ranges of the external magnetic field ($\theta_{H}=\pi/2$,
$\pi/2\ll\theta_{H}\ll\pi$, and $\theta_{H}=\pi$). Our results show that the
tunnel splittings, the tunneling rates and the crossover temperatures depend on
the orientation of the external magnetic field distinctly, which provides a
possible experimental test for magnetic quantum tunneling in nanometer-scale
single-domain ferromagnets.",0005373v1
2000-05-29,Quantum nucleation in ferromagnets with tetragonal and hexagonal symmetries,"The phenomenon of quantum nucleation is studied in a ferromagnet in the
presence of a magnetic field at an arbitrary angle. We consider the
magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal
symmetry, respectively. By applying the instanton method in the
spin-coherent-state path-integral representation, we calculate the dependence
of the rate of quantum nucleation and the crossover temperature on the
orientation and strength of the field for a thin film and for a bulk solid. Our
results show that the rate of quantum nucleation and the crossover temperature
depend on the orientation of the external magnetic field distinctly, which
provides a possible experimental test for quantum nucleation in nanometer-scale
ferromagnets.",0005491v2
2000-11-01,"Magnetism, Spin-Orbit Coupling, and Superconducting Pairing in UGe$_2$","A consistent picture on the mean-field level of the magnetic properties and
electronic structure of the superconducting itinerant ferromagnet UGe$_2$ is
shown to require inclusion of correlation effects beyond the local density
approximation (LDA). The ""LDA+U"" approach reproduces both the magnitude of the
observed moment, composed of strongly opposing spin and orbital parts, and the
magnetocrystalline anisotropy. The largest Fermi surface sheet is comprised
primarily of spin majority states with orbital projection $m_{\ell}$=0,
suggesting a much simpler picture of the pairing than is possible for general
strong spin-orbit coupled materials. This occurrence, and the
quasi-two-dimensional geometry of the Fermi surface, support the likelihood of
magnetically mediated p-wave triplet pairing.",0011026v1
2000-11-24,Relativistic corrections in magnetic systems,"We present a weak-relativistic limit comparison between the Kohn-Sham-Dirac
equation and its approximate form containing the exchange coupling, which is
used in almost all relativistic codes of density-functional theory. For these
two descriptions, an exact expression of the Dirac Green's function in terms of
the non-relativistic Green's function is first derived and then used to
calculate the effective Hamiltonian, i.e., Pauli Hamiltonian, and effective
velocity operator in the weak-relativistic limit. We point out that, besides
neglecting orbital magnetism effects, the approximate Kohn-Sham-Dirac equation
also gives relativistic corrections which differ from those of the exact
Kohn-Sham-Dirac equation. These differences have quite serious consequences: in
particular, the magnetocrystalline anisotropy of an uniaxial ferromagnet and
the anisotropic magnetoresistance of a cubic ferromagnet are found from the
approximate Kohn-Sham-Dirac equation to be of order $1/c^2$, whereas the
correct results obtained from the exact Kohn-Sham-Dirac equation are of order
$1/c^4$ . We give a qualitative estimate of the order of magnitude of these
spurious terms.",0011426v3
2002-01-22,Magnetocrystalline Anisotropy in a Single Crystal of CeNiGe2,"We report measurements on single crystals of orthorhombic CeNiGe2, which is
found to exhibit highly anisotropic magnetic and transport properties. The
magnetization ratio M(H//b)/M(H^b) at 2 K is observed to be about 18 at 4 T and
the electrical resistivity ratio r//b/r^b is about 70 at room temperature. It
is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at 4
and 3 K, as reported for polycrystalline samples. The application of magnetic
field along the b axis (the easy magnetization axis) stabilizes a ferromagnetic
correlation between the Ce ions and enhances the hopping of carriers. This
results in large negative magnetoresistance along the b axis.",0201399v1
2002-01-23,Spin tunneling properties in mesoscopic magnets: effects of a magnetic field,"The tunneling of a giant spin at excited levels is studied theoretically in
mesoscopic magnets with a magnetic field at an arbitrary angle in the easy
plane. Different structures of the tunneling barriers can be generated by the
magnetocrystalline anisotropy, the magnitude and the orientation of the field.
By calculating the nonvacuum instanton solution explicitly, we obtain the
tunnel splittings and the tunneling rates for different angle ranges of the
external magnetic field ($\theta_{H}=\pi/2$ and $\pi/2<\theta_{H}<\pi$). The
temperature dependences of the decay rates are clearly shown for each case. It
is found that the tunneling rate and the crossover temperature depend on the
orientation of the external magnetic field. This feature can be tested with the
use of existing experimental techniques.",0201406v1
2003-02-20,Dynamical Nuclear Polarization by Electrical Spin Injection in Ferromagnet-Semiconductor Heterostructures,"Electrical spin injection from Fe into Al$_x$Ga$_{1-x}$As quantum well
heterostructures is demonstrated in small (< 500 Oe) in-plane magnetic fields.
The measurement is sensitive only to the component of the spin that precesses
about the internal magnetic field in the semiconductor. This field is much
larger than the applied field and depends strongly on the injection current
density. Details of the observed hysteresis in the spin injection signal are
reproduced in a model that incorporates the magnetocrystalline anisotropy of
the epitaxial Fe film, spin relaxation in the semiconductor, and the dynamical
polarization of nuclei by the injected spins.",0302391v1
2003-11-19,Shape memory ferromagnets,"In ferromagnetic alloys with shape memory large reversible strains can be
obtained by rearranging the martensitic domain structure by a magnetic field.
Magnetization through displacement of domain walls is possible in the presence
of high magnetocrystalline anisotropy, when martensitic structure rearrangement
is energetically favorable compared to the reorientation of magnetic moments.
In ferromagnetic Heusler alloys Ni$_{2+x}$Mn$_{1-x}$Ga the Curie temperature
exceeds the martensitic transformation temperature. The fact that these two
temperatures are close to room temperature offers the possibility of
magnetically controlling the shape and size of ferromagnets in the martensitic
state. In Ni$_{2+x}$Mn$_{1-x}$Ga single crystals, a reversible strain of $\sim
6$% is obtained in fields of $\sim 1$ T.",0311433v1
2005-04-19,Nature of magnetism in Ca$_3$Co$_2$O$_6$,"We find using LSDA+U band structure calculations that the novel
one-dimensional cobaltate Ca$_3$Co$_2$O$_6$ is not a ferromagnetic half-metal
but a Mott insulator. Both the octahedral and the trigonal Co ions are formally
trivalent, with the octahedral being in the low-spin and the trigonal in the
high-spin state. The inclusion of the spin-orbit coupling leads to the
occupation of the minority-spin $d_{2}$ orbital for the unusually coordinated
trigonal Co, producing a giant orbital moment (1.57 $\mu_{B}$). It also results
in an anomalously large magnetocrystalline anisotropy (of order 70 meV),
elucidating why the magnetism is highly Ising-like. The role of the oxygen
holes, carrying an induced magnetic moment of 0.13 $\mu_{B}$ per oxygen, for
the exchange interactions is discussed.",0504490v2
2005-09-16,Mesoscopic Resistance Fluctuations in Cobalt Nanoparticles,"We present measurements of mesoscopic resistance fluctuations in cobalt
nanoparticles and study how the fluctuations with bias voltage, bias
fingerprints, respond to magnetization reversal processes. Bias fingerprints
rearrange when domains are nucleated or annihilated. The domain-wall causes an
electron wavefunction phase-shift of $\approx 5\pi$. The phase-shift is not
caused by the Aharonov-Bohm effect; we explain how it arises from the
mistracking effect, where electron spins lag in orientation with respect to the
moments inside the domain-wall. Dephasing time in Co at $0.03K$ is short,
$\tau_\phi\sim ps$, which we attribute to the strong magnetocrystalline
anisotropy.",0509452v3
2006-05-15,Domain Wall Assisted Magnetic Recording,"Using numerical and analytical micromagnetics we calculated the switching
fields and energy barriers of the composite (exchange spring) magnetic
recording media, which consist of layers with high and low magnetocrystalline
anisotropy. We demonstrate that the ultimate potential of the composite media
is realized if the interfacial domain wall fits inside the layers. The
switching occurs via domain wall nucleation, compression in the applied field,
de-pinning and propagation through the hard/soft interface. This domain wall
assisted switching results in a significant reduction of the switching field
without substantial decrease of the for thermal activation energy barrier. We
demonstrate that the Domain Wall Assisted Magnetic Recording (DWAMR) offers up
to a three-fold areal density gain over conventional single layer recording.",0605368v1
2006-11-21,"Valence, spin, and orbital state of the Co ions in the one-dimensional Ca3Co2O6: an x-ray absorption and magnetic circular dichroism study","We have investigated the valence, spin, and orbital state of the Co ions in
the one-dimensional cobaltate Ca3Co2O6 using x-ray absorption and x-ray
magnetic circular dichroism at the Co-L2,3 edges. The Co ions at both the
octahedral Co_oct and trigonal Co_trig sites are found to be in a 3+ state.
  From the analysis of the dichroism we established a low-spin state for the
Co_oct and a high-spin state with an anomalously large orbital moment of 1.7
muB at the Co3+ trig ions. This large orbital moment along the c-axis chain and
the unusually large magnetocrystalline anisotropy can be traced back to the
double occupancy of the d2 orbital in trigonal crystal field.",0611545v1
2006-11-22,Substrate effects on surface magetetism of Fe/W(110) from first principles,"Surface magnetic properties of the pseudomorphic Fe(110) monolayer on a
W(110) substrate are investigated from first principles as a function of the
substrate thickness (up to eight layers). Analyzing the magnetocrystalline
anisotropy energies, we find stable (with respect to the number of substrate
layers) in-plane easy and hard axes of magnetization along the [1[overline 1]0]
and [001] directions, respectively, reaching a value in good agreement with
experiment for thick substrates. Additionally, the changes to the magnetic spin
moments and the density of the Fe d states are analyzed with respect to the
number of substrate layers as well as with respect to the direction of
magnetization. With respect to the number of W(110) substrate layers beneath
the Fe(110) surface, we find that the first four substrate layers have a large
influence on the electronic and magnetic properties of the surface. Beyond the
fourth layer, the substrate has only marginal influence on the surface
properties.",0611581v1
2007-09-20,Local electronic structure and magnetic properties of LaMn0.5Co0.5O3 studied by x-ray absorption and magnetic circular dichroism spectroscopy,"We have studied the local electronic structure of LaMn0.5Co0.5O3 using
soft-x-ray absorption spectroscopy at the Co-L_3,2 and Mn-L_3,2 edges. We found
a high-spin Co^{2+}--Mn^{4+} valence state for samples with the optimal Curie
temperature. We discovered that samples with lower Curie temperatures contain
low-spin nonmagnetic Co^{3+} ions. Using soft-x-ray magnetic circular dichroism
we established that the Co^{2+} and Mn^{4+} ions are ferromagnetically aligned.
We revealed also that the Co^{2+} ions have a large orbital moment:
m_orb/m_spin ~ 0.47. Together with model calculations, this suggests the
presence of a large magnetocrystalline anisotropy in the material and predicts
a non-trivial temperature dependence for the magnetic susceptibility.",0709.3243v2
2008-02-12,"Domain walls in (Ga,Mn)As diluted magnetic semiconductor","We report experimental and theoretical studies of magnetic domain walls in an
in-plane magnetized (Ga,Mn)As dilute moment ferromagnetic semiconductor. Our
high-resolution electron holography technique provides direct images of domain
wall magnetization profiles. The experiments are interpreted based on
microscopic calculations of the micromagnetic parameters and
Landau-Lifshitz-Gilbert simulations. We find that the competition of uniaxial
and biaxial magnetocrystalline anisotropies in the film is directly reflected
in orientation dependent wall widths, ranging from approximately 40 nm to 120
nm. The domain walls are of the N\'eel type and evolve from near-$90^{\circ}$
walls at low-temperatures to large angle [1$\bar{1}$0]-oriented walls and small
angle [110]-oriented walls at higher temperatures.",0802.1574v1
2008-02-22,"Lithographically and electrically controlled strain effects on anisotropic magnetoresistance in (Ga,Mn)As","It has been demonstrated that magnetocrystalline anisotropies in (Ga,Mn)As
are sensitive to lattice strains as small as 10^-4 and that strain can be
controlled by lattice parameter engineering during growth, through post growth
lithography, and electrically by bonding the (Ga,Mn)As sample to a
piezoelectric transducer. In this work we show that analogous effects are
observed in crystalline components of the anisotropic magnetoresistance (AMR).
Lithographically or electrically induced strain variations can produce
crystalline AMR components which are larger than the crystalline AMR and a
significant fraction of the total AMR of the unprocessed (Ga,Mn)As material. In
these experiments we also observe new higher order terms in the
phenomenological AMR expressions and find that strain variation effects can
play important role in the micromagnetic and magnetotransport characteristics
of (Ga,Mn)As lateral nanoconstrictions.",0802.3344v2
2008-03-03,X-ray absorption and x-ray magnetic dichroism study on Ca3CoRhO6 and Ca3FeRhO6,"Using x-ray absorption spectroscopy at the Rh-L_2,3, Co-L_2,3, and Fe-L_2,3
edges, we find a valence state of Co^2+/Rh^4+ in Ca3CoRhO6 and of Fe^3+/Rh^3+
in Ca3FeRhO6. X-ray magnetic circular dichroism spectroscopy at the Co-L_2,3
edge of Ca3CoRhO6 reveals a giant orbital moment of about 1.7mu_B, which can be
attributed to the occupation of the minority-spin d_0d_2 orbital state of the
high-spin Co^2+ (3d^7) ions in trigonal prismatic coordination. This active
role of the spin-orbit coupling explains the strong magnetocrystalline
anisotropy and Ising-like magnetism of Ca3CoRhO6.",0803.0293v1
2009-02-20,Residual attractive force between superparamagnetic nanoparticles,"A superparamagnetic nanoparticle (SPN) is a nanometre-sized piece of a
material that would, in bulk, be a permanent magnet. In the SPN the individual
atomic spins are aligned via Pauli effects into a single giant moment that has
easy orientations set by shape or magnetocrystalline anisotropy. Above a
size-dependent blocking temperature $T_{b}(V,\tau_{obs})$, thermal fluctuations
destroy the average moment by flipping the giant spin between easy orientations
at a rate that is rapid on the scale of the observation time $\tau_{obs}$.
  We show that, depite the vanising of the average moment, two SPNs experience
a net attractive force of magnetic origin, analogous to the van der Waals force
between molecules that lack a permanent electric dipole. This could be relevant
for ferrofluids, for the clumping of SPNs used for drug delivery, and for
ultra-dense magnetic recording media.",0902.3684v1
2009-05-28,Tunneling anisotropic magnetoresistance in organic spin valves,"We report the observation of tunneling anisotropic magnetoresistance (TAMR)
in an organic spin-valve-like structure with only one ferromagnetic electrode.
The device is based on a new high mobility perylene diimide-based n-type
organic semiconductor. The effect originates from the tunneling injection from
the LSMO contact and can thus occur even for organic layers which are too thick
to support the assumption of tunneling through the layer. Magnetoresistance
measurements show a clear spin-valve signal, with the typical two step
switching pattern caused by the magnetocrystalline anisotropy of the epitaxial
magnetic electrode.",0905.4573v2
2009-06-29,Adaptive modulations of martensites,"Modulated phases occur in numerous functional materials like giant
ferroelectrics and magnetic shape memory alloys. To understand the origin of
these phases, we review and generalize the concept of adaptive martensite. As a
starting point, we investigate the coexistence of austenite, adaptive 14M phase
and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial
films. The modulated martensite can be constructed from nanotwinned variants of
a tetragonal martensite phase. By combining the concept of adaptive martensite
with branching of twin variants, we can explain key features of modulated
phases from a microscopic view. This includes phase stability, the sequence of
6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.",0906.5365v1
2009-10-28,"Magnetocrystalline anisotropy in RAu_{2}Ge_{2} (R = La, Ce and Pr) single crystals","Anisotropic magnetic properties of single crystalline RAu_{2}Ge_{2} (R = La,
Ce and Pr) compounds are reported. LaAu_{2}Ge_{2} exhibit a Pauli-paramagnetic
behavior whereas CeAu_{2}Ge_{2} and PrAu_{2}Ge_{2} show an antiferromagnetic
ordering with N\grave{e}el temperatures T_{N} = 13.5 and 9 K, respectively. The
anisotropic magnetic response of Ce and Pr compounds establishes [001] as the
easy axis of magnetization and a sharp spin-flip type metamagnetic transition
is observed in the magnetic isotherms. The resistance and magnetoresistance
behavior of these compounds, in particular LaAu_{2}Ge_{2}, indicate an
anisotropic Fermi surface. The magnetoresistivity of CeAu_{2}Ge_{2} apparently
reveals the presence of a residual Kondo interaction. A crystal electric field
analysis of the anisotropic susceptibility in conjunction with the
experimentally inferred Schottky heat capacity enables us to propose a crystal
electric field level scheme for Ce and Pr compounds. For CeAu_{2}Ge_{2} our
values are in excellent agreement with the previous reports on neutron
diffraction. The heat capacity data in LaAu_{2}Ge_{2} show clearly the
existence of Einstein contribution to the heat capacity.",0910.5310v1
2010-11-03,Issues with J-dependence in the LSDA+U method for non-collinear magnets,"We re-examine the commonly used density functional theory plus Hubbard
\textit{U} (DFT$+U$) method for the case of non-collinear magnets. While many
studies neglect to explicitly include the exchange correction parameter
\textit{J}, or consider its exact value to be unimportant, here we show that in
the case of non-collinear magnetism calculations the \textit{J} parameter can
strongly affect the magnetic ground state. We illustrate the strong
\textit{J}-dependence of magnetic canting and magnetocrystalline anisotropy by
calculating trends in the magnetic lithium orthophosphate family LiMPO$_4$ (M =
Fe and Ni) and difluorite family MF$_2$ (M = Mn, Fe, Co and Ni). Our results
can be readily understood by expanding the usual DFT$+U$ equations within the
spinor scheme, in which the \textit{J} parameter acts directly on the
off-diagonal components which determine the spin canting.",1011.0939v1
2011-04-25,"Spin canted magnetism, decoupling of charge and spin ordering in NdNiO$_3$","We report detailed magnetization measurements on the perovskite oxide
NdNiO$_3$. This system has a first order metal-insulator (M-I) transition at
about 200 K which is associated with charge ordering. There is also a
concurrent paramagnetic to antiferromagnetic spin ordering transition in the
system. We show that the antiferromagnetic state of the nickel sublattice is
spin canted. We also show that the concurrency of the charge ordering and spin
ordering transitions is seen only while warming up the system from low
temperature. The transitions are not concurrent while cooling the system
through the M-I transition temperature. This is explained based on the fact
that the charge ordering transition is first order while the spin ordering
transition is continuous. In the magnetically ordered state the system exhibits
ZFC-FC irreversibilities, as well as history-dependent magnetization and aging.
Our analysis rules out the possibility of spin-glass or superparamagnetism and
suggests that the irreversibilities originate from magnetocrystalline
anisotropy and domain wall pinning.",1104.4766v2
2011-05-09,An Energy-Efficient Bennett Clocking Scheme for 4-State Multiferroic Logic,"Nanomagnets with biaxial magnetocrystalline anisotropy have four stable
magnetization orientations that can encode 4-state logic bits (00), (01), (11)
and (10). Recently, a 4-state NOR gate derived from three such nanomagnets,
interacting via dipole interaction, was proposed. Here, we devise a Bennett
clocking scheme to propagate 4-state logic bits unidirectionally between such
gates. The nanomagnets are assumed to be made of 2-phase strain-coupled
magnetostrictive/piezoelectric multiferroic elements, such as nickel and lead
zirconate titanate (PZT). A small voltage of 200 mV applied across the
piezoelectric layer can generate enough mechanical stress in the
magnetostrictive layer to rotate its magnetization away from one of the four
stable orientations and implement Bennett clocking. We show that a particular
sequence of positive and negative voltages will propagate 4-state logic bits
unidirectionally down a chain of such multiferroic nanomagnets for logic flow.",1105.1818v1
2011-07-29,Phase transitions in single-crystalline magnetoelectric LiCoPO4,"Specific heat, magnetic torque, and magnetization studies of LiCoPO4 olivine
are presented. They show that an unique set of physical properties of LiCoPO4
leads to the appearance of features characteristic of 2D Ising systems near the
Neel temperature, T_N =21.6 K, and to the appearance of an uncommon effect of
influence of magnetic field on the magnetocrystalline anisotropy. The latter
effect manifests itself as a first-order transition, discovered at ~9 K,
induced by magnetic field of 8 T. Physical nature of this transition was
explained and a model describing experimental dependences satisfactorily was
proposed.",1107.5960v1
2011-08-30,Electrically tunable quantum anomalous Hall effect in 5d transition-metal adatoms on graphene,"The combination of the unique properties of graphene with spin polarization
and magnetism for the design of new spintronic concepts and devices has been
hampered by the small Coulomb interaction and the tiny spin-orbit coupling of
carbon in pristine graphene. Such device concepts would take advantage of the
control of the spin degree of freedom utilizing the widely available electric
fields in electronics or of topological transport mechanisms such as the
conjectured quantum anomalous Hall effect. Here we show, using first-principles
methods, that 5d transition-metal (TM) adatoms deposited on graphene display
remarkable magnetic properties. All considered TM adatoms possess significant
spin moments with colossal magnetocrystalline anisotropy energies as large as
50 meV per TM atom. We reveal that the magneto-electric response of deposited
TM atoms is extremely strong and in some cases offers even the possibility to
switch the spontaneous magnetization direction by a moderate external electric
field. We predict that an electrically tunable quantum anomalous Hall effect
can be observed in this type of hybrid materials.",1108.5915v1
2011-09-26,Electric-field control of magnetic domain wall motion and local magnetization reversal,"Spintronic devices currently rely on magnetic switching or controlled motion
of domain walls by an external magnetic field or spin-polarized current.
Achieving the same degree of magnetic controllability using an electric field
has potential advantages including enhanced functionality and low power
consumption. Here, we report on an approach to electrically control local
magnetic properties, including the writing and erasure of regular ferromagnetic
domain patterns and the motion of magnetic domain walls, in multiferroic
CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer
from ferroelastic domains in ferroelectric media to continuous magnetostrictive
films with negligible magnetocrystalline anisotropy. Optical polarization
microscopy of both ferromagnetic and ferroelectric domain structures reveals
that domain correlations and strong inter-ferroic domain wall pinning persist
in an applied electric field. This leads to an unprecedented electric
controllability over the ferromagnetic microstructure, an accomplishment that
produces giant magnetoelectric coupling effects and opens the way to
multiferroic spintronic devices.",1109.5514v1
2012-12-13,"First-principles study of the structural stability of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds","We investigate the structural stability and magnetic properties of cubic,
tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds
using first-principles density-functional theory. We propose that the cubic
phase plays an important role as an intermediate state in the phase transition
from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge
behave differently from Mn3Sn, because the relative energies of the cubic and
hexagonal phases are different. This result agrees with experimental
observations from these three compounds. The weak ferromagnetism of the
hexagonal phase and the perpendicular magnetocrystalline anisotropy of the
tetragonal phase obtained in our calculations are also consistent with
experiment.",1212.3144v1
2013-04-08,Effects of alloying and strain on the magnetic properties of Fe$_{16}$N$_2$,"The electronic structure and magnetic properties of pure and doped
{Fe$_{16}$N$_2$} systems have been studied in the local-density (LDA) and
quasiparticle self-consistent {\emph{GW}} approximations. The {\emph{GW}}
magnetic moment of pure {Fe$_{16}$N$_2$} is somewhat larger compared to LDA but
not anomalously large. The effects of doping on magnetic moment and exchange
coupling were analyzed using the coherent potential approximation. The
theoretical Curie temperature in pure {Fe$_{16}$N$_2$} is significantly higher
than the measured value, which is attributed to the quality of available
samples and the interpretation of experimental results. We found that different
Fe sites contribute very differently to the magnetocrystalline anisotropy
energy (MAE), which offers a way to increase MAE by small additions of Co or
Ti. MAE also increases under tetragonal strain.",1304.2428v2
2013-04-24,Spin Resolution and Evidence for Superexchange on NiO(001) observed by Force Microscopy,"The spin order of the nickel oxide (001) surface is resolved, employing
non-contact atomic force microscopy at 4.4 K using bulk Fe- and SmCo-tips
mounted on a qPlus sensor that oscillates at sub-50 pm amplitudes. The
spin-dependent signal is hardly detectable with Fe-tips. In contrast, SmCo-tips
yield a height contrast of 1.35 pm for Ni ions with opposite spins. SmCo tips
even show a small height contrast on the O atoms of 0.5 pm within the 2x1 spin
unit cell, pointing to the observation of superexchange. We attribute this to
the increased magnetocrystalline anisotropy energy of SmCo, which stabilizes
the magnetic moment at the apex. Atomic force spectroscopy on the Ni up, Ni
down and O lattice site reveals a magnitude of the exchange energy of merely 1
meV at the closest accessible distance with an exponential decay length of
\lambda_exc = 18 pm.",1304.6515v3
2013-09-17,Tuning the Curie temperature of FeCo compounds by tetragonal distortion,"Combining density-functional theory calculations with a classical Monte Carlo
method, we show that for B2-type FeCo compounds tetragonal distortion gives
rise to a strong reduction of the Curie temperature $T_{\mathrm{C}}$. The
$T_{\mathrm{C}}$ monotonically decreases from 1575 K (for $c/a=1$) to 940 K
(for $c/a=\sqrtwo$). We find that the nearest neighbor Fe-Co exchange
interaction is sufficient to explain the $c/a$ behavior of the
$T_{\mathrm{C}}$. Combination of high magnetocrystalline anisotropy energy with
a moderate $T_{\mathrm{C}}$ value suggests tetragonal FeCo grown on the Rh
substrate with $c/a=1.24$ to be a promising material for heat-assisted magnetic
recording applications.",1309.4232v1
2014-02-11,Weak spin interactions in Mott insulating La2O2Fe2OSe2,"Identifying and characterizing the parent phases of iron-based
superconductors is an important step towards understanding the mechanism for
their high temperature superconductivity. We present an investigation into the
magnetic interactions in the Mott insulator La2O2Fe2OSe2. This iron oxyselenide
adopts a 2-k magnetic structure with low levels of magnetic frustration. This
magnetic ground state is found to be dominated by next-nearest neighbor
interactions J2 and J2' and the magnetocrystalline anisotropy of the Fe2+ site,
leading to 2D-Ising-like spin S=2 fluctuations. In contrast to calculations,
the values are small and confine the spin excitations below ~ 25 meV. This is
further corroborated by sum rules of neutron scattering. This indicates that
superconductivity in related materials may derive from a weakly coupled and
unfrustrated magnetic structure.",1402.2684v1
2014-07-05,Atomistic modeling of magnetization reversal modes in $L1_{0}$ FePt nanodots with magnetically soft edges,"Nanopatterned FePt nano-dots often exhibit low coercivity and a broad
switching field distribution, which could arise due to edge damage during the
patterning process causing a reduction in the $L1_{0}$ ordering required for a
high magnetocrystalline anisotropy. Using an atomistic spin model, we study the
magnetization reversal behavior of $L1_{0}$ FePt nanodots with soft magnetic
edges. We show that reversal is initiated by nucleation for the whole range of
edge widths studied. For narrow soft edges the individual nucleation events
dominate reversal; for wider edges, multiple nucleation at the edge creates a
circular domain wall at the interface which precedes complete reversal. Our
simulations compare well with available analytical theories. The increased edge
width further reduces and saturates the required nucleation field. The
nucleation field and the activation volume manipulate the thermally induced
switching field distribution. By control of the properties of dot edges using
proper patterning methods, it should be possible to realize exchange spring bit
patterned media without additional soft layers.",1407.1363v2
2014-07-14,Magnetic / dielectric anomalies and magnetodielectric / magnetoelectric effects in Z- and W-type hexaferrites,"Two kinds of specimens, with the major phase of Sr3Co2Fe24O41 (Sr3Co2Z) and
SrCo2Fe16O27 (SrCo2W) hexaferrites respectively, were fabricated through
solid-state reaction. The phase composition, magnetic and dielectric
properties, magnetodielectric (MD) effect, magnetoelectric (ME) effect and
pyroelectric properties were studied. Results show that magnetic and dielectric
anomalies are induced by the magnetocrystalline anisotropy (MCA) transition.
They can be considered as characteristic properties (e.g., Sr3Co2Z at 370 K)
but are not a sufficient condition for the MD and ME coupling. The T-block
structure, existing in Sr3Co2Z but absent in SrCo2W, results in the dielectric
response with ferroelectric (FE) and magnetic contributions.",1407.3605v2
2014-08-04,55~Tesla coercive magnetic field in frustrated Sr$_3$NiIrO$_6$,"We have measured extremely large coercive magnetic fields of up to 55~T in
Sr$_3$NiIrO$_6$, with a switched magnetic moment $\approx 0.8~\mu_{\rm B}$ per
formula unit. As far as we are aware, this is the largest coercive field
observed thus far. This extraordinarily hard magnetism has a completely
different origin from that found in conventional ferromagnets. Instead, it is
due to the evolution of a frustrated antiferromagnetic state in the presence of
strong magnetocrystalline anisotropy due to the overlap of spatially-extended
Ir$^{4+}$ 5$d$ orbitals with oxygen 2$p$ and Ni$^{2+}$ 3$d$ orbitals. This work
highlights the unusual physics that can result from combining the extended $5d$
orbitals in Ir$^{4+}$ with the frustrated behaviour of triangular lattice
antiferromagnets.",1408.0758v1
2014-10-24,Strong magnetic coupling in the hexagonal R5Pb3 compounds (R = Gd-Tm),"We have synthesized R5Pb3 (R = Gd-Tm) compounds in polycrystalline form and
performed structural analysis, magnetization, and neutron scattering
measurements. For all R5Pb3 reported here the Weiss temperatures {\theta}W are
several times smaller than the ordering temperatures TORD, while the latter are
remarkably high (TORD up to 275 K for R = Gd) compared to other known R-M
binaries (M = Si, Ge, Sn and Sb). The magnetic order changes from ferromagnetic
in R = Gd, Tb to antiferromagnetic in R = Dy-Tm. Below TORD, the magnetization
measurements together with neutron powder diffraction show complex magnetic
behavior and reveal the existence of up to three additional phase transitions.
We believe this to be a result of crystal electric field effects responsible
for high magnetocrystalline anisotropy. The R5Pb3 magnetic unit cells for R =
Tb-Tm can be described with incommensurate magnetic wave vectors with spin
modulation either along the c axis in R = Tb, Er and Tm or within the ab-plane
in R = Dy and Ho.",1410.6732v1
2015-04-16,Heat capacity study of the magnetic phases in a Nd$_5$Ge$_3$ single crystal,"The different magnetic phases of the intermetallic compound Nd$_5$Ge$_3$ are
studied in terms of the specific heat, in a broad range of temperatures
(350~mK--140~K) and magnetic fields (up to 40 kOe). The expected $T^{3}$ and
$T^{3/2}$ terms are not found in the antiferromagnetic (AFM) and ferromagnetic
(FM) phases respectively, but a gapped $T^2$ contribution that originates from
a mixture of AFM and FM interactions in different dimensionalities under a
large magnetocrystalline anisotropy, is present in both. An almost identical
Schottky anomaly, that arises from the hyperfine splitting of the nuclear
levels of the Nd$^{3+}$ ions, is observed in both phases, which leads us to
state that the magnetic-field induced transition AFM$\to$FM that the system
experiments below $26~\text{K}$ consists in the flip of the magnetic moments of
the Nd ions, conserving the average local moment.",1504.04252v1
2015-04-22,Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations,"The structures and magnetic properties of the Co-Zr-B alloys near the Co5Zr
composition were studied using adaptive genetic algorithm and first-principles
calculations to guide further experimental effort on optimizing their magnetic
performances. Through extensive structural searches, we constructed the contour
maps of the energetics and magnetic moments of the Co-Zr-B magnet alloys as a
function of composition. We found that the Co-Zr-B system exhibits the same
structural motif as the ""Co11Zr2"" polymorphs, which plays a key role in
achieving high coercivity. Boron atoms can either substitute selective cobalt
atoms or occupy the interstitial sites. First-principles calculation shows that
the magnetocrystalline anisotropy energies can be significantly improved
through proper boron doping.",1504.05829v1
2015-04-28,Surface-termination dependent magnetism and strong perpendicular magnetocrystalline anisotropy of a FeRh (001) thin film: A density-functional study,"Magnetism of FeRh (001) films strongly depends on film thickness and surface
terminations. While magnetic ground state of bulk FeRh is G-type
antiferromagnetism, the Rh-terminated films exhibit ferromagnetism with strong
perpendicular MCA whose energy +2.1 meV/$\Box$ is two orders of magnitude
greater than 3$d$ magnetic metals, where $\Box$ is area of two-dimensional unit
cell. While Goodenough-Kanamori-Anderson rule on the superexchange interaction
is crucial in determining the magnetic ground phases of FeRh bulk and thin
films, the magnetic phases are results of interplay and competition between
three mechanisms - the superexchange interaction, the Zener direct-interaction,
and magnetic energy gain.",1504.07349v3
2015-06-11,Magnetism in tetragonal manganese-rich Heusler compounds,"A comprehensive study of the total energy of manganese-rich Heusler compounds
using density functional theory is presented. Starting from a large set of
cubic parent systems, the response to tetragonal distortions is studied in
detail. We single out the systems that remain cubic from those that most likely
become tetragonal. The driving force of the tetragonal distortion and its
effect on the magnetic properties, especially where they deviate from the
Slater--Pauling rule, as well as the trends in the Curie temperatures, are
highlighted. By means of partial densities of states, the electronic structural
changes reveal the microscopic origin of the observed trends. We focus our
attention on the magnetocrystalline anisotropy and find astonishingly high
values for tetragonal Heusler compounds containing heavy transition metals
accompanied by low magnetic moments, which indicates that these materials are
promising candidates for spin-transfer torque magnetization-switching
applications.",1506.03735v1
2015-06-29,"Effect of Misfit Strain in (Ga,Mn)(Bi,As) Epitaxial Layers on their Magnetic and Magneto-Transport Properties","Effect of misfit strain in the layers of (Ga,Mn)(Bi,As) quaternary diluted
magnetic semiconductor, epitaxially grown on either GaAs substrate or (In,Ga)As
buffer, on their magnetic and magneto-transport properties has been
investigated. High-resolution X-ray diffraction, applied to characterize the
structural quality and misfit strain in the layers, proved that the layers were
fully strained to the GaAs substrate or (In,Ga)As buffer under compressive or
tensile strain, respectively. Ferromagnetic Curie temperature and
magnetocrystalline anisotropy of the layers have been examined by using
magneto-optical Kerr effect magnetometry and low-temperature magneto-transport
measurements. Post-growth annealing treatment of the layers has been shown to
enhance the hole concentration and Curie temperature in the layers.",1506.08718v1
2015-07-27,A method for measuring the Neel relaxation time in a frozen ferrofluid,"We report a novel method of determining the average Neel relaxation time and
its temperature dependence by calculating derivatives of the measured time
dependence of temperature for a frozen ferrofluid exposed to an alternating
magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles
(diameter 13.7 nm +/- 4.7 nm), was synthesized via wet chemical precipitation
and characterized by x-ray diffraction and transmission electron microscopy. An
alternating magnetic field of constant amplitude (H0 = 20 kA/m) driven at
frequencies of 171 kHz, 232 kHz and 343 kHz was used to determine the
temperature dependent magnetic energy absorption rate in the temperature range
from 160 K to 210 K. We found that the specific absorption rate of the
ferrofluid decreased monotonically with temperature over this range at the
given frequencies. From these measured data, we determined the temperature
dependence of the Neel relaxation time and estimate a room-temperature
magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with
previously published results.",1507.07471v1
2015-09-03,Investigation of ferromagnetic domain behavior and phase transition at nanoscale in bilayer manganites,"Understanding the underlying mechanism and phenomenology of colossal
magnetoresistance in manganites has largely focused on atomic and nanoscale
physics such as double exchange, phase separation, and charge order. Here we
consider a more macroscopic view of manganite materials physics, reporting on
the ferromagnetic domain behavior in a bilayer manganite sample with a nominal
composition of La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ with $x=0.38$, studied using
in-situ Lorentz transmission electron microscopy. The role of
magnetocrystalline anisotropy on the structure of domain walls was elucidated.
On cooling, magnetic domain contrast was seen to appear first at the Curie
temperature within the $a-b$ plane. With further reduction in temperature, the
change in area fraction of magnetic domains was used to estimate the critical
exponent describing the ferromagntic phase transition. The ferromagnetic phase
transition was accompanied by a distinctive nanoscale granular contrast close
to the Curie temperature, which we infer to be related to the presence of
ferromagnetic nanoclusters in a paramagnetic matrix, which has not yet been
reported in bilayer manganites.",1509.01106v1
2015-11-06,"Structural, magnetic and electrical properties of sputter deposited Mn-Fe-Ga thin films","We investigated structural, magnetic and electrical properties of sputter
deposited Mn-Fe-Ga compounds. The crystallinity of the Mn-Fe-Ga thin films was
confirmed using x-ray diffraction. X-ray reflection and atomic force microscopy
measurements were utilized to investigate the surface properties, roughness,
thickness and density of the deposited Mn-Fe-Ga. Depending on the
stoichiometry, as well as the used substrates (SrTiO3 (001) and MgO (001)) or
buffer layer (TiN) the Mn-Fe-Ga crystallizes in the cubic or the tetragonally
distorted phase. Anomalous Hall effect and alternating gradient magnetometry
measurements confirmed strong perpendicular magnetocrystalline anisotropy. Low
saturation magnetization and hard magnetic behavior was reached by tuning the
composition. Temperature dependent anomalous Hall effect measurements in a
closed cycle He-cryostat showed a slight increase in coercivity with decreasing
temperature (300K to 2K). TiN buffered Mn2.7Fe0.3Ga revealed sharper switching
of the magnetization compared to the unbuffered layers.",1511.02097v2
2015-12-10,Piezomagnetic effect as a counterpart of negative thermal expansion in magnetically frustrated Mn-based antiperovskite nitrides,"Electric-field control of magnetization promises to substantially enhance the
energy efficiency of device applications ranging from data storage to
solid-state cooling. However, the intrinsic linear magnetoelectric effect is
typically small in bulk materials. In thin films electric-field tuning of
spin-orbit interaction phenomena (e.g., magnetocrystalline anisotropy) has been
reported to achieve a partial control of the magnetic state. Here we explore
the piezomagnetic effect (PME), driven by frustrated exchange interactions,
which can induce a net magnetization in an antiferromagnet and reverse its
direction via elastic strain generated piezoelectrically. Our $ab~initio$ study
of PME in Mn-antiperovskite nitrides identified an extraordinarily large PME in
Mn$_3$SnN available at room temperature. We explain the magnitude of PME based
on features of the electronic structure and show an inverse-proportionality
between the simulated zero-temperature PME and the negative thermal expansion
at the magnetic (N\'eel) transition measured by Takenaka et al. in 9
antiferromagnetic Mn$_3$AN systems.",1512.03470v2
2016-04-25,Room temperature tetragonal noncollinear antiferromagnet Pt$_2$MnGa,"Here we present the tetragonal stoichiometric Heusler compound Pt$_2$MnGa
with the noncollinear AFM order stable up to 350 K. It is resolved by the
neutron diffraction as a helical spiral propagating along the tetragonal axis.
Ab-initio calculations suggest a pure exchange origin of the spiral and explain
its helical character being stabilized by a large basal plane
magnetocrystalline anisotropy (MCA). Together with the inversion-symmetric
crystal structure, this provides a bi-stability of a spiral with respect to the
right- and left-handed magnetic helices. Despite the large MCA, the long period
of a helix might greatly facilitate the switch of the helicity by the
precessional reorientation, suggesting Pt$_2$MnGa as a potential candidate for
the vector-helicity based non-volatile magnetic memory.",1604.07137v1
2016-08-26,Optimization of nanocomposite materials for permanent magnets by micromagnetic simulations: effect of the intergrain exchange and the hard grains shape,"In this paper we perform the detailed numerical analysis of remagnetization
processes in nanocomposite magnetic materials consisting of magnetically hard
grains (i.e. grains made of a material with a high magnetocrystalline
anisotropy) embedded into a magnetically soft phase. Such materials are widely
used for the production of permanent magnets, because they combine the high
remanence with the large coercivity. We perform simulations of nanocomposites
with Sr-ferrite as the hard phase and Fe or Ni as the soft phase, concentrating
our efforts on analyzing the effects of ({\it i}) the imperfect intergrain
exchange and ({\it ii}) the non-spherical shape of hard grains. We demonstrate
that - in contrast to the common belief - the maximal energy product is
achieved not for systems with the perfect intergrain exchange, but for
materials where this exchange is substantially weakened. We also show that the
main parameters of the hysteresis loop - remanence, coercivity and the energy
product - exhibit non-trivial dependencies on the shape of hard grains, and
provide detailed explanations for our results. Simulation predictions obtained
in this work open new ways for the optimization of materials for permanent
magnets.",1608.07429v1
2016-09-02,Potential Energy Driven Spin Manipulation via a Controllable Hydrogen Ligand,"Spin-bearing molecules can be stabilized on surfaces and in junctions with
desirable properties such as a net spin that can be adjusted by external
stimuli. Using scanning probes, initial and final spin states can be deduced
from topographic or spectroscopic data, but how the system transitioned between
these states is largely unknown. Here we address this question by manipulating
the total spin of magnetic cobalt hydride complexes on a corrugated boron
nitride surface with a hydrogen- functionalized scanning probe tip by
simultaneously tracking force and conductance. When the additional hydrogen
ligand is brought close to the cobalt monohydride, switching between a corre-
lated S = 1 /2 Kondo state, where host electrons screen the magnetic moment,
and a S = 1 state with magnetocrystalline anisotropy is observed. We show that
the total spin changes when the system is transferred onto a new potential
energy surface defined by the position of the hydrogen in the junction. These
results show how and why chemically functionalized tips are an effective tool
to manipulate adatoms and molecules, and a promising new method to selectively
tune spin systems.",1609.00612v2
2016-09-03,Domain structure of ultrathin ferromagnetic elements in the presence of Dzyaloshinskii-Moriya interaction,"Recent advances in nanofabrication make it possible to produce multilayer
nanostructures composed of ultrathin film materials with thickness down to a
few monolayers of atoms and lateral extent of several tens of nanometers. At
these scales, ferromagnetic materials begin to exhibit unusual properties, such
as perpendicular magnetocrystalline anisotropy and antisymmetric exchange, also
referred to as Dzyaloshinskii-Moriya interaction (DMI), because of the
increased importance of interfacial effects. The presence of surface DMI has
been demonstrated to fundamentally alter the structure of domain walls. Here we
use the micromagnetic modeling framework to analyse the existence and structure
of chiral domain walls, viewed as minimizers of a suitable micromagnetic energy
functional. We explicitly construct the minimizers in the one-dimensional
setting, both for the interior and edge walls, for a broad range of parameters.
We then use the methods of {$\Gamma$}-convergence to analyze the asymptotics of
the two-dimensional mag- netization patterns in samples of large spatial extent
in the presence of weak applied magnetic fields.",1609.00841v1
2016-09-05,Critical Current Oscillations of Josephson Junctions Containing PdFe Nanomagnets,"Josephson junctions with ferromagnetic layers are vital elements in a new
class of cryogenic memory devices. One style of memory device contains a spin
valve with one ""hard"" magnetic layer and one ""soft"" layer. To achieve low
switching fields, it is advantageous for the soft layer to have low
magnetization and low magnetocrystalline anisotropy. A candidate class of
materials that fulfills these criteria is the Pd$_{1-x}$Fe$_{x}$ alloy system
with low Fe concentrations. We present studies of micron-scale
elliptically-shaped Josephson junctions containing Pd$_{97}$Fe$_{3}$ layers of
varying thickness. By applying an external magnetic field, the critical current
of the junctions are found to follow characteristic Fraunhofer patterns. The
maximum value of the critical current, extracted from the Fraunhofer patterns,
oscillates as a function of the ferromagnetic barrier thickness, indicating
transitions in the phase difference across the junction between values of zero
and $\pi$.",1609.01330v1
2016-12-14,"First-principles study of intersite magnetic couplings in NdFe$_{12}$ and NdFe$_{12}$X (X = B, C, N, O, F)","We present a first-principles investigation of NdFe$_{12}$ and NdFe$_{12}$X
(X = B, C, N, O, F) crystals with the ThMn$_{12}$ structure. Intersite magnetic
couplings in these compounds, so-called exchange couplings, are estimated by
Liechtenstein's method. It is found that the Nd--Fe couplings are sensitive to
the interstitial dopant X, with the Nd--Fe(8j) coupling in particular reduced
significantly for X = N. This suggests that the magnetocrystalline anisotropy
decays quickly with rising temperature in the X = N system although
nitrogenation has advantages over the other dopants in terms of enhancing
low-temperature magnetic properties. The Curie temperature is also calculated
from the magnetic couplings by using the mean field approximation. Introduction
of X enhances the Curie temperature, with both structural changes and chemical
effects found to play important roles in this enhancement.",1612.04478v5
2016-12-20,Discovery of room temperature multiferroicity and magneto-electric coupling in Fe3Se4 nanorods,"We report for the first time, that Fe3Se4 is a room temperature, type-II
multiferroic with magnetoelectric coupling. We observed the coexistence of
coupled ferrimagnetic and ferroelectric ordering in Fe3Se4nanorods well above
room temperature, which is a hard magnet with large magnetocrystalline
anisotropy. For the first time, we observed spontaneous, reversible
ferroelectric polarization in Fe3Se4 nanorods below the magnetic Curie
temperature. The coupling is manifested by an anomaly in the dielectric
constant and Raman shift at Tc. We do not completely understand the origin of
the ferroelectric ordering at this point however the simultaneous presence of
magnetic and ferroelectric ordering at room temperature in Fe3Se4 along with
hard magnetic properties will open new research areas for devices.",1612.06512v2
2017-02-01,Superzone gap formation and low lying crystal electric field levels in PrPd$_2$Ge$_2$ single crystal,"The magnetocrystalline anisotropy exhibited in PrPd$_2$Ge$_2$ single crystal
has been investigated by measuring the magnetization, magnetic susceptibility,
electrical resistivity and heat capacity. PrPd$_2$Ge$_2$ crystallizes in the
well known ThCr$_2$Si$_2$\--type tetragonal structure. The antiferromagnetic
ordering is confirmed as 5.1~K with the [001]-axis as the easy axis of
magnetization. A superzone gap formation is observed from the electrical
resistivity measurement when the current is passed along the [001] direction.
The crystal electric field (CEF) analysis on the magnetic susceptibility,
magnetization and the heat capacity measurements confirms a doublet ground
state with a relatively low over all CEF level splitting. The CEF level
spacings and the Zeeman splitting at high fields become comparable and lead to
metamagnetic transition at 34~T due to the CEF level crossing.",1702.00220v1
2017-02-21,Human brain ferritin studied by muon Spin Rotation: a pilot study,"Muon Spin Rotation is employed to investigate the spin dynamics of ferritin
proteins isolated from the brain of an Alzheimer's disease (AD) patient and of
a healthy control, using a sample of horse-spleen ferritin as a reference. A
model based on the N\'eel theory of superparamagnetism is developed in order to
interpret the spin relaxation rate of the muons stopped by the core of the
protein. Using this model, our preliminary observations show that ferritins
from the healthy control are filled with a mineral compatible with
ferrihydrite, while ferritins from the AD patient contain a crystalline phase
with a larger magnetocrystalline anisotropy, possibly compatible with magnetite
or maghemite.",1702.07222v2
2017-03-06,"Spindynamics in the antiferromagnetic phases of the Dirac metals $A$MnBi$_2$ ($A=$ Sr, Ca)","The square Bi layers in $A$MnBi$_2$ ($A =$ Sr, Ca) host Dirac fermions which
coexist with antiferromagnetic order on the Mn sublattice below $T_\mathrm{N} =
290\,$K (Sr) and $270\,$K (Ca). We have measured the spin-wave dispersion in
these materials by triple-axis neutron spectroscopy. The spectra show
pronounced spin gaps of 10.2(2)$\,$meV (Sr) and 8.3(8)$\,$meV (Ca) and extend
to a maximum energy transfer of 61 - 63$\,$meV. The observed spectra can be
accurately reproduced by linear spin-wave theory from an Heisenberg effective
spin Hamiltonian. Detailed global fits of the full magnon dispersion are used
to determine the in-plane and inter-layer exchange parameters as well as on the
magnetocrystalline anisotropy constant. To within experimental error we find no
evidence that the magnetic dynamics are influenced by the Dirac fermions.",1703.01849v1
2017-05-01,One-dimensional in-plane edge domain walls in ultrathin ferromagnetic films,"We study existence and properties of one-dimensional edge domain walls in
ultrathin ferromagnetic films with uniaxial in-plane magnetic anisotropy. In
these materials, the magnetization vector is constrained to lie entirely in the
film plane, with the preferred directions dictated by the magnetocrystalline
easy axis. We consider magnetization profiles in the vicinity of a straight
film edge oriented at an arbitrary angle with respect to the easy axis. To
minimize the micromagnetic energy, these profiles form transition layers in
which the magnetization vector rotates away from the direction of the easy axis
to align with the film edge. We prove existence of edge domain walls as
minimizers of the appropriate one-dimensional micromagnetic energy functional
and show that they are classical solutions of the associated Euler-Lagrange
equation with Dirichlet boundary condition at the edge. We also perform a
numerical study of these one-dimensional domain walls and uncover further
properties of these domain wall profiles.",1705.00700v2
2017-07-13,Simulation of alnico coercivity,"Micromagnetic simulations of alnico show substantial deviations from
Stoner-Wohlfarth behavior due to the unique size and spatial distribution of
the rod-like Fe-Co phase formed during spinodal decomposition in an external
magnetic field. The maximum coercivity is limited by single-rod effects,
especially deviations from ellipsoidal shape, and by interactions between the
rods. Both the exchange interaction between connected rods and magnetostatic
interaction between rods are considered, and the results of our calculations
show good agreement with recent experiments. Unlike systems dominated by
magnetocrystalline anisotropy, coercivity in alnico is highly dependent on
size, shape, and geometric distribution of the Fe-Co phase, all factors that
can be tuned with appropriate chemistry and thermal-magnetic annealing.",1707.04180v1
2017-12-01,Spin waves and stability of zigzag order in the Hubbard model with spin-dependent hopping terms - Application to the honeycomb lattice compounds ${\rm Na_2 Ir O_3}$ and ${\rm α- Ru Cl_3}$,"Spin waves in the zigzag ordered state on a honeycomb lattice are
investigated within a Hubbard model with spin-dependent hopping terms. Roles of
the emergent Kitaev, Heisenberg, Dzyaloshinskii-Moriya, and
symmetric-off-diagonal spin interactions are investigated on the stability of
the zigzag order. While the DM interactions are found to destabilize the zigzag
order, the secondary spin-dependent hopping terms (associated with structural
distortions) are shown to strongly stabilize the zigzag order and account for
magnetocrystalline anisotropy, easy axis, and spin wave gap. The calculated
spin wave dispersion and energy scale are in good agreement with inelastic
neutron scattering measurements on $\rm \alpha - RuCl_3$ and $\rm Na_2 Ir O_3$.",1712.00198v2
2018-01-10,Quantum Theory of Rare-Earth Magnets,"Strong permanent magnets mainly consist of rare earths ($R$) and transition
metals ($T$). The main phase of the neodymium magnet, which is the strongest
magnet, is Nd$_2$Fe$_{14}$B. Sm$_{2}$Fe$_{17}$N$_{3}$ is another magnet
compound having excellent magnetic properties comparable to those of
Nd$_{2}$Fe$_{14}$B. Their large saturation magnetization, strong
magnetocrystalline anisotropy, and high Curie temperature originate from the
interaction between the $T$-3d electrons and $R$-4f electrons. This article
discusses the magnetism of rare-earth magnet compounds. The basic theory and
first-principles calculation approaches for quantitative description of the
magnetic properties are presented, together with applications to typical
compounds such as Nd$_2$Fe$_{14}$B, Sm$_{2}$Fe$_{17}$N$_{3}$, and the recently
synthesized NdFe$_{12}$N.",1801.03455v1
2018-01-12,Control of oxidation and spin state in a single-molecule junction,"The oxidation and spin state of a metal-organic molecule determine its
chemical reactivity and magnetic properties. Here, we demonstrate the
reversible control of the oxidation and spin state in a single Fe-porphyrin
molecule in the force field of the tip of a scanning tunneling microscope.
Within the regimes of half-integer and integer spin state, we can further track
the evolution of the magnetocrystalline anisotropy. Our experimental results
are corroborated by density functional theory and wave function theory. This
combined analysis allows us to draw a complete picture of the molecular states
over a large range of intramolecular deformations.",1801.04162v1
2018-02-16,"Role of typical elements in Nd$_{2}$Fe$_{14}$$X$ ($X$ = B, C, N, O, F)","The magnetic properties and structural stability of Nd$_{2}$Fe$_{14}X$ ($X$ =
B, C, N, O, F) are theoretically studied by first-principles calculations
focusing on the role of $X$. We find that B reduces the magnetic moment (per
formula unit) and magnetization (per volume) in Nd$_{2}$Fe$_{14}$B. The
crystal-field parameter $A_2^0 \langle r^2 \rangle$ of Nd is not enhanced
either, suggesting that B has minor roles in the uniaxial magnetocrystalline
anisotropy of Nd. These findings are in contrast to the long-held belief that B
works positively for the magnetic properties of Nd$_{2}$Fe$_{14}$B. As $X$
changes from B to C, N, O and F, both the magnetic properties and stability
vary significantly. The formation energies of Nd$_{2}$Fe$_{14}X$ and
$\alpha$-Fe relative to that of Nd$_{2}$Fe$_{17}X$ are negative for $X$ = B and
C, whereas they are positive when $X$ = N, O and F. This indicates that B plays
an important role in stabilizing the Nd$_{2}$Fe$_{14}$B phase.",1802.05817v1
2018-05-07,Revealing Controllable Anisotropic Magnetoresistance in Spin Orbit Coupled Antiferromagnet Sr2IrO4,"Antiferromagnetic spintronics actively introduces new principles of magnetic
memory, in which the most fundamental spin-dependent phenomena, i.e.
anisotropic magnetoresistance effects, are governed by an antiferromagnet
instead of a ferromagnet. A general scenario of the antiferromagnetic
anisotropic magnetoresistance effects mainly stems from the magnetocrystalline
anisotropy related to spin-orbit coupling. Here we demonstrate magnetic field
driven contour rotation of the fourfold anisotropic magnetoresistance in bare
antiferromagnetic Sr2IrO4/SrTiO3 (001) thin films hosting a strong spin-orbit
coupling induced Jeff=1/2 Mott state. Concurrently, an intriguing minimal in
the magnetoresistance emerges. Through first principles calculations, the
band-gap engineering due to rotation of the Ir isospins is revealed to be
responsible for these emergent phenomena, different from the traditional
scenario where relatively more conductive state was obtained usually when
magnetic field was applied along the magnetic easy axis. Our findings
demonstrate a new efficient route, i.e. via the novel Jeff=1/2 state, to
realize controllable anisotropic magnetoresistance in antiferromagnetic
materials.",1805.02394v1
2018-06-16,First-principles prediction of sub-10 nm skyrmions in Pd/Fe bilayers on Rh(111),"We show that stable skyrmions with diameters of a few nanometers can emerge
in atomic Pd/Fe bilayers on the Rh(111) surface. Based on density functional
theory we calculate the exchange and the Dzyaloshinskii-Moriya interaction as
well as the magnetocrystalline anisotropy energy. The later two terms are
driven by spin-orbit coupling and significantly reduced compared to Pd/Fe
bilayers on Ir(111) as expected since Rh and Ir are isoelectronic $4d$ and $5d$
transition-metals. However, there is still a spin spiral ground state at zero
magnetic field. Atomistic spin dynamics simulations show that a skyrmion phase
occurs at small magnetic fields of $\sim$ 1 T. Skyrmion diameters amount to 2
to 8 nm and skyrmion lifetimes are up to 1 hour at temperatures of 25 to 45 K.",1806.06234v1
2018-06-29,Stability and magnetic properties of Fe double-layers on Ir (111),"We investigate the interplay between the structural reconstruction and the
magnetic properties of Fe doublelayers on Ir (111)-substrate using
first-principles calculations based on density functional theory and mapping of
the total energies on an atomistic spin model. We show that, if a second Fe
monolayer is deposited on Fe/Ir (111), the stacking may change from hexagonal
close-packed to bcc (110)-like accompanied by a reduction of symmetry from
trigonal to centered rectangular. Although the bcc-like surface has a lower
coordination, we find that this is the structural ground state. This
reconstruction has a major impact on the magnetic structure. We investigate in
detail the changes in the magnetic exchange interaction, the magnetocrystalline
anisotropy, and the Dzyaloshinskii Moriya interaction depending on the stacking
sequence of the Fe double-layer. Based on our findings, we suggest a new
technique to engineer Dzyaloshinskii Moriya interactions in multilayer systems
employing symmetry considerations. The resulting anisotropic
Dzyaloshinskii-Moriya interactions may stabilize higher-order skyrmions or
antiskyrmions.",1806.11339v1
2018-07-17,Extended exchange interactions stabilize long-period magnetic structures in Cr$_{1/3}$NbS$_2$,"The topologically-protected, chiral soliton lattice is a unique state of
matter offering intriguing functionality and it may serve as a robust platform
for storing and transporting information in future spintronics devices. While
the monoaxial chiral magnet Cr$_{1/3}$NbS$_2$ is known to host this exotic
state in an applied magnetic field, its detailed microscopic origin has
remained a matter of debate. Here we work towards addressing this open question
by measuring the spin wave spectrum of Cr$_{1/3}$NbS$_2$ over the entire
Brillouin zone with inelastic neutron scattering. The well-defined spin wave
modes allow us to determine the values of several microscopic interactions for
this system. The experimental data is well-explained by a Heisenberg
Hamiltonian with exchange constants up to third nearest neighbor and an easy
plane magnetocrystalline anisotropy term. Our work shows that both the second
and third nearest neighbor exchange interactions contribute to the formation of
the helimagnetic and chiral soliton lattice states in this robust
three-dimensional magnet.",1807.06665v1
2018-10-01,Mediating exchange bias by Verwey transition in CoO/Fe3O4 thin film,"We report the tunability of the exchange bias effect by the first-order
metal-insulator transition (known as the Verwey transition) of Fe3O4 in CoO (5
nm)/Fe3O4 (40 nm)/MgO (001) thin film. In the vicinity of the Verwey
transition, the exchange bias field is substantially enhanced because of a
sharp increase in magnetocrystalline anisotropy constant from high-temperature
cubic to lowtemperature monoclinic structure. Moreover, with respect to the
Fe3O4 (40 nm)/MgO (001) thin film, the coercivity field of the CoO (5 nm)/Fe3O4
(40 nm)/MgO (001) bilayer is greatly increased for all the temperature range,
which would be due to the coupling between Co spins and Fe spins across the
interface.",1810.00488v1
2018-10-19,Ferromagnetic nodal-line metal in monolayer {\em h}-InC,"Based on first-principles calculations, we predict a new two-dimensional
ferromagnetic material that exhibits exotic Fermi surface topology. We show
that monolayer hexagonal indium carbide ({\em h}-InC) is thermodynamically and
dynamically stable, and it energetically favors the ferromagnetic ordering of
spins. The perfectly planar geometry in two dimensions, together with
ferromagnetism, gives rise to a unique opportunity to encounter intriguing
electronic properties, captured in the Fermi surface and band topology. We show
that multiple nodal lines coexist in momentum space, accompanied by the
electron and hole pockets that touch each other linearly at the nodal lines.
Inclusion of spin-orbit coupling enriches the magnetic and electronic
properties of {\em h}-InC. Spin-orbit coupling leads to an easy-plane type
magnetocrystalline anisotropy, and the nodal lines can be tuned into
topological nodal points, contingent upon the magnetization direction. Symmetry
analysis and a tight-binding model are provided to explain the nodal structure
of the bands. Our findings suggest {\em h}-InC as a new venue for supporting
carbon-based magnetism and exotic band topology in two dimensions.",1810.08563v2
2019-01-04,How to accurately determine a saturation magnetization of the sample in a ferromagnetic resonance experiment?,"The phenomenon of ferromagnetic resonance (FMR) is still being exploited for
determining the magnetocrystalline anisotropy constants of magnetic materials.
We show that one can also determine accurately the saturation magnetization of
the sample using results of FMR experiments after taking into account the
relationship between resonance frequency and curvature of the spatial
distribution of free energy at resonance. Specifically, three examples are
given of calculating saturation magnetization from FMR data: we use historical
Bickford's measurements from 1950 for bulk magnetite, Liu's measurements from
2007 for a 500 mn thin film of a weak ferromagnet (Ga, Mn)As, and Wang's
measurements from 2014 for an ultrathin film of YIG. In all three cases, the
magnetization values we have determined are consistent with the results of
measurements.",1901.01207v1
2019-01-09,Anisotropic magnetic entropy change in Cr$_2$X$_2$Te$_6$ (X = Si and Ge),"Intrinsic, two-dimensional (2D) ferromagnetic semiconductors are an important
class of materials for spintronics applications. Cr$_2$X$_2$Te$_6$ (X = Si and
Ge) semiconductors show 2D Ising-like ferromagnetism, which is preserved in
few-layer devices. The maximum magnetic entropy change associated with the
critical properties around the ferromagnetic transition for Cr$_2$Si$_2$Te$_6$
$-\Delta S_M^{max} \sim$ 5.05 J kg$^{-1}$ K$^{-1}$ is much larger than $-\Delta
S_M^{max} \sim$ 2.64 J kg$^{-1}$ K$^{-1}$ for Cr$_2$Ge$_2$Te$_6$ with an
out-of-plane field change of 5 T. The rescaled $-\Delta S_M(T,H)$ curves
collapse onto a universal curve independent of temperature and field for both
materials. This indicates similar critical behavior and 2D Ising magnetism,
confirming the magnetocrystalline anisotropy that could preserve the long-range
ferromagnetism in few-layers of Cr$_2$X$_2$Te$_6$.",1901.02876v1
2019-02-22,Strongly Enhanced Gilbert Damping in 3d Transition Metal Ferromagnet Monolayers in Contact with Topological Insulator Bi2Se3,"Engineering Gilbert damping of ferromagnetic metal films is of great
importance to exploit and design spintronic devices that are operated with an
ultrahigh speed. Based on scattering theory of Gilbert damping, we extend the
torque method originally used in studies of magnetocrystalline anisotropy to
theoretically determine Gilbert dampings of ferromagnetic metals. This method
is utilized to investigate Gilbert dampings of 3d transition metal ferromagnet
iron, cobalt and nickel monolayers that are contacted by the prototypical
topological insulator Bi2Se3. Amazingly, we find that their Gilbert dampings
are strongly enhanced by about one order in magnitude, compared with dampings
of their bulks and free-standing monolayers, owing to the strong spin-orbit
coupling of Bi2Se3. Our work provides an attractive route to tailoring Gilbert
damping of ferromagnetic metallic films by putting them in contact with
topological insulators.",1902.08700v1
2019-02-26,Oriented Three-Dimensional Magnetic Biskyrmion in MnNiGa Bulk Crystals,"A biskyrmion consists of two bound, topologically stable skyrmion spin
textures. These coffee-bean-shaped objects have been observed in real-space in
thin plates using Lorentz transmission electron microscopy (LTEM). From LTEM
imaging alone, it is not clear whether biskyrmions are surface-confined
objects, or, analogously to skyrmions in non-centrosymmetric helimagnets,
three-dimensional tube-like structures in bulk sample. Here, we investigate the
biskyrmion form factor in single- and polycrystalline MnNiGa samples using
small angle neutron scattering (SANS). We find that biskyrmions are not
long-range ordered, not even in single-crystals. Surprisingly all of the
disordered biskyrmions have their in-plane symmetry axis aligned along certain
directions, governed by the magnetocrystalline anisotropy. This anisotropic
nature of biskyrmions may be further exploited to encode information.",1902.09708v1
2019-03-06,Isolated zero field sub-10 nm skyrmions in ultrathin Co films,"Due to their exceptional topological and dynamical properties magnetic
skyrmions - localized stable spin structures on the nanometre scale - show
great promise for future spintronic applications. To become technologically
competitive, isolated skyrmions with diameters below 10 nm that are stable at
zero magnetic field and room temperature are desired. Despite finding skyrmions
in a wide spectrum of materials, the quest for a material with these envisioned
properties is still ongoing. Here we report zero field isolated skyrmions with
diameters smaller than 5 nm coexisting with 1 nm thin domain walls in Rh/Co
atomic bilayers on the Ir(111) surface. These spin structures are characterized
by spin-polarized scanning tunnelling microscopy and can also be detected using
non-spin-polarized tips due to a large non-collinear magnetoresistance. We
demonstrate that sub-10 nm skyrmions are stabilised in these ferromagnetic Co
films at zero field due to strong frustration of exchange interaction, together
with Dzyaloshinskii-Moriya interaction and a large magnetocrystalline
anisotropy.",1903.02258v1
2019-04-06,Anomalous Hall effect in antiferromagnetic/non-magnetic interfaces,"We report a combined theoretical and experimental investigation of magnetic
proximity and Hall transport in Pt/Cr bilayers. Density functional theory
indicates that an interfacial magnetization can be induced in the Pt layer and
a strong magnetocrystalline anisotropy with an easy axis out of plane arises in
the antiferromagnet. A signal ascribed to the anomalous Hall effect is detected
and associated to the interface between Pt and Cr layers. We show that this
effect originates from the combination of proximity-induced magnetization and a
nontrivial topology of the band structure at the interface.",1904.03541v1
2019-04-08,Anisotropic magnetocaloric effect in Fe$_{3-x}$GeTe$_2$,"We present a comprehensive study on anisotropic magnetocaloric porperties of
the van der Waals weak-itinerant ferromagnet Fe$_{3-x}$GeTe$_2$ that features
gate-tunable room-temperature ferromagnetism in few-layer device. Intrinsic
magnetocrystalline anisotropy is observed to be temperature-dependent and most
likely favors the long-range magnetic order in thin Fe$_{3-x}$GeTe$_2$ crsytal.
The magnetic entropy change $-\Delta S_M$ also reveals an anisotropic
characteristic between $H // ab$ and $H // c$, which could be well scaled into
a universal curve. The peak value $-\Delta S_M^{max}$ of 1.20 J kg$^{-1}$
K$^{-1}$ and the corresponding adiabatic temperature change $\Delta T_{ad}$ of
0.66 K are deduced from heat capacity with out-of-plane field change of 5 T. By
fitting of the field-dependent parameters of $-\Delta S_M^{max}$ and the
relative cooling power RCP, it gives $-\Delta S_M^{max} \propto H^n$ with $n =
0.603(6)$ and $RCP \propto H^m$ with $m = 1.20(1)$ when $H // c$. Given the
high and tunable $T_c$, Fe$_{3-x}$GeTe$_2$ crystals are of interest for
fabricating the heterostructure-based spintronics device.",1904.03873v2
2019-06-10,Giant anisotropic magnetoresistance and nonvolatile memory in canted antiferromagnet Sr2IrO4,"Antiferromagnets have been generating intense interest in the spintronics
community, owing to their intrinsic appealing properties like zero stray field
and ultrafast spin dynamics. While the control of antiferromagnetic (AFM)
orders has been realized by various means, applicably appreciated
functionalities on the readout side of AFM-based devices are urgently desired.
Here, we report the remarkably enhanced anisotropic magnetoresistance (AMR) as
giant as ~ 160% in a simple resistor structure made of AFM Sr2IrO4 without
auxiliary reference layer. The underlying mechanism for the giant AMR is an
indispensable combination of atomic scale giant-MR-like effect and
magnetocrystalline anisotropy energy, which was not accessed earlier.
Furthermore, we demonstrate the bistable nonvolatile memory states that can be
switched in-situ without the inconvenient heat-assisted procedure, and robustly
preserved even at zero magnetic field, due to the modified interlayer coupling
by 1% Ga-doping in Sr2IrO4. These findings represent a straightforward step
toward the AFM spintronic devices.",1906.03782v1
2019-06-18,Increased perpendicular magnetocrystalline anisotropy governed by magnetic boundary in an asymmetrically terminated FeRh(001) thin film,"Rh-terminated FeRh(001) film is known to be stable in a ferromagnetic (FM)
state different from a G-type antiferromagnetic (G-AFM) bulk ground state,
while an Fe-terminated FeRh(001) film has the same ground state as the bulk. In
this paper, we investigate the magnetic properties of asymmetrically terminated
FeRh(001) films: one surface is Fe-terminated and the other is Rh-terminated.
Rh surface only ] (RhSO) FM state in asymmetrically terminated FeRh(001) film
is identified to exhibit 40% increased perpendicular MCA energy as compare to
that of the whole-layer (WL) FM state. This increased MCA energy is governed by
Rh atom which is placed at the magnetic boundary. Since FM and G-AFM states are
mixed up at the magnetic boundary, spin-orbit couplings which give positive
contribution to perpendicular MCA are revealed.",1906.07566v1
2019-07-09,"Magnetization reversal, giant exchange bias effect and magnetoresistance in oxygen vacancy ordered Sr$_{4}$Fe$_{3}$CoO$_{11}$","We report the structural, magnetic, exchange bias and magnetotransport effect
in Sr$_{4}$Fe$_{3}$CoO$_{11}$. The material crystallizes in the orthorhombic
$\textit{Cmmm}$ space group. It shows antiferromagnetic (G-type) transition
(T$_{N}$ = 255 K) along with interesting temperature induced magnetization
reversal (T$_{Comp.}$= 47 K measured at 100 Oe). The magnetic reversal can be
elucidated considering the increased magnetocrystalline anisotropy with Co
substitution. Magnetoresistance measurements shows an interesting crossover
from negative to positive side at $\sim$ 100 K. The negative magnetoresistance
reaches 80 $\%$ at 25 K in 7 T magnetic field. Giant exchange bias effect is
observed below T$_{N}$ under field cooling condition. The origin of the
negative magnetoresistance and giant exchange bias in this sample can be
attributed to the magnetic frustration.",1907.03986v1
2019-08-16,Two-dimensional magnetic semiconductors with room Curie temperatures,"We propose two-dimensional (2D) Ising-type ferromagnetic semiconductors
TcSiTe3, TcGeSe3, and TcGeTe3 with high Curie temperatures around 200-0500 K.
Owing to large spin-orbit couplings, the large magnetocrystalline anisotropy
energy (MAE), large anomalous Hall conductivity, and large magneto-optical Kerr
effect were discovered in these intriguing 2D materials. By comparing all
possible 2D MGeTe3 materials (M = 3d, 4d, 5d transition metals), we found a
large orbital moment around 0.5 $\mu$B per atom and a large MAE for TcGeTe3.
The large orbital moments are revealed to be from the comparable crystal fields
and electron correlations in these Tc-based 2D materials. The microscopic
mechanism of the high Curie temperature is also addressed. Our findings reveal
the unique magnetic behaviors of 2D Tc-based materials and present a family of
2D ferromagnetic semiconductors with large MAE and Kerr rotation angles that
would have wide applications in designing spintronic devices.",1908.05836v2
2019-09-16,Dissipation-induced rotation of suspended ferromagnetic nanoparticles,"We report the precessional rotation of magnetically isotropic ferromagnetic
nanoparticles in a viscous liquid that are subjected to a rotating magnetic
field. In contrast to magnetically anisotropic nanoparticles, the rotation of
which occurs due to coupling between the magnetic and lattice subsystems
through magnetocrystalline anisotropy, the rotation of isotropic nanoparticles
is induced only by magnetic dissipation processes. We propose a theory of this
phenomenon based on a set of equations describing the deterministic magnetic
and rotational dynamics of such particles. Neglecting inertial effects, we
solve these equations analytically, find the magnetization and particle
precessions in the steady state, determine the components of the particle
angular velocity and analyze their dependence on the model parameters. The
possibility of experimental observation of this phenomenon is also discussed.",1909.07450v2
2019-12-07,Role of higher-order exchange interactions for skyrmion stability,"Transition-metal interfaces and multilayers are a very promising class of
systems to realize nanometer-sized, stable magnetic skyrmions for future
spintronic devices. For room temperature applications it is crucial to
understand the interactions which control the stability of isolated skyrmions.
Typically, skyrmion properties are explained by the interplay of pair-wise
exchange interactions, the Dzyaloshinskii-Moriya interaction and the
magnetocrystalline anisotropy energy. Here, we demonstrate that higher-order
exchange interactions -- which have so far been neglected -- can play a key
role for the stability of skyrmions. We use an atomistic spin model
parametrized from first-principles and compare three different ultrathin film
systems. We consider all fourth order exchange interactions and show that in
particular the four-site four spin interaction has a giant effect on the energy
barrier preventing skyrmion and antiskyrmion collapse into the ferromagnetic
state. Our work opens new perspectives to enhance the stability of topological
spin structures.",1912.03474v2
2020-01-12,Magnetic Skyrmions in FePt Square-Based Nanoparticles Around Room-Temperature,"Magnetic skyrmions formed at temperatures around room temperature in
square-based parallelepiped magnetic FePt nanoparticles with perpendicular
magnetocrystalline anisotropy (MCA) were studied during the magnetization
reversal using micromagnetic simulations. Finite Differences (FD) method were
used for the solution of the Landau-Lifshitz-Gilbert equation. Magnetic
configurations exhibiting N\'eel skyrmionic formations were detected. The
magnetic skyrmions can be created in different systems generated by the
variation of external field, side length and width of the squared-based
parallelepiped magnetic nanoparticles. Micromagnetic configurations revealed a
variety of states which include skyrmionic textures with one distinct skyrmion
formed and being stable for a range of external fields around room-temperature.
The size of the formed N\'eel skyrmion is calculated as a function of the
external field, temperature, MCA and nanoparticle's geometrical characteristic
lengths which can be adjusted to produce N\'eel type skyrmions on demand having
diameters down to 12 nm. The micromagnetic simulations revealed that stable
skyrmions at the temperature range 270 - 330 K can be created for FePt magnetic
nanoparticle systems lacking of chiral interactions such as
Dzyaloshinskii-Moriya.",2001.03902v3
2020-05-02,Field-temperature phase diagram of magnetic bubbles spanning charge$/$orbital ordered and metallic phases in La$_{1-x}$Sr$_x$MnO$_3$ ($x = 0.125$),"We report formation of magnetic textures in the ferromagnetic (FM) phase of
La$_{1-x}$Sr$_x$MnO$_3$ for $x =$ 0.125; these textures are magnetic bubbles,
magnetic stripe domains, and forced FM states. In situ Lorentz microscopy (LM)
observations show that magnetic bubbles exist in the FM insulating phase
accompanying the formation of the charge$/$orbital ordering (CO$/$OO).
Furthermore, stable magnetic bubbles still exist in an intermediate temperature
region between the CO$/$OO ($T_{CO} =$ 155 K) and FM ($T_c =$ 190 K) transition
temperatures. These magnetic bubbles are believed to originate from the
magnetocrystalline anisotropy and the dipole-dipole interaction in the FM
phase. Based on in situ LM observations as a function of both temperature and
the strength of the external magnetic field applied, a magnetic
field-temperature phase diagram is constructed, exhibiting the stabilizing
regions of the magnetic bubbles in the FM phase of
La$_{0.875}$Sr$_{0.125}$MnO$_{3}$.",2005.00716v1
2020-07-15,Anisotropic magnetocaloric effect and critical behavior in CrSbSe$_3$,"We report anisotropic magnetocaloric effect and critical behavior in
quasi-one-dimensional ferromagnetic CrSbSe$_3$ single crystal. The maximum
magnetic entropy change $-\Delta S_M^{max}$ is 2.16 J kg$^{-1}$ K$^{-1}$ for
easy $a$ axis (2.03 J kg$^{-1}$ K$^{-1}$ for hard $b$ axis) and the relative
cooling power $RCP$ is 163.1 J kg$^{-1}$ for easy $a$ axis (142.1 J kg$^{-1}$
for hard $b$ axis) near $T_c$ with a magnetic field change of 50 kOe. The
magnetocrystalline anisotropy constant $K_u$ is estimated to be 148.5 kJ
m$^{-3}$ at 10 K, decreasing to 39.4 kJ m$^{-3}$ at 70 K. The rescaled $\Delta
S_M(T,H)$ curves along all three axes collapse onto a universal curve,
respectively, confirming the second order ferromagnetic transition. Further
critical behavior analysis around $T_c \sim$ 70 K gives that the critical
exponents $\beta$ = 0.26(1), $\gamma$ = 1.32(2), and $\delta$ = 6.17(9) for
$H\parallel a$, while $\beta$ = 0.28(2), $\gamma$ = 1.02(1), and $\delta$ =
4.14(16) for $H\parallel b$. The determined critical exponents suggest that the
anisotropic magnetic coupling in CrSbSe$_3$ is strongly dependent on
orientations of the applied magnetic field.",2007.08624v1
2020-08-03,Experimental evidence of hidden spin polarization in silicon by using strain gradient,"The centrosymmetric materials with hidden spin polarization are considered to
be the promising candidates for realization of energy efficient spintronics
systems and devices. However, the control of hidden spin polarization and
resulting transport behavior is not well understood. We hypothesized that
inhomogeneous strain can be the external knob to study and control hidden spin
polarization. In this work, we demonstrate a strain gradient mediated symmetry
breaking to discover the hidden spin polarization in centrosymmetric Si
lattice. The hidden spin polarization gives rise to magnetocrystalline
anisotropy and local magnetic moment along <111> directions in the Si. The
local magnetic moment gives rise to spin-acoustic phonon coupling, which is the
underlying cause of observed spin-Hall effect in both n-Si and p-Si. Discovery
of hidden magnetic moment in Si not only challenges the fundamental
understanding of the origin of the magnetism but also presents a giant leap in
realization of spintronics systems.",2008.01033v3
2020-08-12,Prediction on Properties of Rare-earth 2-17-X Magnets Ce2Fe17-xCoxCN : A Combined Machine-learning and Ab-initio Study,"We employ a combination of machine learning and first-principles calculations
to predict magnetic properties of rare-earth lean magnets. For this purpose,
based on training set constructed out of experimental data, the machine is
trained to make predictions on magnetic transition temperature (Tc), largeness
of saturation magnetization ({\mu}0Ms), and nature of the magnetocrystalline
anisotropy (Ku). Subsequently, the quantitative values of {\mu}0Ms and Ku of
the yet-to-be synthesized compounds, screened by machine learning, are
calculated by first-principles density functional theory. The applicability of
the proposed technique of combined machine learning and first-principles
calculations is demonstrated on 2-17-X magnets, Ce2Fe17-xCoxCN. Further to this
study, we explore stability of the proposed compounds by calculating vacancy
formation energy of small atom interstitials (N/C). Our study indicates a
number of compounds in the proposed family, offers the possibility to become
solution of cheap, and efficient permanent magnet.",2008.05125v1
2020-09-03,MAELAS: MAgneto-ELAStic properties calculation via computational high-throughput approach,"In this work, we present the program MAELAS to calculate magnetocrystalline
anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic
constants in an automated way by Density Functional Theory calculations. The
program is based on the length optimization of the unit cell proposed by Wu and
Freeman to calculate the magnetostrictive coefficients for cubic crystals. In
addition to cubic crystals, this method is also implemented and generalized for
other types of crystals that may be of interest in the study of
magnetostrictive materials. As a benchmark, some tests are shown for well-known
magnetic materials.",2009.01638v3
2020-09-28,Electronic and magnetic characterization of epitaxial CrBr$_3$ monolayers,"The ability to imprint a given material property to another through proximity
effect in layered two-dimensional materials has opened the way to the creation
of designer materials. Here, we use molecular-beam epitaxy (MBE) for a direct
synthesis of a superconductor-magnet hybrid heterostructure by combining
superconducting niobium diselenide (NbSe$_2$) with the monolayer ferromagnetic
chromium tribromide (CrBr$_3$). Using different characterization techniques and
density-functional theory (DFT) calculations, we have confirmed that the
CrBr$_3$ monolayer retains its ferromagnetic ordering with a magnetocrystalline
anisotropy favoring an out-of-plane spin orientation. Low-temperature scanning
tunneling microscopy (STM) measurements show a slight reduction of the
superconducting gap of NbSe$_2$ and the formation of a vortex lattice on the
CrBr$_3$ layer in experiments under an external magnetic field. Our results
contribute to the broader framework of exploiting proximity effects to realize
novel phenomena in 2D heterostructures.",2009.13465v1
2020-11-16,Topologically stable bimerons and skyrmions in vanadium dichalcogenide Janus monolayers,"We investigate the magnetic phase diagram of 1T-vanadium dichalcogenide
monolayers in Janus configuration (VSeTe, VSSe, and VSTe) from first
principles. The magnetic exchange, magnetocrystalline anisotropy and
Dzyaloshinskii-Moriya interaction (DMI) are computed using density functional
theory calculations, while the temperature- and field-dependent magnetic phase
diagram is simulated using large-scale atomistic spin modeling in the presence
of thermal fluctuations. The boundaries between magnetic ordered phases and
paramagnetic phases are determined by cross-analyzing the average topological
charge with the magnetic susceptibility and its derivatives. We find that in
such Janus monolayers, DMI is large enough to stabilize non-trivial chiral
textures. In VSeTe monolayer, an asymmetrical bimeron lattice state is
stabilized for in-plane field configuration whereas skyrmion lattice is formed
for out-of-plane field configuration. In VSSe monolayer, a skyrmion lattice is
stabilized for out-of-plane field configuration. This study demonstrates that
non-centrosymmetric van der Waals magnetic monolayers can support topological
textures close to room temperature.",2011.07813v1
2020-11-16,Microwave spectroscopy of the low-temperature skyrmion state in Cu2OSeO3,"In the cubic chiral magnet Cu2OSeO3 a low-temperature skyrmion state (LTS)
and a concomitant tilted conical state are observed for magnetic fields
parallel to <100>. In this work, we report on the dynamic resonances of these
novel magnetic states. After promoting the nucleation of the LTS by means of
field cycling, we apply broadband microwave spectroscopy in two experimental
geometries that provide either predominantly in-plane or out-of-plane
excitation. By comparing the results to linear spin-wave theory, we clearly
identify resonant modes associated with the tilted conical state, the
gyrational and breathing modes associated with the LTS, as well as the
hybridization of the breathing mode with a dark octupole gyration mode mediated
by the magnetocrystalline anisotropies. Most intriguingly, our findings suggest
that under decreasing fields the hexagonal skyrmion lattice becomes unstable
with respect to an oblique deformation, reflected in the formation of elongated
skyrmions.",2011.07826v1
2020-12-12,Electrically Controllable Crystal Chirality Magneto-Optical Effects in Collinear Antiferromagnets,"The spin chirality, created by magnetic atoms, has been comprehensively
understood to generate and control the magneto-optical effects. In comparison,
the role of the crystal chirality that relates to nonmagnetic atoms has
received much less attention. Here, we theoretically discover the crystal
chirality magneto-optical (CCMO) effects, which depend on the chirality of
crystal structures that originates from the rearrangement of nonmagnetic atoms.
We show that the CCMO effects exist in many collinear antiferromagnets, such as
RuO$_{2}$ and CoNb$_{3}$S$_{6}$, which has a local and global crystal
chirality, respectively. The key character of the CCMO effects is the sign
change if the crystal chirality reverses. The magnitudes of the CCMO spectra
can be effectively manipulated by reorienting the N\'eel vector with the help
of an external electric field, and the spectral integrals are found to be
proportional to magnetocrystalline anisotropy energy.",2012.06693v1
2020-12-21,Magnetic order of Dy$^{3+}$ and Fe$^{3+}$ moments in antiferromagnetic DyFeO$_{3}$ probed by spin Hall magnetoresistance and spin Seebeck effect,"We report on spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE)
in single crystal of the rare-earth antiferromagnet DyFeO$_{3}$ with a thin Pt
film contact. The angular shape and symmetry of the SMR at elevated
temperatures reflect the antiferromagnetic order of the Fe$^{3+}$ moments as
governed by the Zeeman energy, the magnetocrystalline anisotropy and the
Dzyaloshinskii-Moriya interaction. We interpret the observed linear dependence
of the signal on the magnetic field strength as evidence for field-induced
order of the Dy$^{3+}$ moments up to room temperature. At and below the Morin
temperature of 50$\,$K, the SMR monitors the spin-reorientation phase
transition of Fe$^{3+}$ spins. Below 23$\,$K, additional features emerge that
persist below 4$\,$K, the ordering temperature of the Dy$^{3+}$ magnetic
sublattice. We conclude that the combination of SMR and SSE is a simple and
efficient tool to study spin reorientation phase transitions and sublattice
magnetizations.",2012.11469v1
2021-03-30,Thermal annealing enhancement of Josephson critical currents in ferromagnetic CoFeB,"The electrical and structural properties of Co40Fe40B20 (CoFeB) alloy are
tunable with thermal annealing. This is key in the optimization of CoFeB-based
spintronic devices, where the advantageously low magnetic coercivity, high spin
polarization, and controllable magnetocrystalline anisotropy are utilised. So
far, there has been no report on superconducting devices based on CoFeB. Here,
we report Nb/CoFeB/Nb Josephson devices and demonstrate an enhancement of the
critical current by up to 700% following thermal annealing due to increased
structural ordering of the CoFeB. The results demonstrate that CoFeB is a
promising material for the development of superconducting spintronic devices.",2103.16136v1
2021-04-24,Electric-field driven stability control of skyrmions in an ultrathin transition-metal film,"To realize future spintronic applications with magnetic skyrmions --
topologically nontrivial swirling spin structures -- it is essential to achieve
efficient writing and deleting capabilities of these quasi-particles.
Electric-field assisted nucleation and annihilation is a promising route,
however, the understanding of the underlying microscopic mechanisms is still
limited. Here, we show how the stability of individual magnetic skyrmions in an
ultrathin transition-metal film can be controlled via external electric fields.
We demonstrate based on density functional theory that it is important to
consider the changes of all interactions with electric field, i.e., the
pair-wise exchange, the Dzyaloshinskii-Moriya interaction, the
magnetocrystalline anisotropy energy, and the higher-order exchange
interactions. The energy barriers for electric-field assisted skyrmion writing
and deleting obtained via atomistic spin simulations vary by up to a factor of
three more than the variations of the interactions calculated from
first-principles. This surprising effect originates from the electric-field
dependent size of metastable skyrmions at a fixed magnetic field. The large
changes of lifetimes allow the possibility of electric-field assisted thermally
activated writing and deleting of skyrmions.",2104.11986v2
2021-06-24,Large-scale epitaxy of two-dimensional van der Waals room-temperature ferromagnet Fe5GeTe2,"In recent years, two-dimensional van der Waals materials have emerged as an
important platform for the observation of long-range ferromagnetic order in
atomically thin layers. Although heterostructures of such materials can be
conceived to harness and couple a wide range of magneto-optical and
magneto-electrical properties, technologically relevant applications require
Curie temperatures at or above room-temperature and the ability to grow films
over large areas. Here we demonstrate the large-area growth of single-crystal
ultrathin films of stoichiometric Fe5GeTe2 on an insulating substrate using
molecular beam epitaxy. Magnetic measurements show the persistence of soft
ferromagnetism up to room temperature, with a Curie temperature of 293 K, and a
weak out-of-plane magnetocrystalline anisotropy. Surface, chemical, and
structural characterizations confirm the layer-by-layer growth, 5:1:2 Fe:Ge:Te
stoichiometric elementary composition, and single crystalline character of the
films.",2106.12808v1
2021-08-12,Magnetic interactions and spin excitations in van der Waals ferromagnet VI$_3$,"Using a combination of density functional theory (DFT) and spin-wave theory
methods, we investigate the magnetic interactions and spin excitations in
semiconducting VI$_3$. Exchange parameters of monolayer, bilayer, and bulk
forms are evaluated by mapping the magnetic energies of various spin
configurations, calculated using DFT+$U$, onto the Heisenberg model. The
intralayer couplings remain largely unchanged in three forms of VI$_3$, while
the interlayer couplings show stronger dependence on the dimensionality of the
materials. We calculate the spin-wave spectra within a linear spin-wave theory
and discuss how various exchange parameters affect the magnon bands. The
magnon-magnon interaction is further incorporated, and the Curie temperature is
estimated using a self-consistently renormalized spin-wave theory. To
understand the roles of constituent atoms on magnetocrystalline anisotropy
energy (MAE), we resolve MAE into sublattices and find that a strong negative
V-I inter-sublattice contribution is responsible for the relatively small
easy-axis MAE in VI$_3$.",2108.05528v1
2021-09-15,Nonlinear One-Dimensional Constitutive Model for Magnetostrictive Materials,"This paper presents an analytic model of one dimensional magnetostriction. We
show how specific assumptions regarding the symmetry of key micromagnetic
energies (magnetocrystalline, magnetoelastic, and Zeeman) reduce a general
three-dimensional statistical mechanics model to a one-dimensional form with an
exact solution. We additionally provide a useful form of the analytic equations
to help ensure numerical accuracy. Numerical results show that the model
maintains accuracy over a large range of applied magnetic fields and stress
conditions extending well outside those produced in standard laboratory
conditions. A comparison to experimental data is performed for several
magnetostrictive materials. The model is shown to accurately predict the
behavior of Terfenol-D, while two compositions of Galfenol are modeled with
varying accuracy. To conclude we discuss what conditions facilitate the
description of materials with cubic crystalline anisotropy as transversely
isotropic, to achieve peak model performance.",2109.07240v1
2021-10-29,Two types of magnetic bubbles in MnNiGa observed via Lorentz microscopy,"Magnetic bubbles are remarkable spin structures that developed in uniaxial
magnets with strong magnetocrystalline anisotropy. Several contradictory
reports have been published concerning the magnetic bubble structure in a
metallic magnet MnNiGa: Biskyrmions or type-II bubbles. Lorentz microscopy in
polycrystalline MnNiGa was used to explain the magnetic bubble structure.
Depending on the connection between the magnetic easy axis and the observation
plane, two types of magnetic bubbles were formed. Magnetic bubbles with
180{\deg} domains were formed if the easy axis was away from the direction
perpendicular to the observation plane. The contrast of biskyrmion is
reproduced by this form of a magnetic bubble. When the easy axis was
approximately perpendicular to the observing plane, type-II bubbles were
observed in the same specimen. The findings will fill a knowledge gap between
prior reports on magnetic bubbles in MnNiGa.",2110.15507v1
2021-11-09,Design of soft magnetic materials,"We present a strategy for the design of ferromagnetic materials with
exceptionally low magnetic hysteresis, quantified by coercivity. In this
strategy, we use a micromagnetic algorithm that we have developed in previous
research and which has been validated by its success in solving the ""Permalloy
Problem"" -- the well-known difficulty of predicting the composition 78.5% Ni of
lowest coercivity in the Fe-Ni system -- and by the insight, it provides into
the ""Coercivity Paradox"" of W. F. Brown. Unexpectedly, the design strategy
predicts that cubic materials with large saturation magnetization $m_s$ and
large magnetocrystalline anisotropy constant $\kappa_1$ will have low
coercivity on the order of that of Permalloy, as long as the magnetostriction
constants $\lambda_{100}, \lambda_{111}$ are tuned to special values. The
explicit prediction for a cubic material with low coercivity is the
dimensionless number $(c_{11}-c_{12}) \lambda_{100}^2/\kappa_1 = 81$ for
$\langle 100 \rangle$ easy axes. The results would seem to have a broad
potential application, especially to magnetic materials of interest in energy
research.",2111.05456v1
2021-11-16,Nature of Interfacial Dzyaloshinskii-Moriya Interactions in Graphene/Co/Pt(111) Multilayer Heterostructures,"DFT calculations within the generalized Bloch theorem approach show that
interfacial Dzyaloshinskii-Moriya interactions (DMI) at both interfaces of
Graphene/Co$_n$/Pt(111) multilayer heterostructures are decoupled for $n \geq
3$. Unlike the property of magnetocrystalline anisotropy for this system, DMI
is not affected by stacking defects in the Co layer. The effect of Graphene
(Gr) is to invert the chirality of the vaccum/Co interfacial DMI, overall
reducing the DMI of the heterostructure, which is nevertheless dominated by the
strong spin-orbit coupling (SOC) of Pt. A spectral analysis in the reciprocal
space shows that DMI at both the Gr/Co and Co/Pt interfaces have the same
nature, namely SOC-split hybrid bands of $d$-orbital character. This proves
that a DMI model based on a single band, such the Rashba DMI model, is
insuficient to describe the behaviour of this family of Gr-capped $3d/5d$ metal
heterostructures.",2111.08556v1
2022-03-08,Breathing skyrmions in chiral antiferromagnets,"Breathing oscillations of skyrmions in chiral antiferromagnets can be excited
by a temporal modification of the Dzyaloshinskii-Moriya interaction or
magnetocrystalline anisotropy strength. We employ an adiabatic approximation
and derive a formula for the potential that directly implies breathing
oscillations. We study the nonlinear regime and the features of larger
amplitude oscillations. We show that there is a maximum amplitude supported by
the potential. As a consequence, we predict theoretically and observe
numerically skyrmion annihilation events due to excitation of large amplitude
breathing oscillations. The process is efficient when the skyrmion is mildly
excited so that its radius initially grows, while the annihilation event is
eventually induced by the internal breathing dynamics. We reveal the
counter-intuitive property that the skyrmion possesses a nonzero kinetic energy
at the moment of its annihilation. Finally, the frequency of small amplitude
breathing oscillations is determined.",2203.04157v1
2022-04-06,Sensitivity of the MnTe valence band to orientation of magnetic moments,"An effective model of the hexagonal (NiAs-structure) manganese telluride
valence band in the vicinity of the A-point of the Brillouin zone is derived.
It is shown that while for the usual antiferromagnetic order (magnetic moments
in the basal plane) band splitting at A is small, their out-of-plane rotation
enhances the splitting dramatically (to about 0.5 eV). We propose extensions of
recent experiments (Moseley et al., Phys. Rev. Materials 6, 014404) where such
inversion of magnetocrystalline anisotropy has been observed in Li-doped MnTe,
to confirm this unusual sensitivity of a semiconductor band structure to
magnetic order.",2204.04206v3
2022-07-19,Micromagnetic simulation of neutron scattering from spherical nanoparticles: Effect of pore-type defects,"We employ micromagnetic simulations to model the effect of pore-type
microstructural defects on the magnetic small-angle neutron scattering cross
section and the related pair-distance distribution function of spherical
magnetic nanoparticles. Our expression for the magnetic energy takes into
account the isotropic exchange interaction, the magnetocrystalline anisotropy,
the dipolar interaction, and an externally applied magnetic field. The
signatures of the defects and the role of the dipolar energy are highlighted
and the effect of a particle-size distribution is studied. The results serve as
a guideline to the experimentalist.",2207.09164v1
2022-07-23,Coexistence of Weyl semimetal and Weyl nodal loop semimetal phases in a collinear antiferromagnet,"Antiferromagnets (AFMs) with anomalous quantum responses have lead to new
progress for the understanding of their magnetic and electronic structures from
symmetry and topology points of view. Two typical topological states are the
collinear antiferromagnetic Weyl semimetal (WSM) and Weyl nodal loop semimetal
(WNLSM). In comparison with the counterparts in ferromagnets and non-collinear
AFMs, the WSMs and WNLSMs in collinear AFMs are still waiting for experimental
verification. In this work, we theoretically predicted the coexistence of Weyl
points (WPs) and Weyl nodal loops (WNLs) in transition metal oxide RuO2. Owing
to the small magnetocrystalline anisotropy energy, the WPs and WNLs can
transform to each other via tuning the Neel vector. Moreover, since the WPs are
very close to Fermi level and the WNLs are even crossing Fermi level, the
topological states in RuO2 can be easily probed by photoemission and STM
methods. Our result provides a promising material platform for the study of WSM
and WNLSM states in collinear AFMs.",2207.11472v1
2022-08-17,"Magnetic, electronic, and structural investigation of the strongly correlated Y$_{1-x}$Sm$_x$Co$_5$ system","SmCo$_5$ and YCo$_5$ are isostructural compounds both showing large
magnetocrystalline anisotropy, where the former originates mainly from the
crystal-electric field and magnetic interactions. We investigate the
contribution of both interactions by partially substituting Y by Sm in as-cast
polycrystalline Y$_{1-x}$Sm$_{x}$Co$_5$ (with $x$=0, 0.1, 0.2, 0.3, and 0.4)
and measuring their structural, magnetic, and electrical properties through
X-ray diffraction, magnetization, and electrical transport measurements. Our
results suggest an interplay between microstructure strain in as-cast samples
and the electronic and magnetic interactions.",2208.08545v1
2022-08-19,Strain-Driven Zero-Field Near-10 nm Skyrmions in Two-Dimensional van der Waals Heterostructures,"Magnetic skyrmions $-$ localized chiral spin structures $-$ show great
promise for spintronic applications. The recent discovery of two-dimensional
(2D) magnetic materials opened new opportunities for exploring such topological
spin structures in atomically thin van der Waals (vdW) materials. Despite
recent progress in stabilizing metastable skyrmions in 2D magnets, their
diameters are still beyond 100~nm and their lifetime, which is essential for
applications, has not been explored yet. Here, using first-principles
calculations and atomistic spin simulations, we predict that compressive
mechanical strain leads to stabilizing zero-field skyrmions with diameters
close to 10 nm in a Fe$_3$GeTe$_2$/germanene vdW heterostructure. The origin of
these unique skyrmions is attributed to the high tunability of
Dzyaloshinskii-Moriya interaction and magnetocrystalline anisotropy energy by
strain, an effect which is shown to be general for Fe$_3$GeTe$_2$
heterostructures with buckled substrates. Based on our first-principles
parameters for the magnetic interactions, we calculate the energy barriers
protecting skyrmions against annihilation and their lifetimes using
transition-state theory. We show that nanoscale skyrmions in strained
Fe$_3$GeTe$_2$/germanene can be stable for hours at temperatures up to 20 K.",2208.09210v1
2022-09-01,Two-dimensional half Chern-Weyl semimetal with multiple screw axes,"Half topological states of matter and two-dimensional (2D) magnetism have
gained much attention recently. In this paper, we propose a special topological
semimetal phase called a 2D half Chern-Weyl semimetal (HCWS), which is a 2D
magnetic Weyl semimetal bound to the half Chern insulator phase by symmetry,
and the two phases can be converted to each other by manipulating the
magnetization direction. We provide the symmetry conditions to realize this
state in 2D systems with multiple screw axes. Tight-binding models with
multiple basis and a predicted 2D material, monolayer TiTe, are shown as the
concrete examples for HCWSs. The TiTe monolayer was shown to have a high
ferremagnetic Curie temperature (~966 K) as well as a Coulomb
correlation-enhanced spin-orbit coupling (SOC), and further demonstrates the
effect of correlation-enhanced SOC on magnetocrystalline anisotropy energy and
energy gap opening. Our work reveals a state with switchable and spin-resolved
half body charge currents as well as half boundary charge currents, and will
provide a platform for novel and high-performance topological spintronics
devices.",2209.00330v1
2022-10-20,Large orbital magnetic moment in VI3,"The existence of the V3+ ion orbital moment is the open issue of the nature
of magnetism in the van der Waals ferromagnet VI3. The huge magnetocrystalline
anisotropy in conjunction with the significantly reduced ordered magnetic
moment compared to the spin-only value provides strong but indirect evidence of
a significant V orbital moment. We used the unique capability of X-ray magnetic
circular dichroism to determine the orbital component of the total magnetic
moment and provide for the first time a direct proof of an exceptionally
sizable orbital moment of the V3+ ion in VI3. Our ligand field multiplet
simulations of the XMCD spectra in synergy with the results of DFT calculations
agree with the existence of two V sites with different orbital occupations and
therefore different OM magnitudes in the ground state.",2210.11278v1
2022-10-25,Tuning of topological properties in the strongly correlated antiferromagnet Mn$_3$Sn via Fe doping,"Magnetic topological materials, in which strong correlations between magnetic
and electronic properties of matter, give rise to various exotic phenomena such
as anomalous Hall effect (AHE), topological Hall effect (THE), and skyrmion
lattice. Here, we report on the electronic, magnetic, and topological
properties of Mn$_{3-\it{x}}$Fe$_{\it{x}}$Sn single crystals ($\it{x}$=0, 0.25,
and 0.35). Low temperature magnetic properties have been significantly changed
with Fe doping. Most importantly, we observe that large uniaxial
magnetocrystalline anisotropy that is induced by the Fe doping in combination
with competing magnetic interactions at low temperature produce nontrivial
spin-texture, leading to large topological Hall effect in the doped systems at
low temperatures. Our studies further show that the topological properties of
Mn$_{3-\it{x}}$Fe$_{\it{x}}$Sn are very sensitive to the Fe doping.",2210.14150v1
2022-11-21,Inertial dynamics and equilibrium correlation functions of magnetization at short times,"The method of moments is developed and employed to analyze the equilibrium
correlation functions of the magnetization of ferromagnetic nanoparticles in
the case of inertial magnetization dynamics. The method is based on the Taylor
series expansion of the correlation functions and the estimation of the
expansion coefficients. This method significantly reduces the complexity of
analysis of equilibrium correlation functions. Analytical expressions are
derived for the first three coefficients for the longitudinal and transverse
correlation functions for the uniaxial magnetocrystalline anisotropy of
ferromagnetic nanoparticles with a longitudinal magnetic field. The limiting
cases of very strong and negligibly weak external longitudinal fields are
considered. The Gordon sum rule for inertial magnetization dynamics is
discussed. In addition, we show that finite analytic series can be used as a
simple and satisfactory approximation for the numerical calculation of
correlation functions at short times.",2211.11515v2
2023-01-24,Ru$_{2-x}$Mn$_{1+x}$Al thin films,"The cubic Heusler alloy Ru$_{2-x}$Mn$_{1+x}$Al is grown in thin film form on
MgO and MgAl$_2$O$_4$ substrates. It is a highly spin-polarised ferrimagnetic
metal, with weak magnetocrystalline anisotropy. Although structurally and
chemically similar to $\text{Mn}_2\text{Ru}_x\text{Ga}$, it does not exhibit
ferrimagnetic compensation, or large magneto galvanic effects. The differences
are attributed to a combination of atomic order and the hybridisation with the
group 13 element Al or Ga. The spin polarisation is around 50 to 60 %. There is
a gap in the density of states just above the Fermi level in fully ordered
compounds.",2301.10148v2
2023-02-04,"Room Temperature Ferroelectricity, Ferromagnetism, and Anomalous Hall Effect in Half-metallic Monolayer CrTe","Two-dimensional materials hosting ferroelectricity and ferromagnetism are
crucial for low-power and high-speed information processing technologies.
However, intrinsic 2D multiferroics in the monolayer limit are rare. Here, we
demonstrate that monolayer CrTe, obtained by cleaving the [002] surface, is
dynamically stable multiferroic at temperatures beyond room temperature. We
show that it orders ferromagnetically with significant in-plane
magnetocrystalline anisotropy, and it is a half-metal featuring a large
half-metal gap. Remarkably, the broken inversion symmetry and buckled geometry
of monolayer CrTe make it a ferroelectric with a large spontaneous out-of-plane
polarization and significant magnetoelectric coupling. In addition, we
demonstrate polarization or electric field-induced tunability of the anomalous
Hall effect, accompanied by substantial bandstructure modulation. Our findings
establish monolayer CrTe as a room-temperature multiferroic with great
potential for applications in spintronics and ferroelectric devices.",2302.02145v2
2023-03-01,Tailed skyrmions -- an obscure branch of magnetic solitons,"We report tailed skyrmions -- a new class of stable soliton solutions of the
2D chiral magnet model. Tailed skyrmions have elongated shapes and emerge in a
narrow range of fields near the transition between the spin spirals and the
saturated state. We analyze the stability range of these solutions in terms of
external magnetic field and magnetocrystalline anisotropy. Minimum energy paths
and the homotopies (continuous transitions) between tailed skyrmions of the
same topological charge have been calculated using the geodesic nudged elastic
bands method. The discovery of tailed skyrmions extends the diversity of
already-known solutions illustrated by complex morphology solitons, such as
tailed skyrmion bags with and without chiral kinks.",2303.00347v1
2023-03-03,Magneto-optical sensing of the pressure driven magnetic ground states in bulk CrSBr,"Competition between exchange interactions and magnetocrystalline anisotropy
may bring new magnetic states that are of great current interest. An applied
hydrostatic pressure can further be used to tune their balance. In this work we
investigate the magnetization process of a biaxial antiferromagnet in an
external magnetic field applied along the easy axis. We find that the single
metamagnetic transition of the Ising type observed in this material under
ambient pressure transforms under hydrostatic pressure into two transitions, a
first-order spin flop transition followed by a second order transition towards
a polarized ferromagnetic state near saturation. This reversible tuning into a
new magnetic phase is obtained in layered bulk CrSBr at low temperature by
varying the interlayer distance using high hydrostatic pressure, which
efficiently acts on the interlayer magnetic exchange, and is probed by
magneto-optical spectroscopy.",2303.01823v2
2023-04-24,Fast non-volatile electric control of antiferromagnetic states,"Electrical manipulation of antiferromagnetic states, a cornerstone of
antiferromagnetic spintronics, is a great challenge, requiring novel material
platforms. Here we report the full control over antiferromagnetic states by
voltage pulses in the insulating Co$_3$O$_4$ spinel. We show that the strong
linear magnetoelectric effect emerging in its antiferromagnetic state is fully
governed by the orientation of the N\'eel vector. As a unique feature of
Co$_3$O$_4$, the magnetoelectric energy can easily overcome the weak
magnetocrystalline anisotropy, thus, the N\'eel vector can be manipulated on
demand, either rotated smoothly or reversed suddenly, by combined electric and
magnetic fields. We succeed with switching between antiferromagnetic states of
opposite N\'eel vectors by voltage pulses within a few microsecond in
macroscopic volumes. These observations render quasi-cubic antiferromagnets,
like Co$_3$O$_4$, an ideal platform for the ultrafast (pico- to nanosecond)
manipulation of microscopic antiferromagnetic domains and may pave the way for
the realization of antiferromagnetic spintronic devices.",2304.12270v1
2023-07-05,Multi-level recording in dual-layer FePt-C granular film for heat-assisted magnetic recording,"Multi-level magnetic recording is a new concept for increasing the data
storage capacity of hard disk drives. However, its implementation has been
limited by a lack of suitable media capable of storing information at multiple
levels. Herein, we overcome this problem by developing dual FePt-C nanogranular
films separated by a Ru-C breaking layer with a cubic crystal structure. The
FePt grains in the bottom and top layers of the developed media exhibited
different effective magnetocrystalline anisotropies and Curie temperatures. The
former is realized by different degrees of ordering in the L10-FePt grains,
whereas the latter was attributed to the diffusion of Ru, thereby enabling
separate magnetic recordings at each layer under different magnetic fields and
temperatures. Furthermore, the magnetic measurements and heat-assisted magnetic
recording simulations showed that these media enabled 3-level recording and
could potentially be extended to 4-level recording, as the up-down and down-up
states exhibited non-zero magnetization.",2307.02213v1
2023-08-22,Effect of Electron-Phonon Scattering on the Anomalous Hall Conductivity of Fe$_3$Sn: A Kagome Ferromagnetic Metal,"We report on magnetic and magnetotransport studies of a Kagome ferromagnetic
metal, Fe$_3$Sn. Our studies reveal a large anomalous Hall conductivity
($\sigma_{zx}$) in this system, mainly contributed by temperature independent
intrinsic Hall conductivity ($\sigma^{int}_{zx}$=485$\pm$60 S/cm) and
temperature dependent extrinsic Hall conductivity ($\sigma^{ext}_{zx}$) due to
skew-scattering. Although $\sigma^{ext}_{zx}$ value is large and almost
equivalent to the intrinsic Hall conductivity at low temperatures, it
drastically decreases with increasing temperature, following the relation
$\sigma^{ext}_{zx}=\frac{\sigma_{zx0}^{ext}}{(aT+1)^2}$, under the influence of
electron-phonon scattering. The presence of electron-phonon scattering in this
system is also confirmed by the linear dependence of longitudinal electrical
resistivity at higher temperatures [$\rho(T)\propto T$]. We further find that
Fe$_3$Sn is a soft ferromagnet with an easy-axis of magnetization lying in the
$\it{ab}$ plane of the crystal with magnetocrystalline anisotropy energy
density as large as 1.02 $\times$ 10$^6$",2308.11177v1
2023-08-22,"Tuning of Electrical, Magnetic, and Topological Properties of Magnetic Weyl Semimetal Mn$_{3+x}$Ge by Fe doping","We report on the tuning of electrical, magnetic, and topological properties
of the magnetic Weyl semimetal (Mn$_{3+x}$Ge) by Fe doping at the Mn site,
Mn$_{(3+x)-\delta}$Fe$_{\delta}$Ge ($\delta$=0, 0.30, and 0.62). Fe doping
significantly changes the electrical and magnetic properties of Mn$_{3+x}$Ge.
The resistivity of the parent compound displays metallic behavior, the system
with $\delta$=0.30 of Fe doping exhibits semiconducting or bad-metallic
behavior, and the system with $\delta$=0.62 of Fe doping demonstrates a
metal-insulator transition at around 100 K. Further, we observe that the Fe
doping increases in-plane ferromagnetism, magnetocrystalline anisotropy, and
induces a spin-glass state at low temperatures. Surprisingly, topological Hall
state has been noticed at a Fe doping of $\delta$=0.30 that is not found in the
parent compound or with $\delta$=0.62 of Fe doping. In addition, spontaneous
anomalous Hall effect observed in the parent system is significantly reduced
with increasing Fe doping concentration.",2308.11183v1
2023-09-12,Probing spatial variation of magnetic order in strained SrMnO$_3$ thin films using Spin Hall Magnetoresistance,"SrMnO$_{3}$ (SMO) is a magnetic insulator and predicted to exhibit a
multiferroic phase upon straining. Strained films of SMO display a wide range
of magnetic orders, ranging from G-type to C-and A-type, indicative of
competing magnetic interactions. The potential of spin Hall magnetoresistance
(SMR) is exploited as an electrical probe for detecting surface magnetic order,
to read surface magnetic moments in SMO and its spatial variation, by designing
and positioning electrodes of different sizes on the film. The findings
demonstrate antiferromagnetic domains with different magnetocrystalline
anisotropies along with a ferromagnetic order, where the magnetization arises
from double exchange mediated ferromagnetic order and canted antiferromagnetic
moments. Further, from a complete analysis of the SMR, a predominance of
antiferromagnetic domain sizes of 3.5 $\mu$m$^2$ is extracted. This work
enhances the applicability of SMR in unraveling the richness of correlation
effects in complex oxides, as manifested by the detection of coexisting and
competing ground states and lays the foundation for the study of magnon
transport for different magnetoelectric based computing applications.",2309.06279v1
2023-09-16,Colossal linear magnetoelectricity in polar magnet Fe2Mo3O8,"Linear magnetoelectric effect is an attractive phenomenon in condensed
matters and provides indispensable technological functionalities. Here a
colossal linear magnetoelectric effect with diagonal component alfa_33 reaching
up to ~480 ps/m is reported in a polar magnet Fe2Mo3O8, and this effect can
persist in a broad range of magnetic field (~20 T) and is orders of magnitude
larger than reported values in literature. Such an exceptional experimental
observation can be well reproduced by a theoretical model affirmatively
unveiling the vital contributions from the exchange striction, while the sign
difference of magnetocrystalline anisotropy can also be reasonably figured out.",2309.08974v1
2023-11-07,"Magnetism in AV3Sb5 (A = Cs, Rb, K): Complex Landscape of the Dynamical Magnetic Textures","We have investigated the dynamical magnetic properties of the V-based kagome
stibnite compounds by combining the ab-initio calculated magnetic parameters of
a spin Hamiltonian like inter-site exchange parameters, magnetocrystalline
anisotropy and site projected magnetic moments, with full-fledged simulations
of atomistic spin-dynamics. Our calculations reveal that in addition to a
ferromagnetic order along the [001] direction, the system hosts a complex
landscape of magnetic configurations comprised of commensurate and
incommensurate spin-spirals along the [010] direction. The presence of such
chiral magnetic textures may be the key to solve the mystery about the origin
of the experimentally observed inherent breaking of the C6 rotational symmetry-
and the time-reversal symmetry.",2311.04099v1
2023-11-30,Growth of high-quality CrI3 single crystals and engineering of its magnetic properties via V and Mn doping,"CrI3, as a soft van der Waals layered magnetic material, has been widely
concerned and explored for its magnetic complexity and tunability. In this
work, high quality and large size thin CrI3, V and Mn doped single crystals
were prepared by chemical vapor transfer method. A remarkable irreversible
Barkhausen effect was observed in CrI3 and CrMn0.06I3, which can be attributed
to the low dislocation density that facilitates movement of the domain walls.
In addition, the introduction of the doping element Mn allows higher saturation
magnetization intensity. Cr0.5V0.5I3 exhibits substantially increased
coercivity force and larger magnetocrystalline anisotropy compared to CrI3,
while kept similar Curie temperature and good environmental stability. The
first principles calculations suggest direct and narrowed band gaps in
Cr0.5V0.5I3 and VI3 comparing to CrI3. The smaller band gaps and good hard
magnetic property make Cr0.5V0.5I3 an alternative choice to future research of
spintronic devices.",2311.18360v1
2024-01-29,"Magnetic, thermodynamic, and magnetotransport properties of CeGaGe and PrGaGe single crystals","We investigate the physical properties of high-quality single crystals CeGaGe
and PrGaGe using magnetization, heat capacity, and magnetotransport
measurements. Gallium-indium binary flux was used to grow these single crystals
that crystallize in a body-centered tetragonal structure. Magnetic
susceptibility data reveal a magnetic phase transition around 6.0 and 19.4 K in
CeGaGe and PrGaGe, respectively, which is further confirmed by heat capacity
and electrical resistivity data. A number of additional anomalies have been
observed below the ordering temperature in the magnetic susceptibility data,
indicating a complex magnetic structure. The magnetic measurements also reveal
a strong magnetocrystalline anisotropy in both compounds. Our detailed analysis
of the crystalline electric field (CEF) effect as observed in magnetic
susceptibility and heat capacity data suggests that the $J$ = 5/2 multiplet of
CeGaGe splits into three doublets, while the $J$ = 4 degenerate ground state of
PrGaGe splits into five singlets and two doublets. The estimated energy levels
from the CEF analysis are consistent with the magnetic entropy.",2401.15907v1
2024-01-31,Prediction of stable nanoscale skyrmions in monolayer Fe$_5$GeTe$_2$,"Using first-principles calculations and atomistic spin simulations, we
predict stable isolated skyrmions with a diameter below 10 nm in a monolayer of
the two-dimensional van der Waals ferromagnet Fe$_5$GeTe$_2$, a material of
significant experimental interest. A very large Dzyaloshinskii-Moriya
interaction (DMI) is observed due to the intrinsic broken inversion symmetry
and strong spin-orbit coupling for monolayer Fe$_5$GeTe$_2$. We show that the
nearest-neighbor approximation, often used in literature, fails to describe the
DMI. The strong DMI together with moderate in-plane magnetocrystalline
anisotropy energy allows to stabilize nanoscale skyrmions in out-of-plane
magnetic fields above $\approx 2$~T. The energy barriers of skyrmions in
monolayer Fe$_5$GeTe$_2$ are comparable to those of state-of-the-art
transition-metal ultra-thin films. We further predict that these nanoscale
skyrmions can be stable for hours at temperatures up to 20 K.",2401.18000v1
2024-02-09,Configuration of the magnetosome chain: a natural magnetic nanoarchitecture,"Magnetospirillum gryphiswaldense is a microorganism with the ability to
biomineralize magnetite nanoparticles, called magnetosomes, and arrange them
into a chain that behaves like a magnetic compass. Rather than straight lines,
magnetosome chains are slightly bent, as evidenced by electron cryotomography.
Our experimental and theoretical results suggest that due to the competition
between the magnetocrystalline and shape anisotropies, the effective magnetic
moment of individual magnetosomes is tilted out of the [111] crystallographic
easy axis of magnetite. This tilt does not affect the direction of the chain
net magnetic moment, which remains along the [111] axis, but explains the
arrangement of magnetosomes in helical-like shaped chains. Indeed, we
demonstrate that the chain shape can be reproduced by considering an interplay
between the magnetic dipolar interactions between magnetosomes, ruled by the
orientation of the magnetosome magnetic moment, and a lipid/protein-based
mechanism, modeled as an elastic recovery force exerted on the magnetosomes.",2402.06375v1
2024-02-29,Searching for magnetically hard monoborides (and finding a few): A first-principles investigation,"New hard magnetic materials with zero or low rare earth content are in demand
due to the high prices of the rare earth metals. Among the candidates for such
materials, we consider MnB, FeB and their alloys, because previous experiments
suggest that FeB has a relatively high magnetic hardness of about 0.83 at room
temperature. Using first-principles calculations, we examine the full range of
alloys from CrB, through MnB, FeB, to CoB. Furthrmore, we consider alloys of
MnB and FeB with substitutions of 3$d$, 4$d$ and 5$d$ transition metals. For
the above ninety compositions, we determine magnetic moment, magnetocrystalline
anisotropy energy and magnetic hardness. For (Fe-Co)B alloys, the calculated
values of magnetic hardness exceed five, which is an exceptionally high. While
these values are inflated by the virtual crystal approximation used, we still
expect actual magnetic hardnesses well above unity. Furthermore, we classify
considered MnB alloys substituted with transition metals as magnetically soft
or semi-hard and FeB alloys with Sc, Ti, V, Zr, Nb, Mo, Hf, Ta or W as
magnetically hard (with magnetic hardness exceeding unity).",2403.00138v1
2006-03-06,Magnetism of iron: from the bulk to the monoatomic wire,"The magnetic properties of iron (spin and orbital magnetic moments,
magnetocrystalline anisotropy energy) in various geometries and
dimensionalities are investigated by using a parametrized tight-binding model
in an $s$, $p$ and $d$ atomic orbital basis set including spin polarization and
the effect of spin-orbit coupling. The validity of this model is well
established by comparing the results with those obtained by using an ab-initio
code. This model is applied to the study of iron in bulk bcc and fcc phases,
$(110)$ and $(001)$ surfaces and to the monatomic wire, at several interatomic
distances. New results are derived. The variation of the component of the
orbital magnetic moment on the spin quantization axis has been studied as a
function of depth, revealing a significant enhancement in the first two layers,
especially for the $(001)$ surface. It is found that the magnetic anisotropy
energy is drastically increased in the wire and can reach several meV. This is
also true for the orbital moment, which in addition is highly anisotropic.
Furthermore it is shown that when the spin quantization axis is neither
parallel nor perpendicular to the wire the average orbital moment is not
aligned with the spin quantization axis. At equilibrium distance the easy
magnetization axis is along the wire but switches to the perpendicular
direction under compression. The success of this model opens up the possibility
of obtaining accurate results on other elements and systems with much more
complex geometries.",0603121v1
2009-03-13,Connection Between Magnetism and Structure in Fe Double Chains on the Ir(100) Surface,"The magnetic ground state of nanosized systems such as Fe double chains,
recently shown to form in the early stages of Fe deposition on Ir(100), is
generally nontrivial. Using ab initio density functional theory we find that
the straight ferromagnetic (FM) state typical of bulk Fe as well as of isolated
Fe chains and double chains is disfavored after deposition on Ir(100) for all
the experimentally relevant double chain structures considered. So long as
spin-orbit coupling (SOC) is neglected, the double chain lowest energy state is
generally antiferromagnetic (AFM), a state which appears to prevail over the FM
state due to Fe-Ir hybridization. Successive inclusion of SOC adds two further
elements, namely a magnetocrystalline anisotropy, and a Dzyaloshinskii-Moriya
(DM) spin-spin interaction, the former stabilizing the collinear AFM state, the
second favoring a long-period spin modulation. We find that anisotropy is most
important when the double chain is adsorbed on the partially deconstructed
Ir(100) -- a state which we find to be substantially lower in energy than any
reconstructed structure -- so that in this case the Fe double chain should
remain collinear AFM. Alternatively, when the same Fe double chain is adsorbed
in a metastable state onto the (5x1) fully reconstructed Ir(100) surface, the
FM-AFM energy difference is very much reduced and the DM interaction is
expected to prevail, probably yielding a helical spin structure.",0903.2348v1
2013-06-16,Exchange coupling and magnetic anisotropy at Fe/FePt interfaces,"We perform fully relativistic first principles calculations of the exchange
interactions and the magnetocrystalline anisotropy energy (MAE) in an
Fe/FePt/Fe sandwich system in order to elucidate how the presence of Fe/FePt
(soft/hard magnetic) interfaces impacts on the magnetic properties of
Fe/FePt/Fe multilayers. Throughout our study we make comparisons between a
geometrically unrelaxed system and a geometrically relaxed system. We observe
that the Fe layer at the Fe/FePt interface plays a crucial role inasmuch its
(isotropic) exchange coupling to the soft (Fe) phase of the system is
substantially reduced. Moreover, this interfacial Fe layer has a substantial
impact on the MAE of the system. We show that the MAE of the FePt slab,
including the contribution from the Fe/FePt interface, is dominated by
anisotropic inter-site exchange interactions. Our calculations indicate that
the change in the MAE of the FePt slab with respect to the corresponding bulk
value is negative, i.e., the presence of Fe/FePt interfaces appears to reduce
the perpendicular MAE of the Fe/FePt/Fe system. However, for the relaxed
system, this reduction is marginal. It is also shown that the relaxed system
exhibits a reduced interfacial exchange. Using a simple linear chain model we
demonstrate that the reduced exchange leads to a discontinuity in the
magnetisation structure at the interface.",1306.3642v1
2014-11-10,Symmetry-lowering lattice distortion at the spin-reorientation in MnBi single crystals,"Structural and physical properties determined by measurements on large single
crystals of the anisotropic ferromagnet MnBi are reported. The findings support
the importance of magneto-elastic effects in this material. X-ray diffraction
reveals a structural phase transition at the spin reorientation temperature
$T_{SR}$ = 90 K. The distortion is driven by magneto-elastic coupling, and upon
cooling transforms the structure from hexagonal to orthorhombic. Heat capacity
measurements show a thermal anomaly at the crystallographic transition, which
is suppressed rapidly by applied magnetic fields. Effects on the transport and
anisotropic magnetic properties of the single crystals are also presented.
Increasing anisotropy of the atomic displacement parameters for Bi with
increasing temperature above $T_{SR}$ is revealed by neutron diffraction
measurements. It is likely that this is directly related to the anisotropic
thermal expansion in MnBi, which plays a key role in the spin reorientation and
magnetocrystalline anisotropy. The identification of the true ground state
crystal structure reported here may be important for future experimental and
theoretical studies of this permanent magnet material, which have to date been
performed and interpreted using only the high temperature structure.",1411.2448v1
2015-04-14,Magnetization induced local electric dipoles and multiferroic properties of Ba2CoGe2O7,"Ba2CoGe2O7, crystallizing in the noncentrosymmetric but nonpolar structure,
belongs to a special class of multiferroic materials, whose properties are
predetermined by the rotoinversion symmetry. Unlike inversion, the
rotoinversion symmetry can be easily destroyed by the magnetization. Moreover,
due to specific structural pattern, the magnetic structure of Ba2CoGe2O7 is
relatively soft. Altogether, this leads to the rich variety of multiferroic
properties, where the magnetic structure can be easily deformed by the magnetic
field, inducing the electric polarization in the direction, which depends on
the direction of the magnetic field. In this paper, we show that all these
properties can be successfully explained on the basis of realistic low-energy
model, derived from the first-principles electronic structure calculations for
the magnetically active Co 3d bands, and the Berry-phase theory of electric
polarization. Particularly, we argue that the magnetization induced electric
polarization in Ba2CoGe2O7 is essentially local and expressed via the
expectation values of some dipole matrices, calculated in the Wannier basis of
the model, and the site-diagonal density matrices of the magnetic Co sites.
Thus, the basic aspects of the behavior of Ba2CoGe2O7 can be understood already
in the atomic limit, where both magnetic anisotropy and magnetoelectric
coupling are specified by density matrix. Then, the macroscopic polarization
can be found as a superposition of electric dipoles of the individual Co sites.
We discuss the behavior of interatomic magnetic interactions, main
contributions to the magnetocrystalline anisotropy and the spin canting, as
well as the similarities and differences of the proposed picture from the
phenomenological model of spin-dependent p-d hybridization.",1504.03540v1
2017-04-24,Geometrical dependence of domain wall propagation and nucleation fields in magnetic domain wall sensor devices,"We study the key domain wall properties in segmented nanowires loop-based
structures used in domain wall based sensors. The two reasons for device
failure, namely the distribution of domain wall propagation field (depinning)
and the nucleation field are determined with Magneto-Optical Kerr Effect (MOKE)
and Giant Magnetoresistance (GMR) measurements for thousands of elements to
obtain significant statistics. Single layers of Ni$_{81}$Fe$_{19}$, a complete
GMR stack with Co$_{90}$Fe$_{10}$/Ni$_{81}$Fe$_{19}$ as a free layer and a
single layer of Co$_{90}$Fe$_{10}$ are deposited and industrially patterned to
determine the influence of the shape anisotropy, the magnetocrystalline
anisotropy and the fabrication processes. We show that the propagation field is
little influenced by the geometry but significantly by material parameters. The
domain wall nucleation fields can be described by a typical Stoner-Wohlfarth
model related to the measured geometrical parameters of the wires and fitted by
considering the process parameters. The GMR effect is subsequently measured in
a substantial number of devices (3000), in order to accurately gauge the
variation between devices. This reveals a corrected upper limit to the
nucleation fields of the sensors that can be exploited for fast
characterization of working elements.",1704.07371v2
2017-07-13,Role of Square Planar Coordination in the Magnetic Properties of Na4IrO4,"Iridates supply fertile grounds for unconventional phenomena and exotic
electronic phases. With respect to well-studied octahedrally-coordinated
iridates, we pay our attention to a rather unexplored iridate, Na4IrO4, showing
an unusual square-planar coordination. The latter is key to rationalize the
electronic structure and magnetic property of Na4IrO4, which is here explored
by first-principles density functional theory and Monte Carlo simulations. Due
to the uncommon square-planar crystal field, Ir 5d states adopt
intermediate-spin state with double occupation of dz2 orbital, leading to a
sizable local spin moment, at variance with many other iridates. The
square-planar crystal field splitting is also crucial in opening a robust
insulating gap in Na4IrO4, irrespective of the specific magnetic ordering or
treatment of electronic correlations. Spin-orbit coupling plays a minor role in
shaping the electronic structure, but leads to a strong magnetocrystalline
anisotropy. The easy axis perpendicular to the IrO4 plaquette, well explained
using perturbation theory, is again closely related to the square-planar
coordination. Finally, the large single-ion anisotropy suppresses the spin
frustration and stabilizes a collinear antiferromagnetic long-range magnetic
ordering, as confirmed by Monte Carlo simulations predicting a quite low N\'eel
temperature, expected from almost isolated IrO4 square-planar units as
crystalline building blocks.",1707.04052v1
2018-06-04,Site-Specific Spin Reorientation in Antiferromagnetic State of Quantum System SeCuO$_3$,"We report on the magnetocrystalline anisotropy energy (MAE) and spin
reorientation in antiferromagnetic state of spin $S=1/2$ tetramer system
SeCuO$_3$ observed in torque magnetometry measurements in magnetic fields
$H<5$~T and simulated using density functional calculations. We employ simple
phenomenological model of spin reorientation in finite magnetic field to
describe our experimental torque data. Our results strongly support collinear
model for magnetic structure in zero field with possibility of only very weak
canting. Torque measurements also indicate that, contrary to what is expected
for uniaxial antiferromagnet, in SeCuO$_3$ only part of the spins exhibit spin
flop instead all of them, allowing us to conclude that AFM state of SeCuO$_3$
is unconventional and comprised of two decoupled subsystems. Taking into
account previously proposed site-selective correlations and dimer singlet state
formation in this system, our results offer further proof that AFM state in
SeCuO$_3$ is composed of a subsystem of AFM dimers forming singlets immersed in
antiferromagnetically long-range ordered spins, where both states coexist on
atomic scale. Furthermore, we show, using an ab-initio approach, that both
subsystems contribute differently to the MAE, corroborating the existence of
decoupled subnetworks in SeCuO$_3$. Combination of torque magnetometry,
phenomenological approach and DFT simulations to magnetic anisotropy presented
here represents a unique and original way to study site-specific reorientation
phenomena in quantum magnets.",1806.01233v2
2018-11-09,Correlation between site preference and magnetic properties of Zn-Sn-substituted strontium hexaferrite,"The site preference and magnetic properties of Zn, Sn and Zn-Sn substituted
M-type strontium hexaferrite (SrFe$_{12}$O$_{19}$) have been investigated using
first-principles total energy calculations based on density functional theory.
The site occupancy of substituted atoms were estimated by calculating the
substitution energies of different configurations. The distribution of
different configurations during the annealing process at high temperature was
determined using the formation probabilities of configurations to calculate
magnetic properties of substituted strontium hexaferrite. We found that the
magnetization and magnetocrystalline anisotropy are closely related to the
distributions of Zn-Sn ions on the five Fe sites. Our calculation show that in
SrFe$_{11.5}$Zn$_{0.5}$O$_{19}$, Zn atoms prefer to occupy $4f_1$, $12k$, and
$2a$ sites with occupation probability of 78%, 19% and 3%, respectively, while
in SrFe$_{11.5}$SnO$_{19}$, Sn atoms occupy the $12k$ and $4f_2$ sites with
occupation probability of 54% and 46%, respectively. We also found that in
SrFe$_{11}$Zn$_{0.5}$Sn$_{0.5}$O$_{19}$, (Zn,Sn) atom pairs prefer to occupy
the ($4f_1$, $4f_2$), ($4f_1$, $12k$) and ($12k$, $12k$) sites with occupation
probability of 82%, 8% and 6%, respectively. Our calculation shows that the
increase of magnetization and the reduction of magnetic anisotropy in Zn-Sn
substituted M-type strontium hexaferrite as observed experimentally is due to
the occupation of (Zn,Sn) pairs at the ($4f_1$, $4f_2$) sites.",1811.04101v2
2018-11-14,Unusual rotating magnetocaloric effect in the hexagonal ErMnO3 single crystal,"It is known that orthorhombic RMnO3 multiferroics (R = magnetic rare earth)
with low symmetry exhibit a large rotating magnetocaloric effect because of
their strong magnetocrystalline anisotropy. In this paper, we demonstrate that
the hexagonal ErMnO3 single crystals also unveils a giant rotating
magnetocaloric effect that can be obtained by spinning them in constant
magnetic fields around their a or b axes. When the ErMnO3 crystal is rotated
with the magnetic field initially parallel to the c-axis, the resulting entropy
change reaches maximum values of 7, 17 and 20 J/kg K under a constant magnetic
field of 2, 5 and 7 T, respectively. These values are comparable or even larger
than those shown by some of the best orthorhombic phases. More interestingly,
the generated anisotropic thermal effect is about three times larger than that
exhibited by the hexagonal HoMnO3 single crystal. The enhancement of the
rotating magnetocaloric effect in the hexagonal ErMnO3 compound arises from the
unique features of Er3+ magnetic sublattice. In fact, the Er3+ magnetic moments
located at 2a sites experience a first-order metamagnetic transition close to 3
K along the c-axis resulting in a peaked magnetocaloric effect over a narrower
temperature range. In contrast, the (paramagnetic) behaviour of Er3+ magnetic
moments within the ab-plane, produces a larger magnetocaloric effect over a
wider temperature range. Therefore, the magnetocaloric effect anisotropy is
maximized between the c and the ab-directions, leading to a giant rotating
magnetocaloric effect.",1811.05847v1
2019-07-04,Micromagnetic modelling of magnetic domain walls and domains in cylindrical nanowires,"Magnetic cylindrical nanowires are very fascinating objects where the curved
geometry allows many novel magnetic effects and a variety of non-trivial
magnetic structures. Micromagnetic modelling plays an important role in
revealing the magnetization distribution in magnetic nanowires, often not
accessible by imaging methods with sufficient details. Here we review the
magnetic properties of the shape anisotropy-dominated nanowires and the
nanowires with competing shape and magnetocrystalline anisotropies, as revealed
by micromagnetic modelling. We discuss the variety of magnetic walls and
magnetic domains reported by micromagnetic simulations in cylindrical
nanowires. The most known domain walls types are the transverse and vortex
(Bloch point) domain walls and the transition between them is materials and
nanowire diameter dependent. Importantly, the field or current-driven domain
walls in cylindrical nanowires can achieve very high velocities. In recent
simulations of nanowires with larger diameter the skyrmion tubes are also
reported. In nanowires with large saturation magnetization the core of these
tubes may form a helicoidal ('corkscrew') structure. The topology of the
skyrmion tubes play an important role in the pinning mechanism, discussed here
on the example of FeCo modulated nanowires. Other discussed examples include
the influence of antinotches ('bamboo' nanowires) on the remanent magnetization
configurations for hcp Co and FeCo nanowires and Co-Ni multisegmented
nanowires.",1907.02318v1
2019-11-27,Spin flop and crystalline anisotropic magnetoresistance in CuMnAs,"Recent research works have shown that the magnetic order in some
antiferromagnetic materials can be manipulated and detected electrically, due
to two physical mechanisms: Neel-order spin-orbit torques and anisotropic
magnetoresistance. While these observations open up opportunities to use
antiferromagnets for magnetic memory devices, different physical
characterization methods are required for a better understanding of those
mechanisms. Here we report a magnetic field induced rotation of the
antiferromagnetic Neel vector in epitaxial tetragonal CuMnAs thin films. Using
soft x-ray magnetic linear dichroism spectroscopy, x-ray photoemission electron
microscopy, integral magnetometry and magneto-transport methods, we demonstrate
spin-flop switching and continuous spin reorientation in antiferromagnetic
films with uniaxial and biaxial magnetic anisotropies, respectively. From
field-dependent measurements of the magnetization and magnetoresistance, we
obtain key material parameters including the anisotropic magnetoresistance
coefficients, magnetocrystalline anisotropy, spin-flop and exchange fields.",1911.12381v2
2020-08-12,Metastable skyrmion lattices governed by magnetic disorder and anisotropy in $β$-Mn-type chiral magnets,"Magnetic skyrmions are vortex-like topological spin textures often observed
in structurally chiral magnets with Dzyaloshinskii-Moriya interaction. Among
them, Co-Zn-Mn alloys with a $\beta$-Mn-type chiral structure host skyrmions
above room temperature. In this system, it has recently been found that
skyrmions persist over a wide temperature and magnetic field region as a
long-lived metastable state, and that the skyrmion lattice transforms from a
triangular lattice to a square one. To obtain perspective on chiral magnetism
in Co-Zn-Mn alloys and clarify how various properties related to the skyrmion
vary with the composition, we performed systematic studies on
Co$_{10}$Zn$_{10}$, Co$_9$Zn$_9$Mn$_2$, Co$_8$Zn$_8$Mn$_4$ and
Co$_7$Zn$_7$Mn$_6$ in terms of magnetic susceptibility and small-angle neutron
scattering measurements. The robust metastable skyrmions with extremely long
lifetime are commonly observed in all the compounds. On the other hand,
preferred orientation of a helimagnetic propagation vector and its temperature
dependence dramatically change upon varying the Mn concentration. The
robustness of the metastable skyrmions in these materials is attributed to
topological nature of the skyrmions as affected by structural and magnetic
disorder. Magnetocrystalline anisotropy as well as magnetic disorder due to the
frustrated Mn spins play crucial roles in giving rise to the observed change in
helical states and corresponding skyrmion lattice form.",2008.05075v1
2021-02-25,Magnetic order and crystalline electric field excitations of the quantum critical heavy fermion ferromagnet CeRh$_6$Ge$_4$,"CeRh$_6$Ge$_4$ is an unusual example of a stoichiometric heavy fermion
ferromagnet, which can be cleanly tuned by hydrostatic pressure to a quantum
critical point. In order to understand the origin of this anomalous behavior,
we have characterized the magnetic ordering and crystalline electric field
(CEF) scheme of this system. While magnetic Bragg peaks are not resolved in
neutron powder diffraction, coherent oscillations are observed in zero-field
$\mu$SR below $T_{\rm C}$, which are consistent with in-plane ferromagnetic
ordering consisting of reduced Ce moments. From analyzing the magnetic
susceptibility and inelastic neutron scattering, we propose a CEF-level scheme
which accounts for the easy-plane magnetocrystalline anisotropy, where the low
lying first excited CEF exhibits significantly stronger hybridization than the
ground state. These results suggest that the orbital anisotropy of the ground
state and low lying excited state doublets are important for realizing
anisotropic electronic coupling between the $f$- and conduction electrons,
which gives rise to the highly anisotropic hybridization observed in
photoemission experiments.",2102.12788v2
2021-03-30,Thermodynamic evidence of a second skyrmion lattice phase and tilted conical phase in Cu$_2$0SeO$_3$,"Precision measurements of the magnetization and ac susceptibility of
Cu$_2$0SeO$_3$ are reported for magnetic fields along different
crystallographic directions, focussing on the border between the conical and
the field-polarized state for a magnetic field along the $\langle 100 \rangle$
axis, complemented by selected specific heat data. Clear signatures of the
emergence of a second skyrmion phase and a tilted conical phase are observed,
as recently identified by means of small-angle neutron scattering. The
low-temperature skyrmion phase displays strongly hysteretic phase boundaries,
but no dissipative effects. In contrast, the tilted conical phase is
accompanied by strong dissipation and higher-harmonic contributions, while the
transition fields are essentially nonhysteretic. The formation of the second
skyrmion phase and tilted conical phase are found to be insensitive to a
vanishing demagnetization factor. A quantitative estimate of the temperature
dependence of the magnetocrystalline anisotropy may be consistently inferred
from the magnetization and the upper critical field and agrees well with a
stabilization of the low-temperature skyrmion phase and tilted conical state by
conventional cubic magnetic anisotropies.",2103.16238v2
2021-05-11,On the connection between magnetic interactions and the spin-wave gap of the insulating phase of NaOsO$_{3}$,"The scenario of a metal-insulator transition driven by the onset of
antiferromagnetic order in NaOsO$_3$ calls for a trustworthy derivation of the
underlying effective spin Hamiltonian. To determine the latter we rely on {\it
ab initio} electronic-structure calculations, linear spin-wave theory, and
comparison to experimental data of the corresponding magnon spectrum. We arrive
this way to Heisenberg couplings that are $\lesssim$45\% to$\lesssim$63\%
smaller than values presently proposed in the literature and
Dzyaloshinskii-Moriya interactions in the region of 15\% of the Heisenberg
exchange $J$. These couplings together with the symmetric anisotropic exchange
interaction and single-ion magnetocrystalline anisotropy successfully reproduce
the magnon dispersion obtained by resonant inelastic X-ray scattering
measurements. In particular, the spin-wave gap fully agrees with the measured
one. We find that the spin-wave gap is defined from a subtle interplay between
the single-ion anisotropy, the Dzyaloshinskii-Moriya exchange and the symmetric
anisotropic exchange interactions. The results reported here underpin the
local-moment description of NaOsO$_3$, when it comes to analyzing the magnetic
excitation spectra. Interestingly, this comes about from a microscopic theory
that describes the electron system as Bloch states, adjusted to a mean-field
solution to Hubbard-like interactions.",2105.04893v2
2021-11-25,Tunable gigahertz dynamics of low-temperature skyrmion lattice in a chiral magnet,"Recently, it has been shown that the chiral magnetic insulator Cu$_2$OSeO$_3$
hosts skyrmions in two separated pockets in temperature and magnetic field
phase space. It has also been shown that the predominant stabilization
mechanism for the low-temperature skyrmion (LTS) phase is via the crystalline
anisotropy, opposed to temperature fluctuations that stabilize the
well-established high-temperature skyrmion (HTS) phase. Here, we report on a
detailed study of LTS generation by field cycling, probed by GHz spin dynamics
in Cu$_2$OSeO$_3$. LTSs are populated via a field cycling protocol with the
static magnetic field applied parallel to the $\langle{100}\rangle$ crystalline
direction of plate and cuboid-shaped bulk crystals. By analyzing
temperature-dependent broadband spectroscopy data, clear evidence of
low-temperature skyrmion excitations with clockwise (CW), counterclockwise
(CCW), and breathing mode (BR) character at temperatures below $T$ = 40 K are
shown. We find that the mode intensities can be tuned with the number of
field-cycles below the saturation field. By tracking the resonance frequencies,
we are able to map out the field-cycle-generated LTS phase diagram, from which
we conclude that the LTS phase is distinctly separated from the
high-temperature counterpart. We also study the mode hybridization between the
dark CW and the BR modes as a function of temperature. By using two
Cu$_2$OSeO$_3$ crystals with different shapes and therefore different
demagnetization factors, together with numerical calculations, we unambiguously
show that the magnetocrystalline anisotropy plays a central role for the mode
hybridization.",2111.13004v1
2022-06-10,Topological spiral magnetism in the Weyl semimetal SmAlSi,"Weyl electrons are intensely studied due to novel charge transport phenomena
such as chiral anomaly, Fermi arcs, and photogalvanic effect. Recent
theoretical works suggest that Weyl electrons can also participate in magnetic
interactions, and the Weyl-mediated indirect exchange coupling between local
moments is proposed as a new mechanism of spiral magnetism that involves chiral
electrons. Despite reports of incommensurate and non-collinear magnetic
ordering in Weyl semimetals, an actual spiral order has remained hitherto
undetected. Here, we present evidence of Weyl-mediated spiral magnetism in
SmAlSi from neutron diffraction, transport, and thermodynamic data. We show
that the spiral order in SmAlSi results from the nesting between topologically
non-trivial Fermi pockets and weak magnetocrystalline anisotropy, unlike
related materials (Ce,Pr,Nd)AlSi, where a strong anisotropy prevents the spins
from freely rotating. We map the magnetic phase diagram of SmAlSi and reveal an
A-phase where topological magnetic excitations may exist. This is corroborated
by the observation of a topological Hall effect within the A-phase.",2206.05121v1
2022-11-24,Unravelling the role of Sm 4f electrons in the magnetism of SmFeO$_3$,"Magnetic rare-earth orthoferrites $R$FeO$_3$ host a variety of functional
properties from multiferroicity and strong magnetostriction, to
spin-reorientation transitions and ultrafast light-driven manipulation of
magnetism, which can be exploited in spintronics and next-generation devices.
Among these systems, SmFeO$_3$ is attracting a particular interest for its rich
phase diagram and the high temperature Fe-spin magnetic transitions, which
combines with a very low temperature and as yet unclear Sm-spin ordering.
Various experiments suggest that the interaction between the Sm and Fe magnetic
moments (further supported by the magnetic anisotropy), is at the origin of the
complex cascade of transitions, but a conclusive and clear picture has not yet
been reached. In this work, by means of comprehensive first-principles
calculations, we unravel the role of the magnetic Sm ions in the Fe-spin
reorientation transition and in the detected anomalies in the lattice
vibrational spectrum, which are a signature of a relevant spin-phonon coupling.
By including both Sm-$f$ electrons and non-collinear magnetism, we find
frustrated and anisotropic Sm interactions, and a large magnetocrystalline
anisotropy mediated by the SOC of the Sm-$4f$ electrons, which drive the
complex magnetic properties and phase diagram of SmFeO$_3$.",2211.13528v1
2023-02-10,Correlation-driven topological transition in Janus VSiGeP2As2,"The appearance of intrinsic ferromagnetism in 2D materials opens the
possibility of investigating the interplay between magnetism and topology. The
magnetic anisotropy energy (MAE) describing the easy axis for magnetization in
a particular direction is an important yardstick for nanoscale applications.
Here, the first-principles approach is used to investigate the electronic band
structures, the strain dependence of MAE in pristine VSi2Z4 (Z=P, As) and its
Janus phase VSiGeP2As2 and the evolution of the topology as a function of the
Coulomb interaction. In the Janus phase the compound presents a breaking of the
mirror symmetry, which is equivalent to having an electric field, and the
system can be piezoelectric. It is revealed that all three monolayers exhibit
ferromagnetic ground state ordering, which is robust even under biaxial
strains. A large value of coupling J is obtained, and this, together with the
magnetocrystalline anisotropy, will produce a large critical temperature. We
found an out-of-plane (in-plane) magnetization for VSi2P4 (VSi2As4), while
in-plane magnetization for VSiGeP2As2. Furthermore, we observed a
correlation-driven topological transition in the Janus VSiGeP2As2. Our analysis
of these emerging pristine and Janus-phased magnetic semiconductors opens
prospects for studying the interplay between magnetism and topology in
two-dimensional materials.",2302.05146v2
2023-02-23,The influence of crystalline electric field on the magnetic properties of CeCd3X3 (X = P and As),"CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal
ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice
order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline
electric field (CEF) level scheme has been determined by fitting magnetic
susceptibility curves, magnetization isotherms, and Schottky anomalies in
specific heat. The calculated results, incorporating the CEF excitation, Zeeman
splitting, and molecular field, are in good agreement with the experimental
data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the
strong easy-plane magnetic anisotropy that has been observed in this family of
materials. A detailed examination of the CEF parameters suggests that the
fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF
induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a
small $c$-axis moment. The reliability of our CEF analysis is assessed by
comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For
both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$
magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is
achieved at the Weiss temperature $\theta_{p}$. Although the observed magnetic
entropy is reminiscent of delocalized 4$f$-electron magnetism with significant
Kondo screening, the electrical resistivity of these compounds follows a
typical metallic behavior. Measurements of thermoelectric power further
validate the absence of Kondo contribution in CeCd$_{3}X_{3}$.",2302.11714v1
2023-02-28,"Epitaxial growth and characterization of (001) [NiFe/M]$_{20}$ (M = Cu, CuPt and Pt) superlattices","We present optimization of [(15 $\unicode{x212B}$) Ni$_{80}$Fe$_{20}$/(5
$\unicode{xC5}$) M]$_{20}$ single crystal multilayers on (001) MgO, with M
being Cu, Cu$_{50}$Pt$_{50}$ and Pt. These superlattices were characterized by
high-resolution X-ray reflectivity (XRR) and diffraction (XRD) as well as polar
mapping of important crystal planes. It is shown that cube on cube epitaxial
relationship can be obtained when depositing at the substrate temperature of
100 $^\circ$C regardless of the lattice mismatch (5% and 14% for Cu and Pt,
respectively). At lower substrate temperatures poly-crystalline multilayers
were obtained while at higher substrate temperatures {111} planes appear at
$\sim$10$^\circ$ off normal to the film plane. It is also shown that as the
epitaxial strain increases, the easy magnetization axis rotates towards the
direction that previously was assumed to be harder, i.e. from [110] to [100],
and eventually further increase in the strain makes the magnetic hysteresis
loops isotropic in the film plane. Higher epitaxial strain is also accompanied
with increased coercivity values. Thus, the effect of epitaxial strain on the
magnetocrystalline anisotropy is much larger than what was observed previously
in similar, but polycrystalline samples with uniaxial anisotropy (Kateb et al.
2021).",2302.14745v1
2023-05-08,Large magnetocaloric effect in the kagome ferromagnet Li$_9$Cr$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$,"Single-crystal growth, magnetic properties, and magnetocaloric effect of the
$S = 3/2$ kagome ferromagnet Li$_9$Cr$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$
(trigonal, space group: $P\bar{3}c1$) are reported. Magnetization data suggest
dominant ferromagnetic intra-plane coupling with a weak anisotropy and the
onset of ferromagnetic ordering at $T_{\rm C} \simeq 2.6$ K. Microscopic
analysis reveals a very small ratio of interlayer to intralayer ferromagnetic
couplings ($J_{\perp}/J \simeq 0.02$). Electron spin resonance data suggest the
presence of short-range correlations above $T_{\rm C}$ and confirms
quasi-two-dimensional character of the spin system. A large magnetocaloric
effect characterized by isothermal entropy change of $-\Delta S_{\rm m}\simeq
31$ J kg$^{-1}$ K$^{-1}$ and adiabatic temperature change of $-\Delta T_{\rm
ad}\simeq 9$ K upon a field sweep of 7 T is observed around $T_{\rm C}$. This
leads to a large relative cooling power of $RCP \simeq 284$ J kg$^{-1}$. The
large magnetocaloric effect, together with negligible hysteresis render
Li$_9$Cr$_3$(P$_2$O$_7$)$_3$(PO$_4$)$_2$ a promising material for magnetic
refrigeration at low temperatures. The magnetocrystalline anisotropy constant
$K \simeq -7.42 \times 10^4$ erg cm$^{-3}$ implies that the compound is an
easy-plane type ferromagnet with the hard axis normal to the $ab$-plane,
consistent with the magnetization data.",2305.04744v1
2023-06-21,"First-principles prediction of structural, magnetic properties of Cr-substituted strontium hexaferrite, and its site preference","To investigate the structural and magnetic properties of Cr-doped M-type
strontium hexaferrite (SrFe$_{12}$O$_{19}$) with x = (0.0, 0.5, 1.0), we
perform first-principles total-energy calculations relied on density functional
theory. Based on the calculation of the substitution energy of Cr in strontium
hexaferrite and formation probability analysis, we conclude that the doped Cr
atoms prefer to occupy the 2a, 12k, and 4f$_{2}$ sites which is in good
agreement with the experimental findings. Due to Cr$^{3+}$ ion moment, 3
{$\mu_B$}, smaller than that of Fe$^{3+}$ ion, 5 {$\mu_B$}, saturation
magnetization (M$_{s}$) reduce rapidly as the concentration of Cr increases in
strontium hexaferrite. The magnetic anisotropic field $\left(H_{a}\right)$
rises with an increasing fraction of Cr despite a significant reduction of
magnetization and a slight increase of magnetocrystalline anisotropy
$\left(K_{1}\right)$.The cause for the rise in magnetic anisotropy field
$\left(H_{a}\right)$ with an increasing fraction of Cr is further emphasized by
our formation probability study. Cr$^{3+}$ ions prefer to occupy the 2a sites
at lower temperatures, but as the temperature rises, it is more likely that
they will occupy the 12k site. Cr$^{3+}$ ions are more likely to occupy the 12k
site than the 2a site at a specific annealing temperature (>700{\deg}C).",2306.11952v1
2023-11-22,Engineering magnetic domain wall energies in multiferroic BiFeO$_3$ via epitaxial strain,"Epitaxial strain has emerged as a powerful tool to tune magnetic and
ferroelectric properties in functional materials such as in multiferroic
perovskite oxides. Here, we use first-principles calculations to explore the
evolution of magnetic interactions in the antiferromagnetic multiferroic
BiFeO$_3$ (BFO), one of the most promising multiferroics for future technology.
The epitaxial strain in BFO(001) oriented film is varied between
$\varepsilon_{xx,yy}$ $\in$ $[-2\%, +2\%]$. We find that both strengths of the
exchange interaction and Dzyaloshinskii-Moriya interaction (DMI) decrease
linearly from compressive to tensile strain whereas the uniaxial
magnetocrystalline anisotropy follows a parabolic behavior which lifts the
energy degeneracy of the (111) easy plane of bulk BFO. From the trends of the
magnetic interactions we can explain the destruction of cycloidal order in
compressive strain as observed in experiments due to the increasing anisotropy
energy. For tensile strain, we predict that the ground state remains unchanged
as a function of strain. By using the domain wall (DW) energy, we envision the
region where isolated chiral magnetic texture might occur as function of strain
i.e. where the DW and the spin spiral energy are equal. This transition between
$-1.5\%$ and $-0.5\%$ of strain should allow topologically stable magnetic
states such as antiferromagnetic skyrmions and merons to occur. Hence, our work
should trigger experimental and theoretical investigations in this range of
strain.",2311.13215v1
2024-03-01,Spin current control of magnetism,"Exploring novel strategies to manipulate the order parameter of magnetic
materials by electrical means is of great importance, not only for advancing
our understanding of fundamental magnetism, but also for unlocking potential
practical applications. A well-established concept to date uses gate voltages
to control magnetic properties, such as saturation magnetization, magnetic
anisotropies, coercive field, Curie temperature and Gilbert damping, by
modulating the charge carrier population within a capacitor structure. Note
that the induced carriers are non-spin-polarized, so the control via the
electric-field is independent of the direction of the magnetization. Here, we
show that the magnetocrystalline anisotropy (MCA) of ultrathin Fe films can be
reversibly modified by a spin current generated in Pt by the spin Hall effect.
The effect decreases with increasing Fe thickness, indicating that the origin
of the modification can be traced back to the interface. Uniquely, the change
in MCA due to the spin current depends not only on the polarity of the charge
current but also on the direction of magnetization, i.e. the change in MCA has
opposite sign when the direction of magnetization is reversed. The control of
magnetism by the spin current results from the modified exchange splitting of
majority- and minority-spin bands, and differs significantly from the
manipulation by gate voltages via a capacitor structure, providing a
functionality that was previously unavailable and could be useful in advanced
spintronic devices.",2403.00709v1
2016-03-01,"Magnetic properties of Fe$_5$SiB$_2$ and its alloys with P, S, and Co","Fe$_5$SiB$_2$ has been synthesized and magnetic measurements have been
carried out, revealing that M$_{\text{sat}}$ = 0.92 MA/m at T = 300 K. The M vs
T curve shows a broad peak around T = 160 K. The anisotropy constant, K$_1$,
estimated at T = 300 K, is 0.25 MJ/m$^3$. Theoretical analysis of Fe$_5$SiB$_2$
system has been carried out and extended to the full range of
Fe$_5$Si$_{1-x}$P$_x$B$_2$, Fe$_5$P$_{1-x}$S$_x$B$_2$, and
(Fe$_{1-x}$Co$_x$)$_5$SiB$_2$ compositions. The electronic band structures have
been calculated using the Full-Potential Local-Orbital Minimum-Basis Scheme
(FPLO-14). The calculated total magnetic moments are 9.20, 9.15, 9.59 and
2.42$\mu_B$ per formula units of Fe$_5$SiB$_2$, Fe$_5$PB$_2$, Fe$_5$SB$_2$, and
Co$_5$SiB$_2$, respectively. In agreement with experiment, magnetocrystalline
anisotropy energies (MAE's) calculated for T = 0 K changes from a negative
(easy-plane) anisotropy -0.28 MJ/m$^3$ for Fe$_5$SiB$_2$ to the positive
(easy-axis) anisotropy 0.35 MJ/m$^3$ for Fe$_5$PB$_2$. Further increase of the
number of p-electrons in Fe$_5$P$_{1-x}$S$_x$B$_2$ leads to an increase of MAE
up to 0.77 MJ/m$^3$ for the hypothetical Fe$_5$P$_{0.4}$S$_{0.6}$B$_2$
composition. Volume variation and fixed spin moment calculations (FSM)
performed for Fe$_5$SiB$_2$ show an inverse relation between MAE and magnetic
moment in the region down to about 15\% reduction of the spin moment. The
alloying of Fe$_5$SiB$_2$ with Co is proposed as a practical realization of
magnetic moment reduction, which ought to increase MAE. MAE calculated in
virtual crystal approximation (VCA) for a full range of
(Fe$_{1-x}$Co$_x$)$_5$SiB$_2$ compositions reaches the maximum value of 1.16
MJ/m$^3$ at Co concentration x = 0.3, with the magnetic moment 7.75$\mu_B$ per
formula unit. Thus, (Fe$_{0.7}$Co$_{0.3}$)$_5$SiB$_2$ is suggested as a
candidate for a rare-earth free permanent magnet.",1603.00253v1
2018-10-05,Magnetic anisotropy and spin-polarized two-dimensional electron gas in the van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$,"We report a comprehensive experimental investigation on the magnetic
anisotropy in bulk single crystals of Cr$_2$Ge$_2$Te$_6$, a
quasi-two-dimensional ferromagnet belonging to the family of magnetic layered
transition metal trichalcogenides that have attracted recently a big deal of
interest with regard to the fundamental and applied aspects of two-dimensional
magnetism. For this purpose electron spin resonance (ESR) and ferromagnetic
resonance (FMR) measurements have been carried out over a wide frequency and
temperature range. A gradual change in the angular dependence of the ESR
linewidth at temperatures above the ferromagnetic transition temperature
$T_{\rm c}$ reveals the development of two-dimensional spin correlations in the
vicinity of $T_{\rm c}$ thereby proving the intrinsically low-dimensional
character of spin dynamics in Cr$_2$Ge$_2$Te$_6$. Angular and frequency
dependent measurements in the ferromagnetic phase clearly show an easy-axis
type anisotropy of this compound. Furthermore, these experiments are compared
with simulations based on a phenomenological approach, which takes into account
results of static magnetization measurements as well as high temperature $g$
factors obtained from ESR spectroscopy in the paramagnetic phase. As a result
the determined magnetocrystalline anisotropy energy density (MAE) $K_U$ is
$(0.48 \pm 0.02) \times10^6$ erg/cm$^3$. This analysis is complemented by
density functional calculations which yield the experimental MAE value for a
particular value of the electronic correlation strength $U$. The analysis of
the electronic structure reveals that the low-lying conduction band carries
almost completely spin-polarized, quasi-homogeneous, two-dimensional states.",1810.02560v3
2020-02-01,Random magnetic anisotropy driven transitions in layered perovskite LaSrCoO$_4$,"Attempts to unravel the nature of magnetic ordering in LaSrCoO$_4$
(Co$^{3+}$), a compound intermediate between antiferromagnetic (AFM)
La$_2$CoO$_4$ (Co$^{2+}$) and ferromagnetic (FM) Sr$_2$CoO$_4$ (Co$^{4+}$),
have met with a limited success so far. In this report, the results of a
thorough investigation of dc magnetization and ac susceptibility (ACS) in
single-phase LaSrCoO$_4$ provide clinching evidence for a thermodynamic
paramagnetic (PM) - ferromagnetic (FM) phase transition at T$_{c}$ = 220.5 K,
followed at lower temperature (T$_{g}$ = 7.7 K) by a transition to the cluster
spin glass (CSG) state. Analysis of the low-field Arrott plot isotherms, in the
critical region near T$_{c}$, in terms of the Aharony-Pytte scaling equation of
state clearly establishes that the PM-FM transition is basically driven by
random magnetic anisotropy (RMA). For temperatures below $\approx$ 30 K, large
enough RMA destroys long-range FM order by breaking up the infinite FM network
into FM clusters of finite size and leads to the formation of a CSG state at
temperatures T $\lesssim$ 8 K by promoting freezing of finite FM clusters in
random orientations. Increasing strength of the single-ion magnetocrystalline
anisotropy (and hence RMA) with decreasing temperature is taken to reflect an
increase in the number of low-spin (LS) Co$^{3+}$ ions at the expense of that
of high-spin (HS) Co$^{3+}$ ions. At intermediate temperatures (30 K $\lesssim
T \lesssim$ 180 K), spin dynamics has contributions from the infinite FM
network (fast relaxation governed by a single anisotropy energy barrier) and
finite FM clusters (extremely slow stretched exponential relaxation due to
hierarchical energy barriers).",2002.00135v3
2020-09-02,New highly-anisotropic Rh-based Heusler compound for magnetic recording,"The development of high-density magnetic recording media is limited by the
superparamagnetism in very small ferromagnetic crystals. Hard magnetic
materials with strong perpendicular anisotropy offer stability and high
recording density. To overcome the difficulty of writing media with a large
coercivity, heat assisted magnetic recording (HAMR) has been developed, rapidly
heating the media to the Curie temperature Tc before writing, followed by rapid
cooling. Requirements are a suitable Tc, coupled with anisotropic thermal
conductivity and hard magnetic properties. Here we introduce Rh2CoSb as a new
hard magnet with potential for thin film magnetic recording. A
magnetocrystalline anisotropy of 3.6 MJm-3 is combined with a saturation
magnetization of {\mu}0Ms = 0.52 T at 2 K (2.2 MJm-3 and 0.44 T at
room-temperature). The magnetic hardness parameter of 3.7 at room temperature
is the highest observed for any rare-earth free hard magnet. The anisotropy is
related to an unquenched orbital moment of 0.42 {\mu}B on Co, which is
hybridized with neighbouring Rh atoms with a large spin-orbit interaction.
Moreover, the pronounced temperature-dependence of the anisotropy that follows
from its Tc of 450 K, together with a high thermal conductivity of 20 Wm-1K-1,
makes Rh2CoSb a candidate for development for heat assisted writing with a
recording density in excess of 10 Tb/in2.",2009.01034v1
2017-03-16,Discovery of intrinsic ferromagnetism in 2D van der Waals crystals,"It has been long hoped that the realization of long-range ferromagnetic order
in two-dimensional (2D) van der Waals (vdW) crystals, combined with their rich
electronic and optical properties, would open up new possibilities for
magnetic, magnetoelectric and magneto-optic applications. However, in 2D
systems, the long-range magnetic order is strongly hampered by thermal
fluctuations which may be counteracted by magnetic anisotropy, according to the
Mermin-Wagner theorem. Prior efforts via defect and composition engineering,
and proximity effect only locally or extrinsically introduce magnetic
responses. Here we report the first experimental discovery of intrinsic
long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers by scanning
magneto-optic Kerr microscopy. In such a 2D vdW soft ferromagnet, for the first
time, an unprecedented control of transition temperature of ~ 35% - 57%
enhancement is realized via surprisingly small fields (<= 0.3 Tesla in this
work), in stark contrast to the stiffness of the transition temperature to
magnetic fields in the three-dimensional regime. We found that the small
applied field enables an effective anisotropy far surpassing the tiny
magnetocrystalline anisotropy, opening up a sizable spin wave excitation gap.
Confirmed by renormalized spin wave theory, we explain the phenomenon and
conclude that the unusual field dependence of transition temperature
constitutes a hallmark of 2D soft ferromagnetic vdW crystals. Our discovery of
2D soft ferromagnetic Cr2Ge2Te6 presents a close-to-ideal 2D Heisenberg
ferromagnet for studying fundamental spin behaviors, and opens the door for
exploring new applications such as ultra-compact spintronics.",1703.05753v1
2023-03-21,Robust intralayer antiferromagnetism and tricriticality in a van der Waals compound: VBr3 case,"We studied magnetic states and phase transitions in the van der Waals
antiferromagnet VBr3 by specific heat and magnetization measurements of single
crystals in high magnetic fields and by ab initio density functional theory
calculations focused on exchange interactions. The magnetization behavior
resembles Ising antiferromagnets with magnetic moments kept in the out-of-plane
direction by strong uniaxial magnetocrystalline anisotropy. The out-of-plane
magnetic field induces a spin-flip metamagnetic transition, which is of
first-order type at low temperatures while at higher temperatures the
transition becomes continuous. The first-order and continuous transition
segments in the field-temperature phase diagram meet at a tricritical point at
= 12 K. The magnetization response to the in-plane field manifests a continuous
spin-flop transition, which at 2 K terminates at a field mu0Hc = 27 T that can
serve as an estimate of the anisotropy field in VBr3. The magnetization curves
above the metamagnetic transition saturate at the same value of magnetic moment
musat = 1.2 muB/f.u., which is much smaller than the spin-only (S = 1) moment
of the V3+ ion. The reduced moment can be explained by the existence of a
significant orbital magnetic moment antiparallel to the spin. The orbital
moment is a key ingredient of a mechanism responsible for the observed large
anisotropy. The exact energy evaluation of possible magnetic orders
unambiguously shows that the magnetic ground state of VBr3 is the intralayer
zigzag antiferromagnetic order that renders the antiferromagnetic ground state
significantly more stable against the spin-flip transition than the other
options. The calculations also predict that a minimal distortion of the Br ion
sublattice causes a radical change of the orbital occupation in the ground
state, connected with the formation of the orbital moment and the stability of
magnetic order.",2303.11794v2
2022-03-11,Hard ferromagnetism down to the thinnest limit of iron-intercalated tantalum disulfide,"Two-dimensional (2D) magnetic crystals hold promise for miniaturized and
ultralow power electronic devices that exploit spin manipulation. In these
materials, large, controllable magnetocrystalline anisotropy is a prerequisite
for the stabilization and manipulation of long-range magnetic order. In known
2D magnetic crystals, relatively weak magnetocrystalline anisotropy results in
typically soft ferromagnetism. Here, we demonstrate that ferromagnetic order
persists down to the thinnest limit of Fe$_x$TaS$_2$ (Fe-intercalated bilayer
2H-TaS$_2$) with giant coercivities up to 3 tesla. We prepare Fe-intercalated
TaS$_2$ by chemical intercalation of van der Waals layered 2H-TaS$_2$ crystals
and perform variable-temperature quantum transport, transmission electron
microscopy, and confocal Raman spectroscopy measurements to shed new light on
the coupled effects of dimensionality, degree of intercalation, and intercalant
order/disorder on the hard ferromagnetic behavior of Fe$_x$TaS$_2$. More
generally, we show that chemical intercalation gives access to a rich synthetic
parameter space for low-dimensional magnets, in which magnetic properties can
be tailored by the choice of the host material and intercalant identity/amount,
in addition to the manifold distinctive degrees of freedom available in
atomically thin, van der Waals crystals.",2203.05747v2
2007-03-22,Orbital contribution to the magnetic properties of iron as a function of dimensionality,"The orbital contribution to the magnetic properties of Fe in systems of
decreasing dimensionality (bulk, surfaces, wire and free clusters) is
investigated using a tight-binding hamiltonian in an $s, p,$ and $d$ atomic
orbital basis set including spin-orbit coupling and intra-atomic electronic
interactions in the full Hartree-Fock (HF) scheme, i.e., involving all the
matrix elements of the Coulomb interaction with their exact orbital dependence.
Spin and orbital magnetic moments and the magnetocrystalline anisotropy energy
(MAE) are calculated for several orientations of the magnetization. The results
are systematically compared with those of simplified hamiltonians which give
results close to those obtained from the local spin density approximation. The
full HF decoupling leads to much larger orbital moments and MAE which can reach
values as large as 1$\mu_B$ and several tens of meV, respectively, in the
monatomic wire at the equilibrium distance. The reliability of the results
obtained by adding the so-called Orbital Polarization Ansatz (OPA) to the
simplified hamiltonians is also discussed. It is found that when the spin
magnetization is saturated the OPA results for the orbital moment are in
qualitative agreement with those of the full HF model. However there are large
discrepancies for the MAE, especially in clusters. Thus the full HF scheme must
be used to investigate the orbital magnetism and MAE of low dimensional
systems.",0703576v1
2007-07-16,Magnetodipolar interlayer interaction effect on the magnetization dynamics of a trilayer square element with the Landau domain structure,"We present a detailed numerical simulation study of the effects caused by the
magnetodipolar interaction between ferromagnetic (FM) layers of a trilayer
magnetic nanoelement on its magnetization dynamics. As an example we use a
Co/Cu/Ni80Fe20 element with a square lateral shape where the magnetization of
FM layers forms a closed Landau-like domain pattern. First we show that when
the thickness of the non-magnetic (NM) spacer is in the technology relevant
region h ~ 10 nm, magnetodipolar interaction between 90o Neel domain walls in
FM layers qualitatively changes the equilibrium magnetization state of these
layers. In the main of the paper we compare the magnetization dynamics induced
by a sub-nsec field pulse in a single-layer Ni80Fe20 (Py) element and in the
Co/Cu/Py trilayer element. Here we show that (i) due to the spontaneous
symmetry breaking of the Landau state in the FM/NM/FM trilayer its domains and
domain walls oscillate with different frequencies and have different spatial
oscillation patterns; (ii) magnetization oscillations of the trilayer domains
are strongly suppressed due to different oscillation frequencies of domains in
Co and Py; (iii) magnetization dynamics qualitatively depends on the relative
rotation sense of magnetization states in Co and Py layers and on the
magnetocrystalline anisotropy kind of Co crystallites. Finally we discuss the
relation of our findings with experimental observations of magnetization
dynamics in magnetic trilayers, performed using the element-specific
time-resolved X-ray microscopy.",0707.2344v1
2008-01-29,"Anisotropic magnetization studies of $R_2 Co Ga_8$ (R = Gd, Tb, Dy, Ho, Er, Tm, Y and Lu) single crystals","Single crystals of R$_2$CoGa$_8$ series of compounds were grown, for the
first time, by high temperature solution growth (flux) method. These compounds
crystallize in a tetragonal crystal structure with the space group $P4/mmm$. It
has been found that R$_2$CoGa$_8$ phase forms only with the heavier rare
earths, starting from Gd with a relatively large $c/a$ ratio of $\approx$ 2.6.
The resultant anisotropic magnetic properties of the compounds were
investigated along the two principal crystallographic directions of the crystal
viz., along [100] and [001]. The nonmagnetic compounds Y$_2$CoGa$_8$ and
Lu$_2$CoGa$_8$ show diamagnetic behavior down to the lowest temperature (1.8 K)
pointing out the non-magnetic nature of Co in these compounds and a relatively
low density of electronic states at the Fermi level. Compounds with the
magnetic rare earths order antiferromagnetically at temperatures lower than 30
K. The easy axis of magnetization for R$_2$CoGa$_8$ (R = Tb, Dy and Ho) is
found to be along the [001] direction and it changes to [100] direction for
Er$_2$CoGa$_8$ and Tm$_2$CoGa$_8$. The magnetization behavior is analyzed on
the basis of crystalline electric field (CEF) model. The estimated crystal
field parameters explains the magnetocrystalline anisotropy in this series of
compounds.",0801.4518v1
2009-09-09,Tuning of crystal structure and magnetic properties by exceptionally large epitaxial strains,"Huge deformations of the crystal lattice can be achieved in materials with
inherent structural instability by epitaxial straining. By coherent growth on
seven different substrates the in-plane lattice constants of 50 nm thick
Fe70Pd30 films are continuously varied. The maximum epitaxial strain reaches
8,3 % relative to the fcc lattice. The in-plane lattice strain results in a
remarkable tetragonal distortion ranging from c/abct = 1.09 to 1.39, covering
most of the Bain transformation path from fcc to bcc crystal structure. This
has dramatic consequences for the magnetic key properties. Magnetometry and
X-ray circular dichroism (XMCD) measurements show that Curie temperature,
orbital magnetic moment, and magnetocrystalline anisotropy are tuned over broad
ranges.",0909.1728v3
2009-11-18,Structurally-driven magnetic state transition of biatomic Fe chains on Ir(001),"Using first-principles calculations, we demonstrate that the magnetic
exchange interaction and the magnetocrystalline anisotropy of biatomic Fe
chains grown in the trenches of the 5x1 reconstructed Ir(001) surface depend
sensitively on the atomic arrangement of the Fe atoms. Two structural
configurations have been considered which are suggested from recent
experiments. They differ by the local symmetry and the spacing between the two
strands of the biatomic Fe chain. Since both configurations are very close in
total energy they may coexist in experiment. We have investigated collinear
ferro- and antiferromagnetic solutions as well as a collinear state with two
moments in one direction and one in the opposite direction (up-down-up-state).
For the structure with a small interchain spacing, there is a strong exchange
interaction between the strands and the ferromagnetic state is energetically
favorable. In the structure with larger spacing, the two strands are
magnetically nearly decoupled and exhibit antiferromagnetic order along the
chain. In both cases, due to hybridization with the Ir substrate the exchange
interaction along the chain axis is relatively small compared to freestanding
biatomic iron chains. The easy magnetization axis of the Fe chains also
switches with the structural configuration and is out-of-plane for the
ferromagnetic chains with small spacing and along the chain axis for the
antiferromagnetic chains with large spacing between the two strands. Calculated
scanning tunneling microscopy images and spectra suggest the possibility to
experimentally distinguish between the two structural and magnetic
configurations.",0911.3526v1
2010-01-25,Solution growth of Ce-Pd-In single crystals: characterization of the heavy-fermion superconductor Ce2PdIn8,"Solution growth of single crystals of the recently reported new compound
Ce2PdIn8 was investigated. When growing from a stoichiometry in a range 2:1:20
- 2:1:35, single crystals of CeIn3 covered by a thin (~50 um)
single-crystalline layer of Ce2PdIn8 were mostly obtained. Using palladium
richer compositions the thickness of the Ce2PdIn8 layers were increased, which
allowed mechanical extraction of single-phase slabs of the desired compound
suitable for a thorough study of magnetism and superconductivity. In some
solution growth products also CePd3In6 (LaNi3In6 - type of structure) and
traces of phases with the stoichiometry CePd2In7, Ce1.5Pd1.5In7 (determined
only by EDX) have been identified. Magnetic measurements of the Ce2PdIn8 single
crystals reveal paramagnetic behaviour of the Ce3+ ions with significant
magnetocrystalline anisotropy. Above 70 K the magnetic susceptibility follows
the Curie-Weiss law with considerably different values of the paramagnetic
Curie temperature, for the magnetic field applied along the a- (-90 K) and
c-(-50 K) axis. Below the reported critical temperature for superconductivity
Tc (0.69 K) the electrical resistivity drops to zero. Comparative measurements
of the electrical resistivity, heat capacity and AC susceptibility of several
crystals reveal that the superconducting transition is strongly
sample-dependent.",1001.4403v1
2013-03-14,Spin-torque effects in thermally assisted magnetization reversal: Method of statistical moments,"Thermal fluctuations of nanomagnets driven by spin-polarized currents are
treated via the Landau-Lifshitz-Gilbert equation generalized to include both
the random thermal noise field and the Slonczewski spin-transfer torque term.
By averaging this stochastic (Langevin) equation over its realizations, the
explicit infinite hierarchy of differential-recurrence relations for
statistical moments (averaged spherical harmonics) is derived for arbitrary
demagnetizing factors and magnetocrystalline anisotropy for the generic
nanopillar model of a spin-torque device comprising two ferromagnetic strata
representing the free and fixed layers and a nonmagnetic conducting spacer all
sandwiched between two ohmic contacts. The influence of thermal fluctuations
and spin-transfer torques on relevant switching characteristics, such as the
stationary magnetization, the magnetization reversal time, etc., is calculated
by solving the hierarchy for wide ranges of temperature, damping, external
magnetic field, and spin-polarized current indicating new spin-torque effects
in the thermally assisted magnetization reversal comprising several orders of
magnitude. In particular, a pronounced dependence of the switching
characteristics on the directions of the external magnetic field and the spin
polarization exists.",1303.3476v4
2014-08-18,Unquenched $e_g^1$ orbital moment in the Mott insulating antiferromagnet KOsO4,"Applying the correlated electronic structure method based on density
functional theory plus the Hubbard $U$ interaction, we have investigated the
tetragonal scheelite structure Mott insulator KOsO$_4$, whose $e_g^1$
configuration should be affected only slightly by spin-orbit couping (SOC). The
method reproduces the observed antiferromagnetic Mott insulating state,
populating the Os $d_{z^2}$ majority orbital. The quarter-filled $e_g$ manifold
is characterized by a symmetry breaking due to the tetragonal structure, and
the Os ion shows a crystal field splitting $\Delta_{cf}$ = 1.7 eV from the
$t_{2g}$ complex, which is relatively small considering the high formal
oxidation state Os$^{7+}$. The small magnetocrystalline anisotropy before
including correlation (i.e., in the metallic state) is increased by more than
an order of magnitude in the Mott-insulating state, a result of a strong
interplay between large SOC and a strong correlation. In contrast to
conventional wisdom that the $e_g$ complex will not support orbital magnetism,
we find that for the easy axis [100] direction the substantial Os orbital
moment $M_L\approx-0.2 \mu_B$ compensates half of the Os spin moment $M_S$ =
0.4$\mu_B$. The origin of the orbital moment is analyzed and understood in
terms of additional spin-orbital lowering of symmetry, and beyond that due to
structural distortion, for magnetization along [100]. Further interpretation is
assisted by analysis of the spin density and the Wannier function with SOC
included.",1408.4078v2
2015-01-09,Single crystal study of layered U$_{n}$RhIn$_{3n+2}$ materials: case of the novel U$_{2}$RhIn$_{8}$ compound,"We report on the single crystal properties of the novel U$_{2}$RhIn$_{8}$
compound studied in the context of parent URhIn$_{5}$ and UIn$_{3}$ systems.
The compounds were prepared by In self-flux method. U$_{2}$RhIn$_{8}$ adopts
the Ho$_{2}$CoGa$_{8}$-type structure with lattice parameters a $= 4.6056(6)$
\AA\ and c $= 11.9911(15)$ \AA. The behavior of U$_{2}$RhIn$_{8}$ strongly
resembles that of the related URhIn$_{5}$ and UIn$_{3}$ with respect to
magnetization, specific heat and resistivity except for magnetocrystalline
anisotropy developing with lowering dimensionality in the series UIn$_{3}$ vs.
U$_{2}$RhIn$_{8}$ and URhIn$_{5}$. U$_{2}$RhIn$_{8}$ orders
antiferromagnetically below T$_{\textrm{N}}$ $= 117$ K and exhibits a slightly
enhanced Sommerfeld coefficient $\gamma = 47$ mJ$\cdot$mol$^{-1}\cdot$K$^{-2}$.
Magnetic field leaves the value of N\'{e}el temperature for both URhIn$_{5}$
and U$_{2}$RhIn$_{8}$ unaffected up to 9 T. On the other hand, T$_{\textrm{N}}$
is increasing with applying hydrostatic pressure up to 3.2 GPa. The weak
temperature dependence of $\chi(T)$ in all studied compounds might be
attributed to the mainly itinerant nature of 5f electrons. The character of
uranium 5f electron states of U$_{2}$RhIn$_{8}$ was studied by first principles
calculations based on the density functional theory. The overall phase diagram
of U$_{2}$RhIn$_{8}$ is discussed in the context of magnetism in the related
URhX$_{5}$ and UX$_{3}$ (X = In, Ga) compounds.",1501.02154v1
2016-05-08,Exchange bias-like effect in TbFeAl intermetallic induced by atomic disorder,"Exchange bias-like effect observed in the intermetallic compound TbFeAl,
which displays a magnetic phase transition at $T^h_c \approx$ 198~K and a
second one at $T^l_c \approx$ 154~K, is reported. {\em Jump}-like features are
observed in the isothermal magnetization, $M (H)$, at 2~K which disappear above
8~K. The field-cooled magnetization isotherms below 10~K show loop-shifts that
are reminiscent of exchange bias, also supported by {\em training effect}.
Significant coercive field, $H_c \approx$ 1.5~T at 2~K is observed in TbFeAl
which, after an initial increase, shows subsequent decrease with temperature.
The exchange bias field, $H_{eb}$, shows a slight increase and subsequent
leveling off with temperature. It is argued that the inherent crystallographic
disorder among Fe and Al and the high magnetocrystalline anisotropy related to
Tb$^{3+}$ lead to the exchange bias effect. TbFeAl is recently reported to show
magnetocaloric effect and the present discovery of exchange bias makes this
compound a multifunctional one. The result obtained on TbFeAl generalizes the
observation of exchange bias in crystallographically disordered materials and
gives impetus for the search for materials with {\em exchange bias induced by
atomic disorder.}",1605.02381v1
2016-07-07,Deciphering chemical order/disorder and material properties at the single-atom level,"Correlating 3D arrangements of atoms and defects with material properties and
functionality forms the core of several scientific disciplines. Here, we
determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in a
model iron-platinum nanoparticle system to correlate 3D atomic arrangements and
chemical order/disorder with material properties at the single-atom level. We
identified rich structural variety and chemical order/disorder including 3D
atomic composition, grain boundaries, anti-phase boundaries, anti-site point
defects and swap defects. We show for the first time that experimentally
measured 3D atomic coordinates and chemical species with 22 pm precision can be
used as direct input for first-principles calculations of material properties
such as atomic magnetic moments and local magnetocrystalline anisotropy. This
work not only opens the door to determining 3D atomic arrangements and chemical
order/disorder of a wide range of nanostructured materials with high precision,
but also will transform our understanding of structure-property relationships
at the most fundamental level.",1607.02051v1
2016-09-12,Spin structures of textured and isotropic Nd-Fe-B-based nanocomposites: Evidence for correlated crystallographic and spin texture,"We report the results of a comparative study of the magnetic microstructure
of textured and isotropic
$\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}/\alpha$-$\mathrm{Fe}$ nanocomposites
using magnetometry, transmission electron microscopy, synchrotron x-ray
diffraction, and, in particular, magnetic small-angle neutron scattering
(SANS). Analysis of the magnetic neutron data of the textured specimen and
computation of the correlation function of the spin misalignment SANS cross
section suggests the existence of inhomogeneously magnetized regions on an
intraparticle nanometer length scale, about $40-50 \, \mathrm{nm}$ in the
remanent state. Possible origins for this spin disorder are discussed: it may
originate in thin grain-boundary layers (where the materials parameters are
different than in the $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$ grains), or it
may reflect the presence of crystal defects (introduced via hot pressing), or
the dispersion in the orientation distribution of the magnetocrystalline
anisotropy axes of the $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$ grains. X-ray
powder diffraction data reveal a crystallographic texture in the direction
perpendicular to the pressing direction -- a finding which might be related to
the presence of a texture in the magnetization distribution, as inferred from
the magnetic SANS data.",1609.03383v1
2016-11-28,Multiscale examination of strain effects in Nd-Fe-B permanent magnets,"We have performed a combined first-principles and micromagnetic study on the
strain effects in Nd-Fe-B magnets. First-principles calculations on Nd2Fe14B
reveal that the magnetocrystalline anisotropy (K) is insensitive to the
deformation along c axis and the ab in-plane shrinkage is responsible for the K
reduction. The predicted K is more sensitive to the lattice deformation than
what the previous phenomenological model suggests. The biaxial and triaxial
stress states have a greater impact on K. Negative K occurs in a much wider
strain range in the ab biaxial stress state. Micromagnetic simulations of
Nd-Fe-B magnets using first-principles results show that a 3-4% local strain in
a 2-nm-wide region near the interface around the grain boundaries and triple
junctions leads to a negative local K and thus decreases the coercivity by
~60%. The local ab biaxial stress state is more likely to induce a large loss
of coercivity. In addition to the local stress states and strain levels
themselves, the shape of the interfaces and the intergranular phases also makes
a difference in determining the coercivity. Smoothing the edge and reducing the
sharp angle of the triple regions in Nd-Fe-B magnets would be favorable for a
coercivity enhancement.",1611.08940v2
2017-05-12,Pseudo-Goldstone magnons in the frustrated S=3/2 Heisenberg helimagnet ZnCr2Se4 with a pyrochlore magnetic sublattice,"Low-energy spin excitations in any long-range ordered magnetic system in the
absence of magnetocrystalline anisotropy are gapless Goldstone modes emanating
from the ordering wave vectors. In helimagnets, these modes hybridize into the
so-called helimagnon excitations. Here we employ neutron spectroscopy supported
by theoretical calculations to investigate the magnetic excitation spectrum of
the isotropic Heisenberg helimagnet ZnCr2Se4 with a cubic spinel structure, in
which spin-3/2 magnetic Cr3+ ions are arranged in a geometrically frustrated
pyrochlore sublattice. Apart from the conventional Goldstone mode emanating
from the (0 0 q) ordering vector, low-energy magnetic excitations in the
single-domain proper-screw spiral phase show soft helimagnon modes with a small
energy gap of ~0.17 meV, emerging from two orthogonal wave vectors (q 0 0) and
(0 q 0) where no magnetic Bragg peaks are present. We term them
pseudo-Goldstone magnons, as they appear gapless within linear spin-wave theory
and only acquire a finite gap due to higher-order quantum-fluctuation
corrections. Our results are likely universal for a broad class of symmetric
helimagnets, opening up a new way of studying weak magnon-magnon interactions
with accessible spectroscopic methods.",1705.04642v3
2018-02-12,Canted ferrimagnetism and giant coercivity in the non-stoichiometric double perovskite La2Ni1.19Os0.81O6,"The non-stoichiometric double perovskite oxide La2Ni1.19Os0.81O6 was
synthesized by solid state reaction and its crystal and magnetic structures
were investigated by powder x-ray and neutron diffraction. La2Ni1.19Os0.81O6
crystallizes in the monoclinic double perovskite structure (general formula
A2BB'O6) with space group P21/n, where the B site is fully occupied by Ni and
the B' site by 19 % Ni and 81 % Os atoms. Using x-ray absorption spectroscopy
an Os4.5+ oxidation state was established, suggesting presence of about 50 %
paramagnetic Os5+ (5d3, S = 3/2) and 50 % non-magnetic Os4+ (5d4, Jeff = 0)
ions at the B' sites. Magnetization and neutron diffraction measurements on
La2Ni1.19Os0.81O6 provide evidence for a ferrimagnetic transition at 125 K. The
analysis of the neutron data suggests a canted ferrimagnetic spin structure
with collinear Ni2+ spin chains extending along the c axis but a non-collinear
spin alignment within the ab plane. The magnetization curve of
La2Ni1.19Os0.81O6 features a hysteresis with a very high coercive field, HC =
41 kOe, at T = 5 K, which is explained in terms of large magnetocrystalline
anisotropy due to the presence of Os ions together with atomic disorder. Our
results are encouraging to search for rare earth free hard magnets in the class
of double perovskite oxides.",1802.03874v1
2018-02-22,Temperature- and field-driven spin reorientations in triple-layer ruthenate Sr$_4$Ru$_3$O$_{10}$,"Sr$_4$Ru$_3$O$_{10}$, the $n$ = 3 member of the Ruddlesden-Popper type
ruthenate Sr$_{n+1}$Ru$_n$O$_{3n+1}$, is known to exhibit a peculiar
metamagnetic transition in an in-plane magnetic field. However, the nature of
both the temperature- and field-dependent phase transitions remains as a topic
of debate. Here, we have investigated the magnetic transitions of
Sr$_4$Ru$_3$O$_{10}$ via single-crystal neutron diffraction measurements. At
zero field, we find that the system undergoes a ferromagnetic transition with
both in-plane and out-of-plane magnetic components at $T_{c}$ ~ 100 K. Below
$T^{*}$ ~ 50 K, the magnetic moments incline continuously toward the
out-of-plane direction. At $T$ ~ 1.5 K, where the spins are nearly aligned
along the $c$ axis, a spin reorientation occurs above a critical field $B_c$,
giving rise to a spin component perpendicular to the plane defined by the field
direction and the $c$ axis. We suggest that both the temperature- and
field-driven spin reorientations are associated with a change in the
magnetocrystalline anisotropy, which is strongly coupled to the lattice degrees
of freedom. This study elucidates the long-standing puzzles on the zero-field
magnetic orders of Sr$_4$Ru$_3$O$_{10}$ and provides new insights into the
nature of the field-induced metamagnetic transition.",1802.08293v1
2018-03-06,Gate-tunable Room-temperature Ferromagnetism in Two-dimensional Fe$_3$GeTe$_2$,"Material research has been a major driving force in the development of modern
nano-electronic devices. In particular, research in magnetic thin films has
revolutionized the development of spintronic devices; identifying new magnetic
materials is key to better device performance and new device paradigm. The
advent of two-dimensional van der Waals crystals creates new possibilities.
This family of materials retain their chemical stability and structural
integrity down to monolayers and, being atomically thin, are readily tuned by
various kinds of gate modulation. Recent experiments have demonstrated that it
is possible to obtain two-dimensional ferromagnetic order in insulating
Cr$_2$Ge$_2$Te$_6$ and CrI$_3$ at low temperatures. Here, we developed a new
device fabrication technique, and successfully isolated monolayers from layered
metallic magnet Fe$_3$GeTe$_2$ for magnetotransport study. We found that the
itinerant ferromagnetism persists in Fe$_3$GeTe$_2$ down to monolayer with an
out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition
temperature, $T_c$, is suppressed in pristine Fe$_3$GeTe$_2$ thin flakes. An
ionic gate, however, dramatically raises the $T_c$ up to room temperature,
significantly higher than the bulk $T_c$ of 205 Kelvin. The gate-tunable
room-temperature ferromagnetism in two-dimensional Fe$_3$GeTe$_2$ opens up
opportunities for potential voltage-controlled magnetoelectronics based on
atomically thin van der Waals crystals.",1803.02038v1
2018-03-08,Direct imaging of antiferromagnetic domains in Mn$_2$Au manipulated by high magnetic fields,"In the field of antiferromagnetic (AFM) spintronics, information about the
N\'eel vector, AFM domain sizes, and spin-flop fields is a prerequisite for
device applications but is not available easily. We have investigated AFM
domains and spin-flop induced changes of domain patterns in Mn2Au(001)
epitaxial thin films by X-ray magnetic linear dichroism photoemission electron
microscopy (XMLD-PEEM) using magnetic fields up to 70 T. As-prepared Mn$_2$Au
films exhibit AFM domains with an average size $\sim$ 1 $\mu$m. Application of
a 30T field, exceeding the spin-flop field, along a magnetocrystalline easy
axis, dramatically increases the AFM domain size with N\'eel vectors
perpendicular to the applied field direction. The width of N\'eel type domain
walls (DW) is below the spatial resolution of the PEEM and therefore can only
be estimated from an analysis of the DW profile to be smaller than 80 nm.
Furthermore, using the values for the DW width and the spin-flop field, we
evaluate an in-plane anisotropy constant ranging between 1 and 17 $\mu$eV/f.u.",1803.03022v1
2018-04-10,Synthesis and magnetic properties of spin-$\frac{3}{2}$ $γ$-phase of SrCo$_{2}$(PO$_{4}$)$_{2}$ antiferromagnet,"We report on the synthesis of a new $\gamma$-phase of the spin
$S$~=~$\frac{3}{2}$ compound SrCo$_2$(PO$_4$)$_2$ together with a detailed
structural, magnetic and thermodynamic properties. The $\gamma$-phase of
SrCo$_2$(PO$_4$)$_2$ crystallizes in a triclinic crystal structure with the
space group $P\bar{1}$. Susceptibility and specific heat measurements reveal
that SrCo$_2$(PO$_4$)$_2$ orders antiferromagnetically below $T_{\rm N}\simeq
8.5$\,K and the nature of ordering is three dimensional (3D). The magnetic
isotherm at temperatures below $T_{\rm N}$ shows a field-induced spin-flop
transition, related to the magnetocrystalline anisotropy, at an applied field
of $\sim$~4.5~Tesla. Remarkably, heat capacity shows magnetic-field-induced
transitions at $T_{\rm N1}$ = 3.6 K and $T_{\rm N2}$ = 7.4 K. The magnetic long
range ordering (LRO) is also confirmed in both the Knight shift and
spin-lattice relaxation rate ($1/T_{1}$) of the $^{31}$P-NMR measurements.
However, below the LRO we have not detected any NMR signal due to faster
relaxation. We have detected two structurally different phosphorous sites in
$\gamma$-phase of SrCo$_{2}$(PO$_{4}$)$_{2}$ and they shift differently with
temperature.",1804.03464v2
2018-04-24,Antiferromagnetism and phase transitions in non-centrosymmetric UIrSi$_3$,"Magnetization and specific heat measurements on a UIrSi3 single crystal
reveal Ising-like antiferromagnetism below T$_N$ = 41.7 K with easy
magnetization direction along the c-axis of tetragonal structure. The
antiferromagentic ordering is suppressed by magnetic fields > H$_c$
({\mu}$_0$H$_c$ = 7.3 T at 2 K) applied along the c-axis. The first-order
metamagnetic transition at H$_c$ exhibits asymmetric hysteresis reflecting a
slow reentry of the complex ground-state antiferromagnetic structure with
decreasing field. The hysteresis narrows with increasing temperature and
vanishes at 28 K. A second-order metamagnetic transition is observed at higher
temperatures. The point of change of the order of transition in the established
H-T magnetic phase diagram is considered as the tricritical point (at T$_{tc}$
= 28 K and {\mu}$_0$H$_{tc}$ = 5.8 T). The modified-Curie-Weiss-law fits of
temperature dependence of the a- and c-axis susceptibility provide opposite
signs of Weiss temperatures, {\Theta}$_p^a$ ~ -51 K and {\Theta}$_p^c$ ~ +38 K,
respectively. This result and the small value of {\mu}$_0$H$_c$ contrasting to
the high T$_N$ indicate competing ferromagnetic and antiferromagnetic
interactions responsible for the complex antiferromagnetic ground state. The
simultaneous electronic-structure calculations focused on the total energy of
ferromagentic and various antiferromagnetic states, the U magnetic moment and
magnetocrystalline anisotropy provide results consistent with experimental
findings and the suggested physical picture of the system.",1804.08832v1
2018-09-13,Single-layer antiferromagnetic semiconductor CoS2 with the pentagonal structure,"Structure-property relationships have always been guiding principles in
discovering new materials. Here we explore the relationships to discover novel
two-dimensional (2D) materials with the goal of identifying 2D magnetic
semiconductors for spintronics applications. In particular, we report a density
functional theory + $U$ study of single-layer antiferromagnetic (AFM)
semiconductor CoS$_2$ with the pentagonal structure forming the so-called Cairo
Tessellation. We find that this single-layer magnet exhibits an indirect
bandgap of 1.06 eV with light electron and hole effective masses of 0.03 and
0.10 $m_0$, respectively, which may lead to high carrier mobilities. The hybrid
density functional theory calculations correct the bandgap to 2.24 eV. We also
compute the magnetocrystalline anisotropy energy (MAE), showing that the easy
axis of the AFM ordering is out of plane with a sizable MAE of 153 $\mu$eV per
Co ion. We further calculate the magnon frequencies at different spin-spiral
vectors, based on which we estimate the N$\acute{e}$el temperatures to be 20.4
and 13.3 K using the mean field and random phase approximations, respectively.
We then apply biaxial strains to tune the bandgap of single-layer pentagonal
CoS$_2$. We find that the energy difference between the ferromagnetic and AFM
structures strongly depends on the biaxial strain, but the ground state remains
the AFM ordering. Although the low critical temperature prohibits the magnetic
applications of single-layer pentagonal CoS$_2$ at room temperature, the
excellent electrical properties may find this novel single-layer semiconductor
applications in optoelectronic nanodevices.",1809.05055v1
2018-10-02,Building traps for skyrmions by the incorporation of magnetic defects into nanomagnets: pinning and scattering traps by magnetic properties engineering,"In this work we have used micromagnetic simulations to report four ways to
build traps for magnetic skyrmions. Magnetic defects have been modeled as local
variations in the material parameters, such as the exchange stiffness,
saturation magnetization, magnetocrystalline anisotropy and
Dzyaloshinskii-Moriya constant. We observe both pinning (potential well) and
scattering (potential barrier) traps when tuning either a local increase or a
local reduction for each one of these magnetic properties. It is found that the
skyrmion-defect aspect ratio is a crucial parameter to build traps for
skyrmions. In particular, the efficiency of the trap is compromised if the
defect size is smaller than the skyrmion size, because they interact weakly. On
the other hand, if the defect size is larger than the skyrmion diameter, the
skyrmion-defect interaction becomes evident. Thus, the strength of the
skyrmion-defect interaction can be tuned by the modification of the magnetic
properties within a region with suitable size. Furthermore, the basic physics
behind the mechanisms for pinning and for scattering is discussed. In
particular, we discover that skyrmions move towards the magnetic region which
tends to maximize its diameter; it enables the magnetic system to minimize its
energy. Thus, we are able to explain why skyrmions are either attracted or
repelled by a region with modified magnetic properties. Results here presented
are of utmost significance for the development and realization of future
spintronic devices, in which skyrmions will work as information carriers.",1810.03754v2
2018-11-08,Single-Layer Ferromagnetic and Piezoelectric CoAsS with Pentagonal Structure,"Single-layer pentagonal materials are an emerging family of two-dimensional
(2D) materials that could exhibit novel properties due to the building blocks
being pentagons instead of hexagons as in numerous 2D materials. Based on our
recently predicted single-layer pentagonal CoS$_2$ that is an antiferromagnetic
(AFM) semiconductor, we replace two S atoms by As atoms in a unit cell to form
single-layer pentagonal CoAsS. The resulting single-layer material is
dynamically stable ac-cording to the phonon calculations. We find two drastic
changes in the properties of single-layer pentagonal CoAsS in comparison with
those of CoS$_2$. First, we find a magnetic transition from the AFM to FM
ordering. We understand that the transition is caused by the lower
electronegativity of As atoms, leading to the weakened bridging roles on the
superexchange interactions be-tween Co ions. Single-layer pentagonal CoAsS also
shows significantly stronger magnetocrystalline anisotropy energy due to
stronger spin-orbit coupling. We additionally perform Monte Carlo simulations
to calculate the Curie temperature of single-layer pentagonal CoAsS and the
predicted Curie temperature is 103 K. Second, we find that single-layer
pentagonal CoAsS exhibits piezoelectricity, which is absent in single-layer
pentagonal CoS$_2$ due to its center of symmetry. The computed piezoelectric
coefficients are also sizable. The rare coexistence of FM ordering and
piezoelectric properties makes single-layer pentagonal CoAsS a promising
multifunctional 2D material.",1811.03469v1
2019-01-07,Field-induced phases in a heavy-fermion U(Ru$_{0.92}$Rh$_{0.08}$)$_{2}$Si$_{2}$ single crystal,"We report the high-field induced magnetic phases and phase diagram of a high
quality \urxrs~single crystal prepared using a modified Czochralski method. Our
study, that combines high-field magnetization and electrical resistivity
measurements, shows for fields applied along the $c$-axis direction three
field-induced magnetic phase transitions at $\mu_{0} H_{c1}$ = 21.60 T,
$\mu_{0} H_{c2}$ = 37.90 T and $\mu_{0} H_{c3}$ = 38.25 T, respectively. In
agreement with a microscopic up-up-down arrangement of the U magnetic moments
the phase above $H_{c1}$ has a magnetization of about one third of the
saturated value. In contrast the phase between $H_{c2}$ and $H_{c3}$ has a
magnetization that is a factor of two lower than above the $H_{c3}$, where a
polarized Fermi-liquid state with a saturated moment $M_{s}$ $\approx$ 2.1
$\mu_{B}$/U is realized. Most of the respective transitions are reflected in
the electrical resistivity as sudden drastic changes. Most notably, the phase
between $H_{c1}$ and $H_{c2}$ exhibits substantially larger values. As the
temperature increases, transitions smear out and disappear above $\approx$ 15
K. However, a substantial magnetoresistance is observed even at temperatures as
high as 80 K. Due to a strong uniaxial magnetocrystalline anisotropy a very
small field effect is observed for fields apllied perpendicular to the $c$-axis
direction.",1901.01750v1
2019-03-27,Structural and magnetic properties of GdCo$_{5-x}$Ni$_x$,"GdCo$_5$ may be considered as two sublattices - one of Gd and one of Co -
whose magnetizations are in antiparallel alignment, forming a ferrimagnet.
Substitution of nickel in the cobalt sublattice of GdCo$_5$ has been
investigated to gain insight into how the magnetic properties of this prototype
rare-earth/transition-metal magnet are affected by changes in the transition
metal sublattice. Polycrystalline samples of GdCo$_{5-x}$Ni$_x$ for 0 $ \leq x
\leq $ 5 were synthesized by arc melting. Structural characterization was
carried out by powder x-ray diffraction and optical and scanning electron
microscope imaging of metallographic slides, the latter revealing a low
concentration of Gd$_2$(Co, Ni)$_7$ lamellae for $x \leq 2.5$. Compensation -
i.e. the cancellation of the opposing Gd and transition metal moments is
observed for $1 \leq x \leq 3$ at a temperature which increases with Ni
content; for larger $x$, no compensation is observed below 360 K. A peak in the
coercivity is seen at $x \approx 1$ at 10K coinciding with a minimum in the
saturation magnetization. Density-functional theory calculations within the
disordered local moment picture reproduce the dependence of the magnetization
on Ni content and temperature. The calculations also show a peak in the
magnetocrystalline anisotropy at similar Ni concentrations to the
experimentally observed coercivity maximum.",1903.11442v1
2020-02-28,Traps for pinning and scattering of antiferromagnetic skyrmions via magnetic properties engineering,"Micromagnetic simulations have been performed to investigate the
controllability of the skyrmion position in antiferromagnetic nanotracks with
their magnetic properties modified spatially. In this study we have modeled
magnetic defects as local variations on the material parameters, such as the
exchange stiffness, saturation magnetization, perpendicular magnetocrystalline
anisotropy and Dzyaloshinskii-Moriya constant. Thus, we have observed not only
pinning (potential well) but also scattering (potential barrier) of
antiferromagnetic skyrmions, when adjusting either a local increase or a local
reduction for each material parameter. In order to control of the skyrmion
motion it is very important to impose certain positions along the nanotrack
where the skyrmion can stop. Magnetic defects incorporated intentionally in
antiferromagnetic racetracks can be useful for such purpose. In order to
provide guidelines for experimental studies, we vary both material parameters
and size of the modified region. The found results show that the efficiency of
skyrmion trap depends on a suitable combination of magnetic defect parameters.
Furthermore, we discuss the reason why skyrmions are either attracted or
repelled by a region magnetically modified.",2003.00907v2
2020-04-17,Magnetic correlations in subsystems of the misfit [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] cobaltate,"[Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], a two dimensional misfit metallic
compound, is famous for its rich phases accessed by temperature, $i.e.$ high
temperature spin-state transition, metal-insulator transition (MIT) at
intermediate temperature ($\sim$ 100 K) and low temperature spin density wave
(SDW). It enters into SDW phase below T$_{MIT}$ which becomes long range at 27
K. Information on the independent role of misfit layers (rocksalt/Ca$_2$CoO$_3$
\& triangular/CoO$_2$) in these phases is scarce. By combining a set of
complementary macroscopic (DC magnetization and resistivity) and microscopic
(neutron diffraction and X-ray absorption fine structure spectroscopy)
measurements on pure (CCO) and Tb substituted in the rocksalt layer of CCO
(CCO1), magnetic correlations in both subsystems of this misfit compound are
unraveled. CCO is found to exhibit glassiness, as well as exchange bias (EB)
effects, while CCO1 does not exhibit glassiness, albeit it shows weaker EB
effect. By combining local structure investigations from extended X-ray
absorption fine structure (EXAFS) spectroscopy and neutron diffraction results
on CCO, we confirm that the SDW arises in the CoO$_2$ layer. Our results show
that the magnetocrystalline anisotropy associated with the rocksalt layer acts
as a source of pinning, which is responsible for EB effect. Ferromagnetic
clusters in the Ca$_2$CoO$_3$ affects SDW in CoO$_2$ and ultimately glassiness
arises.",2004.08319v2
2020-04-24,Observation of magnetic domain and bubble structures in magnetoelectric Sr$_3$Co$_2$Fe$_{24}$O$_{41}$,"The magnetic domain and bubble structures in the Z-type hexaferrite
Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ were investigated using Lorentz microscopy. This
hexaferrite exhibits a room-temperature magnetoelectric effect that is
attributed to its transverse conical spin structure (TC phase). Upon heating,
the TC phase transforms into a ferrimagnetic phase with magnetic moments in the
hexagonal $ab$ plane between 410 and 480 K (FM2 phase) and into another
ferrimagnetic phase with moments parallel to the $c$ axis between 490 and 680 K
(FM1 phase). Accordingly, in this study, the magnetic domain structures in
Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ were observed to change dramatically with
temperature. In the TC phase, irregular fine magnetic domains were observed
after cooling the specimen from the FM2 to TC phase. In the FM1 phase, striped
magnetic domain walls with pairs of bright and dark contrast were formed
parallel to the $c$ axis. Upon applying an external magnetic field, the striped
magnetic domain walls transformed into magnetic bubbles. The topology of the
magnetic bubbles was dependent on the angle between the external magnetic field
($H$) direction and the easy $c$ axis. Namely, magnetic bubbles with the
topological number $N$ = 1 (type I) were created for $H//c$, whereas magnetic
bubbles with $N$ = 0 (type II) were created when the magnetic field was tilted
from the c axis by 5{\deg}. We attribute the high magnetocrystalline anisotropy
of Sr$_3$Co$_2$Fe$_{24}$O$_{41}$ to the emergence of magnetic bubbles in the
FM1 phase.",2004.11591v1
2020-08-27,"Different universality classes of isostructural U$TX$ compounds ($T$ = Rh, Co, Co$_{0.98}$Ru$_{0.02}$; $X$ = Ga, Al)","Magnetization isotherms of the 5f-electron ferromagnets URhGa, UCoGa and
UCo0.98Ru0.02Al were measured at temperatures in the vicinity of their Curie
temperature in order to investigate the critical behavior near the
ferromagnetic phase transition. These compounds adopt the layered hexagonal
ZrNiAl-type structure and exhibit huge uniaxial magnetocrystalline anisotropy.
The critical \b{eta}, {\gamma} and {\delta} exponents were determined by
analyzing Arrott-Noakes plots, Kouvel-Fisher plots, critical isotherms, scaling
theory and Widom scaling relations. The values obtained for URhGa and UCoGa can
be explained by the results of the renormalization group theory for a 2D Ising
system with long-range interactions similar to URhAl reported by other
investigators. On the other hand, the critical exponents determined for
UCo0.98Ru0.02Al are characteristic of a 3D Ising ferromagnet with short-range
interactions suggested in previous studies also for the itinerant 5f-electron
paramagnet UCoAl situated near a ferromagnetic transition. The change from the
2D to the 3D Ising system is related to the gradual delocalization of 5f
electrons in the series of the URhGa, URhAl, UCoGa to UCo0.98Ru0.02Al and UCoAl
compounds and appears close to the strongly itinerant nonmagnetic limit. This
indicates possible new phenomena that may be induced by the change of
dimensionality in the vicinity of the quantum critical point.",2008.12061v1
2020-09-14,Multifunctional Antiperovskites driven by Strong Magnetostructural Coupling,"Based on density functional theory calculations, we elucidated the origin of
multifunctional properties for cubic antiperovskites with noncollinear magnetic
ground states, which can be attributed to strong isotropic and anisotropic
magnetostructural coupling. 16 out of 54 stable magnetic antiperovskites
M$_3$XZ (M = Cr, Mn, Fe, Co, and Ni; X = selected elements from Li to Bi except
for noble gases and 4f rare-earth metals; and Z = C and N) are found to exhibit
the $\Gamma_{4g}$/$\Gamma_{5g}$ (i.e., characterized by irreducible
representations) antiferromagnetic magnetic configurations driven by frustrated
exchange coupling and strong magnetocrystalline anisotropy. Using the magnetic
deformation as an effective proxy, the isotropic magnetostructural coupling is
characterized, and it is observed that the paramagnetic state is critical to
understand the experimentally observed negative thermal expansion and to
predict the magnetocaloric performance. Moreover, the piezomagnetic and
piezospintronic effects induced by biaxial strain are investigated. It is
revealed that there is not a strong correlation between the induced
magnetization and anomalous Hall conductivities by the imposed strain.
Interestingly, the anomalous Hall/Nernst conductivities can be significantly
tailored by the applied strain due to the fine-tuning of the Weyl points
energies, leading to promising spintronic applications.",2009.06440v1
2020-11-01,"Tunable magneto-optical effect, anomalous Hall effect and anomalous Nernst effect in two-dimensional room-temperature ferromagnet $1T$-CrTe$_2$","Utilizing the first-principles density functional theory calculations
together with group theory analyses, we systematically investigate the spin
order-dependent magneto-optical effect (MOE), anomalous Hall effect (AHE), and
anomalous Nernst effect (ANE) in a recently discovered two-dimensional
room-temperature ferromagnet $1T$-CrTe$_2$. We find that the spin prefers an
in-plane direction by the magnetocrystalline anisotropy energy calculations.
The MOE, AHE, and ANE display a period of $2\pi/3$ when the spin rotates within
the atomic plane, and they are forbidden if there exists a mirror plane
perpendicular to the spin direction. By reorienting the spin from in-plane to
out-of-plane direction, the MOE, AHE, and ANE are enhanced by around one order
of magnitude. Moreover, we establish the layer-dependent magnetic properties
for multilayer $1T$-CrTe$_2$ and predict antiferromagnetism and ferromagnetism
for bilayer and trilayer $1T$-CrTe$_2$, respectively. The MOE, AHE, and ANE are
prohibited in antiferromagnetic bilayer $1T$-CrTe$_2$ due to the existence of
the spacetime inversion symmetry, whereas all of them are activated in
ferromagnetic trilayer $1T$-CrTe$_2$ and the MOE is significantly enhanced
compared to monolayer $1T$-CrTe$_2$. Our results show that the magneto-optical
and anomalous transports proprieties of $1T$-CrTe$_2$ can be effectively
modulated by altering spin direction and layer number.",2011.00394v1
2021-02-10,Magneto-electric Tuning of Pinning-Type Permanent Magnets through Atomic-Scale Engineering of Grain Boundaries,"Pinning-type magnets maintaining high coercivity, i.e. the ability to sustain
magnetization, at high temperature are at the core of thriving clean-energy
technologies. Among these, Sm2Co17-based magnets are excellent candidates owing
to their high-temperature stability. However, despite decades of efforts to
optimize the intragranular microstructure, the coercivity currently only
reaches 20~30% of the theoretical limits. Here, the roles of the grain-interior
nanostructure and the grain boundaries in controlling coercivity are
disentangled by an emerging magneto-electric approach. Through hydrogen
charging/discharging by applying voltages of only ~ 1 V, the coercivity is
reversibly tuned by an unprecedented value of ~ 1.3 T. In situ
magneto-structural measurements and atomic-scale tracking of hydrogen atoms
reveal that the segregation of hydrogen atoms at the grain boundaries, rather
than the change of the crystal structure, dominates the reversible and
substantial change of coercivity. Hydrogen lowers the local magnetocrystalline
anisotropy and facilitates the magnetization reversal starting from the grain
boundaries. Our study reveals the previously neglected critical role of grain
boundaries in the conventional magnetisation-switching paradigm, suggesting a
critical reconsideration of strategies to overcome the coercivity limits in
permanent magnets, via for instance atomic-scale grain boundary engineering.",2102.05315v1
2021-03-05,Ferromagnetic Composite Self-Arrangement in Iron-Implanted Epitaxial Palladium Thin Films,"We report on the formation of the dilute $Pd_{1-x}Fe_x$ compositions with
tunable magnetic properties under an ion-beam implantation of epitaxial Pd thin
films. Binary $Pd_{1-x}Fe_x$ alloys with a mean iron content $x$ of $0.025$,
$0.035$ or $0.075$ were obtained by the implantation of $40 keV$ $Fe^+$ ions
into the palladium films on MgO (001) substrate to the doses of
$0.5\cdot10^{16}, 1.0\cdot10^{16}$ and $3.0\cdot10^{16}$ $ions/cm^2$,
respectively. Structural and magnetic studies have shown that iron atoms occupy
regular fcc-lattice Pd-sites without the formation of any secondary
crystallographic phase. All the iron implanted Pd films reveal ferromagnetism
at low temperatures (below $200 K$) with both the Curie temperature and
saturation magnetization determined by the implanted iron dose. In contrast to
the magnetic properties of the molecular beam epitaxy grown $Pd_{1-x}Fe_x$
alloy films with the similar iron contents, the Fe-implanted Pd films possess
weaker in-plane magnetocrystalline anisotropy, and, accordingly, a lower
coercivity. The observed multiple ferromagnetic resonances in the implanted
$Pd_{1-x}Fe_x$ films indicate a formation of a magnetically inhomogeneous state
due to spinodal decomposition into regions, presumably layers, with identical
crystal symmetry but different iron contents. The multiphase magnetic structure
is robust with respect to the vacuum annealing at $770 K$, though develops
towards well-defined local $Pd-Fe$ compositions.",2103.03562v1
2021-03-22,Field-induced reorientation of helimagnetic order in Cu$_2$OSeO$_3$ probed by magnetic force microscopy,"Cu$_2$OSeO$_3$ is an insulating skyrmion-host material with a magnetoelectric
coupling giving rise to an electric polarization with a characteristic
dependence on the magnetic field $\vec H$. We report magnetic force microscopy
imaging of the helical real-space spin structure on the surface of a bulk
single crystal of Cu$_2$OSeO$_3$. In the presence of a magnetic field, the
helimagnetic order in general reorients and acquires a homogeneous component of
the magnetization, resulting in a conical arrangement at larger fields. We
investigate this reorientation process at a temperature of 10~K for fields
close to the crystallographic $\langle 110\rangle$ direction that involves a
phase transition at $H_{c1}$. Experimental evidence is presented for the
formation of magnetic domains in real space as well as for the microscopic
origin of relaxation events that accompany the reorientation process. In
addition, the electric polarization is measured by means of Kelvin-probe force
microscopy. We show that the characteristic field dependency of the electric
polarization originates in this helimagnetic reorientation process. Our
experimental results are well described by an effective Landau theory
previously invoked for MnSi, that captures the competition between
magnetocrystalline anisotropies and Zeeman energy.",2103.11953v1
2021-04-27,Observation of a phase transition within the domain walls of ferromagnetic Co3Sn2S2,"The ferromagnetic phase of Co$_3$Sn$_2$S$_2$ is widely considered to be a
topological Weyl semimetal, with evidence for momentum-space monopoles of Berry
curvature from transport and spectroscopic probes. As the bandstructure is
highly sensitive to the magnetic order, attention has focused on anomalies in
magnetization, susceptibility and transport measurements that are seen well
below the Curie temperature, leading to speculation that a ""hidden"" phase
coexists with ferromagnetism. Here we report spatially-resolved measurements by
Kerr effect microscopy that identify this phase. We find that the anomalies
coincide with a deep minimum in domain wall (DW) mobility, indicating a
crossover between two regimes of DW propagation. We demonstrate that this
crossover is a manifestation of a 2D phase transition that occurs within the
DW, in which the magnetization texture changes from continuous rotation to
unidirectional variation. We propose that the existence of this 2D transition
deep within the ferromagnetic state of the bulk is a consequence of a giant
quality factor for magnetocrystalline anisotropy unique to this compound. This
work broadens the horizon of the conventional binary classification of DWs into
Bloch and N\'eel walls, and suggests new strategies for manipulation of domain
walls and their role in electron and spin transport.",2104.13381v2
2021-06-03,Macrospin model of an assembly of magnetically coupled core-shell nanoparticles,"Highly sophisticated synthesis methods and experimental techniques allow for
precise measurements of magnetic properties of nanoparticles that can be
reliably reproduced using theoretical models. Here, we investigate the magnetic
properties of ferrite nanoparticles by using theoretical techniques based on
Monte Carlo methods. We introduce three stages of sophistication in the
macromagnetic model. First, by using tailor-made hamiltonians we study single
nanoparticles. In a second stage, the internal structure of the nanoparticle is
taken into consideration by defining an internal (core) and external (shell)
region, respectively. In the last stage, an assembly of core/shell NPs are
considered. All internal magnetic couplings such as inter and intra-atomic
exchange interactions or magnetocrystalline anisotropies have been estimated.
Moreover, the hysteresis loops of the aforementioned three cases have been
calculated and compared with recent experimental measurements. In the case of
the assembly of nanoparticles, the hysteresis loops together with the
zero-field cooling and field cooling curves are shown to be in a very good
agreement with the experimental data. The current model provides an important
tool to understand the internal structure of the nanoparticles together with
the complex internal spin interactions of the core-shell ferrite nanoparticles.",2106.01844v1
2021-06-07,MAELAS 2.0: A new version of a computer program for the calculation of magneto-elastic properties,"MAELAS is a computer program for the calculation of magnetocrystalline
anisotropy energy, anisotropic magnetostrictive coefficients and magnetoelastic
constants in an automated way. The method originally implemented in version 1.0
of MAELAS was based on the length optimization of the unit cell, proposed by Wu
and Freeman, to calculate the anisotropic magnetostrictive coefficients. We
present here a revised and updated version (v2.0) of MAELAS, where we added a
new methodology to compute anisotropic magnetoelastic constants from a linear
fitting of the energy versus applied strain. We analyze and compare the
accuracy of both methods showing that the new approach is more reliable and
robust than the one implemented in version 1.0, especially for non-cubic
crystal symmetries. This analysis also help us to find that the accuracy of the
method implemented in version 1.0 could be improved by using deformation
gradients derived from the equilibrium magnetoelastic strain tensor, as well as
potential future alternative methods like the strain optimization method.
Additionally, we clarify the role of the demagnetized state in the fractional
change in length, and derive the expression for saturation magnetostriction for
polycrystals with trigonal, tetragonal and orthorhombic crystal symmetry. In
this new version, we also fix some issues related to trigonal crystal symmetry
found in version 1.0.",2106.03624v3
2021-06-16,Magnetic and geometrical control of spin textures in the itinerant kagome magnet Fe$_3$Sn$_2$,"Magnetic materials with competing magnetocrystalline anisotropy and dipolar
energies can develop a wide range of domain patterns, including classical
stripe domains, domain branching, as well as topologically trivial and
non-trivial (skyrmionic) bubbles. We image the magnetic domain pattern of
Fe$_3$Sn$_2$ by magnetic force microscopy (MFM) and study its evolution due to
geometric confinement, magnetic fields, and their combination. In Fe$_3$Sn$_2$
lamellae thinner than 3 $\mu$m, we observe stripe domains whose size scales
with the square root of the lamella thickness, exhibiting classical Kittel
scaling. Magnetic fields turn these stripes into a highly disordered bubble
lattice, where the bubble size also obeys Kittel scaling. Complementary
micromagnetic simulations quantitatively capture the magnetic field and
geometry dependence of the magnetic patterns, reveal strong reconstructions of
the patterns between the surface and the core of the lamellae, and identify the
observed bubbles as skyrmionic bubbles. Our results imply that geometrical
confinement together with competing magnetic interactions can provide a path to
fine-tune and stabilize different types of topologically trivial and
non-trivial spin structures in centrosymmetric magnets.",2106.08791v1
2021-07-14,Designing light-element materials with large effective spin-orbit coupling,"Spin-orbit coupling (SOC), the core of numerous condensed-matter phenomena
such as nontrivial band gap, magnetocrystalline anisotropy, etc, is generally
considered to be appreciable only in heavy elements, detrimental to the
synthetization and application of functional materials. Therefore, amplifying
the SOC effect in light elements is of great importance. Here, focusing on 3d
and 4d systems, we demonstrate that the interplay between crystal symmetry and
electron correlation can dramatically enhance the SOC effect in certain
partially occupied orbital multiplets, through the self-consistently reinforced
orbital polarization as a pivot. We then provide design principles and
comprehensive databases, in which we list all the Wyckoff positions and site
symmetries, in all two-dimensional (2D) and three-dimensional crystals that
potentially have such enhanced SOC effect. As an important demonstration, we
predict nine material candidates from our selected 2D material pool as
high-temperature quantum anomalous Hall insulators with large nontrivial band
gaps of hundreds of meV. Our work provides an efficient and straightforward way
to predict promising SOC-active materials, releasing the burden of requiring
heavy elements for next-generation spin-orbitronic materials and devices.",2107.06691v2
2021-07-28,Effect of transition metal doping on magnetic hardness of CeFe$_{12}$-based compounds,"In this work, compositions of CeFe11X and CeFe10X2 with all 3d, 4d, and 5d
transition metal substitutions are considered. Since many previous studies have
focused on the CeFe11Ti compound, this particular compound became the starting
point of our considerations and we gave it special attention. We first
determined the optimal symmetry of the simplest CeFe11Ti structure model. We
then observed that the calculated magnetocrystalline anisotropy energy (MAE)
correlates with the magnetic moment, which in turn strongly depends on the
choice of the exchange-correlation potential. MAE, magnetic moments, and
magnetic hardness were determined for all compositions considered. Moreover,
the calculated dependence of the MAE on the spin magnetic moment allowed us to
predict the upper limits of the MAE. We also showed that it does not depend on
the choice of the exchange-correlation potential form. The economically
justifiable compositions with the highest magnetic hardness values are CeFe11W,
CeFe10W2, CeFe11Mn, CeFe10Mn2, CeFe11Mo, CeFe10Mo2, and CeFe10Nb2. However,
calculations suggest that, like CeFe12, these compounds are not chemically
stable and could require additional treatments to stabilize the composition.
Further alloying of the selected compositions with elements embedded in
interstitial positions confirms the positive effect of such dopants on hard
magnetic properties. Subsequent calculations performed for comparison for
selected isostructural La-based compounds lead to similar MAE results as for
Ce-based compounds, suggesting a secondary effect of 4f electrons. Calculations
were performed using the full-potential local-orbital electronic structure code
FPLO18, whose unique fully relativistic implementation of the fixed spin moment
method allowed us to calculate the MAE dependence of the magnetic moment.",2107.13352v3
2021-08-03,Tuning exchange interactions in antiferromagnetic Fe/W(001) by 4d transition-metal overlayers,"We use first-principles calculations based on density functional theory to
study how the magnetic properties of an Fe monolayer on a W(001) surface --
exhibiting a $c(2 \times 2)$ antiferromagnetic ground state -- can be modified
by an additional 4d transition-metal overlayer. To obtain an overview of how
the 4d-band filling influences the exchange interactions in the Fe layer we
have calculated the energy dispersion of spin spirals for 4d/Fe/2W unsupported
quadlayers, in which the W(001)substrate is represented by only two atomic
layers. Hybridization with the overlayer leads to a reduced ferromagnetic
nearest-neighbor exchange interaction and the next-nearest neighbor exchange
gains in strength. Surprisingly, we find that the $c(2 \times 2)$
antiferromagnetic state is unfavorable for all systems with a 4d overlayer. For
4d overlayers from the beginning (Nb) or end (Pd) of the series we find a
ferromagnetic ground state. As one moves to the center of the series there is a
transition via a spin spiral (Mo, Rh) to a $p (2 \times 1)$ antiferromagnetic
ground state (Tc, Ru). We have studied the Mo, Ru, and Pd overlayer on
Fe/W(001) representing the surface by a sufficiently large number of W layers
to obtain bulk like properties in its center. The energy dispersion of spin
spirals show qualitatively the same results as those from the 4\textit{d}/Fe/2W
quadlayers. The Dzyaloshinskii-Moriya interaction calculated upon including
spin-orbit coupling shows significant strength and considerable frustration
effects. The calculated magnetocrystalline anisotropy energy is large as well.
All 4d/Fe/W(001) films are potential candidates for complex non-collinear spin
structures.",2108.01359v1
2021-08-18,Thermal squeezing and nonlinear spectral shift of magnons in antiferromagnetic insulators,"We investigate the effect of magnon-magnon interactions on the dispersion and
polarization of magnons in collinear antiferromagnetic (AF) insulators at
finite temperatures. In two-sublattice AF systems with either uniaxial or
biaxial magnetocrystalline anisotropies, we implement a self-consistent
Hartree-Fock mean-field approximation to explore the nonlinear thermal
interactions. The resulting nonlinear magnon interactions separate into
two-magnon intra- and interband scattering processes. Furthermore, we compute
the temperature dependence of the magnon bandgap and AF resonance modes due to
nonlinear magnon interactions for square and hexagonal lattices. In addition,
we study the effect of magnon interactions on the polarization of magnon modes.
We find that although the noninteracting eigenmodes in the uniaxial case are
circularly polarized, but in the presence of nonlinear thermal interactions the
local U(1) symmetry of the Hamiltonian is broken. The attractive nonlinear
interactions squeeze the low-energy magnon modes and make them elliptical. In
the biaxial case, on the other hand, the bare eigenmodes of low energy magnons
are elliptically polarized but thermal nonlinear interactions squeeze them
further. Direct measurements of the predicted temperature-dependent AF
resonance modes and their polarization can be used as a tool to probe the
nonlinear interactions. Our findings establish a framework for exploring the
effect of thermal magnon interactions in technologically important magnetic
systems, such as magnetic stability of recently discovered two-dimensional
magnetic materials, coherent transport of magnons, Bose-Einstein condensation
of magnons, and magnonic topological insulators.",2108.08374v4
2021-10-25,Persistent large anisotropic magnetoresistance and insulator to metal transition in spin-orbit coupled antiferromagnets Sr2(Ir1-xGax)O4,"Antiferromagnetic (AFM) spintronics, where magneto-transport is governed by
an antiferromagnet instead of a ferromagnet, opens fascinating new perspectives
for both fundamental research and device technology, owing to their intrinsic
appealing properties like rigidness to magnetic field, absence of stray field,
and ultrafast spin dynamics. One of the urgent challenges, hindering the
realization of the full potential of AFM spintronics, has been the performance
gap between AFM metals and insulators. Here, we demonstrate the insulator-metal
transition and persistently large anisotropic magnetoresistance (AMR) in single
crystals Sr2(Ir1-xGax)O4 (0<x<0.09) which host the same basal-plane AFM lattice
with strong spin-orbit coupling. The non-doped Sr2IrO4 shows the insulating
transport with the AMR as big as ~16.8% at 50 K. The Ga substitution of Ir
allows a gradual reduction of electrical resistivity, and a clear
insulator-to-metal transition is identified in doped samples with x above 0.05,
while the AMR can still have ~1%, sizable in comparison with those in AFM
metals reported so far. Our experiments reveal that all the samples have the
similar fourfold AMR symmetry, which can be well understood in the scenario of
magnetocrystalline anisotropy. It is suggested that the spin-orbit coupled
antiferromagnets Sr2(Ir1-xGax)O4 are promising candidate materials for AFM
spintronics, providing a rare opportunity to integrate the superior spintronic
functionalities of AFM metals and insulators.",2110.12852v1
2021-12-01,Pressure dependent magnetic properties on bulk CrBr3 single crystals,"The van der Waals class of materials offer an approach to two-dimensional
magnetism as their spin fluctuations can be tuned upon exfoliation of layers.
Moreover, it has recently been shown that spin-lattice coupling and long-range
magnetic ordering can be modified with pressure in van der Waals materials. In
this work, the magnetic properties of quasi two-dimensional CrBr3 are reported
applying hydrostatic pressure. The application of pressure (0 - 0.8 GPa) shows
a 72 % decrease in saturation magnetization with small decrease in the Curie
temperature from 33 to 29 K. Density functional theory calculations with
pressure up to 1 GPa show a reduction in volume and interplanar distance as
pressure increases. To further understand magnetic properties with applied
pressure, the magnetocrystalline anisotropy energy (MAE) and exchange coupling
parameter (J) are calculated. There is minimal decrease in MAE and the first
nearest neighbor interaction (J1) (U = 2.7 eV and J = 0.7 eV), shows an
increase in J1 with respect to pressure. Overall, CrBr3 displays ferromagnetic
interlayer coupling and the calculated exchange coupling and MAE parameters
match well with the observations from the experimental work.",2112.00233v1
2021-12-06,A material view on extrinsic magnetic domain wall pinning in cylindrical CoNi nanowires,"Speed and reliability of magnetic domain wall (DW) motion are key parameters
that must be controlled to realize the full potential of DW-based magnetic
devices for logic and memory applications. A major hindrance to this is
extrinsic DW pinning at specific sites related to shape and material defects,
which may be present even if the sample synthesis is well controlled.
Understanding the origin of DW pinning and reducing it is especially desirable
in electrochemically-deposited cylindrical magnetic nanowires (NWs), for which
measurements of the fascinating physics predicted by theoretical computation
have been inhibited by significant pinning. We experimentally investigate DW
pinning in Co$_x$Ni$_{100-x}$ NWs, by applying quasistatic magnetic fields.
Wire compositions were varied with $x=20,30,40$, while the microstructure was
changed by annealing or varying the pH of the electrolyte for deposition. We
conclude that pinning due to grain boundaries is the dominant mechanism,
decreasing inversely with both the spontaneous magnetization and grain size.
Second-order effects include inhomogeneities in lattice strain and the residual
magnetocrystalline anisotropy. Surface roughness, dislocations and impurities
are not expected to play a significant role in DW pinning in these wire
samples.",2112.03132v1
2021-12-28,"Phonon, Electron, and Magnon Excitations in Antiferromagnetic L1$_{0}$-type MnPt","Antiferromagnetic L1$_{0}$-type MnPt is a material with relatively simple
crystal and magnetic structure, recently attracting interest due to its high
N{\'{e}}el temperature and wide usage as a pinning layer in magnetic devices.
While it is experimentally well characterized, the theoretical understanding is
much less developed, in part due to the challenging accuracy requirements
dictated by the small underlying energy scales that govern magnetic ordering in
antiferromagnetic metals. In this work, we use density functional theory, the
Korringa-Kohn-Rostoker formalism, and a Heisenberg model to establish a
comprehensive theoretical description of antiferromagnetic L1$_{0}$-type MnPt,
along with accuracy limits, by thoroughly comparing to available literature
data. Our simulations show that the contribution of the magnetic dipole
interaction to the magnetocrystalline anisotropy energy of $K_{1}$=1.07$\times
10^{6}$\,J/m$^3$ is comparable in magnitude to the spin-orbit contribution.
Using our result for the magnetic susceptibility of $5.25\times10^{-4}$, a
lowest magnon frequency of about 2.02\,THz is predicted, confirming THz spin
dynamics in this material. From our data for electron, phonon, and magnon
dispersion we compute the individual contributions to the total heat capacity
and show that the dominant term at or above 2\,K arises from phonons. From the
Landau-Lifshitz-Gilbert equation, we compute a N\'{e}el temperature of
990--1070 K. Finally, we quantify the magnitude of the magneto-optical Kerr
effect generated by applying an external magnetic field. Our results provide
insight into the underlying physics, which is critical for a deep understanding
of fundamental limits of the time scale of spin dynamics, stability of the
magnetic ordering, and the possibility of magneto-optical detection of
collective spin motion.",2112.13954v1
2022-01-24,Direct observation of strong anomalous Hall effect and proximity-induced ferromagnetic state in SrIrO3,"The 5d iridium-based transition metal oxides have gained broad interest
because of their strong spin-orbit coupling which favors new or exotic quantum
electronic states. On the other hand, they rarely exhibit more mainstream
orders like ferromagnetism due to generally weak electron-electron correlation
strength. Here, we show a proximity-induced ferromagnetic (FM) state with TC =
100 K and strong magnetocrystalline anisotropy in a SrIrO3 (SIO)
heterostructure via interfacial charge transfer by using a ferromagnetic
insulator in contact with SIO. Electrical transport allows to selectively probe
the FM state of the SIO layer and the direct observation of a strong, intrinsic
and positive anomalous Hall effect (AHE). For T < 20 K, the AHE displays
unusually large coercive and saturation field, a fingerprint of a strong
pseudospin-lattice coupling. A Hall angle, sxyAHE/sxx, larger by an order of
magnitude than in typical 3d metals and a FM net moment of about 0.1 mB/Ir, is
reported. This emphasizes how efficiently the nontrivial topological band
properties of SIO can be manipulated by structural modifications and the
exchange interaction with 3d TMOs.",2201.09570v2
2022-06-07,Competition of Magnetocrystalline Anisotropy of Uranium Layers and Zig-Zag Chains in UNi$_{0.34}$Ge$_2$ Single Crystals,"Structural and thermodynamic properties of single-crystalline
UNi$_{1-x}$Ge$_2$ with $x$\,=\,0.66 have been investigated by measuring
magnetization, specific heat, and thermal expansion over a wide range of
temperatures and magnetic fields. The measurements revealed the emergence of a
long-range antiferromagnetic ordering of uranium magnetic moments below the
N{\'e}el temperature $T_{\rm N}$\,=\,45.5\,K and the existence of two easy axes
in the studied compound, namely $b$ and $c$, which correspond to the planes of
the uranium zig-zag chains. Magnetic field applied along these two
crystallographic directions induces in the system a first-order metamagnetic
phase transition (from antiferromagnetism to field-polarized paramagnetism),
and the width of the magnetic hysteresis associated with that transition
reaches as much as 40 kOe at the lowest temperatures. A magnetic phase diagram
developed from the experimental data showed that the metastable region
associated with that magnetic hysteresis forms a funnel that narrows toward the
N{\'e}el point in zero magnetic field. The four-layer Ising model has
successfully predicted the collinear antiferromagnetic structure in
UNi$_{0.34}$Ge$_2$ (known from earlier reports), its magnetic phase diagram,
and temperature and field variations of its magnetization. Moreover, it
suggests that the first-order phase transition extends down to zero magnetic
field, although it is barely detectable in the experiments performed in low
magnetic fields. According to this model, the second-order phase transition
occurs in the compound only in zero field.",2206.03397v2
2022-06-22,Spin wave stiffness and damping in a frustrated chiral helimagnet Co$_8$Zn$_8$Mn$_4$ as measured by small-angle neutron scattering,"Multiple intriguing low temperature phenomena have recently been discovered
in the family of chiral cubic Co-Zn-Mn compounds with $\beta-$Mn-type
structure. In particular, Co$_8$Zn$_8$Mn$_4$ displays a reduction of the
helical spiral pitch on cooling, along with lattice shape transformations of
metastable skyrmions and the manifestation of peculiar magnetic textures due to
strong magnetocrystalline anisotropy. Here we report on temperature-dependent
measurements of helimagnon excitations in the field polarized regime
Co$_8$Zn$_8$Mn$_4$ using the spin wave small-angle neutron scattering (SWSANS)
technique. By applying a new analytical expression to interpret the data,
quantitative estimates for both spin wave stiffness and damping are extracted
across a wide temperature range between 70 K and 250 K. We speculate that their
non-trivial temperature-dependencies arise due to the effects of magnetic
frustration arising from Mn magnetic moments, which is further reflected in
continuous variations of both exchange and Dzyaloshinskii-Moriya interactions.",2206.11006v1
2022-07-14,UI$_3$ -- 5f-electron magnetic van der Waals material,"We grew high-quality single crystals of the 5f electron van der Waals
compound UI$_3$ and investigated them by measurements of specific heat and
magnetization as functions of temperature and magnetic field. UI$_3$ behaves as
an antiferromagnet with a first-order magnetic phase transition at the Ne\'el
temperature $T_N$ = 2.65 K. It is characterized by a sharp symmetric
specific-heat peak which is gradually shifted to lower temperatures by
increasing magnetic field applied along either the a- or b-axis. The behavior
in magnetic fields reveals orthorhombic magnetocrystalline anisotropy with the
hard magnetization direction along the c-axis. The 2-K a- and b-axis
magnetization curves exhibit a metamagnetic transition at the critical field
$H_c$ = 3 T and 1.8 T, respectively. In higher fields, when the long-range
antiferromagnetism is suppressed by a metamagnetic transition, signs of
short-range magnetic ordering of antiferromagnetic correlations in the
paramagnetic state show up both in specific heat and magnetization. The
anomalous S-shape field dependence of a-axis magnetization well above $H_c$ can
be understood as the crossover from the correlated paramagnetic regime to the
high-field polarized paramagnet. The magnetic phase diagrams for the magnetic
field applied along the a- and b-axis, respectively, designed using the
mentioned experimental results are presented. We have also found that the
UI$_3$ crystals are easily cleavable which predisposes this material for direct
investigation of 5f electron magnetism in the 2D limit on exfoliated atomically
thin samples.",2207.06880v1
2022-10-25,"Au4Mn, a localized ferromagnet with strong spin-orbit coupling, long-range ferromagnetic exchange and high Curie temperature","Metallic Mn-based alloys with a nearest-neighbor Mn-Mn distance greater than
0.4 nm exhibit large, well-localized magnetic moments. Here we investigate the
magnetism of tetragonal Au4Mn with a Curie temperature of 385 K, where
manganese has a spin moment of 4.1 muB and its orbital moment is quenched.
Since 80% of the atoms are gold, the spin orbit interaction is strong and Au4Mn
exhibits uniaxial magnetocrystalline anisotropy with surface maze domains at
room temperature. The magnetic hardness parameter of 1.0 is sufficient to
maintain the magnetization along the c-axis for a sample of any shape. Au also
reduces the spin moment of Mn through 5d-3d orbital hybridization. An induced
moment of 0.05 muB was found on Au under a pulsed field of 40 T. Density
functional theory calculations indicate that the Mn-Mn exchange is mediated by
spin-polarized gold 5d and 6p electrons. The distance-dependence shows that it
is ferromagnetic or zero for the first ten shells of Mn neighbors out to 1.041
nm (64 atoms), and very weak and oscillatory thereafter.",2210.14069v1
2022-11-05,Designing magnetic properties in CrSBr through hydrostatic pressure and ligand substitution,"The ability to control magnetic properties of materials is crucial for
fundamental research and underpins many information technologies. In this
context, two-dimensional materials are a particularly exciting platform due to
their high degree of tunability and ease of implementation into nanoscale
devices. Here we report two approaches for manipulating the A-type
antiferromagnetic properties of the layered semiconductor CrSBr through
hydrostatic pressure and ligand substitution. Hydrostatic pressure compresses
the unit cell, increasing the interlayer exchange energy while lowering the
N\'eel temperature. Ligand substitution, realized synthetically through Cl
alloying, anisotropically compresses the unit cell and suppresses the
Cr-halogen covalency, reducing the magnetocrystalline anisotropy energy and
decreasing the N\'eel temperature. A detailed structural analysis combined with
first-principles calculations reveal that alterations in the magnetic
properties are intricately related to changes in direct Cr-Cr exchange
interactions and the Cr-anion superexchange pathways. Further, we demonstrate
that Cl alloying enables chemical tuning of the interlayer coupling from
antiferromagnetic to ferromagnetic, which is unique amongst known
two-dimensional magnets. The magnetic tunability, combined with a high ordering
temperature, chemical stability, and functional semiconducting properties, make
CrSBr an ideal candidate for pre- and post-synthetic design of magnetism in
two-dimensional materials.",2211.02788v1
2023-02-07,Masterthesis: Ab Initio Magnetic Properties of Rare-Earth Lean Nd-based Hard Magnets,"Due to the resource criticality of rare-earths (RE), an alternative to the
well-known Nd$_2$Fe$_{14}$B magnets with a lower amount of critical elements is
required. In this work, density functional theory (DFT) calculations to
investigate the influence of partial Nd substitution with more abundant
elements (X: Y and Ce) in ThMn$_{12}$-type (Nd,X)Fe$_{11}$Ti compounds were
performed. In order to have a systematic understanding, the intrinsic magnetic
properties such as the saturation magnetization $M_S$, Curie temperature $T_C$
and magnetocrystalline anisotropy energy, are screened starting from binaries
RFe$_{12}$ (R: Y, Ce and Nd), and only considering the spin magnetic
contribution in case of the $f$ electrons. Ti is considered for the
thermodynamic stabilization and different concentrations of Ti are taken into
account for ternaries RFe$_{12-y}$Ti$_y$ and quaternaries
(Nd,X)Fe$_{12-y}$Ti$_y$ (0.5$\le$ $y$ $\le$1). In addition, the effect of
nitrogenation is examined for each considered compound. In case of
(Nd,Y)Fe$_{11}$Ti, $|BH|$$_{max}$ is found to be 384 kJ/m$^3$ and $T_C$ is
calculated to be 595 K. Similarly, $|BH|$$_{max}$ and $T_C$ are calculated to
be 365 kJ/m$^3$ and 593 K for (Nd,Ce)Fe$_{11}$Ti magnet, respectively. Both 50
% Nd-lean magnets exhibit higher $|BH|$$_{max}$ compared to Sm$_2$Co$_{17}$ and
$T_C$ than Nd$_2$Fe$_{14}$B. For both cases, the theoretical magnetic hardness
factor $\kappa$ is calculated to be 1.20, which qualifies them as good
candidates for RE-lean permanent magnets.",2302.03417v1
2023-05-29,"Structural, Optical and Single-domain Magnetic Features of the Noncollinear Ferrimagnetic Nano-spinel Chromites ACr$_2$O$_4$ (A = Ni, Co, and Mn)","Spinel chromites ACr$_2$O$_4$ with inherent magnetic geometrical frustration
usually exhibit a noncollinear ferrimagnetic ground state when A are magnetic
ions, with possibly crystallite-size dependent intriguing magnetic features.
Here, we report single-domain magnetic properties of ACr$_2$O$_4$ (A = Ni, Co,
and Mn) nanocrystals, with an average crystallite size of 18, 15 and 10 nm,
exhibiting an optical energy gap of 2.87, 3.05 and 2.9 eV, respectively. The
temperature dependence of magnetization indicates the main bulk magnetic
transitions with a commonly coexisting spin-glass-like state and finite-size
effects on the noncolinear ferrimagnetic transitions. An anomaly observed at Ts
= 15, 24 and 10 K is attributed to the bulk magnetic transition to a canted
antiferromagnetic state in NiCr$_2$O$_4$ and incommensurate spiral orders in
CoCr$_2$O$_4$ and MnCr$_2$O$_4$ NCs, respectively. A further bulk magnetic
transition to a commensurate spiral order is observed for CoCr$_2$O$_4$ NCs at
a lock-in temperature Tl = 5 K much lower than that reported using bulk
samples, while it is completely suppressed in the MnCr$_2$O$_4$ NCs.
Finite-size effects and single-domain magnetic behaviors indicated by anomalous
temperature-dependences of the coercive field and the hysteresis-loop
squareness, mainly driven by a magnetocrystalline anisotropy, are discussed in
comparison to results reported using bulk counterparts.",2305.17856v1
2023-07-20,Stray magnetic field imaging of thin exfoliated iron halides flakes,"Magnetic van der Waals materials are often proposed for use in future
spintronic devices, aiming to leverage the combination of long-range magnetic
order and near-atomic thinness to produce energy-efficient components. One
class of material that has been discussed in this context are the iron halides
FeCl$_2$ and FeBr$_2$, which are A-type antiferromagnets with strong uniaxial
magnetocrystalline anisotropy. However, despite characterization of the bulk
materials, the possibility for sustaining the magnetic behaviors that would
underpin such applications in thin flakes has not been investigated. In this
work, we use nitrogen-vacancy (NV) center microscopy to quantitatively image
magnetism in individual exfoliated flakes of these iron halides, revealing the
absence of magnetic remanence, a weak induced magnetization under bias field
and variable behavior versus temperature. We show that our results are
consistent with the antiferromagnetic behavior of the bulk material with a soft
ferromagnetic uncompensated layer, indicating that extended ($>1~\mu$m)
ferromagnetic domains are not sustained even at low temperatures (down to 4 K).
Finally, we find that the magnetic order is strongly affected by the sample
preparation, with a surprising diamagnetic order observed in a thin, hydrated
sample.",2307.10561v1
2023-07-28,Magnetic Antiskyrmions in Two-Dimensional van der Waals Magnets Engineered by Layer Stacking,"Magnetic skyrmions and antiskyrmions are topologically protected
quasiparticles exhibiting a whirling spin texture in real space. Antiskyrmions
offer some advantages over skyrmions as they are expected to have higher
stability and can be electrically driven with no transverse motion. However,
unlike the widely investigated skyrmions, antiskyrmions are rarely observed due
to the required anisotropic Dzyaloshinskii-Moriya interaction (DMI). Here we
propose to exploit the recently demonstrated van der Waals (vdW) assembly of
two-dimensional (2D) materials that breaks inversion symmetry and creates
conditions for anisotropic DMI. Using a 2D vdW magnet CrI${}_3$ as an example,
we demonstrate, based on density functional theory (DFT) calculations, that
this strategy is a promising platform to realize antiskyrmions. Polar layer
stacking of two centrosymmetric magnetic monolayers of CrI${}_3$ efficiently
lowers the symmetry, resulting in anisotropic DMI that supports antiskyrmions.
The DMI is reversible by switching the ferroelectric polarization inherited
from the polar layer stacking, offering the control of antiskyrmions by an
electric field. Furthermore, we find that the magnetocrystalline anisotropy and
DMI of CrI${}_3$ can be efficiently modulated by Mn doping, creating a
possibility to control the size of antiskyrmions. Using atomistic spin dynamics
simulations with the parameters obtained from our DFT calculations, we predict
the formation of antiskyrmions in a Cr${}_{0.88}$Mn${}_{0.12}$I${}_3$ bilayer
and switching their spin texture with polarization reversal. Our results open a
new direction to generate and control magnetic antiskyrmions in 2D vdW magnetic
systems.",2307.15769v1
2023-09-16,Strain tuned magnetotransport of Jeff=1/2 antiferromagnetic Sr2IrO4 thin films,"In this work, we report observation of strain effect on physical properties
of Sr2IrO4 thin films grown on SrTiO3 (001) and LaAlO3 (001) substrates. It is
found that the film on LaAlO3 with compressive strain has a lower
antiferromagnetic transition temperature (TN~210 K) than the film on SrTiO3
(TN~230 K) with tensile strain, which is probably caused by modified interlayer
coupling. Interestingly, magnetoresistance due to pseudospin-flip of the film
on LaAlO3 is much larger than that of tensile-strained film on SrTiO3, and
robust anisotropic magnetoresistance is observed in the former, but H-driven
reversal behavior is seen in the latter. By performing first principles
calculations, it is revealed that epitaxial strain plays an efficient role in
tuning the canting angle of Jeff=1/2 moments and thus net moment at every IrO2
layer, responsible for the difference in magnetoresistance between the films.
The reversal of anisotropic magnetoresistance in the thin film on SrTiO3 can be
ascribed to stabilization of a metastable stable with smaller bandgap as the
Jeff=1/2 moments are aligned along the diagonal of basal plane by H. However,
theoretical calculations reveal much higher magnetocrystalline anisotropy
energy in the film on LaAlO3. This causes difficulties to drive the Jeff=1/2
moments to reach the diagonal and thereby the metastable state, explaining the
distinct anisotropic magnetoresistance between two samples in a qualitative
sense. Our findings indicate that strain can be a highly efficient mean to
engineer the functionalities of Jeff=1/2 antiferromagnet Sr2IrO4.",2309.08981v1
2024-01-10,Observation of correlation induced metal to half-metal phase transition and large orbital moment in $\mathrm{Sr_2CoO_4}$,"We present a detailed mean-field study to address the fundamental discrepancy
in the ground state magnetization of $\mathrm{Sr_{2}CoO_{4}}$ (SCO). In
contrast to the ferromagnetic metallic ground state obtained from density
functional theory (DFT), DFT+$U$ gives three ferromagnetic solutions converging
to integer moment values (1, 2 \& 3 $\mu_B$/f.u) over a range of $U$.
Interestingly, two of the solutions are found to exhibit half-metallicity with
correspondingly $S$=1/2 and S=3/2 spin states. The half-metallic ferromagnetic
state with $S$=3/2 is found to be the ground state solution for SCO. Co atoms
show a large deviation from the formal +4 oxidation state indicating the
presence of strong covalency effects. Our results suggest a plausible metal to
half-metal phase transition around $U$($J$)=4.4(1.16) eV. The Fermi surface
study shows gradual collapse in states leading to half-metallicity suggesting
\textit{\textbf{k}}-dependence of effective $U$ around the critical region.
Surprisingly, in the presence of spin-orbit coupling (SOC), unexpectedly large
orbital moment ($L_{z}$=0.6) is noted in SCO putting it among the class of 3$d$
based transition metal compounds exhibiting pronounced orbital magnetization.
The calculations give large magnetocrystalline anisotropy energy (MAE) of
$\sim$48 meV. Large values of orbital magnetic moment contribution and MAE, in
the presence of strong correlation effects, provide a better interpretation of
experimental magnetization observed in SCO.",2401.05149v1
2024-03-27,"$J_{eff}$ states in a quasi one dimensional antiferromagnetic spin chain hexagonal Iridates Sr$_3$MIrO$_6$ (M=Mg, Zn, Cd): an $ab-initio$ comparative perspective","We employ first-principles density-functional theory, to perform a
comparative investigation of the effect of the spin-orbit coupling (SOC) on the
electronic and magnetic properties of three experimentally synthesized and
characterized hexagonal perovskites Sr$_3$MIrO$_6$(M=Mg, Zn, Cd). The
electronic structure calculations show that in all the compounds, Ir is the
only magnetically active site in +4[5$d^5$] configuration, whereas M$^{+2}$
(M=Cd, Zn, Mg), remains in nonmagnetic states with Cd/Zn and Mg featuring
$d^{10}$ and $d^{0}$ electronic configurations, respectively. The insulating
gap could be opened by switching on the correlation parameter $U$ for
Sr$_3$CdrO$_6$ and Sr$_3$ZnIrO$_6$ which qualifies it to be a correlated Mott
insulator. However, in the case of Sr$_3$MgIrO$_6$ both $U$ and
antiferromagnetic ordering is not enough and the gap could only be opened by
including the SOC which classifies it to fall under the category of a typical
SOC Mott insulator. The $j_{eff}$ states are visualized from the orbital
projected band structure. The magnetism is studied from the point of view of
exchange interactions and magnetocrystalline anisotropy in the presence of the
SOC. We also present the comparative analysis of the renormalized impact of SOC
on the three compounds, which shows that all the three compounds fall under the
$intermediate$ coupling regime, where Sr$_3$MgIrO$_6$ is comparatively closer
to the atomic $j_{eff}=\frac{1}{2}$ picture from the others.",2403.18408v1
2011-07-16,Intrinsic anomalous Hall effect in nickel: An GGA+U study,"The electronic structure and intrinsic anomalous Hall conductivity of nickel
have been calculated based on the generalized gradient approximation (GGA) plus
on-site Coulomb interaction (GGA+U) scheme. It is found that the intrinsic
anomalous Hall conductivity ($\sigma_{xy}^H$) obtained from the GGA+U
calculations with $U = 1.9$ eV and $J=1.2$ eV, is in nearly perfect agreement
with that measured recently at low temperatures while, in contrast, the
$\sigma_{xy}^H$ from the GGA calculations is about 100% larger than the
measured one. This indicates that, as for the other spin-orbit interaction
(SOI)-induced phenomena in 3$d$ itinerant magnets such as the orbital magnetic
magnetization and magnetocrystalline anisotropy, the on-site electron-electron
correlation, though moderate only, should be taken into account properly in
order to get the correct anomalous Hall conductivity. The intrinsic
$\sigma_{xy}^H$ and the number of valence electrons ($N_e$) have also been
calculated as a function of the Fermi energy ($E_F$). A sign change is
predicted at $E_F = -0.38$ eV ($N_e = 9.57$), and this explain qualitatively
why the theoretical and experimental $\sigma_{xy}^H$ values for Fe and Co are
positive. It is also predicted that fcc Ni$_{(1-x)}$Co(Fe,Cu)$_x$ alloys with
$x$ being small, would also have the negative $\sigma_{xy}^H$ with the
magnitude being in the range of $500\sim 1400$ $\Omega^{-1}$cm$^{-1}$. The most
pronounced effect of including the on-site Coulomb interaction is that all the
$d$-dominant bands are lowered in energy relative to the $E_F$ by about 0.3 eV,
and consequently, the small minority spin X$_2$ hole pocket disappears. The
presence of the small X$_2$ hole pocket in the GGA calculations is attributed
to be responsible for the large discrepancy in the $\sigma_{xy}^H$ between
theory and experiment.",1107.3242v2
2016-04-28,Dynamics of skyrmionic states in confined helimagnetic nanostructures,"In confined helimagnetic nanostructures, skyrmionic states in the form of
incomplete and isolated skyrmion states can emerge as the ground state in
absence of both external magnetic field and magnetocrystalline anisotropy. In
this work, we study the dynamic properties (resonance frequencies and
corresponding eigenmodes) of skyrmionic states in thin film FeGe disk samples.
We employ two different methods in finite-element based micromagnetic
simulation: eigenvalue and ringdown method. The eigenvalue method allows us to
identify all resonance frequencies and corresponding eigenmodes that can exist
in the simulated system. However, using a particular experimentally feasible
excitation can excite only a limited set of eigenmodes. Because of that, we
perform ringdown simulations that resemble the experimental setup using both
in-plane and out-of-plane excitations. In addition, we report the nonlinear
dependence of resonance frequencies on the external magnetic bias field and
disk sample diameter and discuss the possible reversal mode of skyrmionic
states. We compare the power spectral densities of incomplete skyrmion and
isolated skyrmion states and observe several key differences that can
contribute to the experimental identification of the state present in the
sample. We measure the FeGe Gilbert damping, and using its value we determine
what eigenmodes can be expected to be observed in experiments. Finally, we show
that neglecting the demagnetisation energy contribution or ignoring the
magnetisation variation in the out-of-film direction - although not changing
the eigenmode's magnetisation dynamics significantly - changes their resonance
frequencies substantially. Apart from contributing to the understanding of
skyrmionic states physics, this systematic work can be used as a guide for the
experimental identification of skyrmionic states in confined helimagnetic
nanostructures.",1604.08347v2
2018-12-26,"Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: the role of dispersion, nonlinearity, and damping","Nonlocal compensation of magnetic damping by spin injection has been
theoretically shown to establish dynamic, noncollinear magnetization states
that carry spin currents over micrometer distances. Such states can be
generically referred to as dissipative exchange flows (DEFs) because spatially
diffusing spin currents are established by the mutual exchange torque exerted
by neighboring spins. Analytical studies to date have been limited to the weak
spin injection assumption whereby the equation of motion for the magnetization
is mapped to hydrodynamic equations describing spin flow and then linearized.
Here, we analytically and numerically study easy-plane ferromagnetic channels
subject to spin injection of arbitrary strength at one extremum under a unified
hydrodynamic framework. We find that DEFs generally exhibit a nonlinear profile
along the channel accompanied by a nonlinear frequency tuneability. At large
injection strengths, we fully characterize a novel magnetization state we call
a contact-soliton DEF (CS-DEF) composed of a stationary soliton at the
injection site, which smoothly transitions into a DEF and exhibits a negative
frequency tuneability. The transition between a DEF and a CS-DEF occurs at the
maximum precessional frequency and coincides with the Landau criterion: a
subsonic to supersonic flow transition. Leveraging the hydraulic-electrical
analogy, the current-voltage characteristics of a nonlinear DEF circuit are
presented. Micromagnetic simulations of nanowires that include
magnetocrystalline anisotropy and non-local dipole fields are in qualitative
agreement with the analytical results. The magnetization states found here
along with their characteristic profile and spectral features provide
quantitative guidelines to pursue an experimental demonstration of DEFs in
ferromagnetic materials and establishes a unified description for long-distance
spin transport.",1812.10438v3
2019-12-07,Suppression of the skyrmion Hall effect in planar nanomagnets by the magnetic properties engineering: Skyrmion transport on nanotracks with magnetic strips,"Micromagnetic simulations have been performed to investigate the suppression
of the skyrmion Hall effect in nanotracks with their magnetic properties
strategically modified. In particular, we study two categories of magnetically
modified nanotracks. One of them, repulsive edges have been inserted in the
nanotrack and, in the other, an attractive strip has been placed exactly on the
longest axis of the nanotrack. Attractive and repulsive interactions can be
generated from the engineering of magnetic properties. For instance, it is
known that the skyrmion can be attracted to a region where the exchange
stiffness constant is decreased. On the other hand, the skyrmion can be
repelled from a region characterized by a local increase in the exchange
stiffness constant. In order to provide a background for experimental studies,
we vary not only the magnetic material parameters (exchange stiffness,
perpendicular magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya
constant) but also the width of the region magnetically modified, containing
either a local reduction or a local increase for each one of these magnetic
properties. In the numerical simulations, the skyrmion motion was induced by a
spin-polarized current and the found results indicate that it is possible to
transport skyrmions around the longest axis of the nanotrack. In practice, the
skyrmion Hall effect can be completely suppressed in magnetic nanotracks with
strategically modified magnetic properties. Furthermore, we discuss in detail 6
ways to suppress the skyrmion Hall effect by the usage of nanotracks with
repulsive edges and nanotracks with an attractive strip.",1912.03403v2
2019-12-07,Tailoring magnetic interactions in atomic bilayers of Rh and Fe on Re(0001),"Using density functional theory, we investigate the interplay between the
stacking order and sequence of bilayers composed of an Fe and a Rh layer on the
Re(0001) and their magnetic properties. We find that fcc/ffc stacked bilayers
are energetically very unfavorable, while all other combinations of hcp and fcc
stacking are energetically close. The magnetic interactions are evaluated by
mapping the DFT total energies onto a spin model, which contains Heisenberg
exchange, Dzyaloshinskii-Moriya interaction, the magnetocrystalline anisotropy
energy, and higher-order exchange interactions. We find that the stacking
sequence of the bilayer significantly modifies the magnetic interactions. As a
result, we find a DMI driven cycloidal spin spiral ground state with a period
of 11~nm for hcp-Fe/hcp-Rh. For fcc-Fe/hcp-Rh and hcp-Fe/fcc-Rh, we obtain a
ferromagnetic ground state. The spin spiral energy dispersion of hcp-Fe/hcp-Rh
including spin-orbit coupling suggests that isolated skyrmions can be
stabilized in the field-polarized ferromagnetic background at external magnetic
fields. If the Fe layer is sandwiched between the Rh overlayer and the Re(0001)
substrate, there is a competition between the ferromagnetic coupling preferred
by the Rh-Fe hybridization and the antiferromagnetic coupling induced by the
Fe-Re hybridization. Due to the Fe/Re interface the DMI can become very large.
For fcc-Rh/hcp-Fe, we obtain a cycloidal spin spiral with a period of 1.7~nm
which is induced by frustration of exchange interactions and further stabilized
by the DMI. For hcp-Rh/hcp-Fe, we find a DMI driven cycloidal spin spiral with
a period of 4~nm and locally nearly antiparallel magnetic moments due to
antiferromagnetic nearest-neighbor exchange. The higher-order exchange
constants can be significant in the considered films, however, they do not
stabilize multi-$Q$ states.",1912.03465v2
2019-12-20,Spontaneous and externally driven quantum spin fluctuations of 3d and 4d single atoms adsorbed on graphene,"At the heart of current information nanotechnology lies the search for ideal
platforms hosting the smallest possible magnets, i.e. single atoms with
magnetic moments pointing out-of-plane, as requested in a binary-type of
memory. For this purpose, a 2D material such as graphene would be an ideal
substrate thanks to its intrinsic low electron and phonon densities, as well as
its 6-fold symmetry. Here we investigate, from first-principles, a fundamental
mechanism detrimental for the magnetic stability: the zero-point
spin-fluctuations modifying the effective energy landscape perceived by the
local spin moments of 3$d$ and 4$d$ transition metal atoms deposited on a free
standing graphene. Utilizing time-dependent density functional theory and by
virtue of the fluctuation-dissipation theorem, these spontaneous quantum
fluctuations are found to be negligible for most of the 3$d$ elements, in
strong contrast to the 4$d$ atoms. Surprisingly, we find that such fluctuations
can promote the magnetic stability by switching the easy direction of the
magnetic moment of Tc from being initially in-plane to out-of-plane. The
adatom-graphene complex gives rise to impurity states settling in some cases
the magnetocrystalline anisotropy energy --- the quantity that defines the
energy barrier protecting the magnetic moments and, consequently, the
spin-excitation behavior detectable with inelastic scanning tunneling
spectroscopy. A detailed analysis is provided on the impact of electron-hole
excitations, damping and lifetime of the spin-excitations on the dynamical
behavior of the adsorbed magnetic moments on graphene.",1912.09938v1
2020-10-22,"Structure, magnetism and electronic properties in 3$d$-5$d$ based double perovskite (Sr$_{1-x}$Ca$_x$)$_2$FeIrO$_6$ (0 $\leq$ $x$ $\leq$ 1): A combined experimental and theoretical investigation","The 3$d$-5$d$ based double perovskites offer an ideal playground to study the
interplay between electron correlation ($U$) and spin-orbit coupling (SOC)
effect, showing exotic physics. The Sr$_2$FeIrO$_6$ is an interesting member in
this family with ionic distribution of Fe$^{3+}$ (3$d^5$) and Ir$^{5+}$
(5$d^4$) where the later is believed to be nonmagnetic under the picture of
strong SOC. Here, we report detailed investigation of structural, magnetic and
electronic transport properties along with electronic structure calculations in
(Sr$_{1-x}$Ca$_x$)$_2$FeIrO$_6$ series with $x$ from 0 to 1. While the basic
interactions such as, $U$ and SOC are unlikely to be modified but a structural
modification is expected due to ionic size difference between Sr$^{2+}$ and
Ca$^{2+}$ which would influence other properties such as crystal field effect
and band widths. While a nonmonotonic changes in lattice parameters are
observed across the series, the spectroscopic investigations reveal that 3+/5+
charge state of Fe/Ir continue till end of the series. An analysis of magnetic
data suggests similar nonmonotonic evolution of magnetic parameters with
doping. Temperature dependent crystal structure as well as low temperature (5
K) magnetic structure have been determined from neutron powder diffraction
measurements. The whole series shows insulating behavior. The electronic
structure calculations show, SOC enhanced, a noncollinear antiferromagnetic and
Mott-type insulating state is the stable ground state for present series with a
substantial amount of orbital moment, but less than the spin magnetic moment,
at the Ir site and the magnetocrystalline anisotropy. The obtained results
imply that the Ca$^{2+}$ has large influence on the magnetic and transport
properties, further showing a large agreement between experimental results as
well as theoretical calculations.",2010.11412v1
2021-01-03,Magnetic surface reconstruction in the van-der-Waals antiferromagnet Fe$_{1+x}$Te,"Fe$_{1+x}$Te is a two dimensional van der Waals antiferromagnet that becomes
superconducting on anion substitution on the Te site. The parent phase of
Fe$_{1+x}$Te is sensitive to the amount of interstitial iron situated between
the iron-tellurium layers displaying collinear magnetic order coexisting with
low temperature metallic resistivity for small concentrations of interstitial
iron $x$ and helical magnetic order for large values of $x$. While this phase
diagram has been established through scattering [see for example E. E.
Rodriguez $\textit{et al.}$ Phys. Rev. B ${\bf{84}}$, 064403 (2011) and S.
R\""ossler $\textit{et al.}$ Phys. Rev. B ${\bf{84}}$, 174506 (2011)], recent
scanning tunnelling microscopy measurements [C. Trainer $\textit{et al.}$ Sci.
Adv. ${\bf{5}}$, eaav3478 (2019)] have observed a different magnetic structure
for small interstitial iron concentrations $x$ with a significant canting of
the magnetic moments along the crystallographic $c$ axis of $\theta$=28 $\pm$
3$^{\circ}$. In this paper, we revisit the magnetic structure of Fe$_{1.09}$Te
using spherical neutron polarimetry and scanning tunnelling microscopy to
search for this canting in the bulk phase and compare surface and bulk
magnetism. The results show that the bulk magnetic structure of Fe$_{1.09}$Te
is consistent with collinear in-plane order ($\theta=0$ with an error of $\sim$
5$^{\circ}$). Comparison with scanning tunnelling microscopy on a series of
Fe$_{1+x}$Te samples reveals that the surface exhibits a magnetic surface
reconstruction with a canting angle of the spins of $\theta=29.8^{\circ}$. We
suggest that this is a consequence of structural relaxation of the surface
layer resulting in an out-of-plane magnetocrystalline anisotropy. The magnetism
in Fe$_{1+x}$Te displays different properties at the surface when the symmetry
constraints of the bulk are removed.",2101.00569v1
2021-04-06,Magnetic imaging and statistical analysis of the metamagnetic phase transition of FeRh with electron spins in diamond,"Magnetic imaging based on nitrogen-vacancy (NV) centers in diamond has
emerged as a powerful tool for probing magnetic phenomena in fields ranging
from biology to physics. A key strength of NV sensing is its local-probe
nature, enabling high-resolution spatial images of magnetic stray fields
emanating from a sample. However, this local character can also form a drawback
for analysing the global properties of a system, such as a phase transition
temperature. Here, we address this challenge by using statistical analyses of
magnetic-field maps to characterize the first-order temperature-driven
metamagnetic phase transition from the antiferromagnetic to the ferromagnetic
state in FeRh. After imaging the phase transition and identifying the regimes
of nucleation, growth, and coalescence of ferromagnetic domains, we
statistically characterize the spatial magnetic-field maps to extract the
transition temperature and thermal hysteresis width. By analysing the spatial
correlations of the maps and their dependence on an external magnetic field, we
investigate the magnetocrystalline anisotropy and detect a reorientation of
domain walls across the phase transition. The employed statistical approach can
be extended to the study of other magnetic phenomena with NV magnetometry or
other sensing techniques.",2104.02814v1
2021-04-28,Structural transformation and magnetic properties of (Fe$_{0.7}$Co$_{0.3}$)$_2$B alloys doped with 5$d$ elements: A combined first-principles and experimental study,"(Fe,Co)$_2$B-based compounds with specified 5$d$ substitutions are considered
as promising materials for permanent magnets without rare-earth elements. We
conducted a combined first-principles and experimental study focused on
(Fe$_{0.7}$Co$_{0.3}$)$_2$B alloys doped with W and Re. First, we used
full-potential local-orbital scheme to systematically investigate (Fe,Co)$_2$B
alloys with 3$d$, 4$d$, and 5$d$ substitutions. Computational analyses showed a
significant increase in magnetocrystalline anisotropy only for the Re doped
sample. Simultaneously, the structural and magnetic properties of the
(Fe$_{0.7-x}$Co$_{0.3-x}$M$_{2x}$)$_2$B ($M$ = W, Re; $x$ = 0, 0.025) alloys
were investigated experimentally. The desired (Fe,Co)$_2$B tetragonal phase was
synthesized by heat treatment of amorphous precursors. We observed that
isothermal annealing increases the coercive field of all samples. However, the
obtained values, without further optimization, are well below the threshold for
permanent magnet applications. Nevertheless, annealing of substituted samples
at 750$^o$C significantly improves saturation magnetization values.
Furthermore, M\""{o}ssbauer spectroscopy revealed a reduction of the hyperfine
field due to the presence of Co atoms in the (Fe,Co)$_2$B phase, where
additional defect positions are formed by Re and W. Radio-frequency
M\""{o}ssbauer studies showed that (Fe$_{0.7}$Co$_{0.3}$)$_2$B and the
W-substituted sample began to crystallize when exposed to an radio frequency
field of 12 Oe, indicating that the amorphous phase is stabilized by Re
substitution. Improvement of thermal stability of
(Fe$_{0.675}$Co$_{0.275}$Re$_{0.05}$)$_2$B alloy is consistent with the results
of differential scanning calorimetry and thermomagnetic measurements.",2104.13724v2
2022-07-22,FORC Diagram Features of Co Particles due to Reversal by Domain Nucleation,"First Order Reversal Curve (FORC) diagrams are a popular tool in geophysics
and materials science for the characterization of magnetic particles of natural
and synthetic origin. However, there is still a lot of controversy about the
rigorous interpretation of the origin of certain features in a FORC diagram. In
this study, we analyze FORCs computed by micromagnetic simulations of Co cubes
with dimensions of 50, 100 and 150 nm and uniaxial magnetocrystalline
anisotropy. For the larger cubes we observe the formation of a stable
two-domain state. The nucleation of a reversed domain and its subsequent
annihilation are clearly visible as separate peaks in the FORC diagram. They
spread out along the coordinate axis in the FORC diagram, which is associated
with the bias field $H_U$ of a Preisach hysteron. Based on our findings, we
state that a FORC diagram peak spreading along the $H_U$ axis can have its
origin in the step-wise magnetization reversal driven by nucleation of domains
in a single particle. This means that we have identified another mechanism
apart from the well-known magnetostatic interaction between a set of particles
that leads to features in the FORC diagram extending along the $H_U$-axis. Our
study demonstrates that if FORCs shall be used as a quantitative tool to assess
the microstructure of samples containing magnetic material, more information
from other methods will be required to identify the correct physical mechanism
by which a certain ""fingerprint"" in a FORC diagram is produced.",2207.11011v1
2022-10-27,Tuning the magnetic interactions in van der Waals Fe$_3$GeTe$_2$ heterostructures: A comparative study of \textit{ab initio} methods,"We investigate the impact of mechanical strain, stacking order, and external
electric fields on the magnetic interactions of a two-dimensional (2D) van der
Waals (vdW) heterostructure in which a 2D ferromagnetic metallic Fe$_3$GeTe$_2$
monolayer is deposited on germanene. Three distinct computational approaches
based on \textit{ab initio} methods are used, and a careful comparison is
given: (i) The Green's function method, (ii) the generalized Bloch theorem, and
(iii) the supercell approach. First, the shell-resolved exchange constants are
calculated for the three Fe atoms within the unit cell of the freestanding
Fe$_3$GeTe$_2$ monolayer. We find that the results between methods (i) and (ii)
are in good qualitative agreement and also with previously reported values. An
electric field of ${\cal E}= \pm 0.5$~V/{\AA} applied perpendicular to the
Fe$_3$GeTe$_2$/germanene heterostructure leads to significant changes of the
exchange constants. We show that the Dzyaloshinskii-Moriya interaction (DMI) in
Fe$_3$GeTe$_2$/germanene is mainly dominated by the nearest neighbors,
resulting in a good quantitative agreement between methods (i) and (ii).
Furthermore, we demonstrate that the DMI is highly tunable by strain, stacking,
and electric field, leading to a large DMI comparable to that of
ferromagnetic/heavy metal (FM/HM) interfaces. The geometrical change and
hybridization effect explain the origin of the high tunability of the DMI at
the interface. The electric-field driven DMI obtained by method (iii) is in
qualitative agreement with the more accurate \textit{ab initio} method used in
approach (ii). However, the field-effect on the DMI is overestimated by method
(iii) by about 50\%. The magnetocrystalline anisotropy energy can also be
drastically changed by the application of compressive or tensile strain in the
Fe$_3$GeTe$_2$/germanene heterostructure.",2210.15351v2
2022-11-28,Orbital-selective Mott phase and spin nematicity in Ni-substituted FeTe$_{0.65}$Se$_{0.35}$ single crystals,"The normal state in iron chalcogenides is metallic but highly unusual, with
orbital and spin degrees of freedom partially itinerant or localized depending
on temperature, leading to many unusual features. In this work, we report on
the observations of two of such features, the orbital selective Mott phase
(OSMP) and spin nematicity, evidenced in magnetization and magnetotransport
[resistivity, Hall effect, anisotropic magnetoresistance (AMR)] of
Fe$_{1-y}$Ni$_y$Te$_{0.65}$Se$_{0.35}$ single crystals, with $0 < y < 0.21$.
Substitution of Ni dopes crystals with electrons, what eliminates some of the
hole pockets from Fermi level, leaving only one, originating from $d_{xy}$
orbital. This leads to electron-dominated conduction at low $T$ for $y \gtrsim
0.06$. However, at high temperatures, $T \gtrsim 125 \div 178$ K, the
conduction reverses to hole-dominated. Anomalies in magnetization and
resistivity are observed at temperatures which approach high-$T$ boundary of
the electron-dominated region. Analysis of these effects suggests a link with
the appearance of the $d_{z^2}$ hole pockets at X points of the Brillouin zone
in the OSMP phase, facilitated by the localization of $d_{xy}$ orbital, as
recently reported by angular resolved photoemission experiments ($\textit{J.
Huang et al., Commun. Phys. 5, 29 (2022)}$). The low-$T$ AMR shows mixed 4-fold
and 2-fold rotational symmetry of in-plane magnetocrystalline anisotropy, with
the 4-fold term the largest at small $y$, and suppressed at intermediate $y$.
These results are consistent with the mixed stripe/bicollinear magnetic
correlations at small $y$, and suppression of stripe correlations at
intermediate $y$, indicating development of spin nematicity with increasing Ni
doping, which possibly contributes to the suppression of superconductivity.",2211.15189v3
2023-06-16,Tailoring defects and nanocrystal transformation for optimal heating power in bimagnetic $Co_yFe_{1-y}O@Co_xFe_{3-x}O_4$ particles,"The effects of cobalt incorporation in spherical heterostructured iron oxide
nanocrystals (NCs) of sub-critical size have been explored by colloidal
chemistry methods. Synchrotron X-ray total scattering methods suggest that
cobalt (Co) substitution in rock salt iron oxide NCs tends to remedy its vacant
iron sites, offering a higher degree of resistance to oxidative conversion.
Self-passivation still creates a spinel-like shell, but with higher volume
fraction of the rock salt Co-containing phase in the core. The higher divalent
metal stoichiometry in the rock salt phase, with increasing Co content, results
in a population of unoccupied tetrahedral metal sites in the spinel part,
likely through oxidative shell creation, involving an ordered defect-clustering
mechanism, directly correlated to the core stabilization. To shed light on the
effects of Co-substitution and atomic-scale defects (vacant sites), Monte Carlo
simulations suggest that designed NCs, with desirable, enhanced magnetic
properties (cf. exchange bias and coercivity), are developed with
magnetocrystalline anisotropy raised at relatively low content of Co ions in
the lattice. Growth of optimally performing candidates combines also a strongly
exchange-coupled system, secured through a high volumetric ratio rock salt
phase, interfaced by a not so defective spinel shell. In view of these
requirements, Specific Absorption Rate (SAR) calculations demonstrate that the
sufficiently protected from oxidation rock salt core and preserved over time
heterostructure, play a key role in magnetically-mediated heating efficacies,
for potential use of such NCs in magnetic hyperthermia applications.",2306.09684v1
2023-07-11,Structural and magnetic properties of Fe-Co-C alloys with tetragonal deformation: a first-principle study,"Fe-Co alloys with induced tetragonal strain are promising materials for
rare-earth-free permanent magnets. However, as ultrathin-film studies have
shown, tetragonal Fe-Co structures tend to a rapid relaxation toward a cubic
structure as the thickness of the deposited film increases. One of the main
methods of inducing the stable strain in the bulk material is interstitial
doping with small atoms, like B, C, or N. In this work, we present a full
configuration space analysis in density functional theory approach for
(Fe$_{1-x}$Co$_x$)$_{16}$C supercells with a single C impurity in one of the
octahedral interstitial positions and for the full range of Co concentrations
$x$. We discuss all assumptions and considerations leading to calculated
lattice parameters, mixing enthalpies, magnetic moments, and averaged
magnetocrystalline anisotropy energies (MAE). We present a comprehensive
qualitative analysis of the structural and magnetic properties' dependence on
short- and long-range ordering parameters. We analyzed all unique Fe/Co atoms
occupancies at all stoichiometric concentrations possible in 2x2x2 supercell
based on 2-atom tetragonal representation. We rely on the thermodynamic
averaging method and large sample count to obtain accurate MAE values. We
reevaluate several chemical disorder approximation methods, including effective
medium methods (virtual crystal approximation and coherent potential
approximation) and special quasirandom structures method applied to Fe-Co-based
alloys. We observe a structural phase transition from the body-centered
tetragonal structure above 70% Co concentration and confirm the structural
stability of Fe-Co-C alloys in the tetragonal range. We show the presence of a
broad MAE maximum of around 50% Co concentration and notably high MAE values
for Co content $x$ as low as 25%. In addition, we show a positive correlation
between MAE and mixing enthalpy.",2307.05709v1
2023-12-07,Tuning magnetic interactions of Co and 4$d$ transition-metal atomic bilayers on Re(0001) via interface engineering,"Employing $\textit{ab-initio}$ density functional theory (DFT), we performed
a systematic investigation of the electronic structures and the magnetic
properties of atomic bilayers composed of a 4$d$ transition-metal layer (Rh, Pd
and Ru) and a Co layer on the Re(0001) surface. Our DFT calculations reveal the
influence of the bilayer composition and their stacking sequence on the
magnetic ground state and magnetic interactions. We obtain the magnetic
interactions by mapping the total energies onto an effective spin Hamiltonian
which contains the exchange interaction and the Dzyaloshinskii-Moriya
interaction (DMI) as well as the magnetocrystalline anisotropy energy (MAE). We
observe noticeable changes in bilayer hybridization due to variation in bilayer
composition and overlayer symmetry, leading to significant variation in
magnetic interactions. In all considered systems, the nearest-neighbor exchange
interaction is ferromagnetic, however, the value varies by up to a factor of 5.
The effective, nearest-neighbor DMI constant exhibits variation in sign over
the films considered, favoring either right- (clockwise) or left-handed
(anticlockwise) cycloidal spin spirals. The value of the DMI changes by up to a
factor of 27 among the films. For most of the systems, the MAE favors an
out-of-plane easy magnetization axis, however, for hcp-Co/Rh and hcp-Co/Ru
bilayers on Re(0001), it prefers an in-plane magnetization axis. The magnitude
of the MAE varies from a small value of about 0.1 meV/Co atom up to about 2
meV/Co atom for Co/Pd bilayers. The spin spiral energy dispersion curve rises
quite quickly close to the ferromagnetic state for films in which the Co layer
is adjacent to the vacuum indicating a large effective exchange constant which
stabilizes a ferromagnetic ground state in Co/$4d$ bilayers on Re(0001).",2312.04409v1
2024-02-29,"Magnetism, heat capacity and electronic structure of EuCd$_2$P$_2$ in view of its colossal magnetoresistance","The mechanism of the peculiar transport properties around the magnetic
ordering temperature of semiconducting antiferromagnetic EuCd$_2$P$_2$ is not
yet understood. With a huge peak in the resistivity observed above the N\'eel
temperature, $T_{\rm N}=10.6\,\rm K$, it exhibits a colossal magnetoresistance
effect. Recent reports on observations of ferromagnetic contributions above
$T_{\rm N}$ as well as metallic behavior below this temperature have motivated
us to perform a comprehensive characterization of this material, including its
resistivity, heat capacity, magnetic properties and electronic structure. Our
transport measurements revealed quite different temperature dependence of
resistivity with the maximum at $14\,\rm K$ instead of previously reported
$18\,\rm K$. Low-field susceptibility data support the presence of static
ferromagnetism above $T_{\rm N}$ and show a complex behavior of the material at
small applied magnetic fields. Namely, signatures of reorientation of magnetic
domains are observed up to $T=16\,\rm K$. Our magnetization measurements
indicate a magnetocrystalline anisotropy which also leads to a preferred
alignment of the magnetic clusters above $T_{\rm N}$. The momentum-resolved
photoemission experiments at temperatures from $24\,\rm K$ down to $2.5\,\rm K$
indicate the permanent presence of a fundamental band gap without change of the
electronic structure when going through $T_N$ that is in contradiction with
previous results. We performed \textit{ab initio} band structure calculations
which are in good agreement with the measured photoemission data when assuming
an antiferromagnetic ground state. Calculations for the ferromagnetic phase
show a much smaller bandgap, indicating the importance of possible
ferromagnetic contributions for the explanation of the colossal
magnetoresistance effect in the related EuZn$_2$P$_2$.",2402.18911v1
2017-12-15,Anisotropic magneto-crystalline coupling of the skyrmion lattice in MnSi,"We investigate the anisotropic nature of magnetocrystalline coupling between
the crystallographic and skyrmion crystal (SKX) lattices in the chiral magnet
MnSi by magnetic field-angle resolved resonant ultrasound spectroscopy. Abrupt
changes are observed in the elastic moduli and attenuation when the magnetic
field is parallel to the [011] crystallographic direction. These observations
are interpreted in a phenomenological Ginzburg-Landau theory that identifies
switching of the SKX orientation to be the result of an anisotropic
magnetocrystalline coupling potential. Our paper sheds new light on the nature
of magnetocrystalline coupling potential relevant to future spintronic
applications.",1712.05479v2
1998-10-31,Charge screening and magnetic anisotropy in RCo5 compounds,"An analysis of magnetic anisotropy in RCo5 compounds is performed with
account of screening of ion point charges by conduction electrons. A crucial
role of non-uniform distribution of screening electrons (the terms containing
derivatives of charge density) is demonstrated. Influence of anisotropy of
screening, that is connected with the anisotropy of the Fermi surface, on the
magnetic anisotropy sign is discussed.",9811004v1
2008-06-03,A Theoretical Approach for Computing Magnetic Anisotropy in Single Molecule Magnets,"We present a theoretical approach to calculate the molecular magnetic
anisotropy parameters, $D_M$ and $E_M$ for single molecule magnets in any
eigenstate of the exchange Hamiltonian, treating the anisotropy Hamiltonian as
a perturbation. Neglecting inter-site dipolar interactions, we calculate
molecular magnetic anisotropy in a given total spin state from the known
single-ion anisotropies of the transition metal centers. The method is applied
to $Mn_{12}Ac$ and $Fe_8$ in their ground and first few excited eigenstates, as
an illustration. We have also studied the effect of orientation of local
anisotropies on the molecular anisotropy in various eigenstates of the exchange
Hamiltonian. We find that, in case of $Mn_{12}Ac$, the molecular anisotropy
depends strongly on the orientation of the local anisotropies and the spin of
the state. The $D_M$ value of $Mn_{12}Ac$ is almost independent of the
orientation of the local anisotropy of the core $Mn(IV)$ ions. In the case of
$Fe_8$, the dependence of molecular anisotropy on the spin of the state in
question is weaker.",0806.0432v1
2000-07-14,Determination of Azimuthal Anisotropy of Neutral Pions from the Measured Anisotropy of Photons in Ultra-relativistic Nuclear Collisions,"A method is suggested to deduce the anisotropy in neutral pions by measuring
the azimuthal anisotropy of photons in ultra-relativistic nuclear collisions.
The ratio of the estimated anisotropy in photons to the anisotropy in neutral
pions is seen to scale with a parameter which depends on photon multiplicity
and anisotropy. This parameter can be determined from experimental data.",0007016v1
2014-10-16,Anisotropy of Weakly Vibrated Granular Flows,"We experimentally probe the anisotropy of the fabric of weakly vibrated,
flowing granular media. Depending on the driving parameters --- flow rate and
vibration strength --- this anisotropy varies significantly. We show how the
anisotropy collapses when plotted as function of the driving stresses,
uncovering a direct link between stresses and anisotropy. Moreover, our data
suggests that for small anisotropies, the shear stresses vanish. Anisotropy of
the fabric of granular media thus plays a crucial role in determining the
rheology of granular flows.",1410.4335v1
2016-07-17,Magnetic anisotropy dependence of the energy of oriented thick ferromagnetic films,"Heisenberg Hamiltonian was employed to describe the variation of energy of
thick ferromagnetic films with second and fourth order anisotropies. At angle
of 1.36 degrees and anisotropies of 1.25, energy is minimum for thick film of
sc(001) with 1000 layers. Energy becomes minimum at angle of 1.18 degrees and
fourth order anisotropy of 1.15 for thick film of bcc(001) with the same
thickness. According to these simulations, these lattices can be easily
oriented in some certain directions under the influence of some particular
values of anisotropies. Energy varies with second and fourth order anisotropies
in similar passion for both types of lattices. The energy gradually decreases
with second and fourth order anisotropy for both types of lattices in the range
described here.",1611.02227v1
2021-07-26,Anisotropy of localized states in an anisotropic disordered medium,"We study Anderson localization of a scalar wave in an ensemble of resonant
point scatterers embedded in an anisotropic background medium. For uniaxial
anisotropy of moderate strength, the mobility edges and the critical exponent
of the localization transition are found to be unaffected by the anisotropy
provided that the determinant of the anisotropy tensor is kept equal to one
upon introducing the anisotropy. Localized modes have anisotropic spatial
shapes although their anisotropy is weaker than the one expected from purely
geometric considerations. The modes with the longest lifetimes are found to be
the most anisotropic and their anisotropy increases with the size of the
disordered medium.",2107.12199v1
2016-09-09,On the origin of perpendicular magnetic anisotropy in strained Fe-Co(-X) films,"Very high magnetic anisotropies have been theoretically predicted for
strained Fe-Co(-X) and indeed several experiments on epitaxial thin films
seemed to confirm strain induced anisotropy enhancement. This study presents a
critical analysis of the different contributions to perpendicular anisotropy:
volume, interface and surface anisotropies. Tracing these contributions,
thickness series of single layer films as well as multilayers with Au-Cu
buffers/interlayers of different lattice parameters have been prepared. The
analysis of their magnetic anisotropy reveals a negligible influence of the
lattice parameter of the buffer. Electronic effects, originating from both, the
Au-Cu interface and the film surface, outrange the elastic effects. Surface
anisotropy, however, exceeds the interface anisotropy by more than a factor of
three. A comparison with results from Density Functional Theory suggests, that
the experimentally observed strong perpendicular surface anisotropy originates
from a deviation from an ideal oxide-free surface. Accordingly, tailored
Fe-Co-X/oxide interfaces may open a route towards high anisotropy in rare-earth
free materials.",1609.02903v2
2016-07-17,Thick ferromagnetic films and their anisotropies as described by second order perturbed Heisenberg Hamiltonian,"Second and fourth order anisotropy dependence of energy of thick simple cubic
ferromagnetic films with 10000 layers is explained using Heisenberg Hamiltonian
with second order perturbation in this manuscript. The second and fourth order
anisotropy constants were assumed to be constants through out the film. When
the fourth order anisotropy is given by fourth order anisotropy of 6, the
sc(001) ferromagnetic thick films with 10000 layers can be easily oriented in
0.6 radians direction for the energy parameters given this report. Under the
influence of the second order anisotropy given by second order anisotropy of
6.3, the easy direction of sc(001) film with 10000 layers is given by 0.66
radians. Although the energy varies periodically in all cases, the maximum
energy considerably decreases with fourth order anisotropy constant. According
to 3-D plots, energy under influence of second order anisotropy is larger than
energy under influence of fourth order anisotropy.",1611.02228v1
2018-07-10,Modeling Molecular Magnets with Large Exchange and On-Site Anisotropies,"Spins in molecular magnets can experience both anisotropic exchange
interactions and on-site magnetic anisotropy. In this paper we study the effect
of exchange anisotropy on the molecular magnetic anisotropy both with and
without on-site anisotropy. When both the anisotropies are small, we find that
the axial anisotropy parameter $D_M$ in the effective spin Hamiltonian is the
sum of the individual contributions due to exchange and on-site anisotropies.
We find that even for axial anisotropy of about $15\%$, the low energy spectrum
does not correspond to a single parent spin manifold but has intruders states
arising from other parent spin. In this case, the low energy spectrum can not
be described by an effective Hamiltonian spanning the parent spin space. We
study the magnetic susceptibility, specific heat as a function of temperature
and magnetization as a function of applied field to characterize the system in
this limit. We find that there is synergy between the two anisotropies,
particularly for large systems with higher site spins.",1807.03500v1
2023-12-21,Effects of Heliolatitudinal Anisotropy of Solar FUV/EUV Emissions on Lyman-alpha Helioglow,"We present a study of the influence of solar UV anisotropy on the
heliospheric backscatter helioglow generated by resonant scattering of solar
Lyman-alpha photons on interstellar hydrogen atoms around the Sun. Simulations
based on the WawHelioGlow model suggest that the response of the helioglow
pole-to-ecliptic ratio to the anisotropy is linear, but 15% of the anisotropy
(polar darkening) generates 30-40% change in the ratio in the solar minimum and
15-20% in the solar maximum. We attribute this difference to an interplay
between the solar UV anisotropy and the latitudinal structure of the solar wind
in solar minima. The solar UV anisotropy also increases the helioglow intensity
from the downwind direction by 5-10%, due to the influence of the anisotropy on
the ionization losses and trajectories of atoms passing by the Sun in polar
regions. Consequently, mid-latitude regions (in the heliographic and ecliptic
coordinates) are least affected by the UV anisotropy. By comparison of the
simulation results with observations of the SOHO/SWAN satellite instrument, we
derive the day-by-day time evolution of the solar Lyman-alpha anisotropy for
the north and south poles over two solar cycles from 1996 to 2022. The inferred
anisotropy is ~5-10% in solar minima and ~15-25% in solar maxima, the northern
anisotropy being stronger than the southern. Our study suggests that in solar
minima a highly structured solar wind is associated with relatively small solar
UV anisotropy, while in solar maxima the solar wind is more isotropic but a
substantial solar UV anisotropy appears.",2312.14039v1
2006-01-25,Primordial magnetic fields and CMB anisotropies,"Possible signatures of primordial magnetic fields on the Cosmic Microwave
Background (CMB) temperature and polarization anisotropies are reviewed. The
signals that could be searched for include excess temperature anisotropies
particularly at small angular scales below the Silk damping scale, B-mode
polarization, and non-Gaussian statistics. A field at a few nG level produces
temperature anisotropies at the 5 micro Kelvin level, and B-mode polarization
anisotropies 10 times smaller, and is therefore potentially detectable via the
CMB anisotropies. An even smaller field, with B_0 < 0.1 nG, could lead to
structure formation at high redshift z > 15, and hence naturally explain an
early re-ionization of the Universe.",0601570v1
2004-03-01,The anisotropy of granular materials,"The effect of the anisotropy on the elastoplastic response of two dimensional
packed samples of polygons is investigated here, using molecular dynamics
simulation. We show a correlation between fabric coefficients, characterizing
the anisotropy of the granular skeleton, and the anisotropy of the elastic
response. We also study the anisotropy induced by shearing on the subnetwork of
the sliding contacts. This anisotropy provides an explanation to some features
of the plastic deformation of granular media.",0403064v1
2004-12-17,Mesoscopic bound on anisotropy in itinerant ferromagnets,"We calculate the anisotropy energy of a single-domain ferromagnetic particle
in which the only source of anisotropy is the presence of non-magnetic
impurities. We find that such anisotropy takes the form of combined easy-axis
and easy-plane anisotropies, with random orientations of the axes. Typically
the anisotropy energy is of order $N^{1/2} \hbar/tau_{so}$, where $N$ is the
number of electrons in the ferromagnetic particle and $\tau_{so}$ is the
spin-orbit time.",0412488v1
2012-05-03,Anisotropy tuning with the Wilson flow,"We use the Wilson flow to define the gauge anisotropy at a given physical
scale. We demonstrate the use of the anisotropic flow by performing the tuning
of the bare gauge anisotropy in the tree-level Symanzik action for several
lattice spacings and target anisotropies. We use this method to tune the
anisotropy parameters in full QCD, where we also exploit the diminishing effect
of a well chosen smearing on the renormalization of the fermion anisotropy.",1205.0781v1
2012-11-19,Magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders,"The magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders was measured as a
function of temperature by the modified singular point detection technique. In
this method singularities indicating the anisotropy field were determined
analyzing ac susceptibility data. The observed relationship between temperature
dependence of anisotropy constant and temperature dependence of magnetization
was used to deduce the origin of magnetic anisotropy in the nanopowders. It was
shown that magnetic anisotropy of La0.7Sr0.3MnO3 nanopowder is determined by
two-ion (dipolar or pseudodipolar) and single-ion mechanisms.",1211.4355v1
2015-11-16,Transport anisotropy in Ge quantum wells in the absence of quantum oscillations,"Recent study of a high-mobility 2D hole gas in a strained Ge quantum well
revealed strong transport anisotropy in the quantum Hall regime when the
magnetic field was tilted away from the sample normal. In the present study we
demonstrate that the anisotropy persists to such high temperatures and filling
factors that quantum oscillations are no longer observed. This finding rules
out the formation of a stripe phase as a possible origin for the observed
anisotropy. However, we also show that the observed anisotropy is not
consistent with other known anisotropies, such as those arising from finite
thickness effects or surface roughness.",1511.05168v1
2017-11-08,Effective uniaxial anisotropy in easy-plane materials through nanostructuring,"Permanent magnet materials require a high uniaxial magneto-crystalline
anisotropy. Exchange coupling between small crystallites with easy-plane
anisotropy induces an effective uniaxial anisotropy if arranged accordingly.
Nanostructuring of materials with easy-plane anisotropy is an alternative way
to create hard-magnetic materials. The coercivity increases with decreasing
feature size. The resulting coercive field is about 12 percent of the
anisotropy field for a crystal size of 3.4 times the Bloch parameter.",1711.03144v1
2023-04-08,Integral Absorption of Microwave Power by Random-Anisotropy Magnets,"We study analytically and numerically on lattices containing $10^5$ spins,
the integral absorption of microwaves by a random-anisotropy magnet, $\int
d\omega P(\omega)$. It scales as $D^2_R/J$ on the random-anisotropy strength
$D_R$ and the strength of the ferromagnetic exchange $J$ in low-anisotropy
amorphous magnetic materials. At high anisotropy and in low-anisotropy
materials sintered of sufficiently large ferromagnetic grains, the integral
power scales linearly on $D_R$. The maximum bandwidth, combined with the
maximum absorption power, is achieved when the amorphous structure factor, or
grain size, is of an order of the domain wall thickness in a conventional
ferromagnet that is of the order of $(J/D_R)^{1/2}$ lattice spacings.",2304.04121v1
2010-02-02,"Magnetic anisotropy of epitaxial (Ga,Mn)As on (113)A GaAs","The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers
grown by molecular beam epitaxy is studied by means of superconducting quantum
interference device (SQUID) magnetometry as well as by ferromagnetic resonance
(FMR) and magnetooptical effects. Experimental results are described
considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude
of cubic and uniaxial anisotropy constants is found to be proportional to the
fourth and second power of saturation magnetization, respectively. Similarly to
the case of (001) samples, the spin reorientation transition from uniaxial
anisotropy with the easy along the [-1, 1, 0] direction at high temperatures to
the biaxial <100> anisotropy at low temperatures is observed around 25 K. The
determined values of the anisotropy constants have been confirmed by FMR
studies. As evidenced by investigations of the polar magnetooptical Kerr
effect, the particular combination of magnetic anisotropies allows the
out-of-plane component of magnetization to be reversed by an in-plane magnetic
field. Theoretical calculations within the p-d Zener model explain the
magnitude of the out-of-plane uniaxial anisotropy constant caused by epitaxial
strain, but do not explain satisfactorily the cubic anisotropy constant. At the
same time the findings point to the presence of an additional uniaxial
anisotropy of unknown origin. Similarly to the case of (001) films, this
additional anisotropy can be explained by assuming the existence of a shear
strain. However, in contrast to the (001) samples, this additional strain has
an out-of-the-(001)-plane character.",1002.0563v2
2020-01-28,Intrinsic Anisotropy and Pinning Anisotropy in Nanostructured YBa$_2$Cu$_3$O$_{7-δ}$ from Microwave Measurements,"Anisotropy is an intrinsic factor that dictates the magnetic properties of
YBCO, thus with great impact for many applications. Artificial pinning centres
are often introduced in an attempt to mitigate its effect, resulting in less
anisotropic electrical and magnetic properties. However, the nanoengineering of
the superconductor makes the quantification of the anisotropy itself uncertain:
the intrinsic anisotropy due to the layered structure, quantified by the
anisotropy factor $\gamma$, mixes up with the additional anisotropy due to
pinning. As a consequence, there is no consensus on the experimental anisotropy
factor $\gamma$ that can result in YBCO when directional (twin planes,
nanorods) or isotropic defects are present. We present here measurements of the
magnetic field and angular dependent surface impedance in very different
nanostructured YBCO films, grown by chemical route and by pulsed laser
deposition, with different kind of defects (nanorods, twin planes,
nanoparticles). We show that the surface impedance measurements are able to
disentangle the intrinsic anisotropy from the directional pinning anisotropy,
thanks to the possibility to extract the true anisotropic flux--flow
resistivity and by correctly exploiting the angular scaling. We find in all
films that the intrinsic anisotropy $\gamma = 5.3\pm0.7$. By contrast, the
pinning anisotropy determines a much complex, feature--rich and nonuniversal,
sample--dependent angular landscape.",2001.10299v1
2020-04-02,Contrast-to-noise ratio analysis of microscopic diffusion anisotropy indices in q-space trajectory imaging,"Diffusion anisotropy in diffusion tensor imaging (DTI) is commonly quantified
with normalized diffusion anisotropy indices (DAIs). Most often, the fractional
anisotropy (FA) is used, but several alternative DAIs have been introduced in
attempts to maximize the contrast-to-noise ratio (CNR) in diffusion anisotropy
maps. Examples include the scaled relative anisotropy (sRA), the gamma variate
anisotropy index (GV), the surface anisotropy (UAsurf), and the lattice index
(LI). With the advent of multidimensional diffusion encoding it became possible
to determine the presence of microscopic diffusion anisotropy in a voxel, which
is theoretically independent of orientation coherence. In accordance with DTI,
the microscopic anisotropy is typically quantified by the microscopic
fractional anisotropy (uFA). In this work, in addition to the uFA, the four
microscopic diffusion anisotropy indices (uDAIs) usRA, uGV, uUAsurf, and uLI
are defined in analogy to the respective DAIs by means of the average diffusion
tensor and the covariance tensor. Simulations with three representative
distributions of microscopic diffusion tensors revealed distinct CNR
differences when differentiating between isotropic and microscopically
anisotropic diffusion. q-Space trajectory imaging (QTI) was employed to acquire
brain in-vivo maps of all indices. For this purpose, a 15 min protocol
featuring linear, planar, and spherical tensor encoding was used. The resulting
maps were of good quality and exhibited different contrasts, e.g. between gray
and white matter. This indicates that it may be beneficial to use more than one
uDAI in future investigational studies.",2004.00892v1
1997-05-03,Evolution of Tidally Truncated Globular Clusters with Anisotropy,"The evolution of tidally truncated globular clusters is investigated by
integrating two-dimensional Fokker-Planck equation that allows the development
of velocity anisotropy. We start from the isotropic Plummer model with tidal
cut off and followed the evolution through the corecollapse. The heating by
three-binary is included to obtain the evolution past the corecollapse. The
anisotropy in velocity dispersion develops during the precollapse evolution.
However, the anisotropy becomes highly depressed during the post-collapse
evolution because of rapid loss of radial orbits. Maximum radial anisotropy
appears just after the beginning of the expansion, and degree of anisotropy
decreases slowly as the total mass of the cluster decreases. Thus it may be
possible to determine the evolutionary status of a cluster if the velocity
anisotropy can be measured in the sense that the postcollapse clusters always
have very little degree of anisotropy. The structure of the post-collapse
cluster can be well fitted to King models because the degree of anisotropy is
rather small.",9705012v1
2006-01-14,Cosmic Microwave Background Mini-Review,"A compact overview of the status of CMB anisotropy results and their
cosmological interpretation up until the end of 2005. Sections headings:
Introduction; Description of CMB Anisotropies; Cosmological Parameters; Physics
of Anisotropies; Current Anisotropy Data; CMB Polarization; Complications;
Constraints on Cosmologies; Particle Physics Constraints; Fundamental Lessons;
and Future Directions.",0601307v1
2003-11-13,Penetration depth anisotropy in two-band superconductors,"The anisotropy of the London penetration depth is evaluated for two-band
superconductors with arbitrary inter- and intra-band scattering times. If one
of the bands is clean and the other is dirty in the absence of inter-band
scattering, the anisotropy is dominated by the Fermi surface of the clean band
and is weakly temperature dependent. The inter-band scattering also suppress
the temperature dependence of the anisotropy.",0311331v1
2006-02-16,Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies,"We develop a model for ferromagnetic resonance in systems with competing
uniaxial and cubic anisotropies. This model applies to (i) magnetic materials
with both uniaxial and cubic anisotropies, and (ii) magnetic nanoparticles with
effective core and surface anisotropies; We numerically compute the resonance
frequency as a function of the field and the resonance field as a function of
the direction of the applied field for an arbitrary ratio of cubic-to-uniaxial
anisotropy. We also provide some approximate analytical expressions in the case
of weak cubic anisotropy. We propose a method that uses these expressions for
estimating the uniaxial and cubic anisotropy constants, and for determining the
relative orientation of the cubic anisotropy axes with respect to the crystal
principle axes. This method is applicable to the analysis of experimental data
of resonance type measurements for which we give a worked example of an iron
thin film with mixed anisotropy.",0602369v3
2010-01-11,The influence of weak texture on the critical currents in polycrystalline MgB$_2$,"The current transport in polycrystalline MgB$_2$ is strongly influenced by
the intrinsic anisotropy of this superconductor. Untextured bulks and wires are
macroscopically isotropic, but the grains retain their anisotropic properties
and the field dependence of the critical currents is much stronger than in
isotropic superconductors. Weakly or partially textured tapes are
macroscopically anisotropic, but the anisotropy of the zero resistivity (or
irreversibility) field is smaller than the intrinsic upper critical field
anisotropy, $\gamma$. The \Jc-anisotropy is field and temperature dependent and
can be much larger than $\gamma$. The most suitable parameter for the
quantification of the macroscopic anisotropy is, therefore, the anisotropy of
the zero resistivity field. It is difficult to distinguish between a higher
degree of texture at a lower intrinsic anisotropy and a weaker texture at
higher anisotropy and hardly possible based on the field dependence of the
critical current anisotropy alone. The knowledge of the upper critical field is
crucial and angular resolved measurements of either the critical currents or,
better, the resistive in-field transitions are favorable for this purpose.",1001.1678v1
2010-03-09,Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes,"We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes
using thermal pyrolysis method and the effect of shape anisotropy on the static
and dynamic magnetic properties were studied. Shape anisotropy of approximately
10 % was introduced in nanocubes by making nanodiscs using a linear chain amine
surfactant during synthesis process. It has been observed that, ferromagnetism
persisted above room temperature and a sharp drop in magnetic moment at low
temperatures in zero-field cooled magnetization may be associated with the spin
disorder due to the effective anisotropy present in the system. Dynamic
magnetic properties were studied using RF transverse susceptibility
measurements at different temperatures and the singularities due to anisotropy
fields were probed at low temperatures. Symmetrically located broad peaks are
observed in the frozen state at the effective anisotropy fields and the peak
structure is strongly affected by shape anisotropy and temperature.
Irrespective of size the shape anisotropy gave rise to higher coercive fields
and larger transverse susceptibility ratio at all temperatures. The role of
shape anisotropy and the size of the particles on the observed magnetic
behaviour were discussed.",1003.1855v1
2019-02-19,Magnetic interaction and anisotropy axes arrangement in nanoparticle aggregates can enhance or reduce the effective magnetic anisotropy,"The magnetic response of nanostructures plays an important role on biomedical
applications being strongly influenced by the magnetic anisotropy. In this work
we investigate the role of temperature, particle concentration and nanoparticle
arrangement forming aggregates in the effective magnetic anisotropy of Mn-Zn
ferrite-based nanoparticles. Electron magnetic resonance and coercivity
temperature dependence analyses, were critically compared for the estimation of
the anisotropy. We found that the temperature dependence of the anisotropy
follows the Callen-Callen model, while the symmetry depends on the particle
concentration. At low concentration one observes only an uniaxial term, while
increasing a cubic contribution has to be added. The effective anisotropy was
found to increase the higher the particle concentration on magnetic colloids,
as long as the easy axis was at the same direction of the nanoparticle chain.
Increasing even further the concentration up to a highly packed condition
(powder sample) one observes a decrease of the anisotropy, that was attributed
to the random anisotropy axes configuration.",1902.07188v1
2022-02-25,Skyrmion crystals in centrosymmetric triangular magnets under hexagonal and trigonal single-ion anisotropy,"We theoretically report an instability toward a skyrmion crystal in
centrosymmetric magnets under hexagonal and trigonal single-ion anisotropy. The
results are obtained for a minimal spin model with a crystal-dependent
single-ion anisotropy on a triangular lattice by performing simulated
annealing. By constructing magnetic phase diagrams in the presence of six
different types of single-ion anisotropy while changing the amplitudes of
external magnetic field and single-ion anisotropy in a systematic way, we find
that the hexagonal and trigonal single-ion anisotropy becomes a source of the
skyrmion crystal depending on the magnetic-field direction. We show that the
skyrmion crystal is stabilized by the uniaxial-type or trigonal-type single-ion
anisotropy under the out-of-plane magnetic field, while it is stabilized by the
hexagonal-type inplane single-ion anisotropy under the inplane magnetic field.
We also find various multiple-$Q$ spin states depending on the types of the
single-ion anisotropy.",2202.12964v1
2014-02-05,Numerical micromagnetism of strong inhomogeneities,"The size of micromagnetic structures, such as domain walls or vortices, is
comparable to the exchange length of the ferromagnet. Both, the exchange length
of the stray field $l_s$ and the magnetocrystalline exchange length $l_k$ are
material-dependent quantities that usually lie in the nanometer range. This
emphasizes the theoretical challenges associated with the mesoscopic nature of
micromagnetism: the magnetic structures are much larger than the atomic lattice
constant, but at the same time much smaller than the sample size. In computer
simulations, the smallest exchange length serves as an estimate for the largest
cell size admissible to prevent appreciable discretization errors. This general
rule is not valid in special situations where the magnetization becomes
particularly inhomogeneous. When such strongly inhomogeneous structures
develop, micromagnetic simulations inevitably contain systematic and numerical
errors. It is suggested to combine micromagnetic theory with a Heisenberg model
to resolve such problems. We analyze cases where strongly inhomogeneous
structures pose limits to standard micromagnetic simulations, arising from
fundamental aspects as well as from numerical drawbacks.",1402.1142v1
2015-07-30,Manipulating Magnetism at Organic/Ferromagnetic Interfaces by Fullerene-Induced Surface Reconstruction,"Fullerenes have several advantages as potential materials for organic
spintronics. Through a theoretical first-principles study, we report that
fullerene C$_{60}$ adsorption can induce a magnetic reconstruction in a Ni(111)
surface and expose the merits of the reconstructed C$_{60}$/Ni(111)
\emph{spinterface} for molecular spintronics applications. Surface
reconstruction drastically modifies the magnetic properties at both sides of
the C$_{60}$/Ni interface. Three outstanding properties of the reconstructed
structure are revealed, which originate from reconstruction enhanced spin-split
$\mathrm{\pi}$$-$d coupling between C$_{60}$ and Ni(111): 1) the C$_{60}$ spin
polarization and conductance around the Fermi level are enhanced
simultaneously, which can be important for read-head sensor miniaturization; 2)
localized spin-polarized states appear in C$_{60}$ with a spin-filter
functionality, and 3) magnetocrystalline anisotropic energy and exchange
coupling in the outermost Ni layer are reduced enormously. Surface
reconstruction can be realized simply by controlling the annealing temperature
in experiments.",1507.08378v1
2017-01-09,Six-fold crystalline anisotropic magnetoresistance in the (111) LaAlO$_3$/SrTiO$_3$ oxide interface,"We measured the magnetoresistance of the 2D electron liquid formed at the
(111) LaAlO$_3$/SrTiO$_3$ interface. The hexagonal symmetry of the interface is
manifested in a six-fold crystalline component appearing in the anisotropic
magnetoresistance (AMR) and planar Hall data, which agree well with symmetry
analysis we performed. The six-fold component increases with carrier
concentration, reaching 15% of the total AMR signal. Our results suggest the
coupling between higher itinerant electronic bands and the crystal as the
origin of this effect and demonstrate that the (111) oxide interface is a
unique hexagonal system with tunable magnetocrystalline effects.",1701.02153v2
2017-03-24,Intrinsic ferromagnetism and quantum anomalous Hall effect in CoBr2 monolayer,"The electronic, magnetic, and topological properties of CoBr2 monolayer are
studied in the frame-work of the density-functional theory (DFT) combined with
tight-binding (TB) modeling in terms of Wannier basis. Our DFT investigation
and Monte Carlo simulation show that there exists intrinsic two-dimensional
ferromagnetism in the CoBr2 monolayer thanks to large out-of-plane
magnetocrystalline anisotropic energy. Our further study shows that the
spin-orbits coupling makes it become a topologically nontrivial insulator with
quantum anomalous Hall effect and topological Chern number C=4, and its edge
states can be manipulated by changing the width of its nanoribbons and applying
strains. The CoBr2 monolayer can be exfoliated from the layered CoBr2 bulk
material because its exfoliation energy is between those of graphene and MoS2
monolayer and it is dynamically stable. These results make us believe that the
CoBr2 monolayer can make a promising spintronic material for future
high-performance devices.",1703.08565v2
2019-09-13,Fully spin-polarized quadratic non-Dirac bands realized quantum anomalous Hall effect,"The quantum anomalous Hall effect is a intriguing quantum state which
exhibits the chiral edge states in the absence of magnetic field. While the
search for quantum anomalous Hall insulators is still active, the researchers
mainly search for the systems containing magnetic atom. Here, based on
first-principles density functional theory, we predict a new family of chern
insulators with fully spin-polarized quadratic px;y non-Dirac bands in the
alkali earth metal BaX (X = Si, Ge, Sn) system. We show that BaX monolayer has
a half-metallic ferromagnetic ground state. The ferromagnetism is mainly
originated from the p orbitals of Si, Ge and Sn atoms. The 2D BaSn monolayer
exhibits a large magnetocrystalline anisotropic energy of 12.20 meV/cell and a
nontrivial band gap of 159.10 meV. Interestingly, both the spin polarization of
the chiral edge currents and the sign of Chern number can be tuned by doping.
Furthermore, the 4 % compressive strain can drive structural phase transition
but the nontrivial topological properties remain reserve in the 2D BaX systems.
Our findings not only extend the novel concepts but also provide fascinating
opportunities for the realization of quantum anomalous Hall effect
experimentally.",1909.06071v2
2020-01-24,Anisotropic magnetoresistance in spin-orbit semimetal SrIrO3,"SrIrO3, the three-dimensional member of the Ruddlesden-Popper iridates, is a
paramagnetic semimetal characterised by a the delicate interplay between
spin-orbit coupling and Coulomb repulsion. In this work, we study the
anisotropic magnetoresistance (AMR) of SrIrO3 thin films, which is closely
linked to spin-orbit coupling and probes correlations between electronic
transport, magnetic order and orbital states. We show that the low-temperature
negative magnetoresistance is anisotropic with respect to the magnetic field
orientation, and its angular dependence reveals the appearance of a fourfold
symmetric component above a critical magnetic field. We show that this AMR
component is of magnetocrystalline origin, and attribute the observed
transition to a field-induced magnetic state in SrIrO3.",2001.08939v1
2022-12-22,Magnetoelasticity-driven phase inversion of ultrafast spin precession in NixFe100-x thin films,"We present strong evidences for the deterministic role of magnetoelasticity
in ultrafast spin dynamics of ferromagnetic NixFe100-x alloy films. Without a
change in the crystal structure, we observed sudden Pi-phase inversion of the
spin precession in the range of x = 87.0 - 97.5. In addition, it was found that
the phase was continuously changed and reversed its sign by varying the pump
fluence. These cannot be explained simply by temperature dependence of
magnetocrystalline, demagnetizing, and Zeeman fields which have been
conventionally considered so far in describing the spin dynamics. Through the
temperature- and composition-dependent simulations adding the magnetoelastic
field generated from the lattice thermal strain, we revealed that the
conventional and magnetoelastic fields were competing around x = 95.3, where
the spin dynamics showed the largest phase shift. For analytic understanding,
we further show that the temperature-dependent interplay of the Curie
temperature, saturation magnetization, and magnetostriction, which are
demonstrated to be the most important macroscopic parameters, determines the
ultrafast spin dynamics. Our extensive study emphasizes that magnetoelasticity
is the key ingredient for fully understanding the driving mechanism of
ultrafast spin dynamics.",2212.11852v1
2023-11-27,Coherent control of photomagnetic back-switching by double-pump laser pulses,"The control of nonthermal, all-optical magnetization switching under the
regime with an independent state of laser polarization opens up new
opportunities for ultrafast magnetic recording. Here, we investigate the
photo-magnetic back-switching capabilities of the write and erase magnetic
domain pattern using double-pump pulse excitations in an iron garnet film with
pure cubic magnetocrystalline symmetry. It is essential to note that forward
and backward magnetization switching is achievable in two distinctive
scenarios: using identical linearly polarized laser pulses and with pulses
having orthogonal polarization planes. By observing the switch of magnetization
at domains independent of the initial state, one can nonthermally toggle the
magnetization, equivalent to XOR logical operation, at frequencies reaching up
to 50 GHz.",2311.16336v2
2023-09-19,Probing the spatial and velocity anisotropies in stellar halos from the Aquarius simulations,"We analyze the spatial anisotropy and the velocity anisotropy in a set of
mock stellar halos from the Aquarius simulations. The spatial anisotropy in
each mock stellar halo rises progressively with the increasing distance from
the halo centre, eventually reaching a maximum near the periphery. Excluding
the bound satellites leads to a significant reduction of the spatial anisotropy
in each halo. We compare the measured anisotropy in the mock stellar halos with
that from their sphericalized versions where all the shape and substructure
induced anisotropies are erased. The growth of spatial anisotropy persists
throughout the entire halo when the bound satellites are present but remains
limited within the inner halo ($<60 \, h^{-1}\, {\rm kpc}$) after their
exclusion. This indicates that the spatial anisotropy in the inner halo is
induced by the diffuse substructures and the halo shape whereas the outer halo
anisotropy is dominated by the bound satellites. We find that the outer parts
of the stellar halo are kinematically colder than the inner regions. The
stellar orbits are predominantly radial but they become rotationally dominated
at certain radii that are marked by the prominent $\beta$ dips. Most of the
$\beta$ dips disappear after the removal of the satellites. A few shallow and
broad $\beta$ dips arise occasionally due to the presence of diffuse streams
and clouds. Our analysis suggests that a combined study of the spatial and
velocity anisotropies can reveal the structure and the assembly history of the
stellar halos.",2309.10798v1
1995-07-06,Galaxy clusters and microwave background anisotropy,"Previous estimates of the microwave background anisotropies produced by
freely falling spherical clusters are discussed. These estimates are based on
the Swiss-Cheese and Tolman-Bondi models. It is proved that these models give
only upper limits to the anisotropies produced by the observed galaxy clusters.
By using spherically symmetric codes including pressureless matter and a hot
baryonic gas, new upper limits are obtained. The contributions of the hot gas
and the pressureless component to the total anisotropy are compared. The
effects produced by the pressure are proved to be negligible; hence,
estimations of the cluster anisotropies based on N-body simulations are
hereafter justified. After the phenomenon of violent relaxation, any realistic
rich cluster can only produce small anisotropies with amplitudes of order
$10^{-7}$. During the rapid process of violent relaxation, the anisotropies
produced by nonlinear clusters are expected to range in the interval
$(10^{-6},10^{-5})$. The angular scales of these anisotropies are discussed.",9507019v2
1996-03-01,DT/T beyond linear theory,"The major contribution to the anisotropy of the temperature of the Cosmic
Microwave Background (CMB) radiation is believed to come from the interaction
of linear density perturbations with the radiation previous to the decoupling
time. Assuming a standard thermal history for the gas after recombination, only
the gravitational field produced by the linear density perturbations present on
a $\Omega\neq 1$ universe can generate anisotropies at low z (these
anisotropies would manifest on large angular scales). However, secondary
anisotropies are inevitably produced during the nonlinear evolution of matter
at late times even in a universe with a standard thermal history. Two effects
associated to this nonlinear phase can give rise to new anisotropies: the
time-varying gravitational potential of nonlinear structures (Rees-Sciama RS
effect) and the inverse Compton scattering of the microwave photons with hot
electrons in clusters of galaxies (Sunyaev-Zeldovich SZ effect). These two
effects can produce distinct imprints on the CMB temperature anisotropy. We
discuss the amplitude of the anisotropies expected and the relevant angular
scales in different cosmological scenarios. Future sensitive experiments will
be able to probe the CMB anisotropies beyong the first order primary
contribution.",9603001v1
1997-07-29,Spin-Orbit-Induced Magnetic Anisotropy for Impurities in Metallic Samples I. Surface Anisotropy,"Motivated by the recent measurements of Kondo resistivity in thin films and
wires, where the Kondo amplitude is suppressed for thinner samples, the surface
anisotropy for magnetic impurities is studied. That anisotropy is developed in
those cases where in addition to the exchange interaction with the impurity
there is strong spin-orbit interaction for conduction electrons around the
impurity in the ballistic region. The asymmetry in the neighborhood of the
magnetic impurity exhibits the anisotropy axis $n$ which, in the case of a
plane surface, is perpendicular to the surface. The anisotropy energy is
$\Delta E=K_d (nS)^2$ for spin $S$, and the anisotropy constant $K_d$ is
inversionally proportional to distance $d$ measured from the surface and
$K_d>0$. Thus at low temperature the spin is frozen in a singlet or doublet of
lowest energy. The influence of that anisotropy on the electrical resistivity
is the subject of the following paper (part II).",9707298v1
2001-02-28,In-plane upper critical field anisotropy in Sr2RuO4 and CeIrIn5,"Experiments on tetragonal Sr2RuO4 and CeIrIn5 indicate the presence of
superconductivity with a multi-component superconducting order parameter. Such
an order parameter should exhibit an in-plane anisotropy in the upper critical
field near the superconducting transition temperature that does not occur for
single-component superconductors. Here, this anisotropy is determined from
microscopic calculations for arbitrary gap functions. It is shown that this
anisotropy is generally not small and, in some cases, independent of impurity
scattering. Furthermore, this anisotropy is calculated for many detailed
microscopic models of Sr2RuO4. For these models this anisotropy is found to be
large, which is in sharp contrast to the small anisotropy observed
experimentally. However, an accidental cancellation of the anisotropy for gaps
on different Fermi surface sheets can lead to a result that is consistent with
experiment.",0102530v1
2006-03-06,"Effect of the shape anisotropy on the magnetic configuration of (Ga,Mn)As and its evolution with temperature","We study the effect of the shape anisotropy on the magnetic domain
configurations of a ferromagnetic semiconductor (Ga,Mn)As/GaAs(001) epitaxial
wire as a function of temperature. Using magnetoresistance measurements, we
deduce the magnetic configurations and estimate the relative strength of the
shape anisotropy compared with the intrinsic anisotropies. Since the intrinsic
anisotropy is found to show a stronger temperature dependence than the shape
anisotropy, the effect of the shape anisotropy on the magnetic domain
configuration is relatively enhanced with increasing temperature. This
information about the shape anisotropy provides a practical means of designing
nanostructured spin electronic devices using (Ga,Mn)As.",0603126v1
2006-07-14,In-plane Anisotropy of the Magnetic Fluctuations in NaxCoO2-yH2O,"We report the $^{59}$Co NMR studies of the in-plane anisotropy of bilayer
hydrated Na$_{x}\mathrm{CoO_{2}} \cdot$$y\mathrm{H_{2}O}$ using a oriented
powder sample by a magnetic field in Fluorinert FC70. We found for the first
time the $ab$-plane anisotropy of the $^{59}$Co NMR Knight shift $K$, the
nuclear spin-lattice relaxation rate 1/$T_{1}$ and the nuclear spin-spin
relaxation rate 1/$T_{2}$ at a magnetic field $H \sim$ 7.5 T up to 200K. Below
75 K, the anisotropy of $K$ is large compared with that at high temperatures.
The hyperfine coupling constants seem to change around the temperature 150 K,
in which the bulk susceptibility $\chi$ shows broad minimum, suggesting a
change of the electronic state of CoO$_{2}$ plane. 1/$T_{1}$ also shows a
significant anisotropy, which cannot be explained only by the anisotropy of the
hyperfine coupling constants nor the anisotropic uniform spin susceptibility.
The difference in the in-plane anisotropy of $T_{1}$ from that of $K$ indicates
that the magnetic fluctuation at a finite wave vector $\vec{q} \neq 0$ is also
anisotropic and the anisotropy is different from that at $\vec{q} = 0$.",0607368v1
2006-11-30,Influence of weak anisotropy on scaling regimes in a model of advected vector field,"Influence of weak uniaxial small-scale anisotropy on the stability of
inertial-range scaling regimes in a model of a passive transverse vector field
advected by an incompressible turbulent flow is investigated by means of the
field theoretic renormalization group. Weak anisotropy means that parameters
which describe anisotropy are chosen to be close to zero, therefore in all
expressions it is enough to leave only linear terms in anisotropy parameters.
Turbulent fluctuations of the velocity field are taken to have the Gaussian
statistics with zero mean and defined noise with finite correlations in time.
It is shown that stability of the inertial-range scaling regimes in the
three-dimensional case is not destroyed by anisotropy but the corresponding
stability of the two-dimensional system can be destroyed even by the presence
of weak anisotropy. A borderline dimension $d_c$ below which the stability of
the scaling regime is not present is calculated as a function of anisotropy
parameters.",0611060v1
2002-05-25,Flow with PMD: Past and Future,"Measurements of azimuthal distribution of inclusive photons using the fine
granularity preshower photon multiplicity detector (PMD) at CERN SPS are used
to obtain anisotropy in the azimuthal distributions. These results are used to
estimate the anisotropy in the neutral pion distributions. The results are
compared with results of charged particle data, both for first order and second
order anisotropy. Assuming the same anisotropy for charged and neutral pions,
the anisotropy in photons is estimated and compared with the measured
anisotropy. The effect of neutral pion decay on the correlation between the
first order and the second order event plane is also discussed. Data from PMD
can also be used to estimate the reaction plane for studying any anisotropy in
particle emission characteristics in the ALICE experiment at the Large Hadron
Collider. In particular, we show that using the event plane from the PMD, it
will be possible to measure the anisotropy in Jpsi absorption (if any) in the
ALICE experiment.",0205017v1
1997-03-05,A note on the light velocity anisotropy,"In the framework of linear transformations between inertial systems, there
are no physical reasons for assuming any anisotropy in the one-way velocity of
light.",9703006v1
2007-05-11,Effective anisotropies and energy barriers of magnetic nanoparticles with Neel surface anisotropy,"Magnetic nanoparticles with Neel surface anisotropy, different internal
structures, surface arrangements and elongation are modelled as many-spin
systems. The results suggest that the energy of many-spin nanoparticles cut
from cubic lattices can be represented by an effective one-spin potential
containing uniaxial and cubic anisotropies. It is shown that the values and
signs of the corresponding constants depend strongly on the particle's surface
arrangement, internal structure and elongation. Particles cut from a simple
cubic lattice have the opposite sign of the effective cubic term, as compared
to particles cut from the face-centered cubic lattice. Furthermore, other
remarkable phenomena are observed in nanoparticles with relatively strong
surface effects: (i) In elongated particles surface effects can change the sign
of the uniaxial anisotropy. (ii) In symmetric particles (spherical and
truncated octahedral) with cubic core anisotropy surface effects can change its
sign. We also show that the competition between the core and surface
anisotropies leads to a new energy that contributes to both the 2nd- and
4th-order effective anisotropies.",0705.1689v1
2008-02-29,"Detailed transport investigation of the magnetic anisotropy of (Ga,Mn)As","This paper discusses transport methods for the investigation of the (Ga,Mn)As
magnetic anisotropy. Typical magnetoresistance behaviour for different
anisotropy types is discussed, focusing on an in depth discussion of the
anisotropy fingerprint technique and extending it to layers with primarily
uniaxial magnetic anisotropy. We find that in all (Ga,Mn)As films studied,
three anisotropy components are always present. The primary biaxial along
([100] and [010]) along with both uniaxial components along the [110] and [010]
crystal directions which are often reported separately. Various fingerprints of
typical (Ga,Mn)As transport samples at 4 K are included to illustrate the
variation of the relative strength of these anisotropy terms. We further
investigate the temperature dependence of the magnetic anisotropy and the
domain wall nucleation energy with the help of the fingerprint method.",0802.4400v1
2011-06-01,Enhancement of magnetic anisotropy barrier in long range interacting spin systems,"Magnetic materials are usually characterized by anisotropy energy barriers
which dictate the time scale of the magnetization decay and consequently the
magnetic stability of the sample. Here we present a unified description, which
includes coherent rotation and nucleation, for the magnetization decay in
generic anisotropic spin systems. In particular, we show that, in presence of
long range exchange interaction, the anisotropy energy barrier grows as the
volume of the particle for on site anisotropy, while it grows even faster than
the volume for exchange anisotropy, with an anisotropy energy barrier
proportional to $V^{2-\alpha/d}$, where $V$ is the particle volume, $\alpha
\leq d $ is the range of interaction and $d$ is the embedding dimension. These
results shows a relevant enhancement of the anisotropy energy barrier w.r.t.
the short range case, where the anisotropy energy barrier grows as the particle
cross sectional area for large particle size or large particle aspect ratio.",1106.0148v2
2013-03-04,Switching of anisotropy and phase diagram of a Heisenberg square lattice S=1/2 antiferromagnet Cu(pz)2(ClO4)2,"Experiments in the antiferromagnetic phase of a quasi 2D $S=1/2$ quasi-square
lattice antiferromagnet Cu(pz)2(ClO4)2 reveal a biaxial type of the anisotropy,
instead of the easy-plane one, considered before. The weak in-plane anisotropy,
found by means of electron spin resonance spectroscopy and magnetization
measurements, is about an order of magnitude weaker, than the off-plane
anisotropy. The weak in-plane anisotropy results in a spin-flop phase
transition for the magnetic field aligned along easy axis, and, thereby, in a
bicritical point on the phase diagram. A remarkable feature of the weak
in-plane anisotropy is the abrupt change of its sign at the spin-flop point.
This anisotropy switching disappears at the tilting of magnetic field to the
easy axis by the angle of 10$^\circ$ within the plane. The nature of the abrupt
anisotropy reversal remains unclear. The phase diagram is characterized by the
increase of the ordering temperature in the magnetic field used, except for a
dip near the bicritical point.",1303.0619v2
2013-09-18,Chiral Symmetry Breaking: To Probe Anisotropy and Magnetic Field in QGP,"We discuss the (spontaneous) chiral symmetry breaking in a strongly coupled
anisotropic quark-gluon plasma (QGP) in the presence of the magnetic field,
using holography. The physical quantities related to the chiral symmetry
breaking (m;B_c) distinguish between the effects of the anisotropy and magnetic
field on the plasma. Anisotropy affects the system similar to the temperature
and for its larger values heavier quarks can live in the QGP without getting
condensed. Raising the anisotropy in the system will also increase the value of
the critical magnetic field, B_c, at which the spontaneous chiral symmetry
breaking happens. Both of these growths are even more when the magnetic field
is applied perpendicular to the anisotropy direction. Such behaviour persists
in the high temperature limit where the temperature is kept fixed. However,
when the entropy density is held fixed, as one increases the anisotropy,
lighter mesons melt when the magnetic field is applied along the anisotropy
direction, in contrast to when the magnetic field is perpendicular to the
anisotropy direction.",1309.4715v2
2013-11-03,Primordial Anisotropies in Gauged Hybrid Inflation,"We study primordial anisotropies generated in the model of gauged hybrid
inflation in which the complex waterfall field is charged under a $U(1)$ gauge
field. Primordial anisotropies are generated either actively during inflation
or from inhomogeneities modulating the surface of end of inflation during
waterfall transition. We present a consistent $\delta N$ mechanism to calculate
the anisotropic power spectrum and bispectrum. We show that the primordial
anisotropies generated at the surface of end of inflation do not depend on the
number of e-folds and therefore do not produce dangerously large anisotropies
associated with the IR modes. Furthermore, one can find the parameter space
that the anisotropies generated from the surface of end of inflation cancel the
anisotropies generated during inflation, therefore relaxing the constrains on
model parameters imposed from IR anisotropies. We also show that the gauge
field fluctuations induce a red-tilted power spectrum so the averaged power
spectrum from the gauge field can change the total power spectrum from blue to
red. Therefore, hybrid inflation, once gauged under a $U(1)$ field, can be
consistent with the cosmological observations.",1311.0493v2
2014-04-05,Anisotropy-based mechanism for zigzag striped patterns in magnetic thin films,"In this work we studied a two dimensional ferromagnetic system using Monte
Carlo simulations. Our model includes exchange and dipolar interactions, a
cubic anisotropy term, and uniaxial out-of-plane and in-plane ones. According
to the set of parameters chosen, the model including uniaxial out-of-plane
anisotropy has a ground-state which consists of a canted state with stripes of
opposite out-of-plane magnetization. When the cubic anisotropy is introduced
zigzag patterns appear in the stripes at fields close to the remanence. An
analysis of the anisotropy terms of the model shows that this configuration is
related to specific values of the ratio between the cubic and the effective
uniaxial anisotropy. The mechanism behind this effect is related to particular
features of the anisotropy's energy landscape, since a global minima transition
as a function of the applied field is required in the anisotropy terms. This
new mechanism for zigzags formation could be present in monocrystal
ferromagnetic thin films in a given range of thicknesses.",1404.1526v2
2015-12-24,Magnetization of superparamagnetics in the state of mechanical anisotropy,"The internal energy of magnetic anisotropy for some nanoparticles dominates
over the thermal energy even at room temperature. Strong magnetic anisotropy of
nanoparticles can significantly affect the process of magnetization of the
magnetic fluid. This influence is substantial if the system of nanoparticles is
in a state of mechanical anisotropy in which the anisotropy axes of the
particles have the same direction. In this work, it is shown that the
magnetization curve of the magnetic fluid in a state of mechanical anisotropy
is significantly different from that of Langevin. It is located between the
Langevin and hyperbolic tangent curves and with increasing anisotropy takes
progressively the hyperbolic tangent shape. It is also shown that in case of
powder samples, the mechanical anisotropy leads to substantial quantitative
changes in the Curie law.",1512.07751v2
2016-10-18,Dichotomy between in-plane magnetic susceptibility and resistivity anisotropies in extremely strained $BaFe_{2}As_{2}$,"The in-plane resistivity and uniform magnetic susceptibility anisotropies of
$BaFe_{2}As_{2}$ are obtained with a new method, in which a large
symmetry-breaking uniaxial strain is applied using a substrate with a very
anisotropic thermal expansion. The resistivity anisotropy and its corresponding
elastoresistivity exhibit very similar diverging behavior as those obtained
from piezo-stack experiments. This suggests that the resistivity anisotropy is
more a direct measure of magnetism than of nematicity, since the nematic
transition is no longer well-defined under a large strain. In strong contrast
to the large resistivity anisotropy above $T_{N}$, the anisotropy of the
in-plane magnetic susceptibility develops largely below $T_{N}$. Using an
itinerant model, we show that the observed anisotropy ($\chi_{b}>\chi_{a}$) is
determined by spin-orbit coupling and the orientation of the magnetic moments
in the antiferromagnetic phase, and that the anisotropy is dominated by
intra-orbital ($yz,yz$) contributions of the Umklapp susceptibility.",1610.05575v2
2016-12-06,Origin of Small-Scale Anisotropies in Galactic Cosmic Rays,"The arrival directions of Galactic cosmic rays (CRs) are highly isotropic.
This is expected from the presence of turbulent magnetic fields in our Galactic
environment that repeatedly scatter charged CRs during propagation. However,
various CR observatories have identified weak anisotropies of various angular
sizes and with relative intensities of up to a level of 1 part in 1,000.
Whereas large-scale anisotropies are generally predicted by standard diffusion
models, the appearance of small-scale anisotropies down to an angular size of
10 degrees is surprising. In this review, we summarise the current experimental
situation for both the large-scale and small-scale anisotropies. We address
some of the issues in comparing different experimental results and remaining
questions in interpreting the observed large-scale anisotropies. We then review
the standard diffusive picture and its difficulty in producing the small-scale
anisotropies. Having set the stage, we review the various ideas and models put
forward for explaining the small-scale anisotropies.",1612.01873v1
2018-09-07,Anisotropy-driven collisional separation of impurities in magnetized compressing and expanding cylindrical plasmas,"When a cylindrically-symmetric magnetized plasma compresses or expands,
velocity-space anisotropy is naturally generated as a result of the different
adiabatic conservation laws parallel and perpendicular to the magnetic field.
When the compression timescale is comparable to the collision timescale, and
both are much longer than the gyroperiod, this pressure anisotropy can become
significant. We show that this naturally-generated anisotropy can dramatically
affect the transport of impurities in the compressing plasma, even in the
absence of scalar temperature or density gradients, by modifying the azimuthal
frictions that give rise to radial particle transport. Although the impurity
transport direction depends only on the sign of the pressure anisotropy, the
anisotropy itself depends on the pitch magnitude of the magnetic field and the
sign of the radial velocity. Thus, pressure anisotropy effects can drive
impurities either towards or away from the plasma core. These
anisotropy-dependent terms represent a qualitatively new effect, influencing
transport particularly in the sparse edge regions of dynamically-compressing
screw pinch plasmas. Such plasmas are used for both X-ray generation and
magneto-inertial fusion, applications which are sensitive to impurity
concentrations.",1809.02528v1
2024-02-01,Legendre Expansion for Scattering Anisotropy in Analytical 1D Multigroup $S_N$ Equations,"We demonstrate the scattering anisotropy treatment of the previously
developed analytical solution for 1D multigroup $S_N$ equations.",2402.01017v1
2003-05-29,Theoretical Overview of Cosmic Microwave Background Anisotropy,"The theoretical basis for the prediction of anisotropies in the cosmic
microwave background is very well developed. Very low amplitude density and
temperature perturbations produce small gravitational effects, leading to an
anisotropy that is a combination of temperature fluctuations at the surface of
last scattering and gravitational redshifts both at last scattering and along
the path to the observer. All of the primary anisotropy can be handled by
linear perturbation theory, which allows a very accurate calculation of the
predicted anisotropy from different models of the Universe.",0305591v1
2006-11-07,CMB anisotropies due to cosmological magnetosonic waves,"We study scalar mode perturbations (magnetosonic waves) induced by a helical
stochastic cosmological magnetic field and derive analytically the
corresponding cosmic microwave background (CMB) temperature and polarization
anisotropy angular power spectra. We show that the presence of a stochastic
magnetic field, or an homogeneous magnetic field, influences the acoustic
oscillation pattern of the CMB anisotropy power spectrum, effectively acting as
a reduction of the baryon fraction. We find that the scalar magnetic energy
density perturbation contribution to the CMB temperature anisotropy is small
compared to the contribution to the CMB $E$-polarization anisotropy.",0611247v2
2007-01-17,Wind anisotropies and GRB progenitors,"We study the effect of wind anisotropies on the stellar evolution leading to
collapsars. Rotating models of a 60 M$_\odot$ star with $\Omega/\Omega_{\rm
crit}=0.75$ on the ZAMS, accounting for shellular rotation and a magnetic
field, with and without wind anisotropies, are computed at $Z$=0.002 until the
end of the core He-burning phase. Only the models accounting for the effects of
the wind anisotropies retain enough angular momentum in their core to produce a
Gamma Ray Burst (GRB). The chemical composition is such that a type Ic
supernova event occurs. Wind anisotropies appear to be a key physical
ingredient in the scenario leading to long GRBs.",0701494v1
1992-09-18,Discrete to Continuous-Time Crossover due to Anisotropy in Diffusion-Limited Two-Particle Annihilation Reactions,"Diffusion-limited reaction A+A->inert with anisotropic hopping on the d=1
lattice, is solved exactly for a simultaneous updating, discrete time-step
dynamics. Diffusion-dominated processes slow down as the anisotropy increases.
For large times or large anisotropy, one can invoke the appropriate continuum
limits. In these limits the effects of the anisotropy on variation of particle
density can be absorbed in time rescaling. However, in other regimes, when the
discreteness of the time steps is nonnegligible, the anisotropy effects are
nontrivial, although they are always quite small numerically.",9209024v1
1996-02-19,Stress-free Spatial Anisotropy in Phase-Ordering,"We find spatial anisotropy in the asymptotic correlations of two-dimensional
Ising models under non-equilibrium phase-ordering. Anisotropy is seen for
critical and off-critical quenches and both conserved and non-conserved
dynamics. We argue that spatial anisotropy is generic for scalar systems
(including Potts models) with an anisotropic surface tension. Correlation
functions will not be universal in these systems since anisotropy will depend
on, e.g., temperature, microscopic interactions and dynamics, disorder, and
frustration.",9602097v1
1998-11-23,Giant enhancement of anisotropy by electron-phonon interaction,"Anisotropic electron-phonon interaction is shown to lead to the anisotropic
polaron effect. The resulting anisotropy of the polaron band is an exponential
function of the electron-phonon coupling and might be as big as $10^3$. This
also makes anisotropy very sensitive to small changes of coupling and implies
wide variations of anisotropy among compounds of similar structure. The isotope
effect on mass anisotropy is predicted. Polaron masses are obtained by an exact
Quantum Monte Carlo method. Implications for high-temperature superconductors
are briefly discussed.",9811327v1
1999-05-09,A simple solid-on-solid model of epitaxial thin films growth: surface morphology anisotropy,"In this paper we present a generalization of a simple solid-on-solid
epitaxial model of thin films growth, when surface morphology anisotropy is
provoked by anisotropy in model control parameters: binding energy and/or
diffusion barrier. The anisotropy is discussed in terms of the height-height
correlation function. It was experimentally confirmed that the difference in
diffusion barriers yields anisotropy in morphology of the surface. We got
antisymmetric correlations in the two in-plane directions for antisymmetric
binding.",9905111v2
2001-06-18,Phase Transition in the Random Anisotropy Model,"The influence of a local anisotropy of random orientation on a ferromagnetic
phase transition is studied for two cases of anisotropy axis distribution. To
this end a model of a random anisotropy magnet is analyzed by means of the
field theoretical renormalization group approach in two loop approximation
refined by a resummation of the asymptotic series. The one-loop result of
Aharony indicating the absence of a second-order phase transition for an
isotropic distribution of random anisotropy axis at space dimension $d<4$ is
corroborated. For a cubic distribution the accessible stable fixed point leads
to disordered Ising-like critical exponents.",0106334v1
2002-10-04,Surface contribution to the anisotropy of magnetic nanoparticles,"We calculate the contribution of the Neel surface anisotropy to the effective
anisotropy of magnetic nanoparticles of spherical shape cut out of a simple
cubic lattice. The effective anisotropy arises because deviations of atomic
magnetizations from collinearity and thus the energy depends on the orientation
of the global magnetization. The result is second order in the Neel surface
anisotropy, scales with the particle volume and has cubic symmetry with
preferred directions [+-1,+-1,+-1].",0210098v1
2003-04-08,Novel surface anisotropy term in the FMR spectra of amorphous microwires,"Some recent publications on ferromagnetic resonance in amorphous wires
mention presumably new kind of anisotropy, called there circumferential
anisotropy, as an explanation of various spectral features. In this paper we
argue that there is no special reason to speak of the new kind of anisotropy,
since the observed spectra can be well described in terms of more traditional
uniaxial and surface anisotropies alone.",0304195v1
2003-07-17,Surface anisotropy in nanomagnets: transverse or Néel ?,"Through the hysteresis loop and magnetization spatial distribution we study
and compare two models for surface anisotropy in nanomagnets: a model with
transverse anisotropy axes and N\'eel's model. While surface anisotropy in the
transverse model induces several jumps in the hysteresis loop because of the
cluster-wise switching of spins, in the N\'eel model the jumps correspond to
successive {\it coherent partial rotations} of the whole bunch of spins. These
calculations together with experimental results suggest that N\'eel's model for
surface anisotropy is more appropriate.",0307436v2
2004-10-04,Effects of Antiferromagnetic Spin Rotation on Anisotropy of Ferromagnetic/Antiferromagnetic Bilayers,"In epitaxial (111) oriented Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$ bilayers,
we separate two distinct behaviors: unidirectional anisotropy (exchange bias)
in thick Fe$_{50}$Mn$_{50}$, and enhanced coercivity in thin
Fe$_{50}$Mn$_{50}$. By measuring the magnetization response to a rotating
magnetic field, we quantitatively determine the relevant anisotropies, and
demonstrate that the enhanced coercivity is related to the rotatable magnetic
anisotropy of Fe$_{50}$Mn$_{50}$. We also demonstrate the consequences of the
anisotropy changes with temperature.",0410091v1
2005-10-03,Surface-induced cubic anisotropy in nanomagnets,"We investigate the effect of surface anisotropy in a spherical many-spin
magnetic nanoparticle. By computing minor loops, two-dimensional (2D) and 3D
energyscape, and by investigating the behavior of the net magnetization, we
show that in the case of not too strong surface anisotropy the behavior of the
many-spin particle may be modeled by that of a macrospin with an effective
energy containing uniaxial and cubic anisotropy terms. This holds for both the
transverse and N\'eel's surface anisotropy models.",0510047v3
2005-10-21,ESR study of the single-ion anisotropy in the pyrochlore antiferromagnet Gd2Sn2O7,"Single-ion anisotropy is of importance for the magnetic ordering of the
frustrated pyrochlore antiferromagnets Gd2Ti2O7 and Gd2Sn2O7. The anisotropy
parameters for the Gd2Sn2O7 were measured using the electron spin resonance
(ESR) technique. The anisotropy was found to be of the easy plane type, with
the main constant D=140mK. This value is 35% smaller than the value of the
corresponding anisotropy constant in the related compound Gd2Ti2O7.",0510575v1
2006-09-13,Determination of the resistivity anisotropy of SrRuO$_{3}$ by measuring the planar Hall effect,"We have measured the planar Hall effect in epitaxial thin films of the
itinerant ferromagnet SrRuO3 patterned with their current paths at different
angles relative to the crystallographic axes. Based on the results, we have
determined that SrRuO3 exhibits small resistivity anisotropy in the entire
temperature range of our measurements (between 2 to 300 K); namely, both above
and below its Curie temperature (~150 K). It means that in addition to
anisotropy related to magnetism, the resistivity anisotropy of SrRuO3 has an
intrinsic, nonmagnetic source. We have found that the two sources of anisotropy
have competing effects.",0609321v1
2006-12-17,"Lithographic engineering of anisotropies in (Ga,Mn)As","The focus of studies on ferromagnetic semiconductors is moving from material
issues to device functionalities based on novel phenomena often associated with
the anisotropy properties of these materials. This is driving a need for a
method to locally control the anisotropy in order to allow the elaboration of
devices. Here we present a method which provides patterning induced anisotropy
which not only can be applied locally, but also dominates over the intrinsic
material anisotropy at all temperatures.",0612439v1
2007-05-10,Effective anisotropy of thin nanomagnets: beyond the surface anisotropy approach,"We study the effective anisotropy induced in thin nanomagnets by the nonlocal
demagnetization field (dipole-dipole interaction). Assuming a magnetization
independent of the thickness coordinate, we reduce the energy to an
inhomogeneneous onsite anisotropy. Vortex solutions exist and are ground states
for this model. We illustrate our approach for a disk and a square geometry. In
particular, we obtain good agreement between spin-lattice simulations with this
effective anisotropy and micromagnetic simulations.",0705.1555v2
2007-07-28,Long-range order in the A-like phase of superfluid 3He in aerogel,"A mutual action of the random anisotropy brought in the superfluid 3He by
aerogel and of the global anisotropy caused by its deformation is considered.
Strong global anisotropy tends to suppress fluctuations of orientation of the
order parameter and stabilizes ABM order parameter. In a limit of vanishing
anisotropy these fluctuations are getting critical. It is argued that still in
a region of small fluctuations the average order parameter can acquire ""robust""
component. This component maintains a long-range order even in a limit of
vanishing global anisotropy.",0707.4222v2
2007-09-26,Single crystal growth and anisotropy of CeRuPO,"We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction.",0709.4144v2
2009-01-19,Local magnetic anisotropy controlled by a surface nano-modulation,"A topological modulation of magnetic thin films can induce a magnetic
anisotropy of magnetostatic origin. In this letter, we report on the magnetic
properties of NiFe layers deposited on wavy shaped Si substrates. Without any
modulation, our films always present an intrinsic anisotropy. We show
unambiguously that patterning the substrate can overcome this anisotropy and
even impose a different easy axis of magnetization. This allows the definition
of two orthogonal easy axes at different places on the same substrate. This
control of anisotropy both in direction and intensity paves the way to the
realization of high precision bidimensional magnetic sensors.",0901.2617v1
2009-05-01,Finite electric field effects in the large perpendicular magnetic anisotropy surface Pt/Fe/Pt(001),"We have investigated crystalline magnetic anisotropy in the electric field
(EF) for the Fe-Pt surface which have a large perpendicular anisotropy, by
means of the first-principles approach. The anisotropy is reduced linearly with
respect to the inward EF, associated with the induced spin density around the
Fe layer. Although the magnetic anisotropy energy (MAE) density reveals the
large variation around the atoms, the intrinsic contribution to the MAE is
found to mainly come from the Fe layer.",0905.0060v1
2009-11-26,Macrospin limit and configurational anisotropy in nanoscale Permalloy triangles,"In Permalloy submicron triangles, configurational anisotropy - a higher-order
form of shape anisotropy - yields three equivalent easy axes, imposed by the
structures' symmetry order. Supported by micromagnetic simulations, an
experimental method was devised to evaluate the nanostructure dimensions for
which a Stoner-Wohlfarth type of reversal could be used to describe this
particular magnetic anisotropy. In this regime, a straightforward procedure
using an in-plane rotating field allowed us to quantify experimentally the
six-fold anisotropy fields for triangles of different thicknesses and sizes.",0911.5121v1
2009-12-01,Vertically Graded Anisotropy in Co/Pd Multilayers,"Depth-grading of magnetic anisotropy in perpendicular magnetic media has been
predicted to reduce the field required to write data without sacrificing
thermal stability. To study this prediction, we have produced Co/Pd multilayers
with depth-dependent Co layer thickness. Polarized neutron reflectometry shows
that the thickness grading results in a corresponding magnetic anisotropy
gradient. Magnetometry reveals that the anisotropy gradient promotes domain
nucleation upon magnetization reversal - a clear experimental demonstration of
the effectiveness of graded anisotropy for reducing write-field.",0912.0256v1
2010-05-07,On non-linear CMB temperature anisotropy from gravitational perturbations,"Non-linear CMB temperature anisotropies up to the third-order on large scales
are calculated. On large scales and in the Sachs-Wolfe limit, we give the
explicit expression for the observed temperature anisotropy in terms of the
primordial curvature perturbation up to the third-order. We derived the final
bispectrum and trispectrum of anisotropies and the corresponding non-linear
parameters, in which the contributions to the observed non-Gaussianity from
primordial perturbations and from the non-linear mapping from primordial
curvature perturbation to the temperature anisotropy are transparently
separated.",1005.1219v1
2010-08-30,Dynamical electronic nematicity from Mott physics,"Very large anisotropies in transport quantities have been observed in the
presence of very small in-plane structural anisotropy in many strongly
correlated electron materials. By studying the two-dimensional Hubbard model
with dynamical-mean-field theory for clusters, we show that such large
anisotropies can be induced without static stripe order if the interaction is
large enough to yield a Mott transition. Anisotropy decreases at large
frequency. The maximum effect on conductivity anisotropy occurs in the
underdoped regime, as observed in high temperature superconductors.",1008.5118v2
2012-12-05,"Influence of Magnetic Anisotropy on Laser-induced Precession of Magnetization in Ferromagnetic Semiconductor (Ga,Mn)As","The laser-induced precession of magnetization in (Ga,Mn)As samples with
different magnetic anisotropy was studied by the time-resolved magneto-optical
method. We observed that the dependence of the precession amplitude on the
external magnetic field depends strongly on the magnetic anisotropy of
(Ga,Mn)As and we explain this phenomenon in terms of competing cubic and
uniaxial anisotropies. We also show that the corresponding anisotropy fields
can be deduced from the magnetic field dependence of the precession frequency.",1212.0962v1
2013-03-01,Electrically tunable three-dimensional g-factor anisotropy in single InAs self-assembled quantum dots,"Three-dimensional anisotropy of the Lande g-factor and its electrical
modulation are studied for single uncapped InAs self-assembled quantum dots
(QDs). The g-factor is evaluated from measurement of inelastic cotunneling via
Zeeman substates in the QD for various magnetic field directions. We find that
the value and anisotropy of the g-factor depends on the type of orbital state
which arises from the three-dimensional confinement anisotropy of the QD
potential. Furthermore, the g-factor and its anisotropy are electrically tuned
by a side-gate which modulates the confining potential.",1303.0158v1
2013-10-12,Inversion Phenomena of the Anisotropies of the Hamiltonian and the Wave Function in Quantum Spin Chains,"We investigate the inversion phenomena between the XXZ anisotropies of the
Hamiltonian and the wave function in quantum spin chains. We focus on the S=1/2
geometrically frustrated 3-leg ladder system with the XXZ interaction
anisotropy. By use of the degenerate perturbation theory from the strong rung
coupling limit, we have obtained the ground-state phase diagram. In some
parameter regions, the Tomonaga-Luttinger spin liquid state is realized in
spite of the Ising-like anisotropy, and the Neel state in spite of the XY-like
anisotropy.",1310.3394v1
2014-11-06,Phenomenological description of anisotropy effects in some ferromagnetic superconductors,"We study phenomenologically by using the previously derived Landau free
energy, the role of anisotropy in ferromagnetic superconductors UGe2, URhGe,
and UCoGe. The three compounds are separately discussed with the special stress
on UGe2. The main effect comes from the strong uniaxial anisotropy of
magnetization while the anisotropy of Cooper pairs and crystal anisotropy only
slightly change the phase diagram in the vicinity of Curie temperature. The
limitations of this approach are also discussed.",1411.1748v1
2015-02-05,DFT calculations of magnetic anisotropy energy for GeMnTe ferromagnetic semiconductor,"Density functional theory (DFT) calculations of the energy of magnetic
anisotropy for diluted ferromagnetic semiconductor GeMnTe were performed using
using OpenMX package with fully relativistic pseudopotentials. The influence of
hole concentration and magnetic ion neighborhood on magnetic anisotropy energy
is presented. Analysis of microscopic mechanism of magnetic anisotropy is
provided, in particular the role of spin-orbit coupling, spin polarization and
spatial changes of electron density are discussed. The calculations are in
accordance with the experimental observation of perpendicular magnetic
anisotropy in rhombohedral GeMnTe (111) thin layers.",1502.01715v3
2015-04-28,"""Switching"" of Magnetic Anisotropy in a fcc Antiferromagnet with Direction-Dependent Interactions","Direction-dependent anisotropic exchange is a common feature of magnetic
systems with strong spin-orbit coupling. Here we study the effect of such
exchange upon macroscopic magnetic anisotropy for a face-centered-cubic model.
By several theoretical techniques, we show that, both in the paramagnetic and
ordered phases, the magnetic anisotropy is induced by fluctuations. Moreover,
the magnetic anisotropy differs in the paramagnetic and ordered phases: in the
paramagnetic phase the susceptibility is maximum along the $\langle111\rangle$
directions, while the magnetic moments orient along $\langle110\rangle$ or
$\langle100\rangle$ in the ordered phase. We suggest that such ""anisotropy
switching"" can be a common feature of strongly spin-orbit coupled magnets.",1504.07607v1
2015-11-16,Strong Transport Anisotropy in a Ge/SiGe Quantum Well in Tilted Magnetic Fields,"We report on a strong transport anisotropy in a 2D hole gas in a Ge/SiGe
quantum well, which emerges only when both perpendicular and in-plane magnetic
fields are present. The ratio of resistances, measured along and perpendicular
to the in-plane field, can exceed $3\times 10^4$. The anisotropy occurs in a
wide range of filling factors where it is determined {\em primarily} by the
tilt angle. The lack of significant anisotropy without an in-plane field, easy
tunability, and persistence to higher temperatures and filling factors set this
anisotropy apart from nematic phases in GaAs/AlGaAs.",1511.05167v1
2017-08-05,Magnetization reversal of thin ferromagnetic elements with surface anisotropy,"The magnetization reversal process in thin-film ferromagnetic elements with
surface anisotropy of various shapes and sizes is investigated by means of
numerical simulation. The dependence of the perpendicular and in-plane
hysteresis loops on the element thickness and the value of the surface
anisotropy constant is obtained. For sufficiently large values of the surface
anisotropy constant the magnetization reversal of thin-film elements is shown
to occur due to the nucleation of the buckling mode. For an elongated
rectangular element the nucleation field of the buckling mode is proportional
to the absolute value of the surface anisotropy constant, and inversely
proportional to the element thickness.",1708.01802v1
2021-10-27,The nonlinear anisotropic model of the Universe with the linear potential,"In the Bianchi I cosmology some subclasses of the Horndeski theory allow for
the non-standard anisotropy behavior. For example, the anisotropy is damped
near the initial singularity instead of tending to infinity. In this article,
we analyze the nonlinear anisotropic model with the linear potential.We have
considered an example of such theory, for which the anisotropy is always
finite. The anisotropy reaches its a maximum value at the initial moment. The
anisotropy suppression occurs during the inflationary stage, and it approaches
zero at later times. This cosmological model does not contain the singular
point.",2110.14630v2
2022-11-21,Giant Magnetochiral Anisotropy in Weyl-semimetal WTe2 Induced by Diverging Berry Curvature,"The concept of Berry curvature is essential for various transport phenomena.
However, an effect of the Berry curvature on magnetochiral anisotropy, i.e.
nonreciprocal magneto-transport, is still elusive. Here, we report the Berry
curvature originates the large magnetochiral anisotropy. In Weyl-semimetal
WTe2, we observed the strong enhancement of the magnetochiral anisotropy when
the Fermi level is located near the Weyl points. Notably, the maximal figure of
merit $\bar{\gamma}$ reaches $1.2\,{\times}10^{-6} \rm{m^2T^{-1}A^{-1}}$, which
is the largest ever reported in bulk materials. Our semiclassical calculation
shows that the diverging Berry curvature at the Weyl points strongly enhances
the magnetochiral anisotropy.",2211.11231v1
2022-12-29,Localized Spin-Wave Modes and Microwave Absorption in Random-Anisotropy Ferromagnets,"The theory of localized spin-wave excitations in random-anisotropy magnets
has been developed. Starting with a pure Heisenberg ferromagnet, we study the
evolution of standing spin waves in a finite-size sample towards localized
modes on increasing the strength of random anisotropy. Profiles of the
localized modes and their phases are analyzed and visualized in a 2D sample.
Localization length is obtained by several methods and its dependence on random
anisotropy is computed. The connection between the localization of spin
excitations and the broadband nature of the absorption of microwave power by
random-anisotropy magnets is elucidated.",2212.14301v1
2024-01-09,Pulsar Kick by the Chiral Anisotropy Conversion,"We discuss a novel mechanism for the proto-neutron star acceleration assisted
by the chiral separation effect which induces an axial vector current in a
dense medium. We consider the process of neutrinos scattering off the
background axial vector current of electrons. We show that anisotropy of either
magnetic field or density in momentum space is essential for nonzero recoil and
we call this mechanism the chiral anisotropy conversion. Assuming a strong
magnetic field $B \simeq 10^{12}$ T and anisotropy by $\sim 10\%$, we find that
the chiral anisotropy conversion can yield the velocity of order of typical
pulsar kicks, i.e., $v_{\mathrm{kick}} \gtrsim 1000$ km/s.",2401.04568v1
2011-12-06,Domain-Wall Pinning by Local Control of Anisotropy in Pt/Co/Pt strips,"We theoretically and experimentally analyze the pinning of a magnetic domain
wall (DW) at engineered anisotropy variations in Pt/Co/Pt strips with
perpendicular magnetic anisotropy. An analytical model is derived showing that
a step in the anisotropy acts as an energy barrier for the DW. Quantitative
measurements are performed showing that the anisotropy can be controlled by
focused ion beam irradiation with Ga ions. This tool is used to experimentally
study the field-induced switching of nanostrips which are locally irradiated.
The boundary of the irradiated area indeed acts as a pinning barrier for the
domain wall and the pinning strength increases with the anisotropy difference.
Varying the thickness of the Co layer provides an additional way to tune the
anisotropy, and it is shown that a thinner Co layer gives a higher starting
anisotropy thereby allowing tunable DW pinning in a wider range of fields.
Finally, we demonstrate that not only the anisotropy itself, but also the width
of the anisotropy barrier can be tuned on the length scale of the domain wall.",1112.1259v2
2019-03-29,Anisotropy of the Universe via the Pantheon supernovae sample revisited,"We employ the hemisphere comparison (HC) method and the dipole fitting (DF)
method to investigate the cosmic anisotropy in the recently released Pantheon
sample of type Ia supernovae (SNe Ia) and five combinations among Pantheon. For
the HC method, we find the maximum anisotropy level in the full Pantheon sample
is $\mathrm{AL}_{max}=0.361\pm0.070$ and corresponding direction
$(l,b)=({123.05^{\circ}}^{+11.25^{\circ}}_{-4.22^{\circ}},
{4.78^{\circ}}^{+1.80^{\circ}}_{-8.36^{\circ}})$. A robust check shows the
statistical significance of maximum anisotropy level is about $2.1\sigma$. We
also find that the Low-$z$ and SNLS subsamples have decisive impact on the
overall anisotropy while other three subsamples have little impact. Moreover,
the anisotropy level map significantly rely on the inhomogeneous distribution
of SNe Ia in the sky. For the DF method, we find the dipole anisotropy in the
Pantheon sample is very weak. The dipole magnitude is constrained to be less
than $1.16\times10^{-3}$ at $95\%$ confidence level. However, the dipole
direction is well inferred by MCMC method and it points towards
$(l,b)=({306.00^{\circ}}^{+82.95^{\circ}}_{-125.01^{\circ}},
{-34.20^{\circ}}^{+16.82^{\circ}}_{-54.93^{\circ}})$. This direction is very
close to the axial direction to the plane of SDSS subsample. It may imply that
SDSS subsample is the decisive part to the dipole anisotropy in the full
Pantheon sample. All these facts imply that the cosmic anisotropy found in
Pantheon sample significantly rely on the inhomogeneous distribution of SNe Ia
in the sky. More homogeneous distribution of SNe Ia is necessary to search for
a more convincing cosmic anisotropy.",1903.12401v2
2022-08-05,Validation of EEG forward modeling approaches in the presence of anisotropy in the source space,"The quality of the inverse approach in electroencephalography (EEG) source
analysis is - among other things - depending on the accuracy of the forward
modeling approach, i.e., the simulation of the electric potential for a known
dipole source in the brain. Here, we use multilayer sphere modeling scenarios
to investigate the performance of three different finite element method (FEM)
based EEG forward approaches - subtraction, Venant and partial integration - in
the presence of tissue conductivity anisotropy in the source space. In our
studies, the effect of anisotropy on the potential is related to model errors
when ignoring anisotropy and to numerical errors, convergence behavior and
computational speed of the different FEM approaches. Three different source
space anisotropy models that best represent adult, child and premature baby
volume conduction scenarios, are used. Major findings of the study include (1)
source space conductivity anisotropy has a significant effect on electric
potential computation: The effect increases with increasing anisotropy ratio;
(2) with numerical errors far below anisotropy effects, all three FEM
approaches are able to model source space anisotropy accordingly, with the
Venant approach offering the best compromise between accuracy and computational
speed; (3) FE meshes have to be fine enough in the subdomain between the source
and the sensors that capture its main activity. We conclude that, especially
for the analysis of cortical development, but also for more general
applications using EEG source analysis techniques, source space conductivity
anisotropy should be modeled and the FEM Venant approach is an appropriate
method.",2208.03081v1
2003-05-29,Evolution of In-Plane Magnetic Anisotropy In Sputtered FeTaN/TaN/FeTaN Sandwich Films,"FeTaN/TaN/FeTaN sandwich films, FeTaN/TaN and TaN/FeTaN bilayers were
synthesized by using RF magnetron sputtering. The magnetic properties,
crystalline structures, microstructures and surface morphologies of the
as-deposited samples were characterized using angle-resolved M-H loop tracer,
VSM, XRD, TEM, AES and AFM. An evolution of the in-plane anisotropy was
observed with the changing thickness of the nonmagnetic TaN interlayer in the
FeTaN/TaN/FeTaN sandwiches, such as the easy-hard axis switching and the
appearing of biaxial anisotropy. It is ascribed to three possible mechanisms,
which are interlayer magnetic coupling, stress, and interface roughness,
respectively. Interlayer coupling and stress anisotropies may be the major
reasons to cause the easy-hard axis switching in the sandwiches. Whereas,
magnetostatic and interface anisotropies may be the major reasons to cause
biaxial anisotropy in the sandwiches, in which magnetostatic anisotropy is the
dominant one.",0305688v1
2007-01-19,"Control of magnetic anisotropy in (Ga,Mn)As by lithography-induced strain relaxation","We obtain control of magnetic anisotropy in epitaxial (Ga,Mn)As by
anisotropic strain relaxation in patterned structures. The strain in the
structures is characterized using sophisticated X-ray techniques. The magnetic
anisotropy before patterning of the layer, which shows biaxial easy axes along
[100] and [010], is replaced by a hard axis in the direction of large elastic
strain relaxation and a uniaxial easy axis in the direction where pseudomorphic
conditions are retained. This strong anisotropy can not be explained by shape
anisotropy and is attributed solely to lattice strain relaxation. Upon
increasing the uniaxial strain anisotropy in the (Ga,Mn)As stripes, we also
observe an increase in magnetic anisotropy.",0701479v1
2008-04-11,Anisotropies in the Cosmic Neutrino Background after WMAP 5-year Data,"We search for the presence of cosmological neutrino background (CNB)
anisotropies in recent WMAP 5-year data using their signature imprinted on
modifications to cosmic microwave background (CMB) anisotropy power spectrum.
By parametrizing the neutrino background anisotropies with the speed viscosity
parameter $c_\vis$, we find that the WMAP 5-year data alone provide only a weak
indication for CNB anisotropies with $c_\vis^2 > 0.06$ at the 95% confidence
level. When we combine CMB anisotropy data with measurements of galaxy
clustering, SN-Ia Hubble diagram, and other cosmological information, the
detection increases to $c_\vis^2 > 0.16$ at the same 95% confidence level.
Future data from Planck, combined with a weak lensing survey such as the one
expected with DUNE from space, will be able to measure the CNB anisotropy
parameter at about 10% accuracy. We discuss the degeneracy between neutrino
background ansiotropies and other cosmological para meters such as the number
of effective neutrinos species and the dark energy equation of state.",0804.1925v2
2008-04-28,Anisotropy of Galactic Cosmic Rays and New Discoveries in Its Measurements,"We discuss recently published results of two-dimensional measurements of the
cosmic ray anisotropy in the energy range 1-100 TeV. It is demonstrated that,
in spite of pretence of the authors to measure the anisotropy in more detail
than it was done in one-dimensional measurements of the first harmonic of CR
intensity in sidereal time, new measurements give nothing essentially new.
Moreover, two-dimensional picture is misleading creating an illusion that the
true direction of the anisotropy is observed, while, as before, only the
projection of the anisotropy onto the equatorial plane is measured and the
phase of the anisotropy remains to be the only directly measured parameter. The
sophisticated interpretations of the results of 2D measurements made by their
authors are invalid, since they are based on the false assumption that the
equatorial excess and deficit of CR intensity seen on the difference maps
represent the real anisotropy.",0804.4381v1
2008-05-14,Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies,"The interplay between intrinsic and surface/interface-induced magnetic
anisotropies strongly in- fluences magnetization processes in nanomagnetic
systems. We develop a micromagnetic theory to describe the field-driven
reorientation in nanomagnets with cubic and uniaxial anisotropies. Spin
configurations in competing phases and parameters of accompanying multidomain
states are calculated as functions of the applied field and the magnetic
anisotropies. The constructed magnetic phase diagrams allow to classify
different types of the magnetization reversal and to provide detailed analysis
of the switching processes in magnetic nanostructures. The calculated
magnetization profiles of isolated domain walls show that the equilibrium
parameters of such walls are extremely sensitive to applied magnetic field and
values of the competing anisotropies and can vary in a broad range. For
nanolayers with perpendicular anisotropy the geometrical parameters of stripe
domains have been calculated as functions of a bias field. The results are
applied to analyse the magnetization processes as observed in various
nanosystems with competing anisotropies, mainly, in diluted magnetic
semiconductor films (Ga,Mn)As.",0805.1984v2
2009-02-18,Splitting of the Kondo resonance in anisotropic magnetic impurities on surfaces,"Using the numerical renormalization group method, we study the splitting of
the Kondo resonance by a magnetic field applied in different directions in the
Kondo model for anisotropic magnetic impurities. Several types of magnetic
anisotropy are considered: the XXZ exchange coupling anisotropy J_perp J_z, the
longitudinal magnetic anisotropy DS_z^2, and the transverse magnetic anisotropy
E(S_x^2-S_y^2). In the spin-1/2 model with the XXZ exchange coupling anisotropy
we find very small direction dependence in the magnitude of the splitting. In
the spin-3/2 model with the easy-plane (D>0) anisotropy, we observe very
unequal magnitudes with further differences between x and y directions in the
presence of an additional transverse anisotropy. A simple and rather intuitive
interpretation is that the splitting is larger in magnetically soft directions.
The magnitude of the splitting is directly related to the energy differences
between spin states and it is only weakly modified by some multiplicative
factor due to Kondo screening. The results for the S=3/2 model are in good
agreement with recent scanning tunneling spectroscopy studies of Co impurities
adsorbed on CuN islands on Cu(100) surfaces [A. F. Otte et al., Nature Physics
4, 847 (2008)]",0902.3119v1
2010-06-17,Constrained Monte Carlo Method and Calculation of the Temperature Dependence of Magnetic Anisotropy,"We introduce a constrained Monte Carlo method which allows us to traverse the
phase space of a classical spin system while fixing the magnetization
direction. Subsequently we show the method's capability to model the
temperature dependence of magnetic anisotropy, and for bulk uniaxial and cubic
anisotropies we recover the low-temperature Callen-Callen power laws in M. We
also calculate the temperature scaling of the 2-ion anisotropy in L10 FePt, and
recover the experimentally observed M^2.1 scaling. The method is newly applied
to evaluate the temperature dependent effective anisotropy in the presence of
the N'eel surface anisotropy in thin films with different easy axis
configurations. In systems having different surface and bulk easy axes, we show
the capability to model the temperature-induced reorientation transition. The
intrinsic surface anisotropy is found to follow a linear temperature behavior
in a large range of temperatures.",1006.3507v1
2011-06-03,Single-ion versus two-ion anisotropy in magnetic compounds: A neutron scattering study,"Anisotropy effects can significantly control or modify the ground-state
properties of magnetic systems. Yet the origin and the relative importance of
the possible anisotropy terms is difficult to assess experimentally and often
ambiguous. Here we propose a technique which allows a very direct distinction
between single-ion and two-ion anisotropy effects. The method is based on
high-resolution neutron spectroscopic investigations of magnetic cluster
excitations. This is exemplified for manganese dimers and tetramers in the
mixed compounds CsMnxMg1-xBr3 (0.05\leqx\leq0.40). Our experiments provide
evidence for a pronounced anisotropy of the order of 3% of the dominant
bilinear exchange interaction, and the anisotropy is dominated by the
single-ion term. The detailed characterization of magnetic cluster excitations
offers a convenient way to unravel anisotropy effects in any magnetic material.",1106.0615v1
2011-11-16,Macrospin approximation and quantum effects in models for magnetization reversal,"The thermal activation of magnetization reversal in magnetic nanoparticles is
controlled by the anisotropy-energy barrier. Using perturbation theory, exact
diagonalization and stability analysis of the ferromagnetic spin-s Heisenberg
model with coupling or single-site anisotropy, we study the effects of quantum
fluctuations on the height of the energy barrier. Opposed to the classical
case, there is no critical anisotropy strength discriminating between reversal
via coherent rotation and via nucleation/domain-wall propagation. Quantum
fluctuations are seen to lower the barrier depending on the anisotropy
strength, dimensionality and system size and shape. In the weak-anisotropy
limit, a macrospin model is shown to emerge as the effective low-energy theory
where the microscopic spins are tightly aligned due to the ferromagnetic
exchange. The calculation provides explicit expressions for the anisotropy
parameter of the effective macrospin. We find a reduction of the
anisotropy-energy barrier as compared to the classical high spin-s limit.",1111.3900v1
2012-08-08,Effect of Co doping on the in-plane anisotropy in the optical spectrum of underdoped Ba(Fe1-xCox)2As2,"We investigated the anisotropy in the in-plane optical spectra of detwinned
Ba(Fe1-xCox)2As2. The optical conductivity spectrum of BaFe2As2 shows
appreciable anisotropy in the magnetostructural ordered phase, whereas the dc
resistivity is almost isotropic at low temperatures. Upon Co doping, the
resistivity becomes highly anisotropic, while the finite-energy intrinsic
anisotropy is suppressed. It is found that anisotropy in resistivity arises
from anisotropic impurity scattering from doped Co atoms, extrinsic in origin.
Intensity of a specific optical phonon mode is also found to show striking
anisotropy in the ordered phase. The anisotropy induced by Co impurity and that
observed in the optical phonon mode are hallmarks of the highly polarizable
electronic state in the ordered phase.",1208.1581v1
2012-10-18,Single-domain shape anisotropy in near-macroscopic Ni$_{80}$Fe$_{20}$ thin-film rectangles,"Shape anisotropy provides a simple mechanism to adjust the local bias field
in patterned structures. It is well known that for ellipsoidal particles $<1$
$\mu$m in size, a quasi-single domain state can be realized with uniform
anisotropy field. For larger patterned ferromagnetic thin-film elements, domain
formation is thought to limit the effectiveness of shape anisotropy. In our
work we show that very soft lithographically patterned Ni$_{80}$Fe$_{20}$ films
with control of induced magnetic anisotropy can exhibit shape anisotropy fields
in agreement with single-domain models, for both hysteresis loop measurements
at low field and ferromagnetic resonance measurements at high field. We show
the superiority of the fluxmetric form over the magnetometric form of
anisotropy estimate for thin films with control dimensions from 10 $\mu$m to
150 $\mu$m and in-plane aspect ratios above 10.",1210.5251v3
2013-08-05,$π$ phase shift induced by interface anisotropy in precession of magnetization initiated by laser heating,"Laser-induced magnetization precession of a thick Pt/Co/Pt film with
perpendicular interface anisotropy was studied using time resolved
magneto-optical Kerr effect. Although the demagnetization energy dominates the
interface anisotropy for the Co thickness considered, and the Co layer can be
characterized by an effective easy-plane anisotropy, we found that an
additional $\pi$ shift in the initial phase for the magnetization precession is
needed to describe the measured data using only the effective easy-plane
anisotropy. The additional $\pi$ phase is rendered by the dependence on the
phonon temperature of the interface anisotropy, in contrast to the dependence
on the electron temperature of the demagnetization energy. Our observation that
the precession phase is affected by both the electron and phonon temperature
warrants a detailed knowledge about the forms of anisotropy present in the
system under investigation for a complete description of laser-induced
magnetization precession.",1308.0976v5
2013-09-05,A viable explanation of the CMB dipolar statistical anisotropy,"The presence of a dipolar statistical anisotropy in the spectrum of cosmic
microwave background (CMB) fluctuations was reported by the Wilkinson Microwave
Anisotropy Probe (WMAP), and has recently been confirmed in the Planck 2013
analysis of the temperature anisotropies. At the same time, the Planck 2013
results report a stringent bound on the amplitude of the local-type
non-Gaussianity. We show that the non-linear effect of the dipolar anisotropy
generates not only a quadrupole moment in the CMB but also a local-type
non-Gaussianity. Consequently, it is not easy to build models having a large
dipolar modulation and at the same time a sufficiently small quadrupole and
level of local bispectral anisotropy to agree with the present data. In
particular, most models proposed so far are almost excluded, or are at best
marginally consistent with observational data. We present a simple alternative
scenario that may explain the dipolar statistical anisotropy while satisfying
the observational bounds on both the quadrupole moment and local-type
non-Gaussianity.",1309.1350v2
2013-12-26,Where is magnetic anisotropy field pointing to?,"The desired result of magnetic anisotropy investigations is the determination
of value(s) of various anisotropy constant(s). This is sometimes difficult,
especially when the precise knowledge of saturation magnetization is required,
as it happens in ferromagnetic resonance (FMR) studies. In such cases we
usually resort to `trick' and fit our experimental data to the quantity called
\emph{anisotropy field}, which is strictly proportional to the ratio of the
searched anisotropy constant and saturation magnetization. Yet, this quantity
is scalar, simply a number, and is therefore of little value for modeling or
simulations of the magnetostatic or micromagnetic structures. Here we show how
to `translate' the values of magnetic anisotropy constants into the complete
vector of magnetic anisotropy field. Our derivation is rigorous and covers the
most often encountered cases, from uniaxial to cubic anisotropy.",1312.7130v1
2014-09-11,Proton temperature-anisotropy-driven instabilities in weakly collisional plasmas: Hybrid simulations,"Kinetic instabilities in weakly collisional, high beta plasmas are
investigated using two-dimensional hybrid expanding box simulations with
Coulomb collisions modeled through the Langevin equation (corresponding to the
Fokker-Planck one). The expansion drives a parallel or perpendicular
temperature anisotropy (depending on the orientation of the ambient magnetic
field). For the chosen parameters the Coulomb collisions are important with
respect to the driver but are not strong enough to keep the system stable with
respect to instabilities driven by the proton temperature anisotropy. In the
case of the parallel temperature anisotropy the dominant oblique fire hose
instability efficiently reduces the anisotropy in a quasilinear manner. In the
case of the perpendicular temperature anisotropy the dominant mirror
instability generates coherent compressive structures which scatter protons and
reduce the temperature anisotropy. For both the cases the instabilities
generate temporarily enough wave energy so that the corresponding (anomalous)
transport coefficients dominate over the collisional ones and their properties
are similar to those in collisionless plasmas.",1409.3407v1
2015-06-10,Imprints of expansion onto the local anisotropy of solar wind turbulence,"We study the anisotropy of II-order structure functions defined in a frame
attached to the local mean field in three-dimensional (3D) direct numerical
simulations of magnetohydrodynamic turbulence, including or not the solar wind
expansion. We simulate spacecraft flybys through the numerical domain by taking
increments along the radial (wind) direction that forms an angle of $45^o$ with
the ambient magnetic field. We find that only when expansion is taken into
account, do the synthetic observations match the 3D anisotropy observed in the
solar wind, including the change of anisotropy with scales. Our simulations
also show that the anisotropy changes dramatically when considering increments
oblique to the radial directions. Both results can be understood by noting that
expansion reduces the radial component of the magnetic field at all scales,
thus confining fluctuations in the plane perpendicular to the radial. Expansion
is thus shown to affect not only the (global) spectral anisotropy, but also the
local anisotropy of second-order structure functions by influencing the
distribution of the local mean field, which enters this higher-order
statistics.",1506.03450v1
2015-07-17,Time evolution of the anisotropies of the hydrodynamically expanding sQGP,"In high energy heavy ion collisions of RHIC and LHC, a strongly interacting
quark gluon plasma (sQGP) is created. This medium undergoes a hydrodynamic
evolution, before it freezes out to form a hadronic matter. The initial state
of the sQGP is determined by the initial distribution of the participating
nucleons and their interactions. Due to the finite number of nucleons, the
initial distribution fluctuates on an event-by-event basis. The transverse
plane anisotropy of the initial state can be translated into a series of
anisotropy coefficients or eccentricities: second, third, fourth-order
anisotropy etc. These anisotropies then evolve in time, and result in
measurable momentum-space anisotropies, to be measured with respect to their
respective symmetry planes. In this paper we investigate the time evolution of
the anisotropies. With a numerical hydrodynamic code, we analyze how the speed
of sound and viscosity influence this evolution.",1507.05005v2
2015-09-18,Three dimensional solar anisotropy of galactic cosmic rays near the recent solar minimum 23/24,"Three dimensional (3D) galactic cosmic ray (GCR) anisotropy has been studied
for 2006- 2012. The GCR anisotropy, both in the ecliptic plane and in polar
direction, were obtained based on the neutron monitors (NMs) and Nagoya muon
telescopes (MT) data. We analyze two dimensional (2D) GCR anisotropy in the
ecliptic plane and north-south anisotropy normal to the ecliptic plane. We
reveal quasi-periodicities - the annual and 27-days waves in the GCR anisotropy
in 2006-2012. We investigate the relationship of the 27-day variation of the
GCR anisotropy in the ecliptic plane and in the polar direction with the
parameters of solar activity and solar wind.",1509.05718v1
2016-01-21,Multiscale model of global inner-core anisotropy induced by hcp-alloy plasticity,"$\bullet$ Multiscale model of inner-core anisotropy produced by hcp alloy
deformation$\bullet$ 5 to 20% single-crystal elastic anisotropy and plastic
deformation by pyramidal slip $\bullet$ Low-degree inner-core formation model
with faster crystallization at the equatorThe Earth's solid inner-core exhibits
a global seismic anisotropy of several percents. It results from a coherent
alignment of anisotropic Fe-alloy crystals through the inner-core history that
can be sampled by present-day seismic observations. By combining
self-consistent polycrystal plasticity, inner-core formation models,
Monte-Carlo search for elastic moduli, and simulations of seismic measurements,
we introduce a multiscale model that can reproduce a global seismic anisotropy
of several percents aligned with the Earth's rotation axis. Conditions for a
successful model are an hexagonal-close-packed structure for the inner-core
Fe-alloy, plastic deformation by pyramidal \textless{}c+a\textgreater{} slip,
and large-scale flow induced by a low-degree inner-core formation model. For
global anisotropies ranging between 1 and 3%, the elastic anisotropy in the
single crystal ranges from 5 to 20% with larger velocities along the c-axis.",1601.05674v1
2016-01-28,A New Maximum-Likelihood Technique for Reconstructing Cosmic-Ray Anisotropy at All Angular Scales,"The arrival directions of TeV-PeV cosmic rays show weak but significant
anisotropies with relative intensities at the level of one per mille. Due to
the smallness of the anisotropies, quantitative studies require careful
disentanglement of detector effects from the observation. We discuss an
iterative maximum-likelihood reconstruction that simultaneously fits cosmic ray
anisotropies and detector acceptance. The method does not rely on detector
simulations and provides an optimal anisotropy reconstruction for ground-based
cosmic ray observatories located in the middle latitudes. It is particularly
well suited to the recovery of the dipole anisotropy, which is a crucial
observable for the study of cosmic ray diffusion in our Galaxy. We also provide
general analysis methods for recovering large- and small-scale anisotropies
that take into account systematic effects of the observation by ground-based
detectors.",1601.07877v2
2016-04-03,Spin relaxation signature of colossal magnetic anisotropy in platinum atomic chains,"Recent experimental data demonstrate emerging magnetic order in platinum
atomically thin nanowires. Furthermore, an unusual form of magnetic anisotropy
-- colossal magnetic anisotropy (CMA) -- was earlier predicted to exist in
atomically thin platinum nanowires. Using spin dynamics simulations based on
first-principles calculations, we here explore the spin dynamics of atomically
thin platinum wires to reveal the spin relaxation signature of colossal
magnetic anisotropy, comparing it with other types of anisotropy such as
uniaxial magnetic anisotropy (UMA). We find that the CMA alters the spin
relaxation process distinctly and, most importantly, causes a large speed-up of
the magnetic relaxation compared to uniaxial magnetic anisotropy. The magnetic
behavior of the nanowire exhibiting CMA should be possible to identify
experimentally at the nanosecond time scale for temperatures below 5 K. This
time-scale is accessible in e.g., soft x-ray free electron laser experiments.",1604.00626v1
2017-01-02,Submicron scale tissue multifractal anisotropy in polarized light scattering,"A number of disordered systems exhibit local anisotropy in the fractal or
multifractal correlation and in the resulting scaling behavior, which contain
wealth of information on the system. Here, we demonstrate that the spatial
dielectric fluctuations in a random medium like biological tissue exhibit such
multifractal anisotropy, leaving its unique signature in the wavelength
variation of the light scattering Mueller matrix and manifesting as an
intriguing spectral diattenuation effect. We have thus developed an inverse
analysis method for the quantification of the multifractal anisotropy from the
scattering Mueller matrix. The method is based on processing the relevant
Mueller matrix elements in Fourier domain using Born approximation followed by
multifractal analysis. Application of this technique on tissues of human cervix
ex vivo demonstrate the potential of the multifractal anisotropy parameters as
novel biomarkers for screening subtle micro-structural changes associated with
precancers. Sensing structural anisotropy in the sub-micron length scale via
the multifractal anisotropy parameters may prove valuable for non-invasive
characterization of a wide class of complex materials and disordered scattering
media.",1701.00348v2
2017-02-06,Higher-order anisotropies in the Blast-Wave Model - disentangling flow and density field anisotropies,"We formulate a generalisation of the blast-wave model which is suitable for
the description of higher order azimuthal anisotropies of the hadron
production. The model includes anisotropy in the density profile as well as an
anisotropy in the transverse expansion velocity field. We then study how these
two kinds of anisotropies influence the single-particle distributions and the
correlation radii of two-particle correlation functions. Particularly we focus
on the third-order anisotropy and consideration is given to the averaging over
different orientation of the event plane.",1702.01735v2
2017-03-03,Search for Cosmic-Ray Electron and Positron Anisotropies with Seven Years of Fermi Large Area Telescope Data,"The Large Area Telescope on board the Fermi Gamma-ray Space Telescope has
collected the largest ever sample of high-energy cosmic-ray electron and
positron events since the beginning of its operation. Potential anisotropies in
the arrival directions of cosmic-ray electrons or positrons could be a
signature of the presence of nearby sources. We use almost seven years of data
with energies above 42 GeV processed with the Pass~8 reconstruction. The
present data sample can probe dipole anisotropies down to a level of $10^{-3}$.
We take into account systematic effects that could mimic true anisotropies at
this level. We present a detailed study of the event selection optimization of
the cosmic-ray electrons and positrons to be used for anisotropy searches.
Since no significant anisotropies have been detected on any angular scale, we
present upper limits on the dipole anisotropy. The present constraints are
among the strongest to date probing the presence of nearby young and
middle-aged sources.",1703.01073v1
2017-11-04,Spin excitation anisotropy in optimal-isovalent-doped superconductor BaFe2(As0.7P0.3)2,"We use neutron polarization analysis to study spin excitation anisotropy in
the optimal-isovalent-doped superconductor BaFe2(As0.7P0.3)2 (Tc = 30 K).
Different from optimally hole and electron-doped BaFe2As2, where there is a
clear spin excitation anisotropy in the paramagnetic tetragonal state well
above Tc, we find no spin excitation anisotropy for energies above 2 meV in the
normal state of BaFe2(As0.7P0.3)2. Upon entering the superconducting state,
significant spin excitation anisotropy develops at the antiferromagnetic (AF)
zone center QAF = (1, 0, L = odd), while magnetic spectrum is isotropy at the
zone boundary Q = (1, 0, L = even). By comparing temperature, wave vector, and
polarization dependence of the spin excitation anisotropy in BaFe2(As0.7P0.3)2
and hole-doped Ba0.67K0.33Fe2As2 (Tc = 38 K), we conclude that such anisotropy
arises from spin-orbit coupling and is associated with the nearby AF order and
superconductivity.",1711.01497v1
2018-04-19,Anisotropy of the DC conductivity due to orbital-selective spin fluctuations in the nematic phase of iron superconductors,"We study the dc conductivity of iron-based superconductors within the
orbital-selective spin fluctuation scenario. Within this approach, the
anisotropy of spin fluctuations below the spin-nematic transition at T$_S$ is
also responsible for the orbital ordering, induced by nematic self-energy
corrections to the quasiparticle dispersion. As a consequence, the anisotropy
of the dc conductivity below T$_S$ is determined not only by the anisotropy of
the scattering rates as expected within a spin-nematic scenario, but also by
the modification of the Fermi velocity due to the orbital reconstruction. More
interestingly, it turns out that these two effects contribute to the
dc-conductivity anisotropy with opposite signs. By using realistic
band-structure parameters we compute the conductivity anisotropy for both 122
and FeSe compounds, discussing the possible origin of the different
dc-conductivity anisotropy observed experimentally in these two families of
iron-based superconductors.",1804.07293v4
2018-10-09,Large nonvolatile control of magnetic anisotropy in CoPt by a ferroelectric ZnO-based tunneling barrier,"The electric control of magnetic anisotropy has important applications for
nonvolatile memory and information processing. By first-principles
calculations, we show a large nonvolatile control of magnetic anisotropy in
ferromagnetic/ferroelectric CoPt/ZnO interface. Using the switched electric
polarization of ZnO, the density-of-states and magnetic anisotropy at the CoPt
surface show a large change. Due to a strong Co/Pt orbitals hybridization and a
large spin-orbit coupling, a large control of magnetic anisotropy was found. We
experimentally measured the change of effective anisotropy by tunneling
resistance measurements in CoPt/Mg-doped ZnO/Co junctions. Additionally, we
corroborate the origin of the control of magnetic anisotropy by observations on
tunneling anisotropic magnetoresistance.",1810.03838v1
2019-04-11,Fermi-Surface Selective Determination of the $\mathbf{g}$-Factor Anisotropy in URu$_2$Si$_2$,"The $g$-factor anisotropy of the heavy quasiparticles in the hidden order
state of URu$_2$Si$_2$ has been determined from the superconducting upper
critical field and microscopically from Shubnikov-de Haas (SdH) oscillations.
We present a detailed analysis of the $g$-factor for the $\alpha$, $\beta$ and
$\gamma$ Fermi-surface pockets. Our results suggest a strong $g$-factor
anisotropy between the $c$ axis and the basal plane for all observed Fermi
surface pockets. The observed anisotropy of the $g$-factor from the quantum
oscillations is in good agreement with the anisotropy of the superconducting
upper critical field at low temperatures, which is strongly limited by the
paramagnetic pair breaking along the easy magnetization axis $c$. However, the
anisotropy of the initial slope of the upper critical field near $T_c$ cannot
be explained by the anisotropy of the effective masses and Fermi velocities
derived from quantum oscillations.",1904.05567v1
2019-05-13,Extraordinary temperature dependent magnetic anisotropy of the non-collinear antiferromagnet IrMn,"The magnetic anisotropy of antiferromagnets plays a crucial role in
stabilising the magnetisation of many spintronic devices. In non-collinear
antiferromagnets such as IrMn the symmetry and temperature dependence of the
effective anisotropy are poorly understood. Theoretical and experimental
calculations of the effective anisotropy constant for IrMn differ by two orders
of magnitude, while the symmetry has been calculated as uniaxial in
contradiction to the assumed relationship between crystallographic symmetry and
temperature dependence of the anisotropy from the Callen-Callen law. In this
letter we determine the effective anisotropy energy surface of \Lonetwo - \IrMn
using an atomistic spin model and constrained Monte Carlo simulations. We find
that meta-stable spin structures lower the overall energy barrier to a tenth of
that estimated from simple geometrical considerations, significantly reducing
the discrepancy between experiment and theory. The temperature scaling of the
anisotropy energy barrier shows an exponent of \factor, close to a uniaxial
exponent of 3. Our results demonstrate the importance of non-collinear spin
states on the thermal stability of antiferromagnets with consequences for the
practical application of antiferromagnets in devices operating at elevated
temperatures.",1905.05069v1
2020-01-10,Studying Anisotropy of Compressible Magnetohydrodynamic Turbulence by Synchrotron Polarization Intensity,"Based on statistical analysis of synchrotron polarization intensity, we study
the anisotropic properties of compressible magnetohydrodynamic (MHD)
turbulence. The second-order normalized structure function, quadrupole ratio
modulus and anisotropic coefficient are synergistically used to characterize
the anisotropy of the polarization intensity. On the basis of pre-decomposition
data cubes, we first explore the anisotropy of the polarization intensity in
different turbulence regimes and find that the most significant anisotropy
occurs in the sub-Alfv\'enic regime. Using post-decomposition data cubes in
this regime, we then study the anisotropy of the polarization intensity from
Alfv\'en, slow and fast modes. Statistics of polarization intensity from
Alfv\'en and slow modes demonstrate the significant anisotropy while statistics
of polarization intensity from fast modes show isotropic structures, which is
consistent with the earlier results provided in Cho & Lazarian (2002). As a
result, both quadrupole ratio modulus and anisotropic coefficient for
polarization intensities can quantitatively recover the anisotropy of
underlying compressible MHD turbulence. The synergistic use of the two methods
helps enhance the reliability of the magnetic field measurement.",2001.03276v1
2020-01-20,The impact of anisotropy on ITER scenarios,"We report on the impact of anisotropy to tokamak plasma configuration and
stability. Our focus is on analysis of the impact of anisotropy on ITER
pre-fusion power operation 5~MA, $B=1.8$~T ICRH scenarios. To model ITER
scenarios remapping tools are developed to distinguish the impact of pressure
anisotropy from the change in magnetic geometry caused by an
anisotropy-modified current profile. The remappings iterate the
anisotropy-modified current profile to produce the same $q$ profile with
matched thermal energy. The analysis is a step toward equilibria that are
kinetically self-consistent for a prescribed scenario. We find characteristic
detachment of flux surfaces from pressure surfaces, and an outboard (inboard)
shift of peak density for $T_{\parallel}>T_\perp$ ( $T_{\parallel}<T_\perp$).
Differences in the poloidal current profile are evident, albeit not as
pronounced as for the spherical tokamak. We find that the incompressional
continuum is largely unchanged in the presence of anisotropy, and the mode
structure of gap modes is largely unchanged. The compressional branch however
exhibits significant differences in the continuum. We report on the implication
of these modifications.",2001.06996v1
2022-02-15,Pressure and temperature dependence of fluorescence anisotropy of Green Fluorescent Protein,"We have studied the effect of high hydrostatic pressure and temperature on
the steady state fluorescence anisotropy of Green Fluorescent Protein (GFP). We
find that the fluorescence anisotropy of GFP at a constant temperature
decreases with increasing pressure. At atmospheric pressure, anisotropy
decreases with increasing temperature but exhibits a maximum with temperature
for pressure larger than 20 MPa. The temperature corresponding to the maximum
of anisotropy increases with increasing pressure. By taking into account of the
rotational correlation time changes of GFP with the pressure-temperature
dependent viscosity of the solvent, we argue that viscosity increase with
pressure is not a major contributing factor to the decrease in anisotropy with
pressure. Our results suggest that the decrease of fluorescence anisotropy with
pressure may result from changes in H-bonding environment around the
chromophore.",2202.07534v1
2022-03-01,Driven Superconducting Vortex Dynamics in Systems with Two-Fold Anisotropy in the Presence of Pinning,"We examine the dynamics of superconducting vortices with two-fold anisotropic
interaction potentials driven over random pinning and compare the behavior
under drives applied parallel and perpendicular to the anisotropy direction.
The number of topological defects reaches a maximum near depinning and then
drops with increasing driving force as the vortices form one-dimensional
chains. This coincides with a transition from a pinned nematic to a moving
smectic aligned with the soft direction of the anisotropy. The system is
generally more ordered when the drive is applied along the soft direction of
the anisotropy, while for driving along the hard direction, there is a critical
value of the anisotropy above which the system remains aligned with the soft
direction. We also observe hysteresis in the dynamics, with one-dimensional
aligned chains persisting during a decreasing drive sweep to drives below the
threshold for chain formation during the increasing drive sweep. More
anisotropic systems have a greater amount of structural disorder in the moving
state. For lower anisotropy, the system forms a moving smectic-A state, while
at higher anisotropy, a moving nematic state appears instead.",2203.00617v1
2022-10-19,Generalised form of the magnetic anisotropy field in micromagnetic and atomistic spin models,"We present a general approach to the derivation of the effective anisotropy
field which determines the dynamical behaviour of magnetic spins according to
the Landau-Lifshitz-Gilbert equation. The approach is based on the gradient in
spherical polar coordinates with the final results being expressed in Cartesian
coordinates as usually applied in atomistic and micromagnetic model
calculations. The approach is generally valid for all orders of anisotropies
including higher order combinations of azimuthal and rotational anisotropies
often found in functional magnetic materials such as permanent magnets and an
emerging class of antiferromagnetic materials with applications in spintronics.
Anisotropies are represented in terms of spherical harmonics which have the
important property of rational temperature scaling. Effective field vectors are
given for anisotropies up to sixth order, presenting a unified framework for
implementing higher order magnetic anisotropies in numerical simulations.",2210.10916v4
2022-12-27,Elastic anisotropy in heterogeneous materials,"Heterogeneous materials exhibit anisotropy to varying extent that is
influenced by factors such as individual phase properties and microstructural
configuration. A review of the existing anisotropy measures proposed in the
context of single crystals reveal that they do not account for the material and
microstructural descriptors influencing the extent of anisotropy in
heterogeneous materials. To overcome this limitation, existing anisotropy
indices have been re-interpreted by considering the effective elastic
properties of heterogeneous materials obtained by appropriate homogenization
techniques. Anisotropy quantification has been demonstrated considering two
phase composite materials highlighting the role of constituent volume
fractions, secondary phase shape and elastic contrast in influencing the extent
of anisotropy. Specific cases leading to overall isotropy in two phase
composite materials and extension of the approach to consider porosity and
cracks have also been presented demonstrating the applicability of the approach
to any class of heterogeneous materials thus filling a crucial gap in the
existing literature.",2212.13503v3
2023-03-21,Inducing or suppressing the anisotropy in multilayers based on CoFeB,"Controlling the uniaxial magnetic anisotropy is of practical interest to a
wide variety of applications. We study Co$_{40}$Fe$_{40}$B$_{20}$ single films
grown on various crystalline orientations of LiNbO$_3$ substrates and on
oxidized silicon. We identify the annealing conditions that are appropriate to
induce or suppress uniaxial anisotropy. Anisotropy fields can be increased by
annealing up to 11 mT when using substrates with anisotropic surfaces. They can
be decreased to below 1 mT when using isotropic surfaces. In the first case,
the observed increase of the anisotropy originates from the biaxial strain in
the film caused by the anisotropic thermal contraction of the substrate when
back at room temperature after strain relaxation during annealing. In the
second case, anisotropy is progressively removed by applying successive
orthogonal fields that are assumed to progressively suppress any chemical
ordering within the magnetic film. The method can be applied to CoFeB/Ru/CoFeB
synthetic antiferromagnets but the tuning of the anisotropy comes with a
decrease of the interlayer exchange coupling and a drastic change of the
exchange stiffness.",2303.11718v1
2024-01-01,Inverse anisotropic catalysis and complexity,"In this work the effect of anisotropy on computational complexity is
considered by CA proposal in holographic two-sided black brane dual of a
strongly coupled gauge theory. It is shown that due to
confinement-deconfinement phase transition there are two different behaviors:
by increase in anisotropy there would be an increase in complexity growth rate
in small anisotropy and a decreases in the complexity growth rate in large
anisotropy. In the extreme case the very large anisotropy leads to the unity of
the complexity growth rate and complexity itself, it means that in this case
getting the target state from the reference state is reachable by no effort.
Moreover, we suggest that $\frac{1}{M}\frac{dC}{dt}$ is a better representation
of system degrees of freedom rather than the complexity growth rate
$\frac{dC}{dt}$ and show that how it is related to inverse anisotropic
catalysis. In addition, we consider the one-sided black brane dual to the
quantum quench and showed that increase in anisotropy comes with decrease in
complexity regardless of the anisotropy value which is due to the fact that the
system do not experience a phase transition.",2401.00732v1
1998-01-05,Calculation of the Ostriker-Vishniac Effect in Cold Dark Matter Models,"We present a new derivation of the cosmic microwave background anisotropy
spectrum from the Ostriker-Vishniac effect for an open, flat, or closed
Universe, and calculate the anisotropy expected in cold dark-matter (CDM)
models. We provide simple semi-analytic fitting formulas for the Vishniac power
spectrum that can be used to evaluate the expected anisotropy in CDM models for
any arbitrary ionization history. In a flat Universe, CDM models normalized to
cluster abundances produce rms temperature anisotropies of 0.8--2.4 $\mu$K on
arcminute angular scales for a constant ionization fraction of unity, whereas
an ionization fraction of 0.2 yields rms anisotropies of 0.3--0.8 $\mu$K. In an
open and/or high-baryon-density Universe, the level of anisotropy is somewhat
higher. The signal in some of these models may be detectable with planned
interferometry experiments. The damping of the acoustic peaks in the
primary-anisotropy spectrum at degree angular scales depends primarily on the
optical depth and only secondarily on the epoch of reionization. On the other
hand, the amplitude of Ostriker-Vishniac anisotropies depends sensitively on
the epoch of reionization. Therefore, when combined with the estimate of the
reionization optical depth provided by maps of degree-scale anisotropies, the
Ostriker-Vishniac effect can provide a unique probe of the epoch of
reionization.",9801022v3
2007-05-28,Dynamical models with a general anisotropy profile,"Both numerical simulations and observational evidence indicate that the outer
regions of galaxies and dark matter haloes are typically mildly to
significantly radially anisotropic. The inner regions can be significantly
non-isotropic, depending on the dynamical formation and evolution processes. In
an attempt to break the lack of simple dynamical models that can reproduce this
behaviour, we explore a technique to construct dynamical models with an
arbitrary density and an arbitrary anisotropy profile. We outline a general
construction method and propose a more practical approach based on a
parameterized anisotropy profile. This approach consists of fitting the density
of the model with a set of dynamical components, each of which have the same
anisotropy profile. Using this approach we avoid the delicate fine-tuning
difficulties other fitting techniques typically encounter when constructing
radially anisotropic models. We present a model anisotropy profile that
generalizes the Osipkov-Merritt profile, and that can represent any smooth
monotonic anisotropy profile. Based on this model anisotropy profile, we
construct a very general seven-parameter set of dynamical components for which
the most important dynamical properties can be calculated analytically. We use
the results to look for simple one-component dynamical models that generate
simple potential-density pairs while still supporting a flexible anisotropy
profile. We present families of Plummer and Hernquist models in which the
anisotropy at small and large radii can be chosen as free parameters. We also
generalize these two families to a three-parameter family that
self-consistently generates the set of Veltmann potential-density pairs.
(Abridged...)",0705.4109v1
2009-04-09,"Magnetic anisotropy in (Ga,Mn)As: Influence of epitaxial strain and hole concentration","We present a systematic study on the influence of epitaxial strain and hole
concentration on the magnetic anisotropy in (Ga,Mn)As at 4.2 K. The strain was
gradually varied over a wide range from tensile to compressive by growing a
series of (Ga,Mn)As layers with 5% Mn on relaxed graded (In,Ga)As/GaAs
templates with different In concentration. The hole density, the Curie
temperature, and the relaxed lattice constant of the as-grown and annealed
(Ga,Mn)As layers turned out to be essentially unaffected by the strain.
Angle-dependent magnetotransport measurements performed at different magnetic
field strengths were used to probe the magnetic anisotropy. The measurements
reveal a pronounced linear dependence of the uniaxial out-of-plane anisotropy
on both strain and hole density. Whereas the uniaxial and cubic in-plane
anisotropies are nearly constant, the cubic out-of-plane anisotropy changes
sign when the magnetic easy axis flips from in-plane to out-of-plane. The
experimental results for the magnetic anisotropy are quantitatively compared
with calculations of the free energy based on a mean-field Zener model. An
almost perfect agreement between experiment and theory is found for the
uniaxial out-of-plane and cubic in-plane anisotropy parameters of the as-grown
samples. In addition, magnetostriction constants are derived from the
anisotropy data.",0904.1565v1
2012-03-22,Non-Parametric Approximations for Anisotropy Estimation in Two-dimensional Differentiable Gaussian Random Fields,"Spatially referenced data often have autocovariance functions with elliptical
isolevel contours, a property known as geometric anisotropy. The anisotropy
parameters include the tilt of the ellipse (orientation angle) with respect to
a reference axis and the aspect ratio of the principal correlation lengths.
Since these parameters are unknown a priori, sample estimates are needed to
define suitable spatial models for the interpolation of incomplete data. The
distribution of the anisotropy statistics is determined by a non-Gaussian
sampling joint probability density. By means of analytical calculations, we
derive an explicit expression for the joint probability density function of the
anisotropy statistics for Gaussian, stationary and differentiable random
fields. Based on this expression, we obtain an approximate joint density which
we use to formulate a statistical test for isotropy. The approximate joint
density is independent of the autocovariance function and provides conservative
probability and confidence regions for the anisotropy parameters. We validate
the theoretical analysis by means of simulations using synthetic data, and we
illustrate the detection of anisotropy changes with a case study involving
background radiation exposure data. The approximate joint density provides (i)
a stand-alone approximate estimate of the anisotropy statistics distribution
(ii) informed initial values for maximum likelihood estimation, and (iii) a
useful prior for Bayesian anisotropy inference.",1203.5010v2
2013-07-03,Self-Consistent Ion Cyclotron Anisotropy-Beta Relation for Solar Wind Protons,"We derive a set of self-consistent marginally stable states for a system of
ion-cyclotron waves propagating parallel to the large-scale magnetic field
through a homogeneous proton-electron plasma. The proton distributions and the
wave dispersions are related through the condition that no further
ion-cyclotron resonant particle scattering or wave growth/damping may take
place. The thermal anisotropy of the protons in these states therefore defines
the threshold value for triggering the proton-cyclotron anisotropy instability.
A number of recent papers have noted that the anisotropy of solar wind protons
at 1 AU does not seem to be limited by the proton-cyclotron anisotropy
threshold, even at low plasma beta. However, this puzzle seems to be due solely
to the estimation of this anisotropy threshold under the assumption that the
protons have a bi-Maxwellian distribution. We note that bi-Maxwellian
distributions are never marginally stable to the resonant cyclotron
interaction, so these estimates do not represent physically valid thresholds.
The threshold anisotropies obtained from our marginally stable states are much
larger, as a function of proton parallel beta, than the bi-Maxwellian
estimates, and we show that the measured data remains below these more rigorous
thresholds. Thus, the results of this paper resolve the apparent contradiction
presented by the solar wind anisotropy observations at 1 AU: The bi-Maxwellian
anisotropies are not rigorous thresholds, and so do not limit the proton
distributions in the solar wind.",1307.1059v1
2013-07-25,Effects of anisotropy of turbulent convection in mean-field solar dynamo models,"We study how anisotropy of turbulent convection affects diffusion of
large-scale magnetic fields and the dynamo process on the Sun. The effect of
anisotropy is calculated in a mean-field magneto-hydrodynamics framework using
the minimal $\tau$-approximation. We examine two types of mean-field dynamo
models: the well-known benchmark flux-transport model, and a distributed-dynamo
model with the subsurface rotational shear layer. For both models we
investigate effects of the double-cell meridional circulation, recently
suggested by helioseismology. We introduce a parameter of anisotropy as a ratio
of the radial and horizontal intensity of turbulent mixing, to characterize the
anisotropy effects. It is found that the anisotropy of turbulent convection
affects the distribution of magnetic fields inside the convection zone. The
concentration of the magnetic flux near the bottom and top boundaries of the
convection zone is greater when the anisotropy is stronger. It is shown that
the critical dynamo number and the dynamo period approach to constant values
for the large anisotropy parameter. The anisotropy reduces the overlap of the
toroidal fields of subsequent cycles in the time-latitude ``butterfly' diagram.
If we assume that sunspots are formed in the vicinity of the subsurface shear
layer, then the distributed dynamo model with anisotropic diffusivity satisfies
the observational constraints from heloseismology results and is consistent
with the value of effective turbulent diffusion, estimated from the dynamics of
surface magnetic fields.",1307.6651v3
2015-07-27,Interplay between effective mass anisotropy and Pauli paramagnetic effects in a multiband superconductor--Application to Sr2RuO4--,"We investigate the mixed state properties in a type II multiband
superconductor with uniaxial anisotropy under the Pauli paramagnetic effects.
Eilenberger theory extended to a multiband superconductor is utilized to
describe the detailed vortex lattice properties, such as the flux line form
factors, the vortex lattice anisotropy and magnetic torques. We apply this
theory to Sr$_2$RuO$_4$ to analyze those physical quantities obtained
experimentally, focusing on the interplay between the strong two-dimensional
anisotropy and the Pauli paramagnetic effects. This study allows us to
understand the origin of the disparity between the vortex lattice anisotropy
($\sim$60) and the $H_{\rm c2}$ anisotropy ($\sim$20). Among the three bands;
$\gamma$ with the effective mass anisotropy $\sim$180, $\alpha$ with $\sim$120,
and $\beta$ with $\sim$60, the last one is found to be the major band,
responsible for various magnetic responses while the minor $\gamma$ band plays
an important role in the vortex formation. Namely, in a field orientation
slightly tilted away from the two dimensional basal plane those two bands
cooperatively form the optimal vortex anisotropy which exceeds that given by
the effective mass formula with infinite anisotropy. This is observed by small
angle neutron scattering experiments on Sr$_2$RuO$_4$. The pairing symmetry of
Sr$_2$RuO$_4$ realized is either spin singlet or spin triplet with the d-vector
strongly locked in the basal plane. The gap structure is that the major $\beta$
band has a full gap and the minor $\gamma$ band has a $d_{x^2-y^2}$ like gap.",1507.07364v1
2015-11-06,Velocity anisotropy in tidally limited star clusters,"We explore the long-term evolution of the anisotropy in the velocity space of
star clusters starting with different structural and kinematical properties. We
show that the evolution of the radial anisotropy strength and its radial
variation within a cluster contain distinct imprints of the cluster initial
structural properties, dynamical history, and of the external tidal field of
its host galaxy. Initially isotropic and compact clusters with small initial
values of the ratio of the half-mass to Jacobi radius, $r_h/r_J$, develop a
strong radial anisotropy during their long-term dynamical evolution. Many
clusters, if formed with small values of $r_h/r_J$, should now be characterized
by a significant radial anisotropy increasing with the distance from the
cluster centre, reaching its maximum at a distance between 0.2 $r_J$ and 0.4
$r_J$, and then becoming more isotropic or mildly tangentially anisotropic in
the outermost regions. A similar radial variation of the anisotropy can also
result from an early violent relaxation phase. In both cases, as a cluster
continues its evolution and loses mass, the anisotropy eventually starts to
decrease and the system evolves toward an isotropic velocity distribution.
However, in order to completely erase the strong anisotropy developed by these
compact systems during their evolution, they must be in the advanced stages of
their evolution and lose a large fraction of their initial mass. Clusters that
are initially isotropic and characterized by larger initial values of
$r_h/r_J$, on the other hand, never develop a significant radial anisotropy.",1511.02236v1
2016-02-11,Ginzburg-Landau theory of the superheating field anisotropy of layered superconductors,"We investigate the effects of material anisotropy on the superheating field
of layered superconductors. We provide an intuitive argument both for the
existence of a superheating field, and its dependence on anisotropy, for
$\kappa = \lambda / \xi$ (the ratio of magnetic to superconducting healing
lengths) both large and small. On the one hand, the combination of our
estimates with published results using a two-gap model for MgB${}_2$ suggests
high anisotropy of the superheating field near zero temperature. On the other
hand, within Ginzburg-Landau theory for a single gap, we see that the
superheating field shows significant anisotropy only when the crystal
anisotropy is large and the Ginzburg-Landau parameter $\kappa$ is small. We
then conclude that only small anisotropies in the superheating field are
expected for typical unconventional superconductors near the critical
temperature. Using a generalized form of Ginzburg Landau theory, we do a
quantitative calculation for the anisotropic superheating field by mapping the
problem to the isotropic case, and present a phase diagram in terms of
anisotropy and $\kappa$, showing type I, type II, or mixed behavior (within
Ginzburg-Landau theory), and regions where each asymptotic solution is
expected. We estimate anisotropies for a number of different materials, and
discuss the importance of these results for radio-frequency cavities for
particle accelerators.",1602.03752v3
2016-04-20,Extending Velocity Channel Analysis for Studying Turbulence Anisotropies,"We extend the velocity channel analysis (VCA), introduced by Lazarian &
Pogosyan, of the intensity fluctuations in the velocity slices of
position-position-velocity (PPV) spectroscopic data from Doppler broadened
lines to study statistical anisotropy of the underlying velocity and density
that arises in a turbulent medium from the presence of magnetic field. In
particular, we study analytically how the anisotropy of the intensity
correlation in the channel maps changes with the thickness of velocity
channels. In agreement with the earlier VCA studies we find that the anisotropy
in the thick channels reflects the anisotropy of the density field, while the
relative contribution of density and velocity fluctuations to the thin velocity
channels depends on the density spectral slope. We show that the anisotropies
arising from Alfven, slow and fast magnetohydrodynamical modes are different,
in particular, the anisotropy in PPV created by fast modes is opposite to that
created by Alfven and slow modes, and this can be used to separate their
contributions. We successfully compare our results with the recent numerical
study of the PPV anisotropies measured with synthetic observations. We also
extend our study to the medium with self-absorption as well as to the case of
absorption lines. In addition, we demonstrate how the studies of anisotropy can
be performed using interferometers.",1604.06102v2
2016-08-18,Anisotropies in the HI gas distribution toward 3C196,"The local Galactic HI gas was found to contain cold neutral medium (CNM)
filaments that are aligned with polarized dust emission. These filaments appear
to be dominated by the magnetic field and in this case turbulence is expected
to show distinct anisotropies. We use the Galactic Effelsberg--Bonn HI Survey
(EBHIS) to derive 2D turbulence spectra for the HI distribution in direction to
3C196 and two more comparison fields. Prior to Fourier transform we apply a
rotational symmetric 50% Tukey window to apodize the data. We derive average as
well as position angle dependent power spectra. Anisotropies in the power
distribution are defined as the ratio of the spectral power in orthogonal
directions. We find strong anisotropies. For a narrow range in position angle,
in direction perpendicular to the filaments and the magnetic field, the
spectral power is on average more than an order of magnitude larger than
parallel. In the most extreme case the anisotropy reaches locally a factor of
130. Anisotropies increase on average with spatial frequency as predicted by
Goldreich and Sridhar, at the same time the Kolmogorov spectral index remains
almost unchanged. The strongest anisotropies are observable for a narrow range
in velocity and decay with a power law index close to --8/3, almost identical
to the average isotropic spectral index of $-2.9 < \gamma < -2.6$. HI
filaments, associated with linear polarization structures in LOFAR observations
in direction to 3C196, show turbulence spectra with marked anisotropies.
Decaying anisotropies appear to indicate that we witness an ongoing shock
passing the HI and affecting the observed Faraday depth.",1608.05369v3
2017-01-23,Transference of Fermi Contour Anisotropy to Composite Fermions,"There has been a surge of recent interest in the role of anisotropy in
interaction-induced phenomena in two-dimensional (2D) charged carrier systems.
A fundamental question is how an anisotropy in the energy-band structure of the
carriers at zero magnetic field affects the properties of the interacting
particles at high fields, in particular of the composite fermions (CFs) and the
fractional quantum Hall states (FQHSs). We demonstrate here tunable anisotropy
for holes and hole-flux CFs confined to GaAs quantum wells, via applying
\textit{in situ} in-plane strain and measuring their Fermi wavevector
anisotropy through commensurability oscillations. For strains on the order of
$10^{-4}$ we observe significant deformations of the shapes of the Fermi
contours for both holes and CFs. The measured Fermi contour anisotropy for CFs
at high magnetic field ($\alpha_\mathrm{CF}$) is less than the anisotropy of
their low-field hole (fermion) counterparts ($\alpha_\mathrm{F}$), and closely
follows the relation: $\alpha_\mathrm{CF} = \sqrt{\alpha_\mathrm{F}}$. The
energy gap measured for the $\nu = 2/3$ FQHS, on the other hand, is nearly
unaffected by the Fermi contour anisotropy up to $\alpha_\mathrm{F} \sim 3.3$,
the highest anisotropy achieved in our experiments.",1701.06684v2
2018-01-31,Anatomy of magnetic anisotropy induced by Rashba spin-orbit interactions,"Magnetic anisotropy controls the orientational stability and switching
properties of magnetic states, and therefore plays a central role in
spintronics. First-principles density-functional-theory calculations are able,
in most cases, to provide a satisfactory description of bulk and interface
contributions to the magnetic anisotropy of particular film/substrate
combinations. In this paper we focus on achieving a simplified understanding of
some trends in interfacial magnetic anisotropy based on a simple tight-binding
model for quasiparticle states in a heavy-metal/ferromagnetic-metal bilayer
film. We explain how to calculate the magnetic anisotropy energy of this model
from the quasiparticle spin-susceptibility, compare with more conventional
approaches using either a perturbative treatment of spin-orbit interactions or
a direct calculation of the dependence of the energy on the orientation of the
magnetization, and show that the magnetic anisotropy can be interpreted as a
competition between a Fermi-sea term favoring perpendicular anisotropy and a
Fermi-surface term favoring in-plane anisotropy. Based on this finding, we
conclude that perpendicular magnetic anisotropy should be expected in an
itinerant electron thin film when the spin magnetization density is larger than
the product of the band exchange splitting and the Fermi level
density-of-states of the magnetic state.",1801.10482v2
2020-02-06,Temperature scaling of two-ion anisotropy in pure and mixed anisotropy systems,"Magnetic anisotropy plays an essential role in information technology
applications of magnetic materials, providing a means to retain the long-term
stability of a magnetic state in the presence of thermal fluctuations.
Anisotropy consists of a single-ion contribution stemming from the crystal
structure and two-ion terms attributed to the exchange interactions between
magnetic atoms. A lack of robust theory crucially limits the understanding of
the temperature dependence of the anisotropy in pure two-ion and mixed
single-ion and two-ion systems. Here, we use Green's function theory and
atomistic Monte Carlo simulations to determine the temperature scaling of the
effective anisotropy in ferromagnets in these pure and mixed cases, from
saturated to vanishing magnetization. At low temperature, we find that the pure
two-ion anisotropy scales with the reduced magnetization as $k(m) \sim
m^{2.28}$, while the mixed scenario describes the diversity of the temperature
dependence of the anisotropy observed in real materials. The temperature
dependence of the mixed anisotropy determined here is expected to considerably
contribute to the understanding and the control of the thermal properties of
magnetic materials.",2002.02548v2
2020-03-20,"Anisotropy of the transport properties of NdFeAs(O,F) thin films grown on vicinal substrates","NdFeAs(O,F) thin films having different fluorine contents were grown on 5
deg. or 10 deg. vicinal cut MgO and CaF2 single crystalline substrates by
molecular beam epitaxy. Structural characterisations by reflection high-energy
electron diffraction and x-ray diffraction confirmed the epitaxial growth of
NdFeAs(O,F). The resistivities of the ab-plane and along the c-axis were
derived from the resistivity measurements in the longitudinal and transversal
directions. The c-axis resistivity was always higher than the ab-plane
resistivity, resulting from the anisotropic electronic structure. The
resistivity anisotropy at 300 K was almost constant in the range of 50-90
irrespective of the F content. On the other hand, the resistivity anisotropy at
56 K showed a strong fluorine dependence: the resistivity anisotropy was over
200 for the films with optimum F contents (superconducting transition
temperature Tc around 50 K), whereas the resistivity anisotropy was around 70
for the films in the under-doped regime (Tc between 35 and 45 K). The mass
anisotropy are the effective masses along the c-axis and on the ab-plane) close
to Tc derived from the anisotropic Ginzburg-Landau approach using the
angular-dependency of the ab-plane resistivity was in the range from 2 to 5. On
the assumption that the square of the mass anisotropy is equal to the
resistivity anisotropy, those values are small compared to the normal state
anisotropy.",2003.09105v1
2021-04-11,The Solar Cycle Variations of the Anisotropy of Taylor Scale and Correlation Scale in the Solar Wind Turbulence,"The field-aligned anisotropy of the solar wind turbulence, which is
quantified by the ratio of the parallel to the perpendicular correlation (and
Taylor) length scales, is determined by simultaneous two-point correlation
measurements during the time period 2001-2017. Our results show that the
correlation scale along the magnetic field is the largest, and the correlation
scale in the field-perpendicular directions is the smallest, at both solar
maximum and solar minimum. However, the Taylor scale reveals inconsistent
results for different stages of the solar cycles. During the years 2001-2004,
the Taylor scales are slightly larger in the field-parallel directions, while
during the years 2004-2017, the Taylor scales are larger in the
field-perpendicular directions. The correlation coefficient between the sunspot
number and the anisotropy ratio is employed to describe the effects of solar
activity on the anisotropy of solar wind turbulence. The results show that the
correlation coefficient regarding the Taylor scale anisotropy (0.65) is larger
than that regarding the correlation scale anisotropy (0.43), which indicates
that the Taylor scale anisotropy is more sensitive to the solar activity. The
Taylor scale and the correlation scale are used to calculate the effective
magnetic Reynolds number, which is found to be systematically larger in the
field-parallel directions than in the field-perpendicular directions. The
correlation coefficient between the sunspot number and the magnetic Reynolds
number anisotropy ratio is -0.75. Our results will be meaningful for
understanding the solar wind turbulence anisotropy and its long-term
variability in the context of solar activity.",2104.04920v1
2021-12-23,Stress-tailoring magnetic anisotropy of V$_2$O$_3$/Ni bilayers,"We report on a temperature-driven reversible change of the in-plane magnetic
anisotropy of V$_2$O$_3$/Ni bilayers. This is caused by the rhombohedral to
monoclinic structural phase transition of V$_2$O$_3$ at $T_C$ = 160 K. The
in-plane magnetic anisotropy is uniaxial above $T_C$, but as the bilayer is
cooled through the structural phase transition, a secondary magnetic easy axis
emerges. Ferromagnetic resonance measurements show that this change in magnetic
anisotropy is reversible with temperature. We identify two structural
properties of the V$_2$O$_3$/Ni bilayers affecting the in-plane magnetic
anisotropy: (1) a growth-induced uniaxial magnetic anisotropy associated with
step-like terraces in the bilayer microstructure and (2) a low-temperature
strain-induced biaxial anisotropy associated with the V$_2$O$_3$ structural
phase transition. Magnetoresistance measurements corroborate the change in
magnetic anisotropy across the structural transition and suggest that the
negative magnetostriction of Ni leads to the emergence of a strain-induced
easy-axis. This shows that a temperature-dependent structural transition in
V$_2$O$_3$ may be used to tune the magnetic anisotropy in an adjacent
ferromagnetic thin film.",2112.12826v1
2022-10-27,The influence of anisotropy on the evolution of interfacial morphologies in directional solidification: A phase-field study,"By adjusting the interface energy, curvature, and velocity, the anisotropy
plays an important role in the interaction between interfacial processes and
transport processes, determining the solidification structures. In this paper,
through the quantitative phase-field model, the influence of anisotropy on the
evolution of interfacial morphologies in directional solidification is
investigated. To represent different interfacial anisotropies, the
solidification processes with different preferred crystallographic orientations
are performed. Then the effect of anisotropy on morphological evolution is
discussed systematically. At the planar growth stage, the interfacial
anisotropy makes no difference in the transport processes and morphological
evolution. At the onset time of planar instability, the anisotropy determines
the detailed evolution by adjusting the interface stiffness. At the
planar-cellular-transition stage, with the influence of anisotropy, the
interfacial curvature decreases from {\theta}0=0{\deg} to {\theta}0=40{\deg}.
Hence, the solute concentration ahead of the interface increases from
{\theta}0=0{\deg} to {\theta}0=40{\deg}, while the instantaneous velocity of
the interface decreases from {\theta}0=0{\deg} to {\theta}0=40{\deg}. At the
quasi-steady-state stage, the anisotropy determines the growth direction and
tip velocity of the primary dendrite, as well as the onset of sidebranches.",2210.15673v1
2023-04-15,Temperature-anisotropy conjugate magnon squeezing in antiferromagnets,"Quantum squeezing is an essential asset in the field of quantum science and
technology. In this study, we investigate the impact of temperature and
anisotropy on squeezing of quantum fluctuations in two-mode magnon states
within uniaxial antiferromagnetic materials. Through our analysis, we discover
that the inherent nonlinearity in these bipartite magnon systems gives rise to
a conjugate magnon squeezing effect across all energy eigenbasis states, driven
by temperature and anisotropy. We show that temperature induces amplitude
squeezing, whereas anisotropy leads to phase squeezing. In addition, we observe
that the two-mode squeezing characteristic of magnon eigenenergy states is
associated with amplitude squeezing. This highlights the constructive impact of
temperature and the destructive impact of anisotropy on two-mode magnon
squeezing. Nonetheless, our analysis shows that the destructive effect of
anisotropy is bounded. We demonstrate this by showing that, at a given
temperature, the squeezing of the momentum (phase) quadrature (or equivalently,
the stretching of the position (amplitude) quadrature) approaches a constant
function of anisotropy after a finite value of anisotropy. Moreover, our study
demonstrates that higher magnon squeeze factors can be achieved at higher
temperatures, smaller levels of anisotropy, and closer to the Brillouin zone
center. All these characteristics are specific to low-energy magnons in the
uniaxial antiferromagnetic materials that we examine here.",2304.07602v2
2023-09-18,Polarized anisotropic synchrotron emission and absorption and its application to Black Hole Imaging,"Low-collisionality plasma in a magnetic field generically develops anisotropy
in its distribution function with respect to the magnetic field direction.
Motivated by the application to radiation from accretion flows and jets, we
explore the effect of temperature anisotropy on synchrotron emission. We derive
analytically and provide numerical fits for the polarized synchrotron emission
and absorption coefficients for a relativistic bi-Maxwellian plasma (we do not
consider Faraday conversion/rotation). Temperature anisotropy can significantly
change how the synchrotron emission and absorption coefficients depend on
observing angle with respect to the magnetic field. The emitted linear
polarization fraction does not depend strongly on anisotropy, while the emitted
circular polarization does. We apply our results to black hole imaging of Sgr
A* and M87* by ray-tracing a GRMHD simulation and assuming that the plasma
temperature anisotropy is set by the thresholds of kinetic-scale
anisotropy-driven instabilities. We find that the azimuthal asymmetry of the
230 GHz images can change by up to a factor of 3, accentuating ($T_\perp >
T_\parallel$) or counteracting ($T_\perp < T_\parallel$) the image asymmetry
produced by Doppler beaming. This can change the physical inferences from
observations relative to models with an isotropic distribution function, e.g.,
by allowing for larger inclination between the line of sight and spin direction
in Sgr A*. The observed image diameter and the size of the black hole shadow
can also vary significantly due to plasma temperature anisotropy. We describe
how the anisotropy of the plasma can affect future multi-frequency and photon
ring observations. In Appendices we calculate kinetic anisotropy-driven
instabilities (mirror, whistler, and firehose) for relativistically hot
plasmas.",2309.10029v1
1994-07-15,Temperature Anisotropies in a Universe with Global Defects,"We present a technique of calculating microwave anisotropies from global
defects in a reionised universe. We concentrate on angular scales down to one
degree where we expect the nongaussianity of the temperature anisotropy in
these models to become apparent.",9407051v1
1996-12-02,Coherence and Sakharov Oscillations in the Microwave Sky,"I discuss the origin of the ``Sakharov oscillations'' (or ``secondary Doppler
peaks'') in standard angular power spectra of the Cosmic Microwave Background
anisotropies calculated for inflationary models. I contrast this with the
production of CMB anisotropies in `active' models and argue that the presence
or absence of Sakharov oscillations will reveal fundamental properties of the
primordial perturbations.",9612015v1
2001-06-23,Interlayer pair tunneling and gap anisotropy in YBa$_2$Cu$_3$O$_{7-δ}$,"Recent ARPES measurement observed a large $ab$-axis gap anisotropy,
$\Delta(0,\pi)/\Delta(\pi,0)=1.5$, in clean YBa$_2$Cu$_3$O$_{7-\delta}$. This
indicates that some sub-dominant component may exist in the $d_{x^2-y^2}$-wave
dominant gap. We propose that the interlayer pairing tunneling contribution can
be determined through the investigation of the order parameter anisotropy.
Their potentially observable features in transport and spin dynamics are also
studied.",0106480v1
2002-01-07,Temperature-dependent $H_{c2}$ anisotropy in MgB$_2$ as inferred from measurements on polycrystals,"We present data on temperature-dependent anisotropy of the upper critical
field of MgB$_2$ obtained from the analysis of measurements on high purity, low
resistivity polycrystals. The anisotropy decreases in a monotonic fashion with
increase of temperature.",0201085v1
2004-04-29,"Implications evinced by the phase diagram, anisotropy, magnetic penetration depths, isotope effects and conductivities of cuprate superconductors","Anisotropy, thermal and quantum fluctuations and their dependence on dopant
concentration appear to be present in all cuprate superconductors, interwoven
with the microscopic mechanisms responsible for superconductivity. Here we
review anisotropy, in-plane and c-axis penetration depths, isotope effect and
conductivity measurements to reassess the universal behavior of cuprates as
revealed by the doping dependence of these phenomena and of the transition
temperature.",0404702v1
2002-09-24,Nano-constraints on the spatial anisotropy of the Gravitational Constant,"We present constraints from various experimental data that limit any spatial
anisotropy of the Gravitational constant to less than a part per billion or
even smaller. This rules out with a wide margin the recently reported claim of
a spatial anisotropy of G with a diurnal temporal signature.",0209093v1
2000-10-03,Isotropy vs anisotropy in small-scale turbulence,"The decay of large-scale anisotropies in small-scale turbulent flow is
investigated. By introducing two different kinds of estimators we discuss the
relation between the presence of a hierarchy for the isotropic and the
anisotropic scaling exponents and the persistence of anisotropies. Direct
measurements from a channel flow numerical simulation are presented.",0010006v1
2006-05-16,Large-scale anisotropy in scalar turbulence,"The effect of anisotropy on the statistics of a passive tracer transported by
a turbulent flow is investigated. We show that under broad conditions an
arbitrarily small amount of anisotropy propagates to the large scales where it
eventually dominates the structure of the concentration field. This result is
obtained analytically in the framework of an exactly solvable model and
confirmed by numerical simulations of scalar transport in two-dimensional
turbulence.",0605033v1
2004-05-19,Azimuthal anisotropy in high-energy heavy-ion collisions at RHIC energies,"Directed and elliptic event anisotropy parameters measured in the experiments
at relativistic heavy-ion collider are presented. The possible origin of the
measured elliptic anisotropy parameter $v_2$ and its sensitivity to the early
phase of the high-energy heavy-ion collisions are discussed.",0405016v1
2006-08-22,The effect of anisotropy and external magnetic filed on the thermal entanglement in a two-spin-qutrit system,"We study the thermal entanglement in a two-spin-qutrit system with anisotropy
in the exchange coupling between two spins. We use the realignment criterion to
distinguish the entangled states, and the negativity for measuring the
entanglement in this system. We see that the anisotropy can provide an
additional parameter for enhancing the entanglement.",0608169v1
2008-02-01,"Rapid change of electronic anisotropy in overdoped (Y,Ca)Ba2Cu3O7-d","Electronic anisotropy was studied for overdoped (Y,Ca)Ba2Cu3O7-d with various
doping levels (p). It was found that the pseudogap-like behavior in the
resistivity disappear when p exceeds 0.17, independent of the oxygen
deficiency. The anisotropy ratio (g) estimated from upper critical fields
showed a rapid decrease at around p = 0.18, approaching g = 3 for p > 0.20.",0802.0061v1
2008-07-07,Heisenberg antiferromagnets with uniaxial exchange and cubic anisotropies in a field,"Classical Heisenberg antiferromagnets with uniaxial exchange anisotropy and a
cubic anisotropy term in a field on simple cubic lattices are studied with the
help of ground state considerations and extensive Monte Carlo simulations.
Especially, we analyze the role of non-collinear structures of biconical type
occurring in addition to the well-known antiferromagnetic and spin-flop
structures. Pertinent phase diagrams are determined, and compared to previous
findings.",0807.1019v1
2009-07-23,Heisenberg antiferromagnets with exchange and cubic anisotropies,"We study classical Heisenberg antiferromagnets with uniaxial exchange
anisotropy and a cubic anisotropy term on simple cubic lattices in an external
magnetic field using ground state considerations and extensive Monte Carlo
simulations. In addition to the antiferromagnetic phase field--induced
spin--flop and non--collinear, biconical phases may occur. Phase diagrams and
critical as well as multicritical phenomena are discussed. Results are compared
to previous findings.",0907.4173v1
2010-11-13,Renormalization of the tunnel splitting in a rotating nanomagnet,"We study spin tunneling in a magnetic nanoparticle with biaxial anisotropy
that is free to rotate about its anisotropy axis. Exact instanton of the
coupled equations of motion is found that connects degenerate classical energy
minima. We show that mechanical freedom of the particle renormalizes magnetic
anisotropy and increases the tunnel splitting.",1011.3134v1
2012-11-05,Multicritical points in the three-dimensional XXZ antiferromagnet with single-ion anisotropy,"The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy,
the XXZ model, and competing planar single-ion anisotropy in a magnetic field
on a simple cubic lattice is studied with the help of extensive Monte Carlo
simulations. The biconical (supersolid) phase, bordering the antiferromagnetic
and spin-flop phases, is found to become thermally unstable well below the
onset of the disordered, paramagnetic phase, leading to interesting
multicritical points.",1211.1052v1
2016-10-13,Development of Particle-in-Cell Simulation in a Two Dimensional Trench Geometry,"A two dimensional electrostatic Particle-in-Cell simulation code is developed
to investigate anisotropy of ions in a trench geometry for plasma etching. The
numerical simulation results suggest that if the trench width is larger than
Debye length scale, anisotropy can be lost due to potential development across
the trench. Furthermore, the effects of ion charge build up on the trench
bottom is investigated, which can degrade the anisotropy.",1610.03918v1
2020-11-25,Noncoplanar multiple-$Q$ spin textures by itinerant frustration: Effects of single-ion anisotropy and bond-dependent anisotropy,"We theoretically investigate multiple-$Q$ spin textures, which are composed
of superpositions of spin density waves with different wave numbers, for an
effective spin model of centrosymmetric itinerant magnets. Our focus is on the
interplay between biquadratic interactions arising from the spin-charge
coupling and magnetic anisotropy caused by the spin-orbit coupling. Taking into
account two types of the magnetic anisotropy, single-ion anisotropy and
bond-dependent anisotropy, we elucidate magnetic phase diagrams for an
archetypal triangular-lattice system in the absence and presence of an external
magnetic field. In the case of the single-ion anisotropy, we find a plethora of
multiple-$Q$ instabilities depending on the strength and the sign of the
anisotropy (easy plane or easy axis), including a skyrmion crystal with
topological number of two. In an external magnetic field, we find that a
skyrmion crystal with topological number of one is stabilized by the in-plane
(out-of-plane) magnetic field under the easy-plane (easy-axis) anisotropy. We
also examine the stability of the field-induced skyrmion crystal by rotating
the field direction. As a biproduct, we show that a triple-$Q$ state with
nonzero chirality appears in the presence of the biquadratic interaction and
the easy-axis anisotropy. Meanwhile, we find that the bond-dependent anisotropy
also stabilizes both types of skyrmion crystals. We show that, however, for the
skyrmion crystal with topological number of one, Bloch- and N\'eel-type
skyrmion crystals are selectively realized depending on the sign of the
bond-dependent anisotropy. Moreover, we find yet another multiple-$Q$ states,
including two types of meron crystals with the skyrmion numbers of one and two.
The systematic investigation will provide a reference to complex magnetic
textures in centrosymmetric magnetic metals.",2011.13040v2
2021-04-22,Quasi-periodic changes of three dimensional solar anisotropy of galactic cosmic rays for 1965-2014,"We study features of the 3D anisotropy of galactic cosmic rays (GCR) for
1965-2014. We analyze the 27-day variations of the 2D GCR anisotropy in the
ecliptic plane, and the north-south anisotropy normal to the ecliptic plane. We
study the dependence of the 27-day variation of the 3D GCR anisotropy on the
solar cycle and solar magnetic cycle. We demonstrate that the 27-day variations
of the GCR intensity and anisotropy can be used as an important tool to study
solar wind, solar activity and heliosphere. We use the components of the 3D GCR
anisotropy found based on hourly data of neutron monitors (NMs) and muon
telescopes (MTs) using the harmonic analyses and spectrographic methods. We
correct 2D diurnal variation of the GCR intensity for the influence of the
Earth magnetic field. We derive the north-south component of the GCR anisotropy
based on the GG index calculated as the difference in GCR intensities of Nagoya
multidirectional MTs. We show that behavior of the 27-variation of the 3D
anisotropy verifies an existence of a stable long-lived active heliolongitudes
on the sun. This finding illustrates usefulness of the 27-day variation of the
GCR anisotropy as a unique proxy to study solar wind, solar activity and
heliosphere. We distinguish a tendency of the 22-year changes of the amplitudes
of the 27-day variation of the 2D anisotropy connected with the solar magnetic
cycle. We demonstrate that the amplitudes of the 27-day variation of the
north-south component of the anisotropy vary upon the 11 year solar cycle,
however, a dependence of the solar magnetic polarity hardly can be recognized.
We show that the 27-day recurrences of the $GG$ index and At component are in a
high positive correlation, and both are highly correlated with By component of
the heliospheric magnetic field.",2104.11279v1
2021-05-25,Study of Anisotropy on Ferromagnetic Electrodes of a Magnetic Tunnel Junction (MTJ)-Based Molecular Spintronics Device (MTJMSD),"Magnetic tunnel junction-based molecular spintronics devices (MTJMSDs) are
designed by covalently connecting the paramagnetic molecules across two
ferromagnets (FM) electrodes of a magnetic tunnel junction (MTJ). MTJMSD
provides opportunities to connect FM electrodes of a vast range of anisotropy
properties to a variety of molecules of length scale. Our prior studies showed
that the paramagnetic molecules can produce strong antiferromagnetic coupling
with FM electrodes. The device properties of MTJMSD depend upon various factors
such as anisotropy, spin fluctuation, thermal energy, etc. In this paper, we
report a theoretical Monte Carlo Simulation (MCS) study to explain the impact
of anisotropy on the MTJMSD equilibrium properties. We studied the energy
variation of the MTJMSD system with time as a function of FM electrode
anisotropy. Experimentally designed FM electrodes of MTJMSD contain
multi-layers of different ferromagnetic materials. These materials possess
in-plane and out-of-plane magnetic anisotropy characteristics. To understand
the competing effect of in-plane and out-of-plane anisotropy, we have
computationally applied anisotropies on the left FM electrode. For the MCS
study, the orientation of the device was kept along YZ plane. As a result, the
applied anisotropy along the X-direction (\mathbit{A}_{\mathbit{Lx}}) and
Y-direction (\mathbit{A}_{\mathbit{Ly}}) represent out-of-plane and in-plane
anisotropy, respectively. We found that increasing anisotropy strength starts
exhibiting diverse domain structures within an FM electrode. Increasing the
magnitude of anisotropy was found to create stripe-shaped domains with opposite
spins. These domains represent the different magnetic phases. However, the
application of equal magnitude of in-plane and out-of-plane cancels the strip
domain formation and lowers the magnetic moment of overall MTJMSD.",2105.11635v1
2022-07-01,Extinction of the TeV Gamma-Ray Background by Sunlight,"I show that pair production on sunlight introduces a sizable anisotropy in
the cosmic background of TeV gamma-rays. The anisotropy amplitude in the
direction of the Sun exceeds the cosmic dipole anisotropy from the motion of
the Sun relative to the cosmic rest-frame.",2207.00671v1
1995-04-18,The Physics of Microwave Background Anisotropies,"Cosmic microwave background anisotropies provide a vast amount of information
on both structure formation in the universe and the background dynamics and
geometry. The full physical content and detailed structure of anisotropies can
be understood in a simple and intuitive fashion through a systematic
investigation of the individual mechanisms for anisotropy formation, based on
elementary gravitational and fluid dynamics.",9504057v1
1996-09-17,Results from the First Flight of BAM,"A new instrument, BAM (Balloon-borne Anisotropy Measurement), designed to
measure cosmic microwave background (CMB) anisotropy at medium angular scales
was flown for the first time in July of 1995. BAM is unique in that it uses a
cryogenic differential Fourier transform spectrometer coupled to a lightweight
off-axis telescope. The very successful first flight of BAM demonstrates the
potential of the instrument for obtaining high quality CMB anisotropy data.",9609108v1
1997-11-25,Microwave Background Anisotropy and Large Scale Structure in Warm Dark Matter Models,"Large scale structure and microwave background anisotropies are studied for
warm dark matter models. Two warm dark matter candidates are considered:
gravitinos and sterile neutrinos. Linear large scale structure properties such
as $\sigma_{8}$ and the excess power are calculated, as well as microwave
background anisotropies. A rather robust feature of warm dark matter models is
that the large scale structure properties are similar to those of mixed dark
matter, but that the microwave background anisotropy is very similar to that of
standard cold dark matter.",9711304v1
1998-06-01,Massless (pseudo-)scalar seeds of CMB anisotropy,"A primordial stochastic background of very weakly coupled massless
(pseudo-)scalars can seed CMB anisotropy, when large-scale fluctuations of
their stress-tensor re-enter the horizon during the matter-dominated era. A
general relation between multipole coefficients of the CMB anisotropy and the
seed's energy spectrum is derived. Magnitude and tilt of the observed
anisotropies can be reproduced for the nearly scale-invariant axion spectra
that are predicted in a particularly symmetric class of string cosmology
backgrounds.",9806015v1
1999-10-28,First Results from Viper: Detection of Small-Scale Anisotropy at 40 GHZ,"Results of a search for small-scale anisotropy in the cosmic microwave
background (CMB) are presented. Observations were made at the South Pole using
the Viper telescope, with a .26 degree (FWHM) beam and a passband centered at
40 GHz. Anisotropy band-power measurements in bands centered at l = 108, 173,
237, 263, 422 and 589 are reported. Statistically significant anisotropy is
detected in all bands.",9910503v1
2000-03-17,Non-Gaussian signature induced by the SZ effect of galaxy clusters,"We apply statistical tests, based on the study of thecoefficients in a
wavelet decomposition, to a cosmological signal: the Cosmic Microwave
Background (CMB) anisotropies. The latter represent the superposition of
primary anisotropy imprints of the initial density perturbations and secondary
anisotropies due to photon interactions after recombination. In an inflationary
scenario with Gaussian distributed fluctuations, we study the statistical
signature of the secondary effects. More specifically, we investigate the
dominant effects arising from the Sunyaev-Zel'dovich effect of galaxy clusters.
Our study predicts the non-Gaussian signature of these secondary anisotropies
and its detectability in the context of the future CMB satellite Planck
Surveyor.",0003256v1
2001-05-19,The Imprint of Lithium Recombination on the Microwave Background Anisotropies,"Following Loeb (2001), we explore the imprint of the resonant 6708A line
opacity of neutral lithium on the temperature and polarization anisotropies of
the cosmic microwave background (CMB) at observed wavelengths of 250-350 micron
(0.9-1.2 THz). We show that if lithium recombines in the redshift range of
z=400-500 as expected, then the standard CMB anisotropies would be
significantly modified in this wavelength band. The modified polarization
signal could be comparable to the expected polarization anisotropies of the
far-infrared background on sub-degree angular scales (l>100). Detection of the
predicted signal can be used to infer the primordial abundance of lithium, and
to probe structure in the Universe at z~500.",0105345v1
2001-09-27,The theory of CMB anisotropies,"This is a review of the theory of CMB anisotropies, an updated version of a
course given at the troisieme cycle de la Suisse Romande. An introduction to
gauge invariant cosmological perturbation theory is given and the theory CMB
anisotropies is develiped in this context. Simple analytical approximations for
the acoustic peak positions for adiabatic and isocurvature perturbations are
derived. Silk damping is discussed by an analytic approximation. A short
description of the present status of observations and parameter estimation
followed by a critical discussion terminate the review. The full system of
differential equations for CMB anisotropies and polarization needed in a
numerical treatment is also developed and given in an appendix.",0109522v1
2002-03-07,TACMB-1: The Theory of Anisotropies in the Cosmic Microwave Background (Bibliographic Resource Letter),"This Resource Letter provides a guide to the literature on the theory of
anisotropies in the cosmic microwave background. Journal articles, web pages,
and books are cited for the following topics: discovery, cosmological origin,
early work, recombination, general CMB anisotropy references, primary CMB
anisotropies (numerical, analytical work), secondary effects,
Sunyaev-Zel'dovich effect(s), lensing, reionization, polarization, gravity
waves, defects, topology, origin of fluctuations, development of fluctuations,
inflation and other ties to particle physics, parameter estimation, recent
constraints, web resources, foregrounds, observations and observational issues,
and gaussianity.",0203120v1
2002-09-26,CMB observations using the SKA,"We examine the prospects for observations of CMB anisotropy with the SKA; we
discuss the advantages of interferometric SKA imaging, observing strategies,
calibration issues and the achievable sensitivity. Although the SKA will
probably operate at cm wavelengths, where discrete source confusion dominates
the CMB anisotropy, its extreme sensitivity to point sources will make it
possible to subtract the source contamination at these wavelengths and thereby
image the low surface brightness CMB anisotropies on small angular scales. The
SKA, operating at 10-20 GHz, may usefully make high-l observations of the CMB
anisotropy spectrum and survey the sky for Sunyaev-Zeldovich decrements.",0209569v1
2004-06-24,Cosmic Background Radiation Mini-Review,"This is a complete re-write of the mini-review for the Review of Particle
Physics (a.k.a the Partcicle Data Book), which includes an assessment of the
CMB anisotropy results and their interpretation up until the end of 2003. It
forms a compact overview of the field at this time. Sections headings are:
Introduction; Description of CMB Anisotropies; Cosmological Parameters; Physics
of Anisotropies; Current Anisotropy Data; CMB Polarization; Complications;
Constraints on Cosmologies; Particle Physics Constraints; Fundamental Lessons;
and Future Directions.",0406567v1
2004-06-25,The Anisotropy of Electron MHD Turbulence,"We present numerical studies of 3-dimensional electron magnetohydrodynamic
(EMHD) turbulence. We investigate cascade timescale and anisotropy of freely
decaying strong EMHD turbulence with zero electron skin depth. Cascade time
scales with $k^{-4/3}$. Our numerical results clearly show scale-dependent
anisotropy. We discuss that the observed anisotropy is consistent with $k_{\|}
\propto k_{\perp}^{1/3}$, where $k_{\|}$ and $k_{\perp}$ are wave numbers
parallel and perpendicular to (local) mean magnetic field, respectively.",0406595v1
2005-12-17,Light-cone anisotropy in 21cm fluctuations during the epoch of reionization,"The delay in light travel time along the line of sight generates an
anisotropy in the power spectrum of 21cm brightness fluctuations from the epoch
of reionization. We show that when the fluctuations in the neutral hydrogen
fraction become non-linear at the later stages of reionization, the light-cone
anisotropy becomes of order unity on scales >50 comoving Mpc. During this
period the density fluctuations and the associated anisotropy generated by
peculiar velocities are negligible in comparison.",0512453v2
1994-02-04,Enhancement of Anisotropy due to Fluctuations in Quasi-One-Dimensional Antiferromagnets,"It is shown that the observed anisotropy of magnetization at high magnetic
fields in RbMnBr3 , a quasi-one-dimensional antiferromagnet on a distorted
stacked triangular lattice, is due to quantum and thermal fluctuations. These
fluctuations are taken into account in the framework of linear spin-wave theory
in the region of strong magnetic fields. In this region the divergent
one-dimensional integrals are cut off by magnetic field and the bare easy-plane
anisotropy. Logarithmical dependence on the cutoff leads to the ""enhancement""
of the anisotropy in magnetization. Comparison between magnetization data and
our theory with parameters obtained from neutron scattering experiments has
been done.",9402024v1
1998-05-19,Magnetic Anisotropy in Quantum Hall Ferromagnets,"We show that the sign of magnetic anisotropy energy in quantum Hall
ferromagnets is determined by a competition between electrostatic and exchange
energies. Easy-axis ferromagnets tend to occur when Landau levels whose states
have similar spatial profiles cross. We report measurements of integer QHE
evolution with magnetic-field tilt. Reentrant behavior observed for the $\nu =
4$ QHE at high tilt angles is attributed to easy-axis anisotropy. This
interpretation is supported by a detailed calculation of the magnetic
anisotropy energy.",9805240v1
2000-02-24,Numerical studies of domains and bubbles of Langmuir monolayers,"A numerical algorithm based on the finite element methods has been developed
to accurately determine the shape of the boundary of a domain containing
``boojum'' textures. Within the context of the simple model we adopt, the
effects of both bulk elastic anisotropy and line-tension anisotropy on the
domain boundary can be examined. It is found that line-tension anisotropy must
be present in order to account for domains with protruding features. Both
elastic anisotropy and anisotropic line-tension can result in domains with
indentations. The numerical algorithm has been extended to investigate the
problem of a bubble in extended region ordered phase.",0002367v1
2000-12-03,Magnetic Anisotropy of a Single Cobalt Nanoparticle,"Using a new microSQUID set-up, we investigate magnetic anisotropy in a single
1000-atoms cobalt cluster. This system opens new fields in the characterization
and the understanding of the origin of magnetic anisotropy in such
nanoparticles. For this purpose, we report three-dimensional switching field
measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix.
We are able to separate the different magnetic anisotropy contributions and
evidence the dominating role of the cluster surface.",0012029v1
2001-03-01,Longitudinal and transversal piezoresistive response of granular metals,"In this paper, we study the piezoresistive response and its anisotropy for a
bond percolation model of granular metals. Both effective medium results and
numerical Monte Carlo calculations of finite simple cubic networks show that
the piezoresistive anisotropy is a strongly dependent function of bond
probability p and of bond conductance distribution width \Delta g. We find that
piezoresistive anisotropy is strongly suppressed as p is reduced and/or \Delta
g is enhanced and that it vanishes at the percolation thresold p=p_c. We argue
that a measurement of the piezoresistive anisotropy could be a sensitive tool
to estimate critical metallic concentrations in real granular metals.",0103035v1
2002-05-01,Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB$_2$,"We examine the superconducting anisotropy $\gamma_c = (m_c / m_{ab})^{1/2}$
of a metallic high-$T_c$ superconductor MgB$_2$ by measuring the magnetic
torque of a single crystal. The anisotropy $\gamma_c$ does not depend
sensitively on the applied magnetic field at 10 K. We obtain the anisotropy
parameter $\gamma_c = 4.31 \pm 0.14$. The torque curve shows the sharp
hysteresis peak when the field is applied parallel to the boron layers. This
comes from the intrinsic pinning and is experimental evidence for the
occurrence of superconductivity in the boron layers.",0205010v1
2002-06-10,Magnetic anisotropy of BaCu2Si2O7: theory and antiferromagnetic resonance,"Antiferromagnetic resonance (AFMR) of BaCu2Si2O7 and a microscopic theory of
the magnetic anisotropy of spin 1/2 chain compounds with folded CuO3 geometry
being in good agreement with the available data are presented. The AFMR studies
at 4.2 K show the existence of two gaps (40 and 76 GHz) at zero magnetic field
and of two spin re-orientation transitions for H||c. The microscopic origin of
the two gaps is shown to be Hund's rule coupling which leads to a ""residual
anisotropy"" beyond the compensation of the Dzyaloshinskii-Moriya term by the
symmetric anisotropy which would be valid without Hund's coupling.",0206151v1
2002-09-25,Crossed-anisotropy films for magnetic tunnel junctions and magnetic memory applications,"A prototype of magnetoresistive random access memory (MRAM) based on magnetic
tunnel junctions (MTJ) was fabricated with crossed-anisotropy of magnetic
layers on either side of the tunnelling barrier layer. It is demonstrated that
the introduction of crossed-anisotropy results in smaller switching fields and
better switching times compared to the conventional case of aligned
anisotropies. The magnetoresistive properties of fabricated devices are in good
agreement with the micromagnetic model.",0209578v1
2002-11-14,Inhomogeneous States in a Small Magnetic Disk with Single-Ion Surface Anisotropy,"We investigate analytically and numerically the ground and metastable states
for easy-plane Heisenberg magnets with single-ion surface anisotropy and disk
geometry. The configurations with two half-vortices at the opposite points of
the border are shown to be preferable for strong anisotropy. We propose a
simple analytical description of the spin configurations for all values of a
surface anisotropy. The effects of lattice pinning leads to appearance of a set
of metastable configurations.",0211265v2
2003-03-19,Many-body Green's function theory for thin ferromagnetic anisotropic Heisenberg films: treatment of the exchange anisotropy,"The many-body Green's function theory developed in our previous work for
treating the reorientation of the magnetization of thin ferromagnetic films is
extended to include the exchange anisotropy. This leads to additional momentum
dependencies which require some non-trivial changes in the formalism. The
theory is developed for arbitrary spin values S and for multilayers. The
effects of the exchange anisotropy and the single-ion anisotropy, which was
treated in our earlier work, on the magnetic properties of thin ferromagnetic
films are compared.",0303389v1
2003-07-16,Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers,"A vector spin model is used to show how frustrations within a multisublattice
antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting
on an exchange coupled ferromagnetic film. Possibilities for the existence of
exchange bias are examined and shown to exist for the case of weak chemical
disorder at the interface in an otherwise perfect structure. A sensitive
dependence on interlayer exchange is found for anisotropies acting on the
ferromagnet through the exchange coupling, and we show that a wide range of
anisotropies can appear even for a perfect crystalline structure with an
ideally flat interface.",0307384v1
2003-11-17,Critical Hysteresis from Random Anisotropy,"Critical hysteresis in ferromagnets is investigated through a $N$-component
spin model with random anisotropies, more prevalent experimentally than the
random fields used in most theoretical studies. Metastability, and the
tensorial nature of anisotropy, dictate its physics. Generically, random field
Ising criticality occurs, but other universality classes exist. In particular,
proximity to $\mathcal{O}(N)$ criticality may explain the discrepancy between
experiment and earlier theories. The uniaxial anisotropy constant, which can be
controlled in magnetostrictive materials by an applied stress, emerges as a
natural tuning parameter.",0311393v2
2003-11-20,Single-ion versus exchange anisotropy in calculating anisotropic susceptibilities of thin ferromagnetic Heisenberg films within many-body Green's function theory,"We compare transverse and parallel static susceptibilities of in-plane
uniaxial anisotropic ferromagnetic Heisenberg films calculated in the framework
of many-body Green's function theory using single-ion anisotropies with the
previously investigated case of exchange anisotropies. On the basis of the
calculated observables (easy and hard axes magnetizations and susceptibilities)
no significant differences are found, i. e. it is not possible to propose an
experiment that might decide which kind of anisotropy is acting in an actual
ferromagnetic film.",0311482v1
2004-01-26,"Evidence for granularity, anisotropy and lattice distortions in cuprate superconductors and their implications","Granularity, anisotropy, local lattice distortions and their dependence on
dopant concentration appear to be present in all cuprate superconductors,
interwoven with the microscopic mechanisms responsible for superconductivity.
Here we review anisotropy and penetration depth measurements to reassess the
evidence for granularity, as revealed by the notorious rounded phase
transition, the evidence for the three dimensional nature of superconductivity,
uncovered by the doping dependence of transition temperature and anisotropy,
and to reassess the relevance of the electron-lattice coupling, emerging from
the oxygen isotope effects.",0401505v1
2004-04-30,In-Plane Conductivity Anisotropy in Underdoped Cuprates in the Spin-Charge Gauge Approach,"Applying the recently developed spin-charge gauge theory for the pseudogap
phase in cuprates, we propose a self-consistent explanation of several peculiar
features of the far-infrared in-plane AC conductivity, including a broad peak
as a function of frequency and significant anisotropy at low temperatures,
along with a similar temperature-dependent in-plane anisotropy of DC
conductivity in lightly doped cuprates. The anisotropy of the metal-insulator
crossover scale is considered to be responsible for these phenomena. The
obtained results are in good agreement with experiments. An explicit proposal
is made to further check the theory.",0404726v1
2004-06-28,Critical properties of random anisotropy magnets,"The problem of critical behaviour of three dimensional random anisotropy
magnets, which constitute a wide class of disordered magnets is considered.
Previous results obtained in experiments, by Monte Carlo simulations and within
different theoretical approaches give evidence for a second order phase
transition for anisotropic distributions of the local anisotropy axes, while
for the case of isotropic distribution such transition is absent. This outcome
is described by renormalization group in its field theoretical variant on the
basis of the random anisotropy model. Considerable attention is paid to the
investigation of the effective critical behaviour which explains the
observation of different behaviour in the same universality class.",0406692v1
2004-07-07,Influence of surface anisotropy on the magnetization reversal of nanoparticles,"The influence of surface anisotropy on the magnetization processes of
maghemite nanoparticles with ellipsoidal shape is studied by means of Monte
Carlo simulations. Radial surface anisotropy is found to favor the formation of
hedgehog-like spin structures that become more stable as the surface anisotropy
constant at the surface $k_S$ is increased form the value at the core. We have
studied the change in the low temperature hysteresis loops with the particle
aspect ratio and with $k_S$, finding a change in the magnetization reversal
mode as $k_S$ or the particle elongation is increased.",0407176v1
2005-05-11,"Annealing-induced changes of the magnetic anisotropy of (Ga,Mn)As epilayers","The dependence of the magnetic anisotropy of As-capped (Ga,Mn)As epilayers on
the annealing parameters - temperature and time - has been investigated. A
uniaxial magnetic anisotropy is evidenced, whose orientation with respect to
the crystallographic axes changes upon annealing from [-110] for the as-grown
samples to [110] for the annealed samples. Both cubic an uniaxial anisotropies
are tightly linked to the concentration of charge carriers, the magnitude of
which is controlled by the annealing process.",0505278v1
2005-12-02,Exchange enhanced anisotropy in ferromagnetic/antiferromagnetic multilayers: dynamic consequences,"The phenomena of exchange anisotropy is well known in terms of static
magnetization properties such as enhanced coercivity and magnetization loop
shifts. These effects are primarily associated with effective anisotropies
introduced into the ferromagnet by exchange coupling with a strongly
anisotropic antiferromagnet. These effective anisotropies can be understood as
manifestations of a more fundamental exchange induced susceptibility. We show
that a consequence of this view is that a class of unusual dynamic effects
associated with the exchange susceptibility should also exist. The effects
become apparent near the ordering temperature of the antiferromagnet and affect
domain wall velocities, domain wall resonances, and precessional switching of
the ferromagnet.",0512034v1
2006-02-17,Theory of high-symmetry tetramer single molecule magnets,"We present a microscopic theory of single molecule magnets. From our exact
single-ion spin matrix elements for four arbitrary spins, we study the
single-ion anisotropy of equal spins exhibiting $T_d$, $D_{2d}$, or $C_{4v}$
molecular group symmetry. Each group generates site-dependent single-ion
anisotropy. For weak anisotropy, accurate Hartree expressions for the
magnetization, specific heat, electron paramagnetic resonance (EPR) absorption,
and inelastic neutron scattering cross-section are given. For $D_{2d}$,
azimuthal single-ion anisotropy leads to the observed Ni$_4$ EPR splittings.",0602417v2
2006-11-09,Phase diagram of the spin-1 XXZ Heisenberg ferromagnet with a single-ion anisotropy,"Phase diagram of the spin-1 quantum Heisenberg model with both exchange as
well as single-ion anisotropy is constructed within the framework of pair
approximation formulated as a variational procedure based on the
Gibbs-Bogoliubov inequality. In this form adapted variational approach is used
to obtain the results equivalent with the Oguchi's pair approximation. It is
shown that the single-ion anisotropy induces a tricritical behaviour in the
considered model system and a location of tricritical points is found in
dependence on the exchange anisotropy strength.",0611254v3
1997-12-19,Equilibrium of Spheres with Local Anisotropy in Postnewtonian Gravity. Application to White Dwarfs,"Static solutions of white dwarfs with spherical symmetry and local anisotropy
are studied in the post-Newtonian approximation. It is argued that the
condition for equilibrium must be that the total energy is a minimum for given
baryon number and the question whether there is local isotropy or anisotropy
inside the star should follow from that condition, rather than be postulated ""a
priori"". It is shown show that, in post-Newtonian gravity, there are stable
configurations with local anisotropy for masses above the Chandrasekhar limit.",9712081v1
2001-08-29,Kaluza-Klein anisotropy in the CMB,"We show that 5-dimensional Kaluza-Klein graviton stresses can slow the decay
of shear anisotropy on the brane to observable levels, and we use cosmic
microwave background anisotropies to place limits on the initial anisotropy
induced by these stresses. An initial shear to Hubble distortion of only \sim
10^{-3}\Omega_0h_0^2 at the 5D Planck time would allow the observed large-angle
CMB signal to be a relic mainly of KK tidal effects.",0108073v2
2002-03-15,A method for analysing the jet azimuthal anisotropy in ultrarelativistic heavy ion collisions,"The azimuthal anisotropy of jet spectra due to energy loss of jet partons in
azimuthally non-symmetric volume of dense quark-gluon matter is considered for
semi-central nuclear interactions at collider energies. We develop the
techniques for event-by-event analysing the jet azimuthal anisotropy using
particle and energy elliptic flow, and suggest a method for calculation of
coefficient of jet azimuthal anisotropy without reconstruction of nuclear
reaction plane.",0203144v2
1998-07-07,Event Anisotropy in High Energy Nucleus-Nucleus Collisions,"The predictions of event anisotropy parameters from transport model RQMD are
compared with the recent experimental measurements for 158$A$ GeV Pb+Pb
collisions. Using the same model, we study the time evolution of event
anisotropy at 2$A$ GeV and 158$A$ GeV for several colliding systems. For the
first time, both momentum and configuration space information are studied using
the Fourier analysis of the azimuthal angular distribution. We find that, in
the model, the initial geometry of the collision plays a dominant role in
determining the anisotropy parameters.",9807021v1
2007-08-11,Vorticity and Magnetic Field Generation from Initial Anisotropy in Ultrarelativistic Gamma-Ray Burst Blastwaves,"Because conical segments of quasispherical ultrarelativistic blastwaves are
causally disconnected on angular scales larger than the blastwave inverse
Lorentz factor, astrophysical blastwaves can sustain initial anisotropy,
imprinted by the process that drives the explosion, while they remain
relativistic. We show that initial angular energy fluctuations in
ultrarelativistic blastwaves imply a production of vorticity in the blastwave,
and calculate the vortical energy production rate. In gamma-ray burst (GRB)
afterglows, the number of vortical eddy turnovers as the shocked fluid crosses
the blastwave shell is about unity for marginally nonlinear anisotropy. Thus
the anisotropy must be nonlinear to explain the magnetic energy density
inferred in measured GRB spectra.",0708.1588v1
2007-11-05,Polarization-anisotropy induced spatial anisotropy of polariton amplification in planar semiconductor microcavities,"Based on a microscopic many-particle theory we investigate the amplification
of polaritons in planar semiconductor microcavities. We study a spatially
perfectly isotropic microcavity system and excitation geometry. For this
system, our analysis shows that a pump-induced vectorial polarization
anisotropy can lead to a spatial anisotropy in the stimulated amplification of
polaritons. This effect is brought about by the interplay of the
longitudinal-transverse cavity mode splitting (TE-TM splitting) and the
spin-dependence of the polariton-polariton scattering processes.",0711.0768v1
2008-01-16,CMB Anisotropies: Their Discovery and Utilization,"This article is a written and modified version of a talk presented at the
conference `A Century of Cosmology' held at San Servolo, Venice, Italy, in
August 2007. The talk focuses on some of the cosmology history leading to the
discovery and exploitation of Cosmic Microwave Background (CMB) Radiation
anisotropies. We have made tremendous advances first in the development of the
techniques to observe these anisotropies and in observing and interpreting them
to extract their contained cosmological information. CMB anisotropies are now a
cornerstone in our understanding of the cosmos and our future progress in the
field. This is an outcome that Dennis Sciama hoped for and encouraged.",0801.2563v1
2008-10-19,Magnetic anisotropy of single 3d spins on CuN surface,"First-principles calculations of the magnetic anisotropy energy for Mn- and
Fe-atoms on CuN/Cu(001) surface are performed making use of the torque method.
The easy magnetization direction is found to be different for Mn and Fe atoms
in accord with the experiment. It is shown the magnetic anisotropy has a
single-ion character and mainly originates from the local magnetic moment of
Mn- and Fe-atoms. The uniaxial magnetic anisotropy constants are calculated in
reasonable agreement with the experiment.",0810.3389v1
2009-07-16,Galactic magnetic fields and the large-scale anisotropy at MILAGRO,"The air-shower observatory Milagro has detected a large-scale anisotropy of
unknown origin in the flux of TeV cosmic rays. We propose that this anisotropy
is caused by galactic magnetic fields, in particular, that it results from the
combined effects of the regular and the turbulent (fluctuating) magnetic fields
in our vicinity. Instead of a diffusion equation, we integrate Boltzmann's
equation to show that the turbulence may define a preferred direction in the
cosmic-ray propagation that is orthogonal to the local regular magnetic field.
The approximate dipole anisotropy that we obtain explains well Milagro's data.",0907.2889v2
2009-08-26,Magnetic anisotropy in Li-phosphates and origin of magnetoelectricity in LiNiPO4,"Li-based phosphates are paradigmatic materials for magnetoelectricity. By
means of first-principles calculations, we elucidate the microscopic origin of
spin anisotropy and of magnetoelectric effects in LiNiPO4. The comparison with
LiCoPO4 reveals that Co-d7 and Ni-d8 electronic clouds show distinct orbital
shapes, which in turn result in an opposite trend of the local spin anisotropy
with respect to the surrounding O6 cages. Due to magnetic anisotropy, the
Ni-based phosphate shows a peculiar ""angled-cross"" spin ground-state, which is
responsible for magnetoelectricity. In this respect, we show that, under a
magnetic field Hx, an electronic polarization Pz arises, with an estimated
linear magneto-electric coefficient in good agreement with experiments.",0908.3802v1
2010-02-10,Spin-orbit coupling induced anisotropy effects in bimetallic antiferromagnets: A route towards antiferromagnetic spintronics,"Magnetic anisotropy phenomena in bimetallic antiferromagnets Mn$_2$Au and
MnIr are studied by first-principles density functional theory calculations. We
find strong and lattice-parameter dependent magnetic anisotropies of the ground
state energy, chemical potential, and density of states, and attribute these
anisotropies to combined effects of large moment on the Mn 3$d$ shell and large
spin-orbit coupling on the 5$d$ shell of the noble metal. Large magnitudes of
the proposed effects can open a route towards spintronics in compensated
antiferromagnets without involving ferromagnetic elements.",1002.2151v1
2010-05-04,Cosmic Microwave Background Mini-review,"A compact overview of the status of CMB anisotropy results and their
cosmological interpretation. Section headings: Introduction; CMB Spectrum;
Description of CMB Anisotropies; Cosmological Parameters; Physics of
Anisotropies; Current Anisotropy Data; CMB Polarization; Complications;
Constraints on Cosmological Parameters; Particle Physics Constraints;
Fundamental Lessons; and Future Directions. This 2023 replacement is a
substantial update compared with earlier versions of this review posted to the
arXiv.",1005.0555v2
2010-08-19,Duality-based Asymptotic-Preserving method for highly anisotropic diffusion equations,"The present paper introduces an efficient and accurate numerical scheme for
the solution of a highly anisotropic elliptic equation, the anisotropy
direction being given by a variable vector field. This scheme is based on an
asymptotic preserving reformulation of the original system, permitting an
accurate resolution independently of the anisotropy strength and without the
need of a mesh adapted to this anisotropy. The counterpart of this original
procedure is the larger system size, enlarged by adding auxiliary variables and
Lagrange multipliers. This Asymptotic-Preserving method generalizes the method
investigated in a previous paper [arXiv:0903.4984v2] to the case of an
arbitrary anisotropy direction field.",1008.3405v1
2010-12-06,Anisotropies in the diffuse gamma-ray background measured by the Fermi-LAT,"The contribution of unresolved sources to the diffuse gamma-ray background
could produce anisotropies in this emission on small angular scales. Recent
studies have considered the angular power spectrum and other anisotropy metrics
as tools for identifying contributions to diffuse emission from unresolved
source classes, such as extragalactic and Galactic dark matter as well as
various astrophysical gamma-ray source populations. We present preliminary
results of an anisotropy analysis of the diffuse emission measured by the
Fermi-LAT.",1012.1206v1
2011-02-04,Anisotropy in transport and magnetic properties of K0.64Fe1.44Se2,"We report a study of anisotropy in transport and magnetic properties of
K0.64Fe1.44Se2.00 single crystals. The anisotropy in resistivity is up to one
order of magnitude between 1.8 K and 300 K. Magnetic susceptibility exhibits
weak temperature dependence in the normal state with decrease in temperature
with no significant anomalies. The lower critical fields Hc1 of
K0.64Fe1.44Se2.00 are only about 3 Oe and the anisotropy of Hc1,c/Hc1,ab is
about 1. The critical currents for H||ab and H||c are about 10-10^3 A/cm2,
smaller than in iron pnictides and in FeTe_{1-x}Se_{x} and nearly isotropic.",1102.1010v3
2011-02-17,The ordering of XY spin glasses,"Ordering properties of XY-like spin-glass magnets with an easy-plane magnetic
anisotropy are studied based on a symmetry consideration and the results of
recent numerical simulations on the pure Heisenberg and XY spin-glass models.
The effects of an easy-plane-type uniaxial anisotropy, a random magnetic
anisotropy and an applied magnetic field are investigated. In the XY regime in
zero field, the ""spin-chirality decoupling"" persists even under the random
magnetic anisotropy, escaping the ""spin-chirality recoupling"" phenomenon which
inevitably occurs in the Heisenberg regime. Contrast between the scalar chiral
order and the vector chiral order is emphasized. Implications to experiments
are discussed.",1102.3496v1
2011-05-31,Chemical order and size effects on the magnetic anisotropy of FePt and CoPt nanoparticles,"We investigate the consequence of the dimension reduction on the magnetic
anisotropy of FePt and CoPt nanoparticles. Using an extension of the magnetic
anisotropy model of N\'eel, we show that, due to a statistical finite size
effect, chemically disordered clusters can display a magnetic anisotropy energy
(MAE) as high as 0.5\times10^6 J/m3, more than one order of magnitude higher
than the bulk MAE. Concerning L10 ordered clusters, we show that the surface
induces a reduction of the MAE as compared to the bulk, due to the symmetry
breaking at the cluster surface, which modifies the chemical order.",1105.6292v1
2011-06-28,Anisotropies in the Gravitational-Wave Stochastic Background,"We consider anisotropies in the stochastic background of gravitational-waves
(SBGW) arising from random fluctuations in the number of gravitational-wave
sources. We first develop the general formalism which can be applied to
different cosmological or astrophysical scenarios. We then apply this formalism
to calculate the anisotropies of SBGW associated with the fluctuations in the
number of cosmic string loops, considering both cosmic string cusps and kinks.
We calculate the anisotropies as a function of angle and frequency.",1106.5555v2
2011-08-31,Optical diode based on the one-way light-speed anisotropy,"We report that a triangular Fabry-Perot resonator filled with a parity-odd
linear anisotropic medium exhibiting the one-way light speed anisotropy acts as
a perfect diode. A Linear crystal such as the nematic liquid crystals whose
molecular structures break parity can exhibit the one-way light speed
anisotropy. The one-way light speed anisotropy also can be induced in a
non-linear medium in the presence of constant electric and magnetic field
strengths.",1108.6162v3
2011-12-13,Phase Diagram of the mixed spin-2 and spin-5/2 Ising system with two different single-ion anisotropies,"In this paper we present a study of the effects of two different single-ion
anisotropies in the phase diagram and in the compensation temperature of the
mixed spin-2 and spin-5/2 Ising ferrimagnetic system. We employed the
mean-field theory based on the Bogoliubov inequality for the Gibbs free energy.
Also we found the Landau expansion of the free energy in the order parameter to
describe the phase diagrams. In the plane critical temperature versus
single-ion anisotropie the phase diagram displays tricritical behavior. The
critical and compensation temperatures increase when the single-ion
anisotropies increase.",1112.2989v1
2012-04-11,On the large magnetic anisotropy of Fe_{2}P,"We present an investigation on the large magnetic anisotropy of Fe_{2}P,
based on {\it Ab Initio} density-functional theory calculations, with a full
potential linear muffin-tin orbital (FP-LMTO) basis. We obtain an uniaxial
magnetic anisotropy energy (MAE) of 664 \mu eV/f.u., which is in decent
agreement with experimental observations. Based on a band structure analysis
the microscopical origin of the large magnetic anisotropy is explained. We also
show that by straining the crystal structure, the MAE can be enhanced further.",1204.2419v2
2012-10-02,Numerical resolution of an anisotropic non-linear diffusion problem,"This paper is devoted to the numerical resolution of an anisotropic
non-linear diffusion problem involving a small parameter \varepsilon, defined
as the anisotropy strength reciprocal. In this work, the anisotropy is carried
by a variable vector function b. The equation being supplemented with Neumann
boundary conditions, the limit \varepsilon \infty 0 is demonstrated to be a
singular perturbation of the original diffusion equation. To address
efficiently this problem, an Asymptotic-Preserving scheme is derived. This
numerical method does not require the use of coordinates adapted to the
anisotropy direction and exhibits an accuracy as well as a computational cost
independent of the anisotropy strength.",1210.0681v1
2012-10-09,Thermopower as sensitive probe of electronic nematicity in iron pnictides,"We study the in-plane anisotropy of the thermoelectric power and electrical
resistivity on detwinned single crystals of isovalent substituted
EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_2$. Compared to the resistivity anisotropy the
thermopower anisotropy is more pronounced and clearly visible already at
temperatures much above the structural and magnetic phase transitions. Most
remarkably, the thermopower anisotropy changes sign below the structural
transition. This is associated with the interplay of two contributions due to
anisotropic scattering and orbital polarization, which dominate at high- and
low-temperatures, respectively.",1210.2634v2
2013-02-12,Granular Brownian Motors: role of gas anisotropy and inelasticity,"We investigate the motion of a wedge-shaped object (a granular Brownian
motor), which is restricted to move along the x-axis and cannot rotate, as gas
particles collide with it. We show that its steady-state drift, resulting from
inelastic gas-motor collisions, is dramatically affected by anisotropy in the
velocity distribution of the gas. We identify the dimensionless parameter
providing the dependence of this drift on shape, masses, inelasticity, and
anisotropy: the anisotropy leads to a dramatic breaking of equipartition, which
should easily be visible in experimental realizations.",1302.2877v2
2013-05-07,Local control of single atom magneto-crystalline anisotropy,"Individual Fe atoms on a Cu2N/Cu(100) surface exhibit strong magnetic
anisotropy due to the crystal field. Using atom manipulation in a
low-temperature STM we demonstrate that the anisotropy of one Fe atom is
significantly influenced by local strain due to a second Fe atom placed nearby.
Depending on the relative positions of the two atoms on the Cu2N lattice we can
controllably enhance or reduce the uniaxial anisotropy. We present a model that
explains the observed behavior qualitatively in terms of first principles.",1305.1616v2
2013-06-03,Non-Bunch-Davies Anisotropy,"We introduce a generic mechanism that can extend the effects of relic
anisotropies at the beginning of inflation to relatively much shorter scales in
density perturbations. This is induced by non-Bunch-Davies states of the
quantum fluctuations, and can show up in the non-oscillatory components of the
density perturbations. This mechanism works for general forms of anisotropies,
and, to illustrate it, we use an example of relic vector field. The detailed
scale-dependence of these anisotropies can be used to probe the initial quantum
state of our universe.",1306.0609v1
2013-06-11,Incompressible States of Dirac Fermions in Graphene with Anisotropic Interactions,"We report on the properties of incompressible states of Dirac fermions in
graphene in the presence of anisotropic interactions and a quantizing magnetic
field. We introduce the necessary formalism to incorporate the anisotropy in
the system. The incopmpressible state in graphene is found to survive the
anisotropy upto a critical value of the anisotropy parameter. The anisotropy
also introduces two branches in the collective excitations of the corresponding
Laughlin state. It strongly influences the short-range behavior of the
pair-correlation functions in the incompressible ground state.",1306.2408v1
2013-06-29,Perpendicular magnetization of Co20Fe50Ge30 films induced by MgO interface,"Epitaxial growth of Co20Fe50Ge30 thin film on single crystal MgO (001)
substrate is reported. Structure characterization revealed (001)-oriented B2
order of CoFeGe well lattice matched with the MgO barrier. Perpendicular
magnetic anisotropy (PMA) was achieved in the MgO/CoFeGe/MgO structure with an
optimized magnetic anisotropy energy density (K) of 3 106 erg/cm3. The magnetic
anisotropy is found to depend strongly on the thickness of the MgO and CoFeGe
layers, indicating that the PMA of CoFeGe is contributed by the interfacial
anisotropy between CoFeGe and MgO. With reported low damping constant, CoFeGe
films are promising spintronic materials for achieving low switching current.",1307.0104v1
2014-04-02,Perpendicular magnetic anisotropy of cobalt films intercalated under graphene,"Magnetic properties of nanometer thick Co films intercalated at the
graphene/Ir(111) interface are investigated using spin-polarized low-energy
electron microscopy (SPLEEM) and Auger electron spectroscopy. We show that the
graphene top layer promotes perpendicular magnetic anisotropy in the Co film
underneath, even for relatively thick intercalated deposits. The magnetic
anisotropy energy is significantly larger for the graphene/Co interface than
for the free Co surface. Hybridization of the graphene and Co electron orbitals
is believed to be at the origin of the observed perpendicular magnetic
anisotropy.",1404.0705v1
2014-05-11,Tuning perpendicular magnetic anisotropy in the MgO/CoFeB/Ta thin films,"Understanding the magnetic anisotropy at ferromagnetic metal/oxide interface
is a fundamental and intriguing subject. Here we propose an approach to
manipulate the strength of perpendicular magnetic anisotropy (PMA) by varying
MgO thickness in the MgO/CoFeB/Ta thin films. We identify that the PMA at the
MgO/CoFeB interface is tuned by the crystalline structure of bulk MgO layer and
decreases dramatically due to the onset of crystalline MgO forming with the
increase of MgO thickness. Our work opens an avenue to manipulate the magnetic
anisotropy by the modification of the ferromagnetic metal/oxide interface.",1405.2551v2
2014-05-16,Statistical Anisotropies in Gravitational Waves in Solid Inflation,"Solid inflation can support a long period of anisotropic inflation. We
calculate the statistical anisotropies in the scalar and tensor power spectra
and their cross-correlation in anisotropic solid inflation. The tensor-scalar
cross-correlation can either be positive or negative, which impacts the
statistical anisotropies of the TT and TB spectra in CMB map more significantly
compared with the tensor self-correlation. The tensor power spectrum contains
potentially comparable contributions from quadrupole and octopole angular
patterns, which is different from the power spectra of scalar, the
cross-correlation or the scalar bispectrum, where the quadrupole type
statistical anisotropy dominates over octopole.",1405.4179v1
2014-09-16,On the anisotropy of stress-distribution induced in glasses and crystals by non-ablative femtosecond laser exposure,"Femtosecond laser exposure in the non-ablative regime induces a variety of
bulk structural modifications, in which anisotropy may depend on the
polarization of the writing beam. In this work, we investigate the correlation
between polarization state and stress anisotropy. In particular, we introduce a
methodology that allows for rapid analysis and visualization of laser-induced
stress anisotropy in glasses and crystals. Using radial and azimuthal
polarization, we also demonstrate stress states that are nearly isotropic.",1409.4578v1
2015-06-23,Effects of magnetic anisotropy on spin dynamics of ferromagnetic frustrated chain,"By exploiting density-matrix renormalization group techniques, we investigate
the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing
ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied
magnetic fields. Numerical results of spin excitation spectra show that in the
field-induced spin quadrupole regime, the longitudinal component has a gapless
mode and the transverse component has a gapped mode irrespective of the
exchange anisotropy. The excitation gap of the transverse spin excitation
increases as the exchange anisotropy increases over the XY-like and Ising-like
regions, demonstrating that two-magnon bound states are stabilized due to the
easy-axis anisotropy.",1506.06883v1
2015-11-30,Mobility anisotropy in monolayer black phosphorus due to charged impurities,"We study the charged impurity limited mobility in black phosphorus, a highly
anisotropic layered material. We compute the mobility within the Boltzmann
transport equation under detailed balance condition, and taking into account
the anisotropy in transport and electronic structure. For carrier densities
accessible in experiments, we obtained an anisotropy ratio of 3 ~ 4 at zero
temperature, two-folds larger than that observed in experiments on multilayers
samples. We discuss also how the anisotropy depends on carrier density and
impurity distribution.",1511.09151v1
2015-12-22,Orbit anisotropy of dark matter haloes with Schwarzschild modelling,"We apply the Schwarzschild orbit superposition method to mock data in order
to investigate the accuracy of recovering the profile of the orbit anisotropy.
The mock data come from four numerical realizations of dark matter haloes with
well defined anisotropy profiles. We show that when assuming a correct mass
distribution we are able to determine the anisotropy with high precision and
clearly distinguish between the models.",1512.07266v1
2015-12-29,Solitary structures with ion and electron thermal anisotropy,"Formation of electrostatic solitary structures are analysed for a magnetised
plasma with ion and electron thermal anisotropies. The ion thermal anisotropy
is modelled with the help of the Chew-Goldberger-Low (CGL) double adiabatic
equations of state while the electrons are treated as inertia-less species with
an anisotropic bi-Maxwellian velocity distribution function. A negative
electron thermal anisotropy $(T_{e\perp}/T_e{\parallel}>1)$ is found to help
form large amplitude solitary structures which are in agreement with
observational data.",1512.08633v1
2016-02-03,Anisotropy in broad component of H$α$ line in the magnetospheric device RT-1,"Temperature anisotropy in broad component of H$\alpha$ line was found in the
ring trap 1 (RT-1) device by Doppler spectroscopy. Since hot hydrogen neutrals
emitting a broad component are mainly produced by charge exchange between
neutrals and protons, the anisotropy in the broad component is the evidence of
proton temperature anisotropy generated by betatron acceleration.",1602.01165v1
2016-04-18,Phase field modelling of interfacial anisotropy driven faceting of precipitates,"We use extended Cahn-Hilliard (ECH) equations to study faceted precipitate
morphologies; specifically, we obtain four sided precipitates (in 2-D) and
dodecahedron (in 3-D) in a system with cubic anisotropy, and, six-sided
precipitates (in 2-D, in the basal plane), hexagonal dipyramids and hexagonal
prisms (in 3-D) in systems with hexagonal anisotropy. Our listing of these ECH
equations is fairly comprehensive and complete (upto sixth rank tensor terms of
the Taylor expansion of the free energy). We also show how the parameters that
enter the model are to be obtained if either the interfacial energy anisotropy
or the equilibrium morphology of the precipitate is known.",1604.05208v1
2016-05-17,Effects of spin fluctuation on the magnetic anisotropy constant of itinerant electron magnets,"In the disordered local moment picture, we calculated the magnetization (M)
and magnetic anisotropy energy (MAE) of FePt, CoPt, and MnAl ordered alloys and
body-centered tegragonal FeCo (bct-FeCo) disordered alloy, assuming spatially
fluctuated spin configurations at finite temperatures. All alloys exhibit the
relation K1(T)/K1(0)=(M(T)/M(0))^n with the exponent (n) around 2. This is
consistent with the two-ion anisotropy model, in contrast to the usual
single-ion anisotropy model exhibiting n=3. Because these systems have
different mechanisms of MAE, we suggest that this relation is a general rule
for itinerant electron systems.",1605.05058v1
2016-06-08,Magnetic energy of sc ferromagnetic films with three layers as described by third order perturbed Heisenberg Hamiltonian,"The solution of third order perturbed Heisenberg Hamiltonian of simple cubic
ferromagnetic ultra-thin films with three layers were found. All the magnetic
energy parameters such as spin exchange interaction, magnetic dipole
interaction, second order magnetic anisotropy, fourth order magnetic
anisotropy, applied magnetic field, demagnetization factor and stress induced
anisotropy were included in the third order perturbed Heisenberg Hamiltonian.
3-D plots of stress induced anisotropy, out of plane magnetic field,
demagnetization factor and spin exchange interaction are presented in this
manuscript. Magnetic easy and hard directions were determined using these 3-D
plots. MATLAB program was employed to solve the equation with seven parameters.",1606.02439v1
2016-09-26,Anisotropies of Gravitational Wave Backgrounds: A Line Of Sight Approach,"In the weak field regime, gravitational waves can be considered as being made
up of collisionless, relativistic tensor modes that travel along null geodesics
of the perturbed background metric. We work in this geometric optics picture to
calculate the anisotropies in gravitational wave backgrounds resulting from
astrophysical and cosmological sources. Our formalism yields expressions for
the angular power spectrum of the anisotropies. We show how the anisotropies
are sourced by intrinsic, Doppler, Sachs-Wolfe, and Integrated Sachs-Wolfe
terms in analogy with Cosmic Microwave Background photons.",1609.08168v1
2016-10-18,Engineering Curvature Induced Anisotropy in Thin Ferromagnetic Films,"The large curvature effects on micromagnetic energy of a thin ferromagnetic
film with nonlocal dipolar energy are considered. We predict that the dipolar
interaction and surface curvature can produce perpendicular anisotropy which
can be controlled by engineering a special type of periodic surface shape
structure. Similar effects can be achieved by a significant surface roughness
in the film. We show that in general the anisotropy can point in an arbitrary
direction depending on the surface curvature. We provide simple examples of
these periodic surface structures to demonstrate how to engineer particular
anisotropies in the film.",1610.05574v1
2017-04-18,Quantitative analysis of the influence of keV He ion bombardment on exchange bias layer systems,"The mechanism of ion bombardment induced magnetic patterning of exchange bias
layer systems for creating engineered magnetic stray field landscapes is still
unclear. We compare results from vectorial magneto-optic Kerr effect
measurements to a recently proposed model with time dependent rotatable
magnetic anisotropy. Results show massive reduction of rotational magnetic
anisotropy compared to all other magnetic anisotropies. We disprove the
assumption of comparable weakening of all magnetic anisotropies and show that
ion bombardment mainly influences smaller grains in the antiferromagnet.",1704.05487v1
2017-06-29,The sign of the polarizability anisotropy of polar molecules is obtained faithfully from terahertz Kerr effect,"Optically heterodyned detected terahertz Kerr effect of gases of polar
molecules is reported. Strikingly, the birefringence signal from fluoroform is
found to have opposite polarity compared to water and acetonitrile. This
behavior is a hallmark of the opposite sign of the polarizability anisotropy of
these molecules. Resonant excitation of the rotational degrees of freedom of
the molecules aligns their permanent dipoles along the terahertz electric
field. This alignment is translated into an optical birefringence through the
polarizability anisotropy of each molecule. Therefore, the resulting net signal
scales with the polarizability anisotropy, whose sign is imprinted faithfully
onto the transient birefringence signal.",1706.09623v1
2017-07-20,General kinetic solution for the Biermann battery with an associated pressure anisotropy generation,"Fully kinetic analytic calculations of an initially Maxwellian distribution
with arbitrary density and temperature gradients exhibit the development of
temperature anisotropies and magnetic field growth associated with the Biermann
battery. The calculation, performed by taking a small order expansion of the
ratio of the Debye length to the gradient scale, predicts anisotropies and
magnetic fields as a function of space given an arbitrary temperature and
density profile. These predictions are shown to qualitatively match the values
measured from particle-in-cell simulations, where the development of the Weibel
instability occurs at the same location and with a wavenumber aligned with the
predicted temperature anisotropy.",1707.06390v1
2017-08-08,Reinvestigation on large perpendicular magnetic anisotropy in Fe/MgO interface from first-principles approach,"We investigated electronic structure and magnetic anisotropy in the Fe/MgO
interface of magnetic metal and dielectric insulator under the Cr layer of
small electronegativity, by means of the first-principles density functional
approach. The result indicates that the interface resonance state gets occupied
unlike a typical rigid band picture as the number of Fe layers decreases,
finding large perpendicular anisotropies in the oscillating behavior for
thickness dependence. We discuss scenarios of the two dimensional van Hove
singularity associated with flat band dispersions, and also the accuracies of
anisotropy energy in comparison with the available experimental data.",1708.02400v1
2018-02-23,3D superconducting gap in FeSe from ARPES,"We present a systematic angle-resolved photoemission spectroscopy study of
the superconducting gap in FeSe. The gap function is determined in a full
Brillouin zone including all Fermi surfaces and kz-dependence. We find
significant anisotropy of the superconducting gap in all momentum directions.
While the in-plane anisotropy can be explained by both, nematicity-induced
pairing anisotropy and orbital-selective pairing, the kz-anisotropy requires
additional refinement of theoretical approaches.",1802.08668v1
2018-09-23,Ferromagnetic resonance in thin ferromagnetic film with surface anisotropy,"The ferromagnetic resonance frequencies are obtained for a thin ferromagnetic
film with surface anisotropy for the cases when the external magnetic field is
applied perpendicularly or parallel to the film surface, and for various
combinations of boundary conditions on the film surface. It is shown that in
the presence of surface anisotropy the ferromagnetic resonance frequency
essentially depends both on the film thickness and on the value of the surface
anisotropy constant. The results obtained provide a basis for the correct
interpretation of experimental data obtained by means of broadband
ferromagnetic resonance in thin film structures.",1809.08644v1
2019-02-11,Measuring hole g-factor anisotropies using transverse magnetic focusing,"Recent theoretical and experimental results from quasi-one dimensional heavy
hole systems have suggested that heavy hole gases have a strongly anisotropic g
factor. In this theoretical paper, we propose a method for measuring this
anisotropy using transverse magnetic focusing (TMF). We demonstrate that for
experimentally accessible fields, the g factor anisotropy leads to a relative
variation in the characteristic of spin-splitting of the TMF spectrum which
allows for the measurement of the anisotropy of the g factor. We show that this
variation is insensitive to additional spin-orbit interactions, and is
resolvable with current devices.",1902.03709v1
2019-12-10,Study on Sub monolayer Epitaxy Growth under Anisotropic Detachment,"We have performed Kinetic Monte Carlo simulation to study the effect of
diffusion anisotropy and bonding anisotropy on island formation at different
temperatures during the sub-monolayer film growth in Molecular Beam Epitaxy. We
use simple cubic solid on solid model and event based Bortz, Kalos and
Labowitch (BKL) algorithm on Kinetic Monte Carlo method to simulate the
physical phenomena. We have found that surface anisotropy has no significant
role on island elongation however it influences on the island morphology,
growth exponent and island size distribution. Elongated islands were obtained
when bonding anisotropy was included.",1912.04877v1
2020-06-08,The effect of anisotropy on phase transitions in graphene,"We study the effect of anisotropy (strain) on dynamical gap generation in
graphene. We work with a low energy effective theory obtained from a
tight-binding Hamiltonian expanded around the Dirac points in momentum space.
We use a non-perturbative Schwinger-Dyson approach and calculate a coupled set
of five momentum dependent dressing functions. Our results show that the
critical coupling depends only weakly on the anisotropy parameter, and
increases with greater anisotropy.",2006.04790v2
2020-06-19,Anisotropy of Electric Field Fluctuations Spectrum of Solar Wind Turbulence,"To investigate the power and spectral index anisotropy in the inertial range
of solar wind turbulence, we use 70 intervals of electric field data
accumulated by Cluster spacecraft in the free solar wind. We compute the
electric field fluctuation power spectra using wavelet analysis technique and
study its spectral index variation with the change in angle between the
heliocentric radial direction and the local mean magnetic field. We find clear
power and spectral index anisotropy in the frequency ranging from 0.01 Hz to
0.1 Hz, with more power in parallel fluctuations than perpendicular. We also
report our study of anisotropy as a function of solar activity.",2006.10954v2
2022-01-28,Theory of spin-excitation anisotropy in the nematic phase of FeSe obtained from RIXS measurements,"Recent resonant inelastic x-ray scattering (RIXS) experiments have detected a
significant high-energy spin-excitation anisotropy in the nematic phase of the
enigmatic iron-based superconductor FeSe, whose origin remains controversial.
We apply an itinerant model previously used to describe the spin-excitation
anisotropy as measured by neutron scattering measurements, with magnetic
fluctuations included within the RPA approximation. The calculated RIXS cross
section exhibits overall agreement with the RIXS data, including the high
energy spin-excitation anisotropy.",2201.12008v2
2022-05-03,"Tuning the perpendicular anisotropy of ferromagnetic films by thickness, width, and profile","Perpendicular magnetic anisotropy was found to be highly sensitive to the
nominal thickness and morphology of laterally heterogeneous CoPd films in the
vicinity of the metal insulator transition. We used the effect to tune the
anisotropy by the width of lithographically patterned stripes with non-uniform
cross-sectional thickness profiles. The phenomenon and the method can be
suitable to control the local anisotropy of spintronic logic circuitry elements
by their shape and lateral dimensions.",2205.01408v1
2022-09-20,Field-Induced Spin Nematic Liquid of the $S=1/2$ Bond-Alternating Chain with the Anisotropy,"The $S=1/2$ ferromagnetic-antiferromagnetic bond-alternating spin chain with
the anisotropy on the ferromagnetic exchange interaction in magnetic field is
investigated using the numerical diagonalization and the density matrix
renormalization group analyses. It is found that the nematic-spin-dominant
Tomonaga-Luttinger liquid phase is induced by the external magnetic field for
sufficiently large anisotropy. The phase diagram with respect to the anisotropy
and the magnetization is presented.",2209.09740v1
2009-06-26,Kinematic deprojection and mass inversion of spherical systems of known velocity anisotropy,"Traditionally, the mass / velocity anisotropy degeneracy (MAD) inherent in
the spherical, stationary, non-streaming Jeans equation has been handled by
assuming a mass profile and fitting models to the observed kinematical data.
Here, the opposite approach is considered: the equation of anisotropic
kinematic projection is inverted for known arbitrary anisotropy to yield the
space radial velocity dispersion profile in terms of an integral involving the
radial profiles of anisotropy and isotropic dynamical pressure. Then, through
the Jeans equation, the mass profile is derived in terms of double integrals of
observable quantities. Single integral formulas for both deprojection and mass
inversion are provided for several simple anisotropy models (isotropic, radial,
circular, general constant, Osipkov-Merritt, Mamon-Lokas and
Diemand-Moore-Stadel). Tests of the mass inversion on NFW models with these
anisotropy models yield accurate results in the case of perfect observational
data, and typically better than 70% (in 4 cases out of 5) accurate mass
profiles for the sampling errors expected from current observational data on
clusters of galaxies. For the NFW model with mildly increasing radial
anisotropy, the mass is found to be insensitive to the adopted anisotropy
profile at 7 scale radii and to the adopted anisotropy radius at 3 scale radii.
This anisotropic mass inversion method is a useful complementary tool to
analyze the mass and anisotropy profiles of spherical systems. It provides the
practical means to lift the MAD in quasi-spherical systems such as globular
clusters, round dwarf spheroidal and elliptical galaxies, as well as groups and
clusters of galaxies, when the anisotropy of the tracer is expected to be
linearly related to the slope of its density.",0906.4971v3
2011-05-23,Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. II: anisotropy,"We investigate the effects of stochasticity in the spatial and temporal
distribution of supernova remnants on the anisotropy of cosmic rays observed at
Earth. The calculations are carried out for different choices of the diffusion
coefficient D(E) for propagation in the Galaxy. The propagation and spallation
of nuclei are taken into account. At high energies we assume that
$D(E)\sim(E/Z)^{\delta}$, with $\delta=1/3$ and $\delta=0.6$ being the
reference scenarios. The large scale distribution of supernova remnants in the
Galaxy is modeled following the distribution of pulsars with and without
accounting for the spiral structure of the Galaxy. Our calculations allow us to
determine the contribution to anisotropy resulting from both the large scale
distribution of SNRs in the Galaxy and the random distribution of the nearest
remnants. The naive expectation that the anisotropy amplitude scales as D(E) is
shown to be an oversimplification which does not reflect in the predicted
anisotropy for any realistic distribution of the sources. The fluctuations in
the anisotropy pattern are dominated by nearby sources, so that predicting or
explaining the observed anisotropy amplitude and phase becomes close to
impossible. We find however that the very weak energy dependence of the
anisotropy amplitude below $10^{5}$ GeV and the rise at higher energies, can
best be explained if the diffusion coefficient is $D(E)\sim E^{1/3}$. Faster
diffusion, for instance with $\delta=0.6$, leads in general to an exceedingly
large anisotropy amplitude. The spiral structure introduces interesting trends
in the energy dependence of the anisotropy pattern, which qualitatively reflect
the trend seen in the data. For large values of the halo size we find that the
anisotropy becomes dominated by the large scale regular structure of the source
distribution, leading indeed to a monotonic increase of $\delta_A$ with energy.",1105.4529v2
2012-07-18,Spin transport in the Neel and collinear antiferromagnetic phase of the two dimensional spatial and spin anisotropic Heisenberg model on a square lattice,"We analyze and compare the effect of spatial and spin anisotropy on spin
conductivity in a two dimensional S=1/2 Heisenberg quantum magnet on a square
lattice. We explore the model in both the Neel antiferromagnetic (AF) phase and
the collinear antiferromagnetic (CAF) phase. We find that in contrast to the
effects of spin anisotropy in the Heisenberg model, spatial anisotropy in the
AF phase does not suppress the zero temperature regular part of the spin
conductivity in the zero frequency limit - rather it enhances it. We also
explore the finite temperature effects on the Drude weight in the AF phase for
various spatial and spin anisotropy parameters. We find that the Drude weight
goes to zero as the temperature approaches zero. At finite temperatures (within
the collision less approximation) enhancing spatial anisotropy increases the
Drude weight value and increasing spin anisotropy decreases the Drude weight
value. In the CAF phase (within the non-interacting approximation) the zero
frequency spin conductivity has a finite value for non-zero values of the
spatial anisotropy parameter. In the CAF phase increasing the spatial
anisotropy parameter suppresses the regular part of the spin conductivity
response at zero frequency. Furthermore, we find that the CAF phase displays a
spike in the spin conductivity not seen in the AF phase. Inclusion of the
smallest amount of spin anisotropy causes a gap to develop in the spin
conductivity response of both the AF and CAF phase. Based on these studies we
conclude that materials with spatial anisotropy are better spin conductors than
those with spin anisotropy both at zero and finite temperatures. We utilize
exchange parameter ratios for real material systems as inputs to the
computation of spin conductivity.",1207.4389v1
2019-01-12,"Revisit to electrical and thermal conductivities, Lorenz number and Knudsen number in thermal QCD in a strong magnetic field","We have explored how the electrical ($\sigma_{\rm el}$) and thermal
($\kappa$) conductivities in a thermal QCD medium get affected in weak-momentum
anisotropies arising either due to a strong magnetic field or due to asymptotic
expansion. This study facilitates to understand the longevity of strong
magnetic field through $\sigma_{el}$, Lorenz number in Wiedemann-Franz law, and
the validity of equilibrium by the Knudsen number. We calculate the
conductivities by solving relativistic Boltzmann transport equation in
relaxation-time approximation within quasiparticle model at finite T and strong
B. We have found that $\sigma_{el}$ and $\kappa$ get enhanced in a magnetic
field-driven anisotropy, but $\sigma_{el}$ decreases with temperature, opposite
to its faster increase in expansion-driven anisotropy. Whereas $\kappa$
increases slowly with temperature, contrary to its rapid increase in
expansion-driven anisotropy. The above findings are broadly attributed to three
factors: the stretching and squeezing of distribution function in anisotropies
generated by the magnetic field and asymptotic expansion, respectively, the
dispersion relation and resulting phase-space factor, the relaxation-time in
absence and presence of strong magnetic field. So $\sigma_{\rm el}$ extracts
the time-dependence of magnetic field, which decays slower than in vacuum but
expansion-driven anisotropy makes the decay faster. The variation in $\kappa$
transpires that Knudsen number decreases with T but expansion-driven anisotropy
reduces its value and magnetic field-driven anisotropy raises its value but to
less than one, thus the system can still be in equilibrium. The ratio,
$\kappa/\sigma_{el}$ in magnetic field-driven anisotropy increases linearly
with temperature but with a value smaller than in expansion-driven anisotropy.
Thus the Lorenz number can make the distinction between different anisotropies.",1901.03855v2
2020-01-31,Momentum and its affiliated transport coefficients for a hot QCD matter in a strong magnetic field,"We have studied the effects of anisotropies on the momentum transport in a
QCD matter by shear ($\eta$) and bulk ($\zeta$) viscosities. The anisotropies
arise either by the strong magnetic field or by the preferential expansion.
This study helps to understand the fluidity and location of transition point of
matter through $\eta/s$ and $\zeta/s$ ($s$ is entropy density), respectively,
the sound attenuation through the Prandtl number (Pl), the nature of flow by
the Reynolds number (Rl), and the competition between momentum and charge
diffusions. The viscosities are calculated in the relaxation time approximation
of kinetic theory within the quasiparticle model. Compared to isotropic medium,
both $\eta$ and $\zeta$ get increased in magnetic field-driven (B-driven)
anisotropy, contrary to the decrease in expansion-driven anisotropy. $\eta$
increases with temperature faster in former case than in latter case whereas
$\zeta$ in former case decreases with temperature and in latter case, it is
meagre and diminishes at a specific temperature. So the viscosities can
distinguish aforesaid anisotropies. Thus, $\eta/s$ gets enhanced in former case
and in latter case, it becomes smaller than isotropic one. Similarly $\zeta/s$
gets amplified but decreases faster with the temperature in a strong magnetic
field. The Prandtl number gets increased in B-induced anisotropy and gets
decreased in expansion-induced anisotropy, compared to isotropic one. Since, Pl
is found larger than 1, the sound attenuation is governed by momentum
diffusion. The B-driven anisotropy makes the Reynolds number smaller than one,
whereas the expansion-driven anisotropy makes it larger. The ratio
($\frac{\eta}{s}/\frac{\sigma_{\rm el}}{T}$) gets amplified in B-driven
anisotropy whereas it gets reduced in expansion-driven anisotropy. Since, the
ratio is always more than one, the momentum diffusion prevails over the charge
diffusion.",2001.11788v2
1995-02-02,CMB ANISOTROPIES: AN OVERVIEW,"A brief outline of the current status of CMB anisotropies and what they might
mean, heavily biased towards the perspective of Berkeley theorists. Based on a
talk presented at the 17th Texas Symposium on Relativistic Astrophysics held in
Munich, December 1994.",9502011v1
1999-03-30,Are you sure that the anisotropies in the microwave background radiation are really cosmological rather than purely Galactic in origin?,"New calculations of the Galactic contamination over microwave background
radiation anisotropies are carried out. On one hand, when a frequency-dependent
contrast of molecular clouds with respect to the Galactic background of the
diffuse interstellar medium is taken into account, the anisotropic amplitude
produced by Galactic dust is increased with respect to previous calculations
and this is of the same order as that of the data from the observations. On the
other hand, if we take into account rotational dust emission, for instance, a
frequency independence of anisotropies in the microwave range may be obtained.
  This leads to the possibility that under some particular, but not impossible,
conditions all the microwave background radiation anisotropies may be due to
Galactic foregrounds rather than cosmological in origin. Moreover, a suspected
coincidence between the typical angular sizes of the microwave background
radiation anisotropies and those of nearby molecular clouds makes more
plausible the hypothesis of a purely Galactic origin for these anisotropies. It
is also argued that the correlation among structures at different frequencies,
the comparison of the power spectrum at different frequencies and the galactic
latitude dependence of the anisotropies are not yet proofs in favour of either
a cosmological or Galactic origin.",9903460v2
1999-04-25,The Limits on Cosmological Anisotropies and Inhomogeneities from COBE Data,"Assuming that the cosmological principle holds, Maartens, Ellis and Stoeger
(MES) recently constructed a detailed scheme linking anisotropies in the cosmic
background radiation (CMB) with anisotropies and inhomogeneities in the large
scale structure of the universe and showed how to place limits on those
anisotropies and inhomogeneities simply by using CMB quadrupole and octupole
limits. First we indicate and discuss the connection between the covariant
multipole moments of the temperature anisotropy used in the MES scheme and the
quadrupole and octupole results from COBE. Then we introduce those results into
the MES limit equations to obtain definite quantitative limits on the complete
set of cosmological measures of anisotropy and inhomogeneity.
  We find that all the anisotropy measures are less than 10^{-4} in the case of
those not affected by the expansion rate H, and less than 10^{-6} Mpc^{-1} in
the case of those which are. These results quantitatively demonstrate that the
observable universe is indeed close to Friedmann-Lemaitre-Robertson-Walker
(FLRW) on the largest scales, and can be adequately modelled by an almost-FLRW
model -- that is, the anisotropies and inhomogeneities characterizing the
observable universe on the largest scales are not too large to be considered
perturbations to FLRW.",9904346v1
1998-12-21,Cosmological Birefringence and the Microwave Background,"We show that significant anisotropy in electromagnetic propagation generates
a distinctive signature in the microwave background. The anisotropy may be
determined by looking at the cross correlator of the $E$-mode and $B$-mode
polarisation spectrum.",9812077v1
2005-10-03,Tuning anisotropies for dynamical gauge configurations,"We present methods and results for the tuning of quark and gluon anisotropies
for improved actions in N_f = 2 QCD.",0510016v1
2011-01-14,Observational Scan Induced Artificial CMB Anisotropy,"To reliably detect the cosmic microwave background (CMB) anisotropy is of
great importance in understanding the birth and evolution of the Universe. One
of the difficulties in CMB experiments is the domination of measured CMB
anisotropy maps by the Doppler dipole moment from the motion of the antenna
relative to the CMB. For each measured temperature the expected dipole
component has to be calculated separately and then subtracted from the data. A
small error in dipole direction, antenna pointing direction, sidelobe pickup
contamination, and/or timing synchronism, can raise significant deviation in
the dipole cleaned CMB temperature. After a full-sky observational scan, the
accumulated deviations will be structured with a pattern closely correlated to
the observation pattern with artificial anisotropies on large scales, including
artificial quadrupole, octopole etc in the final CMB map. Such scan-induced
anisotropies on large scales can be predicted by the true dipole moment and
observational scan scheme. Indeed, the expected scan-induced quadrupole pattern
of the WMAP mission is perfectly in agreement with the published WMAP
quadrupole. With the scan strategy of the Planck mission, we predict that
scan-induced anisotropies will also produce an artificially aligned quadrupole.
The scan-induced anisotropy is a common problem for all sweep missions and,
like the foreground emissions, has to be removed from observed maps. Without
doing so, CMB maps from COBE, WMAP, and Planck as well, are not reliable for
studying the CMB anisotropy.",1101.2720v2
2013-08-26,Constraints on the source of ultra-high energy cosmic rays using anisotropy vs chemical composition,"The joint analysis of anisotropy signals and chemical composition of
ultra-high energy cosmic rays offers strong potential for shedding light on the
sources of these particles. Following up on an earlier idea, this paper studies
the anisotropies produced by protons of energy >E/Z, assuming that anisotropies
at energy >E have been produced by nuclei of charge Z, which share the same
magnetic rigidity. We calculate the number of secondary protons produced
through photodisintegration of the primary heavy nuclei. Making the extreme
assumption that the source does not inject any proton, we find that the
source(s) responsible for anisotropies such as reported by the Pierre Auger
Observatory should lie closer than ~20-30, 80-100 and 180-200 Mpc if the
anisotropy signal is mainly composed of oxygen, silicon and iron nuclei
respectively. A violation of this constraint would otherwise result in the
secondary protons forming a more significant anisotropy signal at lower
energies. Even if the source were located closer than this distance, it would
require an extraordinary metallicity >120, 1600, 1100 times solar metallicity
in the acceleration zone of the source, for oxygen, silicon and iron
respectively, to ensure that the concomitantly injected protons not to produce
a more significant low energy anisotropy. This offers interesting prospects for
constraining the nature and the source of ultra-high energy cosmic rays with
the increase in statistics expected from next generation detectors.",1308.5699v2
2015-01-28,In-plane anisotropy effect on critical transition field in nanogranular films with perpendicular anisotropy,"The influence of the in-plane anisotropy on the magnetization of a
nanogranular film with perpendicular anisotropy has been studied. It is shown
that if a magnetic field is tilted with respect to the film normal, a critical
transition from the inhomogeneous magnetic state of granules with noncollinear
directions of their moments to the homogeneous one with parallel orientation of
granular magnetic moments takes place. The in-plane anisotropy is found to
affect the angular dependence of the critical field. The ensemble of oriented
biaxial particles is theoretically described in the double-well potential
approximation. Despite the biaxial magnetic anisotropy of particles, their
ensemble, if in the inhomogeneous state, is divided into two subensembles, with
the magnetic moments of particles being collinear in each of them. In the
critical field, a transition from the inhomogeneous state with two subensembles
into the homogeneous one takes place. The results of theoretical calculations
are compared with experimental data for a nanogranular Co/Al2On film with
perpendicular anisotropy containing 74.5 at.% Co, which exceeds the percolation
threshold. The magnetic moment of this film is a sum of two contributions: from
nanogranules with biaxial anisotropy and a phase forming the percolation
cluster. The magnetic properties of nanogranules, whose contribution is
separated from the total film magnetization, agree well with the calculation
data.",1501.07252v1
2016-06-23,Molecules associated to Hardy spaces with pointwise variable anisotropy,"In this paper we introduce molecules associated to Hardy spaces with
pointwise variable anisotropy, and prove that each molecule can be represented
as a sum of atoms.",1606.07245v1
2016-08-14,Axisymmetric equilibria with pressure anisotropy and plasma flow,"In this Master thesis we investigate the influence of pressure anisotropy and
incompressible flow of arbitrary direction on the equilibrium properties of
magnetically confined, axisymmetric toroidal plasmas. The main novel
contribution is the derivation of a pertinent generalised Grad-Shafranov
equation. This equation includes six free surface functions and recovers known
Grad-Shafranov-like equations in the literature as well as the usual static,
isotropic one. The form of the generalised equation indicates that pressure
anisotropy and flow act additively on equilibrium. In addition, two sets of
analytical solutions, an extended Solovev one with a plasma reaching the
separatrix and an extended Hernegger-Maschke one for a plasma surrounded by a
fixed boundary possessing an X-point, are constructed, particularly in
relevance to the ITER and NSTX tokamaks. Furthermore, the impacts both of
pressure anisotropy, through an anisotropy function assumed to be uniform on
the magnetic surfaces, and plasma flow, via the variation of an Alfvenic Mach
function, on these equilibria are examined.
  It turns out that depending on the maximum value and the shape of an
anisotropy function, the anisotropy can act either paramagnetically or
diamagnetically. Also, in most of the cases considered both the anisotropy and
the flow have stronger effects on NSTX equilibria than on ITER ones. We
conjecture that these effects may have an influence on plasma stability and
transport, and play a role in the transitions to the improved confinement
regimes in tokamaks.",1608.04083v1
2017-06-29,Characterization of the velocity anisotropy of accreted globular clusters,"Galactic globular clusters (GCs) are believed to have formed in-situ in the
Galaxy as well as in dwarf galaxies later accreted onto the Milky Way. However,
to date, there is no unambiguous signature to distinguish accreted GCs. Using
specifically designed $N$-body simulations of GCs evolving in a variety of
time-dependent tidal fields (describing the potential of a dwarf galaxy-Milky
Way merger), we analyze the effects imprinted to the internal kinematics of an
accreted GC. In particular, we look at the evolution of the velocity
anisotropy. Our simulations show that at early phases, the velocity anisotropy
is determined by the tidal field of the dwarf galaxy and subsequently the
clusters will adapt to the new tidal environment, losing any signature of their
original environment in a few relaxation times. At 10 Gyr, GCs exhibit a
variety of velocity anisotropy profiles, namely, isotropic velocity
distribution in the inner regions and either isotropy or radial/tangential
anisotropy in the intermediate and outer regions. Independently of an accreted
origin, the velocity anisotropy primarily depends on the strength of the tidal
field cumulatively experienced by a cluster. Tangentially anisotropic clusters
correspond to systems that have experienced stronger tidal fields and are
characterized by higher tidal filling factor, $r_{50}/r_j\gtrsim0.17$, higher
mass loss $\gtrsim60\%$ and relaxation times $t_{rel}\lesssim10^9$ Gyr.
Interestingly, we demonstrate that the presence of tidal tails can
significantly contaminate the measurements of velocity anisotropy when a
cluster is observed in projection. Our characterization of the velocity
anisotropy profiles in different tidal environments provides a theoretical
benchmark for the interpretation of the unprecedented amount of
three-dimensional kinematic data progressively available for Galactic GCs.",1706.09815v1
2018-04-05,Phase-field modeling of equilibrium precipitate shapes under the influence of coherency stresses,"Coherency misfit stresses and their related anisotropies are known to
influence the equilibrium shapes of precipitates. Additionally, mechanical
properties of the alloys are also dependent on the shapes of the precipitates.
Therefore, in order to investigate the mechanical response of a material which
undergoes precipitation during heat treatment, it is important to derive the
range of precipitate shapes that evolve. In this regard, several studies have
been conducted in the past using sharp interface approaches where the influence
of elastic energy anisotropy on the precipitate shapes has been investigated.
In this paper, we propose a diffuse interface approach which allows us to
minimize grid-anisotropy related issues applicable in sharp-interface methods.
In this context, we introduce a novel phase-field method where we minimize the
functional consisting of the elastic and surface energy contributions while
preserving the precipitate volume. Using this method we reproduce the
shape-bifurcation diagrams for the cases of pure dilatational misfit that have
been studied previously using sharp interface methods and then extend them to
include interfacial energy anisotropy with different anisotropy strengths which
has not been a part of previous sharp-interface models. While we restrict
ourselves to cubic anisotropies in both elastic and interfacial energies in
this study, the model is generic enough to handle any combination of
anisotropies in both the bulk and interfacial terms. Further, we have examined
the influence of asymmetry in dilatational misfit strains along with
interfacial energy anisotropy on precipitate morphologies.",1804.01763v1
2018-11-28,Effect of magnetic anisotropy on Skyrmions with a high topological number in itinerant magnets,"We report our numerical results for the effect of magnetic anisotropy on a
Skyrmion crystal with a high topological number of two, which was recently
discovered in an itinerant electron model [R. Ozawa, S. Hayami, and Y. Motome,
Phys. Rev. Lett. 118, 147205 (2017)]. By performing numerical simulations based
on the kernel polynomial method and the Langevin dynamics for the Kondo lattice
model on a triangular lattice, we find that the topological property remains
robust against the single-ion anisotropy, while the magnetic texture is
deformed continuously. The resultant spin structure is characterized by three
wave numbers (triple-$Q$ state), in which the $xy$ component of spins forms a
magnetic vortex crystal and the $z$ component of spins behaves a sinusoidal
wave. For larger anisotropy, we show that the system exhibits a phase
transition from the Skyrmion crystal to topologically trivial phases with
vanishing scalar chirality: a single-$Q$ collinear and double-$Q$ noncoplanar
states for the easy-axis and easy-plane anisotropy, respectively. We also
examine the effect of the single-ion anisotropy in an external magnetic field,
and find that the field range of the Skyrmion crystal is rather insensitive to
the anisotropy, in contrast to another Skyrmion crystal with the topological
number of one whose field range is considerably extended (reduced) by the
easy-axis (easy-plane) anisotropy.",1811.11336v1
2019-02-09,Antiferromagnetic phase transition in $Cr_{2}As$ via anisotropy of exchange interactions,"The electronic structure of anti-ferromagnetic $Cr_{2}As$ is investigated.
Anisotropy of exchange interactions between chrome sub-lattices is determined
($J^{X}(Cr_{I}-Cr_{II}) =4.77 meV,J^{Y}(Cr_{I}-Cr_{II}) =-6.36 meV$). The
behavior of exchange integrals from magnetic structure is analyzed.",1902.03337v1
2019-04-08,Three-dimensional local anisotropy of velocity fluctuations in the solar wind,"We analyse velocity fluctuations in the solar wind at magneto-fluid scales in
two datasets, extracted from Wind data in the period 2005-2015, that are
characterised by strong or weak expansion. Expansion affects measurements of
anisotropy because it breaks axisymmetry around the mean magnetic field.
Indeed, the small-scale three-dimensional local anisotropy of magnetic
fluctuations ({\delta}B) as measured by structure functions (SF_B) is
consistent with tube-like structures for strong expansion. When passing to weak
expansion, structures become ribbon-like because of the flattening of SFB along
one of the two perpendicular directions. The power-law index that is consistent
with a spectral slope -5/3 for strong expansion now becomes closer to -3/2.
This index is also characteristic of velocity fluctuations in the solar wind.
We study velocity fluctuations ({\delta}V) to understand if the anisotropy of
their structure functions (SF_V ) also changes with the strength of expansion
and if the difference with the magnetic spectral index is washed out once
anisotropy is accounted for. We find that SF_V is generally flatter than SF_B.
When expansion passes from strong to weak, a further flattening of the
perpendicular SF_V occurs and the small-scale anisotropy switches from
tube-like to ribbon-like structures. These two types of anisotropy, common to
SF_V and SF_B, are associated to distinct large-scale variance anisotropies of
{\delta}B in the strong- and weak-expansion datasets. We conclude that SF_V
shows anisotropic three-dimensional scaling similar to SF_B, with however
systematic flatter scalings, reflecting the difference between global spectral
slopes.",1904.04118v1
2019-11-29,"Filaments and striations: anisotropies in observed, supersonic, highly-magnetised turbulent clouds","Stars form in highly-magnetised, supersonic turbulent molecular clouds. Many
of the tools and models that we use to carry out star formation studies rely
upon the assumption of cloud isotropy. However, structures like high-density
filaments in the presence of magnetic fields, and magnetosonic striations
introduce anisotropies into the cloud. In this study we use the two-dimensional
(2D) power spectrum to perform a systematic analysis of the anisotropies in the
column density for a range of Alfv\'en Mach numbers ($\mathcal{M}_A=0.1$--$10$)
and turbulent Mach numbers ($\mathcal{M}=2$--$20$), with 20 high-resolution,
three-dimensional (3D) turbulent magnetohydrodynamic simulations. We find that
for cases with a strong magnetic guide field, corresponding to
$\mathcal{M}_A<1$, and $\mathcal{M}\lesssim 4$, the anisotropy in the column
density is dominated by thin striations aligned with the magnetic field, while
for $\mathcal{M}\gtrsim 4$ the anisotropy is significantly changed by
high-density filaments that form perpendicular to the magnetic guide field.
Indeed, the strength of the magnetic field controls the degree of anisotropy
and whether or not any anisotropy is present, but it is the turbulent motions
controlled by $\mathcal{M}$ that determine which kind of anisotropy dominates
the morphology of a cloud.",1911.13090v1
2020-11-11,Vital role of anisotropy in cubic chiral skyrmion hosts,"The impact of magnetic anisotropy on the skyrmion lattice (SkL) state in
cubic chiral magnets has been overlooked for long, partly because a
semi-quantitative description of the thermodynamically stable SkL phase pocket
forming near the Curie temperature could be achieved without invoking
anisotropy effects. However, there has been a range of phenomena reported
recently in these materials, such as the formation of low-temperature tilted
conical and SkL states as well as temperature-induced transformations of
lattice geometry in metastable SkL states, where anisotropy was suspected to
play a key role. To settle this issue on experimental basis, we quantified the
cubic anisotropy in a series of CoZnMn-type cubic chiral magnets. We found that
the strength of anisotropy is highly enhanced towards low temperatures in all
the compounds, moreover, not only the magnitude but also the character of cubic
anisotropy drastically varies upon changing the Co/Mn ratio. We correlate these
changes with temperature- and composition-induced variations of the helical
modulation vectors, the anharmonicity and structural rearrangements of the
metastable SkLs and the spin relaxation rates. Similar systematic studies on
magnetic anisotropy may not only pave the way for a quantitative and unified
description of the stable and metastable modulated spin textures in cubic
chiral magnets but would also help exploring further topological spin textures
in this large class of skyrmion hosts.",2011.05967v1
2021-02-10,"Screening, Friedel oscillations, RKKY interaction, and Drude transport in anisotropic two-dimensional systems","We investigate the effect of the mass anisotropy on Friedel Oscillations,
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, screening properties, and
Boltzmann transport in two dimensional (2D) metallic and doped semiconductor
systems. We calculate the static polarizability and the dielectric function
within the random phase approximation with the mass anisotropy fully taken into
account without making any effective isotropic approximation in the theory. We
find that carrier screening exhibits an isotropic behavior for small momenta
despite the anisotropy of the system, and becomes strongly anisotropic above a
certain threshold momentum. Such an anisotropy of screening leads to
anisotropic Friedel oscillations, and an anisotropic RKKY interaction
characterized by a periodicity dependent on the direction between the localized
magnetic moments. We also explore the disorder limited dc transport properties
in the presence of mass anisotropy based on the Boltzmann transport theory.
Interestingly, we find that the anisotropy ratio of the short range disorder
limited resistivity along the heavy- and light-mass directions is always the
same as the mass anisotropy ratio whereas for the long range disorder limited
resistivity the anisotropy ratio is the same as the mass ratio only in the low
density limit, and saturates to the square root of the mass ratio in the high
density limit. Our theoretical work should apply to many existing and
to-be-discovered anisotropic 2D systems.",2102.05659v2
2021-02-26,Evidence of a thick halo for the spatial-dependent propagation model with Cosmic Ray anisotropy,"The spatial-dependent propagation (SDP) model with a nearby source works well
to reproduce the co-evolving features of both cosmic ray (CR) nuclei spectra
and anisotropy. However, it is well known that the Sun is offset from the
Galactic plane. This will lead to a dominating anisotropy in perpendicular
direction, which is discrepant with observations. Thus it is necessary to
reboot further investigation into the effect of the solar offset. In this work,
for the first time the combined studies of the solar offset, nuclei spectra and
anisotropy are performed based on the SDP model. As a result, to reproduce CR
spectra and anisotropy, the thickness of the halo $\rm (\xi z_h)$ increases
linearly with the displacement of the Sun. When the offset is $\rm \sim8~pc$ as
estimated from the matter-borne methods, $\rm \xi z_h$ is about 0.9 kpc, which
is a much thicker halo than usually. Moreover, the PeV anisotropy could
estimate the value of diffusion coefficient, thus breaking the degeneracy of
diffusion coefficient and halo thickness. Therefore it is a good messenger to
constrain the halo thickness. On the other hand, the anisotropy in PeV energy
region, as a new probe, might also shed new light to constrain the solar
offset. We hope that the anisotropy at the energies of $\rm \sim TeV$ to $\rm
PeV$ can be finely measured by LHAASO experiment, leading to a better
understanding about the thick halo.",2102.13498v2
2021-08-11,Instabilities of spin-1 Kitaev spin liquid phase in presence of single-ion anisotropies,"We study the spin-one Kitaev model on the honeycomb lattice in the presence
of single-ion anisotropies. We consider two types of single ion anisotropies: A
$D_{111}$ anisotropy which preserves the symmetry between $X$, $Y$, and $Z$
bonds but violates flux conservation and a $D_{100}$ anisotropy that breaks the
symmetry between $X$, $Y$, and $Z$ bonds but preserves flux conservation. We
use series expansion methods, degenerate perturbation theory, and exact
diagonalization to study these systems. Large positive $D_{111}$ anisotropy
leads to a simple product ground state with conventional magnon-like
excitations, while large negative $D_{111}$ leads to a broken symmetry and
degenerate ground states. For both signs there is a phase transition at a small
$|D_{111}| \approx 0.12$ separating the more conventional phases from the
Kitaev spin liquid phase. With large $D_{100}$ anisotropy, the ground state is
a simple product state, but the model lacks conventional dispersive excitations
due to the large number of conservation laws. Large negative $D_{100}$ leads to
decoupled one-dimensional systems and many degenerate ground states. No
evidence of a phase transition is seen in our numerical studies at any finite
$D_{100}$. Convergence of the series expansion extrapolations all the way to
$D_{100}=0$ suggests that the nontrivial Kitaev spin liquid is a singular limit
of this type of single-ion anisotropy going to zero, which also restores
symmetry between the $X$, $Y$, and $Z$ bonds.",2108.05040v2
2022-03-16,Theoretical analysis of single-ion anisotropy in $d^3$ Mott insulators,"An effective spin model for Mott insulators is determined by the symmetries
involved among magnetic sites, electron fillings, and their interactions. Such
a spin Hamiltonian offers insight to mechanisms of magnetic orders and magnetic
anisotropy beyond the Heisenberg model. For a spin moment S bigger than 1/2,
single-ion anisotropy is in principle allowed. However, for $d^3$ Mott
insulators with large cubic crystal field splitting, the single-ion anisotropy
is absent within the LS coupling, despite S = 3/2 local moment. On the other
hand, preferred magnetic moment directions in $d^3$ materials have been
reported, which calls for a further theoretical investigation. Here we derive
the single-ion anisotropy interaction using the strong-coupling perturbation
theory. The cubic crystal field splitting including $e_g$ orbitals, trigonal
distortions, Hund's coupling, and spin-orbit coupling beyond the LS scheme are
taken into account. For compressed distortion, the spin-orbit coupling at
magnetic sites can favor either the easy-axis or the easy-plane while that of
anions leads to easy-axis anisotropy. We apply the theory on $\rm{CrX}_3$ with
X = Cl and I, and show the dependence of the single-ion anisotropy on the
strength of the spin-orbit couplings of both magnetic and anion sites.
Significance of the single-ion anisotropy in ideal two-dimensional magnets is
also discussed.",2203.08836v3
2022-08-06,Representing the stress and strain energy of elastic solids with initial stress and transverse texture anisotropy,"Real-world solids, such as rocks, soft tissues, and engineering materials,
are often under some form of stress. Most real materials are also, to some
degree, anisotropic due to their microstructure, a characteristic often called
the `texture anisotropy'. This anisotropy can stem from preferential grain
alignment in polycrystalline materials, aligned micro-cracks, or structural
reinforcement, such as collagen bundles in biological tissues, steel rods in
prestressed concrete and reinforcing fibres in composites. Here we establish a
framework for initially stressed solids with transverse texture anisotropy. We
consider that the strain energy per unit mass of the reference is an explicit
function of the elastic deformation gradient, the initial stress tensor, and
the texture anisotropy. We determine the corresponding constitutive relations
and develop examples of nonlinear strain energies which depend explicitly on
the initial stress and direction of texture anisotropy. As an application, we
then employ these models to analyse the stress distribution of an inflated
initially stressed cylinder with texture anisotropy, and the tension of a
welded metal plate. We also deduce the elastic moduli needed to describe linear
elasticity from stress reference with transverse texture anisotropy. As an
example we show how to measure the stress with small-amplitude shear waves.",2208.03502v1
2022-11-02,Electronic anisotropy in magic-angle twisted trilayer graphene,"Due to its potential connection with nematicity, electronic anisotropy has
been the subject of intense research effort on a wide variety of material
platforms. The emergence of spatial anisotropy not only offers a
characterization of material properties of metallic phases, which cannot be
accessed via conventional transport techniques, but it also provides a unique
window into the interplay between Coulomb interaction and broken symmetry
underlying the electronic order. In this work, we utilize a new scheme of
angle-resolved transport measurement (ARTM) to characterize electron anisotropy
in magic-angle twisted trilayer graphene. By analyzing the dependence of
spatial anisotropy on moir\'e band filling, temperature and twist angle, we
establish the first experimental link between electron anisotropy and the
cascade phenomenon, where Coulomb interaction drives a number of isospin
transitions near commensurate band fillings. Furthermore, we report the
coexistence between electron anisotropy and a novel electronic order that
breaks both parity and time reversal symmetry. Combined, the link between
electron anisotropy, cascade phenomenon and PT-symmetry breaking sheds new
light onto the nature of electronic order in magic-angle graphene moir\'e
systems.",2211.01352v1
2023-05-04,Is the Universe anisotropic right now? Comparing the real Universe with the Kasner's space-time,"We investigate possible astronomical manifestations of space-time anisotropy.
The homogeneous vacuum Kasner solution was chosen as a reference anisotropic
cosmological model because there are no effects caused by inhomogeneity in this
simple model with a constant degree of anisotropy. This anisotropy cannot
become weak. The study of its geodesic structure made it possible to clarify
the properties of this space-time. It showed that the degree of manifestation
of anisotropy varies significantly depending on the travel time of the light
from the observed object. For nearby objects, for which it does not exceed half
the age of the universe, the manifestations of anisotropy are very small.
Distant objects show more pronounced manifestations, for example, in the
distribution of objects over the sky and over photometric distances. These
effects for each of the individual objects decrease with time, but in general,
the manifestations of anisotropy in the Kasner space-time remain constant due
to the fact that new sources emerging from beyond the cosmological horizon.We
analyse observable signatures of the Kasner-type anisotropy and compare it to
observations. These effects were not found in astronomical observations,
including the study of the CMB. We can assume that the Universe has always been
isotropic or almost isotropic since the recombination era. This does not
exclude the possibility of its significant anisotropy at the moment of the Big
Bang followed by rapid isotropization during the inflationary epoch.",2305.02726v2
2023-05-09,Exploring the spectrum of stochastic gravitational-wave anisotropies with pulsar timing arrays,"Anisotropies in the nanohertz gravitational-wave background are a compelling
next target for pulsar timing arrays (PTAs). Measurements or informative upper
limits to the anisotropies are expected in the near future and can offer
important clues about the origin of the background and the properties of the
sources. Given that each source is expected (in the simplest scenario of
circular inspirals) to emit at a fixed frequency, the anisotropy will most
generally vary from one frequency to another. The main result presented in this
work is an analytical model for the anisotropies produced by a population of
inspiralling supermassive black-hole binaries (SMBHBs). This model can be
immediately connected with parametrizations of the SMBHB mass function and can
be easily expanded to account for new physical processes taking place within
the PTA frequency band. We show that a variety of SMBHB models predict
significant levels of anistropy at the highest frequencies accessible to PTA
observations and that measurements of anisotropies can offer new information
regarding this population beyond the isotropic component. We also model the
impact of additional dynamical effects driving the binary towards merger and
show that, if these processes are relevant within the PTA band, the
detectability of anisotropies relative to the isotropic background will be
enhanced. Finally, we use the formalism presented in this work to predict the
level anisotropy of the circular and linear polarizations of the SGWB due to
the distribution of binary orientation angles with respect to the line of
sight.",2305.05690v1
2023-09-27,Impact of surface anisotropy on the spin-wave dynamics in thin ferromagnetic film,"The spin-wave dynamics in the thin CoFeB film in Damon-Eshbach geometry are
studied in three cases of boundary conditions -- free boundary conditions,
symmetrical surface anisotropy, and one-sided surface anisotropy. The
analytical model created by Wolfram and De Wames was extended to include
perpendicular surface anisotropy in boundary conditions. Its comparison with
numerical simulations demonstrate perfect agreement between the approaches. The
analysis of the dispersion relation indicates that the presence of surface
anisotropy increases the avoided crossing size between Damon-Eshbach mode and
perpendicular standing modes. Additionally, asymmetrical one-sided surface
anisotropy induces nonreciprocity in the dispersion relation. In-depth analysis
of the avoided crossing size is conducted for systems with different boundary
conditions, different thicknesses, surface anisotropy constant values, and
external magnetic fields. It shows the significant role of the strength of
surface localization of Damon-Eshbach mode and the symmetry of perpendicular
standing modes in the avoided crossing broadening. Interestingly, for specific
set of parameters the interaction between the particular modes can be
suppressed, resulting in a mode crossing. Such a crossing, which occurs only on
one side of the dispersion relation in a one-sided surface anisotropy system,
can be utilized in nonreciprocal devices.",2309.15583v1
2023-12-31,Anisotropy of quadratic forms over a global field of odd characteristic is diophantine,"We prove that the anisotropy of quadratic forms over any global field of
characteristic not equal to 2 is diophantine, by using a generalization of the
method of Koenigsmann and some known results in diophantine sets and quadratic
forms.",2401.00537v1
2024-03-11,On convex comparison for exterior Bernoulli problems with discontinuous anisotropy,"We give a new proof of a convex comparison principle for exterior Bernoulli
free boundary problems with discontinuous anisotropy.",2403.07212v1
2024-02-20,Exploring magnetic anisotropy in bcc-structured ferromagnetic thin films with three spin layers using the fourth order perturbed Heisenberg Hamiltonian,"This study investigates into the analysis of ferromagnetic thin films with a
body centered cubic lattice and three spin layers, utilizing the solution of
the fourth-order perturbed Heisenberg Hamiltonian equation with seven magnetic
energy parameters. Spin-exchange interaction, magnetic dipole interaction,
second-order magnetic anisotropy,fourth-order magnetic anisotropy, applied
magnetic field, demagnetization energy, and stress-induced anisotropy were all
taken into account. According to 3D plots, the minimum order of energy was
observed when the second order magnetic anisotropy constant in the middle spin
layer is less than those of the bottom and top spin layers. In all cases, the
values of stress-induced anisotropy at the maxima of 3D plots are exactly the
same when the values of the second-order magnetic anisotropy constants of the
bottom, middle, and top spin layers are interchanged with each other. In 2D
plots, the angle between consecutive magnetic easy and hard directions is
approximately 90 degrees in all cases. Additionally, the magnetic easy and hard
directions were observed to have exactly the same values when the second-order
magnetic anisotropy constant of the spin layers changes. These results were
compared with the results obtained using the second and third order perturbed
Heisenberg Hamiltonian.",2403.13817v1
2024-04-03,In-situ tunable giant electrical anisotropy in a grating gated AlGaN/GaN two-dimensional electron gas,"Materials with in-plane electrical anisotropy have great potential for
designing artificial synaptic devices. However, natural materials with strong
intrinsic in-plane electrical anisotropy are rare. We introduce a simple
strategy to produce extremely large electrical anisotropy via grating gating of
a semiconductor two-dimensional electron gas (2DEG) of AlGaN/GaN. We show that
periodically modulated electric potential in the 2DEG induces in-plane
electrical anisotropy, which is significantly enhanced in a magnetic field,
leading to an ultra large electrical anisotropy. This is induced by a giant
positive magnetoresistance and a giant negative magnetoresistance under two
orthogonally oriented in-plane current flows, respectively. This giant
electrical anisotropy is in-situ tunable by tailoring both the grating gate
voltage and the magnetic field. Our semiconductor device with controllable
giant electrical anisotropy will stimulate new device applications, such as
multi-terminal memtransistors and bionic synapses.",2404.02427v1
1994-06-17,A Two-Fluid Approximation for Calculating the Cosmic Microwave Background Anisotropies,"We present a simple, yet accurate approximation for calculating the cosmic
microwave background anisotropy power spectrum in adiabatic models. It consists
of solving for the evolution of a two-fluid model until the epoch of
recombination and then integrating over the sources to obtain the CMB
anisotropy power spectrum. The approximation is useful both for a physical
understanding of CMB anisotropies, as well as for a quantitative analysis of
cosmological models. Comparison with exact calculations shows that the accuracy
is typically better than 20 percent over a large range of angles and
cosmological models, including those with curvature and cosmological constant.
Using this approximation we investigate the dependence of the CMB anisotropies
on the cosmological parameters. We identify six dimensionless parameters that
uniquely determine the anisotropy power spectrum within our approximation. CMB
experiments on different angular scales could in principle provide information
on all these parameters. In particular, mapping of the Doppler peaks would
allow an independent determination of baryon mass density, matter mass density
and Hubble constant.",9406050v1
1996-09-05,Large Angular Scale CMB Anisotropy Induced by Cosmic Strings,"We simulate the anisotropy in the cosmic microwave background (CMB) induced
by cosmic strings. By numerically evolving a network of cosmic strings we
generate full-sky CMB temperature anisotropy maps. Based on $192$ maps, we
compute the anisotropy power spectrum for multipole moments $\ell \le 20$. By
comparing with the observed temperature anisotropy, we set the normalization
for the cosmic string mass-per-unit-length $\mu$, obtaining $G\mu/c^2=1.05
{}^{+0.35}_{-0.20} \times10^{-6}$, which is consistent with all other
observational constraints on cosmic strings. We demonstrate that the anisotropy
pattern is consistent with a Gaussian random field on large angular scales.",9609038v1
1999-09-22,An intrinsic anisotropy in the angular distribution of gamma-ray bursts,"The anisotropy of the sky distribution of 2025 gamma-ray bursts (GRBs)
collected in Current BATSE catalog is confirmed. It is shown that the
quadrupole term being proportional to $\sim \sin 2b \sin l$ is non-zero with a
probability 99.9%. The occurrence of this anisotropy term is then supported by
the binomial test even with the probability 99.97%. It is also argued that this
anisotropy cannot be caused exclusively by instrumental effects due to the
non-uniform sky exposure of BATSE instrument; there should exist also some
intrinsic anisotropy in the angular distribution of GRBs. Separating GRBs into
short and long subclasses, it is shown that the 251 short ones are distributed
anisotropically, but the 681 long ones seem to be distributed still
isotropically. The 2-sample Kolmogorov-Smirnov test shows that they are
distributed differently with a 98.7% probability. The character of anisotropy
suggests that the cosmological origin of short GRBs further holds, and there is
no evidence for their Galactical origin. The work in essence contains the key
ideas and results of a recently published paper (\cite{balazs}), to which the
new result following from the 2-sample Kolmogorov-Smirnov test is added, too.",9909379v1
2000-05-02,Anisotropy of the Hubble Constant in a Cosmological Model with a Local Void on Scales of ~ 200 Mpc,"A spherical cosmological model with a local void on scales of $\sim 200$ Mpc
and with an inhomogeneous Hubble constant was proposed in recent two papers.
This model explains consistently the observed properties of the cosmic bulk
flow, the accelerating behavior of type Ia supernovae and the CMB dipole
anisotropy without invoking a cosmological constant. As we are in a position
deviated from the center in the model, the anisotropy of the Hubble constant
appears owing to the directional difference of the distance from the observer
to the boundary of the void region. It is found that the anisotropy is
maximally about 6% of the constant in the region of $200 \sim 500$ Mpc from us.
This inhomogeneity and anisotropy of the Hubble constant are not so large as to
be inconsistent with the present observation. The detection of this anisotropy
in the future will be useful to clarify the implication of the inhomogeneity of
the Hubble constant.",0005031v2
2000-02-03,Band-theoretical prediction of magnetic anisotropy in uranium monochalcogenides,"Magnetic anisotropy of uranium monochalcogenides, US, USe and UTe, is studied
by means of fully-relativistic spin-polarized band structure calculations
within the local spin-density approximation. It is found that the size of the
magnetic anisotropy is fairly large (about 10 meV/unit formula), which is
comparable with experiment. This strong anisotropy is discussed in view of a
pseudo-gap formation, of which crucial ingredients are the exchange splitting
of U 5f states and their hybridization with chalcogen p states (f-p
hybridization). An anomalous trend in the anisotropy is found in the series
(US>>USe<UTe) and interpreted in terms of competition between localization of
the U 5f states and the f-p hybridization. It is the spin-orbit interaction on
the chalcogen p states that plays an essential role in enlarging the strength
of the f-p hybridization in UTe, leading to an anomalous systematic trend in
the magnetic anisotropy.",0002044v1
2000-06-07,Theory of Magnetic Anisotropy in III_{1-x}Mn_{x}V Ferromagnets,"We present a theory of magnetic anisotropy in ${\rm III}_{1-x}{\rm
Mn}_{x}{\rm V}$ diluted magnetic semiconductors with carrier-induced
ferromagnetism. The theory is based on four and six band envelope functions
models for the valence band holes and a mean-field treatment of their exchange
interactions with ${\rm Mn}^{++}$ ions. We find that easy-axis reorientations
can occur as a function of temperature, carrier density $p$, and strain. The
magnetic anisotropy in strain-free samples is predicted to have a $p^{5/3}$
hole-density dependence at small $p$, a $p^{-1}$ dependence at large $p$, and
remarkably large values at intermediate densities. An explicit expression,
valid at small $p$, is given for the uniaxial contribution to the magnetic
anisotropy due to unrelaxed epitaxial growth lattice-matching strains. Results
of our numerical simulations are in agreement with magnetic anisotropy
measurements on samples with both compressive and tensile strains. We predict
that decreasing the hole density in current samples will lower the
ferromagnetic transition temperature, but will increase the magnetic anisotropy
energy and the coercivity.",0006093v1
2001-09-21,Hysteretic properties of a magnetic particle with strong surface anisotropy,"We study the influence of surface anisotropy on the zero-temperature
hysteretic properties of a small single-domain magnetic particle, and give an
estimation of the anisotropy constant for which deviations from the
Stoner-Wohlfarth model are observed due to non-uniform reversal of the
particle's magnetisation. For this purpose, we consider a spherical particle
with simple cubic crystalline structure, a uniaxial anisotropy for core spins
and radial anisotropy on the surface. The hysteresis loop is obtained by
solving the local (coupled) Landau-Lifschitz equations for classical spin
vectors. We find that when the surface anisotropy constant is at least of the
order of the exchange coupling, large deviations are observed with respect to
the Stoner-Wohlfarth model in the hysteresis loop and thereby the
limit-of-metastability curve, since in this case the magnetisation reverses its
direction in a non-uniform manner via a progressive switching of spin clusters.
In this case the critical field, as a function of the particle's size, behaves
as observed in experiments.",0109411v3
2001-12-03,Effect of surface anisotropy on the hysteretic properties of a magnetic particle,"We study the influence of surface anisotropy on the zero-temperature
hysteretic properties of a small single-domain magnetic particle, and give an
estimation of the anisotropy constant for which deviations from the
Stoner-Wohlfarth model are observed. We consider a spherical particle with
simple cubic crystalline structure, a uniaxial anisotropy for core spins and
radial anisotropy on the surface, and compute the hysteresis loop by solving
the local Landau-Lifshitz equations for classical spin vectors. We find that
when the surface anisotropy constant is at least of the order of the exchange
coupling, large deviations are observed with respect to the Stoner-Wohlfarth
model in the hysteresis loop and thereby the limit-of-metastability curve, due
to the non-uniform cluster-wise reversal of the magnetisation.",0112032v1
2002-07-14,Magnetoresistance and magnetic anisotropy in La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$ film,"The magnetic and transport properties of La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$
film grown on a LaAlO$_3$ substrate by pulsed-laser deposition are studied. The
properties are found to be influenced by a combined influence of the magnetic
anisotropy and inhomogeneity. Magnetoresistance anisotropy is determined by the
shape anisotropy and the strain-induced magnetic anisotropy due to the
film-substrate lattice interaction. Indications of the temperature-driven spin
reorientation transition from an out-of plane orderded state at low
temperatures to an in-plane ordered state at high temperatures as a result of
competition between the mentioned anisotropy sources are found.",0207346v1
2003-07-10,Axial and off-axial dynamic transitions in uniaxially anisotropic Heisenberg ferromagnet: A comparison,"Uniaxially anisotropic Heisenberg ferromagnet, in the presence of a magnetic
fieldvarying sinusoidally in time, is studied by Monte Carlo Simulation. The
axial (field applied only along the direction of anisotropy) and off-axial
(field applied only along the direction which is prependicular to the direction
of anisotropy) dynamic transitions are studied. By studying the distribution of
the dynamic order parameter component, it is observed that the axial transition
is discontinuous for low anisotropy and becomes continuous in high anisotropy.
The off-axial transition is found to be continuous for all values of
anisotropy. In the infinite anisotropy limit, both types of transitions are
compared with athat observed in an Ising ferromagnet for the same value of the
field and frequency. The infinitely anisotropic axial transition and dynamic
transition in the Ising ferromagnet occur at different temperatures, whereas
the infinitely anisotropic off-axial transition and the equilibrium ferro-para
transition in the Ising model occur at the same temperature.",0307225v1
2004-07-09,"Pressure Dependence of the Magnetic Anisotropy in the ""Single-Molecule Magnet"" [Mn4O3Br(OAc)3(dbm)3]","The anisotropy splitting in the ground state of the single-molecule magnet
[Mn4O3Br(OAc)3(dbm)3] is studied by inelastic neutron scattering as a function
of hydrostatic pressure. This allows a tuning of the anisotropy and thus the
energy barrier for slow magnetisation relaxation at low temperatures. The value
of the negative axial anisotropy parameter $D_{\rm cluster}$ changes from
-0.0627(1) meV at ambient to -0.0603(3) meV at 12 kbar pressure, and in the
same pressure range the height of the energy barrier between up and down spins
is reduced from 1.260(5) meV to 1.213(9) meV. Since the $\rm Mn-Br$ bond is
significantly softer and thus more compressible than the $\rm Mn-O$ bonds,
pressure induces a tilt of the single ion Mn$^{3+}$ anisotropy axes, resulting
in the net reduction of the axial cluster anisotropy.",0407235v1
2005-04-14,Inversion phenomenon and phase diagram of the $S=1/2$ distorted diamond chain with the $XXZ$ interaction anisotropy,"We discuss the anisotropies of the Hamiltonian and the wave-function in an
$S=1/2$ distorted diamond chain. The ground-state phase diagram of this model
is investigated using the degenerate perturbation theory up to the first order
and the level spectroscopy analysis of the numerical diagonalization data. In
some regions of the obtained phase diagram, the anisotropy of the Hamiltonian
and that of the wave-function are inverted, which we call inversion phenomenon;
the N\'{e}el phase appears for the XY-like anisotropy and the spin-fluid phase
appears for the Ising-like anisotropy. Three key words are important for this
nature, which are frustration, the trimer nature, and the $XXZ$ anisotropy.",0504360v1
2002-09-11,Semiclassical gravitation and quantization for the Bianchi type I universe with large anisotropy,"We use a perturbative method to evaluate the effective action of a free
scalar field propagating in the Bianchi type I spacetime with large space
anisotropy. The zeta- function regularization method is used to evaluate the
action to the second order in the Schwinger perturbative formula. As the
quantum corrections contain fourth derivative in the metric we apply the method
of iterative reduction to reduce it to the second-order form to obtain the
self-consistent solution of the semiclassical gravity theory, The reduced
Einstein equation shows that the space anisotropy, which will be smoothed out
during the evolution of universe, may play an important role in the dynamics of
early universe. We quantize the corresponding minisuperspace model to
investigate the behavior of the space anisotropy in the initial epoch. From the
wavefunction of the Wheeler-DeWitt equation we see that the probability for the
Bianchi type I spacetime with large anisotropy is less then that with a small
anisotropy.",0209092v1
2003-03-12,Cosmological Anisotropy and the Cycling of Universe,"In this paper, we analyze the anisotropy of the scale factor in the
Kantowski-Sachs spacetime. We show that the anisotropy will not increase when
the expansion rate is greater than certain values while it will increase when
the expansion rate is less than that value or the Universe is contracting. It
is manifested that the matter dominated and radiation dominated era favor the
flat spacetime if the anisotropy does not develop significantly. The relation
between the cosmological anisotropy and the red-shift of the supernovae, which
could be used to verify the anisotropy through the observation, has been
derived.",0303110v3
2007-11-22,Globally Anisotropic High Porosity Silica Aerogels,"We discuss two methods by which high porosity silica aerogels can be
engineered to exhibit global anisotropy. First, anisotropy can be introduced
with axial strain. In addition, intrinsic anisotropy can result during growth
and drying stages and, suitably controlled, it can be correlated with
preferential radial shrinkage in cylindrical samples. We have performed small
angle X-ray scattering (SAXS) to characterize these two types of anisotropy. We
show that global anisotropy originating from either strain or shrinkage leads
to optical birefringence and that optical cross-polarization studies are a
useful characterization of the uniformity of the imposed global anisotropy.",0711.3495v1
2008-02-28,"An extensive comparison of anisotropies in MBE grown (Ga,Mn)As material","This paper reports on a detailed magnetotransport investigation of the
magnetic anisotropies of (Ga,Mn)As layers produced by various sources
worldwide. Using anisotropy fingerprints to identify contributions of the
various higher order anisotropy terms, we show that the presence of both a
[100] and a [110] uniaxial anisotropy in addition to the primary ([100] +
[010]) anisotropy is common to all medium doped (Ga,Mn)As layers typically used
in transport measurement, with the amplitude of these uniaxial terms being
characteristic of the individual layers.",0802.4206v1
2008-05-21,Friedel oscillations induced surface magnetic anisotropy,"We present detailed numerical studies of the magnetic anisotropy energy of a
magnetic impurity near the surface of metallic hosts (Au and Cu), that we
describe in terms of a realistic tight-binding surface Green's function
technique. We study the case when spin-orbit coupling originates from the
d-band of the host material and we also investigate the case of a strong local
spin-orbit coupling on the impurity itself. The splitting of the impurity's
spin-states is calculated to leading order in the exchange interaction between
the impurity and the host atoms using a diagrammatic Green's function
technique. The magnetic anisotropy constant is an oscillating function of the
separation d from the surface: it asymptotically decays as 1/d2 and its
oscillation period is determined by the extremal vectors of the host's Fermi
Surface. Our results clearly show that the host-induced magnetic anisotropy
energy is by several orders of magnitude smaller than the anisotropy induced by
the local mechanism, which provides sufficiently large anisotropy values to
explain the size dependence of the Kondo resistance observed experimentally.",0805.3275v1
2008-05-28,Primordial statistical anisotropy generated at the end of inflation,"We present a new mechanism for generating primordial statistical anisotropy
of curvature perturbations. We introduce a vector field which has a non-minimal
kinetic term and couples with a waterfall field in hybrid inflation model. In
such a system, the vector field gives fluctuations of the end of inflation and
hence induces a subcomponent of curvature perturbations. Since the vector has a
preferred direction, the statistical anisotropy could appear in the
fluctuations. We present the explicit formula for the statistical anisotropy in
the primordial power spectrum and the bispectrum of curvature perturbations.
Interestingly, there is the possibility that the statistical anisotropy does
not appear in the power spectrum but does appear in the bispectrum. We also
find that the statistical anisotropy provides the shape dependence to the
bispectrum.",0805.4265v6
2008-06-15,Tricritical transition in the classical XY model on Kagomé lattice under local anisotropy,"Using mean-field theory and high resolution Monte Carlo simulation technique
based on multi-histogram method, we have investigated the critical properties
of an antiferromagnetic XY model on the 2D Kagom\'e lattice, with single ion
easy-axes anisotropy. The mean-field theory predicts second-order phase
transition from disordered to all-in all-out state for any value of anisotropy
for this model. However, Monte Carlo simulations result in first order
transition for small values of anisotropy which turns to second order with
increasing strength of anisotropy, indicating the existence of a tricritical
point for this model. The critical exponents, obtained by finite-size scaling
methods, show that the transition is in Ising universality class for large
values of anisotropy, while the critical behaviour of the system deviates from
2D-$\phi^6$ model near the tricritical point. This suggests the possibility for
existence of a new tricritical universality in two-dimensions.",0806.2432v1
2008-11-19,Transport Anisotropy as a Probe of the Interstitial Vortex State in Superconductors with Artificial Pinning Arrays,"We show using simulations that when interstitial vortices are present in
superconductors with periodic pinning arrays, the transport in two
perpendicular directions can be anisotropic. The degree of the anisotropy
varies as a function of field due to the fact that the interstitial vortex
lattice has distinct orderings at different matching fields. The anisotropy is
most pronounced at the matching fields but persists at incommensurate fields,
and it is most prominent for triangular, honeycomb, and kagome pinning arrays.
Square pinning arrays can also show anisotropic transport at certain fields in
spite of the fact that the perpendicular directions of the square pinning array
are identical. We show that the anisotropy results from distinct vortex
dynamical states and that although the critical depinning force may be lower in
one direction, the vortex velocity above depinning may also be lower in the
same direction for ranges of external drives where both directions are
depinned. For honeycomb and kagome pinning arrays, the anisotropy can show
multiple reversals as a function of field. We argue that when the pinning sites
can be multiply occupied such that no interstitial vortices are present, the
anisotropy is strongly reduced or absent.",0811.3178v1
2008-11-25,Evidence for two distinct anisotropies in the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and NdFeAsO_(0.8)F_(0.2),"Single crystals of the oxypnictide superconductors SmFeAsO_(0.8)F_(0.2) and
NdFeAsO_(0.8)F_(0.2) with T_c in the range of 44 K to 48 K were investigated by
torque magnetometry. An analysis of the data in terms of a recently proposed
model for the anisotropic magnetization in the superconducting state, treating
the penetration depth anisotropy differently than the upper critical field
anisotropy, provides evidence that in the oxypnictide superconductors two
distinct anisotropies are present. As a result the penetration depth anisotropy
differs significantly in magnitude and in temperature dependence from the upper
critical field anisotropy, analogous to MgB_2 but with a reversed sign of
slope. This scenario strongly suggests a new multi-band mechanism in the novel
class of oxypnictide high-temperature superconductors.",0811.4047v3
2009-09-11,Consistency criteria for generalized Cuddeford systems,"General criteria to check the positivity of the distribution function
(phase-space consistency) of stellar systems of assigned density and anisotropy
profile are useful starting points in Jeans-based modeling. Here we
substantially extend previous results, and we present the inversion formula and
the analytical necessary and sufficient conditions for phase-space consistency
of the family of multi-component Cuddeford spherical systems: the distribution
function of each density component of these systems is defined as the sum of an
arbitrary number of Cuddeford distribution functions with arbitrary values of
the anisotropy radius, but identical angular momentum exponent. The radial
trend of anisotropy that can be realized by these models is therefore very
general. As a surprising by-product of our study, we found that the ``central
cusp-anisotropy theorem'' (a necessary condition for consistency relating the
values of the central density slope and of the anisotropy parameter) holds not
only at the center, but at all radii in consistent multi-component generalized
Cuddeford systems. This last result suggests that the so--called
mass--anisotropy degeneracy could be less severe than what is sometimes feared.",0909.2156v1
2010-08-30,Searches for Cosmic-Ray Electron Anisotropies with the Fermi Large Area Telescope,"The Large Area Telescope on board the \textit{Fermi} satellite
(\textit{Fermi}-LAT) detected more than 1.6 million cosmic-ray
electrons/positrons with energies above 60 GeV during its first year of
operation. The arrival directions of these events were searched for
anisotropies of angular scale extending from $\sim$ 10 $^\circ$ up to
90$^\circ$, and of minimum energy extending from 60 GeV up to 480 GeV. Two
independent techniques were used to search for anisotropies, both resulting in
null results. Upper limits on the degree of the anisotropy were set that
depended on the analyzed energy range and on the anisotropy's angular scale.
The upper limits for a dipole anisotropy ranged from $\sim0.5%$ to $\sim10%$.",1008.5119v3
2010-09-13,Radiative energy loss in an anisotropic Quark-Gluon-Plasma,"We calculate radiative energy loss of heavy and light quarks in anisotropic
medium (static) in first order opacity expansion. Such an anisotropy can result
from the initial rapid longitudinal expansion of the matter, created in
relativistic heavy ion collisions. Significant dependency of the energy loss on
the anisotropy parameter ($\xi$) and the direction of propagation of the
partons with respect to the anisotropy axis is found. It is shown that the
introduction of early time momentum-space anisotropy can enhance the fractional
energy loss in the direction of the anisotropy, whereas it decreases when the
parton propagates perpendicular to the direction of the anisotropy.",1009.2304v3
2010-10-01,Ferromagnetic resonance study of Co/Pd/Co/Ni multilayers with perpendicular anisotropy irradiated with Helium ions,"We present a ferromagnetic resonance (FMR) study of the effect of Helium ion
irradiation on the magnetic anisotropy, the linewidth and the Gilbert damping
of a Co/Ni multilayer coupled to Co/Pd bilayers. The perpendicular magnetic
anisotropy decreases linearly with He ion fluence, leading to a transition to
in-plane magnetization at a critical fluence of 5x10^{14} ions/cm^2. We find
that the damping is nearly independent of fluence but the FMR linewidth at
fixed frequency has a maximum near the critical fluence, indicating that the
inhomogeneous broadening of the FMR line is a non-monotonic function of the He
ion fluence. Based on an analysis of the angular dependence of the FMR
linewidth, the inhomogeneous broadening is associated with spatial variations
in the magnitude of the perpendicular magnetic anisotropy. These results
demonstrate that ion irradiation may be used to systematically modify the
magnetic anisotropy and distribution of magnetic anisotropy parameters of
Co/Pd/Co/Ni multilayers for applications and basic physics studies.",1010.0268v2
2010-12-13,Distinct electronic nematicities between electron and hole underdoped iron pnictides,"We systematically investigated the in-plane resistivity anisotropy of
electron-underdoped $EuFe_{2-x}Co_xAs_2$ and $BaFe_{2-x}Co_xAs_2$, and
hole-underdoped $Ba_{1-x}K_xFe_2As_2$. Large in-plane resistivity anisotropy
was found in the former samples, while {\it tiny} in-plane resistivity
anisotropy was detected in the latter ones. When it is detected, the anisotropy
starts above the structural transition temperature and increases smoothly
through it. As the temperature is lowered further, the anisotropy takes a
dramatic enhancement through the magnetic transition temperature. We found that
the anisotropy is universally tied to the presence of non-Fermi liquid T-linear
behavior of resistivity. Our results demonstrate that the nematic state is
caused by electronic degrees of freedom, and the microscopic orbital
involvement in magnetically ordered state must be fundamentally different
between the hole and electron doped materials.",1012.2731v1
2011-06-20,Effects of Single-site Anisotropy on Mixed Diamond Chains with Spins 1 and 1/2,"Effects of single-site anisotropy on mixed diamond chains with spins 1 and
1/2 are investigated in the ground states and at finite temperatures. There are
phases where the ground state is a spin cluster solid, i.e., an array of
uncorrelated spin-1 clusters separated by singlet dimers. The ground state is
nonmagnetic for the easy-plane anisotropy, while it is paramagnetic for the
easy-axis anisotropy. Also, there are the N\'eel, Haldane, and large-$D$
phases, where the ground state is a single spin cluster of infinite size and
the system is equivalent to the spin-1 Heisenberg chain with alternating
anisotropy. The longitudinal and transverse susceptibilities and entropy are
calculated at finite temperatures in the spin-cluster-solid phases. Their
low-temperature behaviors are sensitive to anisotropy.",1106.3846v2
2011-07-30,Comprehensive Control of Optical Polarization Anisotropy in Semiconducting Nanowires,"The demonstration of strong photoluminescence polarization anisotropy in
semiconducting nanowires embodies both technological promise and scientific
challenge. Here we present progress on both fronts through the study of the
photoluminescence polarization anisotropy of randomly oriented nanowire
ensembles in materials without/with crystalline anisotropy, small/wide bandgap,
and both III-V/II-VI chemistry (InP/ZnO nanowires, respectively). Comprehensive
control of the polarization anisotropy is realized by dielectric matching with
conformally deposited Ta2O5 (dielectric ratios of 9.6:4.41 and 4.0:4.41 for InP
and ZnO, respectively). After dielectric matching, the polarization anisotropy
of the nanowire ensembles is reduced by 86% for InP:Ta2O5 and 84% for
ZnO:Ta2O5.",1108.0033v1
2011-09-11,Mössbauer study of the field induced uniaxial anisotropy in electro-deposited FeCo alloy films,"Thin ferromagnetic films with in-plane magnetic anisotropy are promising
materials for obtaining high microwave permeability. The paper reports on the
M\""ossbauer study of the field induced in-plane uniaxial anisotropy in
electro-deposited $FeCo$ alloy films. The $FeCo$ alloy films have been prepared
by electro-deposition method with and without external magnetic field applied
parallel to the film plane during deposition. The vibrating sample magnetometry
and M\""ossbauer spectroscopy measurements at room temperature indicate that the
film deposited in external field shows an in-plane uniaxial anisotropy with an
easy direction coincides with the external field direction and a hard direction
perpendicular to the field direction, whereas the film deposited without
external field doesn't show any in-plane anisotropy. M\""ossbauer spectra taken
in three geometric arrangements show that the magnetic moments are almost
constrained in the film plane for the film deposited with applied magnetic
field. And the magnetic moments are tend to align in the direction of the
applied external magnetic field during deposition, indicating that the observed
anisotropy should be attributed to directional ordering of atomic pairs.",1109.2286v1
2011-11-10,Local Magnetic Turbulence and TeV-PeV Cosmic Ray Anisotropies,"In the energy range from ~ 10^12 eV to ~ 10^15 eV, the Galactic cosmic ray
flux has anisotropies both on large scales, with an amplitude of the order of
0.1%, and on scales between ~ 10 and ~ 30 degrees, with amplitudes smaller by a
factor of a few. With a diffusion coefficient inferred from Galactic cosmic ray
chemical abundances, the diffusion approximation predicts a dipolar anisotropy
of comparable size, but does not explain the smaller scale anisotropies. We
demonstrate here that energy dependent smaller scale anisotropies naturally
arise from the local concrete realization of the turbulent magnetic field
within the cosmic ray scattering length. We show how such anisotropies could be
calculated if the magnetic field structure within a few tens of parsecs from
Earth were known.",1111.2536v2
2012-01-19,"Local Anisotropy, Higher Order Statistics, and Turbulence Spectra","Correlation anisotropy emerges dynamically in magnetohydrodynamics (MHD),
producing stronger gradients across the large-scale mean magnetic field than
along it. This occurs both globally and locally, and has significant
implications in space and astrophysical plasmas, including particle scattering
and transport, and theories of turbulence. Properties of local correlation
anisotropy are further documented here by showing through numerical experiments
that the effect is intensified in more localized estimates of the mean field.
The mathematical formulation of this property shows that local anisotropy mixes
second-order with higher order correlations. Sensitivity of local statistical
estimates to higher order correlations can be understood in connection with the
stochastic coordinate system inherent in such formulations. We demonstrate this
in specific cases, illustrate the connection to higher order statistics by
showing the sensitivity of local anisotropy to phase randomization, and thus
establish that the local structure function is not a measure of the energy
spectrum. Evidently the local enhancement of correlation anisotropy is of
substantial fundamental interest, and this phenomenon must be understood in
terms of higher order correlations, fourth-order and above.",1201.4127v1
2012-05-08,Anisotropy of strong pinning in multi-band superconductors,"The field-angular dependence and anisotropy of the critical current density
in iron-based superconductors is evaluated using a phenomenological approach
featuring distinct anisotropy factors for the penetration depth and the
coherence length. Both the weak collective pinning limit, and the strong
pinning limit relevant for iron-based superconductors at low magnetic fields
are considered. It is found that in the more anisotropic materials, such as
SmFeAsO and NdFeAsO, the field-angular dependence is completely dominated by
the coherence-length (upper-critical field) anisotropy, thereby explaining
recent results on the critical current in these materials. In less anisotropic
superconductors, strong pinning can lead to an apparent inversion of the
anisotropy. Finally, it is shown that, under all circumstances, the ratio of
c-axis and ab-plane critical current densities for magnetic field along the
ab-plane directly yields the coherence length anisotropy factor
{\epsilon}{\xi}.",1205.1741v3
2012-08-08,Anisotropy of the in-plane resistivity of underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ superconductors induced by impurity scattering in the antiferromagnetic orthorhombic phase,"We investigated the in-plane resistivity anisotropy for underdoped
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals with improved quality. We
demonstrate that the anisotropy in resistivity in the magnetostructural ordered
phase arises from the anisotropy in the residual component which increases in
proportion to the Co concentration $x$. This gives evidence that the anisotropy
originates from the impurity scattering by Co atoms substituted for the Fe
sites, rather than so far proposed mechanism such as the anisotropy of Fermi
velocities of reconstructed Fermi surface pockets. As doping proceeds to the
paramagnetic-tetragonal phase, a Co impurity transforms to a weak and isotropic
scattering center.",1208.1575v2
2012-09-24,Field Dependence of the Superconducting Basal Plane Anisotropy of TmNi2B2C,"The superconductor TmNi2B2C possesses a significant four-fold basal plane
anisotropy, leading to a square Vortex Lattice (VL) at intermediate fields.
However, unlike other members of the borocarbide superconductors, the
anisotropy in TmNi2B2C appears to decrease with increasing field, evident by a
reentrance of the square VL phase. We have used Small Angle Neutron Scattering
measurements of the VL to study the field dependence of the anisotropy. Our
results provide a direct, quantitative measurement of the decreasing
anisotropy. We attribute this reduction of the basal plane anisotropy to the
strong Pauli paramagnetic effects observed in TmNi2B2C and the resulting
expansion of vortex cores near Hc2.",1209.5414v1
2012-10-26,Novel Techniques for Decomposing Diffuse Backgrounds,"The total anisotropy of a diffuse background composed of two or more sources,
such as the Fermi-LAT--measured gamma-ray background, is set by the anisotropy
of each source population and the contribution of each population to the total
intensity. The total anisotropy as a function of energy (the anisotropy energy
spectrum) will modulate as the relative contributions of the sources change,
implying that the anisotropy energy spectrum also encodes the intensity
spectrum of each source class. We develop techniques, applicable to any such
diffuse background, for unraveling the intensity spectrum of each component
source population given a measurement of the total intensity spectrum and the
total anisotropy energy spectrum, without introducing \emph{a priori}
assumptions about the spectra of the source classes. We demonstrate the
potential of these methods by applying them to example scenarios for the
composition of the Fermi-LAT gamma-ray background consistent with current data
and feasible within 10 years of observation.",1210.7239v2
2012-11-29,"Electric-field control of the magnetic anisotropy in an ultrathin (Ga,Mn)As/(Ga,Mn)(As,P) bilayer","We report on the electric control of the magnetic anisotropy in an ultrathin
ferromagnetic (Ga,Mn)As/(Ga,Mn)(As,P) bilayer with competing in-plane and
out-of-plane anisotropies. The carrier distribution and therefore the strength
of the effective anisotropy is controlled by the gate voltage of a field effect
device. Anomalous Hall Effect measurements confirm that a depletion of carriers
in the upper (Ga,Mn)As layer results in the decrease of the in-plane
anisotropy. The uniaxial anisotropy field is found to decrease by a factor ~ 4
over the explored gate-voltage range, so that the transition to an out-of-plane
easy-axis configuration is almost reached.",1211.7055v1
2013-02-10,Measurement of orbital asymmetry and strain in Co90Fe10/Ni multilayers and alloys: Origins of perpendicular anisotropy,"We use broadband ferromagnetic resonance spectroscopy and x-ray diffraction
to investigate the fundamental origin of perpendicular anisotropy in
Co90Fe10/Ni multilayers. By careful evaluation of the spectroscopic g-factor,
we determine the orbital moment along the out-of-plane and in-plane directions.
For the multilayers, we find a direct relationship between the orbital moment
asymmetry and the perpendicular anisotropy, consistent with the theory of Bruno
[P.Bruno, Phys. Rev. B, 39, 865 (1989)]. A systematic x-ray diffraction study
revealed the presence of a trigonal strain as high as 0.7 % in some samples.
However, we found no direct correlation between the strain and the anisotropy,
indicating that the anisotropy is not dominated by magnetoelastic effects. In
order to further study the interface structure on the anisotropy, we prepared a
set of equivalent alloy samples. The strain in the alloy samples was comparable
to that of the multilayer samples; however the orbital moment asymmetry in the
alloy samples showed a very different trend allowing us to isolate the effect
of the interfaces in the multilayers.",1302.2366v1
2013-03-21,Asymptotic Preserving scheme for strongly anisotropic parabolic equations for arbitrary anisotropy direction,"This paper deals with the numerical study of a strongly anisotropic heat
equation. The use of standard schemes in this situation leads to poor results,
due to the high anisotropy. Furthermore, the recently proposed
Asymptotic-Preserving method [arXiv:1203.6739] allows to perform simulations
regardless of the anisotropy strength but its application is limited to the
case, where the anisotropy direction is given by a field with all field lines
open. In this paper we introduce a new Asymptotic-Preserving method, which
overcomes those limitations without any loss of precision or increase in the
computational costs. The convergence of the method is shown to be independent
of the anisotropy parameter $0 < \eps <1$, and this for fixed coarse Cartesian
grids and for variable anisotropy directions. The context of this work are
magnetically confined fusion plasmas.",1303.5219v3
2013-08-01,"Observation of TeV-PeV cosmic ray anisotropy with IceCube, IceTop and AMANDA","The study of cosmic ray anisotropy in the TeV-PeV energy range could provide
clues about the origin and propagation of cosmic rays in our galactic
neighborhood. Because the observed anisotropy is very small, below the
per-mille level, large event volumes are needed in order to characterize it in
sufficient detail. Over the last six years, the IceCube Observatory has
collected 150 billion cosmic ray induced muon events. This large data sample
made it possible to detect anisotropies in the southern hemisphere, down to the
10$^{-5}$ level, at primary energies in excess of 10 TeV. The observed
anisotropy is not a simple dipole, but it can be described as composed of
multipole components of the spherical harmonic expansion, to about
10$^{\circ}$. A change in topological structure of the cosmic ray arrival
distribution is observed above 100 TeV. Data collected with the air shower
array IceTop above 300 TeV confirm the observations up to the PeV energy scale.
Moreover, the addition of data collected with the AMANDA neutrino telescope,
which operated between 2000 and 2007, has enabled us to search for time
variability in the observed TeV anisotropy.",1308.0246v1
2013-08-13,Anatomy of perpendicular magnetic anisotropy in Fe/MgO magnetic tunnel junctions: First principles insight,"Using first-principles calculations, we elucidate microscopic mechanisms of
perpendicular magnetic anisotropy (PMA)in Fe/MgO magnetic tunnel junctions
through evaluation of orbital and layer resolved contributions into the total
anisotropy value. It is demonstrated that the origin of the large PMA values is
far beyond simply considering the hybridization between Fe-3d$ and O-2p
orbitals at the interface between the metal and the insulator. On-site
projected analysis show that the anisotropy energy is not localized at the
interface but it rather propagates into the bulk showing an attenuating
oscillatory behavior which depends on orbital character of contributing states
and interfacial conditions. Furthermore, it is found in most situations that
states with $d_{yz(xz)}$ and $d_{z^2}$ character tend always to maintain the
PMA while those with $d_{xy}$ and $d_{x^2-y^2}$ character tend to favor the
in-plane anisotropy. It is also found that while MgO thickness has no influence
on PMA, the calculated perpendicular magnetic anisotropy oscillates as a
function of Fe thickness with a period of 2ML and reaches a maximum value of
3.6 mJ/m$^2$.",1308.2909v1
2013-09-05,Voltage-induced strain control of the magnetic anisotropy in a Ni thin film on flexible substrate,"Voltage-induced magnetic anisotropy has been quantitatively studied in
polycrystalline Ni thin film deposited on flexible substrate using microstrip
ferromagnetic resonance. This anisotropy is induced by a piezoelectric actuator
on which the film/substrate system was glued. In our work, the control of the
anisotropy through the applied elastic strains is facilitated by the compliant
elastic behavior of the substrate. The in-plane strains in the film induced by
the piezoelectric actuation have been measured by the digital image correlation
technique. Non-linear variation of the resonance field as function of the
applied voltage is found and well reproduced by taking into account the non
linear and hysteretic variations of the induced in-plane strains as function of
the applied voltage. Moreover, we show that initial uniaxial anisotropy
attributed to compliant substrate curvature is fully compensated by the voltage
induced anisotropy.",1309.1417v1
2013-12-23,Implications of primordial power spectra with statistical anisotropy on CMB temperature fluctuation and polarizations,"Both the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck observations
reported the hemispherical asymmetry of the cosmic microwave background (CMB)
temperature fluctuation. The hemispherical asymmetry might be stemmed from the
primordial statistical anisotropy during the inflationary era of the universe.
In this paper, we study possible implications of the primordial power spectra
with dipolar anisotropy on the CMB temperature fluctuation and polarizations.
We explicitly show that the statistical dipolar anisotropy may induce the
off-diagonal (\(\ell'\neq\ell\)) $TT$, $EE$, $BB$, and $TE$ correlations, as
well as the diagonal (\(\ell'=\ell\)) $TB$ and $EB$ spectra. In particular,
these correlation coefficients are expected to be \(m\)-dependent generically.
These signals of statistical anisotropy might be tested by CMB observations in
future.",1312.6575v2
2014-02-28,Anisotropic optical properties of Fe/GaAs(001) nanolayers from first principles,"We investigate the anisotropy of the optical properties of thin Fe films on
GaAs(001) from first-principles calculations. Both intrinsic and
magnetization-induced anisotropy are covered by studying the system in the
presence of spin-orbit coupling and external magnetic fields. We use the
linearized augmented plane wave method, as implemented in the WIEN2k density
functional theory code, to show that the $C_{2v}$ symmetric anisotropy of the
spin-orbit coupling fields at the Fe/GaAs(001) interface manifests itself in
the corresponding anisotropy of the optical conductivity and the polar
magneto-optical Kerr effect. While their magnetization-induced anisotropy is
negligible, the intrinsic anisotropy of the optical properties is significant
and reflects the underlying $C_{2v}$ symmetry of the Fe/GaAs(001) interface.
This suggests that the effects of anisotropic spin-orbit coupling fields in
experimentally relevant Fe/GaAs(001) slabs can be studied by purely optical
means.",1402.7370v1
2014-03-28,On radial anisotropy limits in stellar systems,"Following earlier authors, we re-examine constraints on the radial velocity
anisotropy of generic stellar systems using arguments for phase space density
positivity, stability, and separability. It is known that although the majority
of commonly used systems have an maximum anisotropy of less than half of the
logarithmic density slope \emph{i.e.} $\beta < \gamma/2$, there are exceptions
for separable models with large central anisotropy. Here we present a new
exceptional case with above-threshold anisotropy locally but with an isotropic
center nevertheless. These models are non-separable and we maintain positivity.
Our analysis suggests that regions of above-threshold anisotropy are more
related to regions of possible secular instability, which might be observed in
self-consistent galaxies in a short-lived phase. s an equilibrium solution for
a collisionless system.",1403.7396v2
2014-05-19,An observable electron-positron anisotropy cannot be generated by dark matter,"I demonstrate that if an anisotropy in the arrival direction of high-energy
cosmic-ray electrons and positrons is observed then, barring local anisotropic
diffusion, dark matter annihilation is ruled out as an explanation to the
positron excess. For an observable anisotropy to originate from dark matter
annihilation, the high-energy electrons and positrons must be produced in a
nearby clump. I consider the annihilation pathway producing the smallest flux
of gamma rays versus electrons and positrons, and the combination of clump
distance and luminosity that minimizes the gamma-ray flux. I show that if an
anisotropy from such a clump were detected, and if such anisotropy did not
generate from anisotropic diffusion effects, then the clump would be clearly
detectable as an anomalous, bright gamma-ray source with the Fermi Large Area
Telescope. I also point out that the non-detection of an anisotropy is
perfectly compatible with an astrophysical origin for the excess positrons that
has nothing to do with dark matter.",1405.4884v2
2014-05-20,Resistive anisotropy due to spin-fluctuation scattering in the nematic phase of iron pnictides,"The large in-plane anisotropy of the resistivity is a hallmark of the nematic
state of the iron pnictides. Solving the Boltzmann transport equation, we show
that the prominent doping dependence as well as the large values of the
anisotropy can be well explained by momentum-dependent spin-fluctuation
scattering without assuming anisotropic impurity states. Due to the
forward-scattering corrections, the hot spots contribute to the resistive
anisotropy even in the case of strong spin fluctuations, which makes large
values of the anisotropy possible. The ellipticity of the electron pockets
plays an important role in explaining the dominance of positive values of the
anisotropy, i.e., larger resistivity in the direction with weaker spin
fluctuations, throughout the doping range.",1405.5084v3
2014-07-03,Magnetic fields and cosmic ray anisotropies at TeV energies,"Several cosmic-ray observatories have provided a high accuracy map of the sky
at TeV--PeV energies. The data reveals an O(0.1%) deficit from north galactic
directions that peaks at 10 TeV and then evolves with the energy, together with
other anisotropies at smaller angular scales. Using Boltzmann's equation we
derive expressions for the cosmic-ray flux that fit most of these features. The
anisotropies depend on the local interstellar magnetic field B_{IS}, on the
average galactic field B_{R} in our vicinity, and on the distribution of
dominant cosmic-ray sources. We show that the initial dipole anisotropy along
B_{IS} can be modulated by changes in the global cosmic ray wind, and that a
variation in the dipole direction would imply a given radius of coherence for
B_{IS}. We also show that small and medium-scale anisotropies may appear when
the full-sky anisotropy finds a turbulence acting as a magnetic lens.",1407.0850v3
2014-07-09,AC susceptibility of an assembly of nanomagnets: combined effects of surface anisotropy and dipolar interactions,"We compute the AC susceptibility of a weakly dipolar-interacting monodisperse
assembly of magnetic nanoclusters with oriented anisotropy. For this purpose we
first compute the relaxation rate in a longitudinal magnetic field of a single
nanomagnet taking account of both dipolar interactions in the case of dilute
assemblies and surface anisotropy. We then study the behavior of the real and
imaginary components of the AC susceptibility as functions of temperature,
frequency, surface anisotropy and inter-particle interactions. We find that the
surface anisotropy induces an upward shift of the temperature at the maximum of
the AC susceptibility components and that its effects may be tuned so as to
screen out the effects of interactions. The phenomenological Vogel-Fulcher law
for the effect of dipolar interaction on the relaxation rate is revisited
within our formalism and a semi-analytical expression is given for the
effective temperature is given in terms of inter alia the applied field,
surface anisotropy and dipolar interaction.",1407.2503v2
2014-12-18,Can galactic dark matter substructure contribute to the cosmic gamma-ray anisotropy?,"The annihilation of dark matter (DM) particles in the Milky Way can
contribute to the diffuse gamma-ray background (DGRB). Due to the presence of
substructures, this emission will appear anisotropic in a predictable way. We
generate full-sky maps of the gamma-ray emission in galactic substructures from
results of the high-resolution Via Lactea II N-body simulation of the Milky Way
DM halo. We calculate the anisotropy pattern, taking into account different
radial profiles of the DM distribution in substructures, cosmic variance, and
the detection threshold, and compare it to the anisotropy in the DGRB observed
by the Fermi Large Area Telescope (LAT). By comparing the upper limits on the
DM self-annihilation cross-section, <$\sigma v$>, implied by the anisotropy to
the intensity of the DGRB and detected sources in the LAT 2-yr Point Source
Catalog, we find that galactic substructure cannot contribute to the
anisotropies in the DGRB without strongly violating these observations. Our
results challenge the perception that small-scale anisotropies in the DGRB can
be used as a probe of DM annihilation in galactic subhaloes.",1412.5749v1
2015-01-26,Vortex Polarity Switching in Magnets with Surface Anisotropy,"Vortex core reversal in magnetic particle is essentially influenced by a
surface anisotropy. Under the action of a perpendicular static magnetic field
the vortex core undergoes a shape deformationof pillow- or barrel-shaped type,
depending on the type of the surface anisotropy. This deformation plays a key
point in the switching mechanism: We predict that the vortex polarity switching
is accompanied (i) by a linear singularity in case of Heisenberg magnet with
bulk anisotropy only and (ii) by a point singularities in case of surface
anisotropy or exchange anisotropy. We study in details the switching process
using spin-lattice simulations and propose a simple analytical description
using a wired core model, which provides an adequate description of the Bloch
point statics, its dynamics and the Bloch point mediated switching process. Our
analytical predictions are confirmed by spin-lattice simulations for Heisenberg
magnet and micromagnetic simulations for nanomagnet with account of a dipolar
interaction.",1501.06548v1
2015-02-04,Is inner core seismic anisotropy a marker of plastic flow of cubic iron?,"This paper investigates whether observations of seismic anisotropy are
compatible with a cubic structure of the inner core Fe alloy. We assume that
anisotropy is the result of plastic deformation within a large scale flow
induced by preferred growth at the inner core equator. Based on elastic moduli
from the literature, bcc- or fcc-Fe produce seismic anisotropy well below
seismic observations ($\textless{}0.4\%$). A Monte-Carlo approach allows us to
generalize this result to any form of elastic anisotropy in a cubic system.
Within our model, inner core global anisotropy is not compatible with a cubic
structure of Fe alloy. Hence, if the inner core material is indeed cubic, large
scale coherent anisotropic structures, incompatible with plastic deformation
induced by large scale flow, must be present.",1502.01270v1
2015-04-26,Gaussian Anisotropy In Strange Quark Stars,"In this paper for studying the anisotropic strange quark stars, we assume
that the radial pressure inside the anisotropic star is a superposition of
pressure in an isotropic case plus a Gaussian perturbation term. Considering a
proportionality between electric charge density and the density of matter, we
solve the TOV equation for different cases numerically. Our results indicate
that anisotropy increases the maximum mass $M_{max}$ and also its corresponding
radius $R$ for a typical strange quark star. According to our calculations, an
anisotropy amplitude of $A=3\times10^{33}Nm^{-2}$ with a standard deviation of
$\sigma=3\times10^{3}m$ leads to a neutron star of 1.97$M_{\odot}$.
Furthermore, electric charge not only increases the maximum mass and its
corresponding radius, but also raises up the anisotropy factor. We can see that
the tangential pressure $p_{t}$ and anisotropy factor $\Delta$ unlike the
radial pressure $p_{r}$ have a maximum on the surface and this maximum
increases by adding electric charge effect. However, we show that anisotropy
can be more effective than electric charge in rasing maximum mass of strange
quark stars.",1504.06805v1
2015-07-02,Magnetic anisotropy energy in disordered Ge_{1-x}Mn_{x}Te,"We theoretically analyze the influence of chemical disorder on magnetic
anisotropy in Ge_{1-x}Mn_{x}Te semiconductor layers known to exhibit
carrier-induced ferromagnetism and ferroelectric distortion of rhombohedral
crystal lattice. Using DFT method we determine the local changes in the crystal
structure due to Mn ions substitution for Ge and due to the presence in
Ge_{1-x}Mn_{x}Te of very high concentration of cation vacancies. We calculate
the effect of this structural and chemical disorder on single ion magnetic
anisotropy mechanism and show that its contribution is order of magnitude
smaller as compared to magnetic anisotropy mechanism originating from the spin
polarization induced by Mn ions into neighboring Te and Ge ions. We also
discuss magnetic anisotropy effects due to pairs of Mn ions differently
allocated in the lattice. The spatial averaging over chemical disorder strongly
reduces the strength of this magnetic anisotropy mechanism and restores the
global rhombohedral symmetry of magnetic system.",1507.00762v1
2015-09-01,Generalization of the van der Waals equation for anisotropic fluids in porous media,"The generalized van der Waals equation of state for anisotropic liquids in
porous media consists of two terms.One of them is based on the equation of
state for hard spherocylinders in random porous media obtained from the scaled
particle theory.The second term is expressed in terms of the mean value of
attractive intermolecular interactions.The obtained equation is used for the
investigation of the gas-liquid-nematic phase behavior of a molecular system
depending on the anisotropy of molecule shapes, anisotropy of attractive
intermolecular interactions, and porosity of a porous medium.It is shown that
the anisotropic phase is formed by the anisotropy of attractive intermolecular
interactions and by the anisotropy of molecular shapes.The anisotropy of
molecular shapes shifts the phase diagram to lower densities and higher
temperatures.The anisotropy of attractive interactions widens significantly the
coexistence region between the isotropic and anisotropic phases and shifts it
to the region of lower densities and higher temperatures.It is shown that, for
sufficiently long spherocylinders, the liquid-gas transition is localized
completely within the nematic region.For all the considered cases, the decrease
of the porosity shifts the phase diagram to the region of lower densities and
lower temperatures.",1509.00242v1
2015-09-22,Nonlocal Response and Anamorphosis: the Case of Few-Layer Black Phosphorus,"Few-layer black phosphorus was recently rediscovered as a narrow-bandgap
atomically thin semiconductor and has already attracted unprecedented attention
due to its interesting properties. One feature of this material that sets it
apart from other atomically thin crystals is its structural in-plane anisotropy
which manifests in strongly anisotropic transport characteristics. However,
traditional angle-resolved conductance measurements present a challenge for
nanoscale systems such as black phosphorus, calling for new approaches in
precision studies of transport anisotropy. Here we show that the nonlocal
response, being exponentially sensitive to the anisotropy value, provides a
powerful tool for determining the anisotropy. This is established by combining
measurements of the orientation-dependent nonlocal resistance response with the
analysis based on the anamorphosis relations. We demonstrate that the nonlocal
response can differ by orders of magnitude for different crystallographic
directions even when the anisotropy is at most order-one, allowing us to
extract accurate anisotropy values.",1509.06537v1
2015-11-15,Origin of the Resistivity Anisotropy in the Nematic Phase of FeSe,"The in-plane resistivity anisotropy is studied in strain-detwinned single
crystals of FeSe. In contrast to other iron-based superconductors, FeSe does
not develop long-range magnetic order below the nematic/structural transition
at $T_{s}\approx$90~K. This allows for the disentanglement of the contributions
to the resistivity anisotropy due to nematic and magnetic orders. Comparing
direct transport and elastoresistivity measurements, we extract the intrinsic
resistivity anisotropy of strain-free samples. The anisotropy peaks slightly
below $T_{s}$ and decreases to nearly zero on cooling down to the
superconducting transition. This behavior is consistent with a scenario in
which the in-plane resistivity anisotropy in FeSe is dominated by inelastic
scattering by anisotropic spin fluctuations.",1511.04757v1
2016-01-09,Bubble and Skyrmion Crystals in Frustrated Magnets with Easy-Axis Anisotropy,"We clarify the conditions for the emergence of multiple-${\bf Q}$ structures
out of lattice and easy-axis spin anisotropy in frustrated magnets. By
considering magnets whose exchange interaction has multiple global minima in
momentum space, we find that both types of anisotropy stabilize triple-${\bf
Q}$ orderings. Moderate anisotropy leads to a magnetic field-induced skyrmion
crystal, which evolves into a bubble crystal for increasing spatial or spin
anisotropy. The bubble crystal exhibits a quasi-continuous (devil's staircase)
temperature dependent ordering wave-vector, characteristic of the competition
between frustrated exchange and strong easy-axis anisotropy.",1601.02064v2
2016-01-11,Drag and Diffusion of Heavy Quarks in a hot and anisotropic QCD medium,"The propagation of heavy quarks (HQs) in a medium was quite often modeled by
the Fokker-Plank (FP) equation. Since the transport coefficients, related to
drag and diffusion processes are the main ingredients in the FP equation, the
evolution of HQs is thus effectively controlled by them. At the initial stage
of the relativistic heavy ion collisions, asymptotic weak-coupling causes the
free-streaming motions of partons in the beam direction and the expansion in
transverse directions are almost frozen, hence an anisotropy in the momentum
space sets in. Since HQs are too produced in the same time therefore the study
of the effect of momentum anisotropy on the drag and diffusion coefficients
becomes advertently desirable. In this article we have thus studied the drag
and diffusion of HQs in the anisotropic medium and found that the presence of
the anisotropy reduces both drag and diffusion coefficients. In addition, the
anisotropy introduces an angular dependence to both the drag and diffusion
coefficients, as a result both coefficients get inflated when the partons are
moving transverse to the direction of anisotropy than parallel to the direction
of anisotropy.",1601.02341v1
2016-03-01,Axisymmetric equilibria with pressure anisotropy and plasma flow,"A generalised Grad-Shafranov equation that governs the equilibrium of an
axisymmetric toroidal plasma with anisotropic pressure and incompressible flow
of arbitrary direction is derived. This equation includes six free surface
functions and recovers known Grad-Shafranov-like equations in the literature as
well as the usual static, isotropic one. The form of the generalised equation
indicates that pressure anisotropy and flow act additively on equilibrium. In
addition, two sets of analytical solutions, an extended Solovev one with a
plasma reaching the separatrix and an extended Hernegger-Maschke one for a
plasma surrounded by a fixed boundary possessing an X-point, are constructed,
particularly in relevance to the ITER and NSTX tokamaks. Furthermore, the
impacts both of pressure anisotropy and plasma flow on these equilibria are
examined. It turns out that depending on the maximum value and the shape of an
anisotropy function, the anisotropy can act either paramagnetically or
diamagnetically. Also, in most of the cases considered both the anisotropy and
the flow have stronger effects on NSTX equilibria than on ITER ones.",1603.00445v1
2016-03-31,"Influence of the different strains components on the uniaxial magnetic anisotropy constants for (Ga,Mn)As bulk system: a First-Principles Study","We present a computational study of the magnetic anisotropy energy for a
given concentration of the Mn ions in the GaAs host, in the framework of the
density functional theory. We focus on the influence of a different kind of
strains on the uniaxial magnetic anisotropy constants $K_1$ and $K_2$, which
reflect the magnetic anisotropy energy out- and in- (001) plane, respectively.
We have shown that the general trends for the applied biaxial strain on
anisotropy constants are consistent with the experimental data. We have
predicted the critical strains, for which the magnetization vector changes its
direction. Our results have shown that it is not possible to modify
considerably the uniaxial magnetic anisotropy constants, exposing (Ga,Mn)As to
hydrostatic pressure of a magnitude reasonable from experimental point of view.",1603.09546v3
2016-04-25,Higher order anisotropies in the Buda-Lund model: Disentangling flow and density field anisotropies,"The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and
fits the observed elliptic flow and oscillating HBT radii successfully. Due to
fluctuations in energy depositions, the fireball shape however fluctuates on an
event-by-event basis. The transverse plane asymmetry can be translated into a
series of multipole anisotropy coefficients. These anisotropies then result in
measurable momentum-space anisotropies, to be measured with respect to their
respective symmetry planes. In this paper we detail an extension of the
Buda-Lund model to multipole anisotropies and investigate the resulting flow
coefficients and oscillations of HBT radii.",1604.07470v2
2016-05-16,Polarization and dilepton anisotropy in pion-nucleon collisions,"Hadronic polarization and the related anisotropy of the dilepton angular
distribution are studied for the reaction $\pi N \rightarrow Ne^+ e^-$. We
employ consistent effective interactions for baryon resonances up to spin-5/2,
where non-physical degrees of freedom are eliminated, to compute the anisotropy
coefficients for isolated intermediate baryon resonances. It is shown that the
spin and parity of the intermediate baryon resonance is reflected in the
angular dependence of the anisotropy coefficient. We then compute the
anisotropy coefficient including the $N(1520)$ and $N(1440)$ resonances, which
are essential at the collision energy of the recent data obtained by the HADES
collaboration on this reaction. We conclude that the anisotropy coefficient
provides useful constraints for unravelling the resonance contributions to this
process.",1605.04954v2
2016-05-28,"Effects of $c/a$ Anisotropy and Local Crystal Structure on Superconductivity in $A\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($A$=Ba$_{1-y}$Sr$_y$, Sr$_{1-y}$Ca$_y$ and Eu)","We investigated the effects of $c/a$ anisotropy and local crystal structure
on superconductivity (SC) in As/P solid solution systems,
$A\mathrm{Fe_{2}}(\mathrm{As}_{1-x}\mathrm{P}_{x}\mathrm{)_{2}}$ ($A$122P) with
various $A$ ions. With decreasing $A$ site atomic size from $A$=Ba to Eu, the
structural anisotropy decreases, and the rate of decreasing with $x$ also
increases. The rapid narrowing of the region of antiferromagnetic composition
($x$) can be considered to be a result of this anisotropy change due mainly to
the change in the Fermi surface (FS) nesting condition. By contrast, although
the structural anisotropy systematically changes, the maximum $T_{\mathrm{c}}$
values are almost the same in all $A$122P systems except for Eu122P. These
results indicate that the modification of the FS topology via the structural
anisotropy does not affect SC. However local structural parameters, such as
pnictogen height, are crucial for $T_{\mathrm{c}}$.",1605.08914v1
2016-05-30,"An integrated approach to doped thin films with strain tunable magnetic anisotropy: Powder synthesis, target preparation and pulsed laser deposition of Bi:YIG","We present a synthesis/processing method for fabricating ferrimagnetic
insulator (Bi-doped yttrium iron garnet) thin films with tunable magnetic
anisotropy. Since the desired magnetic properties rely on controllable
thickness and successful doping, we pay attention to the entire
synthesis/processing procedure (nanopowder synthesis, nanocrystalline target
preparation and pulsed laser deposition (PLD)). Atomically flat films were
deposited by PLD on (111)-orientated yttrium aluminum garnet. We show a
significant enhancement of perpendicular anisotropy in the films, caused by
strain-induced anisotropy. In addition, the perpendicular anisotropy is tunable
by decreasing the film thickness and overwhelms the shape anisotropy at a
critical thickness of 3.5 nm.",1605.09084v2
2016-06-30,On anisotropy function in crystal growth simulations using Lattice Boltzmann equation,"In this paper, we present the ability of the Lattice Boltzmann (LB) equation,
usually applied to simulate fluid flows, to simulate various shapes of
crystals. Crystal growth is modeled with a phase-field model for a pure
substance, numerically solved with a LB method in 2D and 3D. This study focuses
on the anisotropy function that is responsible for the anisotropic surface
tension between the solid phase and the liquid phase. The anisotropy function
involves the unit normal vectors of the interface, defined by gradients of
phase-field. Those gradients have to be consistent with the underlying lattice
of the LB method in order to avoid unwanted effects of numerical anisotropy.
Isotropy of the solution is obtained when the directional derivatives method,
specific for each lattice, is applied for computing the gradient terms. With
the central finite differences method, the phase-field does not match with its
rotation and the solution is not any more isotropic. Next, the method is
applied to simulate simultaneous growth of several crystals, each of them being
defined by its own anisotropy function. Finally, various shapes of 3D crystals
are simulated with standard and non standard anisotropy functions which favor
growth in <100>-, <110>- and <111>-directions.",1606.09432v1
2016-10-26,Effects of the Lorentz invariance violation in Coulomb interaction in nuclei and atoms,"Anisotropy in the speed of light that has been constrained by
Michelson-Morley-type experiments also generates anisotropy in the Coulomb
interactions. This anisotropy can manifest itself as an energy anisotropy in
nuclear and atomic experiments. Here the experimental limits on Lorentz
violation in 21Ne are used to improve the limits on the Lorentz symmetry in the
photon sector, namely the anisotropy of the speed of light and the Coulomb
interactions, by 7 orders of magnitude in comparison with previous experiments:
the speed of light is isotropic to a part in E-28.",1610.08188v3
2016-11-30,Temperature-dependent magnetic anisotropy from directional-dependent interactions,"Magnetic anisotropy of spin models with directional-dependent interactions in
the high-temperature paramagnetic phase is theoretically studied. Using a high
temperature expansion, we show that the Ising type directional-dependent
interaction gives rise to magnetic anisotropy which depends on the temperature
as $\propto T^{-5}$. This phenomenon arises from the anisotropic exchange
interaction, and is distinct from the orbital effect, such as van Vleck
susceptibility. It is shown that while the quadratic term in the magnetization
favors to point the spins along the bond, the fourth order term in
magnetization prefers to point spins to the perpendicular direction. The theory
is applied to the Heisenberg-Kitaev model on the honeycomb lattice and a cubic
lattice model that is potentially relevant to perovskite iridates. We show
that, in these models, the anisotropic terms in quadratic order cancels out,
and the leading order for the magnetic anisotropy arises from the fourth order
contribution. The result shows that the anisotropy from the
directional-dependent interaction gives rise to $\langle100\rangle$ magnetic
anisotropy. These results are potentially relevant to heavy transition metal
oxides such as iridates. Experimental observation of the magnitude of
anisotropic interactions using magnetic torque measurement is also discussed.",1612.00057v1
2017-02-13,Effective field theory of statistical anisotropies for primordial bispectrum and gravitational waves,"We present the effective field theory studies of primordial statistical
anisotropies in models of anisotropic inflation. The general action in unitary
gauge is presented to calculate the leading interactions between the gauge
field fluctuations, the curvature perturbations and the tensor perturbations.
The anisotropies in scalar power spectrum and bispectrum are calculated and the
dependence of these anisotropies to EFT couplings are presented. In addition,
we calculate the statistical anisotropy in tensor power spectrum and the
scalar-tensor cross correlation. Our EFT approach incorporates anisotropies
generated in models with non-trivial speed for the gauge field fluctuations and
sound speed for scalar perturbations such as in DBI inflation.",1702.03744v1
2017-03-02,Specific Heat and Effects of Uniaxial Anisotropy of a $p$-wave Pairing Interaction in a Strongly Interacting Ultracold Fermi Gas,"We investigate the specific heat $C_V$ at constant volume and effects of
uniaxial anisotropy of a $p$-wave attractive interaction in the normal state of
an ultracold Fermi gas. Within the framework of the strong-coupling theory
developed by Nozi\`eres and Schmitt-Rink, we evaluate this thermodynamic
quantity as a function of temperature, in the whole interaction regime. While
the uniaxial anisotropy is not crucial for $C_V$ in the weak-coupling regime,
$C_V$ is found to be sensitive to the uniaxial anisotropy in the
strong-coupling regime. This originates from the population imbalance among
$p_i$-wave molecules ($i=x,y,z$), indicating that the specific heat is a useful
observable to see which kinds of $p$-wave molecules dominantly exist in the
strong-coupling regime when the $p$-wave interaction has uniaxial anisotropy.
Using this strong point, we classify the strong-coupling regime into some
characteristic regions. Since a $p$-wave pairing interaction with uniaxial
anisotropy has been discovered in a $^{40}$K Fermi gas, our results would be
useful in considering strong-coupling properties of a $p$-wave interacting
Fermi gas, when the interaction is uniaxially anisotropic.",1703.00585v1
2017-04-12,On the origin of magnetic anisotropy in two dimensional CrI$_3$,"The observation of ferromagnetic order in a monolayer of CrI$_3$ has been
recently reported, with a Curie temperature of 45 Kelvin and off-plane easy
axis. Here we study the origin of magnetic anisotropy, a necessary ingredient
to have magnetic order in two dimensions, combining two levels of modeling,
density functional calculations and spin model Hamiltonians. We find two
different contributions to the magnetic anisotropy of the material, both
favoring off-plane magnetization and contributing to open a gap in the spin
wave spectrum. First, ferromagnetic super-exchange across the $\simeq $ 90
degree Cr-I-Cr bonds, are anisotropic, due to the spin orbit interaction of the
ligand I atoms. Second, a much smaller contribution that comes from the single
ion anisotropy of the $S=3/2$ Cr atom. Our results permit to establish the XXZ
Hamiltonian, with a very small single ion anisotropy, as the adequate spin
model for this system. Using spin wave theory we estimate the Curie temperature
and we highlight the essential role played by the gap that magnetic anisotropy
induces on the magnon spectrum.",1704.03849v4
2017-05-26,Tuning of Fermi Contour Anisotropy in GaAs (001) 2D Holes via Strain,"We demonstrate tuning of the Fermi contour anisotropy of two-dimensional (2D)
holes in a symmetric GaAs (001) quantum well via the application of in-plane
strain. The ballistic transport of high-mobility hole carriers allows us to
measure the Fermi wavevector of 2D holes via commensurability oscillations as a
function of strain. Our results show that a small amount of in-plane strain, on
the order of $10^{-4}$, can induce significant Fermi wavevector anisotropy as
large as 3.3, equivalent to a mass anisotropy of 11 in a parabolic band. Our
method to tune the anisotropy \textit{in situ} provides a platform to study the
role of anisotropy on phenomena such as the fractional quantum Hall effect and
composite fermions in interacting 2D systems.",1705.09430v1
2017-06-26,Perpendicular magnetic anisotropy in insulating ferrimagnetic gadolinium iron garnet thin films,"We present experimental control of the magnetic anisotropy in a gadolinium
iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by
simply changing the sample temperature. The magnetic hysteresis loops obtained
by SQUID magnetometry measurements unambiguously reveal a change of the
magnetically easy axis from out-of-plane to in-plane depending on the sample
temperature. Additionally, we confirm these findings by the use of temperature
dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to
determine the effective magnetization, we utilize the intrinsic advantage of
FMR spectroscopy which allows to determine the magnetic anisotropy independent
of the paramagnetic substrate, while magnetometry determines the combined
magnetic moment from film and substrate. This enables us to quantitatively
evaluate the anisotropy and the smooth transition from in-plane to
perpendicular magnetic anisotropy. Furthermore, we derive the temperature
dependent $g$-factor and the Gilbert damping of the GdIG thin film.",1706.08488v1
2017-08-23,Structural Transitions in Vortex Systems with Anisotropic Interactions,"We introduce a model of vortices in type-II superconductors with a four-fold
anisotropy in the vortex-vortex interaction potential. Using numerical
simulations we show that the vortex lattice undergoes structural transitions as
the anisotropy is increased, with a triangular lattice at low anisotropy, a
rhombic intermediate state, and a square lattice for high anisotropy. In some
cases we observe a multi-$q$ state consisting of an Archimedean tiling that
combines square and triangular local ordering. At very high anisotropy, domains
of vortex chain states appear. We discuss how this model can be generalized to
higher order anisotropy as well as its applicability to other particle-based
systems with anisotropic particle-particle interactions.",1708.07116v1
2017-09-06,Record High Magnetic Anisotropy in Chemically Engineered Iridium Dimer,"Exploring giant magnetic anisotropy in small magnetic nanostructures is of
both fundamental interest and technological merit for information storage. To
prevent spin flipping at room temperature due to thermal fluctuation, large
magnetic anisotropy energy (MAE) over 50 meV in magnetic nanostructure is
desired for practical applications. We chose one of the smallest magnetic
nanostructures-Ir2 dimer, to investigate its magnetic properties and explore
possible approach to engineer the magnetic anisotropy. Through systematic
first-principles calculations, we found that the Ir2 dimer already possesses
giant MAE of 77 meV. We proposed an effective way to enhance the MAE of the Ir2
dimer to 223~294 meV by simply attaching a halogen atom at one end of the Ir-Ir
bond. The underlying mechanism for the record high MAE is attributed to the
modification of the energy diagram of the Ir2 dimer by the additional
halogen-Ir bonding, which alters the spin-orbit coupling Hamiltonian and hence
the magnetic anisotropy. Our strategy can be generalized to design other
magnetic molecules or clusters with giant magnetic anisotropy.",1709.01878v1
2017-11-30,On the Relationship Between Scintillation Anisotropy and Crystal Structure in Pure Crystalline Organic Scintillator Materials,"The scintillation anisotropy effect for proton recoil events has been
investigated in five pure organic crystalline materials: anthracene,
trans-stilbene, p-terphenyl, bibenzyl, and diphenylacetylene. These
measurements include characterization of the scintillation response for one
hemisphere of proton recoil directions in each crystal. In addition to standard
measurements of the total light output and pulse shape at each angle, the
prompt and delayed light anisotropies are analyzed, allowing for investigation
of the singlet and triplet molecular excitation behaviors independently. This
work provides new quantitative and qualitative observations that make progress
toward understanding the physical mechanisms behind the scintillation
anisotropy. These measurements show that the relationship between the prompt
and delayed light anisotropies is correlated with crystal structure, as it
changes between the pi-stacked crystal structure materials (anthracene and
p-terphenyl) and the herringbone crystal structure materials (stilbene,
bibenzyl, and diphenylacetylene). The observations are consistent with a model
in which there are preferred directions of kinetic processes for the molecular
excitations. These processes and the impact of their directional dependencies
on the scintillation anisotropy are discussed.",1711.11188v2
2018-03-12,Chiral skyrmions in an anisotropy gradient driven by spin-Hall effect,"A strategy to drive skyrmion motion by a combination of an anisotropy
gradient and spin Hall effect has recently been demonstrated. Here, we study
the fundamental properties of this type of motion by combining micromagnetic
simulations and a generalized Thiele equation. We find that the anisotropy
gradient drives the skyrmion mainly along the direction perpendicular to the
gradient, due to the conservative part of the torque. There is some slower
motion along the direction parallel to the anisotropy gradient due to damping
torque. When an appropriate spin Hall torque is added, the skyrmion velocity in
the direction of the anisotropy gradient can be enhanced. This motion gives
rise to acceleration of the skyrmion as this moves to regions of varying
anisotropy. This phenomenon should be taken into account in experiments for the
correct evaluation of the skyrmion velocity. We employ a Thiele like formalism
and derive expressions for the velocity and the acceleration of the skyrmion
that match very well with micromagnetic simulation results.",1803.04160v1
2018-03-14,Electronically Mediated Magnetic Anisotropy in Vibrating Magnetic Molecules,"We address the electronically induced anisotropy field acting on a spin
moment comprised in a vibrating magnetic molecule located in the junction
between ferromagnetic metals. Under weak coupling between the electrons and
molecular vibrations, the nature of the anisotropy can be changed from favoring
a high spin (easy axis) magnetic moment to a low spin (easy plane) by applying
a temperature difference or a voltage bias across the junction. For unequal
spin-polarizations in the ferromagnetic metals it is shown that the character
of the anisotropy is essentially determined by the properties of the weaker
ferromagnet. By increasing the temperature in this metal, or introducing a
voltage bias, its influence can be suppressed such that the dominant
contribution to the anisotropy is interchanged to the stronger ferromagnet.
With increasing coupling strength between the molecular vibrations and the
electrons, the nature of the anisotropy is locked into favoring easy plane
magnetism.",1803.05480v1
2018-03-28,Effective anisotropy due to the surface of magnetic nanoparticles,"Analytical solution has been found for the second-order effective anisotropy
of magnetic nanoparticles of a cubic shape due to the surface anisotropy (SA)
of the N\'eel type. Similarly to the spherical particles, for the simple cubic
lattice the grand-diagonal directions $\left(\pm1,\pm1,\pm1\right)$ are favored
by the effective cubic anisotropy but the effect is twice as strong. Uniaxial
core anisotropy and applied magnetic field cause screening of perturbations
from the surface at the distance of the domain-wall width and reduce the effect
of SA near the energy minima. However, screening disappears near the uniaxial
energy barrier, and the uniform barrier state of larger particles may become
unstable. For these effects the analytical solution is obtained as well, and
the limits of the additive formula with the uniaxial and effective cubic
anisotropies for the particle are established. Thermally-activated
magnetization-switching rates have been computed by the pulse-noise technique
for the stochastic Landau-Lifshitz equation for a system of spins.",1803.10406v1
2018-05-21,Searching for All-Scale Anisotropies in the Arrival Directions of Cosmic Rays above the Ankle,"The Pierre Auger Observatory has recently reported the detection of a dipole
anisotropy in the arrival directions of cosmic rays above 8 EeV with a
post-trial significance of more than 5.2$\sigma$. This observation has profound
consequences for the distribution and composition of candidate sources of
cosmic rays above the ankle (3-5 EeV). In this paper we search for the presence
of anisotropies on all angular scales in public Auger data. The analysis
follows a likelihood-based reconstruction method that automatically accounts
for variations in the observatory's angular acceptance and background rate. Our
best-fit dipole anisotropy in the equatorial plane has an amplitude of 5.3
$\pm$ 1.3 percent and right ascension angle of 103 $\pm$ 15 degrees, consistent
with the results of the Pierre Auger Collaboration. We do not find evidence for
the presence of medium- or small-scale anisotropies. The method outlined in
this paper is well-suited for the future analyses of cosmic ray anisotropies
below the ankle, where cosmic ray detection in surface arrays is not fully
efficient and dominated by systematic uncertainties.",1805.08220v2
2018-07-13,Beaming electromagnetic (or heat-flux) instabilities from the interplay with the electron temperature anisotropies,"In space plasmas kinetic instabilities are driven by the beaming (drifting)
components and/or the temperature anisotropy of charged particles. The
heat-flux instabilities are known in the literature as electromagnetic modes
destabilized by the electron beams (or strahls) aligned to the interplanetary
magnetic field. A new kinetic approach is proposed here in order to provide a
realistic characterization of heat-flux instabilities under the influence of
electrons with temperature anisotropy. Numerical analysis is based on the
kinetic Vlasov-Maxwell theory for two electron counter-streaming (core and
beam) populations with temperature anisotropies, and stationary, isotropic
protons. The main properties of electromagnetic heat-flux instabilities are
found to be markedly changed by the temperature anisotropy of electron beam
$A_b = T_\perp / T_\parallel \ne 1$, leading to stimulation of either the
whistler branch if $A_b > 1$, or the firehose branch for $A_b<1$. For a high
temperature anisotropy whistlers switch from heat-flux to a standard regime,
when their instability is inhibited by the beam.",1807.05178v1
2018-08-27,Dynamics of the antiferromagnetic skyrmion induced by a magnetic anisotropy gradient,"The dynamics of antiferromagnets is a current hot topic in condensed matter
physics and spintronics. However, the dynamics of insulating antiferromagnets
cannot be excited by an electric current, which is a method usually used to
manipulate ferromagnetic metals. Here, we propose to use the voltage-controlled
magnetic anisotropy gradient as an excitation source to manipulate insulating
antiferromagnetic textures. We analytically and numerically study the dynamics
of an antiferromagnetic skyrmion driven by a magnetic anisotropy gradient. Our
analytical calculations demonstrate that such a magnetic anisotropy gradient
can effectively drive an antiferromagnetic skyrmion towards the area of lower
magnetic anisotropy. The micromagnetic simulations are in good agreement with
our analytical solution. Furthermore, the magnetic anisotropy gradient induced
velocity of an antiferromagnetic skyrmion is compared with that of a
ferromagnetic skyrmion. Our results are useful for the understanding of
antiferromagnetic skyrmion dynamics and may open a new way for the design of
antiferromagnetic spintronic devices.",1808.08664v2
2018-10-17,Testing isotropy in the Universe using photometric and spectroscopic data from the SDSS,"We analyze two volume limited galaxy samples from the SDSS photometric and
spectroscopic data to test the isotropy in the local Universe. We use
information entropy to quantify the global anisotropy in the galaxy
distribution at different length scales and find that the galaxy distribution
is highly anisotropic on small scales. The observed anisotropy diminishes with
increasing length scales and nearly plateaus out beyond a length scale of 200
Mpc/h in both the datasets. We compare these anisotropies with those predicted
by the mock catalogues from the N-body simulations of the Lambda CDM model and
find a fairly good agreement with the observations. We find a small residual
anisotropy on large scales which decays in a way that is consistent with the
linear perturbation theory. The slopes of the observed anisotropy converge to
the slopes predicted by the linear theory beyond a length scale of ~ 200 Mpc/h
indicating a transition to isotropy. We separately compare the anisotropies
observed across the different parts of the sky and find no evidence for a
preferred direction in the galaxy distribution.",1810.07410v2
2019-01-02,Understanding the galactic cosmic ray dipole anisotropy with a nearby single source under the spatially-dependent propagation scenario,"Recently studies of the dipole anisotropy in the arrival directions of
Galactic cosmic rays indicate that the TeV-PeV dipole anisotropy amplitude is
not described by a simple power law, moreover a rapid phase change exists at an
energy of $0.1\sim0.3$ PeV. In this work we argue that the dipole anisotropy
amplitude and phase evolution with energies can be reproduced under the
spatially-dependent propagation scenario with a nearby single source added. Our
results indicate a nearby single source have significant influence to the
cosmic ray gradient below $0.1\sim0.3$ PeV under the spatially-dependent
propagation scenario, which leads the dipole anisotropy phase change at this
energy region. The dipole anisotropy amplitude of the galactic cosmic rays can
also be maintained at a lower level, which are consistent with observations by
underground muons and air shower experiments.",1901.00249v1
2019-02-08,Including off-diagonal anisotropies in anisotropic hydrodynamics,"In this paper we present a method for efficiently including the effects of
off-diagonal local rest frame momentum anisotropies in leading-order
anisotropic hydrodynamics. The method relies on diagonalization of the
space-like block of the anisotropy tensor and allows one to reduce the
necessary moments of the distribution function in the off-diagonal case to a
linear combination of diagonal-anisotropy integrals. Once reduced to
diagonal-anisotropy integrals, the results can be computed efficiently using
techniques described previously in the literature. We present a general
framework for how to accomplish this and provide examples for off-diagonal
anisotropy moments entering into the energy-momentum tensor and viscous update
equations which emerge when performing anisotropic pressure matching.",1902.03303v3
2019-12-30,Magnetic resonance assessment of effective confinement anisotropy with orientationally-averaged single and double diffusion encoding,"Porous or biological materials comprise a multitude of micro-domains
containing water. Diffusion-weighted magnetic resonance measurements are
sensitive to the anisotropy of the thermal motion of such water. This
anisotropy can be due to the domain shape, as well as the (lack of) dispersion
in their orientations. Averaging over measurements that span all orientations
is a trick to suppress the latter, thereby untangling it from the influence of
the domains' anisotropy on the signal. Here, we consider domains whose
anisotropy is modeled as being the result of a Hookean (spring) force, which
has the advantage of having a Gaussian diffusion propagator while still
retaining the fact of finite spatial range for the diffusing particles.
Analytical expressions for the powder-averaged signal under this assumption are
given for so-called single and double diffusion encoding schemes, which
sensitize the MR signal to the diffusive displacement of particles in,
respectively, one or two consecutive time intervals.",1912.12760v1
2020-03-06,Anisotropy in Antiferromagnets,"Due to the advent of antiferromagnetic (AF) spintronics there is a burgeoning
interest in AF materials for a wide range of potential and actual applications.
Generally, AFs are characterized via the ordering at the Neel temperature (TN)
but, to have a stable AF configuration, it is necessary that the material have
a sufficient level of anisotropy so as to maintain the orientation of the given
magnetic state fixed in one direction. Unlike the case for ferromagnets there
is little established data on the anisotropy of AFs and in particular its
origins and those factors which control it. In this paper these factors are
reviewed in the light of recent and established experimental data.
Additionally, there is no recognized technique for the first principle
determination of the anisotropy of an AF which can only be found indirectly via
the exchange bias phenomenon. This technique is reviewed and in particular the
implications for the nature of the anisotropy that is measured and its
distribution. Finally, a strategy is proposed that would allow for the
development of AF materials with controlled anisotropy for future applications.",2003.03324v1
2020-03-09,Interplay between chemical order and magnetic properties in L1$_0$ FeNi (tetrataenite): A First-Principles Study,"We use first-principles-based calculations to investigate the interplay
between chemical order and the magnetic properties of $L1_0$ FeNi. In
particular, we investigate how deviations from perfect chemical order affect
the energy difference between the paramagnetic and ferromagnetic states as well
as the important magneto-crystalline anisotropy energy. Our calculations
demonstrate a strong effect of the magnetic order on the chemical
order-disorder transition temperature, and conversely, a strong enhancement of
the magnetic transition temperature by the chemical order. Most interestingly,
our results indicate that the magnetic anisotropy does not decrease
significantly as long as the deviations from perfect order are not too large.
Moreover, we find that in certain cases a slight disorder can result in a
higher anisotropy than for the fully ordered structure. We further analyze the
correlation between the magneto-crystalline anisotropy and the orbital magnetic
moment anisotropy, which allows to study the effect of the local chemical
environment on both quantities, potentially enabling further optimization of
the magneto-crystalline anisotropy with respect to chemical order and
stoichiometric composition.",2003.04181v2
2020-06-20,Two-fold symmetry of in-plane magnetoresistance anisotropy in the superconducting states of BiCh2-based LaO0.9F0.1BiSSe single crystal,"Recently, two-fold symmetric in-plane anisotropy of the superconducting
properties have been observed in a single crystal of BiCh2-based (Ch: S, Se)
layered superconductor LaO0.5F0.5BiSSe having a tetragonal
(four-fold-symmetric) in-plane structure; the phenomena are very similar to
those observed in nematic superconductors. To explore the origin of the
two-fold symmetric anisotropy in the BiCh2-based system, we have investigated
the electron-doping dependence on the anisotropy by examining the in-plane
anisotropy of the magnetoresistance in the superconducting states for a single
crystal of LaO0.9F0.1BiSSe under high magnetic fields up to 15 T. We observed a
two-fold symmetry of in-plane anisotropy of magnetoresistance for
LaO0.9F0.1BiSSe. The results obtained for LaO0.9F0.1BiSSe are quite similar to
those observed for LaO0.5F0.5BiSSe, which has a higher electron doping
concentration than LaO0.9F0.1BiSSe. Our present finding suggests that the
emergence of the in-plane symmetry breaking in the superconducting state is
robust to the carrier concentration in the series of LaO1-xFxBiSSe.",2006.11576v1
2020-08-12,Velocity Centroids Anisotropy and the Signature of different MHD Modes in the Turbulent ISM,"Magnetic turbulence is anisotropic as the directions of motion are
constrained by the magnetic field. Such anisotropy can be observed in velocity
centroids obtained from spectroscopic observations. We use magnetohydrodynamics
(MHD) simulations to produce synthetic spectroscopic observations
(position-position-velocity data) and study the anisotropy in the structure
function of velocity centroid maps. We decomposed the velocity in the
simulations into Alfv\'en, slow and fast-modes and studied how each of them
contribute to the observed anisotropy. We found that when the angle between the
line of sight and the mean magnetic field is large the Alfv\'en-mode dominates
the observed anisotropy, while for smaller angles the anisotropy is not large
enough to be used to probe the magnetization of the media, and it is dominated
by the slow-mode. Our results are in fair agreement with the theoretical
predictions in Kandel et al.(2016,2017).",2008.05393v1
2021-03-07,Bright correlated twin-beam generation and radiation shaping in high-gain parametric down-conversion with anisotropy,"Uniaxial anisotropy in nonlinear birefringent crystals limits the efficiency
of nonlinear optical interactions and breaks the spatial symmetry of light
generated in the parametric down-conversion (PDC) process. Therefore, this
effect is usually undesirable and must be compensated for. However, high gain
may be used to overcome the destructive role of anisotropy and instead to use
it for the generation of bright two-mode correlated twin-beams. In this work,
we provide a rigorous theoretical description of the spatial properties of
bright squeezed light in the presence of strong anisotropy. We investigate a
single-crystal and a two-crystal configuration and demonstrate the generation
of bright correlated twin-beams in such systems at high gain due to anisotropy.
We explore the mode structure of the generated light and show how anisotropy,
together with crystal spacing, can be used for radiation shaping.",2103.04305v1
2021-05-21,Stability of skyrmion crystal phase in antiferromagnetic triangular lattice with DMI and single-ion anisotropy,"We study a frustrated antiferromagnetic Heisenberg model on a triangular
lattice with the Dzyaloshinskii-Moriya interaction (DMI) in the presence of an
external magnetic field and a single-ion anisotropy. Phase diagrams in the
temperature-field plane for both easy-axis and easy-plane anisotropy of a
varying strength are constructed in the regimes of a moderate and strong DMI by
parallel tempering Monte Carlo simulations. For the considered range of
parameters the phase diagrams featuring up to four ordered phases are
identified. A skyrmion lattice (SkX) phase is found to be stabilized within
some temperature and field window for sufficiently large DMI and not too strong
anisotropy. For the systems with moderate (larger) DMI, a small easy-plane
(easy-axis) anisotropy is concluded to be beneficial by extending (shifting)
the field window of the SkX appearance to lower values. The Metropolis dynamics
is employed to probe the persistence of SkX upon quenching the field to zero or
small finite values. The most favorable conditions for the skyrmions
persistence are confirmed at low temperatures, small DMI and small easy-plane
anisotropy values.",2105.10206v1
2021-06-23,"Magnetic anisotropy in uranium monosulfide, probed by the magnetic torque measurements","We have studied the magnetic torque in uranium monosulfide (US) single
crystals to explore the magnetic anisotropy in this material. Uranium
monosulfide crystallizes in cubic, NaCl-type of crystal structure and exhibits
the largest magneto-crystalline anisotropy observed in cubic systems. By
performing detailed torque measurements we observe a strongly anisotropic
behavior in the paramagnetic phase due to crystal defects and quadrupolar pair
interactions. Our studies also confirm the presence of a large anisotropy in
the ferromagnetic state of the US system with the <100>, <111>, and <110>
directions being hard, easy, and intermediate axis, respectively. Furthermore,
the anisotropy in the paramagnetic phase shows similar characteristics to the
anisotropy observed in the ferromagnetic phase, as characterized by second and
fourth rank susceptibility terms. The similarity of the anisotropic behaviors
in paramagnetic and ferromagnetic phases is the consequence of strong
magneto-elastic properties in this system, which possibly lead to the
rhombohedral structural distortion, not only in the ferromagnetic phase but
also in the paramagnetic phase (induced by applied magnetic fiield).",2106.12464v1
2021-08-11,Enhancement of in-plane anisotropy in MoS2/CoFeB bilayers,"Transition metal dichalcogenides (TMD) possess novel properties which makes
them potential candidates for various spintronic applications. Heterostructures
of TMD with magnetic thin film have been extensively considered for
spin-orbital torque, enhancement of perpendicular magnetic anisotropy etc.
However, the effect of TMD on magnetic anisotropy in heterostructures of
in-plane magnetization has not been studied so far. Further the effect of the
TMD on the domain structure and magnetization reversal of the ferromagnetic
system is another important aspect to be understood. In this context we study
the effect of MoS2, a well-studied TMD material, on magnetic properties of
CoFeB in MoS2/CoFeB heterostructures. The reference CoFeB film possess a weak
in-plane anisotropy. However, when the CoFeB is deposited on MoS2 the in-plane
anisotropy is enhanced as observed from magneto optic Kerr effect (MOKE)
microscopy as well as ferromagnetic resonance (FMR). Magnetic domain structure
and magnetization reversal have also been significantly modified for the
MoS2/CoFeB bilayer as compared to the reference CoFeB layer. Frequency and
angle dependent FMR measurement show that the magnetic anisotropy of CoFeB
increases with increase in thickness of MoS2 in the MoS2/CoFeB
heterostructures.",2108.05130v1
2021-09-07,Testing the Early Universe with Anisotropies of the Gravitational Wave Background,"In this work we analyse in detail the possibility of using small and
intermediate-scale gravitational wave anisotropies to constrain the
inflationary particle content. First, we develop a phenomenological approach
focusing on anisotropies generated by primordial tensor-tensor-scalar and
purely gravitational non-Gaussianities. We highlight the quantities that play a
key role in determining the detectability of the signal. To amplify the power
of anisotropies as a probe of early universe physics, we consider
cross-correlations with CMB temperature anisotropies. We assess the size of the
signal from inflationary interactions against so-called induced anisotropies.
In order to arrive at realistic estimates, we obtain the projected constraints
on the non-linear primordial parameter $F_{\rm NL}$ for several upcoming
gravitational wave probes in the presence of the astrophysical gravitational
wave background. We further illustrate our findings by considering a concrete
inflationary realisation and use it to underscore a few subtleties in the
phenomenological analysis.",2109.03077v1
2021-09-25,Phase transitions in rare-earth ferrimagnets with surface anisotropy near the magnetization compensation point,"We report of a theoretical model for calculating the H-T phase diagrams of a
rare-earth ferrimagnet, taking into account anisotropies originated by both
magnetization sublattices' and by the surface. The possibility of an exchange
spring formation due to surface anisotropy is considered. This situation is
realized in heterostructures containing a ferrimagnet and a heavy metal. We
derive the stability lose lines of the collinear phase from the free energy of
the two sublattice ferrimagnet. We numerical calculate the magnetic phase
diagrams for the cases when the magnetic field applied along and perpendecular
to the easy axis. We demonstrate that tricritical point down at the low field
range due to surface anisotropy effect. Moreover, the line of the first order
phase transition between angular and collinear phases reduces due to surface
anisotropy. In the case when magnetic field is applied perpendicular to the
easy axis we show the possibility of the first order phase transition between
two collinear phases in contrast to the phase diagram without surface
anisotropy.",2109.12377v2
2021-10-26,The magnetic anisotropy of individually addressed spin states,"Controlling magnetic anisotropy is a key requirement for the fundamental
understanding of molecular magnetism and is a prerequisite for numerous
applications in magnetic storage, spintronics, and all-spin logic devices. In
order to address the question of molecular magnetic anisotropy experimentally,
we have synthesized single-crystals of a molecular spin system containing four
antiferromagnetically coupled s = 5/2 manganese(II) ions. Using low-temperature
cantilever magnetometry, we demonstrate the selective population of the S = 0,
1, . . . , 10 spin states upon application of magnetic fields up to 33 T and
map the magnetic anisotropy of each of these states. We observe a strong
dependence of the shape and size of the magnetic anisotropy on the populated
spin states, and, in particular, reveal an anisotropy reversal upon going from
the lowest to the highest spin-state.",2110.13685v1
2022-06-01,Scattering anisotropy in HgTe (013) quantum well,"We report on a detailed experimental study of the electron transport
anisotropy in HgTe (013) quantum well of 22 nm width in the directions $[100]$
and $[03\bar{1}]$ as the function of the electron density $n$. The anisotropy
is absent at minimal electron density near the charge neutrality point. The
anisotropy increases with the increase of n and reaches about 10% when the
Fermi level is within the first subband H1. There is a sharp increase of the
anisotropy (up to 60%) when the Fermi level reaches the second subband E2. We
conclude that the first effect is due to the small intra-subband anisotropic
interface roughness scattering, and the second one is due to the strongly
anisotropic inter-subband roughness scattering, but the microscopical reason of
such a strong change in the anisotropy remains unknown.",2206.00306v2
2022-07-20,Modelling bubble collapse anisotropy in complex geometries,"A gas or vapor bubble collapsing in the vicinity of a rigid boundary
displaces towards the boundary and produces a high-speed jet directed at the
boundary. This behavior has been shown to be a function of the 'anisotropy' of
the collapse, measured by a dimensionless representation of the Kelvin impulse
known as the anisotropy parameter [Supponen et al., J. Fluid Mech. 802, 263-293
(2016)]. However, characterisation of the anisotropy parameter in different
geometries has been limited to simplified analytic solutions. In this work we
develop an inexpensive numerical model, based on the Boundary Element Method,
capable of predicting the anisotropy parameter for any rigid complex geometry.
We experimentally explore a robust measure of bubble displacement, showing that
the bubble displacement in a range of complex geometries behaves as a single
function of the predicted anisotropy parameter values.",2207.09970v2
2023-01-06,Interfacial magnetic anisotropy controlled spin pumping in Co60Fe20B20/Pt stack,"Controlled spin transport in magnetic stacks is required to realize pure spin
current-driven logic and memory devices. The control over the generation and
detection of the pure spin current is achieved by tuning the spin to charge
conversion efficiency of the heavy metal interfacing with ferromagnets. Here,
we demonstrate the direct tunability of spin angular momentum transfer and
thereby spin pumping, in CoFeB/Pt stack, with interfacial magnetic anisotropy.
The ultra-low thickness of CoFeB thin film tilts the magnetic easy axis from
in-plane to out-of-plane due to surface anisotropy. The Ferromagnetic resonance
measurements are performed to investigate the magnetic anisotropy and spin
pumping in CoFeB/Pt stacks. We clearly observe tunable spin pumping effect in
the CoFeB/Pt stacks with varying CoFeB thicknesses. The spin current density,
with varying ferromagnetic layer thickness, is found to increase from 0.11 to
0.24 MA/m2, with increasing in-plane anisotropy field. Such interfacial
anisotropy-controlled generation of pure spin current can potentially lead to
next-generation anisotropic spin current-controlled spintronic devices.",2301.02370v1
2023-05-25,Origin of magnetic anisotropy in $La_{(1\-x)}Sr_{x}MnO_{3}$,"Here, we report the origin of magnetic anisotropy in Sr-doped infinite layer
manganites $La_{(1\-x)}Sr_{x}MnO_{3}$ (0.125 \leq x \leq 0.400). Magnetic
anisotropy is responsible for the large difference in the temperature
dependence of field-cooled and zero-field-cooled magnetization. Translational
symmetry breaking in the context of spins around the boundary between the
ferromagnetic (FM) antiferromagnetic (AFM) region leads to FM-AFM interaction
and results in magnetic anisotropy (exchange anisotropy). Here, we propose that
FM-AFM interaction around the boundary between FM clusters or domains in the
AFM background or between AFM clusters or domains in the ferromagnetic
background is responsible for doping-dependent nonmonotonic behavior and the
origin of magnetic anisotropy.",2305.16493v1
2023-06-13,Is Anisotropy Inherent to Transformers?,"The representation degeneration problem is a phenomenon that is widely
observed among self-supervised learning methods based on Transformers. In NLP,
it takes the form of anisotropy, a singular property of hidden representations
which makes them unexpectedly close to each other in terms of angular distance
(cosine-similarity). Some recent works tend to show that anisotropy is a
consequence of optimizing the cross-entropy loss on long-tailed distributions
of tokens. We show in this paper that anisotropy can also be observed
empirically in language models with specific objectives that should not suffer
directly from the same consequences. We also show that the anisotropy problem
extends to Transformers trained on other modalities. Our observations tend to
demonstrate that anisotropy might actually be inherent to Transformers-based
models.",2306.07656v1
2023-07-27,Sensitivity of the IceCube-Gen2 Surface Array for Cosmic-Ray Anisotropy Studies,"The energy of the transition from Galactic to extra-galactic origin of cosmic
rays is one of the major unresolved issues of cosmic-ray physics. However,
strong constraints can be obtained from studying the anisotropy in the arrival
directions of cosmic rays. The sensitivity to cosmic-ray anisotropy is, in
particular, a matter of statistics. Recently, the cosmic ray anisotropy
measurements in the TeV to PeV energy range were updated from IceCube using 11
years of data. The IceCube-Gen2 surface array will cover an area about 8 times
larger than the existing IceTop surface array with a corresponding increase in
statistics and capability to investigate cosmic-ray anisotropy with higher
sensitivity. In this contribution, we present details on the performed
simulation studies and sensitivity to the cosmic-ray anisotropy signal for the
IceCube-Gen2 surface array.",2307.14655v1
2023-09-23,Anisotropies of Diffusive Ultra-high Energy Cosmic Rays in $f(R)$ Gravity Theory,"Understanding the anisotropy of ultra high-energy cosmic rays (UHECRs) is
crucial for unraveling the origins and propagation mechanisms of these
enigmatic particles. In this work, we studied the dipolar anisotropy of UHECRs
in the diffusive regime by considering three cosmological models: the standard
$\Lambda$CDM model, $f(R)$ gravity power-law model and the Starobinsky model.
This work aims to see the role of the $f(R)$ gravity theory in understanding
the anisotropy of UHECRs without condoning the standard cosmology. We found
that the amplitude of the dipolar anisotropy is sensitive to these cosmological
models, with the $f(R)$ power-law model predicting the largest amplitude, while
the $\Lambda$CDM model predicting the smallest amplitude at most of the
energies in the range considered. The predicted amplitude of the Starobinsky
model lies within the range of the $\Lambda$CDM one. This work not only
provides a way for exploration of UHECRs anisotropy within different
cosmological contexts but also may pave the way for new avenues of research at
the intersection of high-energy astrophysics.",2309.14361v1
2023-11-15,Exotic magnetic anisotropy near digitized dimensional Mott boundary,"The magnetic anisotropy of low-dimensional Mott systems exhibits unexpected
magnetotransport behavior useful for spin-based quantum electronics. Yet, the
anisotropy of natural materials is inherently determined by the crystal
structure, highly limiting its engineering. We demonstrate the magnetic
anisotropy modulation near a digitized dimensional Mott boundary in artificial
superlattices composed of a correlated magnetic monolayer SrRuO3 and
nonmagnetic SrTiO3. The magnetic anisotropy is initially engineered by
modulating the interlayer coupling strength between the magnetic monolayers.
Interestingly, when the interlayer coupling strength is maximized, a nearly
degenerate state is realized, in which the anisotropic magnetotransport is
strongly influenced by both the thermal and magnetic energy scales. Our results
offer a new digitized control for magnetic anisotropy in low-dimensional Mott
systems, inspiring promising integration of Mottronics and spintronics.",2311.09322v1
2023-12-22,Induced Cosmological Anisotropies and CMB Anomalies by a non-Abelian Gauge-Gravity Interaction,"We present a non-abelian cousin of the model presented in [1] which induces
cosmological anisotropies on top of standard FLRW geometry. This is in some
sense doing a cosmological mean field approximation, where the mean field
cosmological model under consideration would be the standard FLRW, and the
induced anisotropies are small perturbative corrections on top of it. Here we
mostly focus on the non-abelian $SU(2)$ gauge fields coupled to the gravity to
generate the anisotropies, which can be a viable model for the axion-like
particle (ALP) dark sector. The induced anisotropies are consequences of the
non-trivial back-reaction of the gauge fields on the gravity sector, and by a
clever choice of the parametrization, one can generate the Bianchi model we
have studied in this note. We also show that the anisotropies influence the
Sachs-Wolfe effect and we discuss the implications.",2312.14513v2
2024-01-22,Anisotropy Is Inherent to Self-Attention in Transformers,"The representation degeneration problem is a phenomenon that is widely
observed among self-supervised learning methods based on Transformers. In NLP,
it takes the form of anisotropy, a singular property of hidden representations
which makes them unexpectedly close to each other in terms of angular distance
(cosine-similarity). Some recent works tend to show that anisotropy is a
consequence of optimizing the cross-entropy loss on long-tailed distributions
of tokens. We show in this paper that anisotropy can also be observed
empirically in language models with specific objectives that should not suffer
directly from the same consequences. We also show that the anisotropy problem
extends to Transformers trained on other modalities. Our observations suggest
that anisotropy is actually inherent to Transformers-based models.",2401.12143v2
2024-03-01,Cooperatively Modulating Magnetic Anisotropy and Colossal Magnetoresistance via Atomic-Scale Buffer Layers in Highly Strained La0.7Sr0.3MnO3 Films,"Simultaneous control of magnetic anisotropy and magnetoresistance, especially
with atomic scale precision, remains a pivotal challenge for realizing advanced
spintronic functionalities. Here we demonstrate cooperative continuous control
over both magnetoresistance and magnetic anisotropy in highly strained
La0.7Sr0.3MnO3 (LSMO) thin films. By inserting varying perovskite buffer
layers, compressively strained LSMO films transition from a ferromagnetic
insulator with out-of-plane magnetic anisotropy to a metallic state with
in-plane anisotropy. Atomic-scale buffer layer insertion enables remarkably
acute, precise control to sharply modulate this magnetic phase transformation.
A gigantic 10,000% modulation of the colossal magnetoresistance (CMR) and an
exceptionally sharp transition from out-of-plane to in-plane magnetic
anisotropy are attained in just a few contiguous layers. These atomic-scale
correlations among electronic, magnetic, and structural order parameters yield
flexible multifunctional control promising for next-generation oxide
spintronics.",2403.00361v1
2008-09-01,Surface anisotropy broadening of the energy barrier distribution in magnetic nanoparticles,"The effect of surface anisotropy on the distribution of energy barriers in
magnetic fine particles of nanometer size is discussed within the framework of
the $T\ln(t/\tau_0)$ scaling approach. The comparison between the distributions
of the anisotropy energy of the particle cores, calculated by multiplying the
volume distribution by the core anisotropy, and of the total anisotropy energy,
deduced by deriving the master curve of the magnetic relaxation with respect to
the scaling variable $T\ln(t/\tau_0)$, enables the determination of the surface
anisotropy as a function of the particle size. We show that the contribution of
the particle surface to the total anisotropy energy can be well described by a
size--independent value of the surface energy per unit area which permits the
superimposition of the distributions corresponding to the particle core and
effective anisotropy energies. The method is applied to a ferrofluid composed
of non-interacting Fe$_{3-x}$O$_{4}$ particles of 4.9 nm in average size and
$x$ about 0.07. Even though the size distribution is quite narrow in this
system, a relatively small value of the effective surface anisotropy constant
$K_{s}=2.9\times 10^{-2}$ erg cm$^{-2}$ gives rise to a dramatic broadening of
the total energy distribution. The reliability of the average value of the
effective anisotropy constant, deduced from magnetic relaxation data, is
verified by comparing it to that obtained from the analysis of the shift of the
ac susceptibility peaks as a function of the frequency.",0809.0203v2
2016-03-03,Thermodynamic conditions during growth determine the magnetic anisotropy in epitaxial thin-films of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$,"The suitability of a particular material for use in magnetic devices is
determined by the process of magnetization reversal/relaxation, which in turn
depends on the magnetic anisotropy. Therefore, designing new ways to control
magnetic anisotropy in technologically important materials is highly desirable.
Here we show that magnetic anisotropy of epitaxial thin-films of half-metallic
ferromagnet La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) is determined by the proximity
to thermodynamic equilibrium conditions during growth. We performed a series of
X-ray diffraction and ferromagnetic resonance (FMR) experiments in two
different sets of samples: the first corresponds to LSMO thin-films deposited
under tensile strain on (001) SrTiO$_{3}$ by Pulsed Laser Deposition (PLD; far
from thermodynamic equilibrium); the second were deposited by a slow Chemical
Solution Deposition (CSD) method, under quasi-equilibrium conditions. Thin
films prepared by PLD show a in-plane cubic anisotropy with an overimposed
uniaxial term. A large anisotropy constant perpendicular to the film plane was
also observed in these films. However, the uniaxial anisotropy is completely
suppressed in the CSD films. The out of plane anisotropy is also reduced,
resulting in a much stronger in plane cubic anisotropy in the chemically
synthesized films. This change is due to a different rotation pattern of
MnO$_{6}$ octahedra to accomodate epitaxial strain, which depends not only on
the amount of tensile stress imposed by the STO substrate, but also on the
growth conditions. Our results demonstrate that the nature and magnitude of the
magnetic anisotropy in LSMO can be tuned by the thermodynamic parameters during
thin-film deposition.",1603.01127v1
2020-05-07,Correlations Between Fission Fragment and Neutron Anisotropies in Neutron-Induced Fission,"Several sources of angular anisotropy for fission fragments and prompt
neutrons have been studied in neutron-induced fission reactions. These include
kinematic recoils of the target from the incident neutron beam and the
fragments from the emission of the prompt neutrons, preferential directions of
the emission of the fission fragments with respect to the beam axis due to the
population of particular transition states at the fission barrier, and
forward-peaked angular distributions of pre-equilibrium neutrons which are
emitted before the formation of a compound nucleus. In addition, there are
several potential sources of angular anisotropies that are more difficult to
disentangle: the angular distributions of prompt neutrons from fully
accelerated fragments or from scission neutrons, and the emission of neutrons
from fission fragments that are not fully accelerated. In this work, we study
the effects of the first group of anisotropy sources, particularly exploring
the correlations between the fission fragment anisotropy and the resulting
neutron anisotropy. While kinematic effects were already accounted for in our
Hauser-Feshbach Monte Carlo code, $\mathtt{CGMF}$, anisotropic angular
distributions for the fission fragments and pre-equilibrium neutrons resulting
from neutron-induced fission on $^{233,234,235,238}$U, $^{239,241}$Pu, and
$^{237}$Np have been introduced for the first time. The effects of these
sources of anisotropy are examined over a range of incident neutron energies,
from thermal to 20 MeV, and compared to experimental data from the Chi-Nu
liquid scintillator array. The anisotropy of the fission fragments is reflected
in the anisotropy of the prompt neutrons, especially as the outgoing energy of
the prompt neutrons increases, allowing for an extraction of the fission
fragment anisotropy to be made from a measurement of the neutrons.",2005.03206v1
1993-01-21,Minimal Microwave Anisotropy from Perturbations Induced at Late Times,"Aside from primordial gravitational instability of the cosmological fluid,
various mechanisms have been proposed to generate large-scale structure at
relatively late times, including, e.g., ``late-time'' cosmological phase
transitions. In these scenarios, it is envisioned that the universe is nearly
homogeneous at the time of last scattering and that perturbations grow rapidly
sometime after the primordial plasma recombines. On this basis, it was
suggested that large inhomogeneities could be generated while leaving
relatively little imprint on the cosmic microwave background (MBR) anisotropy.
In this paper, we calculate the minimal anisotropies possible in any
``late-time'' scenario for structure formation, given the level of
inhomogeneity observed at present. Since the growth of the inhomogeneity
involves time-varying gravitational fields, these scenarios inevitably generate
significant MBR anisotropy via the Sachs-Wolfe effect. Moreover, we show that
the large-angle MBR anisotropy produced by the rapid post-recombination growth
of inhomogeneity is generally greater than that produced by the same
inhomogeneity grown via gravitational instability. In ``realistic'' scenarios
one can decrease the anisotropy compared to models with primordial adiabatic
fluctuations, but only on very small angular scales. The value of any
particular measure of the anisotropy can be made small in late-time models, but
only by making the time-dependence of the gravitational field sufficiently
``pathological''.",9301011v1
1996-01-26,On the microwave background anisotropy produced by big voids in open universes,"The Tolman-Bondi solution of the Einstein equations is used in order to model
the time evolution of the void observed in Bo\""otes. The present density
contrast of the central region ($\sim -0.75$) and its radius ($\sim 30h^{-1} \
Mpc$) are fixed, while the density parameter of the Universe, the amplitude of
the density contrast inside the void wall, the width of this wall and the
distance from the void centre to the Local Group are appropriately varied. The
microwave background anisotropy produced by Bo\""otes-like voids is estimated
for a significant set of locations. All the voids are placed far from the last
scattering surface. It is shown that the anisotropy generated by these voids
strongly depends on the density parameter, the wall structure and the void
location. The Doppler dipole and quadrupole are subtracted and the residual
anisotropy is calculated. In the case of some isolated Bo\""otes-like voids
placed at redshifts between 1 and 10 in an open universe with density parameter
$\Omega_{0}=0.2$, the residual anisotropy appears to be a few times $10^{-6}$
on scales of a few degrees. This anisotropy is about one order of magnitude
greater than previous estimates corresponding to other cases. The anisotropy
produced by a distribution of voids is qualitatively studied in the light of
this result. Comparisons with previous estimates are discussed.",9601154v2
2005-03-10,What will anisotropies in the clustering pattern in redshifted 21 cm maps tell us?,"The clustering pattern in high redshift HI maps is expected to be anisotropic
due to two distinct reasons, the
  Alcock-Paczynski effect and the peculiar velocities, both of which are
sensitive to the cosmological parameters. The signal is also expected to be
sensitive to the details of the HI distribution at the epoch when the radiation
originated. We use simple models for the HI distribution at the epoch of
reionizaation and the post-reionization era to investigate exactly what we hope
to learn from future observations of the anisotropy pattern in HI maps. We find
that such observations will probably tell us more about the HI distribution
than about the background cosmological model. Assuming that reionization can be
described by spherical, ionized bubbles all of the same size with their centers
possibly being biased with respect to the dark matter, we find that the
anisotropy pattern at small angles is expected to have a bump at the
characteristic angular size of the individual bubbles whereas the large scale
anisotropy pattern will reflect the size and the bias of the bubbles. The
anisotropy also depends on the background cosmological parameters, but the
dependence is much weaker. Under the assumption that the HI in the
post-reionization era traces the dark matter with a possible bias, we find that
changing the bias and changing the background cosmology has similar effects on
the anisotropy pattern. Combining observations of the anisotropy with
independent estimates of the bias, possibly from the bi-spectrum, may allow
these observations to constrain cosmological parameters.",0503237v2
1996-07-26,Detection of Anisotropies in the Gravitational-Wave Stochastic Background,"By correlating the signals from a pair of gravitational-wave detectors, one
can undertake sensitive searches for a stochastic background of gravitational
radiation. If the stochastic background is anisotropic, then this correlated
signal varies harmonically with the earth's rotation. We calculate how the
harmonics of this varying signal are related to the multipole moments which
characterize the anisotropy, and give a formula for the signal-to-noise ratio
of a given harmonic. The specific case of the two LIGO (Laser Interferometric
Gravitational Observatory) detectors, which will begin operation around the
year 2000, is analyzed in detail. We consider two possible examples of
anisotropy. If the gravitational-wave stochastic background contains a dipole
intensity anisotropy whose origin (like that of the Cosmic Background
Radiation) is motion of our local system, then that anisotropy will be
observable by the advanced LIGO detector (with 90% confidence in one year of
observation) if \Omega_{gw} > 5.3 \times 10^{-8} h_{100}^{-2}. We also study
the signal produced by stochastic sources distributed in the same way as the
luminous matter in the galactic disk, and in the same way as the galactic halo.
The anisotropy due to sources distributed as the galactic disk or as the
galactic halo will be observable by the advanced LIGO detector (with 90%
confidence in one year of observation) if \Omega_{gw} > 1.8 \times 10^{-10}
h_{100}^{-2} or \Omega_{gw} > 6.7 \times 10^{-8} h_{100}^{-2}, respectively.",9607068v2
2008-12-30,Anisotropy of the Optimally-Doped Iron Pnictide Superconductor Ba(Fe0.926Co0.074)2As2,"Anisotropies of electrical resistivity, upper critical field, London
penetration depth and critical currents have been measured in single crystals
of the optimally doped iron pnictide superconductor
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, $x$=0.074 and $T_c \sim$23 K. The normal state
resistivity anisotropy was obtained by employing both the Montgomery technique
and direct measurements on samples cut along principal crystallographic
directions. The ratio $\gamma_{\rho} = \rho_c /\rho_a$ is about 4$\pm$1 just
above $T_c$ and becomes half of that at room temperature. The anisotropy of the
upper critical field, $\gamma_{H} = H_{c2,ab} /H_{c2,c} $, as determined from
specific heat measurements close to $T_c$, is in the range of 2.1 to 2.6,
depending on the criterion used. A comparable low anisotropy of the London
penetration depth, $\gamma_{\lambda}=\lambda_{c}/\lambda_{ab}$, was recorded
from TDR measurements and found to persist deep into the superconducting state.
An anisotropy of comparable magnitude was also found in the critical currents,
$\gamma_j=j_{c,ab}/j_{c,c}$, as determined from both direct transport
measurements ($\sim$1.5) and from the analysis of the magnetization data
($\sim$3). Overall, our results show that iron pnictide superconductors
manifest anisotropies consistent with essentially three-dimensional
intermetallic compound and bear little resemblance to cuprates.",0812.4991v1
2011-02-06,Experimental study of the influence of anisotropy on the inertial scales of turbulence,"We ask whether the scaling exponents or the Kolmogorov constants depend on
the anisotropy of the velocity fluctuations in a turbulent flow with no shear.
According to our experiment, the answer is no for the Eulerian second-order
transverse velocity structure function. The experiment consisted of 32
loudspeaker-driven jets pointed toward the centre of a spherical chamber. We
generated anisotropy by controlling the strengths of the jets. We found that
the form of the anisotropy of the velocity fluctuations was the same as that in
the strength of the jets. We then varied the anisotropy, as measured by the
ratio of axial to radial root-mean-square (RMS) velocity fluctuations, between
0.6 and 2.3. The Reynolds number was approximately constant at around
$R_\lambda$ = 481. In a central volume with a radius of 50 mm, the turbulence
was approximately homogeneous, axisymmetric, and had no shear and no mean flow.
We observed that the scaling exponent of the structure function was $0.70 \pm
0.03$, independent of the anisotropy and regardless of the direction in which
we measured it. The Kolmogorov constant, $C_2$, was also independent of
direction and anisotropy to within the experimental error of 4%.",1102.1197v2
2011-03-01,Magnetothermal instabilities in magnetized anisotropic plasmas,"Using the transport equations for an ideal anisotropic collisionless plasma
derived from the Vlasov equation by the 16-moment method, we analyse the
influence of pressure anisotropy exhibited by collisionless magnetized plasmas
on the magnetothermal (MTI) and heat-flux-driven buoyancy (HBI) instabilities.
We calculate the dispersion relation and the growth rates for these
instabilities in the presence of a background heat flux and for configurations
with static pressure anisotropy, finding that when the frequency at which heat
conduction acts is much larger than any other frequency in the system (i.e.
weak magnetic field) the pressure anisotropy has no effect on the MTI/HBI,
provided the degree of anisotropy is small. In contrast, when this ordering of
timescales does not apply the instability criteria depend on pressure
anisotropy. Specifically, the growth time of the instabilities in the
anisotropic case can be almost one order of magnitude smaller than its
isotropic counterpart. We conclude that in plasmas where pressure anisotropy is
present the MTI/HBI are modified. However, in environments with low magnetic
fields and small anisotropy such as the ICM the results obtained from the
16-moment equations under the approximations considered are similar to those
obtained from ideal MHD.",1103.0310v3
2012-02-23,Joint anisotropy and source count constraints on the contribution of blazars to the diffuse gamma-ray background,"We place new constraints on the contribution of blazars to the large-scale
isotropic gamma-ray background (IGRB) by jointly analyzing the measured source
count distribution (logN-logS) of blazars and the measured intensity and
anisotropy of the IGRB. We find that these measurements point to a consistent
scenario in which unresolved blazars make less than 20% of the IGRB intensity
at 1-10 GeV while accounting for the majority of the measured anisotropy in
that energy band. These results indicate that the remaining fraction of the
IGRB intensity is made by a component with a low level of intrinsic anisotropy.
We determine upper limits on the anisotropy from non-blazar sources, adopting
the best-fit parameters of the measured source count distribution to calculate
the unresolved blazar anisotropy. In addition, we show that the anisotropy
measurement excludes some recently proposed models of the unresolved blazar
population.",1202.5309v2
2012-10-17,Measurements of electron anisotropy in solar flares using albedo with RHESSI X-ray data,"The angular distribution of electrons accelerated in solar flares is a key
parameter in the understanding of the acceleration and propagation mechanisms
that occur there. However, the anisotropy of energetic electrons is still a
poorly known quantity, with observational studies producing evidence for an
isotropic distribution and theoretical models mainly considering the strongly
beamed case. We use the effect of photospheric albedo to infer the pitch angle
distribution of X-ray emitting electrons using Hard X-ray data from RHESSI. A
bi-directional approximation is applied and a regularized inversion is
performed for eight large flare events to deduce the electron spectra in both
downward (towards the photosphere) and upward (away from the photosphere)
directions. The electron spectra and the electron anisotropy ratios are
calculated for broad energy range from about 10 and up to ~ 300 keV near the
peak of the flares. The variation of electron anisotropy over short periods of
time intervals lasting 4, 8 and 16 seconds near the impulsive peak has been
examined. The results show little evidence for strong anisotropy and the mean
electron flux spectra are consistent with the isotropic electron distribution.
The 3-sigma level uncertainties, although energy and event dependent, are found
to suggest that anisotropic distribution with anisotropy larger than ~ 3 are
not consistent with the hard X-ray data. At energies above 150-200 keV, the
uncertainties are larger and thus the possible electron anisotropies could be
larger.",1210.4757v1
2013-04-04,Reconnection and electron temperature anisotropy in sub-proton scale plasma turbulence,"Turbulent behavior at sub-proton scales in magnetized plasmas is important
for a full understanding of the energetics of astrophysical flows such as the
solar wind. We study the formation of electron temperature anisotropy due to
reconnection in the turbulent decay of sub-proton scale fluctuations using two
dimensional, particle-in-cell (PIC) plasma simulations with realistic
electron-proton mass ratio and a guide field out of the simulation plane. A
fluctuation power spectrum with approximately power law form is created down to
scales of order the electron gyroradius. In the dynamic magnetic field
topology, which gradually relaxes in complexity, we identify the signatures of
collisionless reconnection at sites of X-point field geometry. The reconnection
sites are generally associated with regions of strong parallel electron
temperature anisotropy. The evolving topology of magnetic field lines connected
to a reconnection site allows spatial mixing of electrons accelerated at
multiple, spatially separated reconnection regions. This leads to the formation
of multi-peaked velocity distribution functions with a strong parallel
temperature anisotropy. In a three-dimensional system, supporting the
appropriate wave vectors, the multi-peaked distribution functions would be
expected to be unstable to kinetic instabilities, contributing to dissipation.
The proposed mechanism of anisotropy formation is also relevant to space and
astrophysical systems where the evolution of the plasma is constrained by
linear temperature anisotropy instability thresholds. The presence of
reconnection sites leads to electron energy gain, nonlocal velocity space
mixing and the formation of strong temperature anisotropy; this is evidence of
an important role for reconnection in the dissipation of turbulent
fluctuations.",1304.1444v2
2013-09-12,Origin and spectroscopic determination of trigonal anisotropy in a heteronuclear single-molecule magnet,"W-band ({\nu} ca. 94 GHz) electron paramagnetic resonance (EPR) spectroscopy
was used for a single-crystal study of a star-shaped Fe3Cr single-molecule
magnet (SMM) with crystallographically imposed trigonal symmetry. The high
resolution and sensitivity accessible with W-band EPR allowed us to determine
accurately the axial zero-field splitting terms for the ground (S =6) and first
two excited states (S =5 and S =4). Furthermore, spectra recorded by applying
the magnetic field perpendicular to the trigonal axis showed a pi/6 angular
modulation. This behavior is a signature of the presence of trigonal transverse
magnetic anisotropy terms whose values had not been spectroscopically
determined in any SMM prior to this work. Such in-plane anisotropy could only
be justified by dropping the so-called 'giant spin approach' and by considering
a complete multispin approach. From a detailed analysis of experimental data
with the two models, it emerged that the observed trigonal anisotropy directly
reflects the structural features of the cluster, i.e., the relative orientation
of single-ion anisotropy tensors and the angular modulation of single-ion
anisotropy components in the hard plane of the cluster. Finally, since
high-order transverse anisotropy is pivotal in determining the spin dynamics in
the quantum tunneling regime, we have compared the angular dependence of the
tunnel splitting predicted by the two models upon application of a transverse
field (Berry-phase interference).",1309.3098v1
2013-12-31,Orthogonal invariant sets of the diffusion tensor and the development of a curvilinear set suitable for low-anisotropy tissues,"We develop a curvilinear invariant set of the diffusion tensor which may be
applied to Diffusion Tensor Imaging measurements on tissues and porous media.
This new set is an alternative to the more common invariants such as fractional
anisotropy and the diffusion mode. The alternative invariant set possesses a
different structure to the other known invariant sets; the second and third
members of the curvilinear set measure the degree of orthotropy and
oblateness/prolateness, respectively. The proposed advantage of these
invariants is that they may work well in situations of low diffusion anisotropy
and isotropy, as is often observed in tissues such as cartilage.
  We also explore the other orthogonal invariant sets in terms of their
geometry in relation to eigenvalue space; a cylindrical set, a spherical set
(including fractional anisotropy and the mode), and a log-Euclidean set. These
three sets have a common structure. The first invariant measures the magnitude
of the diffusion, the second and third invariants capture aspects of the
anisotropy; the magnitude of the anisotropy and the shape of the diffusion
ellipsoid (the manner in which the anisotropy is realised). We also show a
simple method to prove the orthogonality of the invariants within a set.",1401.0165v1
2014-01-19,Electronic nematic phase transition in the presence of anisotropy,"We study the phase diagram of electronic nematic instability in the presence
of xy anisotropy. While a second order transition cannot occur in this case,
mean-field theory predicts that a first order transition occurs near van Hove
filling and its phase boundary forms a wing structure, which we term a
Griffiths wing, referring to his original work of He3-He4 mixtures. When
crossing the wing, the anisotropy of the electronic system exhibits a
discontinuous change, leading to a meta-nematic transition, i.e., the analog to
a meta-magnetic transition in a magnetic system. The upper edge of the wing
corresponds to a critical end line, which shows a non-monotonic temperature
dependence as a function of the external anisotropy and vanishes at a quantum
critical end point for a strong anisotropy. The mean-field phase diagram is,
however, very sensitive to fluctuations of the nematic order parameter,
yielding a topologically different phase diagram. The Griffiths wing is broken
into two pieces. A tiny wing appears close to zero anisotropy and the other is
realized for a strong anisotropy. Consequently three quantum critical end
points are realized. We discuss that these results can be related to various
materials including a cold atom system.",1401.4628v3
2014-05-06,Giant dielectric anisotropy via homogenization,"A random mixture of two isotropic dielectric materials, one composed of
oriented spheroidal particles of relative permittivity $\epsilon_a$ and the
other composed of oriented spheroidal particles of relative permittivity
$\epsilon_b$, was considered in the long wavelength regime. The permittivity
dyadic of the resulting homogenized composite material (HCM) was estimated
using the Bruggeman homogenization formalism. The HCM was an orthorhombic
biaxial material if the symmetry axes of the two populations of spheroids were
mutually perpendicular and a uniaxial material if these two axes were mutually
aligned. The degree of anisotropy of the HCM, as gauged by the ratio of the
eigenvalues of the HCM's permittivity dyadic, increased as the shape of the
constituent particles became more eccentric. The greatest degrees of HCM
anisotropy were achieved for the limiting cases wherein the constituent
particles were shaped as needles or discs. In these instances explicit formulas
for the HCM anisotropy were derived from the dyadic Bruggeman equation. Using
these formulas it was found that the degrees of HCM anisotropy are proportional
to $\sqrt{\epsilon_b}$ or $\epsilon_b$, at fixed values of volume fraction and
$\epsilon_a$, for $\epsilon_b > \epsilon_a$. Thus, in principle, there is no
limit to degree of anisotropy that may be attained via homogenization. In
practice, the degree of anisotropy would be limited by the available value of
$\epsilon_b$ (and/or $\epsilon_a$).",1405.1198v1
2014-07-11,Fermi-LAT gamma-ray anisotropy and intensity explained by unresolved Radio-Loud Active Galactic Nuclei,"Radio-loud active galactic nuclei (AGN) are expected to contribute
substantially to both the intensity and anisotropy of the isotropic gamma-ray
background (IGRB). In turn, the measured properties of the IGRB can be used to
constrain the characteristics of proposed contributing source classes. We
consider individual subclasses of radio-loud AGN, including low-,
intermediate-, and high-synchrotron-peaked BL Lacertae objects, flat-spectrum
radio quasars, and misaligned AGN. Using updated models of the gamma-ray
luminosity functions of these populations, we evaluate the energy-dependent
contribution of each source class to the intensity and anisotropy of the IGRB.
We find that collectively radio-loud AGN can account for the entirety of the
IGRB intensity and anisotropy as measured by the Fermi Large Area Telescope
(LAT). Misaligned AGN provide the bulk of the measured intensity but a
negligible contribution to the anisotropy, while high-synchrotron-peaked BL
Lacertae objects provide the dominant contribution to the anisotropy. In
anticipation of upcoming measurements with the Fermi-LAT and the forthcoming
Cherenkov Telescope Array, we predict the anisotropy in the broader energy
range that will be accessible to future observations.",1407.3275v2
2014-08-21,Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited,"The dynamics of the interstellar medium (ISM) are strongly affected by
turbulence, which shows increased anisotropy in the presence of a magnetic
field. We expand upon the Esquivel & Lazarian method to estimate the Alfven
Mach number using the structure function anisotropy in velocity centroid data
from position-position-velocity maps. We utilize 3D magnetohydrodynamic (MHD)
simulations of fully developed turbulence, with a large range of sonic and
Alfvenic Mach numbers, to produce synthetic observations of velocity centroids
with observational characteristics such as thermal broadening, cloud
boundaries, noise, and radiative transfer effects of carbon monoxide. In
addition, we investigate how the resulting anisotropy-Alfven Mach number
dependency found in Esquivel & Lazarian (2011) might change when taking the
second moment of the position-position-velocity cube or when using different
expressions to calculate the velocity centroids. We find that the degree of
anisotropy is related primarily to the magnetic field strength (i.e. Alfven
Mach number) and the line-of-sight orientation, with a secondary effect on
sonic Mach number. If the line-of-sight is parallel to up to ~45 deg off of the
mean field direction, the velocity centroid anisotropy is not prominent enough
to distinguish different Alfvenic regimes. The observed anisotropy is not
strongly affected by including radiative transfer, although future studies
should include additional tests for opacity effects. These results open up the
possibility of studying the magnetic nature of the ISM using statistical
methods in addition to existing observational techniques.",1408.4858v1
2015-03-02,Anisotropy and Strong-Coupling Effects on the Collective Mode Spectrum of Chiral Superconductors: Application to Sr$_2$RuO$_4$,"Recent theories of Sr$_2$RuO$_4$ based on the interplay of strong
interactions, spin-orbit coupling and multi-band anisotropy predict chiral or
helical ground states with strong anisotropy of the pairing states, with deep
minima in the excitation gap, as well as strong phase anisotropy for the chiral
ground state. We develop time-dependent mean field theory to calculate the
Bosonic spectrum for the class of 2D chiral superconductors spanning $^3$He-A
to chiral superconductors with strong anisotropy. Chiral superconductors
support a pair of massive Bosonic excitations of the time-reversed pairs
labeled by their parity under charge conjugation. These modes are degenerate
for 2D $^3$He-A. Crystal field anisotropy lifts the degeneracy. Strong
anisotropy also leads to low-lying Fermions, and thus to channels for the decay
of the Bosonic modes. Selection rules and phase space considerations lead to
large asymmetries in the lifetimes and hybridization of the Bosonic modes with
the continuum of un-bound Fermion pairs. We also highlight results for the
excitation of the Bosonic modes by microwave radiation that provide clear
signatures of the Bosonic modes of an anisotropic chiral ground state.",1503.00624v2
2015-06-02,Clustering Fossil from Primordial Gravitational Waves in Anisotropic Inflation,"Inflationary models can correlate small-scale density perturbations with the
long-wavelength gravitational waves (GW) in the form of the
Tensor-Scalar-Scalar (TSS) bispectrum. This correlation affects the
mass-distribution in the Universe and leads to the off-diagonal correlations of
the density field modes in the form of the quadrupole anisotropy.
Interestingly, this effect survives even after the tensor mode decays when it
re-enters the horizon, known as the fossil effect. As a result, the
off-diagonal correlation function between different Fourier modes of the
density fluctuations can be thought as a way to probe the large-scale GW and
the mechanism of inflation behind the fossil effect. Models of single field
slow roll inflation generically predict a very small quadrupole anisotropy in
TSS while in models of multiple fields inflation this effect can be observable.
Therefore this large scale quadrupole anisotropy can be thought as a
spectroscopy for different inflationary models. In addition, in models of
anisotropic inflation there exists quadrupole anisotropy in curvature
perturbation power spectrum. Here we consider TSS in models of anisotropic
inflation and show that the shape of quadrupole anisotropy is different than in
single field models. In addition in these models the quadrupole anisotropy is
projected into the preferred direction and its amplitude is proportional to
$g_* N_e$ where $N_e$ is the number of e-folds and $g_*$ is the amplitude of
quadrupole anisotropy in curvature perturbation power spectrum. We use this
correlation function to estimate the large scale GW as well as the preferred
direction and discuss the detectability of the signal in the galaxy surveys
like Euclid and 21 cm surveys.",1506.00958v1
2015-06-17,"Consequences of viscous anisotropy in a deforming, two-phase aggregate. Why is porosity-band angle lowered by viscous anisotropy?","In laboratory experiments that impose shear deformation on partially molten
aggregates of initially uniform porosity, melt segregates into high-porosity
sheets (bands in cross-section). The bands emerge at 15-20 degrees to the shear
plane. A model of viscous anisotropy can explain these low angles whereas
previous, simpler models have failed to do so. The anisotropic model is
complex, however, and the reason that it produces low-angle bands has not been
understood. Here we show that there are two mechanisms: (i) suppression of the
well-known tensile instability, and (ii) creation of a new, shear-driven
instability. We elucidate these mechanisms using linearised stability analysis
in a coordinate system that is aligned with the perturbations. We consider the
general case of anisotropy that varies dynamically with deviatoric stress, but
approach it by first considering uniform anisotropy that is imposed a priori
and showing the difference between static and dynamic cases. We extend the
model of viscous anisotropy to include a strengthening in the direction of
maximum compressive stress. Our results support the hypothesis that viscous
anisotropy is the cause of low band-angles in experiments.",1506.05286v2
2015-08-23,Fire Hose instability driven by alpha particle temperature anisotropy,"We investigate properties of a solar wind-like plasma including a secondary
alpha particle population exhibiting a parallel temperature anisotropy with
respect to the background magnetic field, using linear and quasi-linear
predictions and by means of one-dimensional hybrid simulations. We show that
anisotropic alpha particles can drive a parallel fire hose instability
analogous to that generated by protons, but that, remarkably, the instability
can be triggered also when the parallel plasma beta of alpha particles is below
unity. The wave activity generated by the alpha anisotropy affects the
evolution of the more abundant protons, leading to their anisotropic heating.
When both ion species have sufficient parallel anisotropies both of them can
drive the instability, and we observe generation of two distinct peaks in the
spectra of the fluctuations, with longer wavelengths associated to alphas and
shorter ones to protons. If a non-zero relative drift is present, the unstable
modes propagate preferentially in the direction of the drift associated with
the unstable species. The generated waves scatter particles and reduce their
temperature anisotropy to marginally stable state, and, moreover, they
significantly reduce the relative drift between the two ion populations. The
coexistence of modes excited by both species leads to saturation of the plasma
in distinct regions of the beta/anisotropy parameter space for protons and
alpha particles, in good agreement with in situ solar wind observations. Our
results confirm that fire hose instabilities are likely at work in the solar
wind and limit the anisotropy of different ion species in the plasma.",1508.05638v1
2015-08-26,Anatomy and giant enhancement of the perpendicular magnetic anisotropy of cobalt-graphene heterostructures,"We report strongly enhanced perpendicular magnetic anisotropy (PMA) of Co
films by graphene coating from both first-principles and experiments. Our
calculations show that graphene can dramatically boost the surface anisotropy
of Co films up to twice the value of its pristine counterpart and can extend
the out-of-plane effective anisotropy up to unprecedented thickness of 25~\AA.
These findings are supported by our experiments on graphene coating on Co films
grown on Ir substrate. Furthermore, we report layer-resolved and
orbital-hybridization-resolved anisotropy analysis which help understanding the
physical mechanisms of PMA and more practically can help design structures with
giant PMA. As an example, we propose super-exchange stabilized Co-graphene
heterostructures with a robust out-of-plane constant effective PMA and linearly
increasing interfacial anisotropy as a function of film thickness. These
findings point towards possibilities to engineer graphene/ferromagnetic metal
heterostructures with giant magnetic anisotropy more than 20 times larger
compared to conventional multilayers, which constitutes a hallmark for future
graphene and traditional spintronic technologies.",1508.06681v1
2015-11-10,Primordial Statistical Anisotropies: The Effective Field Theory Approach,"In this work we present the effective field theory of primordial statistical
anisotropies generated during anisotropic inflation involving a background
$U(1)$ gauge field. Besides the usual Goldstone boson associated with the
breaking of time diffeomorphism we have two additional Goldstone bosons
associated with the breaking of spatial diffeomorphisms. We further identify
these two new Goldstone bosons with the expected two transverse degrees of the
$U(1)$ gauge field fluctuations. Upon defining the appropriate unitary gauge,
we present the most general quadratic action which respects the remnant
symmetry in the unitary gauge. The interactions between various Goldstone
bosons leads to statistical anisotropy in curvature perturbation power
spectrum. Calculating the general results for power spectrum anisotropy, we
recover the previously known results in specific models of anisotropic
inflation. In addition, we present novel results for statistical anisotropy in
models with non-trivial sound speed for inflaton fluctuations. Also we identify
the interaction which leads to birefringence-like effects in anisotropic power
spectrum in which the speed of gauge field fluctuations depends on the
direction of the mode propagation and the two polarization of gauge field
fluctuations contribute differently in statistical anisotropy. As another
interesting application, our EFT approach naturally captures interactions
generating parity violating statistical anisotropies.",1511.03218v1
2015-12-04,Measures of Three-Dimensional Anisotropy and Intermittency in Strong Alfvénic Turbulence,"We measure the local anisotropy of numerically simulated strong Alfv\'enic
turbulence with respect to two local, physically relevant directions: along the
local mean magnetic field and along the local direction of one of the
fluctuating Elsasser fields. We find significant scaling anisotropy with
respect to both these directions: the fluctuations are ""ribbon-like"" ---
statistically, they are elongated along both the mean magnetic field and the
fluctuating field. The latter form of anisotropy is due to scale-dependent
alignment of the fluctuating fields. The intermittent scalings of the
$n$th-order conditional structure functions in the direction perpendicular to
both the local mean field and the fluctuations agree well with the theory of
Chandran et al. 2015, while the parallel scalings are consistent with those
implied by the critical-balance conjecture. We quantify the relationship
between the perpendicular scalings and those in the fluctuation and parallel
directions, and find that the scaling exponent of the perpendicular anisotropy
(i.e., of the aspect ratio of the Alfv\'enic structures in the plane
perpendicular to the mean magnetic field) depends on the amplitude of the
fluctuations. This is shown to be equivalent to the anticorrelation of
fluctuation amplitude and alignment at each scale. The dependence of the
anisotropy on amplitude is shown to be more significant for the anisotropy
between the perpendicular and fluctuation-direction scales than it is between
the perpendicular and parallel scales.",1512.01461v1
2016-01-15,Limits on the ions temperature anisotropy in turbulent intracluster medium,"Turbulence in the weakly collisional intracluster medium of galaxies (ICM) is
able to generate strong thermal velocity anisotropies in the ions (with respect
to the local magnetic field direction), if the magnetic moment of the particles
is conserved in the absence of Coulomb collisions. In this scenario, the
anisotropic pressure magnetohydrodynamic (AMHD) turbulence shows a very
different statistical behaviour from the standard MHD one and is unable to
amplify seed magnetic fields, in disagreement with previous cosmological MHD
simulations which are successful to explain the observed magnetic fields in the
ICM. On the other hand, temperature anisotropies can also drive plasma
instabilities which can relax the anisotropy. This work aims to compare the
relaxation rate with the growth rate of the anisotropies driven by the
turbulence. We employ quasilinear theory to estimate the ions scattering rate
due to the parallel firehose, mirror, and ion-cyclotron instabilities, for a
set of plasma parameters resulting from AMHD simulations of the turbulent ICM.
We show that the ICM turbulence can sustain only anisotropy levels very close
to the instabilities thresholds. We argue that the AMHD model which bounds the
anisotropies at the marginal stability levels can describe the Alfvenic
turbulence cascade in the ICM.",1601.03837v3
2016-07-17,Second order perturbed Heisenberg Hamiltonian of Fe3O4 ultra-thin films,"Due to the wide range of applications, theoretical models of Fe3O4 films are
found to be important. Ultra thin Fe3O4 films with ferrite structure have been
theoretically investigated using second order perturbed modified Heisenberg
Hamiltonian. Matrices for ultra thin films with two and three spin layers are
presented in this manuscript. Total magnetic energy was expressed in terms of
spin exchange interaction, magnetic dipole interaction, second order magnetic
anisotropy and stress induced magnetic anisotropy. Magnetic properties were
observed for films with two spin layers and variant second order magnetic
anisotropy. For the film with three spin layers, second order anisotropy
constant was fixed to avoid tedious derivations. Magnetic easy axis rotates
toward the in plane direction as the number of spin layers is increased from
two to three because the stress induced anisotropy energy dominates at higher
number of spin layers. According to some other experimental data, the magnetic
easy axis of thin films rotates toward the in plane direction as the thickness
is increased. For ferrite film with two spin layers, magnetic easy and hard
directions can be observed at 0.75 and 1.2 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 3.9. For ferrite film with three spin layers, magnetic easy and
hard directions can be observed at 2.4 and 2.3 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 4.2.",1611.02225v2
2016-12-03,Shaping the solar wind temperature anisotropy by the interplay of electron and proton instabilities,"A variety of nonthermal characteristics like kinetic, e.g., temperature,
anisotropies and suprathermal populations (enhancing the high energy tails of
the velocity distributions) are revealed by the in-situ observations in the
solar wind indicating quasistationary states of plasma particles out of thermal
equilibrium. Large deviations from isotropy generate kinetic instabilities and
growing fluctuating fields which should be more efficient than collisions in
limiting the anisotropy (below the instability threshold) and explain the
anisotropy limits reported by the observations. The present paper aims to
decode the principal instabilities driven by the temperature anisotropy of
electrons and protons in the solar wind, and contrast the instability
thresholds with the bounds observed at 1~AU for the temperature anisotropy. The
instabilities are characterized using linear kinetic theory to identify the
appropriate (fastest) instability in the relaxation of temperature anisotropies
$A_{e,p} = T_{e,p,\perp}/ T_{e,p,\parallel} \ne 1$. The analysis focuses on the
electromagnetic instabilities driven by the anisotropic protons ($A_p \lessgtr
1$) and invokes for the first time a dynamical model to capture the interplay
with the anisotropic electrons by correlating the effects of these two species
of plasma particles, dominant in the solar wind.",1612.01012v1
2016-12-09,Discovery of ferromagnetism with large magnetic anisotropy in ZrMnP and HfMnP,"ZrMnP and HfMnP single crystals are grown by a self-flux growth technique and
structural as well as temperature dependent magnetic and transport properties
are studied. Both compounds have an orthorhombic crystal structure. ZrMnP and
HfMnP are ferromagnetic with Curie temperatures around $370$~K and $320$~K
respectively. The spontaneous magnetizations of ZrMnP and HfMnP are determined
to be $1.9$~$\mu_\textrm{B}$/f.u. and $2.1$~$\mu_\textrm{B}$/f.u. respectively
at $50$~K. The magnetocaloric effect of ZrMnP in term of entropy change
($\Delta S$) is estimated to be $-6.7$ kJm$^{-3}$K$^{-1}$ around $369$~K. The
easy axis of magnetization is [100] for both compounds, with a small anisotropy
relative to the [010] axis. At $50$~K, the anisotropy field along the [001]
axis is $\sim4.6$~T for ZrMnP and $\sim10$~T for HfMnP. Such large magnetic
anisotropy is remarkable considering the absence of rare-earth elements in
these compounds. The first principle calculation correctly predicts the
magnetization and hard axis orientation for both compounds, and predicts the
experimental HfMnP anisotropy field within 25 percent. More importantly, our
calculations suggest that the large magnetic anisotropy comes primarily from
the Mn atoms suggesting that similarly large anisotropies may be found in other
3d transition metal compounds.",1612.03166v1
2017-01-25,Northern sky Galactic Cosmic Ray anisotropy between 10-1000 TeV with the Tibet Air Shower Array,"We report the analysis of the $10-1000$ TeV large-scale sidereal anisotropy
of Galactic cosmic rays (GCRs) with the data collected by the Tibet Air Shower
Array from October, 1995 to February, 2010. In this analysis, we improve the
energy estimate and extend the declination range down to $-30^{\circ}$. We find
that the anisotropy maps above 100 TeV are distinct from that at multi-TeV
band. The so-called ""tail-in"" and ""loss-cone"" features identified at low
energies get less significant and a new component appears at $\sim100$ TeV. The
spatial distribution of the GCR intensity with an excess (7.2$\sigma$
pre-trial, 5.2$\sigma$ post-trial) and a deficit ($-5.8\sigma$ pre-trial) are
observed in the 300 TeV anisotropy map, in a good agreement with IceCube's
results at 400 TeV. Combining the Tibet results in the northern sky with
IceCube's results in the southern sky, we establish a full-sky picture of the
anisotropy in hundreds of TeV band. We further find that the amplitude of the
first order anisotropy increases sharply above $\sim100$ TeV, indicating a new
component of the anisotropy. All these results may shed new light on
understanding the origin and propagation of GCRs.",1701.07144v2
2017-02-20,Recovering the mass profile and orbit anisotropy of mock dwarf galaxies with Schwarzschild modelling,"We present a new study concerning the application of the Schwarzschild orbit
superposition method to model spherical galaxies. The method aims to recover
the mass and the orbit anisotropy parameter profiles of the objects using
measurements of positions and line-of-sight velocities usually available for
resolved stellar populations of dwarf galaxies in the Local Group. To test the
reliability of the method, we used different sets of mock data extracted from
four numerical realizations of dark matter haloes. The models shared the same
density profile but differed in anisotropy profiles, covering a wide range of
possibilities, from constant to increasing and decreasing with radius. The
tests were done in two steps, first assuming that the mass profile of the dwarf
is known and employing the method to retrieve the anisotropy only, and then
varying also the mass distribution. We used two kinds of data samples:
unrealistically large ones based on over 270 000 particles from the numerical
realizations and small ones matching the amount of data available for the
Fornax dwarf. For the large data samples we recover both the mass and the
anisotropy profiles with very high accuracy. For the realistically small ones
we also find a reasonably good agreement between the fitted and the input
anisotropies, however the total density profiles can be significantly biased as
a result of their oversensitivity to the available data. Our results therefore
provide convincing evidence in favour of the applicability of the Schwarzschild
method to break the mass-anisotropy degeneracy in dwarf galaxies.",1702.06065v2
2017-04-10,Modeling Magnetic Anisotropy of Single Chain Magnets in $|d/J| \geq 1$ Regime,"Single molecule magnets (SMMs) with single-ion anisotropies $\mathbf d$,
comparable to exchange interactions J, between spins have recently been
synthesized. In this paper, we provide theoretical insights into the magnetism
of such systems. We study spin chains with site spins, s=1, 3/2 and 2 and
on-site anisotropy $\mathbf d$ comparable to the exchange constants between the
spins. We find that large $\mathbf d$ leads to crossing of the states with
different $M_S$ values in the same spin manifold of the $\mathbf d = 0$ limit.
For very large $\mathbf d$'s we also find that the $M_S$ states of the higher
energy spin states descend below the $M_S$ states of the ground state spin
manifold. Total spin in this limit is no longer conserved and describing the
molecular anisotropy by the constants $D_M$ and $E_M$ is not possible. However,
the total spin of the low-lying large $M_S$ states is very nearly an integer
and using this spin value it is possible to construct an effective spin
Hamiltonian and compute the molecular magnetic anisotropy constants $D_M$ and
$E_M$. We report effect of finite sizes, rotations of site anisotropies and
chain dimerization on the effective anisotropy of the spin chains.",1704.02825v2
2017-06-12,Discriminating Local Sources of High-Energy Cosmic Electrons and Positrons by Current and Future Anisotropy Measurements,"The Fermi-LAT detects no significant anisotropy of the cosmic-ray (CR)
electrons and positrons ($e^-+e^+$) with seven years of data, which provides
the strongest restriction to the $e^-+e^+$ anisotropy up to now. As next
generation CR observatory, HERD is expected to have a better capability of
anisotropy detection than Fermi-LAT. In this paper, we discuss several models
aimed to explain the AMS-02 data by the present and future anisotropy
measurements. We find that the upper limits of Fermi-LAT disfavor Vela SNR as
the dominant source in sub-TeV, while other cases that remain safe under the
constraint of Fermi-LAT are expected to be distinguished from each other by
HERD. We then discuss the possibilities of remarkable TeV spectral features,
and test the corresponding anisotropies. We find the conditions under which the
TeV model can have a prominent spectral feature and avoid the constraint of
Fermi-LAT at the same time. Furthermore, the expected performance of HERD is
sensitive enough to detect the anisotropies of all these TeV models, and even
for the case of a featureless TeV spectrum. Thus HERD may play a crucial part
in the study of the origin of cosmic electrons and positrons.",1706.03745v2
2018-06-28,Readout of field induced magnetic anisotropy in a magnetoactive elastomer,"It is shown that in external magnetic fields, a uniaxial magnetic anisotropy
comes into being in a magnetoactive elastomer (MAE). The magnitude of the
induced uniaxial anisotropy grows with the increasing external magnetic field.
The filler particles are immobilized in the matrix if the MAE sample is cooled
below 220 K, where the anisotropy can be read out. The cooling of the sample is
considered as an alternative methodological approach to the experimental
investigation of the magnetized state of MAEs. The appearance of magnetic
anisotropy in MAE is associated with restructuring of the filler during
magnetization, which leads to an additional effective field felt by the
magnetization. It is found that the magnitude of the effective magnetic
anisotropy constant of the MAE is approximately two times larger than its
effective shear modulus in the absence of magnetic field. It is proposed that
the experimentally observed large (about 40) ratio of the magnetic anisotropy
constant of the filler to the shear modulus of the matrix deserves attention
for the explanation of magnetic and magnetoelastic properties of MAEs. It may
lead to additional rigidity of the elastic subsystem increasing the shear
modulus of the composite material through the magnetomechanical coupling.",1806.11014v1
2019-03-10,The decisive role of magnetic anisotropy in honeycomb layered Li$_3$Ni$_2$SbO$_6$ and Na$_3$Ni$_2$SbO$_6$,"The decisive role of magnetic anisotropy even in systems with small
anisotropy is illustrated for the honeycomb-layered antiferromagnets The
decisive role of magnetic anisotropy in honeycomb layered Li$_3$Ni$_2$SbO$_6$
and Na$_3$Ni$_2$SbO$_6$ with $A$ = Li and Na. Both systems evolve long range
magnetic order below $T_{\rm N}$ = 14 and 16.5~K, respectively. The magnetic
phase diagrams obtained from static magnetisation studies up to 15~T imply
competing antiferromagnetic phases and a tricritical point at $T_{\rm N}$. The
phase boundaries are visible in the dynamic response of the antiferromagnetic
resonance modes, too, which investigation by means of high frequency/high field
electron spin resonance enables precise determination of magnetic anisotropy.
The anisotropy gap amounts to $\Delta = 360 \pm 2$~GHz in Na$_3$Ni$_2$SbO$_6$
while in Li$_3$Ni$_2$SbO$_6$ orthorhombicity is associated with $\Delta = 198
\pm 4$ and $218 \pm 4$~GHz. Above $T_{\rm N}$, the data imply short-range
antiferromagnetic order up to at least 80~K. The data suggest a crucial role of
anisotropy for selecting the actual spin structure at $B=0$~T.",1903.04041v1
2019-04-08,Estimating the dark matter velocity anisotropy to the cluster edge,"Dark matter dominates the properties of large cosmological structures such as
galaxy clusters, and the mass profiles of the dark matter have been measured
for these equilibrated structures for years using X-rays, lensing or galaxy
velocities. A new method has been proposed, which should allow us to estimate a
dynamical property of the dark matter, namely the velocity anisotropy. For the
gas a similar velocity anisotropy is zero due to frequent collisions, however,
the collisionless nature of dark matter allows it to be non-trivial. Numerical
simulations have for years found non-zero and radially varying dark matter
velocity anisotropies. Here we employ the method proposed by Hansen and
Pifaretti (2007), and developed by Host et al. (2009) to estimate the dark
matter velocity anisotropy in the bright galaxy cluster Perseus, to near 5
times the radii previously obtained. We find the dark matter velocity
anisotropy to be consistent with the results of numerical simulations, however,
still with large error-bars. At half the virial radius we find the velocity
anisotropy to be non-zero at 1.7 standard deviations, lending support to the
collisionless nature of dark matter.",1904.04260v3
2019-08-09,Magnetic and thermodynamic properties of the octanuclear nickel phosphonate-based cage,"We report a detailed theoretical investigation into the influence of
anisotropy on the magnetic and thermodynamic properties of an octanuclear
nickel phosphonate cage with butterfly-shaped molecular geometry, namely
$\mathrm{Ni}_8(\mu_3-\mathrm{OH})_4(\mathrm{OMe})_2(\mathrm{O}_3\mathrm{PR}_1)_2
(\mathrm{O}_2\mathrm{C}^t\mathrm{Bu})_6
(\mathrm{HO}_2\mathrm{C}^t\mathrm{Bu})_8$. To validate our exact
diagonalization approach, we firstly compare results with simulations and
experiment in the isotropic case. Having established concurrence, we then
introduce uniaxial single-ion anisotropy and Heisenberg exchange anisotropy
between interacted nickel atoms. We then examine effects of both anisotropy
parameters on the magnetization process, as well as on the specific heat of the
model. We predict intermediate magnetization plateaus, including zero plateau,
and magnetization jumps with magnetic ground-state phase transitions at low
temperature $T=1$K. The magnetization plateaus are strongly dependent on both
the levels of exchange anisotropy and single-ion anisotropy. Varying the former
leads to change in width and magnetic position of all intermediate plateaus
while they become wider upon increasing the latter. The specific heat of the
model manifests a Schottky-type maximum at moderate temperature in the presence
of weak magnetic fields, when the system is isotropic. The introducion of
aniostropy results in substantial variations in the thermal behavior of the
specific heat. Indeed, by tuning anisotropy parameters the Schottky peak
convert to a double-peak temperature dependence that coincided with the
magnetization jumps. We call for these theoretical predictions to be verified
experimentally at low temperature.",1908.03614v2
2020-05-30,Re-Examining the Evidence of the Hercules-Corona-Borealis Great Wall,"In the {\Lambda}-CDM paradigm of cosmology, anisotropies larger than 260 Mpc
shouldn't exist. However, the existence of the Hercules-Corona Borealis Great
Wall (HCB) is purported to challenge this principle by some with an estimated
size exceeding 2000 Mpc. Recently, some have challenged the assertion of the
existence of the HCB, attributing the anisotropy to sky exposure effects. It
has never been explained why the original methods purporting the existence of
the HCB produce anisotropies, even if sky-exposure effects are taken into
account. In this paper, I apply the methods of the original papers purporting
the existence of the HCB in various Monte-Carlo simulations that assume
isotropy to analyze the empirical meaning of the significance levels of the
original tests used. I find that, although the statistical tests at first
glance show significant anisotropies present in the suspect sample, Monte-Carlo
simulations can easily reproduce the sample in most cases, and if not, the
differences can be accounted for by other statistical considerations. An
updated sample raises the probability of drawing the observed clustering from
an isotropic sample ten-fold in some cases. Thus the statistical tests used in
prior studies overestimate the significance of the observed anisotropy, and an
updated sample returns even less significant probabilities. Given the ability
to reproduce the observed anisotropy in Monte-Carlo simulations, the new,
higher probabilities of being drawn from isotropy for an updated sample, and
the work of previous papers attributing anisotropies to sky-selection effects,
the existence of the HCB must be treated as doubtful at best.",2006.00141v1
2020-05-30,Magnetization dynamics in proximity-coupled superconductor/ferromagnet/superconductor multilayers,"In this work, magnetization dynamics is studied in
superconductor/ferromagnet/superconductor three-layered films in a wide
frequency, field, and temperature ranges using the broad-band ferromagnetic
resonance measurement technique. It is shown that in presence of both
superconducting layers and of superconducting proximity at both
superconductor/ferromagnet interfaces a massive shift of the ferromagnetic
resonance to higher frequencies emerges. The phenomenon is robust and
essentially long-range: it has been observed for a set of samples with the
thickness of ferromagnetic layer in the range from tens up to hundreds of
nanometers. The resonance frequency shift is characterized by proximity-induced
magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the
drop of magnetization. The shift and the corresponding uniaxial anisotropy grow
with the thickness of the ferromagnetic layer. For instance, the anisotropy
reaches 0.27~T in experiment for a sample with 350~nm thick ferromagnetic
layer, and about 0.4~T in predictions, which makes it a ferromagnetic film
structure with the highest anisotropy and the highest natural resonance
frequency ever reported. Various scenarios for the superconductivity-induced
magnetic anisotropy are discussed. As a result, the origin of the phenomenon
remains unclear. Application of the proximity-induced anisotropies in
superconducting magnonics is proposed as a way for manipulations with a
spin-wave spectrum.",2006.00348v1
2020-06-10,Dynamical masses of brightest cluster galaxies I: stellar velocity anisotropy and mass-to-light ratios,"We investigate the stellar and dynamical mass profiles in the centres of 25
brightest cluster galaxies (BCGs) at redshifts of 0.05 $\leq z \leq$ 0.30. Our
spectroscopy enables us to robustly measure the Gauss-Hermite higher order
velocity moments $h_{3}$ and $h_{4}$, which we compare to measurements for
massive early-type galaxies, and central group galaxies. We measure positive
central values for $h_{4}$ for all the BCGs. We derive the stellar
mass-to-light ratio ($\Upsilon_{\star \rm DYN}$), and velocity anisotropy
($\beta$) based on a Multi-Gaussian Expansion (MGE) and axisymmetric Jeans
Anisotropic Methods (JAM, cylindrically- and spherically-aligned). We
explicitly include a dark matter halo mass component, which is constrained by
weak gravitational lensing measurements for these clusters. We find a strong
correlation between anisotropy and velocity dispersion profile slope, with
rising velocity dispersion profiles corresponding to tangential anisotropy and
decreasing velocity dispersion profiles corresponding to radial anisotropy. The
rising velocity dispersion profiles can also indicate a significant
contribution from the intracluster light (ICL) to the total light (in
projection) in the centre of the galaxy. For a small number of BCGs with rising
velocity dispersion profiles, a variable stellar mass-to-light ratio can also
account for the profile shape, instead of tangential anisotropy or a
significant ICL contribution. We note that, for some BCGs, a variable
$\beta_{z}(r)$ (from radial to tangential anisotropy) can improve the model fit
to the observed kinematic profiles. The observed diversity in these properties
illustrates that BCGs are not the homogeneous class of objects they are often
assumed to be.",2006.05706v1
2020-09-22,Numerical equilibria with pressure anisotropy and incompressible plasma rotation parallel to the magnetic field,"It is believed that plasma rotation can affect the transitions to the
advanced confinement regimes in tokamaks. In addition, in order to achieve
fusion temperatures modern tokamaks rely on auxiliary heating methods. These
methods generate pressure anisotropy in the plasma. For incompressible rotation
with pressure anisotropy the equilibrium is governed by a Generalized
Grad-Shafranov (GGS) equation and a decoupled Bernoulli-type equation for the
effective pressure, $\bar{p}=(p_\parallel+p_\perp)/2$, where $p_\parallel$
($p_\perp$) is the pressure tensor element parallel (perpendicular) to the
magnetic field. In the case of plasma rotation parallel to the magnetic field
the GGS equation can be transformed to one equation identical in form with the
GS equation. In this study by making use of the aforementioned property of the
GGS equation for parallel plasma rotation we have constructed ITER-like
numerical equilibria by extending HELENA, an equilibrium fixed-boundary solver
and examined the impact of rotation and anisotropy on certain equilibrium
quantities. The main conclusions are that the addition of pressure anisotropy
to rotation allows the profile shaping of the equilibrium quantities in much
more extent thus favouring the confinement and allows extension of the
parametric space of the Mach number corresponding to higher values.
Furthermore, the impact of pressure anisotropy in the equilibrium quantities is
stronger than that of the rotation, for most of the quantities examined. For
the pressure components the impact of the pressure anisotropy is the same
regardless of whether the power is deposited parallel or perpendicular to the
magnetic surfaces, thus implying that there is no preferable heating direction,
while for the current density, the heating parallel to the magnetic surfaces
seems to be beneficial for the current-gradient driven instabilities.",2009.10422v1
2020-10-19,From high $p_\perp$ theory and data to inferring anisotropy of Quark-Gluon Plasma,"High $p_\perp$ theory and data are commonly used to study high $p_\perp$
parton interactions with QGP, while low $p_\perp$ data and corresponding models
are employed to infer QGP bulk properties. On the other hand, with a proper
description of high $p_\perp$ parton-medium interactions, high $p_\perp$ probes
become also powerful tomography tools, since they are sensitive to global QGP
features, such as different temperature profiles or initial conditions. This
tomographic role of high $p_\perp$ probes can be utilized to assess the spatial
anisotropy of the QCD matter. With our dynamical energy loss formalism, we show
that a (modified) ratio of $R_{AA}$ and $v_2$ presents a reliable and robust
observable for straightforward extraction of initial state anisotropy. We
analytically estimated the proportionality between the $v_2/(1-R_{AA})$ and
anisotropy coefficient $\epsilon_{2L}$, and found surprisingly good agreement
with full-fledged numerical calculations. Within the current error bars, the
extraction of the anisotropy from the existing data using this approach is
still inaccessible. However, with the expected accuracy improvement in the
upcoming LHC runs, the anisotropy of the QGP formed in heavy ion collisions can
be straightforwardly derived from the data. Such a data-based anisotropy
parameter would present an important test to models describing the initial
stages of heavy-ion collision and formation of QGP, and demonstrate the
usefulness of high $p_\perp$ theory and data in obtaining QGP properties.",2010.09773v1
2020-11-02,The chain length of anisotropic paramagnetic particles in a rotating field,"In this article, the maximal length of a chain of paramagnetic particles with
magnetic anisotropy in a rotating magnetic field is studied. The theory of
paramagnetic particle chains usually assumes that the particles are
magnetically isotropic and do not rotate in a rotating field. In experiments it
is seen that spherical paramagnetic particles rotate, which can be explained by
small magnetic anisotropy. In this article, the maximal chain length is
calculated for paramagnetic particles with magnetic anisotropy in a rotating
magnetic field. Results show that the maximal chain length as a function of
field frequency has the same trend for isotropic magnetic particles and
particles with magnetic anisotropy if the field frequency is much higher or
much lower than the critical frequency of an individual particle. blue
Initially randomly distributed particles will form chains that will collide and
exchange with particles till they obtain a typical chain length. The typical
chain length of a small cluster is shorter than the maximal chain length of an
isolated chain for the same field frequency. The distribution of chain lengths
in a small cluster of chains is narrower for particles with higher magnetic
anisotropy. Due to the narrower distribution of chain lengths, particles with
magnetic anisotropy can suit better for mass-production. This article will show
how magnetic anisotropy parameters of paramagnetic particles influence chain
length of chains which form in a rotating magnetic field.",2011.01003v2
2020-12-23,Small-scale CMB anisotropies induced by the primordial magnetic fields,"The primordial magnetic fields (PMFs) produced in the early universe are
expected to be the origin of the large-scale cosmic magnetic fields. The PMFs
are considered to leave a footprint on the cosmic microwave background (CMB)
anisotropies due to both the electromagnetic force and gravitational
interaction. In this paper, we investigate how the PMFs affect the CMB
anisotropies on smaller scales than the mean-free-path of the CMB photons. We
solve the baryon Euler equation with Lorentz force due to the PMFs, and we show
that the vector-type perturbations from the PMFs induce the CMB anisotropies
below the Silk scale as $\ell>3000$. Based on our calculations, we put a
constraint on the PMFs from the combined CMB temperature anisotropies obtained
by Planck and South Pole Telescope (SPT). We have found that the
highly-resolved temperature anisotropies of the SPT 2017 bandpowers at $\ell
\lesssim 8000$ favor the PMF model with a small scale-dependence. As a result,
the Planck and SPT's joint-analysis puts a constraint on the PMF spectral index
as $n_B<-1.14$ at 95% confidence level (C.L.), and this is more stringent
compared with the Planck-only constraint $n_B<-0.28$. We show that the PMF
strength normalized on the co-moving 1 Mpc scale is also tightly constrained as
$B_{1\mathrm{Mpc}}<1.5$ nG with Planck and SPT at 95% C.L., while
$B_{1\mathrm{Mpc}}<3.2$ nG only with the Planck data at 95% C.L. We also
discuss the effects on the cosmological parameter estimate when including the
SPT data and CMB anisotropies induced by the PMFs.",2012.12542v2
2021-10-01,Statistically study the optimal local sources for cosmic ray nuclei and electron,"The local sources, such as Geminga SNR, may play important role for the
anomaly of proton, electron and anisotropy in the past works. In fact, there
exists twelve SNRs around solar system within $1$ kpc. One question is that can
other SNRs also possibly contribute the spectra of nuclei and electron and
explain the special structure of anisotropy? In this work, under the
spatial-dependent propagation, we systematically study the contribution of all
local SNRs within 1 kpc around solar to the spectra of nuclei and electron, as
well as the energy dependence of anisotropy. As a result, only Geminga,
Monogem, and Vela SNRs have quantitive contribution to the nuclei and electron
spectra and anisotropy. Here, Geminga SNR is the sole optimal candidate and
Monogem SNR is controversial due to the tension of anisotropy between model
calculation and observations. The Vela SNR contributes a new spectral structure
beyond TeV energy, hinted by HESS, VERITAS, DAMPE and CALET measurements. More
interesting is that the electron anisotropy satisfies the Fermi-LAT limit below
TeV energy, but rises greatly and reaches $10\%$ at several TeV. This new
structure will shed new light to check our model. We hope that the new
structure of electron spectrum and anisotropy can be observed by space-borne
DAMPE and HERD and ground-based HAWC and LHAASO experiments in the near future.",2110.00501v2
2021-12-02,Anisotropy of phase transition gravitational wave and its implication for primordial seeds of the Universe,"We quantitatively study how the primordial density fluctuations are imprinted
on the anisotropy of the phase transition gravitational wave (PTGW). Generated
long before recombination and free from Silk damping, the anisotropic PTGW
might reveal the density perturbation seeded from inflation or alternatives. We
find new behaviors of the PTGW anisotropy power spectrum. The PTGW anisotropy
is stronger than the anisotropy of the cosmic microwave background temperature
at all scales, and the high-$\ell$ multiples are enhanced about 1 order due to
the early integrated Sachs-Wolfe effect. Furthermore, differences in primordial
power spectra at small scales manifest themselves more significantly on the
angular power spectrum of PTGW anisotropy compared to that of the cosmic
microwave background. These properties might provide a novel clue to
understanding the primordial density perturbation of our early Universe and
thereby complete our understanding of inflation theory. Taking nanohertz PTGW
from dark matter models as a typical example, we obtain amplitudes of PTGW
anisotropy which are about 4 or 3 orders weaker than the isotropic PTGW energy
spectra.",2112.01409v4
2022-01-17,Understanding the phase reversals of Galactic cosmic ray anisotropies,"The energy spectra and anisotropies are very important probes of the origin
of cosmic rays. Recent measurements show that complicated but very interesting
structures exist, at similar energies, in both the spectra and energy-dependent
anisotropies, indicating a common origin of these structures. Particularly
interesting phenomenon is that there is a reversal of the phase of the dipole
anisotropies, which challenges a theoretical modeling. In this work, for the
first time, we identify that there might be an additional phase reversal at
$\sim 100$ GeV energies of the dipole anisotropies as indicated by a few
underground muon detectors and the first direct measurement by the Fermi
satellite, coincident with the hundreds of GV hardenings of the spectra. We
propose that these two phase reversals, together with the energy-evolution of
the amplitudes and spectra, can be naturally explained with a nearby source
overlapping onto the diffuse background. As a consequence, the spectra and
anisotropies can be understood as the scalar and vector components of this
model, and the two reversals of the phases characterize just the competition of
the cosmic ray streamings between the nearby source and the background. The
alignment of the cosmic ray streamings along the local large-scale magnetic
field may play an important but sub-dominant role in regulating the cosmic ray
propagation. More precise measurements of the anisotropy evolution at both low
energies by space detectors and high energies by air shower experiments for
individual species will be essential to further test this scenario.",2201.06234v2
2022-02-15,Investigation of the magnetoelastic coupling anisotropy in the Kitaev material $α$-RuCl$_3$,"The Kitaev material $\alpha$-RuCl$_3$ is among the most prominent candidates
to host a quantum spin-liquid state endowed with fractionalized excitations.
Recent experimental and theoretical investigations have separately revealed the
importance of both the magnetoelastic coupling and the magnetic anisotropy, in
dependence of the applied magnetic field direction. In this combined
theoretical and experimental research, we investigate the anisotropic magnetic
and magnetoelastic properties for magnetic fields applied along the main
crystallographic axes as well as for fields canted out of the honeycomb plane.
We found that the magnetostriction anisotropy is unusually large compared to
the anisotropy of the magnetization, which is related to the strong
magnetoelastic $\widetilde{\Gamma'}$-type coupling in our \textit{ab-initio}
derived model. We observed large, non-symmetric magnetic anisotropy for
magnetic fields canted out of the honeycomb $ab$-plane in opposite directions,
namely towards the $+c^*$ or $-c^*$ axes, respectively. The observed
directional anisotropy is explained by considering the relative orientation of
the magnetic field with respect to the co-aligned RuCl$_6$ octahedra.
Magnetostriction measurements in canted fields support this non-symmetric
magnetic anisotropy, however these experiments are affected by magnetic torque
effects. Comparison of theoretical predictions with experimental findings allow
us to recognize the significant contribution of torque effects in experimental
setups where $\alpha$-RuCl$_3$ is placed in canted magnetic fields.",2202.07102v1
2022-04-07,Orientation Controlled Anisotropy in Single Crystals of Quasi-1D BaTiS3,"Low-dimensional materials with chain-like (one-dimensional) or layered
(twodimensional) structures are of significant interest due to their
anisotropic electrical, optical, thermal properties. One material with
chain-like structure, BaTiS3 (BTS), was recently shown to possess giant
in-plane optical anisotropy and glass-like thermal conductivity. To understand
the origin of these effects, it is necessary to fully characterize the optical,
thermal, and electronic anisotropy of BTS. To this end, BTS crystals with
different orientations (aand c-axis orientations) were grown by chemical vapor
transport. X-ray absorption spectroscopy (XAS) was used to characterize the
local structure and electronic anisotropy of BTS. Fourier transform infrared
(FTIR) reflection/transmission spectra show a large inplane optical anisotropy
in the a-oriented crystals, while the c-axis oriented crystals were nearly
isotropic in-plane. BTS platelet crystals are promising uniaxial materials for
IR optics with their optic axis parallel to the c-axis. The thermal
conductivity measurements revealed a thermal anisotropy of ~4.5 between the c-
and a-axis. Time-domain Brillouin scattering showed that the longitudinal sound
speed along the two axes is nearly the same suggesting that the thermal
anisotropy is a result of different phonon scattering rates.",2204.03680v1
2022-08-22,Monte Carlo study of the phase transitions in the classical XY ferromagnets with random anisotropy,"The three-dimensional anisotropic classical XY ferromagnet has been
investigated by extensive Monte Carlo simulation using the Metropolis single
spin flip algorithm. The magnetization ($M$) and the susceptibility ($\chi$)
are measured and studied as functions of the temperature of the system. For
constant anisotropy, the ferro-para phase transition has been found to take
place at a higher temperature than that observed in the isotropic case. The
system gets ordered at higher temperatures for higher values of the strength of
anisotropy. The opposite scenario is observed in the case of random anisotropy.
For all three different kinds of statistical distributions (uniform, Gaussian,
and bimodal) of random anisotropy, the system gets ordered at lower
temperatures for higher values of the width of the distribution of anisotropy.
We have provided the phase boundaries in the case of random anisotropy. The
critical exponents for the scaling laws $M \sim L^{-{{\beta} \over {\nu}}}$ and
$\chi \sim L^{{{\gamma} \over {\nu}}} $ are estimated through the finite size
analysis.",2208.10109v8
2022-09-01,Towards Morphologically Induced Anisotropy in Thermally Hysteretic Dielectric Properties of Vanadium Dioxide,"The Bruggeman homogenization formalism was used to numerically investigate
the dielectric properties of a columnar thin film (CTF) made from vanadium
dioxide. For visible and near-infrared wavelengths, the CTF is
electromagnetically equivalent to a homogeneous orthorhombic material. Over the
58 deg C -- 72 deg C temperature range, the eigenvalues of the CTF's relative
permittivity dyadic are highly sensitive to temperature, and vary according to
whether the CTF is being heated or cooled. The anisotropy revealed through the
eigenvalues, and the anisotropy of the associated hysteresis, were investigated
in relation to temperature for CTFs of different porosities and columnar cross
sections. When the free-space wavelength is 800 nm, the CTF is a dissipative
dielectric material that exhibits temperature-dependent anisotropy and
anisotropic hysteresis. In contrast, when the free-space wavelength is 1550 nm,
the CTF can be either a dissipative dielectric material, a hyperbolic material
or a metal-like material, depending on the temperature and the porosity of the
CTF. As the porosity of the CTF decreases from 0.55 to 0.3, the anisotropy of
the CTF becomes more pronounced, as does the anisotropy of the hysteresis. Only
relatively modest variations in anisotropy and hysteresis arise in response to
varying the columnar cross-sectional shape, as compared to the variations
induced by varying the porosity.",2209.00492v1
2023-01-22,FCC structured ferromagnetic ultra-thin films with two spin layers described by fourth order perturbed Heisenberg Hamiltonian,"Fourth order perturbation was applied to study a small variation of the
azimuthal angle of spin of fcc structured ferromagnetic thin films with two
spin layers. The variation of magnetic energy and the orientation of magnetic
easy axis with the fourth order magnetic anisotropy constant in two spin layers
was investigated. When the second order magnetic anisotropy constant at the top
spin layer is higher than that of bottom spin layer, the total magnetic energy
is slightly higher. Some spikes appeared in the 2D plot of of magnetic energy
versus azimuthal angle of spin. According to the 3D plots, the peak value of
the magnetic energy gradually decreases with the increase of the stress induced
anisotropy constant, and thereafter the peak value of the magnetic energy
gradually increases with the increase of the stress induced anisotropy
constant. The angle between magnetic easy and hard directions was not 90
degrees. The magnetic easy and hard directions of the film with a higher second
order magnetic anisotropy constant of top layer are different from the magnetic
easy and hard directions of the film with a lower second order magnetic
anisotropy constant of top layer. When the second order magnetic anisotropy
constant of the bottom layer is increased, the total magnetic energy does not
change.",2301.09137v1
2023-10-11,Flux gradient relations and their dependence on turbulence anisotropy,"Monin-Obukhov similarity theory (MOST) is used in virtually every Earth
System Model (ESM) to parameterize the near-surface turbulent exchanges,
however there is high uncertainty in the literature about the appropriate
parameterizations to be used. In addition, MOST has limitations in very stable
and unstable regimes, over heterogeneous terrain and complex orography, and has
been found to incorrectly represent the surface fluxes. A new approach
including turbulence anisotropy as a scaling parameter has recently been
developed, allowing to overcome these limitations and generalize the
flux-variance relations to complex terrain. In this paper we analyze the
flux-gradient relations for five well known datasets. The scaling relations
show substantial scatter and highlight the uncertainty in the choice of
parameterization even over canonical conditions. We show that by including
information on turbulence anisotropy as an additional scaling parameter, the
original scatter becomes well bounded and new formulations can be developed,
that drastically improve the accuracy of the flux-gradient relations for wind
shear ($\phi_M$) in unstable conditions, and for temperature gradient
($\phi_H$) both in unstable and stable regime. This analysis shows that both
$\phi_M$ and $\phi_H$ are strongly dependent on turbulence anisotropy and
allows to finally settle the longly discussed free convection regime for
$\phi_M$, which clearly exhibits a $-{1/3}$ power law when anisotropy is
accounted for. Furthermore we show that the eddy diffusivities for momentum and
heat and the turbulent Prandtl number are strongly dependent on anisotropy and
that the latter goes to zero in the free convection limit. These results
highlight the necessity to include anisotropy in the study of near surface
atmospheric turbulence and lead the way for theoretically more robust
simulations of the boundary layer over complex terrain.",2310.07503v1
2023-12-01,Hydrogen-induced switching of perpendicular magnetic anisotropy in amorphous ferrimagnetic thin films,"Unraveling the mechanisms responsible for perpendicular magnetic anisotropy
(PMA) in amorphous rare earth-transition metal alloys has proven challenging,
primarily due to the intrinsic complexity of the amorphous structure. Here, we
investigated the atomic origin of PMA by applying an approach of voltage-driven
hydrogen insertion in interstitial sites, which serve as a perturbation and
probe in local atomic structure. After hydrogen charging, PMA in amorphous TbCo
thin films diminished and switched to in-plane anisotropy, accompanied by
distinct magnetic domain structures. By analyzing the mechanism behind the
anisotropy switching, we unveiled the decisive role of Tb-Co/Tb-Tb bonding in
shaping the magnetic anisotropy using both angle-dependent X-ray magnetic
dichroism and ab initio calculations. Hydrogen insertion induced a
reorientation of the local anisotropy axis, initially along the Tb-Co bonding
direction, due to the distortion of crystal field around Tb. Our approach not
only shows the atomic origin of Tb-Co bonding in inducing PMA, but also enables
the voltage-driven tailoring of magnetic anisotropy in amorphous alloys.",2312.00643v1
2024-02-27,Measuring kinematic anisotropies with pulsar timing arrays,"Recent Pulsar Timing Array (PTA) collaborations show strong evidence for a
stochastic gravitational wave background (SGWB) with the characteristic
Hellings-Downs inter-pulsar correlations. The signal may stem from supermassive
black hole binary mergers, or early universe phenomena. The former is expected
to be strongly anisotropic while primordial backgrounds are likely to be
predominantly isotropic with small fluctuations. In case the observed SGWB is
of cosmological origin, our relative motion with respect to the SGWB rest frame
is a guaranteed source of anisotropy, leading to $\mathcal{O}(10^{-3})$ energy
density fluctuations of the SGWB. These kinematic anisotropies are likely to be
larger than the intrinsic anisotropies, akin to the cosmic microwave background
(CMB) dipole anisotropy. We assess the sensitivity of current PTA data to the
kinematic dipole anisotropy and also provide forecasts with which the magnitude
and direction of the kinematic dipole may be measured in the future with an
SKA-like experiment. We also discuss how the spectral shape of the SGWB and the
location of pulsar observed affects the prospects of detecting the kinematic
dipole with PTA. A detection of this anisotropy may even help resolve the
discrepancy in the magnitude of the kinematic dipole as measured by CMB and
large-scale structure observations.",2402.17312v1
2010-05-03,Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films,"We present a detailed study on the magnetic properties, including anisotropy,
reversal fields, and magnetization reversal processes, of well characterized
half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3
(STO) substrates with three different surface orientations, i.e. (001), (110)
and (1-18). The latter shows step edges oriented parallel to the [110]
(in-plane) crystallographic direction. Room temperature high resolution
vectorial Kerr magnetometry measurements have been performed at different
applied magnetic field directions in the whole angular range. In general, the
magnetic properties of the LSMO films can be interpreted with just the uniaxial
term with the anisotropy axis given by the film morphology, whereas the
strength of this anisotropy depends on both structure and film thickness. In
particular, LSMO films grown on nominally flat (110)-oriented STO substrates
presents a well defined uniaxial anisotropy originated from the existence of
elongated in-plane [001]-oriented structures, whereas LSMO films grown on
nominally flat (001)-oriented STO substrates show a weak uniaxial magnetic
anisotropy with the easy axis direction aligned parallel to residual substrate
step edges. Elongated structures are also found for LSMO films grown on vicinal
STO(001) substrates. These films present a well-defined uniaxial magnetic
anisotropy with the easy axis lying along the step edges and its strength
increases with the LSMO thickness. It is remarkable that this step-induced
uniaxial anisotropy has been found for LSMO films up to 120 nm thickness. Our
results are promising for engineering novel half-metallic magnetic devices that
exploit tailored magnetic anisotropy.",1005.0553v3
2017-06-02,Small-scale anisotropy induced by spectral forcing and by rotation in non-helical and helical turbulence,"We study the effect of large-scale spectral forcing on the scale-dependent
anisotropy of the velocity field in direct numerical simulations of homogeneous
incompressible turbulence. Two forcing methods are considered: the steady ABC
single wavenumber scheme and the unsteady non-helical or helical Euler scheme.
The results are also compared with high resolution data obtained with the
negative viscosity scheme. A fine-grained characterization of anisotropy,
consisting in measuring some quantities related to the two-point velocity
correlations, is used: we perform a modal decomposition of the spectral
velocity tensor into energy, helicity and polarization spectra. Moreover, we
include the explicit dependence of these three spectra on the wavevector
direction. The conditions that allow anisotropy to develop in the small scales
due to forcing alone are clearly identified. It is shown that, in turbulent
flows expected to be isotropic, the ABC forcing yields significant energy and
helicity directional anisotropy down to the smallest resolved scales, like the
helical Euler scheme when an unfavourable forcing scale is used. The
direction-and scale-dependent anisotropy is then studied in rotating
turbulence. It is first shown that, in the ABC-forced simulations the slope of
the energy spectrum is altered and the level of anisotropy is similar to that
obtained at lower Rossby number in Euler-forced runs, a result due both to the
nature of the forcing itself and to the fact that it allows an inverse cascade
to develop. Second, we show that, even at low rotation rate, the natural
anisotropy induced by the Coriolis force is visible at all scales. Finally, we
identify two different wavenumber ranges in which anisotropy behaves
differently, and show that if the Rossby number is not too low the
characteristic lenghscale separating them is the one at which rotation and
dissipation effects balance.",1706.00651v1
2022-10-07,Giant and tunable excitonic optical anisotropy in single-crystal CsPbX$_3$ halide perovskites,"During the last years, giant optical anisotropy demonstrated its paramount
importance for light manipulation which resulted in numerous applications
ranging from subdiffraction light guiding to switchable nanolasers. In spite of
recent advances in the field, achieving continuous tunability of optical
anisotropy remains an outstanding challenge. Here, we present a solution to the
problem through chemical alteration of the ratio of halogen atoms (X = Br or
Cl) in single-crystal CsPbX$_3$ halide perovskites. It turns out that the
anisotropy originates from an excitonic resonance in the perovskite, which
spectral position and strength are determined by the halogens composition. As a
result, we manage to continually modify the optical anisotropy by 0.14. We also
discover that the halide perovskite can demonstrate optical anisotropy up to
0.6 in the visible range -- the largest value among non-van der Waals
materials. Moreover, our results reveal that this anisotropy could be in-plane
and out-of-plane, depending on perovskite shape -- rectangular and square.
Hence, it can serve as an additional degree of freedom for anisotropy
manipulation. As a practical demonstration, we created perovskite anisotropic
nanowaveguides and show a significant impact of anisotropy on high-order
guiding modes. These findings pave the way for halide perovskites as a
next-generation platform for tunable anisotropic photonics.",2210.03541v1
1994-11-01,Toward Understanding CMB Anisotropies and Their Implications,"Working toward a model independent understanding of cosmic microwave
background (CMB) anisotropies and their significance, we undertake a
comprehensive and self-contained study of scalar perturbation theory. Initial
conditions, evolution, thermal history, matter content, background dynamics,
and geometry all play a role in determining the anisotropy. By employing {\it
analytic} techniques to illuminate the numerical results, we are able to
separate and identify each contribution. We thus bring out the nature of the
{\it total} Sachs-Wolfe effect, acoustic oscillations, diffusion damping,
Doppler shifts, and reionization, as well as their particular manifestation in
a critical, curvature, or cosmological constant dominated universe. By studying
the full angular {\it and} spatial content of the resultant anisotropies, we
isolate the signature of these effects from the dependence on initial
conditions. Whereas structure in the Sachs-Wolfe anisotropy depends strongly on
the underlying power spectra, the acoustic oscillations provide features which
are nearly model independent. This may allow for future determination of the
matter content of the universe as well as the adiabatic and/or isocurvature
nature of the initial fluctuations.",9411008v1
1995-01-17,The Imprint of Proper Motion of Nonlinear Structures on the Cosmic Microwave Background,"We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in an $\Omega=1$, Cold Dark Matter (CDM) model
universe. Temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from the beginning of decoupling until the
present epoch. The underlying density field produced by the inhomogeneities is
followed from the linear, through the weakly clustered, into the fully
nonlinear regime. We concentrate on CMB temperature distortions arising from
variations in the gravitational potentials of nonlinear structures. We find two
sources of temperature fluctuations produced by time-varying potentials: (1)
anisotropies due to intrinsic changes in the gravitational potentials of the
inhomogeneities and (2) anisotropies generated by the peculiar, bulk motion of
the structures across the microwave sky. Both effects generate CMB anisotropies
in the range of $10^{-7} \siml \Delta T/T \siml 10^{-6}$ on scales of $ \sim
1^{\circ}$. For isolated structures, anisotropies due to proper motion exhibit
a dipole-like signature in the CMB sky that in principle could yield
information on the transverse velocity of the structures.",9501059v1
1995-10-24,Anisotropy and inhomogeneity of the universe from $ΔT/T$,"A recent paper (Martinez--Gonzalez & Sanz 1995) showed that if the universe
is homogeneous but anisotropic, then the small quadrupole anisotropy in the
cosmic microwave background radiation implies that the spacetime anisotropy is
very small. We point out that more general results may be established, without
assuming a priori homogeneity. We have proved that small anisotropies in the
microwave background imply that the universe is almost
Friedmann--Robertson--Walker. Furthermore, the quadrupole and octopole place
direct and explicit limits on the degree of anisotropy and inhomogeneity, as
measured by the shear, vorticity, Weyl tensor and density gradients. In the
presence of inhomogeneity, it is only possible to set a much weaker limit on
the shear than that given by Martinez--Gonzalez & Sanz.",9510126v1
1996-03-22,Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy,"We estimate the level of confusion to Cosmic Microwave Background anisotropy
measurements caused by extragalactic infrared sources. CMB anisotropy
observations at high resolution and high frequencies are especially sensitive
to this foreground. We use data from the COBE satellite to generate a Galactic
emission spectrum covering mm and sub-mm wavelengths. Using this spectrum as a
template, we predict the microwave emission of the 5319 brightest infrared
galaxies seen by IRAS. We simulate skymaps over the relevant range of
frequencies (30-900 GHz) and instrument resolutions (10'-10 degrees Full Width
Half Max). Analysis of the temperature anisotropy of these skymaps shows that a
reasonable observational window is available for CMB anisotropy measurements.",9603121v2
1996-09-21,CMB anisotropy at degree angular scales and the thermal history of the Universe,"We study the anisotropy of the cosmic microwave background (CMB) in cold and
mixed dark matter (CDM and MDM) models, with non scale-invariant primordial
power spectra (i.e. $n \neq 1$) and a late, sudden reionization of the
intergalactic medium at redshift $z_{rh}$. We test these models against recent
detections of CMB anisotropy at large and intermediate angular scales. We find
that current CMB anisotropy measurements cannot discriminate between CDM and
MDM models. Our likelihood analysis indicates that models with blue power
spectra ($n \simeq 1.2$) and a reionization at $z_{rh} \sim 20$ are most
consistent with the anisotropy data considered here. Without reionization our
analysis gives $1.0 \le n \le 1.26$ (95 % C.L.) for $\Omega_b = 0.05$.",9609154v1
1996-10-29,Anisotropies in the Cosmic Microwave Background: Theoretical Foundations,"The analysis of anisotropies in the cosmic microwave background (CMB) has
become an extremely valuable tool for cosmology. We even have hopes that
planned CMB anisotropy experiments may revolutionize cosmology. Together with
determinations of the CMB spectrum, they represent the first cosmological
precision measurements. This is illustrated in the talk by Anthony Lasenby. The
value of CMB anisotropies lies to a big part in the simplicity of the
theoretical analysis. Fluctuations in the CMB can be determined almost fully
within linear cosmological perturbations theory and are not severely influenced
by complicated nonlinear physics. In this contribution the different physical
processes causing or influencing anisotropies in the CMB are discussed. The
geometry perturbations at and after last scattering, the acoustic oscillations
in the baryon-photon-plasma prior to recombination, and the diffusion damping
during the process of recombination. The perturbations due to the fluctuating
gravitational field, the so called Sachs-Wolfe contribution, is described in a
very general form using the Weyl tensor of the perturbed geometry.",9610234v1
1996-12-19,The Power Spectrum of Microwave Background Temperature Anisotropies Measured by the Tenerife Experiment,"We determine the slope of the power spectrum of the matter perturbations from
the Tenerife observations of the cosmic background radiation temperature
anisotropies. We compute the projected radiation anisotropy power spectrum
measured by this experiment and study its dependence with respect to the slope
of the temperature anisotropy spectrum on the sky. We show that Tenerife alone
implies the upper bound on the spectral index of $m \le 3$. Stronger
conclusions can not be reached due to the small data set. The method proposed
can be applied to any small scale experiment. Sampling the same region of the
skywith different window functions could probe the slope of the radiation
anisotropy power spectrum at different scales and confirm the presence of
Doppler peaks.",9612195v1
1997-03-29,Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions. III. Multi-Mass Clusters,"The evolution of globular clusters driven by two-body relaxation is
investigated by means of numerical integration of the two-dimensional
Fokker-Planck equation in energy--angular momentum space. The two- dimensional
Fokker-Planck equation allows the development of velocity anisotropy. We
include a spectrum of stellar masses in this paper. The radial anisotropy
develops, that is, the radial velocity dispersion exceeds the tangential one,
in the outer halo of multi-mass clusters as in single-mass clusters. However,
the evolution of the velocity anisotropy depends significantly on the stellar
mass in some cases. In fact the tangential velocity dispersion becomes dominant
around the half-mass radius for massive components in clusters with a steep
mass function. The development of this tangential anisotropy is closely related
to the initial cooling of the massive components toward energy equipartition.
Our simulation results indicate that multi-mass anisotropic King-Michie models
are not always appropriate for describing the velocity anisotropy in globular
clusters.",9703190v1
1997-04-16,CMB Anisotropy Induced by Cosmic Strings on Angular Scales $>~ 15'$,"We have computed an estimate of the angular power spectrum of the Cosmic
Microwave Background (CMB) induced by cosmic strings on angular scales $>~
15'$, using a numerical simulation of a cosmic string network; and decomposed
this pattern into scalar, vector, and tensor parts. We find no evidence for
strong acoustic oscillations in the scalar anisotropy but rather a broad peak.
The anisotropies from vector modes dominate except on very small angular scales
while the tensor anisotropies are sub-dominant on all angular scales. The
anisotropies generated after recombination are even more important than in
adiabatic models. We expect that these qualitative features are robust to the
varying of cosmological parameters, a study which has not yet been done.",9704160v1
1997-09-18,Secondary gravitational anisotropies in open universes,"The applicability of the potential approximation in the case of open
universes is tested. Great Attractor-like structures are considered in the
test. Previous estimates of the Cosmic Microwave background anisotropies
produced by these structures are analyzed and interpreted. The anisotropies
corresponding to inhomogeneous ellipsoidal models are also computed. It is
proved that, whatever the spatial symmetry may be, Great Attractor-like objects
with extended cores (radius $\sim 10h^{-1}$),located at redshift $z=5.9$ in an
open universe with density parameter $\Omega_{0}=0.2$, produce secondary
gravitational anisotropies of the order of $10^{-5}$ on angular scales of a few
degrees. This anisotropy appears to be an integrated effect along the photon
geodesics. Its angular scale is much greater than that subtended by the Great
Attractor itself. This is understood taking into account that the integrated
effect is produced by the variations of the gravitational potential, which seem
to be important in large regions subtending angular scales of various degrees.
As a result of the large size of these regions, the spatial curvature of the
universe becomes important and, consequently, significant errors ($\sim 30$ per
cent) arise in estimations based on the potential approximation.",9709181v1
1997-12-11,Effect of Void Network on CMB Anisotropy,"We study the effect of a void network on the CMB anisotropy in the
Einstein-de Sitter background using Thompson &Vishniac's model. We consider
comprehensively the Sacks-Wolfe effect, the Rees-Sciama effect and the
gravitational lensing effect. Our analysis includes the model of primordial
voids existing at recombination, which is realized in some inflationary models
associated with a first-order phase transition. If there exist primordial voids
whose comoving radius is larger than $\sim10h^{-1}$Mpc at recombination, not
only the Sachs-Wolfe effect but also the Rees-Sciama effect is appreciable even
for multipoles $l\lsim1000$ of the anisotropy spectrum. The gravitational
lensing effect, on the other hand, slightly smoothes the primary anisotropy;
quantitatively, our results for the void model are similar to the previous
results for a CDM model. All the effects, together, would give some constraints
on the configuration or origin of voids with high-resolution data of the CMB
anisotropy.",9712153v2
1998-02-09,A Vishniac type contribution to the polarisation of the CMBR?,"Radiation which has a quadrupole component of anisotropy, can get polarized
by Thomson scattering from charged particles. In the cosmological context, the
microwave background photons develop significant quadrupole anisotropy as they
free stream away from the the epoch of standard recombination. Reionization in
the post recombination era can provide free electrons to Thomson scatter the
incident anisotropic $CMBR$ photons. We compute the resulting polarisation
anisotropy on small (arc-minute) angular scales. We look for significant
non-linear contributions, as in the case of Vishniac effect in temperature
anisotropy, due to the coupling of small-scale electron density fluctuations,
at the new last scattering surface, and the temperature quadrupole. We show
that, while, in cold dark matter type models, this does not lead to very
significant signals ($\sim 0.02 - 0.04 \mu K$), a larger small angular scale
polarization anisotropy, ($\sim 0.1 - 0.5\mu K$), can result in isocurvature
type models.",9802099v1
1998-11-19,Contribution of Bright Extragalactic Radio Sources to Microwave Anisotropy,"We estimate the contribution of extragalactic radio sources to fluctuations
in sky temperature over the range of frequencies (10-300 GHz) used for Cosmic
Microwave Background (CMB) anisotropy measurements. CMB anisotropy observations
at high resolution and low frequencies are especially sensitive to this
foreground. We have compiled a catalog of 2207 bright radio sources, including
758 sources with flux measurements at 90 GHz. We develop a method to
extrapolate the source spectra and predict skymaps of extragalactic radio
sources at instrument resolutions of 10 arcmin to 10 degrees FWHM. Our results
indicate that the brightest sources will dominate microwave anisotropy for a
wide range of resolutions and frequencies. Our skymaps predict the location and
flux of the brightest radio sources at each frequency, making it
straightforward to develop a template for masking the pixels containing them.
This masking should be sufficient to protect high resolution CMB anisotropy
observations from unacceptable radio source confusion.",9811311v1
2000-04-03,Cosmic Ray Anisotropy Analysis with a Full-Sky Observatory,"A cosmic ray observatory with full-sky coverage can exploit standard
anisotropy analysis methods that do not work if part of the celestial sphere is
never seen. In particular, the distribution of arrival directions can be fully
characterized by a list of spherical harmonic coefficients. The dipole vector
and quadrupole tensor are of special interest, but the full set of harmonic
coefficients constitutes the anisotropy fingerprint that may be needed to
reveal the identity of the cosmic ray sources. The angular power spectrum is a
coordinate-independent synopsis of that fingerprint. The true cosmic ray
anisotropy can be measured despite non-uniformity in celestial exposure,
provided the observatory is not blind to any region of the sky. This paper
examines quantitatively how the accuracy of anisotropy measurement depends on
the number of arrival directions in a data set.",0004016v1
2001-03-30,Probing the Universe After Cosmological Recombination Through the Effect of Neutral Lithium on the Microwave Background Anisotropies,"I show that neutral lithium couples strongly to the cosmic microwave
background (CMB) through its 6708A resonant transition after it recombines at
z~500. At observed wavelengths of <335 micron, the CMB anisotropies are
significantly altered since the optical depth for resonant scattering by
neutral lithium is substantial, of order 0.5. The scattering would suppress the
original anisotropies, but will generate strong new anisotropies in the CMB
temperature and polarization on sub-degree scales (l>100). Observations at
different wavelengths in this spectral regime can probe different thin slices
of the early universe. The anisotropy noise contributed by continuum radiation
from foreground far--infrared sources could be taken out by subtracting maps at
slightly different wavelengths. Detection of the above effects can be used to
study structure at z<500 and to constrain the primordial abundance and
recombination history of lithium.",0103505v2
2003-02-07,MAXIMA: Observations of CMB Anisotropy,"This document describes the Millimeter Anisotropy eXperiment IMaging Array
(MAXIMA), a balloon-borne experiment measuring the temperature anisotropy of
the Cosmic Microwave Background (CMB) on angular scales of 10 arcminutes to 5
degrees. MAXIMA maps the CMB using 16 bolometric detectors observing in
spectral bands centered at 150 GHz, 230 GHz, and 410 GHz, with 10 arcminute
resolution at all frequencies. The combined receiver sensitivity to CMB
anisotropy is 40 micro-K*(sec^0.5). During two flights with a total of 8.5
hours of CMB observations, 300 square degrees of the sky were mapped. MAXIMA
data are used to discriminate between cosmological models and to determine
cosmological parameters; results are presented from the 1998 flight. The
angular power spectrum derived from these data shows a narrow peak near l=200,
and is consistent with inflationary Big Bang models. Cosmological parameters
are estimated, including total density Omega(total)=0.9(-0.16,+0.18), baryon
density Omega(b)h^2=0.033(+/-0.013), and power spectrum normalization
C(10)=690(-125,+200) micro-K^2. The final chapter is a discussion CMB
polarization anisotropy, including an overview of MAXIPOL, the polarization
sensitive follow-up to MAXIMA.",0302159v1
2003-06-17,CMB Anisotropies in the Presence of Extra Dimensions,"We discuss the effect of the time evolution of extra dimensions on CMB
anisotropies and large-scale structure formation. We study the impact of scalar
fields in a low-energy effective description of a general class of brane world
models on the temperature anisotropy power spectrum. We show that when the
coupling between these scalar fields and matter evolves over cosmological
timescales, current observations of the CMB anisotropies can constrain
primordial values of the fields in a manner complementary to local, late-time
tests of gravity. We also present the effect of these fields on the
polarization anisotropy spectra and the growth of large-scale structure,
showing that future CMB observations will constrain theories of the Universe
involving extra dimensions even further.",0306343v1
2003-09-10,The CMB Quadrupole in a Polarized Light,"The low quadrupole of the cosmic microwave background (CMB), measured by COBE
and confirmed by WMAP, has generated much discussion recently. We point out
that the well-known correlation between temperature and polarization
anisotropies of the CMB further constrains the low multipole anisotropy data.
This correlation originates from the fact that the low-multipole polarization
signal is sourced by the CMB quadrupole as seen by free electrons during the
relatively recent cosmic history. Consequently, the large-angle temperature
anisotropy data make restrictive predictions for the large-angle polarization
anisotropy, which depend primarily on the optical depth for electron scattering
after cosmological recombination, tau. We show that if current cosmological
models for the generation of large angle anisotropy are correct and the
COBE/WMAP data are not significantly contaminated by non-CMB signals, then the
observed C_te amplitude on the largest scales is discrepant at the 99.8% level
with the observed C_tt for the concordance LCDM model with tau=0.10. Using
tau=0.17, the preferred WMAP model-independent value, the discrepancy is at the
level of 98.5%.",0309281v2
2004-08-10,Observation by an Air-Shower Array in Tibet of the Multi-TeV Cosmic-Ray Anisotropy due to Terrestrial Orbital Motion Around the Sun,"We report on the solar diurnal variation of the galactic cosmic-ray intensity
observed by the Tibet III air shower array during the period from 1999 to 2003.
In the higher-energy event samples (12 TeV and 6.2 TeV), the variations are
fairly consistent with the Compton-Getting anisotropy due to the terrestrial
orbital motion around the sun, while the variation in the lower-energy event
sample (4.0 TeV) is inconsistent with this anisotropy. This suggests an
additional anisotropy superposed at the multi-TeV energies, e.g. the solar
modulation effect. This is the highest-precision measurement of the
Compton-Getting anisotropy ever made.",0408187v1
2004-11-02,The Physics of CMBR Anisotropies,"The observed structures in the universe are thought to have arisen from
gravitational instability acting on small fluctuations generated in the early
universe. These spatial fluctuations are imprinted on the CMBR as angular
anisotropies. The physics which connects initial fluctuations in the early
universe to the observed anisotropies is fairly well understood, since for most
part it involves linear perturbation theory. This makes CMBR anisotropies one
of the cleanest probes of the initial fluctuations, various cosmological
parameters governing their evolution and also the geometry of the universe. We
review here in a fairly pedagogical manner the physics of the CMBR anisotropies
and explain the role they play in probing cosmological parameters, especially
in the light of the latest observations from the WMAP satellite.",0411049v1
2005-05-09,Second-order gravitational effects of local inhomogeneities on CMB anisotropies in nonzero-Lambda flat cosmological models,"Nonlinear gravitational effects of large-scale inhomogeneities on Cosmic
Microwave Background (CMB) anisotropies are studied. based on the relativistic
second-order theory of perturbations in nonzero-Lambda flat cosmological
models, which has been analytically derived by the present author, and on the
second-order formula of CMB anisotropies derived by Mollerach and Matarrese. In
this paper we derive the components of the CMB anisotropy power spectra in the
range of l = 1 -22 which are caused by asymmetric local inhomogeneities on
scales of 300 Mpc. Using our results it is found that there is a possibility to
explain the small north-south asymmetry of CMB anisotropies which has recently
been observed.",0505157v6
2005-07-13,A closer look at the spectrum and small scale anisotropies of UHECRs,"We present results of numerical simulations of the propagation of ultra high
energy cosmic rays (UHECRs) over cosmological distances, aimed at quantifying
the statistical significance of the highest energy data on the spectrum and
small scale anisotropies as detected by the AGASA experiment. We assess the
significance of the lack of a GZK feature and its compatibility with the
reported small scale anisotropies.
  Assuming that UHECRs are protons from extragalactic sources, we find that the
small scale anisotropies are incompatible with the reported spectrum at a
probability level of $2 \times 10^{-5}$. Our analysis of the AGASA results
shows the power of combining spectrum and small scale anisotropy data in future
high statistics experiments, such as Auger.",0507324v1
2006-01-13,The Anisotropy of Galactic Cosmic Rays as a Product of Stochastic Supernova Explosions,"We study the effect of the stochastic character of supernova explosions on
the anisotropy of galactic cosmic rays below the knee. We conclude that if the
bulk of cosmic rays are produced in supernova explosions the observed small and
nearly energy independent amplitude of the anisotropy and its phase are to the
large extent determined by the history of these explosions in the vicinity of
the solar system, namely by the location and the age of the supernova remnants,
within a few kpc, which give the highest contribution to the total intensity at
the present epoch. Among the most important factors which result in the small
magnitude and the energy independence of the anisotropy amplitude are the mixed
primary mass composition, the effect of the Single Source and the Galactic
Halo. Special attention is given to the phase of the anisotropy. It is shown
that the excessive flux from the Outer Galaxy can be due to the location of the
solar system at the inner edge of the Orion Arm which has the enhanced density
and rate of supernova explosions.",0601290v1
2006-09-13,Imprint of spatial curvature on inflation power spectrum,"If the universe had a large curvature before inflation there is a deviation
from the scale invariant perturbations of the inflaton at the beginning of
inflation. This may have some effect on the CMB anisotropy at large angular
scales. We calculate the density perturbations for both open and closed
universe cases using the Bunch-Davies vacuum condition on the initial state. We
use our power spectrum to calculate the temperature anisotropy spectrum and
compare the results with the WMAP three year data. We find that our power
spectrum gives a lower quadrupole anisotropy when $\Omega-1 >0$, but matches
the temperature anisotropy calculated from the standard Ratra-Peebles power
spectrum at large $l$. The determination of spatial curvature from temperature
anisotropy data is not much affected by the different power spectra which arise
from the choice of different boundary conditions for the inflaton perturbation.",0609349v4
2006-10-05,Anisotropy of Magnetohydrodynamic Turbulence and Polarization of the Spectral Lines of Molecules,"The anisotropy of velocities in MHD turbulence is demonstrated explicitly by
calculating the velocity gradients as a function of direction in representative
simulations of decaying turbulence. It follows that the optical depths of
spectral lines are anisotropic when there is MHD turbulence, and that this
anisotropy influences the polarization characteristics of the emergent
radiation. We calculate the linear polarization that results for the microwave
lines of the CO molecule in star-forming gas and show that it is comparable to
the polarization that is observed. This and our earlier result--that the
anisotropy of MHD turbulence may be the cause for the absence of the Zeeman
$\pi $-components in the spectra of OH mainline masers--are the first
demonstrations of the occurrence of anisotropy in the optical depths caused by
MHD turbulence. A non-local approximation is developed for the radiative
transfer and the results are compared with those from a local (LVG)
approximation.",0610144v1
2006-10-23,Anisotropy and Corotation of Galactic Cosmic Rays,"The intensity of Galactic cosmic rays is nearly isotropic because of the
influence of magnetic fields in the Milky Way. Here, we present two-dimensional
high-precision anisotropy measurement for energies from a few to several
hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air
Shower Arrays. Besides revealing finer details of the known anisotropies, a new
component of Galactic cosmic ray anisotropy in sidereal time is uncovered
around the Cygnus region direction. For cosmic-ray energies up to a few hundred
TeV, all components of anisotropies fade away, showing a corotation of Galactic
cosmic rays with the local Galactic magnetic environment. These results have
broad implications for a comprehensive understanding of cosmic rays,
supernovae, magnetic fields, and heliospheric and Galactic dynamic
environments.",0610671v1
2007-01-29,The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB,"The inhomogeneous ionization state of the universe when the first sources of
ionizing radiation appeared should lead to anisotropies in the polarization of
the cosmic microwave background. We use cosmological simulations of the process
by which the first sources ionized the intergalactic medium to study the
induced polarization anisotropies. We find that the polarization anisotropies
have rms of order ~0.01 \mu K, and local peak values of ~0.1 \mu K, smaller
than those due to gravitational lensing on small scales. The polarization
direction is highly coherent over degree scales. This directional coherence is
not expected from either primary anisotropy or gravitational lensing effects,
making the largest signals due to inhomogeneous ionization relatively easy to
isolate, should experiments achieve the necessary very low noise levels.",0701784v1
2007-03-20,CMB Spectral Distortions from the Scattering of Temperature Anisotropies,"Thomson scattering of CMBR temperature anisotropies will cause the spectrum
of the CMBR to differ from blackbody even when one resolves all anisotropies. A
formalism for computing the anisotropic and inhomogeneous spectral distortions
of intensity and polarization is derived in terms of Lorentz invariant central
moments of the temperature distribution. The formalism is non-perturbative,
requiring neither small anisotropies nor small metric or matter
inhomogeneities; but it does assume cold electrons. The low order moments are
not coupled to the higher order moments allowing one to truncate the equations
without any loss of accuracy. This formalism is applied to a standard
Lambda-CDM cosmology after reionization where the temperature anisotropies are
dominated by the Doppler effect for the bulk motion of the gas with respect to
the CMBR frame. The resultant spectral distortion is parameterized by u ~ 3e-8,
where in this case u is observationally degenerate with the Sunyaev-Zel'dovich
(SZ) y parameter. In comparison the expected thermal SZ y-distortion from the
hot IGM is expected to be >30 times larger. However at z >5 the effect
described here would have been the dominant source of spectral distortions. The
effect could be much larger in non-standard cosmologies.",0703541v1
1997-01-16,Exchange Anisotropy in Epitaxial and Polycrystalline NiO/NiFe Bilayers,"(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001)
substrates by ion beam sputtering in order to determine the effect that the
crystalline orientation of the NiO antiferromagnetic layer has on the
magnetization curve of the NiFe ferromagnetic layer. Simple models predict no
exchange anisotropy for the (001)-oriented surface, which in its bulk
termination is magnetically compensated. Nonetheless exchange anisotropy is
present in the epitaxial films, although it is approximately half as large as
in polycrystalline films that were grown simultaneously. Experiments show that
differences in exchange field and coercivity between polycrystalline and
epitaxial NiFe/NiO bilayers couples arise due to variations in induced surface
anisotropy and not from differences in the degree of compensation of the
terminating NiO plane. Implications of these observations for models of induced
exchange anisotropy in NiO/NiFe bilayer couples will be discussed.",9701115v1
1998-10-15,Ordering in magnetic films with surface anisotropy,"Effects of the surface exchange anisotropy on ordering of ferromagnetic films
are studied for the exactly solvable classical spin-vector model with D \to
\infty components. For small surface anisotropy \eta'_s << 1 (defined relative
to the exchange interaction), the shift of T_c in a film consisting of N >> 1
layers behaves as T_c^{\rm bulk} - T_c(N) ~ (1/N)\ln(1/\eta'_s) in three
dimensions. The finite-size-scaling limit T_c^{\rm bulk} - T_c(N) \propto
1/(\eta'^{1/2}N^2), which is realized for the model with a bulk anisotropy
\eta' << 1 in the range N\eta'^{1/2} >~ 1, never appears for the model with the
pure surface anisotropy. Here for N\exp(-1/\eta'_s) >~ 1 in three dimensions,
film orders at a temperature above T_c^{\rm bulk} (the surface phase
transition). In the semi-infinite geometry, the surface phase transition occurs
for whatever small values of \eta'_s (i.e., the special phase transition
corresponds to T_c^{\rm bulk}) in dimensions three and lower.",9810182v1
1999-03-02,Triangular anisotropies in Driven Diffusive Systems: reconciliation of Up and Down,"Deterministic coarse-grained descriptions of driven diffusive systems (DDS)
have been hampered by apparent inconsistencies with kinetic Ising models of
DDS. In the evolution towards the driven steady-state, ``triangular''
anisotropies in the two systems point in opposite directions with respect to
the drive field. We show that this is non-universal behavior in the sense that
the triangular anisotropy ``flips'' with local modifications of the Ising
interactions. The sign and magnitude of the triangular anisotropy also vary
with temperature. We have also flipped the anisotropy of coarse-grained models,
though not yet at the latest stages of evolution. Our results illustrate the
comparison of deterministic coarse-grained and stochastic Ising DDS studies to
identify universal phenomena in driven systems. Coarse-grained systems are
particularly attractive in terms of analysis and computational efficiency.",9903049v1
1999-12-16,Viscous fingering in liquid crystals: Anisotropy and morphological transitions,"We show that a minimal model for viscous fingering with a nematic liquid
crystal in which anisotropy is considered to enter through two different
viscosities in two perpendicular directions can be mapped to a two-fold
anisotropy in the surface tension. We numerically integrate the dynamics of the
resulting problem with the phase-field approach to find and characterize a
transition between tip-splitting and side-branching as a function of both
anisotropy and dimensionless surface tension. This anisotropy dependence could
explain the experimentally observed (reentrant) transition as temperature and
applied pressure are varied. Our observations are also consistent with previous
experimental evidence in viscous fingering within an etched cell and
simulations of solidification.",9912312v1
2000-02-24,High Frequency EPR Spectra of [Fe8O2(OH)12(tacn)6]Br8. A Critical Appraisal of the Barrier for the Reorientation of the Magnetization in Single Molecule Magnets,"A detailed multifrequency high field - high frequency EPR (95-285 GHz) study
has been performed on the single-molecule magnet of formula
  [Fe8O2(OH)12(tacn)6]Br8 9H2O, where tacn=1,4,7-triazacyclononane.
Polycrystalline powder spectra have allowed estimating the zero field splitting
parameters up to the fourth order terms.
  The single crystal spectra have provided the principal directions of the
magnetic anisotropy of the cluster. These results have been compared to an
evaluation of the intra-cluster dipolar contribution to the magnetic
anisotropy, suggesting that single ion anisotropy is mainly contributing to the
magnetic anisotropy.
  The role of the transverse magnetic anisotropy in determining the height of
the barrier for the reversal of the magnetization is also discussed.",0002386v1
2000-05-26,Finite-temperature ordering in two-dimensional magnets,"We study the two dimensional quantum Heisenberg antiferromagnet on the square
lattice with easy-axis exchange anisotropy. By the semiclassical method called
pure-quantum self-consistent harmonic approximation we analyse several
thermodynamic quantities and investigate the existence of a finite temperature
transition, possibly describing the low-temperature critical behaviour
experimentally observed in many layered real compounds.
  We find that an Ising-like transition characterizes the model even when the
anisotropy is of the order of $10^{-2}J$ ($J$ being the intra-layer exchange
integral), as in most experimental situations. On the other hand, typical
features of the isotropic Heisenberg model are observed for both values of
anisotropy considered, one in the {\it quasi}-isotropic limit and the other in
a more markedly easy-axis region.
  The good agreement found between our theoretical results and the experimental
data relative to the real compound Rb$_2$MnF$_4$ shows that the insertion of
the easy-axis exchange anisotropy, with quantum effects properly taken into
account, provides a quantitative description and explanation of the
experimental data, thus allowing to recognize in such anisotropy the main agent
for the observed onset of finite temperature long-range order.",0005464v1
2000-12-29,Hysteresis and Avalanches in the Random Anisotropy Ising Model,"The behaviour of the Random Anisotropy Ising model at T=0 under local
relaxation dynamics is studied. The model includes a dominant ferromagnetic
interaction and assumes an infinite anisotropy at each site along local
anisotropy axes which are randomly aligned. Two different random distributions
of anisotropy axes have been studied. Both are characterized by a parameter
that allows control of the degree of disorder in the system. By using numerical
simulations we analyze the hysteresis loop properties and characterize the
statistical distribution of avalanches occuring during the metastable evolution
of the system driven by an external field. A disorder-induced critical point is
found in which the hysteresis loop changes from displaying a typical
ferromagnetic magnetization jump to a rather smooth loop exhibiting only tiny
avalanches. The critical point is characterized by a set of critical exponents,
which are consistent with the universal values proposed from the study of other
simpler models.",0012508v1
2001-08-31,Inversion Phenomena of the Anisotropies of the Hamiltonian and the Wave-Function in the Distorted Diamond Type Spin Chain,"We investigate the ground-sate phase diagram of the XXZ version of the S=1/2
distorted diamond chain by use of the degenerate perturbation theory near the
truncation point. In case of the XY-like interaction anisotropy, the phase
diagram consists of the Neel phase and the spin-fluid phase. For the Ising-like
interaction anisotropy case, it consists of three phases: the ferrimagnetic
phase, the Neel phase and the spin-fluid phase. The magnetization in the
ferrimagnetic phase is 1/3 of the saturation magnetization. The remarkable
nature of the phase diagram is the existence of the Neel phase, although the
interaction anisotropy is XY-like. And also, the spin-fluid phase appears in
spite of the Ising-like interaction anisotropy. We call these regions
""inversion regions"".",0108528v1
2002-01-08,Many-body Green's function theory for thin ferromagnetic films: exact treatment of the single-ion anisotropy,"A theory for the magnetization of ferromagnetic films is formulated within
the framework of many-body Green's funtion theory which considers all
components of the magnetization. The model Hamiltonian includes a Heisenberg
term, an external field, a second- and fourth-order uniaxial single-ion
anisotropy, and the magnetic dipole-dipole coupling. The single-ion anisotropy
terms can be treated exactly by introducing higher-order Green's functions and
subsequently taking advantage of relations between products of spin operators
which leads to an automatic closure of the hierarchy of the equations of motion
for the Green's functions with respect to the anisotropy terms. This is an
improvement on the method of our previous work, which treated the corresponding
terms only approximately by decoupling them at the level of the lowest-order
Green's functions. RPA-like approximations are used to decouple the exchange
terms in both the low-order and higher-order Green's functions. As a first
numerical example we apply the theory to a monolayer for spin S=1 in order to
demonstrate the superiority of the present treatment of the anisotropy terms
over the previous approximate decouplings.",0201097v1
2002-04-09,In-plane anisotropy on the transport properties in the modulated Bi_2O_2-based conductors Bi-2212 and Bi-Sr-Co-O,"We investigated the in-plane anisotropy on the resistivity and thermopower of
the Bi_2Sr_2CaCu_2O_{8+\delta} (Bi-2212) and Bi-Sr-Co-O (BiCo) single crystals.
In Bi-2212, the b-axis resistivity is higher than the a-axis resistivity, and
is expressed as a sum of the a-axis resistivity and an additional residual
resistivity. A downward deviation due to pseudogap is observed below a
characteristic temperature T^*, which is isotropic in the form of conductivity.
These results suggest that the modulation structure along the b-axis works as
an anisotropic scattering center, but does not affect the pseudogap formation.
On the other hand, the anisotropy of the resistivity and the thermopower in
Pb-doped BiCo is substantial, probably owing to the misfit structure between
the hexagonal CoO_2 layer and the rock salt Bi_2O_2 layer. However, the
anisotropy in the resistivity in Pb-free BiCo is very small, suggesting that
the in-plane anisotropy is averaged by the modulation structure, whose
direction is tilted by 45 deg from the a- and b-axes.",0204187v1
2002-07-06,Square-lattice s=1/2 XY model and the Jordan-Wigner fermions: The ground-state and thermodynamic properties,"Using the 2D Jordan-Wigner transformation we reformulate the square-lattice
s=1/2 XY (XZ) model in terms of noninteracting spinless fermions and examine
the ground-state and thermodynamic properties of this spin system. We consider
the model with two types of anisotropy: the spatial anisotropy interpolating
between 2D and 1D lattices and the anisotropy of the exchange interaction
interpolating between isotropic XY and Ising interactions. We compare the
obtained (approximate) results with exact ones (1D limit, square-lattice Ising
model) and other approximate ones (linear spin-wave theory and exact
diagonalization data for finite lattices of up to N=36 sites supplemented by
finite-size scaling). We discuss the ground-state and thermodynamic properties
in dependence on the spatial and exchange interaction anisotropies. We pay
special attention to the quantum phase transition driven by the exchange
interaction anisotropy as well as to the appearance/disappearance of the
zero-temperature magnetization in the quasi-1D limit.",0207179v1
2002-08-16,In-plane dipole coupling anisotropy of a square ferromagnetic Heisenberg monolayer,"In this study we calculate the dipole-coupling-induced quartic in-plane
anisotropy of a square ferromagnetic Heisenberg monolayer. This anisotropy
increases with an increasing temperature, reaching its maximum value close to
the Curie temperature of the system. At T=0 the system is isotropic, besides a
small remaining anisotropy due to the zero-point motion of quantum mechanical
spins. The reason for the dipole-coupling-induced anisotropy is the disturbance
of the square spin lattice due to thermal fluctuations ('order-by-disorder'
effect). For usual ferromagnets its strength is small as compared to other
anisotropic contributions, and decreases by application of an external magnetic
field. The results are obtained from a Heisenberg Hamiltonian by application of
a mean field approach for a spin cluster, as well as from a many-body Green's
function theory within the Tyablikov-decoupling (RPA).",0208324v1
2002-12-20,"Temperature Dependent Magnetic Anisotropy in (Ga,Ma)As Layers","It is demonstrated by SQUID magnetization measurements that (Ga,Mn)As films
can exhibit rich characteristics of magnetic anisotropy depending not only to
the epitaxial strain but being strongly influenced by the hole and Mn
concentration, and temperature. This behavior reflects the spin anisotropy of
the valence subbands and corroborates predictions of the mean field Zener model
of the carrier mediated ferromagnetism in III-V diluted magnetic semiconductors
with Mn. At the same time the existence of in-plane uniaxial anisotropy with
[110] the easy axis is evidenced. This is related to the top/bottom symmetry
breaking, resulting in the lowering of point symmetry of (Ga,Mn)As to the
C_{2v} symmetry group. The latter mechanism coexists with the hole-induced
cubic anisotropy, but takes over close to T_C.",0212511v2
2003-06-23,Anisotropic magnetoresistive and magnetic properties of La_{0.5}Sr_{0.5}CoO_{3-δ} film,"The magnetic and transport properties of La_{0.5}Sr_{0.5}CoO_{3-\delta} film
grown on a LaAlO_3 substrate by pulsed-laser deposition are studied. The
properties are found to be influenced by the magnetic anisotropy and
inhomogeneity. Magnetoresistance anisotropy is determined by the shape
anisotropy of the magnetization and the strain-induced magnetic anisotropy due
to the film-substrate lattice interaction. Indications of the
temperature-driven spin reorientation transition from an out-of plane orderded
state at low temperatures to an in-plane ordered state at high temperatures as
a result of competition between the mentioned sources of magnetic anisotropy
are found.",0306565v1
2003-10-29,Magnetic nanoparticles as many-spin systems,"We present a review of recent advances in the study of many-body effects in
magnetic nanoparticles. Considering classical spins on a lattice coupled by the
exchange interaction in the presence of the bulk and surface anisotropy, we
investigate the effects of finite size, free boundaries, and surface anisotropy
on the average and local magnetization for zero and finite temperatures and
magnetic fields. Superparamagnetism of magnetic particles necessitates
introducing two different, induced and intrinsic, magnetizations. We check the
validity of the much used relation between them within different theoretical
models. We show that the competition between the exchange and surface
anisotropy leads to spin canting dependent on the orientation of the average
magnetization with respect to the crystallographic axes and thus to a
second-order effective anisotropy of the particle. We have also investigated
the switching mechanism of the magnetization upon varying the surface
anisotropy constant. Some cases of more realistic particles are also dealt
with.",0310694v1
2004-03-08,Reversible magnetization measurement of the anisotropy of the London penetration depth in MgB2 single crystals,"We have studied the anisotropy of the London penetration depth, which was
obtained from reversible magnetization measurements with the magnetic field
both parallel and perpendicular to the c-axis. The anisotropy of the London
penetration depth has a smaller magnitude than the anisotropy of the upper
critical field and increases with temperature while that of the upper critical
field decreases as reported earlier. This behavior is in sharp contrast with
the behaviors of superconductors with one superconducting energy gap. The
temperature dependence of the anisotropies of the London penetration depth and
of the upper critical field can be well explained within the theory of two-gap
superconductivity in MgB2.",0403198v1
2004-07-29,Anisotropy in Ferromagnetic Nanoparticles: Level-to-Level Fluctuations of a Collective Effect,"We calculate the mesoscopic fluctuations of the magnetic anisotropy of
ferromagnetic nanoparticles. A microscopic spin-orbit Hamiltonian considered as
a perturbation of the much stronger exchange interaction first yields an
explicit expression for the anisotropy tensor. Then, assuming a simple random
matrix model for the spin-orbit coupling allows us to describe the fluctuation
of such a tensor. In the case of uniaxial anisotropy, we calculate the
distribution of the anisotropy constant for a given number of electrons, and
its variation upon increasing this number by one. The magnitude of the latter
is sufficient to account for the experimental data.",0407771v2
2004-09-13,Thermal and magnetic properties of spin-1 magnetic chain compounds with large single-ion and in-plane anisotropies,"The thermal and magnetic properties of spin-1 magnetic chain compounds with
large single-ion and in-plane anisotropies are investigated via the integrable
su(3) model in terms of the quantum transfer matrix method and the recently
developed high temperature expansion method for exactly solved models. It is
shown that large single-ion anisotropy may result in a singlet gapped phase in
the spin-1 chain which is significantly different from the standard Haldane
phase. A large in-plane anisotropy may destroy the gapped phase. On the other
hand, in the vicinity of the critical point a weak in-plane anisotropy leads to
a different phase transition than the Pokrovsky-Talapov transition. The
magnetic susceptibility, specific heat and magnetization evaluated from the
free energy are in excellent agreement with the experimental data for the
compounds NiC_2H_8N_2)_2Ni(CN)_4 and Ni(C_{10}H_8N_2)_2Ni(CN)_4.H_2O.",0409310v1
2005-02-28,Magnetization of nanomagnet assemblies: Effects of anisotropy and dipolar interactions,"We investigate the effect of anisotropy and weak dipolar interactions on the
magnetization of an assembly of nanoparticles with distributed magnetic
moments, i.e., assembly of magnetic nanoparticles in the one-spin
approximation, with textured or random anisotropy.
  The magnetization of a free particle is obtained either by a numerical
calculation of the partition function or analytically in the low and high field
regimes, using perturbation theory and the steepest-descent approximation,
respectively. The magnetization of an interacting assembly is computed
analytically in the range of low and high field, and numerically using the
Monte Carlo technique.
  Approximate analytical expressions for the assembly magnetization are
provided which take account of the dipolar interactions, temperature, magnetic
field, and anisotropy. The effect of anisotropy and dipolar interactions are
discussed and the deviations from the Langevin law they entail are
investigated, and illustrated for realistic assemblies with the lognormal
moment distribution.",0502660v2
2005-04-20,The loss of anisotropy in MgB2 with Sc substitution and its relationship with the critical temperature,"The electrical conductivity anisotropy of the sigma-bands is calculated for
the (Mg,Sc)B2 system using a virtual crystal model. Our results reveal that
anisotropy drops with relatively little scandium content (< 30%); this
behaviour coincides with the lowering of Tc and the reduction of the Kohn
anomaly. This anisotropy loss is also found in the Al and C doped systems. In
this work it is argued that the anisotropy, or 2D character, of the sigma-bands
is an important parameter for the understanding of the high Tc found in MgB2.",0504495v2
2005-07-18,Single-ion anisotropy in the gadolinium pyrochlores studied by an electron paramagnetic resonance,"The electron paramagnetic resonance is used to measure the single-ion
anisotropy of Gd3+ ions in the pyrochlore structure of (Y{1-x}Gdx)2Ti2O7. A
rather strong easy-plane type anisotropy is found. The anisotropy constant D is
comparable to the exchange integral J in the prototype Gd2Ti2O7, D~0.75J and
exceeds the dipolar energy scale. Physical implications of an easy-plane
anisotropy for a pyrochlore antiferromagnet are considered. We calculate the
magnetization curves at T=0 and discuss phase transitions in magnetic field.",0507413v1
2006-01-03,Ginzburg-Landau theory of crystalline anisotropy for bcc-liquid interfaces,"The weak anisotropy of the interfacial free-energy $\gamma$ is a crucial
parameter influencing dendritic crystal growth morphologies in systems with
atomically rough solid-liquid interfaces. The physical origin and quantitative
prediction of this anisotropy are investigated for body-centered-cubic (bcc)
forming systems using a Ginzburg-Landau theory where the order parameters are
the amplitudes of density waves corresponding to principal reciprocal lattice
vectors. We find that this theory predicts the correct sign,
$\gamma_{100}>\gamma_{110}$, and magnitude, $(\gamma_{100}-\gamma_{110}) /
(\gamma_{100}+\gamma_{110})\approx 1%$, of this anisotropy in good agreement
with the results of MD simulations for Fe. The results show that the
directional dependence of the rate of spatial decay of solid density waves into
the liquid, imposed by the crystal structure, is a main determinant of
anisotropy. This directional dependence is validated by MD computations of
density wave profiles for different reciprocal lattice vectors for $\{110\}$
crystal faces. Our results are contrasted with the prediction of the reverse
ordering $\gamma_{100}<\gamma_{110}$ from an earlier formulation of
Ginzburg-Landau theory [Shih \emph{et al.}, Phys. Rev. A {\bf 35}, 2611
(1987)].",0601057v2
2006-04-05,Critical behavior of the random-anisotropy model in the strong-anisotropy limit,"We investigate the nature of the critical behavior of the random-anisotropy
Heisenberg model (RAM), which describes a magnetic system with random uniaxial
single-site anisotropy, such as some amorphous alloys of rare earths and
transition metals. In particular, we consider the strong-anisotropy limit
(SRAM), in which the Hamiltonian can be rewritten as the one of an Ising
spin-glass model with correlated bond disorder. We perform Monte Carlo
simulations of the SRAM on simple cubic L^3 lattices, up to L=30, measuring
correlation functions of the replica-replica overlap, which is the order
parameter at a glass transition. The corresponding results show critical
behavior and finite-size scaling. They provide evidence of a finite-temperature
continuous transition with critical exponents $\eta_o=-0.24(4)$ and
$\nu_o=2.4(6)$. These results are close to the corresponding estimates that
have been obtained in the usual Ising spin-glass model with uncorrelated bond
disorder, suggesting that the two models belong to the same universality class.
We also determine the leading correction-to-scaling exponent finding $\omega =
1.0(4)$.",0604124v2
2006-05-07,Giant magnetic anisotropy at nanoscale: overcoming the superparamagnetic limit,"It has been recently observed for palladium and gold nanoparticles, that the
magnetic moment at constant applied field does not change with temperature over
the range comprised between 5 and 300 K. These samples with size smaller than
2.5 nm exhibit remanence up to room temperature. The permanent magnetism for so
small samples up to so high temperatures has been explained as due to blocking
of local magnetic moment by giant magnetic anisotropies. In this report we
show, by analysing the anisotropy of thiol capped gold films, that the orbital
momentum induced at the surface conduction electrons is crucial to understand
the observed giant anisotropy. The orbital motion is driven by localised charge
and/or spin through spin orbit interaction, that reaches extremely high values
at the surfaces. The induced orbital moment gives rise to an effective field of
the order of 103 T that is responsible of the giant anisotropy.",0605171v1
2006-06-30,Anisotropic Aerogels for Studying Superfluid $^3$He,"It may be possible to stabilize new superfluid phases of $^{3}$He with
anisotropic silica aerogels. We discuss two methods that introduce anisotropy
in the aerogel on length scales relevant to superfluid $^{3}$He. First,
anisotropy can be induced with uniaxial strain. A second method generates
anisotropy during the growth and drying stages. We have grown cylindrical
$\sim$98% aerogels with anisotropy indicated by preferential radial shrinkage
after supercritical drying and find that this shrinkage correlates with small
angle x-ray scattering (SAXS). The growth-induced anisotropy was found to be
$\sim90^\circ$ out of phase relative to that induced by strain. This has
implications for the possible stabilization of superfluid phases with specific
symmetry.",0606784v2
2006-07-18,Magnetic properties of Fe/Dy multilayers: a Monte Carlo investigation,"We investigate the magnetic properties of a Heisenberg ferrimagnetic
multilayer by using Monte Carlo simulations. The aim of this work is to study
the local structural anisotropy model which is a possible origin of the
perpendicular magnetic anisotropy in transition metal/rare earth amorphous
multilayers. We have considered a face centered cubic lattice where each site
is occupied by a classical Heisenberg spin. We have introduced in our model of
amorphous multilayers a small fraction of crystallized Fe-Dy nanoclusters with
a mean anisotropy axis along the deposition direction. We show that a
competition in the energy terms takes place between the mean uniaxial
anisotropy of the Dy atoms in the nanoclusters and the random anisotropy of the
Dy atoms in the matrix.",0607437v1
2006-09-23,Effects of spin non-collinearities in magnetic nanoparticles,"In a many-spin approach that takes account of the internal structure,
microscopic interactions and single-site anisotropies, we investigate the
effect of spin non-collinearities induced by the boundary and surface
anisotropy on the behaviour of individual magnetic nanoparticles.
  Through analytical and numerical calculations, we show that there are mainly
two regimes separated by some critical value of the surface anisotropy constant
$K_s$ which controls the intensity of spin non-collinearities: i) the so called
Stoner-Wohlfarth or N\'eel-Brown regime of a macrospin undergoing a coherent
switching, ii) the many-spin regime where the strong spin non-collinearities
invalidate the coherent mechanism, and where the particle's magnetic state and
switching mechanisms can no longer be modeled by a macrospin.
  For small-to-intermediate values of $K_s$, and within two models of surface
anisotropy (transverse and N\'eel), the behaviour of the nanoparticle can be
modeled by that of a macrospin with an effective potential energy containing a
uniaxial and cubic anisotropy terms. This effective spin model provides a
crossover between the two regimes.",0609606v1
2006-10-18,A new type of temperature driven reorientation transition in magnetic thin films,"We present a new type of temperature driven spin reorientation transition
(SRT) in thin films. It can occur when the lattice and the shape anisotropy
favor different easy directions of the magnetization. Due to different
temperature dependencies of the two contributions the effective anisotropy may
change its sign and thus the direction of the magnetization as a function of
temperature may change. Contrary to the well-known reorientation transition
caused by competing surface and bulk anisotropy contributions the reorientation
that we discuss is also found in film systems with a uniform lattice
anisotropy. The results of our theoretical model study may have experimental
relevance for film systems with positive lattice anisotropy, as e.g. thin iron
films grown on copper.",0610504v1
2006-10-27,Optical response of high-$T_c$ cuprates: possible role of scattering rate saturation and in-plane anisotropy,"We present a generalized Drude analysis of the in-plane optical conductivity
$\sigma_{ab}$($T$,$\omega$) in cuprates taking into account the effects of
in-plane anisotropy. A simple ansatz for the scattering rate
$\Gamma$($T$,$\omega$), that includes anisotropy, a quadratic frequency
dependence and saturation at the Mott-Ioffe-Regel limit, is able to reproduce
recent normal state data on an optimally doped cuprate over a wide frequency
range. We highlight the potential importance of including anisotropy in the
full expression for $\sigma_{ab}$($T$,$\omega$) and challenge previous
determinations of $\Gamma$($\omega$) in which anisotropy was neglected and
$\Gamma$($\omega$) was indicated to be strictly linear in frequency over a wide
frequency range. Possible implications of our findings for understanding
thermodynamic properties and self-energy effects in high-$T_c$ cuprates will
also be discussed.",0610763v1
2006-11-06,"Transport Characterization of the Magnetic Anisotropy of (Ga,Mn)As","The rich magnetic anisotropy of compressively strained (Ga,Mn)As has
attracted great interest recently. Here we discuss a sensitive method to
visualize and quantify the individual components of the magnetic anisotropy
using transport. A set of high resolution transport measurements is compiled
into color coded resistance polar plots, which constitute a fingerprint of the
symmetry components of the anisotropy. As a demonstration of the sensitivity of
the method, we show that these typically reveal the presence of both the [-110]
and the [010] uniaxial magnetic anisotropy component in (Ga,Mn)As layers, even
when most other techniques reveal only one of these components.",0611156v1
2007-01-25,Theory of the in-plane anisotropy of magnetic excitations in YBa_{2}Cu_{3}O_{6+y},"A pronounced xy-anisotropy was observed in recent neutron scattering
experiments for magnetic excitations in untwinned YBa_{2}Cu_{3}O_{6+y} (YBCO).
The small anisotropy of the bare band structure due to the orthorhombic crystal
symmetry seems to be enhanced by correlation effects. A natural possibility is
that the system is close to a Pomeranchuk instability associated with a d-wave
Fermi surface deformation (dFSD). We investigate this possibility in the
bilayer t-J model within a self-consistent slave-boson mean-field theory. We
show that the dFSD correlations drive a pronounced xy-anisotropy of magnetic
excitations at low doping and at relatively high temperatures, providing a
scenario for the observed xy-anisotropy in optimally doped as well as
underdoped YBCO, including the pseudogap phase.",0701625v1
1995-11-27,Statistics of the Microwave Background Anisotropies Caused by Cosmological Perturbations of Quantum-Mechanical Origin,"The genuine quantum gravity effects can already be around us. It is likely
that the observed large-angular-scale anisotropies in the microwave background
radiation are induced by cosmological perturbations of quantum-mechanical
origin. Such perturbations are placed in squeezed vacuum quantum states and,
hence, are characterized by large variances of their amplitude. The statistical
properties of the anisotropies should reflect the underlying statistics of the
squeezed vacuum quantum states. In this paper, the theoretical variances for
the temperature angular correlation function are described in detail. It is
shown that they are indeed large and must be present in the observational data,
if the anisotropies are truly caused by the perturbations of quantum-mechanical
origin. Unfortunately, these large theoretical statistical uncertainties will
make the extraction of cosmological information from the measured anisotropies
a much more difficult problem than we wanted it to be. This contribution to the
Proceedings is largely based on references~[42,8]. The Appendix contains an
analysis of the ``standard'' inflationary formula for density perturbations.",9511074v1
2000-11-29,Anisotropy dissipation in brane-world inflation,"We examine the behavior of an anisotropic brane-world in the presence of
inflationary scalar fields. We show that, contrary to naive expectations, a
large anisotropy does not adversely affect inflation. On the contrary, a large
initial anisotropy introduces more damping into the scalar field equation of
motion, resulting in greater inflation. The rapid decay of anisotropy in the
brane-world significantly increases the class of initial conditions from which
the observed universe could have originated. This generalizes a similar result
in general relativity. A unique feature of Bianchi I brane-world cosmology
appears to be that for scalar fields with a large kinetic term the initial
expansion of the universe is quasi-isotropic. The universe grows more
anisotropic during an intermediate transient regime until anisotropy finally
disappears during inflationary expansion.",0011105v3
2006-09-16,Bounds on the basic physical parameters for anisotropic compact general relativistic objects,"We derive upper and lower limits for the basic physical parameters
(mass-radius ratio, anisotropy, redshift and total energy) for arbitrary
anisotropic general relativistic matter distributions in the presence of a
cosmological constant. The values of these quantities are strongly dependent on
the value of the anisotropy parameter (the difference between the tangential
and radial pressure) at the surface of the star. In the presence of the
cosmological constant, a minimum mass configuration with given anisotropy does
exist. Anisotropic compact stellar type objects can be much more compact than
the isotropic ones, and their radii may be close to their corresponding
Schwarzschild radii. Upper bounds for the anisotropy parameter are also
obtained from the analysis of the curvature invariants. General restrictions
for the redshift and the total energy (including the gravitational
contribution) for anisotropic stars are obtained in terms of the anisotropy
parameter. Values of the surface redshift parameter greater than two could be
the main observational signature for anisotropic stellar type objects.",0609061v1
1998-08-25,Non-perturbative determination of anisotropy coefficients and pressure gap at the deconfining transition of QCD,"We propose a new non-perturbative method to compute derivatives of gauge
coupling constants with respect to anisotropic lattice spacings (anisotropy
coefficients). Our method is based on a precise measurement of the finite
temperature deconfining transition curve in the lattice coupling parameter
space extended to anisotropic lattices by applying the spectral density method.
We determine the anisotropy coefficients for the cases of SU(2) and SU(3) gauge
theories. A longstanding problem, when one uses the perturbative anisotropy
coefficients, is a non-vanishing pressure gap at the deconfining transition
point in the SU(3) gauge theory. Using our non-perturbative anisotropy
coefficients, we find that this problem is completely resolved.",9808034v1
1992-07-14,Contribution of Long Wavelength Gravitational Waves to the CMB Anisotropy,"We present an in depth discussion of the production of gravitational waves
from an inflationary phase that could have occurred in the early universe,
giving derivations for the resulting spectrum and energy density. We also
consider the large-scale anisotropy in the cosmic microwave background
radiation coming from these waves. Assuming that the observed quadrupole
anisotropy comes mostly from gravitational waves (consistent with the
predictions of a flat spectrum of scalar density perturbations and the measured
dipole anisotropy) we describe in detail how to derive a value for the scale of
inflation of $(1.5-5)\times 10^{16}$GeV, which is at a particularly interesting
scale for particle physics. This upper limit corresponds to a 95\% confidence
level upper limit on the scale of inflation assuming only that the quadrupole
anisotropy from gravitational waves is not cancelled by another source. Direct
detection of gravitational waves produced by inflation near this scale will
have to wait for the next generation of detectors.",9207239v1
2003-08-23,Braneworld cosmological models with anisotropy,"For a cosmological Randall-Sundrum braneworld with anisotropy, i.e., of
Bianchi type, the modified Einstein equations on the brane include components
of the five-dimensional Weyl tensor for which there are no evolution equations
on the brane. If the bulk field equations are not solved, this Weyl term
remains unknown, and many previous studies have simply prescribed it ad hoc. We
construct a family of Bianchi braneworlds with anisotropy by solving the
five-dimensional field equations in the bulk. We analyze the cosmological
dynamics on the brane, including the Weyl term, and shed light on the relation
between anisotropy on the brane and Weyl curvature in the bulk. In these
models, it is not possible to achieve geometric anisotropy for a perfect fluid
or scalar field -- the junction conditions require anisotropic stress on the
brane. But the solutions can isotropize and approach a Friedmann brane in an
anti-de Sitter bulk.",0308158v1
2000-05-31,Anomalous scaling of a passive scalar in the presence of strong anisotropy,"Field theoretic renormalization group and the operator product expansion are
applied to a model of a passive scalar field, advected by the Gaussian strongly
anisotropic velocity field. Inertial-range anomalous scaling behavior is
established, and explicit asymptotic expressions for the n-th order structure
functions of scalar field are obtained; they are represented by superpositions
of power laws with nonuniversal (dependent on the anisotropy parameters)
anomalous exponents. In the limit of vanishing anisotropy, the exponents are
associated with tensor composite operators built of the scalar gradients, and
exhibit a kind of hierarchy related to the degree of anisotropy: the less is
the rank, the less is the dimension and, consequently, the more important is
the contribution to the inertial-range behavior. The leading terms of the even
(odd) structure functions are given by the scalar (vector) operators. For the
finite anisotropy, the exponents cannot be associated with individual operators
(which are essentially ``mixed'' in renormalization), but the aforementioned
hierarchy survives for all the cases studied. The second-order structure
function is studied in more detail using the renormalization group and
zero-mode techniques.",0005067v1
2001-09-09,Light scattering by optically anisotropic scatterers II: T--matrix computations for radially and uniformly anisotropic droplets,"This is the second paper in a series on light scattering from optically
anisotropic scatterers embedded in an isotropic medium. The apparently complex
T-matrix theory involving mixing of angular momentum components turns out to be
an efficient approach to calculating scattering in these systems. We present
preliminary results of numerical calculations of the scattering by spherical
droplets in some simple cases. The droplets contain optically anisotropic
material with local radial or uniform anisotropy. We concentrate on cases in
which the scattering is due only to the local optical anisotropy within the
scatterer. For radial anisotropy we find non-monotonic dependence of the
scattering cross-section on the degree of anisotropy can occur in a regime for
which both the Rayleigh and semi-classical theories are inapplicable. For
uniform anisotropy the cross-section is strongly dependent on the angle between
the incident light and the optical axis, and for larger droplets this
dependence is non-monotonic.",0109023v1
2007-04-06,Model C critical dynamics of random anisotropy magnets,"We study the relaxational critical dynamics of the three-dimensional random
anisotropy magnets with the non-conserved n-component order parameter coupled
to a conserved scalar density. In the random anisotropy magnets the structural
disorder is present in a form of local quenched anisotropy axes of random
orientation. When the anisotropy axes are randomly distributed along the edges
of the n-dimensional hypercube, asymptotical dynamical critical properties
coincide with those of the random-site Ising model. However structural disorder
gives rise to considerable effects for non-asymptotic critical dynamics. We
investigate this phenomenon by a field-theoretical renormalization group
analysis in the two-loop order. We study critical slowing down and obtain
quantitative estimates for the effective and asymptotic critical exponents of
the order parameter and scalar density. The results predict complex scenarios
for the effective critical exponent approaching an asymptotic regime.",0704.0896v1
2007-08-13,Angle dependent magnetoresistance measurements in Tl$_2$Ba$_2$CuO$_{6+δ}$ and the need for anisotropic scattering,"The angle-dependent interlayer magnetoresistance of overdoped
Tl$_2$Ba$_2$CuO$_{6+\delta}$ has been measured in high magnetic fields up to 45
Tesla. A conventional Boltzmann transport analysis with no basal-plane
anisotropy in the cyclotron frequency $\omega_c$ or transport lifetime $\tau$
is shown to be inadequate for explaining the data. We describe in detail how
the analysis can be modified to incorporate in-plane anisotropy in these two
key quantities and extract the degree of anisotropy for each by assuming a
simple four-fold symmetry. While anisotropy in $\omega_c$ and other Fermi
surface parameters may improve the fit, we demonstrate that the most important
anisotropy is that in the transport lifetime, thus confirming its role in the
physics of overdoped superconducting cuprates.",0708.1666v1
2007-11-04,Secondary anisotropies of the CMB,"The Cosmic Microwave Background fluctuations provide a powerful probe of the
dark ages of the universe through the imprint of the secondary anisotropies
associated with the reionisation of the universe and the growth of structure.
We review the relation between the secondary anisotropies and and the primary
anisotropies that are directly generated by quantum fluctuations in the very
early universe. The physics of secondary fluctuations is described, with
emphasis on the ionisation history and the evolution of structure. We discuss
the different signatures arising from the secondary effects in terms of their
induced temperature fluctuations, polarisation and statistics. The secondary
anisotropies are being actively pursued at present, and we review the future
and current observational status.",0711.0518v1
2007-12-08,Thermal and surface anisotropy effects on the magnetization reversal of a nanocluster,"The relaxation rate and temperature-dependent switching field curve of a
spherical magnetic nanocluster are calculated by taking into account the effect
of surface anisotropy via an effective anisotropy model. In particular, it is
shown that surface anisotropy may change the thermally activated magnetization
reversal by more than an order of magnitude, and that temperature-dependent
switching field curves noticeably deviate from the Stoner-Wohlfarth astroid.
With recent and future $\mu$-SQUID measurements in mind, we indicate how
comparison of our results with experimental data on isolated clusters may allow
one to obtain valuable information on surface anisotropy.",0712.1305v3
2007-12-12,Analysis of anisotropy crossover due to oxygen in Pt/Co/MOx trilayer,"Extraordinary Hall effect and X-ray spectroscopy measurements have been
performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta...) in order to
investigate the role of oxidation in the onset of perpendicular magnetic
anisotropy at the Co/MOx interface. It is observed that varying the oxidation
time modifies the magnetic properties of the Co layer, inducing a magnetic
anisotropy crossover from in-plane to out-of-plane. We focused on the influence
of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The
interfacial electronic structure is analyzed via X-ray photoelectron
spectroscopy measurements. It is shown that the maximum of out-of-plane
magnetic anisotropy corresponds to the appearance of a significant density of
Co-O bondings at the Co/AlOx interface.",0712.1905v1
2008-01-22,The trispectrum of 21-cm background anisotropies as a probe of primordial non-Gaussianity,"The 21-cm anisotropies from the neutral hydrogen distribution prior to the
era of reionization is a sensitive probe of primordial non-Gaussianity. Unlike
the case with cosmic microwave background, 21-cm anisotropies provide
multi-redshift information with frequency selection and is not damped at
arcminute angular scales. We discuss the angular trispectrum of the 21-cm
background anisotropies and discuss how the trispectrum signal generated by the
primordial non-Gaussianity can be measured with the three-to-one correlator and
the corresponding angular power spectrum. We also discuss the separation of
primordial non-Gaussian information in the trispectrum with that generated by
the subsequent non-linear gravitational evolution of the density field. While
with the angular bispectrum of 21-cm anisotropies one can limit the second
order corrections to the primordial fluctuations below f_NL< 1, using the
trispectrum information we suggest that the third order coupling term, f_2 or
g_NL, can be constrained to be arounde 10 with future 21-cm observations over
the redshift interval of 50 to 100.",0801.3463v1
2008-01-30,Particle-scale origins of shear strength in granular media,"The shear strength of cohesionless granular materials is generally attributed
to the compactness or anisotropy of their microstructure. An open issue is how
such compact or anisotropic microstructures, and thus the shear strength,
depend on the particle properties. We first recall the role of fabric and force
anisotropies with respect to the critical-state shear stress. Then, a model of
accessible geometrical states in terms of particle connectivity and contact
anisotropy is presented. This model incorporates in a simple way the fact that,
due to steric exclusions, the highest levels of connectivity and anisotropy
cannot be reached simultaneously, a property that affects seriously the shear
strength. We also analyze the force anisotropy in the light of the specific
role of weak forces in sustaining strong force chains and thus the main
mechanism that underlies anisotropic force patterns. Finally, we briefly
discuss the effect of interparticle friction, particle shape, size
polydispersity and adhesion.",0801.4722v1
2008-02-14,Magnetically Aligned Velocity Anisotropy in the Taurus Molecular Cloud,"Velocity anisotropy induced by MHD turbulence is investigated using
computational simulations and molecular line observations of the Taurus
molecular cloud. A new analysis method is presented to evaluate the degree and
angle of velocity anisotropy using spectroscopic imaging data of interstellar
clouds. The efficacy of this method is demonstrated on model observations
derived from three dimensional velocity and density fields from the set of
numerical MHD simulations that span a range of magnetic field strengths. The
analysis is applied to 12CO J=1-0 imaging of a sub-field within the Taurus
molecular cloud. Velocity anisotropy is identified that is aligned within 10
degrees of the mean local magnetic field direction derived from optical
polarization measurements. Estimated values of the field strength based on
velocity anisotropy are consistent with results from other methods. When
combined with new column density measurements for Taurus, our magnetic field
strength estimate indicates that the envelope of the cloud is magnetically
subcritical. These observations favor strong MHD turbulence within the low
density, sub-critical, molecular gas substrate of the Taurus cloud.",0802.2084v1
2008-07-08,Monte Carlo investigation of the magnetic anisotropy in Fe/Dy multilayers,"By Monte Carlo simulations in the canonical ensemble, we have studied the
magnetic anisotropy in Fe/Dy amorphous multilayers. This work has been
motivated by experimental results which show a clear correlation between the
magnetic perpendicular anisotropy and the substrate temperature during
elaboration of the samples. Our aim is to relate macroscopic magnetic
properties of the multilayers to their structure, more precisely their
concentration profile. Our model is based on concentration dependent exchange
interactions and spin values, on random magnetic anisotropy and on the
existence of locally ordered clusters that leads to a perpendicular
magnetisation. Our results evidence that a compensation point occurs in the
case of an abrupt concentration profile. Moreover, an increase of the
noncollinearity of the atomic moments has been evidenced when the Dy anisotropy
constant value grows. We have also shown the existence of inhomogeneous
magnetisation profiles along the samples which are related to the concentration
profiles.",0807.1262v1
2008-08-28,Giant magnetic anisotropy of the bulk antiferromagnets IrMn and IrMn3,"Theoretical predictions of the magnetic anisotropy of antiferromagnetic
materials are demanding due to a lack of experimental techniques which are
capable of a direct measurement of this quantity. At the same time it is highly
significant due to the use of antiferromagnetic components in magneto-resistive
sensor devices where the stability of the antiferromagnet is of upmost
relevance. We perform an ab-initio study of the ordered phases of IrMn and
IrMn3, the most widely used industrial antiferromagnets. Calculating the form
and the strength of the magnetic anisotropy allows the construction of an
effective spin model, which is tested against experimental measurements
regarding the magnetic ground state and the Neel temperature. Our most
important result is the extremely strong second order anisotropy for IrMn3
appearing in its frustrated triangular magnetic ground state, a surprising fact
since the ordered L12 phase has a cubic symmetry. We explain this large
anisotropy by the fact that cubic symmetry is locally broken for each of the
three Mn sub-lattices.",0808.3900v1
2008-09-04,Properties of anisotropic magnetic impurities on surfaces,"Using numerical renormalization group techniques, we study static and dynamic
properties of a family of single-channel Kondo impurity models with axial
magnetic anisotropy $DS_z^2$ terms; such models are appropriate to describe
magnetic impurity atoms adsorbed on non-magnetic surfaces, which may exhibit
surface Kondo effect. We show that for positive anisotropy $D$ and for any spin
$S$, the systems behave at low temperatures as regular Fermi liquids with fully
compensated impurity spin. The approach to the stable fixed point depends on
the value of the spin $S$ and on the ratio $D/T_K^{(0)}$, where $T_K^{(0)}$ is
the Kondo temperature in the absence of the anisotropy. For S=1, the screening
occurs in two stages if $D<T_K^{(0)}$; the second Kondo temperature is
exponentially reduced in this case. More generally, there is an effective
spin-1/2 Kondo effect for any integer $S$ if $D<T_K^{(0)}$ and for any
half-integer $S$ if $D>T_K^{(0)}$. For negative anisotropy $D$, the system is a
non-Fermi liquid with residual anisotropic exchange interaction. However, the
presence of transverse magnetic anisotropy $E(S_x^2-S_y^2)$ restores
Fermi-liquid behavior in real systems.",0809.0759v1
2008-10-28,Competition between Surface Energy and Elastic Anisotropies in the Growth of Coherent Solid State Dendrites,"A new phase field model of microstructural evolution is presented that
includes the effects of elastic strain energy. The model's thin interface
behavior is investigated by mapping it onto a recent model developed by
Echebarria et al (Phys Rev E, 70:061604,2004). Exploiting this thin interface
analysis the growth of solid state dendrites are simulated with diffuse
interfaces and the phase field and mechanical equilibrium equations are solved
in real space on an adaptive mesh. A morphological competition between surface
energy anisotropy and elastic anisotropy is examined. Two dimensional
simulations are reported that show that solid state dendritic structures
undergo a transition from a surface dominated [10] growth direction to an
elastically driven [11] growth direction by changes in the elastic anisotropy,
the surface anisotropy and the supersaturation. Using the curvature and strain
corrections to the equilibrium interfacial composition and linear stability
theory for isotropic precipitates as calculated by Mullins and Sekerka, the
dominant growth morphology is predicted.",0810.4978v1
2008-11-03,Using CMBR analysis tools for flow anisotropies in relativistic heavy-ion collisions,"Recently we have shown that there are crucial similarities in the physics of
cosmic microwave background radiation (CMBR) anisotropies and the flow
anisotropies in relativistic heavy-ion collision experiments (RHICE). We also
argued that, following CMBR anisotropy analysis, a plot of root-mean square
values of the flow coefficients, calculated in a lab fixed frame for RHICE, can
yield important information about the nature of initial state anisotropies and
their evolution. Here we demonstrate the strength of this technique by showing
that elliptic flow for non-central collisions can be directly determined from
such a plot without any need for the determination of event-plane.",0811.0292v2
2008-12-04,Might we eventually understand the origin of the dark matter velocity anisotropy?,"The density profile of simulated dark matter structures is fairly
well-established, and several explanations for its characteristics have been
put forward. In contrast, the radial variation of the velocity anisotropy has
still not been explained. We suggest a very simple origin, based on the shapes
of the velocity distributions functions, which are shown to differ between the
radial and tangential directions. This allows us to derive a radial variation
of the anisotropy profile which is in good agreement with both simulations and
observations. One of the consequences of this suggestion is that the velocity
anisotropy is entirely determined once the density profile is known. We
demonstrate how this explains the origin of the \gamma-\beta relation, which is
the connection between the slope of the density profile and the velocity
anisotropy. These findings provide us with a powerful tool, which allows us to
close the Jeans equations.",0812.1048v1
2008-12-20,Magnetic anisotropy modulation of magnetite in Fe3O4/BaTiO3(100) epitaxial structures,"Temperature dependent magnetometry and transport measurements on epitaxial
Fe3O4 films grown on BaTiO3(100) single crystals by molecular beam epitaxy show
a series of discontinuities, that are due to changes in the magnetic anisotropy
induced by strain in the different crystal phases of BaTiO3. The magnetite film
is under tensile strain at room temperature, which is ascribed to the lattice
expansion of BaTiO3 at the cubic to tetragonal transition, indicating that the
magnetite film is relaxed at the growth temperature. From the magnetization
versus temperature curves, the variation in the magnetic anisotropy is
determined and compared with the magnetoelastic anisotropies. These results
demonstrate the possibility of using the piezoelectric response of BaTiO3 to
modulate the magnetic anisotropy of magnetite films.",0812.3930v1
2009-02-02,Critical Anisotropies of a Geometrically-Frustrated Triangular-Lattice Antiferromagnet,"This work examines the critical anisotropy required for the local stability
of the collinear ground states of a geometrically-frustrated triangular-lattice
antiferromagnet (TLA). Using a Holstein-Primakoff expansion, we calculate the
spin-wave frequencies for the 1, 2, 3, 4, and 8-sublattice (SL) ground states
of a TLA with up to third neighbor interactions. Local stability requires that
all spin-wave frequencies are real and positive. The 2, 4, and 8-SL phases
break up into several regions where the critical anisotropy is a different
function of the exchange parameters. We find that the critical anisotropy is a
continuous function everywhere except across the 2-SL/3-SL and 3-SL/4-SL phase
boundaries, where the 3-SL phase has the higher critical anisotropy.",0902.0359v1
2009-03-04,"Resistivity Anisotropy of $AE$Fe$_2$As$_2$ ($AE$ =Ca, Sr, Ba): direct versus Montgomery technique measurements","The anisotropy of electrical resistivity was measured in parent compounds of
the iron-arsenic high temperature superconductors, AEFe2As2 with Alkali Earth
elements AE=Ca,Sr, Ba. Measurements were performed using both the Montgomery
technique and direct resistivity measurements on samples cut along principal
crystallographic directions. The anisotropy ratio \gamma_\rho=\rho_c/\rho_a is
well below 10 for all compounds in the whole temperature range studied (4 to
300 K), in notable contrast to previous reports. The anisotropy at room
temperature increases from about 2 in Ca, to about 4 in Sr and Ba. In all
compounds the resistivity ratio decreases on cooling through the
structural/antiferromagnetic transition temperature T_{SM}, with the change
mainly coming from stronger variation in \rho_a as compared with \rho_c. This
suggests that the transitions stronger affect the two-dimensional parts of the
Fermi surface. We compare our experimental observations with band structure
calculations, and find similar trend in the evolution of anisotropy with the
size of AE ion. Our results show that the electronic structure of the iron
pnictides has large contribution from three-dimensional areas of the Fermi
surface.",0903.0820v1
2009-03-19,Magnetic Anisotropy and Magnetization Dynamics of Individual Atoms and Clusters of Fe and Co on Pt(111),"The recently discovered giant magnetic anisotropy of single magnetic Co atoms
raises the hope of magnetic storage in small clusters. We present a joint
experimental and theoretical study of the magnetic anisotropy and the spin
dynamics of Fe and Co atoms, dimers, and trimers on Pt(111). Giant anisotropies
of individual atoms and clusters as well as lifetimes of the excited states
were determined with inelastic scanning tunneling spectroscopy. The short
lifetimes due to hybridization-induced electron-electron scattering oppose the
magnetic stability provided by the magnetic anisotropies.",0903.3337v1
2009-06-08,Tunable magnetic properties of arrays of Fe(110) nanowires grown on kinetically-grooved W(110) self-organized templates,"We report a detailed magnetic study of a new type of self-organized nanowires
disclosed briefly previously [B. Borca et al., Appl. Phys. Lett. 90, 142507
(2007)]. The templates, prepared on sapphire wafers in a kinetically-limited
regime, consist of uniaxially-grooved W(110) surfaces, with a lateral period
here tuned to 15nm. Fe deposition leads to the formation of (110) 7 nm-wide
wires located at the bottom of the grooves. The effect of capping layers (Mo,
Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was
studied. Significant discrepancies with figures known for thin flat films are
evidenced and discussed in terms of step anisotropy and strain-dependent
surface anisotropy. Demagnetizing coeffcients of cylinders with a triangular
isosceles cross-section have also been calculated, to estimate the contribution
of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the
interface element was used to tune the blocking temperature of the wires, here
from 50K to 200 K.",0906.1510v1
2009-07-02,Large Scale Cosmic Ray Anisotropy With IceCube,"We report on a study of the anisotropy in the arrival direction of cosmic
rays with a median energy per Cosmic Ray (CR) particle of ~ 14 TeV using data
from the IceCube detector. IceCube is a neutrino observatory at the
geographical South Pole, when completed it will comprise 80 strings plus 6
additional strings for the low energy array Deep Core. The strings are deployed
in the deep ice between 1,450 and 2,450 meters depth, each string containing 60
optical sensors. The data used in this analysis were collected from April 2007
to March 2008 with 22 deployed strings. The data contain ~ 4.3 billion downward
going muon events. A two-dimensional skymap is presented with an evidence of
0.06% large scale anisotropy. The energy dependence of this anisotropy at
median energies per CR particle of 12 TeV and 126 TeV is also presented in this
work. This anisotropy could arise from a number of possible effects; it could
further enhance the understanding of the structure of the galactic magnetic
field and possible cosmic ray sources.",0907.0498v2
2009-08-07,Estimators for CMB Statistical Anisotropy,"We use quadratic maximum-likelihood (QML) estimators to constrain models with
Gaussian but statistically anisotropic Cosmic Microwave Background (CMB)
fluctuations, using CMB maps with realistic sky-coverage and instrumental
noise. This approach is optimal when the anisotropy is small, or when checking
for consistency with isotropy. We demonstrate the power of the QML approach by
applying it to the WMAP data to constrain several models which modulate the
observed CMB fluctuations to produce a statistically anisotropic sky. We first
constrain an empirically motivated spatial modulation of the observed CMB
fluctuations, reproducing marginal evidence for a dipolar modulation pattern
with amplitude 7% at L < 60, but demonstrate that the effect decreases at
higher multipoles and is 1% at L~500. We also look for evidence of a
direction-dependent primordial power spectrum, finding a very statistically
significant quadrupole signal nearly aligned with the ecliptic plane; however
we argue this anisotropy is largely contaminated by observational systematics.
Finally, we constrain the anisotropy due to a spatial modulation of adiabatic
and isocurvature primordial perturbations, and discuss the close relationship
between anisotropy and non-Gaussianity estimators.",0908.0963v4
2009-08-10,Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind,"The proton temperature anisotropy in the solar wind is known to be
constrained by the theoretical thresholds for pressure anisotropy-driven
instabilities. Here we use approximately 1 million independent measurements of
gyroscale magnetic fluctuations in the solar wind to show for the first time
that these fluctuations are enhanced along the temperature anisotropy
thresholds of the mirror, proton oblique firehose, and ion cyclotron
instabilities. In addition, the measured magnetic compressibility is enhanced
at high plasma beta ($\beta_\parallel \gtrsim 1$) along the mirror instability
threshold but small elsewhere, consistent with expectations of the mirror mode.
The power in this frequency (the 'dissipation') range is often considered to be
driven by the solar wind turbulent cascade, an interpretation which should be
qualified in light of the present results. In particular, we show that the
short wavelength magnetic fluctuation power is a strong function of
collisionality, which relaxes the temperature anisotropy away from the
instability conditions and reduces correspondingly the fluctuation power.",0908.1274v1
2009-09-07,Bianchi type III models with anisotropic dark energy,"The general form of the anisotropy parameter of the expansion for Bianchi
type-III metric is obtained in the presence of a single diagonal imperfect
fluid with a dynamically anisotropic equation of state parameter and a
dynamical energy density in general relativity. A special law is assumed for
the anisotropy of the fluid which reduces the anisotropy parameter of the
expansion to a simple form. The exact solutions of the Einstein field
equations, under the assumption on the anisotropy of the fluid, are obtained
for exponential and power-law volumetric expansions. The isotropy of the fluid,
space and expansion are examined. It is observed that the universe can approach
to isotropy monotonically even in the presence of an anisotropic fluid. The
anisotropy of the fluid also isotropizes at later times for accelerating models
and evolves into the well-known cosmological constant in the model for
exponential volumetric expansion.",0909.1025v1
2010-01-07,Jet-photons from an anisotropic {\em Quark-Gluon-Plasma},"We calculate the $p_T$ distributions of jet conversion photons from {\em
Quark Gluon Plasma} with pre-equilibrium momentum-space anisotropy. A
phenomenological model has been used for the time evolution of hard momentum
scale $p_{\rm hard}(\tau)$ and anisotropy parameter $\xi(\tau)$. As a result of
pre-equilibrium momentum-space anisotropy, we find significant modification of
the jet conversion photon $p_T$ distribution. For example, with {\em fixed
initial condition} (FIC) pre-equilibrium anisotropy, we predict significant
enhancement of the jet-photon $p_T$ distribution in the entire region, whereas
for pre-equilibrium anisotropy with {\em fixed final multiplicity} (FFM),
suppression of the jet conversion photons $p_T$ distribution is observed. The
results with FFM (as it is the most realistic situation) have been compared
with high $p_T$ PHENIX photon data. It is found that the data is reproduced
well if the isotropization time lies within $1.5$ fm/c.",1001.1054v2
2010-01-20,On the global density slope-anisotropy inequality,"Starting from the central density slope-anisotropy theorem of An and Evans
(2006), recent investigations have shown that the involved density
slope-anisotropy inequality holds not only at the center, but at all radii
(i.e. globally) in a very large class of spherical systems with positive
phase-space distribution function. Here we present some additional analytical
cases that further extend the validity of the global density slope-anisotropy
inequality. These new results, several numerical evidences, and the absence of
known counter-examples, lead us to conjecture that the global density
slope-anisotropy inequality could actually be a universal property of spherical
systems with positive distribution function.",1001.3632v1
2010-02-11,Electron temperature anisotropy in an expanding plasma: Particle-in-Cell simulations,"We perform fully-kinetic particle-in-cell simulations of an hot plasma that
expands radially in a cylindrical geometry. The aim of the paper is to study
the consequent development of the electron temperature anisotropy in an
expanding plasma flow as found in a collisionless stellar wind. Kinetic plasma
theory and simulations have shown that the electron temperature anisotropy is
controlled by fluctuations driven by electromagnetic kinetic instabilities. In
this study the temperature anisotropy is driven self-consistently by the
expansion. While the expansion favors an increase of parallel anisotropy
($T_\parallel>T_\perp$), the onset of the firehose instability will tend to
decrease it. We show the results for a supersonic, subsonic, and static
expansion flows, and suggest possible applications of the results for the solar
wind and other stellar winds.",1002.2349v1
2010-03-02,Non-detection of a statistically anisotropic power spectrum in large-scale structure,"We search a sample of photometric luminous red galaxies (LRGs) measured by
the Sloan Digital Sky Survey (SDSS) for a quadrupolar anisotropy in the
primordial power spectrum, in which P(\vec{k}) is an isotropic power spectrum
P(k) multiplied by a quadrupolar modulation pattern. We first place limits on
the 5 coefficients of a general quadrupole anisotropy. We also consider
axisymmetric quadrupoles of the form P(\vec{k}) = P(k){1 +
g_*[(\hat{k}\cdot\hat{n})^2-1/3]} where \hat{n} is the axis of the anisotropy.
When we force the symmetry axis \hat{n} to be in the direction (l,b)=(94
degrees,26 degrees) identified in the recent Groeneboom et al. analysis of the
cosmic microwave background, we find g_*=0.006+/-0.036 (1 sigma). With uniform
priors on \hat{n} and g_* we find that -0.41<g_*<+0.38 with 95% probability,
with the wide range due mainly to the large uncertainty of asymmetries aligned
with the Galactic Plane. In none of these three analyses do we detect evidence
for quadrupolar power anisotropy in large scale structure.",1003.0673v2
2010-04-19,Analytic formulae for the off-center CMB anisotropy in a general spherically symmetric universe,"The local void model has recently attracted considerable attention because it
can explain the apparent accelerated expansion of the present universe without
introducing dark energy. However, in order to justify this model as an
alternative to the standard $\Lambda$CDM cosmology, the model should be tested
by various observations, such as the CMB temperature anisotropy, besides the
distance-redshift relation of SNIa. For this purpose, we derive analytic
formulae for the dipole and quadrupole moments of the CMB temperature
anisotropy that hold for any spherically symmetric universe model and can be
used to compare consequences of such a model with observations of the CMB
temperature anisotropy rigorously. We check that our formulae are consistent
with the numerical studies previously made for the CMB temperature anisotropy
in the void model. We also update the constraints concerning the location of
the observers in the void model by applying our analytic dipole formula with
the latest WMAP data.",1004.3089v2
2010-05-10,Anisotropy of Magnetic Interactions in the Spin-Ladder Compound (C$_5$H$_{12}$N)$_2$CuBr$_4$,"Magnetic excitations in the spin-ladder material (C$_5$H$_{12}$N)$_2$CuBr$_4$
[BPCB] are probed by high-resolution multi-frequency electron spin resonance
(ESR) spectroscopy. Our experiments provide a direct evidence for a biaxial
anisotropy ($\sim 5\%$ of the dominant exchange interaction), that is in
contrast to a fully isotropic spin-ladder model employed for this system
previously. It is argued that this anisotropy in BPCB is caused by spin-orbit
coupling, which appears to be important for describing magnetic properties of
this compound. The zero-field zone-center gap in the excitation spectrum of
BPCB, $\Delta_0/k_{B}=16.5$ K, is detected directly. Furthermore, an ESR
signature of the inter-ladder exchange interactions is obtained. The detailed
characterization of the anisotropy in BPCB completes the determination of the
full spin hamiltonian of this exceptional spin-ladder material and shows ways
to study anisotropy effects in spin ladders.",1005.1474v1
2010-06-11,How general is the global density slope-anisotropy inequality?,"Following the seminal result of An & Evans, known as the central density
slope-anisotropy theorem, successive investigations unexpectedly revealed that
the density slope-anisotropy inequality holds not only at the center, but at
all radii in a very large class of spherical systems whenever the phase-space
distribution function is positive. In this paper we derive a criterion that
holds for all spherical systems in which the augmented density is a separable
function of radius and potential: this new finding allows to unify all the
previous results in a very elegant way, and opens the way for more general
investigations. As a first application, we prove that the global density
slope-anisotropy inequality is also satisfied by all the explored additional
families of multi-component stellar systems. The present results, and the
absence of known counter-examples, lead us to conjecture that the global
density slope-anisotropy inequality could actually be a universal property of
spherical systems with positive distribution function.",1006.2344v1
2010-06-18,Azimuthal anisotropy of neutral pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV: Path-length dependence of jet quenching and the role of initial geometry,"We have measured the azimuthal anisotropy of pi0's for 1 < pT < 18 GeV/c for
Au+Au collisions at sqrt s_NN = 200 GeV. The observed anisotropy shows a
gradual decrease in 3 < pT < 7 - 10 GeV/c, but remains positive beyond 10
GeV/c. The magnitude of this anisotropy is under-predicted, up to at least 10
GeV/c, by current perturbative QCD (pQCD) energy-loss model calculations. An
estimate of the increase in anisotropy expected from initial-geometry
modification due to gluon saturation effects and initial-geometry fluctuations
is insufficient to account for this discrepancy. Calculations which implement a
path length dependence steeper than what is implied by current pQCD energy-loss
models, show reasonable agreement with the data.",1006.3740v1
2010-07-20,Conductivity anisotropy in the antiferromagnetic state of iron pnictides,"Recent experiments on iron pnictides have uncovered a large in-plane
resistivity anisotropy with a surprising result: the system conducts better in
the antiferromagnetic x direction than in the ferromagnetic y direction. We
address this problem by calculating the ratio of the Drude weight along the x
and y directions, Dx/Dy, for the mean-field Q=(\pi,0) magnetic phase diagram of
a five-band model for the undoped pnictides. We find that Dx/Dy ranges between
0.3 < D_x/D_y < 1.4 for different interaction parameters. Large values of
orbital ordering favor an anisotropy opposite to the one found experimentally.
On the other hand D_x/D_y is strongly dependent on the topology and morfology
of the reconstructed Fermi surface. Our results points against orbital ordering
as the origin of the observed conductivity anisotropy, which may be ascribed to
the anisotropy of the Fermi velocity.",1007.3483v2
2010-09-09,A Theoretical Diagnosis on Light Speed Anisotropy from GRAAL Experiment,"The light speed anisotropy, i.e., the variation of the light speed with
respect to the direction in an ""absolute"" reference frame, is a profound issue
in physics. The one-way experiment, performed at the GRAAL facility of the
European Synchrotron Radiation Facility (ESRF) in Grenoble, reported results on
the light speed anisotropy by Compton scattering of laser photons on
high-energy electrons. So far, most articles concerned with the GRAAL data have
established only the upper bounds on the anisotropy parameters based on
available theories. We use a new theory of the Lorentz invariance violation to
analyse the available GRAAL data and obtain the stringent upper limit of the
order $2.4\times10^{-14}$ on the Lorentz violation parameters. In the meantime,
we also can reproduce the allowed light speed anisotropy appearing in the
azimuthal distribution of the GRAAL experimental data, and find that the
best-fit parameters are compatible with the competitive upper bounds.",1009.1675v2
2010-09-09,Translation of collision geometry fluctuations into momentum anisotropies in relativistic heavy-ion collisions,"We develop a systematic framework for the study of the initial collision
geometry fluctuations in relativistic heavy-ion collisions and investigate how
they evolve through different stages of the fireball history and translate into
final particle momentum anisotropies. We find in our event-by-event analysis
that only the few lowest momentum anisotropy parameters survive after the
hydrodynamical evolution of the system. The geometry of the produced medium is
found to be affected by the pre-equilibrium evolution of the medium and the
thermal smearing of the discretized event-by-event initial conditions, both of
which tend to smear out the spatial anisotropies. We find such effects to be
more prominent for higher moments than for lower moments. The correlations
between odd and even spatial anisotropy parameters during the pre-equilibrium
expansion are quantitatively studied and found to be small. Our study provides
a theoretical foundation for the understanding of initial state fluctuations
and the collective expansion dynamics in relativistic heavy-ion collisions.",1009.1847v2
2010-09-29,Effects of the galactic magnetic field upon large scale anisotropies of extragalactic Cosmic Rays,"The large scale pattern in the arrival directions of extragalactic cosmic
rays that reach the Earth is different from that of the flux arriving to the
halo of the Galaxy as a result of the propagation through the galactic magnetic
field. Two different effects are relevant in this process: deflections of
trajectories and (de)acceleration by the electric field component due to the
galactic rotation. The deflection of the cosmic ray trajectories makes the flux
intensity arriving to the halo from some direction to appear reaching the Earth
from another direction. This applies to any intrinsic anisotropy in the
extragalactic distribution or, even in the absence of intrinsic anisotropies,
to the dipolar Compton-Getting anisotropy induced when the observer is moving
with respect to the cosmic rays rest frame. For an observer moving with the
solar system, cosmic rays traveling through far away regions of the Galaxy also
experience an electric force coming from the relative motion (due to the
rotation of the Galaxy) of the local system in which the field can be
considered as being purely magnetic. This produces small changes in the
particles momentum that can originate large scale anisotropies even for an
isotropic extragalactic flux.",1009.5891v1
2010-10-20,On the universality of the global slope -- anisotropy inequality,"Recently, some intriguing results have lead to speculations whether the
central density slope -- velocity dispersion anisotropy inequality (An & Evans)
actually holds at all radii for spherical dynamical systems. We extend these
studies by providing a complete analysis of the global slope -- anisotropy
inequality for all spherical systems in which the augmented density is a
separable function of radius and potential. We prove that these systems indeed
satisfy the global inequality if their central anisotropy is $\beta_0\leq 1/2$.
Furthermore, we present several systems with $\beta_0 > 1/2$ for which the
inequality does not hold, thus demonstrating that the global density slope --
anisotropy inequality is not a universal property. This analysis is a
significant step towards an understanding of the relation for general spherical
systems.",1010.4301v1
2010-11-06,Effect of anisotropy on the field induced quantum critical properties of the three dimensional s=1/2 Heisenberg model,"The field induced quantum critical properties of the three dimensional
spin-1/2 anisotropic antiferromagnetic Heisenberg model has been studied. We
have investigated the quantum phase transition between the spiral order and
field induced ferromagnetic order by means of Bose-Einstein condensation of
magnons in terms of a bosonic representation. The effect of in-plane anisotropy
on the critical properties has been studied via the bosonic model by Green's
function approach. We have found an analytic expression for the gap exponent in
addition to numerical results for the critical magnetic field in terms of
anisotropy parameter. The in-plane anisotropy breaks the U(1) symmetry
explicitly which changes the universal behavior by a drastic change on the gap
exponent. Moreover, the critical magnetic field depends strongly on the
in-plane anisotropies. The divergence of the transverse structure factor at the
antiferromagnetic wave vector confirms the onset of the magnetic order which
scales with the negative value of gap exponent as the magnetic field approaches
the critical one. The transverse staggered magnetization as an order parameter
vanishes with exponent $\beta=0.5$ when the magnetic field reaches its critical
value in low field region.",1011.1574v1
2010-11-24,Anisotropies in the gamma-ray sky from millisecond pulsars,"Pulsars emerge in the Fermi era as a sizable population of gamma-ray sources.
Millisecond pulsars (MSPs) constitute an older subpopulation whose sky
distribution extends to high Galactic latitudes, and it has been suggested that
unresolved members of this class may contribute a significant fraction of the
measured large-scale isotropic gamma-ray background (IGRB). We investigate the
possible energy-dependent contribution of unresolved MSPs to the anisotropy of
the Fermi-measured IGRB. For observationally-motivated MSP population models,
we show that the preliminary Fermi anisotropy measurement places an interesting
constraint on the abundance of MSPs in the Galaxy and the typical MSP flux,
about an order of magnitude stronger than constraints on this population
derived from the intensity of the IGRB alone. We also examine the possibility
of a MSP component in the IGRB mimicking a dark matter signal in
anisotropy-based searches, and conclude that the energy dependence of an
anisotropy signature would distinguish MSPs from all but very light dark matter
candidates.",1011.5501v2
2010-12-06,Ab-initio description of the magnetic shape anisotropy due to the Breit interaction,"A quantum-mechanical description of the magnetic shape anisotropy, that is
usually ascribed to the classical magnetic dipole-dipole interaction, has been
developed. This is achieved by including the Breit-interaction, that can be
seen as an electronic current-current interaction in addition to the
conventional Coulomb interaction, within fully relativistic band structure
calculations. The major sources of the magnetic anisotropy, spin-orbit coupling
and the Breit-interaction, are treated coherently this way. This seems to be
especially important for layered systems for which often both sources
contribute with opposite sign to the magnetic anisotropy energy. Applications
to layered transition metal systems are presented to demonstrate the
implications of this new approach in treating the magnetic shape anisotropy.",1012.1115v1
2011-03-15,Amplitudes of thermal and kinetic Sunyaev-Zel'dovich signals from small-scale CMB anisotropies,"While the arcminute-scale Cosmic Microwave Background (CMB) anisotropies are
due to secondary effects, point sources dominate the total anisotropy power
spectrum. At high frequencies the point sources are primarily in the form of
dusty, star-forming galaxies. Both Herschel and Planck have recently measured
the anisotropy power spectrum of cosmic infrared background (CIB) generated by
dusty, star-forming galaxies from degree to sub-arcminute angular scales,
including the non-linear clustering of these galaxies at multipoles of 3000 to
6000 relevant to CMB secondary anisotropy studies. We scale the CIB angular
power spectra to CMB frequencies and interpret the combined WMAP-7 year and
arcminute-scale Atacama Cosmology Telescope (ACT) and South Pole Telescope
(SPT) CMB power spectra measurements to constrain the Sunyaev-Zel'dovich (SZ)
effects. Allowing the CIB clustering amplitude to vary, we constrain the
amplitudes of thermal and kinetic SZ power spectra at 150 GHz.",1103.3051v2
2011-03-31,Constraints on velocity anisotropy of spherical systems with separable augmented densities,"If the augmented density of a spherical anisotropic system is assumed to be
multiplicatively separable to functions of the potential and the radius, the
radial function, which can be completely specified by the behavior of the
anisotropy parameter alone, also fixes the anisotropic ratios of every
higher-order velocity moment. It is inferred from this that the non-negativity
of the distribution function necessarily limits the allowed behaviors of the
radial function. This restriction is translated into the constraints on the
behavior of the anisotropy parameter. We find that not all radial variations of
the anisotropy parameter satisfy these constraints and thus that there exist
anisotropy profiles that cannot be consistent with any separable augmented
density.",1104.0014v2
2011-04-11,Asymmetric magnetization splitting in diamond domain structure: Dependence on exchange interaction and anisotropy,"The distributions of magnetization orientation for both Landau and diamond
domain structures in nano-rectangles have been investigated by micromagnetic
simulation with various exchange coefficient and anisotropy constant. Both
symmetric and asymmetric magnetization splitting are found in diamond domain
structure, as well as only symmetric magnetization splitting in Landau
structure. In the Landau structure, the splitting angle increases with the
exchange coefficient but decreases slightly with the anisotropy constant,
suggesting that the exchange interaction mainly contributes to the
magnetization splitting in Landau structure. However in the diamond structure,
the splitting angle increases with the anisotropy constant but derceases with
the exchange coefficient, indicating that the magnetization splitting in
diamond structure is resulted from magnetic anisotropy.",1104.1819v1
2011-05-23,Orbitally and Magnetically Induced Anisotropy in Iron-based Superconductors,"Recent experimental developments in the iron pnictides have unambiguously
demonstrated the existence of in-plane electronic anisotropy in the absence of
the long-range magnetic order. Such anisotropy can arise from orbital ordering,
which is described by an energy splitting between the two otherwise degenerate
$d_{xz}$ and $d_{yz}$ orbitals. By including this phenomenological orbital
order into a five-orbital Hubbard model, we obtain the mean-field solutions
where the magnetic order is determined self-consistently. Despite sensitivity
of the resulting states to the input parameters, we find that a weak orbital
order that places the $d_{yz}$ orbital slightly higher in energy than the
$d_{xz}$ orbital, combined with intermediate on-site interactions, produces
band dispersions that are compatible with the photoemission results. In this
regime, the stripe antiferromagnetic order is further stabilized and the
resistivity displays the observed anisotropy. We also calculate the optical
conductivity and show that it agrees with the temperature evolution of the
anisotropy seen experimentally.",1105.4630v3
2011-07-14,Microstructure and magnetic anisotropy of electrospun Cu$_{1-x}$Zn$_x$Fe$_2$O$_4$ nanofibers: A local probe study,"Understanding the phenomena at the nanometer scale is of fundamental
importance for future improvements of desired properties of nanomaterials. We
report a detailed investigation of the microstructure and the resulting
magnetic anisotropy by magnetic, transmission electron microscope (TEM) and
M\""ossbauer measurements of the electrospun Cu$_{1-x}$Zn$_x$Fe$_2$O$_4$
nanofibers. Our results show that the electrospun Cu$_{1-x}$Zn$_x$Fe$_2$O$_4$
nanofibers exhibit nearly isotropic magnetic anisotropy. TEM measurements
indicate that the nanofibers are composed of loosely connected and randomly
aligned nanograins. As revealed by the Henkel plot, these nanofibers and the
nanograins within the nanofibers are dipolar coupled, which reduces the
effective shape anisotropy leading to a nearly random configuration of the
magnetic moments inside the nanofibers, hence, the observed nearly isotropic
magnetic anisotropy can be easily understood.",1107.2820v2
2011-08-19,Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films,"This paper shows the correlation between chemical order, lattice strains and
magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A
detailed magnetic characterization has been performed using vector field
magnetometery combined with numerical Stoner-Wohlfarth analysis. We demonstrate
the presence of three types of in-plane anisotropies: one biaxial, as expected
for the cubic symmetry, and other two uniaxial ones. The three anisotropies
show different behavior with the annealing temperature. The biaxial anisotropy
shows a monotonous increase. The uniaxial anisotropy, parallel with the hard
biaxial axes, related to the chemical homogeneity, decreases, while the other,
supposed to have magnetostatic origin, remains constant.",1108.4043v2
2011-10-12,Origin of perpendicular anisotropy in thin Co/Pt bilayers grown on alumina,"We investigate in this paper the origin of perpendicular anisotropy in Co
(1.6 nm)/Pt (3.0 nm) bilayers grown on alumina and annealed up to
650$^{\circ}$C. Above 350$^{\circ}$C, all layers exhibit perpendicular
anisotropy. Then coercive fields increase linearly with annealing temperature
following two different rates: 0.05 T/100$^{\circ}$C below 550$^{\circ}$C and
0.8 T/100$^{\circ}$C above. By making careful structural characterizations
using x-ray diffraction and transmission electron microscopy, we demonstrate
the presence of short range correlation of L1$_{1}$ type below 550$^{\circ}$C
whereas above 550$^{\circ}$C, L1$_{0}$ chemical ordering is observed. We
conclude that perpendicular anisotropy observed in Co/Pt bilayers grown on
alumina and annealed may not only be due to interface anisotropy as usually
invoked but also to CoPt alloying and chemical ordering that take place during
post-growth annealing.",1110.2628v1
2011-11-08,Issues on Generating Primordial Anisotropies at the End of Inflation,"We revisit the idea of generating primordial anisotropies at the end of
inflation in models of inflation with gauge fields. To be specific we consider
the charged hybrid inflation model where the waterfall field is charged under a
U(1) gauge field so the surface of end of inflation is controlled both by
inflaton and the gauge fields. Using delta N formalism properly we find that
the anisotropies generated at the end of inflation from the gauge field
fluctuations are exponentially suppressed on cosmological scales. This is
because the gauge field evolves exponentially during inflation while in order
to generate appreciable anisotropies at the end of inflation the spectator
gauge field has to be frozen and scale invariant. We argue that this is a
generic feature, that is, one can not generate observable anisotropies at the
end of inflation within an FRW background.",1111.1919v3
2011-10-26,Testing for Anisotropy of Space via an Extension of Special Relativity,"In special relativity, testing for spatial anisotropy usually means testing
for anisotropic propagation of light. This paper explores a different
possibility, in which light is still assumed to propagate isotropically in all
frames with an invariant speed, yet other physical effects exhibit a direction
dependence. If spatial isotropy is not assumed in the derivation of the
coordinates transformations, the resulting equations differ from the Lorentz
relations by an additional factor $(\dfrac{c - v}{c + v})^{\kappa}$, where
$\kappa$ is the anisotropy exponent, which depends on the direction chosen as
the x-axis. Time dilation and length contractions become direction dependent.
The anisotropy exponent is frame-independent, so no preferred isotropic frame
exists if $\kappa$ is non-vanishing. The Doppler shift can be used to measure
this exponent and determine experimentally the degree of anisotropy our
universe actually possesses.",1111.4423v1
2012-01-20,The Relation between Ion Temperature Anisotropy and Formation of Slow Shocks in Collisionless Magnetic Reconnection,"We perform a two-dimensional simulation by using an electromagnetic hybrid
code to study the formation of slow-mode shocks in collisionless magnetic
reconnection in low beta plasmas, and we focus on the relation between the
formation of slow shocks and the ion temperature anisotropy enhanced at the
shock downstream region. It is known that as magnetic reconnection develops,
the parallel temperature along the magnetic field becomes large in association
with the anisotropic PSBL (plasma sheet boundary layer) ion beams, and this
temperature anisotropy has a tendency to suppress the formation of slow shocks.
Based on our simulation result, we found that the slow shock formation is
suppressed due to the large temperature anisotropy near the X-type region, but
the ion temperature anisotropy relaxes with increasing the distance from the
magnetic neutral point. As a result, two pairs of current structures, which are
the strong evidence of dissipation of magnetic field in slow shocks, are formed
at the distance x > 115 ion inertial lengths from the neutral point.",1201.4213v1
2012-03-12,A Search for Small-Scale Anisotropy of PeV Cosmic Rays,"Recent results of Milagro, Tibet, ARGO-YBJ and IceCube experiments on the
small-scale anisotropy of Galactic cosmic rays (CRs) with energies from units
up to a few hundred TeV arise a question on a possible nature of the observed
phenomenon, as well as on the anisotropy of CRs at higher energies. An analysis
of a small-scale anisotropy of CRs with energies at around PeV registered with
the EAS MSU array presented in the article, reveals a number of regions with an
excessive flux. A typical size of the regions varies from 3 up to 12 degrees.
We study correlation of these regions with positions of potential astrophysical
sources of CRs and discuss a possible origin of the observed anisotropy.",1203.2472v1
2012-04-03,Tuning entanglement and ergodicity in two-dimensional spin systems using impurities and anisotropy,"We consider the entanglement in a two dimensional XY model in an external
magnetic field h. The model consists of a set of 7 localized spin-1/2 particles
in a two dimensional triangular lattice coupled through nearest neighbor
exchange interaction J. We examine the effect of single and double impurities
in the system as well as the degree of anisotropy on the nearest neighbor
entanglement and ergodicity of the system. We have found that the entanglement
of the system at the different degrees of anisotropy mimics that of the one
dimensional spin systems at the extremely small and large values of the
parameter h/J. The entanglement of the Ising and partially anisotropic system
show phase transition in the vicinity of h/J = 2 while the entanglement of the
isotropic system suddenly vanishes there. Also we investigate the dynamic
response of the system containing single and double impurities to an external
exponential magnetic field at different degrees of anisotropy. We have
demonstrated that the ergodicity of the system can be controlled by varying the
strength and location of the impurities as well as the degree of anisotropy of
the coupling.",1204.0759v1
2012-04-06,Measurement of the elliptic anisotropy of charged particles produced in PbPb collisions at nucleon-nucleon center-of-mass energy = 2.76 TeV,"The anisotropy of the azimuthal distributions of charged particles produced
in PbPb collisions with a nucleon-nucleon center-of-mass energy of 2.76 TeV is
studied with the CMS experiment at the LHC. The elliptic anisotropy parameter
defined as the second coefficient in a Fourier expansion of the particle
invariant yields, is extracted using the event-plane method, two- and
four-particle cumulants, and Lee--Yang zeros. The anisotropy is presented as a
function of transverse momentum (pt), pseudorapidity (eta) over a broad
kinematic range: 0.3 < pt < 20 GeV, abs(eta) < 2.4, and in 12 classes of
collision centrality from 0 to 80%. The results are compared to those obtained
at lower center-of-mass energies, and various scaling behaviors are examined.
When scaled by the geometric eccentricity of the collision zone, the elliptic
anisotropy is found to obey a universal scaling with the transverse particle
density for different collision systems and center-of-mass energies.",1204.1409v2
2012-05-08,Asymmetric velocity anisotropies in remnants of collisionless mergers,"Dark matter haloes in cosmological N-body simulations are affected by
processes such as mergers, accretion and the gravitational interaction with
baryonic matter. Typically the analysis of dark matter haloes is performed in
spherical or elliptical bins and the velocity distributions are often assumed
to be constant within those bins. However, the velocity anisotropy, which
describes differences between the radial and tangential velocity dispersion,
has recently been show to have a strong dependence on direction in the triaxial
halos formed in cosmological simulations. In this study we derive properties of
particles in cones parallel or perpendicular to the collision axis of merger
remnants. We find that the velocity anisotropy has a strong dependence on
direction. The finding that the direction-dependence of the velocity anisotropy
of a halo depends on the merger history, explains the existence of such trends
in cosmological simulations. It also explains why a large diversity is seen in
the velocity anisotropy profiles in the outer parts of high-resolution
simulations of cosmological haloes.",1205.1799v2
2012-05-17,Anisotropy of TeV and PeV cosmic rays with IceCube and IceTop,"The interaction of high energy cosmic rays with the Earth's atmosphere
produces extensive air showers of secondary particles with a large muon
component. By exploiting the sensitivity of neutrino telescopes to high energy
muons, it is possible to use these detectors for precision cosmic ray studies.
The high rate of cosmic-ray muon events provides a high-statistics data sample
that can be used to look for anisotropy in the arrival directions of the parent
particles at the per-mille level.
  This paper reports on the observation of anisotropy in the cosmic ray data
collected with the IceCube neutrino telescope in the 20-400 TeV energy range at
multiple angular scales. New data from the IceTop air shower array, located on
the ice surface above IceCube, shows an anisotropy that is consistent with the
high-energy IceCube results. The sensitivity of IceTop to all the components of
the extensive air shower will allow us to explore in more detail the
characteristics of the primary cosmic rays associated with the observed
anisotropy.",1205.3969v1
2012-05-23,On the Accuracy of Anisotropic Fast Marching,"The fast marching algorithm, and its variants, solves numerically the
generalized eikonal equation associated to an underlying riemannian metric. A
major challenge for these algorithms is the non-isotropy of the riemannian
metric. Applications of the eikonal equation to image processing often involve
pronounced anisotropies, which motivated the design of new algorithms.
  A recently introduced variant of the fast marching algorithm addresses the
problem of large anisotropies using an algebraic tool named lattice basis
reduction. The numerical complexity of this algorithm is insensitive to
anisotropy, under weak assumptions. We establish in this paper, in the
simplified setting of a constant riemannian metric, that the accuracy of this
algorithm is also extremely robust to anisotropy : in an average sense, it is
independent of the anisotropy ratio. We also extend this algorithm to higher
dimension.",1205.5300v1
2012-07-06,Ferromagnetic Quantum critical behavior in three-dimensional Hubbard model with transverse anisotropy,"One-band Hubbard model with transverse anisotropy is considered at density of
electrons $n=0.4$. It is shown that when the anisotropy is appropriately
chosen, the ground state is ferromagnetic with magnetic order perpendicular to
the anisotropy. The increasing of the ratio $\frac tU$, where $t$ is the
hopping parameter and $U$ is the Coulomb repulsion, decreases the Curie
temperature, and the system arrives at the quantum critical point $(T_C=0)$.
The result is obtained introducing Schwinger bosons and slave Fermions
representation of the electron operators. Integrating out the spin-singlet
Fermi fields an effective Heisenberg model with ferromagnetic exchange constant
is obtained for vectors which identifies the local orientation of the spin of
the itinerant electrons. The amplitude of the spin vectors is an effective spin
of the itinerant electrons accounting for the fact that some sites, in the
ground state, are doubly occupied or empty. Owing to the anisotropy, the magnon
fluctuations drive the system to quantum criticality and when the effective
spin is critically small these fluctuations suppress the magnetic order.",1207.1674v1
2013-01-10,Spectrum and Anisotropy of Cosmic Rays at TeV-PeV-energies and Contribution of Nearby Sources,"The role of nearby galactic sources, the supernova remnants, in formation of
observed energy spectrum and anisotropy of high-energy cosmic rays is studied.
The list of these sources is made up based on radio, X-ray and gamma-ray
catalogues. The distant sources are treated statistically as ensemble of
sources with random positions and ages. The source spectra are defined based on
the modern theory of cosmic ray acceleration in supernova remnants while the
propagation of cosmic rays in the interstellar medium is described in the
frameworks of galactic diffusion model. Calculations of anisotropy are made to
reproduce the experimental procedure of getting the two-dimensional anisotropy.
The detailed comparison of calculations with cosmic ray data is made. We
explained simultaneously the new cosmic ray data on a fine structure of all
particle spectra around the knee and the amplitude and direction of the dipole
component of anisotropy in the wide energy range 1 TeV - 1 EeV. Made
assumptions do not look exotic, and they confirm the modern understanding of
cosmic ray origin.",1301.2028v2
2013-01-20,Anisotropy in a Nonsingular Bounce,"Following recent claims relative to the question of large anisotropy
production in regular bouncing scenarios, we study the evolution of such
anisotropies in a model where an Ekpyrotic phase of contraction is followed by
domination of a Galileon-type Lagrangian which generates a non-singular bounce.
We show that the anisotropies decrease during the phase of Ekpyrotic
contraction (as expected) and that they can be constrained to remain small
during the non-singular bounce phase (a non-trivial result). Specifically, we
derive the e-folding number of the phase of Ekpyrotic contraction which leads
to a present-day anisotropy in agreement with current observational bounds.",1301.4703v2
2013-06-27,Amorphous GdFeCo Films Exhibiting Large and Tunable Perpendicular Magnetic Anisotropy,"We report the compositional and temperature dependence of magnetic
compensation in amorphous GdFeCo films. Magnetic compensation is attributed to
the competition between antiferromagnetic coupling of rare-earth with
transition-metal (TM) ions and ferromagnetic interaction between the TM ions.
The low-Gd region from 20 to 34 at. % was found to exhibit compensation
phenomena characterized by a low saturation magnetization and perpendicular
magnetic anisotropy (PMA) near the compensation temperature. Compensation
temperature was not observed in previously unreported high-Gd region from 52 to
59 at. %, in qualitative agreement with results from recent model calculations.
However, low magnetization was achieved at room temperature, accompanied by a
large PMA with coercivity reaching ~6.6 kOe. The observed perpendicular
magnetic anisotropy of amorphous GdFeCo films probably has a structural origin
consistent with certain aspects of the atomic-scale anisotropy. Our findings
have broadened the composition range of transition metal-rare earth alloys for
designing PMA films, making it attractive for tunable magnetic anisotropy in
nanoscale devices.",1306.6451v1
2013-07-01,Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets,"We study the interplay between the effects of surface anisotropy and dipolar
interactions in monodisperse assemblies of nanomagnets with oriented
anisotropy. We derive asymptotic formulas for the assembly magnetization taking
account of temperature, applied field, core and surface anisotropy, and dipolar
inter-particle interactions. We find that the interplay between surface
anisotropy and dipolar interactions is well described by the analytical
expression of the assembly magnetization derived here: the overall sign of the
product of the two parameters governing the surface and the dipolar
contributions determines whether intrinsic and collective terms compete or have
synergistic effects on the magnetization. This is illustrated by the
magnetization curves of $\gamma-Fe_{2}O_{3}$ nanoparticles assemblies in the
low concentration limit.",1307.0342v2
2013-08-15,Shape-induced anisotropy in antiferromagnetic nanoparticles,"High fraction of the surface atoms considerably enhances the influence of
size and shape on the magnetic and electronic properties of nanoparticles.
Shape effects in ferromagnetic nanoparticles are well understood and allow to
set and control the parameters of a sample that affect its magnetic anisotropy
during production. In the present paper we study the shape effects in the other
widely used magnetic materials -- antiferromagnets, -- which possess
vanishingly small or zero macroscopic magnetization. We take into account the
difference between the surface and bulk magnetic anisotropy of a nanoparticle
and show that the effective magnetic anisotropy depends on the particle shape
and crystallographic orientation of its faces. Corresponding shape-induced
contribution to the magnetic anisotropy energy is proportional to the particle
volume, depends on magnetostriction, and can cause formation of equilibrium
domain structure. Crystallographic orientation of the nanoparticle surface
determines the type of domain structure. The proposed model allows to predict
the magnetic properties of antiferromagnetic nanoparticles depending on their
shape and treatment.",1308.3327v1
2013-09-04,On the Anisotropy of the Gravitational Wave Background from Massless Preheating,"When a light scalar field is present during inflation, its value will vary on
superhorizon scales, modulating the preheating process at the end of inflation.
Consequently, the amplitude of the gravitational wave (GW) background produced
during preheating will also be modulated. The observed energy density of this
background will therefore appear anisotropic at different angles in the sky. We
provide a master formula for the angular power spectrum C_l of the anisotropies
in the GW background from preheating, valid for any scenario where the
anisotropies are due to the superhorizon modulation of a light degree of
freedom. Using lattice field theory simulations of massless preheating with
g^2/\lambda = 2, we find a flat angular spectrum l(l+1)C_l \approx 3x10^{-4},
which represents a strong anisotropy of order 1% variations on large angular
scales. For our choice of couplings, long wavelengths are amplified most
strongly during parametric resonance, which is crucial for the development of
the anisotropies. If future direct detection GW observatories are capable of
detecting backgrounds of cosmological origin, they should be able to detect
this effect. This could eventually become a powerful tool to discriminate among
inflationary and preheating scenarios.",1309.1148v1
2013-11-01,"Derivation of the anisotropy profile, constraints on the local velocity dispersion, and implications for direct detection","We study the implications of a pseudo-phase-space density power-law for the
anisotropy profile of a Milky Way-like dark matter halo. Requiring that the
anisotropy parameter does not take non-physical values within the virial radius
places a maximum value on the local radial velocity dispersion. For a plausible
range of halo parameters, it is possible to take a local total velocity
dispersion of up to about $300\,\mathrm{km/s}$. Making this choice uniquely
specifies the anisotropy and dispersion profiles. We introduce a way to model
the local velocity distribution that incorporates this anisotropy and study the
impact on direct detection.",1311.0256v3
2013-11-05,Chiral skyrmions in cubic helimagnet films: the role of uniaxial anisotropy,"This paper reports on magnetometry and magnetoresistance measurements of MnSi
epilayers performed in out-of-plane magnetic fields. We present a theoretical
analysis of the chiral modulations that arise in confined cubic helimagnets
where the uniaxial anisotropy axis and magnetic field are both out-of-plane. In
contrast to in-plane field measurements (Wilson et al., Phys. Rev. B 86, 144420
(2012)), the hard-axis uniaxial anisotropy in MnSi/Si(111) increases the energy
of (111)-oriented skyrmions and in-plane helicoids relative to the cone phase,
and makes the cone phase the only stable magnetic texture below the saturation
field. While induced uniaxial anisotropy is important in stabilizing skyrmion
lattices and helicoids in other confined cubic helimagnets, the particular
anisotropy in MnSi/Si(111) entirely suppresses these states in an out-of-plane
magnetic field. However, it is predicted that isolated skyrmions with enlarged
sizes exist in MnSi/Si(111) epilayers in a broad range of out-of-plane magnetic
fields.",1311.1191v2
2013-12-09,Memory function approach to in-plane anisotropic resistivity in the antiferromagnetic phase of iron arsenide superconductors,"We theoretically examine anisotropy of in-plane resistivity in the striped
antiferromagnetic phase of an iron arsenide superconductor by applying a memory
function approach to the ordered phase with isotropic nonmagnetic impurity. We
find that the anisotropy of the scattering rate is independent of carrier
density when the topology of the Fermi surface is changed after the
introduction of holes. On the other hand, the anisotropy of the Drude weight
monotonically decreases reflecting the distortion of the Dirac Fermi surface
and eventually leads to the reverse of anisotropy of resistivity, being
consistent with experiment. The origin of the anisotropy is thus attributed to
the interplay of impurity scattering and anisotropic electronic states.",1312.2322v3
2013-12-13,Phase diagram of a three-dimensional antiferromagnet with random magnetic anisotropy,"Three-dimensional (3D) antiferromagnets with random magnetic anisotropy (RMA)
experimentally studied to date do not have random single-ion anisotropies, but
rather have competing two-dimensional and three-dimensional exchange
interactions which can obscure the authentic effects of RMA. The magnetic phase
diagram Fe$_{x}$Ni$_{1-x}$F$_{2}$ epitaxial thin films with true random
single-ion anisotropy was deduced from magnetometry and neutron scattering
measurements and analyzed using mean field theory. Regions with uniaxial,
oblique and easy plane anisotropies were identified. A RMA-induced glass region
was discovered where a Griffiths-like breakdown of long-range spin order
occurs.",1312.3687v2
2013-12-17,Control of the in-plane anisotropy in off-stoichiometric NiMnSb,"NiMnSb is a ferromagnetic half-metal which, because of its rich anisotropy
and very low Gilbert damping, is a promising candidate for applications in
information technologies. We have investigated the in-plane anisotropy
properties of thin, MBE-grown NiMnSb films as a function of their Mn
concentration. Using ferromagnetic resonance (FMR) to determine the uniaxial
and four-fold anisotropy fields, 2KU/Ms and 2K1/Ms, we find that a small
variation in composition is sufficient to change the film from primarily
four-fold to primarily uniaxial behavior, allowing for continuous tuning of the
anisotropy. This provides valuable flexibility in designing new device
geometries.",1312.4781v2
2014-02-24,Spiraling elliptic breathers in saturable nonlinear media with linear anisotropy,"We have introduced a class of spiraling elliptic breathers in saturable
nonlinear media with linear anisotropy. Two kinds of evolution behaviors of the
breathers, rotating and pendulum-like librating, are both predicted by the
variational approach, and confirmed by the numerical simulation.The spiraling
elliptic breathers can rotate even though they have no initial orbital angular
momentum (OAM). Due to the linear anisotropy of the media, the OAM is no longer
conserved. Therefore, the angular velocity is found to be not a constant but a
periodic function of the propagation distance. When the linear anisotropy is
large enough, the spiraling elliptic breathers can librate like the pendulum.
The spiraling elliptic breathers exist in the media with not only the saturable
nonlinearity but also the nonlocal nonlinearity, as a matter of fact, they are
universal in the nonlinear media with the linear anisotropy.",1402.5736v1
2014-03-10,Effective anisotropy gradient in pressure graded [Co/Pd] multilayers,"A vertically graded anisotropy profile has been proposed as an optimized
balance of low coercivity and thermal stability for multilayers used in
magnetic media. Deposition pressure is known to have a profound effect on the
magnetic reversal properties of Co/Pd multilayers, making it an attractive
control parameter for achieving an anisotropy gradient. We have used polarized
neutron reflectometry to study the depth-dependent reversal behavior of
""pressure-graded"" Co/Pd, and observed pronounced gradients in the saturation
magnetization and in the rate at which magnetization changes with field (the
effective anisotropy). While the anisotropy gradient likely arises from a
combination of factors intrinsic to deposition pressure, micromagnetic
simulations indicate that the observed saturation magnetization gradient alone
has a major effect on the resulting coercivity.",1403.2126v2
2014-03-19,Low anisotropy of the upper critical field in a strongly anisotropic layered cuprate: Evidence for paramagnetically limited superconductivity,"We study angular-dependent magnetoresistance in a low $T_c$ layered cuprate
Bi$_{2.15}$Sr$_{1.9}$CuO$_{6+\delta}$. The low $T_c$ ~ 4 K allows complete
suppression of superconductivity by modest magnetic fields and facilitate
accurate analysis of the upper critical field $H_{c2}$. We observe an universal
exponential decay of fluctuation conductivity in a broad range of temperatures
above $T_c$ and propose a new method for extraction of $H_{c2}(T)$ from the
scaling analysis of the fluctuation conductivity at $T>T_c$. Our main result is
observation of a surprisingly low $H_{c2}$ anisotropy ~ 2, which is much
smaller than the effective mass anisotropy of the material ~ 300. We show that
the anisotropy is decreasing with increasing field and saturates at a small
value when the field reaches the paramagnetic limit. We argue that the dramatic
discrepancy of high field and low field anisotropies is a clear evidence for
paramagnetically limited superconductivity.",1403.4817v2
2014-03-25,Large-Scale Distribution of Arrival Directions of Cosmic Rays Detected at the Pierre Auger Observatory Above $10~$PeV,"Searches for large-scale anisotropies in the distribution of arrival
directions of cosmic rays detected above $\simeq 10 $PeV at the Pierre Auger
Observatory are presented. Although no significant deviation from isotropy is
revealed at present, some of the measurements suggest that future data will
provide hints for large-scale anisotropies over a wide energy range. Those
anisotropies would have amplitudes which are too small to be significantly
observed within the current statistics. Assuming that the cosmic ray anisotropy
is dominated by dipole and quadrupole moments in the EeV-energy range, some
consequences of the present upper limits on their amplitudes are presented.",1403.6314v1
2014-04-14,Impurity induced enhancement of perpendicular magnetic anisotropy in Fe/MgO tunnel junctions,"Using first-principles calculations, we investigated the impact of chromium
(Cr) and vanadium (V) impurities on the magnetic anisotropy and spin
polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated using
layer resolved anisotropy calculation technique, that while the impurity near
the interface has a drastic effect in decreasing the perpendicular magnetic
anisotropy (PMA), its position within the bulk allows maintaining high surface
PMA. Moreover, the effective magnetic anisotropy has a strong tendency to go
from in-plane to out-of-plane character as a function of Cr and V concentration
favoring out-of-plane magnetization direction for ~1.5 nm thick Fe layers at
impurity concentrations above 20 %. At the same time, spin polarization is not
affected and even enhanced in most situations favoring an increase of tunnel
magnetoresistance (TMR) values.",1404.3523v1
2014-05-19,Beyond the Ginzburg-Landau theory of freezing: Anisotropy of the interfacial free energy in the Phase-Field Crystal model,"This paper re-visits the weakly fourth order anisotropic Ginzburg-Landau (GL)
theory of freezing. First we determine the anisotropy of the interfacial free
energy in the Phase-Field Crystal (PFC) model analytically, and prove that it
remains finite at the critical point as a direct consequence of the one-mode
dominance of the model. Next, we derive the leading order PFC amplitude model
and show the formal analogy to traditional weakly 4th order anisotropic GL
theories. We conclude that the material-independent anisotropy appearing in
emergent GL theory coincides with the remnant anisotropy of the generating PFC
model. As a result, we show that the reduced temperature {\epsilon} does not
enter into the interfacial free energy anisotropy for metallic materials in
both the Phase-Field Crystal model and the emerging Ginzburg-Landau theories.
Finally, we investigate the possible pathways of calibrating anisotropic
Ginzburg-Landau theories.",1405.4680v1
2014-06-08,Perpendicular magnetic anisotropy and magnetization process in CoFeB/Pd multilayer films,"Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal
process in [CoFeB $t$ nm/Pd 1.0 nm]$_n$ ($t$ = 0.4, 0.6, 0.8, 1.0, and 1.2 nm;
$n$ = 2 - 20) multilayer films have been studied by means of magnetic
hysteresis and Kerr effect measurements. Strong and controllable PMA with an
effective uniaxial anisotropy up to 7.7$\times$ 10$^6$ J.m$^{-3}$ and a
saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial
anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is
separated from the effective uniaxial anisotropy of the films, and appears to
increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic
domains during a magnetization reversal process using polar magneto-optical
Kerr microscopy shows the detailed behavior of nucleation and displacement of
the domain walls.",1406.2028v1
2014-08-11,Hole spin dynamics and hole $g$ factor anisotropy in coupled quantum well systems,"Due to its p-like character, the valence band in GaAs-based heterostructures
offers rich and complex spin-dependent phenomena. One manifestation is the
large anisotropy of Zeeman spin splitting. Using undoped, coupled quantum wells
(QWs), we examine this anisotropy by comparing the hole spin dynamics for high-
and low-symmetry crystallographic orientations of the QWs. We directly measure
the hole $g$ factor via time-resolved Kerr rotation, and for the low-symmetry
crystallographic orientations (110) and (113a), we observe a large in-plane
anisotropy of the hole $g$ factor, in good agreement with our theoretical
calculations. Using resonant spin amplification, we also observe an anisotropy
of the hole spin dephasing in the (110)-grown structure, indicating that
crystal symmetry may be used to control hole spin dynamics.",1408.2360v1
2014-10-01,Transverse anisotropy effects on spin-resolved transport through large-spin molecules,"The transport properties of a large-spin molecule strongly coupled to
ferromagnetic leads in the presence of transverse magnetic anisotropy are
studied theoretically. The relevant spectral functions, linear-response
conductance and the tunnel magnetoresistance are calculated by means of the
numerical renormalization group method. We study the dependence of transport
characteristics on orbital level position, uniaxial and transverse
anisotropies, external magnetic field and temperature. It is shown that while
uniaxial magnetic anisotropy leads to the suppression of the Kondo effect,
finite transverse anisotropy can restore the Kondo resonance. The effect of
Kondo peak restoration strongly depends on the magnetic configuration of the
device and leads to nontrivial behavior of the tunnel magnetoresistance. We
show that the temperature dependence of the conductance at points where the
restoration of the Kondo effect occurs is universal and shows a scaling typical
for usual spin-one-half Kondo effect.",1410.0315v1
2014-12-15,Antagonistic in-plane resistivity anisotropies from competing fluctuations in underdoped cuprates,"One of the prime manifestations of an anisotropic electronic state in
underdoped cuprates is the in-plane resistivity anisotropy
$\Delta\rho\equiv(\rho_{a}-\rho_{b})/\rho_{b}$. Here we use a
Boltzmann-equation approach to compute the contribution to $\Delta\rho$ arising
from scattering by anisotropic charge and spin fluctuations, which have been
recently observed experimentally. While the anisotropy in the charge
fluctuations is manifested in the correlation length, the anisotropy in the
spin fluctuations emerges only in the structure factor. As a result, we find
that spin fluctuations favor $\Delta\rho>0$, whereas charge fluctuations
promote $\Delta\rho<0$, which are both consistent with the doping dependence of
$\Delta\rho$ observed in YBa$_{2}$Cu$_{3}$O$_{7}$. We also discuss the role
played by CuO chains in these materials, and propose transport experiments in
strained HgBa$_{2}$CuO$_{4}$ and Nd$_{2}$CuO$_{4}$ to probe directly the
different resistivity anisotropy regimes.",1412.4745v2
2015-01-05,Magnetization of Quantum Dots: A Measure of Anisotropy and the Rashba Interaction,"The magnetization of anisotropic quantum dots in the presence of the Rashba
spin-orbit interaction has been studied for three interacting electrons in the
dot. We observe unique behaviors of magnetization that are direct reflections
of the anisotropy and the spin-orbit interaction parameters independently or
concurrently. In particular, there are saw-tooth structures in the magnetic
field dependence of the magnetization, as caused by the electron-electron
interaction, that are strongly modified in the presence of large anisotropy and
high strength of the spin-orbit interactions. We report the temperature
dependence of magnetization that indicates the temperature beyond which these
structures due to the interactions disappear. Additionally, we found the
emergence of a weak saw-tooth structure in magnetization in the high anisotropy
and large spin-orbit interaction limit that was explained as a result of
merging of two low-energy curves when the level spacings evolve with increasing
values of the anisotropy and the spin-orbit interaction strength.",1501.01025v1
2015-02-12,Effects of Interatomic Coupling on Magnetic Anisotropy and Order of Spins on Metallic Surfaces,"Both quantum and classical behavior of single atomic spins on surfaces is
determined by the local anisotropy of adatoms and their coupling to the
immediate electronic environment. Yet adatoms seldom reside on surfaces alone
and it is generally acknowledged that substrated-mediated interactions can
couple single spins among each other impacting their magnetic behavior. Here we
show that also magnetic anisotropy, which is usually considered to be a
constant determined by the local crystal field, can be extremely sensitive to
such interactions. By the example of Co dimers on Cu(001) and Pt(001) surfaces
we highlight the intricate interplay of exchange coupling and magnetic
anisotropy providing a much sought possibility to tune the latter through
deliberate adjustment of the adatoms' separation. As a technologically relevant
implication we demonstrate the impact of such emergent non-local anisotropy on
the hysterectic properties of single-atom magnetization curves.",1502.03743v2
2015-02-27,Accurate calculation of the transverse anisotropy in perpendicularly magnetized multilayers,"The transverse anisotropy constant and the related D\""oring mass density are
key parameters of the one-dimensional model to describe the motion of magnetic
domain walls. So far, no general framework is available to determine these
quantities from static characterizations such as magnetometry measurements.
Here, we derive a universal analytical expression to calculate the transverse
anisotropy constant for the important class of perpendicular magnetic
multilayers. All the required input parameters of the model, such as the number
of repeats, the thickness of a single magnetic layer, and the layer
periodicity, as well as the effective perpendicular anisotropy, the saturation
magnetization, and the static domain wall width are accessible by static sample
characterizations. We apply our model to a widely used multilayer system and
find that the effective transverse anisotropy constant is a factor 7 different
from the when using the conventional approximations, showing the importance of
using our analysis scheme.",1502.07937v1
2015-05-13,Benefits of Carrier Pocket Anisotropy to Thermoelectric Performance: The case of $p$-type AgBiSe$_2$,"We study theoretically the effects of anisotropy on the thermoelectric
performance of $p$-type AgBiSe$_2$. We present an apparent realization of the
thermoelectric benefits of one-dimensional ""plate-like"" carrier pocket
anisotropy in the valence band of this material. Based on first principles
calculations we find a substantial anisotropy in the electronic structure,
likely favorable for thermoelectric performance, in the valence bands of the
hexagonal phase of the silver chalcogenide thermoelectric AgBiSe$_2$, while the
conduction bands are more isotropic, and in our experiments do not attain high
performance. AgBiSe$_2$ has already exhibited a $ZT$ value of 1.5 in a
high-temperature disordered fcc phase, but room-temperature performance has not
been demonstrated. We develop a theory for the ability of anisotropy to
decouple the density-of-states and conductivity effective masses, pointing out
the influence of this effect in the high performance thermoelectrics
Bi$_2$Te$_3$ and PbTe. From our first principles and Boltzmann transport
calculations we estimate the performance of $p$-type AgBiSe$_{2}$.",1505.03379v1
2015-06-24,Implications of a temperature-dependent magnetic anisotropy for superparamagnetic switching,"The macroscopic magnetic moment of a superparamagnetic system has to overcome
an energy barrier in order to switch its direction. This barrier is formed by
magnetic anisotropies in the material and may be surmounted typically after
10^9 to 10^12 attempts per second by thermal fluctuations. In a first step, the
associated switching rate may be described by a Neel-Brown-Arrhenius law, in
which the energy barrier is assumed as constant or a given temperature. Yet,
magnetic anisotropies in general depend on temperature themselves which is
known to modify the Neel-Brown-Arrhenius law. We illustrate quantitatively the
implications of a temperature-dependent anisotropy on the switching rate and in
particular for the interpretation of the prefactor as an attempt frequency. In
particular, we show that realistic numbers for the attempt frequency are
obtained when the temperature dependence of the anisotropy is taken into
account.",1506.07333v2
2015-06-24,Effects of anisotropy and disorder on the conductivity of Weyl semimetals,"We study dc conductivity of a Weyl semimetal with uniaxial anisotropy (Fermi
velocity ratio $\xi= v_\bot/v_\parallel\neq1$) considering the scattering of
charge carriers by a wide class of impurity potentials, both short- and
long-range. We obtain the ratio of transverse and longitudinal (with respect to
the anisotropy axis) conductivities as a function of both $\xi$ and
temperature. We find that the transverse and longitudinal conductivities
exhibit different temperature dependence in the case of short-range disorder.
For general long-range disorder, the temperature dependence ($\sim T^4$) of the
conductivity turns out to be insensitive of the anisotropy in the limits of
strong ($\xi\gg$ and $\ll1$) and weak ($\xi\approx1$) anisotropy.",1506.07556v1
2015-08-12,A Dzyaloshinskii-Moriya Anisotropy in Nanomagnets with in-plane Magnetization,"We report on a new source of in-plane anisotropy in nanomagnets due to the
presence of Dzyaloshinskii-Moriya interaction (DMI). This anisotropy depends on
the shape of the magnet, and is orthogonal to the demagnetization shape
anisotropy. This effect originates from the DMI energy reduction due to an
out-of-plane tilt of the spins at edges oriented perpendicular to the
magnetization. Our investigation combining experimental, numerical and
analytical results demonstrate that this energy reduction can compensate the
demagnetization shape anisotropy energy in magnets of elongated shape, provided
that their volumes is small enough and thus that their magnetization is
quasi-uniform.",1508.02961v1
2015-09-14,Thickness-Dependent Magnetoelasticity and its Effects on Perpendicular Magnetic Anisotropy in Ta|CoFeB|MgO Thin Films,"We report measurements of the in-plane magnetoelastic coupling in ultra-thin
Ta|CoFeB|MgO layers as a function of uniaxial strain, conducted using a
four-point bending apparatus. For annealed samples, we observe a strong
dependence on the thickness of the CoFeB layer in the range 1.3-2.0 nm, which
can be modeled as arising from a combination of effective surface and volume
contributions to the magnetoelastic coupling. We point out that if similar
thickness dependence exists for magnetoelastic coupling in response to biaxial
strain, then the standard N\'eel model for the magnetic anisotropy energy
acquires a term inversely proportional to the magnetic layer thickness. This
contribution can significantly change the overall magnetic anisotropy, and
provides a natural explanation for the strongly nonlinear dependence of
magnetic anisotropy energy on magnetic layer thickness that is commonly
observed for ultrathin annealed CoFeB|MgO films with perpendicular magnetic
anisotropy.",1509.04134v1
2015-10-14,Full-Sky Analysis of Cosmic-Ray Anisotropy with IceCube and HAWC,"During the past two decades, experiments in both the Northern and Southern
hemispheres have observed a small but measurable energy-dependent sidereal
anisotropy in the arrival direction distribution of galactic cosmic rays. The
relative amplitude of the anisotropy is $10^{-4} - 10^{-3}$. However, each of
these individual measurements is restricted by limited sky coverage, and so the
pseudo-power spectrum of the anisotropy obtained from any one measurement
displays a systematic correlation between different multipole modes $C_\ell$.
To address this issue, we present the preliminary status of a joint analysis of
the anisotropy on all angular scales using cosmic-ray data from the IceCube
Neutrino Observatory located at the South Pole ($90^\circ$ S) and the
High-Altitude Water Cherenkov (HAWC) Observatory located at Sierra Negra,
Mexico ($19^\circ$ N). We describe the methods used to combine the IceCube and
HAWC data, address the individual detector systematics and study the region of
overlapping field of view between the two observatories.",1510.04134v2
2015-11-09,Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe1.9Ni0.1As2,"We use inelastic neutron scattering to study the temperature and energy
dependence of the spin excitation anisotropy in uniaxial-strained
electron-doped iron pnictide BaFe$_{1.9}$Ni$_{0.1}$As$_2$ near optimal
superconductivity ($T_c=20$ K). Our work has been motivated by the observation
of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of
electron-underdoped iron pnictides under uniaxial pressure, which has been
attributed to a spin-driven Ising-nematic state or orbital ordering. Here we
show that the spin excitation anisotropy, a signature of the spin-driven
Ising-nematic phase, exists for energies below $\sim$60 meV in
uniaxial-strained BaFe$_{1.9}$Ni$_{0.1}$As$_2$. Since this energy scale is
considerably larger than the energy splitting of the $d_{xz}$ and $d_{yz}$
bands of uniaxial-strained Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ near optimal
superconductivity, spin Ising-nematic correlations is likely the driving force
for the resistivity anisotropy and associated electronic nematic correlations.",1511.02759v1
2015-11-30,Small-scale anisotropies of cosmic rays from relative diffusion,"The arrival directions of multi-TeV cosmic rays show significant anisotropies
at small angular scales. It has been argued that this small scale structure is
reflecting the local, turbulent magnetic field in the presence of a global
dipole anisotropy in cosmic rays as determined by diffusion. This effect is
analogous to weak gravitational lensing of temperature fluctuations of the
cosmic microwave background. We show that the non-trivial power spectrum in
this setup can be related to the properties of relative diffusion and we study
the convergence of the angular power spectrum to a steady-state as a function
of backtracking time. We also determine the steady-state solution in an
analytical approach based on a modified BGK ansatz. A rigorous mathematical
treatment of the generation of small scale anisotropies will help in unraveling
the structure of the local magnetic field through cosmic ray anisotropies.",1511.09451v1
2015-12-21,Elliptic Anisotropy $v_2$ May Be Dominated by Particle Escape instead of Hydrodynamic Flow,"It is commonly believed that azimuthal anisotropies in relativistic heavy ion
collisions are generated by hydrodynamic evolution of the strongly interacting
quark-gluon plasma. Here we use transport models to study how azimuthal
anisotropies depend on the number of collisions that each parton suffers. We
find that the majority of $v_2$ comes from the anisotropic escape of partons,
not from the parton collective flow, for semi-central Au+Au collisions at 200A
GeV. As expected, the fraction of $v_2$ from the anisotropic particle escape is
even higher for smaller systems such as d+Au. Our transport model results also
confirm that azimuthal anisotropies would be dominated by hydrodynamic flow at
unrealistically-high parton cross sections. Our finding thus naturally explains
the similarity of azimuthal anisotropies in small and large systems; however,
it presents a challenge to the paradigm of anisotropic flow.",1512.06465v1
2015-12-22,Large Angular Scale CMB Anisotropy from an Excited Initial Mode,"According to inflationary cosmology, the CMB anisotropy gives an opportunity
to test predictions of new physics hypotheses. The initial state of quantum
fluctuations is one of the important options at high energy scale, as it can
affect observables such as the CMB power spectrum. In this study a quasi-de
Sitter inflationary background with approximate de Sitter mode function built
over the Bunch-Davies mode is applied to investigate the scale-dependency of
the CMB anisotropy. The recent Planck constraint on spectral index motivated us
to examine the effect of a new excited mode function (instead of pure de Sitter
mode) on the CMB anisotropy at large angular scales. In so doing, it is found
that the angular scale-invariance in the CMB temperature fluctuations is broken
and in the limit $ \ell<200 $ a tiny deviation appears. Also, it is shown that
the power spectrum of CMB anisotropy is dependent on a free parameter with mass
dimension $H<<M_{*}<M_{p}$ and on the slow-roll parameter $\epsilon $.",1512.07018v2
2016-01-02,Field theory and anisotropy of cubic ferromagnet near Curie point,"Critical fluctuations are known to change the effective anisotropy of cubic
ferromagnet near the Curie point. If the crystal undergoes phase transition
into orthorhombic phase and the initial anisotropy is not too strong, effective
anisotropy acquires at T_c the universal value A* = v*/u* where u* and v* are
coordinates of the cubic fixed point entering the scaling equation of state and
expressions for nonlinear susceptibilities. In the paper, the numerical value
of the anisotropy parameter A at the critical point is estimated using the
\epsilon-expansion and pseudo-\epsilon-expansion techniques. Pade resummation
of six-loop pseudo-$\epsilon$-expansions for u*, v*, and A* leads to the
estimate A* = 0.13 close to that extracted from the five-loop
\epsilon-expansion but differing considerably from the value A* = 0.089 given
by the analysis of six-loop expansions of the \beta-functions themselves. This
discrepancy is discussed and its roots are cleared up.",1601.00147v2
2016-02-10,Effects of electron temperature anisotropy on proton mirror instability evolution,"Proton mirror modes are large amplitude nonpropagating structures frequently
observed in the magnetosheath. It has been suggested that electron temperature
anisotropy can enhance the proton mirror instability growth rate while leaving
the proton cyclotron instability largely unaffected, therefore causing the
proton mirror instability to dominate the proton cyclotron instability in
Earth's magnetosheath. Here, we use particle-in-cell simulations to investigate
the electron temperature anisotropy effects on proton mirror instability
evolution. Contrary to the hypothesis, electron temperature anisotropy leads to
excitement of the electron whistler instability. Our results show that the
electron whistler instability grows much faster than the proton mirror
instability and quickly consumes the electron free energy, so that there is no
electron temperature anisotropy left to significantly impact the evolution of
the proton mirror instability.",1602.03411v1
2016-02-22,Effect of transverse anisotropy on inelastic tunneling spectroscopy of atomic-scale magnetic chains,"We theoretically investigate the effect of transverse magnetic anisotropy on
spin-flip assisted tunneling through atomic spin chains. Using a
phenomenological approach and first-order perturbation theory, we analytically
calculate the inelastic tunneling current, differential conductance and atomic
spin transition rates. We predict the appearance of additional steps in the
differential conductance and a pronounced increase in the spin-flip transition
rate which at low voltages scale quadratically with the ratio of the transverse
anisotropy energy and the sum of the longitudinal anisotropy energy and the
exchange energy. Our results provide intuitive quantitative insight in the role
played by transverse anisotropy in inelastic tunneling spectroscopy of atomic
chains and can be observed under realistic experimental conditions.",1602.06839v2
2016-02-29,Tunable magnetic anisotropy from higher-harmonics exchange scattering on the surface of a topological insulator,"We show that higher-harmonics exchange scattering from a magnetic adatom on
the surface of a three dimensional topological insulator leads to a magnetic
anisotropy whose magnitude and sign may be tuned by adjusting the chemical
potential of the helical surface band. As chemical potential moves from the
Dirac point towards the surface band edge, the surface normal is found to
change from magnetic easy, to hard axis. Hexagonal warping is shown to diminish
the region with easy axis anisotropy, and to suppress the anisotropy
altogether. This indirect contribution can be comparable in magnitude to the
intrinsic term arising from crystal field splitting and atomic spin-orbit
coupling, and its tunability with chemical potential makes the two
contributions experimentally discernible, and endows this source of anisotropy
with potentially interesting magnetic functionality.",1602.08926v2
2016-04-01,Anisotropies in the gravitational wave background as a probe of the cosmic string network,"Pulsar timing arrays are one of the powerful tools to test the existence of
cosmic strings through searching for the gravitational wave background. The
amplitude of the background connects to information on cosmic strings such as
the tension and string network properties. In addition, one may be able to
extract more information on properties of cosmic strings by measuring
anisotropies in the gravitational wave (GW) background. In this paper, we
provide estimates of the level of anisotropy expected in the GW background
generated by cusps on cosmic strings. We find that the anisotropy level
strongly depends on the initial loop size $\alpha$, and thus we may be able to
put constraint on $\alpha$ by measuring the anisotropy of the GW background. We
also find that certain regions of the parameter space can be probed by shifting
the observation frequency of GWs.",1604.00332v2
2016-04-04,"Imry-Ma disordered state induced by defects of ""random local anisotropy"" type in the system with O(n) symmetry","For the system with the n-component order parameter (O(n)-model), conditions
for initiation of the Imry-Ma disordered state resulting from the influence of
defects of the ""random local anisotropy"" type were discovered. The initiation
of such a state was shown to be possible if the distribution of local
anisotropy axes directions in the order parameter space is nearly isotropic,
and the limiting degree of the distribution anisotropy was found. For a higher
anisotropy in the distribution of local axes directions, the long-range order
in the system holds true even in the presence of defects of the given type.",1604.00957v1
2016-05-10,Grain size correlated rotatable magnetic anisotropy in polycrystalline exchange bias systems,"Angular resolved measurements of the exchange bias field and the coercive
field are a powerful tool to distinguish between different competing magnetic
anisotropies in polycrystalline exchange bias layer systems. No simple
analytical model is as yet available, which considers time dependent effects
like enhanced coercivity arising from the grain size distribution of the
antiferromagnet. In this work we expand an existing model class describing
polycrystalline exchange bias systems by a rotatable magnetic anisotropy term
to describe grain size correlated effects. Additionally, we performed angular
resolved magnetization curve measurements using vectorial magnetooptic Kerr
magnetometry. Comparison of the experimental data with the proposed model shows
excellent agreement and reveals the ferromagnetic anisotropy and properties
connected to the grain size distribution of the antiferromagnet. Therefore, a
distinction between the different influences on coercivity and anisotropy
becomes available.",1605.02958v2
2016-05-18,Chiral anomaly and giant magnetochiral anisotropy in noncentrosymmetric Weyl semimetals,"We theoretically propose that giant magnetochiral anisotropy is achieved in
Weyl semimetals in noncentrosymmetric crystals as a consequence of the chiral
anomaly. The magnetochiral anisotropy is the nonlinearity of the resistivity
$\rho$ that depends on the current $\boldsymbol{I}$ and the magnetic field
$\boldsymbol{B}$ as $\rho=\rho_0 (1 + \gamma \boldsymbol{I} \cdot
\boldsymbol{B})$, and can be applied to rectifier devices controlled by
$\boldsymbol{B}$. We derive the formula for the coefficient $\gamma$ in
noncentrosymmetric Weyl semimetals. The obtained formula for $\gamma$ shows
that the magnetochiral anisotropy is strongly enhanced when the chemical
potential is tuned to Weyl points, and that noncentrosymmetric Weyl semimetals
such as TaAs can exhibit much larger magnetochiral anisotropy than that
observed in other materials so far.",1605.05409v2
2016-07-01,Evolution of superconducting gap anisotropy in hole-doped 122 iron pnictides,"Motivated by recent experimental findings, we investigate the evolution of
the superconducting gap anisotropy in 122 iron pnictides as a function of hole
doping. Employing both a functional and a weak coupling renormalization group
approach (FRG and WRG), we analyse the Fermi surface instabilities of an
effective 122 model band structure at different hole dopings x, and derive the
gap anisotropy from the leading superconducting instability. In the transition
regime from collinear magnetism to s_{\pm}-wave, where strong correlations are
present, we employ FRG to identify a non- monotonous change of the gap
anisotropy in qualitative agreement with new experimental findings. From the
WRG, which is asymptotically exact in the weak coupling limit, we find an
s_{\pm}-wave to d-wave transition as a function of hole doping, complementing
previous findings from FRG [Thomale et al., Phys. Rev. Lett. 107, 117001
(2011)]. The gap anisotropy of the s_{\pm}-wave monotonously increases towards
the transition to d-wave as a function of x.",1607.00412v1
2016-08-18,The role of electron confinement in Pd films for the oscillatory magnetic anisotropy in an adjacent Co layer,"We demonstrate the interplay between quantum well states in Pd and the
magnetic anisotropy in Pd/Co/Cu(001) by combined scanning tunneling
spectroscopy (STS) and magneto optical Kerr effect (MOKE) measurements. Low
temperature scanning tunneling spectroscopy reveals occupied and unoccupied
quantum well states (QWS) in atomically flat Pd films on Co/Cu(001). These
states give rise to sharp peaks in the differential conductance spectra. A
quantitative analysis of the spectra reveals the electronic dispersion of the
Pd(001) d-band ($\Delta$$_5$-type) along the $\Gamma$-X direction.
\textit{In-situ} MOKE experiments on Pd/Co/Cu(1, 1, 13) uncover a periodic
variation of the in-plane uniaxial magnetic anisotropy as a function of Pd
thickness with a period of 6 atomic layers Pd. STS shows that QWS in Pd cross
the Fermi level with the same periodicity of 6 atomic layers. Backed by
previous theoretical work we ascribe the variation of the magnetic anisotropy
in Co to QWS in the Pd overlayer. Our results suggest a novel venue towards
tailoring uniaxial magnetic anisotropy of ferromagnetic films by exploiting QWS
in an adjacent material with large spin-orbit coupling.",1608.05227v1
2016-08-22,Quark self-energy in an ellipsoidally anisotropic quark-gluon plasma,"We calculate the quark self-energy in a quark-gluon plasma that possesses an
ellipsoidal momentum-space anisotropy in the local rest frame. By introducing
additional transverse momentum anisotropy parameters into the parton
distribution functions, we generalize previous results which were obtained for
the case of a spheroidal anisotropy. Our results demonstrate that the presence
of anisotropies in the transverse directions affects the real and imaginary
parts of quark self-energy and, consequently, the self-energy depends on both
the polar and azimuthal angles in the local rest frame of the matter. Our
results for the quark self-energy set the stage for the calculation of the
effects of ellipsoidal momentum-space anisotropy on quark-gluon plasma photon
spectra and collective flow.",1608.06018v1
2016-09-07,Thermodynamics of anisotropic branes,"We study the thermodynamics of flavor D7-branes embedded in an anisotropic
black brane solution of type IIB supergravity. The flavor branes undergo a
phase transition between a `Minkowski embedding', in which they lie outside of
the horizon, and a `black hole embedding', in which they fall into the horizon.
This transition depends on the black hole temperature, its degree of
anisotropy, and the mass of the flavor degrees of freedom. It happens either at
a critical temperature or at a critical anisotropy. A general lesson we learn
from this analysis is that the anisotropy, in this particular realization,
induces similar effects as the temperature. In particular, increasing the
anisotropy bends the branes more and more into the horizon. Moreover, we
observe that the transition becomes smoother for higher anisotropies.",1609.02167v2
2016-09-30,Precision ESR Measurements of Transverse Anisotropy in the Single-molecule Magnet Ni$_4$,"We present a method for precisely measuring the tunnel splitting in
single-molecule magnets using electron-spin resonance, and use these
measurements to precisely and independently determine the underlying transverse
anisotropy parameter, given a certain class of transitions. By diluting samples
of the SMM Ni$_4$ via co-crystallization in a diamagnetic isostructural
analogue we obtain markedly narrower resonance peaks than are observed in
undiluted samples. Using custom loop-gap resonators we measure the transitions
at several frequencies, allowing a precise determination of the tunnel
splitting. Because the transition under investigation occurs at zero field, and
arises due to a first-order perturbation from the transverse anisotropy, we can
determine the magnitude of this anisotropy independent of any other Hamiltonian
parameters. This method can be applied to other SMMs with tunnel splittings
arising from first-order transverse anisotropy perturbations.",1609.09859v2
2016-10-14,Anisotropy of a Cubic Ferromagnet at Criticality,"Critical fluctuations change the effective anisotropy of cubic ferromagnet
near the Curie point. If the crystal undergoes phase transition into
orthorhombic phase and the initial anisotropy is not too strong, reduced
anisotropy of nonlinear susceptibility acquires at $T_c$ the universal value
$\delta_4^* = {{2v^*} \over {3(u^* + v^*)}}$ where $u^*$ and $v^*$ --
coordinates of the cubic fixed point on the flow diagram of renormalization
group equations. In the paper, the critical value of the reduced anisotropy is
estimated within the pseudo-$\epsilon$ expansion approach. The six-loop
pseudo-$\epsilon$ expansions for $u^*$, $v^*$, and $\delta_4^*$ are derived for
the arbitrary spin dimensionality $n$. For cubic crystals ($n = 3$)
higher-order coefficients of the pseudo-$\epsilon$ expansions obtained turn out
to be so small that use of simple Pad\'e approximants yields reliable numerical
results. Pad\'e resummation of the pseudo-$\epsilon$ series for $u^*$, $v^*$,
and $\delta_4^*$ leads to the estimate $\delta_4^* = 0.079 \pm 0.006$
indicating that detection of the anisotropic critical behavior of cubic
ferromagnets in physical and computer experiments is certainly possible.",1610.04332v1
2016-10-19,Large-Scale Cosmic-Ray Anisotropy as a Probe of Interstellar Turbulence,"We calculate the large-scale cosmic-ray (CR) anisotropies predicted for a
range of Goldreich-Sridhar (GS) and isotropic models of interstellar
turbulence, and compare them with IceTop data. In general, the predicted CR
anisotropy is not a pure dipole; the cold spots reported at 400 TeV and 2 PeV
are consistent with a GS model that contains a smooth deficit of
parallel-propagating waves and a broad resonance function, though some other
possibilities cannot, as yet, be ruled out. In particular, isotropic fast
magnetosonic wave turbulence can match the observations at high energy, but
cannot accommodate an energy dependence in the shape of the CR anisotropy. Our
findings suggest that improved data on the large-scale CR anisotropy could
provide a valuable probe of the properties - notably the power-spectrum - of
the interstellar turbulence within a few tens of parsecs from Earth.",1610.06134v2
2016-10-27,Evolution of CMB spectral distortion anisotropies and tests of primordial non-Gaussianity,"Anisotropies in distortions to the frequency spectrum of the cosmic microwave
background (CMB) can be created through spatially varying heating processes in
the early Universe. For instance, the dissipation of small-scale acoustic modes
does create distortion anisotropies, in particular for non-Gaussian primordial
perturbations. In this work, we derive approximations that allow describing the
associated distortion field. We provide a systematic formulation of the problem
using Fourier-space window functions, clarifying and generalizing previous
approximations. Our expressions highlight the fact that the amplitudes of the
spectral-distortion fluctuations induced by non-Gaussianity depend also on the
homogeneous value of those distortions. Absolute measurements are thus required
to obtain model-independent distortion constraints on primordial
non-Gaussianity. We also include a simple description for the evolution of
distortions through photon diffusion, showing that these corrections can
usually be neglected. Our formulation provides a systematic framework for
computing higher order correlation functions of distortions with CMB
temperature anisotropies and can be extended to describe correlations with
polarization anisotropies.",1610.08711v2
2016-11-27,Theoretical study on the stimulated Brillouin scattering in a sub-wavelength anisotropic waveguide: Acousto-optical coupling coefficients and effects of transverse anisotropies,"A theoretical study on the stimulated Brillouin scattering (SBS) in a
sub-wavelength anisotropic waveguide is conducted. The optical, photoelastic
and mechanical anisotropies of the waveguide materials are all taken into
account. First, the integral formulae for calculating the acousto-optical
coupling coefficients (AOCCs) due to the photoelastic and moving interface
effects in SBS are extended to an optically anisotropic waveguide. Then, with
the extended formulae, the SBSs in an elliptical nanowire with strong
transverse anisotropies are simulated. In the simulations, the elastic fields
are computed with the inclusion of mechanical anisotropy. Observable effects of
the strong transverse anisotropies are found in numerical results. Most
notably, the SBS gains of some elastic modes are found to be very sensitive to
the small misalignment between the waveguide axes and the principal material
axes. Detailed physical interpretations of this interesting phenomenon are
provided. This interesting phenomenon implies an attractive way for more
sensitive tuning of the SBS gain without significantly changing the phononic
frequency.",1611.08792v3
2016-12-28,In-plane anisotropy of transport coefficients in the electronic nematic states: Universal origin of the nematicity in Fe-based superconductors,"The origin of the electronic nematicity and its remarkable
material-dependence are famous longstanding unsolved issues in Fe-based
superconductors. To attack these issues, we focus on the in-plane anisotropy of
the resistivity: In the nematic state in FeSe, the relation $\rho_x>\rho_y$
holds, where $\rho_{x(y)}$ is the resistivity along the longer (shorter) Fe-Fe
axis. In contrast, the opposite anisotropy $\rho_x<\rho_y$ is realized in other
undoped Fe-based superconductors. Such nontrivial material dependence is
naturally explained in terms of the strongly orbital-dependent inelastic
quasiparticle scattering realized in the orbital-ordered state. The opposite
anisotropy between FeSe ($\rho_x>\rho_y$) and other undoped compounds
($\rho_x<\rho_y$) reflects the difference in the number of hole-pockets. We
also explain the large in-plane anisotropy of the thermoelectric power in the
nematic state.",1612.08841v1
2016-12-31,Enhancement of perpendicular magnetic anisotropy and its electric field-induced change through interface engineering in Cr/Fe/MgO,"Recently, perpendicular magnetic anisotropy (PMA) and its voltage control
(VC) was demonstrated for Cr/Fe/MgO (Physical Review Applied 5, 044006 (2016)).
In this study, we shed a light on the origin of large voltage-induced
anisotropy change in Cr/Fe/MgO. Analysis of the chemical structure of Cr/Fe/MgO
revealed the existence of Cr atoms in the proximity of the Fe/MgO interface,
which can affect both magnetic anisotropy (MA) and its VC. We showed that PMA
and its VC can be enhanced by controlled Cr doping at the Fe/MgO interface. For
Cr/Fe (5.9 {\AA})/Cr (0.7 {\AA})/MgO with an effective PMA of 0.8 MJ/m3, a
maximum value of the voltage-controlled magnetic anisotropy (VCMA) effect of
370 fJ/Vm was demonstrated.",1701.00048v1
2017-01-05,Anisotropies in GeV-TeV cosmic ray electrons and positrons,"High energy cosmic ray electrons and positrons probe the local properties of
our Galaxy. In fact, electromagnetic energy losses limit the typical
propagation scale of GeV-TeV electrons and positrons to a few kpc. In the
diffusion model, nearby and dominant sources may produce an observable dipole
anisotropy in the cosmic ray fluxes. We present a detailed study on the role of
anisotropies from nearby sources in the interpretation of the observed GeV-TeV
cosmic ray electron and positrons fluxes. We compute predictions for the
anisotropies from known astrophysical sources as supernova remnants and pulsar
wind nebulae of the ATNF catalog. Our results are compared with current
anisotropy upper limits from the Fermi- LAT, AMS-02 and PAMELA experiments.",1701.01418v1
2017-01-20,The Wavefunction of Anisotropic Inflationary Universes With No-Boundary Conditions,"We study the emergence of anisotropic (Bianchi IX) inflationary universes
with no-boundary conditions in the path integral approach to quantum gravity.
In contrast to previous work, we find no evidence for any limit to how large
the anisotropies can become, although for increasing anisotropies the shape of
the instantons becomes significantly different from Hawking's original
no-boundary instanton. In all cases an inflationary phase is reached, with the
anisotropies decaying away. Larger anisotropies are associated with a much
larger imaginary part of the action, implying that the highly anisotropic
branches of the wavefunction are heavily suppressed. Interestingly, the
presence of anisotropies causes the wavefunction to become classical much more
slowly than for isotropic inflationary universes. We derive the associated
scaling of the WKB classicality conditions both numerically and analytically.",1701.05753v1
2017-01-15,Anisotropic inflation in Brans-Dicke gravity,"We study anisotropic inflation in the Brans-Dicke gravity in the presence of
an abelian gauge field where the gauge field is non-minimally coupled to the
inflaton. We show that the degree of anisotropy, under slow-roll
approximations, is proportional to slow roll parameter of the theory. As
demonstration, we consider the displaced quadratic potential for the inflation.
We do the numerical calculation of the model to investigate the behavior of
anisotropy by changing the parameter in the Brans-Dicke model. We find out
that, the solution is an attractor in the phase space, and anisotropy grows
with number of e-folds. Anisotropy depends on Brans-Dicke parameter, $ \omega
$, initial values of the scalar field and constant parameter of the coupling
function of the scalar field and the abelian gauge field, $ c $. If we consider
upper bound on the number of e-folds from CMB i.e. $ 60 $ e-folds, by
increasing $ \omega $ and $ c $, anisotropy do not have time to exit the
horizon and suppressed.",1701.06890v3
2017-02-04,Direction-Dependent Stability of skyrmion lattice in helimagnets induced by Exchange Anisotropy,"Exchange anisotropy provides a direction dependent mechanism for the
stability of the skyrmion lattice phase in noncentrosymmetric bulk chiral
magnets. Based on the Fourier representation of the skyrmion lattice, we
explain the direction dependence of the temperature-magnetic field phase
diagram for bulk MnSi through a phenomenological mean-field model incorporating
exchange anisotropy. Through quantitative comparison with experimental results,
we clarify that the stability of the skyrmion lattice phase in bulk MnSi is
determined by a combined effect of negative exchange anisotropy and thermal
fluctuation. The effect of exchange anisotropy and the order of Fourier
representation on the equilibrium properties of the skyrmion lattice is
discussed in detail.",1702.01212v3
2017-02-08,Spin-valley skyrmions in graphene at filling factor $ν=-1$,"We model quantum Hall skyrmions in graphene monolayer at quarter filling by a
theory of CP3 fields and study the energy minimizing skyrmions in presence of
valley pseudospin anisotropy and Zeeman coupling. We present a diagram of all
types of skyrmions in a wide range of the anisotropy parameters. For each type
of skyrmion, we visualize it on three Bloch spheres, and present the profiles
of its texture on the graphene honeycomb lattice, thus providing references for
the STM/STS imaging of spin-pseudospin textures in graphene monolayer in
quantum Hall regime. Besides the spin and pseudospin skyrmions for the
corresponding degrees of freedom of an electron in the N=0 Landau level, we
discuss two unusual types -- the ""entanglement skyrmion"" whose texture lies in
the space of the entanglement of spin and pseudospin, as well as the ""deflated
pseudospin skyrmion"" with partial entanglement. For all skyrmion types, we
study the dependence of the energy and the size of a skyrmion on the anisotropy
parameters and perpendicular magnetic field. We also propose three ways to
modify the anisotropy energy, namely the sample tilting, the substrate
anisotropy and the valley pseudospin analogue of Zeeman coupling.",1702.02438v1
2017-02-09,Gate Switchable Transport and Optical Anisotropy in 90° Twisted Bilayer Black Phosphorus,"Anisotropy describes the directional dependence of a material's properties
such as transport and optical response. In conventional bulk materials,
anisotropy is intrinsically related to the crystal structure, and thus not
tunable by the gating techniques used in modern electronics. Here we show that,
in bilayer black phosphorus with an interlayer twist angle of 90{\deg}, the
anisotropy of its electronic structure and optical transitions is tunable by
gating. Using first-principles calculations, we predict that a
laboratory-accessible gate voltage can induce a hole effective mass that is 30
times larger along one Cartesian axis than along the other axis, and the two
axes can be exchanged by flipping the sign of the gate voltage. This
gate-controllable band structure also leads to a switchable optical linear
dichroism, where the polarization of the lowest-energy optical transitions
(absorption or luminescence) is tunable by gating. Thus, anisotropy is a
tunable degree of freedom in twisted bilayer black phosphorus.",1702.02679v1
2017-02-20,Virtual photon polarization in ultrarelativistic heavy-ion collisions,"The polarization of direct photons produced in an ultrarelativistic heavy-ion
collision reflects the momentum anisotropy of the quark-gluon plasma created in
the collision. This paper presents a general framework, based on the photon
spectral functions in the plasma, for analyzing the angular distribution and
thus the polarization of dileptons in terms of the plasma momentum
anisotropies. The rates of dilepton production depend, in general, on four
independent spectral functions, corresponding to two transverse polarizations,
one longitudinal polarization, and -- in plasmas in which the momentum
anisotropy is not invariant under parity in the local rest frame of the matter
-- a new spectral function, $\rho_n$, related to the anisotropy direction in
the collision. The momentum anisotropy appears in the difference of the two
transverse spectral functions, as well as in $\rho_n$. As an illustration, we
delineate the spectral functions for dilepton pairs produced in the lowest
order Drell-Yan process of quark-antiquark annihilation to a virtual photon.",1702.05906v1
2017-02-25,Unveiling the role of Co-O-Mg bond in magnetic anisotropy of Pt/Co/MgO using atomically controlled deposition and in-situ electrical measurement,"Despite the crucial role of interfacial perpendicular magnetic anisotropy in
Co(Fe)/MgO based magnetic tunnel junction, the underlying mechanism is still
being debated. Here, we report an anatomical study of oxygen and Mg effect on
Pt/Co bilayers through repeated in-situ anomalous Hall effect measurements,
controlled oxygen exposure and Mg deposition in an ultrahigh vacuum system. We
found that chemisorbed oxygen not only quenches the effective magnetic moment
of the Co surface layer, but also softens its magnetic anisotropy. However, a
subsequent Mg dusting on the oxygen pre-exposed Pt/Co surface can recover the
magnetic anisotropy. The ab initio calculations on the exchange splitting and
orbital hybridization near the Fermi level give a clear physical explanation of
the experimental observations. Our results suggest that Co(Fe)-O-M bond plays a
more important role than the widely perceived Co(Fe)-O bond does in realizing
interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO heterostructures.",1702.07852v1
2017-03-03,Testing isotropy in the Two Micron All-Sky redshift survey with information entropy,"We use information entropy to test the isotropy in the nearby galaxy
distribution mapped by the Two Micron All-Sky redshift survey (2MRS). We find
that the galaxy distribution is highly anisotropic on small scales. The radial
anisotropy gradually decreases with increasing length scales and the observed
anisotropy is consistent with that expected for an isotropic Poisson
distribution beyond a length scale of $90 \, h^{-1}\, {\rm Mpc}$. Using mock
catalogues from N-body simulations, we find that the galaxy distribution in the
2MRS exhibits a degree of anisotropy compatible with that of the $\Lambda$CDM
model after accounting for the clustering bias of the 2MRS galaxies. We also
quantify the polar and azimuthal anisotropies and identify two directions
$(l,b)=(150^{\circ}, -15^{\circ})$, $(l,b)=(310^{\circ},-15^{\circ})$ which are
significantly anisotropic compared to the other directions in the sky. We
suggest that their preferential orientations on the sky may indicate a possible
alignment of the Local Group with two nearby large scale structures. Despite
the differences in the degree of anisotropy on small scales, we find that the
galaxy distributions in both the 2MRS and the $\Lambda$CDM model are isotropic
on a scale of $90 \, h^{-1}\, {\rm Mpc}$.",1703.01184v1
2017-06-26,Spin excitation anisotropy in the paramagnetic tetragonal phase of BaFe2 As2,"We use neutron polarization analysis to study temperature dependence of the
spin excitation anisotropy in BaFe$_2$As$_2$, which has a
tetragonal-to-orthorhombic structural distortion at $T_s$ and antiferromagnetic
(AF) phase transition at $T_N$ with ordered moments along the orthorhombic
$a$-axis below $T_s\approx T_N\approx 136$ K. In the paramagnetic tetragonal
state at 160 K, spin excitations are isotropic in spin space with
$M_a=M_b=M_c$, where $M_a$, $M_b$, and $M_c$ are spin excitations polarized
along the $a$, $b$, and $c$-axis directions of the orthorhombic lattice,
respectively. On cooling towards $T_N$, significant spin excitation anisotropy
with $M_a>M_b\approx M_c$ develops below 3 meV with a diverging $M_a$ at $T_N$.
The in-plane spin excitation anisotropy in the tetragonal phase of
BaFe$_2$As$_2$ is similar to those seen in the tetragonal phase of its electron
and hole-doped superconductors, suggesting that spin excitation anisotropy is a
direct probe of doping dependence of spin-orbit coupling and its connection to
superconductivity in iron pnictides.",1706.08258v1
2017-08-25,A Search for Cosmic-ray Proton Anisotropy with the Fermi Large Area Telescope,"In eight years of operation, the Fermi Large Area Telescope (LAT) has
detected a large sample of cosmic-ray protons. The LAT's wide field of view and
full-sky coverage make it an excellent instrument for studying anisotropy in
the arrival directions of protons at all angular scales. These capabilities
enable the LAT to make a full-sky 2D measurement of cosmic-ray proton
anisotropy complementary to many recent TeV measurements, which are only
sensitive to the right ascension component of the anisotropy. Any detected
anisotropy probes the structure of the local interstellar magnetic field or
could indicate the presence of a nearby source. We present the first results
from the Fermi-LAT Collaboration on the full-sky angular power spectrum of
protons from approximately 100 GeV - 10 TeV.",1708.07796v1
2017-09-25,Dynamical vs geometric anisotropy in relativistic heavy-ion collisions: which one prevails?,"We study the influence of geometric and dynamical anisotropies on the
development of flow harmonics and, simultaneously, on the second- and
third-order oscillations of femtoscopy radii. The analysis is done within the
Monte Carlo event generator HYDJET++, which was extended to dynamical
triangular deformations. It is shown that the merely geometric anisotropy
provides the results which anticorrelate with the experimental observations of
either $v_2$ (or $v_3$) or second-order (or third-order) oscillations of the
femtoscopy radii. Decays of resonances significantly increase the emitting
areas but do not change the phases of the radii oscillations. In contrast to
the spatial deformations, the dynamical anisotropy alone provides the correct
qualitative description of the flow and the femtoscopy observables
simultaneously. However, one needs both types of the anisotropy to match
quantitatively the experimental data.",1709.08602v2
2017-10-22,Nonlinear anisotropy growth in Bianchi-I spacetime in metric $f(R)$ cosmology,"The present work is related to anisotropic cosmological evolution in metric
$f(R)$ theory of gravity. The initial part of the paper develops the general
cosmological dynamics of homogeneous anisotropic Bianchi-I spacetime in $f(R)$
cosmology. The anisotropic spacetime is pervaded by a barotropic fluid which
has isotropic pressure. The paper predicts nonlinear growth of anisotropy in
such spacetimes. In the later part of the paper we display the predictive power
of the nonlinear differential equation responsible for the cosmological
anisotropy growth in various relevant cases. We present the exact solutions of
anisotropy growth in Starobinsky inflation driven by quadratic gravity and
exponential gravity theory. Semi-analytical results are presented for the
contraction phase in quadratic gravity bounce. The various examples of
anisotropy growth in Bianchi-I model universe shows the complex nature of the
problem at hand.",1710.07906v4
2017-11-10,Impact of organic capping layer on the magnetic anisotropy of ultrathin Co films,"Using combined magnetometry and ferromagnetic resonance studies, it is shown
that introduction of a hydrocarbon cover layer leads to an increase of the
contribution of the surface anisotropy to the effective magnetic anisotropy
energy of hexagonal close-packed 0001 cobalt films, largely enhancing the
perpendicular anisotropy. Due to a weak electronic interaction of the organic
molecules with the Co atoms, an increase of surface anisotropy could be
explained by the presence of an electric field at the organic-material/Co
interface and by modification of surface atoms charge configuration.",1711.03858v1
2017-11-30,Magnetic anisotropy by Rashba spin-orbit coupling in antiferromagnetic thin films,"Magnetic anisotropy in an antiferromagnet (AFM) with inversion symmetry
breaking (ISB) is investigated. The magnetic anisotropy energy (MAE) resulting
from the Rashba spin-orbit and s-d type exchange interactions is determined for
two different models of AFMs. The global ISB model, representing the effect of
a surface, an interface, or a gating electric field, results in an easy-plane
magnetic anisotropy. In contrast, for a local ISB model, i.e., for a
noncentrosymmetric AFM, perpendicular magnetic anisotropy (PMA) arises. Both
results differ from the ferromagnetic case, in which the result for PMA depends
on the band structure and dimensionality. These MAE contributions play a key
role in determining the direction of the Neel order parameter in
antiferromagnetic nanostructures, and reflect the possibility of
electrical-field control of the Neel vector.",1711.11184v2
2017-12-13,Anisotropy and spin-fluctuation effects on the spectral properties of Shiba impurities,"We theoretically consider a quantum magnetic impurity coupled to a
superconductor, and obtain the local density of states at the position of the
impurity taking into account the effect of spin-fluctuations and single-ion
magnetic anisotropy. We particularly focus on the spectrum of subgap
Yu-Shiba-Rusinov (YSR or Shiba) states induced by a quantum impurity with easy-
or hard-axis uniaxial anisotropy. Although this is a relevant experimental
situation in, e.g., magnetic adatoms on the surface of clean metals, it is
customary that theoretical descriptions assume a classical-spin approximation
which is not able to account for single-ion anisotropy and other quantum
effects. Here, quantum fluctuations of the spin are taken into account in the
equations of motion of the electronic Green's function in the weak-coupling
limit, and considerably modify the energy of the Shiba states compared to the
classical-spin approximation. Our results point towards the importance of
incorporating quantum fluctuations and anisotropy effects for the correct
interpretation of scanning tunneling microscopy (STM) experiments.",1712.04920v2
2017-12-23,Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions,"Nanoscale magnetic tunnel junction plays a pivotal role in magnetoresistive
random access memories. Successful implementation depends on a simultaneous
achievement of low switching current for the magnetization switching by
spin-transfer torque and high thermal stability, along with a continuous
reduction of junction size. Perpendicular-easy-axis CoFeB/MgO stacks possessing
interfacial anisotropy have paved the way down to 20-nm scale, below which a
new approach needs to be explored. Here we show magnetic tunnel junctions that
satisfy the requirements at ultrafine scale by revisiting shape anisotropy,
which is a classical part of magnetic anisotropy but has not been fully
utilized in the current perpendicular systems. Magnetization switching solely
driven by current is achieved for junctions smaller than 10 nm where sufficient
thermal stability is provided by shape anisotropy without adopting new material
systems. This work is expected to push forward the development of magnetic
tunnel junctions towards single-digit-nm-scale nano-magnetics/spintronics.",1712.08774v1
2018-01-04,Properties of polycrystalline nanoparticles with uniaxial and cubic types of magnetic anisotropy of individual grains,"The influence of the crystal structure inhomogeneities on the magnetic
properties of cobalt nanoparticles with different aspect ratio and spherical
nanoparticles of chromium dioxide, cobalt ferrite and magnetite has been
studied by means of numerical simulation. The polycrystalline nanoparticles are
modeled by means of subdivision of the nanoparticle volume into tightly bound
single-crystal granules with randomly distributed directions of the easy
anisotropy axes. The probability of appearance of quasi uniform and vortex
states in sufficiently large assemblies of polycrystalline nanoparticles of
various types have been calculated depending on the nanoparticle diameter. It
is shown that the subdivision of a nanoparticle into single-crystal granules
with different orientations of the easy anisotropy axes substantially reduces
the effective single-domain diameters for particles with uniaxial type of
anisotropy of individual granules. However, for particles with cubic type of
magnetic anisotropy the influence of the crystal structure inhomogeneities on
the equilibrium properties of the particles is not so important even for
magnetically hard cobalt ferrite nanoparticles. It is practically absent for
magnetically soft magnetite nanoparticles.",1801.01266v1
2018-01-11,General relativistic polytropes in anisotropic stars,"Spherically symmetric relativistic stars with the polytropic equation of
state (EoS), which possess the local pressure anisotropy, are considered within
the framework of general relativity. The generalized Lane-Emden equations are
derived for the arbitrary anisotropy parameter $\Delta=p_t-p_r$ ($p_t$ and
$p_r$ being the transverse and radial pressure, respectively). They are then
applied to some special ansatz for the anisotropy parameter in the form of the
differential relation between the anisotropy parameter $\Delta$ and the metric
function $\nu$. The analytical solutions of the obtained equations are found
for incompressible fluid stars and then used for getting their mass-radius
relation, gravitational and binding energy. Also, following the Chandrasekhar
variational approach, the dynamical stability of incompressible anisotropic
fluid stars with the polytropic EoS against radial oscillations is studied. It
is shown that the local pressure anisotropy with $p_t>p_r$ can make the
incompressible fluid stars unstable with respect to radial oscillations, in
contrast to incompressible isotropic fluid stars with the polytropic EoS which
are dynamically stable.",1801.03745v1
2018-01-13,Quantum phase transitions in spin-1 XXZ chains with rhombic single-ion anisotropy,"We explore the fidelity susceptibility and the quantum coherence along with
the entanglement entropy in the ground-state of one-dimensional spin-1 XXZ
chains with the rhombic single-ion anisotropy. By using the techniques of
density matrix renormalization group, effects of the rhombic single-ion
anisotropy on a few information theoretical measures are investigated, such as
the fidelity susceptibility, the quantum coherence and the entanglement
entropy. Their relations with the quantum phase transitions are also analyzed.
The phase transitions from the Y-N\'{e}el phase to the Large-$E_x$ or the
Haldane phase can be well characterized by the fidelity susceptibility. The
second-order derivative of the ground-state energy indicates all the
transitions are of second order. We also find that the quantum coherence, the
entanglement entropy, the Schmidt gap can be used to detect the critical points
of quantum phase transitions. Conclusions drawn from these quantum information
observables agree well with each other. Finally we provide a ground-state phase
diagram as functions of the exchange anisotropy $\Delta$ and the rhombic
single-ion anisotropy $E$.",1801.04922v2
2018-01-31,Polarization and dilepton angular distribution in pion-nucleon collisions,"We study hadronic polarization and the related anisotropy of the dilepton
angular distribution for the reaction $\pi N \to Ne^+e^-$. We employ consistent
effective interactions for baryon resonances up to spin-5/2 to compute their
contribution to the anisotropy coefficient. We show that the spin and parity of
the intermediate baryon resonance is reflected in the angular dependence of the
anisotropy coefficient. We present results for the anisotropy coefficient
including the $N(1520)$ and $N(1440)$ resonances, which are essential at the
collision energy of the recent data obtained by the HADES collaboration on this
reaction. We conclude that the anisotropy coefficient provides useful
constraints for unraveling the resonance contributions to this process.",1802.00062v1
2018-03-05,Reconstruction method of $f(R)$ gravity for isotropic and anisotropic spacetimes,"We present the reconstruction method of $f(R)$ gravity for the homogeneous
and anisotropic Bianchi-I spacetime, which was previously formulated only for
homogeneous and isotropic FLRW spacetime. We argue in this paper that for
anisotropic spacetimes, the total anisotropy behaves as an independent metric
degree of freedom on top of the average scale factor in $f(R)$ gravity. This is
not like $GR$, where specifying the form of the average scale factor as a
function of time also specify the total anisotropy as a function of time
uniqely. We link this peculiar fact to an interesting intertwining between the
definition of Ricci scalar for anisotropic metric and anisotropy evolution
equation in $f(R)$ gravity. Consequently, specifying an anisotropic solution of
$f(R)$ gravity implies specifying both the average scale factor and the total
anisotropy as functions of time. The reconstruction method hence formulated is
applied to two scenarios where anisotropy suppression is important, namely, a
quasi de-Sitter expansion as required in inflation, and a power law contraction
as required in ekpyrotic bounce models.",1803.01594v2
2018-03-22,Searching for a possible dipole anisotropy on acceleration scale with 147 rotationally supported galaxies,"We report a possible dipole anisotropy on acceleration scale $g_{\dag}$ with
147 rotationally supported galaxies in local Universe. It is found that a
monopole and dipole correction for the radial acceleration relation can better
describe the SPARC data set. The monopole term is negligible but the dipole
magnitude is significant. It is also found that the dipole correction is mostly
induced by the anisotropy on the acceleration scale. The magnitude of
$\hat{g}_{\dag}$-dipole reaches up to $0.25\pm0.04$, and its direction is
aligned to $(l,b) = (171.30^{\circ}\pm7.18^{\circ},
-15.41^{\circ}\pm4.87^{\circ})$, which is very close to the maximum anisotropy
direction from the hemisphere comparison method. Furthermore, robust check
shows that the dipole anisotropy couldn't be reproduced by isotropic mock data
set. However, it is still premature to claim that the Universe is anisotropic
due to the small data samples and uncertainty in the current observations.",1803.08344v2
2018-05-03,Symmetry broken spin reorientation transition in epitaxial MgO/Fe/MgO layers with competing anisotropies,"The observation of perpendicular magnetic anisotropy (PMA) at MgO/Fe
interfaces boosted the development of spintronic devices based on ultrathin
ferromagnetic layers. Yet, magnetization reversal in the standard magnetic
tunnel junctions (MTJs) with competing PMA and in-plane anisotropies remains
unclear. Here we report on the field induced nonvolatile broken symmetry
magnetization reorientation transition from the in-plane to the perpendicular
(out of plane) state at temperatures below 50K. The samples were 10 nm thick Fe
in MgO/Fe(100)/MgO as stacking components of V/MgO/Fe/MgO/Fe/Co double barrier
MTJs. Micromagnetic simulations with PMA and different second order
anisotropies at the opposite Fe/MgO interfaces qualitatively reproduce the
observed broken symmetry spin reorientation transition. Our findings open the
possibilities to develop multistate epitaxial spintronics based on competing
magnetic anisotropies.",1805.01304v2
2018-05-22,Thermoelectric anisotropy in Ba(Fe1-xCox)2As2 iron-based superconductor,"We report the in-plane anisotropy of the Seebeck and Nernst coefficients as
well as of the electrical resistivity determined for the series of the
strain-detwinned single crystals of Ba(Fe1-xCox)2As2. Two underdoped samples (x
= 0.024, 0.045) exhibiting the transition from the tetragonal paramagnetic
phase to the orthorhombic spin density wave (SDW) phase (at Ttr = 100 and 60 K,
respectively) show an onset of the Nernst anisotropy at temperatures above 200
K, which is significantly higher than Ttr. In the optimally doped sample (x =
0.06) the transport properties also appear to be in-plane anisotropic below T =
120 K, despite the fact that this particular composition does not show any
evidence of long-range magnetic order. However, the anisotropy observed in the
optimally doped crystal is rather small and for the Seebeck and Nernst
coefficients the difference between values measured along and across the
uniaxial strain has opposite sign to those observed for underdoped crystals
with x = 0.024 and 0.045. For these two samples, insensitivity of the Nernst
anisotropy to the SDW transition suggests that the nematicity might be of other
than magnetic origin.",1805.08510v1
2018-05-23,Testing the anisotropy of cosmic acceleration from Pantheon supernovae sample,"In this paper, we study the anisotropy of cosmic acceleration the using
Pantheon sample, which includes 1048 spectroscopically confirmed Type Ia
supernovae (SNe Ia) covering the redshift range $0.01 < z < 2.3$. In hemisphere
comparison method, we find the dipole direction is $(l = 37 \pm 40^{\circ}, b =
33 \pm 16^{\circ})$ with the maximum anisotropy level of $\delta=0.136
{}^{+0.009}_{-0.005}$. From the dipole fitting method, we find that the
magnitude of anisotropy is $A = (3.7 {}^{+2.5}_{-3.7}) \times 10^{-4}$, and the
direction of the dipole $(l = 329^{\circ}{}^{+ 101^{\circ}}_{-28^{\circ}}, b =
37^{\circ}{}^{+ 52^{\circ}}_{-21^{\circ}})$ in the galactic coordinate system.
The result is weakly dependent on redshift from the redshift tomography
analysis. The anisotropy is small and the isotropic cosmological model is an
excellent approximation.",1805.09195v2
2018-06-18,Current-driven domain wall motion along ferromagnetic strips with periodically-modulated perpendicular anisotropy,"The dynamics of magnetic domain walls along ferromagnetic strips with
spatially modulated perpendicular magnetic anisotropy is theoretically studied
by means of micromagnetic simulations. Ferromagnetic layers with a periodic
sawtooth profile of the anisotropy depict a well-defined set of energy minima
where the walls are pinned in the absence of external stimuli, and favor the
unidirectional propagation of domain walls. The performance of the
current-driven domain wall motion along these ratchet-like systems is compared
to the field-driven case. Our study indicates that the current-driven domain
wall motion exhibits significant improvements with respect to the field-driven
case in terms of bit shifting speed and storage density, and therefore, it is
suggested for the development of novel devices. The feasibility of these
current-driven ratchet devices is studied by means of realistic micromagnetic
simulations and supported by a one-dimensional model updated to take into
account the periodic sawthooth anisotropy profile. Finally, the current-driven
domain wall motion is also evaluated in systems with a triangular modulation of
the anisotropy designed to promote the bidirectional shifting of series of
walls, a functionality that cannot be achieved by magnetic fields.",1806.06585v1
2018-07-09,Engineering Phonon Polaritons in van der Waals Heterostructures to Enhance In-Plane Optical Anisotropy,"Van der Waals heterostructures assembled from layers of 2D materials have
attracted considerable interest due to their novel optical and electrical
properties. Here we report a scattering-type scanning near field optical
microscopy study of hexagonal boron nitride on black phosphorous (h-BN/BP)
heterostructures, demonstrating the first direct observation of in-plane
anisotropic phonon polariton modes in vdW heterostructures. Strikingly, the
measured in-plane optical anisotropy along armchair and zigzag crystal axes
exceeds the ratio of refractive indices of BP in the x-y plane. We explain that
this enhancement is due to the high confinement of the phonon polaritons in
h-BN. We observe a maximum in-plane optical anisotropy of {\alpha}_max=1.25 in
the 1405-1440 cm-1 frequency spectrum. These results provide new insights on
the behavior of polaritons in vdW heterostructures, and the observed anisotropy
enhancement paves the way to novel nanophotonic devices and to a new way to
characterize optical anisotropy in thin films.",1807.03339v1
2018-08-29,On the effect of turbulent anisotropy on pulsation stability of stars,"Within the framework of non-local time-dependent stellar convection theory,
we study in detail the effect of turbulent anisotropy on stellar pulsation
stability. The results show that anisotropy has no substantial influence on
pulsation stability of g modes and low-order (radial order $n_\mathrm{r}<5$) p
modes. The effect of turbulent anisotropy increases as the radial order
increases. When turbulent anisotropy is neglected, most of high-order
($n_\mathrm{r}>5$) p modes of all low-temperature stars become unstable.
Fortunately, within a wide range of the anisotropic parameter $c_3$, stellar
pulsation stability is not sensitive to the specific value of $c_3$. Therefore
it is safe to say that calibration errors of the convective parameter $c_3$ do
not cause any uncertainty in the calculation of stellar pulsation stability.",1808.09625v1
2018-09-19,Large phase-transition-induced magnetic anisotropy change in (Co/Pt)2/VO2 heterostructure,"We report the phase-transition controlled magnetic anisotropy modulation in
the (Co/Pt)2/VO2 heterostructure, where VO2 is introduced into the system to
applied an interfacial strain by its metal-insulator transition. A large
reversible modulation of the perpendicular magnetic anisotropy (PMA) reaching
38 kJ/m3 is observed during this process. The calculated energy density
variation of interfacial anisotropy reaches 100 mJ/m2, which shows significant
advantage over traditional modulation strategies. Further experimental results
including magnetization change versus temperature, strain buffered modulation
and pre-strained sample comparison prove that the interfacial coupling between
VO2 and PMA layers plays a crucial role in this modulation. This work,
demonstrating the great potential of phase-transition material in efficient
magnetic anisotropy modulation, would benefit the exploration for low-power
consumption devices.",1809.06999v1
2018-09-29,Perpendicular magnetic anisotropy in bulk and thin-film CuMnAs for antiferromagnetic memory applications,"CuMnAs with perpendicular magnetic anisotropy is proposed as an active
material for antiferromagnetic memory. Information can be stored in the
antiferromagnetic domain state, while writing and readout can rely on the
existence of the surface magnetization. It is predicted, based on
first-principles calculations, that easy-axis anisotropy can be achieved in
bulk CuMnAs by substituting a few percent of As atoms by Ge, Si, Al, or B. This
effect is attributed to the changing occupation of certain electronic bands
near the Fermi level induced by the hole doping. The calculated temperature
dependence of the magnetic anisotropy does not exhibit any anomalies. Thin
CuMnAs(001) films are also predicted to have perpendicular magnetic anisotropy.",1810.00249v1
2018-10-09,Statistical anisotropy in CMB spectral distortions,"Measurements of the cosmic microwave background (CMB) spectral $y$-distortion
anisotropy offer a test for the statistical isotropy of the primordial density
perturbations on $0.01\lesssim k{\rm Mpc}\lesssim 1$. We compute the 1-point
ensemble averages of the $y$-distortion anisotropies which vanish for the
statistically isotropic perturbations. For the quadrupole statistical
anisotropy, we find $4\pi\langle y_{2m}\rangle=-6.8A_2\times
10^{-9}Y_{2m}(\mathbf d )$ with the quadruple Legendre coefficient of the
anisotropic powerspectrum $A_2$ and the $\ell=2$ spherical harmonics
$Y_{2m}(\mathbf d )$ for the preferred direction $\mathbf d $. Also, we discuss
the cosmic variance of the $y$-distortion anisotropy in the statistically
anisotropic Universe.",1810.03928v2
2018-10-31,Visualizing Intramolecular Distortions as the Origin of Transverse Magnetic Anisotropy,"The magnetic properties of metal-organic complexes are strongly influenced by
conformational changes in the ligand. The flexibility of
Fe-tetra-pyridyl-porphyrin molecules leads to different adsorption
configurations on a Au(111) surface. By combining low-temperature scanning
tunneling spectroscopy and atomic force microscopy, we resolve a correlation of
the molecular configuration with different spin states and magnitudes of
magnetic anisotropy. When the macrocycle exhibits a laterally-undistorted
saddle shape, the molecules lie in a S=1 state with axial anisotropy arising
from a square-planar ligand field. If the symmetry in the molecular ligand
field is reduced by a lateral distortion of the molecule, we find a finite
contribution of transverse anisotropy. Some of the distorted molecules lie in a
S=2 state, again exhibiting substantial transverse anisotropy.",1811.00059v1
2018-11-19,Small Anisotropy in Stellar Objects in Modified Theories of Gravity,"Interior structures of stellar objects might have small pressure anisotropy
due to several reasons, including rotation and the presence of magnetic fields.
Here, retaining the approximation of spherical symmetry, we study the possible
role of small anisotropy in stellar interiors in theories of modified gravity,
that are known to alter the hydrostatic equilibrium condition inside stars. We
show how anisotropy may put lower and upper bounds on the modified gravity
parameter depending on the polytropic equation of state, and determine them
numerically. We also study the mass of stellar objects in these theories,
assuming such equations of state, and find that the Chandrasekhar mass limit in
white dwarf stars gets substantially modified compared to the isotropic case,
even without assuming the presence of extreme magnetic fields. Effects of small
pressure anisotropy on the Hydrogen burning limit in low mass stars are also
briefly commented upon. It is shown that here the isotropic case can predict a
theoretical lower bound on the scalar tensor parameter, in addition to a known
upper bound.",1811.07685v1
2018-12-23,Indication of nearby source signatures of cosmic rays from energy spectra and anisotropies,"The origin of Galactic cosmic rays (GCRs) remains a mystery after more than
one century of their discovery. The diffusive propagation of charged particles
in the turbulent Galactic magnetic field makes us unable to trace back to their
acceleration sites. Nevertheless, nearby GCR source(s) may leave imprints on
the locally measured energy spectra and the anisotropies of the arrival
direction. In this work we propose a simple but natural description of the GCR
production and propagation, within a two-zone disk-halo diffusion scenario
together with a nearby source, to understand the up-to-date precise
measurements of the energy spectra and anisotropies of GCRs. We find that a
common energy scale of $\sim100$ TeV appears in both energy spectra of protons
and Helium nuclei measured recently by CREAM and large-scale anisotropies
detected by various experiments. These results indicate that one or more local
sources are very likely important contributors to GCRs below $100$ TeV. This
study provides a probe to identify source(s) of GCRs by means of joint efforts
of spectral and anisotropy measurements.",1812.09673v2
2018-12-31,Electric field switching of the uniaxial magnetic anisotropy of an antiferromagnet,"Electric field control of magnetic anisotropy in ferromagnets has been
intensively pursued in spintronics to achieve efficient memory and computing
devices with low energy consumption. Compared with ferromagnets,
antiferromagnets hold huge potential in high-density information storage for
their ultrafast spin dynamics and vanishingly small stray field. However, the
switching of magnetic anisotropy of antiferromagnets via electric field remains
elusive. Here we use ferroelastic strain from piezoelectric materials to switch
the uniaxial magnetic anisotropy and the N\'eel order reversibly in
antiferromagnetic Mn2Au films with an electric field of only a few kV/cm at
room temperature. Owing to the uniaxial magnetic anisotropy, a ratchet-like
switching behavior driven by the N\'eel spin-orbit torque is observed in the
Mn2Au, which can be reversed by electric fields.",1812.11868v1
2019-02-26,Tensor-valued diffusion MRI in under 3 minutes: An initial survey of microscopic anisotropy and tissue heterogeneity in intracranial tumors,"Purpose: To evaluate the feasibility of a 3-minute b-tensor encoding protocol
for diffusion MRI-based assessment of the microscopic anisotropy and tissue
heterogeneity in a wide range of intracranial tumors. Methods: B-tensor
encoding was performed in 42 patients with intracranial tumors (gliomas,
meningiomas, adenomas, metastases). Microscopic anisotropy and tissue
heterogeneity were evaluated by estimating the anisotropic kurtosis ($MK_A$)
and isotropic kurtosis ($MK_I$), respectively. An extensive imaging protocol
was compared with a faster 3-minute protocol. Results: The fast imaging
protocol yielded parameters with characteristics in terms of bias and precision
similar to the full protocol. Glioblastomas had lower microscopic anisotropy
than meningiomas $(MK_A = 0.29 \pm 0.06$ versus $0.45\pm0.08, p = 0.003)$.
Metastases had higher tissue heterogeneity $(MK_I = 0.57\pm0.07)$ than both the
glioblastomas $(0.44\pm0.06, p < 0.001)$ and meningiomas $(0.46\pm0.06, p =
0.03)$. Conclusion: Evaluation of the microscopic anisotropy and tissue
heterogeneity in intracranial tumor patients is feasible in clinically relevant
times frames.",1902.09986v1
2019-03-05,Anisotropy-based robust performance criteria for statistically uncertain linear continuous time invariant stochastic systems,"This paper is concerned with robust performance criteria for linear
continuous time invariant stochastic systems driven by statistically uncertain
random processes. The uncertainty is understood as the deviation of imprecisely
known probability distributions of the input disturbance from those of the
standard Wiener process. Using a one-parameter family of conformal maps of the
unit disk in the complex plane onto the right half-plane for discrete and
continuous time transfer functions, the deviation from the nominal Gaussian
white-noise model is quantified by the mean anisotropy for the input of a
discrete-time counterpart of the original system. The parameter of this
conformal correspondence specifies the time scale for filtered versions of the
input and output of the system, in terms of which the worst-case root mean
square gain is formulated subject to an upper constraint on the mean
anisotropy. The resulting two-parameter counterpart of the
anisotropy-constrained norm of the system for the continuous time case is
amenable to state-space computation using the methods of the anisotropy-based
theory of stochastic robust filtering and control, originated by the author in
the mid 1990s.",1903.01692v1
2019-04-02,On temperature-dependent anisotropies of upper critical field and London penetration depth,"We show on a few examples of one-band materials with spheroidal Fermi
surfaces and anisotropic order parameters that anisotropies $\gamma_H$ of the
upper critical field and $\gamma_\lambda$ of the London penetration depth
depend on temperature, the feature commonly attributed to multi-band
superconductors. The parameters $\gamma_H$ and $\gamma_\lambda$ may have
opposite temperature dependencies or may change in the same direction depending
on Fermi surface shape and on character of the gap nodes. For two-band systems,
the behavior of anisotropies is affected by the ratios of bands densities of
states, Fermi velocities, anisotropies, and order parameters. We investigate in
detail the conditions determining the directions of temperature dependences of
the two anisotropy factors.",1904.01161v2
2019-04-11,Triangular array of iron-oxide nanoparticles: A simulation study of intra- and inter-particle magnetism,"A study of spherical maghemite nanoparticles on a two dimensional triangular
array was carried out using a stochastic Landau-Lifshitz-Gilbert (sLLG)
approach. The simulation method was first validated with a triangular array of
simple dipoles, where results show the expected phase transition to a
ferromagnetic state at a finite temperature. The ground state exhibited a
continuous degeneracy that was lifted by an order-from-disorder mechanism at
infinitesimal temperatures with the appearance of a six-fold planar anisotropy.
The nanoparticle array consisted of 7.5 nm diameter maghemite spheres with
bulk-like superexchange interactions between Fe-ions in the core, and weaker
exchange between surface Fe-ions and a radial anisotropy. The triangular
nanoparticle array ordered at the same reduced temperature as the simple dipole
array, but exhibited different behaviour at low temperatures due to the surface
anisotropy. We find that the vacancies on the octahedral sites in the
nanoparticles combine with the surface anisotropy to produce an effective
random temperature-dependent anisotropy for each particle. This leads to a
reduction in the net magnetization of the nanoparticle array at zero
temperature compared to the simple dipole array.",1904.05515v1
2019-04-16,Stochastic gravitational wave background anisotropies in the mHz band: astrophysical dependencies,"We show that the anisotropies of the astrophysical stochastic gravitational
wave background in the mHz band have a strong dependence on the modelling of
galactic and sub-galactic physics. We explore a wide range of self-consistent
astrophysical models for stellar evolution and for the distribution of orbital
parameters, all calibrated such that they predict the same number of resolved
mergers to fit the number of detections during LIGO/Virgo O1+O2 observations
runs. We show that different physical choices for the process of black hole
collapse and cut-off in the black hole mass distribution give fractional
differences in the angular power spectrum of anisotropies up to 50\% on all
angular scales. We also point out that the astrophysical information which can
be extracted from anisotropies is complementary to the isotropic background and
individual mergers. These results underline the interest in the anisotropies of
the stochastic gravitational wave background as a new and potentially rich
field of research, at the cross-road between astrophysics and cosmology.",1904.07757v2
2019-04-22,Strain-Induced Reversible Manipulation of Orbital Magnetic Moments in Ni/Cu Multilayers on Ferroelectric BaTiO3,"Controlling magnetic anisotropy by orbital magnetic moments related to
interfacial strains has considerable potential for the development of future
devices using spins and orbitals. For the fundamental physics, the relationship
between strain and orbital magnetic moment is still unknown, because there are
few tools to probe changes of orbital magnetic moment. In this study, we
developed an electric-field- (E)-induced X-ray magnetic circular dichroism
(EXMCD) technique to apply E to a ferroelectric BaTiO3 substrate. We reversibly
tuned the interfacial lattice constants of Ni/Cu multilayers on BaTiO3 using
this technique. As the domain structures in BaTiO3 are modulated by E, EXMCD
measurements reveal that the changes in the magnetic anisotropy of Ni/Cu films
are induced through the modulation of orbital magnetic moments in Ni with
magneto-elastic contributions. The strained Ni layer that induces the
perpendicular magnetic anisotropy without E is released at E = 8 kV/cm, and
in-plane magnetization also occurs. We observed that EXMCD measurements
clarified the origin of the reversible changes in perpendicular magnetic
anisotropy and established the relationship between macroscopic inverse
magnetostriction effects and microscopic orbital moment anisotropy.",1904.09719v1
2019-06-01,Influence of initial-state momentum anisotropy on the final-state collectivity in small collision systems,"A multi-phase transport model is used to understand the origin of long-range
collective azimuthal correlations in small-system collisions. To disentangle
between collectivity associated with initial-state intrinsic momentum
anisotropy and the collectivity arising as a final-state response to the
collision geometry, we studied the development of collectivity in 5.02 TeV
$p$+Pb collisions with both initial-state and final-state effects included. We
find that the initial momentum anisotropy may not be fully isotropized through
parton interactions, and the final-state partonic collectivity in general are
correlated with both the initial momentum anisotropy and the shape of the
collision geometry. The initial momentum anisotropy also influences the event
by event fluctuation of collective flow. Therefore the mere evidence of
geometry response of the collective flow can not rule out the presence of large
contributions from the initial state.",1906.01422v1
2019-09-05,The role of faceting and elongation on the magnetic anisotropy of magnetite Fe3O4 nanocrystals,"Fe3O4 nanoparticles are one of the most promising candidates for biomedical
applications such as magnetic hyperthermia and theranostics due to their
bio-compatibility, structural stability and good magnetic properties. However,
much is unknown about the nanoscale origins of the observed magnetic properties
of particles due to the dominance of surface and finite size effects. Here we
have developed an atomistic spin model of elongated magnetite nanocrystals to
specifically address the role of faceting and elongation on the magnetic shape
anisotropy. We find that for faceted particles simple analytical formulae
overestimate the magnetic shape anisotropy and that the underlying cubic
anisotropy makes a significant contribution to the energy barrier for
moderately elongated particles. Our results enable a better estimation of the
effective magnetic anisotropy of highly crystalline magnetite nanoparticles and
is a step towards quantitative prediction of the heating effects of magnetic
nanoparticles.",1909.02470v1
2019-09-19,Large- and Medium-Scale Anisotropies in the Arrival Directions of Cosmic Rays observed with KASCADE-Grande,"We search for anisotropies in the arrival directions of cosmic rays observed
by the KASCADE-Grande air shower experiment. The analysis is based on public
data of about 23.7 million events with reconstructed primary energies above 1
PeV. We apply a novel maximum-likelihood reconstruction method for the cosmic
ray anisotropy, that compensates for spurious anisotropies induced by local
detector effects. We find no evidence for a large-scale dipole anisotropy in
the data, consistent with official results based on the conventional East-West
derivative method. On the other hand, a subset of cosmic rays with median
energy of 33 PeV shows strong evidence for a medium-scale feature with an
angular diameter of 40 degrees. After accounting for the look-elsewhere effect,
the post-trial significance of this medium-scale feature is at the level of
4$\sigma$.",1909.09222v2
2019-10-03,Photoemission Spectrum of Ca2RuO4: Spin Polaron Physics in an S=1 Antiferromagnet with Anisotropies,"We derive an S=1 spin polaron model which describes the motion of a single
hole introduced into the S=1 spin antiferromagnetic ground state of Ca2RuO4. We
solve the model using the self-consistent Born approximation and show that its
hole spectral function qualitatively agrees with the experimentally observed
high-binding energy part of the Ca2RuO4 photoemission spectrum. We explain the
observed peculiarities of the photoemission spectrum by linking them to two
anisotropies present in the employed model---the spin anisotropy and the
hopping anisotropy. We verify that these anisotropies, and not the possible
differences between the ruthenate (S=1) and the cuprate (S=1/2) spin polaron
models, are responsible for the strong qualitative differences between the
photoemission spectrum of Ca2RuO4 and of the undoped cuprates.",1910.01605v1
2019-10-15,Constraining the anisotropy of the Universe via Pantheon supernovae sample,"We test the possible dipole anisotropy of a Finslerian cosmological model and
other three dipole-modulated cosmological models, i.e., the dipole-modulated
$\rm{\Lambda}$CDM, $w$CDM and Chevallier--Polarski--Linder (CPL) model by using
the recently released Pantheon sample of SNe Ia. The Markov chain Monte Carlo
(MCMC) method is used to explore the whole parameter space. We find that the
dipole anisotropy is very weak in all cosmological models used. Although the
dipole amplitudes of four cosmological models are consistent with zero within
$1\sigma$ uncertainty, the dipole directions are close to the axial direction
to the plane of SDSS subsample among Pantheon. It may imply that the weak
dipole anisotropy in the Pantheon sample originates from the inhomogeneous
distribution of the SDSS subsample. More homogeneous distribution of SNe Ia is
necessary to constrain the cosmic anisotropy.",1910.06883v1
2019-12-10,Effects of substrate anisotropy and edge diffusion on submonolayer growth during molecular beam epitaxy: A Kinetic Monte Carlo study,"We have performed Kinetic Monte Carlo simulation work to study the effect of
diffusion anisotropy, bonding anisotropy and edge diffusion on island formation
at different temperatures during the sub-monolayer film growth in Molecular
Beam Epitaxy. We use simple cubic solid on solid model and event based Bortz,
Kalos and Labowitch (BKL) algorithm on the Kinetic Monte Carlo method to
simulate the physical phenomena. We have found that the island morphology and
growth exponent are found to be influenced by substrate anisotropy as well as
edge diffusion, however they do not play a significant role in island
elongation. The growth exponent and island size distribution are observed to be
influenced by substrate anisotropy but are negligibly influenced by edge
diffusion. We have found fractal islands when edge diffusion is excluded and
compact islands when edge diffusion is included.",1912.05918v1
2020-01-10,Unidirectional tilt of domain walls in equilibrium in biaxial stripes with Dzyaloshinskii-Moriya interaction,"The orientation of a chiral magnetic domain wall in a racetrack determines
its dynamical properties. In equilibrium, magnetic domain walls are expected to
be oriented perpendicular to the stripe axis. We demonstrate the appearance of
a unidirectional domain wall tilt in out-of-plane magnetized stripes with
biaxial anisotropy and Dzyaloshinskii--Moriya interaction (DMI). The tilt is a
result of the interplay between the in-plane easy-axis anisotropy and DMI. We
show that the additional anisotropy and DMI prefer different domain wall
structure: anisotropy links the magnetization azimuthal angle inside the domain
wall with the anisotropy direction in contrast to DMI, which prefers the
magnetization perpendicular to the domain wall plane. Their balance with the
energy gain due to domain wall extension defines the equilibrium magnetization
the domain wall tilting. We demonstrate that the Walker field and the
corresponding Walker velocity of the domain wall can be enhanced in the system
supporting tilted walls.",2001.03408v1
2020-02-10,"Phase diagram of the mixed-spin (1,3/2) Ising ferrimagnetic system with two different anisotropies","In this work, we have performed Monte Carlo simulations to study phase
transitions in a mixed spin-1 and spin-3/2 Ising ferrimagnetic system on the
square and cubic lattices and with two different single-ion anisotropies. This
lattice is divided in two interpenetrating sublattices with spins $S^A = 1$
(states $\pm1$ and 0) on the sublattice $A$ and $S^B = 3/2$ (states $\pm 3/2$,
$\pm 1/2$) on the sublattice $B$. We have used single-ion anisotropies $D_{A}$
and $D_{B}$ acting on the sites of the sublattice $A$ and $B$, receptively. We
have determined the phase diagrams of the model in the temperature $T$ versus
the single-ion anisotropies strength $D_A$ and $D_B$ plane and shown that the
system exhibits both second- and first-order phase transitions. We also have
shown that this system displays compensation points for some values of the
anisotropies.",2002.08421v1
2020-02-20,Dynamics of quantum anisotropies in a Taub Universe in the WKB approximation,"We analyze the dynamics of a Taub cosmological model in the presence of a
massless minimally coupled scalar field and a cosmological constant, in the
limit when both the Universe volume and the scalar field live in a
quasi-classical approximation. By other words, we study the dynamics of a
quantum small anisotropy evolving on a de Sitter background and in the presence
of a kinetic term of the inflaton field. We demonstrate that the quantum
anisotropy exponentially decays during the Universe expansion, approaching a
finite and small value. This result suggests that the quantum isotropization of
the Universe during a de Sitter phase is much weaker than the corresponding
classical evolution, favouring the survival of certain degree of anisotropy to
the de Sitter phase. Finally we analyze the case when also the scalar field is
considered as quantum variable, by showing how its variance naturally spreads
because of no potential term significantly affects its dynamics. This behaviour
results to be different from the anisotropy which is subjected to the potential
coming out from the spatial curvature.",2002.08687v3
2020-02-28,Experimental determination of the orientation of tilted magnetic anisotropy by measuring Hall voltage,"The orientation of the tilted magnetic anisotropy has crucial importance in
many spintronic devices. However, it is very challenging to determine it
especially in very small structures produced by lithography. Here, we propose a
new experimental method to directly and accurately measure both the polar and
azimuthal angles of a tilted magnetic anisotropy. By using the proposed
experimental method, we have successfully determined the out-of-plane and
in-plane angles of the tilted magnetic anisotropy in a micro-structured
multilayer thin film. The orientation of the tilted magnetic anisotropy in the
sample has also been confirmed by the theoretical simulations proving the
accuracy of the method.",2003.00038v1
2020-03-27,Effect of random anisotropy in stabilization of topological chiral textures,"Ever increasing demand of skyrmion manipulation in nanodevices has brought up
interesting research to 8 understand the stabilization of these topologically
protected chiral structures. To understand the actual shape 9 and size of
skyrmion observed experimentally, we have performed micromagnetic simulations
to investigate 10 skyrmion stabilization in presence of random anisotropy in
magnetic thin film system. Previous experimental 11 reports of skyrmion imaging
in thin films depicts that the skyrmion shape is not perfectly circular. Here
we 12 show via simulations that the shape of a skyrmion can get distorted due
to the presence of different local 13 anisotropy energy. The values of uniaxial
anisotropy constant (Ku) and random aniostropy constant (Kr) 14 are varied to
understand the change in shape and size of a skyrmion and an antiskyrmion
stabilized in a 15 square magnetic nanoelement. The skyrmion shape gets
distorted and the size gets constant for high random 16 anisotropy energy in
the system.",2003.12481v1
2020-04-11,Studying the local magnetic field and anisotropy of magnetic turbulence by synchrotron polarization derivative,"Due to the inevitable accumulation of the observed information in the
direction of the line of sight, it is difficult to measure the local magnetic
field of MHD turbulence. However, the correct understanding of the local
magnetic field is a prerequisite for reconstructing the Galactic 3D magnetic
field. We study how to reveal the local magnetic field direction and the eddy
anisotropy on the basis of the statistics of synchrotron polarization
derivative with respect to the squared wavelength $dP/d\lambda^2$. In the low
frequency and strong Faraday rotation regime, we implement numerical
simulations in the combination of multiple statistic techniques, such as
structure function, quadrupole ratio modulus, spectral correlation function,
correlation function anisotropy and spatial gradient techniques. We find that
(1) statistic analysis of $dP/d\lambda^2$ indeed reveals the anisotropy of
underlying MHD turbulence, the degree of which increases with the increase of
the radiation frequency; (2) the synergy of both correlation function
anisotropy and gradient calculation of $dP/d\lambda^2$ enables the measurement
of the local magnetic field direction.",2004.05270v1
2020-06-22,Searching for anisotropy in the distribution of binary black hole mergers,"The standard model of cosmology is underpinned by the assumption of the
statistical isotropy of the Universe. Observations of the cosmic microwave
background, galaxy distributions, and supernovae, among other media, support
the assumption of isotropy at scales $\gtrsim 100$\,Mpc. The recent detections
of gravitational waves from merging stellar-mass binary black holes provide a
new probe of anisotropy; complementary and independent of all other probes of
the matter distribution in the Universe. We present an analysis using a
spherical harmonic model to determine the level of anisotropy in the first
LIGO/Virgo transient catalog. We find that the ten binary black hole mergers
within the first transient catalog are consistent with an isotropic
distribution. We carry out a study of simulated events to assess the prospects
for future probes of anisotropy. Within a single year of operation,
third-generation gravitational-wave observatories will probe anisotropies with
an angular scale of $\sim36^\circ$ at the level of $\lesssim0.1\%$.",2006.11957v2
2020-07-19,Isostructural spin-density-wave and superconducting gap anisotropies in iron-arsenide superconductors,"When passing through a phase transition, electronic system saves energy by
opening energy gaps at the Fermi level. Delineating the energy gap anisotropy
provides insights into the origin of the interactions that drive the phase
transition. Here, we report the angle-resolved photoemission spectroscopy
(ARPES) study on the detailed gap anisotropies in both the tetragonal magnetic
and superconducting phases in Sr$_{1-x}$Na$_x$Fe$_2$As$_2$. First, we found
that the spin-density-wave (SDW) gap is strongly anisotropic in the tetragonal
magnetic phase. The gap magnitude correlates with the orbital character of
Fermi surface closely. Second, we found that the SDW gap anisotropy is
isostructural to the superconducting gap anisotropy regarding to the angular
dependence, gap minima locations, and relative gap magnitudes. Our results
indicate that the superconducting pairing interaction and magnetic interaction
share the same origin. The intra-orbital scattering plays an important role in
constructing these interactions resulting in the orbital-selective magnetism
and superconductivity in iron-based superconductors.",2007.09572v1
2020-07-27,Effect of momentum anisotropy on quark matter in the quark-meson model,"We investigate the chiral phase structure of quark matter with spheroidal
momentum-space anisotropy specified by one anisotropy parameter $\xi$ in the
2+1 flavor quark-meson model. We find that the chiral phase diagram and the
location of the critical endpoint (CEP) are affected significantly by the value
of $\xi$. With the increase of $\xi$, the CEP is shifted to smaller
temperatures and larger quark chemical potentials. And the temperature of the
CEP is more sensitive to the anisotropy parameter than the corresponding quark
chemical potential, which is opposite to the study for finite system volume
effect. Furthermore, the effects of momentum anisotropy on the thermodynamic
properties and scalar (pseudoscalar) meson masses are also studied at vanishing
quark chemical potential. The numerical results show that an increase of $\xi$
can hinder the restoration of chiral symmetry. We also find that shear
viscosity and electrical conductivity decrease as $\xi$ grows. However, bulk
viscosity exhibits a significant non-trivial behavior with $\xi$ in the entire
temperature domain of interest.",2007.13580v3
2020-08-20,Two-dimensional ferromagnetic semiconductor VBr3 with tunable anisotropy,"Two-dimensional (2D) ferromagnets (FMs) have attracted widespread attention
due to their prospects in spintronic applications. Here we explore the
electronic structure and magnetic properties of the bulk and monolayer of
VBr$_{3}$ in the honeycomb lattice, using first-principles calculations,
crystal field level analyses, and Monte Carlo simulations. Our results show
that VBr$_{3}$ bulk has the $e'_{g}$$^2$ ($S$=1) ground state and possesses a
small orbital moment and weak in-plane magnetic anisotropy. Those results well
explain the recent experiments. More interestingly, we find that a tensile
strain on the semiconducting VBr$_{3}$ monolayer tunes the ground state into
$a_{1g}$$^1$$e'_{g}$$^1$ and thus produces a large orbital moment and a strong
out-of-plane anisotropy. Then, the significantly enhanced FM superexchange and
single ion anisotropy (SIA) would raise $T_{\rm C}$ from 20 K for the bare
VBr$_{3}$ monolayer to 100-115 K under a 2.5$\%$-5$\%$ strain. Therefore,
VBr$_{3}$ would be a promising 2D FM semiconductor with a tunable anisotropy.",2008.09232v2
2020-09-28,Bi-directional streaming of particles accelerated at the STEREO-A shock on 9th March 2008,"We present an interpretation of anisotropy and intensity of supra-thermal
ions near a fast quasi-perpendicular reverse shock measured by Solar
Terrestrial Relations Observatory Ahead (ST-A) on 2008 March 9th. The measured
intensity profiles of the supra-thermal particles exhibit an enhancement, or
""spike"", at the time of the shock arrival and pitch-angle anisotropies before
the shock arrival are bi-modal, jointly suggesting trapping of
near-scatter-free ions along magnetic field lines that intersect the shock at
two locations. We run test-particle simulations with pre-existing upstream
magnetostatic fluctuations advected across the shock. The measured bi-modal
upstream anisotropy, the nearly field-aligned anisotropies up to ~15 minutes
upstream of the shock, as well as the ""pancake-like"" anisotropies up to ~10
minutes downstream of the shock are well reproduced by the simulations. These
results, in agreement with earlier works, suggest a dominant role of the
large-scale structure (100s of supra-thermal proton gyroradii) of the magnetic
field in forging the early-on particle acceleration at shocks.",2009.13662v1
2020-10-01,"Anisotropic spin distribution and perpendicular magnetic anisotropy in the layered ferromagnetic semiconductor (Ba,K)(Zn,Mn)$_{2}$As$_{2}$","Perpendicular magnetic anisotropy of the new ferromagnetic semiconductor
(Ba,K)(Zn,Mn)$_{2}$As$_{2}$ is studied by angle-dependent x-ray magnetic
circular dichroism measurements. The large magnetic anisotropy with the
anisotropy field of 0.85 T is deduced by fitting the Stoner-Wohlfarth model to
the magnetic-field-angle dependence of the projected magnetic moment.
Transverse XMCD spectra highlights the anisotropic distribution of Mn 3$d$
electrons, where the $d_{xz}$ and $d_{yz}$ orbitals are less populated than the
$d_{xy}$ state because of the $D_{2d}$ splitting arising from the elongated
MnAs$_{4}$ tetrahedra. It is suggested that the magnetic anisotropy originates
from the degeneracy lifting of $p$-$d_{xz}$, $d_{yz}$ hybridized states at the
Fermi level and resulting energy gain due to spin-orbit coupling when spins are
aligned along the $z$ direction.",2010.00158v1
2020-10-08,Anisotropy and multifractal analysis of turbulent velocity and temperature in the roughness sublayer of a forested canopy,"Anisotropy and multifractality in velocity and temperature time series
sampled at multiple heights in the roughness sublayer (RSL) over a boreal
mixed-coniferous forest are reported. In particular, a turbulent-stress
invariant analysis along with a scalewise version of it are conducted to
elucidate the nature of relaxation of large-scale anisotropy to quasi-isotropic
states at small scales. As the return to isotropy is linked to nonlinear
interactions and correlations between different fluctuating velocity components
across scales, we study the velocity and temperature time series by using
multifractal detrended fluctuation analysis and multiscale multifractal
analysis to assess the effects of thermal stratification and surface roughness
on turbulence in the RSL. The findings are compared so as to quantify the
anisotropy and multifractality ubiquitous to RSL turbulent flow. As we go up in
the RSL, (a) the length scale at which return to isotropy commences increases
because of the weakening of the surface effects and (b) the largest scales
become increasingly anisotropic. The anisotropy in multifractal exponents for
the velocity fluctuations is diminished when we use the
extended-self-similarity procedure to extract the multifractal-exponent ratios.",2010.04194v1
2020-11-11,Field and anisotropy driven transformations of spin spirals in cubic skyrmion hosts,"We discuss distinctive features of spiral states in bulk chiral magnets such
as MnSi and Cu$_2$OSeO$_3$ that stem from the effect of the cubic
magneto-crystalline anisotropy. First of all, at both the helical-to-conical
and the conical-to-ferromagnetic transitions, taking place at H$_{c1}$ and
H$_{c2}$, respectively, the cubic anisotropy leads to reversible or
irreversible jump-like reorientations of the spiral wavevectors. The subtle
interplay between the easy and hard anisotropy axes gives rise to a phase
transition between elliptically distorted conical states almost without any
detectable change in the period. We show that the competition between on-site
cubic and exchange anisotropy terms can also lead to oblique spiral states. Our
work gives clear directions for further experimental studies to reveal
theoretically predicted spiral states in cubic helimagnets beyond the
aforementioned well-established states thus, can help to understand the
magnetic phase diagram of these archetypal skyrmion hosts. In addition, we show
that properties of isolated skyrmions such as inter-skyrmion attraction,
orientation and/or nucleation are also rooted in the properties of host spirals
states, in which skyrmions are stabilized.",2011.05501v1
2020-11-13,Magnetic anisotropy of individual maghemite mesocrystals,"Interest in creating magnetic metamaterials has led to methods for growing
superstructures of magnetic nanoparticles. Mesoscopic crystals of maghemite
($\gamma\text{-Fe}_2\text{O}_3$) nanoparticles can be arranged into highly
ordered body-centered tetragonal lattices of up to a few micrometers. Although
measurements on disordered ensembles have been carried out, determining the
magnetic properties of individual mesoscopic crystals is challenging due to
their small total magnetic moment. Here, we overcome these challenges by
utilizing sensitive dynamic cantilever magnetometry to study individual
micrometer-sized $\gamma\text{-Fe}_2\text{O}_3$ mesocrystals. These
measurements reveal an unambiguous cubic anisotropy, resulting from the
crystalline anisotropy of the constituent maghemite nanoparticles and their
alignment within the mesoscopic lattice. The signatures of anisotropy and its
orgins come to light because we combine the self-assembly of highly ordered
mesocrystals with the ability to resolve their individual magnetism. This
combination is promising for future studies of the magnetic anisotropy of other
nanoparticles, which are too small to investigate individually.",2011.06885v1
2020-11-18,Suppression of transport anisotropy at the Anderson localization transition in three-dimensional anisotropic media,"We study the transport of classical waves through three-dimensional (3D)
anisotropic media close to the Anderson localization transition. Time-,
frequency-, and position-resolved ultrasonic measurements are performed on
anisotropic slab-shaped mesoglass samples to probe the dynamics and the
anisotropy of the multiple scattering halo, and hence to investigate the
influence of disorder on the nature of wave transport and its anisotropy. These
experiments allow us to address conflicting theoretical predictions that have
been made about whether or not the transport anisotropy is affected by the
interference effects that lead to Anderson localization. We find that the
transport anisotropy is significantly reduced as the mobility edge is
approached---a behavior similar to the one predicted recently for matter waves
in infinite anisotropic 3D media.",2011.09560v1
2021-01-07,Mechanisms behind large Gilbert damping anisotropies,"A method with which to calculate the Gilbert damping parameter from a
real-space electronic structure method is reported here. The anisotropy of the
Gilbert damping with respect to the magnetic moment direction and local
chemical environment is calculated for bulk and surfaces of Fe$_{50}$Co$_{50}$
alloys from first principles electronic structure in a real space formulation.
The size of the damping anisotropy for Fe$_{50}$Co$_{50}$ alloys is
demonstrated to be significant. Depending on details of the simulations, it
reaches a maximum-minimum damping ratio as high as 200%. Several microscopic
origins of the strongly enhanced Gilbert damping anisotropy have been examined,
where in particular interface/surface effects stand out, as do local
distortions of the crystal structure. Although theory does not reproduce the
experimentally reported high ratio of 400% [Phys. Rev. Lett. 122, 117203
(2019)], it nevertheless identifies microscopic mechanisms that can lead to
huge damping anisotropies.",2101.02794v2
2021-01-25,Correlation between initial spatial anisotropy and final momentum anisotropies in relativistic heavy ion collisions,"The particle momentum anisotropy ($v_n$) produced in relativistic nuclear
collisions is considered to be a response of the initial geometry or the
spatial anisotropy $\epsilon_n$ of the system formed in these collisions. The
linear correlation between $\epsilon_n$ and $v_n$ quantifies the efficiency at
which the initial spatial eccentricity is converted to final momentum
anisotropy in heavy ion collisions. We study the transverse momentum, collision
centrality, and beam energy dependence of this correlation for different
charged particles using a hydrodynamical model framework. The ($\epsilon_n
-v_n$) correlation is found to be stronger for central collisions and also for
n=2 compared to that for n=3 as expected. However, the transverse momentum
($p_T$) dependent correlation coefficient shows interesting features which
strongly depends on the mass as well as $p_T$ of the emitted particle. The
correlation strength is found to be larger for lighter particles in the lower
$p_T$ region. We see that the relative fluctuation in anisotropic flow depends
strongly in the value of $\eta/s$ specially in the region $p_T <1$ GeV unlike
the correlation coefficient which does not show significant dependence on
$\eta/s$.",2101.09998v1
2021-03-10,Anisotropy with respect to the applied magnetic field of spin qubit decoherence times,"Electron spin qubits are a promising platform for quantum computation.
Environmental noise impedes coherent operations by limiting the qubit
relaxation ($T_1$) and dephasing ($T_{\phi}$) times. There are multiple sources
of such noise, which makes it important to devise experimental techniques that
can detect the spatial locations of these sources and determine the type of
source. In this paper, we propose that anisotropy in $T_1$ and $T_{\phi}$ with
respect to the direction of the applied magnetic field can reveal much about
these aspects of the noise. We investigate the anisotropy patterns of charge
noise, evanescent-wave Johnson noise, and hyperfine noise in hypothetical
devices. It is necessary to have a rather well-characterized sample to get the
maximum benefit from this technique. The general anisotropy patterns are
elucidated. We calculate the expected anisotropy for a particular model of a
Si/SiGe quantum dot device.",2103.05865v3
2021-03-14,Fusion yield of plasma with velocity-space anisotropy at constant energy,"Velocity-space anisotropy can significantly modify fusion reactivity. The
nature and magnitude of this modification depends on the plasma temperature, as
well as the details of how the anisotropy is introduced. For plasmas that are
sufficiently cold compared to the peak of the fusion cross-section, anisotropic
distributions tend to have higher yields than isotropic distributions with the
same thermal energy. At higher temperatures, it is instead isotropic
distributions that have the highest yields. However, the details of this
behavior depend on exactly how the distribution differs from an isotropic
Maxwellian. This paper describes the effects of anisotropy on fusion yield for
the class of anisotropic distribution functions with the same energy
distribution as a 3D isotropic Maxwellian, and compares those results with the
yields from bi-Maxwellian distributions. In many cases, especially for plasmas
somewhat below reactor-regime temperatures, the effects of anisotropy can be
substantial.",2103.07834v2
2021-03-16,Complete mapping of magnetic anisotropy for prototype Ising van der Waals FePS$_3$,"Several Ising-type magnetic van der Waals (vdW) materials exhibit stable
magnetic ground states. Despite these clear experimental demonstrations, a
complete theoretical and microscopic understanding of their magnetic anisotropy
is still lacking. In particular, the validity limit of identifying their
one-dimensional (1-D) Ising nature has remained uninvestigated in a
quantitative way. Here we performed the complete mapping of magnetic anisotropy
for a prototypical Ising vdW magnet FePS$_3$ for the first time. Combining
torque magnetometry measurements with their magnetostatic model analysis and
the relativistic density functional total energy calculations, we successfully
constructed the three-dimensional (3-D) mappings of the magnetic anisotropy in
terms of magnetic torque and energy. The results not only quantitatively
confirm that the easy axis is perpendicular to the $ab$ plane, but also reveal
the anisotropies within the $ab$, $ac$, and $bc$ planes. Our approach can be
applied to the detailed quantitative study of magnetism in vdW materials.",2103.09029v1
2021-03-29,Controlling anisotropy in 2D microscopic models of growth,"The quantitative knowledge of interface anisotropy in lattice models is a
major issue, both for the parametrization of continuum interface models, and
for the analysis of experimental observations. In this paper, we focus on the
anisotropy of line tension and stiffness, which plays a major role both in
equilibrium shapes and fluctuations, and in the selection of nonequilibrium
growth patterns. We consider a 2D Ising Hamiltonian on a square lattice with
first and second-nearest-neighbor interactions. The surface stiffness and line
tension are calculated by means of a broken-bond model for arbitrary
orientations. The analysis of the interface energy allows us to determine the
conditions under which stiffness anisotropy is minimal. These results are
supported by a quantitative comparison with kinetic Monte Carlo simulations,
based on the coupling of a field of mobile atoms to a condensed phase.
Furthermore, we introduce a generic smoothing parameter which allows one to
mimic the finite resolution of experimental microscopy techniques. Our results
provide a method to fine-tune the interface energy in models of nanoscale
non-equilibrium processes, where anisotropy and fluctuations combine and give
rise to non-trivial morphologies.",2103.15535v2
2021-04-15,Geminga SNR: Possible candidate of local cosmic-ray factory,"The precise measurements of energy spectra and anisotropy could help us
uncover the local cosmic-ray accelerators. Our recent works have shown that
spectral hardening above $200$ GeV in the energy spectra and transition of
large-scale anisotropy at $\sim 100$ TeV are of local source origin. Less than
$100$ TeV, both spectral hardening and anisotropy explicitly indicate the
dominant contribution from nearby sources. In this work, we further investigate
the parameter space of sources allowed by the observational energy spectra and
anisotropy amplitude. To obtain the best-fit source parameters, a numerical
package to compute the parameter posterior distributions based on Bayesian
inference, which is applied to perform an elaborate scan of parameter space. We
find that by combining the energy spectra and anisotropy data, the permissible
range of location and age of local source is considerably reduced. When
comparing with the current local SNR catalog, only Geminga SNR could be the
proper candidate of the local cosmic-ray source.",2104.07321v1
2021-04-16,CMB anisotropies generated by cosmic string loops,"We investigate the contribution of cosmic string loops to the Cosmic
Microwave Background (CMB) anisotropies. This is done by extending the
Unconnected Segment Model (USM) to include the contribution of the cosmic
string loops created throughout the cosmological evolution of a cosmic string
network to the stress-energy tensor. We then implement this extended USM in the
publicly available CMBACT code and obtain the linear CDM power spectrum and the
CMB angular power spectra generated by cosmic string loops. We find that the
shape of the angular power spectra generated by loops is, in general, similar
to that of long strings. However, there is generally an enhancement of the
anisotropies on small angular scales. Vector modes produced by loops dominate
over those produced by long strings for large multipole moments $\ell$. The
contribution of loops to the CMB anisotropies generated by cosmic string
networks may reach a level of $10\%$ for large loops but decreases as the size
of loops decreases. This contribution may then be significant and, thus, this
extension provides a more accurate prediction of the CMB anisotropies generated
by cosmic string networks.",2104.08375v2
2021-05-30,Anisotropy in interface stress at the BCC-iron solid-melt interface: molecular dynamics and phase field crystal modelling,"The interface stresses at of the solid-melt interface are, in general,
anisotropic. The anisotropy in the interfacial stress can be evaluated using
molecular dynamics (MD) and phase field crystal (PFC) models. In this paper, we
report our results on the evaluation of the anisotropy in interface stress in a
BCC solid with its melt. Specifically, we study Fe using both MD and PFC
models. We show that while both MD and PFC can be used for the evaluation, and
the PFC and the amplitude equations based on PFC give quantitatively consistent
results, the MD and PFC results are qualitatively the same but do not match
quantitatively. We also find that even though the interfacial free energy is
only weakly anisotropic in BCC interfacial stress anisotropy is strong. This
strong anisotropy has implications for the equilibrium shapes, growth
morphologies and other properties at nano-scale in these materials.",2105.14521v1
2021-07-01,Large-scale anisotropy of Galactic cosmic rays as a probe of local cosmic-ray propagation,"Recent studies have shown that the anisotropy is of great value to decipher
cosmic rays' origin and propagation. We have built an unified scenario to
describe the observations of the energy spectra and the large-scale anisotropy
and called attention to their synchronously evolution with energy. In this
work, the impact of of the local regular magnetic field (LRMF) and
corresponding anisotropic diffusion on large-scale anisotropy have been
investigated. When the perpendicular diffusion coefficient is much smaller than
the parallel one, the dipole anisotropy points to the LRMF and the
observational phase below $100$ TeV could be reproduced. Moreover we find that
the dipole phase above $100$ TeV strongly depends on the evolution of local
diffusion. But the current measurements at that energy are still scarce. We
suggest that more precise measurements at that energy could be carried out to
unveil the local diffusion and further the local turbulence.",2107.00313v4
2021-07-15,Hierarchical single-ion anisotropies in spin-1 Heisenberg antiferromagnets on the honeycomb lattice,"We examine the thermal properties of the spin-1 Heisenberg antiferromagnet on
the honeycomb lattice in the presence of an easy-plane single-ion anisotropy as
well as the effects of an additional weak in-plane easy-axis anisotropy. In
particular, using large-scale quantum Monte Carlo simulations, we analyze the
scaling of the correlation length near the thermal phase transition into the
ordered phase. This allows us to quantify the temperature regime above the
critical point in which -- in spite of the additional in-plane easy-axis
anisotropy -- characteristic easy-plane physics, such as near a
Berezinskii-Kosterlitz-Thouless transition, can still be accessed. Our
theoretical analysis is motivated by recent neutron scattering studies of the
spin-1 compound BaNi${}_2$V${}_2$O${}_8$ in particular, and it addresses basic
quantum spin models for generic spin-1 systems with weak anisotropies, which we
probe over the full range of experimentally relevant correlation length scales.",2107.07182v2
2021-07-30,"Effect of an uniaxial single-ion anisotropy on the quantum and thermal entanglement of a mixed spin-(1/2,$S$) Heisenberg dimer","Exact analytical diagonalization is used to study the bipartite entanglement
of the antiferromagnetic mixed spin-(1/2,$S$) Heisenberg dimer (MSHD) with the
help of negativity. Under the assumption of uniaxial single-ion anisotropy
affecting higher spin-$S$ ($S\!>\!1/2$) entities only, the ground-state
degeneracy $2S$ is partially lifted and the ground state is two-fold degenerate
with the total magnetization per dimer $\pm(S\!-\!1/2)$. It is shown that the
largest quantum entanglement is reached for the antiferromagnetic ground state
of MSHD with arbitrary half-odd-integer spins $S$, regardless of the exchange
and single-ion anisotropies. Contrary to this, the degree of a quantum
entanglement in MSHD with an integer spin $S$ for the easy-plane single-ion
anisotropy, exhibits an increasing tendency with an obvious spin-$S$ driven
crossing point. It is shown that the increasing spin magnitude is a crucial
driving mechanism for an enhancement of a threshold temperature above which the
thermal entanglement vanishes. The easy-plane single-ion anisotropy together
with an enlargement of the spin-$S$ magnitude is other significant driving
mechanism for an enhancement of the thermal entanglement in MSHD.",2107.14620v1
2021-11-08,All-carbon approach to inducing electrical and optical anisotropy in graphene,"Owing to its array of unique properties, graphene is a promising material for
a wide variety of applications. Being two-dimensional, the properties of
graphene are also easily tuned via proximity to other materials. In this work,
we investigate the possibility of inducing electrical and optical anisotropy in
graphene by interfacing it with other anisotropic carbon systems, including
nanoporous graphene and arrays of graphene nanoribbons. We find that such
materials do indeed induce such anisotropy in graphene, while also preserving
the unique properties offered by graphene's Dirac band structure, namely its
superior charge transport and long-wavelength optical absorption. The optical
anisotropy makes such heterostructures interesting for their use in
applications related to long-wavelength polarimetry, while the electrical
anisotropy may be valuable for enhancing the performance of graphene
photothermoelectric detectors.",2111.04571v1
2022-01-20,Small-angle neutron scattering by spatially inhomogeneous ferromagnets with a nonzero average uniaxial anisotropy,"Micromagnetic small-angle neutron scattering theory is well established for
analyzing spin-misalignment scattering data of bulk ferromagnets. Here, this
theory is extended to allow for a global uniaxial magnetic anisotropy (texture)
of the material, in addition to the already included random zero-average local
anisotropy. Macroscopic cross-sections and spin-misalignment response functions
are computed analytically for several practically relevant mutual anisotropy
and external magnetic field orientations in both parallel and perpendicular
scattering geometries for field magnitudes both above and below the rotational
saturation. Some of these expressions are tested on published experimental data
of magnetic-field-annealed Vitroperm and plastically-deformed Ni, allowing to
determine the corresponding global uniaxial anisotropy quality factors.",2201.08334v1
2022-03-07,Detection of Travel Time Anisotropy from Subsurface Horizontal Magnetic Fields,"A time-distance measurement technique is derived to isolate phase travel time
anisotropy caused by subsurface horizontal magnetic fields, and a method which
uses the measured anisotropy to estimate the field's orientation is also
derived. A simulation of acoustic waves propagating in a uniform, inclined
magnetic field with solar background structure is used to verify the derived
technique. Then, the procedure is applied to a numerical simulation of a
sunspot, for which the subsurface state is known, to provide context for the
results obtained from the study of several sunspots observed by the
Helioseismic and Magnetic Imager. Significant anisotropies are detected, on the
order of one minute, and the subsurface field's azimuth is estimated and
compared with the azimuth of the surface magnetic field. In all cases, the
subsurface azimuth is found to be well-aligned with that of the surface, and
the results from the numerical simulation are used to interpret features in the
detected travel time anisotropy.",2203.03495v1
2022-03-18,Prediction of novel two-dimensional rare-earth material with room-temperature ferromagnetism and large perpendicular magnetic anisotropy,"Novel 2D ferromagnets with high Curie temperature and large perpendicular
magnetic anisotropy are especially attractive owing to the future promising
application in modern spintronics, but meanwhile the 2D ferromagnetic materials
with high Curie temperature and large perpendicular magnetic anisotropy are
rarely reported. Based on density functional theory (DFT) calculations, we
predict a new kind of 2D ferromagnetic materials - GdB2N2, which possesses
large magnetic moment, high Curie temperature (335 K) and large perpendicular
magnetic anisotropy (10.38 meV/f.u.). Biaxial strain ranging from -0.5% to 5%
and different concentrations of charge-carrier doping are applied to reveal the
influence on the Curie temperature and magnetic anisotropy energy (MAE).
Besides, magnetic coupling process within GdB2N2 is found to be via a
Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. In summary, our work here
predicts a novel 2D rare-earth material GdB2N2, which not only enriches the
category of 2D room-temperature ferromagnets, but also proposes a new
possibility of combining traditional 2D materials and rare-earth materials to
achieve more intriguing magnetic properties, finally it carves out the path for
the next-generation spintronic devices and sensors.",2203.10969v1
2022-03-31,Primordial Stochastic Gravitational Wave Background Anisotropies: in-in Formalization and Applications,"Primordial non-Gaussianities of the scalar(tensor)-tensor-tensor type
supporting a non-trivial squeezed component are known to induce anisotropies in
the stochastic gravitational wave background. We derive the explicit form of
such anisotropies by making use, for the first time in this context, of the
in-in formalism for cosmological correlation functions. After illustrating the
general method and using it for the minimal single-field slow-roll case, we
apply it to multi-field models, providing both a tree-level and a one-loop
example. First, we make contact with previous results on anisotropies due to
the presence of an extra spin-2 field during inflation. Secondly, we calculate
the 1-loop scalar-tensor-tensor three-point function in the context of
so-called supersolid inflation. The corresponding gravitational wave anisotropy
is induced atop a gravitational signal that may be sufficiently large for
detection.",2203.17192v2
2022-04-20,Collective modes of gluons in an anisotropic thermo-magnetic medium,"We study the collective modes of gluons in an anisotropic thermal medium in
the presence of a constant background magnetic field using the hard-thermal
loop (HTL) perturbation theory. The momentum space anisotropy of the medium has
been incorporated through the generalized $`$Romatschke-Strickland' form of the
distribution function, whereas, the magnetic modification arising from the
quark loop contribution has been taken into account in the lowest Landau level
approximation. We consider two special cases: (i) a spheroidal anisotropy with
the anisotropy vector orthogonal to the external magnetic field and (ii) an
ellipsoidal anisotropy with two mutually orthogonal vectors describing
aniostropies along and orthogonal to the field direction. The general structure
of the polarization tensor in both cases are equivalent and consists of six
independent basis tensors. We find that the introduction of momentum anisotropy
ingrains azimuthal angular dependence in the thermo-magnetic collective modes.
Our study suggests that the presence of a strong background magnetic field can
significantly reduce the growth rate of the unstable modes which may have
important implications in the equilibration of magnetized quark-gluon plasma.",2204.09646v2
2022-05-09,Primordial Clocks within Stochastic Gravitational Wave Anisotropies,"A first-order phase transition in the early universe can give an observable
stochastic gravitational background (SGWB), which will necessarily have
primordial anisotropies across the sky. In multi-field inflationary scenarios,
these anisotropies may have a significant isocurvature component very different
from adiabatic fluctuations, providing an alternate discovery channel for high
energy physics at inflationary scales. Here, we consider classically
oscillating heavy fields during inflation that can imprint distinctive
scale-invariance-breaking features in the power spectrum of primordial
anisotropies. While such features are highly constrained in the cosmic
microwave background, we show that their amplitude can be observably large in
isocurvature SGWB, despite both probing a similar period of inflation.
Measuring SGWB multipoles at the required level, $\ell \sim {\cal O}(10-100)$,
will be technologically challenging. However, we expect that early detection of
a strong isotropic SGWB, and the guarantee of anisotropies, would spur
development of next-generation detectors with sufficient sensitivity, angular
resolution, and foreground discrimination.",2205.04482v1
2022-06-07,The Origin of Deformation Induced Topological Anisotropy in Silica Glass,"Oxide glasses with a network structure are omnipresent in daily life. Often,
they are regarded as isotropic materials; however, structural anisotropy can be
induced through processing in mechanical fields and leads to unique materials
properties. Unfortunately, due to the lack of local, atomic-scale analysis
methods, the microscopic mechanisms leading to anisotropy remained elusive.
Using novel analysis methods on glasses generated by molecular dynamics
simulations, this paper provides a microscopic understanding of topological
anisotropy in silica (SiO$_2$) glass under mechanical loads. The anisotropy
observed in silica glass originates from a preferred orientation of SiO$_4$
tetrahedra at both short- and medium-range levels that can be controlled via
the mode of mechanical loading. The findings elucidate the relation between the
deformation protocol and the resulting anisotropic structure of the silica
network (involving both persistent and transient effects), and thus provide
important insight for the design of oxide glasses with tailored materials
properties.",2206.03039v2
2022-06-08,Observational constraints on anisotropies for bouncing alternatives to inflation,"We calculate how primordial anisotropies in the background space-time affect
the evolution of cosmological perturbations for bouncing alternatives to
inflation, like ekpyrosis and the matter bounce scenario. We find that the
leading order effect of anisotropies in the contracting phase of the universe
is to induce anisotropies in the cosmic microwave background with a very
concrete form: a scale-invariant quadrupolar angular distribution. Sub-leading
effects are the generation of higher-order moments in the angular distribution,
as well as cross-correlations between scalar and tensor modes. We also find
that observational constraints from the cosmic microwave background on the
quadrupole moment provide strong bounds on allowed anisotropies for bouncing
alternatives to inflation that are significantly more constraining than the
bounds previously obtained using scaling arguments based on the conjectured
Belinski-Khalatnikov-Lifshitz instability.",2206.04037v3
2022-07-22,Frustrated ferromagnetic transition in AB-stacked honeycomb bilayer,"In two-dimensional (2D) ferromagnets, anisotropy is essential for the
magnetic ordering as dictated by the Mermin-Wagner theorem. But when competing
anisotropies are present, the phase transition becomes nontrivial. Here,
utilizing highly sensitive susceptometry of scanning superconducting quantum
interference device microscopy, we probe the spin correlations of ABC-stacked
CrBr3 under zero magnetic field. We identify a plateau feature in
susceptibility above the critical temperature (Tc) in thick samples. It
signifies a crossover regime induced by the competition between easy-plane
intralayer exchange anisotropy versus uniaxial interlayer anisotropy. The
evolution of the critical behavior from the bulk to 2D shows that the
competition between the anisotropies is magnified in the reduced dimension. It
leads to a strongly frustrated ferromagnetic transition in the bilayer with
fluctuation on the order of Tc, which is distinct from both the monolayer and
the bulk. Our observation potentially offers a 2D localized spin system on
honeycomb lattice to explore magnetic frustration.",2207.10945v1
2022-08-15,The origin of enhanced interfacial perpendicular magnetic anisotropy in LiF-inserted Fe/MgO interface,"The Fe/MgO interface is an essential ingredient in spintronics as it shows
giant tunneling magnetoresistance and strong perpendicular magnetic anisotropy
(PMA). A recent study demonstrated that the insertion of an ultra-thin LiF
layer between the Fe and MgO layers enhances PMA significantly. In this study,
we perform x-ray magnetic circular dichroism measurements on Fe/LiF/MgO
multilayers to reveal the origin of the PMA enhancement. We find that the LiF
insertion increases the orbital-magnetic-moment anisotropy and thus the
magnetic anisotropy energy. We attribute the origin of this
orbital-magnetic-moment-anisotropy enhancement to the stronger electron
localization and electron-electron correlation or the better interface quality
with fewer defects.",2208.07007v1
2022-09-03,Cosmic-Ray Convection-Diffusion Anisotropy,"Under nonuniform convection, the distribution of diffusive particles can
exhibit dipole and quadrupole anisotropy induced by the fluid inertial and
shear force, respectively. These convection-related anisotropies, unlike the
Compton-Getting effect, typically increase with the cosmic-ray (CR) energy, and
are thus candidate contributors for the CR anisotropy. In consideration of the
inertial effect, CR observational data can be used to set an upper limit on the
average acceleration of the local interstellar medium in the equatorial plane
to be on the order of 100 $ \mu \text{m}/\text{s}^2 $. Using Oort constants,
the quadrupole anisotropy above 200 TeV may be modeled with the shear effect
arising from the Galactic differential rotation.",2209.01412v2
2022-10-16,Magnetic damping anisotropy in the two-dimensional van der Waals material Fe$_3$GeTe$_2$ from first principles,"Magnetization relaxation in the two-dimensional itinerant ferromagnetic van
der Waals material Fe$_3$GeTe$_2$, below the Curie temperature, is
fundamentally important for applications to low-dimensional spintronics
devices. We use first-principles scattering theory to calculate the
temperature-dependent Gilbert damping for bulk and single-layer Fe$_3$GeTe$_2$.
The calculated damping frequency of bulk Fe$_3$GeTe$_2$ increases monotonically
with temperature because of the dominance of resistivitylike behavior. By
contrast, a very weak temperature dependence is found for the damping frequency
of a single layer, which is attributed to strong surface scattering in this
highly confined geometry. A systematic study of the damping anisotropy reveals
that orientational anisotropy is present in both bulk and single-layer
Fe3GeTe2. Rotational anisotropy is significant at low temperatures for both the
bulk and a single layer and is gradually diminished by temperature-induced
disorder. The rotational anisotropy can be significantly enhanced by up to 430%
in gated single-layer Fe$_3$GeTe$_2$.",2210.08429v1
2023-01-30,Constraining the Surface Curvature of an Anisotropic Neutron Star,"The anisotropy of pressure arises due to the various complex phenomena that
happen inside the neutron star (NS). In this study, we calculate the degree of
anisotropy inside the NS using the scalar pressure anisotropy model.
Macroscopic properties such as mass, radius, compactness, redshift, tidal
deformability, the moment of inertia, and surface curvature (SC) are computed
for the anisotropic NS with the equation of states spanning from relativistic
to nonrelativistic cases. The variation of SC as the functions of the
above-mentioned quantities are computed by changing the degree of anisotropy.
Pressure anisotropy has significant effects on the magnitude of SC. The
universal relations between the canonical SC$-\Lambda$ and SC$-\bar{I}$ are
studied. From the GW170817 tidal deformability data constraints on SC are found
to be SC$_{1.4}(10^{14}) = 3.44_{-1.0}^{+0.4}, 2.85_{-1.20}^{+0.62}, \ {\rm
and} \ 2.52_{-1.02}^{+0.61}$ for $\lambda_{\rm BL} = 0.0, 1.0$, and $2.0$
respectively.",2301.12673v2
2023-03-14,Cosmic Microwave Background anisotropies generated by cosmic strings with small-scale structure,"We study the impact of kinks on the cosmic microwave background (CMB)
anisotropies generated by cosmic string networks. To do so, we extend the
Unconnected Segment Model to describe the stress-energy tensor of a network of
cosmic strings with kinks and implement this extension in CMBACT to compute the
CMB anisotropies generated by these wiggly string networks. Our results show
that the inclusion of kinks leads, in general, to an enhancement of the
temperature and polarization angular power spectra, when compared to those
generated by cosmic string networks without small-scale structure with the same
energy density, on scales corresponding to the distance between kinks. This
enhancement, that is more prominent in the case of the temperature
anisotropies, is essentially caused by a significant increase of the
vector-mode anisotropies, since kinks, due to their shape, generate vortical
motions of matter -- a phenomenon that is not taken into account when resorting
to an effective description of wiggly cosmic strings.",2303.07548v2
2023-05-22,Fluid pulsation modes and tidal deformability of anisotropic strange stars in light of the GW$170817$ event,"The effects of the anisotropy on the fluid pulsation modes adopting the
so-called Cowling approximation and tidal deformability of strange quark stars
are investigated by using the numerical integration of the hydrostatic
equilibrium, nonradial oscillations, and tidal deformability equations, being
these equations modified from their standard form to include the anisotropic
effects. The fluid matter inside the compact stars is described by the MIT bag
model equation of state. For the anisotropy profile, we consider a local
anisotropy that is both regular at the center and null at the star's surface.
We find that the effect of the anisotropy is reflected in the fluid pulsation
modes and tidal deformability. Finally, we analyze the correlation between the
tidal deformability of the GW$170817$ event with the anisotropy.",2305.13468v2
2023-07-07,Effects of anisotropy on the high field magnetoresistance of Weyl semimetals,"We study the effects of anisotropy on the magnetoresistance of Weyl
semimetals (WSMs) in the ultraquantum regime. We utilize the fact that many
Weyl semimetals are approximately axially anisotropic. We find that anisotropy
manifests itself in the strong dependence of the magnetoresistance on the polar
and azimuthal angles determining the orientation of the anisotropy axis with
respect to the applied magnetic field and electric current. We also predict
that the ratio of magnetoresistances in the geometries, where the magnetic
field and anisotropy axes are aligned and where they are orthogonal, scales as
$(v_\bot/v_\parallel)^2$ where $v_\bot$ and $v_\parallel$ are the corresponding
Fermi velocities.",2307.03772v1
2023-07-18,Measuring Scale-dependent Shape Anisotropy by Coarse-Graining: Application to Inhomogeneous Rayleigh-Taylor Turbulence,"We generalize the `filtering spectrum' [1] to probe scales along different
directions by spatial coarse-graining. This multi-dimensional filtering
spectrum quantifies the spectral content of flows that are not necessarily
homogeneous. From multi-dimensional spectral information, we propose a simple
metric for shape anisotropy at various scales. The method is applied to
simulations of 2D and 3D Rayleigh-Taylor (RT) turbulence, which is
inhomogeneous and anisotropic. We show that 3D RT has clear shape anisotropy at
large scales with approximately $4:3$ vertical to horizontal aspect ratio, but
tends toward isotropy at small scales as expected [2,3,4]. In sharp contrast,
we find that RT in 2D simulations, which are still the main modeling framework
for many applications, is isotropic at large scales and its shape anisotropy
increases at smaller scales where structures tend to be horizontally elongated.
While this may be surprising, it is consistent with recent results in [5];
large-scale isotropy in 2D RT is due to the generation of a large-scale
overturning circulation via an upscale cascade, while small scale anisotropy is
due to the stable stratification resultant from such overturning and the
inefficient mixing in 2D.",2307.08918v2
2023-09-11,Magnetic anisotropy driven by ligand in 4d transition metal oxide SrRuO3,"The origin of magnetic anisotropy in magnetic compounds is a longstanding
issue in solid state physics and nonmagnetic ligand ions are considered to
contribute little to magnetic anisotropy. Here, we introduce the concept of
ligand driven magnetic anisotropy in a complex transition-metal oxide. We
conducted X ray absorption and X ray magnetic circular dichroism spectroscopies
at the Ru and O edges in the 4d ferromagnetic metal SrRuO3. Systematic
variation of the sample thickness in the range below 10 nm allowed us to
control the localization of Ru 4d t2g states, which affects the magnetic
coupling between the Ru and O ions. We found that the orbital magnetization of
the ligand induced via hybridization with the Ru 4d orbital determines the
magnetic anisotropy in SrRuO3.",2309.05228v2
2023-10-24,Cubic anisotropy of hole Zeeman splitting in semiconductor nanocrystals,"We study theoretically cubic anisotropy of Zeeman splitting of a hole
localized in semiconductor nanocrystal. This anisotropy originates from three
contributions: crystallographic cubically-symmetric spin and kinetic energy
terms in the bulk Luttinger Hamiltonian and the spatial wave function
distribution in a cube-shaped nanocrystal. From symmetry considerations, an
effective Zeeman Hamiltonian for the hole lowest even state is introduced,
containing a spherically symmetric and a cubically symmetric term. The values
of these terms are calculated numerically for spherical and cube-shaped
nanocrystals as functions of the Luttinger Hamiltonian parameters. We
demonstrate that the cubic shape of the nanocrystal and the cubic anisotropy of
hole kinetic energy (so called valence band warping) significantly affect
effective $g$ factors of hole states. In both cases, the effect comes from the
cubic symmetry of the hole wave functions in zero magnetic field. Estimations
for the effective $g$ factor values in several semiconductors with zinc-blende
crystal lattices are made. Possible experimental manifestations and potential
methods of measurement of the cubic anisotropy of the hole Zeeman splitting are
suggested.",2310.15876v1
2023-11-10,The Shape of Learning: Anisotropy and Intrinsic Dimensions in Transformer-Based Models,"In this study, we present an investigation into the anisotropy dynamics and
intrinsic dimension of embeddings in transformer architectures, focusing on the
dichotomy between encoders and decoders. Our findings reveal that the
anisotropy profile in transformer decoders exhibits a distinct bell-shaped
curve, with the highest anisotropy concentrations in the middle layers. This
pattern diverges from the more uniformly distributed anisotropy observed in
encoders. In addition, we found that the intrinsic dimension of embeddings
increases in the initial phases of training, indicating an expansion into
higher-dimensional space. Which is then followed by a compression phase towards
the end of training with dimensionality decrease, suggesting a refinement into
more compact representations. Our results provide fresh insights to the
understanding of encoders and decoders embedding properties.",2311.05928v2
2024-01-08,Atom-by-Atom Mapping and Understanding of In-Plane Anisotropy in GaTe,"Main-group chalcogenides with layered crystal structures and high in-plane
anisotropy are attracting increasing interest for a range of practical
applications. The III-VI semiconductor, monoclinic gallium monotelluride
(m-GaTe), has been recently used in high-sensitivity
photodetectors/phototransistors and electronic memory applications due to its
anisotropic properties yielding superior optical and electrical performance.
Despite these applications, the origin of such anisotropy, namely the complex
structural and bonding environments in GaTe nanostructures remain to be fully
understood. In the present work, we report a comprehensive atomic-scale
characterization of m-GaTe by state-of-the-art element-resolved atomic-scale
microscopy experiments. By performing imaging for two different view
directions, we are able to directly measure the in-plane anisotropy of m-GaTe
at the sub-Angstrom level, and show that it compares well with the results of
first-principles modeling. Quantum-chemical bonding analyses provide a detailed
picture of the atomic neighbor interactions within the layers, revealing that
vertical Ga-Ga homopolar bonds get stronger when they are distorted and
rotated, inducing the strong in-plane anisotropy.",2401.03731v1
2024-01-18,Realistic Anisotropic Neutron Stars: Pressure Effects,"In this paper, we study the impact of anisotropy on neutron stars with
different equations of state, which have been modeled by a piecewise polytropic
function with continuous sound speed. Anisotropic pressure in neutron stars is
often attributed to interior magnetic fields, rotation, and the presence of
exotic matter or condensates. We quantify the presence of anisotropy within the
star by assuming a quasi-local relationship. We find that the radial and
tangential sound velocities constrain the range of anisotropy allowed within
the star. As expected, the anisotropy affects the macroscopic properties of
stars, and it can be introduced to reconcile them with astrophysical
observations. For instance, the maximum mass of anisotropic neutron stars can
be increased by up to 15\% compared to the maximum mass of the corresponding
isotropic configuration. This allows neutron stars to reach masses greater than
$2.5M_\odot$, which may explain the secondary compact object of the GW190814
event. Additionally, we propose a universal relation for the binding energy of
an anisotropic neutron star as a function of the star's compactness and the
degree of anisotropy.",2401.10311v1
2024-03-20,Hydrodynamics of a disk in a thin film of weakly nematic fluid subject to linear friction,"To make progress towards the development of a theory on the motion of
inclusions in thin structured films and membranes, we here consider as an
initial step a circular disk in a two-dimensional, uniaxially anisotropic fluid
layer. We assume overdamped dynamics, incompressibility of the fluid, and
global alignment of the axis of anisotropy. Motion within this layer is
affected by additional linear friction with the environment, for instance, a
supporting substrate. We investigate the induced flows in the fluid when the
disk is translated parallel or perpendicular to the direction of anisotropy.
Moreover, expressions for corresponding mobilities and resistance coefficients
of the disk are derived. Our results are obtained within the framework of a
perturbative expansion in the parameters that quantify the anisotropy of the
fluid. Good agreement is found for moderate anisotropy when compared to
associated results from finite-element simulations. At pronounced anisotropy,
the induced flow fields are still predicted qualitatively correctly by the
perturbative theory, although quantitative deviations arise. We hope to
stimulate with our investigations corresponding experimental analyses, for
example, concerning fluid flows in anisotropic thin films on uniaxially rubbed
supporting substrates.",2403.13755v1
2012-10-04,Structural and Correlation Effects in the Itinerant Insulating Antiferromagnetic Perovskite NaOsO3,"The orthorhombic perovskite NaOsO3 undergoes a continuous metal-insulator
transition (MIT), accompanied by antiferromagnetic (AFM) order at T_N=410 K,
suggested to be an example of the rare Slater (itinerant) MIT. We study this
system using ab initio and related methods, focusing on the origin and nature
of magnetic ordering and the MIT. The rotation and tilting of OsO6 octahedra in
the GdFeO3 structure result in moderate narrowing the band width of the t_{2g}
manifold, but sufficient to induce flattening of bands and AFM order within the
local spin density approximation (LSDA), where it remains metallic but with a
deep pseudogap. Including on-site Coulomb repulsion U, at U_c ~2 eV a MIT
occurs only in the AFM state. Effects of spin-orbit coupling (SOC) on the band
structure seem minor as expected for a half-filled $t_{2g}^{3}$ shell, but SOC
doubles the critical value U_c necessary to open a gap and also leads to large
magnetocrystalline energy differences in spite of normal orbital moments no
greater than 0.1$\mu_B$. Our results are consistent with a Slater MIT driven by
magnetic order, induced by a combination of structurally-induced band narrowing
and moderate Coulomb repulsion, with SOC necessary for a full picture. Strong
p-d hybridization reduces the moment, and when bootstrapped by the reduced
Hund's rule coupling (proportional to the moment) gives a calculated moment of
~1 $\mu_B$, consistent with the observed moment and only a third of the formal
$d^3$ value. We raise and discuss one important question: since this AFM
ordering is at q=0 (in the 20 atom cell) where nesting is a moot issue, what is
the microscopic driving force for ordering and the accompanying MIT?",1210.1286v2
1993-03-26,The Imprint of Gravitational Waves on the Cosmic Microwave Background,"Long-wavelength gravitational waves can induce significant temperature
anisotropy in the cosmic microwave background. Distinguishing this from
anisotropy induced by energy density fluctuations is critical for testing
inflationary cosmology and theories of large-scale structure formation. We
describe full radiative transport calculations of the two contributions and
show that they differ dramatically at angular scales below a few degrees. We
show how anisotropy experiments probing large- and small-angular scales can
combine to distinguish the imprint due to gravitational waves.",9303014v1
1993-10-29,Reionization and Cosmic Microwave Anisotropies,"The effects of reionization, occurring after standard recombination in cold
dark matter-dominated models, on CMB anisotropies are investigated. Late-time
reionization reduces the CMB anisotropies, in particular, on degree scales. It
is found that constraints on cold dark matter-dominated models from the highest
frequency channel of the 9-point South Pole data are significantly relaxed for
models which are consistent with Big Bang nucleosynthesis if reionization is
assumed to have occurred by redshift $\sim 20.$",9310051v1
1994-05-11,Microwave background anisotropy in low-$Ω_0$ inflationary models and the scale of homogeneity in the Universe,"We study the microwave background anisotropy due to superhorizon-size
perturbations (the Grischuk-Zel'dovich effect) in open universes with negative
spatial curvature. Using COBE results on the low-order temperature multipole
moments, we find that if the homogeneity of the observable Universe arises from
an early epoch of inflation, the present density parameter cannot differ from
unity by more than the observed quadrupole anisotropy, $|1-\Omega_0| \alt Q
\simeq 5\times 10^{-6}$. Thus, inflation models with low $\Omega_0$ either do
not fit the microwave background observations or they do not solve the horizon
problem.",9405024v1
1994-07-14,Cosmic Microwave Background Radiation Anisotropy Induced by Cosmic Strings,"We report on a current investigation of the anisotropy pattern induced by
cosmic strings on the cosmic microwave background radiation (MBR). We have
numerically evolved a network of cosmic strings from a redshift of $Z = 100$ to
the present and calculated the anisotropies which they induce. Based on a
limited number of realizations, we have compared the results of our simulations
with the observations of the COBE-DMR experiment. We have obtained a
preliminary estimate of the string mass-per-unit-length $\mu$ in the cosmic
string scenario.",9407042v1
1994-07-20,Cosmic Microwave Background Anisotropies and the Geometry of the Universe,"In this talk, I review some recent work on cosmic microwave background (CMB)
anisotropies in an open universe. I emphasize that the observed CMB
anisotropies are still consistent with a low value of $\Omega$, and I address
the question of whether future CMB measurements will be able to provide
information on the geometry of the Universe.",9407062v1
1994-10-12,Foreground Contributions to 0.2-2 Degree CMB Anisotropies,"We examine the extent to which galactic and extragalactic foregrounds can
hamper the detection of primordial Cosmic Microwave Background (CMB)
anisotropies. We limit our discussion to intermediate angular scales,
$10^{\prime}\lsim \theta \lsim 2^{\circ}$, since many current as well as future
experiments have been designed to map CMB anisotropies at these angular scales.
In fact, scales of $\gsim 10^{\prime}$ are of crucial importance to test both
the conditions in the early Universe and current theories of the gravitational
collapse.",9410037v1
1995-01-06,"LIMITS ON ANISOTROPY AND INHOMOGENEITY FROM THE COSMIC BACKGROUND RADIATION,","We consider directly the equations by which matter imposes anisotropies on
freely propagating background radiation, leading to a new way of using
anisotropy measurements to limit the deviations of the Universe from a
Friedmann-Robertson-Walker (FRW) geometry. This approach is complementary to
the usual Sachs-Wolfe approach: the limits obtained are not as detailed, but
they are more model-independent. We also give new results about combined
matter-radiation perturbations in an almost-FRW universe, and a new exact
solution of the linearised equations.",9501016v1
1995-05-22,Echoes of Gravity,"The study of anisotropies in the Cosmic Microwave Background radiation is
progressing at a phenomenal rate, both experimentally and theoretically. These
anisotropies can teach us an enormous amount about the way that fluctuations
were generated and the way they subsequently evolved into the clustered
galaxies which are observed today. In particular, on sub-degree scales the rich
structure in the anisotropy spectrum is the consequence of gravity-driven
acoustic oscillations occurring before the matter in the universe became
neutral. The frozen-in phases of these sound waves imprint a dependence on many
cosmological parameters, that we may be on the verge of extracting.",9505102v1
1995-06-20,Gravitational Lensing and Anisotropies of CBR on the Small Angular Scales,"We investigate the effect of gravitational lensing, produced by linear
density perturbations, for anisotropies of the Cosmic Background Radiation
(CBR) on scales of arcminutes. In calculations, a flat universe ($\Omega=1$)
and the Harrison-Zel'dovich spectrum ($n=1$) are assumed. The numerical results
show that on scales of a few arcminutes, gravitational lensing produces only
negligible anisotropies in the temperature of the CBR. Our conclusion disagrees
with that of Cay\'{o}n {\it et al.} who argue that the amplification of $\Delta
T/T$ on scales $\le 3'$ may even be larger than 100\%.",9506102v1
1995-12-23,CMB Anisotropy in COBE-DMR-Normalized Flat $Λ$ CDM Cosmogony,"We compute the cosmic microwave background (CMB) anisotropy in a low-density,
flat, cosmological constant, cold dark matter model which is normalized to the
two-year COBE DMR sky map. Although conclusions regarding model viability must
remain tentative until systematic effects are better understood, there are mild
indications that these models have more intermediate scale power than is
indicated by presently available CMB anisotropy observational data, with old
($t_0 \geq 15-16$Gyr), high baryon density ($\Omega_B \geq 0.0175 h^{-2}$), low
density ($\Omega_0 \sim 0.2-0.4$) models doing the worst.",9512157v1
1996-04-28,The Physics of Microwave Background Anisotropies,"Cosmic microwave background anisotropies provide a vast amount of
cosmological information. Their full physical content and detailed structure
can be understood in a simple and intuitive fashion through a systematic
investigation of the individual mechanisms for anisotropy formation.",9604166v1
1996-05-20,How Anisotropic is our Universe?,"Large-scale cosmic microwave background anisotropies in homogeneous, globally
anisotropic cosmologies are investigated. We perform a statistical analysis in
which the four-year data from the Cosmic Background Explorer satellite is
searched for the specific anisotropy patterns predicted by these models and
thereby set definitive upper limits on the amount of shear, $(\sigma/H)_0$ and
vorticity, $(\omega/H)_0$, which are orders of magnitude stronger than previous
constraints. We comment on how these results might impact our understanding of
primordial global anisotropy.",9605123v1
1996-09-10,The Damping Tail of CMB Anisotropies,"By decomposing the damping tail of CMB anisotropies into a series of transfer
functions representing individual physical effects, we provide ingredients that
will aid in the reconstruction of the cosmological model from small-scale CMB
anisotropy data. We accurately calibrate the model-independent effects of
diffusion and reionization damping which provide potentially the most robust
information on the background cosmology. Removing these effects, we uncover
model-dependent processes such as the acoustic peak modulation and
gravitational enhancement that can help distinguish between alternate models of
structure formation and provide windows into the evolution of fluctuations at
various stages in their growth.",9609079v1
1996-10-24,Small-angle anisotropies in the CMBR from active sources,"We consider the effects of photon diffusion on the small-angle microwave
background anisotropies due to active source models. We find that fluctuations
created just before the time of last scattering allow anisotropy to be created
on scales much smaller than allowed by standard Silk damping. Using simple
models for string and texture structure functions as examples, we illustrate
the differences in the angular power spectrum at scales of order a few
arcminutes. In particular, we find that the Doppler peak heights are modified
by 10-50% and the small-angle fall-off is power law rather than exponential.",9610197v1
1996-12-20,Microwave Background Anisotropies Induced by Global Scalar Fields: The Large N Limit,"We present an analysis of CMB anisotropies induced by global scalar fields in
the large N limit. In this limit, the CMB anisotropy spectrum can be determined
without cumbersome 3D simulations. We determine the source functions and their
unequal time correlation functions and show that they are quite similar to the
corresponding functions in the texture model. This leads us to the conclusion
that the large N limit provides a 'cheap approximation' to the texture model of
structure formation.",9612202v1
1997-02-19,Cosmic microwave background measurements can discriminate among inflation models,"Quantum fluctuations during inflation may be responsible for temperature
anisotropies in the cosmic microwave background (CMB). Observations of CMB
anisotropies can be used to falsify many currently popular models. In this
paper we discuss the prospectus for observations of CMB anisotropies at the
accuracy of planned satellite missions to reject currently popular inflation
models and to provide some direction for model building.",9702166v1
1997-02-21,Using SuZIE arcminute-scale CMB anisotropy data to probe open and flat-ΛCDM cosmogonies,"We use arcminute-scale data from the Sunyaev-Zel'dovich Infrared Experiment
to set limits on anisotropies in the cosmic microwave background radiation in
open and spatially-flat-Lambda cold dark matter cosmogonies. There are no
2-sigma detections for the models tested. The upper limits obtained are
consistent with the amplitude of anisotropy detected by the COBE/DMR
experiment.",9702186v1
1998-07-09,Microwave Background Anisotropies from Alfven waves,"We investigate microwave background anisotropies in the presence of
primordial magnetic fields. We show that a homogeneous field with fixed
direction can amplify vector perturbations. We calculate the correlations of
$\delta T/T$ explicitly and show that a large scale coherent field induces
correlations between $a_{\ell-1,m}$ and $a_{\ell+1,m}$. We discuss constraints
on amplitude and spectrum of a primordial magnetic field imposed by
observations of CMB anisotropies.",9807089v1
2000-02-02,The Cosmic Microwave Background Radiation,"We summarize the theoretical and observational status of the study of the
Cosmic Microwave Background radiation. Its thermodynamic spectrum is a robust
prediction of the Hot Big Bang cosmology and has been confirmed
observationally. There are now 76 observations of Cosmic Microwave Background
anisotropy, which we present in a table with references. We discuss the
theoretical origins of these anisotropies and explain the standard jargon
associated with their observation.",0002044v1
2000-06-26,Cosmic Microwave Background Radiation anisotropy with primordial magnetic fields,"Galactic magnetic fields are observed of order $\sim 10^{-6}G$, but their
origin is not definitely known yet. In this paper we consider the primordial
magnetic fields generated in the early universe and analyse their effects on
the density perturbations and the CMBR anisotropy. We assume that the random
magnetic fields have the power law spectrum and satisfy the force-free field
condition.
  The peak heights of the CMBR anisotropy are shown to be shifted upward
depending on the magnetic field strengths relative to the no-magnetic field
case.",0006357v1
2000-08-30,Secondary CMB Anisotropies from Cosmological Reionization,"We use numerical simulation of cosmological reionization to calculate the
secondary CMB anisotropies in a representative flat low density cosmological
model. We show that the kinetic Sunyaev-Zel'dovich effect (scattering off of
moving electrons in the ionized intergalactic medium) is dominated by the
nonlinear hydrodynamic and gravitational evolution of the density and velocity
fields, rather than the detailed distribution of the ionization fraction
(``patchy reionization'') on all angular scales. Combining our results with the
recent calculation of secondary CMB anisotropies by Springel et al., we are
able to accurately predict the power spectrum of the kinetic SZ effect on
almost all angular scales.",0008469v3
2000-10-31,Reproducing the observed Cosmic microwave background anisotropies with causal scaling seeds,"During the last years it has become clear that global O(N) defects and U(1)
cosmic strings do not lead to the pronounced first acoustic peak in the power
spectrum of anisotropies of the cosmic microwave background which has recently
been observed to high accuracy. Inflationary models cannot easily accommodate
the low second peak indicated by the data. Here we construct causal scaling
seed models which reproduce the first and second peak. Future, more precise CMB
anisotropy and polarization experiments will however be able to distinguish
them from the ordinary adiabatic models.",0010633v2
2000-11-28,Peculiarities of anisotropy and polarization as an indicator of noises in the CMB maps,"We discuss some new problems of the modern cosmology which arose after the
BOOMERANG and MAXIMA-1 successful missions. Statistics of high peaks of the CMB
anisotropy is analyzed and we discuss possible inner structure of such peaks in
the observational data of future MAP and PLANCK missions. We have investigated
geometrical and statistical properties of the CMB polarization around such high
isolated peaks of anisotropy in the presence of a polarized pixel noise and
point sources. The structure of polarization fields in the vicinity of singular
points with zero polarization is very sensitive to the level of pixel noises
and point sources in the CMB maps.",0011521v1
2000-12-11,The MAP satellite mission to map the CMB anisotropy,"The Microwave Anisotropy Probe (MAP) satellite is scheduled to launch in
mid-2001. MAP's goal is to produce a map of the anisotropy in the cosmic
microwave background of unprecedented accuracy and precision. The guiding
design principle has been the minimization of systematic effects. The
instrument design and mapping strategy work in concert to take advantage of the
unique opportunities afforded by deep space. We give an overview of the mission
and compare the projected MAP error bars to recent measurements.",0012214v1
2001-07-19,Observing the CMB with the AMiBA,"I discuss the capabilities and limitations of the AMiBA for imaging CMB
anisotropies. Michael Kesteven (ATNF-CSIRO) has proposed drift-scanning as an
observing strategy for measuring and rejecting any instrumental response that
the close-packed interferometers may have to the local environment. The
advantages of mosaic imaging CMB anisotropies using a co-mounted
interferometric array in a drift-scanning observing mode are discussed. A
particular case of mosaic imaging a sky strip using a two-element AMiBA
prototype interferometer is considered and the signal-to-noise ratio in the
measurement of sky anisotropy using this observing strategy is analysed.",0107363v1
2001-08-17,Small Scale Anisotropies of UHECRs from Super-Heavy Halo Dark Matter,"The decay of very heavy metastable relics of the Early Universe can produce
ultra-high energy cosmic rays (UHECRs) in the halo of our own Galaxy. In this
model, no Greisen-Zatsepin-Kuzmin cutoff is expected because of the short
propagation distances. We show here that, as a consequence of the hierarchical
build up of the halo, this scenario predicts the existence of small scale
anisotropies in the arrival directions of UHECRs, in addition to a large scale
anisotropy, known from previous studies. We also suggest some other observable
consequences of this scenario which will be testable with upcoming experiments,
as Auger, EUSO and OWL.",0108288v1
2001-08-27,ATCA and CMB anisotropies,"Australia Telescope Compact Array (ATCA) observations in sky regions selected
to be low in foreground confusion have been used to infer limits on
arcmin-scale CMB anisotropy in total intensity and polarization. These deep
searches have, hitherto, been made using the East-West ATCA in an ultra-compact
1-D array configuration and in the highest available frequency band at 3-cm
wavelength. The ATCA is being upgraded for operation at mm wavelengths and in
2-D array configurations: the enhanced capabilities present a new opportunity
for pursuing CMB anisotropy related observations with reduced foreground
confusion and at smaller angular scales.",0108409v1
2001-09-10,Principal Component Analysis of the Cosmic Microwave Background Anisotropies: Revealing The Tensor Degeneracy,"A principal component analysis of cosmic microwave background (CMB)
anisotropy measurements is used to investigate degeneracies among cosmological
parameters. The results show that a degeneracy with tensor modes -- the `tensor
degeneracy' -- dominates uncertainties in estimates of the baryon and cold dark
matter densities, omega_b = Omega_b h2, omega_c = \Omega_c h^2, from an
analysis of CMB anisotropies alone. The principal component analysis agrees
well with a maximum likelihood analysis of the observations, identifying the
main degeneracy directions and providing an impression of the effective
dimensionality of the parameter space.",0109151v1
2001-12-11,The primordial baryonic clouds and their contribution to the CMB anisotropy and polarization formation,"We discuss possible distortions of the ionization history of the Universe in
the model with small scale baryonic clouds. The corresponding scales of the
clouds are much smaller than the typical galactic mass scales. These clouds are
considered in a framework of the cosmological model with the isocurvature and
adiabatic perturbations. In this model the baryonic clouds do not influence on
the cosmic microwave background anisotropy formation directly as an additional
sources of perturbations, but due to change of the kinetics of the hydrogen
recombination . We also study the corresponding distortions of the anisotropy
and polarization power spectra in connection with the launched MAP and future
PLANCK missions.",0112247v1
2002-07-31,Braneworld Tensor Anisotropies in the CMB,"Cosmic microwave background (CMB) observations provide in principle a
high-precision test of models which are motivated by M theory. We set out the
framework of a program to compute the tensor anisotropies in the CMB that are
generated in braneworld models. In the simplest approximation, we show the
braneworld imprint as a correction to the power spectra for standard
temperature and polarization anisotropies.",0208015v2
2003-03-10,Anisotropy in the angular distribution of the long gamma-ray bursts?,"The gamma-ray bursts detected by the BATSE instrument may be separated into
""short"", ""intermediate"" and ""long"" subgroups. Previous statistical tests found
an anisotropic sky-distribution on large angular scales for the intermediate
subgroup, and probably also for the short subgroup. In this article the
description and the results of a further statistical test - namely the nearest
neighbour analysis - are given. Surprisingly, this test gives an anisotropy for
the long subgroup on small angular scales. The discussion of this result
suggests that this anisotropy may be real.",0303207v1
2003-12-15,Large scale cosmic-ray anisotropy with KASCADE,"The results of an analysis of the large scale anisotropy of cosmic rays in
the PeV range are presented. The Rayleigh formalism is applied to the right
ascension distribution of extensive air showers measured by the KASCADE
experiment.The data set contains about 10^8 extensive air showers in the energy
range from 0.7 to 6 PeV. No hints for anisotropy are visible in the right
ascension distributions in this energy range. This accounts for all showers as
well as for subsets containing showers induced by predominantly light
respectively heavy primary particles. Upper flux limits for Rayleigh amplitudes
are determined to be between 10^-3 at 0.7 PeV and 10^-2 at 6 PeV primary
energy.",0312375v1
2004-03-25,Hyperbolic Universes with a Horned Topology and the CMB Anisotropy,"We analyse the anisotropy of the cosmic microwave background (CMB) in
hyperbolic universes possessing a non-trivial topology with a fundamental cell
having an infinitely long horn. The aim of this paper is twofold. On the one
hand, we show that the horned topology does not lead to a flat spot in the CMB
sky maps in the direction of the horn as stated in the literature. On the other
hand, we demonstrate that a horned topology having a finite volume could
explain the suppression of the lower multipoles in the CMB anisotropy as
observed by COBE and WMAP.",0403597v2
2004-11-01,Are Clusters as Indicators of the Cosmic Ray Anisotropy ?,"The clusters (doublets) in ultrahigh energy cosmic rays are considered based
on Yakutsk and AGASA extensive air shower array data. The problem of cluster
origin is discussed. It is found that arrival directions of the clusters can
point to a cosmic ray anisotropy. As a result of analysis of clusters, the
conclusion on composition and origin of ultrahigh energy cosmic rays has been
made.",0411022v1
2004-12-02,Indication for Primordial Anisotropies in the Neutrino Background from WMAP and SDSS,"We demonstrate that combining Cosmic Microwave Background anisotropy
measurements from the 1st year WMAP observations with clustering data from the
SLOAN galaxy redshift survey yields an indication for primordial anisotropies
in the cosmological Neutrino Background.",0412066v2
2005-12-12,The Big Bang Problems: Anisotropy of z <= 6 Redshifts,"The three-dimensional space distribution of 48921 quasars and 16113 Seyfert
galaxies with redshifts z <= 6 is investigated. The global anisotropy caused by
the shift of the observer place by \simeq 50 Mpc from a center of their
symmetry (supposed center of the Metagalaxy) to the side of the vector with
equatorial coordinates \alpha \simeq 13 degrees and \delta \simeq 70 degrees
has been found in the placement of these objects. In the opposite direction
there exists the extensive region where the progressive decrease of redshifts
up to a minimum (near \alpha \simeq 193 degrees, \delta \simeq -70 degrees) is
observed. The influence of gravitational potential and possible rotation of the
Metagalaxy on the anisotropy of redshifts of the cosmological objects has been
considered.",0512276v1
2006-09-14,CMB Anisotropies from Outflows in Lyman Break Galaxies,"Thomson scattering of the Cosmic Microwave Background (CMB) on moving
electrons in the outflows of Lyman Break Galaxies (LBGs) at redshifts 2-8
contributes to the small-scale CMB anisotropies. The net effect produced by
each outflow depends on its level of deviation from spherical symmetry, caused
either by an anisotropic energy injection from the nuclear starburst or quasar
activity, or by an inhomogeneous intergalactic environment. We find that for
plausible outflow parameters consistent with spectroscopic observations of
LBGs, the induced CMB anisotropies on arcminute scales reach up to $\sim 1
\mu$K, comparable to the level produced during the epoch of reionization.",0609399v1
2006-10-05,Anisotropy studies around the galactic center,"We present the first results for anisotropy searches around the galactic
center at EeV energies using data from the Pierre Auger Observatory. Our
analysis, based on a substantially larger data set, do not support previous
claim of anisotropy found in this region by the AGASA and Sugar experiment.
Furthermore we place un upper limit on a possible point like source located at
the galactic center which exclude several scenarios predicting neutron sources
in this location.",0610160v1
2006-10-05,Cosmic Microwave Background anisotropies: the power spectrum and beyond,"Most of the cosmological information extracted from the CMB has been obtained
through the power spectrum, however there is much more to be learnt from the
statistical distribution of the temperature random field. We review some recent
developments in the study of the Cosmic Microwave Background (CMB) anisotropies
and present a description of the novel tools developed to analyse the
properties of the CMB anisotropies beyond the power spectrum.",0610162v1
2006-10-29,Anisotropies and clustering of extragalactic cosmic rays,"Deviations from isotropy have been a key tool to identify the sources and the
primary type of cosmic rays (CRs) at low energies. We argue that anisotropies
due to blind regions induced by the Galactic magnetic field, the cosmological
Compton-Getting effect, medium-scale anisotropies reflecting the large-scale
distribution of CR sources and the small-scale clustering of the CR arrival
directions at the highest energies may play the same role for extragalactic
CRs.",0610862v1
1994-10-25,Thermal Conductivity Anisotropy in Superconducting $UPt_3$,"Recent thermal conductivity measurements on $UPt_3$ single crystals by
Lussier et al. indicate the existence of a strong b--c anisotropy in the
superconducting state. We calculate the thermal conductivity in various
unconventional candidate states appropriate for the $UPt_3$ ``B phase"" and
compare with experiment, specifically the $E_{2u}$ and $E_{1g}$ $(1,i)$ states
predicted in some Ginzburg-Landau analyses of the phase diagram. For the
simplest realizations of these states over spherical or ellipsoidal Fermi
surfaces, the normalized $E_{2u}$ conductivity is found, surprisingly, to be
completely isotropic. We discuss the effects of inelastic scattering and
realistic Fermi surface anisotropy, and deduce constraints on the symmetry
class of the $UPt_3$ ground state.",9410087v1
1996-06-18,Partially Solvable Anisotropic t-J Model with Long-Range Interactions,"A new anisotropic t-J model in one dimension is proposed which has long-range
hopping and exchange. This t-J model is only partially solvable in contrast to
known integrable models with long-range interaction. In the high-density limit
the model reduces to the XXZ chain with the long-range exchange. Some exact
eigenfunctions are shown to be of Jastrow-type if certain conditions for an
anisotropy parameter are satisfied. The ground state as well as the excitation
spectrum for various cases of the anisotropy parameter and filling are derived
numerically. It is found that the Jastrow-type wave function is an excellent
trial function for any value of the anisotropy parameter.",9606128v1
1997-02-26,Effect of randomness and anisotropy on Turing patterns in reaction-diffusion systems,"We study the effect of randomness and anisotropy on Turing patterns in
reaction-diffusion systems. For this purpose, the Gierer-Meinhardt model of
pattern formation is considered. The cases we study are: (i)randomness in the
underlying lattice structure, (ii)the case in which there is a probablity p
that at a lattice site both reaction and diffusion occur, otherwise there is
only diffusion and lastly, the effect of (iii) anisotropic and (iv) random
diffusion coefficients on the formation of Turing patterns. The general
conclusion is that the Turing mechanism of pattern formation is fairly robust
in the presence of randomness and anisotropy.",9702230v1
1997-03-24,A theoretical investigation of the specific heat of superlattices in a magnetic field,"We analyze the specific heat variations as a function of an external magnetic
field of a simple model of superlattice that includes (i) in--plane
ferromagnetic exchange, (ii) interplane ferromagnetic exchange, (iii) dipolar
interactions, (iv) magnetocristalline anisotropy. The calculations are carried
out at the spin wave level. The interplay between the existence of a canting
transition and the anisotropy of the structure generates non trivial behavior
for the spin wave contribution to the low temperature specific heat as a
function of an external magnetic field when dipolar interactions and
magnetocristalline anisotropy are taken into account.",9703202v1
1997-04-14,The Effect of Anisotropy on Vortex Lattice Structure and Flux Flow in d-Wave Superconductors,"We describe effects of anisotropy caused by the crystal lattice in d-wave
superconductors using effective free energy approach in which only one order
parameter, the d-wave order parameter field, is used. All the effects of
rotational symmetry breaking, including that of the s-wave mixing, can be
parametrized by a single four derivative term. We find solutions for single
vortex and the vortex lattice. Extending the formalism to include the time
dependence, effects of anisotropy on moving vortex structure are calculated.
Both direct and Hall I-V curves as functions of the angle between the current
and the crystal lattice orientation are obtained.",9704116v1
1997-06-30,Anisotropy effects in a mixed quantum-classical Heisenberg model in two dimensions,"We analyse a specific two dimensional mixed spin Heisenberg model with
exchange anisotropy, by means of high temperature expansions and Monte Carlo
simulations. The goal is to describe the magnetic properties of the compound
(NBu_{4})_{2}Mn_{2}[Cu(opba)]_{3}\cdot 6DMSO\cdot H_{2}O which exhibits a
ferromagnetic transition at $T_{c}=15K$. Extrapolating our analysis on the
basis of renormalisation group arguments, we find that this transition may
result from a very weak anisotropy effect.",9706298v1
1997-11-18,Combined effect of nonmagnetic and magnetic scatterers on critical temperatures of superconductors with different gap anisotropy,"The combined effect of nonmagnetic and magnetic defects and impurities on
critical temperatures of superconductors with different gap anisotropy is
studied theoretically within the weak coupling limit of the BCS model. An
expression is derived which relates the critical temperature to relaxation
rates of charge carriers by nonmagnetic and magnetic scatterers, as well as to
the coefficient of anisotropy of the superconducting order parameter on the
Fermi surface. Particular cases of d-wave, (s+d)-wave, and anisotropic s-wave
superconductors are briefly discussed.",9711175v1
1998-04-01,Magnetic Reversal on Vicinal Surfaces,"We present a theoretical study of in-plane magnetization reversal for vicinal
ultrathin films using a one-dimensional micromagnetic model with
nearest-neighbor exchange, four-fold anisotropy at all sites, and two-fold
anisotropy at step edges. A detailed ""phase diagram"" is presented that catalogs
the possible shapes of hysteresis loops and reversal mechanisms as a function
of step anisotropy strength and vicinal terrace length. The steps generically
nucleate magnetization reversal and pin the motion of domain walls. No sharp
transition separates the cases of reversal by coherent rotation and reversal by
depinning of a ninety degree domain wall from the steps. Comparison to
experiment is made when appropriate.",9804009v1
1998-08-26,Evolution of the pairing pseudogap in the spectral function with interplane anisotropy,"We study the pairing pseudogap in the spectral function as a function of
interplane coupling. The analytical expressions for the self-energy in the
critical regime are obtained for any degree of anisotropy. The frequency
dependence of the self-energy is found to be qualitatively different in two and
three dimensions, and the crossover from two to three dimensional behavior is
discussed. In particular, by considering the anisotropy of the Fermi velocity
and gap along the Fermi surface, we can qualitatively explain recent
photoemission experiments on high temperature superconductors concerning the
temperature dependent Fermi arcs seen in the pseudogap phase.",9808298v1
1998-09-25,Absence of anisotropic universal transport in YBCO,"There exists significant in-plane anisotropy between $a$ and $b$ axis for
various properties in YBCO. However recent thermal conductivity measurement by
Chiao et al. which confirms previous microwave conductivity measurement by
Zhang et al., shows no obvious anisotropy in the context of universal
transport. We give a possible explanation of why the anisotropy is seen in most
properties but not seen in the universal transport.",9809341v1
1998-10-19,Polymer Shape Anisotropy and the Depletion Interaction,"We calculate the second and third virial coefficients of the effective
sphere-sphere interaction due to polymer depletion. By utilizing the anisotropy
of a typical polymer conformation, we can consider polymers that are roughly
the same size as the spherical inclusions. We argue that recent experiments can
confirm this anisotropy.",9810234v2
1998-12-15,Self-consistent calculation of the autolocalization barrier for quasiparticles in anisotropic crystal,"The energy of the electron wave packet interacting with lattice distortion,
is considered in anisotropic crystal. Anisotropy of the electron and phonon
spectra as well as of the electron-phonon interaction are taken into account.
The height of the barrier between free and self-trapped states is calculated in
dependence on the anisotropy parameters. The calculation is done numerically,
using continual aproximation. The analytical solution is obtained for some
cases of quasi-two and quasi-one-dimensional spectra. Key words: anisotropy;
polarons; barrier.",9812246v1
1998-12-16,Quasi-long range order in the random anisotropy Heisenberg model,"The large distance behaviors of the random field and random anisotropy
Heisenberg models are studied with the functional renormalization group in
$4-\epsilon$ dimensions. The random anisotropy model is found to have a phase
with the infinite correlation radius at low temperatures and weak disorder. The
correlation function of the magnetization obeys a power law $<{\bf m}({\bf
r}_1) {\bf m}({\bf r}_2)>\sim| {\bf r}_1-{\bf r}_2|^{-0.62\epsilon}$. The
magnetic susceptibility diverges at low fields as $\chi\sim
H^{-1+0.15\epsilon}$. In the random field model the correlation radius is found
to be finite at the arbitrarily weak disorder.",9812280v1
1999-04-08,Magnetic and quadrupolar order in a one-dimensional ferromagnet with cubic crystal-field anisotropy,"The zero temperature phase diagram of a one-dimensional S=2 Heisenberg
ferromagnet with single-ion cubic anisotropy is studied numerically using the
density-matrix renormalization group method. Evidence is found that although
the model does not involve quadrupolar couplings, there is a purely quadrupolar
phase for large values of the anisotropy. The phase transition between the
magnetic and quadrupolar phases is continuous and it seems to be characterized
by Ising critical exponents.",9904109v1
1999-05-25,Field-tilt Anisotropy Energy in Quantum Hall Stripe States,"Recently reported giant anisotropy in the longitudinal resistivity of a 2D
electron system with valence Landau level index $N \ge 2$ has been interpreted
as a signal of unidirectional charge density wave (UCDW) ground states. We
report on detailed Hartree-Fock calculations of the UCDW orientation energy
induced by a tilted magnetic field. We find that for current experimental
samples stripes are oriented perpendicular to the in-plane field, consistent
with experiment. For wider 2D electron systems we predict tilt-induced stripe
states with variable anisotropy energy sign.",9905353v2
1999-08-31,Four-fold basal plane anisotropy of the nonlocal magnetization of YNi2B2C,"Studies of single crystal YNi2B2C have revealed a four-fold anisotropy of the
equilibrium magnetization in the square crystallographic basal plane. This pi/2
periodicity occurs deep in the superconductive mixed state. In this crystal
symmetry, an ordinary superconductive mass anisotropy (as in usual London
theory) allows only a constant, isotropic response. In contrast, the
experimental results are well described by generalized London theory
incorporating non-local electrodynamics, as needed for this clean,
intermediate-k superconductor.",9908483v1
1999-11-01,Competing effects of mass anisotropy and spin Zeeman coupling on the upper critical field of a mixed $d$- and s-wave superconductor,"Based on the linearized Eilenberger equations, the upper critical field
$(H_{c2})$ of mixed d- and s-wave superconductors has been microscopically
studied with an emphasis on the competing effects of mass anisotropy and spin
Zeeman coupling. We find the mass anisotropy always enhance $H_{c2}$ while the
Zeeman interaction suppresses $H_{c2}$. As required by the thermodynamics, we
find $H_{c2}$ is saturated at zero temperature. We compare the theoretical
calculations with recent experimental data of
YBa$_{2}$Cu$_{3}$O$_{7-+AFw-delta}$.",9910522v1
2000-03-03,Breakdown of the Onsager reaction field theory in two dimensions,"It is shown that for the spin 1/2 anisotropic Heisenberg model the result for
the transition temperature is completely insensitive to the anisotropy within
the Onsager reaction field theory, which yields a vanishing T_c in two
dimensions, in total conflict with the expected finite T_c, increasing with
anisotropy. This establishes that the breakdown of the Onsager reaction field
theory in two dimensions is not limited to the Ising model, but actually
extends over the whole range of anisotropy. Therefore, for the isotropic case,
the results of vanishing T_c and exponential dependence of spin correlation
length should be seen as mere coincidence.",0003040v1
2001-01-04,Strong anisotropy of superexchange in the copper-oxygen chains of La_{14-x}Ca_{x}Cu_{24}O_{41},"Electron spin resonance data of Cu^{2+} ions in La_{14-x}Ca_{x}Cu_{24}O_{41}
crystals (x=9,11,12) reveal a very large width of the resonance line in the
paramagnetic state. This signals an unusually strong anisotropy of ~10% of the
isotropic Heisenberg superexchange in the Cu-O chains of this compound. The
strong anisotropy can be explained by the specific geometry of two symmetrical
90 degree Cu-O-Cu bonds, which boosts the importance of orbital degrees of
freedom. Our data show the apparent limitations of the applicability of an
isotropic Heisenberg model to the low dimensional cuprates.",0101040v1
2001-01-24,Effects of geometric anisotropy on local field distribution: Ewald-Kornfeld formulation,"We have applied the Ewald-Kornfeld formulation to a tetragonal lattice of
point dipoles, in an attempt to examine the effects of geometric anisotropy on
the local field distribution. The various problems encountered in the
computation of the conditionally convergent summation of the near field are
addressed and the methods of overcoming them are discussed. The results show
that the geometric anisotropy has a significant impact on the local field
distribution. The change in the local field can lead to a generalized
Clausius-Mossotti equation for the anisotropic case.",0101361v1
2001-03-16,Mean-field theory of magnetic properties of Mn$_x$III$_{1-x}$V semiconductors,"We present a mean-field theory of carrier-induced ferromagnetism in
Mn$_x$III$_{1-x}$V diluted magnetic semiconductors with a special emphasis
placed on the magnetic anisotropy. The valence band holes are described using
the six band Kohn-Luttinger model. We find that the magnetic anisotropy is a
complicated function of sample parameters such as hole density or strain.
Results of our numerical simulations are in agreement with magnetic anisotropy
measurements on samples with both compressive and tensile strains.",0103341v1
2001-06-15,Real-Space Renormalization Group Study of Effects of Anisotropy on S=1 Random Antiferromagnetic Chain,"We investigate S=1 antiferromagnetic quantum spin chain, whose exchange
couplings are strongly disordered. By the real-space renomalization group
method, introduced by Ma, Dasgupta, and Hu, the renormalization group flows are
analyzed numerically in a plain of the anisotoropy of the exchange coupling vs.
the staggered magnetic field. As the result, the Heisenberg point, which has a
zero average of the exchange coupling anisotropy, is specified as the unstable
fixed point against the anisotropy.",0106289v2
2001-06-23,Anisotropy of Quasiparticle Lifetimes and the Role of Disorder for Ultrafast Electron Dynamics in Graphite,"Femtosecond time-resolved photoemission of photoexcited electrons in highly
oriented pyrolytic graphite (HOPG) provides strong evidence for anisotropies of
quasiparticle (QP) lifetimes. Indicative of such anisotropies is a pronounced
anomaly in the energy dependence of QP lifetimes between 1.1 eV and 1.5 eV -
the vicinity of a saddle point in the graphite bandstructure. This is supported
by recent ab initio calculations and a comparison with experiments on
defect-enriched HOPG which reveal that disorder, e.g. defects or phonons,
increases electron energy relaxation rates.",0106486v1
2001-08-13,Stripes and spin-incommensurabilities are favored by lattice anisotropies,"Structural distortions in cuprate materials give a natural origin for
anisotropies in electron properties. We study a modified one-band t-J model in
which we allow for different hoppings and antiferromagnetic couplings in the
two spatial directions ($t_x \ne t_y$ and $J_x \ne J_y$). Incommensurate peaks
in the spin structure factor show up only in the presence of a lattice
anisotropy, whereas charge correlations, indicating enhanced fluctuations at
incommensurate wave vectors, are almost unaffected with respect to the
isotropic case.",0108198v1
2002-01-08,Field dependent anisotropy change in a supramolecular Mn(II)-[3x3] grid,"The magnetic anisotropy of a novel Mn(II)-[3x3] grid complex was investigated
by means of high-field torque magnetometry. Torque vs. field curves at low
temperatures demonstrate a ground state with S > 0 and exhibit a torque step
due to a field induced level-crossing at B* \approx 7.5 T, accompanied by an
abrupt change of magnetic anisotropy from easy-axis to hard-axis type. These
observations are discussed in terms of a spin Hamiltonian formalism.",0201090v1
2002-01-19,Vibrationally induced fourth-order magnetic anisotropy and tunnel splittings in Mn_{12},"From density-functional-theory (DFT) based methods we calculate the
vibrational spectrum of the Mn_{12}O_{12}(COOH)_{16}(H_2 O)_4 molecular magnet.
Calculated infrared intensities are in accord with experimental studies. There
have been no ab initio attempts at determining which interactions account for
the fourth-order anisotropy. We show that vibrationally induced distortions of
the molecule contribute to the fourth-order anisotropy Hamiltonian and that the
magnitude and sign of the effect (-6.2 K) is in good agreement with all
experiments. Vibrationally induced tunnel splittings in isotopically pure and
natural samples are predicted.",0201353v2
2002-02-25,Spin Relaxation Anisotropy in Two-Dimensional Semiconductor Systems,"Spin relaxation is investigated theoretically in two-dimensional systems.
Various semiconductor structures of both n- and p-types are studied in detail.
The most important spin relaxation mechanisms are considered. The spin
relaxation times are calculated taking into account the contributions to the
spin--orbit interaction due to both the bulk inversion asymmetry and the
structure inversion asymmetry. It is shown that in-plane anisotropy of electron
spin relaxation appears in III--V asymmetrical heterostructures. This
anisotropy may be controlled by external parameters, and the spin relaxation
times differ by several orders of magnitude.",0202437v1
2002-02-28,Anisotropy of ultra-thin ferromagnetic films and the spin reorientation transition,"The influence of uniaxial anisotropy and the dipole interaction on the
direction of the magnetization of ultra-thin ferromagnetic films in the
ground-state is studied. The ground-state energy can be expressed in terms of
anisotropy constants which are calculated in detail as function of the system
parameters and the film thickness. In particular non-collinear spin
arrangements are taken into account. Conditions for the appearance of a spin
reorientation transition are given and analytic results for the width of the
canted phase and its shift in applied magnetic fields associated with this
transition are derived.",0202534v1
2002-03-27,Piezoresistive anisotropy of percolative granular metals,"The piezoresistive response of granular metals under uniaxial strain is
strongly dependent on the concentration of the conducting phase. Here we show
that the piezoresistive anisotropy is reduced as the system approaches its
percolation thresold, following a power law behavior in the critical region. We
propose a simple relation between the conductance and the piezoresistive
anisotropy which could be used in relation to real materials and notably to the
thick film resistors.",0203557v1
2002-04-01,Macroscopic anisotropy in superconductors with anisotropic gaps,"It is shown within the weak-coupling model that the macroscopic
superconducting anisotropy for materials with the gap varying on the Fermi
surface cannot be characterized by a single number, unlike the case of clean
materials with isotropic gaps. For clean uniaxial materials, the anisotropy
parameter $\gamma (T)$ defined as the ratio of London penetration depths,
$\lambda_c/\lambda_{ab}$, is evaluated for all $T$'s. Within the two-gap model
of MgB$_2$, $\gamma (T)$ is an increasing function of $T$.",0204038v1
2002-04-25,"Comment on ""Anisotropic s-wave superconductivity in MgB_2""","An analytical result for renormalization of the jump of the heat capacity
Delta C/C_N by the anisotropy of the order parameter is derived in the
framework of the model proposed by Haas and Maki [Phys. Rev. B 65, 020502(R)
(2001)], for both prolate and oblate anisotropy. The graph of Delta C/C_N
versus the ratio of the gaps on the equator and the pole, Delta_e/Delta_p, of
the Fermi surface allows a direct determination of the gap anisotropy parameter
Delta_e/Delta_p using data from specific heat measurements.",0204545v1
2002-05-08,Superconductor-to-Spin-Density-Wave Transition in Quasi-One-Dimensional Metals with Ising Anisotropy,"We study a mechanism for superconductivity in quasi-one-dimensional materials
with Ising anisotropy. In an isolated chain Ising anisotropy opens a spin gap;
if inter-chain coupling is sufficiently weak, single particle hopping is
suppressed and the physics of coupled chains is controlled by a competition
between pair hopping and exchange interaction. Spin density wave and triplet
superconductivity phases are found separated by a first order phase transition.
For particular parameter values a second order transition described by SO(4)
symmetry is found.",0205166v1
2002-07-26,Coherence lengths and anisotropy in MgB2 superconductor,"Field and temperature microwave measurements have been carried out on MgB2
thin film grown on Al2O3 substrate. The analysis reveals the mean field
coherence length xi_{MF} in the mixed state and a temperature independent
anisotropy ratio gamma_{MF} = xi_{MF}^{ab} / xi_{MF}^c approximately 2. At the
superconducting transition, the scaling of the fluctuation conductivity yields
the Ginzburg-Landau coherence length with a different anisotropy ratio
gamma_{GL} = 2.8, also temperature independent.",0207655v1
2002-07-29,Free energy and torque for superconductors with different anisotropies of H_{c2} and lambda,"The free energy is evaluated for a uniaxial superconductor with the
anisotropy of the upper critical field, gamma_H = H_{c2,ab}/H_{c2,c}, different
from the anisotropy of the penetration depth gamma_{lambda} =
lambda_c/lambda_{ab}. With increasing difference between gamma_H and
gamma_{lambda}, the equilibrium orientation of the crystal relative to the
applied field may shift from theta = pi/2 (theta is the angle between the field
and the c axis) to lower angles and reach theta = 0 for large enough gamma_H.
These effects are expected to take place in MgB_2.",0207688v1
2002-09-04,Correlation Effects on Magnetic Anisotropy in Fe and Ni,"We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra-atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean-field theory in the static limit is derived.
The effects of strong correlations are studied along several paths in $(U,J)$
parameter space. Both experimental magnitude of MAE and direction of
magnetization are predicted correctly near $U=1.9 eV$, $J=1.2 eV$ for Ni and
$U=1.2 eV$, $J=0.8 eV$ for Fe. The modified one-electron spectra by strong
correlations are emphasized in conjunction with magnetic anisotropy.",0209073v1
2002-11-11,Possible Jahn-Teller effect in Si-inverse layers,"Jahn-Teller effect in bivalley Si(100) MOSFET under conditions of quantum
Hall effect at integer filling factors nu=1,2,3 is studied. This system is
described by SU(4) hidden symmetry. At nu=2 static and dynamic lattice
deformation creates an easy-plane anisotropy and antiferromagnetic exchange and
lifts the valley degeneracy. At nu=1,3 Coulomb interaction is essential to
produce weak easy-plane anisotropy. Three phases: ferromagnetic, canted
antiferromagnetic and spin-singlet, have been found. Anisotropy energy of
charged skyrmion excitation in every phase is found.",0211214v1
2002-12-13,Step bunching during Si(001) homoepitaxy caused by the surface diffusion anisotropy,"Scanning tunneling microscopy experiments show that the unstable growth
morphology observed during molecular beam homoepitaxy on slightly vicinal
Si(001) surfaces consists of straight step bunches. The instability occurs
under step- flow growth conditions and vanishes both during low-temperature
island growth and at high temperatures. An instability with the same
characteristics is observed in a 2D Kinetic Monte Carlo model of growth with
incorporated Si(001)- like diffusion anisotropy. This provides strong evidence
that the diffusion anisotropy destabilizes growth on Si(001) and similar
surfaces towards step bunching. This new instability mechanism is operational
without any additional step edge barriers.",0212331v1
2003-01-07,Anisotropy of the Mobility of Pentacene from Frustration,"The bandstructure of pentacene is calculated using first-principles density
functional theory. A large anisotropy of the hole and electron effective masses
within the molecular planes is found. The band dispersion of the HOMO and the
LUMO is analyzed with the help of a tight-binding fit. The anisotropy is shown
to be intimately related to the herringbone structure.",0301078v1
2003-03-17,Anisotropic susceptibility of ferromagnetic ultrathin Co films on vicinal Cu,"We measure the magnetic susceptibility of ultrathin Co films with an in-plane
uniaxial magnetic anisotropy grown on a vicinal Cu substrate. Above the Curie
temperature the influence of the magnetic anisotropy can be investigated by
means of the parallel and transverse susceptibilities along the easy and hard
axes. By comparison with a theoretical analysis of the susceptibilities we
determine the isotropic exchange interaction and the magnetic anisotropy. These
calculations are performed in the framework of a Heisenberg model by means of a
many-body Green's function method, since collective magnetic excitations are
very important in two-dimensional magnets.",0303320v1
2003-04-15,Shape and surface anisotropy effects on the hysteresis of ferrimagnetic nanoparticles,"We present the results of Monte Carlo simulations of a model of a single
maghemite ferrimagnetic nanoparticle with the aim to clarify the role played by
the increased anisotropy at the surface and by the shape (spherical or
elliptical) of the particle on the magnetization processes at low temperatures.
The formation of hedgehog-like structures for high enough surface anisotropy is
responsible for a change in the reversal mechanism of the particles.",0304330v1
2003-05-08,Current percolation and anisotropy in polycrystalline MgB$_2$,"The influence of anisotropy on the transport current in MgB$_2$
polycrystalline bulk samples and wires is discussed. A model for the critical
current density is proposed, which is based on anisotropic London theory, grain
boundary pinning and percolation theory. The calculated currents agree
convincingly with experimental data and the fit parameters, especially the
anisotropy, obtained from percolation theory agree with experiment or
theoretical predictions.",0305168v1
2003-07-11,Quantum phase transition in easy-axis antiferromagnetic integer-spin chains,"Antiferromagnetic Heisenberg integer-spin chains are characterized by a
spin-liquid ground state with no long-range order, due to the relevance of
quantum fluctuations. Spin anisotropy, however, freezes quantum fluctuations,
and the system is magnetized in the presence of a sufficiently large easy-axis
anisotropy. We numerically investigate the case S=1, by means of the
density-matrix renormalization group, and find that the freezing of the spin
liquid into a N\'eel spin solid, with increasing easy-axis anisotropy, is a
continuous quantum phase transition. Numerical evidence indicates that the
transition is not in the two-dimensional Ising universality class.",0307266v1
2003-07-17,"Anisotropy and universality: the Oslo model, the rice pile experiment and the quenched Edwards-Wilkinson equation","We show that any amount of anisotropy moves the Oslo model to another known
universality class, the exponents of which can be derived exactly. This amounts
to an exact solution of the quenched Edwards-Wilkinson equation with a drift
term. We argue that anisotropy is likely to be experimentally relevant and may
explain why consistent exponents have not been extracted in the rice pile
experiments.",0307443v1
2003-07-27,Anisotropy of the incommensurate fluctuations in Sr2RuO4: a study with polarized neutrons,"The anisotropy of the magnetic incommensurate fluctuations in Sr2RuO4 has
been studied by inelastic neutron scattering with polarized neutrons. We find a
sizeable enhancement of the out of plane component by a factor of two for
intermediate energy transfer which appears to decrease for higher energies. Our
results qualitatively confirm calculations of the spin-orbit coupling, but the
experimental anisotropy and its energy dependence are weaker than predicted.",0307662v1
2003-08-14,Anisotropy and percolation threshold in a multifractal support,"Recently a multifractal object, $Q_{mf}$, was proposed to study percolation
properties in a multifractal support. The area and the number of neighbors of
the blocks of $Q_{mf}$ show a non-trivial behavior. The value of the
probability of occupation at the percolation threshold, $p_{c}$, is a function
of $\rho$, a parameter of $Q_{mf}$ which is related to its anisotropy. We
investigate the relation between $p_{c}$ and the average number of neighbors of
the blocks as well as the anisotropy of $Q_{mf}$.",0308291v1
2003-10-08,Magnetic Anisotropy of SrCu$_2$(BO$_3$)$_2$ System as Revealed by X-Band ESR,"X-band ESR measurements on a single crystal of the highly frustrated
SrCu$_2$(BO$_3$)$_2$ system are shown to provide an essential inspection of the
magnetic anisotropy present in this compound. The very broad absorption lines
seem to be consistent with the largest anisotropy term, namely, the
antisymmetric Dzyaloshinsky-Moriya (DM) interaction allowed by symmetry.
However, the previously well-accepted model of only interdimer interaction is
generalized with additional intradimer DM terms. Moreover, spin-phonon coupling
is recognized as the cause on the linewidth broadening with increasing
temperature.",0310178v1
2004-04-07,Temperature Anisotropy in a Driven Granular Gas,"When smooth granular material is fluidized by vertically shaking a container,
we find that the temperature in the direction of energy input always exceeds
the temperature in the other directions. An analytical model is presented which
shows how the anisotropy can be traced back to the inelasticity of the
interparticle collisions and the collisions with the wall. The model compares
very well with molecular dynamics simulations. It is concluded that any
non-isotropic driving of a granular gas in a steady state necessarily causes
anisotropy of the granular temperature.",0404174v2
2004-08-04,Quasiparticle dynamics and in-plane anisotropy in $Y Ba_2 Cu_3 O_y$ system near onset of superconductivity,"We report on an infrared study of carrier dynamics within the CuO$_{2}$
planes in heavily underdoped detwinned single crystals of YBa$_{2}$Cu$_{3}$O$%
_{y}$. In an effort to reveal the electronic structure near the onset of
superconductivity, we investigate the strong anisotropy of the electromagnetic
response due to an enhancement of the scattering rate along the a-axis. We
propose that the origin of this anisotropy is related to a modulation of the
electron density within the CuO$_{2}$ planes.",0408097v1
2004-10-01,"Mixed magnetic phases in (Ga,Mn)As epilayers","Two different ferromagnetic-paramagnetic transitions are detected in
(Ga,Mn)As/GaAs(001) epilayers from ac susceptibility measurements: transition
at a higher temperature results from (Ga,Mn)As cluster phases with [110]
uniaxial anisotropy and that at a lower temperature is associated with a
ferromagnetic (Ga,Mn)As matrix with <100> cubic anisotropy. A change in the
magnetic easy axis from [100] to [110] with increasing temperature can be
explained by the reduced contribution of <100> cubic anisotropy to the magnetic
properties above the transition temperature of the (Ga,Mn)As matrix.",0410022v1
2004-11-18,Giant optical anisotropy in a single InAs quantum dot in a very dilute quantum-dot ensemble,"We present the experimental evidence of giant optical anisotropy in single
InAs quantum dots. Polarization-resolved photoluminescence spectroscopy reveals
a linear polarization ratio with huge fluctuations, from one quantum dot to
another, in sign and in magnitude with absolute values up to 82%. Systematic
measurements on hundreds of quantum dots coming from two different laboratories
demonstrate that the giant optical anisotropy is an intrinsic feature of dilute
quantum-dot arrays.",0411484v1
2004-12-02,One-Dimensional S=1 Spin-Orbital Model with Uniaxial Single-Ion Anisotropy,"We investigate ground-state properties of a one-dimensional S=1 spin-orbital
model with or without uniaxial single-ion anisotropy. By means of the density
matrix renormalization group method, we compute the ground-state energy, the
magnetization curves and the correlation functions. We discuss how the
ground-state properties depend on the two exchange couplings for orbital and
spin sectors. The phase diagram obtained is compared with that for the S=1/2
model. We also address the effect of uniaxial single-ion anisotropy.",0412067v1
2005-02-08,Pressure and isotope effect on the anisotropy of MgB$_{2}$,"We analyze the data for the pressure and boron isotope effect on the
temperature dependence of the magnetization near $T_{c}$. Invoking the
universal scaling relation for the magnetization at fixed magnetic field it is
shown that the relative shift of $T_{c}$, induced by pressure or boron isotope
exchange, mirrors essentially that of the anisotropy. This uncovers a novel
generic property of anisotropic type II superconductors, inexistent in the
isotropic case. For MgB$_{2}$ it implies that the renormalization of the Fermi
surface topology due to pressure or isotope exchange is dominated by a
mechanism controlling the anisotropy.",0502202v1
2005-04-11,Lattice pinning of magnetic domains in the helimagnet Ba_2CuGe_2O_7,"The layered magnetic compound Ba_2CuGe_2O_7 exhibits spiral antiferromagnetic
order thanks to a Dzyaloshinskii-Moriya (DM) anisotropy that is allowed by
crystal symmetry. Here we theoretically examine some finer issues such as the
experimentally observed lattice pinning of the propagation vector of helical
magnetic domains. We find that DM anisotropy alone would lead to incorrect
pinning, but agreement with experiment is restored upon including an additional
exchange anisotropy that is also consistent with symmetry. The present results
shed light on the so-called bisection rule which has been abstracted from
experiment in presence of an in-plane magnetic field.",0504262v1
2005-04-19,Spin-glass behavior in the random-anisotropy Heisenberg model,"We perform Monte Carlo simulations in a random anisotropy magnet at a
intermediate exchange to anisotropy ratio. We focus on the out of equilibrium
relaxation after a sudden quenching in the low temperature phase, well below
the freezing one. By analyzing both the aging dynamics and the violation of the
Fluctuation Dissipation relation we found strong evidence of a spin--glass like
behavior. In fact, our results are qualitatively similar to those
experimentally obtained recently in a Heisenberg-like real spin glass.",0504483v2
2005-07-07,Magnetic plateaus in the 1D antiferromagnetic spin-3/2 and spin-2 Ising chains with single-ion anisotropy,"In this study, we have employed the classical transfer matrix technique to
investigate the magnetization plateaus, phase diagrams and other
thermodynamical properties of the one-dimensional antiferromagnetic spin-3/2
and spin-2 Ising chains with single-ion anisotropy in the presence of an
external magnetic field at very low temperature. We have showed that single
ion-anisotropy is one of the indispensable ingredients for an energy gap which
leads to magnetic plateau mechanism in one-dimensional antiferromagnetic Ising
spin chains. Other thermodynamical predictions seem to be provide this
argument.",0507177v1
2005-07-07,"Reorientation Transition in Single-Domain (Ga,Mn)As","We demonstrate that the interplay of in-plane biaxial and uniaxial anisotropy
fields in (Ga,Mn)As results in a magnetization reorientation transition and an
anisotropic AC susceptibility which is fully consistent with a simple single
domain model. The uniaxial and biaxial anisotropy constants vary respectively
as the square and fourth power of the spontaneous magnetization across the
whole temperature range up to T_C. The weakening of the anisotropy at the
transition may be of technological importance for applications involving
thermally-assisted magnetization switching.",0507187v1
2005-08-01,Investigation of the anisotropy of dissipation processes in single crystal of Yba2Cu3O7-d system,"By means of contactless mechanical method of the measurement of energy losses
in superconductors, the anisotropy of dissipation processes has been studied in
single crystal high-temperature layered superconductors of Yba2Cu3O7-d system,
being in mixed state. The observed anisotropy of energy losses indicates the
possibility of the existence of the symmetry of order parameter of dx2-y2 type
in these single crystals.",0508050v1
2005-11-11,Pairing States of Superfluid 3He in Uniaxially Anisotropic Aerogel,"Stable pairing states of superfluid 3He in aerogel are examined in the case
with a global uniaxial anisotropy which may be created by applying an uniaxial
stress to the aerogel. Due to such a global anisotropy, the stability region of
an ABM pairing state becomes wider. In an uniaxially stretched aerogel, the
pure polar pairing state with a horizontal line node is predicted to occur, as
a 3d superfluid phase, over a measurable width just below the superfluid
transition at T_c(P). A possible relevance of the present results to the case
with no global anisotropy is also discussed.",0511280v2
2005-12-06,Hc2 of anisotropy two-band superconductors by Ginzburg-Landau approach,"The purpose of this research is to study the upper critical field (Hc2) of
two-band superconductors by two-band Ginzburg - Landau approach. The analytical
formula of Hc2 included anisotropy of order parameter and anisotropy of
effective-mass are found . The parameters of the upper critical field in
ab-plane and c-axis can be found by fitting to the experimental data . Finally,
we can find the ratio of upper critical field that temperature dependent in the
range of experimental result .",0512105v1
2006-01-19,A significant influence of the substrate on the magnetic anisotropy of monatomic nanowires,"The magnetic anisotropy energy of Fe and Co monatomic nanowires both
free-standing and at the step edge of a Pt surface is investigated within the
framework of the density-functional theory and local-spin-density (LSDA)
approximation. Various types of the analysis of the calculated data reveal that
the spin-orbit interaction of the Pt atoms and the hybridization between the
electronic states have an important impact on the direction of the easy axis
and on the magnitude of the magnetic anisotropy, both by a direct contribution
localized at the Pt atoms and by an indirect contribution due to the
modification of the Co-localized part via hybridization effects.",0601445v1
2006-02-07,Angular dependence of the magnetic-field driven superconductor-insulator transition in thin films of amorphous indium-oxide,"A significant anisotropy of the magnetic-field driven
superconductor-insulator transition is observed in thin films of amorphous
indium-oxide. The anisotropy is largest for more disordered films which have a
lower transition field. At higher magnetic field the anisotropy reduces and
even changes sign beyond a sample specific and temperature independent magnetic
field value. The data are consistent with the existence of more that one
mechanism affecting transport at high magnetic fields.",0602160v1
2006-05-03,Anisotropic Elastic Model for Short DNA Loops,"Effect of bending anisotropy on a planar DNA loop, using energy minimization
and neglecting entropic effects, is studied. We show that the anisotropy
results in polygonal shape of the loop and increasing the anisotropy makes the
edges sharper. Calculating the energy of such a loop lets us to find effective
persistence length as the geometrical mean of hard and soft rigidities, which
is quite different from harmonic mean for an unconstrained long DNA.",0605086v2
2006-10-31,Magnetic anisotropies of late transition metal atomic clusters,"We analyze the impact of the magnetic anisotropy on the geometric structure
and magnetic ordering of small atomic clusters of palladium, iridium, platinum
and gold, using Density Functional Theory. Our results highlight the absolute
need to include self-consistently the spin orbit interaction in any simulation
of the magnetic properties of small atomic clusters, and a complete lack of
universality in the magnetic anisotropy of small-sized atomic clusters.",0610879v2
2000-05-09,Cosmic microwave background anisotropies seeded by incoherent sources,"The cosmic microwave background anisotropies produced by active seeds, such
as topological defects, have been computed recently for a variety of models by
a number of authors. In this paper we show how the generic features of the
anisotropies caused by active, incoherent, seeds (that is the absence of
acoustic peaks at small scales) can be obtained semi-analytically, without
entering into the model dependent details of their formation, structure and
evolution.",0005024v1
2001-10-19,Anisotropic Lattices and Dynamical Fermions,"We report results from full QCD calculations with two flavors of dynamical
staggered fermions on anisotropic lattices. The physical anisotropy as
determined from spatial and temporal masses, their corresponding dispersion
relations, and spatial and temporal Wilson loops is studied as a function of
the bare gauge anisotropy and the bare velocity of light appearing in the Dirac
operator. The anisotropy dependence of staggered fermion flavor symmetry
breaking is also examined. These results will then be applied to the study of
2-flavor QCD thermodynamics.",0110171v1
1998-02-20,Galactic Anisotropy as Signature of ``Top-Down'' Mechanisms of Ultra-High Energy Cosmic Rays,"We show that ``top-down'' mechanisms of Ultra-High Energy Cosmic Rays which
involve heavy relic particle-like objects predict Galactic anisotropy of
highest energy cosmic rays at the level of minimum $\sim 20%$. This anisotropy
is large enough to be either observed or ruled out in the next generation of
experiments.",9802382v2
1998-10-19,Galactic anisotropy of Ultra-High Energy Cosmic Rays produced by CDM-related mechanisms,"We briefly review current theoretical and experimental status of Ultra-High
Energy Cosmic Rays. We show that ``top-down'' mechanisms of UHE CR which
involve heavy relic particle-like objects predict Galactic anisotropy of
highest energy cosmic rays at the level of minimum $\sim 20%$. This anisotropy
is large enough to be either observed or ruled out in the next generation of
experiments.",9810401v1
2000-02-24,Anisotropy of Dynamical Fluctuations as a Probe for Soft and Hard Processes in High Energy Collisions,"It is shown using Lund Monte Carlo that, unlike the average properties of the
hadronic system inside jets, the anisotropy of dynamical fluctuations in these
systems changes abruptly with the variation of the cut parameter $y_cut$. A
transition point exists, where the dynamical fluctuations in the hadronic
system inside jet behave like those in soft hadronic collisions. Thus the
anisotropy property of the dynamical fluctuations can serve as a probe for the
soft and hard processes in high energy collisions.",0002244v2
2001-02-13,Pressure and intermittency in passive vector turbulence,"We investigate the scaling properties a model of passive vector turbulence
with pressure and in the presence of a large-scale anisotropy. The leading
scaling exponents of the structure functions are proven to be anomalous. The
anisotropic exponents are organized in hierarchical families growing without
bound with the degree of anisotropy. Nonlocality produces poles in the
inertial-range dynamics corresponding to the dimensional scaling solution. The
increase with the P\'{e}clet number of hyperskewness and higher odd-dimensional
ratios signals the persistence of anisotropy effects also in the inertial
range.",0102017v1
2001-05-01,Rectangular microwave resonators with magnetic anisotropy. Mapping onto pseudo integrable rhombus,"The rectangular microwave resonator filed by a ferrite with uniaxial magnetic
anisotropy is considered. It is shown that this task can be reduced to an empty
rhombus resonator with vertex angle defined by external magnetic field provided
the magnetic anisotropy of the ferrite is strong. Therefore statistics of eigen
frequencies for TM modes is described by the Brody or semi-Poisson distribution
with some exceptional cases.",0105001v1
2005-06-16,Scaling properties of azimuthal anisotropy of mesons and baryons at RHIC,"Detailed measurements of the azimuthal anisotropy (\v2) for identified
charged particles are reported as a function of transverse momentum ($p_T$) and
centrality for Au+Au collisions at \sqrtsNN = 200 GeV. The measurements
indicate clear evidence for eccentricity and particle flavor scaling over a
broad range of centralities and transverse rapidity $y_T$, indicating a
hydrodynamical origin of the fine structure of azimuthal anisotropy at RHIC.
The observed scaling supports the picture of a suddenly hadronizing
(recombining) fluid of quarks. An apparent breaking of flavor scaling at
relatively large values of $y_T$ points to an important change in the mechanism
for particle emission.",0506019v1
2005-10-08,The azimuthal anisotropy of electrons from heavy flavor decays in sqrt(s_NN) = 200 GeV Au-Au collisions by PHENIX,"The transverse momentum dependence of the azimuthal anisotropy parameter
v_{2}, the second harmonic of the azimuthal distribution, for electrons at
mid-rapidity (|eta|<0.35) has been measured with the PHENIX detector in Au+Au
collisions at sqrt(s_NN) = 200 GeV with respect to the reaction plane defined
at high rapidities (|eta|=3-4). From the result we have calculated non-photonic
electron v_{2}, which is expected to reflect the heavy-flavor azimuthal
anisotropy, by subtracting v_{2} of electrons from other sources such as photon
conversions, Dalitz decay etc.",0510027v1
2006-07-18,Centrality Dependence of Azimuthal Anisotropy of Strange Hadrons in 200 GeV Au+Au Collisions,"Measurements of azimuthal anisotropy for strange and multi-strange hadrons
are presented for the first time in their centrality dependence. The high
statistics results of v2(pT) allow for a more detailed comparison to
hydrodynamical model calculations. Number-of-constituent-quark scaling was
tested for different centrality classes separately. Higher order anisotropies
like v4(pT) are measured for multi-strange hadrons. While we observe agreement
between measured data and models a deeper understanding and refinement of the
models seem to be necessary in order to fully understand the details of the
data.",0607021v1
2001-04-05,Is there elliptic flow without transverse flow?,"Azimuthal anisotropy of final particle distributions was originally
introduced as a signature of transverse collective flow. We show that finite
anisotropy in momentum space can result solely from the shape of the particle
emitting source. However, by comparing the differential anisotropy to recent
data from STAR collaboration we can exclude such a scenario, but instead show
that the data favour strong flow as resulting from a hydrodynamical evolution.",0104020v1
2005-09-30,Azimthally sensitive femtoscopy and v2,"I investigate the correlation between spatial and flow anisotropy in
determining the elliptic flow and azimuthal dependence of the HBT correlation
radii in non-central nuclear collisions. It is shown that the correlation radii
are in most cases dominantly sensitive to the anisotropy in space. In case of
v2, the correlation depends strongly on particle species. A procedure for
disentangling the spatial and the flow anisotropy is proposed.",0509100v1
2006-03-13,Finite driving rate and anisotropy effects in landslide modeling,"In order to characterize landslide frequency-size distributions and
individuate hazard scenarios and their possible precursors, we investigate a
cellular automaton where the effects of a finite driving rate and the
anisotropy are taken into account. The model is able to reproduce observed
features of landslide events, such as power-law distributions, as
experimentally reported. We analyze the key role of the driving rate and show
that, as it is increased, a crossover from power-law to non power-law behaviors
occurs. Finally, a systematic investigation of the model on varying its
anisotropy factors is performed and the full diagram of its dynamical behaviors
is presented.",0603100v1
2006-07-13,Persistence of small-scale anisotropy of magnetic turbulence as observed in the solar wind,"The anisotropy of magnetophydrodynamic turbulence is investigated by using
solar wind data from the Helios 2 spacecraft. We investigate the behaviour of
the complete high-order moment tensors of magnetic field increments and we
compare the usual longitudinal structure functions which have both isotropic
and anisotropic contributions, to the fully anisotropic contribution. Scaling
exponents have been extracted by an interpolation scaling function. Unlike the
usual turbulence in fluid flows, small-scale magnetic fluctuations remain
anisotropic. We discuss the radial dependence of both anisotropy and
intermittency and their relationship.",0607128v1
2007-05-01,Non-abelian plasma instabilities for strong anisotropy,"We numerically investigate gauge field instabilities in anisotropic SU(2)
plasmas using weak field initial conditions. The growth of unstable modes is
stopped by non-abelian effects for moderate anisotropy. If we increase the
anisotropy the growth continues beyond the non-abelian saturation bound. We
find strong indications that the continued growth is not due to over-saturation
of infrared field modes, but instead due to very rapid growth of high momentum
modes which are not unstable in the weak field limit. The saturation amplitude
strongly depends on the initial conditions. For strong initial fields we do not
observe the sustained growth.",0705.0180v1
2007-06-18,Search for large-scale anisotropies with the Auger Observatory,"We use more than two years of data from the Pierre Auger Observatory to
search for anisotropies on large scales in different energy windows. We account
for various systematics in the acceptance, in particular due to the array
growth and weather variations. We present the results of analyses and
consistency checks looking for patterns in the right ascension modulation of
the cosmic ray distribution. No significant anisotropies of this kind are
observed.",0706.2640v1
2007-07-13,Multiphoton antiresonance in large-spin systems,"We study nonlinear response of a spin $S>1/2$ with easy-axis anisotropy. The
response displays sharp dips or peaks when the modulation frequency is
adiabatically swept through multiphoton resonance. The effect is a consequence
of a special symmetry of the spin dynamics in a magnetic field for the
anisotropy energy $\propto S_z^2$. The occurrence of the dips or peaks is
determined by the spin state. Their shape strongly depends on the modulation
amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps
in the response as function of frequency. The results bear on the dynamics of
molecular magnets in a static magnetic field.",0707.2107v1
2008-01-09,Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2,"We have investigated anisotropy in magnetic and electrical transport
properties of Fe1-xCrxSb2 (0<= x <=1) single crystals. The magnetic ground
state of the system evolves from paramagnetic to antiferromagnetic with gradual
substitution of Fe with Cr. Anisotropy in electrical transport diminishes with
increased Cr substitution and fades away by x=0.5. We find that the variable
range hopping (VRH) conduction mechanism dominates at low temperatures for
0.4<= x <=0.75.",0801.1351v2
2008-03-02,Dewetting of an ultrathin solid film on a lattice-matched or amorphous substrate,"An evolution partial differential equation for the surface of a non-wetting
single-crystal film in an attractive substrate potential is derived and used to
study the dynamics of a pinhole for the varying initial depth of a pinhole and
the strengths of the potential and the surface energy anisotropy. The results
of the simulations demonstrate how the corresponding parameters may lead to
complete or partial dewetting of the film. Anisotropy of the surface energy,
through faceting of the pinhole walls, is found to most drastically affect the
time to film rupture. In particular, the similations support the conjecture
that the strong anisotropy is capable of the complete suppression of dewetting
even when the attractive substrate potential is strong.",0803.0126v1
2008-03-11,Metastable anisotropy orientation of nematic quantum Hall fluids,"We analyze the experimental observation of metastable anisotropy resistance
orientation at half filled quantum Hall fluids by means of a model of a quantum
nematic liquid in an explicit symmetry breaking potential. We interpret the
observed ``rotation'' of the anisotropy axis as a process of nucleation of
nematic domains and compute the nucleation rate within this model. By comparing
with experiment, we are able to predict the critical radius of nematic bubbles,
$R_c\sim 2.6 \mu m $. Each domain contains about $10^4$ electrons.",0803.1578v2
2008-04-09,Electric field control of spin-orbit splittings in GaAs/AlGaAs coupled quantum wells,"Electron spin dynamics is investigated in n-i-n GaAs/AlGaAs coupled quantum
wells. The electron spin dephasing time is measured as a function of an
external electrical bias under resonant excitation of the 1sHH intrawell
exciton using a time-resolved Kerr rotation technique. It is found a strong
electron spin dephasing time anisotropy caused by an interference of the
structure inversion asymmetry and the bulk inversion asymmetry. This anisotropy
is shown to be controlled by an electrical bias. A theoretical analysis of
electron spin dephasing time anisotropy is developed. The ratio of Rashba and
Dresselhaus spin splittings is studied as a function of applied bias.",0804.1483v1
2008-04-24,Current-induced domain wall motion in a nanowire with perpendicular magnetic anisotropy,"We study theoretically the current-induced magnetic domain wall motion in a
metallic nanowire with perpendicular magnetic anisotropy. The anisotropy can
reduce the critical current density of the domain wall motion. We explain the
reduction mechanism and identify the maximal reduction conditions. This result
facilitates both fundamental studies and device applications of the current-
induced domain wall motion.",0804.3864v1
2008-08-26,Magnetic anisotropy and reversal in epitaxial Fe/MgO(001) films revisited,"We investigate the magnetization reversal in Fe/MgO(001) films with fourfold
in-plane magnetic anisotropy and an additional uniaxial anisotropy whose
orientation and strength are tuned using different growth geometries and post
growth treatments. The previously adopted mechanism of 180^{o} domain wall
nucleation clearly fails to explain the observed 180^{o} magnetization
reversal. A new reversal mechanism with two successive domain wall nucleations
consistently predicts the switching fields for all field orientations. Our
results are relevant for a correct interpretation of magnetization reversal in
many other epitaxial metallic and semiconducting thin films.",0808.3543v2
2008-08-29,The anisotropy of two dimensional percolation clusters of self-affine models,"The anisotropy parameter of two-dimensional equilibrium clusters of site
percolation process in long-range self-affine correlated structures are studied
numerically. We use a fractional Brownian Motion(FBM) statistic to produce both
persistent and anti-persistent long-range correlations in 2-D models. It is
seen that self affinity makes the shape of percolation clusters slightly more
isotropic. Moreover, we find that the sign of correction to scaling term is
determined by the nature of correlation. For persistent correlation the
correction to scaling term adds a negative contribution to the anisotropy of
percolation clusters, while for the anti-persistent case it is positive.",0808.4033v1
2008-09-05,Interplay between one-dimensional confinement and crystallographic anisotropy in ballistic hole quantum wires,"We study the Zeeman splitting in induced ballistic 1D quantum wires aligned
along the [233] and [011] axes of a high mobility (311)A undoped
heterostructure. Our data shows that the g-factor anisotropy for magnetic
fields applied along the high symmetry [011] direction can be explained by the
1D confinement only. However when the magnetic field is along [233] there is an
interplay between the 1D confinement and 2D crystal anisotropy. This is
highlighted for the [233] wire by an unusual non-monotonic behavior of the
g-factor as the wire is made narrower.",0809.0969v1
2008-10-08,Mixed spin-1/2 and spin-1 Ising model with uniaxial and biaxial single-ion anisotropy on Bethe lattice,"The mixed spin-1/2 and spin-1 Ising model on the Bethe lattice with both
uniaxial as well as biaxial single-ion anisotropy terms is exactly solved by
combining star-triangle and triangle-star mapping transformations with exact
recursion relations. Magnetic properties (magnetization, phase diagrams and
compensation phenomenon) are investigated in detail. The particular attention
is focused on the effect of uniaxial and biaxial single-ion anisotropies that
basically influence the magnetic behavior of the spin-1 atoms.",0810.1371v2
2008-10-11,Polarization singularity anisotropy: determining monstardom,"C points, that is isolated points of circular polarization in transverse
fields of varying polarization, are classified morphologically into three
distinct types, known as lemons, stars and monstars. These morphologies are
interpreted here according to two natural parameters associated with the
singularity, namely the anisotropy of the C point, and the polarization azimuth
on the anisotropy axis. In addition to providing insight into singularity
morphology, this observation applies to the densities of the various
morphologies in isotropic random polarization speckle fields.",0810.2002v1
2008-11-20,Effect of Bending Anisotropy on the 3D Conformation of Short DNA Loops,"The equilibrium three dimensional shape of relatively short loops of DNA is
studied using an elastic model that takes into account anisotropy in bending
rigidities. Using a reasonable estimate for the anisotropy, it is found that
cyclized DNA with lengths that are not integer multiples of the pitch take on
nontrivial shapes that involve bending out of planes and formation of kinks.
The effect of sequence inhomogeneity on the shape of DNA is addressed, and
shown to enhance the geometrical features. These findings could shed some light
on the role of DNA conformation in protein--DNA interactions.",0811.3315v1
2009-02-13,Exposing the Noncollectivity in Elliptic Flow,"We show that backward-forward elliptic anisotropy correlation provides an
experimentally accessible observable which distinguishes between collective and
non-collective contributions to the observed elliptic anisotropy $v_2$ in
relativistic heavy ion collisions. The measurement of this observable will
reveal the momentum scale at which collective expansion seizes and where the
elliptic anisotropy is dominated by (semi)-hard processes.",0902.2377v2
2009-03-28,An asymptotic preserving scheme for strongly anisotropic elliptic problems,"In this article we introduce an asymptotic preserving scheme designed to
compute the solution of a two dimensional elliptic equation presenting large
anisotropies. We focus on an anisotropy aligned with one direction, the
dominant part of the elliptic operator being supplemented with Neumann boundary
conditions. A new scheme is introduced which allows an accurate resolution of
this elliptic equation for an arbitrary anisotropy ratio.",0903.4984v2
2009-06-06,Stable two-dimensional ferromagnets made of regular single-layered lattices of single-molecule nanomagnets on substrates,"We propose that stable two-dimensional (2D) ferromagnets can be made of
regular single-layered lattices of single-molecule nanomagnets with enough
uniaxial magnetic anisotropy on appropriate substrates by controlling the
inter-nanomagnet magnetic interaction. Our Monte Carlo simulated results show
that such ideal 2D ferromagnets are thermodynamically stable when the
anisotropy is strong enough. If the anisotropy energy equals 80 K,
approximately that of the Mn12, the T_c varies from zero to 15 K depending on
different inter-nanomagnet coupling constants. Such stable spin systems,
experimentally accessible, should be promising for information applications.",0906.1298v1
2009-06-06,Memory and aging effects in interacting sub-10nm nanomagnets with large uniaxial anisotropy,"Using a nonequilibrium Monte Carlo method suitable to nanomagnetism, we
investigate representative systems of interacting sub-10nm grained nanomagnets
with large uniaxial anisotropy. Various magnetization memory and aging effects
are found in such systems. We explain these dynamical effects using the
distributed relaxation times of the interacting nanomagnets due to their large
anisotropy energies.",0906.1300v1
2009-07-07,"Tunneling Anisotropic Spin Polarization in lateral (Ga,Mn)As/GaAs spin Esaki diode devices","We report here on anisotropy of spin polarization obtained in lateral
all-semiconductor all-electrical spin injection devices, employing
$p^{+}-$(Ga,Mn)As/$n^{+}-$GaAs Esaki diode structures as spin aligning
contacts, resulting from the dependence of the efficiency of spin tunneling on
the orientation of spins with respect to different crystallographic directions.
We observed an in-plane anisotropy of $~8%$ in case of spins oriented either
along $[1\bar{1}0]$ or $[110]$ directions and $~25%$ anisotropy between
in-plane and perpendicular-to-plane orientation of spins.",0907.1202v1
2009-07-23,Quantum Heisenberg antiferromagnetic chains with exchange and single--ion anisotropies,"Using density matrix renormalization group calculations, ground state
properties of the spin-1 Heisenberg chain with exchange and quadratic
single-ion anisotropies in an external field are studied, for special choices
of the two kinds of anisotropies. In particular, the phase diagram includes
antiferromagnetic, spin-liquid (or spin-flop), (10), and supersolid (or
biconical) phases. Especially, new features of the spin-liquid and supersolid
phases are discussed. Properties of the quantum chains are compared to those of
corresponding classical spin chains.",0907.4168v1
2009-08-10,Phase diagram of an anisotropic frustrated ferromagnetic spin-1/2 chain in a magnetic field: a density matrix renormalization group study,"We study the phase diagram of a frustrated spin-1/2 ferromagnetic chain with
anisotropic exchange interactions in an external magnetic field, using the
density matrix renormalization group method. We show that an easy-axis
anisotropy enhances the tendency towards multimagnon bound states, while an
easy-plane anisotropy favors chirally ordered phases. In particular, a moderate
easy-plane anisotropy gives rise to a quantum phase transition at intermediate
magnetization. We argue that this transition is related to the finite-field
phase transition experimentally observed in the spin-1/2 compound LiCuVO_4.",0908.1281v2
2009-08-12,On quarkonium in an anisotropic quark gluon plasma,"We reconsider a plasma with an anisotropy imposed on the momentum
distribution of the system and study the real time static potential for
quarkonia. The distribution function is normalised so as to preserve the
particle number in an ideal gas, as required in the Keldysh-Schwinger
formalism. In contrast to recent findings without this normalisation, a weak
anisotropy does not lead to an increase in the melting temperature for bound
states. To test for the maximal effect, we also investigate a gluonic medium in
the limit of an asymptotically strong anisotropy. The spectral function of
quarkonium is calculated for this case and found to be in remarkable agreement
with the corresponding results for an isotropic medium.",0908.1746v1
2009-09-25,Nernst effect anisotropy as a sensitive probe of Fermi surface distortions from electron-nematic order,"We analyze the thermoelectric response in layered metals with spontaneously
broken rotation symmetry. We identify the anisotropy of the quasiparticle
Nernst signal as an extremely sensitive probe of Fermi surface distortions
characteristic of the ordered state. This is due to a subtle interplay of
different transport anisotropies which become additionally enhanced near
van-Hove singularities. Applied to recent experiments, our results reinforce
the proposal that the underdoped cuprate superconductor YBCO displays such
``electron-nematic'' order in the pseudogap regime.",0909.4534v2
2009-10-17,Intrinsic anisotropy of thermal conductance in graphene nanoribbons,"Thermal conductance of graphene nanoribbons (GNRs) with the width varying
from 0.5 to 35 nm is systematically investigated using nonequilibrium Green's
function method. Anisotropic thermal conductance is observed with the room
temperature thermal conductance of zigzag GNRs up to ~ 30% larger than that of
armchair GNRs. At room temperature, the anisotropy is found to disappear until
the width is larger than 100 nm. This intrinsic anisotropy originate from
different boundary condition at ribbon edges, and can be used to tune thermal
conductance, which have important implications for the applications of GNRs in
nanoelectronics and thermoelectricity.",0910.3267v1
2009-10-22,Theory of exciton fine structure in semiconductor quantum dots: quantum dot anisotropy and lateral electric field,"Theory of exciton fine structure in semiconductor quantum dots and its
dependence on quantum dot anisotropy and external lateral electric field is
presented. The effective exciton Hamiltonian including long range electron-hole
exchange interaction is derived within the k*p effective mass approximation
(EMA). The exchange matrix elements of the Hamiltonian are expressed explicitly
in terms of electron and hole envelope functions. The matrix element
responsible for the ""bright"" exciton splitting is identified and analyzed. An
excitonic fine structure for a model quantum dot with quasi- two-dimensional
anisotropic harmonic oscillator (2DLAHO) confining potential is analyzed as a
function of the shape anisotropy, size and applied lateral electric field.",0910.4345v1
2009-11-30,Magnetization reversal in amorphous Fe/Dy multilayers: a Monte Carlo study,"The Monte Carlo method in the canonical ensemble is used to investigate
magnetization reversal in amorphous transition metal - rare earth multilayers.
Our study is based on a model containing diluted clusters which exhibit an
effective uniaxial anisotropy in competition with random magnetic anisotropy in
the matrix. We simulate hysteresis loops for an abrupt profile and a diffuse
one obtained from atom probe tomography analyses. Our results evidence that the
atom probe tomography profile favors perpendicular magnetic anisotropy in
agreement with magnetic measurements. Moreover, the hysteresis loops calculated
at several temperatures qualitatively agree with the experimental ones.",0911.5653v1
2010-03-30,Colossal anisotropy in diluted magnetic topological insulators,"We consider dilute magnetic doping in the surface of a three dimensional
topological insulator where a two dimensional Dirac electron gas resides. We
find that exchange coupling between magnetic atoms and the Dirac electrons has
a strong and peculiar effect on both. First, the exchange-induced single ion
magnetic anisotropy is very large and favors off-plane orientation. In the case
of ferromagnetically ordered phase we find a colossal magnetic anisotropy
energy, of the order of the critical temperature. Second, a persistent
electronic current circulates around the magnetic atom and, in the case of a
ferromagnetic phase, around the edges of the surface.",1003.5931v1
2010-04-02,Late-time anisotropy and radiation drag within the cosmic microwave background,"I investigate the effect of the radiation drag force on a star moving
relative to the Cosmic Microwave Background (CMB) at z = 0. As expected, the
perturbation is extremely small and has no observable consequences on orbital
motions of stars within a galaxy or on orbital motions of galaxies within a
cluster. The energy dissipated by cubic meter in a galaxy via this mechanism is
10^{14} smaller than the energy density of the CMB and, thus, is a negligible
source of anisotropy. However, from the last scattering surface to population
III stars (30 < z < 1000), radiation drag on particles may have played a major
role in the apparition of anisotropy and rapid formation of densities.",1004.0328v1
2010-05-10,Impact on cosmology of the celestial anisotropy of the short gamma-ray bursts,"Recently the anisotropy of the short gamma-ray bursts detected by BATSE was
announced (Vavrek et al. 2008). The impact of this discovery on cosmology is
discussed. It is shown that the anisotropy found may cause the breakdown of the
cosmological principle.",1005.1558v1
2010-07-19,CMB anisotropies in the presence of a stochastic magnetic field,"Primordial magnetic fields present since before the epoch of matter-radiation
equality have an effect on the anisotropies of the cosmic microwave background.
The CMB anisotropies due to scalar perturbations are calculated in the gauge
invariant formalism for magnetized adiabatic initial conditions. Furthermore
the linear matter power spectrum is calculated. Numerical solutions are
complemented by a qualitative analysis.",1007.3163v2
2010-09-29,Cosmic microwave anisotropies in an inhomogeneous compact flat universe,"The anisotropies of the cosmic microwave background (CMB) are computed for
the half-turn space E_2 which represents a compact flat model of the Universe,
i.e. one with finite volume. This model is inhomogeneous in the sense that the
statistical properties of the CMB depend on the position of the observer within
the fundamental cell. It is shown that the half-turn space describes the
observed CMB anisotropies on large scales better than the concordance model
with infinite volume. For most observer positions it matches the temperature
correlation function even slightly better than the well studied 3-torus
topology.",1009.5880v2
2010-10-01,"Mapping the magnetic exchange interactions from first principles: Anisotropy anomaly and application to Fe, Ni, and Co","Mapping the magnetic exchange interactions from model Hamiltonian to density
functional theory is a crucial step in multi-scale modeling calculations.
Considering the usual magnetic force theorem but with arbitrary rotational
angles of the spin moments, a spurious anisotropy in the standard mapping
procedure is shown to occur provided by bilinear-like contributions of high
order spin interactions. The evaluation of this anisotropy gives a hint on the
strength of non-bilinear terms characterizing the system under investigation.",1010.0273v2
2010-11-11,Anisotropic spin Hall effect from first principles,"We report on first principles calculations of the anisotropy of the intrinsic
spin Hall conductivity (SHC) in nonmagnetic hcp metals and in antiferromagnetic
Cr. For most of the metals of this study we find large anisotropies. We derive
the general relation between the SHC vector and the direction of spin
polarization and discuss its consequences for hcp metals. Especially, it is
predicted that for systems where the SHC changes sign due to the anisotropy the
spin Hall effect may be tuned such that the spin polarization is parallel
either to the electric field or to the spin current.",1011.2714v2
2011-01-10,Magnetic measurement of the critical current anisotropy in coated conductors,"We determine the critical current anisotropy at maximum Lorentz force from
hysteresis loops in a vibrating sample magnetometer. To eliminate the signal of
spurious variable Lorentz force currents it is sufficient to cut the sample to
a specific length, which is calculated from the position dependent sensitivity
of the instrument. The procedure increases the resolution of the measurement
and the results compare well to transport data on the same sample. As the
electric field in magnetisation measurements is lower than in transport
experiments the anisotropy at high currents (low temperatures and fields) can
be measured without the need of making current contacts or any special sample
preparation.",1101.1788v1
2011-02-18,Perpendicular magnetic anisotropy of full-Heusler films in Pt/Co2FeAl/MgO trilayers,"We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO
sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is
thermally stable that the anisotropy energy density Ku is 1.3{\times}106
erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 oC. The
thicknesses of Co2FeAl and MgO layers greatly affect the PMA. Our results
provide an effective way to realize relative thick perpendicularly magnetized
Heusler alloy films.",1102.3802v1
2011-05-09,A multiscale autocorrelation function for anisotropy studies,"In recent years many procedures have been proposed to check the anisotropy of
a dataset. We present a new simple procedure, based on a scale dependent
approach, to detect anisotropy signatures in a given distribution with
particular attention to small dataset. The method provides a good
discrimination power for both large and small datasets, even in presence of
strong contaminating isotropic background. We present some applications to
simulated datasets of events to investigate statistical features of the method
and present and inspect its behavior under both the null or the alternative
hypothesis.",1105.1604v1
2011-06-22,Anisotropic super-spin at the end of a carbon nanotube,"Interaction-induced magnetism at the ends of carbon nanotubes is studied
theoretically, with a special focus on magnetic anisotropies. Spin-orbit
coupling, generally weak in ordinary graphene, is strongly enhanced in
nanotubes. In combination with Coulomb interactions, this enhanced spin-orbit
coupling gives rise to a super-spin at the ends of carbon nanotubes with an XY
anisotropy on the order of 10 mK. Furthermore, it is shown that this anisotropy
can be enhanced by more than one order of magnitude via a partial suppression
of the super-spin.",1106.4549v1
2011-07-29,Electron spin resonance shift in spin ladder compounds,"We analyze the effects of different coupling anisotropies in spin-1/2 ladder
on the Electron Spin Resonance (ESR) shift. Combining a perturbative expression
in the anisotropies with temperature dependent Density Matrix Renormalization
Group (T-DMRG) computation of the short range correlations, we provide the full
temperature and magnetic field evolution of the ESR paramagnetic shift. We show
that for well chosen parameters the ESR shift can be in principle used to
extract quantitatively the anisotropies and, as an example, discuss the
material $\mathrm{(C_5H_{12}N)_2CuBr_4}$ (BPCB).",1107.5965v2
2011-08-10,A route towards finding large magnetic anisotropy in nano-composites: application to a W$_{1-x}$Re$_x$/Fe multilayer,"We suggest here a novel nano-laminate, 5[Fe]/2[W$_x$Re$_{1-x}$] (x=0.6-0.8),
with enhanced magnetic hardness in combination with a large saturation moment.
The calculated magnetic anisotropy of this material reaches values of 5.3-7.0
MJ/m$^3$, depending on alloying conditions. We also propose a recipe in how to
identify other novel magnetic materials, such as nano-laminates and
multilayers, with large magnetic anisotropy in combination with a high
saturation moment.",1108.2105v1
2011-09-07,Magnetic-field tuned anisotropy in superconducting Rb(x)Fe(2-y)Se(2),"The anisotropic superconducting properties of a Rb(x)Fe(2-y)Se(2) single
crystal with transition temperature 32 K were investigated by means of SQUID
and torque magnetometry, probing the effective magnetic penetration depth and
the magnetic penetration depth anisotropy. Interestingly, the anisotropy is
found to be temperature independent in the superconducting state, but strongly
field dependent. This unusual anisotropic behavior, together with a large
zero-temperature effective magnetic penetration depth is possibly related to a
superconducting state heavily biased by the coexisting antiferromagnetic phase.",1109.1430v2
2011-11-14,Electron spin resonance study of anisotropic interactions in a two-dimensional spin gap magnet PHCC,"Fine details of the excitation spectrum of the two-dimensional spin-gap
magnet PHCC are revealed by electron spin resonance investigations. The values
of anisotropy parameters and the orientations of the anisotropy axes are
determined by accurate measurements of the angular, frequency-field and
temperature dependences of the resonance absorption. The properties of a
spin-gap magnet in the vicinity of critical field are discussed in terms of
sublevel splittings and g-factor anisotropy.",1111.3223v1
2012-01-06,Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: a tight binding approach,"Using an advanced tight-binding approach, we estimate the anisotropy of the
tunnel transmission associated with the rotation of the 5/2 spin of a single Mn
atom forming an acceptor state in GaAs and located near an AlGaAs tunnel
barrier. Significant anisotropies in both in-plane and out-of-plane geometries
are found, resulting from the combination of the large spin-orbit coupling
associated with the p-d exchange interaction, cubic anisotropy of heavy-hole
dispersion and the low C2v symmetry of the chemical bonds.",1201.1439v1
2012-01-11,Local magnetic anisotropy in BaFe$_2$As$_2$: a polarized inelastic neutron scattering study,"The anisotropy of the magnetic excitations in BaFe$_2$As$_2$ was studied by
polarized inelastic neutron scattering which allows one to separate the
components of the magnetic response. Despite the in-plane orientation of the
static ordered moment we find the in-plane polarized magnons to exhibit a
larger gap than the out-of-plane polarized ones indicating very strong
single-ion anisotropy within the layers. It costs more energy to rotate a spin
within the orthorhombic {\it a-b} plane than rotating it perpendicular to the
FeAs layers.",1201.2332v1
2012-01-23,Strong Enhancement of Rashba spin-orbit coupling with increasing anisotropy in the Fock-Darwin states of a quantum dot,"We have investigated the electronic properties of elliptical quantum dots in
a perpendicular external magnetic field, and in the presence of the Rashba
spin-orbit interaction. Our work indicates that the Fock-Darwin spectra display
strong signature of Rashba spin-orbit coupling even for a low magnetic field,
as the anisotropy of the quantum dot is increased. An explanation of this
pronounced effect with respect to the anisotropy is presented. The strong
spin-orbit coupling effect manifests itself prominently in the corresponding
dipole-allowed optical transitions, and hence is susceptible to direct
experimental observation.",1201.4842v2
2012-01-26,Self-assembly of anisotropic soft particles in two dimensions,"The self assembly of core-corona discs interacting via anisotropic potentials
is investigated using Monte Carlo computer simulations. A minimal interaction
potential that incorporates anisotropy in a simple way is introduced. It
consists in a core-corona architecture in which the center of the core is
shifted with respect to the center of the corona. Anisotropy can thus be tuned
by progressively shifting the position of the core. Despite its simplicity, the
system self organize in a rich variety of structures including stripes,
triangular and rectangular lattices, and unusual plastic crystals. Our results
indicate that the amount of anisotropy does not alter the lattice spacing and
only influences the type of clustering (stripes, micells, etc.) of the
individual particles.",1201.5440v1
2012-02-15,Origin of bulk uniaxial anisotropy in zinc-blende dilute magnetic semiconductors,"It is demonstrated that the nearest neighbor Mn pair on the GaAs (001)
surface has a lower energy for the [-110] direction comparing to the [110]
case. According to the group theory and the Luttinger's method of invariants,
this specific Mn distribution results in bulk uniaxial in-plane and
out-of-plane anisotropies. The sign and magnitude of the corresponding
anisotropy energies determined by a perturbation method and ab initio
computations are consistent with experimental results.",1202.3295v1
2012-02-29,Dynamic Critical Behavior of the Heisenberg Model with Strong Easy Plane Anisotropy,"The dynamic critical behavior of the Heisenberg model with a strong
anisotropy of the exchange constant in the z direction is investigated. The
main features of the time evolution of this model are revealed. The static and
dynamic critical behavior of planar magnetic models is shown to be described
well by the Heisenberg model with strong easy plane anisotropy.",1202.6509v1
2012-03-23,Magnetic dispersion and anisotropy in multiferroic BiFeO3,"We have determined the full magnetic dispersion relations of multiferroic
BiFeO3. In particular, two excitation gaps originating from magnetic
anisotropies have been clearly observed. The direct observation of the gaps
enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction
and the single ion anisotropy. The DM interaction supports a strong
magneto-electric coupling in this compound.",1203.5294v3
2012-03-30,Highly anisotropic temperature balance equation and its asymptotic-preserving resolution,"This paper deals with the numerical study of a nonlinear, strongly
anisotropic heat equation. The use of standard schemes in this situation leads
to poor results, due to the high anisotropy. An Asymptotic-Preserving method is
introduced in this paper, which is second-order accurate in both, temporal and
spacial variables. The discretization in time is done using an L-stable
Runge-Kutta scheme. The convergence of the method is shown to be independent of
the anisotropy parameter $0 < \eps <1$, and this for fixed coarse Cartesian
grids and for variable anisotropy directions. The context of this work are
magnetically confined fusion plasmas.",1203.6739v1
2012-04-17,Magnetic anisotropy of YbNi4P2,"We report on transport and magnetic measurements between 1.8 and 400 K on
single crystalline YbNi4P2, which was recently reported to be a heavy fermion
system with a low lying ferromagnetic transition at T_C=0.17 K, based on data
from polycrystals. The tetragonal crystal structure of YbNi4P2 presents
quasi-one-dimensional Yb chains along the c direction. Here we show that at
high temperatures, the magnetic anisotropy of YbNi4P2 is dominated by the
crystal electrical field effect with an Ising-type behaviour, which gets more
pronounced towards lower temperatures. The electrical resistivity also reflects
the strong anisotropy of the crystal structure and favours transport along c,
the direction of the Yb chains.",1204.3759v1
2012-06-05,Cosmic ray transport and anisotropies,"We show that the large-scale cosmic ray anisotropy at ~10 TeV can be
explained by a modified Compton-Getting effect in the magnetized flow field of
old supernova remnants. This approach suggests an optimum energy scale for
detecting the anisotropy. Two key assumptions are that propagation is based on
turbulence following a Kolmogorov law and that cosmic ray interactions are
dominated by transport through stellar winds of the exploding stars. A
prediction is that the amplitude is smaller at lower energies due to incomplete
sampling of the velocity field and also smaller at larger energies due to
smearing.",1206.0828v1
2012-06-26,Entanglement and Sources of Magnetic Anisotropy in Radical Pair-Based Avian Magnetoreceptors,"One of the principal models of magnetic sensing in migratory birds rests on
the quantum spin-dynamics of transient radical pairs created photochemically in
ocular cryptochrome proteins. We consider here the role of electron spin
entanglement and coherence in determining the sensitivity of a radical
pair-based geomagnetic compass and the origins of the directional response. It
emerges that the anisotropy of radical pairs formed from spin-polarized
molecular triplets could form the basis of a more sensitive compass sensor than
one founded on the conventional hyperfine-anisotropy model. This property
offers new and more flexible opportunities for the design of biologically
inspired magnetic compass sensors.",1206.5946v1
2012-07-17,The anisotropy properties of a background radiation in the fractal cosmological model,"We consider the anisotropy properties of a background radiation in the
fractal cosmological model. The space of this model includes self-similar
domains. The metric tensors of any two domains are connected by the discrete
scaling transformation. Photons of the background radiation cross the domain
and their energy change. Any observer receives these photons from different
domains and detects spots with different brightness. The power spectrum of the
brightness anisotropy of the background radiation in the fractal cosmological
model is calculated. It is shown this spectrum is closed to the observed
angular power spectrum of the SDSS-quasar distribution on the celestial sphere.
Only qualitatively it conforms to the angular power spectrum of CMB (WMAP-7).",1207.4615v1
2012-08-10,Transversal Magnetic Anisotropy in Nanoscale PdNi-Strips,"We investigate submicron ferromagnetic PdNi thin-film strips intended as
contact electrodes for carbon nanotube-based spintronic devices. The magnetic
anisotropy and micromagnetic structure are measured as function of temperature
and aspect ratio. Contrary to the expectation from shape anisotropy, magnetic
hysteresis measurements of Pd0.3Ni0.7 on arrays containing strips of various
width point towards a magnetically easy axis in the sample plane, but
transversal to the strip direction. Anisotropic magnetoresistance measured on
individual Pd0.3Ni0.7 contact strips and magnetic force microscopy images
substantiate that conclusion.",1208.2163v2
2012-08-29,Implications of mirror dark matter kinetic mixing for CMB anisotropies,"Mirror dark matter is a dissipative and self-interacting multiparticle dark
matter candidate which can explain the DAMA, CoGeNT and CRESST-II direct
detection experiments. This explanation requires photon-mirror photon kinetic
mixing of strength $\epsilon \sim 10^{-9}$. Mirror dark matter with such
kinetic mixing can potentially leave distinctive signatures on the CMB
anisotropy spectrum. We show that the most important effect of kinetic mixing
on the CMB anisotropies is the suppression of the height of the third and
higher odd peaks. If $\epsilon \stackrel{>}{\sim} 10^{-9}$ then this feature
can be observed by the PLANCK mission in the near future.",1208.6022v2
2012-09-12,Coherent spin control by electrical manipulation of the magnetic anisotropy,"High-spin paramagnetic manganese defects in polar piezoelectric zinc oxide
exhibit a simple almost axial anisotropy and phase coherence times of the order
of a millisecond at low temperatures. The anisotropy energy is tunable using an
externally applied electric field. This can be used to control electrically the
phase of spin superpositions and to drive spin transitions with resonant
microwave electric fields.",1209.2745v2
2012-10-24,Origin of the Large Anisotropy in the χ_3 Anomaly in URu_2Si_2,"Motivated by recent quantum oscillations experiments on URu_2Si_2, we discuss
the microscopic origin of the large anisotropy observed many years ago in the
anomaly of the nonlinear susceptibility in this same material. We show that the
magnitude of this anomaly emerges naturally from hastatic order, a proposal for
hidden order that is a two-component spinor arising from the hybridization of a
non-Kramers Gamma_5 doublet with Kramers conduction electrons. A prediction is
made for the angular anisotropy of the nonlinear susceptibility anomaly as a
test of this proposed order parameter for URu_2Si_2.",1210.6425v1
2012-11-22,Power spectrum and anisotropy of super inflation in loop quantum cosmology,"We investigate the scalar mode of perturbation of super inflation in the
version of loop quantum cosmology in which the gauge invariant holonomy
corrections are considered. Given a background solution, we calculate the power
spectrum of the perturbation in the classical and LQC conditions. Then we
compute the anisotropy originated from the perturbation. It is found that in
the presence of the gauge invariant holonomy corrections the power spectrum is
exponentially blue and the anisotropy also grows exponentially in the epoch of
super inflation.",1211.5310v2
2012-12-28,A Study on Anisotropy in the Arrival Directions of Ultra-High-Energy Cosmic Rays Observed by Pierre Auger Observatory,"We study the anisotropy in the arrival directions of PAO UHECRs, using the
point source correlational angular distance distribution. The result shows that
the anisotropy is characterized by one prominent excess region and one void
region. The excess region is located near the Centaurus A direction, supporting
that the Centaurus A is a promising UHECR source. The void region near the
south pole direction may be used to limit the diffuse isotropic background
contribution.",1212.6479v1
2013-02-02,Physics in a general length space-time geometry: Call for experimental revision of the light speed anisotropy,"We present a phenomenological model for the nature in the Finsler and Randers
space-time geometries. We show that the parity-odd light speed anisotropy
perpendicular to the gravitational equipotential surfaces encodes the deviation
from the Riemann geometry toward the Randers geometry. We utilize an
asymmetrical ring resonator and propose a setup in order to directly measure
this deviation. We address the constraints that the current technology will
impose on the deviation should the anisotropy be measured on the Earth surface
and the orbits of artificial satellites.",1302.1194v1
2013-05-23,Searches for Large-Scale Anisotropies of Cosmic Rays: Harmonic Analysis and Shuffling Technique,"The measurement of large scale anisotropies in cosmic ray arrival directions
is generally performed through harmonic analyses of the right ascension
distribution as a function of energy. These measurements are challenging due to
the small expected anisotropies and meanwhile the relatively large modulations
of observed counting rates due to experimental effects. In this paper, we
present a procedure based on the shuffling technique to carry out these
measurements, applicable to any cosmic ray detector without any additional
corrections for the observed counting rates.",1305.5401v1
2013-06-21,Specific Heat and Upper Critical Field of Sc5Ir4Si10 Superconductor,"Temperature and magnetic field dependent specific heat of textured Sc5Ir4Si10
superconductor was investigated in detail. Based on the fitting of zero-field
electronic specific heat by different gap structures as well as the discussion
on field-induced specific heat coefficient, Sc5Ir4Si10 is proved to be an
anisotropic s-wave superconductor with a gap anisotropy of 0.53. The anisotropy
of upper critical field suggests the weakly one-dimensional Fermi surface, and
the value is consistent with the gap anisotropy result obtained from the
specific heat data.",1306.5027v1
2013-07-12,Non-Stationary Measurements of Chiral Magnetic Effect,"We discuss Chiral Magnetic Effect from quantum theory of measurements point
of view for non-stationary measurements. The effect of anisotropy for
fluctuations of electric currents in magnetic field is addressed. It is shown
that anisotropy caused by nonzero axial chemical potential is indistinguishable
in this framework from anisotropy caused by finite measurement time or finite
lifetime of the magnetic field, and in all cases it is related to abelian
triangle anomaly. Possible P-odd effects for central heavy ions collisions
(where Chiral Magnetic Effect is absent) are discussed in this context.",1307.3444v1
2013-09-11,Non compound nucleus fission events and standard saddle-point statistical model,"The large body of experimental data on the fission fragments anisotropies are
analyzed in several heavy-ion induced fission reaction systems. The entrance
channel mass asymmetry parameters of these systems put on the both sides of the
Businaro-Gallone mass asymmetry parameters. The role of the mass numbers of the
projectile and the target in the prediction of a normal or an anomalous
behavior in angular anisotropy, as well as the validity of standard
saddle-point statistical model are considered. The average contribution of non
compound nucleus fission for the systems with an anomalous behavior in
anisotropy are also determined. PACS numbers: 25.70.Jj *Corresponding author:
s.soheyli@basu.ac.ir",1309.2738v1
2013-09-11,Geometry of Compressible and Incompressible Quantum Hall States: Application to Anisotropic Composite Fermion Liquids,"Haldane's geometrical description of fractional quantum Hall states is
generalized to compressible states. It is shown that anisotropy in the
composite fermion Fermi surface is a direct reflection of this intrinsic
geometry. A simple model is introduced in which the geometric parameter can be
obtained exactly from other parameters including electron mass anisotropy. Our
results compare favorably with recent measurements of anisotropy in composite
fermion Fermi surface [D. Kamburov, Y. Liu, M. Shayegan, L. N. Pfeiffer, K. W.
West, and K. W. Baldwin, Phys. Rev. Lett. 110, 206801 (2013)]. Broader
implications of our results are discussed.",1309.2830v2
2013-09-12,Structural control of magnetic anisotropy in a strain driven multiferroic EuTiO3 thin film,"Octahedral distortion plays a key role in engineering the physical properties
of heterostructures composed of perovskite oxides. We observe a strong in-plane
uniaxial magnetic anisotropy in a strain-enabled multiferroic EuTiO3 thin film
epitaxially grown on a (110)o DyScO3 substrate. First principles calculations
show that the magnetic anisotropy is closely correlated with the uniaxial TiO6
octahedral tilting and the ferroelectric polarization of the film, indicating
potential strong magnetoelectric coupling in the strain-engineered multiferroic
system.",1309.3185v1
2013-11-27,Effects of Surface Anisotropy on Magnetic Vortex Core,"The vortex core shape in the three dimensional Heisenberg magnet is
essentially influenced by a surface anisotropy. We predict that depending of
the surface anisotropy type there appears barrel- or pillow-shaped deformation
of the vortex core along the magnet thickness. Our theoretical study is well
confirmed by spin-lattice simulations.",1311.6882v1
2014-01-06,Anisotropic Hydrodynamics: Motivation and Methodology,"In this proceedings contribution I review recent progress in our
understanding of the bulk dynamics of relativistic systems that possess
potentially large local rest frame momentum-space anisotropies. In order to
deal with these momentum-space anisotropies, a reorganization of relativistic
viscous hydrodynamics can been made around an anisotropic background, and the
resulting dynamical framework has been dubbed ""anisotropic hydrodynamics."" I
also discuss expectations for the degree of momentum-space anisotropy of the
quark gluon plasma generated in relativistic heavy ion collisions at RHIC and
LHC from second-order viscous hydrodynamics, strong-coupling approaches, and
weak-coupling approaches.",1401.1188v1
2014-01-25,A holographic superconductor model in a spatially anisotropic background,"We investigate an anisotropic model of superconductors in the
Einstein-Maxwell-dilaton theory with a charged scalar field. It is found that
the critical temperature decreases as the anisotropy becomes large. We then
estimate the energy gap of the superconductor, and find that the ratio of the
energy gap to the critical temperature increases as the anisotropy increases
and so it is larger than that in the isotropic case. We also find that peudogap
appears due to the anisotropy.",1401.6501v3
2014-02-24,Compensation of anisotropy effects in the generation of two-photon light,"We analyse a method to compensate for anisotropy effects in the spatial
distribution of parametric down-conversion (PDC) radiation in bulk crystals. In
this method, a single nonlinear crystal is replaced by two consecutive crystals
with opposite transverse walk-off directions. We implement a simple numerical
model to calculate the spatial distribution of intensity and correlations, as
well as the Schmidt mode structure, with an account for the anisotropy.
Experimental results are presented which prove the validity of both the model
and the method.",1402.5888v1
2014-08-27,Anderson Localization of Matter Waves in 3D Anisotropic Disordered Potentials,"Using a cutoff-free formulation of the coherent transport theory, we show
that the interference terms at the origin of localization strongly affect the
transport anisotropy. In contrast to the common hypothesis, we then find that
the anisotropies of incoherent and coherent diffusion are significantly
different, in particular at criticality. There, we show that the coherent
transport anisotropy is mainly determined by the properties of the
disorder-averaged effective scattering medium while the incoherent transport
contributions become irrelevant.",1408.6387v2
2014-10-05,Models for Quark Stars with Charged Anisotropic Matter,"In this paper, we found new exact solutions to the Einstein- Maxwell system
of equations within the framework of MIT Bag Model considering a particular
form for the measure of anisotropy and a gravitational potential which depends
on an adjustable parameter {\alpha}. Variables as the energy density, radial
pressure, tangential pressure, electric field intensity and the metric
functions are written in terms of elementary and polinominal functions. We show
that the form chosen for the gravitational potential and the anisotropy allows
obtain physically acceptable solutions with any value of the adjustable
parameter.",1410.1524v1
2014-10-26,"Drag force in strongly coupled, anisotropic plasma at finite chemical potential","We employ methods of gauge/string duality to analyze the drag force on a
heavy quark moving through a strongly coupled, anisotropic \mathcal{N}=4, SU(N)
super Yang- Mills plasma in the presence of a finite U(1) chemical potential.
We present numerical results valid for any value of the anisotropy parameter
and the U(1) charge density and arbitrary direction of the quark velocity with
respect to the direction of anisotropy. In the small anisotropy limit we are
also able to furnish analytical results.",1410.7040v1
2014-11-30,Spin dynamics of the anisotropic spin-1 antiferromagnetic chain at finite magnetic fields,"We present results of a study of the antiferromagnetic spin-1 chain, subject
to the simultaneous presence of single-ion anisotropy and external magnetic
fields. Using quantum Monte-Carlo based on the stochastic series expansion
method we first uncover a rich quantum phase diagram comprising N\'eel,
Haldane, Luttinger liquid, and large anisotropy phases. Second, we scan across
this phase diagram over a wide range of parameters, evaluating the transverse
dynamic structure factor, which we show to exhibit sharp massive modes, as well
as multi particle continua. For vanishing anisotropy and fields, comparison
with existing results from other analytic and numerical approaches shows
convincing consistency.",1412.0208v2
2014-12-11,Possible origin of nonlinear magnetic anisotropy variation in electric field effect in a double interface system,"We investigated the effect of an electric field on the interface magnetic
anisotropy of a thin MgO/Fe/MgO layer using density functional theory. The
perpendicular magnetic anisotropy energy (MAE) increases not only under
electron depletion but also under some electron accumulation conditions,
showing a strong correlation with the number of electrons on the interface Fe
atom. The reverse variation in the MAE under the electric field is ascribed to
novel features on the charged interface, such as electron leakage. We discuss
the origin of the variation in terms of the electronic structures.",1412.3577v1
2015-01-08,Theoretical evaluation on the temperature dependence of magnetic anisotropy constants of Nd2Fe14B - Effects of exchange field and crystal field strength -,"To identify the possible mechanism of coercivity (Hc) degradation of Nd-Fe-B
sintered magnets, we study the roles of the exchange field acting on the 4f
electrons in Nd ions and theoretically investigate how the variation of the
exchange field affects the values of the magnetic anisotropy constants K1 and
K2. We find that, with decreasing exchange field strength, both values decrease
as a result of the lower asphericity of the 4f electron cloud, indicating that
the local anisotropy constants might become small around the grain boundaries
where the exchange fields are decreased owing to the smaller coordination
number.",1501.01782v1
2015-03-04,Geodesic Acoustic Mode in Toroidally Rotating Anisotropic Tokamaks,"Effects of anisotropy on the geodesic acoustic mode (GAM) is analyzed by
using gyro-kinetic equations applicable to low-frequency microinstabilities in
a toroidally rotating tokamak plasma. Dispersion relation in the presence of
arbitrary Mach number $M$, anisotropy strength $\sigma$, and the temperature
ration $\tau$ is analytically derived. It is shown that when $\sigma$ is less
than $ 3 + 2 \tau$, the increased electron temperature with fixed ion parallel
temperature increases the normalized GAM frequency. When $\sigma$ is larger
than $ 3 + 2 \tau$, the increasing of electron temperature decreases the GAM
frequency. The anisotropy $\sigma$ always tends to enlarge the GAM frequency.
The Landau damping rate is dramatically decreased by the increasing $\tau$ or
$\sigma$.",1503.01315v1
2015-05-20,Ultra-directional super-scattering of homogenous spherical particles with radial anisotropy,"We study the light scattering of homogenous radially-anisotropic spherical
particles. It is shown that radial anisotropy can be employed to tune
effectively the electric resonances, and thus enable flexible overlapping of
electric and magnetic dipoles of various numbers, which leads to unidirectional
forward super-scattering at different spectral positions. We further reveal
that through adjusting the radial anisotropy parameters, electric and magnetic
resonances of higher orders can be also made overlapped, thus further
collimating the forward scattering lobes. The ultra-directional
super-scattering we have obtained with individual homogenous radially
anisotropic spherical particles may shed new light to the design of compact and
efficient nanoantennas, which may find various applications in solar cells,
bio-sensing and many other antenna based researches.",1505.05340v1
2015-12-07,Power spectrum of flow fluctuations in relativistic heavy-ion collisions,"We carry out hydrodynamical simulation of the evolution of fluid in
relativistic heavy-ion collisions with random initial fluctuations. The time
evolution of power spectrum of momentum anisotropies shows very strong
correspondence with the physics of cosmic microwave anisotropies as was earlier
predicted by some of us. In particular our results demonstrate suppression of
superhorizon fluctuations and the correspondence between the location of the
first peak in the power spectrum of momentum anisotropies and the length scale
of fluctuations and expected freezeout time scale (more precisely, the sound
horizon size at freezeout).",1512.02136v1
2015-12-08,Anisotropic Inflation with General Potentials,"Anomalies in recent observational data indicate that there might be some
""anisotropic hair"" generated in an inflation period. To obtain general
information about the effects of this anisotropic hair to inflation models, we
studied anisotropic inflation models that involve one vector and one scalar
using several types of potentials. We determined the general relationship
between the degree of anisotropy and the fraction of the vector and scalar
fields, and concluded that the anisotropies behave independently of the
potentials. We also generalized our study to the case of multi-directional
anisotropies.",1512.02316v1
2015-12-09,Pressure anisotropy generation in a magnetized plasma configuration with a shear flow velocity,"The nonlinear evolution of the Kelvin Helmholtz instability in a magnetized
plasma with a perpendicular flow close to, or in, the supermagnetosonic regime
can produce a significant parallel-to-perpendicular pressure anisotropy. This
anisotropy, localized inside the flow shear region, can make the configuration
unstable either to the mirror or to the firehose instability and, in general,
can affect the development of the KHI. The interface between the solar wind and
the Earth's magnetospheric plasma at the magnetospheric equatorial flanks
provides a relevant setting for the development of this complex nonlinear
dynamics.",1512.02917v1
2016-02-29,Anisotropic thermal expansion of bismuth from first principles,"Some anisotropy in both mechanical and thermodynamical properties of bismuth
is expected. A combination of density functional theory total energy
calculations and density functional perturbation theory in the local density
approximation is used to compute the elastic constants at 0 K using a finite
strain approach and the thermal expansion tensor in the quasiharmonic
approximation. The overall agreement with experiment is good. Furthermore, the
anisotropy in the thermal expansion is found to arise from the anisotropy in
both the directional compressibilities and the directional Gr\""uneisen
functions.",1602.08959v1
2016-03-10,"The anisotropy induced by defects of ""random local field"" type in O(n) models and suppression of the Imry-Ma inhomogeneous state","We demonstrate that in the system with anisotropic distribution of the
defect-induced random local field directions in the n-dimensional space of
vector order parameter with the O(n) symmetry, the defect-induced effective
anisotropy arises for the space dimensionality 2<d<4. If the anisotropy
constant exceeds the threshold value, then an inhomogeneous state predicted by
Imry and Ma becomes energetically unfavorable, and the system goes back to the
state with the long-range order.",1603.03360v1
2016-03-13,Perpendicular magnetic anisotropy in Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si,"We report perpendicular magnetic anisotropy (PMA) in the half-metallic
ferromagnetic Heusler alloy Co$_2$Fe$_{0.4}$Mn$_{0.6}$Si (CFMS) in a
MgO/CFMS/Pd trilayer stack. PMA is found for CFMS thicknesses between 1 and 2
nm, with a magnetic anisotropy energy density of $K_U = 1.5\times 10^6$
erg/cm$^3$ for t$_{\tiny \textrm{CFMS}} = 1.5$ nm. Both the MgO and Pd layer
are necessary to induce the PMA. We measure a tunable anomalous Hall effect,
where its sign and magnitude vary with both the CFMS and Pd thickness.",1603.04072v1
2016-04-12,Magnetization distribution and domain wall dynamics in nanotube with surface anisotropy,"The period of magnetization oscillations that occur near the surface of a
nanotube or nanowire under the influence of surface magnetic anisotropy is
determined by means of numerical simulation as a function of nanowire geometry
and material parameters. The hopping mode is observed for stationary movement
of a head-to-head domain wall along nanowire axis in applied magnetic field.
The average speed of the domain wall in the hopping mode is found to be several
times less than the stationary velocity of the wall in the absence of surface
anisotropy.",1604.03523v1
2016-04-14,A comparison of functional summary statistics to detect anisotropy of three-dimensional point patterns,"The growing availability of three-dimensional point process data asks for a
development of suitable analysis techniques. In this paper, we focus on two
recently developed summary statistics, the conical and the cylindrical
$K$-function, which may be used to detect anisotropies in 3D point patterns. We
give some recommendations on choosing their arguments and investigate their
ability to detect two special types of anisotropy. Finally, both functions are
compared on some real data sets from neuroscience and glaciology.",1604.04211v1
2016-04-16,Beyond the upper limit of magnetic anisotropy in two-dimensional transition metal dichalcogenides,"Exploring an upper limit of magnetic anisotropy in two-dimensional materials,
such as graphene and transition metal dichalcogenides, is at the heart of
spintronics research. Herein, an atomic-scale perpendicular magnetic anisotropy
up to an order of 100 meV per atom, which is far beyond the ordinarily obtained
value in graphene and pristine transition metal dichalcogenides, is
demonstrated in individual ruthenium and osmium adatoms at a monosulfur vacancy
in molybdenum disulfide. We further propose a phenomenological model where a
spin state transition that involves hybridization between molybdenum a1 and
adatomic e' orbitals is a possible mechanism for magnetization reorientation.",1604.04708v1
2016-04-19,Multichannel Scattering and Loss Processes of Ultracold Atoms in Anisotropic Harmonic Waveguides,"We have developed the general grid method for multi-channel scattering of
bosonic atoms inside a harmonic waveguide with transverse anisotropy. This
approach is employed to analyze elastic as well as inelastic multi-channel
confined scattering. For the elastic scattering, the effects of the range and
form of interatomic potential and the waveguide anisotropy on the confinement
induced resonance are studied. We have also investigated quantitatively the
reactive rate constant in confined atom-atom collisions. It is found that a
slight anisotropy to the confining trap considerably enhances the reactive rate
constant in multi-channel regime.",1604.05457v2
2016-05-20,Interlayer interaction in multilayer CoPt/Co structures,"We report a study of interlayer exchange interaction in multilayer CoPt/Co
structures consisting of periodic CoPt multilayer film with an ""easy axis""
anisotropy and thick Co layer with an ""easy plane"" anisotropy separated by Pt
spacer with variable thickness. The magnetooptical Kerr effect (MOKE) and
ferromagnetic resonance (FMR) measurements show up the essentially
non-collinear state of magnetic moments of the layers and strong exchange
coupling between CoPt and Co subsystems. The estimation of effective anisotropy
and exchange coupling in a simple model based on the Landau-Lifshitz-Gilbert
equation describing magnetization dynamics was performed.",1605.06468v1
2016-06-09,Spacetime anisotropy affects cosmological entanglement,"Most existing cosmological entanglement studies are focused on the isotropic
Robertson-Walker (RW) spacetime. Here we go beyond this limitation and study
the influence of anisotropy on entanglement generated by dynamical spacetime.
Since the isotropic spacetime is viewed as a background medium and the
anisotropy is incorporated as perturbation, we decompose entanglement entropy
into isotropic and anisotropic contributions. The latter is shown to be
non-negligible by analyzing two cosmological models with weak and conformal
coupling. We also show the possibility of using entanglement to infer about
universe features.",1606.03005v1
2016-06-10,Self-induced glassiness and pattern formation in spin systems subject to long-range interactions,"We study the glass formation in two- and three-dimensional Ising and
Heisenberg spin systems subject to competing interactions and uniaxial
anisotropy with a mean-field approach. In three dimensions, for sufficiently
strong anisotropy the systems always modulates in a striped phase. Below a
critical strength of the anisotropy, a glassy phase exists in a finite range of
temperature, and it becomes more stable as the system becomes more isotropic.
In two dimension the criticality is always avoided and the glassy phase always
exists.",1606.03458v1
2016-06-30,"Helicity, anisotropies and their competition in a multiferroic magnet: insight from the phase diagram","Motivated by the complex phase diagram of MnWO4, we investigate competition
between anisotropy, magnetic field, and helicity for the anisotropic
next-nearest-neighbor Heisenberg model. Apart from two competing exchanges,
which favor a spiral magnetic structure, the model features the bi-axial
single-ion anisotropy. The model is treated in the real-space mean-field
approximation and the phase diagram containing various incommensurate and
commensurate states is obtained for different field orientations. We discuss
similarities and differences of the theoretical phase diagram and the
experimental diagram of MnWO4.",1606.09381v2
2016-08-25,Thermodynamic Measurement of Angular Anisotropy at the Hidden Order Transition of URu$_2$Si$_2$,"The heavy fermion compound URu$_2$Si$_2$ continues to attract great interest
due to the unidentified hidden order it develops below 17.5K. The unique Ising
character of the spin fluctuations and low temperature quasiparticles is well
established. We present detailed measurements of the angular anisotropy of the
nonlinear magnetization that reveal a $\cos^4 \theta$ Ising anisotropy both at
and above the ordering transition. With Landau theory, we show this implies a
strongly Ising character of the itinerant hidden order parameter.",1608.07009v1
2016-09-09,Probing pre-inflationary anisotropy with directional variations in the gravitational wave background,"We perform a detailed analysis on a primordial gravitational-wave background
amplified during a Kasner-like pre-inflationary phase allowing for general
triaxial anisotropies. It is found that the predicted angular distribution map
of gravitational-wave intensity on large scales exhibits topologically
distinctive patterns according to the degree of the pre-inflationary
anisotropy, thereby serving as a potential probe for the pre-inflationary early
universe with future all-sky observations of gravitational waves. We also
derive an observational limit on the amplitude of such anisotropic
gravitational waves from the B-mode polarisation of the cosmic microwave
background.",1609.02785v1
2016-09-21,Mobility anisotropy of two-dimensional semiconductors,"The carrier mobility of anisotropic two-dimensional (2D) semiconductors under
longitudinal acoustic (LA) phonon scattering was theoretically studied with the
deformation potential theory. Based on Boltzmann equation with relaxation time
approximation, an analytic formula of intrinsic anisotropic mobility was
deduced, which shows that the influence of effective mass to the mobility
anisotropy is larger than that of deformation potential constant and elastic
modulus. Parameters were collected for various anisotropic 2D materials (black
phosphorus, Hittorf's phosphorus, BC$_2$N, MXene, TiS$_3$, GeCH$_3$) to
calculate their mobility anisotropy. It was revealed that the anisotropic ratio
was overestimated in the past.",1609.06416v1
2016-10-26,Classical spin liquid instability driven by off-diagonal exchange in strong spin-orbit magnets,"We show that the off-diagonal exchange anisotropy drives Mott insulators with
strong spin-orbit coupling to a classical spin liquid regime, characterized by
an infinite number of ground states and Ising variables living on closed or
open strings. Depending on the sign of the anisotropy, quantum fluctuations
either fail to lift the degeneracy down to very low temperatures, or select
non-collinear magnetic states with unconventional spin correlations. The
results apply to all 2D and 3D tri-coordinated materials with bond-directional
anisotropy, and provide a consistent interpretation of the suppression of the
x-ray magnetic circular dichroism signal reported recently for
$\beta$-Li$_2$IrO$_3$ under pressure.",1610.08463v1
2016-11-16,Perpendicular magnetic anisotropy in Co$_2$MnGa,"We report perpendicular magnetic anisotropy in the ferromagnetic Heusler
alloy Co$_2$MnGa in a MgO/Co$_2$MnGa/Pd trilayer stack for Co$_2$MnGa
thicknesses up to 3.5 nm. There is a thickness- and temperature-dependent spin
reorientation transition from perpendicular to in-plane magnetic anisotropy
which we study through the anomalous Hall effect. From the temperature
dependence of the anomalous Hall effect, we observe the expected scaling of
$\rho_{xy}^{AHE}$ with $\rho_{xx}$, suggesting the intrinsic and side-jump
mechanisms are largely responsible for the anomalous Hall effect in this
material.",1611.05110v1
2016-12-28,Search for Cosmic Ray Anisotropy with the Alpha Magnetic Spectrometer on the International Space Station,"The search for cosmic ray anisotropy has been performed using particles
collected by the Alpha Magnetic Spectrometer after the first five years of
operation. The positron to electron ratio is consistent with isotropy at all
energies and angular scales. The limit on the dipole anisotropy at the 95%
confidence level for energies above 16GeV is $\delta<0.020$ for positrons and
$\delta<0.006$ for electrons. In the case of high rigidity protons the upper
limit in the rigidity range from 80 to 1800GV is $\delta<0.003$. No indication
of seasonal excess is observed for all particle species within the present
statistics.",1612.08957v1
2017-01-31,Effect of radiation-like solid on small-scale CMB anisotropies,"We compute the CMB angular power spectrum in the presence of a radiation-like
solid - elastic matter with the same pressure to energy density ratio as
radiation but with nonzero shear modulus. For the values of shear modulus that
are close enough to zero, so that the effect of the solid on large-scale
anisotropies remains within cosmic variance, we find that there is an
observable effect of the solid on small-scale anisotropies.",1701.09061v2
2017-02-06,Polarimetric analysis of stress anisotropy in nanomechanical silicon nitride resonators,"We realise a circular gray-field polariscope to image stress-induced
birefringence in thin (submicron thick) silicon nitride (SiN) membranes and
strings. This enables quantitative mapping of the orientation of principal
stresses and stress anisotropy, complementary to, and in agreement with, finite
element modeling (FEM). Furthermore, using a sample with a well known stress
anisotropy, we extract a new value for the photoelastic (Brewster) coefficient
of silicon nitride, $C \approx (3.4~\pm~0.1)\times~10^{-6}~\mathrm{MPa}^{-1}$.
We explore possible applications of the method to analyse and quality-control
stressed membranes with phononic crystal patterns",1702.01732v1
2017-04-14,Structure of virtual photon polarization in ultrarelativistic heavy-ion collisions,"Anisotropy in heavy-ion collisions leads to polarization of both direct and
virtual photons, the latter detected via internal conversion to dileptons
pairs. Thus measurement of photon polarization probes the anisotropy at all
stages of collisions. In order to characterize the polarization of virtual
photons, we derive here the general structure of the photon polarization
operator, rho^(mu nu), in an anisotropic medium, in terms of the four spectral
functions, two transverse and one longitudinal, as usual, plus a new spectral
function that reflects anisotropy in asymmetric collisions; and derive the
local production rate of dilepton pairs in terms of these four functions.",1704.04526v1
2017-06-05,Study of the one-way speed of light anisotropy with particle beams,"Concepts of high precision studies of the one-way speed of light anisotropy
are discussed. The high energy particle beam allows measurement of a one-way
speed of light anisotropy (SOLA) via analysis of the beam momentum variation
with sidereal phase without the use of synchronized clocks. High precision beam
position monitors could provide accurate monitoring of the beam orbit and
determination of the particle beam momentum with relative accuracy on the level
of $10^{-10}$, which corresponds to a limit on SOLA of $10^{-18}$ with existing
storage rings. A few additional versions of the experiment are also presented.",1706.01267v1
2017-07-19,The fully kinetic Biermann battery and associated generation of pressure anisotropy,"The dynamical evolution of a fully kinetic, collisionless system with imposed
background density and temperature gradients is investigated analytically. The
temperature gradient leads to the generation of temperature anisotropy, with
the temperature along the gradient becoming larger than that in the direction
perpendicular to it. This causes the system to become unstable to pressure
anisotropy driven instabilities, dominantly to electron Weibel. When both
density and temperature gradients are present and non-parallel to each other,
we obtain a Biermann-like linear in time magnetic field growth. Accompanying
particle in cell numerical simulations are shown to confirm our analytical
results.",1707.06069v1
2017-08-05,Phase field modelling of precipitate morphologies in systems with tetragonal interfacial free energy anisotropy,"A wide variety of morphologies arise due to the tetragonal anisotropy in
interfacial free energy. In this paper, we report on a family of Extended
Cahn-Hilliard (ECH) models for incorporating tetragonal anisotropy in
interfacial free energy. We list the non-zero and independent parameters that
are introduced in our model and list the constraints on them. For appropriate
choice of these parameters, our model can produce a many of the morphologies
seen in tetragonal systems such as di-pyramids, rods, plates and their
truncated variants. We analyse these morphologies and show that they indeed are
equilibrium morphologies consistent with the Wulff construction.",1708.01712v1
2017-09-25,Dynamics of elastically strained islands in presence of an anisotropic surface energy,"The equilibrium solutions and coarsening dynamics of strained semi-conductor
islands are investigated analytically and numerically. We develop an analytical
model to study the effect of surface energy anisotropy on the dynamics
coarsening of islands. We propose a simple model to explain the effect of this
anisotropy on the coarsening time. We find that the anisotropy slows down the
coarsening. This effect is rationalised using a quasi-analytical description of
the island profile.",1709.08570v1
2017-10-30,Tunneling Devices with Perpendicular Magnetic Anisotropy Electrodes on Atomically Thin van der Waals Heterostructures,"We report the fabrication of perpendicular ferromagnetic electrodes for
tunneling devices consist of van der Waals heterostructure. We found MgO/Co/Pt
films on Hexagonal BN shows perpendicular magnetic anisotropy (PMA) with the
easy axis perpendicular to the substrate. Vacuum annealing enhances the
perpendicular anisotropy. The easy axis along the perpendicular direction
persists up to room temperature with the Pt layer thickness ranges from 1.5 to
5 nm. We employed the PMA electrodes to construct tunneling devices on graphene
and monolayer WSe2, where spin injection characteristics and field effect
transistor behavior were demonstrated without strong Schottky barrier
formation.",1710.10743v1
2017-12-15,Effect of the Canting of Local Anisotropy Axes on Ground-State Properties of a Ferrimagnetic Chain with Regularly Alternating Ising and Heisenberg Spins,"The effect of the canting of local anisotropy axes on the ground-state phase
diagram and magnetization of a ferrimagnetic chain with regularly alternating
Ising and Heisenberg spins is exactly examined in an arbitrarily oriented
magnetic field. It is shown that individual contributions of Ising and
Heisenberg spins to the total magnetization basically depend on the spatial
orientation of the magnetic field and the canting angle between two different
local anisotropy axes of the Ising spins.",1712.05622v1
2018-02-13,Integrable Toda system as a quantum approximation to the anisotropy of Mixmaster,"We present a regularisation approach to the study of the quantum dynamics of
the Mixmaster universe which allows to approximate the anisotropy potential
with the explicitly integrable periodic 3-particle Toda system. This approach
is based on a covariant Weyl-Heisenberg integral quantization. Such a procedure
naturally amplifies the dynamical role of the underlying Toda system by
smoothing out the three canyons of the anisotropy potential. Since the
respective eigenfunctions can be explicitly constructed, our finding paves the
way to a novel perturbative approach to the quantum Mixmaster dynamics.",1802.04662v2
2018-07-26,Are 10 EeV cosmic rays extragalactic? Theory of cosmic ray diffusion at high energy,"Auger Collaboration has reported a large-scale anisotropy in the arrival
directions of cosmic rays above 8 EeV. The dipole direction, at 125$^\circ$
from the Galactic center, is taken as an indication of an extragalactic origin
of these cosmic rays. We show, both theoretically and by direct numerical
simulations, that this is not necessarily true. Intermediate mass nuclei
originating in the Galaxy and diffusing in the Galactic magnetic field can have
a dipole anisotropy pointing away from the Galactic center. Our theory predicts
a quadrupole anisotropy of the same order of magnitude as the dipole.",1808.00041v1
2018-08-24,Hunting for Statistical Anisotropy in Tensor Modes with B-mode Observations,"We investigate a possibility of constraining statistical anisotropies of the
primordial tensor perturbations by using future observations for the Cosmic
Microwave Background (CMB) B-mode polarization. By parameterizing a
statistically-anisotropic tensor power spectrum as $P_h ({\boldsymbol{k}}) =
P_h (k) \sum_n g_n \cos^n \theta_{\boldsymbol{k}}$, where
$\theta_{\boldsymbol{k}}$ is an angle of the direction of
$\hat{k}={\boldsymbol{k}}/k$ from a preferred direction, we find that it would
be possible for future B-mode observations such as CMB-S4 to detect the tensor
statistical anisotropy at the level of $g_n \sim {\mathcal O} (0.1)$.",1808.08044v1
2018-09-05,Spiral plane flops in frustrated helimagnets in external magnetic field,"We discuss theoretically frustrated Heisenberg spiral magnets in magnetic
field $\bf H$. We demonstrate that small anisotropic spin interactions
(single-ion biaxial anisotropy or dipolar forces) select the plane in which
spins rotate (spiral plane) and can lead to the spiral plane flop upon in-plane
field increasing. Expressions for the critical fields $H_{flop}$ are derived.
It is shown that measuring of $H_{flop}$ is an efficient and simple method of
quantifying the anisotropy in the system (as the measurement of spin-flop
fields in collinear magnets with axial anisotropy). Corresponding recent
experiments are considered in spiral magnets some of which are multiferroics of
spin origin.",1809.01680v1
2018-11-02,New magnetic states in nanorings created by anisotropy gradients,"Magnetic nanorings have been widely studied due to their potential
applications in spintronic and magnonic devices. In this work, by means of
analytical calculations and micromagnetic simulations we have analyzed the
magnetic energy of nanorings with variable anisotropy along their radius. Four
magnetic states, including two new magnetic configurations, here called meron
and knot-like states, are considered, looking to the relative lower energy
states as a function of anisotropy. Phase diagrams with this states are
presented.",1811.01069v1
2018-11-06,Anisotropic diffusion and the cosmic ray anisotropy,"We argue that the diffusion of cosmic rays in the Galactic magnetic field has
to be strongly anisotropic. As a result, the number of CR sources contributing
to the local CR flux is reduced by a factor $\sim 200$. The CR density is
therefore less smooth, and the contribution of individual sources to the CR
dipole anisotropy becomes more prominent. In the case of anisotropic diffusion,
the observed plateau in the CR dipole anisotropy around 2-20 TeV can be
explained by a 2-3 Myr old CR source which dominates the local CR flux in this
energy range.",1811.02419v1
2018-11-20,The Dipole Anisotropy of Galactic Cosmic Rays,"The arrival directions of Galactic cosmic rays exhibit anisotropies up to the
level of one per-mille over various angular scales. Recent observations of
TeV-PeV cosmic rays show that the dipole anisotropy has a strong energy
dependence with a phase-flip around 100 TeV. We argue that this behavior can be
well understood by the combination of various effects: the anisotropic
diffusion of cosmic rays, the presence of nearby sources, the Compton-Getting
effect from our relative motion and the reconstruction bias of ground-based
observatories.",1811.08136v1
2018-11-30,Giant superconducting proximity effect on spintronic anisotropy,"We investigate theoretically the interplay of proximity effects due to the
presence of a superconductor and normal ferromagnetic leads on the formation of
the spintronic quadrupolar exchange field in a large-spin molecule. We show
that the spintronic anisotropy can be enhanced by a few orders of magnitude,
and tuned by changing the strength of coupling to the superconductor.
Especially large anisotropy is generated in the vicinity of the charge parity
changing transition of the molecule. We also provide predictions of measurable
spectral properties being the hallmarks of these phenomena.",1811.12733v2
2018-12-17,Symmetry and polarity of the voltage-controlled magnetic anisotropy studied by the Anomalous Hall effect,"The voltage-controlled magnetic anisotropy (VCMA) effect in FeB and FeB/W
films was measured by four independent methods. All measurements are consistent
and show the same tendency. The coercive field, Hall angle, anisotropy field,
the magnetization switching time and retention time linearly decrease when the
gate voltage increases and they linearly increase when the gate voltage
decreases.",1812.07077v1
2019-01-01,Puzzles of the cosmic ray anisotropy,"We discuss three of the known puzzles of the cosmic ray anisotropy in the PeV
and sub-PeV energy region. They are: (1) the so called inverse anisotropy, (2)
the irregularity in the energy dependence of the amplitude and phase of the
first harmonic and (3) the contribution of the single source.",1901.00160v4
2019-01-24,Weak Lensing Effect on CMB in the Presence of a Dipole Anisotropy,"We investigate weak lensing effect on cosmic microwave background (CMB) in
the presence of dipole anisotropy. The approach of flat-sky approximation is
considered. We determine the functions $\sigma_0^2$ and $\sigma_2^2$ that
appear in expressions of the lensed CMB power spectrum in the presence of a
dipole anisotropy. We determine the correction to B-mode power spectrum which
is found to be appreciable at low multipoles ($l$). However, the temperature
and E-mode power spectrum are not altered significantly.",1901.08595v1
2019-06-24,On relations of anisotropy and linear inhomogeneity using Backus average,"The anisotropy of an equivalent medium resulting from the Backus (1962)
average is induced by the vertical inhomogeneity among its constituent layers.
The velocity field of the constituent isotropic layers increases linearly with
depth, which is assumed to be a good seismological description of sedimentary
layers Slotnick (1959). We derive an analytical relationship between the
anisotropy, characterized by the Thomsen (1986) parameters, and the linear
inhomogeneity parameters, which forms a system of three equations for nine
unknowns. To obtain well-posedness, we constrain the problem by considering two
seismological methods applied to field data. We use the results from the two
methods, for a particular region of interest, to assess the validity of the
analytical relation.",1906.10196v1
2019-08-30,Turbulence in a stably stratified fluid: Onset of global anisotropy as a function of the Richardson number,"It is necessary to introduce an external forcing to induce turbulence in a
stably stratified fluid. The Heisenberg eddy viscosity technique should in this
case suffice to calculate a space-time averaged quantity like the global
anisotropy parameter as a function of the Richardson number. We find
analytically that the anisotropy increases linearly with the Richardson number,
with a small quadratic correction. A numerical simulation of the complete
equations shows the linear behaviour.",1908.11767v1
2019-11-12,On the future of solutions to the massless Einstein-Vlasov system in a Bianchi I cosmology,"We show that massless solutions to the Einstein-Vlasov system in a Bianchi I
space-time with small anisotropy, i.e. small shear and small trace-free part of
the spatial energy momentum tensor, tend to a radiation fluid in an Einstein-de
Sitter space-time with the anisotropy $\Sigma^a_b\Sigma^b_a$ and $\tilde{w}^i_j
\tilde{w}^j_i$ decaying as $O(t^{-\frac12})$.",1911.04937v2
2020-02-05,Spherical harmonic analysis of anisotropies in polarized stochastic gravitational wave background with interferometry experiments,"We study the interferometric observation of intensity and polarization
anisotropies of a stochastic gravitational wave background (SGWB). We show that
the observed correlated data is defined in the group manifold of the
three-dimensional rotation. Explicit correlation between two detectors in the
interferometry experiments such as LIGO-Virgo and KAGRA is constructed in terms
of the Wigner D-functions. Our results may provide a tool for constructing data
pipelines to estimate the power spectra of the SGWB anisotropies.",2002.01606v3
2020-03-27,Substrate Induced Optical Anisotropy in Monolayer MoS$_2$,"In-plane optical anisotropy has been detected from monolayer MoS$_2$ grown on
a-plane (11-20) sapphire substrate in the ultraviolet-visible wavelength range.
Based on the measured optical anisotropy, the energy differences between the
optical transitions polarized along the ordinary and extraordinary directions
of the underlying sapphire substrate have been determined. The results
corroborate comprehensively with the dielectric environment induced
modification on the electronic band structure and exciton binding energy of
monolayer MoS$_2$ predicted recently by first principle calculations. The
output of this study proposes the symmetry as a new degree of freedom for
dielectric engineering of the two-dimensional materials.",2003.12235v1
2020-04-07,Critical behavior of the spin-3/2 Blume Capel quantum model with two random transverse single-ion anisotropies,"Using the approach based on the Bogoliubov inequality for free energy, we
have studied the magnetic properties of the spin-3/2 Blume-Capel quantum model
in the presence of the random transverse single-ion anisotropy (RTSIA). By
analyzis of the phase diagrams in $\tau \times \varphi_{x} $, $m \times
\varphi_{x}$ and $m \times \tau$ plans, we have obtained information about how
the presence of anisotropy affects the properties of the system. We have shown
that the RTSIA is responsible for changing the topology of the phase diagrams,
compared to the pure model, leading to the appearance tricritical point (TCP).",2004.03527v1
2020-06-19,Anisotropic generalization of Vaidya-Tikekar superdense star,"We study superdense relativistic stars with anisotropic matter distributions
with spheroidal spatial hypersurfaces. We propose a methodology to make an
anisotropic generalization of the Vaidya-Tikekar superdense star model. The
anisotropic Einstein field equations can be solved in terms of hypergeometric
functions for our choice of gravitational potential and anisotropy. Particular
parameter choices allow us to generate models of anisotropic stars in terms of
elementary functions. Also, isotropic stars can be generated in the limit of
vanishing anisotropy. In particular, we obtain the well known superdense models
of Tikekar which are isotropic and have specific spheroidal geometries. The
impact of anisotropy on the gross physical behaviour of a compact star is
studied.",2006.12266v1
2020-10-13,Modeling evolution of composition patterns in a binary surface alloy,"Evolution of composition patterns in the annealed, single-crystal surface
alloy film is considered in the presence of the spinodal decomposition, the
compositional stress and the diffusion anisotropy. While the former two effects
contribute to overall phase separation, the anisotropy, correlated with the
surface crystallographic orientation, guides the in-plane formation and
orientation of a pattern. The impacts of the anisotropy parameters on patterns
are systematically computed for [110], [100], and [111]-oriented fcc cubic
alloy surfaces.",2010.06838v1
2021-03-29,Atomistic modelling of frictional anisotropy of palladium nanoparticles on graphene,"This article is a continuation of our previous studies of the frictional
anisotropy of metal nanoparticles on the surface of a graphene substrate for
other temperature conditions. The friction force acting on palladium
nanoparticles on a graphene sheet in various lateral directions is investigated
using classical molecular dynamics modelling. Anisotropy is studied at high
sliding speeds of nanoparticles consisting of 10000 atoms on the surface of
graphene. The effect of incommensurability and short-range order of the contact
surfaces of nanoparticles, as well as the graphene deformation lead to the
absence of an expressed angular dependence of the friction force.",2103.15494v1
2021-05-03,Anisotropy-Exchange Resonance as a Mechanism for Entangled State Switching,"We explore the three-particle spin model of an $S_{1}=\frac{1}{2}$ particle
(e.g. a stationary electron) interacting with two spin-coupled $S_{\text{2,3}}$
particles with exchange coupling and magnetic anisotropy. We find that in the
case of $S_{2,3}=1$ particles, the coupled particle entanglement states can be
prepared, controlled, and read by the $S_{1}$ particle. We also find that for
particular resonance conditions of the magnetic anisotropy strength $D$ and
exchange coupling strength $J$, the entanglement state switching behavior is
maximized and is robust against a range of anisotropic application of the
exchange coupling.",2105.01126v1
2021-09-10,An Efficient High-order Numerical Solver for Diffusion Equations with Strong Anisotropy,"In this paper, we present an interior penalty discontinuous Galerkin finite
element scheme for solving diffusion problems with strong anisotropy arising in
magnetized plasmas for fusion applications. We demonstrate the accuracy
produced by the high-order scheme and develop an efficient preconditioning
technique to solve the corresponding linear system, which is robust to the mesh
size and anisotropy of the problem. Several numerical tests are provided to
validate the accuracy and efficiency of the proposed algorithm.",2109.05085v1
2021-10-05,Jet-temperature anisotropy revealed through high-$p_\perp$ data,"We explore to what extent, and how, high-$p_\perp$ data and predictions
reflect the shape and anisotropy of the QCD medium formed in ultrarelativistic
heavy-ion collisions. To this end, we use our recently developed DREENA-A
framework, which can accommodate any temperature profile within the dynamical
energy loss formalism. We show that the ratio of high-$p_\perp$ $v_2$ and
$(1-R_{AA})$ predictions reaches a well-defined saturation value, which is
directly proportional to the time-averaged anisotropy of the evolving QGP, as
seen by the jets.",2110.02029v2
2022-05-16,Magnetic neutron scattering from spherical nanoparticles with Neel surface anisotropy: Atomistic simulations,"We consider a dilute ensemble of randomly-oriented noninteracting spherical
nanomagnets and investigate its magnetization structure and ensuing
neutron-scattering response by numerically solving the Landau-Lifshitz
equation. Taking into account the isotropic exchange interaction, an external
magnetic field, a uniaxial magnetic anisotropy for the particle core, and in
particular the Neel surface anisotropy, we compute the magnetic small-angle
neutron scattering cross section and pair-distance distribution function from
the obtained equilibrium spin structures. The numerical results are compared to
the well-known analytical expressions for uniformly magnetized particles and
provide guidance to the experimentalist. Moreover, the effect of a
particle-size distribution function is modeled.",2205.07552v1
2022-05-16,Feedback of non-local $d_{xy}$ nematicity on the magnetic anisotropy in FeSe,"We analyze theoretically the magnetic anisotropy in the nematic phase of FeSe
by computing the spin and the orbital susceptibilities from the microscopic
multiorbital model. In particular, we take into account both the $xz/yz$ and
the recently proposed non-local $xy$ nematic ordering and show that the latter
one could play a crucial role in reproducing the experimentally-measured
temperature dependence of the magnetic anisotropy. This provides a direct
fingerprint of the different nematic scenarios on the magnetic properties of
FeSe.",2205.07718v1
2022-06-15,Optimization of the anisotropic Cheeger constant with respect to the anisotropy,"Given an open, bounded set $\Omega$ in $\mathbb{R}^N$, we consider the
minimization of the anisotropic Cheeger constant $h_K(\Omega)$ with respect to
the anisotropy $K$, under a volume constraint on the associated unit ball. In
the planar case, under the assumption that $K$ is a convex, centrally symmetric
body, we prove the existence of a minimizer. Moreover, if $\Omega$ is a ball,
we show that the optimal anisotropy $K$ is not a ball and that, among all
regular polygons, the square provides the minimal value.",2206.07436v2
2022-10-16,On the angular anisotropy of the randomly-averaged magnetic neutron scattering cross section of nanoparticles,"We calculate the magnetic SANS cross section of dilute ensembles of uniformly
magnetized and randomly-oriented Stoner-Wohlfarth particles using the
Landau-Lifshitz equation. The focus of our study is on the angular anisotropy
of the magnetic SANS signal as it can be seen on a two-dimensional
position-sensitive detector. Depending on the symmetry of the magnetic
anisotropy of the particles (e.g. uniaxial, cubic), an anisotropic magnetic
SANS pattern may result, even in the demagnetized state or at the coercive
field. The case of inhomogeneously magnetized particles and the effects of a
particle-size distribution and interparticle correlations are discussed.",2210.08406v1
2022-10-30,Controlling magnetic anisotropy in amplitude expansion of phase field crystal model,"The amplitude expansion for a magnetic phase-field-crystal (magnetic APFC)
model enables a convenient coarse-grained description of crystalline structures
under the influence of magnetic fields. Considering higher-order magnetic
coupling terms, we demonstrate the possibility of tuning the magnetic
anisotropy in these models. This allows for reproducing the easy and hard
direction of magnetization. Such a result can be achieved without increasing
the computational cost, enabling simulations of the manipulation of dislocation
networks and microstructures in ferromagnetic materials. As a demonstration, we
report on the simulation of the shrinkage of a spherical grain with the
magnetic anisotropy of Fe.",2210.16855v1
2022-11-24,Effects of target anisotropy on harmonic measure and mean first-passage time,"In this paper, we investigate the influence of target anisotropy on two
characteristics of diffusion-controlled reactions: harmonic measure density and
mean first-passage time. First, we compute the volume-averaged harmonic measure
density on prolate and oblate spheroidal targets inside a confining domain in
three dimensions. This allows us to quantify the uniformity of this density in
the small target limit. Second, we derive an explicit expression of the mean
first-passage time to such targets and analyze the effect of anisotropy. In
particular, we illustrate the accuracy of the capacitance approximation for
small targets.",2212.00011v2
2023-06-08,Magnetic anisotropy of superconducting transition in S/AF heterostructures with spin-orbit coupling,"The influence of Rashba spin-orbit coupling (SOC) on superconducting
correlations in thin-film superconductor/antiferromagnet (S/AF) structures with
compensated interfaces is studied. A unique effect of anisotropic enhancement
of proximity-induced triplet correlations by the SOC is predicted. It manifests
itself in the anisotropy of the superconducting critical temperature Tc with
respect to orientation of the Neel vector relative to the S/AF interface, which
is opposite to the behaviour of Tc in superconductor/ferromagnet structures. We
show that the anisotropy is controlled by the chemical potential of the
superconductor and, therefore, can be adjusted in (quasi)2D structures.",2306.05055v1
2023-08-14,Probing extreme astrophysical accelerators through neutrino anisotropy,"We present the extent to which anisotropies in the ultrahigh energy neutrino
sky can probe the distribution of extreme astrophysical accelerators in the
universe. In this talk, we discuss the origin of an anisotropic neutrino sky
and show how observers can use this anisotropy to measure the evolution of
ultrahigh energy neutrino sources - and therefore, the sources of ultrahigh
energy cosmic rays - for the very first time.",2308.07211v2
2023-08-30,Neutrino anisotropy as a probe of extreme astrophysical accelerators,"We consider how the cutoff of the ultrahigh energy neutrino spectrum
introduces an effective neutrino horizon, allowing for future neutrino
detectors to measure an anisotropy in neutrino arrival directions driven by the
local large-scale structure. We show that measurement of the level of this
anisotropy along with features of the neutrino spectrum will allow for a
measurement of the evolution of ultrahigh energy neutrino sources, which are
expected to also be the sources of ultrahigh energy cosmic rays.",2308.16225v1
2023-10-03,Analysis of Local Anisotropy Fluctuations in Compact Objects,"Mathematical modeling within the framework of the general theory of
relativity has been used to explain the behavior and structure of massive
objects as neutron stars, quasars, black holes, pulsars and white dwarfs and
requires finding the exact solutions of the Einstein-Maxwell system. In this
paper we study the effects induced by fluctuations of local anisotropy in a new
family of anisotropic solutions depending on a parameter, with a specific value
that provides a radial pressure having the same functional dependence on the
radial coordinate as the Schwarzschild solution. It is shown the effect the
functional dependence on the radial coordinate has in the occurrence of
cracking within the sphere when anisotropy fluctuations are allowed.",2310.01730v1
2023-12-03,Thermally Averaged Magnetic Anisotropy Tensors via Machine Learning Based on Gaussian Moments,"We propose a machine learning method to model molecular tensorial quantities,
namely the magnetic anisotropy tensor, based on the Gaussian-moment
neural-network approach. We demonstrate that the proposed methodology can
achieve an accuracy of 0.3--0.4 cm$^{-1}$ and has excellent generalization
capability for out-of-sample configurations. Moreover, in combination with
machine-learned interatomic potential energies based on Gaussian moments, our
approach can be applied to study the dynamic behavior of magnetic anisotropy
tensors and provide a unique insight into spin-phonon relaxation.",2312.01415v1
2023-12-18,Peculiarities of spin-orbit interaction systematically measured in FeCoB nanomagnets,"This study introduces a method to measure strength of spin-orbit interaction
(SO) in a nanomagnet, investigating fundamental phenomena governing magnetic
anisotropy. The method explores the fundamental property of SO in its linear
proportionality to the external magnetic field, a relationship validated
through experimental observation. Systematic study of SO in FeCoB nanomagnets
reveals distinct SO behaviors in bulk and at an interface, its substantial
disparities in single- and multi-layer nanomagnets, intriguing periodic
oscillations in SO strength, and the systematic relationship between SO
strength, demagnetization field, and magnetic anisotropy based on surface
imperfections. These findings provide crucial insights into diverse spin-orbit
interaction behaviors, crucial for understanding and optimizing magnetic
anisotropy and nanomagnet properties.",2312.11056v1
1993-12-08,Large-Angle Cosmic Microwave Background Anisotropies in an Open Universe,"If the Universe is open, scales larger than the curvature scale may be probed
by large-angle fluctuations in the cosmic microwave background (CMB). We
consider primordial adiabatic perturbations and discuss power spectra that are
power laws in volume, wavelength, and eigenvalue of the Laplace operator. The
resulting large-angle anisotropies of the CMB are computed. The amplitude
generally increases as $\Omega$ is decreased, but decreases as $h$ is
increased. Interestingly enough, for all three ansatzes, anisotropies on
angular scales larger than the curvature scale are suppressed relative to the
anisotropies on scales smaller than the curvature scale. Models with
$0.2<\Omega h<0.3$ appear compatible with CMB fluctuations detected by COBE and
Tenerife and with the amplitude and spectrum of fluctuations of galaxy counts
in galaxy surveys. COBE normalization for these models yields $\sigma_8\simeq
0.5-0.7$. Models with smaller values of $\Omega h$ when normalized to COBE
require bias factors in excess of 2 to be compatible with the observed galaxy
counts on the $8/h$ Mpc scale. Requiring that the age of the universe exceed 10
Gyr implies that $\Omega>0.25$, while requiring that the age exceed 13 Gyr
implies that $\Omega>0.35$. Unlike in the flat-Universe case where the
anisotropy comes only from the last-scattering term in the Sachs-Wolfe formula,
large-angle anisotropies come primarily from the decay of potential
fluctuations at $z<1/\Omega$. Thus, if the Universe is open, COBE has been
detecting fluctuations produced at moderate redshift rather than at $z\sim
1300$.",9312017v1
1995-10-04,Cosmic Microwave Background Anisotropies from the Rees-Sciama Effect in $Ω_{0} \le 1$ Universes,"We investigate the imprint of nonlinear matter condensations on the Cosmic
Microwave Background (CMB) in $\Omega_{0}<1$ cold dark matter (CDM) model
universes. We consider simulation domains ranging from $120h^{-1}$ Mpc to
$360h^{-1}$ Mpc in size. We concentrate on the secondary temperature
anisotropies induced by time varying gravitational potentials occurring after
decoupling. Specifically, we investigate the importance of the Rees-Sciama
effect due to: (1) intrinsic changes in the gravitational potential of forming,
nonlinear structures, (2) proper motion of nonlinear structures, and (3) late
time decay of gravitational potential perturbations in open universes. CMB
temperature anisotropies are obtained by numerically evolving matter
inhomogeneities and CMB photons from an early, linear epoch ($z=100$) to the
present, nonlinear epoch $(z=0)$. We test the dependence and relative
importance of these secondary temperature anisotropies as a function of the
scale of the underlying matter (voids, superclusters) and as a function of
$\Omega_{0}$. The results of the $\Omega_{0}<1$ models are compared to a
similarly executed $\Omega_{0}=1.0$ simulation. We find that in low density
models all three sources of anisotropy could be relevant and reach levels of
$\Delta T/T \sim 10^{-6}$. In particular, we find that for $\Omega_{0}<1$ at
large scales, secondary temperature anisotropies are dominated by the decaying
potential.",9510019v1
1996-10-30,"Stellar systems following the R^{1/m} luminosity law. II Anisotropy, velocity profiles, and the FP of elliptical galaxies","We study the dynamical properties of spherical galaxies with surface
luminosity profile described by the R^{1/m}-law, in which a variable degree of
orbital anisotropy is allowed. The parameter m for the present models covers
the range [1,10]. For these models we study the self-consistently generated
phase-space distribution function (DF), and we derive - as a function of m -
the minimum value of the anisotropy radius for the model consistency (i.e., in
order to have a nowhere negative DF). Then we study the region in the parameter
space where the R^{1/m} models are likely to be stable against radial-orbit
instability, and we compare its size with that of the larger region
corresponding to the consistency requirement. For stable anisotropic models the
spatial and projected velocity dispersion profiles are obtained solving the
Jeans equation, and compared to those of the globally isotropic case, already
discussed in Paper I. The relevance of the results in connection with the
Fundamental Plane (FP) of elliptical galaxies is pointed out: the effect on the
projected velocity dispersion due to the maximum orbital anisotropy allowed by
the stability requirement is well within the FP thickness, and so no
fine-tuning for anisotropy is required. Finally, the Velocity Profiles are
constructed as function of the projected radius and for various degrees of
anisotropy, and their deviations from a gaussian discussed.",9610251v1
1997-08-02,Skewness in the Cosmic Microwave Background Anisotropy from Inflationary Gravity Wave Background,"In the context of inflationary scenarios, the observed large angle anisotropy
of the Cosmic Microwave Background (CMB) temperature is believed to probe the
primordial metric perturbations from inflation. Although the perturbations from
inflation are expected to be gaussian random fields, there remains the
possibility that nonlinear processes at later epochs induce ``secondary''
non-gaussian features in the corresponding CMB anisotropy maps. The
non-gaussianity induced by nonlinear gravitational instability of scalar
(density) perturbations has been investigated in existing literature. In this
paper, we highlight another source of non-gaussianity arising out of higher
order scattering of CMB photons off the metric perturbations. We provide a
simple and elegant formalism for deriving the CMB temperature fluctuations
arising due to the Sachs-Wolfe effect beyond the linear order. In particular,
we derive the expression for the second order CMB temperature fluctuations. The
multiple scattering effect pointed out in this paper leads to the possibility
that tensor metric perturbation, i.e., gravity waves (GW) which do not exhibit
gravitational instability can still contribute to the skewness in the CMB
anisotropy maps. We find that in a flat $\Omega =1$ universe, the skewness in
CMB contributed by gravity waves via multiple scattering effect is comparable
to that from the gravitational instability of scalar perturbations for equal
contribution of the gravity waves and scalar perturbations to the total rms CMB
anisotropy. The secondary skewness is found to be smaller than the cosmic
variance leading to the conclusion that inflationary scenarios do predict that
the observed CMB anisotropy should be statistically consistent with a gaussian
random distribution.",9708015v1
1999-06-25,"Projection, Spatial Correlations, and Anisotropies in a Large and Complete Sample of Abell Clusters","An analysis of R >= 1 Abell clusters is presented for samples containing
recent redshifts from the MX Northern Abell Cluster Survey. The newly obtained
redshifts from the MX Survey as well as those from the ESO Nearby Abell Cluster
Survey (ENACS) provide the necessary data for the largest magnitude-limited
correlation analysis of rich clusters in the entire sky (excluding the galactic
plane) to date. We find 19.4 <= r_0 <= 23.3 h^-1Mpc, -1.92 <= gamma <= -1.83
for four different subsets of Abell/ACO clusters, including a large sample
(N=104) of cD clusters. We have used this dataset to look for line-of-sight
anisotropies within the Abell/ACO catalogs. We show that the strong
anisotropies present in previously studied Abell cluster datasets are not
present in our R >= 1 samples. There are, however, indications of residual
anisotropies which we show are the result of two elongated superclusters, Ursa
Majoris and Corona Borealis, whose axes lie near the line-of-sight. After
rotating these superclusters so that their semi-major axes are prependicular to
the line-of-sight, we find no anisotropies as indicated by the correlation
function. The amplitude and slope of the two-point correlation function remain
the same before and after these rotations. We also remove a subset of R = 1
Abell/ACO clusters that show sizable foreground/background galaxy contamination
and again find no change in the amplitude or slope of the correlation function.
We conclude that the correlation length of R >= 1 Abell clusters is not
artificially enhanced by line-of-sight anisotropies.",9906414v1
2001-02-23,Gaussianity of Degree-Scale Cosmic Microwave Background Anisotropy Observations,"We present results from a first test of the Gaussianity of degree-scale
cosmic microwave background (CMB) anisotropy. We investigate Gaussianity of the
CMB anisotropy by studying the topology of CMB anisotropy maps from the QMAP
and Saskatoon experiments. We also study the QMASK map, a combination map of
the QMAP and Saskatoon data. We measure the genus from noise-suppressed
Wiener-filtered maps at an angular scale of about 1.5 degrees. To test the
Gaussianity of the observed anisotropy, we compare these results to those
derived from a collection of simulated maps for each experiment in a Gaussian
spatially-flat cosmological constant dominated cold dark matter model. The
genus-threshold level relations of the QMAP and Saskatoon maps are consistent
with Gaussianity. While the combination QMASK map has a mildly non-Gaussian
genus curve which is not a consequence of known foreground contamination, this
result is not statistically significant at the 2 sigma level. These results
extend previous upper limits on the non-Gaussianity of the large angular scale
(> 10 degrees) CMB anisotropy (measured by the COBE DMR experiment) down to
degree angular scales.",0102406v2
2002-10-22,Microwave anisotropies from the Galactic halo,"Models in which a large fraction of the Galactic dark matter takes the form
of cold gas clouds imply that there is thermal microwave emission from the
Galactic dark halo. Such models can therefore be directly constrained by data
on the microwave sky, and in particular the very sensitive observations of
microwave anisotropies which are now being made. To this end we have computed
the anisotropy power-spectrum expected for a Galactic dark halo made of cold,
dense gas clouds, including the effects of clustering with a CDM-like mass
spectrum of mini-halo substructure. The power-spectrum displays two peaks: one,
at l~50, is the Poisson noise for the mini-halos, and the second, much larger
and at much higher l, is the Poisson noise of the individual clouds. Because it
appears on small (milli-arcsecond) angular scales, where the instrumental
sensitivity is inevitably very poor, the latter signal is not directly
detectable. By contrast, clusters of cold gas clouds may contribute
significantly to the observed anisotropies if their emission has a grey-body
spectrum. In this case the peak fluctuation, at l~50, amounts to 4/|sin b|
micro-K in the Rayleigh-Jeans limit, and is the dominant Galactic foreground
between 40 and 80 GHz. It will be possible to constrain this foreground
component using low-latitude data from the MAP satellite, providing that its
spectrum conforms to a grey-body. If the spectrum is ``dusty'' there will be
relatively little power at frequencies below the thermal peak, and in this case
the predicted anisotropies are shown to be negligible.",0210483v2
2005-02-28,Cosmic 21-cm Delensing of Microwave Background Polarization and the Minimum Detectable Energy Scale of Inflation,"The curl (B) modes of cosmic microwave background (CMB) polarization
anisotropies are a unique probe of the primordial background of inflationary
gravitational waves (IGWs). Unfortunately, the B-mode polarization anisotropies
generated by gravitational waves at recombination are confused with those
generated by the mixing of gradient-mode (E-mode) and B-mode polarization
anisotropies as CMB photons propagate through the Universe and are
gravitationally lensed. We describe here a method for delensing CMB
polarization anisotropies using observations of anisotropies in the cosmic
21-cm radiation emitted or absorbed by neutral hydrogen atoms at redshifts 10
to 200. While the detection of cosmic 21-cm anisotropies at high resolution is
challenging, a combined study with a relatively low-resolution (but
high-sensitivity) CMB polarization experiment could probe inflationary energy
scales well below the Grand Unified Theory (GUT) scale of 10^{16} GeV --
constraining models with energy scales below 10^{15} GeV (the detectable limit
derived from CMB observations alone). The ultimate theoretical limit to the
detectable inflationary energy scale via this method may be as low as 3 \times
10^{14} GeV.",0502549v1
2007-03-22,Anisotropy Studies of the Unresolved Far-infrared Background,"Dusty, starforming galaxies and active galactic nuclei that contribute to the
integrated background intensity at far-infrared wavelengths trace the
large-scale structure. Below the point source detection limit, correlations in
the large-scale structure lead to clustered anisotropies in the unresolved
component of the far-infrared background (FIRB). The angular power spectrum of
the FIRB anisotropies could be measured in large-area surveys with the Spectral
and Photometric Imaging Receiver (SPIRE) on the upcoming Herschel observatory.
To study statistical properties of these anisotropies, the confusion from
foreground Galactic dust emission needs to be reduced even in the ``cleanest''
regions of the sky.The multi-frequency coverage of SPIRE allows the foreground
dust to be partly separated from the extragalactic background composed of dusty
starforming galaxies as well as faint normal galaxies. The separation improves
for fields with sizes greater than a few hundred square degrees and when
combined with Planck data. We show that an area of about $\sim$ 400 degrees$^2$
observed for about 1000 hours with Herschel-SPIRE and complemented by Planck
provides maximal information on the anisotropy power spectrum. We discuss the
scientific studies that can be done with measurements of the unresolved FIRB
anisotropies including a determination of the large scale bias and the
small-scale halo occupation distribution of FIRB sources with fluxes below the
point-source detection level.",0703592v2
1995-07-17,Magneto-Conductance Anisotropy and Interference Effects in Variable Range Hopping,"We investigate the magneto-conductance (MC) anisotropy in the variable range
hopping regime, caused by quantum interference effects in three dimensions.
When no spin-orbit scattering is included, there is an increase in the
localization length (as in two dimensions), producing a large positive MC. By
contrast, with spin-orbit scattering present, there is no change in the
localization length, and only a small increase in the overall tunneling
amplitude. The numerical data for small magnetic fields $B$, and hopping
lengths $t$, can be collapsed by using scaling variables $B_\perp t^{3/2}$, and
$B_\parallel t$ in the perpendicular and parallel field orientations
respectively. This is in agreement with the flux through a `cigar'--shaped
region with a diffusive transverse dimension proportional to $\sqrt{t}$. If a
single hop dominates the conductivity of the sample, this leads to a
characteristic orientational `finger print' for the MC anisotropy. However, we
estimate that many hops contribute to conductivity of typical samples, and thus
averaging over critical hop orientations renders the bulk sample isotropic, as
seen experimentally. Anisotropy appears for thin films, when the length of the
hop is comparable to the thickness. The hops are then restricted to align with
the sample plane, leading to different MC behaviors parallel and perpendicular
to it, even after averaging over many hops. We predict the variations of such
anisotropy with both the hop size and the magnetic field strength. An
orientational bias produced by strong electric fields will also lead to MC
anisotropy.",9507066v1
2002-02-26,Increasing Superconducting Tc's by a Factor of 1000 with StripeLike Hopping Anisotropies,"We have studied the enhancement of the superconducting transition
temperature, Tc, in a t-J-U model of electrons moving on a square lattice in
which anisotropic electronic hopping is introduced. The inclusion of such
hopping mimics, in a approximate fashion, a potentially important
characteristic of materials possessing stripelike charge and spin correlations.
For this model we have calculated Tc for singlet pairing using the non
self-consistent Thouless criterion, and find a dramatic enhancement of Tc
induced by hopping anisotropies. Further, the maximum increase in Tc is
obtained when the system is pushed towards the extreme anisotropy limit, that
is, when the hopping of electrons is confined to occur in 1+0^+ dimensions. We
demonstrate that in this limit the increase in Tc, with respect to the
isotropic system, can be of the order of 1000. We have also determined that in
the extreme anisotropy limit the superconducting gap is an equal mixture of s
and d pairing symmetries (two choices of such a combination being s + d and s +
id) owing to the reduced (square to rectangular) symmetry of the system in the
presence of hopping anisotropies. Thus, the presence of d-wave superconducting
features in materials whose symmetry is very different from that of a
two-dimensional square lattice, with the anisotropy produced by the appearance
of stripes, is not unexpected.",0202478v1
2003-05-29,Magnetic anisotropy and magnetoresistance of sputtered [(FeTaN)/(TaN)](n) multilayers,"We studied the in-plane magnetic anisotropy of rf (radio frequency) sputtered
[(FeTaN)/(TaN)](n) multilayers synthesized on Si substrates. In the multilayers
where n=5, the FeTaN thickness is fixed at 30 nm and the thickness of TaN,
t(TaN), is varied from 0 to 6.0 nm, we observed a clear trend that, with
increasing t(TaN), the values of coercivity, grain size, and amplitude of
maximum magnetoresistance (MR) of the samples all decrease first and then
increase after reaching a minimum when t(TaN) is around 2.0-4.0 nm. This trend
is also associated with an evolution of in-plane magnetic anisotropy, where the
multilayers change from uniaxial anisotropy to biaxial at t(TaN) around 4.0 nm
and above. We attribute the phenomena to the interlayer coupling effect of
FeTaN films as a function of the coupling layer (TaN) thickness, rather than to
the thickness dependence observed in single-layered FeTaN films, where the
direction of easy axis switches 90degrees when the film is thicker than 300 nm.
The in-plane anisotropy of the [(FeTaN)/(TaN)](n) multilayers also shows signs
of oscillation when the number of coupling layers varies. The MR effects
observed are mainly due to anisotropy MR (AMR), while the grain size and
exchange coupling may also contribute to the change of maximum MR ratios in the
multilayers with changing t(TaN).",0305687v2
2004-04-14,Flux melting in BSCCO: Incorporating both electromagnetic and Josephson couplings,"Multilevel Monte Carlo simulations of a BSCCO system are carried out
including both Josephson as well as electromagnetic couplings for a range of
anisotropies. A first order melting transition of the flux lattice is seen on
increasing the temperature and/or the magnetic field. The phase diagram for
BSCCO is obtained for different values of the anisotropy parameter $\gamma$.
The best fit to the experimental results of D. Majer {\it et al.} [Phys. Rev.
Lett. {\bf 75}, 1166 (1995)] is obtained for $\gamma\approx 250$ provided one
assumes a temperature dependence $\lambda^2(0)/\lambda^2(T)=1-t$ of the
penetration depth with $t=T/T_c$. Assuming a dependence
$\lambda^2(0)/\lambda^2(T)=1-t^2$ the best fit is obtained for $ \gamma\approx
450$. For finite anisotropy the data is shown to collapse on a straight line
when plotted in dimensionless units which shows that the melting transition can
be satisfied with a single Lindemann parameter whose value is about 0.3. A
different scaling applies to the $\gamma=\infty$ case. The energy jump is
measured across the transition and for large values of $\gamma$ it is found to
increase with increasing anisotropy and to decrease with increasing magnetic
field. For infinite anisotropy we see a 2D behavior of flux droplets with a
transition taking place at a temperature independent of the magnetic field. We
also show that for smaller values of anisotropy it is reasonable to replace the
electromagnetic coupling with an in-plane interaction represented by a Bessel
function of the second kind ($K_0$), thus justifying our claim in a previous
paper.",0404336v1
2004-07-07,Many-body Green's function theory of ferromagnetic Heisenberg systems with single-ion anisotropies in more than one direction,"The behaviour of ferromagnetic systems with single-ion anisotropies in more
than one direction is investigated with many-body Green's function theory
generalizing earlier work with uniaxial anisotropies only. It turns out to be
of advantage to construct Green's functions in terms of the spin operators S^x,
S^y and S^z, instead of the commonly used S^+,S^- and S^z operators. The
exchange energy terms are decoupled by RPA and the single-ion anisotropy terms
by a generalization of the Anderson-Callen decoupling. We stress that in the
derivation of the formalism none of the three spatial axes is special, so that
one is always able to select a reference direction along which a magnetization
component is not zero. Analytical expressions are obtained for all three
components of the magnetization and the expectation values <(S^x)^2>, <(S^y)^2>
and <(S^z)^2> for any spin quantum number S. The formalism considers both
in-plane and out-of-plane anisotropies. Numerical calculations illustrate the
behaviour of the magnetization for 3-dimensional and 2-dimensional systems for
various parameters. In the 2-dimensional case, the magnetic dipole-dipole
coupling is included, and a comparison is made between in-plane and
out-of-plane anisotropies.",0407171v2
2005-05-23,Anisotropy of incommensurate spin and charge fluctuations in detwinned YBa$_2$Cu$_3$O$_{6+δ}$,"Motivated by a recent neutron scattering experiment on detwinned
YBa$_2$Cu$_3$O$_{6+\delta}$ superconductor, we examine the frequency and doping
dependence of the anisotropy in the spin and charge fluctuation arising from
the coupling between the plane and the chain. Starting from the two-dimensional
$t$-$t^{'}$-$J$ model and using the random-phase approximation (RPA), we find a
pronounced anisotropy of the incommensurate (IC) peaks in the spin channel,
namely the peak intensity at the $(\pi\pm\delta,\pi)$ direction is stronger
than that at the $(\pi,\pi\pm\delta)$ direction in a wide frequency range from
$\omega=0.2J$ to the resonance frequency $\omega_r=0.35J$. Above the resonance
frequency, the IC peaks reemerge. Their intensities shift to the diagonal
direction and no anisotropy exists along the two diagonal directions. We find
that this anisotropy is robust with respect to the possible variation of the
RPA correction factor and to the dopings. The charge fluctuation is also found
to be incommensurate for all energies considered and peak at $(0,\delta)$ and
$(\delta,0)$. An anisotropy in its IC peak intensity along the $k_x$ and the
$k_y$ direction exists, but in sharp contrast to the spin channel, the maximum
intensity of the IC peak is along the $k_y$ direction. Moreover, the IC peak in
the charge channel exhibits an upward dispersion, in contrast to the downward
dispersion below the spin resonance frequency for the spin IC peak. We explain
these features based on the effect of the plane-chain coupling on the topology
of the Fermi surface.",0505545v1
2004-01-16,Anisotropy in Bianchi-type brane cosmologies,"The behavior near the initial singular state of the anisotropy parameter of
the arbitrary type, homogeneous and anisotropic Bianchi models is considered in
the framework of the brane world cosmological models. The matter content on the
brane is assumed to be an isotropic perfect cosmological fluid, obeying a
barotropic equation of state. To obtain the value of the anisotropy parameter
at an arbitrary moment an evolution equation is derived, describing the
dynamics of the anisotropy as a function of the volume scale factor of the
Universe. The general solution of this equation can be obtained in an exact
analytical form for the Bianchi I and V types and in a closed form for all
other homogeneous and anisotropic geometries. The study of the values of the
anisotropy in the limit of small times shows that for all Bianchi type
space-times filled with a non-zero pressure cosmological fluid, obeying a
linear barotropic equation of state, the initial singular state on the brane is
isotropic. This result is obtained by assuming that in the limit of small times
the asymptotic behavior of the scale factors is of Kasner-type. For brane
worlds filled with dust, the initial values of the anisotropy coincide in both
brane world and standard four-dimensional general relativistic cosmologies.",0401069v1
2000-09-07,Jet Quenching and Azimuthal Anisotropy of Large $p_T$ Spectra in Non-central High-energy Heavy-ion Collisions,"Parton energy loss inside a dense medium leads to the suppression of large
$p_T$ hadrons and can also cause azimuthal anisotropy of hadron spectra at
large transverse momentum in non-central high-energy heavy-ion collisions. Such
azimuthal anisotropy is studied qualitatively in a parton model for heavy-ion
collisions at the RHIC energies. The coefficient $v_2(p_T)$ of the elliptic
anisotropy at large $p_T$ is found to be very sensitive to parton energy loss.
It decreases slowly with $p_T$ contrary to its low $p_T$ behavior where $v_2$
increases very rapidly with $p_T$. The turning point signals the onset of
contributions of hard processes and the magnitude of parton energy loss. The
centrality dependence of $v_2(p_T)$ is shown to be sensitive to both size and
density dependence of the parton energy loss and the later can also be studied
via variation of the colliding energy. The anisotropy coefficient
$v_2/\epsilon$ normalized by the spatial ellipticity $\epsilon$ is found to
decrease significantly toward semi-peripheral collisions, differing from the
hydrodynamic results for low $p_T$ hadrons. Constrained by the existing WA98
experimental data at the SPS energy on parton energy loss, both hadron spectra
suppression and azimuthal anisotropy at high $p_T$ are predicted to vanish for
$b>$7-8 fm in $Au+Au$ collisions at $\sqrt{s}=$130-200 GeV when the hadron
rapidity density per unit area of the initial overlapped region is less than
what is achieved in the central $Pb+Pb$ collisions at the SPS energy.",0009019v2
2008-06-11,Study of reconnection-associated multi-scale fluctuations with Cluster and Double Star,"The objective of the paper is to asses the specific spectral scaling
properties of magnetic reconnection associated fluctuations/turbulence at the
Earthward and tailward outflow regions observed simultaneously by the Cluster
and Double Star (TC-2) spacecraft on September 26, 2005. Systematic comparisons
of spectral characteristics, including variance anisotropy and scale-dependent
spectral anisotropy features in wave vector space were possible due to the
well-documented reconnection events, occurring between the positions of Cluster
(X = -14--16 $R_e$) and TC-2 (X = -6.6 $R_e$). Another factor of key importance
is that the magnetometers on the spacecraft are similar. The comparisons
provide further evidence for asymmetry of physical processes in
Earthward/tailward reconnection outflow regions. Variance anisotropy and
spectral anisotropy angles estimated from the multi-scale magnetic fluctuations
in the tailward outflow region show features which are characteristic for
magnetohydrodynamic cascading turbulence in the presence of a local mean
magnetic field. The multi-scale magnetic fluctuations in the Earthward outflow
region are exhibiting more power, lack of variance and scale dependent
anisotropies, but also having larger anisotropy angles. In this region the
magnetic field is more dipolar, the main processes driving turbulence are flow
breaking/mixing, perhaps combined with turbulence ageing and non-cascade
related multi-scale energy sources.",0806.1829v1
2008-11-03,Two-component galaxy models: the effect of density profile at large radii on the phase-space consistency,"It is well known that the density and anisotropy profile in the inner regions
of a stellar system with positive phase-space distribution function are not
fully independent. Here we study the interplay between density profile and
orbital anisotropy at large radii in physically admissible (consistent) stellar
systems. The analysis is carried out by using two-component (n-gamma,gamma_1)
spherical self-consistent galaxy models, in which one density distribution
follows a generalized gamma profile with external logarithmic slope n, and the
other a standard gamma_1 profile (with external slope 4). The necessary and
sufficient conditions for phase-space consistency are determined analytically,
also in presence of a dominant massive central black hole, and the analytical
phase-space distribution function of (n-gamma,1) models, and of n-gamma models
with a central black hole, is derived for gamma=0,1,2. It is found that the
density slope in the external regions of a stellar system can play an important
role in determining the amount of admissible anisotropy: in particular, for
fixed density slopes in the central regions, systems with a steeper external
density profile can support more radial anisotropy than externally flatter
models. This is quantified by an inequality formally identical to the ``cusp
slope-central anisotropy'' theorem (An & Evans 2006), relating at all radii
(and not just at the center) the density logarithmic slope and the anisotropy
indicator in all Osipkov-Merritt systems [Abridged].",0811.0322v1
2009-01-30,Ferromagnetism in Co7(TeO3)4Br6: A byproduct of complex antiferromagnetic order and single-ion anisotropy,"Pronounced anisotropy of magnetic properties and complex magnetic order of a
new oxi-halide compound Co7(TeO3)4Br6 has been investigated by powder and
single crystal neutron diffraction, magnetization and ac susceptibility
techniques. Anisotropy of susceptibility extends far into the paramagnetic
temperature range. A principal source of anisotropy are anisotropic properties
of the involved octahedrally coordinated single Co(2+) ions, as confirmed by
angular-overlap-model calculations presented in this work. Incommensurate
antiferromagnetic order sets in at TN=34 K. Propagation vector is strongly
temperature dependent reaching k1=(0.9458(6), 0, 0.6026(5)) at 30 K. A
transition to a ferrimagnetic structure with k2=0 takes place at TC=27 K.
Magnetically ordered phase is characterized by very unusual anisotropy as well:
while M-H scans along b-axis reveals spectacularly rectangular but otherwise
standard ferromagnetic hysteresis loops, M-H studies along other two principal
axes are perfectly reversible, revealing very sharp spin flop (or spin flip)
transitions, like in a standard antiferromagnet (or metamagnet). Altogether,
the observed magnetic phenomenology is interpreted as an evidence of competing
magnetic interactions permeating the system, first of all of the single ion
anisotropy energy and the exchange interactions. Different coordinations of the
Co(2+)-ions involved in the low-symmetry C2/c structure of Co7(TeO3)4Br6 render
the exchange-interaction network very complex by itself. Temperature dependent
changes in the magnetic structure, together with an abrupt emergence of a
ferromagnetic component, are ascribed to continual spin reorientations
described by a multi-component, but yet unknown, spin Hamiltonian.",0901.4878v1
2009-05-04,Magnetization Plateaux in the Antiferromagnetic Ising Chain with Single-Ion Anisotropy,"Two one-dimensional spin-1 antiferromagnetic Ising models with a single-ion
anisotropy under external magnetic field at low temperatures are exactly
investigated by the transfer-matrix technique. The magnetization per spin ($m$)
is obtained for the two types of models (denoted by model 1 and 2) as an
explicit function of the magnetic field ($H$%) and of the anisotropy parameter
($D$). Model 1 is an extension of the recently one treated by Ohanyan and
Ananikian [\emph{Phys. Lett. A} \textbf{% 307} (2003) 76]: we have generalized
their model to the spin-1 case and a single-ion anisotropy term have been
included. In the limit of positive (or null) anisotropy ($D\geq 0$) and strong
antiferromagnetic coupling ($\alpha =J_{A}/J_{F}\geq 3$) the $m \times H$
curves are qualitatively the same as for the spin $S=1/2$ case, with the
presence of only one plateau at $m/m_{sat}=1/3$. On the other hand, for
negative anisotropy ($D<0$) we observe more plateaux ($m=1/6$ and 2/3), which
depend on the values of $D$ and $% \alpha $. The second model (model 2) is the
same as the one recently studied by Chen et al. [\emph{J. Mag. Mag. Mat.
}\textbf{262} (2003) 258)] using Monte Carlo simulation; here, the model is
treated within an exact transfer-matrix framework.",0905.0505v1
2009-07-29,"Domain walls, canted states and stripe width variation in ultrathin magnetic films with perpendicular anisotropy","Stripe width variation in ultrathin magnetic films is a well known phenomenon
still not well understood. We analyze this problem considering a 2D Heisenberg
model with ferromagnetic exchange interactions, dipolar interactions and
perpendicular anisotropy, relevant e.g. in Fe/Cu(001) films. By extending a
classic result of Yafet & Gyorgy (YG) and using Monte Carlo simulations we
calculate the complete zero temperature phase diagram of the model. Through
this calculation we analyze the correlation between domain walls structure and
stripe width variation, as the perpendicular anisotropy changes. In particular,
we found evidences that the recently detected canted state becomes the ground
state of the system close to the Spin Reorientation Transition (SRT) for any
value of the exchange to dipolar couplings ratio. Far away of the SRT the
canted ground state is replaced by a saturated stripes state, in which
in--plane magnetization components are only present inside the walls. We find
that the domain wall structure strongly depends on the perpendicular
anisotropy: close to SRT it is well described by YG approximation, but a strong
departure is observed in the large anisotropy limit. Moreover, we show that
stripe width variation is directly related to domain wall width variation with
the anisotropy.",0907.5153v1
2010-01-22,Non-Gaussianity and the Cosmic Microwave Background Anisotropies,"We review in a pedagogical way the present status of the impact of
non-Gaussianity (NG) on the Cosmic Microwave Background (CMB) anisotropies. We
first show how to set the initial conditions at second-order for the (gauge
invariant) CMB anisotropies when some primordial NG is present. However, there
are many sources of NG in CMB anisotropies, beyond the primordial one, which
can contaminate the primordial signal. We mainly focus on the NG generated from
the post-inflationary evolution of the CMB anisotropies at second-order in
perturbation theory at large and small angular scales, such as the ones
generated at the recombination epoch. We show how to derive the equations to
study the second-order CMB anisotropies and provide analytical computations to
evaluate their contamination to primordial NG (complemented with numerical
examples). We also offer a brief summary of other secondary effects. This
review requires basic knowledge of the theory of cosmological perturbations at
the linear level.",1001.3957v1
2010-04-22,Numerical study on the emergence of anisotropy in artificial flocks: A BOIDS modeling and simulations of empirical findings,"In real flocks, it was revealed that the angular density of nearest neighbors
shows a strong {\it anisotropic structure} of individuals by very recent
extensive field studies by Ballerini et al [{\it Proceedings of the National
Academy of Sciences USA} {\bf 105}, pp.1232-1237 (2008)]. In this paper, we
show that this empirical evidence in real flocks, namely, the structure of
anisotropy also emerges in an artificial flock simulation based on the {\it
BOIDS} by Reynolds [{\it Computer Graphics} {\bf 21}, pp.25-34 (1987)]. We
numerically find that appropriate combinations of the weights for just only
three essential factors of the BOIDS, namely, `Cohesion', `Alignment' and
`Separation' lead to a strong anisotropy in the flock. This result seems to be
highly counter-intuitive and also provides a justification of the hypothesis
that the anisotropy emerges as a result of self-organization of interacting
intelligent agents (birds for instance). To quantify the anisotropy, we
evaluate a useful statistics (a kind of {\it order parameters} in statistical
physics), that is to say, the so-called $\gamma$-value defined as an inner
product between the vector in the direction of the lowest angular density of
flocks and the vector in the direction of the moving of the flock. Our results
concerning the emergence of the anisotropy through the $\gamma$-value might
enable us to judge whether an arbitrary flock simulation seems to be {\it
realistic} or not.",1004.3837v1
2010-05-04,CMB in a box: causal structure and the Fourier-Bessel expansion,"This paper makes two points. First, we show that the line-of-sight solution
to cosmic microwave anisotropies in Fourier space, even though formally defined
for arbitrarily large wavelengths, leads to position-space solutions which only
depend on the sources of anisotropies inside the past light-cone of the
observer. This happens order by order in a series expansion in powers of the
visibility $\gamma=e^{-\mu}$, where $\mu$ is the optical depth to Thompson
scattering. We show that the CMB anisotropies are regulated by spacetime window
functions which have support only inside the past light-cone of the point of
observation. Second, we show that the Fourier-Bessel expansion of the physical
fields (including the temperature and polarization momenta) is an alternative
to the usual Fourier basis as a framework to compute the anisotropies. In that
expansion, for each multipole $l$ there is a discrete tower of momenta
$k_{i,l}$ (not a continuum) which can affect physical observables, with the
smallest momenta being $k_{1,l} ~ l$. The Fourier-Bessel modes take into
account precisely the information from the sources of anisotropies that
propagates from the initial value surface to the point of observation - no
more, no less. We also show that the physical observables (the temperature and
polarization maps), and hence the angular power spectra, are unaffected by that
choice of basis. This implies that the Fourier-Bessel expansion is the optimal
scheme with which one can compute CMB anisotropies. (Abridged)",1005.0563v1
2010-08-07,T=0 phase diagram and nature of domains in ultrathin ferromagnetic films with perpendicular anisotropy,"We present the complete zero temperature phase diagram of a model for
ultrathin films with perpendicular anisotropy. The whole parameter space of
relevant coupling constants is studied in first order anisotropy approximation.
Because the ground state is known to be formed by perpendicular stripes
separated by Bloch walls, a standard variational approach is used, complemented
with specially designed Monte Carlo simulations. We can distinguish four
regimes according to the different nature of striped domains: a high anisotropy
Ising regime with sharp domain walls, a saturated stripe regime with thicker
walls inside which an in-plane component of the magnetization develops, a
narrow canted-like regime, characterized by a sinusoidal variation of both the
in-plane and the out of plane magnetization components, which upon further
decrease of the anisotropy leads to an in-plane ferromagnetic state via a spin
reorientation transition (SRT). The nature of domains and walls are described
in some detail together with the variation of domain width with anisotropy, for
any value of exchange and dipolar interactions. Our results, although strictly
valid at $T=0$, can be valuable for interpreting data on the evolution of
domain width at finite temperature, a still largely open problem.",1008.1353v1
2010-11-30,Dark matter electron anisotropy: a universal upper limit,"We study the dipole anisotropy in the arrival directions of high energy CR
electrons and positrons (CRE) of Dark Matter (DM) origin. We show that this
quantity is very weakly model dependent and offers a viable criterion to
discriminate among CRE from DM or from local discrete sources, like e.g.
pulsars. In particular, we find that the maximum anisotropy which DM can
provide is to a very good approximation a universal quantity and, as a
consequence, if a larger anisotropy is detected, this would constitute a strong
evidence for the presence of astrophysical local discrete CRE sources, whose
anisotropy, instead, can be naturally larger than the DM upper limit. We
further find that the main source of anisotropy from DM is given by the
fluctuation in the number density of DM sub-structures in the vicinity of the
observer and we thus devote special attention to the study of the variance in
the sub-structures realization implementing a dedicated Montecarlo simulation.
Such scenarios will be probed in the next years by Fermi-LAT, providing new
hints, or constraints, about the nature of DM.",1012.0041v3
2011-01-27,Anisotropy as a Probe of the Galactic Cosmic Ray Propagation and the Galactic Halo Magnetic Field,"The anisotropy of cosmic rays (CRs) in the solar vicinity is generally at-
tributed to the CR streaming due to the discrete distribution of CR sources or
local magnetic field modulation. Recently, the two dimensional large scale CR
anisotropy has been measured by many experiments in TeV-PeV energy range in
both hemispheres. The tail-in excess along the tangential direction of the
local spiral arm and the loss cone deficit pointing to the north Galactic pole
direction agree with what have been obtained in tens to hundreds of GeV. The
persistence of the two large scale anisotropy structures in such a wide range
of energy suggests that the anisotropy might be due to a global streaming of
the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy
picture from solar system to the whole galaxy. In such a case, we can find a
new interesting signature, a loop of GCR streaming, of the GCR propagation. We
further calculate the overall GCR streaming induced magnetic field, and find a
qualitative consistence with the observed structure of the halo magnetic field.",1101.5273v3
2011-06-14,The East-West method: an exposure-independent method to search for large scale anisotropies of cosmic rays,"The measurement of large scale anisotropies in cosmic ray arrival directions
at energies above 10^13 eV is performed through the detection of Extensive Air
Showers produced by cosmic ray interactions in the atmosphere. The observed
anisotropies are small, so accurate measurements require small statistical
uncertainties, i.e. large datasets. These can be obtained by employing ground
detector arrays with large extensions (from 10^4 to 10^9 m^2) and long
operation time (up to 20 years). The control of such arrays is challenging and
spurious variations in the counting rate due to instrumental effects (e.g. data
taking interruptions or changes in the acceptance) and atmospheric effects
(e.g. air temperature and pressure effects on EAS development) are usually
present. These modulations must be corrected very precisely before performing
standard anisotropy analyses, i.e. harmonic analysis of the counting rate
versus local sidereal time. In this paper we discuss an alternative method to
measure large scale anisotropies, the ""East-West method"", originally proposed
by Nagashima in 1989. It is a differential method, as it is based on the
analysis of the difference of the counting rates in the East and West
directions. Besides explaining the principle, we present here its mathematical
derivation, showing that the method is largely independent of experimental
effects, that is, it does not require corrections for acceptance and/or for
atmospheric effects. We explain the use of the method to derive the amplitude
and phase of the anisotropy and we demonstrate its power under different
conditions of detector operation.",1106.2651v1
2011-07-21,An Estimator for statistical anisotropy from the CMB bispectrum,"Various data analyses of the Cosmic Microwave Background (CMB) provide
observational hints of statistical isotropy breaking. Some of these features
can be studied within the framework of primordial vector fields in inflationary
theories which generally display some level of statistical anisotropy both in
the power spectrum and in higher-order correlation functions. Motivated by
these observations and the recent theoretical developments in the study of
primordial vector fields, we develop the formalism necessary to extract
statistical anisotropy information from the three-point function of the CMB
temperature anisotropy. We employ a simplified vector field model and
parametrize the bispectrum of curvature fluctuations in such a way that all the
information about statistical anisotropy is encoded in some parameters
lambda_{LM} (which measure the anisotropic to the isotropic bispectrum
amplitudes). For such a template bispectrum, we compute an optimal estimator
for lambda_{LM} and the expected signal-to-noise ratio. We estimate that, for
f_{NL} ~ 30, an experiment like Planck can be sensitive to a ratio of the
anisotropic to the isotropic amplitudes of the bispectrum as small as 10%. Our
results are complementary to the information coming from a power spectrum
analysis and particularly relevant for those models where statistical
anisotropy turns out to be suppressed in the power spectrum but not negligible
in the bispectrum.",1107.4304v2
2012-06-20,Models of the Contribution of Blazars to the Anisotropy of the Extragalactic Diffuse Gamma-ray Background,"We study the relation between the measured anisotropies in the extragalactic
diffuse gamma-ray background (DGRB) and the DGRB spectral intensity, and their
potential origin from the unresolved blazar population. Using a
physical-evolution model for blazars with a luminosity dependent evolution
(LDDE) and an observationally-determined luminosity-dependent blazar spectral
energy distribution (SED), we find that blazars can account for the observed
anisotropy of the DGRB consistent with their observed source-count
distribution, but are in turn constrained in contributing significantly to the
observed DGRB intensity. For the best-fit LDDE model accounting for the DGRB
anisotropy and source-count distribution, blazars only contribute
5.7^{+2.1}_{-1.0}% (68% CL) of the DGRB intensity above 1 GeV. Requiring a
higher fraction of the DGRB intensity contribution by blazars overproduces the
DGRB anisotropy, and therefore blazars in the LDDE+SED-sequence model cannot
simultaneously account for the DGRB intensity as well as anisotropy. We discuss
the limitations of LDDE models. However, these models do not require the many
unjustified and observationally-inconsistent simplifying
assumptions---including a single power law for all blazar spectra and a simple
broken power-law model for their source-count distribution---that are present
in much previous work.",1206.4734v2
2012-10-08,Magnetic anisotropy in strained manganite films and bicrystal junctions,"Transport and magnetic properties of LSMO manganite thin films and bicrystal
junctions were investigated. Manganite films were epitaxially grown on STO,
LAO, NGO and LSAT substrates and their magnetic anisotropy were determined by
two techniques of magnetic resonance spectroscopy. Compare with cubic
substrates a small (about 0.3 persentage), the anisotropy of the orthorhombic
NGO substrate leads to a uniaxial anisotropy of the magnetic properties of the
films in the plane of the substrate. Samples with different tilt of
crystallographic basal planes of manganite as well as bicrystal junctions with
rotation of the crystallographic axes (RB - junction) and with tilting of basal
planes (TB - junction) were investigated. It was found that on vicinal NGO
substrates the value of magnetic anisotropy could be varied by changing the
substrate inclination angle from 0 to 25 degrees. Measurement of magnetic
anisotropy of manganite bicrystal junction demonstrated the presence of two
ferromagnetically ordered spin subsystems for both types of bicrystal
boundaries RB and TB. The magnitude of the magnetoresistance for TB - junctions
increased with decreasing temperature and with the misorientation angle even
misorientation of easy axes in the parts of junction does not change. Analysis
of the voltage dependencies of bicrystal junction conductivity show that the
low value of the magnetoresistance for the LSMO bicrystal junctions can be
caused by two scattering mechanisms with the spin- flip of spin - polarized
carriers due to the strong electron - electron interactions in a disordered
layer at the bicrystal boundary at low temperatures and the spin-flip by anti
ferromagnetic magnons at high temperatures.",1210.2261v1
2012-10-08,The behaviour of shape and velocity anisotropy in dark matter haloes,"Dark matter haloes from cosmological N-body simulations typically have
triaxial shapes and anisotropic velocity distributions. Recently it has been
shown that the velocity anisotropy, beta, of cosmological haloes and major
merger remnants depends on direction in such a way that beta is largest along
the major axis and smallest along the minor axis. In this work we use a wide
range of non-cosmological N-body simulations to examine halo shapes and
direction-dependence of velocity anisotropy profiles. For each of our simulated
haloes we define 48 cones pointing in different directions, and from the
particles inside each cone we compute velocity anisotropy profiles. We find
that elongated haloes can have very distinct velocity anisotropies. We group
the behaviour of haloes into three different categories, that range from
spherically symmetric profiles to a much more complex behaviour, where
significant differences are found for beta along the major and minor axes. We
encourage future studies of velocity anisotropies in haloes from cosmological
simulations to calculate beta-profiles in cones, since it reveals information,
which is hidden from a spherically averaged profile. Finally, we show that
spherically averaged profiles often obey a linear relation between beta and the
logarithmic density slope in the inner parts of haloes, but this relation is
not necessarily obeyed, when properties are calculated in cones.",1210.2392v1
2013-01-21,Increase of magnetic hyperthermia efficiency due to dipolar interactions in low anisotropy magnetic nanoparticles : theoretical and experimental results,"When magnetic nanoparticles (MNPs) are single-domain and magnetically
independent, their magnetic properties and the conditions to optimize their
efficiency in magnetic hyperthermia applications are now well-understood.
However, the influence of magnetic interactions on magnetic hyperthermia
properties is still unclear. Here, we report hyperthermia and high-frequency
hysteresis loop measurements on a model system consisting of MNPs with the same
size but a varying anisotropy, which is an interesting way to tune the relative
strength of magnetic interactions. A clear correlation between the MNP
anisotropy and the squareness of their hysteresis loop in colloidal solution is
observed : the larger the anisotropy, the smaller the squareness. Since low
anisotropy MNPs display a squareness higher than the one of magnetically
independent nanoparticles, magnetic interactions enhance their heating power in
this case. Hysteresis loop calculations of independent and coupled MNPs are
compared to experimental results. It is shown that the observed features are a
natural consequence of the formation of chains and columns of MNPs during
hyperthermia experiments: in these structures, when the MNP magnetocristalline
anisotropy is small enough to be dominated by magnetic interactions, the
hysteresis loop shape tends to be rectangular, which enhance their efficiency.
On the contrary, when MNPs do not form chains and columns, magnetic
interactions reduces the hysteresis loop squareness and the efficiency of MNPs
compared to independent ones. The present work should improve the understanding
and interpretation of magnetic hyperthermia experiments.",1301.5590v1
2013-06-20,"Magnetic orders, excitations, and phase transitions in Fe_1+yTe","We study the magnetic properties of Fe_1+y Te, a parent compound of the
iron-based high-temperature superconductors. Motivated by recent neutron
scattering experiments, we show that a spin-1 exchange model, supplemented by a
single-ion spin anisotropy, accounts well for the experimentally observed low
temperature magnetic phase diagram, that exhibits a commensurate bicollinear
order at low Fe dopings (y < 0.12) and an incommensurate spin-spiral order at
high Fe dopings (y > 0.12). We suggest that the commensurate-incommensurate
transition at y = 0.12 is due to the competition between the exchange
interaction and the local spin anisotropy. At low Fe dopings, the single-ion
spin anisotropy is strong and pins the spins along the easy axis, which,
together with the spatially anisotropic exchanges, induces a unusual
bicollinear commensurate magnetic order. The low-energy spin-wave excitation is
gapped due to the explict breaking of spin-rotational symmetry by the local
spin anisotropy. At high Fe dopings, the single-ion anisotropy is weak, and the
exchange favors an incommensurate coplanar state. The incommensurate magnetic
wavevector averages out the spin anisotropy so that a gapless low-energy
spin-wave excitation is obtained. We also analyze the low-energy hydrodynamic
model and use it to describe the magneto-structural transition and the static
and dynamical spin structure factors across the magnetic ordering transitions.",1306.4730v2
2013-06-23,Characterising gravitational wave stochastic background anisotropy with Pulsar Timing Arrays,"Detecting a stochastic gravitational wave background, particularly radiation
from individually unresolvable super-massive black hole binary systems, is one
of the primary targets for Pulsar Timing Arrays. Increasingly more stringent
upper limits are being set on these signals under the assumption that the
background radiation is isotropic. However, some level of anisotropy may be
present and the characterisation of the power at different angular scales
carries important information. We show that the standard analysis for isotropic
backgrounds can be generalised in a conceptually straightforward way to the
case of generic anisotropic background radiation by decomposing the angular
distribution of the gravitational wave power on the sky into multipole moments.
We introduce the concept of generalised overlap reduction functions which
characterise the effect of the anisotropy multipoles on the correlation of the
timing residuals from the pulsars timed by a Pulsar Timing Array. In a search
for a signal characterised by a generic anisotropy, the generalised overlap
reduction functions play the role of the so-called Hellings and Downs curve
used for isotropic radiation. We compute the generalised overlap reduction
functions for a generic level of anisotropy and Pulsar Timing Array
configuration. We also provide an order of magnitude estimate of the level of
anisotropy that can be expected in the background generated by super-massive
black hole binary systems.",1306.5394v2
2013-08-19,Dipole Anisotropy in Integrated Linearly Polarized Flux Density in NVSS Data,"We study the dipole anisotropy in integrated linearly polarization flux
density in NRAO VLA Sky Survey (NVSS). We extract the anisotropy parameters in
the number counts, number counts weighted by polarization observables, i.e.
degree of polarization (p) and polarization flux (P). We also determine the
anisotropy in the degree of polarization per source and polarization flux per
source. We consider data with several different cuts on the flux density,
S>10,20,30,40,50 mJy. For studies with degree of polarization we impose the
additional cut 0.01<p<1. Similarly for polarization flux we impose, 0.5<P<100
mJy. We find a very significant signal of dipole, both in number counts and P
(or p) weighted number counts. For the case of P weighted number counts the
significance ranges from 8 \sigma to 5 \sigma for S>20 mJy to S>50 mJy. The
corresponding direction parameters are found to be stable with the cut on flux
density. The significance is even higher for the case of p weighted number
counts. The observed anisotropy is found to be much larger in comparison to the
CMBR expectations. We find that polarization observables show a much higher
level of anisotropy in comparison to pure number counts or flux weighted number
counts.",1308.3970v2
2013-09-27,The Effect of 45° Grain Boundaries and associated Fe particles on Jc and resistivity in Ba(Fe0.9Co0.1)2As2 Thin Films,"The anisotropy of the critical current density Jc depends in general on both
the properties of the flux lines (such as line tension, coherence length and
penetration depth) and the properties of the defects (such as density, shape,
orientation etc.). Whereas the Jc anisotropy in microstructurally clean films
can be scaled to an effective magnetic field containing the Ginzburg-Landau
anisotropy term, it is in general not possible (or only in a limited field
range) for samples containing extended defects. Here, the Jc anisotropy of a
Co-doped BaFe2As2 sample with 45{\deg} [001] tilt grain boundaries (GBs), i.e.
grain boundaries created by 45{\deg} in-plane rotated grains, as well as
extended Fe particles is investigated. This microstructure leads to c-axis
correlated pinning, both due to the GBs and the Fe particles and manifests in a
c-axis peak in the Jc anisotropy at low magnetic fields and a deviation from
the anisotropic Ginzburg-Landau scaling at higher fields. Strong pinning at
ellipsoidal extended defects, i.e. the Fe particles, is discussed, and the full
Jc anisotropy is fitted successfully with the vortex path model. The results
are compared to a sample without GBs and Fe particles. 45{\deg} GBs seem to be
good pinning centers rather than detrimental to current flow.",1309.7182v1
2014-04-07,Cross-correlation of cosmic far-infrared background anisotropies with large scale structures,"We measure the cross-power spectra between luminous red galaxies (LRGs) from
the Sloan Digital Sky Survey (SDSS)-III Data Release Eight (DR8) and cosmic
infrared background (CIB) anisotropies from Planck and data from the Improved
Reprocessing (IRIS) of the Infrared Astronomical Satellite (IRAS) at 353, 545,
857, and 3000 GHz, corresponding to 850, 550, 350 and 100 micron, respectively,
in the multipole range 100<l<1000. Using approximately 6.5 10^5 photometrically
determined LRGs in 7760 deg^2 of the northern hemisphere in the redshift range
0.45 < z < 0.65, we model the far-infrared background (FIRB) anisotropies with
an extended version of the halo model. With these methods, we confirm the basic
picture obtained from recent analyses of FIRB anisotropies with Herschel and
Planck, that the most efficient halo mass at hosting star forming galaxies is
log(M_ eff/M_\odot)=12.84+/-0.15. We estimate the percentage of FIRB
anisotropies correlated with LRGs as approximately 11.8 %, 3.9 %, 1.8 %, and
1.0 % of the total at 3000, 857, 545, and 353 GHz, respectively. At redshift
z~0.55, the bias of FIRB galaxies with respect to the dark matter density field
has the value b_{FIRB}~1.45, and the mean dust temperature of FIRB galaxies is
T_d=26 K. Finally, we discuss the impact of present and upcoming
cross-correlations with far-infrared background anisotropies on the
determination of the global star formation history and the link between
galaxies and dark matter.",1404.1933v2
2014-04-15,Anisotropic upper critical field of BiS2-based superconductor LaO0.5F0.5BiS2,"Superconducting properties under high magnetic fields for the novel
BiS2-based layered superconductor LaO0.5F0.5BiS2 (polycrystalline sample
prepared using the high-pressure synthesis method) have been investigated. The
anisotropy of the upper critical field was discussed by analyzing the
temperature dependence of the temperature derivative of resistivity. The
temperature dependence of upper critical field showed an anomalous behavior
with a characteristic magnetic field of 8 T. We revealed that the anomalous
behavior was caused by the existence of three kinds of upper critical field,
HC2max, HC2mid and HC2min in LaO0.5F0.5BiS2. The lowest upper critical field
HC2min is regarded as the Hc2 where the superconducting states of the grains
with an orientation of H // c are suppressed. The HC2max and HC2mid are
regarded as the Hc2 where the superconducting states of the grains with an
orientation of H // ab are suppressed. The difference between the HC2max and
HC2mid could be explained by the anisotropy of superconducting states within
the Bi-S plane. The estimated anisotropy parameter of the upper critical fields
was about 7.4 for the high-pressure-synthesized LaO0.5F0.5BiS2 polycrystalline
sample. Since the value was clearly lower than the anisotropy parameter of over
30 observed in the previous report on the LaO0.5F0.5BiS2 single crystals grown
under ambient pressure, we concluded that a larger anisotropy of
superconductivity was not essential for the enhancement of Tc, and lower
anisotropy might be important for a higher Tc in LaO1-xFxBiS2.",1404.3798v1
2014-05-14,Shrinkage anisotropy characteristics from soil structure and initial sample/layer size,"The objective of this work is a physical prediction of such soil shrinkage
anisotropy characteristics as variation with drying of (i) different
sample/layer sizes and (ii) the shrinkage geometry factor. With that, a new
presentation of the shrinkage anisotropy concept is suggested through the
sample/layer size ratios. The work objective is reached in two steps. First,
the relations are derived between the indicated soil shrinkage anisotropy
characteristics and three different shrinkage curves of a soil relating to:
small samples (without cracking at shrinkage), sufficiently large samples (with
internal cracking), and layers of similar thickness. Then, the results of a
recent work with respect to the physical prediction of the three shrinkage
curves are used. These results connect the shrinkage curves with the initial
sample size/layer thickness as well as characteristics of soil texture and
structure (both inter- and intra-aggregate) as physical parameters. The
parameters determining the reference shrinkage curve (relating to the small
samples) and initial sample size/layer thickness are needed for the prediction
of the above soil shrinkage anisotropy characteristics. Using the available
data on two soils and samples of two essentially different sizes, illustrative
estimates of the relative sample sizes, new characteristic of the shrinkage
anisotropy, and shrinkage geometry factor are given as the physically predicted
values.",1405.3409v1
2015-05-11,Imprint of a 2 Myr old source on the cosmic ray anisotropy,"We study numerically the anisotropy of the cosmic ray (CR) flux emitted by a
single source calculating the trajectories of individual CRs. We show that the
contribution of a single source to the observed anisotropy is instead
determined solely by the fraction the source contributes to the total CR
intensity, its age and its distance,and does not depend on the CR energy at
late times. Therefore the observation of a constant dipole anisotropy indicates
that a single source dominates the CR flux in the corresponding energy range. A
natural explanation for the plateau between 2--20 TeV observed in the CR
anisotropy is thus the presence of a single, nearby source. For the source age
of 2 Myr, as suggested by the explanation of the antiproton and positron data
from PAMELA and AMS-02 through a local source [arXiv:astro-ph/1504.06472], we
determine the source distance as $\sim 200$ pc. Combined with the contribution
of the global CR sea calculated in the escape model, we can explain
qualitatively the data for the dipole anisotropy. Our results suggest that the
assumption of a smooth CR source distribution should be abandoned between 200
GeV and 1 PeV.",1505.02720v2
2015-06-09,Macroscopic model with anisotropy based on micro-macro informations,"Physical experiments can characterize the elastic response of granular
materials in terms of macroscopic state-variables, namely volume (packing)
fraction and stress, while the microstructure is not accessible and thus
neglected. Here, by means of numerical simulations, we analyze dense,
frictionless, granular assemblies with the final goal to relate the elastic
moduli to the fabric state, i.e., to micro-structural averaged contact network
features as contact number density and anisotropy.
  The particle samples are first isotropically compressed and later
quasi-statically sheared under constant volume (undrained conditions). From
various static, relaxed configurations at different shear strains, now
infinitesimal strain steps are applied to ""measure"" the effective elastic
response; we quantify the strain needed so that plasticity in the sample
develops as soon as contact and structure rearrangements happen. Because of the
anisotropy induced by shear, volumetric and deviatoric stresses and strains are
cross-coupled via a single anisotropy modulus, which is proportional to the
product of deviatoric fabric and bulk modulus (i.e. the isotropic fabric).
Interestingly, the shear modulus of the material depends also on the actual
stress state, along with the contact configuration anisotropy.
  Finally, a constitutive model based on incremental evolution equations for
stress and fabric is introduced. By using the previously measured dependence of
the stiffness tensor (elastic moduli) on the microstructure, the theory is able
to predict with good agreement the evolution of pressure, shear stress and
deviatoric fabric (anisotropy) for an independent undrained cyclic shear test,
including the response to reversal of strain.",1506.02992v2
2015-07-27,Ultrafast laser-induced changes of the magnetic anisotropy in a low-symmetry iron garnet film,"We explore a thermal mechanism of changing the anisotropy by femtosecond
laser pulses in dielectric ferrimagnetic garnets by taking a low symmetry
(YBiPrLu)3(FeGa)5O12 film grown on the (210)-oriented Gd3Ga5O12 substrate as a
model media. We demonstrate by means of spectral magneto-optical pump-probe
technique and phenomenological analysis, that the magnetization precession in
such a film is triggered by laser-induced changes of the growth-induced
magnetic anisotropy along with the well-known ultrafast inverse Faraday effect.
The change of magnetic anisotropy is mediated by the lattice heating induced by
laser pulses of arbitrary polarization on a picosecond time scale. We show that
the orientation of the external magnetic field with respect to the
magnetization easy plane noticeably affects the precession excited via the
anisotropy change. Importantly, the relative contributions from the ultrafast
inverse Faraday effect and the change of different growth-induced anisotropy
parameters can be controlled by varying the applied magnetic field strength and
direction. As a result, the amplitude and the initial phase of the excited
magnetization precession can be gradually tuned.",1507.07437v2
2015-09-02,Cosmic Ray Small Scale Anisotropies and Local Turbulent Magnetic Fields,"Cosmic ray anisotropy has been observed in a wide energy range and at
different angular scales by a variety of experiments over the past decade.
However, no comprehensive or satisfactory explanation has been put forth to
date. The arrival distribution of cosmic rays at Earth is the convolution of
the distribution of their sources and of the effects of geometry and properties
of the magnetic field through which particles propagate. It is generally
believed that the anisotropy topology at the largest angular scale is
adiabatically shaped by diffusion in the structured interstellar magnetic
field. On the contrary, the medium- and small-scale angular structure could be
an effect of non-diffusive propagation of cosmic rays in perturbed magnetic
fields. In particular, a possible explanation of the observed small-scale
anisotropy observed at TeV energy scale, may come from the effect of particle
scattering in turbulent magnetized plasmas. We perform numerical integration of
test particle trajectories in low-$\beta$ compressible magnetohydrodynamic
turbulence to study how the cosmic rays arrival direction distribution is
perturbed when they stream along the local turbulent magnetic field. We utilize
Liouville's theorem for obtaining the anisotropy at Earth and provide the
theoretical framework for the application of the theorem in the specific case
of cosmic ray arrival distribution. In this work, we discuss the effects on the
anisotropy arising from propagation in this inhomogeneous and turbulent
interstellar magnetic field.",1509.00892v2
2015-09-15,Overlap distributions for quantum quenches in the anisotropic Heisenberg chain,"The dynamics after a quantum quench is determined by the weights of the
initial state in the eigenspectrum of the final Hamiltonian, i.e., by the
distribution of overlaps in the energy spectrum. We present an analysis of such
overlap distributions for quenches of the anisotropy parameter in the
one-dimensional anisotropic spin-1/2 Heisenberg model (XXZ chain). We provide
an overview of the form of the overlap distribution for quenches from various
initial anisotropies to various final ones, using numerical exact
diagonalization. We show that if the system is prepared in the
antiferromagnetic N\'eel state (infinite anisotropy) and released into a
non-interacting setup (zero anisotropy, XX point) only a small fraction of the
final eigenstates gives contributions to the post-quench dynamics, and that
these eigenstates have identical overlap magnitudes. We derive expressions for
the overlaps, and present the selection rules that determine the final
eigenstates having nonzero overlap. We use these results to derive concise
expressions for time-dependent quantities (Loschmidt echo, longitudinal and
transverse correlators) after the quench. We use perturbative analyses to
understand the overlap distribution for quenches from infinite to small nonzero
anisotropies, and for quenches from large to zero anisotropy.",1509.04666v1
2015-10-29,Strain-induced perpendicular magnetic anisotropy in La$_2$CoMnO$_{6-ε}$ thin films and its dependence with film thickness,"Ferromagnetic insulating La$_2$CoMnO$_{6-\epsilon}$ (LCMO) epitaxial thin
films grown on top of SrTiO$_3$ (001) substrates presents a strong magnetic
anisotropy favoring the out of plane orientation of the magnetization with a
strong anisotropy field ($\sim 70$ kOe for film thickness of about 15 nm) and
with a coercive field of about 10 kOe. The anisotropy can be tuned by modifying
the oxygen content of the film which indirectly has two effects on the unit
cell: i) change of the orientation of the LCMO crystallographic axis over the
substrate (from c in-plane to c out-of-plane) and ii) shrinkage of the out of
plane cell parameter, which implies increasing tensile strain of the films. In
contrast, LCMO films grown on (LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ and
LaAlO$_3$ substrates (with a larger out-of-plane lattice parameter and
compressive stress) display in-plane magnetic anisotropy. Thus, we link the
strong magnetic anisotropy observed in La$_2$CoMnO$_{6-\epsilon}$ to the
relation between in-plane and out-of-plane parameters and so to the film
stress.",1510.08685v4
2015-12-11,Large anisotropy of electron and hole g factors in infrared-emitting InAs/InAlGaAs self-assembled quantum dots,"A detailed study of the $g$-factor anisotropy of electrons and holes in
InAs/In$_{0.53}$Al$_{0.24}$Ga$_{0.23}$As self-assembled quantum dots emitting
in the telecom spectral range of $1.5-1.6$ $\mu$m (around 0.8 eV photon energy)
is performed by time-resolved pump-probe ellipticity technique using a
superconducting vector magnet. All components of the $g$-factor tensors are
measured, including their spread in the quantum dot (QD) ensemble.
Surprisingly, the electron $g$ factor shows a large anisotropy changing from
$g_{\mathrm{e},x}= -1.63$ to $g_{\mathrm{e},z}= -2.52$ between directions
perpendicular and parallel to the dot growth axis, respectively, at an energy
of 0.82 eV. The hole $g$-factor anisotropy at this energy is even stronger:
$|g_{\text{h},x}|= 0.64$ and $|g_{\text{h},z}|= 2.29$. On the other hand, the
in-plane anisotropies of electron and hole $g$ factors are small. The
pronounced out-of-plane anisotropy is also observed for the spread of the $g$
factors, determined from the spin dephasing time. The hole longitudinal $g$
factors are described with a theoretical model that allows us to estimate the
QD parameters. We find that the QD height-to-diameter ratio increases while the
indium composition decreases with increasing QD emission energy.",1512.03544v3
2016-02-12,Effects of suprathermal electrons on the proton temperature anisotropy in space plasmas: Electromagnetic ion-cyclotron instability,"In collision-poor plasmas from space, e.g., the solar wind and planetary
magnetospheres, the kinetic anisotropy of the plasma particles is expected to
be regulated by the kinetic instabilities. Driven by an excess of ion (proton)
temperature perpendicular to the magnetic field $(~T_\perp >T_\parallel)$, the
electromagnetic ion-cyclotron (EMIC) instability is fast enough to constrain
the proton anisotropy, but the observations do not conform to the instability
thresholds predicted by the standard theory for bi-Maxwellian models of the
plasma particles. This paper presents an extended investigation of the EMIC
instability in the presence of suprathermal electrons which are ubiquitous in
these environments. The analysis is based on the kinetic (Vlasov-Maxwell)
theory assuming that both species, protons and electrons, may be anisotropic,
and the EMIC unstable solutions are derived numerically providing an accurate
description for conditions typically encountered in space plasmas. The effects
of suprathermal populations are triggered by the electron anisotropy and the
temperature contrast between electrons and protons. For certain conditions the
anisotropy thresholds exceed the limits of the proton anisotropy measured in
the solar wind considerably restraining the unstable regimes of the EMIC modes.",1602.04051v2
2016-02-18,Second order anisotropy contribution in perpendicular magnetic tunnel junctions,"Magnetoresistance loops under in-plane applied field were measured on
perpendicularly magnetized magnetic tunnel junction (pMTJ) pillars with nominal
diameters ranging from 50 to 150 nm. By fitting the hard-axis magnetoresistance
loops to an analytical model, the effective anisotropy fields in both free and
reference layers were derived and their variations in temperature range between
340K and 5K were determined. It is found that an accurate fitting is possible
only if a second-order anisotropy term of the form $-K_{2}cos^4{\theta}$, is
added to the fitting model. This higher order contribution exists both in the
free and reference layers and its sign is opposite to that of the first order
anisotropy constant, $K_{1}$. At room temperatures the estimated $-K_{2}/K_{1}$
ratios are 0.1 and 0.24 for the free and reference layers, respectively. The
ratio is more than doubled at low temperatures altering the ground state of the
reference layer from 'easy-axis' to 'easy-cone' regime. Easy-cone state has
clear signatures in the shape of the hard-axis magnetoresistance loops. The
same behavior was observed in all measured devices regardless of their
diameter. The existence of this higher order anisotropy was confirmed
experimentally on FeCoB/MgO sheet films by ferromagnetic resonance technique.
It is of interfacial nature and is believed to be linked to spatial
fluctuations at the nanoscale of the anisotropy parameter at the FeCoB/MgO
interface, in agreement with Dieny-Vedyayev model.",1602.05815v1
2016-04-10,Entanglement robustness in Heisenberg spin chains coupled to dissipative environment at finite temperature,"We consider a finite one-dimensional Heisenberg XYZ spin chain under the
influence of dissipative Lindblad environment obeying the Born-Markovian
constrain in presence of an external magnetic field. We apply both closed and
open boundary conditions at zero and finite temperature. We present an exact
numerical solution for the Lindblad master equation of the system in the
Liouville space. we find that, in the free spin chain (in absence of any
environment), the entanglement at all ranges evolve in time in a non-uniform
oscillatory form that changes significantly depending on the initial state,
system size and the spatial anisotropy. The oscillatory behavior is suppressed
once the system is coupled to the environment. Furthermore, the asymptotic
behavior of the entanglement, nearest neighbor and beyond, in the system under
the influence of the environment at zero temperature is very sensitive to the
x-y spatial anisotropy, which causes them to reach either a zero or a finite
sustainable steady state value regardless of the initial state of the system.
The anisotropy in the $z-$direction may enhance the entanglement depending on
the interplay with the magnetic field applied in the same direction. As the
temperature is raised, the steady state of the short range entanglements is
found to be robust within very small non-zero temperature range, which depends
critically on the spatial anisotropy of the system. The entanglement at each
range depends differently on the spatial anisotropy. Moreover, the end to end
entanglement transfer time and speed through the open boundary chain vary
significantly based on the degree of anisotropy and the temperature of the
environment.",1604.02689v1
2016-07-18,Effects of Crystal Anisotropy on Optical Phonon Resonances in the Mid-Infrared Second Harmonic Response of SiC,"We study the effects of crystal anisotropy on optical phonon resonances in
the second harmonic generation (SHG) from silicon carbide (SiC) in its
Reststrahl region. By comparing experiments and simulations for isotropic
3C-SiC and anisotropic 4H-SiC in two crystal cuts, we identify several
pronounced effects in the nonlinear response which arise solely from the
crystal anisotropy. Specifically, we demonstrate that the axial and planar
transverse optical phonon resonances selectively and exclusively appear in the
corresponding tensor elements of the nonlinear susceptibility, enabling
observation of an intense SHG peak originating from a weak phonon mode due to
zone-folding along the c-axis of 4H-SiC. Similarly, we identify an anisotropy
factor $\zeta \equiv \epsilon_\perp/\epsilon_\parallel$ responsible for a steep
enhancement of the transmitted fundamental fields at the axial longitudinal
optical phonon frequency, resulting in strongly enhanced SHG. We develop a
general recipe to extract all these features that is directly applicable to all
wurtzite-structure polar dielectrics, where a very similar behavior is
expected. Our model study illustrates the opportunities for utilizing the
crystal anisotropy for selectively enhancing nonlinear-optical effects in polar
dielectrics, which could potentially be extended to built-in anisotropy in
artificially designed hybrid materials.",1607.05207v2
2016-09-17,Magnetic-anisotropy induced spin blockade in a single-molecule transistor,"We present a new mechanism for a spin blockade effect associated with a
change in the type of magnetic anisotropy over oxidation state in a single
molecule transistor, by taking an example of an individual
Eu$_{2}$(C$_{8}$H$_{8}$)$_{3}$ molecule weakly coupled to non-magnetic
electrodes without linker groups. The molecule switches its magnetization
direction from in-plane to out-of-plane when it is charged. In other words, the
magnetic anisotropy of the molecule changes from easy plane to easy axis when
the molecule is charged. By solving the master equation based on model
Hamiltonian, we find that current through the molecule is highly suppressed at
low bias independently of gate voltage due to the interplay between spin
selection rules and the change in the type of magnetic anisotropy. Transitions
between the lowest magnetic levels in successive charge states are forbidden
because the magnetic levels differ by $|\Delta M| > 1/2$ due to the change in
the type of magnetic anisotropy, although the total spins differ by $|\Delta
S|=1/2$. This current suppression can be lifted by significant B field, and the
threshold B field varies as a function of the field direction and the strength
of magnetic anisotropy. The spin blockade effect shed light on switching the
magnetization direction by non-spin-polarized current and on exploring effects
of this property coupled to other molecular degrees of freedom.",1609.05269v1
2016-11-17,Anisotropy induces non-Fermi-liquid behavior and nematic magnetic order in three-dimensional Luttinger semimetals,"We illuminate the intriguing role played by spatial anisotropy in
three-dimensional Luttinger semimetals featuring quadratic band touching and
long-range Coulomb interactions. We observe the anisotropy to be subject to an
exceptionally slow renormalization group (RG) evolution so that it can be
considered approximately constant when computing the impact of quantum
fluctuations on the remaining couplings of the system. Using perturbative RG we
then study the competition of all local short-range interactions that are
generated from the long-range interactions for fixed anisotropy. Two main
effects come to light for sufficiently strong anisotropy. First, the
three-dimensional system features an Abrikosov non-Fermi liquid ground state.
Second, there appear qualitatively new fixed points which describe quantum
phase transitions into phases with nemagnetic orders - higher-rank tensor
orders that break time-reversal symmetry, and thus have both nematic and
magnetic character. In real materials these phases may be realized through
sufficiently strong microscopic short-range interactions. On the pyrochlore
lattice, the anisotropy-induced fixed points determine the onset of
all-in-all-out or spin ice ordering of local magnetic moments of the electrons.",1611.05904v2
2016-11-23,"Cubic anisotropy created by defects of ""random local anisotropy"" type, and phase diagram of the O(n) model","The expression for the cubic-type-anisotropy constant created by defects of
""random local anisotropy"" type is derived. It is shown that the Imry-Ma theorem
stating that in space dimensions d<4 the introduction of an arbitrarily small
concentration of defects of the ""random local anisotropy"" type in a system with
continuous symmetry of the n-component vector order parameter (O(n) model)
leads to the long-range order collapse and to occurrence of a disordered state,
is not true if an anisotropic distribution of the defect-induced random easy
axes directions in the order parameter space creates a global effective
anisotropy of the ""easy axis"" type. For a weakly anisotropic distribution of
the easy axes, in space dimensions 2<d<4 there exists some critical defect
concentration, when exceeded, the inhomogeneous Imry-Ma state can exist as an
equilibrium one. At lower defect concentration the long-range order takes place
in the system. For a strongly anisotropic distribution of the easy axes, the
Imry-Ma state is suppressed completely and the long-range order state takes
place at any defect concentration.",1611.07948v1
2016-12-01,Spin anisotropy due to spin-orbit coupling in optimally hole-doped Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$,"We use polarized inelastic neutron scattering to study the temperature and
energy dependence of spin space anisotropies in the optimally hole-doped iron
pnictide Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ ($T_{{\rm c}}=38$ K). In the
superconducting state, while the high-energy part of the magnetic spectrum is
nearly isotropic, the low-energy part displays a pronouced anisotropy,
manifested by a $c$-axis polarized resonance. We also observe that the spin
anisotropy in superconducting Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ extends to
higher energies compared to electron-doped BaFe$_{2-x}TM_{x}$As$_{2}$ ($TM=$Co,
Ni) and isovalent-doped BaFe$_{2}$As$_{1.4}$P$_{0.6}$, suggesting a connection
between $T_{\rm c}$ and the energy scale of the spin anisotropy. In the normal
state, the low-energy spin anisotropy for optimally hole- and electron-doped
iron pnictides onset at temperatures similar to the temperatures at which the
elastoresistance deviate from Curie-Weiss behavior, pointing to a possible
connection between the two phenomena. Our results highlight the relevance of
the spin-orbit coupling to the superconductivity of the iron pnictides.",1612.00379v2
2017-01-07,Velocity Anisotropy in Self-Gravitating Molecular Clouds. I: Simulation,"The complex interplay between turbulence, magnetic fields, and self-gravity
leads to the formation of molecular clouds out of the diffuse interstellar
medium (ISM). One avenue of studying this interplay is by analyzing statistical
features derived from observations, where the interpretation of these features
is greatly facilitated by comparisons with numerical simulations. Here we focus
on the statistical anisotropy present in synthetic maps of velocity centroid
data, which we derive from three-dimensional magnetohydrodynamic simulations of
a turbulent, magnetized, self-gravitating patch of ISM. We study how the
orientation and magnitude of the velocity anisotropy correlate with the
magnetic field and with the structures generated by gravitational collapse.
  Motivated by recent observational constraints, our simulations focus on the
supersonic (sonic Mach number $\mathcal{M} \approx 2 - 17$) but sub- to
trans-alfvenic (alfvenic Mach number $\mathcal{M}_A \approx 0.2 - 1.2$)
turbulence regime, and we consider clouds which are barely to mildly
magnetically supercritical (mass-to-flux ratio equal to once or twice the
critical value). Additionally we explore the impact of the turbulence driving
mechanism (solenoidal or compressive) on the velocity anisotropy.
  While we confirm previous findings that the velocity anisotropy generally
aligns well with the plane-of-sky magnetic field, our inclusion of the effects
of self-gravity reveals that in regions of higher column density, the velocity
anisotropy may be destroyed or even reoriented to align with the
gravitationally formed structures. We provide evidence that this effect is not
necessarily due to the increase of $\mathcal{M}_A$ inside the high-density
regions.",1701.01806v1
2017-05-08,The influence of magnetic order on the magnetoresistance anisotropy of Fe$_{1+δ-x}$Cu$_{x}$Te,"We performed resistance measurements on Fe$_{1+\delta-x}$Cu$_{x}$Te with
$x_{EDX}\leq 0.06$ in the presence of in-plane applied magnetic fields,
revealing a resistance anisotropy that can be induced at a temperature far
below the structural and magnetic zero-field transition temperatures. The
observed resistance anisotropy strongly depends on the field orientation with
respect to the crystallographic axes, as well as on the field-cooling history.
Our results imply a correlation between the observed features and the
low-temperature magnetic order. Hysteresis in the angle-dependence indicates a
strong pinning of the magnetic order within a temperature range that varies
with the Cu content. The resistance anisotropy vanishes at different
temperatures depending on whether an external magnetic field or a remnant field
is present: the closing temperature is higher in the presence of an external
field. For $x_{EDX} = 0.06$ the resistance anisotropy closes above the
structural transition, at the same temperature at which the zero-field
short-range magnetic order disappears and the sample becomes paramagnetic. Thus
we suggest that under an external magnetic field the resistance anisotropy
mirrors the magnetic order parameter. We discuss similarities to nematic order
observed in other iron pnictide materials.",1705.02849v1
2018-01-11,Modeling the Oblique Spin Precession in Lateral Spin Valves for Accurate Determination of Spin Lifetime Anisotropy: Effect of Finite Contact Resistance and Channel Length,"The spin lifetime anisotropy is an important quantity for investigating the
spin relaxation mechanisms in graphene and in heterostructures of
two-dimensional materials. We generalize the diffusive spin transport equations
of oblique spin precession in a lateral spin valve with finite contact
resistance. This yields a method to determine the spin lifetime anisotropy
ratio {\xi}={\tau}$_{\perp}$/{\tau}$_{\parallel}$, which is the ratio between
lifetimes of spin polarized perpendicular and parallel to the graphene surface.
By solving the steady-state Bloch equations, we show that the line-shape of the
oblique spin precession signal can be described with six dimensionless
parameters, which can be solved analytically. We demonstrate that the
anisotropic spin precession characteristics can be strongly suppressed by
contact induced spin relaxation originating from conductance mismatch between
the channel material and electrodes. To extract the spin lifetime anisotropy
ratio accurately, we develop a closed form equation that includes the effect of
finite contact resistance. Furthermore, we demonstrate that in the high contact
resistance regime, the minimum channel length required for accurately
determining the spin lifetime anisotropy for a sufficiently low external
magnetic field is only determined by the diffusion coefficient of the channel
material, as opposed to the spin diffusion length. Our work provides an
accurate model to extract the spin lifetime anisotropy ratio from the oblique
spin precession measurement, and can be used to guide the device design for
such measurements.",1801.03606v1
2018-02-27,"3D Anisotropy of Solar Wind Turbulence, Tubes, or Ribbons?","We study the anisotropy with respect to the local magnetic field of turbulent
magnetic fluctuations at magnetofluid scales in the solar wind. Previous
measurements in the fast solar wind obtained axisymmetric anisotropy, despite
that the analysis method allows nonaxisymmetric structures. These results are
probably contaminated by the wind expansion that introduces another symmetry
axis, namely, the radial direction, as indicated by recent numerical
simulations. These simulations also show that while the expansion is strong,
the principal fluctuations are in the plane perpendicular to the radial
direction. Using this property, we separate 11 yr of Wind spacecraft data into
two subsets characterized by strong and weak expansion and determine the
corresponding turbulence anisotropy. Under strong expansion, the small-scale
anisotropy is consistent with the Goldreich & Sridhar critical balance. As in
previous works, when the radial symmetry axis is not eliminated, the turbulent
structures are field-aligned tubes. Under weak expansion, we find 3D anisotropy
predicted by the Boldyrev model, that is, turbulent structures are ribbons and
not tubes. However, the very basis of the Boldyrev phenomenology, namely, a
cross-helicity increasing at small scales, is not observed in the solar wind:
the origin of the ribbon formation is unknown.",1802.09837v2
2018-06-05,Observing small-scale $γ$-ray anisotropies with the Cherenkov Telescope Array,"Disentangling the composition of the diffuse gamma-ray background (DGRB) is a
major challenge in gamma-ray astronomy. It is presumed that at the highest
energies, the DGRB is dominated by relatively few, still unresolved point
sources. This conjecture has recently been supported by the measurement of
small-scale anisotropies in the DGRB by the Fermi Large Area Telescope (LAT) up
to energies of 500 GeV. We show how such anisotropies can be searched for with
the forthcoming Earth-bound Cherenkov Telescope Array (CTA) up to the TeV
range. We investigate different observation modes to analyse CTA data for
small-scale anisotropies and propose the projected extragalactic large-area sky
survey as the most promising data set. Relying on an up-to-date model of the
performance of the southern CTA, we find that CTA will be able to probe
anisotropies in the DGRB from unresolved point sources at a relative amplitude
of $C_{\rm P}^I/I^2_{\rm DGRB}\gtrsim 4\times 10^{-3}\,{\rm sr}$ at energies
above 30 GeV and angular scales $\lesssim 1.5^{\circ}$. Such DGRB anisotropies
have not yet been ruled out by the Fermi-LAT. The proposed analysis would
primarily clarify the contribution from blazars and misaligned active galactic
nuclei to the very-high-energy regime of the DGRB, as well as provide insight
into dark matter annihilation in Galactic and extragalactic density structures.
Finally, it constitutes a measurement with complementary systematic
uncertainties compared to the Fermi-LAT.",1806.01839v2
2018-11-28,Inverse Anisotropic Catalysis in Holographic QCD,"We investigate the effects of anisotropy on the chiral condensate in a
holographic model of QCD with a fully backreacted quark sector at vanishing
chemical potential. The high temperature deconfined phase is a neutral and
anisotropic plasma showing different pressure gradients along different spatial
directions, similar to the state produced in noncentral heavy-ion collisions.
We find that the chiral transition occurs at a lower temperature in the
presence of anisotropy. Equivalently, we find that anisotropy acts
destructively on the chiral condensate near the transition temperature. These
are precisely the same footprints as the ""inverse magnetic catalysis"" i.e. the
destruction of the condensate with increasing magnetic field observed earlier
on the lattice, in effective field theory models and in holography. Based on
our findings we suggest, in accordance with the conjecture of [1], that the
cause for the inverse magnetic catalysis may be the anisotropy caused by the
presence of the magnetic field instead of the charge dynamics created by it. We
conclude that the weakening of the chiral condensate due to anisotropy is more
general than that due to a magnetic field and we coin the former ""inverse
anisotropic catalysis"". Finally, we observe that any amount of anisotropy
changes the IR physics substantially: the geometry is $\text{AdS}_4 \times
\mathbb{R}$ up to small corrections, confinement is present only up to a
certain scale, and the particles acquire finite widths.",1811.11724v3
2018-12-06,CMB statistical isotropy confirmation at all scales using multipole vectors,"We present an efficient numerical code and conduct, for the first time, a
null and model-independent CMB test of statistical isotropy using Multipole
Vectors (MVs) at all scales. Because MVs are insensitive to the angular power
spectrum $C_\ell$, our results are independent from the assumed cosmological
model. We avoid a posteriori choices and use pre-defined ranges of scales
$\ell\in[2,30]$, $\ell\in[2,600]$ and $\ell\in[2,1500]$ in our analyses. We
find that all four masked Planck maps, from both 2015 and 2018 releases, are in
agreement with statistical isotropy for $\ell\in[2,30]$, $\ell\in[2,600]$. For
$\ell\in[2,1500]$ we detect anisotropies but this is indicative of simply the
anisotropy in the noise: there is no anisotropy for $\ell < 1300$ and an
increasing level of anisotropy at higher multipoles. Our findings of no
large-scale anisotropies seem to be a consequence of avoiding \emph{a
posteriori} statistics. We also find that the degree of anisotropy in the full
sky (i.e. unmasked) maps vary enormously (between less than 5 and over 1000
standard deviations) among the different mapmaking procedures and data
releases.",1812.02654v5
2018-12-08,Resolution-induced anisotropy in LES,"Large eddy simulation (LES) of turbulence in complex geometries and domains
is often conducted with high aspect ratio resolution cells of varying shapes
and orientations. The effects of such anisotropic resolution are often
simplified or neglected in subgrid model formulation. Here, we examine
resolution induced anisotropy and demonstrate that, even for isotropic
turbulence, anisotropic resolution induces mild resolved Reynolds stress
anisotropy and significant anisotropy in second-order resolved velocity
gradient statistics. In large eddy simulations of homogeneous isotropic
turbulence with anisotropic resolution, it is shown that commonly used subgrid
models, including those that consider resolution anisotropy in their
formulation, perform poorly. The one exception is the anisotropic minimum
dissipation model proposed by Rozema et al. (Phys. of Fluids 27, 085107, 2015).
A simple new model is presented here that is formulated with an anisotropic
eddy diffusivity that depends explicitly on the anisotropy of the resolution.
It also performs well, and is remarkable because unlike other LES subgrid
models, the eddy diffusivity only depends on statistical characteristics of the
turbulence (in this case the dissipation rate), not on fluctuating quantities.
In other subgrid modeling formulations, such as the dynamic procedure, limiting
flow dependence to statistical quantities in this way could have advantages.",1812.03261v2
2019-01-04,Anisotropies and magnetic phase transitions in insulating antiferromagnets determined by a Spin-Hall magnetoresistance probe,"We demonstrate that we can determine the antiferromagnetic anisotropies and
the bulk Dzyaloshinskii-Moriya fields of the insulating iron oxide hematite,
{\alpha}-Fe2O3, using a surface sensitive spin-Hall magnetoresistance (SMR)
technique. We develop an analytical model that in combination with SMR
measurements, allow for the identification of the material parameters of this
prototypical antiferromagnet over a wide range of temperatures and magnetic
field values. Using devices with different orientations, we demonstrate that
the SMR response strongly depends on the direction of the charge current with
respect to the magneto-crystalline anisotropies axis. We show that we can
extract the anisotropies over a wide temperature range including across the
Morin phase transition. We observe that the electrical response is dominated by
the orientation of the antiferromagnetic N\'eel order parameter, rather than by
the emergent weak magnetic moment. Our results highlight that the surface
sensitivity of the SMR allows accessing the magnetic anisotropies of
antiferromagnetic crystals and in particular thin films where other methods to
determine anisotropies such as bulk-sensitive magnetic susceptibility
measurements do not provide sufficient sensitivity.",1901.01213v1
2019-03-07,A Search for Cosmic-ray Proton Anisotropy with the Fermi Large Area Telescope,"The Fermi Large Area Telescope (LAT) has amassed a large data set of primary
cosmic-ray protons throughout its mission. The LAT's wide field of view and
full-sky survey capabilities make it an excellent instrument for studying
cosmic-ray anisotropy. As a space-based survey instrument, the LAT is sensitive
to anisotropy in both right ascension and declination, while ground-based
observations only measure the anisotropy in right ascension. We present the
results of the first ever proton anisotropy search using Fermi LAT. The data
set uses eight years of data and consists of approximately 179 million protons
above 78 GeV, enabling it to probe dipole anisotropy below an amplitude of
$10^{-3}$, resulting in the most stringent limits on the declination dependence
of the dipole to date. We measure a dipole amplitude $\delta = 3.9\pm1.5 \times
10^{-4}$ with a p-value of 0.01 (pre-trials) for protons with a minimum energy
of 78 GeV. We discuss various systematic effects that could give rise to a
dipole excess and calculate upper limits on the dipole amplitude as a function
of minimum energy. The 95% CL upper limit on the dipole amplitude is
$\delta_{UL}=1.3\times 10^{-3}$ for protons with a minimum energy of 78 GeV and
$\delta_{UL}=1.2 \times 10^{-3}$ for protons with a minimum energy of 251 GeV.",1903.02905v1
2019-05-29,Anisotropies of different mass compositions of cosmic rays,"The spectral hardenings of cosmic ray nuclei above $\sim 200$ GV followed by
softenings around 10 TV, the knee of the all-particle spectrum around PeV
energies, as well as the pattern change of the amplitude and phase of the
large-scale anisotropies around 100 TeV indicate the complexities of the origin
and transportation of Galactic cosmic rays. It has been shown that nearby
source(s) are most likely to be the cause of such spectral features of both the
spectra and the anisotropies. In this work, we study the anisotropy features of
different mass composition (or mass groups) of cosmic rays in this nearby
source model. We show that even if the spectral features from the nearby source
component is less distinctive compared with the background component from e.g.,
the population of distant sources, the anisotropy features are more remarkable
to be identified. Measurements of the anisotropies of each mass composition
(group) of cosmic rays by the space experiments such as DAMPE and HERD and the
ground-based experiments such as LHAASO in the near future are expected to be
able to critically test this scenario.",1905.12505v3
2019-07-19,Particle-In-Cell simulations of the parallel proton firehose instability influenced by the electron temperature anisotropy in solar wind conditions,"In situ observations of the solar wind show a limited level of particle
temperature anisotropy with respect to the interplanetary magnetic field
direction. Kinetic electromagnetic instabilities are efficient to prevent the
excessive growth of the anisotropy of particle velocity distribution functions.
Among them, the firehose instabilities are often considered to prevent the
increase of the parallel temperature and hence to shape the velocity
distribution functions of electrons and protons in the solar wind. We present a
non-linear modeling of the parallel firehose instability, retaining a kinetic
description for both the electrons and protons. One-dimensional (1D) fully
kinetic Particle-In-Cell simulations using the Energy Conserving semi-implicit
method (ECsim) are performed to clarify the role of the electron temperature
anisotropy in the development of the parallel proton firehose instability. We
found that in the presence of an electron temperature anisotropy, such that the
temperature parallel to the background magnetic field is higher than the
temperature in the perpendicular direction, the onset of the parallel proton
firehose instability occurs earlier and its growth rate is faster. The enhanced
wave fluctuations contribute to the particle scattering reducing the
temperature anisotropy to a stable, nearly isotropic state. The simulation
results compare well with linear theory. A test case of 1D simulations at
oblique angles with respect to the magnetic field is also considered, as a
first step to study the cumulative effect of protons and electrons on the full
spectrum of instabilities.",1907.08502v2
2019-08-17,Hybrid Color Glass Condensate and hydrodynamic description of the Relativistic Heavy Ion Collider small system scan,"Multi-particle correlation observables in the Relativistic Heavy Ion Collider
small system scan are computed in a framework that contains both initial state
momentum anisotropies from the Color Glass Condensate effective theory and
final state hydrodynamic evolution. The initial state is computed using the
IP-Glasma model and coupled to viscous relativistic hydrodynamic simulations,
which are followed by microscopic hadronic transport. All parameters of the
calculation were previously constrained using experimental data on Au+Au
collisions at the same center of mass energy. We find that the qualitative
features of the experimental data, such as the system and centrality dependence
of the charged hadron momentum anisotropy, can only be reproduced when final
state interactions are present. On the other hand, we also demonstrate that the
details of the initial state are crucially important for the quantitative
description of observables in the studied small systems, as neglecting the
initial transverse flow profile or the initial shear stress tensor, which
contain information on the momentum anisotropy from the Color Glass Condensate,
has dramatic effects on the produced final state anisotropy. We further show
that the initial state momentum anisotropy is correlated with the observed
elliptic flow in all small systems, with the effect increasing with decreasing
multiplicity. We identify the precise measurement of $v_2$ in d+Au and Au+Au
collisions at RHIC energy at the same multiplicity as a means to reveal effects
of the initial state momentum anisotropy.",1908.06212v1
2019-10-30,Transverse momentum and process dependent azimuthal anisotropies in $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV $p$+Pb collisions with the ATLAS detector,"The azimuthal anisotropy of charged particles produced in
$\sqrt{s_{\mathrm{NN}}}=8.16$ TeV $p$+Pb collisions is measured with the ATLAS
detector at the LHC. The data correspond to an integrated luminosity of $165$
$\mathrm{nb}^{-1}$ that was collected in 2016. Azimuthal anisotropy
coefficients, elliptic $v_2$ and triangular $v_3$, extracted using two-particle
correlations with a non-flow template fit procedure, are presented as a
function of particle transverse momentum ($p_\mathrm{T}$) between $0.5$ and
$50$ GeV. The $v_2$ results are also reported as a function of centrality in
three different particle $p_\mathrm{T}$ intervals. The results are reported
from minimum-bias events and jet-triggered events, where two jet $p_\mathrm{T}$
thresholds are used. The anisotropies for particles with $p_\mathrm{T}$ less
than about $2$ GeV are consistent with hydrodynamic flow expectations, while
the significant non-zero anisotropies for $p_\mathrm{T}$ in the range $9$-$50$
GeV are not explained within current theoretical frameworks. In the
$p_\mathrm{T}$ range $2$-$9$ GeV, the anisotropies are larger in minimum-bias
than in jet-triggered events. Possible origins of these effects, such as the
changing admixture of particles from hard scattering and the underlying event,
are discussed.",1910.13978v2
2019-12-21,Extreme acoustic anisotropy in crystals visualized by diffraction tensor,"Acoustic wave propagation in single crystals, metamaterials and composite
structures is a basic mechanism in acoustic, acousto-electronic and
acousto-optic devices. Acoustic anisotropy of crystals provides a variety of
device performances and application fields, but its role in pre-estimation of
achievable device characteristics and location of crystal orientations with
desired properties is often underestimated. A geometrical image of acoustic
anisotropy can be an important tool in design of devices based on wave
propagation in single crystals or combinations of anisotropic materials. We
propose a fast and robust method for survey and visualization of acoustic
anisotropy based on calculation of the eigenvalues of bulk acoustic wave (BAW)
diffraction tensor (curvature of the slowness surface). The stereographic
projection of these eigenvalues clearly reveals singular directions of BAW
propagation (acoustic axes) in anisotropic media and areas of fast or slow
variation of wave velocities. The method is illustrated by application to three
crystals of different symmetry used in different types of acoustic devices:
paratellurite, lithium niobate, and potassium gadolinium tungstate. The
specific features of acoustic anisotropy are discussed for each crystal in
terms of their potential application in devices. In addition, we demonstrate
that visualization of acoustic anisotropy of lithium niobate helps to find
orientations supporting propagation of high-velocity surface acoustic waves.",1912.10270v1
2020-02-25,Strain-Tuned Magnetic Anisotropy in Sputtered Thulium Iron Garnet Ultrathin Films and TIG/Au/TIG Valve Structures,"Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in
ferrimagnetic insulators films by controlling the strain, while maintaining
high-quality surfaces, is desirable for spintronic and magnonic applications.
We investigate ways to tune the anisotropy of amorphous sputtered ultrathin
thulium iron garnet (TIG) films, and thus tailor their magnetic properties by
the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and
crystallization process. We correlate morphological and structural properties
with the magnetic anisotropy of post-growth annealed films. 30 nm thick films
annealed at 600 {\deg}C show compressive strain favoring an in-plane magnetic
anisotropy (IPMA), whereas films annealed above 800 {\deg}C are under a tensile
strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films
present a high degree of crystallinity and magnetization saturation close to
the bulk value. These results lead to successful fabrication of trilayers
TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness.
These results will facilitate the use of TIG to create various in situ clean
hybrid structures for fundamental interface exchange studies, and towards the
development of complex devices. Moreover, the sputtering technique is
advantageous as it can be easily scaled up for industrial applications.",2002.10608v2
2020-06-28,Observable signatures of initial state momentum anisotropies in nuclear collisions,"We show that the correlation between the elliptic momentum anisotropy, $v_2$,
and the average transverse momentum, $[p_T]$, at fixed multiplicity in small
system nuclear collisions carries information on the origin of the observed
momentum anisotropy. A calculation using a hybrid
IP-Glasma+\textsc{Music}+UrQMD model that includes contributions from final
state response to the initial geometry as well as initial state momentum
anisotropies of the Color Glass Condensate, predicts a characteristic sign
change of the correlator $\hat{\rho}(v_2^2,[p_T])$ as a function of charged
particle multiplicity in p+Au and d+Au collisions at $\sqrt{s}=200\,{\rm GeV}$,
and p+Pb collisions at $\sqrt{s}=5.02\,{\rm TeV}$. This sign change is absent
in calculations without initial state momentum anisotropies. The model further
predicts a qualitative difference between the centrality dependence of
$\hat{\rho}(v_2^2,[p_T])$ in Au+Au collisions at $\sqrt{s}=200\,{\rm GeV}$ and
Pb+Pb collisions at $\sqrt{s}=5.02\,{\rm TeV}$, with only the latter showing a
sign change in peripheral events. Predictions for O+O collisions at different
collision energy show a similar behavior. Experimental observation of these
distinct qualitative features of $\hat{\rho}(v_2^2,[p_T])$ in small and large
systems would constitute strong evidence for the presence and importance of
initial state momentum anisotropies predicted by the Color Glass Condensate
effective theory.",2006.15721v1
2020-07-22,Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method,"Modeling blocking temperature in molecular magnets has been a long standing
problem in the field of molecular magnetism. We investigate this problem using
a kinetic Monte Carlo (kMC) approach on an assembly of 100,000 short molecular
magnetic chains (SMMCs), each of six identical spins with nearest neighbour
anisotropic ferromagnetic exchange interactions. Each spin is also anisotropic
with an uniaxial anisotropy. The site spin on these SMMCs take values $1$,
$3/2$ or $2$. Using eigenstates of these SMMCs as the states of Markov chain,
we carry out a kMC simulation starting with an initial state in which all SMMCs
are completely spin polarized and assembled on a one-dimensional lattice so as
to experience ferromagnetic spin-dipolar interaction with each other. From
these simulations we obtain the relaxation time $\tau_r$ as a function of
temperature and the associated blocking temperature. We study this for
different exchange anisotropy, on-site anisotropy and strength of dipolar
interactions. The magnetization relaxation times show non-Arrhenius behaviour
for weak on-site interactions. The energy barrier to magnetization relaxation
increases with increase in on-site anisotropy, exchange anisotropy and strength
of spin dipolar interactions; more strongly on the last parameter. In all cases
the barrier saturates at large on-site anisotropy. The barrier also increases
with site spin. The large barrier observed in rare-earth single ion magnets can
be attributed to large dipolar interactions due to short intermolecular
distances, owing to their small size and large spin of the rare earth ion in
the molecule.",2007.11342v4
2020-08-28,Testing cosmic anisotropy with Pantheon sample and quasars at high redshifts,"In this paper, we investigate the cosmic anisotropy from the SN-Q sample,
consisting of the Pantheon sample and quasars, by employing the hemisphere
comparison (HC) method and the dipole fitting (DF) method. Compared to the
Pantheon sample, the new sample has a larger redshift range, a more homogeneous
distribution, and a larger sample size. For the HC method, we find that the
maximum anisotropy level is $AL_{max}=0.142\pm0.026$ in the direction ($l$,
$b$) = $({316.08^{\circ}}^{+27.41}_{-129.48}$,
${4.53^{\circ}}^{+26.29}_{-64.06})$. The magnitude of anisotropy is $A$ =
($-$8.46 $^{+4.34}_{-5.51}$)$\times$$10^{-4}$ and the corresponding preferred
direction points toward $(l$, $b)$ = ($29.31^{\circ}$$^{+30.59}_{-30.54}$,
$71.40^{\circ}$$^{+9.79}_{-9.72}$) for the quasar sample from the DF method.
The combined SN and quasar sample is consistent with the isotropy hypothesis.
The distribution of the dataset might impact the preferred direction from the
dipole results. The result is weakly dependent on the redshift from the
redshift tomography analysis. There is no evidence of cosmic anisotropy in the
SN-Q sample. Though some results obtained from the quasar sample are not
consistent with the standard cosmological model, we still do not find any
distinct evidence of cosmic anisotropy in the SN-Q sample.",2008.12439v1
2020-09-18,The effect of the surface magnetic anisotropy of the neodymium atoms on the coercivity in the neodymium permanent magnet,"The Nd permanent magnet (Nd$_{2}$Fe$_{14}$B) is an indispensable material
used in modern energy conversion devices. The realization of high coercivity at
finite temperatures is a burning issue. One of the important ingredients for
controlling the coercive force is the surface property of magnetic grains. It
has been reported by first-principles studies that the Nd atoms in the first
(001) surface layer facing the vacuum have in-plane anisotropy perpendicular to
the $c$ axis, which may decrease the coercivity. Focusing on the surface
anisotropy effect on the coercivity, we examine the coercivity at zero and
finite temperatures by using an atomistic model reflecting the lattice
structure of the Nd magnet with a stochastic Landau-Lifshitz-Gilbert equation
method. We study general three cases, in which the Nd atoms in surface layers
have (1) no anisotropy, (2) in-plane anisotropy, and (3) reinforced anisotropy
for two types of surfaces, (001) and (100) surfaces. We find that in contrast
to the zero-temperature case, due to the thermal fluctuation effect, the
modification of only the first surface layer has little effect on the
coercivity at finite temperatures. However, the modification of a few layers
results in significant effects. We discuss the details of the dependence of the
coercivity on temperature, type of surface, and modified layer depth, and also
the features of domain growth in magnetization reversal.",2009.08572v1
2020-10-16,"Physical Explanation for the Galaxy Distribution on the $(λ_{\rm R}, \varepsilon)$ and $(V/σ, \varepsilon)$ Diagrams or for the Limit on Orbital Anisotropy","In the $(\lambda_{\rm R}, \varepsilon)$ and $(V/\sigma, \varepsilon)$
diagrams for characterizing dynamical states, the fast-rotator galaxies (both
early-type and spirals) are distributed within a well-defined leaf-shaped
envelope. This was explained as due to an upper limit to the orbital anisotropy
increasing with galaxy intrinsic flattening. However, a physical explanation
for this empirical trend was missing. Here we construct Jeans Anisotropic
Models (JAM), with either cylindrically or spherically aligned velocity
ellipsoid (two extreme assumptions), and each with either spatially-constant or
-variable anisotropy. We use JAM to build mock samples of axisymmetric
galaxies, assuming on average an oblate shape for the velocity ellipsoid (as
required to reproduce the rotation of real galaxies), and limiting the radial
anisotropy $\beta$ to the range allowed by physical solutions. We find that all
four mock samples naturally predict the observed galaxy distribution on the
$(\lambda_{\rm R}, \varepsilon)$ and $(V/\sigma, \varepsilon)$ diagrams,
without further assumptions. Given the similarity of the results from quite
different models, we conclude that the empirical anisotropy upper limit in real
galaxies, and the corresponding observed distributions in the $(\lambda_{\rm
R}, \varepsilon)$ and $(V/\sigma, \varepsilon)$ diagrams, are due to the lack
of physical axisymmetric equilibrium solutions at high $\beta$ anisotropy when
the velocity ellipsoid is close to oblate.",2010.08586v1
2020-10-20,The primordial information content of Rayleigh Anisotropies,"Anisotropies in the cosmic microwave background (CMB) are primarily generated
by Thomson scattering of photons by free electrons. Around recombination, the
Thomson scattering probability quickly diminishes as the free electrons combine
with protons to form neutral hydrogen off which CMB photons can scatter through
Rayleigh scattering. Unlike Thomson scattering, Rayleigh scattering is
frequency dependent resulting in the generation of anisotropies with a
different spectral dependence. Unfortunately the Rayleigh scattering efficiency
rapidly decreases with the expansion of the neutral universe, with the result
that only a small percentage of photons are scattered by neutral hydrogen.
Although the effect is very small, future CMB missions with higher sensitivity
and improved frequency coverage are poised to measure Rayleigh scattering
signal. The uncorrelated component of the Rayleigh anisotropies contains unique
information on the primordial perturbations that could potentially be leveraged
to expand our knowledge of the early universe. In this paper we explore whether
measurements of Rayleigh scattering anisotropies can be used to constrain
primordial non-Gaussianity (NG) and examine the hints of anomalies found by
WMAP and \textit{Planck} satellites. We show that the additional Rayleigh
information has the potential to improve primordial NG constraints by $30\%$,
or more. Primordial bispectra that are not of the local type benefit the most
from these additional scatterings, which we attribute to the different scale
dependence of the Rayleigh anisotropies. Unfortunately this different scaling
means that Rayleigh measurements can not be used to constrain anomalies or
features on large scales. On the other hand, anomalies that may persist to
smaller scales, such as the potential power asymmetry seen in WMAP and
\textit{Planck}, could be improved by the addition of Rayleigh measurements.",2010.10481v1
2020-11-10,Frictional anisotropy of 3D-printed fault surfaces,"The surface morphology of faults controls the spatial anisotropy of their
frictional properties, and hence their mechanical stability. Such anisotropy is
only rarely studied in seismology models of fault slip, although it might be
paramount to understand the seismic rupture in particular areas, notably where
slip occurs in a direction different from that of the main striations of the
fault. To quantify how the anisotropy of fault surfaces affects the friction
coefficient during sliding, we sheared synthetic fault planes made of plaster
of Paris. These fault planes were produced by 3D-printing real striated fault
surfaces whose 3D roughness was measured in the field at spatial scales from
millimeters to meters. Here, we show how the 3D-printing technology can help
for the study of frictional slip. Results show that fault anisotropy controls
the coefficient of static friction, with the friction coefficient along the
striations being three to four times smaller than the friction coefficient
along the direction perpendicular to the striations. This is true both at the
meter and the millimeter scales. The anisotropy in friction and the average
coefficient of static friction are also shown to decrease with the normal
stress applied to the faults, as a result of the increased surface wear under
increased loading.",2011.05012v2
2020-12-16,A tool to predict coercivity in magnetic materials,"Magnetic coercivity is often viewed to be lower in alloys with negligible (or
zero) values of the anisotropy constant. However, this explains little about
the dramatic drop in coercivity in FeNi alloys at a non-zero anisotropy value.
Here, we develop a theoretical and computational tool to investigate the
fundamental interplay between material constants that govern coercivity in bulk
magnetic alloys. The two distinguishing features of our coercivity tool are
that: (a) we introduce a large localized disturbance, such as a spike-like
magnetic domain, that provides a nucleation barrier for magnetization reversal;
and (b) we account for magneto-elastic energy -- however small -- in addition
to the anisotropy and magnetostatic energy terms. We apply this coercivity tool
to show that the interactions between local instabilities and material
constants, such as anisotropy and magnetostriction constants, are key factors
that govern magnetic coercivity in bulk alloys. Using our model, we show that
coercivity is minimum at the permalloy composition (Fe-21.5Ni-78.5) at which
the alloy's anisotropy constant is not zero. We systematically vary the values
of the anisotropy and magnetostriction constants, around the permalloy
composition, and identify new combinations of material constants at which
coercivity is small. More broadly, our coercivity tool provides a theoretical
framework to potentially discover novel magnetic materials with low coercivity.",2012.09320v1
2021-01-08,"Stability, Evolution and Switching of Ferroelectric Domain Structures in Lead-free BaZr$_{0.2}$Ti$_{0.8}$O$_3$-Ba$_{0.7}$Ca$_{0.3}$TiO$_3$ System: Thermodynamic Analysis and Phase-field Simulations","Enhanced room-temperature electromechanical coupling in the lead-free
ferroelectric system $(1-x)$BaZr$_{0.2}$Ti$_{0.8}$O$_{3}$ -
$x$Ba$_{0.7}$Ca$_{0.3}$TiO$_{3}$ (abbreviated as BZCT) at $x=0.5$ is attributed
to the existence of a morphotropic phase region (MPR) containing an
intermediate orthorhombic ($O$) phase between terminal rhombohedral ($R$) BZT
and tetragonal ($T$) BCT phases. However, there is ambiguity regarding the
morphotropic phase transition in BZCT at room temperature - while some
experiments suggest a single $O$ phase within the MPR, others indicate
coexistence of three polar phases ($T+R+O$). Therefore, to understand the
thermodynamic stability of polar phases and its relation to electromechanical
switching during morphotropic phase transition in BZCT, we develop a Landau
potential based on the theory of polar anisotropy. Since intrinsic
electrostrictive anisotropy changes as a function of electromechanical
processing, we establish a correlation between the parameters of our potential
and the coefficients of electrostriction. We also conducted phase-field
simulations based on this potential to demonstrate changes in domain
configuration from single-phase $O$ to three-phase $T+R+O$ at the equimolar
composition with the increase in electrostrictive anisotropy. Diffusionless
phase diagrams and the corresponding piezoelectric coefficients obtained from
our model compare well with the experimental findings. Increase in
electrostrictive anisotropy increases the degeneracy of the free energy at
ambient temperature and pressure leading to decreasing polar anisotropy,
although there is an accompanying increase in the electromechanical anisotropy
manifested by an increase in the difference between effective longitudinal and
transverse piezo-coefficients, $d_{33}$ and $d_{31}$.",2101.03066v1
2021-02-26,Anisotropy of Solar-Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations,"The anisotropy of solar wind turbulence is a critical issue in understanding
the physics of energy transfer between scales and energy conversion between
fields and particles in the heliosphere. Using the measurement of \emph{Parker
Solar Probe} (\emph{PSP}), we present an observation of the anisotropy at
kinetic scales in the slow, Alfv\'enic, solar wind in the inner heliosphere.
\textbf{The magnetic compressibility behaves as expected for kinetic Alfv\'enic
turbulence below the ion scale.} A steepened transition range is found between
the inertial and kinetic ranges in all directions with respect to the local
background magnetic field direction. The anisotropy of $k_\perp \gg
k_\parallel$ is found evident in both transition and kinetic ranges, with the
power anisotropy $P_\perp/P_\parallel > 10$ in the kinetic range leading over
that in the transition range and being stronger than that at 1 au. The spectral
index varies from $\alpha_{t\parallel}=-5.7\pm 1.0$ to $\alpha_{t\perp}=-3.7\pm
0.3$ in the transition range and $\alpha_{k\parallel}=-3.12\pm 0.22$ to
$\alpha_{k\perp}=-2.57\pm 0.09$ in the kinetic range. The corresponding
wavevector anisotropy has the scaling of $k_\parallel \sim k_\perp^{0.71\pm
0.17}$ in the transition range, and changes to $k_\parallel \sim
k_\perp^{0.38\pm 0.09}$ in the kinetic range, consistent with the kinetic
Alfv\'enic turbulence at sub-ion scales.",2102.13294v2
2021-03-04,WawHelioGlow: a model of the heliospheric backscatter glow. II. The helioglow buildup and the potential significance of the anisotropy in the solar EUV output,"The helioglow is a fluorescence of interstellar atoms inside the heliosphere,
where they are excited by the solar EUV. Because the mean free path between
collisions for the interstellar gas is comparable to the size of the
heliosphere, the distribution function of this gas inside the heliosphere
strongly varies in space and with time and is non-Maxwellian. Coupling between
realistically modeled solar factors and the distribution function of
interstellar neutral gas is accounted for in a helioglow model that we have
developed. WawHelioGlow is presented in the accompanying Paper I. Here, we
present the evolution of the gas density, solar illumination, helioglow source
function, and other relevant parameters building up the helioglow signal for
selected lines of sight observed at 1 au. We compare these elements for various
phases of the solar cycle and we present the sensitivity of the results to
heliolatitudinal anisotropy of the solar EUV output. We assume a realistic
latitudinal anisotropy of the solar wind flux using results from analysis of
interplanetary scintillations. We compare the simulated helioglow with with
selected maps observed by the SOHO/SWAN instrument. We demonstrate that
WawHelioGlow is able to reproduce fundamental features of the sky distribution
of the helioglow. For some phases of the solar cycle, the model with an
anisotropy of the solar EUV output better reproduces the observations, while
for other phases no EUV anisotropy is needed. In all simulated cases, the solar
wind anisotropy following insight from interplanetary scintillation
measurements is present.",2103.02802v1
2021-05-01,Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors,"Spintronics-based nonvolatile components in neuromorphic circuits offer the
possibility of realizing novel functionalities at low power. Current-controlled
electrical switching of magnetization is actively researched in this context.
Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA),
consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material
contenders. Utilizing the crystal orientation, magnetic anisotropy in such
simple heterostructures can be tuned to either exhibit a perfect or slightly
tilted PMA. Here, we investigate current-induced magnetization modulation in
such tailored ferromagnetic layers with a material with strong spin-orbit
coupling (Pt), exploiting the spin Hall effect. We find significant differences
in the magnetic anisotropy between the SRO/STO heterostructures, as manifested
in the first and second harmonic magnetoresistance measurements.
Current-induced magnetization switching can be realized with spin-orbit
torques, but for systems with perfect PMA this switching is probabilistic as a
result of the high symmetry. Slight tilting of the PMA can break this symmetry
and allow the realization of deterministic switching. Control over the magnetic
anisotropy of our heterostructures therefore provides control over the manner
of switching. Based on our findings, we propose a three-terminal spintronic
memristor, with a magnetic tunnel junction design, that shows several resistive
states controlled by electric charge. Non-volatile states can be written
through SOT by applying an in-plane current, and read out as a tunnel current
by applying a small out-of-plane current. Depending on the anisotropy of the
SRO layer, the writing mechanism is either deterministic or probabilistic
allowing for different functionalities to emerge. We envisage that the
probabilistic MTJs could be used as synapses while the deterministic devices
can emulate neurons",2105.00269v1
2021-05-05,Superconductivity assisted change of the perpendicular magnetic anisotropy in V/MgO/Fe junctions,"Controlling the perpendicular magnetic anisotropy (PMA) in thin films has
received considerable attention in recent years due to its technological
importance. PMA based devices usually involve heavy-metal
(oxide)/ferromagnetic-metal bilayers, where, thanks to interfacial spin-orbit
coupling (SOC), the in-plane (IP) stability of the magnetization is broken.
Here we show that in V/MgO/Fe(001) epitaxial junctions with competing in-plane
and out-of-plane (OOP) magnetic anisotropies, the SOC mediated interaction
between a ferromagnet (FM) and a superconductor (SC) enhances the effective PMA
below the superconducting transition. This produces a partial magnetization
reorientation without any applied field for all but the largest junctions,
where the IP anisotropy is more robust; for the smallest junctions there is a
reduction of the field required to induce a complete OOP transition
($H_\text{OOP}$) due to the stronger competition between the IP and OOP
anisotropies. Our results suggest that the degree of effective PMA could be
controlled by the junction lateral size in the presence of superconductivity
and an applied electric field. We also discuss how the $H_\text{OOP}$ field
could be affected by the interaction between magnetic stray fields and
superconducting vortices. Our experimental findings, supported by numerical
modelling of the ferromagnet-superconductor interaction, open pathways to
active control of magnetic anisotropy in the emerging dissipation-free
superconducting spin electronics.",2105.02050v4
2021-05-17,On the Temperature-dependent Characteristics of Perpendicular Shape Anisotropy-Spin Transfer Torque-Magnetic Random Access Memories (PSA-STT-MRAMs),"The perpendicular shape anisotropy-spin transfer torque-magnetic random
access memories (PSASTT-MRAMs) takes advantage of the nanopillar free-layer
geometry for securing a good thermal stability factor from the shape anisotropy
of the nanomagnet. Such a concept is particularly well-suited for small
junctions down to a few nanometers. At such a volume size, the nanopillar can
be effectively modeled as a Stoner-Wohlfarth (SW) particle, and the shape
anisotropy scales with the spontaneous magnetization by ~ Ms^2. For almost all
ferromagnets, Ms is a strong function of temperature, therefore, the
temperature-dependent shape anisotropy is an important factor to be considered
in any modeling of the temperature-dependent performance of PSA-STT-MRAMs. In
this work, we summarize and discuss various possible temperature-dependent
contributions to the thermal stability factor and coercivity of the
PSA-STT-MRAMs by modeling and comparing different temperature scaling and
parameters. We reveal nontrivial corrections to the thermal stability factor by
considering both temperature-dependent shape and interfacial anisotropies. The
coercivity, blocking temperature, and electrical switching characteristics that
resulted from incorporating such a temperature dependence are also discussed,
in conjugation with the nanomagnet dimension and coherence volume.",2105.07801v1
2021-08-27,Effects of anisotropy on strongly magnetized neutron and strange quark stars in general relativity,"We investigate the properties of anisotropic, spherically symmetric compact
stars, especially neutron stars and strange quark stars, made of strongly
magnetized matter. The neutron stars are described by SLy equation of state,
the strange quark stars by an equation of state based on the MIT Bag model. The
stellar models are based on an a priori assumed density dependence of the
magnetic field and thus anisotropy. Our study shows that not only the presence
of a strong magnetic field and anisotropy, but also the orientation of the
magnetic field itself, have an important influence on the physical properties
of stars. Two possible magnetic field orientations are considered, a radial
orientation, where the local magnetic fields point in the radial direction, and
a transverse orientation, where the local magnetic fields are perpendicular to
the radial direction. Interestingly, we find that for a transverse orientation
of the magnetic field, the stars become more massive with increasing anisotropy
and magnetic field strength and increase in size, since the repulsive,
effective anisotropic force increases in this case. In the case of a radially
orientated magnetic field, however, the masses and radii of the stars decrease
with increasing magnetic field strength, because of the decreasing effective
anisotropic force. Importantly, we also show that in order to achieve
hydrostatic equilibrium configurations of magnetized matter, it is essential to
account for both the local anisotropy effects as well as the anisotropy effects
caused by a strong magnetic field. Otherwise, hydrostatic equilibrium is not
achieved for magnetized stellar models.",2108.12436v1
2021-11-08,Anisotropy and quench dynamics of quasiholes in fractional quantum Hall liquids,"We present a microscopic study of quasiholes in bosonic fractional quantum
Hall (FQH) liquids at filling factor $\nu=1/2$ in the lowest Landau level with
anisotropic band mass tensors. We use the spatial density profile to
characterize the shape of a quasihole and analyze its anisotropy. We then
compare the quasihole's anisotropy with the intrinsic geometric metric of the
system that is extracted from the maximal overlap between the numerically
obtained quasihole ground state and a set of model wave functions of
anisotropic quasiholes. For a static system, we find that the quasihole's
anisotropy, similar to the intrinsic metric, grows with the anisotropy of the
band mass tensor. When the quasihole develops well, we observe a correspondence
between the anisotropy of the quasihole and the intrinsic metric of the
underlying anisotropic FQH state. We also drive the system out of equilibrium
by suddenly changing the band mass tensor. In this case, the shape of the
quasihole evolves with time and shows similar dynamics with the intrinsic
metric of the postquench state. The evolving frequency matches the energy of a
spin-$2$ quadrupole degree of freedom in the system. Our results suggest that
the density profile of a quasihole is a useful tool to estimate the intrinsic
metric and capture the dynamics of an FQH system.",2111.04214v2
2022-01-06,Impact of Warm Dark Matter on the Cosmic Neutrino Background Anisotropies,"The Cosmic Neutrino Background (C$\nu$B) anisotropies for massive neutrinos
are a unique probe of large-scale structure formation. The redshift-distance
measure is completely different for massive neutrinos as compared to
electromagnetic radiation. The C$\nu$B anisotropies in massive neutrinos grow
in response to non-relativistic motion in gravitational potentials seeded by
relatively high $k$-modes. Differences in the early phases of large-scale
structure formation in Warm Dark Matter (WDM) versus Cold Dark Matter (CDM)
cosmologies have an impact on the magnitude of the C$\nu$B anisotropies for
contributions to the angular power spectrum that peak at high $k$-modes. We
take the examples of WDM consisting of 2, 3 or 7 keV sterile neutrinos and show
that the C$\nu$B anisotropies for 0.05 eV neutrinos drop off at high-$l$
multipole moment in the angular power spectrum relative to CDM. At the same
angular scales that one can observe baryonic acoustical oscillations in the
CMB, the C$\nu$B anisotropies begin to become sensitive to differences in WDM
and CDM cosmologies. The precision measurement of high-$l$ multipoles in the
C$\nu$B neutrino sky map is a potential possibility for the PTOLEMY experiment
with thin film targets of spin-polarized atomic tritium superfluid that exhibit
significant quantum liquid amplification for non-relativistic relic neutrino
capture.",2201.01888v2
2022-02-08,Tunable Magnetic Anisotropy in Patterned SrRuO3 Quantum Structures: Competition between Lattice Anisotropy and Oxygen Octahedral Rotation,"Artificial perovskite-oxide nanostructures possess intriguing magnetic
properties due to their tailorable electron-electron interactions, which are
extremely sensitive to the oxygen coordination environment. To date,
perovskite-oxide nanodots with sizes below 50 nm have rarely been reported.
Furthermore, the oxygen octahedral distortion and its relation to magnetic
properties in perovskite oxide nanodots remain unexplored yet. Here, we have
studied the magnetic anisotropy in patterned SrRuO3 (SRO) nanodots as small as
30 nm while performing atomic-resolution electron microscopy and spectroscopy
to directly visualize the constituent elements, in particular oxygen ions. We
observe that the magnetic anisotropy and RuO6 octahedra distortion in SRO
nanodots are both nanodots' size-dependent but remain unchanged in the first
3-unit-cell interfacial SRO monolayers regardless of the dots' size. Combined
with the first principle calculations, we unravel a unique structural mechanism
behind the nanodots' size-dependent magnetic anisotropy in SRO nanodots,
sugguesting that the competition between lattice anisotropy and oxygen
octahedral rotation mediates anisotropic exchange interactions in SRO nanodots.
These findings demonstrate a new avenue towards tuning magnetic properties of
correlated perovskite oxides and imply that patterned nanodots could be a
promising playground for engineering emergent functional behaviors.",2202.03820v1
2022-05-13,Isotropic orbital magnetic moments in magnetically anisotropic SrRuO3 films,"Epitaxially strained SrRuO3 films have been a model system for understanding
the magnetic anisotropy in metallic oxides. In this paper, we investigate the
anisotropy of the Ru 4d and O 2p electronic structure and magnetic properties
using high-quality epitaxially strained (compressive and tensile) SrRuO3 films
grown by machine-learning-assisted molecular beam epitaxy. The element-specific
magnetic properties and the hybridization between the Ru 4d and O 2p orbitals
were characterized by Ru M2,3-edge and O K-edge soft X-ray absorption
spectroscopy and X-ray magnetic circular dichroism measurements. The
magnetization curves for the Ru 4d and O 2p magnetic moments are identical,
irrespective of the strain type, indicating the strong magnetic coupling
between the Ru and O ions. The electronic structure and the orbital magnetic
moment relative to the spin magnetic moment are isotropic despite the
perpendicular and in-plane magnetic anisotropy in the compressive-strained and
tensile-strained SrRuO3 films; i.e., the orbital magnetic moments have a
negligibly small contribution to the magnetic anisotropy. This result
contradicts Bruno model, where magnetic anisotropy arises from the difference
in the orbital magnetic moment between the perpendicular and in-plane
directions. Contributions of strain-induced electric quadrupole moments to the
magnetic anisotropy are discussed, too.",2205.06563v1
2022-08-01,Observation of gigantic spin conversion anisotropy in bismuth,"Whilst the g-factor can be anisotropic due to the spin-orbit interaction
(SOI), its existence in solids cannot be simply asserted from a band structure,
which hinders progress on studies from such the viewpoints. The g-factor in
bismuth (Bi) is largely anisotropic; especially for holes at T-point, the
g-factor perpendicular to the trigonal axis is negligibly small (< 0.112),
whereas the g-factor along the trigonal axis is very large (62.7). We clarified
in this work that the large g- factor anisotropy gives rise to the gigantic
spin conversion anisotropy in Bi from experimental and theoretical approaches.
Spin-torque ferromagnetic resonance was applied to estimate the spin conversion
efficiency in rhombohedral (110) Bi to be 17%, which is unlike the negligibly
small efficiency in Bi(111). Harmonic Hall measurements supports the large spin
conversion efficiency in Bi(110). This is the first observation of gigantic
spin conversion anisotropy as the clear manifestation of the g-factor
anisotropy. Beyond the emblematic case of Bi, our study unveiled the
significance of the g-factor anisotropy in condensed-matter physics and can
pave a pathway toward establishing novel spin physics under g-factor control.",2208.00589v3
2022-08-31,Large Magnetic Anisotropy and Magnetostriction in Thin Films of CoV$_2$O$_4$,"Spinel Cobalt Vanadate CoV$_2$O$_4$ has been grown on (001) SrTiO$_3$
substrates. Using torque magnetometry experiments, we find that the previously
observed temperature induced anisotropy change, where the easy axis changes
from the out of plane [001] direction to a biaxial anisotropy with planar <100>
easy axes, occurs in a gradual second-order structural phase transition. This
work characterizes this transition and the magnetic anisotropies in the (001),
(100), and (-110) rotation planes, and explores their field dependence up to
30~T. Below 80~K, hysteretic features appear around the hard axes, i.e., the
out-of-plane direction in (-110) and (010) rotations and the planar <110>
directions in (001) rotations. This is due to a Zeeman Energy that originates
from the lag of the magnetization with respect to the applied magnetic field as
the sample is rotated. The appearance of the hysteresis, which persist up to
very high fields, shows that the anisotropy at low temperature is rather
strong. Additionally, field dependent distortions to the symmetry of the torque
response in increasing applied fields shows that magnetostriction plays a large
role in determining the direction and magnitude of the anisotropy.",2209.00047v2
2022-11-16,Continuous Electrical Manipulation of Magnetic Anisotropy and Spin Flopping in van der Waals Ferromagnetic Devices,"Controlling the magnetic anisotropy of ferromagnetic materials plays a key
role in magnetic switching devices and spintronic applications. Examples of
spin-orbit torque devices with different magnetic anisotropy geometries
(in-plane or out-of-plane directions) have been demonstrated with novel
magnetization switching mechanisms for extended device functionalities.
Normally, the intrinsic magnetic anisotropy in ferromagnetic materials is
unchanged within a fixed direction, and thus, it is difficult to realize
multifunctionality devices. Therefore, continuous modulation of magnetic
anisotropy in ferromagnetic materials is highly desired but remains
challenging. Here, we demonstrate a gate-tunable magnetic anisotropy transition
from out-of-plane to canted and finally to in-plane in layered Fe$_5$GeTe$_2$
by combining the measurements of the angle-dependent anomalous Hall effect and
magneto-optical Kerr effect with quantitative Stoner-Wohlfarth analysis. The
magnetic easy axis continuously rotates in a spin-flop pathway by gating or
temperature modulation. Such observations offer a new avenue for exploring
magnetization switching mechanisms and realizing new spintronic
functionalities.",2211.08909v1
2023-01-22,Easy-plane spin Hall oscillator,"Spin Hall oscillators (SHOs) based on bilayers of a ferromagnet (FM) and a
non-magnetic heavy metal (HM) are electrically tunable nanoscale microwave
signal generators. Achieving high output power in SHOs requires driving
large-amplitude magnetization dynamics by a direct spin Hall current. The
maximum possible amplitude of such oscillations with the precession cone angle
nearing $90^\circ$ is predicted for FM layers with easy-plane magnetic
anisotropy and spin Hall current polarization perpendicular to the easy plane.
While many FMs exhibit natural easy-plane anisotropy in the FM film plane, the
spin Hall current in a HM|FM bilayer is polarized in this plane and thus cannot
drive large-amplitude magneto-dynamics. Here we present a new type of SHO
engineered to have the easy-plane anisotropy oriented normal to the film plane,
enabling large-amplitude easy-plane dynamics driven by spin Hall current. Our
experiments and micromagnetic simulations demonstrate that the desired
easy-plane anisotropy can be achieved by tuning the magnetic shape anisotropy
and perpendicular magnetic anisotropy in a nanowire SHO, leading to a
significant enhancement of the generated microwave power. The easy-plane SHO
experimentally demonstrated here is an ideal candidate for realization of a
spintronic spiking neuron. Our results provide a new approach to design of
high-power SHOs for wireless communications, neuromorphic computing, and
microwave assisted magnetic recording.",2301.09228v1
2023-04-26,Exploring the origins of perpendicular magnetic anisotropy in amorphous Tb-Co via changes in medium-range ordering,"Amorphous thin films of Tb$_{17}$Co$_{83}$ (a-Tb-Co) grown by magnetron
co-sputtering exhibit changes in magnetic anisotropy with varying growth and
annealing temperatures. The magnetic anisotropy constant increases with
increasing growth temperature, which is reduced or vanishes upon annealing at
temperatures above the growth temperature. The proposed explanation for this
growth-induced anisotropy in high orbital moment Tb-based transition metal
alloys such as a-Tb-Co is an amorphous phase texturing with preferential
in-plane and out-of-plane local bonding configurations for the rare-earth and
transition metal atoms. Scanning nanodiffraction performed in a transmission
electron microscope (TEM) is applied to a-Tb$_{17}$Co$_{83}$ films deposited
over a range of temperatures to measure relative changes in medium-range
ordering (MRO). These measurements reveal an increase in MRO with higher growth
temperatures and a decrease in MRO with higher annealing temperatures. The
trend in MRO indicates a relationship between the magnetic anisotropy and local
atomic ordering. Tilting select films between 0$^{\circ}$ and 40$^{\circ}$ in
the TEM measures variations in the local atomic structure a function of
orientation within the films. The findings support claims that preferential
ordering along the growth direction results from temperature-mediated adatom
configurations during deposition, and that oriented MRO correlates with the
larger anisotropy constants.",2304.13208v3
2023-04-26,Bond-dependent anisotropy and magnon decay in cobalt-based Kitaev triangular antiferromagnet,"The Kitaev model, a honeycomb network of spins with bond-dependent
anisotropic interactions, is a rare example of having a quantum spin liquid
ground state. Although most Kitaev model candidate materials eventually order
magnetically due to inevitable non-Kitaev terms, their bond-dependent
anisotropy manifests in unusual spin dynamics. It has recently been suggested
that bond-dependent anisotropy can stabilise novel magnetic phases and exotic
spin dynamics on the geometrically frustrated triangular lattice. However, few
materials have been identified with simultaneous geometric frustration and
bond-dependent anisotropy. Here, we report a frustrated triangular lattice with
bond-dependent anisotropy in the cobalt-based triangular van der Waals
antiferromagnet CoI2. Its momentum and energy-resolved spin dynamics exhibit
substantial magnon breakdown and complex level repulsion, as measured by
inelastic neutron scattering. A thorough examination of excitations in both the
paramagnetic and magnetically ordered states reveals that the bond-dependent
anisotropy is the origin of the spiral order and the magnon breakdown found in
CoI2. Our result paves the way toward a new research direction for the Kitaev
model with geometrical frustration.",2304.13236v3
2023-05-22,On the isotropy of SnIa absolute magnitudes in the Pantheon+ and SH0ES samples,"We use the hemisphere comparison method to test the isotropy of the SnIa
absolute magnitudes of the Pantheon+ and SH0ES samples in various
redshift/distance bins. We compare the identified levels of anisotropy in each
bin with Monte-Carlo simulations of corresponding isotropised data to estimate
the frequency of such levels of anisotropy in the context of an underlying
isotropic cosmological. We find that the identified levels of anisotropy in all
bins are consistent with the Monte-Carlo isotropic simulated samples. However,
in the real samples for both the Pantheon+ and the SH0ES cases we find sharp
changes of the level of anisotropy occuring at distances less than $40Mpc$. For
the Pantheon+ sample we find that the redshift bin $[0.005,0.01]$ is
significantly more anisotropic than the other 5 redshift bins considered. For
the SH0ES sample we find a sharp drop of the anisotropy level at distances
larger than about $30Mpc$. These anisotropy transitions are relatively rare in
the Monte-Carlo isotropic simulated data and occur in $2\%$ of the SH0ES
simulated data and at about $7\%$ of the Pantheon+ isotropic simulated samples.
This effect is consistent with the experience of an off center observer in a
$30Mpc$ bubble of distinct physics or systematics.",2305.12819v1
2023-10-30,Strong in-plane magnetic anisotropy (Co0.15Fe0.85)5GeTe2/graphene van der Waals heterostructure spin-valve at room temperature,"Van der Waals (vdW) magnets are promising owing to their tunable magnetic
properties with doping or alloy composition, where the strength of magnetic
interactions, their symmetry, and magnetic anisotropy can be tuned according to
the desired application. However, most of the vdW magnet based spintronic
devices are so far limited to cryogenic temperatures with magnetic anisotropies
favouring out-of-plane or canted orientation of the magnetization. Here, we
report room-temperature lateral spin-valve devices with strong in-plane
magnetic anisotropy of the vdW ferromagnet (Co0.15Fe0.85)5GeTe2 (CFGT) in
heterostructures with graphene. Magnetization measurements reveal above
room-temperature ferromagnetism in CFGT with a strong in-plane magnetic
anisotropy. Density functional theory calculations show that the magnitude of
the anisotropy depends on the Co concentration and is caused by the
substitution of Co in the outermost Fe layer. Heterostructures consisting of
CFGT nanolayers and graphene were used to experimentally realize basic building
blocks for spin valve devices such as efficient spin injection and detection.
The spin transport and Hanle spin precession measurements prove a strong
in-plane and negative spin polarization at the interface with graphene, which
is supported by the calculated spin-polarized density of states of CFGT. The
in-plane magnetization of CFGT at room temperature proves its usefulness in
graphene lateral spin-valve devices, thus opening further opportunities for
spintronic technologies.",2310.19618v1
2023-11-09,Signature of surface anisotropy in the spin-flip neutron scattering cross section of spherical nanoparticles: atomistic simulations and analytical theory,"We investigate the signature of magnetic surface anisotropy in nanoparticles
in their spin-flip neutron scattering cross section. Taking into account the
isotropic exchange interaction, an external magnetic field, a uniaxial or cubic
magnetic anisotropy for the particle's core, and several models for the surface
anisotropy (N\'eel, conventional, random), we compute the spin-flip small-angle
neutron scattering (SANS) cross section from the equilibrium spin structures
obtained using the Landau-Lifshitz equation. The sign of the surface anisotropy
constant, which is related to the appearance of tangential- or radial-like spin
textures, can be distinguished from the momentum-transfer dependence of the
spin-flip signal. The data cannot be described by the well-known and often-used
analytical expressions for uniformly magnetized spherical or core-shell
particles, in particular at remanence or at the coercive field. Based on a
second-order polynomial expansion for the magnetization vector field, we
develop a novel minimal model for the azimuthally-averaged magnetic SANS cross
section. The theoretical expression considers a general magnetization
inhomogeneity and is not restricted to the presence of surface anisotropy. It
is shown that the model describes very well our simulation data as well as more
complex spin patterns such as vortex-like structures. Only seven expansion
coefficients and some basis functions are sufficient to describe the scattering
behavior of a very large number of atomic spins.",2311.05706v1
2023-11-30,Effects of anisotropic pressure on interacting quark star structure,"Perturbative Quantum Chromodynamics (pQCD) corrections and color
superconductivity predict that strongly interacting matter can reveal new
physical phenomena under extreme conditions. Taking into account these
interaction effects, we investigate the role of anisotropic pressure in quark
stars composed of interacting quark matter. Adopting two physically
well-motivated anisotropy profiles, we numerically solve the stellar structure
equations in order to explore the consequences of anisotropic pressure on
various macroscopic properties such as radius, gravitational mass, surface
redshift, moment of inertia, tidal Love number and oscillation spectrum.
Remarkably, for both anisotropy models, negative anisotropies increase the
radial stability of interacting quark stars, while the opposite occurs for
positive anisotropies. However, for the Bowers-Liang profile, the central
density corresponding to the maximum-mass point does not coincide with the
central density where the squared oscillation frequency vanishes, indicating
that the existence of stable anisotropic interacting quark stars is possible
beyond the maximum mass for negative anisotropies. Additionally, we compare our
theoretical predictions with several observational mass-radius measurements and
tidal deformability constraints, which suggest that both strong interaction
effects and anisotropy effects play a crucial role in describing compact stars
observed in the Universe.",2311.18770v2
2024-02-03,Magnetosheath ion field-aligned anisotropy and implications for ion leakage to the foreshock,"The ion foreshock is highly dynamic, disturbing the bow shock and the
magnetosphere-ionosphere system. To forecast foreshock-driven space weather
effects, it is necessary to model foreshock ions as a function of upstream
shock parameters. Case studies in the accompanying paper show that
magnetosheath ions sometimes exhibit strong field-aligned anisotropy towards
the upstream direction, which may be responsible for enhancing magnetosheath
leakage and therefore foreshock ion density. To understand the conditions
leading to such an anisotropy and the potential for enhanced leakage, we
perform case studies and a statistical study of magnetosheath and foreshock
region data surrounding ~500 THEMIS bow shock crossings. We quantify the
anisotropy using the heat flux along the field-aligned direction. We show that
the strong field-aligned heat flux persists across the entire magnetosheath
from the magnetopause to the bow shock. Ion distribution functions reveal that
the strong heat flux is caused by a secondary thermal population. We find that
stronger anisotropy events exhibit heat flux preferentially towards the
upstream direction near the bow shock and occur under larger IMF strength and
larger solar wind dynamic pressure and/or energy flux. Additionally, we show
that near the bow shock, magnetosheath leakage is a significant contributor to
foreshock ions, and through enhancing the leakage the magnetosheath ion
anisotropy can modulate the foreshock ion velocity and density. Our results
imply that likely due to field line draping and compression against the
magnetopause that leads to a directional mirror force, modeling the foreshock
ions necessitates a more global accounting of downstream conditions.",2402.01978v1
2024-03-16,Nonequilibrium tricritical behaviour in anisotropic XY ferromagnet driven by elliptically polarised propagating magnetic field wave,"Three dimensional anisotropic XY ferromagnet driven by elliptically polarized
propagating magnetic field wave has been extensively investigated by Monte
Carlo simulation with Metropolis single spin flip algorithm. Both the effects
of the bilinear exchange type and the single site anisotropies are thoroughly
investigated. The time average magnetisation (over the complete cycle of the
elliptically polarized propagating magnetic field wave) components play the
role of dynamic order parameter. For fixed set of values of the strength of
anisotropy and the field amplitudes, the system has been found to get
dynamically ordered at a pseudocritical temperature. The pseudocritical
temperature of such dynamic nonequilibrium phase transition has been found to
depend on both the strength of anisotropy and the amplitudes of the
elliptically polarized propagating magnetic field wave. A comprehensive phase
diagram is represented here in the form of image plot of the pseudocritical
temperature in the plane formed by the strength of anisotropy and field
amplitudes. Interestingly, this nonequilibrium phase transition has been found
discontinuous (first order) for higher values of the field amplitude and lower
values of the anisotropy. On the other hand, the continuous (second order)
transition has been noticed for lower values of the field amplitude and higher
values of the anisotropy.",2403.10975v2
1995-01-24,A Calculation of Cosmic Variance in Cosmic Microwave Background Anisotropy,"We present a theoretical calculation of the variance $\Delta C_l$ of the CMB
anisotropy power spectrum $\langle C_l\rangle$ caused by gravitational waves
based on quantum field theory in an inflationary cosmology.",9501088v2
1996-06-11,Microwave Anisotropies from Random Sources,"I report on recent developments in the theory of cosmic background radiation
perturbations. I describe ways of modeling alternatives to the canonical
Gaussian theories within the standard framework of cosmological perturbation
theory. Some comments are made on using these techniques to resolve the
uncertainties in theories of structure formation with topological defects. (To
appear in the proceedings of the XXXIth Moriond meeting, ``Microwave Background
Anisotropies'')",9606068v1
1996-11-27,Theoretical implications of microwave background radiation anisotropy experiments,"Observational results from several experiments such as COBE, SP, Saskatoon,
PYTHON, ARGO, MAX, MSAM, Tenerife and CAT are considered and a comparison is
made with predictions from several models. Conclusions are reached about the
viability of current structure formation models.",9611228v1
1997-05-13,The Cosmic Microwave Background Spectrum,"This paper given at the Strasbourg NATO school on the CMB and cosmology
reports the contents of four hours of lectures on the CMB spectrum, potential
distortions, and implications. It was followed by 6 hours of lectures on CMB
anisotropy. This paper reviews the observations and theoretical implications
for the CMB frequency spectrum - both for the monopole (essentially total
power) and the dipole and higher order anisotropies including the
Sunyaev-Zeldovich effect.",9705101v2
1997-05-21,On the Computation of CMBR Anisotropies from Simulations of Topological Defects,"Techniques for computing the CMBR anisotropy from simulations of topological
defects are discussed with an eye to getting as much information from a
simulation as possible. Here we consider the practical details of which sums
and multiplications to do and how many terms there are.",9705177v1
1997-07-09,Polarization-Temperature Correlation from a Primordial Magnetic Field,"We propose a new method for constraining a primordial homogeneous magnetic
field with the cosmic microwave background. Such a field will induce an
observable parity odd cross correlation between the polarization anisotropy and
the temperature anisotropy by Faraday rotation. We analyze the necessary
experimental features to match, and improve, current constraints of such a
field by measuring this correlation.",9707115v1
1998-04-14,CMB anisotropy measurements using stratospheric balloons,"We review the topic of Cosmic Microwave Background Anisotropy measurements
carried out by means of balloon-borne telescopes. After a short description of
the experimental methodology, we outline the peculiar problems of these
experiments, and we describe the main results obtained and the perspects for
future developments.",9804138v1
1998-10-30,Polarization of the CMB Anisotropy,"I review why we expect the CMB anisotropy to be polarized, what we can learn
from studying polarization and the level of the experimental challenge it
presents. A discussion of current and future polarization sensitive experiments
will focus on the expected sensitivity of PLANCK.",9810506v1
1999-11-29,Cosmic Microwave Background Anisotropies: Inflation versus Topological Defects,"I present a briefly summary of the current status of inflationary models
versus topological defects scenarios, as the mechanisms which could have
induced the initial density perturbations, which left an imprint on the cosmic
microwave backgound radiation anisotropies.",9911497v1
2000-02-15,Sachs-Wolfe effect in space-times with torsion,"Cartan torsion contribution to Sachs-Wolfe effect in the inflationary phase
of the Universe is discussed.From the COBE data of the microwave anisotropy is
possible to compute the spin-density in the Universe as $10^{16}$ mks units.The
spin-density fluctuations at the hadron era is shown to coincide with the
anisotropy temperature fluctuations.",0002301v1
2000-09-18,Complex Visibilities of Cosmic Microwave Background Anisotropies,"We study the complex visibilities of the cosmic microwave background
anisotropies that are observables in interferometric observations of the cosmic
microwave background, using the multipole expansion methods commonly adopted in
analyzing single-dish experiments. This allows us to recover the properties of
the visibilities that is obscured in the flat-sky approximation. Discussions of
the window function, multipole resolution, instrumental noise, pixelization,
and polarization are given.",0009277v1
2000-10-23,Precision of inflationary predictions and recent CMB anisotropy data,"Inflationary predictions of the cosmic microwave background anisotropy are
often based on the slow-roll approximation. We study the precision of these
predictions and compare them with the recent data from BOOMERanG and MAXIMA-1.",0010453v1
2000-11-23,Issues and methods for CMB anisotropy data reduction,"Major issues and existing methods for the reduction of CMB anisotropy data
are reviewed. An emphasis is put on the proper modelling of the data. It is
suggested that the robustness of methods could be improved by taking into
account the uncertainty of the model for finding optimal solutions.",0011444v1
2001-05-16,Window Function for Non-Circular Beam CMB Anisotropy Experiment,"We develop computationally rapid methods to compute the window function for a
cosmic microwave background anisotropy experiment with a non-circular beam
which scans over large angles on the sky. To concretely illustrate these
methods we compute the window function for the Python V experiment which scans
over large angles on the sky with an elliptical Gaussian beam.",0105270v1
2001-06-07,Anisotropy analysis of EAS data in the knee region,"Based on MAKET-ANI EAS data the distributions of equatorial coordinates of
EAS core directions are obtained in the knee region. Anisotropy of primary
cosmic rays is displayed only by declination equatorial coordinates (20+/-3
degrees) at primary energies more than 5-10 PeV. The fraction of anisotropic
component turns out ~10% in the knee region.",0106124v1
2001-09-17,Physics of Cosmic Microwave Background anisotropies and primordial fluctuations,"The physics of the origin and evolution of CMB anisotropies is described. I
explain the idea and status of cosmic parameter estimation and follow it up
with critical comments on its dependence on model assumptions and initial
conditions.",0109274v1
2003-02-13,Probing the star formation epoch with Wilkinson Microwave Anisotropy Probe (WMAP) data and high-redshift QSOs,"Using the values of the cosmological parameters obtained from Wilkinson
Microwave Anisotropy Probe (WMAP) and the cosmological chemical clock observed
by high-redshift quasars, it is shown that star formation should have started
by the redshift $z_F > 9.5$, and that $z_F$ is sensitive only to $\omegamz h^2$
in flat $\Lambda$CDM cosmology.",0302263v1
2004-01-30,Anisotropies in Ultrahigh Energy Cosmic Rays,"The present status of anisotropy studies for the highest energy cosmic rays
is presented including the first full sky survey. Directions and prospects for
the future are also discussed in light of new statistical methods and the last
quantities of data expected in the near future from the Pierre Auger
Observatory.",0401632v1
2004-12-01,Initial power spectrum shape,"Mainly used to set constraints on cosmological parameters, CMB anisotropies
can give information on primordial universe. Unfortunately, initial conditions
and late time cosmology are degenerated. I focus on the effect of the shape of
the initial power spectrum of fluctuations on the cosmological parameter
estimation from CMB temperature anisotropies. Strong constraints obtained using
a priori knowledge of the initial spectrum disappear when the latter is let
free.",0412022v1
2006-07-05,A No-Truncation Approach to Cosmic Microwave Background Anisotropies,"We offer a method of calculating the source term in the line-of-sight
integral for cosmic microwave background anisotropies without using a truncated
partial-wave expansion in the Boltzmann hierarchy.",0607076v2
2007-02-11,Ellipsoidal Universe Induces Large Scale CMB Polarization,"We calculate the large scale polarization of the cosmic microwave background
induced by the anisotropy of the spatial geometry of our universe. Assuming an
eccentricity at decoupling of about $0.64 10^{-2}$, we find $\Delta T_{pol}/
T_0 \simeq 0.53 10^{-6}$ quite close to the average level of polarization
detected by the Wilkinson Microwave Anisotropy Probe.",0702293v2
1997-10-28,Field-induced quasi-particle coherence effects in certain small magnets,"Small ferromagnets and anti-ferromagnets with an easy-plane anisotropy have a
ground to first excited state (tunnel) splitting which is quasi-periodic in the
magnitude of a field applied perpendicular to a principal anisotropy axis. The
associated oscillations in thermodynamic quantities might be used to prove the
existence of a coherent ground state even when the tunnel splitting itself
cannot be directly detected.",9710302v1
1998-05-15,Gauge Equivalence between Two-Dimensional Heisenberg Ferromagnets with Single-Site Anisotropy and Zakharov Equations,"Gauge equivalence between the two-dimensional continuous classical Heisenberg
ferromagnets(CCHF) of spin 1/2 - the M-I equation with single site anisotropy
and the Zakharov equation(ZE) is established for the easy axis case. The
anisotropic CCHF is shown to be gauge equivalent to the isotropic CCHF.",9805188v1
1999-04-18,Orientational phase transitions in anisotropic rare-earth magnets at low temperatures,"Orientational phase transitions are investigated within the Heisenberg model
with single-site anisotropy. The temperature dependence of the cone angle is
calculated within the spin-wave theory. The role of the quantum
renormalizations of anisotropy constants is discussed. A comparison with the
experimental data on the cone-plane orientational transition in holmium is
performed.",9904251v1
2001-01-31,Spin-orbit induced anisotropy in the magnetoconductance of two-dimensional metals,"It is shown that the spin-orbit coupling due to structure inversion asymmetry
leads to a characteristic anisotropy in the magnetoconductance of
two-dimensional metals. Relevance for recent experiments is discussed.",0101473v1
2001-04-13,Dipolar induced anisotropy in the random-field Ising model,"The crystalline ferromagnet with dipole-dipole interactions is studied within
the framework of the three-dimensional random-field Ising model. The field
distribution function and the analytic expression for temperature dependent
free energy are found. The dipolar induced magnetic anisotropy energy of bulk
cubic ferromagnetic materials is calculated.",0104246v1
2001-06-18,A microscopic model for exchange bias,"The domain state model for exchange bias has been further investigated by
considering vector spins for the antiferromagnet instead of Ising spins used in
the earlier studies. The qualitative results are similar to those with infinite
anisotropy for the antiferromagnet. However, under certain conditions softer
spins can lead to an even stronger bias field. The study shows a nontrivial
dependence of the exchange bias on the antiferromagnetic anisotropy.",0106333v1
2001-08-05,Low Energy Behaviour of XXZ Antiferromagnetic Spin Chain,"Zero temperature phase diagram of XXZ spin chain in external magnetic field
is investigated at low energies using path integral approach.It has been shown
by spin wave analysis and then by nonlinear sigma model transformation that
below some critical field the system undergoes quantum Kosterlitz-Thouless
phase transition.Above that critical field for low anisotropies the system is
saturated while at strong anisotropy the system has Ising antiferromagnetic
order.",0108086v1
2002-03-13,Comment on: Weak Anisotropy and Disorder Dependence of the In-Plane Magnetoresistance in High-Mobility (100) Si Inversion Layers,"Comment on: Weak Anisotropy and Disorder Dependence of the In-Plane
Magnetoresistance in High-Mobility (100) Si Inversion Layers",0203276v1
2002-07-05,Anisotropy of the upper critical field in superconductors with anisotropic gaps. Anisotropy parameters of MgB2,"The upper critical field Hc2 is evaluated for weakly-coupled two-band
superconductors. By modeling the actual bands and the gap distribution of MgB2
by two Fermi surface spheroids with average parameters of the real material, we
show that H_{c2,ab}/H_{c2,c} increases with decreasing temperature in agreement
with available data.",0207146v1
2004-02-09,Evidence of large anisotropy in the magnetization of Na0.35CoO2.1.3H2O quasi-single-crystal superconductors,"Quasi-single crystals (up to 2x2x1 mm3) of Na0.35CoO2.1.3H2O-superconductor
have been grown. Magnetization M(H, T) and M(T, H) curves with magnetic field
approximately parallel and perpendicular to c-axis indicates on large
anisotropy, comparable with Bi-based high-temperature superconducting (HTS)
phases.",0402235v1
2005-11-21,Magnetization reversal in the anisotropy-dominated regime using time-dependent magnetic fields,"We study magnetization reversal using various r.f. magnetic pulses. We show
numerically that switching is possible with simple sinusoidal pulses; however
the optimum approach is to use a frequency-swept (chirped) r.f. magnetic pulse,
the shape of which can be derived analytically. Switching times of the order of
nanoseconds can be achieved with relatively small r.f. fields, independent of
the anisotropy's strength.",0511497v1
2006-06-14,Anisotropy of heat capacity in Pauli limited unconventional superconductors,"Diamagnetically coupled magnetic field can be used as a probe of nodal
positions in unconventional superconductors. The heat capacity depends on the
angle $\phi_0$ between the magnetic field and the nodal directions. We show
that the anisotropy $C(\phi_0)$ persists even in systems with strong
paramagnetic coupling to the electrons's spins.",0606390v1
2007-03-11,Time-dependent fields and anisotropy dominated magnetic media,"We use a single dipole approximation to analyze the behavior of
anisotropy-dominated magnetic nanoparticles subjected to an external r.f.
field. We identify the steady state oscillations and analyze their stability.
We also analyze the case when the external r.f. field has a time-dependent
frequency which insures the most effective switching of the magnetization.",0703272v1
1994-05-25,Density Perturbations of Quantum Mechanical Origin and Anisotropy of the Microwave Background,"If the large-angular-scale anisotropy in the cosmic microwave background
radiation is caused by the long-wavelength cosmological perturbations of
quantum mechanical origin, they are, most likely, gravitational waves, rather
than density perturbations or rotational perturbations.",9405059v1
1998-11-03,A note on light velocity anisotropy,"It is proved that in experiments on or near the Earth, no anisotropy in the
one-way velocity of light may be detected. The very accurate experiments which
have been performed to detect such an effect are to be considered significant
tests of both special relativity and the equivalence principle",9811008v1
2003-06-23,Modern Michelson-Morley experiments and gravitationally-induced anisotropy of c,"The recent, precise Michelson-Morley experiment performed by Muller et al.
suggests a tiny anisotropy of the speed of light. I propose a quantitative
explanation of the observed effect based on the interpretation of gravity as a
density fluctuation of the Higgs condensate.",0306105v1
2005-01-11,"Quasi-spherical gravitational collapse and the role of initial data, anisotropy and inhomogeneity","In this paper, the role of anisotropy and inhomogeneity has been studied in
quasi-spherical gravitational collapse. Also the role of initial data has been
investigated in characterizing the final state of collapse. Finally, a linear
transformation on the initial data set has been presented and its impact has
been discussed.",0501035v1
1999-12-01,Seeds of Large Scale Anisotropy in Pre-Big-Bang Cosmology,"Within a string cosmology context, the large scale temperature anisotropies
may arise from the contribution of seeds to the metric fluctuations. We study
the cases of electromagnetic and axion seeds. We find that massless or very
light axions can lead to a flat or slightly tilted blue spectrum, that fits
current data.",9912207v1
2003-11-25,Cosmological constraints from Microwave Background Anisotropy and Polarization,"The recent high-quality measurements of the Cosmic Microwave Background
anisotropies have presented cosmologists with the possibility of studying the
large scale properties of our universe with unprecedented precision. Here I
review the current status of observations and constraints on theoretical
models.",0311319v1
2004-01-22,Noncommutative inflation and the large-scale damping in the CMB anisotropy,"We show that a certain class of short-distance cutoff can give rise to large
suppression on the CMB anisotropies at large angular scales.",0401153v2
2005-09-25,Hamiltonian formalism of the Landau-Lifschitz equation for a spin chain with full anisotropy,"The Hamiltonian formalism of the Landau-Lifschitz equation for a spin chain
with full anisotropy is formulated completely, which constructs a stable base
for further investigations.",0509042v1
2004-04-08,"Event anisotropy of identified $π^{0}$, photon and electron compared to charged $π$, $K$, $p$ and deuteron in $\sqrt{s_{NN}}$ = 200 GeV Au+Au at PHENIX","We report the recent results of event anisotropy analysis focused on $v_2$ in
$\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions at PHENIX.",0404014v1
2001-02-14,Effects of anisotropy on thermal entanglement,"We study the thermal entanglement in the two-qubit anisotropic XXZ model and
the Heisenberg model with Dzyaloshinski-Moriya (DM) interactions. The DM
interaction is another kind of anisotropic antisymmetric exchange interaction.
The effects of these two kinds of anisotropies on the thermal entanglement are
studied in detail for both the antiferromagnetic and ferromagnetic cases.",0102072v1
2007-05-20,Anisotropy and asymmetry in fully developed turbulence,"Using experimental longitudinal and transverse velocities data for very high
Reynolds number turbulence, we study both anisotropy and asymmetry of
turbulence. These both seem to be related to small scale turbulent structures,
and to intermittency. We may assume that the large scale velocity shear gives
an impact into the small scale turbulence, resulting in non-locality, and
related anomalous events.",0705.2890v1
2007-10-08,Lensing and CMB Anisotropies by Cosmic Strings at a Junction,"The metric around straight arbitrarily-oriented cosmic strings forming a
stationary junction is obtained at the linearized level. It is shown that the
geometry is flat. The sum rules for lensing by this configuration and the
anisotropies of the CMB are obtained.",0710.1636v1
2008-01-10,Order parameter configurations in the Lifshitz-type incommensurate ferroelectric thin films,"The Dzialoshinskii model of periodic and helicoidal structures has been
analyzed without neglecting of the amplitude function oscillations. The
amplitude function oscillations are shown to be important for understanding of
the nature of the phase function. Analytic consideration is carried out in the
limit of small anisotropy (neglecting the cosine term in the Hamiltonian).
Surprisingly, the phase jumps survive even in the limit of the vanishing
anisotropy.",0801.1583v1
2008-05-20,A Search for Cosmic Microwave Background Anisotropies on Arcminute Scales with Bolocam,"We have surveyed two science fields totaling one square degree with Bolocam
at 2.1 mm to search for secondary CMB anisotropies caused by the Sunyaev-
Zel'dovich effect (SZE). The fields are in the Lynx and Subaru/XMM SDS1 fields.
Our survey is sensitive to angular scales with an effective angular multipole
of l_eff = 5700 with FWHM_l = 2800 and has an angular resolution of 60
arcseconds FWHM. Our data provide no evidence for anisotropy. We are able to
constrain the level of total astronomical anisotropy, modeled as a flat
bandpower in C_l, with frequentist 68%, 90%, and 95% CL upper limits of 590,
760, and 830 uKCMB^2. We statistically subtract the known contribution from
primary CMB anisotropy, including cosmic variance, to obtain constraints on the
SZE anisotropy contribution. Now including flux calibration uncertainty, our
frequentist 68%, 90% and 95% CL upper limits on a flat bandpower in C_l are
690, 960, and 1000 uKCMB^2. When we instead employ the analytic spectrum
suggested by Komatsu and Seljak (2002), and account for the non-Gaussianity of
the SZE anisotropy signal, we obtain upper limits on the average amplitude of
their spectrum weighted by our transfer function of 790, 1060, and 1080
uKCMB^2. We obtain a 90% CL upper limit on sigma8, which normalizes the power
spectrum of density fluctuations, of 1.57. These are the first constraints on
anisotropy and sigma8 from survey data at these angular scales at frequencies
near 150 GHz.",0805.3151v2
2008-05-26,Magnetic anisotropy in ferromagnetic Josephson junctions,"Magnetotransport measurements were done on $\Nb/\Al_2\O_3/\Cu/\Ni/\Nb$
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Depending on ferromagnetic $\Ni$ interlayer thickness and geometry the standard
(1d) magnetic field dependence of critical current deviates from the text-book
model for Josephson junctions. The results are qualitatively explained by a
short Josephson junction model based on anisotropy and 2d remanent
magnetization.",0805.3925v2
2008-07-26,CMB Temperature Anisotropy from Broken Spatial Isotropy due to an Homogeneous Cosmological Magnetic Field,"We derive the cosmic microwave background temperature anisotropy two-point
correlation function (including off-diagonal correlations) from broken spatial
isotropy due to an arbitrarily oriented homogeneous cosmological magnetic
field.",0807.4239v2
2009-05-23,Influence of a Transport Current on Magnetic Anisotropy in Gyrotropic Ferromagnets,"Current-induced torques are commonly used to manipulate non-collinear
magnetization configurations. In this article we discuss current-induced
torques present in a certain class of collinear magnetic systems, relating them
to current-induced changes in magnetic anisotropy energy. We present a
quantitative estimate of their characteristics in uniform strained
ferromagnetic (Ga,Mn)As.",0905.3856v1
2009-06-27,The mass and anisotropy profiles of galaxy clusters from the projected phase space density: testing the method on simulated data,"We present a new method of constraining the mass and velocity anisotropy
profiles of galaxy clusters from kinematic data. The method is based on a model
of the phase space density which allows the anisotropy to vary with radius
between two asymptotic values. The characteristic scale of transition between
these asymptotes is fixed and tuned to a typical anisotropy profile resulting
from cosmological simulations. The model is parametrized by two values of
anisotropy, at the centre of the cluster and at infinity, and two parameters of
the NFW density profile, the scale radius and the scale mass. In order to test
the performance of the method in reconstructing the true cluster parameters we
analyze mock kinematic data for 20 relaxed galaxy clusters generated from a
cosmological simulation of the standard LCDM model. We use Bayesian methods of
inference and the analysis is carried out following the Markov Chain Monte
Carlo approach. The parameters of the mass profile are reproduced quite well,
but we note that the mass is typically underestimated by 15 percent, probably
due to the presence of small velocity substructures. The constraints on the
anisotropy profile for a single cluster are in general barely conclusive.
Although the central asymptotic value is determined accurately, the outer one
is subject to significant systematic errors caused by substructures at large
clustercentric distance. The anisotropy profile is much better constrained if
one performs joint analysis of at least a few clusters. In this case it is
possible to reproduce the radial variation of the anisotropy over two decades
in radius inside the virial sphere.",0906.5071v1
2009-08-03,Killing vectors and anisotropy,"We consider an action that can generate fluids with three unequal stresses
for metrics with a spacelike Killing vector. The parameters in the action are
directly related to the stress anisotropies. The field equations following from
the action are applied to an anisotropic cosmological expansion and an
extension of the Gott-Hiscock cosmic string.",0908.0354v1
2009-09-01,Effects of anisotropy in geostrophic turbulence,"The Boussinesq model of convection in a flat layer with heating from below is
considered. We analyze the effects of anisotropy caused by rapid rotation in
physical and wave spaces and demonstrate the suppression of energy transfer by
rotation. We also examine the structure of the wave triangle in nonlinear
interaction. The range of parameters is adapted to the models of convection in
the geodynamo.",0909.0149v1
2009-10-26,The Cosmic Neutrino Background Anisotropy - Linear Theory,"The cosmic neutrino background anisotropy is calculated for massive neutrino
states by solving the full Boltzmann equation. The effect of weak gravitational
lensing, including the Limber approximation, is also derived for massive
particles, and subsequently applied to the case of massive neutrinos.",0910.4578v1
2009-11-02,Dynamical Toroidal Hopfions in a Ferromagnet with Easy-Axis Anisotropy,"Three-dimensional toroidal precession solitons with a nonzero Hopf index,
which uniformly move along the anisotropy axis in a uniaxial ferromagnet, have
been found. The structure and existence region of the solitons have been
numerically determined by solving the Landau-Lifshitz equation.",0911.0451v1
2010-01-20,Note on Anisotropy of Resistivity in Hidden Ordered State of URu_2Si_2,"On an assumption that the HO is the antiferro-quadrupolar order with
\Gamma_{5} (Q_{z(x+y)} and Q_{z(x-y)}) symmetry, the anisotropy in temperature
dependence of resistivity (\rho_{c}\propto T^{2}, and \rho_{ab}\propto T) in
the HO phase of URu_2Si_2 is explained.",1001.3516v1
2010-05-06,The importance of anisotropy for relativistic fluids with spherical symmetry,"It is shown that an effective anisotropic spherically symmetric fluid model
with heat flow can absorb the addition to a perfect fluid of pressure
anisotropy, heat flow, bulk and shear viscosity, electric field and null fluid.
In most cases the induction of effective heat flow can be avoided.",1005.1047v1
2010-08-12,Anisotropy of DC Electric Field Influence on Acoustic Wave Propagation in Piezoelectric Plate,"Anisotropy of dc electric field influence on the different types of acoustic
waves in piezoelectric plate has been investigated by means of computer
simulation. Detail calculations have made for bismuth germanium oxide crystals.",1008.2058v1
2011-04-29,90-Degree Bloch Domain Wall Structure in a Cubic Crystal with a Negative Magnetic Anisotropy,"An influence of strong sample demagnetization field on the structure of plane
90-degree Bloch domain walls in a cubic (001)-crystal with a negative first
constant of magnetic anisotropy is considered.",1105.0013v1
2011-08-05,On discrete symmetries and relic radiation anisotropy,"It is argued that large scale angle correlations of the Cosmic Microwave
Background Radiation (CMBR) temperature fluctuations measured by Wilkinson
Microwave Anisotropy Probe (WMAP) mission may have a trace of discrete
symmetries of quantum gravity",1108.1254v2
2012-02-17,CMB Tensor Anisotropies in Metric f(R) Gravity,"We present a description of CMB anisotropies generated by tensor
perturbations in f(R) theories of gravity. The temperature power spectrum in
the special case of $f(R)=R^n$ is computed using a modified version of CAMB
package.",1202.3862v1
2012-09-11,Towards azimuthal anisotropy of direct photons,"Intensive radiation of magnetic bremsstrahlung type (synchrotron radiation)
resulting from the interaction of escaping quarks with the collective confining
colour field is discussed as a new possible mechanism of observed direct photon
anisotropy.",1209.2380v3
2012-12-25,Hysteresis behavior of the anisotropic quantum Heisenberg model,"The effect of the anisotropy in the exchange interaction on the hysteresis
loops within the anisotropic quantum Heisenberg model has been investigated
with the effective field theory for two spin cluster. Particular attention has
been devoted on the behavior of the hysteresis loop area, coercive field and
remanent magnetization with the anisotropy in the exchange interaction for both
ferromagnetic and paramagnetic phases.",1212.5997v1
2013-02-04,An optimality result about sample path properties of Operator Scaling Gaussian Random Fields,"We study the sample paths properties of Operator scaling Gaussian random
fields. Such fields are anisotropic generalizations of anisotropic self-similar
random fields as anisotropic Fractional Brownian Motion. Some characteristic
properties of the anisotropy are revealed by the regularity of the sample
paths. The sharpest way of measuring smoothness is related to these
anisotropies and thus to the geometry of these fields.",1302.0818v1
2013-02-04,A strong optimality result for anisotropic self--similar textures,"In previous works, we proposed a method to characterize jointly
self-similarity and anisotropy properties of a large class of self--similar
Gaussian random fields. We provide here a mathematical analysis of our
approach, proving that the sharpest way of measuring smoothness is related to
these anisotropies and thus to the geometry of these fields.",1302.0819v1
2013-02-12,Anisotropy and superconductivity,"The mean field method is applied for analysis of valence electrons in metals.
It is shown that at low temperatures electrons have two wave-vector
distribution patterns. Isotropic distribution refers to the first pattern.
Anisotropic distribution refers to another pattern, particularly to specific
wave-vector values occurred nearby the Fermi sphere. It is shown that it is the
anisotropy that makes the metal obtain its specific superconductor features.",1302.5066v1
2013-02-22,CMB Anisotropies by Collapsing Textures,"CMB photons passing through a collapsing texture knot receive an energy
shift, creating characteristic cold and hot spots on the sky. We calculate the
anisotropy pattern produced by collapsing texture knots of arbitrary shape. The
texture dynamics are solved numerically on a Minkowski background.",1302.5627v1
2013-05-29,The problem of small angular scale structure in the cosmic ray anisotropy data,"Recent observations have revealed structure on small angular scales in the
anisotropy data of cosmic rays at multi TeV energies. Even though the absolute
amplitudes are very small, these effects are somewhat surprising and a wide
range of possible causes have been discussed. A possible origin associated with
heliospheric electric fields is proposed.",1305.6752v1
2013-06-27,The anisotropy of a three- and a one-form,"We calculate the anisotropic signal associated with the coupling of a
three-form with an Abelian vector gauge field. In the simplest examples of
three-form inflation the amplification of the vector fluctuations is
exponential; this makes it almost certain that a large anisotropy will develop,
severely constraining the viability of the coupling.",1306.6429v1
2014-01-08,Light cone anisotropy in 21 cm signal from the epoch of reionization,"Using a suite of detailed numerical simulations we estimate the level of
anisotropy generated by the time evolution along the light cone of the 21cm
signal from the epoch of reionization. Our simulations include the physics
necessary to model the signal during both the late emission regime and the
early absorption regime, namely X-ray and Lyman-band 3D radiative transfer in
addition to the usual dynamics and ionizing UV transfer. The signal is analysed
using correlation functions perpendicular and parallel to the line of sight
(LOS). We reproduce general findings from previous theoretical studies: the
overall amplitude of the correlations and the fact that the light cone
anisotropy is visible only on large scales (100 cMpc). However, the detailed
behaviour is different. At 3 different epochs, the amplitude of the
correlations along and perpendicular to the LOS differ from each other,
indicating anisotropy. These 3 epochs are associated with 3 events of the
global reionization history: the overlap of ionized bubbles, the onset of mild
heating by X-rays in regions around the sources, and the onset of efficient
Lyman-alpha coupling in regions around the sources. A 20x20 deg^2 survey area
may be necessary to mitigate sample variance when we use the directional
correlation functions. On a 100 cMpc scale the light cone anisotropy dominates
over the anisotropy generated by peculiar velocity gradients computed in the
linear regime. By modelling instrumental noise and limited resolution, we find
that the anisotropy should be easily detectable by the SKA, assuming perfect
foreground removal, the limiting factor being a large enough survey size. In
the case of the LOFAR, it is likely that only first anisotropy episode will
fall in the observing frequency range and will be detectable only if sample
variance is much reduced (i.e. a larger than 20x20 deg^2 survey, which is not
presently planned).",1401.1807v1
2014-05-21,Anisotropy results from 193 GeV U+U collisions at RHIC,"We report the measurement of azimuthal anisotropy $v_{n}$ for n = 1-5 as a
function of transverse momentum $p_{T}$ and centrality in U+U collisions at
$\sqrt{s_{NN}}$ = 193 GeV, recorded with the STAR detector at RHIC. We also
present results on $v_{2}$ and azimuthal correlator related to charge
separation across the reaction plane due to local parity violation(LPV) in the
ultra-central collisions.",1405.5510v1
2014-07-21,Implications of the primordial anisotropy for a scalar field with non-minimal kinetic coupling,"We consider a scalar field with a kinetic term non-minimally coupled to
gravity in an anisotropic background. Various potentials for the scalar field
are considered. By explicit examples, we show that how the anisotropy can
change the dynamics of the scalar field compared with the isotropic background.",1407.5421v1
2015-03-24,Nuclear modification and azimuthal anisotropy of D mesons produced in relativistic heavy ion collision,"In this paper we present a phenomenological treatment of charm quark energy
loss before fragmenting into D mesons and calculate nuclear modification
factor, '$R_{AA}$' and azimuthal anisotropy, '$v_2$' of D mesons for lead on
lead collision at LHC energy of $\sqrt{s}$=2.76 A TeV.",1503.06936v1
2015-06-11,Hysteresis Behavior of Anisotropic Heisenberg Model in Thin Film Geometry,"The effect of the anisotropy in the exchange interaction and film thickness
on the hysteresis behavior of the anisotropic Heisenberg thin film has been
investigated with effective field formulation in a two spin cluster using the
decoupling approximation. The behaviors of the hysteresis loop area, coersive
field and remanent magnetization with the film thickness and anisotropy in the
exchange interaction have been obtained.",1506.03641v2
2015-09-18,27-day Variation of the Three Dimensional Solar Anisotropy of Galactic Cosmic Ray: 1965-2014,"The temporal evaluation of the 27-day variation of the three dimensional (3D)
galactic cosmic ray (GCR) anisotropy has been studied for 1965-2014. 3D
anisotropy vector was obtained based on the neutron monitors and Nagoya muon
telescopes data. We analyze the 27-day variation of the (1) two dimensional
(2D) GCR anisotropy in the ecliptic plane, and (2) north-south anisotropy
normal to the ecliptic plane. Studying the time line of the 27-day variation of
the 2D GCR anisotropy, we confirm that the average amplitude in the minimum
epoch of solar activity is polarity dependent, as it is expected from the drift
theory. The amplitude in the negative polarity epochs is less as we had shown
before. The feeble 11-year variation connected with solar cycle and strong
22-year pattern connected with solar magnetic cycle is visible in the 27-day
variation of the 2D anisotropy for 1965-2014. We show that the 27-day variation
of the GG index (being a measure of the north-south asymmetry) varies in
accordance to solar cycle with a period of 11-years, being in good agreement
with the 27-day variation of the At component of the GCR anisotropy calculated
by the IZMIRAN group. Detailed analysis are presented for the solar minimum
2007-2008 of solar cycle no.23 and solar maximum 2013-2015 of solar cycle no
24. In the solar cycle no. 24 GG index, calculated by Nagoya telescopes data,
is highly anticorrelated with By component of the interplanetary magnetic field
(IMF) and shows a clear recurrent changes related to the Sun's rotation.",1509.05770v1
2015-12-04,Primordial gravity wave background anisotropies,"We consider the primordial gravity wave background produced by inflation. We
compute the small anisotropy produced by the primordial scalar fluctuations.",1512.01531v3
2016-03-28,Electric-field modulation of exchange stiffness in MgO/CoFeB with perpendicular anisotropy,"We observe magnetic domain structures of MgO/CoFeB with a perpendicular
magnetic easy axis under an electric field. The domain structure shows a maze
pattern with electric-field dependent isotropic period. We find that the
electric-field modulation of the period is explained by considering the
electric-field modulation of the exchange stiffness constant in addition to the
known magnetic anisotropy modulation.",1603.08280v1
2016-09-05,Numerical examination of commutativity between Backus and Gazis et al. averages,"Dalton and Slawinski (2016) show that, in general, the Backus (1962) average
and the Gazis et al. (1963) average do not commute. Herein, we examine the
extent of this noncommutativity. We illustrate numerically that the extent of
noncommutativity is a function of the strength of anisotropy. The averages
nearly commute in the case of weak anisotropy.",1609.01034v1
2016-11-28,Numerical Study of Pseudo-gap Anisotropy for a Tight Binding Band,"The Fermi surface anisotropy of a pseudo-gap in the spectral weight, caused
by superconducting fluctuations or anti-ferromagnetic fluctuations, is
calculated for a tight binding band. The importance of the Fermi surface saddle
point, or hot spot, is illustrated. A peak-dip-hump structure due to a finite
frequency mode, is briefly explored. The connection to high temperature
superconducting copper-oxides is discussed.",1611.09305v1
2017-08-01,Effect of radiation-like solid on CMB anisotropies,"We compute the CMB angular power spectrum in the presence of the
radiation-like solid with the same pressure to energy density ratio as for the
radiation but with nonzero shear modulus. The effect can be observable not only
for large-angle anisotropies as shown by Balek and \v{S}kovran [2015] but also
for very small-angle ones.",1708.00237v1
2017-11-14,Generalized crystalline evolutions as limits of flows with smooth anisotropies,"We prove existence and uniqueness of weak solutions to anisotropic and
crystalline mean curvature flows, obtained as limit of the viscosity solutions
to flows with smooth anisotropies.",1711.04997v1
2018-07-04,Magnetic properties in the metallic magnets with large anisotropy,"We study low temperature properties in the metallic magnets, considering the
itinerant electron mediated ferromagnetism. Applying the Monte Carlo
simulations to the extended double exchange model, we discuss reorientation
phase transition and anisotropy field for the metallic magnets.",1807.01405v1
2018-10-30,Q-operators for higher spin eight vertex models with a rational anisotropy parameter,"Q-operators for generalised eight vertex models associated to higher spin
representations of the Sklyanin algebra are constructed by Baxter's first
method and Fabricius's method, when the anisotropy parameter is rational.",1810.12969v1
2019-04-12,Quasilinear approach of the cumulative whistler instability in fast solar winds: Constraints of electron temperature anisotropy,"Context. Solar outflows are a considerable source of free energy which
accumulates in multiple forms like beaming (or drifting) components and/or
temperature anisotropies. However, kinetic anisotropies of plasma particles do
not grow indefinitely and particle-particle collisions are not efficient enough
to explain the observed limits of these anisotropies. Instead, the
self-generated wave instabilities can efficiently act to constrain kinetic
anisotropies, but the existing approaches are simplified and do not provide
satisfactory explanations. Thus, small deviations from isotropy shown by the
electron temperature ($T$) in fast solar winds are not explained yet.
  Aims. This paper provides an advanced quasilinear description of the whistler
instability driven by the anisotropic electrons in conditions typical for the
fast solar winds. The enhanced whistler-like fluctuations may constrain the
upper limits of temperature anisotropy $A \equiv T_\perp /T_\parallel > 1$,
where $\perp, \parallel$ are defined with respect to the magnetic field
direction.
  Methods. Studied are the self-generated whistler instabilities, cumulatively
driven by the temperature anisotropy and the relative (counter)drift of the
electron populations, e.g., core and halo electrons. Recent studies have shown
that quasi-stable states are not bounded by the linear instability thresholds
but an extended quasilinear approach is necessary to describe them in this
case.
  Results. Marginal conditions of stability are obtained from a quasilinear
theory of the cumulative whistler instability, and approach the quasi-stable
states of electron populations reported by the observations.The instability
saturation is determined by the relaxation of both the temperature anisotropy
and the relative drift of electron populations.",1904.06202v2
2019-07-24,"Exact Thermodynamic Properties of (1,1/2) Mixed Diamond Chains with Strong Single-Site Anisotropy","The ground states and finite-temperature properties of mixed diamond chains
with spins 1 and 1/2 are investigated in the limit of strong easy-axis
anisotropy on the spin-1 sites. Magnetization curves, entropy, specific heat
and magnetic susceptibility are exactly calculated using the method of
\v{C}anov\`a et al. [J. Phys.: Condens. Matter 18 4967 (2006)].",1907.10467v1
2019-11-01,Discrimination of Dark Matter Mass and Velocity Distribution by Directional Detection,"The velocity distribution of dark matter is supposed to be isotropic Maxwell-
Boltzmann distribution in most cases, however, its anisotropy is suggested by
some simulations. We investigate conditions to give constraints on the
anisotropy with directional direct detections.",1911.00170v1
2020-11-18,On the interplay between magnetic field and anisotropy in holographic QCD,"We investigate the combined effects of anisotropy and a magnetic field in
strongly interacting gauge theories by the gauge/gravity correspondence. Our
main motivation is the quark-gluon plasma produced in off-central heavy-ion
collisions which exhibits large anisotropy in pressure gradients as well as
large external magnetic fields. We explore two different configurations, with
the anisotropy either parallel or perpendicular to the magnetic field, focusing
on the competition and interplay between the two. A detailed study of the RG
flow in the ground state reveals a rich structure where depending on which of
the two, anisotropy or magnetic field, is stronger, intermediate geometries
with approximate AdS$_4\times \mathbb{R}$ and AdS$_3\times \mathbb{R}^2$
factors arise. This competition is also manifest in the phase structure at
finite temperature, specifically in the dependence of the chiral transition
temperature on anisotropy and magnetic field, from which we infer the presence
of inverse magnetic and anisotropic catalyses of the chiral condensate.
Finally, we consider other salient observables in the theory, including the
quark-antiquark potential, shear viscosity, entanglement entropy and the
butterfly velocity. We demonstrate that they serve as good probes of the
theory, in particular, distinguishing between the effects of the magnetic field
and anisotropy in the ground and plasma states. We also find that the butterfly
velocity, which codifies how fast information propagates in the plasma,
exhibits a rich structure as a function of temperature, anisotropy and magnetic
field, exceeding the conformal value in certain regimes.",2011.09474v3
2021-04-22,Features of the Galactic Cosmic Ray Anisotropy in the Solar Cycle 24 and Solar Minima 23/24 and 24/25,"We study the role of drift effect in the temporal changes of the anisotropy
of galactic cosmic rays (GCRs) and the influence of the sector structure of the
heliospheric magnetic field on it. We analyze the GCRs anisotropy in the Solar
Cycle 24 and solar minimum 23_24 with negative polarity for the period of
2007-2009 and near minimum 24_25 with positive polarity in 2017-2018 using data
of global network of Neutron Monitors. We use the harmonic analyses method to
calculate the radial and tangential components of the anisotropy of GCRs for
different sectors (plus corresponds to the positive and minus to the negative
directions) of the heliospheric magnetic field. We compare the analysis of GCRs
anisotropy using different evaluations of the mean GCRs rigidity related to
Neutron Monitor observations. Then the radial and tangential components are
used for characterizing the GCRs modulation in the heliosphere. We show that in
the solar minimum 23_24 in 2007-2009 when negative, the drift effect is not
visibly evident in the changes of the radial component, i.e. the drift effect
is found to produce 4 % change in the radial component of the GCRs anisotropy
for 2007-2009. Hence the diffusion dominated model of GCRs transport is more
acceptable in 2007-2009. In turn, near the solar minimum 24_25 in 2017-2018
when positive, the drift effect is evidently visible and produce 40% change in
the radial component of the GCRs anisotropy for 2017-2018. So in the period of
2017-2018 diffusion model with noticeably manifested drift is acceptable. The
results of this work are in good agreement with the drift theory of GCRs
modulation, according to which during negative (positive) polarity cycles, a
drift stream of GCRs is directed toward (away from) the Sun, thus giving rise
to a 22-year cycle variation of the radial GCRs anisotropy.",2104.11277v1
2022-02-12,Renormalization group analysis of the finite 2DXY model with fourfold anisotropy: Application to the magnetic susceptibility of a ferromagnetic ultrathin film,"The renormalization group equations describing a finite 2DXY system with
fourfold anisotropy are solved in two steps, in order to study the magnetic
transition to paramagnetism in an ultrathin film. First, the equations are
linearized near the critical coupling $K=J/k_BT=2/\pi$. An exact solution of
the linearized equations confirms that a finite-size Kosterlitz-Thouless (KT)
transition occurs in the presence of weak fourfold anisotropy, and that an
Ising transition occurs for strong anisotropy. The behaviour of a given system
is determined by the product of an anisotropy parameter and the logarithm of
the system size. The linearized RG equations are not quantitatively reliable
across the full temperature range of the finite-size transition, but they
define the parameter space where a second approach, where the fourfold
anisotropy is treated as a perturbation, is valid. This perturbative treatment
provides a quantitative determination of the renormalized exchange coupling,
vortex density, and anisotropy throughout the transition. In particular, the
coupling has a universal point of inflection where vortex-antivortex pairs
unbind (as opposed to a ""universal jump""), and goes to zero asymptotically in
the paramagnetic state, as is expected for a finite system. These results are
used to calculate the magnetic susceptibility as the system moves from one
dominated by spin waves to one dominated by a free vortex gas. The presence of
anisotropy makes it necessary to include both the susceptibility $\chi_{||}$
due to fluctuations of the magnitude of the magnetization, and $\chi_\perp$ due
to angular fluctuations of the magnetization about a fourfold easy axis. A
comparison to recent measurements of the magnetic susceptibility of ultrathin
Fe/W(001) films is very encouraging.",2202.06100v2
2022-02-24,Temperature Anisotropy of the CMBR and the Non-zero Cosmological Constant,"We analyze the effect of a spherically symmetric clump on the anisotropy of
the cosmic microwave background radiation temperature in the framework of the
standard model of cosmology with a non-zero cosmological constant $\Lambda$ and
we show that it weakens the Rees-Sciama effect.",2202.12105v2
2022-04-18,Tomography of stellar halos: what does anisotropy in a stellar halo tell us?,"The stellar halo of the Milky Way is known to have a highly lumpy structure
due to the presence of tidal debris and streams accreted from the satellite
galaxies. The abundance and distribution of these substructures can provide a
wealth of information on the assembly history of the Milky Way. We use some
information-theoretic measures to study the anisotropy in a set of Milky
Way-sized stellar halos from the Bullock & Johnston suite of simulations that
uses a hybrid approach coupling semi-analytic and N-body techniques. Our
analysis shows that the whole-sky anisotropy in each stellar halo increases
with the distance from its centre and eventually plateaus out beyond a certain
radius. All the stellar halos have a very smooth structure within a radius of
$\sim 50$ kpc and a highly anisotropic structure in the outskirts. At a given
radius, the anisotropies at a fixed polar or azimuthal angle have two distinct
components: (i) an approximately isotropic component and (ii) a component with
large density fluctuations on small spatial scales. We remove the contributions
of the substructures and any non-spherical shape of the halo by randomizing the
polar and azimuthal coordinates of the stellar particles while keeping their
radial distances fixed. We observe that the fluctuating part of the anisotropy
is completely eliminated, and the approximately uniform component of the
anisotropy is significantly reduced after the sphericalization. A comparison
between the original halos and their sphericalized versions reveals that the
approximately uniform part of the anisotropy originates from the discreteness
noise and the non-spherical shape of the halo whereas the substructures
contribute to the fluctuating part. We show that such distinction between the
anisotropies has the potential to constrain the shape of the stellar halo and
its substructures.",2204.08425v2
2022-07-31,Possible Enhancements of Collective Flow Anisotropy Induced by Uncertainty Relation for Fluid Element,"In the stochastic formulation of viscous hydrodynamics, the velocity of a
fluid element fluctuates satisfying a similar relation to the
quantum-mechanical uncertainty relation. Using a non-relativistic toy model, we
show that the presence of such a velocity fluctuation increases the local
anisotropy of the momentum distributions of produced hadrons, and thus the
collective flow parameters such as $v_2$ is emphasized.",2208.00452v1
2023-03-11,Instability of a plane Poiseuille flow bounded between inhomogeneous anisotropic porous layers,"The linear stability analysis of a plane Poiseuille flow in a channel with
anisotropic and inhomogeneous porous layers is performed. The effect of
anisotropy and inhomogeneous permeability on the stability characteristics is
addressed in detail. The stability characteristics of the anisotropy parameter
(the ratio of permeability in the streamwise and the transverse direction) and
the inhomogeneity function are presented in detail",2305.07654v1
2023-05-25,Detector induced anisotropies on the angular distribution of gravitational wave sources and opportunities of constraining horizon scale anisotropies,"The cosmological principle has been verified using electromagnetic (EM)
observations. However its verification with high accuracy is challenging due to
various foregrounds and selection effects, and possible violation of the
cosmological principle has been reported in the literature. In contrast,
gravitational wave (GW) observations are free of these foregrounds and related
selection biases. This may enable future GW experiments to test the
cosmological principle robustly with full sky distribution of millions of
standard bright/dark sirens. However, the sensitivities of GW detectors are
highly anisotropic, resulting in significant instrument induced anisotropies in
the observed GW catalog. We investigate these instrumental effects for 3rd
generation detector networks in term of multipoles $a_{\ell m}$ of the observed
GW source distribution, using Monte Carlo simulations. (1) We find that the
instrument induced anisotropy primarily exists at the $m=0$ modes on large
scales ($\ell \lesssim 10$), with amplitude $\langle |a_{\ell 0}|^2 \rangle
\sim 10^{-3}$ for two detectors (ET-CE) and $\sim 10^{-4}$ for three detectors
(ET-2CE). This anisotropy is correlated with the sky distribution of
signal-to-noise ratio (SNR) and localization accuracy. Such anisotropy sets a
lower limit on the detectable cosmological $a_{\ell 0}$. (2) However, we find
that the instrument induced anisotropy is efficiently canceled by rotation of
the Earth in $m\neq 0$ components of $a_{\ell m}$. Therefore $a_{\ell m}$
($m\neq 0$) are clean windows to detect cosmological anisotropies. (3) We
investigate the capability of 3rd generation GW experiments to measure the
cosmic dipole. Through Monte Carlo simulations, we find that cosmic dipole with
an amplitude of $\sim 10^{-2}$ reported in the literature can be detected/ruled
out by ET-CE and ET-2CE robustly, through the measurement of $a_{11}$.",2305.15946v2
2023-08-09,Concave solutions to Finsler $p$-Laplace type equations,"We prove concavity properties for solutions to anisotropic quasi-linear
equations, extending previous results known in the Euclidean case. We focus the
attention on nonsmooth anisotropies and in particular we also allow the
functions describing the anisotropies to be not even.",2308.05069v2
1993-03-19,Cosmic Variance in CMB Anisotropies: From $1^{\circ}$ to COBE,"Cosmic Microwave Background (CMB) anisotropies that result from quantum
fluctuations during inflation are explored and the impact of their ``cosmic
variance'' on the ability to use existing data to probe inflationary models is
studied. We calculate the rms temperature fluctuation, and its cosmic variance,
for a number of experiments and for models with primordial power spectra which
range from $n={1\over 2}$ to $1$. We find: (1) cosmic variance obscures the
information which can be extracted, so a comparison of the rms temperature
fluctuation on small scales with the COBE result can fix $n$ to only
$\approx\pm 0.2$ at best; (2) measurements of the rms fluctuation on
$1^{\circ}$ scales may not allow one to unambiguously infer the tensor
contribution to the COBE anisotropy; (3) comparison of this contribution with
the predictions of inflation are ambiguous if the quadrupole anisotropy alone
is utilized. We discuss means for minimizing the uncertainty due to cosmic
variance in comparisons between experiments.",9303009v2
1994-01-04,Small-Scale Cosmic Microwave Background Anisotropies as a Probe of the Geometry of the Universe,"We perform detailed calculations of cosmic microwave background (CMB)
anisotropies in a CDM-dominated open universe with primordial adiabatic density
perturbations for a variety of reionization histories. We show that to a great
extent, the CMB anisotropies depend only on the geometry of the Universe, which
in a matter dominated universe is determined by $\Omega$, and the optical depth
to the surface of last scattering. In particular, the location of the primary
Doppler peak depends primarily on $\Omega$ and is fairly insensitive to the
other unknown parameters, such as $\Omega_b$, $h$, $\Lambda$, and the shape of
the power spectrum. Therefore, measurements of CMB anisotropies on small scales
may be used to determine $\Omega$.",9401003v1
1994-09-27,The Effect of Gravitational Scattering on the Anisotropy of the Cosmic Background Radiation,"The homogeneity of the cosmic microwave background radiation (CBR) is one of
the most severe constraint for theories of the structure formation in the
universe. We investigated the effect of the gravitational scattering (lensing)
of galaxies, clusters of galaxies, and superclusters on the anisotropy of the
CBR by numerical simulations. Although this effect was thought to be
unimportant, we found that the gravitational scatterings by superclusters can
significantly reduce the anisotropy of the CBR. We took into account the
exponential growth of the distance between two rays due to multiple
scatterings. The bending angle of each ray grows through the random walk
process. On the other hand, difference between two rays grows exponentially
while it is small. This exponential growth is caused by coherent scatterings
that two rays suffer, and was neglected in the previous studies. The
gravitational scattering by superclusters reduces the observed temperature
anisotropy of the CBR at present time approximately by 40--60 $\%$ from that at
the recombination time for angular scale up to a few degrees if the
supercluster were formed at $z=$2--4.",9409069v1
1995-11-27,Concepts in CMB Anisotropy Formation,"These lecture notes form a primer on the theory of cosmic microwave
background (CMB) anisotropy formation. With emphasis on conceptual aspects
rather than technical issues, we examine the physical foundations of anisotropy
evolution in relativistic kinetic and perturbation theory as well as the
manifestation of these principles in primary and secondary anisotropies. We
discuss gauge choice and gauge invariance and their use in understanding the
CMB. Acoustic, gravitational redshift and ionization effects have robust
signatures in the CMB spectrum and may allow determination of classical
cosmological parameters as well as reveal general distinctions between models
for structure formation. We develop the tight and weak coupling approximations
as analytic tools to help understand these effects and the robustness of their
signatures.",9511130v1
1996-06-16,Sub-degree Scale Microwave Anisotropies from Cosmic Defects,"If current ideas about unified field theories are correct, macroscopic cosmic
defects may well exist. The observation of such an entity would have enormous
significance for our understanding of fundamental physics. This paper points
out a novel observable signature of cosmic texture and global monopoles, namely
strong hot spots in the cosmic microwave anisotropy pattern on subdegree
scales. This signal should be readily detectable by the next generation of
anisotropy mapping experiments. The signature arises from overdensities in the
photon-baryon fluid generated by the gravitational attraction of the defects.
The angular power spectrum of the anisotropy fluctuations on subdegree scales
is also calculated, for cosmic string, global monopoles, and texture.",9606087v1
1996-09-04,Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions. II. Post-Collapse Evolution,"The evolution of spherical single-mass star clusters driven by two-body
relaxation was followed beyond core collapse by numerically solving the
orbit-averaged Fokker-Planck equation in energy--angular momentum space. The
heating effect by three-body binaries was incorporated in the Fokker-Planck
models. The development of velocity anisotropy after the core collapse is
discussed in detail. The anisotropy in the outer regions continues to increase
slowly after the collapse. In clusters comprising a relatively small number of
stars ($N \ltsim 10000$), the post-collapse expansion is nearly self-similar
and the anisotropy at each of inner Lagrangian radii is nearly constant. In
clusters comprising a larger number of stars ($N \gtsim 10000$), gravothermal
oscillations occur and the anisotropy at each of the inner radii oscillates
with the core oscillations. There is no qualitative difference in the nature of
the gravothermal oscillations between the isotropic and anisotropic
Fokker-Planck models.",9609025v1
1996-11-27,Anisotropy in the Microwave Sky: Results from the First Flight of BAM,"Results are reported from the first flight of a new balloon-borne instrument,
BAM (Balloon-borne Anisotropy Measurement), designed to search for cosmic
microwave background (CMB) anisotropy. The instrument uses a cryogenic
differential Fourier transform spectrometer to obtain data in five spectral
channels whose central frequencies lie in the range 3.7 cm^{-1} to 8.5 cm^{-1}.
The spectrometer is coupled to an off-axis prime focus telescope; the
combination yields difference spectra of two regions on the sky defined by
0\fdg 7 FWHM beams separated by 3\fdg 6. Single differences obtained at ten sky
positions show statistically significant fluctuations. Assuming Gaussian
correlated anisotropy, for the band average 3.1 cm^{-1} to 9.2 cm^{-1}, one
finds $\Delta T/T = 3.1^{+3.1}_{1.1}\times 10^{-5}$ (90% confidence interval)
for a correlation angle of 1\fdg 2. This corresponds to $Q_{flat} =
35.9^{17.7}_{6.3} \mu K$ (1\sigma).",9611225v1
1997-01-13,Constraints on a Primordial Magnetic Field,"We derive an upper limit of $B_0<3.4\times 10^{-9}(\Omega_0h_{50}^2)^{1/2}$
Gauss on the present strength of any primordial homogeneous magnetic field. The
microwave background anisotropy created by cosmological magnetic fields is
calculated in the most general flat and open anisotropic cosmologies containing
expansion-rate and 3-curvature anisotropies. Our limit is derived from a
statistical analysis of the 4-year Cosmic Background Explorer data for
anisotropy patterns characteristic of homogeneous anisotropy averaged over all
possible sky orientations with respect to the COBE receiver. The limits we
obtain are considerably stronger than those imposed by primordial
nucleosynthesis and ensure that other magnetic field effects on the microwave
background structure are unobservably small.",9701063v1
1997-02-24,Open inflation models and gravitational wave anisotropies in the CMB,"We study the large scale power spectrum of gravitational wave perturbations
of the microwave background in the context of single-bubble open inflation
models. We compute the ratio of tensor to scalar contributions to the CMB
anisotropies as a function of $\Omega_0$, the spectral index $n_S$ and the
tunneling parameter $2\pi GS_1/H$. We find that gravitational wave anisotropies
can be very large at small values of this tunneling parameter. We also consider
the contribution of supercurvature and bubble wall modes and find constraints
on the parameters of open inflation models from the observed temperature
anisotropies of the CMB. We show that the induced gravity and open hybrid
scenarios are compatible with present observations for a reasonable range of
parameters.",9702211v2
1997-02-26,CMB anisotropies caused by gravitational waves: A parameter study,"Anisotropies in the cosmic microwave background radiation due to gravity
waves are investigated. An initial spectrum of gravity waves may have been
induced during an epoch of inflation. We study the propagation of such a
spectrum in a Friedmann background of hot and cold dark matter, radiation and
(possibly) a cosmological constant. We finally calculate its imprint as
anisotropies on the cosmic microwave background. We also take into account that
massless particles can source gravity waves by their anisotropic stresses. We
consider general mixed dark matter models with and without cosmological
constant. For a given, scale invariant input spectrum of gravity we determine
the dependence of the resulting spectrum of CMB anisotropies on the different
model parameters.",9702226v2
1997-02-27,Cosmic Microwave Background anisotropies from second order gravitational perturbations,"This paper presents a complete analysis of the effects of second order
gravitational perturbations on Cosmic Microwave Background anisotropies, taking
explicitly into account scalar, vector and tensor modes. We also consider the
second order perturbations of the metric itself obtaining them, for a universe
dominated by a collision-less fluid, in the Poisson gauge, by transforming the
known results in the synchronous gauge. We discuss the resulting second order
anisotropies in the Poisson gauge, and analyse the possible relevance of the
different terms. We expect that, in the simplest scenarios for structure
formation, the main effect comes from the gravitational lensing by scalar
perturbations, that is known to give a few percent contribution to the
anisotropies at small angular scales.",9702234v2
1997-05-13,Cosmology with Sunyaev-Zeldovich observations from space,"In order to assess the potential of future microwave anisotropy space
experiments for detecting clusters by their Sunyaev-Zeldovich (SZ) thermal
effect, we have simulated maps of the large scale distribution of their Compton
parameter $y$ and of the temperature anisotropy $\Delta T/T$ induced by their
proper motion. Our model is based on a predicted distribution of clusters per
unit redshift and flux density using a Press-Schecter approach. These maps were
used to create simulated microwave sky by adding them to the microwave
contributions of the emissions of our Galaxy and the primary Cosmic Microwave
Background (CMB) anisotropies. In order to simulate measurements representative
of what current technology should achieve, ``observations'' were performed
according to the instrumental characteristics of the COBRAS/SAMBA space
mission. We then analyzed the resulting $y$ and $\Delta T/T$ maps which now
include both the primary anisotropies and those superimposed due to cluster
motions.",9705092v1
1997-06-25,"The Scalar, Vector and Tensor Contributions to CMB anisotropies from Cosmic Defects","Recent work has emphasised the importance of vector and tensor contributions
to the large scale microwave anisotropy fluctuations produced by cosmic
defects. In this paper we provide a general discussion of these contributions,
and how their magnitude is constrained by the fundamental assumptions of
causality, scaling, and statistical isotropy. We discuss an analytic model
which illustrates and explains how the ratios of isotropic and anisotropic
scalar, vector and tensor microwave anisotropies are determined. This provides
a check of the results from large scale numerical simulations, confirming the
numerical finding that vector and tensor modes provide substantial
contributions to the large angle anisotropies. This leads to a suppression of
the scalar normalisation and consequently of the Doppler peaks.",9706250v2
1997-09-09,A Complete Treatment of CMB Anisotropies in a FRW Universe,"We generalize the total angular momentum method for computing Cosmic
Microwave Background anisotropies to Friedman-Robertson-Walker (FRW) spaces
with arbitrary geometries. This unifies the treatment of temperature and
polarization anisotropies generated by scalar, vector and tensor perturbations
of the fluid, seed, or a scalar field, in a universe with constant comoving
curvature. The resulting formalism generalizes and simplifies the calculation
of anisotropies and, in its integral form, allows for a fast calculation of
model predictions in linear theory for any FRW metric.",9709066v2
1997-10-01,Correlation Functions of CMB Anisotropy and Polarization,"We give a full analysis of the auto- and cross-correlations between the
Stokes parameters of the cosmic microwave background. In particular, we derive
the windowing function for an antenna with Gaussian response in polarization
experiment, and construct correlation function estimators corrected for
instrumental noise. They are applied to calculate the signal to noise ratios
for future anisotropy and polarization measurements. While the
small-angular-scale anisotropy-polarization correlation would be likely
detected by the MAP satellite, the detection of electric and magnetic
polarization would require higher experimental sensitivity. For
large-angular-scale measurements such as the being planned SPOrt/ISS, the
expected signal to noise ratio for polarization is greater than one only for
reionized models with high reionization redshifts, and the ratio is less for
anisotropy-polarization correlation. Correlation and covariance matrices for
likelihood analyses of ground-based and satellite data are also given.",9710012v2
1998-03-17,Secondary CMB anisotropies in a universe reionized in patches,"In a universe reionized in patches, the Doppler effect from Thomson
scattering off free electrons generates secondary cosmic microwave background
(CMB) anisotropies. For a simple model with small patches and late
reionization, we analytically calculate the anisotropy power spectrum. Patchy
reionization can, in principle, be the main source of anisotropies on arcminute
scales. On larger angular scales, its contribution to the CMB power spectrum is
a small fraction of the primary signal and is only barely detectable in the
power spectrum with even an ideal, i.e. cosmic variance limited, experiment and
an extreme model of reionization. Consequently patchy reionization is unlikely
to affect cosmological parameter estimation from the acoustic peaks in the CMB.
Its detection on small angles would help determine the ionization history of
the universe, in particular the typical size of the ionized region and the
duration of the reionization process.",9803188v1
1998-07-01,Anisotropy of the sky distribution of gamma-ray bursts,"The isotropy of gamma-ray bursts collected in Current BATSE catalog is
studied. It is shown that the quadrupole term being proportional to $\sim \sin
2b \sin l$ is non-zero with a probability 99.9%. The occurrence of this
anisotropy term is then confirmed by the binomial test even with the
probability 99.97 %. Hence, the sky distribution of all known gamma-ray bursts
is anisotropic. It is also argued that this anisotropy cannot be caused
exclusively by instrumental effects due to the nonuniform sky exposure of BATSE
instrument. Separating the GRBs into short and long subclasses, it is shown
that the short ones are distributed anisotropically, but the long ones seem to
be distributed still isotropically. The character of anisotropy suggests that
the cosmological origin of short GRBs further holds, and there is no evidence
for their Galactical origin.",9807006v1
1998-07-04,The Anisotropy of Cosmic Ray Arrival Directions around 10$^{18}$eV,"Anisotropy in the arrival directions of cosmic rays with energies above
10$^{17}$eV is studied using data from the Akeno 20 km$^2$ array and the Akeno
Giant Air Shower Array (AGASA), using a total of about 117,000 showers observed
during 11 years. In the first harmonic analysis, we have found strong
anisotropy of $\sim$ 4% around 10$^{18}$eV, corresponding to a chance
probability of 0.2%. With two dimensional analysis in right ascension and
declination, this anisotropy is interpreted as an excess of showers near the
directions of the Galactic Center and the Cygnus region.",9807045v2
1998-10-19,Anisotropy of Ultra High Energy Cosmic Rays in the Dark Matter Halo Model,"The harmonic analysis of anisotropy of Ultra High Energy Cosmic Rays is
performed for the Dark Matter halo model. In this model the relic superheavy
particles comprise part of the Dark Matter and are concentrated in the Galactic
halo. The Ultra High Energy Cosmic Rays are produced by the decays of these
particles. Anisotropy is caused by the non-central position of the Sun in the
Galactic halo. The calculated anisotropy is in reasonable agreement with the
AGASA data. For more precise test of the model a comparison of fluxes in the
directions of the Galactic Center and Anticenter is needed.",9810277v3
1998-11-10,Observational Constraints on Microwave Anisotropy from Point Sources,"Applying basic physical principles to recent observational results, we derive
upper and lower limits on microwave anisotropy from point sources over the
range of frequencies 10-1000 GHz. We examine the level of noise in the
observations as a possible indication of source confusion at subarcminute
scales. We also derive an upper limit on microwave anisotropy caused by the
sources responsible for the Far-Infrared Background radiation detected in FIRAS
data. Our upper limit on point source confusion of DeltaT/T=10^{-5} for a 10'
beam at 100 GHz would cause severe foreground contamination for CMB anisotropy
observations, although the actual contamination level is probably much lower.
This upper limit constrains the long-feared possibility of an undetected
population of sources with emission peaking near 100 GHz. Source detections
closer to 100 GHz are needed to improve our knowledge of galaxy evolution at
high redshift and to predict the level of point source confusion.",9811148v1
1999-01-17,The Gravitational-Wave contribution to the CMB anisotropies,"We study the possible contribution of a stochastic gravitational wave
background to the anisotropy of the cosmic microwave background (CMB) in cold
and mixed dark matter (CDM and MDM) models. We test this contribution against
recent detections of CMB anisotropy at large and intermediate angular scales.
Our likelihood analysis indicates that models with blue power spectra ($n
\simeq 1.2$) and a tensor to the scalar quadrupole ratio of $R = C_2^T /C_2^S
\sim 2$ are most consistent with the anisotropy data considered here. We find
that by including the possibility of such background in CMB data analysis it
can drastically alter the conclusion on the remaining cosmological parameters.",9901220v1
1999-04-19,An almost isotropic cosmic microwave temperature does not imply an almost isotropic universe,"In this letter we will show that, contrary to what is widely believed, an
almost isotropic cosmic microwave background (CMB) temperature does not imply
that the universe is ``close to a Friedmann-Lemaitre universe''. There are two
important manifestations of anisotropy in the geometry of the universe, (i) the
anisotropy in the overall expansion, and (ii) the intrinsic anisotropy of the
gravitational field, described by the Weyl curvature tensor, although the
former usually receives more attention than the latter in the astrophysical
literature. Here we consider a class of spatially homogeneous models for which
the anisotropy of the CMB temperature is within the current observational
limits but whose Weyl curvature is not negligible, i.e. these models are not
close to isotropy even though the CMB temperature is almost isotropic.",9904252v1
1999-12-01,Limits on Arcminute Scale Cosmic Microwave Background Anisotropy with the BIMA Array,"We have used the Berkeley-Illinois-Maryland-Association (BIMA) millimeter
array outfitted with sensitive cm-wave receivers to search for Cosmic Microwave
Background (CMB) anisotropies on arcminute scales. The interferometer was
placed in a compact configuration which produces high brightness sensitivity,
while providing discrimination against point sources. Operating at a frequency
of 28.5 GHz, the FWHM primary beam of the instrument is 6.6 arcminutes. We have
made sensitive images of seven fields, five of which where chosen specifically
to have low IR dust contrast and be free of bright radio sources. Additional
observations with the Owens Valley Radio Observatory (OVRO) millimeter array
were used to assist in the location and removal of radio point sources.
Applying a Bayesian analysis to the raw visibility data, we place limits on CMB
anisotropy flat-band power Q_flat = 5.6 (+3.0 -5.6) uK and Q_flat < 14.1 uK at
68% and 95% confidence. The sensitivity of this experiment to flat band power
peaks at a multipole of l = 5470, which corresponds to an angular scale of
approximately 2 arcminutes. The most likely value of Q_flat is similar to the
level of the expected secondary anisotropies.",9912010v1
1999-12-01,On the existence of the intrinsic anisotropies in the angular distributions of gamma-ray bursts,"This articles is concerned primarily with the intrinsic anisotropy in the
angular distribution of 2281 gamma-ray bursts (GRBs) collected in Current BATSE
Gamma-Ray Burst Catalog until the end of year 1998, and, second, with intrinsic
anisotropies of three subclasses (""short"", ""intermediate"", ""long"") of GRBs.
Testing based on spherical harmonics of each class, in equatorial coordinates,
is presented. Because the sky exposure function of BATSE instrument is not
dependent on the right ascension $\alpha$, any non-zero spherical harmonic
proportional either to $P_n^m(\sin \delta) \sin m \alpha$ or to $P_n^m(\sin
\delta) \cos m\alpha$ with $m \neq 0$ ($\delta$ is the declination),
immediately indicates an intrinsic non-zero term. It is a somewhat surprising
result that the ""intermediate"" subclass shows an intrinsic anisotropy at the
$97\%$ significance level caused by the high non-zero $P_3^1(\sin \delta) \sin
m \alpha$ harmonic. The remaining two subclasses, and the full sample of GRBs,
remain isotropic.",9912037v1
2000-06-24,Ultra High Energy Cosmic Rays: propagation in the Galaxy and anisotropy,"We considered propagation of Ultra High Energy Cosmic Rays (UHECR) through
the galaxy. We investigated models with sources of UHECR distributed in the
same way as Cold Dark Matter (CDM) in a self-consistent way, taking into
account both extra-galactic and Galactic contributions. Using a very simple toy
model of galactic magnetic field we showed that in the case of galactic origin
of UHECRs the anisotropy can reach considerable values. In the case of
extragalactic UHECRs origin the anisotropy appears to be non-vanishing only for
electron and photon components due to synchrotron losses, but it hardly can be
reassured. The reason is an extremely low flux of UHE electrons and a too low
level of gamma-ray anisotropy.",0006349v3
2001-12-01,Archeops: A balloon experiment to measure CMB anisotropies with a broad range of angular sizes,"The Cosmic Microwave Background Radiation is the oldest photon radiation that
can be observed, having been emitted when the Universe was about 300,000 year
old. It is a blackbody at 2.73 K, and is almost perfectly isotropic, the
anisotropies being about one part to 100,000. However, these anisotropies,
detected by the COBE satellite in 1992, constrain the cosmological parameters
such as the curvature of the Universe.
  Archeops is a balloon-borne experiment designed to map these anisotropies.
The instrument is composed of a 1.5 m telescope and bolometers cooled at 85 mK
to detect radiation between 150 and 550 GHz. To lower atmosphere parasitic
signal, the instrument is lifted at 32 km altitude with a stratospheric balloon
during the arctic night. This instrument is also a preparation for the Planck
satellite mission, as its design is similar.
  We discuss here the results of the first scientific flight from Esrange (near
Kiruna, Sweden) to Russia on January 29th 2001, which led to a 22 %
(sub)millimetre sky coverage unprecedented at this resolution.",0112012v1
2002-03-07,Cosmic Microwave Background anisotropies beyond the third peak,"Forthcoming CMB experiments will allow us to accurately investigate the power
spectrum at very small scales ($\ell > 1000$). We predict the level of the
primary anisotropies, given the actual CMB measurements. The secondary
anisotropies generated after matter-radiation decoupling contribute additional
power in the tail of the CMB power spectrum. Together with the primary
anisotropies, we compute the predicted power spectra for three dominant
secondary effects induced by photon scattering. We predict these secondary
contributions in flat cosmological models for parameters in agreement (to
$2\sigma$) with the values allowed by current parameter estimates.",0203112v2
2002-10-31,CMB Temperature and Polarization Anisotropy Fundamentals,"The tremendous experimental progress in cosmic microwave background (CMB)
temperature and polarization anisotropy studies over the last few years has
helped establish a standard paradigm for cosmology at intermediate epochs and
has simultaneously raised questions regarding the physical processes at the two
opposite ends of time. What is the physics behind the source of structure in
the universe and the dark energy that is currently accelerating its expansion?
We review the acoustic phenomenology that forms the cornerstone of the standard
cosmological model and discuss internal consistency relations which lend
credence to its interpretation. We discuss future milestones in the study of
CMB anisotropy that have implications for inflationary and dark energy models.
These include signatures of gravitational waves and gravitational lensing in
the polarization fields and secondary temperature anisotropy from the transit
of CMB photons across the large-scale structure of the universe.",0210696v1
2003-08-27,The Anisotropy Search Program For the Pierre Auger Observatory,"The Pierre Auger Southern Observatory in Argentina has begun taking data as
it is being developed up to a final enclosed area of 3000 square kilometres. A
key aspect of the project is to provide information on the origin of the
highest energy cosmic rays through understanding the arrival directions of
those particles. To avoid claims of a spurious anisotropy detection because
trials have not been properly accounted, the Auger Collaboration has agreed 'a
priori' to the analysis prescription presented here. It specifies the
following:
  1. The accumulation time for the (future) data set to be analyzed.
  2. The anisotropy 'targets', each assigned a chance probability level.
  3. The analysis procedure for each trial.
  A positive result will be claimed for any target search only if its chance
probability is less than its assigned level. The levels are chosen so that the
total chance probability for one or more positive results is 0.001.
  Exploratory searches beyond this prescription will be encouraged, but the
Auger Collaboration will not assign any confidence level to anisotropies that
may be discovered that way. Any such discovery would identify a good target for
a prescription to be used with a subsequent Auger data set.",0308494v1
2003-09-29,Interpretation of the Global Anisotropy in the Radio Polarizations of Cosmologically Distant Sources,"We present a detailed statistical study of the observed anisotropy in radio
polarizations from distant extragalactic objects. This anisotropy was earlier
found by Birch (1982) and reconfirmed by Jain and Ralston (1999) in a larger
data set. A very strong signal was seen after imposing the cut
$|RM-\bar{RM}|>6$ rad/m$^2$, where $RM$ is the rotation measure and $\bar{RM}$
its mean value. In this paper we show that there are several indications that
this anisotropy cannot be attributed to bias in the data.
  We also find that a generalized statistic shows a very strong signal in the
entire data without imposing the RM dependent cut. Finally we argue that an
anisotropic background pseudoscalar field can explain the observations.",0309776v2
2004-03-15,Anisotropies in the Cosmic Microwave Background,"The linear anisotropies in the temperature of the cosmic microwave background
(CMB) radiation and its polarization provide a clean picture of fluctuations in
the universe some 370 kyr after the big bang. Simple physics connects these
fluctuations with those present in the ultra-high-energy universe, and this
makes the CMB anisotropies a powerful tool for constraining the fundamental
physics that was responsible for the generation of structure. Late-time effects
also leave their mark, making the CMB temperature and polarization useful
probes of dark energy and the astrophysics of reionization. In this review we
discuss the simple physics that processes primordial perturbations into the
linear temperature and polarization anisotropies. We also describe the role of
the CMB in constraining cosmological parameters, and review some of the
highlights of the science extracted from recent observations and the
implications of this for fundamental physics.",0403344v1
2004-04-13,Angular Power Spectrum Estimation of Cosmic Ray Anisotropies with Full or Partial Sky Coverage,"We study the angular power spectrum estimate in order to search for large
scale anisotropies in the arrival directions distribution of the highest-energy
cosmic rays. We show that this estimate can be performed even in the case of
partial sky coverage and validated over the full sky under the assumption that
the observed fluctuations are statistically spatial stationary. If this
hypothesis - which can be tested directly on the data - is not satisfied, it
would prove, of course, that the cosmic ray sky is non isotropic but also that
the power spectrum is not an appropriate tool to represent its anisotropies,
whatever the sky coverage available. We apply the method to simulations of the
Pierre Auger Observatory, reconstructing an input power spectrum with the
Southern site only and with both Northern and Southern ones. Finally, we show
the improvement that a full-sky observatory brings to test an isotropic
distribution, and we discuss the sensitivity of the Pierre Auger Observatory to
large scale anisotropies.",0404253v2
2004-06-16,Statistical Isotropy of the Wilkinson Microwave Anisotropy Probe Data: A Bipolar Power Spectrum Analysis,"The statistical expectation values of the temperature fluctuations of the
Cosmic Microwave Background (CMB) are assumed to be preserved under rotations
of the sky. We investigate the Statistical Isotropy (SI) of the CMB anisotropy
maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using
Bipolar Power Spectrum (BiPS) proposed in [Hajian & Souradeep 2003]. The method
can probe specific regions in multipole space using appropriate window
functions. The BiPS is estimated for full sky CMB anisotropy maps based on the
first year WMAP data using a range of window functions. The BiPS spectra
computed for both full sky maps for all our window functions are consistent
with zero, roughly within $2 \sigma$. The null BiPS results may be interpreted
as an absence of strong violation of statistical isotropy in the first-year
WMAP data on angular scales larger than that corresponding to $l\sim60$.
However, pending a careful direct comparison, our results do not necessarily
conflict with the specific SI related anomalies reported using other
statistical tests.",0406354v2
2005-02-12,Statistical isotropy of CMB anisotropy from WMAP,"The statistical expectation values of the temperature fluctuations of cosmic
microwave background (CMB) are assumed to be preserved under rotations of the
sky. We investigate the statistical isotropy of the CMB anisotropy maps
recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using
bipolar spherical harmonic power spectrum proposed in Hajian & Souradeep 2003.
The Bipolar Power Spectrum (BiPS) is estimated for the full sky CMB anisotropy
maps of the first year WMAP data. The method allows us to isolate regions in
multipole space and study each region independently. This search shows no
evidence for violation of statistical isotropy in the first-year WMAP data on
angular scales larger than that corresponding to l~60.",0502248v1
2005-04-01,CMB Anisotropy Due to Tangled magnetic fields in re-ionized models,"Primordial tangled cosmological Magnetic Fields source rotational velocity
perturbations of the baryon fluid, even in the post-recombination universe.
These vortical modes inturn leave a characteristic imprint on the temperature
anisotropy of the Cosmic Microwave Background (CMB), if the CMB photons can be
re-scatterred after recombination. Observations from WMAP indicate that the
Universe underwent a relatively early re-ionization ($z_{ri} \sim 15$), which
does indeed lead to a significant optical depth for re-scattering of CMB
photons after the re-ionization epoch. We compute the resulting additional
temperature anisotropies, induced by primordial magnetic fields in the
post-recombination universe. We show that in models with early re-ionization, a
nearly scale-invariant spectrum of tangled magnetic fields which redshift to a
present value of $B_0 \sim 3 \times 10^{-9}$ Gauss, produce vector mode
perturbations which in turn induce additional temperature anisotropy of about
0.3 to 0.4 $ \mu$K over very small angular scales, with $ l$ upto $\sim 10000 $
or so.",0504007v1
2005-07-21,Coverage and large scale anisotropies estimation methods for the Pierre Auger Observatory,"When searching for anisotropies in the arrival directions of Ultra High
Energy Cosmic Rays, one must estimate the number of events expected in each
direction of the sky in the case of a perfect isotropy. We present in this
article a new method, developed for the Auger Observatory, based on a smooth
estimate of the zenith angle distribution obtained from the data itself (which
is essentially unchanged in the case of the presence of a large scale
anisotropy pattern). We also study the sensitivity of several methods to detect
large-scale anisotropies in the cosmic ray arrival direction distribution :
Rayleigh analysis, dipole fitting and angular power spectrum estimation.",0507517v1
2005-09-26,Separate the Tensor Perturbation From the CMB Temperature Anisotropy Power Spectrum,This paper has been withdrawn.,0509753v3
2005-09-27,A universal density slope - velocity anisotropy relation,"One can solve the Jeans equation analytically for equilibrated dark matter
structures, once given two pieces of input from numerical simulations. These
inputs are 1) a connection between phase-space density and radius, and 2) a
connection between velocity anisotropy and density slope, the \alpha-\beta
relation. The first (phase-space density v.s. radius) has been analysed through
several different simulations, however the second (\alpha-\beta relation) has
not been quantified yet. We perform a large set of numerical experiments in
order to quantify the slope and zero-point of the \alpha-\beta relation. When
combined with the assumption of phase-space being a power-law in radius this
allows us to conclude that equilibrated dark matter structures indeed have zero
central velocity anisotropy, central density slope of \alpha_0 = -0.8, and
outer anisotropy of approximately \beta_\infinity = 0.5.",0509799v1
2005-10-05,Did WMAP see Moving Local Structures?,"The divergence of the momentum density field of the large scale structure
generates a secondary anisotropy contribution to the Cosmic Microwave
Background (CMB). While the effect is best described as a non-linear extension
to the well-known integrated Sachs-Wolfe effect, due to mathematical
coincidences, the anisotropy contribution is also described as the lensing of
the dipole seen in the rest-frame of a moving mass. Given the closeness, there
is a remote possibility that local concentrations of mass in the form of the
Great Attractor and the Shapley concentration generate large angular scale
fluctuations in CMB and could potentially be responsible, at least partly, for
some of the low-multipole anomalies in WMAP data. While the local anisotropy
contribution peaks at low multipoles, for reasonable models of the mass and
velocity distributions associated with local super structures we find that the
amplitude of temperature anisotropies is at most at a level of 10$^{-2}$ $\mu$K
and is substantially smaller than primordial fluctuations. It is extremely
unlikely that the momentum density of local mass concentrations is responsible
for any of the large angular scale anomalies in WMAP data.",0510137v1
2005-10-12,CMB Temperature Anisotropy Quadrupole Generated by Tensor Perturbation,This paper has been withdrawn.,0510355v2
2005-10-21,The velocity anisotropy - density slope relation,"One can solve the Jeans equation analytically for equilibrated dark matter
structures, once given two pieces of input from numerical simulations. These
inputs are 1) a connection between phase-space density and radius, and 2) a
connection between velocity anisotropy and density slope, the \alpha-\beta
relation. The first (phase-space density v.s. radius) has already been analysed
through several different simulations, however the second (\alpha-\beta
relation) has not been quantified yet. We perform a large set of numerical
experiments in order to quantify the slope and zero-point of the \alpha-\beta
relation. We find strong indication that the relation is indeed an attractor.
When combined with the assumption of phase-space being a power-law in radius,
this allows us to conclude that equilibrated dark matter structures indeed have
zero central velocity anisotropy \beta_0 = 0, central density slope of \alpha_0
= -0.8, and outer anisotropy of \beta_\infty = 0.5.",0510656v1
2005-10-24,Anisotropic thermal emission from magnetized neutron stars,"The thermal emission from isolated neutron stars is not well understood. The
X-ray spectrum is very close to a blackbody but there is a systematic optical
excess flux with respect to the extrapolation to low energy of the best
blackbody fit. This fact, in combination with the observed pulsations in the
X-ray flux, can be explained by anisotropies in the surface temperature
distribution.We study the thermal emission from neutron stars with strong
magnetic fields in order to explain the origin of the anisotropy. We find
(numerically) stationary solutions in axial symmetry of the heat
transportequations in the neutron star crust and the condensed envelope. The
anisotropy in the conductivity tensor is included consistently. The presence of
magnetic fields of the expected strength leads to anisotropy in the surface
temperature. Models with toroidal components similar to or larger than the
poloidal field reproduce qualitatively the observed spectral properties and
variability of isolated neutron stars. Our models also predict spectral
features at energies between 0.2 and 0.6 keV.",0510684v2
2005-10-28,Search for Global Metric Anisotropy in Type Ia Supernova Data,"We examine the Type 1a supernova data in order to determine if it shows any
signal of large scale anisotropy. The anisotropy is modelled by an extended
G\""{o}del metric, which incorporates expansion along with rotation. The model
is smoothly connected to the usual FRW type, while expressing anisotropic
metric effects depending on certain parameters. We find no significant signal
of anisotropy in the data. We obtain bounds on an anisotropic redshift versus
magnitude relationship, and accompanying parameters of the G\""{o}del-Obukhov
metric.",0510803v3
2006-07-07,Angular distribution of satellite galaxies from the Sloan Digital Sky Survey Data Release 4,"We explore the angular distribution of two samples of satellite galaxies
orbiting isolated hosts extracted from the Sloan Digital Sky Survey Data
Release 4. We find a clear alignment of the satellites along the major axis of
their hosts when restricting the analysis to red hosts. The anisotropy is most
pronounced for red satellites of red hosts. We find that the distribution of
the satellites about blue, isolated hosts is consistent with isotropy. We show
that under the assumption that the true, underlying distribution of satellites
of blue hosts exhibits the same anisotropy as the satellites of red hosts, the
sample of blue hosts is too small to measure this anisotropy at a
statistically-significant level. The anisotropy that we detect for satellites
about red primaries is independent of the projected radius. In particular, it
is evident at large projected distances from primaries (300 < r_p < 500 kpc).",0607139v1
2006-08-25,The r-Process in the Proto-Neutron-Star Winds with Anisotropic Neutrino Emission,"The astrophysical origin of the r-process nuclei is still unknown. Even the
most promising scenario, the neutrino-driven winds from a nascent neutron star,
encounters severe difficulties in obtaining requisite entropy and short dynamic
timescale for the r-process. In this study, the effect of anisotropy in
neutrino emission from a proto-neutron star surface is examined with
semi-analytic neutrino-driven wind models. The increase of neutrino number
density in the wind owing to the anisotropy is modeled schematically by
enhancing the effective neutrino luminosity. It is shown that the neutrino
heating rate from neutrino-antineutrino pair annihilation into
electron-positron pairs can significantly increase owing to the anisotropy and
play a dominant role for the heating of wind material. A factor of five
increase in the effective neutrino luminosity results in 50% higher entropy and
a factor of ten shorter dynamic timescale owing to this enhanced neutrino
heating. The nucleosynthesis calculations show that this change is enough for
the robust r-process, producing the third abundance peak A = 195 and beyond.
Future multi-dimensional studies with accurate neutrino transport will be
needed if such anisotropy relevant for the current scenario (more than a factor
of a few) is realized during the wind phase (~1-10 s).",0608539v1
2006-09-29,Separating the Weak Lensing and Kinetic SZ Effects from CMB Temperature Maps,"A new generation of CMB experiments will soon make sensitive high resolution
maps of the microwave sky. At angular scales less than $\sim$10 arcminutes,
most CMB anisotropies are generated at z $< 1000$, rather than at the surface
of last scattering. Therefore, these maps potentially contain an enormous
amount of information about the evolution of structure. Whereas spectral
information can distinguish the thermal Sunyaev-Zeldovich (tSZ) effect from
other anisotropies, the spectral form of anisotropies generated by the
gravitational lensing and the kinetic Sunyaev-Zeldovich (kSZ) effects are
identical. While spectrally identical, the statistical properties of these
effects are different. We introduce a new real-space statistic, $<\theta
(\hat{n})^3 \theta (\hat{m})>_c$, and show that it is identically zero for
weakly lensed primary anisotropies and, therefore, allows a direct measurement
of the kSZ effect. Measuring this statistic can offer a new tool for studing
the reionization epoch. Models with the same optical depth, but different
reionization histories, can differ by more than a factor of 3 in the amplitude
of the kSZ-generated non-Gaussian signal.",0610007v2
2006-12-13,Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies: The Effect of a Cosmological Constant,"We explore the large angular scale temperature anisotropies in the cosmic
microwave background (CMB) due to homogeneous local dust-filled voids in a flat
Friedmann-Robertson-Walker universe with a cosmological constant. In comparison
with the equivalent dust-filled void model in the Einstein-de Sitter
background, we find that the anisotropy for compensated asymptotically
expanding local voids can be larger because second-order effects enhance the
linear integrated Sachs-Wolfe (ISW) effect. However, for local voids that
expand sufficiently faster than the asymptotic velocity of the wall, the
second-order effect can suppress the fluctuation due to the linear ISW effect.
A pair of quasi-linear compensated asymptotic local voids with radius
(2-3)*10^2 ~h^{-1} Mpc and a matter density contrast ~-0.3 can be observed as
cold spots with a temperature anisotropy Delta T/T~O(10^{-5}) that might help
explain the observed large-angle CMB anomalies. We predict that the associated
anisotropy in the local Hubble constant in the direction of the voids could be
as large as a few percent.",0612347v2
2006-12-26,Anisotropy of dark matter annihilation with respect to the Galactic plane,"We describe the anisotropy of dark matter clump distribution caused by tidal
destruction of clumps in the Galactic disk. A tidal destruction of clumps with
orbit planes near the disk plane occurs more efficiently as compared with
destruction of clumps at near-polar orbits. A corresponding annihilation of
dark matter particles in small-scale clumps produces the anisotropic gamma-ray
signal with respect to the Galactic disk. This anisotropy is rather small, 9%,
and superimposed on that due to off-centering position of the Sun in the
Galaxy. The anisotropy of annihilation signal with respect to the Galactic disk
provides a possibility to discriminate dark matter annihilation from the
diffuse gamma-ray backgrounds of other origin.",0612733v2
1994-11-04,Theoretical Study of Time-Resolved Fluorescence Anisotropy from Coupled Chromophore Pairs,"Calculations of time-resolved fluorescence anisotropy from a pair of
chromophores coupled by an excitation transfer interaction are presented. For
the purpose of investigating the effects of nuclear motion on the energy
transfer and anisotropy, an illustrative model is developed that provides each
chromophore with a single intramolecular vibrational mode. Account is taken of
non-instantaneous excitation and time- and frequency-resolved detection.
Effects of excitation pulse duration, detection window duration and frequency
resolution, and excitation transfer coupling strength on the time-resolved
anisotropy are examined in detail. Effects of vibrational relaxation and
dephasing are also examined using a simplified Redfield description of the
effects of coupling to a thermal bath.",9411004v1
1995-07-14,Density of States Driven Anisotropies Induced by Momentum Decoupling in High-Tc Superconductors,"Momentum decoupling arises when small momentum transfer processes dominate
the electron-phonon scattering and implies that anisotropies in
superconductivity are driven by the anisotropies of the density of states.
Considering an isotropic s-wave interaction in the momentum decoupling regime
we give a natural simultaneous explanation to various aspects of ARPES and
tunnel experiments on $Bi_2Sr_2CaCu_2O_8$, including the correlation of gap
magnitude and visibility of the dip above the gap, the enhancement of
anisotropy with temperature, the presence of gap minima away from the
$\Gamma-X$ direction and a gap maximum in the $\Gamma-X$ direction, the
similarity of tunnel and ARPES spectra in the $\Gamma-\bar{M}$ direction and
the asymmetry in the SIN tunnel spectra where the dip structure is present only
at negative sample bias.",9507052v1
1996-07-29,Spin-one ferromagnets with single-ion anisotropy in a perpendicular external field,"In this paper, the conventional Holstein-Primakoff method is generalized with
the help of the characteristic angle transformation [Lei Zhou and Ruibao Tao,
J. Phys. A {\bf 27} 5599 (1994)] for the spin-one magnetic systems with
single-ion anisotropies. We find that the weakness of the conventional method
for such systems can be overcome by the new approach. Two models will be
discussed to illuminate the main idea, which are the ``easy-plane"" and the
``easy-axis"" spin-one ferromagnet, respectively. Comparisons show that the
current approach can give reasonable ground state properties for the magnetic
system with ``easy-plane"" anisotropy though the conventional method never can,
and can give a better representation than the conventional one for the magnetic
system with ``easy-axis"" anisotropy though the latter is usually believed to be
a good approximation in such case. Study of the easy-plane model shows that
there is a phase transition induced by the external field, and the
low-temperature specific heat may have a peak as the field reaches the critical
value.",9607207v1
1997-07-29,Spin-Orbit-Induced Magnetic Anisotropy for Impurities in Metallic Samples II. Finite Size Dependence in the Kondo Resistivity,"The electrical resistivity including the Kondo resistivity increase at low
temperature is calculated for thin films of dilute magnetic alloys. Assuming
that in the non-magnetic host the spin-orbit interaction is strong like in Au
and Cu, the magnetic impurities have a surface anisotropy calculated in part I.
That anisotropy hinders the motion of the spin. Including that anisotropy the
effective electron-impurity coupling is calculated by using the second order
renormalization group equations. The amplitude of the Kondo resistivity
contribution is reduced as the position of the impurity approaches the surface
but the increase occurs approximately at the bulk Kondo temperature. Different
proximity effects observed by Giordano are also explained qualitatively where
the films of magnetic alloys are covered by pure second films with different
mean free path. The theory explains the experimental results in those cases
where a considerable amount of impurities is at the surface inside the
ballistic region.",9707299v1
1997-11-12,Phase-transitions induced by easy-plane anisotropy in the classical Heisenberg antiferromagnet on a triangular lattice: a Monte Carlo simulation,"We present the results of Monte Carlo simulations for the antiferromagnetic
classical XXZ model with easy-plane exchange anisotropy on the triangular
lattice, which causes frustration of the spin alignment. The behaviour of this
system is similar to that of the antiferromagnetic XY model on the same
lattice, showing the signature of a Berezinskii-Kosterlitz-Thouless transition,
associated to vortex-antivortex unbinding, and of an Ising-like one due to the
chirality, the latter occurring at a slightly higher temperature. Data for
internal energy, specific heat, magnetic susceptibility, correlation length,
and some properties associated with the chirality are reported in a broad
temperature range, for lattice sizes ranging from 24x24 to 120x120; four values
of the easy-plane anisotropy are considered. Moving from the strongest towards
the weakest anisotropy (1%) the thermodynamic quantities tend to the isotropic
model behaviour, and the two transition temperatures decrease by about 25% and
22%, respectively.",9711104v2
1998-01-15,Magnetization switching in a Heisenberg model for small ferromagnetic particles,"We investigate the thermally activated magnetization switching of small
ferromagnetic particles driven by an external magnetic field. For low uniaxial
anisotropy the spins can be expected to rotate coherently, while for sufficient
large anisotropy they should behave Ising-like, i.e., the switching should then
be due to nucleation. We study this crossover from coherent rotation to
nucleation for the classical three-dimensional Heisenberg model with a finite
anisotropy. The crossover is influenced by the size of the particle, the
strength of the driving magnetic field, and the anisotropy. We discuss the
relevant energy barriers which have to be overcome during the switching, and
find theoretical arguments which yield the energetically favorable reversal
mechanisms for given values of the quantities above. The results are confirmed
by Monte Carlo simulations of Heisenberg and Ising models.",9801154v2
1998-05-01,Band structures and optical properties of GaInAs quantum wires grown by strain-induced lateral ordering,"Band structures and optical matrix elements of strained multiple
quantum-wires (QWR's) are investigated theoretically via the effective
bond-orbital model, which takes into account the effects of valence-band
anisotropy and the band mixing. In particular, the Ga$_{1-x}$In$_x$As QWR's
grown by strain-induced lateral ordering (SILO) are considered. Recently, long
wavelength Ga$_{1-x}$In$_x$As QWR lasers have been fabricated via a single step
molecular beam epitaxy technique which uses the SILO process.[1] Low threshold
current and high optical anisotropy have been achieved. Multi-axial strains
[combinations of biaxial strains in the (001) and (110) planes] for QWR's are
considered, Our calculated anisotropy in optical matrix elements (for light
polarized parallel versus perpendicular to the QWR's axis) is in good agreement
with experiment. We also find that the strain tends to increase the quantum
confinement and enhance the anisotropy of the optical transitions.",9805016v1
1998-05-29,Scaling theory of magnetic ordering in the Kondo lattices with anisotropic exchange interactions,"The lowest-order scaling consideration of the magnetic state formation in the
Kondo lattices is performed within the $s-f$ model with inclusion of anisotropy
for both the $f-f$ coupling and $s-f$ exchange interaction. The Kondo
renormalizations of the effective transverse and longitudinal $s-f$ coupling
parameters, spin-wave frequency, gap in the magnon spectrum and ordered moment
are calculated in the case of both ferro- and antiferromagnets. The
anisotropy-driven change of the scaling behavior (e.g., critical value of $g$
for entering the strong-coupling region and the corresponding critical
exponents) is investigated numerically for N=2 and analytically in the large-N
limit. The dependence of the effective Kondo temperature on the bare $s-f$
coupling parameter $g$ weakens in the presence of anisotropy. The relative
anisotropy parameters for both the $s-f$ and $f-f$ coupling are demonstrated to
decrease during the renormalization process. The role of next-nearest exchange
interactions for this effect in the antiferromagnet is discussed.",9805390v2
1998-09-17,Magnetization Switching in Small Ferromagnetic Particles: Nucleation and Coherent Rotation,"The mechanisms of thermally activated magnetization switching in small
ferromagnetic particles driven by an external magnetic field are investigated.
For low uniaxial anisotropy the spins rotate coherently while for sufficiently
large uniaxial anisotropy they behave Ising-like, i.e. the switching then is
due to nucleation. The crossover from coherent rotation to nucleation is
studied for the classical three-dimensional Heisenberg model with uniaxial
anisotropy by Monte Carlo simulations. From the temperature dependence of the
metastable lifetime the energy barrier of a switching process can be
determined. For the case of infinite anisotropy we compare numerical results
from simulations of the Ising model with theoretical results for energy
barriers for both, single-droplet and multi-droplet nucleation. The simulated
barriers are in agreement with the theoretical predictions.",9809237v1
1999-02-11,A Comparative Study of the Magnetization Process of Two-Dimensional Antiferromagnets,"Plateaux in the magnetization curves of the square, triangular and hexagonal
lattice spin-1/2 XXZ antiferromagnet are investigated. One finds a zero
magnetization plateau (corresponding to a spin-gap) on the square and hexagonal
lattice with Ising-like anisotropies, and a plateau with one third of the
saturation magnetization on the triangular lattice which survives a small
amount of easy-plane anisotropy. Here we start with transfer matrix
computations for the Ising limit and continue with series in the XXZ-anisotropy
for plateau-boundaries using the groundstates of the Ising limit. The main
focus is then a numerical computation of the magnetization curves with
anisotropies in the vicinity of the isotropic situation. Finally, we discuss
the universality class associated to the asymptotic behaviour of the
magnetization curve close to saturation, as observed numerically in two and
higher dimensions.",9902163v1
1999-02-16,Dependence of Magnetic Anisotropy and Magnetoresistance of Ni81Fe19-Films on Annealing,"Permalloy (Py:Ni81Fe19) exhibits an anisotropic magnetoresistance (AMR) which
is very often used to read magnetic signals from storage devices. Py-films of
thickness 20nm were prepared by dc-magnetron sputtering in a magnetic field
onto thermally oxidized Si-wafers and annealed ex situ at temperatures up to
1000K in order to investigate the dependence of the magnetic anisotropy and the
AMR on heat treatments. The films exhibit an uniaxial anisotropy after
preparation which changes during annealing above 520K. The AMR along the former
magnetically easy axis as well as the corresponding field sensitivity are
increased by a heat treatment around 700K reaching maxima of about 8% and a
maximum sensitivity of 1.5%/Oe, respectively. We discuss possible sources for
the change in anisotropy, i.e. strain effects, inhomogeneities, and changes of
the local atomic order.",9902222v1
1999-05-12,Effects of dimensionality and anisotropy on the Holstein polaron,"We apply weak-coupling perturbation theory and strong-coupling perturbation
theory to the Holstein molecular crystal model in order to elucidate the
effects of anisotropy on polaron properties in D dimensions. The ground state
energy is considered as a primary criterion through which to study the effects
of anisotropy on the self-trapping transition, the self-trapping line
associated with this transition, and the adiabatic critical point. The effects
of dimensionality and anisotropy on electron-phonon correlations and polaronic
mass enhancement are studied, with particular attention given to the polaron
radius and the characteristics of quasi-1D and quasi-2D structures.
Perturbative results are confirmed by selected comparisons with variational
calculations and quantum Monte Carlo data.",9905148v2
1999-05-31,Magnetoelastic mechanism of spin-reorientation transitions at step-edges,"The symmetry-induced magnetic anisotropy due to monoatomic steps at strained
Ni films is determined using results of first - principles relativistic
full-potential linearized augmented plane wave (FLAPW) calculations and an
analogy with the N\'eel model. We show that there is a magnetoelastic
anisotropy contribution to the uniaxial magnetic anisotropy energy in the
vicinal plane of a stepped surface. In addition to the known spin-direction
reorientation transition at a flat Ni/Cu(001) surface, we propose a
spin-direction reorientation transition in the vicinal plane for a stepped
Ni/Cu surface due to the magnetoelastic anisotropy. We show that with an
increase of Ni film thickness, the magnetization in the vicinal plane turns
perpendicular to the step edge at a critical thickness calculated to be in the
range of 16-24 Ni layers for the Ni/Cu(1,1,13) stepped surface.",9905437v1
1999-10-18,Field-induced magnetic reorientation and effective anisotropy of a ferromagnetic monolayer within spin wave theory,"The reorientation of the magnetization of a ferromagnetic monolayer is
calculated with the help of many-body Green's function theory. This allows, in
contrast to other spin wave theories, a satisfactory calculation of magnetic
properties over the entire temperature range of interest since interactions
between spin waves are taken into account. A Heisenberg Hamiltonian plus a
second-order uniaxial single-ion anisotropy and an external magnetic field is
treated by the Tyablikov (Random Phase Approximation: RPA) decoupling of the
exchange interaction term and the Anderson-Callen decoupling of the anisotropy
term. The orientation of the magnetization is determined by the spin components
$\la S^\alpha\ra$ ($\alpha=x,y,z$), which are calculated with the help of the
spectral theorem. The knowledge of the orientation angle $\Theta_0$ allows a
non-perturbative determination of the temperature dependence of the effective
second-order anisotropy coefficient. Results for the Green's function theory
are compared with those obtained with mean-field theory (MFT). We find
significant differences between these approaches.",9910280v1
1999-11-19,Superconducting properties of Y_xLu_(1-x)Ni2B2C and La3Ni2B2N3: A comparison between experiment and Eliashberg theory,"Specific heat and resistivity measurements were performed on polycrystalline
samples of the solid-solution Y_xLu_(1-x)Ni2B2C in order to determine
thermodynamic properties such as the specific-heat difference, the
thermodynamic critical field H_c(T), as well as the upper critical field
H_{c2}(T). These properties were analyzed within the Eliashberg theory
including anisotropy effects, yielding electron-phonon coupling anisotropy
parameters <a_k^2> ranging beween 0.02 and 0.03 for the whole series, and Fermi
velocity anisotropy parameters of <b_k^2> = 0.245-0.3. Excellent agreement
between theory and experiment was achieved for these parameters, the Sommerfeld
constant and model phonon spectra determined from specific heat measurements.
An analysis of the previously investigated boronitride La3Ni2B2N3 for
comparison revealed the electron-phonon anisotropy to be of great significance
in describing its thermodynamic properties and the calculations yielded <a_k^2>
\~ 0.08 and <b_k^2> ~ 0.245. The T_c-behavior within the series
Y_xLu_(1-x)Ni2B2C is discussed in terms of coupling and impurity effects, and
the density of states at the Fermi level N(0).",9911305v2
1999-12-02,Generalized Phase Field Model for Computer Simulation of Grain Growth in Anisotropic Systems,"We study the dynamics and morphology of grain growth with anisotropic energy
and mobility of grain boundaries using a generalized phase field model. In
contrast to previous studies, both inclination and misorientation of the
boundaries are considered. The model is first validated against exact
analytical solutions for the classical problem of an island grain embedded in
an infinite matrix. It is found that grain boundary energy anisotropy has a
much stronger effect on grain shape than that of mobility anisotropy. In a
polycrystalline system with mobility anisotropy, we find that the system
evolves in a non-self-similar manner and grain shape anisotropy develops.
However, the average area of the grains grows linearly with time, as in an
isotropic system.",9912044v1
1999-12-21,Schwinger boson theory of anisotropic ferromagnetic ultrathin films,"Ferromagnetic thin films with magnetic single-ion anisotropies are studied
within the framework of Schwinger bosonization of a quantum Heisenberg model.
Two alternative bosonizations are discussed. We show that qualitatively correct
results are obtained even at the mean-field level of the theory, similar to
Schwinger boson results for other magnetic systems. In particular, the
Mermin-Wagner theorem is satisfied: a spontaneous magnetization at finite
temperatures is not found if the ground state of the anisotropic system
exhibits a continuous degeneracy. We calculate the magnetization and effective
anisotropies as functions of exchange interaction, magnetic anisotropies,
external magnetic field, and temperature for arbitrary values of the spin
quantum number. Magnetic reorientation transitions and effective anisotropies
are discussed. The results obtained by Schwinger boson mean-field theory are
compared with the many-body Green's function technique.",9912382v2
2000-08-17,Vortex Lines or Vortex-Line Chains at the Lower Critical Field in Anisotropic Superconductors?,"The vortex state at the lower critical field, H_{c1}, in clean anisotropic
superconductors placed in an external field tilted with respect to the axis of
anisotropy (c-axis) is considered assuming two possible arrangements: dilute
vortex-lines or dilute vortex-line chains. By minimizing the Gibbs free
energies in the London limit for each possibility we obtain the corresponding
lower critical fields as a function of the tilt angle. The equilibrium
configuration at H_{c1} for a given tilt angle is identified with that for
which H_{c1} is the smallest. We report results for parameter values typical of
strong and moderate anisotropy. We find that for strong anisotropy vortex-line
chains are favored for small tilt angles (< 7.9^o) and that at 7.9^o there is
coexistence between this configuration and a vortex-line one. For moderate
anisotropy we find that there is little difference between the vortex-line and
the vortex-chain lower critical fields.",0008261v1
2000-08-23,Weak ferromagnetism and field-induced spin reorientation in K2V3O8,"Magnetization and neutron diffraction measurements indicate long-range
antiferromagnetic ordering below TN=4 K in the 2D, S=1/2 Heisenberg
antiferromagnet K2V3O8. The ordered state exhibits ``weak ferromagnetism'' and
novel, field-induced spin reorientations. These experimental observations are
well described by a classical, two-spin Heisenberg model incorporating
Dzyaloshinskii-Moriya interactions and an additional c-axis anisotropy. This
additional anisotropy can be accounted for by inclusion of the symmetric
anisotropy term recently described by Kaplan, Shekhtman, Entin-Wohlman, and
Aharony. This suggests that K2V3O8 may be a very unique system where the
qualitative behavior relies on the presence of this symmetric anisotropy.",0008351v1
2001-01-17,Phenomenological theory of magnetic anisotropy in thin films and multilayers,"Within a phenomenological approach the density of induced uniaxial anisotropy
in nanostructures K(r) is treated as a physical field additional to the
magnetization M(r). The equilibrium distributions of K(r) are formed under the
influence of the surfaces and internal interactions. The functions K(r) and
M(r) are calculated for a magnetic layer between two nonmagnetic spacers. It is
shown that the transition from the phase with magnetization in plane to the
perpendicular phase occurs continuously via an intermediate phase which is
inhomogeneous across the layer-thickness. The theory explains experimentally
observed thickness dependences of the effective anisotropy and gives a method
to obtain values of the characteristic parameters for the theory from
experimental data. It is shown that the separation of the induced anisotropy
into volume and surface contribution is valid only for thick films.",0101262v1
2001-02-12,Lattice anisotropy as microscopic origin of static stripes in cuprates,"Structural distortions in cuprate materials offer a microscopic origin for
anisotropies in electron transport in the basal plane. Using a real-space
Hartree-Fock approach, we consider the ground states of the anisotropic Hubbard
(t_x \ne t_y) and t-J (t_x \ne t_y, J_x \ne J_y) models. Symmetrical but
inhomogeneous (``polaronic'') charge structures in the isotropic models are
altered even by rather small anisotropies to one-dimensional, stripe-like
features. We find two distinct types of stripe, namely uniformly filled,
antiphase domain walls and non-uniform, half-filled, in-phase ones. We
characterize their properties, energies and dependence on the model parameters,
including filling and anisotropy in t (and J). We discuss the connections among
these results, other theoretical studies and experimental observation.",0102201v1
2001-06-08,Reduced symmetry of heterointerfaces and orientational pinning of quantum Hall stripe phase,"In a 2D electron system in (001) GaAs/AlGaAs upon filling high Landau levels,
it was recently observed a new class of collective states, which are recognized
now to relate to the spontaneous formation of a charge density wave (``stripe
phase''). Here we analyze one of the possible mechanisms of the stripe pinning
along the crystallographic direction [110]--the native effective mass
anisotropy of 2D electrons. It is shown that for a symmetric quantum well this
anisotropy is a linear function of applied perpendicular-to-plane electric
field. So, if it is the anisotropy that defines the direction of the stripes,
the critical in-plane magnetic field, when the stripes rotate, will strongly
depend on the bias. The proper experiment will answer the question whether the
native anisotropy of the effective mass is the mechanism of the pinning.",0106162v1
2001-08-03,Electrical Resistivity Anisotropy from Self-Organized One-Dimensionality in High-Temperature Superconductors,"We investigate the manifestation of the stripes in the in-plane resistivity
anisotropy in untwinned single crystals of La_{2-x}Sr_{x}CuO_{4} (x = 0.02 -
0.04) and YBa_{2}Cu_{3}O_{y} (y = 6.35 - 7.0). It is found that both systems
show strongly temperature-dependent in-plane anisotropy in the lightly
hole-doped region and that the anisotropy in YBa_{2}Cu_{3}O_{y} grows with
decreasing y below about 6.60 despite the decreasing orthorhombicity, which
gives most direct evidence that electrons self-organize into a macroscopically
anisotropic state. The transport is found to be easier along the direction of
the spin stripes already reported, demonstrating that the stripes are
intrinsically conducting in cuprates.",0108053v2
2001-11-07,Critical behavior of the two-dimensional N-component Landau-Ginzburg Hamiltonian with cubic anisotropy,"We study the two-dimensional N-component Landau-Ginzburg Hamiltonian with
cubic anisotropy. We compute and analyze the fixed-dimension perturbative
expansion of the renormalization-group functions to four loops. The relations
of these models with N-color Ashkin-Teller models, discrete cubic models,
planar model with fourth order anisotropy, and structural phase transition in
adsorbed monolayers are discussed. Our results for N=2 (XY model with cubic
anisotropy) are compatible with the existence of a line of fixed points joining
the Ising and the O(2) fixed points. Along this line the exponent $\eta$ has
the constant value 1/4, while the exponent $\nu$ runs in a continuous and
monotonic way from 1 to $\infty$ (from Ising to O(2)). For N\geq 3 we find a
cubic fixed point in the region $u, v \geq 0$, which is marginally stable or
unstable according to the sign of the perturbation. For the physical relevant
case of N=3 we find the exponents $\eta=0.17(8)$ and $\nu=1.3(3)$ at the cubic
transition.",0111118v2
2001-12-10,Temperature and field dependence of the anisotropy of MgB2,"The anisotropy gamma of the superconducting state of high quality
single-crystals of MgB2 was determined, using torque magnetometry with two
different methods. The anisotropy of the upper critical field was found to be
temperature dependent, decreasing from gamma = 6 at 15 K to 2.8 at 35 K.
Reversible torque data near Tc reveal a field dependent anisotropy, increasing
nearly linearly from gamma = 2 in zero field to 3.7 in 10 kOe. The unusual
temperature dependence is a true bulk property and can be explained by
non-local effects of anisotropic pairing and/or the wave vector dependence of
the effective mass tensor.",0112166v3
2002-01-02,Anisotropies of the Hamiltonian and the Wave Function: Inversion Phenomena in Quantum Spin Chains,"We investigate the inversion phenomenon between the XXZ anisotropies of the
Hamiltonian and the wave function in quantum spin chains, mainly focusing on
the S=1/2 trimerized XXZ model with the next-nearest-neighbor interactions. We
have obtained the ground-state phase diagram by use of the degenerate
perturbation theory and the level spectroscopy analysis of the numerical data
calculated by the Lanczos method. In some parameter regions, the spin-fluid is
realized for the Ising-like anisotropy, and the Neel state for the XY-like
anisotropy, against the ordinary situation.",0201014v1
2002-04-11,In-plane Anisotropy on Resistivity and Thermopower in The Misfit Layered Oxide Bi2-xPbxSr2Co2Oy,"We investigated the in-plane anisotropy on the resistivity and thermopower of
Bi2-xPbxSr2Co2Oy single crystals, which have a misfit structure between the
hexagonal CoO2 layer and the rock salt Bi2Sr2O4 layer. The resistivity and
thermopower show significantly large anisotropy, which exceeds two at maximum.
This anisotropy would come from the anisotropic pseudogap formation enhanced by
the misfit structure. The thermopower changes with Pb doping to take a maximum
at x=0.4. The misfit structure improves the thermoelectric properties through
chemical pressure. The power factor is as large as 9 muW/cmK2 at 100 K for
x=0.6, which is the highest value for thermoelectric oxides at 100 K.",0204245v1
2002-06-11,Dynamics of Low Anisotropy Morphologies in Directional Solidification,"We report experimental results on quasi-two-dimensional diffusion limited
growth in directionally solidified succinonitrile with small amounts of
poly(ethylene oxide), acetone, or camphor as a solute. Seaweed growth, or dense
branching morphology, is selected by growing grains close to the $\{111\}$
plane, where the in-plane surface tension is nearly isotropic. The observed
growth morphologies are very sensitive to small anisotropies in surface tension
caused by misorientations from the $\{111\}$ plane. Different seaweed
morphologies are found, including the degenerate, the stabilized, and the
strongly tilted seaweeds. The degenerate seaweeds show a limited fractal
scaling range and, with increased undercooling, suggests a transition from
""fractal"" to ""compact"" seaweed. Strongly tilted seaweeds demonstrate a
significant twofold anisotropy. In addition, seaweed-dendrite transitions are
observed in low anisotropy growth.",0206179v1
2002-06-21,"Comment on ""Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB2""","In a recent paper [Phys. Rev. B 66, 012501 (2002)], torque data measured on a
MgB2 single crystal in fields from 10 to 60 kOe at 10 K were presented. The
authors obtained the anisotropy gamma by fitting a theoretical expression to
the data and concluded that the anisotropy is field independent gamma \approx
4.3. They also reported the observation of ""intrinsic pinning"", which they take
as experimental evidence for the occurence of superconductivity in the boron
layers. In this comment, we discuss the range of validity of the theoretical
expression used by the authors and show that the conclusion of a field
independent anisotropy does not hold. Furthermore, we present torque data
measured on two crystals of MgB2, establishing the extrinsic nature of the peak
in the irreversible torque observed in some crystals.",0206407v1
2002-07-25,Ground State Phase Diagram of the Distorted S=1 Kagomé Heisenberg Antiferromagnets with Single-site Anisotropy,"The ground state phase transitions in the distorted S=1 kagome Heisenberg
antiferromagnet (KHAF) with single-site anisotropy D are studied by the
numerical exact diagonalization method. For strong easy plane anisotropy, the
hexgonal singlet solid (HSS) ground state of the uniform KHAF is destroyed and
large-D state is realized. The quantum phase transition between these two
states is analogous to the Haldane-large-D transition in the S=1
antiferromagnetic Heisenberg chain. The combined effect of the sqrt(3) times
sqrt(3) lattice distortion and single site anisotropy is also investigated. The
ground state phase diagram expected from the numerical results is presented.
The presence of this transition is consistent with the HSS picture of the
ground state of the uniform S=1 KHAF and supports its validity.",0207595v1
2002-08-12,"Fe/V and Fe/Co (001) superlattices: growth, anisotropy, magnetisation and magnetoresistance","Some physical properties of bcc Fe/V and Fe/Co (001) superlattices are
reviewed. The dependence of the magnetic anisotropy on the in-plane strain
introduced by the lattice mismatch between Fe and V is measured and compared to
a theoretical derivation. The dependence of the magnetic anisotropy (and
saturation magnetisation) on the layer thickness ratio Fe/Co is measured and a
value for the anisotropy of bcc Co is derived from extrapolation. The
interlayer exchange coupling of Fe/V superlattices is studied as a function of
the layer thickness V (constant Fe thickness) and layer thickness of Fe
(constant V thickness). A region of antiferromagnetic coupling and GMR is found
for V thicknesses 12-14 monolayers. However, surprisingly, a 'cutoff' of the
antiferromagnetic coupling and GMR is found when the iron layer thickness
exceeds about 10 monolayers.",0208229v1
2002-10-08,Microwave Surface Resistance and Upper-Critical-Field Anisotropy of MgB2 Superconductor,"The field-induced variations of the microwave surface resistance are
investigated in two different samples of powdered MgB2. The experimental
results can be justified in the framework of the Coffey and Clem model with
fluxons moving in the flux-flow regime, provided that the anisotropy of the
upper critical field is taken into due account. Assuming the angular dependence
of the upper critical field expected from the anisotropic Ginzburg-Landau
theory, we determine the anisotropy factor by fitting the experimental data of
the field dependence of the microwave surface resistance. We show that the
anisotropy factor is constant in a range of temperatures of about 3 K below Tc
and it takes on different values for the two samples, even though they have
similar shape.",0210178v1
2002-10-31,Anisotropy of the superconducting state properties and phase diagram of MgB2 by torque magnetometry on single crystals,"The angular and temperature dependence of the upper critical field Hc2 in
MgB2 was determined from torque magnetometry measurements on single crystals.
The Hc2 anisotropy gamma_H was found to decrease with increasing temperature,
in disagreement with the anisotropic Ginzburg-Landau theory, which predicts
that the gamma_H is temperature independent. This behaviour can be explained by
the two band nature of superconductivity in MgB2. An analysis of measurements
of the reversible torque in the mixed state yields a field dependent effective
anisotropy gamma_eff, which can be at least partially explained by different
anisotropies of the penetration depth and the upper critical field. It is shown
that a peak effect in fields of about 0.85 Hc2 is a manifestation of an
order-disorder phase transition of vortex matter. The H-T phase diagram of MgB2
for H//c correlates with the intermediate strength of thermal fluctuations in
MgB2, as compared to those in high and low Tc superconductors.",0210701v1
2003-02-26,In-plane magnetic reorientation in coupled ferro- and antiferromagnetic thin films,"By studying coupled ferro- (FM) and antiferromagnetic (AFM) thin film
systems, we obtain an in-plane magnetic reorientation as a function of
temperature and FM film thickness. The interlayer exchange coupling causes a
uniaxial anisotropy, which may compete with the intrinsic anisotropy of the FM
film. Depending on the latter the total in-plane anisotropy of the FM film is
either enhanced or reduced. Eventually a change of sign occurs, resulting in an
in-plane magnetic reorientation between a collinear and an orthogonal magnetic
arrangement of the two subsystems. A canted magnetic arrangement may occur,
mediating between these two extremes. By measuring the anisotropy below and
above the N\'eel temperature the interlayer exchange coupling can be
determined. The calculations have been performed with a Heisenberg-like
Hamiltonian by application of a two-spin mean-field theory.",0302535v1
2003-03-18,Calculation of magnetic anisotropy energy in SmCo5,"SmCo5 is an important hard magnetic material, due to its large magnetic
anisotropy energy (MAE). We have studied the magnetic properties of SmCo5 using
density functional theory (DFT) calculations where the Sm f-bands, which are
difficult to include in DFT calculations, have been treated within the LDA+U
formalism. The large MAE comes mostly from the Sm f-shell anisotropy, stemming
from an interplay between the crystal field and the spin-orbit coupling. We
found that both are of similar strengths, unlike some other Sm compounds,
leading to a partial quenching of the orbital moment (f-states cannot be
described as either pure lattice harmonics or pure complex harmonics), an
optimal situation for enhanced MAE. A smaller portion of the MAE can be
associated with the Co-d band anisotropy, related to the peak in the density of
states at the Fermi energy. Our result for the MAE of SmCo5, 21.6 meV/f.u.,
agrees reasonably with the experimental value of 13-16 meV/f.u., and the
calculated magnetic moment (including the orbital component) of 9.4 mu_B agrees
with the experimental value of 8.9 mu_B.",0303368v1
2003-04-09,Field-induced magnetic anisotropy in La0.7Sr0.3CoO3,"Magnetic anisotropy has been measured for the ferromagnetic La0.7Sr0.3CoO3
perovskite from an analysis of the high-field part of the magnetization vs.
field curves, i.e., the magnetic saturation regime. These measurements give a
magnetic anistropy one order of magnitude higher than that of reference
manganites. Surprisingly, the values of the magnetic anisotropy calculated in
this way do not coincide with those estimated from measurements of coercive
fields which are one order of magnitude smaller. It is proposed that the reason
of this anomalous behaviour is a transition of the trivalent Co ions under the
external magnetic field from a low-spin to an intermediate-spin state. Such a
transition converts the Co3+ ions into Jahn-Teller ions having an only
partially quenched orbital angular momentum, which enhances the intra-atomic
spin-orbit coupling and magnetic anisotropy.",0304211v1
2003-05-05,Spin Anisotropy and Slow Dynamics in Spin Glasses,"We report on an extensive study of the influence of spin anisotropy on spin
glass aging dynamics. New temperature cycle experiments allow us to compare
quantitatively the memory effect in four Heisenberg spin glasses with various
degrees of random anisotropy and one Ising spin glass. The sharpness of the
memory effect appears to decrease continuously with the spin anisotropy.
Besides, the spin glass coherence length is determined by magnetic field change
experiments for the first time in the Ising sample. For three representative
samples, from Heisenberg to Ising spin glasses, we can consistently account for
both sets of experiments (temperature cycle and magnetic field change) using a
single expression for the growth of the coherence length with time.",0305088v2
2003-06-13,Modification of the classical Heisenberg helimagnet by weak uniaxial anisotropy and magnetic field,"Classical ground state of the isotropic Heisenberg spin Hamiltonian on a
primitive Bravais lattice is known to be a single-Q planar spin spiral. A
uniaxial anisotropy and external magnetic field distort this structure by
generating the higher-order Fourier harmonics at wave-vectors nQ in the spatial
spin configuration. These features are not captured in the formalism based on
the Luttinger-Tisza theorem, where the classical ground state energy is
minimized under the ``weak'' condition on the length of the spins. We discuss
why the correct solution is lost in that approach and present an alternative
microscopic treatment of the problem. It allows to find the classical ground
state for general Q for both easy-axis and easy-plane uniaxial second-order
anisotropy, and for any orientation of the magnetic field, by treating the
effect of anisotropy (but not the field) as a perturbation to the exchange
structure. As a result, the classical ground state energy, the uniform
magnetization, and the magnetic Bragg peak intensities that are measured in
experiment, are calculated.",0306370v1
2003-06-19,Exchange anisotropy and the dynamic phase transition in thin ferromagnetic Heisenberg films,"Monte Carlo simulations have been performed to investigate the dependence of
the dynamic phase behavior on the bilinear exchange anisotropy of a classical
Heisenberg spin system. The system under consideration is a planar thin
ferromagnetic film with competing surface fields subject to a pulsed
oscillatory external field. The results show that the films exhibit a single
discontinuous dynamic phase transition (DPT) as a function of the anisotropy of
the bilinear exchange interaction in the Hamiltonian. Furthermore there is no
evidence of stochastic resonance (SR) associated with the DPT. These results
are in marked contrast to the continuous DPT observed in the same system as a
function of temperature and applied field strength for a fixed bilinear
exchange anisotropy.",0306502v1
2003-07-17,Vortex-vacancy interactions in two-dimensional easy-plane magnets,"For a model with isotropic nearest neighbor exchange combined with easy-plane
exchange or single-ion anisotropies, the static effects of a magnetic vacancy
site on a nearby magnetic vortex are analyzed on square, hexagonal and
triangular lattices. Numerical energy minimization and linear stability
analysis using the vortex instability mode are employed. When the vortex is
centered on a vacancy, the critical anisotropies where the stable vortex
structure switches from out-of-plane to planar form are determined, and the
vortex energies and magnetizations are found as functions of anisotropy.
Consistent with square lattice calculations by Zaspel et al, the strength of
anisotropy needed to stabilize a vortex in the planar form is reduced when the
vortex is centered on a vacancy, for all three lattices studied. The
vortex-on-vacancy energy is found to be smaller than the typical energy of a
vortex centered between lattice sites in a system without vacancies. For a
vortex separated from a vacancy, the energy found as a function of separation
demonstrates an attractive potential between the two.",0307448v1
2003-08-14,In-Plane Magnetic Anisotropy In RF Sputtered Fe-N Thin Films,"We have fabricated Fe(N) thin films with varied N2 partial pressure and
studied the microstructure, morphology, magnetic properties and resistivity by
using X-ray diffraction, atomic force microscopy, transmission electron
microscopy, vibrating-sample magnetometer and angle-resolved M-H hysteresis
Loop tracer and standard four-point probe method. In the presence of low N2
partial pressure, Fe(N) films showed a basic bcc a-Fe structure with a
preferred (110) texture. A variation of in-plane magnetic anisotropy of the
Fe(N) films was observed with the changing of N component. The evolution of
in-plane anisotropy in the films was attributed to the directional order
mechanism. Nitrogen atoms play an important role in refining the a-Fe grains
and inducing uniaxial anisotropy.",0308274v1
2003-08-31,Josephson vortices and solitons inside pancake vortex lattice in layered superconductors,"In very anisotropic layered superconductors a tilted magnetic field generates
crossing vortex lattices of pancake and Josephson vortices (JVs). We study the
properties of an isolated JV in the lattice of pancake vortices. JV induces
deformations in the pancake vortex crystal, which, in turn, substantially
modify the JV structure. The phase field of the JV is composed of two types of
phase deformations: the regular phase and vortex phase. The phase deformations
with smaller stiffness dominate. The contribution from the vortex phase
smoothly takes over with increasing magnetic field. We find that the structure
of the cores experiences a smooth yet qualitative evolution with decrease of
the anisotropy. At large anisotropies pancakes have only small deformations
with respect to position of the ideal crystal while at smaller anisotropies the
pancake stacks in the central row smoothly transfer between the neighboring
lattice positions forming a solitonlike structure. We also find that even at
high anisotropies pancake vortices strongly pin JVs and strongly increase their
viscous friction.",0309021v1
2003-09-04,Orbital-dependent two-band superconductivity in MgB2,"We show that a two-band model with ${\bf k}$-dependent superconducting gaps
well describes the transmission and optical conductivity measured for MgB$_2$
thin films. It is also shown that the two-band anisotropic model consistently
describes the specific-heat jump and thermodynamic critical magnetic field
$H_c$. A single-gap anisotropic model is shown to be insufficient to understand
consistently optical and thermodynamic behaviors. In our model, the pairing
symmetry in each band has an anisotropic characteristic which is determined
almost uniquely; the superconducting gap in the $\sigma$-band has anisotropy in
the ab-plane and the gap in the $\pi$-band has a prolate form exhibiting
anisotropy in the c-direction. The anisotropy in the $\sigma$-band produces
rather small effects on the physical properties compared to the anisotropy in
the $\pi$-band.",0309095v1
2003-10-08,The Role of Nonlocality in the Pinning Properties of Borocarbides Materials,"An experimental review on the influence of nonlocal electrodynamics in the
vortex pinning properties of non-magnetic borocarbide superconductors is
presented. We show that the pinning force density Fp exhibits a rich and
complex anisotropic behavior that sharply contrast with the small mass
anisotropy of these compounds. For magnetic fields H applied parallel to the
crystallographic c-axis, the first order reorientation transition between two
rhombic lattices manifests itself as a kink in Fp(H). For H perpendicular to
the c-axis, a much larger Fp(H) and a slower relaxation rate is observed. In
this field configuration, nonlocality induces a fourfold periodicity in Fp when
H is rotated within the square basal plane. Unlike the out-of-plane anisotropy,
which persists for increasing impurity levels, the in-plane fourfold anisotropy
can be strongly suppressed by reducing the electronic mean free path. This
result unambiguously demonstrate that the in-plane anisotropy is a consequence
of nonlocal effects.",0310188v2
2003-10-31,Instability of planar vortices in two-dimensional easy-plane Heisenberg model with distance-dependent interactions,"It is known that magnetic vortices in two dimensional Heisenberg models with
easy-plane anisotropy exhibit an instability depending on the anisotropy
strength. In this paper, we study the statistic behavior of the two-dimensional
easy-plane Heisenberg models with distance-dependent interactions, $J_{xy}(r)$
and $J_z(r)$ for in-plane and out-of-plane components. We develop analytical
and numerical methods for accurate determination of critical anisotropy, above
which out-of-plane vortices are stable. In particular, we explore the vortex
formation of the Gaussian-type interaction model and determine the critical
anisotropy accurately for square, hexagonal and triangular lattices.",0310753v2
2003-12-18,Anisotropy of the orbital methods and the magnetic dipole term $T_z$ in ${\rm CrO_2}$: An {\it ab-initio} studt,"A systematic study is performed by the {\it ab-initio} density functional
theory of the anisotropy of the orbital moments $<l_z>$ and the magnetic dipole
term $<T_z>$ in bulk ${\rm CrO_2}$. Two different band-structure techniques are
used (FLAPW and LMTO-ASA), and the electronic correlations are treated by the
local-spin-density approximation (LSDA), the LSDA+ orbital polarization method,
and the LSDA+$U$ method. The calculated anisotropies of $<l_z>$ and $<T_z>$ are
very large compared to Fe, Ni and Co but still a factor of 5 and 2 smaller than
the anisotropies obtained from a recently suggested analysis of the X-ray
magnetic circular dichroism spectra for a thick layer of ${\rm CrO_2}$.",0312468v1
2004-04-16,Symmetry of Magnetic Quantum Tunneling in the Single-Molecule Magnet Mn12-Acetate,"The symmetry of magnetic quantum tunneling (MQT) in the single molecule
magnet Mn12-acetate has been determined by sensitive low-temperature magnetic
measurements in the pure quantum tunneling regime and high frequency EPR
spectroscopy in the presence of large transverse magnetic fields. The combined
data set definitely establishes the transverse anisotropy terms responsible for
the low temperature quantum dynamics. MQT is due to a disorder induced locally
varying quadratic transverse anisotropy associated with rhombic distortions in
the molecular environment (2nd order in the spin-operators). This is
superimposed on a 4th order transverse magnetic anisotropy consistent with the
global (average) S4 molecule site symmetry. The hard axes associated with these
forms of the transverse anisotropy are not collinear, leading to a complex
interplay between local and global symmetries, the consequences of which are
analyzed in detail.",0404390v2
2004-05-20,Anisotropy and internal field distribution of MgB2 in the mixed state at low temperatures,"Magnetization and muon spin relaxation on MgB2 were measured as a function of
field at 2 K. Both indicate an inverse-squared penetration depth strongly
decreasing with increasing field H below about 1 T. Magnetization also suggests
the anisotropy of the penetration depth to increase with increasing H,
interpolating between a low Hc1 and a high Hc2 anisotropy. Torque vs angle
measurements are in agreement with this finding, while also ruling out drastic
differences between the mixed state anisotropies of the two basic length scales
penetration depth and coherence length.",0405495v1
2004-06-30,Helical anisotropy and magnetoimpedance of CoFeSiB wires under torsional stress,"Recent measurements of the magnetoimpedance (at a fixed frequency of 1 MHz)
of cobalt-rich wires subjected to torsion stress show an asymmetry as a
function of torsion angle stemming from residual anisotropies induced during
wire fabrication. We interpret these measurements with a simple model based on
the competition between a circumferential magnetic anisotropy and another one
induced by torsional and residual stress. This allows extraction of the
physical parameters of the wire and explains the positive and negative torsion
cases. The agreement between theoretical and experimental results provides a
firm support for the model describing the behaviour of the anisotropy field
versus static magnetic field for all torsion angles.",0406767v2
2004-07-14,Ferromagnetic resonance study of free hole contribution to magnetization and magnetic anisotropy in modulation-doped Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As:Be,"Ferromagnetic resonance (FMR) is used to study magnetic anisotropy of GaMnAs
in a series of Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As heterostructures
modulation-doped by Be. The FMR experiments provide a direct measure of cubic
and uniaxial magnetic anisotropy fields, and their dependence on the doping
level. It is found that the increase in doping -- in addition to rising the
Curie temperature of the Ga$_{1 - x}$Mn$_{x}$As layers -- also leads to a very
significant increase of their uniaxial anisotropy field. The FMR measurements
further show that the effective $g$-factor of Ga$_{1 - x}$Mn$_{x}$As is also
strongly affected by the doping. This in turn provides a direct measure of the
contribution from the free hole magnetization to the magnetization of Ga$_{1 -
x}$Mn$_{x}$As system as a whole.",0407371v1
2004-07-19,Fermi-liquid based theory for the in-plane magnetic anisotropy in untwinned high-T$_c$ superconductors,"Using a generalized RPA-type theory we calculate the in-plane anisotropy of
the magnetic excitations in hole-doped high-$T_c$ superconductors. Extending
our earlier Fermi-liquid based studies on the resonance peak by inclusion of
orthorhombicity we still find two-dimensional spin excitations, however, being
strongly anisotropic. This reflects the underlying anisotropy of the hopping
matrix elements and of the resultant superconducting gap function. We compare
our calculations with new experimental data on {\it fully untwinned}
${YBa}_2{Cu}_3{O}_{6.85}$ and find good agreement. Our results are in contrast
to earlier interpretations on the in-plane anisotropy in terms of stripes (H.
Mook {\it et al.}, Nature {\bf 404}, 729 (2000)), but reveal a conventional
solution to this important problem.",0407487v2
2004-10-05,Micellar shape anisotropy and elastic constants in discotic lyotropic liquid crystals,"The elastic constants of a discotic lyotropic nematic liquid crystal are
calculated by means of a pseudo-molecular approach as functions of the micellar
shape anisotropy. By assuming that the temperature dependence of the ratio of
the elastic constants comes from the temperature dependence of the micellar
shape anisotropy, the theoretical predictions are connected with experimental
measurements for the ratio $K_{33}/K_{11}$. This procedure permits to
determine, in a phenomenological way, the temperature dependence for the ratio
of elastic constants and for the micellar shape anisotropy near the
nematic-isotropic transition in agreement with the experimental data.",0410128v1
2004-10-22,Influence of disorder on Hc2-anisotropy and flux pinning in MgB2,"The upper critical field and flux pinning in MgB2 single crystals were
investigated. The implications of these properties for technical applications
are discussed and compared with transport properties of polycrystalline bulk
samples and wires. In these untextured materials current percolation is
important, especially at high magnetic fields. It is shown that the anisotropy
of the upper critical field influences the ""irreversibility line"" and that the
application range of MgB2 is limited by the smallest upper critical field
(i.e., for the field direction perpendicular to the boron planes). Disorder,
introduced by irradiation with neutrons, enhances the upper critical field,
reduces the anisotropy and drastically changes flux pinning. While the enhanced
Hc2 and the reduced anisotropy generally improve the transport properties of
the polycrystalline samples, the contribution of the radiation-induced defects
to flux pinning is small compared to the as-grown defect structure (grain
boundary pinning).",0410573v1
2004-11-21,Anisotropy of in-plane magnetization due to nodal gap structure in the vortex state,"We examine the interplay between anisotropy of the in-plane magnetization and
the nodal gap structure on the basis of the approximate analytic solution in
the quasiclassical formalism. We show that a four-fold oscillation appears in
the magnetization, and its amplitude changes sign at an intermediate field. The
high-field oscillation originates from the anisotropy of the upper critical
field, while the low-field behavior can be understood by the thermally
activated quasiparticles near nodes depending on the applied field angles. The
temperature dependence of the magnetization also shows a similar sign change.
The anisotropy of the magnetization offers a possible measurement to identify
the gap structure directly for a wide class of type II superconductors.",0411540v1
2004-12-21,Permeability anisotropy induced by a shear displacement,"The permeability anisotropy that results from a shear displacement 'u'
between the complementary self-affine walls of a rough fracture is
investigated. Experiments in which a dyed fluid displaces a transparent one as
it is radially injected into a transparent fracture exhibit a clear anisotropy
in the presence of shear displacements, and allow us to estimate the ratio of
the permeabilities for flows parallel and perpendicular to 'u'. A simple model
which accounts for the development of channels perpendicular to 'u'
qualitatively explains these results, and predicts a permeability decreasing
(increasing) linearly with the variance of the aperture field for flow parallel
(perpendicular) to the shear displacement. These predictions are then compared
to the results of numerical simulations performed using a lattice-Boltzmann
technique and to the anisotropies measured in displacement experiments.",0412586v1
2005-01-26,Anisotropic diffusion limited aggregation in three dimensions - universality and non-universality,"We explore the macroscopic consequences of lattice anisotropy for Diffusion
Limited Aggregation (DLA) in three dimensions. Simple cubic and BCC lattice
growths are shown to approach universal asymptotic states in a coherent
fashion, and the approach is accelerated by the use of noise reduction. These
states are strikingly anisotropic dendrites with a rich hierarchy of structure.
For growth on an FCC lattice, our data suggest at least two stable fixed points
of anisotropy, one matching the BCC case. Hexagonal growths, favouring six
planar and two polar directions, appear to approach a line of asymptotic states
with continuously tunable polar anisotropy. The more planar of these growths
visually resemble real snowflake morphologies.
  Our simulations use a new and dimension-independent implementation of the
Diffusion Limited Aggregation (DLA) model. The algorithm maintains a hierarchy
of sphere-coverings of the growth, supporting efficient random walks onto the
growth by spherical moves. Anisotropy was introduced by restricting growth to
certain preferred directions.",0501645v2
2005-02-03,Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy,"The giant magnetoimpedance effect in composite wires consising of a
non-magnetic inner core and soft magnetic shell is studied theoretically. It is
assumed that the magnetic shell has a helical anisotropy. The current and field
distributions in the composite wire are found by means of a simultaneous
solution of Maxwell equations and the Landau-Lifshitz equation. The expressions
for the diagonal and off-diagonal impedance are obtained for low and high
frequencies. The dependences of the impedance on the anisotropy axis angle and
the shell thickness are analyzed. Maximum field sensitivity is shown to
correspond to the case of the circular anisotropy in the magnetic shell. It is
demonstrated that the optimum shell thickness to obtain maximum impedance ratio
is equal to the effective skin depth in the mahnetic material.",0502086v2
2005-06-10,Anisotropy of the antiferromagnetic spin correlations in the superconducting state of YBa_2Cu_3O_7 and YBa_2Cu_4O_8,"We present evidence that the antiferromagnetic spin correlations in optimally
doped YBa_2Cu_3O_7 and underdoped YBa_2Cu_4O_8 develop a surprisingly strong
anisotropy in the superconducting state. Comparing the ratio of the nuclear
spin-lattice relaxation rates of the planar copper and oxygen, measured at the
lowest and highest temperatures as well as at T_c, we conclude that the
antiferromagnetic in-plane correlations vanish as the temperature goes to zero.
This observation is corroborated by the measurement of the copper linewidth in
YBa_2Cu_4O_8. In contrast, the out-of-plane correlations do not change
appreciably between T=T_c and T=0. Within a model of fluctuating fields this
extreme anisotropy of the antiferromagnetic correlations also explains the
observed temperature dependence of the anisotropy of the copper relaxation
measured in a low external magnetic field.",0506245v2
2005-06-10,"Anisotropic Magnetoresistance and Magnetic Anisotropy in High-quality (Ga,Mn)As Films","We have performed a systematic investigation of magnetotransport of a series
of as-grown and annealed Ga1-xMnxAs samples with 0.011 <= x <= 0.09. We find
that the anisotropic magnetoresistance (AMR) generally decreases with
increasing magnetic anisotropy, with increasing Mn concentration and on low
temperature annealing. We show that the uniaxial magnetic anisotropy can be
clearly observed from AMR for the samples with x >= 0.02. This becomes the
dominant anisotropy at elevated temperatures, and is shown to rotate by 90o on
annealing. We find that the in-plane longitudinal resistivity depends not only
on the relative angle between magnetization and current direction, but also on
the relative angle between magnetization and the main crystalline axes. The
latter term becomes much smaller after low temperature annealing. The planar
Hall effect is in good agreement with the measured AMR indicating the sample is
approximately in a single domain state throughout most of the magnetisation
reversal, with a two-step magnetisation jump ascribed to domain wall nucleation
and propagation.",0506250v1
2005-06-22,Influence of the upper critical field anisotropy on the transport properties of polycrystalline MgB$_{2}$,"The intrinsic properties of MgB$_2$ form the basis for all applications of
this superconductor. We wish to emphasize that the application range of
polycrystalline MgB$_2$ is limited by the upper critical field H$_{c2}$ and its
anisotropy. In wires or tapes, the MgB$_2$ grains are randomly oriented or only
slightly textured and the anisotropy of the upper critical field leads to
different transport properties in different grains, if a magnetic field is
applied and the current transport becomes percolative. The irreversibility line
is caused by the disappearance of a continuous superconducting current path and
not by depinning as in high temperature superconductors. Based on a percolation
model, we demonstrate how changes of the upper critical field and its
anisotropy and how changes of flux pinning will influence the critical currents
of a wire or a tape. These predictions are compared to results of neutron
irradiation experiments, where these parameters were changed systematically.",0506562v1
2005-08-03,Effects of an external magnetic field on the gaps and quantum corrections in an ordered Heisenberg antiferromagnet with Dzyaloshinskii-Moriya anisotropy,"We study the effects of external magnetic field on the properties of an
ordered Heisenberg antiferromagnet with the Dzyaloshinskii-Moriya (DM)
interaction. Using the spin-wave theory quantum correction to the energy,
on-site magnetization, and uniform magnetization are calculated as a function
of the field H and the DM anisotropy constant D. It is shown that the spin-wave
excitations exhibit an unusual field-evolution of the gaps. This leads to
various non-analytic dependencies of the quantum corrections on H and D. It is
also demonstrated that, quite generally, the DM interaction suppresses quantum
fluctuations, thus driving the system to a more classical ground state. Most of
the discussion is devoted to the spin-S, two-dimensional square lattice
antiferromagnet, whose S=1/2 case is closely realized in K2V3O8 where at H=0
the DM anisotropy is hidden by the easy-axis anisotropy but is revealed in a
finite field. The theoretical results for the field-dependence of the
spin-excitation gaps in this material are presented and the implications for
other systems are discussed.",0508114v2
2005-11-01,Quasi-uniform in plane magnetization state of thin cylindrical dots in a square array and related anisotropy,"The energy (magnetostatic, exchange and Zeeman terms) of a square array of
cylindrical sub-micron dots made of soft ferromagnetic material is calculated
analytically and minimized, taking into account quasi-uniformity of dots
magnetization. The dependence of the equilibrium energy of the array on the
direction of the externally applied magnetic field in the array plane is
recovered, exhibiting the four-fold anisotropy. The anisotropy constant is
calculated. Its values for different array geometries are in excellent
agreement to the recent independent experiments. New eight-fold anisotropy
effect is predicted. Theory involves no adjustable parameters.",0511020v3
2006-04-14,Can the Ising critical behavior survive in non-equilibrium synchronous cellular automata?,"Universality classes of Ising-like phase transitions are investigated in
series of two-dimensional synchronously updated probabilistic cellular automata
(PCAs), whose time evolution rules are either of Glauber type or of
majority-vote type, and degrees of anisotropy are varied. Although early works
showed that coupled map lattices and PCAs with synchronously updating rules
belong to a universality class distinct from the Ising class, careful
calculations reveal that synchronous Glauber PCAs should be categorized into
the Ising class, regardless of the degree of anisotropy. Majority-vote PCAs for
the system size considered yield exponents $\nu$ which are between those of the
two classes, closer to the Ising value, with slight dependence on the
anisotropy. The results indicate that the Ising critical behavior is robust
with respect to anisotropy and synchronism for those types of non-equilibrium
PCAs. There are no longer any PCAs known to belong to the non-Ising class.",0604379v3
2006-04-27,Frozen metastable states in ordered systems of ultrafine magnetic particles,"For studying the interplay of dipolar interaction and anisotropy energy in
systems of ultrafine magnetic particles we consider simple cubic systems of
magnetic dipoles with anisotropy axes pointing into the $z$-direction. Using
Monte Carlo simulations we study the magnetic relaxation from several initial
states. We show explicitely that, due to the combined influence of anisotropy
energy and dipole interaction, magnetic chains are formed along the
$z$-direction that organize themselves in frozen metastable domains of columnar
antiferromagnetic order. We show that the domains depend explicitely on the
history and relax only at extremely large time scales towards the ordered
state. We consider this as an indication for the appearence of frozen
metastable states also in real sytems, where the dipoles are located in a
liquid-like fashion and the anisotropy axes point into random directions.",0604620v1
2006-05-08,Antiferromagnetic and spin gap phases of the anisotropic Kondo necklace model,"We have studied the effect of anisotropies on the quantum phase transition of
the Kondo necklace model in dimensions D=1, 2 and 3. Both the anisotropy
$\delta$ of the inter-site interaction term and anisotropy $\Delta$ of the
on-site Kondo interaction have been included. We use a bond operator method
with constraints implemented in mean field approximation. Starting from the
paramagnetic phase we determine the critical ratio $(t/J)_c$ of the quantum
critical point and associated scaling exponents of the Kondo-singlet gap. We
show that in the case of easy-axis type anisotropy $\delta >1$ a qualitatively
new behavior in comparison to the conventional Kondo necklace model with
($\delta$,$\Delta$)=(0,1) appears. We have also obtained the antiferromagnetic
order parameter in the long range ordered phase for $t > t_c$.",0605191v2
2006-06-08,An ab-initio theory for the temperature dependence of magnetic anisotropy,"We present a first-principles theory of the variation of magnetic anisotropy,
K, with temperature, T, in metallic ferromagnets. It is based on relativistic
electronic structure theory and calculation of magnetic torque. Thermally
induced `local moment' magnetic fluctuations are described within the
relativistic generalisation of the `disordered local moment' (R-DLM) theory
from which the T dependence of the magnetisation, m, is found. We apply the
theory to a uniaxial magnetic material with tetragonal crystal symmetry,
L1_0-ordered FePd, and find its uniaxial K consistent with a magnetic easy axis
perpendicular to the Fe/Pd layers for all m and proportional to m squared for a
broad range of values of m. This is the same trend that we have previously
found in L1_0-ordered FePt and which agrees with experiment. This account,
however, differs qualitatively from that extracted from a single ion anisotropy
model. We also study the magnetically soft cubic magnet, the Fe(50)Pt(50) solid
solution, and find that its small magnetic anisotropy constant K_1 rapidly
diminishes from 8 micro-eV to zero. K evolves from being proportional to the
seventh power of m at low T to the fourth power near the Curie temperature.",0606219v1
2006-07-03,Monte Carlo study of the transverse susceptibility in ordered arrays of magnetic nanoparticles,"We present Monte Carlo simulations of the reversible transverse
susceptibility (RTS) for a hexagonal array of dipolar interacting magnetic
nanoparticles with random anisotropy. RTS curves with the bias-field in-plane
and out-of-plane are compared. With increasing temperature the RTS curves
evolve from a three-peak structure to a double-peak and eventually a
single-peak at the blocking temperature of the system. This trend is preserved
for weak interactions. Dipolar interactions at low temperature are responsible
for the suppression of the coercivity peak in the out-of-plane geometry and its
progressive merge to the anisotropy peak with decreasing interparticle
separation in the in-plane geometry. The anisotropy peaks are located at higher
field values in the out-of-plane geometry relative to the in-plane one. When
the bias field lies in-plane (out-of-plane) the anisotropy peaks are shown to
shift to lower (higher) field values with decreasing interparticle separation.
The coercivity peak shifts to lower field values in both geometries. Our
results are compared with recent experimental findings in self-assembled arrays
of Fe nanoparticles.",0607037v2
2006-10-06,Sensitivity of the interlayer magnetoresistance of layered metals to intralayer anisotropies,"Many of the most interesting and technologically important electronic
materials discovered in the past two decades have two common features: a
layered crystal structure and strong interactions between electrons. Two of the
most fundamental questions about such layered metals concern the origin of
intralayer anisotropies and the coherence of interlayer charge transport. We
show that angle dependent magnetoresistance oscillations (AMRO) are sensitive
to anisotropies around an intralayer Fermi surface. Hence, AMRO can be a probe
of intralayer anisotropies that is complementary to angle-resolved
photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM).
However, AMRO are not very sensitive to the coherence of the interlayer
transport. We illustrate this with comparisons to recent AMRO experiments on an
overdoped cuprate.",0610191v2
2006-11-08,Phase diagram of the spin-1 anisotropic Heisenberg model with a single-ion anisotropy,"The spin-1 anisotropic Heisenberg model with a single-ion anisotropy is
studied using the Oguchi's pair approximation. Although the theory is developed
for lattices with general coordination number, we treat in detail the
three-dimensional lattice with the lowest coordination number, i.e. diamond
lattice, where the critical and tricritical behavior of the system is analyzed
as a function of both the single-ion anisotropy and exchange anisotropy.",0611212v2
2006-11-10,Rotational hysteresis of the exchange anisotropy direction in Co/FeMn thin films,"We have investigated the effects of rotating an applied field on the exchange
anisotropy in Co/FeMn thin films. When the applied field is initially along the
cooling field direction, the longitudinal hysteresis loop has a maximum
coercivity and the transverse hysteresis loop is flat, indicating that the
exchange field is along the cooling field direction. When the applied field
angle is rotated away and then restored to the original field cooling
direction, the exchange anisotropy direction has changed. The rotation of the
exchange field direction trails the applied field and is hysteretic. The
rotational hysteresis of the exchange field direction is due to the weak
anisotropy in thin FeMn layers, and decreases with increasing FeMn thickness.",0611294v1
2006-11-17,Anisotropy and Penetration Depth of MgB$_{2}$ from ${}^{11}$B NMR,"The ${}^{11}$B NMR spectra in polycrystalline MgB$_2$ were measured for
several magnetic fields (1.97 T and 3.15 T) as a function of temperature from 5
K to 40 K. The composite spectra in the superconducting state can be understood
in terms of anisotropy of the upper critical field, $\gamma_{H}$, which is
determined to be 5.4 at low temperature. Using Brandt's algorithm\cite{Brandt}
the full spectrum, including satellites, was simulated for the temperature 8 K
and a magnetic field of 1.97 T. The penetration depth $\lambda$ was determined
to be $1,152\pm50$ {\AA}, and the anisotropy of the penetration depth,
$\gamma_{\lambda}$, was estimated to be close to one at low temperature.
Therefore, our findings establish that there are two different anisotropies for
upper critical field and penetration depth at low temperatures.",0611473v2
2006-12-14,Importance of In-Plane Anisotropy in the Quasi Two-Dimensional Antiferromagnet BaNi$_{2}$V$_{2}$O$_{8}$,"The phase diagram of the quasi two-dimensional antiferromagnet
BaNi$_{2}$V$_{2}$O$_{8}$ is studied by specific heat, thermal expansion,
magnetostriction, and magnetization for magnetic fields applied perpendicular
to $\mathbf{c}$. At $\mu_0H^{*}\simeq1.5$ T, a crossover to a high-field state,
where $T_N(H)$ increases linearly, arises from a competition of intrinsic and
field-induced in-plane anisotropies. The pressure dependences of $T_N$ and
$H^{*}$ are interpreted using the picture of a pressure-induced in-plane
anisotropy. Even at zero field and ambient pressure, in-plane anisotropy cannot
be neglected, which implies deviations from pure
Berezinskii-Kosterlitz-Thouless behavior.",0612357v2
2007-01-10,Anisotropic susceptibility of the geometrically frustrated spin-chain compound Ca3Co2O6,"Ca3Co2O6 is a system exhibiting a series of fascinating properties, including
magnetization plateaus and remarkably slow dynamics at low-T. These properties
are intimately related to the geometrical frustration, which results from a
particular combination of features: (i) the chains are arranged on a triangular
lattice; (ii) there is a large uniaxial anisotropy; (iii) the intrachain and
interchain couplings are ferromagnetic and antiferromagnetic, respectively.
  The uniaxial anisotropy is thus an issue of crucial importance for the
analysis of the physical properties of Ca3Co2O6. However, it turns out that no
precise investigation of this magnetic anisotropy has been performed so far. On
the basis of susceptibility data directly recorded on single crystals, the
present study reports on quantitative information about the anisotropy of
Ca3Co2O6.",0701192v1
2007-01-25,Shape-induced phenomena in the finite size antiferromagnets,"It is of common knowledge that the direction of easy axis in the finite-size
ferromagnetic sample is controlled by its shape. In the present paper we show
that a similar phenomenon should be observed in the compensated
antiferromagnets with strong magnetoelastic coupling. Destressing energy which
originates from the long-range magnetoelastic forces is analogous to
demagnetization energy in ferromagnetic materials and is responsible for the
formation of equilibrium domain structure and anisotropy of macroscopic
magnetic properties. In particular, crystal shape may be a source of additional
uniaxial magnetic anisotropy which removes degeneracy of antiferromagnetic
vector or artificial 4th order anisotropy in the case of a square cross-section
sample. In a special case of antiferromagnetic nanopillars shape-induced
anisotropy can be substantially enhanced due to lattice mismatch with the
substrate. These effects can be detected by the magnetic rotational torque and
antiferromagnetic resonance measurements.",0701631v2
2007-01-29,"Magnetic Anisotropy, Spin Pinning and Exchange Constants of (Ga,Mn)As films","We present a detailed investigation of exchange-dominated nonpropagating
spin-wave modes in a series of 100 nm Ga$_{1 - x}$Mn$_{x}$As films with Mn
concentrations $x$ ranging from 0.02 to 0.08. The angular and Mn concentration
dependences of spin wave resonance modes have been studied for both as-grown
and annealed samples. Our results indicate that the magnetic anisotropy terms
of Ga$_{1 - x}$Mn$_{x}$As depend on the Mn concentration $x$, but are also
strongly affected by sample growth conditions; moreover, the magnetic
anisotropy of Ga$_{1 - x}$Mn$_{x}$As films is found to be clearly linked to the
Curie temperature. The spin wave resonance spectra consist of a series of well
resolved standing spin-wave modes. The observed mode patterns are consistent
with the Portis volume-inhomogeneity model, in which a spatially nonuniform
anisotropy field acts on the Mn spins. The analysis of these exchange-dominated
spin wave modes, including their angular dependences, allows us to establish
the exchange stiffness constants for Ga$_{1 - x}$Mn$_{x}$As films.",0701717v1
2007-02-12,Anisotropy and Order of Epitaxial Self-Assembled Quantum Dots,"Epitaxial self-assembled quantum dots (SAQDs) represent an important step in
the advancement of semiconductor fabrication at the nanoscale that will allow
breakthroughs in electronics and optoelectronics. In these applications, order
is a key factor. Here, the role of crystal anisotropy in promoting order during
early stages of SAQD formation is studied through a linear analysis of a
commonly used surface evolution model. Elastic anisotropy is used a specific
example. It is found that there are two relevant and predictable correlation
lengths. One of them is related to crystal anisotropy and is crucial for
determining SAQD order. Furthermore, if a wetting potential is included in the
model, it is found that SAQD order is enhanced when the deposited film is
allowed to evolve at heights near the critical surface height for
three-dimensional film growth.",0702278v1
1995-04-26,Statistics of the Microwave Background Anisotropies Caused by the Squeezed Cosmological Perturbations,"It is likely that the observed large-angular-scale anisotropies in the
microwave background radiation are induced by the cosmological perturbations of
quantum-mechanical origin. Such perturbations are now placed in squeezed vacuum
quantum states and, hence, are characterized by large variances of their
amplitude. The statistical properties of the anisotropies should reflect the
underlying statistics of the squeezed vacuum quantum states. The theoretical
variances for the temperature angular correlation function are derived and
described quantitatively. It is shown that they are indeed large.
Unfortunately, these large theoretical statistical uncertainties will make the
extraction of cosmological information from the measured anisotropies a much
more difficult problem than we wanted it to be.",9504045v1
2005-09-16,Evidence for an anisotropy of the speed of light,"By comparing with the most recent experimental results, we point out the
model dependence of the present bounds on the anisotropy of the speed of light.
In fact, by replacing the CMB with a class of preferred frames that can better
account for the experimental data, one obtains values of the RMS anisotropy
parameter (1/2 -beta + delta) that are one order of magnitude larger than the
presently quoted ones. The resulting non-zero anisotropy can be understood
starting from the observation that the speed of light in the Earth's
gravitational field is not the basic parameter c=1 entering Lorentz
transformations. In this sense, light can propagate isotropically only in one
`preferred' frame.",0509066v1
1998-06-06,Non-perturbative determination of anisotropy coefficients in lattice gauge theories,"We propose a new non-perturbative method to compute derivatives of gauge
coupling constants with respect to anisotropic lattice spacings (anisotropy
coefficients), which are required in an evaluation of thermodynamic quantities
from numerical simulations on the lattice. Our method is based on a precise
measurement of the finite temperature deconfining transition curve in the
lattice coupling parameter space extended to anisotropic lattices by applying
the spectral density method. We test the method for the cases of SU(2) and
SU(3) gauge theories at the deconfining transition point on lattices with the
lattice size in the time direction $N_t=4$ -- 6. In both cases, there is a
clear discrepancy between our results and perturbative values. A longstanding
problem, when one uses the perturbative anisotropy coefficients, is a
non-vanishing pressure gap at the deconfining transition point in the SU(3)
gauge theory. Using our non-perturbative anisotropy coefficients, we find that
this problem is completely resolved: we obtain $\Delta p/T^4 = 0.001(15)$ and
$-0.003(17)$ on $N_t=4$ and 6 lattices, respectively.",9806007v1
2001-08-06,Classically Perfect Gauge Actions on Anisotropic Lattices,"We present a method for constructing classically perfect anisotropic actions
for SU(3) gauge theory based on an isotropic Fixed Point Action. The action is
parametrised using smeared (``fat'') links. The construction is done explicitly
for anisotropy $\xi=a_s/a_t=2$ and 4. The corresponding renormalised
anisotropies are determined using the torelon dispersion relation. The
renormalisation of the anisotropy is small and the parametrisation describes
the true action well. Quantities such as the static quark-antiquark potential,
the critical temperature of the deconfining phase transition and the low-lying
glueball spectrum are measured on lattices with anisotropy $\xi=2$. The mass of
the scalar $0^{++}$ glueball is determined to be 1580(60) MeV, while the tensor
$2^{++}$ glueball is at 2430(60) MeV.",0108005v1
2002-08-06,One loop calculation of the renormalised anisotropy for improved anisotropic gluon actions on a lattice,"Using the infrared dispersion relation of the on shell gluon, we calculate
the renormalisation of the the anisotropy to one loop in perturbation theory
for lattice Yang-Mills theories, including the Wilson action and actions with
Symanzik and/or tadpole improvement. Using twisted boundary conditions as a
gauge invariant infrared regulator, we show for an SU(3) gauge group in D=3+1
dimensions that the one loop anisotropy is accurate to O(3%) for a range of g^2
and chi covering current simulations. In doing so we also present Feynman rules
for SU(N) gauge groups with generic anisotropy structure (including `3+1' and
`2+2' cases).",0208010v2
2004-01-06,Numerical study of staggered quark action on quenched anisotropic lattices,"The staggered quark action on anisotropic lattices is studied. We carry out
numerical simulations in the quenched approximation at three values of lattice
spacing ($a_{\sigma}^{-1}=1-2$ GeV) with the anisotropy $\xi=
a_{\sigma}/a_{\tau}=4$, where $a_{\sigma}$ and $a_{\tau}$ are the spatial and
temporal lattice spacings, respectively. The bare anisotropy $\gamma_F$ in the
quark action is numerically tuned through the ratio of meson masses in the fine
and coarse directions, and through the dispersion relation of a meson, so that
the renormalized fermionic anisotropy coincides with that of the gauge field.
The discrepancy between these two calibration schemes provides an estimate of
the finite lattice artifact, which is found to be sizable in the range of
cutoff explored in this work. We also compute the meson masses using
correlators with the wall source at the tuned anisotropy parameter. The flavor
symmetry breaking effect smoothly decreases as $\beta$ increases. The effect of
uncertainty in $\gamma_F$ on the meson masses are examined. We also discuss a
perspective on dynamical simulations.",0401009v1
2005-09-13,Fermion propagators in QED3 with velocity anisotropies,"QED3 with fermi and gap anisotropies is considered to be a candidate
effective field theory of high temperature superconductors. Simulations of a
variant of the theory have demonstrated that there is evidence consistent with
a phase transition to a chirally restored phase as the velocity anisotropy
increases, and that the correlation lengths of pions in spatial directions
behave in a manner consistent with the anisotropy being a relevant parameter of
the theory. We present the first measurements of the fermion propagator in
Landau gauge for this theory and suggest that the structure of this theory is
more complex than previously thought.",0509038v2
1993-05-13,Degree Scale Microwave Anisotropies in NonGaussian Theories of Cosmic Structure Formation,"The COBE satellite's maps of the cosmic microwave background (CMB) anisotropy
do not have the resolution to discriminate between theories of cosmic structure
formation based on inflation, and those based on field ordering following a
symmetry breaking phase transition. For this purpose it is critical to resolve
the CMB anisotropy on degree scales. In this paper we report on detailed
calculations of the degree scale anisotropies predicted in the global string,
monopole, texture and nontopological texture scenarios of structure formation,
emphasising their distinct character from those predicted by inflation, and
commenting on the prospects of their detection in the near future.",9305261v1
2004-06-17,Collective modes of an Anisotropic Quark-Gluon Plasma II,"We continue our exploration of the collective modes of an anisotropic quark
gluon plasma by extending our previous analysis to arbitrary Riemann sheets. We
demonstrate that in the presence of momentum-space anisotropies in the parton
distribution functions there are new relevant singularities on the neighboring
unphysical sheets. We then show that for sufficiently strong anisotropies that
these singularities move into the region of spacelike momentum and their effect
can extend down to the physical sheet. In order to demonstrate this explicitly
we consider the polarization tensor for gluons propagating parallel to the
anisotropy direction. We derive analytic expressions for the gluon structure
functions in this case and then analytically continue them to unphysical
Riemann sheets. Using the resulting analytic continuations we numerically
determine the position of the unphysical singularities. We then show that in
the limit of infinite contraction of the distribution function along the
anisotropy direction that the unphysical singularities move onto the physical
sheet and result in real spacelike modes at large momenta for all
""out-of-plane"" angles of propagation.",0406188v1
2004-08-25,Collisional Energy Loss of a Heavy Quark in an Anisotropic Quark-Gluon Plasma,"We compute the leading-order collisional energy loss of a heavy quark
propagating through a quark-gluon plasma in which the quark and gluon
distributions are anisotropic in momentum space. Following the calculation
outlined for QED in an earlier work we indicate the differences encountered in
QCD and their effect on the collisional energy loss results. For a 20 GeV
bottom quark we show that momentum space anisotropies can result in the
collisional heavy quark energy loss varying with the angle of propagation by up
to 50%. For low velocity quarks we show that anisotropies result in energy gain
instead of energy loss with the energy gain focused in such a way as to
accelerate particles along the anisotropy direction thereby reducing the
momentum-space anisotropy. The origin of this negative energy loss is
explicitly identified as being related to the presence of plasma instabilities
in the system.",0408275v1
2004-11-17,Anomalous scaling of passively advected magnetic field in the presence of strong anisotropy,"Inertial-range scaling behavior of high-order (up to order N=51) structure
functions of a passively advected vector field has been analyzed in the
framework of the rapid-change model with strong small-scale anisotropy with the
aid of the renormalization group and the operator-product expansion. It has
been shown that in inertial range the leading terms of the structure functions
are coordinate independent, but powerlike corrections appear with the same
anomalous scaling exponents as for the passively advected scalar field. These
exponents depend on anisotropy parameters in such a way that a specific
hierarchy related to the degree of anisotropy is observed. Deviations from
power-law behavior like oscillations or logarithmic behavior in the corrections
to structure functions have not been found.",0411040v1
2005-07-23,Discrete Solitons and Vortices on Anisotropic Lattices,"We consider effects of anisotropy on solitons of various types in
two-dimensional nonlinear lattices, using the discrete nonlinear
Schr{\""{o}}dinger equation as a paradigm model. For fundamental solitons, we
develop a variational approximation, which predicts that broad quasi-continuum
solitons are unstable, while their strongly anisotropic counterparts are
stable. By means of numerical methods, it is found that, in the general case,
the fundamental solitons and simplest on-site-centered vortex solitons (""vortex
crosses"") feature enhanced or reduced stability areas, depending on the
strength of the anisotropy. More surprising is the effect of anisotropy on the
so-called ""super-symmetric"" intersite-centered vortices (""vortex squares""),
with the topological charge $S$ equal to the square's size $M$: we predict in
an analytical form by means of the Lyapunov-Schmidt theory, and confirm by
numerical results, that arbitrarily weak anisotropy results in dramatic changes
in the stability and dynamics in comparison with the \emph{degenerate}, in this
case, isotropic limit.",0507048v1
2006-09-28,Numerical Investigation of Scaling Regimes in a Model of Anisotropically Advected Vector Field,"Influence of strong uniaxial small-scale anisotropy on the stability of
inertial-range scaling regimes in a model of a passive transverse vector field
advected by an incompressible turbulent flow is investigated by means of the
field theoretic renormalization group. Turbulent fluctuations of the velocity
field are taken in the form of a Gaussian statistics with zero mean and defined
noise with finite correlations in time. It is shown that stability of the
inertial-range scaling regimes in the three-dimensional case is not destroyed
by anisotropy but the corresponding stability of the two-dimensional system can
be corrupted by the presence of anisotropy. A borderline dimension $d_c$ below
which the stability of the scaling regime is not present is calculated as a
function of anisotropy parameters.",0609067v1
2004-06-21,Azimuthal Anisotropy of Photon and Charged Particle Emission in Pb+Pb Collisions at 158 A GeV/c,"The azimuthal distributions of photons and charged particles with respect to
the event plane are investigated as a function of centrality in Pb + Pb
collisions at 158 A GeV/c in the WA98 experiment at the CERN SPS. The
anisotropy of the azimuthal distributions is characterized using a Fourier
analysis. For both the photon and charged particle distributions the first two
Fourier coefficients are observed to decrease with increasing centrality. The
observed anisotropies of the photon distributions compare well with the
expectations from the charged particle measurements for all centralities.",0406022v2
1996-01-12,Dilepton anisotropy from $p + Be$ and $Ca + Ca$ collisions at BEVALAC energies,"A full calculation of lepton-pair angular characteristics is carried out for
$e^+e^-$ pairs created in $p + Be$ and $Ca + Ca$ collisions from 1.0 to 2.1
GeV/A. It is demonstrated that the dilepton decay anisotropy depends
sensitively on the different sources and may be used for their disentangling.
Due to the dominance of the $\eta$-and $\Delta$-Dalitz decays and only a small
anisotropy coefficient for $\pi^+\pi^-$ annihilation, the expected anisotropy
coefficients show a decrease with invariant mass of the dilepton pair and
change only moderately when comparing $p + Be$ and $Ca + Ca$ reactions at the
same bombarding energy.",9601018v1
1996-05-17,Probing Hadronic Polarizations with Dilepton Anisotropies,"We investigate the production of $e^+e^-$ pairs from $p + Be$ and
nucleus-nucleus collisions from 2 GeV/A to 200 GeV/A within a covariant
transport approach and focus on the dilepton angular anisotropies as a function
of the dilepton invariant mass. Whereas the low mass regime yields information
about the Dalitz decays of the $\Delta, \eta$ and $\omega$, above M $\approx
$0.5 GeV the angular anisotropies provide additional information about the
$\pi^+\pi^- \to \rho^0 \to e^+e^-$ channel in the medium. The anisotropy
coefficient is found to change its sign for M $>$ 0.5 GeV in case of
nucleus-nucleus reactions when increasing the bombarding energy from 2 GeV/A to
200 GeV/A which sheds some light on the $\pi \pi \to \rho$ dynamics.",9605025v1
2001-06-04,Passive scalar anisotropy in a heated turbulent wake: new observations and implications for LES,"The effects of passive scalar anisotropy on subgrid-scale (SGS) physics and
modeling for Large-Eddy Simulations are studied experimentally. Measurements
are performed across a moderate Reynolds number wake flow generated by a heated
cylinder, using an array of four X-wire and four cold-wire probes. By varying
the separation distance among probes in the array, we obtain filtered and
subgrid quantities at three different filter sizes. We compute several terms
that comprise the subgrid dissipation tensor of kinetic energy and
scalar-variance and test for isotropic behavior, as a function of filter scale.
We find that whereas the kinetic energy dissipation tensor tends towards
isotropy at small scales, the SGS scalar-variance dissipation remains
anisotropic independent of filter scale. The eddy-diffusion model predicts
isotropic behavior, whereas the nonlinear (or tensor eddy diffusivity) model
reproduces the correct trends, but overestimates the level of scalar
dissipation anisotropy. These results provide some support for so-called mixed
models but raise new questions about the causes of the observed anisotropy.",0106014v1
2001-11-21,Interpreting Compton anisotropy of ice Ih: a cluster partitioning method,"We propose a simple cluster-based method with application to calculations of
Compton profile anisotropies of ice. The convergence of the method is checked
with respect to Crystal95 results. Increasing both basis-set quality and
cluster sizes results in a decrease of the magnitude of theoretical Compton
anisotropies. The agreement with experimental data is therefore improved
towards previously calculated anisotropies. Moreover, analyzing directional
autocorrelation functions shows an evidence for both anti-bonding and
polarization effects.",0111157v2
2006-12-21,Re-Analysis of the Marinov Light-Speed Anisotropy Experiment,"The anisotropy of the speed of light at 1 part in 10^3 has been detected by
Michelson and Morley (1887), Miller (1925/26), Illingworth (1927), Joos (1930),
Jaseja et al. (1964), Torr and Kolen (1984), De Witte (1991) and Cahill (2006)
using a variety of experimental techniques, from gas-mode Michelson
interferometers (with the relativistic theory for these only determined in
2002) to one-way RF coaxial cable propagation timing. All agree on the speed,
right ascension and declination of the anisotropy velocity. The Stephan Marinov
experiment (1984) detected a light speed anisotropy using a mechanical coupled
shutters technique which has holes in co-rotating disks, essentially a one-way
version of the Fizeau mechanical round-trip speed-of-light experiment. The
Marinov data is re-analysed herein because the velocity vector he determined is
in a very different direction to that from the above experiments. No
explanation for this difference has been uncovered.",0612201v2
2007-05-29,A Study on anisotropy of cosmic ray distribution with a small array of water-cherenkov detectors,"The study of the anisotropy of the arrival directions is an essential tool to
investigate the origin and propagation of cosmic rays primaries. A simple way
of recording many cosmic rays is to record coincidences between a number of
detectors. We have monitored multi-TeV cosmic rays by a small array of water
cherenkov detectors in Tehran(35 43 N, 51 20 E, 1200m a.s.l). More than
1.1*10^6 extensive air shower events were recorded. In addition to the Compton-
Getting effect due to the motion of the earth in the Galaxy, an anisotropy has
been observed which is due to a unidirectional anisotropy of cosmic ray flow
along the Galactic arms.",0705.4234v1
2007-06-21,Tuning the domain wall orientation in thin magnetic strips by induced anisotropy,"We report on a method to tune the orientation of in-plane magnetic domains
and domain walls in thin ferromagnetic strips by manipulating the magnetic
anisotropy. Uniaxial in-plane anisotropy is induced in a controlled way by
oblique evaporation of magnetic thin strips. A direct correlation between the
magnetization direction and the domain wall orientation is found experimentally
and confirmed by micromagnetic simulations. The domain walls in the strips are
always oriented along the oblique evaporation-induced easy axis, in spite of
the shape anisotropy. The controlled manipulation of domain wall orientations
could open new possibilities for novel devices based on domain-wall
propagation.",0706.3106v1
2007-07-06,Zero-temperature behavior of the random-anisotropy model in the strong-anisotropy limit,"We consider the random-anisotropy model on the square and on the cubic
lattice in the strong-anisotropy limit. We compute exact ground-state
configurations, and we use them to determine the stiffness exponent at zero
temperature; we find $\theta = -0.275(5)$ and $\theta \approx 0.2$ respectively
in two and three dimensions. These results show that the low-temperature phase
of the model is the same as that of the usual Ising spin-glass model. We also
show that no magnetic order occurs in two dimensions, since the expectation
value of the magnetization is zero and spatial correlation functions decay
exponentially. In three dimensions our data strongly support the absence of
spontaneous magnetization in the infinite-volume limit.",0707.1005v1
2007-07-17,The behavior of non-linear anisotropies in bouncing Bianchi I models of loop quantum cosmology,"In homogeneous and isotropic loop quantum cosmology, gravity can behave
repulsively at Planckian energy densities leading to the replacement of the big
bang singularity with a big bounce. Yet in any bouncing scenario it is
important to include non-linear effects from anisotropies which typically grow
during the collapsing phase. We investigate the dynamics of a Bianchi I
anisotropic model within the framework of loop quantum cosmology. Using
effective semi-classical equations of motion to study the dynamics, we show
that the big bounce is still predicted with only differences in detail arising
from the inclusion of anisotropies. We show that the anisotropic shear term
grows during the collapsing phase, but remains finite through the bounce.
Immediately following the bounce, the anisotropies decay and with the inclusion
of matter with equation of state $w < +1$, the universe isotropizes in the
expanding phase.",0707.2548v1
2007-09-17,X-Ray Analysis of Oxygen-induced Perpendicular Magnetic Anisotropy in Pt/Co/AlOx trilayer,"X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlOx
trilayers to investigate the role of Co oxidation in the perpendicular magnetic
anisotropy of the Co/AlOx interface. It is observed that high temperature
annealing modifies the magnetic properties of the Co layer, inducing an
enhancement of the perpendicular magnetic anisotropy. The microscopic
structural properties are analyzed via X-ray Absorption Spectroscopy, X-ray
Magnetic Circular Dichroism and X-ray Photoelectron Spectroscopy measurements.
It is shown that annealing enhances the amount of interfacial oxide, which may
be at the origin of a strong perpendicular magnetic anisotropy.",0709.2581v2
2007-10-03,Evidence of random magnetic anisotropy in ferrihydrite nanoparticles based on analysis of statistical distributions,"We show that the magnetic anisotropy energy of antiferromagnetic ferrihydrite
depends on the square root of the nanoparticles volume, using a method based on
the analysis of statistical distributions. The size distribution was obtained
by transmission electron microscopy, and the anisotropy energy distributions
were obtained from ac magnetic susceptibility and magnetic relaxation. The
square root dependence corresponds to random local anisotropy, whose average is
given by its variance, and can be understood in terms of the recently proposed
single phase homogeneous structure of ferrihydrite.",0710.0864v1
2007-12-08,The shape of invasion perclation clusters in random and correlated media,"The shape of two-dimensional invasion percolation clusters are studied
numerically for both non-trapping (NTIP) and trapping (TIP) invasion
percolation processes. Two different anisotropy quantifiers, the anisotropy
parameter and the asphericity are used for probing the degree of anisotropy of
clusters. We observe that in spite of the difference in scaling properties of
NTIP and TIP, there is no difference in the values of anisotropy quantifiers of
these processes. Furthermore, we find that in completely random media, the
invasion percolation clusters are on average slightly less isotropic than
standard percolation clusters. Introducing isotropic long-range correlations
into the media reduces the isotropy of the invasion percolation clusters. The
effect is more pronounced for the case of persisting long-range correlations.
The implication of boundary conditions on the shape of clusters is another
subject of interest. Compared to the case of free boundary conditions, IP
clusters of conventional rectangular geometry turn out to be more isotropic.
Moreover, we see that in conventional rectangular geometry the NTIP clusters
are more isotropic than TIP clusters.",0712.1287v2
2007-12-13,Breakdown of an intermediate plateau in the magnetization process of anisotropic spin-1 Heisenberg dimer: theory vs. experiment,"The magnetization process of the spin-1 Heisenberg dimer model with axial and
rhombic single-ion anisotropy terms is particularly investigated in connection
with recent experimental high-field measurements performed on the
single-crystal sample of the homodinuclear nickel(II) compound
[Ni2(Medpt)2(ox)(H2O)2](ClO4)2.2H2O (Medpt=methyl-bis(3-aminopropyl)amine). The
results obtained from the exact numerical diagonalization reveal a striking
magnetization process with a marked spatial dependence on the applied magnetic
field for arbitrary but non-zero single-ion anisotropy. It is demonstrated that
the field range, which corresponds to an intermediate magnetization plateau
emerging at a half of the saturation magnetization, basically depends on
single-ion anisotropy terms as well as a spatial orientation of the applied
field. The breakdown of the intermediate magnetization plateau is discussed at
length in relation to the single-ion anisotropy strength.",0712.2109v2
2007-12-14,The Spin Reorientation Transition and Phase Diagram of Ultrathin Ferromagnetic Films,"We show results from Monte Carlo simulations of a two dimensional Heisenberg
model for ultrathin films with perpendicular anisotropy. A complete phase
diagram is obtained as a function of anisotropy and temperature, spanning a
wide range of behavior. We discuss our results in relation with experimental
findings in different ultrathin films. We observe and characterize a line of
Spin Reorientation Transitions . This transition from out of plane stripe order
to in plane ferromagnetic order presents a paramagnetic gap in between in a
finite region in parameter space, as reported in experiments. For large
anisotropies direct transitions from a low temperature stripe phase to a
paramagnetic or tetragonal phase with dominant perpendicular magnetization is
observed, also in agreement with experiments.
  We also show the phase diagram for a system without exchange, i.e. with pure
dipolar and anisotropy interactions. It shows a similar behavior to the
ferromagnetic case with antiferromagnetic instead of stripe phases at low
temperatures. A Spin Reorientation Transition is also found in this case.",0712.2426v1
2007-12-15,Second-order power spectra of CMB anisotropies due to primordial random perturbations in flat cosmological models,"Second-order power spectra of Cosmic Microwave Background (CMB) anisotropies
due to random primordial perturbations at the matter dominant stage are
studied, based on the relativistic second-order theory of perturbations in flat
cosmological models and on the second-order formula of CMB anisotropies derived
by Mollerach and Matarrese. So far the second-order integrated Sachs-Wolfe
effect has been analyzed using the three-point correlation or bispectrum. In
this paper we derive the second-order term of power spectra given using the
two-point correlation of temperature fluctuations.
  The second-order density perturbations are small, compared with the
first-order ones. The second-order power spectra of CMB anisotropies, however,
are not small at all, compared with the first-order power spectra, because at
the early stage the first-order integrated Sachs-Wolfe effect is very small and
the second-order integrated Sachs-Wolfe effect may be dominant over the
first-order ones. So their characteristic behaviors may be measured through the
future precise observation and bring useful informations on the structure and
evolution of our universe in the future.",0712.2511v3
2008-01-30,Femtosecond Control of the Magnetization in Ferromagnetic Semiconductors,"We develop a theory of collective spin dynamics triggered by ultrafast
optical excitation of ferromagnetic semiconductors. Using the density matrix
equations of motion in the mean field approximation and including magnetic
anisotropy and hole spin dephasing effects, we predict the development of a
light--induced magnetization tilt during ultra--short time intervals comparable
to the pulse duration. This femtosecond dynamics in the coherent temporal
regime is governed by the interband nonlinear optical polarizations and is
followed by a second temporal regime governed by the magnetic anisotropy of the
Fermi sea. We interpret our numerical results by deriving a
Landau--Gilbert--like equation for the collective spin, which demonstrates an
ultrafast correction to the magnetic anisotropy effective field due to second
order coherent nonlinear optical processes. Using the Lindblad semigroup
method, we also derive a contribution to the interband polarization dephasing
determined by the Mn spin and the hole spin dephasing. Our predicted
magnetization tilt and subsequent nonlinear dynamics due to the magnetic
anisotropy can be controlled by varying the optical pulse intensity, duration,
and helicity and can be observed with pump--probe magneto--optical
spectroscopy.",0801.4641v1
2008-03-27,Tuning for Three-flavors of Anisotropic Clover Fermions with Stout-link Smearing,"In this work we perform the parameter tuning of three flavors of dynamical
clover quarks on anisotropic lattices. The fermion action uses
three-dimensional spatial stout-link smearing. The gauge anisotropy is
determined in a small box with Schr\""odinger background using Wilson-loop
ratios. The fermion anisotropy is obtained from studying the meson dispersion
relation with antiperiodic boundary conditions in the time direction. The
spatial and temporal clover coefficients are fixed to the tree-level
tadpole-improved values, and we demonstrate that they satisfy the
nonperturbative conditions as determined by the Schr\""odinger functional
method. For the desired lattice spacing $a_s\approx 0.12$ fm and renormalized
anisotropy $\xi=3.5$, we find the gauge and fermionic anisotropies can be fixed
to quark mass independent values up through the strange quark mass. This work
lays the foundation needed for further studies of the excited-state hadron
spectrum.",0803.3960v2
2008-04-07,Cosmic Strings as the Source of Small-Scale Microwave Background Anisotropy,"Cosmic string networks generate cosmological perturbations actively
throughout the history of the universe. Thus, the string sourced anisotropy of
the cosmic microwave background is not affected by Silk damping as much as the
anisotropy seeded by inflation. The spectrum of perturbations generated by
strings does not match the observed CMB spectrum on large angular scales
(l<1000) and is bounded to contribute no more than 10% of the total power on
those scales. However, when this bound is marginally saturated, the anisotropy
created by cosmic strings on small angular scales l>2000 will dominate over
that created by the primary inflationary perturbations. This range of angular
scales in the CMB is presently being measured by a number of experiments; their
results will test this prediction of cosmic string networks soon.",0804.0810v2
2008-04-15,Anisotropy and Morphology of Strained III-V Heteroepitaxial Films,"Strained coherent heteroepitaxy of III-V semiconductor films such as
In$_x$Ga$_{1-x}$As/GaAs has potential for electronic and optoelectronic
applications such as high density logic, quantum computing architectures, laser
diodes, and other optoelectronic devices. Crystal symmetry can have a large
effect on the morphology of these films and their spatial order. Often the
formation of group IV strained heterostructures such as Ge deposited on Si is
analyzed using analytic models based on the Asaro-Tiller-Grinfeld instability.
However, the governing dynamics of III-V 3D heterostructure formation has
different symmetry and is more anisotropic. The additional anisotropy appears
in both the surface energy and the diffusivity. Here, the resulting anisotropic
governing dynamics are studied to linear order. The resulting possible film
morphologies are compared with experimentally observed In$_x$Ga$_{1-x}$As/GaAs
films. Notably it is found that surface-energy anisotropy plays a role at least
as important as surface diffusion anisotropy if not more so, in contrast to
previous suppositions.",0804.2438v3
2008-04-18,Effect of anisotropic hopping on the Bose Hubbard model phase diagram: strong-coupling perturbation theory on a square lattice,"There has been a recent resurgence of experimental efforts to quantitatively
determine the phase diagram of the Bose Hubbard model by carefully analyzing
experiments with ultracold bosonic atoms on an optical lattice. In many
realizations of these experiments, the hopping amplitudes are not homogeneous
throughout the lattice, but instead, the lattice has an anisotropy where
hopping along one direction is not exactly equal to hopping along a
perpendicular direction. In this contribution, we examine how an anisotropy in
the hopping matrix elements affects the Mott lobes of the Bose Hubbard model.
For weak anisotropy, we find the phase diagram is only slightly modified when
expressed in terms of the average hopping, while for strong anisotropy, one
expects to ultimately see dimensional crossover effects.",0804.3040v1
2008-06-18,Space-time anisotropy: theoretical issues and the possibility of an observational test,"The specific astrophysical data collected during the last decade causes the
need for the modification of the expression for the Einstein-Hilbert action,
and several attempts sufficing this need are known. The modification suggested
in this paper stems from the possible anisotropy of space-time and this means
the natural change of the simplest scalar in the least action principle. To
provide the testable support to this idea, the optic-metrical parametric
resonance is regarded - an experiment on the galactic scale based on the
interaction between the electromagnetic radiation of cosmic masers and
periodical gravitational waves emitted by close double systems or pulsars.
Since the effect depends on the space-time metric, the possible anisotropy
could reveal itself through observations. To give the corresponding theory
predicting the corrections to the expected results of the experiment, the
specific mathematical formalism of Finsler geometry was chosen. It was found
that in case the anisotropy of the space-time exists, the orientation of the
astrophysical systems suitable for observations would show it. In the obtained
geodesics equation there is a direction dependent term.",0806.3066v2
2008-09-05,CMB Anisotropy Induced by a Moving Straight Cosmic String,"We showed that the part of strings could be detected by optical method is
only 20% from the total available amount of such objects, therefore the
gravitational lensing method has to be ""completed"" by CMB one. We found the
general structure of the CMB anisotropy generated by a cosmic string for simple
model of straight string moving with constant velocity. For strings with
deficit angle 1-2 arcsec the amplitude of generated anisotropy has to be 15-30
muK (the corresponding string linear density is (G mu) ~ 10^{-7} and energy is
GUT one, 10^{15} GeV). To use both radio and optical methods the deficit angle
has to be from 0.1 arcsec to 5-6 arcsec. If cosmic string can be detected by
optical method, the length of corresponding brightness spot of anisotropy has
to be no less than 100 degrees.",0809.0992v1
2008-09-26,Photons from anisotropic Quark-Gluon-Plasma,"We calculate medium photons due to Compton and annihilation processes in an
anisotropic media. The effects of time-dependent momentum-space anisotropy of
{\em Quark-Gluon-Plasma} (QGP) on the medium photon production are discussed.
Such an anisotropy can results from the initial rapid longitudinal expansion of
the matter, created in relativistic heavy ion collisions. A phenomenological
model for the time-dependence of the parton hard momentum scale,
$p_{hard}(\tau)$, and anisotropy parameter, $\xi(\tau)$, has been used to
describe the plasma space-time evolution. We find significant dependency of
photon yield on the isotropization time ($\tau_{iso}$). It is shown that the
introduction of early time momentum-space anisotropy can enhance the photon
production by a factor of $10 (1.5)$ (in the central rapidity region) for {\em
free streaming} ({\em collisionally-broadened}) {\em interpolating} model if we
assume fixed initial condition. On the other hand, enforcing the fixed final
multiplicity significantly reduces the enhancement of medium photon production.",0809.4596v3
2008-12-30,Quasistatic behavior and force transmission in packing of irregular polyhedral particles,"Dense packings composed of irregular polyhedral particles are investigated by
numerical simulations under quasistatic triaxial compression. The Contact
Dynamics method is used for this investigation with 40 000 particles. The
effect of particle shape is analyzed by comparing this packing with a packing
of similar particle size distribution but with spherical particles. We analyze
the origin of the higher shear strength of the polyhedra packing by considering
various anisotropy parameters characterizing the microstructure and force
transmission. Remarkably, we find that the polyhedra packing has a lower fabric
anisotropy in terms of branch vectors (joining the particle centers) than the
sphere packing. In contrast, the polyhedra packing shows a much higher force
anisotropy which is at the origin of its higher shear strength. The force
anisotropy in the polyhedra packing is shown to be related to the formation of
face-face contacts. In particular, most face-face contacts belong to strong
force chains along the major principal stress direction whereas vertex-face and
edge-edge contacts are correlated with weak forces and oriented on average
along the minor principal stress direction in steady shearing.",0812.5060v1
2009-01-05,Anisotropic spatially heterogeneous dynamics on the $α$ and $β$ relaxation time scales studied via a four-point correlation function,"We examine the anisotropy of a four-point correlation function
$G_4(\vec{k},\vec{r};t)$ and it's associated structure factor
$S_4(\vec{k},\vec{q};t)$ calculated using Brownian Dynamics computer
simulations of a model glass forming system. These correlation functions
measure the spatial correlations of the relaxation of different particles, and
we examine the time and temperature dependence of the anisotropy. We find that
the anisotropy is strongest at nearest neighbor distances at time scales
corresponding to the peak of the non-Gaussian parameter $\alpha_2(t) = 3 <
\delta r^4(t) >/[ 5 < \delta r^2(t) >^2] - 1$, but is still pronounced around
the $\alpha$ relaxation time. We find that the structure factor
$S_4(\vec{k},\vec{q};t)$ is anisotropic even for the smallest wave vector
accessible in our simulation suggesting that our system (and other systems
commonly used in computer simulations) may be too small to extract the $\vec{q}
\to 0$ limit of the structure factor. We find that the determination of a
dynamic correlation length from $S_4(\vec{k},\vec{q};t)$ is influenced by the
anisotropy. We extract an effective anisotropic dynamic correlation length from
the small $q$ behavior of $S_4(\vec{k},\vec{q};t)$.",0901.0493v1
2009-01-21,Finite-size anisotropy in statistically uniform porous media,"Anisotropy of the permeability tensor in statistically uniform porous media
of sizes used in typical computer simulations is studied. Although such systems
are assumed to be isotropic by default, we show that de facto their anisotropic
permeability can give rise to significant changes of transport parameters such
as permeability and tortuosity. The main parameter controlling the anisotropy
is $a/L$, being the ratio of the obstacle to system size. Distribution of the
angle $\alpha$ between the external force and the volumetric fluid stream is
found to be approximately normal, and the standard deviation of $\alpha$ is
found to decay with the system size as $(a/L)^{d/2}$, where $d$ is the space
dimensionality. These properties can be used to estimate both
anisotropy-related statistical errors in large-scale simulations and the size
of the representative elementary volume.",0901.3219v1
2009-02-17,"10-100 TeV cosmic ray anisotropy measured at Baksan EAS ""Carpet"" array","Preliminary results of one year anisotropy measurement in the energy range
10^{13} -10^{14} eV as a function of energy are presented. The results are
compared for two methods of data analysis: the standard one with meteo
correction approach in use and another one so-called ""East minus West"" method.
Amplitudes and phases of anisotropy for three median energies E = 25 TeV, E =
75 TeV and E = 120 TeV are reported. Brief consideration of amplitude-phase
dependence of anisotropy on energy is expounded.",0902.2967v1
2009-03-20,Quarkonium dissociation in the presence of a small momentum space anisotropy,"We consider the dissociation of heavy quarkonium in a medium close to thermal
equilibrium but with a small momentum space anisotropy. Dissociation is defined
to take place when the width of the ground state equals its binding energy. We
show that if the anisotropic medium is obtained isentropically from the
equilibrium one, then to first order in the anisotropy parameter the
dissociation temperature remains unchanged. If, in contrast, the
non-equilibrium system has a smaller entropy density than the equilibrium one,
then the dissociation temperature increases with respect to the isotropic case,
by up to 10% for modest anisotropies.",0903.3467v2
2009-05-22,Semiclassical suppression of weak anisotropies of a generic Universe,"A semiclassical mechanism which suppresses the weak anisotropies of an
inhomogeneous cosmological model is developed. In particular, a wave function
of this Universe having a meaningful probabilistic interpretation is obtained
that is in agreement with the Copenhagen School. It describes the evolution of
the anisotropies with respect to the isotropic scale factor which is regarded
as a semiclassical variable playing an observer-like role. Near the
cosmological singularity the solution spreads over all values of the
anisotropies while, when the Universe expands sufficiently, the closed
Friedmann-Robertson-Walker model appears to be the favorite state.",0905.3695v2
2009-05-25,Sky maps without anisotropies in the cosmic microwave background are a better fit to WMAP's uncalibrated time ordered data than the official sky maps,"The purpose of this reanalysis of the WMAP uncalibrated time ordered data
(TOD) was two fold. The first was to reassess the reliability of the detection
of the anisotropies in the official WMAP sky maps of the cosmic microwave
background (CMB). The second was to assess the performance of a proposed
criterion in avoiding systematic error in detecting a signal of interest. The
criterion was implemented by testing the null hypothesis that the uncalibrated
TOD was consistent with no anisotropies when WMAP's hourly calibration
parameters were allowed to vary. It was shown independently for all 20 WMAP
channels that sky maps with no anisotropies were a better fit to the TOD than
those from the official analysis. The recently launched Planck satellite should
help sort out this perplexing result.",0905.3971v3
2009-06-15,Appearance of classical Mixmaster Universe from the No-Boundary Quantum State,"We investigate the appearance of the classical anisotropic universe from the
no-boundary quantum state according to the prescription proposed by Hartle,
Hawking and Hertog. Our model is homogeneous, anisotropic, closed universes
with a minimally coupled scalar field and cosmological constant. We found that
there are an ensemble of classical Lorentzian histories with anisotropies and
experience inflationary expansion at late time, and the probability of
histories with anisotropies are lower than isotropic histories. Thus the
no-boundary condition may be able to explain the emergence of our universe. If
the classical late time histories are extended back, some become singular by
the existence of initial anisotropies with large accelerations. However we do
not find any chaotic behavior of anisotropies near the initial singularity.",0906.2616v1
2009-08-10,CMB anisotropies induced by tensor modes in Massive Gravity,"We study Gravitational Waves (GWs) in the context of Massive Gravity, an
extension to General Relativity (GR) where the fluctuations of the metric have
a nonzero mass, and specifically investigate the effect of the tensor modes on
the Cosmic Microwave Background (CMB) anisotropies. We first study the time
evolution of the tensor modes in Massive Gravity and show that there is a
graviton mass limit $m_l=10^{-66}g\sim 10^{-29}cm^{-1}$, so that for masses
$m\leq m_l$ the tensor perturbations in Massive Gravity are indistinguishable
from the corresponding ones in GR. Also, we show that short wavelength massive
modes behave almost indistinguishably from their massless counterparts. Later
on, we show that massive gravitons with masses within the range $m=
10^{-27}cm^{-1}$ - $m=10^{-26}cm^{-1}$ would leave a clear signature on the
lower multipoles ($\ell< 30$) in the CMB anisotropy power spectrum. Hence, our
results show that CMB anisotropies measurements might be decisive to show
whether the tensor modes are massive or not.",0908.1360v2
2009-08-24,Anisotropic microwave conductivity of cuprate superconductors in the presence of CuO chain induced impurities,"The anisotropy in the microwave conductivity of the ortho-II
YBa$_2$Cu$_3$O$_{6.50}$ is studied within the kinetic energy driven
superconducting mechanism. The ortho-II YBa$_2$Cu$_3$O$_{6.50}$ is
characterized by a periodic alternative of filled and empty $\hat{b}$-axis CuO
chains. By considering the CuO chain induced extended anisotropy impurity
scattering, the main features of the anisotropy in the microwave conductivity
of the ortho-II YBa$_2$Cu$_3$O$_{6.50}$ are reproduced based on the nodal
approximation of the quasiparticle excitations and scattering processes,
including the intensity and lineshape of the energy and temperature dependence
of the $\hat{a}$-axis and $\hat{b}$-axis microwave conductivities. Our results
also confirm that the $\hat{b}$-axis CuO chain induced impurity is the main
source of the anisotropy.",0908.3355v1
2009-09-09,Nonequilibrium dynamics of vortex arrest in a finite-temperature Bose-Einstein condensate,"We perform finite-temperature dynamical simulations of the arrest of a
rotating Bose-Einstein condensate by a fixed trap anisotropy, using a
Hamiltonian classical-field method. We consider a quasi-two-dimensional
condensate containing a single vortex in equilibrium with a rotating thermal
cloud. Introducing an elliptical deformation of the trapping potential leads to
the loss of angular momentum from the system. We identify the condensate and
the complementary thermal component of the nonequilibrium field, and compare
the evolution of their angular momenta and angular velocities. By varying the
trap anisotropy we alter the relative efficiencies of the vortex-cloud and
cloud-trap coupling. For strong trap anisotropies the angular momentum of the
thermal cloud may be entirely depleted before the vortex begins to decay. For
weak trap anisotropies, the thermal cloud exhibits a long-lived steady state in
which it rotates at an intermediate angular velocity.",0909.1683v2
2009-09-14,Interpreting Power Anisotropy Measurements in Plasma Turbulence,"A relationship is derived between power anisotropy and wavevector anisotropy
in turbulent fluctuations. This can be used to interpret plasma turbulence
measurements, for example in the solar wind. If fluctuations are anisotropic in
shape then the ion gyroscale break point in spectra in the directions parallel
and perpendicular to the magnetic field would not occur at the same frequency,
and similarly for the electron gyroscale break point. This is an important
consideration when interpreting solar wind observations in terms of anisotropic
turbulence theories. Model magnetic field power spectra are presented assuming
a cascade of critically balanced Alfven waves in the inertial range and kinetic
Alfven waves in the dissipation range. The variation of power anisotropy with
scale is compared to existing solar wind measurements and the similarities and
differences are discussed.",0909.2683v2
2009-09-30,A solution to the anisotropy problem in bouncing cosmologies,"Bouncing cosmologies are often proposed as alternatives to standard inflation
for the explanation of the homogeneity and flatness of the universe. In such
scenarios, the present cosmological expansion is preceded by a contraction
phase. However, during the contraction, in general the anisotropy of the
universe grows and eventually leads to a chaotic mixmaster behavior. This would
either be hard to reconcile with observations or even lead to a singularity
instead of the bounce. In order to preserve a smooth and isotropic bounce, the
source for the contraction must have a super-stiff equation of state with
$P/\rho=w>1$. In this letter we propose a new mechanism to solve the anisotropy
problem for any low-energy value of $w$ by arguing that high energy physics
leads to a modification of the equation of state, with the introduction of
non-linear terms. In such a scenario, the anisotropy is strongly suppressed
during the high energy phase, allowing for a graceful isotropic bounce, even
when the low-energy value of $w$ is smaller than unity.",0909.5611v1
2009-11-17,"Anisotropy of Earth's D"" layer and stacking faults in the MgSiO3 post-perovskite phase","The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral
phase of the Earth's lowermost mantle (the D"" layer). Its properties explain
numerous geophysical observations associated with this layer - for example, the
D'' discontinuity, its topography and seismic anisotropy within the layer. Here
we use a novel simulation technique, first-principles metadynamics, to identify
a family of low-energy polytypic stacking-fault structures intermediate between
the perovskite and post-perovskite phases. Metadynamics trajectories identify
plane sliding involving the formation of stacking faults as the most favourable
pathway for the phase transition, and as a likely mechanism for plastic
deformation of perovskite and postperovskite. In particular, the predicted slip
planes are (010) for perovskite (consistent with experiment) and (110) for
postperovskite (in contrast to the previously expected (010) slip planes).
Dominant slip planes define the lattice preferred orientation and elastic
anisotropy of the texture. The (110) slip planes in post-perovskite require a
much smaller degree of lattice preferred orientation to explain geophysical
observations of shear-wave anisotropy in the D"" layer.",0911.3185v1
2009-11-19,Magnetic Anistropy due to the Casimir Effect,"We consider the Casimir interaction between a ferromagnetic and a
non-magnetic mirror, and show how the Casimir effect gives rise to a magnetic
anisotropy in the ferromagnetic layer. The anisotropy is out-of-plane if the
non-magnetic plate is optically isotropic. If the non-magnetic plate shows a
uniaxial optical anisotropy (with optical axis in the plate plane), we find an
in-plane magnetic anisotropy. In both cases, the energetically most favorable
magnetization orientation is given by the competition between polar,
longitudinal and transverse contributions to the magneto-optical Kerr effect,
and will therefore depend on the interplate distance. Numerical results will be
presented for a magnetic plate made out of iron, and non-magnetic plates of
gold (optically isotropic), quartz, calcite and barium titanate (all uniaxially
birefringent).",0911.3854v1
2009-12-09,The detectability of dark matter annihilation with Fermi using the anisotropy energy spectrum of the gamma-ray background,"The energy-dependence of the anisotropy (the anisotropy energy spectrum) of
the large-scale diffuse gamma-ray background can reveal the presence of
multiple source populations. Annihilating dark matter in the substructure of
the Milky Way halo could give rise to a modulation in the anisotropy energy
spectrum of the diffuse gamma-ray emission measured by Fermi, enabling the
detection of a dark matter signal. We determine the detectability of a
dark-matter-induced modulation for scenarios in which unresolved blazars are
the primary contributor to the measured emission above ~1 GeV and find that in
some scenarios pair-annihilation cross sections of order the value expected for
thermal relic dark matter can produce a detectable feature. We anticipate that
the sensitivity of this technique to specific dark matter models could be
improved by tailored likelihood analysis methods.",0912.1854v3
2010-01-04,The single-ion anisotropy in LaFeAsO,"We use Green's function method to study the Heisenberg model of LaFeAsO with
the striped antiferromagnetic collinear spin structure. In addition to the
intra-layer spin couplings $J_{1a},J_{1b},J_2$ and the inter-layer coupling
$J_c$, we further consider the contributions of the single-ion anisotropy
$J_s$. The analytical expressions for the magnetic phase-transition temperature
$T_N$ and the spin spectrum gap $\Delta$ are obtained. According to the
experimental temperature $T_N=138$K and the previous estimations of the
coupling interactions, we make a further discussion about the magnitude and the
effects of the single-ion anisotropy $J_s$. We find that the magnitudes of
$J_s$ and $J_c$ can compete. The dependences of the transition temperature
$T_N$, the zero-temperature average spin and the spin spectrum gap on the
single-ion anisotropy are investigated. We find they both increase as $J_s$
increases. The spin spectrum gap at low temperature $T\to0$ is calculated as a
function of $J_s$, the result of which is a useful reference for the future
experimental researches.",1001.0431v1
2010-01-04,Large Magnetic Susceptibility Anisotropy of Metallic Carbon Nanotubes,"Through magnetic linear dichroism spectroscopy, the magnetic susceptibility
anisotropy of metallic single-walled carbon nanotubes has been extracted and
found to be 2-4 times greater than values for semiconducting single-walled
carbon nanotubes. This large anisotropy is consistent with our calculations and
can be understood in terms of large orbital paramagnetism of electrons in
metallic nanotubes arising from the Aharonov-Bohm-phase-induced gap opening in
a parallel field. We also compare our values with previous work for
semiconducting nanotubes, which confirm a break from the prediction that the
magnetic susceptibility anisotropy increases linearly with the diameter.",1001.0524v1
2010-01-05,Power law behavior for the zigzag transition in a Yukawa cluster,"We provide direct experimental evidence that the one-dimensional (1D) to
two-dimensional (2D) zigzag transition in a Yukawa cluster exhibits power law
behavior. Configurations of a six-particle dusty (complex) plasma confined in a
biharmonic potential well are characterized as the well anisotropy is reduced.
When the anisotropy is large the particles are in a 1D straight line
configuration. As the anisotropy is decreased the cluster undergoes a zigzag
transition to a 2D configuration. The measured dependence of cluster width on
anisotropy is well described by a power law. A second transition from the
zigzag to an elliptical configuration is also observed. The results are in very
good agreement with a model for particles interacting through a Yukawa
potential.",1001.0753v1
2010-01-17,Variational Studies of Triangular Heisenberg Antiferromagnet in Magnetic Field,"We present a variational study of the Heisenberg antiferromagnet on the
spatially anisotropic triangular lattice in magnetic field. First we construct
a simple yet accurate wavefunction for the 1/3-magnetization plateau uud phase
on the isotropic lattice. Beginning with this state, we obtain natural
extensions to nearby commensurate coplanar phases on either side of the
plateau. The latter occur also for low lattice anisotropy, while the uud state
extends to much larger anisotropy. Far away from the 1/3 plateau and for
significant anisotropy, incommensurate states have better energetics, and we
address competition between coplanar and non-coplanar states in the high field
regime. For very strong anisotropy, our study is dominated by quasi-1d physics.
The variational study is supplemented by exact diagonalization calculations
which provide a reference for testing the energetics of our trial wavefunctions
as well as helping to identify candidate phases.",1001.2863v2
2010-03-19,Anisotropy of the superconducting state parameters and intrinsic pinning in low-level Pr-doped YBa2Cu3O(7-delta) single crystals,"The influence of low-level Pr substitution in Y1-xPrxBa2Cu3O(7-delta) single
crystals on the anisotropy of the superconducting state parameters was
investigated by torque magnetometry in magnetic fields of up to 9 T. An
averaged anisotropy parameter, \gamma, of 7.4 was found and no influence of the
Pr ion concentration on \gamma was observed up to a Pr content of 2.4%. A
pronounced maximum at angles between 0.5 and 1 degree out of the ab-plane was
observed in all crystals in the irreversible angular dependence of the torque.
This maximum is attributed to intrinsic pinning associated with kinked
vortices. The variation of the irreversible torque with the substitution level
indicates the influence of the Pr content on pinning within the CuO2 planes,
even though the anisotropy of the superconducting state parameters is not
affected.",1003.3793v1
2010-04-27,Nonequilibrium relaxation study of the anisotropic antiferromagnetic Heisenberg model on the triangular lattice,"Effect of exchange anisotropy on the relaxation time of spin and vector
chirality is studied for the antiferromagnetic classical Heisenberg model on
the triangular lattice by using the nonequilibrium relaxation Monte Carlo
method. We identify the Berezinskii-Kosterlitz-Thouless (BKT) transition and
the chiral transition in a wide range of the anisotropy, even for very small
anisotropy of $\sim$ 0.01%. As the anisotropy decreases, both the critical
temperatures steeply decrease, while the BKT critical region becomes
divergently wide. We elucidate a sharp ""V shape"" of the phase diagram around
the isotropic Heisenberg point, which suggests that the isotropic case is
exceptionally singular and the associated Z vortex transition will be isolated
from the BKT and chiral transitions. We discuss the relevance of our results to
peculiar behavior of the spin relaxation time observed experimentally in
triangular antiferromagnets.",1004.4927v1
2010-06-18,Magnetic anisotropy in thin films of Prussian blue analogues,"The magnetic anisotropy of thin (~ 200 nm) and thick (~ 2 $\mu$m) films and
of polycrystalline (diameters ~ 60 nm) powders of the Prussian blue analogue
Rb$_{0.7}$Ni$_{4.0}$[Cr(CN)$_6$]$_{2.9} \cdot n$H$_2$O, a ferromagnetic
material with $T_c \sim 70$ K, have been investigated by magnetization, ESR at
50 GHz and 116 GHz, and variable-temperature x-ray diffraction (XRD). The
origin of the anisotropic magnetic response cannot be attributed to the direct
influence of the solid support, but the film growth protocol that preserves an
organized two-dimensional film is important. In addition, the anisotropy does
not arise from an anisotropic g-tensor nor from magneto-lattice variations
above and below $T_c$. By considering effects due to magnetic domains and
demagnetization factors, the analysis provides reasonable descriptions of the
low and high field data, thereby identifying the origin of the magnetic
anisotropy.",1006.3801v2
2010-07-19,Evidence for a temperature dependent anisotropy of the superconducting state parameters in underdoped SmBa2Cu3Ox,"The temperature dependence of the anisotropy of the superconducting state
parameters, {\gamma}, was studied by torque magnetometry for the high
temperature superconductor SmBa2Cu3Ox in magnetic fields of up to 9 T. The
measurements were performed on four underdoped single crystals with oxygen
contents corresponding to Tc's varying from 42.8 to 63.6 K. The anisotropy was
found to be strongly temperature dependent, while only a weak dependence on the
magnetic field was observed. No evidence for a field dependent superfluid
density was found. Possible origins of the temperature dependence of the
anisotropy are discussed.",1007.3152v1
2010-09-14,Anisotropy-axis orientation effect on the magnetization of γ-Fe2O3 frozen ferrofluid,"The effect of magnetic anisotropy-axis alignment on the superparamagnetic
(SPM) and superspin glass (SSG) states in a frozen ferrofluid has been
investigated. The ferrofluid studied here consists of maghemite nanoparticles
(\gamma-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume
fraction of ~15%. In the high temperature SPM state, the magnetization of
aligned ferrofluid increased by a factor varying between 2 and 4 with respect
to that in the randomly oriented state. The negative interaction energy
obtained from the Curie-Weiss fit to the high temperature susceptibility in the
SPM states as well as the SSG phase onset temperature determined from the
linear magnetization curves were found to be rather insensitive to the
anisotropy axis alignment. The low temperature aging behaviour, explored via
""zero-field cooled magnetization"" (ZFCM) relaxation measurements, however, show
distinct difference in the aging dynamics in the anisotropy-axis aligned and
randomly oriented SSG states.",1009.2610v1
2010-10-01,"Surface morphology and magnetic anisotropy in (Ga,Mn)As","Atomic Force Microscopy and Grazing incidence X-ray diffraction measurements
have revealed the presence of ripples aligned along the $[1\bar{1}0]$ direction
on the surface of (Ga,Mn)As layers grown on GaAs(001) substrates and buffer
layers, with periodicity of about 50 nm in all samples that have been studied.
These samples show the strong symmetry breaking uniaxial magnetic anisotropy
normally observed in such materials. We observe a clear correlation between the
amplitude of the surface ripples and the strength of the uniaxial magnetic
anisotropy component suggesting that these ripples might be the source of such
anisotropy.",1010.0112v2
2010-11-24,Impact of anisotropy on vortex clusters and their dynamics,"We investigate the effects of anisotropy on the stability and dynamics of
vortex cluster states which arise in Bose-Einstein condensates. Sufficiently
strong anisotropies are shown to stabilize states with arbitrary numbers of
vortices that are highly unstable in the isotropic limit. Conversely,
anisotropy can be used to destabilize states which are stable in the isotropic
limit. Near the linear limit, we identify the bifurcations of vortex states
including their emergence from linear eigenstates, while in the strongly
nonlinear limit, a particle-like description of the dynamics of the vortices in
the anisotropic trap is developed. Both are in very good agreement with
numerical results. Collective modes of stabilized many vortex cluster states
are demonstrated.",1011.5350v1
2010-12-27,Transport properties and anisotropy of Rb0.8Fe2Se2 single crystals,"Single crystals of Rb{0.8}Fe2Se2 are successfully synthesized with the
superconducting transition temperatures T_c{onset}= 31 K and T_c{zero}= 28 K. A
clear anomaly of resistivity was observed in the normal state at about 150 K,
as found in a similar system KxFe2Se2. The upper critical field has been
determined with the magnetic field along ab-plane and c-axis, yielding an
anisotropy of about 3.5. The angle dependent resistivity measured below T_c
allow a perfect scaling feature based on the anisotropic Ginzburg-Landau
theory, leading to a consistent value of the anisotropy which decreases from
about 3.6 at around T_c to 2.9 at 27 K. Comparing to the anisotropy determined
for Ba0.6K0.4Fe2As2 and Ba(Fe0.92Co0.08)2As2 using the same method, we find
that the present sample is more anisotropic and the Fermi surfaces with
stronger two dimensional characters are expected.",1012.5637v3
2011-02-15,Magnetic torque study of the temperature dependent anisotropy parameter in overdoped superconducting single-crystal YBa_2Cu_3O_7,"An overdoped YBa2Cu3O7 single crystal was studied by SQUID and torque
magnetometry in order to investigate the temperature dependence of the
anisotropy parameter close to the transition temperature T_c (0.87 T_c < T <
T_c). Angle dependent torque measurements were performed and analyzed with the
widely used Kogan model [Phys. Rev. B 38, 7049 (1988)] as well as with an
extended model by Hao and Clem [Phys. Rev. Lett. 67, 2371 (1991)], taking into
account the influence of the vortex cores on the magnetization. Both approaches
yield similar results, with an out-of-plane anisotropy parameter around 6.5
which slightly increases with decreasing temperature, and a temperature
independent in-plane anisotropy parameter gamma_ab}= 1.12(5).",1102.2990v3
2011-02-24,The role of magnetic anisotropy in spin filter junctions,"We have fabricated oxide based spin filter junctions in which we demonstrate
that magnetic anisotropy can be used to tune the transport behavior of spin
filter junctions. Until recently, spin filters have been largely comprised of
polycrystalline materials where the spin filter barrier layer and one of the
electrodes are ferromagnetic. These spin filter junctions have relied on the
weak magnetic coupling between one ferromagnetic electrode and a barrier layer
or the insertion of a nonmagnetic insulating layer in between the spin filter
barrier and electrode. We have demonstrated spin filtering behavior in
La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where
the interface anisotropy plays a significant role in determining transport
behavior. Detailed studies of chemical and magnetic structure at the interfaces
indicate that abrupt changes in magnetic anisotropy across the
non-isostructural interface is the cause of the significant suppression of
junction magnetoresistance in junctions with MnCr2O4 barrier layers.",1102.4978v1
2011-03-04,Temporal response to harmonic driving in electroconvection,"The temporal evolution of the spatially periodic electroconvection (EC)
patterns has been studied within the period of the driving ac voltage by
monitoring the light intensity diffracted from the pattern. Measurements have
been carried out on a variety of nematic systems, including those with negative
dielectric and positive conductivity anisotropy, exhibiting ""standard EC""
(s-EC), those with both anisotropies negative exhibiting ""non-standard EC""
(ns-EC), as well as those with the two anisotropies positive. Theoretical
predictions have been confirmed for stationary s-EC and ns-EC patterns.
Transitions with Hopf bifurcation have also been studied. While traveling had
no effect on the temporal evolution of dielectric s-EC, traveling conductive
s-EC and ns-EC patterns exhibited a substantially altered temporal behavior
with a dependence on the Hopf frequency. It has also been shown that in
nematics with both anisotropies positive, the pattern develops and decays
within an interval much shorter than the period, even at relatively large
driving frequencies.",1103.0898v1
2011-03-31,Anisotropy of magnetic emulsions induced by magnetic and electric fields,"The anisotropy of magnetic emulsions induced by simultaneously acting
electric and magnetic fields is theoretically and experimentally investigated.
Due to the anisotropy, the electric conductivity and magnetic permeability of a
magnetic emulsion are no longer scalar coefficients, but are tensors. The
electric conductivity and magnetic permeability tensors of sufficiently diluted
emulsions in sufficiently weak electric and magnetic fields are found as
functions of the electric and magnetic intensity vectors. The theoretically
predicted induced anisotropy was verified experimentally. The experimental data
are analyzed and compared with theoretical predictions. The results of the
analysis and comparison are discussed.",1103.6251v2
2011-05-02,Quantifying the anisotropy in the infrared emission of powerful AGN,"We use restframe near- and mid-IR data of an isotropically selected sample of
quasars and radio galaxies at 1.0 \leq z \leq 1.4, which have been published
previously, to study the wavelength-dependent anisotropy of the IR emission.
For that we build average SEDs of the quasar subsample (= type 1 AGN) and radio
galaxies (= type 2 AGN) from ~1-17 {\mu}m and plot the ratio of both average
samples. From 2 to 8 {\mu}m restframe wavelength the ratio gradually decreases
from 20 to 2 with values around 3 in the 10{\mu}m silicate feature. Longward of
12{\mu}m the ratio decreases further and shows some high degree of isotropy at
15 {\mu}m (ratio ~1.4). The results are consistent with upper limits derived
from the X-ray/mid-IR correlation of local Seyfert galaxies. We find that the
anisotropy in our high-luminosity radio-loud sample is smaller than in
radio-quiet lower-luminosity AGN which may be interpreted in the framework of a
receding torus model with luminosity-dependent obscuration properties. It is
also shown that the relatively small degree of anisotropy is consistent with
clumpy torus models.",1105.0429v1
2011-05-09,Properties of magnetic nanodots with perpendicular anisotropy,"Nanodots with magnetic vortices have many potential applications, such as
magnetic memories (VRAMs) and spin transfer nano-oscillators (STNOs). Adding a
perpendicular anisotropy term to the magnetic energy of the nanodot it becomes
possible to tune the vortex core properties. This can be obtained, e.g., in Co
nanodots by varying the thickness of the Co layer in a Co/Pt stack. Here we
discuss the spin configuration of circular and elliptical nanodots for
different perpendicular anisotropies; we show for nanodisks that micromagnetic
simulations and analytical results agree. Increasing the perpendicular
anisotropy, the vortex core radii increase, the phase diagrams are modified and
new configurations appear; the knowledge of these phase diagrams is relevant
for the choice of optimum nanodot dimensions for applications. MFM measurements
on Co/Pt multilayers confirm the trend of the vortex core diameters with
varying Co layer thicknesses.",1105.1813v1
2011-06-03,Origin of in-plane uniaxial magnetic anisotropy in CoFeB amorphous ferromagnetic thin-films,"Describing the origin of uniaxial magnetic anisotropy (UMA) is generally
problematic in systems other than single crystals. We demonstrate an in-plane
UMA in amorphous CoFeB films on GaAs(001) which has the expected symmetry of
the interface anisotropy in ferromagnetic films on GaAs(001), but strength
which is independent of, rather than in inverse proportion to, the film
thickness. We show that this volume UMA is consistent with a bond-orientational
anisotropy, which propagates the interface-induced UMA through the thickness of
the amorphous film. It is explained how, in general, this mechanism may
describe the origin of in-plane UMAs in amorphous ferromagnetic films.",1106.0606v1
2011-06-07,Evolution of curvature and anisotropy near a nonsingular bounce,"We consider bouncing cosmologies in which an ekpyrotic contraction phase with
w >> 1 is followed by a bouncing phase with w < -1 that violates the null
energy condition. The bouncing phase, induced by ghost condensation, is
designed to produce a classically nonsingular bounce at a finite value of the
scale factor. We show that the initial curvature and anisotropy, though diluted
during the ekpyrotic phase, grow back exponentially during the bouncing phase.
Moreover, curvature perturbations and anisotropy are generated by quantum
fluctuations during the ekpyrotic phase. In the bouncing phase, however, an
adiabatic curvature perturbation grows to dominate and contributes a blue
spectrum that spoils the scale-invariance. Meanwhile, a scalar shear
perturbation grows nonlinear and creates an overwhelming anisotropy that
disrupts the nonsingular bounce altogether.",1106.1416v2
2011-06-17,Electromagnetic signatures of a strongly coupled anisotropic plasma,"In heavy-ion collisions, quark-gluon plasma is likely to be produced with
sizable initial pressure anisotropy, which may leave an imprint on
electromagnetic observables. In order to model a strongly coupled anisotropic
plasma, we use the AdS/CFT correspondence to calculate the current-current
correlator of a weakly gauged U(1) subgroup of R symmetry in an N=4
super-Yang-Mills plasma with a (temporarily) fixed anisotropy. The dual
geometry, obtained previously by Janik and Witaszczyk, contains a naked
singularity which however permits purely infalling boundary conditions and
therefore the usual definition of a retarded correlator. We obtain numerical
results for the cases of wave vector parallel and orthogonal to the direction
of anisotropy, and we compare with previous isotropic results. In the
(unphysical) limit of vanishing frequency (infinite time) we obtain a vanishing
DC conductivity for any amount of anisotropy, but the anisotropic AC
conductivities smoothly approach the isotropic case in the limit of high
frequencies. We also discuss hard photon production from an anisotropic plasma
and compare with existing hard-loop resummed calculations.",1106.3539v3
2011-07-29,$Bi_2Te_3$: Implications of the rhombohedral k-space texture on the evaluation of the in-plane/out-of-plane conductivity anisotropy,"Different computational scheme for calculating surface integrals in
anisotropic Brillouin zones are compared. The example of the transport
distribution function (plasma frequency) of the thermoelectric Material \BiTe
near the band edges will be discussed. The layered structure of the material
together with the rhombohedral symmetry causes a strong anisotropy of the
transport distribution function for the directions in the basal (in-plane) and
perpendicular to the basal plane (out-of-plane). It is shown that a thorough
reciprocal space integration is necessary to reproduce the
in-plane/out-of-plane anisotropy. A quantitative comparison can be made at the
band edges, where the transport anisotropy is given in terms of the anisotropic
mass tensor.",1108.0023v1
2011-07-30,Spiraling elliptic solitons in nonlocal nonlinear media without anisotropy,"The optical spatial solitons with ellipse-shaped spots have generally been
considered to be a result of either linear or nonlinear anisotropy. In this
paper, we introduce a class of spiraling elliptic solitons in the nonlocal
nonlinear media without both linear and nonlinear anisotropy. The spiraling
elliptic solitons carry the orbital angular momentum, which plays a key role in
the formation of such solitons, and are stable for any degree of nonlocality
except the local case when the response function of the material is Gaussian
function. The formation of such solitons can be attributable to the effective
anisotropic diffraction (linear anisotropy) resulting from the orbital angular
momentum. Our variational analytical result is confirmed by direct numerical
simulation of the nonlocal nonlinear Schrodinger equation.",1108.0055v1
2011-08-17,Magnetic properties of Mn impurities on GaAs (110) surfaces,"We present a computational study of individual and pairs of substitutional Mn
impurities on the (110) surface of GaAs samples based on density functional
theory. We focus on the anisotropy properties of these magnetic centers and
their dependence on on-site correlations, spin-orbit interaction and
surface-induced symmetry-breaking effects. For a Mn impurity on the surface,
the associated acceptor-hole wavefunction tends to be more localized around the
Mn than for an impurity in bulk GaAs. The magnetic anisotropy energy for
isolated Mn impurities is of the order of 1 meV, and can be related to the
anisotropy of the orbital magnetic moment of the Mn acceptor hole. Typically Mn
pairs have their spin magnetic moments parallel aligned, with an exchange
energy that strongly depends on the pair orientation on the surface. The spin
magnetic moment and exchange energies for these magnetic entities are not
significantly modified by the spin-orbit interaction, but are more sensitive to
on-site correlations. Correlations in general reduce the magnetic anisotropy
for most of the ferromagnetic Mn pairs.",1108.3440v2
2011-08-29,Anisotropy of the coherence length from critical currents in the stoichiometric superconductor LiFeAs,"Miniature Hall-probe arrays were used to measure the critical current
densities for the three main directions of vortex motion in the stoichiometric
LiFeAs superconductor. These correspond to vortices oriented along the c-axis
moving parallel to the ab-plane, and to vortices in the ab-plane moving
perpendicular to, and within the plane, respectively. The measurements were
carried out in the low-field regime of strong vortex pinning, in which the
critical current anisotropy is solely determined by the coherence length
anisotropy parameter, {\epsilon}_{\xi}. This allows extraction of
{\epsilon}_{\xi} at magnetic fields far below the upper critical field B_c2. We
find that increasing magnetic field decreases the anisotropy of the coherence
length.",1108.5583v3
2011-09-01,Electronic structure and transport anisotropy of Bi2Te3 and Sb2Te3,"On the basis of detailed ab initio studies the influence of strain on the
anisotropy of the transport distribution of the thermoelectrics Bi$_2$Te$_3$
and Sb$_2$Te$_3$ was investigated. Both tellurides were studied in their own,
as well as in their co-partners lattice structure to gain insight to the
electrical transport in epitaxial heterostructures composed of both materials.
It is shown, that the anisotropy of the transport distribution overestimates
the experimental findings for Bi$_2$Te$_3$, implying anisotropic scattering
effects. An increase of the in-plane lattice constant leads to an enhancement
of the transport anisotropy for $p$-doping, whereas the opposite occurs for
$n$-doping. The recent findings and special features of the transport
distribution are discussed in detail in relation to the topology of the band
structures.",1109.0186v1
2011-09-05,Direction Dependence of the Deceleration Parameter,"In this paper we study the possibly existing anisotropy in the acceleration
expansion by use of the full sample of Union2 data. Using the hemisphere
comparison method to search for a preferred direction, we take the deceleration
parameter q0 as the diagnostic to quantify the anisotropy level in the wCDM
model. We find that the maximum accelerating expansion direction is
$(l,b)=(314_{+20^{\circ}}^{\circ-13^{\circ}},28_{+11^{\circ}}^{\circ-33^{\circ}})$,with
the maximum anisotropy level of $\delta
q_{0,max}/\bar{q}_0=0.79_{+0.27}^{-0.28}$, and that the anisotropy is more
prominent when only low redshift data ($z\leq0.2$) are used. We also discuss
this issue in the $CPL$ parameterized model, showing a similar result.",1109.0941v6
2011-09-24,Interface-Roughening Phase Diagram of the Three-Dimensional Ising Model for All Interaction Anisotropies from Hard-Spin Mean-Field Theory,"The roughening phase diagram of the d=3 Ising model with uniaxially
anisotropic interactions is calculated for the entire range of anisotropy, from
decoupled planes to the isotropic model to the solid-on-solid model, using
hard-spin mean-field theory. The phase diagram contains the line of ordering
phase transitions and, at lower temperatures, the line of roughening phase
transitions, where the interface between ordered domains roughens. Upon
increasing the anisotropy, roughening transition temperatures settle after the
isotropic case, whereas the ordering transition temperature increases to
infinity. The calculation is repeated for the d=2 Ising model for the full
range of anisotropy, yielding no roughening transition.",1109.5294v2
2011-10-03,Phase transitions in spin-orbital models with spin-space anisotropies for iron-pnictides: A study through Monte Carlo simulations,"The common phase diagrams of superconducting iron pnictides show interesting
material specificities in the structural and magnetic phase transitions. In
some cases the two transitions are separate and second order, while in others
they appear to happen concomitantly as a single first order transition. We
explore these differences using Monte Carlo simulations of a two-dimensional
Hamiltonian with coupled Heisenberg-spin and Ising-orbital degrees of freedom.
In this spin-orbital model, the finite-temperature orbital-ordering transition
results in a tetragonal-to-orthorhombic symmetry reduction and is associated
with the structural transition in the iron-pnictide materials. With a zero or
very small spin space anisotropy, the magnetic transition separates from the
orbital one in temperature, and the orbital transition is found to be in the
Ising universality class. With increasing anisotropy, the two transitions
rapidly merge together and tend to become weakly first order. We also study the
case of a single-ion anisotropy and propose that the preferred spin-orientation
along the antiferromagnetic direction in these materials is driven by orbital
order.",1110.0434v2
2011-10-04,Trans-Alfvenic Motions in the Taurus Molecular Cloud,"Magnetically aligned velocity anisotropy over varying physical conditions and
environments within the Taurus Molecular Cloud is evaluated from analysis of
wide field spectroscopic imaging of 12CO and 13CO J=1-0 emission. Such
anisotropy is a result of MHD turbulence in the strong magnetic field regime
and provides an indirect measure of the role of magnetic fields upon the gas.
Velocity anisotropy aligned with the local, projected mean magnetic field
direction is limited to fields with low surface brightness 12CO emission
corresponding to regions of low visual extinction and presumably, low gas
volume density. The more optically thin 13CO J=1-0 emission shows little
evidence for velocity anisotropy. We compare our results with computational
simulations with varying degrees of magnetic field strength and Alfvenic Mach
numbers. In the diffuse, molecular envelope of the cloud, a strong magnetic
field and sub-Alfvenic turbulent motions are inferred. Super-Alfvenic motions
are present within the high column density filaments of the Taurus cloud. From
this trans-Alfvenic flow, we constrain the scaling exponent, kappa, of the
magnetic field density relation (B ~ n^kappa) to be near zero as expected for
ambipolar diffusion or material loading of magnetic flux tubes.",1110.0808v1
2011-10-10,Observation of Anisotropy in the Arrival Direction Distribution of Cosmic Rays above TeV Energies with Icecube,"Between May 2009 and May 2010, the IceCube neutrino detector recorded 32
billion of atmospheric muons generated in air showers produced by cosmic rays
in the TeV energy range. With such high statistics sample it is possible to
observe, for the first time in the southern hemisphere, an energy dependence in
the Galactic cosmic ray anisotropy up to a few hundred TeV. This study shows
that the same large-scale anisotropy observed at median energies around 20 TeV
is not present at 400 TeV; the anisotropy observed at 400 TeV shows substantial
differences with respect to that at lower energy. In addition to the
large-scale features observed at 20 TeV in the form of strong dipole and
quadrupole moments, the data include several localized regions of excess and
deficit on scales between 10{\degree} to 30{\degree}. The features observed at
both large and small scale are statistically significant, but their origin is
currently unknown.",1110.2079v1
2011-10-13,Nonaxisymmetric Anisotropy of Solar Wind Turbulence as a Direct Test for the Models of Magnetohydrodynamic Tubulence,"Single point spacecraft observations of the turbulent solar wind flow exhibit
a characteristic nonaxisymmetric anisotropy that depends sensitively on the
perpendicular power spectral exponent. For the first time we use this
nonaxisymmetric anisotropy as a function of wave vector direction to test
models of magnetohydrodynamic (MHD) turbulence. Using Ulysses magnetic field
observations in the fast, quiet polar solar wind we find that the
Goldreich-Sridhar model of MHD turbulence is not consistent with the observed
anisotropy, whereas the observations are well reproduced by the ""Slab + 2D""
model. The Golderich-Sridhar model alone can not account for the observations
unless an additional component is also present.",1110.2932v1
2011-10-25,"Magnetoresistance of individual ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires","We investigate, angle dependent, the magnetoresistance (MR) of individual
self-assembled ferromagnetic GaAs/(Ga,Mn)As core-shell nanowires at cryogenic
temperatures. The shape of the MR traces and the observed strong anisotropies
in transport can be ascribed to the interplay of the negative magnetoresistance
effect and a strong uniaxial anisotropy with the magnetic easy direction
pointing along the wire axis. The magnetoresistance can be well described by a
quantitative analysis based on the concept of the effective magnetic field,
usually used to describe ferromagnetic resonance phenomena. The nanowires we
investigate exhibit a uniaxial anisotropy which is approximately 5 times larger
than the strain induced anisotropy observed in lithographically prepared
(Ga,Mn)As stripes.",1110.5507v1
2011-11-03,Doping - dependent superconducting gap anisotropy in the two-dimensional 10-3-8 pnictide Ca$_{10}$(Pt$_3$As$_8$)[(Fe$_{1-x}$Pt$_{x}$)$_2$As$_2$]$_5$,"The characteristic features of
Ca$_{10}$(Pt$_3$As$_8$)[(Fe$_{1-x}$Pt$_x$)$_2$As$_2$]$_5$ (""10-3-8"")
superconductor are relatively high anisotropy and a clear separation of
superconductivity and structural/magnetic transitions, which allows studying
the superconducting gap without complications due to the coexisting order
parameters. The London penetration depth, measured in underdoped single
crystals of 10-3-8 ($x =$ 0.028, 0.041, 0.042, and 0.097), shows behavior
remarkably similar to other Fe-based superconductors, exhibiting robust
power-law, $\Delta \lambda(T) = A T^n$. The exponent $n$ decreases from 2.36
($x =$ 0.097, close to optimal doping) to 1.7 ($x =$ 0.028, a heavily
underdoped composition), suggesting that the superconducting gap becomes more
anisotropic at the dome edge. A similar trend is found in low-anisotropy
superconductors based on BaFe$_2$As$_2$ (""122""), implying that it is an
intrinsic property of superconductivity in iron pnictides, unrelated to the
coexistence of magnetic order and superconductivity or the anisotropy of the
normal state. Overall this doping dependence is consistent with $s_{\pm}$
pairing competing with intra-band repulsion.",1111.1003v1
2011-11-11,Temperature anisotropy and differential streaming of solar wind ions -- Correlations with transverse fluctuations,"We study correlations of the temperature ratio (which is an indicator for
perpendicular ion heating) and the differential flow of the alpha particles
with the power of transverse fluctuations that have wave numbers between 0.01
and 0.1 (normalized to $k_p=1/l_p$, where $l_p$ is the proton inertial length).
We found that both the normalized differential ion speed, $V_{\alpha
p}/V_\mathrm{A}$ (where $V_\mathrm{A}$ is the Alfv\'en speed) and the proton
temperature anisotropy, $T_{\perp p}/T_{\parallel p}$, increase when the
relative wave power is growing. Furthermore, if the normalized differential ion
speed stays below 0.5, the alpha-particle temperature anisotropy, $T_{\perp
\alpha}/T_{\parallel \alpha}$, correlates positively with the relative power of
the transverse fluctuations. However, if $V_{\alpha p}/V_\mathrm{A}$ is higher
than 0.6, then the alpha-particle temperature anisotropy tends to become lower
and attain even values below unity despite the presence of transverse
fluctuations of relatively high amplitudes. Our findings appear to be
consistent with the expectations from kinetic theory for the resonant
interaction of the ions with Alfv\'en/ion-cyclotron waves and the resulting
wave dissipation.",1111.2724v1
2011-11-13,Anisotropy of TeV Cosmic Rays and the Outer Heliospheric Boundaries,"Cosmic rays in the energy range from about 10's GeV to several 100's TeV are
observed on Earth with an energy-dependent anisotropy of order 0.01-0.1%, and a
consistent topology that appears to significantly change at higher energy. The
nearest and most recent galactic cosmic ray sources might stochastically
dominate the observation and possibly explain a change in orientation of the
anisotropy as a function of energy. However, the diffusion approximation is not
able to explain its non-dipolar structure and, in particular, the significant
contribution of small angular scale features. Particle propagation within the
mean free path in the local interstellar medium might have a major role in
determining the properties of galactic cosmic rays, such as their arrival
distribution. In particular, scattering on perturbations induced in the local
interstellar magnetic field by the heliosphere wake, may cause a
re-distribution of anisotropic cosmic rays below about 100 TeV toward the
direction of the elongated heliotail and of the local interstellar magnetic
field in the outer heliosphere. Such scattering processes are considered
responsible of the observed TeV cosmic ray global anisotropy and its fine
angular structure.",1111.3075v2
2011-11-17,Field-induced Magnetic Transition in Cobalt-Ferrite,"We present magnetostriction and magnetization measurements of a cobalt
ferrite Co0.8Fe2.2O4 single crystal. We observe unusual behaviour in the
magnetic hard axis of the single crystal which manifests in a jump of the
magnetization curve at a critical field. This first order magnetization process
(FOMP) which is explained as an anisotropy driven transition is visible at
temperatures lower than 150 K. By analyzing the anisotropy constants we found
that the higher order anisotropy constant K2 dominates the anisotropy energy.
In the magnetostriction measurements the FOMP is clearly visible as a huge jump
in the [111] direction, which can be explained by means of a geometric model.",1111.4027v2
2011-12-03,Observation of CR Anisotropy with ARGO-YBJ,"The measurement of the anisotropies of cosmic ray arrival direction provides
important informations on the propagation mechanisms and on the identification
of their sources. In this paper we report the observation of anisotropy regions
at different angular scales. In particular, the observation of a possible
anisotropy on scales between $\sim$ 10 $^{\circ}$ and $\sim$ 30 $^{\circ}$
suggests the presence of unknown features of the magnetic fields the charged
cosmic rays propagate through, as well as potential contributions of nearby
sources to the total flux of cosmic rays. Evidence of new weaker few-degree
excesses throughout the sky region $195^{\circ}\leq$ R.A. $\leq 315^{\circ}$ is
reported for the first time.",1112.0666v2
2011-12-11,Anisotropies in the cosmic radiation observed with ARGO-YBJ,"Important informations on the origin and the propagation mechanisms of cosmic
rays may be provided by the measurement of the anisotropies of their arrival
direction. In this paper the observation of anisotropy regions at different
angular scales is reported. In particular, the observation of a possible
anisotropy on scales between $\sim10^{\circ}$ and $\sim30^{\circ}$ may be a
key-detection for speculations on the presence of unknown features of the
magnetic fields the charged cosmic rays propagate through, as well as to
potential contributions of nearby sources to the total flux of cosmic rays.
Evidence of new weaker few-degree excesses throughout the sky region
$195^{\circ}\leq$ R.A. $\leq 315^{\circ}$ is also reported.",1112.2375v1
2011-12-22,Initial state anisotropies and their uncertainties in ultrarelativistic heavy-ion collisions from the Monte Carlo Glauber model,"In hydrodynamical modeling of heavy-ion collisions, the initial-state spatial
anisotropies are translated into momentum anisotropies of the final-state
particle distributions. Thus, understanding the origin of the initial-state
anisotropies and their uncertainties is important before extracting specific
QCD matter properties, such as viscosity, from the experimental data. In this
work we review the wounded nucleon approach based on the Monte Carlo Glauber
model, charting in particular the uncertainties arising from modeling of the
nucleon-nucleon interactions between the colliding nucleon pairs and
nucleon-nucleon correlations inside the colliding nuclei. We discuss the
differences between the black disk model and a probabilistic profile function
approach for the inelastic nucleon-nucleon interactions, and investigate the
influence of initial-state correlations using state-of-the-art modeling of
these.",1112.5306v2
2011-12-26,Different types of the dimensional crossover in the quasi-one-dimensional spinless fermion systems,"It is known that many-body correlations qualitatively modify the properties
of a one-dimensional metal. However, for a quasi-one-dimensional metal these
correlations are suppressed, at least partially. We study conditions under
which the one-dimensional effects significantly influence the dimensional
crossover of a quasi-one-dimensional metal. It is proved (i) that even a system
with very high anisotropy of the single-particle hopping might behave on both
sides of the crossover as an ordinary weakly non-ideal Fermi gas. Further, (ii)
to demonstrate well-developed signatures of one-dimensional correlations the
system must have extremely (exponentially) high anisotropy. Between cases (i)
and (ii) an intermediate regime lies: (iii) the one-dimensional phenomena
affect the two-particle susceptibilities, but do not reveal themselves in
single-particle quantities. Unlike the normal state properties, (iv) the
ordering transition is always very sensitive to the anisotropy: the mean field
theory quickly becomes invalid as the anisotropy increases. An expression for
the transition temperature is derived. The attributes (i-iv) are used to
classify the weakly interacting quasi-one-dimensional fermion systems.",1112.5852v1
2012-01-10,Effect of anisotropy on small magnetic clusters,"The effect of dipolar interaction and local uniaxial anisotropy on the
magnetic response of small spin clusters where spins are located on the
vertices of icosahedron, cuboctahedron, tetrahedron and square geometry have
been investigated. We consider the ferromagnetic and antiferromagnetic spin-1/2
and spin-1 Heisenberg model with uniaxial anisotropy and dipolar interaction
and apply numerical exact diagonalization technique in order to study the
influence of frustration and anisotropy on the ground state properties of the
spin-clusters. The ground state magnetization, spin-spin correlation and
several thermodynamic quantities such as entropy and specific heat are
calculated as a function of temperature and magnetic field.",1201.2088v1
2012-01-13,Strong single-ion anisotropy and anisotropic interactions of magnetic adatoms induced by topological surface states,"The nature of the magnetism brought about by Fe adatoms on the surface of the
topological insulator Bi2Se3 was examined in terms of density functional
calculations. The Fe adatoms exhibit strong easy-axis magnetic anisotropy in
the dilute adsorption limit due to the topological surface states (TSS). The
spin exchange J between the Fe adatoms follows a Ruderman-Kittel-Kasuya-Yosida
(RKKY) behavior with substantial anisotropy, and the Dzyaloshinskii-Moriya (DM)
interaction between them is quite strong with |D/J|~0.3 under the mediation by
the TSS, and can be further raised to ~0.6 by an external electric field. The
apparent single-ion anisotropy of a Fe adatom is indispensable in determining
the spin orientation.",1201.2857v1
2012-01-20,Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background,"The intergalactic magnetic field (IGMF) may leave an imprint on the angular
anisotropy of the extragalactic gamma-ray background through its effect on
electromagnetic cascades triggered by interactions between very high energy
photons and the extragalactic background light. A strong IGMF will deflect
secondary particles produced in these cascades and will thus tend to isotropize
lower energy cascade photons, thereby inducing a modulation in the anisotropy
energy spectrum of the gamma-ray background. Here we present a simple,
proof-of-concept calculation of the magnitude of this effect and demonstrate
that current Fermi data already seem to prefer non-negligible IGMF values. The
anisotropy energy spectrum of the Fermi gamma-ray background could thus be used
as a probe of the IGMF strength.",1201.4405v3
2012-01-30,"Fractional calculus, completely monotonic functions, a generalized Mittag-Leffler function and phase-space consistency of separable augmented densities","Under the separability assumption on the augmented density, a distribution
function can be always constructed for a spherical population with the
specified density and anisotropy profile. Then, a question arises, under what
conditions the distribution constructed as such is non-negative everywhere in
the entire accessible subvolume of the phase-space. We rediscover necessary
conditions on the augmented density expressed with fractional calculus. The
condition on the radius part R(r^2) -- whose logarithmic derivative is the
anisotropy parameter -- is equivalent to R(1/w)/w being a completely monotonic
function whereas the condition on the potential part is stated as its
derivative up to the order not greater than 3/2-b being non-negative (where b
is the central limiting value for the anisotropy parameter). We also derive the
set of sufficient conditions on the separable augmented density for the
non-negativity of the distribution, which generalizes the condition derived for
the generalized Cuddeford system by Ciotti & Morganti to arbitrary separable
systems. This is applied for the case when the anisotropy is parameterized by a
monotonic function of the radius of Baes & Van Hese. The resulting criteria are
found based on the complete monotonicity of generalized Mittag-Leffler
functions.",1201.6113v1
2012-03-02,Single Magnetic Atom on a Surface: Anisotropy Energy and Spin Density,"Studying single-atom magnetic anisotropy on surfaces enables the exploration
of the smallest magnetic storage bit that can be built. In this work, magnetic
anisotropy of a single rare-earth atom on a surface is studied computationally
for the first time. The single adatom and its substrate surface are chosen to
be a Dysprosium (Dy) atom and a copper-nitrite surface, respectively, where
single transition-metal magnetic atoms on the same surface were previously
studied one atom at a time by scanning tunneling microscopes. We propose
unconventional f and d subshell symmetries so that following the
first-principles calculations, simple pictorial analyses of the spin-density
distribution can be performed for the first time, independently for both a
rare-earth atom Dy and a transition-metal Fe. The magnetic anisotropy energy of
Dy on the surface is calculated to be a factor of five larger than the previous
highest one, reaching a record-high value of 31 meV.",1203.0420v1
2012-03-02,Mismatch of conductivity anisotropy in the mixed and normal states of type-II superconductors,"We have calculated the Bardeen-Stephen contribution to the vortex viscosity
for uniaxial anisotropic superconductors within the time-dependent
Ginzburg-Landau (TDGL) theory. We focus our attention on superconductors with a
mismatch of anisotropy of normal and superconducting characteristics. Exact
asymptotics for the Bardeen-Stephen contribution have been derived in two
limits: the cases of small and large electric field penetration depth (as
compared to the coherence length). Also we suggest a variational procedure
which allows us to calculate the vortex viscosity for superconductors with
arbitrary ratio of the coherence lenght to the electric field penetration
depth. The approximate analytical result is compared with numerical
calculations. Finally, using a generalized TDGL theory, we prove that the
viscosity anisotropy and, thus, the flux-flow conductivity anisotropy may
depend on temperature.",1203.0459v2
2012-03-09,Fractional quantum Hall states in two-dimensional electron systems with anisotropic interactions,"We study the anisotropic effect of the Coulomb interaction on a 1/3-filling
fractional quantum Hall system by using an exact diagonalization method on
small systems in torus geometry. For weak anisotropy the system remains to be
an incompressible quantum liquid, although anisotropy manifests itself in
density correlation functions and excitation spectra. When the strength of
anisotropy increases, we find the system develops a Hall-smectic-like phase
with a one-dimensional charge density wave order and is unstable towards the
one-dimensional crystal in the strong anisotropy limit. In all three phases of
the Laughlin liquid, Hall-smectic-like, and crystal phases the ground state of
the anisotropic Coulomb system can be well described by a family of model wave
functions generated by an anisotropic projection Hamiltonian. We discuss the
relevance of the results to the geometrical description of fractional quantum
Hall states proposed by Haldane [ Phys. Rev. Lett. 107 116801 (2011)].",1203.1982v2
2012-03-09,Role of Fermi surface anisotropy in the study of gap anisotropy using magnetic-field-angle dependence of thermal oscillations in AyFe2-xSe2 superconductors,"We present a numerical study of the field-angle resolved oscillations of the
thermal conductivity and specific heat under rotated magnetic field in the
$A_y$Fe$_{2-x}$Se$_2$ [$A$=K,Rb,Cs,(Tl,K)] superconductors, using realistic
two-band Fermi surface parameterization. Our key finding is that even for
isotropic pairing on an anisotropic Fermi surface, the thermodynamic quantities
exhibit substantial oscillatory behavior in the superconducting state, even
much below the upper critical field. Furthermore, in multiband systems the
competition of anisotropies between two Fermi surfaces can cause a double sign
reversal of oscillations as a function of temperature, irrespective of gap
anisotropy. Our findings put severe constraints on simple interpretations of
field-angle resolved measurements widely used to identify the angular structure
of the superconducting gap.",1203.2211v2
2012-03-15,Azimuthal anisotropy in a jet absorption model with fluctuating initial geometry in heavy ion collisions,"The azimuthal anisotropy due to path-length dependent jet energy loss is
studied in a simple jet absorption model that include event by event
fluctuating Glauber geometry. Significant anisotropy coefficients v_n are
observed for n=1,2 and 3, but they are very small for n>3. These coefficients
are expected to result in a ""ridge"" for correlations between two independently
produced jets. The correlations between the orientation of the n^{th}-order
anisotropy induced by jet absorption (\Phi_n^{QP}) and the n^{th}-order
participant plane (\Phi_n^{PP}) responsible for harmonic flow are studied.
Tight correlations are observed for n=2 in mid-central collisions, but they
weaken significantly for n\neq2. The correlations are positive for n>=3, but
become negative in central collisions for n>3. The dispersion between
\Phi_n^{QP} and \Phi_n^{PP} is expect to break the factorization of the Fourier
coefficients from two-particle correlation v_{n,n} into the single particle
v_n, and has important implications for the high-pT ridge phenomena.",1203.3265v2
2012-04-09,Azimuthal anisotropy of charged particles at high transverse momenta in PbPb collisions at sqrt(s[NN]) = 2.76 TeV,"The azimuthal anisotropy of charged particles in PbPb collisions at
nucleon-nucleon center-of-mass energy of 2.76 TeV is measured with the CMS
detector at the LHC over an extended transverse momentum (pt) range up to
approximately 60 GeV. The data cover both the low-pt region associated with
hydrodynamic flow phenomena and the high-pt region where the anisotropies may
reflect the path-length dependence of parton energy loss in the created medium.
The anisotropy parameter (v2) of the particles is extracted by correlating
charged tracks with respect to the event-plane reconstructed by using the
energy deposited in forward-angle calorimeters. For the six bins of collision
centrality studied, spanning the range of 0-60% most-central events, the
observed v2 values are found to first increase with pt, reaching a maximum
around pt = 3 GeV, and then to gradually decrease to almost zero, with the
decline persisting up to at least pt = 40 GeV over the full centrality range
measured.",1204.1850v2
2012-05-03,Cosmic Topology of Prism Double-Action Manifolds,"The cosmic microwave background (CMB) anisotropies in spherical 3-spaces with
a non-trivial topology are studied. This paper discusses the special class of
the so-called double-action manifolds, which are for the first time analysed
with respect to their CMB anisotropies. The CMB anisotropies are computed for
all prism double-action manifolds generated by a binary dihedral and a cyclic
group with a group order of up to 180 leading to 33 different topologies.
Several spaces are found which show a suppression of the CMB anisotropies on
large angular distances as it is found on the real CMB sky. It turns out that
two of these spaces possess Dirichlet domains which are not very far from
highly symmetric polyhedra like Platonic or Archimedean ones.",1205.0660v2
2012-05-10,"Multiboson spin-wave theory for Ba2CoGe2O7, a spin-3/2 easy-plane Neel antiferromagnet with strong single-ion anisotropy","We consider the square-lattice antiferromagnetic Heisenberg Hamiltonian
extended with a single-ion axial anisotropy term as a minimal model for the
multiferroic Ba2CoGe2O7. Developing a multiboson spin-wave theory, we
investigate the dispersion of the spin excitations in this spin-3/2 system. As
a consequence of a strong single-ion anisotropy, a stretching (longitudinal)
spin-mode appears in the spectrum. The inelastic neutron scattering spectra of
Zheludev et al. [Phys. Rev. B 68, 024428 (2003)] are successfully reproduced by
the low energy modes in the multiboson spin-wave theory, and we anticipate the
appearance of the spin stretching modes at 4meV that can be identified using
the calculated dynamical spin structure factors. We expect the appearance of
spin stretching modes for any S>1/2 compound where the single-ion anisotropy is
significant.",1205.2196v2
2012-05-21,Theoretical study of magnetic domain walls through a cobalt nanocontact,"To calculate the magnetic ground state of nanoparticles we present a
self-consistent first principles method in terms of a fully relativistic
embedded cluster multiple scattering Green's function technique. Based on the
derivatives of the band energy, a Newton-Raphson algorithm is used to find the
ground state configuration. The method is applied to a cobalt nanocontact that
turned out to show a cycloidal domain wall configuration between oppositely
magnetized leads. We found that a wall of cycloidal spin-structure is about 30
meV lower in energy than the one of helical spin-structure. A detailed analysis
revealed that the uniaxial on-site anisotropy of the central atom is mainly
responsible to this energy difference. This high uniaxial anisotropy energy is
accompanied by a huge enhancement and anisotropy of the orbital magnetic moment
of the central atom. By varying the magnetic orientation at the central atom,
we identified the term related to exchange couplings (Weiss-field term),
various on-site anisotropy terms, and also those due to higher order
spin-interactions.",1205.4579v1
2012-06-25,Initial state anisotropies in ultrarelativistic heavy-ion collisions from the Monte Carlo Glauber model,"In hydrodynamicalmodeling of heavy-ion collisions the initial state spatial
anisotropies translate into momentum anisotropies of the final state particle
distributions. Thus, understanding the origin of the initial anisotropies and
quantifying their uncertainties is important for the extraction of specific QCD
matter properties, such as viscosity, from the experimental data. In this work
we study the wounded nucleon approach in the Monte Carlo Glauber model
framework, focusing especially on the uncertainties which arise from the
modeling of the nucleon-nucleon interactions between the colliding nucleon
pairs and nucleon-nucleon correlations inside the colliding nuclei. We compare
the black disk model and a probabilistic profile function approach for the
inelastic nucleon-nucleon interactions, and study the effects of initial state
correlations using state-of-theart modeling of these.",1206.5720v1
2012-06-29,Light-induced magnetization reversal of high-anisotropy TbCo alloy films,"Magnetization reversal using circularly polarized light provides a new way to
control magnetization without any external magnetic field and has the potential
to revolutionize magnetic data storage. However, in order to reach ultra-high
density data storage, high anisotropy media providing thermal stability are
needed. Here, we evidence all-optical magnetization switching for different
TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching
for films with anisotropy fields reaching 6 T corresponding to anisotropy
constants of 3x106 ergs/cm3. Optical magnetization switching is observed only
for alloys which compensation temperature can be reached through sample
heating.",1206.6978v1
2012-08-12,Measurement of the azimuthal anisotropy of neutral pions in PbPb collisions at sqrt(s(NN)) = 2.76 TeV,"First measurements of the azimuthal anisotropy of neutral pions produced in
PbPb collisions at a center-of-mass energy of sqrt(s(NN)) = 2.76 TeV are
presented. The amplitudes of the second Fourier component (v2) of the neutral
pion azimuthal distributions are extracted using an event-plane technique. The
values of v2 are studied as a function of the neutral pion transverse momentum
(pt) for different classes of collision centrality in the kinematic range 1.6 <
pt < 8.0 GeV, within the pseudorapidity interval abs(eta) < 0.8. The CMS
measurements of v2(pt) are similar to previously reported neutral pion
azimuthal anisotropy results from sqrt(s(NN)) = 200 GeV AuAu collisions at
RHIC, despite a factor of about 14 increase in the center-of-mass energy. In
the momentum range 2.5 < pt < 5.0 GeV, the neutral pion anisotropies are found
to be smaller than those observed by CMS for inclusive charged particles.",1208.2470v2
2012-08-27,Understanding TeV-band cosmic-ray anisotropy,"We investigate the temporal and spectral correlations between flux and
anisotropy fluctuations of TeV-band cosmic rays in the light of recent data
taken with IceCube. We find that for a conventional distribution of cosmic-ray
sources the dipole anisotropy is higher than observed, even if source
discreteness is taken into account. Moreover, even for a shallow distribution
of galactic cosmic-ray sources and a reacceleration model, fluctuations arising
from source discreteness provide a probability only of the order of 10% that
the cosmic-ray anisotropy limits of the recent IceCube analysis are met. This
probability estimate is nearly independent of the exact choice of source rate,
but generous for a large halo size. The location of the intensity maximum far
from the Galactic Center is naturally reproduced.",1208.5338v1
2012-08-27,Anisotropy of photon production: Initial eccentricity or magnetic field,"Recent measurements of the azimuthal anisotropy of direct photons in
heavy-ion collisions at the energies of RHIC show that it is of the same order
as the hadronic one. This finding appears to contradict the expected dominance
of photon production from a quark-gluon plasma at an early stage of a heavy-ion
collision. A possible explanation of the strong azimuthal anisotropy of the
photons, given recently, is based on the presence of a large magnetic field in
the early phase of a collision. In this letter, we propose a method to
experimentally measure the degree to which a magnetic field in heavy-ion
collisions is responsible for the observed anisotropy of photon production. The
experimental test proposed in this letter may potentially change our
understanding of the non-equilibrium stage and possible thermalization in
heavy-ion collisions.",1208.5502v3
2012-09-01,Anisotropy and universality: Critical Binder cumulant of the two-dimensional Ising model,"We reanalyze transfer matrix and Monte Carlo results for the critical Binder
cumulant U* of an anisotropic two-dimensional Ising model on a square lattice
in a square geometry with periodic boundary conditions. Spins are coupled
between nearest neighboring sites and between next-nearest neighboring sites
along one of the lattice diagonals. We find that U* depends only on the
asymptotic critical long-distance features of the anisotropy, irrespective of
its realization through ferromagnetic or antiferromagnetic next-nearest
neighbor couplings. We modify an earlier renormalization-group calculation to
obtain a quantitative description of the anisotropy dependence of U*. Our
results support our recent claim towards the validity of universality for
critical phenomena in the presence of a weak anisotropy.",1209.0105v2
2012-10-05,Anisotropy of spin relaxation in metals,"The concept of anisotropy of spin relaxation in non-magnetic metals with
respect to the spin direction of the injected electrons relative to the crystal
orientation is introduced. The effect is related to an anisotropy of the
Elliott-Yafet parameter, arising from a modulation of the decomposition of the
spin-orbit Hamiltonian into spin-conserving and spin-flip terms as the spin
quantization axis is varied. This anisotropy, reaching gigantic values for
uniaxial transition-metals (e.g. 830% for hcp Hf) as density-functional
calculations show, is related to extended ""spin-flip hot areas"" on the Fermi
surface created by the proximity of extended sheets of the surface, or
""spin-flip hot loops"" at the Brillouin zone boundary, and has no theoretical
upper limit. Possible ways of measuring the effect as well as consequences in
application are briefly outlined.",1210.1801v1
2012-10-10,Distance-Redshift Relations in an Anisotropic Cosmological Model,"In this paper we study an anisotropic model generated from a particular
Bianchi type-III metric, which is a generalization of G\""odel's metric and an
exact solution of Einstein's field equations. We analyse type Ia supernova
data, namely the SDSS sample calibrated with the MLCS2k2 fitter, and we verify
in which ranges of distances and redshifts the anisotropy could be observed. We
also consider, in a joint analysis, the position of the first peak in the CMB
anisotropy spectrum, as well as current observational constraints on the Hubble
constant. We conclude that a small anisotropy is permitted by the data, and
that more accurate measurements of supernova distances above z = 2 might
indicate the existence of such anisotropy in the universe.",1210.2909v2
2012-10-24,Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3,"We report on domain formation and magnetization reversal in epitaxial Fe
films on ferroelectric BaTiO3 substrates with ferroelastic a-c stripe domains.
The Fe films exhibit biaxial magnetic anisotropy on top of c domains with
out-of-plane polarization, whereas the in-plane lattice elongation of a domains
induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The
strong modulation of magnetic anisotropy symmetry results in full imprinting of
the a-c domain pattern in the Fe films. Exchange and magnetostatic interactions
between neighboring magnetic stripes further influence magnetization reversal
and pattern formation within the a and c domains.",1210.6533v2
2012-11-02,Symmetry Conditions for Non-reciprocal Light Propagation in Magnetic Crystals,"Recent studies demonstrated the violation of reciprocity in optical processes
in low-symmetry magnetic crystals. In these crystals the speed of light can be
different for counter-propagating beams. Correspondingly, they can show strong
directional anisotropies such as direction dependent absorption also called
directional dichroism[S. Bord\'acs et al., Nat. Phys. 8, 734 (2012); M. Saito
et al., J. Phys. Soc. Jpn. 77, 013705 (2008)]. Based on symmetry
considerations, we identify the magnetic point groups of materials which can
host such directional anisotropies and also provide a list of possible
candidate materials to observe these phenomena. In most of these cases, the
symmetry of the crystal allows directional anisotropy not only for optical
processes but also for the propagation of beams of particles and scalar waves.
We also predict new types of directional optical anisotropies -- besides the
optical magnetoelectric effect and the magnetochiral dichroism investigated so
far -- and specify the magnetic point groups of crystals where they can emerge.",1211.0530v2
2012-11-27,Monte Carlo simulation of the effects of higher order anisotropy on the spin reorientation transition in the two dimensional Heisenberg model with long range interactions,"The strength of perpendicular anisotropy is known to drive the spin
reorientation in thin magnetic films. Here we consider the effect different
order anisotropies have on two phase transitions; the spin reorientation
transition and the orientational order transition. We find that the relative
magnitude of different order anisotropies can significantly enhance or suppress
the degree to which the system reorients. Specifically Monte Carlo simulations
reveal significant changes in the cone angle and planar magnetization. In order
to facilitate rapid computation we have developed a stream processing
technique, suitable for use on GPU systems, for computing the transition
probabilities in two dimensional systems with dipole interactions.",1211.6234v1
2012-12-13,Constraints on the origin of cosmic rays above $10^{18}$ eV from large scale anisotropy searches in data of the Pierre Auger Observatory,"A thorough search for large scale anisotropies in the distribution of arrival
directions of cosmic rays detected above $10^{18}$ eV at the Pierre Auger
Observatory is reported. For the first time, these large scale anisotropy
searches are performed as a function of both the right ascension and the
declination and expressed in terms of dipole and quadrupole moments. Within the
systematic uncertainties, no significant deviation from isotropy is revealed.
Upper limits on dipole and quadrupole amplitudes are derived under the
hypothesis that any cosmic ray anisotropy is dominated by such moments in this
energy range. These upper limits provide constraints on the production of
cosmic rays above $10^{18}$ eV, since they allow us to challenge an origin from
stationary galactic sources densely distributed in the galactic disk and
emitting predominantly light particles in all directions.",1212.3083v1
2012-12-24,Excited states of the quasi-one-dimensional hexagonal quantum antiferromagnets,"We investigate the excited states of the quasi-one-dimensional quantum
antiferromagnets on hexagonal lattices, including the longitudinal modes based
on the magnon-density waves. A model Hamiltonian with a uniaxial single-ion
anisotropy is first studied by a spin-wave theory based on the one-boson
method; the ground state thus obtained is employed for the study of the
longitudinal modes. The full energy spectra of both the transverse modes (i.e.,
magnons) and the longitudinal modes are obtained as functions of the
nearest-neighbor coupling and the anisotropy constants. We have found two
longitudinal modes due to the non-collinear nature of the triangular
antiferromagnetic order, similar to that of the phenomenological field theory
approach by Affleck. The excitation energy gaps due to the anisotropy and the
energy gaps of the longitudinal modes without anisotropy are then investigated.
We then compare our results for the longitudinal energy gaps at the magnetic
wavevectors with the experimental results for several antiferromagnetic
compounds with both integer and non-integer spin quantum numbers, and we find
good agreement after the higher-order contributions are included in our
calculations.",1212.5924v3
2012-12-28,Study of the magnetic anisotropy in a planar model of the La2CuO4,"We study the anisotropy energy in a planar model for the Cu-O layers of the
La2CuO4 investigated in previous works. The Tight-Binding (TB) potential of the
model was extended out of the validity region with the purpose of incorporate
it in the potential. Next, the spin-orbit operator was considered in the
Hartree Fock solution of the full HF problem. It follows that in spite of the
fact that the extended potential possesses the square symmetry of the
crystalline structure, the anisotropy energy vanishes in its purely 2D
formulation. The result indicates that for the prediction by the model of the
observed non vanishing magnetic anisotropy at zero doping and temperature in
La2CuO4, its formulation requires of a 3D representation of its Wannier
orbitals and the use of d like orbitals. The consideration of more realistic 3D
character of the model, by including multiple CuO planes, also could be
important due to the argued absence of long range order in 2D.",1212.6460v1
2013-01-23,The investigations of anisotropy in orientations of galaxies,"In 1994 Parnovsky, Karachentsev and Karachentseva suggested a modified method
for investigation of the orientations of galaxies. Using this method they
analyzed galaxies from the UGC and ESO catalogues, as well as from their's own
catalogue inclusive of flat, edge-on galaxies. They found statistically
significant anisotropy in the galaxies orientations'. In 1995 Flin suggested
that this anisotropy has to be specific to LOcal Supercluster (LSC) In the
present paper, using the method proposed by Parnovsky, Karachentsev and
Karachentseva in 1994, we analyzed orientation of galaxies in the sample of
galaxies belonging to LSC founding only a weak anisotropy. The relation of this
method to Hawley and Peebles (1975) method of the investigation of the
orientation of galaxies was discussed as well.",1301.5477v1
2013-02-22,Constraints on spacetime anisotropy and Lorentz violation from the GRAAL experiment,"The GRAAL experiment could constrain the variations of the speed of light.
The anisotropy of the speed of light may imply that the spacetime is
anisotropic. Finsler geometry is a reasonable candidate to deal with the
spacetime anisotropy. In this paper, the Lorentz invariance violation (LIV) of
the photon sector is investigated in the locally Minkowski spacetime. The
locally Minkowski spacetime is a class of flat Finsler spacetime and refers a
metric with the anisotropic departure from the Minkowski one. The LIV matrices
used to fit the experimental data are represented in terms of these metric
deviations. The GRAAL experiment constrains the spacetime anisotropy to be less
than \(10^{-14}\). In addition, we find that the simplest Finslerian photon
sector could be viewed as a geometric representation of the photon sector in
the minimal standard model extension (SME).",1302.5486v2
2013-03-14,Thermal Stability and Electrical Control of Magnetization of Heusler/Oxide Interface and Non-collinear Spin Transport of Its Junction,"Towards next-generation spintronics devices, such as computer memories and
logic chips, it is necessary to satisfy high thermal stability, low-power
consumption and high spin-polarization simultaneously. Here, from
first-principles, we investigate thermal stability (both structure and
magnetization) and the electric field control of magnetic anisotropy on Co2FeAl
(CFA)/MgO. A phase diagram of structural thermal stability of the CFA/MgO
interface is illustrated. An interfacial perpendicular-anisotropy, coming from
the Fe-O orbital hybridization, provides high magnetic thermal stability and a
low stray field. We find an electric-field-induced giant modification of such
perpendicular-anisotropy via a great magnetoelectric effect (the anisotropy
energy coefficient beta~10-7 erg/V cm). Our spin electronic-structure and
non-collinear transport calculations indicate high spin-polarized interfacial
states and good magnetoresistance properties of CFA/MgO/CFA perpendicular
magnetic tunnel junctions.",1303.3473v2
2013-03-25,Field-angle-resolved anisotropy in superconducting CeCoIn5 using realistic Fermi surfaces,"We compute the field-angle-resolved specific heat and thermal conductivity
using realistic model band structure for the heavy-fermion superconductor
CeCoIn5 to identify the gap structure and location of nodes. We use a two-band
tight-binding parametrization of the band dispersion as input for the
self-consistent calculations in the quasiclassical formulation of the
superconductivity. Systematic analysis shows that modest in-plane anisotropy in
the density of states and Fermi velocity in tetragonal crystals significantly
affects the fourfold oscillations in thermal quantities, when the magnetic
field is rotated in the basal plane. The Fermi surface anisotropy substantially
shifts the location of the lines in the H-T plane, where the oscillations
change sign compared to quasicylindrical model calculations. In particular, at
high fields, the anisotropy and sign reversal are found even for isotropic
gaps. Our findings imply that a simultaneous analysis of the specific heat and
thermal conductivity, with an emphasis on the low energy sector, is needed to
restrict potential pairing scenarios in multiband superconductors. We discuss
the impact of our results on recent measurements of the Ce-115 family, namely
CeTIn5 with T=Co,Rh,Ir.",1303.6258v1
2013-03-29,Anisotropic Non-Gaussianity from a Two-Form Field,"We study an inflationary scenario with a two-form field to which an inflaton
couples non-trivially. First, we show that anisotropic inflation can be
realized as an attractor solution and that the two-form hair remains during
inflation. A statistical anisotropy can be developed because of a cumulative
anisotropic interaction induced by the background two-form field. The power
spectrum of curvature perturbations has a prolate-type anisotropy, in contrast
to the vector models having an oblate-type anisotropy. We also evaluate the
bispectrum and trispectrum of curvature perturbations by employing the in-in
formalism based on the interacting Hamiltonians. We find that the non-linear
estimators $f_{NL}$ and $\tau_{NL}$ are correlated with the amplitude $g_*$ of
the statistical anisotropy in the power spectrum. Unlike the vector models,
both $f_{NL}$ and $\tau_{NL}$ vanish in the squeezed limit. However, the
estimator $f_{NL}$ can reach the order of 10 in the equilateral and enfolded
limits. These results are consistent with the latest bounds on $f_{NL}$
constrained by Planck.",1303.7340v2
2013-04-11,Theory of magnetic small-angle neutron scattering of two-phase ferromagnets,"Based on micromagnetic theory we have derived analytical expressions for the
magnetic small-angle neutron scattering (SANS) cross section of a two-phase
particle-matrix-type ferromagnet. The approach---valid close to magnetic
saturation---provides access to several features of the spin structure such as
perturbing magnetic anisotropy and magnetostatic fields. Depending on the
applied magnetic field and on the magnitude $H_p$ of the magnetic anisotropy
field relative to the magnitude $\Delta M$ of the jump in the longitudinal
magnetization at the particle-matrix interface, we observe a variety of angular
anisotropies in the magnetic SANS cross section. In particular, the model
explains the ""clover-leaf""-shaped angular anisotropy which was previously
observed for several nanostructured magnetic materials, and it provides access
to the magnetic interaction parameters such as the average exchange-stiffness
constant. It is also shown that the ratio $H_p / \Delta M$ decisively
determines the asymptotic power-law exponent and the range of spin-misalignment
correlations.",1304.3214v1
2013-04-10,Environment-induced anisotropy and the sensitivity of the radical pair mechanism in the avian compass,"Several experiments over the years have shown that the Earth's magnetic field
is essential for orientation in birds migration. The most promising explanation
for this orientation is the photo-stimulated radical pair (RP) mechanism. In
order to define a reference frame for the orientation task radicals must have
an intrinsic anisotropy. We show that this kind of anisotropy, and consequently
the entanglement in the model, are not necessary for the proper functioning of
the compass. Classically correlated initial conditions for the RP, subjected to
a fast decoherence process, are able to provide the anisotropy required. Even a
dephasing environment can provide the necessary frame for the compass to work,
and also implies fast decay of any quantum correlation in the system without
damaging the orientation ability. This fact significantly expands the range of
applicability of the RP mechanism providing more elements for experimental
search.",1304.3452v2
2013-04-19,Energetic Particle Diffusion In Critically Balanced Turbulence,"Observations and modelling suggest that the fluctuations in magnetised
plasmas exhibit scale-dependent anisotropy, with more energy in the
fluctuations perpendicular to the mean magnetic field than in the parallel
fluctuations and the anisotropy increasing at smaller scales. The
scale-dependence of the anisotropy has not been studied in full-orbit
simulations of particle transport in turbulent plasmas so far. In this paper,
we construct a model of critically balanced turbulence, as suggested by
\cite{GoSr1995}, and calculate energetic particle spatial diffusion
coefficients using full-orbit simulations. The model uses an enveloped
turbulence approach, where each 2-dimensional wave mode with wavenumber
$k_\perp$ is packed into envelopes of length $L$ following the critical balance
condition, $L\propto k_\perp^{-2/3}$, with the wave mode parameters changing
between envelopes. Using full-orbit particle simulations, we find that both the
parallel and perpendicular diffusion coefficients increase by a factor 2,
compared to previous models with scale-independent anisotropy.",1304.5399v1
2013-05-08,Magnetic Exchange Coupling and Anisotropy of 3d Transition-Metal Nanowire on the Surface of Graphyne Sheet,"Using density functional theory plus Hubbard-U (DFT+U) approach, we find that
quasi one-dementation(1D) 3d transition metal(TM) zigzag nanowire can be
constructed by TM adsorbed on the surface of graphyne sheet. The results show
that the TM exchange coupling of the zigzag nanowire mediated by sp hybridized
carbon atoms gives rise to long range ferromagnetic order except for Cr with
anti-ferromagnetic order. The magnetic exchange interaction of TM chains
follows like-Zener's p_z-d exchange mechanism: the coexistence of out-of plane
p_z-d and in-plane p_x-y-d exchange. Finally, by including spin-orbit
interactions within spin-DFT, we calculate the magnetic anisotropy energy of
the TM chain on graphyne. We find that the Fe and Co chains show considerable
magnetic anisotropy energy (MAE) and orbital magnetic moment. The easy axis of
V, Cr, Mn and Fe chains is perpendicular to the surface, whereas the easy axis
of Co lies in the surface. Moreover, only V chain shows relatively larger
in-plane anisotropy. Our results open a new route to realize the applications
of graphyne in spintronics.",1305.1791v2
2013-05-09,Review of Anisotropic Terahertz Material Response,"Anisotropy is ubiquitous in solids and enhanced in low-dimensional materials.
In response to an electromagnetic wave, anisotropic absorptive and refractive
properties result in dichroic and birefringent optical phenomena both in the
linear and nonlinear optics regimes. Such material properties have led to a
diverse array of useful polarization components in the visible and
near-infrared, but mature technology is non-existent in the terahertz (THz).
Here, we review several novel types of anisotropic material responses observed
in the THz frequency range, including both linear and circular anisotropy,
which have long-term implications for the development of THz polarization
optics. We start with the extreme linear anisotropy of macroscopically aligned
carbon nanotubes, arising from their intrinsically anisotropic dynamic
conductivity. Magnetically induced anisotropy will then be reviewed, including
the giant Faraday effects observed in semiconductors, semimetals, and
two-dimensional electron systems.",1305.1987v1
2013-05-10,Effects of spacetime anisotropy on the galaxy rotation curves,"The observations on galaxy rotation curves show significant discrepancies
from the Newtonian theory. This issue could be explained by the effect of the
anisotropy of the spacetime. Conversely, the spacetime anisotropy could also be
constrained by the galaxy rotation curves. Finsler geometry is a kind of
intrinsically anisotropic geometry. In this paper, we study the effect of the
spacetime anisotropy at the galactic scales in the Finsler spacetime. It is
found that the Finslerian model has close relations with the Milgrom's MOND. By
performing the best-fit procedure to the galaxy rotation curves, we find that
the anisotropic effects of the spacetime become significant when the Newtonian
acceleration \(GM/r^2\) is smaller than the critical acceleration \(a_0\).
Interestingly, the critical acceleration \(a_0\), although varies between
different galaxies, is in the order of magnitude \(cH_0/2\pi\sim 10^{-10}
\rm{m\,\, s^{-2}}\).",1305.2314v2
2013-06-05,Constraints on Spatial Variations in the Fine-Structure constant from Planck,"We use the Cosmic Microwave Background (CMB) anisotropy data from Planck to
constrain the spatial fluctuations of the fine-structure constant \alpha.
Through Thompson scattering of CMB photons, spatial anisotropies of \alpha lead
to higher-order correlations in the CMB anisotropies. We use a quadratic
estimator based on the four-point correlation function of the CMB temperature
anisotropy to extract the angular power spectrum of the spatial variation of
the fine-structure constant projected along the line of sight at the last
scattering surface. At tens of degree angular scales and above, we constrain
the rms fluctuations of the fine structure constant to be \delta
\alpha/\alpha_0= (1.34 +/- 5.82) x 10^-2 at the 95% confidence level with
respect to the standard value \alpha_0. We find no evidence for a spatially
varying \alpha at a redshift of 10^3.",1306.1232v1
2013-06-20,Review of the anisotropy working group at UHECR-2012,"The study of ultra-high energy cosmic rays (UHECRs) has recently experienced
a jump in statistics as well as improved instrumentation. This has allowed a
better sensitivity in searching for anisotropies in the arrival directions of
cosmic rays. In this written version of the presentation given by the
inter-collaborative ""Anisotropy Working Group"" at the International Symposium
on Future Directions in UHECR physics at CERN in February 2012, we report on
the current status for anisotropy searches in the arrival directions of UHECRs.",1306.4998v1
2013-06-28,Velocity Anisotropy and Shape Bias in the Caustic Technique,"We use the Millennium Simulation to quantify the statistical accuracy and
precision of the escape velocity technique for measuring cluster-sized halo
masses at z~0.1. We show that in 3D, one can measure nearly unbiased (<4%) halo
masses (>1.5x10^14 M_solar h^-1) with 10-15% scatter. Line-of-sight projection
effects increase the scatter to ~25%, where we include the known velocity
anisotropies. The classical ""caustic"" technique incorporates a calibration
factor which is determined from N-body simulations. We derive and test a new
implementation which eliminates the need for calibration and utilizes only the
observables: the galaxy velocities with respect to the cluster mean v, the
projected positions r_p, an estimate of the Navarro-Frenk-White (NFW) density
concentration and an estimate of the velocity anisotropies, beta. We find that
differences between the potential and density NFW concentrations induce a 10%
bias in the caustic masses. We also find that large (100%) systematic errors in
the observed ensemble average velocity anisotropies and concentrations
translate to small (5%-10%) biases in the inferred masses.",1307.0018v1
2013-07-09,Effects of anisotropy in a nonlinear crystal for squeezed vacuum generation,"Squeezed vacuum (SV) can be obtained by an optical parametric amplifier (OPA)
with the quantum vacuum state at the input. We are interested in a degenerate
type-I OPA based on parametric down-conversion (PDC) where due to phase
matching requirements, an extraordinary polarized pump must impinge onto a
birefringent crystal with a large \chi(2) nonlinearity. As a consequence of the
optical anisotropy of the medium, the direction of propagation of the pump
wavevector does not coincide with the direction of propagation of its energy,
an effect known as transverse walk-off. For certain pump sizes and crystal
lengths, the transverse walk-off has a strong influence on the spatial spectrum
of the generated radiation, which in turn affects the outcome of any experiment
in which this radiation is employed. In this work we propose a method that
reduces the distortions of the two-photon amplitude (TPA) of the states
considered, by using at least two consecutive crystals instead of one. We show
that after anisotropy compensation the TPA becomes symmetric, allowing for a
simple Schmidt expansion, a procedure that in practice requires states that
come from experimental systems free of anisotropy effects.",1307.2405v1
2013-07-09,Temperature dependence of the switching field distributions in all-perpendicular spin-valve nanopillars,"We present temperature dependent switching measurements of the Co/Ni
multilayered free element of 75 nm diameter spin-valve nanopillars. Angular
dependent hysteresis measurements as well as switching field measurements taken
at low temperature are in agreement with a model of thermal activation over a
perpendicular anisotropy barrier. However, the statistics of switching (mean
switching field and switching variance) from 20 K up to 400 K are in
disagreement with a N\'{e}el-Brown model that assumes a temperature independent
barrier height and anisotropy field. We introduce a modified N\'{e}el-Brown
model thats fit the experimental data in which we take a $T^{3/2}$ dependence
to the barrier height and the anisotropy field due to the temperature dependent
magnetization and anisotropy energy.",1307.2496v1
2013-07-10,Cherenkov sound on a surface of a topological insulator,"Topological insulators are currently of considerable interest due to peculiar
electronic properties originating from helical states on their surfaces. Here
we demonstrate that the sound excited by helical particles on surfaces of
topological insulators has several exotic properties fundamentally different
from sound propagating in non-helical or even isotropic helical systems.
Specifically, the sound may have strictly forward propagation absent for
isotropic helical states. Its dependence on the anisotropy of the realistic
surface-states is of distinguished behavior which may be used as an alternative
experimental tool to measure the anisotropy strength. Fascinating from the
fundamental point of view backward, or anomalous, Cherenkov sound is excited
above the critical angle $\pi/2$ when the anisotropy exceeds a critical value.
Strikingly, at strong anisotropy the sound localizes into a few forward and
backward beams propagating along specific directions.",1307.2777v2
2013-08-04,Anisotropy studies with the Pierre Auger Observatory,"We report recent results from the Pierre Auger Observatory about the study of
the anisotropy in the arrival directions of ultra-high energy cosmic rays. We
present the results of the search for a dipolar anisotropy at the EeV energy
scale. Measurements of the phase and the amplitude of the first harmonic
modulation in the right-ascension distribution are discussed. For cosmic rays
with energies above 55 EeV, we present an update of the search for correlations
between their arrival directions and the positions of active galactic nuclei
from the Veron-Cetty and Veron catalog. We also discuss the results of
correlation analyses applied to other populations of extragalactic objects.
Finally we present the search for anisotropies in the data without the usage of
astronomical catalogues.",1308.0820v1
2013-08-15,Magnetic fields from inflation: The CMB temperature anisotropies,"The cosmic microwave background (CMB) temperature anisotropies from
primordial magnetic fields are studied. In addition to the known passive and
the compensated mode we discuss an inflationary magnetic mode in the curvature
perturbation, present when magnetic fields are generated during inflation. This
mode is absent if the generation mechanism is causal, e.g. a phase transition.
We compute and discuss the effect of this mode on the observed CMB anisotropy
spectrum, in comparison with the passive and compensated ones. We find that it
dominates the CMB anisotropy, and consequently leads to stronger constraints on
the amplitude $B_{1\,{\rm Mpc}}$ and spectral index $n_B$ of the magnetic field
than what usually found in CMB analyses from the compensated mode. This happens
in particular for spectral indexes $n_B>-3$: the inflationary magnetic mode is
always scale invariant, therefore through this mode even a magnetic field with
a spectrum which is not scale invariant can leave a detectable signal in the
CMB at large scales.",1308.3348v2
2013-08-18,Spin excitation anisotropy as a probe of orbital ordering in the paramagnetic tetragonal phase of superconducting BaFe1.904Ni0.096As2,"We use polarized neutron scattering to demonstrate that in-plane spin
excitations in electron doped superconducting BaFe1.904Ni0.096As2 (Tc=19.8 K)
change from isotropic to anisotropic in the tetragonal phase well above the
antiferromagnetic (AF) ordering and tetragonal-to-orthorhombic lattice
distortion temperatures (Tn=Ts=33 K) without an uniaxial pressure. While the
anisotropic spin excitations are not sensitive to the AF order and
tetragonal-to-orthorhombic lattice distortion, superconductivity induces
further anisotropy for spin excitations along the [1,1,0] and [1,-1,0]
directions. These results indicate that the spin excitation anisotropy is a
probe of the electronic anisotropy or orbital ordering in the tetragonal phase
of iron pnictides.",1308.3858v1
2013-09-16,Optical Anisotropy in Bismuth Titanate: An Experimental and Theoretical Study,"We report experimental and theoretical investigation of anisotropy in optical
properties and their origin in the ferroelectric and paraelectric phases of
bismuth titanate. Room temperature ellipsometric measurements performed on
pulsed laser deposited bismuth titanate thin films of different orientations
show anisotropy in the dielectric and optical constants, Subsequent
first-principles calculations performed on the ground state structures of
ferroelectric and high temperature paraelectric phases of bismuth titanate show
that the material demonstrates anisotropic optical behavior in both
ferroelectric and paraelectric phases. We further show that O 2p to Ti 3d
transition is the primary origin of optical activity of the material while
optical anisotropy results from the asymmetrically oriented Ti-O bonds in TiO6
octehdra in the unit cell.",1309.4056v1
2013-10-04,In-plane spin excitation anisotropy in the paramagnetic phase of NaFeAs,"We use unpolarized and polarized inelastic neutron scattering to study
low-energy spin excitations in NaFeAs, which exhibits a
tetragonal-to-orthorhombic lattice distortion at $T_s\approx 58$ K followed by
a collinear antiferromagnetic (AF) order below $T_N\approx 45$ K. In the AF
ordered state ($T<T_N$), spin waves are entirely c-axis polarized below
$\sim$10 meV, exhibiting a gap of $\sim4$ meV at the AF zone center and
disperse to $\sim$7 meV near the c-axis AF zone boundary. On warming to the
paramagnetic state with orthorhombic lattice distortion ($T_N<T<T_s$), spin
excitations become anisotropic within the FeAs plane. Upon further warming to
the paramagnetic tetragonal state ($T>T_s$), spin excitations become more
isotropic. Since similar magnetic anisotropy is also observed in the
paramagnetic tetragonal phase of superconducting
BaFe$_{1.904}$Ni$_{0.096}$As$_2$, our results suggest that the spin excitation
anisotropy in superconducting iron pnictides originates from similar anisotropy
already present in their parent compounds.",1310.1143v1
2013-10-23,Anisotropy parameters in two-colour two-photon above threshold ionization,"We employ the time-dependent R-Matrix (TDRM) method to calculate anisotropy
parameters for positive and negative sidebands of selected harmonics generated
by two-color two-photon above threshold ionization of argon. We consider odd
harmonics of an 800 nm field ranging from the 13th to 19th harmonic, overlapped
by a fundamental 800 nm IR field. The anisotropy parameters obtained using the
TDRM method are compared with those obtained using a second order perturbation
theory with a model potential (MP) approach and a soft photon approximation
(SPA) approach. Where available, a comparison is also made to published
experimental results. All three theoretical approaches provide similar values
for anisotropy parameters. The TDRM approach obtains values that are closest to
published experimental values. At high photon energies, the differences between
each of the theoretical methods become less significant.",1310.6190v1
2013-11-05,Effect of disorder on the resistivity anisotropy near the electronic nematic phase transition in pure and electron-doped BaFe$_2$As$_2$,"We show that the strain-induced resistivity anisotropy in the tetragonal
state of the representative underdoped Fe-arsenides BaFe$_2$As$_2$,
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ is
independent of disorder over a wide range of defect and impurity
concentrations. This result demonstrates that the anisotropy in the in-plane
resistivity in the paramagnetic orthorhombic state of this material is not due
to elastic scattering from anisotropic defects, and is most easily understood
in terms of an intrinsic anisotropy in the electronic structure.",1311.0933v2
2013-11-22,Full-Heusler Co2FeSi alloy thin films with perpendicular magnetic anisotropy induced by MgO-interface,"The authors demonstrated that L21-ordered full-Heusler Co2FeSi (CFS) alloy
film with thickness of 100 nm were formed by facing targets sputtering (FTS)
method at a substrate temperature TS = 300 deg C. Degrees of L21- and B2- order
for the film were 0.37, and 0.96, respectively. Furthermore, full-Heusler CFS
alloy thin films with perpendicular magnetic anisotropy (PMA) induced by
MgO-interface magnetic anisotropy were successfully formed by the FTS method.
The CFS/MgO stacking layers showed PMA when dCFS was 0.6 nm <= dCFS <= 1.0 nm.
The PMA in these structures resulted from the CFS/MgO interfacial perpendicular
magnetic anisotropy.",1311.5670v2
2013-12-03,Depth dependent magnetization profiles of hybrid exchange springs,"We report on the magnetization depth profile of a hybrid exchange spring
system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to
a CoFeB thin film with in-plane anisotropy. The competition between these two
orthogonal anisotropies promotes a strong depth dependence of the magnetization
orientation. The angle of the magnetization vector is sensitive both to the
strength of the individual anisotropies and to the local exchange constant, and
is thus tunable by changing the thickness of the CoFeB layer and by
substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic
depth profiles are directly probed by element specific x-ray magnetic circular
dichroism (XMCD) of the Co, Fe, and Ni layers located at different average
depths. The experimental results are corroborated by micromagnetic simulations.",1312.0878v1
2013-12-04,Rashba Spin-Orbit Anisotropy and the Electric Field Control of Magnetism,"The control of the magnetism of ultra-thin ferromagnetic layers using an
electric field rather than a current, if large enough, would lead to many
technologically important applications. To date, while it is usually assumed
the changes in the magnetic anisotropy, leading to such a control, arises from
surface charge doping of the magnetic layer, a number of key experiments cannot
be understood within such a scenario. Much studied is the fact that, for
non-magnetic metals or semi-conductors, a large surface electric field gives
rise to a Rashba spin-orbit coupling which leads to a spin-splitting of the
conduction electrons. For a magnet, this splitting is modified by the exchange
field resulting in a large magnetic anisotropy energy via the
Dzyaloshinskii-Moriya mechanism. This different, yet traditional, path to an
electrically induced anisotropy energy can explain the electric field,
thickness, and material dependence reported in many experiments.",1312.1021v1
2013-12-04,Anisotropies of ultra-high energy cosmic rays diffusing from extragalactic sources,"We obtain the dipolar anisotropies in the arrival directions of ultra-high
energy cosmic rays diffusing from nearby extragalactic sources. We discuss both
the energy regime of spatial diffusion and the quasi-rectilinear one leading to
just angular diffusion at higher energies. We obtain analytic results for the
anisotropies from a single source which are validated using two different
numerical simulations. For a scenario with a few sources in the local
supercluster (with the closest source at a typical distance of few to tens of
Mpc), we discuss the possible transition between the case in which the
anisotropies are dominated by a few sources at energies below few EeV towards
the regime in which many sources contribute at higher energies. The effect of a
non-isotropic source distribution is also discussed, showing that it can
significantly affect the observed dipole.",1312.1366v1
2013-12-05,Hysteresis behavior of the anisotropic quantum Heisenberg model driven by periodic magnetic field,"Dynamic behavior of a quantum Heisenberg ferromagnet in the presence of a
periodically oscillating magnetic field has been analyzed by means of the
effective field theory with two spin cluster. The dynamic equation of motion
has been constructed with the help of a Glauber type stochastic process and
solved for a simple cubic lattice. After the phase diagrams given, the behavior
of the hysteresis loop area, coercive field and remanent magnetization with the
anisotropy in the exchange interaction has been investigated in detail.
Especially, by comparing of the magnitudes of the hysteresis loop area in the
high anisotropy limit (i.e. Ising model) and low anisotropy limit (i.e.
isotropic Heisenberg model), detailed description of the hysteresis loop area
with the anisotropy in the exchange interaction given. Some interesting
features have been obtained about this behavior as well as in phase diagrams
such as tricritical points.",1312.1647v1
2013-12-13,Combined Flux and Anisotropy Searches Improve Sensitivity to Gamma Rays from Dark Matter,"Searches for dark matter annihilation signals in the diffuse gamma-ray
background are promising. We present the first comprehensive study utilizing
both flux and anisotropy, using the example of a spectral line signal. Besides
improving sensitivity, a combined analysis will help separately determine the
particle properties of dark matter and the cosmological aspects of its clumping
into halo substructure. The significance of a signal in a shot-noise-dominated
anisotropy analysis increases linearly with time $t$, as opposed to $\sqrt{t}$
for a flux analysis, so a flux hint might be confirmed with an anisotropy
signal. A first combined line search with Fermi-LAT would provide powerful new
sensitivity; one with the proposed GAMMA-400 would be dramatically better.",1312.3945v1
2013-12-28,Heavy Quark Diffusion in Strongly Coupled Anisotropic Plasmas,"We study the Langevin diffusion of a relativistic heavy quark in anisotropic
strongly coupled theories in the local limit. Firstly, we use the axion
space-dependent deformed anisotropic N=4 sYM, where the geometry anisotropy is
always prolate, while the pressure anisotropy may be prolate or oblate. For
motion along the anisotropic direction we find that the effective temperature
for the quark can be larger than the heat bath temperature, in contrast to what
happens in the isotropic theory. The longitudinal and transverse Langevin
diffusion coefficients depend strongly on the anisotropy, the direction of
motion and the transverse direction considered. We analyze the anisotropy
effects to the coefficients and compare them to each other and to them of the
isotropic theory. To examine the dependence of the coefficients on the type of
the geometry, we consider another bottom-up anisotropic model. Changing the
geometry from prolate to oblate, certain diffusion coefficients interchange
their behaviors. In both anisotropic backgrounds we find cases that the
transverse diffusion coefficient is larger than the longitudinal, but we find
no negative excess noise.",1312.7474v1
2014-01-04,Anisotropy of Conductivity in Bilayer Graphene with Relatively Shifted Layers,"A transformation of the band structure in bilayer graphene (BLG) with
relatively shifted layers has been studied in the framework of the
tight-binding model. BLG is demonstrated to remain a zero-gap material in the
whole range of experimentally attainable shifts, but the positions of contact
points between the conduction and valence bands depend substantially on the
shift direction. The shift results in a considerable anisotropy of the band
spectrum, which is, in turn, responsible for a substantial (10-20%) anisotropy
of the conductivity in BLG. A possibility of using this anisotropy in
high-sensitive sensors of a mechanical tension and for the generation of a
purely valley current in multivalley anisotropic BLG in the case where both the
average spin and the average current of electrons are equal to zero is
discussed.",1401.0820v1
2013-12-10,Anisotropy mapping in rat brains using Intermolecular Multiple Quantum Coherence Effects,"This document reports an unconventional and rapidly developing approach to
magnetic resonance imaging (MRI) using intermolecular multiple-quantum
coherences (iMQCs). Rat brain images are acquired using iMQCs. We detect iMQCs
between spins that are 10 {\mu}m to 500 {\mu}m apart. The interaction between
spins is dependent on different directions. We can choose the directions on
physical Z, Y and X axis by choosing correlation gradients along those
directions. As an important application, iMQCs can be used for anisotropy
mapping. In the rat brains, we investigate tissue microstructure. We simulated
images expected from rat brains without microstructure. We compare those with
experimental results to prove that the dipolar field from the overall shape
only has small contributions to the experimental iMQC signal. Because of the
underlying low signal to noise ratio (SNR) in iMQCs, this anisotropy mapping
method still has comparatively large potentials to grow. The ultimate goal of
my project is to develop creative and effective methods of tissue
microstructure anisotropy mapping. Recently we found that combining phase data
of iMQCs images with phase data of modified-crazed images is very promising to
construct microstructure maps. Some information and initial results are shown
in this document.",1401.3772v1
2014-01-21,Analysing the impact of anisotropy pressure on tokamak equilibria,"Neutral beam injection or ion cyclotron resonance heating induces pressure
anisotropy. The axisymmetric plasma equilibrium code HELENA has been upgraded
to include anisotropy and toroidal flow. With both analytical and numerical
methods, we have studied the determinant factors in anisotropic equilibria and
their impact on flux surfaces, magnetic axis shift, the displacement of
pressures and density contours from flux surface. With $p_\parallel/p_\perp
\approx 1.5$, $p_\perp$ can vary 20% on $s=0.5$ flux surface, in a MAST like
equilibrium. We have also re-evaluated the widely applied approximation to
anisotropy in which $p^*=(p_\parallel + p_\perp)/2$, the average of parallel
and perpendicular pressure, is taken as the approximate isotropic pressure. We
find the reconstructions of the same MAST discharge with $p_\parallel/p_\perp
\approx 1.25$, using isotropic and anisotropic model respectively, to have a 3%
difference in toroidal field but a 66% difference in poloidal current.",1401.5520v2
2014-01-22,Sensitivity of orbiting JEM-EUSO to large-scale cosmic-ray anisotropies,"The two main advantages of space-based observation of extreme-energy
($\gtrsim 10^{19}$~eV) cosmic-rays (EECRs) over ground-based observatories are
the increased field of view, and the all-sky coverage with nearly uniform
systematics of an orbiting observatory. The former guarantees increased
statistics, whereas the latter enables a partitioning of the sky into spherical
harmonics. We have begun an investigation, using the spherical harmonic
technique, of the reach of \J\ into potential anisotropies in the
extreme-energy cosmic-ray sky-map. The technique is explained here, and
simulations are presented. The discovery of anisotropies would help to identify
the long-sought origin of EECRs.",1401.5757v1
2014-01-31,Phase diagram of the Hubbard model on the anisotropic triangular lattice,"We investigate the Hubbard model on the anisotropic triangular lattice as a
suggested effective description of the Mott phase in various triangular organic
compounds. Employing the variational cluster approximation and the ladder
dual-fermion approach as complementary methods to adequately treat the
zero-temperature and the finite-temperature domains, we obtain a consistent
picture of the phase diagram as a function of anisotropy and interaction
strength. The metal-insulator transition substantially depends on the
anisotropy, and so does the nature of magnetism and the emergence of a
nonmagnetic insulating phase. We further find that geometric anisotropy
significantly influences the thermodynamics of the system. For increased
frustration induced by anisotropy, the entropy of the system increases with
interaction strength, opening the possibility of adiabatically cooling a
frustrated system by an enhancement of electronic correlations.",1401.8198v3
2014-02-04,Self-gravitating Newtonian models of fermions with anisotropy and cutoff energy in their distribution function,"Systems of self-gravitating fermions constitute a topic of great interest in
astrophysics, due to the wide field of applications. In this paper, we consider
the gravitational equilibrium of spherically symmetric Newtonian models of
collisionless semidegenerate fermions. We construct numerical solutions by
taking into account the effects of the anisotropy in the distribution function
and considering the prevalence of tangential velocity. In this way, our models
generalize the solutions obtained for isotropic Fermi-Dirac statistics. We also
extend the analysis to equilibrium configurations in the classical regime and
in the fully degenerate limit, recovering, for different levels of anisotropy,
hollow equilibrium configurations obtained in Maxwellian regime. Moreover, in
the limit of full degeneracy, we find a direct expression relating the
anisotropy with the mass of the particles composing the system.",1402.0756v5
2014-02-12,Magnetic anisotropy of thin sputtered MgB2 films on MgO substrates in high magnetic fields,"We investigated the magnetic anisotropy ratio of thin sputtered
polycrystalline MgB2 films on MgO substrates. Using high magnetic field
measurements, we estimated an anisotropy ratio of 1.35 for T=0 K with an upper
critical field of 31.74 T in the parallel case and 23.5 T in the perpendicular
case. Direct measurements of a magnetic-field sweep at 4.2 K show a linear
behavior, confirmed by a linear fit for magnetic fields perpendicular to the
film plane. Furthermore, we observed a change of up to 12% of the anisotropy
ratio in dependence of the film thickness.",1402.2901v1
2014-03-21,Anisotropy enhancement of the Casimir-Polder force between a nanoparticle and graphene,"We derive the analytical expressions for the thermal Casimir-Polder energy
and force between a spheroidal nanoparticle above a semi-infinite material and
a graphene covered interface. We analyze in detail the Casimir-Polder force
between a gold nanoparticle and a single sheet of pristine graphene focusing on
the impact of anisotropy. We show that the effect of anisotropy, i.e. the shape
and orientation of the spheroidal nanoparticle, has a much larger influence on
the force than the tunability of graphene. The effect of tuning and anisotropy
both add up such that we observe a force which is between 20-50% of that in the
ideal metal case which is much larger than the results found for the Casimir
force between a metal halfspace and a layer of graphene.",1403.5476v2
2014-03-28,Magnetic and structural properties of Co2FeAl thin films grown on Si substrate,"The correlation between magnetic and structural properties of Co_{2} FeAl
(CFA) thin films of different thickness (10 nm<d< 100 nm) grown at room
temperature on MgO-buffered Si/SiO2 substrates and annealed at
600\lyxmathsym{\textdegree}C has been studied. XRD measurements revealed an
(011) out-of-plane texture growth of the films. The deduced lattice parameter
increases with the film thickness. Moreover, pole figures showed no in-plane
preferential growth orientation. The magneto-optical Kerr effect hysteresis
loops showed the presence of a weak in-plane uniaxial anisotropy with a random
easy axis direction. The coercive field measured with an applied field along
the easy axis direction and the uniaxial anisotropy field increase linearly
with the inverse of the CFA thickness. The microstrip line ferromagnetic
resonance measurements for in-plane and perpendicular applied magnetic fields
revealed that the effective magnetization and the uniaxial in-palne anisotropy
field follow a linear variation versus the inverse CFA thickness. This allows
deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2",1403.7566v1
2014-04-22,Constituents of magnetic anisotropy and a screening of spin-orbit coupling in solids,"Using quantum mechanical perturbation theory (PT) we analyze how the energy
of perturbation of different orders is renormalized in solids. We test the
validity of PT analysis by considering a specific case of spin-orbit coupling
as a perturbation. We further compare the relativistic energy and the magnetic
anisotropy from the PT approach with direct density functional calculations in
FePt, CoPt, FePd, MnAl, MnGa, FeNi, and tetragonally strained FeCo. In addition
using decomposition of anisotropy into contributions from individual sites and
different spin components we explain the microscopic origin of high anisotropy
in FePt and CoPt magnets.",1404.5546v2
2014-04-23,The role of the Galactic Halo and the Single Source in the formation of the cosmic ray anisotropy,"The existence of the cosmic ray Halo in our Galaxy has been discussed for
more than half a century. If it is real it could help to explain some puzzling
features of the cosmic ray flux: its small radial gradient, nearly perfect
isotropy and the low level of the fine structure in the energy spectra of the
various particles. All these features could be understood if: (a) the Halo has
a big size (b) cosmic rays in the Halo have a unform spatial distribution and
(c) the cosmic ray density in the Halo is comparable or even higher than that
in the Galactic Disk. The main topic of the paper concerns the present status
of the anisotropy and a model for its formation. In our model the extremely
small amplitude of the dipole anisotropy is due to the dilution of the
anisotropy in the Disk by the dominating isotropic cosmic rays from the Halo.
Some minor deviations from complete isotropy in the sub-PeV and PeV energy
regions point out to the possible contribution of the Single Source with the
phase of its first harmonic opposite to the phase produced by the Disk.",1404.5918v1
2014-04-28,Effect of anisotropy in the $S=1$ underscreened Kondo lattice,"We study the effect of crystal field anisotropy in the underscreened $S=1$
Kondo lattice model. Starting from the two orbital Anderson lattice model and
including a local anisotropy term, we show, through Schrieffer-Wolff
transformation, that local anisotropy is equivalent to an anisotropic Kondo
interaction ($J_{\parallel} \neq{J_{\perp}}$). The competition and coexistence
between ferromagnetism and Kondo effect in this effective model is studied
within a generalized mean-field approximation. Several regimes are obtained,
depending on the parameters, exhibiting or not coexistence of magnetic order
and Kondo effect. Particularly, we show that a re-entrant Kondo phase at low
temperature can be obtained. We are also able to describe phases where the
Kondo temperature is smaller than the Curie temperature ($T_K<T_C$). We propose
that some aspects of uranium and neptunium compounds that present coexistence
of Kondo effect and ferromagnetism, can be understood within this model.",1404.6864v1
2014-05-05,Planar array of self-assembled Ga$_{x}$Fe$_{4-x}$N nanocrystals in GaN: Magnetic anisotropy determined via ferromagnetic resonance,"The magnetic anisotropy of a planar array of Ga$_{x}$Fe$_{4-x}$N nanocrystals
(NCs) embedded in a GaN host is studied by ferromagnetic resonance. X-ray
diffraction and transmission electron microscopy are employed to determine the
phase and distribution of the nanocrystals. The magnetic anisotropy is found to
be primarily uniaxial with the hard axis normal to the NCs plane and to have a
comparably weak in-plane hexagonal symmetry. The origin of the magnetic
anisotropy is discussed taking into consideration the morphology of the
nanocrystals, the epitaxial relations, strain effects and magnetic coupling
between the NCs.",1405.0906v2
2014-05-09,Deformed Flux Tubes Produce Azimuthal Anisotropy in Heavy Ion Collisions,"We investigate the azimuthal anisotropy $v_2$ of particle production in
nucleus-nucleus collisions in the maximum entropy approach. This necessitates
two new phenomenological input parameters $\delta$ and $\lambda_2$ compared
with integrated multiplicity distributions. The parameter $\delta$ describes
the deformation of a flux tube and can be theoretically calculated in a bag
model with a bag constant which depends on the density of surrounding flux
tubes. The parameter $\lambda_2$ defines the anisotropy of the particle
distribution in momentum space and can be connected to $\delta$ via the
uncertainty relation. In this framework we compute the anisotropy $v_2$ as a
function of centrality, transverse momentum and rapidity in qualitative
agreement with LHC data.",1405.2248v2
2014-05-09,Effect of equatorial line nodes on upper critical field and London penetration depth,"The upper critical field $H_{c2}$ and its anisotropy are calculated for order
parameters with line nodes at equators, $k_z=0$, of the Fermi surface of
uniaxial superconductors. It is shown that characteristic features found in
Fe-based materials -- a nearly linear $H_{c2}(T)$ in a broad $T$ domain, a low
and increasing on warming anisotropy $\gamma_H= H_{c2,ab}/ H_{c2,c}\, $ -- can
be caused by competing effects of the equatorial nodes and of the Fermi surface
anisotropy. For certain material parameters, $\gamma_H(T)-1$ may change sign on
warming in agreement with recorded behavior of FeTeS system. It is also shown
that the anisotropy of the penetration depth $\gamma_\lambda=
\lambda_c/\lambda_{ab} $ decreases on warming to reach $\gamma_H$ at $T_c$ in
agreement with data available. For some materials $\gamma_\lambda(T)$ may
change on warming from $\gamma_\lambda>1$ at low $T$s to $\gamma_\lambda<1$ at
high $T$s.",1405.2359v1
2014-05-13,Constraining the Anisotropy of the Universe from Supernovae and Gamma-ray Bursts,"Recently, an anisotropic cosmological model was proposed. An arbitrary
1-form, which picks out a privileged axis in the universe, was added to the
Friedmann-Robertson-Walker line element. The distance-redshift relation was
modified such that it is direction dependent. In this paper, we use the Union2
dataset and 59 high-redshift gamma-ray bursts to give constraints on the
anisotropy of the universe. The results show that the magnitude of anisotropy
is about $D=-0.044\pm0.018$, and the privileged axis points towards the
direction $(l_0,b_0)=(306.1^{\circ}\pm 18.7^{\circ},-18.2^{\circ}\pm
11.2^{\circ})$ in the galactic coordinate system. The anisotropy is small and
the isotropic cosmological model is an excellent approximation.",1405.3074v1
2014-05-17,Application of the Enhanced Semidefinite Relaxation Method to Construction of the Optimal Anisotropy Function,"In this paper we propose and apply the enhanced semidefinite relaxation
technique for solving a class of non-convex quadratic optimization problems.
The approach is based on enhancing the semidefinite relaxation methodology by
complementing linear equality constraints by quadratic-linear constrains. We
give sufficient conditions guaranteeing that the optimal values of the primal
and enhanced semidefinite relaxed problems coincide. We apply this approach to
the problem of resolving the optimal anisotropy function. The idea is to
construct an optimal anisotropy function as a minimizer for the anisotropic
interface energy functional for a given Jordan curve in the plane. We present
computational examples of resolving the optimal anisotropy function. The
examples include boundaries of real snowflakes.",1405.4382v3
2014-06-02,CMB $μ$ distortion from primordial gravitational waves,"We propose a new mechanism of generating the $\mu$ distortion in cosmic
microwave background (CMB) originated from primordial gravitational waves. Such
$\mu$ distortion is generated by the damping of the temperature anisotropies
through the Thomson scattering, even on scales larger than that of Silk
damping. This mechanism is in sharp contrast with that from the primordial
curvature (scalar) perturbations, in which the temperature anisotropies mainly
decay by Silk damping effects. We estimate the size of the $\mu$ distortion
from the new mechanism, which can be used to constrain the amplitude of
primordial gravitational waves on smaller scales independently from the CMB
anisotropies, giving more wide-range constraint on their spectral index by
combining the amplitude from the CMB anisotropies.",1406.0451v2
2014-06-26,Spin-torque diode radio-frequency detector with voltage tuned resonance,"We report on a voltage tunable radio-frequency (RF) detector based on a
magnetic tunnel junction (MTJ). The spin-torque diode effect is used to excite
and/or detect RF oscillations in the magnetic free layer of the MTJ. In order
to reduce the overall in-plane magnetic anisotropy of the free layer, we take
advantage of the perpendicular magnetic anisotropy at the interface between
ferromagnetic and insulating layers. The applied bias voltage is shown to have
a significant influence on the magnetic anisotropy, and thus on the resonance
frequency of the device. This influence also depends on the voltage polarity.
The obtained results are accounted for in terms of the interplay of
spin-transfer-torque and voltage-controlled magnetic anisotropy effects.",1406.6935v1
2014-07-01,Measuring Anisotropies in the Cosmic Neutrino Background,"Neutrino capture on tritium has emerged as a promising method for detecting
the cosmic neutrino background (CvB). We show that relic neutrinos are captured
most readily when their spin vectors are anti-aligned with the polarization
axis of the tritium nuclei and when they approach along the direction of
polarization. As a result, CvB observatories may measure anisotropies in the
cosmic neutrino velocity and spin distributions by polarizing the tritium
targets. A small dipole anisotropy in the CvB is expected due to the peculiar
velocity of the lab frame with respect to the cosmic frame and due to late-time
gravitational effects. The PTOLEMY experiment, a tritium observatory currently
under construction, should observe a nearly isotropic background. This would
serve as a strong test of the cosmological origin of a potential signal. The
polarized-target measurements may also constrain non-standard neutrino
interactions that would induce larger anisotropies and help discriminate
between Majorana versus Dirac neutrinos.",1407.0393v1
2014-07-20,Probing Transverse Magnetic Anisotropy by Electronic Transport through a Single-Molecule Magnet,"By means of electronic transport, we study the transverse magnetic anisotropy
of an individual Fe$_4$ single-molecule magnet (SMM) embedded in a
three-terminal junction. In particular, we determine in situ the transverse
anisotropy of the molecule from the pronounced intensity modulations of the
linear conductance, which are observed as a function of applied magnetic field.
The proposed technique works at temperatures exceeding the energy scale of the
tunnel splittings of the SMM. We deduce that the transverse anisotropy for a
single Fe$_4$ molecule captured in a junction is substantially larger than the
bulk value.",1407.5265v2
2014-07-28,Collective effects in light-heavy ion collisions,"We present results for the azimuthal anisotropy of charged hadron
distributions in A+A, p+A, d+A, and He3+A collisions within the IP-Glasma+MUSIC
model. Obtained anisotropies are due to the fluid dynamic response of the
system to the fluctuating initial geometry of the interaction region. While the
elliptic and triangular anisotropies in peripheral Pb+Pb collisions at
root-s=2.76 TeV are well described by the model, the same quantities in
root-s=5.02 TeV p+Pb collisions underestimate the experimental data. This
disagreement can be due to neglected initial state correlations or the lack of
a detailed description of the fluctuating spatial structure of the proton, or
both. We further present predictions for azimuthal anisotropies in p+Au, d+Au,
and He3+Au collisions at root-s=200 GeV. For d+Au and 3He+Au collisions we
expect the detailed substructure of the nucleon to become less important.",1407.7557v1
2014-08-07,Ferromagnetic resonance of a magnetic dimer with dipolar coupling,"We develop a general formalism for analyzing the ferromagnetic resonance
characteristics of a magnetic dimer consisting of two magnetic elements (in a
horizontal or vertical configuration) coupled by dipolar interaction, taking
account of their finite-size and aspect ratio. We study the effect on the
resonance frequency and resonance field of the applied magnetic field (in
amplitude and direction), the inter-element coupling, and the uniaxial
anisotropy in various configurations. We obtain analytical expressions for the
resonance frequency in various regimes of the interlayer coupling. We
(numerically) investigate the behavior of the resonance field in the
corresponding regimes. The critical value of the applied magnetic field at
which the resonance frequency vanishes may be an increasing or a decreasing
function of the dimer's coupling, depending on the anisotropy configuration. It
is also a function of the nanomagnets aspect ratio in the case of in-plane
anisotropy. This and several other results of this work, when compared with
experiments using the standard ferromagnetic resonance with fixed frequency, or
the network analyzer with varying frequency and applied magnetic field, provide
a useful means for characterizing the effective anisotropy and coupling within
systems of stacked or assembled nanomagnets.",1408.1594v1
2014-08-07,Tuning Perpendicular Anisotropy Gradient in Co/Pd Multilayers by Ion Irradiation,"The tunability of Ar+ ion irradiation of Co/Pd multilayers has been employed
to create depth-dependent perpendicular anisotropy gradients. By adjusting the
Ar+ kinetic energy and fluence, the depth and lateral density of the local
structural modification are controlled. First-order reversal curve analysis
through X-ray magnetic circular dichroism and conventional magnetometry studies
show that the local structural damage weakens the perpendicular anisotropy near
the surface, leading to a magnetization tilting towards the in-plane direction.
The ion irradiation method is complementary to, and may be used in conjunction
with, other synthesis approaches to maximize the anisotropy gradient.",1408.1659v1
2014-08-13,Temperature-Dependent Interplay of Dzyaloshinskii-Moriya Interaction and Single-Ion Anisotropy in Multiferroic BiFeO$_3$,"Low-energy magnon excitations in multiferroic BiFeO$_3$ were measured in
detail as a function of temperature around several Brillouin zone centers by
inelastic neutron scattering experiments on single crystals. Unique features
around 1 meV are directly associated with the interplay of the
Dzyaloshinskii-Moriya interaction and a small single-ion anisotropy. The
temperature dependence of these and the exchange interactions were determined
by fitting the measured magnon dispersion with spin-wave calculations. The
spectra best fits an easy-axis type magnetic anisotropy and the deduced
exchange and anisotropy parameters enable us to determine the anharmonicity of
the magnetic cycloid. We then draw a direct connection between the changes in
the parameters of spin Hamiltonian with temperature and the physical properties
and structural deformations of BiFeO$_3$.",1408.2942v2
2014-09-09,Most spin-1/2 transition-metal ions do have single ion anisotropy,"The cause for the preferred spin orientation in magnetic systems containing
spin-1/2 transition-metal ions was explored by studying the origin of the
easy-plane anisotropy of the spin-1/2 Cu2+ ions in CuCl2.2H2O, LiCuVO4, CuCl2
and CuBr2 on the basis of density functional theory and magnetic dipole-dipole
energy calculations as well as a perturbation theory treatment of the
spin-orbit coupling. We find that the spin orientation observed for these
spin-1/2 ions is not caused by their anisotropic spin exchange interactions,
nor by their magnetic dipole-dipole interactions, but by the spin-orbit
coupling associated with their crystal-field split d-states. Our study also
predicts in-plane anisotropy for the Cu2+ ions of Bi2CuO4 and Li2CuO2. The
results of our investigations dispel the mistaken belief that magnetic systems
with spin-1/2 ions have no magnetic anisotropy induced by spin-orbit coupling.",1409.2795v2
2014-10-15,Low artificial anisotropy cellular automaton model and its applications to the cell-to-dendrite transition in directional solidification,"A low artificial anisotropy cellular automaton (CA) model is developed for
the simulation of microstructure evolution in directional solidification. The
CA model's capture rule was modified by a limited neighbor solid fraction
(LNSF) method. Various interface curvature calculation methods have been
compared. The simulated equilibrium shapes agree with the theoretical shapes,
when the interface energy anisotropy coefficient is {\epsilon}=0.01,
{\epsilon}=0.03 and {\epsilon}=0.05, respectively.The low artificial anisotropy
CA model is used in the numerical simulation of the cell-to-dendrite transition
(CDT) in directional solidification. The influence of physical parameters
({\Gamma}, Dl, k0, ml) on CDT has been investigated. The main finding in this
paper is the discovery of the changing behavior of the Vcd when the solute
partition coefficient k0 is larger than a critical value. When k0 is less than
0.125, the Vcd follows the Kurz and Fisher criterion Vc/k0; while when
k0>0.125, the Vcd equals to 8Vc. The experimental data of
succinonitrile-acetone (SCN-ace, k0=0.1) and SCN-camphor (k0=0.33) support the
conclusion from CA simulations.",1410.3907v1
2014-10-21,Anisotropic fluid star model in isotropic coordinates,"We present a spherically symmetric solution of the general relativistic field
equations in isotropic coordinates for anisotropic neutral fluid, compatible
with a super dense star modeling by considering a specific choice of anisotropy
factor that includes a positive constant defined as anisotropy parameter, which
varies the relation between the radial and tangential pressure. Further, we
have constructed a super-dense star model with all degree of suitability. We
have found that the maximum mass decreases with the increase of anisotropy
parameter. The robustness of our result is that it matches with the recent
discoveries.",1410.5808v1
2014-11-03,Curvature effects in statics and dynamics of low dimensional magnets,"We develop an approach to treat magnetic energy of a ferromagnet for
arbitrary curved wires and shells on the assumption that the anisotropy
contribution much exceeds the dipolar and other weak interactions. We show that
the curvature induces two effective magnetic interactions: effective magnetic
anisotropy and effective Dzyaloshinskii-like interaction. We derive an equation
of magnetisation dynamics and propose a general static solution for the limit
case of strong anisotropy. To illustrate our approach we consider the
magnetisation structure in a ring wire and a cone surface: ground states in
both systems essentially depend on the curvature excluding strictly tangential
solutions even in the case of strong anisotropy. We derive also the spectrum of
spin waves in such systems.",1411.0646v2
2014-11-26,Electrical manipulation of orbital occupancy and magnetic anisotropy in manganites,"Electrical manipulation of lattice, charge, and spin has been realized
respectively by the piezoelectric effect, field-effect transistor, and electric
field control of ferromagnetism, bringing about dramatic promotions both in
fundamental research and industrial production. However, it is generally
accepted that the orbital of materials are impossible to be altered once they
have been made. Here we use electric-field to dynamically tune the electronic
phase transition in (La,Sr)MnO3 films with different Mn^4+/(Mn^3+ + Mn^4+)
ratios. The orbital occupancy and corresponding magnetic anisotropy of these
thin films are manipulated by gate voltage in a reversible and quantitative
manner. Positive gate voltage increases the proportion of occupancy of the
orbital and magnetic anisotropy that were initially favored by strain
(irrespective of tensile and compressive), while negative gate voltage reduces
the concomitant preferential orbital occupancy and magnetic anisotropy. Besides
its fundamental significance in orbital physics, our findings might advance the
process towards practical oxide-electronics based on orbital.",1411.7128v1
2014-12-18,Scaling of Coercivity in a 3d Random Anisotropy Model,"The random-anisotropy Heisenberg model is numerically studied on lattices
containing over ten million spins. The study is focused on hysteresis and
metastability due to topological defects, and is relevant to magnetic
properties of amorphous and sintered magnets. We are interested in the limit
when ferromagnetic correlations extend beyond the size of the grain inside
which the magnetic anisotropy axes are correlated. In that limit the coercive
field computed numerically roughly scales as the fourth power of the random
anisotropy strength and as the sixth power of the grain size. Theoretical
arguments are presented that provide an explanation of numerical results. Our
findings should be helpful for designing amorphous and nanosintered materials
with desired magnetic properties.",1412.6182v1
2014-12-23,The Anisotropy of the Extragalactic Radio Background from Dark Matter Annihilation,"Observations of the extragalactic radio background have uncovered a
significant isotropic emission across multiple frequencies spanning from 22 MHz
to 10 GHz. The intensity of this non-thermal emission component significantly
exceeds the expected contribution from known astrophysical sources.
Interestingly, models have indicated that the annihilation of dark matter
particles may reproduce both the flux and spectrum of the excess. However, the
lack of a measurable anisotropy in the residual emission remains challenging
for both dark matter and standard astrophysical interpretations of the ARCADE-2
data. We calculate the expected synchrotron anisotropy from dark matter
annihilation and show that these models can produce very small anisotropies,
though this requires galaxy clusters to have large substructure contributions
and strong magnetic fields. We show that this constraint can be significantly
relaxed, however, in scenarios where electrons produced via dark matter
annihilation can be efficiently reaccelerated by Alfv\'en waves in the
intra-Cluster medium. Our analysis indicates that any source capable of
explaining the intensity and isotropy of the extragalactic radio excess must
have a spatial extension far larger than typical for baryons in galaxies,
suggesting a novel physics interpretation.",1412.7545v1
2015-01-05,Reversed anisotropy of the in-plane resistivity in the antiferromagnetic phase of iron tellurides,"We systematically investigated the anisotropic in-plane resistivity of the
iron telluride including three kinds of impurity atoms: excess Fe, Se
substituted for Te, and Cu substituted for Fe. Sizable resistivity anisotropy
was found in the magneto-structurally ordered phase whereas the sign is
opposite ($\rho_a$ $>$ $\rho_b$, where the $b$-axis parameter is shorter than
the $a$-axis one) to that observed in the transition-metal doped iron arsenides
($\rho_a$ $<$ $\rho_b$). On the other hand, our results demonstrate that the
magnitude of the resistivity anisotropy in the iron tellurides is correlated
with the amount of impurities, implying that the resistivity anisotropy
originates from an exotic impurity effect like that in the iron arsenides. This
suggests that the anisotropic carrier scattering by impurities is a universal
phenomenon in the magneto-structurally ordered phase of the iron-based
materials.",1501.00774v1
2015-01-14,Dilepton production from the quark-gluon plasma using (3+1)-dimensional anisotropic dissipative hydrodynamics,"We compute dilepton production from the deconfined phase of the quark-gluon
plasma using leading-order (3+1)-dimensional anisotropic hydrodynamics. The
anisotropic hydrodynamics equa- tions employed describe the full spatiotemporal
evolution of the transverse temperature, spheroidal momentum-space anisotropy
parameter, and the associated three-dimensional collective flow of the matter.
The momentum-space anisotropy is also taken into account in the computation of
the dilepton production rate, allowing for a self-consistent description of
dilepton production from the quark-gluon plasma. For our final results, we
present predictions for high-energy dilepton yields as a function of invariant
mass, transverse momentum, and pair rapidity. We demonstrate that high- energy
dilepton production is extremely sensitive to the assumed level of initial
momentum-space anisotropy of the quark-gluon plasma. As a result, it may be
possible to experimentally constrain the early-time momentum-space anisotropy
of the quark-gluon plasma generated in relativistic heavy ion collisions using
high-energy dilepton yields.",1501.03418v1
2015-01-21,Universal distribution of magnetic anisotropy of impurities in ordered and disordered nano-grains,"We examine the distribution of the magnetic anisotropy (MA) experienced by a
magnetic impurity embedded in a metallic nano-grain. As an example of a generic
magnetic impurity with partially filled $d$-shell, we study the case of $d^{1}$
impurities imbedded into ordered and disordered Au nano-grains, described in
terms of a realistic band structure. Confinement of the electrons induces a
magnetic anisotropy that is large, and can be characterized by 5 real
parameters, coupling to the quadrupolar moments of the spin. In ordered
(spherical) nano-grains, these parameters exhibit symmetrical structures and
reflect the symmetry of the underlying lattice, while for disordered grains
they are randomly distributed and, - for stronger disorder, - their
distribution is found to be characterized by random matrix theory. As a result,
the probability of having small magnetic anisotropies $K_L$ is suppressed below
a characteristic scale $\Delta_E$, which we predict to scale with the number of
atoms $N$ as $\Delta_E\sim 1/N^{3/2}$. This gives rise to anomalies in the
specific heat and the susceptibility at temperatures $T\sim \Delta_E$ and
produces distinct structures in the magnetic excitation spectrum of the
clusters, that should be possible to detect experimentally.",1501.05346v1
2015-02-23,Can modified gravity models reconcile the tension between CMB anisotropy and lensing maps in Planck-like observations?,"Planck-2015 data seem to favour a large value of the lensing amplitude
parameter, $A_{\rm L}=1.22\pm0.10$, in CMB spectra. This result is in $2\sigma$
tension with the lensing reconstruction result, $A_{\rm
L}^{\phi\phi}=0.95\pm0.04$. In this paper, we simulate several CMB anisotropy
and CMB lensing spectra based on Planck-2015 best-fit cosmological parameter
values and Planck blue book beam and noise specifications. We analyse several
modified gravity models within the effective field theory framework against
these simulations and find that models whose effective Newton constant is
enhanced can modulate the CMB anisotropy spectra in a way similar to that of
the $A_{\rm L}$ parameter. However, in order to lens the CMB anisotropies
sufficiently, like in the Planck-2015 results, the growth of matter
perturbations is substantially enhanced and gives a high $\sigma_8$ value. This
in turn proves to be problematic when combining these data to other probes,
like weak lensing from CFHTLenS, that favour a smaller amplitude of matter
fluctuations.",1502.06599v1
2015-03-09,"Alternating magnetic anisotropy of Li$_2$(Li$_{1-x}T_x$)N with $T$ = Mn, Fe, Co, and Ni","Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be
substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and
temperature-dependent magnetization measurements reveal local magnetic moments
with magnitudes significantly exceeding the spin-only value. The additional
contributions stem from unquenched orbital moments that lead to rare-earth-like
behavior of the magnetic properties. Accordingly, extremely large magnetic
anisotropies have been found. Most notably, the magnetic anisotropy alternates
as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$
easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co
$\rightarrow$ Ni. This behavior can be understood based on a perturbation
approach in an analytical, single-ion model. The calculated magnetic
anisotropies show a surprisingly good agreement with the experiment and capture
the basic features observed for the different transition metals.",1503.02501v2
2015-04-04,Design of Black Phosphorus 2D Nanomechanical Resonators by Exploiting the Intrinsic Mechanical Anisotropy,"Black phosphorus (P), a layered material that can be isolated down to
individual 2D crystalline sheets, exhibits highly anisotropic mechanical
properties due to its corrugated crystal structure in each atomic layer, which
are intriguing for 2D nanomechanical devices. Here we lay the framework for
describing the mechanical resonant responses in free-standing black P
structures, by using a combination of analytical modeling and numerical
simulation. We find that thicker devices (>100nm) operating in the elastic
plate regime exhibit pronounced signatures of mechanical anisotropy, and can
lead to new multimode resonant characteristics in terms of mode sequences,
shapes, and orientational preferences that are unavailable in nanomechanical
resonators made of isotropic materials. In addition, through investigating
devices with different geometries, we identify the resonant response's
dependence on crystal orientation in asymmetric devices, and evaluate the
effects from the degree of anisotropy. The results suggest a pathway towards
harnessing the mechanical anisotropy in black P for building novel 2D
nanomechanical devices and resonant transducers with engineerable multimode
functions.",1504.01060v1
2015-04-10,Influence of magnetic surface anisotropy on spin wave reflection from the edge of ferromagnetic film,"We study propagation of the Gaussian beam of spin waves and its reflection
from the edge of thin yttrium-iron-garnet film with in-plane magnetization
perpendicular to this edge. We have performed micromagnetic simulations
supported by analytical calculations to investigate influence of the surface
magnetic anisotropy present at the film edge on the reflection, especially in
the context of the Goos-Hanchen effect. We have shown the appearance of a
negative lateral shift between reflected and incident spin wave beams' spots.
This shift is particularly sensitive to the surface magnetic anisotropy value
and is a result of the Goos-Hanchen shift which is sensitive to the magnitude
of the anisotropy and of the bending of spin wave beam. We have demonstrated
that the demagnetizing field provide graded increase of the refractive index
for spin waves, which is responsible for the bending.",1504.02668v2
2015-04-26,Origin of the resistive anisotropy in the electronic nematic phase of BaFe$_2$As$_2$ revealed by optical spectroscopy,"We perform, as a function of uniaxial stress, an optical-reflectivity
investigation of the representative 'parent' ferropnictide BaFe$_2$As$_2$ in a
broad spectral range, across the tetragonal-to-orthorhombic phase transition
and the onset of the long-range antiferromagnetic order (AFM). The infrared
response reveals that the $dc$ transport anisotropy in the orthorhombic AFM
state is determined by the interplay between the Drude spectral weight and the
scattering rate, but that the dominant effect is clearly associated with the
metallic spectral weight. In the paramagnetic tetragonal phase, though, the
$dc$ resistivity anisotropy of strained samples is almost exclusively due to
stress-induced changes in the Drude weight rather than in the scattering rate,
definitively establishing the anisotropy of the Fermi surface parameters as the
primary effect driving the $dc$ transport properties in the electronic nematic
state.",1504.06829v1
2015-05-05,In-plane transport anisotropy in BSCCO-Ag multi-filamentary tapes,"Composite structures such as High-Tc multi-filamentary tapes display a
complex anisotropy arising from the combination of the intrinsic anisotropy of
the Bi-2223 grains, and that associated to the superconducting phase
distribution in the superconductor-metal composite, as well as cracks and other
defects. In this paper we characterize the in-plane anisotropy of BSCCO-Ag
tapes, i.e., the difference between the transport properties along the
longitudinal axis and those along the transverse direction also lying on the
wide face of the tape. In particular, we demonstrate that the dissipation
associated to transport along the transverse direction approaches that of the
longitudinal direction as the temperature or the current increase, which may be
relevant to transport applications in situations where the superconducting
properties have significantly degraded.",1505.01190v1
2015-05-13,The electronic origin of shear-induced direct to indirect gap transition and anisotropy diminution in phosphorene,"Artificial monolayer black phosphorus, the so-called phosphorene has
attracted global interest with its distinguished anisotropic optoelectronic and
electronic properties. Here, we unraveled the shear-induced direct to indirect
gap transition and anisotropy diminution in phosphorene based on
first-principles calculations. Lattice dynamic analysis demonstrated that
phosphorene can sustain up to 10% applied shear strain. The band gap of
phosphorene experiences a direct to indirect transition when 5% shear strain is
applied. The electronic origin of direct to indirect gap transition from 1.54
eV at ambient condition to 1.22 eV at 10% shear strains for phosphorene was
explored and the anisotropy diminution in phosphorene is discussed by
calculating the maximum sound velocities, effective mass and decomposed charge
density, which signals the undesired shear-induced direct to indirect gap
transition in the applications of phosphorene for electronics and
optoelectronics. On the other hand, the shear-induced electronic anisotropy
properties suggest that phosphorene can be applied as the switcher in the nano
electronic applications.",1505.03353v1
2015-06-17,Small-Scale Anisotropies of Cosmic Rays from Relative Diffusion,"The arrival directions of multi-TeV cosmic rays show significant anisotropies
at small angular scales. It has been argued that this small-scale structure can
naturally arise from cosmic ray scattering in local turbulent magnetic fields
that distort a global dipole anisotropy set by diffusion. We study this effect
in terms of the power spectrum of cosmic ray arrival directions and show that
the strength of small-scale anisotropies is related to properties of relative
diffusion. We provide a formalism for how these power spectra can be inferred
from simulations and motivate a simple analytic extension of the
ensemble-averaged diffusion equation that can account for the effect.",1506.05488v2
2015-06-19,Statistics of the CMB polarised anisotropies,"This PhD thesis (defended in 2014) is focused on the estimation of the CMB
polarised anisotropies power spectra on a masked sky and on forecasts of
constraints set on the primordial universe physics thanks to these
anisotropies. After an introduction on the light polarisation, the standard
model of cosmology and the CMB properties, I show the results obtained on the
use and efficiency of pseudospectrum methods to correct for the so-called
E-to-B leakage. Afterwards, I present the forecasts obtained on the detection
of the tensor-to-scalar ratio r and on the detection of chiral gravity, using
the pure pseudospectrum method. The study of forecasts of a primordial magnetic
field detection using the CMB polarised anisotropies is finally briefly
tackled.",1506.05940v1
2015-06-25,Dirac electrons and domain walls: a realization in junctions of ferromagnets and topological insulators,"We study a system of Dirac electrons with finite density of charge carriers
coupled to an external electromagnetic field in two spatial dimensions, with a
domain wall (DW) mass term. The interface between a thin-film ferromagnet and a
three-dimensional topological insulator provides a condensed-matter realization
of this model, when an out-of-plane domain wall magnetization is coupled to the
TI surface states. We show how, for films with very weak intrinsic in-plane
anisotropies, the torque generated by the edge electronic current flowing along
the DW competes with an effective in-plane anisotropy energy, induced by
quantum fluctuations of the chiral electrons bound to the wall, in a mission to
drive the internal angle of the DW from a Bloch configuration towards a N\'eel
configuration. Both the edge current and the induced anisotropy contribute to
stabilize the internal angle, so that for weak intrinsic in-plane anisotropies
DW motion is still possible without suffering from an extremely early Walker
breakdown.",1506.07668v1
2015-07-19,Fabrication of Flexible Oriented Magnetic Thin Films with Large in-plane Uniaxial Anisotropy by Roll-to-roll Nanoimprint Lithography,"Here, we report wafer scale fabrication of densely packed Fe nanostripe-based
magnetic thin films on a flexible substrate and their magnetic anisotropy
properties. We find that Fe nanostripes exhibit large in-plane uniaxial
anisotropy and nearly square hysteresis loops with energy products (BH)max
exceeding 3 MGOe at room temperature. High density Fe nanostripes were
fabricated on 70 nm flexible polyethylene terephthalate (PET) gratings, which
were made by roll-to-roll (R2R) UV nanoimprintlithography technique. Observed
large in-plane uniaxial anisotropies along the long dimension of nanostripes
are attributed to the shape. Temperature dependent hysteresis measurements
confirm that the magnetization reversal is driven by non-coherent rotation
reversal processes.",1507.05252v1
2015-07-23,Anisotropies of ultra-high energy cosmic ray nuclei diffusing from extragalactic sources,"We obtain the dipolar anisotropies in the arrival directions of ultra-high
energy cosmic ray nuclei diffusing from nearby extragalactic sources. We
consider mixed-composition scenarios in which different cosmic ray nuclei are
accelerated up to the same maximum rigidity, so that $E<ZE_\text{max}^p$, with
$Z$ the atomic number and $E_\text{max}^p$ the maximum proton energy. We adopt
$E_\text{max}^p\simeq 6$ EeV so as to account for an increasingly heavier
composition above the ankle. We obtain the anisotropies through Monte Carlo
simulations that implement the cosmic ray diffusion in extragalactic turbulent
fields as well as the effects of photo-disintegrations and other energy losses.
Dipolar anisotropies at the level of 5 to 10\% at energies $\sim 10$~EeV are
predicted for plausible values of the source density and magnetic fields.",1507.06585v1
2015-08-19,Observation of Anisotropy in the Arrival Direction Distribution of TeV Cosmic Rays with HAWC,"The High-Altitude Water Cherenkov (HAWC) Observatory, located 4100 m above
sea level near Sierra Negra (19$^\circ$ N) in Mexico, is sensitive to gamma
rays and cosmic rays at TeV energies. The arrival direction distribution of
cosmic rays at these energies shows significant anisotropy on several angular
scales, with a relative intensity ranging between 10$^{-3}$ and 10$^{-4}$. We
present the results of a study of cosmic-ray anisotropy based on more than 86
billion cosmic-ray air showers recorded with HAWC since June 2013. The HAWC
cosmic-ray sky map, which has a median energy of 2 TeV, exhibits several
regions of significantly enhanced cosmic-ray flux. We present the energy
dependence of the anisotropy and the cosmic-ray spectrum in the regions of
significant excess.",1508.04781v1
2015-08-31,Edge-modulated perpendicular magnetic anisotropy in [Co/Pd]n and L10-FePt thin film wires,"Thickness modulation at the edges of nanostructured magnetic thin films is
shown to have important effects on their perpendicular magnetic anisotropy.
Thin film wires with tapered edges were made from [Co/Pd]20 multilayers or
L10-FePt films using liftoff with a double layer resist. The effect of edge
taper on the reversal process was studied using magnetic force microscopy and
micromagnetic modeling. In [Co/Pd]20 the anisotropy was lower in the tapered
edge regions which switched at a lower reverse field compared to the center of
the wire. The L10-FePt wires showed opposite behavior with the tapered regions
exhibiting higher anisotropy.",1508.07948v2
2015-09-03,Magnetic alignment of block copolymer microdomains by intrinsic chain anisotropy,"We examine the role of intrinsic chain susceptibility anisotropy in magnetic
field directed self-assembly of a block copolymer using \textit{in situ} X-ray
scattering. Alignment of a lamellar mesophase is observed on cooling across the
disorder-order transition with the resulting orientational order inversely
proportional to the cooling rate. We discuss the origin of the susceptibility
anisotropy, $\Delta\chi$, that drives alignment, and calculate its magnitude
using coarse-grained molecular dynamics to sample conformations of
surface-tethered chains, finding $\Delta\chi\approx 2\times10^{-8}$. From
field-dependent scattering data we estimate grains of $\approx1.2$ $\mu$m are
present during alignment. These results demonstrate that intrinsic anisotropy
is sufficient to support strong field-induced mesophase alignment and suggest a
versatile strategy for field control of orientational order in block
copolymers.",1509.01292v1
2015-09-22,Long-lived Neel states in antiferromagnetic quantum spin chains with strong uniaxial anisotropy for atomic-scale antiferromagnetic spintronics,"It has been experimentally established that magnetic adatoms on surfaces can
be arranged to form antiferromagnetic quantum spin chains with strong uniaxial
anisotropy and Neel states in such spin systems can be used to realize
information storage. Here, we investigate eigen states, quantum spin dynamics,
and life times of Neel states in short antiferromagnetic quantum spin chains
with strong uniaxial anisotropy on the basis of numerical exact diagonalization
method. We show rigorously that as long as the uniaxial anisotropy is very
strong, the ground state and the first excitation state, being nearly
degenerate, are safely separated from the other states and thus dominate the
quantum dynamics of the Neel states. Through further numerical analysis, we
achieve a powerful life-time expression of the Neel states for arbitrary spin
and model parameters. It is interesting that for the famous Fe adatom chains on
Cu$_2$N surface, 14 or 16 Fe adatoms are enough to obtain a practical long
life-time for Neel state storage of information. These should be applicable to
other similar antiferromagnetic spin systems for atomic-scale antiferromagnetic
spintronics.",1509.06597v1
2015-10-20,Monte Carlo Simulations of ABC Stacked Kagome Lattice Thin Films,"Properties of thin films of geometrically frustrated ABC stacked
antiferromagnetic kagome layers are examined using Metropolis Monte Carlo
simulations. The impact of having an easy-axis anisotropy on the surface layers
and cubic anisotropy in the interior layers is explored. The spin structure at
the surface is shown to be different from that of the bulk 3D fcc system, where
surface axial anisotropy tends to align spins along the surface [111] normal
axis. This alignment tendency then propagates only weakly to the interior
layers through exchange coupling. Results are shown for the specific heat,
magnetization and sub-lattice order parameters for both surface and interior
spins in three and six layer films as a function of increasing axial surface
anisotropy. Relevance to the exchange bias phenomenon in IrMn$_3$ thin films is
discussed.",1510.05924v1
2015-10-31,"Investigating the anisotropic scintillation response in anthracene through neutron, gamma-ray, and muon measurements","This paper reports a series of measurements that characterize the directional
dependence of the scintillation response of crystalline anthracene to incident
DT neutrons, DD neutrons, Cs-137 gamma rays, and, for the first time, cosmic
ray muons. The neutron measurements give the amplitude and pulse shape
dependence on the proton recoil direction over one hemisphere of the crystal,
confirming and extending previous results in the literature. In similar
measurements using incident gamma rays, no directional effect is evident, and
any anisotropy with respect to the electron recoil direction is constrained to
have a magnitude of less than a tenth of that present in the proton recoil
events. Cosmic muons are measured at two directions, and no anisotropy is
observed. This set of observations indicates that high dE/dx is necessary for
an anisotropy to be present for a given type of scintillation event, which in
turn could be used to discriminate among different hypotheses for the
underlying causes of the anisotropy, which are not well understood.",1511.00081v1
2015-12-08,Orbital anisotropy underlying the superconducting dome in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ superconductors,"We investigate the in-plane anisotropy of Fe 3d orbitals occurring in a wide
temperature and composition range of BaFe2(As1-xPx)2 system. By employing the
angle-resolved photoemission spectroscopy, the lifting of degeneracy in dxz and
dyz orbitals at the Brillouin zone corners can be obtained as a measure of the
orbital anisotropy. In the underdoped regime, it starts to evolve on cooling
from high temperatures above both antiferromagnetic and orthorhombic
transitions. With increasing x, it well survives into the superconducting
regime, but gradually gets suppressed and finally disappears around the
non-superconducting transition (x = 0.7). The observed spontaneous in-plane
orbital anisotropy, possibly coupled with anisotropic lattice and magnetic
fluctuations, implies the rotational-symmetry broken electronic state working
as the stage for the superconductivity in BaFe2(As1-xPx)2.",1512.02389v1
2015-12-11,A new method for testing isotropy with Shannon entropy,"We propose a novel method for testing isotropy of a three-dimensional
distribution using Shannon entropy. We test the method on some Monte Carlo
simulations of isotropic and anisotropic distributions and find that the method
can effectively identify and characterize different types of hemispherical
asymmetry inputted in a distribution. We generate anisotropic distributions by
introducing pockets of different densities inside homogeneous and isotropic
distributions and find that the proposed method can effectively quantify the
degree of anisotropy and determine the geometry of the pockets introduced. We
also considered spherically symmetric radially inhomogeneous distributions
which are anisotropic at all points other than the centre and find that such
anisotropy can be easily characterized by our method. We use a semi analytic
galaxy catalogue from the Millennium simulation to study the anisotropies
induced by the redshift space distortions and find that the method can separate
such anisotropies from a general one. The method may be also suitably adapted
for any two dimensional maps on the celestial sphere to study the hemispherical
asymmetry in other cosmological observations.",1512.03562v2
2015-12-16,"On the existence conditions of surface spin wave modes in (Ga,Mn)As thin films","Spin-wave resonance (SWR) is a newly emerged method for studying surface
magnetic anisotropy and surface spin-wave modes (SSWMs) in (Ga,Mn)As thin
films. The existence of SSWMs in (Ga,Mn)As thin films has recently been
reported in the literature; SSWMs have been observed in the in-plane
configuration (with variable azimuth angle $\phi_M$ between the in-plane
magnetization of the film and the surface [100] crystal axis), in the azimuth
angle range between two in-plane critical angles $\phi_{c1}$ and $\phi_{c2}$.
We show here that cubic surface anisotropy is an essential factor determining
the existence conditions of the above-mentioned SSWMs: conditions favorable for
the occurrence of surface spin-wave modes in a (Ga,Mn)As thin film in the
in-plane configuration are fulfilled for those azimuth orientations of the
magnetization of the sample that lie around the hard axes of cubic magnetic
anisotropy. This implies that a hard cubic anisotropy axis can be regarded in
(Ga,Mn)As thin films as an easy axis for surface spin pinning.",1512.05140v1
2016-01-06,Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy,"Multifunctional materials composed of ultrathin magnetic films with
perpendicular magnetic anisotropy combined with ferroelectric substrates
represent a new approach toward low power, fast, high density spintronics. Here
we demonstrate Co/Ni multilayered films with tunable saturation magnetization
and perpendicular anisotropy grown directly on ferroelectric PZT
[Pb(Zr_xTi_1-x)O_3] substrate plates. Electric fields up to +/- 2 MV/m expand
the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni
multilayered film. Modifying the strain with a voltage can reduce the coercive
field by over 30%. We also demonstrate that alternating in-plane tensile and
compressive strains (less than 0.01%) can be used to propagate magnetic domain
walls. This ability to manipulate high anisotropy magnetic thin films could
prove useful for lowering the switching energy for magnetic elements in future
voltage-controlled spintronic devices.",1601.01349v1
2016-01-12,Ultrafast magneto-photocurrents as probe of anisotropy relaxation in GaAs,"We induce ultrafast photocurrents in a GaAs crystal exposed to a magnetic
field by optical femtosecond excitation. The magneto-photocurrents are studied
by time-resolved detection of the simultaneously emitted THz radiation. We find
that their dynamics differ considerably from the dynamics of other
photocurrents which are expected to follow the temporal shape of the optical
intensity. We attribute this difference to the influence of carrier-anisotropy
relaxation on the magneto-photocurrents. Our measurements show that the
anisotropy relaxation for carrier densities ranging between $10^{16}$ cm$^{-3}$
and $5 \times 10^{17}$ cm$^{-3}$ occurs on two different time scales. While the
slow time constant is approximately 100 fs long and most likely governed by
electron-phonon scattering, the fast time constant is on the order of 10 fs and
presumably linked to the valence band. Our studies not only help to better
understand the microscopic origins of optically induced currents but - being
even more important - show that magneto-photocurrents can be employed as novel
probe of anisotropy relaxation in GaAs. This technique is applicable to all
non-centrosymmetric bulk semiconductors.",1601.02962v1
2016-01-25,"Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory","The Fermi-surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several
elemental metals are studied by \emph{ab initio} calculations. We focus first
on the anisotropy of the EYP as a function of the direction of the
spin-quantization axis [Phys.~Rev.~Lett.\ \textbf{109}, 236603 (2012)]. We
analyze in detail the origin of the gigantic anisotropy in $5d$ hcp metals as
compared to $5d$ cubic metals by band-structure calculations and discuss the
stability of our results against an applied magnetic field. We further present
calculations of light (4$d$ and 3$d$) hcp crystals, where we find a huge
increase of the EYP anisotropy, reaching colossal values as large as $6000\%$
in hcp Ti. We attribute these findings to the reduced strength of spin-orbit
coupling, which promotes the anisotropic spin-flip hot loops at the Fermi
surface.
  In order to conduct these investigations, we developed an adapted
tetrahedron-based method for the precise calculation of Fermi surfaces of
complicated shape and accurate Fermi-surface integrals within the
full-potential relativistic Korringa-Kohn-Rostoker Green-function method.",1601.06605v1
2016-02-23,Impact of momentum anisotropy and turbulent chromo-fields on thermal particle production in quark-gluon plasma medium,"Momentum anisotropy present during the hydrodynamic evolution of Quark-Gluon
Plasma (QGP) in RHIC may lead to chromo-Weibel instability and turbulent
chromo-fields.The dynamics of the quark and gluon momentum distributions in
this case is governed by an effective diffusive Vlasov equation (linearized).
The solution of this linearized transport equation for the modified momentum
distribution functions lead to the mathematical form of non-equilibrium
momentum distribution functions of quarks/antiquarks and gluons. The
modification to these distributions encode the physics of turbulent color
fields and momentum anisotropy. In the present manuscript, we employ these
distribution functions to to estimate thermal dilepton production rate in the
QGP medium. The production rate is seen to have appreciable sensitivity to the
strength of the anisotropy.",1602.07142v3
2016-03-02,Blocking temperature of interacting magnetic nanoparticles with uniaxial and cubic anisotropies from Monte Carlo simulations,"The low temperature behavior of densely packed interacting spherical single
domain nanoparticles (MNP) is investigated by Monte Carlo simulations in the
framework of an effective one spin model. The particles are distributed through
a hard sphere like distribution with periodic boundary conditions and interact
through the dipole dipole interaction (DDI) with an anisotropy energy including
both cubic and uniaxial symmetry components. The cubic component is shown to
play a sizable role on the value of the blocking temperature $T_b$ only when
the MNP easy axes are parallel to the cubic easy direction ([111] direction for
a negative cubic anisotropy constant). The nature of the collective low
temperature state, either ferromagnetic or spin glass like, is found to depend
on the ratio of the anisotropy to the dipolar energies characterizing partly
the disorder in the system.",1603.00605v1
2016-03-11,A Mechanism of Long-Range Order Induced by Random Local Fields: Effective Anisotropy Created by Defects,"We propose a microscopic mechanism of the long-range order in two-dimensional
space induced by random local fields of crystal defects. The anisotropic
distribution of defect-induced random local field directions in the
n-dimensional space of vector order parameter with the O(n) symmetry is shown
to give rise to the defect-induced effective anisotropy in the system. The
expression for the effective anisotropy constant is found. A weak anisotropy of
the ""easy axis"" type transforms the X-Y model and the Heisenberg model to the
class of Ising models, and brings into existence the long-range order in the
system.",1603.03687v1
2016-03-20,Reconstruction of CMB Temperature Anisotropies with Primordial CMB Induced Polarization in Galaxy Clusters,"Scattering of cosmic microwave background (CMB) radiation in galaxy clusters
induces polarization signals determined by the quadrupole anisotropy in the
photon distribution at the location of clusters. This ""remote quadrupole""
derived from the measurements of the induced polarization in galaxy clusters
provides an opportunity of reconstruction of local CMB temperature
anisotropies. In this {\em Letter} we develop an algorithm of the
reconstruction through the estimation of the underlying primordial
gravitational potential, which is the origin of the CMB temperature and
polarization fluctuations and CMB induced polarization in galaxy clusters. We
found a nice reconstruction for the quadrupole and octopole components of the
CMB temperature anisotropies with the assistance of the CMB induced
polarization signals. The reconstruction can be an important consistency test
on the puzzles of CMB anomaly, especially for the low quadrupole and axis of
evil problems reported in WMAP and Planck data.",1603.06166v1
2016-04-01,Conductivities in an anisotropic medium,"In order to imitate anisotropic medium of a condensed matter system, we take
into account an Einstein-Maxwell-dilaton-axion model as a dual gravity theory
where the anisotropy is caused by different momentum relaxations. This gravity
model allows an anisotropic charged black hole solution. On this background, we
investigate how the linear responses of vector modes like electric,
thermoelectric, and thermal conductivities rely on the anisotropy. We find that
the electric conductivity in low frequency limit shows a Drude peak and that in
the intermediate frequency regime it reveals the power law behavior.
Especially, when the anisotropy increases the exponent of the power law becomes
smaller. In addition, we find that there exist a critical value for the
anisotropy at which the DC conductivity reaches to its maximum value.",1604.00156v1
2016-04-23,Interplay between anisotropy and spatial dispersion in metamaterial waveguide,"We analyze spectrum of waveguide modes of an arbitrary uniaxial anisotropic
metamaterial slab with non-local electromagnetic response whose permittivity
tensor could be described within Drude approximation. Spatial dispersion was
introduced within the hydrodynamical model. Both anisotropy and spatial
dispersion were considered as perturbations. This helps to distinguish their
effect on the spectrum of the slab and to analyze lifting of the degeneracy of
eigenmodes at plasma frequency in detail. Spatial dispersion is shown to result
in break of the singularity in the den- sity of optical states in the
hyperbolic regime and in suppression of negative dispersion induced by
anisotropy. Mutual effect of spatial dispersion and anisotropy can bring light
to a complete stop at certain frequencies.",1604.06925v1
2016-05-02,A computational scheme to evaluate Hamaker constants of molecules with practical size and anisotropy,"We propose a computational scheme to evaluate Hamaker constants, $A$, of
molecules with practical sizes and anisotropies. Upon the increasing
feasibility of diffusion Monte Carlo (DMC) methods to evaluate binding curves
for such molecules to extract the constants, we discussed how to treat the
averaging over anisotropy and how to correct the bias due to the
non-additivity. We have developed a computational procedure for dealing with
the anisotropy and reducing statistical errors and biases in DMC valuations,
based on possible validations on predicted $A$. We applied the scheme to
cyclohexasilane molecule, Si$_6$H$_{12}$, used in 'printed electronics'
fabrications, getting $A \sim 105 \pm 2$ [zJ], being in plausible range
supported even by other possible extrapolations. The scheme provided here would
open a way to use handy {\it ab initio} evaluations to predict wettabilities as
in the form of materials informatics over broader molecules.",1605.00580v3
2016-05-10,Latent heat at the first order phase transition point of SU(3) gauge theory,"We calculate the energy gap (latent heat) and pressure gap between the hot
and cold phases of the SU(3) gauge theory at the first order deconfining phase
transition point. We perform simulations around the phase transition point with
the lattice size in the temporal direction Nt=6, 8 and 12 and extrapolate the
results to the continuum limit. We also investigate the spatial volume
dependence. The energy density and pressure are evaluated by the derivative
method with non-perturabative anisotropy coefficients. We adopt a multi-point
reweighting method to determine the anisotropy coefficients. We confirm that
the anisotropy coefficients approach the perturbative values as Nt increases.
We find that the pressure gap vanishes at all values of Nt when the
non-perturbative anisotropy coefficients are used. The spatial volume
dependence in the latent heat is found to be small on large lattices.
Performing extrapolation to the continuum limit, we obtain $ \Delta
\epsilon/T^4 = 0.75 \pm 0.17 $ and $ \Delta (\epsilon -3 p)/T^4 = 0.623 \pm
0.056.$",1605.02997v1
2016-05-11,Anisotropy of spin coherence in high mobility quantum wells with arbitrary magnetic fields,"We present a theoretical study of the anisotropy of the spin relaxation and
decoherence in typical quantum wells with an arbitrary magnetic field. In such
systems, the orientation of the magnetic field relative to the main
crystallographic directions is crucial, owing to the lack of spin-rotation
symmetry. For typical high mobility samples, relaxation anisotropies in the
motional narrowing limit owing to the interplay of Rashba and Dresselhaus spin
orbit coupling are calculated. We also include the effect of the
cubic-in-momentum terms. Although commonly ignored in literature, the latter
were experimentally evidenced by the observation of strong anisotropy in spin
decoherence measurements by different experimental groups and has long remained
unexplained.",1605.03399v2
2016-05-25,Linear theory of random textures of 3He-A in aerogel,"Spacial variation of the orbital part of the order parameter of $^3$He-A in
aerogel is represented as a random walk of the unit vector $\mathbf{l}$ in a
field of random anisotropy produced by the strands of aerogel. For a range of
distances, where variation of $\mathbf{l}$ is small in comparison with its
absolute value correlation function of directions of $\mathbf{l}(\mathbf{r})$
is expressed in terms of the correlation function of the random anisotropy
field. With simplifying assumptions about this correlation function a spatial
dependence of the average variation $\langle\delta\mathbf{l}^2\rangle$ is found
analytically for isotropic and axially anisotropic aerogels. Average
projections of $\mathbf{l}$ on the axes of anisotropy are expressed in terms of
characteristic parameters of the problem. Within the ""model of random
cylinders"" numerical estimations of characteristic length for disruption of the
long-range order and of the critical anisotropy for restoration of this order
are made and compared with other estimations .",1605.07828v3
2016-07-24,Morphology dependent optical anisotropies in the n-type polymer P(NDI2OD-T2),"Organic semiconductors tend to self-assemble into highly ordered and oriented
morphologies with anisotropic optical properties. Studying these optical
anisotropies provides insight into processing-dependent structural properties
and informs the photonic design of organic photovoltaic and light-emitting
devices. Here, we measure the anisotropic optical properties of spin-cast films
of the n-type polymer P(NDI2OD-T2) using momentum-resolved absorption and
emission spectroscopies. We quantify differences in the optical anisotropies of
films deposited with distinct face-on and edge-on morphologies. In particular,
we infer a substantially larger out-of-plane tilt angle of the optical
transition dipole moment in high temperature annealed, edge-on films.
Measurements of spectral differences between in-plane and out-of-plane dipoles,
further indicate regions of disordered polymers in low temperature annealed
face-on films that are otherwise obscured in traditional X-ray and optical
characterization techniques. The methods and analysis developed in this work
provide a way to identify and quantify subtle optical and structural
anisotropies in organic semiconductors that are important for understanding and
designing highly efficient thin film devices.",1607.07066v1
2016-08-24,Anisotropic spin fluctuations in Sr$_2$RuO$_4$: role of spin-orbit coupling and induced strain,"We analyze the spin anisotropy of the magnetic susceptibility of Sr$_2$RuO$4$
in presence of spin-orbit coupling and anisotropic strain using
quasi-two-dimensional tight-binding parametrization fitted to the ARPES
results. Similar to the previous observations we find the in-plane polarization
of the low ${\bf q}$ magnetic fluctuations and the out-of-plane polarization of
the incommensurate magnetic fluctuation at the nesting wave vector ${\bf Q}_1 =
(2/3 \pi ,2/3 \pi)$ but also nearly isotropic fluctuations near ${\bf
Q}_2=(\pi/6,\pi/6)$. Furthermore, one finds that apart from the high-symmetry
direction of the tetragonal Brillouin zone the magnetic anisotropy is maximal,
i.e. $\chi^{xx} \neq \chi^{yy} \neq \chi^{zz}$. This is the consequence of the
orbital anisotropy of the $xz$ and $yz$ orbitals in the momentum space. We also
study how the magnetic anisotropy evolves in the presence of the strain and
find strong Ising-like ferromagnetic fluctuations near the Lifshitz transition
for the $xy$-band.",1608.06786v1
2016-09-25,Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via Nanomechanical Multimode Resonance Spectromicroscopy,"Black phosphorus (P) has emerged as a layered semiconductor with a unique
crystal structure featuring corrugated atomic layers and strong in-plane
anisotropy in its physical properties. Here, we demonstrate that the crystal
orientation and mechanical anisotropy in free-standing black P thin layers can
be precisely determined by spatially resolved multimode nanomechanical
resonances. This offers a new means for resolving important crystal orientation
and anisotropy in black P device platforms in situ beyond conventional optical
and electrical calibration techniques. Furthermore, we show that
electrostatic-gating-induced straining can continuously tune the mechanical
anisotropic effects on multimode resonances in black P electromechanical
devices. Combined with finite element modeling (FEM), we also determine the
Young's moduli of multilayer black P to be 116.1 and 46.5 GPa in the zigzag and
armchair directions, respectively.",1609.07801v1
2016-09-26,Ferromagnetic resonance study of composite Co/Ni - FeCoB free layers with perpendicular anisotropy,"We study the properties of composite free layers with perpendicular
anisotropy. The free layers are made of a soft FeCoB layer ferromagnetically
coupled by a variable spacer (Ta, W, Mo) to a very anisotropic [Co/Ni]
multilayer embodied in a magnetic tunnel junction meant for spin torque memory
applications. For this we use broadband ferromagnetic resonance to follow the
field dependence of the acoustical and optical excitation of the composite free
layer in both in-plane and out-of-plane applied fields. The modeling provides
the interlayer exchange coupling, the anisotropies and the damping factors. The
popular Ta spacer are outperformed by W and even more by Mo, which combines the
strongest interlayer exchange coupling without sacrificing anisotropies,
damping factors and transport properties.",1609.07863v1
2016-09-26,Supernovae anisotropy power spectrum,"We contribute another anisotropy study to this field of research using Type
Ia supernovae (SNe Ia). In this work, we utilise the power spectrum calculation
method and apply it to both the current SNe Ia data and simulation. Using the
Union2.1 data set at all redshifts, we compare the spectrum of the residuals of
the observed distance moduli to that expected from an isotropic universe
affected by the Union2.1 observational uncertainties at low multipoles. Through
this comparison we find a dipolar anisotropy with tension of less that
$2\sigma$ towards $l =171^\circ \pm 21^\circ$ and $b=-26^\circ \pm 28^\circ$
which is mainly induced by anisotropic spatial distribution of the SNe with $z
> 0.2$ rather than being a cosmic effect. Furthermore, we find a tension of
$\sim 4\sigma$ at $\ell=4$ between the two spectra. Our simulations are
constructed with the characteristics of the upcoming surveys like the Large
Synoptic Survey Telescope (LSST), which shall bring us the largest SNe Ia
collection to date. We make predictions for the amplitude of a possible dipolar
anisotropy that would be detectable by future SNe Ia surveys.",1609.08012v3
2016-10-10,Determination of the resistivity anisotropy of orthorhombic materials via transverse resistivity measurements,"Measurements of the resistivity anisotropy can provide crucial information
about the electronic structure and scattering processes in anisotropic and
low-dimensional materials, but quantitative measurements by conventional means
often suffer very significant systematic errors. Here we describe a novel
approach to measuring the resistivity anisotropy of orthorhombic materials,
using a single crystal and a single measurement, that is derived from a
$\frac{\pi}{4}$ rotation of the measurement frame relative to the
crystallographic axes. In this new basis the transverse resistivity gives a
direct measurement of the resistivity anisotropy, which combined with the
longitudinal resistivity also gives the in-plane elements of the conventional
resistivity tensor via a 5-point contact geometry. This is demonstrated through
application to the charge-density wave compound ErTe$_3$, and it is concluded
that this method presents a significant improvement on existing techniques in
many scenarios.",1610.03122v1
2016-10-19,Anomalous Thermal Diffusivity in Underdoped YBa$_2$Cu$_3$O$_{6+x}$,"We present local optical measurements of thermal diffusivity in the $ab$
plane of underdoped YBCO crystals. We find that the diffusivity anisotropy is
comparable to reported values of the electrical resistivity anisotropy,
suggesting that the anisotropies have the same origin. The anisotropy drops
sharply below the charge order transition. We interpret our results through a
strong electron-phonon scattering picture and find that both electronic and
phononic contributions to the diffusivity saturate a proposed bound. Our
results suggest that neither well-defined electron nor phonon quasiparticles
are present in this material.",1610.05845v2
2016-10-27,Giant variation of the perpendicular magnetic anisotropy at Fe/MgO interfaces by oxygen migration: a first-principles study,"A characteristic dependence of voltage control of perpendicular magnetic
anisotropy (VCMA) on oxygen migration at Fe/MgO interfaces was revealed by
performing systematic {\it ab initio} study of the energetics of the oxygen
path around the interface. We find that the surface anisotropy energy exhibits
a Boltzmann sigmoidal behavior as a function of the migrated O-atoms
concentration. The obtained variation of the VCMA efficiency factor $\beta$
reveals a saturation limit beyond a critical concentration of migrated O, about
$54\%$, at which the anisotropy switches from perpendicular to in plane.
Furthermore, depending on the range of variation of the applied voltage, two
regimes associated with reversible or irreversible ions displacement are
predicted to occur, yielding different VCMA response. According to our
findings, one can distinguish from the order of magnitude of $\beta$ the VCMA
driving mechanism: an effect of several tens of fJ/(V.m) is likely associated
to charge-mediated effect combined with slight reversible oxygen displacements
whereas an effect of the order of thousands of fJ/(V.m) is more likely
associated with irreversible oxygen ionic migration.",1610.08859v2
2016-11-15,Recent progress in anisotropic hydrodynamics,"The quark-gluon plasma created in a relativistic heavy-ion collisions
possesses a sizable pressure anisotropy in the local rest frame at very early
times after the initial nuclear impact and this anisotropy only slowly relaxes
as the system evolves. In a kinetic theory picture, this translates into the
existence of sizable momentum-space anisotropies in the underlying partonic
distribution functions, <p_L^2> << <p_T^2>. In such cases, it is better to
reorganize the hydrodynamical expansion by taking into account momentum-space
anisotropies at leading-order in the expansion instead of as a perturbative
correction to an isotropic distribution. The resulting anisotropic
hydrodynamics framework has been shown to more accurately describe the dynamics
of rapidly expanding systems such as the quark-gluon plasma. In this
proceedings contribution, I review the basic ideas of anisotropic
hydrodynamics, recent progress, and present a few preliminary phenomenological
predictions for identified particle spectra and elliptic flow.",1611.05056v1
2016-11-25,Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions,"Minijets and jets are produced in large numbers in nuclear collisions at TeV
energies, so that there are many of them in a single fireball. They deposit
non-negligible amount of momentum and energy into the hydrodynamically
expanding bulk and cause anisotropies of the expansion. Moreover, due to their
multiple production in a single event the resulting anisotropies are correlated
with the collision geometry and thus contribute positively also to
event-averaged anisotropies in non-central collisions. Using simulations with
three-dimensional ideal hydrodynamic model we demonstrate the importance of
this effect. It must be taken into account if conclusions about the properties
of the hot matter are to be drawn.",1611.08577v1
2016-11-28,Fine-tuning challenges for the matter bounce scenario,"A bouncing universe with a long period of contraction during which the
average density is pressureless (the same equation of state as matter) as
cosmologically observable scales exit the Hubble horizon has been proposed as
an explanation for producing a nearly scale-invariant spectrum of adiabatic
scalar perturbations. A well-known problem with this scenario is that, unless
suppressed, the energy density associated with anisotropy grows faster than
that of the pressureless matter, so the matter-like phase is unstable. Previous
models introduce an ekpyrotic phase after the matter-like phase to prevent the
anisotropy from generating chaotic mixmaster behavior. In this work, though, we
point out that, unless the anisotropy is suppressed first, the matter-like
phase will never start and that suppressing the anisotropy requires
extraordinary, exponential fine-tuning.",1611.08972v1
2016-12-07,Size-Resolved Photoelectron Anisotropy of Gas Phase Water Clusters and Predictions for Liquid Water,"We report the first measurement of size-resolved photoelectron angular
distributions for the valence orbitals of water clusters with up to 20
molecules. A systematic decrease of the photoelectron anisotropy is found for
clusters with up to 5-6 molecules, and most remarkably, convergence of the
anisotropy for larger clusters. We suggest the latter to be the result of a
local short-range scattering potential that is fully described by a unit of 5-6
molecules. The cluster data and a detailed electron scattering model are used
to predict liquid water anisotropies. Reasonable agreement with experimental
liquid jet data is found.",1612.02338v1
2017-01-16,Electric field modulation of the non-linear areal magnetic anisotropy energy,"We study the ferromagnetic layer thickness dependence of the
voltage-controlled magnetic anisotropy (VCMA) in gated CoFeB/MgO
heterostructures with heavy metal underlayers. When the effective CoFeB
thickness is below ~1 nm, the VCMA efficiency of Ta/CoFeB/MgO heterostructures
considerably decreases with decreasing CoFeB thickness. We find that a high
order phenomenological term used to describe the thickness dependence of the
areal magnetic anisotropy energy can also account for the change in the areal
VCMA efficiency. In this structure, the higher order term competes against the
common interfacial VCMA, thereby reducing the efficiency at lower CoFeB
thickness. The areal VCMA efficiency does not saturate even when the effective
CoFeB thickness exceeds ~1 nm. We consider the higher order term is related to
the strain that develops at the CoFeB/MgO interface: as the average strain of
the CoFeB layer changes with its thickness, the electronic structure of the
CoFeB/MgO interface varies leading to changes in areal magnetic anisotropy
energy and VCMA efficiency.",1701.04150v1
2017-01-26,Numerical study of anisotropy in a composite Fermi liquid,"We perform density-matrix renormalization group studies of a two-dimensional
electron gas in a high magnetic field and with an anisotropic band mass. At
half-filling in the lowest Landau level, such a system is a Fermi liquid of
composite fermions. By measuring the Fermi surface of these composite fermions,
we determine a relationship between the anisotropy of composite fermion
dispersion, $\alpha_{CF}$, and the original anisotropy $\alpha_F$ of the
fermion dispersion at zero magnetic field. For systems where the electrons
interact via a Coulomb interaction, we find $\alpha_{CF}=\sqrt{\alpha_F}$
within our numerical accuracy. The same result has been found concurrently in
recent experiments. We also show results with other forms of the
electron-electron interaction; this allows us (a) to benchmark our procedure
against known exact results and (b) to show that the relationship between the
anisotropies is dependent on the form of the interaction.",1701.07832v2
2017-01-16,Bianchi-V String Cosmological model with Dark Energy Anisotropy,"The role of anisotropic components on the dark energy and the dynamics of the
universe is investigated. An anisotropic dark energy fluid with different
pressures along different spatial directions is assumed to incorporate the
effect of anisotropy. One dimensional cosmic strings aligned along x-direction
supplement some kind of anisotropy. Anisotropy in the dark energy pressure is
found to evolve with cosmic expansion at least at late times. At an early
phase, the anisotropic effect due to the cosmic strings substantially affect
the dynamics of the accelerating universe.",1701.08632v4
2017-02-02,Radial anisotropy in omega Cen limiting the room for an intermediate-mass black hole,"Finding an intermediate-mass black hole (IMBH) in a globular cluster (or
proving its absence) would provide valuable insights into our understanding of
galaxy formation and evolution. However, it is challenging to identify a unique
signature of an IMBH that cannot be accounted for by other processes.
Observational claims of IMBH detection are indeed often based on analyses of
the kinematics of stars in the cluster core, the most common signature being a
rise in the velocity dispersion profile towards the centre of the system.
Unfortunately, this IMBH signal is degenerate with the presence of
radially-biased pressure anisotropy in the globular cluster. To explore the
role of anisotropy in shaping the observational kinematics of clusters, we
analyse the case of omega Cen by comparing the observed profiles to those
calculated from the family of LIMEPY models, that account for the presence of
anisotropy in the system in a physically motivated way. The best-fit radially
anisotropic models reproduce the observational profiles well, and describe the
central kinematics as derived from Hubble Space Telescope proper motions
without the need for an IMBH.",1702.00725v1
2017-02-03,Cosmic-Ray Anisotropy and the Local Interstellar Turbulence,"We study the role of local interstellar turbulence in shaping the large-scale
anisotropy in the arrival directions of TeV-PeV cosmic-rays (CRs) on the sky.
Assuming pitch-angle diffusion of CRs in a magnetic flux tube containing the
Earth, we compute the CR anisotropy for Goldreich-Sridhar turbulence, and for
isotropic fast modes. The narrow deficits in the 400 TeV and 2 PeV data sets of
IceTop can be fitted for some parameters of the turbulence. The data also rule
out a part of the parameter space. The shape of the CR anisotropy may be used
as a local probe of the still poorly known properties of the interstellar
turbulence and of CR transport.",1702.01001v1
2017-02-12,"Micromagnetic study of a feasibility of the magnetic anisotropy engineering in nano-structured epitaxial films of (III,Mn)V ferromagnetic semiconductors","The attainability of modification of the apparent magnetic anisotropy in
(III,Mn)V ferromagnetic semiconductors is probed by means of the
finite-elements-based modelling. The most representative case of (Ga,Mn)As and
its in-plane uniaxial anisotropy is investigated. The hysteresis loops of the
continuous films of a ferromagnetic semiconductor as well as films structured
with the elliptic antidots are modelled for various eccentricity, orientation,
and separation of the anti dots. The effect of anti-dots on the magnetic
anisotropy is confirmed but overall is found to be very weak. The subsequent
modelling for (Ga,Mn)As film with the elliptic dots comprising of metallic NiFe
shows much stronger effect, revealing switching of the magnetic moment in the
ferromagnetic semiconductor governed by the switching behavior of the metallic
inclusions.",1702.03509v1
2017-02-12,Excitonic mass gap in uniaxially strained graphene,"We study the conditions for spontaneously generating an excitonic mass gap
due to Coulomb interactions between anisotropic Dirac fermions in uniaxially
strained graphene. The mass gap equation is realized as a self-consistent
solution for the self-energy within the Hartree-Fock mean-field and static
random phase approximations. It depends not only on momentum, due to the
long-range nature of the interaction, but also on the velocity anisotropy
caused by the presence of uniaxial strain. We solve the nonlinear integral
equation self-consistently by performing large scale numerical calculations on
variable grid sizes. We evaluate the mass gap at the charge neutrality (Dirac)
point as a function of the dimensionless coupling constant and anisotropy
parameter. We also obtain the phase diagram of the critical coupling, at which
the gap becomes finite, against velocity anisotropy. Our numerical study
indicates that with an increase in uniaxial strain in graphene the strength of
critical coupling decreases, which suggests anisotropy supports formation of
excitonic mass gap in graphene.",1702.03551v2
2017-03-21,Experimental determination of Rashba and Dresselhaus parameters and $g^*$-factor anisotropy via Shubnikov-de Haas oscillations,"The spin splitting of conduction band electrons in inversion-asymmetric
InGaAs/InP quantum wells is studied by Shubnikov-de Haas measurements combining
the analysis of beating patterns and coincidence measurements in doubly tilted
magnetic fields. The method allows us to determine the absolute values of the
Rashba and linear Dresselhaus spin-orbit interaction coefficients, their
relative sign and the full Land\'e g-tensor. This is achieved by analyzing the
anisotropy of the beat node positions with respect to both polar and azimuthal
angles between the magnetic field direction and the quantum well normal. We
show that the spin-orbit interaction is dominated by a large Rashba coefficient
together with a linear Dresselhaus coefficient that is 10 $\%$ of the Rashba
coefficient. Their relative sign is found to be positive. The g-tensor is found
to have a marked out-of-plane anisotropy and a smaller but distinct in-plane
anisotropy due to spin-orbit interaction.",1703.07143v1
2017-03-23,Effect of anisotropy distribution on local nucleation field in bistable ferromagntic microwires,"Critical parameters defining the local nucleation field in amorphous
ferromagnetic microwires with positive magnetostriction are obtained
analytically through scaling procedures. Exact value of the nucleation field is
obtained numerically as a function of geometric parameters of anisotropy
distribution, which is fully taken into account instead of being averaged out.
It is established that the value of nucleation field depends predominantly on
the steepness of anisotropy change withing the boundary between axial and
radial domains, while the maximal value of anisotropy inside the wire or an
overall average is not relevant.",1703.08066v5
2017-04-10,Limits on statistical anisotropy from BOSS DR12 galaxies using bipolar spherical harmonics,"We measure statistically anisotropic signatures imprinted in
three-dimensional galaxy clustering using bipolar spherical harmonics (BipoSHs)
in both Fourier space and configuration space. We then constrain a well-known
quadrupolar anisotropy parameter $g_{2M}$ in the primordial power spectrum,
parametrized by $P(\vec{k}) = \bar{P}(k) [ 1 + \sum_{M} g_{2M} Y_{2M}(\hat{k})
]$, with $M$ determining the direction of the anisotropy. Such an anisotropic
signal is easily contaminated by artificial asymmetries due to specific survey
geometry. We precisely estimate the contaminated signal and finally subtract it
from the data. Using the galaxy samples obtained by the Baryon Oscillation
Spectroscopic Survey Data Release 12, we find no evidence for violation of
statistical isotropy, $g_{2M}$ for all $M$ to be of zero within the $2\sigma$
level. The $g_{2M}$-type anisotropy can originate from the primordial curvature
power spectrum involving a directional-dependent modulation $g_* (\hat{k} \cdot
\hat{p})^2$. The bound on $g_{2M}$ is translated into $g_*$ as $-0.09 < g_* <
0.08$ with a $95\%$ confidence level when $\hat{p}$ is marginalized over.",1704.02868v2
2017-04-18,Heavy decaying dark matter and large-scale anisotropy of high-energy cosmic rays,"We examine the role of the large--scale anisotropy of the high--energy cosmic
ray distribution in a search for the heavy decaying dark matter (DM) signal.
Using recent anisotropy measurements from the extensive air shower (EAS)
observatories we constrain the lifetime of the DM particles with masses
$10^{7}~\leq~M_X~\leq~10^{16}$ GeV. These constraints appear to be weaker than
that obtained with the high energy gamma-ray limits. We also estimate the
desired precision level for the anisotropy measurements to discern the decaying
DM signal marginally allowed by the gamma-ray limits and discuss the prospects
of the DM search with the modern EAS facilities.",1704.05300v2
2017-04-18,Instability constraints for the electron temperature anisotropy in the slow solar wind. Thermal core vs. suprathermal halo,"This letter presents the results of an advanced parametrization of the solar
wind electron temperature anisotropy and the instabilities resulting from the
interplay of the (bi-)Maxwellian core and (bi-)Kappa halo populations in the
slow solar wind. A large set of observational data (from the Ulysses, Helios
and Cluster missions) is used to parametrize these components and establish
their correlations. The instabilities are significantly stimulated in the
presence of suprathermals, and the instability thresholds shape the limits of
the temperature anisotropy for both the core and halo populations re-stating
the incontestable role that the selfgenerated instabilities can play in
constraining the electron anisotropy. These results confirm a particular
implication of the suprathermal electrons which are less dense but hotter than
thermal electrons.",1704.05311v2
2017-04-18,On commutativity and near commutativity of translational and rotational averages: Analytical proofs and numerical examinations,"We show that, in general, the translational average over a spatial
variable---discussed by Backus \cite{backus}, and referred to as the
equivalent-medium average---and the rotational average over a symmetry group at
a point---discussed by Gazis et al. \cite{gazis}, and referred to as the
effective-medium average---do not commute. However, they do commute in special
cases of particular symmetry classes, which correspond to special relations
among the elasticity parameters. We also show that this noncommutativity is a
function of the strength of anisotropy. Surprisingly, a perturbation of the
elasticity parameters about a point of weak anisotropy results in the
commutator of the two types of averaging being of the order of the {\it
square\/} of this perturbation. Thus, these averages nearly commute in the case
of weak anisotropy, which is of interest in such disciplines as quantitative
seismology, where the weak-anisotropy assumption results in empirically
adequate models.",1704.05541v3
2017-04-21,Charge/quadrupole fluctuations and gap anisotropy in BiS$_2$-based superconductors,"Recent angle-resolved spectroscopy in BiS$_2$-based superconductors has
indicated that the superconducting gap amplitude possesses remarkable
anisotropy and/or a sign change on a small Fermi pocket around $X$ point. It
implies a possibility of an unconventional pairing state. Here we study the gap
anisotropy in superconductivity mediated by inherent charge/quadrupole
fluctuations in an extended Hubbard model, which includes inter-site
interaction between Bi and S atoms. The first-principles downfolded band
structure is composed of Bi $6p_x/p_y$ and S $3p_x/p_y$ orbitals on a BiS$_2$
single layer. Evaluating the linearized gap equation, we find that the ferroic
charge/quadrupole fluctuation driven by the inter-site interaction leads to a
fully-gapped $d_{x^2-y^2}$-wave pairing state, in which the gap amplitude has
sizable anisotropy on the Fermi surface.",1704.06396v1
2017-05-08,Angular dependence of magnetization reversal in epitaxial chromium telluride thin films with perpendicular magnetic anisotropy,"We investigate magnetic anisotropy and magnetization reversal mechanism in
chromium telluride thin films grown by molecular beam epitaxy. We report
existence of strong perpendicular anisotropy in these thin films, along with a
relatively strong second order anisotropy contribution. The angular variation
of the switching field observed from the magnetoresistance measurement is
explained quantitatively using a one-dimensional defect model. The model
reveals the relative roles of nucleation and pinning in the magnetization
reversal, depending on the applied field orientation. Micromagnetic simulations
are performed to visualize the domain structure and switching process.",1705.03121v1
2017-05-09,Large magnetic anisotropy in $Fe_xTaS_2$ single crystals,"In intercalated transition metal dichalcogenide $Fe_xTaS_2$ (0.2 $\leq$ x
$\leq$ 0.4) single crystals, large magnetic anisotropy is observed. Transport
property measurements indicate that heavy Fe-doping leads to a large anisotropy
of resistivity ($\rho$$_{c}$/$\rho$$_{ab}$). A sharp M-H hysteresis curve is
observed with magnetic field along c-axis, while a linear magnetization appears
with magnetic field applied in the ab-plane. The angular dependent magnetic
susceptibility from in-plane to out-of-plane indicates that magnetic moments
are strongly pinned along the c-axis in an unconventional manner and the
coercive field reaches as large as 6 T at T = 5 K. First-principles calculation
clearly suggests that the strong spin-orbital coupling give rise to such a
large anisotropy of magnetism. The strong pinning effect of magnetic moments
along c-axis makes this material a very promising candidate for the development
of spin-aligner in spintronics devices.",1705.03139v1
2017-05-31,Giant Spin Lifetime Anisotropy in Graphene Induced by Proximity Effects,"We report on fundamental aspects of spin dynamics in graphene interfaced with
transition metal dichalcogenides (TMDCs). By using realistic models derived
from first principles we compute the spin lifetime anisotropy, defined as the
ratio of lifetimes for spins pointing out of the graphene plane to those
pointing in the plane. In the presence of strong intervalley scattering the
anisotropy can reach unprecedented values of tens to hundreds, while it reduces
to 1/2 for weak disorder. This behavior is mediated by spin-valley locking,
which is strong in TMDCs and is imprinted onto graphene. Such giant spin
transport anisotropy, driven by proximity effects, provides an exciting
paradigm for designing novel spin device functionalities.",1705.10972v2
2017-06-08,Current-Voltage Characteristics of Borophene and Borophane Sheets,"Motivated by recent experimental and theoretical research on a monolayer of
Boron atoms, Borophene, current-voltage characteristics of three different
Borophene sheets, 2Pmmn, 8Pmmn and 8Pmmm, are calculated using density
functional theory combined with nonequilibriumGreen function formalism.
Borophene sheets with two and eight atoms in a unit cell are considered and
bandstructure, electron density and structural anisotropy of them are analyzed
in details. Results show that 8Pmmn and 8Pmmm structures which have eight atoms
in the unit cell have less anisotropy than 2Pmmn. In addition, although 8Pmmn
shows a Dirac cone in the bandstructure, its current is lower than two others.
We also consider a fully hydrogenated Borophene, Borophane, and find that the
hydrogenation process reduces the structural anisotropy and the current
significantly. Our findings reveal that the current-voltage characteristics of
the Borophene sheets can be used to detect the kind and the growth direction of
the sample because it is strongly dependent on the direction of the electron
transport, anisotropy and details of the unit cell of the Borophene.",1706.02511v1
2017-06-26,CMB anisotropies at all orders: the non-linear Sachs-Wolfe formula,"We obtain the non-linear generalization of the Sachs-Wolfe + integrated
Sachs-Wolfe (ISW) formula describing the CMB temperature anisotropies. Our
formula is valid at all orders in perturbation theory, is also valid in all
gauges and includes scalar, vector and tensor modes. A direct consequence of
our results is that the maps of the logarithmic temperature anisotropies are
much cleaner than the usual CMB maps, because they automatically remove many
secondary anisotropies. This can for instance, facilitate the search for
primordial non-Gaussianity in future works. It also disentangles the non-linear
ISW from other effects. Finally, we provide a method which can iteratively be
used to obtain the lensing solution at the desired order.",1706.08428v2
2017-06-30,Stability of the spin-$1/2$ kagome ground state with breathing anisotropy,"We numerically study the spin-$1/2$ breathing kagome lattice. In this
variation of the kagome Heisenberg antiferromagnet, the spins belonging to
upward and downward facing triangles have different coupling strengths. Using
the density matrix renormalization group (DMRG) method and exact
diagonalization, we show that the kagome antiferromagnet spin liquid is
extremely robust to this anisotropy. Materials featuring this anisotropy -- and
especially the recently studied vanadium compound
$[{\mathrm{NH}}_{4}{]}_{2}[{\mathbf{C}}_{7}{\mathbf{H}}_{14}\mathbf{N}][{\mathbf{V}}_{7}{\mathbf{O}}_{6}{\mathbf{F}}_{18}]$
(DQVOF) -- may thus be very good candidates to realize the much studied kagome
spin liquid. Further, we closely examine the limit of strong breathing
anisotropy and find indications of a transition to a nematic phase.",1706.10105v1
2017-07-07,Nonlinear electric field effect on perpendicular magnetic anisotropy in Fe/MgO interfaces,"The electric field effect on magnetic anisotropy was studied in an ultrathin
Fe(001) monocrystalline layer sandwiched between Cr buffer and MgO tunnel
barrier layers, mainly through post-annealing temperature and measurement
temperature dependences. A large coefficient of the electric field effect of
more than 200 fJ/Vm was observed in the negative range of electric field, as
well as an areal energy density of perpendicular magnetic anisotropy (PMA) of
around 600 uJ/m2. More interestingly, nonlinear behavior, giving rise to a
local minimum around +100 mV/nm, was observed in the electric field dependence
of magnetic anisotropy, being independent of the post-annealing and measurement
temperatures. The insensitivity to both the interface conditions and the
temperature of the system suggests that the nonlinear behavior is attributed to
an intrinsic origin such as an inherent electronic structure in the Fe/MgO
interface. The present study can contribute to the progress in theoretical
studies, such as ab initio calculations, on the mechanism of the electric field
effect on PMA.",1707.02067v1
2017-07-18,Large Magnetic Anisotropy of an Iron-Porphyrin Complex on Metal Substrate,"Single magnetic atoms or molecules with large single-ion magnetic anisotropy
are highly desired for future applications in high-density data storage and
quantum computation. Here we have synthesized an Fe-porphyrin complex on
Au(111) substrate in a controlled way, and revealed large magnetic anisotropy
energy of more than 15 meV by low-temperature scanning tunneling microscopy and
spectroscopy. Two magnetic states with opposite spin directions are
discriminated by inelastic electron tunneling spectroscopy in varied magnetic
field, and are found to have long spin lifetimes. First-principle calculations
reveal that the weak ligand filed in this complex keeps the Fe atom in a
high-spin state and preserves its large orbital angular momentum, which gives
rise to an easy-axis perpendicular to the molecular plane and large magnetic
anisotropy energy by spin-orbit coupling.",1707.05434v1
2017-07-23,A core-shell-surface layer model to explain the size dependence of effective magnetic anisotropy in magnetic nanoparticles,"The particle size (D) dependence of the effective magnetic anisotropy Keff of
magnetic nanoparticles (NPs) usually shows Keff increasing with decreasing D.
This dependence is often interpreted using the Eq.: Keff = Kb + (6Ks/D) where
Kb and Ks are the anisotropy constants of the spins in the bulk-like core and
surface layer, respectively. Here, we show that this model is inadequate to
explain the observed size-dependency of Keff for smaller nanoparticles with D <
5 nm. Instead the results in NPs of maghemite ({\gamma}-Fe2O3), NiO and Ni are
best described by an extension of the above model leading to the variation
given by Keff = Kb + (6Ks/D) +Ksh{[1-(2d/D)]^(-3) -1}, where the last term is
due to the spins in a shell of thickness d with anisotropy Ksh. The validation
of this core-shell-surface layer (CSSL) model for three different magnetic NPs
systems viz. ferrimagnetic {\gamma}-Fe2O3, ferromagnetic Ni and
antiferromagnetic NiO suggests its possible applicability for all magnetic
nanoparticles.",1707.07241v1
2017-07-28,An Introduction to the Planck Mission,"The Cosmic Microwave Background (CMB) is the oldest light in the universe. It
is seen today as black body radiation at a near-uniform temperature of 2.73K
covering the entire sky. This radiation field is not perfectly uniform, but
includes within it temperature anisotropies of order delta(T)/T ~ 10E-5.
Physical processes in the early universe have left their fingerprints in these
CMB anisotropies, which later grew to become the galaxies and large scale
structure we see today. CMB anisotropy observations are thus a key tool for
cosmology. The Planck Mission was the European Space Agency's (ESA) probe of
the CMB. Its unique design allowed CMB anisotropies to be measured to greater
precision over a wider range of scales than ever before. This article provides
an introduction to the Planck Mission, including its goals and motivation, its
instrumentation and technology, the physics of the CMB, how the contaminating
astrophysical foregrounds were overcome, and the key cosmological results that
this mission has so far produced.",1707.09220v1
2017-08-05,Third order perturbed Heisenberg Hamiltonian of sc ferromagnetic films with fifty spin layers,"Magnetic energy of simple cubic structured ferromagnetic films with 10 to 50
spin layers was determined using third order perturbed Heisenberg Hamiltonian.
By plotting 3-D plot of energy versus angle and stress induced anisotropy, the
values of stress induced anisotropy corresponding to energy minimums and
maximums were determined. By plotting the graphs of energy versus angle at
these different stress induced anisotropy values, the easy and hard directions
were determined. Magnetic easy and hard directions are related to energy
minimums and maximums of the curve. Similar graphs were plotted for spin
exchange interaction to determine the easy and hard directions. Graphs of
energy versus angle were plotted by keeping all the magnetic energy parameters
at constant values for each number of spin layers to determine the variation of
magnetic easy directions, hard direction and corresponding energies with the
number of spin layers. The magnetic easy axis gradually rotates from out of
plane to in plane direction as the number of spin layers is increased. In
addition, the magnetic anisotropy energy increases with the number of spin
layers.",1708.02996v1
2017-08-31,Antiferromagnetic anisotropy determination by spin Hall magnetoresistance,"An electric method for measuring magnetic anisotropy in antiferromagnetic
insulators (AFIs) is proposed. When a metallic film with strong spin-orbit
interactions, e.g., platinum (Pt), is deposited on an AFI, its resistance
should be affected by the direction of the AFI N eel vector due to the spin
Hall magnetoresistance (SMR). Accordingly, the direction of the AFI N eel
vector, which is affected by both the external magnetic field and the magnetic
anisotropy, is reflected in resistance of Pt. The magnetic field angle
dependence of the resistance of Pt on AFI is calculated by consider- ing the
SMR, which indicates that the antiferromagnetic anisotropy can be obtained
experimentally by monitoring the Pt resistance in strong magnetic fields.
Calculations are performed for realistic systems such as Pt/Cr2O3, Pt/NiO, and
Pt/CoO.",1708.09564v1
2017-09-05,Semianalytic calculation of cosmic microwave background anisotropies from wiggly and superconducting cosmic strings,"We study how the presence of world-sheet currents affects the evolution of
cosmic string networks, and their impact on predictions for the cosmic
microwave background (CMB) anisotropies generated by these networks. We provide
a general description of string networks with currents and explicitly
investigate in detail two physically motivated examples: wiggly and
superconducting cosmic string networks. By using a modified version of the
CMBact code, we show quantitatively how the relevant network parameters in both
of these cases influence the predicted CMB signal. Our analysis suggests that
previous studies have overestimated the amplitude of the anisotropies for
wiggly strings. For superconducting strings the amplitude of the anisotropies
depends on parameters which presently are not well known - but which can be
measured in future high-resolution numerical simulations.",1709.01839v4
2017-09-23,"Electron Mobility in Monoclinic β-Ga2O3 - Effect of Plasmon-phonon Coupling, Anisotropy, and Confinement","This work reports an investigation of electron transport in monoclinic
\beta-Ga2O3 based on a combination of density functional perturbation theory
based lattice dynamical computations, coupling calculation of lattice modes
with collective plasmon oscillations and Boltzmann theory based transport
calculations. The strong entanglement of the plasmon with the different
longitudinal optical (LO) modes make the role LO-plasmon coupling crucial for
transport. The electron density dependence of the electron mobility in
\beta-Ga2O3 is studied in bulk material form and also in the form of
two-dimensional electron gas. Under high electron density a bulk mobility of
182 cm2/ V.s is predicted while in 2DEG form the corresponding mobility is
about 418 cm2/V.s when remote impurities are present at the interface and
improves further as the remote impurity center moves away from the interface.
The trend of the electron mobility shows promise for realizing high electron
mobility in dopant isolated electron channels. The experimentally observed
small anisotropy in mobility is traced through a transient Monte Carlo
simulation. It is found that the anisotropy of the IR active phonon modes is
responsible for giving rise to the anisotropy in low-field electron mobility.",1709.08117v1
2017-10-18,Collective modes in multicomponent condensates with anisotropy,"We report the effects of anisotropy in the confining potential on two
component Bose-Einstein condensates (TBECs) through the properties of the low
energy quasiparticle excitations. Starting from generalized Gross Pitaevskii
equation, we obtain the Bogoliubov de-Gennes (BdG) equation for TBECs using the
Hartree-Fock-Bogoliubov (HFB) theory. Based on this theory, we present the
influence of radial anisotropy on TBECs in the immiscible or the
phase-separated domain. In particular, the TBECs of $^{85}$Rb~-$^{87}$Rb and
$^{133}$Cs~-$^{87}$Rb TBECs are chosen as specific examples of the two possible
interface geometries, shell-structured and side by side, in the immiscible
domain. We also show that the dispersion relation for the TBEC shell-structured
interface has two branches, and anisotropy modifies the energy scale and
structure of the two branches.",1710.06673v1
2017-10-20,Out-of-plane Enhanced Magnetic Anisotropy Energy in Ni$_{3}$Bz$_{3}$ molecule,"Organometallic complexes formed by transition metals clusters and benzene
molecules have already been synthesized, and in selected cases display magnetic
properties controlled by external magnetic fields. We have studied Ni$_n$Bz$_n$
complexes made of nickel atoms surrounded by benzene molecules and here we
focus specifically on the magnetic molecule Ni$_{3}$Bz$_{3}$. By means of
calculations including relativistic spin-orbit terms, we show that this
molecule reveals a large magnetic anisotropy energy of approximately 8 meV,
found with the easy axis perpendicular to the metal atoms plane. Note that the
matching bare Ni$_{3}$ cluster have similar magnetic anisotropy, however the
easy axis is in-plane. Covering with benzene molecules is thus switching the
easy axis from in-plane for Ni$_3$ to out-of-plane for Ni$_{3}$Bz$_{3}$. The
large out-of-plane magnetic anisotropy of Ni$_{3}$Bz$_{3}$ suggests that this
molecule could indeed be used as part in the design of molecular magnetic
memories.",1710.07519v2
2017-10-31,Constraints on Patchy Reionization from Planck CMB Temperature Trispectrum,"We present constraints on the patchy reionization by measuring the
trispectrum of the Planck 2015 cosmic microwave background (CMB) temperature
anisotropies. The patchy reionization leads to anisotropies in the CMB optical
depth, and the statistics of the observed CMB anisotropies is altered. We
estimate the trispectrum of the CMB temperature anisotropies to constrain
spatial variation of the optical depth. We show that the measured trispectrum
is consistent with that from the standard lensed CMB simulation at $2\sigma$.
While no evidence of the patchy reionization is found in the Planck 2015
temperature trispectrum, the CMB constraint on the patchy reionization is
significantly improved from previous works. Assuming the analytic bubble-halo
model of Wang and Hu (2006), the constraint obtained in this work rules out the
typical bubble size at the ionization fraction of $\sim0.5$ as $R\gtrsim 10$
Mpc. Further, our constraint implies that large-scale $B$-modes from the patchy
reionization are not a significant contamination in detecting the primordial
gravitational waves of $r\gtrsim0.001$ if the $B$ mode induced by the patchy
reionization is described by Dvorkin et al. (2009). The CMB trispectrum data
starts to provide meaningful constraints on the patchy reionization.",1711.00058v2
2017-11-17,The parametric instability of Alfvén waves: effects of temperature anisotropy,"We study the stability of large amplitude, circularly polarized Alfv\'en
waves in an anisotropic plasma described by the double-adiabatic/CGL closure,
and in particular the effect of a background thermal pressure anisotropy on the
well-known properties of Alfv\'en wave parametric decay in Magnetohydrodynamics
(MHD). Anisotropy allows instability over a much wider range of values of
parallel plasma beta ($\beta_\parallel$) when $\xi=p_{0\bot}/p_{0\parallel} >
1$. When the pressure anisotropy exceeds a critical value, $\xi\geq\xi^*$ with
$\xi^*\simeq2.7$, there is a new regime in which the parametric instability is
no longer quenched at high $\beta_\parallel$ and in the limit
$\beta_\parallel\gg1$ the growth rate becomes independent of $\beta_\parallel$.
In the opposite case of $\xi< \xi^*$, the instability is strongly suppressed
with increasing parallel plasma beta, similarly to the MHD case. We analyze
marginal stability conditions for parametric decay in the
$(\xi,\,\beta_\parallel)$ parameter space, and discuss possible implications
for Alfv\'enic turbulence in the solar wind.",1711.06371v1
2017-11-27,Deriving galaxy cluster velocity anisotropy profiles from a joint analysis of dynamical and weak lensing data,"We present an analytic approach to lift the mass-anisotropy degeneracy in
clusters of galaxies by utilizing the line-of-sight velocity dispersion of
clustered galaxies jointly with weak lensing inferred masses. More
specifically, we solve the spherical Jeans equation by assuming a simple
relation between the line-of-sight velocity dispersion and the radial velocity
dispersion and recast the Jeans equation as a Bernoulli differential equation
that has a well-known analytic solution. We first test our method in
cosmological N-body simulations and then derive the anisotropy profiles for 35
archival data galaxy clusters with an average redshift of $\langle
{z}_{c}\rangle =0.25$. The resulting profiles yield a weighted average global
value of $\langle \beta (0.2\leqslant R/{R}_{200}\leqslant 1)\rangle =0.35\pm
0.28$ (stat) \pm 0.15 (sys). This indicates that clustered galaxies tend to
globally fall on radially anisotropic orbits. We note that this is the first
attempt to derive velocity anisotropy profiles for a cluster sample of this
size utilizing joint dynamical and weak lensing data",1711.10018v2
2018-01-03,Effect of low anisotropy on cosmological models by using supernova data,"By using the supernovae type Ia data we study influence of the anisotropy
(although low) on the evolution of the universe and compare ${\Lambda}$CDM
model with 6 representative parametrizations of the recent Hubble expansion
history $H(z)$. To compare these models we use the the maximum likelihood
method for find that the best fit dynamical $\omega(z)$ and $q(z)$ obtained
from the SNIa dataset. In particular we find the best fit value of $\Lambda$CDM
model $(\Omega_{\sigma_0}= 0.013$, $\chi^2_{min}=197.56)$. The analysis shows
that by considering the anisotropy, it leads to more best fit parameters in all
models (except of SCDM) with SNIa data. We also use two statistical tests such
as the usual $\chi^2_{min}/dof$ and p-test to compare different dark energy
models. According to both statistical tests and considering anisotropy, the
linear parametrization model that is providing the best fit to $\Lambda$CDM
model.",1801.01094v3
2018-02-02,Testing the anisotropy of the universe using the simulated gravitational wave events from advanced LIGO and Virgo,"The detection of gravitational waves (GWs) provides a powerful tool to
constrain the cosmological parameters. In this paper, we investigate the
possibility of using GWs as standard sirens in testing the anisotropy of the
universe. We consider the GW signals produced by the coalescence of binary
black hole systems and simulate hundreds of GW events from the advanced Laser
Interferometer Gravitational-Wave Observatory (LIGO) and Virgo. It is found
that the anisotropy of the universe can be tightly constrained if the redshift
of the GW source is precisely known. The anisotropic amplitude can be
constrained with an accuracy comparable to the Union2.1 complication of type-Ia
supernovae if $\gtrsim 400$ GW events are observed. As for the preferred
direction, $\gtrsim 800$ GW events are needed in order to achieve the accuracy
of Union2.1. With 800 GW events, the probability of pseudo anisotropic signals
with an amplitude comparable to Union2.1 is negligible. These results show that
GWs can provide a complementary tool to supernovae in testing the anisotropy of
the universe.",1802.00642v2
2018-02-02,Spin-orbit coupling induced magnetic anisotropy and large spin wave gap in $\rm Na Os O_3$,"The role of spin-orbit coupling and Hund's rule coupling on magnetic
ordering, anisotropy, and excitations are investigated within a minimal
three-orbital model for the $5d^3$ compound $\rm Na Os O_3$. Asymmetry between
the magnetic moments for the $xy$ and $xz,yz$ orbitals, arising from the
hopping asymmetry generated by the $\rm Os O_6$ octahedral tilting and
rotation, together with the weak correlation effect, are shown to be crucial
for the large SOC induced magnetic anisotropy and spin wave gap observed in
this compound. Due to the intrinsic SOC-induced changes in the electronic
densities under rotation of the staggered field, their coupling with the
orbital energy offset is also found to contribute significantly to the magnetic
anisotropy energy.",1802.01449v2
2018-02-22,Gravitational decoupled anisotropies in compact stars,"Simple generic extensions of isotropic Durgapal--Fuloria stars to the
anisotropic domain are presented. These anisotropic solutions are obtained by
guided minimal deformations over a self gravitating isotropic system. When the
isotropic and the anisotropic sector interacts in a purely gravitational
manner, the conditions to decouple both sectors by means of the minimal
geometric deformation approach are satisfied. Hence the anisotropic field
equations are isolated resulting a more treatable set. The simplicity of the
equations allows one to manipulate the anisotropies that can be implemented in
a systematic way to obtain different realistic models for anisotropic
configurations. Later on, observational effects of such anisotropies when
measuring the redshift are discussed. To conclude, the application of the
method over anisotropic solutions is generalized. In this manner, different
anisotropic sectors can be isolated of each other and modeled in a simple and
systematic way. Besides, a generic property of the minimal geometric
deformation approach, its noncommutativity, is discussed. This property
duplicates the solutions obtained through this approach; anisotropies applied
in the reversed order give different physically acceptable configurations.",1802.08000v1
2018-03-26,Uniaxial anisotropy and enhanced magnetostriction of CoFe$_2$O$_4$ induced by reaction under uniaxial pressure with SPS,"In this study, we have compared magnetic and magnetostrictive properties of
polycrystalline CoFe$_2$O$_4$ pellets, produced by three different methods,
focusing on the use of Spark Plasma Sintering (SPS). This technique allows a
very short heat treatment stage while a uniaxial pressure is applied. SPS was
utilized to sinter cobalt ferrite but also to make the reaction and the
sintering (reactive sintering) of the same ceramic composition. Magnetic and
magnetostrictive measurements show that the reactive sintering with SPS induces
a uniaxial anisotropy, while it is not the case with a simple sintering
process. The induced anisotropy is then expected to be a consequence of the
reaction under uniaxial pressure. This anisotropy enhanced the magnetostrictive
properties of the sample, where a maximum longitudinal magnetostriction of
$-229$~ppm is obtained. This process can be a promising alternative to the
magnetic-annealing because of the short processing time required (22 minutes).",1803.09656v1
2018-03-30,Gate-controlled anisotropy in Aharonov-Casher spin interference: signatures of Dresselhaus spin-orbit inversion and spin phases,"The coexistence of Rashba and Dresselhaus spin-orbit interactions (SOIs) in
semiconductor quantum wells leads to an anisotropic effective field coupled to
carriers' spins. We demonstrate a gate-controlled anisotropy in Aharonov-Casher
(AC) spin interferometry experiments with InGaAs mesoscopic rings by using an
in-plane magnetic field as a probe. Supported by a perturbation-theory
approach, we find that the Rashba SOI strength controls the AC resistance
anisotropy via spin dynamic and geometric phases and establish ways to
manipulate them by employing electric and magnetic tunings. Moreover, assisted
by two-dimensional numerical simulations, we identify a remarkable anisotropy
inversion in our experiments attributed to a sign change in the renormalized
linear Dresselhaus SOI controlled by electrical means, which would open a door
to new possibilities for spin manipulation.",1803.11371v2
2018-03-31,Vibration-induced modulation of magnetic anisotropy in a magnetic molecule,"We theoretically analyze the spectrum of a magnetic molecule when its charge
and spin can couple to the molecular vibrations. More specifically, we show
that the interplay between charge-vibron and spin-vibron coupling leads to a
renormalization of the magnetic anisotropy parameters of the molecule. This
effect is discussed for a model device consisting of an individual magnetic
molecule embedded in a junction. We study the transport properties of the
device and illustrate how the differential conductance is affected by the
vibrationally induced renormalization of the magnetic anisotropy. Depending on
the total molecular spin and the bare (intrinsic) magnetic anisotropy, the
induced modulation can lead to visible shifts and crossings in the spectrum,
and it can even be the cause of a transport blockade. It is therefore of
particular interest to use mechanically controllable break junctions, since in
such a case, the relevant coupling between the molecular spin and vibrations
can be controlled via deformations of the molecule when stretching or
compressing the junction.",1804.00142v2
2018-04-18,Ferromagnetic resonance linewidth in coupled layers with easy-plane and perpendicular magnetic anisotropies,"Magnetic bilayers with different magnetic anisotropy directions are
interesting for spintronic appli- cations as they offer the possibility to
engineer tilted remnant magnetization states. We investigate the ferromagnetic
resonance (FMR) linewidth of modes associated with two interlayer exchange-
coupled ferromagnetic layers, the first a CoNi multilayer with a perpendicular
magnetic anisotropy, and the second a CoFeB layer with an easy-plane
anisotropy. For antiferromagnetic interlayer ex- change coupling, elevated FMR
linewidths are observed below a characteristic field. This is in contrast to
what is found in uncoupled, ferromagnetically coupled and single ferromagnetic
layers in which the FMR linewidth increases monotonically with field. We show
that the characteristic field at which there is a dramatic increase in FMR
linewidth can be understood using a macrospin model with Heisenberg-type
exchange coupling between the layers.",1804.06796v1
2018-04-25,Spin precession in anisotropic media,"We generalize the diffusive model for spin injection and detection in
nonlocal spin structures to account for spin precession under an applied
magnetic field in an anisotropic medium, for which the spin lifetime is not
unique and depends on the spin orientation.We demonstrate that the spin
precession (Hanle) line shape is strongly dependent on the degree of anisotropy
and on the orientation of the magnetic field. In particular, we show that the
anisotropy of the spin lifetime can be extracted from the measured spin signal,
after dephasing in an oblique magnetic field, by using an analytical formula
with a single fitting parameter. Alternatively, after identifying the
fingerprints associated with the anisotropy, we propose a simple scaling of the
Hanle line shapes at specific magnetic field orientations that results in a
universal curve only in the isotropic case. The deviation from the universal
curve can be used as a complementary means of quantifying the anisotropy by
direct comparison with the solution of our generalized model. Finally, we
applied our model to graphene devices and find that the spin relaxation for
graphene on silicon oxide is isotropic within our experimental resolution.",1804.09426v1
2018-05-04,GETMe.anis: On geometric polygon transformations leading to anisotropy,"This work contributes to the analysis of linear geometric polygon
transformations with the aim to force a desired shape by an iterative
procedure.",1805.01767v1
2018-05-10,Zener Pinning through Coherent Precipitates: A Phase Field Study,"A novel phase field model has been developed to study the effect of coherent
precipitate on the Zener pinning of matrix grain boundaries. The model accounts
for misfit strain between precipitate and matrix as well as the elastic
inhomogeneity and anisotropy between them. The results show that increase in
elastic misfit, elastic inhomogeneity, and elastic anisotropy increases the
coarsening rate of the precipitates. Increased coarsening of precipitates in
turn decreases the pinning of grain boundaries. Therefore, increase in misfit
strain, elastic inhomogeneity and anisotropy negatively affect the Zener
pinning through coherent precipitate. This study shows elastic anisotropy gives
rise to the needle shape precipitate. It has also been shown that these needle
shaped precipitates are not very effective in Zener pinning. This study
provides an understanding into the effect of coherent precipitate on the Zener
pinning of matrix grain boundaries.",1805.03831v2
2018-05-31,Observation of spin-valley coupling induced large spin lifetime anisotropy in bilayer graphene,"We report the first observation of a large spin lifetime anisotropy in
bilayer graphene (BLG) fully encapsulated between hexagonal boron nitride. We
characterize the out-of-plane ($\tau_\perp$) and in-plane ($\tau_\parallel$)
spin lifetimes by oblique Hanle spin precession. At 75~K and the charge
neutrality point (CNP) we observe a strong anisotropy of
$\tau_\perp/\tau_\parallel$ = 8 $\pm$ 2. This value is comparable to
graphene/TMD heterostructures, whereas our high quality BLG provides with
$\tau_\perp$ up to 9~ns, a more than two orders of magnitude larger spin
lifetime. The anisotropy decreases to 3.5 $\pm$ 1 at a carrier density of n =
$6\times 10^{11}~$cm$^{-2}$. Temperature dependent measurements show above 75~K
a decrease of $\tau_\perp/\tau_\parallel$ with increasing temperature, reaching
the isotropic case close to room temperature. We explain our findings with
electric field induced spin-valley coupling arising from the small intrinsic
spin orbit fields in BLG of 12~$\mu$eV at the CNP.",1805.12420v1
2018-06-05,Anisotropies in the astrophysical gravitational-wave background: Predictions for the detection of compact binaries by LIGO and Virgo,"We develop a detailed anisotropic model for the astrophysical
gravitational-wave background, including binary mergers of two stellar-mass
black holes, two neutron stars, or one of each, which are expected to be the
strongest contributions in the LIGO-Virgo frequency band. The angular spectrum
of the anisotropies, quantified by the $C_\ell$ components, is calculated using
two complementary approaches: (i) a simple, closed-form analytical expression,
and (ii) a detailed numerical study using an all-sky mock light cone galaxy
catalogue from the Millennium simulation. The two approaches are in excellent
agreement at large angular scales, and differ by a factor of order unity at
smaller scales. These anisotropies are considerably larger in amplitude than
e.g. those in the temperature of the cosmic microwave background, confirming
that it is important to model these anisotropies, and indicating that this is a
promising avenue for future theoretical and observational work.",1806.01718v2
2018-06-08,The measurements of matter density perturbations amplitude from cosmological data,"We compare various physically different measurements of linear matter density
perturbation amplitude, $sigma_8$, which are obtained from the observations of
CMB anisotropy, galaxy cluster mass function, weak gravitation lensing, matter
power spectrum and redshift space distortions. We show that $\sigma_8$
measurement from CMB gravitational lensing signal based on Planck CMB
temperature anisotropy data at high multipoles, $\ell>1000$, contradict to all
other measurements obtained both from remaining Planck CMB anisotropy data and
from other cosmological data, at about $3.7\sigma$ significance level.
Therefore, these data currently should not be combined with other data to
constrain cosmological parameters.
  With the exception of Planck CMB temperature anisotropy data at high
multipoles, all other measurements are in good agreement between each other and
give the following measurements of linear density perturbation amplitude:
$\sigma_8=0.792\pm0.006$, mean density of the Universe:
$\Omega_m=0.287\pm0.007$, and Hubble constant: $H_0 = 69.4\pm
0.6$~km~s$^{-1}$~Mpc$^{-1}$. Taking in account the data on baryon acoustic
oscillations and (or) direct measurements of the Hubble constant, one can
obtain different constraints on sum of neutrino mass and number of relativistic
species.",1806.03261v3
2018-07-05,Domain wall dynamics for an in-plane magnetized thin film with large perpendicular hard axis anisotropy including Dzyaloshinskii-Moriya interaction,"We consider a thin ferromagnetic layer to which an external field or a
current are applied along an in plane easy axis. The perpendicular hard axis
anisotropy constant is large so that the out of plane magnetization component
is smaller than the in plane components. A perturbation approach is used to
obtain the profile and velocity of the moving domain wall. The dynamics of the
in plane components of the magnetization is governed by a reaction diffusion
equation which determines the speed of the profile. We find a simple analytic
expression for the out of plane magnetization showing a symmetric distortion
due to the motion in addition to the asymmetric component due to the
Dzyaloshinskii--Moriya interaction. The results obtained complement previous
studies in which either the Dzyalozhinskii vector or the out of plane hard axis
anisotropy were assumed small. In the regime studied the Walker breakdown is
not observed but the reaction diffusion dynamics predicts a slowing down of the
domain wall for sufficiently large magnetic field. The transition point depends
on the applied field, saturation magnetization and easy axis anisotropy.",1807.02032v1
2018-07-30,Surface anisotropy in a magnetic cylinder induced by the displacement of a vortex core,"In this article we investigate the induction of a surface anisotropy due to
the displacement of the vortex core in a cylindrical nanostructure. In fact,
the effect of the displacement of the vortex core in the dipolar energy can be
modeled simply as a surface anisotropy of the form $E_s = K_s
\int_{\mathcal{S}_m} d\mathcal{S} \, (\hat{n} \cdot \hat{m})^2/2$. Moreover,
the surface anisotropy constant $K_s$ is proportional to the cylinder in-plane
demagnetizing factor in the direction of the core deviation, $N_y(L/R)$, i.e.,
$K_s = \mu_0 M_0^2 R \, N_y(L/R)$, where $R$ and $L$ are the radius and the
thickness of the cylinder, respectively. Our results show that the term of the
nontrivial dipolar energy caused by the charges in the cylinder mantle can be
replaced by a simple integral $E_s$ that increases the efficiency of the
numerical calculations in the analytical study of the displacement of the
vortex core in magnetic vortices.",1807.11349v1
2018-08-02,Longitudinal and transverse magnetoresistance in films with tilted out-of-plane magnetic anisotropy,"Tilted off-plane magnetic anisotropy induces two unusual characteristic
magnetotransport phenomena: extraordinary Hall effect in the presence of an
in-plane magnetic field, and non-monotonic anisotropic magnetoresistance in the
presence of a field normal to the sample plane. We show experimentally that
these effects are generic, appearing in multiple ferromagnetic systems with
tilted anisotropy introduced either by oblique deposition from a single source
or in binary systems co-deposited from separate sources. We present a
theoretical model demonstrating that these observations are natural results of
the standard extraordinary Hall effect and anisotropic magnetoresistance, when
the titled anisotropy is properly accounted for. Such a scenario may help
explaining various previous intriguing measurements by other groups.",1808.00846v2
2018-08-09,Helical edge transport in the presence of a magnetic impurity: the role of local anisotropy,"Helical edge modes of 2D topological insulators are supposed to be protected
from time-reversal invariant elastic backscattering. Yet substantial deviations
from the perfect conductance are typically observed experimentally down to very
low temperatures. To resolve this conundrum we consider the effect of a single
magnetic impurity with arbitrary spin on the helical edge transport. We
consider the most general structure of the exchange interaction between the
impurity and the edge electrons. Moreover, for the first time, we take into the
account the local anisotropy for the impurity and show that it strongly affects
the backscattering current in a wide range of voltages and temperatures. We
show that the sensitivity of the backscattering current to the presence of the
local anisotropy is different for half-integer and integer values of the
impurity spin. In the latter case the anisotropy can significantly increase the
backscattering correction to the current.",1808.03084v2
2018-08-30,CMB anisotropy power spectrum of 3-sphere universe for low $l$,"We calculate the CMB anisotropy power spectrum of a closed universe for large
angle (i.e., low $l$) due to a scale invariant fluctuation of primordial
universe by considering the spherical harmonics for 3-sphere. In particular,
contrary to the wide belief, we show that this consideration affects the CMB
anisotropy power spectrum; instead of constant $l(l+1)C_l$, our consideration
results in the supression for $l=2$, currently explained by the cosmic
variance. As a more concrete proof of our analysis, from the low $l$ CMB
anisotropy data \emph{alone}, we obtained
$\Omega_{\mathrm{tot}}=1.0018^{+0.0031}_{-0.0007}$, which agrees with
$\Omega_{\mathrm{tot}}=1.0023^{+ 0.0056}_{- 0.0054}$ from the previous anlaysis
of WMAP+BAO+$H_0$. Thus, we conclude that our Universe is closed.",1808.10757v4
2018-09-11,Scaling behavior in interacting systems: joint effect of anisotropy and compressibility,"Motivated by the ubiquity of turbulent flows in realistic conditions, effects
of turbulent advection on two models of classical non-linear systems are
investigated. In particular, we analyze model A (according to the
Hohenberg-Halperin classification [1]) of a non-conserved order parameter and a
model of the direct bond percolation process. Having two paradigmatic
representatives of distinct stochastic dynamics, our aim is to elucidate to
what extent velocity fluctuations affect their scaling behavior. The main
emphasis is put on an interplay between anisotropy and compressibility of the
velocity flow on their respective scaling regimes. Velocity fluctuations are
generated by means of the Kraichnan rapid-change model, in which the anisotropy
is due to a distinguished spatial direction n and a correlator of the velocity
field obeys the Gaussian distribution law with prescribed statistical
properties. As the main theoretical tool, the field-theoretic perturbative
renormalization group is adopted. Actual calculations are performed in the
leading (one-loop) approximation. Having obtained infra-red stable asymptotic
regimes, we have found four possible candidates for macroscopically observable
behavior for each model. In contrast to the isotropic case, anisotropy brings
about enhancement of non-linearities and non-trivial regimes are proved to be
more stable.",1809.03781v1
2018-09-13,Magnetic anisotropy of ferromagnetic metals in low-symmetry systems,"We have constructed an analytic formula to treat the perpendicular magnetic
anisotropy energy in ferromagnetic metals with low symmetry, such as C4V and
C3V. We find that the anisotropy energy is proportional to a part of the
expectation values of the orbital angular momentum and magnetic dipole
operator. Although the result is similar to the model proposed by Laan [J.
Phys.: Condens. Matter 10, 3239 (1998)], we have derived a concrete expression
for the spin-flip virtual excitation process term, which can be dominant in
atoms with small magnetic moments and/or small exchange splitting. Pt monatomic
layer with proximity-induced spin polarization grown on Fe is an example of
this. Other multilayer systems such as Co/Pd and Co/Ni and bilayer systems such
as Fe(CoB)/MgO can be discussed similarly. Moreover, the relation between
perpendicular magnetic anisotropy energy and measurable physical parameters is
discussed based on X-ray magnetic circular dichroism spectroscopy.",1809.04749v4
2018-09-27,On conditions for long-wave equivalent medium to be isotropic and on analysis of parameters indicating anisotropy of equivalent TI medium,"In this paper, we consider a long-wave equivalent medium to a finely
parallel-layered inhomogeneous medium, obtained using the Backus average.
Following the work of Postma and Backus, we show explicitly the derivations of
the conditions to obtain the equivalent isotropic medium. We demonstrate that
there cannot exist a transversely isotropic (TI) equivalent medium with the
coefficients $c^{\overline{\rm TI}}_{1212} \neq c^{\overline{\rm TI}}_{2323}$,
$c^{\overline{\rm TI}}_{1111} = c^{\overline{\rm TI}}_{3333}$ and
$c^{\overline{\rm TI}}_{1122} = c^{\overline{\rm TI}}_{1133}$. Moreover, we
consider a new parameter, $\varphi$, indicating the anisotropy of the
equivalent medium, and we show its range and properties. Subsequently, we
compare $\varphi$ to the Thomsen parameters, emphasizing its usefulness as a
supportive parameter showing the anisotropy of the equivalent medium or as an
alternative parameter to $\delta$. We argue with certain Berryman et al.
considerations regarding the properties of the anisotropy parameters $\epsilon$
and $\delta$. Additionally, we show an alternative way---to the one mentioned
by Berryman et al.---of indicating changing fluid content in layered Earth.",1809.10385v1
2018-09-27,Crystalline anisotropy induces a second antiferromagnetic phase in the absence of SDW in the heavily hydrogen-doped LaFeAsO$_{1-x}$H$_x$ $(x\sim0.5 )$,"Electronic and magnetic properties of the heavily H-doped
LaFeAsO$_{1-x}$H$_x$ $(x\sim0.5 )$ were studied in the framework of the density
functional theory combined with the dynamical mean field theory (DFT+DMFT). We
found a stripe-like-ordered structure of hydrogen and oxygen atoms, as a ground
state, with the same configuration as the antiferromagnetic (AF) order. The new
configuration could explain the existing experimental results related to the
heavily H-doped LaFeAsO$_{1-x}$H$_x$, such as an in-plane electronic anisotropy
and a non-uniform magnetic behavior. A significant anisotropy was observed
between Fe- 3d$_{xz}$ (xz) and Fe-3d$_{yz}$ (yz) orbitals in the ground state
in the absence of the pseudogap resulting from the spin density wave phase,
which was found to originate from the crystalline anisotropy. Magnetic moments
were not spatially uniform and were sensitive to the crystal configuration. We
found that a non-uniform magnetic behavior is associated with the As-Fe-As bond
angle in the structure. Our findings would clarify the importance of crystal
details and orbital degrees of freedom in iron-based superconductors.",1809.10641v1
2018-10-12,Controlling solid-liquid interfacial energy anisotropy through the isotropic liquid,"Although the anisotropy of the solid-liquid interfacial free energy for most
alloy systems is very small, it plays a crucial role in the growth rate,
morphology and crystallographic growth direction of dendrites. Previous work
posited a dendrite orientation transition via compositional additions. In this
work we examine experimentally the change in dendrite growth behaviour in the
Al-Sm (Samarium) system as a function of solute concentration and study its
interfacial properties using molecular dynamics simulations. We observe a
dendrite growth direction which changes from <100> to <110> as Sm content
increases. The observed change in dendrite orientation is consistent with the
simulation results for the variation of the interfacial free energy anisotropy
and thus provides definitive confirmation of conjecture in previous works. In
addition, our results provide physical insight into the atomic structural
origin of the concentration dependent anisotropy, and deepens our fundamental
understanding of solid-liquid interfaces in binary alloys.",1810.05298v2
2018-10-15,TeV-PeV Cosmic-Ray Anisotropy and Local Interstellar Turbulence,"We calculate the shape of the large-scale anisotropy of TeV-PeV cosmic-rays
(CR) in different models of the interstellar turbulence. In general, the
large-scale CR anisotropy (CRA) is not a dipole, and its shape can be used as a
new probe of the turbulence. The 400 TeV and 2 PeV data sets of IceTop can be
fitted with Goldreich-Sridhar turbulence and a broad resonance function, but
other possibilities are not excluded. We then present our first numerical
calculations of the CRA down to 3 TeV energies in 3D isotropic Kolmogorov
turbulence. At these low energies, the large-scale CRA aligns well with the
direction of local magnetic field lines around the observer. In this type of
turbulence, the CR intensity is flat in a broad region perpendicular to field
lines. Even though the CRA is quite gyrotropic, we show that the local
configuration of the turbulence around the observer does result in the
appearance of weak, ""non-gyrotropic"" small-scale anisotropies, which contain
information on the local turbulence level.",1810.06396v1
2018-10-16,Drude weight anisotropy in the doped iron pnictides: the primary role of orbital weight redistribution along the reconstructed Fermi surfaces,"We explore the anisotropy in low frequency conductivity as a function of hole
doping in multiorbital models of pnictides by analyzing the Drude weight in the
$x$ and $y$ directions of a ($\pi$, 0) spin-density wave state. A reduction in
the conductivity anisotropy with increased hole doping, and subsequent sign
reversal, both observed in experiments, is found to be a common trend in these
models. This behavior arises due to the interplay of low energy
orbitally-resolved density of states and the geometrical features of the Fermi
surface. An understanding of anisotropy in the electron doped regime, however,
would require additional ingredients.",1810.06842v2
2018-10-26,Reliable mass calculation in spherical gravitating systems,"We present an innovative approach to the methodology of dynamical modelling,
allowing practical reconstruction of the underlying dark matter mass without
assuming both the density and anisotropy functions. With this, the
mass-anisotropy degeneracy is reduced to simple model inference, incorporating
the uncertainties inherent with observational data, statistically circumventing
the mass-anisotropy degeneracy in spherical collisionless systems. We also
tackle the inadequacy that the Jeans method of moments has on small datasets,
with the aid of Generative Adversarial Networks: we leverage the power of
artificial intelligence to reconstruct non-parametrically the projected
line-of-sight velocity distribution. We show with realistic numerical
simulations of dwarf spheroidal galaxies that we can distinguish between
competing dark matter distributions and recover the anisotropy and mass profile
of the system.",1810.11375v1
2018-10-05,Zero-field dynamics stabilized by in-plane shape anisotropy in MgO-based spin-torque oscillators,"Here we demonstrate numerically that shape anisotropy in MgO-based
spin-torque nano-oscillators consisting of an out-of-plane magnetized free
layer and an in-plane polarizer is necessary to stabilize out-of-plane
magnetization precession without the need of external magnetic fields. As the
in-plane anisotropy is increased, a gradual tilting of the magnetization
towards the in-plane easy direction is introduced, favouring zero-field
dynamics over static in-plane states. Above a critical value, zero-field
dynamics are no longer observed. The optimum ratio of in-plane shape to
out-of-plane uniaxial anisotropy, for which large angle out-of-plane zero-field
dynamics occur within the widest current range, is reported.",1811.00106v1
2018-11-08,Thermodynamics at Strong Coupling on Anisotropic Lattices,"Lattice QCD with staggered fermions at strong coupling has long been studied
in a dual representation to circumvent the finite baryon density sign problem.
Monte Carlo simulations at finite temperature and density require anisotropic
lattices. Recent results that established the non-perturbative functional
dependence between the bare anisotropy $\gamma$ and the physical anisotropy
$a_s/a_t$ in the chiral limit are now extended to finite quark mass. We
illustrate how the calibration of the anisotropy works and discuss the
consequences of the anisotropy on thermodynamic observables. We also show first
results on the energy density and pressure in the QCD phase diagram in the
strong coupling regime.",1811.03584v1
2018-11-12,Current direction anisotropy of the spin Hall magnetoresistance in nickel ferrite thin films with bulk-like magnetic properties,"We utilize spin Hall magnetoresistance (SMR) measurements to experimentally
investigate the pure spin current transport and magnetic properties of nickel
ferrite (NiFe2O4,NFO)/normal metal (NM) thin film heterostructures. We use
(001)-oriented NFO thin films grown on lattice-matched magnesium gallate
substrates by pulsed laser deposition, which significantly improves the
magnetic and structural properties of the ferrimagnetic insulator. The NM in
our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude
for charge currents applied in the [100]- and [110]-direction of NFO yields a
change of 50% for Pt at room temperature. We also investigated the temperature
dependence of this current direction anisotropy and find that it is
qualitatively different for the conductivity and the SMR magnitude. From our
results we conclude that the observed current direction anisotropy may
originate from an anisotropy of the spin mixing conductance or of the spin Hall
effect in these Pt and Ta layers, and/or additional spin-galvanic contributions
from the NFO/NM interface.",1811.04696v1
2018-11-17,Unconventional anisotropic even-denominator fractional quantum Hall state in a system with mass anisotropy,"The fractional quantum Hall state (FQHS) observed at a half-filled Landau
level in an interacting two-dimensional electron system (2DES) is among the
most exotic states of matter as its quasiparticles are expected to be Majoranas
with non-Abelian statistics. We demonstrate here the unexpected presence of
such a state in a novel 2DES with a strong band-mass anisotropy. The FQHS we
observe has unusual characteristics. While its Hall resistance is
well-quantized at low temperatures, it exhibits highly-anisotropic in-plane
transport resembling compressible stripe/nematic charge-density-wave phases.
More striking, the anisotropy sets in suddenly below a critical temperature,
suggesting a finite-temperature phase transition. Our observations highlight
how anisotropy modifies the many-body phases of a 2DES, and should further fuel
the discussion surrounding the enigmatic even-denominator FQHS.",1811.07094v1
2018-11-22,On the Emission Pattern of Nanoscopic Emitters in Planar Anisotropic Matrix and Nanoantenna Structures,"Single nanoscopic emitters embedded in crystalline matrix have become a
valuable resource for emerging nanophotonic and quantum technologies. The
generally anisotropic nature of the matrix strongly affects the emission
properties of the quantum emitters, in particular, when the matrix is assembled
in nanophotonic structures. We report on rigorous analysis and engineering of
spontaneous emission from single emitters coupled to nanoantenna and planar
anisotropic antenna structures. By developing a convenient theoretical method
with efficient numerical implementation, we show that accurate modeling of the
anisotropy is essential in predicting the emission pattern for many important
systems, such as single molecules in solid-state matrix, isolated defects in 2D
materials and so on. In particular, we illustrate the amplified effects of
material anisotropy and geometrical anisotropy for emitters coupled to planar
antenna and nanoantenna structures. We show that with proper design of the
anisotropies strong enhancement of the emission rate and nearly collimated beam
from single emitters can be simultaneously achieved.",1811.09052v1
2019-01-01,Micro-mechanics of fabric and failure in granular materials,"The paper addresses the underlying source of two forms of induced anisotropy
in granular materials: contact orientation anisotropy and contact force
anisotropy. A rational, mathematical structure is reviewed for the manner in
which fabric anisotropy emerges and evolves during loading. Fabric is expressed
as an orientation density, and transport phenomena such as convection, contact
generation, and diffusion control the rate of fabric evolution during loading.
The paper proposes specific measurable forms for all terms, based upon the
micro-mechanics of particle interactions. Discrete element (DEM) simulations
are used to verify and quantify these terms, so that the theory can be applied
to general loading conditions. The DEM simulations are of densely packed
durable spheres, and the emphasis is on soil behavior at large strains,
specifically on fabric and strength at the critical state. Once the theory has
been developed and quantified, it is applied to predict the effect of the
intermediate principal stress on strength.",1901.07341v1
2019-01-25,Current-Induced Torques with Dresselhaus Symmetry Due to Resistance Anisotropy in 2D Materials,"We report measurements of current-induced torques in heterostructures of
Permalloy (Py) with TaTe$_2$, a transition-metal dichalcogenide (TMD) material
possessing low crystal symmetry, and observe a torque component with
Dresselhaus symmetry. We suggest that the dominant mechanism for this
Dresselhaus component is not a spin-orbit torque, but rather the Oersted field
arising from a component of current that flows perpendicular to the applied
voltage due to resistance anisotropy within the TaTe$_2$. This type of
transverse current is not present in wires made from a single uniform layer of
a material with resistance anisotropy, but will result whenever a material with
resistance anisotropy is integrated into a heterostructure with materials
having different resistivities, thereby producing a spatially non-uniform
pattern of current flow. This effect will therefore influence measurements in a
wide variety of heterostructures incorporating 2D TMD materials and other
materials with low crystal symmetries.",1901.08908v1
2019-02-07,Unidirectional anisotropy in cubic FeGe with antisymmetric spin-spin-coupling,"We report strong unidirectional anisotropy in bulk polycrystalline B20 FeGe
measured by ferromagnetic resonance spectroscopy. Bulk and micron-sized samples
were produced and analytically characterized. FeGe is a B20 compound with
inherent Dzyaloshinskii-Moriya interaction. Lorenz microscopy confirms a
skyrmion lattice at $190 \; \text{K}$ in a magnetic field of 150 mT.
Ferromagnetic resonance was measured at $276 \; \text{K} \pm 1 \; \text{K}$,
near the Curie temperature. Two resonance modes were observed, both exhibit a
unidirectional anisotropy of $K=1153 \; \text{J/m}^3 \pm 10 \; \text{J/m}^3$ in
the primary, and $K=28 \; \text{J/m}^3 \pm 2 \; \text{J/m}^3$ in the secondary
mode, previously unknown in bulk ferromagnets. Additionally, about 25 standing
spin wave modes are observed inside a micron-sized FeGe wedge, measured at room
temperature ($\sim \; 293$ K). These modes also exhibit unidirectional
anisotropy.",1902.02665v2
2019-02-12,Numerical Anisotropy in Finite Differencing,"Numerical solutions to hyperbolic partial differential equations, involving
wave propagations in one direction, are subject to several specific errors,
such as numerical dispersion, dissipation or aliasing. In multi-dimensions,
where the waves propagate in all directions, there is an additional specific
error resulting from the discretization of spatial derivatives along grid
lines. Specifically, waves or wave packets in multi-dimensions propagate at
different phase or group velocities, respectively, along different directions.
A commonly used term for the aforementioned multidimensional discretization
error is the numerical anisotropy or isotropy error. In this review, the
numerical anisotropy is briefly described in the context of the wave equation
in multi-dimensions. Then, several important studies that were focused on
optimizations of finite difference schemes with the objective of reducing the
numerical anisotropy are discussed.",1902.04466v1
2019-02-21,Mean flow anisotropy without waves in rotating turbulence,"We tackle the question of how anisotropy in flows subject to background
rotation favours structures elongated along the rotation axis, especially in
turbulent flows. A new, wave-free mechanism is identified that challenges the
current understanding of the process. Inertial waves propagating near the
rotation axis are generally accepted as the most efficient mechanism to
transport energy anisotropically. They have been shown to transfer energy to
large anisotropic, columnar structures. Nevertheless, they cannot account for
the formation of simpler steady anisotropic phenomena such as Taylor columns.
Here, we experimentally show that more than one mechanism involving the
Coriolis force may promote anisotropy. In particular, in the limit of fast
rotation, that is at low Rossby number, anisotropy favouring the direction of
rotation of the average of a turbulent flow arises neither because of inertial
waves nor following the same mechanism as in steady Taylor columns, but from an
interplay between the Coriolis force and average advection.",1902.07984v2
2019-03-02,Evolution of Internal Granular Structure at the Flow-Arrest Transition,"The evolution of the internal granular structure in shear-arrested and
shear-flowing states of granular materials is characterized using fabric
tensors as descriptors of the internal contact and force networks. When a
dilute system of frictional grains is subjected to a constant pressure and
shear stress, the bulk stress ratio is well-predicted from the anisotropy of
its contact and force networks during transient flow prior to steady shear flow
or shear arrest. Although the onset of shear arrest is a stochastic process,
the fabric tensors upon arrest are distributed around nearly equal
contributions of force and contact network anisotropy to the bulk stress ratio.
The distribution becomes seemingly narrower with increasing system size. The
anisotropy of the contact network in shear-arrested states is reminiscent of
the fabric anisotropy observed in shear-jammed packings.",1903.00599v2
2019-03-11,Effect of Anisotropy on Defect Mode Peculiariries in Chiral Liquid Crystals,"The effect of anisotropy on defect mode peculiarities in cholesteric liquid
crystals is investigated. The problem is solved by Ambartsumians layer addition
modified method. Two cases are considered. In the first case, it is assumed
that the defect layer is not absorbing and the effect of refraction anisotropy
on the reflection, relative photonic density of states and the total field
intensity aroused in the defect layer are studied . In the second case, defect
layer is assumed to be isotropic for refraction and anisotropic for absorption,
and the influence of defect layer absorption anisotropy on reflection,
absorption, relative photonic density of states and the total field intensity
aroused in the defect layer are investigated.",1903.04924v1
2019-04-06,The prospects of gravitational waves on constraining the anisotropy of the Universe,"The observation of GW150914 indicated a new independent measurement of the
luminosity distance of a gravitational wave event. In this paper, we constrain
the anisotropy of the Universe by using gravitational wave events. We simulate
hundreds of events of binary neutron star merging that may be observed by
Einstein Telescope. Full simulation for producing process of gravitational wave
data is employed. We find that 200 of binary neutron star merging in redshift
$(0,1)$ observed by Einstein Telescope may constrain the anisotropy with an
accuracy comparable to the result from Union2.1 supernovae. This result shows
that gravitational waves can be a powerful tool in investigating the
cosmological anisotropy.",1904.03460v1
2019-04-09,\txtit{In situ} determination of the anisotropy field in ferromagnetic films using magnetic susceptibility measurements by MOKE,"An alternate method of measuring anisotropy fields in thin film ferromagnets
is demonstrated. The method relies on the magnetic susceptibility in a small
a.c. magnetic field, measured \txtit{in situ} using the magneto-optic Kerr
effect (MOKE), and will be useful in situations where more specialized
apparatus are not available, or constraints discourage the use of a large,
static magnetic field. The method is demonstrated for Co/W(110) films, where it
yields anisotropy fields in agreement with previous studies using more
conventional torque magnetometry. The sensitivity of the method is demonstrated
using CoO/Co/W(110) bilayer films, where the anisotropy due to interfacial
exchange coupling is detected and used to find the N\'{e}el temperature of the
thin CoO layer.",1904.04855v1
2019-04-25,Low damping magnetic properties and perpendicular magnetic anisotropy with strong volume contribution in the Heusler alloy Fe1.5CoGe,"We present a study of the dynamic magnetic properties of TiN-buffered
epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series
annealed at different temperatures are prepared and the magnetic damping is
measured, a lowest value of $\alpha=2.18\times 10^{-3}$ is obtained. The
perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also
characterized. The evolution of the interfacial perpendicular anisotropy
constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and
compared with the widely used CoFeB/MgO interface. A large volume contribution
to the perpendicular anisotropy of $(4.3\pm0.5)\times 10^{5}$ $\rm J/m^3$ is
also found, in contrast with vanishing bulk contribution in common Co- and
Fe-based Heusler alloys.",1904.11247v1
2019-05-01,A partial inventory of observational anisotropies in single-dish line-intensity mapping,"Line-intensity mapping, being an imperfect observation of the line-intensity
field in a cosmological volume, will be subject to various anisotropies
introduced in observation. Existing literature in the context of CO and [C II]
line-intensity mapping often predicts only the real-space, spherically averaged
line-intensity power spectrum, with some works considering anisotropies while
examining projection of interloper emission. We explicitly consider a
simplified picture of redshift-space distortions and instrumental effects due
to limited resolution, and how these distort an isotropic line-intensity signal
in real space and introduce strong apparent anisotropies. The results suggest
that while signal loss due to limited instrumental resolution is unavoidable,
measuring the quadrupole power spectrum in addition to the monopole would still
break parameter degeneracies present in monopole-only constraints, even without
a measurement of the full anisotropic power spectrum.",1905.00209v3
2019-05-22,Magnetic ripple domain structure in FeGa/MgO thin films,"The magnetic domain structure is studied in epitaxial
Fe$_{100-x}$Ga$_x$/MgO(001) films with 0 $<$ x $<$ 30 and thicknesses below 60
nm by magnetic force microscopy. For low gallium content, domains with the
magnetization lying in the film plane and domain walls separating micrometric
areas are observed. Above x $\approx$ 20, the magnetic contrast shows a fine
corrugation, ranging from 300 to 900 nm, suggesting a ripple substructure with
a periodic oscillation of the magnetization. We discuss the presence of a
random magnetic anisotropy contribution, that superimposed to the cubic
coherent anisotropy, is able to break the uniform orientation of the
magnetization. The origin of that random anisotropy is attributed to several
factors: coexistence of crystal phases in the films, inhomogeneous distribution
of both internal strain and Ga-Ga next nearest neighbor pairs and interface
magnetic anisotropy due to the Fe-O bond.",1905.09180v2
2019-06-06,Interaction-dependent anisotropy of fractional quantum Hall states,"A fractional quantum Hall (FQH) system with broken rotational symmetry
exploits its geometric degree of freedom to minimize its ground state energy.
The mass anisotropy of bare particles interacting isotropically is partially
inherited by the many-body FQH state, and the extent to which it does so
depends on the type of interaction, filling fraction and ground state phase.
Using numerical infinite density matrix renormalization group simulations, we
investigate the transference of elliptical ($C_2$-symmetric) anisotropy from
the band mass of the bare particles to the FQH states, for various power law
interactions. We map out the response of FQH states to small anisotropy as a
function of power law exponent, filling, and statistics (bosonic or fermionic)
of the constituents. Interestingly, we find a non-analyticity in the linear
response of the FQH state at a special filling-dependent value of the power law
exponent, above which the interaction effectively becomes zero-range
(point-like). We also investigate the the effect of $C_4$-symmetric band
distortions, where we observe a strikingly different dependence on filling.",1906.02835v1
2019-06-20,High-energy cosmic rays from compact galactic star clusters: particle fluxes and anisotropy,"It has been shown that supernova blast waves interacting with winds from
massive stars in compact star clusters may be capable of producing cosmic-ray
(CR) protons to above $10^{17}$ eV. We give a brief description of the
colliding-shock-flows mechanism and look at generalizations of the diffusion of
~ 100 PeV CRs in the turbulent galactic magnetic field present in the galactic
disk. We calculate the temporal evolution of the CR anisotropy from a possible
distribution of young compact massive star clusters assuming the sources are
intermittent on time scales of a few million years, i.e., comparable to their
residence time in the Milky Way. Within the confines of our model, we determine
the galactic/extra-galactic fraction of high-energy CRs resulting in
anisotropies consistent with observed values. We find that galactic star
clusters may contribute a substantial fraction of ~ 100 PeV CRs without
producing anisotropies above observed limits.",1906.08813v1
2019-06-23,Effect of elastic anisotropy on phase separation in ternary alloys: A phase-field study,"The precipitate shape, size and distribution are crucial factors which
determine the properties of several technologically important alloys. Elastic
interactions between the inclusions modify their morphology and align them
along elastically favourable crystallographic directions. Among the several
factors contributing to the elastic interaction energy between precipitating
phases, anisotropy in elastic moduli is decisive in the emergence of modulated
structures during phase separation in elastically coherent alloy systems. We
employ a phase-field model incorporating elastic interaction energy between the
misfitting phases to study microstructural evolution in ternary three-phase
alloy systems when the elastic moduli are anisotropic. The spatiotemporal
evolution of the composition field variables is governed by solving a set of
coupled Cahn-Hilliard equations numerically using a semi-implicit Fourier
spectral technique. We methodically vary the misfit strains, alloy chemistry
and elastic anisotropy to investigate their influence on domain morphology
during phase separation. The coherency strains between the phases and alloy
composition alter the coherent phase equilibria and decomposition pathways. The
degree of anisotropy in elastic moduli modifies the elastic interaction energy
between the precipitates depending on the sign and magnitude of relative
misfits, and thus determines the shape and alignment of the inclusions in the
microstructure.",1906.09637v1
2019-07-03,Large spin-relaxation anisotropy in bilayer-graphene/WS$_2$ heterostructures,"We study spin-transport in bilayer-graphene (BLG), spin-orbit coupled to a
tungsten di sulfide (WS$_2$) substrate, and measure a record spin lifetime
anisotropy ~40-70, i.e. ratio between the out-of-plane $\tau_{\perp}$ and
in-plane spin relaxation time $\tau_{||}$. We control the injection and
detection of in-plane and out-of-plane spins via the shape-anisotropy of the
ferromagnetic electrodes. We estimate $\tau_{\perp}$ ~ 1-2 ns via Hanle
measurements at high perpendicular magnetic fields and via a new tool we
develop: Oblique Spin Valve measurements. Using Hanle spin-precession
experiments we find a low $\tau_{||}$ ~ 30 ps in the electron-doped regime
which only weakly depends on the carrier density in the BLG and conductivity of
the underlying WS$_2$, indicating proximity-induced spin-orbit coupling (SOC)
in the BLG. Such high $\tau_{\perp}$ and spin lifetime anisotropy are clear
signatures of strong spin-valley coupling for out-of-plane spins in BLG/WS$_2$
systems in the presence of SOC, and unlock the potential of BLG/transition
metal dichalcogenide heterostructures for developing future spintronic
applications.",1907.01975v1
2019-07-08,Metadynamics study of the temperature dependence of magnetic anisotropy and spin-reorientation transitions in ultrathin films,"We employ metadynamics simulations to calculate the free energy landscape of
thin ferromagnetic films and perform a systematic study of the temperature
dependence of magnetic anisotropy and of the spin-reorientation transitions. By
using a simple spin model we recover the well-known power-law behavior of the
magnetic anisotropy energy against magnetization and present a rather detailed
analysis of the spin-reorientation transitions in ultrathin films. Based on
tensorial exchange interactions and anisotropy parameters derived from
first-principles calculations we perform simulations for Fe double layers
deposited on Au(001) and W(110). In case of Fe$_2$W(110) our simulations
display an out-of-plane to in-plane spin-reorientation transition in agreement
with experiments.",1907.03616v1
2019-07-17,Suppression of twinning and enhanced electronic anisotropy of SrIrO3 films,"The spin-orbit coupling and electron correlation in perovskite SrIrO3 (SIO)
strongly favor new quantum states and make SIO very attractive for next
generation quantum information technology. In addition, the small electronic
band-width offers the possibility to manipulate anisotropic electronic
transport by strain. However, twinned film growth of SIO often masks electronic
anisotropy which could be very useful for device applications. We demonstrate
that the twinning of SIO films on (001) oriented SrTiO3 (STO) substrates can be
strongly reduced for thin films with thickness t less than 30 nm by using
substrates displaying a TiO2-terminated surface with step-edge alignment
parallel to the a- or b-axis direction of the substrate. This allows us to
study electronic anisotropy of strained SIO films which hitherto has been
reported only for bulk-like SIO. For films with t < 30 nm electronic anisotropy
increases with increasing t and becomes even twice as large compared to nearly
strain-free films grown on (110) DyScO3. The experiments demonstrate the high
sensitivity of electronic transport towards structural distortion and the
possibility to manipulate transport by substrate engineering.",1907.07520v1
2019-07-27,Magnetization plateau of the $S=2$ antiferromagnetic Heisenberg chain with anisotropies,"We investigate the $S=2$ antiferromagnetic quantum spin chain with the
exchange and single-ion anisotropies in a magnetic field, using the numerical
exact diagonalization of finite-size clusters and the level spectroscopy
analysis. It is found that a magnetization plateau possibly appears at a half
of the saturation magnetization for some suitable anisotropy parameters. The
level spectroscopy analysis indicates that the 1/2 magnetization plateau is
formed by two different mechanisms, depending on the anisotropy parameters. The
phase diagram of the 1/2 plateau states and some typical magnetization curves
are also presented. In addition the biquadratic interaction is revealed to
enhance the plateau induced by the Haldane mechanism.",1907.11931v2
2019-08-01,Anisotropies and non-Gaussianity of the Cosmological Gravitational Wave Background,"The Stochastic Gravitational Wave Background (SGWB) is expected to be a key
observable for Gravitational Wave (GW) interferometry. Its detection will open
a new window on early universe cosmology and on the astrophysics of compact
objects. Using a Boltzmann approach, we study the angular anisotropies of the
GW energy density, which is an important tool to disentangle the different
cosmological and astrophysical contributions to the SGWB. Anisotropies in the
cosmological background are imprinted both at its production, and by GW
propagation through the large-scale scalar and tensor perturbations of the
universe. The first contribution is not present in the Cosmic Microwave
Background (CMB) radiation (as the universe is not transparent to photons
before recombination), causing an order one dependence of the anisotropies on
frequency. Moreover, we provide a new method to characterize the cosmological
SGWB through its possible deviation from a Gaussian statistics. In particular,
the SGWB will become a new probe of the primordial non-Gaussianity of the
large-scale cosmological perturbations.",1908.00527v1
2019-09-23,Criticality of the $O(2)$ model with cubic anisotropies from nonperturbative renormalization,"We study the $O(2)$ model with $\mathbb{Z}_4$-symmetric perturbations within
the framework of nonperturbative renormalization group (RG) for spatial
dimensionality $d=2$ and $d=3$. In a unified framework we resolve the
relatively complex crossover behavior emergent due to the presence of multiple
RG fixed points. In $d=3$ the system is controlled by the $XY$, Ising, and
low-$T$ fixed points in presence of a dangerously irrelevant anisotropy
coupling $\lambda$. In $d=2$ the anisotropy coupling is marginal and the
physical picture is governed by the interplay between two distinct lines of RG
fixed points, giving rise to nonuniversal critical behavior; and an isolated
Ising fixed point. In addition to inducing crossover behavior in universal
properties, the presence of the Ising fixed point yields a generic, abrupt
change of critical temperature at a specific value of the anisotropy field.",1909.10600v1
2019-09-30,Effects of exchange and weak Dzyaloshinsky-Moriya anisotropies on thermodynamic characteristics of spin-gapped magnets,"We study the modification of low temperature properties of quantum magnets
such as magnetization, heat capacity, energy spectrum, and densities of
condensed and noncondensed quasiparticles (triplons) due to anisotropies in the
framework of mean-field based approach. We show that in contrast to exchange
anisotropy (EA) interaction, Dzyaloshinsky-Moriya (DM) interaction modifies the
physics dramatically. Particularly, it changes the sign of the anomalous
density in the whole range of temperatures. Its critical behavior is slightly
modified also by the EA. We have found that the shift of the critical
temperature of phase transition (or crossover caused by DM interaction) is
positive and significant. Using the experimental data on the magnetization of
the compound TlCuCl$_3$, we have found optimal values for the strengths of EA
and DM interactions. The spectrum of the energy of low lying excitations has
also been investigated and found to develop a linear dispersion similar to
Goldstone mode with a negligibly small anisotropy gap.",1909.13641v2
2019-10-25,Local magnetic anisotropy by polarized neutron powder diffraction: application of magnetically induced preferred crystallite orientation,"Polarized neutron diffraction allows to determine the local susceptibility
tensor on the magnetic site both in single crystals and powders. It is widely
used in the studies of single crystals, but it is still hardly applicable to a
number of highly interesting powder materials, like molecular magnets or
nanoscale systems because of the low luminosity of existing instruments and the
absence of an appropriate data analysis software. We show that these
difficulties can be overcome by using a large area detector in combination with
the two-dimensional Rietveld method and powder samples with magnetically
induced preferred crystallite orientation. This is demonstrated by revisiting
two test powder compounds, namely, low anisotropy (soft) ferrimagnetic compound
Fe3O4 and spin-ice compound Ho2Ti2O7 with high local anisotropy. The values of
magnetic moments in Fe3O4 and the susceptibility tensors of Ho2Ti2O7 at various
temperatures and fields were found in perfect agreement with these found
earlier in single crystal experiments. The magnetically induced preferred
crystallite orientation was used to study the local susceptibility of a
single-molecule magnet Co([(CH3)2N]2CS)2Cl2. Hence, the studies of local
magnetic anisotropy in powder systems might now become accessible.",1910.11822v1
2019-10-30,"Anomalous Gravitational TTT Vertex, Temperature Inhomogeneity, and Pressure Anisotropy","The conformal anomaly in curved spacetime generates a nontrivial anomalous
vertex, given by the three-point correlation function $TTT$ of the
energy-momentum tensor $T^{\mu\nu}$. We show that a temperature inhomogeneity
in a gas of charged massless particles generates, via the $TTT$ vertex, a
pressure anisotropy with respect to the axis of the temperature variation. This
very particular signature may provide an experimental access to the elusive
gravitational coefficient $b$ which determines the anomaly contribution of the
Weyl tensor to the trace of the energy-momentum tensor in curved spacetime. We
present an estimate of the pressure anisotropy both for fermionic
quasiparticles in the solid-state environment of Dirac semimetals as well as
for a quark-gluon plasma in relativistic heavy-ion collisions. In both cases,
the pressure anisotropy is small compared to the mean thermal pressure.",1910.13727v3
2019-11-26,Preserving the accuracy of numerical methods discretizing anisotropic elliptic problems,"In this paper we study the loss of precision of numerical methods
discretizing anisotropic problems and propose alternative approaches free from
this drawback. The deterioration of the accuracy is observed when the
coordinates and the mesh are unrelated to the anisotropy direction. While this
issue is commonly addressed by increasing the scheme approximation order, we
demonstrate that, though the gains are evident, the precision of these
numerical methods remain far from optimal and limited to moderate anisotropy
strengths. This is analysed and explained by an amplification of the
approximation error related to the anisotropy strength. We propose an approach
consisting in the introduction of an auxiliary variable aimed at removing the
amplification of the discretization error. By this means the precision of the
numerical approximation is demonstrated to be independent of the anisotropy
strength.",1911.11482v1
2019-11-29,Reflection anisotropy experiments to study non-equilibrium dynamics of electronic nematicity,"Electronic nematicity have attracted a great deal of interest in the
unconventional superconductivity research. We present an experimental method to
investigate reflectivity anisotropy by the electronic nematicity and its
non-equilibrium dynamics. Our experimental results on
Ba(Fe$_{0.955}$Co$_{0.045}$)$_{2}$As$_{2}$ single crystal clearly feature the
broken four-fold symmetry along directions parallel to Fe-Fe bonding. Numerical
simulations using WVASE from Woollam Co. demonstrate that our method is highly
reliable under various experimental conditions. Finally, we perform
time-resolved reflectivity anisotropy measurement confirming that
photo-excitation by 1.55 eV photons suppresses the reflectivity anisotropy due
to nematic order.",1911.12920v1
2019-12-19,Characterizing the Cosmological Gravitational Wave Background Anisotropies and non-Gaussianity,"A future detection of the Stochastic Gravitational Wave Background (SGWB)
with GW experiments is expected to open a new window on early universe
cosmology and on the astrophysics of compact objects. In this paper we study
SGWB anisotropies, that can offer new tools to discriminate between different
sources of GWs. In particular, the cosmological SGWB inherits its anisotropies
both (i) at its production and (ii) during its propagation through our
perturbed universe. Concerning (i), we show that it typically leads to
anisotropies with order one dependence on frequency. We then compute the effect
of (ii) through a Boltzmann approach, including contributions of both
large-scale scalar and tensor linearized perturbations. We also compute for the
first time the three-point function of the SGWB energy density, which can allow
one to extract information on GW non-Gaussianity with interferometers. Finally,
we include non-linear effects associated with long wavelength scalar
fluctuations, and compute the squeezed limit of the 3-point function for the
SGWB density contrast. Such limit satisfies a consistency relation,
conceptually similar to what found in the literature for the case of CMB
perturbations.",1912.09433v1
2019-12-22,"Two-dimensional O(n) Models with Defects of ""Random Local Anisotropy"" Type","The phase diagram of two-dimensional systems with continuous symmetry of the
vector order parameter containing defects of the ""random local anisotropy"" type
is investigated. In the case of a weakly anisotropic distribution of the easy
anisotropy axes in the space of the order parameter, with decreasing
temperature, a smooth transition takes place from the paramagnetic phase with
dynamic fluctuations of the order parameter to the Imri-Ma phase with its
static fluctuations. In the case when the anisotropic distribution of the easy
axes induces a global anisotropy of the ""easy axis"" type that exceeds a
critical value, the system goes into the Ising class of universality, and a
phase transition to the ordered state occurs in it at a finite temperature.",1912.10444v1
2019-12-23,Spin-$\frac{1}{2}$ kagome Heisenberg antiferromagnet with strong breathing anisotropy,"We study the zero-temperature phase diagram of the spin-$\frac{1}{2}$
Heisenberg model with breathing anisotropy (i.e., with different coupling
strength on the upward and downward triangles) on the kagome lattice. Our study
relies on large scale tensor network simulations based on infinite projected
entangled-pair state and infinite projected entangled-simplex state methods
adapted to the kagome lattice. Our energy analysis suggests that the U(1)
algebraic quantum spin-liquid (QSL) ground-state of the isotropic Heisenberg
model is stable up to very large breathing anisotropy until it breaks down to a
critical lattice-nematic phase that breaks rotational symmetry in real space
through a first-order quantum phase transition. Our results also provide
further insight into the recent experiment on vanadium oxyfluoride compounds
which has been shown to be relevant platforms for realizing QSL in the presence
of breathing anisotropy.",1912.10756v2
2020-01-06,Galactic Magnetic Field Bias on Inferences from UHECR Data,"A consequence of Liouville's theorem indicates that the recently observed
large scale anisotropy in the arrival direction of Ultra-High-Energy Cosmic
Rays (UHECRs) cannot be produced by the Galactic magnetic field, thus this
anisotropy already needs to be present outside our Galaxy. But in this case,
the observed energy spectrum and composition of UHECRs differs from the one
outside of the Milky Way, due to the suppression or the amplification of the
UHECR flux from certain directions by the Galactic magnetic field. In this
work, we investigate this effect for the case of a dipole and a quadrupole
anisotropy, respectively, for the widely-used JF12 magnetic field model. We
investigate boundaries on the maximal amplitude of the observed anisotropy and
the maximal charge number of UHECRs. Furthermore, the flux modification is
discussed in the light of the Auger data on the recent dipole and also the
chemical composition. We find that this modification effect yields a
modification of the observed flux of up to $\sim 10\%$ for the investigated
magnetic field model and the observed dipole, in particular for a heavy
chemical composition of UHECRs as suggested by the 'EPOS-LHC' model.",2001.01530v2
2020-01-14,Low power switching of magnetization using enhanced magnetic anisotropy with short-voltage-pulse application,"A low power magnetization switching scheme based on the voltage control of
magnetic anisotropy (VCMA) is proposed. In contrast to the conventional
switching scheme using VCMA, where the magnetic anisotropy is eliminated during
the voltage pulse, the magnetic anisotropy is enhanced to induce precession
around the axis close to the easy axis. After turning off the voltage
proximately at a half of precession period, the magnetization relaxes to the
opposite equilibrium direction. We perform numerical simulations and show that
the pulse duration of the proposed switching scheme is as short as a few tens
of pico seconds. Such a short pulse duration is beneficial for low power
consumption because of the reduction of energy loss by Joule heating.",2001.11088v1
2020-03-31,Discrimination of Dark Matter Mass and Velocity Distribution by Directional Detection,"Velocity distribution of dark matter is assumed to be isotropic in most
cases, however, anisotropy is suggested in some simulations. Directional direct
detection of dark matter is a hopeful way to discriminate the anisotropy of
dark matter velocity distribution. We simulate the dark matter and target
scattering in the directional direct detection, and investigate conditions
required to discriminate the anisotropy. If dark matter mass is known,
$O(10^3)-O(10^4)$ events are required for the discrimination if the dark matter
mass is known by other experiments. We also study the case that the dark matter
mass is not known, and in analysis using both the recoil energy and the
scattering angle data, both the dark matter mass and the anisotropy can be
restricted much better than the analysis only with either of them.",2003.14220v1
2020-04-03,Spin-Excitations Anisotropy in the Bilayer Iron-Based Superconductor CaKFe$_4$As$_4$,"We use polarized inelastic neutron scattering to study the spin-excitations
anisotropy in the bilayer iron-based superconductor CaKFe$_4$As$_4$ ($T_c$ = 35
K). In the superconducting state, both odd and even $L-$modulations of spin
resonance have been observed in our previous unpolarized neutron scattering
experiments (T. Xie {\it et al.} Phys. Rev. Lett. {\bf 120}, 267003 (2018)).
Here we find that the high-energy even mode ($\sim 18$ meV) is isotropic in
spin space, but the low-energy odd modes consist of a $c-$axis polarized mode
around 9 meV along with another partially overlapped in-plane mode around 12
meV. We argue that such spin anisotropy is induced by the spin-orbit coupling
in the spin-vortex-type fluctuations of this unique compound. The spin
anisotropy is strongly affected by the superconductivity, where it is weak
below 6 meV in the normal state and then transferred to higher energy and
further enhanced in the odd mode of spin resonance below $T_c$.",2004.01405v1
2020-04-06,Growth morphology and symmetry selection of interfacial instabilities in anisotropic environments,"The displacement of a fluid by another less viscous one in a quasi-two
dimensional geometry typically leads to complex fingering patterns. In an
isotropic system, dense-branching growth arises, which is characterized by
repeated tip-splitting of evolving fingers. When anisotropy is present in the
interfacial dynamics, the growth morphology changes to dendritic growth
characterized by regular structures. We introduce anisotropy by engraving a
six-fold symmetric lattice of channels on a Hele-Shaw cell. We show that the
morphology transition in miscible fluids depends not only on the previously
reported degree of anisotropy set by the lattice topography, but also on the
viscosity ratio between the two fluids. Remarkably, the viscosity ratio and the
degree of anisotropy also govern the global features of the dendritic patterns,
inducing a systematic change from six-fold towards twelve-fold symmetric
dendrites. Varying either control parameter provides a new method to tune the
symmetry of complex patterns, which may also have relevance for analogous
phenomena of gradient-driven interfacial dynamics, such as directional
solidification or electrodeposition.",2004.02371v2
2020-04-06,Theoretical Study of the Anisotropy Spectra of the Valine Zwitterion and Glyceraldehyde,"The electronic absorption (EA), circular dichroism (ECD), and anisotropy
spectra of the L-valine zwitterion and D-glyceraldehyde are calculated by
time-dependent density functional theory (TDDFT) with the M06-2X and B3LYP
functionals. It is found that the absorption and ECD spectra from TDDFT/M06-2X
agree well with experimental results measured from amorphous film of L-valine.
Moreover, the calculations reproduce all three major peaks observed in the
experimental anisotropy spectra. For D-glyceraldehyde, the TDDFT/M06-2X
calculations indicate that the excitation wavelengths of the first excited
state of 32 stable conformers distribute from 288 to 322 nm, giving rise to two
ECD peaks with opposite signs centered at 288 nm and 322 nm. The very weak
absorption of the first excited state (S1) induces two high peaks in the
anisotropy spectra of D-glyceraldehyde, which should be seen in future
experimental works.",2004.02455v3
2020-04-21,Magnetization plateaux cascade in the frustrated quantum antiferromagnet Cs$_2$CoBr$_4$,"We have found an unusual competition of two frustration mechanisms in the 2D
quantum antiferromagnet Cs$_2$CoBr$_4$. The key actors are the alternation of
single-ion planar anisotropy direction of the individual magnetic Co$^{2+}$
ions, and their arrangement in a distorted triangular lattice structure. In
particular, the uniquely oriented Ising-type anisotropy emerges from the
competition of easy-plane ones, and for a magnetic field applied along this
axis one finds a cascade of five ordered phases at low temperatures. Two of
these phases feature magnetization plateaux. The low-field one is supposed to
be a consequence of a collinear ground state stabilized by the anisotropy,
while the other plateau bears characteristics of an ""up-up-down"" state
exclusive for lattices with triangular exchange patterns. Such coexistence of
the magnetization plateaux is a fingerprint of competition between the
anisotropy and the geometric frustration in Cs$_2$CoBr$_4$.",2004.09893v2
2020-04-25,Pulse-assisted magnetization switching in magnetic nanowires at picosecond and nanosecond timescales with low energy,"Detailed understanding of spin dynamics in magnetic nanomaterials is
necessary for developing ultrafast, low-energy and high-density spintronic
logic and memory. Here, we develop micromagnetic models and analytical
solutions to elucidate the effect of increasing damping and uniaxial anisotropy
on magnetic field pulse-assisted switching time, energy and field requirements
of nanowires with perpendicular magnetic anisotropy and yttrium iron
garnet-like spin transport properties. A nanowire is initially magnetized using
an external magnetic field pulse (write) and self-relaxation. Next, magnetic
moments exhibit deterministic switching upon receiving 2.5 ns-long external
magnetic pulses in both vertical polarities. Favorable damping
({\alpha}~0.1-0.5) and anisotropy energies (10^4-10^5 J m^-3) allow for as low
as picosecond magnetization switching times. Magnetization reversal with fields
below coercivity was observed using spin precession instabilities. A
competition or a nanomagnetic trilemma arises among the switching rate, energy
cost and external field required. Developing magnetic nanowires with optimized
damping and effective anisotropy could reduce the switching energy barrier down
to 3163kBT at room temperature. Thus, pulse-assisted picosecond and low energy
switching in nanomagnets could enable ultrafast nanomagnetic logic and cellular
automata.",2004.12243v1
2020-05-19,Magnetic hard-direction ordering in anisotropic Kondo systems,"We present a generic mechanism that explains why many Kondo materials show
magnetic ordering along directions that are not favoured by the crystal-field
anisotropy. Using a renormalization-group (RG) analysis of single impurity
Kondo models with single-ion anisotropy, we demonstrate that strong
fluctuations above the Kondo temperature drive a moment re-orientation over a
wide range of parameters, e.g. for different spin values $S$ and number of
Kondo channels $N$. In tetragonal systems this can happen for both easy-plane
or easy axis anisotropy. The characteristic crossing of magnetic
susceptibilities is not an artefact of the weak-coupling RG treatment but can
be reproduced in brute-force perturbation theory. Employing numerical
renormalization group (NRG), we show that for an under-screened moment ($S=1$,
$N=1$) with easy-plane anisotropy, a crossing of magnetic susceptibilities can
also occur in the strong-coupling regime (below the Kondo temperature). This
suggests that collective magnetic ordering of such under-screened moments would
develop along the magnetic hard axis.",2005.09533v3
2020-05-22,The nonlinear patterns of the cosmic anisotropy in the late time universe,"In this manuscript, we investigate the patterns satisfied by the cosmological
anisotropy under the hypothesis of the observers being co-moving with a perfect
fluid whose induced space sections are homogeneous with vanishing scalar
curvature. We describe the positive increment $\Delta R$ that the Hubble
parameter in the anisotropic model will have as it is compared to its isotropic
counterpart. In general, it has an exponential awakening at a specific redshift
$z_A$. We also show that the deceleration and the jerk along the principal
directions of the anisotropy are constrained by simple algebraic equations that
do not depend on the type of matter present. These characteristic patterns form
a valuable framework to distinguish the cosmological anisotropy from any other
kind, thus adding a useful tool to probe its upper limits in the supernovae
surveys, which are orders of magnitude away from those observed in the CMB.",2005.11250v2
2020-05-26,Classifying local anisotropy formed by rigid molecules: symmetries and tensors,"We consider an infinitesimal volume where there are many rigid molecules of
the same kind, and discuss the description and classification of the local
anisotropy in this volume by tensors. First, we examine the symmetry of a rigid
molecule, which is described by a point group in $SO(3)$. For each point group
in $SO(3)$, we find the tensors invariant under the rotations in the group.
These tensors shall be symmetric and traceless. We write down the explicit
expressions. The order parameters to describe the local anisotropy are then
chosen as some of the invariant tensors averaged about the density function.
Next, we discuss the classification of local anisotropy by the symmetry of the
whole infinitesimal volume. This mesoscopic symmetry can be recognized by the
value of the order parameter tensors in the sense of maximum entropy state. For
some sets of order parameter tensors involving different molecular symmetries,
we give the classification of mesoscopic symmetries, in which the three-fold,
four-fold and polyhedral symmetries are examined.",2005.12480v1
2020-06-22,Spin-orbit torque induced magnetisation dynamics and switching in CoFeB/Ta/CoFeB system with mixed magnetic anisotropy,"Spin-orbit torque (SOT) induced magnetisation switching in CoFeB/Ta/CoFeB
trilayer with two CoFeB layers exhibiting in-plane magnetic anisotropy (IPMA)
and perpendicular magnetic anisotropy (PMA) is investigated. Interlayer
exchange coupling (IEC), measured using ferromagnetic resonance technique is
modified by varying thickness of Ta spacer. The evolution of the IEC leads to
different orientation of the magnetic anisotropy axes of two CoFeB layers: for
thicker Ta layer where magnetisation prefers antiferromagnetic ordering and for
thinner Ta layer where ferromagnetic coupling exists. Magnetisation state of
the CoFeB layer exhibiting PMA is controlled by the spin-polarized current
originating from SOT in $\mu m$ sized Hall bars. The evolution of the critical
SOT current density with Ta thickness is presented, showing an increase with
decreasing $t_\mathrm{Ta}$, which coincides with the coercive field dependence.
In a narrow range of $t_\mathrm{Ta}$ corresponding to the ferromagnetic IEC,
the field-free SOT-induced switching is achieved.",2006.12068v1
2020-07-08,Anisotropic properties of monolayer 2D materials: an overview from the C2DB database,"We analyze the occurrence of in-plane anisotropy in the electronic, magnetic,
elastic and transport properties of more than one thousand 2D materials from
the C2DB database. We identify hundreds of anisotropic materials and classify
them according to their point group symmetry and degree of anisotropy. A
statistical analysis reveals that a lower point group symmetry and a larger
amount of different elements in the structure favour all types of anisotropies,
which could be relevant for future materials design approaches. Besides, we
identify novel compounds, predicted to be easily exfoliable from a parent bulk
compound, with anisotropies that largely outscore those of already known 2D
materials. Our findings provide a comprehensive reference for future studies of
anisotropic response in atomically-thin crystals and point to new previously
unexplored materials for the next generation of anisotropic 2D devices.",2007.04152v2
2020-07-08,Susceptibility anisotropy and its disorder evolution in models for Kitaev materials,"Mott insulators with strong spin-orbit coupling display a strongly
anisotropic response to applied magnetic fields. This applies in particular to
Kitaev materials, with $\alpha$-RuCl$_3$ and Na$_2$IrO$_3$ representing two
important examples. Both show a magnetically ordered zigzag state at low
temperatures, and considerable effort has been devoted to properly modeling
these systems in order to identify routes towards realizing a quantum spin
liquid. Here, we investigate the relevant Heisenberg-Kitaev-$\Gamma$ model
primarily at elevated temperatures, focusing on the characteristic anisotropy
between the in-plane and out-of-plane uniform susceptibility. For
$\alpha$-RuCl$_3$, we find that the experimentally observed anisotropy,
including its temperature dependence, can be reproduced by combining a large
off-diagonal $\Gamma_1$ coupling with a moderate $g$-factor anisotropy.
Moreover, we study in detail the effect of magnetic dilution and provide
predictions for the doping evolution of the temperature-dependent
susceptibilities.",2007.04339v2
2020-07-21,Orbital anisotropy of heavy fermion Ce$_{2}$IrIn$_{8}$ under crystalline electric field and its energy scale,"We investigate the temperature ($T$)-evolution of orbital anisotropy and its
effect on spectral function and optical conductivity in Ce$_{2}$IrIn$_{8}$,
using a first principles dynamical mean field theory combined with density
functional theory. The orbital anisotropy develops by lowering $T$ and it is
intensified below a temperature corresponding to the crystalline-electric field
(CEF) splitting size. Interestingly, the depopulation of CEF excited states
leaves a spectroscopic signature, ""shoulder"", in the $T$-dependent spectral
function at the Fermi level. From the two-orbital Anderson impurity model, we
demonstrate that CEF splitting size is the key ingredient influencing the
emergence and the position of the ""shoulder"". Besides the two conventional
temperature scales $T_{K}$ and $T^{*}$, we introduce an additional temperature
scale to deal with the orbital anisotropy in heavy fermion systems.",2007.10641v3
2020-08-07,Voltage-controlled magnetic anisotropy in antiferromagnetic MgO-capped MnPt films,"The magnetic anisotropy in MgO-capped MnPt films and its voltage control are
studied using first-principles calculations. Sharp variation of the magnetic
anisotropy with film thickness, especially in the Pt-terminated film, suggests
that it may be widely tuned by adjusting the film thickness. In thick films the
linear voltage control coefficient is as large as 1.5 and $-0.6$ pJ/Vm for
Pt-terminated and Mn-terminated interfaces, respectively. The combination of a
widely tunable magnetic anisotropy energy and a large voltage-control
coefficient suggest that MgO-capped MnPt films can serve as a versatile
platform for magnetic memory and antiferromagnonic applications.",2008.03249v2
2020-08-12,"Equilibrium, radial stability and non-adiabatic gravitational collapse of anisotropic neutron stars","In this work we construct families of anisotropic neutron stars for an
equation of state compatible with the constraints of the gravitational-wave
event GW170817 and for four anisotropy ansatze. Such stars are subjected to a
radial perturbation in order to study their stability against radial
oscillations and we develop a dynamical model to describe the non-adiabatic
gravitational collapse of the unstable anisotropic configurations whose
ultimate fate is the formation of a black hole. We find that the standard
criterion for radial stability $dM/d\rho_c >0$ is not always compatible with
the calculation of the oscillation frequencies for some anisotropy ansatze, and
each anisotropy parameter is constrained taking into account the recent
restriction of maximum mass of neutron stars. We further generalize the TOV
equations within a non-adiabatic context and we investigate the dynamical
behaviour of the equation of state, heat flux, anisotropy factor and mass
function as an unstable anisotropic star collapses. After obtaining the
evolution equations we recover, as a static limit, the background equations.",2008.05331v1
2020-09-09,Magnetic Anisotropy in Spin-3/2 with Heavy Ligand in Honeycomb Mott Insulators: Application to CrI$_3$,"Ferromagnetism in the two-dimensional CrI$_3$ has generated a lot of
excitement, and it was recently proposed that the spin-orbit coupling (SOC) in
Iodine may generate bond-dependent spin interactions leading to magnetic
anisotropy. Here we derive a microscopic spin model of S=3/2 on transition
metals surrounded by heavy ligands in honeycomb Mott insulators using a
strong-coupling perturbation theory. For ideal octahedra we find Heisenberg and
Kitaev interactions, which favor the magnetic moment along the cubic axis via
quantum fluctuations. When a slight trigonal distortion of the octahedra is
present together with the SOC, three additional interactions arise, comprised
of the off-diagonal symmetric $\Gamma$ and $\Gamma^\prime$, and single-ion
anisotropy. The resulting magnetic anisotropy pins the moment perpendicular to
the honeycomb plane as observed in a single-layer of CrI$_3$, suggesting the
significance of SOC and trigonal distortion in understanding magnetism of two
dimensional Mott insulators. Comparison to the spin-orbit coupled $J_{\rm
eff}$= 1/2 and S=1 models is also presented.",2009.04475v2
2020-10-01,Charge density waves and their transitions in anisotropic quantum Hall systems,"In recent experiments, external anisotropy has been a useful tool to tune
different phases and study their competitions. In this paper, we look at the
quantum Hall charge density wave states in the $N=2$ Landau level. Without
anisotropy, there are two first-order phase transitions between the Wigner
crystal, the $2$-electron bubble phase, and the stripe phase. By adding mass
anisotropy, our analytical and numerical studies show that the $2$-electron
bubble phase disappears and the stripe phase significantly enlarges its domain
in the phase diagram. Meanwhile, a regime of stripe crystals that may be
observed experimentally is unveiled after the bubble phase gets out. Upon
increase of the anisotropy, the energy of the phases at the transitions becomes
progressively smooth as a function of the filling. We conclude that all
first-order phase transitions are replaced by continuous phase transitions,
providing a possible realisation of continuous quantum crystalline phase
transitions.",2010.00611v2
2020-10-05,"Properties of amorphous CoZr(RE) (RE=Gd, Sm, Dy) films with various uniaxial anisotropies, prepared by a new process","If a DC magnetic field is applied parallel to the plane of amorphous CoZr(RE)
thin films during sputter depositing, a uniaxial anisotropy is formed the
direction of which depends upon the choice of RE substituted and its
concentration. When RE = Gd a perpendicular anisotropy K, forms over a large
concentration range, a spin reorientation process being at the origin of the
process. A well-defined K, is developed also in CoFeZrGd and CoZrGdSm films.
CoZrGdDy films exhibit simultaneously a perpendicular and an in-plane uniaxial
anisotropy. The related magnetization process and domain structures are quite
peculiar.",2010.01831v1
2020-10-30,"Phase transitions between helices, vortices, and hedgehogs driven by spatial anisotropy in chiral magnets","Superpositions of spin helices can yield topological spin textures, such as
two-dimensional vortices and skyrmions, and three-dimensional hedgehogs. Their
topological nature and spatial dimensionality depend on the number and relative
directions of the constituent helices. This allows mutual transformation
between the topological spin textures by controlling the spatial anisotropy.
Here we theoretically study the effect of anisotropy in the magnetic
interactions for an effective spin model for chiral magnetic metals. By
variational calculations for both cases with triple and quadruple
superpositions, we find that the hedgehog lattices, which are stable in the
isotropic case, are deformed by the anisotropy, and eventually changed into
other spin textures with reduced dimension, such as helices and vortices. We
also clarify the changes of topological properties by tracing the real-space
positions of magnetic monopoles and antimonopoles as well as the emergent
magnetic field generated by the noncoplanar spin textures. Our results suggest
possible control of the topological spin textures, e.g., by uniaxial pressure
and chemical substitution in chiral materials.",2010.16187v1
2020-11-04,Large angle precession of magnetization maintained by a microwave voltage,"Effects of a microwave voltage on magnetization precession are analyzed based
on a macrospin model. The microwave voltage induces the oscillating anisotropy
field through the voltage controlled magnetic anisotropy (VCMA) effect, and
then stimulates the magnetization. The large angle precession is maintained if
the magnetization synchronizes with the microwave voltage. The effective
equations of motion of the magnetization with an oscillating anisotropy field
are derived, and the mechanism of the synchronization is clarified by analyzing
the derived equations of motion. The conditions of the angular frequency
detuning and the amplitude of the oscillating anisotropy field for
synchronization are obtained. The results are useful for development of the
VCMA-based energy-efficient spintronics devices using magnetization precession
such as a VCMA-based magnetoresistive random access memory and a nano-scale
microwave magnetic field generator.",2011.02104v1
2020-11-05,Antiferromagnetic resonance in a spin-gap magnet with strong single-ion anisotropy,"Quasi-one-dimensional magnet NiCl$_2\cdot$4SC(NH$_2$)$_2$, usually
abbreviated as DTN, does not order at zero field down to $T=0$: due to the
strong single-ion anisotropy of the ""easy plane"" type acting on $S=1$ Ni$^{2+}$
ions, the $S_z=0$ ground state is separated from $S_z=\pm 1$ excitations by an
energy gap. Once the magnetic field is applied along the main anisotropy axis,
the gap closes at $B_{c1}=2.18$ T and the field-induced antiferromagnetic order
arises. The low-energy excitations spectrum of this field-induced ordered state
includes two branches of excitations, one of them have to be a gapless
Goldstone mode. Recent studies of excitations spectrum in a field-induced
ordered state of DTN (T.Soldatov et.al, Phys.Rev.B 101, 104410 (2020)) have
revealed that Goldstone mode became gapped as magnetic field deviates from the
main symmetry axis. This paper proposes simple description of antiferromagnetic
resonance modes of quasi-one-dimensional quantum $S=1$ magnet with strong
single-ion anisotropy. The approach used is based on a combination of the
strong coupling model for the anisotropic spin chain with the conventional
mean-field model of antiferromagnetic resonance. The resulting model fits to
the known experimental results without additional tuning parameters.",2011.02715v1
2020-11-05,Testing Short Distance Anisotropy in Space,"The isotropy of space is not a logical requirement but rather is an empirical
question; indeed there is suggestive evidence that universe might be
anisotropic. A plausible source of these anisotropies could be quantum gravity
corrections. If these corrections happen to be between the electroweak scale
and the Planck scale, then these anisotropies can have measurable consequences
at short distances and their effects can be measured using ultra sensitive
condensed matter systems. We investigate how such anisotropic quantum gravity
corrections modify low energy physics through an anisotropic deformation of the
Heisenberg algebra. We discuss how such anisotropies might be observed using a
scanning tunneling microscope.",2011.03340v2
2020-11-06,Covariant formulation of gluon self-energy in presence of ellipsoidal anisotropy,"In this work, a covariant formulation of the gluon self-energy in presence of
ellipsoidal anisotropy is considered. It is shown that the general structure of
the gluon self-energy can be written in terms of six linearly independent
projection tensors. Similar to the spheroidal anisotropy, mass scales can be
introduced for each of the collective modes considering the static limits. With
a simplified ellipsoidal generalization of the Romatschke-Strickland form, the
angular dependencies of the mass scales are studied. It is observed that,
compared to the spheroidal case, additional unstable mode may appear in
presence of ellipsoidal anisotropy depending upon the choice of the parameters.",2011.03374v2
2020-11-14,Voltage-controlled magnetic anisotropy under the electronic structure modulation in quantum wells,"Voltage-controlled magnetic anisotropy (VCMA) offers an emerging approach to
realize energy-efficient magnetization switching in spintronic devices such as
magnetic random access memories (MRAMs). Here, we show that manipulating the
condensed states, i.e., introducing quantum well (QW) can significantly
influence the VCMA in a Cr/Fe-QW/MgAl2O4 based magnetic tunnel junction (MTJ).
Only for the MTJ with an even number of Fe atomic layers, we observed a novel
A-shaped VCMA curve for a particular QW state, where magnetic anisotropy energy
(MAE) reaches a local maximum at zero bias and reduces when applying both
positive and negative bias, i.e., a novel bi-polar VCMA effect. Our ab initio
calculations demonstrate that the QW states give an additional contribution to
perpendicular magnetic anisotropy (PMA), which can explain not only the
A-shaped VCMA but also the Fe-layer-number parity dependence of VCMA. The
present study suggests that the QW-modulated VCMA should open a new pathway to
design VCMA-assisted MRAM.",2011.07217v1
2020-11-25,Investigation of superconducting properties and possible nematic superconductivity in self-doped BiCh2-based superconductor CeOBiS1.7Se0.3,"We investigate the superconducting properties and possible nematic
superconductivity of self-doped BiCh2-based (Ch: S, Se) superconductor
CeOBiS1.7Se0.3 through the measurements of in-plane anisotropy of
magnetoresistance. Single crystals of CeOBiS1.7Se0.3 were grown using a flux
method. Single-crystal structural analysis revealed that the crystal structure
at room temperature is tetragonal (P4/nmm). Bulk superconductivity with a
transition temperature of 3.3 K was observed through electrical resistivity and
magnetization measurements. Investigation of anisotropy of upper critical field
suggested relatively low anisotropy in the crystal as compared to other
BiCh2-based superconductors. In the superconducting states of CeOBiS1.7Se0.3,
two-fold symmetric in-plane anisotropy of magnetoresistance was observed, which
indicates the in-plane rotational symmetry breaking in the tetragonal structure
and hence the possibility of nematic superconductivity in CeOBiS1.7Se0.3.",2011.12708v1
2020-12-24,Relationship between polytropic index and temperature anisotropy in space plasmas,"The paper develops a theoretical relationship between the polytropic index
and the temperature anisotropy that may characterize space plasmas. The
derivation is based on the correlation among the kinetic energies of particles
with velocities described by anisotropic kappa distributions. The correlation
coefficient depends on the effective dimensionality of the velocity
distribution function, having its shape determined by the temperature
anisotropies caused by the ambient magnetic field; on the other hand, the
effective dimensionality is directly dependent on the polytropic index. This
analysis leads to the connection between the correlation coefficient, effective
dimensionality of velocity space, and the polytropic index, with the ratio of
temperature anisotropy. Moreover, a data and statistical analysis is performed
to test the application of the theoretically developed model, in the solar wind
proton plasma near 1 AU. The derived theoretical relationship is in good
agreement with observations, showing that the lowest and classical value of the
adiabatic polytropic index occurs in the isotropic case, while higher indices
characterize anisotropic plasmas. Finally, possible extensions of the theory
considering (i) non-adiabatic polytropic behavior, and (ii) more general
distributions, are further discussed.",2012.13222v1
2021-01-04,Absorption of Microwaves by Random-Anisotropy Magnets,"Microscopic model of the interaction of spins with a microwave field in a
random-anisotropy magnet has been developed. Numerical results show that
microwave absorption occurs in a broad range of frequencies due to the
distribution of Imry-Ma domains on sizes and effective anisotropy. That
distribution is also responsible for the weak dependence of the absorption on
the damping. At a fixed frequency of the ac-field the spatial pattern of the
amplitude of spin oscillations exhibits maxima corresponding to the
oscillations of resonant magnetic domains. The dependence of the peak
absorption frequency on the ratio of the magnitude of per-spin random
anisotropy to the strength of the ferromagnetic exchange agrees with the
scaling derived from the Imry-Ma argument. The effect noticeably increases in
low-dimensional systems, suggesting that materials comprised of microscopic
amorphous leaves and wires can be promising candidates for enhanced microwave
absorption.",2101.01230v1
2021-01-05,Tunable Single-Ion Anisotropy in Spin-1 Models Realized with Ultracold Atoms,"Mott insulator plateaus in optical lattices are a versatile platform to study
spin physics. Using sites occupied by two bosons with an internal degree of
freedom, we realize a uniaxial single-ion anisotropy term proportional to
$(S^z)^2$, which plays an important role in stabilizing magnetism for
low-dimensional magnetic materials. Here we explore non-equilibrium spin
dynamics and observe a resonant effect in the spin anisotropy as a function of
lattice depth when exchange coupling and on-site anisotropy are similar. Our
results are supported by many-body numerical simulations and are captured by
the analytical solution of a two-site model.",2101.01316v1
2021-01-07,Optically Facet-Resolved Reaction Anisotropy in Two-Dimensional Transition Metal Dichalcogenides,"Quantifying anisotropy in the chemical reactions of mesoscopic crystals has
mostly resorted on the combination of electron microscopy and diffraction. In
this work, we established crystal-facet-resolved kinetic measurements of
oxidation reactions in 2D transition metal dichalcogenides (TMDs) using optical
second-harmonic generation spectroscopy and scanning probe microscopy. We show
the in-plane anisotropy of their bond-breaking reactions is governed by their
structure and strongly material-dependent among four TMDs. The facet-resolved
analysis directly revealed that the reactions proceed fastest (slowest) for
chalcogen (metal)-terminated zigzag edges with armchair edges in the middle.
The degree of the anisotropy inducing trigonal oxidation patterns was much
higher in MoS2 and MoSe2 than WS2 and WSe2. Kinetic Wulff construction based on
edge-specific reaction rates verified the material-dependent mesoscopic
reaction patterns. We also show that the reactions are initiated at
substrate-mediated defects located on the bottom and top surfaces of 2D TMDs.",2101.02376v2
2021-01-13,Self-organization in the one-dimensional Landau-Lifshitz-Gilbert-Slonczewski equation with non-uniform anisotropy fields,"In magnetic films driven by spin-polarized currents, the
perpendicular-to-plane anisotropy is equivalent to breaking the time
translation symmetry, i.e., to a parametric pumping. In this work, we
numerically study those current-driven magnets via the
Landau-Lifshitz-Gilbert-Slonczewski equation in one spatial dimension. We
consider a space-dependent anisotropy field in the parametric-like regime. The
anisotropy profile is antisymmetric to the middle point of the system. We find
several dissipative states and dynamical behavior and focus on localized
patterns that undergo oscillatory and phase instabilities. Using numerical
simulations, we characterize the localized states' bifurcations and present the
corresponding diagram of phases.",2101.05263v1
2021-01-19,Cosmic Ray transport in mixed magnetic fields and their role on the observed anisotropies,"There is a growing set of observational data demonstrating that cosmic rays
exhibit small-scale anisotropies (5-30 deg) with amplitude deviations lying
between 0.01-0.1 percent that of the average cosmic ray flux. A broad range of
models have been proposed to explain these anisotropies ranging from
finite-scale magnetic field structures to dark matter annihilation. The
standard diffusion transport methods used in cosmic ray propagation do not
capture the transport physics in a medium with finite-scale or coherent
magnetic field structures. Here, we present a Monte Carlo transport method,
applying it to a series of finite-scale magnetic field structures to determine
the requirements of such fields in explaining the observed cosmic
ray,small-scale anisotropies.",2101.07759v1
2021-02-08,Nanoscale decoupling of electronic nematicity and structural anisotropy in FeSe thin films,"In a material prone to a nematic instability, anisotropic strain in principle
provides a preferred symmetry-breaking direction for the electronic nematic
state to follow. This is consistent with experimental observations, where
electronic nematicity and structural anisotropy typically appear hand-in-hand.
In this work, we discover that electronic nematicity can be locally decoupled
from the underlying structural anisotropy in strain-engineered iron-selenide
(FeSe) thin films. We use heteroepitaxial molecular beam epitaxy to grow FeSe
with a nanoscale network of modulations that give rise to spatially varying
strain. We map local anisotropic strain by analyzing scanning tunneling
microscopy topographs, and visualize electronic nematic domains from
concomitant spectroscopic maps. While the domains form so that the energy of
nemato-elastic coupling is minimized, we observe distinct regions where
electronic nematic ordering fails to flip direction, even though the underlying
structural anisotropy is locally reversed. The findings point towards a
nanometer-scale stiffness of the nematic order parameter.",2102.04381v1
2021-02-14,Heavy quark transport in an anisotropic hot QCD medium: Collisional and Radiative processes,"The impact of momentum anisotropy on the heavy quark transport coefficients
due to collisional and radiative processes in the QCD medium has been studied
within the ambit of kinetic theory. Anisotropic aspects (momentum) are
incorporated into the heavy quark dynamics through the non-equilibrium momentum
distribution function of quarks, antiquarks, and gluons. These non-equilibrium
distribution functions that encode the physics of momentum anisotropy and
turbulent chromo-fields have been obtained by solving the ensemble-averaged
diffusive Vlasov-Boltzmann equation. The momentum dependence of heavy quark
transport coefficients in the medium is seen to be sensitive to the strength of
the anisotropy for both collisional and radiative processes. In addition, the
collisional and radiative energy loss of the heavy quark in the anisotropic hot
QCD medium have been analyzed. The effects of anisotropy on the drag and
diffusion coefficients are observed to have a visible impact on the nuclear
suppression factor both at the RHIC and LHC.",2102.07082v2
2021-03-07,"Magnetic anisotropy and exchange interactions of two-dimensional FePS$_3$, NiPS$_3$ and MnPS$_3$ from first principles calculations","The van der Waals bonded transition metal phosphorous trichalcogenides
FePS$_3$, NiPS$_3$ and MnPS$_3$ have recently attracted renewed attention due
to the possibility of exfoliating them into their monolayers. Although the
three compounds have similar electronic structure, the magnetic structure
differs due to subtle differences in exchange and magnetic anisotropy and the
materials thus comprise a unique playground for studying different aspects of
magnetism in 2D. Here we calculate the exchange and anisotropy parameters of
the three materials from first principles paying special attention to the
choice of Hubbard parameter U. We find a strong dependence of the choice of U
and show that the calculated N\'eel temperature of FePS$_3$ varies by an order
of magnitude over commonly applied values of U for the Fe $d$-orbitals. The
results are compared with parameters fitted to experimental spin-wave spectra
of the bulk materials and we find excellent agreement between the exchange
constants when a proper value of U is chosen. However, the anisotropy
parameters are severely underestimated by DFT and we discuss possible origins
of this discrepancy.",2103.04474v1
2021-03-24,Quantifying the anisotropic density structure of the Central Molecular Zone -- a 2D correlation function approach,"The Central Molecular Zone (CMZ) is a ring-like structure sitting at the
center of the Milky Way. Using the 870 $\mu$m continuum map from the APEX
Telescope Large Area Survey of the Galaxy (ATLASGAL), we study the anisotropy
of the density structure of the gas in the Central Molecular Zone (CMZ) using
the 2D correlation function. To quantify the spatial anisotropy, we define the
critical angle $\theta_{\rm half}$, as well as the anisotropy parameter
$A\equiv \frac{\pi}{4\theta_{\rm half}}-1$. We find that the density structure
is strongly anisotropic at the large scale (~ 100 pc), and the degree of
spatial anisotropy decreases with the decreasing scale. At the scale of ~ 10
pc, the structure is still mildly anisotropic. In our analyses, we provide a
quantitative description of the anisotropic density structure of gas in the
CMZ, and the formalism can be applied to different regions to study their
differences.",2103.13048v2
2021-04-19,Anisotropic quantum Hall states in the presence of interactions with fourfold rotational symmetry,"We study the effects of anisotropic interactions in the quantum Hall effect
in the presence of a fourfold discrete rotational ($C_4$) symmetry. Employing
the density matrix renormalization group technique on an infinite cylinder
geometry (iDMRG), we calculate the anisotropy response of the Laughlin state at
$\nu=1/3$ and the composite-Fermi liquid (CFL) state at $\nu=1/2$. We find that
the anisotropy transferred from the interaction potential to the $\nu=1/3$
state is stronger when compared to the complementary case of an anisotropic
band. Further, the strength of anisotropy reduces as the interaction is made
shorter ranged. Quite surprisingly, at $\nu=1/2$, we find that the deformation
in the CF Fermi-surface changes sign as the interaction range is reduced. Our
results imply that the short-distance and long-distance parts of the
interaction potential have opposite effects on the CFL state in the presence of
$C_4$-symmetric anisotropy.",2104.09670v2
2021-04-26,Switching between Magnetic Bloch and Néel Domain Walls with Anisotropy Modulations,"It has been shown previously that the presence of a Dzyaloshinskii-Moriya
interaction in perpendicularly magnetized thin films stabilizes N\'eel type
domain walls. We demonstrate, using micromagnetic simulations and analytical
modeling, that the presence of a uniaxial in-plane magnetic anisotropy can also
lead to the formation of N\'eel walls in the absence of a Dzyaloshinskii-Moriya
interaction. It is possible to abruptly switch between Bloch and N\'eel walls
via a small modulation of both the in-plane, but also the perpendicular
magnetic anisotropy. This opens up a route towards electric field control of
the domain wall type with small applied voltages through electric field
controlled anisotropies.",2104.12400v2
2021-05-07,CMB Mode Coupling with Isotropic Polarization Rotation,"We provide a new analysis technique to measure the effect of the isotropic
polarization rotation, induced by e.g. the isotropic cosmic birefringence from
axion-like particles and a miscalibration of CMB polarization angle, via mode
coupling in the cosmic microwave background (CMB). Several secondary effects
such as gravitational lensing and CMB optical-depth anisotropies lead to mode
coupling in observed CMB anisotropies, i.e., non-zero off-diagonal elements in
the observed CMB covariance. To derive the mode coupling, however, we usually
assume no parity violation in the observed CMB anisotropies. We first derive a
new contribution to the CMB mode coupling arising from parity violation in
observed CMB. Since the isotropic polarization rotation leads to parity
violation in the observed CMB anisotropies, we then discuss the use of the new
mode coupling for constraining the isotropic polarization angle. We find that
constraints on the isotropic polarization angle by measuring the new
mode-coupling contribution are comparable to that using the $EB$ cross-power
spectrum in future high-sensitivity polarization experiments such as CMB-S4 and
LiteBIRD. Thus, this technique can be used to cross-check results obtained by
the use of the $EB$ cross-power spectrum.",2105.03367v1
2021-05-08,Breaking of Ginzburg-Landau description in the temperature dependence of the anisotropy in the nematic superconductor,"Nematic superconductors are characterized by an apparent crystal symmetry
breaking that results in the anisotropy of the in-plane upper critical magnetic
field $H_{c2}$. The symmetry breaking is usually attributed to the strain of
the crystal lattice. The nature and the value of the strain are debatable. We
perform systematic measurements of the $H_{c2}$ anisotropy in the high-quality
Sr$_x$Bi$_2$Se$_3$ single crystals in the temperature range 1.8~K$<T<T_c\approx
2.7$~K using temperature stabilization with an accuracy of 0.0001 K. We observe
that in all tested samples the anisotropy is weakly temperature dependent when
$T<0.8\,T_c$ and smoothly decreases at higher temperatures without any sign of
singularity when $T\rightarrow T_c$. Such a behavior {is in a drastic
contradiction with the prediction of} the Ginzburg-Landau theory for the
nematic superconductors. We discuss possible reasons for this discrepancy.",2105.03696v2
2021-05-10,Role of Majorana fermions in spin transport of anisotropic Kitaev model,"We study a quantum spin Kitaev model with zigzag edges to clarify the effects
of anisotropy in the exchange couplings on the spin propagation. We simulate
the spin and Majorana dynamics triggered by a magnetic pulse, using the
real-space time-dependent Majorana mean-field theory. When the anisotropy is
small, the dispersion of the itinerant Majorana fermions remains gapless, where
the velocity of the spin propagation matches the group velocity of the
itinerant Majorana fermions at the nodal points. On the other hand, in the
gapped system with a large anisotropy, the spin propagation is strongly
suppressed although its nature depends on the shape of the pulse. The spin
transport in the junction system described by the Kitaev models with distinct
anisotropies is also dressed.",2105.04094v1
2021-05-10,Is there Anisotropy in Structural Bias?,"Structural Bias (SB) is an important type of algorithmic deficiency within
iterative optimisation heuristics. However, methods for detecting structural
bias have not yet fully matured, and recent studies have uncovered many
interesting questions. One of these is the question of how structural bias can
be related to anisotropy. Intuitively, an algorithm that is not isotropic would
be considered structurally biased. However, there have been cases where
algorithms appear to only show SB in some dimensions. As such, we investigate
whether these algorithms actually exhibit anisotropy, and how this impacts the
detection of SB. We find that anisotropy is very rare, and even in cases where
it is present, there are clear tests for SB which do not rely on any
assumptions of isotropy, so we can safely expand the suite of SB tests to
encompass these kinds of deficiencies not found by the original tests.
  We propose several additional testing procedures for SB detection and aim to
motivate further research into the creation of a robust portfolio of tests.
This is crucial since no single test will be able to work effectively with all
types of SB we identify.",2105.04480v1
2021-05-18,Bumblebee field as a source of cosmological anisotropies,"In this work, a bumblebee field is adopted in order to generate cosmological
anisotropies. For that purpose, we assume a Bianchi I cosmology, as the
background geometry, and a bumblebee field coupled to it. Bumblebee models are
examples of a mechanism for the Lorentz symmetry violation by assuming a
nonzero vacuum expectation value for the bumblebee field. When coupled to the
Bianchi I geometry, which is not in agreement with a cosmological principle,
the bumblebee field plays the role of a source of anisotropies and produces a
preferred axis. Thus, a fraction of the cosmic anisotropies would come from the
Lorentz symmetry violation. In the last part of the article, we try to assume
an upper bound on the bumblebee field using the quadrupole and octopole moments
of the cosmic microwave background radiation.",2105.08659v3
2021-05-21,Elastic anisotropy of nematic liquid crystals in the two-dimensional Landau-de Gennes model,"We study the effects of elastic anisotropy on the Landau-de Gennes critical
points for nematic liquid crystals, in a square domain. The elastic anisotropy
is captured by a parameter, $L_2$, and the critical points are described by
three degrees of freedom. We analytically construct a symmetric critical point
for all admissible values of $L_2$, which is necessarily globally stable for
small domains i.e., when the square edge length, $\lambda$, is small enough. We
perform asymptotic analyses and numerical studies to discover at least $5$
classes of these symmetric critical points - the $WORS$, $Ring^{\pm}$,
$Constant$ and $pWORS$ solutions, of which the $WORS$, $Ring^+$ and $Constant$
solutions can be stable. Furthermore, we demonstrate that the novel $Constant$
solution is energetically preferable for large $\lambda$ and large $L_2$, and
prove associated stability results that corroborate the stabilising effects of
$L_2$ for reduced Landau-de Gennes critical points. We complement our analysis
with numerically computed bifurcation diagrams for different values of $L_2$,
which illustrate the interplay of elastic anisotropy and geometry for nematic
solution landscapes, at low temperatures.",2105.10253v1
2021-05-26,Quarkonium dissociation properties of hot QCD medium at momentum-anisotropy in the N-dimensional space using Quasi-particle Debye mass with finite baryonic chemical potential,"The analytical exact iteration method (AEIM) have been used to calculate the
N-dimensional radial schrodinger equation with the real part of complex-valued
potential and it is generalized to the finite value of anisotropy ({\xi}),
temperature and baryonic chemical potential. In N-dimensional space the energy
eigen values have been calculated for any states (n,l). The present results
have been used to study the properties of quarkonium states (i.e, the binding
energy and mass spectra in the N-dimensional space). The influences of
anisotropy ({\xi}) on the dissociation temperature(TD) has been also calculated
for the ground state of quarkonia at N=0 and \mu = 300MeV . The anisotropy in
oblate case, thus obtained, makes the dissociation temperature(TD) lower as
compared to the isotropic case . We also seen that Leading order Debye mass is
greater than that of Quasi-particle Debye mass after introducing the baryonic
chemical potential.",2105.12346v3
2021-05-28,Anisotropic Magnon Spin Transport in Ultra-thin Spinel Ferrite Thin Films -- Evidence for Anisotropy in Exchange Stiffness,"We report measurements of magnon spin transport in a spinel ferrite,
magnesium aluminum ferrite $\mathrm{MgAl_{0.5}Fe_{1.5}O_4}$ (MAFO), which has a
substantial in-plane four-fold magnetic anisotropy. We observe spin diffusion
lengths $> 0.8$ $\mathrm{\mu m}$ at room temperature in 6 nm films, with spin
diffusion length 30% longer along the easy axes compared to the hard axes. The
sign of this difference is opposite to the effects just of anisotropy in the
magnetic energy for a uniform magnetic state. We suggest instead that
accounting for anisotropy in exchange stiffness is necessary to explain these
results.",2105.13943v1
2021-06-07,Influence of microstructural and crystallographic inhomogeneity on tensile anisotropy in thick-section Al-Li-Cu-Mg plates,"Thick-section plates made from a recently developed Al-Cu-Mg-Li alloy have
been evaluated to understand the influence of microstructure on the anisotropy
of tensile strengths after natural and artificial ageing treatment.
Pancake-shaped grains with a coarse substructure and strong crystallographic
texture with a beta-fibre orientation at the mid-thickness position are
observed. In addition, an inhomogeneous distribution of T1 precipitates through
the plate thickness has been revealed with the volume fraction of intragranular
precipitates ~ 40% higher at the plate centre than the thickness position.
Altogether these microstructural features contribute to the in-plane anisotropy
of tensile strengths that is ~ 5% higher at the mid-thickness position than the
1/4 thickness position. The variation of ageing-induced T1 precipitates through
the plate thickness further contributes to the through-thickness anisotropy
that is ~ 3% higher in T8 temper as compared to T3 temper.",2106.03644v1
2021-07-07,Shape anisotropy enhances the elasticity of colloidal gels through mechanisms that act multiplicatively,"The physical gelation of colloids produces elastic structures that are
commonly used to stabilize complex fluids in multiple industries. However, the
ability to control the level of elastic modulus of these materials is limited
by the universality of the arrested spinodal decomposition mechanism that
governs their formation. We demonstrate that manipulating particle shape can
yield very large shifts in gel elasticity relative to this universal behavior,
and that these changes are generated by a set of independent mechanisms that
act multiplicatively. Modeling demonstrates that this efficient generation of
elasticity is the consequence of the combined effects of shape anisotropy on
the hierarchical fractal microstructure of the gel network, the anisotropy of
the attractive interparticle pair potentials, and the volumetric compactness of
the fractal cluster. The findings show how and why particle anisotropy can be
exploited to generate elasticity at ultra-low colloidal volume fractions in
this important class of soft matter.",2107.03422v1
2021-07-08,Nontrivial temperature dependence of magnetic anisotropy in multiferroics Ba$_2$MnGe$_2$O$_7$,"We measured the temperature dependences of the static magnetization and the
spin excitation in a square-lattice multiferroics Ba$_2$MnGe$_2$O$_7$. An
anisotropy gap of the observed low energy mode is scaled by electric
polarization rather than a power of sublattice moment. Spin nematic interaction
in effective spin Hamiltonian, which is equivalent to interaction of electric
polarization, is responsible for the easy-axis anisotropy. The nontrivial
behavior of the anisotropy gap can be rationalized as change of the hybridized
$d$-$p$ orbital with temperature, leading to the temperature dependence of the
spin nematic interaction.",2107.03928v1
2021-08-20,Probing anisotropy in epitaxial Fe/Pt bilayers by spin-orbit torque ferromagnetic resonance,"We report the generation and detection of spin-orbit torque ferromagnetic
resonance (STFMR) in micropatterned epitaxial Fe/Pt bilayers grown by molecular
beam epitaxy. The magnetic field dependent measurements at an in-plane magnetic
field angle of 45 degrees with respect to the microwave-current direction
reveal the presence of two distinct voltage peaks indicative of a strong
magnetic anisotropy. We show that STFMR can be employed to probe the underlying
magnetic properties including the anisotropies in the Fe layer. We compare our
STFMR results with broadband ferromagnetic resonance spectroscopy of the
unpatterned bilayer thin films. The experimental STFMR measurements are
interpreted using an analytical formalism and further confirmed using
micromagnetic modeling, which shed light on the field-dependent magnetization
alignment in the microstructures responsible for the STFMR rectification. Our
results demonstrate a simple and efficient method for determining magnetic
anisotropies in microstructures by means of rf spectroscopy.",2108.09132v1
2021-08-24,Out-of-plane magnetic anisotropy in bulk ilmenite $\text{CoTiO}_3$,"Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are
analyzed in the framework of density functional theory (DFT), using the
generalized gradient approximation (GGA) and Hubbard-corrected approaches. We
find that the G-type antiferromagnetic (G-AFM) structure, which consists of
antiferromagnetically coupled ferromagnetic $ab$ planes, is the ground-state of
the system, in agreement with experiments. Furthermore, cobalt titanates
present two critical temperatures related to the breaking of the inter- and
intra-layer magnetic ordering. This would result in the individual planes
remaining ferromagnetic even at temperatures above the N\'{e}el temperature.
When spin-orbit coupling is included in our calculations, we find an
out-of-plane magnetic anisotropy, which can be converted to an in-plane
anisotropy with a small doping of electrons corresponding to about 2.5% Ti
substitution for Co, consistent with experimental expectations. We thus present
a disorder-dependent study of the magnetic anisotropy in bulk $\text{CoTiO}_3$,
which will determine its magnon properties, including topological aspects.",2108.10847v2
2021-09-06,On optimal cloaking-by-mapping transformations,"A central ingredient of cloaking-by-mapping is the diffeomorphisn which
transforms an annulus with a small hole into an annulus with a finite size
hole, while being the identity on the outer boundary of the annulus. The
resulting meta-material is anisotropic, which makes it difficult to
manufacture. The problem of minimizing anisotropy among radial transformations
has been studied in [4]. In this work, as in [4], we formulate the problem of
minimizing anisotropy as an energy minimization problem. Our main goal is to
provide strong evidence for the conjecture that for cloaks with circular
boundaries, non-radial transformations do not lead to lower degree of
anisotropy. In the final section, we consider cloaks with non-circular
boundaries and show that in this case, non-radial cloaks may be advantageous,
when it comes to minimizing anisotropy.",2109.02397v1
2021-09-21,Effect of uniaxial single-ion anisotropy on a stability of intermediate magnetization plateaus of a spin-1 Heisenberg diamond cluster,"Ground-state phase diagrams and magnetization curves of a spin-1 Heisenberg
diamond cluster with two different coupling constants and uniaxial single-ion
anisotropy are investigated in a presence of the external magnetic field with
the help of exact diagonalization methods. It is shown that the spin-1
Heisenberg diamond cluster exhibits several remarkable quantum ground states,
which are manifested in zero- and low-temperature magnetization curves as
intermediate plateaus at one-quarter, one-half and three-quarters of the
saturation magnetization. It is found that the width of the fractional
magnetization plateaus depends basically on a relative strength of the coupling
constants as well as uniaxial single-ion anisotropy, which may substantially
shrink or even cause full breakdown of some intermediate magnetization
plateaus. It is evidenced that a relatively weak uniaxial single-ion anisotropy
of the easy-axis type considerably improves a theoretical fit of
low-temperature magnetization curves of the tetranuclear nickel complex
[Ni4(CO3)2(aetpy)8](ClO4)4 in a low-field region without spoiling the previous
fit based on the fully isotropic Heisenberg model in a high-field region.",2109.10030v1
2021-10-25,Emergent anisotropy in the Fulde-Ferrell-Larkin-Ovchinnikov state,"Exotic superconductivity is formed by unconventional electron pairing and
exhibits various unique properties that cannot be explained by the basic
theory. The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state is known as an exotic
superconducting state in that the electron pairs have a finite center-of-mass
momentum leading to a spatially modulated pattern of superconductivity. The
spatial modulation endows the FFLO state with emergent anisotropy. However, the
anisotropy has never been experimentally verified despite numerous efforts over
the years. Here, we report detection of anisotropic acoustic responses
depending on the sound propagation direction appearing above the Pauli limit.
This anisotropy reveals that the two-dimensional FFLO state has a
center-of-mass momentum parallel to the nesting vector on the Fermi surface.
The present findings will facilitate our understanding of not only
superconductivity in solids but also exotic pairings of various particles.",2110.12774v2
2021-10-29,"Stripe order, impurities, and symmetry breaking in a diluted frustrated magnet","We investigate the behavior of the frustrated $J_1$-$J_2$ Ising model on a
square lattice under the influence of random dilution and spatial anisotropies.
Spinless impurities generate a random-field type disorder for the spin-density
wave (stripe) order parameter. These random fields destroy the long-range
stripe order in the case of spatially isotropic interactions. Combining
symmetry arguments, percolation theory and large-scale Monte Carlo simulations,
we demonstrate that arbitrarily weak spatial interaction anisotropies restore
the stripe phase. More specifically, the transition temperature $T_c$ into the
stripe phase depends on the interaction anisotropy $\Delta J$ via $T_c \sim
1/|\ln (\Delta J)|$ for small $\Delta J$. This logarithmic dependence implies
that very weak anisotropies are sufficient to restore the transition
temperature to values comparable to that of the undiluted system. We analyze
the critical behavior of the emerging transition and find it to belong to the
disordered two-dimensional Ising universality class, which features the clean
Ising critical exponents and universal logarithmic corrections. We also discuss
the generality of our results and their consequences for experiments.",2111.00101v2
2021-11-15,On the phase diagram of a three-dimensional dipolar model,"The magnetic phase diagram at zero external field of an ensemble of dipoles
with uniaxial anisotropy on a FCC lattice has been investigated from tempered
Monte Carlo simulations. The uniaxial anisotropy is characterized by a random
distribution of easy axes and its magnitude $\lambda_u$ is the driving force of
disorder and consequently frustration. The phase diagram, separating the
paramagnetic, ferromagnetic and spin-glass regions, was thus considered in the
temperature, $\lambda_u$ plane. Here we interpret this phase diagram in terms
of the more convenient variables namely the bare dipolar interaction and
anisotropy energies $\epsilon_d$ and $\epsilon_u$ on the one hand and the
volume fraction $\Phi$ on the other hand and compare the result with that
corresponding to the random distribution of particles in the absence of
anisotropy. We also display the nature of the ordered phase reached at low
temperature by the ensemble of dipoles on the FCC lattice in terms of both the
dipolar coupling and the texturation of the easy axes distribution when the
latter is no more random. This system is aimed at modeling the magnetic phase
diagram of supracrystals of magnetic nanoparticles.",2111.07709v1
2022-01-03,Susceptibility of Polar Flocks to Spatial Anisotropy,"We consider the effect of spatial anisotropy on polar flocks by investigating
active $q$-state clock models in two dimensions. In contrast to what happens in
equilibrium, we find that, in the large-size limit, any amount of anisotropy
changes drastically the phenomenology of the rotationally-invariant case,
destroying long-range correlations, pinning the direction of global order, and
transforming the traveling bands of the coexistence phase into a single moving
domain. All this happens beyond a lengthscale that diverges in the $q\to\infty$
limit. A phenomenology akin to that of the Vicsek model can thus be observed in
a finite system for large enough values of $q$. We provide a scaling argument
which rationalizes why anisotropy has so different effects in the passive and
active cases.",2201.00704v2
2022-01-11,Non-resonant relaxation of anisotropic globular clusters,"Globular clusters are dense stellar systems whose core slowly contracts under
the effect of self-gravity. The rate of this process was recently found to be
directly linked to the initial amount of velocity anisotropy: tangentially
anisotropic clusters contract faster than radially anisotropic ones.
Furthermore, initially anisotropic clusters are found to generically tend
towards more isotropic distributions during the onset of contraction.
Chandrasekhar's ""non-resonant"" (NR) theory of diffusion describes this
relaxation as being driven by a sequence of local two-body deflections along
each star's orbit. We explicitly tailor this NR prediction to anisotropic
clusters, and compare it with $N$-body realisations of Plummer spheres with
varying degrees of anisotropy. The NR theory is shown to recover remarkably
well the detailed shape of the orbital diffusion and the associated initial
isotropisation, up to a global multiplicative prefactor which increases with
anisotropy. Strikingly, a simple effective isotropic prescription provides
almost as good a fit, as long as the cluster's anisotropy is not too strong.
For these more extreme clusters, accounting for long-range resonant relaxation
may be necessary to capture these clusters' long-term evolution.",2201.03985v1
2022-02-17,A Three-component Model for Cosmic-ray Spectrum and Dipole Anisotropy,"Using a three-component, multi-scale diffusion model, we show that the
cosmic-ray (CR) proton and helium spectra and the dipole anisotropy can be
explained with reasonable parameters. The model includes a nearby source
associated with the supernova remnant (SNR) that gave rise to the Geminga
pulsar, a source at the Galactic center, and a component associated with the
Galactic disk. The CR flux below TeV is dominated by the disk component. The
center source with a continuous injection of CRs starting about 18 Myr ago is
needed to explain the anisotropy above 100 TeV. With the assumption of
universal CR spectra injected by all SNRs, the nearby source can produce a TeV
spectral bump observed at Earth via slow diffusion across the interstellar
magnetic field, which needs to have an angle $ \theta \approx 5^{\circ} $
between the field line and the line of sight toward the source, and have weak
magnetic turbulence with the Alfv\'{e}n Mach number $ M_{\text{A}}\approx 0.1
$. Considering the modulation of the Galactic-scale anisotropy by this magnetic
field, in a quasi-local approach the field may be directed at a right ascension
about $ -90^{\circ} $ and a declination about $ -7.4^{\circ} $ in the
equatorial coordinate system.",2202.08491v1
2022-04-15,Dipole Anisotropy in Gravitational Wave Source Distribution,"Our local motion with respect to the cosmic frame of rest is believed to be
dominantly responsible for the observed dipole anisotropy in the Cosmic
Microwave Background Radiation (CMBR). We study the effect of this motion on
the sky distribution of gravitational wave (GW) sources. We determine the
resulting dipole anisotropy in GW source number counts, mass weighted number
counts, which we refer to as mass intensity, and mean mass per source. The mass
M dependence of the number density n(M) distribution of BBH is taken directly
from the data. We also test the anisotropy in the observable mean mass per
source along the direction of the CMB dipole. The current data sample is
relatively small and consistent with isotropy. The number of sources required
for this test is likely to become available in the near future.",2204.07472v3
2022-04-16,On the anisotropy theorem of Papadakis and Petrotou,"We study the anisotropy theorem for Stanley-Reisner rings of simplicial
homology spheres in characteristic 2 by Papadakis and Petrotou. This theorem
implies the Hard Lefschetz theorem as well as McMullen's g-conjecture for such
spheres. Our first result is an explicit description of the quadratic form. We
use this description to prove a conjecture stated by Papadakis and Petrotou.
All anisotropy theorems for homology spheres and pseudo-manifolds in
characteristic 2 follow from this conjecture. Using a specialization argument,
we prove anisotropy for certain homology spheres over the field $\mathbb{Q}$.
These results provide another self-contained proof of the g-conjecture for
homology spheres in characteristic 2.",2204.07758v3
2022-05-11,Enhancing gravitational wave anisotropies with peaked scalar sources,"Gravitational wave (GW) backgrounds of cosmological origin are expected to be
nearly isotropic, with small anisotropies resembling those of the cosmic
microwave background. We analyse the case of a scalar-induced GW background and
clarify in the process the relation between two different approaches to
calculating GW anisotropies. We focus on GW scenarios sourced by a
significantly peaked scalar spectrum, which are frequently considered in the
context of primordial black holes production. We show that the resulting GW
anisotropies are characterised by a distinct frequency dependence. We explore
the observational consequences concentrating on a GW background enhanced in the
frequency band of space-based GW detectors. We study the detectability of the
signal through both cross-correlations among different space-based GW
detectors, and among GW and CMB experiments.",2205.05644v2
2022-05-22,Rashba spin-orbit interaction induced modulation of magnetic anisotropy,"In past few decades, Rashba spin-orbit coupling (SOC) has been successfully
employed for the emergence of exotic phenomena at the quantum oxide interfaces.
In these systems, the combined effect of charge transfer, broken symmetries and
SOC yields intriguing interfacial magnetism and transport properties. Here, we
provide an insight to control and tune interfacial phenomena in CaMnO3/CaIrO3
based 3d-5d oxide heterostructures by the charge transfer driven Rashba SOC.
Anomalous Hall effect in these canted antiferromagnetic heterostructures
originates from the intrinsic contribution associated with the topology of the
electronic band structure and it is mostly confined to the interface. Rashba
SOC reconstructs the Berry curvature and enhances the anomalous Hall
conductivity by two orders of magnitude. From the anisotropy magnetoresistance
measurements we demonstrate that Rashba SOC is instrumental in tailoring
magnetic anisotropy where magnetization easy-axis rotates from the out-of-plane
direction to the in-plane direction. The ability to tune Rashba SOC and
resulting competing magnetic anisotropy provides a route to manipulate
electronic band structure for the origin of non-trivial spin texture useful for
spin-orbitronics applications.",2205.10859v1
2022-06-01,Spectral Recognition of Magnetic Nanoparticles with Artificial Neural Networks,"Ferromagnetic resonance (FMR) spectroscopy is a powerful method for
quantifying internal magnetic anisotropy fields in nanoparticles, which is
important in a wide range of biomedical and storage applications. The
interpretation of FMR spectra, however, can only be achieved with the use of an
appropriate model, and no inverse methods are available to extract internal
fields from FMR spectra. Here, we present the use of artificial neural networks
for spectral recognition, i.e., to identify the internal magnetic anisotropy
field from the FMR spectrum. We trained two different types of networks, a
convolutional neural network and a multi-layer perceptron, by feeding the
networks pre-computed FMR spectra labeled with the corresponding anisotropy
fields. Testing of the trained networks with unseen spectra showed that they
successfully predict the correct anisotropy fields and, surprisingly, the
networks performed well for data that was beyond their training range. These
results show the promise of using artificial neural networks for accelerated
high-throughput analysis of magnetic materials and nanostructures; for example
they could serve in automatizing and optimizing exploration missions where
nanomagnetic signals are often used as proxies.",2206.00166v1
2022-06-05,Evidence of Magnon-Mediated Orbital Magnetism in a Quasi-2D Topological Magnon Insulator,"We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon
insulator. The results show that the thermal evolution of Land\'e $g$-factor
($g$) is anisotropic: $g_\textrm{in-plane}$ reduces while
$g_\textrm{out-plane}$ increases with increasing temperature $T$. Moreover, the
anisotropy of the $g$-factor ($\Delta g$) and the anisotropy of saturation
magnetization ($\Delta M_\textrm{s}$) are correlated below 4 K, but they
diverge above 4 K. We show that the electronic orbital moment contributes to
the $g$ anisotropy at lower $T$, while the topological orbital moment induced
by thermally excited spin chirality dictates the $g$ anisotropy at higher $T$.
Our work suggests an interplay among topology, spin chirality, and orbital
magnetism in Cu(1,3-bdc).",2206.02191v1
2022-06-30,Ce and Dy substitutions in Nd$_{2}$Fe$_{14}$B: site-specific magnetic anisotropy from first-principles,"A first-principles approach combining density functional and dynamical
mean-field theories in conjunction with a quasi-atomic approximation for the
strongly localized 4$f$ shell is applied to Nd$_{2}$Fe$_{14}$B-based hard
magnets in order to evaluate crystal-field and exchange-field parameters at
rare-earth sites and their corresponding single-ion contribution to the
magnetic anisotropy. In pure Nd$_2$Fe$_{14}$B, our calculations reproduce the
easy-cone to easy axis transition; theoretical magnetization curves agree
quantitatively with experiment. Our study reveals that the rare-earth
single-ion anisotropy in the ""2-14-1"" structure is strongly site-dependent,
with the $g$ rare-earth site exhibiting a larger value. In particular, we
predict that increased $f$ and $g$-site occupancy of $R=$ Ce and Dy,
respectively, leads to an increase of the magnetic anisotropy of the
corresponding (Nd,$R$)$_{2}$Fe$_{14}$B substituted compounds.",2206.15093v1
2022-08-02,Novel setup for detecting short-range anisotropic corrections to gravity,"In this paper we argue that, even though there are strong theoretical and
empirical reasons to expect a violation of spatial isotropy at short distances,
contemporary setups for probing gravitational interactions at short distances
have not been configured to measure such spatial anisotropies. We propose a
simple modification to the state-of-the-art torsion pendulum design and
numerically demonstrate that it suppresses signals due to the large
spatially-isotropic component of the gravitational force while maintaining a
high sensitivity to short-range spatial anisotropies. We incorporate anisotropy
using both Yukawa-type and power-law-type short-distance corrections to
gravity. The proposed differential torsion pendulum is shown to be capable of
making sensitive measurements of small gravitational anisotropies and the
resulting anisotropic torques are largely independent of the details of the
underlying short-distance modification to gravity. Thus, if there is an
anisotropic modification to gravity, from any theory, in any form of the
modified potential, the proposed setup provides a practical means of detecting
it.",2208.01645v3
2022-08-11,Nearby active galactic nuclei and starburst galaxies as sources of the measured UHECRs anisotropy signal,"The Pierre Auger and the Telescope Array observatories have measured
independent and statistical significant anisotropy in the arrival direction of
ultra-high-energy cosmic rays (UHECR). Three hotspot regions with relative
excess of events and a dipole signal have been identified in different regions
of the sky and energy ranges. In this paper, we investigate the conditions
under which these anisotropy signal could be generated by nearby (<23 Mpc)
active galactic nuclei (AGN) and/or starburst galaxies (SBG). We studied a wide
range of possibilities including injected nuclei (p, He, N, Si, and Fe), three
UHECR luminosity proxies and three extragalactic magnetic field models. The
results shows that both local AGN and SBG are needed to describe all the
anisotropy signal. The contribution of AGN to hotspots and to the generation of
the dipole is dominant in most cases. SBG is required only to explain the
hotspot measured by the Telescope Array Observatory.",2208.05849v2
2022-08-16,Anisotropy of the Optical Properties of Pentacene:Black Phosphorus Interfaces,"Black phosphorus (BP) is a layered material with anisotropic properties. We
study interfaces formed by a pentacene monolayer adsorbed on monolayer BP, a
prototypical system for BP surface passivation. We place the pentacene
monolayer along the zigzag and armchair directions of the BP substrate,
respectively, to examine the anisotropy of the heterogeneous interfaces. We
perform first-principles $GW$ plus Bethe-Salpeter equation ($GW$-BSE)
calculations to determine the quasiparticle and optical properties. To
quantitatively analyze the anisotropy of the optical properties, we develop a
general computational scheme to decompose the interface excitons into different
contributions. We find a distinct charge-transfer exciton formed when the
monolayer pentacene is placed along the armchair direction, and discuss how the
anisotropy of each component is modulated by the interface. Our results shine a
light on the understanding of the BP surface passivation via molecular
adsorption and provide a benchmark for future experimental and computational
studies.",2208.07780v1
2022-08-31,Bose-Einstein condensation in honeycomb dimer magnets and $\rm Yb_2 \rm Si_2 \rm O_7$,"An asymmetric Bose-Einstein condensation (BEC) dome was observed in a recent
experiment on the quantum dimer magnet $\rm Yb_2Si_2O_7$, which is modeled by a
""breathing"" honeycomb lattice Heisenberg model with possible anisotropies. We
report a remarkable agreement between key experimental features and predictions
from numerical simulations of the magnetic model. Both critical fields, as well
as critical temperatures of the BEC dome, can be accurately captured, as well
as the occurrence of two regimes inside the BEC phase. Furthermore, we
investigate the role of anisotropies in the exchange coupling and the
$g$-tensor. While we confirm a previous proposal that anisotropy can induce a
zero temperature phase transition at magnetic fields smaller than the fully
polarizing field strength, we find that this effect becomes negligible at
temperatures above the anisotropy scale. Instead, the two regimes inside the
BEC dome are found to be due to a non-linear magnetization behavior of the
isotropic breathing honeycomb Heisenberg antiferromagnet. Our analysis is
performed by combining the density matrix renormalization group (DMRG) method
with the finite-temperature techniques of minimally entangled typical thermal
states (METTS) and quantum Monte Carlo (QMC).",2209.00032v1
2022-09-13,On the response of the Einstein Telescope to Doppler anisotropies,"We study the response function of the Einstein Telescope to kinematic Doppler
anisotropies, which represent one of the guaranteed properties of the
stochastic gravitational wave background. If the frequency dependence of the
stochastic background changes slope within the detector frequency band, the
Doppler anisotropic contribution to the signal can not be factorized in a part
depending on frequency, and a part depending on direction. For the first time,
we study the detector response function to Doppler anisotropies without making
any factorizable Ansatz. Moreover, we do not assume that kinematic effects are
small, and we derive general formulas valid for any relative velocity among
frames. We apply our findings to three well-motivated examples of background
profiles: power-law, broken power-law, and models with a resonance motivated by
primordial black hole scenarios. We derive the signal-to-noise ratio associated
with an optimal estimator for the detection of non-factorizable kinematic
anisotropies, and we study it for representative examples.",2209.05770v2
2022-09-29,Effect of temperature anisotropy on the dynamics of geodesic acoustic modes,"In this work, we revisit the linear gyro-kinetic theory of geodesic acoustic
modes (GAMs) and derive a general dispersion relation for an arbitrary
equilibrium distribution function of ions. A bi-Maxwellian distribution of ions
is then used to study the effects of ion temperature anisotropy on GAM
frequency and growth rate. We find that ion temperature anisotropy yields
sensible modifications to both the GAM frequency and growth rate as both tend
to increase with anisotropy and these results are strongly affected by the
electron to ion temperature ratio.",2209.14874v2
2022-10-11,Disorder effects on the metastability of classical Heisenberg ferromagnets,"In the present work, we investigate the effects of disorder on the reversal
time ($\tau$) of classical anisotropic Heisenberg ferromagnets in three
dimensions by means of Monte Carlo simulations. Starting from the pure system,
our analysis suggests that $\tau$ increases with increasing anisotropy
strength. On the other hand, for the case of randomly distributed anisotropy,
generated from various statistical distributions, a set of results is obtained:
(i) For both bimodal and uniform distributions the variation of $\tau$ with the
strength of anisotropy strongly depends on temperature. (ii) At lower
temperatures, the decrement in $\tau$ with increasing width of the distribution
is more prominent. (iii) For the case of normally distributed anisotropy, the
variation of $\tau$ with the width of the distribution is non-monotonic,
featuring a minimum value that decays exponentially with the temperature.
Finally, we elaborate on the joint effect of longitudinal ($h_z$) and
transverse ($h_x$) fields on $\tau$, which appear to obey a scaling behavior of
the form $\tau h_z^{n} \sim f(h_x)$.",2210.05510v2
2022-10-14,Higher-order magnetic anisotropy in soft-hard magnetic materials,"We have computationally studied the properties of higher-order magnetic
anisotropy constants in an L10/A1-FePt coreshell system which is characterized
by a strong second-order 2-ion Fe-Pt anisotropy component. We show that the
coreshell structure induces an unexpected fourth-order anisotropy constant K2
the magnitude of which varies non-monotonically with the core-size ratio R
reaching a peak at R = 0.50. Furthermore, we find that K2 scales with the
normalized magnetization by (M/Ms)^2.2 at temperatures below the Curie
temperature - a remarkable deviation from the established Callen-Callen theory
which instead predicts a scaling exponent of 10. We construct an analytic model
which demonstrates K2 arises from the canting of the core and shell
magnetization, and successfully reproduces and justifies the scaling exponent
obtained from numerical simulation.",2210.07875v1
2022-10-25,How can we explain last UHERC anisotropies?,"We consider the recent results on UHECR (Ultra High Energy Cosmic Ray),
clustering, composition, distribution in the sky, from the energy of several
EeV with the dipole anisotropy up to the highest ones. We have suggested since
2008 and we reconfirm here that UHECR at 40 up to 70 EeV are mostly made by
light and lightest nuclei. The remarkable Virgo absence and the few localized
nearby extragalactic sources as CenA, NG 253, M82 may be well understood by the
lightest nuclei fragility and opacity within Mpc distances. We comment also on
the role of a few galactic UHECR sources at ten EeV that may be partially
feeding the Auger dipole UHECR anisotropy. The recent anisotropy in the UHECR
spectral composition of lightest and heavy nuclei, outside and along the
galactic plane, could also be a first confirmation of our previous claims
(2012). The interplay of the heavier and most energetic UHECR galactic nuclei
with the mainly local (Mpcs) extragalactic signals ruled by lightest nuclei,
seems to fit the main pieces of UHECR puzzle.",2210.14365v1
2022-10-27,Spectro-spatial evolution of the CMB II: generalised Boltzmann hierarchy,"In this paper, we formulate a generalised photon Boltzmann hierarchy that
allows us to model the evolution and creation of spectral distortion
anisotropies in the early Universe. We directly build on our first paper in
this series, extending the thermalisation Green's function treatment to the
anisotropic case. We show that the problem can be described with the common
Boltzmann hierarchy for the photon field extended by new spectral parameters --
a step that reduces the complexity of the calculation by at least two orders of
magnitude. Our formalism describes the effects of i) Doppler and potential
driving, ii) spectral evolution by Compton scattering, iii) perturbed
thermalisation and iv) anisotropic heating on the distortion anisotropies. We
highlight some of the main physical properties of the equations and also
outline the steps for computing CMB power spectra including distortion
anisotropies. Limitations and extensions of the formulation are also briefly
discussed. The novel Boltzmann hierarchy given here is the basis for a series
of companion papers studying how distortion anisotropies evolve in the
perturbed Universe and which physical processes could be constrained using
future CMB imaging techniques.",2210.15308v1
2022-11-07,Simulation of the Einstein-de Haas effect combining molecular and spin dynamics,"The spin and lattice dynamics of a ferromagnetic nanoparticle are studied via
molecular dynamics and with semi-classical spin dynamics simulations where spin
and lattice degrees of freedom are coupled via a dynamic uniaxial anisotropy
term. We show that this model conserves total angular momentum, whereas spin
and lattice angular momentum are not conserved. We carry out simulations of the
the Einstein-de Haas effect for a Fe nanocluster with more than 500 atoms that
is free to rotate, using a modified version of the open-source spinlattice
dynamics code (SPILADY). We show that the rate of angular momentum transfer
between spin and lattice is proportional to the strength of the magnetic
anisotropy interaction. The addition of the anisotropy allows full spin-lattice
relaxation to be achieved on previously reported timescales of \sim 100 ps and
for tight-binding magnetic anisotropy energies comparable to those of small Fe
nanoclusters.",2211.03706v1
2022-11-09,Anomalous anisotropy of spin current in a cubic spin source with noncollinear antiferromagnetism,"Cubic materials host high crystal symmetry and hence are not expected to
support anisotropy in transport phenomena. In contrast to this common
expectation, here we report an anomalous anisotropy of spin current can emerge
in the (001) film of Mn${_3}$Pt, a noncollinear antiferromagnetic spin source
with face-centered cubic structure. Such spin current anisotropy originates
from the intertwined time reversal-odd ($T$-odd) and time reversal-even
($T$-even) spin Hall effects. Based on symmetry analyses and experimental
characterizations of the current-induced spin torques in Mn${_3}$Pt-based
heterostructures, we find that the spin current generated by Mn${_3}$Pt (001)
exhibits exotic dependences on the current direction for all the spin
components, deviating from that in conventional cubic systems. We also
demonstrate that such an anisotropic spin current can be used to realize
low-power spintronic applications such as the efficient field-free switching of
the perpendicular magnetizations.",2211.04970v1
2023-01-07,Crucial role of Fe in determining the hard magnetic properties of Nd$_2$Fe$_{14}$B,"Nd$_2$Fe$_{14}$B's unsurpassed, hard magnetic properties for a wide range of
temperatures result from a combination of a large volume magnetization from Fe
and a strong single-ion anisotropy from Nd. Here, using finite temperature
first-principles calculations, we focus on the other crucial roles played by
the Fe atoms in maintaining the magnetic order on the Nd sublattices, and hence
the large magnetic anisotropy, and directly generating significant uniaxial
anisotropy at high temperatures. We identify effective spins for atomistic
modelling from the material's interacting electrons and {quantify pairwise and
higher order, non-pairwise magnetic interactions among them. We find the Nd
spins couple most strongly to spins on sites belonging to two specific Fe
sublattices, 8$j_1$, 8$j_2$. Moreover the Fe 8$j_1$ sublattice also provides
the electronic origin of the unusual, nonmonotonic temperature dependence of
the anisotropy of Y$_2$Fe$_{14}$B.} Our work provides atomic-level resolution
of the properties of this fascinating magnetic material.",2301.02868v1
2023-01-08,Diffusive Pseudo-Conformal Mapping: Anisotropy-Free Transformation Thermal Media with Perfect Interface Matching,"Transformation media provide a fundamental paradigm for field regulation, but
their tricky anisotropy challenges fabrication. Though optical conformal
mapping has been utilized to eliminate anisotropy, two key factors still hinder
its development in thermotics, i.e., the distinct diffusion nature and
inevitable interface mismatching. Here, we put forth the concept of diffusive
pseudo-conformal mapping, overcoming the inherent difference between diffusion
and waves and achieving perfect interface matching. The proposed mapping
directly leads to heat guiding and expanding functions with anisotropy-free
transformation thermal media, whose feasibility is confirmed by experiments or
simulations. Besides diverse applications, we provide a unified perspective for
two distinct types of prevailing bilayer cloaks by uncovering their profound
ties with pseudo-conformal mapping. These results greatly simplify the
preparation of transformation thermotics and have implications for regulating
other diffusion and wave phenomena.",2301.02963v1
2023-01-16,Possible realization of hyperbolic plasmons in a few-layered rhenium disulfide,"The in-plane structural anisotropy in low-symmetric layered compound rhenium
disulfide ($\text{ReS}_2$) makes it a candidate to host and tune
electromagnetic phenomena specific for anisotropic media. In particular,
optical anisotropy may lead to the appearance of hyperbolic plasmons, a highly
desired property in optoelectronics. The necessary condition is a strong
anisotropy of the principal components of the dielectric function, such that at
some frequency range, one component is negative and the other is positive,
i.e., one component is metallic, and the other one is dielectric. Here, we
study the effect of anisotropy in $\text{ReS}_2$ and show that it can be a
natural material to host hyperbolic plasmons in the ultraviolet frequency
range. The operating frequency range of the hyperbolic plasmons can be tuned
with the number of $\text{ReS}_2$ layers.",2301.06521v1
2023-01-19,Intrinsic limits on the detection of the anisotropies of the Stochastic Gravitational Wave Background,"For any given network of detectors, and for any given integration time, even
in the idealized limit of negligible instrumental noise, the intrinsic time
variation of the isotropic component of the Stochastic Gravitational Wave
Background (SGWB) induces a limit on how accurately the anisotropies in the
SGWB can be measured. We show here how this sample limit can be calculated and
apply this to three separate configurations of ground-based detectors placed at
existing and planned sites. Our results show that in the idealized, best-case
scenario individual multipoles of the anisotropies at $\ell \leq 8$ can only be
measured to $\sim 10^{-5} - 10^{-4}$ level over 5 years of observation as a
fraction of the isotropic component. As the sensitivity improves as the square
root of the observation time, this poses a very serious challenge for the
measurement of the anisotropies of SGWB of cosmological origin, even in the
case of idealised detectors with arbitrarily low instrumental noise.",2301.08074v1
2023-02-11,Spatial magnetization profile in spherical nanomagnets with surface anisotropy: Green's function approach,"We consider a single spherical nanomagnet and investigate the spatial
magnetization profile $\mathbf{m}\left(\mathbf{r}\right)$ in the continuum
approach, using the Green's function formalism. The energy of the (many-spin)
nanomagnet comprises an isotropic exchange interaction, a uniaxial anisotropy
in the core and N\'eel's surface anisotropy, and an external magnetic field. We
derive a semi-analytical expression for the magnetization vector field
$\mathbf{m}\left(\mathbf{r}\right)$ for an arbitrary position $\mathbf{r}$
within and on the boundary of the nanomagnet, as a solution of a homogeneous
Helmholtz equation with inhomogeneous Neumann boundary conditions.
  ...
  For a more plausible comparison with experiments, e.g. using the technique of
small-angle magnetic neutron scattering, we have averaged over the direction
solid angle and derived the spatial profile in terms of the distance $r$. We
believe that the predictions of the present study could help to characterize
and understand the effects of size and surface anisotropy on the magnetization
configurations in nanomagnet assemblies such as arrays of well-spaced
platelets.",2302.05773v3
2023-02-13,Density jump as a function of magnetic field strength for parallel collisionless shocks with anisotropic upstream pressure,"The properties of collisionless shocks are frequently assessed in the
magnetohydrodynamics (MHD) model. Yet, in a collisionless plasma, an ambient
magnetic field can sustain a stable anisotropy in the upstream or the
downstream, resulting in a departure from the MHD predicted behavior. We
present a model allowing to derive the downstream anisotropy, hence the shock
density jump, in terms of the upstream quantities. For simplicity, the case of
a parallel shock in pair plasma is considered. Contrary to previous works where
the upstream was assumed isotropic, here the upstream anisotropy
$A=T_\perp/T_\parallel$ is a free parameter. The strong sonic shock regime is
formally identical to the isotropic upstream case. Yet, for intermediate sonic
Mach numbers, a variety of behaviors appear as a result of the anisotropy of
the upstream.",2302.06521v1
2023-02-23,In-situ Growth of Ultrathin Magnetic Films and Tuning the Magnetic Properties by Ion-sculpting,"Magnetic anisotropy is a key parameter of magnetic materials as it decides
the response in the presence of an external magnetic field. The artificial
tailoring of magnetic anisotropy by manipulating surface and interface
morphology is attracting widespread interest for its application in spintronic
and magnetic memory devices. In this perspective, the primary focus of this
thesis has been inducing and tailoring magnetic anisotropy in thin film-based
systems via the engineering of structure and surface/interfacial morphology.
For this purpose, instead of multistep, expensive lithographic techniques, we
have utilized low-energy IBE as a handy, cost-effective, and useful tool for
producing magnetic nanostructures and tailoring its surface structure,
morphology and magnetic anisotropy. Furthermore, we have also proposed various
new and unconventional methods (oblique angle deposition on the rippled
substrate, sequential deposition-erosion) for enhancement of UMA and proved its
effectiveness via experiments. We have performed most of the present thesis
work in-situ utilizing a UHV chamber to get genuine characteristics and
understand their interdependencies. However, advanced synchrotron-based
techniques such as GISAXS and NFS were also utilized to complement the in-situ
observations.",2302.11941v1
2023-05-02,GW_CLASS: Cosmological Gravitational Wave Background in the Cosmic Linear Anisotropy Solving System,"The anisotropies of the Cosmological Gravitational Wave Background (CGWB)
retain information about the primordial mechanisms that source the
gravitational waves and about the geometry and the particle content of the
universe at early times. In this work, we discuss in detail the computation of
the angular power spectra of CGWB anisotropies and of their cross correlation
with Cosmic Microwave Background (CMB) anisotropies, assuming different
processes for the generation of these primordial signals. We present an
efficient implementation of our results in a modified version of CLASS which
will be publicly available. By combining our new code GW_CLASS with
MontePython, we forecast the combined sensitivity of future gravitational wave
interferometers and CMB experiments to the cosmological parameters that
characterize the cosmological gravitational wave background.",2305.01602v2
2023-05-02,Probing the global 21-cm background by velocity-induced dipole and quadrupole anisotropies,"The motion of an observer in the rest frame of the cosmic 21-cm background
induces an anisotropy in the observed background, even when the background is
isotropic. The induced anisotropy includes a dipole and a quadrupole, in the
order decreasing in amplitude. If observed, these multipole anisotropies can be
used as additional probes of the spectral shape of the global 21-cm background
for mitigating the ambiguity in the monopole spectrum probed by single-element
radio telescopes such as EDGES and SARAS. This could also help with
understanding the astrophysical and cosmological processes that occurred during
the cosmic dawn and the epoch of reionization, and even improving on the
estimation of the solar velocity and the foreground spectra. Here, we study the
feasibility of such observations and present science drivers for the
measurement of the 21-cm dipole and quadrupole.",2305.01672v2
2023-05-15,Post-growth shaping and transport anisotropy in 2D InAs nanofins,"We report on the post-growth shaping of free-standing 2D InAs nanofins that
are grown by selective-area epitaxy and mechanically transferred to a separate
substrate for device fabrication. We use a citric acid based wet etch that
enables complex shapes, e.g., van der Pauw cloverleaf structures, with
patterning resolution down to 150 nm as well as partial thinning of the nanofin
to improve the gate response. We exploit the high sensitivity of the cloverleaf
structures to transport anisotropy to address the fundamental question of
whether there is a measurable transport anisotropy arising from
wurtzite/zincblende polytypism in 2D InAs nanostructures. We demonstrate a
mobility anisotropy of order 2-4 at room temperature arising from polytypic
stacking faults in our nanofins. Our work highlights a key materials
consideration for devices featuring self-assembled 2D III-V nanostructures
using advanced epitaxy methods.",2305.08309v1
2023-05-25,The Impact of Anisotropy on Neutron Star Properties: Insights from I-f-C Universal Relations,"This study presents a universal relation for anisotropic neutron stars,
called the $I-f-C$ relation, which accounts for the local anisotropic pressure
using the Quasi-Local (QL) Model proposed by Horvat et al. \cite{QL_Model} to
describe the anisotropy inside the neutron star. This study analyzes
approximately 60 unified tabulated EoS-ensembles, spanning from relativistic to
non-relativistic mean-field models, that comply with multimessenger constraints
and cover a broad range of stiffness. The results indicate that the
relationship between the parameters becomes more robust with positive
anisotropy, while it weakens with negative anisotropy. With the help of the
GW170817 \& GW190814 tidal deformability limit, a theoretical limit for the
canonical $f$-mode frequency for both isotropic and anisotropic stars is
established. For isotropic case the canonical $f$-mode frequency for event
GW170817 \& GW190814 is $f_{1.4} = 2.605^{+0.487} _ {-0.459}\ \mathrm{kHz}$ and
$ f_{1.4} = 2.093^{+0.150} _ {-0.125} \ \mathrm{kHz}$ respectively. These
established relationships have the potential to serve as a reliable tool to
limit the equation of state of nuclear matter when measurements of relevant
observables are obtained.",2305.15724v2
2023-06-01,Anisotropic behavior of S-wave and P-wave states of heavy quarkonia at finite magnetic field,"We studied the effect of momentum space anisotropy on heavy quarkonium states
using an extended magnetized effective fugacity quasiparticle model (EQPM).
Both the real and imaginary part of the potential has been modified through the
dielectric function by including the anisotropic parameter $\xi$. The real part
of the medium modified potential becomes more attractive in the presence of the
anisotropy and constant magnetic field. The binding energy of the 1S, 2S, and
1P quarkonium states including anisotropy effects for both the oblate and the
isotropic case were studied. We find that the binding energy of quarkonium
states becomes stronger in the presence of anisotropy. However, the magnetic
field is found to reduce the binding energy. The thermal width of the
charmonium and bottomonium 1S states have been studied at constant magnetic
field eB = 0.3 GeV2 for isotropic and prolate cases. The effect of magnetic
field on the mass spectra of the 1P state for the oblate case was also
examined. The dissociation temperature for the 1S, 2S, and 1P charmonium and
bottomonium have been determined to be higher for the oblate case with respect
to the isotropic case",2306.00908v1
2023-06-13,Heavy quark radiation in an anisotropic hot QCD medium,"The impact of momentum anisotropy on the heavy quarks (HQs) dynamics has been
investigated in a hot QCD medium while considering both collisional and
radiative processes within the ambit of the Fokker-Planck approach. The
relative orientation of the HQs motion (momentum vector) with respect to the
direction of anisotropy is responsible for the character of transport
coefficients. Therefore, the drag and diffusion coefficients of the HQs are
decomposed, respectively, into two and four components by considering a general
tensor basis. Each component of the drag and diffusion coefficient of the HQs
has been analyzed in detail. It is observed that the anisotropy has a
significant impact on the transport coefficients of the HQ for both the
collisional and the radiational processes. The nuclear suppression factor,
$R_{AA}$, has been computed considering the anisotropic medium. It is observed
that the momentum anisotropy affects the $R_{AA}$ of the HQs significantly in
both elastic and inelastic cases.",2306.07966v2
2023-06-20,Engineering magnetic anisotropy and the surface of epitaxial Fe films using ion beam erosion; unveiling self-assembly and tunability,"The engineering of surface morphology and structure of the thin film is one
of the essential technological assets for regulating the physical properties
and functionalities of thin film-based devices. This study investigates the
evolution of surface structure and magnetic anisotropy in epitaxially grown
ultrathin Fe films on MgO (001) substrates subjected to multiple cycles of ion
beam erosion (IBE) after growth. Ultrathin Fe film grows in 3D island mode and
exhibits intrinsic fourfold magnetic anisotropy. After a few cycles of IBE, the
film displays an induced uniaxial magnetic anisotropy that leads to a split in
the hysteresis loop. In addition, clear and conclusive evidence of IBE mediated
(2x2) reconstruction of the Fe surface has been observed. We also demonstrate
that thermal annealing can reversibly tune the induced UMA and surface
reconstruction. The feasibility of the IBE technique by properly selecting ion
beam parameters for modification of surface structure has been highlighted
apart from conventional methods of tailoring the morphology for tuning of UMA.
Thus, the present work paves a way to explore the IBE-induced self-assembling
phenomena further.",2306.11516v1
2023-07-14,Photon and dilepton emission anisotropy for magnetized quark-gluon plasma,"We study the higher-order anisotropy coefficients $v_4$ and $v_6$ in the
photon and dilepton emission from a hot magnetized quark-gluon plasma. Together
with the earlier predictions for $v_2$, these results show a distinctive
pattern of the anisotropy coefficients in several kinematic regimes. In the
case of photon emission, nonzero coefficients $v_n$ (with even $n$) have
opposite signs at small and large values of the transverse momentum (i.e.,
$k_T\lesssim \sqrt{|eB|}$ and $k_T\gtrsim \sqrt{|eB|}$, respectively).
Additionally, the $v_n$ signs alternate with increasing $n$, and their
approximate values decrease as $1/n^2$ in magnitude. The anisotropy of dilepton
emission is well-pronounced only at large transverse momenta and small
invariant masses (i.e., when $k_T\gtrsim \sqrt{|eB|}$ and $M\lesssim
\sqrt{|eB|}$). The corresponding $v_4$ and $v_6$ coefficients are of the same
magnitude and show a similar sign-alternative pattern with increasing $n$ as in
the photon emission.",2307.07557v1
2023-07-21,Tailoring giant quantum transport anisotropy in disordered nanoporous graphenes,"During the last 15 years bottom-up on-surface synthesis has been demonstrated
as an efficient way to synthesize carbon nanostructures with atomic precision,
opening the door to unprecedented electronic control at the nanoscale.
Nanoporous graphenes (NPGs) fabricated as two-dimensional arrays of graphene
nanoribbons (GNRs) represent one of the key recent breakthroughs in the field.
NPGs interestingly display in-plane transport anisotropy of charge carriers,
and such anisotropy was shown to be tunable by modulating quantum interference.
Herein, using large-scale quantum transport simulations, we show that
electrical anisotropy in NPGs is not only resilient to disorder but can further
be massively enhanced by its presence. This outcome paves the way to systematic
engineering of quantum transport in NPGs as a novel concept for efficient
quantum devices and architectures.",2307.11480v1
2023-07-31,"Multi-particle correlations, cumulants, and moments sensitive to fluctuations in rare-probe azimuthal anisotropy in heavy ion collisions","Correlations of two or more particles have been an essential tool for
understanding the hydrodynamic behavior of the quark-gluon plasma created in
ultra-relativistic nuclear collisions. In this paper, we extend that framework
to introduce a mathematical construction of multi-particle correlators that
utilize correlations between arbitrary numbers of particles of interest (e.g.
particles selected for their strangeness, heavy flavor, and conserved charges)
and inclusive reference particles to estimate the azimuthal anisotropies of
rare probes. To estimate the fluctuations and correlations in the azimuthal
anisotropies of these particle of interest, we use these correlators in a
system of cumulants, raw moments, and central moments. We finally introduce two
classes of observables that can compare the fluctuations in the azimuthal
anisotropies of particles of interest with reference particles at each order.",2307.16796v2
2023-08-07,Frustration relief and reorientation transition in the kagome-like dolerophanite Cu$_2$OSO$_4$,"We present a theoretical study of dolerophanite Cu$_2$OSO$_4$, a layered
kagome-like spin-$\frac{1}{2}$ magnetic insulator that can be described either
as a system of chains coupled through dimers or as a kagome lattice where every
third spin is replaced by a ferromagnetic spin dimer. Building on insights from
ab initio calculations, classical numerical minimizations, and semiclassical
expansions, we arrive at a minimal microscopic description that accounts for
the experimental data reported so far, including the nature of the magnetic
order, the reported spin length, and the observed anisotropy. The latter arises
by a peculiar competition between the antisymmetric (Dzyaloshinskii-Moriya) and
the symmetric part of the exchange anisotropy, which gives rise to a two-step
re-orientation process involving two successive continuous phase transitions.
Our work uncovers mechanisms stabilizing canted ferrimagnetic order in kagome
systems, and highlights strong magnetic anisotropy in the presence if
dissimilar magnetic orbitals on crystallographically nonequivalent Cu sites. We
also show how these anisotropy terms affect the spin-wave spectrum and how they
can be tracked experimentally.",2308.03599v2
2023-08-21,"Anisotropies, large and small","We report on several new results using anisotropies of UHECRs. We improve and
extend the work of Ding, Globus and Farrar, who modeled the UHECR dipole
assuming sources follow the dark matter distribution, accounting for
deflections in the Galactic and extragalactic magnetic fields but using a
simplified treatment of interactions during propagation. The work presented
here employs an accurate and self-consistent treatment of the evolution of
composition during propagation, allows for and explores the impact of ""bias"" in
the relation between UHECR sources and the dark matter distribution, and
investigates the possible generation of arrival-direction-dependent composition
anisotropies. Limits on the source number density consistent with the observed
anisotropies are derived for the case where UHECR sources follow the dark
matter distribution, and compared to a homogeneous source distribution case.",2308.10678v1
2023-08-22,Measures of azimuthal anisotropy in high-energy collisions,"Azimuthal anisotropy is a key observation made in ultrarelativistic heavy-ion
collisions. This phenomenon has played a crucial role in the development of the
field over the last two decades. In addition to its interest for studying the
quark-gluon plasma, which was the original motivation, it is sensitive to the
properties of incoming nuclei, in particular to the nuclear deformation and to
the nuclear skin. The azimuthal anisotropy is therefore of crucial importance
when relating low-energy nuclear structure to high-energy nuclear collisions.
This article is an elementary introduction to the various observables used in
order to characterize azimuthal anisotropy, which go under the names of
$v_2\{2\}$, $v_3\{2\}$, $v_2\{4\}$, etc. The intended audience is primarily
physicists working in the field of nuclear structure.",2308.11674v2
2023-08-28,Azimuthal Anisotropy at high transverse momentum in $p$-$p$ and $p$-$A$ collisions,"We explore the possibility that the initial transverse momentum distribution
of unpolarized and polarized partons within unpolarized nucleons, both with and
without the anisotropy of unpolarized hadrons produced in the fragmentation of
outgoing partons, could lead to the observed azimuthal anisotropy of high
transverse momentum (high-$p_T$) hadrons produced in high energy proton-proton
($p$-$p$) or proton-ion ($p$-$A$) collisions. Including simple Gaussian forms
for transverse momentum dependent parton distribution functions (PDF) and
fragmentation functions, and assuming an $A^{1/3}$ enhancement of a PDF in
$p$-$Pb$ collisions, we show that the observed anisotropy, with \emph{no
modification} to the angle integrated spectra ($R_{pA}=1$) for 5~GeV~$\lesssim
p_T\lesssim 50$~GeV, can be straightforwardly understood as arising from a few
processes dominated by gluon-gluon to gluon-gluon scattering.",2308.14702v4
2023-09-01,Kinematic anisotropies and pulsar timing arrays,"Doppler anisotropies, induced by our relative motion with respect to the
source rest frame, are a guaranteed property of stochastic gravitational wave
backgrounds of cosmological origin. If detected by future pulsar timing array
measurements, they will provide interesting information on the physics sourcing
gravitational waves, which is hard or even impossible to extract from
measurements of the isotropic part of the background only. We analytically
determine the pulsar response function to kinematic anisotropies, including
possible effects due to parity violation, to features in the frequency
dependence of the isotropic part of the spectrum, as well as to the presence of
extra scalar and vector polarizations. For the first time, we show how the
sensitivity to different effects crucially depends on the pulsar configuration
with respect to the relative motion among frames. Correspondingly, we propose
examples of strategies of detection, each aimed at exploiting future
measurements of kinematic anisotropies for characterizing distinct features of
the cosmological gravitational wave background.",2309.00403v3
2023-09-06,Shaping magnetization dynamics in a planar square dot by adjusting its surface anisotropy,"A planar square dot is one of the simplest structures confined to three
dimensions. Despite its geometrical simplicity, the description of the spin
wave modes in this structure is not trivial due to the competition of dipolar
and exchange interactions. An additional factor that makes this description
challenging are the boundary conditions depend both on non-local dipolar
interactions and local surface parameters such as surface anisotropy. In the
presented work, we showed how the surface anisotropy applied at the lateral
faces of the dot can tune the frequency of fundamental mode in the planar CoFeB
dot, magnetized in an out-of-plane direction. Moreover, we analyzed the spin
wave profile of the fundamental mode and the corresponding dynamic stray field.
We showed that the asymmetric application of surface anisotropy produces an
asymmetric profile of dynamic stray field for square dot and can be used to
tailor inter-dot coupling. The calculations were performed with the use of the
finite-element method.",2309.02984v1
2023-09-09,Anisotropy-assisted thermodynamic advantage of a local-spin thermal machine,"We study quantum Otto thermal machines with a two-spin working system coupled
by anisotropic interaction. Depending on the choice of different parameters,
the quantum Otto cycle can function as different thermal machines, including a
heat engine, refrigerator, accelerator and heater. We aim to investigate how
the anisotropy plays a fundamental role in the performance of the quantum Otto
engine operating in different time scales. We find that while the efficiency of
the engine efficiency increases with the increase in anisotropy for the
quasistatic operation, quantum internal friction and incomplete thermalization
degrade the performance in a finite time cycle. Further, we study the QOE with
one of the spins, the local spin, as the working system. We show that the
efficiency of such an engine can surpass the standard quantum Otto limit, along
with maximum power, thanks to the anisotropy. This can be attributed to quantum
interference effects. We demonstrate that the enhanced performance of a
local-spin QOE originates from the same interference effects, as in a
measurement-based QOE for their finite time operation.",2309.04757v1
2023-09-12,Anisotropy-assisted magnon condensation in ferromagnetic thin films,"We theoretically demonstrate that adding an easy-axis magnetic anisotropy
facilitates magnon condensation in thin yttrium iron garnet (YIG) films.
Dipolar interactions in a quasi-equilibrium state stabilize room-temperature
magnon condensation in YIG. Even though the out-of-plane easy-axis anisotropy
generally competes with the dipolar interactions, we show that adding such
magnetic anisotropy may even assist the generation of the magnon condensate
electrically via the spin transfer torque mechanism. We use analytical
calculations and micromagnetic simulations to illustrate this effect. Our
results may explain the recent experiment on Bi-doped YIG and open a pathway
toward applying current-driven magnon condensation in quantum spintronics.",2309.05982v3
2023-10-18,"First-principles study of the magnetic anisotropy of ultrathin B-, C-, and N-doped FeCo films","Iron-based layered systems are of great interest because of their ability to
tune effective material parameters such as magnetic anisotropy energy (MAE).
The influence of the crystallographic structure of Fe, its thickness, and the
presence of other layers above and below the Fe layer on magnetic parameters,
such as the MAE of the studied system, is an intriguing and important topic
from an application point of view. Here, we present a density functional theory
(DFT) study of the magnetic anisotropy of nine-monolayer Fe, FeCo, and FeCo
films with B, C, and N dopants placed in octahedral interstitial positions. The
theoretical study is based on calculations using the full-potential
local-orbital code FPLO and the generalized gradient approximation. The
chemical disorder in the FeCo layers was modeled using the virtual crystal
approximation. The structures of the layers were subjected to optimization of
the geometry of the interlayer spacings and the neighborhood of the dopant
sites. We determined the local magnetic moments and the excess charge at each
layer position. We also identified the influence of dopant atoms on the
magnetic properties of FeCo layers, such as magnetization and magnetic
anisotropy.",2310.12242v1
2023-10-23,Anisotropies in Scalar-Induced Gravitational-Wave Background from Inflaton-Curvaton Mixed Scenario with Sound Speed Resonance,"We propose a new model to generate large anisotropies in the scalar-induced
gravitational wave (SIGW) background via sound speed resonance in the
inflaton-curvaton mixed scenario. Cosmological curvature perturbations are not
only exponentially amplified at a resonant frequency, but also preserve
significant non-Gaussianity of local type described by $f_{\mathrm{nl}}$.
Besides a significant enhancement of energy-density fraction spectrum, large
anisotropies in SIGWs can be generated, because of super-horizon modulations of
the energy density due to existence of primordial non-Gaussianity. A reduced
angular power spectrum $\tilde{C}_{\ell}$ could reach an amplitude of
$[\ell(\ell+1)\tilde{C}_{\ell}]^{1/2} \sim 10^{-2}$, leading to potential
measurements via planned gravitational-wave detectors such as DECIGO. The large
anisotropies in SIGWs would serve as a powerful probe of the early universe,
shedding new light on the inflationary dynamics, primordial non-Gaussianity,
and primordial black hole dark matter.",2310.14606v3
2023-10-25,Intrinsic Piezoelectric Anisotropy of Tetragonal ABO3 Perovskites: A High-Throughput Study,"A comprehensive understand of the intrinsic piezoelectric anisotropy stemming
from diverse chemical and physical factors is a key step for the rational
design of highly anisotropic materials. We performed high-throughput
calculations on tetragonal ABO3 perovskites to investigate the piezoelectricity
and the interplay between lattice, displacement, polarization and elasticity.
Among the 123 types of perovskites, the structural tetragonality is naturally
divided into two categories: normal tetragonal (c/a ratio < 1.1) and
super-tetragonal (c/a ratio > 1.17), exhibiting distinct ferroelectric,
elastic, and piezoelectric properties. Charge analysis revealed the mechanisms
underlying polarization saturation and piezoelectricity suppression in the
super-tetragonal region, which also produces an inherent contradiction between
high d33 and large piezoelectric anisotropy ratio |d33/d31|. The polarization
axis and elastic softness direction jointly determine the maximum longitudinal
piezoelectric response d33 direction. The validity and deficiencies of the
widely utilized |d33/d31| ratio for representing piezoelectric anisotropy were
reevaluated.",2310.16591v1
2023-10-29,Impact of Medium Anisotropy on Quarkonium Dissociation and Regeneration,"Quarkonium production in ultra-relativistic collisions plays a crucial role
in probing the existence of hot QCD matter. This study explores quarkonia
states dissociation and regeneration in the hot QCD medium while considering
momentum anisotropy. The net quarkonia decay width ($\Gamma_{D}$) arises from
two essential processes: collisional damping and gluonic dissociation. The
quarkonia regeneration includes the transition from octet to singlet states
within the anisotropic medium. Our study utilizes a medium-modified potential
that incorporates anisotropy via particle distribution functions. This modified
potential gives rise to collisional damping for quarkonia due to the
surrounding medium, as well as the transition of quarkonia from singlet to
octet states due to interactions with gluons. Furthermore, we employ the
detailed balance approach to investigate the regeneration of quarkonia within
this medium. Our comprehensive analysis spans various temperature settings,
transverse momentum values, and anisotropic strengths. Notably, we find that,
in addition to medium temperatures and heavy quark transverse momentum,
anisotropy significantly influences the dissociation and regeneration of
various quarkonia states.",2310.18909v1
2023-11-11,Single-Phase L1$_{0}$-Ordered High Entropy Thin Films with High Magnetic Anisotropy,"The vast high entropy alloy (HEA) composition space is promising for
discovery of new material phases with unique properties. We explore the
potential to achieve rare-earth-free high magnetic anisotropy materials in
single-phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally
oxidized Si/SiO$_{2}$ substrates at room temperature are magnetically soft,
with a coercivity on the order of 10 Oe. After post-deposition rapid thermal
annealing (RTA), the films exhibit a single face-centered-cubic (fcc) phase,
with an almost 40-fold increase in coercivity. Inclusion of 50 at.% Pt in the
film leads to ordering of a single L1$_{0}$ high entropy intermetallic phase
after RTA, along with high magnetic anisotropy and a 3 orders of magnitude
coercivity increase. These results demonstrate a promising HEA approach to
achieve high magnetic anisotropy materials using RTA.",2311.06618v2
2023-11-13,Magnetogenesis from Anisotropic Universe,"The existence of large-scale anisotropy can not be ruled out by the cosmic
microwave background (CMB) radiation. Over the years, several models have been
proposed in the context of anisotropic inflation to account for CMB's cold spot
and hemispheric asymmetry. However, any small-scale anisotropy, if exists
during inflation, is not constrained due to its nonlinear evolution in the
subsequent phase. This small-scale anisotropy during inflation can play a
non-trivial role in giving rise to the cosmic magnetic field, which is the
subject of our present study. Assuming a particular phenomenological form of an
anisotropic inflationary universe, we have shown that it can generate a
large-scale magnetic field at $1$-Mpc scale with a magnitude $\sim 4\times
10^{-20}~G$, within the observed bound. Because of the anisotropy, the
conformal flatness property is lost, and the Maxwell field is generated even
without explicit coupling. This immediately resolves the strong coupling
problem in the standard magnetogenesis scenario. In addition, assuming very low
conductivity during the reheating era, we can further observe the evolution of
the electromagnetic field with the equation of state (EoS) $\omega_{eff}$ and
its effects on the present-day magnetic field.",2311.07685v1
2023-12-05,Magnetic instability under ferroaxial moment,"Magnetic anisotropy is one of the important factors in determining magnetic
structures. A type of magnetic anisotropy is closely related to the symmetry of
crystals. We theoretically investigate magnetic anisotropy and its related
magnetic instability arising from an electric axial moment, which appears under
the breaking of the mirror symmetry parallel to the moment but does not require
the breakings of both spatial inversion and time-reversal symmetries. By
performing perturbation and mean-field calculations in a complementary way, we
show the appearance of the in-plane magnetic anisotropy when the electric axial
moment occurs, which tends to tilt in-plane spin moments from the crystal axes
in collaboration with relativistic spin--orbit coupling. We demonstrate such a
tendency for single-site and four-site cluster models, the latter of which
leads to the instability toward a spin vortex phase accompanying magnetic
monopole and magnetic toroidal dipole.",2312.02444v1
2024-01-23,Universal relations for anisotropic interacting quark stars,"Interacting quark stars, which are entirely composed of interacting quark
matter including perturbative QCD corrections and color superconductivity, can
meet constraints from various pulsar observations. In realistic scenarios,
pressure anisotropies are expected in the star's interior. Recently, the
stellar structural properties of anisotropic interacting quark stars have been
investigated. In this study, we further explore the universal relations (URs)
related to the moment of inertia $I$, tidal deformability $\Lambda$,
compactness $C$, and the $f$-mode nonradial pulsation frequency for such stars.
Our results reveal that these approximate URs generally hold, being insensitive
to both the EOS variations as well as to the presence of anisotropy.
Specifically, we find that more positive anisotropy tends to enhance the
$I-\Lambda$ and $I-C$ URs, but weakens the $C-\Lambda$ UR. For all the URs
involving $f$-mode frequency, we find that they are enhanced by the inclusion
of anisotropy (whether positive or negative).",2401.12519v1
2024-02-05,Bifurcation to complex dynamics in largely modulated voltage-controlled parametric oscillator,"An experimental demonstration of a parametric oscillation of a magnetization
in a ferromagnet was performed recently by applying a microwave voltage,
indicating the potential to be applied in a switching method in non-volatile
memories. In the previous works, the modulation of a perpendicular magnetic
anisotropy field produced by the microwave voltage was small compared with an
external magnetic field pointing in an in-plane direction. A recent trend is,
however, opposite, where an efficiency of the voltage controlled magnetic
anisotropy (VCMA) effect is increased significantly by material research and
thus, the modulated magnetic anisotropy field can be larger than the external
magnetic field. Here, we solved the Landau-Lifshitz-Gilbert equation
numerically and investigated the magnetization dynamics driven under a wide
range of the microwave VCMA effect. We evaluated bifurcation diagrams, which
summarize local maxima of the magnetization dynamics. For low modulation
amplitudes, the local maximum is a single point because the dynamics is the
periodic parametric oscillation. The bifurcation diagrams show distributions of
the local maxima when the microwave magnetic anisotropy field becomes larger
than the external magnetic field. The appearance of this broadened distribution
indicates complex dynamics such as chaotic and transient-chaotic behaviors,
which were confirmed from an analysis of temporal dynamics.",2402.02742v1
2024-02-12,Quarkonia dissociation at finite magnetic field in the presence of momentum anisotropy,"In this study, we investigate the potential of heavy quarkonia within a
magnetized hot QGP medium having finite momentum anisotropy. The phenomenon of
inverse magnetic catalysis is introduced into the system, influencing the
magnetic field-modified Debye mass and thereby altering the effective quark
masses. Concurrently, the impact of momentum anisotropy in the medium is
considered that influence the particle distribution in the medium. The thermal
decay width and dissociation temperature of quarkonium states, specifically the
1S and 2S states of charmonium and bottomonium, are computed. Our results
reveal that both momentum anisotropy and the inverse magnetic catalysis effects
play a significant role in modifying the thermal decay width and dissociation
temperature of these heavy quarkonia states.",2402.07848v1
2024-02-14,Anisotropy Scaling Functions in Heavy-Ion Collisions: Insights into the `Ultra-Central Flow Puzzle' and Constraints on Transport Coefficients and Nuclear Deformation,"Anisotropy scaling functions, derived from extensive measurements of
transverse momentum- and centrality-dependent anisotropy coefficients
$v_2(p_T,\text{cent})$ and $v_3(p_T,\text{cent})$ in Pb+Pb collisions at 5.02
and 2.76 TeV, and Xe+Xe collisions at 5.44 TeV at the LHC, shed light on the
'ultra-central flow puzzle'. These functions amalgamate diverse measurements
into a unified curve, elucidating anisotropy attenuation across the full $p_T$
and centrality range and unveiling dependencies on key factors including
initial-state eccentricities ($\varepsilon_{n}$), dimensionless size
($\mathbb{R}$), radial flow, viscous correction to the thermal distribution
function ($\delta_f$), the medium's stopping power ($\hat{q}$), and specific
shear viscosity ($\eta/s$). Their analysis provides distinct insights into
transport coefficients and nucleus deformation constraints.",2402.09389v1
2024-02-25,Effect of Magnetic Anisotropy Constants on Skyrmion Formation in Co/Pt,"Skyrmions, which are topologically stable magnetic structures, have
manifested promising features to be used as an information carrier in new-age,
non-volatile data storage devices. In this article, we show how the creation
and stability of skyrmion can be manipulated by external stimuli (here,
nano-second current pulse). Co/Pt square nano-structure with Co free layer
thickness in the range 1 nm to 5 nm and first and second-order anisotropy
constants are taken to study the controlled creation of skyrmions. The
magnetization dynamics controlled by the current-induced spin transfer torque
help to nucleate skyrmions by transformation from perpendicularly magnetized
ground state to a stable state of isolated skyrmions via complex transformation
of Neel wall following its image inversion. Compared with the first-order
anisotropy alone, how the higher-order anisotropy constants (up to second
order) impact the relaxed state of a system has been discussed.",2402.16060v1
2024-02-27,"Impact of strong magnetic field, baryon chemical potential, and medium anisotropy on polarization and spin alignment of hadrons","The recent observation of global polarization of $\Lambda$ ($\bar{\Lambda}$)
hyperons and spin alignment of $\phi$ and $K^{*0}$ vector mesons create
remarkable interest in investigating the particle polarization in the
relativistic fluid produced in heavy-ion collisions at GeV/TeV energies. Among
other sources of polarization, the Debye mass of a medium plays a crucial role
in particle polarization. Any modification brought to the effective mass due to
the temperature, strong magnetic field (eB), baryonic chemical potential
($\mu_{B}$), and medium anisotropy ($\xi$), vorticity, etc., certainly affects
the particle polarization. In this work, we explore the global hyperon
polarization and the spin alignment of vector mesons corresponding to the
strong magnetic field, baryonic chemical potential, and medium anisotropy. We
find that the degree of polarization is flavor-dependent for hyperons.
Meanwhile, vector meson spin alignment depends on the hadronization mechanisms
of initially polarized quarks and anti-quarks. Medium anisotropy significantly
changes the degree of polarization in comparison with the magnetic field and
baryon chemical potential.",2402.17344v1
2001-06-30,Effects of Foreground Contamination on the Cosmic Microwave Background Anisotropy Measured by MAP,"We study the effects of diffuse Galactic, far-infrared extragalactic source,
and radio point source emission on the cosmic microwave background (CMB)
anisotropy data anticipated from the MAP experiment. We focus on the
correlation function and genus statistics measured from mock MAP
foreground-contaminated CMB anisotropy maps generated in a spatially-flat
cosmological constant dominated cosmological model. Analyses of the simulated
MAP data at 90 GHz (0.3 deg FWHM resolution smoothed) show that foreground
effects on the correlation function are small compared with cosmic variance.
However, the Galactic emission, even just from the region with |b| > 20 deg,
significantly affects the topology of CMB anisotropy, causing a negative genus
shift non-Gaussianity signal. Given the expected level of cosmic variance, this
effect can be effectively reduced by subtracting existing Galactic foreground
emission models from the observed data. IRAS and DIRBE far-infrared
extragalactic sources have little effect on the CMB anisotropy. Radio point
sources raise the amplitude of the correlation function considerably on scales
below 0.5 deg. Removal of bright radio sources above a 5 \sigma detection limit
effectively eliminates this effect. Radio sources also result in a positive
genus curve asymmetry (significant at 2 \sigma) on 0.5 deg scales. Accurate
radio point source data is essential for an unambiguous detection of CMB
anisotropy non-Gaussianity on these scales. Non-Gaussianity of cosmological
origin can be detected from the foreground-subtracted CMB anisotropy map at the
2 \sigma level if the measured genus shift parameter |\Delta\nu| >= 0.02 (0.04)
or if the measured genus asymmetry parameter |\Delta g| >= 0.03 (0.08) on a 0.3
(1.0) deg FWHM scale.",0107004v2
2006-10-05,Fundamental Magnetic Properties and Structural Implications for Nanocrystalline Fe-Ti-N Thin Films,"The magnetization (M) as a function of temperature (T) from 2 to 300 K and
in-plane field (H) up to 1 kOe, room temperature easy and hard direction
in-plane field hysteresis loops for fields between -100 and +100 Oe, and 10 GHz
ferromagnetic resonance (FMR) profiles have been measured for a series of
soft-magnetic nano-crystalline 50 nm thick Fe-Ti-N films made by magnetron
sputtering in an in-plane field. The nominal titanium concentration was 3 at. %
and the nitrogen concentrations (xN) ranged from zero to 12.7 at. %. The
saturation magnetization (Ms) vs. T data and the extracted exchange parameters
as a function of xN are consistent with a lattice expansion due to the addition
of interstitial nitrogen in the body-centered-cubic (bcc) lattice and a
structural transition to body-centered-tetragonal (bct) in the 6-8 at. %
nitrogen range. The hysteresis loop and FMR data show a consistent picture of
the changes in both the uniaxial and cubic anisotropy as a function of xN.
Films with xN > 1.9 at. % show an overall uniaxial anisotropy, with an
anisotropy field parameter Hu that increases with xN. The corresponding
dispersion averaged uniaxial anisotropy energy density parameter <Ku> = HuMs/2
is a linear function of xN, with a rate of increase of 950 erg/cm3 per at. %
nitrogen. The estimated uniaxial anisotropy energy per nitrogen atom is 30
J/mol, a value consistent with other systems. For xN below 6 at. %, the scaling
of coercive force Hc data with the sixth power of the grain size D indicate a
grain averaged effective cubic anisotropy energy density parameter <K1> that is
about an order of magnitude smaller that the nominal K1 values for iron, and
give a quantitative <K1> vs. D response that matches predictions for exchange
coupled random grains with cubic anisotropy.",0610160v1
2007-03-29,Anomalous scaling of a passive scalar advected by the turbulent velocity field with finite correlation time and uniaxial small-scale anisotropy,"The influence of uniaxial small-scale anisotropy on the stability of the
scaling regimes and on the anomalous scaling of the structure functions of a
passive scalar advected by a Gaussian solenoidal velocity field with finite
correlation time is investigated by the field theoretic renormalization group
and operator product expansion within one-loop approximation. Possible scaling
regimes are found and classified in the plane of exponents $\epsilon-\eta$,
where $\epsilon$ characterizes the energy spectrum of the velocity field in the
inertial range $E\propto k^{1-2\epsilon}$, and $\eta$ is related to the
correlation time of the velocity field at the wave number $k$ which is scaled
as $k^{-2+\eta}$. It is shown that the presence of anisotropy does not disturb
the stability of the infrared fixed points of the renormalization group
equations which are directly related to the corresponding scaling regimes. The
influence of anisotropy on the anomalous scaling of the structure functions of
the passive scalar field is studied as a function of the fixed point value of
the parameter $u$ which represents the ratio of turnover time of scalar field
and velocity correlation time. It is shown that the corresponding one-loop
anomalous dimensions, which are the same (universal) for all particular models
with concrete value of $u$ in the isotropic case, are different (nonuniversal)
in the case with the presence of small-scale anisotropy and they are continuous
functions of the anisotropy parameters, as well as the parameter $u$. The
dependence of the anomalous dimensions on the anisotropy parameters of two
special limits of the general model, namely, the rapid-change model and the
frozen velocity field model, are found when $u\to \infty$ and $u\to 0$,
respectively.",0703063v1
2008-08-29,Needlet Detection of Features in WMAP CMB Sky and the Impact on Anisotropies and Hemispherical Asymmetries,"We apply spherical needlets to the Wilkinson Microwave Anisotropy Probe
5-year cosmic microwave background (CMB) dataset, to search for imprints of
non-isotropic features in the CMB sky. We use the needlets localization
properties to resolve peculiar features in the CMB sky and to study how these
features contribute to the anisotropy power spectrum of the CMB. In addition to
the now well-known ""cold spot"" of the CMB map in the southern hemisphere, we
also find two hot spots at greater than 99% confidence level, again in the
southern hemisphere and closer to the Galactic plane. While the cold spot
contributes to the anisotropy power spectrum in the multipoles between l=6 to
l=33, the hot spots are found to be dominating the anisotropy power in the
range between l=6 and l=18. Masking both the cold and the two hot spots results
in a reduction by about 15% in the amplitude of the angular power spectrum of
CMB around l=10. The resulting changes to the cosmological parameters when the
power spectrum is estimated masking these features (in addition to the WMAP
team's KQ85 mask) are within the 1$\sigma$ errors published with the WMAP mask
only. We also study the asymmetry between the angular power spectra evaluated
on the northern and southern hemispheres. When the features detected by
needlets are masked, we find that the difference in the power, measured in
terms of the anisotropy variance between l=4 and l=18, is reduced by a factor
2. We make available a mask related to needlet features for more detailed
studies on asymmetries in the CMB anisotropy sky.",0809.0010v2
2013-07-08,Dipole anisotropy in sky brightness and source count distribution in radio NVSS data,"We study the dipole anisotropy in number counts and flux density weighted
number counts {or sky brightness} in the NRAO VLA Sky Survey (NVSS) data. The
dipole anisotropy is expected due to our local motion with respect to the CMBR
rest frame. We analyse data with an improved fit to the number density, n(S),
as a function of the flux density S, which allows deviation from a pure power
law behaviour. We also impose more stringent cuts to remove the contribution
due to clustering dipole. In agreement with earlier results, we find that the
amplitude of anisotropy is significantly larger in comparison to the prediction
based on CMBR measurements. The extracted speed is found to be roughly 3 times
the speed corresponding to CMBR. The significance of deviation is smaller,
roughly 2 sigma, in comparison to earlier estimates. For the cut, S>30 mJy, the
speed is found to be $1110\pm370$ Km/s using the source count analysis. The
direction of the dipole anisotropy is found to be approximately in agreement
with CMBR. We find that the results are relatively insensitive to the lower as
well as upper limit imposed on the flux density. Our results suggest that the
Universe is intrinsically anisotropic with the axis of anisotropy axis pointing
roughly towards the CMBR dipole direction. Finally we present a method which
may allow an independent extraction of the local speed and an intrinsic dipole
anisotropy, provided a larger data set becomes available in future.",1307.1947v4
2013-11-22,Effects of anisotropy on gravitational infall in galaxy clusters using an exact general relativistic model,"We study the effects and implications of anisotropies at the scale of galaxy
clusters by building an exact general relativistic model of a cluster using the
inhomogeneous and anisotropic Szekeres metric. The model is built from a
modified Navarro-Frenk-White (NFW) density profile. We compare this to a
corresponding spherically symmetric structure in the Lemaitre-Tolman (LT) model
and quantify the impact of introducing varying levels of anisotropy. We examine
two physical measures of gravitational infall -- the growth rate of density and
the velocity of the source dust in the model. We introduce a generalization of
the LT dust velocity profile for the Szekeres metric and demonstrate its
consistency with the growth rate of density. We find that the growth rate of
density in one substructure increases by 0.5%, 1.5%, and 3.75% for 5%, 10%, and
15% levels of introduced anisotropy, which is measured as the fractional
displaced mass relative to the spherically symmetric case. The infall velocity
of the dust is found to increase by 2.5, 10, and 20 km/s (0.5%, 2%, and 4.5%),
respectively, for the same three levels of anisotropy. This response to the
anisotropy in a structure is found to be strongly nonlinear with respect to the
strength of anisotropy. These relative velocities correspond to an equivalent
increase in the total mass of the spherically symmetric structure of 1%, 3.8%,
and 8.4%, indicating that not accounting for the presence of anisotropic mass
distributions in cluster models can strongly bias the determination of physical
properties like the total mass.",1311.5651v2
2015-12-09,Anisotropy of X-ray bursts from neutron stars with concave accretion disks,"Emission from neutron stars and accretion disks in low-mass X-ray binaries is
not isotropic. The non-spherical shape of the disk as well as blocking of the
neutron star by the disk and vice versa cause the observed flux to depend on
the inclination angle of the disk with respect to the line of sight. This is of
special importance for the interpretation of Type I X-ray bursts, which are
powered by the thermonuclear burning of matter accreted onto the neutron star.
Because part of the X-ray burst is reflected off the disk, the observed burst
flux depends on the anisotropies for both direct emission from the neutron star
and reflection off the disk. This influences measurements of source distance,
mass accretion rate, and constraints on the neutron star equation of state.
Previous studies made predictions of the anisotropy factor for the total burst
flux, assuming a geometrically flat disk. Recently, detailed observations of
two exceptionally long bursts (so-called superbursts) allowed for the first
time for the direct and the reflected burst flux to each be measured, as
opposed to just their sum. The ratio of the reflected and direct flux (the
reflection fraction) was much higher than what the anisotropies of a flat disk
can account for. We create numerical models to calculate the anisotropy factors
for different disk shapes, including concave disks. We present the anisotropy
factors of the direct and reflected burst flux separately, as well as the
anisotropy of the persistent flux. Reflection fractions substantially larger
than unity are produced in case the inner accretion disk steeply increases in
height, such that part of the star is blocked from view. Such a geometry could
possibly be induced by the X-ray burst, if X-ray heating causes the inner disk
to puff up.",1512.02889v2
2017-06-25,"Magnetic anisotropy of $L1_0$-ordered FePt thin films studied by Fe and Pt $L_{2,3}$-edges x-ray magnetic circular dichroism","The strong perpendicular magnetic anisotropy of $L{\rm1_0}$-ordered FePt has
been the subject of extensive studies for a long time. However, it is not known
which element, Fe or Pt, mainly contributes to the magnetic anisotropy energy
(MAE). We have investigated the anisotropy of the orbital magnetic moments of
Fe 3$d$ and Pt 5$d$ electrons in $L{\rm1_0}$-ordered FePt thin films by Fe and
Pt $L_{2,3}$-edge x-ray magnetic circular dichroism (XMCD) measurements for
samples with various degrees of long-range chemical order $S$. Fe
$L_{2,3}$-edge XMCD showed that the orbital magnetic moment was larger when the
magnetic field was applied perpendicular to the film than parallel to it, and
that the anisotropy of the orbital magnetic moment increased with $S$. Pt
$L_{2,3}$-edge XMCD also showed that the orbital magnetic moment was smaller
when the magnetic field was applied perpendicular to the film than parallel to
it, opposite to the Fe $L_{2,3}$-edge XMCD results although the anisotropy of
the orbital magnetic moment increases with $S$ like the Fe edge. These results
are qualitatively consistent with the first-principles calculation by Solovyev
${\it et\ al.}$ [Phys. Rev. B $\bf{52}$, 13419 (1995).], which also predicts
the dominant contributions of Pt 5$d$ to the magnetic anisotropy energy rather
than Fe 3$d$ due to the strong spin-orbit coupling and the small spin splitting
of the Pt 5$d$ bands in $L{\rm1_0}$-ordered FePt.",1706.08183v1
2017-07-18,HI anisotropies associated with radio-polarimetric filaments. Steep power spectra associated with cold gas,"LOFAR detected toward 3C 196 linear polarization structures which were found
subsequently to be closely correlated with cold filamentary HI structures. The
derived direction-dependent HI power spectra revealed marked anisotropies for
narrow ranges in velocity, sharing the orientation of the magnetic field as
expected for magneto hydrodynamical turbulence. Using the Galactic portion of
the Effelsberg-Bonn HI Survey we continue our study of such anisotropies in the
HI distribution in direction of two WSRT fields, Horologium and Auriga; both
are well known for their prominent radio-polarimetric depolarization canals. At
349 MHz the observed pattern in total intensity is insignificant but polarized
intensity and polarization angle show prominent ubiquitous structures with so
far unknown origin. Apodizing the HI survey data by applying a rotational
symmetric 50 percent Tukey window, we derive average and position angle
dependent power spectra. We fit power laws and characterize anisotropies in the
power distribution. We use a Gaussian analysis to determine relative abundances
for the cold and warm neutral medium. For the analyzed radio-polarimetric
targets significant anisotropies are detected in the HI power spectra; their
position angles are aligned to the prominent depolarization canals, initially
detected by WSRT. HI anisotropies are associated with steep power spectra.
Steep power spectra, associated with cold gas, are detected also in other
fields. Radio-polarimetric depolarization canals are associated with
filamentary HI structures that belong to the cold neutral medium (CNM).
Anisotropies in the CNM are in this case linked to a steepening of the
power-spectrum spectral index, indicating that phase transitions in a turbulent
medium occur on all scales. Filamentary HI structures, driven by thermal
instabilities, and radio-polarimetric filaments are associated with each other.",1707.05672v2
2018-04-29,Stress anisotropy in shear-jammed packings of frictionless disks,"We perform computational studies of repulsive, frictionless disks to
investigate the development of stress anisotropy in mechanically stable (MS)
packings. We focus on two protocols for generating MS packings: 1) isotropic
compression and 2) applied simple or pure shear strain $\gamma$ at fixed
packing fraction $\phi$. MS packings of frictionless disks occur as geometric
families (i.e. parabolic segments with positive curvature) in the
$\phi$-$\gamma$ plane. MS packings from protocol 1 populate parabolic segments
with both signs of the slope, $d\phi/d\gamma >0$ and $d\phi/d\gamma <0$. In
contrast, MS packings from protocol 2 populate segments with $d\phi/d\gamma <0$
only. For both simple and pure shear, we derive a relationship between the
stress anisotropy and dilatancy $d\phi/d\gamma$ obeyed by MS packings along
geometrical families. We show that for MS packings prepared using isotropic
compression, the stress anisotropy distribution is Gaussian centered at zero
with a standard deviation that decreases with increasing system size. For shear
jammed MS packings, the stress anisotropy distribution is a convolution of
Weibull distributions that depend on strain, which has a nonzero average and
standard deviation in the large-system limit. We also develop a framework to
calculate the stress anisotropy distribution for packings generated via
protocol 2 in terms of the stress anisotropy distribution for packings
generated via protocol 1. These results emphasize that for repulsive
frictionless disks, different packing-generation protocols give rise to
different MS packing probabilities, which lead to differences in macroscopic
properties of MS packings.",1804.10962v2
2018-06-21,"The electrical conductivity tensor of $β$-Ga2O3 analyzed by van der Pauw measurements: Inherent anisotropy, off-diagonal element, and the impact of grain boundaries","The semiconducting oxide $\beta$-Gallium Oxide ($\beta$-Ga$_{2}$O$_{3}$)
possesses a monoclinic unit cell whose low symmetry generally leads to
anisotropic physical properties. For example, its electrical conductivity is
generally described by a polar symmetrical tensor of second rank consisting of
four independent components. Using van der Pauw measurements in a well-defined
square geometry on differently-oriented high-quality bulk samples and the
comparison to finite element simulations we precisely determine the ratio of
all elements of the $\beta$-Ga$_{2}$O$_{3}$ 3-dimensional electrical
conductivity tensor. Despite the structural anisotropy a nearly isotropic
conductivity at and above room temperature was found with the principal
conductivities deviating from each other by less than 6% and the off-diagonal
element being $\approx3$% of the diagonal ones. Analysis of the temperature
dependence of the anisotropy and mobility of differently doped samples allows
us to compare the anisotropy for dominant phonon-scattering to that for
dominant ionized-impurity scattering. For both scattering mechanisms, the
conductivites along the $a$ and $b$-direction agree within 2%. In contrast, the
conductivity along $c$-direction amounts to $0.96\times$ and up to $1.12\times$
that along the $b$-direction for phonon and ionized impurity scattering,
respectively. The determined transport anisotropies are larger than the
theoretically predicted effective mass anisotropy, suggesting slightly
anisotropic scattering mechanisms. We demonstrate that significantly higher
anisotropies can be caused by oriented extended structural defects in the form
of low-angle grain boundaries for which we determined energy barriers of
multiple 10 meV.",1806.08162v2
2018-12-19,"Stress-induced anisotropy in granular materials: fabric, stiffness, and permeability","The loading of a granular material induces anisotropies of the particle
arrangement (fabric) and of the material's strength, incremental stiffness, and
permeability. Thirteen measures of fabric anisotropy are developed, which are
arranged in four categories: as preferred orientations of the particle bodies,
the particle surfaces, the contact normals, and the void space. Anisotropy of
the voids is described through image analysis and with Minkowski tensors. The
thirteen measures of anisotropy change during loading, as determined with
three-dimensional discrete element simulations of biaxial plane strain
compression with constant mean stress. Assemblies with four different particle
shapes were simulated. The measures of contact orientation are the most
responsive to loading, and they change greatly at small strains, whereas the
other measures lag the loading process and continue to change beyond the state
of peak stress and even after the deviatoric stress has nearly reached a steady
state. The paper implements a methodology for characterizing the incremental
stiffness of a granular assembly during biaxial loading, with orthotropic
loading increments that preserve the principal axes of the fabric and stiffness
tensors. The linear part of the hypoplastic tangential stiffness is monitored
with oedometric loading increments. This stiffness increases in the direction
of the initial compressive loading but decreases in the direction of extension.
Anisotropy of this stiffness is closely correlated with a particular measure of
the contact fabric. Permeabilities are measured in three directions with
lattice Boltzmann methods at various stages of loading and for assemblies with
four particle shapes. Effective permeability is negatively correlated with the
directional mean free path and is positively correlated with pore width.",1812.08267v1
2019-09-30,Simultaneous individual and dipolar collective properties in binary assemblies of magnetic nanoparticles,"Applications based on aggregates of magnetic nanoparticles are becoming
increasingly widespread, ranging from hyperthermia to magnetic recording.
However, although some uses require a collective behavior, other need a more
individual-like response, the conditions leading to either of these behaviors
are still poorly understood. Here we use nanoscale-uniform binary random dense
mixtures with different proportions of oxide magnetic nanoparticles with
low$/$high anisotropy as a valuable tool to explore the crossover from
individual to collective behavior. Two different anisotropy scenarios have been
studied in two series of binary compacts: M1, comprising maghemite
($\gamma$-Fe$_2$O$_3$) nanoparticles of different sizes (9.0 nm $/$ 11.5 nm)
with barely a factor of 2 between their anisotropy energies and M2, mixing
equally-sized pure maghemite (low-anisotropy) and Co-doped maghemite
(high-anisotropy) nanoparticles with a large difference in anisotropy energy
(ratio $>$ 8). Interestingly, while the M1 series exhibits collective behavior
typical of strongly-coupled dipolar systems, the M2 series presents a more
complex scenario where different magnetic properties resemble either
""individual-like"" or ""collective"", crucially emphasizing that the collective
character must be ascribed to specific properties and not to the system as a
whole. The strong differences between the two series, offer new insight
(systematically ratified by simulations) into the subtle interplay between
dipolar interactions, local anisotropy and sample heterogeneity, to determine
the behavior of dense assemblies of magnetic nanoparticles.",1909.13500v1
2020-05-12,"Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia","We analyze the anisotropy profile of the Milky Way's smooth, diffuse stellar
halo using SDSS/SEGUE blue horizontal branch stars and SDSS/SEGUE and LAMOST K
giants. These intrinsically luminous stars allow us to probe the halo to
approximately 100 kpc from the Galactic center. Line-of-sight velocities,
distances, metallicities, and proper motions are available for all stars via
SDSS/SEGUE, LAMOST, and Gaia, and we use these data to construct a full 7D set
consisting of positions, space motions, and metallicity. We remove substructure
from our samples using integrals of motion based on the method of Xue et al. We
find radially dominated kinematic profiles with nearly constant anisotropy
within 20 kpc, beyond which the anisotropy profile gently declines although
remains radially dominated to the furthest extents of our sample. Independent
of star type or substructure removal, the anisotropy depends on metallicity,
such that the orbits of the stars become less radial with decreasing
metallicity. For $-1.7<$ [Fe/H] $<-1$, the smooth, diffuse halo anisotropy
profile begins to decline at Galactocentric distances $\sim20$ kpc, from
$\beta\sim0.9$ to 0.7 for K giants and from $\beta\sim0.8$ to 0.1 for blue
horizontal branch stars. For [Fe/H] $<-1.7$, the smooth, diffuse halo
anisotropy remains constant along all distances with $0.2<\beta<0.7$ depending
on the metallicity range probed, although independent on star type. These
samples are ideal for estimating the total Galactic mass as they represent the
virialized stellar halo system.",2005.05980v2
2020-06-18,Interplay of Turbulence and Proton-Microinstability Growth in Space Plasmas,"Numerous prior studies have shown that as proton beta increases, a narrower
range of proton temperature anisotropy values is observed. This effect has
often been ascribed to the actions of kinetic microinstabilities because the
distribution of observational data aligns with contours of constant instability
growth rates in the beta-anisotropy plane. However, the linear Vlasov theory of
instabilities assumes a uniform background in which perturbations grow. The
established success of linear-microinstability theories suggests that the
conditions in regions of extreme temperature anisotropy may remain uniform for
a long enough time so that the instabilities have the chance to grow to
sufficient amplitude. Turbulence, on the other hand, is intrinsically
non-uniform and non-linear. Thin current sheets and other coherent structures
generated in a turbulent plasma, may destroy the uniformity fast enough. It is
therefore not a-priori obvious whether the presence of intermittency and
coherent structures favors or disfavors instabilities. To address this
question, we examined the statistical distribution of growth rates associated
with proton temperature-anisotropy driven microinstabilities and local
nonlinear time scales in turbulent plasmas. Linear growth rates are, on
average, substantially less than the local nonlinear rates. However, at the
regions of extreme values of temperature anisotropy, near the ""edges"" of the
populated part of the proton temperature anisotropy-parallel beta plane, the
instability growth rates are comparable or faster than the turbulence time
scales. These results provide a possible answer to the question as to why the
linear theory appears to work in limiting plasma excursions in anisotropy and
plasma beta.",2006.10316v2
2020-09-02,3D modeling from the onset of the SN to the full-fledged SNR: Role of an initial ejecta anisotropy on matter mixing,"The aim of this work is to bridge the gap between CC SNe and their remnants
by investigating how post-explosion anisotropies in the ejecta influence the
structure and chemical properties of the remnant at later times. We performed
three-dimensional magneto-hydrodynamical simulations starting soon after the SN
event and following the evolution of the system in the circumstellar medium
(consisting of the wind of the stellar progenitor), for 5000 years, obtaining
the physical scenario of a SNR. Here we focused the analysis on the case of a
progenitor red supergiant of 19.8 M_sun. We also investigated how a
post-explosion large-scale anisotropy in the SN affects the ejecta distribution
and the matter mixing of heavy elements in the remnant, during the first 5000
years of evolution. In the case of a spherically symmetric SN explosion without
large-scale anisotropies, the remnant roughly keeps memory of the original
onion-like layering of ejecta soon after the SN event. Nevertheless, as the
reverse shock hits the ejecta, the element distribution departs from a
homologous expansion, because of the slowing down of the outermost ejecta
layers due to interaction with the reverse shock. In the case of a large-scale
anisotropy developed after the SN, we found that the chemical stratification in
the ejecta can be strongly modified and the original onion-like layering is not
preserved. The anisotropy may cause spatial inversion of ejecta layers, for
instance leading to Fe/Si-rich ejecta outside the O shell, and may determine
the formation of Fe/Si-rich jet-like features that may protrude the remnant
outline. The level of matter mixing and the properties of the jet-like feature
are sensitive to the initial physical (density and velocity) and geometrical
(size and position) initial characteristics of the anisotropy.",2009.01157v1
2020-11-04,Unveiling temperature dependence mechanisms of perpendicular magnetic anisotropy at Fe/MgO interfaces,"The perpendicular magnetic anisotropy (PMA) at magnetic transition
metal/oxide interfaces is a key element in building out-of-plane magnetized
magnetic tunnel junctions for spin-transfer-torque magnetic random access
memory (STT-MRAM). Size downscaling renders magnetic properties more sensitive
to thermal effects. Thus, understanding the temperature dependence of the
magnetic anisotropy is crucial. In this work, we theoretically address the
correlation between temperature dependence of PMA and magnetization in typical
Fe/MgO-based structures. In particular, the possible mechanisms behind the
experiments reporting deviations from the Callen and Callen scaling power law
are analyzed. At ideal interfaces, first-principles calculations reveal (i)
small high-order anisotropy constants compared to first order and (ii) enhanced
exchange constants. Considering these two intrinsic effects in the atomistic
simulations, the temperature-dependence of the total and layer-resolved
anisotropy are found to follow the Callen and Callen scaling power law, thus
ruling out an intrinsic microscopic mechanism underlying deviations from this
law. Besides, two possible extrinsic macroscopic mechanisms are unveiled namely
the influence of the dead layer, often present in the storage layer of STT-MRAM
cells, and the spatial inhomogeneities of the interfacial magnetic anisotropy.
About the first mechanism, we show that the presence of a dead layer tends to
reduce the scaling exponents. In the second mechanism, increasing the
percentage of inhomogeneity in the interfacial PMA is revealed to decrease the
scaling exponent. These results allow us to explain the difference in scaling
exponents relating anisotropy and magnetization thermal variations reported in
earlier experiments. This is crucial for the understanding of the thermal
stability of the storage layer magnetization in STT-MRAM applications.",2011.02220v3
2021-05-21,Comparative study of superconducting and normal-state anisotropy in Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ superconductors with controlled amounts of interstitial excess Fe,"We report a systematic study of the superconducting (SC) and normal-state
anisotropy of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ single crystals with controlled
amounts of excess Fe ($y$ = 0, 0.07, and 0.14). The SC state anisotropy
$\gamma_{H}$ was obtained by measuring the upper critical fields under high
magnetic fields over 50 T for both $H\parallel ab$ and $H\parallel c$. On the
other hand, the normal state anisotropy $\gamma_{\rho}$ was obtained by
measuring the resistivity with current flowing in the $ab$ plane ($\rho_{ab}$)
and along the $c$ axis ($\rho_c$). To precisely measure $\rho_{ab}$ and
$\rho_c$ in the same part of a specimen avoiding the variation dependent on
pieces or parts, we adopt a new method using a micro-fabricated bridge with an
additional neck part along $c$ axis. The $\gamma_{H}$ decreases from a value
dependent on the amount of excess Fe at $T_{\rm{c}}$ to a common value $\sim$ 1
at 2 K. The different $\gamma_{H}$ at $T_{\rm{c}}$ ($\sim$1.5 for $y$ = 0, and
2.5 for $y$ = 0.14) suggests that the anisotropy of effective mass
$m_c^*/m_{ab}^*$ increases from $\sim$ 2.25 ($y$ = 0) to 6.25 ($y$ = 0.14) with
the excess Fe. The almost isotropic $\gamma_{H}$ at low temperatures is due to
the strong spin paramagnetic effect at $H\parallel ab$. By contrast, the
$\gamma_{\rho}$ shows a much larger value of $\sim$ 17 ($y$ = 0) to $\sim$ 50
($y$ = 0.14) at the temperature just above $T_{\rm{c}}$. Combined the results
of $\gamma_{H}$ and $\gamma_{\rho}$ near $T_{\rm{c}}$, we found out that the
discrepant anisotropies between the SC and normal states originates from a
large anisotropy of scattering time $\tau_{ab}$/$\tau_c$ $\sim$ 7.8. The
$\tau_{ab}$/$\tau_c$ is found to be independent of the excess Fe.",2105.10093v1
2021-08-10,Spin-excitation anisotropy in the nematic state of detwinned FeSe,"The origin of the electronic nematicity in FeSe is one of the most important
unresolved puzzles in the study of iron-based superconductors. In both spin-
and orbital-nematic models, the intrinsic magnetic excitations at
$\mathbf{Q}_1=(1, 0)$ and $\mathbf{Q}_2=(0, 1)$ of twin-free FeSe are expected
to provide decisive criteria for clarifying this issue. Although a
spin-fluctuation anisotropy below 10 meV between $\mathbf{Q}_1$ and
$\mathbf{Q}_2$ has been observed by inelastic neutron scattering around
$T_c\sim 9$ K ($<<T_s\sim 90$ K), it remains unclear whether such an anisotropy
also persists at higher energies and associates with the nematic transition
$T_{\rm s}$. Here we use resonant inelastic x-ray scattering (RIXS) to probe
the high-energy magnetic excitations of uniaxial-strain detwinned FeSe and
{\BFA}. A prominent anisotropy between the magnetic excitations along the $H$
and $K$ directions is found to persist to $\sim200$ meV in FeSe, which is even
more pronounced than the anisotropy of spin waves in {\BFA}. This anisotropy
decreases gradually with increasing temperature and finally vanishes at a
temperature around the nematic transition temperature $T_{\rm s}$. Our results
reveal an unprecedented strong spin-excitation anisotropy with a large energy
scale well above the $d_{xz}/d_{yz}$ orbital splitting, suggesting that the
nematic phase transition is primarily spin-driven. Moreover, the measured
high-energy spin excitations are dispersive and underdamped, which can be
understood from a local-moment perspective. Our findings provide the
much-needed understanding of the mechanism for the nematicity of FeSe and
points to a unified description of the correlation physics across seemingly
distinct classes of Fe-based superconductors.",2108.04484v2
2021-10-20,What can be learnt from UHECR anisotropies observations? Paper I : large-scale anisotropies and composition features,"We investigate the implications of the current data regarding large scale
anisotropies, and examine to what extent they can be used to constrain the
origin of UHECRs and the astrophysical parameters of the source scenarios. We
discuss the possibility of observing an associated anisotropy of the
composition, the potential benefit of the separation of the different nuclear
components and the interest of observing the UHECR sky with larger exposure
future observatories. We simulate UHECR sky maps for various astrophysical
scenarios satisfying the current observational constraints, taking into account
the energy losses of the UHE protons and nuclei and their deflections by
intervening magnetic fields. We investigate scenarios in which the UHECR source
distribution follows that of the galaxies, varying the source composition and
spectrum, the source density and the magnetic field models. We apply similar
analyses as those used by the Auger collaboration. We find that: i) reproducing
the observed dipole anisotropy and its energy evolution is relatively easy
within our assumptions; ii) this agreement can be obtained with different sets
of assumptions on the astrophysical parameters, and is thus not, at this stage,
very constraining for UHECR source scenarios; iii) the actual reconstructed
direction of the dipole appears non natural in essentially all scenarios
investigated, and challenges their main assumptions on the source distribution
or the assumed magnetic field configuration, especially in the Galaxy; iv)
except for protons, the energy range in which the GZK horizon strongly reduces
is a key target for anisotropy searches for each given nuclear species; v) The
composition anisotropy naturally expected in our models is unlikely to account
for that recently reported by Auger unless the observed amplitude is a strong
positive statistical fluctuation of an intrinsically weaker signal.",2110.10761v1
1994-03-18,Anisotropies of the Cosmic Background Radiation in a Reionized Universe,"We trace the evolution of cosmic microwave background photons propagating
through a reionized model universe. The reionization of the intergalactic
medium is achieved by UV photons emitted from the decaying `hot' dark matter
neutrinos. The model universe is represented by a comoving cube through which
we propagate photons and subject them to the Sachs-Wolfe effect and Thomson
scattering off the ionized fraction of the IGM, beginning at z=1900 until the
present z=0. The simulation follows the evolving matter inhomogeneities and
microwave background photons into the present nonlinear regime and yields
temperature maps of the microwave sky as a comoving observer would detect. Our
temperature maps display anisotropies on scales ranging from 2 to 8 degrees
with rms amplitudes ranging from DT/T_{rms} =2.8 to 3.4 times 10^{-5} without
reionization. If we allow the neutrinos to decay and subsequently reionize the
IGM, the level of the temperature anisotropies is reduced to DT/T=0.8 to 1.1
times 10^{-5}. This includes the Doppler shifts suffered by the CMB photons as
they scatter off the moving ionized fraction of the IGM. If, however,
reionization is caused by a late and sudden energy input into the IGM, we find
that some reduction in $\Delta T/T$ occurs, but not enough to make this
scenario consistent with observations. We find that the decaying neutrino
hypothesis is more efficient at reducing primordial anisotropies and generates
smaller Doppler anisotropies than a model reionized via a late and sudden
energy input into the IGM.",9403040v1
1997-02-03,Microwave Background Anisotropies from Scaling Seed Perturbations,"We study microwave background anisotropies induced by scaling seed
perturbations in a universe dominated by cold dark matter. Using a gauge
invariant linear perturbation analysis, we solve the perturbation equations on
super-horizon scales, for CMB anisotropies triggered by generic gravitational
seeds. We find that perturbations induced by seeds --- under very mild
restrictions --- are nearly isocurvature. Thus, compensation, which is mainly
the consequence of physically sensible initial conditions, is very generic.
  We then restrict our study to the case of scaling sources, motivated by
global scalar fields. We parameterize the energy momentum tensor of the source
by ``seed functions'' and calculate the Sachs-Wolfe and acoustic contributions
to the CMB anisotropies. We discuss the dependence of the anisotropy spectrum
on the parameters of the model considered. Even within the restricted class of
models investigated in this work, we find a surprising variety of results for
the position and height of the first acoustic peak as well as for the overall
amplitude. In particular, for certain choices of parameters, the spectrum
resembles very much the well known adiabatic inflationary spectrum, whereas for
others, the position of the first acoustic peak is significantly shifted
towards smaller angular scales.",9702028v4
1997-05-07,Detection of Cosmic Microwave Background Anisotropy by the Third Flight of MSAM,"The third flight of the Medium Scale Anisotropy Measurement (MSAM1), in June
1995, observed a new strip of sky, doubling the sky coverage of the original
MSAM1 dataset. MSAM1 observes with a 0.5 deg beam size in four bands from 5-20
icm. From these four bands we derive measurements of cosmic microwave
background radiation (CMBR) anisotropy and interstellar dust emission. Our
measurement of dust emission correlates well with the 100 um IRAS Sky Survey
Atlas; from this comparison we determine an effective emissivity spectral index
between 100 um and 444 um of 1.46 +/- 0.28. Analysis of our measurement of CMBR
anisotropy shows that for Gaussian-shaped correlation functions with theta_c =
0.3 deg, we place a limit on total rms anisotropy of 2.2 x 10^{-5} < Delta T/T
< 3.9 x 10^{-5} (90% confidence interval, including calibration error). The
band-power limits are <delta T> = <l (l+1)C_l/2 pi>^{1/2} = 50^{+16}_{-11} uK
at l = 160, and <delta T> = 65^{+18}_{-13} uK at l = 270 (1 sigma limits,
including calibration error). The corresponding limits with statistical errors
only are <delta T> = 50^{+13}_{-9} uK and <delta T> = 65^{+14}_{-10} uK
respectively. These measurements are consistent with a standard adiabatic cold
dark matter model; we discuss constraints on h, n, and the redshift of
reionization.",9705041v2
1997-11-04,Recent developments in the calculation of CMB anisotropies,"We discuss three recent developments in the calculation of CMB anisotropies.
First, we consider relativistic corrections to the Sunyaev-Zel'dovich effect.
By extending the Kompaneets equation to the relativistic domain we are able to
derive simple analytic forms for the SZ spectral distortion. Second, we discuss
covariant kinetic theory methods for the gauge-invariant calculation of CMB
anisotropies. We present a covariant version of the Boltzmann equation which we
use to derive covariant and gauge-invariant equations describing a CDM model,
which are independent of background curvature and type of perturbation (scalar,
vector or tensor). By integrating the covariant Boltzmann equation along the
line of sight, and using the instantaneous recombination approximation, we
obtain an expression for the large-scale anisotropy which agrees with an
expression derived recently by Dunsby. Third, we discuss recent accurate
calculations of the CMB anisotropy in global defect models of cosmic structure
formation. In such models the effects of vector modes are significant and when
combined with the effects of decoherence lead to a suppression of the Doppler
peaks. The result is that global defect models may already be at variance with
the growing volume of CMB and large scale structure data.",9711028v3
1997-11-10,Sub-degree CMB anisotropies from inflationary bubbles,"It is well known that processes of first order phase transitions may have
occurred in the inflationary era. If one or more occurred well before the end
of inflation, the nucleated bubbles are stretched to large scales and the
primordial power spectrum contains a scale dependent non-Gaussian component
provided by the remnants of the bubbles. We predict the anisotropies in the
cosmic microwave background (CMB) induced by inflationary bubbles. We build a
general analytic model for describing a bubbly perturbation; we evolve each
Fourier mode using the linear theory of perturbations from reheating until
decoupling; we get the CMB anisotropies by considering the bubbly perturbation
intersecting the last scattering surface. The CMB image of an inflationary
bubble is a series of concentric isothermal rings of different color (sign of
$\delta T/T$) on the scale of the sound horizon at decoupling ($\le 1^{o}$ in
the sky); the resulting anisotropy is therefore strongly non-Gaussian. The mean
amplitude of $\delta T/T$ for a bubble of size $L$ follows the known estimates
for linear perturbations, $\delta T/T\simeq\delta\rho /\rho\cdot
(L/H^{-1})^{2}$. In particular, bubbles with size corresponding to the seeds of
the observed large scale voids (tens of comoving Mpc) induce an interesting
pattern of CMB anisotropies on the sub-degree angular scale, to be further
investigated and compared with the forthcoming high resolution CMB maps
provided by the MAP and the Planck experiments.",9711095v1
1998-06-17,Gravothermal Catastrophe in Anisotropic Spherical Systems,"In this paper we investigate the gravothermal instability of spherical
stellar systems endowed with a radially anisotropic velocity distribution. We
focus our attention on the effects of anisotropy on the conditions for the
onset of the instability and in particular we study the dependence of the
spatial structure of critical models on the amount of anisotropy present in a
system. The investigation has been carried out by the method of linear series
which has already been used in the past to study the gravothermal instability
of isotropic systems.
  We consider models described by King, Wilson and Woolley-Dickens distribution
functions. In the case of King and Woolley-Dickens models, our results show
that, for quite a wide range of amount of anisotropy in the system, the
critical value of the concentration of the system (defined as the ratio of the
tidal to the King core radius of the system) is approximately constant and
equal to the corresponding value for isotropic systems. Only for very
anisotropic systems the critical value of the concentration starts to change
and it decreases significantly as the anisotropy increases and penetrates the
inner parts of the system. For Wilson models the decrease of the concentration
of critical models is preceded by an intermediate regime in which critical
concentration increases, it reaches a maximum and then it starts to decrease.
The critical value of the central potential always decreases as the anisotropy
increases.",9806233v2
1999-03-17,The Standard Cosmological Model and CMB Anisotropies,"This is a course on cosmic microwave background (CMB) anisotropies in the
standard cosmological model, designed for beginning graduate students and
advanced undergraduates. ``Standard cosmological model'' in this context means
a Universe dominated by some form of cold dark matter (CDM) with adiabatic
perturbations generated at some initial epoch, e.g., Inflation, and left to
evolve under gravity alone (which distinguishes it from defect models). The
course is primarily theoretical and concerned with the physics of CMB
anisotropies in this context and their relation to structure formation. Brief
presentations of the uniform Big Bang model and of the observed large--scale
structure of the Universe are given. The bulk of the course then focuses on the
evolution of small perturbations to the uniform model and on the generation of
temperature anisotropies in the CMB. The theoretical development is performed
in the (pseudo--)Newtonian gauge because it aids intuitive understanding by
providing a quick reference to classical (Newtonian) concepts. The fundamental
goal of the course is not to arrive at a highly exact nor exhaustive
calculation of the anisotropies, but rather to a good understanding of the
basic physics that goes into such calculations.",9903260v1
1999-05-11,Searching for the non-gaussian signature of the CMB secondary anisotropies,"In a first paper (Forni & Aghanim 1999), we developed several statistical
discriminators to test the non-gaussian nature of a signal. These tests are
based on the study of the coefficients in a wavelet decomposition basis. In
this paper, we apply them in a cosmological context, to the study of the nature
of the Cosmic Microwave Background (CMB) anisotropies. The latter represent the
superposition of primary anisotropy imprints of the initial density
perturbations and secondary ones due to photon interactions after
recombination. In an inflationary scenario (standard Cold Dark Matter) with
gaussian distributed fluctuations, we study the statistical signature of the
secondary effects. More specifically, we investigate the dominant effects
arising from the Compton scattering of CMB photons in ionised regions of the
Universe: the Sunyaev-Zel'dovich effect of galaxy clusters and the effects of a
spatially inhomogeneous re-ionisation of the Universe. Our study specifies and
predicts the non-gaussian signature of the secondary anisotropies induced by
these scattering effects. We find that our statistical discriminators allow us
to distinguish and highlight the non-gaussian signature of a process even if it
is combined with a larger gaussian one. We investigate the detectability of the
secondary anisotropy non-gaussian signature in the context of the future CMB
satellites (MAP and Planck Surveyor).",9905124v1
1999-06-03,The Anisotropy of Cosmic Ray Arrival Direction around 10^18eV,"Anisotropy in the arrival directions of cosmic rays around 10^{18}eV is
studied using data from the Akeno 20 km^2 array and the Akeno Giant Air Shower
Array (AGASA), using a total of about 216,000 showers observed over 15 years
above 10^{17}eV. In the first harmonic analysis, we have found significant
anisotropy of $\sim$ 4 % around 10^{18}eV, corresponding to a chance
probability of $\sim 10^{-5}$ after taking the number of independent trials
into account. With two dimensional analysis in right ascension and declination,
this anisotropy is interpreted as an excess of showers near the directions of
the Galactic Center and the Cygnus region. This is a clear evidence for the
existence of the galactic cosmic ray up to the energy of 10^{18}eV. Primary
particle which contribute this anisotropy may be proton or neutron.",9906056v1
1999-07-08,Reionization Revisited: Secondary CMB Anisotropies and Polarization,"Secondary CMB anisotropies and polarization provide a laboratory to study
structure formation in the reionized epoch. We consider the kinetic
Sunyaev-Zel'dovich effect from mildly nonlinear large-scale structure and show
that it is a natural extension of the perturbative Vishniac effect. If the gas
traces the dark matter to overdensities of order 10, as expected from
simulations, this effect is at least comparable to the Vishniac effect at
arcminute scales. On smaller scales, it may be used to study the thermal
history-dependent clustering of the gas. Polarization is generated through
Thomson scattering of primordial quadrupole anisotropies, kinetic (second order
Doppler) quadrupole anisotropies and intrinsic scattering quadrupole
anisotropies. Small scale polarization results from the density and ionization
modulation of these sources. These effects generically produce comparable E and
B-parity polarization, but of negligible amplitude (0.001-0.01 uK) in adiabatic
CDM models. However, the primordial and kinetic quadrupoles are observationally
comparable today so that a null detection of B-polarization would set
constraints on the evolution and coherence of the velocity field. Conversely, a
detection of a cosmological B-polarization even at large angles does not
necessarily imply the presence of gravity waves or vorticity. For these
calculations, we develop an all-sky generalization of the Limber equation that
allows for an arbitrary local angular dependence of the source for both scalar
and symmetric trace-free tensor fields on the sky.",9907103v2
2000-05-08,MAXIMA-1: A Measurement of the Cosmic Microwave Background Anisotropy on angular scales of 10 arcminutes to 5 degrees,"We present a map and an angular power spectrum of the anisotropy of the
cosmic microwave background (CMB) from the first flight of MAXIMA. MAXIMA is a
balloon-borne experiment with an array of 16 bolometric photometers operated at
100 mK. MAXIMA observed a 124 square degrees region of the sky with 10
arcminute resolution at frequencies of 150, 240 and 410 GHz. The data were
calibrated using in-flight measurements of the CMB dipole anisotropy. A map of
the CMB anisotropy was produced from three 150 and one 240 GHz photometer
without need for foreground subtractions. Analysis of this CMB map yields a
power spectrum for the CMB anisotropy over the range 36 < l < 785. The spectrum
shows a peak with an amplitude of 78 +/- 6 micro-Kelvin at l ~ 220 and an
amplitude varying between ~40 micro-Kelvin and ~50 micro-Kelvin for 400 < l <
785.",0005123v3
2001-02-15,Binned Cosmic Microwave Background Anisotropy Power Spectra: Peak Location,"We use weighted mean and median statistics techniques to combine individual
cosmic microwave background (CMB) anisotropy detections and determine binned,
multipole-space, CMB anisotropy power spectra. The resultant power spectra are
peaked. The derived weighted-mean CMB anisotropy power spectrum is not a good
representation of the individual measurements in a number of multipole-space
bins, if the CMB anisotropy is Gaussian and correlations between individual
measurements are small. This could mean that some observational error bars are
underestimated, possibly as a consequence of undetected systematic effects.
Discarding the most discrepant 5% of the measurements alleviates but does not
completely resolve this problem. The median-statistics power spectrum of this
culled data set is not as constraining as the weighted-mean power spectrum.
Nevertheless it indicates that there is more power at multipoles $\ell \sim
150-250$ than is expected in an open cold dark matter (CDM) model, and it is
more consistent with a flat CDM model. Unlike the weighted-mean power spectrum,
the median-statistics power spectrum at $\ell \sim 400-500$ does not exclude a
second peak in the flat CDM model.",0102264v1
2002-12-12,High Resolution Observations of the CMB Power Spectrum with ACBAR,"We report the first measurements of anisotropy in the cosmic microwave
background (CMB) radiation with the Arcminute Cosmology Bolometer Array
Receiver (ACBAR). The instrument was installed on the 2.1m Viper telescope at
the South Pole in January 2001; the data presented here are the product of
observations up to and including July 2002. The two deep fields presented here,
have had offsets removed by subtracting lead and trail observations and cover
approximately 24 deg^2 of sky selected for low dust contrast. These results
represent the highest signal to noise observations of CMB anisotropy to date;
in the deepest 150GHz band map, we reached an RMS of 8.0\mu K per 5' beam. The
3 degree extent of the maps, and small beamsize of the experiment allow the
measurement of the CMB anisotropy power spectrum over the range \ell = 150-3000
with resolution of \Delta \ell=150. The contributions of galactic dust and
radio sources to the observed anisotropy are negligible and are removed in the
analysis. The resulting power spectrum is found to be consistent with the
primary anisotropy expected in a concordance \Lambda CDM Universe.",0212289v1
2003-04-01,Decaying neutron propagation in the Galaxy and the Cosmic Ray anisotropy at 1 EeV,"We study the cosmic ray arrival distribution expected from a source of
neutrons in the galactic center at energies around 1 EeV and compare it with
the anisotropy detected by AGASA and SUGAR. Besides the point-like signal in
the source direction produced by the direct neutrons, an extended signal due to
the protons produced in neutron decays is expected. This associated proton
signal also leads to an excess in the direction of the spiral arm. For
realistic models of the regular and random galactic magnetic fields, the
resulting anisotropy as a function of the energy is obtained. We find that for
the anisotropy to become sufficiently suppressed below E\sim 10^{17.9}eV, a
significant random magnetic field component is required, while on the other
hand, this also tends to increase the angular spread of the associated proton
signal and to reduce the excess in the spiral arm direction. The source
luminosity required in order that the right ascension anisotropy be 4% for the
AGASA angular exposure corresponds to a prediction for the point-like flux from
direct neutrons compatible with the flux detected by SUGAR. We also analyse the
distinguishing features predicted for a large statistics southern observatory.",0304023v2
2003-05-09,Trade-off between angular resolution and straylight contamination in CMB anisotropy experiments. I. Pattern simulations,"The study of Cosmic Microwave Background (CMB) anisotropies represents one of
the most powerful Cosmological tools. After the great success of the two NASA's
satellite missions COBE and WMAP, Planck represents the third generation of
mm-wave instruments designed for space observations of CMB anisotropies within
the new Cosmic Vision 2020 ESA Science Programme. The Planck survey will cover
the whole sky with unprecedented sensitivity, angular resolution and frequency
coverage, using two instruments that share the focal region of a 1.5 m off-axis
dual reflector telescope: the Low Frequency Instrument (LFI) and the High
Frequency Instrument (HFI). Within the LFI optical interfaces optimisation
activity, two concurrent demands have to be satisfied: the best angular
resolution (which impacts the ability to reconstruct the anisotropy power
spectrum of the CMB anisotropies at high multipoles) and the lowest level of
straylight contamination (that may be one of the most critical sources of
systematic effects). We present the results of the optical simulations aimed to
establish the trade-off between angular resolution and straylight rejection,
carried out for the 100 GHz channel of Planck Low Frequency Instrument. Antenna
pattern of different models of dual profiled corrugated conical feed horns have
been simulated using advanced simulation techniques, considering the whole
spacecraft geometry in order to obtain truthful sidelobe predictions. Optical
computation accuracy necessary to provide strong straylight evaluation in
reasonable computational time is shown and the inadequacy of a Gaussian feed
model in realistic far pattern predictions is demonstrated. This paper is based
on LFI activities.",0305152v1
2004-02-17,The origin and implications of dark matter anisotropic cosmic infall on ~L* haloes,"We measure the anisotropy of dark matter flows on small scales in the near
environment of haloes using a large set of simulations. We rely on two
different approaches to quantify the anisotropy of the cosmic infall: we
measure the flows at the haloes' virial radius while describing the infalling
matter via fluxes through a spherical shell; we measure the spatial and
kinematical distributions of satellites and substructures around haloes
detected by the subclump finder ADAPTAHOP first described in the appendix. The
two methods are found to be in agreement both qualitatively and quantitatively
via one and two points statistics.The infall takes place preferentially in the
plane perpendicular to the direction defined by the halo's spin. We computed
the excess of equatorial accretion both through rings and via a harmonic
expansion of the infall. The level of anisotropy of infalling matter is found
to be ~15 %. The substructures have their spin orthogonal to their velocity
vector in the halo's rest frame at a level of about 5%, suggestive of an image
of a flow along filamentary structures which provides an explanation for the
measured anisotropy. We conclude that a halo does not see its environment as an
isotropic perturbation, investigate how the anisotropy is propagated inwards
using perturbation theory, and discuss briefly implications for weak lensing,
warps and the thickness of galactic disks.",0402405v1
2004-04-21,Statistical Significance of Small Scale Anisotropy in Arrival Directions of Ultra-High Energy Cosmic Rays,"Recently, the High Resolution Fly's Eye (HiRes) experiment claims that there
is no small scale anisotropy in the arrival distribution of ultra-high energy
cosmic rays (UHECRs) above $E>10^{19}$ eV contrary to the Akeno Giant Air
Shower Array (AGASA) observation. In this paper, we discuss the statistical
significance of this discrepancy between the two experiments. We calculate
arrival distribution of UHECRs above $10^{19}$ eV predicted by the source
models constructed using the Optical Redshift Survey galaxy sample. We apply
the new method developed by us for calculating arrival distribution in the
presence of the galactic magnetic field. The great advantage of this method is
that it enables us to calculate UHECR arrival distribution with lower energy
($\sim 10^{19}$ eV) than previous studies within reasonable time by following
only the trajectories of UHECRs actually reaching the earth. It has been
realized that the small scale anisotropy observed by the AGASA can be explained
with the source number density $\sim 10^{-5 \sim -6}$ Mpc$^{-3}$ assuming weak
extragalactic magnetic field ($B \le 1$ nG). We find that the predicted small
scale anisotropy for this source number density is also consistent with the
current HiRes data. We thus conclude that the statement by the HiRes experiment
that they do not find small scale anisotropy in UHECR arrival distribution is
not statistically significant at present. We also show future prospect of
determining the source number density with increasing amount of observed data.",0404411v2
2004-05-26,Cross-Correlation Studies between CMB Temperature Anisotropies and 21 cm Fluctuations,"During the transition from a neutral to a fully reionized universe,
scattering of cosmic microwave background (CMB) photons via free-electrons
leads to a new anisotropy contribution to the temperature distribution. If the
reionization process is inhomogeneous and patchy, the era of reionization is
also visible via brightness temperature fluctuations in the redshifted 21 cm
line emission from neutral Hydrogen. Since regions containing electrons and
neutral Hydrogen are expected to trace the same underlying density field, the
two are (anti) correlated and this is expected to be reflected in the
anisotropy maps via a correlation between arcminute-scale CMB temperature and
the 21 cm background. In terms of the angular cross-power spectrum,
unfortunately, this correlation is insignificant due to a geometric
cancellation associated with second order CMB anisotropies. The same
cross-correlation between ionized and neutral regions, however, can be studied
using a bispectrum involving large scale velocity field of ionized regions from
the Doppler effect, arcminute scale CMB anisotropies during reionization, and
the 21 cm background. While the geometric cancellation is partly avoided, the
signal-to-noise ratio related to this bispectrum is reduced due to the large
cosmic variance related to velocity fluctuations traced by the Doppler effect.
Unless the velocity field during reionization can be independently established,
it is unlikely that the correlation information related to the relative
distribution of ionized electrons and regions containing neutral Hydrogen can
be obtained with a combined study involving CMB and 21 cm fluctuations.",0405528v1
2005-04-27,"The Surprising Anisotropy of Fast Rotating, Disky Elliptical Galaxies","The projected kinematical properties of unequal-mass merger remnants of disk
galaxies are analysed and shown to agree well with observations of disky, fast
rotating elliptical galaxies. This supports the major merger hypothesis of
early-type galaxy formation. However, in contrast to previous claims, the
merger remnants are very anisotropic with values of the anisotropy parameter
that are similar to equal-mass merger remnants that form boxy, slowly rotating
ellipticals. Including gas in the simulations does not change this result
although the line-of-sight velocity profile and the intrinsic orbital structure
are strongly affected by the presenceof gas. The kinematical difference between
boxy and disky ellipticals appears not to be the amount of anisotropy but
rather rotation and the shape of the velocity dispersion tensor. The apparent
isotropy of observed disky ellipticals is shown to result from inclination
effects. Even small inclination angles strongly reduce the measured anisotropy
of fast rotating systems, seen in projection. A second problem is the limited
amount of information that is available when measuring only the central
velocity dispersion and a characteristic rotation and ellipticity. Methods are
investigated that allow a better determination of the intrinsic anisotropy of
fast rotating early-type galaxies with known inclination angles.",0504595v1
2005-08-08,The trail of discrete X-ray sources in the early-type galaxy NGC4261: anisotropy in the globular cluster distribution?,"Chandra images of the elliptical galaxy NGC4261 have revealed an anisotropy
in the spatial distribution of the off-nuclear X-ray sources, interpreted by
Zezas et al. as evidence of an association with a young stellar population. Our
independent analysis of archive X-ray (Chandra) and optical (INT and HST)
observations confirms the anisotropy of the X-ray sources but conducts to a
different interpretation for their origin. We find that nearly half of the
X-ray sources are associated to a globular cluster (optical counterpart)
suggesting that they are accreting low-mass X-ray binaries. Where color index
information is available, the X-ray sources are found to reside in red
(metal-rich) systems. The luminosity function of the X-ray sources is also
consistent with the one drawn from a population of Low Mass X-ray Binaries. We
further investigate the properties of the sample of point-like sources obtained
from archival optical images that we suggest are good globular cluster
candidates and for which we find that the projected spatial distribution is
non-homogeneous. In addition, we show that the distributions of the optical and
X-ray populations are very similar, which leads us to conclude that the spatial
anisotropy of the X-ray sources in NGC4261 is mostly a reflection of the
anisotropy of the globular cluster population.",0508189v1
2005-11-22,Mapping the large-scale anisotropy in the WMAP data,"Analyses of recent cosmic microwave background (CMB) observations have
provided increasing indications for the existence of large scale anisotropy in
the universe. Given the far reaching consequences of such an anisotropy for our
understanding of the universe, it is important to employ alternative indicators
in order to determine whether the reported anisotropy is cosmological in
origin, and if so extract further information that may be helpful for
identifying its causes. Here we propose a new directional indicator, based on
angular-separation histograms of pairs of pixels with similar temperatures in
the CMB map, which provides a measure of departure from statistical isotropy.
The main advantage of this indicator is that it can be used to generate a sky
map of large-scale anisotropies in the CMB temperature map, thus allowing a
possible additional window into their causes. Using this indicator, we find a
statistically significant (at 95% CL) preferred direction in the CMB data and
discuss how it compares with other such axes recently reported. We also show
that our findings are robust with respect to both the details of the method
used, and the choice of the WMAP CMB maps employed, including the three-year
CMB data released recently.",0511666v4
2006-01-19,The Contribution of the Intergalactic Medium to Cosmic Microwave Background Anisotropies,"We compute the power spectrum of the Cosmic Microwave Background temperature
anisotropies generated by the Intergalactic Medium. To estimate the electron
pressure along the line of sight and its contribution to the Sunyaev-Zeldovich
component of the CMB anisotropies, we assume the non-linear baryonic density
contrast is well described by a log-normal distribution. For model parameters
in agreement with observations and for an experiment operating in the
Rayleigh-Jeans regime, the largest IGM contribution is expected at scales
corresponding to multipole numbers of about 2000. The amplitude is rather
uncertain and could be as large as 100-200 [mikroK]^2, comparable to the
contribution of galaxy clusters. The actual value is strongly dependent on the
gas polytropic index and the amplitude of the matter power spectrum sigma_8. At
all redshifts, the largest contribution comes from scales very close to the
comoving baryon Jeans length. This scale is not yet resolved in numerical
simulations that follow the evolution of gas on cosmological scales. The
anisotropy generated by the Intergalactic Medium could make compatible the
excess of power measured by Cosmic Background Imager (CBI) on scales of l >
2000 with sigma_8=0.9. Taking the CBI result as an upper limit, the polytropic
index can be constrained to < 1.5 at 2-sigma level at redshifts z ~ 0.1-0.4.
With its large frequency coverage, the PLANCK satellite will be able to measure
the secondary anisotropies coming from hot gas. Cluster and Intergalactic
Medium contributions could be separated by cross correlating galaxy/cluster
catalogs with CMB maps. This measurement will determine the state of the gas at
low and intermediate redshifts.",0601424v1
2006-04-13,Unveiling Hidden Patterns in CMB Anisotropy Maps,"Bianchi VII_h models have been recently proposed to explain potential
anomalies in the CMB anisotropy as observed by WMAP. We investigate the
violation of statistical isotropy due to an embedded Bianchi VII_h templates in
the CMB anisotropy maps to determine whether the existence of a hidden Bianchi
template in the WMAP data is consistent with the previous null detection of the
bipolar power spectrum in the WMAP first year maps. We argue that although
correcting the WMAP maps for the Bianchi template may explain some features in
the WMAP data it may cause other anomalies such as preferred directions leading
to detectable levels of violation of statistical isotropy in the Bianchi
corrected maps. We compute the bipolar power spectrum for the low density
Bianchi VII_h models embedded in the background CMB anisotropy maps with the
power spectrum that have been shown in recent literature to best fit the first
year WMAP data. By examining statistical isotropy of these maps, we put a limit
of {\sigma/H}_0 < 2.77E-10 (99% CL) on the shear parameter in Bianchi VII_h
models.",0604279v2
2006-07-20,Is there a chance that the anisotropies in the cosmic microwave background detected by COBE are an artefact of COBE's image reconstruction?,"The COBE time ordered data (TOD) was reanalysed for anisotropies in the
cosmic microwave background with a novel technique that is much simpler and
more robust than used in the official analysis of the COBE TOD. The technique
extends the statistical concept of rejecting the null hypothesis to image
reconstruction by asking if the TOD is consistent with no anisotropies outside
the galactic band. If it is assumed that the instrumentation noise is ideal, as
appears to be the case in the official analysis, the null hypothesis can be
rejected to 28 sigma, a highly significant detection. However, the official
analysis presents no information supporting the ideal noise assumption to the
level required to reject the null hypothesis. The interaction of COBE's
calibration error of roughly 3.0% with the brightest regions of the galactic
band in combination with the reconstruction algorithm may have introduced
artefacts roughly of the size and spectral signature of the 10ppm anisotropies
reported by COBE. Data from follow up missions have similar problems with
calibration errors that may have resulted in similar sky maps to COBE. It is
pointed out that either a few hours of repetitive circular scans using the WMAP
satellite or the single beam antenna of the soon-to-be-launched Planck
satellite should provide definitive evidence as to the existence or non
existence of the 10ppm anisotropies without the use of image reconstruction.",0607484v5
2006-12-16,Dark matter annihilation or unresolved astrophysical sources? Anisotropy probe of the origin of cosmic gamma-ray background,"The origin of the cosmic gamma-ray background (CGB) is a longstanding mystery
in high-energy astrophysics. Possible candidates include ordinary astrophysical
objects such as unresolved blazars, as well as more exotic processes such as
dark matter annihilation. While it would be difficult to distinguish them from
the mean intensity data alone, one can use anisotropy data instead. We
investigate the CGB anisotropy both from unresolved blazars and dark matter
annihilation (including contributions from dark matter substructures), and find
that the angular power spectra from these sources are very different. We then
focus on detectability of dark matter annihilation signals using the anisotropy
data, by treating the unresolved blazar component as a known background. We
find that the dark matter signature should be detectable in the angular power
spectrum of the CGB from two-year all-sky observations with the Gamma Ray Large
Area Space Telescope (GLAST), as long as the dark matter annihilation
contributes to a reasonable fraction, e.g., >~ 0.3, of the CGB at around 10
GeV. We conclude that the anisotropy measurement of the CGB with GLAST should
be a powerful tool for revealing the CGB origin, and potentially for the first
detection of dark matter annihilation.",0612467v2
2000-03-13,Bond and charge density waves in the isotropic interacting two-dimensional quarter-filled band and the insulating state proximate to organic superconductivity,"We report two surprising results regarding the nature of the spatial broken
symmetries in the two-dimensional (2D), quarter-filled band with strong
electron-electron interactions. First, in direct contradiction to the
predictions of one-electron theory, we find a coexisting ``bond-order and
charge density wave'' (BCDW) insulating ground state in the 2D rectangular
lattice for all anisotropies, including the isotropic limit. Second, we find
that the BCDW further coexists with a spin-density wave (SDW) in the range of
large anisotropy. Further, in contrast to the interacting half-filled band, in
the interacting quarter-filled band there are two transitions: first, a similar
singlet-to-AFM/SDW transition for large anisotropy and second, an
AFM/SDW-to-singlet transition at smaller anisotropy. We discuss how these
theoretical results apply to the insulating states that are proximate to the
superconducting states of 2:1 cationic charge-transfer solids (CTS).
  An important consequence of this work is the suggestion that organic
superconductivity is related to the proximate Coulomb-induced BCDW, with the
SDW that coexists for large anisotropies being also a consequence of the BCDW,
rather than the driver of superconductivity.",0003200v2
2000-10-07,Enhanced Bound State Formation in Two Dimensions via Stripe-Like Hopping Anisotropies,"We have investigated two-electron bound state formation in a square
two-dimensional t-J-U model with hopping anisotropies for zero electron
density; these anisotropies are introduced to mimic the hopping energies
similar to those expected in stripe-like arrangements of holes and spins found
in various transition metal oxides. In this report we provide analytical
solutions to this problem, and thus demonstrate that bound-state formation
occurs at a critical exchange coupling, J_c, that decreases to zero in the
limit of extreme hopping anisotropy t_y/t_x -> 0. This result should be
contrasted with J_c/t = 2 for either a one-dimensional chain, or a
two-dimensional plane with isotropic hopping. Most importantly, this behaviour
is found to be qualitatively similar to that of two electrons on the two-leg
ladder problem in the limit of t_interchain/t_intrachain -> 0. Using the latter
result as guidance, we have evaluated the pair correlation function, thus
determining that the bound state corresponds to one electron moving along one
chain, with the second electron moving along the opposite chain, similar to two
electrons confined to move along parallel, neighbouring, metallic stripes. We
emphasize that the above results are not restricted to the zero density limit -
we have completed an exact diagonalization study of two holes in a 12 X 2
two-leg ladder described by the t-J model and have found that the
above-mentioned lowering of the binding energy with hopping anisotropy persists
near half filling.",0010116v1
2003-07-05,Domain-wall profile in the presence of anisotropic exchange interactions: Effective on-site anisotropy,"Starting from a D-dimensional XXZ ferromagnetic Heisenberg model in an
hypercubic lattice, it is demonstrated that the anisotropy in the exchange
coupling constant leads to a D-dependent effective on-site anisotropy
interaction often ignored for D>1. As a result the effective width of the wall
depends on the dimensionality of the system. It is shown that the effective
one-dimensional Hamiltonian is not the one-dimensional XXZ version as assumed
in previous theoretical work. We derive a new expression for the wall profile
that generalizes the standard Landau-Lifshitz form. Our results are found to be
in very good agreement with earlier numerical work using the Monte Carlo
method. Preceding theories concerning the domain wall contribution to
magnetoresistance have considered the role of D only through the modification
of the density of states in the electronic band structure. This Brief Report
reveals that the wall profile itself contains an additional D dependence for
the case of anisotropic exchange interactions.",0307120v2
2005-05-12,"Perpendicular magnetization reversal, magnetic anisotropy, multi-step spin switching, and domain nucleation and expansion in Ga1-xMnxAs films","We present a comprehensive study of the reversal process of perpendicular
magnetization in thin layers of the ferromagnetic semiconductor Ga1-xMnxAs. For
this investigation we have purposely chosen Ga1-xMnxAs with a low Mn
concentration (x ~ 0.02), since in such specimens contributions of cubic and
uniaxial anisotropy parameters are comparable, allowing us to identify the role
of both types of anisotropy in the magnetic reversal process. As a first step
we have systematically mapped out the angular dependence of ferromagnetic
resonance in thin Ga1-xMnxAs layers, which is a highly effective tool for
obtaining the magnetic anisotropy parameters of the material. The process of
perpendicular magnetization reversal was then studied by magneto-transport
(i.e., Hall effect and planar Hall effect measurements). These measurements
enable us to observe coherent spin rotation and non-coherent spin switching
between the (100) and (010) planes. A model is proposed to explain the observed
multi-step spin switching. The agreement of the model with experiment indicates
that it can be reliably used for determining magnetic anisotropy parameters
from magneto-transport data. An interesting characteristic of perpendicular
magnetization reversal in Ga1-xMnxAs with low x is the appearance of a double
hysteresis loops in the magnetization data. This double-loop behavior can be
understood by generalizing the proposed model to include the processes of
domain nucleation and expansion.",0505322v1
2005-12-12,Angular Dependence of Exchange Anisotropy on Cooling Field in FM/Fluoride Thin Films,"Exchange anisotropy in ferromagnet/antiferromagnet (FM/AF) films is usually
introduced along the cooling field or FM magnetization direction. Here we
investigate the dependence of the exchange anisotropy, loop bifurcation, and
reversal mechanism on the cooling field direction using vector magnetometry.
Three types of samples (FM=Fe, Ni /AF = FeF2, MnF2) have been studied where the
AF layer is epitaxial (110), twinned (110), and polycrystalline. With an
epitaxial AF which has one spin axis, the cooling field orients the exchange
field along the spin axis. Applying the cooling field perpendicular to the spin
axis results in bifurcated loops, whose shape evolves with the cooling field
geometry and strength. With a twinned AF where there are two orthogonal spin
axes, the exchange field direction is along the bisector of the spin axes that
encompass the cooling field. With a polycrystalline AF, the exchange field
direction is the same as the cooling field. Transverse hysteresis loops show
that when the exchange field has a component perpendicular to the applied
field, the magnetization reversal occurs by rotation in the direction of the
perpendicular component. Our results demonstrate that in fluoride films, the
exchange field is established primarily by the AF anisotropy direction, and
only to a lesser extent the cooling field or the magnetization direction. The
bifurcated loops are due to a distribution of AF anisotropies and large AF
domain sizes. Furthermore, the magnetization reversal process is extremely
sensitive to the exchange field direction.",0512257v1
2006-06-28,The random-anisotropy model in the strong-anisotropy limit,"We investigate the nature of the critical behaviour of the random-anisotropy
Heisenberg model (RAM), which describes a magnetic system with random uniaxial
single-site anisotropy, such as some amorphous alloys of rare earths and
transition metals. In particular, we consider the strong-anisotropy limit
(SRAM), in which the Hamiltonian can be rewritten as the one of an Ising
spin-glass model with correlated bond disorder: H = - J \sum_{< xy >} j_{xy}
\sigma_x \sigma_y, where j_{xy} = \vec{u}_x \cdot \vec{u}_y and \vec{u}_x is a
random three-component unit vector. We performed Monte Carlo simulations of the
SRAM on simple cubic L^3 lattices, up to L=30, measuring correlation functions
of the replica-replica overlap, which is the order parameter at a glass
transition. The corresponding results show critical behaviour and finite-size
scaling. They provide evidence of a finite-temperature continuous transition
with critical exponents \eta_o=-0.24(4) and \nu_o=2.4(6). These results are
close to the corresponding estimates that have been obtained in the usual Ising
spin-glass model with uncorrelated bond disorder, suggesting that the two
models belong to the same universality class. This is consistent with arguments
that suggest that the disorder correlations present in the SRAM are irrelevant.",0606728v1
2004-11-03,Probing anisotropies of gravitational-wave backgrounds with a space-based interferometer: geometric properties of antenna patterns and their angular power,"We discuss the sensitivity to anisotropies of stochastic gravitational-wave
backgrounds (GWBs) observed via space-based interferometer. In addition to the
unresolved galactic binaries as the most promising GWB source of the planned
Laser Interferometer Space Antenna (LISA), the extragalactic sources for GWBs
might be detected in the future space missions. The anisotropies of the GWBs
thus play a crucial role to discriminate various components of the GWBs. We
study general features of antenna pattern sensitivity to the anisotropies of
GWBs beyond the low-frequency approximation. We show that the sensitivity of
space-based interferometer to GWBs is severely restricted by the data
combinations and the symmetries of the detector configuration. The spherical
harmonic analysis of the antenna pattern functions reveals that the angular
power of the detector response increases with frequency and the detectable
multipole moments with effective sensitivity h_{eff} \sim 10^{-20} Hz^{-1/2}
may reach $\ell \sim$ 8-10 at $f \sim f_*=10$ mHz in the case of the single
LISA detector. However, the cross correlation of optimal interferometric
variables is blind to the monopole (\ell=0) intensity anisotropy, and also to
the dipole (\ell=1) in some case, irrespective of the frequency band. Besides,
all the self-correlated signals are shown to be blind to the odd multipole
moments (\ell=odd), independently of the frequency band.",0411017v2
2007-01-27,Thermodynamics of Ideal Boson and Fermion Gases in the Static Taub Universe,"Some thermodynamic quantities of nonrelativistic ideal boson and fermion
gases in the static Taub universe are derived to first order in a small
anisotropy parameter d which measuring the deformation from the spherical
Einstein universe. They are used to investigate the problem of how the
curvature anisotropy affects the thermodynamic behaviors of an ideal gas. It is
found that, when the universe is in the oblate configuration (i.e., d > 0), the
effect of curvature anisotropy is to increase the number of the fraction in the
Bose-Einstein condensation and to decrease the fermion distribution function at
low temperature. When the universe is in the prolate configuration (i.e., d <
0), the effects of curvature anisotropy on the thermodynamic quantities is
contrary to that in the oblate configuration. The density matrix of a two
particle system is evaluated and it is used to define the ""statistical
interparticle potential"" as an attempt to give a ""statistical interpretation""
about the found thermodynamic behaviors. It is found that when the universe is
in the oblate (prolate) configuration the curvature anisotropy will enhance
(reduce) both the ""statistic attraction"" among the bosons and ""statistical
repulsion"" among the fermions. It is expected that such a behavior will also be
shown in the relativistic system.",0701147v1
2000-10-16,Anomalous scaling in two models of the passive scalar advection: Effects of anisotropy and compressibility,"The problem of the effects of compressibility and large-scale anisotropy on
anomalous scaling behavior is considered for two models describing passive
advection of scalar density and tracer fields. The advecting velocity field is
Gaussian, $\delta$-correlated in time, and scales with a positive exponent
$\epsilon$. Explicit inertial-range expressions for the scalar correlation
functions are obtained; they are represented by superpositions of power laws
with nonuniversal amplitudes and universal (dependent only on $\epsilon$ and
$\alpha$, the compressibility parameter) anomalous exponents. The complete set
of anomalous exponents for the pair correlation functions is found
nonperturbatively, in any space dimension d, using the zero-mode technique. For
higher-order correlation functions, the anomalous exponents are calculated to
$O(\epsilon^{2})$ using the renormalization group. Like in the incompressible
case, the exponents exhibit a hierarchy related to the degree of anisotropy:
the leading contributions to the even correlation functions are given by the
exponents from the isotropic shell, in agreement with the idea of restored
small-scale isotropy. As the degree of compressibility increases, the
corrections become closer to the leading terms. The small-scale anisotropy
reveals itself in the odd ratios of correlation functions: the skewness factor
is slowly decreasing going down to small scales for the incompressible case,
but becomes increasing if $\alpha$ is large enough. The higher odd
dimensionless ratios (hyperskewness etc.) increase, thus signalling the
persistent small-scale anisotropy; this effect becomes more pronounced for
larger values of $\alpha$.",0010029v1
2002-08-02,Field-dependent surface impedance tensor in amorphous wires with two types of magnetic anisotropy: helical and circumferential,"This paper concerns the theoretical and experimental investigation of the
magneto-impedance (MI) effect in amorphous wires in terms of the surface
impedance tensor. Physical concepts of MI and problems of significant practical
importance are discussed using the results obtained. The theoretical analysis
is based on employing the asymptotic-series expansion method of solving the
Maxwell equations for a ferromagnetic wire with an ac permeability tensor of a
general form associated with magnetisation rotation. The magnetic
structure-dependent impedance tensor is calculated for any frequency and
external magnetic field, and is not restricted to the case when only strong
skin-effect is present. This approach allows us to develop a rigorous
quantitative analysis of MI characteristics in wires, depending on the type of
magnetic anisotropy, the magnitude of dc bias current, and an excitation
method. The theoretical model has been tested by comparing the obtained results
with experiment. For the sake of an adequate comparison, the full impedance
tensor is measured in CoFeSiB and CoSiB amorphous wires having a
circumferential and helical anisotropy, respectively, by determining the S21
parameter. In cases, when the rotational dynamics is responsible for the
impedance behaviour, there is a reasonable agreement between the experimental
and theoretical results. Such effects as the ac biased asymmetrical MI in wires
with a circumferential anisotropy, the transformation in MI behaviour caused by
a dc current (from that having a symmetric hysteresis to an asymmetric
anhysteretic one) in wires with a helical anisotropy are discussed.",0208012v1
2006-10-11,A New Light-Speed Anisotropy Experiment: Absolute Motion and Gravitational Waves Detected,"Data from a new experiment measuring the anisotropy of the one-way speed of
EM waves in a coaxial cable, gives the speed of light as 300,000+/-400+/-20km/s
in a measured direction RA=5.5+/-2hrs, Dec=70+/-10deg S, is shown to be in
excellent agreement with the results from seven previous anisotropy
experiments, particularly those of Miller (1925/26), and even those of
Michelson and Morley (1887). The Miller gas-mode interferometer results, and
those from the RF coaxial cable experiments of Torr and Kolen (1983), De Witte
(1991) and the new experiment all reveal the presence of gravitational waves,
as indicated by the last +/- variations above, but of a kind different from
those supposedly predicted by General Relativity. The understanding of the
operation of the Michelson interferometer in gas-mode was only achieved in 2002
and involved a calibration for the interferometer that necessarily involved
Special Relativity effects and the refractive index of the gas in the light
paths. The results demonstrate the reality of the Fitzgerald-Lorentz
contraction as an observer independent relativistic effect. A common
misunderstanding is that the anisotropy of the speed of light is necessarily in
conflict with Special Relativity and Lorentz symmetry - this is explained. All
eight experiments and theory show that we have both anisotropy of the speed of
light and relativistic effects, and that a dynamical 3-space exists - that
absolute motion through that space has been repeatedly observed since 1887.
These developments completely change fundamental physics and our understanding
of reality.",0610076v1
1997-03-19,Quantum Noise and Polarization Fluctuations in Vertical Cavity Surface Emitting Lasers,"We investigate the polarization fluctuations caused by quantum noise in
quantum well vertical cavity surface emitting lasers (VCSELs). Langevin
equations are derived on the basis of a generalized rate equation model in
which the influence of competing gain-loss and frequency anisotropies is
included. This reveals how the anisotropies and the quantum well confinement
effects shape the correlations and the magnitude of fluctuations in ellipticity
and in polarization direction. According to our results all parameters used in
the rate equations may be obtained experimentally from precise time resolved
measurements of the intensity and polarization fluctuations in the emitted
laser light. To clarify the effects of anisotropies and of quantum well
confinement on the laser process in VCSELs we therefore propose time resolved
measurements of the polarization fluctuations in the laser light. In
particular, such measurements allow to distinguish the effects of frequency
anisotropy and of gain-loss anisotropy and would provide data on the spin
relaxation rate in the quantum well structure during cw operation as well as
representing a new way of experimentally determinig the linewidth enhancement
factor alpha.",9703034v1
2007-04-09,Excitation Spectrum Gap and Spin-Wave Stiffness of XXZ Heisenberg Chains: Global Renormalization-Group Calculation,"The anisotropic XXZ spin-1/2 Heisenberg chain is studied using
renormalization-group theory. The specific heats and nearest-neighbor spin-spin
correlations are calculated thoughout the entire temperature and anisotropy
ranges in both ferromagnetic and antiferromagnetic regions, obtaining a global
description and quantitative results. We obtain, for all anisotropies, the
antiferromagnetic spin-liquid spin-wave velocity and the Isinglike
ferromagnetic excitation spectrum gap, exhibiting the spin-wave to spinon
crossover. A number of characteristics of purely quantum nature are found: The
in-plane interaction s_i^x s_j^x + s_i^y s_j^y induces an antiferromagnetic
correlation in the out-of-plane s_i^z component, at higher temperatures in the
antiferromagnetic XXZ chain, dominantly at low temperatures in the
ferromagnetic XXZ chain, and, in-between, at all temperatures in the XY chain.
We find that the converse effect also occurs in the antiferromagnetic XXZ
chain: an antiferromagnetic s_i^z s_j^z interaction induces a correlation in
the s_i^xy component. As another purely quantum effect, (i) in the
antiferromagnet, the value of the specific heat peak is insensitive to
anisotropy and the temperature of the specific heat peak decreases from the
isotropic (Heisenberg) with introduction of either type (Ising or XY)
anisotropy; (ii) in complete contrast, in the ferromagnet, the value and
temperature of the specific heat peak increase with either type of anisotropy.",0704.1064v2
2007-06-18,Some physical displays of the space anisotropy relevant to the feasibility of its being detected at a laboratory,"The impact of local space anisotropy on the transverse Doppler effect is
examined. Two types of laboratory experiments aimed at seeking and measuring
the local space anisotropy are proposed. In terms of the conventional special
relativity theory, which treats 3D space to be locally isotropic, the
experiments are of the type of ``null-experiments''. In the first-type
experiments, a feasible Doppler shift of frequency is measured by the
M\""ossbauer effect, with the M\""ossbauer source and absorber being located at
two identical and diametrically opposed distances from the center of a rapidly
rotating rotor, while the $\gamma$-quanta are recorded by two stationary and
oppositely positioned proportional counters. Either of the counters records
only those $\gamma$-quanta that passed through the absorber at the moment of
the passage of the latter near a counter. The second-type experiments are made
using the latest radio physics techniques for generating monochromatic
oscillations and for recording weak signals. The effect expected due to space
anisotropy consists in frequency modulation of the harmonic oscillations coming
to a receiver that rotates at a constant velocity around the monochromatic wave
emitter. In this case the modulation depth proves to be proportional to the
space anisotropy magnitude.",0706.2621v1
2008-04-08,Piezo-control of magnetic anisotropy in GaMnAs: Reversible manipulation of magnetization orientation and irreversible magnetization switching,"We have investigated the magnetic properties of a piezoelectric
actuator/ferromagnetic semiconductor hybrid structure. Using a GaMnAs epilayer
as the ferromagnetic semiconductor and applying the piezo-stress along its
[110] direction, we quantify the magnetic anisotropy as a function of the
voltage V_p applied to the piezoelectric actuator using anisotropic
magnetoresistance techniques. We find that the easy axis of the strain-induced
uniaxial magnetic anisotropy contribution can be inverted from the [110] to the
[1-10] direction via the application of appropriate voltages V_p. At T=5K the
magnetoelastic term is a minor contribution to the magnetic anisotropy.
Nevertheless, we show that the switching fields of rho(H) loops are shifted as
a function of V_p at this temperature. At 50K - where the magnetoelastic term
dominates the magnetic anisotropy - we are able to tune the magnetization
orientation by about 70 degree solely by means of the electrical voltage V_p
applied. Furthermore, we derive the magnetostrictive constant lambda_111 as a
function of temperature and find values consistent with earlier results. We
argue that the piezo-voltage control of magnetization orientation is directly
transferable to other ferromagnetic/piezoelectric hybrid structures, paving the
way to innovative multifunctional device concepts. As an example, we
demonstrate piezo-voltage induced irreversible magnetization switching at
T=40K, which constitutes the basic principle of a nonvolatile memory element.",0804.1336v1
2009-01-28,A Measurement of Arcminute Anisotropy in the Cosmic Microwave Background with the Sunyaev-Zel'dovich Array,"We present 30 GHz measurements of the angular power spectrum of the cosmic
microwave background (CMB) obtained with the Sunyaev-Zel'dovich Array. The
measurements are sensitive to arcminute angular scales, where secondary
anisotropy from the Sunyaev-Zel'dovich effect (SZE) is expected to dominate.
For a broad bin centered at multipole 4066 we find 67+77-50 uK^2, of which
26+/-5 uK^2 is the expected contribution from primary CMB anisotropy and
80+/-54 uK^2 is the expected contribution from undetected radio sources. These
results imply an upper limit of 155 uK^2 (95% CL) on the secondary contribution
to the anisotropy in our maps. This level of SZE anisotropy power is consistent
with expectations based on recent determinations of the normalization of the
matter power spectrum, i.e., sigma_8~0.8.",0901.4342v2
2009-05-18,Structure of energy level degeneracy of a single-spin model from a view point of symmetry of the spin anisotropy and its nontrivial spin($S$)-dependence on the higher order anisotropy,"We study structure of the gapless points (diabolical points) at zero magnetic
field ($H_z=0$) of single-spin models with spin anisotropies. Nontrivial
appearance of diabolical points at finite transverse field $H_x$ has been
studied from the view point of interference of the Berry phase, and related
phenomena have been experimentally found in the single molecular magnet Fe$_8$.
We study effects of the orthorhombic single-ion anisotropy $E(S_+^2+S_-^2)$ and
find a symmetry associated with the degeneracy, which provides a clear picture
of the global structure of energy level diagram including the excited states.
Moreover, we study effects of the higher order anisotropy $C(S_+^4+S_-^4)$, and
find that, in contrast to the semiclassical limit $(S\to\infty)$, location of a
pair annihilation of the diabolical point does not coincides with a point at
which a pair of diabolical points appears in nonzero $H_y$ space(bifurcation
points). Distance between the annihilation and bifurcation points vanishes when
$S\to\infty$, which restores the semiclassical result. We obtain a complete
structure of the diabolical points in the $(C,H_x)$ plane.",0905.2780v2
2009-09-18,Detecting Gamma-Ray Anisotropies from Decaying Dark Matter: Prospects for Fermi LAT,"Decaying dark matter particles could be indirectly detected as an excess over
a simple power law in the energy spectrum of the diffuse extragalactic
gamma-ray background. Furthermore, since the Earth is not located at the center
of the Galactic dark matter halo, the exotic contribution from dark matter
decay to the diffuse gamma-ray flux is expected to be anisotropic, offering a
complementary method for the indirect search for decaying dark matter
particles. In this paper we discuss in detail the expected dipole-like
anisotropies in the dark matter signal, taking also into account the radiation
from inverse Compton scattering of electrons and positrons from dark matter
decay. A different source for anisotropies in the gamma-ray flux are the dark
matter density fluctuations on cosmic scales. We calculate the corresponding
angular power spectrum of the gamma-ray flux and comment on observational
prospects. Finally, we calculate the expected anisotropies for the decaying
dark matter scenarios that can reproduce the electron/positron excesses
reported by PAMELA and the Fermi LAT, and we estimate the prospects for
detecting the predicted gamma-ray anisotropy in the near future.",0909.3514v2
2009-11-18,Anisotropic nonlinear elasticity in a spherical bead pack: influence of the fabric anisotropy,"Stress-strain measurements and ultrasound propagation experiments in glass
bead packs have been simultaneously conducted to characterize the
stress-induced anisotropy under uniaxial loading. These measurements, realized
respectively with finite and incremental deformations of the granular assembly,
are analyzed within the framework of the effective medium theory based on the
Hertz-Mindlin contact theory. Our work shows that both compressional and shear
wave velocities and consequently the incremental elastic moduli agree fairly
well with the effective medium model by Johnson et al. [J. Appl. Mech. 65, 380
(1998)], but the anisotropic stress ratio resulting from finite deformation
does not at all. As indicated by numerical simulations, the discrepancy may
arise from the fact that the model doesn't properly allow the grains to relax
from the affine motion approximation. Here we find that the interaction nature
at the grain contact could also play a crucial role for the relevant prediction
by the model; indeed, such discrepancy can be significantly reduced if the
frictional resistance between grains is removed. Another main experimental
finding is the influence of the inherent anisotropy of granular packs, realized
by different protocols of the sample preparation. Our results reveal that
compressional waves are more sensitive to the stress-induced anisotropy,
whereas the shear waves are more sensitive to the fabric anisotropy, not being
accounted in analytical effective medium models.",0911.3542v1
2010-05-05,Anisotropies in the Diffuse Gamma-Ray Background from Dark Matter with Fermi LAT: a closer look,"We perform a detailed study of the sensitivity to the anisotropies related to
Dark Matter (DM) annihilation in the Isotropic Gamma-Ray Background (IGRB) as
measured by the Fermi Large Area Telescope (Fermi-LAT). For the first time, we
take into account the effects of the Galactic foregrounds and use a realistic
representation of the Fermi-LAT. We consider DM anisotropies of extra-galactic
origin and of Galactic origin (which can be generated through annihilation in
the Milky Way sub-structures) as opposed to a background of anisotropies
generated by sources of astrophysical origin, blazars for example. We find that
with statistics from 5 years of observation Fermi is sensitive to a DM
contribution at the level of the thermal-relic cross section depending on the
DM mass and annihilation mode. The anisotropy method for DM searches has a
sensitivity comparable to the usual methods based only on the energy spectrum
and thus constitutes an independent and complementary piece of information in
the DM puzzle. (abridged)",1005.0843v2
2010-07-28,Cosmological density perturbations from conformal scalar field: infrared properties and statistical anisotropy,"We consider a scenario in which primordial scalar perturbations are generated
when complex conformal scalar field rolls down its negative quartic potential.
Initially, these are the perturbations of the phase of this field; they are
converted into the adiabatic perturbations at a later stage. A potentially
dangerous feature of this scenario is the existence of perturbations in the
radial field direction, which have red power spectrum. We show, however, that
to the linear order in the small parameter - the quartic self-coupling - the
infrared effects are completely harmless, as they can be absorbed into field
redefinition. We then evaluate the statistical anisotropy inherent in the model
due to the existence of the long-ranged radial perturbations. To the linear
order in the quartic self-coupling the statistical anisotropy is free of the
infrared effects. The latter show up at the quadratic order in the
self-coupling and result in the mild (logarithmic) enhancement of the
corresponding contribution to the statistical anisotropy. The resulting
statistical anisotropy is a combination of a larger term which, however, decays
as momentum increases, and a smaller term which is independent of momentum.",1007.4949v2
2010-09-03,Local Anisotropy of Fluids using Minkowski Tensors,"Statistics of the free volume available to individual particles have
previously been studied for simple and complex fluids, granular matter,
amorphous solids, and structural glasses. Minkowski tensors provide a set of
shape measures that are based on strong mathematical theorems and easily
computed for polygonal and polyhedral bodies such as free volume cells (Voronoi
cells). They characterize the local structure beyond the two-point correlation
function and are suitable to define indices $0\leq \beta_\nu^{a,b}\leq 1$ of
local anisotropy. Here, we analyze the statistics of Minkowski tensors for
configurations of simple liquid models, including the ideal gas (Poisson point
process), the hard disks and hard spheres ensemble, and the Lennard-Jones
fluid. We show that Minkowski tensors provide a robust characterization of
local anisotropy, which ranges from $\beta_\nu^{a,b}\approx 0.3$ for vapor
phases to $\beta_\nu^{a,b}\to 1$ for ordered solids. We find that for fluids,
local anisotropy decreases monotonously with increasing free volume and
randomness of particle positions. Furthermore, the local anisotropy indices
$\beta_\nu^{a,b}$ are sensitive to structural transitions in these simple
fluids, as has been previously shown in granular systems for the transition
from loose to jammed bead packs.",1009.0601v2
2010-11-11,Competition between supersolid phases and magnetisation plateaux in the frustrated easy-axis antiferromagnet on a triangular lattice,"The majority of magnetic materials possess some degree of magnetic
anisotropy, either at the level of a single ion, or in the exchange
interactions between different magnetic ions. Where these exchange interactions
are also frustrated, the competition between them and anisotropy can stabilize
a wide variety of new phases in applied magnetic field. Motivated by the
hexagonal delafossite 2H-AgNiO 2, we study the Heisenberg antiferromagnet on a
layered triangular lattice with competing first- and second-neighbour
interactions and single-ion easy-axis anisotropy. Using a combination of
classical Monte Carlo simulation, mean-field analysis, and Landau theory, we
establish the magnetic phase diagram of this model as a function of temperature
and magnetic field for a fixed ratio of exchange interactions, but with values
of easy-axis anisotropy D extending from the Heisenberg (D =0) to the Ising
(D=&#8734) limits. We uncover a rich variety of different magnetic phases.
These include several phases which are magnetic supersolids (in the sense of
Matsuda and Tstuneto or Liu and Fisher), one of which may already have been
observed in AgNiO 2. We explore how this particular supersolid arises through
the closing of a gap in the spin-wave spectrum, and how it competes with rival
collinear phases as the easy-axis anisotropy is increased. The finite
temperature properties of this phase are found to be different from those of
any previously studied magnetic supersolid.",1011.2698v2
2011-03-22,Dipolar Interactions between Iron-Oxide Nanoparticles in Frozen Ferrofluids and Ferronematics,"We present a detailed study of the magnetic behavior of iron-oxide
(gamma-Fe2O3 and Fe3O4) nanoparticles constituents of ferrofluids (FF's) with
average particle sizes <d> = 2.5 and 10 nm. The particles were dispersed in the
frozen liquid carrier (pure FF) and in a frozen lyotropic liquid crystalline
matrix in the nematic phase or ferronematic (FN) (ferrolyomesophase). Both FF
and FN phases displayed superparamagnetic (SPM) behaviour at room temperature,
with blocking temperatures T_B ~ 10 and 100 K for <d> = 2.5 and 10 nm,
respectively. Dynamic ac susceptibility measurements showed a thermally
activated N\'eel-Brown dependence of the blocking temperature with applied
frequency. Our results show that dipolar interactions are small, but
non-negligible, as compared to the single-particle energy barriers from
magnetic anisotropy. From the fit of ac susceptibility we calculated the
effective magnetic anisotropy constant K_{eff} for 2.5 nm maghemite particles.
Although interparticle interactions present in highly diluted samples do not
appreciably modify the dynamic magnetic behavior of isolated particles, the
calculated magnetic anisotropy were abut one order of magnitude larger that the
bulk materials, suggesting the existence of large surface anisotropy. Using the
thermally activated model to fit the dynamic data yielded effective energy
barriers Ea = 3.5x10^{-21} J. From these data, we obtained K_{eff} = 422 kJ/m^3
for the single-particle effective magnetic anisotropy.",1103.4403v1
2011-03-23,"On the origin of non-monotonic doping dependence of the in-plane resistivity anisotropy in Ba(Fe$_{1-x}T_x$)$_2$As$_2$, $T$ = Co, Ni and Cu","The in-plane resistivity anisotropy has been measured for detwinned single
crystals of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$.
The data reveal a non-monotonic doping dependence, similar to previous
observations for Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Magnetotransport measurements
of the parent compound reveal a non-linear Hall coefficient and a strong linear
term in the transverse magnetoresistance. Both effects are rapidly suppressed
with chemical substitution over a similar compositional range as the onset of
the large in-plane resistivity anisotropy. It is suggested that the relatively
small in-plane anisotropy of the parent compound in the spin density wave state
is due to the presence of an isotropic, high mobility pocket of reconstructed
Fermi surface. Progressive suppression of the contribution to the conductivity
arising from this isotropic pocket with chemical substitution eventually
reveals the underlying in-plane anisotropy associated with the remaining FS
pockets.",1103.4535v2
2011-03-31,Phase diagram for the $ν=0$ quantum Hall state in monolayer graphene,"The $\nu=0$ quantum Hall state in a defect-free graphene sample is studied
within the framework of quantum Hall ferromagnetism. We perform a systematic
analysis of the pseudospin anisotropies, which arise from the valley and
sublattice asymmetric short-range electron-electron (e-e) and electron-phonon
(e-ph) interactions. The phase diagram, obtained in the presence of generic
pseudospin anisotropy and the Zeeman effect, consists of four phases
characterized by the following orders: spin-polarized ferromagnetic, canted
antiferromagnetic, charge density wave, and Kekul\'{e} distortion. We take into
account the Landau level mixing effects and show that they result in the key
renormalizations of parameters. First, the absolute values of the anisotropy
energies become greatly enhanced and can significantly exceed the Zeeman
energy. Second, the signs of the anisotropy energies due to e-e interactions
can change upon renormalization. A crucial consequence of the latter is that
the short-range e-e interactions alone could favor any state on the phase
diagram, depending on the details of interactions at the lattice scale. On the
other hand, the leading e-ph interactions always favor the Kekul\'{e}
distortion order. The possibility of inducing phase transitions by tilting the
magnetic field is discussed.",1103.6285v2
2011-08-02,Velocity Anisotropy as a Diagnostic of the Magnetization of the Interstellar Medium and Molecular clouds,"We use a set of magnetohydrodynamics (MHD) simulations of fully-developed
(driven) turbulence to study the anisotropy in the velocity field that is
induced by the presence of the magnetic field. In our models we study
turbulence characterized by sonic Mach numbers M_s from 0.7 to 7.5, and Alfven
Mach numbers M_A from 0.4 to 7.7. These are used to produce synthetic
observations (centroid maps) that are analyzed. To study the effect of large
scale density fluctuations and of white noise we have modified the density
fields and obtained new centroid maps, which are analyzed. We show that
restricting the range of scales at which the anisotropy is measured makes the
method robust against such fluctuations. We show that the anisotropy in the
structure function of the maps reveals the direction of the magnetic field for
M_A \lesssim 1.5, regardless of the sonic Mach number. We found that the degree
of anisotropy can be used to determine the degree of magnetization (i.e. M_A)
for M_A \lesssim 1.5. To do this, one needs an additional measure of the sonic
Mach number and an estimate of the LOS magnetic field, both feasible by other
techniques, offering a new opportunity to study the magnetization state of the
interstellar medium.",1108.0693v1
2011-09-19,Anisotropic spin-fluctuations in SmCoPO revealed by 31^P NMR measurement,"31^P NMR spectral features in polycrystalline SmCoPO reveal an axially
symmetric local magnetic field. At low temperature, the anisotropy of the
internal magnetic field increases rapidly, with K_ab increasing faster than
that of K_c. The dominant contribution to this anisotropy arises from Sm-4f
electron contribution over that of Co-3d. The intrinsic width 2*(Beta) deviates
from linearity with respect to bulk susceptibility below 170 K due to the
enhancement of (1/T_2)dynamic, which along with the continuous increase of
anisotropy in the internal magnetic field is responsible for the wipe out
effect of the NMR signal, well above T_C. 1/T_1 shows large anisotropy
confirming a significant contribution of Sm-4f electron spin fluctuations to
1/T_1, arising from indirect RKKY type exchange interaction indicating a
non-negligible hybridization between Sm-4f orbitals and the conduction band,
over the itinerant character of the Co-3d spins. This anisotropy in originates
from the orientation dependence of chi""(q,omega). The 3d-spin fluctuations in
the ab plane is 2D FM in nature, while along the c-axis, a signature of a weak
2D AFM spin fluctuations superimposed on weak FM spin-fluctuations even in a
field of 7 T and far above T_N is observed. The enhancement of this AFM
fluctuations of the Co-3d spins along c-axis, at further low temperature is
responsible to drive the system to an AFM ordered state.",1109.3955v3
2011-10-28,Large peculiar motion of the solar system from the dipole anisotropy in sky brightness due to distant radio sources,"According to the cosmological principle, the Universe should appear
isotropic, without any preferred directions, to an observer whom we may
consider to be fixed in the co-moving co-ordinate system of the expanding
Universe. Such an observer is stationary with respect to the average
distribution of the matter in the Universe and the sky brightness at any
frequency should appear uniform in all directions to such an observer. However
a peculiar motion of such an observer, due to a combined effect of Doppler
boosting and aberration, will introduce a dipole anisotropy in the observed sky
brightness; in reverse an observed dipole anisotropy in the sky brightness
could be used to infer the peculiar velocity of the observer with respect to
the average Universe. We determine the peculiar velocity of the solar system
relative to the frame of distant radio sources, by studying the anisotropy in
the sky brightness from discrete radio sources, i.e., an integrated emission
from discrete sources per unit solid angle. Our results give a direction of the
velocity vector in agreement with the Cosmic Microwave Background Radiation
(CMBR) value, but the magnitude ($\sim 1600\pm 400$ km/s) is $\sim 4$ times the
CMBR value ($369\pm 1$ km/s) at a statistically significant ($\sim 3\sigma$)
level. A genuine difference between the two dipoles would imply anisotropic
Universe, with the anisotropy changing with the epoch. This would violate the
cosmological principle where the isotropy of the Universe is assumed for all
epochs, and on which the whole modern cosmology is based upon.",1110.6260v1
2012-02-24,Band mass anisotropy and the intrinsic metric of fractional quantum Hall systems,"It was recently pointed out that topological liquid phases arising in the
fractional quantum Hall effect (FQHE) are not required to be rotationally
invariant, as most variational wavefunctions proposed to date have been.
Instead, they possess a geometric degree of freedom corresponding to a shear
deformation that acts like an intrinsic metric. We apply this idea to a system
with an anisotropic band mass, as is intrinsically the case in many-valley
semiconductors such as AlAs and Si, or in isotropic systems like GaAs in the
presence of a tilted magnetic field, which breaks the rotational invariance. We
perform exact diagonalization calculations with periodic boundary conditions
(torus geometry) for various filling fractions in the lowest, first and second
Landau levels. In the lowest Landau level, we demonstrate that FQHE states
generally survive the breakdown of rotational invariance by moderate values of
the band mass anisotropy. At 1/3 filling, we generate a variational family of
Laughlin wavefunctions parametrized by the metric degree of freedom. We show
that the intrinsic metric of the Laughlin state adjusts as the band mass
anisotropy or the dielectric tensor are varied, while the phase remains robust.
In the n=1 Landau level, mass anisotropy drives transitions between
incompressible liquids and compressible states with charge density wave
ordering. In n>=2 Landau levels, mass anisotropy selects and enhances stripe
ordering with compatible wave vectors at partial 1/3 and 1/2 fillings.",1202.5586v1
2012-06-05,"Underscreened Kondo effect in S=1 magnetic quantum dots: Exchange, anisotropy and temperature effects","We present a theoretical analysis of the effects of uniaxial magnetic
anisotropy and contact-induced exchange field on the underscreened Kondo effect
in S=1 magnetic quantum dots coupled to ferromagnetic leads. First, by using
the second-order perturbation theory we show that the coupling to
spin-polarized electrode results in an effective exchange field $B_{\rm eff}$
and an effective magnetic anisotropy $D_{\rm eff}$. Second, we confirm these
findings by using the numerical renormalization group method, which is employed
to study the dependence of the quantum dot spectral functions, as well as
quantum dot spin, on various parameters of the system. We show that the
underscreened Kondo effect is generally suppressed due to the presence of
effective exchange field and can be restored by tuning the anisotropy constant,
when $|D_{\rm eff}| = |B_{\rm eff}|$. The Kondo effect can also be restored by
sweeping an external magnetic field, and the restoration occurs twice in a
single sweep. From the distance between the restored Kondo resonances one can
extract the information about both the exchange field and the effective
anisotropy. Finally, we calculate the temperature dependence of linear
conductance for the parameters where the Kondo effect is restored and show that
the restored Kondo resonances display a universal scaling of $S=1/2$ Kondo
effect.",1206.1034v2
2012-06-21,A Novel Approach to Constrain the Escape Fraction and Dust Content at High Redshift Using the Cosmic Infrared Background Fractional Anisotropy,"The Cosmic Infrared Background (CIB) provides an opportunity to constrain
many properties of the high redshift (z>6) stellar population as a whole. This
background, specifically, from 1 to 200 microns, will contain any information
about the era of reionization and the stars responsible for producing these
ionizing photons. In this paper, we look at the fractional anisotropy delta I/I
of this high redshift population, which is the ratio of the magnitude of the
fluctuations (delta I) and the mean intensity (I). We show that this can be
used to constrain the escape fraction of the population as a whole. The
magnitude of the fluctuations of the CIB depend on the escape fraction, while
the mean intensity does not. This results in lower values of the escape
fraction producing higher values of the fractional anisotropy. This difference
is predicted to be larger at the longer wavelengths bands (above 10 microns),
albeit it is also much harder to observe in that range. We show that the
fractional anisotropy can also be used to separate a dusty from a dust-free
population. Finally, we discuss the constraints provided by current
observations on the CIB fractional anisotropy.",1206.4934v2
2012-07-23,Vlasov simulations of multi-ion plasma turbulence in the solar wind,"Hybrid Vlasov-Maxwell simulations are employed to investigate the role of
kinetic effects in a two-dimensional turbulent multi-ion plasma, composed of
protons, alpha particles and fluid electrons. In the typical conditions of the
solar-wind environment, and in situations of decaying turbulence, the numerical
results show that the velocity distribution functions of both ion species
depart from the typical configuration of thermal equilibrium. These
non-Maxwellian features are quantified through the statistical analysis of the
temperature anisotropy, for both protons and alpha particles, in the reference
frame given by the local magnetic field. Anisotropy is found to be higher in
regions of high magnetic stress. Both ion species manifest a preferentially
perpendicular heating, although the anisotropy is more pronounced for the alpha
particles, according with solar wind observations. Anisotropy of the alpha
particle, moreover, is correlated to the proton anisotropy, and also depends on
the local differential flow between the two species. Evident distortions of the
particle distribution functions are present, with the production of bumps along
the direction of the local magnetic field. The physical phenomenology recovered
in these numerical simulations reproduces very common measurements in the
turbulent solar wind, suggesting that the multi-ion Vlasov model constitutes a
valid approach to the understanding of the nature of complex kinetic effects in
astrophysical plasmas.",1207.5379v1
2012-09-04,On the orbital and internal evolution of cluster galaxies,"Galaxies inhabiting a cluster environment experience significant evolution in
their orbital motions throughout time; this is accompanied by changes in the
anisotropy parameter, measuring the relative importance of radial and
tangential motions for a given class of objects. Along with orbital changes,
galaxies in clusters are well known to undergo severe alteration in their
hot/cold gas content and star formation properties. Understanding the link
between the changes in the internal properties of galaxies and their orbital
motion is of crucial importance in the study of galaxy evolution, as it could
unveil the primary mechanism responsible for its environmental dependence. Do
the changes in the internal properties happen in parallel with those in the
orbital motion? Or are the orbital features at the time of infall what
determines the fate of the member galaxies? Alternatively: are the properties
of galaxies at a given time related to the coeval orbital anisotropy or are
they better related to the anisotropy at infall? In order to answer these
questions, we studied the orbital evolution of different galaxy populations in
the semi-analytic models of Guo et al. (2011) applied on to the Millennium
Simulation. For each class of objects, characterised by different internal
properties (such as age, star formation rate and colour), we studied the
anisotropy profile at redshift zero and its evolution by tracing the
progenitors back in time. We conclude that the orbital properties at infall
strongly influence the subsequent evolution of the internal features of
galaxies and that the overall anisotropy of the galaxy population tends to
increase with time.",1209.0586v1
2012-10-12,A search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger Observatory,"Observations of cosmic ray arrival directions made with the Pierre Auger
Observatory have previously provided evidence of anisotropy at the 99% CL using
the correlation of ultra high energy cosmic rays (UHECRs) with objects drawn
from the Veron-Cetty Veron catalog. In this paper we report on the use of three
catalog independent methods to search for anisotropy. The 2pt-L, 2pt+ and 3pt
methods, each giving a different measure of self-clustering in arrival
directions, were tested on mock cosmic ray data sets to study the impacts of
sample size and magnetic smearing on their results, accounting for both angular
and energy resolutions. If the sources of UHECRs follow the same large scale
structure as ordinary galaxies in the local Universe and if UHECRs are
deflected no more than a few degrees, a study of mock maps suggests that these
three methods can efficiently respond to the resulting anisotropy with a
P-value = 1.0% or smaller with data sets as few as 100 events. Using data taken
from January 1, 2004 to July 31, 2010 we examined the 20, 30,..., 110 highest
energy events with a corresponding minimum energy threshold of about 49.3 EeV.
The minimum P-values found were 13.5% using the 2pt-L method, 1.0% using the
2pt+ method and 1.1% using the 3pt method for the highest 100 energy events. In
view of the multiple (correlated) scans performed on the data set, these
catalog-independent methods do not yield strong evidence of anisotropy in the
highest energy cosmic rays.",1210.3602v1
2012-12-10,Proton temperature anisotropy and magnetic reconnection in the solar wind: effects of kinetic instabilities on current sheet stability,"We investigate the role of kinetic instabilities driven by a proton
anisotropy on the onset of magnetic reconnection by means of 2-D hybrid
simulations. The collisionless tearing of a current sheet is studied in the
presence of a proton temperature anisotropy in the surrounding plasma. Our
results confirm that anisotropic protons within the current sheet region can
significantly enhance/stabilize the tearing instability of the current.
Moreover, fluctuations associated to linear instabilities excited by large
proton temperature anisotropies can significantly influence the stability of
the plasma and perturb the current sheets, triggering the tearing instability.
We find that such a complex coupling leads to a faster tearing evolution in a
regime with larger perpendicular temperature when an ion-cyclotron instability
is generated by the anisotropic proton distribution functions. On the contrary,
in the presence of the opposite anisotropy, fire hose fluctuations excited by
the unstable background protons with larger parallel temperature are not able
to efficiently destabilize the current sheets, which remain stable for a long
time after fire hose saturation. We discuss possible influences of this novel
coupling on the solar wind and heliospheric plasma dynamics.",1212.2101v1
2013-04-11,Sign-reversal of the in-plane resistivity anisotropy in iron pnictides,"The concept of an electronically-driven breaking of the rotational symmetry
of a crystal, without involving magnetic order, has found experimental support
in several systems, from semiconductor heterostructures and ruthenates, to
cuprate and iron-pnictide superconductors. In the pnictide BaFe$_{2}$As$_{2}$,
such an ""electronic nematic state"" appears above the magnetic transition dome,
over a temperature range that can be controlled by external strain. Here, by
measuring the in-plane resistivity anisotropy, we probe the electronic
anisotropy of this material over the entire nematic/magnetic dome, whose end
points coincide with the optimal superconducting transition temperatures.
Counter-intuitively, we find that, unlike other materials, the resistivity
anisotropy in BaFe$_{2}$As$_{2}$ changes sign across the doping phase diagram,
even though the signs of the magnetic, nematic, and orthorhombic order
parameters are kept fixed. This behavior is explained by the Fermi surface
reconstruction in the magnetic phase and spin-fluctuation scattering in the
nematic phase. The unique behavior of the transport anisotropy unveils that the
primary role is played by magnetic scattering in the normal state transport
properties of the iron pnictides, suggesting a close connection between
magnetism, nematicity, and unconventional superconductivity.",1304.3490v1
2013-05-04,Effect of perpendicular uniaxial anisotropy on the annihilation fields of magnetic vortices,"The magnetic vortex structure, that is present in several nanoscopic systems,
is stable and can be manipulated through the application of a magnetic field or
a spin polarized current. The size and shape of the core are strongly affected
by the anisotropy, however its role on the core behavior has not yet been
clarified. In the present work we investigate the influence of a perpendicular
anisotropy on the annihilation and shape of magnetic vortex cores in permalloy
disks. We have used both micromagnetic simulations with the OOMMF code, and an
analytical model that assumes that the shape of the core does not change during
the hysteresis cycle, known as the rigid core model, to calculate the
annihilation fields. In both cases we found that the annihilation fields
decrease with increasing perpendicular anisotropy for almost all the structures
investigated. The simulations show that for increasing anisotropy or dot
thickness, or both, the vortex core profile changes its shape, becoming
elongated. For every dot thickness, this change does not depend on the dot
radius, but on the relative distance of the core from the center of the dot.",1305.0942v2
2013-05-19,Self-Similar Anisotropic Texture Analysis: the Hyperbolic Wavelet Transform Contribution,"Textures in images can often be well modeled using self-similar processes
while they may at the same time display anisotropy. The present contribution
thus aims at studying jointly selfsimilarity and anisotropy by focusing on a
specific classical class of Gaussian anisotropic selfsimilar processes. It will
first be shown that accurate joint estimates of the anisotropy and
selfsimilarity parameters are performed by replacing the standard 2D-discrete
wavelet transform by the hyperbolic wavelet transform, which permits the use of
different dilation factors along the horizontal and vertical axis. Defining
anisotropy requires a reference direction that needs not a priori match the
horizontal and vertical axes according to which the images are digitized, this
discrepancy defines a rotation angle. Second, we show that this rotation angle
can be jointly estimated. Third, a non parametric bootstrap based procedure is
described, that provides confidence interval in addition to the estimates
themselves and enables to construct an isotropy test procedure, that can be
applied to a single texture image. Fourth, the robustness and versatility of
the proposed analysis is illustrated by being applied to a large variety of
different isotropic and anisotropic self-similar fields. As an illustration, we
show that a true anisotropy built-in self-similarity can be disentangled from
an isotropic self-similarity to which an anisotropic trend has been
superimposed.",1305.4384v1
2013-06-11,Bethe ansatz description of edge-localization in the open-boundary XXZ spin chain,"At large values of the anisotropy \Delta, the open-boundary Heisenberg
spin-1/2 chain has eigenstates displaying localization at the edges. We present
a Bethe ansatz description of this `edge-locking' phenomenon in the entire
\Delta>1 region. We focus on the simplest spin sectors, namely the highly
polarized sectors with only one or two overturned spins, i.e., one-particle and
two-particle sectors. Edge-locking is associated with pure imaginary solutions
of the Bethe equations, which are not commonly encountered in periodic chains.
In the one-particle case, at large anisotropies there are two eigenstates with
imaginary Bethe momenta, related to localization at the two edges. For any
finite chain size, one of the two solutions become real as the anisotropy is
lowered below a certain value. For two particles, a richer scenario is
observed, with eigenstates having the possibility of both particles locked on
the same or different edge, one locked and the other free, and both free either
as single magnons or as bound composites corresponding to `string' solutions.
For finite chains, some of the edge-locked spins get delocalized at certain
values of the anisotropy (`exceptional points'), corresponding to imaginary
solutions becoming real. We characterize these phenomena thoroughly by
providing analytic expansions of the Bethe momenta for large chains, large
anisotropy, and near the exceptional points. In the large-chain limit all the
exceptional points coalesce at the isotropic point (\Delta=1) and edge-locking
becomes stable in the whole \Delta>1 region.",1306.2666v3
2013-07-07,Instabilities Driven by the Drift and Temperature Anisotropy of Alpha Particles in the Solar Wind,"We investigate the conditions under which parallel-propagating
Alfv\'en/ion-cyclotron (A/IC) waves and fast-magnetosonic/whistler (FM/W) waves
are driven unstable by the differential flow and temperature anisotropy of
alpha particles in the solar wind. We focus on the limit in which $w_{\parallel
\alpha} \gtrsim 0.25 v_{\mathrm A}$, where $w_{\parallel \alpha} $ is the
parallel alpha-particle thermal speed and $v_{\mathrm A}$ is the Alfv\'en
speed. We derive analytic expressions for the instability thresholds of these
waves, which show, e.g., how the minimum unstable alpha-particle beam speed
depends upon $w_{\parallel \alpha}/v_{\mathrm A}$, the degree of alpha-particle
temperature anisotropy, and the alpha-to-proton temperature ratio. We validate
our analytical results using numerical solutions to the full hot-plasma
dispersion relation. Consistent with previous work, we find that temperature
anisotropy allows A/IC waves and FM/W waves to become unstable at significantly
lower values of the alpha-particle beam speed $U_\alpha$ than in the
isotropic-temperature case. Likewise, differential flow lowers the minimum
temperature anisotropy needed to excite A/IC or FM/W waves relative to the case
in which $U_\alpha =0$. We discuss the relevance of our results to alpha
particles in the solar wind near 1 AU.",1307.1823v2
2013-08-06,Anisotropic Lyman-alpha Emission,"As a result of resonant scatterings off hydrogen atoms, Lyman-alpha (Lya)
emission from star-forming galaxies provides a probe of the (hardly isotropic)
neutral gas environment around them. We study the effect of the environmental
anisotropy on the observed Lya emission by performing radiative transfer
calculations for models of neutral hydrogen clouds with prescriptions of
spatial and kinematic anisotropies. The environmental anisotropy leads to
corresponding anisotropy in the Lya flux and spectral properties and induces
correlations among them. The Lya flux (or observed luminosity) depends on the
viewing angle and shows an approximate correlation with the initial Lya optical
depth in the viewing direction relative to those in all other directions. The
distribution of Lya flux from a set of randomly oriented clouds is skewed to
high values, providing a natural contribution to the Lya equivalent width (EW)
distribution seen in observation. A narrower EW distribution is found at a
larger peak offset of the Lya line, similar to the trend suggested in
observation. The peak offset appears to correlate with the line shape (full
width at half maximum and asymmetry), pointing to a possibility of using Lya
line features alone to determine the systemic redshifts of galaxies. The study
suggests that anisotropies in the spatial and kinematic distributions of
neutral hydrogen can be an important ingredient in shaping the observed
properties of Lya emission from star-forming galaxies. We discuss the
implications of using Lya emission to probe the circumgalactic and
intergalactic environments of galaxies.",1308.1405v2
2014-02-19,"Solar wind protons at 1 AU: trends and bounds, constraints and correlations","The proton temperature anisotropy in the solar wind exhibits apparent bounds
which are compatible with the theoretical constraints imposed by
temperature-anisotropy driven kinetic instabilities. Recent statistical
analyses based on conditional averaging indicate that near these theoretical
constraints the solar wind protons have typically enhanced temperatures and a
weaker collisionality. Here we carefully analyze the solar wind data and show
that these results are a consequence of superposition of multiple correlations
in the solar wind, namely, they mostly result from the correlation between the
proton temperature and the solar wind velocity and from the superimposed
anti-correlation between the proton temperature anisotropy and the proton
parallel beta in the fast solar wind. Colder and more collisional data are
distributed around temperature isotropy whereas hotter and less collisional
data have a wider range of the temperature anisotropy anti-correlated with the
proton parallel beta with signatures of constraints owing to the
temperature-anisotropy driven instabilities. However, most of the hot and
weakly collisional data, including the hottest and least collisional ones, lies
far from the marginal stability regions. Consequently, we conclude that there
is no clear relation between the enhanced temperatures and instability
constraints and that the conditional averaging used for these analyses must be
used carefully and need to be well tested.",1402.4611v1
2014-05-19,Peculiar motion of the solar system derived from a dipole anisotropy in the redshift distribution of distant quasars,"An observer stationary with respect to comoving coordinates of the expanding
universe should find the redshift distribution to be isotropic. However, a
peculiar motion of the observer would introduce a dipole anisotropy in the
observed redshift distribution. Conversely, a dipole anisotropy in observed
redshift distribution could be exploited to infer our peculiar motion, or
rather of our solar system. We determine here our peculiar velocity by studying
the dipole anisotropy in the redshift distribution of a large sample of
quasars. The magnitude of the peculiar velocity thus determined turns out to be
$2350\pm280$ km s$^{-1}$, not only much larger than 370 km s$^{-1}$ determined
from the dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR),
but also nearly in an opposite direction. Such large values for peculiar
velocity have been found in a couple of radio surveys too, but with a direction
along the CMBR dipole. Large genuine differences in the inferred motion,
whether in magnitude or direction, are rather disconcerting since a solar
peculiar velocity should not depend upon the method of its determination. Such
discordant dipoles imply perhaps an anisotropic universe, violating the
cosmological principle, a cornerstone of the modern cosmology.",1405.4796v4
2014-06-13,Kinematical fingerprints of star cluster early dynamical evolution,"We study the effects of the external tidal field on the violent relaxation
phase of star clusters dynamical evolution, with particular attention to the
kinematical properties of the equilibrium configurations emerging at the end of
this phase.We show that star clusters undergoing the process of violent
relaxation in the tidal field of their host galaxy can acquire significant
internal differential rotation and are characterized by a distinctive radial
variation of the velocity anisotropy. These kinematical properties are the
result of the symmetry breaking introduced by the external tidal field in the
collapse phase and of the action of the Coriolis force on the orbit of the
stars. The resulting equilibrium configurations are characterized by
differential rotation, with a peak located between one and two half-mass radii.
As for the anisotropy, similar to clusters evolving in isolation, the systems
explored in this Letter are characterized by an inner isotropic core, followed
by a region of increasing radial anisotropy. However for systems evolving in an
external tidal field the degree of radial anisotropy reaches a maximum in the
cluster intermediate regions and then progressively decreases, with the cluster
outermost regions being characterized by isotropy or a mild tangential
anisotropy. Young or old but less-relaxed dynamically young star clusters may
keep memory of these kinematical fingerprints of their early dynamical
evolution.",1406.3634v1
2014-10-09,A CMB Gibbs sampler for localized secondary anisotropies,"As well as primary fluctuations, CMB temperature maps contain a wealth of
additional information in the form of secondary anisotropies. Secondary effects
that can be identified with individual objects, such as the thermal and kinetic
Sunyaev-Zel'dovich (SZ) effects due to galaxy clusters, are difficult to
unambiguously disentangle from foreground contamination and the primary CMB
however. We develop a Bayesian formalism for rigorously characterising
anisotropies that are localised on the sky, taking the TSZ and KSZ effects as
an example. Using a Gibbs sampling scheme, we are able to efficiently sample
from the joint posterior distribution for a multi-component model of the sky
with many thousands of correlated physical parameters. The posterior can then
be exactly marginalised to estimate properties of the secondary anisotropies,
fully taking into account degeneracies with the other signals in the CMB map.
We show that this method is computationally tractable using a simple
implementation based on the existing Commander component separation code, and
also discuss how other types of secondary anisotropy can be accommodated within
our framework.",1410.2544v2
2014-11-23,Slowly Rotating Anisotropic Neutron Stars in General Relativity and Scalar-Tensor Theory,"Some models (such as the Skyrme model, a low-energy effective field theory
for QCD) suggest that the high-density matter prevailing in neutron star
interiors may be significantly anisotropic. Anisotropy is known to affect the
bulk properties of nonrotating neutron stars in General Relativity. In this
paper we study the effects of anisotropy on slowly rotating stars in General
Relativity. We also consider one of the most popular extensions of Einstein's
theory, namely scalar-tensor theories allowing for spontaneous scalarization (a
phase transition similar to spontaneous magnetization in ferromagnetic
materials). Anisotropy affects the moment of inertia of neutron stars (a
quantity that could potentially be measured in binary pulsar systems) in both
theories. We find that the effects of scalarization increase (decrease) when
the tangential pressure is bigger (smaller) than the radial pressure, and we
present a simple criterion to determine the onset of scalarization by
linearizing the scalar-field equation. Our calculations suggest that binary
pulsar observations may constrain the degree of anisotropy or even, more
optimistically, provide evidence for anisotropy in neutron star cores.",1411.6286v3
2015-01-16,Direct measurement of the magnetic anisotropy field in Mn--Ga and Mn--Co--Ga Heusler films,"The static and dynamic magnetic properties of tetragonally distorted Mn--Ga
based alloys were investigated. Static properties are determined in magnetic
fields up to 6.5~T using SQUID magnetometry. For the pure Mn$_{1.6}$Ga film,
the saturation magnetisation is 0.36~MA/m and the coercivity is 0.29~T. Partial
substitution of Mn by Co results in Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$. The
saturation magnetisation of those films drops to 0.2~MA/m and the coercivity is
increased to 1~T.
  Time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the
high-frequency dynamics of Mn--Ga. The ferromagnetic resonance frequency
extrapolated to zero-field is found to be 125~GHz with a Gilbert damping,
$\alpha$, of 0.019. The anisotropy field is determined from both SQUID and
TR-MOKE to be 4.5~T, corresponding to an effective anisotropy density of
0.81~MJ/m$^3$.
  Given the large anisotropy field of the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film,
pulsed magnetic fields up to 60~T are used to determine the field strength
required to saturate the film in the plane. For this, the extraordinary Hall
effect was employed as a probe of the local magnetisation. By integrating the
reconstructed in--plane magnetisation curve, the effective anisotropy energy
density for Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ is determined to be 1.23~MJ/m$^3$.",1501.03973v1
2015-03-02,Predicted Impacts of Proton Temperature Anisotropy on Solar Wind Turbulence,"Particle velocity distributions measured in the weakly collisional solar wind
are frequently found to be non-Maxwellian, but how these non-Maxwellian
distributions impact the physics of plasma turbulence in the solar wind remains
unanswered. Using numerical solutions of the linear dispersion relation for a
collisionless plasma with a bi-Maxwellian proton velocity distribution, we
present a unified framework for the four proton temperature anisotropy
instabilities, identifying the associated stable eigenmodes, highlighting the
unstable region of wavevector space, and presenting the properties of the
growing eigenfunctions. Based on physical intuition gained from this framework,
we address how the proton temperature anisotropy impacts the nonlinear dynamics
of the \Alfvenic fluctuations underlying the dominant cascade of energy from
large to small scales and how the fluctuations driven by proton temperature
anisotropy instabilities interact nonlinearly with each other and with the
fluctuations of the large-scale cascade. We find that the nonlinear dynamics of
the large-scale cascade is insensitive to the proton temperature anisotropy,
and that the instability-driven fluctuations are unlikely to cause significant
nonlinear evolution of either the instability-driven fluctuations or the
turbulent fluctuations of the large-scale cascade.",1503.00695v2
2015-03-10,In-plane electronic anisotropy in the antiferromagnetic-orthorhombic phase of isovalent-substituted Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$,"We have studied the anisotropy in the in-plane resistivity and the electronic
structure of isovalent Ru-substituted BaFe$_2$As$_2$ in the
antiferromagnetic-orthorhombic phase using well-annealed crystals. The
anisotropy in the residual resistivity component increases in proportional to
the Ru dopant concentration, as in the case of Co-doped compounds. On the other
hand, both the residual resistivity and the resistivity anisotropy induced by
isovalent Ru substitution is found to be one order of magnitude smaller than
those induced by heterovalent Co substitution. Combined with angle-resolved
photoemission spectroscopy results, which show almost the same anisotropic band
structure both for the parent and Ru-substituted compounds, we confirm the
scenario that the anisotropy in the residual resistivity arises from
anisotropic impurity scattering in the magneto-structurally ordered phase
rather than directly from the anisotropic band structure of that phase.",1503.02855v1
2015-06-29,Influence of interphase anisotropy on lamellar eutectic growth patterns,"It is well documented in many experiments that crystallographic effects play
an important role in the generation of two-phase patterns during the
solidification of eutectic alloys. In particular, in lamellar composites, large
patches of perfectly aligned lamellae are frequently observed. Moreover, the
growth direction of the lamellae often markedly differs from the direction of
the temperature gradient (the lamellae are tilted with respect to the main
growth direction). Both of these effects cannot be explained either by the
standard theory or the available numerical models of eutectic growth, which all
assume the interfaces to be isotropic. We have developed a phase-field model in
which the anisotropy of each interface (solid-liquid and solid-solid) can be
separately controlled, and we have investigated the effect of interface
anisotropy on the growth dynamics. We have found that anisotropy of the
solid-solid interphase boundary free energy dramatically alters the growth
dynamics. Tilted lamellae result from the modified equilibrium condition at the
triple lines, in good agreement with a theoretical conjecture proposed
recently. In three dimensions, the interphase boundaries tend to align with
directions of minimal energy. We have also performed simulations in which two
grains with different anisotropies are in competition. In all cases, the grain
containing the boundaries with the lowest energies was selected after a
transient. These results shed new light on the selection of growth patterns in
eutectic solidification.",1506.08893v1
2015-10-09,Magnetic anisotropy of polycrystalline high-temperature ferromagnetic Mn$_x$Si$_{1-x}$ ($x\approx0.5$) alloy films,"A set of thin film Mn$_x$Si$_{1-x}$ alloy samples with different manganese
concentration x = 0.44 - 0.63 grown by the pulsed laser deposition (PLD) method
onto the Al$_2$O$_3$(0001) substrate was investigated in the temperature range
4 - 300 K using ferromagnetic resonance (FMR) measurements in the wide range of
frequencies (f = 7 - 60 GHz) and magnetic fields (H = 0 - 30 kOe). For samples
with x = 0.52 - 0.55, FMR data show clear evidence of ferromagnetism with high
Curie temperatures T$_\text{C}$ ~ 300 K. These samples demonstrate complex and
unusual character of magnetic anisotropy described in the frame of
phenomenological model as a combination of the essential second order easy
plane anisotropy contribution and the additional forth order uniaxial
anisotropy contribution with easy direction normal to the film plane. We
explain the obtained results by a polycrystalline (mosaic) structure of the
films caused by the film-substrate lattice mismatch. The existence of extra
strains at the crystallite boundaries leads to an essential inhomogeneous
magnetic anisotropy in the film plane.",1510.02634v1
2015-11-01,RKKY-like contributions to the magnetic anisotropy energy: 3d adatoms on Pt(111) surface,"The magnetic anisotropy energy defines the energy barrier that stabilizes a
magnetic moment. Utilizing density functional theory based simulations and
analytical formulations, we establish that this barrier is strongly modified by
long-range contributions very similar to Frieden oscillations and
Rudermann-Kittel-Kasuya-Yosida interactions. Thus, oscillations are expected
and observed, with different decaying factors and highly anisotropic in
realistic materials, which can switch non-trivially the sign of the magnetic
anisotropy energy. This behavior is general and for illustration we address
transition metals adatoms, Cr, Mn, Fe and Co deposited on Pt(111) surface. We
explain in particular the mechanisms leading to the strong site-dependence of
the magnetic anisotropy energy observed for Fe adatoms on Pt(111) surface as
revealed previously via first-principles based simulations and inelastic
scanning tunneling spectroscopy (A. A. Khajetoorians et al. Phys. Rev. Lett.
111, 157204 (2013)). The same mechanisms are probably active for the
site-dependence of the magnetic anisotropy energy obtained for Fe adatoms on Pd
or Rh(111) surfaces and for Co adatoms on Rh(111) surface (P. Blonski et al.
Phys. Rev. B 81, 104426 (2010)).",1511.00232v2
2016-02-10,Orientational ordering of confined hard rods: the effect of shape anisotropy on surface ordering and capillary nematization,"We examine the ordering properties of rectangular hard rods with length L and
diameter D at a single planar wall and between two parallel hard walls using
the second-virial density functional theory. The theory is implemented in the
three-state Zwanzig approximation, where only three mutually perpendicular
directions are allowed for the orientations of hard rods. The effect of varying
shape anisotropy is examined at L/D=10, 15 and 20. In contact with a single
hard wall, the density profiles show planar ordering, damped oscillatory
behavior, and wall induced surface ordering transition below the coexisting
isotropic density of bulk isotropic-nematic (I-N) phase transition. Upon
approaching the coexisting isotropic density, the thickness of nematic film
diverges logarithmically, i.e. the nematic wetting is complete for any shape
anisotropy. In the case of confinement between two parallel hard walls, it is
found that the continuous surface ordering transition depends strongly on the
distance between confining walls (H) for H<L, while it depends weakly on H for
H>L. The minimal density at which a surface ordering transition can be realized
is located at around H~2D for all studied shape anisotropies due to the strong
interference effect between the two hard walls. The first order I-N phase
transition of the bulk system becomes surface ordered isotropic (IB)-capillary
nematic (NB) phase transition in the slit pore. This first order IB-NB
transition weakens with decreasing pore width and terminates in a critical
point for all studied shape anisotropies.",1602.03485v1
2016-03-12,Non-monotonic anisotropy in charge conduction induced by antiferrodistortive transition in metallic SrTiO$_{3}$,"Cubic SrTiO$_{3}$ becomes tetragonal below 105 K. The antiferrodistortive
(AFD) distortion leads to clockwise and counter-clockwise rotation of adjacent
TiO$_{6}$ octahedra. This insulator becomes a metal upon the introduction of
extremely low concentration of n-type dopants. However, signatures of the
structural phase transition in charge conduction have remained elusive.
Employing the Montgomery technique, we succeed in resolving the anisotropy of
charge conductivity induced by the AFD transition, in the presence of different
types of dopants. We find that the slight lattice distortion ($<6 \times
10^{-4}$) gives rise to a twenty percent anisotropy in charge conductivity, in
agreement with the expectations of band calculations. Application of uniaxial
strain amplifies the detectable anisotropy by disfavoring one of the three
possible tetragonal domains. In contrast with all other known anisotropic Fermi
liquids, the anisotropy has opposite signs for elastic and inelastic
scattering. Increasing the concentration of dopants leads to a drastic shift in
the temperature of the AFD transition either upward or downward. The latter
result puts strong constraints on any hypothetical role played by the AFD soft
mode in the formation of Cooper pairs and the emergence of superconductivity in
SrTiO$_3$.",1603.03831v2
2016-02-26,The Electron Temperature and Anisotropy in the Solar Wind. I. Comparison of the Core and Halo Populations,"Estimating the temperature of the solar wind particles and their anisotropies
is particularly important for understanding the origin of these deviations from
thermal equilibrium as well as their effects. In the absence of energetic
events the velocity distribution of electrons reveal a dual structure with a
thermal (Maxwellian) core and a suprathermal (Kappa) halo. This paper presents
a detailed observational analysis of these two components, providing
estimations of their temperatures and temperature anisotropies and decoding any
potential interdependence that their properties may indicate. The data set used
in this study includes more than 120$\,$000 the events detected by three
missions in the ecliptic within an extended range of heliocentric distances
from 0.3 to over 4~AU. The anti-correlation found for the core and halo
temperatures is consistent with the radial evolution of the Kappa model,
clarifying an apparent contradiction in previous observational analysis and
providing valuable clues about the temperature of the Kappa-distributed
populations. However, these two components manifest a clear tendency to deviate
from isotropy in the same direction, that seems to confirm the existence of
mechanisms with similar effects on both components, e.g., the solar wind
expansion, or the particle heating by the fluctuations. On the other hand, the
existence of plasma states with anti-correlated anisotropies of the core and
halo populations suggests a dynamic interplay of these components, mediated,
most probably, by the anisotropy-driven instabilities.",1603.08392v1
2016-05-05,Anisotropy of the monomer random walk in a polymer melt: local-order and connectivity effects,"The random walk of a bonded monomer in a polymer melt is anisotropic due to
local order and bond connectivity. We investigate both effects by
molecular-dynamics simulations on melts of fully-flexible linear chains ranging
from dimers ($M=2$) up to entangled polymers ($M=200$). The corresponding
atomic liquid is also considered as reference system. To disentangle the
influence of the local geometry and the bond arrangements, and reveal their
interplay, we define suitable measures of the anisotropy emphasising either the
former or the latter aspect. Connectivity anisotropy, as measured by the
correlation between the initial bond orientation and the direction of the
subsequent monomer displacement, shows a slight enhancement due to the local
order at times shorter than the structural relaxation time. At intermediate
times - when the monomer displacement is comparable to the bond length - a
pronounced peak and then decays slowly as $t^{-1/2}$, becoming negligible when
the displacements is as large as about five bond lengths, i.e. about four
monomer diameters or three Kuhn lengths. Local-geometry anisotropy, as measured
by the correlation between the initial orientation of a characteristic axis of
the Voronoi cell and the subsequent monomer dynamics, is affected at shorter
times than the structural relaxation time by the cage shape with antagonistic
disturbance by the connectivity. Differently, at longer times, the connectivity
favours the persistence of the local-geometry anisotropy which vanishes when
the monomer displacement exceeds the bond length. Our results strongly suggest
that the sole consideration of the local order is not enough to understand the
microscopic origin of the rattling amplitude of the trapped monomer in the cage
of the neighbours.",1605.01568v1
2016-07-11,Significance of Natural Scene Statistics in Understanding the Anisotropies of Perceptual Filling-in at the Blind Spot,"Psychophysical experiments reveal our horizontal preference in perceptual
filling-in at the blind spot. On the other hand, vertical preference is
exhibited in the case of tolerance in filling-in. What causes this anisotropy
in our perception? Building upon the general notion, that the functional
properties of the early visual system are shaped by the innate specification as
well as the statistics of the environment, we reasoned that the anisotropy in
filling-in could be understood in terms of anisotropy in orientation
distribution inherent to natural scene statistics. We examined this proposition
by investigating filling-in of bar stimuli on a Hierarchical Predictive Coding
model network. In response to bar stimuli, the model network, trained with
natural images, exhibited anisotropic filling-in performance at the blind spot
similar to reported in psychophysical experiments i.e. horizontal preference in
filling-in and vertical preference in tolerance of filling-in. We suggest that
the over-representation of horizontal contours in the natural scene contribute
to the observed horizontal superiority while the broader distribution of
vertical contours contributes to the observed vertical superiority in
tolerance. These results indicate that natural scene statistics plays a
significant role in determining the filling-in performance at the blind spot
and shaping the associated anisotropies.",1607.02865v2
2016-07-14,Study of velocity centroids based on the theory of fluctuations in position-position-velocity space,"We study possibility of obtaining velocity spectra by studying turbulence in
an optically thick medium using velocity centroids (VCs).We find that the
regime of universal, i.e. independent of underlying turbulence statistics,
fluctuations discovered originally within the velocity channel analysis (VCA)
carries over to the statistics of VCs. In other words, for large absorptions
the VC lose their ability to reflect the spectra of turbulence. Combining our
present study with the earlier studies of centroids in Esquivel & Lazarian, we
conclude that centroids are applicable for studies subsonic/transsonic
turbulence for the range of scales that is limited by the absorption effects.
We also consider VCs based on absorption lines and define the range of their
applicability. We address the problem of analytical description of spectra and
anisotropies of fluctuations that are available through studies using VC. We
obtain spectra and anisotropy of VC fluctuations arising from Alfv\'en, slow
and fast modes that constitute the compressible MHD cascade to address the
issue of anisotropy of VC statistics, and show how the VC anisotropy can be
used to find the media magnetization as well as to identify and separate
contributions from Alfv\'en, slow and fast modes. Our study demonstrates that
VCs are complementary to the tools provided by the VCA. In order to study
turbulent volume for which the resolution of single dish telescopes is
insufficient, we demonstrate how the studies of anisotropy can be performed
using interferometers.",1607.04316v1
2016-09-20,Magnetic anisotropy and the phase diagram of chiral MnSb2O6,"The magnetic phase diagram and low-energy magnon excitations of structurally
and magnetically chiral MnSb2O6 are reported. The specific heat and the static
magnetization are investigated in magnetic fields up to 9 and 30 T,
respectively, while the dynamicmagnetic properties are probed by X-band as well
as tunable high-frequency electron spin-resonance spectroscopy. Below TN = 11.5
K, we observe antiferromagnetic resonance modes which imply small but finite
planar anisotropy showing up in a zero-field splitting of 20 GHz. The data are
well described by means of an easy-plane two-sublattice model with the
anisotropy field BA = 0.02 T. The exchange field BE = 13 T is obtained from the
saturation field derived from the pulsed-field magnetization. A crucial role of
the small anisotropy for the spin structure is reflected by competing
antiferromagnetic phases appearing, at T = 2 K, in small magnetic fields at BC1
$\approx$ 0.5 T and BC2 = 0.9 T. We discuss the results in terms of spin
reorientation and of small magnetic fields favoring helical spin structure over
the cycloidal ground state which, at B = 0, is stabilized by the planar
anisotropy. Above TN, short-range magnetic correlations up to >=60 K and
magnetic entropy changes well above TN reflect the frustrated triangular
arrangement of Mn2+ ions in MnSb2O6.",1609.06105v1
2016-11-18,Dipole anisotropy in cosmic electrons and positrons: inspection on local sources,"The cosmic electrons and positrons have been measured with unprecedented
statistics up to several hundreds GeV, thus permitting to explore the role that
close single sources can have in shaping the flux at different energies. In the
present analysis, we consider electrons and positrons in cosmic rays to be
produced by spallations of hadron fluxes with the interstellar medium, by a
smooth Supernova Remnant (SNR) population, by all the ATNF catalog pulsars, and
by few discrete, local SNRs. We test several source models on the $e^++e^-$ and
$e^+$ AMS-02 flux data. For the configurations compatible with the data, we
compute the dipole anisotropy in $e^++e^-$, $e^+$, $e^+/e^-$ from single
sources. Our study includes a dedicated analysis to the Vela SNR. We show that
Fermi-LAT present data on dipole anisotropy of $e^++e^-$ start to explore some
of the models for the Vela SNR selected by AMS-02 flux data. We also
investigate how the observed anisotropy could result from a combination of
local sources. Our analysis shows that the search of anisotropy in the lepton
fluxes up to TeV energies can be an interesting tool for the inspection of
properties of close SNRs, complementary to the high precision flux data.",1611.06237v1
2017-02-28,Measuring X-ray anisotropy in solar flares. Prospective stereoscopic capabilities of STIX and MiSolFA,"During the next solar maximum, two upcoming space-borne X-ray missions, STIX
on board Solar Orbiter and MiSolFA, will perform stereoscopic X-ray
observations of solar flares at two different locations: STIX at 0.28 AU (at
perihelion) and up to inclinations of $\sim25^{\circ}$, and MiSolFA in a
low-Earth orbit. The combined observations from these cross-calibrated
detectors will allow us to infer the electron anisotropy of individual flares
confidently for the first time. We simulated both instrumental and physical
effects for STIX and MiSolFA including thermal shielding, background and X-ray
Compton backscattering (albedo effect) in the solar photosphere. We predict the
expected number of observable flares available for stereoscopic measurements
during the next solar maximum. We also discuss the range of useful spacecraft
observation angles for the challenging case of close-to-isotropic flare
anisotropy. The simulated results show that STIX and MiSolFA will be capable of
detecting low levels of flare anisotropy, for M1-class or stronger flares, even
with a relatively small spacecraft angular separation of 20-30{\deg}. Both
instruments will directly measure the flare X-ray anisotropy of about 40 M- and
X-class solar flares during the next solar maximum. Near-future stereoscopic
observations with Solar Orbiter/STIX and MiSolFA will help distinguishing
between competing flare-acceleration mechanisms, and provide essential
constraints regarding collisional and non-collisional transport processes
occurring in the flaring atmosphere for individual solar flares.",1702.08795v2
2017-03-12,GdRh$_2$Si$_2$: An exemplary tetragonal system for antiferromagnetic order with weak in-plane anisotropy,"The anisotropy of magnetic properties commonly is introduced in textbooks
using the case of an antiferromagnetic system with Ising type anisotropy. This
model presents huge anisotropic magnetization and a pronounced metamagnetic
transition and is well-known and well-documented both, in experiments and
theory. In contrast, the case of an antiferromagnetic $X$-$Y$ system with weak
in-plane anisotropy is only poorly documented. We studied the anisotropic
magnetization of the compound GdRh$_2$Si$_2$ and found that it is a perfect
model system for such a weak-anisotropy setting because the Gd$^{3+}$ ions in
GdRh$_2$Si$_2$ have a pure spin moment of S=7/2 which orders in a simple AFM
structure with ${\bf Q} = (001)$. We observed experimentally in $M(B)$ a
continuous spin-flop transition and domain effects for field applied along the
$[100]$- and the $[110]$-direction, respectively. We applied a mean field model
for the free energy to describe our data and combine it with an Ising chain
model to account for domain effects. Our calculations reproduce the
experimental data very well. In addition, we performed magnetic X-ray
scattering and X-ray magnetic circular dichroism measurements, which confirm
the AFM propagation vector to be ${\bf Q} = (001)$ and indicate the absence of
polarization on the rhodium atoms.",1703.04114v1
2017-06-04,The uncertainty of local background magnetic field orientation in anisotropic plasma turbulence,"In order to resolve and characterize anisotropy in turbulent plasma flows a
proper estimation of the background magnetic field is crucially important.
Various approaches to calculate the background magnetic fields, ranging from
local fields to globally averaged fields, are commonly used in the analysis of
turbulent data. Here we investigate how the uncertainty in the orientation of a
scale dependent background magnetic field influences the ability to resolve
anisotropy. Therefore we introduce a quantitative measure, the angle
uncertainty, which characterizes the uncertainty of the orientation of the
background magnetic field which turbulent structures are exposed to. The angle
uncertainty can be used as a condition to estimate the ability to resolve
anisotropy with certain accuracy. We apply our description to resolve spectral
anisotropy in fast solar wind data. We show that if the angle uncertainty grows
too large, the power of the turbulent fluctuations is attributed to false local
magnetic field angles, which may lead to an incorrect estimation of spectral
indices. In our results an apparent robustness of the spectral anisotropy to
false local magnetic field angles is observed, which can be explained by a
stronger increase of power for lower frequencies when the scale of the local
magnetic field is increased. The frequency dependent angle uncertainty is a
measure which can be applied to any turbulent system.",1706.01126v1
2017-07-03,Searching for a cosmological preferred direction with 147 rotationally supported galaxies,"It is well known that the Milgrom's MOND (modified Newtonian dynamics)
explains well the mass discrepancy problem in galaxy rotation curves. The MOND
predicts a universal acceleration scale below which the Newtonian dynamics is
invalid yet. The universal acceleration scale we got from the SPARC dataset is
$g_{\dag}=1.02\times10^{-10} \rm m~s^{-2}$. Milgrom suggested that the
acceleration scale may be a fingerprint of cosmology on local dynamics and
related with the Hubble constant $g_{\dag}\sim cH_0$. In this paper, we use the
hemisphere comparison method with the SPARC dataset to investigate the spatial
anisotropy on the acceleration scale. We find that the hemisphere of the
maximum acceleration scale is in the direction $(l,b) =
({175.5^\circ}^{+6^\circ}_{-10^\circ}, {-6.5^\circ}^{+8^\circ}_{-3^\circ})$
with $g_{\dag,max}=1.10\times10^{-10} \rm m~s^{-2}$, while the hemisphere of
the minimum acceleration scale is in the opposite direction $(l,b) =
({355.5^\circ}^{+6^\circ}_{-10^\circ}, {6.5^\circ}^{+3^\circ}_{-8^\circ})$ with
$g_{\dag,min}=0.76\times10^{-10} \rm m~s^{-2}$. The maximum anisotropy level
reaches up to $0.37\pm0.04$. Robust tests present that such a level of
anisotropy can't be reproduced by a statistically isotropic data. In addition,
we show that the spatial anisotropy on the acceleration scale has little
correlation with the non-uniform distribution of the SPARC data points in sky.
We also find that the maximum anisotropy direction is close with other
cosmological preferred directions, especially the direction of the ""Australia
dipole"" for the fine structure constant.",1707.00417v1
2017-08-18,Skyrmion robustness in non-centrosymmetric magnets with axial symmetry: The role of anisotropy and tilted magnetic fields,"We investigate the stability of N\'eel skyrmions against tilted magnetic
fields, in polar magnets with uniaxial anisotropy ranging from easy-plane to
easy-axis type. We construct the corresponding phase diagrams and investigate
the internal structure of skewed skyrmions with displaced cores. We find that
moderate easy-plane anisotropy increases the stability range of N\'eel
skyrmions for fields along the symmetry axis, while moderate easy-axis
anisotropy enhances their robustness against tilted magnetic fields. We stress
that the direction, along which the skyrmion cores are shifted, depends on the
symmetry of the underlying crystal lattice. The cores of N\'eel skyrmions,
realized in polar magnets with C$_{nv}$ symmetry, are displaced either along or
opposite to the off-axis (in-plane) component of the magnetic field depending
on the rotation sense of the magnetization, dictated by the sign of the
Dzyaloshinskii constant. The core shift of antiskyrmions, present in chiral
magnets with D$_{2d}$ symmetry, depends on the in-plane orientation of the
magnetic field and can be parallel, anti-parallel, or perpendicular to it. We
argue that the role of anisotropy in magnets with axially symmetric crystal
structure is different from that in cubic helimagnets. Our results can be
applied to address recent experiments on polar magnets with C$_{3v}$ symmetry,
GaV$_4$S$_8$ and GaV$_4$Se$_8$.",1708.05505v1
2017-10-16,Anisotropies of Ultra-high Energy Cosmic Rays Dominated by a Single Source in the Presence of Deflections,"This work presents a scenario of ultra-high energy cosmic ray source
distribution where a nearby source is solely responsible for the anisotropies
in arrival directions of cosmic rays while the rest of the sources contribute
only isotropically. An analytical approach focused on large-scale anisotropies,
which are influenced by deflections in a Kolmogorov-type turbulent magnetic
field, is employed to provide more general results. When the recent Pierre
Auger Observatory angular power spectrum above 8 EeV is used the restricted
model gives, under the assumption of the small angle approximation, a solution
where the RMS deflection with respect to the line of sight is $\alpha_{\rm rms}
= \left(50^{+11}_{-10}\right)^\circ$, while the relative flux from the single
source $\eta=0.03\pm 0.01$. Furthermore, the solution can be translated into
constraints on the source distance, luminosity, and extra-galactic magnetic
field strength. For Centaurus A and the Virgo cluster the required relation
between the coherence length and the RMS magnetic field strength is obtained: a
coherence length of $~\sim 100\,\mathrm{kpc}$ would imply the RMS field
strength around $1\,\mathrm{nG}$ for iron dominated and above $10\,\mathrm{nG}$
for proton dominated composition. We also performed trajectory simulations with
our publicly available code CRPropa to show that our analytical model can serve
as a good approximation as long as the deflections in cosmic magnetic fields
can be described as a random walk. The simulations showed that generally
structured fields tend to suppress large-scale anisotropies, especially the
dipole, compared to anisotropies at smaller scales described by higher
multipoles.",1710.05517v3
2017-11-08,Polarization of Sunyaev-Zeldovich signal due to electron pressure anisotropy in galaxy clusters,"We describe polarization of the Sunyaev-Zel'dovich (SZ) effect associated
with electron pressure anisotropy likely present in the intracluster medium
(ICM). The ICM is an astrophysical example of a weakly collisional plasma where
the Larmor frequencies of charged particles greatly exceed their collision
frequencies. This permits formation of pressure anisotropies, driven by
evolving magnetic fields via adiabatic invariance, or by heat fluxes. SZ
polarization arises in the process of Compton scattering of the cosmic
microwave background (CMB) photons off the thermal ICM electrons due to the
difference in the characteristic thermal velocities of the electrons along two
mutually orthogonal directions in the sky plane. The signal scales linearly
with the optical depth of the region containing large-scale correlated
anisotropy, and with the degree of anisotropy itself. It has the same spectral
dependence as the polarization induced by cluster motion with respect to the
CMB frame (kinematic SZ effect polarization), but can be distinguished by its
spatial pattern. { For the illustrative case of a galaxy cluster with a cold
front, where electron transport is mediated by Coulomb collisions, we estimate
the CMB polarization degree at the level of 10$^{-8}$ ($\sim 10$ nK). An
increase of the effective electron collisionality due to plasma instabilities
will reduce the effect. Such polarization, therefore, may be an independent
probe of the electron collisionality in the ICM, which is one of the key
properties of a high-$\beta$ weakly collisional plasma from the point of view
of both astrophysics and plasma theory.",1711.03084v1
2017-11-25,Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2,"Superconducting vortex cores have been extensively studied for magnetic
fields applied perpendicular to the surface by mapping the density of states
(DOS) through Scanning Tunneling Microscopy (STM). Vortex core shapes are often
linked to the superconducting gap anisotropy---quasiparticle states inside
vortex cores extend along directions where the superconducting gap is smallest.
The superconductor 2H-NbSe$_2$ crystallizes in a hexagonal structure and
vortices give DOS maps with a sixfold star shape for magnetic fields
perpendicular to the surface and the hexagonal plane. This has been associated
to a hexagonal gap anisotropy located on quasi two-dimensional Fermi surface
tubes oriented along the $c$ axis. The gap anisotropy in another,
three-dimensional, pocket is unknown. However, the latter dominates the STM
tunneling conductance. Here we measure DOS in magnetic fields parallel to the
surface and perpendicular to the $c$ axis. We find patterns of stripes due to
in-plane vortex cores running nearly parallel to the surface. The patterns
change with the in-plane direction of the magnetic field, suggesting that the
sixfold gap anisotropy is present over the whole Fermi surface. Due to a slight
misalignment between the vector of the magnetic field and the surface, our
images also show outgoing vortices. Their shape is successfully compared to
detailed calculations of vortex cores in tilted fields. Their features merge
with the patterns due to in plane vortices, suggesting that they exit at an
angle with the surface. Measuring the DOS of vortex cores in highly tilted
magnetic fields with STM can thus be used to study the superconducting gap
structure.",1711.09269v1
2018-05-01,Black Arsenic: A Layered Semiconductor with Extreme in-plane Anisotropy,"Two-dimensional (2D) layered materials emerge in recent years as a new
platform to host novel electronic, optical or excitonic physics and develop
unprecedented nanoelectronic and energy applications. By definition, these
materials are strongly anisotropic between within the basal plane and cross the
plane. The structural and property anisotropies inside their basal plane,
however, are much less investigated. Herein, we report a rare chemical form of
arsenic, called black-arsenic (b-As), as an extremely anisotropic layered
semiconductor. We have performed systematic characterization on the structural,
electronic, thermal and electrical properties of b-As single crystals, with
particular focus on its anisotropies along two in-plane principle axes,
armchair (AC) and zigzag (ZZ). Our analysis shows that b-As exhibits higher or
comparable electronic, thermal and electric transport anisotropies between the
AC and ZZ directions than any other known 2D crystals. Such extreme in-plane
anisotropies are able to potentially implement novel ideas for scientific
research and device applications.",1805.00418v1
2018-05-13,Pressure-induced spin reorientation transition in layered ferromagnetic insulator Cr2Ge2Te6,"Anisotropic magnetoresistance (AMR) of Cr2Ge2Te6 (CGT), a layered
ferromagnetic insulator, is investigated under an applied hydrostatic pressure
up to 2 GPa. The easy axis direction of the magnetization is inferred from the
AMR saturation feature in the presence and absence of the applied pressure. At
zero applied pressure, the easy axis is along the c-direction or perpendicular
to the layer. Upon application of a hydrostatic pressure>1 GPa, the uniaxial
anisotropy switches to easy-plane anisotropy which drives the equilibrium
magnetization from the c-axis to the ab-plane at zero magnetic field, which
amounts to a giant magnetic anisotropy energy change (>100%). As the
temperature is increased across the Curie temperature, the characteristic AMR
effect gradually decreases and disappears. Our first-principles calculations
confirm the giant magnetic anisotropy energy change with moderate pressure and
assign its origin to the increased off-site spin-orbit interaction of Te atoms
due to a shorter Cr-Te distance. Such a pressure-induced spin reorientation
transition is very rare in three-dimensional ferromagnets, but it may be common
to other layered ferromagnets with similar crystal structures to CGT, and
therefore offers a unique way to control magnetic anisotropy.",1805.04937v1
2018-05-23,Detection and Removal of B-mode Dust Foregrounds with Signatures of Statistical Anisotropy,"Searches for inflationary gravitational wave signals in the CMB B-mode
polarisation are expected to reach unprecedented power over the next decade. A
major difficulty in these ongoing searches is that galactic foregrounds such as
dust can easily mimic inflationary signals. Though typically foregrounds are
separated from primordial signals using the foregrounds' different frequency
dependence, in this paper we investigate instead the extent to which the
galactic dust B-modes' statistical anisotropy can be used to distinguish them
from inflationary B-modes, building on the work of Kamionkowski and Kovetz
(2014). In our work, we extend existing anisotropy estimators and apply them to
simulations of polarised dust to forecast their performance for future
experiments. Considering the application of this method as a null-test for dust
contamination to CMB-S4, we find that we can detect residual dust levels
corresponding to $r\sim0.001$ at $2\sigma$, which implies that statistical
anisotropy estimators will be a powerful diagnostic for foreground residuals
(though our results show some dependence on the dust simulation used). Finally,
considering applications beyond a simple null test, we demonstrate how
anisotropy statistics can be used to construct an estimate of the dust B-mode
map, which could potentially be used to clean the B-mode sky.",1805.09177v2
2018-06-07,Null Signal for the Cosmic Anisotropy in the Pantheon Supernovae Data,"The cosmological principle assumes that the universe is homogeneous and
isotropic on cosmic scales. There exist many works testing the cosmic
homogeneity and/or the cosmic isotropy of the universe in the literature. In
fact, some observational hints of the cosmic anisotropy have been claimed.
However, we note that the paucity of the data considered in the literature
might be responsible for the `found' cosmic anisotropy. So, it might disappear
in a large enough sample. Very recently, the Pantheon sample consisting of 1048
type Ia supernovae (SNIa) has been released, which is the largest
spectroscopically confirmed SNIa sample to date. In the present work, we test
the cosmic anisotropy in the Pantheon SNIa sample by using three methods, and
hence the results from different methods can be cross-checked. All the results
obtained by using the hemisphere comparison (HC) method, the dipole fitting
(DF) method and HEALPix suggest that no evidence for the cosmic anisotropy is
found in the Pantheon SNIa sample.",1806.02773v3
2018-07-29,"A family of high-temperature ferromagnetic monolayers with locked spin-dichroism-mobility anisotropy: MnNX and CrCX (X=Cl, Br, I; C=S, Se, Te)","Two-dimensional magnets have received increasing attention since Cr2Ge2Te6
and CrI3 were experimentally exfoliated and measured in 2017. Although layered
ferromagnetic metals were demonstrated at room temperature, a layered
ferromagnetic semiconductor with high Curie temperature (Tc) is yet to be
unveiled. Here, we theoretically predicted a family of high Tc ferromagnetic
monolayers, namely MnNX and CrCX (X=Cl, Br and I; C=S, Se and Te). Their Tc
values were predicted from over 100 K to near 500 K with Monte Carlo
simulations using an anisotropic Heisenberg model. Eight members among them
show semiconducting bandgaps varying from roughly 0.23 to 1.85 eV. These
semiconducting monolayers also show extremely large anisotropy, i.e. ~101 for
effective masses and ~102 for carrier mobilities, along the two in-plane
lattice directions of these layers. Additional orbital anisotropy leads to a
spin-locked linear dichroism, in different from previously known circular and
linear dichroisms in layered materials. Together with the mobility anisotropy,
it offers a spin-, dichroism- and mobility-anisotropy locking. These results
manifest the potential of this 2D family for both fundamental research and high
performance spin-dependent electronic and optoelectronic devices.",1807.11000v3
2018-08-06,Cosmic-Ray Anisotropy from Large Scale Structure and the effect of magnetic horizons,"Motivated by the ~7 % dipole anisotropy in the distribution of ultra-high
energy cosmic-rays (UHECRs) above 8 EeV, we explore the anisotropy induced by
the large scale structure, using constrained simulations of the local Universe
and taking into account the effect of magnetic fields. The value of the
intergalactic magnetic field (IGMF) is critical as it determines the UHECR
cosmic horizon. We calculate the UHECR sky maps for different values of the
IGMF variance and show the effect of the UHECR horizon on the observed
anisotropy. The footprint of the local ($\lesssim350$ Mpc) Universe on the
UHECR background, a small angular scale enhancement in the Northern Hemisphere,
is seen. At 11.5 EeV (the median value of the energy bin at which the dipole
has been reported), the LSS-induced dipole amplitude is $A_1\sim10\%$, for IGMF
in the range [0.3-3] nG for protons, helium and nitrogen, compatible with the
rms value derived from the cosmic power spectrum. However at these energies the
UHECRs are also influenced by the Galactic Magnetic Field (GMF) and we discuss
its effect on the LSS-induced anisotropy.",1808.02048v2
2018-09-02,Probing physical origin of anisotropic thermal transport in black phosphorus nanoribbons,"Black phosphorus (BP) has emerged as a promising candidate for next
generation electronics and optoelectronics among the 2D family materials due to
its extraordinary electrical/optical/optoelectronic properties. Interestingly,
BP shows strong anisotropic transport behaviour because of its puckered
honeycomb structure. Previous studies have demonstrated the thermal transport
anisotropy of BP and theoretically attribute this to the anisotropy in both
phonon dispersion relation and phonon relaxation time. However, the exact
origin of such strong anisotropy lacks clarity and has yet to be proven
experimentally. In this work, we probe the thermal transport anisotropy of BP
nanoribbons (NRs) by an electron beam technique. We provide direct evidence
that the origin of this anisotropy is dominated by the anisotropic phonon group
velocity for the first time, verified by Young modulus measurements along
different directions. It turns out that the ratio of thermal conductivity
between zigzag (ZZ) and armchair (AC) ribbons is almost same as that of the
corresponding Young modulus values. The results from first-principles
calculation are consistent with this experimental observation, where
anisotropic phonon group velocity between ZZ and AC is shown. Our results
provide fundamental insight into the anisotropic thermal transport in low
symmetric crystals.",1809.00302v1
2018-10-30,Anisotropy effects on the critical magnetic field in CaC$_{6}$ superconductor,"The calcium intercalated graphite (CaC$_{6}$) is considered to be a
representative material of the graphite intercalated superconductors, which
exhibits sizable anisotropy of the Fermi surface (FS). Herein, the influence of
the FS anisotropy on the critical magnetic field ($H_{C}$) in CaC$_{6}$
superconductor is comprehensively analyzed within the Migdal-Eliashberg (M-E)
formalism. To precisely account for the mentioned anisotropy effects, the
analysis is conducted in the framework of the six-band approximation, hitherto
not employed for calculations of the $H_{C}$ function in CaC$_{6}$ material.
For convenience, the obtained results are compared with the available one- and
three-band estimates reported by using the M-E theory. A notable signatures of
the increased number of bands are observed for the temperature dependent
$H_{C}$ functions. In particular, the $H_{C}$ function decreases at T=0 K as
the number of the considered bands is higher. Moreover, it is argued that the
six-band formalism yields the most physically relevant shape of the $H_{C}$
function among all considered approximations. Therefore, the six-band model
introduces not only quantitative but also qualitative changes to the results,
in comparison to the other discussed FS approximations. This observation
supports postulate that the six-band model constitutes minimal structure for FS
of CaC$_{6}$, but also magnify importance of anisotropy effects for the
critical magnetic field calculations.",1810.12878v1
2018-11-13,Interplay between Kitaev interaction and single ion anisotropy in ferromagnetic CrI$_3$ and CrGeTe$_3$ monolayers,"Magnetic anisotropy is crucially important for the stabilization of
two-dimensional (2D) magnetism, which is rare in nature but highly desirable in
spintronics and for advancing fundamental knowledge. Recent works on CrI$_3$
and CrGeTe$_3$ monolayers not only led to observations of the long-time-sought
2D ferromagnetism, but also revealed distinct magnetic anisotropy in the two
systems, namely Ising behavior for CrI$_3$ versus Heisenberg behavior for
CrGeTe$_3$. Such magnetic difference strongly contrasts with structural and
electronic similarities of these two materials, and understanding it at a
microscopic scale should be of large benefits. Here, first-principles
calculations are performed and analyzed to develop a simple Hamiltonian, to
investigate magnetic anisotropy of CrI$_3$ and CrGeTe$_3$ monolayers. The
anisotropic exchange coupling in both systems is surprisingly determined to be
of Kitaev-type. Moreover, the interplay between this Kitaev interaction and
single ion anisotropy (SIA) is found to naturally explain the different
magnetic behaviors of CrI$_3$ and CrGeTe$_3$. Finally, both the Kitaev
interaction and SIA are further found to be induced by spin-orbit coupling of
the heavy ligands (I of CrI$_3$ or Te of CrGeTe$_3$) rather than the commonly
believed 3d magnetic Cr ions.",1811.05413v1
2019-01-21,Paramagnetic squeezing of a uniformly expanding quark-gluon plasma in and out of equilibrium,"The plasma of quarks and gluons created in ultrarelativistic heavy-ion
collisions turns out to be paramagnetic. In the presence of a background
magnetic field, this paramagnetism thus leads to a pressure anisotropy, similar
to anisotropies appearing in a viscous fluid. In the present paper, we use this
analogy, and develop a framework similar to anisotropic hydrodynamics, to take
the pressure anisotropy caused, in particular, by the nonvanishing
magnetization of a plasma of quarks and gluons into account. We consider the
first two moments of the classical Boltzmann equation in the presence of an
electromagnetic source in the relaxation-time approximation, and derive a set
of coupled differential equations for the anisotropy parameter $\xi_0$ and the
effective temperature $\lambda_0$ of an ideal fluid with nonvanishing
magnetization. We also extend this method to a dissipative fluid with finite
magnetization in the presence of a strong and dynamical magnetic field. We
present a systematic method leading to the one-particle distribution function
of this magnetized dissipative medium in a first-order derivative expansion,
and arrive at analytical expressions for the shear and bulk viscosities in
terms of the anisotropy parameter $\xi$ and effective temperature $\lambda$. We
then solve the corresponding differential equations for $(\xi_0,\lambda_0)$ and
$(\xi,\lambda)$ numerically, and determine, in this way, the proper time and
temperature dependence of the energy density, directional pressures, speed of
sound, and the magnetic susceptibility of a longitudinally expanding magnetized
quark-gluon plasma in and out of equilibrium.",1901.06928v2
2019-03-26,The orbital anisotropy profiles of nearby globular clusters from Gaia Data Release 2,"Gaia Data Release 2 provides a wealth of data to study the internal structure
of nearby globular clusters. We use this data to investigate the internal
kinematics of 11 nearby globular clusters, with a particular focus on their
poorly-studied outer regions. We apply a strict set of selection criteria to
remove contaminating sources and create pure cluster-member samples over a
significant fraction of the radial range of each cluster. We confirm previous
measurements of rotation (or a lack thereof) in the inner regions of several
clusters, while extending the detection of rotation well beyond where it was
previously measured and finding a steady decrease in rotation with radius. We
also determine the orbital anisotropy profile and determine that clusters have
isotropic cores, are radially anisotropic out to $\approx$ 4 half-light radii
or $35\%$ of their limiting radii, and are then isotropic out to the limits of
our datasets. We detect for the first time the presence of radial anisotropy in
M 22, while confirming previous detections of radial anisotropy in 47 Tuc, M 3,
M 13, M 15, and $\omega$ Cen's innermost regions. The implications of these
measurements are that clusters can be separated into two categories: 1)
clusters with observed radial anisotropy that likely formed tidally
under-filling or are dynamically young, and 2) clusters that are primarily
isotropic that likely formed tidally filling or are dynamically old.",1903.11070v1
2019-04-05,Tailoring anomalous Nernst effect in stressed magnetostrictive film grown onto flexible substrate,"The anomalous Nernst effect in nanostructured magnetic materials is a key
phenomenon to optimally control and employ the internal energy dissipated in
electronic devices, being dependent on for instance the magnetic anisotropy of
the active element. Thereby, here we report a theoretical and experimental
investigation of the magnetic properties and anomalous Nernst effect in a
flexible magnetostrictive film with induced uniaxial magnetic anisotropy and
under external stress. Specifically, we calculate the magnetization behavior
and the thermoelectric voltage response from a theoretical approach for a
planar geometry and with a magnetic free energy density which takes into
account the induced uniaxial and magnetoelastic anisotropy contributions.
Experimentally, we verify modifications of the effective magnetic anisotropy
and thermoelectric voltage with the stress and explore the possibility of
tailoring the anomalous Nernst effect in a flexible magnetostrictive film by
modifying both, the magnetic field and external stress. We find quantitative
agreement between experiment and numerical calculations, thus elucidating the
magnetic and thermoelectric voltage behaviors, as well as providing evidence to
confirm the validity of the theoretical approach to describe the magnetic
properties and anomalous Nernst effect in ferromagnetic magnetostrictive films
having uniaxial magnetic anisotropy and submitted to external stress. Hence,
the results place flexible magnetostrictive systems as a promising candidate
for active elements in functionalized touch electronic devices.",1904.03125v1
2019-04-10,The search for anisotropy in the gravitational-wave background with pulsar-timing arrays,"Pulsar-timing arrays (PTAs) are seeking gravitational waves from
supermassive-black-hole binaries, and there are prospects to complement these
searches with stellar-astrometry measurements. Theorists still disagree,
however, as to whether the local gravitational-wave background will be
statistically isotropic, as arises if it is the summed contributions from many
SMBH binaries, or whether it exhibits the type of statistical anisotropy that
arises if the local background is dominated by a handful (or even one) bright
source. Here we derive, using bipolar spherical harmonics, the optimal PTA
estimators for statistical anisotropy in the GW background and simple estimates
of the detectability of this anisotropy. We provide results on the smallest
detectable amplitude of a dipole anisotropy (and several other low-order
multipole moments) and also the smallest detectable amplitude of a ""beam"" of
gravitational waves. Results are presented as a function of the signal-to-noise
with which the GW signal is detected and as a function of the number of pulsars
(assuming uniform distribution on the sky and equal sensitivity per pulsar). We
provide results first for measurements with a single time-domain window
function and then show how the results are augmented with the inclusion of
time-domain information. The approach here is intended to be conceptually
straightforward and to complement the results of more detailed (but
correspondingly less intuitive) modeling of the actual measurements.",1904.05348v3
2019-04-12,"Unusual thermoelectric transport anisotropy in quasi-2D, rhombohedral GeTe","In this study, we calculate the $T$=300 K scattering and thermoelectric
transport properties of rhombohedral GeTe using first-principles modeling. The
room-temperature phase of GeTe has a layered structure, with cross-plane and
in-plane directions oriented parallel and perpendicular to [111], respectively.
Based on rigorous electron-phonon scattering, our transport calculations reveal
unusual anisotropic properties; n-type GeTe has a cross-plane electrical
conductivity that is roughly 3$\times$ larger than in-plane. p-type GeTe,
however, displays opposite anisotropy with in-plane conducting roughly
2$\times$ more than cross-plane, as is expected in quasi-2D materials. The
power factor shows the same anisotropy as the electrical conductivity, since
the Seebeck coefficient is relatively isotropic. Interestingly, cross-plane
n-GeTe shows the largest mobility and power factor approaching 500 cm$^2$/V-s
and 32 $\mu$W/cm-K$^2$, respectively. The thermoelectric figure-of-merit, $zT$,
is enhanced as a result of this unusual anisotropy in n-GeTe since the lattice
thermal conductivity is minimized along cross-plane. This decouples the
preferred transport directions of electrons and phonons, leading to a threefold
increase in $zT$ along cross-plane compared to in-plane. The n-type anisotropy
results from high-velocity electron states formed by Ge p-orbitals that span
across the interstitial region. This surprising behavior, that would allow the
preferential conduction direction to be controlled by doping, could be observed
in other quasi-2D materials and exploited to achieve higher-performance
thermoelectrics.",1904.06439v2
2019-06-02,Comparison of Shear and Compression Jammed Packings of Frictional Disks,"We compare the structural and mechanical properties of mechanically stable
(MS) packings of frictional disks in two spatial dimensions (2D) generated with
isotropic compression and simple shear protocols from discrete element modeling
(DEM) simulations. We find that the average contact number and packing fraction
at jamming onset are similar (with relative deviations $< 0.5\%$) for MS
packings generated via compression and shear. In contrast, the average stress
anisotropy $\langle {\hat \Sigma}_{xy} \rangle = 0$ for MS packings generated
via isotropic compression, whereas $\langle {\hat \Sigma}_{xy} \rangle >0$ for
MS packings generated via simple shear. To investigate the difference in the
stress state of MS packings, we develop packing-generation protocols to first
unjam the MS packings, remove the frictional contacts, and then rejam them.
Using these protocols, we are able to obtain rejammed packings with nearly
identical particle positions and stress anisotropy distributions compared to
the original jammed packings. However, we find that when we directly compare
the original jammed packings and rejammed ones, there are finite stress
anisotropy deviations $\Delta {\hat \Sigma}_{xy}$. The deviations are smaller
than the stress anisotropy fluctuations obtained by enumerating the force
solutions within the null space of the contact networks generated via the DEM
simulations. These results emphasize that even though the compression and shear
jamming protocols generate packings with the same contact networks, there can
be residual differences in the normal and tangential forces at each contact,
and thus differences in the stress anisotropy.",1906.00438v1
2019-07-17,Neutron Scattering Study of Magnetic Anisotropy in a Tetragonal Antiferromagnet Bi$_2$CuO$_4$,"We present a comprehensive study of magnon excitations in the tetragonal
easy-plane anti-ferromagnet Bi$_2$CuO$_4$ using inelastic neutron scattering
and spin wave analyses. The nature of low energy magnons, and hence the
anisotropy in this material, has been controversial. We show unambiguously that
the low energy magnon spectrum consists of a gapped and a gapless mode, which
we attribute to out-of-plane and in-plane spin fluctuations, respectively. We
modelled the observed magnon spectrum using linear spin wave analysis of a
minimal anisotropic spin model motivated by the lattice symmetry. By studying
the magnetic field dependence of the (1, 0, 0) Bragg peak intensity and the
in-plane magnon intensity, we observed a spin-flop transition in the $ab$ plane
at $\sim0.4$~T which directly indicates the existence of a small in-plane
anisotropy that is classically forbidden. It is only by taking into account
magnon zero-point fluctuations beyond the linear spin wave approximation, we
could explain this in-plane anisotropy and its magnitude, the latter of which
is deduced from critical field of the spin-flop transition. The microscopic
origins of the observed anisotropic interactions are also discussed. We found
that our data is inconsistent with a large Dzyaloshinskii-Moriya interaction,
which suggests a potential departure of Bi$_2$CuO$_4$ from the conventional
theories of magnetic anisotropy for other cuprates.",1907.07784v2
2019-09-23,Effective macrospin model for $Co_{x}Fe_{3-x}O_{4}$ nanoparticles: decreasing the anisotropy by Co-doping?,"$Co$-doping of $Fe_{3}O_{4}$ magnetic nanoparticles is an effective way to
tailor their magnetic properties. When considering the two extreme cases of the
$Co_{x}Fe_{3-x}O_{4}$ series, i.e. the $x=0$ and $x=1$ values, one finds that
the system evolves from a negative cubic-anisotropy energy constant,
$K_{C}^{-}<0$, to a positive one, $K_{C}^{+}>0$. Thus, what happens for
intermediate $x$-compositions? In this work we present a very simple
phenomenological model for the anisotropy, under the \textit{macrospin}
approximation, in which the resultant anisotropy is just directly proportional
to the amount of $Co$. First, we perform a detailed analysis on a rather ideal
system in which the extreme values have the same magnitude (i.e.
$|K_{C}^{-}|=|K_{C}^{+}|$) and then we focus on the real $Co_{x}Fe_{3-x}O_{4}$
system, for which $|K_{C}^{+}|\sim 18|K_{C}^{-}|$. Remarkably, the approach
reproduces rather well the experimental values of the heating performance of
$Co_{x}Fe_{3-x}O_{4}$ nanoparticles, suggesting that our simple approach may in
fact be a good representation of the real situation. This gives rise to an
intriguing related possibility arises: a $Co$-doping composition should exist
for which the effective anisotropy tends to zero, estimated here as 0.05.",1909.10643v1
2019-10-04,Spin-wave directional anisotropies in antiferromagnetic Ba$_{3}$NbFe$_{3}$Si$_{2}$O$_{14}$,"Ba$_{3}$NbFe$_{3}$Si$_{2}$O$_{14}$ (langasite) is structurally and
magnetically single domain chiral with the magnetic helicity induced through
competing symmetric exchange interactions. Using neutron scattering, we show
that the spin-waves in antiferromagnetic langasite display directional
anisotropy. On applying a time reversal symmetry breaking magnetic field along
the $c$-axis, the spin wave energies differ when the sign is reversed for
either the momentum transfer $\pm$ $\vec{Q}$ or applied magnetic field $\pm$
$\mu_{0}$H. When the field is applied within the crystallographic $ab$-plane,
the spin wave dispersion is directionally \textit{isotropic} and symmetric in
$\pm$ $\mu_{0}$H. However, a directional anisotropy is observed in the spin
wave intensity. We discuss this directional anisotropy in the dispersion in
langasite in terms of a field induced precession of the dynamic unit cell
staggered magnetization. Directional anisotropy, or often referred to as non
reciprocal responses, can occur in antiferromagnetic phases in the absence of
the Dzyaloshinskii-Moriya interaction or other effects resulting from
spin-orbit coupling.",1910.01977v2
2019-10-14,Ultrafast domain wall motion in ferrimagnets induced by magnetic anisotropy gradient,"The ultrafast magnetic dynamics in compensated ferrimagnets not only provides
information similar to antiferromagnetic dynamics, but more importantly opens
new opportunities for future spintronic devices [Kim et al., Nat. Mater. 16,
1187 (2017)]. One of the most essential issues for device design is searching
for low-power-consuming and high-efficient methods of controlling domain wall.
In this work, we propose to use the voltage-controlled magnetic anisotropy
gradient as an excitation source to drive the domain wall motion in
ferrimagnets. The ultrafast wall motion under the anisotropy gradient is
predicted theoretically based on the collective coordinate theory, which is
confirmed by the atomistic micromagnetic simulations. The antiferromagnetic
spin dynamics is realized at the angular momentum compensation point, and the
wall shifting has a constant speed under small gradient and can be slightly
accelerated under large gradient due to the broadened wall width during the
motion. For nonzero net angular momentum, the Walker breakdown occurs at a
critical anisotropy gradient significantly depending on the second anisotropy
and interfacial Dzyaloshinkii-Moriya interaction, which is highly appreciated
for further experiments including the materials selection and device geometry
design. More importantly, this work unveils a low-power-consuming method of
controlling the domain wall in ferrimagnets, benefiting to future spintronic
applications.",1910.05918v1
2019-10-14,CMB anisotropy and BBN constraints on pre-recombination decay of dark matter to visible particles,"Injection of high energy electromagnetic particles around the recombination
epoch can modify the standard recombination history and therefore the CMB
anisotropy power spectrum. Previous studies have put strong constraints on the
amount of electromagnetic energy injection around the recombination era
(redshifts $z\lesssim 4500$). However, energy injected in the form of energetic
($>$ keV) visible standard model particles is not deposited instantaneously.
The considerable delay between the time of energy injection and the time when
all energy is deposited to background baryonic gas and CMB photons, together
with the extraordinary precision with which the CMB anisotropies have been
measured, means that CMB anisotropies are sensitive to energy that was injected
much before the epoch of recombination. We show that the CMB anisotropy power
spectrum is sensitive to energy injection even at $z = 10000$, giving stronger
constraints compared to big bang nucleosynthesis and CMB spectral distortions.
We derive, using Planck CMB data, the constraints on long-lived unstable
particles decaying at redshifts $z\lesssim 10000$ (lifetime $\tau_X\gtrsim
10^{11}$s) by explicitly evolving the electromagnetic cascades in the expanding
Universe, thus extending previous constraints to lower particle lifetimes. We
also revisit the BBN constraints and show that the delayed injection of energy
is important for BBN constraints. We find that the constraints can be weaker by
a factor of few to almost an order of magnitude, depending on the energy, when
we relax the quasi-static or on-the-spot assumptions.",1910.06272v2
2019-10-19,Mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles in PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 2.76 and 5.02 TeV,"Anisotropies in the initial energy density distribution of the quark-gluon
plasma created in high energy heavy ion collisions lead to anisotropies in the
azimuthal distributions of the final-state particles known as collective flow.
Fourier harmonic decomposition is used to quantify these anisotropies. The
higher-order harmonics can be induced by the same order anisotropies (linear
response) or by the combined influence of several lower order anisotropies
(nonlinear response) in the initial state. The mixed higher-order anisotropic
flow and nonlinear response coefficients of charged particles are measured as
functions of transverse momentum and centrality in PbPb collisions at
nucleon-nucleon center-of-mass energies $\sqrt{s_\mathrm{NN}} =$ 2.76 and 5.02
TeV with the CMS detector. The results are compared with viscous hydrodynamic
calculations using several different initial conditions, as well as microscopic
transport model calculations. None of the models provides a simultaneous
description of the mixed higher-order flow harmonics and nonlinear response
coefficients.",1910.08789v2
2019-10-21,Overlooked transportation anisotropies in d-band correlated rare-earth perovskite nickelates,"Anisotropies in electronic transportations conventionally originate from the
nature of low symmetries in crystal structures, and were not anticipated for
perovskite oxides, the crystal asymmetricity of which is far below, e.g. van
der Waals or topological crystal. Beyond conventional expectations, herein we
demonstrate pronounced anisotropies in the inter-band coulomb repulsion
dominated electronic transportation behaviors under low-dimensional confinement
for the perovskite family of rare-earth nickelates (ReNiO3). From one aspect,
imparting bi-axial interfacial strains upon various lattice planes results in
extrinsic anisotropies in the abrupt orbital transitions of ReNiO3, and their
metal to insulator transition behaviors that elevates the transition
temperature beyond the existing merit. From the other aspect, the in-plane
orbital entropy associated to the in-plane symmetry of the NiO6 octahedron
within ReNiO3 causes intrinsic anisotropies for the gradually orbital
transition with temperature to further improve their thermistor transportation
properties. The present work unveils the overlooked role of the electronic
orbital directionality within low dimensional correlated perovskites that can
trigger anisotropic transportation behaviors, in spite of their relatively
symmetric crystal structures. Establishing anisotropic transportations
integrating the electron correlation and quantum confinement effects will bring
in a new freedom for achieving further improvement in transportation properties
of multi-functional perovskite oxides.",1910.09160v1
2019-11-04,Validation and noise robustness assessment of microscopic anisotropy estimation with clinically feasible double diffusion encoding MRI,"Purpose: Double diffusion encoding (DDE) MRI enables the estimation of
microscopic diffusion anisotropy, yielding valuable information on tissue
microstructure. A recent study proposed that the acquisition of rotationally
invariant DDE metrics, typically obtained using a spherical ""5-design"", could
be greatly simplified by assuming Gaussian diffusion, facilitating reduced
acquisition times that are more compatible with clinical settings. Here, we aim
to validate the new minimal acquisition scheme against the standard DDE
5-design, and to quantify the proposed method's noise robustness to facilitate
future clinical use. Methods: DDE MRI experiments were performed on both ex
vivo and in vivo rat brains at 9.4 T using the 5-design and the proposed
minimal design and taking into account the difference in the number of
acquisitions. The ensuing microscopic fractional anisotropy ({\mu}FA) maps were
compared over a range of b-values up to 5000 s/mm2. Noise robustness was
studied using analytical calculations and numerical simulations. Results: The
minimal protocol quantified {\mu}FA at an accuracy comparable to the estimates
obtained via the more theoretically robust DDE 5-design. {\mu}FA's sensitivity
to noise was found to strongly depend on compartment anisotropy and tensor
magnitude in a non-linear fashion. When {\mu}FA < 0.75 or when mean diffusivity
is particularly low, very high signal to noise ratio (SNR) is required for
precise quantification of {\mu}FA. Conclusion: Our work supports using DDE for
quantifying microscopic diffusion anisotropy in clinical settings but raises
hitherto overlooked precision issues when measuring {\mu}FA with DDE and
typical clinical SNR.",1911.01148v1
2019-11-13,Extended FLRW Models: dynamical cancellation of cosmological anisotropies,"We investigate a corner of the Bianchi models that has not received much
attention: ""extended FLRW models"" (eFLRW) defined as a cosmological model with
underlying anisotropic Bianchi geometry that nevertheless expands isotropically
and can be mapped onto a reference FLRW model with the same expansion history.
In order to investigate the stability and naturalness of such models in a
dynamical systems context, we consider spatially homogeneous models that
contain a massless scalar field $\varphi$ and a non-tilted perfect fluid
obeying an equation of state $p=w\rho$. Remarkably, we find that matter
anisotropies and geometrical anisotropies tend to cancel out dynamically.
Hence, the expansion is asymptotically isotropic under rather general
conditions. Although extended FLRW models require a special matter sector with
anisotropies that are 'fine-tuned"" relative to geometrical anisotropies, our
analysis shows that such solutions are dynamically preferred attractors in
general relativity. Specifically, we prove that all locally rotationally
symmetric Bianchi type III universes with space-like $\nabla_\mu\varphi$ are
asymptotically shear-free, for all $w\in[-1,1]$. Moreover, all shear-free
equilibrium sets with anisotropic spatial curvature are proved to be stable
with respect to all homogeneous perturbations for $w\geq -1/3$.",1911.05793v2
2020-01-29,Stationary and dynamical properties of two harmonically trapped bosons in the crossover from two dimensions to one,"We unravel the stationary properties and the interaction quench dynamics of
two bosons, confined in a two-dimensional anisotropic harmonic trap. A
transcendental equation is derived giving access to the energy spectrum and
revealing the dependence of the energy gaps on the anisotropy parameter. The
relation between the two and the one dimensional scattering lengths as well as
the Tan contacts is established. The contact, capturing the two-body short
range correlations, shows an increasing tendency for a larger anisotropy.
Subsequently, the interaction quench dynamics from attractive to repulsive
values and vice versa is investigated for various anisotropies. A closed
analytical form of the expansion coefficients of the two-body wavefunction,
during the time evolution is constructed. The response of the system is studied
by means of the time-averaged fidelity, the spectra of the spatial extent of
the cloud in each direction and the one-body density. It is found that as the
anisotropy increases, the system becomes less perturbed independently of the
interactions while for fixed anisotropy quenches towards the non-interacting
regime perturb the system in the most efficient manner. Furthermore, we
identify that in the tightly confined direction more frequencies are involved
in the dynamics stemming from higher-lying excited states.",2001.10722v3
2020-02-16,Using anisotropic 3D Minkowski functionals for trabecular bone characterization and biomechanical strength prediction in proximal femur specimens,"The ability of Anisotropic Minkowski Functionals (AMFs) to capture local
anisotropy while evaluating topological properties of the underlying gray-level
structures has been previously demonstrated. We evaluate the ability of this
approach to characterize local structure properties of trabecular bone
micro-architecture in ex vivo proximal femur specimens, as visualized on
multi-detector CT, for purposes of biomechanical bone strength prediction. To
this end, volumetric AMFs were computed locally for each voxel of volumes of
interest (VOI) extracted from the femoral head of 146 specimens. The local
anisotropy captured by such AMFs was quantified using a fractional anisotropy
measure; the magnitude and direction of anisotropy at every pixel was stored in
histograms that served as a feature vectors that characterized the VOIs. A
linear multi-regression analysis algorithm was used to predict the failure load
(FL) from the feature sets; the predicted FL was compared to the true FL
determined through biomechanical testing. The prediction performance was
measured by the root mean square error (RMSE) for each feature set. The best
prediction performance was obtained from the fractional anisotropy histogram of
AMF Euler Characteristic (RMSE = 1.01 +- 0.13), which was significantly better
than MDCT-derived mean BMD (RMSE = 1.12 +- 0.16, p<0.05). We conclude that such
anisotropic Minkowski Functionals can capture valuable information regarding
regional trabecular bone quality and contribute to improved bone strength
prediction, which is important for improving the clinical assessment of
osteoporotic fracture risk.",2002.07156v1
2020-02-24,A Generalized framework of weak value amplification in path interference of polarized light for the enhancement of all possible polarization anisotropy effects,"Using the profound interferometric philosophy of weak value amplification, we
propose a simple, general and a robust polarization method for the
amplification and quantification of small magnitudes of all possible
polarization anisotropy effects in a single experimental embodiment. The
approach is experimentally realized by introducing a weak coupling between the
polarization degree of freedom of light and the path degree of freedom in a
Mach-Zehnder interferometer in the presence of a weak anisotropy effect. Real
and imaginary weak value amplifications of different polarization anisotropy
effects are manifested as characteristic changes in relevant Stokes vector
elements at the exit port of the interferometer, which follow orthogonal
trajectories in the Poincare sphere. The proof of concept experiment
demonstrates that using this scheme, one can faithfully extract and quantify
anisotropy parameter that is smaller than the typical sensitivity of
measurement of a given Stokes parameter of a traditional polarimeter by a large
weak value amplification factor. This opens up possibility of a sample
measuring weak value polarimeter for studying rich variety of fundamental
optical effects and for materials characterization and precision metrology.",2002.10093v2
2020-03-28,Acoustic Wave Induced FMR Assisted Spin-Torque Switching of Perpendicular MTJs with Anisotropy Variation,"We have investigated Surface Acoustic Wave (SAW) induced ferromagnetic
resonance (FMR) assisted Spin Transfer Torque (STT) switching of perpendicular
MTJ (p-MTJ) with inhomogeneities using micromagnetic simulations that include
the effect of thermal noise. With suitable frequency excitation, the SAW can
induce ferromagnetic resonance in magnetostrictive materials, and the
magnetization can precesses in a cone with high deflection from the
perpendicular direction. With incorporation of inhomogeneity via lateral
anisotropy variation as well as room temperature thermal noise, the
magnetization precession in different gains can be significantly incoherent.
Interestingly, the precession in different grains are found to be in phase,
even though the precession amplitude (angle of deflection from the
perpendicular direction) vary across grains of different anisotropy.
Nevertheless, the high mean deflection angle can complement the STT switching
by reducing the STT current significantly; even though the applied stress
induced change in anisotropy is much lower than the total anisotropy barrier.
This work indicates that SAW assisted switching can improve energy efficiency
while being scalable to very small dimensions, which is technologically
important for STT-RAM and elucidates the physical mechanism for the potential
robustness of this paradigm in realistic scenarios with thermal noise and
material inhomogeneity",2003.12903v1
2020-04-11,Investigation of Magnetic Anisotropy and Heat Dissipation in Thin Films of Compensated Antiferromagnet CuMnAs by Pump-probe Experiment,"We recently reported on a method to determine the easy axis position in a 10
nm thick film of the fully compensated antiferromagnet CuMnAs. The film had a
uniaxial magnetic anisotropy and the technique utilized a magneto-optical pump
and probe experiment [Nature Photonics 11, 91 (2017)]. In this contribution we
discuss the applicability of this method for the investigation of a broader set
of epitaxial CuMnAs films having different thicknesses. This work reveals that
the equilibrium magnetic anisotropy can be studied only in samples where this
anisotropy is rather strong. However, in the majority of CuMnAs films, the
impact of a strong pump pulse induces nano-fragmentation of the magnetic
domains and, therefore, the magnetic anisotropy measured by the pump-probe
technique differs substantially from that in the equilibrium conditions. We
also demonstrate that optical pump-probe experiment can be used very
efficiently to study the local heating and heat dissipation in CuMnAs epitaxial
layers. In particular, we determined the electron-phonon relaxation time in
CuMnAs. We also observed that for a local film heating by a focused laser the
thinner films are heated more, but the heat is dissipated considerably faster
than in the case of thicker films. This illustrates that the optical pump-probe
experiment is a valuable characterization tool for the heat management
optimization in the CuMnAs memory devices and can be applied in a similar way
to those used during heat-assisted magnetic recording (HAMR) technology
development for the latest generation of hard drive disks.",2004.05360v2
2020-04-23,Correlation-driven eightfold magnetic anisotropy in a two-dimensional oxide monolayer,"Engineering magnetic anisotropy in two-dimensional systems has enormous
scientific and technological implications. The uniaxial anisotropy universally
exhibited by two-dimensional magnets has only two stable spin directions,
demanding 180 degrees spin switching between states. We demonstrate a novel
eightfold anisotropy in magnetic SrRuO3 monolayers by inducing a spin
reorientation in (SrRuO3)1/(SrTiO3)N superlattices, in which the magnetic easy
axis of Ru spins is transformed from uniaxial <001> direction (N = 1 and 2) to
eightfold <111> directions (N = 3, 4 and 5). This eightfold anisotropy enables
71 and 109 degrees spin switching in SrRuO3 monolayers, analogous to 71 and 109
degrees polarization switching in ferroelectric BiFeO3. First-principle
calculations reveal that increasing the SrTiO3 layer thickness induces an
emergent correlation-driven orbital ordering, tuning spin-orbit interactions
and reorienting the SrRuO3 monolayer easy axis. Our work demonstrates that
correlation effects can be exploited to substantially change spin-orbit
interactions, stabilizing unprecedented properties in two-dimensional magnets
and opening rich opportunities for low-power, multi-state device applications.",2004.10939v1
2020-05-04,Anisotropy of electronic correlations: On the applicability of local theories to layered materials,"Besides the chemical constituents, it is the lattice geometry that controls
the most important material properties. In many interesting compounds, the
arrangement of elements leads to pronounced anisotropies, which reflect into a
varying degree of quasi two-dimensionality of their low-energy excitations.
Here, we start by classifying important families of correlated materials
according to a simple measure for the tetragonal anisotropy of their ab initio
electronic (band) structure. Second, we investigate the impact of a
progressively large anisotropy in driving the non-locality of many-body
effects. To this end, we tune the Hubbard model from isotropic cubic in three
dimensions to the two-dimensional limit and analyze it using the dynamical
vertex approximation. For sufficiently isotropic hoppings, we find the
self-energy to be well separable into a static non-local and a dynamical local
contribution. While the latter could potentially be obtained from dynamical
mean-field approaches, we find the former to be non-negligible in all cases.
Further, by increasing the model-anisotropy, we quantify the degree of quasi
two-dimensionality which causes this ""space-time separation"" to break down. Our
systematic analysis improves the general understanding of electronic
correlations in anisotropic materials, heterostructures and ultra-thin films,
and provides useful guidance for future realistic studies.",2005.01369v1
2020-05-11,Skyrmion confinement and dynamics in tracks patterned with magnetic anisotropy: theory and simulations,"Skyrmion is a topologically protected spin texture excited in magnetic thin
films. The radii of skyrmions are typically 10-100 nm. Because of the size, the
skyrmion is expected to be a candidate for memory and novel-device usages. To
realize the futuristic devices that will be using the skyrmion circuit, the
tracks which guide the motion of skyrmions are needed. The tracks patterned
with differences in the magnetic-anisotropy energy are well-paved without a
potential pocket, whereas the tracks carved out of magnetic films have the
potential pockets at corners due to the demagnetizing field. Therefore, the
tracks patterned with the magnetic anisotropy plays a key role in making the
skyrmion circuits. The experiment along this idea has been conducted for the
hub and bent tracks. However, we have little known the motion of skyrmions in
these tracks. This work aims to identify the forces acting between skyrmions
and walls of the tracks. The static force on a skyrmion can be expressed as
minus the gradient of the potential energy caused by the magnetic-anisotropy
undulation. The potential can be estimated numerically, modeling the shape of
skyrmions with their radii and domain wall widths. We find that the forces
depend not only on the distance from the wall but also on the shape of
skyrmions. We have also performed micromagnetic simulations where the Magnus
force and the acceleration by the magnetic-anisotropy gradient are taken into
account as well as the force by the walls. The simulation results show good
agreement with those calculated from the modeled skyrmions.",2005.04860v1
2020-06-01,Giant optical anisotropy in transition metal dichalcogenides for next-generation photonics,"Large optical anisotropy observed in a broad spectral range is of paramount
importance for efficient light manipulation in countless devices. Although a
giant anisotropy was recently observed in the mid-infrared wavelength range,
for visible and near-infrared spectral intervals, the problem remains acute
with the highest reported birefringence values of 0.8 in BaTiS3 and h-BN
crystals. This inspired an intensive search for giant optical anisotropy among
natural and artificial materials. Here, we demonstrate that layered transition
metal dichalcogenides (TMDCs) provide an answer to this quest owing to their
fundamental differences between intralayer strong covalent bonding and weak
interlayer van der Walls interaction. To do this, we carried out a correlative
far- and near-field characterization validated by first-principle calculations
that reveals an unprecedented birefringence of 1.5 in the infrared and 3 in the
visible light for MoS2. Our findings demonstrate that this outstanding
anisotropy allows for tackling the diffraction limit enabling an avenue for
on-chip next-generation photonics.",2006.00884v3
2020-06-04,Observational quantification of three-dimensional anisotropies and scalings of space plasma turbulence at kinetic scales,"A statistical survey of spectral anisotropy of space plasma turbulence is
performed using five years measurements from MMS in the magnetosheath. By
measuring the five-point second-order structure functions of the magnetic
field, we have for the first time quantified the three-dimensional anisotropies
and scalings at sub-ion-scales ($<$ 100 km). In the local reference frame
$(\hat L_{\perp}, \hat l_{\perp}, \hat l_{\parallel})$ defined with respect to
local mean magnetic field $\boldsymbol {B}_0$ (Chen et al. 2012), the
""statistical eddies"" are found to be mostly elongated along $\boldsymbol {B}_0$
and shortened in the direction perpendicular to both $\boldsymbol {B}_0$ and
local field fluctuations. From several $d_i$ (ion inertial length) toward
$\sim$ 0.05 $d_i$, the ratio between eddies' parallel and perpendicular lengths
features a trend of rise then fall, whereas the anisotropy in the perpendicular
plane appears scale-invariant. Specifically, the anisotropy relations for the
total magnetic field at 0.1-1.0 $d_i$ are obtained as $l_{\parallel} \simeq
2.44 \cdot l_{\perp}^{0.71}$, and $L_{\perp} \simeq 1.58 \cdot
l_{\perp}^{1.08}$, respectively. Our results provide new observational evidence
to compare with phenomenological models and numerical simulations, which may
help to better understand the nature of kinetic scale turbulence.",2006.02722v1
2020-07-14,QCD Axions and CMB Anisotropy,"In this paper, we consider a possibility that the temperature anisotropy of
cosmic microwave background (CMB) is dominantly generated by the primordial
fluctuations of QCD-axion like particles under a circumstance that inflaton's
perturbation is too small to explain the CMB anisotropy. Since the axion
potential is generated by acquiring its energy from radiation, the primordial
fluctuations of the axion field generated in the inflation era are correlated
with the CMB anisotropies. Consequently, the observations stringently constrain
a model of the axion and the early universe scenario. The following conditions
must be satisfied: (i) sufficient amplitudes of the CMB anisotropy (ii)
consistency with the axion isocurvature constraint and (iii) the
non-Gaussianity constraint. To satisfy these conditions, a large energy
fraction $\Omega_A^{}$ of the axion is necessary at the QCD scale when the
axion-potential is generated, but simultaneously, it must become tiny at the
present era due to the isocurvature constraint. Thus an additional scenario of
the early universe, such as low scale thermal inflation, is inevitable to
dilute the axions after the QCD scale. We investigate such a model and obtain
its allowed parameter region.",2007.06802v2
2020-07-16,Stability of in-plane and out-of-plane chiral skyrmions in epitaxial MnSi(111)/Si(111) thin films: surface twists versus easy-plane anisotropy,"The revisited theoretical phase diagrams for thin films of cubic helimagnets
with the easy-plane anisotropy are shown to have different topology as
previously reported [Phys. Rev. B 85, 094429 (2012)]. For both in-plane and
out-of-plane directions of an applied magnetic field, the phase diagrams
exhibit extensive areas of stable skyrmions, which overlap for a wide range of
anisotropy parameters. Although the existence of the out-of-plane skyrmions was
contradicted within the previous theoretical models, we prove that additional
surface twists lead to their stability, while the moderate easy-plane
anisotropy increases the stability range of in-plane skyrmions. Moreover, the
interplay between the anisotropy and the surface twists gives rise to a stable
spiral state canted with respect to the surfaces. Being absent in bulk
helimagnets, this oblique spiral occupies vast areas at the phase diagrams in
thin-film nanosystems and serves as a connecting-link between cones and
helicoids. Our theory gives clear directions for renewed experimental studies
of in-plane and out-of-plane skyrmions in epitaxial MnSi(111)/Si(111) thin
films.",2007.08065v1
2020-08-31,Single-ion anisotropy effects on the critical behaviors of quantum entanglement and correlation in the spin-1 Heisenberg chain,"Quantum entanglement and correlations in the spin-1 Heisenberg chain with
single-ion anisotropy are investigated using the quantum renormalization group
method. Negativity and quantum discord (QD) are calculated with various
anisotropy parameters $\bigtriangleup$ and single-ion anisotropy parameters
$D$. We focus on the relations between two abovementioned physical quantities
and on transitions between the N\'eel, Haldane, and Large-D phases. It is found
that both negativity and QD exhibit step-like patterns in different phases as
the size of the system increases. Interestingly, the single-ion anisotropy
parameter $D$, which can be modulated using nuclear electric resonance (2020
\textit{Nature} \textbf{579} 205), plays an important role in tuning the
quantum phase transition (QPT) of the system. Both the first partial derivative
of the negativity and quantum discord with respect to $D$ or $\bigtriangleup$
exhibit nonanalytic behavior at the phase transition points, which corresponds
directly to the divergence of the correlation length. The quantum correlation
critical exponents derived from negativity and QD are equal, and are the
reciprocal of the correlation length exponent at each critical point. This work
extends the application of quantum entanglement and correlations as tools for
depicting QPTs in spin-1 systems.",2008.13641v3
2020-09-09,Minimum variance estimation of statistical anisotropy via galaxy survey,"We consider the benefits of measuring cosmic statistical anisotropy from
redshift-space correlators of the galaxy number density fluctuation and the
peculiar velocity field without adopting the plane-parallel (PP) approximation.
Since the correlators are decomposed using the general tripolar spherical
harmonic (TripoSH) basis, we can deal with wide-angle contributions untreatable
by the PP approximation, and at the same time, target anisotropic signatures
can be cleanly extracted. We, for the first time, compute the covariance of the
TripoSH decomposition coefficient and the Fisher matrix to forecast the
detectability of statistical anisotropy. The resultant expression of the
covariance is free from nontrivial mixings between each multipole moment caused
by the PP approximation and hence the detectability is fully optimized.
Compared with the analysis under the PP approximation, the superiority in
detectability is always confirmed, and it is highlighted, especially in the
cases that the shot noise level is large and that target statistical anisotropy
has a blue-tilted shape in Fourier space. The application of the TripoSH-based
analysis to forthcoming all-sky survey data could result in constraints on
anisotropy comparable to or tighter than the current cosmic microwave
background ones.",2009.04355v2
2020-09-14,"Effect of controlled point-like disorder induced by 2.5 MeV electron irradiation on nematic resistivity anisotropy of hole-doped (Ba,K)Fe$_2$As$_2$","In-plane anisotropy of electrical resistivity was studied in samples of the
hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ in the composition range $0.21 \leq x
\leq 0.26$ where anisotropy changes sign. Low-temperature ($\sim$20~K)
irradiation with relativistic 2.5 MeV electrons was used to control the level
of disorder and residual resistivity of the samples. Modification of the
stress-detwinning technique enabled measurements of the same samples before and
after irradiation, leading to conclusion of anisotropic character of
predominantly inelastic scattering processes. Our main finding is that the
resistivity anisotropy is of the same sign irrespective of residual
resistivity, and remains the same in the orthorhombic $C_2$ phase above the
re-entrant tetragonal transition. Unusual $T$-linear dependence of the
anisotropy $\Delta \rho \equiv \rho_a(T)-\rho_b(T)$ is found in pristine
samples with $x=$0.213 and $x=$0.219, without similar signatures in either
$\rho_a(T)$ or $\rho_b(T)$. We show that this feature can be reproduced by a
phenomenological model of R.~M.~Fernandes {\it et al.} Phys. Rev. Lett. {\bf
107},217002 (2011). We speculate that onset of fluctuations of nematic order on
approaching the instability towards the re-entrant tetragonal phase contributes
to this unusual dependence.",2009.06753v1
2020-10-02,Singular magnetic anisotropy in the nematic phase of FeSe,"FeSe is arguably the simplest, yet the most enigmatic, iron-based
superconductor. Its nematic but non-magnetic ground state is unprecedented in
this class of materials and stands out as a current puzzle. Here, our NMR
measurements in the nematic state of mechanically detwinned FeSe reveal that
both the Knight shift and the spin-lattice relaxation rate 1/T_1 possess an
in-plane anisotropy opposite to that of the iron pnictides LaFeAsO and
BaFe2As2. Using a microscopic electron model that includes spin-orbit coupling,
our calculations show that an opposite quasiparticle weight ratio between the
d_xz and d_yz orbitals leads to an opposite anisotropy of the orbital magnetic
susceptibility, which explains our Knight shift results. We attribute this
property to a different nature of nematic order in the two compounds,
predominantly bond-type in FeSe and onsite ferro-orbital in pnictides. The T_1
anisotropy is found to be inconsistent with existing neutron scattering data in
FeSe, showing that the spin fluctuation spectrum reveals surprises at low
energy, possibly from fluctuations that do not break C_4 symmetry. Therefore,
our results reveal that important information is hidden in these anisotropies
and they place stringent constraints on the low-energy spin correlations as
well as on the nature of nematicity in FeSe.",2010.01020v1
2020-10-02,Electron Temperature Anisotropy and Electron Beam Constraints From Electron Kinetic Instabilities in the Solar Wind,"Electron temperature anisotropies and electron beams are nonthermal features
of the observed nonequilibrium electron velocity distributions in the solar
wind. In collision-poor plasmas these nonequilibrium distributions are expected
to be regulated by kinetic instabilities through wave-particle interactions.
This study considers electron instabilities driven by the interplay of core
electron temperature anisotropies and the electron beam, and firstly gives a
comprehensive analysis of instabilities in arbitrary directions to the
background magnetic field. It clarifies the dominant parameter regime (e.g.,
parallel core electron plasma beta $\beta_{\mathrm{ec\parallel}}$, core
electron temperature anisotropy $A_{\mathrm{ec}}\equiv
T_{\mathrm{ec\perp}}/T_{\mathrm{ec\parallel}}$, and electron beam velocity
$V_{\mathrm{eb}}$) for each kind of electron instability (e.g., the electron
beam-driven electron acoustic/magnetoacoustic instability, the electron
beam-driven whistler instability, the electromagnetic electron cyclotron
instability, the electron mirror instability, the electron firehose
instability, and the ordinary-mode instability). It finds that the electron
beam can destabilize electron acoustic/magnetoacoustic waves in the
low-$\beta_{\mathrm{ec\parallel}}$ regime, and whistler waves in the medium-
and large-$\beta_{\mathrm{ec\parallel}}$ regime. It also finds that a new
oblique fast-magnetosonic/whistler instability is driven by the electron beam
with $V_{\mathrm{eb}}\gtrsim7V_{\mathrm{A}}$ in a regime where
$\beta_{\mathrm{ec\parallel}}\sim0.1-2$ and $A_{\mathrm{ec}}<1$. Moreover, this
study presents electromagnetic responses of each kind of electron instability.
These results provide a comprehensive overview for electron instability
constraints on core electron temperature anisotropies and electron beams in the
solar wind.",2010.01066v1
2020-10-10,Highly anisotropic two-dimensional metal in monolayer MoOCl$_2$,"Anisotropy is a general feature in materials. Strong anisotropy could lead to
interesting physical properties and useful applications. Here, based on
first-principles calculations and theoretical analysis, we predict a stable
two-dimensional (2D) material---the monolayer MoOCl$_2$, and show that it
possesses intriguing properties related to its high anisotropy. Monolayer
MoOCl$_2$ can be readily exfoliated from the van der Waals layered bulk, which
has already been synthesized. We show that a high in-plane anisotropy manifests
in the structural, phononic, mechanical, electronic, and optical properties of
monolayer MoOCl$_2$. The material is a metal with highly anisotropic Fermi
surfaces, giving rise to open orbits at the Fermi level, which can be probed in
magneto-transport. Remarkably, the combination of high anisotropy and metallic
character makes monolayer MoOCl$_2$ an almost ideal hyperbolic material. It has
two very wide hyperbolic frequency windows from 0.41 eV (99 THz) to 2.90 eV
(701 THz), and from 3.63 eV (878 THz) to 5.54 eV (1340 THz). The former window
has a large overlap with the visible spectrum, and the dissipation for most
part of this window is very small. The window can be further tuned by the
applied strain, such that at a chosen frequency, a transition between elliptic
and hyperbolic character can be induced by strain. Our work discovers a highly
anisotropic 2D metal with extraordinary properties, which holds great potential
for electronic and optical applications.",2010.04923v1
2020-10-30,Effect of Single-ion Anisotropy on Magnetocaloric Properties of Frustrated Spin-$s$ Ising Nanoclusters,"Effects of a single-ion anisotropy on magnetocaloric properties of selected
spin-$s\geq 1$ antiferromagnetic Ising clusters with frustration-inducing
triangular geometry are studied by exact enumeration. It is found that
inclusion of the single-ion anisotropy parameter $D$ can result in a much more
complex ground-state behavior, which is also reflected in a magnetocaloric
effect (MCE) at finite temperatures. For negative $D$ (easy-plane anisotropy)
with increasing $s$ the ground-state magnetization as a function of the
external field gradually shows increasing number of plateaus of various
heights. Except for the cases of integer $s$ with $D < D_0 \leq 0$, the first
magnetization plateau is of non-zero height. This property facilitates an
enhanced MCE in the adiabatic demagnetization process in the form of an abrupt
decrease in temperature as the magnetic field vanishes to zero. The cooling
rate can be considerably enhanced in the systems with larger $s$ and $D>0$
(easy-axis anisotropy), albeit its dependence on these parameters is strongly
dependent on the cluster geometry. From the studied systems more favorable
conditions for observing a giant MCE were found in the 2CS cluster, consisting
of two corner-sharing tetrahedra, the experimental realization of which could
be technologically used for efficient refrigeration to ultra-low temperatures.",2010.16287v1
2021-02-18,The relationship between transport anisotropy and nematicity in FeSe,"The mechanism behind the nematicity of FeSe is not known. Through
elastoresitivity measurements it has been shown to be an electronic
instability. However, so far measurements have extended only to small strains,
where the response is linear. Here, we apply large elastic strains to FeSe, and
perform two types of measurements. (1) Using applied strain to control
twinning, the nematic resistive anisotropy at temperatures below the nematic
transition temperature Ts is determined. (2) Resistive anisotropy is measured
as nematicity is induced through applied strain at fixed temperature above Ts.
In both cases, as nematicity strengthens the resistive anisotropy peaks about
about 7%, then decreases. Below ~40 K, the nematic resistive anisotropy changes
sign. We discuss possible implications of this behaviour for theories of
nematicity. We report in addition: (1) Under experimentally accessible
conditions with bulk crystals, stress, rather than strain, is the conjugate
field to the nematicity of FeSe. (2) At low temperatures the twin boundary
resistance is ~10% of the sample resistance, and must be properly subtracted to
extract intrinsic resistivities. (3) Biaxial inplane compression increases both
in-plane resistivity and the superconducting critical temperature Tc,
consistent with a strong role of the yz orbital in the electronic correlations.",2102.09212v1
2021-03-22,Intensity and anisotropies of the stochastic Gravitational Wave background from merging compact binaries in galaxies,"We investigate the isotropic and anisotropic components of the Stochastic
Gravitational Wave Background (SGWB) originated from unresolved merging compact
binaries in galaxies. We base our analysis on an empirical approach to galactic
astrophysics that allows to follow the evolution of individual systems. We then
characterize the energy density of the SGWB as a tracer of the total matter
density, in order to compute the angular power spectrum of anisotropies with
the Cosmic Linear Anisotropy Solving System (CLASS) public code in full
generality. We obtain predictions for the isotropic energy density and for the
angular power spectrum of the SGWB anisotropies, and study the prospect for
their observations with advanced Laser Interferometer Gravitational-Wave and
Virgo Observatories and with the Einstein Telescope. We identify the
contributions coming from different type of sources (binary black holes, binary
neutron stars and black hole-neutron star) and from different redshifts. We
examine in detail the spectral shape of the energy density for all types of
sources, comparing the results for the two detectors. We find that the power
spectrum of the SGWB anisotropies behaves like a power law on large angular
scales and drops at small scales: we explain this behaviour in terms of the
redshift distribution of sources that contribute most to the signal, and of the
sensitivities of the two detectors. Finally, we simulate a high resolution full
sky map of the SGWB starting from the power spectra obtained with CLASS and
including Poisson statistics and clustering properties.",2103.12037v2
2021-04-01,"Scale-dependent anisotropy, energy transfer and intermittency in bubble-laden turbulent flows","Data from Direct Numerical Simulations of disperse bubbly flows in a vertical
channel are used to study the effect of the bubbles on the carrier-phase
turbulence. A new method is developed, based on the barycentric map approach,
that allows to quantify the anisotropy and componentiality of the flow at any
scale. Using this the bubbles are found to significantly enhance flow
anisotropy at all scales compared with the unladen case, and for some bubble
cases, very strong anisotropy persists down to the smallest flow scales. The
strongest anisotropy observed was for the cases involving small bubbles.
Concerning the inter-scale energy transfer, our results indicate that for the
bubble-laden cases, the energy transfer is from large to small scales, just as
for the unladen case. However, there is evidence of an upscale transfer when
considering the transfer of energy associated with particular components of the
velocity field. Although the direction of the energy transfer is the same with
and without the bubbles, the transfer is much stronger for the bubble-laden
cases, suggesting that the bubbles play a strong role in enhancing the activity
of the nonlinear term in the flow. The normalized forms of the fourth and
sixth-order structure functions are also considered, and reveal that the
introduction of bubbles into the flow strongly enhances intermittency in the
dissipation range, but suppresses it at larger scales. This strong enhancement
of the dissipation scale intermittency has significant implications for
understanding how the bubbles might modify the mixing properties of turbulent
flows.",2104.00449v1
2021-05-17,Computing Curie temperature of two-dimensional ferromagnets in the presence of exchange anisotropy,"We compare three first-principles methods of calculating the Curie
temperature in two-dimensional (2D) ferromagnetic materials (FM), modeled using
the Heisenberg model, and propose a simple formula for estimating the Curie
temperature with high accuracy that works for all common 2D lattice types.
First, we study the effect of exchange anisotropy on the Curie temperature
calculated using the Monte-Carlo (MC), the Green's function method, and the
renormalized spin-wave (RNSW). We find that the Green's function overestimates
the Curie temperature in high-anisotropy regimes compared to MC, whereas RNSW
underestimates the Curie temperature compared to the MC and the Green's
function. Next, we propose a closed-form formula for calculating the Curie
temperature of 2D FMs, which provides an estimate of the Curie temperature
greatly improving over the mean-field expression for magnetic material
screening. We apply the closed-form formula to predict the Curie temperature 2D
magnets screened from the C2DB database and discover several high Curie
temperature FMs with Fe2F2 and MoI2 emerging as the most promising 2D
ferromagnets. Finally, comparing to experimental results for CrI3, CrCl3, and
CrBr3, we conclude that for small effective anisotropies, the Green's
function-based equations are preferable, while, for larger anisotropies
MC-based results are more predictive.",2105.07958v3
2021-05-24,Tuning of magnetic structures topology via single-ion anisotropy and magnetic field in frustrated 2D semiconductors,"The effects of competing magnetic interactions in stabilizing different spin
configurations are drawing a renewed attention in order to both unveil emerging
topological spin textures and to highlight microscopic mechanisms leading to
their stabilization. The possible key role of the two-site exchange anisotropy
in selecting specific helicity and vorticity of skyrmionic lattices has only
recently been proposed. In this work we explore the phase diagram of a
frustrated localized magnet on a two-dimensional centrosymmetric triangular
lattice, focusing on the interplay between the two-ion anisotropy (TIA) and the
single-ion anisotropy (SIA). The effects of an external magnetic field applied
perpendicularly to the magnetic layer are also investigated. By means of Monte
Carlo simulations, we find a profusion of different spin configurations, going
from trivial to high-order Q skyrmionic and meronic lattices. In closer detail,
we find that a dominant role is played by the two-ion over the single-ion
anisotropy in determining the planar spin texture, whereas the strength and
sign of SIA, together with the magnitude of the magnetic field, tune the
perpendicular spin components, mostly affecting the polarity (and, in turn, the
topology) of the spin-texture. Our analysis confirms the crucial role of
anisotropic symmetric exchange in systems with dominant short-range
interactions, at the same time predicting a rich variety of complex magnetic
textures that may arise from a fine tuning of competing anisotropic mechanisms.",2105.11411v1
2021-07-01,Controllable inter-skyrmion attractions and resulting skyrmion-lattice structures in two-dimensional chiral magnets with in-plane anisotropy,"We study inter-skyrmion interactions and stable spin configurations in a 2D
chiral magnet with in-plane anisotropies of a tilted magnetic field and the
magneto-crystalline anisotropy on a (011) thin film. We find that in both cases
a small deformation of a skyrmion shape makes the inter-skyrmion interaction
anisotropic, and that the skyrmions are weakly bounded along a certain
direction due to an emergent attractive interaction. Furthermore, when the
magneto-crystalline anisotropy is comparable to the Zeeman energy, skyrmions
embedded in a uniform magnetization are tightly bound by creating a magnetic
domain between them. The formation of the magnetic domain, and thus the
strength of the inter-skyrmion interaction, can be controlled by the direction
of an external magnetic field. The anisotropic interaction also affects the
skyrmion alignment in the skyrmion crystal (SkX) phase. By employing the Monte
Carlo simulation and the micromagnetic simulation, we obtain an elongated
triangular lattice structure in the SkX phase. In particular, in the presence
of a strong magneto-crystalline anisotropy, magnetic domains appear in the
background of the lattice structure, and bimerons aligned on the domain walls
form an elongated triangular lattice. We also find a parameter region that the
SkX phase is stabilized due to the inter-skyrmion attraction.",2107.00201v1
2021-08-05,Metamagnetic Transitions in Few-Layer CrOCl Controlled by Magnetic Anisotropy Flipping,"The pivotal role of magnetic anisotropy in stabilising two-dimensional (2D)
magnetism has been widely accepted, however, direct correlation between
magnetic anisotropy and long-range magnetic ordering in the 2D limit is yet to
be explored. Here, using angle- and temperature-dependent tunnelling
magnetoresistance, we report unprecedented metamagnetic phase transitions in
atomically-thin CrOCl, triggered by magnetic easy-axis flipping instead of the
conventional spin flop mechanism. Few-layer CrOCl tunnelling devices of various
thicknesses consistently show an in-plane antiferromagnetic (AFM) ground state
with the easy axis aligned along the Cr-O-Cr direction (b-axis). Strikingly,
with the presence of a magnetic field perpendicular to the easy-axis (H||c),
magnetization of CrOCl does not follow the prevalent spin rotation and
saturation pattern, but rather exhibits an easy-axis flipping from the in-plane
to out-of-plane directions. Such magnetic anisotropy controlled metamagnetic
phase transitions are manifested by a drastic upturn in tun- nelling current,
which shows anomalous shifts towards higher H when temperature increases. By 2D
mapping of tunnelling currents as a function of both temperature and H, we
determine a unique ferrimagnetic state with a superstructure periodicity of
five unit cells after the field-induced metam- agnetic transitions. The
feasibility to control 2D magnetism by manipulating magnetic anisotropy may
open enormous opportunities in spin-based device applications.",2108.02825v1
2021-09-05,Lateral modulation of magnetic anisotropy in tricolor 3d-5d oxide superlattices,"Manipulating magnetic anisotropy (MA) purposefully in transition metal oxides
(TMOs) enables the development of oxide-based spintronic devices with practical
applications. Here, we report a pathway to reversibly switch the lateral
magnetic easy-axis via interfacial oxygen octahedral coupling (OOC) effects in
3d-5d tricolor superlattices, i.e. [SrIrO3,mRTiO3,SrIrO3,2La0.67Sr0.33MnO3]10
(RTiO3: SrTiO3 and CaTiO3). In the heterostructures, the anisotropy energy
(MAE) is enhanced over one magnitude to ~106 erg/cm3 compared to
La0.67Sr0.33MnO3 films. Moreover, the magnetic easy-axis is reversibly
reoriented between (100)- and (110)-directions by changing the RTiO3. Using
first-principles density functional theory calculations, we find that the
SrIrO3 owns a large single-ion anisotropy due to its strong spin-orbit
interaction. This anisotropy can be reversibly controlled by the OOC, then
reorient the easy-axis of the superlattices. Additionally, it enlarges the MAE
of the films via the cooperation with a robust orbital hybridization between
the Ir and Mn atoms. Our results indicate that the tricolor superlattices
consisting of 3d and 5d oxides provide a powerful platform to study the MA and
develop oxide-based spintronic devices.",2109.02062v1
2021-10-01,Measurement of the Anisotropy Power Spectrum of the Radio Synchrotron Background,"We present the first targeted measurement of the power spectrum of
anisotropies of the radio synchrotron background, at 140 MHz where it is the
overwhelmingly dominant photon background. This measurement is important for
understanding the background level of radio sky brightness, which is dominated
by steep-spectrum synchrotron radiation at frequencies below 0.5 GHz and has
been measured to be significantly higher than that which can be produced by
known classes of extragalactic sources and most models of Galactic halo
emission. We determine the anisotropy power spectrum on scales ranging from 2
degrees to 0.2 arcminutes with LOFAR observations of two 18 square degree
fields -- one centered on the Northern hemisphere coldest patch of radio sky
where the Galactic contribution is smallest and one offset from that location
by 15 degrees. We find that the anisotropy power is higher than that
attributable to the distribution of point sources above 100 micro-Jy in flux.
This level of radio anisotropy power indicates that if it results from point
sources, those sources are likely at low fluxes and incredibly numerous, and
likely clustered in a specific manner.",2110.00499v3
2021-11-11,"No longer ballistic, not yet diffusive--the formation of cosmic ray small-scale anisotropies","The arrival directions of TeV-PeV cosmic rays are remarkably uniform due to
the isotropization of their directions by scattering on turbulent magnetic
fields. Small anisotropies can exist in standard diffusion models, however,
only on the largest angular scales. Yet, high-statistics observatories like
IceCube and HAWC have found significant deviations from isotropy down to small
angular scales. Here, we explain the formation of small-scale anisotropies by
considering pairs of cosmic rays that get correlated by their transport through
the same realisation of the turbulent magnetic field. We argue that the
formation of small-scale anisotropies is the reflection of the particular
realisation of the turbulent magnetic field experienced by cosmic rays on time
scales intermediate between the early, ballistic regime and the late, diffusive
regime. We approach this problem in two different ways: First, we run test
particle simulations in synthetic turbulence, covering for the first time the
TV rigidities of observations with realistic turbulence parameters. Second, we
extend the recently introduced mixing matrix approach and determine the
steady-state angular power spectrum. Throughout, we adopt magneto-static,
slab-like turbulence. We find excellent agreement between the predicted angular
power spectra in both approaches over a large range of rigidities. In the
future, measurements of small-scale anisotropies will be valuable in
constraining the nature of the turbulent magnetic field in our Galactic
neighborhood.",2111.06419v1
2022-03-01,Bianchi Type I model of universe with customized scale factors,"According to standard cosmology, the universe is homogeneous and isotropic at
large scales. However, some anisotropies can be observed at the local scale in
the universe through various ways. Here we have studied the Bianchi type I
model with customizing the scale factors to understand the anisotropic nature
of the universe. We have considered two cases with slight modifications of
scale factors in different directions in the generalized Bianchi Type I metric
equation, and compared the results with the $\Lambda$CDM model and also with
available cosmological observational data. Through this study, we also want to
predict the possible degree of anisotropy present in the early universe and its
evolution to current time by calculating the value of density parameter for
anisotropy ($\Omega_{\sigma}$) for both low and high redshift (z) along with
the possible relative anisotropy that exist among different directions. It is
found that there was a significant amount of anisotropy in the early universe
and the anisotropic nature of the universe vanishes at the near past and the
present epochs. Thus at near past and present stages of the universe there is
no effective distinction between this anisotropic model and the standard
$\Lambda$CDM model.",2203.00385v2
2022-03-20,Anisotropy of Magnetic Field Spectra at Kinetic Scales of Solar Wind Turbulence as Revealed by Parker Solar Probe in the Inner Heliosphere,"Using the Parker Solar Probe data taken in the inner heliosphere, we
investigate the power and spatial anisotropy of magnetic-field spectra at
kinetic scales (i.e., around sub-ion scales) in solar wind turbulence in the
inner heliosphere. We find that strong anisotropy of magnetic spectra occurs at
kinetic scales with the strongest power in the perpendicular direction with
respect to the local magnetic field (forming an angle theta_B with the mean
flow velocity). The spectral index of magnetic spectra varies from -3.2 to -5.8
when the angle theta_B changes from 90 to 180 (or 0) deg, indicating that
strong anisotropy of the spectral indices occurs at kinetic scales in the solar
wind turbulence. Using a diagnosis based on the magnetic helicity, we show that
the anisotropy of the spectral indices can be explained by the nature of the
plasma modes that carry the cascade at kinetic scales. We discuss our findings
in light of existing theories and current development in the field.",2203.10475v1
2022-03-25,Phase diagrams and excitations of anisotropic $S=1$ quantum magnets on the triangular lattice,"The $S=1$ bilinear-biquadratic Heisenberg exchange model on the triangular
lattice with a single-ion anisotropy has previously been shown to host a number
of exotic magnetic and nematic orders [Moreno-Cardoner $\textit{et al.}$, Phys.
Rev. B $\textbf{90}$, 144409 (2014)], including an extensive region of
""supersolid"" order. In this work, we amend the model by an XXZ anisotropy in
the exchange interactions. Tuning to the limit of an exactly solvable $S=1$
generalized Ising-/Blume-Capel-type model provides a controlled limit to access
phases at finite transverse exchange. Notably, we find an additional
macroscopically degenerate region in the phase diagram and study its fate under
perturbation theory. We further map out phase diagrams as a function of the XXZ
anisotropy parameter, ratio of bilinear and biquadratic interactions and
single-ion anisotropy, and compute corrections to the total ordered moment in
various phases using systematically constructed linear flavor-wave theory. We
also present linear flavor-wave spectra of various states, finding that the
lowest-energy band in three-sublattice generalized (i.e. with $S^z=\pm1,0$)
Ising/Blume-Capel states, stabilized by strong exchange anisotropies, is
remarkably flat, opening up the way to flat-band engineering of magnetic
excitation via stabilizing non-trivial Ising-ordered ground states.",2203.13490v1
2022-06-20,Forecasting pulsar timing array sensitivity to anisotropy in the stochastic gravitational wave background,"Statistical anisotropy in the nanohertz-frequency gravitational-wave
background (GWB) is expected to be detected by pulsar timing arrays (PTAs) in
the near future. By developing a frequentist statistical framework that
intrinsically restricts the GWB power to be positive, we establish scaling
relations for multipole-dependent anisotropy decision thresholds that are a
function of the noise properties, timing baselines, and cadences of the pulsars
in a PTA. We verify that $(i)$ a larger number of pulsars, and $(ii)$ factors
that lead to lower uncertainty on the cross-correlation measurements between
pulsars, lead to a higher overall GWB signal-to-noise ratio, and lower
anisotropy decision thresholds with which to reject the null hypothesis of
isotropy. Using conservative simulations of realistic NANOGrav datasets, we
predict that an anisotropic GWB with angular power $C_{l=1} > 0.3\,C_{l=0}$ may
be sufficient to produce tension with isotropy at the $p = 3\times10^{-3}$
($\sim3\sigma$) level in near-future NANOGrav data with a $20$~yr baseline. We
present ready-to-use scaling relationships that can map these thresholds to any
number of pulsars, configuration of pulsar noise properties, and sky coverage.
We discuss how PTAs can improve the detection prospects for anisotropy, as well
as how our methods can be adapted for more versatile searches.",2206.09936v1
2022-06-28,Probing parity-odd bispectra with anisotropies of GW $V$ modes,"It is well known that non-trivial squeezed tensor bispectra can lead to
anisotropies in the inflationary stochastic gravitational wave (GW) background,
providing us with an alternative and complementary window to primordial
non-Gaussianities (NGs) with respect to the CMB. Previous works have
highlighted the detection prospects of parity-even tensor NGs via the GW
$I$-mode anisotropies. In this work we extend this by analysing for the first
time the additional information carried by GW $V$-mode anisotropies due to
squeezed NGs. We show that GW $V$ modes allow us to probe parity-odd squeezed
$\langle \rm tts \rangle$ and $\langle \rm ttt \rangle$ bispectra. These
bispectra break parity at the non-linear level and can be introduced by
allowing alternative symmetry breaking patterns during inflation, like those
comprised in solid inflation. Considering a BBO-like experiment, we find that a
non-zero detection of squeezed $\langle \rm tts \rangle$ parity-odd bispectra
in the $V$ modes dipole is possible without requiring any short-scale
enhancement of the GW power spectrum amplitude over the constraints set by the
CMB. We also briefly discuss the role of $V$-CMB cross-correlations. Our work
can be extended in several directions and motivates a systematic search for
polarized GW anisotropies in the next generations of GW experiments.",2206.14173v3
2022-07-23,Large-scale anisotropies of extragalactic cosmic rays below the ankle,"We study the anisotropies on large angular scales which can be present in the
flux of cosmic rays reaching the Earth from a population of extragalactic
sources, focusing on the energy range between the second knee and the ankle. In
this energy range the particles are significantly affected by the Galactic
magnetic field, which then plays a relevant role in shaping the expected
anisotropies. The Galactic magnetic field deflects the cosmic-ray trajectories
and thus modifies the anisotropies present outside the halo of the Galaxy, in
particular the dipolar one associated with the translational motion of the
observer (Compton-Getting effect). Also, due to the Galactic rotation, in the
reference frame of an observer at Earth there is an electric component of the
Galactic field that produces a small change in the particles' momentum. This
acceleration depends on the cosmic-ray arrival direction and it hence induces
anisotropies in the flux observed in a given energy range. We analyse the
expected amplitude and phase of the resulting dipolar component of the flux and
discuss the possibility to explain via these effects the change in the phase of
the right-ascension distribution which is observed at energies around 1 EeV.",2207.11540v2
2022-09-30,Induced cosmological anisotropy by a gauge-gravity interaction,"We present a simple model which generates cosmological anisotropies on top of
standard FLRW geometry. This is in some sense reminiscent of the mean field
approximation, where the mean field cosmological model under consideration
would be the standard FLRW, and the anisotropy is a small perturbative
correction on top of it. Using a supergravity-inspired model, we confirm that
the stable fixed point of our model corresponds to standard FLRW cosmology. We
use a Bianchi VII$_0$-type model supplemented with a scalar and $U(1)$ gauge
fields, and we show that the anisotropies of the geometry are generated by the
non-trivial interaction between the gravity sector and the $U(1)$ gauge sector.
Studying the attractor flow, we show that the anisotropies are present at early
times (high redshift) and decay asymptotically to an FLRW attractor fixed
point. With such a mechanism, observations of non-isotropy are not
contradictory to FLRW geometry or indeed the $\Lambda$CDM model. Such models
could in principle shed some insights on the present cosmological tensions.",2209.15225v3
2022-11-24,A Simplified Method of the Assessment of Magnetic Anisotropy of Commonly Used Sapphire Substrates in SQUID Magnetometers,"Solid state wafers are indispensable components in material science as
substrates for epitaxial homo- or hetero-structures or carriers for
two-dimensional materials. However, a reliable determination of magnetic
properties of nanomaterials in volume magnetometry is frequently affected by
unexpectedly rich magnetism of these substrates, including significant magnetic
anisotropy. Here, we describe a simplified experimental routine of magnetic
anisotropy assessment, which we exemplify and validate for epi-ready sapphire
wafers from various sources. Both the strength and the sign of magnetic
anisotropy is obtained from carefully designed temperature dependent
measurements, which mitigate all known pitfalls of volume SQUID magnetometry
and are substantially faster than traditional approaches. Our measurements
indicate that in all the samples two types of net paramagnetic contributions
coexists with diamagnetism. The first one can be as strong as 10% of the base
diamagnetism of sapphire [-3.7(1) x 10-7 emu/gOe], and, when exceeds 2% mark,
it exhibits pronounced magnetic anisotropy with the easy axis oriented
perpendicularly to the face of c-plane wafers. The other is much weaker but
exhibit ferromagnetic-like appearance. These findings form an important message
that non-standard magnetism of common substrates can significantly influence
the results of precise magnetometry of nanoscale materials and its existence
must be taken for granted by both industry and academia.",2211.13690v1
2022-12-08,"Thin film epitaxial [111] Co$_{50}$Pt$_{50}$: Structure, magnetisation, and spin polarisation","Ferromagnetic films with perpendicular magnetic anisotropy are of interest in
spintronics and superconducting spintronics. Perpendicular magnetic anisotropy
can be achieved in thin ferromagnetic multilayer structures, when the
anisotropy is driven by carefully engineered interfaces. Devices with multiple
interfaces are disadvantageous for our application in superconducting
spintronics, where the current perpendicular to plane is affected by the
interfaces. Robust intrinsic PMA can be achieved in certain Co$_x$Pt$_{100-x}$
alloys and compounds at any thickness, without increasing the number of
interfaces. Here, we grow equiatomic Co$_{50}$Pt$_{50}$ and report a
comprehensive study on the structural, magnetic, and spin-polarisation
properties in the $L1_1$ and $L1_0$ ordered compounds. Primarily, interest in
Co$_{50}$Pt$_{50}$ has been in the $L1_0$ crystal structure, where layers of Pt
and Co are stacked alternately in the [100] direction. There has been less work
on $L1_1$ crystal structure, where the stacking is in the [111] direction. For
the latter $L1_1$ crystal structure, we find magnetic anisotropy perpendicular
to the film plane. For the former $L1_0$ crystal structure, the magnetic
anisotropy is perpendicular to the [100] plane, which is neither in-plane or
out-of-plane in our samples. We obtain a value for the ballistic spin
polarisation of the $L1_1$ and $L1_0$ Co$_{50}$Pt$_{50}$ to be $47\pm3\%$.",2212.04370v2
2023-02-01,Temperature-independent ferromagnetic resonance shift in Bi-doped YIG garnets through magnetic anisotropy tuning,"Thin garnet films are becoming central for magnon-spintronics and
spin-orbitronics devices as they show versatile magnetic properties together
with low magnetic losses. These fields would benefit from materials in which
heat does not affect the magnetization dynamics, an effect known as the
non-linear thermal frequency shift. In this study, low damping Bi substituted
Iron garnet (Bi:YIG) ultra-thin films have been grown using Pulsed Laser
Deposition. Through a fine tuning of the growth parameters, the precise control
of the perpendicular magnetic anisotropy allows to achieve a full compensation
of the dipolar magnetic anisotropy. Strikingly, once the growth conditions are
optimized, varying the growth temperature from 405 {\deg}C to 475 {\deg}C as
the only tuning parameter induces the easy-axis to go from out-of-plane to
in-plane. For films that are close to the dipolar compensation, Ferromagnetic
Resonance measurements yield an effective magnetization $\mu _{0}M_{eff} (T)$
that has almost no temperature dependence over a large temperature range (260 K
to 400 K) resulting in an anisotropy temperature exponent of 2. These findings
put Bi:YIG system among the very few materials in which the temperature
dependence of the magnetic anisotropy varies at the same rate than the
saturation magnetization. This interesting behavior is ascribed
phenomenologically to the sizable orbital moment of $Bi^{3+}$.",2302.00585v1
2023-02-17,Significantly increased magnetic anisotropy in Co nano-columnar multilayer structure via a unique sequential oblique-normal deposition approach,"Oblique/normal sequential deposition technique is used to create Co based
unique multilayer structure [Co-oblique(4.4nm)/Co-normal (4.2 nm)]x10, where
each Co-oblique layer is deposited at an oblique angle of 75deg, to induce
large in-plane uniaxial magnetic anisotropy (UMA). Compared to the previous
ripple, stress and oblique angle deposition (OAD) related studies on Cobalt in
literature, one-order higher UMA with the easy axis of magnetization along the
projection of the tilted nano-columns in the multilayer plane is observed. The
multilayer retains magnetic anisotropy even after annealing at 450C. The
in-plane UMA in this multilayer is found to be the combination of shape, and
magneto-crystalline anisotropy (MCA) confirmed by the temperature-dependent
grazing incidence small angle X-ray scattering (GISAXS), in situ reflection
high energy electron diffraction (RHEED) and grazing incidence X-ray
diffraction (GIXRD) measurements. The crystalline texturing of hcp Co in the
multilayer minimizes spin-orbit coupling energy along the column direction,
which couples with the shape anisotropy energies and results in preferential
orientation of the easy magnetic axis along the projection of the columns in
the multilayer plane. Reduction in UMA after annealing is attributed to
diffusion/merging of columns and annihilating crystallographic texturing. The
obtained one-order high UMA demonstrates the potential application of the
unique structure engineering technique, which may have far-reaching advantages
in magnetic thin films/multilayers and spintronic devices.",2302.08739v1
2023-04-30,Feedback-driven anisotropy in the circumgalactic medium for quenching galaxies in the SIMBA simulations,"We use the SIMBA galaxy formation simulation suite to explore anisotropies in
the properties of circumgalactic gas that result from accretion and feedback
processes. We particularly focus on the impact of bipolar active galactic
nuclei (AGN) jet feedback as implemented in SIMBA, which quenches galaxies and
has a dramatic effect on large-scale gas properties. We show that jet feedback
at low redshifts is most common in the stellar mass range $(1-5)\times
10^{10}M_\odot$, so we focus on galaxies with active jets in this mass range.
In comparison to runs without jet feedback, jets cause lower densities and
higher temperatures along the galaxy minor axis (SIMBA jet direction) at radii
>=$0.5r_{200c}-4r_{200c}$ and beyond. This effect is less apparent at higher or
lower stellar masses, and is strongest within green valley galaxies. The
metallicity also shows strong anisotropy out to large scales, driven by star
formation feedback. We find substantially stronger anisotropy at
<=$0.5r_{200c}$, but this also exists in runs with no explicit feedback,
suggesting that it is due to anisotropic accretion. Finally, we explore
anisotropy in the bulk radial motion of the gas, finding that both star
formation and AGN wind feedback contribute to pushing the gas outwards along
the minor axis at <=1 Mpc, but AGN jet feedback further causes bulk outflow
along the minor axis out to several Mpc, which drives quenching via gas
starvation. These results provide observational signatures for the operation of
AGN feedback in galaxy quenching.",2305.00602v2
2023-05-18,Compass-like manipulation of electronic nematicity in Sr$_3$Ru$_2$O$_7$,"Electronic nematicity has been found in a wide range of strongly correlated
electron materials, resulting in the electronic states having a symmetry that
is lower than that of the crystal that hosts them. One of the most astonishing
examples is Sr$_3$Ru$_2$O$_7$, in which a small in-plane component of a
magnetic field induces significant resistivity anisotropy. The direction of
this anisotropy follows the direction of the in-plane field. The microscopic
origin of this field-induced nematicity has been a long-standing puzzle, with
recent experiments suggesting a field-induced spin density wave driving the
anisotropy. Here, we report spectroscopic imaging of a field-controlled
anisotropy of the electronic structure at the surface of Sr$_3$Ru$_2$O$_7$. We
track the electronic structure as a function of the direction of the field,
revealing a continuous change with the angle. This continuous evolution
suggests a mechanism based on spin-orbit coupling resulting in compass-like
control of the electronic bands. The anisotropy of the electronic structure
persists to temperatures about an order of magnitude higher compared to the
bulk, demonstrating novel routes to stabilize such phases over a wider
temperature range.",2305.11210v2
2023-07-12,Quasi-static magnetization dynamics in a compensated ferrimagnetic half-metal -- Mn$_2$Ru$_x$Ga,"Exploring anisotropy and diverse magnetization dynamics in specimens with
vanishing magnetic moments presents a significant challenge using traditional
magnetometry, as the low resolution of existing techniques hinders the ability
to obtain accurate results. In this study, we delve deeper into the examination
of magnetic anisotropy and quasi-static magnetization dynamics in \mrg\,(MRG)
thin films, as an example of a compensated ferrimagnetic half-metal, by
employing anomalous Hall effect measurements within a tetragonal crystal
lattice system. Our research proposes an innovative approach to accurately
determine the complete set of anisotropy constants of these MRG thin films. To
achieve this, we perform anomalous Hall voltage curve fitting, using torque
models under the macrospin approximation, which allow us to obtain out-of-plane
anisotropy constants $K_1=4.0\times10^4$ J m$^{-3}$ ($K_1/M=0.655$\,T) and
$K_2=2.54\times10^4$ J m$^{-3}$ ($K_2/M=0.416$\,T), along with a weaker
in-plane anisotropy constant $K_3=3.48\times10^3$ J m$^{-3}$
($K_3/M=0.057$\,T). By additionally employing first-order reversal curves
(FORC) and classical Preisach hysteresis (hysterons) models, we are able to
validate the efficacy of the macrospin model in capturing the magnetic behavior
of MRG thin films. Furthermore, our investigation substantiates that the
complex quasi-static magnetization dynamics of MRG thin films can be
effectively modelled using a combination of hysteronic and torque models. This
approach facilitates the exploration of both linear and non-linear quasi-static
magnetization dynamics, in the presence of external magnetic field and/or
current-induced effective fields, generated by the spin-orbit torque and spin
transfer torque mechanisms.",2307.06403v1
2023-08-11,Piezostrain-induced in-plane anisotropy of superconducting transition temperature for FeSe0.5Te0.5 thin films,"Superconductivity is a macroscopic quantum phenomenon and it is commonly
believed that the in-plane superconducting transition temperature (Tc) should
be isotropic for superconductors with crystal structures of stacking layers
(quasi two-dimensional). Here, we report the observation of piezostrain-induced
in-plane anisotropy of Tc in FeSe0.5Te0.5 (FST) thin films grown on
ferroelectrics. The as-prepared FST shows tetragonal phase with equal in-plane
lattice parameters and absence of in-plane anisotropy of Tc. Upon applying
electric fields, piezostrain induces difference of the in-plane lattice
parameters (a-b) and in-plane anisotropy of Tc. The in-plane anisotropy of Tc
correlates with a-b and becomes more remarkable for larger values of a-b. Some
possible extrinsic effects were ruled out by experiments and analysis. It is
suggested that electronic nematicity with one direction induced by piezostrain
and inhomogeneous superconductivity in FST are involved in this unusual
phenomenon. This work reveals the exotic behavior of FST and will stimulate
exploration of similar behavior in other unconventional superconductors.",2308.05919v1
2023-09-22,Influence of surface energy anisotropy on nucleation and crystallographic texture of polycrystalline deposits,"This paper aims to elucidate the role of interface energy anisotropy in
orientation selection during nucleation of new grains in a polycrystalline film
growth. An assessment of (heterogeneous) nucleation probability as function of
orientation of both the bottom grain and of the nucleus was developed (using
the concepts of classical nucleation theory). Novel solutions to the
generalized Winterbottom construction were described in cases of very strong
anisotropy and arbitrary orientations. In order to demonstrate the effect on
the film crystallographic texture, a 2D Monte Carlo algorithm for anisotropic
polycrystalline growth was used to simulate growth of films with columnar
microstructure. The effect of strength of anisotropy, the deposition rate and
initial texture were investigated. Results showed that with larger strength of
anisotropy, the nucleation rate is less dependent on the driving force, but
more dependent on the initial texture. With certain initial textures, the
anisotropic nucleation may even be either impossible or having probability
close to one irrespective of the driving force. Depending on the conditions,
the anisotropic nucleation could hasten the evolution towards the
interface-energy minimizing texture or retard it. Based on these insights, a
hypothesis was offered to explain a peculiar texture evolution in
electrodeposited nickel.",2309.12889v2
2023-10-24,Spin wave excitations in low dimensional systems with large magnetic anisotropy,"The low energy excitation spectrum of a two-dimensional ferromagnetic
material is dominated by single-magnon excitations that show a gapless
parabolic dispersion relation with the spin wave vector. This occurs as long as
magnetic anisotropy and anisotropic exchange are negligible compared to
isotropic exchange. However, to maintain magnetic order at finite temperatures,
it is necessary to have sizable anisotropy to open a gap in the spin wave
excitation spectrum. We consider four real two-dimensional systems for which
ferromagnetic order at finite temperature has been observed or predicted.
Density functional theory calculations of the total energy differences for
different spin configurations permit us to extract the relevant parameters and
connect them with a spin Hamiltonian. The corresponding values of the Curie
temperature are estimated using a simple model and found to be mostly
determined by the value of the isotropic exchange. The exchange and anisotropy
parameters are used in a toy model of finite-size periodic chains to study the
low-energy excitation spectrum, including single-magnon and two-magnon
excitations. At low energies we find that single-magnon excitations appear in
the spectrum together with two-magnon excitations. These excitations present a
gap that grows particularly for large values of the magnetic anisotropy or
anisotropic exchange, relative to the isotropic exchange.",2310.15942v1
2023-10-26,Pitch-Angle Anisotropy Imprinted by Relativistic Magnetic Reconnection,"Radiation emitted by nonthermal particles accelerated during relativistic
magnetic reconnection is critical for understanding the nonthermal emission in
a variety of astrophysical systems, including blazar jets, black hole coronae,
pulsars, and magnetars. By means of fully kinetic Particle-in-Cell (PIC)
simulations, we demonstrate that reconnection-driven particle acceleration
imprints an energy-dependent pitch-angle anisotropy and gives rise to broken
power laws in both the particle energy spectrum and the pitch-angle anisotropy.
The particle distributions depend on the relative strength of the
non-reconnecting (guide field) versus the reconnecting component of the
magnetic field ($B_g/B_0$) and the lepton magnetization ($\sigma_0$). Below the
break Lorentz factor $\gamma_0$ (injection), the particle energy spectrum is
ultra-hard ($p_< < 1$), while above $\gamma_0$, the spectral index $p_>$ is
highly sensitive to $B_g/B_0$. Particles' velocities align with the magnetic
field, reaching minimum pitch angles $\alpha$ at a Lorentz factor $\gamma_{\min
\alpha}$ controlled by $B_g/B_0$ and $\sigma_0$. The energy-dependent
pitch-angle anisotropy, evaluated through the mean of $\sin^2 \alpha$ of
particles at a given energy, exhibits power-law ranges with negative ($m_<$)
and positive ($m_>$) slopes below and above $\gamma_{\min \alpha}$, becoming
steeper as $B_g/B_0$ increases. The generation of anisotropic pitch angle
distributions has important astrophysical implications. We address their
effects on regulating synchrotron luminosity, spectral energy distribution,
polarization, particle cooling, the synchrotron burnoff limit, emission
beaming, and temperature anisotropy.",2310.17560v2
2023-12-05,Constraints on UHECR sources and extragalactic magnetic fields from directional anisotropies,"A dipole anisotropy in ultra-high-energy cosmic ray (UHECR) arrival
directions, of extragalactic origin, is now firmly established at energies E >
8 EeV. Furthermore, the UHECR angular power spectrum shows no power at smaller
angular scales than the dipole, apart from hints of possible individual hot or
warm spots for energy thresholds $\gtrsim$40 EeV. Here, we exploit the
magnitude of the dipole and the limits on smaller-scale anisotropies to place
constraints on two quantities: the extragalactic magnetic field (EGMF) and the
number density of UHECR sources or the volumetric event rate if UHECR sources
are transient. We also vary the bias between the extragalactic matter and the
UHECR source densities, reflecting whether UHECR sources are preferentially
found in over- or under-dense regions, and find that little or no bias is
favored. We follow Ding et al. (2021) in using the Cosmic Flows 2 density
distribution of the local universe as our baseline distribution of UHECR
sources, but we improve and extend that work by employing an accurate and
self-consistent treatment of interactions and energy losses during propagation.
Deflections in the Galactic magnetic field are treated using both the full JF12
magnetic field model, with random as well as coherent components, or just the
coherent part, to bracket the impact of the GMF on the dipole anisotropy. This
Large Scale Structure (LSS) model gives good agreement with both the direction
and magnitude of the measured dipole anisotropy and forms the basis for
simulations of discrete sources and the inclusion of EGMF effects.",2312.02645v3
2023-12-08,Role of initial transverse momentum in a hybrid approach,"The purpose of this work is to study the effect of exchanging initial
condition models in a modular hybrid approach. The focus lies on the
event-by-event correlations of elliptic and triangular flow. This study is
performed in the hybrid approach SMASH-vHLLE, composed of the hadronic
transport approach SMASH and the (3+1)d viscous hydrodynamic code vHLLE. The
initial condition models investigated are SMASH IC, Trento and IP-Glasma.
Correlations are calculated on an event-by-event basis between the
eccentricities and momentum anisotropies of the initial state as well as the
momentum anisotropies in the final state, both for ultra-central and
off-central collisions for AuAu collisions at $\sqrt{s_{NN}} = 200$ GeV. This
work demonstrates that, although averaged values for the eccentricities of
these models are very similar, substantial differences exist both in the
distributions of eccentricities, the correlations amongst the initial state
properties as well as in the correlations between initial state and final state
properties. Notably, whereas initial state momentum anisotropy is shown to not
affect the final state flow, the presence of radial flow affects the emergence
of final state momentum anisotropies. Inclusion of radial flow in the linear
fit improves the prediction of final state flow from initial state properties.
The presence of momentum in the initial state has an effect on the emergence of
flow and is therefore a relevant part of initial state models, challenging the
common understanding of final state momentum anisotropies being a linear
response to initial state eccentricity only.",2312.05001v1
2024-01-06,From ergodicity to Stark many-body localization in spin chains with single-ion anisotropy,"The principles of ergodicity and thermalization constitute the foundation of
statistical mechanics, positing that a many-body system progressively loses its
local information as it evolves. Nevertheless, these principles can be
disrupted when thermalization dynamics lead to the conservation of local
information, as observed in the phenomenon known as many-body localization.
Quantum spin chains provide a fundamental platform for exploring the dynamics
of closed interacting quantum many-body systems. This study explores the
dynamics of a spin chain with $S\geq 1/2$ within the Majumdar-Ghosh model,
incorporating a non-uniform magnetic field and single-ion anisotropy. Through
the use of exact numerical diagonalization, we unveil that a nearly
constant-gradient magnetic field suppress thermalization, a phenomenon termed
Stark many-body localization (SMBL), previously observed in $S=1/2$ chains.
Furthermore, our findings reveal that the sole presence of single-ion
anisotropy is sufficient to prevent thermalization in the system.
Interestingly, when the magnitudes of the magnetic field and anisotropy are
comparable, they compete, favoring delocalization. Despite the potential
hindrance of SMBL by single-ion anisotropy in this scenario, it introduces an
alternative mechanism for localization. Our interpretation, considering local
energetic constraints and resonances between degenerate eigenstates, not only
provides insights into SMBL but also opens avenues for future experimental
investigations into the enriched phenomenology of disordered free localized
$S\geq 1/2$ systems.",2401.03111v1
2024-01-08,On using the counting method to constrain the anisotropy of kilonova radiation,"A large number of binary neutron star (BNS) mergers are expected to be
detected by gravitational wave (GW) detectors and the electromagnetic (EM)
counterparts (e.g., kilonovae) of a fraction of these mergers may be detected
in multi-bands by large area survey telescopes. For a given number of BNS
mergers detected by their GW signals, the expected numbers of their EM
counterparts that can be detected by a survey with given selection criteria
depend on the kilonova properties, including the anisotropy. In this paper, we
investigate whether the anisotropy of kilonova radiation and the kilonova model
can be constrained statistically by the counting method, i.e., using the
numbers of BNS mergers detected via GW and multi-band EM signals. Adopting
simple models for the BNS mergers, afterglows, and a simple two (blue and
red)-component model for kilonovae, we generate mock samples for GW detected
BNS mergers, their associated kilonovae and afterglows detected in multi-bands.
By assuming some criteria for searching the EM counterparts, we simulate the
observations of these EM counterparts and obtain the EM observed samples in
different bands. With the numbers of BNS mergers detected by GW detectors and
EM survey telescopes in different bands, we show that the anisotropy of
kilonova radiation and the kilonova model can be well constrained by using the
Bayesian analysis. Our results suggest that the anisotropy of kilonova
radiation may be demographically and globally constrained by simply using the
detection numbers of BNS mergers by GW detectors and EM survey telescopes in
multi-bands.",2401.03710v1
2024-01-24,Reversible out-of-plane to in-plane magnetic transition by electrical and thermal cycling in Ni$_{90}$Fe$_{10}$/BaTiO$_3$(001),"The study investigates the manipulation of the magnetic anisotropy in a thick
(1 $\mu$m) Ni$_{90}$Fe$_{10}$ layer electrodeposited on a ferroelectric
BaTiO$_3$(001) substrate, using a combination of Magneto-optical Kerr Effect,
Photoemission Electron Microscopy with X-ray circular magnetic dichroism and
X-ray diffraction. In the as-grown state, the system shows weak perpendicular
magnetic anisotropy and characteristic stripe domains. Upon out-of-plane
electrical poling of the BaTiO$_3$ substrate, the magnetic anisotropy switches
to in-plane with a strong uniaxial behavior. This change is ascribed to the
magnetoelastic effect due to the switching of the BaTiO$_3$ ferroelectric [001]
axis into the sample plane, as evidenced by XRD. The strong mechanical
interaction with the thick Ni$_{90}$Fe$_{10}$ overlayer prevents the full
inversion of the substrate. The perpendicular magnetic anisotropy can be
recovered by a mild thermal annealing above the BaTiO$_3$ tetrahedral to cubic
phase transition and can be cycled by repeated electrical poling/thermal
annealing. This method opens the path to a reversible control of the magnetic
anisotropy in Ni$_{90}$Fe$_{10}$/BaTiO$_3$ heterostructures from perpendicular
to in-plane.",2401.13487v2
2024-01-29,Superexchange interactions and magnetic anisotropy in MnPSe$_3$ monolayer,"Two-dimensional van der Waals magnetic materials are of great current
interest for their promising applications in spintronics. In this work, using
density functional theory calculations in combination with the maximally
localized Wannier functions method and the magnetic anisotropy analyses, we
study the electronic and magnetic properties of MnPSe$_3$ monolayer. Our
results show that it is a charge transfer antiferromagnetic (AF) insulator. For
this Mn$^{2+}$ $3d^5$ system, although it seems straightforward to explain the
AF ground state using the direct exchange, we find that the near 90$^\circ$
Mn-Se-Mn charge transfer type superexchange plays a dominant role in
stabilizing the AF ground state. Moreover, our results indicate that although
the shape anisotropy favors an out-of-plane spin orientation, the spin-orbit
coupling (SOC) leads to the experimentally observed in-plane spin orientation.
We prove that the actual dominant contribution to the magnetic anisotropy comes
from the second-order perturbation of the SOC, by analyzing its distribution
over the reciprocal space. Using the AF exchange and anisotropy parameters
obtained from our calculations, our Monte Carlo simulations give the N\'eel
temperature $T_{\rm N}=47$ K for MnPSe$_3$ monolayer, which agrees with the
experimental 40 K. Furthermore, our calculations show that under a uniaxial
tensile (compressive) strain, N\'eel vector would be parallel (perpendicular)
to the strain direction, which well reproduces the recent experiments. We also
predict that $T_{\rm N}$ would be increased by a compressive strain.",2401.16154v1
2024-02-05,The nonflow issue in connecting anisotropy measurements to hydrodynamics in relativistic heavy-ion collisions,"Hydrodynamics can describe majority of the measured azimuthal anisotropies in
relativistic heavy-ion collisions. Many of the anisotropy measurements are
contaminated by nonflow correlations (i.e., those unrelated to global
event-wise correlations). Those nonflow contamination can cause incorrectness
or compromise the accuracy of the physics extracted from data-hydrodynamics
comparison, particularly when one relies on subtle difference in the
measurements. In the recent preprint by STAR (arXiv:2401.06625) extracting the
Uranium nucleus deformation parameter, nonflow contamination is assessed by
subevents in the limited STAR acceptance. In this note, we demonstrate that
such assessment is inadequate and illustrate how large an effect nonflow can
cause by using the HIJING model, in which all correlations are nonflow and
non-hydrodynamic. We thereby conclude that the extracted Uranium deformation
parameter is premature and emphasize the importance of an earnest assessment of
or correction for nonflow contamination, not only for this STAR analysis but
more generally for studies relying on comparing anisotropy measurements to
hydrodynamic calculations.",2402.03222v1
2024-02-07,Anisotropy of Density Fluctuations in the Solar Wind at 1 au,"A well-known property of solar wind plasma turbulence is the observed
anisotropy of the autocorrelations, or equivalently the spectra, of velocity
and magnetic field fluctuations. Here we explore the related but apparently not
well-studied issue of the anisotropy of plasma density fluctuations in the
energy-containing and inertial ranges of solar wind turbulence. Using 10 years
(1998-2008) of in situ data from the Advanced Composition Explorer (ACE)
mission, we find that the density correlation scale is slightly larger in
directions quasi-parallel to the large-scale mean magnetic field as compared to
quasi-perpendicular directions. The effect is present in both fast and slow
winds. The anisotropy as a function of the level of correlation is also
explored. We find at small correlation levels, i.e., at energy-containing
scales and larger, the density fluctuations are close to isotropy, but in fact
slightly favor more rapid decorrelation in perpendicular directions. At
relatively smaller turbulence inertial range scales where the correlation
values are larger, the sense of anisotropy is reversed in all speed ranges,
implying a more ``slab-like'' structure, especially prominent in the fast wind
samples. We contrast this finding with published results on velocity and
magnetic field correlations.",2402.05191v1
2024-02-12,Jet Suppression and Azimuthal Anisotropy from RHIC to LHC,"Azimuthal anisotropies of high-$p_T$ particles produced in heavy-ion
collisions are understood as an effect of a geometrical selection bias.
Particles oriented in the direction in which the QCD medium formed in these
collisions is shorter, suffer less energy loss, and thus, are over-represented
in the final ensemble compared to those oriented in the direction in which the
medium is longer. In this work we present the first semi-analytical
predictions, including propagation through a realistic, hydrodynamical
background, of the azimuthal anisotropies for jets, obtaining a quantitative
agreement with available experimental data as function of the jet $p_T$, its
cone size $R$ and the collisions centrality. Jets are multi-partonic, extended
objects and their energy loss is sensitive to substructure fluctuations. This
is determined by the physics of color coherence that relates to the ability of
the medium to resolve those partonic fluctuations. Namely, color dipoles whose
angle is smaller than a critical angle, $\theta_c$, are not resolved by the
medium and they effectively act as a coherent source of energy loss. We find
that jet azimuthal anisotropies have a specially strong dependence on coherence
physics due to the marked length-dependence of $\theta_c$. By combining our
predictions for the collision systems and center of mass energies studied at
RHIC and the LHC, covering a wide range of typical values of $\theta_c$, we
show that the relative size of jet azimuthal anisotropies for jets with
different cone-sizes $R$ follow a universal trend that indicates a transition
from a coherent regime of jet quenching to a decoherent regime. These results
suggest a way forward to reveal the role played by the physics of jet color
decoherence in probing deconfined QCD matter.",2402.07869v1
2024-03-23,The role of rare-earth atoms in the anisotropy and antiferromagnetic exchange coupling at a hybrid metal-organic interface,"Magnetic anisotropy and magnetic exchange interactions are crucial parameters
that characterize the hybrid metal-organic interface, key component of an
organic spintronic device. We show that the incorporation of 4$f$ RE atoms to
hybrid metal-organic interfaces of CuPc/REAu$_2$ type (RE= Gd, Ho) constitutes
a feasible approach towards on-demand magnetic properties and functionalities.
The GdAu$_2$ and HoAu$_2$ substrates differ in their magnetic anisotropy
behavior. Remarkably, the HoAu$_2$ surface boosts the inherent out-of-plane
anisotropy of CuPc, owing to the match between the anisotropy axis of substrate
and molecule. Furthermore, the presence of RE atoms leads to a spontaneous
antiferromagnetic (AFM) exchange coupling at the interface, induced by the
3$d$-4$f$ superexchange interaction between the unpaired 3$d$ electron of CuPc
and the 4$f$ electrons of the RE atoms. We show that 4$f$ RE atoms with
unquenched quantum orbital momentum ($L$), as it is the case of Ho, induce an
anisotropic interfacial exchange coupling.",2403.15774v1
2024-04-04,Towards tailored magnetic anisotropy: A first-principles study of L1$_0$ FeNi ultrathin films,"In previous experiments, thin films of L1$\mathrm{_0}$ FeNi with different
surfaces, including (001), (110) and (111), were produced and studied. Each
surface defines a different alignment of the crystallographic tetragonal axis
with respect to the film's plane, resulting in different magnetic anisotropies.
In this study, we use density functional theory calculations to examine three
series of L1$\mathrm{_0}$ FeNi films with surfaces (001), (010), and (111), and
with thicknesses ranging from 0.5 to 3 nm (from 4 to 16 atomic monolayers). Our
results show that films (001) have perpendicular magnetic anisotropy, while
(010) favor in-plane magnetization, with a clear preference for the tetragonal
axis [001]. We propose calling this type of in-plane anisotropy fixed in plane.
A film with surface (111) and a thickness of four atomic monolayers has the
magnetization easy axis almost perpendicular to the plane of the film. As the
thickness of the (111) film increases, the direction of magnetization rotates
towards a tetragonal axis [001], positioned at an angle of about 45$^{o}$ to
the plane of the film. Furthermore, the magnetic moment of ultrathin films
increases by a maximum of 5%, and the most significant changes in spin and
orbital magnetic moments occur at a depth of about three near-surface atomic
monolayers. The presented results could be useful for experimental efforts to
synthesize ultrathin L1$\mathrm{_0}$ FeNi films with different surfaces.
Ultrathin L1$\mathrm{_0}$ FeNi films with varying magnetic anisotropies may
find applications in spintronic devices.",2404.03416v1
1995-12-12,Measurements of Anisotropy in the Cosmic Microwave Background Radiation at 0\fdg5 Scales near the Stars HR5127 and Phi Herculis,"We present measurements of cosmic microwave background (CMB) anisotropy near
the stars HR5127 and Phi Herculis from the fifth flight of the Millimeter-wave
Anisotropy eXperiment (MAX). We scanned 8\arcdeg\ strips of the sky with an
approximately Gaussian 0\fdg5 FWHM beam and a 1\fdg4 peak to peak sinusoidal
chop. The instrument has four frequency bands centered at 3.5, 6, 9, and
14~cm$^{-1}$. The IRAS 100~\micron\ map predicts that these two region have low
interstellar dust contrast. The HR5127 data are consistent with CMB anisotropy.
The Phi Herculis data, which were measured at lower flight altitudes, show time
variability at 9 and 14~cm$^{-1}$ which we believe to be due to atmospheric
emission. However, the Phi Herculis data at 3.5 and 6~cm$^{-1}$ are essentially
independent of this atmospheric contribution and are consistent with CMB
anisotropy. Confusion from galactic foregrounds is unlikely based on the
spectrum and amplitude of the structure at these frequencies. If the observed
HR5127 structure and the atmosphere independent Phi Herculis structure are
attributed to CMB anisotropy, then we find $\Delta T/T =
\langle\frac{l(l+1)C_l}{2\pi}\rangle^{1/2} = 1.2^{+0.4}_{-0.3}\times 10^{-5}$
for HR5127 and $1.9^{+0.7}_{-0.4}\times 10^{-5}$ for Phi Herculis in the flat
band approximation. The upper and lower limits represent a 68\% confidence
interval added in quadrature with a 10\% calibration uncertainty.",9512067v1
2003-05-02,Two band superconductivity in MgB2: basic anisotropic properties and phase diagram,"Magnesium diboride MgB2 has been an extraordinarily hot research topic since
the discovery of superconductivity below 40 K, due to the vast amount of
unusual properties originating from the involvement in superconductivity of two
sets of bands that are of a different dimensionality. We review, with a strong
focus on results obtained by torque magnetometry, how this leads to a complex
behavior of the anisotropic superconducting state properties. The different
dimensionality of the two sets of bands is manifested in the upper critical
field Hc2 anisotropy, which was found to strongly decrease with increasing
temperature. While the angular dependence of Hc2 follows roughly the
predictions of anisotropic Ginzburg-Landau theory AGLT, small, but systematic
deviations were observed near Tc. This, and the temperature dependent
anisotropy, witness a breakdown of the AGLT description of MgB2, even close to
Tc. Theoretical calculations are in qualitative agreement with the observed
angle dependence, but suggest a much lower penetration depth anisotropy at low
temperatures. Reversible torque vs angle curves in the mixed state indicate
that the penetration depth anisotropy in intermediate fields has to be higher
than currently available theoretical estimates. The observed field dependent
effective anisotropies can be accounted for qualitatively by the faster
depression of superconductivity in the more isotropic bands by the applied
field. The vortex matter phase diagram is drawn, based on measurements of the
reversible and irreversible torque in the mixed state. In the irreversible
torque, a peak effect (PE) was observed in fields of about 0.85 Hc2. History
effects of the critical current density in the PE region suggest that the PE
signifies an order-disorder transition of vortex matter.",0305048v2
2007-08-08,Small-Angle CMB Temperature Anisotropies Induced by Cosmic Strings,"We use Nambu-Goto numerical simulations to compute the cosmic microwave
background (CMB) temperature anisotropies induced at arcminute angular scales
by a network of cosmic strings in a Friedmann-Lemaitre-Robertson-Walker (FLRW)
expanding universe. We generate 84 statistically independent maps on a 7.2
degree field of view, which we use to derive basic statistical estimators such
as the one-point distribution and two-point correlation functions. At high
multipoles, the mean angular power spectrum of string-induced CMB temperature
anisotropies can be described by a power law slowly decaying as \ell^{-p}, with
p=0.889 (+0.001,-0.090) (including only systematic errors). Such a behavior
suggests that a nonvanishing string contribution to the overall CMB
anisotropies may become the dominant source of fluctuations at small angular
scales. We therefore discuss how well the temperature gradient magnitude
operator can trace strings in the context of a typical arcminute
diffraction-limited experiment. Including both the thermal and nonlinear
kinetic Sunyaev-Zel'dovich effects, the Ostriker-Vishniac effect, and the
currently favored adiabatic primary anisotropies, we find that, on such a map,
strings should be ``eye visible,'' with at least of order ten distinctive
string features observable on a 7.2 degree gradient map, for tensions U down to
GU \simeq 2 x 10^{-7} (in Planck units). This suggests that, with upcoming
experiments such as the Atacama Cosmology Telescope (ACT), optimal
non-Gaussian, string-devoted statistical estimators applied to small-angle CMB
temperature or gradient maps may put stringent constraints on a possible cosmic
string contribution to the CMB anisotropies.",0708.1162v2
2008-11-04,Sky-maps of the sidereal anisotropy of galactic cosmic ray intensity and its energy dependence,"We analyze the sidereal daily variations observed between 1985 and 2006 at
Matsushiro, Japan (MAT) and between 1993 and 2005 at Liapootah, Tasmania (LPT).
These stations comprise the two hemisphere network (THN) of underground muon
detectors in Japan and Australia. Yearly mean harmonic vectors at MAT and LPT
are more or less stable without any significant change in phase and amplitude
in correlation with either the solar activity- or magnetic-cycles. In this
paper, therefore, we analyze the average anisotropy over the entire observation
periods, i.e. 1985-2006 for MAT and 1993-2005 for LPT. We apply to the THN data
a best-fitting analysis based on a model anisotropy in space identical to that
adopted by Amenomori et al. (2007) for Tibet III data. The median energies of
primary cosmic rays recorded are ~0.5 TeV for THN and ~5 TeV for the Tibet III
experiment. It is shown that the intensity distribution of the best-fit
anisotropy is quite similar to that derived from Tibet III data, regardless of
the order of magnitude difference in energies of primary particles. This,
together with the THN observations, confirms that the analysis by Amenomori et
al. (2007) based on the Tibet III experiment in the northern hemisphere is not
seriously biased. The best-fit amplitudes of the anisotropy, on the other hand,
are only one third or less of those reported by the Tibet III experiment,
indicating attenuation due to solar modulation. The rigidity dependence of the
anisotropy amplitude in the sub-TeV region is consistent with the spectrum
reported by Hall et al. (1999), smoothly extending to the Tibet III result in
the multi-TeV region. The amplitude at higher energies appears almost constant
or gradually decreasing with increasing rigidity.",0811.0422v2
2009-07-09,Anisotropy vs chemical composition at ultra-high energies,"This paper proposes and discusses a test of the chemical composition of
ultra-high energy cosmic rays that relies on the anisotropy patterns measured
as a function of energy. In particular, we show that if one records an
anisotropy signal produced by heavy nuclei of charge Z above an energy E_{thr},
one should record an even stronger (possibly much stronger) anisotropy at
energies >E_{thr}/Z due to the proton component that is expected to be
associated with the sources of the heavy nuclei. This conclusion remains robust
with respect to the parameters characterizing the sources and it does not
depend at all on the modelling of astrophysical magnetic fields. As a concrete
example, we apply this test to the most recent data of the Pierre Auger
Observatory. Assuming that the anisotropy reported above 55EeV is not a
statistical accident, and that no significant anisotropy has been observed at
energies <10EeV, we show that the apparent clustering toward Cen A cannot be
attributed to heavy nuclei. Similar conclusions are drawn regarding the
apparent excess correlation with nearby active galactic nuclei. We then discuss
a robust lower bound to the magnetic luminosity that a source must possess in
order to be able to accelerate particles of charge Z up to 100EeV,
L_B>10^{45}Z^{-2}erg/s. Using this bound in conjunction with the above
conclusions, we argue that the current PAO data does not support the model of
cosmic ray origin in active radio-quiet or even radio-loud galaxies. Finally,
we demonstrate that the apparent clustering in the direction of Cen A can be
explained by the contribution of the last few gamma-ray bursts or magnetars in
the host galaxy thanks to the scattering of the cosmic rays on the magnetized
lobes.",0907.1354v1
2010-03-11,Magnetic moment and magnetic anisotropy of linear and zigzag 4{\it d} and 5{\it d} transition metal nanowires: First-principles calculations,"An extensive {\it ab initio} study of the physical properties of both linear
and zigzag atomic chains of all 4$d$ and 5$d$ transition metals (TM) within the
GGA by using the accurate PAW method, has been carried out. All the TM linear
chains are found to be unstable against the corresponding zigzag structures.
All the TM chains, except Nb, Ag and La, have a stable (or metastable) magnetic
state in either the linear or zigzag or both structures. Magnetic states appear
also in the sufficiently stretched Nb and La linear chains and in the largely
compressed Y and La chains. The spin magnetic moments in the Mo, Tc, Ru, Rh, W,
Re chains could be large ($\geq$1.0 $\mu_B$/atom). Structural transformation
from the linear to zigzag chains could suppress the magnetism already in the
linear chain, induce the magnetism in the zigzag structure, and also cause a
change of the magnetic state (ferromagnetic to antiferroamgetic or vice verse).
The calculations including the spin-orbit coupling reveal that the orbital
moments in the Zr, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir and Pt chains could be
rather large ($\geq$0.1 $\mu_B$/atom). Importantly, large magnetic anisotropy
energy ($\geq$1.0 meV/atom) is found in most of the magnetic TM chains,
suggesting that these nanowires could have fascinating applications in
ultrahigh density magnetic memories and hard disks. In particular, giant
magnetic anisotropy energy ($\geq$10.0 meV/atom) could appear in the Ru, Re,
Rh, and Ir chains. Furthermore, the magnetic anisotropy energy in several
elongated linear chains could be as large as 40.0 meV/atom. A
spin-reorientation transition occurs in the Ru, Ir, Ta, Zr, La and Zr, Ru, La,
Ta and Ir linear chains when they are elongated. Remarkably, all the 5$d$ as
well as Tc and Pd chains show the colossal magnetic anisotropy (i.e., it is
impossible to rotate magnetization into certain directions). Finally, the
electronic band structure and density of states of the nanowires have also been
calculated in order to understand the electronic origin of the large magnetic
anisotropy and orbital magnetic moment as well as to estimate the conduction
electron spin polarization.",1003.2254v1
2010-07-12,Simple models for dynamic hysteresis loops calculation: Application to hyperthermia optimization,"To optimize the heating properties of magnetic nanoparticles (MNPs) in
magnetic hyperthermia applications, it is necessary to calculate the area of
their hysteresis loops in an alternating magnetic field. The three types of
theories suitable for describing the hysteresis loops of MNPs are presented and
compared to numerical simulations: equilibrium functions, Stoner-Wohlfarth
model based theories (SWMBTs) and linear response theory (LRT). Suitable
formulas to calculate the hysteresis area of major cycles are deduced from
SWMBTs and from numerical simulations; the domain of validity of the analytical
formula is explicitly studied. In the case of minor cycles, the hysteresis area
calculations are based on the LRT. A perfect agreement between LRT and
numerical simulations of hysteresis loops is obtained. The domain of validity
of the LRT is explicitly studied. Formulas to calculate the hysteresis area at
low field valid for any anisotropy of the MNP are proposed. Numerical
simulations of the magnetic field dependence of the area show it follows
power-laws with a large range of exponents. Then, analytical expressions
derived from LRT and SWMBTs are used for a theoretical study of magnetic
hyperthermia. It is shown that LRT is only pertinent for MNPs with strong
anisotropy and that SWMBTs should be used for weak anisotropy MNPs. The optimum
volume of MNPs for magnetic hyperthermia as function of material and
experimental parameters is derived. The maximum specific absorption rate (SAR)
achievable is calculated versus the MNP anisotropy. It is shown that an optimum
anisotropy increases the SAR and reduces the detrimental effects of size
distribution. The optimum anisotropy is simple to calculate and depends on the
magnetic field used in the hyperthermia experiments and on the MNP
magnetization only. The theoretical optimum parameters are compared to the one
of several magnetic materials.",1007.2009v2
2011-05-07,An accurate measurement of the anisotropies and mean level of the Cosmic Infrared Background at 100 and 160 um,"The measurement of the anisotropies in the cosmic infrared background (CIB)
is a powerful mean of studying the evolution of galaxies and large-scale
structures. These anisotropies have been measured by a number of experiments,
from the far-infrared to the millimeter. One of the main impediments to an
accurate measurement on large scales is the contamination of the foreground
signal by Galactic dust emission. Our goal is to show that we can remove the
Galactic cirrus contamination using HI data, and thus accurately measure the
clustering of starburst galaxies in the CIB. We use observations of the ELAIS
N1 field at far-infrared (100 and 160{\mu}m) and radio (21 cm) wavelengths. We
compute the correlation between dust emission, traced by far-infrared
observations, and HI gas traced by 21cm observations, and derive dust
emissivities that enable us to subtract the cirrus emission from the
far-infrared maps. We then derive the power spectrum of the CIB anisotropies,
as well as its mean level at 100{\mu}m and 160{\mu}m. We also combine the HI
data and Spitzer total power mode absolute measurements to determine the CIB
mean level at 160{\mu}m. We find B160=0.77\pm0.04\pm0.12MJy/sr,where the first
error is statistical and the second systematic. Combining this measurement with
the B100/B160 color of the correlated anisotropies, we also derive the CIB mean
at 100 {\mu}m, B100=0.24\pm0.08\pm0.04 MJy/sr. This measurement is in line with
values obtained with recent models of infrared galaxy evolution and
Herschel/PACS data, but is much smaller than the previous DIRBE measurements.
The use of high-angular resolution Hi data is mandatory to accurately
differentiate the cirrus from the CIB emission. The 100 {\mu}m IRAS map (and
thus the map developed by Schlegel and collaborators) in such extragalactic
fields is highly contaminated by the CIB anisotropies and hence cannot be used
as a Galactic cirrus tracer.",1105.1463v3
2011-06-29,Profiles of Dark Matter Velocity Anisotropy in Simulated Clusters,"We report statistical results for dark matter (DM) velocity anisotropy,
\beta, from a sample of some 6000 cluster-size halos (at redshift zero)
identified in a \Lambda CDM hydrodynamical adaptive mesh refinement simulation
performed with the Enzo code. These include profiles of \beta\ in clusters with
different masses, relaxation states, and at several redshifts, modeled both as
spherical and triaxial DM configurations. Specifically, although we find a
large scatter in the DM velocity anisotropy profiles of different halos (across
elliptical shells extending to at least ~$1.5 r_{vir}$), universal patterns are
found when these are averaged over halo mass, redshift, and relaxation stage.
These are characterized by a very small velocity anisotropy at the halo center,
increasing outward to about 0.27 and leveling off at about $0.2 r_{vir}$.
Indirect measurements of the DM velocity anisotropy fall on the upper end of
the theoretically expected range. Though measured indirectly, the estimations
are derived by using two different surrogate measurements - X-ray and galaxy
dynamics. Current estimates of the DM velocity anisotropy are based on very
small cluster sample. Increasing this sample will allow testing theoretical
predictions, including the speculation that the decay of DM particles results
in a large velocity boost. We also find, in accord with previous works, that
halos are triaxial and likely to be more prolate when unrelaxed, whereas
relaxed halos are more likely to be oblate. Our analysis does not indicate that
there is significant correlation (found in some previous studies) between the
radial density slope, \gamma, and \beta\ at large radii, $0.3 r_{vir} < r <
r_{vir}$.",1106.6048v2
2012-09-26,Radioactivity and fragmentation of UHECR: Correlating gamma anisotropy and neutrino PeV events,"UHECR (Ultra High Energy Cosmic Rays) were expected to be protons, to fly
straight and to suffer from a GZK (opacity on CMB radiation) cut off. AUGER
suggested in 2007 that such early UHECR anisotropy was compatible with the
foreseen Super-Galactic plane, while both HIRES and AUGER confirmed this
apparent GZK cut-off in the spectra. However, the same AUGER composition since
2007 had favored nuclei (and not nucleons). The recent absence of narrow angle
clustering in UHECR maps, as it should be expected for protons, the missing of
events along the nearest Cluster Virgo, the wide spread (nearly 16 degree
angle) of UHECR along Cen A are in disagreement with the first proton-UHECR
AUGER understanding. Since 2008 we had claimed a light nuclei role for the Cen
A crowded area. However the ICECUBE absence of TeV neutrino clustering or
anisotropy, its spectra steepening favors mostly a ruling atmospheric neutrino
noise up to tens TeV. However two recent PeV neutrino event, cannot easily
coexist or been extrapolated with such an atmospheric ruling scenario, or with
GZK (either nucleons or nuclei) secondary expected spectra. Finally tens of TeV
gamma anisotropy in ARGO-MILAGRO-ICECUBE maps may hardly be associated with
known hadronic sources. We imagine such anisotropy ruled by diffused gamma
secondaries, shining along UHECR bending and flight: radioactive (Ni,Co,Al,D,
neutron) light and heavy UHECR nuclei in GRB-SGRs-jet, while scattering or
decaying in flight, may paint in the sky (by gamma, electrons and neutrinos
secondaries) their trajectories and bending, connecting UHECR spread events
with TeV anisotropy, and also offering a very realistic source of first,
otherwise puzzling, observed PeV neutrinos. Evidences for such relativistic Ni
jet in 4U1630-47 system has been observed recently by D\'iaz Trigo
collaboration.",1209.6090v3
2013-03-08,Orbital anisotropy in cosmological haloes revisited,"The velocity anisotropy of particles inside dark matter (DM) haloes is an
important physical quantity, which is required for the accurate modelling of
mass profiles of galaxies and clusters of galaxies. It is typically measured
using the ratio of the radial-to-tangential velocity dispersions at a given
distance from the halo centre. However, this measure is insufficient to
describe the dynamics of realistic haloes, which are typically quite elongated.
Studying the velocity distribution in massive DM haloes in cosmological
simulations, we find that in the inner parts of the haloes the local velocity
ellipsoids are strongly aligned with the major axis of the halo, the alignment
being stronger for more relaxed haloes. In the outer regions of the haloes, the
alignment becomes gradually weaker and the orientation is more random. These
two distinct regions of different degree of the alignment coincide with two
characteristic regimes of the DM density profile: shallower and steeper than
\rho r^{-2}. This alignment of the local velocity ellipsoids requires
reinterpretation of features found in measurements based on the spherically
averaged ratio of the radial-to-tangential velocity dispersions. In particular,
we show that the velocity distribution in the central halo regions is highly
anisotropic. For cluster-size haloes with mass 10^{14}-10^{15} h^-1 Msun, the
velocity anisotropy along the major axis is nearly independent of radius and is
equal to \beta=1-\sigma^2_{perp}/\sigma^2_{radial}=0.4, which is significantly
larger than the previously estimated spherically averaged velocity anisotropy.
The alignment of density and velocity anisotropies, and the radial trends may
also have some implications for the mass modelling based on kinematical data of
such objects as galaxy clusters or dwarf spheroidals, where the orbital
anisotropy is a key element in an unbiased mass inference.",1303.2056v2
2013-07-31,Lower Limits on the Anisotropy of the Extragalactic Gamma-Ray Background implied by the 2FGL and 1FHL Catalogs,"In principle, the angular anisotropy in the extragalactic gamma-ray
background (EGRB) places severe constraints upon putative populations of
unresolved gamma-ray point sources. Existing estimates of the EGRB anisotropy
have been constructed by excising known point sources, e.g., taken from the
First or 2 Year Fermi-LAT Source Catalog (1FGL or 2FGL, respectively) and
statistically analyzing the residual gamma-ray sky maps. We perform an
independent check of the EGRB anisotropy limits by comparing the values
obtained from the 1FGL-masked sky maps to the signal implied by sources that
lie below the 1FGL detection threshold in the more sensitive 2FGL and 1FHL
(First Fermi-LAT catalog of >10 GeV sources). As such, our analysis provides an
internal consistency check of implications for source counts and spectral index
distributions of gamma-ray bright active galactic nuclei obtained from
Fermi-LAT data. Based on this, we find evidence for substantially larger
anisotropies than those previously reported at energies above 5 GeV, where BL
Lac objects are likely to provide the bulk of their contribution to the EGRB.
This uncertainty in the EGRB anisotropy cautions against using it as an
independent constraint for the high-redshift gamma-ray universe. Moreover, this
would suggest that contrary to previous claims, smooth extensions of the
resolved point-source population may be able to simultaneously explain both the
isotropic and anisotropic components of the EGRB.",1308.0015v2
2014-01-06,Anisotropy expectations for ultra-high-energy cosmic rays with future high statistics experiments,"UHECRs have attracted a lot of attention due to their challengingly high
energies and their potential value to constrain physical processes and
astrophysical parameters in the most energetic sources of the universe. Current
detectors have failed to detect significant anisotropies which had been
expected to allow source identification. Some indications about the UHECR
composition, which may become heavier at the highest energies, has even put
into question the possibility that such a goal could be achieved soon.
  We investigate the potential value of a new-generation detector, with 10
times larger exposure, to overcome the current situation and make significant
progress in the detection of anisotropies and thus in the study of UHECRs. We
take as an example the expected performances of the JEM-EUSO, assuming a
uniform full-sky coverage with a total exposure of 300,000 km2 sr yr.
  We simulate realistic UHECR sky maps for a wide range of possible
astrophysical scenarios allowed by the current constraints, taking into account
the energy losses and photo-dissociation of the UHECRs, as well as their
deflections by magnetic fields. These sky maps, built for the expected
statistics of JEM-EUSO as well as for the current Auger statistics, as a
reference, are analyzed from the point of view of their intrinsic anisotropies,
using the two-point correlation function. A statistical study of the resulting
anisotropies is performed for each astrophysical scenario, varying the UHECR
source composition and spectrum as well as the source density.
  We find that significant anisotropies are expected to be detected by a
next-generation UHECR detector, for essentially all the astrophysical scenarios
studied, and give precise, quantitative meaning to this statement. Our results
show that a gain of one order of magnitude in exposure would make a significant
difference compared to the existing detectors.",1401.1119v1
2014-05-28,Scale and shape dependent non-Gaussianity in the presence of inflationary vector fields,"We consider cosmological inflationary models in which vector fields play some
role in the generation of the primordial curvature perturbation $\zeta$. Such
models are interesting because the involved vector fields naturally seed
statistical anisotropy in the primordial fluctuations which could eventually
leave a measurable imprint on the cosmic microwave background fluctuations. In
this article, we estimate the scale and shape dependent effects on the
non-Gaussianity (NG) parameters due to the scale dependent statistical
anisotropy in the distribution of the fluctuations. For concreteness, we use a
power spectrum (PS) of the fluctuations of the quadrupolar form:
$P_\zeta(\vec{k})\equiv P_\zeta(k)[1+g_\zeta(k)(\hat{n} \cdot \hat{k})^2 ]$,
where $g_{\zeta}(k)$ is the only quantity which parametrizes the level of
statistical anisotropy and $\hat{n}$ is a unitary vector which points towards
the preferred direction. Then, we evaluate the contribution of the running of
$g_{\zeta}(k)$ on the NG parameters by means of the $\delta N$ formalism. We
focus specifically on the details for the $f_{\rm NL}$ NG parameter, associated
with the bispectrum $B_\zeta$, but the structure of higher order NG parameters
is straightforward to generalize. Although the level of statistical anisotropy
in the PS is severely constrained by recent observations, the importance of
statistical anisotropy signals in higher order correlators remains to be
determined, this being the main task that we address here. The precise
measurement of the shape and scale dependence (or running) of statistical
parameters such as the NG parameters and the statistical anisotropy level could
provide relevant elements for model building and for the determination of the
presence (or nonpresence) of inflationary vector fields and their role in the
inflationary mechanism.",1405.7374v2
2014-07-30,The expected anisotropy in solid inflation,"Solid inflation is an effective field theory of inflation in which isotropy
and homogeneity are accomplished via a specific combination of anisotropic
sources (three scalar fields that individually break isotropy). This results in
specific observational signatures that are not found in standard models of
inflation: a non-trivial angular dependence for the squeezed bispectrum, and a
possibly long period of anisotropic inflation (to drive inflation, the ""solid""
must be very insensitive to any deformation, and thus background anisotropies
are very slowly erased). In this paper we compute the expected level of
statistical anisotropy in the power spectrum of the curvature perturbations of
this model. To do so, we account for the classical background values of the
three scalar fields that are generated on large (superhorizon) scales during
inflation via a random walk sum, as the perturbation modes leave the horizon.
Such an anisotropy is unavoidably generated, even starting from perfectly
isotropic classical initial conditions. The expected level of anisotropy is
related to the duration of inflation and to the amplitude of the squeezed
bispectrum. If this amplitude is close to its current observational limit (so
that one of the most interesting predictions of the model can be observed in
the near future), we find that a level of statistical anisotropy $\gtrsim 3\%$
in the power spectrum is to be expected, if inflation lasted $\gtrsim 20-30$
e-folds more than the final $50-60$ efolds required to generare the CMB modes.
We also comment and point out various similarities between solid inflation and
models of inflation where a suitable coupling of the inflaton to a vector
kinetic term $F^{2}$ gives frozen and scale invariant vector perturbations on
superhorizon scales.",1407.8053v1
2015-09-21,Search for anisotropies in cosmic-ray positrons detected by the PAMELA experiment,"The PAMELA detector was launched on board of the Russian Resurs-DK1 satellite
on June 15, 2006. Data collected during the first four years have been used to
search for large-scale anisotropies in the arrival directions of cosmic-ray
positrons. The PAMELA experiment allows for a full sky investigation, with
sensitivity to global anisotropies in any angular window of the celestial
sphere. Data samples of positrons in the rigidity range 10 GV $\leq$ R $\leq$
200 GV were analyzed. This article discusses the method and the results of the
search for possible local sources through analysis of anisotropy in positron
data compared to the proton background. The resulting distributions of arrival
directions are found to be isotropic. Starting from the angular power spectrum,
a dipole anisotropy upper limit \delta = 0.166 at 95% C.L. is determined.
Additional search is carried out around the Sun. No evidence of an excess
correlated with that direction was found.",1509.06249v2
2016-06-14,Direct probe of anisotropy in atom-molecule collisions via quantum scattering resonances,"Anisotropy is a fundamental property of particle interactions. It occupies a
central role in cold and ultra-cold molecular processes, where long range
forces have been found to significantly depend on orientation in ultra-cold
polar molecule collisions. Recent experiments have demonstrated the emergence
of quantum phenomena such as scattering resonances in the cold collisions
regime due to quantization of the intermolecular degrees of freedom. Although
these states have been shown to be sensitive to interaction details, the effect
of anisotropy on quantum resonances has eluded experimental observation so far.
Here, we directly measure the anisotropy in atom-molecule interactions via
quantum resonances by changing the quantum state of the internal molecular
rotor. We observe that a quantum scattering resonance at a collision energy of
$k_B$ x 270 mK appears in the Penning ionization of molecular hydrogen with
metastable helium only if the molecule is rotationally excited. We use state of
the art ab initio and multichannel quantum molecular dynamics calculations to
show that the anisotropy contributes to the effective interaction only for
$H_2$ molecules in the first excited rotational state, whereas rotationally
ground state $H_2$ interacts purely isotropically with metastable helium.
Control over the quantum state of the internal molecular rotation allows us to
switch the anisotropy on or off and thus disentangle the isotropic and
anisotropic parts of the interaction. These quantum phenomena provide a
challenging benchmark for even the most advanced theoretical descriptions,
highlighting the advantage of using cold collisions to advance the microscopic
understanding of particle interactions.",1606.04384v1
2016-10-13,When the Jeans don't fit: How stellar feedback drives stellar kinematics and complicates dynamical modeling in low-mass galaxies,"In low-mass galaxies, stellar feedback can drive gas outflows that generate
non-equilibrium fluctuations in the gravitational potential. Using cosmological
zoom-in baryonic simulations from the Feedback in Realistic Environments (FIRE)
project, we investigate how these fluctuations affect stellar kinematics and
the reliability of Jeans dynamical modeling in low-mass galaxies. We find that
stellar velocity dispersion and anisotropy profiles fluctuate significantly
over the course of galaxies' starburst cycles. We therefore predict an
observable correlation between star formation rate and stellar kinematics:
dwarf galaxies with higher recent star formation rates should have systemically
higher stellar velocity dispersions. This prediction provides an observational
test of the role of stellar feedback in regulating both stellar and dark-matter
densities in dwarf galaxies. We find that Jeans modeling, which treats galaxies
as virialized systems in dynamical equilibrium, overestimates a galaxy's
dynamical mass during periods of post-starburst gas outflow and underestimates
it during periods of net inflow. Short-timescale potential fluctuations lead to
typical errors of $\sim 20\%$ in dynamical mass estimates, even if full
3-dimensional stellar kinematics -- including the orbital anisotropy -- are
known exactly. When orbital anisotropy is $\textit{not}$ known a priori,
typical mass errors arising from non-equilibrium fluctuations in the potential
are larger than those arising from the mass-anisotropy degeneracy. However,
Jeans modeling alone $\textit{cannot}$ reliably constrain the orbital
anisotropy, and problematically, it often favors anisotropy models that do not
reflect the true profile. If galaxies completely lose their gas and cease
forming stars, fluctuations in the potential subside, and Jeans modeling
becomes much more reliable.",1610.04232v2
2016-11-27,Features of collisionless turbulence in the intracluster medium from simulated Faraday rotation maps II: the effects of instabilities feedback,"Statistical analysis of Faraday Rotation Measure (RM) maps of the
intracluster medium (ICM) of galaxy clusters provides a unique tool to evaluate
some spatial features of the magnetic fields there. Its combination with
numerical simulations of magnetohydrodynamic (MHD) turbulence allows the
diagnosis of the ICM turbulence. Being the ICM plasma weakly collisional, the
thermal velocity distribution of the particles naturally develops anisotropies
as a consequence of the large scale motions and the conservation of the
magnetic moment of the charged particles. A previous study (Paper I) analyzed
the impact of large scale thermal anisotropy on the statistics of RM maps
synthesized from simulations of turbulence; these simulations employed a
collisionless MHD model which considered a tensor pressure with uniform
anisotropy. In the present work, we extend that analysis to a collisionless MHD
model in which the thermal anisotropy develops according to the conservation of
the magnetic moment of the thermal particles. We also consider the effect of
anisotropy relaxation caused by the micro-scale mirror and firehose
instabilities. We show that if the relaxation rate is fast enough to keep the
anisotropy limited by the threshold values of the instabilities, the dispersion
and power spectrum of the RM maps are indistinguishable from those obtained
from collisional MHD. Otherwise, there is a reduction in the dispersion and
steepening of the power spectrum of the RM maps (compared to the collisional
case). Considering the first scenario, the use of collisional MHD simulations
for modeling the RM statistics in the ICM becomes better justified.",1611.10183v1
2017-01-06,Magnetization in narrow ribbons: curvature effects,"A ribbon is a surface swept out by a line segment turning as it moves along a
central curve. For narrow magnetic ribbons, for which the length of the line
segment is much less than the length of the curve, the anisotropy induced by
the magnetostatic interaction is biaxial, with hard axis normal to the ribbon
and easy axis along the central curve. The micromagnetic energy of a narrow
ribbon reduces to that of a one-dimensional ferromagnetic wire, but with
curvature, torsion and local anisotropy modified by the rate of turning. These
general results are applied to two examples, namely a helicoid ribbon, for
which the central curve is a straight line, and a M\""obius ribbon, for which
the central curve is a circle about which the line segment executes a
$180^\circ$ twist. In both examples, for large positive tangential anisotropy,
the ground state magnetization lies tangent to the central curve. As the
tangential anisotropy is decreased, the ground state magnetization undergoes a
transition, acquiring an in-surface component perpendicular to the central
curve. For the helicoid ribbon, the transition occurs at vanishing anisotropy,
below which the ground state is uniformly perpendicular to the central curve.
The transition for the M\""obius ribbon is more subtle; it occurs at a positive
critical value of the anisotropy, below which the ground state is nonuniform.
For the helicoid ribbon, the dispersion law for spin wave excitations about the
tangential state is found to exhibit an asymmetry determined by the geometric
and magnetic chiralities.",1701.01691v1
2017-06-16,Anisotropic spin-density distribution and magnetic anisotropy of strained La$_{1-x}$Sr$_x$MnO$_3$ thin films: Angle-dependent x-ray magnetic circular dichroism,"Magnetic anisotropies of ferromagnetic thin films are induced by epitaxial
strain from the substrate via strain-induced anisotropy in the orbital magnetic
moment and that in the spatial distribution of spin-polarized electrons.
However, the preferential orbital occupation in ferromagnetic metallic
La$_{1-x}$Sr$_x$MnO$_3$ (LSMO) thin films studied by x-ray linear dichroism
(XLD) has always been found out-of-plane for both tensile and compressive
epitaxial strain and hence irrespective of the magnetic anisotropy. In order to
resolve this mystery, we directly probed the preferential orbital occupation of
spin-polarized electrons in LSMO thin films under strain by angle-dependent
x-ray magnetic circular dichroism (XMCD). Anisotropy of the spin-density
distribution was found to be in-plane for the tensile strain and out-of-plane
for the compressive strain, consistent with the observed magnetic anisotropy.
The ubiquitous out-of-plane preferential orbital occupation seen by XLD is
attributed to the occupation of both spin-up and spin-down out-of-plane
orbitals in the surface magnetic dead layer.",1706.05183v5
2017-09-15,Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability,"In collisionless and weakly collisional plasmas, such as hot accretion flows
onto compact objects, the magnetorotational instability (MRI) can differ
significantly from the standard (collisional) MRI. In particular, pressure
anisotropy with respect to the local magnetic-field direction can both change
the linear MRI dispersion relation and cause nonlinear modifications to the
mode structure and growth rate, even when the field and flow perturbations are
small. This work studies these pressure-anisotropy-induced nonlinearities in
the weakly nonlinear, high-ion-beta regime, before the MRI saturates into
strong turbulence. Our goal is to better understand how the saturation of the
MRI in a low collisionality plasma might differ from that in the collisional
regime. We focus on two key effects: (i) the direct impact of self-induced
pressure-anisotropy nonlinearities on the evolution of an MRI mode, and (ii)
the influence of pressure anisotropy on the ""parasitic instabilities"" that are
suspected to cause the mode to break up into turbulence. Our main conclusions
are: (i) The mirror instability regulates the pressure anisotropy in such a way
that the linear MRI in a collisionless plasma is an approximate nonlinear
solution once the mode amplitude becomes larger than the background field (just
as in MHD). This implies that differences between the collisionless and
collisional MRI become unimportant at large amplitudes. (ii) The break up of
large amplitude MRI modes into turbulence via parasitic instabilities is
similar in collisionless and collisional plasmas. Together, these conclusions
suggest that the route to magnetorotational turbulence in a collisionless
plasma may well be similar to that in a collisional plasma, as suggested by
recent kinetic simulations. As a supplement to these findings, we offer
guidance for the design of future kinetic simulations of magnetorotational
turbulence.",1709.05428v2
2018-05-11,Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and $Gaia$,"The anisotropy parameter $\beta$ characterizes the extent to which orbits in
stellar systems are predominantly radial or tangential, and is likely to
constrain, for the stellar halo of the Milky Way, scenarios for its formation
and evolution. We have measured the anisotropy $\beta$ as a function of
Galactocentric radius from $5-100$ kpc for over 8600 metal poor ([Fe/H]
$<-1.3$) halo K giants from the LAMOST catalog with line-of-sight velocities
and distances, matched to proper motions from the second $Gaia$ data release.
We construct full 6-D positions and velocities for the K giants to directly
measure the 3 components of the velocity dispersion $(\sigma_r, \sigma_\theta,
\sigma_\phi)$ (in spherical coordinates). We find that the orbits in the halo
are radial over our full Galactocentric distance range reaching over 100 kpc.
The anisotropy remains remarkably unchanged with Galactocentric radius from
approximately 5 to 25 kpc, with an amplitude that depends on the metallicity of
the stars, dropping from $\beta \approx 0.9$ for $-1.8 \leq$ [Fe/H] $< -1.3$
(for the bulk of the stars) to $\beta \approx 0.6$ for the lowest metallicities
([Fe/H] $< -1.8$). Considering our sample as a whole, $\beta\approx0.8$ and,
beyond 25 kpc, the orbits gradually become less radial and anisotropy decreases
to $\beta<0.3$ past 100 kpc. Within 8 kpc, $\beta<0.8$. The measurement of
anisotropy is affected by substructure and streams, particularly beyond a
Galactocentric distance of approximately 25 kpc, where the Sagittarius stream
is prominent in the data. These results are complimentary to recent analysis of
simulations by Loebman et al. and of SDSS/$Gaia$ DR1 data by Belokurov et al.",1805.04503v2
2018-07-25,A mass-velocity anisotropy relation in galactic stellar disks,"The ellipsoid of stellar random motions is a fundamental ingredient of galaxy
dynamics. Yet it has long been difficult to constrain this component in disks
others than the Milky Way. This article presents the modeling of the
azimuthal-to-radial axis ratio of the velocity ellipsoid of galactic disks from
stellar dispersion maps using integral field spectroscopy data of the CALIFA
survey. The measured azimuthal anisotropy is shown to be not strongly dependent
on the assumed vertical-to-radial dispersion ratio of the ellipsoid. The
anisotropy distribution shows a large diversity in the orbital structure of
disk galaxies from tangential to radial stellar orbits. Globally, the orbits
are isotropic in inner disk regions and become more radial as a function of
radius, although this picture tends to depend on galaxy morphology and
luminosity. The Milky Way orbital anisotropy profile measured from the Second
Gaia Data Release is consistent with those of CALIFA galaxies. A new
correlation is evidenced, linking the absolute magnitude or stellar mass of the
disks to the azimuthal anisotropy. More luminous disks have more radial orbits
and less luminous disks have isotropic and somewhat tangential orbits. This
correlation is consistent with the picture in galaxy evolution in which orbits
become more radial as the mass grows and is redistributed as a function of
time. With the help of circular velocity curves, it is also shown that the
epicycle theory fails to reproduce the diversity of the azimuthal anisotropy of
stellar random motions, as it predicts only nearly radial orbits in the
presence of flat curves. The origin of this conflict is yet to be identified.
It also questions the validity of the vertical-to-radial axis ratio of the
velocity ellipsoid derived by many studies in the framework of the epicyclic
approximation.",1807.09833v2
2018-08-15,Large magneto-optical effects and magnetic anisotropy energy in two-dimensional Cr$_2$Ge$_2$Te$_6$,"By performing systematic $ab$ $initio$ density functional calculations, here
we study two relativity-induced properties of atomically thin ferromagnetic
(FM) Cr$_2$Ge$_2$Te$_6$ films [monolayer (ML), bilayer (BL) and trilayer (TL)
as well as bulk], namely, magnetic anisotropy energy (MAE) and magneto-optical
(MO) effects. Competing contributions of both magneto-crystalline anisotropy
energy (C-MAE) and magnetic dipolar anisotropy energy (D-MAE) to the MAE, are
computed. Calculated MAEs of these materials are large, being in the order of
$\sim$0.1 meV/Cr. Interestingly, we find that the out-of-plane magnetic
anisotropy is preferred in all the systems except the ML where an in-plane
magnetization is favored because here the D-MAE is larger than the C-MAE.
Crucially, this explains why long-range FM order was observed in all the
few-layer Cr$_2$Ge$_2$Te$_6$ except the ML because the out-of-plane magnetic
anisotropy would open a spin-wave gap and thus suppress magnetic fluctuations
so that long-range FM order could be stabilized at finite temperature. In the
visible frequency range, large Kerr rotations up to $\sim$1.0 deg in these
materials are predicted and they are comparable to that observed in famous MO
materials such as PtMnSb and Y$_3$Fe$_5$O$_{12}$. Moreover, they are $\sim$100
times larger than that of 3$d$ transition metal MLs deposited on Au surfaces.
Faraday rotation angles in these 2D materials are also large, being up to
$\sim$120 deg/$\mu$m, and are thus comparable to the best-known MO
semiconductor Bi$_3$Fe$_5$O$_{12}$. These findings thus suggest that with large
MAE and MO effects, atomically thin Cr$_2$Ge$_2$Te$_6$ films would have
potential applications in novel magnetic, MO and spintronic nanodevices.",1808.05086v1
2019-12-09,Proton Temperature Anisotropy Variations in Inner Heliosphere Estimated with First Parker Solar Probe Observations,"We report proton temperature anisotropy variations in the inner heliosphere
with Parker Solar Probe (PSP) observations. Using a linear fitting method, we
derive proton temperature anisotropy with temperatures measured by the Solar
Probe Cup (SPC) from the SWEAP instrument suite and magnetic field observations
from the FIELDS instrument suite. The observed radial dependence of temperature
variations in the fast solar wind implies stronger perpendicular heating and
parallel cooling than previous results from Helios measurements made at larger
radial distances. The anti-correlation between proton temperature anisotropy
and parallel plasma beta is retained in fast solar wind. However, the
temperature anisotropies of the slow solar wind seem to be well constrained by
the mirror and parallel firehose instabilities. The perpendicular heating of
the slow solar wind inside 0.24 AU may contribute to its same trend up against
mirror instability thresholds as fast solar wind. These results suggest that we
may see stronger anisotropy heating than expected in inner heliosphere.",1912.03871v2
2020-01-07,Full-sky searches for anisotropies in UHECR arrival directions with the Pierre Auger Observatory and the Telescope Array,"The arrival directions of ultra-high-energy cosmic rays appear to be
approximately isotropically distributed over the whole sky, but the
last-generation UHECR detector arrays, the Pierre Auger Observatory (Auger) and
the Telescope Array (TA), have detected thousands of events, allowing us to
study small deviations from isotropy. So far, Auger has detected a large-scale
anisotropy consistent with a $\sim 6.5\%$ dipole moment in the distribution of
cosmic rays with $E > 8$~EeV, and both collaborations have reported indications
for smaller-scale anisotropies at higher energies. On the other hand, neither
array has full-sky coverage, the Auger field of view being limited to
declinations $\delta < +45^\circ$ and the TA one to $\delta > -16^\circ$.
Searches for anisotropies with full-sky coverage thus require combining data
from both arrays. A working group with members from both collaborations has
been established for this task. Since even a minor systematic error in the
energy determinations at either of the arrays could result in a sizeable
spurious anisotropy along the north--south axis, we devised a method to
cross-calibrate the energy scales of the two experiments with respect to each
other by using events in a declination band within the intersection of their
fields of view. In this contribution, we report on both updates on blind
searches for anisotropies and the first full-sky studies of flux models based
on possible local extragalactic sources.",2001.01864v1
2020-04-02,Introducing Anisotropic Minkowski Functionals and Quantitative Anisotropy Measures for Local Structure Analysis in Biomedical Imaging,"The ability of Minkowski Functionals to characterize local structure in
different biological tissue types has been demonstrated in a variety of medical
image processing tasks. We introduce anisotropic Minkowski Functionals (AMFs)
as a novel variant that captures the inherent anisotropy of the underlying
gray-level structures. To quantify the anisotropy characterized by our
approach, we further introduce a method to compute a quantitative measure
motivated by a technique utilized in MR diffusion tensor imaging, namely
fractional anisotropy. We showcase the applicability of our method in the
research context of characterizing the local structure properties of trabecular
bone micro-architecture in the proximal femur as visualized on multi-detector
CT. To this end, AMFs were computed locally for each pixel of ROIs extracted
from the head, neck and trochanter regions. Fractional anisotropy was then used
to quantify the local anisotropy of the trabecular structures found in these
ROIs and to compare its distribution in different anatomical regions. Our
results suggest a significantly greater concentration of anisotropic trabecular
structures in the head and neck regions when compared to the trochanter region
(p < 10-4). We also evaluated the ability of such AMFs to predict bone strength
in the femoral head of proximal femur specimens obtained from 50 donors. Our
results suggest that such AMFs, when used in conjunction with multi-regression
models, can outperform more conventional features such as BMD in predicting
failure load. We conclude that such anisotropic Minkowski Functionals can
capture valuable information regarding directional attributes of local
structure, which may be useful in a wide scope of biomedical imaging
applications.",2004.01185v1
2020-06-23,Unlocking the synergy between CMB spectral distortions and anisotropies,"Measurements of the cosmic microwave background (CMB) spectral distortions
(SDs) will open a new window on the very early universe, providing new
information complementary to that gathered from CMB temperature and
polarization anisotropies. In this paper, we study their synergy as a function
of the characteristics of the considered experiments. In particular, we examine
a wide range of sensitivities for possible SD measurements, spanning from FIRAS
up to noise levels 1000 times better than PIXIE, and study their constraining
power when combined with current or future CMB anisotropy experiments such as
Planck or LiteBIRD plus CMB-S4. We consider a number of different cosmological
models such as the $\Lambda$CDM, as well as its extensions with the running of
the scalar spectral index, the decay or the annihilation of dark matter (DM)
particles. While upcoming CMB anisotropy experiments will be able to decrease
the uncertainties on inflationary parameters such as $A_s$ and $n_s$ by about a
factor 2 in the $\Lambda$CDM case, we find that an SD experiment 100 times more
sensitive than PIXIE (comparable to the proposed Super-PIXIE satellite) could
potentially further contribute to constrain these parameters. This is even more
significant in the case of the running of the scalar spectral index.
Furthermore, as expected, constraints on DM particles decaying at redshifts
probed by SDs will improve by orders of magnitude even with an experiment 10
times worse than PIXIE as compared to CMB anisotropies or Big Bang
Nucleosynthesis bounds. On the contrary, DM annihilation constraints will not
significantly improve over CMB anisotropy measurements. Finally, we forecast
the constraints obtainable with sensitivities achievable either from the ground
or from a balloon.",2006.12886v2
2021-04-09,"Joint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo","We present multi-tracer dynamical models of the low mass ($M_{*} \sim
10^{7}$), isolated dwarf irregular galaxy WLM in order to simultaneously
constrain the inner slope of the dark matter (DM) halo density profile
($\gamma$) and flattening ($q_\mathrm{DM}$), and the stellar orbital anisotropy
($\beta_{z}, \beta_{r}$). For the first time, we show how jointly constraining
the mass distribution from the HI gas rotation curve and solving the Jeans'
equations with discrete stellar kinematics leads to a factor of $\sim2$
reduction in the uncertainties on $\gamma$. The mass-anisotropy degeneracy is
also partially broken, leading to reductions on uncertainty by $\sim 30\%$ on
$M_\mathrm{vir}$ (and $\sim 70\%$ at the half-light radius) and $\sim 25\%$ on
anisotropy. Our inferred value of $\gamma = 0.3 \pm 0.1$ is robust to the halo
geometry, and in excellent agreement with predictions of stellar feedback
driven DM core creation. The derived prolate geometry of the DM halo with
$q_\mathrm{DM} = 2 \pm 1$ is consistent with $\Lambda$CDM simulations of dwarf
galaxy halos. While self-interacting DM (SIDM) models with $\sigma/m_{X} \sim
0.6$ can reproduce this cored DM profile, the interaction events may
sphericalise the halo. The simultaneously cored and prolate DM halo may
therefore present a challenge for SIDM. Finally we find that the radial profile
of stellar anisotropy in WLM ($\beta_{r}$) follows a nearly identical trend of
increasing tangential anisotropy to the classical dSphs, Fornax and Sculptor.
Given WLM's orbital history, this result may call into question whether such
anisotropy is a consequence of tidal stripping in only one pericentric passage
or if it instead is a feature of the largely self-similar formation and
evolutionary pathways for some dwarf galaxies.",2104.04273v1
2021-08-31,Strain-controlled Domain Wall injection into nanowires for sensor applications,"We investigate experimentally the effects of externally applied strain on the
injection of 180$^\circ$ domain walls (DW) from a nucleation pad into magnetic
nanowires, as typically used for DW-based sensors. In our study the strain,
generated by substrate bending, induces in the material a uniaxial anisotropy
due to magnetoelastic coupling. To compare the strain effects,
$Co_{40}Fe_{40}B_{20}$, $Ni$ and $Ni_{82}Fe_{18}$ samples with in-plane
magnetization and different magnetoelastic coupling are deposited. In these
samples, we measure the magnetic field required for the injection of a DW, by
imaging differential contrast in a magneto-optical Kerr microscope. We find
that strain increases the DW injection field, however, the switching mechanism
depends strongly on the direction of the strain with respect to the wire axis.
We observe that low magnetic anisotropy facilitates the creation of a domain
wall at the junction between the pad and the wire, whereas a strain-induced
magnetic easy axis significantly increases the coercive field of the nucleation
pad. Additionally, we find that the effects of mechanical strain can be
counteracted by a magnetic uniaxial anisotropy perpendicular to the
strain-induced easy axis. In $Co_{40}Fe_{40}B_{20}$, we show that this
anisotropy can be induced by annealing in a magnetic field. We perform
micromagnetic simulations to support the interpretation of our experimental
findings. Our simulations show that the above described observations can be
explained by the effective anisotropy in the device. The anisotropy influences
the switching mechanism in the nucleation pad as well as the pinning of the DW
at the wire entrance. As the DW injection is a key operation for sensor
performances, the observations show that strain is imposing a lower limit for
the sensor field operating window.",2108.13881v1
2021-10-27,Leverage on small-scale primordial non-Gaussianity through cross-correlations between CMB $E$-mode and $μ$-distortion anisotropies,"Multi-field inflation models and non-Bunch-Davies vacuum initial conditions
both predict sizeable non-Gaussian primordial perturbations and anisotropic
$\mu$-type spectral distortions of the cosmic microwave background (CMB)
blackbody. While CMB anisotropies allow us to probe non-Gaussianity at
wavenumbers $k\simeq 0.05\,{\rm Mpc^{-1}}$, $\mu$-distortion anisotropies are
related to non-Gaussianity of primordial perturbation modes with much larger
wavenumbers, $k\simeq 740\,{\rm Mpc^{-1}}$. Through cross-correlations between
CMB and $\mu$-distortion anisotropies, one can therefore shed light on the
aforementioned inflation models. We investigate the ability of a future CMB
satellite imager like LiteBIRD to measure $\mu T$ and $\mu E$ cross-power
spectra between anisotropic $\mu$-distortions and CMB temperature and $E$-mode
polarization anisotropies in the presence of foregrounds, and derive LiteBIRD
forecasts on ${f_{\rm NL}^\mu(k\simeq 740\,{\rm Mpc^{-1}})}$. We show that $\mu
E$ cross-correlations with CMB polarization provide more constraining power on
$f_{\rm NL}^\mu$ than $\mu T$ cross-correlations in the presence of
foregrounds, and the joint combination of $\mu T$ and $\mu E$ observables adds
further leverage to the detection of small-scale primordial non-Gaussianity. We
find that LiteBIRD would detect ${f_{\rm NL}^\mu}=4500$ at $5\sigma$
significance after foreground removal, and achieve a minimum error of
${\sigma(f_{\rm NL}^\mu=0) \simeq 800}$ at 68\% CL by combining CMB temperature
and polarization. Due to the huge dynamic range of wavenumbers between CMB and
$\mu$-distortion anisotropies, such large $f^\mu_{\rm NL}$ values would still
be consistent with current CMB constraints in the case of very mild
scale-dependence of primordial non-Gaussianity. Anisotropic spectral
distortions thus provide a new path, complementary to CMB $B$-modes, to probe
inflation with LiteBIRD.",2110.14664v2
2022-01-19,On the Energy Dependence of Galactic Cosmic Ray Anisotropies in the Very Local Interstellar Medium,"We report on the energy dependence of galactic cosmic rays (GCRs) in the very
local interstellar medium (VLISM) as measured by the Low Energy Charged
Particle (LECP) instrument on the Voyager 1 (V1) spacecraft. The LECP
instrument includes a dual-ended solid state detector particle telescope
mechanically scanning through 360 deg across eight equally-spaced angular
sectors. As reported previously, LECP measurements showed a dramatic increase
in GCR intensities for all sectors of the >=211 MeV count rate (CH31) at the V1
heliopause (HP) crossing in 2012, however, since then the count rate data have
demonstrated systematic episodes of intensity decrease for particles around
90{\deg} pitch angle. To shed light on the energy dependence of these GCR
anisotropies over a wide range of energies, we use V1 LECP count rate and pulse
height analyzer (PHA) data from >=211 MeV channel together with lower energy
LECP channels. Our analysis shows that while GCR anisotropies are present over
a wide range of energies, there is a decreasing trend in the amplitude of
second-order anisotropy with increasing energy during anisotropy episodes. A
stronger pitch-angle scattering at the higher velocities is argued as a
potential cause for this energy dependence. A possible cause for this velocity
dependence arising from weak rigidity dependence of the scattering mean free
path and resulting velocity-dominated scattering rate is discussed. This
interpretation is consistent with a recently reported lack of corresponding GCR
electron anisotropies.",2201.07844v1
2022-01-20,Event-by-event jet anisotropy and hard-soft tomography of the quark-gluon plasma,"Suppression of jet spectra or jet quenching in high-energy heavy-ion
collisions is caused by jet energy loss in the dense medium. The azimuthal
anisotropy of jet energy loss in non-central heavy-ion collisions can lead to
jet anisotropy which in turn can provide insight into the path-length
dependence of jet quenching. This is investigated within the Linear Boltzmann
Transport (LBT) model which simulates both elastic scattering and
medium-induced gluon radiation based on perturbative QCD for jet shower and
medium recoil partons as well as radiated gluons as they propagate through the
quark-gluon plasma (QGP). The dynamical evolution of the QGP in each event of
heavy-ion collisions is provided by the (3+1)D CLVisc hydrodynamic model with
fully fluctuating initial conditions. This framework has been shown to describe
the suppression of single inclusive jet spectra well. We calculate in this
study the elliptic ($v_{2}^{\rm jet}$) and triangular ($v_{3}^{\rm jet}$)
anisotropy coefficients of the single inclusive jet spectra in Pb+Pb collisions
at the LHC energies. We investigate the colliding energy, centrality, jet
transverse momentum dependence of the jet anisotropy, as well as their
event-by-event correlation with the flow coefficients of the soft bulk hadrons.
An approximate linear correlation between jet and bulk $v_2$ is found. Effect
of the bulk $v_n$ fluctuation on $v_n^{\rm jet}$ is found negligible. The
jet-induced medium excitation, which is influenced by radial flow, is shown to
enhance $v_{2}^{\rm jet}$ and the enhancement increases with the jet cone size.
The jet elliptic anisotropy $v_{2}^{\rm jet}$ is also found to be slightly
enhanced by the shear viscosity of the bulk medium in comparison to the LBT
results when jets propagate through an ideal hydrodynamic QGP medium.",2201.08408v1
2022-02-17,"Doping control of magnetic anisotropy for stable antiskyrmion formation in schreibersite (Fe,Ni)$_3$P with $S_4$ symmetry","Magnetic skyrmions, vortex-like topological spin textures, have attracted
much interest in a wide range of research fields from fundamental physics to
spintronics applications. Recently, growing attention has also been paid to
antiskyrmions emerging in opposite topological charge in non-centrosymmetric
magnets with $D_{2\mathrm{d}}$ or $S_4$ symmetry. In these magnets, complex
interplay among anisotropic Dzyaloshinskii-Moriya interaction, uniaxial
magnetic anisotropy, and magnetic dipolar interactions generates a variety of
magnetic structures. However, the relation between the stability of
antiskyrmions and these magnetic interactions remains to be elucidated. In this
work, we control the uniaxial magnetic anisotropy of schreibersite (Fe,Ni)$_3$P
with $S_4$ symmetry by doping and investigate its impact on the stability of
antiskyrmions. Our magnetometry study, supported by ferromagnetic resonance
spectroscopy, shows that the variation of the Ni content and slight doping with
4$d$ transition metals considerably change the magnetic anisotropy. In
particular, doping with Pd induces easy-axis anisotropy, giving rise to
formation of antiskyrmions, while a temperature-induced spin reorientation is
observed in a Rh-doped compound. In combination with Lorentz transmission
electron microscopy and micromagnetic simulations, we quantitatively analyze
the stability of antiskyrmion as functions of uniaxial anisotropy and
demagnetization energy, and demonstrate that subtle balance between them is
necessary to stabilize the antiskyrmions.",2202.08483v1
2023-02-20,Pressure anisotropy and viscous heating in weakly collisional plasma turbulence,"Pressure anisotropy can strongly influence the dynamics of weakly
collisional, high-beta plasmas, but its effects are missed by standard
magnetohydrodynamics (MHD). Small changes to the magnetic-field strength
generate large pressure-anisotropy forces, heating the plasma, driving
instabilities, and rearranging flows, even on scales far above the particles'
gyroscales where kinetic effects are traditionally considered important. Here,
we study the influence of pressure anisotropy on turbulent plasmas threaded by
a mean magnetic field (Alfv\'enic turbulence). Extending previous results that
were concerned with Braginskii MHD, we consider a wide range of regimes and
parameters using a simplified fluid model based on drift kinetics with heat
fluxes calculated using a Landau-fluid closure. We show that viscous
(pressure-anisotropy) heating dissipates between a quarter and half of the
turbulent cascade power injected at large scales; this does not depend strongly
on either plasma beta or the ion-to-electron temperature ratio. This will in
turn influence the plasma's thermodynamics by regulating energy partition
between different dissipation channels (e.g., electron and ion heat). Due to
the pressure anisotropy's rapid dynamical feedback onto the flows that create
it -- an effect we term `magneto-immutability' -- the viscous heating is
confined to a narrow range of scales near the forcing scale, supporting a
nearly conservative, MHD-like inertial-range cascade, via which the rest of the
energy is transferred to small scales. Despite the simplified model, our
results -- including the viscous heating rate, distributions, and turbulent
spectra -- compare favourably to recent hybrid-kinetic simulations. This is
promising for the more general use of extended-fluid (or even MHD) approaches
to model weakly collisional plasmas such as the intracluster medium, hot
accretion flows, and the solar wind.",2303.00468v2
2023-09-13,Beyond the Background: Gravitational Wave Anisotropy and Continuous Waves from Supermassive Black Hole Binaries,"Pulsar timing arrays have found evidence for a low-frequency gravitational
wave background (GWB). Assuming the GWB is produced by supermassive black hole
binaries (SMBHBs), the next gravitational wave (GW) signals astronomers
anticipate are Continuous Waves (CWs) from single SMBHBs and their associated
GWB anisotropy. The prospects for detecting CWs and anisotropy are highly
dependent on the astrophysics of SMBHB populations. Thus, information from
single sources can break degeneracies in astrophysical models and place much
more stringent constraints than the GWB alone. We simulate and evolve SMBHB
populations, model their GWs, and calculate their anisotropy and detectability.
We investigate how varying components of our semi-analytic model, including the
galaxy stellar mass function, the SMBH--host galaxy relation
($M_\mathrm{BH}$--$M_\mathrm{bulge}$), and the binary evolution prescription
impact the expected detections. The CW occurrence rate is greatest for few
total binaries, high SMBHB masses, large scatter in
$M_\mathrm{BH}$--$M_\mathrm{bulge}$, and long hardening times. The occurrence
rate depends most on the binary evolution parameters, implying that CWs offer a
novel avenue to probe binary evolution. The most detectable CW sources are in
the lowest frequency bin for a 16.03-year PTA, have masses from
$\sim\!\!10^9-10^{10}\mathrm{M}_\odot$, and are $\sim\!\!1$ Gpc away. The level
of anisotropy increases with frequency, with the angular power spectrum over
multipole modes $\ell$ varying in low-frequency $C_{\ell>0}/C_0$ from
$\sim\!\!5\times 10^{-3}$ to $\sim\!\!2\times10^{-1}$, depending on the model;
typical values are near current upper limits. Observing this anisotropy would
support SMBHB models for the GWB over cosmological models, which tend to be
isotropic.",2309.07227v2
2024-02-09,Crossover From Individual to Collective Magnetism in Dense Nanoparticle Systems: Local Anisotropy Versus Dipolar Interactions,"Dense systems of magnetic nanoparticles may exhibit dipolar collective
behavior. However, two fundamental questions remain unsolved: i) whether the
transition temperature may be affected by the particle anisotropy or it is
essentially determined by the intensity of the interparticle dipolar
interactions, and ii) what is the minimum ratio of dipole-dipole interaction
($E_\text{dd}$) to nanoparticle anisotropy ($K_{\text{ef}}V$, anisotropy
$\times$ volume) energies necessary to crossover from individual to collective
behavior. A series of particle assemblies with similarly intense dipolar
interactions but widely varying anisotropy is studied. The $K_\text{ef}$ is
tuned through different degrees of cobalt-doping in maghemite nanoparticles,
resulting in a variation of nearly an order of magnitude. All the bare particle
compacts display collective behavior, except the one made with the highest
anisotropy particles, which presents ``marginal'' features. Thus, a threshold
of $K_{\text{ef}} V/E_{\text{dd}} \approx 130$ to suppress collective behavior
is derived, in good agreement with Monte Carlo simulations. This translates
into a crossover value of $\approx 1.7$ for the easily accessible parameter
$T_\text{MAX}$(interacting)$/T_\text{MAX}$(non-interacting) (ratio of the peak
temperatures of the zero-field-cooled magnetization curves of interacting and
dilute particle systems), which is successfully tested against the literature
to predict the individual-like$/$collective behavior of any given interacting
particle assembly comprising relatively uniform particles.",2402.06583v1
2024-03-29,Influence of pressure anisotropy and non-metricity parameter on mass-radius relation and stability of millisecond pulsar in $f(Q)$ gravity,"In this study we explore the astrophysical implications of pressure
anisotropy on the physical characteristics of millisecond pulsars within the
framework of $f(Q)$ gravity. Starting off with the field equations for
anisotropic matter distributions, we adopt the physically salient
Durgapal-Fuloria ansatz together with a well-motivated anisotropic factor for
the interior matter distribution. This leads to a nonlinear second order
differential equation which is integrated to give the complete gravitational
and thermodynamical properties of the stellar object. The resulting model is
subjected to rigorous tests to ensure that it qualifies as a physically viable
compact object within the $f(Q)$-gravity framework. We study in detail two
factors, one being non-metricity (gravitational interaction) and the other the
pressure anisotropy (matter variation) and their contributions to the mass,
radius and stability of the star. Our analyses indicate that our models are
well-behaved, singularity-free and can account for the existence of a wide
range of observed pulsars with masses ranging from 2.08 to 2.67 $M_{\odot}$,
with the upper value being in the so-called {\em mass gap} regime observed in
gravitational events such as GW190814. A novel finding of this work is
two-fold: an increase in the non-metricity factor (fixed anisotropy) leads to a
spectrum of pulsars with radii ranging from a minimum of 10 km whereas a
variation in anisotropy (fixed non-metricity) restricts the radii to a narrow
window between ($12 - 13.2$) km for a 450 Hz pulsar. In addition, contributions
from anisotropy outweigh the impact of nonmetricity in predicting the masses of
pulsars with the ratio, $\left(\frac{M_\Delta}{M_Q}\right)_{max} \approx 2.43 $
for low mass pulsars.",2403.20011v1
1993-05-09,Testing for Gaussianity Through the Three Point Temperature Correlation Function,"One of the crucial aspects of density perturbations that are produced by the
standard inflation scenario is that they are Gaussian where seeds produced by
topological defects tend to be non-Gaussian. The three point correlation
function of the temperature anisotropy of the cosmic microwave background
radiation (CBR) provides a sensitive test of this aspect of the primordial
density field. In this paper, this function is calculated in the general
context of various allowed non-Gaussian models. It is shown that by COBE and
the forthcoming South Pole and Balloon CBR anisotropy data may be able to test
provide a crucial test of Gaussianity.",9305009v1
1993-09-01,Implications of MAX for CDM,"We analyze the Gamma Ursae Minoris (GUM) and Mu Pegasii (MuP) scans of the
Millimeter-wave Anisotropy eXperiment in the context of cold dark matter (CDM)
models of structure formation, paying particular attention to the
two-dimensional nature of the GUM scan. If all of the structure in the
(foreground subtracted) data is attributed to cosmic microwave background
anisotropy, then there is a detection in each scan. For a standard CDM model,
the amplitudes of the signals are individually compatible with the COsmic
Background Explorer measurement, but marginally inconsistent with each other.",9309006v1
1993-09-28,Measuring Cosmological Parameters with Cosmic Microwave Background Experiments,"The cosmic microwave background anisotropy is sensitive to the slope and
amplitude of primordial energy density and gravitational wave fluctuations, the
baryon density, the Hubble constant, the cosmological constant, the ionization
history, {\it etc.} In this Letter, we examine the degree to which these
factors can be separately resolved from combined small- and large-angular scale
anisotropy observations. We isolate directions of degeneracy in this cosmic
parameter space, but note that other cosmic observations can break the
degeneracy. (Correction to Eq. 4)",9309041v2
1993-10-26,Gravitational Waves and the Polarisation of the Cosmic Microwave Background,"We discuss the influence of gravitational waves (GWs) upon the polarisation
of the Cosmic Microwave Background Radiation (CMBR). We show how to compute the
{\em rms} temperature anisotropy and polarisation of the CMBR induced by GWs of
arbitrary wavelength. We find that the ratio of polarisation, $\Pi$, to
anisotropy, $A$, can be as large as $\sim 40$\%, but is sensitively dependent
upon the GW spectrum and the cosmological ionisation history. We argue that
CMBR polarisation measurements can provide useful constraints on cosmological
models.",9310045v1
1994-02-16,How Well Can Cosmological Parameters Be Estimated from CMB Observations?,"The CMB anisotropy depends sensitively upon the slope and amplitude of
primordial density and gravitational wave fluctuations, the baryon density, the
Hubble constant, the cosmological constant, the ionization history, {\it etc.}
We report on recent work showing how well multi-scale measurements of the
anisotropy power spectrum can resolve these factors. We identify a hypersurface
in cosmic parameter space that can be accurately localized by observations, but
along which the likelihood will hardly vary. Other cosmic observations will be
needed to break this degeneracy.",9402041v1
1994-04-29,On Fractal Structure of Quantum Gravity and Relic Radiation Anisotropy,"It is argued that large-scale ($>7^o$) cosmic microwave background anisotropy
detected in COBE cosmic experiment can be considered as a trace of the quantum
gravity fractal structure.",9404076v3
1994-06-21,Quoting Experimental Information,"There was a question raised at this meeting as to the best way to present the
results of experiments measuring anisotropies in the CMB. Here we will make
some simple comments about the 3 main competing methods and some suggestions.
In particular we will give an over-simplified but hopefully useful method of
comparing GACF numbers with other power spectra, and a simple rule-of-thumb for
converting between the two main conventions.",9406060v1
1994-06-27,"CBR Anisotropy in an Open Inflation, CDM Cosmogony","We compute the cosmic background radiation anisotropy, produced by
energy-density fluctuations generated during an early epoch of inflation, in an
open cosmological model based on the cold dark matter scenario. At $\Omega_0
\sim$ 0.3 -- 0.4, the COBE normalized open model appears to be consistent with
most observations.",9406069v1
1994-07-13,Detectability of Tensor Perturbations Through CBR Anisotropy (final published version),"Detection of the tensor perturbations predicted in inflationary models is
important for testing inflation as well as for reconstructing the inflationary
potential. We show that because of cosmic variance the tensor contribution to
the square of the CBR quadrupole anisotropy must be greater than about 20\% of
the scalar contribution to ensure a statistically significant detection of
tensor perturbations. This sensitivity could be achieved by full-sky
measurements on angular scales of $3^{\circ}$ and $0.5^\circ$.",9407037v3
1994-07-15,Skewness of CMB Anisotropies in an Inflationary Isocurvature Baryon Model,"We investigate the cosmic variance of the skewness of the cosmic microwave
background (CMB) anisotropies in an inflationary model which leads to the
baryon isocurvature scenario for the cosmic structure formation. In this model,
the baryon number fluctuations are given by a sinusoidal function of a random
Gaussian field. We find that the skewness is very small in comparison with that
of the fluctuations which obey Gaussian statistics.",9407046v1
1995-01-13,"SUB--DEGREE ANISOTROPY OBSERVATIONS: GROUND--BASED, BALLOON--BORNE AND SPACE EXPERIMENTS","Extensive, accurate imaging of the Cosmic Background Radiation temperature
anisotropy at sub--degree angular resolution is widely recognized as one of the
most crucial goals for cosmology and astroparticle physics in the next decade.
We review the scientific case for such measurements in relation with sky
coverage, attainable sensitivity, confusing foreground radiation components,
and experimental strategies. Although ground--based and balloon--borne
experiments will provide valuable results, only a well--designed, far--Earth
orbit space mission covering a wide spectral range and a significant part of
all the sky will provide decisive answers on the mechanism of structure
formation.",9501043v1
1995-08-16,Anisotropy of the Microwave Sky at 90 GHz: Results from Python II,"We report on additional observations of degree scale anisotropy at 90~GHz
from the Amundsen-Scott South Pole Station in Antarctica. Observations during
the first season with the Python instrument yielded a statistically significant
sky signal; in this paper we report the confirmation of that signal with data
taken in the second year, and on results from an interleaving set of fields.",9508065v1
1995-09-02,The Topology of The Cosmic Microwave Background Anisotropy on The Scale 1 degree,"In this paper we develop the theory of clusterization of peaks in a Gaussian
random field. We have obtained new mathematical results from this theory and
the theory of percolation and have proposed a topological method of analysis of
sky maps based on these results. We have simulated $10^o\times10^o$ sky maps of
the cosmic microwave background anisotropy expected from different cosmological
models with $0.5^o-1^o$ resolution in order to demonstrate how this method can
be used for detection of non-Gaussian noise in the maps and detection of the
Doppler-peak in the spectrum of perturbation of $\gD T/T$.",9509008v1
1995-09-07,"CMB Anisotropies, Large-Scale Structure and the Future","We are now beginning to learn detailed information about cosmological
parameters from the shapes of the matter and radiation power spectra, together
with their relative normalization. As more high quality data are gathered from
galaxy surveys and from microwave anisotropies, the range of allowed models is
expected to get incrementally smaller. The amount of information potentially
available from a high-resolution satellite experiment should allow a
determination of essentially {\it all} currently discussed cosmological
parameters to less than ~10%.",9509035v1
1995-12-22,CMB Anisotropy in COBE-DMR-Normalized Open CDM Cosmogony,"We compute the CMB anisotropy in an open inflation CDM model which is
normalized to the two-year DMR sky map. Presently available CMB data is
consistent with $\Omega_0 \sim 0.3 - 0.4$, but does not strongly disfavour
either $\Omega_0 \sim 0.1$ or $\Omega_0 \sim 1$. Accumulating CMB data should
strengthen the observational discriminative power, however, a better
understanding of systematic effects will be needed before it will be possible
to draw robust conclusions about model viability.",9512148v1
1996-03-15,"Comment on a Paper by Fang, Huang, and Wu","Before decoupling in the early universe, the tightly coupled photon/electron
gas underwent acoustic oscillations. These oscillations should be visible today
in the spectrum of anisotropies. Recently Fang, Huang, and Wu (1996) claimed
that when random processes are accounted for, the phases of these oscillations
are no longer coherent. In fact, they claim that the well-defined peaks will be
completely smoothed out. We show here that their claim is incorrect. The
standard Boltzmann treatment determining the anisotropies is sufficient; random
processes do not change the standard result.",9603079v1
1996-06-21,Testing Inflation with Small Scale CMB Anisotropies,"We discuss ability of the harmonic pattern of peaks in the CMB angular power
spectrum to test inflation. By studying robust features of alternate models,
which must all be isocurvature in nature, we reveal signatures unique to
inflation. Inflation thus could be validated by the next generation of
experiments.",9606138v1
1996-07-22,A Causal Source which Mimics Inflation,"How unique are the inflationary predictions for the cosmic microwave
anisotropy pattern? In this paper, it is asked whether an arbitrary causal
source for perturbations in the standard hot big bang could effectively mimic
the predictions of the simplest inflationary models. A surprisingly simple
example of a `scaling' causal source is found to closely reproduce the
inflationary predictions. This letter extends the work of a previous paper
(ref. 6) to a full computation of the anisotropy pattern, including the Sachs
Wolfe integral. I speculate on the possible physics behind such a source.",9607109v1
1996-10-12,Cosmic Parameter Estimation Combining Sub-Degree CMB Experiments with COBE,"We describe the Bayesian-based signal-to-noise eigenmode method for
cosmological parameter estimation, show how it can be used to optimally
compress large CMB anisotropy data sets to manageable sizes, and apply it to
the DMR 4-year, South Pole and Saskatchewan data, individually and in
combination. A simple prior probability method is used to include large scale
structure observations. Estimates of the Hubble parameter, vacuum energy
density, baryon fraction and primordial spectral tilt derived from the combined
data are given.",9610091v1
1996-11-26,Radio frequency foreground emission and the separation of microwave anisotropies from foreground contamination,"The effects on CMB measurements of foreground contamination due to
synchrotron radiation, free-free emission and discrete sources are considered.
Estimates of the level and power spectrum of the Galactic fluctuations are made
using low frequency maps and recent Tenerife data. New methods for achieving a
frequency-based separation of Galactic and CMB components are discussed, and a
positive/negative maximum entropy algorithm shown to be particularly powerful
in this respect.",9611214v1
1997-01-27,Tensor Anisotropies in an Open Universe,"We calculate the anisotropies in the cosmic microwave background induced by
long-wavelength primordial gravitational waves in a universe with negative
spatial curvature, such as are produced in the ``open inflation'' scenario. The
impact of these results on the COBE normalization of open models is discussed.",9701210v2
1997-03-12,"Fast Spherical Harmonic Analysis: a quick algorithm for generating and/or inverting full sky, high resolution CMB Anisotropy maps","We present a fast algorithm for generating full sky, high resolution ($\sim
5'$) simulations of the CMB anisotropy pattern. We also discuss the inverse
problem, that of evaluating from such a map the full set of $a_{\ell m}$'s and
the spectral coefficients $C_\ell$. We show that using an Equidistant
Cylindrical Projection of the sky substantially speeds up the calculations.
Thus, generating and/or inverting a full sky, high resolution map can be easily
achieved with present day computer technology.",9703084v1
1997-04-18,CMB Experiment Baseline Determination by Minimizing Pixel Observations Dispersion,"This paper discusses a couple of approaches to removing instrument gain and
baseline variation from observations of the CMB anisotropy. These techniques
were tested on the COBE DMR data, a balloon experiment, and by monte carlo
simulations. This work, though considered technical, is made available because
CMB anisotropy mapping data processing is currently very active and a
significant number of groups are working on this issue. Specifically,
time-ordered estimates of the gain and baseline via fitting to limited sections
of data or to the full or a large section of data are considered and compared.
An expression is given for the correlation between pixels introduced by the
residual baseline and removal technique.",9704193v2
1997-06-04,Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation,"In this note we provide a simple explanation of the recent finding of
anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston
(astro-ph/9704196). We consider, as a possible origin of such effect, the
effective coupling between EM fields and some tiny background torsion field.
The coupling is obtained after integrating out charged fermions, it is gauge
invariant and does not require the introduction of any new physics.",9706044v2
1997-10-24,Using White Dish CMB Anisotropy Data to Probe Open and Flat-Lambda CDM Cosmogonies,"We use data from the White Dish experiment to set limits on cosmic microwave
background radiation anisotropies in open and spatially-flat-Lambda cold dark
matter cosmogonies. We account for the White Dish calibration uncertainty, and
marginalize over the offset and gradient removed from the data. Our 2-sigma
upper limits are larger than those derived previously. These upper limits are
consistent with those derived from the $COBE$-DMR data for all models tested.",9710270v1
1997-11-19,The CMBR and the Seeds of Galaxies,"The Cosmic Microwave Background Radiation (CMBR) is the radiation left over
from the hot Big Bang. Its blackbody spectrum and small anisotropy provide
clues about the origin and early evolution of the Universe. In particular, the
spectrum of the CMBR rules out many non-gravitational models of structure
formation, and the anisotropy of the CMBR provides a measure of the
gravitational potential at the time of last scattering, about 300,000 years
after the Big Bang. The density inhomogeneities needed to produce the
gravitational potential perturbations traced by the CMBR have grown to become
the galaxies, clusters of galaxies, and superclusters that we see today.",9711220v1
1997-12-05,The Two-Point Angular Correlation Function and BATSE Sky Exposure,"The Two-Point Angular Correlation Function is a standard analysis tool used
to study angular anisotropies. Since BATSE's sky exposure (the angular sampling
of gamma-ray bursts) is anisotropic, the TPACF should at some point identify
anisotropies in BATSE burst catalogs due to sky exposure. The effects of BATSE
sky exposure are thus explored here for BATSE 3B and 4B catalogs. Sky-exposure
effects are found to be small.",9712094v1
1997-12-15,Interferometric Observation of Cosmic Microwave Background Anisotropies,"We present a formalism for analyzing interferometric observations of Cosmic
Microwave Background (CMB) anisotropy and polarization data. The formalism is
based upon the ell-space expansion of the angular power spectrum favoured in
recent years. Explicit discussions of maximum likelihood analysis, power
spectrum reconstruction, parameter estimation, imaging and polarization are
given. As an example, several calculations for the Degree Angular Scale
Interferometer (DASI) and Cosmic Background Interferometer (CBI) experiments
are presented.",9712195v2
1998-01-13,The anisotropy of inverse beta decay and antineutrino detection,"The anisotropy of the positrons emitted in the reaction $\bar{\nu}_{e}+p\to
n+e^{+}$ has to be taken into account for extracting an antineutrino signal in
Superkamiokande. For the Sun, this effect allows a sensitivity to
$\nu_{e}\to\bar{\nu}_{e}$ transition probability at the 3% level already with
the statistics collected in the first hundred days. For a supernova in the
Galaxy, the effect is crucial for extracting the correct ratio of $\nu-e$ to
$\bar\nu_{e}-p$ events.",9801111v1
1998-06-08,Cosmic Background Radiation Temperature Anisotropy: Position of First Doppler Peak,"The purpose of the Cosmic Background Radiation (CBR) experiments is to
measure the temperature anisotropy via the autocorrelation function. The
partial wave $l_1$ corresponding to the first Doppler peak caused by
baryon-photon oscillations at the surface of last scattering depends on the
present density $\Omega_0$ and the cosmological constant contribution
$\Omega_{\Lambda}$. We discuss this dependence on the basis of perspicuous
figures.",9806118v1
1998-08-25,Cosmic microwave background anisotropy power spectrum statistics for high precision cosmology,"As the era of high precision cosmology approaches, the empirically determined
power spectrum of the microwave background anisotropy, $C_l$, will provide a
crucial test for cosmological theories. We present a unified semi-analytic
framework for the study of the statistical properties of the $C_l$ coefficients
computed from the results of balloon, ground based, and satellite experiments.
An illustrative application shows that commonly used approximations {\it bias}
the estimation of the baryon parameter $\Omega_b$ at the 1% level even for a
satellite capturing as much as $\sim 70$% of the sky.",9808292v1
1998-11-04,COBE-DMR constraints on a inflation model with non-minimal scalar field,"We derive the power spectra of the scalar- and tensor-type structures
generated in a chaotic-type inflation model based on non-minimally coupled
scalar field with a self interaction. By comparing contributions of
both-structures to the anisotropy of the cosmic microwave background radiation
with the four-year COBE-DMR data on quadrupole anisotropy we derive constraints
on the ratio of self-coupling and non-minimal coupling constants, and the
expansion rate in the inflation era, Eq. (12). The requirement of successful
amount of inflation further constrains the relative amount of tensor-type
contribution, Eq. (16).",9811069v1
1999-03-23,Generating Non-Gaussian Adiabatic Fluctuations from Inflation,"As the quality of cosmological data continue to improve, it is natural to
test the statistics of primordial fluctuations: are they Gaussian or
non-Gaussian? I review a model which generates non-Gaussian adiabatic
fluctuations from inflation. Current investigations suggest that there may
possibly be a non-Gaussian signal in large angle cosmic microwave background
anisotropy data. Statistics of microwave anisotropies could thus serve as a
powerful probe of the very early Universe.",9903327v1
1999-08-04,Inhomogeneous reionization and the polarization of the cosmic microwave background,"In a universe with inhomogeneous reionization, the ionized patches create a
second order signal in the cosmic microwave background polarization anisotropy.
This signal originates in the coupling of the free electron fluctuation to the
quadruple moment of the temperature anisotropy. We examine the contribution
from a simple inhomogeneous reionization model and find that the signal from
such a process is below the detectable limits of the Planck Surveyor mission.
However t he signal is above the fundamental uncertainty limit from cosmic
variance, so th at a future detection with a high accuracy experiment on
sub-arcminute scales is possible.",9908033v2
1999-10-15,Topological Defects and CMB anisotropies : Are the predictions reliable ?,"We consider a network of topological defects which can partly decay into
neutrinos, photons, baryons, or Cold Dark Matter. We find that the degree-scale
amplitude of the cosmic microwave background (CMB) anisotropies as well as the
shape of the matter power spectrum can be considerably modified when such a
decay is taken into account. We conclude that present predictions concerning
structure formation by defects might be unreliable.",9910290v2
1999-11-10,Efficient Computation of CMB anisotropies in closed FRW models,"We implement the efficient line of sight method to calculate the anisotropy
and polarization of the cosmic microwave background for scalar and tensor modes
in almost-Friedmann-Robertson-Walker models with positive spatial curvature. We
present new results for the polarization power spectra in such models.",9911177v2
2000-02-11,CMB Anisotropies and the Determination of Cosmological Parameters,"I review the basic theory of the cosmic microwave background anisotropies in
adiabatic cold dark matter cosmologies. The latest observational results on the
CMB power spectrum are consistent with the simplest inflationary models and
indicate that the Universe is close to spatially flat with a nearly scale
invariant fluctuation spectrum. We are also beginning to see interesting
constraints on the density of CDM, with a best fit value of omega_c = Omega_c
h^2 of about 0.1. The CMB constraints, when combined with observations of
distant Type Ia supernovae, are converging on a Lambda-dominated Universe with
Omega_m approx 0.3 and Omega_Lambda approx 0.7.",0002249v1
2000-03-22,Correlated mixtures of adiabatic and isocurvature cosmological perturbations,"The Cosmic Microwave Background (CMB) anisotropies measurements can provide
many clues about the Universe. Although the common belief is that they will
allow a very precise measurement of the cosmological parameters (that is, the
current state of the Universe), they will alternatively give interesting
informations about the state of the initial perturbations (that is, the state
of the Universe at the end of inflation). In this paper, we study the
observational consequences on the CMB anisotropies of some wide set of inital
conditions, with a correlated mixture of adiabatic and isocurvature
perturbations.",0003339v1
2000-11-29,Cosmic Microwave Background in Closed Multiply Connected Universes,"We have investigated the cosmic microwave background (CMB) anisotropy in
closed multiply connected universes
  (flat and hyperbolic) with low matter density. We show that the COBE
constraints on these low matter density models with non-trivial topology are
less stringent since a large amount of CMB anisotropy on large angular scales
can be produced due to the decay of the gravitational potential at late time.",0011539v1
2000-11-29,Data Analysis for the Microwave Anisotropy Probe (MAP) Mission,"We present an overview of the upcoming Microwave Anisotropy Probe (MAP)
mission, with an emphasis on those aspects of the mission that simplify the
data analysis. The method used to make sky maps from the differential
temperature data is reviewed and we present some of the noise properties
expected from these maps. An overview of the method we plan to use to mine the
angular power spectrum from the mega-pixel sky maps closes the paper.",0011555v1
2001-04-02,Reproducing Cosmic Microwave Background anisotropies with mixed isocurvature perturbations,"Recently high quality data of the cosmic microwave background anisotropies
have been published. In this work we study to which extent the cosmological
parameters determined by using this data depend on assumptions about the
initial conditions. We show that for generic initial conditions, not only the
best fit values are very different but, and this is our main result, the
allowed parameter range enlarges dramatically.",0104017v2
2001-06-28,Studying the anisotropy of the gravitational wave stochastic background with LISA,"A plethora of gravitational wave stochastic backgrounds populate the
sensitivity window of the Laser Interferometer Space Antenna. We show that LISA
can detect the anisotropy of the background corresponding to the multipole
moments of order l=2 and 4. The signal-to-noise ratio generated by galactic
white dwarf binary systems could be as high as 60 for 3 yrs of integration, and
LISA could provide valuable information on the spatial distribution of a
variety of galactic sources. We also show that the cross-correlation of the
data sets from two interferometers could marginally lead to meaningful
upper-limits on the degree of isotropy of the primordial gravitational wave
background.",0106538v1
2001-10-09,Archeops: a large sky coverage millimeter experiment for mapping Cosmic Microwave Background anisotropies,"We present Archeops, a balloon-borne bolometer experiment designed to map a
large part of the sky at millimeter and submillimeter wavelengths. The main
scientific goal is to study the Cosmic Microwave Background anisotropies on all
scales, in order to properly derive the cosmological parameters of the
Universe. We present the sky coverage map of the first scientific flight.",0110221v1
2001-10-30,CMB anisotropy: deviations from Gaussianity due to non-linear gravity,"Non-linear evolution of cosmological energy density fluctuations triggers
deviations from Gaussianity in the temperature distribution of the cosmic
microwave background. A method to estimate these deviations is proposed. N-body
simulations -- in a $\Lambda$CDM cosmology -- are used to simulate the strongly
non-linear evolution of cosmological structures. It is proved that these
simulations can be combined with the potential approximation to calculate the
statistical moments of the CMB anisotropies produced by non-linear gravity.
Some of these moments are computed and the resulting values are different from
those corresponding to Gaussianity.",0110664v1
2001-11-08,Cosmic Microwave Background Anisotropy in models with Quintessence,"We study the Cosmic Microwave Background (CMB) anisotropies produced by
cosine-type quintessence models. In our analysis, effects of the adiabatic and
isocurvature fluctuations are both taken into account. For purely adiabatic
fluctuations with scale invariant spectrum, we obtain a stringent constraint on
the model parameters using the CMB data from COBE, BOOMERanG and MAXIMA.
Furthermore, it is shown that isocurvature fluctuations have significant
effects on the CMB angular power spectrum at low multipoles in some parameter
space, which may be detectable in future satellite experiments. Such a signal
may be used to test the cosine-type quintessence models.",0111159v1
2001-12-06,What's Behind Acoustic Peaks in the Cosmic Microwave Background Anisotropies,"We give a brief review of the physics of acoustic oscillations in Cosmic
Microwave Background (CMB) anisotropies. As an example of the impact of their
detection in cosmology, we show how the present data on CMB angular power
spectrum on sub-degree scales can be used to constrain dark energy cosmological
models.",0112149v1
2002-03-19,Dynamical effects of the neutrino gravitational clustering at Planck angular scales,"We study the CMB anisotropy induced by the non-linear perturbations in the
massive neutrino density associated to the non-linear gravitational clustering
proceses. Our results show that for the neutrino fraction in agreement with
that indicated by the astroparticle and nuclear physics experiments and a
cosmological accreting mass comparable with the mass of known clusters, the
angular resolution and the sensitivity of the CMB anisotropy measurements from
the Planck surveyor will allow the detection of the dynamical effects of the
neutrino gravitational clustering.",0203306v1
2002-04-25,New Limits on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales,"We update the limit from the 90 GHz PIQUE ground-based polarimeter on the
magnitude of any polarized anisotropy of the cosmic microwave radiation. With a
second year of data, we have now limited both Q and U on a ring of 1 degree
radius. The window functions are broad: for E-mode polarization, the effective
l is <l> = 191 +143 -132. We find that the E-mode signal can be no greater than
8.4 microK (95% CL), assuming no B-mode polarization. Limits on a possible
B-mode signal are also presented.",0204438v1
2002-07-05,"Cosmic ray drift, the second knee and galactic anisotropies","We show that the second knee in the cosmic ray spectrum (i.e. the steepening
occurring at $E\simeq 4\times 10^{17}$ eV) could be related to drift effects
affecting the heaviest nuclear component, the iron group nuclei, in a scenario
in which the knee at $3\times 10^{15}$ eV indicates the onset of drift effects
in the lighter proton component. We also study the anisotropies resulting from
diffusion and drift currents in the Galaxy, showing their potential relevance
to account for the AGASA observations at $E\sim 10^{18}$ eV, before the
extragalactic component becomes dominant.",0207143v1
2002-09-25,"Effects of halo triaxiality, anisotropy and small scale clumping on WIMP direct detection exclusion limits","Weakly Interacting Massive Particle (WIMP) direct detection experiments are
closing in on the region of parameter space where neutralinos may constitute
the Galactic halo dark matter. Numerical simulations and observations of galaxy
halos indicate that the standard Maxwellian halo model is likely to be a poor
approximation to the dark matter distribution. We examine how halo models with
triaxiality and/or velocity anisotropy affect exclusion limits, before
discussing the consequences of the possible survival of small scale clumps.",0209528v2
2002-12-12,Cosmological Constraints from a Combined Analysis of the Cluster Mass Function and Microwave Background Anisotropies,"We present constraints on several cosmological parameters from a combined
analysis of the most recent Cosmic Microwave Background anisotropy data and the
Sloan Digital Sky Survey cluster mass function. We find that the combination of
the two data sets breaks several degeneracies among the parameters and provides
the following constraints: $\sigma_8=0.76\pm0.09$,
$\Omega_m=0.26^{+0.06}_{-0.07}$, $h=0.66^{+0.05}_{-0.06}$, $n=0.96 \pm 0.05$,
$\tau_c=0.07^{+0.07}_{-0.05}$.",0212276v1
2003-03-05,Is the Low CMB Quadrupole a Signature of Spatial Curvature?,"The temperature anisotropy power spectrum measured with the Wilkinson
Microwave Anisotropy Probe (WMAP) at high multipoles is in spectacular
agreement with an inflationary Lambda-dominated cold dark matter cosmology.
However, the low order multipoles (especially the quadrupole) have lower
amplitudes than expected from this cosmology, indicating a need for new
physics. Here we speculate that the low quadrupole amplitude is associated with
spatial curvature. We show that positively curved models are consistent with
the WMAP data and that the quadrupole amplitude can be reproduced if the
primordial spectrum truncates on scales comparable to the curvature scale.",0303127v2
2003-05-12,Numerical Likelihood Analysis of Cosmic Ray Anisotropies,"A numerical likelihood approach to the determination of cosmic ray
anisotropies is presented which offers many advantages over other approaches.
It allows a wide range of statistically meaningful hypotheses to be compared
even when full sky coverage is unavailable, can be readily extended in order to
include measurement errors, and makes maximum unbiased use of all available
information.",0305206v1
2003-05-19,Cosmic Microwave Background and Supernova Constraints on Quintessence: Concordance Regions and Target Models,"We perform a detailed comparison of the Wilkinson Microwave Anisotropy Probe
(WMAP) measurements of the cosmic microwave background (CMB) temperature and
polarization anisotropy with the predictions of quintessence cosmological
models of dark energy. We consider a wide range of quintessence models,
including: a constant equation-of-state; a simply-parametrized, time-evolving
equation-of-state; a class of models of early quintessence; scalar fields with
an inverse-power law potential. We also provide a joint fit to the CBI and
ACBAR CMB data, and the type 1a supernovae. Using these select constraints we
identify viable, target models for further analysis.",0305334v1
2003-05-22,Goodness--of--fit Statistics and CMB Data Sets,"Application of a Goodness--of--fit (GOF) statistic is an essential element of
parameter estimation. We discuss the computation of GOF when estimating
parameters from anisotropy measurements of the cosmic microwave background
(CMB), and we propose two GOF statistics to be used when employing approximate
band--power likelihood functions. They are based on an approximate form for the
distribution of band--power estimators that requires only minimal experimental
information to construct. Monte Carlo simulations of CMB experiments show that
the proposed form describes the true distributions quite well. We apply these
GOF statistics to current CMB anisotropy data and discuss the results.",0305428v1
2003-05-26,Observing the CMB at High-l using the VSA and AMI,"We discuss two experiments - the Very Small Array (VSA) and the Arcminute
MicroKelvin Imager (AMI) - and their prospects for observing the CMB at high
angular multipoles. Whilst the VSA is primarily designed to observe primary
anisotropies in the CMB, AMI is designed to image secondary anisotropies via
the Sunyaev-Zel'dovich effect. The combined l-range of these two instruments is
between l = 150 and ~10000.",0305485v1
2003-06-20,Constraining superheavy dark matter model of UHECR with SUGAR data,"Models which associate the origin of the ultra-high energy cosmic rays
(UHECR) with decays of relic superheavy particles predict the anisotropy of
UHECR flux toward the Galactic center. We use the existing SUGAR data, which
covered the Galactic center best so far, to look for such a signal and limit
the fraction of UHECR produced by this mechanism. The absence of anisotropy
toward the Galactic center in the SUGAR data implies at 95% confidence level
that the fraction of SHDM-related cosmic rays should be less than 20% at
$E>1\times10^{19}$ eV and less than 50% at $E>4\times10^{19}$ eV.",0306413v1
2003-07-18,Model-independent dark energy test with sigma_8 using results from the Wilkinson Microwave Anisotropy Probe,"By combining the recent WMAP measurements of the cosmic microwave background
anisotropies and the results of the recent luminosity distance measurements to
type-Ia supernovae, we find that the normalization of the matter power spectrum
on cluster scales, sigma_8, can be used to discriminate between dynamical
models of dark energy (quintessence models) and a conventional cosmological
constant model (LCDM).",0307346v2
2003-08-12,Correlated Isocurvature Fluctuation in Quintessence and Suppressed CMB Anisotropies at Low Multipoles,"We consider cosmic microwave background (CMB) anisotropy in models with
quintessence taking into account of isocurvature fluctuation in the
quintessence. It is shown that, if the primordial fluctuation of the
quintessence has a correlation with the adiabatic density fluctuations, CMB
angular power spectrum $C_l$ at low multipoles can be suppressed without
affecting $C_l$ at high multipoles. Possible scenario of generating correlated
mixture of the quintessence and adiabatic fluctuations is also discussed.",0308208v2
2003-10-15,Early Quintessence and the CMB,"We examine the cosmic microwave background (CMB) anisotropy for signatures of
early quintessence dark energy -- a non-negligible quintessence energy density
during the recombination and structure formation eras. In contrast to a
$\Lambda$CDM cosmology, early quintessence leads to a larger suppression of
structure growth. Because of this influence on the clustering of dark matter
and the baryon-photon fluid, we may expect to find trace signals in the CMB and
the mass fluctuation power spectrum. In detail, we demonstrate that suppressed
clustering power on small length-scales, as suggested by the combined Wilkinson
Microwave Anisotropy Probe (WMAP) / CMB / large scale structure data set, is
characteristic of early quintessence.",0310412v1
2003-11-19,Extended self-similarity of the small-scale cosmic microwave background anisotropy,"The Extended Self-Similarity (ESS) of cosmic microwave background (CMB)
radiation has been studied using recent data obtained by the space-craft based
Wilkinson Microwave Anisotropy Probe. Using the ESS and the high angular scale
resolution (arcminutes) of the data it is shown that the CMB temperature space
{\it increments} exhibit considerable and systematic declination from
Gaussianity for high order moments at the small angular scales. Moreover, the
CMB space increment ESS exponents have remarkably close values to the ESS
exponents observed in turbulence (in magnetohydrodynamic turbulence).",0311444v1
2004-05-17,Global Anisotropies in Supernova Explosions and Pulsar Recoil,"We show by two-dimensional and first three-dimensional simulations of
neutrino-driven supernova explosions that low (l=1,2) modes can dominate the
flow pattern in the convective postshock region on timescales of hundreds of
milliseconds after core bounce. This can lead to large global anisotropy of the
supernova explosion and pulsar kicks in excess of 500 km/s.",0405311v2
2004-06-02,Mean diurnal variations of cosmic ray intensity as measured by Andyrchi air shower array and Baksan underground scintillation telescope,"The results of measuring diurnal variations of extensive air showers with
energy above 100 TeV detected by the Andyrchi air shower array in 1995-2002 are
presented. It is shown that solar diurnal wave of intensity is formed by
pressure variations and Compton-Getting effect (due to the orbital motion of
the Earth). The data on cosmic ray anisotropy of the Baksan underground
scintillation telescope (BUST) are also presented for energies above 2.5 TeV
covering the period 1982-1998. The diurnal sidereal wave measured by both
Andyrchi and BUST is due to anisotropy of the cosmic rays.",0406059v1
2004-06-21,Search for Cosmic Strings in CMB Anisotropies,"We have searched the 1st-year WMAP W-Band CMB anisotropy map for evidence of
cosmic strings. We have set a limit of $\delta = 8 \pi G \mu / c^2 < 8.2 \times
10^{-6}$ at 95% CL for statistical search for a significant number of strings
in the map. We also have set a limit using the uniform distribution of strings
model in the WMAP data with $\delta = 8 \pi G \mu / c^2 < 7.34 \times 10^{-5}$
at 95% CL. And the pattern search technique we developed here set a limit
$\delta = 8 \pi G \mu / c^2 < 1.54 \times 10^{-5}$ at 95% CL.",0406432v2
2004-09-01,Full-sky correlation functions for CMB experiments with asymmetric window functions,"We discuss full-sky convolution of the instrumental beam with the CMB sky
signal in CMB single-dish and interferometry experiments, using the method
(Challinor et al. 2000) that the measured temperature and polarization
anisotropies are defined globally on the group manifold of the
three-dimensional rotation by means of Wigner D-functions. We re-derive the
anisotropy and polarization correlation functions incorporated with asymmetric
window functions, which are then explicitly calculated for a single-dish
elliptical Gaussian beam and an interferometric Gaussian beam.",0409007v2
2004-11-01,Magnetic turbulence in compressible fluids,"We present high resolution numerical simulations of compressible
magnetohydrodynamic (MHD) turbulence. We concentrate on studies of spectra and
anisotropy of velocity and density. We describe a technique of separating
different magnetohydrodynamic (MHD) modes (slow, fast and Alfven) and apply it
to our simulations. For the mildly supersonic case, velocity and density show
anisotropy. However, for the highly supersonic case, we observe steepening of
the slow mode velocity spectrum and isotropization of density. Our present
studies show that the spectrum of density gets substantially
  {\it flatter} than the Kolmogorov one.",0411031v1
2005-04-18,Rotation and anisotropy of galaxies revisited,"The use of the tensor virial theorem (TVT) as a diagnostic of anisotropic
velocity distributions in galaxies is revisited. The TVT provides a rigorous
global link between velocity anisotropy, rotation and shape, but the quantities
appearing in it are not easily estimated observationally. Traditionally use has
been made of a centrally averaged velocity dispersion and the peak rotation
velocity. Although this procedure cannot be rigorously justified, tests on
model galaxies show that it works surprisingly well. With the advent of
integral-field spectroscopy it is now possible to establish a rigorous
connection between the TVT and observations. The TVT is reformulated in terms
of sky-averages, and the new formulation is tested on model galaxies.",0504387v1
2005-09-29,Footprints of Statistical Anisotropies,"We propose and develop a formalism to describe and constrain statistically
anisotropic primordial perturbations. Starting from a decomposition of the
primordial power spectrum in spherical harmonics, we find how the temperature
fluctuations observed in the CMB sky are directly related to the coefficients
in this harmonic expansion. Although the angular power spectrum does not
discriminate between statistically isotropic and anisotropic perturbations, it
is possible to define analogous quadratic estimators that are direct measures
of statistical anisotropy. As a simple illustration of our formalism we test
for the existence of a preferred direction in the primordial perturbations
using full-sky CMB maps. We do not find significant evidence supporting the
existence of a dipole component in the primordial spectrum.",0509893v1
2005-12-19,The Full Second-Order Radiation Transfer Function for Large-Scale CMB Anisotropies,"We calculate the full second-order radiation transfer function for Cosmic
Microwave Background anisotropies on large angular scales in a flat universe
filled with matter and cosmological constant. It includes (i) the second-order
generalization of the Sachs-Wolfe effect, and of (ii) both the early and late
Integrated Sachs-Wolfe effects, (iii) the contribution of the second-order
tensor modes, and is valid for a generic set of initial conditions specifying
the level of primordial non-Gaussianity.",0512481v1
2006-02-14,Contribution of a nearby Pulsar to Cosmic Rays observed at Earth,"Contribution of nearby pulsars to the cosmic rays observed at Earth has been
studied. It is found that the experimental bound on amplitude of cosmic ray
anisotropy may produce significant constraint on the efficiency of converting
pulsar rotational energy to emitted particles kinetic energy. Cosmic ray fluxes
from two well known nearby gamma ray pulsars, namely the Vela and Geminga
pulsars, are estimated. The analysis suggests that observed bound on cosmic ray
anisotropy restricts the contributions of the Vela and the Geminga pulsars to
at most 1 % of the observed cosmic rays below the knee.",0602301v1
2006-05-01,Anisotropy of the primary cosmic-ray flux in Super-Kamiokande,"A first-ever 2-dimensional celestial map of primary cosmic-ray flux was
obtained from 2.10x10^8 cosmic-ray muons accumulated in 1662.0 days of
Super-Kamiokande. The celestial map indicates an (0.104 \pm 0.020)% excess
region in the constellation of Taurus and a -(0.094 \pm 0.014)% deficit region
toward Virgo. Interpretations of this anisotropy are discussed.",0605020v2
2006-06-27,Cosmological science enabled by Planck,"Planck will be the first mission to map the entire cosmic microwave
background (CMB) sky with mJy sensitivity and resolution better than 10'. The
science enabled by such a mission spans many areas of astrophysics and
cosmology. In particular it will lead to a revolution in our understanding of
primary and secondary CMB anisotropies, the constraints on many key
cosmological parameters will be improved by almost an order of magnitude (to
sub-percent levels) and the shape and amplitude of the mass power spectrum at
high redshift will be tightly constrained.",0606643v1
2006-07-07,Testing Global Isotropy of Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Data: Temperature Analysis,"We examine statistical isotropy of large scale anisotropies of the Internal
Linear Combination (ILC) map, based on three year WMAP data. Our study reveals
no significant deviation from statistical isotropy on large angular scales of
3-year ILC map. Comparing statistical isotropy of 3-year ILC map and 1-year ILC
map, we find a significant improvement in 3-year ILC map which can be due to
the gain model, improved ILC map processing and foreground minimization.",0607153v1
2006-09-20,The signature of local cosmic structures on the ultra-high energy cosmic ray anisotropies,"Current experiments collecting high statistics in ultra-high energy cosmic
rays (UHECRs) are opening a new window on the universe facing the possibility
to perform UHECR astronomy. Here we discuss a large scale structure (LSS) model
for the UHECR origin for which we evaluate the expected large scale anisotropy
in the UHECR arrival distribution. Employing the IRAS PSCz catalogue as tracer
of the LSS, we derive the minimum statistics needed to reject or assess the
correlation of the UHECRs with the baryonic distribution in the universe, in
particular providing a forecast for the Auger experiment.",0609577v1
2006-12-12,CMB Alignment in Multi-Connected Universes,"The low multipoles of the cosmic microwave background (CMB) anisotropy
possess some strange properties like the alignment of the quadrupole and the
octopole, and the extreme planarity or the extreme sphericity of some
multipoles, respectively. In this paper the CMB anisotropy of several
multi-connected space forms is investigated with respect to the maximal angular
momentum dispersion and the Maxwellian multipole vectors in order to settle the
question whether such spaces can explain the low multipole anomalies in the
CMB.",0612308v1
2006-12-23,Hemispherical transport equation: modeling of quasiparallel collisionless shocks,"Using a so-called hemispherical model we derive a general transport equation
for cosmic ray and thermal particles scattered in pitch angle by magnetic
inhomogeneities in a moving collisionless plasma. The weak scattering through
90 degrees results in isotropic particle distributions in each hemisphere. The
consideration is not limited by small anisotropies and by the condition that
particle velocities are higher than characteristic flow velocity differences.
For high velocities and small anisotropies the standard cosmic ray transport
equation is recovered. We apply the equations derived for investigation of
injection and acceleration of particles by collisionless shocks.",0612715v1
1992-04-21,Image of the Energy Gap Anisotropy in the Vibrational Spectum of a High Temperature Superconductor,"We present a new method of determining the anisotropy of the gap function in
layered high-Tc superconductors. Careful inelastic neutron scattering
measurements at low temperature of the phonon dispersion curves in the (100)
direction in La_(1.85)Sr_(.15)CuO_4 would determine whether the gap is
predominately s-wave or d-wave. We also propose an experiment to determine the
gap at each point on a quasi-two-dimensional Fermi surface.",9204008v1
1993-02-09,Kinetics of Ordering in Cu3Au: An Atomistic Approach,"We study the kinetics of ordering in Cu3Au using a model Hamiltonian derived
from the effective medium theory of chemical bonding. Monte Carlo simulations
are used to investigate universal and non-universal features of the growth
kinetics. Anisotropic scaling of the structure factor is observed in late-stage
growth of ordered domains. The anisotropy is a non-universal feature determined
by details of the microscopic model, and we find that the anisotropy observed
in the simulations is in excellent agreement with experiments on Cu3Au. The
simulations are discussed in the context of theories of unstable growth. To our
knowledge, this is the first study of kinetics in a realistic model Hamiltonian
describing the material-specific properties of Cu3Au.",9302014v1
1993-08-13,Boundary-induced anisotropy of the avalanches in the sandpile automaton,"We study numerically the avalanches in a two--dimensional critical height
sandpile model with sand grains added at the center of the system. Smaller
avalanches near the center of the system are isotropic. Larger avalanches are,
however, affected by the boundary of the system, to a degree that increases
with the avalanche size. Up to linear system size $L=1001$, we did not find an
obvious indication for lattice--induced anisotropy.",9308021v1
1994-06-07,Temperature Dependent Gap Anisotropy from Interlayer Tunneling,"A recent experiment by Ma and collaborators shows that the gap anisotropy in
${\rm Bi}_2 {\rm Sr}_2 {\rm Ca}_1 {\rm Cu}_2 {\rm O}_{8+x}$ is strongly
temperature dependent. In particular, the superconducting gap along the $\Gamma
- M$ direction shows a weaker temperature dependence than the gap along the
$\Gamma - X$ direction which decreases rapidly with temperature. We explain
this novel feature as a natural consequence of the interlayer tunneling
mechanism of superconductivity.",9406046v1
1994-09-19,The Role of Spin Anisotropy in the Unbinding of Interfaces,"We study the ground state of a classical X-Y model with $p \ge 3$-fold spin
anisotropy $D$ in a uniform external field, $H$. An interface is introduced
into the system by a suitable choice of boundary conditions. For large $D$, as
$H \to 0$, we prove using an expansion in $D^{-1}$ that the interface unbinds
from the surface through an infinite series of layering transitions. Numerical
work shows that the transitions end in a sequence of critical end points.",9409078v1
1994-10-27,Multiparticle Reactions with Spatial Anisotropy,"We study the effect of anisotropic diffusion on the one-dimensional
annihilation reaction kA->inert with partial reaction probabilities when
hard-core particles meet in groups of k nearest neighbors. Based on scaling
arguments, mean field approaches and random walk considerations we argue that
the spatial anisotropy introduces no appreciable changes as compared to the
isotropic case. Our conjectures are supported by numerical simulations for slow
reaction rates, for k=2 and 4.",9410103v1
1995-04-05,Josephson Junction Ladders: Ground State and Relaxation Phenomena,"This paper considers a Josephson Junction array with the geometry of a ladder
and anisotropy in the Josephson couplings. The ground state problem for the
ladder corresponds to the one for the one-dimensional chiral XY model in a
two-fold anisotropy field, which allows of a rigorous characterization of the
ground state phase diagram and the relevant elementary excitations for the
system. The approach to equilibrium, which we study using Langevin dynamics,
shows slow relaxation, typical of systems whose energy landscape in the
configuration space consists of a wealthy of metastable states, dynamically
disconnected.",9504015v1
1995-08-23,Acoustic Attenuation in High-$T_c$ Superconductors,"We analyze the acoustic attenuation rate in high-$T_c$ superconductors, and
find that this method offers an additional way to examine the anisotropy of the
superconducting order parameter in these materials. We argue that it should be
possible to distinguish the electronic contribution to the acoustic
attenuation, which has a strong temperature dependence near $T_c$, from the
lattice contribution, which does not show a strong temperature dependence near
$T_c$. We propose that this can be utilized to measure the anisotropy of the
order parameter by measuring the attenuation rate near $T_c$ in different
directions.",9508102v1
1995-08-29,Characterization of the reorientation transition in classical Heisenberg models with dipole interaction,"In this paper the thermodynamics of thin ferromagnetic films are studied in
the framework of the classical Heisenberg model with uniaxial anisotropy and
long--range dipole interaction. The dependence of the order of the
reorientation transition in these systems on the number of layers and on the
distribution of anisotropies is investigated using both mean field theory and
Monte-Carlo simulations.",9508131v1
1995-09-08,Heat Transport and the Nature of the Order Parameter in Superconducting $UPt_3$,"Recent thermal conductivity data on the heavy fermion superconductor $UPt_3$
have been interpreted as offering support for an $E_{2u}$ model of the order
parameter as opposed to an $E_{1g}$ model. In this paper, we analyze this issue
from a theoretical standpoint including the detailed effects of Fermi surface
and gap anisotropy. Our conclusion is that although current data put strong
constraints on the gap anisotropy, they cannot definitively distinguish between
these two models. Measurements on samples of varying quality could be decisive
in this regard, however.",9509045v1
1996-06-03,Vortex-Loop Unbinding and Flux-Line Lattice Melting in Superconductors,"We study the interplay between a novel vortex-loop unbinding in finite
magnetic field at T=T_V and flux-line lattice (FLL) melting at T=T_M in type-II
superconductors. The FLL melts due to nucleation of vortex loops parallel to
c-axis, connected to flux lines. For moderate anisotropy, phase coherence along
c-axis is lost at T_V > T_M due to an ab-plane vortex-loop unbinding with loops
located close to thermal FLL fluctuations. For large anisotropy, phase
coherence along c-axis is lost at T_V < T_M due to nucleation of ab-plane
vortex-loops uncorrelated to flux lines.",9606002v1
1996-07-30,The phase diagram of high-Tc's: Influence of anisotropy and disorder,"We propose a phase diagram for the vortex structure of high temperature
superconductors which incorporates the effects of anisotropy and disorder. It
is based on numerical simulations using the three-dimensional Josephson
junction array model. We support the results with an estimation of the internal
energy and configurational entropy of the system. Our results give a unified
picture of the behavior of the vortex lattice, covering from the very
anysotropic BiSrCaCuO to the less anisotropic YBaCuO, and from the first order
melting ocurring in clean samples to the continuous transitions observed in
samples with defects.",9607219v1
1996-09-20,Exact results for quantum phase transitions in random XY spin chains,"The effect of disorder on the quantum phase transitions induced by a
transverse field, anisotropy, and dimerization in XY spin chains is
investigated. The low-energy behavior near the critical point is described by a
Dirac-type equation with a random mass for which an exact analytic treatment is
possible. Results obtained for the dynamical critical exponent, the specific
heat, and transverse susceptibility agree with results recently obtained using
a real space renormalization group decimation technique, supporting Fisher's
claim that it is exact. A non-zero transverse field changes the universality
class of the anisotropy transition.",9609195v1
1996-10-30,A unified treatment of Ising model magnetizations,"We show how the spontaneous bulk, surface and corner magnetizations in the
square lattice Ising model can all be obtained within one approach. The method
is based on functional equations which follow from the properties of corner
transfer matrices and vertex operators and which can be derived graphically. In
all cases, exact analytical expressions for general anisotropy are obtained.
Known results, including several for which only numerical computation was
previously possible, are verified and new results related to general anisotropy
and corner angles are obtained.",9610212v2
1997-01-08,Reorientation transition of ultrathin ferromagnetic films,"We demonstrate that the reorientation transition from out-of-plane to
in-plane magnetization with decreasing temperature as observed experimentally
in Ni-films on Cu(001) can be explained on a microscopic basis. Using a
combination of mean field theory and perturbation theory, we derive an analytic
expression for the temperature dependent anisotropy. The reduced magnetization
in the film surface at finite temperatures plays a crucial role for this
transition as with increasing temperature the influence of the uniaxial
anisotropies is reduced at the surface and is enhanced inside the film.",9701043v2
1997-01-10,Effect of Anisotropy on the Localization in a Bifractal System,"Bifractal is a highly anisotropic structure where planar fractals are stacked
to form a 3-dimensional lattice. The localization lengths along fractal
structure for the Anderson model defined on a bifractal are calculated. The
critical disorder and the critical exponent of the localization lengths are
obtained from the finite size scaling behavior. The numerical results are in a
good agreement with previous results which have been obtained from the
localization lengths along the perpendicular direction. This suggests that the
anisotropy of the embedding lattice structure is irrelevant to the critical
properties of the localization.",9701065v1
1997-10-30,Magnetization plateau in S=3/2 antiferromagnetic Heisenberg chain with anisotropy,"The magnetization process of the S=3/2 antiferromagnetic Heisenberg chain
with the single-ion anisotropy D at T=0 is investigated by the exact
diagonalization of finite clusters and finite-size scaling analyses. It is
found that a magnetization plateau appears at m=1/2 for $D>D_c=0.93 \pm 0.01$.
The phase transition with respect to D at D_c is revealed to be the
Kosterlitz-Thouless-type. The magnetization curve of the infinite system is
also presented for some values of D.",9710327v1
1997-12-15,Shape anisotropy and magnetic domain structures in striped monolayers,"We study the effect of dipolar interactions on a magnetic striped monolayer
with a microscopic unit cell of square symmetry, and of size $(N_x\times N_y)$
spins. Even if the aspect ratio $r=N_x/N_y$ is very large, an in-plane shape
anisotropy is always negligible, except if $N_y$ is fairly small $(N_y<40)$.
In-plane domains are not possible, except for values of the dipolar coupling
larger than the domain wall energy.",9712158v1
1997-12-17,Domain structures in ultrathin magnetic films,"Domain structures appear in ultrathin magnetic films, if an easy-axis
anisotropy, favouring the direction perpendicular to the film, overcomes the
shape anisotropy. We will study the nature of the magnetic ground state and how
the different parameters influence the domain structure. Both Ising and
Heisenberg spins will be considered: in the latter case, a reorientation phase
transition may take place. Domains are expected to appear just before such
transition. Domain structures at finite temperature will be described in terms
of a two dimensional array of domain walls, whose behaviour resembles a liquid
crystal.",9712207v1
1998-01-13,Skyrmion in a real magnetic film,"Skyrmions are the magnetic defects in an ultrathin magnetic film, similar to
the bubble domains in the thicker films. Even weak uniaxial anisotropy
determines its radius unambiguously. We consider the dynamics of the skyrmion
decay. We show that the discreteness of the lattice in an isotropic 2D magnet
leads to a slow rotation of the local magnetization in the skyrmion and,
provided a small dissipation, to decay of the skyrmion. The radius of such a
skyrmion as a function of time is calculated. We prove that uniaxial anisotropy
stabilizes the skyrmion and study the relaxation process.",9801114v1
1998-01-27,Electronic Structure of Ladder Cuprates,"We study the electronic structure of the ladder compounds (SrCa)CuO 14-24-41
and SrCuO 123. LDA calculations for both give similar Cu 3d-bands near the
Fermi energy. The hopping parameters estimated by fitting LDA energy bands show
a strong anisotropy between the t_perp t_par intra-ladder hopping and small
inter-ladder hopping. A downfolding method shows that this anisotropy arises
from the ladder structure.The conductivity perpendicular to the ladders is
computed assuming incoherent tunneling giving a value close to experiment.",9801280v1
1998-02-12,Behavior of a polymer chain in a critical binary solvent,"We present a field-theoretic renormalization group analysis of a polymer
chain immersed in a binary good solvent close to its critical demixing point.
We first show that this problem can be mapped on a bicritical field theory,
i.e. a $(\Phi^{2})^{2}$-model with a mass anisotropy. This implies that the
end-to-end distance of the polymer is now controlled by a new critical exponent
$\nu_{B}$ related to the quadratic mass anisotropy operator $B$. To show this
we solve the RG equation and calculate explicitly the exponents and the mean
end-to-end length of the chain.",9802130v1
1998-03-02,Field induced transition of the S=1 antiferromagnetic chain with anisotropy,"The ground state magnetization process of the S=1 antiferromagnetic chain
with the easy-axis single-ion anisotropy described by negative $D$ is
investigated. It is numerically found that a phase transition between two
different gapless phases occurs at an intermediate magnetic field between the
starting and saturation points of the magnetization for $-1.49<D<-0.35$. The
transition is similar to the spin flopping, but it is second-order and not
accompanied with any significant anomalous behaviors in the magnetization
curve. We also present the phase diagrams in the m-D and H-D planes which
reveal a possible re-entrant transition.",9803022v2
1998-03-31,Crossover between polariton and phonon local states. Anisotropy-induced localization threshold,"We consider the impurity-induced polariton local states in a dipole-active
medium. These states present the local optical vibrations which are coherently
coupled with the induced electromagnetic field. We show that the crossover
between the polariton and phonon local states takes place within the
relativistically narrow interval near the bottom of the polariton gap. However,
the resonant phonon-photon interaction leads to the absence of the lower
threshold of the impurity strength. These results are due to the singularity of
the density of the polariton states, which is generic for any isotropic
dipole-active phonon mode with the negative dispersion. We show that a weak
anisotropy removes this singularity and sets a finite threshold for the local
polariton states.",9803375v1
1998-04-06,Stochastic equation for the erosion of inclined topography,"We present a stochastic equation to model the erosion of topography with
fixed inclination. The inclination causes the erosion to be anisotropic. A
zero-order consequence of the anisotropy is the dependence of the prefactor of
the surface height-height correlations on direction. The lowest higher-order
contribution from the anisotropy is studied by applying the dynamic
renormalization group. In this case, assuming an inhomogenous distribution of
soil material, we find a one-loop estimate of the roughness exponents. The
predicted exponents are in good agreement with new measurements made from
seafloor topography.",9804066v1
1998-05-21,Two-Coupled Chains with Spin-Anisotropic Backward Scattering,"By applying renormalization group method to the bosonized Hamiltonian of
two-coupled chains with repulsive intrachain interaction, we have examined a
role of backward scattering with a spin-anisotropy which competes with
interchain hopping. From calculation of a dominant state in the limit of low
energy, it is found that superconducting state moves into spin density wave
state when the anisotropy becomes larger than a critical value. Further phase
diagram is shown on the plane of g-ology.",9805270v2
1998-10-31,The Kosterlitz-Thouless and magnetic transition temperatures in layered magnets with a weak easy-plane anisotropy,"The two-dimensional (2D) Heisenberg magnet with a weak easy-plane anisotropy
is considered. A renormalization group (RG) analysis in this model is performed
for both quantum and classical cases. A crossover from the Heisenberg to 2D XY
model is discussed. The magnetic transition owing to the interlayer coupling is
considered. Analytical results for the Kosterlitz-Thouless and Curie (Neel)
temperatures are derived with account of two-loop corrections. The results are
compared with experimental data, e.g. on K2CuF4, and turn out to provide a
quantitative description, unlike the standard one-loop results.",9811003v1
1998-12-04,Fundamental constraints for the mechanism of superconductivity in cuprates,"Considerable progress has been made over the last decade in understanding the
phenomenological properties of the cuprate high-T$_{c}$ superconductors and in
producing well characterized high quality materials. Nevertheless, the pairing
mechanism itself remains controversial. We establish a criterion to test
theories for layered superconductors relying on a substantial interlayer
contribution. The criterion is based on the ratio of the interlayer
contribution to the total superfluid density, which is traced back to the
inverse squared effective mass anisotropy. The anisotropy can be measured
rather accurately by various experimental techniques. It turns out that models
relying on interlayer pairing cannot be considered as serious candidates for
the mechanism of superconductivity in cuprate superconductors.",9812081v1
1999-01-04,On the magnetoresistance anisotropy of a 2-dimensional electron gas with large half-integer filling factors,"The unsymmetric confinement of the electrons in a typical 2-dimensional
electron gas (2DEG) breaks the full cubic symmetry of the in-plane transport
properties. A rigorous invariance of the transport under rotation by pi/2 about
the cubic axis perpendicular to the plane of the gas no longer holds, even for
structurally perfect samples, and asymmetries under rotation by pi/2 are
allowed. It is proposed that this symmetry breaking plays a role in the recent
observation, by Little et al., of the pronounced anisotropy of the
magnetoresistance of a 2DEG at very low temperatures, at large half-integer
filling factors of the Landau levels in such a system.",9901016v1
1999-02-22,Broken Symmetries in Scanning Tunneling Images of Carbon Nanotubes,"Scanning tunneling images of carbon nanotubes frequently show electron
distributions which break the local sixfold symmetry of the graphene sheet. We
present a theory of these images which relates these anisotropies to the off
diagonal correlations in the single particle density matrix, and allows one to
extract these correlations from the observed images. The theory is applied to
images of the low energy states reflected at the end of a tube or by point
defects, and to states propagating on defect free semiconducting tubes. The
latter exhibit a novel switching of the anisotropy in the tunneling image with
the sign of the tunneling bias.",9902303v1
1999-03-28,Anisotropic Transport of Two-Dimensional Holes in High Landau Levels,"Magnetoresistance data taken along $[\bar{2}33]$ and $[01\bar{1}]$ directions
in a GaAs/AlGaAs two-dimensional hole sample with van der Pauw geometry exhibit
significant anisotropy at half-integer filling factors. The anisotropy appears
to depend on both the density and symmetry of the hole charge distribution.",9903405v2
1999-04-01,First principles calculation of uniaxial magnetic anisotropy and magnetostriction in strained CMR films,"We performed first - principles relativistic full-potential linearized
augmented plane wave calculations for strained tetragonal ferromagnetic
La(Ba)MnO$_3$ with an assumed experimental structure of thin strained
tetragonal La$_{0.67}$Ca$_{0.33}$MnO$_3$ (LCMO) films grown on SrTiO$_3$[001]
and LaAlO$_3$[001] substrates. The calculated uniaxial magnetic anisotropy
energy (MAE) values, are in good quantitative agreement with experiment for
LCMO films on SrTiO$_3$ substrate. We also analyze the applicability of linear
magnetoelastic theory for describing the stain dependence of MAE, and estimate
magnetostriction coefficient $\lambda_{001}$.",9903460v1
1999-04-19,"Dynamic transverse susceptibility in Au-Fe-Au ""nano-onions""","A precision radio-frequency (RF) transverse modulation technique based on a
resonant tunnel diode oscillator (TDO) has been used to study the dynamic
susceptibility in novel ring-shaped single domain Fe nanoparticles synthesized
using reverse-micelle chemistry. Hysteresis loops measured using a SQUID
magnetometer indicate a large coercivity (Hc = 400Oe) below the blocking
temperature (TB ~52K). The dynamic susceptibility shows remarkable consistency
with the M-H data and exhibits peaks at characteristic anisotropy fields.
Overall, these RF experiments are well suited to probe the magnetic anisotropy
in nanophase materials.",9904267v1
1999-04-30,Does spin-orbit coupling play a role in metal-nonmetal transition in two-dimensional systems?,"We propose an experiment, which would allow to pinpoint the role of
spin-orbit coupling in the metal-nonmetal transition observed in a number of
two-dimensional systems at low densities. Namely, we demonstrate that in a
parallel magnetic field the interplay between the spin-orbit coupling and the
Zeeman splitting leads to a characteristic anisotropy of resistivity with
respect to the direction of the in-plane magnetic field. Though our analytic
calculation is done in the deeply insulating regime, the anisotropy is expected
to persist far beyond that regime.",9904451v2
1999-05-21,Breakdown of a Magnetization Plateau due to Anisotropy in Heisenberg Mixed-Spin Chains,"We discuss the critical behavior of the spin-(1,1/2) Heisenberg ferrimagnetic
chain in a magnetic field, whose magnetization curve exhibits a plateau at a
third of the full magnetization. A bond alternation stabilizes the massive
state, whereas an exchange anisotropy causes the breakdown of the plateau and
the onset of a gapless spin-fluid state, where the transition, lying in the XY
but ferromagnetic region, is of Kosterlitz-Thouless type. In order to elucidate
significant quantum effects, we investigate the model of classical version as
well.",9905311v1
1999-07-20,Conductivity of Layered Crystals,"We show that the resistive anisotropy of an anisotropic medium is determined
by the ratio of the phase coherence lengths. In layered crystals in which the
interlayer transport is incoherent, the out-of-plane phase coherence length is
fixed and temperature independent. This leads to a temperature dependent
resistive anisotropy and to the coexistence of metallic in-plane and
non-metallic out-of-plane conductivities. Our approach provides a description
of the c-axis conductivity in the highly nonclassical regime, characteristic of
layered cuprates.",9907306v1
1999-11-23,Magnetization-plateau state of the S=3/2 spin chain with single ion anisotropy,"We reexamine the numerical study of the magnetized state of the S=3/2 spin
chain with single ion anisotropy D(> 0) for the magnetization M=M_{S}/3, where
M_{S} is the saturation magnetization. We find at this magnetization that for
D<D_{c1}=0.387 the system is critical and the magnetization plateau does not
appear. For D > D_{c1}, the parameter region is divided into two parts D_{c1} <
D < D_{c2}=0.943 and D_{c2} < D. In each region, the system is gapful and the
M=M_{S}/3 magnetization plateau appears in the magnetization process. From our
numerical calculation, the intermediate region D_{c1} < D < D_{c2} should be
characterized by a magnetized valence-bond-solid state.",9911364v1
1999-12-13,Spin Anisotropy and Quantum Hall Effect in the Kagome Lattice - Chiral Spin State based on a Ferromagnet-,"A ferromagnet with spin anisotropies on the 2D Kagome lattice is
theoretically studied. This is a typical example of the flat-band ferromagnet.
The Berry phase induced by the tilting of the spins opens the band gap and
quantized Hall conductance \sigma_{xy}=\pm e^2/h is realized without external
magnetic field. This is the most realistic chiral spin state based on the
ferromagnetism. We also discuss the implication of our results to anomalous
Hall effect observed in the metallic pyrochlore ferromagnets R_2Mo_2O_7(R=Nd,
Sm, Gd).",9912206v1
2000-01-14,Anisotropy of the Energy Gap in the Insulating Phase of the U-t-t' Hubbard Model,"We apply a diagrammatic expansion method around the atomic limit (U >> t) for
the U-t-t' Hubbard model at half filling and finite temperature by means of a
continued fraction representation of the one-particle Green's function. From
the analysis of the spectral function A(\vec{k},\omega) we find an energy
dispersion relation with a (cos k_x-cos k_y)^2 modulation of the energy gap in
the insulating phase. This anisotropy is compared with experimental ARPES
results on insulating cuprates.",0001210v2
2000-02-09,Fluctuating spin g-tensor in small metal grains,"In the presence of spin-orbit scattering, the splitting of an energy level in
a generic small metal grain due to the Zeeman coupling to a magnetic field B
depends on the direction of B, as a result of mesoscopic fluctuations. The
anisotropy is described by the eigenvalues g_j^2 (j=1,2,3) of a tensor G,
corresponding to the (squares of) g-factors along three principal axes. We
consider the statistical distribution of G and find that the anisotropy is
enhanced by eigenvalue repulsion between the g_j.",0002139v1
2000-02-10,Shape anisotropy and Voids,"Numerical simulations on a 2-dimensional model system showed that voids are
induced primarily due to shape anisotropy in binary mixtures of interacting
disks. The results of such a simple model account for the key features seen in
a variety of flux experiments using liposomes and biological membranes.",0002148v1
2000-03-02,Spinning up and down a Boltzmann gas,"Using the average method, we derive a close set of linear equations that
describes the spinning up of an harmonically trapped gas by a rotating
anisotropy. We find explicit expressions for the needed to transfer angular
momentum as well as the decay time induced by a static residual anisotropy.
These different time scales are compared with the measured nucleation time and
lifetime of vortices by the ENS group. We find a good agreement that may
emphasize the role played by the non-condensed component in thoses experiments.",0003024v1
2000-03-17,Spin-triplet superconductivity due to antiferromagnetic spin-fluctuation in Sr_2RuO_4,"A mechanism leading to the spin-triplet superconductivity is proposed based
on the antiferromagnetic spin fluctuation. The effects of anisotropy in spin
fluctuation on the Cooper pairing and on the direction of d vector are examined
in the one-band Hubbard model with RPA approximation. The gap equations for the
anisotropic case are derived and applied to Sr_2RuO_4. It is found that a
nesting property of the Fermi surface together with the anisotropy leads to the
triplet superconductivity with the d=z(sin{k_x}\pm isin{k_y}), which is
consistent with experiments.",0003296v1
2000-03-30,Observation of harmonic generation and nonlinear coupling in the collective dynamics of a Bose condensate,"We report the observation of harmonic generation and strong nonlinear
coupling of two collective modes of a condensed gas of rubidium atoms. Using a
modified TOP trap we changed the trap anisotropy to a value where the frequency
of the m=0 high-lying mode corresponds to twice the frequency of the m=0
low-lying mode, thus leading to strong nonlinear coupling between these modes.
By changing the anisotropy of the trap and exciting the low-lying mode we
observed significant frequency shifts of this fundamental mode and also the
generation of its second harmonic.",0003495v1
2000-06-23,Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni,"We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra-atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean-field theory in the static limit is
emphasized. Both experimental magnitude of MAE and direction of magnetization
are predicted correctly near U=4 eV for Ni and U=3.5 eV for Fe. Correlations
modify one-electron spectra which are now in better agreement with experiments.",0006385v1
2000-07-10,Experimental evidence for the formation of stripe phases in Si/SiGe,"We observe pronounced transport anisotropies in magneto-transport experiments
performed in the two-dimensional electron system of a Si/SiGe heterostructure.
They occur when an in-plane field is used to tune two Landau levels with
opposite spin to energetic coincidence. The observed anisotropies disappear
drastically for temperatures above 1 K. We propose that our experimental
findings may be caused by the formation of a unidirectional stripe phase
oriented perpendicular to the in-plane field.",0007148v1
2000-07-14,Dissipative dynamics of vortex arrays in anisotropic traps,"We discuss the dissipative dynamics of vortex arrays in trapped
Bose-condensed gases and analyze the lifetime of the vortices as a function of
trap anisotropy and the temperature. In particular, we distinguish the two
regimes of the dissipative dynamics, depending on the relative strength of the
mutual friction between the vortices and the thermal component, and the
friction of the thermal particles on the trap anisotropy. We study the effects
of heating of the thermal cloud by the escaping vortices on the dynamics of the
system.",0007246v1
2000-09-22,Highly anisotropic commensurability oscillations in two-dimensional holes at the GaAs/AlGaAs (311)A interface,"Measurements of commensurability oscillations in GaAs/AlGaAs two-dimensional
(2D) hole systems grown on GaAs (311)A substrates reveal a remarkable
anisotropy: the amplitude of the measured commensurability oscillations along
the [$\bar{2}$33] direction is about 100 times larger than along [01$\bar{1}$].
For 2D electron systems at similar interfaces, however, we observe nearly
isotropic oscillations, suggesting that the anomalous anisotropy is intrinsic
to GaAs 2D holes at the (311)A interface.",0009363v1
2000-12-10,Anisotropic scattering and quantum magnetoresistivities of a periodically modulated 2D electron gas,"We calculate the longitudinal conductivities of a two-dimensional
noninteracting electron gas in a uniform magnetic field and a lateral electric
or magnetic periodic modulation in one spatial direction, in the quantum
regime. We consider the effects of the electron-impurity scattering anisotropy
through the vertex corrections on the Kubo formula, which are calculated with
the Bethe-Salpeter equation, in the self-consistent Born approximation. We find
that due to the scattering anisotropy the band conductivity increases, and the
scattering conductivities decrease and become anisotropic. Our results are in
qualitative agreement with recent experiments.",0012165v1
2001-02-19,Phase diagram of a random-anisotropy mixed-spin Ising model,"We investigate the phase diagram of a mixed spin-1/2--spin-1 Ising system in
the presence of quenched disordered anisotropy. We carry out a mean-field and a
standard self-consistent Bethe--Peierls calculation. Depending on the amount of
disorder, there appear novel transition lines and multicritical points. Also,
we report some connections with a percolation problem and an exact result in
one dimension.",0102336v1
2001-02-28,Stripe orientation in an anisotropic t-J model,"The tilt pattern of the CuO_6 octahedra in the LTT phase of the cuprate
superconductors leads to planar anisotropies for the exchange coupling and
hopping integrals. Here, we show that these anisotropies provide a possible
structural mechanism for the orientation of stripes. A t_x-t_y-J_x-J_y model
thus serves as an effective Hamiltonian to describe stripe formation and
orientation in LTT-phase cuprates.",0102524v1
2001-03-13,Anisotropic superconducting properties of aligned MgB2 crystallites,"Samples of aligned MgB2 crystallites have been prepared, allowing for the
first time the direct identification of an upper critical field anisotropy
Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40
A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background
signal was identified, possibly related to the raw materials purity.",0103287v4
2001-05-17,"Anisotropy of p states and 11B nuclear spin-lattice relaxation in (Mg,Al)B2","We calculated the nuclear spin-lattice relaxation rate in the (Mg,Al)B2
system and found that the orbital relaxation mechanism dominates over the
dipolar and Fermi-contact mechanisms in MgB2, whereas in AlB2 due to a smaller
density of states and strong anisotropy of boron p orbitals the relaxation is
completely determined by Fermi-contact interaction. The results for MgB2 are
compared with existing experimental data, whereas our results for the doped
alloy and AlB2 can be used in future experiments to verify the theoretical
predictions about the electronic structure of this system.",0105356v1
2001-05-26,Time-resolved ferromagnetic resonance in epitaxial Fe1-xCox films,"Magnetodynamics in epitaxial Fe1-xCox films on GaAs (100) are studied using
time-resolved ferromagnetic resonance, in which the free precession of the
magnetization after an impulsive excitation is measured using the polar Kerr
effect. The sample is rotated with respect to the static and pulsed field
directions, providing a complete mapping of the free energy surface and
characteristic relaxation times. The magnetic response can be simulated with a
simple coherent rotation model except in the immediate vicinity of switching
fields. Bulk and surface anisotropies are identified, and unusual dynamics
associated with the coexistence of cubic and uniaxial anisotropies are
observed.",0105513v1
2001-07-03,Importance of Correlation Effects on Magnetic Anisotropy in Fe and Ni,"We calculate magnetic anisotropy energy of Fe and Ni by taking into account
the effects of strong electronic correlations, spin-orbit coupling, and
non-collinearity of intra--atomic magnetization. The LDA+U method is used and
its equivalence to dynamical mean--field theory in the static limit is
emphasized. Both experimental magnitude of MAE and direction of magnetization
are predicted correctly near U=1.9 eV, J=1.2 eV for Ni and U=1.2 eV, J=0.8 eV
for Fe. Correlations modify the one--electron spectra which are now in better
agreement with experiments.",0107063v1
2001-07-05,Magnetization in quasiperiodic magnetic multilayers with biquadratic exchange and uniaxial anisotropy,"A theoretical study is made of the magnetization versus applied field curves
of ferromagnetic/nonmagnetic multilayers constructed according to a Fibonacci
quasiperiodic sequence. The ferromagnetic films are assumed to have uniaxial
anisotropy and are coupled by both bilinear and biquadratic effective exchange.
The effects of quasiperiodicity in the magnetic phases are illustrated
numerically for Fe/Cr systems.",0107127v1
2001-07-25,Complementary Theories of Energy Gaps in HTSC,"We examine experiments on energy gaps in high temperature superconductors
(HTSC) in terms of experimental probes that utilize momentum, position, or
neither. Experiments on very high quality mechanical tunnel junctions show a
sharp energy gap with a maximum anisotropy of ~ 10%, while ultrahigh precision
ARPES experiments show 100% anisotropy (d-wave pairing). We resolve this
conbflict by showing that the latter result is caused by the
momentum-projective nature of ARPES and glassy orthorhombic dopant
correlations. The latter appear to be a universal feature of the intermediate
phase tha is responsible for HTSC. Apparent large inconsistencies between
position-projective STM gap data and tunnel junction data on severely
underdoped BSCCO are also resolved.",0107531v1
2001-07-26,Direct Investigation of Superparamagnetism in Co Nanoparticle Films,"A direct probe of superparamagnetism was used to determine the complete
anisotropy energy distribution of Co nanoparticle films. The films were
composed of self-assembled lattices of uniform Co nanoparticles 3 nm or 5 nm in
diameter, and a variable temperature scanning-SQUID microscope was used to
measure temperature-induced spontaneous magnetic noise in the samples. Accurate
measurements of anisotropy energy distributions of small volume samples will be
critical to magnetic optimization of nanoparticle devices and media.",0107556v1
2001-07-30,Giant Spin Relaxation Anisotropy in Zinc-Blende Heterostructures,"Spin relaxation in-plane anisotropy is predicted for heterostructures based
on zinc-blende semiconductors. It is shown that it manifests itself especially
brightly if the two spin relaxation mechanisms (D'yakonov-Perel' and Rashba)
are comparable in efficiency. It is demonstrated that for the quantum well
grown along the [0 0 1] direction, the main axes of spin relaxation rate tensor
are [1 1 0] and [1 -1 0].",0107599v1
2001-08-05,Studies on the Anisotropic Properties of MgB2,"This paper presents a brief review on the reported anisotropic properties of
MgB2, in the superconducting state (e.g. upper critical field Hc2, field
penetration depth, coherence length, energy gap) as well as in the normal state
(e.g., magnetoresistance, compressibility, thermal expansion). So far, the
reported results have been obtained using aligned crystallites, c-axis oriented
thin films and sub-millimeter crystals. Since impurity scattering affects
directly the gap anisotropy it could be one of the main reasons for the
different values observed in the Hc2 anisotropy ratio, ranging between 1.3 and
2.6.",0108093v1
2001-08-09,Magnetic Anisotropy Variations and Non-Equilibrium Tunneling in a Cobalt Nanoparticle,"We present detailed measurements of the discrete electron-tunneling level
spectrum within nanometer-scale cobalt particles as a function of magnetic
field and gate voltage, in this way probing individual quantum many-body
eigenstates inside ferromagnetic samples. Variations among the observed levels
indicate that different quantum states within one particle are subject to
different magnetic anisotropy energies. Gate-voltage studies demonstrate that
the low-energy tunneling spectrum is affected dramatically by the presence of
non-equilibrium spin excitations.",0108166v1
2001-11-12,Quadratic transverse anisotropy term due to dislocations in Mn12-Ac directly obtained by EPR spectroscopy,"High-Sensitivity Electron Paramagnetic Resonance experiments have been
carried out in fresh and stressed Mn12-Acetate single crystals for frequencies
ranging from 40 GHz up to 110 GHz. The high number of crystal dislocations
formed in the stressing process introduces a E(S_x^2-S_y^2) transverse
anisotropy term in the spin hamiltonian. From the behaviour of the resonant
absorptions on the applied transverse magnetic field we have obtained an
average value for E = 22 mK, corresponding to a concentration of dislocations
per unit cell of c = 10^-3.",0111208v1
2001-11-23,Optical responses through dilute anisotropic composites: Numerical calculations via Green's-function formalism,"We investigate the linear and nonlinear optical responses of dilute
anisotropic networks using the Green's-function formalism (GFF)[Gu Y et al.
1999 Phys. Rev. B 59 12847]. For the different applied fields, numerical
calculations indicate that a large third order nonlinear enhancement and a
broad infrared absorption arise from the geometric anisotropy. It is also shown
the overlap and separation between the absorption peak and nonlinear
enhancement peak when the applied field is parallel, perpendicular to the
anisotropy respectively. In terms of the inverse participation ratios (IPR)
with q=2 and spectral distribution of optical responses, the results can be
understood.",0111459v1
2001-12-03,Multiple Field-Induced Phase Transitions in a Geometrically-Frustrated Dipolar Magnet - Gd2Ti2O7,"Field-driven phase transitions generally arise from competition between
Zeeman energy and exchange or crystal-field anisotropy.
  Here we present the phase diagram of a frustrated pyrochlore magnet Gd2Ti2O7,
where crystal field splitting is small compared to the dipolar energy. We find
good agreement between zero-temperature critical fields and those obtained from
a mean-field model. Here, dipolar interactions couple real-space and
spin-space, so the transitions in Gd2Ti2O7 arise from field-induced
""cooperative anisotropy"" reflecting the broken spatial symmetries of the
pyrochlore lattice.",0112022v1
2002-01-15,Rigorous Bounds to Retarded Learning,"We show that the lower bound to the critical fraction of data needed to infer
(learn) the orientation of the anisotropy axis of a probability distribution,
determined by Herschkowitz and Opper [Phys.Rev.Lett. 86, 2174 (2001)], is not
always valid. If there is some structure in the data along the anisotropy axis,
their analysis is incorrect, and learning is possible with much less data
points.",0201256v1
2002-03-14,Modeling exchange bias microscopically,"Exchange bias is a horizontal shift of the hysteresis loop observed for a
ferromagnetic layer in contact with an antiferromagnetic layer. Since exchange
bias is related to the spin structure of the antiferromagnet, for its
fundamental understanding a detailed knowledge of the physics of the
antiferromagnetic layer is inevitable. A model is investigated where domains
are formed in the volume of the AFM stabilized by dilution. These domains
become frozen during the initial cooling procedure carrying a remanent net
magnetization which causes and controls exchange bias. Varying the anisotropy
of the antiferromagnet we find a nontrivial dependence of the exchange bias on
the anisotropy of the antiferromagnet.",0203297v2
2002-04-01,Ground-State Phase Diagram of Frustrated Antiferromagnetic S=1 Chain with Uniaxial Single-Ion-Type Anisotropy,"The ground-state phase diagram of a frustrated S=1 Heisenberg spin chain with
uniaxial single-ion-type anisotropy is studied using the infinite-system
density-matrix renormalization-group method. Particular attention is paid to
""chiral"" phases, in which the long-range order parameter is a vector chirality.
It is found that, in addition to the Haldane, large-D (LD), and double-Haldane
phases, the phase diagram includes three different chiral phases, i.e., the
gapless chiral, chiral-Haldane, and chiral-LD phases. These chiral phases are
distinguished from each other by the energy gap and the string long-range
order.",0204020v1
2002-04-02,Effects of La substitution on superconducting state of CeCoIn5,"We report effects of La substitution on superconducting state of heavy
fermion superconductor CeCoIn5, as seen in transport and magnetization
measurements. As opposed to the case of conventional superconductors, pair
breaking by nonmagnetic La results in depression of Tc and indicates strong gap
anisotropy. Upper critical field Hc2 values decrease with increased La
concentration, but the critical field anisotropy, gamma=Hc2(a)/Hc2(c), does not
change in the Ce_{1-x}La_xCoIn5 (x=0-0.15). The electronic system is in the
clean limit for all values of x.",0204059v1
2002-04-14,Raman scattering through surfaces having biaxial symmetry,"Magnetic Raman scattering in two-leg spin ladder materials and the
relationship between the anisotropic exchange integrals are analyzed by P. J.
Freitas and R. R. P. Singh in Phys. Rev. B, {\bf 62}, 14113 (2000). The angular
dependence of the two-magnon scattering is shown to provide information for the
magnetic anisotropy in the Sr_14Cu_24O_41 and La_6Ca_8Cu_24O_41 compounds. We
point out that the experimental results of polarized Raman measurements at
arbitrary angles with respect to the crystal axes have to be corrected for the
light ellipticity induced inside the optically anisotropic crystals. We refer
quantitatively to the case of Sr_14Cu_24O_41 and discuss potential implications
for spectroscopic studies in other materials with strong anisotropy.",0204312v1
2002-06-15,Effect of a Staggered Magnetic Field on the S=1 Haldane Chain with Single-ion Anisotropy,"We analyze the gaps in the excitation spectrum of a Haldane chain with
single-ion anisotropy in a staggered field. We show that the gap along the
direction of the field increases at a faster rate than the others, while its
spectral weight decreases, being transferred to a two-magnon continuum.",0206288v1
2002-07-02,Internal localized eigenmodes on spin discrete breathers in antiferromagnetic chains with on-site easy axis anisotropy,"We investigate internal localized eigenmodes of the linearized equation
around spin discrete breathers in 1D antiferromagnets with on-site easy axis
anisotropy. The threshold of occurrence of the internal localized eigenmodes
has a typical structure in parameter space depending on the frequency of the
spin discrete breather. We also performed molecular dynamics simulation in
order to show the validity of our linear analysis.",0207053v1
2002-07-19,Nonlinear Mechanical Response of DNA due to Anisotropic Bending Elasticity,"The response of a short DNA segment to bending is studied, taking into
account the anisotropy in the bending rigidities caused by the double-helical
structure. It is shown that the anisotropy introduces an effective nonlinear
twist-bend coupling that can lead to the formation of kinks and modulations in
the curvature and/or in the twist, depending on the values of the elastic
constants and the imposed deflection angle. The typical wavelength for the
modulations, or the distance between the neighboring kinks is found to be set
by half of the DNA pitch.",0207477v1
2002-07-19,"Conduction Anisotropy, Hall Effect, and Magnetoresistance of (TMTSF)2ReO4 at High Temperatures","We investigated the transport properties of the quasi one-dimensional organic
metal (TMTSF)2ReO4 above the anion-ordering metal-insulator transition (T_{AO}
\approx 180K). The pronounced conductivity anisotropy, a small and smoothly
temperature dependent Hall effect, and a small, positive and temperature
dependent magnetoresistance are analyzed within the existing Fermi-liquid and
non-Fermi liquid models. We propose that the transport properties of quasi
one-dimensional Bechgaard salts at high temperatures can be described within
the Fermi liquid description.",0207479v2
2002-07-28,Anisotropy of Mott-Hubbard gap transitions due to spin and orbital ordering in LaVO3 and YVO3,"Anisotropic optical spectra coupled with antiferromagnetic spin ordering (SO)
and orbital ordering (OO) have been investigated for single crystals of
LaVO_{3} and YVO_{3}. The orbital-dependent Mott-Hubbard gap transitions are
observed around 2 eV. The transitions composed of the two peaks show distinct
anisotropy and selection rules, reflecting the respective SO and OO patterns.
The temperature dependence of the anisotropic transitions clearly indicates the
SO/OO correlation and the evolution of the order parameters.",0207664v1
2002-09-11,Magnetic Anisotropy in La_0.8Sr_0.2MnO_3: Electron Spin Resonance,"We report on Ferromagnetic-Resonance experiments in a single crystal of
La_0.8Sr_0.2MnO_3 in the temperature range from 4 to 300 K. The observed
anisotropy of the resonance line changes on crossing the transition from the
orthorhombic O-phase to the rhombohedral R-phase at T~100 K and indicates a
reorientation of the spins at about 130 K.",0209257v1
2002-10-04,The Effects of the Misfit Structure on Thermoelectric Properties of Bi2-xPbxSr2Co2Oy Single Crystals,"In-plane anisotropy of the resistivity and thermopower was measured for
single crystal Bi2-xPbxSr2Co2Oy. There is large in-plane anisotropy, which is
attributed to the anisotropic pseudogap formation due to the different crystal
symmetry between the square Bi2Sr2O4 layer and the triangular CuO2 layer. The
magnitude of the thermopower both along a- and b-axis direction increases with
Pb doping from x=0 to 0.4, where we observe discontinuous shrink of b-axis
length. We attribute this to the enhancement of the misfitness. Thus, we can
improve the thermoelectric properties by tuning the misfitness.",0210087v1
2002-10-08,Coulomb Correlations and Magnetic Anisotropy in ordered $L1_0$ CoPt and FePt alloys,"We present results of the magneto-crystalline anisotropy energy (MAE)
calculations for chemically ordered $L1_0$ CoPt and FePt alloys taking into
account the effects of strong electronic correlations and spin-orbit coupling.
The local spin density + Hubbard U approximation (LSDA+U) is shown to provide a
consistent picture of the magnetic ground state properties when intra-atomic
Coulomb correlations are included for both 3$d$ and 5$d$ elements. Our results
demonstrate significant and complex contribution of correlation effects to
large MAE of these material.",0210157v2
2002-11-07,Piezoresistivity and conductance anisotropy of tunneling-percolating systems,"Percolating networks based on interparticle tunneling conduction are shown to
yield a logarithmic divergent piezoresistive response close to the critical
point as long as the electrical conductivity becomes nonuniversal. At the same
time, the piezoresistivity or, equivalently, the conductivity anisotropy
exponent $\lambda$ remains universal also when the conductive exponent is not,
suggesting a purely geometric origin of $\lambda$. We discuss our results in
relation to the nature of transport for a variety of materials such as
carbon-black--polymer composites and RuO_2-glass systems which show
nonuniversal transport properties and coexistence between tunneling and
percolating behaviors.",0211133v2
2002-11-12,Electronic structure and magnetic anisotropy of the [Co_4(hmp)_4(CH_3OH)_4Cl_4] molecule,"Accurate density-functional based calculations have been performed on the
Co_4(hmp)_4(CH_3OH)_4Cl_4 molecular magnet where hmp is deprotonated
hydroxymethyl pyridine. In addition to the experimentally observed staggered
geometry, we identify two isomers, referred to as eclipsed and
half-staggered/half-eclipsed, that are reasonably low in energy. Our
calculations show that the magnetic anisotropy is strongly dependent on the
pyridine-pyridine separation and that the three structures exhibit easy axis,
easy plane and triaxial behavior. Other effects such as partial reprotonation
of the hmp is considered.",0211221v1
2002-11-29,Anisotropic Magnetoresistance in GaMnAs films,"The magnetoresistance in a series of Ga1-xMnxAs samples with 0.2 =< x =< 0.8
have been measured for three mutually orthogonal orientations of the external
magnetic field. The anisotropy magnetoresistance decreases with increasing of
the Mn content, which means that the magnetic disorder or defects scattering
increases with increasing of Mn content. And also the magneto-crystalline
anisotropy increases with increasing of Mn concentration.",0211697v1
2002-12-03,Thermal stability of coupled ferromagnetic and superparamagnetic particles,"We consider a single-domain ferromagnetic particle with uniaxial anisotropy
coupled to a single-domain soft ferromagnetic particle (superparamagnetic
particle). The problem of thermally agitated magnetization reversal in this
case can be reduced to the random magnetization dynamics of the first particle
with an effectively larger anisotropy field. The magnetic external field is
also altered in a manner that depends on the sign of the coupling and can be
either enhanced or suppressed.",0212041v1
2002-12-16,Anisotropy parameters of superconducting MgB$_2$,"Data on macroscopic superconducting anisotropy of MgB$_2$ are reviewed. The
data are described within a weak coupling two-gaps anisotropic s-wave model of
superconductivity. The calculated ratio of the upper critical fields
$\gamma_H=H_{c2,ab}/H_{c2,c}$ increases with decreasing temperature in
agreement with available data, whereas the calculated ratio of London
penetration depths $\gamma_{\lambda}=\lambda_c/\lambda_{ab}$ decreases to reach
$\approx 1.1$ at T=0. Possible macroscopic consequences of
$\gamma_{\lambda}\ne\gamma_H$ are discussed.",0212383v1
2002-12-17,"Comment on ""First-principles calculation of the superconducting transition in MgB2 within the anisotropic Eliashberg formalism""","Choi et al. [Phys. Rev. B 66, 020513 (2002)] recently presented first
principles calculations of the electron-phonon coupling and superconductivity
in MgB2, emphasizing the importance of anisotropy and anharmonicity. We point
out that (1) variation of the superconducting gap inside the sigma- or the
pi-bands can hardly be observed in real samples, and (2) taking the anisotropy
of the Coulomb repulsion into account influences the size of the small gap,
Delta_pi.",0212417v3
2003-03-20,On a dual model for 5f electrons,"We study the effect of intra-atomic correlations on anisotropies of hopping
of 5f electrons. It is shown that they may considerably enhance these
anisotropies to the extend that electrons in some of the 5f orbitals remain
localized. This provide a microscopic basis for a previously made assumption
that some of the 5f electrons must be partially localized when Fermi surfaces
and effective masses of the component are calculated. Calculations are
performed on two- and three-sites clusters. They include phase diagrams in the
presence and absence of an external magnetic field as function of anisotropic
hopping.",0303414v1
2003-05-01,"Reply to the comment on the paper ""Thermodynamics of two-dimensional magneto nanoparticles (P. Vargas, D. Altbir, M.Knobel and D. Laroze)"" by H. Buettner and Yu. Gaididei","It is shown that there is bi-stability in a two dimensional system consisting
of non interacting magnetic nanoparticles with equal uniaxial anisotropies. It
is also shown that bi-stability still remains in three dimensions. The only
consideration is that the applied magnetic field has to be perpendicular to the
anisotropy axis.",0305023v1
2003-06-24,Doping dependence of the gap anisotropy in LCCO studied by millimeter-wave spectroscopy,"We measure the penetration depth of optimally doped and underdoped
La2-xCexCuO4 in the millimeter frequency domain (4 - 7 cm-1) and for
temperatures 2 K < T < 300 K. The penetration depth as function of temperature
reveals significant changes on electron doping. It shows quadratic temperature
dependence in underdoped samples, but increases almost exponentially at optimal
doping. Significant changes in the gap anisotropy (or even in the gap symmetry)
may account for this transition.",0306606v1
2003-09-23,On the Field Dependence of the Interface Energy in Af/FM Bilayers,"In the investigations of antiferromagnetic (AF)/ ferromagnetic (FM) bilayer
samples, often distinct experimental techniques yield different values for the
measured exchange anisotropy field (HE). We propose that the observed
discrepancy may be accounted in part by the dependence of the unidirectional
anisotropy with the value of the external applied field (h). Using a simple
microscopic model for representing the AF/FM interface, which incorporates the
effect of interface roughness, we show that the interface energy between the AF
and FM layer indeed varies with h, as recently observed in anisotropic
magnetoresistance measurements, lending support to our proposal.",0309535v1
2003-12-18,Controlled normal and inverse magnetoresistance and current-driven magnetization switching in magnetic nanopillars,"Combining pairs of ferromagnetic metals with different signs of scattering
anisotropies, let us independently invert the magnetoresistance and the
direction of current-driven switching in
ferromagnetic/non-magnetic/ferromagnetic metal nanopillars. We show all four
combinations of normal and inverse behaviors, at both room temperature and
4.2K. In all cases studied, the direction of switching is set by the net
scattering anisotropy of the fixed (polarizing) ferromagnet. We provide simple
arguments for what we see.",0312475v1
2004-02-14,Depolarization of backscattered linearly polarized light,"We formulate a quantitative description of backscattered linearly polarized
light using an extended photon diffusion formalism taking explicitly into
account the scattering anisotropy parameter g of the medium. From diffusing
wave spectroscopy measurements the characteristic depolarization length for
linearly polarized light is deduced. We investigate the dependance of this
length on the scattering anisotropy parameter g spanning an extended range from
-1 (backscattering) to 1 (forward scattering). Good agreement is found with
Monte Carlo simulations of multiply scattered light.",0402391v1
2004-02-16,Triplet superconductivity vs. easy-plane ferromagnetism in a 1D itinerant electron system with transverse spin anisotropy,"In this paper we study the ground state phase diagram of a one-dimensional
$t-U-J$ model, at half-filling. In the large-bandwidth limit and for
ferromagnetic exchange with easy-plane anisotropy, a phase with gapless charge
and massive spin excitations, characterized by the coexistence of triplet
superconducting and spin density wave instabilities is realized in the ground
state. With reduction of the bandwidth, a transition into an insulating phase
showing properties of the spin-1/2 XY model takes place.",0402405v1
2004-02-25,Spin Dynamics of a Canted Antiferromagnet in a Magnetic Field,"The spin dynamics of a canted antiferromagnet with a quadratic spin-wave
dispersion near $\vq =0$ is shown to possess a unique signature. When the
anisotropy gap is negligible, the spin-wave stiffness $\dsw (\vq, B) =
(\omega_{\vq}-B)/q^2$ depends on whether the limit of zero field or zero
wavevector is taken first. Consequently, $\dsw $ is a strong function of
magnetic field at a fixed wavevector. Even in the presence of a sizeable
anisotropy gap, the field dependence of both $\dsw $ and the gap energy
distinguishes a canted antiferromagnet from a phase-separated mixture
containing both ferromagnetic and antiferromagnetic regions.",0402633v2
2004-03-16,Anisotropy-induced ordering in the quantum J1-J2 antiferromagnet,"We study the effect of spin anisotropies on a frustrated quantum
antiferromagnet using the J_1-J_2^{XXZ} model on the square lattice. The T=0
and finite-T phase diagrams of this model are obtained utilizing spin-wave
theory, exact diagonalization, and quantum Monte Carlo. We find that
anisotropic frustration tends to stabilize XY- and Ising-like ordered phases,
while the disordered spin-liquid phase is restricted to a small region of the
phase diagram. The ordered phases are separated by first-order transitions and
exhibit a non-trivial reentrance phenomenon.",0403375v1
2004-03-23,Field dependence of the zero energy density of states around vortices in an anisotropic gap superconductor,"It is shown theoretically that the Sommerfeld coefficient $\gamma(B)$ in the
mixed state contains useful information on the gap topology in a
superconductor. We accurately evaluate $\gamma(B)$ against magnetic induction
$B$ by using microscopic quasi-classical theory. The linear portion in
{$\gamma(\propto B)$} relative to $B_{\rm c2}$ and its slope in low field
faithfully corresponds to the gap anisotropy, so that we can distinguish the
nodal gap and the anisotropic full gap, and estimate the magnitude of the gap
anisotropy.",0403589v1
2004-04-03,"Pinning a Domain Wall in (Ga,Mn)As with Focused Ion Beam Lithography","We utilize a focused beam of Ga+ ions to define magnetization pinning sites
in a ferromagnetic epilayer of (Ga,Mn)As. The nonmagnetic defects locally
increase the magneto-crystalline anisotropy energies, by which a domain wall is
pinned at a given position. We demonstrate techniques for manipulating domain
walls at these pinning sites as probed with the giant planar Hall effect
(GPHE). By varying the magnetic field angle relative to the crystal axes, an
upper limit is placed on the local effective anisotropy energy.",0404068v1
2004-04-14,Evidence of gap anisotropy in superconducting YNi2B2C using directional point contact spectroscopy,"We present a study of the anisotropy in the superconducting energy gap in a
single crystal of YNi2B2C (Tc~14.6K) using directional point contact
spectroscopy. The superconducting energy gap at 2.7K, when measured for I||c,
is 4.5 times larger than that for I||a. The energy gaps in the two directions
also have different temperature dependences. Our results support a scenario
with s+g like symmetry.",0404322v1
2004-04-16,Changes in magnetic scattering anisotropy at a ferromagnetic/superconducting interface,"We show that some metals and alloys (X = Cu, Ag, FeMn, or Cu and Ag combined
with each other), sputtered between ferromagnetic Co and superconducting Nb,
produce no change in current-perpendicular-to-plane magnetoresistance (CPP-MR)
in a carefully designed CPP-spin-valve. In contrast, other metals (Ru or Au) or
combinations (Cu or Ag combined with Au, Ru, or FeMn) change the CPP-MR, in
some cases even reversing its sign. We ascribe these changes to activation of
magnetic scattering anisotropies at a ferromagnetic/superconducting interface,
apparently by strong spin-flipping between the Co and Nb layers.",0404396v1
2004-04-18,Anisotropy of superconductivity of as-grown MgB$_2$ thin films by molecular beam epitaxy,"Superconducting thin films of magnesium diboride (MgB$_2$) were prepared on
MgO (001) substrate by a molecular beam epitaxy (MBE) method with the
co-evaporation conditions of low deposition rate in ultra-high vacuum. The
structural and physical properties of the films were studied by RHEED, XRD,
XPS, resistivity and magnetization measurements.All films demonstrated
superconductivity without use of any post-annealing process.The highest {\it
T}$_{c,onset}$ determined by resistivity measurement was about 33K in the
present samples.Anisotropic superconducting properties were evaluated by the
resistivity and magnetic measurements.We will discuss the anisotropy of
superconductivity for as-grown MgB$_2$ thin films.",0404415v1
2004-05-01,Anisotropy of Resonant Inelastic X-Ray Scattering at the K Edge of Si:Theoretical Analysis,"We investigate theoretically the resonant inelastic x-ray scattering (RIXS)
at the $K$ edge of Si on the basis of an ab initio calculation. We calculate
the RIXS spectra with systematically varying transfered-momenta,
incident-photon energy and incident-photon polarization. We confirm the
anisotropy of the experimental spectra by Y. Ma {\it et al}. (Phys. Rev. Lett.
74, 478 (1995)), providing a quantitative explanation of the spectra.",0405009v4
2004-05-24,Determination of the magnetic anisotropy axes of single-molecule magnets,"Simple methods are presented allowing the determination of the magnetic
anisotropy axes of a crystal of a single-molecule magnet (SMM). These methods
are used to determine an upper bound of the easy axis tilts in a standard
Mn12-Ac crystal. The values obtained in the present study are significately
smaller than those reported in recent high frequency electron paramagnetic
resonance (HF-EPR) studies which suggest distributions of hard-axes tilts.",0405565v1
2004-06-09,Anisotropy in double negative permittivity and permeability materials or left-handed materials : the effect on guided wave propagating electromagnetic fields,"Effect of anisotropy in the physical tensor description of the negative index
of refraction material (left-handed material, LHM) acting as a substrate is
found on the electromagnetic field distributions. Field distributions are
provided in the GHz region in the cross-section of the uniform microstrip
guided wave structure. It is found from ab initio Green's function calculations
that modifying the tensor can allow control because the wave changes
volumetrically, or switches from volumetric to surface, in its distribution of
fields. Comparison is made of the LHM results to ordinary right-handed material
(RHM) acting as a substrate.",0406219v2
2004-07-09,Magnetic order in lightly doped La_{2-x}Sr_{x}CuO_{4},"We study long wavelength magnetic excitations in lightly doped
La_{2-x}Sr_{x}CuO_{4} (x < 0.03) detwinned crystals. The lowest energy magnetic
anisotropy induced gap can be understood in terms of the antisymmetric spin
interaction inside the antiferromagnetic (AF) phase. The second magnetic
resonace, analyzed in terms of in-plane spin anisotropy, shows unconventional
behavior within the AF state and led to the discovery of collective spin
excitations pertaining to a field induced magnetically ordered state. This
state persists in a 9 T field to more than 100 K above the N\'{e}el temperature
in x = 0.01.",0407248v1
2004-08-13,Finite lattice size effect in the ground state phase diagram of quasi-two-dimensional magnetic dipolar dots array with perpendicular anisotropy,"A prototype Hamiltonian for the generic patterned magnetic structures, of
dipolar interaction with perpendicular anisotropy, is investigated within the
finite-size framework by Landau-Lifshift-Gilbert classical spin dynamics.
Modifications on the ground state phase diagram are discussed with an emphasis
on the disappearance of continuous degeneracy in the ground state of in-plane
phase due to the finite lattice size effect. The symmetry-governed ground state
evolution upon the lattice size increase provides a critical insight into the
systematic transition to the infinite extreme.",0408324v1
2004-09-01,Momentum space anisotropy in doped Mott insulators,"We study the single hole tt't''J-model numerically to address the momentum
space anisotropy found in doped Mott insulators. A simple two band picture to
understand how the doped hole is screened by the spin background in states of
different momenta is proposed. In this picture, the disparity between the nodal
and antinodal regions, observed by experiments in the underdoped cuprate
superconductors, follows from local energetic considerations and amounts to the
distinction between well defined quasiparticle behavior and spin-charge
separation related phenomenology.",0409002v3
2004-10-21,"Implications of the isotope effects on the magnetization, magnetic torque and susceptibility","We analyze the magnetization, magnetic torque and susceptibility data of
La2-xSrxCu(16,18)O4 and YBa2(63,65)CuO7-x near Tc in terms of the universal
3D-XY scaling relations. It is shown that the isotope effect on Tc mirrors that
on the anisotropy. Invoking the generic behavior of the anisotropy the doping
dependence of the isotope effects on the critical properties, including Tc,
correlation lengths and magnetic penetration depths are traced back to a change
of the mobile carrier concentration.",0410547v1
2004-10-28,Complex shape evolution of electromigration-driven single-layer islands,"The shape evolution of two-dimensional islands through periphery diffusion
biased by an electromigration force is studied numerically using a continuum
approach. We show that the introduction of crystal anisotropy in the mobility
of edge atoms induces a rich variety of migration modes, which include
oscillatory and irregular behavior. A phase diagram in the plane of anisotropy
strength and island size is constructed. The oscillatory motion can be
understood in terms of stable facets which develop on one side of the island
and which the island then slides past. The facet orientations are determined
analytically.",0410745v2
2004-11-11,Anisotropic Diamagnetic Response in Type-II Superconductors with Gap and Fermi-Surface Anisotropies,"Effects of anisotropic gap structures on a diamagnetic response are
investigated in order to demonstrate that the field-angle-resolved
magnetization ($M_L(\chi)$) measurement can be used as a spectroscopic method
to detect gap structures. Our microscopic calculation based on the
quasiclassical Eilenberger formalism reveals that $M_L(\chi)$ in a
superconductor with four-fold gap displays a four-fold oscillation reflecting
the gap and Fermi surface anisotropies, and the sign of this oscillation
changes at a field between $H_{c1}$ and $H_{c2}$. As a prototype of
unconventional superconductors, magnetization data for borocarbides are also
discussed.",0411290v2
2004-11-25,Magnetoresistance in metals with embedded magnetic nano-clusters,"We propose a kinetic theory of transport in metals embedded with
ferromagnetic nanoclusters, describing the dependence of the form of
magnetoresistance on anisotropy characteristics of the ensemble of clusters and
the influence of the electron spin depolarisation by clusters. We note that
this effect is strongest when all the clusters have the same intrinsic
easy-axis anisotropy.",0411655v2
2004-12-15,Effects of edges in spin-1/2 bond-alternating Heisenberg chains: Matrix-product variational approach,"We make a matrix-product variational approach to spin-1/2
ferromagnetic-antiferromagnetic bond-alternating chains with anisotropy on
their ferromagnetic bonds, especially under the open boundary condition. The
rich phase diagram containing the Haldane, large-D, and two types of Neel
phases is well reproduced with only two variational parameters. The on-bond
anisotropy has a significant effect on the ferromagnetic coupling between
neighboring spins and induces novel edge states peculiar to spin-1/2 chains.",0412390v1
2004-12-17,Hysteresis loops of magnetic thin films with perpendicular anisotropy,"We model the magnetization of quasi two-dimensional systems with easy
perpendicular (z-)axis anisotropy upon change of external magnetic field along
z. The model is derived from the Landau-Lifshitz-Gilbert equation for
magnetization evolution, written in closed form in terms of the z component of
the magnetization only. The model includes--in addition to the external
field--magnetic exchange, dipolar interactions and structural disorder. The
phase diagram in the disorder/interaction strength plane is presented, and the
different qualitative regimes are analyzed. The results compare very well with
observed experimental hysteresis loops and spatial magnetization patterns, as
for instance for the case of Co-Pt multilayers.",0412461v1
2005-02-12,Does Optical Anisotropy Lead to Negative Refraction at an Interface?,"This is a comment inspired by recently published results [Y. Zhang et al.,
Phys. Rev. Lett. 91, 157404 (2003)] that introduced the name ""amphoteric
refraction"" for the fact that at the interface with an optically anisotropic
material there can be a range of incidence angles for which the component of
the Poynting vector parallel to the interface changes sign upon refraction. The
latter effect is a well-known consequence of optical anisotropy, but it was
described as a new negative refraction phenomenon that can be put in the same
class as the negative refraction observed at an interface with a left-handed
material with negative refractive index.",0502308v2
2005-02-24,Pressure effects on the superconducting properties of YBa_2Cu_4O_8,"Measurements of the magnetization under high hydrostatic pressure (up to 10.2
kbar) in YBa_2Cu_4O_8 were carried out. From the scaling analysis of the
magnetization data the pressure induced shifts of the transition temperature
T_c, the volume V and the anisotropy \gamma have been obtained. It was shown
that the pressure induced relative shift of T_c mirrors essentially that of the
anisotropy. This observation uncovers a novel generic property of anisotropic
type II superconductors, that inexistent in the isotropic case.",0502576v1
2005-05-10,"Nanomechanical Measurements of Magnetostriction and Magnetic Anisotropy in (Ga,Mn)As","A (Ga,Mn)As nanoelectromechanical resonator is used to obtain the first
direct measurement of magnetostriction in a dilute magnetic semiconductor.
Field-dependent magnetoelastic stress induces shifts in resonance frequency
that can be discerned with a high resolution electromechanical transduction
scheme. By monitoring the field dependence, the magnetostriction and anisotropy
field constants can be simultaneously mapped over a wide range of temperatures.
These results, when compared with theoretical predictions, appear to provide
insight into a unique form of magnetoelastic behavior mediated by holes.",0505222v1
2005-06-10,Spin-charge-orbital ordering on triangle-based lattices,"We investigate the ground-state property of an e_g-orbital Hubbard model at
quarter filling on a zigzag chain by exploiting the density matrix
renormalization group method. When two orbitals are degenerate, the zigzag
chain is decoupled to a doble-chain spin system to suppress the spin
frustration due to the spatial anisotropy of the occupied orbital. On the other
hand, when the level splitting is increased and the orbital anisotropy
disappears, a characteristic change in the spin incommnsurability is observed
due to the revival of the spin frustration.",0506242v1
2005-06-15,Enhanced Magnetic Anisotropy of Mn12-acetate,"Thin films of the Single Molecule Magnet (Mn12-acetate) have been fabricated
on a Si-substrate by the Dip-and-Dry method, a simple and robust technique.
Atomic force microscopy and X-ray photoelectron spectroscopy characterizations
reveal that homogeneous, thin films of a few molecular layers with smoothness
at the molecular level are deposited. Significant changes in magnetic
properties of Mn12-acetate exposed to the same solvent were observed in
zero-field-cooled and field-cooled magnetization, as well as ac-susceptibility
measurements. The blocking temperature was found to increase to TB > 10 K at
low magnetic fields, indicating an enhanced magnetic anisotropy.",0506378v1
2005-06-16,Orbital order and spin-orbit coupling in BaVS3,"The correlated 3d sulphide BaVS3 undergoes a sequence of three symmetry
breaking transitions which are reflected in the temperature dependence of the
magnetic susceptibility, and its anisotropy. We introduce a microscopic model
based on the coexistence of wide band a(1g) and localized e(g) d-electrons, and
give the classification of the order parameters under the double space group
and time reversal symmetries. Allowing for the relativistic spin-orbit
coupling, the d-shell multipoles acquire a mixed spin-orbital character. It
follows that orbital ordering is accompanied by a change in the susceptibility
anisotropy",0506409v1
2005-06-19,Anisotropic Hubbard model on a triangular lattice -- spin dynamics in Ho Mn O_3,"The recent neutron-scattering data for spin-wave dispersion in $\rm Ho Mn
O_3$ are well described by an anisotropic Hubbard model on a triangular lattice
with a planar (XY) spin anisotropy. Best fit indicates that magnetic
excitations in $\rm Ho Mn O_3$ correspond to the strong-coupling limit $U/t >
\sim 15$, with planar exchange energy $J=4t^2/U \simeq 2.5$meV and planar
anisotropy $\Delta U \simeq 0.35$meV.",0506475v3
2005-07-06,Orientational symmetry-breaking correlations in square lattice t-J model,"We study a tendency to orientational symmetry breaking of the square lattice
t-J model by applying the exact diagonalization technique. We introduce a small
external anisotropy to t and J, and calculate the induced anisotropy of
hole-hole correlations as a response. It is found that the response is strongly
enhanced for particular band parameters, meaning that the system has a strong
tendency to orientational symmetry breaking. The analysis of the momentum
distribution function indicates that the correlation develops when the Fermi
surface is close to (pi,0) and (0,pi). Some properties of high-Tc cuprates
previously attributed to stripes can also be understood from orientational
symmetry breaking alone.",0507146v1
2005-08-15,Opening of pseudogaps due to superconducting critical fluctuations in quasi-two dimensions,"We examine the role of the anisotropy of superconducting thermal critical
fluctuations in the opening of pseudogaps in quasi-two dimensions. When the
anisotropy of coherence or correlation lengths of the fluctuations is large
enough and critical temperatures T_c are high enough, the energy dependence of
the selfenergy deviates from that of Landau's normal Fermi liquid in critical
regions; its imaginary part has no minimum at the chemical potential. Prominent
pseudogaps open in such a non-Fermi liquid phase. Pseudogaps must be absent or
subtle in quasi-two dimensional superconductors with low T_c and almost
isotropic three dimensional superconductors.",0508344v1
2005-08-15,Electronic structure and anisotropic transport properties in hexagonal YPtIn and LuAgGe ternary compounds,"We present anisotropic, zero applied magnetic field, temperature dependent
resistivity measurements on hexagonal, non-magnetic, YPtIn and LuAgGe single
crystals. For these materials the in-plane resistivity, $\rho_{ab}$, is
significantly higher than the $c$ - axis one, $\rho_c$, with $\rho_{ab}/\rho_c
\approx 1.4$ for YPtIn and $\approx 4.2 - 4.7$ for LuAgGe. The connection
between the electronic structure and the anisotropic transport properties is
discussed using density functional calculations that link the observed
anisotropy with a specific shape of Fermi surface and anisotropy of the Fermi
velocities.",0508346v1
2005-09-29,Comment to: Correlation Between Superfluid Density and T_{c} of Underdoped YBa2Cu3O6+x Near the Superconductor-Insulator Transition,"Zuev et al. reported measurements of the in-plane magnetic penetration depth
of supposedly underdoped films of YBa2Cu3O6+x, with Tc from 6 to 50 K. They
argue that their data is inconsistent with a linear relationship between Tc and
the inversw of the T=0 in-plane penetration depth squared, as expected for a
two dimensional quantum superconductor to insulator (2D-QSI) transition where
Tc vanishes and the anisotropy diverges. It is shown that the data of Zuev et
al. do not fall onto the regime where the linear relationship applies, because
the observed reduction of Tc is not associated with an increase of the
anisotropy.",0509768v1
2005-10-07,Perpendicular magnetic anisotropy in nanoclusters caused by surface segregation and shape,"The growth of binary alloy clusters on a weakly interacting substrate through
codeposition of two atomic species is studied by kinetic Monte Carlo
simulation. Our model describes salient features of CoPt$_3$-nanoclusters, as
obtained recently by the molecular-beam epitaxy technique. The clusters display
perpendicular magnetic anisotropy (PMA) in a temperature window of growth
favorable for applications. This temperature window is found to arise from the
interplay of Pt surface segregation and aspect ratio for cluster shapes.
Conclusions are drawn how to optimize growth parameters with respect to PMA.",0510196v1
2005-11-22,Influence of anisotropic next-nearest-neighbor hopping on diagonal charge-striped phases,"We consider the model of strongly-correlated system of electrons described by
an extended Falicov-Kimball Hamiltonian where the stability of some axial and
diagonal striped phases was proved. Introducing a next-nearest-neighbor
hopping, small enough not to destroy the striped structure, we examine
rigorously how the presence of the next-nearest-neighbor hopping anisotropy
reduces the $\pi/2$-rotation degeneracy of the diagonal-striped phase. The
effect appears to be similar to that in the case of anisotropy of the
nearest-neighbor hopping: the stripes are oriented in the direction of the
weaker next-nearest-neighbor hopping.",0511557v1
2005-11-23,Phase separation in the trapped spinor gases with anisotropic spin-spin interaction,"We investigate the effect of the anisotropic spin-spin interaction on the
ground state density distribution of the one dimensional spin-1 bosonic gases
within a modified Gross-Pitaevskii theory both in the weakly interaction regime
and in the Tonks-Girardeau (TG) regime. We find that for ferromagnetic spinor
gas the phase separation occurs even for weak anisotropy of the spin-spin
interaction, which becomes more and more obvious and the component of $m_F=0$
diminishes as the anisotropy increases. However, no phase separation is found
for anti-ferromagnetic spinor gas in both regimes.",0511581v2
2005-11-28,Quantum tunneling induced Kondo effect in single molecular magnets,"We consider transport through a single-molecule magnet strongly coupled to
metallic electrodes. We demonstrate that for half-integer spin of the molecule
electron- and spin-tunneling \emph{cooperate} to produce both quantum tunneling
of the magnetic moment and a Kondo effect in the linear conductance. The Kondo
temperature depends sensitively on the ratio of the transverse and easy-axis
anisotropies in a non-monotonic way. The magnetic symmetry of the transverse
anisotropy imposes a selection rule on the total spin for the occurrence of the
Kondo effect which deviates from the usual even-odd alternation.",0511664v2
2005-12-07,Finite-size scaling in anisotropic systems,"We present analytical results for the finite-size scaling in d--dimensional
O(N) systems with strong anisotropy where the critical exponents (e.g. \nu_{||}
and \nu_{\perp}) depend on the direction. Prominent examples are systems with
long-range interactions, decaying with the interparticle distance r as
r^{-d-\sigma} with different exponents \sigma in corresponding spatial
directions, systems with space-""time""a anisotropy near a quantum critical point
and systems with Lifshitz points. The anisotropic properties involve also the
geometry of the systems. We consider systems confined to a d-dimensional layer
with geometry L^{m}\times\infty^{n}; m+n=d and periodic boundary conditions
across the finite m dimensions. The arising difficulties are avoided using a
technics of calculations based on the analytical properties of the generalized
Mittag-Leffler functions.",0512146v1
2005-12-07,Effect of spin-orbit interaction on a magnetic impurity in the vicinity of a surface,"We propose a new mechanism for surface-induced magnetic anisotropy to explain
the thickness-dependence of the Kondo resistivity of thin films of dilute
magnetic alloys. The surface anisotropy energy, generated by spin-orbit
coupling on the magnetic impurity itself, is an oscillating function of the
distance d from the surface and decays as 1/d^2. Numerical estimates based on
simple models suggest that this mechanism, unlike its alternatives, gives rise
to an effect of the desired order of magnitude.",0512154v1
2006-02-15,Effect of step stiffness and diffusion anisotropy on the meandering of a growing vicinal surface,"We study the step meandering instability on a surface characterized by the
alternation of terraces with different properties, as in the case of Si(001).
The interplay between diffusion anisotropy and step stiffness induces a finite
wavelength instability corresponding to a meandering mode. The instability sets
in beyond a threshold value which depends on the relative magnitudes of the
destabilizing flux and the stabilizing stiffness difference. The meander
dynamics is governed by the conserved Kuramoto-Sivashinsky equation, which
display spatiotemporal coarsening.",0602353v1
2006-03-07,Reentrant anisotropic phases in a two-dimensional hole system,"Anisotropic charge transport is observed in a two-dimensional (2D) hole
system in a perpendicular magnetic field at filling factors nu=7/2 and nu=11/2
for temperatures below 150mK. In stark contrast, the transport at nu=9/2 is
isotropic for all temperatures. Our results for a two-dimensional hole system
differ substantially from 2D electron transport where no anisotropy has been
observed at nu=7/2, the strongest anisotropy occurs at nu=9/2, and reentrant
behavior is not evident. We attribute this difference to strong spin-orbit
coupling in the hole system.",0603173v1
2006-03-20,Triplet superconductivity in a 1D itinerant electron system with transverse spin anisotropy,"In this paper we study the ground state phase diagram of a one-dimensional
t-J-U model away from half-filling. In the large-bandwidth limit and for
ferromagnetic exchange with easy-plane anisotropy a phase with gapless charge
and massive spin excitations, characterized by the coexistence of triplet
superconducting and spin density wave instabilities is realized in the ground
state. With increasing ferromagnetic exchange transitions into a ferrometallic
and then a spin gapped triplet superconducting phase take place.",0603504v1
2006-05-06,Nutations of spin in the quasi-isotropic superfluid A-like phase of 3He,"The order parameter of the quasi-isotropic superfluid A-like phase of 3He is
rewritten in a simple form. Effect of anisotropy of magnetic susceptibility of
this phase on the frequencies of the spatially uniform oscillations of spin and
the spin part of its order parameter are found. Anisotropy of susceptibility
has pronounced effect on the low-frequency mode, which is analogous to
nutations of the asymmetric top. Possibility of observation of the
nutation-like mode is discussed.",0605126v1
2006-05-22,Kondo-transport spectroscopy of single molecule magnets,"We demonstrate that in a single molecule magnet (SMM) strongly coupled to
electrodes the Kondo effect involves all magnetic excitations. This Kondo
effect is induced by the quantum tunneling of the magnetic moment (QTM).
Importantly, the Kondo temperature $T_K$ can be much larger than the magnetic
splittings. We find a strong modulation of the Kondo effect as function of the
transverse anisotropy parameter or a longitudinal magnetic field. For both
integer and half-integer spin this can be used for an accurate transport
spectroscopy of the magnetic states in low magnetic fields on the order of the
easy-axis anisotropy parameter. We set up a relationship between the Kondo
effects for successive integer and half-integer spins.",0605514v1
2006-06-27,Compressed Silica Aerogels for the Study of Superfluid 3He,"We have performed Small Angle X-ray Scattering (SAXS) on uniaxially strained
aerogels and measured the strain-induced structural anisotropy. We use a model
to connect our SAXS results to anisotropy of the 3He quasiparticle mean free
path in aerogel.",0606702v1
2006-08-19,Spin dynamics in molecular ring nanomagnets: Significant effect of acoustic phonons and magnetic anisotropies,"The nuclear spin-lattice relaxation rate 1/T_1_ is calculated for magnetic
ring clusters by fully diagonalizing their microscopic spin Hamiltonians.
Whether the nearest-neighbor exchange interaction J is ferromagnetic or
antiferromagnetic, 1/T_1_ versus temperature T in ring nanomagnets may be
peaked at around k_B_T=|J| provided the lifetime broadening of discrete energy
levels is in proportion to T^3^. Experimental findings for ferromagnetic and
antiferromagnetic Cu^II^ rings are reproduced with crucial contributions of
magnetic anisotropies as well as acoustic phonons.",0608438v1
2006-08-23,Influence of impurity on isotope coefficient of superconductors,"We study the influence of anisotropy of the impurity potential on isotope
coefficient of an impure superconductor in Born limit. From the isotope
coefficient of non-magnetic and magnetic impurities including an angle-resolved
Fermi surface density of state, anisotropy order parameter and impure
potential, we make the assumption that the form of them are in the harmonic
form and are investigated. Our numerical calculation of isotope coefficient can
fit well with experimental data of high-Tc superconductors.",0608497v1
2006-09-06,"Magnitude and crystalline anisotropy of hole magnetization in (Ga,Mn)As","Theory of hole magnetization Mc in zinc-blende diluted ferromagnetic
semiconductors is developed relaxing the spherical approximation of earlier
approaches. The theory is employed to determine Mc for (Ga,Mn)As over a wide
range of hole concentrations and a number of crystallographic orientations of
Mn magnetization. It is found that anisotropy of Mc is practically negligible
but the obtained magnitude of Mc is significantly greater than that determined
in the spherical approximation. Its sign and value compares favorably with the
results of available magnetization measurements and ferromagnetic resonance
studies.",0609128v1
2006-09-25,"Light-Induced Magnetic Precession in (Ga,Mn)As Slabs: Hybrid Standing-Wave Damon-Eshbach Modes","Coherent oscillations associated with spin precessions were observed in
ultrafast optical experiments on ferromagnetic (Ga,Mn)As films. Using a
complete theoretical description of the processes by which light couples to the
magnetization, values for the exchange and anisotropy constants were obtained
from the field-dependence of the magnon frequencies and the
oscillation-amplitude ratios. Results reveal a relatively large negative
contribution to the energy due to surface anisotropy leading to excitations
that are a mixture of bulk waves and surface modes.",0609646v1
2006-10-23,Mechanism of temperature dependence of the magnetic anisotropy energy in ultrathin Cobalt and Nickel films,"Temperature dependent FMR-measurements of Ni and Co films are analysed using
a microscopic theory for ultrathin metallic systems. The mechanism governing
the temperature dependence of the magnetic anisotropy energy is identified and
discussed. It is reduced with increasing temperature. This behavior is found to
be solely caused by magnon excitations.",0610649v1
2006-10-27,Charge and spin transport in spin valves with anisotropic spin relaxation,"We investigate effects of spin-orbit splitting on electronic transport in a
spin valve consisting of a large quantum dot defined on a two-dimensional
electron gas with two ferromagnetic contacts. In the presence of both structure
inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) a giant anisotropy
in the spin-relaxation times has been predicted. We show how such an anisotropy
affects the electronic transport properties such as the angular
magnetoresistance and the spin-transfer torque. Counterintuitively, anisotropic
spin-relaxation processes sometimes enhance the spin accumulation.",0610770v1
2006-11-30,NMR of superfluid 3He in anisotropic aerogel,"We report on orientation of the order parameter in the 3He-A and 3He-B phases
caused by aerogel anisotropy. In 3He-A we have observed relatively homogeneous
NMR line with an anomalously large negative frequency shift. We can attribute
this effect to an orientation of orbital momentum along the axis of density
anisotropy. The similar orientation effect we have seen in 3He-B. We can
measure the A-phase Leggett frequency, which shows the same energy gap
suppression as in the B-phase. We observe a correlation of A - B transition
temperature and NMR frequency shift.",0612007v1
2006-12-22,Magnon Dispersion and Anisotropies in SrCu$_2$(BO$_3$)$_2$,"We study the dispersion of the magnons (triplet states) in
SrCu$_2$(BO$_3$)$_2$ including all symmetry-allowed Dzyaloshinskii-Moriya
interactions. We can reduce the complexity of the general Hamiltonian to a new
simpler form by appropriate rotations of the spin operators. The resulting
Hamiltonian is studied by both perturbation theory and exact numerical
diagonalization on a 32-site cluster. We argue that the dispersion is dominated
by Dzyaloshinskii-Moriya interactions. We point out which combinations of these
anisotropies affect the dispersion to linear-order, and extract their
magnitudes.",0612598v2
2007-01-19,"Exploiting Locally Imposed Anisotropies in (Ga,Mn)As: a Non-volatile Memory Device","Progress in (Ga,Mn)As lithography has recently allowed us to realize
structures where unique magnetic anisotropy properties can be imposed locally
in various regions of a given device. We make use of this technology to
fabricate a device in which we study transport through a constriction
separating two regions whose magnetization direction differs by 90 degrees. We
find that the resistance of the constriction depends on the flow of the
magnetic field lines in the constriction region and demonstrate that such a
structure constitutes a non-volatile memory device.",0701478v1
2007-02-12,Multicritical behavior of two-dimensional anisotropic antiferromagnets in a magnetic field,"We study the phase diagram and multicritical behavior of anisotropic
Heisenberg antiferromagnets on a square lattice in the presence of a magnetic
field along the easy axis. We argue that, beside the Ising and XY critical
lines, the phase diagram presents a first-order spin-flop line starting from
T=0, as in the three-dimensional case. By using field theory we show that the
multicritical point where these transition lines meet cannot be O(3) symmetric
and occurs at finite temperature. We also predict how the critical temperature
of the transition lines varies with the magnetic field and the uniaxial
anisotropy in the limit of weak anisotropy.",0702273v1
2007-02-17,Magnetic Anisotropy of Co2+ as Signature of Intrinsic Ferromagnetism in ZnO:Co,"We report on the magnetic properties of thoroughly characterized Zn1-xCoxO
epitaxial thin films, with low Co concentration, x=0.003-0.005. Magnetic and
EPR measurements, combined with crystal field theory, reveal that isolated Co2+
ions in ZnO possess a strong single ion anisotropy which leads to an ""easy
plane"" ferromagnetic state when the ferromagnetic Co-Co interaction is
considered. We suggest that the peculiarities of the magnetization process of
this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co
materials.",0702410v1
2007-02-21,Magnetic Anisotropy of Deposited Transition Metal Clusters,"We present results of magnetic torque calculations using the fully
relativistic spin-polarized Korringa-Kohn-Rostoker approach applied to small Co
and Fe clusters deposited on the Pt(111) surface. From the magnetic torque one
can derive among others the magnetic anisotropy energy (MAE). It was found that
this approach is numerically much more stable and also computationally less
demanding than using the magnetic force theorem that allows to calculate the
MAE directly. Although structural relaxation effects were not included our
results correspond reasonably well to recent experimental data.",0702483v1
1993-10-06,Cosmological Rotation of Quantum-Mechanical Origin and Anisotropy of the Microwave Background,"It is shown that rotational cosmological perturbations can be generated in
the early Universe, similarly to gravitational waves. The generating mechanism
is quantum-mechanical in its nature, and the created perturbations should now
be placed in squeezed vacuum quantum states. The physical conditions under
which the phenomenon can occur are formulated. The generated perturbations can
contribute to the large-angular-scale anisotropy of the cosmic microwave
background radiation. An exact formula is derived for the angular correlation
function of the temperature variations caused by the quantum-mechanically
generated rotational perturbations. The multipole expansion begins from the
dipole component. The comparison with the case of gravitational waves is made.",9310011v1
1994-10-18,Cosmological Perturbations of Quantum Mechanical Origin and Anisotropy of the Microwave Background Radiation,"A theory of quantum-mechanical generation of cosmological perturbations is
considered. The conclusion of this study is that if the large-angular-scale
anisotropy in the cosmic microwave background radiation is caused by the
long-wavelength cosmological perturbations of quantum mechanical origin, they
are, most likely, gravitational waves, rather than density perturbations or
rotational perturbations. Some disagreements with previous publications are
clarified. This contribution to the Proceedings is based on Reference~[34].",9410025v1
1996-04-05,Stochastic Processes and Diffusion on Spaces with Local Anisotropy,"The purpose of this work is to extend the formalism of stochastic calculus to
the case of spaces with local anisotropy (modeled as vector bundles with
compatible nonlinear and distinguished connections and metric structures and
containing as particular cases different variants of Kaluza--Klein and
generalized Lagrange and Finsler spaces). We shall examine nondegenerate
diffusions on the mentioned spaces and theirs horizontal lifts.",9604014v1
1996-09-27,The Implications of the Microwave Background Anisotropies for Laser-Interferometer-Tested Gravitational Waves,"The observed microwave background anisotropies in combination with the theory
of quantum mechanically generated cosmological perturbations predict a well
measurable amount of relic gravitational waves in the frequency intervals
tested by LISA and ground-based laser interferometers.",9609062v2
1996-11-29,Inflation for Bianchi IX model,"The influence of Inflation on initial (i.e. at Planck's epoch) large
anisotropy of the Universe is studied, considering a more general metric than
the isotropic one: the locally rotationally symmetric (L.R.S.) Bianchi IX
metric. We find, then, a large set of initial conditions of intrinsic curvature
and shear allowing an inflationary epoch that make the anisotropy negligible.
These are not trivial because of the non-linearity of the Einstein's equations.",9612001v1
1997-11-03,On the role of density inhomogeneity and local anisotropy in the fate of spherical collapse,"We obtain an expression for the active gravitational mass of a collapsing
fluid distribution, which brings out the role of density inhomogeneity and
local anisotropy in the fate of spherical collapse.",9711002v1
1998-06-25,Local anisotropy of space in a frame of reference co-moving with the Earth,"We consider, in the framework of General Relativity, the linear approximation
of the gravitational field of the Earth taking into account its mass, its
quadrupole moment, its shape and its diurnal rotation.
  We conclude that in the frame of reference co-moving with the Earth the local
anisotropy of the space is of the order of $10^{-12}-10^{-13}$ and could be
observed.",9806099v1
2000-01-21,Quantum Evolution of the Bianchi Type I Model,"The behaviour of the flat anisotropic model of the Universe with a scalar
field is explored within the framework of quantum cosmology. The principal
moment of the account of an anisotropy is the presence either negative
potential barrier or positive repelling wall. In the first case occur the above
barrier reflection of the wave function of the Universe, in the second one
there is bounce off a potential wall. The further evolution of the Universe
represents an exponential inflating with fast losses of an anisotropy and
approach to the standard cosmological scenario.",0001065v2
2000-10-06,General Relativistic Contribution to Polarization of the Cosmic Microwave Background Anisotropy,"We solve the wave equation for the electromagnetic field tensors associated
with the CMBR photons in a universe with scalar metric perturbations. We show
that the coupling of the electromagnetic fields with the curvature associated
with the scalar perturbations gives rise to an optical rotation of the
microwave background photons. The magnitude of the gravitationally generated
V-Stokes parameter anisotropy $\Delta_V$, is however very small compared to the
linear polarisation caused by Thomson scattering.",0010022v1
2002-10-22,Bianchi type I universes with dilaton and magnetic fields,"We consider the dynamics of a Bianchi type I spacetime in the presence of
dilaton and magnetic fields. The general solution of the Einstein-Maxwell
dilaton field equations can be obtained in an exact parametric form. Depending
on the numerical values of the parameters of the model there are three distinct
classes of solutions. The time evolution of the mean anisotropy, shear and
deceleration parameter is considered in detail and it is shown that a
magnetic-dilaton anisotropic Bianchi type I geometry does not isotropize, the
initial anisotropy being present in the universe for all times.",0210073v1
2004-03-02,Annual modulation of the Galactic binary confusion noise bakground and LISA data analysis,"We study the anisotropies of the Galactic confusion noise background and its
effects on LISA data analysis. LISA has two data streams of the gravitational
waves signals relevant for low frequency regime. Due to the anisotropies of the
background, the matrix for their confusion noises has off-diagonal components
and depends strongly on the orientation of the detector plane. We find that the
sky-averaged confusion noise level $\sqrt {S(f)}$ could change by a factor of 2
in three months, and would be minimum when the orbital position of LISA is
either around the spring or autumn equinox.",0403014v1
2005-09-07,A locally anisotropic geometrical model of space-time based on CMBR,"We study a locally anisotropic model of General Relativity in the framework
of a more general geometrical structure than the Riemannian one. In this model
the observable anisotropy of the CMBR (WMAP) is represented by a tensor of
anisotropy and it is included in the metric structure of space-time. As well,
some interesting special cases of spaces are considered.",0509020v3
2005-11-30,Indications for a preferred reference frame from an ether-drift experiment,"We present a fully model-independent analysis of the extensive observations
reported by a recent ether-drift experiment in Berlin. No a priori assumption
is made on the nature of a hypothetical preferred frame. We find a remarkable
consistency with an Earth's cosmic motion exhibiting an average declination
angle |\gamma|\sim 43^o and with values of the RMS anisotropy parameter
(1/2-\beta+\delta) that are one order of magnitude larger than the presently
quoted ones. This might represent the first modern indication for a preferred
frame and for a non-zero anisotropy of the speed of light.",0511160v1
2002-05-22,Azimuthal anisotropy of K0s and Lambda prduction at mid-rapidity from Au+Au collisions at root s = 130 GeV,"We report STAR results on the azimuthal anisotropy parameter v2 for strange
particles K0S, L and Lbar at midrapidity in Au+Au collisions at sNN = 130 GeV
at RHIC. The value of v2 as a function of transverse momentum of the produced
particles pt and collision centrality is presented for both particles up to pt
3.0 GeV/c. A strong pt dependence in v2 is observed up to 2.0 GeV/c. The v2
measurement is compared with hydrodynamic model calculations. The physics
implications of the pt integrated v2 magnitude as a function of particle mass
are also discussed.",0205072v1
1996-10-28,One-loop anisotropy for improved actions,"We determine the one-loop correction to the anisotropy factor for the square
Symanzik improved lattice action, extracted fromthe finite volume effective
action for SU(N) gauge theories in the background of a zero-momentum gauge
field. The result is smaller by approximately a factor 3 than the one-loop
correction for the anisotropic Wilson action. We also comment on the
Hamiltonian limit.",9610036v1
1999-08-30,Some effects of the anisotropy in a simple lattice gauge model at finite temperature,"Monte Carlo simulations are carried out on the (3+1)-dimensional Z(2)
anisotropic lattice model, and a new method to simulate extremely anisotropic
lattice systems with discrete symmetries is proposed. Dependence of the
temporal and spatial average plaquette, Wilson loops on the anisotropy
parameter is presented.",9908053v1
2000-06-22,Casimir scaling of SU(3) static potentials,"Potentials between static colour sources in eight different representations
are computed in four dimensional SU(3) gauge theory. The simulations have been
performed with the Wilson action on anisotropic lattices where the renormalised
anisotropies have been determined non-perturbatively. After an extrapolation to
the continuum limit we are able to exclude any violations of the Casimir
scaling hypothesis that exceed 5% for source separations of up to 1 fm.",0006022v2
2001-03-29,Non-perturbative computation of the bubble nucleation rate in the cubic anisotropy model,"At first order phase transitions the transition proceeds through droplet
nucleation and growth. We discuss a lattice method for calculating the droplet
nucleation rate, including the complete dynamical factors. The method is
especially suitable for very strongly suppressed droplet nucleation, which is
often the case in physically interesting transitions. We apply the method to
the 3-dimensional cubic anisotropy model in a parameter range where the model
has a radiatively induced strong first order phase transition, and compare the
results with analytical approaches.",0103036v1
2002-09-03,Dynamical fermions on anisotropic lattices,"We report on our study of two-flavor full QCD on anisotropic lattices using
$O(a)$-improved Wilson quarks coupled with an RG-improved glue. The bare gauge
and quark anisotropies corresponding to the renormalized anisotropy
$\xi=a_s/a_t = 2$ are determined as functions of $\beta$ and $\kappa$, using
the Wilson loop and the meson dispersion relation at several lattice cutoffs
and quark masses.",0209026v2
2003-12-06,Numerical study of staggered fermion on anisotropic lattices,"We study calibration procedures of the staggered quarks on anisotropic
lattices in the quenched approximation and in $N_f = 2$ dynamical simulations.
For the calibration conditions we adopt the hadronic radii $r_0$ and the meson
masses in the temporal and spatial directions. On the quenched lattice, we
calibrate the quark field and compare the result with the result determined
using the meson dispersion relation. In dynamical simulations, we determine the
anisotropy parameters $\gamma_G$ and $\gamma_F$ simultaneously within 1%
accuracy at renormalized anisotropy $\xi = a_s/a_t = 4$.",0312010v1
2006-03-15,Static Quark Potential and the Renormalized Anisotropy on Tadpole Improved Anisotropic Lattices,"Static quark potential is studied using a tadpole improved gauge lattice
action. The scale is set using the potential for a wide range of bare
parameters.
  The renormalized anisotropy of the lattice is also measured.",0603015v1
1992-07-16,"COBE, Inflation, and Light Scalars","Comparison of theobservedanisotropy with that predicted iadiabaticDM models
suggest that much of thserved signal may be due to long wavelenh gravitational
waves. In inflationary models this requires the generation of tensor
fluctuations to be at least comparable to scalar density fltuations. This i is
feasible, but depends sensitively on the inflaton potential. Alternatively,
isocurvature quantum fluctuations in an axion-like field could produce a
quadrupole anisotropy proportional to the gravitational wave anisotropy,k
independent of the inflaton potential. These could also produce large scale
structure with more power on larger scales than their adiabatic counterparts.",9207243v1
1992-10-24,Topological Defect Models of Structure Formation After the COBE Discovery of CMB Anisotropies,"The COBE satellite has discovered anisotropies in the cosmic microwave
background (CMB) consistent with a scale invariant spectrum of density
perturbations. As reviewed in this lecture, topological defect models of
structure formation generically produce such a spectrum. We give a summary of
the cosmic string and global texture models, focusing on distinct observational
signatures in large-scale structure surveys and in the microwave background. It
is shown that the amplitude of the CMB quadrupole detected by COBE is in good
agreement with the predictions of the cosmic string model.",9210261v1
1996-10-22,"$ε$ expansion analysis of very weak first-order transitions in the cubic anisotropy model, Part II","A companion article analyzed very weakly first-order phase transitions in the
cubic anisotropy model using $\eps$ expansion techniques. We extend that
analysis to a calculation of the relative discontinuity of specific heat across
the transition.",9610448v2
2001-12-13,Azimuthal anisotropy of jet quenching at LHC,"We analyze the azimuthal anisotropy of jet spectra due to energy loss of hard
partons in quark-gluon plasma, created initially in nuclear overlap zone in
collisions with non-zero impact parameter. The calculations are performed for
semi-central Pb-Pb collisions at LHC energy.",0112180v1
2003-04-01,Extracting the jet azimuthal anisotropy from higher order cumulants,"We analyze the method for calculation of a coefficient of jet azimuthal
anisotropy without reconstruction of the nuclear reaction plane considering the
higher order correlators between the azimuthal position of jet axis and the
angles of particles not incorporated in the jet. The reliability of this
technique in the real physical situation under LHC conditions is illustrated.",0304009v1
2003-10-31,"Detectability of the Sgr Dwarf Leading Tidal Stream with Auger, EUSO or OWL","We point out that if heavy metastable particles composing the dark matter of
our galaxy are responsible for the ultra-high energy cosmic rays (UHECR) then
the leading tidal stream of the Sagittarius dwarf galaxy could be detected
through UHECR. The signal would be an anisotropy in the UHECR flux smaller than
the telltale anisotropy towards the galactic center that would first establish
unstable dark matter as the origin of the UHECR.",0311001v2
1992-03-12,New Integrable Deformations of Higher Spin Heisenberg-Ising Chains,"We show that the anisotropic Heisenberg-Ising chains with higher spin allow,
for special values of the anisotropy, integrable deformations intimately
related to the theory of quantum groups at roots of unity. For the spin one
case we construct and study the symmetries of the hamiltonian which depends on
a spectral variable belonging to an elliptic curve. One of the points of this
curve yields the Fateev-Zamolodchikov hamiltonian of spin one and anisotropy
$\Delta = \frac{ q^2 + q^{-2}}{2} $ with $q$ a cubic root of unity. In some
other special points the spin degrees of freedom as well as the hamiltonian
splits into pieces governed by a larger symmetry.",9203035v1
1999-12-27,Ground State of the Quantum Symmetric Finite Size XXZ Spin Chain with Anisotropy Parameter $Δ= {1/2}$,"We find an analytic solution of the Bethe Ansatz equations (BAE) for the
special case of a finite XXZ spin chain with free boundary conditions and with
a complex surface field which provides for $U_q(sl(2))$ symmetry of the
Hamiltonian. More precisely, we find one nontrivial solution, corresponding to
the ground state of the system with anisotropy parameter $\Delta = {1/2}$
corresponding to $q^3 = -1$.",9912252v1
2001-05-10,Chiral stabilization of the renormalization group for flavor and color anisotropic current interactions,"We propose an all-orders beta function for current-current interactions in 2d
with flavor anisotropy. When the number of left-moving and right-moving flavors
are unequal, the beta function has a non-trivial fixed point at finite values
of the couplings. We also extend the computation to simple cases with both
flavor and color anisotropy.",0105092v2
1996-07-11,Anisotropy of Growth of the Close-Packed Surfaces of Silver,"The growth morphology of clean silver exhibits a profound anisotropy: The
growing surface of Ag(111) is typically very rough while that of Ag(100) is
smooth and flat. This serious and important difference is unexpected, not
understood, and hitherto not observed for any other metal. Using density
functional theory calculations of self-diffusion on flat and stepped Ag(100) we
find, for example, that at flat regions a hopping mechanism is favored, while
across step edges diffusion proceeds by an exchange process. The calculated
microscopic parameters explain the experimentally reported growth properties.",9607007v1
2000-04-09,A twist localizes three-dimensional patterns,"A mechanism for the localization of spatially periodic, self-organized
patterns in anisotropic media which requires systems extended in all three
spatial dimensions is presented: When the anisotropy axis is twisted the
pattern becomes localized in planes parallel to the anisotropy axis. An
analytic description of the effect is developed and used to interpret recent
experiments in the high-frequency regime of electroconvection by Bohatsch and
Stannarius [Phys. Rev. E {\bf 60}, 5591 (1999)]. The localization width is
found to be of the order of magnitude of the geometrical average of pattern
wavelength and the inverse twist.",0004014v2
2000-05-09,Manifestation of anisotropy persistence in the hierarchies of MHD scaling exponents,"The first example of a turbulent system where the failure of the hypothesis
of small-scale isotropy restoration is detectable both in the `flattening' of
the inertial-range scaling exponent hierarchy, and in the behavior of odd-order
dimensionless ratios, e.g., skewness and hyperskewness, is presented.
Specifically, within the kinematic approximation in magnetohydrodynamical
turbulence, we show that for compressible flows, the isotropic contribution to
the scaling of magnetic correlation functions and the first anisotropic ones
may become practically indistinguishable. Moreover, skewness factor now
diverges as the P\'eclet number goes to infinity, a further indication of
small-scale anisotropy.",0005019v1
1997-11-07,Reconstructing azimuthal distributions in nucleus-nucleus collisions,"Azimuthal distributions of particles produced in nucleus-nucleus collisions
are measured with respect to an estimated reaction plane which, because of
finite multiplicity fluctuations, differs in general from the true reaction
plane. It follows that the measured distributions do not coincide with the true
ones. I propose a general method of reconstructing the Fourier coefficients of
the true azimuthal distributions from the measured ones. This analysis suggests
that the Fourier coefficients are the best observables to characterize
azimuthal anisotropies because, unlike other observables such as the in-plane
anisotropy ratio or the squeeze-out ratio, they can be reconstructed
accurately.",9711003v2
2002-06-10,Azimuthal anisotropy and correlations in the hard scattering regime at RHIC,"Azimuthal anisotropy ($v_2$) and two-particle angular correlations of high
$p_T$ charged hadrons have been measured in Au+Au collisions at
$\sqrt{s_{NN}}$=130 GeV for transverse momenta up to 6 GeV/c, where hard
processes are expected to contribute significantly. The two-particle angular
correlations exhibit elliptic flow and a structure suggestive of fragmentation
of high $p_T$ partons. The monotonic rise of $v_2(p_T)$ for $p_T<2$ GeV/c is
consistent with collective hydrodynamical flow calculations. At $\pT>3$ GeV/c a
saturation of $v_2$ is observed which persists up to $p_T=6$ GeV/c.",0206006v2
2002-08-22,Azimuthal anisotropy of K^0_S and Lambda production at mid-rapidity from Au+Au collisions at root s_NN = 130 GeV,"We report STAR results on the azimuthal anisotropy parameter v2 for strange
particles K0S and Lambda at midrapidity in Au+Au collisions at /s_NN = 130 GeV
at RHIC. The value of v2 as a function of transverse momentum pt and collision
centrality is presented for both particles and compared to model calculations.
A strong pt dependence in v2 is observed up to pt ~2.0 GeV/c where v2 begins to
saturate.",0208013v1
2002-10-02,Two Particle Azimuthal Correlation Measurements in PHENIX,"Two particle azimuthal correlation functions are presented for charged
hadrons produced in Au-Au collisions at RHIC sqrt(s_NN)=200 GeV.The correlation
functions indicate sizeable asymmetries and anisotropies. The trend of the
asymmetries is compatible with the presence of emission patterns associated
with mini-jets. The magnitude and the trend of the differential anisotropies
v_2(p_T) and v_2(N_Part), provide important model constraints.",0210007v2
2002-10-18,Azimuthal Anisotropy of Charged and Identified High $p_T$ Hadrons in Au+Au Collisions at RHIC,"We report new results on $v_2(p_T)$ for Au+Au collisions at
$\sqrt{s_{NN}}$=200 GeV for charged hadrons, pions, kaons, (anti)protons,
$K^0_s$, and $\Lambda$. The analysis is extended to $p_T=12$ GeV/c for charged
hadrons and $p_T=4$ GeV/c for identified particles. A comparison of the
azimuthal anisotropy of charged hadrons measured at \sqrtsNN=130 and 200 GeV is
presented. The $p_T$-dependence of baryon versus meson elliptic flow is
discussed.",0210027v2
2002-11-13,Transverse Dynamics at RHIC,"Studies of <p_{T}>, transverse momentum spectra and anisotropy flow from
nuclear collisions at RHIC indicate early thermalization and strong collective
expansion. We propose a systematic study of the anisotropy parameter $v_2$ and
the transverse momentum distributions of $\phi, \Omega, D^0, \Lambda_C$ and $J
/ \psi$ in order to extract information on partonic collective flow.",0211012v1
2002-12-12,Flow and non-flow event anisotropies at the SPS,"A study of differential elliptic event anisotropies (v_2) of charged
particles and high-pt pions in 158 AGeV/c Pb+Au collisions is presented.
Results from correlations with respect to the event plane and from two-particle
azimuthal correlations are compared. The latter give systematically higher v_2
values at pt>1.2GeV/c providing possibly an evidence of a non-flow semihard
component.",0212013v2
2005-02-26,Effect of Finite Granularity of Detectors on Anisotropy Coefficients,"The coefficients that describe the anisotropy in the azimuthal distribution
of particles are lower when the particles are recorded in a detector with
finite granularity and measures only hits. This arises due to loss of
information because of multiple hits in any channel. The magnitude of this loss
of signal depends both on the occupancy and on the value of the coefficient.
These correction factors are obtained for analysis methods differing in detail,
and are found to be different.",0502023v2
2005-11-21,PHENIX Measurement of Particle Yields at High pT with Respect toReaction Plane in Au+Au Collisions at sqrt(s) = 200 GeV,"The PHENIX Run 4 Au+Au dataset provides a powerful opportunity for exploring
the angular anisotropy of identified particle yields at high pT. Complementing
traditional v2 measurements, we present pi0 yields as a function of angle with
reaction plane, up to pT 10 GeV/c. The centrality dependence of the angular
anisotropy allows us to probe the density and path-length dependence of the
energy loss of hard-scattered partons. We will discuss various mechanisms for
particle production in this high pT region.",0511039v1
2006-07-10,High-pT Particle Production with Respect to the Reaction Plane,"The PHENIX Run4 data-set provides a powerful opportunity for exploring the
angular anisotropy of identified particle yields at high pT. Complementing
traditional v2 measurements, we present pi0 yields as a function of emission
angle with respect to the reaction plane in Au+Au collisions at sqrt(s) = 200
GeV/c. The centrality dependence of the angular anisotropy allows us to probe
the density and path-length dependence of the energy loss of hard-scattered
partons.",0607009v1
1994-12-14,Fragment Flow and the Nuclear Equation of State,"We use the Boltzmann-Uehling-Uhlenbeck model with a momentum-dependent
nuclear mean field to simulate the dynamical evolution of heavy ion collisions.
We re-examine the azimuthal anisotropy observable, proposed as sensitive to the
equation of state of nuclear matter. We obtain that this sensitivity is maximal
when the azimuthal anisotropy is calculated for nuclear composite fragments, in
agreement with some previous calculations. As a test case we concentrate on
semi-central $^{197}{\rm Au}\ +\ ^{197}{\rm Au}$ collisions at 400 $A$ MeV.",9412020v1
2001-08-14,Hydrodynamical analysis of flow at RHIC,"We use a hydrodynamical model to describe the evolution of the collision
system at collision energies sqrt{s}=130 and 200 GeV. At lower sqrt{s}=130 GeV
energy we compare the results obtained assuming fast or slow thermalization
(thermalization times tau_0=0.6 and 4.1 fm/c, respectively) and show that slow
thermalization fails to reproduce the observed anisotropy of particle
distribution. At sqrt{s}=200 GeV collision energy our results show anisotropies
similar to those observed at sqrt{s}=130 GeV.",0108033v1
2004-02-13,Momentum anisotropies in the quark coalescence model,"Based on the quark coalescence model, we derive relations among the momentum
anisotropies of mesons and baryons in relativistic heavy ion collisions from a
given, but arbitrary azimuthal distribution for the partons. Besides the
familiar even Fourier coefficients such as the elliptic flow, we also pay
attention to odd Fourier coefficients such as the directed flow, which has been
observed at finite rapidity even at RHIC energies.",0402049v1
2004-09-30,Disentangling spatial and flow anisotropy,"Two generalisations of the blast-wave model to non-central nuclear collisions
are constructed, and elliptic flow as well as azimuthal dependence of
correlation radii are calculated. Particular attention is paid to how different
azimuthal dependences of transverse flow direction can cause qualitatively
different anisotropic fireballs to give same v_2 as a function of the
transverse momentum. The simultaneous dependence of v_2 and the oscillation of
correlation radii on both spatial and flow anisotropy is studied in great
detail.",0409074v2
2003-06-05,Statistical anisotropy of magnetohydrodynamic turbulence,"Direct numerical simulations of decaying and forced magnetohydrodynamic (MHD)
turbulence without and with mean magnetic field are analyzed by higher-order
two-point statistics. The turbulence exhibits statistical anisotropy with
respect to the direction of the local magnetic field even in the case of global
isotropy. A mean magnetic field reduces the parallel-field dynamics while in
the perpendicular direction a gradual transition towards two-dimensional MHD
turbulence is observed with $k^{-3/2}$ inertial-range scaling of the
perpendicular energy spectrum. An intermittency model based on the Log-Poisson
approach, $\zeta_p=p/g^2 +1 -(1/g)^{p/g}$, is able to describe the observed
structure function scalings.",0306045v1
2003-09-15,Local phase structure of wave dislocation lines: twist and twirl,"Generic wave dislocations (phase singularities, optical vortices) in three
dimensions have anisotropic local structure, which is analysed, with emphasis
on the twist of surfaces of equal phase along the singular line, and the
rotation of the local anisotropy ellipse (twirl). Various measures of twist and
twirl are compared in specific examples, and a theorem is found relating the
(quantised) topological twist and twirl for a closed dislocation loop with the
anisotropy C line index threading the loop.",0309069v2
2004-11-21,Plateau Instability of Liquid Crystalline Cylinder in Magnetic Field,"The capillary instability of a LC cylinder in magnetic field is considered
using an energy approach. The boundary problem is solved in the linear
approximation of the anisotropy $\chi_a$ of the magnetic susceptibility $\chi$.
The effect of anisotropy, in the region $1\gg|\chi|>|\chi_a|\gg \chi^2$, can be
strong enough to counteract and even reverse the tendency of the field to
enhance stabilization by enlarging the cut--off wave number $k_s$ beyond the
conventional one set by Rayleigh.",0411200v1
2004-07-17,Quantum teleportation via two qubit Heisenberg XY chain - Effects of anisotropy and magnetic field,"In this paper, we study the influence of anisotropy on the usefulness, of the
entanglement in a two-qubit Heisenberg XY chain at thermal equilibrium in the
presence of an external magnetic field, as resource for quantum teleportation
via the standard teleportation protocol. We show that the nonzero thermal
entanglement produced by adjusting the external magnetic field strength beyond
some critical strength is a useful resource. We also considered entanglement
teleportation via two two-qubit Heisenberg XY chains.",0407137v1
2007-04-22,Sm2Al: Another ferromagnet with spin-orbital compensation?,"We report the observation of a compensation point in the temperature
dependence of magnetization data of polycrystalline Sm2Al. Magnetization
measurements show that this compound magnetically orders at about 150 K. Below
this temperature, the magnetization data shows a compensation point, which
shifts with field. Hysteresis loops obtained below the compensation temperature
show that the compound possesses exchange anisotropy. Both the exchange
anisotropy field and the coercive field are found to be quite large and
comparable to those of the classical spin-orbit compensated ferromagnet
(Sm,Gd)Al2. The heat capacity data also suggest that there are similarities
between (Sm,Gd)Al2 and Sm2Al.",0704.2864v1
2007-04-23,Dynamical stability for finite quantum spin chains against a time-periodic inhomogeneous perturbation,"We investigate dynamical stability of the ground state against a
time-periodic and spatially-inhomogeneous magnetic field for finite quantum XXZ
spin chains. We use the survival probability as a measure of stability and
demonstrate that it decays as $P(t) \propto t^{-1/2}$ under a certain
condition. The dynamical properties should also be related to the level
statistics of the XXZ spin chains with a constant spatially-inhomogeneous
magnetic field. The level statistics depends on the anisotropy parameter and
the field strength. We show how the survival probability depends on the
anisotropy parameter, the strength and frequency of the field.",0704.2922v1
2007-05-08,Anisotropic probabilistic cellular automaton for a predator-prey system,"We consider a probabilistic cellular automaton to analyze the stochastic
dynamics of a predator-prey system. The local rules are Markovian and are based
in the Lotka-Volterra model. The individuals of each species reside on the
sites of a lattice and interact with an unsymmetrical neighborhood. We look for
the effect of the space anisotropy in the characterization of the oscillations
of the species population densities. Our study of the probabilistic cellular
automaton is based on simple and pair mean-field approximations and explicitly
takes into account spatial anisotropy.",0705.1053v1
2007-05-27,The transition temperature of Ising ferromagnetic thin film with aniaxial anisotropy,"The magnetic properties in the Ising ferromagnetic thin films are studied. By
transfer matrix method, the transition temperatures are calculated as a
function of the intra- and interlayer exchange interactions. The transition
temperatures in the Ising ferromagnetic thin films with uniaxial anisotropy are
also studied. The results show that the transition temperature changes with the
film thickness.",0705.3955v3
2007-06-04,Non-Abelian Plasma Instabilities for Extreme Anisotropy,"Thermalization of quark-gluon plasmas in heavy-ion collisions is a difficult
theoretical problem. One theoretical goal has been to understand the physics of
thermalization in the relatively simplifying limit of arbitrarily high energy
collisions, where the running coupling alpha_s is weak. One of the current
roadblocks to achieving this goal is lack of knowledge about the behavior of
plasma instabilities when particle distributions are highly anisotropic. In
particular, it has not been known how the magnetic fields generated by plasma
instabilities scale with anisotropy. In this paper, we use numerical
simulations in a first attempt to determine this scaling.",0706.0490v1
2007-06-12,Temperature dependence of magnetic anisotropy in bulk and nanoparticles of Pr_0.5Sr_0.5MnO_3,"Nanoparticles (size 20, 40 and 60 nm) of Pr_0.5Sr_0.5MnO_3 are prepared by
sol-gel technique and their magnetic properties are studied using ferromagnetic
resonance and magnetization measurements. A comparison with the properties of
the bulk material shows that the ferromagnetic transition at 265 K remains
unaffected but the anti-ferromagnetic transition at T_N = 150 K disappears in
the nanoparticles. Further, the temperature dependence of magnetic anisotropy
shows a complex behavior, being higher in the nanoparticles at high
temperatures and lower at lower temperatures in comparison with the bulk.",0706.1662v1
2007-06-15,Evolution of Anisotropy of Parton System from Relativistic Heavy-Ion Collisions,"Evolution of anisotropy in momentum and coordinate space of the parton system
produced in relativistic heavy-ion collisions is discussed within the
free-streaming approximation. The momentum distribution evolves from the
prolate shape - elongated along the beam - to the oblate one - squeezed along
the beam. At the same time the eccentricity in the coordinate space, which
occurs at finite values of impact parameter, decreases. It is argued that the
parton system reaches local thermodynamic equilibrium before the momentum
distribution becomes oblate.",0706.2273v3
2007-06-16,Maxwell Equations with Accounting of Tensor Properties of Time,"The Maxwell equations with accounting for tensors properties of time have
been considered. The effects that follow from such consideration are described.
These are the appearance of vacuum polarization, anisotropy of electromagnetic
wave velocity in vacuum, anisotropy of the vacuum dielectric permittivity,
rotation of light polarization plane, as well as the existence of longitudinal
components of electromagnetic wave and the rotational (non-potential) component
of electric field caused by electric charges.",0706.2414v1
2007-06-19,A search for possible anisotropies of cosmic rays with 0.1<E<10 EeV in the region of the Galactic Centre,"We present updated results for anisotropy searches in the direction of the
Galactic Center (GC) at energies in the ranges: 0.1<E<1 EeV and 1<E<10 EeV. We
use data from the Pierre Auger Observatory up to March, 2007. Present analyzes
are therefore based on a substantially larger data set than our previous
published results. A limit on the flux coming from a hypothetical point-like
neutron source at the GC for 1<E<10 EeV was imposed, and searches for extended
excesses were also performed.",0706.2669v2
2007-06-24,Gabay-Toulouse Phase Transition in Heisenberg Spin-Glasses in Three Dimensions,"We examine three-dimensional $\pm J$ Heisenberg models with and without
random anisotropies in a magnetic field. We calculate both the stiffness
exponent $\theta_s$ at absolute zero temperature and spin-glass correlation
lengths for the longitudinal and transverse spin components at finite
temperatures. We suggest that, contrary to a chirality scenario predicted by
Kawamura and his co-workers, a Gabay-Toulouse phase transition occurs when the
anisotropies are absent, although no phase transition occurs when they are
present.",0706.3493v1
2007-06-26,Measuring the Expansion of the Universe Through Changes in the CMB Photosphere,"The expansion of the universe may be observed in ``realtime'' by measuring
changes in the patterns of the anisotropy in the CMB. As the universe ages, the
surface of decoupling--or the CMB photosphere--moves away from us and samples a
different gravitational landscape. The response of the CMB to this new
landscape results in a different pattern than we observe today. The largest
change occurs at l~900. We show that with an array of detectors that we may
envision having in a couple of decades, one can in principle measure the change
in the anisotropy with two high precision measurements separated by a century.",0706.3908v1
2007-06-27,Correlation in the velocity of a Brownian particle induced by frictional anisotropy and magnetic field,"We study the motion of charged Brownian particles in an external magnetic
field. It is found that a correlation appears between the components of
particle velocity in the case of anisotropic friction, approaching
asymptotically zero in the stationary limit. If magnetic field is smaller
compared to the critical value, determined by frictional anisotropy, the
relaxation of the correlation is non-oscillating in time. However, in a larger
magnetic field this relaxation becomes oscillating. The phenomenon is related
to the statistical dependence of the components of transformed random force
caused by the simultaneous influence of magnetic field and anisotropic
dissipation.",0706.4090v2
2007-07-11,Orbital-Driven Electronic Structure Changes and the Resulting Optical Anisotropy of the Quasi-Two-Dimensional Spin Gap Compound La4Ru2O10,"We investigated the electronic response of the quasi-two-dimensional spin gap
compound La4Ru2O10 using optical spectroscopy. We observed drastic changes in
the optical spectra as the temperature decreased, resulting in anisotropy in
the electronic structure of the spin-singlet ground state. Using the
orbital-dependent hopping analysis, we found that orbital ordering plays a
crucial role in forming the spin gap state in the non-one-dimensional material.",0707.1564v1
2007-07-27,"Photo-induced precession of magnetization in ferromagnetic (Ga,Mn)As","Precession of magnetization induced by pulsed optical excitation is observed
in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical
measurements. It appears as complicated oscillations of polarization plane of
linearly-polarized probe pulses, but is reproduced by gyromagnetic theory
incorporating an impulsive change in an effective magnetic field due to changes
in magnetic anisotropy. It is inferred from the shape of the impulse that the
changes in anisotropy result from non-equilibrium carrier population: cooling
of hot photo-carriers and subsequent annihilation of photo-carriers.",0707.4055v2
2007-08-24,The role of pressure anisotropy on the maximum mass of cold compact stars,"We study the physical features of a class of exact solutions for cold compact
anisotropic stars. The effect of pressure anisotropy on the maximum mass and
surface redshift is analysed in the Vaidya-Tikekar model. It is shown that
maximum compactness, redshift and mass increase in the presence of anisotropic
pressures; numerical values are generated which are in agreement with
observation.",0708.3305v1
2007-08-24,On surface tension for compact stars,"In an earlier treatment it was demonstrated that general relativity gives
higher values of surface tension in strange stars with quark matter than
neutron stars.We generate the modified Tolman-Oppenheimer-Volkoff equation to
incorporate anisotropic matter and use this to show that pressure anisotropy
provides for a wide range of behaviour in the surface tension than is the case
with isotropic pressures. In particular it is possible that anisotropy
drastically decreases the value of the surface tension.",0708.3317v1
2007-08-27,Anisotropic conductivity of disordered 2DEGs due to spin-orbit interactions,"We show that the conductivity tensor of a disordered two-dimensional electron
gas becomes anisotropic in the presence of both Rashba and Dresselhaus
spin-orbit interactions (SOI). This anisotropy is a mesoscopic effect and
vanishes with vanishing charge dephasing time. Using a diagrammatic approach
including zero, one, and two-loop diagrams, we show that a consistent
calculation needs to go beyond a Boltzmann equation approach. In the absence of
charge dephasing and for zero frequency, a finite anisotropy \sigma_{xy}
e^2/lhpf arises even for infinitesimal SOI.",0708.3504v2
2007-09-20,Spin wave resonances in La_{0.7}Sr_{0.3}MnO_{3} films: measurement of spin wave stiffness and anisotropy field,"We studied magnetic field dependent microwave absorption in epitaxial
La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films using an X-band Bruker ESR spectrometer. By
analyzing angular and temperature dependence of the ferromagnetic and spin-wave
resonances we determine spin-wave stiffness and anisotropy field. The spin-wave
stiffness as found from the spectrum of the standing spin-wave resonances in
thin films is in fair agreement with the results of inelastic neutron
scattering studies on a single crystal of the same composition [Vasiliu-Doloc
et al., J. Appl. Phys. \textbf{83}, 7343 (1998)].",0709.3204v2
2007-10-12,Probing Non-Gaussianity In The Cosmic Microwave Background Anisotropies: One Point Distribution Function,"We analyze WMAP 3 year data using the one-point distribution functions to
probe the non-Gaussianity in the Cosmic Microwave Background (CMB) Anisotropy
data. Computer simulations are performed to determine the uncertainties of the
results. We report the non-Gaussianity parameter f_NL is constrained to
26<f_NL<82 for Q-band, 12<f_NL<67 for V-band, 7<f_NL<64 for W-band and
23<f_NL<75 for Q+V+W combined data at 95% confidence level (CL).",0710.2371v3
2007-11-05,Magnetic excitations in vanadium spinels,"We study magnetic excitations in vanadium spinel oxides AV$_2$O$_4$ (A=Zn,
Mg, Cd) using two models: first one is a superexchange model for vanadium S=1
spins, second one includes in addition spin-orbit coupling, and crystal
anisotropy. We show that the experimentally observed magnetic ordering can be
obtained in both models, however the orbital ordering is different with and
without spin-orbit coupling and crystal anisotropy. We demonstrate that this
difference strongly affects the spin-wave excitation spectrum above the
magnetically ordered state, and argue that the neutron measurement of such
dispersion is a way to distinguish between the two possible orbital orderings
in AV$_2$O$_4$.",0711.0732v1
2007-11-06,Quantum Weibel Instability,"The Weibel instability is analyzed for quantum plasmas described by the
Wigner-Maxwell model. For a suitable class of electromagnetic potentials, the
Wigner-Maxwell system is linearized yielding a general dispersion relation for
transverse electromagnetic waves. For a double Gaussian equilibrium with
temperature anisotropy, the derived dispersion relation generalizes the
classical Weibel instability equation. More detailed analytical results are
obtained for the cases of extreme temperature anisotropy and for a
three-dimensional water bag distribution. In all cases, quantum effects tends
to weaken or suppress the instability. Applications are discussed for dense
astrophysical objects like white dwarfs and neutron stars as well as for
tunnel-ionized plasmas with controllable perpendicular plasma temperature.",0711.0851v1
2007-11-19,Azimuthal anisotropy of direct photons,"The electromagnetic bremsstrahlung produced by a quark interacting with
nucleons or nuclei is azimuthally asymmetric. In the light-cone dipole approach
this effect is related to the orientation dependent dipole cross section. Such
a radiation anisotropy is expected to contribute to the azimuthal asymmetry of
direct photons in pA and AA collisions, as well as in DIS and in the production
of dileptons.",0711.3010v4
2007-12-03,In-plane magnetic field phase diagram of superconducting Sr2RuO4,"We develop the Ginzburg - Landau theory of the upper critical field in the
basal plane of a tetragonal multiband metal in two-component superconducting
state. It is shown that typical for the two component superconducting state the
upper critical field basal plane anisotropy and the phase transition splitting
still exist in a multiband case. However, the value of anisotropy can be
effectively smaller than in the single band case. The results are discussed in
the application to the superconducting Sr2RuO4.",0712.0286v3
2007-12-23,Orthogonalization Properties of Linear Deterministic Polarization Elements,"The conditions under which a linear anisotropic polarization element
orthogonalizes several polarization states of input totally polarized light
were studied in the paper. The criterion for orthogonalization was obtained in
the form of inequality for anisotropy parameters. Orthogonalization properties
of polarization elements with the most important anisotropy types were
investigated. The parameters under which orthogonalization occurs, and the
states that are orthogonalized were found. The loci of these states on the
Poincare sphere were given for sake of illustration in each case.",0712.3888v1
2008-01-04,Diagonal charge modulation in the insulating La$_{2-x}$Sr$_x$CuO$_4$,"We show that, due to the Dzyaloshinskii-Moriya and the XY anisotropies, the
disordered diagonal spin spiral in the insulating La$_{2-x}$Sr$_x$CuO$_4$
generates a diagonal charge density wave (CDW) with the wave vector twice of
that of the spin spiral. The amplitude of the CDW depends on values of the
anisotropies, the doping level, and on the density of states at the chemical
potential. Based on available experimental data we estimate that for 4% doping
the amplitude of CDW is about 1/10 of the doping level. We believe that this
mechanism explains the CDW observed recently in Zn-codoped detwinned
La$_{2-x}$Sr$_x$CuO$_4$.",0801.0614v1
2008-01-09,Anisotropy in magnetic and transport properties of Fe1-xCoxSb2,"Anisotropic magnetic and electronic transport measurements were carried out
on large single crystals of Fe1-xCoxSb2 (0<= x <=1). The semiconducting state
of FeSb2 evolves into metallic and weakly ferromagnetic by substitution of Fe
with Co for x<0.5. Further doping induces structural transformation from
orthorhombic Pnnm structure of FeSb2 to monoclinic P21/c structure of CoSb2
where semiconducting and diamagnetic ground state is restored again. Large
magnetoresistance and anisotropy in electronic transport were observed.",0801.1350v2
2008-01-11,Anisotropy of Electrical Transport and Superconductivity in Metal Chains of Nb2Se3,"In this work we have shown bulk superconductivity and studied the anisotropy
in both the normal and superconducting states in quasi-1D conductor Nb2Se3.
Electron - electron Umklapp scattering dominates electronic transport along the
direction of Nb metal chains as well as perpendicular to it. The
superconducting state is rather anisotropic with possible multi - band
features.",0801.1682v1
2008-01-12,Critical fluctuations and random-anisotropy glass transition in nematic elastomers,"We carry out a detailed deuterium NMR study of local nematic ordering in
polydomain nematic elastomers. This system has a close analogy to the
random-anisotropy spin glass. We find that, in spite of the quadrupolar nematic
symmetry in 3-dimensions requiring a first-order transition, the order
parameter in the quenched ``nematic glass'' emerges via a continuous phase
transition. In addition, by a careful analysis of the NMR line shape, we deduce
that the local director fluctuations grow in a critical manner around the
transition point. This could be the experimental evidence for the Aizenman-Wehr
theorem about the quenched impurities changing the order of discontinuous
transition.",0801.1894v1
2008-01-20,Strain-induced Fermi contour anisotropy of GaAs 2D holes,"We report measurements of magneto-resistance commensurability peaks, induced
by a square array of anti-dots, in GaAs (311)A two-dimensional holes as a
function of applied in-plane strain. The data directly probe the shapes of the
Fermi contours of the two spin subbands that are split thanks to the spin-orbit
interaction and strain. The experimental results are in quantitative agreement
with the predictions of accurate energy band calculations, and reveal that the
majority spin-subband has a severely distorted Fermi contour whose anisotropy
can be tuned with strain.",0801.3106v1
2008-01-29,Interplay among the azimuthally dependent HBT radii and the elliptic flow,"We present a calculation of the elliptic flow and azimuthal dependence of the
correlation radii in the ellipsoidally symmetric generalization of the
Buda-Lund model. The elliptic flow is shown to depend only on the flow
anisotropy while in case of correlation radii both flow and space anisotropy
play an important role in determining their azimuthal oscillation. We also
outline a simple procedure for determining the parameters of the model from
data.",0801.4434v2
2008-02-08,Theory of reduced singlet pairing without the underlying state of charge stripes in the high-temperature superconductor YBa_2Cu_3O_6.45,"Recently, a strongly enhanced xy anisotropy of magnetic excitations was
observed in YBa_2Cu_3O_y (YBCO_y) with y=6.45 and Tc=35 K [Science 319, 597
(2008)]. Unlike the observation in YBCO_6.6 and YBCO_6.85, the anisotropy grows
to be pronounced at lower temperature and at lower energy, and is not
suppressed by the onset of superconductivity. We propose that the effect of
singlet pairing is substantially reduced in YBCO_6.45. This reduction
concomitantly enhances an order competing with singlet pairing, a strong
tendency of the so-called d-wave Pomeranchuk instability, leading to the
magnetic excitations observed experimentally.",0802.1149v2
2008-02-25,Lecture Notes on CMB Theory: From Nucleosynthesis to Recombination,"These lecture notes comprise an informal but pedagogical introduction to the
well established physics and phenomenology of the cosmic microwave background
(CMB) between big bang nucleosynthesis and recombination. The dominant
properties of the spectrum, temperature anisotropy and polarization anisotropy
of the CMB all arise from this period. We review the physical processes
involved and show how they are related to the observed phenomenology.",0802.3688v1
2008-03-06,Swap Action in a Solid-State Controllable Anisotropic Heisenberg Model,"Correct swap action can be realized via the control of the anisotropic
Heisenberg interaction in solid-state quantum systems. The conditions of
performing a swap are derived by the dynamics of arbitrary bipartite pure
state. It is found that swap errors can be eliminated in the presence of
symmetric anisotropy. In realistic quantum computers with unavoidable
fluctuations, the gate fidelity of swap action is estimated. The scheme of
quantum computation via the anisotropic Heisenberg interaction is implemented
in a one dimensional quantum dots. The slanting and static magnetic field can
be used to adjust the anisotropy.",0803.0767v1
2008-03-07,Strong electron-phonon interaction in multiband superconductors,"We discuss the effects of anisotropy on superconducting critical temperature
and order parameter in a strongly coupled regime. The multiband representation
is used as a model for anisotropy. We show that strong coupling effects in
multiband superconductors lead to pair-breaking due to interband coupling
because soft phonon modes play the same role as usual impurities. This effect
makes the order parameters in different bands equal to each other and limits
the upper bound on critical temperature.",0803.1103v1
2008-03-08,The Impact of Stochastic Primordial Magnetic Fields on the Scalar Contribution to Cosmic Microwave Background Anisotropies,"We study the impact of a stochastic background of primordial magnetic fields
on the scalar contribution of CMB anisotropies and on the matter power
spectrum. We give the correct initial conditions for cosmological perturbations
and the exact expressions for the energy density and Lorentz force associated
to the stochastic background of primordial magnetic fields, given a power-law
for their spectra cut at a damping scale. The dependence of the CMB temperature
and polarization spectra on the relevant parameters of the primordial magnetic
fields is illustrated.",0803.1246v1
2008-04-22,Anisotropic spectra of acoustic type turbulence,"We consider the problem of spectra for acoustic type of turbulence generated
by shocks being randomly distributed in space. We show that for turbulence with
a weak anisotropy such spectra have the same dependence in $k$-space as the
Kadomtsev-Petviashvili (KP) spectrum: $E(k)\sim k^{-2}$. However, the frequency
spectrum has always the falling $\sim \omega^{-2}$, independently on
anisotropy. In the strong anisotropic case the energy distribution relative to
wave vectors takes anisotropic dependence forming in the large $% k $ region
the spectra of the jet type.",0804.3540v1
2008-04-26,"Comments on gap anisotropy and nodal constant Fermi velocity in a superconductor, BSCCO","On the basis of both the inhomogeneity of a superconductor, BSCCO-2212, and
the effect of measurement, we reveal that an anomalously large gap anisotropy
known as evidence of dx2-y2-wave symmetry [Phys. Rev. Lett. 70 (1993) 1553] is
not intrinsic, and that the constant Fermi velocity at node as an unsolved
problem [Nature 423 (2003) 398] is due to the dx2-y2-wave insulator-metal
transition.",0804.4209v1
2008-05-13,Correlation of the HIghest Energy Cosmic Rays with the Supergalactic Plane,"We examine the anisotropy of the arrival directions of twenty seven ultra
high energy cosmic rays detected by the Pierre Auger Collaboration. We confirm
the anisotropy of the arrival directions of these events and find a significant
correlation with the updated definition of the supergalactic plane at distances
up to 70 Mpc, A Monte Carlo calculation of isotropic source distribution
suggests a chance probability for isotropic event arrival direction
distribution of 2-6$\times10^{-4}$.",0805.1746v2
2008-05-14,Giant optical anisotropy in cylindrical self-assembled InAs/GaAs quantum rings,"Using a single-particle atomistic pseudopotential method followed by a
many-particle configuration interaction method, we investigate the geometry,
electronic structure and optical transitions of a self-assembled InAs/GaAs
quantum ring (QR), changing its shape continously from a lens-shaped quantum
dot (QD) to a nearly one dimensional ring. We find that the biaxial strain in
the ring is strongly asymmetric in the plane perpendicular to the QR growth
direction, leading to giant optical anisotropy.",0805.1962v1
2008-05-14,Enhancement of evanescent waves inside media with extreme optical anisotropy,"Significant enhancement of evanescent spatial harmonics inside the slabs of
media with extreme optical anisotropy is revealed. This phenomenon results from
the pumping of standing waves and has the feature of being weakly sensitive to
the material losses. Such characteristics may enable subwavelength imaging at
considerable distances away from the objects.",0805.2080v3
2008-06-05,Jet quenching and broadening: the transport coefficient $\hat{q}$ in an anisotropic plasma,"The jet quenching parameter $\hat{q}$ is analyzed for a quark jet propagating
in an anisotropic plasma. The momentum anisotropy is calculated at high
temperature of the underlying quark-gluon plasma. $\hat{q}$ is explicitly
estimated in leading-logarithmic approximation by the broadening of the
massless quark interacting via gluon exchange. A plasma instability is present.
Strong indications are found that $\hat{q}$ is increasing with increasing
anisotropy. Possible implications for the saturation scale $Q_s$ in $A-A$
collisions are pointed out.",0806.0954v1
2008-06-16,Spontaneous order in the highly frustrated spin-1/2 Ising-Heisenberg model on the triangulated Kagome lattice due to the Dzyaloshinskii-Moriya anisotropy,"The spin-1/2 Ising-Heisenberg model on the triangulated Kagome
(triangles-in-triangles) lattice is exactly solved by establishing a precise
mapping correspondence to the simple spin-1/2 Ising model on Kagome lattice. It
is shown that the disordered spin liquid state, which otherwise occurs in the
ground state of this frustrated spin system on assumption that there is a
sufficiently strong antiferromagnetic intra-trimer interaction, is eliminated
from the ground state by arbitrary but non-zero Dzyaloshinskii-Moriya
anisotropy.",0806.2568v1
2008-06-25,Anomalous Anisotropic Magnetoresistance in Heavy-Fermion PrFe4P12,"We have investigated the anisotropy of the magnetoresistance in the Pr-based
HF compound PrFe4P12. The large anisotropy of effective mass and its strong
field dependence have been confirmed by resistivity measurements. Particularly
for H||[111], where the effective mass is most strongly enhanced, the non-Fermi
liquid behavior has been observed. Also, we have found the angular dependence
of the magnetoresistance sharply enhanced at H||[111], which is evidently
correlated with both the non-Fermi liquid behavior and the high-field ordered
state (B-phase).",0806.4047v1
2008-07-16,Analytical solution of the equation of motion for a rigid domain wall in a magnetic material with perpendicular anisotropy,"This paper reports the solution of the equation of motion for a domain wall
in a magnetic material which exhibits high magneto-crystalline anisotropy.
Starting from the Landau-Lifschitz-Gilbert equation for field-induced motion,
we solve the equation to give an analytical expression, which specifies the
domain wall position as a function of time. Taking parameters from a Co/Pt
multilayer system, we find good quantitative agreement between calculated and
experimentally determined wall velocities, and show that high field uniform
wall motion occurs when wall rigidity is assumed.",0807.2604v3
2008-07-28,Gap anisotropy and universal pairing scale in a spin fluctuation model for cuprates,"We consider the evolution of d-wave pairing, mediated by nearly critical spin
fluctuations, with the coupling strength. We show that the onset temperature
for pairing, T*, smoothly evolves between weak and strong coupling, passing
through a broad maximum at intermediate coupling. At strong coupling, T* is of
order the magnetic exchange energy J. We argue that for all couplings, pairing
is confined to the vicinity of the Fermi surface. We also find that thermal
spin fluctuations only modestly reduce T*, even at criticality, but they
substantially smooth the gap anisotropy. The latter evolves with coupling,
being the largest at weak coupling.",0807.4404v1
2008-08-11,Superhorizon Perturbations and the Cosmic Microwave Background,"Superhorizon perturbations induce large-scale temperature anisotropies in the
cosmic microwave background (CMB) via the Grishchuk-Zel'dovich effect. We
analyze the CMB temperature anisotropies generated by a single-mode adiabatic
superhorizon perturbation. We show that an adiabatic superhorizon perturbation
in a LCDM universe does not generate a CMB temperature dipole, and we derive
constraints to the amplitude and wavelength of a superhorizon potential
perturbation from measurements of the CMB quadrupole and octupole. We also
consider constraints to a superhorizon fluctuation in the curvaton field, which
was recently proposed as a source of the hemispherical power asymmetry in the
CMB.",0808.1570v1
2008-08-18,Quantum teleportation via a two-qubit Heisenberg XXZ chain-effects of anisotropy and magnetic field,"We study quantum teleportation via a two-qubit Heisenberg XXZ chain under an
inhomogeneous magnetic field. We first consider entanglement teleportation, and
then focus on the teleportation fidelity under different conditions. The
effects of anisotropy and the magnetic field, both uniform and inhomogeneous,
are discussed. We also find that, though entanglement teleportation does
require an entangled quantum channel, a nonzero critical value of minimum
entanglement is not always necessary.",0808.2406v1
2008-08-21,On the role of pressure anisotropy for relativistic stars admitting conformal motion,"We investigate the spacetime of anisotropic stars admitting conformal motion.
The Einstein field equations are solved using different ansatz of the surface
tension. In this investigation, we study two cases in details with the
anisotropy as: [1] $p_t = n p_r$ [2] $p_t - p_r = \frac{1}{8
\pi}(\frac{c_1}{r^2} + c_2)$ where, n, $c_1$ and $c_2$ are arbitrary constants.
The solutions yield expressions of the physical quantities like pressure
gradients and the mass.",0808.2927v3
2008-08-26,Spin-Orbit Integrated Ground State and Magnetic Anisotropy in Sr$_2$IrO$_4$,"We present a microscopic model for the anisotropic exchange interactions in
Sr$_{2}$IrO$_{4}$. A direct construction of Wannier functions from
first-principles calculations proves the $j_{\mathrm{eff}}$=1/2 character of
the spin-orbit integrated states at the Fermi level. An effective
$j_{\mathrm{eff}}$-spin Hamiltonian explains the observed weak ferromagnetism
and anisotropy of antiferromagnetically ordered magnetic state, which arise
naturally from the $j_{\mathrm{eff}}$=1/2 state with a rotation of IrO$_{6}$
octahedra. It is suggested that Sr$_{2}$IrO$_{4}$ is a unique class of
materials with effective exchange interactions in the spin-orbital Hilbert
space.",0808.3491v2
2008-08-30,Control of Domain Wall Position by Electrical Current in Structured Co/Ni Wire with Perpendicular Magnetic Anisotropy,"We report the direct observation of the current-driven domain wall (DW)
motion by magnetic force microscopy in a structured Co/Ni wire with
perpendicular magnetic anisotropy. The wire has notches to define the DW
position. It is demonstrated that single current pulses can precisely control
the DW position from notch to notch with high DW velocity of 40 m/s.",0809.0047v1
2008-10-31,Optical Anisotropy of Electronic Excitations in Elliptical Quantum Dots,"The authors report that anisotropic confining potentials in laterally-coupled
semiconductor quantum dots (QDs) have large impacts in optical transitions and
energies of inter-shell collective electronic excitations. The observed
anisotropies are revealed by inelastic light scattering as a function of the
in-plane direction of light polarization and can be finely controlled by
modifying the geometrical shape of the QDs. These experiments show that the
tuning of the QD confinement potential offers a powerful method to manipulate
electronic states and far-infrared inter-shell optical transitions in quantum
dots.",0810.5649v1
2008-11-04,Three-Component Fermi Gas in a one-dimensional Optical Lattice,"We investigate the effect of the anisotropy between the s-wave scattering
lengths of a three-component atomic Fermi gas loaded into a one-dimensional
optical lattice. We find four different phases which support trionic
instabilities made of bound states of three fermions. These phases distinguish
themselves by the relative phases between the 2$k_F$ atomic density waves
fluctuations of the three species. At small enough densities or strong
anisotropies we give further evidences for a decoupling and the stabilization
of more conventional BCS phases. Finally our results are discussed in light of
a recent experiment on $^{6}$Li atoms.",0811.0555v2
2008-11-05,Quantum Phase Diagram and Excitations for the One-Dimensional S=1 Heisenberg Antiferromagnet with Single-Ion Anisotropy,"We investigate the zero-temperature phase diagram of the one-dimensional S=1
Heisenberg antiferromagnet with single-ion anisotropy. By employing high-order
series expansions and quantum Monte Carlo simulations we obtain accurate
estimates for the critical points separating different phases in the quantum
phase diagram. Additionally, excitation spectra and gaps are obtained.",0811.0646v2
2008-11-07,Translational Invariance and the Anisotropy of the Cosmic Microwave Background,"Primordial quantum fluctuations produced by inflation are conventionally
assumed to be statistically homogeneous, a consequence of translational
invariance. In this paper we quantify the potentially observable effects of a
small violation of translational invariance during inflation, as characterized
by the presence of a preferred point, line, or plane. We explore the imprint
such a violation would leave on the cosmic microwave background anisotropy, and
provide explicit formulas for the expected amplitudes $<a_{lm}a_{l'm'}^*>$ of
the spherical-harmonic coefficients.",0811.1086v3
2008-11-11,Anisotropy due to Brans-Dicke Theory,"It is well known that the viscous Bianchi type-I metric of the Kasner form is
not able to describe an anisotropic universe, which satisfies the second law of
thermodynamics and the dominant energy condition in Einstein's theory of
gravity. We investigate this problem in Brans-Dicke theory of gravity using the
Bianchi type-I metric with the perfect fluid. We show that it is possible to
have the dominant energy condition and the growth of entropy in this model.
Also we apply this model to explain the anomaly concerning the low quadrupole
amplitude of the angular power spectrum of the temperature anisotropy observed
in WMAP data.",0811.1643v1
2008-11-13,Effects of anisotropy on optimal dense coding,"We study optimal dense coding with thermal entangled states of a two-qubit
anisotropic \emph{XXZ} model and a Heisenberg model with Dzyaloshinski-Moriya
(DM) interactions. The DM interaction is another kind of anisotropic
antisymmetric exchange interaction. The effects of these two kinds of
anisotropies on dense coding are studied in detail for both the
antiferromagnetic and ferromagnetic cases. For the two models, we give the
conditions that the parameters of the models have to satisfy for a valid dense
coding. We also found that even though there is entanglement, it is unavailable
for our optimal dense coding, which is the same as entanglement teleportation.",0811.2017v1
2008-11-13,Magnetoelastic coupling in BaTiO3-based multiferroic structures,"Analytical expressions for the magnetoelastic anisotropy constants of cubic
magnetic systems are derived for rectangular and oblique distortions
originating from epitaxial growth on substrates with lower crystal symmetry. In
particular, the temperature variation of the magnetic properties of magnetic
films grown on barium titanate (BaTiO3) substrates are explained in terms of
strain-induced magnetic anisotropies caused by the temperature dependent phase
transitions of BaTiO3. Our results quantify the experimental observations in
ferromagnet/\bto-based structures, which have been proposed as templates for
magnetoelectric composite heterostructures.",0811.2146v1
2008-11-26,Gate control of a quantum dot single-electron spin in realistic confining potentials: anisotropy effects,"Among recent proposals for next-generation, non-charge-based logic is the
notion that a single electron can be trapped and its spin can be manipulated
through the application of gate potentials. In this paper, we present numerical
simulations of such spins in single electron devices for realistic (asymmetric)
confining potentials in two-dimensional electrostatically confined quantum
dots. Using analytical and numerical techniques we show that breaking the
in-plane rotational symmetry of the confining potential leads to a significant
effect on the tunability of the g-factor with applied gate potentials. In
particular, anisotropy extends the range of tunability to larger quantum dots.",0811.4201v1
2008-12-10,Magnetic Bianchi I Universe in Loop Quantum Cosmology,"We examine the dynamical consequences of homogeneous cosmological magnetic
fields in the framework of loop quantum cosmology. We show that a big-bounce
occurs in a collapsing magnetized Bianchi I universe, thus extending the known
cases of singularity-avoidance. Previous work has shown that perfect fluid
Bianchi I universes in loop quantum cosmology avoid the singularity via a
bounce. The fluid has zero anisotropic stress, and the shear anisotropy in this
case is conserved through the bounce. By contrast, the magnetic field has
nonzero anisotropic stress, and shear anisotropy is not conserved through the
bounce. After the bounce, the universe enters a classical phase. The addition
of a dust fluid does not change these results qualitatively.",0812.1889v1
2008-12-13,A Novel Temperature-Induced Magnetization Transition in Pt/Co/Pt Sandwiches,"It is found in the Pt/Co/Pt(111) sandwiches that perpendicular magnetic
anisotropy weakens associated with the dramatic magnetization enhancement as
the temperature decreases below a critical temperature, T_cri, which increases
with the Pt overlayer thickness t_Pt. For the sandwich with enough thick Pt
overlayer, it trends to an unusual state with weak perpendicular magnetic
anisotropy in the absence of obvious easy direction behavior at low
temperature. It suggests that Pt is more significantly polarized in the film
with thicker Pt overlayer. The results reveal the strong influence of both
thick nonmagnetic coverage and temperature on the electronic structure of the
Pt/Co/Pt(111) sandwich.",0812.2512v1
2009-01-11,Magnetic soliton transport over topological spin texture in chiral helimagnet with strong easy-plane anisotropy,"We show the existence of an isolated soliton excitation over the topological
ground state configuration in chiral helimagnet with the Dzyaloshinskii-Moryia
exchange and the strong easy-plane anisotropy. The magnetic field perpendicular
to the helical axis stabilizes the kink crystal state which plays a role of
""topological protectorate"" for the traveling soliton with a definite
handedness. To find new soliton solution, we use the B\""{a}cklund
transformation technique. It is pointed out that the traveling soliton carries
the magnon density and a magnetic solition transport may be realized.",0901.1423v1
2009-01-14,Spin-1 Heisenberg antiferromagnetic chain with exchange and single-ion anisotropies,"Using density matrix renormalization group calculations, ground state
properties of the spin-1 Heisenberg chain with exchange and single-ion
anisotropies in an external field are studied. Our findings confirm and refine
recent results by Sengupta and Batista, Physical Review Letters 99, 217205
(2007) (2007), on the same model applying Monte Carlo techniques. In
particular, we present evidence for two types of biconical (or supersolid) and
for two types of spin-flop (or superfluid) structures. Basic features of the
quantum phase diagram may be interpreted qualitatively in the framework of
classical spin models.",0901.2081v2
2009-01-15,On Anisotropy of Ultra-High Energy Cosmic-Rays,"We briefly summarize our study on anisotropy of Ultra-High Energy Cosmic-Rays
(UHECRs), in which we define a statistics that measures the correlation between
UHECRs and Large Scale Structure (LSS). We also comment here on recently
published paper by Koers and Tinyakov that compared our statistics to improved
KS statistics.",0901.2256v2
2009-01-21,"Lateral magnetic anisotropy superlattice out of a single (Ga,Mn)As layer","We use lithographically induced strain relaxation to periodically modulate
the magnetic anisotropy in a single (Ga,Mn)As layer. This results in a lateral
magnetoresistance device where two non-volatile magnetic states exist at zero
external magnetic field with resistances resulting from the orientation of two
lithographically defined regions in a single and contiguous layer.",0901.3210v1
2009-03-12,Simulation of a spin-wave instability from atomistic spin dynamics,"We study the spin dynamics of a Heisenberg model at finite temperature in the
presence of an external field or a uniaxial anisotropy. For the case of the
uniaxial anisotropy our simulations show that the macro moment picture breaks
down. An effect which we refer to as a spin-wave instability (SWI) results in a
non-dissipative Bloch-Bloembergen type relaxation of the macro moment where the
size of the macro moment changes, and can even be made to disappear. This
relaxation mechanism is studied in detail by means of atomistic spin dynamics
simulations.",0903.2186v1
2009-03-25,On the Experimental Substantiation of Anisotropy of Inertial Mass of Body in the Earth Gravitation Field,"On the basis of the field concept of gravitation and gravitational analogue
of the Faradays induction law the difference of inertial mass of a body at its
accelerated movement in horizontal and vertical directions relative to the
Earth is shown. For an illustration of such a distinction the results of
comparison of a motion of balance mechanical watch at horizontal and vertical
orientations of balance axis are given. The expediency of statement of
precision mechanical experiments with measurement of anisotropy of the inertial
mass is noted, allowing to estimate the validity of the field approach in the
description of gravitation.",0903.4433v1
2009-03-30,Lecture notes on the physics of cosmic microwave background anisotropies,"We review the theory of the temperature anisotropy and polarization of the
cosmic microwave background (CMB) radiation, and describe what we have learned
from current CMB observations. In particular, we discuss how the CMB is being
used to provide precise measurements of the composition and geometry of the
observable universe, and to constrain the physics of the early universe. We
also briefly review the physics of the small-scale CMB fluctuations generated
during and after the epoch of reionization, and which are the target of a new
breed of arcminute-resolution instruments.",0903.5158v1
2009-03-30,Origin of Gap Anisotropy in Spin Fluctuation Models of the Fe-pnictides,"We discuss the large gap anisotropy found for the A1g (s-wave) state in RPA
spin-fluctuation and functional renormalization group calculations and show how
the simple arguments leading to isotropic sign-switched s-wave states in these
systems need to be supplemented by a consideration of pair scattering within
Fermi surface sheets and between the individual electron sheets as well. In
addition, accounting for the orbital makeup of the states on the Fermi surface
is found to be crucial.",0903.5216v1
2009-04-01,Current-induced microwave excitation of a domain wall confined in a magnetic wire with bi-axial anisotropy,"We studied the current-induced magnetization dynamics of a domain wall
confined in a magnetic wire with bi-axial anisotropy. We showed that above the
threshold current density, breathing-mode excitation, where the thickness of
the domain wall oscillates, is induced by spin-transfer torque. We found that
the breathing-mode can be applied as a source of microwave oscillation because
the resistance of the domain wall is a function of the domain wall thickness.
In a current sweep simulation, the frequency of the breathing-mode exhibits
hysteresis because of the confinement.",0904.0044v1
2009-05-14,Plasticity-induced structural anisotropy of silica glass,"Amorphous silica density at ambient pressure is known to depend on thermal
history (through the quenching rate) but also, at room temperature, on the
maximum pressure applied in the past. Here we show that beyond density, a
mechanical loading can endow the structure with an orientational order.
Molecular dynamics simulations show evidence that amorphous silica develops a
permanent anisotropic structure after extended shear plastic flow. This
anisotropy which survives for an unstressed specimen is revealed markedly by
the fabric tensor computed over the Si-O-Si orientations, albeit the SiO4
tetrahedra microstructure remains mostly unaltered.",0905.2319v1
2009-05-15,Planar superconductor/ferromagnet hybrids: Anisotropy of resistivity induced by magnetic templates,"We investigated experimentally the transport properties of a superconducting
cross-shaped aluminium microbridge fabricated on top of ferromagnetic BaFe12O19
single crystal. It was demonstrated that a one-dimensional domain structure in
the ferromagnetic substrate can induce the formation of superconducting
channels above magnetic domains. This leads to a giant anisotropy of
resistivity of the superconducting bridge, caused by the appearance of
continuous paths of supercurrents flowing along domain walls.",0905.2590v1
2009-05-27,Magnetic response of magnetic molecules with non-collinear local d-tensors,"Investigations of molecular magnets are driven both by prospective
applications in future storage technology or quantum computing as well as by
fundamental questions. Nowadays numerical simulation techniques and computer
capabilities make it possible to investigate spin Hamiltonians with realistic
arrangements of local anisotropy tensors. In this contribution I will discuss
the magnetic response of a small spin system with special emphasis on
non-collinear alignments of the local anisotropy axes.",0905.4375v2
2009-05-28,Anisotropy of the interface tension of the three-dimensional Ising model,"We determine the interface tension for the 100, 110 and 111 interface of the
simple cubic Ising model with nearest-neighbour interaction using novel
simulation methods. To overcome the droplet/strip transition and the droplet
nucleation barrier we use a newly developed combination of the multimagnetic
algorithm with the parallel tempering method. We investigate a large range of
inverse temperatures to study the anisotropy of the interface tension in
detail.",0905.4569v1
2009-06-12,Six-fold configurational anisotropy and magnetic reversal in nanoscale Permalloy triangles,"Six-fold configurational anisotropy was studied in Permalloy triangles, in
which the shape symmetry order yields two energetically non-degenerate
micromagnetic configurations of the spins, the so-called ""Y"" and ""buckle""
states. A twelve pointed switching astroid was measured using magneto-optical
experiments and successfully reproduced numerically, with different polar
quadrants identified as specific magnetic transitions, thereby giving a
comprehensive view of the magnetic reversal in these structures. A detailed
analysis highlighted the necessity to include the physical rounding of the
structures in the simulations to account for the instability of the Y state.",0906.2322v1
2009-06-22,Anisotropy in the sky distributions of the short and intermediate gamma-ray bursts: Breakdown of the cosmological principle?,"After the discovery of the anisotropy in the sky-distribution of intermediate
gamma-ray bursts recently also the distribution of the short gamma-ray bursts
is proven to be anisotropic. The impact of these behaviors on the validity of
the cosmological principle is shortly discussed.",0906.4034v1
2009-07-26,Nematic Anchoring on Carbon Nanotubes,"A dilute suspension of carbon nanotubes (CNTs) in a nematic liquid crystal
(LC) does not disturb the LC director. Due to a strong LC-CNT anchoring energy
and structural symmetry matching, CNT long axis follows the director field,
possessing enhanced dielectric anisotropy. This strong anchoring energy
stabilizes local pseudo-nematic domains, resulting in non-zero dielectric
anisotropy in the isotropic phase. These anisotropic domains respond to
external electric fields and show intrinsic frequency response. The presence of
these domains makes the isotropic phase field-responsive, giving rise to a
large dielectric hysteresis effect.",0907.4455v2
2009-09-10,Circumstantial evidence for a non-Maxwellian plasma from femtosecond laser-matter interaction,"We study ion acceleration mechanisms in laser-plasma interactions using
neutron spectroscopy. We consider different types of ion-collision mechanisms
in the plasma, which cause the angular anisotropy of the observed neutron
spectra. These include the collisions between an ion in the plasma and an ion
in the target, and the collisions between two ions in the hot plasma. By
analyzing the proton spectra, we suggest that the laser-generated plasma
consists of at least two components, one of which collectively accelerated and
can also produce anisotropy in the angular distribution of fusion neutrons.",0909.2048v1
2009-09-25,Tunable steady-state domain wall oscillator with perpendicular magnetic anisotropy,"We theoretically study domain wall oscillations upon the injection of a dc
current through a geometrically constrained wire with perpendicular magnetic
anisotropy. The oscillation frequency spectrum can be tuned by the injected
current density, but additionally by the application of an external magnetic
field independent of the power. The results of analytical calculations are
supported by micromagnetic simulations based on the Landau-Lifshitz-Gilbert
equation. The simple concept of our localized steady-state oscillator might
prove useful as a nanoscale microwave generator with possible applications in
telecommunication or for rf-assisted writing in magnetic hard drives.",0909.4733v1
2009-09-30,Collapse of triaxial bright solitons in atomic Bose-Einstein condensates,"We study triaxial bright solitons made of attractive Bose-condensed atoms
characterized by the absence of confinement in the longitudinal axial direction
but trapped by an anisotropic harmonic potential in the transverse plane. By
numerically solving the three-dimensional Gross-Pitaevskii equation we
investigate the effect of the transverse trap anisotropy on the critical
interaction strength above which there is the collapse of the condensate. The
comparison with previous predictions [Phys. Rev. A {\bf 66}, 043619 (2002)]
shows significant differences for large anisotropies.",0910.0035v1
2009-10-02,Single-Species Weibel Instability of Radiationless Plasma,"A Particle-in-Cell (PIC) numerical simulation of the electron Weibel
instability is applied in a frame of Darwin (radiationless) approximation of
the self-consistent fields of sparse plasma. As a result, we were able to
supplement the classical picture of the instability and, in particular, to
obtain the dependency of the basic characteristics (the time of development and
the maximum field energy) of the thermal anisotropy parameter, to trace the
dynamic restructuring of current filaments accompanying the nonlinear stage of
the instability and to trace in detail the evolution of the initial anisotropy
of the electron component of plasma.",0910.0361v2
2009-11-10,Direct and inverse measurement of thin films magnetostriction,"Two techniques of measurements of thin film magnetostriction are compared:
direct, when changes of the substrate curvature caused by the film
magnetization are controlled, and inverse (""indirect""), when the modification
of the magnetic anisotropy induced by the substrate deformation (usually
bending) is measured. We demonstrate how both the elastic strength of the
substrate and the effective magneto-mechanical coupling between the substrate
deformation and magnetic anisotropy of the film depend on different conditions
of bending. Equations to be used for magnetostriction value determination in
typical cases are given and critical parameters for the corresponding
approximations are identified.",0911.1914v1
2009-11-14,Rotational States of Magnetic Molecules,"We study a magnetic molecule that exhibits spin tunneling and is free to
rotate about its anisotropy axis. Exact low-energy eigenstates of the molecule
that are superpositions of spin and rotational states are obtained. We show
that parameter $\alpha = 2(\hbar S)^2/(I\Delta)$ determines the ground state of
the molecule. Here $\hbar S$ is the spin, $I$ is the moment of inertia, and
$\Delta$ is the tunnel splitting. The magnetic moment of the molecule is zero
at $\alpha < \alpha_c = [1-1/(2S)^{2}]^{-1}$ and non-zero at $\alpha >
\alpha_c$. At $\alpha \to \infty$ the spin of the molecule localizes in one of
the directions along the anisotropy axis.",0911.2810v1
2009-12-21,Polarization dependent spontaneous-emission rate of single quantum dots in photonic crystal membranes,"We have measured the variation of the spontaneous emission rate with
polarization for self-assembled single quantum dots in two-dimensional photonic
crystal membranes. We observe a maximum anisotropy factor of 6 between the
decay rates of the two bright exciton states. This large anisotropy is
attributed to the substantially different projected local density of optical
states for differently oriented dipoles in the photonic crystal.",0912.4109v2
2009-12-29,On asimuthal anisotropy in fragmentation of classical relativistic string,"A fragmenting relativistic string is widely used for modelling particle
production via quark-gluon strings formed in hadron inelastic interactions of
high energies. In this note we focus on motion and fragmentation of
relativistic string with non-zero transverse separation of its ends and study
this scenario as a possible mechanism bringing anisotropy into the asimuthal
angle disribution of produced particles in inelastic interactions of hadrons.",0912.5377v1
2010-01-11,Nonlocal effects on magnetism in the diluted magnetic semiconductor Ga_{1-x}Mn_{x}As,"The magnetic properties of the diluted magnetic semiconductor
Ga_{1-x}Mn_{x}As are studied within the dynamical cluster approximation. We use
the k-dot-p Hamiltonian to describe the electronic structure of GaAs with
spin-orbit coupling and strain effects. We show that nonlocal effects are
essential for explaining the experimentally observed transition temperature and
saturation magnetization. We also demonstrate that the cluster anisotropy is
very strong and induces rotational frustration and a cube-edge direction
magnetic anisotropy at low temperature. With this, we explain the
temperature-driven spin reorientation in this system.",1001.1716v1
2010-01-29,Variations of decay rates of radio-active elements and their connections with global anisotropy of physical space,"The analysis of correlations between fluctuations of alpha- and beta-decay
rates for different radio-active elements is carried out. These fluctuations
exceed significantly errors of measurements in many cases. They have the
periodical character and reveal definite spatial directions. We suggest that
the observed fluctuations are caused by the unique physical reason connected
with the global anisotropy of physical space and by the new force.",1001.5383v1
2010-02-26,25 years of Cosmic Microwave Background research at INPE,"This article is a report of 25 years of Cosmic Microwave Background
activities at INPE. Starting from balloon flights to measure the dipole
anisotropy caused by the Earth's motion inside the CMB radiation field, whose
radiometer was a prototype of the DMR radiometer on board COBE satellite,
member of the group cross the 90s working both on CMB anisotropy and foreground
measurements. In the 2000s, there was a shift to polarization measurements and
to data analysis, mostly focusing on map cleaning, non-gaussianity studies and
foreground characterization.",1002.4902v1
2010-02-28,Asymmetric Beams and CMB Statistical Anisotropy,"Beam asymmetries result in statistically-anisotropic cosmic microwave
background (CMB) maps. Typically, they are studied for their effects on the CMB
power spectrum, however they more closely mimic anisotropic effects such as
gravitational lensing and primordial power asymmetry. We discuss tools for
studying the effects of beam asymmetry on general quadratic estimators of
anisotropy, analytically for full-sky observations as well as in the analysis
of realistic data. We demonstrate this methodology in application to a
recently-detected 9 sigma quadrupolar modulation effect in the WMAP data,
showing that beams provide a complete and sufficient explanation for the
anomaly.",1003.0198v2
2010-03-01,Anisotropy of the Stone-Wales Defect and Warping of Graphene Nano-ribbons: A First-principles Analysis,"Stone-Wales (SW) defects, analogous to dislocations in crystals, play an
important role in mechanical behavior of $sp^2$-bonded carbon based materials.
Here, we show using first-principles calculations that a marked anisotropy in
the interaction among the SW defects has interesting consequences when such
defects are present near the edges of a graphene nano-ribbon: depending on
their orientation with respect to edge, they result in compressive or tensile
stress, and the former is responsible to depression or warping of the graphene
nano-ribbon. Such warping results in delocalization of electrons in the defect
states.",1003.0479v1
2010-06-01,Geometric signature of reversal modes in ferromagnetic nanowires,"Magnetic nanowires are a good platform to study fundamental processes in
Magnetism and have many attractive applications in recording such as
perpendicular storage and in spintronics such as non-volatile magnetic memory
devices (MRAM) and magnetic logic devices. In this work, nanowires are used to
study magnetization reversal processes through a novel geometric approach.
Reversal modes imprint a definite signature on a parametric curve representing
the locus of the critical switching field. We show how the different modes
affect the geometry of this curve depending on the nature of the anisotropy
(uniaxial or cubic anisotropy), demagnetization and exchange effects. The
samples we use are electrochemically grown Nickel and Cobalt nanowires.",1006.0105v1
2010-06-08,Strong-interaction approximation for transfer matrix method,"Using transfer-matrix method a correspondence between $2D$ classical spin
systems ($2D$ Ising model and six-vertex model) and $1D$ quantum spin systems
is considered. We find the transfer matrix in two limits - in a well-known
strong-anisotropy limit and a novel strong-interaction limit. In contrast to
the usual strong-anisotropy approximation, within the strong-interaction
approximation we take into account the non-commutativity of transfer-matrix
components. The latter approximation is valid for low temperatures or strong
interaction in one spatial dimension. We observe that the Hamiltonian of the
corresponding quantum chains contains multispin interactions.",1006.1608v1
2010-06-08,Horava-Lifshitz modifications of the Casimir effect,"We study the modifications induced by spacetime anisotropy on the Casimir
effect in the case of two parallel plates. Nonperturbative and perturbative
regimes are analyzed. In the first case the Casimir force either vanishes or it
reverses its direction which, in any case, makes the proposal untenable. On the
other hand, the perturbative model enables us to incorporate appropriately the
effects of spacetime anisotropy.",1006.1635v1
2010-07-13,Current-induced exchange switching magnetic junctions with cubic anisotropy of the free layer,"The stability is analyzed of the equilibrium configurations of a magnetic
junction with a free layer that has cubic symmetry and two anisotropy axes in
the layer plane. Different variants of the switching between various
configurations are considered. A possibility is shown of the substantial
lowering of the threshold current density needed for the switching. Numerical
simulation is made of the switching dynamics for various configurations.",1007.2097v1
2010-07-16,"Equation of State, Stability, Anisotropy and Nonlinear Elasticity of Diamond-Cubic (ZB) Silicon by Phonon Imaging at High Pressure","Experimental phonon imaging in diamond anvils cell is demonstrated to be an
adequate tool to extract the complete set of elastic constants of
single-crystalline silicon up to the ZB$\rightarrow \beta-$Sn transition (10
GPa). Contrary to what was commonly admitted, we demonstrate that the
development of the strain-energy density in terms of strains cannot be stopped,
for silicon, after the terms containing the third-order elastic constants.
Nonlinear elasticity, degree of anisotropy and pressure-induced mechanical
stability of the cubic silicon structure are thus revisited and investigated in
more detail.",1007.2730v1
2010-08-02,Elliptic flow from color strings,"It is shown that the elliptic flow can be successfully described in the color
string picture with fusion and percolation provided anisotropy of particle
emission from the fused string is taken into account. Two possible sources of
this anisotropy are considered, propagation of the string in the transverse
plane and quenching of produced particles in the strong color field of the
string. Calculations show that the second source gives an overwhelming
contribution to the flow at accessible energies.",1008.0245v1
2010-08-05,Anisotropic magnetocaloric effect in all-ferromagnetic (La0.7Sr0.3MnO3/SrRuO3) superlattices,"We exploit the magnetic interlayer coupling in La0.7Sr0.3MnO3/SrRuO3
superlattices to realize a crossover between inverse and conventional magnetic
entropy changes. Our data reveal a strong anisotropic nature of the
magnetocaloric effect due to the magnetic anisotropy of the superlattice.
Therefore, artificial superlattices built from ferromagnetic materials that can
be used to alter the magnetic structure as well as the magnetic anisotropy,
could also be utilized for tuning the magnetocaloric properties, which may open
a constructive approach for magnetic refrigeration applications.",1008.1041v1
2010-08-26,Two-electron entanglement in elliptically deformed quantum dots,"Entropic entanglement measures of a two-dimensional system of two
Coulombically interacting particles confined in an anisotropic harmonic
potential are discussed in dependence on the anisotropy and the interaction
strength. The harmonic approximation appears exact in the strong interaction
limit, allowing determination of the asymptotic expression for the linear
entropy. Entanglement properties are dramatically influenced by the anisotropy
of the confining potential in the strong-correlation regime.",1008.4605v1
2010-09-11,Anisotropic charge transport in non-polar GaN QW: polarization induced charge and interface roughness scattering,"Charge transport in GaN quantum well (QW) devices grown in non-polar
direction has been theoretically investigated . Emergence of anisotropic line
charge scattering mechanism originating as a result of anisotropic rough
surface morphology in conjunction with in-plane built-in polarization has been
proposed. It has shown that in-plane growth anisotropy leads to large
anisotropic carrier transport at low temperatures. At high temperatures, this
anisotropy in charge transport is partially washed out by strong isotropic
optical phonon scattering in GaN QW.",1009.2156v2
2010-09-22,Shape anisotropy of polymers in disordered environment,"We study the influence of structural obstacles in a disordered environment on
the size and shape characteristics of long flexible polymer macromolecules. We
use the model of self-avoiding random walks on diluted regular lattices at the
percolation threshold in space dimensions d=2, 3. Applying the Pruned-Enriched
Rosenbluth Method (PERM), we numerically estimate rotationally invariant
universal quantities such as the averaged asphericity A_d and prolateness S of
polymer chain configurations. Our results quantitatively reveal the extent of
anisotropy of macromolecules due to the presence of structural defects.",1009.4358v2
2010-09-28,Spin-orbit anisotropy measured using ballistic spin resonance,"Spin relaxation can be greatly enhanced in narrow channels of two-dimensional
electron gas due to ballistic spin resonance, which is mediated by spin-orbit
interaction for trajectories that bounce rapidly between channel walls. The
channel orientation determines which momenta affect the relaxation process, so
comparing relaxation for two orientations provides a direct determination of
spin-orbit anisotropy. Electrical measurements of pure spin currents are shown
to reveal an order of magnitude stronger relaxation for channels fabricated
along the [110] crystal axis in a GaAs electron gas compared to [-110]
channels, believed to result from interference between structural and bulk
inversion asymmetries.",1009.5702v1
2010-09-29,Spin quadrupoletronics: moving spin anisotropy around,"We show that spin anisotropy can be transferred to an isotropic system by
transport of spin quadrupole moment. We derive the quadrupole moment current
and continuity equation and study a high-spin valve structure consisting of two
ferromagnets coupled to a quantum dot probing an impurity spin. The quadrupole
back-action on their coupled spin results in spin torques and anisotropic spin
relaxation which do not follow from standard spin current considerations. We
demonstrate the detection of the impurity spin by charge transport and its
manipulation by electric fields.",1009.5874v2
2010-10-19,Third-order Elsässer moments in axisymmetric MHD turbulence,"Incompressible MHD turbulence is investigated under the presence of a uniform
magnetic field $\bb0$. Such a situation is described in the correlation space
by a divergence relation which expresses the statistical conservation of the
Els\""asser energy flux through the inertial range. The ansatz is made that the
development of anisotropy, observed when $B_0$ is strong enough, implies a
foliation of space correlation. A direct consequence is the possibility to
derive a vectorial law for third-order Els\""asser moments which is parametrized
by the intensity of anisotropy. We use the so-called critical balance
assumption to fix this parameter and find a unique expression.",1010.3823v1
2010-10-21,The effect of Dzyaloshinskii-Moriya interactions on the phase diagram and magnetic excitations of SrCu2(BO3)2,"The orthogonal dimer structure in the SrCu2(BO3)2 spin-1/2 magnet provides a
realization of the Shastry-Sutherland model. Using a dimer-product variational
wave function, we map out the phase diagram of the Shastry-Sutherland model
including anisotropies. Based on the variational solution, we construct a
bond-wave approach to obtain the excitation spectra as a function of magnetic
field. The characteristic features of the experimentally measured neutron and
ESR spectra are reproduced, like the anisotropy induced zero field splittings
and the persistent gap at higher fields.",1010.4476v2
2010-10-23,High spin polarization in epitaxial films of ferrimagnetic Mn3Ga,"Ferrimagnetic Mn3Ga exhibits a unique combination of low saturation
magnetization (Ms = 0.11 MA m-1) and high perpendicular anisotropy with a
uniaxial anisotropy constant of Ku = 0.89 MJ m-3. Epitaxial c-axis films
exhibit spin polarization as high as 58%, measured using point contact Andreev
reflection. These epitaxial films will be able to support thermally stable
sub-10 nm bits for spin transfer torque memories.",1010.4872v1
2010-10-27,CoIr-carbon complexes with magnetic anisotropies larger than 0.2 eV: a density-functional-theory prediction,"We report a density-functional study of the heteronuclear CoIr dimer adsorbed
on benzene or graphene. In either case CoIr prefers an upright position above
the center of a carbon hexagon with the Co atom next to it. The Ir atom stays
away from the carbon ring and thus preserves its free-atom-like properties.
This results in a very large magnetic anisotropy of more than 0.2 eV per dimer.
So high a value should suffice for long-term data storage at the temperature of
liquid nitrogen.",1010.5663v1
2010-11-12,"Comprehensive transport studies of anisotropy and ordering phenomena in quasi-one-dimensional (TMTTF)2X salts (X = PF6, AsF6, SbF6; BF4, ClO4, ReO4)","The temperature dependent dc resistivity of the quasi-one-dimensional organic
salts (TMTTF)2X ( X = PF6, AsF6, SbF6; BF4, ClO4, ReO4) has been measured in
all three crystal directions in order to investigate anisotropy, localization
effects, charge and anion ordering phenomena at low temperatures. For all
compounds and directions we extract the transport mechanisms in different
regimes. The data are thoroughly analyzed, related to structural properties,
and extensively discussed in view of previous studies and latest theories. It
becomes apparent that the anions have a severe influence on the physical
properties of the TMTTF salts.",1011.2856v1
2010-11-18,Lost and found: The missing diabolical points in the Fe$_8$ molecular magnet,"Certain diabolical points in the tunneling spectrum of the single-molecule
magnet Fe$_8$ were previously believed to be have been eliminated as a result
of a weak fourth-order anisotropy. As shown by Bruno, this is not so, and the
points are only displaced in the magnetic field space along the medium
anisotropy direction. The previously missing points are numerically located by
following the lines of the Berry curvature. The importance of an experimental
search for these rediscovered points is discussed.",1011.4326v2
2010-11-19,"Anisotropic spin fluctuations and superconductivity in ""115'' heavy fermion compounds: 59Co NMR study in PuCoGa5","We report results of $^{59}$Co nuclear magnetic resonance measurements on a
single crystal of superconducting PuCoGa5 in its normal state. The nuclear
spin-lattice relaxation rates and the Knight shifts as a function of
temperature reveal an anisotropy of spin fluctuations with finite wave vector
q. By comparison with the isostructural members, we conclude that
antiferromagnetic XY-type anisotropy of spin fluctuations plays an important
role in mediating superconductivity in these heavy fermion materials.",1011.4466v1
2010-11-29,Measuring the thermalization time,"A new method of measuring the pressure anisotropy in the early stage of
heavy-ion collisions is discussed. It is shown that the transverse momentum
spectra, elliptic flow and interferometry radii are not sensitive to the early
anisotropy. We propose the directed flow as a measure of the early transverse
and longitudinal pressures. Calculations indicate that the transverse and
longitudinal pressures equilibrate in less than 0.25 fm/c.",1011.6210v1
2010-12-01,Size dependent electric voltage-controlled magnetic anisotropy in multiferroic heterostructures: Interface-charge and strain co-mediated magnetoelectric coupling,"We present a phenomenological scheme to study the size-dependent electric
voltage-controlled magnetic anisotropy in ferromagnetic (FM)/ferroelectric (FE)
heterostructures. The FM layers are either metallic Fe(001), Ni(001), Co(0001),
or half-metallic (La, Sr)MnO3 films. Two magnetoelectric mechanisms, i.e.,
interface-charge and strain-mediated couplings, are considered. We show that
the interface-charge mediated coupling is the main mechanism for the
magnetoelectic coupling when the FM film thickness is below a certain
transition thickness dtr while the strain-mediated coupling dominates above
dtr.",1012.0088v1
2010-12-08,Directional Anisotropy of Swift Gamma-Ray Bursts,"Swift satellite measurements contributed substantially to the gamma-ray burst
(GRB) redshift observations through fast slewing to the source of the GRBs.
Still, a large number of bursts are without redshift. We study the celestial
distribution of bursts with various methods and compare them to a random
catalog using Monte-Carlo simulations. We find an anisotropy in the
distribution of the intermediate class of bursts and find that the short and
long population are distributed isotropically.",1012.1757v2
2010-12-22,Transport properties of the new Fe-based superconductor KxFe2Se2 (Tc = 33 K),"We synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystals.
The obtained single crystal exhibited a sharp superconducting transition, and
the onset and zero-resistivity temperature was estimated to be 33 and 31.8 K,
respectively. A high upper critical field of 192 T was obtained. Anisotropy of
superconductivity of K0.8Fe2Se2 was ~3.6. Both the high upper critical field
and comparably low anisotropy are advantageous for the application under high
magnetic field.",1012.4950v1
2011-01-06,Towards a first observation of magneto-electric directional anisotropy and linear birefringence in gases,"In this contribution to PSAS'2010 we report on recent progress on an
experiment aimed at measuring small optical directional anisotropies by
frequency metrology in a high finesse ring cavity. We focus on our first
experimental goal, the measurement of magneto-electric effects in gases. After
a review of the expected effects in our set-up, we present the apparatus and
the measurement procedure, showing that we already have the necessary
sensitivity to start novel experiments.",1101.1174v1
2011-01-11,Deconfined criticality for the S=1 spin model on the spatially anisotropic triangular lattice,"The quantum S=1 spin model on the spatially anisotropic triangular lattice is
investigated numerically. The nematic and valence-bond-solid (VBS) phases are
realized by adjusting the spatial anisotropy and the biquadratic interaction.
The phase transition between the nematic and VBS phases is expected to be a
continuous one with unconventional critical indices (deconfined criticality).
The geometrical character (spatial anisotropy) is taken into account by
imposing the screw-boundary condition (Novotny's method). Diagonalizing the
finite-size cluster with N \le 20 spins, we observe a clear indication of
continuous phase transition. The correlation-length critical exponent is
estimated as \nu=0.92(10).",1101.1999v1
2011-01-13,The three dimensional Heisenberg spin glass under a weak random anisotropy,"We perform a finite size scaling study of the three-dimensional Heisenberg
spin glass in the presence of weak random anisotropic interactions, up to sizes
L=32. Anisotropies have a major impact on the phase transition. The
chiral-glass susceptibility does not diverge, due to a large anomalous
dimension. It follows that the anisotropic spin-glass belongs to a Universality
Class different from the isotropic model, which questions the applicability of
the chirality scenario.",1101.2509v2
2011-02-14,Interaction of spin and vibrations in transport through single-molecule magnets,"We study linear electron transport through a single-molecule magnet (SMM) and
the interplay of its anisotropic spin with quantized vibrational distortions of
the molecule. We show that, despite the longitudinal anisotropy barrier and
small transverse anisotropy, vibrational fluctuations can induce quantum
spin-tunneling (QST) and a QST-Kondo effect. The interplay of spin scattering,
QST and molecular vibrations can strongly enhance the Kondo effect and induce
an anomalous magnetic field dependence of vibrational Kondo side-bands.",1102.2798v1
2011-02-15,Adaptation to anisotropy and inhomogeneity via dyadic piecewise polynomial selection,"This article is devoted to nonlinear approximation and estimation via
piecewise polynomials built on partitions into dyadic rectangles. The
approximation rate is studied over possibly inhomogeneous and anisotropic
smoothness classes that contain Besov classes. Highlighting the interest of
such a result in statistics, adaptation in the minimax sense to both
inhomogeneity and anisotropy of a related multivariate density estimator is
proved. Besides, that estimation procedure can be implemented with a
computational complexity simply linear in the sample size.",1102.3108v1
2011-02-24,Anisotropy studies with multiscale autocorrelation function,"We present a novel method, based on a multiscale approach, for detecting
anisotropy signatures in the arrival direction distribution of the highest
energy cosmic rays. This method is catalog independent, i.e. it does not depend
on the choice of a particular catalog of candidate sources, and it provides a
good discrimination power even in presence of contaminating isotropic
background. We present applications to simulated data sets of events
corresponding to plausible scenarios for events detected, in the last decades,
by world-wide surface detector-based observatories for charged particles.",1102.5007v1
2011-03-06,Spin-wave energy dispersion of a frustrated spin-1/2 Heisenberg antiferromagnet on a stacked square lattice,"Effects of interlayer coupling and spatial anisotropy on spin-wave excitation
spectra of a three-dimensional spatially anisotropic, frustrated spin-$\half$
Heisenberg antiferromagnet (HAFM) is investigated for the two ordered phases
using second-order spin-wave expansion. We show that the second-order
corrections to the spin-wave energies are significant and find that the energy
spectra of the three-dimensional HAFM shares similar qualitative features with
the energy spectra of the two-dimensional HAFM on a square lattice. We also
discuss the features that can provide experimental measures for the strength of
the interlayer coupling, spatial anisotropy parameter, and magnetic
frustration.",1103.1155v1
2011-03-08,Quantum Phase Transitions around the Staggered Valence Bond Solid,"Motivated by recent numerical results, we study the quantum phase transitions
between Z_2 spin liquid, Neel ordered, and various valence bond solid (VBS)
states on the honeycomb and square lattices, with emphasis on the staggered
VBS. In contrast to the well-understood columnar VBS order, the staggered VBS
is not described by an XY order parameter with Z_N anisotropy close to these
quantum phase transitions. Instead, we demonstrate that on the honeycomb
lattice, the staggered VBS is more appropriately described as an O(3) or CP(2)
order parameter with cubic anisotropy, while on the square lattice it is
described by an O(4) or CP(3) order parameter.",1103.1638v1
2011-03-15,Ellipsoidal anisotropy in elasticity for rocks and rock masses,"One of the interesting features with the ellipsoidal models of anisotropy
presented in this paper is their acceptance of analytical solutions for some of
the basic elasticity problems. It was shown by Pouya (2000) and Pouya and Zaoui
(2006) that many closed-form solutions for basic problems involving linear
isotropic materials could be extended by linear transformation to cover a
variety of ""ellipsoidal"" materials. This paper will describe two main varieties
of ellipsoidal elastic models and show how well they fit the in situ data for
sedimentary rocks; numerical homogenization results for several varieties of
fractured rock masses will also be provided.",1103.3033v1
2011-04-12,Upper critical fields and superconducting anisotropy of K0.70Fe1.55Se1.01S0.99 and K0.76Fe1.61Se0.96S1.04 single crystals,"We have investigated temperature and angular dependence of resistivity of
K0.70(7)Fe1.55(7)Se1.01(2)S0.99(2) and K0.76(5)Fe1.61(5)Se0.96(4)S1.04(5)
single crystals. The upper critical fields Hc2(T) for both field directions
decrease with the increase in S content. On the other hand, the angle-dependent
magnetoresistivity for both compounds can be scaled onto one curve using the
anisotropic Ginzburg-Landau theory. The obtained anisotropy of Hc2(T) increases
with S content, implying that S doping might decrease the dimensionality of
certain Fermi surface parts, leading to stronger two dimensional character.",1104.2318v2
2011-04-14,The Cosmic Linear Anisotropy Solving System (CLASS) I: Overview,"The Cosmic Linear Anisotropy Solving System (CLASS) is a new accurate
Boltzmann code, designed to offer a more user-friendly and flexible coding
environment to cosmologists. CLASS is very structured, easy to modify, and
offers a rigorous way to control the accuracy of output quantities. It is also
incidentally a bit faster than other codes. In this overview, we present the
general principles of CLASS and its basic structure. We insist on the
friendliness and flexibility aspects, while accuracy, physical approximations
and performances are discussed in a series of companion papers.",1104.2932v2
2011-04-28,Temperature dependent anisotropy and elastic effects in ferromagnetic nanowire arrays,"Temperature dependent Ferromagnetic Resonance measurements performed as a
function of diameter on Nickel nanowire arrays reveal several interesting
features in these systems. With diameter decrease from 100 nm to 15 nm, a
transition induced by surface anisotropy increase is observed at 50 nm in easy
axis orientation from parallel to perpendicular with respect to individual
nanowire geometric axis. Analysis of resonance field $H_{res}$ temperature
variation (between liquid Helium and room temperature) reveals underlying
strong magneto-elastic effects in small and large diameter nanowire arrays with
potential applications in recording and spintronics.",1104.5348v3
2011-06-21,Josephson effect through an anisotropic magnetic molecule,"We study the Josephson effect through a magnetic molecule with anisotropic
properties. Performing calculations in the tunneling regime, we show that the
exchange coupling between the electron spin on the molecule and the molecular
spin can trigger a transition from the $\pi$ state to the 0 state, and we study
how the spin anisotropy affects this transition. We show that the behavior of
the critical current as a function of an external magnetic field can give
access to valuable information about the spin anisotropy of the molecule.",1106.4193v2
2011-06-22,Magnetic anisotropy at nanoscale,"Nanoscale objects often behave differently than their 'normal-sized'
counterparts. Sometimes it is enough to be small in just one direction to
exhibit unusual features. One example of such a phenomenon is a very specific
in-plane magnetic anisotropy observed sometimes in very thin layers of various
materials. Here we recall a peculiar form of the free energy functional nicely
describing the experimental findings but completely irrelevant and thus never
observed in larger objects.",1106.4515v1
2011-07-13,Multichannel Effects near Confinement-Induced Resonances in Harmonic Waveguides,"We analyze the impact of multichannel scattering in harmonic waveguides on
the positions and widths of confinement-induced resonances for both isotropic
and anisotropic transversal confinement. Multichannel scattering amplitudes and
transmission coefficients are calculated and used to characterize the resonant
behaviour of atomic collisions with varying anisotropy. A mechanism is
established which leads to a splitting of the confinement-induced resonance in
the presence of anisotropy.",1107.2501v2
2011-08-12,Universal amplitude ratios for scaling corrections on Ising strips with fixed boundary conditions,"We study the (analytic) finite-size corrections in the Ising model on the
strip with fixed ($+ -$) boundary conditions. We find that subdominant
finite-size corrections to scaling should be to the form $a_k/N^{2k-1}$ for the
free energy $f_N$ and $b_k^{(n)}/N^{2k-1}$ for inverse correlation length
$\xi_n^{-1}$, with integer value of $k$. We investigate the set $\{a_k,
b_k^{(n)}\}$ by exact evaluation and their changes upon varying anisotropy of
coupling. We find that the amplitude ratios $b_k^{(n)}/a_k$ remain constant
upon varying coupling anisotropy. Such universal behavior are correctly
reproduced by the conformal perturbative approach.",1108.2574v1
2011-08-31,Extensibility enables locomotion under isotropic drag,"Anisotropic viscous drag is usually believed to be a requirement for the low
Reynolds number locomotion of slender bodies such as flagella and cilia. Here
we show that locomotion under isotropic drag is possible for extensible slender
bodies. After general considerations, a two-ring swimmer and a model
dinoflagellate flagellum are studied analytically to illustrate how
extensibility can be exploited for self-propulsion without drag anisotropy.
This new degree of freedom could be useful for some complex swimmer geometries
and locomotion in complex fluid environments where drag anisotropy is weak or
even absent.",1109.0047v1
2011-09-03,Thermomagnetic instability of standing flux-antiflux front in layered type-II superconductors,"Stability of standing flux-antiflux front in anisotropic layered
superconductors is considered. We describe two assisting mechanisms
destabilizing the standing vortex-antivortex front. There are anisotropy of the
layered superconductors and the heat, released by the vortex dynamics. We
present the conditions of the front stability for various anisotropy and
heating parameters. We predict that even small vortex-antivortex heating can
result in front instability. The characteristic size of the unstable pattern is
estimated.",1109.0637v1
2011-09-09,Theoretical Investigation of the Magnetic Order in FeAs,"The magnetic structure of the iron monoarsenide FeAs is studied using
first-principles calculations. We consider the collinear and non-collinear
(spin-spiral wave) magnetic ordering and magnetic anisotropy. It is
analitically shown that a magnetic triaxial anisotropy results in a sum of two
spin-spiral waves with opposite directions of wave vectors and different spin
amplitudes, so that the magnetic moments in two perpendicular directions do not
equal each other.",1109.1924v1
2011-09-09,Non-Gaussianity in the Cosmic Microwave Background Anisotropies at Recombination in the Squeezed limit,"We estimate analytically the second-order cosmic microwave background
temperature anisotropies at the recombination epoch in the squeezed limit and
we deduce the contamination to the primordial local non-Gaussianity. We find
that the level of contamination corresponds to f_NL^{con}=O(1) which is below
the sensitivity of present experiments and smaller than the value O(5) recently
claimed in the literature.",1109.2043v2
2011-11-07,"Spatially fractional-order viscoelasticity, non-locality and a new kind of anisotropy","Spatial non-locality of space-fractional viscoelastic equations of motion is
studied. Relaxation effects are accounted for by replacing second-order time
derivatives by lower-order fractional derivatives and their generalizations. It
is shown that space-fractional equations of motion of an order strictly less
than 2 allow for a new kind anisotropy, associated with angular dependence of
non-local interactions between stress and strain at different material points.
Constitutive equations of such viscoelastic media are determined. Explicit
fundamental solutions of the Cauchy problem are constructed for some cases
isotropic and anisotropic non-locality.",1111.1680v1
2011-11-22,Role of anisotropy in the Förster energy transfer from a semiconductor quantum well to an organic crystalline overlayer,"We consider the non-radiative resonant energy transfer from a two-dimensional
Wannier exciton (donor) to a Frenkel exciton of a molecular crystal overlayer
(acceptor). We characterize the effect of the optical anisotropy of the organic
subsystem on this process. Using realistic values of material parameters, we
show that it is possible to change the transfer rate within typically a factor
of two depending on the orientation of the crystalline overlayer. The resonant
matching of donor and acceptor energies is also partly tunable via the organic
crystal orientation.",1111.5154v1
2011-11-22,Basic Properties of MHD Turbulence in the Inertial Range,"We revisit the issue of spectral slope of MHD turbulence in the inertial
range and argue that numerics favor Goldreich-Sridhar -5/3 slope rather than
-3/2 slope. We also did precision measurements of anisotropy of MHD turbulence
and determined the anisotropy constant C_A=0.34 of Alfvenic turbulence.
Together with previously measured Kolmogorov constant C_K=4.2, or 3.3 for
purely Alfvenic case, it constitutes a full description of MHD cascade in terms
of spectral quantities, which is of high practical value for astrophysics.",1111.5329v2
2011-11-26,Orientation selection of equiaxed dendritic growth by three-dimensional cellular automaton model,"A three-dimensional (3-D) adaptive mesh refinement (AMR) cellular automata
(CA) model is developed to simulate the equiaxed dendritic growth of pure
substance. In order to reduce the mesh induced anisotropy by CA capture rules,
a limited neighbor solid fraction (LNSF) method is presented. An expansion
description using two interface free energy anisotropy parameters (\epsilon1,
\epsilon2) is used in present 3-D CA model. The dendrite growths with the
orientation selection between <100> and <110> are discussed using the different
\epsilon1 with \epsilon2=-0.02. It is found that the simulated morphologies by
present CA model are as expected from the minimum stiffness criterion.",1111.6159v1
2011-12-16,Competition between superconductivity and nematic order : anisotropy of superconducting coherence length,"We study the interplay between nematic order and superconductivity, motivated
by a recent experiment on FeSe observing strongly distorted vortex shapes (Song
et al., Science 332, 1410 (2011)). We show that the nematic order strongly
enhances the anisotropy in the superconducting coherence length, beyond that
expected from considerations of the Ginzburg-Landau theory. We obtain universal
functions describing the coupling between the nematic order and
superconductivity, and discuss connections of our results to the experiments.",1112.3973v2
2012-01-17,Spin wave excitation in magnetic insulators by spin-transfer torque,"We study the excitation of spin waves in magnetic insulators by the
current-induced spin-transfer torque. We predict preferential excitation of
surface spin waves induced by an easy-axis surface anisotropy with critical
current inversely proportional to the penetration depth and surface anisotropy.
The surface modes strongly reduce the critical current and enhance the
excitation power of the current-induced magnetization dynamics.",1201.3442v1
2012-01-23,Local lattice distortions around $\rm{Mn^{2+}}$ cause in-plane uniaxial magnetic anisotropy in Ga(Mn)As,"We theoretically investigate the interplay between local lattice distortions
around $\rm{Mn^{2+}}$ ion impurity and the ion's magnetic polarization,
mediated through spin-orbit coupling of hole. We show that the tetrahedral
symmetry around $\rm{Mn^{2+}}$ ion impurity is spontaneously broken even in the
paramagnetic regime. Modest local lattice distortions around the impurity
$\rm{Mn^{2+}}$ ion, along with the growth strain, stabilize magnetization along
$< 110 >$ directions, in the ferromagnetic regime. We explain the
experimentally observed in-plane uniaxial magnetic anisotropy seen in this
system using this symmetry-breaking mechanism.",1201.4879v2
2012-01-26,Thermal switching rate of a ferromagnetic material with uniaxial anisotropy,"The field dependence of the thermal switching rate of a ferromagnetic
material with uniaxial anisotropy was studied by solving the Fokker-Planck
equation. We derived the analytical expression of the thermal switching rate
using the mean first-passage time approach, and found that Brown's formula
[Phys. Rev. 130, 1677 (1963)] is applicable even in the low barrier limit by
replacing the attempt frequency with the proper factor which is expressed by
the error function.",1201.5460v2
2012-01-26,Ground-state correlation properties of charged bosons trapped in strongly anisotropic harmonic potentials,"We study systems of a few charged bosons contained within a strongly
anisotropic harmonic trap. A detailed examination of the ground-state
correlation properties of two-, three-, and four-particle systems is carried
out within the framework of the single-mode approximation of the transverse
components. The linear correlation entropy of the quasi-1D systems is discussed
in dependence on the confinement anisotropy and compared with a strictly 1D
limit. Only at weak interaction the correlation properties depend strongly on
the anisotropy parameter.",1201.5504v1
2012-01-31,Statistical Anisotropy from Anisotropic Inflation,"We review an inflationary scenario with the anisotropic expansion rate. An
anisotropic inflationary universe can be realized by a vector field coupled
with an inflaton, which can be regarded as a counter example to the cosmic
no-hair conjecture. We show generality of anisotropic inflation and derive a
universal property. We formulate cosmological perturbation theory in
anisotropic inflation. Using the formalism, we show anisotropic inflation gives
rise to the statistical anisotropy in primordial fluctuations. We also explain
a method to test anisotropic inflation using the cosmic microwave background
radiation (CMB).",1201.6434v2
2012-02-15,Measurement of Cosmic Ray spectrum and Anisotropy with ARGO-YBJ,"In this paper we report on the observation of the anisotropy of cosmic ray
arrival direction at different angular scales with ARGO-YBJ. Evidence of new
few-degree excesses throughout the sky region 195$^{\circ}\leq$ R.A. $\leq$
315$^{\circ}$ is presented for the first time. We report also on the
measurement of the light-component (p+He) spectrum of primary cosmic rays in
the range 5 - 200 TeV.",1202.3379v1
2012-02-21,High-Directional Wave Propagation in Periodic Gain/Loss Modulated Materials,"Amplification/attenuation of light waves in artificial materials with a
gain/loss modulation on the wavelength scale can be sensitive to the
propagation direction. We give a numerical proof of the high anisotropy of the
gain/loss in two dimensional periodic structures with square and rhombic
lattice symmetry by solving the full set of Maxwell's equations using the
finite difference time domain method. Anisotropy of amplification/attenuation
leads to the narrowing of the angular spectrum of propagating radiation with
wavevectors close to the edges of the first Brillouin Zone. The effect provides
a novel and useful method to filter out high spatial harmonics from noisy
beams.",1202.4585v1
2012-02-23,Domain structure in CoFeB thin films with perpendicular magnetic anisotropy,"Domain structures in CoFeB-MgO thin films with a perpendicular easy
magnetization axis were observed by magneto-optic Kerr-effect microscopy at
various temperatures. The domain wall surface energy was obtained by analyzing
the spatial period of the stripe domains and fitting established domain models
to the period. In combination with SQUID measurements of magnetization and
anisotropy energy, this leads to an estimate of the exchange stiffness and
domain wall width in these films. These parameters are essential for
determining whether domain walls will form in patterned structures and devices
made of such materials.",1202.5128v1
2012-04-04,CMBR anisotropy in the framework of cosmological extrapolation of MOND,"A modified gravity involving a critical acceleration, as empirically
established at galactic scales and successfully tested by data on supernovae of
type Ia, can fit the measured multipole spectrum of anisotropy in the cosmic
microwave background radiation, so that a dark sector of Universe is
constructively mimicked as caused by the dynamics beyond the general
relativity. Physical consequences, verifiable predictions and falsifiable
issues are listed and discussed.",1204.0869v2
2012-04-30,Statistically anisotropic curvature perturbation generated during the waterfall,"If the waterfall field of hybrid inflation couples to a U(1) gauge field, the
waterfall can generate a statistically anisotropic contribution to the
curvature perturbation. We investigate this possibility, generalising in
several directions the seminal work of Yokoyama and Soda. The statistical
anisotropy of the bispectrum could be detectable by PLANCK even if the
statistical anisotropy of the spectrum is too small to detect.",1204.6619v1
2012-05-25,Higher order spectra from an initially anisotropic universe,"In this paper, we present the higher order spectra of a scalar field produced
through the higher derivative interactions in the initially anisotropic
universe. Although we ignore the backreaction of the scalar field on the
geometry, our analysis should have much overlap with the quantum fluctuations
of the inflaton field in the anisotropic universe. We also include the planar
modes whose momenta are along the plane which is perpendicular to the
primordial preferred direction, for which effects of the initial anisotropy are
not suppressed. The presence of a negative frequency mode produces features
distinguishable from the case of the de Sitter inflation. We also show that
richer features appear in the trispectra due to the primordial anisotropy.",1205.5600v1
2012-05-27,Superfluid state of repulsively interacting three-component fermionic atoms in optical lattices,"We investigate the superfluid state of repulsively interacting
three-component (color) fermionic atoms in optical lattices. When the
anisotropy of the three repulsive interactions is strong, atoms of two of the
three colors form Cooper pairs and atoms of the third color remain a Fermi
liquid. An effective attractive interaction is induced by density fluctuations
of the third-color atoms. This superfluid state is stable against changes in
filling close to half filling. We determine the phase diagrams in terms of
temperature, filling, and the anisotropy of the repulsive interactions.",1205.5964v1
2012-05-29,Anisotropic excitation spectrum of a dipolar quantum Bose gas,"We measure the excitation spectrum of a dipolar Chromium Bose Einstein
Condensate with Raman-Bragg spectroscopy. The energy spectrum depends on the
orientation of the dipoles with respect to the excitation momentum,
demonstrating an anisotropy which originates from the dipole-dipole
interactions between the atoms. We compare our results with the Bogoliubov
theory based on the local density approximation, and, at large excitation
wavelengths, with numerical simulations of the time dependent Gross-Pitaevskii
equation. Our results show an anisotropy of the speed of sound",1205.6305v1
2012-06-13,Anisotropic Friedmann-Robertson-Walker universe from nonlinear massive gravity,"In the scope of the nonlinear massive gravity, we study fixed points of
evolution equations for a Bianchi type--I universe. We find a new attractor
solution with non-vanishing anisotropy, on which the physical metric is
isotropic but the Stuckelberg configuration is anisotropic. As a result, at the
background level, the solution describes a homogeneous and isotropic universe,
while a statistical anisotropy is expected from perturbations, suppressed by
smallness of the graviton mass.",1206.2723v2
2012-06-23,Interacting Anisotropic Dirac Fermions in Strained Graphene and Related Systems,"We study the role of long-range electron-electron interactions in a system of
two-dimensional anisotropic Dirac fermions, which naturally appear in
uniaxially strained graphene, graphene in external potentials, some strongly
anisotropic topological insulators, and engineered anisotropic graphene
structures. We find that while for small interactions and anisotropy the system
restores the conventional isotropic Dirac liquid behavior, strong enough
anisotropy can lead to the formation of a quasi-one dimensional electronic
phase with dominant charge order (anisotropic excitonic insulator).",1206.5427v2
2012-06-27,Domain wall propagation through spin wave emission,"We theoretically study field-induced domain wall (DW) motion in an
electrically insulating ferromagnet with hard- and easy-axis anisotropies. DWs
can propagate along a dissipationless wire through spin wave emission locked
into the known soliton velocity at low fields. In the presence of damping, the
mode appears before the Walker breakdown field for strong out-of-plane magnetic
anisotropy, and the usual Walker rigid-body propagation mode becomes unstable
when the field is between the maximal-DW-speed field and Walker breakdown
field.",1206.6244v1
2012-07-27,A Theory for Diffusionless Structural Phase Transitions in BaTiO3 and PZT Single Crystals,"A phenomenological theory has been proposed for the diffusionless structural
phase transitions in crystalline solids here. It has been found that for BaTiO3
single crystal, both the phase transitions and the crystal structures can be
predicted with the crystalline anisotropy constants and order parameter
dependent strain constants that depend on the temperature. The results have
also shown that the morphotropic phase boundaries in PZT crystals arise from
the crystalline anisotropy.",1207.6532v2
2012-08-03,Quantum measurements and chiral magnetic effect,"The effect of anisotropy for fluctuations of electric currents in magnetic
field is addressed within framework of quantum measurements theory. It is shown
that for free fermions in uniform magnetic field the anisotropy is of the same
sign as one expects for chiral magnetic effect and is related to triangle
anomaly. The corresponding decoherence functional contains anomalous
off-diagonal terms leading to correlation of fluctuations between observables
of opposite P-parity.",1208.0777v2
2012-08-13,Highly anisotropic dissipative hydrodynamics,"The quark gluon plasma generated in ultrarelativistic heavy ion collisions
may possess sizable momentum-space anisotropies that cause the longitudinal and
transverse pressures in the local rest frame to be significantly different. We
review recent attempts to derive a dynamical framework that can reliably
describe systems that possess a high degree of momentum-space anisotropy. The
dynamical framework that has been developed can describe the evolution of the
quark gluon plasma ranging from the longitudinal free-streaming limit to the
ideal hydrodynamical limit.",1208.2626v2
2012-09-24,Control of the magnetism and magnetic anisotropy of a single-molecule magnet with an electric field,"Through systematics density functional calculations, the mechanism of the
substrate induced spin reorientation transition in FePc/O-Cu(110) was explained
in terms of charge transfer and rearrangement of Fe-d orbitals. Moreover, we
found giant magnetoelectric effects in this system, manifested by the sensitive
dependences of its magnetic moment and magnetic anisotropy energy on external
electric field. In particular, the direction of magnetization of FePc/O-Cu(110)
is switchable between in-plane and perpendicular axes, simply by applying an
external electric field of 0.5 eV/{\AA} along the surface normal.",1209.5453v3
2012-10-05,Anisotropic Fermi Contour of (001) GaAs Holes in Parallel Magnetic Fields,"We report a severe, spin-dependent, Fermi contour anisotropy induced by
parallel magnetic field in a high-mobility (001) GaAs two-dimensional hole
system. Employing commensurability oscillations created by a unidirectional,
surface-strain-induced, periodic potential modulation, we directly probe the
anisotropy of the two spin subband Fermi contours. Their areas are obtained
from the Fourier transform of the Shubnikov-de Haas oscillations. Our findings
are in semi-quantitative agreement with the results of parameter-free
calculations of the energy bands.",1210.1672v1
2012-10-17,Topological transition of Dirac points in a microwave experiment,"By means of a microwave tight-binding analogue experiment of a graphene-like
lattice, we observe a topological transition between a phase with a point-like
band gap characteristic of massless Dirac fermions and a gapped phase. By
applying a controlled anisotropy on the structure, we investigate the
transition directly via density of states measurements. The wave function
associated with each eigenvalue is mapped and reveals new states at the Dirac
point, localized on the armchair edges. We find that with increasing
anisotropy, these new states are more and more localized at the edges.",1210.4642v2
2012-10-27,Nonlinear optical anisotropy due to freed electrons,"We present a computational study of the pump-probe response of a single atom
to assess any microscopic nonlinear optical anisotropy due to freed electrons
for non-resonant optical excitation. Using simulations of the Schr\""odinger
equation for an atom exposed to a strong, short-duration linearly polarized
pump, we calculate the induced dipole moment along probe directions parallel
and perpendicular to the pump polarization. Our simulations show birefringence
ratios of approximately 0.78-0.9 on the timescale of tens of femtoseconds
following the excitation pulse.",1210.7285v1
2012-11-06,Spin Wave Scattering in Ferromagnetic Cross,"Spin wave scattering in the right angle ferromagnetic cross was measured.
Shape anisotropy defined magnetization ground states at zero biasing magnetic
fields. Scattering of the spin waves in the center of ferromagnetic cross is
strongly dependent on the amplitude and angle of the biasing magnetic field.
Micromagnetic simulations indicate that low in-plane biasing magnetic fields
rotate the magnetization of the cross center while the arms stay axially
magnetized due to the shape anisotropy. We discuss effect of biasing magnetic
fields on the spin wave scattering and approaches to an effective spin wave
switch based on the fabricated structure.",1211.1259v1
2012-11-20,Novel Two-dimensional Carbon Allotrope with Strong Electronic Anisotropy,"Two novel two-dimensional carbon allotropes comprised of octagons and
pentagons are proposed based on the first-principles calculations. The two
carbon allotropes, named OPG-L and OPG-Z, are found to have distinct
properties. OPG-L is metallic, while OPG-Z is a gapless semimetal. Remarkably,
OPG-Z exhibits pronounced electronic anisotropy with highly anisotropic Dirac
points at the Fermi level. A tight-binding model is suggested to describe the
low-energy quasiparticles, which clarifies the origin of the anisotropic Dirac
points. Such an anisotropic electronic characteristic of OPG-Z is expected to
have wide implications in nano-electronics.",1211.4680v2
2012-11-30,Ab initio study of magnetic anisotropy in cobalt doped zinc oxide with electron-filling,"Based on first-principles calculation, it has been predicted that the
magnetic anisotropy energy (MAE) in Co-doped ZnO (Co:ZnO) depends on
electron-filling. Results show that the charge neutral Co:ZnO presents a ""easy
plane"" magnetic state. While modifying the total number of electrons, the easy
axis rotates from in-plane to out-of-plane. The alternation of the MAE is
considered to be the change of the ground state of Co ion, resulting from the
relocating of electrons on Co d-orbitals with electron-filling.",1211.7287v2
2012-12-13,Measurement of J/{psi} Azimuthal Anisotropy in Au+Au Collisions at {sqrt{s_{NN}}} = 200 GeV,"The measurement of J/{psi} azimuthal anisotropy is presented as a function of
transverse momentum for different centralities in Au+Au collisions at
{sqrt{s_{NN}}} = 200 GeV. The measured J/{psi} elliptic flow is consistent with
zero within errors for transverse momentum between 2 and 10 GeV/c. Our
measurement suggests that J/{psi} with relatively large transverse momentum are
not dominantly produced by coalescence from thermalized charm quarks, when
comparing to model calculations.",1212.3304v2
2012-12-15,Event plane resolution correction for azimuthal anisotropy in wide centrality bins,"We provide a method to correct the observed azimuthal anisotropy in heavy-ion
collisions for the event plane resolution in a wide centrality bin. This new
procedure is especially useful for rare particles, such as Omega baryons and
J/psi mesons, which are difficult to measure in small intervals of centrality.
Based on a Monte Carlo calculation with simulated v_2 and multiplicity, we show
that some of the commonly used methods have a bias of up to 15%.",1212.3650v2
2013-01-17,Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet,"The electric (E) field control of magnetic properties opens the prospects of
an alternative to magnetic field or electric current activation to control
magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have
proven to be particularly sensitive to the influence of an E-field due to the
interfacial origin of their anisotropy. In these systems, E-field effects have
been recently applied to assist magnetization switching and control domain wall
(DW) velocity. Here we report on two new applications of the E-field in a
similar material : controlling DW nucleation and stopping DW propagation at the
edge of the electrode.",1301.4007v1
2013-01-24,Pressure effects in hollow and solid iron oxide nanoparticles,"We report a study on the pressure response of the anisotropy energy of hollow
and solid maghemite nanoparticles. The differences between the maghemite
samples are understood in terms of size, magnetic anisotropy and shape of the
particles. In particular, the differences between hollow and solid samples are
due to the different shape of the nanoparticles and by comparing both pressure
responses it is possible to conclude that the shell has a larger pressure
response when compared to the core.",1301.5708v1
2013-01-29,Continuum random sequential adsorption of polymer on a flat and homogeneous surface,"Random sequential adsorption (RSA) of polymer, modeled as a chain of
identical spheres, is systematically studied. In order to control precisely
anisotropy and number of degrees of freedom, two different kinds of polymers
are used. In the first one, monomers are placed along a straight line, whereas
in the second, relative orientations of particles are random. Such polymers
fill a flat homogeneous surface randomly. The paper focuses on maximal random
coverage ratio and adsorption kinetics dependence on polymer size, shape
anisotropy, and numbers of degrees of freedom. Obtained results were discussed
and compared with other numerical experiments and theoretical predictions.",1301.6964v2
2013-02-07,CMB Tensor Anisotropies in f(R) Gravity,"The cosmic microwave background (CMB) carries information from the last
scattering surface that puts constraints on the multitude of proposed
cosmological models and the gravitation theories they are based on. One class
of such theories is $f(R)$ gravity, which has become an interesting endeavour
to correct for the degeneracies of the concordance model.
  We presents a description of CMB anisotropies generated by tensor
perturbations in $f(R)$ theories of gravity. The temperature and the $E$-mode
polarisation power spectra in the special case of $f(R)=R^n$ are computed using
a modified version of CAMB package.",1302.1887v1
2013-02-09,Existence and uniqueness for planar anisotropic and crystalline curvature flow,"We prove short-time existence of \phi-regular solutions to the planar
anisotropic curvature flow, including the crystalline case, with an additional
forcing term possibly unbounded and discontinuous in time, such as for instance
a white noise. We also prove uniqueness of such solutions when the anisotropy
is smooth and elliptic. The main tools are the use of an implicit variational
scheme in order to define the evolution, and the approximation with flows
corresponding to regular anisotropies.",1302.2216v1
2013-02-28,Polarization dependences of terahertz radiation emitted by hot charge carriers in p-Te,"Polarization dependences of the terahertz radiation emitted by hot charge
carriers in p-Te have been studied both theoretically and experimentally. The
angular dependences of the spontaneous radiation emission by hot carriers is
shown to originate from the anisotropy of their dispersion law and the
anisotropy of the dielectric permittivity of a tellurium crystal. We have shown
that the polarization dependences of radiation are determined by the angle
between the crystallographic axis C3 in p-Te and the polarization vector; they
are found to have a periodic character.",1302.7182v1
2013-03-08,Central compact objects in magnetic lethargy,"Central Compact Objects are peculiar young neutron stars, with very low
external magnetic fields combined with high fluxes in the X-ray band and
surface temperature anisotropies. However, in their crust the magnetic field
can be strong, result of its burial during a short post-supernova hypercritical
accretion episode. The implications of this latter scenario for the temperature
anisotropy, pulsed fraction and luminosity are discussed.",1303.1997v1
2013-04-04,Spin-orbit coupling induced Fulde-Ferrell-Larkin-Ovchinnikov-like Cooper pairing and skyrmion-like polarization textures in trapped optical lattices,"We study the interplay between the Zeeman field and spin-orbit coupling (SOC)
in harmonically trapped Fermi gases loaded into a two-dimensional single-band
tight-binding optical lattice. Using the Bogoliubov-de Gennes theory, we find
that the Zeeman field combined with a Rashba SOC gives rise to $(i)$
Fulde-Ferrell-like superfluidity and $(ii)$ skyrmion-like polarization textures
near the edges of the system. We also discussed the effects of interaction,
temperature, SOC anisotropy and Zeeman field anisotropy on the superfluid
ground state and polarization textures.",1304.1473v2
2013-04-10,Effect of anisotropic Fermi surface on the flux-flow resistivity under rotating magnetic field,"We numerically investigate the effect of in-plane anisotropic Fermi surface
(FS) on the flux-flow resistivity $\rho_{\rm f}$ under rotating magnetic field
on the basis of the quasiclassical Green's function method. We demonstrate that
one can detect the phase in pairing potential of Cooper pair through the
field-angular dependence of $\rho_{\rm f}$ even if the FS has in-plane
anisotropy. In addition, we point out one can detect the gap-node directions
irrespective of the FS anisotropy by measuring $\rho_{\rm f}$ under rotating
field.",1304.3164v1
2013-04-19,Spin nematic states in spin-1 antiferromagnets with easy-axis anisotropy,"It is well known that spin nematic phases can appear in either frustrated
magnets or in those described by Hamiltonians with large exotic non-Heisenberg
terms like biquadratic exchange. We show in the present study that
non-frustrated spin-1 1D, 2D and 3D antiferromagnets with single-ion easy-axis
anisotropy can show nematic phases in strong magnetic field. For 1D case we
support our analytical results by numerical ones.",1304.5467v1
2013-05-01,Azimuthal Anisotropy in U+U Collisions at $\sqrt{s_{NN}} = 193 $ GeV with STAR Detector at RHIC,"We report the measurement of first (\textit {n} = 1) and higher
order(\textit{n} = 2-5) harmonic coefficients ($v_{n}$) of the azimuthal
anisotropy in the distribution of the particles produced in U+U collisions at
$\sqrt{s_{NN}}$ =193 GeV, recorded with the STAR detector at RHIC. The
differential measurement of $(v_{n})$ is presented as a function of transverse
momentum ($p_{T}$) and centrality. We also present $v_{n}$ measurement in the
ultra-central collisions. These data may provide strong constraints on the
theoretical models of the initial condition in heavy ion collisions and the
transport properties of the produced medium.",1305.0173v1
2013-05-06,Anisotropy of Interfacial Energy in Five Dimensions,"Anisotropy of interfacial energy is the principal driving force for material
microstructure evolution yet its origins remain uncertain and a quantitative
description lacking. We present and justify a concise hypothesis on the
topography and topology of the functional space of grain boundary energies and,
based on this hypothesis, construct a closed-form function that quantitatively
describes energy variations in the entire 5-space of macroscopic parameters
defining grain boundary geometry. The new function is found to be universal for
the crystallography class of face-centered cubic metals.",1305.1282v1
2013-05-07,Spin Wave Excitation in Magnetic Insulator Thin Films by Spin-Transfer Torque,"We describe excitation of dipole-exchange spin waves in insulating magnetic
thin films by spin current injection at the surface of the film. An easy-axis
magnetic surface anisotropy can induce a non-chiral surface spin wave mode with
penetration depth inversely proportional to the strength of the surface
anisotropy, which strongly reduces the critical current and enhances the
excitation power. The importance of the interface spin wave modes on the
excitation spectrum is reduced by spin pumping, which depends on the quality of
the interface as expressed by the spin mixing conductance.",1305.1364v2
2013-06-27,Speed of sound of a Bose--Einstein condensate with dipole--dipole interactions,"In the present work the case of a chromium Bose-Einstein condensate is
considered. The model includes not only the presence of the so-called contact
interaction but also a long range and anisotropic dipole-dipole interaction has
been included. Some thermodynamical properties are analyzed. For instance, the
size of the condensate, chemical potential, speed of sound, number of
particles, etc., are deduced. It will be shown that this dipole-dipole
interaction implies the emergence of anisotropy, for example, in the speed of
sound. The possible use of this anisotropy as a tool for the analyze of
dissipative mechanisms, for instance, Landau's criterion for superfluidity,
will be also discussed.",1306.6680v1
2013-07-02,Size Dependence of Domain Pattern Transfer in Multiferroic Heterostructures,"Magnetoelectric coupling in multiferroic heterostructures can produce large
lateral modulations of magnetic anisotropy enabling the imprinting of
ferroelectric domains into ferromagnetic films. Exchange and magnetostatic
interactions within ferromagnetic films oppose the formation of such domains.
Using micromagnetic simulations and a 1-D model, we demonstrate that competing
energies lead to the breakdown of domain pattern transfer below a critical
domain width. Moreover, rotation of the magnetic field results in abrupt
transitions between two scaling regimes with different magnetic anisotropy.",1307.0605v2
2013-07-24,Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy,"We present a method to map the saturation magnetization of soft ultrathin
films with perpendicular anisotropy, and we illustrate it to assess the
compositional dependence of the magnetization of CoFeB(1 nm)/MgO films. The
method relies on the measurement of the dipolar repulsion of parallel domain
walls that define a linear domain. The film magnetization is linked to the
field compressibility of the domain. The method also yields the minimal
distance between two walls before their merging, which sets a practical limit
to the storage density in spintronic devices using domain walls as storage
entities.",1307.6479v1
2013-08-12,Anisotropic Heisenberg Model on Core-Shell Structured Nanotube Geometry,"The effect of the anisotropy in the exchange interaction on the critical
temperature and the order parameter of the anisotropic Heisenberg model on a
core-shell structured nanotube geometry has been investigated. As a
formulation, effective field theory with the differential operator technique
and decoupling approximation within the 4-spin cluster (EFT-4) has been used.
The variation of the critical temperature with the anisotropy in the exchange
interaction has been obtained. Besides, suitability of the effective field
theory in small clusters as a formulation for the Heisenberg nanotube has been
discussed and it is concluded that minimum size of the cluster is 4-spin
cluster, which can give the correct critical description of the system.",1308.2511v2
2013-09-05,Fine structures in the spectrum of the open-boundary Heisenberg chain at large anisotropies,"At large anisotropies, the spectrum of the Heisenberg XXZ spin chain
separates into `bands' with energies largely determined by the number of domain
walls. The band structure is richer with open boundary conditions: there are
more bands and the bands develop intricate fine structures. We characterize and
explain these structures and substructures in the open-boundary chain. The fine
structures are explained using degenerate perturbation theory. We also present
some dynamical consequences of these sub-band structures, through explicit time
evolution of the wavefunction from initial states motivated by the fine
structure analysis.",1309.1471v2
2013-10-23,Magnetization Characteristic of Ferromagnetic Thin Strip by Measuring Anisotropic Magnetoresistance and Ferromagnetic Resonance,"The magnetization characteristic in a permalloy thin strip is investigated by
electrically measuring the anisotropic magnetoresistance and ferromagnetic
resonance in in-plane and out-of-plane configurations. Our results indicate
that the magnetization vector can rotate in the film plane as well as out of
the film plane by changing the intensity of external magnetic field of certain
direction. The magnetization characteristic can be explained by considering
demagnetization and magnetic anisotropy. Our method can be used to obtain the
demagnetization factor, saturated magnetic moment and the magnetic anisotropy.",1310.6117v1
2013-10-23,Hamiltonian Theory of Anisotropic Fractional Quantum Hall States,"Rotationally invariant fractional quantum Hall (FQH) states have long been
understood in terms of composite bosons or composite fermions. Recent
investigations of both incompressible and compressible states in highly tilted
fields, which renders them anisotropic, have revealed puzzling features which
have so far defied quantitative explanation. The author's work with R. Shankar
in constructing and analyzing an operator-based theory in the rotationally
invariant FQHE is generalized here to the anisotropic case. We compute the
effective anisotropies of many principal fraction states in the lowest and the
first Landau levels and find good agreement with previous theoretical results.
We compare the effective anisotropy in a model potential with finite sample
thickness and find good agreement with experimental results.",1310.6215v1
2013-11-14,Chromo-Natural Model in Anisotropic Background,"In this work we study the chromo-natural inflation model in the anisotropic
setup. Initiating inflation from Bianchi type-I cosmology, we analyze the
system thoroughly during the slow-roll inflation, from both analytical and
numerical points of view. We show that the isotropic FRW inflation is an
attractor of the system. In other words, anisotropies are damped within few
$e$--folds and the chromo-natural model respects the cosmic no-hair conjecture.
Furthermore, we demonstrate that in the slow-roll limit, the anisotropies in
both chromo-natural and gauge-flation models share the same dynamics.",1311.3361v2
2013-11-20,"Brownian motion in strongly coupled, anisotropic Yang-Mills plasma: A holographic approach","We employ methods of gauge/string duality to analyze the Brownian motion and
the concomitant Langevin equation of a heavy quark in a strongly coupled,
thermal, anisotropic Yang-Mills plasma. We consider fluctuations both along and
perpendicular to the direction of anisotropy and study the effects of
anisotropy on the drag coefficient, the diffusion constant and the Langevin
coefficient for both the directions. We also verify the fluctuation-dissipation
theorem for Brownian motion in an anisotropic medium.",1311.5023v2
2013-12-09,"Full susceptibility tensor for localized spin models with S=1, 3/2, 2, 5/2 and with rhombic anisotropy","A general discussion of the simulation procedure of the full susceptibility
tensor and isothermal magnetization pseudovector for compounds comprising
weakly-interacting magnetic centers is presented. A single-crystal-sample as
well as a powder-sample case are considered. The procedure is used to obtain
explicit expressions for the full susceptibility tensor for spins S=1, 3/2, 2,
and 5/2 for non-vanishing rhombic local anisotropy and any form of
spectroscopic tensor.",1312.2401v1
2014-01-30,Optical fiber Sagnac interferometer for sensing scalar directional refraction: application to magnetochiral birefringence,"We present a set-up dedicated to the measurement of the small scalar
directional anisotropies associated to the magnetochiral interaction. The
apparatus, based on a polarization-independent fiber Sagnac interferometer, is
optimized to be insensitive to circular anisotropies and to residual
absorption. It can thus characterize samples of biological interests, for which
the two enantiomers are not available and/or which present poor transmission.
The signal-to-noise ratio is shown to be limited only by the source intensity
noise, leading to a detection limit of Df = 500 nrad.Hz-1/2. It yields a limit
on the magnetochiral index nMC < 4 10-13 T-1 at 1550 nm for the organic
molecules tested.",1401.7765v1
2014-02-03,Magnetism and Magnetic Anisotropy of Transition Metal-Phthalocyanine Molecules,"Search for single-molecule magnets (SMMs) with high blocking temperature (TB)
is urgent for practical applications in magnetic recording, molecular
spintronics and quantum computing. Based on the First-principles calculations,
magnetic anisotropy energies (MAE) of the transition metal-Phthalocyanine
(TM-Pc) molecules are investigated and the mechanism that determines the MAE of
TM-Pc molecules is established. In particular, colossal MAE > 100 meV can be
obtained by adding an Os atom on RuPc and OsPc, so these molecules may offer
ultrahigh thermal stability in devices.",1402.0278v1
2014-02-05,Tunable Thermal Conduction in Graphane Nanoribbons,"Graphane and graphene are both two-dimensional materials but of different
bonding configurations, which can result in distinct thermal conduction
properties. We simulate thermal conduction in graphane nanoribbons (GANRs)
using the nonequilibrium Green's function method. It is found that GANRs have
lower ballistic thermal conductance and stronger thermal conductance anisotropy
than the graphene counterparts. Furthermore, hydrogen vacancies of GANRs
considerably suppress thermal conduction, accompanied by enhanced thermal
conductance anisotropy. The tunable thermal conduction, realized by controlling
the width, edge shape and hydrogen vacancy concentration of GANRs, could be
useful for thermal management and thermoelectric applications.",1402.1212v1
2014-02-07,Dielectron Azimuthal Anisotropy at mid-rapidity in Au+Au collisions at $\sqrt{s_{_{NN}}} = 200$ GeV,"We report on the first measurement of the azimuthal anisotropy ($v_2$) of
dielectrons ($e^{+}e^{-}$ pairs) at mid-rapidity from $\sqrt{s_{_{NN}}} = 200$
GeV Au+Au collisions with the STAR detector at RHIC, presented as a function of
transverse momentum ($p_T$) for different invariant-mass regions. In the mass
region $M_{ee}\!<1.1$ GeV/$c^2$ the dielectron $v_2$ measurements are found to
be consistent with expectations from $\pi^{0}$, $\eta$, $\omega$ and $\phi$
decay contributions. In the mass region $1.1\!<M_{ee}\!<2.9$ GeV/$c^2$, the
measured dielectron $v_2$ is consistent, within experimental uncertainties,
with that from the $c\bar{c}$ contributions.",1402.1791v2
2014-02-18,Effect of radiation-like solid on CMB anisotropies,"We compute the power in the lowest multipoles of CMB anisotropies in the
presence of radiation-like solid, a hypothetical new kind of radiation with
nonzero shear modulus. If only the ordinary Sachs-Wolfe effect is taken into
account, the shear modulus to energy density ratio must be in absolute value of
order $10^{-5}$ or less for the theory to be consistent with observations
within cosmic variance. With the integrated Sachs-Wolfe effect switched on, the
constraint is relaxed almost by two orders of magnitude.",1402.4434v2
2014-02-26,Spin nematic interaction in multiferroic compound Ba$_{2}$CoGe$_{2}$O$_{7}$,"We demonstrate the existence of the spin nematic interactions in an
easy-plane type antiferromagnet Ba$_{2}$CoGe$_{2}$O$_{7}$ by exploring the
magnetic anisotropy and spin dynamics. Combination of neutron scattering and
magnetic susceptibility measurements reveals that the origin of the in-plane
anisotropy is an antiferro-type interaction of the spin nematic operator. The
relation between the nematic operator and the electric polarization in the
ligand symmetry of this compound is presented. The introduction of the spin
nematic interaction is useful to understand the physics of spin and electric
dipole in multiferroic compounds.",1402.6436v1
2014-03-10,Nematicons in liquid crystals with negative dielectric anisotropy,"We report a theoretical and experimental work on the nematicon in the planar
cell containing the nematic liquid crystal with negative dielectric anisotropy,
aligned homeotropically in the presence of an externally applied voltage. The
formation of the soliton is resulted from the balance between the linear
difrraction and the nonlocal nonlinearity due to molecular reorientation.",1403.2154v2
2014-03-14,Cosmology from weak lensing of CMB,"The weak lensing effect on the cosmic microwave background (CMB) induces
distortions in spatial pattern of CMB anisotropies, and statistical properties
of CMB anisotropies become a weakly non-Gaussian field. We first summarize the
weak lensing effect on the CMB (CMB lensing) in the presence of scalar, vector
and tensor perturbations. Then we focus on the lensing effect on CMB statistics
and methods to estimate deflection angles and their power spectrum. We end by
summarizing recent observational progress and future prospect.",1403.3569v1
2014-03-20,Anisotropic Atom-Surface Interactions in the Casimir-Polder Regime,"The distance-dependence of the anisotropic atom-wall interaction is studied.
The central result is the 1/z^6 quadrupolar anisotropy decay in the retarded
Casimir-Polder regime. Analysis of the transition region between non-retarded
van der Waals regime (in 1/z^3) and Casimir-Polder regime shows that the
anisotropy cross-over occurs at very short distances from the surface, on the
order of 0.03 Lambda, where Lambda is the atom characteristic wavelength.
Possible experimental verifications of this distance dependence are discussed.",1403.5216v1
2014-03-26,Large Scale Anisotropy of Cosmic Rays and Directional Neutrino Signals from Galactic Sources,"We investigate the neutrino - cosmic ray connection for sources in the Galaxy
in terms of two observables: the shape of the energy spectrum and the
distribution of arrival directions. We also study the associated gamma ray
emission from these sources.",1403.6628v2
2014-04-04,Thermally assisted domain wall nucleation in perpendicular anisotropy trilayer nanowires,"We study thermally assisted domain wall generation in perpendicular magnetic
anisotropy CoFeB trilayer nanowires by the effect of Joule heating. The
anomalous Hall effect is utilized to detect magnetization reversal in order to
study the domain wall generation. We observe a statistical distribution in the
switching process which is consistent with the thermal activation process. Our
results show that the proposed method provides an efficient way for generating
domain walls in perpendicular magnetic nanowires at predefined locations.",1404.1135v1
2014-05-01,Multi-region relaxed magnetohydrodynamics with anisotropy and flow,"We present an extension of the multi-region relaxed magnetohydrodynamics
(MRxMHD) equilibrium model that includes pressure anisotropy and general plasma
flows. This anisotropic extension to our previous isotropic model is motivated
by Sun and Finn's model of relaxed anisotropic magnetohydrodynamic equilibria.
We prove that as the number of plasma regions becomes infinite, our anisotropic
extension of MRxMHD reduces to anisotropic ideal MHD with flow. The
continuously nested flux surface limit of our MRxMHD model is the first
variational principle for anisotropic plasma equilibria with general flow
fields.",1405.0061v1
2014-05-03,Axial quadrupole phase of a uniaxial spin-1 magnet,"Uniaxial phase of the axial quadrupole spin-1 magnet in an external magnetic
field is investigated. A case where the system includes single-ion anisotropy
and anisotropic biquadratic exchange interaction the most general form, is
considered. It is proved, that the molecular field approximation of the
relative magnetization does not depend on temperature and increases linearly
with the external magnetic field. Two branches of the spin excitation spectrum
are derived. Condition of mitigation of the spectrum defines the boundary
between the axial quadrupole and angular phases. The critical temperature of
the corresponding phase transition depends considerably on the anisotropy
constants of the biquadratic exchange interaction.",1405.0606v1
2014-05-08,Anisotropy of acoustooptic figure of merit in optically isotropic media,"We suggest a new approach for analyzing spatial anisotropy of acoustooptic
figure of merit (AOFM). The relations for the effective elastooptic
coefficients and the AOFM are derived for all possible types of acoustooptic
(AO) interactions in optically isotropic media, including non-solid-state and
solid-state amorphous media, and crystals belonging to the cubic system. Our
approach allows for finding the optimal geometries of AO interactions
characterized by the highest AOFM for a given material. The analysis is carried
out on the examples of cubic KBr and KAl(SO4)2x12H2O crystals which represent
different subgroups of the cubic symmetry class.",1405.1919v1
2014-06-04,Growth and superconducting anisotropies of F-substituted LaOBiSe2 single crystals,"F-substituted LaOBiSe2 single crystals were grown using CsCl flux. The
obtained single crystals showed a plate-like shape with a size of about 1.0 mm
square. The c-axis lattice constant of the grown crystals was determined to be
14.114(3) {\AA}. The superconducting critical temperature of the single crystal
was approximately 3.5 K. The superconducting anisotropies were determined to be
49 and 24 using the upper critical field and the effective mass model,
respectively.",1406.0921v1
2014-06-07,Anisotropy in Inflation with Non-minimal Coupling,"We study a new anisotropic inflation model, with an inflaton field
nonminimally coupled with the gravity and a vector field. We find that the
anisotropic attractor solution exists not only in the weak curvature coupling
limit, but more interestingly in the strong curvature coupling limit as well.
We show that in the strong curvature coupling limit, the contribution from the
anisotropy is greatly suppressed.",1406.1874v2
2014-06-13,Low thermal conductivity and triaxial phononic anisotropy of SnSe,"In this theoretical study, we investigate the origins of the very low thermal
conductivity of tin selenide (SnSe) using ab-initio calculations. We obtained
high-temperature lattice thermal conductivity values that are close to those of
amorphous compounds. We also found a strong anisotropy between the three
crystallographic axes: one of the in-plane directions conducts heat much more
easily than the other. Our results are compatible with most of the experimental
literature on SnSe, and differ markedly from the more isotropic values reported
by a recent study.",1406.3532v2
2014-07-04,Hexagonal type Ising nanowire with spin-1 core and spin-2 shell structure,"}Thermodynamic properties and phase diagrams of a mixed spin-(1, 2) Ising
ferrimagnetic system with single ion anisotropy on hexagonal nanowire are
studied by using effective-field theory with correlations. The susceptibility,
internal energy and specific heat of the system are numerically examined and
some interesting phenomena in these quantities are found. The effect of the
Hamiltonian parameters on phase diagrams are examined in detail. Besides
second-order phase transition, lines of first-order transition and tricritical
points are found. In particular, we found that for some negative values of
single-ion anisotropies, there exist first-order phase transitions.",1407.1147v1
2014-07-26,Late time Acceleration and Role of Skewness in Anisotropic models,"We study cosmological models with anisotropy in expansion rates in the
context of the recent observations predicting an accelerating universe. In the
absence of any anisotropy in the cosmic fluid, it is shown that the role of
skewness in directional Hubble rates is crucial in deciding the behavior of the
model. We find that incorporation of skewness leads to a more evolving
effective equation of state parameter.",1407.7791v1
2014-08-04,Universal parameterization of initial-state fluctuations and its applications to event-by-event anisotropy,"We propose Elliptic Power and Power parameterizations for the probability
distribution of initial state anisotropies in heavy-ion collisions. By assuming
a linear eccentricity scaling, the new parameterizations can also be applied to
fluctuations of harmonic flow. In particular, we analyze flow multi-particle
cumulants and event-by-event distributions, both of which are recently measured
at the LHC.",1408.0709v1
2014-08-05,Non-Local Transport Mediated by Spin-Supercurrents,"In thin film ferromagnets with perfect easy-plane anisotropy, the component
of total spin perpendicular to the easy plane is a good quantum number and the
corresponding spin supercurrent can flow without dissipation. In this Letter we
explain how spin supercurrents couple spatially remote spin-mixing vertical
transport channels, even when easy-plane anisotropy is imperfect, and discuss
the possibility that this effect can be used to fabricate new types of
electronic devices.",1408.1100v1
2014-08-06,Medium-induced optical effects for prompt photons,"Electromagnetic aspects of a QCD matter have been a hot topic in recent
years. High-energy heavy-ion experiments revealed that flow harmonics of direct
photons are not explained by most hydrodynamic models. In this work I discuss
possible effects of refraction by the hot medium since it can work as a lens
which converts its geometrical anisotropy into momentum anisotropy of photons.
Then elliptic flow and higher-order harmonics of prompt photons are estimated
numerically. The results indicate that they could be small but have
phenomenologically non-trivial consequences.",1408.1410v1
2014-08-10,Anisotropy universe in doubly warped product scheme,"We study the GMGHS spacetimes to analyze the evolution of the anisotropy
universe, which can be treated as a doubly warped products manifold possessing
warping functions (or scale factor) having the Kantowski-Sachs solution which
represents homogeneous but anisotropically expanding(contracting) cosmology. We
investigate the curvature associated with three phases in the evolution of the
universe.",1408.2182v4
2014-08-21,Evidence of a small crystal field anisotropy in GdCoIn$_5$,"We investigate the effects of an applied magnetic field on the magnetic
properties of the antiferromagnet GdCoIn$_5$. The prominent anisotropy observed
in the susceptibility below $T_N$ is rapidly suppressed by a field of just a
few Tesla. Further evidence of this low energy-scale is obtained from
magnetoresistance and magnetostriction experiments. The lattice lenght,
particulary, shows a sudden change below 2 Tesla when the magnetic field is
applied perpendicular to the crystallographic $\hat{c}$-axis. The experimental
results as a whole can be attributed to a small but non negligible higher-order
crystalline electric field.",1408.5156v1
2014-09-12,Nowhere to hide: closing in on cosmological homogeneity,"Homogeneity is a crucial, but poorly tested, assumption in cosmology. We
introduce a new approach which allows us to place limits on the presence of
localized structures within essentially our entire observable volume, using
cosmic microwave background secondary anisotropies. We find that structures
cannot exceed roughly 20 times their expected amplitude over most of our
observable volume. Similarly, we place tight constraints on statistical
inhomogeneity within our volume, performing the first power spectrum
reconstruction using secondary anisotropies alone. We find that the standard
model passes this important new consistency test. Our approach probes
homogeneity over vastly larger volumes and scales than previous studies based
on surveys.",1409.3831v1
2014-09-22,Anisotropic flow of the fireball fed by hard partons,"In nuclear collisions at highest accessible LHC energies, often more than one
dijet pairs deposit momentum into the deconfined expanding medium. With the
help of 3+1 dimensional relativistic hydrodynamic simulation we show that this
leads to measurable contribution to the anisotropy of collective transverse
expansion. Hard partons generate streams in plasma which merge if they come
close to each other. This mechanism correlates the resulting contribution to
flow anisotropy with the fireball geometry and causes an increase of the
elliptic flow in non-central collisions.",1409.6116v2
2014-09-22,Are EeV cosmic rays isotropic at intermediate scales?,"We study anisotropy of cosmic rays in the energy range 0.2-1.4 EeV at
intermediate angular scales using the public data set of the Pierre Auger
Observatory. At certain scales, the analysis reveals a number of deviations
from the isotropic distribution with the statistical significance above three
standard deviations. It also demonstrates that the anisotropy evolves with
energy. If confirmed with the complete Auger or Telescope Array data sets, the
result can shed new light on the structure of galactic magnetic fields and the
problem of transition from galactic to extragalactic cosmic rays.",1409.6138v1
2014-09-30,Relativistic Viscous Universe Models,"The research on relativistic universe models with viscous fluids is reviewed.
Viscosity may have been of significance during the early inflationary era, and
may also be of importance for the late time evolution of the Universe. Bulk
viscosity and shear viscosity cause exponential decay of anisotropy, while
nonlinear viscosity causes power-law decay of anisotropy. We consider also the
influence from turbulence, in connection with future singularities of the
universe (Big Rip and Little Rip). Finally, we review some recent developments
of causal cosmology theories.",1409.8561v1
2014-10-13,Eilenberger theory and London theory for transverse components of flux line lattice form factors in uniaxial superconductors,"We theoretically study the magnetic field orientation dependence of
longitudinal and transverse flux line lattice form factors in uniaxial
superconductors with anisotropy ratio corresponding to YBa_2_Cu_3_O_{7-delta}.
We discuss influences of the anisotropy ratio of coherence length, and
differences between the s-wave and the d_{x^2-y^2}-wave pairings. The
calculations are performed by two methods, the Eilenberger theory and the
London theory comparatively, and we study the cutoff function of the extended
London theory, which will be helpful in the analysis of the small angle neutron
scattering in the vortex states.",1410.3204v1
2014-10-14,Skyrmion-like states in multilayer exchange coupled ferromagnetic nanostructures with distinct anisotropy directions,"We report the experimental observation of magnetic skyrmion-like states in
patterned ferromagnetic nanostructures consisting of perpendicular magnetized
Co/Pt multilayer film exchange coupled with Co nanodisks in vortex state. The
magnetic force microscopy and micromagnetic simulations show that depending on
the magnitude of Co/Pt perpendicular anisotropy in these systems two different
modes of skyrmion formation are realized.",1410.4174v1
2014-10-23,Conductivity anisotropy helps to reveal the microscopic structure of a density wave at imperfect nesting,"Superconductivity or metallic state may coexist with density wave ordering at
imperfect nesting of the Fermi surface. In addition to the macroscopic spatial
phase separation, there are, at least, two possible microscopic structures of
such coexistence: (i) the soliton-wall phase and (ii) the ungapped
Fermi-surface pockets. We show that the conductivity anisotropy allows to
distinguish between these two microscopic density-wave structures. The results
obtained may help to analyze the experimental observations in layered organic
metals (TMTSF)$_{2}$PF$_{6}$, (TMTSF)$_{2}$ClO$_{4}$, $\alpha
$-(BEDT-TTF)$_{2}$KHg(SCN)$_{4}$ and in other compounds.",1410.6314v1
2014-10-31,Elliptic flow of thermal photons in chemically non-equilibrated QCD medium,"Heavy-ion experiments have recently revealed that azimuthal momentum
anisotropy -- elliptic flow -- of direct photons from a QCD medium is a few
times larger than hydrodynamic predictions. I present a possible explanation
for the enhancement based on late quark chemical equilibration. The color glass
theory indicates that the medium is initially gluon-rich. Thermal photons are
then mainly produced after quarks are produced, at which point large flow
anisotropy is developed. The numerical estimations indicate that slow chemical
equilibration visibly enhances the elliptic flow of thermal photons.",1410.8621v1
2014-12-05,A Relativistic Plasma Polarizer: Impact of Temperature Anisotropy on Relativistic Transparency,"3D particle-in-cell simulations demonstrate that the enhanced transparency of
a relativistically hot plasma is sensitive to how the energy is partitioned
between different degrees of freedom. For an anisotropic electron distribution,
propagation characteristics, like the critical density, will depend on the
polarization of the electromagnetic wave. Despite the onset of the Weibel
instability in such plasmas, the anisotropy can persist long enough to affect
laser propagation. This plasma can then function as a polarizer or a waveplate
to dramatically alter the pulse polarization.",1412.1865v1
2015-02-03,Modeling anisotropic charged neutron star in isotropic coordinates,"We present a spherically symmetric solution of the general relativistic field
equations in isotropic coordinates for charged fluid with pressure anisotropy,
compatible with a super dense star modeling. Further, we have constructed an
anisotropic model of super dense star with all degree of suitability. We also
observed that by increasing anisotropy, the maximum mass of super dense stars
also decreases.",1502.03378v1
2015-02-24,Spin rectification for collinear and non-collinear magnetization and external magnetic field configurations,"Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically
detected for collinear and non-collinear magnetization and external magnetic
field configurations. The line shape, line width and signal polarity are
analysed. The spin rectication theory has been much extended by taking the
magneto-crystalline anisotropy and shape anisotropy into account, which
explained non-collinear resonances and agrees very well with experimental data.
Thus, a comprehensive understanding of spin rectification in ferromagnetic
metal was demonstrated in this work.",1502.06859v1
2015-04-20,URu2Si2: hidden order and amplitude of quantum oscillations,"It is shown that the hidden ordered (HO) state in heavy fermionic metal
URu2Si2 is either nonconventional charge density wave (CDW) or
antiferroelectric (AFE) commensurate ordering. Similar to antiferromagnetic
(AF) order an antiferroelectric order creates momentum dependence of conducting
electrons $g$-factor. This even modest anisotropy along with the anisotropy of
heavy cyclotron mass can produce multiple effect of so called zero-spin
splitting in the amplitude of the de Haas - van Alphen and the Shubnikov - de
Haas signals as function of direction of magnetic field.",1504.05020v2
2015-04-29,"L1$_0$ stacked binaries as candidates for hard magnets: FePt, MnAl and MnGa","A novel strategy of stacking binary magnets to enhance the magneto
crystalline anisotropy is explored. This strategy is used in the search for
hard magnets by studying FePt/MnGa and FePt/MnAl stacks. The choice of these
binaries is motivated by the fact that they already possess large magneto
crystalline anisotropy. Several possible alternative structures for these
materials are explored in order to reduce the amount of Pt owing to its high
cost.",1504.07827v1
2015-05-15,Dilepton production from the quark-gluon plasma using leading-order (3+1)D anisotropic hydrodynamics,"Dilepton production from the quark-gluon plasma (QGP) phase of
ultra-relativistic heavy-ion collisions is computed using the leading-order
(3+1)-dimensional anisotropic hydrodynamics. It is shown that high-energy
dilepton spectrum is sensitive to the initial local-rest-frame momentum-space
anisotropy of the QGP. Our findings suggest that it may be possible to
constrain the early-time momentum-space anisotropy in relativistic heavy-ion
collisions using high-energy dilepton yields.",1505.04018v1
2015-05-26,Quantum correlations in Ising-XYZ diamond chain structure under an external magnetic field,"In this paper, we consider an entangled Ising-XYZ diamond chain structure.
Quantum correlations for this model is investigated by using of quantum discord
and trace distance discord. Quantum correlations is obtained for different
values of the anisotropy parameter, magnetic field and temperature. By
comparison between quantum correlations, we show trace distance discord is
always larger than quantum discord. Finally, some novel effects, such as
increasing the quantum correlations with temperature and constructive role of
anisotropy parameter which may paly to the quantum correlations were observed.",1505.06820v2
2015-05-27,Excitation of magnetic precession in bismuth iron garnet via a polarization-independent impulsive photomagnetic effect,"A polarization-independent, nonthermal optical effect on the magnetization in
bismuth iron garnet is found, in addition to the circular
polarization-dependent inverse Faraday effect and the linear
polarization-dependent photoinduced magnetic anisotropy. Its impulsive
character is demonstrated by the field dependence of the amplitude of the
resulting precession, which cannot be explained by a long-living photo or
heat-induced anisotropy.",1505.07447v1
2015-06-09,Hysteresis behaviors of a spin-1 anisotropic Heisenberg model,"The hysteresis behaviors of anisotropic S-1 Heisenberg model have been
studied within the effective field theory with two spin cluster. After giving
the phase diagrams, the effect of the crystal field and anisotropy in the
exchange interaction on the hysteresis loops have been determined. One
important finding is double hysteresis loop behavior of the system in the low
temperature and negative crystal field region, which disappears with the
decreasing anisotropy in the exchange interaction. This behavior was carefully
investigated and physical explanation has also been given.",1506.02859v1
2015-06-24,Inflation after Planck and BICEP2,"We discuss the inflationary paradigm, how it can be tested, and how various
models of inflation fare in the light of data from Planck and BICEP2. We
introduce inflation and reheating, and discuss temperature and polarisation
anisotropies in the cosmic microwave background radiation due to quantum
fluctuations during inflation. Fitting observations of the anisotropies with
theoretical realisations obtained by varying various parameters of the
curvature power spectrum and cosmological parameters enables one to obtain the
allowed ranges of these parameters. We discuss how to relate these parameters
to inflation models which allows one to rule in or out specific models of
inflation.",1506.07433v1
2015-07-02,Flow anisotropies due to momentum deposition from hard partons,"In nuclear collisions at the LHC large number of hard partons are created in
initial partonic interactions, so that it is reasonable to suppose that they do
not thermalise immediately but deposit their energy and momentum later into the
evolving hot quark-gluon fluid. We show that this mechanism leads to
contribution to flow anisotropies at all orders which are non-negligible and
should be taken into account in realistic simulations.",1507.00499v1
2015-09-03,Dynamic Entanglement Evolution of Two-qubit XYZ Spin Chain in Markovian Environment,"We propose a new approach called Ket-Bra Entangled State (KBES) Method for
converting master equation into Schr\""{o}dinger-like equation. With this
method, we investigate decoherence process and entanglement dynamics induced by
a $2$-qubit spin chain that each qubit coupled with reservoir. The spin chain
is an anisotropy $XYZ$ Heisenberg model in the external magnetic field $B$, the
corresponding master equation is solved concisely by KBES method; Furthermore,
the effects of anisotropy, temperature, external field and initial state on
concurrence dynamics is analyzed in detail for the case that initial state is
Extended Wenger-Like(EWL) state. Finally we research the coherence and
concurrence of the final state (namely the density operator for time tend to
infinite)",1509.01001v1
2015-09-16,High-speed measurement of rotational anisotropy nonlinear optical harmonic generation using position sensitive detection,"We present a method of performing high-speed rotational anisotropy nonlinear
optical harmonic generation experiments at rotational frequencies of several
hertz by projecting the harmonic light reflected at different angles from a
sample onto a stationary position sensitive detector. The high rotational speed
of the technique, $10^3$ to $10^4$ times larger than existing methods, permits
precise measurements of the crystallographic and electronic symmetries of
samples by averaging over low frequency laser power, beam pointing, and pulse
width fluctuations. We demonstrate the sensitivity of our technique by
resolving the bulk four-fold rotational symmetry of GaAs about its [001] axis
using second harmonic generation.",1509.04779v1
2015-09-17,On anisotropic black branes with Lifshitz scaling,"In this paper, based on the method of scalar perturbations, we construct the
\textit{anisotropic} charged Lifshitz background perturbatively upto leading
order in the anisotropy. We perform our analysis both in the extremal as well
as in the non extremal limit. Finally, we probe the so called superfluid phase
of the boundary theory and explore the effects of anisotropy on the
superconducting condensate.",1509.05229v2
2015-10-11,Crystal Field Excitations in Breathing Pyrochlore Antiferromagnet Ba3Yb2Zn5O11,"Inelastic neutron scattering measurement is performed on a breathing
pyrochlore antiferromagnet Ba3Yb2Zn5O11. The observed dispersionless
excitations are explained by a crystalline electric field (CEF) Hamiltonian of
Kramers ion Yb3+ of which the local symmetry exhibits C3v point group symmetry.
The magnetic susceptibility previously reported is consistently reproduced by
the energy scheme of the CEF excitations. The obtained wave functions of the
ground state Kramers doublet exhibit the planer-type anisotropy. The result
demonstrates that Ba3Yb2Zn5O11 is an experimental realization of breathing
pyrochlore antiferromagnet with a pseudospin S = 1/2 having easy-plane
anisotropy.",1510.03049v1
2015-10-13,Probing strongly coupled anisotropic plasmas from higher curvature gravity,"We consider five-dimensional AdS-axion-dilaton gravity with a Gauss-Bonnet
term and use a black brane solution displaying spatial anisotropy as the
gravity dual of a strongly coupled anisotropic plasma. We compute several
observables relevant to the study of the plasma, namely, the drag force, the
jet quenching parameter, the quarkonium potential and the thermal photon
production. The effects of higher derivative corrections and of the anisotropy
are discussed and compared with previous results.",1510.03774v3
2015-10-16,Reaction diffusion dynamics and the Schryer-Walker solution for domain walls of the Landau-Lifshitz-Gilbert equation,"We study the dynamics of the equation obtained by Schryer and Walker for the
motion of domain walls. The reduced equation is a reaction diffusion equation
for the angle between the applied field and the magnetization vector. If the
hard axis anisotropy $K_d$ is much larger than the easy axis anisotropy $K_u$,
there is a range of applied fields where the dynamics does not select the
Schryer-Walker solution. We give analytic expressions for the speed of the
domain wall in this regime and the conditions for its existence.",1510.04927v1
2015-11-14,Incoherent magnetization dynamics in strain mediated switching of magnetostrictive nanomagnets,"Micromagnetic studies of the magnetization change in magnetostrictive
nanomagnets subjected to stress are performed for nanomagnets of different
sizes. The interplay between demagnetization, exchange and stress anisotropy
energies is used to explain the rich physics of size-dependent magnetization
dynamics induced by modulating stress anisotropy in planar nanomagnets. These
studies have important implications for strain mediated ultralow energy
magnetization change in nanomagnets and its application in energy-efficient
nanomagnetic computing systems.",1511.04617v1
2015-11-21,Hybridization and anisotropy in the exchange interaction in 3D Dirac semimetals,"We study the Ruderman-Kittel-Kasuya-Yosida interaction in 3D Dirac
semimetals. Using retarded Green's functions in real space, we obtain and
analyze asymptotic expressions for the interaction, with magnetic impurities at
different distances and relative angle with respect to high symmetry directions
on the lattice. We show that the Fermi velocity anisotropy in these materials
produces a strong renormalization of the magnitude of the interaction, as well
as a correction to the frequency of oscillation in real space. Hybridization of
the impurities to different conduction electron orbitals are shown to result in
interesting anisotropic spin-spin interactions which can generate spiral spin
structures in doped samples.",1511.06933v1
2015-12-01,Wave Propagation in Undulated Structural Lattices,"This work investigates wave propagation in undulated square structural
lattices. The undulated pattern is obtained by imposing an initial curvature to
the lattice's elements. The study considers both periodic undulated structures,
in which the undulation is uniform throughout the structure as well as graded
undulated patterns, in which the undulation is modulated within the lattice.
Undulation is specifically considered in relation to its ability to induce
anisotropy in the equivalent mechanical properties and to break the symmetry of
the straight square lattice. Results show that wave motion is inhibited within
specified frequency ranges owing to the generation of band gaps, and in
specific directions as a result of the undulation-induced anisotropy.",1512.00114v1
2015-12-07,Anisotropy of the magnetic properties of the FeTe0.65Se0.35 superconductor,"The magnetization anisotropy of a layered superconductor FeTe0.65Se0.35
sample is experimentally studied in a magnetic field directed either along the
layers of the plane, or perpendicular to them. The value of the vortex pinning
potential in a weak magnetic field, and the critical current density ratio are
determined for these directions. The results are discussed within the framework
of presenting the sample as layers of fine single crystals, divided by weak
interlayer superconducting bonds with magnetic inclusions.",1512.02027v1
2015-12-09,Scaling laws for the critical current density in anisotropic biaxial superconductors,"To understand the anisotropy of flux pinning and critical current density in
technological superconductors, the scaling law for the anisotropy of
single-vortex collective pinning in uniaxial superconductors is extended to
flux-bundle collective pinning in biaxial superconductors. The scaling results
show that in a system of random uncorrected point defects, the critical current
density is described by a unified function with the magnetic field of the
scaled isotropic superconductor. The obtained angular dependence of the
critical current density depicts the main features of experimental
observations, considering possible corrections due to the strong-pinning
interaction.",1512.02774v1
2015-12-19,The effect of momentum deposition during fireball evolution on flow anisotropy,"The highest LHC energies give rise to production of many pairs of hard
partons which deposit four-momentum into the expanding fireball matter. We
argue that it is necessary to include momentum deposition during fireball
evolution into 3+1 dimensional hydrodynamic simulations of the collision. This
influence cannot be accounted for simply by modifying initial conditions of the
simulation. The resulting contribution to flow anisotropy is correlated with
the fireball geometry and causes an increase of the elliptic flow in
non-central collisions. The results are presented for various scenarios with
energy and momentum deposition to clearly demonstrate this effect.",1512.06215v2
2016-01-18,Anisotropic solutions in f(R) Gravity,"Anisotropic cosmological models are investigated in the frame work of $f(R)$
gravity in the metric formalism. Plane symmetric models are considered to
incorporate anisotropy in the expansion rates along different spatial
directions. The anisotropy in expansion rates are assumed to be maintained
throughout the cosmic evolution. Two accelerating models are constructed by
considering different functional forms for f(R). The viability of these models
are tested through a stability analysis.",1601.05019v1
2016-02-26,Reorientation of quantum Hall stripes within a partially filled Landau level,"We investigate the effect of the filling factor on transport anisotropies,
known as stripes, in high Landau levels of a two-dimensional electron gas. We
find that at certain in-plane magnetic fields, the stripes orientation is
sensitive to the filling factor within a given Landau level. This sensitivity
gives rise to the emergence of stripes away from half-filling while an
orthogonally-oriented, native stripes reside at half-filling. This switching of
the anisotropy axes within a single Landau level can be attributed to a strong
dependence of the native symmetry breaking potential on the filling factor.",1602.08395v1
2016-04-03,Soliton collisions in soft magnetic nanotube with uniaxial anisotropy,"The structure of stable magnetic solitons of various orders in soft magnetic
nanotube with uniaxial magnetic anisotropy has been studied using numerical
simulation. Solitons of even order are immobile in axially applied magnetic
field. Odd solitons show decreased mobility with respect to that of head-to
head domain wall. Solitons of various orders can participate in nanotube
magnetization reversal process. Various coalescence and decomposition processes
in soliton assembly are considered. It is shown that the general magnetization
state of magnetic nanotube consists of chains of magnetic solitons of various
orders.",1604.00614v1
2016-04-17,Angular anisotropy of time delay in XUV/IR photoionization of H$_2^+$,"We develop a novel technique for modeling of atomic and molecular ionization
in superposition of XUV and IR fields with characteristics typical for
attosecond streaking and RABBITT experiments. The method is based on solving
the time-dependent Schr\""odinger equation in the coordinate frame expanding
along with the photoelectron wave packet. The efficiency of the method is
demonstrated by calculating angular anisotropy of photoemission time delay of
the H$_2^+$ ion in a field configuration of recent RABBITT experiments.",1604.04938v1
2016-04-19,Ultrahigh Energy Cosmic Rays: A Galactic Origin?,"It is suggested that essentially all of the UHECRs we detect, including those
at the highest energy, originate in our Galaxy. It is shown that even if the
density of sources decreases with Galactic radius, then the anisotropy and
composition can be understood. Inward anisotropy, as recently reported by the
Auger collaboration can be understood as drift along the current sheet of
UHECRs originating outside the solar circle, as predicted in Kumar and Eichler
(2014), while those originating within the solar circle exit the Galaxy at high
latitudes.",1604.05721v1
2016-05-03,Ion collisional transport coefficients in the solar wind at 1 AU,"Proton and alpha particle collisional transport coefficients (isotropization,
relative deceleration frequencies and heating rates) at 1 AU are quantified
using the WIND/SWE data. In agreement with previous studies the ion-ion Coulomb
collisions are generally important for slow solar wind streams and tend to
reduce the temperature anisotropies, the differential streaming and the
differences between proton and alpha particle temperatures. In slow solar wind
streams the Coulomb collisions between protons and alpha particles are
important for the overall proton energetics as well as for the relative
deceleration between the two species. It is also shown that ion temperature
anisotropies and differential streaming need to be generally taken into account
for evaluation of the collisional transport coefficients.",1605.00804v1
2016-05-11,Proton structure in high-energy high-multiplicity p-p collisions,"A few-body proton image, expected to be derivable from QCD in the
renormalization group procedure for effective particles, is used within the
Monte Carlo Glauber model to calculate the anisotropy coefficients in the
initial collision-state of matter in high-energy high-multiplicity
proton-proton interaction events. We estimate the ridge-like correlations in
the final hadronic state by assuming their proportionality to the initial
collision-state anisotropy. In our estimates, some distinct few-body proton
structures appear capable of accounting for the magnitude of p-p ridge effect,
with potentially discernible differences in dependence on multiplicity.",1605.03488v1
2016-05-28,Unidirectional superscattering by multilayered cavities of effective radial anisotropy,"We achieve unidirectional forward superscattering by multilayered spherical
cavities which are effectively radially anisotropic. It is demonstrated that,
relying on the large effective anisotropy, the electric and magnetic dipoles
can be tuned to spectrally overlap in such cavities, which satisfies the
Kerker's condition of simultaneous backward scattering suppression and forward
scattering enhancement. We show such scattering pattern shaping can be obtained
in both all-dielectric and plasmonic multilayered cavities, and believe that
the mechanism we have revealed provides extra freedom for scattering shaping,
which may play a significant role in many scattering related applications and
also in optoelectronic devices made up of intrinsically anisotropic two
dimensional materials.",1605.08895v1
2016-06-21,Characterization of the scintillation anisotropy in crystalline stilbene scintillator detectors,"This paper reports a series of measurements that characterize the directional
dependence of the scintillation response of crystalline melt-grown and
solution-grown stilbene to incident DT and DD neutrons. These measurements give
the amplitude and pulse shape dependence on the proton recoil direction over
one hemisphere of the crystal, confirming and extending previous results in the
literature for melt-grown stilbene and providing the first measurements for
solution-grown stilbene. In similar measurements of liquid and plastic
detectors, no directional dependence was observed, confirming the hypothesis
that the anisotropy in stilbene and other organic crystal scintillators is a
result of internal effects due to the molecular or crystal structure and not an
external effect on the measurement system.",1606.06715v1
2016-06-30,The effect of minijet on hadron spectra and azimuthal anisotropy in heavy-ion collisions,"Here I review the transverse momentum distributions of identified hadrons
produced in Au-Au collisions at RHIC and Pb-Pb collisions at LHC in the
framework of recombination model. Minijets play an important role in generating
shower partons in the intermediate $p_T$ region. At LHC, the resultant soft
shower partons are even found to dominate over the thermal partons in the
non-strange sector. The azimuthal anisotropy of the produced hadrons could also
be explained as the consequence of the effects of minijets. Harmonic analysis
of the $\phi$ dependence leads to $v_n(p_T, b)$ that can be well produced
without reference to flow.",1606.09373v1
2016-07-28,The random anisotropy model revisited,"We revisit the thermodynamic behavior of the random-anisotropy O($N$) model
by investigating its large-$N$ limit. We focus on the system at zero
temperature where the mean-field-like artifacts of the large-$N$ limit are less
severe. We analyze the connection between the description in terms of
self-consistent Schwinger-Dyson equations and the functional renormalization
group. We provide a unified description of the phase diagram and critical
behavior of the model and clarify the nature of the possible ""glassy"" phases.
Finally we discuss the implications of our findings for the finite-$N$ and
finite-temperature systems.",1607.08515v1
2016-10-21,Concurrency of anisotropy and spatial dispersion in low refractive index dielectric composites,"The article demonstrates uncommon manifestation of spatial dispersion in low
refractive index contrast 3D periodic dielectric composites with periods of
about one tenth of the wavelength. First principles simulations by the well
established plane wave method reveal that spatial dispersion leads to
appearance of additional optical axes and can compensate anisotropy in certain
directions.",1610.06828v2
2016-11-04,Spontaneous generation of a temperature anisotropy in a strongly coupled magnetized plasma,"A magnetic field was recently shown to enhance field-parallel heat conduction
in a strongly correlated plasma whereas cross-field conduction is reduced. Here
we show that in such plasmas, the magnetic field has the additional effect of
inhibiting the isotropization process between field-parallel and cross-field
temperature components thus leading to the emergence of strong and long-lived
temperature anisotropies when the plasma is locally perturbed. An extended heat
equation is shown to describe this process accurately.",1611.01397v1
2016-11-29,Odd Azimuthal Anisotropy of the Glasma for pA Scattering,"In this paper we analytically extract the odd azimuthal anisotropy in the
Classical Yang-Mills equations for the Glasma for pA collisions. We compute the
first non-trivial term in the expansion of the proton sources of color charge.
The computation is valid in the limit of a large nucleus when the produced
particle momenta are larger than the saturation momentum of the proton.",1611.09870v4
2016-11-30,Two-dimensional Phononic Crystals with Acoustic-Band Negative Refraction,"A two-dimensional phononic crystal (PC) can exhibit longitudinal-mode
negative energy refraction on its lowest (acoustical) frequency pass band. The
effective elastodynamic properties of a typical PC are calculated and it is
observed that the components of the effective density tensor can achieve
negative values at certain low frequencies on the acoustical branches for the
longitudinal-mode pass-band, and that negative refraction may be accompanied by
either positive or negative effective density. Furthermore, such a PC has a
high anisotropy ratio at certain low frequencies, offering potential for
application to acoustic cloaking where effective material anisotropy is
essential.",1612.00037v1
2016-11-28,On Cracking of Charged Anisotropic Polytropes,"Recently in \cite{34}, the role of electromagnetic field on the cracking of
spherical polytropes has been investigated without perturbing charge parameter
explicitly. In this study, we have examined the occurrence of cracking of
anisotropic spherical polytropes through perturbing parameters like anisotropic
pressure, energy density and charge. We consider two different types of
polytropes in this study. We discuss the occurrence of cracking in two
different ways $(i)$ by perturbing polytropic constant, anisotropy and charge
parameter $(ii)$ by perturbing polytropic index, anisotropy and charge
parameter for each case. We conclude that cracking appears for a wide range of
parameters in both cases. Also, our results are reduced to \cite{33} in the
absence of charge.",1612.00290v1
2016-12-22,Spin Superfluidity in Biaxial Antiferromagnetic Insulators,"Antiferromagnets may exhibit spin superfluidity since the dipole interaction
is weak. We seek to establish that this phenomenon occurs in insulators such as
NiO, which is a good spin conductor according to previous studies. We
investigate nonlocal spin transport in a planar antiferromagnetic insulator
with a weak uniaxial anisotropy. The anisotropy hinders spin superfluidity by
creating a substantial threshold that the current must overcome. Nevertheless,
we show that applying a high magnetic field removes this obstacle near the
spin-flop transition of the antiferromagnet. Importantly, the spin
superfluidity can then persist across many micrometers, even in dirty samples.",1612.07440v2
2017-01-01,Electrical Transport of perpendicularly magnetized L10-MnGa and MnAl films,"Ferromagnetic films of L10-ordered MnGa and MnAl that exhibit giant
perpendicular magnetic anisotropy and great controllability in the magnetism
and structural disorders show promise not only in the applications in magnetic
recording, permanent magnets and spintronics, but also in controllable studies
of disorder-relevant electrical transport phenomena. In this article, we review
the intriguing experimental observations of the orbital two-channel Kondo
effect and anomalous Hall effect in L10-ordered MnGa and MnAl thin films with
perpendicular magnetic anisotropy. We also give a perspective with regards to
the future technological and fundamental applications of these perpendicularly
magnetized Mn-based binary alloy films.",1701.00191v1
2017-02-16,Domain wall nucleation in ferromagnetic nanowire with perpendicular magnetization stimulated by stray field of V-shaped magnetic particle,"We report the results of micromagnetic simulations of domain wall (DW)
nucleation and pinning/depinning processes in ferromagnetic planar structure
consisting of nanowire (NW) with perpendicular anisotropy and special V-shaped
nanoparticle (NP) with in-plane anisotropy located on top of NW. The
magnetization reversal features of this system in an external magnetic field
are investigated depending on the direction of particle magnetic moment.
Possible variants of magnetic logic cells (LCs) based on such system are
discussed.",1702.05416v1
2017-02-19,Width of the confinement-induced resonance in a quasi-one-dimensional trap with transverse anisotropy,"We theoretically study the width of the s-wave confinement-induced resonance
(CIR) in quasi-one-dimensional atomic gases under tunable transversely
anisotropic confinement. We find that the width of the CIR can be tuned by
varying the transverse anisotropy. The change in the width of the CIR can
manifest itself in the position of the discontinuity in the interaction energy
density, which can be probed experimentally.",1702.05761v3
2017-03-10,Effects on the CMB from magnetic field dissipation before recombination,"Magnetic fields present before decoupling are damped due to radiative
viscosity. This energy injection affects the thermal and ionization history of
the cosmic plasma. The implications for the CMB anisotropies and polarization
are investigated for different parameter choices of a non helical stochastic
magnetic field. Assuming a Gaussian smoothing scale determined by the magnetic
damping wave number at recombination it is found that magnetic fields with
present day strength less than 0.1 nG and negative magnetic spectral indices
have a sizeable effect on the CMB temperature anisotropies and polarization.",1703.03650v1
2017-04-26,Superscattering pattern shaping for radially anisotropic nanowires,"We achieve efficient shaping of superscattering by radially anisotropic
nanowires relying on resonant multipolar interferences. It is shown that the
radial anisotropy of refractive index can be employed to resonantly overlap
electric and magnetic multipoles of various orders, and as a result effective
superscattering with different engineered angular patterns can be obtained. We
further demonstrate that such superscattering shaping relying on unusual radial
anisotropy parameters can be directly realised with isotropic multi-layered
nanowires, which may shed new light to many fundamental researches and various
applications related to scattering particles.",1704.07994v2
2017-05-04,Reduced models for ferromagnetic thin films with periodic surface roughness,"We investigate the influence of periodic surface roughness in thin
ferromagnetic films on shape anisotropy and magnetization behavior inside the
ferromagnet. Starting from the full micromagnetic energy and using methods of
homogenization and $\Gamma$-convergence we derive a two dimensional local
reduced model. Investigation of this model provides an insight on the formation
mechanism of {\it perpendicular magnetic anisotropy} and uniaxial anisotropy
with an {\it arbitrary} preferred direction of magnetization.",1705.01742v1
2017-06-10,Dynamical features of an anisotropic cosmological model,"The dynamical features of Bianchi type $VI_h$ $(BVI_h)$ universe are
investigated in $f(R,T)$ theory of gravity. The field equations and the
physical properties of the model are derived considering a power law expansion
of the universe. The effect of anisotropy on the dynamics of the universe as
well on the energy conditions are studied. The assumed anisotropy of the model
is found to have substantial effects on the energy condition and dynamical
parameters.",1706.03767v2
2017-06-15,Can decaying particle explain cosmic infrared background excess?,"Recently the CIBER experiment measured the diffuse cosmic infrared background
(CIB) flux and claimed an excess compared with integrated emission from
galaxies. We show that the CIB spectrum can be fitted by the additional photons
produced by the decay of a new particle. However, it also contributes too much
to the anisotropy of the CIB, which is in contradiction with the anisotropy
measurements by the CIBER and Hubble Space Telescope.",1706.04921v1
2017-06-16,Nanoconstriction spin-Hall oscillator with perpendicular magnetic anisotropy,"We experimentally study spin-Hall nano-oscillators based on [Co/Ni]
multilayers with perpendicular magnetic anisotropy. We show that these devices
are capable of single-frequency auto-oscillations at current densities
comparable to those in the in-plane magnetized oscillators. The demonstrated
oscillators exhibit large magnetization precession amplitudes, and their
oscillation frequency is highly tunable by the electric current. These features
make them promising for applications in high-speed integrated microwave
circuits.",1706.05302v1
2017-06-21,Quantum Phase Transition in the Twisted Three-Leg Spin Tube,"We investigate the spin-1/2 twisted three-leg antiferromagnetic quantum spin
tube in the presence of the easy-plane anisotropy, using the numerical
diagonalization of finite-size clusters. And we observe cases of the existence
and the absence of magnetization plateau at 1/3 height of saturation
magnetization when the anisotropy is tuned. The
phenomenological-renormalization analysis indicates a quantum phase transition
between the 1/3 magnetization plateau phase and the plateauless one. The phase
diagram is also presented.",1706.06947v1
2017-08-10,Control of the gyration dynamics of magnetic vortices by the magnetoelastic effect,"The influence of a strain-induced uniaxial magnetoelastic anisotropy on the
magnetic vortex core dynamics in microstructured magnetostrictive
Co$_{40}$Fe$_{40}$B$_{20}$ elements was investigated with time-resolved
scanning transmission x-ray microscopy. The measurements revealed a
monotonically decreasing eigenfrequency of the vortex core gyration with the
increasing magnetoelastic anisotropy, which follows closely the predictions
from micromagnetic modeling.",1708.03123v1
2017-08-16,The Microscopic Model of BiFeO$_3$,"Many years and great effort have been spent constructing the microscopic
model for the room temperature multiferroic BiFeO3 However, earlier models
implicitly assumed that the cycloidal wavevector q was confined to one of the
three-fold symmetric axis in the hexagonal plane normal to the electric
polarization. Because recent measurements indicate that q can be rotated by a
magnetic field, it is essential to properly treat the anisotropy that confines
q at low fields. We show that the anisotropy energy $-K_3 S^6 \sin^6 \theta
\cos 6 \phi $ confines the wavevectors q to the three-fold axis $\phi =0$ and
$+-2 \pi/3$ within the hexagonal plane with $\theta = \pi /2$.",1708.04925v1
2017-08-25,"Classification of symmetry properties of waveguide modes in presence of gain/losses, anisotropy/bianisotropy, or continuous/discrete rotational symmetry","We study the symmetric properties of waveguide modes in presence of
gain/losses, anisotropy/bianisotropy, or continuous/discrete rotational
symmetry. We provide a comprehensive approach to identity the modal symmetry by
constructing a $4\times4$ waveguide Hamiltonian and searching the symmetric
operation in association with the corresponding waveguides. We classify the
chiral/time reversal/parity/parity time/rotational symmetry for different
waveguides, and provide the criterion for the aforementioned symmetry
operations. Lastly, we provide examples to illustrate how the symmetry
operations can be used to classify the modal properties from the symmetric
relation between modal profiles of several different waveguides.",1708.07600v1
2017-08-27,Direct Photon Production and Azimuthal Anisotropy at Low Transverse Momentum measured in PHENIX,"The PHENIX experiment discovered a large excess of low-$p_{T}$ direct photons
in Au+Au collisions at 200 GeV compared to reference p+p collisions, which has
been attributed to thermal radiation from the medium produced in the
collisions. At the same time the excess photons show a large azimuthal
anisotropy, expressed as Fourier coefficients $v_{2}$ and $v_{3}$. These
surprising results have not yet been fully described by theoretical models. We
will present the results obtained from real photons in the electromagnetic
calorimeter and photons converted on the outer shell of the Hadron Blind
Detector. PHENIX has also developed a new technique to identify conversion
photons without assuming the radius where the conversion happened. This method
greatly increases the available statistics and reduces systematic
uncertainties.",1708.08088v1
2017-09-24,"Anisotropic cosmological reconstruction in $f(R,T)$ gravity","Anisotropic cosmological models are constructed in $f(R,T)$ gravity theory to
investigate the dynamics of universe concerning the late time cosmic
acceleration. Using a more general and simple approach, the effect of the
coupling constant and anisotropy on the cosmic dynamics have been investigated.
Cosmic anisotropy is found affect substantially the cosmic dynamics.",1709.10399v2
2017-10-25,Flux tubes in $N_f=2+1$ QCD with external magnetic fields,"We study the behavior of the confining flux tube in $N_f=2+1$ QCD at the
physical point, discretized with the stout smearing improved staggered quark
action and the tree level Symanzik gauge action. We discuss how it depends on a
uniform external magnetic field, showing how it displays anisotropies with
respect to the magnetic field direction. Moreover, we compare the observed
anisotropy pattern with that of the static quark-antiquark potential we
obtained in our previous works.",1710.09215v1
2017-11-15,Anisotropy of thermal dileptons,"The meaningful specific anisotropy in the angle distribution of leptons with
respect to the three-momentum of pair is predicted as a feasibility signature
of synchrotron-like mechanism resulting from the quarks interacting with a
collective confining color field in the heavy ion collisions. The lepton pair
production rate and the spectrum of pair invariant mass are presented for this
new dilepton source that is apparently not taken into consideration in the
available phenomenological estimates.",1711.05459v2
2017-11-28,Massive gravity and the suppression of anisotropies and gravitational waves in a matter-dominated contracting universe,"We consider a modified gravity model with a massive graviton, but which
nevertheless only propagates two gravitational degrees of freedom and which is
free of ghosts. We show that non-singular bouncing cosmological background
solutions can be generated. In addition, the mass term for the graviton
prevents anisotropies from blowing up in the contracting phase and also
suppresses the spectrum of gravitational waves compared to that of the scalar
cosmological perturbations. This addresses two of the main problems of the
matter bounce scenario.",1711.10472v1
2017-11-30,"Does Anisotropic ""Inflation"" Produce a Small Statistical Anisotropy?","Anisotropic inflation is an interesting model with an U(1) gauge field and it
predicts the statistical anisotropy of the curvature perturbation characterized
by a parameter $g_*$. However, we find that the background gauge field does not
follow the classical attractor solution due to the stochastic effect. We
develop the stochastic formalism of a vector field and solve Langevin and
Fokker-Planck equations. It is shown that this model is excluded by the CMB
constraint $g_*\le 10^{-2}$ with a high probability about $99.999\%$.",1711.11539v1
2018-02-06,Co/Ni multilayers for spintronics: high spin-polarization and tunable magnetic anisotropy,"In this paper we analyze in details the electronic properties of (Co/Ni)
multilayers, a model system for spintronics devices. We use magneto-optical
Kerr (MOKE), spin-polarized photoemission spectroscopy (SRPES), x-ray magnetic
circular dichroism (XMCD) and anomalous surface diffraction experiments to
investigate the electronic properties and perpendicular magnetic anisotropy
(PMA) in [Co(x)/Ni(y)] single-crystalline stacks grown by molecular beam
epitaxy.",1802.02020v1
2018-02-07,Virtual photon polarization and dilepton anisotropy in relativistic nucleus-nucleus collisions,"The polarization of virtual photons produced in relativistic nucleus-nucleus
collisions provides information on the conditions in the emitting medium. In a
hydrodynamic framework, the resulting angular anisotropy of the dilepton final
state depends on the flow as well as on the transverse momentum and invariant
mass of the photon. We illustrate these effects in dilepton production from
quark-antiquark annihilation in the QGP phase and $\pi^+\pi^-$ annihilation in
the hadronic phase for a static medium in global equilibrium and for a
longitudinally expanding system.",1802.02479v2
2018-03-05,Holographic Entanglement Entropy Decomposition in an Anisotropic Gauge Theory,"We study holographic entanglement entropy in spatially anisotropic field
theory. We observe that for the background we consider in this paper, to a good
approximation, the holographic entanglement entropy can be decomposed into two
terms. One of them is the entanglement entropy of the isotropic field theory at
fixed temperature and the other term is only a function of anisotropy
parameter. Moreover, for large enough values of anisotropy parameter, our
numerical results indicate that the entanglement entropy in the perpendicular
direction to anisotropic direction is greater than the parallel case.",1803.01754v1
2018-03-18,Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials,"Spin resonance in the superconducting state of Fe-based materials within the
multiorbital model with unequal anisotropic gaps on different Fermi surface
sheets is studied. On the basis of the model gap function and the one
calculated within the spin fluctuation theory of pairing, I show that the
resonance peak shifts to higher frequencies with increasing the zero-amplitude
gap magnitude. On the contrary, with increasing the gap anisotropy, it shifts
to lower frequencies and lose some intensity.",1803.06736v2
2018-03-22,Hyperbolic Blockade: Suppression of the Photonic Density of States and the Spontaneous Emission Rate at the Interface with Conducting Medium,"Surface scattering of free electrons strongly modifies the electromagnetic
response near the interface. Due to the inherent anisotropy of the surface
scattering that necessarily reverses the normal the interface component of the
electron velocity while its tangential component may remain the same, a thin
layer near a high-quality interface shows strong dielectric anisotropy. The
formation of the resulting hyperbolic dispersion layers near the
metal-dielectric interface strongly modifies the local density of states, and
leads to orders of magnitude changes in all associated phenomena.",1803.08191v1
2018-03-22,Engineering giant magnetic anisotropy in single-molecule magnets by dimerizing heavy transition-metal atoms,"Search for single-molecule magnets with large magnetic anisotropy energy
(MAE) is essential for the development of molecular spintronics devices used at
room temperature. Through systematic first-principles calculations, we found
that an Os-Os or Ir-Ir dimer embedded in the (5,5'-Br2-Salophen) molecule gives
rise to large MAE of 41.6 or 51.4 meV which is large enough to hold the spin
orientation at room temperature. Analysis of electronic structures reveals that
the top Os and Ir atoms are most responsible for the spin moments and large
MAEs of the molecules.",1803.08213v1
2018-05-07,Anisotropy of dark matter velocity distribution,"Direct detection of dark matter with directional sensitivity has the
potential to discriminate the dark matter velocity distribution. Especially, it
will be suitable to discriminate isotropic distribution from anisotropic one.
Analyzing data produced with Monte-Carlo simulation, required conditions for
the discrimination is estimated. If energy threshold of detector is optimized,
$O(10^3-10^4)$ event number is required to discriminate the anisotropy.",1805.02472v1
2018-07-15,"Anisotropy of Neel ""orange-peel"" coupling in magnetic multilayers","We calculate the energy of the magnetostatic interaction between two
ferromagnetic films with uniform magnetization and correlated interfaces (the
""orange-peel"" effect). The ""orange-peel"" coupling is anisotropic: the
interaction is ferromagnetic when the films are magnetized in-plane; and it is
antiferromagnetic when magnetization is out-of-plane. The interaction
anisotropy can be used to distinguish the ""orange-peel"" effect from the
interlayer exchange coupling.",1807.05590v1
2018-09-27,Measurements of Fourier harmonics of azimuthal anisotropy in Pb+Pb and Xe+Xe collisions,"The high-statistics data sets collected by the LHC experiments during the
heavy-ion runs allow for a detailed study of the azimuthal anisotropy of
charged particles. This report presents the selected results of $v_{n}$
measured in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV and Xe+Xe
collisions at $\sqrt{s_\mathrm{NN}} = 5.44$ TeV, with emphasis on the higher
order Fourier coefficients, $v_{n}$, sensitive to initial state fluctuations of
the medium created in ultra-relativistic heavy-ion collisions.",1809.10648v2
2018-10-03,Orbital-Flop Transition of Angular Momentum in a Topological Superfluid,"The direction of the orbital angular momentum of the $B$-phase of superfluid
$^3$He can be controlled by engineering the anisotropy of the silica aerogel
framework within which it is imbibed. In this work, we report our discovery of
an unusual and abrupt `orbital-flop' transition of the superfluid angular
momentum between orientations perpendicular and parallel to the anisotropy
axis. The transition has no hysteresis, warming or cooling, as expected for a
continuous thermodynamic transition, and is not the result of a competition
between strain and magnetic field. This demonstrates the spontaneous
reorientation of the order parameter of an unconventional BCS condensate.",1810.01901v1
2018-10-17,Interface enhanced magnetic anisotropy in Pt/EuO films,"We report proximity effects of spin-orbit coupling in EuO$_{1-x}$ films
capped with a Pt overlayer. Transport measurements suggest that current flows
along a conducting channel at the interface between the Pt and EuO. The
temperature dependence of the resistivity picks up the critical behaviors of
EuO, i.e., the metal-to-insulator transition. We also find an unusual
enhancement of the magnetic anisotropy in this structure from its bulk value
which results from strong spin-orbit coupling across the Pt/EuO interface.",1810.07336v1
2018-11-13,Confinement transition in a Kitaev-like honeycomb model with bond anisotropy,"The honeycomb $K-\Gamma$ model is known to have both deconfined spin liquid
and confined phases. We study here a confinement transition between the Kitaev
spin liquid and a dimerized phase in the limit of strong bond anisotropy. By
partially projecting out Majorana states we are able to map the model onto a
model of weakly coupled Ising chains in a transverse field. Within this mapping
the ordered Ising phase corresponds to the condensation of $Z_2$ fluxes, or
confinement. Our results may improve our understanding of the extensively
studied spin liquid candidate material $\alpha$-RuCl$_3$, where $K-\Gamma$
interactions are dominant.",1811.05499v1
2018-11-19,Dilepton production and elliptic flow from an anisotropic quark-gluon plasma,"We calculate the yield and elliptic flow of mid-rapidity dileptons emitted
from the quark-gluon plasma generated in Pb-Pb collisions at LHC. We use
relativistic anisotropic hydrodynamics for the 3+1 dimensional evolution of the
quark-gluon plasma and convolve this with the momentum-anisotropic local rest
frame production rate for dileptons. The effects of momentum anisotropy of the
quark distribution functions, viscosity to entropy density ratio, centrality of
the collisions, and initial momentum anisotropy on the results are investigated
and discussed.",1811.07486v2
2018-11-26,Fluctuating shapes of the fireballs in heavy-ion collisions,"We argue that energy and momentum deposition from hard partons into
quark-gluon plasma induces an important contribution to the final state hadron
anisotropies. We also advocate a novel method of Event Shape Sorting which
allow to analyse the azimuthal anisotropies of the fireball dynamics in more
detail. A use of the method in femtoscopy is demonstrated.",1811.10349v1
2018-12-06,Entanglement in anisotropic expanding spacetime,"We study the effect of space anisotropy in the entanglement generated by
expanding universe on spin 0 and 1/2 fields. For massive scalar field we find
revivals of entanglement entropy vs momentum after decreasing from the maximum
at k = 0. In massive Dirac field the effect is a slight distortion of the
non-monotonic profile giving rise to the maximum of entanglement entropy at k >
0. More interestingly, massless field of both type can only get entangled
through anisotropy, with a maximum of entanglement entropy occurring at k > 0.",1812.02835v1
2018-12-14,The cubic Schr{ö}dinger regime of the Landau-Lifshitz equation with a strong easy-axis anisotropy,"We pursue our work on the asymptotic regimes of the Landau-Lifshitz equation
for bi-axial ferromagnets. We put the focus on the cubic Schr{\""o}dinger
equation, which is known to describe the dynamics in a regime of strong
easy-axis anisotropy. In any dimension, we rigorously prove this claim for
solutions with sufficient regularity. In this regime, we additionally classify
the one-dimensional solitons of the Landau-Lifshitz equation and quantify their
convergence towards the solitons of the one-dimensional cubic Schr{\""o}dinger
equation.",1812.05854v1
2019-01-17,$\mathbb{B}_0$-Valued Monogenic Functions to the theory of Plane Anisotropy,"A solution of the elliptic type PDE of the 4th order, being a reduction of
the Eqs. of stress function corresponding to any case of plane anisotropy which
is not equal to isotropy (proved by S.\,G.~Mikhlin), is described in terms of
hypercomplex `analytic' functions with values in two-dimensional semisimple
algebra over the field of complex numbers in case when a domain under
consideration is bounded and simply-connected. A boundary value problem on
finding a function which satisfies this PDE in the considered domain (bounded
and simply-connected) and permits continuations (to the boundary) of operators
$\frac{\partial}{\partial x}$ and $\frac{\partial}{\partial y}$ acted to it, is
reduced to certain BVP for these hypercomplex functions.",1901.05882v1
2019-01-23,Cracking and Stability of Non-Rotating Relativistic Spheres with Anisotropic Internal Stresses,"The stability of static uncharged spheres with anisotropic internal stresses
is studied in general relativity. It has been noticed that pressure anisotropy
plays an important role for stability of stellar structure. It is shown that
radial profile of the stress anisotropy can be considered to decide potentially
stable/unstable regions. Finally, pontentially stable/unstable regions of two
known models of relativistic star have been examined.",1901.09808v2
2019-03-01,Recent results from the Pierre Auger Observatory,"In this paper some recent results from the Pierre Auger Collaboration are
presented. These are the measurement of the energy spectrum of cosmic rays over
a wide range of energies ($10^{17.5}$ to above $10^{20}$ eV), studies of the
cosmic-ray mass composition with the fluorescence and surface detector of the
Observatory, the observation of a large-scale anisotropy in the arrival
direction of cosmic rays above 8 x $10^{18}$ eV and indications of anisotropy
at intermediate angular scales above 4 x $10^{19}$ eV. The astrophysical
implications of the spectrum and composition results are also discussed.
Finally the progress of the upgrade of the Observatory, AugerPrime is
presented.",1903.00529v1
2019-03-08,Anisotropy and controllable band structure in supra-wavelength polaritonic metasurfaces,"In this letter we exploit the extended coherence length of mixed
plasmon/exciton states to generate active metasurfaces. For this purpose,
periodic stripes of organic dye are deposited on a continuous silver film.
Typical metasurface effects, such as effective behavior and geometry
sensitivity, are measured for periods exceeding the polaritonic wavelength by
more than one order of magnitude. By adjusting the metasurface geometry,
anisotropy, modified band structure and unidimensional polaritons are
computationally simulated and experimentally observed in reflectometry as well
as in emission.",1903.03328v1
2019-04-13,Reversible electric-field-driven magnetization in a columnar nanocomposite film,"Magnetic hysteresis loops show a moderate perpendicular anisotropy of the
magnetostrictive CFO pillars, which is related to their vertical compression.
The application of an electric field to the electromechanical PMN-PT substrate
produced significant and reversible changes in the magnetization due to an
additional strain-induced magnetic anisotropy. This demonstrates completely
reversible, room-temperature electric-field-assisted control of magnetization
in self-assembled vertical nanocomposites of CFO and BFO.",1904.06568v1
2019-05-16,The Effect of Anisotropy on Holographic Entanglement Entropy and Mutual Information,"We study the effect of anisotropy on holographic entanglement entropy (HEE)
and holographic mutual information (MI) in the Q-lattice model, by exploring
the HEE and MI for infinite strips along arbitrary directions. We find that the
lattice always enhances the HEE. The MI, however, is enhanced by lattice for
large sub-regions; while for small sub-regions, the MI is suppressed by the
lattice. We also discuss how these phenomena result from the deformation of
geometry caused by Q-lattices.",1905.06808v2
2019-06-04,Deterministic magnetization switching by voltage-control of magnetic anisotropy and Dzyaloshinskii-Moriya interaction under in-plane magnetic field,"Based on the micromagnetic simulations the magnetization switching in a
triangle magnetic element by voltage-control of magnetic anisotropy and
Dzyaloshinskii-Moriya interaction under in-plane magnetic field is proposed.
The proposed switching scheme is not the toggle switching but the deterministic
switching where the magnetic state is determined by the polarity of the applied
voltage pulse. The mechanism and conditions for the switching are clarified.
The results provide a fast and low-power writing method for magnetoresistive
random access memories.",1906.01254v1
2019-06-10,"Linking dissipation, anisotropy and intermittency in rotating stratified turbulence","Analyzing a large data base of high-resolution three-dimensional direct
numerical simulations of decaying rotating stratified flows, we show that
anomalous mixing and dissipation, marked anisotropy, and strong intermittency
are all observed simultaneously in an intermediate regime of parameters in
which both waves and eddies interact nonlinearly. A critical behavior governed
by the stratification occurs at Richardson numbers of order unity, and with the
flow close to being in a state of instability. This confirms the central
dynamical role, in rotating stratified turbulence, of large-scale
intermittency, which occurs in the vertical velocity and temperature
fluctuations, as an adjustment mechanism of the energy transfer in the presence
of strong waves.",1906.04302v2
2019-06-19,Anisotropic Tolman VII solution by gravitational decoupling,"Using the gravitational decoupling by the minimal geometric deformation
approach, we build an anisotropic version of the well-known Tolman VII
solution, determining an exact and physically acceptable interior two-fluid
solution that can represent behavior of compact objects. Comparison of the
effective density and density of the perfect fluid is demonstrated explicitly.
We show that the radial and tangential pressure are different in magnitude
giving thus the anisotropy of the modified Tolman VII solution. The dependence
of the anisotropy on the coupling constant is also shown.",1906.08368v1
2019-06-28,Fine-tuning of orbital angular momentum in an optical parametric oscillator,"We investigate the dynamical properties of a type-II optical parametric
oscillator pumped by a structured light beam carrying orbital angular momentum.
Different dynamical regimes are theoretically derived and experimentally
demonstrated, depending on the anisotropy effects imposed by the nonlinear
medium. In a weakly anisotropic regime, fine-tuning of the orbital angular
momentum transfer is obtained by adjusting the crystal parameters. Under strong
anisotropy, orbital angular momentum transfer is not possible and a sharp
dynamical behavior is observed, with abrupt switching between different
transverse modes.",1907.00026v1
2019-07-06,Angle-resolved broadband ferromagnetic resonance apparatus enabled through a spring-loaded sample mounting manipulator,"Broadband ferromagnetic resonance is a useful technique to determine the
magnetic anisotropy and study the magnetization dynamics of magnetic thin
films. We report a spring-loaded sample loading manipulator for reliable sample
mounting and rotation. The manipulator enables maximum signal, enhances system
stability and is particularly useful for fully automated in-plane-field
angle-resolved measurements. This angle-resolved broadband ferromagnetic
resonance apparatus provides a viable method to study anisotropic damping and
weak magnetic anisotropies, both vital for fundamental research and
applications.",1907.03097v1
2019-08-06,Position-space curved-sky anisotropy quadratic estimation,"This document supplements the release of the Planck 2018 CMB lensing
pipeline, now made publicly available. It collects calculations relevant to
curved-sky separable quadratic estimators in the spin-weight, position-space
correlation function formalism, including analytic calculations of estimator
responses and Gaussian noise biases between arbitrary pairs of quadratic
estimators. It also contains the derivation of optimal, joint gradient and curl
mode quadratic estimators for parametrized anisotropy of arbitrary spin.",1908.02016v1
2019-09-02,Extreme anisotropy and gyrotropy of surface polaritons in Weyl semimetals,"Weyl semimetals possess unique electrodynamic properties due to a combination
of strongly anisotropic and gyrotropic bulk conductivity, surface conductivity,
and surface dipole layer. We explore the potential of popular tip-enhanced
optical spectroscopy techniques for studies of bulk and surface topological
electron states in these materials. Anomalous dispersion, extreme anisotropy,
and the optical Hall effect for surface polaritons launched by a nanotip
provides information about Weyl node position and separation in the Brillouin
zone, the value of the Fermi momentum, and the matrix elements of the optical
transitions involving both bulk and surface electron states.",1909.00861v1
2019-09-19,Dark Matter Mass and Anisotropy in Directional Detector,"Velocity distribution of dark matter is supposed to be isotropic
Maxwell-Boltzmann distribution in most cases, however, other distribution
models including anisotropic one are suggested by simulations. Directional
direct detection of dark matter is expected to be a hopeful way to discriminate
isotropic distribution from anisotropic one. We investigate the possibility to
obtain the anisotropy and WIMP mass by Monte-Carlo simulation supposing the
directional detector.",1909.08861v1
2019-11-22,Modeling anisotropic magnetized strange quark stars,"Compact objects have an intrinsic anisotropy due to the presence of strong
magnetic fields that cause considerable modifications on the equations of state
(EoS). In this work, we study the impact of this anisotropy in the size and
shape of magnetized strange quark stars using an axially symmetric metric in
spherical coordinates, the gamma-metric. The results are compared with those
obtained with the standard Tolman-Oppenheimer-Volkoff (TOV) equations for the
parallel and perpendicular pressures independently. Differences in the results
are discussed.",1911.10224v1
2020-01-22,Beyond classical anisotropy and a new look to relativistic stars: a gravitational decoupling approach,"In this article, we propose a physical condition to extend interior isotropic
solutions to anisotropic domains by gravitational decoupling in the framework
of the Minimal Geometric Deformation approach. In particular, it is found that
by using an expression reminiscent of the classical anisotropy factor, we can
close the decoupling system of equations and a new anisotropic solution can be
found. As an example, we extend the well--known Tolman IV.",2001.07961v2
2020-01-27,Bidirectional switching assisted by interlayer exchange coupling in asymmetric magnetic tunnel junctions,"We study the combined effects of spin transfer torque, voltage modulation of
interlayer exchange coupling and magnetic anisotropy on the switching behavior
of perpendicular magnetic tunnel junctions (p-MTJs). In asymmetric p-MTJs, a
linear-in-voltage dependence of interlayer exchange coupling enables the
effective perpendicular anisotropy barrier to be lowered for both voltage
polarities. This mechanism is shown to reduce the critical switching current
and effective activation energy. Finally, we analyze the possibility of having
switching via interlayer exchange coupling only.",2001.10024v1
2020-02-18,Polarization loss in reflecting coating,"In laser gravitational waves detectors optical loss restricts sensitivity. We
discuss polarization scattering as one more possible mechanism of optical
losses. Circulated inside interferometer light is polarized and after
reflection its plane of polarization can turn a little due to reflecting
coating of mirror can have slightly different refraction index along axes $x,\,
y$ in plane of mirror surface (optical anisotropy). This anisotropy can be
produced during manufacture of coating (elasto-optic effect). This orthogonal
polarized light, enhanced in cavity, produces polarization optical loss.
Polarization map of mirrors is very important and we propose to measure it.
Polarization loss can be important in different precision optical experiments
based on usage of polarized light, for example, in quantum speed meter.",2002.08271v1
2020-03-12,Minimizing movements for forced anisotropic mean curvature flow of partitions with mobilities,"Under suitable assumptions on the family of anisotropies, we prove the
existence of a weak global $\frac{1}{n+1}$-H\""older continuous in time mean
curvature flow with mobilities of a bounded anisotropic partition in any
dimension using the method of minimizing movements. The result is extended to
the case when suitable driving forces are present. We improve the H\""older
exponent to $\frac12$ in the case of partitions with the same anisotropy and
the same mobility and provide a weak comparision result in this setting for a
weak anisotropic mean curvature flow of a partition and an anisotropic mean
curvature two-phase flow.",2003.05761v1
2020-04-08,Role of anisotropy to the compensation in the Blume-Capel trilayered ferrimagnet,"The trilayered Blume-Capel ($S=1$) magnet with nearest neighbour intralayer
ferromagnetic and nearest neighbour interlayer antiferromagnetic interaction is
studied by Monte Carlo simulation. Depending on the relative interaction
strength and the value of anisotropy the critical temperature (where all the
sublattice magnetisations and consequently the total magnetisation vanishes)
and the compensation temperature (where the total magnetisation vanishes for a
special combination of nonzero sublattice magnetisations) are estimated. The
comprehensive phase diagrams with lines of critical temperatures and
compensation temperatures for different parameter values are drawn.",2004.03930v3
2020-04-28,The effects of collisions on the generation and suppression of temperature anisotropies and the Weibel instability,"The expansion of plasma with non-parallel temperature and density gradients,
and the generation of magnetic field via the Biermann battery is modeled using
particle-in-cell simulations that include collisional effects via Monte Carlo
methods. A scaling of the degree of collisionality shows that an anisotropy can
be produced, and drive the Weibel instability, for gradient scales shorter than
the mean free path. For larger collision rates, the Biermann battery dominates
as the cause of magnetic field generation. When the most energetic particles
remain collisionless, the Nernst effect causes the Biermann field to be dragged
with the heat flux, piled up, and enhanced.",2004.13365v1
2020-07-23,Mathematical modeling of glioma invasion: acid- and vasculature mediated go-or-grow dichotomy and the influence of tissue anisotropy,"Starting from kinetic transport equations and subcellular dynamics we deduce
a multiscale model for glioma invasion relying on the go-or-grow dichotomy and
the influence of vasculature, acidity, and brain tissue anisotropy. Numerical
simulations are performed for this model with multiple taxis, in order to
assess the solution behavior under several scenarios of taxis and growth for
tumor and endothelial cells. An extension of the model to incorporate the
macroscopic evolution of normal tissue and necrotic matter allows us to perform
tumor grading.",2007.12204v1
2020-07-28,Maximal Function Characterizations of Hardy Spaces on ${\mathbb{R}}^{n}$ with Pointwise Variable Anisotropy,"In 2011, Dekel et al. developed highly geometric Hardy spaces $H^p(\Theta)$,
for the full range $0<p\leq 1$, which are constructed by continuous multi-level
ellipsoid covers $\Theta$ of $\mathbb{R}^n$ with high anisotropy in the sense
that the ellipsoids can change shape rapidly from point to point and from level
to level. In this article, if the cover $\Theta$ is pointwise continuous, then
the authors further obtain some real-variable characterizations of
$H^p(\Theta)$ in terms of the radial, the non-tangential and the tangential
maximal functions, which generalize the known results on the anisotropic Hardy
spaces of Bownik.",2007.14211v2
2020-09-07,Anomalous In-plane Magnetic Anisotropy in Strain-mediated Converse Magnetoelectric Coupling,"Magnetic axis rotation (MAR) in ferromagnetic (FM) layers is crucial for
strain-mediated converse magnetoelectric coupling. Employing the density
functional theory (DFT), we computationally study the magnetic anisotropy of
selected deformed FM materials such as body-centered iron. The results show
that the short axis is more energy-favorable at high in-plane strain difference
than previously predicted phenomenologically. This anomalous trend and the
complex energy behaviors at different strain conditions explain why
spin-lattice dynamics (SLD) simulation does not produce in-plane MAR and imply
couplings between different energy terms together with high order coefficient
contributions.",2009.03045v2
2020-09-08,Critical dynamics of non-conserved strongly anisotropic permutation symmetric three-vector model,"We explore, employing the renormalization-group theory, the critical scaling
behavior of the permutation symmetric three-vector model that obeys
non-conserving dynamics and has a relevant anisotropic perturbation which
drives the system into a non-equilibrium steady state. We explicitly find the
independent critical exponents with corrections up to two loops. They include
the static exponents $\nu$ and $\eta$, the off equilibrium exponent
$\widetilde{\eta}$, the dynamic exponent $z$ and the strong anisotropy exponent
$\Delta$. We also express the other anisotropy exponents in terms of these.",2009.03965v1
2020-10-20,Cosmic ray anisotropies from transient extragalactic sources,"We study the spectrum and anisotropies of ultrahigh energy cosmic ray
transient sources, accounting for the effects of their propagation through the
turbulent extragalactic magnetic fields. We consider either bursting sources or
sources emitting since a given initial time. We analyse in detail the
transition between the diffusive and the quasi-rectilinear regimes, describing
some new features that could be present",2010.10629v2
2020-12-13,Tunneling magnetoresistance in ensembles of ferromagnetic granules with exchange interaction and random easy axes of magnetic anisotropy,"We study the tunneling magnetoresistance in the ensembles of ferromagnetic
granules with random easy axes of magnetic anisotropy taking into account the
exchange interaction between granules. It is shown that due to the exchange
interaction magnetoresistance is effectively decoupled from magnetization, i.e.
the strongest negative magnetoresistance can be observed at the field where
magnetization is almost saturated. Under some conditions, the sign of
magnetoresistance can be reversed and tunneling magnetoresistance can become
positive at certain magnetic fields. Our theory agrees with measurements of
magnetoresistance in ensembles of Fe granules in SiCxNy matrix.",2012.07114v1
2020-12-21,Chiral Bosonic Topological Insulator on the Honeycomb Lattice with Anisotropic Interactions,"We study hard-core bosons on the honeycomb lattice in the presence of
anisotropic nearest-neighbor repulsive interactions. Using a quantum Monte
Carlo (QMC) technique, we extract the phase diagram of the model in terms of
the filling and the anisotropy. At half-filling we find a dimer insulator phase
near maximum anisotropy that is characterized by a finite topological
entanglement entropy $\ln(2)/2$, indicative of a fractional quantum Hall state
for bosons. We identify the presence of edge states and derive a QMC-based
method to extract and verify their chirality. Remarkably, this phase arises in
the absence of magnetic flux and without explicit lattice frustration.",2012.11461v1
2020-12-27,On volume-preserving crystalline mean curvature flow,"In this work we consider the global existence of volume-preserving
crystalline curvature flow in a non-convex setting. We show that a natural
geometric property, associated with reflection symmetries of the Wulff shape,
is preserved with the flow. Using this geometric property, we address global
existence and regularity of the flow for smooth anisotropies. For the
non-smooth case we establish global existence results for the types of
anisotropies known to be globally well-posed.",2012.13839v1
2021-02-10,Weibel instability beyond bi-Maxwellian anisotropy,"The shape of the anisotropic velocity distribution function, beyond the realm
of strict Maxwellians can play a significant role in determining the evolution
of the Weibel instability dictating the dynamics of self-generated magnetic
fields. For non-Maxwellian distribution functions, we show that the direction
of the maximum growth rate wavevector changes with shape. We investigate
different laser-plasma interaction model distributions which show that their
Weibel generated magnetic fields may require closer scrutiny beyond the second
moment (temperature) anisotropy ratio characterization.",2102.05499v3
2021-02-15,From n-layer planar ordering to the monolayer homeotropic structure of confined hard rods: The effect of shape anisotropy and wall-to-wall separation,"Using the Parsons Lee theory we examined the effect of shape anisotropy and
the wall to wall separation on the phase behavior of the hard parallelepiped
rods with dimensions L, D, and D (L>D) in such narrow slitlike pores which only
one homeotropic layer can form. The phase structures, including biaxiality,
planar nematic layering transition as well as planar to homeotropic, were
studied for some separations in the range 2.5D<H<10.0D for H-D<L<H.",2102.07853v1
2021-02-26,Distinctive magnetic properties of CrI3 and CrBr3 monolayers caused by spin-orbit coupling,"After the discovery of magnetism in monolayer CrI3, the magnetic properties
of different 2D materials from the chromium-trihalide family are intuitively
assumed to be similar, yielding magnetic anisotropy from the spin-orbit
coupling on halide ligands. Here we reveal significant differences between the
CrI3 and CrBr3 magnetic monolayers in their magnetic anisotropy, resulting
Curie temperature, hysteresis in external magnetic field, and evolution of
magnetism with strain, all predominantly attributed to distinctly different
interplay of atomic contributions to spin-orbit coupling in two materials.",2102.13325v1
2021-04-29,Thickness Dependence of Magneto-transport Properties in Tungsten Ditelluride,"We investigate the electronic structure of tungsten ditelluride (WTe$_2$)
flakes with different thicknesses in magneto-transport studies. The
temperature-dependent resistance and magnetoresistance (MR) measurements both
confirm the breaking of carrier balance induced by thickness reduction, which
suppresses the `turn-on' behavior and large positive MR. The Shubnikov-de-Haas
oscillation studies further confirm the thickness-dependent change of
electronic structure of WTe$_2$ and reveal a possible temperature-sensitive
electronic structure change. Finally, we report the thickness-dependent
anisotropy of Fermi surface, which reveals that multi-layer WTe$_2$ is an
electronic 3D material and the anisotropy decreases as thickness decreases.",2104.14464v1
2021-06-03,Magnon spin transport around the compensation magnetic field in easy-plane antiferromagnetic insulators,"In this work, we theoretically study the magnon spin transport in easy-plane
antiferromagnetic insulators in the presence of an in-plane magnetic field. By
exactly calculating the magnon spectrum, we find the band splitting due to the
magnetic anisotropy can be fully compensated by the external field at a
particular strength, which makes its dynamics nearly equivalent to an easy-axis
antiferromagnet. As a result, the intrinsic magnon spin Hall effect due to the
dipole-dipole interaction, previously predicted in easy-axis antiferromagnets
is activated in easy-plane antiferromagnets. The compensation feature also
allows the field control of magnon spin lifetime and hence the spin diffusion
length. The compensation feature is robust against the biaxial anisotropy.",2106.02178v1
2021-06-12,Anisotropic generalization of Buchdahl bound for specific stellar models,"Anisotropy is one factor that appears to be significantly important in the
studies of relativistic compact stars. In this paper, we make a generalization
of the Buchdahl limit by incorporating an anisotropic effect for a selected
class of exact solutions describing anisotropic stellar objects. In the
isotropic case of a homogeneous distribution, we regain the Buchdahl limit
$2M/R \leq 8/9$. Our investigation shows a direct link between the maximum
allowed compactness and pressure anisotropy vi-a-vis geometry of the associated
$3$-space.",2106.08156v1
2021-08-30,Anisotropic Optical Properties of Hexagonal Boron Nitride Thin Films,"Few-layer flakes of hexagonal boron nitride were prepared by ultrasonication
of bulk crystals and agglomerated to form thin films. The transmission and
reflection spectra of the thin films were measured. The spectral dependences of
the linear and circular polarization revealed a hidden anisotropy of the films
over the whole sample area which could not be explained by the anisotropy of
the chaotically-oriented individual particles. Statistical analysis of optical
microscopy images showed a macroscopic particle density distribution with
ordering corresponding to the optical axis observed in the polarization data.",2108.13267v1
2021-09-05,Pearl vortices in anisotropic superconducting films,"The magnetic field of vortices in anisotropic superconducting films is
considered in the framework of anisotropic London approach. It is found that at
distances large relative to the core size, the magnetic field normal to the
film surface may change sign.
  We find that the magnetic field attenuates at large distances as $1/r^3$ as
it does in isotropic films, but the anisotropy induces an angular dependence to
the supercurrents which causes the sign of the field to change for anisotropy
parameters $\gamma=\lambda_2/\lambda_1>\sqrt{2}$ in some parts of the $(x,y)$
plane.",2109.01966v1
2021-10-13,Signatures of electronic correlations and spin-susceptibility anisotropy in nuclear magnetic resonance,"We present a methodology for probing the details of electronic susceptibility
through minimally-invasive nuclear magnetic resonance techniques. Specifically,
we classify electron-mediated long-range interactions in an ensemble of nuclear
spins by revealing their effect on simple spin echo experiments. We find that
pulse strength and applied field orientation dependence of these spin echo
measurements resolves the spatial extent and anisotropy of electronic spin
susceptibility. This work provides an alternate explanation to NMR results in
superconducting and magnetically-ordered systems. The methodology has direct
applications for sensing and characterizing emergent electronic phases.",2110.06811v1
2021-10-19,Recent results of $\text{D}^{0}$ mesons azimuthal anisotropy using the CMS detector,"In a relativistic heavy ion collision, heavy flavor (charm and bottom) quarks
are mostly created via hard processes at the early stage of the collisions. We
present the latest results of the azimuthal anisotropy coefficients
$v_{\text{n}}$ for prompt and nonprompt $\text{D}^{0}$ mesons in PbPb, pPb, and
pp collisions from the CMS experiment. The studies are about collectivity
phenomena in smaller systems (pp and pPb collisions), searches for the effects
of very strong electromagnetic fields created in the initial stages of
ultrarelativistic PbPb collisions, and charm quark energy loss in the
quark-gluon plasma.",2110.09878v1
2021-10-27,Planar Hall effect in Cu intercalated PdTe$_2$,"We present the Planar Hall effect studies on the Cu intercalated type-II
Dirac semimetal PdTe$_{2}$. The electrical resistivity exhibits a positive
field dependence both in perpendicular and parallel field directions, causing
non-zero anisotropy. The longitudinal magnetoresistance shows almost linear
field dependence at low temperatures. A tilted prolate spheroid shaped orbits
are observed in parametric plot between transverse and longitudinal
resistivities. Our study suggest that for the type-II Dirac semimetal materials
with positive longitudinal magnetoresistance, the origin of Planar Hall effect
cannot be asserted with certainty to the topological or non-topological without
taking into account the anisotropy of Fermi surface.",2110.14251v1
2021-11-08,Azimuthal anisotropy measurement of multi-strange hadrons in Au+Au collision at $\sqrt{s_{NN}}$ = 27 and 54.4 GeV at STAR,"In these proceedings, we present the second order ($v_{2}$) and the third
order ($v_{3}$) azimuthal anisotropy measurements of strange and multi-strange
hadrons such as $K^{0}_{S}$, $\Lambda$, $\bar{\Lambda}$, $\phi$, $\Xi^{-}$,
$\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$ in Au+Au collisions at
$\sqrt{s_{NN}}$ = 27 and 54.4 GeV at STAR. The centrality dependence of $v_{2}$
and $v_{3}$ as well as the number of constituent quark scaling (NCQ scaling)
for all the particles mentioned above are discussed. The ratio of $v_{2}$ of
$\phi$ mesons to that of $\bar{p}$ is presented at $\sqrt{s_{NN}}$ = 54.4 GeV
which gives a hint of mass ordering violation at low $p_{T}$.",2111.04743v1
2022-01-12,The Ellipsoidal Universe and the Hubble tension,"The Hubble tension resides in a statistically significant discrepancy between
early time and late time determinations of the Hubble constant. We discuss the
Hubble tension within the Ellipsoidal Universe cosmological model. We suggest
that allowing small anisotropies in the large-scale spatial geometry could
alleviate the tension. We, also, show that the discrepancy in the measurements
of the Hubble constant is reduced to a statistically acceptable level if we
assume sizeable cosmological anisotropies during the Dark Age. In addition, we
argue that the Ellipsoidal Universe cosmological model should resolve the $S_8$
tension.",2201.04548v4
2022-02-09,Electron Beam Weibel Instability in the Collisionless Shock with Low Mach Number,"The electron beam Weibel instability in the electrostatic collisionless shock
is studied via particle in cell simulation. When the non-relativistic incoming
plasmas collide with cold dilute plasmas, an electrostatic shock forms near the
interface. Following that, a filamentary out-of-plane magnetic field is formed
as a result of the Weibel instability. It is demonstrated that the anisotropy
of incoming hot electrons is insufficient to trigger the Weibel instability.
And the Weibel instability is excited by cold electrons in dilute plasmas.
After being accelerated to relativistic velocities by the shock electric field
into the dense plasmas, electrons in the dilute plasma have considerable
anisotropy and can trigger the Weibel instability",2202.04341v1
2022-02-27,Dual function spin-wave logic gates based on electric field control magnetic anisotropy boundary,"Spin waves (SWs) have been considered a promising candidate for encoding
information with lower power consumption. Here, we propose the dual function SW
logic gates based on the electric field controlling the SW propagation in the
Fe film of Fe/BaTiO3 heterostructure with the motion of magnetic anisotropy
boundary (MAB). We show micromagnetic simulations to validate the AND-OR and
NAND-NOR logic gates. Our research may find a path for simplifying integrated
logic circuits using such dual function SW logic gates.",2202.13258v1
2022-03-04,Effect of the field self-interaction of General Relativity on the Cosmic Microwave Background Anisotropies,"Field self-interactions are at the origin of the non-linearities inherent to
General Relativity. We study their effects on the Cosmic Microwave Background
anisotropies. We find that they can reduce or alleviate the need for dark
matter and dark energy in the description of the Cosmic Microwave Background
power spectrum.",2203.02350v2
2022-04-30,Piezoelectric ferromagnetism in two dimensional FeCl$_2$,"We predict that monolayer FeCl$_2$ is a two-dimensional piezoelectric
ferromagnet (PFM) with easy-axis magnetism and a Curie temperature of 260 K.
Our ab-initio calculations combined with data mining reveal 2H-FeCl$_2$ as the
only easy-axis 2D monolayer PFM, and that its magnetic anisotropy increases
many-fold with moderate hole doping. We develop an analysis based on magnetic
anisotropy energy densities that explain the magnetic and doping-dependent
behavior of FeCl$_2$, as well as VSe$_2$ and CrI$_3$, and can enable the design
of future 2D magnetically ordered materials.",2205.00300v1
2022-05-06,Emergent anisotropy in magnetic metamaterials,"We demonstrate directional dependence of the self-modification of internal
mesospin textures in magnetic metamaterials, arising from the coupling of the
atomic- and mesoscopic length-scales. Dressing the mesospins in different
directions enables the quantification of the degree of texture in the internal
magnetization and its impact on the interaction energy of the mesospins. The
emerging anisotropy is manifested in a directional dependence of the remanent
magnetization with temperature.",2205.03134v1
2022-05-14,Magnetization Plateau of the Distorted Diamond Spin Chain with Anisotropic Ferromagnetic Interaction,"The $S=1/2$ distorted diamond spin chain with the anisotropic ferromagnetic
interaction is investigated using the numerical diagonalization and the level
spectroscopy analysis. It is known that the system exhibits a plateau of the
magnetization curve at the 1/3 of the saturation. The present study indicates
that as the anisotropy is varied the quantum phase transition occurs between
two different mechanisms of the 1/3 magnetization plateau. The phase diagram
with respect to the anisotropy and the ferromagnetic coupling is also
presented.",2205.07027v1
2022-05-18,Anisotropy of Halo Main Sequence Turnoff Stars Measured with New MMT Radial Velocities and Gaia Proper Motions,"We measure the anisotropy of the Milky Way stellar halo traced by a dense
sample of 18<r<21 mag F-type main sequence turnoff stars using Gaia eDR3 proper
motions and new radial velocity measurements published here.",2205.09755v1
2022-06-21,Phase transitions in anisotropic graphene,"We study the effect of anisotropy on phase transitions in graphene. We work
with an low energy effective field theory which is strongly coupled, and solve
a coupled set of Schwinger-Dyson equations. We show that the effect of
anisotropy is to reduce the critical coupling.",2206.10111v1
2022-07-11,Contribution to the theory of waves in multi-dimensional linear dispersive media,"The asymptotic solutions for linear waves generated by oscillating source of
elliptic shape in the motionless media is constructed with the recently
developed Reference Solution Approach (RSA). Pronounced anisotropy of the
solutions is found for elongated sources both for amplitudes and phases of the
resulting wave pattern. The classic Kelvin angles of the ship wave patterns
determine specific directions of this anisotropy, thus, demonstrating the role
of wave dispersion. The analytical results within the RSA are shown to agree
remarkably well with exact solutions of the linear wave problem.",2207.04938v1
2022-08-18,Giant thermoelectric power factor anisotropy in PtSb$_{1.4}$Sn$_{0.6}$,"We report giant anisotropy in thermoelectric power factor ($S^2\sigma$) of
marcasite structure-type PtSb$_{1.4}$Sn$_{0.6}$. PtSb$_{1.4}$Sn$_{0.6}$,
synthesized using ambient pressure flux growth method upon mixing Sb and Sn on
the same atomic site, is a new phase different from both PtSb$_2$ and PtSn$_2$
that crystallize in the cubic $Pa\bar{3}$ pyrite and $Fm\bar{3}m$ fluorite unit
cell symmetry, respectively. Giant difference in $S^2\sigma$ for heat flow
applied along different principal directions of the orthorhombic unit cell
mostly stems from anisotropic Seebeck coefficients.",2208.08647v1
2022-11-14,Studies of decoherence in strongly anisotropic spin triangles with toroidal or general non-collinear easy axes,"Magnetic molecules are investigated with respect to their usability as units
in future quantum devices. In view of quantum computing, a necessary
prerequisite is a long coherence time of superpositions of low-lying levels. In
this article, we investigate by means of numerical simulations whether a
toroidal structure of single-ion easy anisotropy axes is advantageous as often
conjectured. Our results demonstrate that there is no general advantage of
toroidal magnetic molecules, but that arrangements of tilted anisotropy axes
perform best in many cases.",2211.07281v2
2022-11-18,Temperature dependence of spin-model parameters in antiferromagnets,"The temperature dependence of mesoscopic spin-model parameters is derived in
two-sublattice antiferromagnetically aligned systems based on Green's function
theory. It is found that transversal spin correlations decrease the anisotropy
terms while increasing the Heisenberg and Dzyaloshinsky--Moriya exchange
interactions and the latter's contribution to the anisotropy. The obtained
temperature dependences show quantitative agreement with the results for
ferromagnets, and they also agree well with numerical atomistic simulations
which treat the spin correlations without approximations. Possible applications
of the results in multiscale modelling are discussed.",2211.10204v2
2022-12-03,Bulk ReSe2: record high refractive index and biaxially anisotropic material for all-dielectric nanophotonics,"We show that bulk rhenium diselenide, ReSe2 is characterized by record high
value of the refractive index exceeding 5 in near-infrared frequency range. We
use back focal plane reflection spectroscopy to extract the components of the
ReSe2 permittivity tensor and reveal its extreme biaxial anisotropy. We also
demonstrate the good agreement between the experimental data and the
predictions of the density functional theory. The combination of the large
refractive index and giant optical anisotropy makes ReSe2 a perspective
material for all-dielectric nanophotonics in the near-infrared frequency range.",2212.01501v2
2022-12-24,Anisotropic acoustics in dipolar Fermi gases,"We consider plane wave modes in ultracold, but not quantum degenerate,
dipolar Fermi gases in the hydrodynamic limit. Longitudinal waves present
anisotropies in both the speed of sound and their damping, and experience a
small, undulatory effect in their flow velocity. Two distinct types of shear
waves appear, a ``familiar"" one, and another that is accompanied by nontrivial
density and temperature modulations. We propose these shear modes as an
experimental means to measure the viscosity coefficients, including their
anisotropies.",2212.12659v1
2022-12-29,Magnetically enhanced thin film coarsening by a magnetic XPFC model allowing to decouple magnetic anisotropy and magnetostriction,"External magnetic fields provide a macroscopic control mechanism to influence
the microstructure of polycrystalline materials. We model the influence of
strong magnetic fields on grain growth in thin films with a magnetic extended
phase field crystal (XPFC) model. The magneto-structural effects are
incorporated into the correlation function in reciprocal space. With this
approach magnetic anisotropy, magnetostriction and mobility of grain boundary
can be controlled and a variety of geometrical and topological properties
consistent with experimental results can be determined.",2212.14416v1
2023-01-10,Semi-Classical quantisation of 3-particles Toda lattice augmented; Application to the Mixmaster anisotropy Hamiltonian,"Usual approaches to quantisation of a 3-Toda lead to numerical calculations
requiring many steps that can be time consuming to insure their reliability. In
order to reduce as much as possible the numerical part of the EKB quantisation
procedure, and then to ease numerical calculations, we propose a reformulation
of the mathematical framework with more adapted variables. The resulting
equations and procedure might be easily implemented in a short Mathematica
code. This more explicit framework will be useful for studying quantum
Toda-Bianchi IX models in quantum cosmology where the true Bianchi IX
anisotropy Hamiltonian can be approximated by a 3-particle Toda system.",2301.03929v1
2023-02-14,Anisotropy effects on the quantum transport of atomic matter waves,"We discuss effects of anisotropic scattering in transport properties of
ultracold atoms in three-dimensional optical potentials. Within the realm of
the first Born approximation, we calculate the self energy, the scattering mean
free time, the scattering mean free path, and the anisotropy factor. The
behavior of the diffusion constant as a function of the wavenumber is also
examined in diffusive and weak localization regimes. We show that these
quantities are affected by quantum corrections due to the interference caused
by disorder. The dimensionless conductance is also evaluated using the scaling
theory of localization. Our results are compared with previous theoretical and
the experimental results.",2302.07367v1
2023-03-08,Majorana Gap Formation in the Anisotropic Kitaev Model with Ordered Flux Configuration,"We study the Kitaev model with direction dependent interactions to
investigate how the flux configuration and/or the anisotropy in the exchanges
affect the Majorana excitations. Systematic numerical calculations demonstrate
how the anisotropy of the exchange couplings and flux configuration make the
Majorana excitation gapped. The induced gapped quantum spin liquid states are
distinct from the gapped one realized in the large anisotropic limit. The
nature of gapped states can be explained by the superlattice potential due to
flux configuration.",2303.04295v1
2023-03-21,Unique Itinerant Ferromagnetism in 4d-electron System Ca2RuO4,"We have studied the magnetic properties of pressure-induced ferromagnet
Ca2RuO4 to reveal the uniqueness of the 4d-electron ferromagnetism in the
quasi-two-dimensional conductor. The magnetic parameters have been estimated
from the paramagnetic susceptibility and the magnetisation process under
pressure up to 2 GPa. The parameters can well be interpreted on the basis of
the self-consistent renormalization theory of spin fluctuation for 3D-itinerant
ferromagnet. Nevertheless, the metallic Ca2RuO4 shows quite strong anisotropy
not only in the conductivity but also in the magnetisation process. Such the
strong anisotropy is rare for an itinerant ferromagnet and is a unique
characteristic of the 4d electron system Ca2RuO4.",2303.11604v1
2023-03-18,Some new models of anisotropic relativistic stars in linear and quadratic regime,"Taking local anisotropy into consideration, in this paper, some new
analytical models of relativistic anisotropic charged quark stars in linear and
quadratic regime have been developed. The Einstein-Maxwell field equations have
been solved with a particular form of metric potential and electric field
intensity. The plots generated show that physical variables such as metric
potentials, radial pressure, energy density, charge density, anisotropy, radial
speed sound are consistent with realistic stellar models. We obtained some
models consistent with stellar objects as 4U 1538-52, Cyg X-2, OGLE-TR-122b and
red dwarf Proxima Centauri.",2303.12161v1
2023-06-07,Versatile Parametric Classes of Covariance Functions that Interlace Anisotropies and Hole Effects,"Covariance functions are a fundamental tool for modeling the dependence
structure of spatial processes. This work investigates novel constructions for
covariance functions that enable the integration of anisotropies and hole
effects in complex and versatile ways, having the potential to provide more
accurate representations of dependence structures arising with real-world data.
We show that these constructions extend widely used covariance models,
including the Mat\'ern, Cauchy, compactly-supported hypergeometric and cardinal
sine models. We apply our results to a geophysical data set from a
rock-carbonate aquifer and demonstrate that the proposed models yield more
accurate predictions at unsampled locations compared to basic covariance
models.",2306.04483v1
2023-06-17,Polarized Photons from the Early Stages of Relativistic Heavy-Ion Collisions,"The polarization of real photons emitted from early-time heavy-ion collisions
is calculated, concentrating on the contribution from bremsstrahlung and
quark-antiquark annihilation processes at leading order in the strong coupling.
The effect of an initial momentum space anisotropy of the parton distribution
is evaluated using a model for the non-equilibrium scattering kernel for
momentum broadening. The effect on the photon polarization is reported for
different degrees of anisotropy. The real photons emitted early during
in-medium interactions will be dominantly polarized along the beam axis.",2306.10307v1
2023-07-28,Analysis of magneto-optical Kerr spectra of ferrimagnetic Mn$_4$N,"Simulations of magneto-optical Kerr effect in biaxially strained Mn$_4$N are
performed using density functional theory and linear response theory. We
consider three ferrimagnetic phases, two collinear and one noncollinear, which
have been corroborated separately by earlier studies. The simulated spectra are
compared to magneto-optical data available in recent literature. A collinear
ferrimagnetic phase with a small saturation magentization, a large
perpendicular anisotropy, and Curie temperature above 700~K is found to be
consistent with the measured spectra. We hypothesise that an admixture of the
noncollinear phase, which could explain the lower than predicted net moment and
magnetic anisotropy observed experimentally, is also present.",2307.15246v1
2023-11-15,"Ultralight vector dark matter, anisotropies and cosmological adiabatic modes","In this work we study the early-time behavior and the background evolution of
ultra-light vector dark matter. We present a model for vector dark matter in an
anisotropic Bianchi type I universe. Vector fields source anisotropies in the
early universe characterized by a shear tensor which rapidly decays once the
fields start oscillating, making them viable dark matter candidates. We present
the set of equations needed to evolve scalar cosmological perturbations in the
linear regime, both in Synchronous gauge and Newtonian gauge. We show that the
shear tensor has to be taken into account in the calculation of adiabatic
initial conditions.",2311.09373v1
2023-12-11,Experimental verification of the inverse Anomalous spin Hall effect with perpendicular magnetic anisotropy Materials,"In this work, the spin pumping technique was employed to investigate the
anomalous inverse spin Hall effect in BIG/NiO/Fe samples where
BIG[(Bi,Tm)3(Fe,Ga)5O12] exhibits perpendicular magnetic anisotropy. Our
results reveal an intriguing phenomenon: when the magnetizations of both
ferromagnetic layers align perpendicularly, a distinct spin-to-charge current
conversion mechanism occurs. This conversion is intricately linked to the
magnetization of the converting layer, spin polarization, and the spin current
orientation.",2312.06819v1
2023-12-17,Thermal leptogenesis in anisotropic cosmology,"There is no evidence that the universe must have been homogeneous and
isotropic before the big bang nucleosynthesis. The Bianchi type-I cosmology is
the simplest homogeneous but anisotropic cosmology. In this work, we
investigate thermal leptogenesis, as a baryogenesis scenario, in the Bianchi
type-I cosmology. Our results show that for specific values of the anisotropy,
the modified thermal leptogenesis generated more baryon asymmetry than the
standard one. In this way, anisotropy can help to achieve low-scale
leptogenesis.",2312.10677v1
2023-12-18,On the consequences of Raychaudhuri equation in Kantowski-Sachs space-time,"The paper aims to study the geometry and physics of the Raychaudhuri equation
(RE) in the background of a homogeneous and anisotropic space-time described by
Kantowski-Sachs (KS) metric. Role of anisotropy/shear in the context of
convergence and possible avoidance of singularity has been analyzed subject to
a physically motivated constraint. Moreover, using a suitable transformation
the first order RE has been converted to a second order differential equation
analogous to a Harmonic Oscillator and criterion for convergence has been shown
to be associated with the time varying frequency of the Oscillator. Finally,
the paper points out a geometric and physical notion of anisotropy along with
their corresponding behavior towards convergence.",2312.11134v1
2023-12-19,Measurements of azimuthal anisotropies in $^{16}$O+$^{16}$O and $γ$+Au collisions from STAR,"In this proceeding, we present the first measurements of azimuthal
anisotropies, $v_2$ and $v_3$, in $^{16}$O+$^{16}$O collisions at 200 GeV as a
function of transverse momentum and multiplicity, by using two- and
four-particle correlation methods. We compare our measurements with STAR
measurements of $v_n$ in \dau and \heau collisions to provide insight into the
impact of system symmetry on initial condition for small systems. We also
investigate the ratio $v_2\{4\}/v_2\{2\}$ as a function of centrality, which is
expected to be sensitive to nucleon-nucleon correlation in the $^{16}$O
nucleus.",2312.12167v1
2023-12-24,A Novel Field-Free SOT Magnetic Tunnel Junction With Local VCMA-Induced Switching,"By integrating the local voltage-controlled magnetic anisotropy (VCMA)
effect, Dzyaloshinskii-Moriya interaction (DMI) effect, and spin-orbit torque
(SOT) effect, we propose a novel device structure for field-free magnetic
tunnel junction (MTJ). Micromagnetic simulation shows that the device utilizes
the chiral symmetry breaking caused by the DMI effect to induce a non-collinear
spin texture under the influence of SOT current. This, combined with the
perpendicular magnetic anisotropy (PMA) gradient generated by the local VCMA
effect, enables deterministic switching of the MTJ state without an external
field. The impact of variations in DMI strength and PMA gradient on the
magnetization dynamics is analyzed.",2312.15481v1
2024-01-09,Modelling the elliptical instability of magnetic skyrmions,"Two recently developed methods of modelling chiral magnetic soliton
elliptical instability are applied in two novel scenarios, the tilted
ferromagnetic phase of chiral magnets dominated by easy-plane anisotropy and
the general case of the chiral magnet with tilted applied field and arbitrary
uniaxial anisotropy. In the former case, the analytical predictions are found
to exactly match previous numerical results. In the latter case, instability of
isolated chiral skyrmions has not yet been studied, although the predictions
correspond interestingly to previous numerical investigation of the phase
diagram.",2401.04569v1
2024-01-21,Structure-property relationships for weak-ferromagnetic perovskites,"Despite several decades of active experimental and theoretical studies of
rare-earth orthoferrites, the mechanism of the formation of specific magnetic,
magnetoelastic, optical, and magneto-optical properties remains a subject of
discussion. This paper provides an overview of simple theoretical model
approaches to quantitatively describing the structure-property relationships,
in particular, interplay between FeO$_6$ octahedral deformations/rotations and
main magnetic and optic characteristics such as N\'{e}el temperature, overt and
hidden canting of magnetic sublattices, magnetic and magnetoelastic anisotropy,
optic and photoelastic anisotropy.",2401.11424v1
2024-02-26,Small-Scale Anisotropies of Cosmic Rays from Turbulent Flow,"Within the classical convection--diffusion approximation, we show that the
angular distribution of cosmic rays (CRs) in a highly turbulent flow may
exhibit significant small-scale anisotropies. The CR intensity angular power
spectrum $ C_\ell $ is then a direct reflection of interstellar turbulence,
from which one expects $ C_\ell\propto\ell^{-\gamma -1} $ for $ \ell\gg 1 $,
where $ \gamma $ is the power-law turbulence spectral index. Observations by
IceCube and HAWC at TeV energies can be explained approximately with the
Kolmogorov law $ \gamma =5/3 $ with a convection velocity dispersion of 20 km/s
on the scale of 10 pc.",2402.16554v1
2024-02-26,On the causal discontinuity of Morse spacetimes,"Morse spacetime is a model of singular Lorentzian manifold, built upon a
Morse function which serves as a global time function outside its critical
points. The Borde-Sorkin conjecture states that a Morse spacetime is causally
continuous if and only if the index and coindex of critical points of the
corresponding Morse function are both different from 1. The conjecture has
recently been confirmed by Garcia Heveling for the case of small anisotropy and
Euclidean background metric. Here, we provide a complementary counterexample: a
four dimensional Morse spacetime whose critical point has index 2 and large
enough anisotropy is causally discontinuous and thus the Borde-Sorkin
conjecture does not hold. The proof features a low regularity causal structure
and causal bubbling.",2402.16571v1
2024-02-20,Effects of anisotropy in an anisotropic extension of $w$CDM model,"In this paper, we derive observational constraints on an anisotropic $w$CDM
model from observational data including Baryonic Acoustic Oscillations (BAOs),
Cosmic Chronometer (CC), Big Bang Nucleosynthesis (BBN), Pantheon Plus (PP)
compilation of Type Ia supernovae, and SH0ES Cepheid host distance anchors. We
find that anisotropy is of the order $10^{-13}$, and its presence in the $w$CDM
model reduces $H_0$ tension by $\sim 2\sigma$ and $\sim 1\sigma$ in the
analyses with BAO+CC+BBN+PP and BAO+CC+BBN+PPSH0ES data combinations,
respectively. In both analyses, the quintessence form of dark energy is favored
at 95\% CL.",2402.16885v1
1994-06-28,The Nature versus Nurture of Anisotropies,"With the rapidly growing number of cosmic microwave background measurements
on various scales, there is real hope that the number of acceptable models for
structure formation will be limited to a very few in the near future. Yet any
given model can always be saved by introducing and tuning extraneous free
parameters. To better understand this question of ``nature versus nurture'' for
temperature fluctuations, it is useful to know not only the general features of
anisotropy predictions but also their causes. Extracting the physical content
of our other works, we present here a {\it simple} account of cosmic microwave
background anisotropies on all scales. In particular, we show that analytic
approximations can trace the structure of the so-called ``Doppler peaks,''
which arise due to the {\it adiabatic} oscillations in the photon-baryon fluid.
We also show how the finite thickness of the last scattering surface and the
Silk damping mechanism can be described in a unified way by photon diffusion.
In order to present a specific example, we focus on comparing the primordial
isocurvature baryon (PIB) model with the standard cold dark matter model (CDM).
In particular, we explain why PIB generically predicts larger {\it
non}-oscillatory anisotropies from the 1$^\circ$ to 10$^\circ$ scale which may
already be in conflict with experiments.",9406071v1
1994-07-28,Anisotropies in the Cosmic Microwave Background: An Analytic Approach,"We introduce a simple yet powerful {\it analytic} method which obtains the
structure of cosmic microwave background anisotropies to better than 5-10\% in
temperature fluctuations on {\it all} scales. It is applicable to {\it any}
model in which the potential fluctuations at recombination are both linear and
known. Moreover, it recovers and explains the presence of the ``Doppler peaks''
at degree scales as {\it driven} acoustic oscillations of the photon-baryon
fluid. We treat in detail such subtleties as the time dependence of the
gravitational driving force, anisotropic stress from the neutrino quadrupole,
and damping during the recombination process, again all from an analytic
standpoint. We apply this formalism to the standard cold dark matter model to
gain physical insight into the anisotropies, including the dependence of the
peak locations and heights on cosmological parameters such as $\Omega_b$ and
$h$, as well as model parameters such as the ionization history. Damping due to
the finite thickness of the last scattering surface and photon diffusion are
further more shown to be identical. In addition to being a powerful probe into
the nature of anisotropies, this treatment can be used in place of the standard
Boltzmann code where 5-10\% accuracy in temperature fluctuations is
satisfactory and/or speed is essential. Equally importantly, it can be used as
a portable standard by which numerical codes can be tested and compared.",9407093v1
1994-12-31,Large-angle Polarization of the Cosmic Microwave Background Radiation and Reionization,"We discuss the effect of matter reionization on the large-angular-scale
anisotropy and polarization of the cosmic microwave background radiation (CMBR)
in the standard CDM model. We separate three cases in which the anisotropy is
induced by pure scalar, pure tensor, and mixed metric perturbations
respectively. It is found that, if reionization occurs early enough, the
polarization can reach a detectable level of sequentially $6\%$, $9\%$, and
$6.5\%$ of the anisotropy. In general, a higher degree of polarization implies
a dominant contribution from the tensor mode or reionization at high redshift.
Since early reionization will suppress small-scale CMBR anisotropies and
polarizations significantly, measuring the polarization on few degree scales
can be a direct probe of the reionization history of the early universe.",9412097v2
1995-07-13,Perturbation growth and cosmic microwave background anisotropies in the string-like matter dominated universe,"It is well known that the $\Lambda$-term is a very good candidate for the
smooth component of the universe since it resolves the so-called
``$\Omega$-problem'' giving, at the same time, sufficiently large age of the
universe. However, the constant $\Lambda$-term is not the only possibility.
Some people consider the $\Lambda$-term varying in time according to the law
$\Lambda\approx R^{-2}$. Moreover the global texture in a closed universe and
the network of cosmic strings obeying the same law of variation ($\rho\approx
R^{-2}$) seem to be good candidates as well. We call the ``exotic'' form of
matter scaling according to this law -- string-like matter. In the paper we
discuss perturbation growth and anisotropies of the CMB in the string-like
dominated universe. One can show that the perturbations cannot grow in the
curvature dominated universe. Since the energy density of the string-like
matter scales with the expansion in the same way as the curvature term one
asserts that the perturbations cannot grow in the string-like matter dominated
universe either. We find this generally accepted statement not quite correct
and one of the purposes of the paper is to clear up this point. The second
purpose of the paper is to check whether the eventual existence of the
string-like matter may have an impact on the large-angular-scale anisotropies
of the CMB. We show that such exotic matter has no effect on the value of the
anisotropy amplitude $\delta T/T(theta).$",9507049v1
1997-02-19,CMB Anisotropies: Total Angular Momentum Method,"A total angular momentum representation simplifies the radiation transport
problem for temperature and polarization anisotropy in the CMB. Scattering
terms couple only the quadrupole moments of the distributions and each moment
corresponds directly to the observable angular pattern on the sky. We develop
and employ these techniques to study the general properties of anisotropy
generation from scalar, vector and tensor perturbations to the metric and the
matter, both in the cosmological fluids and from any seed perturbations (e.g.
defects) that may be present. The simpler, more transparent form and derivation
of the Boltzmann equations brings out the geometric and model-independent
aspects of temperature and polarization anisotropy formation. Large angle
scalar polarization provides a robust means to distinguish between isocurvature
and adiabatic models for structure formation in principle. Vector modes have
the unique property that the CMB polarization is dominated by magnetic type
parity at small angles (a factor of 6 in power compared with 0 for the scalars
and 8/13 for the tensors) and hence potentially distinguishable independent of
the model for the seed. The tensor modes produce a different sign from the
scalars and vectors for the temperature-polarization correlations at large
angles. We explore conditions under which one perturbation type may dominate
over the others including a detailed treatment of the photon-baryon fluid
before recombination.",9702170v3
1997-03-24,The Anisotropy of Low Prandtl Number Turbulent Convection,"A model for homogeneous anisotropic incompressible turbulence is proposed.
The model generalizes the GISS model of homogeneous isotropic turbulence; the
generalization involves the solution of the GISS equations along a set of
integration paths in wavenumber (k-) space. In order to make the problem
tractable, these integration paths (""cascade lines"") must be chosen in such a
way that the behaviour of the energy spectral function along different cascade
lines should be reasonably similar. In practice this is realized by defining
the cascade lines as the streamlines of a cascade flow; in the simplest case
the source of this flow may be identified with the source function of the
turbulence. Owing to the different approximations involved, the resulting
energy spectral function is not exact but is expected to give good
approximative values for the bulk quantities characterising the turbulent
medium, and for the measure of the anisotropy itself in particular.
  The model is then applied to the case of low Prandtl number thermal
convection. The energy spectral function and the bulk quantities characterizing
the flow are derived for different values of the parameter $S=Ra \sigma$. The
most important new finding is that unlike the anisotropy of the most unstable
mode in linear stability analysis the anisotropy of the turbulence does not
grow indefinitely with increasing S but it rather saturates to a relatively
moderate finite asymptotic value.",9703155v1
1997-04-17,The Spectrum of the CMB Anisotropy from the Combined COBE FIRAS and DMR Observations,"We analyze the Cosmic Microwave Background (CMB) anisotropy data from the
independent COBE FIRAS and DMR observations. We extract the frequency spectrum
of the FIRAS signal that has the spatial distribution seen by DMR and show that
it is consistent with CMB temperature fluctuations in the radiation well into
the Wien region of the spectrum. Conversely, we form a map of the Planckian
component of the sky temperature from FIRAS and show that it correlates with
the DMR anisotropy map. The rms fluctuations at angular scales of 7 degrees are
48 \pm 14 uK for the FIRAS data compared with 35 \pm 2 uK for the DMR data and
31 \pm 6 uK for the correlated combination (1 sigma uncertainties). The
consistency of these data, from very different instruments with very different
observing strategies, provide compelling support for the interpretation that
the signal seen by DMR is, in fact, temperature anisotropy of cosmological
origin. The data also limit rms fluctuations in the Compton y parameter,
observable via the Sunyaev- Zel'dovich effect, to Delta_y < 3 x 10^{-6} (95%
CL) on 7 degree angular scales.",9704176v1
1997-05-07,Multi-component models for disk galaxies. I. Stellar rotation and anisotropy,"We present here a self-consistent, tridimensional model of a disc galaxy
composed by a number of ellipsoidal distributions of matter having different
flattening and density profile. The model is self-consistent and takes into
account the observed luminosity distribution, the flattening profile and the
stellar rotation- and velocity dispersion- curves. In this paper we considered
the particular case of a disc galaxy composed by two spheroidal bodies: an
exponential disc and a bulge following the r^{1/4} law. We studied the behavior
of the stellar rotation- and velocity dispersion- profiles along the sequence
of S0s and Spirals, identified by an increasing disc-to-bulge ratio. Inside
every class, kinematic curves were produced by changing the relative
concentration of the two components and the inclination of the galaxy with
respect to the line of sight. The comparison with observational data requires
only two scaling factors: the total mass of the galaxy, and the effective
radius.
  The model allows also to detect the presence of anisotropy in the velocity
distribution. In the special case of S0s, we explored the sensitivity of the
kinematics of the model by changing the anisotropy and the flattening of the
bulge. For intermediate flattening (0.4<b/a<0.85) it is possible to distinguish
a change of anisotropy of 15%.
  To show a real case, the model has been applied to the photometric and
kinematic data of NGC 5866. We plan to apply these models to a larger database
of S0 galaxies in a future paper.",9705042v2
1997-06-25,Bayesian Analysis of the Polarization of Distant Radio Sources: Limits on Cosmological Birefringence,"A recent study of the rotation of the plane of polarization of light from 160
cosmological sources claims to find significant evidence for cosmological
anisotropy. We point out methodological weaknesses of that study, and reanalyze
the same data using Bayesian methods that overcome these problems. We find that
the data always favor isotropic models for the distribution of observed
polarizations over counterparts that have a cosmological anisotropy of the type
advocated in the earlier study. Although anisotropic models are not completely
ruled out, the data put strong lower limits on the length scale $\lambda$ (in
units of the Hubble length) associated with the anisotropy; the lower limits of
95% credible regions for $\lambda$ lie between 0.43 and 0.62 in all anisotropic
models we studied, values several times larger than the best-fit value of
$\lambda \approx 0.1$ found in the earlier study. The length scale is not
constrained from above. The vast majority of sources in the data are at
distances closer than 0.4 Hubble lengths (corresponding to a redshift of
$\approx$0.8); the results are thus consistent with there being no significant
anisotropy on the length scale probed by these data.",9706258v1
1997-08-22,MAX 4 and MAX 5 CMB anisotropy measurement constraints on open and flat-Lambda CDM cosmogonies,"We account for experimental and observational uncertainties in likelihood
analyses of cosmic microwave background (CMB) anisotropy data from the MAX 4
and MAX 5 experiments. These analyses use CMB anisotropy spectra predicted in
open and spatially-flat Lambda cold dark matter cosmogonies. Amongst the models
considered, the combined MAX data set is most consistent with the CMB
anisotropy shape in Omega_0 ~ 0.1-0.2 open models and less so with that in old
(t_0 >~ 15 - 16 Gyr, i.e., low h), high baryon density (Omega_B >~ 0.0175/h^2),
low density (Omega_0 ~ 0.2 - 0.4), flat-Lambda models. The MAX data alone do
not rule out any of the models we consider at the 2-sigma level.
  Model normalizations deduced from the combined MAX data are consistent with
those drawn from the UCSB South Pole 1994 data, except for the flat bandpower
model where MAX favours a higher normalization. The combined MAX data
normalization for open models with Omega_0 ~ 0.1-0.2 is higher than the upper
2-sigma value of the DMR normalization. The combined MAX data normalization for
old (low h), high baryon density, low-density flat-Lambda models is below the
lower 2-sigma value of the DMR normalization. Open models with Omega_0 ~
0.4-0.5 are not far from the shape most favoured by the MAX data, and for these
models the MAX and DMR normalizations overlap. The MAX and DMR normalizations
also overlap for Omega_0 = 1 and some higher h, lower Omega_B, low-density
flat-Lambda models.",9708202v1
1998-04-29,1+3 Covariant Cosmic Microwave Background anisotropies I: Algebraic relations for mode and multipole representations,"This is the first of a series of papers extending a covariant and gauge
invariant (CGI) treatment of kinetic theory in curved space-times to a
treatment of Cosmic Background Radiation (CBR) temperature anisotropies arising
from inhomogeneities in the early universe. This paper deals with algebraic
issues, both generically and in the context of models linearised about RW
geometries.
  The approach represents radiation anisotropies by PSTF tensors. The Angular
correlation functions for the mode coefficients are found in terms of these
quantities, following the Wilson-Silk approach, but derived and dealt with in
CGI form. The covariant multipole and mode-expanded angular correlation
functions are related to the usual treatments in the literature. The CGI mode
expansion is related to the coordinate approach by linking the Legendre
functions to the PSTF representation, using a covariant addition theorem for
the tensors to generate the Legendre Polynomial recursion relation.
  This paper lays the foundation for further papers in the series, which use
this formalism in a CGI approach to develop solutions of the Boltzmann and
Liouville equations for the CBR before and after decoupling, thus providing a
unified CGI derivation of the variety of approaches to CBR anisotropies in the
current literature.",9804316v3
1999-01-13,CMB in Open Inflation,"The possibility to have an infinite open inflationary universe inside a
bubble of a finite size is one of the most interesting realizations extensively
discussed in the literature. The original idea was based on the theory of
tunneling and bubble formation in the theories of a single scalar field.
However, for a long time we did not have any consistent models of this type, so
it was impossible to compare predictions of such models with the observational
data on the CMB anisotropy. The first semi-realistic model of this type was
proposed only very recently, in hep-ph/9807493. Here we present the results of
our investigation of the scalar and tensor perturbation spectra and the
resulting CMB anisotropy in such models. In all models which we have studied
there are no supercurvature perturbations. The spectrum of scalar CMB
anisotropies has a minimum at small l and a plateau at l > O(10) for low
Omega_0. Meanwhile tensor CMB anisotropies are peaked at l=2. Relative
magnitude of the scalar CMB spectra versus tensor CMB spectra at small l
depends on the parameters of the models.",9901135v2
1999-03-09,"Modelling elliptical galaxies: phase-space constraints on two-component (gamma1,gamma2) models","In the context of the study of the properties of the mutual mass distribution
of the bright and dark matter in elliptical galaxies, present a family of
two-component, spherical, self-consistent galaxy models, where one density
distribution follows a gamma_1 profile, and the other a gamma_2 profile
[(gamma_1,gamma_2) models], with different total masses and ``core'' radii. A
variable amount of Osipkov-Merritt (radial) orbital anisotropy is allowed in
both components. For these models, I derive analytically the necessary and
sufficient conditions that the model parameters must satisfy in order to
correspond to a physical system. Moreover, the possibility of adding a black
hole at the center of radially anisotropic gamma models is discussed,
determining analytically a lower limit of the anisotropy radius as a function
of gamma. The analytical phase-space distribution function for (1,0) models is
presented, together with the solution of the Jeans equations and the quantities
entering the scalar virial theorem. It is proved that a globally isotropic
gamma=1 component is consistent for any mass and core radius of the
superimposed gamma=0 model; on the contrary, only a maximum value of the core
radius is allowed for the gamma=0 model when a gamma=1 density distribution is
added. The combined effects of mass concentration and orbital anisotropy are
investigated, and an interesting behavior of the distribution function of the
anisotropic gamma=0 component is found: there exists a region in the parameter
space where a sufficient amount of anisotropy results in a consistent model,
while the structurally identical but isotropic model would be inconsistent.",9903123v1
1999-03-23,Cosmic microwave background anisotropy from wiggly strings,"We investigate the effect of wiggly cosmic strings on the cosmic microwave
background radiation anisotropy and matter power spectrum by modifying the
string network model used by Albrecht et al.. We employ the wiggly equation of
state for strings and the one-scale model for the cosmological evolution of
certain network characteristics. For the same choice of simulation parameters
we compare the results with and without including wiggliness in the model and
find that wiggliness together with the accompanying low string velocities lead
to a significant peak in the microwave background anisotropy and to an
enhancement in the matter power spectrum. For the cosmologies we have
investigated (standard CDM, and, CDM plus cosmological constant), and within
the limitations of our modeling of the string network, the anisotropy is in
reasonable agreement with current observations but the COBE normalized
amplitude of density perturbations is lower than what the data suggests. In the
case of a cosmological constant and CDM model, a bias factor of about 2 is
required.",9903361v4
1999-06-26,Line-of-Sight Anisotropies within X-ray Luminous Cluster Samples,"We present the results from two-point spatial correlation analyses on X-ray
confirmed northern Abell clusters. The cluster samples are subsets of a
volume-limited ROSAT All-Sky Survey study of 294 Abell clusters of which 240
are X-ray luminous. We examined magnitude- and volume-complete samples for
differences according to richness and X-ray luminosity. For R>=1 clusters, we
find r_0 = 22h^-1Mpc and gamma = -1.7, which is consistent with previous
analyses of visually selected clusters. We also find no indications of
line-of-sight anisotropies. For R >= 0 clusters, we find r_0= 17.5h^-1Mpc which
is considerably lower than recent determinations of r_0 for similar X-ray
bright cluster samples (e.g. the XBACs and the RASS1 clusters). All of the R>=0
X-ray confirmed samples, including the XBACs and RASS1 clusters, show
line-of-sight anisotropies. Since X-ray emissions confirm a cluster's reality,
we conclude that these anisotropies are not the result of spuriously selected
clusters. We also examine the Abell clusters for the depedence of r_0 and gamma
on X-ray luminosity, and find no evidence for r_0 to grow with increasing X-ray
luminosity thresholds. This is contrary to similar L_x vs. r_0 analyses of the
RASS1 and XBACs cluster samples. We describe selection effects within the
flux-limited XBACs and RASS1 samples and suggest how they can affect both the
size of r_0 and its dependence on L_x.",9906423v1
1999-11-01,Polarization of Thermal Emission from Aligned Dust Grains Under an Anisotropic Radiation Field,"If aspherical dust grains are immersed in an anisotropic radiation field,
their temperature depends on the cross-sections projected in the direction of
the anisotropy.It was shown that the temperature difference produces polarized
thermal emission even without alignment, if the observer looks at the grains
from a direction different from the anisotropic radiation. When the dust grains
are aligned, the anisotropy in the radiation makes various effects on the
polarization of the thermal emission, depending on the relative angle between
the anisotropy and alignment directions. If the both directions are parallel,
the anisotropy produces a steep increase in the polarization degree at short
wavelengths. If they are perpendicular, the polarization reversal occurs at a
wavelength shorter than the emission peak. The effect of the anisotropic
radiation will make a change of more than a few % in the polarization degree
for short wavelengths and the effect must be taken into account in the
interpretation of the polarization in the thermal emission. The anisotropy in
the radiation field produces a strong spectral dependence of the polarization
degree and position angle, which is not seen under isotropic radiation. The
dependence changes with the grain shape to a detectable level and thus it will
provide a new tool to investigate the shape of dust grains. This paper presents
examples of numerical calculations of the effects and demonstrates the
importance of anisotropic radiation field on the polarized thermal emission.",9910560v1
1999-12-07,CMB Anisotropy in Compact Hyperbolic Universes I: Computing Correlation Functions,"CMB anisotropy measurements have brought the issue of global topology of the
universe from the realm of theoretical possibility to within the grasp of
observations. The global topology of the universe modifies the correlation
properties of cosmic fields. In particular, strong correlations are predicted
in CMB anisotropy patterns on the largest observable scales if the size of the
Universe is comparable to the distance to the CMB last scattering surface. We
describe in detail our completely general scheme using a regularized method of
images for calculating such correlation functions in models with nontrivial
topology, and apply it to the computationally challenging compact hyperbolic
spaces. Our procedure directly sums over images within a specified radius,
ideally many times the diameter of the space, effectively treats more distant
images in a continuous approximation, and uses Cesaro resummation to further
sharpen the results. At all levels of approximation the symmetries of the space
are preserved in the correlation function. This new technique eliminates the
need for the difficult task of spatial eigenmode decomposition on these spaces.
Although the eigenspectrum can be obtained by this method if desired, at a
given level of approximation the correlation functions are more accurately
determined. We use the 3-torus example to demonstrate that the method works
very well. We apply it to power spectrum as well as correlation function
evaluations in a number of compact hyperbolic (CH) spaces. Application to the
computation of CMB anisotropy correlations on CH spaces, and the observational
constraints following from them, are given in a companion paper.",9912124v1
2000-03-27,The Anisotropy of MHD Alfvénic Turbulence,"We perform direct 3-dimensional numerical simulations for magnetohydrodynamic
(MHD) turbulence in a periodic box of size $2\pi$ threaded by strong uniform
magnetic fields. We use a pseudo-spectral code with hyperviscosity and
hyperdiffusivity to solve the incompressible MHD equations. We analyze the
structure of the eddies as a function of scale. A straightforward calculation
of anisotropy in wavevector space shows that the anisotropy is scale-{\it
independent}. We discuss why this is {\it not} the true scaling law and how the
curvature of large-scale magnetic fields affects the power spectrum and leads
to the wrong conclusion. When we correct for this effect, we find that the
anisotropy of eddies depends on their size: smaller eddies are more elongated
than larger ones along {\it local} magnetic field lines. The results are
consistent with the scaling law $\tilde{k}_{\parallel} \sim
\tilde{k}_{\perp}^{2/3}$ proposed by Goldreich and Sridhar (1995, 1997). Here
$\tilde{k}_{\|}$ (and $\tilde{k}_{\perp}$) are wavenumbers measured relative to
the local magnetic field direction. However, we see some systematic deviations
which may be a sign of limitations to the model, or our inability to fully
resolve the inertial range of turbulence in our simulations.",0003403v2
2000-09-04,Secondary CMB anisotropies from the kinetic SZ effect,"We present an analytic model, based on previous works which tackled the
reionization history of the universe, which allows us to describe the
generation of the secondary CMB anisotropies due to the kinetic SZ effect. We
take into account the ""patchy pattern"" of reionization (HII bubbles), the
cross-correlations of these ionized regions, the small-scale fluctuations of
the matter density field and the contribution from collapsed objects. For an
open universe, we find that the power-spectrum $l(l+1)C_l/(2\pi)$ exhibits a
plateau of height $10^{-13}$ in the range $10^3 < l < 10^6$. We find that for
large wavenumbers $l > 10^4$ the signal is dominated by the contribution from
collapsed halos while for $l < 10^4$ it is governed by the large-scale
correlations of HII bubbles. This implies that one cannot discriminate
reionization by stars from a quasar-driven scenario since the size of ionized
regions never dominates the behaviour of the anisotropies. Moreover, the
secondary CMB anisotropies arise from a broad range of redshifts (7.5<z<10 for
the IGM and 0<z<7 for galactic halos). The signal expected in our model might
bias the cosmological parameter estimation from CMB experiments such as Planck
and could be detected by future mm-wavelength interferometers (e.g., ALMA).",0009040v2
2000-12-04,Mass profiles and anisotropies of early-type galaxies,"We discuss the problem of using stellar kinematics of early-type galaxies to
constrain the galaxies' orbital anisotropies and radial mass profiles. We
demonstrate that compressing a galaxy's light distribution along the line of
sight produces approximately the same signature in the line-of-sight velocity
profiles as radial anisotropy. In particular, fitting spherically symmetric
dynamical models to apparently round, isotropic face-on flattened galaxies
leads to a spurious bias towards radial orbits in the models, especially if the
galaxy has a weak face-on stellar disk. Such face-on stellar disks could
plausibly be the cause of the radial anisotropy found in spherical models of
intermediate luminosity ellipticals such as NGC 2434, NGC 3379 and NGC 6703.
  In the light of this result, we use simple dynamical models to constrain the
outer mass profiles of a sample of 18 round, early-type galaxies. The galaxies
follow a Tully-Fisher relation parallel to that for spiral galaxies, but
fainter by at least 0.8 mag (I-band) for a given mass. The most luminous
galaxies show clear evidence for the presence of a massive dark halo, but the
case for dark haloes in fainter galaxies is more ambiguous. We discuss the
observations that would be required to resolve this ambiguity.",0012071v1
2000-12-06,A Preliminary Detection of Arcminute Scale Cosmic Microwave Background Anisotropy with the BIMA Array,"We have used the Berkeley-Illinois-Maryland-Association (BIMA) array
outfitted with sensitive cm-wave receivers to expand our search for arcminute
scale anisotropy of the Cosmic Microwave Background (CMB). The interferometer
was placed in a compact configuration toobtain high brightness sensitivity on
arcminute scales over its 6.6' FWHM field of view. The sensitivity of this
experiment to flat band power peaks at a multipole of l=5530 which corresponds
to an angular scale of ~2'. We present the analysis of a total of 470 hours of
on-source integration time on eleven independent fields which were selected
based on their low IR contrast and lack of bright radio sources. Applying a
Bayesian analysis to the visibility data, we find CMB anisotropy flat band
power Q_flat = 6.1(+2.8/-4.8) microKelvin at 68% confidence. The confidence of
a non- zero signal is 76% and we find an upper limit of Q_flat < 12.4
microKelvin at 95% confidence. We have supplemented our BIMA observations with
concurrent observations at 4.8 GHz with the VLA to search for and remove point
sources. We find the point sources make an insignificant contribution to the
observed anisotropy.",0012151v2
2001-11-14,Cosmic Background Anisotropy due to Neutrino Oscillations Revisited,"This paper has been withdrawn by the author due to a crucial error in several
equations.",0111264v3
2001-12-01,Archeops: A CMB anisotropy balloon experiment measuring a broad range of angular scales,"The Cosmic Microwave Background Radiation is the oldest photon radiation that
can be observed, having been emitted when the Universe was about 300,000 year
old. It is a blackbody at 2.73 K, and is almost perfectly isotropic, the
anisotropies being about one part to 100,000. However, these anisotropies,
detected by the COBE satellite in 1992, constrain the cosmological parameters
such as the curvature of the Universe. Archeops is a balloon-borne experiment
designed to map these anisotropies. The instrument is composed of a 1.5 m
telescope and bolometers cooled at 85 mK to detect radiation between 150 and
550 GHz. To lower parasitic signals, the instrument is borne by a stratospheric
balloon during the arctic night. This instrument is also a preparation for the
Planck satellite mission, as its design is similar to HFI. We discuss here the
results of the first scientific flight from Esrange (near Kiruna, Sweden) to
Russia on January 29th 2001, which led to a 22 % (sub)millimetre sky coverage
unprecedented at this resolution. Here, we put some emphasis on interstellar
dust foreground emission observations.",0112010v1
2001-12-17,High precision cosmology,"I review the current status of cosmology as emerging from recent observations
of cosmic microwave background anisotropies as well as from other sources of
cosmological information.",0112394v1
2002-01-24,Radial orbital anisotropy and the Fundamental Plane of elliptical galaxies,"The existence of the Fundamental Plane (FP) imposes strong constraints on the
structure and dynamics of elliptical galaxies, and thus contains important
information on the processes of their formation and evolution. Here we focus on
the relations between the FP thinness and tilt and the amount of radial orbital
anisotropy. By using N-body simulations of galaxy models characterized by
observationally motivated density profiles, and also allowing for the presence
of live, massive dark matter halos, we explore the impact of radial orbital
anisotropy and instability on the FP properties. The numerical results confirm
a previous semi--analytical finding: the requirement of stability matches
almost exactly the thinness of the FP. In other words, galaxy models that are
radially anisotropic enough to be found outside the observed FP (with their
isotropic parent models lying on the FP) are unstable, and their end--products
fall back on the FP itself. We also find that a systematic increase of radial
orbit anisotropy with galaxy luminosity cannot explain by itself the whole tilt
of the FP, becoming the galaxy models unstable at moderately high luminosities:
at variance with the previous case their end--products are found well outside
the FP itself (abridged).",0201402v1
2002-05-16,Measuring CMB Polarization with ESA PLANCK SubMM-Wave Telescope,"We analyze the polarization properties of the tilted off-axis dual-reflector
submillimeter-wave telescope on the ESA PLANCK Surveyor designed for measuring
the temperature anisotropies and polarization characteristics of the cosmic
microwave background.",0205262v1
2002-05-20,Small-scale microwave background anisotropies due to tangled primordial magnetic fields,"An inhomogeneous cosmological magnetic field creates vortical perturbations
that survive Silk damping on much smaller scales than compressional modes. This
ensures that there is no sharp cut-off in anisotropy on arc-minute scales. As
we had pointed out earlier, tangled magnetic fields, if they exist, will then
be a potentially important contributor to small-angular scale CMBR
anisotropies. Several ongoing and new experiments, are expected to probe the
very small angular scales, corresponding to multipoles with l>1000. In view of
this observational focus, we revisit the predicted signals due to primordial
tangled magnetic fields, for different spectra and different cosmological
parameters. We also identify a new regime, where the photon mean-free path
exceeds the scale of the perturbation, which dominates the predicted signal at
very high l. A scale-invariant spectrum of tangled fields which redshifts to a
present value B_{0}=3\times 10^{-9} Gauss, produces temperature anisotropies at
the 10 micro Kelvin level between l ~ 1000-3000. Larger signals result if the
univese is lambda dominated, if the baryon density is larger, or if the
spectral index of magnetic tangles is steeper, n > -3. The signal will also
have non-Gaussian statistics. We predict the distinctive form of the increased
power expected in the microwave background at high l in the presence of
significant tangled magnetic fields. We may be on the verge of detecting or
ruling out the presence of tangled magnetic fields which are strong enough to
influence the formation of large-scale structure in the Universe.",0205312v1
2002-12-30,Dark Energy: Is it Q or Lambda ?,"New observations of Cosmic Microwave Background Anisotropies, Supernovae
luminosity distances and Galaxy Clustering are sharpening our knowledge about
dark energy. Here we present the latest constraints.",0212566v1
2003-01-29,Statistical Isotropy of CMB and Cosmic Topology,"The breakdown of statistical homogeneity and isotropy of cosmic perturbations
is a generic feature of ultra large scale structure of the cosmos, in
particular, of non trivial cosmic topology. The statistical isotropy (SI) of
the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is
sensitive to this breakdown on largest scales comparable to, and even beyond
the cosmic horizon. We study a set of measures, $\kappa_\ell$ ($\ell=1,2,3,
>...$) which for non-zero values indicate and quantify statistical isotropy
violations in a CMB map. The main goal here is to interpret the $\kappa_\ell$
spectrum and relate it to characteristic patterns in the correlation function
of CMB anisotropy arising from cosmic topology. We numerically compute the
predicted $\kappa_\ell$ spectrum for CMB anisotropy in flat torus universe
models. The essential features are captured in the leading order approximation
to the correlation function where $\kappa_\ell$ can be calculated analytically.
The $\kappa_\ell$ spectrum is shown to reflect the number, importance and
relative orientation of principal directions in the CMB correlation dictated by
the shape of the Dirichlet domain (DD) of the compact space and its size
relative to cosmic horizon. Hence, besides detecting cosmic topology,
$\kappa_\ell$ can discriminate between different topology of the universe
complementing ongoing search for cosmic topology in CMB anisotropy data.",0301590v2
2003-05-19,3-point temperature anisotropies in WMAP: Limits on CMB non-Gaussianities and non-linearities,"We present a study of the 3-pt angular correlation function w_3= <delta_1
delta_2 delta_3> of (adimensional) temperature anisotropies measured by the
Wilkinson Microwave Anisotropy Probe (WMAP). Results can be normalized to the
2-point function w_2 = <delta_1 delta_2> in terms of the hierarchical: q_3 ~
w_3/w_2^2 or dimensionless: d_3 ~ w_2/w_2^{3/2}$ amplitudes. Strongly
non-Gaussian models are generically expected to show d_3 > 1 or q_3 > 10^3 d_3.
Unfortunately, this is comparable to the cosmic variance on large angular
scales. For Gaussian primordial models, q_3 gives a direct measure of the
non-linear corrections to temperature anisotropies in the sky: delta = delta_L
+ f_{NLT} (delta_L^2 - <delta_L^2>) with f_{NLT} = q_3/2 for the leading order
term in w_2^2. We find good agreement with the Gaussian hypothesis d_3 ~ 0
within the cosmic variance of LCDM simulations (with or without a low
quadrupole). The strongest constraints on q_3 come from scales smaller than 1
degree. We find q_3 =19 +/-141 for (pseudo) collapsed configurations and an
average of q_3 = 336 +/-218 for non-collapsed triangles. The corresponding
non-linear coupling parameter, f_{NL}, for curvature perturbations Phi, in the
Sachs-Wolfe (SW) regime is: f_{NL}^{SW} = q_3/6, while on degree scales, the
extra power in acoustic oscillations produces f_{NL} ~ q_3/30 in the LCM model.
Errors are dominated by cosmic variance, but for the first time they begin to
be small enough to constrain the leading order non-linear effects with coupling
of order unity.",0305327v2
2003-06-04,The effect of imperfect corrections of PSF anisotropy on cosmic shear measurements,"Current measurements of the weak lensing signal induced by large scale
structure provide useful constraints on a range of cosmological parameters.
However, the ultimate succes of this technique depends on the accuracy with
which one can correct for the effect of the Point Spread Function (PSF). In
this paper we examine the accuracy of the PSF anisotropy correction using
images of fields with a large number of stars. The ellipticity correlation
function of the residuals is studied to quantify the effect of imperfect
corrections for PSF anisotropy on cosmic shear studies. These imperfections
occur on the chip scale and consequently the systematic signal decreases
rapidly with increasing angular scale. Separation of the signal into ``E''
(curl-free) and ``B'' (curl) components can help to identify the presence of
residual systematics, but in general, the amplitude of the ``B''-mode is
different from that of the ``E''-mode. The study of fields with many stars can
be beneficial in finding a proper description of the variation of PSF
anisotropy, and consequently help to significantly improve the accuracy with
which the cosmic shear signal can be measured. We show that with such an
approach it is feasible that the accuracy of future cosmic shear studies is
limited by the statistical noise introduced by the intrinsic shapes of the
sources. In particular, the prospects for accurate measurements of the cosmic
shear signal on scales larger than ~10 arcminutes are excellent.",0306097v1
2003-06-25,"How reliable is the kinematical evidence for dark matter: the effects of non-sphericity, substructure and streaming motions","Using cosmological $N$-body simulations of dark matter haloes, we study the
effects of non-sphericity, substructure and streaming motions in reproducing
the structure and internal kinematics of clusters of galaxies from kinematical
measurements. Fitting an NFW model to the 3D density profile, we determine the
virial mass, concentration parameter and velocity anisotropy of the haloes, and
then calculate the profiles of projected velocity moments, as they would be
measured by a distant observer. Using these mock data, we apply a Jeans
analysis for spherical objects to reproduce the line-of-sight velocity
dispersion and kurtosis and fit the three parameters. We find that the
line-of-sight velocity dispersion and kurtosis profiles of a given halo can
vary considerably with the angle of view of the observer. We show that the
virial mass, concentration parameter and velocity anisotropy of the haloes can
be reproduced satisfactorily independently of the halo shape, although the
virial mass tends to be underestimated, the concentration parameter
overestimated, while the recovered anisotropy is typically more tangential than
the true one. The mass, concentration and velocity anisotropy of haloes are
recovered with better precision when their mean velocity profiles are near
zero.",0306520v2
2003-08-20,Correlations Between the WMAP and MAXIMA Cosmic Microwave Background Anisotropy Maps,"We cross-correlate the cosmic microwave background temperature anisotropy
maps from the WMAP, MAXIMA-I, and MAXIMA-II experiments. We use the
cross-spectrum, which is the spherical harmonic transform of the angular
two-point correlation function, to quantify the correlation as a function of
angular scale. We find that the three possible pairs of cross-spectra are in
close agreement with each other and with the power spectra of the individual
maps. The probability that there is no correlation between the maps is smaller
than 1 * 10^(-8). We also calculate power spectra for maps made of differences
between pairs of maps, and show that they are consistent with no signal. The
results conclusively show that the three experiments not only display the same
statistical properties of the CMB anisotropy, but also detect the same features
wherever the observed sky areas overlap. We conclude that the contribution of
systematic errors to these maps is negligible and that MAXIMA and WMAP have
accurately mapped the cosmic microwave background anisotropy.",0308355v3
2003-08-22,First Star Signature in Infrared Background Anisotropies,"(Abridged) Recent cosmic microwave background anisotropy results from the
Wilkinson Microwave Anisotropy Probe suggest that the universe was reionized at
a redshift around 20. Such an early reionization could arise through the
ionizing radiation emitted by metal-free population III stars at redshifts of
10 and higher. We discuss infrared background (IRB) surface brightness spatial
fluctuations from such a generation of early star formation. We show that the
spatial clustering of these stars at tens of arcminute scales generates a
contribution to the angular power spectrum of the IRB anisotropies at the same
angular scales. This excess can be potentially detected when resolved
foreground galaxies out to a redshift of a few is removed from the clustering
analysis. Additionally, assuming a population III stellar spectrum, we suggest
that the clustering excess related to the first generation of stars can be
separated from brightness fluctuations resulting from other foreground sources
and galaxies using multifrequency observations in the wavelength range of ~ 1
to 5 microns. In addition to removing the low-redshift galaxy population, the
multifrequency data are essential to account for certain foreground
contaminants such zodiacal light, which, if varying spatially over degree
scales, can be a significant source of confusion for the proposed study. Using
various instruments, we study the extent to which spatial fluctuations of the
IRB can be studied in the near future.",0308407v2
2003-09-15,MAXIMA: A Balloon-Borne Cosmic Microwave Background Anisotropy Experiment,"We describe the Millimeter wave Anisotropy eXperiment IMaging Array (MAXIMA),
a balloon-borne experiment designed to measure the temperature anisotropy of
the Cosmic Microwave Background (CMB) on angular scales of 10' to 5 degrees .
MAXIMA mapped the CMB using 16 bolometric detectors in spectral bands centered
at 150 GHz, 240 GHz, and 410 GHz, with 10' resolution at all frequencies. The
combined receiver sensitivity to CMB anisotropy was ~40 microK/rt(sec).
Systematic parasitic contributions were minimized by using four uncorrelated
spatial modulations, thorough crosslinking, multiple independent CMB
observations, heavily baffled optics, and strong spectral discrimination.
Pointing reconstruction was accurate to 1', and absolute calibration was better
than 4%. Two MAXIMA flights with more than 8.5 hours of CMB observations have
mapped a total of 300 deg^2 of the sky in regions of negligible known
foreground emission. MAXIMA results have been released in previous
publications. MAXIMA maps, power spectra and correlation matrices are publicly
available at http://cosmology.berkeley.edu/maxima",0309414v1
2003-10-29,The Effect of Proton Temperature Anisotropy on the Solar Minimum Corona and Wind,"A semi-empirical, axisymmetric model of the solar minimum corona is developed
by solving the equations for conservation of mass and momentum with prescribed
anisotropic temperature distributions. In the high-latitude regions, the proton
temperature anisotropy is strong and the associated mirror force plays an
important role in driving the fast solar wind; the critical point where the
outflow velocity equals the parallel sound speed is reached already at 1.5 Rsun
from Sun center. The slow wind arises from a region with open field lines and
weak anisotropy surrounding the equatorial streamer belt. The model parameters
were chosen to reproduce the observed latitudinal extent of the equatorial
streamer in the corona and at large distance from the Sun. We find that the
magnetic cusp of the closed-field streamer core lies at about 1.95 Rsun. The
transition from fast to slow wind is due to a decrease in temperature
anisotropy combined with the non-monotonic behavior of the non-radial expansion
factor in flow tubes that pass near the streamer cusp. In the slow wind, the
plasma beta is of order unity and the critical point lies at about 5 Rsun, well
beyond the magnetic cusp. The predicted outflow velocities are consistent with
OVI Doppler dimming measurements from UVCS/SOHO. We also find good agreement
with polarized brightness (pB) measurements from LASCO/SOHO and HI Ly-alpha
images from UVCS/SOHO.",0310846v1
2003-11-10,Anisotropy in the Distribution of Satellite Galaxy Orbits,"Nearby clusters such as Virgo and Coma possess galaxy distributions which
tend to be aligned with the principal axis of the cluster itself. This has also
been confirmed by a recent statistical analysis of some 300 Abell clusters
where the effect has been linked to the dynamical state of the cluster.
Moreover, the orbits of satellite galaxies in galactic systems like our own
Milky Way also demonstrate a high degree of anisotropy - the so-called Holmberg
effect, the origin of which has been the subject of debate for more than 30
years. This study presents the analysis of cosmological simulations focusing on
the orbits of satellite galaxies within dark matter halos. The apocentres of
the orbits of these satellites are preferentially found within a cone of
opening angle ~40 around the major axis of the host halo, in accordance with
the observed anisotropy found in galaxy clusters. We do, however, note that a
link to the dynamical age of the cluster is not well established as both our
oldest dark matter halos do show a clear anisotropy signal. Further analysis
connects this distribution to the infall pattern of satellites along the
filaments: the orbits are determined rather by the environment of the host halo
than some ""dynamical selection"" during their life within the host's virial
radius.",0311202v1
2003-11-26,Detection and discrimination of cosmological non-Gaussian signatures by multi-scale methods,"Recent Cosmic Microwave Background (CMB) observations indicate that the
temperature anisotropies arise from quantum fluctuations in the inflationary
scenario. In the simplest inflationary models, the distribution of CMB
temperature fluctuations should be Gaussian. However, non-Gaussian signatures
can be present. They might have different origins and thus different
statistical and morphological characteristics.
  In this context and motivated by recent and future CMB experiments, we search
for, and discriminate between, different non-Gaussian signatures. We analyse
simulated maps of three cosmological sources of temperature anisotropies:
Gaussian distributed CMB anisotropies from inflation, temperature fluctuations
from cosmic strings and anisotropies due to the kinetic Sunyaev-Zel'dovich (SZ)
effect both showing a non-Gaussian character. We use different multi-scale
methods, namely, wavelet, ridgelet and curvelet transforms. The sensitivity and
the discriminating power of the methods is evaluated using simulated data sets.
  We find that the bi-orthogonal wavelet transform is the most powerful for the
detection of non-Gaussian signatures and that the curvelet and ridgelet
transforms characterise quite precisely and exclusively the cosmic strings.
They allow us thus to detect them in a mixture of CMB + SZ + cosmic strings. We
show that not one method only should be applied to understand non-Gaussianity
but rather a set of different robust and complementary methods should be used.",0311577v1
2003-12-31,CMB Observational Techniques and Recent Results,"The Cosmic Microwave Background (CMB) consists of photons that were last
created about 2 months after the Big Bang, and last scattered about 380,000
years after the Big Bang. The spectrum of the CMB is very close to a blackbody
at 2.725 K and upper limits on any deviations of the CMB from a blackbody place
strong constraints on energy transfer between the CMB and matter at all
redshifts less than 2,000,000. The CMB is very nearly isotropic, but a dipole
anisotropy of +/-3.346(17) mK shows that the Solar System barycenter is moving
at 368+/-2 km/sec relative to the observable Universe. The dipole corresponds
to a spherical harmonic index l=1. The higher indices l geq 2 indicate
intrinsic inhomogeneities in the Universe that existed at the time of last
scattering. While the photons have traveled freely only since the time of last
scattering, the inhomogeneities traced by the CMB photons have been in place
since the inflationary epoch only 10^{-35} sec after the Big Bang. These
intrinsic anisotropies are much smaller in amplitude than the dipole
anisotropy, with Delta T leq 100 microK. Electron scattering of the anisotropic
radiation field produces an anisotropic linear polarization in the CMB with
amplitudes less than 5 microK. Detailed studies of the angular power spectrum
of the temperature and linear polarization anisotropies have yielded precise
values for many cosmological parameters. This paper will discuss the techniques
necessary to measure signals that are 100 million times smaller than the
emission from the instrument and briefly describe results from experiments up
to WMAP.",0401001v1
2004-01-20,Detecting Population III stars through observations of near-IR cosmic infrared background anisotropies,"Following the successful mapping of the last scattering surface by WMAP and
balloon experiments, the epoch of the first stars, when Population III stars
formed, is emerging as the next cosmological frontier. It is not clear what
these stars' properties were, when they formed or how long their era lasted
before leading to the stars and galaxies we see today. We show that these
questions can be answered with the current and future measurements of the
near-IR cosmic infrared background (CIB). Theoretical arguments suggest that
Population III stars were very massive and short-lived stars that formed at
$z\sim 10-20$ at rare peaks of the density field in the cold-dark-matter
Universe. Because Population III stars probably formed individually in small
mini-halos, they are not directly accessible to current telescopic studies. We
show that these stars left a strong and measurable signature via their
contribution to the CIB anisotropies for a wide range of their formation
scenarios. The excess in the recently measured near-IR CIB anisotropies over
that from normal galaxies can be explained by contribution from early
Population III stars. These results imply that Population III were indeed very
massive stars and their epoch started at $z\sim 20$ and lasted past $z\lsim
13$. We show the importance of accurately measuring the CIB anisotropies
produced by Population III with future space-based missions.",0401401v2
2004-02-23,Imaging the first light: experimental challenges and future perspectives in the observation of the Cosmic Microwave Background Anisotropy,"Measurements of the cosmic microwave background (CMB) allow high precision
observation of the Last Scattering Surface at redshift $z\sim$1100. After the
success of the NASA satellite COBE, that in 1992 provided the first detection
of the CMB anisotropy, results from many ground-based and balloon-borne
experiments have showed a remarkable consistency between different results and
provided quantitative estimates of fundamental cosmological properties. During
2003 the team of the NASA WMAP satellite has released the first improved
full-sky maps of the CMB since COBE, leading to a deeper insight into the
origin and evolution of the Universe. The ESA satellite Planck, scheduled for
launch in 2007, is designed to provide the ultimate measurement of the CMB
temperature anisotropy over the full sky, with an accuracy that will be limited
only by astrophysical foregrounds, and robust detection of polarisation
anisotropy. In this paper we review the experimental challenges in high
precision CMB experiments and discuss the future perspectives opened by second
and third generation space missions like WMAP and Planck.",0402528v1
2004-05-10,Cosmological Magnetic Fields vs. CMB,"I present a short review of the effects of a cosmological magnetic field on
the CMB temperature and polarization anisotropies. Various possibilities for
constraining the magnetic field amplitude are discussed.",0405184v1
2005-04-07,The Kinetic Sunyaev-Zel'dovich Effect from Reionization,"During the epoch of reionization, local variations in the ionized fraction
(patchiness) imprint arcminute-scale temperature anisotropies in the CMB
through the kinetic Sunyaev-Zel'dovich (kSZ) effect. We employ an improved
version of an analytic model of reionization devised in Furlanetto et al.(2004)
to calculate the kSZ anisotropy from patchy reionization. This model uses
extended Press-Schechter theory to determine the distribution and evolution of
HII bubbles and produces qualitatively similar reionization histories to those
seen in recent numerical simulations. We find that the angular power spectrum
of the kSZ anisotropies depends strongly on the size distribution of the HII
bubbles and on the duration of reionization. In addition, we show that upcoming
measurements of the kSZ effect should be able to distinguish between several
popular reionization scenarios. In particular, the amplitude of the patchy
power spectrum for reionization scenarios in which the IGM is significantly
ionized by Population III stars (or by mini-quasars/decaying particles) can be
larger (or smaller) by over a factor of 3 than the amplitude in more
traditional reionization histories (with temperature anisotropies that range
between 0.5 and 3 micro-Kelvin at l = 5000). We highlight the differences in
the kSZ signal between many possible reionization morphologies and discuss the
constraints that future observations of the kSZ will place on this epoch.",0504189v2
2005-04-13,An indirect limit on the amplitude of primordial Gravitational Wave Background from CMB-Galaxy Cross Correlation,"While large scale cosmic microwave background (CMB) anisotropies involve a
combination of the scalar and tensor fluctuations, the scalar amplitude can be
independently determined through the CMB-galaxy cross-correlation. Using
recently measured cross-correlation amplitudes, arising from the
cross-correlation between galaxies and the Integrated Sachs Wolfe effect in CMB
anisotropies, we obtain a constraint r < 0.5 at 68% confidence level on the
tensor-to-scalar fluctuation amplitude ratio. The data also allow us to exclude
gravity waves at a level of a few percent, relative to the density field, in a
low - Lambda dominated universe(Omega_Lambda~0.5). In future, joining
cross-correlation ISW measurements, which captures cosmological parameter
information, with independent determinations of the matter density and CMB
anisotropy power spectrum, may constrain the tensor-to-scalar ratio to a level
above 0.05. This value is the ultimate limit on tensor-to-scalar ratio from
temperature anisotropy maps when all other cosmological parameters except for
the tensor amplitude are known and the combination with CMB-galaxy correlation
allows this limit to be reached easily by accounting for degeneracies in
certain cosmological parameters.",0504290v2
2005-05-08,Radio Emission from Anisotropic Electron Distributions,"The effect of pitch-angle anisotropy of fast electrons on generation of
nonthermal radio emission is studied. Incoherent gyrosynchrotron radiation is
shown to depend strongly on the anisotropy. In particular, the spectral index
of gyrosynchrotron radiation increases up to a factor of 3-4 compared with the
isotropic case. The degree of polarization (X-mode) increases for loss-cone
distributions, while decreases for beam-like distributions. Ample evidence of
the pitch-angle anisotropy effect on (1) spatial distribution of the radio
brightness, (2) spatially resolved light curves of the intensity and
polarization, (3) spectral hardness of microwave bursts, is found by exploring
observations performed with Nobeyama Radioheliograph and Owens Valley Solar
Array. Above some threshold in the angular gradient, the electron cyclotron
maser instability (coherent gyrosynchrotron emission) can develop, provided
that standard gyrosynchrotron emission is accompanied by a lower-frequency
intense coherent emission. The coherent emission is studied in detail for a
realistic distribution of fast electrons over the energy and pitch-angle. In
agreement with observations of narrowband radio spikes, it is found that (1)
hard (power-law) distributions over energy are preferable to produce the
coherent emission, (2) the threshold of the instability corresponds to quite an
anisotropic electron distribution, thus, the pitch-angle anisotropy derived
from the properties of the continuum gyrosynchrotron radiation will not
necessarily give rise to coherent emission (either enhanced isotropization
implied by quasilnear saturation of the instability).",0505146v1
2005-08-22,Observation of the Anisotropy of 10 TeV Primary Cosmic Ray Nuclei Flux with the Super-Kamiokande-I Detector,"The relative sidereal variation in the arrival direction of primary cosmic
ray nuclei of median energy 10 TeV was measured using downward, through-going
muons detected with the Super-Kamiokande-I detector. The projection of the
anisotropy map onto the right ascension axis has a first harmonic amplitude of
$(6.64 \pm 0.98 {stat.} \pm 0.55 {syst.}) \times 10^{-4}$ and a phase at
maximum at $(33.2^\circ \pm 8.2^\circ {stat.} \pm 5.1^\circ {syst.})$ right
ascension. A sky map in equatorial coordinates indicates an excess region in
the constellation of Taurus and a deficit region toward Virgo. The excess
region is centered at $(\alpha_T, \delta_T) = (75^\circ \pm 7^\circ, -5^\circ
\pm 9^\circ)$ with a half opening angle $\chi_T = (39 \pm 7)^\circ$; the excess
flux is ($0.104 \pm 0.020$)% above the isotropic expectation. The corresponding
parameters for the deficit region are $(\alpha_V, \delta_V) = (205^\circ \pm
7^\circ, 5^\circ \pm 10^\circ)$, $\chi_V = (54 \pm 7)^\circ$, and $(-0.094 \pm
0.014)$%. The data do not allow us to rule out a pure dipole form for the
anisotropy (allowed at 13% confidence level); they are better described by the
excess and deficit cones described above. We explored the implications under
the assumption that the true anisotropy is not distorted too much by the
analysis filter so that it is well-described by the observed excess and deficit
cones.",0508468v4
2005-09-08,Nonlinear Evolution of Cosmic Magnetic Fields and Cosmic Microwave Background Anisotropies,"In this work we investigate the effects of the primordial magnetic fields on
cosmic microwave background anisotropies (CMB). Based on cosmological
magnetohydrodynamic (MHD) simulations we calculate the CMB anisotropy spectra
and polarization induced by fluid fluctuations (Alfv\'en modes) generated by
primordial magnetic fields. The strongest effect on the CMB spectra comes from
the transition epoch from a turbulent regime to a viscous regime. The balance
between magnetic and kinetic energy until the onset of the viscous regime
provides a one to one relation between the comoving coherence length $L$ and
the comoving magnetic field strength $B$, such as $L \sim 30 (B/10^{-9}{\rm
G})^3 \rm pc$. The resulting CMB temperature and polarization anisotropies are
somewhat different from the ones previously obtained by using linear
perturbation theory. Our calculation gives a constraint on the magnetic field
strength in the intermediate scale of CMB observations. Upper limits are set by
WMAP and BOOMERANG results for comoving magnetic field strength of $B < 28 \rm
nG$ with a comoving coherence length of $L > 0.7 \rm Mpc$ for the most extreme
case, or $B < 30 \rm nG$ and $L> 0.8 \rm Mpc$ for the most conservative case.",0509220v2
2005-11-02,Searching For Integrated Sachs-Wolfe Effect Beyond Temperature Anisotropies: CMB E-mode Polarization-Galaxy Cross Correlation,"The cross-correlation between cosmic microwave background (CMB) temperature
anisotropies and the large scale structure (LSS) traced by the galaxy
distribution, or sources at different wavelengths, is now well known. This
correlation results from the integrated Sachs-Wolfe (ISW) effect in CMB
anisotropies generated at late times due to the dark energy component of the
Universe. In a reionized universe, the ISW quadrupole rescatters and
contributes to the large-scale polarization signal. Thus, in principle, the
large-scale polarization bump in the E-mode should also be correlated with the
galaxy distribution. Unlike CMB temperature-LSS correlation that peaks for
tracers at low redshifts this correlation peaks mostly at redshifts between 1
and 3. Under certain conditions, mostly involving a low optical depth to
reionization, if the Universe reionized at a redshift around 6, the cross
polarization-source signal is marginally detectable, though challenging as it
requires all-sky maps of the large scale structure at redshifts between 1 and
3. If the Universe reionized at a redshift higher than 10, it is unlikely that
this correlation will be detectable even with no instrumental noise all-sky
maps. While our estimates do not guarantee a detection unknown physics related
to the dark energy as well as still uncertain issues related to the large
angular scale CMB and polarization anisotropies may motivate attempts to
measure this correlation using upcoming CMB polarization E-mode maps.",0511054v2
2006-02-09,Constraints on the Evolution of the Primordial Magnetic Field from the Small-Scale Cosmic Microwave Background Angular Anisotropy,"Recent observations of the cosmic microwave background (CMB) have extended
the measured power spectrum to higher multipoles $l\gtrsim$1000, and there
appears to be possible evidence for excess power on small angular scales. The
primordial magnetic field (PMF) can strongly affect the CMB power spectrum and
the formation of large scale structure. In this paper, we calculate the CMB
temperature anisotropies generated by including a power-law magnetic field at
the photon last-scattering surface (PLSS). We then deduce an upper limit on the
PMF based on our theoretical analysis of the power excess on small angular
scales. We have taken into account several important effects such as the
modified matter sound speed in the presence of a magnetic field. An upper limit
to the field strength of $|B_\lambda|\lesssim$ 4.7 nG at the present scale of 1
Mpc is deduced. This is obtained by comparing the calculated theoretical result
including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the
small-scale CMB anisotropies from the $Wilkinson Microwave Anisotropy Probe$
(WMAP), the Cosmic Background Imager (CBI), and the Arcminute Cosmology
Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for
the generation and evolution of the PMF.",0602224v5
2006-03-30,The velocity dispersion and mass profile of the Milky Way,"We re-analyse the velocity-dispersion profile sigma(r) at radii r>10 kpc in
the Galactic stellar halo, recently derived by Battaglia et al. (2005), who
concluded that, for constant velocity anisotropy of the tracers, these data
rule out a flat circular-speed curve for the Milky Way. However, we demonstrate
that if one makes the natural assumption that the tracer density is truncated
at r_t >~ 160 kpc and falls off significantly more steeply than r^-3.5 at r >~
80 kpc, then these data are consistent with a flat circular-speed curve and a
constant velocity anisotropy comparable to that observed for halo stars in the
Solar neighbourhood. We also consider a more detailed mass model with an
exponential stellar disc and an extended non-isothermal dark-matter halo. In
this two-component model, the Milky Way's virial radius and mass are r_vir =
200 kpc and M_vir = 1.5 x 10^12 M_sun. Still assuming the tracers' velocity
anisotropy to be constant (at beta=0.5) we again find good agreement with the
observed sigma(r), so long as the tracer density is truncated near the virial
radius. These data by themselves do not allow to differentiate between
different dark-halo or total-mass models for the Milky Way, nor between
different velocity-anisotropy profiles for the tracers.",0603825v1
2006-04-07,Weak Lensing of the Cosmic Microwave Background by Foreground Gravitational Waves,"Weak lensing distortion of the background cosmic microwave background (CMB)
temperature and polarization patterns by the foreground density fluctuations is
well studied in the literature. We discuss the gravitational lensing
modification to CMB anisotropies and polarization by a stochastic background of
primordial gravitational waves between us and the last scattering surface.
While density fluctuations perturb CMB photons via gradient-type deflections
only, foreground gravitational waves distort CMB anisotropies via both
gradient- and curl-type displacements. The latter is a rotation of background
images, while the former is related to the lensing convergence. For a
primordial background of inflationary gravitational waves, with an amplitude
corresponding to a tensor-to-scalar ratio below the current upper limit of
$\sim$ 0.3, the resulting modifications to the angular power spectra of CMB
temperature anisotropy and polarization are below the cosmic variance limit. At
tens of arcminute angular scales and below, these corrections, however, are
above the level at which systematics must be controlled in all-sky anisotropy
and polarization maps with no instrumental noise and other secondary and
foreground signals.",0604179v5
2006-07-25,Measuring Statistical Isotropy of CMB Anisotropy,"The statistical expectation values of the temperature fluctuations and
polarization of cosmic microwave background (CMB) are assumed to be preserved
under rotations of the sky. We investigate the statistical isotropy (SI) of the
CMB maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP)
using the bipolar spherical harmonic formalism proposed in Hajian & Souradeep
2003 for CMB temperature anisotropy and extended to CMB polarization in Basak,
Hajian & Souradeep 2006. The Bipolar Power Spectrum (BiPS) had been measured
for the full sky CMB anisotropy maps of the first year WMAP data and now for
the recently released three years of WMAP data. We also introduce and measure
directional sensitive reduced Bipolar coefficients on the three year WMAP ILC
map. Consistent with our published results from first year WMAP data we have no
evidence for violation of statistical isotropy on large angular scales.
Preliminary analysis of the recently released first WMAP polarization maps,
however, indicate significant violation of SI even when the foreground
contaminated regions are masked out. Further work is required to confirm a
possible cosmic origin and rule out the (more likely) origin in observational
artifact such as foreground residuals at high galactic latitude.",0607577v1
2006-10-09,"Primordial magnetic field constrained from CMB anisotropies,and its generation and evolution before, during and after the BBN","The primordial magnetic field (PMF) can strongly affect the cosmic microwave
background (CMB) power spectrum and the formation of large scale structure. In
this presentation, we calculate the CMB temperature anisotropies generated by
including a power-law magnetic field at the photon last scattering surface
(PLSS). We then deduce an upper limit on the primordial magnetic field based
upon our theoretical analysis of the power excess on small angular scales. We
have taken into account several important effects such as the modified matter
sound speed in the presence of a magnetic field. An upper limit to the field
strength of $|B_\lambda|\lesssim$ 4.7 nG at the present scale of 1 Mpc is
deduced. This is obtained by comparing the calculated theoretical result
including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the
small scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe
(WMAP), the Cosmic Background Imager (CBI) and the Arcminute Cosmology
Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for
the generation and evolution of the PMF before, during and after the BBN.",0610234v1
2006-11-15,On the Influence of Resonant Scattering on Cosmic Microwave Background Polarisation Anisotropies,"We implement the theory of resonant scattering in the context of Cosmic
Microwave Background (CMB) polarisation anisotropies. We compute the changes in
the E-mode polarisation (EE) and Temperature E-mode (TE) CMB power spectra
introduced by the scattering on a resonant transition with a given optical
depth $\tau_X$ and polarisation coefficient $E_1$. The latter parameter,
accounting for how anisotropic the scattering is, depends on the exchange of
angular momentum in the transition and enables, {\it a priori}, to distinguish
among different possible resonances. We use this formalism in two different
scenarios: cosmological recombination and cosmological reionisation. In the
context of cosmological recombination, we compute predictions in frequency and
multipole space for the change in the TE and EE power spectra introduced by
scattering on the $H_{\alpha}$ and $P_{\alpha}$ lines of Hydrogen. This
constitutes a fundamental test for the standard model of recombination, and the
sensitivity it requires is comparable to that needed in measuring the
primordial CMB B-mode polarisation component. In the context of reionisation,
we study the scattering off metals and ions produced by the first stars, and
find that polarisation anisotropies, apart from providing a consistency test
for intensity measurements, give some insight on how reionisation evolved:
since they keep memory of how anisotropic the line scattering is, they should
be able to discern the OI 63.2$\mu$m transition from other possible transitions
associated to OIII, NII, NIII, etc. The amplitude of these signals are,
however, between 10 to 100 times below the (already challenging) level of CMB
B-mode polarisation anisotropies.",0611497v1
2006-12-01,Slow evolution of elliptical galaxies induced by dynamical friction III. Role of density concentration and pressure anisotropy,"In this paper we study the infall, by dynamical friction, of rigid
""satellites"" taken in a variety of initial configurations and models. We thus
measure how dynamical friction depends on the density concentration and on the
pressure anisotropy of the host galaxy and, separately, the response of the
galaxy during the process.
  The investigation is carried out by using a numerical laboratory set up in
previous papers of this series.
  We find that the pressure anisotropy present in the host galaxy has little
effect on dynamical friction. Instead, the shape of the galaxy density profile
is very important. The classical idealized description appears to be applicable
to galaxy models characterized by a small density gradient but not to
concentrated models. In contrast to the behavior found in small density
gradient models, the orbits of satellites captured in concentrated models are
not circularized by dynamical friction.
  The induced evolution in the host galaxy reflects the initial conditions
adopted for the captured satellite. Satellites spiraling in on quasi-circular
orbits tend to modify the pressure tensor of the host galaxy in the tangential
direction and the galaxy shape from spherical to oblate, while satellites
captured along quasi-radial orbits tend to induce pressure anisotropy in the
radial direction and to generate a prolate shape. This result suggests that the
shape of early-type galaxies may result from occasional mergers rather than
being directly related to the effectiveness of the radial-orbit instability
during the process of formation via collisionless collapse, as often argued in
the past.",0612020v1
2007-01-18,The haloes of merger remnants,"We perform collisionless N-body simulations of 1:1 galaxy mergers, using
models which include a galaxy halo, disc and bulge, focusing on the behaviour
of the halo component. The galaxy models are constructed without recourse to a
Maxwellian approximation. We investigate the effect of varying the galaxies'
orientation, their mutual orbit, and the initial velocity anisotropy or cusp
strength of the haloes upon the remnant halo density profiles and shape, as
well as on the kinematics. We observe that the halo density profile (determined
as a spherical average, an approximation we find appropriate) is exceptionally
robust in mergers, and that the velocity anisotropy of our remnant haloes is
nearly independent of the orbits or initial anisotropy of the haloes. The
remnants follow the halo anisotropy - local density slope (\beta-\gamma)
relation suggested by Hansen & Moore (2006} in the inner parts of the halo, but
\beta is systematically lower than this relation predicts in the outer parts.
Remnant halo axis ratios are strongly dependent on the initial parameters of
the haloes and on their orbits. We also find that the remnant haloes are
significantly less spherical than those described in studies of simulations
which include gas cooling.",0701541v2
1995-11-27,Superconducting state properties of a d-wave superconductor with mass anisotropy,"YBa$_2$Cu$_3$O$_7$ (YBCO) exhibits a large anisotropy between the $a$ and $b$
axes in the CuO$_2$ planes because of the presence of CuO chains. In order to
account for such an anisotropy we develop a Ginzburg-Landau (GL) theory for an
anisotropic d-wave superconductor in an external magnetic field, based on an
anisotropic effective mass approximation within CuO$_2$ planes. The anisotropic
parameter $\lambda=m_x/m_y$, where $m_x$ ($m_y$) is the effective mass in the
$x$ ($y$) direction, is found to have significant physical consequences: In the
bulk case, there exist both the $s$- and $d$-wave order parameters with the
same transition temperature, as long as $\lambda\ne 1$. The GL equations are
also solved both analytically and numerically for the vortex state, and it is
shown that both the $s$- and $d$-wave components show a two-fold symmetry, in
contrast to the four-fold symmetry around the vortex, as expected for the
purely $d$-wave vortex. With the deviation of $\lambda$ from unity, the
opposite winding between the $s$- and $d$-wave components observed in the
purely $d$-wave case is gradually taken over by the same winding number. The
vortex lattice is found to have oblique structure in a wide temperature range
with the precise shape depending on the anisotropy.",9511130v1
1997-04-15,Static and Dynamical Anisotropy Effects in Mixed State of D - Wave Superconductors,"We describe effects of anisotropy caused by the crystal lattice in d-wave
superconductors with s-wave mixing using the effective free energy approach.
Only the d-wave order parameter field $d$ is introduced, while the effect of
the s wave mixing as well as other effects breaking the rotational symmetry
down to the fourfold symmetry of the crystal are represented by a single four
(covariant) derivative term: $\eta d^{*}(\Pi _{y}^{2}-\Pi_{x}^{2})^{2}d $. The
single vortex solution in a phenomenologically interesting range of parameters
is almost identical to the two order parameters approach. We analytically
consider the most general oblique lattice and orientation, but find that only
rectangular body centered lattices are realized. A critical value $\eta _{c} $
at which a phase transition from the rectangular lattice to the square lattice
takes place. The influence on the phase transition line is discussed. The
formalism is extended to the time dependent anisotropic Ginzburg-Landau
equations in order to calculate the effect of the anisotropy on the flux flow.
The moving vortex structure is established and the magnetization as function of
the current is calculated. Although the linear conductivity tensor is
rotationally invariant due to the fourfold symmetry, the nonlinear one shows
anisotropy. We calculate dependence of both direct and Hall I-V curves on the
angle between the current and the crystal lattice orientation.",9704131v1
2001-05-16,Angular dependence of the bulk nucleation field Hc2 of aligned MgB2 crystallites,"Studies on the new MgB2 superconductor, with a critical temperature Tc ~ 39
K, have evidenced its potential for applications although intense magnetic
relaxation effects limit the critical current density, Jc, at high magnetic
fields. This means that effective pinning centers must be added into the
material microstructure, in order to halt dissipative flux movements.
Concerning the basic microscopic mechanism to explain the superconductivity in
MgB2, several experimental and theoretical works have pointed to the relevance
of a phonon-mediated interaction, in the framework of the BCS theory. Questions
have been raised about the relevant phonon modes, and the gap and Fermi surface
anisotropies, in an effort to interpret spectroscopic and thermal data that
give values between 2.4 and 4.5 for the gap energy ratio. Preliminary results
on the anisotropy of Hc2 have shown a ratio, between the in-plane and
perpendicular directions, around 1.7 for aligned MgB2 crystallites and 1.8 for
epitaxial thin films. Here we show a study on the angular dependence of Hc2
pointing to a Fermi velocity anisotropy around 2.5. This anisotropy certainly
implies the use of texturization techniques to optimize Jc in MgB2 wires and
other polycrystalline components.",0105332v2
2001-09-04,Magnetotransport of CeRhIn5,"We report measurements of the temperature-dependent anisotropic resistivity
and in-plane magnetoresistance on single crystals of the tetragonal
heavy-fermion antiferromagnet (TN = 3.8 K) CeRhIn5. The measurements are
reported in the temperature range 1.4 K to 300 K and in magnetic fields to 18
tesla. The resistivity is moderately anisotropic, with a room-temperature
c-axis to in-plane resistivity ratio rho_c/rho_a(300 K) = 1.7. rho(T)
measurements on the non-magnetic analog LaRhIn5 indicate that the anisotropy in
the CeRhIn5 resistivity stems predominately from anisotropy in Kondo-derived
magnetic scattering. In the magnetically ordered regime an applied field H
reduces TN only slightly due to the small ordered moment (0.37mu_B) and
magnetic anisotropy. The magnetoresistance (MR) below TN is positive and varies
linearly with H. In the paramagnetic state a positive MR is present below 7.5
K, while a high-field negative contribution is evident at higher temperatures.
The positive contribution decreases in magnitude with increasing temperature.
Above 40 K the positive contribution is no longer observable, and the MR is
negative. The low-T positive MR results from interactions with the
Kondo-coherent state, while the high-T negative MR stems from single-impurity
effects. The H and T-dependent magnetotransport reflects the magnetic
anisotropy and Kondo interactions at play in CeRhIn5.",0109062v1
2002-05-02,Super-conducting critical fields and anisotropy of a MgB2 single crystal,"Despite the intense activity in the year since the discovery of
superconductivity in MgB2, key parameters, in particular the upper and lower
critical fields Hc2 and Hc1 and their anisotropies, are not well-established,
largely because of the difficulty of growing MgB2 crystals. Attempts have been
made to deduce these parameters from experiments on polycrystalline material,
but they have substantial uncertainties. Hc2 is particularly important for
applications, as it is the field which quenches bulk super-conductivity. In
terms of understanding MgB2, it is now clear that the conventional
electron-phonon interaction is strong enough to account for the high transition
temperature Tc, but the consequences of the double super-conducting gap for the
anisotropy and its dependence on temperature, are uncertain. Here we describe
detailed direct measurements of Hc1(T) and Hc2(T) for the two principal
crystallographic directions in a clean single crystal of MgB2. For fields in
the c-direction, $\mu_0 H^c_{c1}(0)$ = $0.28 +- 0.01T$ and $\mu_0 H^c_{c2}(0)$
is $3 +- 0.5T$; this ratio of critical fields is rather low and implies that
MgB2 is only just a Type II super-conductor. The anisotropies of both critical
fields are close to 2.",0205036v2
2002-06-14,"Reply to Comment on ""Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers""",Reply to the Comment by V.T. Dolgopolov and A.V. Gold [cond-mat/0203276].,0206279v1
2002-09-06,The Transition State in Magnetization Reversal,"We consider a magnet with uniaxial anisotropy in an external magnetic field
along the anisotropy direction, but with a field magnitude smaller than the
coercive field. There are three representative magnetization configurations
corresponding to three extrema of the free energy. The equilibrium and
metastable configurations, which are magnetized approximately parallel and
antiparallel to the applied field, respectively, both correspond to local
free-energy minima. The third extremum configuration is the saddle point
separating these minima. It is also called the transition state for
magnetization reversal. The free-energy difference between the metastable and
transition-state configurations determines the thermal stability of the magnet.
However, it is difficult to determine the location of the transition state in
both experiments and numerical simulations. Here it is shown that the
computational Projective Dynamics method, applied to the time dependence of the
total magnetization, can be used to determine the transition state. From
large-scale micromagnetic simulations of a simple model of magnetic nanowires
with no crystalline anisotropy, the magnetization associated with the
transition state is found to be linearly dependent on temperature, and the
free-energy barrier is found to be dominated by the entropic contribution at
reasonable temperatures and external fields. The effect of including
crystalline anisotropy is also discussed. Finally, the influence of the spin
precession on the transition state is determined by comparison of the
micromagnetic simulations to kinetic Monte Carlo simulations of precession-free
(overdamped) dynamics.",0209166v1
2002-09-13,Quantum Monte Carlo study of S=1/2 weakly-anisotropic antiferromagnets on the square lattice,"We study the finite-temperature behaviour of two-dimensional S=1/2 Heisenberg
antiferromagnets with very weak easy-axis and easy-plane exchange anisotropies.
By means of quantum Monte Carlo simulations, based on the continuous-time loop
and worm algorithm, we obtain a rich set of data that allows us to draw
conclusions about both the existence and the type of finite-temperature
transition expected in the considered models. We observe that the essential
features of the Ising universality class, as well as those of the
Berezinskii-Kosterlitz-Thouless (BKT) one, are preserved even for anisotropies
as small as 10^{-3} times the exchange integral; such outcome, being referred
to the most quantum case S=1/2, rules out the possibility for quantum
fluctuations to destroy the long or quasi-long range order, whose onset is
responsible for the Ising or BKT transition, no matter how small the
anisotropy. Besides this general issue, we use our results to extract, out of
the isotropic component, the features which are peculiar to weakly anisotropic
models, with particular attention for the temperature region immediately above
the transition. By this analysis we aim to give a handy tool for understanding
the experimental data relative to those real compounds whose anisotropies are
too weak for a qualitative description to accomplish the goal of singling out
the genuinely two-dimensional critical behaviour.",0209316v2
2003-10-14,"Exchange anisotropy, disorder and frustration in diluted, predominantly ferromagnetic, Heisenberg spin systems","Motivated by the recent suggestion of anisotropic effective exchange
interactions between Mn spins in Ga$_{1-x}$Mn$_x$As (arising as a result of
spin-orbit coupling), we study their effects in diluted Heisenberg spin
systems. We perform Monte Carlo simulations on several phenomenological model
spin Hamiltonians, and investigate the extent to which frustration induced by
anisotropic exchanges can reduce the low temperature magnetization in these
models and the interplay of this effect with disorder in the exchange. In a
model with low coordination number and purely ferromagnetic (FM) exchanges, we
find that the low temperature magnetization is gradually reduced as exchange
anisotropy is turned on. However, as the connectivity of the model is
increased, the effect of small-to-moderate anisotropy is suppressed, and the
magnetization regains its maximum saturation value at low temperatures unless
the distribution of exchanges is very wide. To obtain significant suppression
of the low temperature magnetization in a model with high connectivity, as is
found for long-range interactions, we find it necessary to have both
ferromagnetic and antiferromagnetic (AFM) exchanges (e.g. as in the RKKY
interaction). This implies that disorder in the sign of the exchange
interaction is much more effective in suppressing magnetization at low
temperatures than exchange anisotropy.",0310322v1
2004-05-04,Effect of extra electrons on the exchange and magnetic anisotropy in the anionic single-molecule magnet Mn12,"To understand the effect of molecular environment on the electronic and
magnetic properties of the single-molecule magnet (SMM) Mn$_{12}$, we explore
two possible means for adding extra electrons to molecule. We explore both
substitution of Mn ions by Fe ions and the inclusion of neighboring electronic
donors. For both possibilities we calculate, within density-functional theory,
the electronic structure, the total ground-state spin and ordering, the
magnetic anisotropy barrier, the transverse magnetic anisotropy parameter $E$
which is responsible for some measured tunneling, and the tilting angle of the
easy axis from the z axis. Our calculations show that the total spin increases
with increasing number of extra electrons except for the case of Mn$_{8}$Fe$_4$
where the resulting ground state has a low spin. The calculated energy gaps
between the unoccupied and the occupied orbitals exhibit no clear trend as a
function of number of extra electrons. The calculated magnetic anisotropy
barrier decreases with increasing number of extra electrons and can be directly
chased to a quenching of Jahn-Teller distortions at the sites where the
additional electrons are localized. The values of $E$ and the easy-axis tilting
angles for the geometries with one- and two-extra electrons are significantly
larger than those induced by solvent disorder.",0405059v1
2005-07-30,GaMnAs grown on (311) GaAs substrates: modified Mn incorporation and new magnetic anisotropies,"We report the results of a detailed study of the structural, magnetic and
magnetotransport properties of as-grown and annealed Ga0.91Mn0.09As thin films
grown on (311)A and (311)B GaAs substrates. The high Curie temperature and hole
density of the (311)B material are comparable to those of GaMnAs grown on (001)
GaAs under the same growth conditions, while they are much lower for the (311)A
material. We find evidence that Mn incorporation is more efficient for (311)B
than for (001) and significantly less efficient for (311)A which is consistent
with the bonding on these surfaces. This indicates that growth on (311)B may be
a route to increased Curie temperatures in GaMnAs. A biaxial magnetic
anisotropy is observed for the (311) material with easy axes along the [010]
and [001] out-of-plane directions. An additional uniaxial in-plane anisotropy
is also observed with the easy axis along for the (311)A material, and along
for the (311)B material. This new observation may be of importance for the
resolution of the outstanding problem of the origin of uniaxial anisotropy in
(001) GaMnAs.",0508021v1
2005-10-25,Effective Electrostatic Interactions in Solutions of Polyelectrolyte Stars with Rigid Rodlike Arms,"In solutions of star-branched polyelectrolytes, electrostatic interactions
between charged arms on neighboring stars can compete with intra-star
interactions and rotational entropy to induce anisotropy in the orientational
distribution of arms. For model stars comprising rigid rodlike arms with evenly
spaced charged monomers interacting via an effective screened-Coulomb (Yukawa)
potential, we explore the influence of arm orientational anisotropy on
effective star-star interactions. Monte Carlo simulation and density-functional
theory are used to compute arm orientational distributions and effective pair
potentials between weakly charged stars. The degree of anisotropy is found to
increase with the strength of electrostatic interactions and proximity of the
stars. As two stars begin to overlap, the forward arms are pushed back by
inter-star arm-arm repulsion, but partially interdigitate due to rotational
entropy. At center-center separations approaching complete overlap, the arms
relax to an isotropic distribution. For nonoverlapping stars,
anisotropy-induced changes in intra- and inter-star arm-arm interactions
largely cancel and the effective pair interactions are then well approximated
by a simple Yukawa potential, as predicted by linear response theory for a
continuum model of isotropic stars [A. R. Denton, Phys. Rev. E 67, 11804
(2003)]. For overlapping stars, the effective pair interactions in the simple
rigid-arm-Yukawa model agree closely with simulations of a molecular model that
includes flexible arms and explicit counterions [A. Jusufi, C. N. Likos, and H.
Lowen, Phys. Rev. Lett. 88, 018301 (2002); J. Chem. Phys. 116, 11011 (2002)].",0510678v1
2006-01-25,Spin anisotropy effects in dimer single molecule magnets,"We present a model of equal spin $s_1$ dimer single molecule magnets. The
spins within each dimer interact via the Heisenberg and the most general set of
four quadratic anisotropic spin interactions with respective strengths $J$ and
$\{J_j\}$, and with the magnetic induction ${\bf B}$. We solve the model
exactly for $s_1=1/2, 1, 5/2$, and for antiferromagnetic Heisenberg couplings
($J<0$), present ${\bf M}({\bf B})$ curves at low $T$ for these cases. Low-$T$
$C_V({\bf B})$ curves for $s_1=1/2$ and electron paramagnetic susceptibility
$\chi({\bf B},\omega)$ for $s_1=1$ are also provided. For weak anisotropy
interactions, we employ a perturbative treatment, and show that the Hartree and
extended Hartree approximations lead to reliable analytic results at low $T$
and large $B$ for these quantities and for the inelastic neutron scattering
cross-section $S({\bf B}, {\bf q},\omega)$. Our results are discussed with
regard to existing ${\bf M}({\bf B})$ experiments on $s_1=5/2$ Fe$_2$ dimer
single molecule magnets, and suggest that one of them contains a substantial
amount of single-ion anisotropy, without any sizeable global spin anisotropy.
We urge further experiments of the above types on single crystals of Fe$_2$ and
on some $s_=9/2$ [Mn$_4$]$_2$ dimers, in order to elucidate the precise values
of the various microscopic interactions.",0601591v1
2006-03-08,Is it really possible to grow isotropic on-lattice diffusion-limited aggregates?,"In a recent paper (Bogoyavlenskiy V A 2002 \JPA \textbf{35} 2533), an
algorithm aiming to generate isotropic clusters of the on-lattice
diffusion-limited aggregation (DLA) model was proposed. The procedure consists
of aggregation probabilities proportional to the squared number of occupied
sites ($k^2$). In the present work, we analyzed this algorithm using the noise
reduced version of the DLA model and large scale simulations. In the noiseless
limit, instead of isotropic patterns, a $45^\circ$ ($30^\circ$) rotation in the
anisotropy directions of the clusters grown on square (triangular) lattices was
observed. A generalized algorithm, in which the aggregation probability is
proportional to $k^\nu$, was proposed. The exponent $\nu$ has a nonuniversal
critical value $\nu_c$, for which the patterns generated in the noiseless limit
exhibit the original (axial) anisotropy for $\nu<\nu_c$ and the rotated one
(diagonal) for $\nu>\nu_c$. The values $\nu_c = 1.395\pm0.005$ and $\nu_c =
0.82\pm 0.01$ were found for square and triangular lattices, respectively.
Moreover, large scale simulations show that there are a nontrivial relation
between noise reduction and anisotropy direction. The case $\nu=2$ (\bogo's
rule) is an example where the patterns exhibit the axial anisotropy for small
and the diagonal one for large noise reduction.",0603218v1
2006-05-19,Spin-flop transition in antiferromagnetic multilayers,"A comprehensive theoretical investigation on the field-driven reorientation
transitions in uniaxial multilayers with antiferromagnetic coupling is
presented. It is based on a complete survey of the one-dimensional solutions
for the basic phenomenological (micromagnetic) model that describes the
magnetic properties of finite stacks made from ferromagnetic layers coupled
antiferromagnetically through spacer layers. The general structure of the phase
diagrams is analysed. At a high ratio of uniaxial anisotropy to
antiferromagnetic interlayer exchange, only a succession of collinear magnetic
states is possible. With increasing field first-order (metamagnetic)
transitions occur from the antiferromagnetic ground-state to a set of
degenerate ferrimagnetic states and to the saturated ferromagnetic state. At
low anisotropies, a first-order transition from the antiferromagnetic
ground-state to an inhomogeneous spin-flop state occurs. Between these two
regions, transitional magnetic phases occupy the range of intermediate
anisotropies. Detailed and quantitative phase diagrams are given for the basic
model of antiferromagnetic multilayer systems with N = 2 to 16 layers. The
connection of the phase diagrams with the spin-reorientation transitions in
bulk antiferromagnets is discussed. The limits of low anisotropy and large
numbers of layers are analysed by two different representations of the magnetic
energy, namely, in terms of finite chains of staggered vectors and in a general
continuum form. It is shown that the phenomena widely described as ``surface
spin-flop'' are driven only by the cut exchange interactions and the
non-compensated magnetic moment at the surface layers of a stacked
antiferromagnetic system.",0605493v1
2006-06-10,Topological solitons in highly anisotropic two dimensional ferromagnets,"e study the solitons, stabilized by spin precession in a classical
two--dimensional lattice model of Heisenberg ferromagnets with non-small
easy--axis anisotropy. The properties of such solitons are treated both
analytically using the continuous model including higher then second powers of
magnetization gradients, and numerically for a discrete set of the spins on a
square lattice. The dependence of the soliton energy $E$ on the number of spin
deviations (bound magnons) $N$ is calculated. We have shown that the
topological solitons are stable if the number $N$ exceeds some critical value
$N_{\rm{cr}}$. For $N < N_{\rm{cr}}$ and the intermediate values of anisotropy
constant $K_{\mathrm{eff}} <0.35J$ ($J$ is an exchange constant), the soliton
properties are similar to those for continuous model; for example, soliton
energy is increasing and the precession frequency $ \omega (N)$ is decreasing
monotonously with $N$ growth. For high enough anisotropy $K_{\mathrm{eff}} >
0.6 J$ we found some fundamentally new soliton features absent for continuous
models incorporating even the higher powers of magnetization gradients. For
high anisotropy, the dependence of soliton energy E(N) on the number of bound
magnons become non-monotonic, with the minima at some ""magic"" numbers of bound
magnons. Soliton frequency $\omega (N)$ have quite irregular behavior with
step-like jumps and negative values of $\omega $ for some regions of $N$. Near
these regions, stable static soliton states, stabilized by the lattice effects,
exist.",0606263v1
2006-07-24,Effect of Y substitution on the structural and magnetic properties of Dy1-xYxCo5 compounds,"Structural and magnetization studies were carried out on Dy1-xYxCo5 [x = 0,
0.2, 0.4, 0.6, 0.8, 1] compounds which crystallize in the hexagonal CaCu5-type
structure. Lattice parameters and unit-cell volume increase with Y
concentration. Large thermomagnetic irreversibility between the field-cooled
and the zero-field cooled magnetization data has been observed in all the
compounds, which has been attributed to the domain wall pinning effect.
Temperature dependence of magnetization data shows that except DyCo5 and YCo5,
all the compounds show spin reorientation transitions in the range of 5-300 K.
The spin reorientation temperature decreases from 266 K for x=0.2 to 100 K for
x=0.8. Powder x-ray diffractograms of the magnetically aligned samples show
that DyCo5 has planar anisotropy at room temperature whereas all the other
compounds possess axial anisotropy. The spin reorientation transition has been
attributed to a change in the easy magnetization direction from the ab-plane to
the c-axis, as the temperature is increased. The anisotropy field and the first
order anisotropy constant are found to be quite high in all the compounds
except DyCo5. The magnetic properties have been explained by taking into
account the variations in contributions arising from the rare earth and
transition metal sublattices.",0607597v1
2006-08-18,Influence of external flows on crystal growth: numerical investigation,"We use a combined phase-field/lattice-Boltzmann scheme [D. Medvedev, K.
Kassner, Phys. Rev. E {\bf 72}, 056703 (2005)] to simulate non-facetted crystal
growth from an undercooled melt in external flows. Selected growth parameters
are determined numerically.
  For growth patterns at moderate to high undercooling and relatively large
anisotropy, the values of the tip radius and selection parameter plotted as a
function of the Peclet number fall approximately on single curves. Hence, it
may be argued that a parallel flow changes the selected tip radius and growth
velocity solely by modifying (increasing) the Peclet number. This has
interesting implications for the availability of current selection theories as
predictors of growth characteristics under flow.
  At smaller anisotropy, a modification of the morphology diagram in the plane
undercooling versus anisotropy is observed. The transition line from dendrites
to doublons is shifted in favour of dendritic patterns, which become faster
than doublons as the flow speed is increased, thus rendering the basin of
attraction of dendritic structures larger.
  For small anisotropy and Prandtl number, we find oscillations of the tip
velocity in the presence of flow. On increasing the fluid viscosity or
decreasing the flow velocity, we observe a reduction in the amplitude of these
oscillations.",0608430v1
2006-10-30,Revised theory of the magnetic surface anisotropy of impurities in metallic mesoscopic samples,"In several experiments the magnitude of the contribution of magnetic
impurities to the Kondo resistivity shows size dependence in mesoscopic
samples. It was suggested ten years ago that magnetic surface anisotropy can be
responsible for the size dependence in cases where there is strong spin-orbit
interaction in the metallic host. The anisotropy energy has the form $\Delta
E=K_d ({\bf n}{\bf S})^2$ where ${\bf n}$ is the vector perpendicular to the
plane surface, ${\bf S}$ is the spin of the magnetic impurity and $K_d>0$ is
inversely proportional to distance $d$ measured from the surface. It has been
realized that in the tedious calculation an unjustified approximation was
applied for the hybridizations of the host atom orbitals with the conduction
electrons which depend on the position of the host atoms. Namely, the momenta
of the electrons were replaced by the Fermi momentum $k_F$. That is
reinvestigated considering the $k$-dependence which leads to singular energy
integrals and in contrary to the previous result $K_d$ is oscillating like
$\sin (2 k_F d)$ and the distance dependence goes like $1/d^3$ in the
asymptotic region. As the anisotropy is oscillating, for integer spin the
ground state is either a singlet or a doublet depending on distance $d$, but in
the case of the doublet there is no direct electron induced transition between
those two states at zero temperature. Furthermore, for half-integer ($S > 1/2$)
spin it is always a doublet with direct transition only in half of the cases.",0610843v2
2007-01-04,Exact solution of the mixed-spin Ising model on a decorated square lattice with two different kinds of decorating spins on horizontal and vertical bonds,"The mixed spin-(1/2, S_B, S_C) Ising model on a decorated square lattice with
two different kinds of decorating spins S_B and S_C placed on its horizontal
and vertical bonds, respectively, is exactly solved by establishing a precise
mapping relationship with the corresponding spin-1/2 Ising model on an
anisotropic square (rectangular) lattice. The effect of uniaxial single-ion
anisotropy acting on both types of decorating spins S_B and S_C is examined in
particular. If decorating spins S_B and S_C are integer and half-odd-integer,
respectively, or if the reverse is the case, the model under investigation
displays a very peculiar critical behavior beared on the spontaneously ordered
'quasi-1D' spin system, which appears as a result of the single-ion anisotropy
strengthening. We have found convincing evidence that this remarkable
spontaneous ordering virtually arises even though all integer-valued decorating
spins tend towards their 'non-magnetic' spin state S=0 and the system becomes
disordered only upon further increase of the single-ion anisotropy. The
single-ion anisotropy parameter is also at an origin of various temperature
dependences of the total magnetization when imposing the pure ferrimagnetic or
the mixed ferro-ferrimagnetic character of the spin arrangement.",0701071v2
1992-11-19,Tunneling in Anisotropic Cosmological Models,"Tunneling rate is investigated in homogenous and anisotropic cosmologies. The
calculations is done by two methods: Euclidean and Hamiltonian approaches. It
is found that the probability decreases exponentialy as anisotropy is
increased.",9211024v1
1997-07-10,A fully covariant description of CMB anisotropies,"Starting from the exact non-linear description of matter and radiation, a
fully covariant and gauge-invariant formula for the observed temperature
anisotropy of the cosmic microwave background (CBR) radiation, expressed in
terms of the electric ($E_{ab}$) and magnetic ($H_{ab}$) parts of the Weyl
tensor, is obtained by integrating photon geodesics from last scattering to the
point of observation today. This improves and extends earlier work by Russ et
al where a similar formula was obtained by taking first order variations of the
redshift. In the case of scalar (density) perturbations, $E_{ab}$ is related to
the harmonic components of the gravitational potential $\Phi_k$ and the usual
dominant Sachs-Wolfe contribution $\delta T_R/\bar{T}_R\sim\Phi_k$ to the
temperature anisotropy is recovered, together with contributions due to the
time variation of the potential (Rees-Sciama effect), entropy and velocity
perturbations at last scattering and a pressure suppression term important in
low density universes. We also explicitly demonstrate the validity of assuming
that the perturbations are adiabatic at decoupling and show that if the surface
of last scattering is correctly placed and the background universe model is
taken to be a flat dust dominated Friedmann-Robertson-Walker model (FRW), then
the large scale temperature anisotropy can be interpreted as being due to the
motion of the matter relative to the surface of constant temperature which
defines the surface of last scattering on those scales.",9707022v1
1998-03-13,The Anisotropic Wilson Gauge Action,"Anisotropic lattices, with a temporal lattice spacing smaller than the
spatial one, allow precision Monte Carlo calculations of problems that are
difficult to study otherwise: heavy quarks, glueballs, hybrids, and high
temperature thermodynamics, for example. We here perform the first step
required for such studies with the (quenched) Wilson gauge action, namely, the
determination of the renormalized anisotropy $\xi$ as a function of the bare
anisotropy $\xi_0$ and the coupling. By, essentially, comparing the
finite-volume heavy quark potential where the quarks are separated along a
spatial direction with that where they are separated along the time direction,
we determine the relation between $\xi$ and $\xi_0$ to a fraction of 1% for
weak and to 1% for strong coupling. We present a simple parameterization of
this relation for $1\leq \xi \leq 6$ and $5.5 \leq \beta \leq \infty$, which
incorporates the known one-loop result and reproduces our non-perturbative
determinations within errors. Besides solving the problem of how to choose the
bare anisotropies if one wants to take the continuum limit at fixed
renormalized anisotropy, this parameterization also yields accurate estimates
of the derivative $\partial\xi_0/\partial\xi$ needed in thermodynamic studies.",9803010v2
2001-07-02,Numerical study of O(a) improved Wilson quark action on anisotropic lattice,"The $O(a)$ improved Wilson quark action on the anisotropic lattice is
investigated. We carry out numerical simulations in the quenched approximation
at three values of lattice spacing ($a_{\sigma}^{-1}=1$--2 GeV) with the
anisotropy $\xi=a_{\sigma}/a_{\tau}=4$, where $a_{\sigma}$ and $a_{\tau}$ are
the spatial and the temporal lattice spacings, respectively. The bare
anisotropy $\gamma_F$ in the quark field action is numerically tuned by the
dispersion relation of mesons so that the renormalized fermionic anisotropy
coincides with that of gauge field. This calibration of bare anisotropy is
performed to the level of 1 % statistical accuracy in the quark mass region
below the charm quark mass. The systematic uncertainty in the calibration is
estimated by comparing the results from different types of dispersion
relations, which results in 3 % on our coarsest lattice and tends to vanish in
the continuum limit. In the chiral limit, there is an additional systematic
uncertainty of 1 % from the chiral extrapolation.
  Taking the central value $\gamma_F=\gamma_F^*$ from the result of the
calibration, we compute the light hadron spectrum. Our hadron spectrum is
consistent with the result by UKQCD Collaboration on the isotropic lattice. We
also study the response of the hadron spectrum to the change of anisotropic
parameter, $\gamma_F \to \gamma_F^* + \delta\gamma_F$. We find that the change
of $\gamma_F$ by 2 % induces a change of 1 % in the spectrum for physical quark
masses. Thus the systematic uncertainty on the anisotropic lattice, as well as
the statistical one, is under control.",0107001v1
2004-12-03,Lattice Study of Anisotropic QED-3,"We present results from a Monte Carlo simulation of non-compact lattice QED
in 3 dimensions on a $16^3$ lattice in which an explicit anisotropy between $x$
and $y$ hopping terms has been introduced into the action. This formulation is
inspired by recent formulations of anisotropic QED$_3$ as an effective theory
of the non-superconducting portion of the cuprate phase diagram, with
relativistic fermion degrees of freedom defined near the nodes of the gap
function on the Fermi surface, and massless photon degrees of freedom
reproducing the dynamics of the phase disorder of the superconducting order
parameter. Using a parameter set corresponding to broken chiral symmetry in the
isotropic limit, our results show that the renormalised anisotropy, defined in
terms of the ratio of correlation lengths of gauge invariant bound states in
the $x$ and $y$ directions, exceeds the explicit anisotropy $\kappa$ introduced
in the lattice action, implying in contrast to recent analytic results that
anisotropy is a relevant deformation of QED$_3$. There also appears to be a
chiral symmetry restoring phase transition at $\kappa_c\simeq4.5$, implying
that the pseudogap phase persists down to T=0 in the cuprate phase diagram.",0412009v2
1997-01-29,Symmetries of BFKL Equation,"We discuss the algebraic structure of the spin chains related to high energy
scattering in QCD. We study the sl(2) Yangian symmetry and possible
generalizations to nonzero spin and anisotropy parameter.",9701174v1
2006-11-28,On the Dirichlet problem of Landau-Lifshitz-Maxwell equations,"We prove the existence and uniqueness of non-trivial stable solutions to
Landau-Lifshitz-Maxwell equations with Dirichlet boundary condition for large
anisotropies and small domains, where the domains are non-simply connected.",0611844v1
2000-01-19,Persistence of small-scale anisotropies and anomalous scaling in a model of magnetohydrodynamics turbulence,"The problem of anomalous scaling in magnetohydrodynamics turbulence is
considered within the framework of the kinematic approximation, in the presence
of a large-scale background magnetic field. The velocity field is Gaussian,
$\delta$-correlated in time, and scales with a positive exponent $\xi$.
Explicit inertial-range expressions for the magnetic correlation functions are
obtained; they are represented by superpositions of power laws with
non-universal amplitudes and universal (independent of the anisotropy and
forcing) anomalous exponents. The complete set of anomalous exponents for the
pair correlation function is found non-perturbatively, in any space dimension
$d$, using the zero-mode technique. For higher-order correlation functions, the
anomalous exponents are calculated to $O(\xi)$ using the renormalization group.
The exponents exhibit a hierarchy related to the degree of anisotropy; the
leading contributions to the even correlation functions are given by the
exponents from the isotropic shell, in agreement with the idea of restored
small-scale isotropy. Conversely, the small-scale anisotropy reveals itself in
the odd correlation functions : the skewness factor is slowly decreasing going
down to small scales and higher odd dimensionless ratios (hyperskewness etc.)
dramatically increase, thus diverging in the $r\to 0$ limit.",0001039v1
2000-07-12,"""Toy models"" of turbulent convection and the hypothesis of the local isotropy restoration","A brief review is given of recent results devoted to the effects of
large-scale anisotropy on the inertial-range statistics of the passive scalar
quantity $\theta(t,{\bf x})$, advected by the synthetic turbulent velocity
field with the covariance $\propto\delta(t-t')|{\bf x}-{\bf x'}|^{\eps}$.
Inertial-range anomalous scaling behavior is established, and explicit
asymptotic expressions for the structure functions $ S_n (\r) \equiv <
[\theta(t,{\bf x}+\r)-\theta(t,{\bf x})]^{n}>$ are obtained; they are
represented by superpositions of power laws with universal (independent of the
anisotropy parameters) anomalous exponents, calculated to the first order in
$\eps$ in any space dimension. The exponents are associated with tensor
composite operators built of the scalar gradients, and exhibit a kind of
hierarchy related to the degree of anisotropy: the less is the rank, the less
is the dimension and, consequently, the more important is the contribution to
the inertial-range behavior. The leading terms of the even (odd) structure
functions are given by the scalar (vector) operators. The small-scale
anisotropy reveals itself in odd correlation functions: for the incompressible
velocity field, $S_{3}/S_{2}^{3/2}$ decreases going down towards to the depth
of the inertial range, while the higher-order odd ratios increase; if the
compressibility is strong enough, the skewness factor also becomes increasing.",0007015v1
2007-01-03,On the angular distribution and spin polarization of the photoelectrons from semi-filled shell atoms,"We present here the results of calculations of photoelectrons' angular
anisotropy and spin-polarization parameters for a number of semi-filled shell
atoms. We consider ionization of outer or in some cases next to the outer
electrons in a number of elements from I, V, and VI groups of the Periodic
Table. All calculations are performed with account of multi-electron
correlations in the frame of the Spin Polarized version of the Random Phase
Approximation with Exchange - SP RPAE. We consider the dipole angular
distribution and spin polarization of photoelectrons from semi-filled subshells
and from closed shells that are neighbors to the semi-filled shells. We have
considered also angular anisotropy and spin-polarization of photoelectrons from
some excited atoms that are formed by spin-flip of one of the outer electrons.
To check the accuracy and consistency of the applied SP RPAE approach and to
see the role of the nuclear charge variation only, we have calculated the
dipole angular anisotropy and spin-polarization parameters of 3p - electrons in
K and compare them to Ar and K+ that have the same configuration. Entirely, we
have calculated the angular anisotropy and spin-polarization parameters for
following subshells of atoms N (2p), P (3p), Ar (3p), K+(3p), K(3p), Cr(3p,
3d), Cr*(3d), Mn(3p, 3d), As(3d, 4p), Mo(4p, 4d), Mo*(4d), Tc(4p, 4d), Sb(4d,
5p), Eu(4f). The peculiarities of obtained parameters as function of photon
frequencies are discussed, as well as some specific features of considered
semi-filled shell objects.",0701040v1
2007-05-18,Angular anisotropy of the fusion-fission and quasifission fragments,"The anisotropy in the angular distribution of the fusion-fission and
quasifission fragments for the $^{16}$O+$^{238}$U, $^{19}$F+$^{208}$Pb and
$^{32}$S+$^{208}$Pb reactions is studied by analyzing the angular momentum
distributions of the dinuclear system and compound nucleus which are formed
after capture and complete fusion, respectively. The orientation angles of
axial symmetry axes of colliding nuclei to the beam direction are taken into
account for the calculation of the variance of the projection of the total spin
onto the fission axis. It is shown that the deviation of the experimental
angular anisotropy from the statistical model picture is connected with the
contribution of the quasifission fragments which is dominant in the
$^{32}$S+$^{208}$Pb reaction. Enhancement of anisotropy at low energies in the
$^{16}$O+$^{238}$U reaction is connected with quasifission of the dinuclear
system having low temperature and effective moment of inertia.",0705.2748v1
2007-06-05,A note on the large-angle anisotropies in the WMAP cut-sky maps,"Recent analyses of the WMAP data seem to indicate the possible presence of
large-angle anisotropy in the Universe. If confirmed, these can have important
consequences for our understanding of the Universe. A number of attempts have
recently been made to establish the reality and nature of such anisotropies in
the CMB data. Among these is a directional indicator recently proposed by the
authors. A distinctive feature of this indicator is that it can be used to
generate a sky map of the large-scale anisotropies of the CMB maps. Applying
this indicator to full-sky temperature maps we found a statistically
significant preferred direction. The full-sky maps used in these analyses are
known to have residual foreground contamination as well as complicated noise
properties. Thus, here we performed the same analysis for a map where regions
with high foreground contamination were removed. We find that the main feature
of the full-sky analysis, namely the presence of a significant axis of
asymmetry, is robust with respect to this masking procedure. Other subtler
anomalies of the full-sky are on the other hand no longer present.",0706.0575v1
2007-06-14,Bianchi Model CMB Polarization and its Implications for CMB Anomalies,"We derive the CMB radiative transfer equation in the form of a multipole
hierarchy in the nearly-Friedmann-Robertson-Walker limit of homogeneous, but
anisotropic, universes classified via their Bianchi type. Compared with
previous calculations, this allows a more sophisticated treatment of
recombination, produces predictions for the polarization of the radiation, and
allows for reionization. Our derivation is independent of any assumptions about
the dynamical behaviour of the field equations, except that it requires
anisotropies to be small back to recombination; this is already demanded by
observations.
  We calculate the polarization signal in the Bianchi VIIh case, with the
parameters recently advocated to mimic the several large-angle anomalous
features observed in the CMB. We find that the peak polarization signal is ~
1.2 micro K for the best-fit model to the temperature anisotropies, and is
mostly confined to multipoles l<10. Remarkably, the predicted large-angle EE
and TE power spectra in the Bianchi model are consistent with WMAP observations
that are usually interpreted as evidence of early reionization. However, the
power in B-mode polarisation is predicted to be similar to the E-mode power and
parity-violating correlations are also predicted by the model; the WMAP
non-detection of either of these signals casts further strong doubts on the
veracity of attempts to explain the large-angle anomalies with global
anisotropy. On the other hand, given that there exist further dynamical degrees
of freedom in the VIIh universes that are yet to be compared with CMB
observations, we cannot at this time definitively reject the anisotropy
explanation.",0706.2075v2
2007-08-30,Some doubts on the validity of the foreground Galactic contribution subtraction from microwave anisotropies,"The Galactic foreground contamination in CMBR anisotropies, especially from
the dust component, is not easily separable from the cosmological or
extragalactic component. In this paper, some doubts will be raised concerning
the validity of the methods used to date to remove Galactic dust emission in
order to show that none of them achieves its goal.
  First, I review the recent bibliography on the topic and discuss critically
the methods of foreground subtraction: the cross-correlation with templates,
analysis assuming the spectral shape of the Galactic components, the ""maximum
entropy method"", ""internal linear combination"", and ""wavelet-based high
resolution fitting of internal templates"". Second, I analyse the galactic
latitude dependence from WMAP data. The frequency dependence is discussed with
the data in the available literature. The result is that all methods of
subtracting the Galactic contamination are inaccurate. The galactic latitude
dependence analysis or the frequency dependence of the anisotropies in the
range 50-250 GHz put a constraint on the maximum Galactic contribution in the
power spectrum to be less than a ~10% (68% C. L.) for a ~1 degree scale, and
possibly higher for larger scales.
  The origin of most of the signal in the CMBR anisotropies is not Galactic. In
any case, the subtraction of the Galaxy is not accurate enough to allow a
""precision Cosmology""; other sources of contamination (extragalactic, solar
system) are also present.",0708.4133v2
2007-10-23,"Three-electron anisotropic quantum dots in variable magnetic fields: exact results for excitation spectra, spin structures, and entanglement","Exact-diagonalization calculations for N=3 electrons in anisotropic quantum
dots, covering a broad range of confinement anisotropies and strength of
inter-electron repulsion, are presented for zero and low magnetic fields. The
excitation spectra are analyzed as a function of the strength of the magnetic
field and for increasing quantum-dot anisotropy. Analysis of the intrinsic
structure of the many-body wave functions through spin-resolved two-point
correlations reveals that the electrons tend to localize forming Wigner
molecules. For certain ranges of dot parameters (mainly at strong anisotropy),
the Wigner molecules acquire a linear geometry, and the associated wave
functions with a spin projection S_z=1/2 are similar to the representative
class of strongly entangled states referred to as W-states. For other ranges of
parameters (mainly at intermediate anisotropy), the Wigner molecules exhibit a
more complex structure consisting of two mirror isosceles triangles. This
latter structure can be viewed as an embryonic unit of a zig-zag Wigner crystal
in quantum wires. The degree of entanglement in three-electron quantum dots can
be quantified through the use of the von Neumann entropy.",0710.4325v1
2007-12-15,Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single molecule magnets,"We study single-ion and exchange anisotropy effects in equal-spin $s_1$
tetramer single molecule magnets exhibiting $T_d$, $D_{4h}$, $D_{2d}$,
$C_{4h}$, $C_{4v}$, or $S_4$ ionic point group symmetry. We first write the
group-invariant quadratic single-ion and symmetric anisotropic exchange
Hamiltonians in the appropriate local coordinates. We then rewrite these local
Hamiltonians in the molecular or laboratory representation, along with the
Dzyaloshinskii-Moriay (DM) and isotropic Heisenberg, biquadratic, and
three-center quartic Hamiltonians. Using our exact, compact forms for the
single-ion spin matrix elements, we evaluate the eigenstate energies
analytically to first order in the microscopic anisotropy interactions,
corresponding to the strong exchange limit, and provide tables of simple
formulas for the energies of the lowest four eigenstate manifolds of
ferromagnetic (FM) and anitiferromagnetic (AFM) tetramers with arbitrary $s_1$.
For AFM tetramers, we illustrate the first-order level-crossing inductions for
$s_1=1/2,1,3/2$, and obtain a preliminary estimate of the microscopic
parameters in a Ni$_4$ from a fit to magnetization data.
  Accurate analytic expressions for the thermodynamics, electron paramagnetic
resonance absorption and inelastic neutron scattering cross-section are given,
allowing for a determination of three of the microscopic anisotropy
interactions from the second excited state manifold of FM tetramers. We also
predict that tetramers with symmetries $S_4$ and $D_{2d}$ should exhibit both
DM interactions and multiferroic states, and illustrate our predictions for
$s_1=1/2, 1$.",0712.2518v2
2008-01-08,Kinematic Sunyaev-Zeldovich Cosmic Microwave Background Temperature Anisotropies Generated by Gas in Cosmic Structures,"If the gas in filaments and halos shares the same velocity field than the
luminous matter, it will generate measurable temperature anisotropies due to
the Kinematic Sunyaev-Zeldovich effect. We compute the distribution function of
the KSZ signal produced by a typical filament and show it is highly
non-gaussian. The combined contribution of the Thermal and Kinematic SZ effects
of a filament of size $L\simeq 5$Mpc and electron density $n_e\simeq
10^3m^{-3}$ could explain the cold spots of $\delta\sim -200\mu$K on scales of
30' found in the Corona Borealis Supercluster by the VSA experiment. PLANCK,
with its large resolution and frequency coverage, could provide the first
evidence of the existence of filaments in this region. The KSZ contribution of
the network of filaments and halo structures to the radiation power spectrum
peaks around $l\sim 400$, a scale very different from that of clusters of
galaxies, with a maximum amplitude $l(l+1)C_l/2\pi\sim 10-25 (\mu K)^2$,
depending on model parameters, i.e., $\sigma_8$ and the Jeans length. About 80%
of the signal comes from filaments with redshift $z\le 0.1$. Adding this
component to the intrinsic Cosmic Microwave Background temperature anisotropies
of the concordance model improves the fit to WMAP 3yr data by
$\Delta\chi^2\simeq 1$. The improvement is not statistically significant but a
more systematic study could demonstrate that gas could significantly contribute
to the anisotropies measured by WMAP.",0801.1198v1
2008-04-30,Coinage-metal capping effects on the spin-reorientations of Co/Ru(0001),"Thin films of Co/Ru(0001) are known to exhibit an unusual spin reorientation
transition (SRT) coupled to the completion of Co atomic layers for Co
thicknesses under 4 layers. By means of spin-polarized low-energy electron
microscopy, we follow in real space the magnetization orientation during the
growth of atomically thick capping layers on Co/Ru(0001). Capping with
coinage-metal (Cu, Ag, Au) elements modifies the SRT depending on the Co and
overlayer thickness and on the overlayer material, resulting in an expanded
range of structures with high perpendicular magnetic anisotropy. The origin of
the SRT can be explained in terms of ab-initio calculations of the
layer-resolved contributions to the magnetic anisotropy energy. Besides the
changes in the SRT introduced by the capping, a quantitative enhancement of the
magnetic anisotropy is identified. A detailed analysis of the interplay between
strain and purely electronic effects allows us to identify the conditions that
lead to a high perpendicular magnetic anisotropy in thin hcp Co films.",0804.4777v2
2008-05-27,Gaussianity,"In this chapter we review the present status of the Gaussianity studies of
the CMB anisotropies, including physical effects producing non-Gaussianity,
methods to test it and observational constraints.",0805.4157v1
2008-06-03,Mass distribution and orbital anisotropy of early-type galaxies: constraints from the Mass Plane,"Massive early-type galaxies are observed to lie on the Mass Plane (MP), a
two-dimensional manifold in the space of effective radius R_e, projected mass
M_p (measured via strong gravitational lensing) and projected velocity
dispersion sigma within R_e/2. The MP is less `tilted' than the Fundamental
Plane, and the two have comparable associated scatter. This means that
c_e2=2*G*M_p/(R_e*sigma^2) is a nearly universal constant in the range
sigma=175-400 km/s. This finding can be used to constrain the mass distribution
and internal dynamics of early-type galaxies. We find that a relatively wide
class of spherical galaxy models has values of c_e2 in the observed range,
because c_e2 is not very strongly sensitive to the mass distribution and
orbital anisotropy. If the total mass distribution is isothermal, a broad range
of stellar luminosity profile and anisotropy is consistent with the
observations, while NFW dark-matter halos require more fine tuning of the
stellar mass fraction, luminosity profile and anisotropy. If future data can
cover a broader range of masses, the MP could be seen to be tilted and the
value of any such tilt would provide a discriminant between models for the
total mass-density profile of the galaxies. [Abridged]",0806.0570v2
2008-06-24,Superfluid Phase Stability of $^3$He in Axially Anisotropic Aerogel,"Measurements of superfluid $^3$He in 98% aerogel demonstrate the existence of
a metastable \emph{A}-like phase and a stable \emph{B}-like phase. It has been
suggested that the relative stability of these two phases is controlled by
anisotropic quasiparticle scattering in the aerogel. Anisotropic scattering
produced by axial compression of the aerogel has been predicted to stabilize
the axial state of superfluid $^3$He. To explore this possiblity, we used
transverse acoustic impedance to map out the phase diagram of superfluid $^3$He
in a $\sim 98$% porous silica aerogel subjected to 17% axial compression. We
have previously shown that axial anisotropy in aerogel leads to optical
birefringence and that optical cross-polarization studies can be used to
characterize such anisotropy. Consequently, we have performed optical
cross-polarization experiments to verify the presence and uniformity of the
axial anisotropy in our aerogel sample. We find that uniform axial anisotropy
introduced by 17% compression does not stabilize the \emph{A}-like phase. We
also find an increase in the supercooling of the \emph{A}-like phase at lower
pressure, indicating a modification to \emph{B}-like phase nucleation in
\emph{globally} anisotropic aerogels.",0806.3927v1
2008-09-25,Two-component galaxies with flat rotation curve,"Dynamical properties of two-component galaxy models whose stellar density
distribution is described by a gamma-model while the total density distribution
has a pure r^(-2) profile, are presented. The orbital structure of the stellar
component is described by Osipkov-Merritt anisotropy, while the dark matter
halo is isotropic. After a description of minimum halo models, the positivity
of the phase-space density (the model consistency) is investigated, and
necessary and sufficient conditions for consistency are obtained analytically
as a function of the stellar inner density slope gamma and anisotropy radius.
The explicit phase-space distribution function is recovered for integer values
of gamma, and it is shown that while models with gamma>4/17 are consistent when
the anisotropy radius is larger than a critical value (dependent on gamma), the
gamma=0 models are unphysical even in the fully isotropic case. The Jeans
equations for the stellar component are then solved analytically; in addition,
the projected velocity dispersion at the center and at large radii are also
obtained analytically for generic values of the anisotropy radius, and it is
found that they are given by remarkably simple expressions. The presented
models, even though highly idealized, can be useful as starting point for more
advanced modeling of the mass distribution of elliptical galaxies in studies
combining stellar dynamics and gravitational lensing.",0809.4444v1
2008-10-24,Detecting the Cosmic Dipole Anisotropy in Large-Scale Radio Surveys,"The detection of a dipole anisotropy in the sky distribution of sources in
large-scale radio surveys can be used to constrain the magnitude and direction
of our local motion with respect to an isotropically distributed extragalactic
radio source population. Such a population is predicted to be present at
cosmological redshifts in an isotropically expanding universe. The
extragalactic radio source population is observed to have a median redshift of
z ~ 1, a much later epoch than the cosmic microwave background (z ~ 1100). I
consider the detectability of a velocity dipole anisotropy in radio surveys
having a finite number of source counts. The statistical significance of a
velocity dipole detection from radio source counts is also discussed in detail.
I find that existing large-scale radio survey catalogs do not have a sufficient
number of sources to detect the expected velocity dipole with statistical
significance, even if survey masking and flux calibration complications can be
completely eliminated (i.e., if both the surveys and observing instruments are
perfect). However, a dipole anisotropy should be easily detectable in future
radio surveys planned with next-generation radio facilities, such as the Low
Frequency Array and the Square Kilometer Array; tight constraints on the dipole
magnitude and direction should be possible if flux calibration problems can be
sufficiently minimized or corrected and contamination from local sources
eliminated.",0810.4520v1
2009-02-20,Techniques to study cosmic ray anisotropies,"These lectures review some of the techniques used to analyze the arrival
direction distribution of Cosmic Rays, and some relevant results on the field.",0902.3601v1
2009-05-11,Cosmic ray electron anisotropies as a tool to discriminate between exotic and astrophysical sources,"Recent results from the PAMELA, ATIC, PPB BETS and Fermi collaborations
extend the energy range in the electron flux measurement up to unexplored
energies in the hundred GeVs range confirming the bump starting at about 10GeV
already suggested by HEAT and AMS01 data . This bump can be explained by
annihilating dark matter in the context of exotic physics, or by nearby
astrophysical sources e.g. pulsars. In order to discriminate between competing
models for primary positron production, the study of anisotropies
,complementary to the spectrum determination, shows up as new tool to look for
the origin of the lepton excess. In this letter we calculate the contribution
to the electron flux given by the collection of all known gamma ray pulsars (as
listed in the ATNF catalogue) and by annihilating dark matter both in case of a
clumpy halo or in case the excess can be atributed to a nearby sizeable dark
matter clump. We address the problem of the electron anisotropy in both
scenarios and estimate the prospect that a small dipole anisotropy can be found
by the Fermi observatory.",0905.1653v3
2009-06-29,"Zero modes, energy gap, and edge states of anisotropic honeycomb lattice in a magnetic field","We present systematic study of zero modes and gaps by introducing effects of
anisotropy of hopping integrals for a tight-binding model on the honeycomb
lattice in a magnetic field. The condition for the existence of zero modes is
analytically derived. From the condition, it is found that a tiny anisotropy
for graphene is sufficient to open a gap around zero energy in a magnetic
field. This gap behaves as a non-perturbative and exponential form as a
function of the magnetic field. The non-analytic behavior with respect to the
magnetic field can be understood as tunneling effects between energy levels
around two Dirac zero modes appearing in the honeycomb lattice, and an explicit
form of the gap around zero energy is obtained by the WKB method near the
merging point of these Dirac zero modes. Effects of the anisotropy for the
honeycomb lattices with boundaries are also studied. The condition for the
existence of zero energy edge states in a magnetic field is analytically
derived. On the basis of the condition, it is recognized that anisotropy of the
hopping integrals induces abrupt changes of the number of zero energy edge
states, which depend on the shapes of the edges sensitively.",0906.5027v2
2009-07-09,Ground states of anisotropic antiferromagnets with single ion and cubic anisotropy,"Anisotropic antiferromagnets in an external magnetic field show a rich
variety of different ground states meeting in transition lines and
multicritical points. We study the dependence of the ground states of these
systems in the three dimensional space on physical parameters as exchange,
single ion and cubic anisotropy.
  One identifies four different ground states: the paramagnetic (PM), the
antiferromagnetic (AF), the spin flop (SF) and the biconical (BC) ground state.
In the case of absence of a cubic anisotropy the transition lines separating
the different ground states can be calculated analytically, otherwise they have
to be calculated numerically. We also considered the behavior of the staggered
magnetization which characterizes the different ground states. From its
behavior the order of the transition from one state to the other is determined.
But also the order of the transition changes along the transition lines when
including the cubic anisotropy, especially at the reeentrant region where a
transition from SF to BC and back to SF by increasing the external field $H$
occurs. Multicritical points are founded which are assumed to be tricritical or
critical endpoints. The results obtained may be relevant for other systems
since the antiferromagnetic model can be mapped to a lattice gas model where
the biconical ground state is interpreted as supersolid phase. Recent
renormalization group calculations show that such a phase would indicate the
existence of a tetracritical point.",0907.1480v1
2009-09-05,The sidereal anisotropy of multi-TeV cosmic rays in an expanding Local Interstellar Cloud,"The sidereal anisotropy of galactic cosmic ray (GCR) intensity observed with
the Tibet Air Shower (AS) experiment still awaits theoretical interpretation.
The observed global feature of the anisotropy is well reproduced by a
superposition of the bi-directional and uni-directional flows (BDF and UDF,
respectively) of GCRs. If the orientation of the deduced BDF represents the
orientation of the local interstellar magnetic field (LISMF), as indicated by
best-fitting a model to the data, the UDF deviating from the BDF orientation
implies a significant contribution from the streaming perpendicular to the
LISMF. This perpendicular streaming is probably due to the drift anisotropy,
because the contribution from the perpendicular diffusion is expected to be
much smaller than the drift effect. The large amplitude deduced for the UDF
indicates a large spatial gradient of the GCR density. We suggest that such a
density gradient can be expected at the heliosphere sitting close to the
boundary of the Local Interstellar Cloud (LIC), if the LIC is expanding. The
spatial distribution of GCR density in the LIC reaches a stationary state
because of the balance between the inward cross-field diffusion and the
adiabatic cooling due to the expansion. We derive the steady-state distribution
of GCR density in the LIC based on radial transport of GCRs in a spherical LIC
expanding at a constant rate. By comparing the expected gradient with the
observation by Tibet experiment, we estimate the perpendicular diffusion
coefficient of multi-TeV GCRs in the local interstellar space.",0909.1029v1
2009-10-30,Resonant x-ray scattering in 3d-transition-metal oxides: Anisotropy and charge orderings,"The structural, magnetic and electronic properties of transition metal oxides
reflect in atomic charge, spin and orbital degrees of freedom. Resonant x-ray
scattering (RXS) allows us to perform an accurate investigation of all these
electronic degrees. RXS combines high-Q resolution x-ray diffraction with the
properties of the resonance providing information similar to that obtained by
atomic spectroscopy (element selectivity and a large enhancement of scattering
amplitude for this particular element and sensitivity to the symmetry of the
electronic levels through the multipole electric transitions). Since electronic
states are coupled to the local symmetry, RXS reveals the occurrence of
symmetry breaking effects such as lattice distortions, onset of electronic
orbital ordering or ordering of electronic charge distributions. We shall
discuss the strength of RXS at the K absorption edge of 3d transition-metal
oxides by describing various applications in the observation of local
anisotropy and charge disproportionation. Examples of these resonant effects
are (I) charge ordering transitions in manganites, Fe3O4 and ferrites and (II)
forbidden reflections and anisotropy in Mn3+ perovskites, spinel ferrites and
cobalt oxides. In all the studied cases, the electronic (charge and/or
anisotropy) orderings are determined by the structural distortions.",0910.5789v1
2009-11-05,Layer World: Living on a layer in 5D SU(3),"We suggest another approach to five-dimensional non-isotropic gauge theory.
Using non-perturbative technique we show that already modest interaction
anisotropy confines heavy bound states to four-dimensional layers, while free
quarks propagate with almost no penalty into the fifth dimension.",0911.1071v1
2009-11-13,Landau hydrodynamic solution for non-central heavy ion collisions,"The manuscript presents generalization of the Landau hydrodynamic solution
for multiparticle production applied for non-central relativistic heavy ion
collisions. Obtained solution enables to calculate anisotropy parameter $v_2$
for different rapidities with respect to the initial conditions for
hydrodynamics.",0911.2677v1
2009-12-12,The fundamental spherically symmetric fluid model,"It is shown that an effective anisotropic spherically symmetric fluid model
with heat flow can absorb the addition to a perfect fluid of pressure
anisotropy, heat flow, bulk and shear viscosity, electric field and null fluid.",0912.2447v1
2010-05-07,Vortex Dynamics in Anisotropic Traps,"We investigate the dynamics of linear vortex lattices in anisotropic traps in
two-dimensions and show that the interplay between the rotation and the
anisotropy leads to a rich but highly regular dynamics.",1005.1262v1
2010-05-25,"Structural, static and dynamic magnetic properties of CoMnGe thin films on a sapphire a-plane substrate","Magnetic properties of CoMnGe thin films of different thicknesses (13, 34,
55, 83, 100 and 200 nm), grown by RF sputtering at 400{\deg}C on single crystal
sapphire substrates, were studied using vibrating sample magnetometry (VSM) and
conventional or micro-strip line (MS) ferromagnetic resonance (FMR). Their
behavior is described assuming a magnetic energy density showing twofold and
fourfold in-plane anisotropies with some misalignment between their principal
directions. For all the samples, the easy axis of the fourfold anisotropy is
parallel to the c-axis of the substrate while the direction of the twofold
anisotropy easy axis varies from sample to sample and seems to be strongly
influenced by the growth conditions. Its direction is most probably monitored
by the slight unavoidable angle of miscut the Al2O3 substrate. The twofold
in-plane anisotropy field is almost temperature independent, in contrast with
the fourfold field which is a decreasing function of the temperature. Finally,
we study the frequency dependence of the observed line-width of the resonant
mode and we conclude to a typical Gilbert damping constant of 0.0065 for the
55-nm-thick film.",1005.4595v3
2010-07-19,Gauge field back-reaction in Born Infeld cosmologies,"In this paper, we investigate the back-reaction of $U(1)$ gauge fields into a
class of inflationary settings. To be more precise, we employ a Bianchi-I
geometry (taken as an anisotropic perturbation of a flat FRW model) within two
types of Born-Infeld theories. Firstly we consider pure Born-Infeld
electromagnetism. For either a constant or a $b(\phi)$ coupling, inflationary
trajectories are modified but anisotropies increase; In particular, for the
former coupling we find that a quadratic inflaton potential, within a constant
ratio for the scalar and gauge energy densities, does not induce sufficient
inflation, while in the latter the back-reaction in the cosmology determines
(from the tensor-scalar ratio) a narrow range where inflation can occur. A
Dirac-Born-Infeld framework is afterwards analysed in both non-relativistic and
relativistic regimes. In the former, for different cases of the coupling
(richer with respect to mere BI setups) between scalar and gauge sectors, we
find that inflationary trajectories are modified, with anisotropy increasing or
decreasing. In particular, a tachyonic solution is studied, allowing for a non
standard ratio between scalar and gauge matter densities, enhancing sufficient
inflation, but with the anisotropy increasing. For the relativistic limit,
inflationary trajectories are also modified and anisotropies increase faster
than in the non-relativistic limit. Finally we discuss how magnetic seed fields
could evolve in these settings.",1007.3299v2
2010-11-02,Electron transport and anisotropy of the upper critical magnetic field in a Ba0.68K0.32Fe2As2 single crystals,"Early work on the iron-arsenide compounds supported the view, that a reduced
dimensionality might be a necessary prerequisite for high-Tc superconductivity.
Later, however, it was found that the zero-temperature upper critical magnetic
field, Hc2(0), for the 122 iron pnictides is in fact rather isotropic. Here, we
report measurements of the temperature dependence of the electrical
resistivity, \Gamma(T), in Ba0.5K0.5Fe2As2 and Ba0.68K0.32Fe2As2 single
crystals in zero magnetic field and for Ba0.68K0.32Fe2As2 as well in static and
pulsed magnetic fields up to 60 T. We find that the resistivity of both
compounds in zero field is well described by an exponential term due to
inter-sheet umklapp electron-phonon scattering between light electrons around
the M point to heavy hole sheets at the \Gamma point in reciprocal space. From
our data, we construct an H-T phase diagram for the inter-plane (H || c) and
in-plane (H || ab) directions for Ba0.68K0.32Fe2As2. Contrary to published data
for underdoped 122 FeAs compounds, we find that Hc2(T) is in fact anisotropic
in optimally doped samples down to low temperatures. The anisotropy parameter,
{\gamma} = Habc2/Hcc2, is about 2.2 at Tc. For both field orientations we find
a concave curvature of the Hc2 lines with decreasing anisotropy and saturation
towards lower temperature. Taking into account Pauli spin paramagnetism we
perfectly can describe Hc2(T) and its anisotropy.",1011.0698v1
2010-11-12,Age- and time-varying proportional hazards models for employment discrimination,"We use a discrete-time proportional hazards model of time to involuntary
employment termination. This model enables us to examine both the continuous
effect of the age of an employee and whether that effect has varied over time,
generalizing earlier work [Kadane and Woodworth J. Bus. Econom. Statist. 22
(2004) 182--193]. We model the log hazard surface (over age and time) as a
thin-plate spline, a Bayesian smoothness-prior implementation of penalized
likelihood methods of surface-fitting [Wahba (1990) Spline Models for
Observational Data. SIAM]. The nonlinear component of the surface has only two
parameters, smoothness and anisotropy. The first, a scale parameter, governs
the overall smoothness of the surface, and the second, anisotropy, controls the
relative smoothness over time and over age. For any fixed value of the
anisotropy parameter, the prior is equivalent to a Gaussian process with linear
drift over the time--age plane with easily computed eigenvectors and
eigenvalues that depend only on the configuration of data in the time--age
plane and the anisotropy parameter. This model has application to legal cases
in which a company is charged with disproportionately disadvantaging older
workers when deciding whom to terminate. We illustrate the application of the
modeling approach using data from an actual discrimination case.",1011.2851v1
2010-11-25,Effects of magnetic field and transverse anisotropy on full counting statistics in single-molecule magnet,"We have theoretically studied the full counting statistics of electron
transport through a single-molecule magnet (SMM) with an arbitrary angle
between the applied magnetic field and the SMM's easy axis above the sequential
tunneling threshold, since the angle $\theta$ cannot be controlled in
present-day SMM experiments. In the absence of the small transverse anisotropy,
when the coupling of the SMM with the incident-electrode is stronger than that
with the outgoing-electrode, i.e., $\Gamma_{L}/\Gamma_{R}\gg1$, the maximum
peak of shot noise first increases and then decreases with increasing $\theta$
from 0 to $0.5\pi$. In particular, the shot noise can reach up to
super-Poissonian value from sub-Poissonian value when considering the small
transverse anisotropy. For $\Gamma_{L}/\Gamma_{R}\ll1$, the maximum peaks of
the shot noise and skewness can be reduced from a super-Poissonian to a
sub-Poissonian value with increasing $\theta$ from 0 to $0.5\pi$; the
super-Poissonian behavior of the skewness is more sensitive to the small
$\theta$ than shot noise, which is suppressed when taking into account the
small transverse anisotropy. These characteristics of shot noise can be
qualitatively attributed to the competition between the fast and slow transport
channels. The predictions regarding of the $\theta$-dependence of high order
current cumulants are very interesting for a better understanding electron
transport through SMM, and will allow for experimental tests in the near
future.",1011.5546v2
2010-12-17,Phenomenology of magnetically active superconductors,"The thermodynamical phenomenological theory of magnetically active
superconducting materials and magnetic-superconducting heterostructures is
presented. The materials may exhibit arbitrarily strong anisotropy, parametric
or structural. Exact anisotropic similarity transformations are found for both
the continuum and layered hybrid systems.",1012.3869v1
2010-12-23,Ellipsoidal anisotropies in linear elasticity Extension of Saint Venant's work to phenomenological modelling of materials,"Several families of elastic anisotropies were introduced by Saint Venant
(1863) for which the polar diagram of elastic parameters in different
directions of the material (indicator surface) are ellipsoidal. These families
recover a large variety of models introduced in recent years for damaged
materials or as effective modulus of heterogeneous materials. On the other
hand, ellipsoidal anisotropy has been used as a guideline in phenomenological
modeling of materials. A question that then naturally arises is to know in
which conditions the assumption that some indicator surfaces are ellipsoidal
allows one to entirely determine the elastic constants. This question has not
been rigorously studied in the literature. In this paper, first several basic
classes of ellipsoidal anisotropy are presented. Then the problem of
determination of the elastic parameters from indicator surfaces is discussed in
several basic cases that can occur in phenomenological modelling. Finally the
compatibility between the assumption of ellipsoidal form for different
indicator surfaces is discussed and in particular, it is shown that if the
indicator surfaces of the fourth root of E(n) and of 1/c(n) where E(n) and c(n)
are respectively the Young's modulus and the elastic coefficient in the
direction n) are ellipsoidal, then the two ellipsoids have necessarily the same
principal axes and the material in this case is orthotropic.",1012.5148v1
2010-12-23,Deep Core muon neutrino rate and anisotropy by mixing and CPT violation,"Neutrinos are allowed to mix and to oscillate among their flavor. Muon and
tau in particular oscillate at largest values.Last Minos experiment claimed
possible difference among their matter and anti-matter masses, leading to a
first violation of the most believed CPT symmetry.Isotropically born
atmospheric muon neutrino at 20-80 GeV, while up-going, they might be partially
suppressed by mixing in analogy to historical SuperKamiokande muon neutrino
disappearance into tau, leading to large scale anisotropy signals. Here we show
an independent muon rate foreseen in Deep Core based on observed SK signals
extrapolated to DeepCore mass and its surrounding. Our rate prediction
partially differ from previous ones. The neutrino muon disappearance into tau
is leading to an anisotropy in vertical up-going muon track: in particular
along channel 3-5 we expect a huge rate (tens of thousand of events) of neutral
current events, charged current electron and inclined crossing muons. Moreover
at channel 6-9 we expect a severe suppression of the rate due to muon
disappearance (in CPT conserved frame). Such an anisotropy might be partially
tested by more than one string detection at E> 45 GeV energy. A CPT violation
may induce a more remarkable suppression of vertical up-going tracks because of
larger anti-neutrino muon reduction for E> 35 GeV.",1012.5271v1
2010-12-31,In-plane anisotropy of electrical resistivity in the strain-detwinned SrFe2As2,"Intrinsic, in-plane anisotropy of electrical resistivity was studied on
mechanically detwinned single crystals of SrFe$_2$As$_2$ above and below the
temperature of the coupled structural/magnetic transition, $T_{\textrm{TO}}$.
Resistivity is smaller for electrical current flow along the orthorhombic $a_o$
direction (direction of antiferromagnetically alternating magnetic moments) and
is larger for transport along the $b_o$ direction (direction of ferromagnetic
chains), which is similar to CaFe$_2$As$_2$ and BaFe$_2$As$_2$ compounds. A
strongly first order structural transition in SrFe$_2$As$_2$ was confirmed by
high-energy x-ray measurements, with the transition temperature, and character
unaffected by moderate strain. For small strain levels, which are just
sufficient to detwin the sample, we find a negligible effect on the resistivity
above $T_{\textrm{TO}}$. With the increase of strain, the resistivity
anisotropy starts to develop above $T_{\textrm{TO}}$, clearly showing the
relation of anisotropy to an anomalously strong response to strain. Our study
suggests that electronic nematicity cannot be observed in the FeAs based
compounds in which the structural transition is strongly first order.",1101.0274v1
2011-01-14,How to distinguish the Haldane/Large-D state and the intermediate-D state in an S=2 quantum spin chain with the XXZ and on-site anisotropies,"We numerically investigate the ground-state phase diagram of an S=2 quantum
spin chain with the $XXZ$ and on-site anisotropies described by ${\mathcal
H}=\sum_j (S_j^x S_{j+1}^x+S_j^y S_{j+1}^y+\Delta S_j^z S_{j+1}^z) + D \sum_j
(S_j^z)^2$, where $\Delta$ denotes the XXZ anisotropy parameter of the
nearest-neighbor interactions and $D$ the on-site anisotropy parameter. We
restrict ourselves to the $\Delta>0$ and $D>0$ case for simplicity. Our main
purpose is to obtain the definite conclusion whether there exists or not the
intermediate-$D$ (ID) phase, which was proposed by Oshikawa in 1992 and has
been believed to be absent since the DMRG studies in the latter half of 1990's.
In the phase diagram with $\Delta>0$ and $D>0$ there appear the XY state, the
Haldane state, the ID state, the large-$D$ (LD) state and the N\'eel state. In
the analysis of the numerical data it is important to distinguish three gapped
states; the Haldane state, the ID state and the LD state. We give a physical
and intuitive explanation for our level spectroscopy method how to distinguish
these three phases.",1101.2799v2
2011-01-20,"Ultra-thin SWNTs Films with Tunable, Anisotropic Transport Properties","Directional transport properties at the nanoscale remain a challenge
primarily due to issues associated with control over the underlying anisotropy
and scalability to macroscopic scales. In this letter, we develop a facile
approach based on template-guided fluidic assembly of high mobility building
blocks - single walled carbon nanotubes (SWNTs) - to fabricate ultra-thin and
anisotropic SWNT films. A major advancement is the complete control over the
anisotropy in the assembled nanostructure, realized by three-dimensional
engineering of dip-coated SWNT thin films into alternating hydrophilic and
hydrophobic micro-line patterns with prescribed intra/inter-line widths and
line thicknesses. Variations in the contact line profile results in an
evaporation-controlled assembly mechanism that leads to the formation of an
alternating, and more importantly, contiguous SWNT network. Evidently, the
nanoscopic thickness modulations are direct reflections of the substrate
geometry and chemistry. The nanostructured film exhibits significant anisotropy
in their electrical and thermal transport properties as well as optical
transparency, as revealed by characterization studies. The direct interplay
between the anisotropy and the 3D micro-line patterns of the substrate combined
with the wafer-level scalability of the fluidic assembly allows us to tune the
transport properties for a host of nanoelectronic applications.",1101.3805v1
2011-04-20,Oscillating Bianchi IX Universe in Horava-Lifshitz Gravity,"We study a vacuum Bianchi IX universe in the context of Ho\v{r}ava-Lifshitz
(HL) gravity. In particular, we focus on the classical dynamics of the universe
and analyze how anisotropy changes the history of the universe. For small
anisotropy, we find an oscillating universe as well as a bounce universe just
as the case of the Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime.
However, if the initial anisotropy is large, we find the universe which ends up
with a big crunch after oscillations if a cosmological constant $\Lambda$ is
zero or negative. For $\Lambda>0$, we find a variety of histories of the
universe, that is de Sitter expanding universe after oscillations in addition
to the oscillating solution and the previous big crunch solution. This fate of
the universe shows sensitive dependence of initial conditions, which is one of
the typical properties of a chaotic system. If the initial anisotropy is near
the upper bound, we find the universe starting from a big bang and ending up
with a big crunch for $\Lambda\leq 0$, while de Sitter expanding universe
starting from a big bang for $\Lambda>0$.",1104.3978v2
2011-05-25,Properties of Turbulence in the Very Local Interstellar Clouds,"We have investigated the degree to which turbulence in the Very Local
Interstellar Clouds resembles the highly-studied turbulence in the solar corona
and the solar wind. The turbulence diagnostics for the Local Clouds are the
absorption line widths measured along 32 lines of sight to nearby stars,
yielding measurements for 53 absorption components (Redfield and Linsky 2004).
We have tested whether the Local Cloud turbulence has the following properties
of turbulence in the solar corona or the solar wind: (a) velocity fluctuations
mainly perpendicular to the average magnetic field, (b) a temperature
anisotropy in the sense that the perpendicular temperature is larger than the
parallel temperature (or at least enhanced relative to expectation), and (c) an
ion temperature which is dependent on the ion Larmor radius, in the sense that
more massive ions have higher temperatures. Our analysis of the data does not
show compelling evidence for any of these properties in Local Cloud turbulence,
indicating possible differences with heliospheric plasmas. In the case of
anisotropy of velocity fluctuations, although the expected observational
signature is not seen, we cannot exclude the possibility of relatively high
degrees of anisotropy (anisotropy parameter $\epsilon \sim 0.50 - 0.70$), if
some other process in the the Local Clouds is causing variations in the
turbulent line width from one line of sight to another. We briefly consider
possible reasons for differences between coronal and solar wind turbulence and
that in the Local Clouds.",1105.5077v1
2011-05-29,Conductance anisotropy and linear magnetoresistance in La2-xSrxCuO4 thin films,"We have performed a detailed study of conductance anisotropy and
magnetoresistance (MR) of La2-xSrxCuO4 (LSCO) thin films (0.10 < x < 0.25).
These two observables are promising for the detection of stripes. Subtle
features of the conductance anisotropy are revealed by measuring the transverse
resistance Rxy in zero magnetic field. It is demonstrated that the sign of Rxy
depends on the orientation of the LSCO Hall bar with respect to the terrace
structure of the substrate. Unit-cell-high substrate step edges must therefore
be a dominant nucleation source for antiphase boundaries during film growth. We
show that the measurement of Rxy is sensitive enough to detect the
cubic-tetragonal phase transition of the SrTiO3(100) (STO) substrate at 105 K.
The MR of LSCO thin films shows for 0.10 < x < 0.25 a non-monotonic temperature
dependence, resulting from the onset of a linear term in the MR above 90 K. We
show that the linear MR scales with the absolute Hall resistivity, with the
constant of proportionality independent of temperature. Such scaling suggests
that the linear MR originates from current distortions induced by structural or
electronic inhomogeneities. The possible role of stripes for both the MR and
the conductance anisotropy is discussed throughout the paper.",1105.6090v1
2011-06-24,Unprecedented anisotropic metallic state in BaFe2As2 revealed by optical spectroscopy,"An ordered phase showing remarkable electronic anisotropy in proximity to the
superconducting phase is now a hot issue in the field of
high-transition-temperature superconductivity. As in the case of copper oxides,
superconductivity in iron arsenides competes or coexists with such an ordered
phase. Undoped and underdoped iron arsenides have a magnetostructural ordered
phase exhibiting stripe-like antiferromagnetic spin order accompanied by an
orthorhombic lattice distortion; both the spin order and lattice distortion
break the tetragonal symmetry of crystals of these compounds. In this ordered
state, anisotropy of in-plane electrical resistivity is anomalous and difficult
to attribute simply to the spin order and/or the lattice distortion. Here, we
present the anisotropic optical spectra measured on detwinned BaFe2As2 crystals
with light polarization parallel to the Fe planes. Pronounced anisotropy is
observed in the spectra, persisting up to an unexpectedly high photon energy of
about 2 eV. Such anisotropy arises from an anisotropic energy gap opening below
and slightly above the onset of the order. Detailed analysis of the optical
spectra reveals an unprecedented electronic state in the ordered phase.",1106.4967v1
2011-06-24,Note on a class of anisotropic Einstein metrics,"A class of anisotropic Einstein metrics is presented. These metrics are axial
symmetric and contains an anisotropy parameter $\alpha$, which is identified as
the amplitude of the proper acceleration of the origin, thus explaining the
ellipsoid shape of the horizon.",1106.5027v1
2011-07-04,Anisotropic in-plane optical conductivity in detwinned Ba(Fe1-xCox)2As2,"We study the anisotropic in-plane optical conductivity of detwinned
Ba(Fe1-xCox)2As2 single crystals for x=0, 2.5% and 4.5% in a broad energy range
(3 meV-5 eV) across their structural and magnetic transitions. For temperatures
below the Neel transition, the topology of the reconstructed Fermi surface,
combined with the distinct behavior of the scattering rates, determines the
anisotropy of the low frequency optical response. For the itinerant charge
carriers, we are able to disentangle the evolution of the Drude weights and
scattering rates and to observe their enhancement along the orthorhombic
antiferromagnetic a-axis with respect to the ferromagnetic b-axis. For
temperatures above Ts, uniaxial stress leads to a finite in-plane anisotropy.
The anisotropy of the optical conductivity, leading to a significant dichroism,
extends to high frequencies in the mid- and near-infrared regions. The
temperature dependence of the dichroism at all dopings scales with the
anisotropy ratio of the dc conductivity, suggesting the electronic nature of
the structural transition. Our findings bear testimony to a large nematic
susceptibility that couples very effectively to the uniaxial lattice strain. In
order to clarify the subtle interplay of magnetism and Fermi surface topology
we compare our results with theoretical calculations obtained from density
functional theory within the full-potential linear augmented plane-wave method.",1107.0670v1
2011-09-07,Improved Models for Cosmic Infrared Background Anisotropies: New Constraints on the IR Galaxy Population,"The power spectrum of cosmic infrared background (CIB) anisotropies is
sensitive to the connection between star formation and dark matter halos over
the entire cosmic star formation history. Here we develop a model that
associates star-forming galaxies with dark matter halos and their subhalos. The
model is based on a parameterized relation between the dust-processed infrared
luminosity and (sub)halo mass. By adjusting 3 free parameters, we attempt to
simultaneously fit the 4 frequency bands of the Planck measurement of the CIB
anisotropy power spectrum. To fit the data, we find that the star-formation
efficiency must peak on a halo mass scale of ~ 5x10^12 solar mass and the
infrared luminosity per unit mass must increase rapidly with redshift. By
comparing our predictions with a well-calibrated phenomenological model for
shot noise, and with a direct observation of source counts, we show that the
mean duty cycle of the underlying infrared sources must be near unity,
indicating that the CIB is dominated by long-lived quiescent star formation,
rather than intermittent short ""star bursts"". Despite the improved flexibility
of our model, the best simultaneous fit to all four Planck channels remains
relatively poor. We discuss possible further extensions to alleviate the
remaining tension with the data. Our model presents a theoretical framework for
a future joint analysis of both background anisotropy and source count
measurements.",1109.1522v1
2011-09-22,Cosmic String constraints from WMAP and the South Pole Telescope,"The predictions of the inflationary LCDM paradigm match today's
high-precision measurements of the cosmic microwave background anisotropy
extremely well. The same data put tight limits on other sources of anisotropy.
Cosmic strings are a particularly interesting alternate source to constrain.
Strings are topological defects, remnants of inflationary-era physics that
persist after the big bang. They are formed in a variety of models of
inflation, including string theory models such as brane inflation. We assume a
""Nambu-Goto"" model for strings, approximated by a collection of unconnected
segments with zero width, and show that measurements of temperature anisotropy
by the South Pole Telescope break a parameter degeneracy in the WMAP data,
permitting us to place a strong upper limit on the possible string contribution
to the CMB anisotropy: the power sourced by zero-width strings must be <1.75%
(95% CL) of the total or the string tension Gmu <1.7x10^{-7}. These limits
imply that the best hope for detecting strings in the CMB will come from B-mode
polarization measurements at arcminute scales rather than the degree scale
measurements pursued for gravitational wave detection.",1109.4947v2
2011-10-05,Anisotropies in the diffuse gamma-ray background measured by Fermi LAT,"The small angular scale fluctuations of the (on large scale) isotropic
gamma-ray background (IGRB) carry information about the presence of unresolved
source classes. A guaranteed contribution to the IGRB is expected from the
unresolved gamma-ray AGN while other extragalactic sources, Galactic gamma-ray
source populations and dark matter Galactic and extragalactic structures (and
sub-structures) are candidate contributors. The IGRB was measured with
unprecedented precision by the Large Area Telescope (LAT) on-board of the Fermi
gamma-ray observatory, and these data were used for measuring the IGRB angular
power spectrum (APS). Detailed Monte Carlo simulations of Fermi-LAT all-sky
observations were performed to provide a reference against which to compare the
results obtained for the real data set. The Monte Carlo simulations are also a
method for performing those detailed studies of the APS contributions of single
source populations, which are required in order to identify the actual IGRB
contributors. We present preliminary results of an anisotropy search in the
IGRB. At angular scales <2deg (e.g. above multipole 155), angular power above
the photon noise level is detected, at energies between 1 and 10 GeV in each
energy bin, with statistical significance between 7.2 and 4.1 sigmas. The
energy not dependence of the fluctuation anisotropy is pointing to the presence
of one or more unclustered source populations, while the energy dependence of
the intensity anisotropy is consistent with source populations having average
photon index 2.40\pm0.07.",1110.1047v2
2011-10-11,Bianchi type II models in the presence of perfect fluid and anisotropic dark energy,"Spatially homogeneous but totally anisotropic and non-flat Bianchi type II
cosmological model has been studied in general relativity in the presence of
two minimally interacting fluids; a perfect fluid as the matter fluid and a
hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field
equations have been solved by applying two kinematical ans\""{a}tze: we have
assumed the variation law for the mean Hubble parameter that yields a constant
value of deceleration parameter, and one of the components of the shear tensor
has been considered proportional to the mean Hubble parameter. We have
particularly dwelled on the accelerating models with non-divergent expansion
anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we
consider in the context of dark energy, can produce results that can be
produced in the presence of isotropic fluid in accordance with the \Lambda CDM
cosmology. However, the derived model gives additional opportunities by being
able to allow kinematics that cannot be produced in the presence of fluids that
yield only isotropic pressure. We have obtained well behaving cases where the
anisotropy of the expansion and the anisotropy of the fluid converge to finite
values (include zero) in the late Universe. We have also showed that although
the metric we consider is totally anisotropic, the anisotropy of the dark
energy is constrained to be axially symmetric, as long as the overall energy
momentum tensor possesses zero shear stress.",1110.2408v2
2011-10-12,High-precision CTE measurement of hybrid C/SiC composite for cryogenic space telescopes,"This paper presents highly precise measurements of thermal expansion of a
""hybrid"" carbon-fiber reinforced silicon carbide composite,
HB-Cesic\textregistered - a trademark of ECM, in the temperature region of
\sim310-10K. Whilst C/SiC composites have been considered to be promising for
the mirrors and other structures of space-borne cryogenic telescopes, the
anisotropic thermal expansion has been a potential disadvantage of this
material. HB-Cesic\textregistered is a newly developed composite using a
mixture of different types of chopped, short carbon-fiber, in which one of the
important aims of the development was to reduce the anisotropy. The
measurements indicate that the anisotropy was much reduced down to 4% as a
result of hybridization. The thermal expansion data obtained are presented as
functions of temperature using eighth-order polynomials separately for the
horizontal (XY-) and vertical (Z-) directions of the fabrication process. The
average CTEs and their dispersion (1{\sigma}) in the range 293-10K derived from
the data for the XY- and Z-directions were 0.805$\pm$0.003\times10$^{-6}$
K$^{-1}$ and 0.837\pm0.001\times10$^{-6}$ K$^{-1}$, respectively. The absolute
accuracy and the reproducibility of the present measurements are suggested to
be better than 0.01\times10$^{-6}$ K$^{-1}$ and 0.001\times(10)^{-6} K^{-1},
respectively. The residual anisotropy of the thermal expansion was consistent
with our previous speculation regarding carbon-fiber, in which the residual
anisotropy tended to lie mainly in the horizontal plane.",1110.2620v1
2012-01-31,Local 2D Particle-in-cell simulations of the collisionless MRI,"The magnetorotational instability (MRI) is a crucial mechanism of angular
momentum transport in a variety of astrophysical accretion disks. In systems
accreting at well below the Eddington rate, such as the central black hole in
the Milky Way (Sgr A*), the rate of Coulomb collisions between particles is
very small, making the disk evolve essentially as a collisionless plasma. We
present a nonlinear study of the collisionless MRI using first-principles
particle-in-cell (PIC) plasma simulations. In this initial study we focus on
local two-dimensional (axisymmetric) simulations, deferring more realistic
three-dimensional simulations to future work. For simulations with net vertical
magnetic flux, the MRI continuously amplifies the magnetic field until the
Alfv\'en velocity, v_A, is comparable to the speed of light, c (independent of
the initial value of v_A/c). This is consistent with the lack of saturation of
MRI channel modes in analogous axisymmetric MHD simulations. The amplification
of the magnetic field by the MRI generates a significant pressure anisotropy in
the plasma (with the perpendicular pressure being larger than the parallel
pressure). We find that this pressure anisotropy in turn excites mirror modes
and that the volume averaged pressure anisotropy remains near the threshold for
mirror mode excitation. Particle energization is due to both reconnection and
viscous heating associated with the pressure anisotropy. Reconnection produces
a distinctive power-law component in the energy distribution function of the
particles, indicating the likelihood of non-thermal ion and electron
acceleration in collisionless accretion disks. This has important implications
for interpreting the observed emission -- from the radio to the gamma-rays --
of systems such as Sgr A*.",1201.6407v1
2012-02-20,Statistical anisotropy of CMB as a probe of conformal rolling scenario,"Search for the statistical anisotropy in the CMB data is a powerful tool for
constraining models of the early Universe. In this paper we focus on the
recently proposed cosmological scenario with conformal rolling. We consider two
sub-scenarios, one of which involves a long intermediate stage between
conformal rolling and conventional hot epoch. Primordial scalar perturbations
generated within these sub-scenarios have different direction-dependent power
spectra, both characterized by a single parameter h^2. We search for the
signatures of this anisotropy in the seven-year WMAP data using quadratic
maximum likelihood method, first applied for similar purposes by Hanson and
Lewis. We confirm the large quadrupole anisotropy detected in V and W bands,
which has been argued to originate from systematic effects rather than from
cosmology. We construct an estimator for the parameter h^2. In the case of the
sub-scenario with the intermediate stage we set an upper limit h^2 < 0.045 at
the 95% confidence level. The constraint on h^2 is much weaker in the case of
another sub-scenario, where the intermediate stage is absent.",1202.4357v3
2012-03-21,Implication of the lopsided growth for the viscosity of Earth's inner core,"Two main seismic features characterize the Earth's inner core: a North-South
polar anisotropy and an East-West asymmetry of P-wave velocity and attenuation.
Anisotropy is expected if shear deformation is induced by convective motions.
Translation has recently been put forward as an important mode of convection of
the inner core. Combined with a simple diffusive grain growth model, this
mechanism is able to explain the observed seismic asymmetry, but not the bulk
anisotropy. The source of anisotropy has therefore to be sought in the shear
motions caused by higher modes of convection. Using a hybrid finite-difference
spherical harmonics Navier-Stokes solver, we investigate the interplay between
translation and convection in a 3D spherical model with permeable boundary
conditions at the inner core boundary. Three parameters act independently:
viscosity, internal heating and convection velocity in the outer core. Our
numerical simulations show the dominance of pure translation for viscosities of
the inner core higher than $10^{20}$ Pas. Translation is almost completely
hampered by convective motions for viscosities lower than $10^{18}$ Pas.
Between these values, translation and convection develop, but convective
downwellings are restricted to the coldest hemisphere where crystallization
occurs. On the opposite side, shear is almost absent, thereby allowing grain
growth. We propose that the coexistence of translation and convection observed
in our numerical models leads to a seismic asymmetry but localizes deformation
only in one hemisphere.",1203.4708v1
2012-03-30,"Transport properties, upper critical field and anisotropy of Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals","The temperature and angle dependent resistivity of
Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ single crystals were measured in magnetic
fields up to 14 T. The temperature dependent resistivity with the magnetic
field aligned parallel to c-axis and ab-planes allow us to derive the slope of
d$H_{c2}^{ab}/dT$ and d$H_{c2}^c/dT$ near $T_c$ yielding an anisotropy ratio
$\Gamma=dH_{c2}^{ab}/dT/dH_{c2}^c/dT \approx$ 2. By scaling the curves of
resistivity vs. angle measured at a fixed temperature but different magnetic
fields within the framework of the anisotropic Ginzburg-Landau theory, we
obtained the anisotropy in an alternative way. Again we found that the
anisotropy $(m_c/m_{ab})^{1/2}$ was close to 2. This value is very similar to
that in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ (K-doped Ba122) and
Ba(Fe$_{0.92}$Co$_{0.08}$)$_2$As$_2$ (Co-doped Ba122). This suggests that the
3D warping effect of the Fermi surface in Ru-doped samples may not be stronger
than that in the K-doped or Co-doped Ba122 samples, therefore the possible
nodes appearing in Ru-doped samples cannot be ascribed to the 3D warping effect
of the Fermi surface.",1203.6793v1
2012-04-17,"Comment on ""Joint Anisotropy and Source Count Constraints on the Contribution of Blazars to the Diffuse Gamma-Ray Background""","We show the conclusions claimed in the manuscript arXiv:1202.5309v1 by Cuoco,
Komatsu and Siegal-Gaskins (CKS) are not generally valid. The results in CKS
are based on a number of simplifying assumptions regarding the source
population below the detection threshold and the threshold flux itself, and do
not apply to many physical models of the blazar population. Physical blazar
population models that match the measured source counts above the observational
threshold can account for 60% of the diffuse gamma-ray background intensity
between 1-10 GeV, while the assumptions in CKS limit the intensity to <30%. The
shortcomings of the model considered in CKS arise from an over-simplified
blazar source model. A number of the simplifying assumptions are unjustified,
including: first, the adoption of an assumed power-law source-count
distribution, dN/dS, to arbitrary low source fluxes, which is not exhibited in
physical models of the blazar population; and, second, the lack of blazar
spectral information in calculating the anisotropy of unresolved gamma-ray
blazar emission. We also show that the calculation of the unresolved blazars'
anisotropy is very sensitive to the spectral distribution of the unresolved
blazars through the adopted source resolution threshold value, and must be
taken into account in an accurate anisotropy calculation.",1204.3870v1
2012-05-02,CMB polarization anisotropies from cosmological reionization: extension to B-modes,"The accurate understanding of the ionization history of the Universe plays a
fundamental role in modern cosmology. It includes a phase of cosmological
reionization after the standard recombination epoch, possibly associated to the
early stages of structure and star formation. While the simple
""{\tau}-parametrization"" of the reionization process and, in particular, of its
imprints on the CMB anisotropy likely represents a sufficiently accurate
modelling for the interpretation of current CMB data, a great attention has
been recently posed on the accurate computation of the reionization signatures
in the CMB for a large variety of astrophysical scenarios and physical
processes. This work is aimed at a careful characterization of the imprints
introduced in the polarization anisotropy, with particular attention to the
B-modes. We have implemented a modified version of CAMB, the Cosmological
Boltzmann code for computing the angular power spectrum (APS) of the
anisotropies of the CMB, to introduce the hydrogen and helium ionization
fractions predicted in astrophysical and phenomenological reionization
histories, beyond the simple {\tau}-parametrization. We compared the results
obtained for these models for all the non-vanishing (in the assumed scenarios)
modes of the CMB APS. The amplitude and shape of the B-mode APS depends, in
particular, on the tensor-to-scalar ratio, r, and on the reionization history,
thus an accurate modeling of the reionization process will have implications
for the precise determination of r or to set more precise constraints on it
through the joint analysis of E and B-mode polarization data available in the
next future and from a mission of next generation. Considering also the
limitation from potential residuals of astrophysical foregrounds, we discussed
the capability of next data to disentangle between different reionization
scenarios in a wide range of r.",1205.0463v1
2012-10-16,The effect of perception anisotropy on particle systems describing pedestrian flows in corridors,"We consider a microscopic model (a system of self-propelled particles) to
study the behaviour of a large group of pedestrians walking in a corridor. Our
point of interest is the effect of anisotropic interactions on the global
behaviour of the crowd. The anisotropy we have in mind reflects the fact that
people do not perceive (i.e. see, hear, feel or smell) their environment
equally well in all directions. The dynamics of the individuals in our model
follow from a system of Newton-like equations in the overdamped limit. The
instantaneous velocity is modelled in such a way that it accounts for the angle
under which an individual perceives another individual. We investigate the
effects of this perception anisotropy by means of simulations, very much in the
spirit of molecular dynamics. We define a number of characteristic quantifiers
(including the polarization index and Morisita index) that serve as measures
for e.g. organization and clustering, and we use these indices to investigate
the influence of anisotropy on the global behaviour of the crowd. The goal of
the paper is to investigate the potentiality of this model; extensive
statistical analysis of simulation data, or reproducing any specific real-life
situation are beyond its scope.",1210.4530v2
2012-11-29,The sensitivity of Cherenkov telescopes to dark matter and astrophysical anisotropies in the diffuse gamma-ray background,"In this article, the capability of present (H.E.S.S., MAGIC, VERITAS) and
planned (CTA) ground-based Cherenkov telescope systems for detecting angular
anisotropies in the diffuse gamma-ray background is investigated. Following up
on a study of the impact of instrumental characteristics (effective area, field
of view, angular resolution, and background rejection efficiency), the first
part examines the influence of different observational strategies, i.e. whether
a single deep observation or a splitting over multiple shallow fields is
preferred. In the second part, the sensitivity to anisotropies generated by
self-annihilating dark matter is studied for different common dark matter
models. We find that a relative contribution of ~10% from dark matter
annihilation to the extra-galactic diffuse gamma-ray background can be detected
with planned configurations of CTA. In terms of the thermally-averaged
self-annihilation cross section, the sensitivity of CTA corresponds to values
below the thermal freeze-out expectation <sigma v> = 3 x 10-26 cm3s-1 for dark
matter particles lighter than ~200 GeV. We stress the importance of
constraining anisotropies from unresolved astrophysical sources with currently
operating instruments already, as a novel and complementary method for
investigating the properties of TeV sources.",1211.6922v2
2012-12-20,Numerical Renormalization Group calculations of the magnetization of isotropic and anisotropic Kondo impurities,"We study a Kondo impurity model with additional uniaxial anisotropy D in a
non-zero magnetic field B using the Numerical Renormalization Group (NRG). The
ratio g_e/g_S of electron and impurity g-factor is regarded as a free parameter
and, in particular, the special cases of a ""local"" (g_e=0) and ""bulk"" (g_e=g_S)
field are considered. For a bulk field, the relationship between the impurity
magnetization M and the impurity contribution to the magnetization M_imp is
investigated. Furthermore, we study how the value of g_e affects the impurity
magnetization curves. In case of an isotropic impurity with g_e=g_S, it is
demonstrated that at zero temperature M(B), unlike M_imp(B), does not display
universal behavior. With additional ""easy axis"" anisotropy, the impurity
magnetization is well described by a shifted and rescaled Brillouin function on
energy scales that are small compared to |D|. In case of ""hard axis""
anisotropy, the magnetization curves can feature steps which are due to
field-induced pseudo-spin-1/2 Kondo effects. For large anisotropy and a local
field, these screening effects are described by an anisotropic spin-1/2 Kondo
model with an additional scattering term that is spin-dependent (in contrast to
ordinary potential scattering). Our study is motivated by the question how the
magnetic properties of a deposited magnetic molecule are modified by the
interaction with a non-magnetic metallic surface.",1212.5007v1
2013-01-08,Magnetic anisotropy in hole-doped superconducting Ba 0.67K 0.33Fe 2As2 probed by polarized inelastic neutron scattering,"We use polarized inelastic neutron scattering (INS) to study spin excitations
of optimally hole-doped superconductor Ba$_{0.67}$K$_{0.33}$Fe$_2$As$_{2}$
($T_c=38$ K).
  In the normal state, the imaginary part of the dynamic susceptibility,
$\chi^{\prime\prime}(Q,\omega)$, shows magnetic anisotropy for energies below
$\sim$7 meV with c-axis polarized spin excitations larger than that of the
in-plane component. Upon entering into the superconducting state, previous
unpolarized INS experiments have shown that spin gaps at $\sim$5 and 0.75 meV
open at wave vectors $Q=(0.5,0.5,0)$ and $(0.5,0.5,1)$, respectively, with a
broad neutron spin resonance at $E_r=15$ meV. Our neutron polarization analysis
reveals that the large difference in spin gaps is purely due to different spin
gaps in the c-axis and in-plane polarized spin excitations, resulting resonance
with different energy widths for the c-axis and in-plane spin excitations. The
observation of spin anisotropy in both opitmally electron and hole-doped
BaFe$_2$As$_2$ is due to their proximity to the AF ordered BaFe$_2$As$_2$ where
spin anisotropy exists below $T_N$.",1301.1397v1
2013-02-04,The flattening of globular clusters: internal rotation or velocity anisotropy?,"Internal rotation is considered to play a major role in determining the
structure and dynamics of some globular clusters. We present a dynamical
analysis of the photometry and three-dimensional kinematics of 47 Tuc and omega
Cen, by means of a new family of self-consistent axisymmetric rotating models.
The combined use of line-of-sight velocities and proper motions allows us to
obtain a global description of the internal dynamical structure of the objects
together with an estimate of their dynamical distances. The well-relaxed
cluster 47 Tuc is very well interpreted by our dynamical models; in particular,
internal rotation is found to explain the observed morphology. For the
partially relaxed cluster omega Cen, the selected model provides a good
representation of its complex three-dimensional kinematics, in general
qualitative agreement with the observed anisotropy profile, which is
characterized by tangential anisotropy in the outer parts; discrepancies are
found between the observed and the expected ellipticity profile and are
ascribed to the presence of a high degree of radial anisotropy in the
intermediate region and to its interplay with rotation.",1302.0717v1
2013-03-06,Magnetic field-induced gluonic (inverse) catalysis and pressure (an)isotropy in QCD,"We study the influence of strong external magnetic fields on gluonic and
fermionic observables in the QCD vacuum at zero and nonzero temperatures, via
lattice simulations with N_f=1+1+1 staggered quarks of physical masses. The
gluonic action density is found to undergo magnetic catalysis at low
temperatures and inverse magnetic catalysis near and above the transition
temperature, similar to the quark condensate. Moreover, the gluonic action
develops an anisotropy: the chromo-magnetic field parallel to the external
field is enhanced, while the chromo-electric field in this direction is
suppressed. We demonstrate that the same hierarchy is obtained using the
Euler-Heisenberg effective action. Conversely, the topological charge density
correlator does not reveal a significant anisotropy up to magnetic fields eB~1
GeV^2. Furthermore, we show that the pressure remains isotropic even for
nonzero magnetic fields, if it is defined through a compression of the system
at fixed external field. In contrast, if the flux of the field is kept fixed
during the compression -- which is the situation realized in the lattice
simulation -- the pressure develops an anisotropy. We estimate the quark and
gluonic contributions to this anisotropy, and relate them to the magnetization
of the QCD vacuum. After performing electric charge renormalization, we obtain
an estimate for the magnetization, which indicates that QCD is paramagnetic.",1303.1328v2
2013-04-05,Probing the Pulsar Origin of the Anomalous Positron Fraction with AMS-02 and Atmospheric Cherenkov Telescopes,"Recent observations by PAMELA, Fermi-LAT, and AMS-02 have conclusively
indicated a rise in the cosmic-ray positron fraction above 10 GeV, a feature
which is impossible to mimic under the paradigm of secondary positron
production with self-consistent Galactic cosmic-ray propagation models. A
leading explanation for the rising positron fraction is an additional source of
electron-positron pairs, for example one or more mature, energetic, and
relatively nearby pulsars. We point out that any one of two well-known nearby
pulsars, Geminga and Monogem, can satisfactorily provide enough positrons to
reproduce AMS-02 observations. A smoking-gun signature of this scenario is an
anisotropy in the arrival direction of the cosmic-ray electrons and positrons,
which may be detectable by existing, or future, telescopes. The predicted
anisotropy level is, at present, consistent with limits from Fermi-LAT and
AMS-02. We argue that the large collecting area of Atmospheric Cherenkov
Telescopes (ACTs) makes them optimal tools for detecting such an anisotropy.
Specifically, we show that much of the proton and gamma-ray background, which
affects measurements of the cosmic-ray electron-positron spectrum with ACTs,
may be controlled in the search for anisotropies. We conclude that observations
using archival ACT data could already constrain or substantiate the pulsar
origin of the positron anomaly, while upcoming instruments (such as the
Cherenkov Telescope Array) will provide strong constraints on the source of the
rising positron fraction.",1304.1791v2
2013-04-10,Constraints on the Sunyaev-Zel'dovich signal from the Warm Hot Intergalactic Medium from WMAP and SPT data,"The fraction of ionized gas in the Warm Hot Intergalactic Medium induces
temperature anisotropies on the Cosmic Microwave Background similar to those of
clusters of galaxies. The Sunyaev-Zel'dovich anisotropies due to these low
density, weakly non-linear, baryon filaments can not be distinguished from that
of clusters using frequency information, but they can be separated since their
angular scales are very different. To determine the relative contribution of
the WHIM SZ signal to the radiation power spectrum of temperature anisotropies,
we explore the parameter space of the concordance LCDM model using Monte Carlo
Markov Chains and the Wilkinson Microwave Anisotropy Probe 7yr and South Pole
Telescope data. We find marginal evidence of a contribution by diffuse gas,
with amplitudes of A_WHIM=10-20 muK^2, but the results are also compatible with
a null contribution from the WHIM, allowing to set an upper limit of A_WHIM <
43 muK^2 (95.4% C.L.). The signal produced by galaxy clusters remains at
A_CL=4.5 muK^2, a value similar to what is obtained when no WHIM is included.
From the measured WHIM amplitude we constrain the temperature-density phase
diagram of the diffuse gas, and find it to be compatible with numerical
simulations. The corresponding baryon fraction in the WHIM varies from 0.43 to
0.47, depending on model parameters. Planck data could set tighter constraints
on the temperature-density relation.",1304.2901v1
2013-05-23,Holographic Photon Production with Magnetic Field in Anisotropic Plasmas,"We investigate the thermal photon production from constant magnetic field in
a strongly coupled and anisotropic plasma via the gauge/gravity duality. The
dual geometry with pressure anisotropy is generated from the axion-dilaton
gravity action introduced by Mateos and Trancancelli and the magnetic field is
coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find
that the photon spectra with different quark mass are enhanced at large
frequency when the photons are emitted parallel to the anisotropic direction
with larger pressure or perpendicular to the magnetic field. However, in the
opposite conditions for the emitted directions, the spectra approximately
saturate isotropic results in the absence of magnetic field. On the other hand,
a resonance emerges at moderate frequency for the photon spectrum with heavy
quarks when the photons move perpendicular to the magnetic field. The resonance
is more robust when the photons are polarized along the magnetic field. On the
contrary, in the presence of pressure anisotropy, the resonance will be
suppressed. There exist competing effects of magnetic field and pressure
anisotropy on meson melting in the strongly coupled super Yang-Mills plasma,
while we argue that the suppression led by anisotropy may not be applied to the
quark gluon plasma.",1305.5509v3
2013-05-26,Rotating Globular Clusters,"Internal rotation is considered to play a major role in the dynamics of some
globular clusters. However, in only few cases it has been studied by
quantitative application of realistic and physically justified global models.
Here we present a dynamical analysis of the photometry and three-dimensional
kinematics of omega Cen, 47 Tuc, and M15, by means of a recently introduced
family of self-consistent axisymmetric rotating models. The three clusters,
characterized by different relaxation conditions, show evidence of differential
rotation and deviations from sphericity. The combination of line-of-sight
velocities and proper motions allows us to determine their internal dynamics,
predict their morphology, and estimate their dynamical distance. The
well-relaxed cluster 47 Tuc is very well interpreted by our model; internal
rotation is found to explain the observed morphology. For M15, we provide a
global model in good agreement with the data, including the central behavior of
the rotation profile and the shape of the ellipticity profile. For the
partially relaxed cluster omega Cen, the selected model reproduces the complex
three-dimensional kinematics; in particular the observed anisotropy profile,
characterized by a transition from isotropy, to weakly-radial anisotropy, and
then to tangential anisotropy in the outer parts. The discrepancy found for the
steep central gradient in the observed line-of-sight velocity dispersion
profile and for the ellipticity profile is ascribed to the condition of only
partial relaxation of this cluster and the interplay between rotation and
radial anisotropy.",1305.6025v1
2013-06-05,Statistical Anisotropy in Inflationary Models with Many Vector Fields and/or Prolonged Anisotropic Expansion,"We study the most general contributions due to scalar field perturbations,
vector field perturbations, and anisotropic expansion to the generation of
statistical anisotropy in the primordial curvature perturbation \zeta. Such a
study is done using the \delta N formalism where only linear terms are
considered. Here, we consider two specific cases that lead to determine the
power spectrum P_\zeta(k) of the primordial curvature perturbation. In the
first one, we consider the possibility that the n-point correlators of the
field perturbations in real space are invariant under rotations in space
(statistical isotropy); as a result, we obtain as many levels of statistical
anisotropy as vector fields present and, therefore, several preferred
directions. The second possibility arises when we consider anisotropic
expansion, which leads us to obtain I+a additional contributions to the
generation of statistical anisotropy of \zeta compared with the former case,
being I and a the number of scalar and vector fields involved respectively.",1306.1150v1
2013-07-29,Chiral Phases of Superfluid 3He in an Anisotropic Medium,"I report theoretical analysis and predictions for the equilibrium phases of
superfluid 3He infused into a low-density, homogeneous uniaxial aerogel.
Ginzburg-Landau (GL) theory for a class of equal-spin-pairing (ESP) states in a
medium with uniaxial anisotropy is developed and used to analyze recent
experiments on uniaxially strained aerogels. For 3He in an axially ""stretched""
aerogel GL theory predicts a transition from normal liquid into a chiral ABM
phase at T_c1 in which the chirality axis, l, is aligned along the strain axis.
This orbitally aligned state, is protected from random fluctuations in the
anisotropy direction, has a positive NMR frequency shift, a sharp NMR resonance
line and is identified with the high-temperature ESP-1 phase of superfluid 3He
in axially stretched aerogel. A second transition into a biaxial phase is
predicted to onset at a slightly lower temperature, T_c2 < T_c1. This phase is
an ESP state, breaks time-reversal symmetry, and is defined by an orbital order
parameter that spontaneously breaks axial rotation symmetry. This transition is
driven by the coupling of an axially aligned 1D ""polar"" order parameter to the
two time-reversed 2D axial ABM states. The biaxial phase has a continuous
degeneracy associated with the projection of its chiral axis in the plane
normal to the anisotropy axis. Theoretical predictions for the NMR frequency
shifts of the biaxial phase provide an identification of the ESP-2 as the
biaxial state, partially disordered by random anisotropy (Larkin-Imry-Ma
effect). The ""width"" of the jump in the NMR frequency shift at T_c2 provides an
estimate of the orbital domain size, xi_LIM ~ 5 mu-m at 18 bar.",1307.7656v1
2013-08-05,Thermally driven domain wall motion in Fe on W(1 1 0),"It has recently been shown that domain walls in ferromagnets can be moved in
the presence of thermal gradients. In this work we study the motion of narrow
domain walls in low-dimensional systems when subjected to thermal gradients.
The system chosen is a monolayer of Fe on W(1 1 0) which is known to exhibit a
large anisotropy while having a soft exchange, resulting in a very narrow
domain wall. The study is performed by means of atomistic spin dynamics
simulations coupled to first-principles calculations. By subjecting the systems
to a thermal gradient we observe a temperature dependent movement of the domain
wall as well as changes of the spatial magnetization profile of the system. The
thermal gradient always makes the domain wall move towards the hotter region of
the sample with a velocity proportional to the gradient. The material specific
study is complemented by model simulations to discern the interplay between the
thermal gradient, magnetic anisotropy and the exchange interaction, and shows
that the larger DW velocities are found for materials with low magnetic
anisotropy. The relatively slow DW motion of the Fe/W(1 1 0) system is hence
primarily caused by its large magnetic anisotropy.",1308.0986v1
2013-09-16,Limits on Alpha Particle Temperature Anisotropy and Differential Flow from Kinetic Instabilities: Solar Wind Observations,"Previous studies have shown that the observed temperature anisotropies of
protons and alpha particles in the solar wind are constrained by theoretical
thresholds for pressure-anisotropy-driven instabilities such as the
Alfv\'en/ion-cyclotron (A/IC) and fast-magnetosonic/whistler (FM/W)
instabilities. In this letter, we use a long period of in-situ measurements
provided by the {\em Wind} spacecraft's Faraday cups to investigate the
combined constraint on the alpha-proton differential flow velocity and the
alpha-particle temperature anisotropy due to A/IC and FM/W instabilities. We
show that the majority of the data are constrained to lie within the region of
parameter space in which A/IC and FM/W waves are either stable or have
extremely low growth rates. In the minority of observed cases in which the
growth rate of the A/IC (FM/W) instability is comparatively large, we find
relatively higher values of $T_{\perp\alpha}/T_{\perp p}$
($T_{\parallel\alpha}/T_{\parallel p}$) when alpha-proton differential flow
velocity is small, where $T_{\perp\alpha}$ and $T_{\perp p}$
($T_{\parallel\alpha}$ and $T_{\parallel p}$) are the perpendicular (parallel)
temperatures of alpha particles and protons. We conjecture that this observed
feature might arise from preferential alpha-particle heating which can drive
the alpha particles beyond the instability thresholds.",1309.4010v2
2013-09-24,Medium scale anisotropy in the TeV cosmic ray flux observed by ARGO-YBJ,"Measuring the anisotropy of the arrival direction distribution of cosmic rays
provides important information on the propagation mechanisms and the
identification of their sources. In fact, the flux of cosmic rays is thought to
be dependent on the arrival direction only due to the presence of nearby cosmic
ray sources or particular magnetic-field structures. Recently, the observation
of unexpected excesses at TeV energy down to angular scale as narrow as
$\sim10\deg$ raised the possibility that the problem of the origin of galactic
cosmic rays may be addressed by studying the anisotropy.
  The ARGO-YBJ experiment is a full-coverage EAS array, sensitive to cosmic
rays with energy threshold of a few hundred GeV. Searching for small-size
deviations from the isotropy, the ARGO-YBJ collaboration explored the
declination region $\delta\sim-20^{\circ}\div 80^{\circ}$, making use of about
3.7$\cdot10^{11}$ events collected from November 2007 to May 2012.
  In this paper the detection of different significant (up to 13 standard
deviations) medium-scale anisotropy regions in the arrival directions of CRs is
reported. The observation was performed with unprecedented detail. The relative
excess intensity with respect to the isotropic flux extends up to 10$^{-3}$.
The maximum excess occurs for proton energies of 10-20 TeV, suggesting the
presence of unknown features of the magnetic fields the charged cosmic rays
propagate through, or some contribution of nearby sources never considered so
far.
  The observation of new weaker few-degree excesses throughout the sky region
$195^{\circ}\leq$ \ra $\leq 290^{\circ}$ is reported for the first time.",1309.6182v1
2013-10-21,"Controlled nucleation of topological defects in the stripe domain patterns of Lateral multilayers with Perpendicular Magnetic Anisotropy: competition between magnetostatic, exchange and misfit interactions","Magnetic lateral multilayers have been fabricated on weak perpendicular
magnetic anisotropy amorphous Nd-Co films in order to perform a systematic
study on the conditions for controlled nucleation of topological defects within
their magnetic stripe domain pattern. A lateral thickness modulation of period
$w$ is defined on the nanostructured samples that, in turn, induces a lateral
modulation of both magnetic stripe domain periods $\lambda$ and average
in-plane magnetization component $M_{inplane}$. Depending on lateral multilayer
period and in-plane applied field, thin and thick regions switch independently
during in-plane magnetization reversal and domain walls are created within the
in-plane magnetization configuration coupled to variable angle grain boundaries
and disclinations within the magnetic stripe domain patterns. This process is
mainly driven by the competition between rotatable anisotropy (that couples the
magnetic stripe pattern to in-plane magnetization) and in-plane shape
anisotropy induced by the periodic thickness modulation. However, as the
structural period $w$ becomes comparable to magnetic stripe period $\lambda$,
the nucleation of topological defects at the interfaces between thin and thick
regions is hindered by a size effect and stripe domains in the different
thickness regions become strongly coupled.",1310.5566v1
2013-11-21,Jet Quenching and Its Azimuthal Anisotropy in AA and possibly High Multiplicity pA and dA Collisions,"We report our calculation of jet quenching and its azimuthal anisotropy in
the high energy AA and high multiplicity pA and dA collisions. The purpose of
this study is twofold. First, we improve our previous event-by-event studies,
by properly implementing $p_t$ dependence in the modeling. We show that, within
the jet ""monography"" scenario featuring a strong near-Tc-enhancement of jet
energy loss, the computed high-$p_t$ nuclear modification factor $R_{AA}$ and
the harmonic coefficients in its azimuthal anisotropy $v_{2,\,3,\,4}$, agree
well with the available data from both Relativistic Heavy Ion Collider (RHIC)
and Large Hadron Collider (LHC). Second, in light of current discussions on
possible final state collective behavior in the high-multiplicity pPb and dAu
collisions, we examine the implication of final state jet attenuation in such
collisions, by applying the same model used in AA collisions and quantifying
the corresponding $R_{pA}$ and $R_{dA}$ and their azimuthal anisotropy. The
high-$p_t$ $V_n$ provide a set of clean indicators of final state energy loss.
In particular we find in the most central pPb (5.02 TeV) and dAu (200 GeV)
collisions, $V_2$ is on the order of $0.01$ and $0.1$ respectively, measurable
with current experimental accuracy. In addition, our high-$p_t$ $R_{dA}$ is
around $0.6$ which is compatible with preliminary dAu results from RHIC.",1311.5463v2
2013-12-13,On Vortex Solutions of Landau-Lifshitz Equations,"We study the Landau-Lifshitz equation of ferromagnetism on $\mathbb{R}^2$
with an easy-axis anisotropy. We give the necessary condition for the existence
of the finite energy vortex solutions and show the behaviors of the solutions.",1312.3816v1
2013-12-23,"Universal fluctuation-driven eccentricities in proton-proton, proton-nucleus and nucleus-nucleus collisions","We show that the statistics of fluctuation-driven initial-state anisotropies
in proton-proton, proton-nucleus and nucleus-nucleus collisions is to a large
extent universal. We propose a simple parametrization for the probability
distribution of the Fourier coefficient $\varepsilon_n$ in harmonic $n$, which
is in good agreement with Monte-Carlo simulations. Our results provide a simple
explanation for the 4-particle cumulant of triangular flow measured in Pb-Pb
collisions, and for the 4-particle cumulant of elliptic flow recently measured
in p-Pb collisions. Both arise as natural consequences of the condition that
initial anisotropies are bounded by unity. We argue that the initial rms
anisotropy in harmonic $n$ can be directly extracted from the measured ratio
$v_n\{4\}/v_n\{2\}$: this gives direct access to a property of the initial
density profile from experimental data. We also make quantitative predictions
for the small lifting of degeneracy between $v_n\{4\}$, $v_n\{6\}$ and
$v_n\{8\}$. If confirmed by future experiments, they will support the picture
that long-range correlations observed in p-Pb collisions at the LHC originate
from collective flow proportional to the initial anisotropy.",1312.6555v3
2014-01-17,Co2FeAl Heusler thin films grown on Si and MgO substrates: annealing temperature effect,"10 nm and 50 nm Co$_{2}$FeAl (CFA) thin films have been deposited on MgO(001)
and Si(001) substrates by magnetron sputtering and annealed at different
temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth
(according to the relation CFA(001)[110]//MgO(001)[100] epitaxial relation),
respectively for CFA films grown on a Si and on a MgO substrate. For these
later, the chemical order varies from the A2 phase to the B2 phase when
increasing the annealing temperature (Ta) while only the A2 disorder type has
been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR)
measurements revealed that the in-plane anisotropy results from the
superposition of a uniaxial and of a fourfold symmetry term for CFA grown on
MgO substrates. This fourfold anisotropy, which disappears completely for
samples grown on Si, is in accord with the crystal structure of the samples.
The fourfold anisotropy field decreases when increasing Ta while the uniaxial
anisotropy field is nearly unaffected by Ta within the investigated range. The
MS-FMR data also allow for concluding that the gyromagnetic factor remains
constant and that the exchange stiffness constant increases with $T_{a}$.
Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement
of the chemical order. We derive a very low intrinsic damping parameter
(1.3*10^-3 and 1.1*10^-3 for films of 50 nm thickness annealed at 615 {\deg}C
grown on MgO and on Si, respectively).",1401.4397v1
2014-02-05,Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers,"We present a comprehensive study of the current-induced spin-orbit torques in
perpendicularly magnetized Ta/CoFeB/MgO layers. The samples were annealed in
steps up to 300 degrees C and characterized using x-ray absorption
spectroscopy, transmission electron microscopy, resistivity, and Hall effect
measurements. By performing adiabatic harmonic Hall voltage measurements, we
show that the transverse (field-like) and longitudinal (antidamping-like)
spin-orbit torques are composed of constant and magnetization-dependent
contributions, both of which vary strongly with annealing. Such variations
correlate with changes of the saturation magnetization and magnetic anisotropy
and are assigned to chemical and structural modifications of the layers. The
relative variation of the constant and anisotropic torque terms as a function
of annealing temperature is opposite for the field-like and antidamping
torques. Measurements of the switching probability using sub-{\mu}s current
pulses show that the critical current increases with the magnetic anisotropy of
the layers, whereas the switching efficiency, measured as the ratio of magnetic
anisotropy energy and pulse energy, decreases. The optimal annealing
temperature to achieve maximum magnetic anisotropy, saturation magnetization,
and switching efficiency is determined to be between 240 degrees and 270
degrees C.",1402.0986v2
2014-02-26,Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li_{1-x}Fe_x)N,"Large magnetic anisotropy and coercivity are key properties of functional
magnetic materials and are generally associated with rare earth elements. Here
we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic
hysteresis in Li2(Li1-xFex)N. An extrapolated, magnetic anisotropy field of 220
Tesla and a coercivity field of over 11 Tesla at 2 Kelvin outperform all known
hard-ferromagnets and single-molecule magnets (SMMs). Steps in the hysteresis
loops and relaxation phenomena in striking similarity to SMMs are particularly
pronounced for x << 1 and indicate the presence of nano-scale magnetic centres.
Quantum tunnelling, in form of temperature-independent relaxation and
coercivity, deviation from Arrhenius behaviour and blocking of the relaxation,
dominates the magnetic properties up to 10 Kelvin. The simple crystal
structure, the availability of large single crystals, and the ability to vary
the Fe concentration make Li2(Li1-xFex)N (i) an ideal model system to study
macroscopic quantum effects at elevated temperatures and (ii) a basis for novel
functional magnetic materials.",1402.6626v1
2014-03-22,Constraining anisotropy of the universe from different groups of type-Ia supernovae,"Recent released Planck data and other astronomical observations show that the
universe may be anisotropic on large scales. Inspired by this, anisotropic
cosmological models have been proposed. We note that the Finsler-Randers
spacetime provides an appropriate framework for the anisotropic cosmology. By
adding an arbitrary 1-form to the Friedmann-Robertson-Walker (FRW) line
element, a privileged axis in the universe is picked out. The distance-redshift
relation is modified to be direction-dependent. We wish that the anisotropic
cosmological model may be tested crossly by independent observations. Type-Ia
supernovae (SNe Ia) calibrated from four different light curve fitters are used
to constrain possible anisotropy of the universe. The magnitudes of anisotropy
are all between 2% --- 5%, but the systematic uncertainty cannot be excluded.
The directions of privileged axis seem to differ from each other. The
statistical significance is not high enough to make a convincing conclusion.
Nevertheless, the $1\sigma$ contours in the $(l,b)$ plane obtained from four
groups of SNe Ia have an overlap, centering at $(l,b)\approx
(170^{\circ},0^{\circ})$. Monte Carlo simulation shows that the anisotropy is
unlikely to be caused by selection effect.",1403.5661v1
2014-04-07,Long term variation of the solar diurnal anisotropy of galactic cosmic rays observed with the Nagoya multi-directional muon detector,"We analyze the three dimensional anisotropy of the galactic cosmic ray (GCR)
intensities observed independently with a muon detector at Nagoya in Japan and
neutron monitors over four solar activity cycles. We clearly see the phase of
the free-space diurnal anisotropy shifting toward earlier hours around solar
activity minima in A>0 epochs, due to the reduced anisotropy component parallel
to the mean magnetic field. The average parallel component is consistent with a
rigidity independent spectrum, while the perpendicular component increases with
GCR rigidity. We suggest that this harder spectrum of the perpendicular
component is due to contribution from the drift streaming. We find that the
bidirectional latitudinal density gradient is positive in A>0 epoch, while it
is negative in A<0 epoch, in accord with the drift model prediction. The radial
density gradient, on the other hand, varies with ~11-year cycle with maxima
(minima) in solar maximum (minimum) periods, but there is no significant
difference seen between average radial gradients in A>0 and A<0 epochs. The
average parallel mean free path is larger in A<0 than in A>0. We also find,
however, that parallel mean free path (radial gradient) appears to persistently
increase (decreasing) in the last three cycles of weakening solar activity. We
suggest that simple differences between these parameters in A>0 and A<0 epochs
are seriously biased by these long-term trends.",1404.1676v2
2014-05-08,Dynamical Condensation in a Holographic Superconductor Model with Anisotropy,"We study dynamical condensation process in a holographic superconductor model
with anisotropy. The time-dependent numerical solution is constructed for the
Einstein-Maxwell-dilaton theory with complex scalar in asymptotic AdS
spacetime. The introduction of dilaton field generates the anisotropy in
boundary spatial directions. In analogy of isotropic case, we have two black
hole solutions below certain critical temperature $T_c$, the anisotropic
charged black hole with and without scalar hair, corresponding respectively to
the supercooled normal phase and superconducting phase in the boundary theory.
We observe a nonlinear evolution from a supercooled anisotropic black hole
without scalar hair to a anisotropic hairy black hole. Via AdS/CFT
correspondence, we extract time evolution of the condensate operator, which
shows an exponential growth and subsequent saturation, similar to the isotropic
case. Furthermore, we obtain a nontrivial time evolution of the boundary
pressure, while in isotropic case it remains a constant. We also generalize
quasinormal modes calculation to anisotropic black holes and shows scalar
quasinormal modes match with relaxation time scale of the condensate operator.
In addition, we present the final temperature and anisotropic pressure as
functions of initial temperature and background anisotropy.",1405.1806v2
2014-05-08,Magnetic anisotropy and chirality of frustrated Cr nanostructures on Au(111),"By using a fully relativistic embedded cluster Green's function technique we
investigated the magnetic anisotropy properties of four different compact Cr
trimers (equilateral triangles) and Cr mono-layers deposited on Au(111) surface
in both fcc and hcp stackings. For all trimers the magnetic ground state was
found a frustrated 120$^\circ$ N\'eel configuration. Applying global spin
rotations to the magnetic ground state, the predictions of an appropriate
second order spin Hamiltonian were reproduced with high accuracy by the first
principles calculations. For the Cr trimers with adjacent Au atoms in similar
geometry we obtained similar values for the in-plane and out-of-plane
anisotropy parameters, however, the Dzyaloshinskii-Moriya (DM) interactions
appeared to differ remarkably. For two kinds of trimers we found an
unconventional magnetic ground state showing 90$^\circ$ in-the-plane rotation
with respect to the high symmetry directions. Due to higher symmetry, the
in-plane anisotropy term was missing for the mono-layers and distinctly
different DM interactions were obtained for the different stackings. The chiral
degeneracy of the N\'eel configurations was lifted by less then 2 meV for the
trimers, while this value raised up to about 15 meV per 3 Cr atoms for the hcp
packed mono-layer.",1405.2057v1
2014-05-16,Mixed configuration ground state in Iron(II) Phthalocyanine,"We calculate the angular dependence of the x-ray linear and circular
dichroism at the $L_{2,3}$ edges of $\alpha$-Fe(II) Phthalocyanine (FePc) thin
films using a ligand field model with full configuration interaction. We find
the best agreement with the experimental spectra for a mixed ground state of
$^3E_{g}(a_{1g}^2e_g^3b_{2g}^1)$ and $^3B_{2g}(a_{1g}^1e_g^4b_{2g}^1)$ with the
two configurations coupled by the spin-orbit interaction. The $^3E_{g}(b)$ and
$^3B_{2g}$ states have an easy axis and plane anisotropies, respectively. Our
model accounts for an easy-plane magnetic anisotropy and the measured
magnitudes of the in-plane orbital and spin moments. The proximity in energy of
the two configurations allows a switching of the magnetic anisotropy from easy
plane to easy axis with a small change in the crystal field, as recently
observed for FePc adsorbed on an oxidized Cu surface. We also discuss the
possibility of a quintet ground state ($^5A_{1g}$ is 250~meV above the ground
state) with planar anisotropy by manipulation of the Fe-C bond length by
depositing the complex on a substrate that is subjected to a mechanical strain.",1405.4313v4
2014-05-23,Evolution of Anisotropic In-plane Resistivity with doping level in Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ Single Crystals,"We measured the in-plane resistivity anisotropy in the underdoped
Ca$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals. The anisotropy (indicated by
$\rho_{\rm b} - \rho_{\rm a}$) appears below a temperature well above magnetic
transition temperature $T_{\rm N}$, being positive ($\rho_{\rm b} - \rho_{\rm
a} > 0$) as $x\leq$ 0.14. With increasing the doping level to $x$ = 0.19, an
intersection between $\rho_{\rm b}$ and $\rho_{\rm a}$ is observed upon
cooling, with $\rho_{\rm b} - \rho_{\rm a} < 0$ at low-temperature deep inside
a magnetically ordered state, while $\rho_{\rm b} - \rho_{\rm a}> 0$ at high
temperature. Subsequently, further increase of hole concentration leads to a
negative anisotropy $\rho_{\rm b} - \rho_{\rm a} < 0$ in the whole temperature
range. These results manifest that the anisotropic behavior of resistivity in
the magnetically ordered state depends strongly on the competition of the
contributions from different mechanisms, and the competition between the two
contributions results in a complicated evolution of the anisotropy of in-plane
resistivity with doping level.",1405.6199v1
2014-06-23,Magnetic phases in the S=1 Shastry-Sutherland model with uniaxial anisotropy,"We explore the field induced magnetic phases of an $S=1$ $XXZ$ model with
single-ion anisotropy and large Ising-like anisotropy on a Shastry Sutherland
lattice over a wide range of Hamiltonian parameters and applied magnetic field.
The multitude of ground state phases are characterized in detail in terms of
their thermodynamic properties and the underlying classical (Ising limit) spin
arrangements for the plateau phases are identified by calculating the static
structure factors. The enlarged local Hilbert space of the $S=1$ spins results
in several new ground state phases that are not realized for $S=1/2$ spins.
These include the quantum paramagnetic state that is ubiquitous to $S=1$ spins
with single ion anisotropy, two different spin supersolid phases (with distinct
longitudinal ordering) and a magnetization plateau that arises as a direct
descendant of the 1/3 plateau due to quantum fluctuations that are not possible
for $S=1/2$ spins. We predict the same mechanism will lead to plateaus at
smaller fractions of 1/3 for higher spins. The full momentum dependence of the
longitudinal and transverse components of the static structure factor is
calculated in the spin supersolid phase to demonstrate the simultaneous
existence of diagonal and off-diagonal long-range order as well as the
different longitudinal orderings.",1406.5856v1
2014-08-20,The redshift-space galaxy two-point correlation function and baryon acoustic oscillations,"Future galaxy surveys will measure baryon acoustic oscillations (BAOs) with
high significance, and a complete understanding of the anisotropies of BAOs in
redshift space will be important to exploit the cosmological information in
BAOs. Here we describe the anisotropies that arise in the redshift-space galaxy
two-point correlation function (2PCF) and elucidate the origin of features that
arise in the dependence of the BAOs on the angle between the orientation of the
galaxy pair and the line of sight. We do so with a derivation of the
configuration-space 2PCF using streaming model. We find that, contrary to
common belief, the locations of BAO peaks in the redshift-space 2PCF are
anisotropic even in the linear theory. Anisotropies in BAO depend strongly on
the method of extracting the peak, showing maximum 3 % angular variation. We
also find that extracting the BAO peak of $r^2\xi(r,\mu)$ significantly reduces
the anisotropy to sub-percent level angular variation. When subtracting the
tilt due to the broadband behavior of the 2PCF, the BAO bump is enhanced along
the line of sight because of local infall velocities toward the BAO bump.
Precise measurement of the angular dependence of the redshift-space 2PCF will
allow new geometrical tests of dark energy beyond the BAO.",1408.4648v1
2014-11-12,Large perpendicular magnetic anisotropy in magnetostrictive Fe$_{1-x}$Ga$_x$ thin films,"In this work we report the appearence of a large perpendicular magnetic
anisotropy (PMA) in Fe$_{1-x}$Ga$_x$ thin films grown onto ZnSe/GaAs(100). This
arising anisotropy is related to the tetragonal metastable phase in as-grown
samples recently reported [M. Eddrief {\it et al.}, Phys. Rev. B {\bf 84},
161410 (2011)]. By means of ferromagnetic resonance studies we measured PMA
values up to $\sim$ 5$\times$10$^5$ J/m$^3$. PMA vanishes when the cubic
structure is recovered upon annealing at 300$^{\circ}$C. Despite the important
values of the magnetoelastic constants measured via the cantilever method, the
consequent magnetoelastic contribution to PMA is not enough to explain the
observed anisotropy values in the distorted state. {\it Ab initio} calculations
show that the chemical ordering plays a crucial role in the appearance of PMA.
Through a phenomenological model we are able to explain that an excess of next
nearest neighbour Ga pairs (B$_2$-like ordering) along the perpendicular
direction arises as the source of PMA in Fe$_{1-x}$Ga$_x$ thin films.",1411.3055v2
2014-11-17,On the Anisotropy of Nuclei Mid-Infrared Radiation in Nearby Active Galactic Nuclei,"In the center of active galactic nuclei (AGN), the dusty torus absorb the
radiation from the central engine and re-emit in mid-infrared (MIR).
Observations have detected moderate anisotropy in the dust MIR emission, in the
way that type 1 AGNs (type1s) are mildly brighter in MIR comparing with type 2
sources (type2s). However, type1s and type2s were found to follow statistically
the same tight MIR -- hard X-ray correlation, suggesting the MIR emission is
highly isotropic assuming the hard X-ray radiation is inclination independent.
We argue this discrepancy could be solved considering the hard X-ray emission
in AGN is also mildly anisotropic as we recently discovered. To verify this
diagram, we compare the sub-arcsecond 12\mu m flux densities of type1s and
type2s using [OIV]$\lambda$25.89\mu m emission line as an isotropic luminosity
indicator. We find that on average type1s are brighter in nuclei 12\mu m
radiation by a factor of $2.6 \pm 0.6$ than type2s at given
[OIV]$\lambda$25.89\mu m luminosities, confirming the mild anisotropy of the
nuclei 12\mu m emission. We show that the anisotropy of the 12\mu m emission we
detected is in good agreement with radiative transfer models of clumpy torus.
The fact that type 1 and type 2 AGNs follow the same tight MIR -- hard X-ray
correlation instead supports that both the MIR and hard X-ray emission in AGNs
are mildly anisotropic.",1411.4585v1
2014-12-08,Voltage Controlled Magnetic Anisotropy Based Low Energy Switching of a Ferromagnet on a Topological Insulator,"We present a novel memory device that consists of a thin ferromagnetic layer
of Fe deposited on topological insulator thin film, Bi2Se3. The ferromagnetic
layer has perpendicular anisotropy, due to MgO deposited on the top surface of
Fe. When current is passed on the surface of Bi2Se3, the surface of the Bi2Se3
becomes spin polarized and strong exchange interaction occurs between the d
electrons in the ferromagnet and the electrons conducting the current on the
surface of the Bi2Se3. Part of the current is shunted through the ferromagnet
which generates spin transfer torque in the ferromagnet. The combination of the
spin transfer torque and exchange interaction torque along with
voltage-controlled magnetic anisotropy (VCMA) allows ultralow-energy switching
of the ferromagnet. We perform micromagnetic simulations and predict switching
time of the order of 2.5 ns and switching energy of the order of 0.45fJ for a
ferromagnetic bit with thermal stability of 43kBT. Such ultralow-energy and
high-speed VCMA-induced switching of a perpendicular anisotropy ferromagnet on
a topological insulator could be utilized for energy-efficient memory design.",1412.2434v3
2014-12-09,Anisotropy-based optimal filtering in linear discrete time invariant systems,"This paper is concerned with a problem of robust filtering for a
finite-dimensional linear discrete time invariant system with two output
signals, one of which is directly observed while the other has to be estimated.
The system is assumed to be driven by a random disturbance produced from the
Gaussian white noise sequence by an unknown shaping filter. The worst-case
performance of an estimator is quantified by the maximum ratio of the
root-mean-square (RMS) value of the estimation error to that of the disturbance
over stationary Gaussian disturbances whose mean anisotropy is bounded from
above by a given parameter $a \ge 0$. The mean anisotropy is a combined entropy
theoretic measure of temporal colouredness and spatial ""nonroundness"" of a
signal. We construct an $a$-anisotropic estimator which minimizes the
worst-case error-to-noise RMS ratio. The estimator retains the general
structure of the Kalman filter, though with modified state-space matrices.
Computing the latter is reduced to solving a set of two coupled algebraic
Riccati equations and an equation involving the determinant of a matrix. In two
limiting cases, where $a = 0$ or $a \to +\infty$, the $a$-anisotropic estimator
leads to the standard steady-state Kalman filter or the $H_{\infty}$-optimal
estimator, respectively.",1412.3010v1
2015-01-05,Anisotropic Strong Coupling Effects on Superfluid 3He in Aerogels - Conventional Spin-Fluctuation Approach -,"Motivated by recent experiments on liquid $^3$He reporting emergence of novel
superfluid phases in globally anisotropic aerogels, our previous theory on
superfluid $^3$He in globally anisotropic aerogels is extended to incorporate
effects of an anisotropy of the quasiparticle scattering cross section on the
strong coupling (SC) contributions to the Ginzburg-Landau (GL) free energy on
the basis of the spin-fluctuation (paramagnon) approach to the SC contributions
developed by Brinkman et al. [Phys. Rev. A {\bf 10}, 2386 (1974)]. In the
globally isotropic case, impurity effects on the SC correction destabilize the
A-phase even at higher pressures of about 30 (bar) and make the B-phase the
only state in equilibrium, while SC contributions accompanied by a global
stretched anisotropy to the GL quartic terms generally tend to broaden the
stability region of the A-phase compared with that of the B-phase. In
particular, in contrast to the cases in bulk and in the isotropic aerogel, the
SC corrections to the GL {\it quadratic} terms are not negligible in the
globally anisotropic case but may change the sign of the apparent anisotropy
depending on the magnitude of the frequency cutoff of the normal paramagnon
propagator. Based on this sign change of the apparent anisotropy, we discuss
different strange observations on superfluid $^3$He in porous media such as
disappearance of the polar superfluid phase at higher pressures seen in
nematically-ordered aerogels and absence of the B-phase and of the A-phase with
planar ${\hat {\bf l}}$-vector in a stretched aerogel.",1501.00795v1
2015-02-02,Giant Phononic Anisotropy and Unusual Anharmonicity of Phosphorene: Interlayer Coupling and Strain Engineering,"Phosphorene, an emerging elemental two-dimensional (2D) direct band gap
semiconductor with fascinating structural and electronic properties
distinctively different from other 2D materials such as graphene and MoS2, is
promising for novel nanoelectronic and optoelectronic applications. Phonons, as
one of the most important collective excitations, are at the heart for the
device performance, as their interactions with electrons and photons govern the
carrier mobility and light-emitting efficiency of the material. Here, through a
detailed first-principles study, it is demonstrated that monolayer phosphorene
exhibits a giant phononic anisotropy, and remarkably, this anisotropy is
squarely opposite to its electronic counterpart and can be tuned effectively by
strain engineering. By sampling the whole Brillouin zone for the mono-layer
phosphorene, several ""hidden"" directions are found, along which small-momentum
phonons are ""frozen"" with strain and possess the smallest degree of
anharmonicity. Unexpectedly, these ""hidden"" directions are intrinsically
different from those usually studied armchair and zigzag directions. Light is
also shed on the anisotropy of interlayer coupling of few-layer phosphorene by
examining the rigid-layer vibrations. These highly anisotropic and
strain-tunable characteristics of phosphorene offer new possibilities for its
applications in thermal management, thermoelectronics, nanoelectronics and
phononics.",1502.00375v1
2015-02-04,Azimuthal anisotropies in p+Pb collisions from classical Yang-Mills dynamics,"We compute single and double inclusive gluon distributions in classical
Yang-Mills simulations of proton-lead collisions and extract the associated
transverse momentum dependent Fourier harmonics $v_2(p_T)$ and $v_3(p_T)$.
Gluons have a large $v_2$ in the initial state, while odd harmonics such as
$v_3$ vanish identically at the initial time $\tau=0^{+}$. By the time $\tau
\lesssim 0.4\,{\rm fm/c}$ final state effects in the classical Yang-Mills
evolution generate a non-zero $v_{3}$ and only mildly modify the gluon $v_{2}$.
Unlike hydrodynamic flow, these momentum space anisotropies are uncorrelated
with the global spatial anisotropy of the collision. A principal ingredient for
the generation of $v_2$ and $v_3$ in this framework is the event-by-event
breaking of rotational invariance in domains the size of the inverse of the
saturation scale $Q_s$. In contrast to our findings in p+Pb collisions
Yang-Mills simulations of lead-lead collisions generate much smaller values of
$v_{2,3} (p_T)$ and additional collective flow effects are needed to explain
experimental data. This is because the locally generated anisotropy due to the
breaking of rotational invariance is depleted with the increase in the number
of uncorrelated domains.",1502.01331v2
2015-02-21,Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets,"The concept of local isotropy in a chemically reacting turbulent wall-jet
flow is addressed using direct numerical simulation (DNS) data. Different DNS
databases with isothermal and exothermic reactions are examined. The chemical
reaction and heat release effects on the turbulent velocity, passive scalar and
reactive species fields are studied using their probability density functions
(PDF) and higher order moments for velocities and scalar fields, as well as
their gradients. With the aid of the anisotropy invariant maps for the Reynolds
stress tensor the heat release effects on the anisotropy level at different
wall-normal locations are evaluated and found to be most accentuated in the
near-wall region. It is observed that the small-scale anisotropies are
persistent both in the near-wall region and inside the jet flame. Two
exothermic cases with different Damkohler number are examined and the
comparison revealed that the Damkohler number effects are most dominant in the
near-wall region, where the wall cooling effects are influential. In addition,
with the aid of PDFs conditioned on the mixture fraction, the significance of
the reactive scalar characteristics in the reaction zone is illustrated. We
argue that the combined effects of strong intermittency and strong persistency
of anisotropy at the small scales in the entire domain can affect mixing and
ultimately the combustion characteristics of the reacting flow.",1502.06113v1
2015-04-09,Consequences of critical interchain couplings and anisotropy on a Haldane chain,"Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNi$_2$V$_2$O$_8$.
Significant effects on low energy excitation spectra are found where the
Haldane gap ($\Delta_0 \approx 0.41J$; where $J$ is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction $J$ = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
$d$ orbital of V ions. The present single crystal study also allows us to
correctly position SrNi$_2$V$_2$O$_8$ in the theoretical $D$-$J_{\perp}$ phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.",1504.02400v1
2015-05-22,Spectral distortions of the CMB dipole,"We consider the distortions of the cosmic microwave background (CMB) dipole
anisotropy related to the primordial recombination radiation (PRR) and
primordial $y$- and $\mu$-distortions. The signals arise due to our motion
relative to the CMB restframe and appear as a frequency-dependent distortion of
the CMB temperature dipole. To leading order, the expected relative distortion
of the CMB dipole does not depend on the particular observation directions and
reaches the level of $10^{-6}$ for the PRR- and $\mu$-distortions and $10^{-5}$
for the $y$-distortion in the frequency range 1 -- 700 GHz. The temperature
differences arising from the dipole anisotropy of the relic CMB distortions
depend on the observation directions. For mutually opposite directions,
collinear to the CMB dipole axis, the temperature differences because of the
PRR- and $\mu$-dipole anisotropy attain values $\Delta T\simeq 10\,$nK in the
considered range. The temperature difference arising from the $y$-dipole
anisotropy may reach values of up to $1\,\mu$K. The key features of the
considered effect are as follow: (i) an observation of the effect does not
require absolute calibration; (ii) patches of sky with minimal foreground
contamination can be chosen. Future measurements of the CMB dipole distortion
thus will provide an alternative method for direct detection of the PRR-, $y$-,
and $\mu$-distortions. The $y$-distortion dipole may be detectable with PIXIE
at a few standard deviations.",1505.06028v2
2015-05-26,Reference Interaction Site Model and Optimized Perturbation theories of colloidal dumbbells with increasing anisotropy,"We investigate thermodynamic properties of anisotropic colloidal dumbbells in
the frameworks provided by the Reference Interaction Site Model (RISM) theory
and an Optimized Perturbation Theory (OPT), this latter based on a fourth-order
high-temperature perturbative expansion of the free energy, recently
generalized to molecular fluids. Our model is constituted by two identical
tangent hard spheres surrounded by square-well attractions with same widths and
progressively different depths. Gas-liquid coexistence curves are obtained by
predicting pressures, free energies, and chemical potentials. In comparison
with previous simulation results, RISM and OPT agree in reproducing the
progressive reduction of the gas-liquid phase separation as the anisotropy of
the interaction potential becomes more pronounced; in particular, the RISM
theory provides reasonable predictions for all coexistence curves, bar the
strong anisotropy regime, whereas OPT performs generally less well. Both
theories predict a linear dependence of the critical temperature on the
interaction strength, reproducing in this way the mean-field behavior observed
in simulations; the critical density~--~that drastically drops as the
anisotropy increases~--~turns to be less accurate. Our results appear as a
robust benchmark for further theoretical studies, in support to the simulation
approach, of self-assembly in model colloidal systems.",1505.06952v1
2015-06-07,Temperature dependent three-dimensional anisotropy of the magnetoresistance in WTe$_2$,"Extremely large magnetoresistance (XMR) was recently discovered in WTe$_2$,
triggering extensive research on this material regarding the XMR origin. Since
WTe$_2$ is a layered compound with metal layers sandwiched between adjacent
insulating chalcogenide layers, this material has been considered to be
electronically two-dimensional (2D). Here we report two new findings on
WTe$_2$: (1) WTe$_2$ is electronically 3D with a mass anisotropy as low as $2$,
as revealed by the 3D scaling behavior of the resistance
$R(H,\theta)=R(\varepsilon_\theta H)$ with $\varepsilon_\theta =(\cos^2 \theta
+ \gamma^{-2}\sin^2 \theta)^{1/2}$, $\theta$ being the magnetic field angle
with respect to c-axis of the crystal and $\gamma$ being the mass anisotropy;
(2) the mass anisotropy $\gamma$ varies with temperature and follows the
magnetoresistance behavior of the Fermi liquid state. Our results not only
provide a general scaling approach for the anisotropic magnetoresistance but
also are crucial for correctly understanding the electronic properties of
WTe$_2$, including the origin of the remarkable 'turn-on' behavior in the
resistance versus temperature curve, which has been widely observed in many
materials and assumed to be a metal-insulator transition.",1506.02214v2
2015-07-18,Tensor anisotropy as a tracer of cosmic voids,"We present a new method to find voids in cosmological simulations based on
the tidal and the velocity shear tensors definitions of the cosmic web. We use
the fractional anisotropy (FA) computed from the eigenvalues of each web scheme
as a void tracer. We identify voids using a watershed transform based on the
local minima of the FA field without making any assumption on the shape or
structure of the voids. We test the method on the Bolshoi simulation and report
on the abundance and radial averaged profiles for the density, velocity and
fractional anisotropy. We find that voids in the velocity shear web are smaller
than voids in the tidal web, with a particular overabundance of very small
voids in the inner region of filaments/sheets. We classify voids as
subcompensated/overcompansated depending on the absence/presence of an
overdense matter ridge in their density profile, finding that close to $65\%$
and $35\%$ of the total population are classified into each category,
respectively. Finally, we find evidence for the existence of universal profiles
from the radially averaged profiles for density, velocity and fractional
anisotropy. This requires that the radial coordinate is normalized to the
effective radius of each void. Put together, all these results show that the FA
is a reliable tracer for voids, which can be used in complementarity to other
existing methods and tracers.",1507.05178v1
2015-08-06,Crossing Statistics of Anisotropic Stochastic Surface,"In this paper, we propose crossing statistics and its generalization, as a
new framework to characterize the anisotropy in a 2D field, e.g. height on a
surface, extendable to higher dimensions. By measuring $\nu^+$, the number of
up-crossing (crossing points with positive slope at a given threshold of height
($\alpha$)), and $N_{tot}$ (the generalized roughness function), it is possible
to distinguish the nature of anisotropy, rotational invariance and Gaussianity
of any given surface. For the case of anisotropic correlated self- or
multi-affine surfaces (even with different correlation lengths in various
directions and/or directional scaling exponents), we analytically derive some
relations between $\nu^+$ and $N_{tot}$ with corresponding scaling parameters.
The method systematically distinguishes the directions of anisotropy, at
$3\sigma$ confidence interval using P-value statistics. After applying a
typical method in determining the corresponding scaling exponents in identified
anisotropic directions, we are able to determine the kind and ratio of
correlation length anisotropy. To demonstrate capability and accuracy of the
method, as well validity of analytical relations, our proposed measures are
calculated on synthetic stochastic rough interfaces and rough interfaces
generated from simulation of ion etching. There are good consistencies between
analytical and numerical computations. The proposed algorithm can be mounted
with a simple software on various instruments for surface analysis and
characterization, such as AFM, STM and etc.",1508.01409v2
2015-08-26,Order and excitations in large-$S$ kagomé-lattice antiferromagnets,"We systematically investigate the ground-state and the spectral properties of
antiferromagnets on a kagom\'{e} lattice with several common types of the
planar anisotropy: $XXZ$, single-ion, and out-of-plane Dzyaloshinskii-Moriya.
Our main focus is on the role of nonlinear, anharmonic terms, which are
responsible for the quantum order-by-disorder effect and for the corresponding
selection of the ground-state spin structure in many of these models. The $XXZ$
and the single-ion anisotropy models exhibit a quantum phase transition between
the ${\bf q}\!=\!0$ and the $\sqrt{3}\times\!\sqrt{3}$ states as a function of
the anisotropy parameter, offering a rare example of the quantum
order-by-disorder fluctuations favoring a ground state which is different from
the one selected by thermal fluctuations. The nonlinear terms are also shown to
be crucial for a very strong near-resonant decay phenomenon leading to the
quasiparticle breakdown in the kagom\'{e}-lattice antiferromagnets whose
spectra are featuring flat or weakly dispersive modes. The effect is shown to
persist even in the limit of large spin values and should be common to other
frustrated magnets with flat branches of excitations. Model calculations of the
spectrum of the $S=5/2$ Fe-jarosite with Dzyaloshinskii-Moriya anisotropy
provide a convincing and detailed characterization of the proposed scenario.",1508.06632v2
2015-09-01,Magnon-driven longitudinal spin Seebeck effect in F|N and N|F|N structures: role of asymmetric in-plane magnetic anisotropy,"The influence of an asymmetric in-plane magnetic anisotropy on the thermally
activated spin current is studied theoretically for two different systems; (i)
the system consisting of a ferromagnetic insulator in a direct contact with a
nonmagnetic metal, and the sandwich structure consisting of a ferromagnetic
insulating part sandwiched between two nonmagnetic metals. It is shown that
when the difference between the temperatures of the two nonmagnetic metals in a
structure is not large, the spin pumping currents from the magnetic part to the
nonmagnetic ones are equal in amplitude and have opposite directions, so only
the spin torque current contributes to the total spin current. The spin current
flows then from the nonmagnetic metal with the higher temperature to the
nonmagnetic metal having a lower temperature. Its amplitude varies linearly
with the difference in temperatures. In addition, we have found that if the
magnetic anisotropy is in the layer plane, then the spin current increases with
the magnon temperature, while in the case of an out-of-plane magnetic
anisotropy the spin current decreases when the magnon temperature enhances.
Enlarging the difference between the temperatures of the nonmagnetic metals,
the linear response becomes important, as confirmed by analytical expressions
inferred from the Fokker-Planck approach and by the results obtained upon a
full numerical integration of the stochastic Landau-Lifshitz-Gilbert equation.",1509.00376v1
2015-10-08,Statistical anisotropy and cosmological quantum relaxation,"We show that cosmological quantum relaxation predicts an anisotropic
primordial power spectrum with a specific dependence on wavenumber k. We
explore some of the consequences for precision measurements of the cosmic
microwave background (CMB). Quantum relaxation is a feature of the de
Broglie-Bohm pilot-wave formulation of quantum theory, which allows the
existence of more general physical states that violate the Born probability
rule. Recent work has shown that relaxation to the Born rule is suppressed for
long-wavelength field modes on expanding space, resulting in a large-scale
power deficit with a characteristic inverse-tangent dependence on k. Because
the quantum relaxation dynamics is independent of the direction of the wave
vector for the relaxing field mode, in the limit of weak anisotropy we are able
to derive an expression for the anisotropic power spectrum that is determined
by the power deficit function. As a result, the off-diagonal terms in the CMB
covariance matrix are also determined by the power deficit. We show that the
lowest-order l-(l+1) inter-multipole correlations have a characteristic scaling
with multipole moment l. Our derived spectrum also predicts a residual
statistical anisotropy at small scales, with an approximate consistency
relation between the scaling of the l-(l+1) correlations and the scaling of the
angular power spectrum at high l. We also predict a relationship between the
l-(l+1) correlations at large and small scales. Cosmological quantum relaxation
appears to provide a single physical mechanism that predicts both a large-scale
power deficit and a range of statistical anisotropies, together with
potentially testable relationships between them.",1510.02523v1
2015-12-28,Monolayer Molybdenum Disulfide Nanoribbons with High Optical Anisotropy,"Two-dimensional Molybdenum Disulfide (MoS2) has shown promising prospects for
the next generation electronics and optoelectronics devices. The monolayer MoS2
can be patterned into quasi-one-dimensional anisotropic MoS2 nanoribbons
(MNRs), in which theoretical calculations have predicted novel properties.
However, little work has been carried out in the experimental exploration of
MNRs with a width of less than 20 nm where the geometrical confinement can lead
to interesting phenomenon. Here, we prepared MNRs with width between 5 nm to 15
nm by direct helium ion beam milling. High optical anisotropy of these MNRs is
revealed by the systematic study of optical contrast and Raman spectroscopy.
The Raman modes in MNRs show strong polarization dependence. Besides that the
E' and A'1 peaks are broadened by the phonon-confinement effect, the modes
corresponding to singularities of vibrational density of states are activated
by edges. The peculiar polarization behavior of Raman modes can be explained by
the anisotropy of light absorption in MNRs, which is evidenced by the polarized
optical contrast. The study opens the possibility to explore
quasione-dimensional materials with high optical anisotropy from isotropic 2D
family of transition metal dichalcogenides.",1512.08338v1
2016-02-04,Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A comparative study,"New classes two-dimensional (2D) materials beyond graphene, including layered
and non-layered, and their heterostructures, are currently attracting
increasing interest due to their promising applications in nanoelectronics,
optoelectronics and clean energy, where thermal transport property is one of
the fundamental physical parameters. In this paper, we systematically
investigated the phonon transport properties of 2D orthorhombic group IV-VI
compounds of $GeS$, $GeSe$, $SnS$ and $SnSe$ by solving the Boltzmann transport
equation (BTE) based on first-principles calculations. Despite the similar
puckered (hinge-like) structure along the armchair direction as phosphorene,
the four monolayer compounds possess diverse anisotropic properties in many
aspects, such as phonon group velocity, Young's modulus and lattice thermal
conductivity ($\kappa$), etc. Especially, the $\kappa$ along the zigzag and
armchair directions of monolayer $GeS$ shows the strongest anisotropy while
monolayer $SnS$ and $SnSe$ shows an almost isotropy in phonon transport. The
origin of the diverse anisotropy is fully studied and the underlying mechanism
is discussed in detail. With limited size, the $\kappa$ could be effectively
lowered, and the anisotropy could be effectively modulated by nanostructuring,
which would extend the applications in nanoscale thermoelectrics and thermal
management. Our study offers fundamental understanding of the anisotropic
phonon transport properties of 2D materials, and would be of significance for
further study, modulation and aplications in emerging technologies.",1602.01766v2
2016-03-07,Cyclotron maser emission from power-law electrons with strong pitch-angle anisotropy,"Energetic electrons with power-law spectrum are most commonly observed in
astrophysics. This paper investigates electron cyclotron maser emission (ECME)
from the power-law electrons, in which strong pitch-angle anisotropy is
emphasized. The electron distribution function proposed in this paper can
describe various types of pitch-angle anisotropy. Results show that the
emission properties of ECME, including radiation growth, propagation, and
frequency properties, depend considerably on the types of electron pitch-angle
anisotropy, and different wave modes show different dependences on the pitch
angle of electrons. In particular, the maximum growth rate of X2 mode rapidly
decreases with respect to the electron pitch-angle cosine $\mu_0$ at which the
electron distribution peaks, while the growth rates for other modes (X1, O1,
O2) initially increase before decreasing as $\mu_0$ increases. Moreover, the O
mode as well as the X mode can be the fastest growth mode, in terms of not only
the plasma parameter but also the type of electron pitch-angle distribution.
This result presents a significant extension of the recent researches on ECME
driven by the lower-energy cutoff of power-law electrons, in which the X mode
is generally the fastest growth mode.",1603.01923v1
2016-03-10,ALICE overview,"Recent results from the ALICE experiment are presented with a particular
emphasis on particle identification, the nuclear modification factor ($R_{AA}$)
and azimuthal anisotropy ($v_2$). Comparison of lead-lead and proton-lead
results reveals evidence of collectivity in small systems.",1603.03320v1
2016-03-15,"Anisotropic, multi-carrier transport at the (111) LaAlO$_3$/SrTiO$_3$ interface","The conducting gas that forms at the interface between LaAlO$_3$ and
SrTiO$_3$ has proven to be a fertile playground for a wide variety of physical
phenomena. The bulk of previous research has focused on the (001) and (110)
crystal orientations. Here we report detailed measurements of the
low-temperature electrical properties of (111) LAO/STO interface samples. We
find that the low-temperature electrical transport properties are highly
anisotropic, in that they differ significantly along two mutually orthogonal
crystal orientations at the interface. While anisotropy in the resistivity has
been reported in some (001) samples and in (110) samples, the anisotropy in the
(111) samples reported here is much stronger, and also manifests itself in the
Hall coefficient as well as the capacitance. In addition, the anisotropy is not
present at room temperature and at liquid nitrogen temperatures, but only at
liquid helium temperatures and below. The anisotropy is accentuated by exposure
to ultraviolet light, which disproportionately affects transport along one
surface crystal direction. Furthermore, analysis of the low-temperature Hall
coefficient and the capacitance as a function of back gate voltage indicates
that in addition to electrons, holes contribute to the electrical transport.",1603.04538v2
2016-04-29,Polarization of thermal bremsstrahlung emission due to electron pressure anisotropy,"Astrophysical plasmas are typically magnetized, with the Larmor radii of the
charged particles many orders of magnitude smaller than their collisional mean
free paths. The fundamental properties of such plasmas, e.g., conduction and
viscosity, may depend on the instabilities driven by the anisotropy of the
particle distribution functions and operating at scales comparable to the
Larmor scales. We discuss a possibility that the pressure anisotropy of thermal
electrons could produce polarization of thermal bremsstrahlung emission. In
particular, we consider coherent large-scale motions in galaxy clusters to
estimate the level of anisotropy driven by stretching of the magnetic-field
lines by plasma flow and by heat fluxes associated with thermal gradients. Our
estimate of the degree of polarization is $\sim 0.1 \%$ at energies $\gtrsim
kT$. While this value is too low for the forthcoming generation of X-ray
polarimeters, it is potentially an important proxy for the processes taking
place at extremely small scales, which are impossible to resolve spatially. The
absence of the effect at the predicted level may set a lower limit on the
electron collisionality in the ICM. At the same time, the small value of the
effect implies that it does not preclude the use of clusters as (unpolarized)
calibration sources for X-ray polarimeters at this level of accuracy.",1604.08669v2
2016-05-06,Testing lowered isothermal models with direct N-body simulations of globular clusters,"Several self-consistent models have been proposed, aiming at describing the
phase space distribution of stars in globular clusters. This study explores the
ability of the recently proposed LIMEPY models (Gieles & Zocchi) to reproduce
the dynamical properties of direct N-body models of a cluster in a tidal field,
during its entire evolution. These dynamical models include prescriptions for
the truncation and the degree of radially-biased anisotropy contained in the
system, allowing us to explore the interplay between the role of anisotropy and
tides in various stages of the life of star clusters. We show that the amount
of anisotropy in an initially tidally underfilling cluster increases in the
pre-collapse phase, and then decreases with time, due to the effect of the
external tidal field on its spatial truncation. This is reflected in the
correspondent model parameters, and the best-fit models reproduce the main
properties of the cluster at all stages of its evolution, except for the phases
immediately preceding and following core collapse. We also notice that the
best-fit LIMEPY models are significantly different from isotropic King models,
especially in the first part of the evolution of the cluster. Our results put
limits on the amount of radial anisotropy that can be expected for clusters
evolving in a tidal field, which is important to understand other factors that
could give rise to similar observational signatures, such as the presence of an
intermediate-mass black hole.",1605.02032v1
2016-05-22,Low Gilbert damping in Co2FeSi and Fe2CoSi films,"Thin highly textured Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si ($0 \leq$ x
$\leq 1$) films were prepared on MgO (001) substrates by magnetron
co-sputtering. The magneto-optic Kerr effect (MOKE) and ferromagnetic resonance
(FMR) measurements were used to investigate the composition dependence of the
magnetization, the magnetic anisotropy, the gyromagnetic ratio and the
relaxation of the films. The effective magnetization for the thin
Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films, determined by FMR measurements,
are consistent with the Slater Pauling prediction. Both MOKE and FMR
measurements reveal a pronounced fourfold anisotropy distribution for all
films. In addition we found a strong influence of the stoichiometry on the
anisotropy as the cubic anisotropy strongly increases with increasing Fe
concentration. The gyromagnetic ratio is only weakly dependent on the
composition. We find low Gilbert damping parameters for all films with values
down to $0.0012\pm0.00012$ for Fe$_{1.75}$Co$_{1.25}$Si. The effective damping
parameter for Co$_2$FeSi is found to be $0.0018\pm 0.0004$. We also find a
pronounced anisotropic relaxation, which indicates significant contributions of
two-magnon scattering processes that is strongest along the easy axes of the
films. This makes thin Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films ideal
materials for the application in STT-MRAM devices.",1605.06797v1
2016-06-01,Monte Carlo analysis for finite temperature magnetism of Nd$_2$Fe$_{14}$B permanent magnet,"We investigate the effects of magnetic inhomogeneities and thermal
fluctuations on the magnetic properties of a rare earth intermetallic compound,
Nd$_2$Fe$_{14}$B. The constrained Monte Carlo method is applied to a
Nd$_2$Fe$_{14}$B bulk system to realize the experimentally observed spin
reorientation and magnetic anisotropy constants $K^{\rm A}_m (m=1, 2, 4)$ at
finite temperatures. % Subsequently, it is found that the temperature
dependence of $K^{\rm A}_1$ deviates from the Callen--Callen law, $K^{\rm
A}_1(T) \propto M(T)^3$, even above room temperature, $T_{\rm R}\sim 300\rm\,
K$, when the Fe (Nd) anisotropy terms are removed to leave only the Nd (Fe)
anisotropy terms. This is because the exchange couplings between Nd moments and
Fe spins are much smaller than those between Fe spins. % It is also found that
the exponent $n$ in the external magnetic field $H_{\rm ext}$ response of
barrier height $\mathcal{F}_{\rm B}=\mathcal{F}_{\rm B}^0(1-H_{\rm ext}/H_0)^n$
is less than $2$ in the low-temperature region below $T_{\rm R}$, whereas $n$
approaches $2$ when $T>T_{\rm R}$, indicating the presence of
Stoner--Wohlfarth-type magnetization rotation. This reflects the fact that the
magnetic anisotropy is mainly governed by the $K^{\rm A}_1$ term in the
$T>T_{\rm R}$ region.",1606.00333v2
2016-06-27,Blume-Capel ferromagnet driven by propagating and standing magnetic field wave: Dynamical modes and nonequilibrium phase transition,"The dynamical responses of Blume-Capel (S=1) ferromagnet to the plane
propagating (with fixed frequency and wavelength) and standing magnetic field
waves are studied sepa- rately in two dimensions by extensive Monte Carlo
simulation. Depending on the values of temperature, amplitude of the
propagating magnetic field and the strength of anisotropy, two different
dynamical phases are observed. For a fixed value of anisotropy and the
amplitude of the propagating magnetic field, the system undergoes a dynamical
phase transition from a driven spin wave propagating phase to a pinned or spin
frozen state as the system is cooled down. The time averaged magnetisation over
a full cycle of the propagating magnetic field plays the role of the dynamic
order parameter. A comprehensive phase diagram is plotted in the plane formed
by the amplitude of the propagating wave and the temperature of the system. It
is found that the phase boundary shrinks inward as the anisotropy increases.
The phase boundary, in the plane described by the strength of the anisotropy
and temperature, is also drawn. This phase boundary was observed to shrink
inward as the field amplitude increases.",1606.08155v3
2016-07-26,Pseudospin anisotropy of trilayer semiconductor quantum Hall ferromagnets,"When two Landau levels are brought to a close coincidence between them and
with the chemical potential in the Integer Quantum Hall regime, the two Landau
levels can just cross or collapse while the external or pseudospin field that
induces the alignment changes. In this work, all possible crossings are
analyzed theoretically for the particular case of semiconductor trilayer
systems, using a variational Hartree-Fock approximation. The model includes
tunneling between neighboring layers, bias, intra-layer and inter-layer Coulomb
interaction among the electrons. We have found that the general pseudospin
anisotropy classification scheme used in bilayers applies also to the trilayer
situation, with the simple crossing corresponding to an easy-axis ferromagnetic
anisotropy analogy, and the collapse case corresponding to an easy-plane
ferromagnetic analogy. An isotropic case is also possible, with the levels just
crossing or collapsing depending on the filling factor and the quantum numbers
of the two nearby levels. While our results are valid for any integer filling
factor $\nu$ (=1,2,3,...), we have analyzed in detail the crossings at $\nu=3$
and $4$, and we have given clear predictions that will help in their
experimental search. In particular, the present calculations suggest that by
increasing the bias, the trilayer system at these two filling factors can be
driven from an easy-plane anisotropy regime to an easy-axis regime, and then
can be driven back to the easy-plane regime. This kind of reentrant behavior is
an unique feature of the trilayers, compared with the bilayers.",1607.07909v1
2016-09-18,Cosmological constraints from the redshift dependence of the Alcock-Paczynski effect: application to the SDSS-III BOSS DR12 galaxies,"We apply the methodology developed in \cite{Li2014,Li2015} to BOSS DR12
galaxies and derive cosmological constraints from the redshift dependence of
the Alcock-Paczynski (AP) effect. The apparent anisotropy in the distribution
of observed galaxies arise from two main sources, the redshift-space distortion
(RSD) effect due to the galaxy peculiar velocities, and the geometric
distortion when incorrect cosmological models are assumed for transforming
redshift to comoving distance, known as the AP effect. Anisotropies produced by
the RSD effect are, although large, maintaining a nearly uniform magnitude over
a large range of redshift, while the degree of anisotropies from the AP effect
varies with redshift by much larger magnitude. We split the DR12 galaxies into
six redshift bins, measure the 2-point correlation function in each bin, and
assess the redshift evolution of anisotropies. We obtain constraints of
$\Omega_m=0.290 \pm 0.053,\ \ w = -1.07 \pm 0.15$, which are comparable with
the current constraints from other cosmological probes such as type Ia
supernovae, cosmic microwave background, and baryon acoustic oscillation (BAO).
Combining these cosmological probes with our method yield tight constraints of
$ \Omega_m = 0.301 \pm 0.006,\ w=-1.054 \pm 0.025$. Our method is complementary
to the other large scale structure probes like BAO and topology. We expect this
technique will play an important role in deriving cosmological constraints from
large scale structure surveys.",1609.05476v1
2016-09-25,Effects of anisotropy and Coulomb interactions on quantum transport in a quadruple quantum-dot structure,"We present analytical and numerical investigation of spectral and transport
properties of a quadruple quantum-dot (QQD) structure which is one of the
popular low-dimensional systems in the context of fundamental quantum physics
study, future electronic applications and quantum calculations. The density of
states, occupation numbers and conductance of the structure were analyzed using
the nonequilibrium Green's functions in the tight binding approach and the
equation-of-motion method. In particular the anisotropy of hopping integrals
and on-site electron energies as well as the effects of the finite intra- and
interdot Coulomb interactions were investigated. It was found out that the
anisotropy of the kinetic processes in the system leads to the Fano-Feshbach
asymmetrical peak. We demonstrated that the conductance of QQD device has a
wide insulating band with steep edges separating triple-peak structures if the
intradot Coulomb interactions are taken into account. The interdot Coulomb
correlations between the central QDs result in the broadening of this band and
the occurrence of an additional band with low conductance due to the Fano
antiresonances. It was shown that in this case the conductance of the
anisotropic QQD device can be dramatically changed by tuning the anisotropy of
on-site electron energies.",1609.07760v1
2016-10-17,Can we reconcile the TA excess and hotspot with Auger observations?,"The Telescope Array (TA) shows a 20$^{\circ}$ hotspot as well as an excess of
UHECRs above 50~EeV when compared with the Auger spectrum. We consider the
possibility that both the TA excess and hotspot are due to a dominant source in
the Northern sky. We carry out detailed simulations of UHECR propagation in
both the intergalactic medium and the Galaxy, using different values for the
intergalactic magnetic field. We consider two general classes of sources:
transients and steady, adopting a mixed UHECR composition that is consistent
with the one found by Auger. The spatial location of the sources is draw
randomly. We generate Auger-like and TA-like data sets from which we determine
the spectrum, the sky maps and the level of anisotropy. We find that, while
steady sources are favored over transients, it is unlikely to account for all
the currently available observational data. While we reproduce fairly well the
Auger spectrum for the vast majority of the simulated data sets, most of the
simulated data sets with a spectrum compatible with that of TA (at most a few
percent depending on density model tested) show a much stronger anisotropy than
the one observed. We find that the rare cases in which both the spectrum and
the anisotropy are consistent require a steady source within $\sim 10$ Mpc, to
account for the flux excess, and a strong extragalactic magnetic field $\sim
10$ nG, to reduce the excessive anisotropy.",1610.05319v2
2016-12-23,Testing parity-violating physics from cosmic rotation power reconstruction,"We study the reconstruction of the cosmic rotation power spectrum produced by
parity-violating physics, with an eye to ongoing and near future cosmic
microwave background (CMB) experiments such as BICEP Array, CMBS4, LiteBIRD and
Simons Observatory. In addition to the inflationary gravitational waves and
gravitational lensing, measurements of other various effects on CMB
polarization open new window into the early Universe. One of these is
anisotropies of the cosmic polarization rotation which probes the Chern-Simons
term generally predicted by string theory. The anisotropies of the cosmic
rotation are also generated by the primordial magnetism and in the Standard
Model extention framework. The cosmic rotation anisotropies can be
reconstructed as quadratic in CMB anisotropies. However, the power of the
reconstructed cosmic rotation is a CMB four-point correlation and is not
directly related to the cosmic-rotation power spectrum. Understanding all
contributions in the four-point correlation is required to extract the cosmic
rotation signal. Assuming a scale-invariant rotation spectrum motivated by the
inflationary cosmic-rotation models, we employ simulation to quantify each
contribution to the four-point correlation and find that (1) a secondary
contraction of the trispectrum increases the total signal-to-noise, (2) a bias
from the lensing-induced trispectrum is significant compared to the statistical
errors in, e.g., LiteBIRD and CMBS4-like experiments, (3) the use of a
realization-dependent estimator decreases the statistical errors by 10%-20%,
depending on experimental specifications, and (4) other higher-order
contributions are negligible at least for near future experiments.",1612.07855v3
2017-03-03,A nonlinear Monte Carlo model of super-diffusive shock acceleration with magnetic field amplification,"Fast collisionless shocks in cosmic plasmas convert their kinetic energy flow
into the hot downstream thermal plasma with a substantial fraction of energy
going into a broad spectrum of superthermal charged particles and magnetic
fluctuations. The superthermal particles can penetrate into the shock upstream
region producing an extended shock precursor. The cold upstream plasma flow is
decelerated by the force provided by the superthermal particle pressure
gradient. In high Mach number collisionless shocks, efficient particle
acceleration is likely coupled with turbulent magnetic field amplification
(MFA) generated by the anisotropic distribution of accelerated particles. This
anisotropy is determined by the fast particle transport making the problem
strongly nonlinear and multi-scale. Here, we present a nonlinear Monte Carlo
model of collisionless shock structure with super-diffusive propagation of
high-energy Fermi accelerated particles coupled to particle acceleration and
MFA which affords a consistent description of strong shocks. A distinctive
feature of the Monte Carlo technique is that it includes the full angular
anisotropy of the particle distribution at all precursor positions. The model
reveals that the super-diffusive transport of energetic particles (i.e.,
Levy-walk propagation) generates a strong quadruple anisotropy in the precursor
particle distribution. The resultant pressure anisotropy of the high-energy
particles produces a non-resonant mirror-type instability which amplifies
compressible wave modes with wavelengths longer than the gyroradii of the
highest energy protons produced by the shock.",1703.01160v2
2017-03-24,Effects of anisotropy in spin molecular-orbital coupling on effective spin models of trinuclear organometallic complexes,"We consider layered decorated honeycomb lattices at two-thirds filling, as
realized in some trinuclear organometallic complexes. Localized $S=1$ moments
with a single-spin anisotropy emerge from the interplay of Coulomb repulsion
and spin molecular-orbit coupling (SMOC). Magnetic anisotropies with bond
dependent exchange couplings occur in the honeycomb layers when the direct
intracluster exchange and the spin molecular-orbital coupling are both present.
We find that the effective spin exchange model within the layers is an XXZ +
120$^\circ$ honeycomb quantum compass model. The intrinsic non-spherical
symmetry of the multinuclear complexes leads to very different transverse and
longitudinal spin molecular-orbital couplings, which greatly enhances the
single-spin and exchange coupling anisotropies. The interlayer coupling is
described by a XXZ model with anisotropic biquadratic terms. As the correlation
strength increases the systems becomes increasingly one-dimensional. Thus, if
the ratio of SMOC to the interlayer hopping is small this stabilizes the
Haldane phase. However, as the ratio increases there is a quantum phase
transition to the topologically trivial `$D$-phase'. We also predict a quantum
phase transition from a Haldane phase to a magnetically ordered phase at
sufficiently strong external magnetic fields.",1703.08343v3
2017-03-30,Anisotropy governed competition of magnetic phases in the honeycomb quantum magnet Na$_3$Ni$_2$SbO$_6$ studied by dilatometry and high-frequency ESR,"Thermodynamic properties as well as low-energy magnon excitations of $S=1$
honeycomb-layered Na$_3$Ni$_2$SbO$_6$ have been investigated by high-resolution
dilatometry, static magnetisation, and high-frequency electron spin resonance
studies in magnetic fields up to 16 T. At $T_{\rm N}$ = 16.5 K, there is a
tricritical point separating two distinct antiferromagnetic phases AF1 and AF2
from the paramagnetic regime. In addition, our data imply short-range
antiferromagnetic correlations at least up to $\sim 5\cdot T_{\rm N}$. Well
below $T_{\rm N}$, the magnetic field $B_{\rm C1}\approx$ 9.5 T is needed to
stabilize AF2 against AF1. The thermal expansion and magnetostriction anomalies
at $T_{\rm N}$ and $B_{\rm C1}$ imply significant magnetoelastic coupling, both
of which associated with a sign change of $\partial L/\partial B$. The
transition at $B_{\rm C1}$ is associated with softening of the
antiferromagnetic resonance modes observed in the electron spin resonance
spectra. The anisotropy gap $\Delta = 360$ GHz implies considerable uniaxial
anisotropy. We conclude the crucial role of axial anisotropy favoring the AF1
spin structure over the AF2 one. While the magnetostriction data disprove a
simple spin-flop scenario at $B_{\rm C1}$, the nature of a second transition at
$B_{\rm C2}\approx$ 13 T remains unclear. Both the sign of the magnetostriction
and Gr\""uneisen analysis suggest the short-range correlations at high
temperatures to be of AF2-type.",1703.10493v1
2017-04-22,Dark Energy Induced Anisotropy in Cosmic Expansion,"In order to understand the nature of the accelerating expansion of the
late-time universe, it is important to experimentally determine whether dark
energy is a cosmological constant or dynamical in nature. If dark energy
already exists prior to inflation, which is a reasonable assumption, then one
expects that a dynamical dark energy would leave some footprint in the
anisotropy of the late-time accelerated expansion. To demonstrate the viability
of this notion, we invoke the quintessence field with the exponential potential
as one of the simplest dynamical dark energy models allowed by observations. We
investigate the effects of its quantum fluctuations (the physical origin of the
perturbation being isocurvature) generated during inflation and having fully
positive correlation with the primordial curvature perturbations, and estimate
the anisotropy of the cosmic expansion so induced. We show that the primordial
amplitude of quantum fluctuations of quintessence field {\delta\phi}_P can be
related to the tensor-to-scalar ratio r, and we calculate the perturbed
luminosity distance to first order and the associated luminosity distance power
spectrum, which is an estimator of anisotropicity of late-time accelerated
expansion. We find that the gravitational potential at large scales and late
times is less decayed in QCDM compared to that in {\Lambda}CDM so that the
smaller the redshift and multipole, the more relative deficit of power in QCDM.
Our results of luminosity distance power spectrum also show the similar
conclusions of suppression as that of the previous investigation regarding the
effect of quantum fluctuations of quintessence field on the CMB temperature
anisotropies.",1704.06797v2
2017-05-03,Quantum phase transitions driven by rhombic-type single-ion anisotropy in the S=1 Haldane chain,"The spin-1 Haldane chain is an example of the symmetry-protected-topological
(SPT) phase in one dimension. Experimental realization of the spin chain
materials usually involves both the uniaxial-type, $D(S^z)^2$, and the
rhombic-type, $E[(S^x)^2-(S^y)^2]$, single-ion anisotropies. Here, we provide a
precise ground-state phase diagram for spin-1 Haldane chain with these
single-ion anisotropies. Using quantum numbers, we find that the $\mathbb{Z}_2$
symmetry breaking phase can be characterized by double degeneracy in the
entanglement spectrum. Topological quantum phase transitions take place on
particular paths in the phase diagram, from the Haldane phase to the
Large-$E_x$, Large-$E_y$, or Large-$D$ phases. The topological critical points
are determined by the level spectroscopy method with a newly developed parity
technique in the density matrix renormalization group [Phys. Rev. B 86, 024403
(2012)], and the Haldane-Large-$D$ critical point is obtained with an
unprecedentedly precision, $(D/J)_c=0.9684713(1)$. Close to this critical
point, a small rhombic single-ion anisotropy $|E|/J\ll1$ can destroy the
Haldane phase and bring the system into a $y$-N\'eel phase. We propose that the
compound [Ni(HF$_2$)(3-Clpy)$_4$]BF$_4$ is a candidate system to search for the
$y$-N\'eel phase.",1705.01558v2
2017-05-18,Magnetization dynamics and its scattering mechanism in thin CoFeB films with interfacial anisotropy,"Studies of magnetization dynamics have incessantly facilitated the discovery
of fundamentally novel physical phenomena, making steady headway in the
development of magnetic and spintronics devices. The dynamics can be induced
and detected electrically, offering new functionalities in advanced electronics
at the nanoscale. However, its scattering mechanism is still disputed.
Understanding the mechanism in thin films is especially important, because most
spintronics devices are made from stacks of multilayers with nanometer
thickness. The stacks are known to possess interfacial magnetic anisotropy, a
central property for applications, whose influence on the dynamics remains
unknown. Here, we investigate the impact of interfacial anisotropy by adopting
CoFeB/MgO as a model system. Through systematic and complementary measurements
of ferromagnetic resonance (FMR), on a series of thin films, we identify
narrower FMR linewidths at higher temperatures. We explicitly rule out the
temperature dependence of intrinsic damping as a possible cause, and it is also
not expected from existing extrinsic scattering mechanisms for ferromagnets. We
ascribe this observation to motional narrowing, an old concept so far neglected
in the analyses of FMR spectra. The effect is confirmed to originate from
interfacial anisotropy, impacting the practical technology of spin-based
nanodevices up to room temperature.",1705.06624v1
2017-05-14,Prediction of plastic anisotropy of textured polycrystalline sheets based on a new single crystal model,"In this paper, we predict the effect of texture on the anisotropy in plastic
properties of polycrystalline metallic sheets. The constituent grain behavior
is modelled using the new single crystal yield criterion developed by Cazacu,
Revil, and Chandola (2017). For ideal texture components, the yield stress and
plastic strain ratios can be obtained analytically. For the case of strongly
textured sheets containing a spread about the ideal texture components, the
polycrystalline response is obtained numerically on the basis of the same
single-crystal criterion. It is shown that for textures with misorientation
scatter width up to 25 degrees, the numerical predictions are very close to
those obtained analytically for an ideal texture. Furthermore, irrespective of
the number of grains in the sample, Lankford coefficients have finite values
for all loading orientations. Illustrative examples for sheets with textures
containing a combination of few ideal texture components are also presented.
The simulations of the predicted polycrystalline behavior based on the new
description of the plastic behavior of the constituent grains capture the
influence of individual texture components on the overall degree of anisotropy.
The polycrystalline simulation results are also compared to analytical
estimates obtained using the closed-form formulas for the ideal components
present in the texture in conjunction with a simple law of mixtures. The
analytical estimates show the same trends as the simulation results. Therefore,
the trends in plastic anisotropy of the macroscopic properties can be
adequately estimated analytically.",1705.10018v1
2017-06-29,Island dynamics and anisotropy during vapor phase epitaxy of m-plane GaN,"Using in situ grazing-incidence x-ray scattering, we have measured the
diffuse scattering from islands that form during layer-by-layer growth of GaN
by metal-organic vapor phase epitaxy on the (1010) m-plane surface. The diffuse
scattering is extended in the (0001) in-plane direction in reciprocal space,
indicating a strong anisotropy with islands elongated along [1 $\overline{2}$
10] and closely spaced along [0001]. This is confirmed by atomic force
microscopy of a quenched sample. Islands were characterized as a function of
growth rate G and temperature. The island spacing along [0001] observed during
the growth of the first monolayer obeys a power-law dependence on growth rate
G$^{-n}$, with an exponent $n = 0.25 \pm 0.02$. Results are in agreement with
recent kinetic Monte Carlo simulations, indicating that elongated islands
result from the dominant anisotropy in step edge energy and not from surface
diffusion anisotropy. The observed power-law exponent can be explained using a
simple steady-state model, which gives n = 1/4.",1706.09955v1
2017-07-04,Can we reconcile the TA excess and hotspot with Auger observations?,"The Telescope Array (TA) shows a 20$^{\circ}$ hotspot as well as an excess of
UHECRs above 50~EeV when compared with the Auger spectrum. We consider the
possibility that both the TA excess and hotspot are due to a dominant source in
the Northern sky. We carry out detailed simulations of UHECR propagation in
both the intergalactic medium and the Galaxy, using different values for the
intergalactic magnetic field. We consider two general classes of sources:
transients and steady, adopting a mixed UHECR composition that is consistent
with the one found by Auger. The spatial location of the sources is draw
randomly. We generate Auger-like and TA-like data sets from which we determine
the spectrum, the sky maps and the level of anisotropy. We find that, while
steady sources are favored over transients, it is unlikely to account for all
the currently available observational data. While we reproduce fairly well the
Auger spectrum for the vast majority of the simulated data sets, most of the
simulated data sets with a spectrum compatible with that of TA (at most a few
percent depending on density model tested) show a much stronger anisotropy than
the one observed. We find that the rare cases in which both the spectrum and
the anisotropy are consistent require a steady source within $\sim 10$ Mpc, to
account for the flux excess, and a strong extragalactic magnetic field $\sim
10$ nG, to reduce the excessive anisotropy.",1707.01177v2
2017-07-10,The Kinematic Richness of Star Clusters I. Isolated Spherical Models with Primordial Anisotropy,"We investigate the dynamical evolution of isolated equal-mass star cluster
models by means of direct N-body simulations, primarily focusing on the effects
of the presence of primordial anisotropy in the velocity space. We found
evidence of the existence of a monotonic relationship between the moment of
core collapse and the amount and flavour of anisotropy in the stellar system.
Specifically, equilibria characterised by the same initial structural
properties (Plummer density profile) and with different degrees of
tangentially-biased (radially-biased) anisotropy, reach core collapse earlier
(later) than isotropic models. We interpret this result in light of an
accelerated (delayed) phase of the early evolution of collisional stellar
systems ""anisotropic-response""), which we have characterised both in terms of
the evolution of the velocity moments and of a fluid model of two-body
relaxation. For the case of the most tangentially anisotropic model the initial
phase of evolution involves a catastrophic collapse of the inner part of the
system which continues until an isotropic velocity distribution is reached.
This study represents a first step towards a comprehensive investigation of the
role played by kinematic richness in the long-term dynamical evolution of
collisional systems.",1707.02792v1
2017-07-11,Planck 2015 constraints on the non-flat $Λ$CDM inflation model,"We study Planck 2015 cosmic microwave background (CMB) anisotropy data using
the energy density inhomogeneity power spectrum generated by quantum
fluctuations during an early epoch of inflation in the non-flat $\Lambda$CDM
model. Unlike earlier analyses of non-flat models, which assumed an
inconsistent power-law power spectrum of energy density inhomogeneities, we
find that the Planck 2015 data alone, and also in conjunction with baryon
acoustic oscillation measurements, are reasonably well fit by a closed
$\Lambda$CDM model in which spatial curvature contributes a few percent of the
current cosmological energy density budget. In this model, the measured Hubble
constant and non-relativistic matter density parameter are in good agreement
with values determined using most other data. Depending on parameter values,
the closed $\Lambda$CDM model has reduced power, relative to the tilted,
spatially-flat $\Lambda$CDM case, and can partially alleviate the low multipole
CMB temperature anisotropy deficit and can help partially reconcile the CMB
anisotropy and weak lensing $\sigma_8$ constraints, at the expense of somewhat
worsening the fit to higher multipole CMB temperature anisotropy data. Our
results are interesting but tentative; a more thorough analysis is needed to
properly gauge their significance.",1707.03452v2
2017-07-16,First Principles Study of the Giant Magnetic Anisotropy Energy in Bulk Na4IrO4,"In 5d transition metal oxides, novel properties arise from the interplay of
electron correlations and spin--orbit interactions. Na4IrO4, where 5d
transition-metal Ir atom occupies the center of the square-planar coordination
environment, is synthesized. Based on density functional theory, we calculate
its electronic and magnetic properties. Our numerical results show that the
Ir-5d bands are quite narrow, and the bands around the Fermi level are mainly
contributed by d_{xy},d_{yz} and d_{zx} orbitals. The magnetic easy-axis is
perpendicular to the IrO4 plane, and the magnetic anisotropy energy (MAE) of
Na4IrO4 is found to be very giant. We estimate the magnetic parameters by
mapping the calculated total energy for different spin configurations onto a
spin model. The next nearest neighbor exchange interaction J2 is much larger
than other intersite exchange interactions and results in the magnetic ground
state configuration. Our study clearly demonstrates that the huge MAE comes
from the single-ion anisotropy rather than the anisotropic interatomic spin
exchange. This compound has a large spin gap but very narrow spin-wave
dispersion, due to the large single-ion anisotropy and relatively small
exchange couplings. Noticing this remarkable magnetic feature originated from
its highly isolated IrO4 moiety, we also explore the possiblity to further
enhance the MAE.",1707.04865v1
2017-07-27,Two-component Jaffe models with a central black hole. I: the spherical case,"Dynamical properties of spherically symmetric galaxy models where both the
stellar and total mass density distributions are described by the Jaffe (1983)
profile (with different scale-lenghts and masses), are presented. The orbital
structure of the stellar component is described by Osipkov--Merritt anisotropy,
and a black hole (BH) is added at the center of the galaxy; the dark matter
halo is isotropic. First, the conditions required to have a nowhere negative
and monothonically decreasing dark matter halo density profile, are derived. We
then show that the phase-space distribution function can be recovered by using
the Lambert-Euler $W$ function, while in absence of the central BH only
elementary functions appears in the integrand of the inversion formula. The
minimum value of the anisotropy radius for consistency is derived in terms of
the galaxy parameters. The Jeans equations for the stellar component are solved
analytically, and the projected velocity dispersion at the center and at large
radii are also obtained analytically for generic values of the anisotropy
radius. Finally, the relevant global quantities entering the Virial Theorem are
computed analytically, and the fiducial anisotropy limit required to prevent
the onset of Radial Orbit Instability is determined as a function of the galaxy
parameters. The presented models, even though highly idealized, represent a
substantial generalization of the models presentd in Ciotti et al. (2009), and
can be useful as starting point for more advanced modeling the dynamics and the
mass distribution of elliptical galaxies.",1707.08822v2
2017-08-03,Evolution of the interfacial perpendicular magnetic anisotropy constant of the Co$_2$FeAl/MgO interface upon annealing,"We investigate thickness series of films of the Heusler alloy Co$_2$FeAl in
order to study the effect of annealing on the interface with a MgO layer and on
the bulk magnetic properties. Our results reveal that while the perpendicular
interface anisotropy constant $K^{\perp}_{\rm S}$ is zero for the as-deposited
samples, its value increases with annealing up to a value of $1.14\, \pm
\,0.07$~mJ/m$^2$ for the series annealed at 320$^{\rm o}$C and of $2.07\, \pm
\,0.7$~mJ/m$^2$ for the 450$^{\rm o}$C annealed series owing to a strong
modification of the interface during the thermal treatment. This large value
ensures a stabilization of a perpendicular magnetization orientation for a
thickness below 1.7~nm. The data additionally shows that the in-plane biaxial
anisotropy constant has a different evolution with thickness in as-deposited
and annealed systems. The Gilbert damping parameter $\alpha$ shows minima for
all series for a thickness of 40~nm and an absolute minimum value of
$2.8\pm0.1\cdot10^{-3}$. The thickness dependence is explained in terms of an
inhomogenous magnetization state generated by the interplay between the
different anisotropies of the system and by crystalline disorder.",1708.01126v2
2017-08-09,Combined Analysis of Cosmic-Ray Anisotropy with IceCube and HAWC,"During the past two decades, experiments in both the northern and southern
hemispheres have observed a small but measurable energy-dependent sidereal
anisotropy in the arrival direction distribution of Galactic cosmic rays with
relative intensities at the level of one per mille. Individually, these
measurements are restricted by limited sky coverage, and so the power spectrum
of the anisotropy obtained from any one measurement displays a systematic
correlation between different multipole modes $C_\ell$. We present the results
of a joint analysis of the anisotropy on all angular scales using cosmic-ray
data collected during 336 days of operation of the High-Altitude Water
Cherenkov (HAWC) Observatory (located at 19$^\circ$ N) and 5 years of data
taking from the IceCube Neutrino Observatory (located at 90$^\circ$ S) The
results include a combined sky map and an all-sky power spectrum in the
overlapping energy range of the two experiments at around 10 TeV. We describe
the methods used to combine the IceCube and HAWC data, address the individual
detector systematics, and study the region of overlapping field of view between
the two observatories.",1708.03005v1
2017-08-21,Crossover from low-temperature to high-temperature fluctuations. II. Nonuniversal thermodynamic Casimir forces of anisotropic systems,"The finite-size renormalization-group approach for isotropic O$(n)$-symmetric
systems introduced previously [V. Dohm, Phys. Rev. Lett. {\bf 110}, 107207
(2013)] is extended to weakly anisotropic O$(n)$-symmetric systems. Our theory
is formulated within the $\varphi^4$ model with lattice anisotropy in a
$d$-dimensional block geometry with periodic boundary conditions. It describes
the crossover from low- to high-temperature fluctuations including
Goldstone-dominated and critical fluctuations for $1\leq n \leq \infty$ in
$2<d<4$ dimensions. An exact representation is derived for the large-distance
behavior of the bulk correlation function of anisotropic systems in terms of
the principal correlation lengths and an anisotropy matrix ${\bf \bar A}$. This
includes the long-ranged correlations with an anisotropic algebraic decay at
low temperatures due to the Goldstone modes for $n>1$. We calculate the
finite-size scaling functions of the excess free energy and thermodynamic
Casimir force. Exact results are derived in the large-$n$ limit. Applications
are given for $L_\parallel^{d-1} \times L$ slab geometries with a finite aspect
ratio $\rho=L/L_\parallel$ as well as for the film limit $\rho \to 0$. For
weakly anisotropic systems two-scale-factor universality is replaced by
multiparameter universality. This implies a substantial reduction of the
predictive power of bulk and finite-size theory for anisotropic systems as
compared to isotropic systems. The validity of multiparameter universality is
confirmed analytically for a nontrivial example of the $d=2,n=1$ universality
class. Anisotropy-dependent minima of the Casimir force scaling function are
found below $T_c$. Both the sign and magnitude of the Casimir amplitude in the
Goldstone and critical regimes are affected by the lattice anisotropy.
Quantitative predictions are made that can be tested by Monte Carlo
simulations.",1708.06272v1
2017-08-29,Probing the chiral magnetic wave in pPb and PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV using charge-dependent azimuthal anisotropies,"Charge-dependent anisotropy Fourier coefficients ($v_n$) of particle
azimuthal distributions are measured in pPb and PbPb collisions at $
\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV with the CMS detector at the
LHC. The normalized difference in the second-order anisotropy coefficients
($v_2$) between positively and negatively charged particles is found to depend
linearly on the observed event charge asymmetry with comparable slopes for both
pPb and PbPb collisions over a wide range of charged particle multiplicity. In
PbPb, the third-order anisotropy coefficient, $v_3$, shows a similar linear
dependence with the same slope as seen for $v_2$. The observed similarities
between the $v_2$ slopes for pPb and PbPb, as well as the similar slopes for
$v_2$ and $v_3$ in PbPb, are compatible with expectations based on local charge
conservation in the decay of clusters or resonances, and constitute a challenge
to the hypothesis that, at LHC energies, the observed charge asymmetry
dependence of $v_2$ in heavy ion collisions arises from a chiral magnetic wave.",1708.08901v2
2017-08-30,The effect of non-sphericity on mass and anisotropy measurements in dSph galaxies with Schwarzschild method,"In our previous work we confirmed the reliability of the spherically
symmetric Schwarzschild orbit-superposition method to recover the mass and
velocity anisotropy profiles of spherical dwarf galaxies. Here we investigate
the effect of its application to intrinsically non-spherical objects. For this
purpose we use a model of a dwarf spheroidal galaxy formed in a numerical
simulation of a major merger of two disky dwarfs. The shape of the stellar
component of the merger remnant is axisymmetric and prolate which allows us to
identify and measure the bias caused by observing the spheroidal galaxy along
different directions, especially the longest and shortest principal axis. The
modelling is based on mock data generated from the remnant that are
observationally available for dwarfs: projected positions and line-of-sight
velocities of the stars. In order to obtain a reliable tool while keeping the
number of parameters low we parametrize the total mass distribution as a
radius-dependent mass-to-light ratio with just two free parameters we aim to
constrain. Our study shows that if the total density profile is known, the
true, radially increasing anisotropy profile can be well recovered for the
observations along the longest axis whereas the data along the shortest axis
lead to the inference an incorrect, isotropic model. On the other hand, if the
density profile is derived from the method as well, the anisotropy is always
underestimated but the total mass profile is well recovered for the data along
the shortest axis whereas for the longest axis the mass content is
overestimated.",1708.09425v2
2017-09-25,Is perpendicular magnetic anisotropy essential to all-optical ultrafast spin reversal in ferromagnets?,"All-optical spin reversal presents a new opportunity for spin manipulations,
free of a magnetic field. Most of all-optical-spin-reversal ferromagnets are
found to have a perpendicular magnetic anisotropy (PMA), but it has been
unknown whether PMA is necessary for the spin reversal. Here we theoretically
investigate magnetic thin films with either PMA or in-plane magnetic anisotropy
(IMA). Our results show that the spin reversal in IMA systems is possible, but
only with a longer laser pulse and within a narrow laser parameter region. The
spin reversal does not show a strong helicity dependence where the left- and
right-circularly polarized light lead to the identical results. By contrast,
the spin reversal in PMA systems is robust, provided both the spin angular
momentum and laser field are strong enough while the magnetic anisotropy itself
is not too strong. This explains why experimentally the majority of all-optical
spin-reversal samples are found to have strong PMA and why spins in Fe
nanoparticles only cant out of plane. It is the laser-induced spin-orbit torque
that plays a key role in the spin reversal. Surprisingly, the same spin-orbit
torque results in laser-induced spin rectification in spin-mixed configuration,
a prediction that can be tested experimentally. Our results clearly point out
that PMA is essential to the spin reversal, though there is an opportunity for
in-plane spin reversal.",1709.08690v1
2017-09-30,Multi-Scale Pipeline for the Search of String-Induced CMB Anisotropies,"We propose a multi-scale edge-detection algorithm to search for the
Gott-Kaiser-Stebbins imprints of a cosmic string (CS) network on the Cosmic
Microwave Background (CMB) anisotropies. Curvelet decomposition and extended
Canny algorithm are used to enhance the string detectability. Various
statistical tools are then applied to quantify the deviation of CMB maps having
a cosmic string contribution with respect to pure Gaussian anisotropies of
inflationary origin. These statistical measures include the one-point
probability density function, the weighted two-point correlation function
(TPCF) of the anisotropies, the unweighted TPCF of the peaks and of the
up-crossing map, as well as their cross-correlation. We use this algorithm on a
hundred of simulated Nambu-Goto CMB flat sky maps, covering approximately
$10\%$ of the sky, and for different string tensions $G\mu$. On noiseless sky
maps with an angular resolution of $0.9'$, we show that our pipeline detects
CSs with $G\mu$ as low as $G\mu\gtrsim 4.3\times 10^{-10}$. At the same
resolution, but with a noise level typical to a CMB-S4 phase II experiment, the
detection threshold would be to $G\mu\gtrsim 1.2 \times 10^{-7}$.",1710.00173v1
2017-10-03,Fission Fragment Angular Anisotropy in Neutron-Induced Fission of $^{235}$U Measured with a Time Projection Chamber,"Fission fragment angular distributions can provide an important constraint on
fission theory, improving predictive fission codes, and are a prerequisite for
a precise ratio cross section measurement. Available anisotropy data is sparse,
especially at neutron energies above 5 MeV. For the first time, a
three-dimensional tracking detector is employed to study fragment emission
angles and provide a direct measurement of angular anisotropy. The Neutron
Induced Fission Fragment Tracking Experiment (NIFFTE) collaboration has
deployed the fission time projection chamber (fissionTPC) to measure nuclear
data with unprecedented precision. The fission fragment anisotropy of $^{235}$U
has been measured over a wide range of incident neutron energies from 180 keV
to 200 MeV; a careful study of the systematic uncertainties complement the
data.",1710.00973v2
2017-10-21,"Size dependence of the effective magnetic anisotropy in Co, Ni, Fe, and magnetite nanoparticles: Testing the core-shell-surface-layer (CSSL) model","The stability of the stored information in recording media depends on the
anisotropy energy Ea = KeffV of nanoparticles (NPs) of volume V or diameter D.
Therefore, the knowledge of how the effective magnetic anisotropy Keff varies
with D for a given system is important for technological applications. In a
recent paper [Appl. Phys. Lett. 110 (22), 222409 (2017)], the variation of Keff
versus D in NPs of maghemite ({\gamma}-Fe2O3) was best described by the Eq.:
Keff = Kb + (6KS/D) +Ksh{[1-(2d/D)]-3 -1}, where Kb, KS, and Ksh are the
anisotropy constants of spins in the core, surface layer, and a shell of
thickness d, respectively. This core-shell-surface layer (CSSL) model is an
extension of the often used core-surface layer (CSL) model described by Keff =
Kb + (6KS/D) [Phys. Rev. Lett. 72, 282 (1994)]. The additional term involving
Ksh was found to be necessary to fit the data for smaller NPs of {\gamma}-Fe2O3
with D < 5 nm. Here we check the validity of the CSSL model for metallic
magnetic NPs of Co, Ni, Fe and magnetite using Keff vs. D data from published
literature. Care was taken in selecting data only for those NPs for which the
effects of interparticle interactions has been taken into account in
determining Keff. The importance of the new CSSL model is that it describes
well the Keff vs. D variation for all particles sizes whereas the core-surface
layer model often fails for smaller particles with the notable exception of Fe
NPs. The verification of the CSSL model for metallic NPs of Co, Ni, and
magnetite along with NPs of NiO and {\gamma}-Fe2O3 validates its general
applicability.",1710.07832v1
2017-10-27,Azimuthal Anisotropy in High Energy Nuclear Collision - An Approach based on Complex Network Analysis,"Recently, a complex network based method of Visibility Graph has been applied
to confirm the scale-freeness and presence of fractal properties in the process
of multiplicity fluctuation. Analysis of data obtained from experiments on
hadron-nucleus and nucleus-nucleus interactions results in values of
Power-of-Scale-freeness-of-Visibility-Graph-(PSVG) parameter extracted from the
visibility graphs. Here, the relativistic nucleus-nucleus interaction data have
been analysed to detect azimuthal-anisotropy by extending the Visibility Graph
method and extracting the average clustering coefficient, one of the important
topological parameters, from the graph. Azimuthal-distributions corresponding
to different pseudorapidity-regions around the central-pseudorapidity value are
analysed utilising the parameter. Here we attempt to correlate the conventional
physical significance of this coefficient with respect to complex-network
systems, with some basic notions of particle production phenomenology, like
clustering and correlation. Earlier methods for detecting anisotropy in
azimuthal distribution, were mostly based on the analysis of statistical
fluctuation. In this work, we have attempted to find deterministic information
on the anisotropy in azimuthal distribution by means of precise determination
of topological parameter from a complex network perspective.",1710.10007v2
2017-10-27,Anisotropy and multiband superconductivity in Sr2RuO4,"Despite numerous studies the exact nature of the order parameter in
superconducting Sr2RuO4 remains unresolved. We have extended previous
small-angle neutron scattering studies of the vortex lattice in this material
to a wider field range, higher temperatures, and with the field applied close
to both the <100> and <110> basal plane directions. Measurements at high field
were made possible by the use of both spin polarization and analysis to improve
the signal-to-noise ratio. Rotating the field towards the basal plane causes a
distortion of the square vortex lattice observed for H // <001>, and also a
symmetry change to a distorted triangular symmetry for fields close to <100>.
The vortex lattice distortion allows us to determine the intrinsic
superconducting anisotropy between the c-axis and the Ru-O basal plane,
yielding a value of ~60 at low temperature and low to intermediate fields. This
greatly exceeds the upper critical field anisotropy of ~20 at low temperature,
reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects
on the unpaired quasiparticles in the vortex cores are observed, but a direct
detection lies below the measurement sensitivity. The superconducting
anisotropy is found to be independent of temperature but increases for fields >
1 T, indicating multiband superconductvity in Sr2RuO4. Finally, the temperature
dependence of the scattered intensity provides further support for gap nodes or
deep minima in the superconducting gap.",1710.10310v1
2017-11-02,Nearly isotropic superconductivity in layered Weyl semimetal WTe$_2$ at 98.5 kbar,"Layered transition metal dichalcogenide WTe$_2$ has recently attracted
significant attention due to the discovery of an extremely large
magnetoresistance, a predicted type-II Weyl semimetallic state, and the
pressure-induced superconducting state. By a careful measurement of the
superconducting upper critical fields as a function of the magnetic field angle
at a pressure as high as 98.5 kbar, we provide the first detailed examination
of the dimensionality of the superconducting condensate in WTe$_2$. Despite the
layered crystal structure, the upper critical field exhibits a negligible field
anisotropy. The angular dependence of the upper critical field can be
satisfactorily described by the anisotropic mass model from 2.2 K
($T/T_c\sim0.67$) to 0.03 K ($T/T_c\sim0.01$), with a practically identical
anisotropy factor $\gamma\sim1.7$. The temperature dependence of the upper
critical field, determined for both $H\perp ab$ and $H\parallel ab$, can be
understood by a conventional orbital depairing mechanism. Comparison of the
upper critical fields along the two orthogonal field directions results in the
same value of $\gamma\sim1.7$, leading to a temperature independent anisotropy
factor from near $T_c$ to $<0.01T_c$. Our findings thus identify WTe$_2$ as a
nearly isotropic superconductor, with an anisotropy factor among one of the
lowest known in superconducting transition metal dichalcogenides.",1711.00666v1
2017-11-08,Coexistence of Magneto-Rotational and Jeans Instabilities in an Axisymmetric Nebula,"We analyze the magneto-rotational instability (MRI) effects on gravitational
collapse and its influence on the instability critical scale. In particular, we
study an axisymmetric nonstratified differentially rotating cloud, embedded in
a small magnetic field, and we perform a local linear stability analysis,
including the self gravity of the system. We demonstrate that the linear
evolution of the perturbations is characterized by the emergence of an
anisotropy degree of the perturbed mass densities. Starting with spherical
growing overdensities, we see that they naturally acquire an anisotropy of
order unity in their shape. Despite the linear character of our analysis, we
infer that such a seed of anisotropy can rapidly grow in a nonlinear regime,
leading to the formation of filament-like structures. However, we show how such
an anisotropy is essentially an intrinsic feature of the Jean instability, and
how MRI only plays a significant role in fixing the critical scale of the mode
spectrum. We then provide a characterization of the present analysis in terms
of the cosmological setting, in order to provide an outlook of how the present
results could concern the formation of large-scale structures across the
Universe.",1711.03010v4
2017-11-08,Jets and large-scale vortices in rotating Rayleigh-Bénard convection,"One of the most prominent dynamical features of turbulent, rapidly-rotating
convection is the formation of large-scale coherent structures, driven by
Reynolds stresses resulting from the small-scale convective flows. In spherical
geometry, such structures consist of intense zonal flows that are invariant
along the rotation axis. In planar geometry, long-lived, depth-invariant
structures also form at large scales, but, in the absence of horizontal
anisotropy, they consist of vortices that grow to the domain size. In this
work, through the introduction of horizontal anisotropy into a numerical model
of planar rotating convection by the adoption of unequal horizontal box sizes
(i.e. $L_x \le L_y$, where the $xy$-plane is horizontal), we investigate
whether unidirectional flows and large-scale vortices can coexist. We find that
only a small degree of anisotropy is required to bring about a transition from
dynamics dominated by persistent large-scale vortices to dynamics dominated by
persistent unidirectional flows parallel to the shortest horizontal direction.
When the anisotropy is sufficiently large, the unidirectional flow consists of
multiple jets, generated on a timescale smaller than a global viscous
timescale, thus signifying that the upscale energy transfer does not
spontaneously feed the largest available mode in the system. That said, the
multiple jets merge on much longer timescales. Large-scale vortices of size
comparable with $L_x$ systematically form in the flanks of the jets and can be
persistent or intermittent. This indicates that large-scale vortices, either
coexisting with jets or not, are a robust dynamical feature of planar rotating
convection.",1711.03030v1
2018-01-03,Investigation of the spin-1 honeycomb antiferromagnet BaNi$_2$V$_2$O$_8$ with easy plane anisotropy,"The magnetic properties of the two-dimensional, S=1 honeycomb antiferromagnet
BaNi$_2$V$_2$O$_8$ have been comprehensively studied using DC susceptibility
measurements and inelastic neutron scattering techniques. The magnetic
excitation spectrum is found to be dispersionless within experimental
resolution between the honeycomb layers, while it disperses strongly within the
honeycomb plane where it consists of two gapped spin-wave modes. The magnetic
excitations are compared to linear spin-wave theory allowing the Hamiltonian to
be determined. The first- and second-neighbour magnetic exchange interactions
are antiferromagnetic and lie within the ranges 10.90meV$\le$J$_n$$\le$13.35
meV and 0.85meV$\le$J$_{nn}$$\le$1.65 meV respectively. The interplane coupling
J$_{out}$ is four orders of magnitude weaker than the intraplane interactions,
confirming the highly two-dimensional magnetic behaviour of this compound. The
sizes of the energy gaps are used to extract the magnetic anisotropies and
reveal substantial easy-plane anisotropy and a very weak in-plane easy-axis
anisotropy. Together these results reveal that BaNi$_2$V$_2$O$_8$ is a
candidate compound for the investigation of vortex excitations and
Berezinsky-Kosterliz-Thouless phenomenona.",1801.00962v1
2017-12-26,An accurate centroid algorithm for PSF reconstruction,"In this work, we present a novel centroiding method based on Fourier space
Phase Fitting(FPF) for Point Spread Function(PSF) reconstruction. We generate
two sets of simulations to test our method. The first set is generated by
GalSim with elliptical Moffat profile and strong anisotropy which shifts the
center of the PSF. The second set of simulation is drawn from CFHT i band
stellar imaging data. We find non-negligible anisotropy from CFHT stellar
images, which leads to $\sim$0.08 scatter in unit of pixels using polynomial
fitting method Vakili and Hogg (2016). And we apply FPF method to estimate the
centroid in real space, this scatter reduces to $\sim$0.04 in SNR=200 CFHT like
sample. In low SNR (50 and 100) CFHT like samples, the background noise
dominates the shifting of the centroid, therefore the scatter estimated from
different methods are similar. We compare polynomial fitting and FPF using
GalSim simulation with optical anisotropy. We find that in all SNR$\sim$50, 100
and 200) samples, FPF performs better than polynomial fitting by a factor of
$\sim$3. In general, we suggest that in real observations there are anisotropy
which shift the centroid, and FPF method is a better way to accurately locate
it.",1801.01015v1
2018-01-08,Strong- and weak-universal critical behaviour of a mixed-spin Ising model with triplet interactions on the Union Jack (centered square) lattice,"The mixed spin-1/2 and spin-S Ising model on the Union Jack (centered square)
lattice with four different three-spin (triplet) interactions and the uniaxial
single-ion anisotropy is exactly solved by establishing a rigorous mapping
equivalence with the corresponding zero-field (symmetric) eight-vertex model on
a dual square lattice. A rigorous proof of the aforementioned exact mapping
equivalence is provided by two independent approaches exploiting either a
graph-theoretical or spin representation of the zero-field eight-vertex model.
An influence of the interaction anisotropy as well as the uniaxial single-ion
anisotropy on phase transitions and critical phenomena is examined in
particular. It is shown that the considered model exhibits a strong-universal
critical behaviour with constant critical exponents when considering the
isotropic model with four equal triplet interactions or the anisotropic model
with one triplet interaction differing from the other three. The anisotropic
models with two different triplet interactions, which are pairwise equal to
each other, contrarily exhibit a weak-universal critical behaviour with
critical exponents continuously varying with a relative strength of the triplet
interactions as well as the uniaxial single-ion anisotropy. It is evidenced
that the variations of critical exponents of the mixed-spin Ising models with
the integer-valued spins S differ basically from their counterparts with the
half-odd-integer spins S.",1801.02676v1
2018-01-19,Detecting Anisotropy in Fingerprint Growth,"From infancy to adulthood, human growth is anisotropic, much more along the
proximal-distal axis (height) than along the medial-lateral axis (width),
particularly at extremities. Detecting and modeling the rate of anisotropy in
fingerprint growth, and possibly other growth patterns as well, facilitates the
use of children's fingerprints for long-term biometric identification. Using
standard fingerprint scanners, anisotropic growth is highly overshadowed by the
varying distortions created by each imprint, and it seems that this difficulty
has hampered to date the development of suitable methods, detecting anisotropy,
let alone, designing models. We provide a tool chain to statistically detect,
with a given confidence, anisotropic growth in fingerprints and its preferred
axis, where we only require a standard fingerprint scanner and a minutiae
matcher. We build on a perturbation model, a new Procrustes-type algorithm, use
and develop several parametric and non-parametric tests for different
hypotheses, in particular for neighborhood hypotheses to detect the axis of
anisotropy, where the latter tests are tunable to measurement accuracy. Taking
into account realistic distortions caused by pressing fingers on scanners, our
simulations based on real data indicate that, for example, already in rather
small samples (56 matches) we can significantly detect proximal-distal growth
if it exceeds medial-lateral growth by only around 5 percent. Our method is
well applicable to future datasets of children fingerprint time series and we
provide an implementation of our algorithms and tests with matched minutiae
pattern data.",1801.06437v1
2018-01-21,Ce$_{3-x}$Mg$_x$Co$_{9}$: transformation of a Pauli paramagnet into a strong permanent magnet,"We report on the synthesis of single crystalline and polycrystalline samples
of Ce$_{3-x}$Mg$_x$Co$_9$ solid solution ($0\leq x \lesssim 1.4$) and
characterization of their structural and magnetic properties. The crystal
structure remains rhombohedral in the whole composition range and Mg partially
replaces Ce in the 6\textit{c} site of the CeCo$_3$ structure. Ferromagnetism
is induced by Mg substitutions starting as low as $x=0.18$ and reaching a Curie
temperature as high as $450$\,K for $x=1.35$. Measurements on single crystals
with $x=1.34$ and $T_\textrm{C}=440$\,K indicate an axial magnetic anisotropy
with the anisotropy field of $6$\,T and a magnetization of $6$\,$\mu_B/$f.u. at
$300$\,K. Coercicity is observed in the polycrystalline samples consistent with
the observed axial magnetic anisotropy. Our discovery of ferromagnetism with
large axial magnetic anisotropy induced by substituting a rare-earth element by
Mg is a very promising result in the search of inexpensive permanent-magnet
materials and suggests other non-magnetic phases, similar to CeCo$_3$, may also
conceal nearby ferromagnetic phases.",1801.06743v2
2018-01-31,"Cubic anisotropy in high homogeneity thin (Ga,Mn)As layers","Historically, comprehensive studies of dilute ferromagnetic semiconductors,
e.g., $p$-type (Cd,Mn)Te and (Ga,Mn)As, paved the way for a quantitative
theoretical description of effects associated with spin-orbit interactions in
solids, such as crystalline magnetic anisotropy. In particular, the theory was
successful in explaining {\em uniaxial} magnetic anisotropies associated with
biaxial strain and non-random formation of magnetic dimers in epitaxial
(Ga,Mn)As layers. However, the situation appears much less settled in the case
of the {\em cubic} term: the theory predicts switchings of the easy axis
between in-plane $\langle 100\rangle$ and $\langle 110\rangle$ directions as a
function of the hole concentration, whereas only the $\langle 100\rangle$
orientation has been found experimentally. Here, we report on the observation
of such switchings by magnetization and ferromagnetic resonance studies on a
series of high-crystalline quality (Ga,Mn)As films. We describe our findings by
the mean-field $p$-$d$ Zener model augmented with three new ingredients. The
first one is a scattering broadening of the hole density of states, which
reduces significantly the amplitude of the alternating carrier-induced
contribution. This opens the way for the two other ingredients, namely the
so-far disregarded single-ion magnetic anisotropy and disorder-driven
non-uniformities of the carrier density, both favoring the $\langle 100\rangle$
direction of the apparent easy axis. However, according to our results, when
the disorder gets reduced a switching to the $\langle 110\rangle$ orientation
is possible in a certain temperature and hole concentration range.",1802.00076v2
2018-02-22,Magnetic properties of metal-organic coordination networks based on 3d transition metal atoms,"The magnetic anisotropy and exchange coupling between spins localized at the
positions of 3d transition metal atoms forming two-dimensional metal-organic
coordination networks (MOCNs) grown on the Au(111) metal surface are studied.
In particular, we consider MOCNs made of Ni or Mn metal centers linked by TCNQ
(7,7,8,8-tetracyanoquinodimethane) organic ligands, which form rectangular
networks with 1:1 stoichiometry. Based on the analysis of X-ray magnetic
circular dichroism (XMCD) data taken at T= 2.5 K, we find that Ni atoms in the
Ni-TCNQ MOCNs are coupled ferromagnetically and do not show any significant
magnetic anisotropy, while Mn atoms in the Mn-TCNQ MOCNs are coupled
antiferromagnetically and do show a weak magnetic anisotropy with
in-planemagnetization. We explain these observations using both
amodelHamiltonian based on mean-fieldWeiss theory and density functional theory
calculations that include spin-orbit coupling. Our main conclusion is that the
antiferromagnetic coupling between Mn spins and the in-plane magnetization of
the Mn spins can be explained neglecting effects due to the presence of the
Au(111) surface, while for Ni-TCNQ the metal surface plays a role in
determining the absence of magnetic anisotropy in the system.",1802.08243v1
2018-03-20,Anisotropy in electrical conductivity and transparency of films of aligned conducting rods,"Numerical simulations by means of the Monte Carlo method have been performed
to study the electrical properties of a two-dimensional composite filled with
rodlike particles. The main goal was to study the effect of the alignment of
such rods on the anisotropy of its electrical conductivity. A continuous model
was used. In this model, the rods have zero-width (i.e. infinite aspect ratio)
and they may intersect each other. To involve both the low conductive host
matrix, and highly conductive fillers (rods) in the consideration, a
discretization algorithm based on the use of a supporting mesh was applied. The
discretization is equivalent to the substitution of rods with the polyominoes.
Once discretized, the Frank--Lobb algorithm was applied to evaluate the
electrical conductivity. Our main findings are (i) the alignment of the rods
essentially affects the electrical conductivity and its anisotropy, (ii)the
discrete nature of computer simulations is crucial. For slightly disordered
system, high electrical anisotropy was observed at small filler content,
suggesting a method to enable the production of optically transparent and
highly anisotropic conducting films.",1803.07354v1
2018-03-26,Enhancement of the magnetoelectric effect in multiferroic CoFe$_2$O$_4$/PZT bilayer by induced uniaxial magnetic anisotropy,"In this study we have compared magnetic, magnetostrictive and piezomagnetic
properties of isotropic and anisotropic cobalt ferrite pellets. The isotropic
sample was prepared by the ceramic method while the sample exhibiting uniaxial
anisotropy was made by reactive sintering using Spark Plasma Sintering (SPS).
This technique permits to induce a magnetic anisotropy in cobalt ferrite in the
direction of the applied pressure during SPS process. Sample with uniaxial
anisotropy revealed a higher longitudinal magnetostriction and piezomagnetism
compared to the isotropic sample, but the transversal magnetostriction and
piezomagnetism were dramatically reduced. In the case of magnetoelectric
layered composite, the magnetoelectric coefficient is directly related to the
sum of the longitudinal and transversal piezomagnetic coefficients. These two
coefficients being opposite in sign, the use of material exhibiting high
longitudinal and low transversal piezomagnetic coefficient (or vice versa) in
ME devices is expected to improve the ME effect. Hence, ME bilayer devices were
made using isotropic and anisotropic cobalt ferrite stuck with a PZT layer. ME
measurements at low frequencies revealed that bilayer with anisotropic cobalt
ferrite exhibits a ME coefficient three times higher than a bilayer with
isotropic cobalt ferrite. We also investigated the behavior of such composites
when excited at resonant frequency.",1803.09677v1
2018-04-08,Statistical tracing of magnetic fields: comparing and improving the techniques,"Magnetohydrodynamic(MHD) turbulence displays velocity anisotropies which
reflect the direction of the magnetic field. This anisotropy has led to the
development of a number of statistical techniques for studying magnetic fields
in the interstellar medium. In this paper, we review and compare three
techniques that use radio position-position-velocity data for determining
magnetic field strength and morphology : the correlation function anisotropy
(CFA), Principal Component Analysis of Anisotropies (PCAA), and the more recent
Velocity Gradient Technique (VGT). We compare these three techniques and
suggest improvements to the CFA and PCAA techniques to increase their accuracy
and versatility. In particular, we suggest and successfully implement a much
faster way of calculating non-periodic correlation functions for the CFA. We
discuss possible improvements to the current implementation of the PCAA. We
show the advantages of the VGT in terms of magnetic field tracing and stress
the complementary nature with the other two techniques.",1804.02732v2
2018-04-13,Enhanced mobility of discrete solitons in anisotropic two-dimensional waveguide arrays with modulated separations,"We consider two-dimensional waveguide arrays with anisotropic coupling
coefficients. We show using numerical and variational calculations that four
stationary soliton types exist: Site-Centered, Bond-Centered, Hybrid-X and
Hybrid-Y. For the isotropic case the last two modes become identical and
equivalent to the known hybrid soliton. With a variational calculation using a
gaussian trial function and six variational parameters corresponding to the
soliton's position, width, and velocity components, the four stationary soliton
types are reproduced and their equilibrium widths are accounted for accurately
for a wide range of anisotropy ratios. We obtained using the variational
calculation the Peierls-Nabarro potential and barrier heights for the four
soliton types and different anisotropy ratios. We have also obtained a phase
diagram showing regions of soliton stability against collapse and subregions of
mobility in terms of the initial kick-in speed and anisotropy ratio. The phase
diagram shows that 2D solitons become highly mobile for anisotropy ratios
larger than some critical values that depend on the initial kick-in speed. This
fact was then exploited to design tracks within the 2D waveguide array along
which the soliton can be accelerated and routed. We have calculated the actual
waveguide separations needed to realist the proposed guided trajectories of 2D
solitons.",1804.04896v1
2018-04-21,"Dipole Anisotropy as an Essential Qualifier for the Monopole Component of the Cosmic-Dawn Spectral Signature, and the Potential of Diurnal Pattern for Foreground Estimation","While the importance of detecting the Global spectral signatures of the
red-shifted 21-cm line of atomic hydrogen from the very early epochs cannot be
overstated, the associated challenges primarily include isolating the weak
signal of interest from the orders of magnitude brighter foregrounds, and
extend equally to reliably establishing the origin of the {\it apparent} global
signal to the very early epochs. This letter proposes a critical dipole test
that the measurements of the monopole component of the spectrum of interest
should necessarily pass. Our criterion is based on a unique correspondence
between the intrinsic monopole spectrum and the differential spectrum as an
imprint of dipole anisotropy resulting from motion of observer with respect to
the rest frame of our source (such as that of our Solar system, interpreted
from the dipole anisotropy in CMBR). More importantly, the spectral
manifestation of the dipole anisotropy gets {\it amplified} by a significant
factor, depending on the monopole spectral slopes, rendering it feasible to
measure. We describe details of such a test, and illustrate its application
with the help of simulations. The letter also alludes to a novel
model-independent path toward isolating the foreground contribution, using the
diurnal pattern readily apparent in drift-scan observations. Such dipole
qualifier for the monopole spectrum, when combined with reliable foreground
estimation, is expected to pave way for in situ validation of spectral
signatures from early epochs, important to presently reported and future
detections of EoR signal.",1804.07993v3
2018-04-23,"Dependence of light scattering properties on porosity, size and composition of dust aggregates","In this work, we study the light scattering properties of dust aggregates
($0.7\mu m \lesssim R_c \lesssim 2.0\mu m$) having a wide range of porosity
($\mathcal{P}$ = 0.59 to 0.98). The simulations are executed using the
Superposition T-matrix code with BCCA, BA, BAM1 and BAM2 clusters of varying
porosity. We investigate the nature and dependencies of the different
scattering parameters on porosity, size and composition of the aggregated
particles for wavelengths 0.45 $\mu$m and 0.65 $\mu$m. We find that the
scattering parameters are strongly correlated with the porosity of the
aggregated structures. Our results indicate that, when the porosity of the
aggregates decreases, keeping characteristic radius of the aggregates ($R_c$)
same for all structures, there is an enhancement in the negative polarization
branch (NPB) which is accompanied by a substantial increase in the anisotropies
present in the material. Also at the exact backscattering region, the
anisotropies are found to be linearly correlated with the porosity of the
aggregated structure. The computational study reveals that, for low absorbing
materials ($k \le 0.1$), the negative polarization minimum ($P_{min}$) is
strongly correlated with the associated anisotropies. Finally, we put forward a
qualitative comparison between our computationally obtained results and some
selected data from the Amsterdam Light Scattering Database for both low and
high absorbing materials. The experimental results also suggest that an
increase in the NPB is always accompanied by an enhancement in the anisotropy
at the backscattering region.",1804.08324v1
2018-06-06,The effect of stellar-mass black holes on the central kinematics of omega Cen: a cautionary tale for IMBH interpretations,"The search for intermediate-mass black holes (IMBHs) in the centre of
globular clusters is often based on the observation of a central cusp in the
surface brightness profile and a rise towards the centre in the velocity
dispersion profiles. Similar signatures, however, could result from other
effects, that need to be taken into account in order to determine the presence
(or the absence) of an IMBH in these stellar systems. Following our previous
exploration of the role of radial anisotropy in shaping these observational
signatures, we analyse here the effects produced by the presence of a
population of centrally concentrated stellar-mass black holes. We fit dynamical
models to omega Cen data, and we show that models with ~5% of their mass in
black holes (consistent with ~100% retention fraction after natal kicks) can
reproduce the data. When simultaneously considering both radial anisotropy and
mass segregation, the best-fit model includes a smaller population of remnants,
and a less extreme degree of anisotropy with respect to the models that include
only one of these features. These results underline that before conclusions
about putative IMBHs can be made, the effects of stellar-mass black holes and
radial anisotropy need to be properly accounted for.",1806.02157v1
2018-06-23,MMS Observations of Beta-Dependent Constraints on Ion Temperature-Anisotropy in Earth's Magnetosheath,"Protons (ionized hydrogen) in the solar wind frequently exhibit distinct
temperatures ($T_{\perp p}$ and $T_{\parallel p}$) perpendicular and parallel
to the plasma's background magnetic-field. Numerous prior studies of the
interplanetary solar-wind have shown that, as plasma beta ($\beta_{\parallel
p}$) increases, a narrower range of temperature-anisotropy ($R_p\equiv T_{\perp
p}\,/\,T_{\parallel p}$) values is observed. Conventionally, this effect has
been ascribed to the actions of kinetic microinstabilities. This study is the
first to use data from the Magnetospheric Multiscale Mission (MMS) to explore
such $\beta_{\parallel p}$-dependent limits on $R_p$ in Earth's magnetosheath.
The distribution of these data across the $(\beta_{\parallel p},R_p)$-plane
reveals limits on both $R_p>1$ and $R_p<1$. Linear Vlasov theory is used to
compute contours of constant growth-rate for the ion-cyclotron, mirror,
parallel-firehose, and oblique-firehose instabilities. These instability
thresholds closely align with the contours of the data distribution, which
suggests a strong association of instabilities with extremes of ion temperature
anisotropy in the magnetosheath. The potential for instabilities to regulate
temperature anisotropy is discussed.",1806.08886v1
2018-07-19,Small system studies: A theory overview,"There is now a substantial body of evidence that a deconfined quark-gluon
plasma is created in ultrarelativistic collisions of heavy nuclei. Some key
observables which are used to gauge the production of the quark-gluon plasma
are the hadronic spectra and multiplicities across many species, azimuthal
anisotropies in the production of various hadrons, jet quenching,
photon/dilepton production, and heavy quarkonium suppression. A key question in
the study of the quark-gluon plasma is what happens to these observables as one
changes the system size. In particular, it is very interesting to study
collisions of `small systems' such as pp, dA, pA, and $e^+ e^-$ since naively
one does not expect to produce a QGP in these cases. One of the surprises from
such studies was the existence of sizable azimuthal anisotropies in the hadron
spectra in the highest multiplicity classes, which led to speculations that one
can generate a QGP in such relatively rare events. This interpretation,
however, is complicated by the fact that there can be multiple sources of
azimuthal anisotropy. I will discuss our current understanding of the different
sources of azimuthal anisotropies and the multiplicity windows in which each
mechanism is expected to dominate. I will also provide a critical discussion of
the reliability of hydrodynamic models applied to small systems. Finally, I
will briefly discuss jet quenching and heavy quarkonium suppression in small
systems and discuss whether or not these observables show any indication of the
production of a small QGP droplet.",1807.07191v2
2018-08-16,Estimating the Anisotropy of Protein Structures from SAXS,"In the field of small angle x-ray scattering (SAXS), the task of estimating
the size of particles in solution is usually synonymous with the Guinier plot.
The approximation behind this plot, developed by Guinier in 1939 provides a
simple yet accurate characterization of the scattering behavior of particles at
low scattering angle $q$, together with a computationally efficient way of
inferring their radii of gyration $R_G$. Moreover, this approximation is valid
beyond spherical scatterers, making its use ubiquitous in the SAXS world.
However, when it is important to estimate further particle characteristics,
such as the anisotropy of the scatterer's shape, no similar or extended
approximations are available. Existing tools to characterize the shape of
scatterers rely either on prior knowledge of the scatterers' geometry or on
iterative procedures to infer the particle shape \textit{ab initio}.\\
  In this work we develop a low angle approximation of the scattering intensity
$I(q)$ for ellipsoids of revolution and show how to extract size and anisotropy
information from the parameters of that approximation. Beyond ideal ellipsoids
of revolution, we show that this approximation can be used to infer the size
and shape of molecules in solution, both in computational and experimental
scenarios. We discuss the limits of our approach and study the impact of a
particle's anisotropy in the Guinier estimate of $R_G$.",1808.05569v1
2018-09-20,Universal Fermi-surface anisotropy renormalization for interacting Dirac fermions with long-range interactions,"Recent experimental and numerical evidence suggest an intriguing universal
relationship between the Fermi surface anisotropy of the non-interacting parent
two-dimensional electron gas and the strongly correlated composite Fermi liquid
formed in a strong magnetic field close to half-filing. Inspired by these
observations, we explore more generally the question of anisotropy
renormalization in interacting 2D Fermi systems. Using a recently developed
non-perturbative and numerically-exact projective quantum Monte Carlo
simulation as well as other numerical and analytic techniques, only for Dirac
fermions with long-range Coulomb interactions do we find a universal
square-root decrease of the Fermi-surface anisotropy. For the half-filled
composite Fermi liquid, this result is surprising since a Dirac fermion ground
state was only recently proposed as an alternative to the usual HLR state. The
importance of the long-range interaction, expected for Dirac systems, is also
consistent with recent transport measurements. Our proposed universality can be
tested in several anisotropic Dirac materials including graphene, topological
insulators organic conductors, and magic-angle twisted bilayer graphene.",1809.07775v2
2018-10-04,Prospects of detecting a large-scale anisotropy of ultra-high-energy cosmic rays from a nearby source with the K-EUSO orbital telescope,"KLYPVE-EUSO (K-EUSO) is a planned orbital detector of ultra-high-energy
cosmic rays (UHECRs), which is to be deployed on board the International Space
Station. K-EUSO is expected to have a uniform exposure over the celestial
sphere and register from 120 to 500 UHECRs at energies above 57 EeV in a 2-year
mission. We employed the TransportCR and CRPropa 3 packages to estimate
prospects of detecting a large-scale anisotropy of ultra-high-energy cosmic
rays from a nearby source with K-EUSO. Nearby active galactic nuclei Centaurus
A, M82, NGC 253, M87 and Fornax A were considered as possible sources of
UHECRs. A minimal model for extragalactic cosmic rays and neutrinos by
Kachelriess, Kalashev, Ostapchenko and Semikoz (2017) was chosen for
definiteness. We demonstrate that an observation of $\gtrsim300$ events will
allow detecting a large-scale anisotropy with a high confidence level providing
the fraction of from-source events is $\simeq$10-15%, depending on a particular
source. The threshold fraction decreases with an increasing sample size. We
also discuss if an overdensity originating from a nearby source can be observed
at around the ankle in case a similar anisotropy is found beyond 57 EeV. The
results are generic and hold for other future experiments with a uniform
exposure of the celestial sphere.",1810.02284v3
2018-10-16,Density jump as a function of magnetic field strength for parallel collisionless shocks in pair plasmas,"Collisionless shocks follow the Rankine-Hugoniot jump conditions to a good
approximation. However, for a shock propagating parallel to a magnetic field,
magnetohydrodynamics states that the shock properties are independent of the
field strength, whereas recent Particle-in-Cell simulations reveal a
significant departure from magnetohydrodynamics behavior for such shocks in the
collisionless regime. This departure is found to be caused by a field-driven
anisotropy in the downstream pressure, but the functional dependence of this
anisotropy on the field strength is yet to be determined. Here, we present a
non-relativistic model of the plasma evolution through the shock front,
allowing for a derivation of the downstream anisotropy in terms of the field
strength. Our scenario assumes double adiabatic evolution of a pair plasma
through the shock front. As a result, the perpendicular temperature is
conserved. If the resulting downstream is firehose stable, then the plasma
remains in this state. If unstable, it migrates towards the firehose stability
threshold. In both cases, the conservation equations, together with the
relevant hypothesis made on the temperature, allows a full determination of the
downstream anisotropy in terms of the field strength.",1810.07319v1
2018-10-20,Data-Driven Modelling of the Reynolds Stress Tensor using Random Forests with Invariance,"A novel machine learning algorithm is presented, serving as a data-driven
turbulence modeling tool for Reynolds Averaged Navier-Stokes (RANS)
simulations. This machine learning algorithm, called the Tensor Basis Random
Forest (TBRF), is used to predict the Reynolds-stress anisotropy tensor, while
guaranteeing Galilean invariance by making use of a tensor basis. By modifying
a random forest algorithm to accept such a tensor basis, a robust, easy to
implement, and easy to train algorithm is created. The algorithm is trained on
several flow cases using DNS/LES data, and used to predict the Reynolds stress
anisotropy tensor for new, unseen flows. The resulting predictions of
turbulence anisotropy are used as a turbulence model within a custom RANS
solver. Stabilization of this solver is necessary, and is achieved by a
continuation method and a modified $k$-equation. Results are compared to the
neural network approach of Ling et al. [J. Fluid Mech, 807(2016):155-166,
(2016)]. Results show that the TBRF algorithm is able to accurately predict the
anisotropy tensor for various flow cases, with realizable predictions close to
the DNS/LES reference data. Corresponding mean flows for a square duct flow
case and a backward facing step flow case show good agreement with DNS and
experimental data-sets. Overall, these results are seen as a next step towards
improved data-driven modelling of turbulence. This creates an opportunity to
generate custom turbulence closures for specific classes of flows, limited only
by the availability of LES/DNS data.",1810.08794v2
2019-01-05,Evolution of magnetic anisotropy in cobalt film on nanopatterned silicon substrate studied in situ using MOKE,"Evolution of magnetization behaviour of cobalt film on nano patterned silicon
substrate, with film thickness, has been studied. In situ magneto-optical Kerr
effect measurements during film deposition allowed us to study genuine
thickness dependence of magnetization behaviour, all other parameters like
surface topology, deposition conditions remaining invariant. The film exhibits
uniaxial magnetic anisotropy, with its magnitude decreasing with increasing
film thickness. Analysis shows that anisotropy has contributions from both, i)
exchange energy which is volume dependent and, ii) stray dipolar fields at the
surface/interface. This suggests that local magnetization follows only
partially the topology of the rippled surface. As expected from energy
considerations, for small film thickness, the local magnetization closely
follows the surface contour of the ripples making the volume term as the
dominant contribution. With increasing film thickness, the local magnetization
gradually deviates from the local slope and approaches towards a uniform
magnetization along the macroscopic film plane making the surface term as the
dominant contribution. Significant deviation from the anisotropy energy
expected on the basis of theoretical considerations can be attributed to
several factors like, deviation of surface topology from an ideal sinusoidal
wave, breaks of continuity along the ripple direction, defects like pattern
dislocations, and possible decrease in surface modulation depth with increasing
film thickness.",1901.01397v1
2019-03-27,High throughput computational screening for 2D ferromagnetic materials: the critical role of anisotropy and local correlations,"The recent observation of ferromagnetic order in two-dimensional (2D)
materials has initiated a booming interest in the subject of 2D magnetism. In
contrast to bulk materials, 2D materials can only exhibit magnetic order in the
presence of magnetic anisotropy. In the present work we have used the
Computational 2D Materials Database (C2DB) to search for new ferromagnetic 2D
materials using the spinwave gap as a simple descriptor that accounts for the
role of magnetic anisotropy. In addition to known compounds we find 12 novel
insulating materials that exhibit magnetic order at finite temperatures. For
these we evaluate the critical temperatures from classical Monte Carlo
simulations of a Heisenberg model with exchange and anisotropy parameters
obtained from first principles. Starting from 150 stable ferromagnetic 2D
materials we find five candidates that are predicted to have critical
temperatures exceeding that of CrI3. We also study the effect of Hubbard
corrections in the framework of DFT+U and find that the value of U can have a
crucial influence on the prediction of magnetic properties. Our work provides
new insight into 2D magnetism and identifies a new set of promising monolayers
for experimental investigation.",1903.11466v2
2019-04-07,Homogenization of Norton-Hoff fibered composites with high contrast,"We study the steady creep flow of a perfectly viscoplastic solid reinforced
by fibers with high viscosity contrast. Our study unveils new effects related
to anisotropy and conditioned by the Norton exponent.",1904.03622v2
2019-04-19,Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression,"Detailed microstructure characterisation and in-situ micropillar compression
were coupled with crystal plasticity-based finite element modelling (CP-FEM) to
study the micro-mechanisms of plastic anisotropy in lamellar TiAl alloys. The
consideration of microstructure in both simulation and in-situ experiments
enables in-depth understanding of micro-mechanisms responsible for the highly
anisotropic deformation response of TiAl on the intra-lamella and inter-lamella
scales. This study focuses on two specific configurations of
{\gamma}/{\alpha}_2 lamellar microstructure with the {\gamma}/{\alpha}_2
interfaces being aligned {25}^o and {55}^o to the loading direction.
Microstructure-based CP-FEM shows that longituginal slip of super and ordinary
dislocations are most responsible for the plastic anisotropy in the {25}^o
micropillar while the anisotropy of the {55}^o micropillar is due to
longitudinal superdislocations and longitudinal twins. In addition, transversal
superdislocations were more active, making the deformation in the {25}^o
micropillar less localised than that in the {55}^o micropillar. Moreover, the
CP-FEM model successfully predicted substantial build-up of internal stresses
at {\gamma}/{\alpha}_2 interfaces, which is believed to be detrimental to the
ductility in TiAl. However, as evidenced by the model, the detrimental internal
stresses can be significantly relieved by the activation of transverse
deformation twinning, suggesting that the ductility of TiAl can be improved by
promoting transverse twins.",1904.09206v1
2019-05-10,Elastic Anisotropy Governs the Decay of Cell-induced Displacements,"The unique nonlinear mechanics of the fibrous extracellular matrix (ECM)
facilitates long-range cell-cell mechanical communications that would be
impossible on linear elastic substrates. Past research has described the
contribution of two separated effects on the range of force transmission,
including ECM elastic non-linearity and fiber alignment. However, the relation
between these different effects is unclear, and how they combine to dictate
force transmission range is still elusive. Here, we combine discrete fiber
simulations with continuum modeling to study the decay of displacements induced
by a contractile cell in fibrous networks. We demonstrate that fiber
non-linearity and fiber reorientation both contribute to the strain-induced
anisotropy of the elastic moduli of the cell local environment. This elastic
anisotropy is a parameter that governs the slow decay of the displacements, and
it depends on the magnitude of applied strain, either an external tension or an
internal contraction as a model of the cell. Furthermore, we show that
accounting for artificially-prescribed elastic anisotropy dictates the
displacement decay induced by a contracting cell. Our findings unify previous
single effects into a mechanical theory that explains force transmission in
fibrous networks. This work provides important insights into biological
processes that involve the coordinated action of distant cells mediated by the
ECM, such that occur in morphogenesis, wound healing, angiogenesis, and cancer
metastasis. It may also provide design parameters for biomaterials to control
force transmission between cells, as a way to guide morphogenesis in tissue
engineering.",1905.04345v1
2019-06-27,An anisotropic model for global climate data,"We present a new, elementary way to obtain axially symmetric Gaussian
processes on the sphere, in order to accommodate for the directional anisotropy
of global climate data in geostatistical analysis.",1906.11585v1
2019-07-19,Impact of main ion pressure anisotropy on stellarator impurity transport,"Main ions influence impurity dynamics through a variety of mechanisms; in
particular, via impurity-ion collisions. To lowest order in an expansion in the
main ion mass over the impurity mass, the impurity-ion collision operator only
depends on the component of the main ion distribution that is odd in the
parallel velocity. These lowest order terms give the parallel friction of the
impurities with the main ions, which is typically assumed to be the main cause
of collisional impurity transport. Next-order terms in the mass ratio expansion
of the impurity-ion collision operator, proportional to the component of the
main ion distribution that is even in the parallel velocity, are usually
neglected. However, in stellarators, the even component of the main ion
distribution can be very large. In this article, such next-order terms in the
mass ratio expansion of the impurity-ion collision operator are retained, and
analytical expressions for the neoclassical radial flux of trace impurities are
calculated in the Pfirsch-Schl\""uter, plateau and $1/\nu$ regimes. The new
terms provide a drive for impurity transport that is physically very different
from parallel friction: they are associated to anisotropy in the pressure of
the main ions, which translates into impurity pressure anisotropy. It is argued
that main ion pressure anisotropy must be taken into account for a correct
description of impurity transport in certain realistic stellarator plasmas.
Examples are given by numerically evaluating the analytical expressions for the
impurity flux.",1907.08482v2
2019-08-03,Nanoscale magnetic and charge anisotropies at manganite interfaces,"Strong correlated manganites are still under intense research owing to their
complex phase diagrams in terms of the Sr-doping and their sensitivity to
intrinsic and extrinsic structural deformations. Here, we performed x-ray
absorption spectroscopy measurements of manganites bilayers to explore the
effects that a local Sr-doping gradient produce on the charge and
antiferromagnetic anisotropies. In order to gradually tune the Sr-doping level
along the axis perpendicular to the samples we have grown a series of bilayers
with different thicknesses of low-doped manganites (from 0 nm to 6 nm)
deposited over a La0.7Sr0.3MnO3 metallic layer. This strategy permitted us to
resolve with high accuracy the thickness region where the charge and spin
anisotropies vary and the critical thickness tc over which the out of plane
orbital asymmetry does not have any further modifications. We found that the
antiferromagnetic spin axis points preferentially out of the sample plane
regardless the capping layer thickness. However, it tilts partially into the
sample plane far from this critical thickness, owing to the jointed
contributions of the external structural strain and electron doping.
Furthermore, we found that the doping level of the capping layer sensibly
affects the critical thickness, giving clear evidence of the influence exerted
by the electron doping on the orbital and magnetic configurations. These
anisotropy changes induce subtle modifications on the domain reorientation of
the La0.7Sr0.3MnO3, as evidenced from the magnetic hysteresis cycles.",1908.01196v1
2019-09-20,A new class of galaxy models with a central BH -- I. The spherical case,"The dynamical properties of spherically symmetric galaxy models, where a
Jaffe (1983) stellar density profile is embedded in a total mass density
decreasing as $r^{-3}$ at large radii, are presented. The orbital structure of
the stellar component is described by the Osipkov--Merritt anisotropy; the dark
matter halo is isotropic, and a black hole is added at the center of the
galaxy. First, the conditions for a nowhere negative and monotonically
decreasing dark matter halo density profile are derived; this profile can be
made asymptotically coincident with a NFW profile at the center and at large
radii. Then the minimum value of the anisotropy radius for phase-space
consistency is derived as a function of the galaxy parameters. The Jeans
equations for the stellar component are solved analytically; the projected
velocity dispersion at the center and at large radii is also obtained, for
generic values of the anisotropy radius. Finally, analytical expressions for
the terms entering the Virial Theorem are derived, and the fiducial anisotropy
limit required to prevent the onset of Radial Orbit Instability is determined
as a function of the galaxy parameters. The presented models, built following
an approach already adopted in our previous works, can be a useful starting
point for a more advanced modeling of the dynamics of elliptical galaxies, and
can be easily implemented in numerical simulations requiring a realistic
dynamical model of a galaxy.",1909.09639v1
2019-09-26,Electrical manipulation of magnetic anisotropy in a Fe$_{81}$Ga$_{19}$/PMN-PZT magnetoelectric multiferroic composite,"Magnetoelectric composites are an important class of multiferroic materials
that pave the way towards a new generation of multifunctional devices directly
integrable in data storage technology and spintronics. This study focuses on
strain-mediated electrical manipulation of magnetization in an extrinsic
multiferroic. The composite includes 5 nm or 60 nm Fe$_{81}$Ga$_{19}$ thin
films coupled to a piezoelectric (011)-PMN-PZT. The magnetization reversal
study reveals a converse magnetoelectric coefficient $\alpha_\mathrm{CME,max}
\approx 2.7 \times {10^{-6}}$ s.m$^{-1}$ at room temperature. This reported
value of $\alpha_\mathrm{CME}$ is among the highest so far compared to previous
reports of single-phase multiferroics as well as composites. An angular
dependency of $\alpha_\mathrm{CME}$ is also shown for the first time, arising
from the intrinsic magnetic anisotropy of FeGa. The highly efficient
magnetoelectric composite FeGa/PMN-PZT demonstrates drastic modifications of
the in-plane magnetic anisotropy, with an almost 90$^{\circ}$ rotation of the
preferential anisotropy axis in the thinner films under an electric field E =
10.8 kV.cm$^{-1}$. Also, the influence of thermal strain on the bilayer's
magnetic coercivity is compared to that of a reference bilayer FeGa/Glass at
cryogenic temperatures. A different evolution is observed as a function of
temperature, revealing a substrate thermo-mechanical influence which has not
yet been reported in FeGa thin films coupled to a piezoelectric material.",1909.12431v1
2019-10-15,Superconducting Correlations in the One-Dimensional Kondo Lattice Models under Magnetic Fields,"We analyze superconducting correlations in the one-dimensional Kondo lattice
models with Ising anisotropy under transverse magnetic fields, using the
density matrix renormalization group. For the spin-1/2 local spin model, the
Ising anisotropy is introduced by the ferromagnetic Ising interaction between
the local spins, while for the spin-1 model, it is taken by the single-ion
anisotropy. The magnetic properties under the transverse fields for the
spin-1/2 model are very similar to those for the spin-1 model [K. Suzuki and K.
Hattori, J. Phys. Soc. Jpn. 88, 024707 (2019).]. For the superconducting
correlations, we analyze various Cooper pairs within nearest-neighbor pairs
including composite ones between the local spins and the electrons. We find
that, for the spin-1/2 model, the superconducting correlations are highly
enhanced in the Tomonaga-Luttinger liquid state near the Kondo-plateau phase,
where the conduction electrons and the local spins are strongly coupled with a
finite spin gap for the Ising axis. This is a clear contrast to the model under
the longitudinal magnetic fields, where there are no noticeable superconducting
correlations. Competitions between the transverse magnetic field and the Kondo
singlet formation lead to this enhanced superconducting correlations. For the
spin-1 model, the single-ion anisotropy suppresses the superconducting
correlation and there is no noticeable enhancement. We also examine the large
Kondo exchange coupling limit. For the moderate ferromagnetic Ising interaction
between the local spins, we find that another type of superconducting
correlation is enhanced inside the ferromagnetic phase. We discuss a possible
relation between our results and reentrant superconductivity in U-based
ferromagnetic superconductors under transverse magnetic fields.",1910.06545v2
2019-11-21,Heat capacity of anisotropic Heisenberg antiferromagnet within the spin Hartree-Fock approach in quasi-1D Regime,"We study the anisotropic quantum Heisenberg antiferromagnet for spin-1/2 that
interpolates smoothly between the one-dimensional (1D) and the two-dimensional
(2D) limits. Using the spin Hartree-Fock approach we construct a quantitative
theory of heat capacity in the quasi-1D regime with a finite coupling between
spin chains. This theory reproduces closely the exact result of Bethe Ansatz in
the 1D limit and does not produces any spurious phase transitions for any
anisotropy in the quasi-1D regime at finite temperatures in agreement with the
Mermin-Wagner theorem. We study the static spin-spin correlation function in
order to analyse the interplay of lattice geometry and anisotropy in these
systems. We compare the square and triangular lattice. For the latter we find
that there is a quantum transition point at an intermediate anisotropy of
$\sim0.6$. This quantum phase transition establishes that the quasi-1D regime
extends upto a particular point in this geometry. For the square lattice the
change from the 1D to 2D occurs smoothly as a function of anisotropy, i.e. it
is of the crossover type. Comparing the newly developed theory to the available
experimental data on the heat capacity of $\rm{Cs}_2\rm{CuBr}_4$ and
$\rm{Cs}_2\rm{CuCl}_4$ we extract the microscopic constants of the exchange
interaction that previously could only be measured using inelastic neutron
scattering in high magnetic fields.",1911.09403v1
2019-12-09,Large Easy Axis Anisotropy in the One-Dimensional Magnet BaMo(PO$_4$)$_2$,"We present an extensive experimental and theoretical study on the
low-temperature magnetic properties of the monoclinic anhydrous alum compound
BaMo(PO$_4$)$_2$. The magnetic susceptibility reveals strong antiferromagnetic
interactions $\theta_{CW} = -167$~K and long-range magnetic order at
$T_N=22$~K, in agreement with a recent report. Powder neutron diffraction
furthermore shows that the order is collinear, with the moments near the $ac$
plane. Neutron spectroscopy reveals a large excitation gap $\Delta = 15$~meV in
the low-temperature ordered phase, suggesting a much larger easy-axis spin
anisotropy than anticipated. However, the large anisotropy justifies the
relatively high ordered moment, N\'{e}el temperature, and collinear order
observed experimentally, and is furthermore reproduced in a first principles
calculations using a new computational scheme. We therefore propose
BaMo(PO$_4$)$_2$ to host $S=1$ antiferromagnetic chains with large easy-axis
anisotropy, which has been theoretically predicted to realize novel excitation
continua.",1912.03969v1
2019-12-10,Magnetic properties of thin epitaxial Pd$_{1-x}$Fe$_x$ alloy films,"In the paper we present the results of extensive studies of palladium-rich
Pd1-xFex alloy films epitaxially grown on MgO single-crystal substrate. In a
composition range of x = 0.01-0.07 these materials are soft ferromagnets, the
saturation magnetization and magnetic anisotropy of which can be tuned by its
composition. Vibrating sample magnetometry was used to study temperature
dependences of spontaneous magnetic moment and to establish the temperature of
magnetic ordering (Curie temperature). Ferromagnetic resonance (FMR)
measurements at low temperatures in the in-plane and out-of-plane geometries
revealed the four-fold in-plane magnetic anisotropy with the easy directions
along the <110> axes of the substrate. The modelling of the angular dependence
of the field for resonance allowed to extract the cubic and tetragonal
contributions to the magnetic anisotropy of the films and establish their
dependence on the concentration of iron in the alloy. Experimental data are
discussed in the framework of existing theories of dilute magnetic alloys.
Using the anisotropy constants established from FMR, the magnetic hysteresis
loops are reproduced utilizing the Stoner-Wohlfarth model thus indicating the
predominant coherent magnetic moment rotation at low temperatures. The obtained
results compile a database of magnetic properties of a palladium-iron alloy
considered as a material for superconducting spintronics.",1912.04852v1
2019-12-17,Hyperbolic wavelet analysis of classical isotropic and anisotropic Besov-Sobolev spaces,"In this paper we introduce new function spaces which we call anisotropic
hyperbolic Besov and Triebel-Lizorkin spaces. Their definition is based on a
hyperbolic Littlewood-Paley analysis involving an anisotropy vector only
occurring in the smoothness weights. Such spaces provide a general and natural
setting in order to understand what kind of anisotropic smoothness can be
described using hyperbolic wavelets (in the literature also sometimes called
tensor-product wavelets), a wavelet class which hitherto has been mainly used
to characterize spaces of dominating mixed smoothness.
  A centerpiece of our present work are characterizations of these new spaces
based on the hyperbolic wavelet transform. Hereby we treat both, the standard
approach using wavelet systems equipped with sufficient smoothness, decay, and
vanishing moments, but also the very simple and basic hyperbolic Haar system.
  The second major question we pursue is the relationship between the novel
hyperbolic spaces and the classical anisotropic Besov-Lizorkin-Triebel scales.
As our results show, in general, both approaches to resolve an anisotropy do
not coincide. However, in the Sobolev range this is the case, providing a link
to apply the newly obtained hyperbolic wavelet characterizations to the
classical setting. In particular, this allows for detecting classical
anisotropies via the coefficients of a universal hyperbolic wavelet basis,
without the need of adaption of the basis or a-priori knowledge on the
anisotropy.",1912.08034v1
2019-12-17,Whistler instabilities from the interplay of electron anisotropies in space plasmas: A quasilinear approach,"Recent statistical studies of observational data unveil relevant correlations
between whistler fluctuations and the anisotropic electron populations present
in space plasmas, e.g., solar wind and planetary magnetospheres. Locally,
whistlers can be excited by two sources of free energy associated with
anisotropic electrons, i.e., temperature anisotropies and beaming populations
carrying the heat flux. However, these two sources of free energy and the
resulting instabilities are usually studied independently preventing a
realistic interpretation of their interplay. This paper presents the results of
a parametric quasilinear study of the whistler instability cumulatively driven
by two counter-drifting electron populations and their anisotropic
temperatures. By comparison to individual regimes dominated either by beaming
population or by temperature anisotropy, in a transitory regime the instability
becomes highly conditioned by the effects of both these two sources of free
energy. Cumulative effects stimulate the instability and enhance the resulting
fluctuations, which interact with electrons and stimulate their diffusion in
velocity space, leading to a faster and deeper relaxation of the beaming
velocity associated with a core heating in perpendicular direction and a
thermalization of the beaming electrons. In particular, the relaxation of
temperature anisotropy to quasi-stable states below the thresholds conditions
predicted by linear theory may explain the observations showing the
accumulation of these states near the isotropy and equipartition of energy.",1912.09283v1
2019-12-23,Fluctuation Dynamo in Collisionless and Weakly Collisional Magnetized Plasmas,"In weakly collisional astrophysical plasmas, such as the intracluster medium
of galaxy clusters, the amplification of cosmic magnetic fields by chaotic
fluid motions is hampered by the adiabatic production of magnetic-field-aligned
pressure anisotropy. This anisotropy drives a viscous stress parallel to the
field that inhibits the plasma's ability to stretch magnetic-field lines. I
demonstrate through the use of kinetic simulations that in high-$\beta$
plasmas, kinetic ion-Larmor scale instabilities sever the adiabatic link
between the thermal and magnetic pressures, reducing this viscous stress and
thereby allowing the dynamo to operate. Two distinct regimes of the fluctuation
dynamo in a magnetized plasma are identified: one in which these instabilities
efficiently regulate the pressure anisotropy and one in which this regulation
is imperfect. I elucidate the role of these kinetic instabilities on the plasma
viscosity and determine how the fields and flows self-organize to allow the
dynamo to operate in the face of parallel viscous stresses. In the case of
efficient pressure-anisotropy regulation, the plasma dynamo closely resembles
its more traditional Pm ~ 1 MHD counterpart. When the regulation is imperfect,
the dynamo exhibits characteristics remarkably similar to those found in the
saturated state of the MHD dynamo. A novel set of microphysical closures for
fluid simulations that bridges these two regimes are constructed, exhibiting
explosive magnetic-field growth caused by a field-strength-dependent viscosity.
The dynamos in both collisionless and weakly collisional plasmas are then
closely compared to each other, revealing substantial differences in how
sub-parallel viscous motions behave. The former (collisionless) scenario
experiences a cascade of stretching motions to sub-Larmor scales that lead to
increasingly fast dynamo as the magnetic Reynolds number is increased.",1912.11072v1
2020-01-14,Anisotropic superconductivity mediated by ferroelectric fluctuations in cubic systems with spin-orbit coupling,"Motivated by the experimental observation that superconductivity in bulk
doped SrTiO$_{3}$ is enhanced as a putative ferroelectric quantum critical
point (FE-QCP) is approached, we study the pairing instability of a cubic
system in which electrons exchange low-energy ferroelectric fluctuations.
Instead of the gradient coupling to the lattice distortion associated with
ferroelectricity, we consider a direct coupling between the electrons and the
bosonic ferroelectric field that appears in the presence of spin-orbit
coupling. Working in the weak-coupling regime, we find that the pairing
interaction is dominated by the soft transverse optical (TO) mode, resulting in
a $T_{c}$ enhancement upon approaching the FE-QCP. Focusing on even-parity
states, we find that although the $s$-wave state always wins, states with
higher Cooper-pair angular momentum become close competitors as the TO mode
softens. We show that the cubic anisotropy of the FE fluctuations mixes the
$s$-wave and $g$-wave states, resulting in a characteristic anisotropy of the
gap function. The gap anisotropy behaves non-monotonically as the FE-QCP is
approached: upon decreasing the TO mode frequency, the gap anisotropy first
changes sign and then increases in magnitude. We discuss the possible
applications of our results to the superconducting state of SrTiO$_{3}$.",2001.04919v1
2020-04-07,Linear stability of magnetic vortex chains in a plasma in the presence of equilibrium electron temperature anisotropy,"The linear stability of chains of magnetic vortices in a plasma is
investigated analytically in two dimensions by means of a reduced fluid model
assuming a strong guide field and accounting for equilibrium electron
temperature anisotropy. The chain of magnetic vortices is modelled by means of
the classical ""cat's eyes"" solutions and the linear stability is studied by
analysing the second variation of a conserved functional, according to the
Energy-Casimir method. The stability analysis is carried out on the domain
bounded by the separatrices of the vortices. Two cases are considered,
corresponding to a ratio between perpendicular equilibrium ion and electron
temperature much greater or much less than unity, respectively. In the former
case, equilibrium flows depend on an arbitrary function. Stability is attained
if the equilibrium electron temperature anisotropy is bounded from above and
from below, with the lower bound corresponding to the condition preventing the
firehose instability. A further condition sets an upper limit to the amplitude
of the vortices, for a given choice of the equilibrium flow. For cold ions, two
sub-cases have to be considered. In the first one, equilibria correspond to
those for which the velocity field is proportional to the local Alfv\'en
velocity. Stability conditions imply: an upper limit on the amplitude of the
flow, which automatically implies firehose stability, an upper bound on the
electron temperature anisotropy and again an upper bound on the size of the
vortices. The second sub-case refers to equilibrium electrostatic potentials
which are not constant on magnetic flux surfaces and the resulting stability
conditions correspond to those of the first sub-case in the absence of flow.",2004.03243v2
2020-04-27,Anisotropy driven reversal of magnetisation in Blume-Capel ferromagnet: A Monte Carlo study,"The two dimensional Spin-1 Blume-Capel ferromagnet is studied by Monte Carlo
simulation with Metropolis algorithm. Starting from initial ordered spin
configuration the reversal of magnetisation is investigated in presence of a
magnetic field ($h$) applied in the opposite direction. The variations of the
reversal time with the strength of single site anisotropy are investigated in
details. The exponential dependence was observed. The systematic variations of
the mean reversal time with positive and negative anisotropy was found. The
mean macroscopic reversal time was observed to be linearly dependent on a
suitably defined microscopic reversal time. The saturated magnetisation $M_f$
after the reversal was noticed to be dependent of the strength of anisotropy
$D$. An interesting scaling relation was obtained, $|M_f| \sim
|h|^{\beta}f(D|h|^{-\alpha})$ with the scaling function of the form $f(x)=
\frac{1}{1+e^{(x-a)/b}}$. The temporal evolution of density of $S_i^z=0$
(surrounded by all $S_i^z=+1$) is observed to be exponentially decaying. The
growth of mean density of $S_i^z=-1$ has been fitted in a function
$\rho_{-1}(t) \sim \frac{1}{a+e^{(t_c-t)/c}}$. The characteristic time shows
$t_c \sim e^{-rD}$ and a crossover in the rate of exponential falling is
observed at $D=1.5$. The metastable volume fraction has been found to obey the
Avrami's law.",2004.12586v4
2020-05-18,A Detailed Examination of Anisotropy and Timescales in Three-dimensional Incompressible Magnetohydrodynamic Turbulence,"When magnetohydrodynamic turbulence evolves in the presence of a large-scale
mean magnetic field, an anisotropy develops relative to that preferred
direction. The well-known tendency is to develop stronger gradients
perpendicular to the magnetic field, relative to the direction along the field.
This anisotropy of the spectrum is deeply connected with anisotropy of
estimated timescales for dynamical processes, and requires reconsideration of
basic issues such as scale locality and spectral transfer. Here analysis of
high-resolution three-dimensional simulations of unforced magnetohydrodynamic
turbulence permits quantitative assessment of the behavior of theoretically
relevant timescales in Fourier wavevector space. We discuss the distribution of
nonlinear times, Alfv\'en times, and estimated spectral transfer rates.
Attention is called to the potential significance of special regions of the
spectrum, such as the two-dimensional limit and the ""critical balance"" region.
A formulation of estimated spectral transfer in terms of a suppression factor
supports a conclusion that the quasi two-dimensional fluctuations
(characterized by strong nonlinearities) are not a singular limit, but may be
in general expected to make important contributions.",2005.08815v2
2020-05-19,Spin transport in a tunable Heisenberg model realized with ultracold atoms,"Simple models of interacting spins play an important role in physics. They
capture the properties of many magnetic materials, but also extend to other
systems, such as bosons and fermions in a lattice, systems with gauge fields,
high-Tc superconductors, and systems with exotic particles such as anyons and
Majorana fermions. In order to study and compare these models, a versatile
platform is needed. Realizing such a system has been a long-standing goal in
the field of ultracold atoms. So far, spin transport has only been studied in
the isotropic Heisenberg model. Here we implement the Heisenberg XXZ model with
adjustable anisotropy and use this system to study spin transport far from
equilibrium after quantum quenches from imprinted spin helix patterns. In the
non-interacting XX model, we find ballistic behavior of spin dynamics, while in
the isotropic XXX model, we find diffusive behavior. For positive anisotropies,
the dynamics ranges from anomalous super-diffusion to sub-diffusion depending
on anisotropy, whereas for negative anisotropies, we observe a crossover in the
time domain from ballistic to diffusive transport. This behavior contrasts with
expectations for the linear response regime and raises new questions in
understanding quantum many-body dynamics far away from equilibrium.",2005.09549v1
2020-06-03,Combining ILC and moment expansion techniques for extracting average-sky signals and CMB anisotropies,"The method of weighted addition of multi-frequency maps, more commonly
referred to as {\it Internal Linear Combination} (ILC), has been extensively
employed in the measurement of cosmic microwave background (CMB) anisotropies
and its secondaries along with similar application in 21cm data analysis. Here
we argue and demonstrate that ILC methods can also be applied to data from
absolutely-calibrated CMB experiments to extract average-sky signals in
addition to the conventional CMB anisotropies. The performance of the simple
ILC method is, however, limited, but can be significantly improved by adding
constraints informed by physics and existing empirical information. In recent
work, a moment description has been introduced as a technique of carrying out
high precision modeling of foregrounds in the presence of inevitable averaging
effects. We combine these two approaches to construct a heavily constrained
form of the ILC, dubbed \milc, which can be used to recover tiny monopolar
spectral distortion signals in the presence of realistic foregrounds and
instrumental noise. This is a first demonstration for measurements of the
monopolar and anisotropic spectral distortion signals using ILC and extended
moment methods. We also show that CMB anisotropy measurements can be improved,
reducing foreground biases and signal uncertainties when using the \milc. While
here we focus on CMB spectral distortions, the scope extends to the 21cm
monopole signal and $B$-mode analysis. We briefly discuss augmentations that
need further study to reach the full potential of the method.",2006.02458v1
2020-07-20,Electrical control of spin relaxation anisotropy during drift transport in a two-dimensional electron gas,"Spin relaxation was studied in a two-dimensional electron gas confined in a
wide GaAs quantum well. Recently, the control of the spin relaxation anisotropy
by diffusive motion was first shown in D. Iizasa et al., arXiv:2006.08253
(2020). Here, we demonstrate electrical control by drift transport in a system
with two-subbands occupied. The combined effect of in-plane and gate voltages
was investigated using time-resolved Kerr rotation. The measured relaxation
time present strong anisotropy with respect to the transport direction. For an
in-plane accelerating electric field along $\left[110\right]$, the lifetime was
strongly suppressed irrespective of the applied gate voltage. Remarkably, for
transport along $\left[1\bar{1}0\right]$, the data shows spin lifetime that was
gate-dependent and longer than in the $\left[110\right]$ direction regardless
of the in-plane voltage. In agreement, independent results of anisotropic spin
precession frequencies are also presented. Nevertheless, the long spin
lifetime, strong anisotropy and drift response seen in the data are beyond the
existing models for spin drift and diffusion.",2007.10425v2
2020-07-31,Giant perpendicular magnetic anisotropy enhancement in MgO-based magnetic tunnel junction by using Co/Fe composite layer,"Magnetic tunnel junctions with perpendicular anisotropy form the basis of the
spin-transfer torque magnetic random-access memory (STT-MRAM), which is
non-volatile, fast, dense, and has quasi-infinite write endurance and low power
consumption. Based on density functional theory (DFT) calculations, we propose
an alternative design of magnetic tunnel junctions comprising
Fe(n)Co(m)Fe(n)/MgO storage layers with greatly enhanced perpendicular magnetic
anisotropy (PMA) up to several mJ/m2, leveraging the interfacial perpendicular
anisotropy of Fe/MgO along with a stress-induced bulk PMA discovered within bcc
Co. This giant enhancement dominates the demagnetizing energy when increasing
the film thickness. The tunneling magnetoresistance (TMR) estimated from the
Julliere model is comparable with that of the pure Fe/MgO case. We discuss the
advantages and pitfalls of a real-life fabrication of the structure and propose
the Fe(3ML)Co(4ML)Fe(3ML) as a storage layer for MgO-based STT-MRAM cells. The
large PMA in strained bcc Co is explained in the framework of Bruno's model by
the MgO-imposed strain and consequent changes in the energies of dyz and dz2
minority-spin bands.",2007.15940v1
2020-08-05,Whistler Waves and Electron Properties in the Inner Heliosphere: Helios Observations,"We present the analysis of narrowband whistler wave signatures observed in
the inner heliosphere (0.3-1 au). These signatures are bumps in the spectral
density in the 10-200 Hz frequency range of the AC magnetic field as measured
by the search coil magnetometer on board the Helios1 spacecraft. We show that
the majority of whistler signatures are observed in the slow solar wind (<500
km/s) and their occurrence increases with the radial distance (R), from ~3% at
0.3 au to ~10% at 0.9 au. In the fast solar wind (>600 km/s), whistler activity
is significantly lower; whistler signatures start to appear for R > 0.6 au and
their number increases from ~0.03% at 0.65 au to ~1% at 0.9 au. We have studied
the variation of the electron core and halo anisotropy, as well as the electron
normalized heat flux as a function of R and of the solar wind speed. We find
that, in the slow wind electron core and halo anisotropy is higher than in fast
one, and also that these anisotropies increase radially in both types of winds,
which is in line with the occurrence of whistler signatures. We hypothesize the
existence of a feedback mechanism to explain the observed radial variations of
the occurrence of whistlers in relation with the halo anisotropy.",2008.02334v1
2020-08-17,Precision Multi-Mode Dielectric Characterization of a Crystalline Perovskite Enables Determination of the Temperature-Dependent Phase Transitions,"Simple perovskite crystals undergo structural phase transitions on cooling to
low temperatures, which significantly change the material properties of the
crystal. In this work we rigorously characterize the temperature evolution of
permittivity of a perovskite crystal as it undergoes phase transitions. In
particular, we have undertaken precision measurements of a single crystal of
Strontium Titanate from 294.6 K to 5.6 K, by measuring the frequency of
multiple microwave transverse electric and magnetic resonant modes
simultaneously. The multi-mode microwave measurement technique of resonant
frequency used in this work allows high precision determination of any induced
anisotropy of the permittivity as the crystal undergoes structural phase
transitions. Compared with previous results we unequivocally show that the
permittivity has an isotropic value of $316.3\pm2.2$ at room temperature,
consistent with its well-known cubic structure, and determine the onset of
dielectric anisotropy as the crystal is cooled to lower temperatures. We show
that the crystal exhibits uniaxial anisotropy in the permittivity below 105 K
when the structure becomes tetragonal, and exhibits biaxial anisotropy in the
permittivity below 51 K when the structure becomes orthorhombic.",2008.07088v2
2020-08-26,An effective parameterization of texture-induced viscous anisotropy in orthotropic materials with application for modeling geodynamical flows,"In this article, we describe the mathematical formulation and the numerical
implementation of an effective parametrization of the viscous anisotropy of
orthorhombic materials produced by crystallographic preferred orientations (CPO
or texture), which can be integrated into 3D geodynamic and materials science
codes. Here, the approach is applied to characterize the texture-induced
viscous anisotropy of olivine polycrystals, the main constituent of the Earth's
upper mantle. The parameterization is based on the Hill (1948) orthotropic
yield criterion. The coefficients of the Hill yield surface are calibrated
based on numerical tests performed using the second order Viscoplastic
Self-consistent (SO-VPSC) model. The parametrization was implemented in a 3D
thermo-mechanical finite-element code developed to model large-scale
geodynamical flows, in the form of a Maxwell rheology combining isotropic
elastic and anisotropic non-linear viscous behaviors. The implementation was
validated by comparison with results of the analytical solution and of the
SO-VPSC model for simple shear and axial compression of a homogeneous
anisotropic material. An application designed to examine the effect of
texture-induced viscous anisotropy on the reactivation of mantle shear zones in
continental plates highlights unexpected couplings between localized
deformation controlled by variations in the orientation and intensity of the
olivine texture in the mantle and the mechanical behavior of the
elasto-viscoplastic overlying crust. Importantly, the computational time only
increases by a factor 2-3 with respect to the classic isotropic Maxwell
viscoelastic rheology.",2008.11494v3
2020-10-07,Correlation of uniaxial magnetic anisotropy axes and principal resistivities in polycrystalline ferromagnetic films,"In the present study, we demonstrate the measurement of resistivity tensor
($\rho$) along the magnetic axes of a polycrystalline film of ferromagnetic
permalloy (Py). To this end, conventional Hall-bar and a more recent extended
van der Pauw methods were utilized for determining 2D $\rho$ in the film plane.
The samples were prepared by normal incidence sputter deposition within an
in-situ magnetic field to induce in-plane uniaxial magnetic anisotropy in the
film. Since $\rho$ might be affected by the internal magnetization of the film,
we performed measurements by rotation of a saturating magnetic field in the
film plane. Both methods indicate that the average resistivity is lower along
the easy axis of the film compared to the hard axis. Since X-ray diffraction
results indicated no dominating texture in the film, we concluded that there is
a correlation between uniaxial magnetic axes and principal resistivity axes.
This is an important finding that allows determining the direction of magnetic
anisotropy axes without magnetometry. The results also verify atomic or pair
ordering to be the origin of uniaxial magnetic anisotropy in the Py since
resistivity is sensitive to the level of order in solids. The extended van der
Pauw utilized here can be easily performed on the as-received samples which is
of practical interest.",2010.03554v3
2020-10-10,Controlling the anisotropy of a van der Waals antiferromagnet with light,"Magnetic van der Waals materials provide an ideal playground for exploring
the fundamentals of low-dimensional magnetism and open new opportunities for
ultrathin spin processing devices. The Mermin-Wagner theorem dictates that as
in reduced dimensions isotropic spin interactions cannot retain long-range
correlations; the order is stabilized by magnetic anisotropy. Here, using
ultrashort pulses of light, we demonstrate all-optical control of magnetic
anisotropy in the two-dimensional van der Waals antiferromagnet NiPS$_3$.
Tuning the photon energy in resonance with an orbital transition between
crystal-field split levels of the nickel ions, we demonstrate the selective
activation of a sub-THz two-dimensional magnon mode. The pump polarization
control of the magnon amplitude confirms that the activation is governed by the
instantaneous magnetic anisotropy axis emergent in response to photoexcitation
of orbital states with a lowered symmetry. Our results establish pumping of
orbital resonances as a universal route for manipulating magnetic order in
low-dimensional (anti)ferromagnets.",2010.05062v1
2020-11-02,Explaining Cosmological Anisotropy: Evidence for Causal Horizons from CMB data,"The origin of power asymmetry and other measures of statistical anisotropy on
the largest scales of the universe, as manifested in Cosmic Microwave
Background (CMB) and large-scale structure data, is a long-standing open
question in cosmology. In this paper we analyze the Planck Legacy temperature
anisotropy data and find strong evidence for a violation of the Cosmological
principle of isotropy, with a probability of being a statistical fluctuation of
order ~ 10^-9. The detected anisotropy is related to large-scale directional
LCDM cosmological parameter variations across the CMB sky, that are sourced by
three distinct patches in the maps with circularly-averaged sizes between 40 to
70 degrees in radius. We discuss the robustness of our findings to different
foreground separation methods and analysis choices, and find consistent results
from WMAP data when limiting the analysis to the same scales. We argue that
these well-defined regions within the cosmological parameter maps may reflect
finite and casually disjoint horizons across the observable universe. In
particular we show that the observed relation between horizon size and mean
dark energy density within a given horizon is in good agreement with
expectations from a recently proposed model of the universe that explains
cosmic acceleration and cosmological parameter tensions between the high and
low redshift universe from the existence of casual horizons within our
universe.",2011.00910v4
2020-11-04,Anisotropic Fermionic Quasiparticles,"We have carried out a comprehensive investigation of the quasiparticle
properties of a two-dimensional electron gas, interacting via the long-range
Coulomb interaction, in the presence of bare mass anisotropy (i.e. with an
elliptic noninteracting Fermi surface) by calculating the self-energy, the
spectral function, the scattering rate, and the effective mass within the
leading order dynamical self-energy approximation. We find novel anisotropic
features of quasiparticle properties that are not captured by the isotropic
approximation where the anisotropic effective mass is replaced by the isotropic
averaged density-of-states mass. Some of these interesting results are: (1) the
renormalization of the quasiparticle spectrum becomes highly anisotropic as the
quasiparticle energy increases away from the Fermi energy; (2) the inelastic
scattering rate features a strong anisotropy, exhibiting an abrupt jump at
different injected energies depending on the momentum direction of the injected
electron; (3) the effective mass anisotropy is reduced by interactions. Our
results and analysis show that the unjustified neglect of the mass anisotropy
can lead to an incorrect description of quasiparticle properties of the
anisotropic system although the use of an equivalent isotropic approximation
using the density-of-states effective mass works as a reasonable approximation
in many situations. We also provide a theory using the plasmon-pole
approximation, commenting on its validity for anisotropic self-energy
calculations. We comment also on the interaction effect on the Fermi surface
topology, finding that the elliptic shape of the bare Fermi surface is
preserved, with suppressed ellipticity, in the interacting system to a high
degree of accuracy. Our theory provides a complete generalization of the
existing isotropic many-body theory of interacting electrons to the
corresponding anisotropic systems.",2011.02481v2
2020-11-18,Breaking Beta: A comparison of mass modelling methods for spherical systems,"We apply four different mass modelling methods to a suite of publicly
available mock data for spherical stellar systems. We focus on the recovery of
the density and velocity anisotropy as a function of radius, using either
line-of-sight velocity data only, or adding proper motion data. All methods
perform well on isotropic and tangentially anisotropic mock data, recovering
the density and velocity anisotropy within their 95% confidence intervals over
the radial range 0.25 < R/Rhalf < 4, where Rhalf is the half light radius.
However, radially-anisotropic mocks are more challenging. For line-of-sight
data alone, only methods that use information about the shape of the velocity
distribution function are able to break the degeneracy between the density
profile and the velocity anisotropy to obtain an unbiased estimate of both.
This shape information can be obtained through directly fitting a global phase
space distribution function, by using higher order 'Virial Shape Parameters',
or by assuming a Gaussian velocity distribution function locally, but
projecting it self-consistently along the line of sight. Including proper
motion data yields further improvements, and in this case, all methods give a
good recovery of both the radial density and velocity anisotropy profiles.",2011.09493v2
2020-11-19,The role of $T_0$ in CMB anisotropy measurements,"The quantity $T_0$, the cosmic microwave background (CMB) monopole, is an
often neglected seventh parameter of the standard cosmological model. As well
as its variation affecting the physics of the CMB, the measurement of $T_0$ is
also used to calibrate the anisotropies, via the orbital dipole. We point out
that it is easy to misestimate the effect of $T_0$ because the CMB anisotropies
are conventionally provided in temperature units. In fact the anisotropies are
most naturally described as dimensionless and we argue for restoring the
convention of working with $\Delta T/T$ rather than $\Delta T$. As a free
cosmological parameter, $T_0$ most naturally only impacts the CMB power spectra
through late-time effects. Thus if we ignore the COBE-FIRAS measurement,
current CMB data only weakly constrain $T_0$. Even ideal future CMB data can at
best provide a percent-level constraint on $T_0$, although adding large-scale
structure data will lead to further improvement. The FIRAS measurement is so
precise that its uncertainty negligibly effects most, but not all, cosmological
parameter inferences for current CMB experiments. However, if we eventually
want to extract all available information from CMB power spectra measured to
multipoles $\ell\simeq5000$, then we will need a better determination of $T_0$
than is currently available.",2011.09616v2
2020-11-20,Anisotropy of the spin-orbit coupling driven by a magnetic field in InAs nanowires,"We use the $\mathbf{k} \cdot \mathbf{p}$ theory and the envelope function
approach to evaluate the Rashba spin-orbit coupling induced in a semiconductor
nanowire by a magnetic field at different orientations, taking explicitely into
account the prismatic symmetry of typical nano-crystals. We make the case for
the strongly spin-orbit-coupled InAs semiconductor nanowires and investigate
the anisotropy of the spin-orbit constant with respect to the field direction.
At sufficiently high magnetic fields perpendicular to the nanowire, a 6-fold
anisotropy results from the interplay between the orbital effect of field and
the prismatic symmetry of the nanowire. A back-gate potential, breaking the
native symmetry of the nano-crystal, couples to the magnetic field inducing a
2-fold anisotropy, with the spin-orbit coupling being maximized or minimized
depending on the relative orientation of the two fields. We also investigate
in-wire field configurations, which shows a trivial 2-fold symmetry when the
field is rotated off the axis. However, isotropic spin-orbit coupling is
restored if a sufficiently high gate potential is applied. Our calculations are
shown to agree with recent experimental analysis of the vectorial character of
the spin-orbit coupling for the same nanomaterial, providing a microscopic
interpretation of the latter.",2011.10483v1
2020-12-07,Monopole Fluctuation of the CMB and its Gauge Invariance,"The standard theoretical description $\Theta(\hat n)$ of the observed CMB
temperature anisotropies is gauge-dependent. It is, however, well known that
the gauge mode is limited to the monopole and the higher angular multipoles
$\Theta_l$ ($l\geq1$) are gauge-invariant. Several attempts have been made in
the past to properly define the monopole fluctuation, but the resulting values
of the monopole power $C_0$ are infinite due to the infrared divergences. The
infrared divergences arise from the contribution of the uniform gravitational
potential to the monopole fluctuation, in violation of the equivalence
principle. Here we present the gauge-invariant theoretical description of the
observed CMB temperature anisotropies and compute the monopole power
$C_0=1.66\times10^{-9}$ in a $\Lambda$CDM model. While the gauge-dependence in
the standard calculations originates from the ambiguity in defining the
hypersurface for the background CMB temperature $\bar T$ today, it is in fact
well defined and one of the fundamental cosmological parameters. We argue that
once the cosmological parameters are chosen, the monopole fluctuation can be
unambiguously inferred from the angle-average of the observed CMB temperature,
making it a model-dependent ''observable''. Adopting simple approximations for
the anisotropy formation, we derive a gauge-invariant analytical expression for
the observed CMB temperature anisotropies to study the CMB monopole fluctuation
and the cancellation of the uniform gravitational potential contributions on
large scales.",2012.03968v2
2020-12-08,Director alignment at the nematic-isotropic interface: elastic anisotropy and active anchoring,"Activity in nematics drives interfacial flows that lead to preferential
alignment that is tangential or planar for extensile systems (pushers) and
perpendicular or homeotropic for contractile ones (pullers). This alignment is
known as active anchoring and has been reported for a number of systems and
described using active nematic hydrodynamic theories. The latter are based on
the one-elastic constant approximation, i.e., they assume elastic isotropy of
the underlying passive nematic. Real nematics, however, have different elastic
constants, which lead to interfacial anchoring. In this paper, we consider
elastic anisotropy in multiphase and multicomponent hydrodynamic models of
active nematics and investigate the competition between the interfacial
alignment driven by the elastic anisotropy of the passive nematic and the
active anchoring. We start by considering systems with translational invariance
to analyze the alignment at flat interfaces and, then, consider two-dimensional
systems and active nematic droplets. We investigate the competition of the two
types of anchoring over a wide range of the other parameters that characterize
the system. The results of the simulations reveal that the active anchoring
dominates except at very low activities, when the interfaces are static. In
addition, we found that the elastic anisotropy does not affect the dynamics but
changes the active length that becomes anisotropic.",2012.04288v2
2021-01-12,The Imprint of Large Scale Structure on the Ultra-High-Energy Cosmic Ray Sky,"Ultra-high-energy cosmic rays (UHECRs) are atomic nuclei from space with
vastly higher energies than any other particles ever observed. Their origin and
chemical composition remain a mystery. As we show here, the large- and
intermediate-angular-scale anisotropies observed by the Pierre Auger
Observatory are a powerful tool for understanding the origin of UHECRs. Without
specifying any particular production mechanism, but only postulating that the
source distribution follows the matter distribution of the local Universe, a
good accounting of the magnitude, direction and energy dependence of the dipole
anisotropy at energies above $8 \times 10^{18}$ eV is obtained, after taking
into account the impact of energy losses during propagation (the ""GZK
horizon""), diffusion in extragalactic magnetic field and deflections in the
Galactic magnetic field (GMF). This is a major step toward the long-standing
hope of using UHECR anisotropies to constrain UHECR composition and magnetic
fields. The observed dipole anisotropy is incompatible with a pure proton
composition in this scenario. With a more accurate treatment of energy losses,
it should be possible to further constrain the cosmic-ray composition and
properties of the extragalactic magnetic field, self-consistently improve the
GMF model, and potentially expose individual UHECR sources.",2101.04564v3
2021-01-11,On the interplay of solar wind proton and electron instabilities: Linear and quasi-linear approaches,"Important efforts are currently made for understanding the so-called kinetic
instabilities, driven by the anisotropy of different species of plasma
particles present in the solar wind and terrestrial magnetosphere. These
instabilities are fast enough to efficiently convert the free energy of plasma
particles into enhanced (small-scale) fluctuations with multiple implications,
regulating the anisotropy of plasma particles. In this paper we use both linear
and quasilinear (QL) frameworks to describe complex unstable regimes, which
realistically combine different temperature anisotropies of electrons and ions
(protons). Thus parameterized are various instabilities, e.g., proton and
electron firehose, electromagnetic ion cyclotron, and whistler instability,
showing that their main linear properties are markedly altered by the interplay
of anisotropic electrons and protons. Linear theory may predict a strong
competition of two instabilities of different nature when their growth rates
are comparable. In the QL phase wave fluctuations grow and saturate at
different levels and temporal scales, by comparison to the individual
excitation of the proton or electron instabilities. In addition, cumulative
effects of the combined proton and electron induced fluctuations can markedly
stimulate the relaxations of their temperature anisotropies. Only whistler
fluctuations inhibit the efficiency of proton firehose fluctuations in the
relaxation of anisotropic protons. These results offer valuable premises for
further investigations in numerical simulations, to decode the full spectrum of
kinetic instabilities resulting from the interplay of anisotropic electrons and
protons in space plasmas.",2101.07689v1
2021-02-19,Improved large scales interstellar dust foreground model and CMB solar dipole measurement,"The Cosmic Microwave Background anisotropies are difficult to measure at
large angular scales. In this paper, we present a new analysis of the \Planck\
High Frequency Instrument data that brings the cosmological part and its major
foreground signal close to the detector noise. The solar dipole signal, induced
by the motion of the solar system with respect to the CMB, is a very efficient
tool to calibrate a detector or a set of detectors with high accuracy. In this
work, the solar dipole signal is used to extract corrections of the frequency
maps offsets reducing significantly uncertainties. The solar dipole parameters
are refined together with the improvement of the high frequency foregrounds,
and of the CMB large scales cosmological anisotropies. The stability of the
solar dipole parameters is a powerful way to control the galactic foregrounds
removal in the component separation process. It is used to build a model for
Spectral Energy Distribution spatial variations of the interstellar dust
emission. The knowledge of these variations will help future CMB analyses in
intensity, and also in polarization to measure faint signal related to the
optical reionization depth and the tensor-to-scalar ratio of the primordial
anisotropies. The results of this work are: improved solar dipole parameters, a
new interstellar dust model, and a large scale cosmological anisotropies map.",2102.10004v1
2021-02-22,Anisotropic cosmological models in Horndeski gravity,"It was found recently that the anisotropies in the homogeneous Bianchi I
cosmology considered within the context of a specific Horndeski theory are
damped near the initial singularity instead of being amplified. In this work we
extend the analysis of this phenomenon to cover the whole of the Horndeski
family. We find that the phenomenon is absent in the K-essence and/or Kinetic
Gravity Braiding theories, where the anisotropies grow as one approaches the
singularity. The anisotropies are damped at early times only in more general
Horndeski models whose Lagrangian includes terms quadratic and cubic in second
derivatives of the scalar field. Such theories are often considered as being
inconsistent with the observations because they predict a non-constant speed of
gravitational waves. However, the predicted value of the speed at present can
be close to the speed of light with any required precision, hence the theories
actually agree with the present time observations. We consider two different
examples of such theories, both characterized by a late self-acceleration and
an early inflation driven by the non-minimal coupling. Their anisotropies show
a maximum at intermediate times and approach zero at early and late times. The
early inflationary stage exhibits an instability with respect to inhomogeneous
perturbations, suggesting that the initial state of the universe should be
inhomogeneous. However, more general Horndeski models may probably be stable.",2102.10981v2
2021-02-27,Strong bulk-surface interaction dominated in-plane anisotropy of electronic structure in GaTe,"Recently, intriguing physical properties have been unraveled in anisotropic
layered semiconductors, in which the in-plane electronic band structure
anisotropy often originates from the low crystallographic symmetry and thus a
thickness-independent character emerges. Here, we apply high-resolution
angle-resolved photoemission spectroscopy to directly image the in-plane
anisotropic energy bands in monoclinic gallium telluride (GaTe). Our
first-principles calculations reveal the in-plane anisotropic energy band
structure of GaTe measured experimentally is dominated by a strong bulk-surface
interaction rather than geometric factors, surface effect and quantum
confinement effect. Furthermore, accompanied by the thickness of GaTe
increasing from mono- to few-layers, the strong interlayer coupling of GaTe
induces direct-indirect-direct band gap transitions and the in-plane anisotropy
of hole effective mass is reversed. Our results shed light on the physical
origins of in-plane anisotropy of electronic structure in GaTe, paving the way
for the design and device applications of nanoelectronics and optoelectronics
based on anisotropic layered semiconductors.",2103.00272v4
2021-03-05,Microstructural origins of crushing strength for inherently anisotropic brittle materials,"We study the crushing strength of brittle materials whose internal structure
(e.g., mineral particles or graining) presents a layered arrangement
reminiscent of sedimentary and metamorphic rocks. Taking a discrete-element
approach, we probe the failure strength of circular-shaped samples intended to
reproduce specific mineral configurations. To do so, assemblies of cells,
products of a modified Voronoi tessellation, are joined in mechanically-stable
layerings using a bonding law. The cells' shape distribution allows us to set a
level of inherent anisotropy to the material. Using a diametral point loading,
and systematically changing the loading orientation with respect to the cells'
configuration, we characterize the failure strength of increasingly anisotropic
structures. This approach ends up reproducing experimental observations and
lets us quantify the statistical variability of strength, the consumption of
the fragmentation energy, and the induced anisotropies linked to the cell's
geometry and force transmission in the samples. Based on a fine description of
geometrical and mechanical properties at the onset of failure, we develop a
micromechanical breakdown of the crushing strength variability using an
analytical decomposition of the stress tensor and the geometrical and force
anisotropies. We can conclude that the origins of failure strength in
anisotropic layered media rely on compensations of geometrical and mechanical
anisotropies, as well as an increasing average radial force between minerals
indistinctive of tensile or compressive components.",2103.03962v1
2021-03-10,Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions,"Using 2D particle-in-cell (PIC) plasma simulations we study electron
acceleration by temperature anisotropy instabilities, assuming conditions
typical of above-the-loop-top (ALT) sources in solar flares. We focus on the
long-term effect of $T_{e,\perp} > T_{e,\parallel}$ instabilities by driving
the anisotropy growth during the entire simulation time, through imposing a
shearing or a compressing plasma velocity ($T_{e,\perp}$ and $T_{e,\parallel}$
are the temperatures perpendicular and parallel to the magnetic field). This
magnetic growth makes $T_{e,\perp}/T_{e,\parallel}$ grow due to electron
magnetic moment conservation, and amplifies the ratio $\omega_{ce}/\omega_{pe}$
from $\sim 0.53$ to $\sim 2$ ($\omega_{ce}$ and $\omega_{pe}$ are the electron
cyclotron and plasma frequencies, respectively). In the regime
$\omega_{ce}/\omega_{pe}\lesssim 1.2-1.7$ the instability is dominated by
oblique, quasi-electrostatic (OQES) modes, and the acceleration is inefficient.
When $\omega_{ce}/\omega_{pe}$ has grown to $\omega_{ce}/\omega_{pe}\gtrsim
1.2-1.7$, electrons are efficiently accelerated by the inelastic scattering
provided by unstable parallel, electromagnetic z (PEMZ) modes. After
$\omega_{ce}/\omega_{pe}$ reaches $\sim 2$, the electron energy spectra show
nonthermal tails that differ between the shearing and compressing cases. In the
shearing case, the tail resembles a power-law of index $\alpha_s \sim$ 2.9 plus
a high-energy bump reaching $\sim 300$ keV. In the compressing runs, $\alpha_s
\sim$ 3.7 with a spectral break above $\sim 500$ keV. This difference can be
explained by the different temperature evolutions in these two types of
simulations, suggesting a critical role played by the type of anisotropy
driving, $\omega_{ce}/\omega_{pe}$ and the electron temperature in the
efficiency of the acceleration.",2103.05805v2
2021-04-01,The oscillatory anisotropy in the spatially flat cosmological models,"In this manuscript, we investigate the oscillatory behaviour of the
anisotropy in the diagonal Bianchi-I spacetimes. Our starting point is a
simplification of Einstein's equations using only observable or physical
variables. As a consequence, we are able to: (a) Prove general results
concerning the existence of oscillations of the anisotropy in the primordial
and the late-time universe. For instance, in the expanding scenario, we show
that a past weakly mixmaster behaviour (oscillations as we approach the Kasner
solutions) might appear even with no violation of the usual energy conditions,
while in the future, the pulsation (oscillations around isotropic solutions)
seems to be most favored; (b) Determine a large scheme for deriving classes of
physically motivated exact solutions, and we give some (including the general
barotropic perfect fluid and the magnetic one); (c) Understand the physical
conditions for the occurrence of the isotropization or anisotropization during
the cosmological evolution; (d) Understand how anisotropy and energy density
are converted one into another. In particular, we call attention to the
presence of a residue in the energy density in a late-time isotropic universe
coming from its past anisotropic behaviour.",2104.00470v1
2021-05-09,Constraining the anisotropy of the Universe with the X-ray and UV fluxes of quasars,"We test the anisotropy in the Finslerian cosmological model with the X-ray
and ultraviolet (UV) fluxes of 808 quasars. The dipole amplitude is
$A_D=0.302_{ -0.124}^{ +0.185}$ and the dipole direction points towards $(l, b)
= ( 288.92_{~ -28.80^{\circ}}^{^{\circ}+23.74^{\circ}}, 6.10_{~
-16.40^{\circ}}^{^{\circ} +16.55^{\circ}} )$. We find that the dipole direction
from the X-ray and UV fluxes of quasars is very close to the dipole direction
given by the ""Joint Light-curve Analysis"" (JLA) compilation in the Finslerian
cosmological model and the angular difference between the two dipole directions
is only $10.44^{\circ}$. We also find the angular difference between the dipole
direction from the 808 quasars in the Finslerian cosmological model and ones
from the supernovae of type Ia (SNe Ia) samples in the dipole-modulated
$\Lambda$CDM model is around $30^{\circ}$. Six gravitationally lensed quasars
are considered to investigate the Hubble constant $H_0$ in the Finslerian
cosmological model. We get a slightly smaller $H_0$ than the result given by
the six gravitationally lensed quasars. Finally, we forecast the future
constraints on the dipole parameters with the X-ray and UV fluxes of quasars.
As the number of simulations increases, the precisions of the parameters
related to anisotropy in the Finslerian cosmological model improve
significantly. The X-ray and UV fluxes of quasars have a promising future as a
probe of anisotropy in Finsler spacetime.",2105.03965v1
2021-05-22,Estimation of lunar surface dielectric constant using MiniRF SAR data,"A new model has been developed to estimate the dielectric constant of the
lunar surface using Synthetic Aperture Radar (SAR) data. Continuous
investigation on the dielectric constant of the lunar surface is a high
priority task due to future lunar mission's goals and possible exploration of
human outposts. For this purpose, derived anisotropy and backscattering
coefficients of SAR images are used. The SAR images are obtained from Miniature
Radio Frequency (MiniRF) radar onboard Lunar Reconnaissance Orbiter (LRO).
These images are available in the form of Stokes parameters, which are used to
derive the coherency matrix. The derived coherency matrix is further
represented in terms of particle anisotropy. This coherency matrix's elements
compared with Cloud's coherency matrix, which results in the new relationship
between particle anisotropy and coherency matrix elements (backscattering
coefficients). Following this, estimated anisotropy is used to determine the
dielectric constant. Our model estimates the dielectric constant of the lunar
surface without parallax error. The produce results are also comparable with
the earlier estimate. As an advantageous, our method estimates the dielectric
constant without any apriori information about the density or composition of
lunar surface materials. The proposed approach can also be useful for
determining the dielectric properties of Mars and other celestial bodies.",2105.10670v1
2021-05-25,"Power Anisotropy, Dispersion Signature and Turbulence Diffusion Region in the 3D Wavenumber Domain of Space Plasma Turbulence","We explore the multi-faceted important features of turbulence (e.g.,
anisotropy, dispersion, diffusion) in the three-dimensional (3D) wavenumber
domain ($k_\parallel$, $k_{\perp,1}$, $k_{\perp,2}$), by employing the
k-filtering technique to the high-quality measurements of fields and particles
from the MMS multi-spacecraft constellation. We compute the 3D power spectral
densities (PSDs) of magnetic and electric fluctuations (marked as
$\rm{PSD}(\delta \mathbf{B}(\mathbf{k}))$ and $\rm{PSD}(\delta
\mathbf{E}'_{\langle\mathbf{v}_\mathrm{i}\rangle}(\mathbf{k}))$), both of which
show a prominent spectral anisotropy in the sub-ion range. We give the first 3D
image of the bifurcation between power spectra of the electric and magnetic
fluctuations, by calculating the ratio between $\rm{PSD}(\delta \mathbf{E}'_{
\langle\mathbf{v}_\mathrm{i}\rangle}(\mathbf{k}))$ and $\rm{PSD}(\delta
\mathbf{B}(\mathbf{k}))$, the distribution of which is related to the
non-linear dispersion relation. We also compute the ratio between electric
spectra in different reference frames defined by the ion bulk velocity, that is
$\mathrm{PSD}(\delta{\mathbf{E}'_{\mathrm{local}\
\mathbf{v}_\mathrm{i}}})/\mathrm{PSD}(\delta{\mathbf{E}'_{
\langle\mathbf{v}_\mathrm{i}\rangle}})$, to visualize the turbulence ion
diffusion region (T-IDR) in wavenumber space. The T-IDR has an anisotropy and a
preferential direction of wavevectors, which is generally consistent with the
plasma wave theory prediction based on the dominance of kinetic Alfv\'en waves
(KAW). This work manifests the worth of the k-filtering technique in diagnosing
turbulence comprehensively, especially when the electric field is involved.",2105.12568v1
2021-06-03,Effect of pseudogap on electronic anisotropy in the strain dependence of the superconducting $T_c$ of underdoped YBa$_2$Cu$_3$O$_y$,"For orthorhombic superconductors we define thermodynamic anisotropy $N \equiv
d T_c/d \epsilon_{22} - dT_c/d \epsilon_{11}$ as the difference in how
superconducting $T_c$ varies with strains $\epsilon_{ii}$, $i=(1, 2)$, along
the in-plane directions. We study the hole doping ($p$) dependence of $N$ on
detwinned single crystals of underdoped YBa$_2$Cu$_3$O$_y$ (YBCO) using
ultrasound technique. While the structural orthorhombicity of YBCO reduces
monotonically with decreasing doping over $0.065 <p<0.16$, we find that the
thermodynamic anisotropy shows an intriguing enhancement at intermediate doping
level, which is of electronic origin. Our theoretical analysis shows that the
enhancement of the electronic anisotropy can be related to the pseudogap
potential in the electronic specturm that itself increases when the Mott
insulating state is approached. Our results imply that the pseudogap is
controlled by a local energy scale that can be tuned by varying the nearest
neighbor Cu-Cu bond length. Our work opens the possibility to strain engineer
the pseudogap potential to enhance the superconducting \Tc.",2106.02055v2
2021-06-09,A new way to test the Cosmological Principle: measuring our peculiar velocity and the large scale anisotropy independently,"We present a novel approach to disentangle two key contributions to the
largest-scale anisotropy of the galaxy distribution: (i) the intrinsic dipole
due to clustering and anisotropic geometry, and (ii) the kinematic dipole due
to our peculiar velocity. Including the redshift and angular size of galaxies,
in addition to their fluxes and positions allows us to measure both the
direction and amplitude of our velocity independently of the intrinsic dipole
of the source distribution. We find that this new approach applied to future
galaxy surveys (LSST and Euclid) and a SKA radio continuum survey will allow to
measure our velocity ($\beta = v/c$) with a relative error in the amplitude
$\sigma(\beta)/\beta \sim (1.3 - 4.5)\%$ and in direction, $\theta_{\beta} \sim
0.9^\circ - 3.9^\circ$, well beyond what can be achieved when analysing only
the number count dipole. We also find that galaxy surveys are able to measure
the intrinsic large-scale anisotropy with a relative uncertainty of $\lesssim
5\%$ (measurement error, not including cosmic variance). Our method enables two
simultaneous tests of the Cosmological Principle: comparing the observations of
our peculiar velocity with the CMB dipole, and testing for a significant
intrinsic anisotropy on large scales which would indicate effects beyond the
standard cosmological model.",2106.05284v2
2021-06-27,Relaxation in Ordered Assembly of Magnetic Nanoparticles,"We study the relaxation characteristics in the two-dimensional ($l^{}_x
\times l^{}_y$) array of magnetic nanoparticles (MNPs) as a function of aspect
ratio $A^{}_r=l^{}_y/l^{}_x$, dipolar interaction strength $h^{}_d$ and
anisotropy axis orientation using computer simulation. The anisotropy axes of
all the MNPs are assumed to have the same direction, $\alpha$ being the
orientational angle. Irrespective of $\alpha$ and $A^{}_r$, the functional form
of the magnetization-decay curve is perfectly exponentially decaying with
$h^{}_d\leq0.2$. There exists a transition in relaxation behaviour at
$h^{}_d\approx0.4$; magnetization relaxes slowly for $\alpha\leq45^\circ$; it
relaxes rapildy with $\alpha>45^\circ$. Interestingly, it decays rapidly for
$h^{}_d>0.6$, irrespective of $\alpha$. It is because the dipolar interaction
promotes antiferromagnetic coupling in such cases. There is a strong effect of
$\alpha$ on the magnetic relaxation in the highly anisotropic system
($A^{}_r\geq25$). Interesting physics unfolds in the case of a huge aspect
ratio $A^{}_r=400$. There is a rapid decay of magnetization with $\alpha$, even
for weakly interacting MNPs. Remarkably, magnetization does not relax even with
a moderate value of $h^{}_d=0.4$ and $\alpha=0^\circ$ because of ferromagnetic
coupling dominance. Surprisingly, there is a complete magnetization reversal
from saturation (+1) to $-1$ state with $\alpha>60^\circ$. The dipolar field
and anisotropy axis tend to get aligned antiparallel to each other in such a
case. The effective N\'eel relaxation time $\tau^{}_N$ depends weakly on
$\alpha$ for small $h^{}_d$ and $A^{}_r\leq25.0$. For large $A^{}_r$, there is
a rapid fall in $\tau^{}_N$ as $\alpha$ is incremented from 0 to $90^\circ$.
These results benefit applications in data and energy storages where such
controlled magnetization alignment and desired structural anisotropy are
desirable.",2106.14271v1
2021-07-16,Giant Anisotropic in-Plane Thermal Conduction Induced by Anomalous Phonons in Nearly-Equilaterally Structured PdSe2,"In two-dimensional materials, structure difference induces the difference in
phonon dispersions, leading to the anisotropy of in-plane thermal transport.
Here, we report an exceptional case in layered PdSe2, where the bonding, force
constants, and lattice constants are nearly-equal along the in-plane
crystallographic axis directions. The phonon dispersions show significant
differences between the Gamma-X and Gamma-Y directions, leading to the
anisotropy of in-plane thermal conductivity with a ratio up to 1.8. Such
anisotropy is not only unexpected in equilaterally structured (in-plane)
materials but also comparable to the record in the non-equilaterally structured
material reported to date. By combining inelastic X-ray scattering and
first-principles calculations, we attribute such anisotropy to the low-energy
phonons along Gamma-X, in particular, their lower group velocities and
""avoided-crossing"" behavior. The different bucking structures between a-
(zigzag-type) and b-axis (flat-type) are mainly responsible for the unique
phonon dynamics properties of PdSe2. The present results illustrate the unusual
thermal conduction mechanism of the equilaterally structured materials and
provide valuable insights on thermal management in electronic devices.",2107.07959v1
2021-09-13,Magnetic anisotropy of the van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$ studied by angular-dependent XMCD,"The van der Waals ferromagnet Cr$_2$Ge$_2$Te$_6$ (CGT) has a two-dimensional
crystal structure where each layer is stacked through van der Waals force. We
have investigated the nature of the ferromagnetism and the weak perpendicular
magnetic anisotropy (PMA) of CGT by means of X-ray absorption spectroscopy and
X-ray magnetic circular dichroism (XMCD) studies of CGT single crystals. The
XMCD spectra at the Cr $L_{2,3}$ edge for different magnetic field directions
were analyzed on the basis of the cluster-model multiplet calculation. The Cr
valence is confirmed to be 3+ and the orbital magnetic moment is found to be
nearly quenched, as expected for the high-spin $t_{2g}$$^3$ configuration of
the Cr$^{3+}$ ion. A large ($\sim 0.2$ eV) trigonal crystal-field splitting of
the $t_{2g}$ level caused by the distortion of the CrTe$_6$ octahedron has been
revealed, while the single-ion anisotropy (SIA) of the Cr atom is found to have
a sign {\it opposite} to the observed PMA and too weak compared to the reported
anisotropy energy. The present result suggests that anisotropic exchange
coupling between the Cr atoms through the ligand Te $5p$ orbitals having strong
spin-orbit coupling has to be invoked to explain the weak PMA of CGT, as in the
case of the strong PMA of CrI$_3$.",2109.05715v1
2021-10-06,"Stacking-order effect on spin-orbit torque, spin-Hall magnetoresistance, and magnetic anisotropy in Ni$_{81}$Fe$_{19}$-IrO$_2$ bilayers","The 5d transition-metal oxides have been an intriguing platform to
demonstrate efficient charge to spin current conversion due to a unique
electronic structure dominated by strong spin-orbit coupling. Here, we report
on stacking-order effect of spin-orbit torque (SOT), spin-Hall
magnetoresistance, and magnetic anisotropy in bilayer Ni$_{81}$Fe$_{19}$-5d
iridium oxide, IrO$_2$. While all the IrO$_2$ and Pt control samples exhibit
large dampinglike-SOT generation stemming from the efficient charge to spin
current conversion, the magnitude of the SOT is larger in the IrO$_2$
(Pt)-bottom sample than in the IrO$_2$ (Pt)-top one. The fieldlike-SOT has even
more significant stack order effect, resulting in an opposite sign in the
IrO$_2$ samples in contrast to the same sign in the Pt samples. Furthermore, we
observe that the magnetic anisotropy energy density and the anomalous Hall
effect are increased in the IrO$_2$ (Pt)-bottom sample, suggesting enhanced
interfacial perpendicular magnetic anisotropy. Our findings highlight the
significant influence of the stack order on spin transport and magnetotransport
properties of Ir oxide/ferromagnet systems, providing useful information on
design of SOT devices including 5d transition-metal oxides.",2110.02517v1
2021-10-27,Geometry of Magnetic Fluctuations near the Sun from PSP,"Solar wind magnetic fluctuations exhibit anisotropy due to the presence of a
mean magnetic field in the form of the Parker spiral. Close to the Sun, direct
measurements were not available until the recently launched Parker Solar Probe
(PSP) mission. The nature of anisotropy and geometry of the magnetic
fluctuations play a fundamental role in dissipation processes and in the
transport of energetic particles in space. Using PSP data, we present
measurements of geometry and anisotropy of the inner heliosphere magnetic
fluctuations, from fluid to kinetic scales. The results are surprising and
different from 1 au observations. We find that fluctuations evolve
characteristically with size scale. However, unlike 1 au solar wind, at the
outer scale, the fluctuations are dominated by wavevectors quasi-parallel to
the local magnetic field. In the inertial range, average wave vectors become
less field-aligned, but still remain more field aligned than near-Earth solar
wind. In the dissipation range, the wavevectors become almost perpendicular to
the local magnetic field in the dissipation range, to a much higher degree than
those indicated by 1 au observations. We propose that this reduced degree of
anisotropy in the outer scale and inertial range is due to the nature of
large-scale forcing outside the solar corona.",2110.14756v1
2021-10-26,CLASS_GWB: robust modeling of the astrophysical gravitational wave background anisotropies,"Gravitational radiation offers a unique possibility to study the large-scale
structure of the Universe, gravitational wave sources and propagation in a
completely novel way. Given that gravitational wave maps contain a wealth of
astrophysical and cosmological information, interpreting this signal requires a
non-trivial multidisciplinary approach. In this work we present the complete
computation of the signal produced by compact object mergers accounting for a
detailed modelling of the astrophysical sources and for cosmological
perturbations. We develop the CLASS_GWB code, which allows for the computation
of the anisotropies of the astrophysical gravitational wave background,
accounting for source and detector properties, as well as effects of
gravitational wave propagation. We apply our numerical tools to robustly
compute the angular power spectrum of the anisotropies of the gravitational
wave background generated by astrophysical sources in the LIGO-Virgo frequency
band. The end-to-end theoretical framework we present can be easily applied to
different sources and detectors in other frequency bands. Moreover, the same
numerical tools can be used to compute the anisotropies of gravitational wave
maps of the sky made using resolved events.",2110.15059v1
2021-11-15,Probing magnetic anisotropy in Kagome antiferromagnetic Mn$_3$Ge with torque magnetometry,"We investigate the magnetic symmetry of the topological antiferromagnetic
material Mn$_3$Ge by using torque measurements. Below the Neel temperature,
detailed angle-dependent torque measurements were performed on Mn$_3$Ge single
crystals in directions parallel and perpendicular to the Kagome basal plane.
The out-of plane torque data exhibit $\pm\sin\theta$ and $\sin2\theta$
behaviors, of which the former results from the spontaneous ferromagnetism
within the basal plane and the latter from the in- and out-of-plane
susceptibility anisotropy. The reversible component of the in-plane torque
exhibits $\sin6\varphi$ behavior, revealing the six-fold symmetry of the
in-plane magnetic free energy. Moreover, we find that the free energy minima
are pinned to the direction of spontaneous ferromagnetism, which correspond to
the maxima of the irreversible component of the in-plane torque. We provide an
effective spin model to describe the in-plane magnetic anisotropy. Our results
demonstrate that the ground state of Mn$_3$Ge is described by the coexistence
of a strong six-fold antichiral order and a weak ferromagnetic order induced by
second-order spin anisotropy.",2111.07587v2
2021-12-20,Temperature independent pseudogap from $^{17}$O and $^{89}$Y NMR and the single component picture,"Nuclear Magnetic Resonance (NMR) is a powerful local quantum probe of the
electronic structure of materials, but in the absence of reliable theory the
interpretation of the NMR data can be challenging. This is true in particular
for the cuprate high-temperature superconductors. Over the years, a large base
of NMR data became available, which makes a review of the early interpretation
possible. Recently, it was shown that all planar $^{17}$O NMR shift and
relaxation data available in the literature point to a temperature independent
but doping dependent pseudogap, very similar to what was proposed from the
electronic entropy. Here we analyze the anisotropy of the shift and relaxation
of planar O to establish whether a single electronic spin component is
applicable, since the planar Cu shift anisotropy clearly fails such a
description. We find that the orbital shift terms deduced from the data are in
agreement with first principle calculations, and the shift data show a
temperature independent anisotropy also in agreement with hyperfine
coefficients predicted by first principles, which also account for the
relaxation anisotropy. Furthermore, we show that the original $^{89}$Y shift
and relaxation data are in agreement with the proposed temperature independent
pseudogap. This pseudogap depends on doping, but also on the family of
materials, and the density of states outside or in the absence of the gap is
universal for the cuprates; this suggests that the entropy should be similar
for all cuprates, as well. Further consequences will be discussed.",2112.10595v1
2021-12-21,CrSbSe3: a pseudo one-dimensional ferromagnetic semiconductor,"Low-dimensional magnetic materials have attracted much attention due to their
novel properties and high potential for spintronic applications. In this work,
we study the electronic structure and magnetic properties of the pseudo
one-dimensional compound CrSbSe$_3$, using density functional calculations,
superexchange model analyses, and Monte Carlo simulations. We find that
CrSbSe$_3$ is a ferromagnetic (FM) semiconductor with a band gap of about 0.65
eV. The FM couplings within each zig-zag spin chain are due to the Cr-Se-Cr
superexchange with the near-90$^\circ$ bonds, and the inter-chain FM couplings
are one order of magnitude weaker. By inclusion of the spin-orbit coupling
(SOC) effects, our calculations reproduce the experimental observation of the
easy magnetization $a$ axis and the hard $b$ axis (the spin-chain direction),
with the calculated moderate magnetic anisotropy of 0.19 meV/Cr. Moreover, we
identify the nearly equal contributions from the single ion anisotropy of Cr,
and from the exchange anisotropy due to the strong SOC of the heavy elements Sb
and Se and their couplings with Cr. Using the parameters of the magnetic
coupling and anisotropy from the above calculations, our Monte Carlo
simulations yield the Curie temperature $T_{\rm{C}}$ of 108 K.",2112.10937v1
2022-01-25,Doppler boosting the stochastic gravitational wave background,"One of the guaranteed features of the stochastic gravitational wave
background (SGWB) is the presence of Doppler anisotropies induced by the motion
of the detector with respect to the rest frame of the SGWB source. We point out
that kinematic effects can be amplified if the SGWB is characterised by large
tilts in its spectrum as a function of frequency, or by sizeable intrinsic
anisotropies. Hence we examine the possibility to use Doppler effects as
complementary probes of the SGWB frequency profile. For this purpose we work in
multipole space, and we study the effect of kinematic modulation and aberration
on the GW energy density parameter and on its angular power spectrum. We
develop a Fisher forecast analysis and we discuss prospects for constraining
parameters controlling kinematically induced anisotropies with future detector
networks. As a case study, we apply our framework to a background component
with constant slope in frequency, potentially detectable by a network of future
ground-based interferometers. For this specific example, we show that a
measurement of kinematic anisotropies with a network of Einstein Telescope and
Cosmic Explorer will allow us to constrain the spectral shape with a precision
of about 16$\%$. Finally, we identify cosmological and astrophysical scenarios
where kinematic effects are enhanced in frequency ranges probed by current and
future GW experiments.",2201.10464v2
2022-02-06,Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2,"Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film
is crucial in spintronic device. One way to modify the magnetic anisotropy is
through the surface of the FM thin film. Here, we report the emergence of a
perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in
a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the
low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide,
WTe2. At the same time, we also observed an enhancement in Gilbert damping in
the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the
Gilbert damping enhancement have no observable WTe2 thickness dependence down
to single quadruple-layer, indicating that the interfacial interaction plays a
critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined
with its previously reported capability to generate out-of-plane damping like
spin torque, makes it desirable for magnetic memory applications.",2202.02834v1
2022-03-09,Self-consistent dynamical models with a finite extent -- I. The uniform density sphere,"The standard method to generate dynamical models with a finite extent is to
apply a truncation in binding energy to the distribution function. This
approach has the disadvantages that one cannot choose the density to start
with, that the important dynamical quantities cannot be calculated
analytically, and that a fraction of the possible bound orbits are excluded a
priori. We explore another route and start from a truncation in radius rather
than a truncation in binding energy. We focus on the simplest truncated density
profile, the uniform density sphere. We explore the most common inversion
techniques to generate distribution functions for the uniform density sphere,
corresponding to a large range of possible anisotropy profiles. We find that
the uniform density sphere cannot be supported by the standard isotropic,
constant anisotropy or Osipkov-Merritt models, as all these models are
characterised by negative distribution functions. We generalise the Cuddeford
inversion method to models with a tangential anisotropy and present a
one-parameter family of dynamical models for the uniform density sphere. Each
member of this family is characterised by an anisotropy profile that smoothly
decreases from an arbitrary value $\beta_0\leqslant0$ at the centre to
completely tangential at the outer radius. All models have a positive
distribution function over the entire phase space, and a nonzero occupancy of
all possible bound orbits. This shows that one can generate nontrivial
self-consistent dynamical models based on preset density profile with a finite
extent.",2203.04715v1
2022-04-04,Angular dependence of the upper critical induction of clean $s$- and $d_{x^2-y^2}$-wave superconductors with self-consistent ellipsoidal effective mass and Zeeman anisotropies,"We employ the Schr{\""o}dinger-Dirac method generalized to an ellipsoidal
effective mass anisotropy in order to treat the spin and orbital effective mass
anisotropies self consistently, which is important when Pauli-limiting effects
on the upper critical field characteristic of singlet superconductivity are
present. By employing the Klemm-Clem transformations to map the equations of
motion into isotropic form, we then calculate the upper critical magnetic
induction $B_{c2}(\theta, \phi, T)$ at arbitrary directions and temperatures
$T$ for isotropic $s$-wave and for anisotropic $d_{x^2-y^2}$-wave
superconducting order parameters. As for anisotropic $s$-wave superconductors,
the reduced upper critical field $b_{c2}$ is largest in the direction of the
lowest effective mass, and is proportional to the universal orientation factor
$\alpha(\theta,\phi)$. However, for $d_{x^2-y^2}$-wave pairing, ${\bm
B}_{c2}(\pi/2,\phi,T)$ exhibits either a four-fold pattern with $C_4$ symmetry
just below the transition temperature $T_c$ that rotates by $\pi/4$ as $T$ is
lowered, or a two-fold pattern with $C_2$ symmetry, depending upon the planar
effective mass anisotropy. This provides a new method to distinguish these
pairing symmetries in clean unconventional superconductors.",2204.01246v1
2022-04-14,Piezoelectric ferromagnetism in Janus monolayer YBrI: a first-principle prediction,"Coexistence of intrinsic ferromagnetism and piezoelectricity, namely
piezoelectric ferromagnetism (PFM), is crucial to advance multifunctional
spintronic technologies. In this work, we demonstrate that Janus monolayer YBrI
is a PFM, which is dynamically, mechanically and thermally stable. Electronic
correlation effects on physical properties of YBrI are investigated by using
generalized gradient approximation plus $U$ (GGA+$U$) approach. For
out-of-plane magnetic anisotropy, YBrI is a ferrovalley (FV) material, and the
valley splitting is larger than 82 meV in considered $U$ range. The anomalous
valley Hall effect (AVHE) can be achieved under an in-plane electric field.
However, for in-plane magnetic anisotropy, YBrI is a common ferromagnetic (FM)
semiconductor. When considering intrinsic magnetic anisotropy, the easy axis of
YBrI is always in-plane with magnetic anisotropy energy (MAE) from 0.309 meV to
0.237 meV ($U$=0.0 eV to 3.0 eV). However, the magnetization can be adjusted
from the in-plane to off-plane direction by external magnetic field, and then
lead to the occurrence of valley polarization. Moreover, missing centrosymmetry
along with mirror symmetry breaking results in both in-plane and out-of-plane
piezoelectricity in YBrI monolayer. At a typical $U$=2.0 eV, the $d_{11}$ is
predicted to be -5.61 pm/V, which is higher than or compared with ones of other
two-dimensional (2D) known materials. The electronic and piezoelectric
properties of YBrI can be effectively tuned by applying a biaxial strain. For
example, tensile strain can enhance valley splitting and $d_{11}$ (absolute
value). The predicted Curie temperature of YBrI is higher than those of
experimentally synthesized 2D ferromagnetic materials $\mathrm{CrI_3}$ and
$\mathrm{Cr_2Ge_2Te_6}$.",2204.06713v1
2022-05-04,Holographic Schwinger effect and electric instability with anisotropy,"According to the gauge-gravity duality, we systematically study the Schwinger
effect and electric instability with anisotropy in a top-down holographic
approach. The anisotropic black brane and bubble (soliton) background in IIB
supergravity are employed and the dual theories in these backgrounds are
expected to be anisotropic theory at finite temperature and anisotropic theory
with confinement respectively. Then performing the potential analysis, we find
due to the anisotropy, the potential barrier behaves oppositely with parallel
and perpendicular electric fields, and this behavior agrees with the previous
study about the quark potential with anisotropy in this system. Afterwards, we
evaluate the pair production rate by solving the equation of motion for a
fundamental string numerically which reveals the consistent behavior with the
potential analysis. Furthermore, the probe D7-brane as flavor is introduced
into the bulk in order to investigate the electric instability. The vacuum
decay rate can be obtained by evaluating the imaginary part of the D7-brane
action which again agrees with our potential analysis. Solving the associated
constraint of gauge field strength on the flavor brane, we finally obtain the
V-A curve displaying the distinct behavior of the conductivity in parallel and
perpendicular direction which is in agreement with some bottom-up and
phenomenologically holographic approaches in anisotropic fluid. Accordingly, we
believe this work may be remarkable to study the electric features in strongly
coupled anisotropic system.",2205.01885v3
2022-05-31,Maximum likelihood kinetic Sunyaev Zel'dovich velocity reconstruction,"The kinetic Sunyaev Zel'dovich (kSZ) effect, cosmic microwave background
(CMB) temperature anisotropies induced by the scattering of CMB photons from
free electrons, will be measured by near-term CMB experiments at high
significance. By combining CMB temperature anisotropies with a tracer of
structure, such as a galaxy redshift survey, previous literature introduced a
number of techniques to reconstruct the radial velocity field. This
reconstructed radial velocity field encapsulates the majority of the
cosmological information contained in the kSZ temperature anisotropies, and can
provide powerful new tests of the standard cosmological model and theories
beyond it. In this paper, we introduce a new estimator for the radial velocity
field based on a coarse-grained maximum likelihood fit for the kSZ component of
the temperature anisotropies, given a tracer of the optical depth. We
demonstrate that this maximum likelihood estimator yields a higher fidelity
reconstruction than existing quadratic estimators in the low-noise and
high-resolution regime targeted by upcoming CMB experiments. We describe
implementations of the maximum likelihood estimator in both harmonic space and
map space, using either direct measurements of the optical depth field or a
galaxy survey as a tracer. We comment briefly on the impact of biases
introduced by imperfect reconstruction of the optical depth field.",2205.15779v1
2022-06-29,Generalizing Monin-Obukhov similarity theory (1954) for complex atmospheric turbulence,"Monin-Obukhov similarity theory (MOST) stands at the center of understanding
of atmospheric surface-layer turbulence. Based on the hypothesis that a single
length scale determined by surface fluxes governs the turbulent exchange of
momentum, mass, and energy between the Earth's surface and the atmosphere, MOST
has been widely used in parametrizations of turbulent processes in virtually
all numerical models of atmospheric flows. However, its inherent limitations to
flat and horizontally homogeneous terrain, the non-scaling of horizontal
velocity variances, and stable turbulence have plagued the theory since its
inception. Thus, the limitations of MOST, and its use beyond its intended range
of validity contribute to large uncertainty in weather, climate, and
air-pollution models, particularly in polar regions and over complex terrain.
Here we present a first generalized extension of MOST encompassing a wide range
of realistic surface and flow conditions. The novel theory incorporates
information on the directionality of turbulence exchange (anisotropy of the
Reynolds stress tensor) as a key missing variable. The constants in the
standard empirical MOST relations are shown to be functions of anisotropy, thus
allowing a seamless transition between traditional MOST and its novel
generalization. The new scaling relations, based on measurements from 13
well-known datasets ranging from flat to highly complex mountainous terrain,
show substantial improvements to scaling under all stratifications. The results
also highlight the role of anisotropy in explaining general characteristics of
complex terrain and stable turbulence, adding to the mounting evidence that
anisotropy fully encodes the information on the complexity of the boundary
conditions.",2206.14592v1
2022-07-29,The role of magnetoelastic coupling and magnetic anisotropy in MnTiO$_3$,"We report the thermodynamic properties studied by thermal expansion,
magnetostriction, magnetisation, and specific heat measurements as well as the
low-energy magnetic excitations of \mto\ and investigate how magneto-elastic
coupling and magnetic anisotropy affect the evolution of long-range order and
the magnetic phase diagram. Specifically, we utilise high-resolution
capacitance dilatometry and antiferromagnetic resonance (AFMR) studies by means
of high-frequency electron spin resonance (HF-ESR) spectroscopy. The role of
anisotropy is reflected by spin-reorientation at $B_{\rm{SF}}$~$\simeq 6$~T and
a corresponding sign change in $\partial T_{\rm N}/\partial B$. Analysis of the
AFMR modes enables us to establish the zero-field excitation gap $\Delta$ as
well as its temperature dependence. We derive the effective anisotropy field
$B_\mathrm{A} = 0.16(1)$~T which predominately originates from out-of-plane
nearest-neighbour dipole-dipole interactions. Despite the nearly fully quenched
orbital moment, our data show pronounced thermal expansion and magnetostriction
anomalies at $T_{\rm N}$ and $B_{\rm{SF}}$ , respectively, which allows the
experimental determination of sizable uniaxial pressure dependencies, i.e.,
$\partial B_{\rm SF}/\partial p_{\rm c} = -0.20(2)$~T/GPa, $\partial T_{\rm N}/
\partial p_b = 0.69(12)$~K/GPa, and $\partial T_{\rm N}/ \partial p_c =
-2.0(4)$~K/GPa. Notably, short-range magnetic order appears up to at least
3$T_{\rm N}$ , as indicated by anisotropic lattice distortion, the violation of
a constant Gr\""uneisen behavior, and the presence of local magnetic fields
detected by HF-ESR.",2207.14750v1
2022-08-04,Anisotropic Magnetodielectric Coupling in Layered Antiferromagnetic FePS$_3$,"We report anisotropic magnetodielectric (MD) coupling in layered van der
Waals (vdW) antiferromagnetic (AFM) FePS$_3$ (N\'eel temperature
$T_{\mathrm{N}}$ $\sim$ 120K) with perpendicular anisotropy. Above $T_N$, while
dielectric response function along \textit{c}-axis shows frequency dependent
relaxations, in-plane data is frequency independent and reveals a deviation
from phonon-anharmonicity in the ordered state, thereby implying a connection
to spin-phonon coupling known to be indicative of onset of magnetic ordering.
At low temperature (below 40 K), atypical anomaly in the dielectric constant is
corroborated with temperature dependent DC and AC susceptibility. The
magnetodielectric response across this anomaly differs significantly for both,
in-plane and out-of-plane cases. We have explained this in terms of
preferential orientation of magnetic AFM-z alignment, implied by the in-plane
structural anisotropy as confirmed by \textit{ab-initio} calculations.
Controlling relative strength of magnetodielectric coupling with magnetic
anisotropy opens up a strategy for tracking subtle modifications of structure,
such as in-plane anisotropy, with potential application to spintronic
technologies.",2208.02729v2
2022-08-07,Strain tunability of perpendicular magnetic anisotropy in van der Waals ferromagnets VI3,"Layered ferromagnets with high coercivity have special applications in
nanoscale memory elements in electronic circuits, such as data storage.
Therefore, searching for new hard ferromagnets and effectively tuning or
enhancing the coercivity are the hottest topics in layered magnets today. Here,
we report a strain tunability of perpendicular magnetic anisotropy in van der
Waals (vdW) ferromagnets VI3 using magnetic circular dichroism measurements.
For an unstrained flake, the M-H curve shows a rectangular-shaped hysteresis
loop with perpendicular magnetic anisotropy and a large coercivity (up to 1.775
T at 10 K). Furthermore, the coercivity can be enhanced to a maximum of 2.6 T
at 10 K under a 2.9% in-plane tensile strain. Our DFT calculations show that
the magnetic anisotropy energy (MAE) can be dramatically increased after
applying an in-plain tensile strain, which contributes to the enhancement of
coercivity in the VI3 flake. Meanwhile, the strain tunability on the coercivity
of CrI3, with a similar crystal structure, is limited. The main reason is the
strong spin-orbital coupling in V3+ in VI6 octahedra in comparison with that in
Cr3+. The strain tunability of coercivity in VI3 flakes highlights its
potential for integration into vdW heterostructures, paving the way toward
nanoscale spintronic devices and applications in the future.",2208.03678v1
2022-08-10,Enhancing the limit of uniaxial magnetic anisotropy induced by ion beam erosion,"The artificial tailoring of magnetic anisotropy by manipulation of
interfacial morphology and film structure are of fundamental interest from
application point of view in spintronic and magnetic memory devices. This
letter reports an approach of engineering and enhancing the strength of oblique
incidence ion beam erosion (IBE) induced in-plane uniaxial magnetic anisotropy
(UMA) by simultaneous modification of film morphology as well as film texture.
To meet this objective, Cobalt film and Si substrate have been taken as a model
system. Unlike conventional post growth IBE of film, we direct our effort to
the sequential deposition and subsequent IBE of the film. Detailed in-situ
investigation insights that the film grows in highly biaxially textured
polycrystalline state with formation of nanometric surface ripples. The film
also exhibits pronounced UMA with easy axis oriented parallel to the surface
ripple direction. Remarkably, the induced UMA is about one order of magnitude
larger than the reported similar kind of earlier studies. The possibility of
imposing in-plane crystallographic texture giving rise to magneto-crystalline
anisotropy, along with long-range dipolar interaction throughout ripple crests
enhances the strength of the UMA. The present findings can be further extended
to systems characterized by different crystallographic structure and magnetic
properties and show the general applicability of the present method.",2208.05249v1
2022-08-23,Crystal anisotropy implications on the intrinsic magnetic and optical properties in van der Waals FePS3,"Antiferromagnetic (AFM) FePS3 has gained significant interest recently for
its potential applications in spin-related devices. A single layer is comprised
of a honeycomb network, stabilized by long-range spin-exchange interactions,
with a zigzag or Neel arrangement of the Fe-atoms. This study exposed, for the
first time, a strong impact of lateral crystal distortion on the magnetic
arrangement and optical properties of FePS3. This impact was deciphered by
correlating photoluminescence (PL) observations with single-crystal XRD which
uncovered anisotropy in the a/b crystallographic plane. Thus, induceing a
breakage in the inversion symmetry in FePS3 causing changes in it's electronic
and optical transitions. The MPL observations exhibited an unexpected band-edge
circularly polarized recombination emission, while off-band-edge transitions
were linearly polarized. Also, temperature-dependent MPL measurements reflected
zigzag-AFM at low temperatures and the coexistence of zigzag or Neel at mid
temperatures. Theoretical calculation implementing anisotropy in spin-exchange
interactions among Fe atom's nearest neighbors revealed stabilized zigzag
arrangement tilted away from the a-axis. Furthermore, DFT calculations of the
electronic band-edge predicted split states in degenerate symmetric points
(K+/K-) for zigzag structure and non-degenerate for the Neel arrangement.
Highlighting the importance of the inclusion of a crystallographic anisotropy
parameter for the simulation of the experimental observations.",2208.10890v1
2022-08-31,Detection of anisotropic satellite quenching in galaxy clusters up to $z\sim1$,"Satellite galaxies in the cluster environment are more likely to be quenched
than galaxies in the general field. Recently, it has been reported that
satellite galaxy quenching depends on the orientation relative to their central
galaxies: satellites along the major axis of centrals are more likely to be
quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to $z\sim1$ based on a large
optically-selected cluster catalogue constructed from the Hyper Suprime-Cam
Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction
as a function of orientation angle measured from the major axis of central
galaxies and find that the quiescent fractions at $0.25<z<1$ are reasonably
fitted by sinusoidal functions with amplitudes of a few percent. Anisotropy is
clearer in inner regions ($<r_\mathrm{200m}$) of clusters and not significant
in cluster outskirts ($>r_\mathrm{200m}$). We also confirm that the observed
anisotropy cannot be explained by differences in local galaxy density or
stellar mass distribution along the two axes. Quiescent fraction excesses
between the two axes suggest that the quenching efficiency contributing to the
anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of $M_{*}=1\times10^{10}\,M_{\odot}$. Finally, we argue that the
physical origins of the observed anisotropy should have shorter quenching
timescales than $\sim1\,\mathrm{Gyr}$, like ram-pressure stripping, because,
for anisotropic quenching to be observed, satellites must be quenched before
their initial orientation angles are significantly changed.",2209.00015v2
2022-09-01,Comparing the counter-beaming and temperature anisotropy driven aperiodic electron firehose instabilities in collisionless plasma environments,"The electron firehose instabilities are among the most studied kinetic
instabilities, especially in the context of space plasmas, whose dynamics is
mainly controlled by collisionless wave-particle interactions. This paper
undertakes a comparative analysis of the aperiodic electron firehose
instabilities excited either by the anisotropic temperature or by the electron
counter-beaming populations. Two symmetric counter-beams provide an effective
kinetic anisotropy similar to the temperature anisotropy of a single
(non-drifting) population, with temperature along the magnetic field direction
larger than that in perpendicular direction. Therefore, the counter-beaming
plasma is susceptible to firehose-like instabilities (FIs), parallel and
oblique branches. Here we focus on the oblique beaming FI, which is also
aperiodic when the free energy is provided by symmetric counter-beams. Our
results show that, for relative small drifts or beaming speeds ($U$), not
exceeding the thermal speed ($\alpha$), the aperiodic FIs exist in the same
interval of wave-numbers and the same range of oblique angles (with respect to
the magnetic field direction), but the growth rates of counter-beaming FI
(CBFI) are always higher than those of temperature anisotropy FI (TAFI). For
$U/\alpha > 1$, however, another electrostatic two-stream instability (ETSI) is
also predicted, which may have growth rates higher than those of CBFI, and may
dominate in that case the dynamics.",2209.00441v1
2022-09-08,The Einasto model for dark matter haloes,"Context: The Einasto model has become one of the most popular models for
describing the density profile of dark matter haloes. There have been
relatively few comprehensive studies on the dynamical structure of the Einasto
model, mainly because only a limited number of properties can be calculated
analytically. Aims: We want to systematically investigate the photometric and
dynamical structure of the family of Einasto models over the entire model
parameter space. Methods: We used the SpheCow code to explore the properties of
the Einasto model. We systematically investigated how the most important
properties change as a function of the Einasto index $n$. We considered both
isotropic models and radially anisotropic models with an Osipkov-Merritt
orbital structure. Results: We find that all Einasto models with $n<\tfrac12$
have a formal isotropic or Osipkov-Merritt distribution function that is
negative in parts of phase space, and hence cannot be supported by such orbital
structures. On the other hand, all models with larger values of $n$ can be
supported by an isotropic orbital structure, or by an Osipkov-Merritt
anisotropy, as long as the anisotropy radius is larger than a critical value.
This critical anisotropy radius is a decreasing function of $n$, indicating
that less centrally concentrated models allow for a larger degree of radial
anisotropy. Conclusions: Studies of the structure and dynamics of models for
galaxies and dark matter haloes should not be restricted to completely
analytical models. Numerical codes such as SpheCow can help open up the range
of models that are systematically investigated. This applies to the Einasto
model discussed here, but also to other proposed models for dark matter haloes,
including different extensions to the Einasto model.",2209.03639v1
2022-09-14,Tuning magnetoelectricity in a mixed-anisotropy antiferromagnet,"Control of magnetization and electric polarization is attractive in relation
to tailoring materials for data storage and devices such as sensors or
antennae. In magnetoelectric materials, these degrees of freedom are closely
coupled, allowing polarization to be controlled by a magnetic field, and
magnetization by an electric field, but the magnitude of the effect remains a
challenge in the case of single-phase magnetoelectrics for application. We
demonstrate that the magnetoelectric properties of the mixed-anisotropy
antiferromagnet LiNi$_{1-x}$Fe$_x$PO$_4$ are profoundly affected by replacing a
fraction of the Ni$^{2+}$ ions with Fe$^{2+}$ on the transition metal site.
This introduces random site-dependent single-ion anisotropy energies and causes
a lowering of the magnetic symmetry of the system. In turn, magnetoelectric
couplings that are symmetry-forbidden in the parent compounds, LiNiPO$_4$ and
LiFePO$_4$, are unlocked and the dominant coupling is enhanced by two orders of
magnitude. Our results demonstrate the potential of mixed-anisotropy magnets
for tuning magnetoelectric properties.",2209.06702v1
2022-09-22,"Single-crystal elastic moduli, anisotropy and the B1-B2 phase transition of NaCl at high pressures: Experiment vs. ab-initio calculations","Single-crystal elastic moduli, Cij, and the B1-B2 phase transition of NaCl
were investigated experimentally, using time-domain Brillouin scattering
(TDBS), and theoretically, via density-functional-theory (DFT), to 41 GPa.
Thus, we largely extended pressure range where Cij and elastic anisotropy of
the solid are measured, including the first experimental data for the
high-pressure B2 phase, NaCl-B2. NaCl-B1 exhibits a strong and growing with
pressure anisotropy, in contrast to NaCl-B2. Theoretical values obtained using
different advanced DFT functionals were compared with our measurements but no
one could satisfactorily reproduce our experimental data for NaCl-B1 and
NaCl-B2 simultaneously. For all available DFT results on the principal shear
moduli and anisotropy, the deviation became pronounced when the degree of
compression increased significantly. Similar deviations could be also
recognized for other cubic solids having the same B1-type structure and similar
bonding, such as CaO, MgO, or (Mg1-x,Fex)O. Furthermore, the available
experimental data suggest that the B1-B2 phase transition of NaCl and the above
mentioned compounds are governed by the Born stability criterion C44(P) - P >
0.",2209.10899v1
2022-10-11,Magnetic anisotropy reversal driven by structural symmetry-breaking in monolayer α-RuCl3,"Layered {\alpha}-RuCl3 is a promising material to potentially realize the
long-sought Kitaev quantum spin liquid with fractionalized excitations. While
evidence of this exotic state has been reported under a modest in-plane
magnetic field, such behavior is largely inconsistent with theoretical
expectations of Kitaev phases emerging only in out-of-plane fields. These
predicted field-induced states have been mostly out of reach due to the strong
easy-plane anisotropy of bulk crystals, however. We use a combination of
tunneling spectroscopy, magnetotransport, electron diffraction, and ab initio
calculations to study the layer-dependent magnons, anisotropy, structure, and
exchange coupling in atomically thin samples. Due to structural distortions,
the sign of the average off-diagonal exchange changes in monolayer
{\alpha}-RuCl3, leading to a reversal of magnetic anisotropy to easy-axis. Our
work provides a new avenue to tune the magnetic interactions in {\alpha}-RuCl3
and allows theoretically predicted quantum spin liquid phases for out-of-plane
fields to be more experimentally accessible.",2210.05733v1
2022-11-01,Observation of oscillating $g$-factor anisotropy arising from strong crystal lattice anisotropy in GaAs spin-3/2 hole quantum point contacts,"Many modern spin-based devices rely on the spin-orbit interaction, which is
highly sensitive to the host semiconductor heterostructure and varies
substantially depending on crystal direction, crystal asymmetry (Dresselhaus),
and quantum confinement asymmetry (Rashba). One-dimensional quantum point
contacts are a powerful tool to probe both energy and directional dependence of
spin-orbit interaction through the effect on the hole $g$-factor. In this work
we investigate the role of cubic crystal asymmetry in driving an oscillation in
the in-plane hole $g$-factor anisotropy when the quantum point contact is
rotated with respect to the crystal axes, and we are able to separate
contributions to the Zeeman Hamiltonian arising from Rashba and cubic crystal
asymmetry spin-orbit interactions. The in-plane $g$-factor is found to be
extremely sensitive to the orientation of the quantum point contact, changing
by a factor of $5$ when rotated by $45^{\circ}$. This exceptionally strong
crystal lattice anisotropy of the in-plane Zeeman splitting cannot be explained
within axially symmetric theoretical models. Theoretical modelling based on the
combined Luttinger, Rashba and Dresselhaus Hamiltonians that we use here
reveals new spin-orbit contributions to the in-plane hole $g$-factor and
provides an excellent agreement with our experimental data.",2211.00253v2
2022-12-03,Measurements of azimuthal anisotropy of nonprompt D$^0$ mesons in PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV,"Measurements of the elliptic ($v_2$) and triangular ($v_3$) azimuthal
anisotropy coefficients are presented for D$^0$ mesons produced in b hadron
decays (nonprompt D$^0$ mesons) in lead-lead collisions at
$\sqrt{s_\mathrm{NN}}$ = 5.02 TeV. The results are compared with previously
published charm meson anisotropies measured using prompt D$^0$ mesons. The data
were collected with the CMS detector in 2018 with an integrated luminosity of
0.58 nb$^{-1}$. Azimuthal anisotropy is sensitive to the interactions of quarks
with the hot and dense medium created in heavy ion collisions. Comparing
results for prompt and nonprompt D$^0$ mesons can assist in understanding the
mass dependence of these interactions. The nonprompt results show lower
magnitudes of $v_2$ and $v_3$ and weaker dependences on the meson transverse
momentum and collision centrality than those found for prompt D$^0$ mesons. The
results are in agreement with theoretical predictions that include a mass
dependence in the interactions of quarks with the medium.",2212.01636v2
2022-12-12,Searching for anisotropic stochastic gravitational-wave backgrounds with constellations of space-based interferometers,"Many recent works have shown that the angular resolution of ground-based
detectors is too poor to characterize the anisotropies of the stochastic
gravitational-wave background (SGWB). For this reason, we asked ourselves if a
constellation of space-based instruments could be more suitable. We consider
the Laser Interferometer Space Antenna (LISA), a constellation of multiple
LISA-like clusters, and the Deci-hertz Interferometer Gravitational-wave
Observatory (DECIGO). Specifically, we test whether these detector
constellations can probe the anisotropies of the SGWB. For this scope, we
considered the SGWB produced by two astrophysical sources: merging compact
binaries and a recently proposed scenario for massive black-hole seed formation
through multiple mergers of stellar remnants. We find that measuring the
angular power spectrum of the SGWB anisotropies is almost unattainable.
However, it turns out that it could be possible to probe the SGWB anisotropies
through cross-correlation with the CMB fluctuations. In particular, we find
that a constellation of two LISA-like detectors and CMB-S4 can marginally
constrain the cross-correlation between the CMB lensing convergence and the
SGWB produced by the black hole seed formation process. Moreover, we find that
DECIGO can probe the cross-correlation between the CMB lensing and the SGWB
from merging compact binaries.",2212.06162v1
2022-12-20,New universal property of cosmological gravitational wave anisotropies,"The anisotropies of the stochastic gravitational wave background, as produced
in the early phases of cosmological evolution, can act as a key probe of the
primordial universe particle content. We point out a new universal property of
gravitational wave anisotropies of cosmological origin: for adiabatic initial
conditions, their angular power spectrum is insensitive to the equation of
state of the cosmic fluid driving the expansion before big-bang
nucleosynthesis. Any deviation from this universal behaviour points to the
presence of non-adiabatic sources of primordial fluctuations. Such scenarios
can be tested by gravitational wave detectors operating at a frequency range
which is fully complementary to CMB experiments. In this work we prove this
general result, and we illustrate its consequences for a representative
realisation of initial conditions based on the curvaton scenario. In the case
of the simplest curvaton setup, we also find a significant cross-correlation
between gravitational wave anisotropies and the CMB temperature fluctuations.
There is a fourfold enhancement vis-\`{a}-vis the purely adiabatic scenario. We
discuss the implications of our findings for identifying the origin of the
(cosmological) gravitational wave background when, as is often the case, this
cannot be determined solely on the basis of its spectral shape.",2212.10316v2
2023-01-10,Compensation of anisotropy in spin-Hall devices for neuromorphic applications,"Spintronic nano-oscillators with reduced non-linearity could offer key
benefits for realizing neuromorphic applications such as spike-based neurons
and frequency multiplexing in neural networks. Here, we experimentally
demonstrate the reduction in non-linearity of a spin-Hall nano-oscillator
(SHNO) by compensation of its effective magnetic anisotropy. The study involves
optimization of Co/Ni multilayer growth to achieve the compensation, followed
by spin diode measurements on patterned microstrips to quantify their
anisotropy. The relation between the second ($H_{k2}$ = 0.47 mT) and the first
order ($H_{k1}^{eff}$ = $-$0.8 mT) anisotropy fields reveals the existence of
an easy cone, thereby validating the presence of compensation. Furthermore, we
demonstrate a synapse based on the compensated spin diode which has a fixed
frequency when the input power is varied. We then study the current-induced
auto-oscillation properties of SHNOs on compensated films by patterning
nano-constrictions of widths 200 and 100 nm. The invariance of the resonance
frequency and linewidth of the compensated SHNO with applied dc current
indicates the absence of non-linearity. This independence is maintained
irrespective of the applied external fields and its orientations. The
compensated SHNO obtained has a linewidth of 1.1 MHz and a peak output power of
up to 1 pW/MHz emulating a nano-neuron with a low linewidth and a fixed
frequency.",2301.03794v1
2023-01-10,Magnetic anisotropy and low-energy spin dynamics in the van der Waals compounds Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$,"We report the detailed high-field and high-frequency electron spin resonance
(HF-ESR) spectroscopic study of the single-crystalline van der Waals compounds
Mn$_{2}$P$_{2}$S$_{6}$ and MnNiP$_{2}$S$_{6}$. Analysis of magnetic excitations
shows that in comparison to Mn$_{2}$P$_{2}$S$_{6}$ increasing the Ni content
yields a larger magnon gap in the ordered state and a larger g-factor value and
its anisotropy in the paramagnetic state. The studied compounds are found to be
strongly anisotropic having each the unique ground state and type of magnetic
order. Stronger deviation of the g-factor from the free electron value in the
samples containing Ni suggests that the anisotropy of the exchange is an
important contributor to the stabilization of a certain type of magnetic order
with particular anisotropy. At temperatures above the magnetic order, we have
analyzed the spin-spin correlations resulting in a development of slowly
fluctuating short-range order. They are much stronger pronounced in
MnNiP$_{2}$S$_{6}$ compared to Mn$_{2}$P$_{2}$S$_{6}$. The enhanced spin
fluctuations in MnNiP$_{2}$S$_{6}$ are attributed to the competition of
different types of magnetic order. Finally, the analysis of the temperature
dependent critical behavior of the magnon gaps below the ordering temperature
in Mn$_{2}$P$_{2}$S$_{6}$ suggests that the character of the spin wave
excitations in this compound undergoes a field induced crossover from a 3D-like
towards 2D XY regime.",2301.04239v2
2023-01-11,Traveling wave enantio-selective electron paramagnetic resonance,"We propose a novel method for enantio-selective electron paramagnetic
resonance spectroscopy based on magneto-chiral anisotropy. We calculate the
strength of this effect and propose a dedicated interferometer setup for its
observation.",2301.04755v1
2023-02-15,"A ""morphogenetic action"" principle for 3D shape formation by the growth of thin sheets","How does growth encode form in developing organisms? Many different
spatiotemporal growth profiles may sculpt tissues into the same target 3D
shapes, but only specific growth patterns are observed in animal and plant
development. In particular, growth profiles may differ in their degree of
spatial variation and growth anisotropy, however, the criteria that distinguish
observed patterns of growth from other possible alternatives are not
understood. Here we exploit the mathematical formalism of quasiconformal
transformations to formulate the problem of ""growth pattern selection""
quantitatively in the context of 3D shape formation by growing 2D epithelial
sheets. We propose that nature settles on growth patterns that are the
'simplest' in a certain way. Specifically, we demonstrate that growth pattern
selection can be formulated as an optimization problem and solved for the
trajectories that minimize spatiotemporal variation in areal growth rates and
deformation anisotropy. The result is a complete prediction for the growth of
the surface, including not only a set of intermediate shapes, but also a
prediction for cell displacement along those surfaces in the process of growth.
Optimization of growth trajectories for both idealized surfaces and those
observed in nature show that relative growth rates can be uniformized at the
cost of introducing anisotropy. Minimizing the variation of programmed growth
rates can therefore be viewed as a generic mechanism for growth pattern
selection and may help to understand the prevalence of anisotropy in
developmental programs.",2302.07839v1
2023-03-12,Investigating the elliptic anisotropy of identified particles in p--Pb collisions with a multi-phase transport model,"The elliptic azimuthal anisotropy coefficient ($v_{2}$) of the identified
particles at midrapidity ($|\eta|<0.8$) was investigated in p--Pb collisions at
$\sqrt{s_\mathrm{NN}}=$ 5.02 TeV using a multi-phase transport model (AMPT).
The calculations of differential $v_{2}$ based on the advanced flow extraction
method of light flavor hadrons (pions, kaons, protons, and $\Lambda$) in small
collision systems were extended to a wider transverse momentum
($p_{\mathrm{T}}$) range of up to 8 GeV/$c$ for the first time. The
string-melting version of the AMPT model provides a good description of the
measured $p_{\mathrm{T}}$-differential $v_{2}$ of the mesons but exhibits a
slight deviation from the baryon $v_{2}$. In addition, we observed the features
of mass ordering at low $p_{\mathrm{T}}$ and the approximate number of
constituent quarks (NCQ) scaled at intermediate $p_{\mathrm{T}}$. Moreover, we
demonstrate that hadronic rescattering does not have a significant impact on
$v_{2}$ in p--Pb collisions for different centrality selections, whereas
partonic scattering dominates in generating the elliptic anisotropy of the
final particles. This study provides further insight into the origin of
collective-like behavior in small collision systems and has referential value
for future measurements of azimuthal anisotropy.",2303.06577v3
2023-03-16,Measuring galaxy cluster mass profiles into the low acceleration regime with galaxy kinematics,"We probe the dynamical mass profiles of 10 galaxy clusters from the HIghest
X-ray FLUx Galaxy Cluster Sample (HIFLUGCS) using galaxy kinematics. We
numerically solve the spherical Jeans equation, and parameterize the dynamical
mass profile and the galaxy velocity anisotropy profile using two general
functions to ensure that our results are not biased towards any specific model.
The mass-velocity anisotropy degeneracy is ameliorated by using two ""virial
shape parameters"" that depend on the fourth moment of velocity distribution.
The resulting velocity anisotropy estimates consistently show a nearly
isotropic distribution in the inner regions, with an increasing radial
anisotropy towards large radii. We compare our derived dynamical masses with
those calculated from X-ray gas data assuming hydrostatic equilibrium, finding
that massive and rich relaxed clusters generally present consistent mass
measurements, while unrelaxed or low-richness clusters have systematically
larger total mass than hydrostatic mass by an average of 50\%. This might help
alleviate current tensions in the measurement of $\sigma_8$, but it also leads
to cluster baryon fractions below the cosmic value. Finally, our approach
probes accelerations as low as $10^{-11}$ m s$^{-2}$, comparable to the
outskirts of individual late-type galaxies. We confirm that galaxy clusters
deviate from the radial acceleration relation defined by galaxies.",2303.10175v2
2023-03-20,Scaling anisotropy with stationary background field in the near-Sun solar wind turbulence,"The scaling of magnetic fluctuations provides crucial information for the
understanding of solar wind turbulence. However, the observed magnetic
fluctuations contain not only turbulence but also magnetic structures, leading
to the violation of the time stationarity. This violation would conceal the
true scaling and influence the determination of the sampling angle with respect
to the local background magnetic field. Here, to investigate the scaling
anisotropy, we utilize an easy but effective criterion $\phi<10^\circ$ to
ensure the time stationarity of the magnetic field, where $\phi$ is the angle
between the two averaged magnetic fields after cutting the interval into two
halves. We study the scaling anisotropy using higher-order statistics of
structure functions under the condition of stationarity for the near-Sun solar
wind turbulence for the first time based on measurements obtained from Parker
Solar Probe (PSP) at 0.17 au. We find that the scaling indices $\xi$ of
magnetic field show a linear dependence on the order $p$ close to $\xi(p)=p/4$.
The multifractal scaling of magnetic-trace structure functions becomes
monoscaling close to $\xi(p)=p/3$ with the local magnetic field perpendicular
to the sampling direction and close to $\xi(p)=p/4$ with the local magnetic
field parallel to the sampling direction when measured with the stationary
background magnetic field. The scaling of velocity-trace structure functions
has similar but less significant changes. The near-Sun solar wind turbulence
displays different scaling anisotropies with the near-Earth solar wind
turbulence, suggesting the evolution of the nonlinear interaction process
during the solar wind expansion.",2303.10810v1
2023-03-20,Violation of Emergent Rotational Symmetry in the Hexagonal Kagome Superconductor CsV3Sb5,"Superconductivity is caused by electron pairs that are canonically isotropic,
whereas some exotic superconductors are known to exhibit non-trivial anisotropy
stemming from unconventional pairings. However, superconductors with hexagonal
symmetry, the highest rotational symmetry allowed in crystals, exceptionally
have strong constraint that is called emergent rotational symmetry (ERS):
anisotropic properties should be very weak especially near the critical
temperature Tc even for unconventional pairings such as d-wave states. Here, we
investigate superconducting anisotropy of the recently-found hexagonal Kagome
superconductor CsV3Sb5, which is known to exhibit various intriguing phenomena
originating from its undistorted Kagome lattice formed by vanadium atoms. Based
on calorimetry performed under accurate two-axis field-direction control, we
discover a combination of six- and two-fold anisotropies in the in-plane upper
critical field. Both anisotropies, robust up to very close to Tc, are beyond
predictions of standard theories. We infer that this clear ERS violation with
nematicity is best explained by multi-component nematic superconducting order
parameter in CsV3Sb5 intertwined with symmetry breakings caused by the
underlying charge-density-wave order.",2303.11072v1
2023-03-27,Strain effects on magnetic compensation and spin reorientation transition of Co/Gd synthetic ferrimagnets,"Synthetic ferrimagnets are an attractive materials class for spintronics as
they provide access to all-optical switching of magnetization and, at the same
time, allow for ultrafast domain wall motion at angular momentum compensation.
In this work, we systematically study the effects of strain on the
perpendicular magnetic anisotropy and magnetization compensation of Co/Gd and
Co/Gd/Co/Gd synthetic ferrimagnets. Firstly, the spin reorientation transition
of a bilayer system is investigated in wedge type samples, where we report an
increase in the perpendicular magnetic anisotropy in the presence of in-plane
strain. Using a model for magnetostatics and spin reorientation transition in
this type of system, we confirm that the observed changes in anisotropy field
are mainly due to the Co magnetoelastic anisotropy. Secondly, the magnetization
compensation of a quadlayer is studied. We find that magnetization compensation
of this synthetic ferrimagnetic system is not altered by external strain. This
confirms the resilience of this material system against strain that may be
induced during the integration process, making Co/Gd ferrimagnets suitable
candidates for spintronics applications.",2303.15191v4
2023-03-28,L1$_0$ FePt thin films with tilted and in-plane magnetic anisotropy: first-principles study,"Ultrathin L1$_0$ films with different $c$-axis orientations relative to the
film plane are promising candidates for data storage materials. In this work,
within the framework of density functional theory, we calculated the magnetic
properties of ultrathin L1$_0$ (111) and (010) films with thicknesses ranging
from 4 to 16 atomic monolayers (from about 0.8 to 3.5~nm). The highest average
magnetic moments are observed for the thinnest films considered, and with
increasing film thickness, the values converge towards the magnetic moment for
bulk. The observed increase comes mainly from enhanced moments in the two
atomic monolayers closest to the surface of the films. The easy axis of
magnetization of (111) films prefers an alignment close to the tetragonal axis,
an example of tilted magnetic anisotropy. The 6-monolayer (111) film (about
1.3~nm thick) inclines the easy axis of magnetization of about 45{\deg} to the
film plane, which can find use in applications. The (010) films show an
in-plane easy magnetization axis in a unique L1$_0$ tetragonal direction. This
is an unusual type of in-plane anisotropy, as the particular direction
preference is very strong. The computational results encourage further
experimental studies of L1$_0$ systems with tilted and in-plane fixed magnetic
anisotropy.",2303.15877v2
2023-04-05,Unstable Anisotropic Neutron Stars: Probing the Limits of Gravitational Collapse,"The aim of this paper is to investigate the effects of anisotropy on the
gravitational collapse of unstable neutron stars. We utilize the BL-Model to
describe the anisotropy inside the neutron star and construct a family of
anisotropic neutron stars for BSk21-EOS. We subject these stars to radial
perturbations to study their stability against radial oscillations, and analyze
the effects of anisotropy on the large frequency separation for systems with
and without crust. To observe the unstable branch in the respective profile
curves, we calculate the properties of anisotropic neutron stars in advance. We
compare the obtained radial stability curve to the standard criterion for
radial stability ($\frac{\partial M}{\partial \rho_c } > 0 $) and find that the
stability limit of anisotropic stars is more accurately described by the radial
stability curve. We filter out all sequence of anisotropic neutron stars that
exceed the stability limit obtained from the radial stability curve. The
ultimate fate of these unstable anisotropic neutron stars is to collapse into a
black hole. To study the dynamical evolution of such unstable anisotropic
neutron stars, we consider a non-ideal fluid in a non-adiabatic background. We
examine the time-evolution of key properties such as mass, density, heat flux,
and anisotropy during the process of gravitational collapse. To better
visualize this process, we perform a contour simulation (Fig.
\ref{fig:ns-params_time_evolution}). Finally, we introduce a few challenging
yet plausible mechanisms for detecting such high-energy gravitational collapse
events.",2304.02439v2
2023-04-13,Element-Specific Study of Magnetic Anisotropy and Hardening in SmCo$_{5-x}$Cu$_{x}$ Thin Films,"This work investigates the effect of copper substitution on the magnetic
properties of SmCo$_{5}$ thin films synthesized by molecular beam epitaxy. A
series of thin films with varying concentrations of Cu were grown under
otherwise identical conditions to disentangle structural and compositional
effects on the magnetic behavior. The combined experimental and theoretical
studies show that Cu substitution at the Co$_{3g}$ sites not only stabilizes
the formation of the SmCo$_{5}$ structure but enhances magnetic anisotropy and
coercivity. Density functional theory calculations indicate that
Sm(Co$_4$Cu$_{3g}$)$_5$ possesses a higher single-ion anisotropy as compared to
pure SmCo$_{5}$. In addition, X-ray magnetic circular dichroism reveals that Cu
substitution causes an increasing decoupling of the Sm 4\textit{f} and Co
3\textit{d} moments. Scanning transmission electron microscopy confirms
predominantly SmCo$_{5}$ phase formation and reveals nanoscale inhomogeneities
in the Cu and Co distribution. Our study based on thin film model systems and
advanced characterization as well as modeling reveals novel aspects of the
complex interplay of intrinsic and extrinsic contributions to magnetic
hysteresis in rare earth-based magnets, \textit{i.e.} the combination of
increased intrinsic anisotropy due to Cu substitution and the extrinsic effect
of inhomogeneous elemental distribution of Cu and Co.",2304.06457v1
2023-05-01,Perpendicular magnetic anisotropy of an ultrathin Fe layer grown on NiO(001),"The magnetic anisotropy and magnetic interactions at the interface between Fe
and NiO(001) were investigated. Depending on the growth conditions of the
NiO(001) layers and the post-annealing temperature, the preferential
magnetization direction of the ultrathin Fe layer grown on a NiO(001) layer
changed from in-plane to a direction perpendicular to the film plane. The
lattice constant of the NiO(001) layers parallel to the growth direction
increased with O$_2$ flow rate, while that parallel to the in-plane were locked
onto the MgO(001) substrate regardless of the growth conditions of the NiO
layers. Moreover, perpendicular magnetization was observed only when the NiO
layer was grown with O$_2$ flow rates higher than 2.0 sccm corresponding to
oxygen-rich NiO. X-ray magnetic circular dichroism measurements revealed an
enhancement in anisotropic orbital magnetic moments similar to the origin of
perpendicular magnetic anisotropy at the Fe/MgO(001) interface. The interfacial
magnetic anisotropy energies were 0.93 and 1.02 mJ/m$^2$ at room temperature
and at 100 K, respectively, indicating less temperature dependence. In
contrast, the coercivity $H_c$ exhibited a significant temperature dependence.
Although no signature of exchange bias or unidirectional loop shift was
observed, $H_c$ was strongly dependent on the NiO layer thickness, indicating
that the exchange interaction at the interface between the ferromagnetic and
antiferromagnetic layers was not negligible, despite the NiO(001) being a
spin-compensated surface.",2305.00672v1
2023-05-15,The influence of anisotropy on the manifestation of aging effects in the magnetoresistance of multilayer structures,"Currently, aging effects occurring in multilayer systems attract much
attention from researchers. In our research we looked at the behavior of
multilayer systems that depend on anisotropy, magnetoresistance and
susceptibility.All these parameters are interrelated and have varying degrees
of influence on the effects of aging. We researched our Co-layers magnetic
system from high-temperature and low-temperature initial states, as well as not
only in the critical temperature region, but in a wide low-temperature range.
The study was carried out with different types of magnetic anisotropy, which
made it possible to identify differences in the behavior of the system
depending on the type of anisotropy. We found that in systems exhibiting a
dimensional transition, aging effects manifest to gain and themselves in a wide
low-temperature range, and not only in a narrow near-critical region, which
ultimately leads us to a wide range of applications of these materials for
practical applications.",2305.08656v4
2023-06-01,"Diffuse Sources, Clustering and the Excess Anisotropy of the Radio Synchrotron Background","We present the largest low frequency (120~MHz) arcminute resolution image of
the radio synchrotron background (RSB) to date, and its corresponding angular
power spectrum of anisotropies (APS) with angular scales ranging from $3^\circ$
to $0.3^\prime$. We show that the RSB around the North Celestial Pole has a
significant excess anisotropy power at all scales over a model of unclustered
point sources based on source counts of known source classes. This anisotropy
excess, which does not seem attributable to the diffuse Galactic emission,
could be linked to the surface brightness excess of the RSB. To better
understand the information contained within the measured APS, we model the RSB
varying the brightness distribution, size, and angular clustering of potential
sources. We show that the observed APS could be produced by a population of
faint clustered point sources only if the clustering is extreme and the size of
the Gaussian clusters is $\lesssim 1'$. We also show that the observed APS
could be produced by a population of faint diffuse sources with sizes $\lesssim
1'$, and this is supported by features present in our image. Both of these
cases would also cause an associated surface brightness excess. These classes
of sources are in a parameter space not well probed by even the deepest radio
surveys to date.",2306.00829v1
2023-06-10,The Central Role of Tilted Anisotropy for Field-Free Spin-Orbit Torque Switching of Perpendicular Magnetization,"The discovery of efficient magnetization switching activated by the spin Hall
effect (SHE)-induced spin-orbit torque (SOT) changed the course of magnetic
random-access memory (MRAM) research and development. However, for systems with
perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by
the necessity of a longitudinal magnetic field to break the magnetic symmetry
to achieve deterministic switching. In this work, we first demonstrate that a
robust and tunable field-free current-driven SOT switching of perpendicular
magnetization can be controlled by the growth protocol in Pt-based magnetic
heterostructures. It is further elucidated that such growth-dependent symmetry
breaking is originated from the laterally tilted magnetic anisotropy of the
ferromagnetic layer with PMA, which has been largely neglected in previous
studies and its critical role should be re-focused. We show by both experiments
and simulations that in a PMA system with tilted anisotropy, the deterministic
field-free switching possesses a conventional SHE-induced damping-like torque
feature and the resulting current-induced effective field has a non-linear
dependence on the applied current density, which could be potentially
misattributed to an unconventional SOT origin.",2306.06357v1
2023-06-20,Magnetic Exciton-Polariton with Strongly Coupled Atomic and Photonic Anisotropies,"Anisotropy plays a key role in science and engineering. However, the
interplay between the material and engineered photonic anisotropies has hardly
been explored due to the vastly different length scales. Here we demonstrate a
matter-light hybrid system, exciton-polaritons in a 2D antiferromagnet, CrSBr,
coupled with an anisotropic photonic crystal (PC) cavity, where the spin,
atomic lattice, and photonic lattices anisotropies are strongly correlated,
giving rise to unusual properties of the hybrid system and new possibilities of
tuning. We show exceptionally strong coupling between engineered anisotropic
optical modes and anisotropic excitons in CrSBr, which is stable against
excitation densities a few orders of magnitude higher than polaritons in
isotropic materials. Moreover, the polaritons feature a highly anisotropic
polarization tunable by tens of degrees by controlling the matter-light
coupling via, for instance, spatial alignment between the material and photonic
lattices, magnetic field, temperature, cavity detuning and cavity
quality-factors. The demonstrated system provides a prototype where atomic- and
photonic-scale orders strongly couple, opening opportunities of photonic
engineering of quantum materials and novel photonic devices, such as compact,
on-chip polarized light source and polariton laser.",2306.11265v2
2023-06-26,Detecting anisotropies of the stochastic gravitational wave background with TianQin,"The investigation of the anisotropy of the stochastic gravitational wave
background (SGWB) using the TianQin detector plays a crucial role in studying
the early universe and astrophysics. In this work, we examine the response of
the $AET$ channel of the TianQin Time Delay Interferometry (TDI) to the
anisotropy of the SGWB. We calculate the corresponding angular sensitivity
curves and find that TianQin is capable of detecting the anisotropy of the
SGWB, with an angular sensitivity reaching $10^{-10}$ for quadrupoles. Due to
the fixed $z$-axis of TianQin pointing towards J0806, its overlap reduction
functions (ORFs) exhibit specific symmetries, enabling the resolution of
different multipole moments $\ell m$. The detection sensitivity is optimal for
the $(2, 0)$ mode, with a sensitivity reaching $10^{-10}$. Using the Fisher
matrix approach, we estimate the parameters and find that in the power-law
spectrum model, higher logarithmic amplitudes lead to more effective
reconstruction of the spectral index for all multipole moments. Under the
optimal scenario with a signal amplitude of $\Omega_{\mathrm{GW}} (f =
f_{\mathrm{c}}) h^2 = 10^{-9}$, the spectral indices can be reconstructed with
uncertainties of $10^{-3}$, $10$, and $10^{-3}$ for $\ell = 0$, $1$, and $2$
multipole moments, respectively. For the cases of $(\ell, m) = (0, 0)$, $(1,
1)$, $(2, 0)$, and $(2, 2)$, the spectral indices can be reconstructed with
uncertainties of $10^{-3}$, $10$, $10^{-3}$, and $10$, respectively.",2306.14439v3
2023-07-22,Magnetization dynamics due to field interplay in field free spin Hall nano-oscillators,"Spin Hall nano oscillators (SHNOs) have shown applications in unconventional
computing schemes and broadband frequency generation in the presence of applied
external magnetic field. However, under field-free conditions, the oscillation
characteristics of SHNOs display a significant dependence on the effective
field, which can be tuned by adjusting the constriction width, thereby
presenting an intriguing area of study. Here we study the effect of nano
constriction width on the magnetization dynamics in anisotropy assisted field
free SHNOs. In uniaxial anisotropy-based field-free SHNOs, either the
anisotropy field or the demagnetization field can dominate the magnetization
dynamics depending on the constriction width. Our findings reveal distinct
auto-oscillation characteristics in narrower constrictions with 20 nm and 30 nm
constriction width compared to their wider counterpart with 100 nm width. The
observed frequency shift variations with input current and constriction widths
stem from the inherent nonlinearity of the system. The interplay between the
B_demag and B_anis, coupled with changes in constriction width, yields rich
dynamics and offers control over frequency tunability, auto oscillation
amplitude, and threshold current. Notably, the spatial configuration of spin
wave wells within the constriction undergoes transformations in response to
changes in both constriction width and anisotropy. The findings highlight the
significant influence of competing fields at the constriction on the field-free
auto oscillations of SHNOs, with this impact intensifying as the constriction
width is varied.",2307.12068v1
2023-09-18,Phase transitions in the anisotropic XY ferromagnet with quenched nonmagnetic impurity,"The three dimensional anisotropic XY ferromagnet has been studied by Monte
Carlo simulation. The ferro-para phase transition has been observed to take
place at a lower temperature for impure anisotropic XY ferromagnet. The
pseudocritical temperature ($T_c^*$) has been found to decrease as the system
gets more and more impure (impurity concentration $p$ increases). In the case
of bilinear exchange type of anisotropy ($\lambda$), the pseudocritical
temperature ($T_c^*$) increases linearly with $\lambda$ for any given
concentration of nonmagnetic impurity ($p$). The slope of this linear function
has been found to depend on the impurity concentration ($p$). The slope
decreases linearly with the impurity concentration ($p$). In the case of the
single site anisotropy ($D$), the pseudocritical temperature ($T_c^*$) has been
found to decrease linearly with $p$ for fixed $D$. The critical temperature
(for a fixed set of parameter values) has been estimated from the temperature
variation of fourth order Binder cumulants ($U_L$) for different system sizes
($L$). The critical magnetisation ($M(T_c)$) and the maximum value of the
susceptibility ($\chi_p$) are calculated for different system sizes ($L$). The
critical exponents for the assumed scaling laws, $M(T_c) \sim L^{-{{\beta}
\over {\nu}}}$ and $\chi_p \sim L^{{{\gamma} \over {\nu}}}$, are estimated
through the finite size analysis. We have estimated, ${{\beta} \over {\nu}}$,
equals to $0.48\pm0.05$ and $0.37\pm0.04$ for bilinear exchange and single site
anisotropy respectively. We have also estimated, ${{\gamma} \over {\nu}}$
equals to $1.78\pm0.05$ and $1.81\pm0.05$ for bilinear exchange and single site
anisotropy respectively.",2309.09659v3
2023-10-05,Study of azimuthal anisotropy of $Υ$(1S) mesons in pPb collisions at $\sqrt{s_\mathrm{NN}}$ = 8.16 TeV,"The azimuthal anisotropy of $\Upsilon$(1S) mesons in high-multiplicity
proton-lead collisions is studied using data collected by the CMS experiment at
a nucleon-nucleon center-of-mass energy of 8.16 TeV. The $\Upsilon$(1S) mesons
are reconstructed using their dimuon decay channel. The anisotropy is
characterized by the second Fourier harmonic coefficients, found using a
two-particle correlation technique, in which the $\Upsilon$(1S) mesons are
correlated with charged hadrons. A large pseudorapidity gap is used to suppress
short-range correlations. Nonflow contamination from the dijet background is
removed using a low-multiplicity subtraction method, and the results are
presented as a function of $\Upsilon$(1S) transverse momentum. The azimuthal
anisotropies are smaller than those found for charmonia in proton-lead
collisions at the same collision energy, but are consistent with values found
for $\Upsilon$(1S) mesons in lead-lead interactions at a nucleon-nucleon
center-of-mass energy of 5.02 TeV.",2310.03233v2
2023-08-29,Multiscale and Anisotropic Characterization of Images Based on Complexity: an Application to Turbulence,"This article presents a multiscale, non-linear and directional statistical
characterization of images based on the estimation of the skewness, flatness,
entropy and distance from Gaussianity of the spatial increments. These
increments are characterized by their magnitude and direction; they allow us to
characterize the multiscale properties directionally and to explore anisotropy.
To describe the evolution of the probability density function of the increments
with their magnitude and direction, we use the skewness to probe the symmetry,
the entropy to measure the complexity, and both the flatness and distance from
Gaussianity to describe the shape. These four quantities allow us to explore
the anisotropy of the linear correlations and non-linear dependencies of the
field across scales. First, we validate the methodology on two-dimensional
synthetic scale-invariant fields with different multiscale properties and
anisotropic characteristics. Then, we apply it on two synthetic turbulent
velocity fields: a perfectly isotropic and homogeneous one, and a channel flow
where boundaries induce inhomogeneity and anisotropy. Our characterization
unambiguously detects the anisotropy in the second case, where our quantities
report scaling properties that depend on the direction of analysis.
Furthermore, we show in both cases that turbulent velocity fluctuations are
always isotropic, when the mean velocity profile is adequately removed.",2310.05946v1
2023-10-24,In memoriam Pal Revesz(1934-2022) The random walk from orthogonality to anisotropy,"A tribute to the life and work of Pal Revesz. The Hungarian mathematical
community lost one of his leading members, when Pal Revesz passed away on 14 of
November 2022.",2310.16163v1
2023-11-07,Spectral scaling of unstably-stratified atmospheric flows: understanding the low frequency spread of Kaimal model,"For more than five decades, a notable spread in the low frequencies of
velocity and temperature spectra, scaled using inertial subrange properties and
Monin-Obukhov similarity theory, has been observed in unstable stratification.
A large ensemble of 14 datasets, over relatively simple terrain (from flat and
homogeneous to gentle slope or valley floor) and very complex terrain (steep
slope, crater rim, mountain top), are used to assess the reasons of this
low-frequency behaviour.
  Turbulence anisotropy is shown to be the primary factor influencing the
spectral energy at the largest scales and the spectral peak position of
streamwise and spanwise velocity spectra, with stability acting as a secondary
factor. On the contrary, the low-frequency behaviour of surface-normal and
temperature spectra is dominated by stability effects, while turbulence
anisotropy plays a secondary role. These observations are valid over both
simple and complex terrain, even though variability of the largest scales of
complex terrain datasets integrate other processes not included in turbulence
anisotropy or stability conditions.
  Using a combination of non-dimensional turbulence parameters - temperature
and velocity variances as well as dissipation of turbulence kinetic energy and
of temperature variance - and of a semi-empirical model provided in the
literature, we are able to describe the behaviour of the velocity and
temperature spectra with only turbulence anisotropy and stability as input
parameters.
  Finally, the paper provides some insights into the nature of anisotropic
eddies, as well as the relationship between the boundary layer height and the
spectral behaviour.",2311.03859v1
2023-11-15,Merger Response of Halo Anisotropy Properties,"Anisotropy properties -- halo spin, shape, position offset, velocity offset,
and orientation -- are an important family of dark matter halo properties that
indicate the level of directional variation of the internal structures of
haloes. These properties reflect the dynamical state of haloes, which in turn
depends on the mass assembly history. In this work, we study the evolution of
anisotropy properties in response to merger activity using the IllustrisTNG
simulations. We find that the response trajectories of the anisotropy
properties significantly deviate from secular evolution. These trajectories
have the same qualitative features and timescales across a wide range of merger
and host properties. We propose explanations for the behaviour of these
properties and connect their evolution to the relevant stages of merger
dynamics. We measure the relevant dynamical timescales. We also explore the
dependence of the strength of the response on time of merger, merger ratio, and
mass of the main halo. These results provide insight into the physics of halo
mergers and their effects on the statistical behaviour of halo properties. This
study paves the way towards a physical understanding of scaling relations,
particularly to how systematics in their scatter are connected to the mass
assembly histories of haloes.",2311.08664v1
2023-12-07,Features of magnetization and spin reorientation in weak ferrimagnets of the YFe$_{1-x}$Cr$_x$O$_3$ type,"A brief critical review is given of the 50-year history of experimental and
theoretical studies of the magnetic properties of a new promising class of weak
ferrimagnets such as RFe$_{1-x}$Cr$_x$O$_3$ with a non-magnetic R-ion (R = La ,
Y, Lu), i.e. systems with competing signs of the Dzyaloshinsky vectors Fe-Fe,
Cr-Cr and Fe-Cr. The spin Hamiltonian of the system is considered taking into
account isotropic exchange, antisymmetric Dzyaloshinsky-Moriya exchange, and
second- and fourth-order single-ion anisotropy. Within the framework of the
molecular field approximation, calculations were made of the Neel temperatures,
the average magnetic moments of $3d$ ions, total and partial magnetizations,
and effective anisotropy constants. The existence in the model system
YFe$_{1-x}$Cr$_x$O$_3$ of two regions of negative magnetization $0.25 \leq
x\leq 0.5$ and $x\approx 0.8$ with the corresponding magnetization reversal
points reaching room temperature at $x\approx 0.45$. The phenomenon of spin
reorientation observed for single-crystal samples in a wide range of
concentrations is explained by a sharp decrease in the contribution of
antisymmetric exchange to magnetic anisotropy with increasing deviation from
the parent compositions and competition between the contributions of single-ion
anisotropy of Fe and Cr ions. It has been suggested that the spatial
orientation of the Neel ${\bf G}$ vector and the $G_{xyz}$ configuration are
the reason for the small value of saturation magnetization observed
experimentally for compositions inside or near the region of negative
magnetization.",2312.04381v2
2023-12-12,Confined magnon dispersion in ferromagnetic and antiferromagnetic thin films in a second quantization approach: the case of Fe and NiO,"We present a methodology based on the calculation of the inelastic scattering
from magnons via the spin scattering function in confined geometries such as
thin films using a second quantization formalism, for both ferromagnetic and
antiferromagnetic materials. The case studies are chosen with an aim to
demonstrate the effects of film thickness and crystal orientation on magnon
modes, using bcc Fe(100) and NiO with (100) and (111) crystallographic
orientations as prototypical systems. Due to the quantization of the
quasi-momentum we observe a granularity in the inelastic spectra in the
reciprocal space path reflecting the orientation of the thin film. This
approach also allows to capture softer modes that appear due to the partial
interaction of magnetic moments close to the surface in a thin film geometry,
in addition to bulk modes. The softer modes are also affected by
crystallographic orientations as illustrated by the different surface-related
peaks of NiO magnon density of states at approximately ~ 65 meV for (100) and ~
42 meV for (111). Additionally, we explore the role of anisotropy on magnon
modes, revealing that introducing anisotropy to both Fe and NiO films increases
the overall hardness of the magnon modes. The introduction of a surface
anisotropy produces a shift of the surface-related magnon DOS peak to higher
energies with increased surface anisotropy, and in some cases leading to
surface confined mode.",2312.07715v1
2024-01-16,Insights into Polycrystalline Microstructure of Blood Films with 3D Mueller Matrix Imaging Approach,"We introduce a 3D Mueller Matrix (MM) image reconstruction technique using
digital holographic approach for the layer-by-layer profiling thin films with
polycrystalline structures, like dehydrated blood smears. The proposed method
effectively extracts optical anisotropy parameters for a detailed quantitative
analysis. The investigation revealed the method sensitivity to subtle changes
in optical anisotropy properties resulting from alterations in the quaternary
and tertiary structures of blood proteins, leading to disturbances in
crystallization structures at the macro level at the very early stage of a
disease. Spatial distributions of linear and circular birefringence and
dichroism are analyzed in partially depolarizing polycrystalline blood films
obtained from healthy tissues and cancerous prostate tissues at various stages
of adenocarcinoma. Changes in the values of the 1st to 4th order statistical
moments, characterizing the distributions of optical anisotropy in different
phase sections of the smear volumes, are observed and quantified. Comparative
analysis of optical anisotropy distributions from healthy patients highlighted
the 3rd and 4th order statistical moments for linear and circular birefringence
and dichroism as the most promising for diagnostic purposes. We achieved an
excellent accuracy (>90%) for early cancer diagnosis and differentiation of its
stages, demonstrating the techniques significant potential for rapid and
accurate definitive cancer diagnosis compared to existing screening approaches.",2401.08340v1
2024-02-04,Infrared Optical Anisotropy in Quasi-1D Hexagonal Chalcogenide BaTiSe3,"Polarimetric infrared detection bolsters IR thermography by leveraging the
polarization of light. Optical anisotropy, i.e., birefringence and dichroism,
can be leveraged to achieve polarimetric detection. Recently, giant optical
anisotropy was discovered in quasi-1D narrow-bandgap hexagonal perovskite
sulfides, A1+xTiS3, specifically BaTiS3[1,2] and Sr9/8TiS3[3,4]. In these
materials, the critical role of atomic-scale structure modulations[4,5] in the
unconventional electrical[5,6], optical[7,8], and thermal[7,9] properties
raises the broader question of other materials that belong to this family. To
address this issue, for the first time, we synthesized high-quality single
crystals of a largely unexplored member of the A1+xTiX3 (X = S, Se) family,
BaTiSe3. Single-crystal X-ray diffraction determined the room-temperature
structure with the P31c space group, which is a superstructure of the earlier
reported[10] P63/mmc structure. The crystal structure of BaTiSe3 features
antiparallel c-axis displacements similar to BaTiS3,[2] but is of lower
symmetry. Polarization-resolved Raman and Fourier transform infrared (FTIR)
spectroscopy were used to characterize the optical anisotropy of BaTiSe3, whose
refractive index along the ordinary (perpendicular to c) and extraordinary
(parallel to c) optical axes was quantitatively determined by combining
ellipsometry studies with FTIR. With a giant birefringence {\Delta}n~0.9,
BaTiSe3 emerges as a new candidate for miniaturized birefringent optics for
mid-wave infrared to long-wave infrared imaging.",2402.02323v1
2024-02-04,Mass-Radius relationship of Strongly Magnetized Super-Chandrasekhar Anisotropic Deformed White Dwarf Stars in presence of $γ$-metric,"The masses and radii of strongly magnetized anisotropic deformed white dwarf
stars are investigated using the stellar structure equations in the
parameterized $\gamma$-metric formalism. The Equation of State (EoS) of a
completely degenerate relativistic electron gas in strong quantizing
density-dependent magnetic field is developed. The fluid and field pressure
anisotropy among the parallel and perpendicular components to the magnetic
field is taken into consideration. This anisotropy in the EoS causes
axisymmetric deformation of the star. We found stable solutions of deformed
super-Chandrasekhar ultramassive white dwarfs. The masses of anisotropic
magnetized white dwarfs at the same central density decrease monotonically with
the increase in the strength of the central magnetic field, while the
equatorial radii increase monotonically. This is in sharp contrast to the
isotropic case where both the mass and radius increase monotonically. High
magnetic field increases anisotropy and oblateness. We also see that the
maximum mass and its corresponding equatorial radius both decrease as central
magnetic field strength increases. We also notice that the maximum mass occurs
at higher central density as the magnetic field increases. This shows that
increasing magnetic field (hence increasing anisotropy) softens the EoS and
makes the star more compact.",2402.02509v1
2024-02-19,Towards Cosmography of the Local Universe,"Anisotropies in the distance-redshift relation of cosmological sources are
expected due to large-scale inhomogeneities in the local Universe. When the
observed sources are tracing a large-scale matter flow in a general spacetime
geometry, the distance-redshift relation with its anisotropies can be described
with a geometrical prediction that generalises the well-known
Friedmann-Lema\^itre-Robertson-Walker result. Furthermore, it turns out that a
finite set of multipole coefficients contain the full information about a
finite-order truncation of the distance-redshift relation of a given observer.
The multipoles of the distance-redshift relation are interesting new
cosmological observables that have a direct physical interpretation in terms of
kinematical quantities of the underlying matter flow. Using light cones
extracted from $N$-body simulations we quantify the anisotropies expected in a
$\Lambda$ cold dark matter cosmology by running a Markov chain Monte Carlo
analysis on the observed data. In this observational approach the survey
selection implements an implicit smoothing scale over which the effective rest
frame of matter is fitted. The perceived anisotropy therefore depends
significantly on the redshift range and distribution of sources. We find that
the multipoles of the expansion rate, as well as the observer's velocity with
respect to the large-scale matter flow, can be determined robustly with our
approach.",2402.12165v1
2024-02-19,Variational properties of local functionals driven by arbitrary anisotropies,"We provide integral representation and $\Gamma$-compactness results for
anisotropic local functionals depending on arbitrary Lipschitz continuous
vector fields. In particular, neither bracket-generating assumptions nor linear
independence conditions are required.",2402.12227v1
2024-02-24,Energy landscape of noncollinear exchange coupled magnetic multilayers,"We conduct an exploration of the energy landscape of two coupled
ferromagnetic layers with perpendicular-to-plane uniaxial anisotropy using
finite-element micromagnetic simulations. These multilayers can be used to
produce noncollinearity in spin-transfer torque magnetic random-access memory
cells, which has been shown to increase the performance of this class of
computer memory. We show that there exists a range of values of the interlayer
exchange coupling constants for which the magnetic state of these multilayers
can relax into two energy minima. The size of this region is determined by the
difference in the magnitude of the layer anisotropies and is minimized when
this difference is large. In this case, there is a wide range of experimentally
achievable coupling constants that can produce desirable and stable
noncollinear alignment. We investigate the energy barriers separating the local
and global minima using string method simulations, showing that the stabilities
of the minima increase with increasing difference in the anisotropy of the
ferromagnetic layers. We provide an analytical solution to the location of the
minima in the energy landscape of coupled macrospins, which has good agreement
with our micromagnetic results for a case involving ferromagnetic layers with
the same thickness and anisotropy, no demagnetization field, and large exchange
stiffness. These results are important to understand how best to employ
noncollinear coupling in the next generation of thin film magnetic devices.",2402.15910v1
2024-03-22,Quantum spin driven Yu-Shiba-Rusinov multiplets and fermion-parity-preserving phase transition in K$_3$C$_{60}$,"Magnetic impurities in superconductors are of increasing interest due to
emergent Yu-Shiba-Rusinov (YSR) states and Majorana zero modes for
fault-tolerant quantum computation. However, a direct relationship between the
YSR multiple states and magnetic anisotropy splitting of quantum impurity spins
remains poorly characterized. By using scanning tunneling microscopy, we
resolve systematically individual transition-metal (Fe, Cr and Ni) impurities
induced YSR multiplets as well as their Zeeman effects in K$_3$C$_{60}$
superconductor. The YSR multiplets show identical $d$ orbital-like wave
functions that are symmetry-mismatched to the threefold K$_3$C$_{60}$(111) host
surface, breaking point-group symmetries of the spatial distribution of YSR
bound states in real space. Remarkably, we identify an unprecedented
fermion-parity-preserving quantum phase transition between ground states with
opposite signs of the uniaxial magnetic anisotropy that can be manipulated by
an external magnetic field. These findings can be readily understood in terms
of anisotropy splitting of quantum impurity spins, and thus elucidate the
intricate interplay between the magnetic anisotropy and YSR multiplets.",2403.14970v1
2024-03-31,On bond anisotropy for the ising model through the geometry of numbers,"We associate to each unit volume lattice of $\R^d$ the Ising model with bond
variables equal to the inverse successive minima of that lattice. This induces
the notion of a critical temperature for a random lattice for which
integrability exponents are proven.",2404.00662v1
1992-12-16,Gravity's rainbow,"Could COBE DMR be detecting the imprint from a spectrum of gravitational
waves generated during inflation? The conventional inflationary prediction had
been that the cosmic microwave anisotropy is dominated by energy density
fluctuations generated during inflation and that the gravitational waves
contribute negligibly. In this paper, we report on recent work (in
collaboration with R. Davis, H. Hodges, and M. Turner) that has shown that the
conventional wisdom may be wrong; specifically, gravitational waves may
dominate the anisotropy in inflationary models where the spectrum of
perturbations deviates significantly from scale invariance (e.g., extended and
power-law inflation models and extreme versions of chaotic inflation). If
gravitational waves do dominate at the large-angular scales measured by COBE
DMR, the expectation and interpretation of anisotropies on small-angular scales
is profoundly altered. Invited Paper for Proceedings of the Journees
Relativistes, Amsterdam, May 14-16, 1992",9212003v1
1993-05-26,Comparing Direct N-Body Integration with Anisotropic Gaseous Models of Star Clusters,"We compare the results for the dynamical evolution of star clusters derived
from anisotropic gaseous models with the data from N-body simulations of
isolated and one-component systems, each having modest number of stars. The
statistical quality of N-body data was improved by averaging results from many
N-body runs, each with the same initial parameters but with different sequences
of random numbers used to initialize positions and velocities of the particles.
We study the development of anisotropy, the spatial evolution and energy
generation by three-body binaries and its N-dependence. We estimate the
following free parameters of anisotropic gaseous models: the time scale for
collisional anisotropy decay and the coefficient in the formulae for energy
generation by three-body binaries. To achieve a fair agreement between N-body
and gaseous models for the core in pre- as well as in post-collapse only the
energy generation by binaries had to be varied by N. We find that anisotropy
has considerable influence on the spatial structure of the cluster particularly
for the intermediate and outer regions.",9305033v1
1993-07-26,"Peculiar Velocity, Cosmic Perturbation Theory and the CMB Anisotropy","This is a somewhat extended version of the original July 93 report. It is
proved that the cosmological density perturbation is associated with a peculiar
velocity field. This allows a simple formulation of cosmological perturbation
theory, which works entirely with quasi-Newtonian fluid flow equations. As an
illustration, the large scale cosmic microwave background anisotropy
(Sachs-Wolfe effect) is calculated without any reference to the metric
perturbation. In addition, assuming the usual adiabatic initial condition on
the density perturbation, we show that the dipole of the anisotropy measures
our peculiar velocity relative to the average peculiar velocity within the last
scattering surface of the microwave background, thus defining its frame of
reference.",9307036v2
1993-11-17,Early Reionization in Cosmology,"The cosmic microwave background (CMB) anisotropies have turned out to
represent one of the most stringent 'bottle necks' for scenarios of large scale
structure formation. As a possibility to relax this constraint, it has been
proposed that early reionization can damp CMB fluctuations on small scales due
to photon diffusion in the ionized plasma. As an example, I investigate the
recently proposed scenario with cold dark matter (CDM) and texture seeds.
There, an analysis of CMB anisotropies shows that early reionization is a
crucial ingredient for this scenario. Without damping, the small scale
anisotropies would dominate and exceed observed limits. In this paper I present
analytical and numerical results for the amount of damping due to early
reionization for CMB perturbations induced by a collapsing texture.
Furthermore, the spectral distortion of the CMB due to Compton scattering of
the hotter plasma electrons is calculated. Next I discuss the physical
processes which lead to a system of coupled ordinary differential equations for
the degree of ionization, the electron temperature and the evolution of the
ionizing radiation.",9311039v1
1993-11-17,Microwave Anisotropies from Texture Seeded Structure Formation,"The cosmic microwave anisotropies in a scenario of large scale structure
formation with cold dark matter and texture are discussed and compared with
recent observational results of the COBE satellite. A couple of important
statistical parameters are determined. The fluctuations are slightly non
gaussian. The quadrupole anisotropy is $1.5\pm 1.2\times 10^{-5}$ and the
fluctuations on a angular scale of 10 degrees are $ (3.8\pm 2.6)\times
10^{-5}$. The COBE are within about one standard deviation of the typical
texture + CDM model discussed in this paper. Furthermore, we calculate
fluctuations on intermediate scales (about 2 degrees) with the result $\De
T/T(\theta \sim 2^o) = 3.9\pm 0.8)\times 10^{-5}$. Collapsing textures are
modeled by spherically symmetric field configurations. This leads to
uncertainties of about a factor of~2.",9311040v1
1994-03-02,Texture-Induced Microwave Background Anisotropies,"We use numerical simulations to calculate the cosmic microwave background
anisotropy induced by the evolution of a global texture field, with special
emphasis on individual textures. Both spherically symmetric and general
configurations are analysed, and in the latter case we consider field
configurations which exhibit unwinding events and also ones which do not. We
compare the results given by evolving the field numerically under both the
expanded core (XCORE) and non-linear sigma model (NLSM) approximations with the
analytic predictions of the NLSM exact solution for a spherically symmetric
self-similar (SSSS) unwinding. We find that the random unwinding configuration
spots' typical peak height is 60--75\% and angular size typically only 10\% of
those of the SSSS unwinding, and that random configurations without an
unwinding event nonetheless may generate indistinguishable hot and cold spots.
The influence of these results on analytic estimates of texture induced
microwave anisotropies is examined, and comparison made with other numerical
work.",9403005v1
1994-06-27,Beyond the Small-Angle Approximation For MBR Anisotropy from Seeds,"In this paper we give a general expression for the energy shift of massless
particles travelling through the gravitational field of an arbitrary matter
distribution as calculated in the weak field limit in an asymptotically flat
space-time. It is {\it not} assumed that matter is non-relativistic. We
demonstrate the surprising result that if the matter is illuminated by a
uniform brightness background that the brightness pattern observed at a given
point in space-time (modulo a term dependent on the oberver's velocity) depends
only on the matter distribution on the observer's past light-cone. These
results apply directly to the cosmological MBR anisotropy pattern generated in
the immediate vicinity of of an object like a cosmic string or global texture.
We apply these results to cosmic strings, finding a correction to previously
published results for in the small-angle approximation. We also derive the
full-sky anisotropy pattern of a collapsing texture knot.",9406067v1
1994-07-01,Models of Galaxies with Central Black Holes: Adiabatic Growth in Spherical Galaxies,"We add black holes to nonrotating, spherical galaxy models, with the
assumption that the black-hole growth is slow compared with the dynamical time
but fast compared with the relaxation time. The outcome differs depending on
whether the core of the initial galaxy does or does not resemble that of an
isothermal sphere. For the isothermal case the previously-known results are
confirmed and sharpened: the black hole induces cusps in the density ($\rho\sim
r^{-3/2}$) and velocity dispersion ($v^2\sim r^{-1}$), and a tangential
anisotropy in the velocity distribution away from the center. For the
non-isothermal case the induced density cusp is steeper, and the induced
anisotropy is larger and penetrates right to the center. The cusp around the
black hole is insensitive to anisotropy in the initial velocity distribution,
and also to the origin of the black hole, unless its mass comes exclusively
from the stars of lowest angular momentum, in which case the cusp is
suppressed. We discuss the implications for the interpretation of evidence for
massive black holes in galactic nuclei.",9407005v1
1994-11-29,The Cosmic Microwave Background Dipole as a Cosmological Effect,"A conventional explanation of the dipole anisotropy of the cosmic microwave
background (CMB) radiation is in terms of the Doppler effect: our galaxy is
moving with respect to CMB frame with $ \sim 600 ~ km ~ s^{-1} $. However, as
the deep redshift surveys fail to reveal a convergence of the large scale flow
to zero at distances as large as $ d \sim H^{-1} 15,000 ~ km ~ s^{-1} $ (Lauer
& Postman, 1994), the uniqueness of the conventional interpretation has to be
investigated. A possible alternative might be a cosmological entropy gradient,
as suggested by Paczy\'nski & Piran (1990). We find that contrary to that
suggestion a quadrupole anisotropy is generically of the same order of
magnitude as the dipole anisotropy (or larger) not only for adiabatic but also
for iso-curvature initial perturbations. Hence, the observed dipole cannot be
explained with a very large scale perturbation which was initially
iso-curvature.",9411111v1
1994-12-17,Constraints onOmega from the IRAS Redshift Surveys,"We measure the anisotropy of the redshift-space power spectrum in the 1.2-Jy
and QDOT redshift surveys of IRAS-selected galaxies. On large scales, this
anisotropy is caused by coherent peculiar motions, and gravitational
instability theory predicts a distortion of the power spectrum that depends
only on the ratio $\beta \equiv f(\Omega)/b \approx \Omega^{0.6}/b$, where
Omega is the cosmological density parameter and $b$ is the bias parameter. On
small scales, the distortion is dominated by the random velocity dispersion in
non-linear structures. We fit the observed anisotropy with an analytic model
that incorporates two parameters, beta, and a small-scale velocity dispersion
sigma_v. Tests on N-body simulations show that this model recovers beta quite
accurately on the scales accessible to the existing IRAS redshift surveys.
  Applying our procedure to the 1.2-Jy and QDOT surveys, we find beta=0.52 +/-
0.13 and beta=0.54 +/- 0.3, respectively. These results imply Omega
approximately 0.35 if galaxies trace mass, or a bias factor of about 2 if
Omega=1.",9412062v1
1995-05-09,Electromagnetic Origin of the CMB Anisotropy in String Cosmology,"In the inflationary scenarios suggested by string theory, the vacuum
fluctuations of the electromagnetic field can be amplified by the
time-evolution of the dilaton background, and can grow large enough to explain
both the origin of the cosmic magnetic fields and of the observed CMB
anisotropy. The normalization of the perturbation spectrum is fixed, and
implies a relation between the perturbation amplitude at the COBE scale and the
spectral index $n$. Working within a generic two-parameter family of
backgrounds, a large scale anisotropy $\Delta T/T\simeq 10^{-5}$ is found to
correspond to a spectral index in the range $n\simeq 1.11 - 1.17$.",9505041v1
1995-05-23,GRAVITATIONAL LENSING EFFECT ON COSMIC MICROWAVE BACKGROUND ANISOTROPIES: A POWER SPECTRUM APPROACH,"The effect of gravitational lensing on cosmic microwave background (CMB)
anisotropies is investigated using the power spectrum approach. The lensing
effect can be calculated in any cosmological model by specifying the evolution
of gravitational potential. Previous work on this subject is generalized to a
non-flat universe and to a nonlinear evolution regime. Gravitational lensing
cannot change the gross distribution of CMB anisotropies, but it may
redistribute the power and smooth the sharp features in the CMB power spectrum.
The magnitude of this effect is estimated using observational constraints on
the power spectrum of gravitational potential from galaxy and cluster surveys
and also using the limits on correlated ellipticities in distant galaxies. For
realistic CMB power spectra the effect on CMB multipole moments is less then a
few percent on degree angular scales, but gradually increases towards smaller
scales. On arcminute angular scales the acoustic oscillation peaks may be
partially or completely smoothed out because of the gravitational lensing.",9505109v2
1995-06-12,COSMICS: Cosmological Initial Conditions and Microwave Anisotropy Codes,"COSMICS is a package of fortran programs useful for computing transfer
functions and microwave background anisotropy for cosmological models, and for
generating gaussian random initial conditions for nonlinear structure formation
simulations of such models. Four programs are provided: {\bf linger\_con} and
{\bf linger\_syn} integrate the linearized equations of general relativity,
matter, and radiation in conformal Newtonian and synchronous gauge,
respectively; {\bf deltat} integrates the photon transfer functions computed by
the linger codes to produce photon anisotropy power spectra; and {\bf grafic}
tabulates normalized matter power spectra and produces constrained or
unconstrained samples of the matter density field.
  Version 1.0 of COSMICS is available at http://arcturus.mit.edu/cosmics/ . The
current release gives fortran-77 programs that run on workstations and
vectorized supercomputers. Unix makefiles are included that make it simple to
build and test the package. A future release will include portable parallel
versions of the linger codes using standard message-passing libraries.",9506070v1
1995-07-14,CMB Anisotropies in the Weak Coupling Limit,"We present a new, more powerful and accurate, analytic treatment of cosmic
microwave background (CMB) anisotropies in the weakly coupled regime. Three
applications are presented: gravitational redshifts in a time dependent
potential, the Doppler effect in reionized scenarios, and the Vishniac effect.
The Vishniac effect can dominate primary anisotropies at small angles even in
late and minimally reionized models in flat dark-matter dominated universes
with Harrison-Zel'dovich initial conditions. The techniques developed here
refine previous calculations yielding a larger coherence angle for the Vishniac
effect and moreover can be applied to non-trivial ionization histories. These
analytic expressions may be used to modify results for the standard cold dark
matter model to its cosmological constant and reionized extensions without
detailed and time consuming recalculation.",9507060v1
1995-10-20,Producing Mega-pixel CMB Maps from Differential Radiometer Data,"A major goal of cosmology is to obtain sensitive, high resolution maps of the
Cosmic Microwave Background (CMB) anisotropy. Such maps, as would be produced
by the recently proposed Microwave Anisotropy Probe (MAP), will contain a
wealth of primary information about conditions in the early universe. To
mitigate systematic effects when observing the microwave background, it is
desirable for the raw data to be collected in differential form: as a set of
temperature differences between points in the sky. However, the production of
large (mega-pixel) maps from a set of temperature differences is a potentially
severe computational challenge. We present a new technique for producing maps
from differential radiometer data that has a computational cost that grows in
the slowest possible way with increasing angular resolution and number of map
pixels. The required central processor (CPU) time is proportional to the number
of differential data points and the required random access memory (RAM) is
proportional to the number of map pixels. We test our technique, and
demonstrate its feasibility, by simulating one year of a space-borne anisotropy
mission.",9510102v1
1995-12-02,A Balloon-Borne Millimeter-Wave Telescope for Cosmic Microwave Background Anisotropy Measurements,"We report on the characteristics and design details of the Medium Scale
Anisotropy Measurement (MSAM), a millimeter-wave, balloon-borne telescope that
has been used to observe anisotropy in the Cosmic Microwave Background
Radiation (CMBR) on 0\fdg5 angular scales. The gondola is capable of
determining and maintaining absolute orientation to a few arcminutes during a
one-night flight. Emphasis is placed on the optical and pointing performance as
well as the weight and power budgets. We also discuss the total balloon/gondola
mechanical system. The pendulation from this system is a ubiquitous
perturbation on the pointing system. A detailed understanding in these areas is
needed for developing the next generation of balloon-borne instruments.",9512006v1
1995-12-29,Tentative Appraisal of Compatibility of Small-Scale CMB Anisotropy Detections in the Context of COBE-DMR-Normalized Open and Flat $Λ$ CDM Cosmogonies,"Goodness-of-fit statistics are used to quantitatively establish the
compatibility of CMB anisotropy predictions in a wide range of DMR-normalized,
open and spatially-flat $\Lambda$, CDM cosmogonies with the set of all
presently available small-scale CMB anisotropy detection data. Conclusions
regarding model viability depend sensitively on the prescription used to
account for the 1$\sigma$ uncertainty in the assumed value of the DMR
normalization, except for low-density, $\Omega_0 \sim 0.3$ -- 0.4, open models
which are compatible with the data for all prescriptions used. While large
baryon-density ($\Omega_B \gap 0.0175 h^{-2}$), old ($t_0 \gap 15$ -- 16 Gyr),
low-density ($\Omega_0 \sim 0.2$ -- 0.4), flat-$\Lambda$ models might be
incompatible, no model is incompatible with the data for all prescriptions. In
fact, some open models seem to fit the data better than should be expected, and
this might be an indication that some error bars are mildly overconservative.",9512168v1
1996-01-11,Search for Supergalactic Anisotropies in the 3B Catalog,"The angular distribution of GRBs is isotropic, while the brightness
distribution of bursts shows a reduced number of faint events. These
observations favor a cosmological burst origin. If GRBs are indeed at
cosmological distances and if they trace luminous matter, we must eventually
find an anisotropic distribution of bright bursts. If a significant number of
bursts originate at redshifts less than z~1, the concentration of nearby
galaxies towards the supergalactic plane is pronounced enough that we could
discover the corresponding clustering of burst locations. We used the 3B
catalog to search for a pattern visible in supergalactic coordinates. No
compelling evidence for anisotropies was found. The absence of anisotropies in
SG coordinates implies a minimum sampling distance of 200h^-1 Mpc.",9601057v1
1996-01-12,2-Point Correlations in the COBE DMR 4-Year Anisotropy Maps,"The 2-point temperature correlation function is evaluated from the 4-year
COBE DMR microwave anisotropy maps. We examine the 2-point function, which is
the Legendre transform of the angular power spectrum, and show that the data
are statistically consistent from channel to channel and frequency to
frequency. The most likely quadrupole normalization is computed for a
scale-invariant power-law spectrum of CMB anisotropy, using a variety of data
combinations. For a given data set, the normalization inferred from the 2-point
data is consistent with that inferred by other methods. The smallest and
largest normalization deduced from any data combination are 16.4 and 19.6 uK
respectively, with a value ~18 uK generally preferred.",9601061v1
1996-01-30,Monte Carlo Simulations of Medium-Scale CMB Anisotropy,"Recent detections of cosmic microwave background (CMB) anisotropy at
half-degree angular scales show considerable scatter in the reported amplitude
even at similar angular resolution. We use Monte Carlo techniques to simulate
the current set of medium-scale CMB observations, including all relevant
aspects of sky coverage and measurement technique. The scatter in the reported
amplitudes is well within the range expected for the standard cold dark matter
(CDM) cosmological model, and results primarily from the restricted sky
coverage of each experiment. Within the context of standard CDM current
observations of CMB anisotropy support the detection of a ``Doppler peak'' in
the CMB power spectrum consistent with baryon density 0.01 < Omega_b < 0.13
(95% confidence) for Hubble constant H_0 = 50 km/s/Mpc. The uncertainties are
approximately evenly divided between instrument noise and cosmic variance
arising from the limited sky coverage.",9601179v1
1996-02-01,A Measurement of the Angular Power Spectrum of the Anisotropy in the Cosmic Microwave Background,"We report on a measurement of the angular power spectrum of the anisotropy in
the Cosmic Microwave Background. The anisotropy is measured in 23 different
multipole bands from l=54 (~3 deg) to l=404 (~0.45 deg) and in 6 frequency
bands from 26 GHz to 46 GHz over three observing seasons. The measurements are
consistent from year to year. The frequency spectral index of the fluctuations
(measured at low l) is consistent with that of the CMB and inconsistent with
either dust or Galactic free-free emission. Furthermore, the observations of
the MSAM1-92 experiment (Cheng et al. 1994) are repeated and confirmed. The
angular spectrum shows a distinct rise from dT_l =
\sqrt{l(2l+1)<|a^m_l|^2>/4pi} = 49(+8,-5) \uK at l=87 to dT_l=85(+10,-8) uK at
l = 237. These values do not include an overall +/-14\% (1sigma) calibration
uncertainty. The analysis and possible systematic errors are discussed.",9601197v1
1996-03-05,A CMBR Measurement Reproduced: A Statistical Comparison of MSAM1-94 to MSAM1-92,"The goal of the second flight of the Medium Scale Anisotropy Measurement
(MSAM1-94) was to confirm the measurement of cosmic microwave background
radiation (CMBR) anisotropy made in the first flight (MSAM1-92). The CMBR
anisotropy and interstellar dust emission signals from the two flights are
compared by forming the sum and difference of those portions of the data with
the same pointings on the sky. The difference data are consistent with a null
detection, while the summed data show significant signal. We conclude that
MSAM1-92 and MSAM1-94 measured the same celestial signal.",9603017v1
1996-06-21,Correlated gravitational lensing of the CMB,"Cosmological inhomogeneities gravitationally deflect radiation propagating
from distant sources, transforming the spatial and angular correlation
functions of intrinsic source properties. For a gaussian distribution of
deflections (e.g. from a primordial gaussian density perturbation spectrum or
from the central limit theorem) we calculate the probability distributions for
geodesic deviations. If the intrinsic variable is also gaussian, e.g. the large
scale velocity flow field or cosmic microwave background temperature
anisotropies, then distributions and correlation functions of the observed
image sky properties can be obtained. Specialising to CMB temperature
fluctuations we rederive simply the influence of independent gravitational
lensing on the anisotropy angular correlation function and calculate the new
effect of lensing correlated with the anisotropies, e.g. arising from the same
primordial gravitational perturbation field. Characteristic magnitudes and
scales are given in terms of the density power spectrum. The correlated
deflection-temperature effect is shown to be negligible.",9606141v1
1996-07-18,Calculation of Cosmic Background Radiation Anisotropies and Implications,"We review the physical processes that are thought to produce anisotropy in
the cosmic microwave background, focusing primarily (but not exclusively) on
the effects of acoustic waves in the early Universe. We attempt throughout to
supply an intuitive, physical picture of the key ideas and to elucidate the
ways in which the predicted anisotropy depends on cosmological parameters such
as Omega and h. The second half of these lectures is devoted to a discussion of
microwave background data analysis techniques, with an emphasis on the analysis
of the COBE DMR data. In particular, the Karhunen-Loeve method of data
compression is described in detail.",9607088v1
1996-08-15,Depolarization of the cosmic microwave background by a primordial magnetic field and its effect upon temperature anisotropy,"We estimate the depolarizing effect of a primordial magnetic field upon the
cosmic microwave background radiation due to differential Faraday rotation
across the last scattering surface. The degree of linear polarization of the
CMB is significantly reduced at frequencies around and below 30 GHz $(B_*
/10^{-2}{\rm Gauss})^{1/2}$, where $B_*$ is the value of the primordial field
at recombination. The depolarizing mechanism reduces the damping of
anisotropies due to photon diffusion on small angular scales. The $l\approx
1000$ multipoles of the CMB temperature anisotropy correlation function in a
standard cold dark matter cosmology increase by up to 7.5\% at frequencies
where depolarization is significant.",9608098v1
1997-01-24,Cosmic Microwave Background Anisotropy in the COBE DMR 4-yr Sky Maps,"The COBE satellite has provided the only comprehensive multi-frequency
full-sky observations of the microwave sky available today. Assessment of the
observations requires a detailed likelihood analysis to extract the maximum
amount of information present in the noisy data. I present a specific method
for estimating the CMB anisotropy power spectrum independent of any assumptions
about the underlying cosmology, and then use standard image processing
techniques to generate the most revealing corresponding maps of the signal. The
consistency of the data at the available frequencies provides strong support to
the assertion that we are being provided with our first glimpse of the last
scattering surface.",9701191v1
1997-01-27,Polarization of the CMB photons crossing the galaxy clusters,"In this paper, I investigate a local effect of polarization of the Cosmic
Microwave Background (CMB) in clusters of galaxies, due to the Thomson
scattering of the anisotropic radiation. A local anisotropy of the CMB is
produced by some gravitational and scattering effects, as, for instance, the
Sunyaev Zel'dovich effect, the Doppler shift due to the cluster motion and the
gravitational lensing. The resulting anisotropy $\Delta I / I$ depends on the
physical properties of the clusters, in particular on their emissivity in the X
band, their size, their gravitational potential and on the peculiar conditions
characterizing the cluster gas. By solving the Boltzmann radiative transfer
equation in presence of such anisotropies I calculate the average polarization
at the centre of some clusters, namely A2218, A576 and A2163, whose properties
are quite well known. I prove the gravitational effects due to the contraction
or to the expansion of the cluster have some importance and dominate the SZ
effect, particularly for high density stuctures.",9701203v1
1997-02-14,Anisotropies in the Cosmic Microwave Background: Theory,"Anisotropies in the Cosmic Microwave Background (CMB) contain a wealth of
information about the past history of the universe and the present values of
cosmological parameters. I ouline some of the theoretical advances of the last
few years. In particular, I emphasize that for a wide class of cosmological
models, theorists can accurately calculate the spectrum to better than a
percent. The specturm of anisotropies today is directly related to the pattern
of inhomogeneities present at the time of recombination. This recognition leads
to a powerful argument that will enable us to distinguish inflationary models
from other models of structure formation. If the inflationary models turn out
to be correct, the free parameters in these models will be determined to
unprecedented accuracy by the upcoming satellite missions.",9702134v1
1997-02-20,Wall fluctuation modes and tensor CMB anisotropy in open inflation models,"We calculate the spectrum of large angle cosmic microwave background (CMB)
anisotropies due to quantum fluctuations of the gravitational wave modes in
one-bubble open inflation models. We find the bubble-wall fluctuation modes,
which had been thought to exist discretely in previous analyses, are actually
contained in the continuous spectrum of gravitational wave modes when the
gravitational coupling is correctly taken into account. Then we find that the
spectrum of the tensor CMB anisotropy can be decomposed into the part due to
the wall fluctuation modes and that due to the usual gravitational wave modes
in a way which is almost model-independent, even when the gravitational
coupling is strong. We also discuss observational constraints on the model
parameters. We find that an appreciable portion of the parameter space is
excluded but the remaining allowable region is still wide enough to leave the
one-bubble scenario viable.",9702174v1
1997-03-18,Getting Around Cosmic Variance,"Cosmic microwave background (CMB) anisotropies probe the primordial density
field at the edge of the observable Universe. There is a limiting precision
(``cosmic variance'') with which anisotropies can determine the amplitude of
primordial mass fluctuations. This arises because the surface of last scatter
(SLS) probes only a finite two-dimensional slice of the Universe. Probing other
SLSs observed from different locations in the Universe would reduce the cosmic
variance. In particular, the polarization of CMB photons scattered by the
electron gas in a cluster of galaxies provides a measurement of the CMB
quadrupole moment seen by the cluster. Therefore, CMB polarization measurements
toward many clusters would probe the anisotropy on a variety of SLSs within the
observable Universe, and hence reduce the cosmic-variance uncertainty.",9703118v1
1997-04-28,Integral Solution for the Microwave Background Anisotropies in Non-fl at Universes,"We present an efficient method to compute CMB anisotropies in non-flat
universes. First we derive the Boltzmann equation for cosmic microwave
background temperature and polarization fluctuations produced by scalar
perturbations in a general Robertson-Walker universe. We then apply the
integral method to solve this equation, writing temperature and polarization
anisotropies as a time integral over a geometrical term and a source term. The
geometrical terms can be written using ultra-spherical Bessel functions, which
depend on curvature. These cannot be precomputed in advance as in flat space.
Instead we solve directly their differential equation for selected values of
the multipoles. The resulting computational time is comparable to the flat
space case and improves over previous methods by 2-3 orders of magnitude. This
allows one to compute highly accurate CMB temperature and polarization spectra,
matter transfer functions and their CMB normalizations for any cosmological
model, thereby avoiding the need to use various approximate fitting formulae
that exist in the literature.",9704265v2
1997-05-19,The Cosmic Microwave Background Anisotropy Experiments,"This paper reports a summary of the contents contents of six hours of
lectures on the CMB anisotropy experiments given at the Strasbourg NATO school
on the CMB and cosmology. (Its companion paper, astro-ph/9705101 reports the
lectures on the CMB spectrum.) A context is set as a bridge from the
theoretical CMB anisotropy lectures and the experimental situation. The COBE
DMR results are reveiwed in detail and as pioneer for future space missions.
Current and planned experiments are discussed in preference to reviewing
already completed observations. The NASA MidEX mission MAP is discussed in some
detail including figures. The ESA M3 mission Max Planck Surveyor is also
reviewed in some detail though its final configuration is not yet fully
settled. The recent history and current versions are presented. Tables and
references for experiments are included.",9705135v1
1997-11-27,"Constraints on the chaotic inflationary scenario with a nonminimally coupled ""inflaton"" field from the cosmic microwave background radiation anisotropy","We investigate a possibility to restrict the chaotic inflationary scenario
with ""large"" nonminimally coupled inflaton(""phi"") field considered by Fakir and
Unruh by means of the observed CMBR anisotropy. We calculate the contributions
of the long wavelength gravitational waves generated in the inflationary period
to CMBR anisotropy quadrupole moment. We obtain the constraint lambda/(xi^2) =
1.8 X 10^(-8)/psi_i, where ""lambda"" is the self coupling, ""xi"" is the
nonminimal coupling constant and ""psi_i"" means the initial value of psi =
8piG(phi^2). Combining this with previously obtained constraint that 2.1 times
squre root of lambda/(xi^2) = dT/T = 1.1 X 10^(-5), we conclude that the
initial value has to be psi_i = 1.6 X 10^3. If the self-coupling has a
reasonably values of order 10^(-2), then xi = 10^4 and phi_i = 10^(-1) times
Planck mass.",9711340v1
1998-01-28,The Effect of the Detector Response Time on Bolometric Cosmic Microwave Background Anisotropy Experiments,"We analyze the effects of the detector response time on bolometric
measurements of the anisotropy of the cosmic microwave background (CMB). We
quantify the effect in terms of a single dimensionless parameter $L$ defined as
the ratio between the time the beam sweeps its own size and the bolometer
response time. As $L$ decreases below $\sim 2.5$ the point source response of
the experiment becomes elongated. We introduce a window function matrix based
on the timestream data to assess the effects of the elongated beam. We find
that the values of the window function matrix elements decrease slowly as a
function $L$. Our analysis and results apply to other cases of beam asymmetry.
For the High Frequency Instrument on board the Planck Surveyor satellite we
show that for a broad range of $L$ the ability of the experiment to extract the
cosmological parameters is not degraded. Our analysis enhances the flexibility
in tuning the design parameters of CMB anisotropy experiments.",9801291v2
1998-03-15,Cosmological-Parameter Determination With Cosmic Microwave Background Temperature Anisotropies and Polarization,"Forthcoming cosmic microwave background experiments (CMB) will provide
precise new tests of structure-formation theories. The geometry of the Universe
may be determined robustly, and the classical cosmological parameters, such as
the cosmological constant, baryon density, and Hubble constant, may be
determined as well. In addition, the ``inflationary observables,'' which
parameterize the shapes and amplitudes of the primordial spectra of density
perturbations and long-wavelength gravitational waves produced by inflation,
may also be measured and thus provide several new tests of inflation. Although
most attention has focussed on the more easily observed temperature
anisotropies, recent work has shown that the CMB polarization provides a wealth
of unique information that may be especially important for determination of the
inflationary observables. Secondary anisotropies at small angular scales
produced by re-scattering of photons from partial reionization may be used to
constrain the ionization history of the Universe.",9803168v1
1998-04-04,Probing Cosmic topology using CMB anisotropy,"The measurements of CMB anisotropy have opened up a window for probing the
global topology of the universe on length scales comparable to and beyond the
Hubble radius. We have developed a new method for calculating the CMB
anisotropy in models with nontrivial topology and apply it to open universe
models with compact spatial topology. We conduct a Bayesian probability
analysis for a selection of models which confronts the theoretical pixel-pixel
temperature correlation function with the COBE-DMR data. Our results
demonstrate that strong constraints on compactness arise: if the universe is
small compared to the `horizon' size, correlations appear in the maps that are
irreconcilable with the observations.",9804042v1
1998-04-16,A covariant and gauge-invariant analysis of cosmic microwave background anisotropies from scalar perturbations,"We present a new, fully covariant and manifestly gauge-invariant expression
for the temperature anisotropy in the cosmic microwave background radiation
resulting from scalar perturbations. We pay particular attention to gauge
issues such as the definition of the temperature perturbation and the placing
of the last scattering surface. In the instantaneous recombination
approximation, the expression may be integrated up to a Rees-Sciama term for
arbitrary matter descriptions in flat, open and closed universes. We discuss
the interpretation of our result in the baryon-dominated limit using numerical
solutions for conditions on the last scattering surface, and confirm that for
adiabatic perturbations the dominant contribution to the anisotropy on
intermediate scales (the location of the Doppler peaks) may be understood in
terms of the spatial inhomogeneity of the radiation temperature in the baryon
rest frame. Finally, we show how this term enters the usual Sachs-Wolfe type
calculations (it is rarely seen in such analyses) when subtle gauge effects at
the last scattering surface are treated correctly.",9804150v1
1998-04-24,Small-scale anisotropy of the cosmic background radiation and scattering by cloudy plasma,"If the first stars formed soon after decoupling of baryons from the thermal
cosmic background radiation (CBR), the radiation may have been last scattered
in a cloudy plasma. We discuss the resulting small-scale anisotropy of the CBR
in the limit where the plasma clouds are small compared to the mean distance
between clouds along a line of sight. This complements the perturbative
analysis valid for mildly nonlinear departures from homogeneity at last
scattering. We conclude that reasonable choices for the cloud parameters imply
CBR anisotropy consistent with the present experimental limits, in agreement
with the perturbative approach. This means the remarkable isotropy of the CBR
need not contradict the early small-scale structure formation predicted in some
cosmogonies.",9804260v1
1998-04-28,Cosmic microwave background anisotropies in the CDM model: a covariant and gauge-invariant approach,"We present a fully covariant and gauge-invariant calculation of the evolution
of anisotropies in the cosmic microwave background (CMB) radiation. We use the
physically appealing covariant approach to cosmological perturbations, which
ensures that all variables are gauge-invariant and have a clear physical
interpretation. We derive the complete set of frame-independent, linearised
equations describing the (Boltzmann) evolution of anisotropy and inhomogeneity
in an almost Friedmann-Robertson-Walker (FRW) cold dark matter (CDM) universe.
These equations include the contributions of scalar, vector and tensor modes in
a unified manner. Frame-independent equations for scalar and tensor
perturbations, which are valid for any value of the background curvature, are
obtained straightforwardly from the complete set of equations. We discuss the
scalar equations in detail, including the integral solution and relation with
the line of sight approach, analytic solutions in the early radiation dominated
era, and the numerical solution in the standard CDM model. Our results confirm
those obtained by other groups, who have worked carefully with non-covariant
methods in specific gauges, but are derived here in a completely transparent
fashion.",9804301v2
1998-08-16,Cosmic microwave background anisotropies: Nonlinear dynamics,"We develop a new approach to local nonlinear effects in cosmic microwave
background anisotropies, and discuss the qualitative features of these effects.
New couplings of the baryonic velocity to radiation multipoles are found,
arising from nonlinear Thomson scattering effects. We also find a new nonlinear
shear effect on small angular scales. The full set of evolution and constraint
equations is derived, including the nonlinear generalizations of the radiation
multipole hierarchy, and of the dynamics of multi-fluids. These equations
govern radiation anisotropies in any inhomogeneous spacetime, but their main
application is to second-order effects in a universe that is close to the
Friedmann models. Qualitative analysis is given here, and quantitative
calculations are taken up in further papers.",9808163v2
1998-10-16,Reconstructing Projected Matter Density from Cosmic Microwave Background,"Gravitational lensing distorts the cosmic microwave background (CMB)
anisotropies and imprints a characteristic pattern onto it. The distortions
depend on the projected matter density between today and redshift $z \sim
1100$. In this paper we develop a method for a direct reconstruction of the
projected matter density from the CMB anisotropies. This reconstruction is
obtained by averaging over quadratic combinations of the derivatives of CMB
field. We test the method using simulations and show that it can successfully
recover projected density profile of a cluster of galaxies if there are
measurable anisotropies on scales smaller than the characteristic cluster size.
In the absence of sufficient small scale power the reconstructed maps have low
signal to noise on individual structures, but can give a positive detection of
the power spectrum or when cross correlated with other maps of large scale
structure. We develop an analytic method to reconstruct the power spectrum
including the effects of noise and beam smoothing. Tests with Monte Carlo
simulations show that we can recover the input power spectrum both on large and
small scales, provided that we use maps with sufficiently low noise and high
angular resolution.",9810257v1
1998-11-10,Temperature Anisotropies and Distortions Induced by Hot Intracluster Gas on the Cosmic Microwave Background,"The power spectrum of temperature anisotropies induced by hot intracluster
gas on the cosmic background radiation is calculated. For low multipoles it
remains constant while at multipoles above $l>2000$ it is exponentially damped.
The shape of the radiation power spectrum is almost independent of the average
intracluster gas density profile, gas evolution history or clusters virial
radii; but the amplitude depends strongly on those parameters and could be as
large as 20% that of intrinsic contribution. The exact value depends on the
global properties of the cluster population and the evolution of the
intracluster gas. The distortion on the Cosmic Microwave Background black body
spectra varies in a similar manner. The ratio of the temperature anisotropy to
the mean Comptonization parameters is shown to be almost independent of the
cluster model and, in first approximation, depends only on the number density
of clusters.",9811158v1
1999-02-04,Cosmic Microwave Background Anisotropy Window Functions Revisited,"The primary results of most observations of cosmic microwave background (CMB)
anisotropy are estimates of the angular power spectrum averaged through some
broad band, called band-powers. These estimates are in turn what are used to
produce constraints on cosmological parameters due to all CMB observations.
Essential to this estimation of cosmological parameters is the calculation of
the expected band-power for a given experiment, given a theoretical power
spectrum. Here we derive the ""band power"" window function which should be used
for this calculation, and point out that it is not equivalent to the window
function used to calculate the variance. This important distinction has been
absent from much of the literature: the variance window function is often used
as the band-power window function. We discuss the validity of this assumed
equivalence, the role of window functions for experiments that constrain the
power in {\it multiple} bands, and summarize a prescription for reporting
experimental results. The analysis methods detailed here are applied in a
companion paper to three years of data from the Medium Scale Anisotropy
Measurement.",9902046v2
1999-03-30,CMB Anisotropy in Compact Hyperbolic Universes,"Measurements of CMB anisotropy are ideal experiments for discovering the
non-trivial global topology of the universe. To evaluate the CMB anisotropy in
multiply-connected compact cosmological models, one needs to compute eigenmodes
of the Laplace-Beltrami operator. We numerically obtain the eigenmodes on a
compact 3-hyperbolic space cataloged as $m003(-2,3)$ in SnapPea (computer
program by Jeff Weeks) using the direct boundary element method, which enables
one to simulate the CMB in multiply-connected compact models with high
precision. The angular power spectra $C_{l}$'s ($2 \leq l\leq18$) are
calculated using computed eigenmodes for $5.4\leqk<10$ and Gaussian random
approximation for the expansion coefficients for $10\leqk<20$. Assuming that
the initial power spectrum is the Harrison-Zeldovich spectrum, the computed
$C_l$'s are consistent with the COBE data for $0.1 \leq\Omega_o \leq 0.6$.
  In low $\Omega_o$ models, the large-angular fluctuations can be produced at
periods after the last scattering as the curvature perturbations decay in the
curvature dominant era.",9903446v2
1999-04-19,Overview of Secondary Anisotropies of the CMB,"While the major contribution to the Cosmic Microwave Background (CMB)
anisotropies are the sought-after primordial fluctuations produced at the
surface of last scattering, other effects produce secondary fluctuations at
lower redshifts. These secondary fluctuations must be carefully accounted for,
in order to isolate primordial fluctuations. In addition, they are interesting
in their own right, since they provide a wealth of information on the geometry
and local properties of the universe. Here, I survey the different sources of
secondary anisotropies and extragalactic foregrounds of the CMB. I show their
relative importance on the multipole-frequency plane. I discuss in particular
their impact in the future CMB missions MAP and Planck Surveyor.",9904235v1
1999-04-26,Constraining the equation of state of the Universe from Distant Type Ia Supernovae and Cosmic Microwave Background Anisotropies,"We analyse the constraints that can be placed on a cosmological constant or
quintessence-like component by combining observations of Type Ia supernovae
with measurements of anisotropies in the cosmic microwave background. We use
the recent supernovae sample of Perlmutter et al and observations of the CMB
anisotropies to constraint the equation of state (w_Q = p/rho) in
quintessence-like models via a likelihood analysis. The 2 sigma upper limits
are w_Q < -0.6 if the Universe is assumed to be spatially flat, and w_Q < -0.4
for universes of arbitrary spatial curvature. The upper limit derived for a
spatially flat Universe is close to the lower limit (w_Q approx -0.7) allowed
for simple potentials, implying that additional fine tuning may be required to
construct a viable quintessence model.",9904356v1
1999-05-20,Models of Universe with an inhomogeneous Big Bang singularity. II. CMBR dipole anisotropy as a byproduct of a conic Big Bang singularity,"The existence of stars and galaxies reqires cosmological models with an
inhomogeneous matter and radiation distribution. But in these models the
initial singularity surface t_0(r) is in general homogeneous (independent of
r). In this second paper of a series devoted to an inhomogeneous Big Bang
singularity, we investigate the cosmic microwave background radiation (CMBR)
dipole. A special Tolman-Bondi Universe is used to study the effect of a
Big-Bang singularity, depending linearly on r, on the CMBR anisotropy. It is
shown that, for an observer located off the ``center'' of this Universe (r=0),
the parameters of the model can be tuned so as to reproduce, with a good
approximation, the dipole and the quadrupole moments of the CMBR anisotropy
observed in recent experiments. If the dipole should prove cosmological, a
slight delaying of the Big-Bang over spatial coordinates would thus be a good
candidate for its interpretation.",9905262v1
1999-06-25,Correlations in the Far Infrared Background,"We compute the expected angular power spectrum of the cosmic Far Infrared
Background (FIRB). We find that the signal due to source correlations dominates
the shot--noise for $\ell \la 1000$ and results in anisotropies with rms
amplitudes $(\sqrt{\ell(\ell+1)C_\ell/2\pi})$ between 5% and 10% of the mean
for $l \ga 150$. The angular power spectrum depends on several unknown
quantities, such as the UV flux density evolution, optical properties of the
dust, biasing of the sources of the FIRB, and cosmological parameters. However,
when we require our models to reproduce the observed DC level of the FIRB, we
find that the anisotropy is at least a few percent in all cases. This
anisotropy is detectable with proposed instruments, and its measurement will
provide strong constraints on models of galaxy evolution and large-scale
structure at redshifts up to at least $z \sim5$.",9906399v3
1999-10-19,On the Numerical Study of the Complexity and Fractal Dimension of CMB Anisotropies,"We consider the problem of numerical computation of the Kolmogorov complexity
and the fractal dimension of the anisotropy spots of Cosmic Microwave
Background (CMB) radiation. Namely, we describe an algorithm of estimation of
the complexity of spots given by certain pixel configuration on a grid and
represent the results of computations for a series of structures of different
complexity. Thus, we demonstrate the calculability of such an abstract
descriptor as the Kolmogorov complexity for CMB digitized maps. The correlation
of complexity of the anisotropy spots with their fractal dimension is revealed
as well. This technique can be especially important while analyzing the data of
the forthcoming space experiments.",9910338v1
1999-11-25,CMB Anisotropies due to Feedback-Regulated Inhomogeneous Reionization,"We calculate the secondary anisotropies in the CMB produced by inhomogeneous
reionization from simulations in which the effects of radiative and stellar
feedback effects on galaxy formation have been included. This allows to
self-consistently determine the beginning ($z_i\approx 30$), the duration ($
\delta z\approx 20$) and the (nonlinear) evolution of the reionization process
for a critical density CDM model. In addition, from the simulated spatial
distribution of ionized regions, we are able to calculate the evolution of the
two-point ionization correlation function, $C_\chi$, and obtain the power
spectrum of the anisotropies, $C_\ell$, in the range $5000 < \ell < 10^6$. The
power spectrum has a broad maximum around $\ell \approx 30000$, where it
reaches the value $2\times 10^{-12}$. We also show that the angular correlation
function $C(\theta)$ is not Gaussian, but at separation angles $% \theta
\lower.5ex\hbox{\ltsima} 10^{-4}$ rad it can be approximated by a modified
Lorentzian shape; at larger separations an anticorrelation signal is predicted.
Detection of signals as above will be possible with future mm-wavelength
interferometers like ALMA, which appears as an optimum instrument to search for
signatures of inhomogeneous reionization.",9911467v1
1999-12-02,Cosmic Glows,"This is the obligatory Cosmic Microwave Background review. I discuss the
current status of CMB anisotropies, together with some points on the related
topic of the Far-Infrared Background. We have already learned a number of
important things from CMB anisotropies. Models which are in good shape have:
approximately flat geometry; cold dark-matter, plus something like a
cosmological constant; roughly scale invariant adiabatic fluctuations; and
close to Gaussian statistics. The constraints from the CMB are beginning to be
comparable to those from other cosmological measurements. With a wealth of new
data coming in, it is expected that CMB anisotropies will soon provide the most
stringent limits on fundamental cosmological parameters, as well as probing
high energy particle physics and the Dark Ages of astrophysics. Nudge, nudge.
Wink, wink. Say no more.",9912038v1
2000-02-29,CMB Anisotropies: A Decadal Survey,"We review the theoretical implications of the past decade of CMB anisotropy
measurements, which culminated in the recent detection of the first feature in
the power spectrum, and discuss the tests available to the next decade of
experiments. The current data already suggest that density perturbations
originated in an inflationary epoch, the universe is spatially flat, and
baryonic dark matter is required. We discuss the underlying assumptions of
these claims and outline the tests required to ensure they are robust. The most
critical test - the presence of a second feature at the predicted location -
should soon be available. Further in the future, secondary anisotropies and
polarization should open new windows to the early and low(er) redshift
universe.",0002520v1
2000-07-06,On the effect of coronal outflow on spectra formation in galactic black hole systems,"We present the results of both analytical and numerical calculations of the
amplitude of the reflection component in X-ray spectra of galactic black hole
systems. We take into account the anisotropy of Compton scattering and the
systematic relativistic bulk motion of the hot plasma. In the case of single
scattering approximation the reflection from the disc surface is significantly
enhanced due to the anisotropy of Compton scattering. On the other hand the
calculations of multiple scattering obtained using the Monte Carlo method show
that the anisotropy effect is much weaker in that case. Therefore, the enhanced
backscattered flux may affect the observed spectra only if the disc surface is
highly ionized, which reduces the absorption in the energy band corresponding
to the first Compton scattering.",0007070v1
2000-07-31,Gravitational Time Delay Effects on CMB Anisotropies,"We study the effect of gravitational time delay on the power spectra and
bispectra of the cosmic microwave background (CMB) temperature and polarization
anisotropies. The time delay effect modulates the spatial surface at
recombination on which temperature anisotropies are observed, typically by ~1
Mpc. While this is a relatively large shift, its observable effects in the
temperature and polarization fields are suppressed by geometric considerations.
The leading order effect is from its correlation with the closely related
gravitational lensing effect. The change to the temperature-polarization cross
power spectrum is of order 0.1% and is hence comparable to the cosmic variance
for the power in the multipoles around l~1000. While unlikely to be extracted
from the data in its own right, its omission in modeling would produce a
systematic error comparable to this limiting statistical error and, in
principle, is relevant for future high precision experiments. Contributions to
the bispectra result mainly from correlations with the Sachs-Wolfe effect and
may safely be neglected in a low density universe.",0008001v1
2000-11-07,From Anisotropy to Omega,"Following the recent measurement of the acoustic peak by the BOOMERanG and
MAXIMA experiments in the CMB anisotropy angular power spectrum, many analyses
have found that the geometry of the Universe is very close to flat, but
slightly closed models are favoured. In this paper we will briefly review how
the CMB anisotropies depend on the curvature, explaining any assumptions we
could make and showing that this skewness towards closed models can be easily
explained by degeneracies in the cosmological parameters. While it is difficult
to give independent constraints on the cosmological constant and/or different
forms of dark energies, we will also show that combining CMB measurements with
other observational data will introduce new and tighter constraints, like
$\Omega_\Lambda > 0$ at high significance.",0011147v2
2001-01-05,Constraints from the damping tail,"The detection of anisotropy in the cosmic microwave background on arcminute
scales by the Cosmic Background Imager (CBI) provides us with our first
measurement of the damping tail and closes one chapter in the CMB story. We now
have experimental verification for all of the features in the temperature
anisotropy spectrum predicted theoretically two decades ago. The CBI result
allows us to constrain both parameterized models based on the inflationary cold
dark matter (CDM) paradigm and to examine model independent constraints on the
matter content, the distance to last scattering and the thickness of the last
scattering surface. By providing a lower limit on the duration of recombination
it implies a lower limit on the polarization of the sub-degree scale anisotropy
which is close to current experimental upper limits.",0101086v2
2001-04-03,Finding out the velocity anisotropy parameter for some globular clusters: the case of stationary model,"The problem of determination of the velocity anisotropy parameter (A) from
star density profiles in globular clusters is considered. The calculations are
performed for following clusters: M3, M12, M13, M15, M55, M56, Palomar 3,
Palomar 14, NGC5139 (Omega Centauri) and NGC6535. We found that for most
clusters is A=0. For M56 the parameter is calculated at limiting magnitudes
B=21.5 and B=19.0 and we found A=0.8 and A=0.3 respectively. For Omega Centauri
the anisotropy parameter is determined in three separate regions and we found:
A=0 for central region, A=0.1 for middle region and A=0.3 for halo.",0104038v1
2001-04-06,The Tensor to Scalar Ratio of Phantom Dark Energy Models,"We investigate the anisotropies in the cosmic microwave background in a class
of models which possess a positive cosmic energy density but negative pressure,
with a constant equation of state w = p/rho < -1. We calculate the temperature
and polarization anisotropy spectra for both scalar and tensor perturbations by
modifying the publicly available code CMBfast. For a constant initial curvature
perturbation or tensor normalization, we have calculated the final anisotropy
spectra as a function of the dark energy density and equation of state w and of
the scalar and tensor spectral indices. This allows us to calculate the
dependence of the tensor-to-scalar ratio on w in a model with phantom dark
energy, which may be important for interpreting any future detection of
long-wavelength gravitational waves.",0104112v1
2001-08-12,CMB Analysis,"We describe the subject of Cosmic Microwave Background (CMB) analysis - its
past, present and future. The theory of Gaussian primary anisotropies, those
arising from linear physics operating in the early Universe, is in reasonably
good shape so the focus has shifted to the statistical pipeline which confronts
the data with the theory: mapping, filtering, comparing, cleaning, compressing,
forecasting, estimating. There have been many algorithmic advances in the
analysis pipeline in recent years, but still more are needed for the forecasts
of high precision cosmic parameter estimation to be realized. For secondary
anisotropies, those arising once nonlinearity develops, the computational state
of the art currently needs effort in all the areas: the Sunyaev-Zeldovich
effect, inhomogeneous reionization, gravitational lensing, the Rees-Sciama
effect, dusty galaxies. We use the Sunyaev-Zeldovich example to illustrate the
issues. The direct interface with observations for these non-Gaussian signals
is much more complex than for Gaussian primary anisotropies, and even more so
for the statistically inhomogeneous Galactic foregrounds. Because all the
signals are superimposed, the separation of components inevitably complicates
primary CMB analyses as well.",0108204v1
2001-10-18,Cosmic Microwave Background Anisotropies,"Cosmic microwave background (CMB) temperature anisotropies have and will
continue to revolutionize our understanding of cosmology. The recent discovery
of the previously predicted acoustic peaks in the power spectrum has
established a working cosmological model: a critical density universe
consisting of mainly dark matter and dark energy, which formed its structure
through gravitational instability from quantum fluctuations during an
inflationary epoch. Future observations should test this model and measure its
key cosmological parameters with unprecedented precision. The phenomenology and
cosmological implications of the acoustic peaks are developed in detail. Beyond
the peaks, the yet to be detected secondary anisotropies and polarization
present opportunities to study the physics of inflation and the dark energy.
The analysis techniques devised to extract cosmological information from
voluminous CMB data sets are outlined, given their increasing importance in
experimental cosmology as a whole.",0110414v1
2001-11-15,Temperature Isotropization in Solar Flare Plasmas due to the Electron Firehose Instability,"The isotropization process of a collisionless plasma with an electron
temperature anisotropy along an external magnetic field ($T_\| ^e\gg
T_\perp^e$, $\|$ and $\perp$ with respect to the background magnetic field) and
isotropic protons is investigated using a particle-in-cell(PIC) code.
Restricting wave growth mainly parallel to the external magnetic field, the
isotropization mechanism is identified to be the Electron Firehose Instability
(EFI). The free energy in the electrons is first transformed into left-hand
circularly polarized transverse low-frequency waves by a non-resonant
interaction. Fast electrons can then be scattered towards higher perpendicular
velocities by gyroresonance, leading finally to a complete isotropization of
the velocity distribution. During this phase of the instability, Langmuir waves
are generated which may lead to the emission of radio waves. A large fraction
of the protons is resonant with the left-hand polarized electromagnetic waves,
creating a proton temperature anisotropy $T_\|^p < T_\perp^p$. The parameters
of the simulated plasma are chosen compatible to solar flare conditions. The
results indicate the significance of this mechanism in the particle
acceleration context: The EFI limits the anisotropy of the electron velocity
distribution, and thus provides the necessary condition for further
acceleration. It enhances the pitch-angle of the electrons and heats the ions.",0111303v1
2001-12-03,The CMB - Contemporary Measurements and Cosmology,"Since the discovery of the Cosmic Microwave Background (CMB) in 1965,
characterization of the CMB anisotropy angular power spectrum has become
somewhat of a holy grail for experimental cosmology. Because CMB anisotropy
measurements are difficult, the full potential of the CMB is only now being
realized. Improvements in experimental techniques and detector technology have
yielded an explosion of progress in the past couple of years resulting in the
ability to use measurements of the CMB to place meaningful constraints on
cosmological parameters. In this review, I discuss the theory behind the CMB
but focus primarily on the experiments, reviewing briefly the history of CMB
anisotropy measurements and focusing on the recent experiments that have
revolutionized this field. Results from these modern experiments are reviewed
and the cosmological implications discussed. I conclude with brief comments
about the future of CMB physics.",0112052v1
2002-03-04,After Acoustic Peaks: What's Next in CMB?,"The advent of high signal-to-noise cosmic microwave background (CMB)
anisotropy experiments has allowed detailed studies on the power spectrum of
temperature fluctuations. The existence of acoustic oscillations in the
anisotropy power spectrum is now established with the detection of the first
two, and possibly the third, peaks. Beyond the acoustic peak structure, we
consider cosmological and astrophysical information that can be extracted by
pushing anisotropy observations to fine angular scales with higher resolution
instruments. At small scales, a variety of contributions allow the use of CMB
photons as a probe of the large scale structure: we outline possible studies
related to understanding detailed physical properties such as the distribution
of dark matter, baryons and pressure, and ways to measure the peculiar,
transverse and rotational velocities of virialized halos such as galaxy
clusters. Beyond the temperature, we consider several useful aspects of the CMB
polarization and comment on an ultimate goal for future CMB experiments
involving the direct detection of inflationary gravity-waves through their
distinct signature in the curl-type polarization.",0203048v3
2002-03-21,Detection of the velocity dipole in the radio galaxies of the NRAO VLA Sky Survey,"We are in motion against the cosmic backdrop. This motion is evidenced by the
systematic temperature shift - or dipole anisotropy - observed in the Cosmic
Microwave Background radiation (CMB). Because of the Doppler effect, the
temperature of the CMB is 0.1 per cent higher in our direction of motion
through the Universe. If our standard cosmological understanding is correct,
this dipole should also be present as an enhancement in the surface density of
distant galaxies. The main obstacle in finding this signal is the very uneven
distribution of nearby galaxies in the Local Supercluster, which drowns out the
small cosmological imprint. Here we report the first detection of the expected
dipole anisotropy in the galaxy distribution, in a survey of galaxies detected
in radio waves. Radio galaxies are mostly located at cosmological distances, so
the contamination from nearby clusters should be small. With local radio
sources removed, we find a dipole anisotropy in the radio galaxy distribution
in the same direction as the CMB, close to the expected amplitude. This result
is confirmation of the standard cosmological interpretation of the CMB.",0203385v1
2002-07-29,CMB-Normalized Predictions for Sunyaev-Zel'dovich effect fluctuations,"We predict the level of small-scale anisotropy in the cosmic microwave
background (CMB) due to the Sunyaev--Zel'dovich (SZ) effect for the ensemble of
cosmological models that are consistent with current measurements of
large-scale CMB anisotropy. We argue that the recently reported detections of
the small-scale (arcminutes) CMB anisotropy are only marginally consistent with
being the SZ effect when cosmological models are calibrated to the existing
primary CMB data on large scales. The discrepancy is at more than 2-2.5 sigma,
and is mainly due to a lower sigma_8 <0.8 favored by the primary CMB and a
higher sigma_8 > 1 favored by the SZ effect. A degeneracy between the optical
depth to Thomson scattering and the CMB-derived value of sigma_8 suggests that
the discrepancy is reduced if the universe was reionized very early, at a
redshift of about 25.",0207633v1
2002-08-16,Weak Lensing of the CMB: Cumulants of the Probability Distribution Function,"We discuss the real-space moments of temperature anisotropies in the cosmic
microwave background (CMB) due to weak gravitational lensing by intervening
large-scale structure. We show that if the probability distribution function of
primordial temperature anisotropies is Gaussian, then it remains unchanged
after gravitational lensing. With finite resolution, however, non-zero
higher-order cumulants are generated both by lensing autocorrelations and by
cross-correlations between the lensing potential and secondary anisotropies in
the CMB such as the Sunayev-Zel'dovich (SZ) effect. Skewness is produced by
these lensing-SZ correlations, while kurtosis receives contributions from both
lensing alone and lensing-SZ correlations. We show that if the projected
lensing potential is Gaussian, all cumulants of higher-order than the kurtosis
vanish. While recent results raise the possibility of detection of the skewness
in upcoming data, the kurtosis will likely remain undetected.",0208325v1
2002-09-11,Anisotropies of the Cosmic Microwave Background,"We review the present status of Cosmic Microwave Background (CMB) anisotropy
observations and discuss the main related astrophysical issues, instrumental
effects and data analysis techniques. We summarise the balloon-borne and
ground-based experiments that, after COBE-DMR, yielded detection or significant
upper limits to CMB fluctuations. A comparison of subsets of combined data
indicates that the acoustic features observed today in the angular power
spectrum are not dominated by undetected systematics. Pushing the accuracy of
CMB anisotropy measurements to their ultimate limits represents one of the best
opportunities for cosmology to develop into a precision science in the next
decade. We discuss the forthcoming sub-orbital and space programs, as well as
future prospects of CMB observations.",0209215v2
2002-09-26,Anisotropy at the end of the cosmic ray spectrum?,"The starburst galaxies M82 and NGC253 have been proposed as the primary
sources of cosmic rays with energies above $10^{18.7}$ eV. For energies $\agt
10^{20.3}$ eV the model predicts strong anisotropies. We calculate the
probabilities that the latter can be due to chance occurrence. For the highest
energy cosmic ray events in this energy region, we find that the observed
directionality has less than 1% probability of occurring due to random
fluctuations. Moreover, during the first 5 years of operation at Auger, the
observation of even half the predicted anisotropy has a probability of less
than $10^{-5}$ to occur by chance fluctuation. Thus, this model can be subject
to test at very small cost to the Auger priors budget and, whatever the outcome
of that test, valuable information on the Galactic magnetic field will be
obtained.",0209546v3
2002-11-07,Dipole anisotropies of IRAS galaxies and the contribution of a large-scale local void,"Recent observations of dipole anisotropies show that the velocity of the
Local Group ($\Vec v_{\rm G}$) induced by the clustering of IRAS galax ies has
an amplitude and direction similar to those of the velocity of Cosmic Microwave
Background dipole anisotropy ($\Vec v_{\rm CMB}$), but the difference $| \Vec
v_{\rm G} - \Vec v_{\rm CMB} |$ is still $\sim 170$ km/s, which is about 28% of
$|\Vec v_{\rm CMB} |$. Here we consider the possibility that the origin of this
difference comes from a hypothetical large-scale local void, with which we can
account for the accelerating behavior of type Ia supernovae due to the spatial
inhomogeneity of the Hubble constant without dark energies and derive the
constraint to the model parameters of the local void. It is found as a result
that the distance between the Local Group and the center of the void must be
$(10 -- 20) h^{-1}$ Mpc, whose accurate value depends on the background model
parameters.",0211137v2
2003-06-18,The Wilkinson Microwave Anisotropy Probe,"The Wilkinson Microwave Anisotropy Probe (WMAP) has mapped the full sky in
five frequency bands between 23 and 94 GHz. The primary goal of the mission is
to produce high-fidelity, all-sky, polarization-sensitive maps that can be used
to study the cosmic microwave background. Systematic errors in the maps are
constrained to new levels: using all-sky data, aspects of the anisotropy may
confidently be probed to sub-microKelvin levels. We give a brief description of
the instrument and an overview of the first results from an analysis of maps
made with one year of data. The highlights are (1) the flat Lambda-CDM model
fits the data remarkably well, whereas an Einstein-de Sitter model does not;
(2) we see evidence of the birth of the first generation of stars at z ~ 20;
(3) when the WMAP data are combined and compared with other cosmological
probes, a cosmic consistency emerges: multiple different lines of inquiry lead
to the same results.",0306381v1
2003-07-31,Measuring Statistical isotropy of the CMB anisotropy,"The statistical expectation values of the temperature fluctuations of cosmic
microwave background (CMB) are assumed to be preserved under rotations of the
sky. This assumption of {\em statistical isotropy} (SI) of the CMB anisotropy
should be observationally verified since detection of violation of SI could
have profound implications for cosmology. We propose a set of measures,
$\kappa_\ell$ ($\ell=1,2,3, ...$) for detecting violation of statistical
isotropy in an observed CMB anisotropy sky map indicated by non zero
$\kappa_\ell$. We define an estimator for the $\kappa_\ell$ spectrum and
analytically compute its cosmic bias and cosmic variance. The results match
those obtained by measuring $\kappa_\ell$ using simulated sky maps. Non-zero
(bias corrected) $\kappa_\ell$ larger than the SI cosmic variance will imply
violation of SI. The SI measure proposed in this paper is an appropriate
statistics to investigate preliminary indication of SI violation in the
recently released WMAP data.",0308001v2
2003-12-04,Signature of HDM clustering at Planck angular scales,"We present the CMB anisotropy induced by the non-linear perturbations in the
massive neutrino density associated to the non-linear gravitational clustering.
We show that the non-linear time varying potential induced by the gravitational
clustering process generates metric perturbations that affect the time
evolution of the density fluctuations in all the components of the expanding
Universe, leaving imprints on the CMB anisotropy power spectrum at subdegree
angular scales. For a neutrino fraction in agreement with that indicated by the
astroparticle and nuclear physics experiments and a cosmological accreting mass
comparable with the mass of known clusters, we find that CMB anisotropy
measurements with {\sc Planck} angular resolution and sensitivity possibly
combined to other precise cosmological observations will allow the detection of
the dynamical, linear and non-linear effects of the neutrino gravitational
clustering.",0312123v1
2003-12-05,Antimatter from the cosmological baryogenesis and the anisotropies and polarization of the CMB radiation,"We discuss the hypotheses that cosmological baryon asymmetry and entropy were
produced in the early Universe by phase transition of the scalar fields in the
framework of spontaneous baryogenesis scenario. We show that annihilation of
the matter-antimatter clouds during the cosmological hydrogen recombination
could distort of the CMB anisotropies and polarization by delay of the
recombination. After recombination the annihilation of the antibaryonic clouds
(ABC) and baryonic matter can produce peak-like reionization at the high
redshifts before formation of quasars and early galaxy formation. We discuss
the constraints on the parameters of spontaneous baryogenesis scenario by the
recent WMAP CMB anisotropy and polarization data and on possible manifestation
of the antimatter clouds in the upcoming PLANCK data.",0312168v2
2004-01-08,"CMB Anisotropies, Cosmological Parameters and Fundamental Physics: Current Status & Perspectives","I describe briefly the Cosmic Microwave Background (hereafter CMB) physics
which explains why high accuracy observations of its spatial structure are a
unique observational tool both for the determination of the global cosmological
parameters and to constrain observationally the physics of the early universe.
I also briefly survey the many experiments which have measured the anisotropies
of the CMB and led to crucial advances in observational Cosmology. The somewhat
frantic series of new results has recently culminated with the outcome of the
WMAP satellite which confirmed earlier results, set new standards of accuracy,
and suggested that the Universe may have reionised earlier than anticipated.
Many more CMB experiments are currently taking data or being planned, with the
Planck satellite on the 2007 Horizon poised to extract all the cosmological
information in the temperature anisotropies, and foray deeply into
polarisation.",0401108v1
2004-02-24,Maps of the Cosmos: The Cosmic Microwave Background,"Since the IAU XXIV meeting in 2000, the CMB anisotropy has matured from being
one of a number of cosmological probes to forming the bedrock foundation for
what is now the standard model of cosmology. The large advances over the past
three years have come from making better and better maps of the cosmos. We
review the state of measurements of the anisotropy and outline some of what we
have learned since 2000. The recent advancements may be placed roughly into
three categories: 1) What we learn from the CMB with minimal input from other
cosmic measurements such as the Hubble constant; 2) What we learn from the CMB
in combination with other probes of large scale structure; and 3) What we learn
by using the CMB as a back light. Future directions are also discussed. It is
clear: we have much more to learn from the CMB anisotropy.",0402547v1
2004-03-30,Looking for Cosmological Alfven Waves in WMAP Data,"A primordial cosmological magnetic field induces and supports vorticity or
Alfven waves, which in turn generate cosmic microwave background (CMB)
anisotropies. A homogeneous primordial magnetic field with fixed direction
induces correlations between the $a_{l-1,m}$ and $a_{l+1,m}$ multipole
coefficients of the CMB temperature anisotropy field. We discuss the
constraints that can be placed on the strength of such a primordial magnetic
field using CMB anisotropy data from the WMAP experiment. We place 3 $\sigma$
upper limits on the strength of the magnetic field of $B < 15$ nG for vector
perturbation spectral index $n=-5$ and $B<1.7$ nG for $n=-7$.",0403695v2
2004-04-06,Study of Small-Scale Anisotropy of Ultrahigh Energy Cosmic Rays Observed in Stereo by HiRes,"The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence
detector which, operating in stereo mode, has a typical angular resolution of
0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes
is thus an excellent instrument for the study of the arrival directions of
ultrahigh energy cosmic rays. We present the results of a search for
anisotropies in the distribution of arrival directions on small scales (<5
degrees) and at the highest energies (>10^19 eV). The search is based on data
recorded between 1999 December and 2004 January, with a total of 271 events
above 10^19 eV. No small-scale anisotropy is found, and the strongest
clustering found in the HiRes stereo data is consistent at the 52% level with
the null hypothesis of isotropically distributed arrival directions.",0404137v2
2004-04-21,Breaking the mass / anisotropy degeneracy in the Coma cluster,"We provide the first direct lifting of the mass/anisotropy degeneracy for a
cluster of galaxies, by jointly fitting the line of sight velocity dispersion
and kurtosis profiles of the Coma cluster, assuming an NFW tracer density
profile, a generalized-NFW dark matter profile and a constant anisotropy
profile. We find that the orbits in Coma must be quasi-isotropic, and find a
mass consistent with previous analyses, but a concentration parameter 50%
higher than expected in cosmological N-body simulations. We then test the
accuracy of our method on realistic non-spherical systems with substructure and
streaming motions, by applying it to the ten most massive structures in a
cosmological N-body simulation. We find that our method yields fairly accurate
results on average (within 20%), although with a wide variation (factor 1.7 at
1 sigma) for the concentration parameter, with decreased accuracy and
efficiency when the projected mean velocity is not constant with radius.",0404415v1
2004-05-27,Stochastic Inflation and the Lower Multipoles in the CMB Anisotropies,"We generalize the treatment of inflationary perturbations to deal with the
non-Markovian colored noise emerging from any realistic approach to stochastic
inflation. We provide a calculation of the power-spectrum of the
gauge-invariant comoving curvature perturbation to first order in the slow-roll
parameters. Properly accounting for the constraint that our local patch of the
Universe is homogeneous on scales just above the present Hubble radius, we find
a blue tilt of the power-spectrum on the largest observable scales, in
agreement with the WMAP data which show an unexpected suppression of the low
multipoles of the CMB anisotropy. Our explanation of the anomalous behaviour of
the lower multipoles of the CMB anisotropies does not invoke any ad-hoc
introduction of new physical ingredients in the theory.",0405544v1
2004-11-15,Cosmological reionization after WMAP: perspectives from PLANCK and future CMB missions,"The WMAP first year detection of a high redshift reionization through its
imprints on CMB anisotropy T and TE mode angular power spectra calls for a
better comprehension of the universe ionization and thermal history after the
standard recombination. Different reionization mechanisms predict different
signatures in the CMB, both in temperature and polarization anisotropies and in
spectral distortions. The Planck capability to distinguish among different
scenarios through its sensitivity to T, TE, and E mode angular power spectra is
discussed. Perspectives open by future high sensitivity experiments on the CMB
polarization anisotropy and spectrum are also presented.",0411415v1
2004-11-16,A universal density slope - velocity anisotropy relation for relaxed structures,"We identify a universal relation between the radial density slope \alpha (r)
and the velocity anisotropy \beta (r) for equilibrated structures. This
relation holds for a variety of systems, including disk galaxy mergers,
spherical collapses, cold dark matter (CDM) halos both with and without
cooling. We argue that the shape of the relation is reasonable from fundamental
principles when the dark matter or stars are assumed to obey Tsallis
statistics, and in that case we fit the \alpha - \beta relation with just one
free parameter. One can use this result to close the Jeans equations, for
example to construct mass models of elliptical galaxies from observational data
or to tune dark matter direct detection experiments. We also predict the
asymptotic central slope and anisotropy of CDM halos to be approximately -1 and
0.",0411473v3
2004-12-21,CMB Anisotropy of the Poincare Dodecahedron,"We analyse the anisotropy of the cosmic microwave background (CMB) for the
Poincare dodecahedron which is an example for a multi-connected spherical
universe. We compare the temperature correlation function and the angular power
spectrum for the Poincare dodecahedral universe with the first-year WMAP data
and find that this multi-connected universe can explain the surprisingly low
CMB anisotropy on large scales found by WMAP provided that the total energy
density parameter Omega_tot is in the range 1.016...1.020. The ensemble average
over the primordial perturbations is assumed to be the scale-invariant
Harrison-Zel'dovich spectrum. The circles-in-the-sky signature is studied and
it is found that the signal of the six pairs of matched circles could be missed
by current analyses of CMB sky maps.",0412569v2
2005-01-31,Relativistic second-order perturbations of nonzero-Λflat cosmological models and CMB anisotropies,"First the second-order perturbations of nonzero-\Lambda cosmological models
are derived with an arbitrary potential function of spatial coordinates, using
the nonlinear version of Lifshitz's method in the synchronous gauge. Their
expression is the generalization (to the nonzero-\Lambda case) of second-order
perturbations in the Einstein-de Sitter model which were derived previously by
the present author. Next the second-order temperature anisotropies of Cosmic
Micriwave Background radiation are derived using the gauge-invariant formula
which was given by Mollerach and Matarrese. Moreover the corresponding
perturbations in the Poisson gauge are derived using the second-order gauge
transformations formulated by Bruni et al. In the second-order it is found in
spite of gauges that tensor (gravitational-wave) perturbations and vector
(shear) perturbations without vorticity are induced from the first-order scalar
perturbations. These results will be useful to analyze the nonlinear effect of
local inhomogeneities on Cosmic Microwave Background anisotropies.",0501663v4
2005-03-02,On the Spectrum of Magnetohydrodynamic Turbulence,"We propose a phenomenological model for incompressible magnetohydrodynamic
turbulence. We argue that nonlinear-wave interaction weakens as the energy
cascade proceeds to small scales, however, the anisotropy of fluctuations along
the large-scale magnetic field increases, which makes turbulence strong at all
scales. To explain the weakening of the interaction, we propose that
small-scale fluctuations of the velocity and magnetic fields become
increasingly dynamically aligned as their scale decreases, so that turbulent
eddies become locally anisotropic in the plane perpendicular to the large-scale
magnetic field. In the limit of weak anisotropy, that is, weak large-scale
magnetic field, our model reproduces the Goldreich-Sridhar spectrum, while the
limit of strong anisotropy, that is, strong large-scale magnetic field,
corresponds to the Iroshnikov-Kraichnan scaling of the spectrum. This is in
good agreement with recent numerical results.",0503053v2
2005-03-04,Elliptic CMB Sky,"The ellipticity of the anisotropy spots of the Cosmic Microwave Background
measured by the Wilkinson Microwave Anisotropy Probe (WMAP) has been studied.
We find an average ellipticity of about 2, confirming with a far larger
statistics similar results found first for the COBE-DMR CMB maps, and then for
the BOOMERanG CMB maps. There are no preferred directions for the obliquity of
the anisotropy spots. The average ellipticity is independent of temperature
threshold and is present on scales both smaller and larger than the horizon at
the last scattering. The measured ellipticity characteristics are consistent
with being the effect of geodesics mixing occurring in an hyperbolic Universe,
and can mark the emergence of CMB ellipticity as a new observable constant
describing the Universe. There is no way of simulating this effect. Therefore
we cannot exclude that the observed behavior of the measured ellipticity can
result from a trivial topology in the popular flat $\Lambda$-CDM model, or from
a non-trivial topology.",0503103v2
2005-03-31,Effects of Cosmological Magnetic Helicity on the Cosmic Microwave Background,"Cosmological magnetic fields induce temperature and polarization fluctuations
in the cosmic microwave background (CMB) radiation. A cosmological magnetic
field with current amplitude of order $10^{-9}$ G is detectable via
observations of CMB anisotropies. This magnetic field (with or without
helicity) generates vector perturbations through vortical motions of the
primordial plasma. This paper shows that magnetic field helicity induces
parity-odd cross correlations between CMB temperature and $B$-polarization
fluctuations and between $E$- and $B$-polarization fluctuations, correlations
which are zero for fields with no helicity (or for any parity-invariant
source). Helical fields also contribute to parity-even temperature and
polarization anisotropies, cancelling part of the contribution from the
symmetric component of the magnetic field. We give analytic approximations for
all CMB temperature and polarization anisotropy vector power spectra due to
helical magnetic fields. These power spectra offer a method for detecting
cosmological helical magnetic fields, particularly when combined with Faraday
rotation measurements which are insensitive to helicity.",0503709v1
2005-05-18,CMB Tomography: Reconstruction of Adiabatic Primordial Scalar Potential Using Temperature and Polarization Maps,"Assuming linearity of the perturbations at the time of decoupling, we
reconstruct the primordial scalar potential from the temperature and
polarization anisotropies in the cosmic microwave background radiation. In
doing so we derive an optimal linear filter which, when operated on the
spherical harmonic coefficients of the anisotropy maps, returns an estimate of
the primordial scalar potential fluctuations in a spherical slice. The
reconstruction is best in a thick shell around the decoupling epoch; the
quality of the reconstruction depends on the redshift of the slice within this
shell. With high quality maps of the temperature and polarization anisotropies
it will be possible to obtain a reconstruction of potential fluctuation on
scales between l=2 and l ~ 300 at the redshift of decoupling, with some
information about the three-dimensional shapes of the perturbations in a shell
of width 250Mpc.",0505386v1
2005-06-17,Non-Gaussianity of Large-Scale Cosmic Microwave Background Anisotropies beyond Perturbation Theory,"We compute the fully non-linear Cosmic Microwave Background (CMB)
anisotropies on scales larger than the horizon at last-scattering in terms of
only the curvature perturbation, providing a generalization of the linear
Sachs-Wolfe effect at any order in perturbation theory. We show how to compute
the n-point connected correlation functions of the large-scale CMB anisotropies
for generic primordial seeds provided by standard slow-roll inflation as well
as the curvaton and other scenarios for the generation of cosmological
perturbations. As an application of our formalism, we compute the three- and
four-point connected correlation functions whose detection in future CMB
experiments might be used to assess the level of primordial non-Gaussianity,
giving the theoretical predictions for the parameters of quadratic and cubic
non-linearities f_NL and g_NL.",0506410v2
2005-08-13,Local virial relation and velocity anisotropy for collisionless self-gravitating systems,"The collisionless quasi-equilibrium state realized after the cold collapse of
self-gravitating systems has two remarkable characters. One of them is the
linear temperature-mass (TM) relation, which yields a characteristic
non-Gaussian velocity distribution. Another is the local virial (LV) relation,
the virial relation which holds even locally in collisionless systems through
phase mixing such as cold-collapse. A family of polytropes are examined from a
view point of these two characters. The LV relation imposes a strong constraint
on these models: only polytropes with index $n \sim 5$ with a flat boundary
condition at the center are compatible with the numerical results, except for
the outer region. Using the analytic solutions based on the static and
spherical Jeans equation, we show that this incompatibility in the outer region
implies the important effect of anisotropy of velocity dispersion. Furthermore,
the velocity anisotropy is essential in explaining various numerical results
under the condition of the local virial relation.",0508308v2
2005-09-18,Second-order gravitational effects of local inhomogeneities on CMB anisotropies and non-Gaussian signatures,"Based on the second-order nonlinear theory of perturbations in non-zero
\Lambda flat cosmological models, we study the gravitational effects of local
inhomogeneities on cosmic microwave background (CMB) anisotropies. As the local
inhomogeneities we consider firstly large-scale dipole and quadruple
distributions of galaxies around us and next an isolated cluster-scale matter
distribution. It is found that, due to the second-order integral Sachs-Wolfe
effect, the north-south asymmetry of CMB anisotropies and non-Gaussian
signatures (in terms of scale-dependent estimators of kurtosis) in a spot-like
object are caused from these matter distributions along light paths. Our
theoretical results seem to be consistent with recent various observational
results which have been shown by Hansen et al., Eriksen et al., Vielva et al.
and Cruz et al.",0509518v4
2005-10-25,Anisotropic k-essence cosmologies,"We investigate a Bianchi type-I (BTI) cosmology with k essence and find the
set of models which dissipate the initial anisotropy. There are cosmological
models with extended tachyon fields and k essence having constant bariotropic
index. We obtain the conditions leading to a regular bounce of the average
geometry and the residual anisotropy on the bounce. For constant potential, we
develop purely kinetic k-essence models which are dust dominated in their early
stages, dissipate the initial anisotropy and end in a stable de Sitter
accelerated expansion scenario. We show that linear k field and polynomial
kinetic function models evolve asymptotically to Friedmann-Robertson-Walker
(FRW) cosmologies. The linear case is compatible with an asymptotic potential
interpolating between $V_l\propto \phi^{-\gamma_l}$, in the shear dominated
regime, and $V_l\propto\phi^{-2}$ at late time. In the polynomial case, the
general solution contains cosmological models with an oscillatory average
geometry. For linear k essence, we find the general solution in the BTI
cosmology when the k field is driven by an inverse square potential. This model
shares the same geometry than a quintessence field driven by an exponential
potential.",0510726v2
2005-12-16,On the Viability of Bianchi Type VIIh Models with Dark Energy,"We generalize the predictions for the CMB anisotropy patterns arising in
Bianchi type VIIh universes to include a dark energy component. We consider
these models in light of the result of Jaffe et al. (2005a,b) in which a
correlation was found on large angular scales between the WMAP data and the
anisotropy structure in a low density Bianchi universe. We find that by
including a term Omega_L > 0, the same best-fit anisotropy pattern is
reproduced by several combinations of cosmological parameters. This sub-set of
models can then be further constrained by current observations that limit the
values of various cosmological parameters. In particular, we consider the
so-called geometric degeneracy in these parameters imposed by the peak
structure of the WMAP data itself. Apparently, despite the additional freedom
allowed by the dark energy component, the modified Bianchi models are ruled out
at high significance.",0512433v1
2006-02-22,Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies I,"We explore the large angular scale temperature anisotropies in the cosmic
microwave background due to expanding homogeneous local voids at redshift z~1.
A compensated spherically symmetric homogeneous dust-filled void with radius
\~3*10^2 h^{-1}Mpc, and density contrast ~-0.3 can be observed as a cold spot
with a temperature anisotropy -1*10^{-5} surrounded by a slightly hotter ring.
We find that a pair of these circular cold spots separated by ~50 degree can
account both for the planarity of the octopole and for the alignment between
the quadrupole and the octopole in the cosmic microwave background (CMB)
anisotropy. The cold spot in the Galactic southern hemisphere which is
anomalous at the ~3sigma level can be explained by such a large void at z~1.
The observed north-south asymmetry in the large-angle CMB power can be
attributed to the asymmetric distribution of these local voids between the two
hemispheres. The statistical significance of the low quadrupole is further
reduced in this interpretation of the large angular scale CMB anomalies.",0602478v2
2006-04-13,Quantum noise and large-scale cosmic microwave background anisotropy,"We propose a new source for the cosmological density perturbation which is
passive fluctuations of the inflaton driven dynamically by a colored quantum
noise as a result of its coupling to other massive quantum fields. The created
fluctuations grow with time during inflation before horizon-crossing. However,
the larger-scale modes cross out the horizon earlier, thus resulting in a
suppression of their density perturbation as compared with those on small
scales. By using current observed CMB data to constrain the parameters
introudced, we find that a significant contribution from the noise-driven
perturbation to the density perturbation is still allowed. It in turn gives
rise to a suppression of the large-scale CMB anisotropy that may be relevant to
the observed low quadrupole in the WMAP CMB anisotropy data. We also briefly
discuss the implications to the energy scale of inflation and the spectral
index and non-Gaussianity of the density perturbation.",0604292v3
2006-04-19,CMB Anisotropies at Second Order I,"We present the computation of the full system of Boltzmann equations at
second-order describing the evolution of the photon, baryon and cold dark
matter fluids. These equations allow to follow the time evolution of the Cosmic
Microwave Background (CMB) anisotropies at second-order at all angular scales
from the early epoch, when the cosmological perturbations were generated, to
the present through the recombination era. This paper sets the stage for the
computation of the full second-order radiation transfer function at all scales
and for a a generic set of initial conditions specifying the level of
primordial non-Gaussianity. In a companion paper, we will present the
computation of the three-point correlation function at recombination which is
so relevant for the issue of non-Gaussianity in the CMB anisotropies.",0604416v4
2006-09-29,Impact of three years of data from the Wilkinson Microwave Anisotropy Probe on cosmological models with dynamical dark energy,"The first three years of observation of the Wilkinson Microwave Anisotropy
Probe (WMAP) have provided the most precise data on the anisotropies of the
cosmic microwave background (CMB) to date. We investigate the impact of these
results and their combination with data from other astrophysical probes on
cosmological models with a dynamical dark energy component. By considering a
wide range of such models, we find that the constraints on dynamical dark
energy are significantly improved compared to the first year data.",0609814v2
2006-10-09,21-cm Background Anisotropies Can Discern Primordial Non-Gaussianity,"The non-Gaussianity of initial perturbations provides information on the
mechanism that generated primordial density fluctuations. The expected
non-Gaussianity for slow-roll inflationary models is well below the ultimate
detection level with cosmic microwave background (CMB) anisotropies or
large-large structure at low redshifts. We find that 21-cm background
anisotropies of the low-frequency radio sky due to inhomogeneous neutral
Hydrogen distribution at redshifts between 30 and 100 captures information on
primordial non-Gaussianity better than any other cosmological probe. An all-sky
21-cm experiment over the frequency range from 14 MHz to 40 MHz using a
bandwidth of 1 MHz and with angular information out to a multipole of 10^5 can
limit the primordial non-Gaussianity parameter f_nl < 0.01. The 21-cm
background should eventually reveal the non-Gaussianity associated with single
field slow-roll inflation.",0610257v2
2006-12-22,The Validity of the Cosmic String Pattern Search with the Cosmic Microwave Background,"We introduce a new technique to detect the discrete temperature steps that
cosmic strings might have left in the cosmic microwave background (CMB)
anisotropy map. The technique provides a validity test on the pattern search of
cosmic strings that could serve as the groundwork for future pattern searches.
The detecting power of the technique is only constrained by two unavoidable
features of CMB data: (1) the finite pixelization of the sky map and (2) the
Gaussian fluctuation from instrumental noise and primordial anisotropy. We set
the upper limit on the cosmic string parameter as $G\mu\lesssim 3.7\times
10^{-6}$ at the 95% confidence level (CL) and find that the amplitude of the
temperature step has to be greater than $44\mu K$ in order to be detected for
the {\it{Wilkinson Microwave Anisotropy Probe (WMAP)}} 3 year data.",0612706v3
2007-03-08,Effect of nearby supernova remnants on local Cosmic-Rays,"We study in detail the effect of different particle release times from
sources on the cosmic-ray (CR) spectrum below $10^{15}eV$ in the Galaxy. We
discuss different possible forms of particle injection such as burst-like
injection, continuous injection for a finite time, injection from a stationary
source and energy dependent injection. When applied to the nearby known
supernova remnants, we find that the observed CR anisotropy data favour the
burst-like particle injection model for the CR diffusion coefficient
$D(E)\propto E^a$ with $a=0.3-0.6$ in the local region. In the study we have
also found that the contribution of the sources G114.3+0.3 and Monogem dominate
if the observed anisotropy is a result of the effect of the nearby sources.
Further study shows that we should not neglect the contribution of the
undetected old sources to the local CR anisotropy.",0703176v2
1993-05-28,Cluster Variation Approach to the Random-Anisotropy Blume-Emery-Griffiths Model,"The random--anisotropy Blume--Emery--Griffiths model, which has been proposed
to describe the critical behavior of $^3$He--$^4$He mixtures in a porous
medium, is studied in the pair approximation of the cluster variation method
extended to disordered systems. Several new features, with respect to mean
field theory, are found, including a rich ground state, a nonzero percolation
threshold, a reentrant coexistence curve and a miscibility gap on the high
$^3$He concentration side down to zero temperature. Furthermore, nearest
neighbor correlations are introduced in the random distribution of the
anisotropy, which are shown to be responsible for the raising of the critical
temperature with respect to the pure and uncorrelated random cases and
contribute to the detachment of the coexistence curve from the $\lambda$ line.",9305036v1
1994-01-31,Comment on `Anomalously Large Gap Anisotropy in the a-b Plane of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$',"Comment on `Anomalously Large Gap Anisotropy in the a-b Plane of Bi$_{{\bf
2}}$Sr$_{{\bf 2}}$CaCu$_{{\bf 2}}$O$_{{\bf 8+}{\delta}}$', Kazumasa Miyake and
Osamu Narikiyo, In a recent Letter, Shen and collaborators [Phys. Rev. Lett.
{\bf 70}, 1555 (1993)] reported that angle-resolved photoemission spectra
(ARPES) in Bi-2212 cuprate superconductor far below $T_{{\rm c}}$ has
anomalously large anisotropy and then concluded that the symmetry of Cooper
pair is likely to be $d_{x^{2}-y^{2}}$, i.e., $\Delta_{{\bf k}}=\Delta(\cos
k_{x}a-\cos k_{y}a)$. In this Comment we point out that the interpretation done
by Shen {\it et al\/.}, where the shift of edge near Fermi level has been
identified with the gap $\Delta_{{\bf k}}$, is not unambiguous, and that a
possibility of $d_{xy}$ pairing, i.e., $\Delta_{{\bf k}}=2\Delta\sin k_{x}a\sin
k_{y}a$, cannot be ruled out.",9401073v1
1994-08-19,Spin Softening in Models with Competing Interactions: A New High Anisotropy Expansion to All Orders,"An expansion in inverse spin anisotropy, which enables us to study the
behaviour of discrete spin models as the spins soften, is developed. In
particular we focus on models, such as the chiral clock model and the $p$-state
clock model with competing first and second neighbour interactions, where there
are special multiphase points at zero temperature at which an infinite number
of ground states are degenerate. The expansion allows calculation of the ground
state phase diagram near these points as the spin anisotropy, which constrains
the spin to take discrete values, is reduced from infinity. Several different
behaviours are found, from a single first order phase boundary to infinite
series of commensurate phases.",9408053v1
1995-01-14,Temperature dependent gap anisotropy in Bi$_{2}$Sr$_{2}$CaCu$_{2}$ O$_{8+x}$ as evidence for a mixed-symmetry ground state,"In a recent experiment, Ma et al. measured the temperature dependence of the
gap anisotropy of oxygen-annealed Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$. Their
measurements were taken along the two directions $\Gamma - M$ and $\Gamma - X$.
They found that the gap along both directions is nonzero at low temperatures
and that the ratio is strongly temperature dependent. We show, using
Ginzburg-Landau theory, that this behavior can be obtained if one assumes the
existence of s-wave and d-wave components for the order parameter. Our theory
predicts orthorhombic anisotropy in the gap and anomalous behavior for the
electronic specific heat below T$_c$.",9501057v1
1995-03-18,Effects of Magnetic Order on the Upper Critical Field of UPt$_3$,"I present a Ginzburg-Landau theory for hexagonal oscillations of the upper
critical field of UPt$_3$ near $T_c$. The model is based on a $2D$
representation for the superconducting order parameter,
$\vec{\eta}=(\eta_1,\eta_2)$, coupled to an in-plane AFM order parameter,
$\vec{m}_s$. Hexagonal anisotropy of $H_{c2}$ arises from the weak in-plane
anisotropy energy of the AFM state and the coupling of the superconducting
order parameter to the staggered field. The model explains the important
features of the observed hexagonal anisotropy [N. Keller, {\it et al.}, Phys.
Rev. Lett. {\bf 73}, 2364 (1994).] including: (i) the small magnitude, (ii)
persistence of the oscillations for $T\rightarrow T_c$, and (iii) the change in
sign of the oscillations for $T> T^{*}$ and $T< T^{*}$ (the temperature at the
tetracritical point). I also show that there is a low-field crossover
(observable only very near $T_c$) below which the oscillations should vanish.",9503105v1
1995-06-29,Modulated structures stabilised by spin softening: an expansion in inverse spin anisotropy,"We develop an analytic approach which allows us to study the behaviour of
spin models with competing interactions and $p$-fold spin anisotropy, $D$, in
the limit where the pinning potential which results from $D$ is large. This is
an expansion in inverse spin anisotropy which must be carried out to all orders
where necessary. Interesting behaviour occurs near where the boundary between
different ground states is infinitely degenerate for infinite $D$. Here as $D$
decreases and the spins are allowed to soften, we are able to demonstrate the
existence of several different behaviours ranging from a single first-order
boundary to infinite series of commensurate phases. The method is illustrated
by considering the soft chiral clock model and the soft clock model with first-
and second-neighbour competing interactions. In the latter case the results are
strongly dependent on the value of $p$.",9506135v1
1995-10-20,"Critical Properties of the transition between the Haldane phase and the large-D phase of the spin-1/2 ferromagnetic-antiferromagnetic Heisenberg chain with on-site anisotropy""","We analytically study the ground-state quantum phase transition between the
Haldane phase and the large-$D$ (LD) phase of the $S=1/2$
ferromagnetic-antiferromagnetic alternating Heisenberg chain with on-site
anisotropy. We transform this model into a generalized version of the
alternating antiferromagnetic Heisenberg model with anisotropy. In the
transformed model, the competition between the transverse and longitudinal bond
alternations yields the Haldane-LD transition. Using the bosonization method,
we show that the critical exponents vary continuously on the Haldane-LD
boundary. Our scaling relations between critical exponents very well explains
the numerical results by Hida.",9510115v2
1996-01-17,On the low temperature properties and specific anisotropy of pure anisotropically paired superconductors,"Dependences of low temperature behavior and anisotropy of various physical
quantities for pure unconventional superconductors upon a particular form of
momentum direction dependence for the superconducting order parameter (within
the framework of the same symmetry type of superconducting pairing) are
considered. A special attention is drawn to the possibility of different
multiplicities of the nodes of the order parameter under their fixed positions
on the Fermi surface, which are governed by symmetry. The problem of an
unambiguous identification of a type of superconducting pairing on the basis of
corresponding experimental results is discussed. Quasiparticle density of
states at low energy for both homogeneous and mixed states, the low temperature
dependences of the specific heat, penetration depth and thermal conductivity,
the I-V curves of SS and NS tunnel junctions at low voltages are examined. A
specific anisotropy of the boundary conditions for unconventional
superconducting order parameter near $T_c$ for the case of specular reflection
from the boundary is also investigated.",9601066v1
1997-03-22,Internal Anisotropy of Collision Cascades,"We investigate the internal anisotropy of collision cascades arising from the
branching structure. We show that the global fractal dimension cannot give an
adequate description of the geometrical structure of cascades because it is
insensitive to the internal anisotropy. In order to give a more elaborate
description we introduce an angular correlation function, which takes into
account the direction of the local growth of the branches of the cascades. It
is demonstrated that the angular correlation function gives a quantitative
description of the directionality and the interrelation of branches. The power
law decay of the angular correlation is evidenced and characterized by an
exponent and an angular correlation length different from the radius of
gyration. It is demonstrated that the overlapping of subcascades has a strong
effect on the angular correlation.",9703194v1
1997-05-28,Effects of gap anisotropy upon the electronic structure around a superconducting vortex,"An isolated single vortex is considered within the framework of the
quasiclassical theory. The local density of states around a vortex is
calculated in a clean type II superconductor with an anisotropy. The anisotropy
of a superconducting energy gap is crucial for bound states around a vortex. A
characteristic structure of the local density of states, observed in the
layered hexagonal superconductor 2H-NbSe2 by scanning tunneling microscopy
(STM), is well reproduced if one assumes an anisotropic s-wave gap in the
hexagonal plane. The local density of states (or the bound states) around the
vortex is interpreted in terms of quasiparticle trajectories to facilitate an
understanding of the rich electronic structure observed in STM experiments. It
is pointed out that further fine structures and extra peaks in the local
density of states should be observed by STM.",9705286v1
1998-01-09,Dynamical Structure Factors of the Spin-1/2 XXZ Chain with Inverse-Square Exchange and Ising Anisotropy,"The dynamical properties of the S=1/2 antiferromagnetic XXZ chain are studied
by the exact diagonalization and the recursion method of finite systems up to
24 sites. Two types of the exchange interaction are considered: one is the
nearest-neighbor type, and the other is the inverse-square one. As the Ising
anisotropy becomes larger, there appears a noticeable difference in the
transverse component S^{xx}(q,\omega) between the two types of the exchange.
For the nearest-neighbor type, the peak frequency of S^{xx}(q,\omega) for each
q approaches the center of the continuum spectrum. On the contrary, the peak
frequency for the inverse-square type moves to the upper edge of the continuum,
and separates from the continuum for the anisotropy larger than the threshold
value. Whether the interaction between domain walls (solitons) is absent or
repulsive in the Ising limit leads to this difference in the behavior of
S^{xx}(q,\omega). In the longitudinal component S^{zz}(q,\omega), on the other
hand, the feature of the dynamics is scarcely different between the two types.
The energy gap and the static properties are also discussed.",9801070v1
1998-01-26,Charge screening and magnetic anisotropy in metallic rare-earth systems,"The calculation of magnetic anisotropy constants is performed beyond the
point charge model for a continuous charge density distribution of screening
conduction electrons. An important role of the non-uniform electron density, in
particular, of the Friedel oscillations, in the formation of crystal field is
demonstrated. Such effects can modify strongly the effective ion (impurity)
charge and even change its sign. This enables one to justify the anion model,
which is often used at discussing experimental data on hydrogen-containing
systems. Possible applications to the pure rare-earth metals and RCo5 compounds
are discussed. The deformation of magnetic structure near the interstitial
positive muon owing to the strong local anisotropy, and the corresponding
contribution to the dipole field at the muon are considered.",9801269v1
1998-02-03,The Anisotropic Bak-Sneppen Model,"The Bak-Sneppen model is shown to fall into a different universality class
with the introduction of a preferred direction, mirroring the situation in spin
systems. This is first demonstrated by numerical simulations and subsequently
confirmed by analysis of the multi-trait version of the model, which admits
exact solutions in the extremes of zero and maximal anisotropy. For
intermediate anisotropies, we show that the spatiotemporal evolution of the
avalanche has a power law ``tail'' which passes through the system for any
non-zero anisotropy but remains fixed for the isotropic case, thus explaining
the crossover in behaviour. Finally, we identify the maximally anisotropic
model which is more tractable and yet more generally applicable than the
isotropic system.",9802028v2
1998-04-28,Ferromagnetism and Temperature-Driven Reorientation Transition in Thin Itinerant-Electron Films,"The temperature-driven reorientation transition which, up to now, has been
studied by use of Heisenberg-type models only, is investigated within an
itinerant-electron model. We consider the Hubbard model for a thin fcc(100)
film together with the dipole interaction and a layer-dependent anisotropy
field. The isotropic part of the model is treated by use of a generalization of
the spectral-density approach to the film geometry. The magnetic properties of
the film are investigated as a function of temperature and film thickness and
are analyzed in detail with help of the spin- and layer-dependent quasiparticle
density of states. By calculating the temperature dependence of the
second-order anisotropy constants we find that both types of reorientation
transitions, from out-of-plane to in-plane (``Fe-type'') and from in-plane to
out-of-plane (``Ni-type'') magnetization are possible within our model. In the
latter case the inclusion of a positive volume anisotropy is vital. The
reorientation transition is mediated by a strong reduction of the surface
magnetization with respect to the inner layers as a function of temperature and
is found to depend significantly on the total band occupation.",9804301v1
1998-06-16,Curie Temperature of Anisotropic Ferromagnetic Films,"Dimensional crossover of ordering in ferromagnetic films with both periodic
and free boundary conditions is studied for the exactly solvable uniaxial model
of classical D-component spin vectors in the limit D \to \infty. Analytical and
numerical solution of the exact equations describing this model shows that for
lattice dimensionalities d>4, finite-size corrections to the bulk values of T_c
are characterized by the mean-field exponents and anisotropy-dependent
amplitudes. For d =< 4, the mean-field behavior is only realized in the region
\kappa_c N >> 1, where \kappa_c is the dimensionlesss inverse transverse (with
respect to the easy axis) bulk correlation length at T_c and N is the number of
layers in the film. In the region \kappa_c N << 1 and the dimensionality range
3 < d =< 4, finite-size corrections are described by the universality class of
the isotropic D=\infty model. For d =< 3, magnetic ordering vanishes in the
isotropic limit, \kappa_c \to 0, since the film behaves as an object of
dimensionality d'=d-1 =< 2 and long-wavelength fluctuations destroy the order.
Here the suppression of T_c of a film can be substantial, depending on the
competition between the weakening anisotropy and the increasing film thickness.
For thick films, T_c becomes small only for very small anisotropy.",9806198v1
1998-08-27,Thickness evolution of coercivity in ultrathin magnetic films,"The thickness evolution of in-plane magnetization reversal in ultrathin films
is studied with a theoretical model that takes account of surface roughness
typical of epitaxial growth. Guided by N\'{e}el's model, step edge sites of
monolayer-height islands are assigned a two-fold anisotropy in addition to a
four-fold anisotropy at all sites. Coercivity is found to depend essentially on
both the film thickness and the partial coverage of the topmost layer. Its
qualitative features are determined primarily by sample geometry and the size
of the step anisotropy compared to the domain wall energy. Magnetostatic
interactions change the results quantitatively, but not qualitatively. Their
effect is understood by comparing calculations with and without their
inclusion.",9808311v1
1998-09-08,Inelastic Neutron Scattering Study of Mn_12-Acetate,"We report zero-field inelastic neutron scattering experiments on a deuterated
powder sample of Mn12-Acetate consisting of a large number of nominally
identical spin-10 magnetic clusters. Our resolution enables us to see a series
of peaks corresponding to transitions between the anisotropy levels within the
spin-10 manifold. A fit to the spin Hamiltonian yields an anisotropy constant
D=0.54 K and a fourth-order diagonal anisotropy coefficient A = 1.2x10^-3 K.
Performed in the absence of a magnetic field, our experiments do not involve
the g-values as fitting parameters, thereby yielding particularly reliable
values of D and A.",9809133v2
1998-09-30,Effect of anisotropy on universal transport in unconventional superconductors,"We investigate the universal electronic transport for a mixed
$d_{x^2-y^2}$+s-wave superconductor in the presence of an anisotropic
elliptical Fermi surface. Similar to the universal low-temperature transport
predicted in a $d_{x^2-y^2}$-wave superconductor with a circular Fermi surface,
anisotropic universal features are found in the low-temperature microwave
conductivity, and thermal conductivity in the anisotropic system. The effects
of anisotropy on the penetration depth, impurity induced $T_c$ suppression, and
the zero-frequency density of states are also considered. While a small amount
of anisotropy can lead to a strong suppression of the effective scattering rate
and hence the density of states at zero frequency, experimental data suggests
that large effects are restored by a negative $s$-component gap admixture.",9809400v1
1999-03-03,Theory of magnetoresistance in films of dilute magnetic alloys,"Earlier a magnetic anisotropy for magnetic impurities nearby the surface of
non-magnetic host was proposed in order to explain the size dependence of the
Kondo effect in dilute magnetic alloys. Recently Giordano has measured the
magnetoresistance of dilute Au(Fe) films for different thicknesses well above
the Kondo temperature $T_K$. In this way he verified the existence of that
anisotropy even for such a case where the Kondo effect is not dominating. For
detailed comparison of that suggestion with experiments, the magnetic field
dependence of the magnetoresistance is calculated in the lowest approximation,
thus in the second order of the exchange coupling. The strength of the
anisotropy is very close to earlier estimates deduced from the size dependence
of the Kondo resistivity amplitude.",9903054v2
1999-03-05,Comment on ``Evidence for Anisotropic State of Two-Dimensional Electrons in High Landau Levels'',"In a recent letter M. Lilly et al [PRL 82, 394 (1999)] have shown that a
highly anisotropic state can arise in certain two dimensional electron systems.
In the large square samples studied, resistances measured in the two
perpendicular directions are found to have a ratio that may be 60 or larger at
low temperature and at certain magnetic fields. In Hall bar measurements, the
anisotropy ratio is found to be much smaller (roughly 5). In this comment we
resolve this discrepancy by noting that the anisotropy of the underlying sheet
resistivities is correctly represented by Hall bar resistance measurements but
shows up exponentially enhanced in resistance measurements on square samples
due to simple geometric effects. We note, however, that the origin of this
underlying resistivity anisotropy remains unknown, and is not addressed here.",9903086v3
1999-03-16,Opening of the Haldane Gap in Anisotropic Two- and Four-Leg Spin Ladders,"We study the opening of the Haldane gap in two-leg and four-leg anisotropic
spin ladders using bosonization and renormalization group methods, and we
determine the phase diagram as a function of the interchain coupling and the
relative anisotropy. It is found that the opening of the Haldane gap is
qualitatively different for the two cases considered. For the two-leg ladder
the Haldane gap opens for arbitrarily small interchain coupling, independent of
the relative anisotropy, and the Haldane phase exists in a large region of
parameter space. For the four-leg ladder the opening of the Haldane gap is
strongly dependent on both the interchain coupling as well as the relative
anisotropy, and the Haldane phase exists only in a narrow region about the
isotropic antiferromagnet.",9903241v1
1999-04-30,Magnetic excitations in charge- ordered NaV2O5,"An investigation of the spin excitation spectrum of charge ordered (CO)
NaV2O5 is presented. We discuss several different exchange models which may be
relevant for this compound, namely in- line and zig-zag chain models with weak
as well as strong inter- chain coupling and also a ladder model and a CO/MV
(mixed valent) model. We put special emphasis on the importance of large
additional exchange across the diagonals of V- ladders and the presence of
exchange anisotropies on the excitation spectrum. It is shown that the observed
splitting of transverse dispersion branches may both be interpreted as
anisotropy effect as well as acoustic- optic mode splitting in the weakly
coupled chain models. In addition we calculate the field dependence of
excitation modes in these models. Furthermore we show that for strong inter-
chain coupling, as suggested by recent LDA+U results, an additional high energy
optical excitation appears and the spin gap is determined by anisotropies. The
most promising CO/MV model predicts a spin wave dispersion perpendicular to the
chains which agrees very well with recent results obtained by inelastic neutron
scattering.",9904443v2
1999-07-08,Quasi-long-range order in the random anisotropy Heisenberg model: functional renormalization group in 4-εdimensions,"The large distance behaviors of the random field and random anisotropy O(N)
models are studied with the functional renormalization group in 4-\epsilon
dimensions. The random anisotropy Heisenberg (N=3) model is found to have a
phase with the infinite correlation radius at low temperatures and weak
disorder. The correlation function of the magnetization obeys a power law <
m(x) m(y) >\sim |x-y|^{-0.62\epsilon}. The magnetic susceptibility diverges at
low fields as \chi \sim H^{-1+0.15\epsilon}. In the random field O(N) model the
correlation radius is found to be finite at the arbitrarily weak disorder for
any N>3. The random field case is studied with a new simple method, based on a
rigorous inequality. This approach allows one to avoid the integration of the
functional renormalization group equations.",9907122v3
1999-08-13,Resistive upper critical fields and irreversibility lines of optimally-doped high-T_c cuprates,"We present the resistively-determined upper critical field H^{\rho}_{c2}(T)
and the irreversibility lines H^{\rho}_{irr}(T) of various high-T_c cuprates,
deduced from measurements in 61-T pulsed magnetic fields applied parallel to
the c-axis. The SHAPE of both H^{\rho}_{c2}(T) and H^{\rho}_{irr}(T) depends
monotonically on the anisotropy of the material and none of the samples show
saturation of H^{\rho}(T) at low temperatures. The anomalous positive
curvature, d^2 H^{\rho}/dT^2 > 0, is the strongest in materials with the
largest normal-state anisotropy, regardless of whether anisotropy is varied by
changing the carrier concentration or by comparing a variety of optimally-doped
compounds.",9908190v1
1999-11-24,Random Field and Random Anisotropy Effects in Defect-Free Three-Dimensional XY Models,"Monte Carlo simulations have been used to study a vortex-free XY ferromagnet
with a random field or a random anisotropy on simple cubic lattices. In the
random field case, which can be related to a charge-density wave pinned by
random point defects, it is found that long-range order is destroyed even for
weak randomness. In the random anisotropy case, which can be related to a
randomly pinned spin-density wave, the long-range order is not destroyed and
the correlation length is finite. In both cases there are many local minima of
the free energy separated by high entropy barriers. Our results for the random
field case are consistent with the existence of a Bragg glass phase of the type
discussed by Emig, Bogner and Nattermann.",9911398v2
2000-03-27,Effects of interlayer coupling on the irreversibility lines of NbN/AlN superconducting multilayers,"We have studied the temperature dependence of the in-plane resistivity of
NbN/AlN multilayer samples with varying insulating layer thickness in magnetic
fields up to 7 Tesla parallel and perpendicular to the films. The upper
critical field shows a crossover from 2D to 3D behavior in parallel fields. The
irreversibility lines have the form (1-T/Tc)^alpha, where alpha varies from 4/3
to 2 with increasing anisotropy. The results are consistent with simultaneous
melting and decoupling transitions for low anisotropy sample, and with melting
of decoupled pancakes in the superconducting layers for higher anisotropy
samples.",0003426v2
2000-05-25,Laplacian growth with separately controlled noise and anisotropy,"Conformal mapping models are used to study competition of noise and
anisotropy in Laplacian growth. For that, a new family of models is introduced
with the noise level and directional anisotropy controlled independently.
Fractalization is observed in both anisotropic growth and the growth with
varying noise. Fractal dimension is determined from cluster size scaling with
its area. For isotropic growth we find d = 1.7, both at high and low noise. For
anisotropic growth with reduced noise the dimension can be as low as d = 1.5
and apparently is not universal. Also, we study fluctuations of particle areas
and observe, in agreement with previous studies, that exceptionally large
particles may appear during the growth, leading to pathologically irregular
clusters. This difficulty is circumvented by using an acceptance window for
particle areas.",0005456v2
2000-06-14,Orientational pinning of quantum Hall striped phase,"In ultra-clean 2D electron systems on (001) GaAs/AlGaAs upon filling high
Landau levels, it was recently observed a new class of collective states, which
can be related to the spontaneous formation of a charge density wave (``striped
phase''). We address to the following unsolved problem: what is the reason for
stripe pinning along the crystallographic direction [110]? It is shown that in
a single heterojunction (001) III-V the effective mass of 2D electrons is
anisotropic. This natural anisotropy is due to the reduced (C_{2v}) symmetry of
the heterojunction and, even being weak (0.1 percent), can govern the stripe
direction. A magnetic field parallel to the interface induces ``magnetic''
anisotropy of the effective mass. The competition of these two types of
anisotropy provides quantitative description of the experiment.",0006226v1
2000-07-18,Shape-induced magnetic anisotropy in dilute magnetic alloys,"We extend the theory of the surface-induced magnetic anisotropy to mesoscopic
samples with arbitrary geometry. The shape-induced anisotropy of impurity spins
in small brick-shaped grains of dilute magnetic alloys is studied in detail.
The surface-induced blocking of a magnetic-impurity spin is shown to be very
sensitive to geometric parameters of a grain. This implies that the apparent
discrepancy between the experimental data of different groups on the size
dependence of the Kondo resistivity can result from different microstructure of
the used samples. In order to interpret recent experimental data on the
anomalous Hall effect in thin polycrystalline Fe doped Au films, we analyse the
magnetisation of impurity spins as a function of the impurity position and of
the grain shape.",0007294v1
2000-08-05,Reversed anisotropies and thermal contraction of FCC (110) surfaces,"The observed anisotropies of surface vibrations for unreconstructed FCC metal
(110) surfaces are often reversed from the ""common sense"" expectation. The
source of these reversals is investigated by performing ab initio density
functional theory calculations to obtain the surface force constant tensors for
Ag(110), Cu(110) and Al(110). The most striking result is a large enhancement
in the coupling between the first and third layers of the relaxed surface,
which strongly reduces the amplitude of out-of-plane vibrations of atoms in the
first layer. This also provides a simple explanation for the thermal
contraction of interlayer distances. Both the anisotropies and the thermal
contraction arise primarily as a result of the bond topology, with all three
(110) surfaces showing similar behavior.",0008088v1
2000-09-04,Current Induced Magnetization Switching in Small Domains of Different Anisotropies,"Several recent experimental studies have confirmed the possibility of
switching the magnetization direction in the small magnetic domains by pumping
large spin-polarized currents through them. On the basis of equations proposed
by J.Slonczewski for the case when magnetization of the domains is almost
uniform, we analyze the stability and switching for two types of magnetic and
shape anisotropies of a magnetic domain in a nanowire and find qualitatively
different behavior, including different shapes of bistable regions. Our study
is analytic as opposed to recent numeric work. Assumed anisotropies can be
realized in experiments and our predictions can be used to experimentally test
the theory of spin-transfer torques. Such test would be especially interesting
since alternative approaches are discussed in the literature.",0009034v1
2001-01-18,Thermodynamic perturbation theory for dipolar superparamagnets,"Thermodynamic perturbation theory is employed to derive analytical
expressions for the equilibrium linear susceptibility and specific heat of
lattices of anisotropic classical spins weakly coupled by the dipole-dipole
interaction. The calculation is carried out to the second order in the coupling
constant over the temperature, while the single-spin anisotropy is treated
exactly. The temperature range of applicability of the results is, for weak
anisotropy (A/kT << 1), similar to that of ordinary high-temperature
expansions, but for moderately and strongly anisotropic spins (A/kT > 1) it can
extend down to the temperatures where the superparamagnetic blocking takes
place (A/kT \sim 25), provided only the interaction strength is weak enough.
Besides, taking exactly the anisotropy into account, the results describe as
particular cases the effects of the interactions on isotropic (A = 0) as well
as strongly anisotropic (A \to \infty) systems (discrete orientation model and
plane rotators).",0101287v2
2001-02-28,Electronic and Optical Properties of Self-Assembled Quantum Wires,"We have studied the band and optical properties of self-assembled quantum
wires. In particular, the band structures and optical matrix elements of
strained multiple quantum-wires (QWR's) are investigated theoretically via the
effective bond-orbital model(EBOM), which takes into account the effects of
valence-band anisotropy and the band mixing. It is found that the strain leads
to further confinement of carriers and enhancement of the anisotropy.
  By using the EBOM and valence-force field model, we systematically studied
the microstrain effects on the electronic and optical properties of
Ga$_{1-x}$In$_x$As self-assembled quantum-wires (QWR's) made of short-period
superlattices with strain-induced lateral ordering. Valence-band anisotropy,
band mixing, and effects due to local strain distribution at the atomistic
level are all taken into account.A comprehensive collection of different
structures in our model are presented.
  Finally, the excitonic absorption spectrum for the SILO quantum wires are
investigated by using our envelope function model.",0102506v2
2001-03-02,Superconducting Gap and Strong In-Plane Anisotropy in Untwinned YBa2Cu3O7-d,"With significantly improved sample quality and instrumental resolution, we
clearly identify in the (pi,0) ARPES spectra from YBa2Cu3O6.993, in the
superconducting state, the long-sought `peak-dip-hump' structure. This advance
allows us to investigate the large a-b anisotropy of the in-plane electronic
structure including, in particular, a 50% difference in the magnitude of the
superconducting gap that scales with the energy position of the hump feature.
This anisotropy, likely induced by the presence of the CuO chains, raises
serious questions about attempts to quantitatively explain the YBa2Cu3O7-d data
from various experiments using models based on a perfectly square lattice.",0103047v1
2001-03-16,Gap Anisotropy and de Haas-van Alphen Effect in Type-II Superconductors,"We present a theoretical study on the de Haas-van Alphen (dHvA) oscillation
in the vortex state of type-II superconductors, with a special focus on the
connection between the gap anisotropy and the oscillation damping. Numerical
calculations for three different gap structures clearly indicate that the
average gap along extremal orbits is relevant for the magnitude of the extra
damping, thereby providing a support for experimental efforts to probe gap
anisotropy through the dHvA signal. We also derive an analytic formula for the
extra damping which gives a good fit to the numerical results.",0103336v3
2001-03-23,Transport and magnetic anisotropy in CMR thin film La_{1-x}Ca_{x}MnO_{3} (x \approx 1/3) induced by a film-substrate interaction,"We present a study of anisotropy of transport and magnetic properties in
La_{1-x}Ca_{x}MnO_{3} (x \approx 1/3) film prepared by pulsed-laser deposition
onto a LaAlO_{3} sunstrate. We found a non-monotonic dependence of
magnetoresistance (MR) on magnetic field H for both H perpendicular and
parallel to the film plane but perpendicular to the current. This rather
complex behavior of MR manifests itself at low temperatures, far below the
Curie temperature. Two main sources of MR anisotropy have been considered in
the explanantion of the results: (1) the existence of preferential directions
of magnetization (due to strains stemming from the lattice film-substrate
mismatch or other reasons); (2) dependence of resistance on the angle between
current and the magnetization, which is inherent in ferromagnets.",0103493v1
2001-04-15,Nonlinear ac response of anisotropic composites,"When a suspension consisting of dielectric particles having nonlinear
characteristics is subjected to a sinusoidal (ac) field, the electrical
response will in general consist of ac fields at frequencies of the
higher-order harmonics. These ac responses will also be anisotropic. In this
work, a self-consistent formalism has been employed to compute the induced
dipole moment for suspensions in which the suspended particles have nonlinear
characteristics, in an attempt to investigate the anisotropy in the ac
response. The results showed that the harmonics of the induced dipole moment
and the local electric field are both increased as the anisotropy increases for
the longitudinal field case, while the harmonics are decreased as the
anisotropy increases for the transverse field case. These results are
qualitatively understood with the spectral representation. Thus, by measuring
the ac responses both parallel and perpendicular to the uniaxial anisotropic
axis of the field-induced structures, it is possible to perform a real-time
monitoring of the field-induced aggregation process.",0104270v1
2001-04-25,Anisotropy of magnetothermal conductivity in Sr2RuO4,"The dependence of in-plane and interplane thermal conductivities of Sr2RuO4
on temperature, as well as magnetic field strength and orientation, is
reported. We found no notable anisotropy in the thermal conductivity for the
magnetic field rotation parallel to the conducting plane in the whole range of
experimental temperatures and fields, except in the vicinity of the upper
critical field Hc2, where the anisotropy of the Hc2 itself plays a dominant
role. This finding imposes strong constraints on the possible models of
superconductivity in Sr2RuO4 and supports the existence of a superconducting
gap with a line of nodes running orthogonal to the Fermi surface cylinder.",0104492v1
2001-04-28,"Electronic anisotropy, magnetic field-temperature phase diagram and their dependence on resistivity in c-axis oriented MgB2 thin films","An important predicted, but so far uncharacterized, property of the new
superconductor MgB2 is electronic anisotropy arising from its layered crystal
structure. Here we report on three c-axis oriented thin films, showing that the
upper critical field anisotropy ratio Hc2par/Hc2perp is 1.8 to 2.0, the ratio
increasing with higher resistivity. Measurements of the magnetic
field-temperature phase diagram show that flux pinning disappears at H* ~
0.8Hc2perp(T) in untextured samples. Hc2par(0) is strongly enhanced by alloying
to 39 T for the highest resistivity film, more than twice that seen in bulk
samples.",0104562v1
2001-05-21,Unusual magnetic susceptibility anisotropy in untwinned La_{2-x}Sr_xCuO_4 single crystals in the lightly-doped region,"We present a study of the magnetic susceptibility in carefully detwinned
La_{2-x}Sr_{x}CuO_4 single crystals in the lightly-doped region (x=0-0.03),
which demonstrates a remarkable in-plane anisotropy of the spin system. This
anisotropy is found to persist after the long-range antiferromagnetic (AF)
order is destroyed by hole doping, suggesting that doped holes break the AF
order into domains in which the spin alignment is kept essentially intact. It
turns out that the freezing of the spins taking place at low temperatures is
also notably anisotropic, implying that the ""spin-glass"" feature is governed by
the domain structure as well.",0105390v1
2001-05-30,Anisotropy in the electronic screening of oxygen lattice modes in YBa(2)Cu(3)O(6.95),"Inelastic neutron scattering data from a twinned single-crystal of
YBa2Cu3O6.95 are presented that show a distinct a-b plane anisotropy in the
oxygen vibrations. The Cu-O bond-stretching type phonons are simultaneously
observed along the a and b directions due to a 4 meV splitting arising from the
orthorhombicity. The present results show the bond-stretching branch along b
(parallel to the chain) has a continuous dispersion, while the branch along a
is discontinuous, suggesting a possibility of short-range cell-doubling along
a. Furthermore, the LO mode along a is split in en-ergy from its TO partner at
non-zero q-vectors, while the b mode is not. These results imply strong
anisotropy in the electronic screening and a one-dimensional character in
underlying charge fluctuations.",0105593v1
2001-06-12,Single ion anisotropy of Mn doped GaAs measured by EPR,"Electron paramagnetic resonance (EPR) study of MBE grown Mn doped GaAs is
presented. The resolved fine structure allows us to evaluate the crystal field
parameters of the spin Hamiltonian. The obtained cubic constant is a= -14.1
10^-4/cm. The axial field parameter, D, increases with Mn concentration, x,
i.e., with the strain of (Ga,Mn)As layers. Extrapolation of D shows that the
single ion anisotropy is the important contribution to the magnetic anisotropy
which is observed in ferromagnetic layers with greater Mn concentrations. The
analysis of the EPR linewidth shows that native defects of the concentration of
5 10^19/cm^3, but not the Mn ions, are the main origin of crystal field
fluctuations.",0106227v1
2001-06-27,A Distribution of Tunnel Splittings in Mn$_{12}$-Acetate,"In magnetic fields applied parallel to the anisotropy axis, the relaxation of
the magnetization of Mn$_{12}$ measured for different sweep rates is shown to
collapse onto a single scaled curve. The form of the scaling implies that the
dominant symmetry-breaking process that gives rise to tunneling is a locally
varying second-order anisotropy, forbidden by tetragonal symmetry in the
perfect crystal, which gives rise to a broad distribution of tunnel splittings
in a real crystal of Mn$_{12}$-acetate. Different forms applied to even and
odd-numbered steps provide a distinction between even step resonances
(associated with crystal anisotropy) and odd resonances (which require a
transverse component of magnetic field).",0106579v3
2001-08-10,Thermodynamics of Two Dimensional Magnetic Nanoparticles,"A two dimensional magnetic particle in the presence of an external magnetic
field is studied. Equilibrium thermodynamical properties are derived by
evaluating analytically the partition function. When the external field is
applied perpendicular to the anisotropy axis the system exhibits a second order
phase transition with order parameter being the magnetization parallel to the
field. In this case the system is isomorph to a mechanical system consisting in
a particle moving without friction in a circle rotating about its vertical
diameter. Contrary to a paramagnetic particle, equilibrium magnetization shows
a maximum at finite temperature. We also show that uniaxial anisotropy in a
system of noninteracting particles can be missinterpreted as a ferromagnetic or
antiferromagnetic coupling among the magnetic particles depending on the angle
between anisotropy axis and magnetic field.",0108178v1
2001-08-20,Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions,"We study the magnetic properties of spherical Co clusters with diameters
between 0.8 nm and 5.4 nm (25 to 7500$ atoms) prepared by sequential sputtering
of Co and Al2O3. The particle size distribution has been determined from the
equilibrium susceptibility and magnetization data and it is compared to
previous structural characterizations. The distribution of activation energies
was independently obtained from a scaling plot of the ac susceptibility.
Combining these two distributions we have accurately determined the effective
anisotropy constant Keff. We find that Keff is enhanced with respect to the
bulk value and that it is dominated by a strong anisotropy induced at the
surface of the clusters. Interactions between the magnetic moments of adjacent
layers are shown to increase the effective activation energy barrier for the
reversal of the magnetic moments. Finally, this reversal is shown to proceed
classically down to the lowest temperature investigated (1.8 K).",0108304v1
2001-08-21,Quasiparticle spectrum of d-wave superconductors in the mixed state: a large Fermi-velocity anisotropy study,"The quasiparticle spectrum of a two-dimensional d-wave superconductor in the
mixed state, H_c1 << H << H_c2, is studied for large values of the ``anisotropy
ratio'' alpha_D = v_F/v_Delta. For a square vortex lattice rotated by 45
degrees from the quasiparticle anisotropy axes (and the usual choice of
Franz--Tesanovic singular gauge transformation) we determine essential features
of the band structure asymptotically for large alpha_D, using an effective
one-dimensional model, and compare them to numerical calculations. We find that
several features of the band structure decay to zero exponentially fast for
large alpha_D. Using a different choice of singular gauge transformation, we
obtain a different band structure, but still find qualitative agreement between
the 1D and full 2D calculations. Finally, we distort the square lattice into a
non-Bravais lattice. Both the one- and two-dimensional numerical calculations
of the energy spectra show a gap around zero-energy, with our gauge choice, and
the two excitation spectra agree reasonably well.",0108324v1
2001-10-11,Anisotropy of Vortex-Liquid and Vortex-Solid Phases in Single Crystals of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$: Violation of the Scaling Law,"The vortex-liquid and vortex-solid phases in single crystals of
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ placed in tilted magnetic fields are studied
by in-plane resistivity measurements using the Corbino geometry to avoid
spurious surface barrier effects. It was found that the anisotropy of the
vortex-solid phase increases with temperature and exhibits a maximum at
$T\approx 0.97 T_c$. In contrast, the anisotropy of the vortex-liquid rises
monotonically across the whole measured temperature range. The observed
behavior is discussed in the context of dimensional crossover and thermal
fluctuations of vortices in the strongly layered system.",0110232v1
2001-10-22,Magnetoconductance of a two-dimensional metal in the presence of spin-orbit coupling,"We show that in the metallic phase of a two dimensional electron gas the
spin-orbit coupling due to structure inversion asymmetry leads to a
characteristic anisotropy in the magnetoconductance. Within the assumption that
the metallic phase can be described by a Fermi liquid, we compute the
conductivity in the presence of an in-plane magnetic field. Both the spin-orbit
coupling and the Zeeman coupling with the magnetic field give rise to two spin
subbands, in terms of which most of the transport properties can be discussed.
  The strongest conductivity anisotropy occurs for Zeeman energies of the order
of the Fermi energy corresponding to the depopulation of the upper spin
subband. The energy scale associated with the spin-orbit coupling controls the
strength of the effect. More in particular, we find that the detailed behavior
and the sign of the anisotropy depends on the underlying scattering mechanism.
Assuming small angle scattering to be the dominant scattering mechanism our
results agree with recent measurement on Si-MOSFET's in the vicinity of the
metal-insulator transition.",0110454v1
2001-10-25,Observation of large anisotropy in c-axis oriented thin films of MgB$_{2}$ prepared by an in situ pulsed laser deposition process,"A large anisotropy in the upper critical field (H$_{C2}$) is observed for
MgB$_{2}$ films grown in situ by a pulsed laser deposition process involving
growth and annealing of Mg and B multilayers. Measurements of resistivity as a
function of temperature and magnetic field yield the estimated zero temperature
values of H$_{C2}$ in the range 100 to 130 T and about 10 T, for the field in
ab plane and along c axis, respectively, depending on the criterion chosen for
the transition temperature. The corresponding anisotropy parameter is thus in
the range 9 to 13. The estimated coherence length in ab plane is about 50
\r{A}, whereas that in the c direction is much smaller (\approx 5 \r{A}). No
significant magnetoresistance is observed in the normal state.",0110541v1
2001-12-07,The origin of second-order transverse magnetic anisotropy in Mn12-acetate,"The problem of the role of transverse fields in Mn12-acetate, a molecular
nanomagnet, is still open. We present structural evidences that the disorder of
the acetic acid of crystallization indices sizeable distortion of the Mn(III)
sites, giving rise to six different isomers, four of them with symmetry lower
than tetragonal. Using a ligand field approach the effect of the structure
modifications on the second order transverse magnetic anisotropy, forbidden in
tetragonal symmetry, has been evaluated. The order of magnitude of the
quadratic transverse anisotropies well agree with the values derived by the
analysis of the field sweep dependence of the hysteresis loops performed by
Mertes et al.
  (Phys. Rev. Lett 87, 227205 (2001)) and allows to better simulate the EPR
spectra.",0112112v1
2001-12-11,Temperature dependence and anisotropy of the bulk upper critical field H_c2 of MgB_2,"The bulk upper critical field H_{c2}(T) of superconducting MgB_2 and its
anisotropy are established by analyzing experimental data on the temperature
and magnetic field dependences of the ab-plane thermal conductivity of a
single-crystalline sample in external magnetic fields oriented both parallel
(H_{c2}^c) and perpendicular (H_{c2}^{ab}) to the c axis of the hexagonal
lattice. From numerical fits we deduce the anisotropy ratio \gamma_0 =
H_{c2}^{ab}(0) / H_{c2}^c(0)=4.2 at T=0 K. Both the values and the temperature
dependences of H_{c2}^c and H_{c2}^{ab} are distinctly different from previous
claims based on measurements of the electrical resistivity.",0112191v2
2002-01-08,The effect of velocity anisotropy on the antiferromagnetic instability of a d-wave superconductor,"We consider the effective 2+1 dimensional electrodynamics (QED_3) of
low-energy quasiparticles coupled to fluctuating vortex loops in the d-wave
superconductor, with the velocity anisotropy: v_F not equal to v_Delta. This
theory should be relevant to the quantum superconductor-insulator transition in
underdoped cuprates. Working in the customary large-N approximation, we find
that weak anisotropy is a marginally irrelevant perturbation to the Lorentz
invariant QED_3, and that the critical number N_c of Dirac fields below which
the theory suffers the antiferromagnetic (chiral) instability stays the same.",0201088v4
2002-01-25,Anisotropic superconducting properties of MgB2 single crystals probed by in-plane electrical transport measurements,"We report on study of the electronic anisotropy of the newly discovered MgB2
superconductor using the in-plane resistivity measurements in magnetic field
applied perpendicular and parallel to Mg and B planes of MgB2 single crystals.
The results show temperature dependent anisotropy of the upper critical field
with anisotropy ratio increasing from 2.2 close to Tc up to about 3 below 30K.
Our estimation of the in-plane and out-of-plane coherence length of about 68A
and 23A and electronic mean-free path 240A and 60A respectively indicates MgB2
single crystal as approaching clean limit type-II superconductor.",0201451v2
2002-03-09,Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau Levels,"We observe density induced 90$^{\circ}$ rotations of the anisotropy axes in
transport measurements at half-filled high Landau levels in the two dimensional
electron system, where stripe states are proposed ($\nu$=9/2, 11/2, etc). Using
a field effect transistor, we find the transition density to be
$2.9\times10^{11}$cm$^{-2}$ at $\nu$=9/2. Hysteresis is observed in the
vicinity of the transition. We construct a phase boundary in the filling
factor-magnetic field plane in the regime $4.4<\nu<4.6$. An in-plane magnetic
field applied along either anisotropy axis always stabilizes the low density
orientation of the stripes.",0203203v1
2002-03-29,Femtosecond quasiparticle relaxation dynamics and probe polarization anisotropy in YBa2Cu4O8,"Femtosecond pump probe experiments are reported on quasiparticle relaxation
and recombination in YBa2Cu4O8 as a function of temperature and polarization.
The data show a 2-component relaxation similar to YBa2Cu3O7-\delta, one
component being assocated with the superconducting transition, and the other
with the pseudogap below T* The relaxation time tau_p associated with the
pseudogap is found to be T-independent, while the relaxation time tau_g of the
component obseved only below Tc exhibits a clear divergence near Tc. A strong
polarisation anisotropy of the picosecond transient is observed below Tc which
is attributed to the anisotropy of the probe transition matrix elements.",0203614v2
2002-04-22,Magnetic Anisotropy in the Molecular Complex V15,"We apply degenerate perturbation theory to investigate the effects of
magnetic anisotropy in the magnetic molecule V15. Magnetic anisotropy is
introduced via Dzyaloshinskii-Moriya (DM) interaction in the full Hilbert space
of the system. Our model provides an explanation for the rounding of
transitions in the magnetization as a function of applied field at low
temperature, from which an estimate for the DM interaction is found. We find
that the calculated energy differences of the lowest energy states are
consistent with the available data. Our model also offers a novel explanation
for the hysteretic nature of the time-dependent magnetization data.",0204435v2
2002-04-22,"Magnetic ordering, electronic structure and magnetic anisotropy energy in the high-spin Mn$_{10}$ single molecule magnet","We report the electronic structure and magnetic ordering of the single
molecule magnet [Mn$_{10}$O$_{4}$(2,2'-biphenoxide)$_{4}$Br$_{12}$]$^{4-}$
based on first-principles all-electron density-functional calculations. We find
that two of the ten core Mn atoms are coupled antiferromagnetically to the
remaining eight, resulting in a ferrimagnetic ground state with total spin
S=13. The calculated magnetic anisotropy barrier is found to be 9 K in good
agreement with experiment. The presence of the Br anions impact the electronic
structure and therefore the magnetic properties of the 10 Mn atoms. However,
the electric field due to the negative charges has no significant effect on the
magnetic anisotropy.",0204479v1
2002-04-30,"S=1 kagomé Ising model with triquadratic interactions, single-ion anisotropy and magnetic field: exact phase diagrams","We consider a S=1 kagom\'e Ising model with triquadratic interactions around
each triangular face of the kagom\'e lattice, single-ion anisotropy and an
applied magnetic field. A mapping establishes an equivalence between the
magnetic canonical partition function of the model and the grand canonical
partition function of a kagom\'e lattice-gas model with localized
three-particle interactions. Since exact phase diagrams are known for
condensation in the one-parameter lattice-gas model, the mapping directly
provides the corresponding exact phase diagrams of the three-parameter S=1
Ising model. As anisotropy competes with interactions, results include the
appearance of confluent singularities effecting changes in the topology of the
phase diagrams, phase boundary curves (magnetic field vs temperature) with
purely positive or negative slopes as well as intermediate cases showing
nonmonotonicity, and coexistence curves (magnetization vs temperature) with
varying shapes and orientations, in some instances entrapping a homogeneous
phase.",0204632v1
2002-05-06,"Comment on ``Anisotropic s-wave superconductivity: comparison with experiments on MgB_2 [A. I. Posazhennikova, T. Dahm and K. Maki, cond-mat/0204272; submitted to Europhys. Lett.]","An analytical result for the renormalization of the jump of the heat capacity
Delta C/C_N by the anisotropy of the order parameter is derived within the
framework of the very recent model proposed by Posazhennikova, Dahm and Maki
[cond-mat/0204272, submitted to Europhys. Lett.], for both oblate and prolate
anisotropy. The graph of Delta C/C_N versus the ratio of the gaps on the
equator and the pole of the Fermi surface, Delta_e/\Delta_p, allows a direct
determination of the gap anisotropy parameter Delta_e/\Delta_p by fitting data
from specific heat measurements Delta C/C_N. Using the experimental value Delta
C/C_N=0.82 +/- 10% by Wang, Plackowski, and Junod [Physica C 355 (2001) 179] we
find Delta_e/\Delta_p = 4.0.",0205104v3
2002-05-10,Macroscopic Anisotropy and Symmetry Breaking in the Pyrochlore Antiferromagnet Gd$_{2}$Ti$_{2}$O$_{7}$},"In the Heisenberg antiferromagnet $Gd_2Ti_2O_7$, the exchange interactions
are geometrically frustrated by the pyrochlore lattice structure. This ESR
study reveals a strong temperature dependent anisotropy with respect to a [111]
body diagonal below a temperature $T_A=80$ K, despite the spin only nature of
the $Gd^{3+}$ ion. Anisotropy and symmetry breaking can nevertheless appear
through the superexchange interaction. The presence of short range planar
correlation restricted to specific Kagom\'{e} planes is sufficient to explain
the two ESR modes studied in this work.",0205224v1
2002-07-04,Specific heat of single crystal MgB_2: a two-band superconductor with two different anisotropies,"Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields
up to 14 T and below 3 K allow the determination of the low-temperature linear
term of the specific heat, its field dependence and its anisotropy. Our results
are compatible with two-band superconductivity, the band carrying the small gap
being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three
different upper critical fields are thus needed to describe the superconducting
state of MgB2.",0207141v3
2002-07-08,Magnetic behavior of single crystalline Ho$_2$PdSi$_3$,"The magnetic behavior of single-crystal Ho$_2$PdSi$_3$, crystallizing in an
AlB$_2$-derived hexagonal structure, is investigated by magnetic susceptibility
($\chi$) and electrical resistivity ($\rho$) measurements along two directions.
There is no dramatic anisotropy in the high temperature Curie-Weiss parameter
or in the $\rho$ and isothermal magnetization data, though there is a
noticeable anisotropy in the magnitude of $\rho$ between two perpendicular
orientations. The degree of anisotropy is overall less prominent than in the Gd
(which is an S-state ion!) and Tb analogues. A point of emphasis is that this
compound undergoes long range magnetic ordering below 8 K as in the case of
analogous Gd and Dy compounds. Considering this fact for these compounds with
well-localised f-orbital, the spin glass freezing noted for isomorphous U
compounds in the recent literature could be attributed to the role of the
f-ligand hybridization, rather than just Pd-Si disorder.",0207199v1
2002-07-18,Effects of superconducting gap anisotropy on the flux flow resistivity in Y(Ni_{1-x}Pt_x)_2B_2C,"The microwave complex surface impedance Z_s of Y(Ni_{1-x}Pt_x)_2B_2C was
measured at 0.5 K under magnetic fields H up to 7T. In nominally pure
YNi_2B_2C, which is a strongly anisotropic s-wave superconductor, the flux flow
resistivity \rho_f calculated from Z_s was twice as large as that expected from
the conventional normal-state vortex core model. In Pt-doped samples where the
gap anisotropy is smeared out, the enhancement of \rho_f is reduced and \rho_f
approaches to the conventional behavior. These results indicate that energy
dissipation in the vortex core is strongly affected by the anisotropy of the
superconducting gap.",0207454v1
2002-07-29,Anisotropic Lattice Models of Electrolytes,"Systems of charged particles on anisotropic three-dimensional lattices are
investigated theoretically using Debye-Huckel theory. It is found that the
thermodynamics of these systems strongly depends on the degree of anisotropy.
For weakly anisotropic simple cubic lattices, the results indicate the
existence of order-disorder phase transitions and a tricritical point, while
the possibility of low-density gas-liquid coexistence is suppressed. For
strongly anisotropic lattices this picture changes dramatically: the
low-density gas-liquid phase separation reappears and the phase diagram
exhibits critical, tricritical and triple points. For body-centered lattices,
the low-density gas-liquid phase coexistence is suppressed for all degrees of
anisotropy. These results show that the effect of anisotropy in lattice models
of electrolytes amounts to reduction of spatial dimensionality.",0207686v1
2002-08-01,"Quantum Hall ferromagnets, cooperative transport anisotropy, and the random field Ising model","We discuss the behaviour of a quantum Hall system when two Landau levels with
opposite spin and combined filling factor near unity are brought into energetic
coincidence using an in-plane component of magnetic field. We focus on the
interpretation of recent experiments under these conditions [Zeitler et al,
Phys. Rev. Lett. 86, 866 (2001); Pan et al, Phys. Rev. B 64, 121305 (2001)], in
which a large resistance anisotropy develops at low temperatures. Modelling the
systems involved as Ising quantum Hall ferromagnets, we suggest that this
transport anisotropy reflects domain formation induced by a random field
arising from isotropic sample surface roughness.",0208024v1
2002-11-12,Reciprocity theorem in high-temperature superconductors,"This article is devoted to the problem of the validity of the reciprocity
theorem in high-temperature superconductors (HTSC). The violation of the
reciprocity theorem in zero external magnetic fields has been studied.
Experimental data obtained for two different superconducting materials:
BiSrCaCuO and YBaCuO are presented. Results show that the basic form of the
reciprocity theorem (without consideration of any additional anisotropy) is not
valid near the critical temperature. We assume that the reciprocity theorem
breaking is connected with the existence of an extraordinary transverse
electric field originated from additional anisotropy and more general form of
the reciprocity relations should be valid. However, the origin of this
anisotropy is not clear yet. We suggest that the vortex-antivortex dynamics
model taking into account vortex guiding can be responsible for the observed
effect. Also the explanation based on weak P and T symmetry breaking in HTSC
which is supported by the observation of the spontaneous magnetisation can not
be excluded.",0211233v1
2002-11-23,Binder Parameter of a Heisenberg Spin-Glass Model in Four Dimensions,"We studied the phase transition of the $\pm J$ Heisenberg model with and
without a random anisotropy on four dimensional lattice $L\times L\times
L\times (L+1)$ $(L\leq 9)$. We showed that the Binder parameters $g(L,T)$'s for
different sizes do not cross even when the anisotropy is present. On the
contrary, when a strong anisotropy exists, $g(L,T)$ exhibits a steep negative
dip near the spin-glass phase transition temperature $T_{\rm SG}$ similarly to
the $p-$state infinite-range Potts glass model with $p \geq 3$, in which the
one-step replica-symmetry-breaking (RSB) occurs. We speculated that a one-step
RSB-like state occurs below $T_{\rm SG}$, which breaks the usual crossing
behavior of $g(L,T)$.",0211521v1
2002-12-02,Anisotropic Optic Conductivities due to Spin and Orbital Orderings in LaVO3 and YVO3: First-Principles Studies,"The anisotropy of low energy (0$\sim$5eV) optical excitations in strongly
correlated transition-metal oxides is closely related to the spin and orbital
orderings. The recent successes of LDA+$U$ method in describing the magnetic
and electronic structures enable us to calculate the optical conductivity from
first-principles. The LaVO$_3$ and YVO$_3$, both of which have $3d^2$
configuration and have various spin and orbital ordered phases at low
temperature, show distinct anisotropy in the optical spectra. The effects of
spin and orbital ordering on the anisotropy are studied in detail based on our
first-principles calculations. The experimental spectra of both compounds at
low temperature phases can be qualitatively explained with our calculations,
while the studies for the intermediate temperature phase of YVO$_3$ suggest the
substantial persistence of the low temperature phase at elevated temperature.",0212024v1
2002-12-09,Fermi surface topology and the upper critical field in two-band superconductors - application to MgB2,"Recent measurements of the anisotropy of the upper critical field Bc2 on MgB2
single crystals have shown a puzzling strong temperature dependence. Here, we
present a calculation of the upper critical field based on a detailed modeling
of bandstructure calculations that takes into account both the unusual Fermi
surface topology and the two gap nature of the superconducting order parameter.
Our results show that the strong temperature dependence of the Bc2 anisotropy
can be understood as an interplay of the dominating gap on the sigma-band,
which possesses a small c-axis component of the Fermi velocity, with the
induced superconductivity on the pi-band possessing a large c-axis component of
the Fermi velocity. We provide analytic formulas for the anisotropy ratio at
T=0 and T=Tc and quantitatively predict the distortion of the vortex lattice
based on our calculations.",0212188v3
2002-12-10,Solution of mass/gap equations for strong velocity anisotropy in the QED3 theory of underdoped cuprates,"The low-lying excitations at the nodes of the d-wave gap in the normal state
for underdoped cuprates, close to the superconducting phase transition, may be
described by an effective QED3 theory. There are three characteristic
velocities: v_F, v_Delta and c. For v_Delta=v_F=c, the model reduces to
N-flavour QED3. Here, in the isotropic limit, for N<N_0c, a critical number of
fermions, a dynamical mass is generated which corresponds to the formation of a
spin density wave. We study the effects of strong velocity anisotropy (v_F \neq
v_\Delta) on dynamical mass generation. Solutions are given for the dynamical
mass at both N=2 and N=100, and so we show that the critical number of fermions
N_c>100. However, we argue that N_c=N_0c, when we go beyond the approximations
used to derive our mass gap equations. We expect, though, that our solution for
N=2 is roughly correct, at low momentum, for large enough anisotropies.
Implications and possible extensions to this work are also discussed.",0212204v2
2003-01-21,Ferromagnetic coupling and magnetic anisotropy in molecular Ni(II) squares,"We investigated the magnetic properties of two isostructural Ni(II) metal
complexes [Ni4Lb8] and [Ni4Lc8]. In each molecule the four Ni(II) centers form
almost perfect regular squares. Magnetic coupling and anisotropy of single
crystals were examined by magnetization measurements and in particular by
high-field torque magnetometry at low temperatures. The data were analyzed in
terms of an effective spin Hamiltonian appropriate for Ni(II) centers. For both
compounds, we found a weak intramolecular ferromagnetic coupling of the four
Ni(II) spins and sizable single-ion anisotropies of the easy-axis type. The
coupling strengths are roughly identical for both compounds, whereas the
zero-field-splitting parameters are significantly different. Possible reasons
for this observation are discussed.",0301373v1
2003-02-14,Anisotropy of heavy hole spin splitting and interference effects of optical polarization in semiconductor quantum wells subjected to an in-plane magnetic field,"Strong effects of optical polarization anisotropy observed previously in the
quantum wells subjected to the in-plane magnetic field arrive at complete
description within microscopic approach. Theory we develop involves two sources
of optical polarization. First source is due to correlations between electron
and heavy hole (HH) phases of $\psi $-functions arising due to electron Zeeman
spin splitting and joint manifestation of low-symmetry and Zeeman interactions
of HH in an in-plane magnetic field. In this case, four possible
phase-controlled electron-HH transitions constitute the polarization effect,
which can reach its maximal amount ($\pm $1) at low temperatures when only one
transition survives. Other polarization source stems from the admixture of
excited light-holes (LH) states to HH by low-symmetry interactions. The
contribution of this mechanism to total polarization is relatively small but it
can be independent of temperature and magnetic field. Analysis of different
mechanisms of HH splitting exhibits their strong polarization anisotropy. Joint
action of these mechanisms can result in new peculiarities, which should be
taken into account for explanation of different experimental situations.",0302301v2
2003-03-06,Strong 3D correlations in vortex system of Bi2212:Pb,"The experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO)
reveals remarkable field penetration pattern alteration (flux configuration
change) and superconducting current anisotropy enhancement by the in-plane
field. The anisotropy increases with the temperature rise up to $T_m = 54 \pm 2
K$. At $T = T_m$ an abrupt change in the flux behavior is found; the
correlation between the in-plane magnetic field and the out-of-plane magnetic
flux penetration disappears. No correlation is observed for $T > T_m$. The
transition temperature $T_m$ does not depend on the magnetic field strength.
The observed flux penetration anisotropy is considered as an evidence of a
strong 3D - correlation between pancake vortices in different CuO planes at $T
< T_m$. This enables understanding of a remarkable pinning observed in
Bi2212:Pb at low temperatures.",0303103v1
2003-03-12,Upper critical field in dirty two-band superconductors: breakdown of the anisotropic Ginzburg-Landau theory,"We investigate the upper critical field in a dirty two-band superconductor
within quasiclassical Usadel equations. The regime of very high anisotropy in
the quasi-2D band, relevant for MgB$_{2}$, is considered. We show that strong
disparities in pairing interactions and diffusion constant anisotropies for two
bands influence the in-plane $H_{c2}$ in a different way at high and low
temperatures. This causes temperature-dependent $H_{c2}$ anisotropy, in
accordance with recent experimental data in MgB$_{2}$. The three-dimensional
band most strongly influences the in-plane $H_{c2}$ near $T_{c}$, in the
Ginzburg-Landau (GL) region. However, due to a very large difference between
the c-axis coherence lengths in the two bands, the GL theory is applicable only
in an extremely narrow temperature range near $T_c$. The angular dependence of
$H_{c2}$ deviates from a simple effective-mass law even near $T_c$.",0303237v1
2003-03-26,Frozen Quasi Long Range Order in Random Anisotropy Heisenberg Magnet,"Extensive Monte Carlo simulations are used to investigate the low-temperature
properties of the random anisotropy Heisenberg model, which describes the
magnetic behavior of amorphous rare-earth-transition metal alloy. We show that
the low-temperature phase in weak-anisotropy region is characterized by a {\it
frozen-in} power-law spin-spin correlation. Numerical observation of the
power-law exponent $\eta$ indicates nonuniversal behavior.",0303552v4
2003-04-01,Study of the influence of surface anisotropy and lattice structure on the behaviour of a small magnetic cluster,"We have studied by Monte Carlo simulations the thermal behaviour of a small
(N=13 particles) cluster described by a Heisenberg model, including
nearest-neighbour ferromagnetic interactions and radial surface anisotropy, in
an applied magnetic field. We have studied three different lattice structures:
hexagonal close packed, face centered cubic and icosahedral. We show that the
zero-field thermal behaviour depends not only on the value of the anisotropy
constant but also on the lattice structure. The behaviour in an applied field,
additionally depends, on the different orientations of the field with respect
to the crystal axes. According to these relative orientations, hysteresis
cycles show different step-like characteristics.",0304015v2
2003-05-26,Macroturbulent Instability of the Flux Line Lattice in Anisotropic Superconductors,"A theory of the macroturbulent instability in the system containing vortices
of opposite directions (vortices and antivortices) in hard superconductors is
proposed. The origin of the instability is connected with the anisotropy of the
current capability in the sample plane. The anisotropy results in the
appearance of tangential discontinuity of the hydrodynamic velocity of vortex
and antivortex motion near the front of magnetization reversal. As is known
from the classical hydrodynamics of viscous fluids, this leads to the
turbulization of flow. The examination is performed on the basis of the
anisotropic power-law current-voltage characteristics. The dispersion equation
for the dependence of the instability increment on the wave number of
perturbation is obtained, solved, and analyzed analytically and numerically. It
is shown that the instability can be observed even at relatively weak
anisotropy.",0305589v1
2003-05-29,Influence of spin structures and nesting on Fermi surface and a pseudogap anisotropy in t-t'-U Hubbard model,"Influence of two type of spin structures on the form of the Fermi surface
(FS) and a photoemission intensity map is studied for t-t'-U Hubbard model.
Mean field calculations are done for the stripe phase and for the spiral spin
structure. It is shown, that unlike a case of electron doping, the hole-doped
models are unstable with respect to formation of such structures. The pseudogap
anisotropies are different for h- and e- doping. In accordance with ARPES data
for La2SrxCuO4 the stripe phase is characterized by quasi-one-dimensional
segments of FS at k=(\pi,0) and by suppression of spectral weight in diagonal
direction. It is shown that spiral structures display the polarisation
anisotropy: different segments of FS correspond to electros with different spin
polarisations.",0305685v1
2003-06-19,Spatial anisotropy of the exciton level in CaF$_2$ at 11.1 eV and its relation to the weak optical anisotropy at 157 nm,"The energy level of the exciton around the $\Gamma$ point in CaF$_2$ at about
11.1 eV was investigated by reflection measurements on oriented surfaces using
dispersed synchrotron radiation. A small but clear energy shift of the exciton
resonance structure was observed which depends on the crystal orientation with
respect to the incoming beam. By interpreting the results in terms of the
complex dielectric function it becomes possible to determin the respective
exciton levels and lifetimes. For crystal samples oriented in the (111)
direction, the exciton has an excitation energy 0.02 eV above the energy of
samples oriented in the (100) direction. The results obtained suggest that the
exciton-energy shift is related to the spatial anisotropy recently measured in
CaF$_2$ at 157 nm.",0306510v1
2003-07-18,Thermodynamics of Electrolytes on Anisotropic Lattices,"The phase behavior of ionic fluids on simple cubic and tetragonal
(anisotropic) lattices has been studied by grand canonical Monte Carlo
simulations. Systems with both the true lattice Coulombic potential and
continuous-space $1/r$ electrostatic interactions have been investigated. At
all degrees of anisotropy, only coexistence between a disordered low-density
phase and an ordered high-density phase with the structure similar to ionic
crystal was found, in contrast to recent theoretical predictions. Tricritical
parameters were determined to be monotonously increasing functions of
anisotropy parameters which is consistent with theoretical calculations based
on the Debye-H\""uckel approach. At large anisotropies a two-dimensional-like
behavior is observed, from which we estimated the dimensionless tricritical
temperature and density for the two-dimensional square lattice electrolyte to
be $T^*_{tri}=0.14$ and $\rho^*_{tri} = 0.70$.",0307472v1
2003-08-26,Anisotropy in the Antiferromagnetic Spin Fluctuations of Sr2RuO4,"It has been proposed that Sr_2RuO_4 exhibits spin triplet superconductivity
mediated by ferromagnetic fluctuations. So far neutron scattering experiments
have failed to detect any clear evidence of ferromagnetic spin fluctuations
but, instead, this type of experiments has been successful in confirming the
existence of incommensurate spin fluctuations near q=(1/3 1/3 0). For this
reason there have been many efforts to associate the contributions of such
incommensurate fluctuations to the mechanism of its superconductivity. Our
unpolarized inelastic neutron scattering measurements revealed that these
incommensurate spin fluctuations possess c-axis anisotropy with an anisotropic
factor \chi''_{c}/\chi''_{a,b} of \sim 2.8. This result is consistent with some
theoretical ideas that the incommensurate spin fluctuations with a c-axis
anisotropy can be a origin of p-wave superconductivity of this material.",0308521v2
2003-09-12,Anisotropy of exchange stiffness and its effect on the properties of magnets,"Using the spin-spiral formulation of the tight-binding linear muffin-tin
orbital method, the principal components of the exchange stiffness tensor are
calculated for typical hard magnets including tetragonal CoPt-type and
hexagonal YCo5 alloys. The exchange stiffness is strongly anisotropic in all
studied alloys. This anisotropy makes the domain wall surface tension
anisotropic. Competition between this anisotropic surface tension and
magnetostatic energy controls the formation and dynamics of nanoscale domain
structures in hard magnets. Anisotropic domain wall bending is described in
detail from the general point of view and with application to cellular Sm-Co
magnets. It is shown that the repulsive cell-boundary pinning mechanism in
these magnets is feasible only due to the anisotropic exchange stiffness if
suitably oriented initial pinning centers are available. In polytwinned
CoPt-type magnets the exchange stiffness anisotropy controls the orientation of
macrodomain wall segments. These segments may reorient both statically during
microstructural coarsening and dynamically during the macrodomain wall
splitting in external field. Reorientation of segments may facilitate their
pinning at antiphase boundaries.",0309321v1
2003-11-19,New Anisotropic Behavior of Quantum Hall Resistance in (110) GaAs Heterostructures at mK Temperatures and Fractional Filling Factors,"Transport experiments in high mobility (110) GaAs heterostructures have been
performed at very low temperatures 8 mK. At higher Landau-Levels we observe a
transport anisotropy that bears some similarity with what is already seen at
half-odd-integer filling on (001) oriented substrates. In addition we report
the first observation of transport anisotropies within the lowest Landau-Level.
This remarkable new anisotropy is independent of the current direction and
depends on the polarity of the magnetic field.",0311454v2
2003-12-10,Second-order transverse magnetic anisotropy induced by disorders in the single-molecule magnet Mn12,"For the single-molecule magnet Mn12, Cornia et al. recently proposed that
solvent molecules may cause the quantum tunneling that requires a lower
symmetry than S4. However, magnetic quantum tunneling and electron paramagnetic
resonance experiments suggested that the proposed theory may not correspond to
the measurements. In this regard, we consider positional disorder induced by
the solvent molecules and orientational disorder by the methyl groups of a Mn12
molecule. We calculate, within density-functional theory, the second-order
transverse magnetic anisotropy parameter E and an easy-axis tilting angle
induced by the positional disorder and the E value by the orientational
disorder. We also calculate the local magnetic anisotropy and the local easy
axis for each inequivalent Mn site in different environments to investigate
their effects on the global E value. We find that the hydrogen bonding between
a Mn12 molecule and the solvent molecule is crucial to obtain a substantial E
value and that the E value increases upon geometry relaxations. Our
calculations on relaxed geometries show that the largest calculated E value is
0.016 K and that the largest tilting angle is 0.5 degrees. Our largest E value
is comparable to experimental results but larger than Cornia et al.'s.",0312261v1
2003-12-19,Magnetisation switching in a ferromagnetic Heisenberg nanoparticle with uniaxial anisotropy: A Monte Carlo investigation,"We investigate the thermal activated magnetisation reversal in a single
ferromagnetic nanoparticle with uniaxial anisotropy using Monte Carlo
simulations. The aim of this work is to reproduce the reversal magnetisation by
uniform rotation at very low temperature in the high energy barrier hypothesis,
that is to realize the N\'eel-Brown model. For this purpose we have considered
a simple cubic nanoparticle where each site is occupied by a classical
Heisenberg spin. The Hamiltonian is the sum of an exchange interaction term, a
single-ion anisotropy term and a Zeeman interaction term. Our numerical data of
the thermal variation of the switching field are compared to an approximated
expression and previous experimental results on Co nanoparticles.",0312536v1
2004-04-03,Macroscopic Quantum Tunneling in Small Antiferromagnetic Particles: Effects of a Strong Magnetic Field,"We consider an effect of a strong magnetic field on the ground state and
macroscopic coherent tunneling in small antiferromagnetic particles with
uniaxial and biaxial single-ion anisotropy. We find several tunneling regimes
that depend on the direction of the magnetic field with respect to the
anisotropy axes. For the case of a purely uniaxial symmetry and the field
directed along the easy axis, an exact instanton solution with two different
scales in imaginary time is constructed. For a rhombic anisotropy the effect of
the field strongly depends on its orientation: with the field increasing, the
tunneling rate increases or decreases for the field parallel to the easy or
medium axis, respectively. The analytical results are complemented by numerical
simulations.",0404069v2
2004-04-14,"Exchange interactions and magnetic anisotropy in the ""Ni_4"" magnetic molecule","Magnetic properties of a tetrahedral ""Ni_4"" molecule are discussed in terms
of the Heisenberg model, with magnetic anisotropy terms included, and on the
basis of first-principle calculations within the density functional theory. It
is shown that the isotropic Heisenberg model does not provide an adequate
description of magnetization at low temperatures; an inclusion of single-site
anisotropy terms does not help to improve the situation either. We suppose that
the magnetostriction of the molecule and hence the dependence of interatomic
coupling parameters on the magnetization might be important for an adequate
description of magnetic properties. The first-principle calculations confirm
the system's general preference for antiferromagnetic coupling, as well as the
failure of the isotropic Heisenberg model. A conjugated-gradient search for the
relaxed structure of the ""Ni_4"" molecule in ferromagnetic and antiferromagnetic
configurations did not show any clear tendency to diversification of
interatomic distances. These calculations however have not yet included the
spin-orbit coupling, which can be essential for analyzing the effects of
magnetostriction.",0404343v1
2004-06-11,Role of surface anisotropy for magnetic impurities in electron dephasing and energy relaxation and their size effect,"Recently the electron dephasing and energy relaxation due to different
magnetic impurities have been extensively investigated experimentally in thin
wires and in this Letter these quantities are theoretically studied. It was
shown earlier that a magnetic impurity in a metallic host with strong
spin-orbit interaction experiences a surface anisotropy of the form $H=K_d
({\bf n}{\bf S})^2$ which causes size effects for impurities with integer spin.
Here we show that the dephasing and the energy relaxation are influenced by the
surface anisotropy in very different ways for integer spin having a singlet
ground state. That must result also in strong size effects and may resolve the
puzzle between the concentrations estimated from the two kind of experiments.",0406277v3
2004-07-20,The interplay between screening properties and colloid anisotropy: towards a reliable pair potential for disc-like charged particles,"The electrostatic potential of a highly charged disc (clay platelet) in an
electrolyte is investigated in detail. The corresponding non-linear
Poisson-Boltzmann (PB) equation is solved numerically, and we show that the
far-field behaviour (relevant for colloidal interactions in dilute suspensions)
is exactly that obtained within linearized PB theory, with the surface boundary
condition of a uniform potential. The latter linear problem is solved by a new
semi-analytical procedure and both the potential amplitude (quantified by an
effective charge) and potential anisotropy coincide closely within PB and
linearized PB, provided the disc bare charge is high enough. This anisotropy
remains at all scales; it is encoded in a function that may vary over several
orders of magnitude depending on the azimuthal angle under which the disc is
seen. The results allow to construct a pair potential for discs interaction,
that is strongly orientation dependent.",0407521v1
2004-07-29,Temperature dependent magnetic anisotropy in metallic magnets from an ab-initio electronic structure theory: L1_0-ordered FePt,"On the basis of a first-principles, relativistic electronic structure theory
of finite temperature metallic magnetism, we investigate the variation of
magnetic anisotropy, K, with magnetisation, M, in metallic ferromagnets. We
apply the theory to the high magnetic anisotropy material, L1_0-ordered FePt,
and find its uniaxial K consistent with a magnetic easy axis perpendicular to
the Fe/Pt layering for all M and to be proportional to M^2 for a broad range of
values of M. For small M, near the Curie temperature, the calculations pick out
the easy axis for the onset of magnetic order. Our results are in good
agreement with recent experimental measurements on this important magnetic
material.",0407774v1
2004-08-02,Ab initio study of reflectance anisotropy spectra of a sub-monolayer oxidized Si(100) surface,"The effects of oxygen adsorption on the reflectance anisotropy spectrum (RAS)
of reconstructed Si(100):O surfaces at sub-monolayer coverage (first stages of
oxidation) have been studied by an ab initio DFT-LDA scheme within a
plane-wave, norm-conserving pseudopotential approach. Dangling bonds and the
main features of the characteristic RAS of the clean Si(100) surface are mostly
preserved after oxidation of 50% of the surface dimers, with some visible
changes: a small red shift of the first peak, and the appearance of a distinct
spectral structure at about 1.5 eV. The electronic transitions involved in the
latter have been analyzed through state-by-state and layer-by-layer
decompositions of the RAS. We suggest that new interplay between present
theoretical results and reflectance anisotropy spectroscopy experiments could
lead to further clarification of structural and kinetic details of the Si(100)
oxidation process in the sub-monolayer range.",0408028v2
2004-08-30,Anisotropy-driven transition from collisionless to collisional regime in the dipolar modes of a trapped gaseous mixture,"We evaluate the dipolar oscillations of a harmonically trapped fermion gas
containing thermal bosonic impurities as a function of the anisotropy of the
trap, from the numerical solution of the Vlasov-Landau equations for the
one-body phase-space distribution functions. Starting from a situation in which
the two components of the gaseous mixture perform almost independent
oscillations inside a spherical trap, we demonstrate that different collision
behaviors arise for oscillations in different directions as the trap is
deformed into an elongated cigar-like shape. An increase in the anisotropy of
the confinement thus suffices to drive a transition of dipolar modes from a
collisionless to a collisional regime.",0408654v2
2004-09-02,Spin-orbit coupling and anisotropy of spin splitting in quantum dots,"In lateral quantum dots, the combined effect of both Dresselhaus and
Bychkov-Rashba spin orbit coupling is equivalent to an effective magnetic field
B_so which has the opposite sign for s_z=1/2 spin electrons. When the external
magnetic field is perpendicular to the planar structure, the field B_so
generates an additional splitting for electron states as compared to the spin
splitting in the in-plane field orientation. The anisotropy of spin splitting
has been measured and then analyzed in terms of spin-orbit coupling in several
AlGaAs/GaAs quantum dots by means of resonanat tunneling spectroscopy. From the
measured values and sign of the anisotropy we are able to determine the
dominating spin-orbit coupling mechanism.",0409054v1
2004-09-08,Incommensurate Transverse Anisotropy Induced by Disorder and Spin-Orbit-Vibron Coupling in Mn12-acetate,"It has been shown within density-functional theory that in Mn$_{12}$-acetate
there are effects due to disorder by solvent molecules and a coupling between
vibrational and electronic degrees of freedom. We calculate the in-plane
principal axes of the second-order anisotropy caused by the second effect and
compare them with those of the fourth-order anisotropy due to the first effect.
We find that the two types of the principal axes are not commensurate with each
other, which results in a complete quenching of the tunnel-splitting
oscillation as a function of an applied transverse field.",0409206v1
2004-10-21,"In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films","We show, by SQUID magnetometry, that in (Ga,Mn)As films the in-plane uniaxial
magnetic easy axis is consistently associated with particular crystallographic
directions and that it can be rotated from the [-110] direction to the [110]
direction by low temperature annealing. We show that this behavior is
hole-density-dependent and does not originate from surface anisotropy. The
presence of uniaxial anisotropy as well its dependence on the
hole-concentration and temperature can be explained in terms of the p-d Zener
model of the ferromagnetism assuming a small trigonal distortion.",0410544v1
2004-12-20,Quasiclassical Theory for Thermodynamic Properties of the Two-Band Superconductor MgB$_2$ under Magnetic Fields,"Consistent account is provided of strongly anisotropic properties in
thermodynamics of MgB$_2$ under magnetic field $H$ using approximate analytic
solution in the quasiclassical formalism. With the strength of the pairing
interactions and the Fermi velocities of two bands as fitting parameters, it is
possible to reproduce in wide regions of the phase diagram the $H$- and
temperature dependences of relevant quantities such as the zero-energy density
of states (ZEDOS), two energy gaps, the specific heat and the $H_{c2}$
anisotropy. It is demonstrated that the velocity ratio of two bands affects
considerably the low-field behavior of the ZEDOS and energy gaps. The ratio
also affects the high-temperature behavior of the $H_{c2}$ anisotropy. The
anisotropy of the coherence length in the $\sigma$ band depends weakly on $H$
and $T$, whereas the coherence length in the $\pi$ band remains isotropic even
in the presence of the inter-band coupling.",0412522v2
2005-01-04,Anisotropy of spin splitting and spin relaxation in lateral quantum dots,"Inelastic spin relaxation and spin splitting $\epsilon_{\mathrm{s}}$ in
lateral quantum dots are studied in the regime of strong in-plane magnetic
field. Due to both g-factor energy dependence and spin-orbit coupling
$\epsilon_{\mathrm{s}}$ demonstrates a substantial non-linear magnetic field
dependence similar to that observed by R.Hanson \textit{et al} [Phys. Rev.
Lett. \textbf{91}, 196802 (2003)]. It also varies with the in-plane orientation
of magnetic field due to crystalline anisotropy of spin-orbit coupling. Spin
relaxation rate is also anisotropic, the anisotropy increasing with the field.
When the magnetic length is less than the 'thickness' of GaAs dot, the
relaxation can be order of magnitude faster for $\mathbf{B}% \Vert\lbrack100]$
than for $\mathbf{B\Vert}[110]$.",0501046v1
2005-04-27,The effect of stripe domain structure on dynamic permeability of thin ferromagnetic films with out-of-plane uniaxial anisotropy,"The permeability is calculated for a thin ferromagnetic film with the stripe
domain structure and out-of-plane uniaxial magnetic anisotropy. Analytical
expressions for the frequency dependence of components of permeability tensor
are derived with the use of the Smit-Beljers method, with the thickness of
domain walls and the domain wall motion being neglected. The effect of the
domain width and the angle between the anisotropy axis and the film plane on
the frequency dependence of the permeability is analyzed. General equations
relating the static permeability components and the ferromagnetic resonance
frequencies are found. The results of the approach are applied to the
derivation of the constraint for the microwave permeability of thin
ferromagnetic films. The analysis of the constraint as a function of the axis
deviation angle, the domain aspect ratio and the damping parameter allows the
conditions to be found for maximal microwave permeability. The results obtained
may be useful in connection with the problem of developing high-permeable
microwave magnetic materials.",0504710v1
2005-05-06,Cascade of two-dimensional Fulde-Ferrell-Larkin-Ovchinnikov phases with anisotropy,"For an isotropic two-dimensional system, when the temperature is lowered
toward T=0, it has been found recently that, for the transition from the normal
to the superfluid state in the paramagnetic limit, the order parameter
describing the Fulde-Ferrell-Larkin-Ovchinnikov phase has an increasingly
complex structure with contributions from an increasing number of wavevectors.
This cascade of phase transitions is directly linked to the fact that, due to
the rotational invariance, all the wavevectors directions which can enter the
order parameter are degenerate. We study how this cascade of phase transitions
is modified when one takes into account the anisotropy arising in a real solid
state compound. For a simple model of anisotropy with elliptical dispersion
relation, we find surprisingly that the cascade of phase transitions is not
modified and the degeneracy with respect to the wavevector direction is still
present. When we take into account a deviation with respect to this elliptical
model, which is treated to first order in perturbation, we find that the
degeneracy is lifted and that, basically, a single wavevector is favored right
at the transition. However when one enters the superfluid phase, additional
wavevectors come in the order parameter and the cascade of transitions is still
present, though in a modified form.",0505155v1
2005-05-07,Polyconvex Model for Materials with Cubic Anisotropy,"Polyconvexity is one of the known conditions which guarantee existence of
solutions of boundary value problems in finite elasticity. In this work we
propose a framework for development of polyconvex strain energy functions for
hyperelastic materials with cubic anisotropy. The anisotropy is captured by a
single fourth order structural tensor for which the minimal polynomial basis is
identified and used for the formulation of the strain energy functions. After
proving the polyconvexity of some polynomial terms, we proceed to propose a
model based on a simple strain energy function. We investigate the behavior of
the model analytically in one dimension and numerically in two and three
dimensions. These investigations allow us conclude that the model possesses the
physically relevant directional properties, in particular, strains in different
directions are different and the lack of any loading symmetries leads to
development of ``shear'' stresses and displacements.",0505178v1
2005-05-08,Quantum analogue of the spin-flop transition for a spin pair,"Quantum (step-like) magnetization curves are studies for a spin pair with
antiferromagnetic coupling in the presence of a magnetic field parallel to the
easy axis of the magnetic anisotropy. The consideration is done both
analytically and numerically for a wide range of the anisotropy constants and
spins up to $S \gtrsim 100$. Depending on the origin of the anisotropy
(exchange or single-ion), the magnetization curve can demonstrate the jumps
more than unity and the concentration of the unit jumps in a narrow range of
the field. We also point the region of the problem parameters, where the
behavior is quasiclassical for $S = 5$, and where system is substantially
quantum in the limit $S \to \infty$.",0505188v1
2005-05-10,Interplay between magnetic anisotropy and interlayer coupling in nanosecond magnetization reversal of spin-valve trilayers,"The influence of magnetic anisotropy on nanosecond magnetization reversal in
coupled FeNi/Cu/Co trilayers was studied using a photoelectron emission
microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic
samples the reversal of the soft FeNi layer is determined by domain wall
pinning that leads to the formation of small and irregular domains. In samples
with uniaxial magnetic anisotropy, the domains are larger and the influence of
local interlayer coupling dominates the domain structure and the reversal of
the FeNi layer.",0505240v1
2005-05-26,Exact results of a mixed spin-1/2 and spin-S Ising model on a bathroom tile (4-8) lattice: effect of uniaxial single-ion anisotropy,"Effect of uniaxial single-ion anisotropy upon magnetic properties of a mixed
spin-1/2 and spin-S (S>=1) Ising model on a bathroom tile (4-8) lattice is
examined within the framework of an exact star-triangle mapping transformation.
The particular attention is focused on the phase diagrams established for
several values of the quantum spin number S. It is shown that the mixed-spin
bathroom tile lattice exhibits very similar phase boundaries as the mixed-spin
honeycomb lattice whose critical points are merely slightly enhanced with
respect to the former ones. The influence of uniaxial single-ion anisotropy
upon the total magnetization vs. temperature dependence is particularly
investigated as well.",0505638v2
2005-06-23,Theory of Anisotropic Hopping Transport due to Spiral Correlations in the Spin-Glass Phase of Underdoped Cuprates,"We study the in-plane resistivity anisotropy in the spin-glass phase of the
high-$T_{c}$ cuprates, on the basis of holes moving in a spiral spin
background. This picture follows from analysis of the extended $t-J$ model with
Coulomb impurities. In the variable-range hopping regime the resistivity
anisotropy is found to have a maximum value of around 90%, and it decreases
with temperature, in excellent agreement with experiments in
La$_{2-x}$Sr$_x$CuO$_4$. In our approach the transport anisotropy is due to the
non-collinearity of the spiral spin state, rather than an intrinsic tendency of
the charges to self-organize.",0506604v3
2005-07-05,Effect of second-rank random anisotropy on critical phenomena of random field O(N) spin model in the large N limit,"We study the critical behavior of a random field O($N$) spin model with a
second-rank random anisotropy term in spatial dimensions $4<d<6$, by means of
the replica method and the 1/N expansion. We obtain a replica-symmetric
solution of the saddle-point equation, and we find the phase transition obeying
dimensional reduction. We study the stability of the replica-symmetric saddle
point against the fluctuation induced by the second-rank random anisotropy. We
show that the eigenvalue of the Hessian at the replica-symmetric saddle point
is strictly positive. Therefore, this saddle point is stable and the
dimensional reduction holds in the 1/N expansion. To check the consistency with
the functional renormalization group method, we obtain all fixed points of the
renormalization group in the large $N$ limit and discuss their stability. We
find that the analytic fixed point yielding the dimensional reduction is
practically singly unstable in a coupling constant space of the given model
with large $N$. Thus, we conclude that the dimensional reduction holds for
sufficiently large $N$.",0507096v2
2005-07-11,Critical slowing down in random anisotropy magnets,"We study the purely relaxational critical dynamics with non-conserved order
parameter (model A critical dynamics) for three-dimensional magnets with
disorder in a form of the random anisotropy axis. For the random axis
anisotropic distribution, the static asymptotic critical behaviour coincides
with that of random site Ising systems. Therefore the asymptotic critical
dynamics is governed by the dynamical exponent of the random Ising model.
However, the disorder influences considerably the dynamical behaviour in the
non-asymptotic regime. We perform a field-theoretical renormalization group
analysis within the minimal subtraction scheme in two-loop approximation to
investigate asymptotic and effective critical dynamics of random anisotropy
systems. The results demonstrate the non-monotonic behaviour of the dynamical
effective critical exponent $z_{\rm eff}$.",0507241v1
2005-07-20,All-optical probe of precessional magnetization dynamics in exchange biased NiFe/FeMn bilayers,"An internal anisotropy pulse field is launched by an 8.3 ps short laser
excitation, which triggers precessional magnetization dynamics of a
polycrystalline NiFe/FeMn exchange bias system on the picosecond timescale. Due
to the excitation the unidirectional anisotropy and, thus, the exchange
coupling across the interface between the ferromagnetic and the
antiferromagnetic layer is reduced, leading to a fast reduction of the exchange
bias field and to a dramatic increase of the zero-field susceptibility. The
fast optical unpinning is followed by a slower recovery of the interfacial
exchange coupling dominated by spin-lattice and heat flow relaxation with a
time constant of the order of 160 ps. The measured picosecond time evolution of
the exchange decoupling and restoration is interpreted as an anisotropy pulse
field giving rise to fast precessional magnetization dynamics of the
ferromagnetic layer. The strength of the internal pulse field and even the
initial magnetization deflection direction from the equilibrium orientation can
be controlled by the absorbed photons. The dependence of the effective Gilbert
damping on both small and large angle precessional motion was studied, yielding
that both cases can be modeled with reasonable accuracy within the
Landau-Lifshitz and Gilbert framework.",0507475v1
2005-09-01,Magnetic resonance study of the spin-reorientation transitions in the quasi-one-dimensional antiferromagnet BaCu2Si2O7,"A quasi-one dimensional antiferromagnet with a strong reduction of the
ordered spin component, BaCu2Si2O7, is studied by the magnetic resonance
technique in a wide field and frequency range. Besides of conventional
spin-flop transition at the magnetic field parallel to the easy axis of spin
ordering, magnetic resonance spectra indicate additional spin-reorientation
transitions in all three principal orientations of magnetic field. At these
additional transitions the spins rotate in the plane perpendicular to the
magnetic field keeping the mutual arrangement of ordered spin components. The
observed magnetic resonance spectra and spin-reorientation phase transitions
are quantitatively described by a model including the anisotropy of transverse
susceptibility with respect to the order parameter orientation. The anisotropy
of the transverse susceptibility and the strong reduction of the anisotropy
energy due to the quantum spin fluctuations are proposed to be the reason of
the spin reorientations which are observed.",0509015v1
2005-09-27,Charge-stripe phases versus a weak anisotropy of nearest-neighbor hopping,"Recently, we demonstrated rigorously the stability of charge-stripe phases in
quantum-particle systems that are described by extended Falicov-Kimball
Hamiltonians, with the quantum hopping particles being either spinless fermions
or hardcore bosons. In this paper, by means of the same methods, we show that
any anisotropy of nearest-neighbor hopping eliminates the $\pi/2$-rotation
degeneracy of the so called dimeric and axial-stripe phases and orients them in
the direction of a weaker hopping. Moreover, due to the same anisotropy the
obtained phase diagrams of fermions show a tendency to become similar to those
of hardcore bosons.",0509698v2
2005-10-13,Spin gaps and magnetic structure of NaxCoO2,"We present two experiments that provide information on spin anisotropy and
the magnetic structure of NaxCoO2. First, we report low-energy neutron
inelastic scattering measurements of the zone-center magnetic excitations in
the magnetically ordered phase of Na0.75CoO2. The energy spectra suggest the
existence of two gaps, and are very well fitted by a spin-wave model with both
in-plane and out-of-plane anisotropy terms. The gap energies decrease with
increasing temperature and both gaps are found to have closed when the
temperature exceeds the magnetic ordering temperature T_m~22 K. Secondly, we
present neutron diffraction studies of Na0.85CoO2 with a magnetic field applied
approximately parallel to the c axis. For fields in excess of ~8T a magnetic
Bragg peak was observed at the (0,0,3) position in reciprocal space. We
interpret this as a spin-flop transition of the A-type antiferromagnetic
structure, and we show that the spin-flop field is consistent with the size of
the anisotropy gap.",0510360v1
2005-11-16,Monte Carlo simulations of ${\rm Ni Fe_2O_4}$ Nanoparticles,"We use Monte Carlo simulations to study ${\rm Ni Fe_2O_4}$ nanoparticles.
Finite size and surface effects differentiate them from their bulk
counterparts. A continuous version of the Wang-Landau algorithm is used to
calculate the joint density of states $g(M_z, E)$ efficiently. From $g(M_z,
E)$, we obtain the Bragg-Williams free energy of the particle, and other
physical quantities. The hysteresis is observed when the nanoparticles have
both surface disorder and surface anisotropy. We found that the finite
coercivity is the result of interplay between surface disorder and surface
anisotropy. If the surface disorder is absent or the surface anisotropy is
relatively weak, the nanoparticles often exhibit superparamagnetism.",0511410v1
2005-11-19,Measurement of spin waves and activation volumes in superparamagnetic Fe films on GaAs(100),"Spin wave frequencies are observed in ultra-thin Fe/GaAs(100) films at
temperatures where the spontaneous zero field magnetization is zero. The films
exhibit good cyrstalline structure, and the effect of magnetic anisotropies is
apparent even though no zero field spin wave energy gap exists. An analysis is
given in terms of a superparamagnetic model in which the film is treated as a
network of non-interacting single domain magnetic islands. A spin wave analysis
provides a means to separate measured values of anisotropy parameters from
products involving anisotropy and island volume. In this way, a measure of the
activation volume associated with superparamagnetic islands is obtained for
different Fe film thicknesses. Results suggest that the island lateral area
increases with increasing film thickness.",0511482v1
2005-11-28,Basal-Plane Magnetic Anisotropies of High-kappa d-Wave Superconductors in a Mixed State: A Quasiclassical Approach,"We study the basal-plane anisotropies of reversible magnetization and torque
in a mixed state of layered d-wave superconductors based on the quasiclassical
version of the BCS-Gor'kov theory. Both the longitudinal magnetization ($M_L$)
and torque ($\tau$) show fourfold oscillations as a function of the field angle
$\chi$. The relationship between the node position and the oscillatory patterns
shown by $M_L$ and $\tau$ is clarified. It is also shown that the sign of the
$\tau (\chi)$-oscillation does not change between $H_{c1}$ and $H_{c2}$, while
the sign of the $M_L (\chi)$-oscillation changes. The newly obtained result for
$\tau$ indicates that the torque experiment can allow us to detect the in-plane
anisotropies of $H_{c2}$ even in a material with strong fluctuations such as
cuprate or organic superconductors, where the $H_{c2}$ itself cannot be
determined experimentally.",0511644v2
2005-12-18,Theory of the algebraic vortex liquid in an anisotropic spin-1/2 triangular antiferromagnet,"We explore spin-1/2 triangular antiferromagnets with both easy-plane and
lattice exchange anisotropies by employing a dual vortex mapping followed by a
fermionization of the vortices. Over a broad range of exchange anisotropy, this
approach leads naturally to a ``critical'' spin liquid--the algebraic vortex
liquid--which appears to be distinct from other known spin liquids. We present
a detailed characterization of this state, which is described in terms of
non-compact QED3 with an emergent SU(4) symmetry. Descendant phases of the
algebraic vortex liquid are also explored, which include the Kalmeyer-Laughlin
spin liquid, a variety of magnetically ordered states such as the well known
coplanar spiral state, and supersolids. In the range of exchange anisotropy
where the ``square lattice'' Neel ground state arises, we demonstrate that
anomalous ``roton'' minima in the excitation spectrum recently reported in
series expansions can be accounted for within our approach.",0512427v1
2006-01-03,In-plane anisotropy of spin excitations in the normal and superconducting states of underdoped YBa$_2$Cu$_3$O$_{6+x}$,"A detailed inelastic neutron scattering study of the in-plane anisotropy of
magnetic excitations in twin-free YBa$_2$Cu$_3$O$_{6.6}$ ($T_c =$ 61 K) reveals
that the spin excitation spectra in the superconducting and normal states are
qualitatively different. Below $T_c$, the spectrum consists of upward- and
downward-dispersing branches with modest in-plane anisotropy merging at an
energy $E_{res} =$ 37.5 meV. In the normal state, the singularity at $E_{res}$
disappears, and the spectrum exhibits a steep dispersion with a strongly
anisotropic in-plane geometry. These data have important implications for
models based on static or dynamic ""stripe"" order of spins and charges.",0601048v2
2006-01-12,Anomalous in-plane magneto-optical anisotropy of self-assembled quantum dots,"We report on a complex nontrivial behavior of the optical anisotropy of
quantum dots that is induced by a magnetic field in the plane of the sample. We
find that the optical axis either rotates in the opposite direction to that of
the magnetic field or remains fixed to a given crystalline direction. A
theoretical analysis based on the exciton pseudospin Hamiltonian unambiguously
demonstrates that these effects are induced by isotropic and anisotropic
contributions to the heavy-hole Zeeman term, respectively. The latter is shown
to be compensated by a built-in uniaxial anisotropy in a magnetic field B_c =
0.4 T, resulting in an optical response typical for symmetric quantum dots.",0601270v1
2006-02-07,Tunable dipolar magnetism in high-spin molecular clusters,"We report on the Fe17 high-spin molecular cluster and show that this system
is an exemplification of nanostructured dipolar magnetism. Each Fe17 molecule,
with spin S=35/2 and axial anisotropy as small as D=-0.02K, is the magnetic
unit that can be chemically arranged in different packing crystals whilst
preserving both spin ground-state and anisotropy. For every configuration,
molecular spins are correlated only by dipolar interactions. The ensuing
interplay between dipolar energy and anisotropy gives rise to macroscopic
behaviors ranging from superparamagnetism to long-range magnetic order at
temperatures below 1K.",0602184v2
2006-02-19,Origin of four-fold anisotropy in square lattices of circular ferromagnetic dots,"We discuss the four-fold anisotropy of in-plane ferromagnetic resonance (FMR)
field $H_r$, found in a square lattice of circular Permalloy dots when the
interdot distance $a$ gets comparable to the dot diameter $d$. The minimum
$H_r$, along the lattice $<11>$ axes, and the maximum, along the $<10>$ axes,
differ by $\sim$ 50 Oe at $a/d$ = 1.1. This anisotropy, not expected in
uniformly magnetized dots, is explained by a non-uniform magnetization
$\bm(\br)$ in a dot in response to dipolar forces in the patterned magnetic
structure. It is well described by an iterative solution of a continuous
variational procedure.",0602447v4
2006-03-01,Correlation functions for the $XY$ model in a Magnetic Field,"Recent studies of the two-dimensional, classical $XY$ magnet in a magnetic
field suggest that it has three distinct vortex phases: a linearly confined
phase, a logarithmically confined phase, and a free vortex phase. In this work
we study spin-spin correlation functions in this model by analytical analysis
and numerical simulations to search for signatures of the various phases. In
all three phases, the order parameter is nonzero and $<\cos(\th({\bf
r}_1))\cos(\th({\bf r}_2))>$ remains nonzero for $r \equiv |{\bf r}_1-{\bf
r}_2|\rightarrow \infty$, indicating the expected long range order. The
correlation function for transverse fluctuations of the spins,
$C(r)=<\sin(\th({\bf r}_1))\sin(\th({\bf r}_2))>$, falls exponentially in all
three phases. A renormalization group analysis suggests that the
logarithmically confined phase should have a spatially anisotropic correlation
length. In addition, there is a generic anisotropy in the prefactor which is
always present. We find that this prefactor anisotropy becomes rather strong in
the presence of a magnetic field, masking the effects of any anisotropy in the
correlation length in the simulations.",0603028v1
2006-03-14,The effect of uniaxial crystal-field anisotropy on magnetic properties of the superexchange antiferromagnetic Ising model,"The generalized Fisher super-exchange antiferromagnetic model with uniaxial
crystal-field anisotropy is exactly investigated using an extended mapping
technique. An exact relation between partition function of the studied system
and that one of the standard zero-field spin-1/2 Ising model on the
corresponding lattice is obtained applying the decoration-iteration
transformation. Consequently, exact results for all physical quantities are
derived for arbitrary spin values S of decorating atoms. Particular attention
is paid to the investigation of the effect of crystal-field anisotropy and
external longitudinal magnetic field on magnetic properties of the system under
investigation. The most interesting numerical results for ground-state and
finite-temperature phase diagrams, thermal dependences of the sublattice
magnetization and other thermodynamic quantities are discussed.",0603377v1
2006-03-31,Large magnetic anisotropy in Ferrihydrite nanoparticles synthesized from reverse micelles,"Six-line ferrihydrite(FH) nanoparticles have been synthesized in the core of
reverse micelles, used as nanoreactors to obtain average particle sizes $<d>$
$\approx$ 2 to 4 nm. The blocking temperatures $T_B^m$ extracted from
magnetization data increased from $\approx 10$ to 20 K for increasing particle
size. Low-temperature \MOS measurements allowed to observe the onset of
differentiated contributions from particle core and surface as the particle
size increases. The magnetic properties measured in the liquid state of the
original emulsion showed that the \FH phase is not present in the liquid
precursor, but precipitates in the micelle cores after the free water is
freeze-dried. Systematic susceptibility $\chi_{ac}(\emph{f},T)$ measurements
showed the dependence of the effective magnetic anisotropy energies $E_{a}$
with particle volume, and yielded an effective anisotropy value of $K_{eff} =
312\pm10$ kJ/m$^3$.",0603852v2
2006-05-04,Magnetic anisotropy of $Co_x Pt_{1-x}$ clusters embedded in matrix: Influences of the cluster chemical composition and the matrix nature,"We report on the magnetic properties of Co$\_x$Pt$\_{1-x}$ clusters embedded
in various matrices. Using a careful analysis of magnetization curves and ZFC
susceptibility measurements, we determine the clusters magnetic anisotropy
energy (MAE) and separate the surface and volume contributions. By comparing
different chemical compositions, we show that a small amount of Pt (15%)
induces an important increase in the volume anisotropy with respect to pure Co
clusters, even in chemically disordered fcc clusters. Comparing the
measurements of clusters embedded in Nb and MgO matrices, we show that the
oxide matrix induces an important increase of the surface MAE attributed to the
formation of an antiferromagnetic CoO shell around the clusters.",0605107v1
2006-06-21,Magnetic anisotropies and magnetization reversal of the Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al Heusler compound,"Magnetic anisotropies and magnetization reversal properties of the epitaxial
Heusler compound Co$_2$Cr$_{0.6}$Fe$_{0.4}$Al (CCFA) deposited on Fe and Cr
buffer layers are studied. Both samples exhibit a growth-induced fourfold
anisotropy, and magnetization reversal occurs through the formation of stripy
domains or 90 degree domains. During rotational magnetometric scans the sample
deposited on Cr exhibits about 2 degree sharp peaks in the angular dependence
of the coercive field, which are oriented along the hard axis directions. These
peaks are a consequence of the specific domain structure appearing in this
particular measurement geometry. A corresponding feature in the sample
deposited on Fe is not observed.",0606542v1
2006-07-03,Dramatic role of critical current anisotropy on flux avalanches in MgB2 films,"Anisotropic penetration of magnetic flux in MgB2 films grown on vicinal
sapphire substrates is investigated using magneto-optical imaging. Regular
penetration above 10 K proceeds more easily along the substrate surface steps,
anisotropy of the critical current being 6%. At lower temperatures the
penetration occurs via abrupt dendritic avalanches that preferentially
propagate {\em perpendicular} to the surface steps. This inverse anisotropy in
the penetration pattern becomes dramatic very close to 10 K where all flux
avalanches propagate in the strongest-pinning direction. The observed behavior
is fully explained using a thermomagnetic model of the dendritic instability.",0607063v1
2006-07-13,Spin-Reorientation Transition of Field-Induced Magnetic Ordering Phases in the Anisotropic Haldane System,"A possible spin-reorientation transition in field-induced magnetic ordering
phases of the S=1 Haldane system with large easy-plane anisotropy is proposed,
using an effective Lagrangian formalism as well as the density matrix
renormalization group method. Such a spin-reorientation transition is predicted
in the case where the applied magnetic field is inclined from the easy axis of
the anisotropy. We point out that this transition has a close connection with a
variation of the order parameter even at zero temperature, although it is
different from a quantum analog of the so-called spin-flop transition proposed
for the system having a strong easy axis anisotropy. In connection with a novel
phase observed recently in the Haldane system at high fields, we discuss
possible implications for the field-induced magnetic ordering.",0607336v1
2006-07-26,Many-body Green's function theory of Heisenberg films,"The treatment of Heisenberg films with many-body Green's function theory
(GFT) is reviewed. The basic equations of GFT are derived in sufficient detail
so that the rest of the paper can be understood without having to consult
further literature. The main part of the paper is concerned with applications
of the formalism to ferromagnetic, antiferromagnetic and coupled
ferromagnetic-antiferromagnetic Heisenberg films based on a generalized
Tyablikov (RPA) decoupling of the exchange interaction and exchange anisotropy
terms and an Anderson-Callen decoupling for a weak single-ion anisotropy. We
not only give a consistent description of our own work but also refer
extensively to related investigations. We discuss in particular the
reorientation of the magnetization as a function of the temperature and film
thickness. If the single-ion anisotropy is strong, it can be treated exactly by
going to higher-order Green's functions. We also discuss the extension of the
theory beyond RPA. Finally the limitations of GFT is pointed out.",0607675v1
2006-12-13,Stability of Random-Field and Random-Anisotropy Fixed Points at large N,"In this note, we clarify the stability of the large-N functional RG fixed
points of the order/disorder transition in the random-field (RF) and
random-anisotropy (RA) O(N) models. We carefully distinguish between infinite
N, and large but finite N. For infinite N, the Schwarz-Soffer inequality does
not give a useful bound, and all fixed points found in cond-mat/0510344 (Phys.
Rev. Lett. 96, 197202 (2006)) correspond to physical disorder. For large but
finite N (i.e. to first order in 1/N) the non-analytic RF fixed point becomes
unstable, and the disorder flows to an analytic fixed point characterized by
dimensional reduction. However, for random anisotropy the fixed point remains
non-analytic (i.e. exhibits a cusp) and is stable in the 1/N expansion, while
the corresponding dimensional-reduction fixed point is unstable. In this case
the Schwarz-Soffer inequality does not constrain the 2-point spin correlation.
We compute the critical exponents of this new fixed point in a series in 1/N
and to 2-loop order.",0612310v1
2006-12-14,Stripes in thin ferromagnetic films with out-of-plane anisotropy,"We examine the T=0 phase diagram of a thin ferromagnetic film with a strong
out-of-plane anisotropy in the vicinity of the reorientation phase transition
(with Co on Pt as an example). The phase diagram in the anisotropy-applied
field plane is universal in the limit where the film thickness is the shortest
length scale. It contains uniform fully magnetized and canted phases, as well
as periodically nonuniform states: a weakly modulated spin-density wave and
strongly modulated stripes. We determine the boundaries of metastability of
these phases and point out the existence of a critical point at which the
difference between the SDW and stripes vanishes. Out-of-plane magnetization
curves exhibit a variety of hysteresis loops caused by the coexistence of one
or more phases. Additionally, we study the effect of a system edge on the
orientation of stripes. We compare our results with recent experiments.",0612346v2
2007-03-16,Nature of the Perpendicular-to-Parallel Spin Reorientation in a Mn-doped GaAs Quantum Well: Canting or Phase Separation?,"It is well known that the magnetic anisotropy in a compressively-strained
Mn-doped GaAs film changes from perpendicular to parallel with increasing hole
concentration $p$. We study this reorientation transition at T=0 in a quantum
well with Mn impurities confined to a single plane. With increasing $p$, the
angle $\theta $ that minimizes the energy $E$ increases continuously from 0
(perpendicular anisotropy) to $\pi /2$ (parallel anisotropy) within some range
of $p$. The shape of $\Emin (p)$ suggests that the quantum well becomes phase
separated with regions containing low hole concentrations and perpendicular
moments interspersed with other regions containing high hole concentrations and
parallel moments. However, due to the Coulomb energy cost associated with phase
separation, the true magnetic state in the transition region is canted with $0
< \theta < \pi /2$.",0703436v1
2007-03-28,Transverse ultrasound absorption in cubic crystals with positive and negative anisotropies of second-order elasticity moduli,"The transverse ultrasound absorption in cubic crystals with positive and
negative anisotropies of the second-order elasticity moduli is analyzed. The
scattering of the ultrasound by defects and during anharmonic scattering
processes is considered. The transverse ultrasound absorption is analyzed as a
function of the wave-vector direction in terms of the anisotropic continuum
model. The Landau-Rumer mechanism is considered for anharmonic scattering
processes. Known values of the second- and third-order elasticity moduli are
used to calculate parameters determining the ultrasound absorption. It is shown
that the angular dependences of the transverse ultrasound absorption differ
qualitatively if the anharmonic scattering processes dominate in cubic crystals
with positive and negative anisotropies of the second-order elasticity moduli.
For the scattering by defects and the anharmonic scattering processes, the
angular dependences of the transverse ultrasound absorption exhibit the inverse
behavior, making it possible to determine the dominating mechanism of the
ultrasound relaxation in the crystals under study.",0703748v1
1998-02-19,Effects of anisotropy and spatial curvature on the pre-big bang scenario,"A class of exact, anisotropic cosmological solutions to the vacuum
Brans-Dicke theory of gravity is considered within the context of the pre-big
bang scenario. Included in this class are the Bianchi type III, V and VI_h
models and the spatially isotropic, negatively curved
Friedmann-Robertson-Walker universe. The effects of large anisotropy and
spatial curvature are determined. In contrast to negatively curved
Friedmann-Robertson-Walker model, there exist regions of the parameter space in
which the combined effects of curvature and anisotropy prevent the occurrence
of inflation. When inflation is possible, the necessary and sufficient
conditions for successful pre-big bang inflation are more stringent than in the
isotropic models. The initial state for these models is established and
corresponds in general to a gravitational plane wave.",9802052v1
1998-04-28,Seeds of large-scale anisotropy in string cosmology,"Pre-big bang cosmology predicts tiny first-order dilaton and metric
perturbations at very large scales. Here we discuss the possibility that other
-- more copiously generated -- perturbations may act, at second order, as
scalar seeds of large-scale structure and CMB anisotropies. We study, in
particular, the cases of electromagnetic and axionic seeds. We compute the
stochastic fluctuations of their energy-momentum tensor and determine the
resulting contributions to the multipole expansion of the temperature
anisotropy. In the axion case it is possible to obtain a flat or slightly
tilted blue spectrum that fits present data consistently, both for massless and
for massive (but very light) axions.",9804076v1
1998-06-18,Weighing the string mass with the COBE data,"In the context of the pre-big bang scenario the large-scale CMB anisotropy
can be seeded by a primordial background of very light (or massless) axion
fluctuations. In that case the slope of the temperature anisotropy spectrum,
allowed by present observations, defines an allowed range of values for the
string mass scale. Conversely, from the theoretical expected value of the
string scale we can predict the slope of the anisotropy spectrum. In both cases
there is a remarkable agreement between observations and theoretical
expectations.",9806073v1
1998-12-07,"Fully Anisotropic String Cosmologies, Maxwell Fields and Primordial Shear","We present a class of exact cosmological solutions of the low energy string
effective action in the presence of a homogeneous magnetic fields. We discuss
the physical properties of the obtained (fully anisotropic) cosmologies paying
particular attention to their vacuum limit and to the possible isotropization
mechanisms. We argue that quadratic curvature corrections are able to
isotropize fully anisotropic solutions whose scale factors describe accelerated
expansion. Moreover, the degree of isotropization grows with the duration of
the string phase. We follow the fate of the shear parameter in a decelerated
phase where, dilaton, magnetic fields and radiation fluid are simultaneously
present. In the absence of any magnetic field a long string phase immediately
followed by radiation is able to erase large anisotropies. Conversely, if a
short string phase is followed by a long dilaton dominated phase the
anisotropies can be present, in principle, also at later times. The presence of
magnetic seeds after the end of the string phase can induce further
anisotropies which can be studied within the formalism reported in this paper.",9812021v1
2002-04-14,Radion and Large Scale Anisotropy on the Brane,"We investigate the effect of the radion on cosmological perturbations in the
brane world. The S^1/Z_2 compactified 5D Anti-de Sitter spacetime bounded by
positive and negative tension branes is considered. The radion is the relative
displacement of the branes in this model. We find two different kinds of the
radion at the linear perturbation order for a cosmological brane. One describes
a ""fluctuation"" of the brane which does not couple to matter on the brane. The
other describes a ""bend"" of the brane which couples to the matter. The bend
determines the curvature perturbation on the brane. At large scales, the radion
interacts with anisotopic perturbations in the bulk. By solving the bulk
anisotropic perturbations, large scale metric perturbations and anisotropies of
the Cosmic Microwave Background (CMB) on the positive tension brane are
calculated. We find an interesting fact that the radion contributes to the CMB
anisotropies. The observational consequences of these effects are discussed.",0204047v2
2005-04-25,Acoustic peaks in the CMB: a matter of standard causal boundary conditions on primordial density anisotropies,"The pattern of acoustic peaks in the sub-horizon power spectrum of primordial
density anisotropies at recombination can be naturally understood in the
framework of standard Friedmann-Robertson-Walker cosmology (without inflation)
as a consequence of the boundary conditions imposed by the causal horizon on
the statistical two-points correlation functions: the sub-horizon spectrum is
discrete (harmonic), with comoving modes located at $k_n = n
\frac{\pi}{H^{-1}_{eq}}$, $n = 1,2,...$, because the causally connected patch
of the universe at recombination is compact, with comoving radius
$H^{-1}_{eq}$. The results presented in this paper complement those presented
in [1], where it was shown that the scale invariance of the primordial density
anisotropies over comoving scales of cosmological size is also a consequence of
the boundary conditions imposed by causality. Together these results lay an
appealing theoretical alternative to the inflationary paradigm as the ultimate
answer for the origin of cosmological structures in standard cosmology.",0504124v1
2006-12-24,Friedmann Robertson-Walker model in generalised metric space-time with weak anisotropy,"A generalized model of space-time is given, taking into consideration the
anisotropic structure of fields which are depended on the position and the
direction (velocity).In this framework a generalized FRW-metric the
Raychaudhouri and Friedmann equations are studied.A long range vector field of
cosmological origin is considered in relation to the physical geometry of
space-time in which Cartan connection has a fundamental role.The generalised
Friedmann equations are produced including anisotropic terms.The variation of
anisotropy $z_t$ is expressed in terms of the Cartan torsion tensor of the
Finslerian space-time.A possible estimation of the anisotropic parameter $z_t$
can be achieved with the aid of the de-Sitter model of the empty flat universe
with weak anisotropy. Finally a physical generalisation for the model of
inflation is also studied.",0612157v4
1996-06-13,Large Self-affine fractality in $\p^+$p and K$^+$p collisions at 250 GeV/$c$,"Taking into account the anisotropy of phase space in multiparticle
production, a self-affine analysis of factorial moments was carried out on the
NA22 data for $\p^+\Pp$ and $\PK^+\Pp$ collisions at 250 GeV/$c$. Within the
transverse plane, the Hurst exponents measuring the anisotropy are consistent
with unit value (i.e. no anisotropy). They are, however, only half that value
when the longitudinal direction is compared to the transverse ones. Fractality,
indeed, turns out to be self-affine rather than self-similar in multiparticle
production. In three-dimensional phase space, power-law scaling is observed to
be better realized in self-affine than in self-similar analysis.",9606005v1
1992-07-31,A Lower Bound on $T_{SR}/{m_{\rm H}}$ in the O(4) Model on Anisotropic Lattices,"Results of an investigation of the $O(4)$ spin model at finite temperature
using anisotropic lattices are presented. In both the large $N$ approximation
and numerical simulations using the Wolff cluster algorithm we find that the
ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass
$m_{\rm H}$ is independent of the anisotropy $\xi$. From the numerical
simulations we obtain a lower bound of $T_{\rm SR} / m_{\rm H} \simeq 0.58 \pm
0.02$ at a value for the Higgs mass $m_{\rm H}a_s \simeq 0.5$, which is lowered
further by about $10\%$ at $m_{\rm H}a_s \simeq 1$. Requiring certain timelike
correlation functions to coincide with their spacelike counterparts, quantum
and scaling corrections to the anisotropy are determined and are found to be
small, i.e., the anisotropy is found to be close to the ratio of spacelike and
timelike lattice spacings.",9207033v1
1999-05-03,Determination of Anisotropy Coefficients for SU(3) Gauge Actions from the Integral and Matching Methods,"We use two non-perturbative methods to obtain the anisotropy derivatives of
the coupling constants (the anisotropy coefficients) of SU(3) lattice gauge
theory. These coefficients appear in the derivative formulae for the energy
density and the pressure. We calculate them for the standard Wilson and two
improved actions, the 2x2 and the Square Symanzik action. Both methods lead for
all investigated actions to compatible results which are clearly different from
their known asymptotic perturbative limits. With increasing beta the limits are
however approached in all cases. Our findings strongly support the equivalence
of the integral and derivative methods for the calculation of energy density
and pressure.",9905002v1
2001-05-31,Perfect Gauge Actions on Anisotropic Lattices,"We present a method for constructing classically perfect anisotropic actions
for SU(3) gauge theory based on a present isotropic Fixed Point Action. The
action is parametrised using smeared (``fat'') links. The construction is done
explicitly for anisotropy $\xi=a_s/a_t=2,4$ and the renormalised anisotropies
are determined using the torelon dispersion relation. Quantities such as the
static quark-antiquark potential, the critical temperature of the deconfining
phase transition and the low-lying glueball spectrum are measured as well. It
turns out that the procedure presented works, the renormalised anisotropy is
small and the parametrisation describes the full action well. Issues such as
the application of the method for scalar fields as well as for the quadratic
approximation to gauge theory, measurements of autocorrelation times of simple
operators and of the computational overhead are also covered. A (more compact)
paper about this classically perfect anisotropic gauge action is in
preparation.",0105033v1
2002-03-24,Heavy quark action on the anisotropic lattice,"We investigate the $O(a)$ improved quark action on anisotropic lattice as a
potential framework for the heavy quark, which may enable precision computation
of hadronic matrix elements of heavy-light mesons. The relativity relations of
heavy-light mesons as well as of heavy quarkonium are examined on a quenched
lattice with spatial lattice cutoff $a_\sigma^{-1} \simeq$ 1.6 GeV and the
anisotropy $\xi=4$. We find that the bare anisotropy parameter tuned for the
massless quark describes both the heavy-heavy and heavy-light mesons within 2%
accuracy for the quark mass $a_\sigma m_Q < 0.8$, which covers the charm quark
mass. This bare anisotropy parameter also successfully describes the
heavy-light mesons in the quark mass region $a_\sigma m_Q \leq 1.2$ within the
same accuracy. Beyond this region, the discretization effects seem to grow
gradually. The anisotropic lattice is expected to extend by a factor $\xi$ the
quark mass region in which the parameters in the action tuned for the massless
limit are applicable for heavy-light systems with well controlled systematic
errors.",0203025v1
2003-03-18,Renormalization of Anisotropy and Glueball Masses on Tadpole Improved Lattice Gauge Action,"The Numerical calculations for tadpole-improved U(1) lattice gauge theory in
three-dimensions on anisotropic lattices have been performed using standard
path integral Monte Carlo techniques. Using average plaquette tadpole
renormalization scheme, simulations were done with temporal lattice spacings
much smaller than the spatial ones and results were obtained for the string
tension, the renormalized anisotropy and scalar glueball masses. We find, by
comparing the `regular' and `sideways' potentials, that tadpole improvement
results in very little renormalization of the bare anisotropy and reduces the
discretization errors in the static quark potential and in the glueball masses.",0303011v3
2003-07-08,"The contribution of O(alpha) radiative corrections to the renormalised anisotropy and application to general tadpole improvement schemes: addendum to ""One loop calculation of the renormalised anisotropy for improved anisotropic gluon actions on a lattice"" [hep-lat/0208010]","General O(alpha) radiative corrections to lattice actions may be interpreted
as counterterms that give additive contributions to the one-loop
renormalisation of the anisotropy. The effect of changing the radiative
coefficients is thus easily calculable. In particular, the results obtained in
a previous paper for Landau mean link improved actions apply in any tadpole
improvement scheme. We explain how this method can be exploited when tuning
radiatively improved actions. Efficient methods for self-consistently tuning
tadpole improvement factors are also discussed.",0307010v1
1992-05-08,"Grand Unification, Gravitational Waves, and the Cosmic Microwave Background Anisotropy","We re-examine the gravitational wave background resulting from inflation and
its effect on the cosmic microwave background radiation. The new COBE
measurement of a cosmic background quadrupole anisotropy places an upper limit
on the vacuum energy during inflation of $\approx 5 \times 10^{16}$ GeV. A
stochastic background of gravitational waves from inflation could produce the
entire observed signal (consistent with the observed dipole anisotropy and a
flat spectrum) if the vacuum energy during inflation was as small as $1.5
\times 10^{16}$ GeV at the 95\% confidence level. This coincides nicely with
the mass scale for Grand Unification inferred from precision measurements of
the electroweak and strong coupling constants, for the SUSY Grand Unified
Theories. Thus COBE could be providing the first direct evidence, via
gravitational waves, for GUTs, and supersymmetry. Further tests of this
possibility are examined, based on analyzing the energy density associated with
gravitational waves from inflation.",9205212v1
1992-08-07,The gravitational wave contribution to CMB anisotropies and the amplitude of mass fluctuations from COBE results,"A stochastic background of primordial gravitational waves may substantially
contribute, via the Sachs--Wolfe effect, to the large--scale Cosmic Microwave
Background (CMB) anisotropies recently detected by COBE. This implies a {\it
bias} in any resulting determination of the primordial amplitude of density
fluctuations. We consider the constraints imposed on $n<1$ (``tilted"")
power--law fluctuation spectra, taking into account the contribution from both
scalar and tensor waves, as predicted by power--law inflation. The
gravitational--wave contribution to CMB anisotropies generally reduces the
required {\it rms} level of mass fluctuation, thereby increasing the linear
{\it bias parameter}, even in models where the spectral index is close to the
Harrison--Zel'dovich value $n=1$. This ``gravitational--wave bias"" helps to
reconcile the predictions of CDM models with observations on pairwise galaxy
velocity dispersion on small scales.",9208214v1
1992-08-10,"Density Perturbations,Gravity Waves and the Cosmic Microwave Background","We asses the contribution to the observed large scale anisotropy of the
cosmic microwave background radiation, arising from both gravity waves as well
as adiabatic density perturbations, generated by a common inflationary
mechanism in the early Universe.
  We find that for inflationary models predicting power law primordial spectra
%$a(t) \propto t^p, p > 1$, $\dk^2 \propto k^n$, the relative contribution to
the quadrupole anisotropy from gravity waves and scalar density perturbations,
depends crucially upon $n$. For $n < 0.87$, gravity waves perturb the CMBR by a
larger amount than density perturbations, whereas for $n > 0.87$ the reverse is
true. %For nearly exponential inflation, on the other hand, the contribution to
the %microwave anisotropy from scalar density perturbations always exceeds
%that due to gravity waves. Normalising the amplitude of the density
perturbation spectrum at large scales, using the observed value of the COBE
quadrupole, we determine $(\delta M /M)_{16}$ -- the rms density contrast on
scales $\sim 16 h_{50}^{-1}$ Mpc, for cosmological models with cold dark
matter. We find that for $n < 0.75$, a large amount of biasing is required in
order to reconcile theory with observations.",9208217v1
1993-10-20,$Π$ in the Sky ? Microwave Anisotropies from Cosmic Defects,"High resolution maps of the anisotropy of the microwave sky will yield
invaluable clues as to the mechanisms involved in cosmic structure formation.
One fundamental question they should answer is whether the fluctuations were
Gaussian random noise, as predicted in inflationary models, or were nonGaussian
as in theories based on symmetry breaking and cosmic defects. In the latter
case there is the prospect of obtaining information regarding symmetry breaking
at high energy scales, specifically the homotopy classes $\Pi_n$ of the vacuum
manifold. In this paper we report on detailed calculations of the degree scale
anisotropies predicted in the cosmic string, monopole texture and
nontopological texture theories of structure formation, emphasising their
distinct character from those predicted by inflation, and the bright prospects
for experimental tests.",9310322v2
1998-12-31,Microwave background anisotropies in quasiopen inflation,"Quasiopenness seems to be generic to multi-field models of single-bubble open
inflation. Instead of producing infinite open universes, these models actually
produce an ensemble of very large but finite inflating islands. In this paper
we study the possible constraints from CMB anisotropies on existing models of
open inflation. The effect of supercurvature anisotropies combined with the
quasiopenness of the inflating regions make some models incompatible with
observations, and severely reduces the parameter space of others. Supernatural
open inflation and the uncoupled two-field model seem to be ruled out due to
these constraints for values of $\Omega_0\lesssim0.98$. Others, such as the
open hybrid inflation model with suitable parameters for the slow roll
potential can be made compatible with observations.",9812533v1
1999-03-23,Measuring the cosmological lepton asymmetry through the CMB anisotropy,"A large lepton asymmetry in the Universe is still a viable possibility and
leads to many interesting phenomena such as gauge symmetry nonrestoration at
high temperature. We show that a large lepton asymmetry changes the predicted
cosmic microwave background (CMB) anisotropy and that any degeneracy in the
relic neutrino sea will be measured to a precision of 1% or better when the CMB
anisotropy is measured at the accuracy expected to result from the planned
satellite missions MAP and Planck. In fact, the current measurements already
put an upper limit on the lepton asymmetry of the Universe which is stronger
than the one coming from considerations of primordial nucleosynthesis and
structure formation.",9903459v3
2000-10-18,Constraints on Natural Inflation from Cosmic Microwave Background,"We study constraints on the natural inflation model from the cosmic microwave
background radiation (CMBR). Inflaton \phi for the natural inflation has a
potential of the form V=\Lambda^4[1-\cos(\phi/\sqrt{2}f_\phi)], which is
parametrized by two parameters f_\phi and \Lambda. Various cosmological
quantities, like the primordial curvature perturbation and the CMBR anisotropy,
are determined as functions of these two parameters. Using recent observations
of the CMBR anisotropy by BOOMERANG and MAXIMA (as well as those from COBE),
constraints on the parameters f_\phi and \Lambda are derived. The model with
f_\phi lower than 8.5\times 10^{18} (5.4\times 10^{18}, 4.5\times 10^{18}) GeV
predicts a power spectrum with index n_{\rm S} smaller than 0.95 (0.9, 0.85)
which suppresses the CMBR anisotropy for smaller angular scale. With such a
small n_{\rm S}, height of the second acoustic peak can become significantly
lower than the case of the scale-invariant Harrison-Zeldovich spectrum.",0010197v2
2001-12-27,Cosmic Microwave Background Anisotropy with Late Time Entropy Production,"We discuss effects of cosmological moduli fields on the cosmic microwave
background (CMB). If a modulus field \phi once dominates the universe, the CMB
we observe today is from the decay of \phi and its anisotropy is affected by
the primordial fluctuation in the amplitude of the modulus field. As a result,
constraints on the inflaton potential from the CMB anisotropy can be relaxed.
In addition, with the cosmological moduli fields, correlated mixture of
adiabatic and isocurvature fluctuations may be generated, which results in
enhanced CMB angular power spectrum at higher multipoles relative to that of
lower ones. Such an enhancement can be an evidence of late time entropy
production due to the cosmological moduli fields, and may be observed at
on-going and future experiments.",0112335v1
2003-11-14,Narrowing the window for millicharged particles by CMB anisotropy,"We calculate the cosmic microwave background (CMB) anisotropy spectrum in
models with millicharged particles of electric charge q\sim 10^{-6}-10^{-1} in
units of electron charge. We find that a large region of the parameter space
for the millicharged particles exists where their effect on the CMB spectrum is
similar to the effect of baryons. Using WMAP data on the CMB anisotropy and
assuming Big Bang nucleosynthesis value for the baryon abundance we find that
only a small fraction of cold dark matter, Omega_{mcp}h_0^2 < 0.007 (at 95%
CL), may consists of millicharged particles with the parameters (charge and
mass) from this region. This bound significantly narrows the allowed range of
the parameters of millicharged particles. In models without paraphoton
millicharged particles are now excluded as a dark matter candidate. We also
speculate that recent observation of 511 keV gamma-rays from the Galactic bulge
may be an indication that a (small) fraction of CDM is comprised of the
millicharged particles.",0311189v2
2003-07-02,Super Heavy Dark Matter Anisotropies from D-particles in the Early Universe,"We discuss a way of producing anisotropies in the spectrum of superheavy Dark
matter, which are due to the distortion of the inflationary space time induced
by the recoil of D-particles upon their scattering with ordinary string matter
in the Early Universe. We calculate such distortions by world-sheet Liouville
string theory (perturbative) methods. The resulting anisotropies are found to
be proportional to the average recoil velocity and density of the D-particles.
In our analysis we employ a regulated version of de Sitter space, allowing for
graceful exit from inflation. This guarantees the asymptotic flatness of the
space time, as required for a consistent interpretation, within an effective
field theory context, of the associated Bogolubov coefficients as particle
number densities. The latter are computed by standard WKB methods.",0307028v1
2004-01-28,Parity-violating Kalb-Ramond-Maxwell interactions and CMB anisotropy in a braneworld,"Following up on a recent paper by two of us (DM and SS), demonstrating the
large enhancement in observable optical activity in radiation from high
redshift sources arising from the string-based coupling of bulk Kalb-Ramond
field to the Maxwell Chern Simons three-form on the brane in a Randall-Sundrum
braneworld, we exhibit here a similar enhancement in parity-violating
temperature-polarization correlations, yet unseen, in the CMB anisotropy due to
a generalized parity-violating Kalb-Ramond axion-photon interaction proposed
earlier by one of us (PM). The non-observation of such correlations in CMB
anisotropies would necessitate unnatural fine tuning of the Kalb-Ramond axion
parameters. As a stringy realization of Randall-Sundrum braneworld scenario is
yet to be understood properly, our work indicates the need of a careful
investigation to establish the connection between string-based phenomenological
models and the Randall-Sundrum braneworld scenario",0401218v2
2001-01-29,Stability of scaling regimes in $d\geq 2$ developed turbulence with weak anisotropy,"The fully developed turbulence with weak anisotropy is investigated by means
of renormalization group approach (RG) and double expansion regularization for
dimensions $d\ge 2$. Some modification of the standard minimal substraction
scheme has been used to analyze stability of the Kolmogorov scaling regime
which is governed by the renormalization group fixed point. This fixed point is
unstable at $d=2$; thus, the infinitesimally weak anisotropy destroyes above
scaling regime in two-dimensional space. The restoration of the stability of
this fixed point, under transition from $d=2$ to $d=3,$ has been demonstrated
at borderline dimension $ 2<d_c<3$. The results are in qualitative agreement
with ones obtained recently in the framework of the usual analytical
regularization scheme.",0101050v1
2001-04-05,"Anomalous scaling, nonlocality and anisotropy in a model of the passively advected vector field","A model of the passive vector quantity advected by a Gaussian
time-decorrelated self-similar velocity field is studied; the effects of
pressure and large-scale anisotropy are discussed. The inertial-range behavior
of the pair correlation function is described by an infinite family of scaling
exponents, which satisfy exact transcendental equations derived explicitly in d
dimensions. The exponents are organized in a hierarchical order according to
their degree of anisotropy, with the spectrum unbounded from above and the
leading exponent coming from the isotropic sector. For the higher-order
structure functions, the anomalous scaling behavior is a consequence of the
existence in the corresponding operator product expansions of ``dangerous''
composite operators, whose negative critical dimensions determine the
exponents. A close formal resemblance of the model with the stirred NS equation
reveals itself in the mixing of operators. Using the RG, the anomalous
exponents are calculated in the one-loop approximation for the even structure
functions up to the twelfth order.",0104012v1
2006-11-30,Influence of anisotropy and compressibility on anomalous scaling of a passive scalar field,"Influence of uniaxial small-scale anisotropy and compressibility on the
stability of scaling regime and on the anomalous scaling of structure functions
of a scalar field is investigated in the model of a passive scalar field
advected by the compressible Gaussian strongly anisotropic velocity field with
the covariance $\propto \delta(t-t^{\prime})|{\bf x}-{\bf
x^{\prime}}|^{2\epsilon}$ by using the field theoretic renormalization group
and the operator product expansion. The inertial-range stability of the
corresponding scaling regime is established. The anomalous scaling of the
single-time structure functions is studied and the corresponding anomalous
exponents are calculated. Their dependence on the compressibility parameter and
anisotropy parameters is analyzed. It is shown that the presence of
compressibility leads to the decreasing of the critical dimensions of the
important composite operators, i.e., the anomalous scaling is more pronounced
in the compressible systems. This result is demonstrated for the structure
function of the third order. All calculations are done to the first order in
$\epsilon$.",0611061v1
1996-10-18,Energy and Charged Particle Flow in 10.8 A GeV/c Au+Au Collisions,"Experimental results and a detailed analysis are presented of the transverse
energy and charged particle azimuthal distributions measured by the E877
collaboration for different centralities of Au+Au collisions at a beam momentum
of 10.8 A GeV/c. The anisotropy of these distributions is studied with respect
to the reaction plane reconstructed on an event-by-event basis using the
transverse energy distribution measured by calorimeters. Results are corrected
for the reaction plane resolution. For semicentral events we observe directed
flow signals of up to ten percent. We observe a stronger anisotropy for slow
charged particles. For both the charged particle and transverse energy
distributions we observe a small but non zero elliptic anisotropy with the
major axis pointing into the reaction plane. Combining the information on
transverse energy and charged particle flow we obtain information on the flow
of nucleons and pions. The data are compared to event generators and the need
to introduce a mean field or nucleon-nucleon potential is discussed.",9610006v1
2002-05-29,Pseudorapidity and centrality dependence of the collective flow of charged particles in Au+Au collisions at sqrt{s_NN} = 130 GeV,"This paper describes the measurement of collective flow for charged particles
in Au+Au collisions at sqrt{s_NN}} = 130 GeV using the PHOBOS detector at the
Relativistic Heavy Ion Collider (RHIC). An azimuthal anisotropy is observed in
the charged particle hit distribution in the PHOBOS multiplicity detector. This
anisotropy is presented over a wide range of pseudorapidity (eta) for the first
time at this energy. The size of the anisotropy (v_{2}) is thought to probe the
degree of equilibration achieved in these collisions. The result here,averaged
over momenta and particle species, is observed to reach 7% for peripheral
collisions at mid-rapidity, falling off with centrality and increasing |eta|.
Data are presented as a function of centrality for |eta|<1.0 and as a function
of eta, averaged over centrality, in the angular region -5.0<eta<5.3. These
results call into question the common assumption of longitudinal boost
invariance over a large region of rapidity in RHIC collisions.",0205021v1
2004-11-19,Saturation of azimuthal anisotropy in Au + Au collisions at sqrt(s_NN) = 62 - 200 GeV,"New measurements are presented for charged hadron azimuthal correlations at
mid-rapidity in Au+Au collisions at sqrt(s_NN) = 62.4 and 200 GeV. They are
compared to earlier measurements obtained at sqrt(s_NN) = 130 GeV and in Pb+Pb
collisions at sqrt(s_NN) = 17.2 GeV. Sizeable anisotropies are observed with
centrality and transverse momentum (p_T) dependence characteristic of elliptic
flow (v_2). For a broad range of centralities, the observed magnitudes and
trends of the differential anisotropy, v_2(p_T), change very little over the
collision energy range sqrt(s_NN) = 62-200 GeV, indicating saturation of the
excitation function for v_2 at these energies. Such a saturation may be
indicative of the dominance of a very soft equation of state for sqrt(s_NN) =
62-200 GeV.",0411040v1
1993-04-13,Maximum Azimuthal Anisotropy of Neutrons from Nb-Nb Collisions at 400 AMeV and the Nuclear Equation of State,"We measured the first azimuthal distributions of triple--differential cross
sections of neutrons emitted in heavy-ion collisions, and compared their
maximum azimuthal anisotropy ratios with Boltzmann--Uehling--Uhlenbeck (BUU)
calculations with a momentum-dependent interaction. The BUU calculations agree
with the triple- and double-differential cross sections for positive rapidity
neutrons emitted at polar angles from 7 to 27 degrees; however, the maximum
azimuthal anisotropy ratio for these free neutrons is insensitive to the size
of the nuclear incompressibility modulus K characterizing the nuclear matter
equation of state.",9304009v1
1995-08-27,Decay Anisotropy of $e^+e^-$ Sources from $pN$ and $pd$ collisions,"A full calculation of lepton-pair angular characteristics is carried out for
$e^+e^-$ pairs created in $pp$, $pn$ and $pd$ collisions at intermediate
energies. It is demonstrated that the proposed new observable, the dilepton
decay anisotropy, quite sensitively changes for different sources and may be
useful for their disentangling. The relevance of the dilepton decay anisotropy
is shown in the context of a puzzling energy behavior for the ratio of the
lepton yield from $pd$ to $pp$ reactions as observed at the BEVALAC.",9508043v1
1999-12-17,A Model of Convergent Extension in Animal Morphogenesis,"In this paper we argue that the pattern of cell movements in the
morphogenetic process known as convergent extension can be understood as a
energy minimization process, provided the cell-cell adhesive energy has a
certain kind of anisotropy. This single simple property is sufficient cause for
the type of cell elongation, alignment, and intercalation of a cellular array
that is the characteristic of convergent extension. We describe the type of
anisotropy required. We show that the final aspect ratio of the array of cells
is independent of the initial configuration and of the degree of cell
elongation. We find how it depends on the anisotropy.",9912038v3
2001-06-14,Influence of Static and Dynamic Disorder on the Anisotropy of Emission in the Ring Antenna Subunits of Purple Bacteria Photosynthetic Systems,"Using the reduced density matrix formalism the time dependence of the exciton
scattering in light-harvesting ring systems of purple bacteria is calculated.
In contrast to the work of Kumble and Hochstrasser (J. Chem. Phys. 109 (1998)
855) static disorder (fluctuations of the site energies) as well as dynamic
disorder (dissipation) is taken into account. For the description of
dissipation we use Redfield theory in exciton eigenstates without secular
approximation. This is shown to be equivalent to the Markovian limit of Capek's
theory in local states. Circular aggregates with 18 pigments are studied to
model the B850 ring of bacteriochlorophyls within LH2 complexes. It can be
demonstrated that the dissipation is important for the time-dependent
anisotropy of the fluorescence. Smaller values of static disorder are
sufficient to produce the same decay rates in the anisotropy in comparison with
the results by Kumble and Hochstrasser.",0106043v1
2002-08-23,Reinterpretation of Matter-Wave Interference Experiments Based on the Local-Ether Wave Equation,"Based on the local-ether wave equation for free particle, the dispersion of
matter wave is examined. From the dispersion relation, the angular frequency
and wavelength of matter wave are derived. These formulas look like the
postulates of de Broglie in conjunction with the Lorentz mass-variation law.
However, the fundamental difference is that for terrestrial particles their
speeds are referred specifically to a geocentric inertial frame and hence
incorporate the speed due to earth's rotation. Thus the local-ether model
predicts an east-west directional anisotropy both in mass and wavelength.
Meanwhile, in spite of the restriction on reference frame, the local-ether
model can account for the matter-wave interference experiments of the Bragg
reflection and the Sagnac effect. For electron wave, the effects of earth's
rotation are negligible and the derived Bragg angle is actually in accord with
the Davisson-Germer experiment, as examined within the present precision. On
the other hand, the local-ether model leads to a directional anisotropy in the
Bragg angle in neutron diffraction. The predicted anisotropy due to earth's
rotation then provide a means to test the local-ether wave equation.",0208085v1
2003-02-26,A New Limit on Signals of Lorentz Violation in Electrodynamics,"We describe the results of an experiment to test for spacetime anisotropy
terms that might exist from Lorentz violations. The apparatus consists of a
pair of cylindrical superconducting cavity-stabilized oscillators operating in
the TM_{010} mode with one axis east-west and the other vertical. Spatial
anisotropy is detected by monitoring the beat frequency at the sidereal rate
and its first harmonic. We see no anisotropy to a part in 10^{13}. This puts a
comparable bound on four linear combinations of parameters in the general
Standard Model extension, and a weaker bound of <4 x 10^{-9} on three others.",0302093v1
2004-07-19,Sharp vorticity gradients in two-dimensional hydrodynamic turbulence,"The appearance of sharp vorticity gradients in two-dimensional hydrodynamic
turbulence and their influence on the turbulent spectra is considered. We have
developed the analog of the vortex line representation as a transformation to
the curvilinear system of coordinates moving together with the di-vorticity
lines. Compressibility of this mapping can be considered as the main reason for
the formation of the vorticity discontinuities at high Reynolds numbers. For
two-dimensional turbulence in the case of strong anisotropy the vorticity
discontinuities can generate spectra with the fall-off at large $k$
proportional to $k^{-3}$ resembling the Kraichnan spectrum for the enstrophy
cascade. For turbulence with weak anisotropy the $k$ dependence of the spectrum
due to discontinuities coincides with that of the Saffman spectrum: $k^{-4}$.
We have compared the analytical predictions with direct numerical solutions of
the two-dimensional Euler equation for decaying turbulence. We observe that the
di-vorticity is reaching very high values and is distributed locally in space
along piecewise straight lines. Thus, indicating strong anisotropy and
accordingly we found a spectrum close to the $k^{-3}$-spectrum.",0407101v1
2004-07-25,Theory of electrical conductivities of ferrogels,"Conductive organic polymers can be formulated with polymers that incorporate
fine dispersed metallic particles.
  In this work, we present a general model for ferrogels which are chemically
cross-linked polymer networks swollen with a ferrofluid. Our aim is to study
the effect of the shape and/or material (conductivity) anisotropy on the
effective electrical conductivity of the ferrogel in the presence of an
external magnetic field. Our theory can reproduce the known results, and
provides a link between the particle property and orientation distribution and
the effective electrical conductivity. To this end, we find that material
(conductivity) anisotropies are more important to yield a high effective
electrical conductivity than shape anisotropies, while magnetic fields can
offer a correction.",0407129v2
2005-06-23,Gigantic transmission band edge resonance in periodic stacks of anisotropic layers,"We consider Fabry-Perot cavity resonance in periodic stacks of anisotropic
layers with misaligned in-plane anisotropy at the frequency close to a photonic
band edge. We show that in-plane dielectric anisotropy can result in a dramatic
increase in field intensity and group delay associated with the transmission
resonance. The field enhancement appears to be proportional to forth degree of
the number N of layers in the stack. By contrast, in common periodic stacks of
isotropic layers, those effects are much weaker and proportional to N^2. Thus,
the anisotropy allows to drastically reduce the size of the resonance cavity
with similar performance. The key characteristic of the periodic arrays with
the gigantic transmission resonance is that the dispersion curve omega(k)at the
photonic band edge has the degenerate form Delta(omega) ~ Delta(k)^4, rather
than the regular form Delta(omega) ~ Delta(k)^2. This can be realized in
specially arranged stacks of misaligned anisotropic layers. The degenerate band
edge cavity resonance with similar outstanding properties can also be realized
in a waveguide environment, as well as in a linear array of coupled multimode
resonators, provided that certain symmetry conditions are in place.",0506174v1
2004-08-09,Effects of the interplay between interaction and disorder in bipartite entanglement,"We use a disordered anti-ferromagnetic spin-1/2 chain with anisotropic
exchange coupling to model an array of interacting qubits. All qubits have the
same level spacing, except two, which are called the defects of the chain. The
level spacings of the defects are equal and much larger than all the others. We
investigate how the entanglement between the two defects depends on the
anisotropy of the system. When the anisotropy coupling is much larger than the
energy difference between a defect and an ordinary qubit, the two defects
become strongly entangled. Small anisotropies, on the contrary, may decrease
the entanglement, which is, in this case, also much affected by the number of
excitations. The analysis is made for nearest neighbor and next-nearest
neighbor defects. The decrease in the entanglement for nearest neighbor defects
is not very significant, especially in large chains.",0408062v2
2007-04-15,Interplay of Anisotropy and Disorder in the Doping-Dependent Melting and Glass Transitions of Vortices in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$,"We study the oxygen doping dependence of the equilibrium first-order melting
and second-order glass transitions of vortices in
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. Doping affects both anisotropy and
disorder. Anisotropy scaling is shown to collapse the melting lines only where
thermal fluctuations are dominant. Yet, in the region where disorder breaks
that scaling, the glass lines are still collapsed. A quantitative fit to
melting and replica symmetry breaking lines of a 2D Ginzburg-Landau model
further reveals that disorder amplitude weakens with doping, but to a lesser
degree than thermal fluctuations, enhancing the relative role of disorder.",0704.1902v1
2007-04-17,Effects of a pre-inflation radiation-dominated epoch to CMB anisotropy,"We consider that the pre-inflation era is radiation-dominated, transiting
smoothly to the inflationary era. We work out in detail the dynamics of
inflaton fluctuations across the phase transition and the proper choices of
initial vacuum states. It is found that this phase transition can suppress
long-wavelength quantum fluctuations of inflaton. This may attribute to the
large-scale CMB anisotropy a lower power than predicted in the standard
$\Lambda$CDM model. In constraining this transitional effect by WMAP anisotropy
data, we use the WMAP best-fit scale-invariant $\Lambda$CDM model with the
density power spectrum replaced by the one found in this work. We find that the
transition occurs at least about 10 e-folds before the comoving scales
comparable to our present horizon size cross the Hubble radius during
inflation.",0704.2095v3
2007-05-02,Effect of temperature-dependent shape anisotropy on coercivity with aligned Stoner-Wohlfarth soft ferromagnets,"The temperature variation effect of shape anisotropy on the coercivity,
HC(T), for the aligned Stoner-Wohlfarth (SW) soft ferromagnets, such as fcc Ni,
fcc Co and bcc Fe, are investigated within the framework of Neel-Brown (N-B)
analysis. An extended N-B equation is thus proposed,by introducing a single
dimensionless correction function, the reduced magnetization, m(\tao) =
MS(T)/MS(0), in which \tao = T/TC is the reduced temperature, MS(T) is the
saturation magnetization, and TC is the Curie temperature. The factor, m(\tao),
accounts for the temperature-dependent effect of the shape anisotropy. The
constants, H0 and E0, are for the switching field at zero temperature and the
potential barrier at zero field, respectively. According to this newly derived
equation, the blocking temperature above which the properties of
superparamagnetism show up is described by the expression, TB =
E0m^2(\tao)/[kBln(t/t0)], with the extra correction factor m^2(\tao). The
possible effect on HC(T) and the blocking temperature, TB, attributed to the
downshift of TC resulting from the finite size effect has been discussed also.",0705.0195v1
2007-05-17,Kagome lattice antiferromagnets and Dzyaloshinsky-Moriya interactions,"We study the consequences of in-plane (D_p) and out-of-plane (D_z)
Dzyaloshinsky-Moriya (DM) interactions on the thermodynamic properties of
spin-1/2} Heisenberg model on the kagome lattice using numerical linked cluster
expansions and exact diagonalization, and contrast them with those of other
perturbations such as exchange anisotropy and dilution. We find that different
combinations of the DM anisotropies lead to a wide variety of thermodynamic
behavior, which are quite distinct from those of most other perturbations. We
argue that the sudden upturn seen experimentally in the susceptibility of the
material ZnCu3(OH)6Cl2 can be understood in terms of Dzyaloshinsky-Moriya
anisotropies with D_p>|D_z|. We also show that the measured specific heat of
the material puts further constraints on the allowed DM parameters.",0705.2591v2
2007-05-24,Nonequilibrium Dynamics of Anisotropic Large Spins in the Kondo Regime: Time-Dependent Numerical Renormalization Group Analysis,"We investigate the time-dependent Kondo effect in a single-molecule magnet
(SMM) strongly coupled to metallic electrodes. Describing the SMM by a Kondo
model with large spin S > 1/2, we analyze the underscreening of the local
moment and the effect of anisotropy terms on the relaxation dynamics of the
magnetization. Underscreening by single-channel Kondo processes leads to a
logarithmically slow relaxation, while finite uniaxial anisotropy causes a
saturation of the SMM's magnetization. Additional transverse anisotropy terms
induce quantum spin tunneling and a pseudospin-1/2 Kondo effect sensitive to
the spin parity.",0705.3654v2
2007-05-25,Probing polarization states of primordial gravitational waves with CMB anisotropies,"We discuss the polarization signature of primordial gravitational waves
imprinted in cosmic microwave background (CMB) anisotropies. The high-energy
physics motivated by superstring theory or M-theory generically yield parity
violating terms, which may produce a circularly polarized gravitational wave
background (GWB) during inflation. In contrast to the standard prediction of
inflation with un-polarized GWB, circularly polarized GWB generates
non-vanishing TB and EB-mode power spectra of CMB anisotropies. We evaluate the
TB and EB-mode power spectra taking into account the secondary effects and
investigate the dependence of cosmological parameters. We then discuss current
constraints on the circularly polarized GWB from large angular scales (l < 16)
of the three year WMAP data. Prospects for future CMB experiments are also
investigated based on a Monte Carlo analysis of parameter estimation, showing
that the circular polarization degree, varepsilon, which is the asymmetry of
the tensor power spectra between right- and left-handed modes normalized by the
total amplitude, can be measured down to |varepsilon| 0.35(r/0.05)^{-0.6}.",0705.3701v3
2007-05-31,Measuring the dark matter velocity anisotropy in galaxy clusters,"The Universe contains approximately 6 times more dark matter than normal
baryonic matter, and a directly observed fundamental difference between dark
matter and baryons would both be significant for our understanding of dark
matter structures and provide us with information about the basic
characteristics of the dark matter particle. We discuss one distinctive feature
of dark matter structures in equilibrium, namely the property that a local dark
matter temperature may depend on direction. This is in stark contrast to
baryonic gases. We used X-ray observations of two nearby, relaxed galaxy
clusters, under the assumptions of hydrostatic equilibrium and identical dark
matter and gas temperatures in the outer cluster region, to measure this dark
matter temperature anisotropy beta_dm, with non-parametric Monte Carlo methods.
We find that beta_dm is greater than the value predicted for baryonic gases,
beta_gas=0, at more than 3 sigma confidence. The observed value of the
temperature anisotropy is in fair agreement with the results of cosmological
N-body simulations and shows that the equilibration of the dark matter
particles is not governed by local point-like interactions in contrast to
baryonic gases.",0705.4680v2
2007-06-24,Nonlinear elastic stress response in granular packings,"We study the nonlinear elastic response of a two-dimensional material to a
localized boundary force, with the particular goal of understanding the
differences observed between isotropic granular materials and those with
hexagonal anisotropy. Corrections to the classical Boussinesq result for the
stresses in an infinite half-space of a linear, isotropic material are
developed in a power series in inverse distance from the point of application
of the force. The breakdown of continuum theory on scales of order of the grain
size is modeled with phenomenological parameters characterizing the strengths
of induced multipoles near the point of application of the external force. We
find that the data of Geng et al. on isotropic and hexagonal packings of
photoelastic grains can be fit within this framework. Fitting the hexagonal
packings requires a choice of elastic coefficients with hexagonal anisotropy
stronger than that of a simple ball and spring model. For both the isotropic
and hexagonal cases, induced dipole and quadrupole terms produce propagation of
stresses away from the vertical direction over short distances. The scale over
which such propagation occurs is significantly enhanced by the nonlinearities
that generate hexagonal anisotropy.",0706.3513v2
2007-07-01,"Giant Anisotropy of Magnetoresistance and ""Spin Valve"" effect in Antiferromagnetic $Nd_{2-x}Ce_xCuO_{4}$","We have studied anisotropic magnetoresistance (MR) and magnetization with
rotating magnetic field (B) within $CuO_2$ plane in lightly doped AF
$Nd_{2-x}Ce_xCuO_{4}$. \emph{A giant anisotropy} in MR is observed at low
temperature below 5 K. The c-axis resistivity can be tuned about one order of
magnitude just by changing B direction within $CuO_2$ plane and a scaling
behavior between out-of-plane and in-plane MR is found. A ""Spin valve"" effect
is proposed to understand the giant anisotropy of out-of-plane MR and the
evolution of scaling parameters with the external field. It is found that the
field-induced spin-flop transition of Nd$^{3+}$ layer under high magnetic field
is the key to understand the giant anisotropy. These results suggest that a
novel entanglement between charge and spin dominates the underlying physics.",0707.0104v3
2007-07-03,Entanglement generation resonances in XY chains,"We examine the maximum entanglement reached by an initially fully aligned
state evolving in an XY Heisenberg spin chain placed in a uniform transverse
magnetic field. Both the global entanglement between one qubit and the rest of
the chain and the pairwise entanglement between adjacent qubits is analyzed. It
is shown that in both cases the maximum is not a monotonous decreasing function
of the aligning field, exhibiting instead a resonant behavior for low
anisotropies, with pronounced peaks (a total of [n/2] peaks in the global
entanglement for an $n$-spin chain), whose width is proportional to the
anisotropy and whose height remains finite in the limit of small anisotropy. It
is also seen that the maximum pairwise entanglement is not a smooth function of
the field even in small finite chains, where it may exhibit narrow peaks above
strict plateaus. Explicit analytical results for small chains, as well as
general exact results for finite n-spin chains obtained through the
Jordan-Wigner mapping, are discussed.",0707.0473v1
2007-07-17,Correlated Anisotropies in the Cosmic Far-Infrared Background Detected by MIPS/Spitzer: Constraint on the Bias,"We report the detection of correlated anisotropies in the Cosmic Far-Infrared
Background at 160 microns. We measure the power spectrum in the Spitzer/SWIRE
Lockman Hole field. It reveals unambiguously a strong excess above cirrus and
Poisson contributions, at spatial scales between 5 and 30 arcminutes,
interpreted as the signature of infrared galaxy clustering. Using our model of
infrared galaxy evolution we derive a linear bias b=1.74 \pm 0.16. It is a
factor 2 higher than the bias measured for the local IRAS galaxies. Our model
indicates that galaxies dominating the 160 microns correlated anisotropies are
at z~1. This implies that infrared galaxies at high redshifts are biased
tracers of mass, unlike in the local Universe.",0707.2443v1
2007-07-31,Violation of the isotropic-$\ell$ approximation in overdoped La_{2-x}Sr_xCuO_4,"Magnetotransport measurements on the overdoped cuprate La_{1.7}Sr_{0.3}CuO_4
are fitted using the Ong construction and band parameters inferred from
angle-resolved photoemission. Within a band picture, the low temperature Hall
data can only be fitted satisfactorily by invoking strong basal-plane
anisotropy in the mean-free-path $\ell$. This violation of the isotropic-$\ell$
approximation supports a picture of dominant small-angle elastic scattering in
cuprates due to out-of-plane substitutional disorder. We show that both band
anisotropy and anisotropy in the elastic scattering channel strongly
renormalize the Hall coefficient in overdoped La_{2-x}Sr_xCuO_4 over a wide
doping and temperature range.",0707.4601v1
2007-09-07,Detecting Cosmic Strings in the CMB with the Canny Algorithm,"Line discontinuities in cosmic microwave background anisotropy maps are a
distinctive prediction of models with cosmic strings. These signatures are
visible in anisotropy maps with good angular resolution and should be
identifiable using edge detection algorithms. One such algorithm is the Canny
algorithm. We study the potential of this algorithm to pick out the line
discontinuities generated by cosmic strings. By applying the algorithm to
small-scale microwave anisotropy maps generated from theoretical models with
and without cosmic strings, we find that, given an angular resolution of
several minutes of arc, cosmic strings can be detected down to a limit of the
mass per unit length of the string which is one order of magnitude lower than
the current upper bounds.",0709.0982v3
2007-09-12,The velocity distribution of SDSS satellites in MOND,"The recent SDSS measured velocity distribution of satellite galaxies has been
modelled in the context of MOND. We show that even when the extra constraint of
adhering to the projected satellite number density profile is added, the two
line of sight (los) velocity dispersion profiles presented in Klypin & Prada
(2007) can be matched simply with a radially varying anisotropy. Interestingly,
the anisotropies required to fit the los velocity dispersions are remarkably
similar to the anisotropies generated by dissipationless collapse simulations
in MOND. The mass-to-light ratios of the two host galaxies used are sensible
and positivity of the distribution function is satisfied.",0709.1966v1
2007-09-22,Measuring Quark-Gluon-Plasma Thermalization Time with Dileptons,"We calculate the medium dilepton yield from a quark-gluon plasma which has a
time-dependent local momentum-space anisotropy. A phenomenological model for
the hard momentum scale, p_hard(tau), and plasma anisotropy parameter, xi(tau),
is constructed which interpolates between free streaming behavior at early
times (tau << tau_iso) and ideal hydrodynamic behavior at late times (tau >>
tau_iso). We show that high-energy dilepton production is sensitive to the
assumed plasma isotropization time, tau_iso, and can therefore be used to
experimentally determine the time of onset for hydrodynamic expansion of a
quark-gluon plasma and the magnitude of expected early-time momentum-space
anisotropies.",0709.3576v3
2007-10-05,Biconical structures in two-dimensional anisotropic Heisenberg antiferromagnets,"Square lattice Heisenberg and XY antiferromagnets with uniaxial anisotropy in
a field along the easy axis are studied. Based on ground state considerations
and Monte Carlo simulations, the role of biconical structures in the transition
region between the antiferromagnetic and spin--flop phases is analyzed. In
particular, adding a single--ion anisotropy to the XXZ antiferromagnet, one
observes, depending on the sign of that anisotropy, either an intervening
biconical phase or a direct transition of first order separating the two
phases. In case of the anisotropic XY model, the degeneracy of the ground
state, at a critical field, in antiferromagnetic, spin--flop, and bidirectional
structures seems to result, as in the case of the XXZ model, in a narrow
disordered phase between the antiferromagnetic and spin--flop phases, dominated
by bidirectional fluctuations.",0710.1251v2
2007-10-06,Global anisotropy of arrival directions of ultra-high-energy cosmic rays: capabilities of space-based detectors,"Planned space-based ultra-high-energy cosmic-ray detectors (TUS, JEM-EUSO and
S-EUSO) are best suited for searches of global anisotropies in the distribution
of arrival directions of cosmic-ray particles because they will be able to
observe the full sky with a single instrument. We calculate quantitatively the
strength of anisotropies associated with two models of the origin of the
highest-energy particles: the extragalactic model (sources follow the
distribution of galaxies in the Universe) and the superheavy dark-matter model
(sources follow the distribution of dark matter in the Galactic halo). Based on
the expected exposure of the experiments, we estimate the optimal strategy for
efficient search of these effects.",0710.1382v2
2007-10-18,FFLO state in thin superconducting films,"We present the analysis of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) superconducting state in thin superconducting films in the parallel
magnetic field. For the tetragonal crystal symmetry (relevant to CeCoIn$_{5}$ -
the most probable candidate for the FFLO state formation) we predict a very
peculiar in-plane angular dependence of the FFLO critical field due to the
orbital effect. In the uniform superconducting state the critical field should
be isotropic. The magnetic field pins also the direction of the FFLO modulation
permitting thus to study the critical current anisotropy. Our calculations
reveal a strong critical current anisotropy in the FFLO state in sharp contrast
with the usual superconducting state. The predicted characteristic anisotropies
of the critical field and critical current may provide an unambiguous probe of
the FFLO phase formation.",0710.3613v1
2007-11-07,Characterization of graphene through anisotropy of constant-energy maps in angle-resolved photoemission,"We show theoretically how constant-energy maps of the angle-resolved
photoemission intensity can be used to test wave function symmetry in graphene.
For monolayer graphene, we demonstrate that the observed anisotropy of ARPES
spectra is a manifestation of what has been recently branded as electronic
chirality. For bilayer graphene, we show that the anisotropy of the
constant-energy maps may be used to extract information about the magnitude and
sign of interlayer coupling parameters and about symmetry breaking inflicted on
a bilayer by the underlying substrate.",0711.1129v2
2007-12-14,Mass modelling of galaxy clusters via velocity moments,"We summarize the method of mass modelling of galaxy clusters based on
reproducing the dispersion and kurtosis of the projected velocity distribution
of galaxies. The models are parametrized within the framework of the NFW
density profile, characterized by the virial mass and concentration, together
with the constant anisotropy of galaxy orbits. The use of velocity dispersion
alone does not allow to constrain all the three parameters from kinematic data
due to the mass-anisotropy degeneracy. The degeneracy is broken by introducing
the fourth velocity moment, the kurtosis. We tested the method based on fitting
both moments on mock data sets drawn from simulated dark matter haloes and
showed it to reproduce reliably the properties of the haloes. The method has
been applied to estimate the mass, concentration and anisotropy of more than 20
clusters which allowed us to confirm, for the first time using kinematic data,
the mass-concentration relation found in N-body simulations.",0712.2368v1
2008-01-06,Avalanches in anisotropic sheared granular media,"We study the influence of particle shape anisotropy on the occurrence of
avalanches in sheared granular media. We use molecular dynamic simulations to
calculate the relative movement of two tectonic plates. % with transform
boundaries. Our model considers irregular polygonal particles constituting the
material within the shear zone. We find that the magnitude of the avalanches is
approximately independent on particle shape and in good agreement with the
Gutenberg-Richter law, but the aftershock sequences are strongly influenced by
the particle anisotropy yielding variations on the exponent characterizing the
empirical Omori's law. Our findings enable one to identify the presence of
anisotropic particles at the macro-mechanical level only by observing the
avalanche sequences of real faults. In addition, we calculate the probability
of occurrence of an avalanche for given values of stiffness or frictional
strength and observe also a significant influence of the particle anisotropy.",0801.0862v1
2008-01-14,Anisotropic Susceptibility of La_2-xSr_xCoO_4 related to the Spin States of Cobalt,"We present a study of the magnetic susceptibility of La_2-xSr_xCoO_4 single
crystals in a doping range 0.3<=x<=0.8. Our data shows a pronounced magnetic
anisotropy for all compounds. This anisotropy is in agreement with a low-spin
ground state (S=0) of Co^3+ for x>=0.4 and a high-spin ground state (S=3/2) of
Co^2+. We compare our data with a crystal-field model calculation assuming
local moments and find a good description of the magnetic behavior for x>=0.5.
This includes the pronounced kinks observed in the inverse magnetic
susceptibility, which result from the anisotropy and low-energy excited states
of Co^2+ and are not related to magnetic ordering or temperature-dependent
spin-state transitions.",0801.2087v1
2008-01-21,Uniaxially anisotropic antiferromagnets in a field on a square lattice,"Classical uniaxially anisotropic Heisenberg and XY antiferromagnets in a
field along the easy axis on a square lattice are analysed, applying ground
state considerations and Monte Carlo techniques. The models are known to
display antiferromagnetic and spin-flop phases. In the Heisenberg case, a
single-ion anisotropy is added to the XXZ antiferromagnet, enhancing or
competing with the uniaxial exchange anisotropy. Its effect on the stability of
non-collinear structures of biconical type is studied. In the case of the
anisotropic XY antiferromagnet, the transition region between the
antiferromagnetic and spin-flop phases is found to be dominated by degenerate
bidirectional fluctuations. The phase diagram is observed to resemble closely
that of the XXZ antiferromagnet without single-ion anisotropy.",0801.3217v1
2008-02-21,Discrete Fracture Model with Anisotropic Load Sharing,"A two-dimensional fracture model where the interaction among elements is
modeled by an anisotropic stress-transfer function is presented. The influence
of anisotropy on the macroscopic properties of the samples is clarified, by
interpolating between several limiting cases of load sharing. Furthermore, the
critical stress and the distribution of failure avalanches are obtained
numerically for different values of the anisotropy parameter $\alpha$ and as a
function of the interaction exponent $\gamma$. From numerical results, one can
certainly conclude that the anisotropy does not change the crossover point
$\gamma_c=2$ in 2D. Hence, in the limit of infinite system size, the crossover
value $\gamma_c=2$ between local and global load sharing is the same as the one
obtained in the isotropic case. In the case of finite systems, however, for
$\gamma\le2$, the global load sharing behavior is approached very slowly.",0802.3003v1
2008-03-10,Distribution Function of Dark Matter with Constant Anisotropy,"N-body simulations of dark matter halos show that the density is cusped near
the center of the halo. The density profile behaves as $r^{-\gamma}$ in the
inner parts, where $\gamma \simeq 1$ for the NFW model and $\gamma \simeq 1.5$
for the Moore's model, but in the outer parts, both models agree with each
other in the asymptotic behavior of the density profile. The simulations also
show the information about anisotropy parameter $\beta(r)$ of velocity
distribution. $\beta\approx 0$ in the inner part and $\beta\approx 0.5$
(radially anisotropic) in the outer part of the halo. We provide some
distribution functions $F(E,L)$ with the constant anisotropy parameter $\beta$
for the two spherical models of dark matter halos: a new generalized NFW model
and a generalized Moore model. There are two parameters $\alpha$ and $\epsilon$
for those two generalized models to determine the asymptotic behavior of the
density profile. In this paper, we concentrate on the situation of
$\beta(r)=1/2$ from the viewpoint of the simulation.",0803.1431v2
2008-03-23,S-Z Power Spectra,"There is some observational evidence for earlier evolution of clusters of
galaxies than predicted in the standard LambdaCDM model with a Gaussian
primordial density fluctuation field, and a low value for the mass variance
parameter sigma_8. Particularly difficult in this model is the interpretation
of possible excess CMB anisotropy on cluster scales as due to the
Sunyaev-Zeldovich (S-Z) effect. We have calculated S-Z power spectra in the
standard model, and in two alternative models which predict higher cluster
abundance - a model with non-Gaussian PDF, and an early dark energy model. As
anticipated, the levels of S-Z power in the latter two models are significantly
higher than in the standard model, and in good agreement with current
measurements of CMB anisotropy at high multipole values. Our results provide a
sufficient basis for testing the viability of the three models by futur high
quality measurements of cluster abundance and the anisotropy induced by the S-Z
effect.",0803.3323v1
2008-03-24,Solution of the Holstein polaron anisotropy problem,"We study Holstein polarons in three-dimensional anisotropic materials. Using
a variational exact diagonalization technique we provide highly accurate
results for the polaron mass and polaron radius. With these data we discuss the
differences between polaron formation in dimension one and three, and at small
and large phonon frequency. Varying the anisotropy we demonstrate how a polaron
evolves from a one-dimensional to a three-dimensional quasiparticle. We thereby
resolve the issue of polaron stability in quasi-one-dimensional substances and
clarify to what extent such polarons can be described as one-dimensional
objects. We finally show that even the local Holstein interaction leads to an
enhancement of anisotropy in charge carrier motion.",0803.3425v2
2008-04-09,Anisotropic interaction of two-level systems with acoustic waves in disordered crystals,"We apply the model introduced in Phys. Rev. B 75, 064202 (2007),
cond-mat/0610469, to calculate the anisotropy effect in the interaction of two
level systems with phonons in disordered crystals. We particularize our
calculations to cubic crystals and compare them with the available experimental
data to extract the parameters of the model. With these parameters we calculate
the interaction of the dynamical defects in the disordered crystal with phonons
(or sound waves) propagating along other crystalographic directions, providing
in this way a method to investigate if the anisotropy comes from the two-level
systems being preferably oriented in a certain direction or solely from the
lattice anisotropy with the two-level systems being isotropically oriented.",0804.1481v1
2008-04-24,Covalency effects on the magnetism of EuRh2P2,"In experiments, the ternary Eu pnictide EuRh2P2 shows an unusual coexistence
of a non-integral Eu valence of about 2.2 and a rather high Neel temperature of
50 K. In this paper, we present a model which explains the non-integral Eu
valence via covalent bonding of the Eu 4f-orbitals to P2 molecular orbitals. In
contrast to intermediate valence models where the hybridization with
delocalized conduction band electrons is known to suppress magnetic ordering
temperatures to at most a few Kelvin, covalent hybridization to the localized
P2 orbitals avoids this suppression. Using perturbation theory we calculate the
valence, the high temperature susceptibility, the Eu single-ion anisotropy and
the superexchange couplings of nearest and next-nearest neighbouring Eu ions.
The model predicts a tetragonal anisotropy of the Curie constants. We suggest
an experimental investigation of this anisotropy using single crystals. From
experimental values of the valence and the two Curie constants, the three free
parameters of our model can be determined.",0804.3905v1
2008-05-02,"Quasistatic rheology, force transmission and fabric properties of a packing of irregular polyhedral particles","By means of contact dynamics simulations, we investigate a dense packing
composed of polyhedral particles under quasistatic shearing. The effect of
particle shape is analyzed by comparing the polyhedra packing with a packing of
similar characteristics except for the spherical shape of the particles. The
polyhedra packing shows higher shear stress and dilatancy but similar
stress-dilatancy relation compared to the sphere packing. A harmonic
approximation of granular fabric is presented in terms of branch vectors
(connecting particle centers) and contact force components along and
perpendicular to the branch vectors. It is found that the origin of enhanced
shear strength of the polyhedra packing lies in its higher force anisotropy
with respect to the sphere packing which has a higher fabric anisotropy.
Various contact types (face-vertex, face-face, etc) contribute differently to
force transmission and fabric anisotropy. In particular, most face-face
contacts belong to strong force chains along the major principal stress
direction whereas vertex-face contacts are correlated with weak forces and
oriented on average along the minor principal stress direction in steady
shearing.",0805.0178v1
2008-05-16,Characterization of Geometric Structures of Biaxial Nematic Phases,"The ordering matrix, which was originally introduced by de Gennes, is a
well-known mathematical device for describing orientational order of biaxial
nematic liquid crystal. In this paper we propose a new interpretation of the
ordering matrix. We slightly modify the definition of the ordering matrix and
call it the geometric order parameter. The geometric order parameter is a
linear transformation which transforms a tensorial quantity of an individual
molecule to a tensorial quantity observed at a macroscopic scale. The degree of
order is defined as the singular value of the geometric order parameter. We
introduce the anisotropy diagram, which is useful for classification and
comparison of various tensorial quantities. As indices for evaluating
anisotropies of tensorial quantities, we define the degree of anisotropy and
the degree of biaxiality. We prove that a simple diagrammatic relation holds
between a microscopic tensor and a macroscopic tensor. We provide a
prescription to formulate the Landau-de Gennes free energy of a system whose
constituent molecules have an arbitrary shape. We apply our prescription to a
system which consists of D_{2h}-symmetric molecules.",0805.2471v2
2008-05-23,AC and DC Conductivity Anisotropies in Lightly Doped La(2-x)Sr(x)CuO(4),"The AC and DC conductivity anisotropies in the low temperature orthorhombic
phase of lightly doped La(2-x)Sr(x)CuO(4) are ascribed to the rotational
symmetry broken, localized impurity states resulting from the trapping of doped
holes by Sr ions. The two lowest-energy p-wave-like states are split by
orthorhombicity and partially filled with holes. This leaves a unique imprint
in AC conductivity, which shows two distinct infrared continuum absorption
energies. Furthermore, the existence of two independent channels for hopping
conductivity, associated to the two orthorhombic directions, explains
quantitatively the observed low temperature anisotropies in DC conductivity.",0805.3609v2
2008-05-26,"Magnetic reversal under external field and current-driven domain wall motion in (Ga,Mn)As: influence of extrinsic pinning","We investigate the anisotropy of magnetic reversal and current-driven domain
wall motion in annealed Ga_0.95Mn_0.05As thin films and Hall bar devices with
perpendicular magnetic anisotropy. Hall bars with current direction along the
[110] and [1-10] crystallographic axes are studied. The [110] device shows
larger coercive field than the [1-10] device. Strong anisotropy is observed
during magnetic reversal between [110] and [1-10] directions. A power law
dependence is found for both devices between the critical current (JC) and the
magnetization (M), with J_C is proportional to M^2.6. The domain wall motion is
strongly influenced by the presence of local pinning centres.",0805.3998v1
2008-06-03,Critical Fields and Anisotropy of NdO0.82F0.18FeAs Single Crystals,"The newly discovered iron-based superconductors have stimulated enormous
interests in the field of superconductivity. Since the new superconductor is a
layered system, the anisotropy is a parameter with the first priority to know.
Meanwhile any relevant message about the critical fields (upper critical field
and irreversibility line) are essentially important. By using flux method, we
have successfully grown the single crystals NdO0.82F0.18FeAs at ambient
pressure. Resistive measurements reveal a surprising discovery that the
anisotropy \Gamma = (mc/mab)^{1/2} is below 5, which is much smaller than the
theoretically calculated results. The data measured up to 400 K show a
continuing curved feature which prevents a conjectured linear behavior for an
unconventional metal. The upper critical fields determined based on the
Werthamer-Helfand-Hohenberg formula are H_{c2}^{H||ab}(T=0 K) = 304 T and
H_{c2}^{H||c}(T=0 K)=62-70 T, indicating a very encouraging application of the
new superconductors.",0806.0532v1
2008-06-23,Evolution of Anisotropies in Eddington-Born-Infeld Cosmology,"Recently a Born-Infeld action for dark energy and dark matter that uses
additional affine connections was proposed. At background level, it was shown
that the new proposal can mimic the standard cosmological evolution. In Bianchi
cosmologies, contrary to the scalar field approach (e.g., Chaplygin gas), the
new approach leads to anisotropic pressure, raising the issues of stability of
the isotropic solution under anisotropic perturbations and, being it stable,
how the anisotropies evolve. In this work, the Eddington-Born-Infeld proposal
is extended to a Bianchi type I scenario and residual post-inflationary
anisotropies are shown to decay in time. Moreover, it is shown that the shears
decay following a damped oscillatory pattern, instead of the standard
exponential-like decay. Allowing for some fine tuning on the initial
conditions, standard theoretical bounds on the shears can be avoided.",0806.3613v3
2008-07-09,Delayed Recombination and Cosmic Parameters,"Current cosmological constraints from Cosmic Microwave Background (CMB)
anisotropies are typically derived assuming a standard recombination scheme,
however additional resonance and ionizing radiation sources can delay
recombination, altering the cosmic ionization history and the cosmological
inferences drawn from CMB data. We show that for recent observations of CMB
anisotropy, from the Wilkinson Microwave Anisotropy Probe satellite mission
5-year survey (WMAP5) and from the ACBAR experiment, additional resonance
radiation is nearly degenerate with variations in the spectral index, n_s, and
has a marked effect on uncertainties in constraints on the Hubble constant, age
of the universe, curvature and the upper bound on the neutrino mass. When a
modified recombination scheme is considered, the redshift of recombination is
constrained to z_*=1078\pm11, with uncertainties in the measurement weaker by
one order of magnitude than those obtained under the assumption of standard
recombination while constraints on the shift parameter are shifted by 1-sigma
to R=1.734\pm0.028. Although delayed recombination limits the precision of
parameter estimation from the WMAP satellite, we demonstrate that this should
not be the case for future, smaller angular scales measurements, such as those
by the Planck satellite mission.",0807.1420v1
2008-07-16,Solid behavior of anisotropic rigid frictionless bead assemblies,"We investigate the structure and mechanical behavior of assemblies of
frictionless, nearly rigid equal-sized beads, in the quasistatic limit, by
numerical simulation. Three different loading paths are explored: triaxial
compression, triaxial extension and simple shear. Generalizing recent results
[1], we show that the material, despite rather strong finite sample size
effects, is able to sustain a finite deviator stress in the macroscopic limit,
along all three paths, without dilatancy. The shape of the yield surface is
adequately described by a Lade-Duncan (rather than Mohr-Coulomb) criterion.
While scalar state variables keep the same values as in isotropic systems,
fabric and force anisotropies are each characterized by one parameter and are
in one-to-one correspondence with principal stress ratio along all three
loading paths.The anisotropy of the pair correlation function extends to a
distance between bead surfaces on the order of 10% of the diameter. The tensor
of elastic moduli is shown to possess a nearly singular, uniaxial structure
related to stress anisotropy. Possible stress-strain relations in monotonic
loading paths are also discussed.",0807.2513v2
2008-07-29,Anisotropic pairing in the iron pnictides,"We determine the anisotropy of the spin fluctuation induced pairing gap on
the Fermi surface of the FeAs based superconductors as function of the exchange
and Hund's coupling $J_{H}$. We find that for sufficiently large $J_{H}$,
nearly commensurate magnetic fluctuations yield a fully gapped
$s^{\pm}$-pairing state with small anisotropy of the gap amplitude on each
Fermi surface sheet, but significant variations of the gap amplitude for
different sheets of the Fermi surface. In particular, we obtain the large
variation of the gap amplitude on different Fermi surface sheets, as seen in
ARPES experiments. For smaller values of Hund's coupling incommensurate
magnetic fluctuations yield an $s^{\pm}$-pairing state with line nodes. Such a
state is also possible once the anisotropy of the material is reduced and three
dimensional effects come into play.",0807.4566v2
2008-08-04,Primordial non-Gaussianity estimator: the inhomogeneous noise effect,"Since the inhomogeneous instrument noise can produce extra non-Gaussianity in
the CMB anisotropy, its effect should be carefully subtracted in the primordial
non-Gaussianity estimation. We calculate the probability distribution function
of the CMB anisotropy for local type of non-Gaussianity, from which the optimal
estimator in the general case (inhomogeneous noise and cut sky) is obtained.
The new estimator obtained here is different from the popular one, since the
inhomogeneous noise and cut sky effects are completely accounted. The CMB
anisotropy in the new estimator is noise weighted. The noise weight is
different from that used by WMAP Group in their 5-year data analysis. Although
it is still difficult to calculate the new estimator rigorously, for the case
of the slightly inhomogeneous noise, there exists a series expansion method to
compute the new estimator. Each order in the series is suppressed by two
factors, $(\frac{\sigma^2}{\sigma^2_{i}}-1)$ and $\frac{C_l}{C^{tot}_{l}}$,
which make the method feasible. Through the Edgeworth expansion we can
generalize our discussion to other types of non-Gaussianity.",0808.0424v1
2008-08-12,Anisotropy and Magnetism in the LSDA+U Method,"Consequences of anisotropy (variation of orbital occupation) and magnetism,
and their coupling, are analyzed for LSDA+U functionals, both the commonly used
ones as well as less commonly applied functionals. After reviewing and
extending some earlier observations for an isotropic interaction, the
anisotropies are examined more fully and related to use with the local density
(LDA) or local spin density (LSDA) approximations. The total energies of all
possible integer configurations of an open $f$ shell are presented for three
functionals, where some differences are found to be dramatic. Differences in
how the commonly used ""around mean field"" (AMF) and ""fully localized limit""
(FLL) functionals perform are traced to such differences. The LSDA+U
interaction term, applied self-consistently, usually enhances spin magnetic
moments and orbital polarization, and the double-counting terms of both
functionals provide an opposing, moderating tendency (""suppressing the magnetic
moment""). The AMF double counting term gives magnetic states a significantly
larger energy penalty than does the FLL counterpart.",0808.1706v3
2008-08-14,Determination of the single-ion anisotropy energy in a S = 5/2 kagome antiferromagnet using X-ray absorption spectroscopy,"We report x-ray absorption and x-ray linear dichroism measurements at the Fe
L2,3 edges of the geometrically frustrated systems of potassium and hydronium
iron jarosite. Comparison with simulated spectra, involving ligand-field
multiplet calculations modelling the 3d-2p hybridization between the iron ion
and the oxygen ligands, has yielded accurate estimates for the ligand metal-ion
hybridization and the resulting single-ion crystal field anisotropy energy.
Using this method we provide an experimentally verified scenario for the
appearance of a single-ion anisotropy in this nominally high-spin 3d5 orbital
singlet 6S system, which accounts for features of the spin-wave dispersion in
the long-range ordered ground state of potassium iron jarosite.",0808.1969v2
2008-08-18,"Upper critical field, anisotropy, and superconducting properties of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals","The temperature dependent resistivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (x =
0.23, 0.25, 0.28 and 0.4) single crystals and the angle dependent resistivity
of superconducting Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystals were
measured in magnetic fields up to 9 T. The measurements of temperature
dependent resistivity for samples with different doping levels revealed very
high upper critical fields which increase with the transition temperature
monotonously, and a very low superconducting anisotropy ratio
$\Gamma=H_{c2}^{ab}/H_{c2}^c \approx$ 2. By scaling the resistivity in the
frame of the anisotropic Ginzburg-Landau theory, the angle dependent
resistivity of the Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystal measured with
different magnetic fields at a certain temperature collapsed onto one curve. As
the only scaling parameter, the anisotropy $\Gamma$ was determined
alternatively for each temperature and was found to be between two and three.",0808.2392v3
2008-08-20,The ground-state magnetic ordering of the spin-1/2 frustrated J1-J2 XXZ model on the square lattice,"Using the coupled-cluster method for infinite lattices and the exact
diagonalization method for finite lattices, we study the influence of an
exchange anisotropy Delta on the ground-state phase diagram of the spin-1/2
frustrated J1-J2 XXZ antiferromagnet on the square lattice. We find that
increasing Delta>1 (i.e. an Ising type easy-axis anisotropy) as well as
decreasing Delta<1 (i.e. an XY type easy-plane anisotropy) both lead to a
monotonic shrinking of the parameter region of the magnetically disordered
quantum phase. Finally, at Delta~1.9 this quantum phase disappears, whereas in
pure XY limit (Delta=0) there is still a narrow region around J2 =0.5J1 where
the quantum paramagnetic ground-state phase exists.",0808.2743v2
2008-09-14,Geometric-Phase-Effect Tunnel-Splitting Oscillations in Single-Molecule Magnets with Fourth-Order Anisotropy Induced by Orthorhombic Distortion,"We analyze the interference between tunneling paths that occurs for a spin
system with both fourth-order and second-order transverse anisotropy. Using an
instanton approach, we find that as the strength of the second-order transverse
anisotropy is increased, the tunnel splitting is modulated, with zeros
occurring periodically. This effect results from the interference of four
tunneling paths connecting easy-axis spin orientations and occurs in the
absence of any magnetic field.",0809.2289v2
2008-09-15,Thermodynamic Properties of Kagome Antiferromagnets with different Perturbations,"We discuss the results of several small perturbations to the thermodynamic
properties of Kagome Lattice Heisenberg Model (KLHM) at high and intermediate
temperatures, including Curie impurities, dilution, in-plane and out of plane
Dzyaloshinski-Moria (DM) anisotropies and exchange anisotropy. We examine the
combined role of Curie impurities and dilution in the behavior of uniform
susceptibility. We also study the changes in specific heat and entropy with
various anisotropies. Their relevance to newly discovered materials
ZnCu3(OH)6Cl2 is explored. We find that the magnetic susceptibility is well
described by about 6 percent impurity and dilution. We also find that the
entropy difference between the material and KLHM is well described by the DM
parameter D_z/J~0.1.",0809.2621v2
2008-10-20,Measurement of the dark matter velocity anisotropy profile in galaxy clusters,"Dark matter particles form halos that contribute the major part of the mass
of galaxy clusters. The formation of these cosmological structures have been
investigated both observationally and in numerical simulations, which have
confirmed the existence of a universal mass profile. However, the dynamic
behaviour of dark matter in halos is not as well understood. We have used
observations of 16 equilibrated galaxy clusters to show that the random
velocities of dark matter particles are larger on average along the radial
direction than along the tangential, and that the magnitude of this velocity
anisotropy is radially varying. Our measurement implies that the collective
behaviour of dark matter particles is fundamentally different from that of
normal particles and the radial variation of the anisotropy velocity agrees
with the predictions of numerical simulation.",0810.3676v1
2008-10-30,Patch coalescence as a mechanism for eukaryotic directional sensing,"Eukaryotic cells possess a sensible chemical compass allowing them to orient
toward sources of soluble chemicals. The extracellular chemical signal triggers
separation of the cell membrane into two domains populated by different
phospholipid molecules and oriented along the signal anisotropy. We propose a
theory of this polarization process, which is articulated into subsequent
stages of germ nucleation, patch coarsening and merging into a single domain.
We find that the polarization time, $t_\epsilon$, depends on the anisotropy
degree $\epsilon$ through the power law $t_\epsilon\propto \epsilon^{-2}$, and
that in a cell of radius $R$ there should exist a threshold value
$\epsilon_\mathrm{th}\propto R^{-1}$ for the smallest detectable anisotropy.",0810.5409v1
2008-11-04,The Anisotropic Spatial Distribution of Hypervelocity Stars,"We study the distribution of angular positions and angular separations of
unbound hypervelocity stars (HVSs). HVSs are spatially anisotropic at the
3-sigma level. The spatial anisotropy is significant in Galactic longitude, not
in latitude, and the inclusion of lower velocity, possibly bound HVSs reduces
the significance of the anisotropy. We discuss how the observed distribution of
HVSs may be linked to their origin. In the future, measuring the distribution
of HVSs in the southern sky will provide additional constraints on the spatial
anisotropy and the origin of HVSs.",0811.0612v2
2008-11-11,Signals of Statistical Anisotropy in WMAP Foreground-Cleaned Maps,"Recently a symmetry-based method to test for statistical isotropy of the
cosmic microwave background was developed. We apply the method to
template-cleaned 3-year and 5-year WMAP-$DA$ maps. We examine a wide range of
angular multipoles from $2 < l < 300$. The analysis detects statistically
signicant signals of anisotropy inconsistent with an isotropic CMB in some of
the foreground cleaned maps. We are unable to resolve whether the anomalies
have a cosmological, local astrophysical or instrumental origin. Assuming the
anisotropy arises due to residual foreground contamination, we estimate the
residual foreground power in the maps. For the W band maps, we also find a
highly improbable degree of isotropy we cannot explain. We speculate that
excess isotropy may be caused by faulty modeling of detector noise.",0811.1639v2
2008-11-13,The flattening and the orbital structure of early-type galaxies and collisionless N-body binary disk mergers,"We use oblate axisymmetric dynamical models including dark halos to determine
the orbital structure of intermediate mass to massive Coma early-type galaxies.
We find a large variety of orbital compositions. Averaged over all sample
galaxies the unordered stellar kinetic energy in the azimuthal and the radial
direction are of the same order, but they can differ by up to 40 percent in
individual systems. In contrast, both for rotating and non-rotating galaxies
the vertical kinetic energy is on average smaller than in the other two
directions. This implies that even most of the rotating ellipticals are
flattened by an anisotropy in the stellar velocity dispersions. Using
three-integral axisymmetric toy models we show that flattening by stellar
anisotropy maximises the entropy for a given density distribution.
Collisionless disk merger remnants are radially anisotropic. The apparent lack
of strong radial anisotropy in observed early-type galaxies implies that they
may not have formed from mergers of disks unless the influence of dissipational
processes was significant.",0811.2130v1
2008-12-03,Quantum communication through anisotropic Heisenberg XY spin chains,"We study quantum communication through an anisotropic Heisenberg XY chain in
a transverse magnetic field. We find that for some time $t$ and anisotropy
parameter $\gamma$, one can transfer a state with a relatively high fidelity.
In the strong-field regime, the anisotropy does not significantly affect the
fidelity while in the weak-field regime the affect is quite pronounced. The
most interesting case is the the intermediate regime where the oscillation of
the fidelity with time is low and the high-fidelity peaks are relatively broad.
This would, in principle, allow for quantum communication in realistic
circumstances. Moreover, we calculate the purity, or tangle, as a measure of
the entanglement between one spin and all the other spins in the chain and find
that the stronger the anisotropy and exchange interaction, the more
entanglement will be generated for a given time.",0812.0645v2
2008-12-08,CMB anisotropy induced by tachyonic perturbations of dark energy,"We study effects of possible tachyonic perturbations of dark energy on the
CMB temperature anisotropy. Motivated by some models of phantom energy, we
consider both Lorentz-invariant and Lorentz-violating dispersion relations for
tachyonic perturbations. We show that in the Lorentz-violating case, the shape
of the CMB anisotropy spectrum generated by the tachyonic perturbations is very
different from that due to adiabatic scalar perturbations and, if sizeable, it
would be straightforwardly distinguished from the latter. The tachyonic
contribution improves slightly the agreement between the theory and data;
however, this improvement is not statistically significant, so our analysis
results in limits on the time scale of the tachyonic instability. In the
Lorentz-invariant case, tachyonic contribution is a rapidly decaying function
of the multipole number $l$, so that the entire observed dipole can be
generated without conflicting the data at higher multipoles. On the
conservative side, our comparison with the data places limit on the absolute
value of the (imaginary) tachyon mass in the Lorentz-invariant case.",0812.1459v2
2008-12-15,Scattering polarization due to light source anisotropy,"We consider the polarization arising from scattering in an envelope
illuminated by a central anisotropic source. Spherical harmonics are used to
describe both the light source anisotropy and the envelope density distribution
functions of the scattering particles. This framework demonstrates how the net
resultant polarization arises from a superposition of three basic ""shape""
functions: the distribution of source illumination, the distribution of
envelope scatterers, and the phase function for dipole scattering. Specific
expressions for the Stokes parameters and scattered flux are derived for the
case of an ellipsoidal light source inside an ellipsoidal envelope, with
principal axes that are generally not aligned. Two illustrative examples are
considered: (a) axisymmetric mass loss from a rapidly rotating star, such as
may apply to some Luminous Blue Variables, and (b) a Roche-lobe filling star in
a binary system with a circumstellar envelope. As a general conclusion, the
combination of source anisotropy with distorted scattering envelopes leads to
more complex polarimetric behavior such that the source characteristics should
be carefully considered when interpreting polarimetric data.",0812.2772v1
2009-01-18,Stable topological textures in a classical 2D Heisenberg model,"We show that stable localized topological soliton textures (skyrmions) with
$\pi_2$ topological charge $\nu \geq 1$ exist in a classical 2D Heisenberg
model of a ferromagnet with uniaxial anisotropy. For this model the soliton
exist only if the number of bound magnons exceeds some threshold value $N_{\rm
cr}$ depending on $\nu $ and the effective anisotropy constant $K_{\rm eff}$.
We define soliton phase diagram as the dependence of threshold energies and
bound magnons number on anisotropy constant. The phase boundary lines are
monotonous for both $\nu=1$ and $\nu >2$, while the solitons with $\nu=2$
reveal peculiar nonmonotonous behavior, determining the transition regime from
low to high topological charges. In particular, the soliton energy per
topological charge (topological energy density) achieves a minimum neither for
$\nu=1$ nor high charges, but rather for intermediate values $\nu=2$ or
$\nu=3$.",0901.2707v1
2009-01-20,"Phase diagram of the frustrated, spatially anisotropic S=1 antiferromagnet on a square lattice","We study the S=1 square lattice Heisenberg antiferromagnet with spatially
anisotropic nearest neighbor couplings $J_{1x}$, $J_{1y}$ frustrated by a
next-nearest neighbor coupling $J_{2}$ numerically using the density-matrix
renormalization group (DMRG) method and analytically employing the
Schwinger-Boson mean-field theory (SBMFT). Up to relatively strong values of
the anisotropy, within both methods we find quantum fluctuations to stabilize
the N\'{e}el ordered state above the classically stable region. Whereas SBMFT
suggests a fluctuation-induced first order transition between the N\'{e}el
state and a stripe antiferromagnet for $1/3\leq J_{1x}/J_{1y}\leq 1$ and an
intermediate paramagnetic region opening only for very strong anisotropy, the
DMRG results clearly demonstrate that the two magnetically ordered phases are
separated by a quantum disordered region for all values of the anisotropy with
the remarkable implication that the quantum paramagnetic phase of the spatially
isotropic $J_{1}$-$J_{2}$ model is continuously connected to the limit of
decoupled Haldane spin chains. Our findings indicate that for S=1 quantum
fluctuations in strongly frustrated antiferromagnets are crucial and not
correctly treated on the semiclassical level.",0901.3141v1
2009-01-31,Anisotropy Studies with the Pierre Auger Observatory,"An anisotropy signal for the arrival directions of ultra-high energy cosmic
rays (UHECR) of more than 99% confidence level was established using data
collected by the Pierre Auger Observatory. Cosmic rays with energy above $\sim
6 \times 10^{19}$ eV show a correlation with the positions of extragalactic
nearby active galactic nuclei (AGN), being maximum for sources at less than
$\sim$100 Mpc and angular separation of a few degrees. The evolution of the
correlation signal with the energy shows that the departure from anisotropy
coincides with the flux suppression observed in the spectrum, being therefore
consistent with the hypothesis that the correlated events have their origin in
extragalactic sources close enough to avoid significant interaction with the
cosmic microwave background (the Greisen-Zatsepin-Kuz'min effect). Even though
the observed signal cannot unambiguously identify AGNs as the production sites
of UHECRs, the potential sources have to be distributed in a similar way. A
number of additional statistical tests were performed in order to further
understand the nature of the correlation signal.",0902.0040v1
2009-03-03,Dzyaloshinskii-Moriya Interaction and Anisotropy effects on the Entanglement of Heisenberg Model,"In this paper the the effect of Dzyaloshinskii-Moriya interaction and
anisotropy on the Entanglement of Heisenberg chain has been studied. While the
anisotropy suppress the entanglement due to favoring of the alignment of spins,
the DM interaction restores the spoiled entanglement via creation of the
quantum fluctuations. Thermodynamic limit of the model and emerging of
non-analytic behavior of the entanglement have also been probed. The
singularities of the entanglement correspond to the critical boundary
separating different phases of the model. The singularity of the entanglement
derivative approaches the critical point from the gapped phase and will be
symmetric if both phase on the boundary are gapped.",0903.0630v2
2009-04-03,Simulations of Electron Magnetohydrodynamic Turbulence,"We present numerical simulations of electron magnetohydrodynamic (EMHD) and
electron reduced MHD (ERMHD) turbulence. Comparing scaling relations, we find
that both EMHD and ERMHD turbulence show similar spectra and anisotropy. We
develop new techniques to study anisotropy of EMHD turbulence. Our detailed
study of anisotropy of EMHD turbulence supports our earlier result of k_par ~
k_perp^(1/3) scaling. We find that the high-order statistics show a scaling
that is similar to the She-Leveque scaling. We observe that the bispectra,
which characterize the interaction of different scales within the turbulence
cascade, are very different for EMHD and MHD turbulence. We show that both
decaying and driven EMHD turbulence have the same statistical properties. We
calculate the probability distribution functions (PDFs) of MHD and EMHD
turbulence and compare them with those of interplanetary turbulence. We find
that, as in the case of the solar wind, the PDFs of the increments of magnetic
field strength in MHD and EMHD turbulence are well described by the Tsallis
distribution. We discuss implications of our results for astrophysical
situations, including the ADAFs and magnetic reconnection.",0904.0661v2
2009-04-12,Erratum: Statistical anisotropy in the inflationary universe,"An error was made when calculating the amplitude of the perturbed scalar mode
after Hubble-radius crossing. When corrected, it eliminates the leading term in
the statistical anisotropy of the power spectrum, reducing it from the
previously claimed upper estimate of $\lesssim 10^{-2}$ to the level of at most
$10^{-6}$, which is beyond the possibility of detection. The general conclusion
is that a single-field inflationary scenario cannot produce statistical
anisotropy of appreciable magnitude.",0904.1887v4
2009-04-18,High-energy dileptons from an anisotropic quark-gluon plasma,"We calculate leading-order dilepton yields from a quark-gluon plasma which
has a time-dependent anisotropy in momentum space. Such anisotropies can arise
during the earliest stages of quark-gluon plasma evolution due to the rapid
longitudinal expansion of the created matter. A phenomenological model for the
proper time dependence of the parton hard momentum scale, p_hard, and the
plasma anisotropy parameter, xi, is proposed. The model describes the
transition of the plasma from a 0+1 dimensional collisionally-broadened
expansion at early times to a 0+1 dimensional ideal hydrodynamic expansion at
late times. We find that high-energy dilepton production is enhanced by
pre-equilibrium emission up to 50% at LHC energies, if one assumes an
isotropization/thermalization time of 2 fm/c. Given sufficiently precise
experimental data this enhancement could be used to determine the plasma
isotropization time experimentally.",0904.2866v2
2009-04-27,Role of Oxygen Electrons in the Metal-Insulator Transition in the Magnetoresistive Oxide La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ Probed by Compton Scattering,"We have studied the [100]-[110] anisotropy of the Compton profile in the
bilayer manganite. Quantitative agreement is found between theory and
experiment with respect to the anisotropy in the two metallic phases (i.e. the
low temperature ferromagnetic and the colossal magnetoresistant phase under a
magnetic field of 7 T). Robust signatures of the metal-insulator transition are
identified in the momentum density for the paramagnetic phase above the Curie
temperature. We interpret our results as providing direct evidence for the
transition from the metallic-like to the admixed ionic-covalent bonding
accompanying the magnetic transition. The number of electrons involved in this
phase transition is estimated from the area enclosed by the Compton profile
anisotropy differences. Our study demonstrates the sensitivity of the Compton
scattering technique for identifying the number and type of electrons involved
in the metal-insulator transition.",0904.4255v1
2009-05-08,A cluster model with random anisotropy for hysteresis jumps in CeNi$_{1-x}$Cu$_{x}$ alloys,"Some Cerium compounds exhibit hysteresis cycles with sharp macroscopic jumps
in the magnetization at very low temperatures. This effect is attributed to the
formation of clusters in which the anisotropy competes with the applied
magnetic field. Here, we present a simple model where a lattice of
ferromagnetically coupled spins is separated in clusters of random sizes and
with random anisotropy. Within this model, we obtain hysteresis cycles
presenting jumps that behave in a similar way that the experimental ones, and
that disappear when increasing the temperature. The results are in good
agreement with the hysteresis cycles measured at very low temperatures in
CeNi$_{1-x}$Cu$_{x}$ and the comparison with these experimental results allows
to discriminate the relative importance of the mechanisms driving the thermal
evolution of the cycles.",0905.1219v1
2009-05-10,Achieving Invisibility of Homogeneous Radially Anisotropic Cylinders by Effective Medium Theory,"In this paper, we establish the full-wave electromagnetic scattering theory
to study the electromagnetic scattering from infinitely long cylinders with
radially anisotropic coatings. We show that the total effective scattering
width can be dramatically reduced by the suitable adjustment of the dielectric
anisotropy of the shell, while it is not the case for tuning the dielectric
anisotropy of the core. Furthermore, we could make the cylindrical objects
invisible when both dielectric and magnetic anisotropies are adjusted. In the
long wavelength limit, we develop effective medium theory to derive the
effective isotropic permittivity and permeability for the anisotropic coated
cylinders, and the invisibility radius ratio derived from the full-wave theory
for small coated cylinders can be well described within the effective medium
theory.",0905.1503v2
2009-05-29,A general framework for multiple scattering of polarized waves including anisotropies and Berry phase,"We develop a framework for the multiple scattering of a polarized wave. We
consider particles with spin propagating in a medium filled with scatterers. We
write the amplitudes of each spin eigenstate in a local, mobile frame. One of
the axes is in the direction of propagation of the particle. We use this
representation to define a directional Green's operator of the homogeneous
medium and also to write the spin-dependent scattering amplitudes. We show that
this representation reveals a Berry phase. We establish a generalized
Green-Dyson equation for the multiple scattering problem in this framework. We
show that the generalized Green-Dyson equation can be solved by linear algebra
if one uses a representation of the rotations based on Wigner D-matrices. The
properties of light scattering are retrieved if we use spin 1 particles. Our
theory allows to take into account several kinds of anisotropies like circular
or linear dichroism and birefringence, Faraday effects andMie scattering within
the same formalism. Several anisotropies can be present at the same time.",0905.4915v2
2009-07-15,The use of Lorentz microscopy for the determination of magnetic reversal mechanism of exchange-biased Co30Fe70/NiMn bilayer,"Lorentz transmission electron microscopy (LTEM) combined with in-situ
magnetizing experiments is a powerful tool for the investigation of the
magnetization of the reversal process at the micron scale. We have implemented
this tool on a conventional transmission electron microscope (TEM) to study the
exchange anisotropy of a polycrystalline Co35Fe65/NiMn bilayer.
Semi-quantitative maps of the magnetic induction were obtained at different
field values by the differential phase contrast (DPC) technique adapted for a
TEM (SIDPC). The hysteresis loop of the bilayer has been calculated from the
relative intensity of magnetic maps. The curve shows the appearance of an
exchange-bias field reveals with two distinct reversal modes of the
magnetization: the first path corresponds to a reversal by wall propagation
when the applied field is parallel to the anisotropy direction whereas the
second is a reversal by coherent rotation of magnetic moments when the field is
applied antiparallel to unidirectional anisotropy direction.",0907.2537v1
2009-07-21,Rapidity distribution of photons from an anisotropic Quark-Gluon-Plasma,"We calculate rapidity distribution of photons due to Compton and annihilation
processes from {\em Quark Gluon Plasma} (QGP) with pre-equilibrium
momentum-space anisotropy. We also include contributions from hadronic matter
with late stage transverse expansion. A phenomenological model has been used
for the time evolution of hard momentum scale $p_{\rm hard}(\tau)$ and
anisotropy parameter $\xi(\tau)$. As a result of pre-equilibrium momentum-space
anisotropy, we find significant modification of photons rapidity distribution.
For example, with {\em fixed initial condition} (FIC) {\em free-streaming}
($\delta=2$) interpolating model we observe significant enhancement of photon
rapidity distribution at fixed $p_T$, where as for FIC {\em
collisionally-broadened} ($\delta=2/3$) interpolating model the yield increases
till $y \sim 1$. Beyond that suppression is observed. With {\em fixed final
multiplicity} (FFM) {\em free-streaming} interpolating model we predict
enhancement of photon yield which is less than the case of FIC. Suppression is
always observed for FFM {\em collisionally-broadened} interpolating model.",0907.3607v2
2009-07-30,Heisenberg Spin Glass Experiments and the Chiral Ordering Scenario,"An overview is given of experimental data on Heisenberg Spin Glass materials
so as to make detailed comparisons with numerical results on model Heisenberg
spin glasses, with particular reference to the chiral driven ordering
transition scenario due to Kawamura and collaborators. On weak anisotropy
systems, experiments show critical exponents which are very similar to those
estimated numerically for the model Heisenberg chiral ordering transition but
which are quite different from those at Ising spin glass transitions. Again on
weak anisotropy Heisenberg spin glasses, experimental torque data show well
defined in-field transverse ordering transitions up to strong applied fields,
in contrast to Ising spin glasses where fields destroy ordering. When samples
with stronger anisotropies are studied, critical and in-field behavior tend
progressively towards the Ising limit. It can be concluded that the essential
physics of laboratory Heisenberg spin glasses mirrors that of model Heisenberg
spin glasses, where chiral ordering has been demonstrated numerically.",0907.5333v1
2009-08-01,"Phosphorous alloying: controlling the magnetic anisotropy in ferromagnetic (Ga,Mn)(As,P) Layers","Phosphorous alloying of GaMnAs thin films has been used for the manipulation
of the magnetic anisotropies in ferromagnetic Ga0.93Mn0.07As1-yPy layers. We
have determined the anisotropy constants as a function of temperature for
phosphorous alloying levels between 0 and 8.8 at % for a Mn doping level of ~
7at%. We show that it is possible to obtain layers with robust ferromagnetism
and either in-plane or out-of plane easy axes with small barriers for
magnetization reorientation by phosphorous alloying with y< 6at% or y> 6at%.
The critical temperatures are not significantly increased by the P alloying.",0908.0063v2
2009-08-04,Crystallographically oriented Co and Ni nanocrystals inside ZnO formed by ion implantation and postannealing,"In the last decade, transition-metal-doped ZnO has been intensively
investigated as a route to room-temperature diluted magnetic semiconductors
(DMSs). However, the origin for the reported ferromagnetism in ZnO-based DMS
remains questionable. Possible options are diluted magnetic semiconductors,
spinodal decomposition, or secondary phases. In order to clarify this question,
we have performed a thorough characterization of the structural and magnetic
properties of Co- and Ni-implanted ZnO single crystals. Our measurements reveal
that Co or Ni nanocrystals (NCs) are the major contribution of the measured
ferromagnetism. Already in the as-implanted samples, Co or Ni NCs have formed
and they exhibit superparamagnetic properties. The Co or Ni NCs are
crystallographically oriented with respect to the ZnO matrix. Their magnetic
properties, e.g., the anisotropy and the superparamagnetic blocking
temperature, can be tuned by annealing. We discuss the magnetic anisotropy of
Ni NCs embedded in ZnO concerning the strain anisotropy.",0908.0458v1
2009-08-27,"A low field technique for measuring magnetic and magneto-resistance anisotropy coefficients applied to (Ga,Mn)As","We demonstrate a simple, low cost, magneto-transport method for rapidly
characterizing the magnetic anisotropy and anisotropic magneto-resistance (AMR)
of ferromagnetic devices with uniaxial magnetic anisotropy. This transport
technique is the analogue of magnetic susceptibility measurements of bulk
material but is applicable to very small samples with low total moment. The
technique is used to characterize devices fabricated from the dilute magnetic
semiconductor (Ga,Mn)As. The technique allows us to probe the behavior of the
parameters close to the Curie temperature, in the limit of the applied magnetic
field tending to zero. This avoids the complications arising from the presence
of paramagnetism.",0908.3960v1
2009-09-03,Late time CMB anisotropies constrain mini-charged particles,"Observations of the temperature anisotropies induced as light from the CMB
passes through large scale structures in the late universe are a sensitive
probe of the interactions of photons in such environments. In extensions of the
Standard Model which give rise to mini-charged particles, photons propagating
through transverse magnetic fields can be lost to pair production of such
particles. Such a decrement in the photon flux would occur as photons from the
CMB traverse the magnetic fields of galaxy clusters. Therefore late time CMB
anisotropies can be used to constrain the properties of mini-charged particles.
We outline how this test is constructed, and present new constraints on
mini-charged particles from observations of the Sunyaev-Zel'dovich effect in
the Coma cluster.",0909.0649v1
2009-09-16,Note on galaxy catalogues in UHECR flux modelling,"We consider the dependence of ultra-high energy cosmic ray (UHECR) flux
predictions on the choice of galaxy catalogue. We demonstrate that model
predictions by Koers & Tinyakov (2009b), based on the so-called KKKST
catalogue, are in good agreement with predictions based on the XSCz catalogue,
a recently compiled catalogue that contains spectroscopic redshifts for a large
fraction of galaxies. This agreement refutes the claim by Kashti (2009) that
the KKKST catalogue is not suited for studies of UHECR anisotropy due to its
dependence on photometric redshift estimates. In order to quantify the effect
of galaxy catalogues on flux predictions, we develop a measure of anisotropies
associated with model flux maps. This measure offers a general criterion to
study the effect of model parameters and assumptions on the predicted strength
of UHECR anisotropies.",0909.3010v1
2009-09-29,Effect of a staggered spin-orbit coupling on the occurrence of a nematic phase in Sr$_3$Ru$_2$O$_7$,"Ultra-clean crystals of Sr$_3$Ru$_2$O$_7$ undergo a metamagnetic transition
at low temperatures. This transition shows a strong anisotropy in the applied
field direction with the critical field $H_c$ ranging from $\sim 5.1$T for
$H\perp c$ to $\sim 8$T for $H\parallel c$. In addition, studies on ultra-pure
samples revealed a bifurcation of the metamagnetic line for fields in
$c$-direction and it is argued that a nematic phase emerges between the
magnetization jumps. The aim of this study is to explain the field-direction
anisotropy of these phenomena. Based on a microscopic tight-binding model, we
introduce the metamagnetic transition by means of a van Hove singularity
scenario. We show that the rotation of the O-octahedra around the c-axis
expected for this material introduces a staggered spin-orbit coupling within
the planes and naturally leads to an anisotropy of the magnetic response. We
describe the low-temperature phase as a nematic state favored by forward
scattering processes. The spin-orbit coupling shows an influence on both, the
critical field $H_c$ and the occurrence of the nematic phase.",0909.5392v2
2009-10-01,First-Principles Study for the Anisotropy of Iron-based Superconductors toward Power and Device Applications,"Performing the first-principles calculations, we investigate the anisotropy
in the superconducting state of iron-based superconductors to gain an insight
into their potential applications. The anisotropy ratio $\gamma_\lambda$ of the
c-axis penetration depth to the ab-plane one is relatively small in BaFe2As2
and LiFeAs, i.e., $\gamma_\lambda \sim 3$, indicating that the transport
applications are promising in these superconductors. On the other hand, in
those having perovskite type blocking layers such as Sr2ScFePO3 we find a very
large value, $\gamma_\lambda \sim 200$, comparable to that in strongly
anisotropic high-Tc cuprate Bi2Sr2CaCu2O{8-\delta}. Thus, the intrinsic
Josephson junction stacks are expected to be formed along the c-axis, and novel
Josephson effects due to the multi-gap nature are also suggested in these
superconductors.",0910.0107v1
2009-10-09,Spin-waves in the $J_{1a}-J_{1b}-J_{2}$ orthorombic square-lattice Heisenberg models: Application to the iron pnictide materials,"Motivated by the observation of spatially anisotropic exchange constants in
the iron pnictide materials, we study the spin-wave spectra of the
$J_{1a}-J_{1b}-J_{2}$ Heisenberg models on a square-lattice with nearest
neighbor exchange $J_{1a}$ along x and $J_{1b}$ along y axis and a second
neighbor exchange $J_2$. We focus on the regime, where the spins order at
($\pi,0$), and compute the spectra by systematic expansions around the Ising
limit. We study both spin-half and spin-one Heisenberg models as well as a
range of parameters to cover various cases proposed for the iron pnictide
materials. The low-energy spectra have anisotropic spin-wave velocities and are
renormalized with respect to linear spin-wave theory by up to 20 percent,
depending on parameters. Extreme anisotropy, consisting of a ferromagnetic
$J_{1b}=- |J_F|$, is best distinguished from a weak anisotropy ($J_{1a}\approx
J_{1b}=J_1$, $J_2>J_1/2$) by the nature of the spin-waves near the wavevectors
($0,\pi$) or ($\pi,\pi$). The reported spectra for the pnictide material
CaFe$_2$As$_2$ clearly imply such an extreme anisotropy.",0910.1793v1
2009-10-28,Rapidly Rotating Fermions in an Anisotropic Trap,"We consider a cold gas of non-interacting fermions in a two dimensional
harmonic trap with two different trapping frequencies $\omega_x \leq \omega_y$,
and discuss the effect of rotation on the density profile. Depending on the
rotation frequency $\Omega$ and the trap anisotropy $\omega_y/\omega_x$, the
density profile assumes two qualitatively different shapes. For small
anisotropy ($\omega_y/\omega_x \ll \sqrt{1+4 \Omega^2/\omega_x^2}$), the
density consists of elliptical plateaus of constant density, corresponding to
Landau levels and is well described by a two dimensional local density
approximation. For large anisotropy ($\omega_y/\omega_x \gg \sqrt{1+4
\Omega^2/\omega_x^2}$), the density profile is Gaussian in the strong confining
direction and semicircular with prominent Friedel oscillations in the weak
direction. In this regime, a one dimensional local density approximation is
well suited to describe the system. The crossover between the two regimes is
smooth where the step structure between the Landau level edges turn into
Friedel oscillations. Increasing the temperature causes the step structure or
the Friedel oscillations to wash out leaving a Boltzmann gas density profile.",0910.5361v1
2009-11-06,Solar cycle dependence of the diurnal anisotropy of 0.6 TeV cosmic ray intensity observed with the Matsushiro underground muon detector,"We analyze the temporal variation of the diurnal anisotropy of sub-TeV cosmic
ray intensity observed with the Matsushiro (Japan) underground muon detector
over two full solar activity cycles in 1985-2008. The average sidereal
amplitude over the entire period is 0.034+-0.003 %, which is roughly one third
of the amplitude reported from AS and deep-underground muon experiments
monitoring multi-TeV GCR intensity suggesting a significant attenuation of the
anisotropy due to the solar modulation. We find, on the other hand, only weak
correlations either with the solar activity- or magnetic-cycles. We examine the
temporal variation of the ""single-band valley depth"" (SBVD) quoted by the
Milagro experiment and, by contrast with recent Milagro reports, we find no
steady increase in the Matsushiro observations in a 7-year period between 2000
and 2007. We suggest, therefore, that the steady increase of the SBVD reported
by the Milagro experiment is not caused by the decreasing solar modulation in
the declining phase of the 23rd solar activity cycle.",0911.1165v2
2009-11-19,In-plane electronic anisotropy in underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ revealed by detwinning in a magnetic field,"We present results of angle-dependent magnetoresistance measurements and
direct optical images of underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ which reveal
partial detwinning by action of a 14T magnetic field. Driven by a substantial
magneto-elastic coupling, this result provides evidence for an electronic
origin of the lattice distortion in underdoped iron pnictides. The observed
anisotropy in these partially detwinned samples implies a substantial in-plane
electronic anisotropy in the broken symmetry state, with a smaller resistivity
along the antiferromagnetic ordering direction.",0911.3878v1
2009-12-02,Constraints on the anisotropy of dark energy,"If the equation of state of dark energy is anisotropic there will be
additional quadrupole anisotropy in the cosmic microwave background induced by
the time dependent anisotropic stress quantified in terms of $\Delta w$.
Assuming that the entire amplitude of the observed quadrupole is due to this
anisotropy, we conservatively impose a limit of $|\Delta w| < 2.1\times
10^{-4}$ for any value of $w\ge -1$ assuming that $\Omega_{\rm m}<0.5$. This is
considerably tighter than that which comes from SNe. Stronger limits, upto a
factor of 10, are possible for specific values of $\Omega_{\rm m}$ and $w$.
Since we assume this component is uncorrelated with the stochastic component
from inflation, we find that both the expectation value and the sample variance
are increased. There no improvement in the likelihood of an anomalously low
quadrupole as suggested by previous work on an elliptical universe.",0912.0397v1
2009-12-10,Modelling the WMAP large-angle anomalies as an effect of a local density inhomogeneity,"We investigate large-angle scale temperature anisotropy in the Cosmic
Microwave Background (CMB) with the Wilkinson Microwave Anisotropy Probe (WMAP)
data and model the large-angle anomalies as the effect of the CMB quadrupole
anisotropies caused by the local density inhomogeneities. The quadrupole caused
by the local density inhomogeneities is different from the special relativity
kinematic quadrupole. If the observer inhabits a strong inhomogeneous region,
the local quadrupole should not be neglected. We calculate such local
quadrupole under the assumption that there is a huge density fluctuation field
in direction $(284^{\circ},74^{\circ})$, where the density fluctuation is
$10^{-3}$, and its center is $\sim 112h^{-1} \rm {Mpc}$ away from us. After
removing such mock signals from WMAP data, the power in quadrupole, $C_2$,
increases from the range $(200\sim260\mu \rm{K^2})$ to $\sim1000\mu \rm{K^2}$.
The quantity S, which is used to estimate the alignment between the quadrupole
and the octopole, decreases from $(0.7\sim0.74)$ to $(0.31\sim0.37)$, while the
model predict that $C_2=1071.5\mu \rm{K^2}$, $S=0.412$. So our local density
inhomogeneity model can, in part, explain the WMAP low-$\ell$ anomalies.",0912.1913v1
2010-01-14,Primordial Power Spectra from Anisotropic Inflation,"We examine cosmological perturbations in a dynamical theory of inflation in
which an Abelian gauge field couples directly to the inflaton, breaking
conformal invariance. When the coupling between the gauge field and the
inflaton takes a specific form, inflation becomes anisotropic and anisotropy
can persist throughout inflation, avoiding Wald's no-hair theorem. After
discussing scenarios in which anisotropy can persist during inflation, we
calculate the dominant effects of a small persistent anisotropy on the
primordial gravitational wave and curvature perturbation power spectra using
the ""in-in"" formalism of perturbation theory. We find that the primordial power
spectra of cosmological perturbations gain significant direction dependence and
that the fractional direction dependence of the tensor power spectrum is
suppressed in comparison to that of the scalar power spectrum.",1001.2301v4
2010-01-14,Lunar Laser-Ranging Detection of Light-Speed Anisotropy and Gravitational Waves,"The Apache Point Lunar Laser-ranging Operation (APOLLO), in NM, can detect
photon bounces from retro-reflectors on the moon surface to 0.1ns timing
resolution. This facility enables not only the detection of light speed
anisotropy, which defines a local preferred frame of reference - only in that
frame is the speed of light isotropic, but also fluctuations/turbulence
(gravitational waves) in the flow of the dynamical 3-space relative to local
systems/observers. So the APOLLO facility can act as an effective
""gravitational wave"" detector. A recently published small data set from
November 5, 2007, is analysed to characterise both the average anisotropy
velocity and the wave/turbulence effects. The results are consistent with some
13 previous detections, with the last and most accurate being from the
spacecraft earth-flyby Doppler-shift NASA data.",1001.2358v2
2010-01-22,Non-Gaussianity and statistical anisotropy from vector field populated inflationary models,"We present a review of vector field models of inflation and, in particular,
of the statistical anisotropy and non-Gaussianity predictions of models with
SU(2) vector multiplets. Non-Abelian gauge groups introduce a richer amount of
predictions compared to the Abelian ones, mostly because of the presence of
vector fields self-interactions. Primordial vector fields can violate isotropy
leaving their imprint in the comoving curvature fluctuations zeta at late
times. We provide the analytic expressions of the correlation functions of zeta
up to fourth order and an analysis of their amplitudes and shapes. The
statistical anisotropy signatures expected in these models are important and,
potentially, the anisotropic contributions to the bispectrum and the
trispectrum can overcome the isotropic parts.",1001.4049v1
2010-01-25,"Interplay between Symmetric Exchange Anisotropy, Uniform Dzyaloshinskii-Moriya Interaction and Magnetic Fields in the Phase Diagram of Quantum Magnets and Superconductors","We theoretically study the joint influence of uniform Dzyaloshinskii-Moriya
(DM) interactions, symmetric exchange anisotropy (with its axis parallel to the
DM vector) and arbitrarily oriented magnetic fields on one-dimensional spin 1/2
antiferromagnets. We show that the zero-temperature phase diagram contains
three competing phases: (i) an antiferromagnet with Neel vector in the plane
spanned by the DM vector and the magnetic field, (ii) a {\em dimerized}
antiferromagnet with Neel vector perpendicular to both the DM vector and the
magnetic field, and (iii) a gapless Luttinger liquid. Phase (i) is destroyed by
a small magnetic field component along the DM vector and is furthermore
unstable beyond a critical value of easy-plane anisotropy, which we estimate
using Abelian and non-Abelian bosonization along with perturbative
renormalization group. We propose a mathematical equivalent of the spin model
in a one-dimensional Josephson junction (JJ) array located in proximity to a
bulk superconductor.
  We discuss the analogues of the magnetic phases in the superconducting
context and comment on their experimental viability.",1001.4290v1
2010-02-10,"Strain, magnetic anisotropy, and anisotropic magnetoresistance in (Ga,Mn)As on high-index substrates: application to (113)A-oriented layers","Based on a detailed theoretical examination of the lattice distortion in
high-index epilayers in terms of continuum mechanics, expressions are deduced
that allow the calculation and experimental determination of the strain tensor
for (hhl)-oriented (Ga,Mn)As layers. Analytical expressions are derived for the
strain-dependent free-energy density and for the resistivity tensor for
monoclinic and orthorhombic crystal symmetry, phenomenologically describing the
magnetic anisotropy (MA) and anisotropic magnetoresistance (AMR) by appropriate
anisotropy and resistivity parameters, respectively. Applying the results to
(113)A orientation with monoclinic crystal symmetry, the expressions are used
to determine the strain tensor and the shear angle of a series of
(113)A-oriented (Ga,Mn)As layers by high-resolution x-ray diffraction and to
probe the MA and AMR at 4.2 K by means of angle-dependent magnetotransport.
Whereas the transverse resistivity parameters are nearly unaffected by the
magnetic field, the parameters describing the longitudinal resistivity are
strongly field dependent.",1002.2179v2
2010-02-11,"Synthesis, anisotropy, and superconducting properties of LiFeAs single crystal","A LiFeAs single crystal with $T_c^{onset}$$\sim$19.7 K was grown successfully
in a sealed tungsten crucible using the Bridgeman method. The electrical
resistivity experiments revealed a ratio of room temperature to residual
resistivity (RRR) of approximately 46 and 18 for the in-plane and out-of plane
directions. The estimated anisotropic resistivity, $\gamma_\rho$=$\rho_c$ /
$\rho_{ab}$, was approximately 3.3 at $T_c^{onset}$. The upper critical fields
had large $H_{c2} ^{\shortparallel ab}$ and $H_{c2}^{\shortparallel c}$ values
of 83.4 T and 72.5 T, respectively, and an anisotropy ratio is
$\gamma_H$=$H_{c2}^{\shortparallel ab}$ / $H_{c2} ^{\shortparallel
c}$$\sim$1.15. The high upper critical field value and small anisotropy
highlight the potential use of LiFeAs in a variety of applications. The
calculated critical current density $(J_c)$ from the $M$-$H$ loop is
approximately 10$^3$ A/cm$^2$",1002.2249v1
2010-02-12,Low magnetization and anisotropy in the antiferromagnetic state of undoped iron pnictides,"We examine the magnetic phase diagram of iron pnictides using a five band
model. For the intermediate values of the interaction expected to hold in the
iron pnictides, we find a metallic low moment state characterized by
antiparallel orbital magnetic moments. The anisotropy of the interorbital
hopping amplitudes is the key to understanding this low moment state. This
state accounts for the small magnetization measured in undoped iron pnictides
and leads to the strong exchange anisotropy found in neutron experiments.
Orbital ordering is concomitant with magnetism and produces the large zx
orbital weight seen at Gamma in photoemission experiments.",1002.2584v2
2010-02-20,Analytic formulae for CMB anisotropy in LTB cosmology,"The local void model has lately attracted considerable attention since it can
explain the present apparent accelerated expansion of the universe without
introducing dark energy. However, in order to justify this model as an
alternative cosmological model to the standard $\Lambda$CDM model (FLRW
universe plus dark energy), one has to test the model by various observations,
such as CMB temperature anisotropy, other than the distance-redshift relation
of SNIa. For this purpose, we derive some analytic formulae that can be used to
rigorously compare consequences of this model with observations of CMB
anisotropy and to place constraints on the position of observers in the void
model.",1002.3855v3
2010-02-24,Role of anisotropy for protein-protein encounter,"Protein-protein interactions comprise both transport and reaction steps.
During the transport step, anisotropy of proteins and their complexes is
important both for hydrodynamic diffusion and accessibility of the binding
site. Using a Brownian dynamics approach and extensive computer simulations, we
quantify the effect of anisotropy on the encounter rate of ellipsoidal
particles covered with spherical encounter patches. We show that the encounter
rate $k$ depends on the aspect ratios $\xi$ mainly through steric effects,
while anisotropic diffusion has only a little effect. Calculating analytically
the crossover times from anisotropic to isotropic diffusion in three
dimensions, we find that they are much smaller than typical protein encounter
times, in agreement with our numerical results.",1002.4485v1
2010-02-24,Monte Carlo Study of Maghemite Nanoparticles,"We consider a simple model of maghemite nanoparticles and study their
magnetic properties using Monte Carlo methods. The particles have a spherical
geometry with diameters ranging from 3 nm to 8 nm. The interior of the
particles consists of core spins with exchange interactions and anisotropy
given by the values in the bulk material. The outer layer of the particles
consists of surface spins with weaker exchange interactions but an enhanced
anisotropy. The thermal behaviour of the total, core and surface magnetizations
are calculated as well as the hysteresis loops due to the application of an
applied field. The effect of the surface anisotropy on the blocking
temperature, the coercive and exchange bias fields is studied.",1002.4648v2
2010-02-25,Statistical anisotropy as a consequence of inflation,"Cosmological inflation remains to be a unique mechanism of generation of
plausible initial conditions in the early universe. In particular, it generates
the primordial quasiclassical perturbations with power spectrum determined by
the fundamental principles of quantum field theory. In this work, we pay
attention to the fact that the quasiclassical perturbations permanently
generated at early stages of inflation break homogeneity and isotropy of the
cosmological background. The evolution of the small-scale quantum vacuum modes
on this inhomogeneous background results in statistical anisotropy of the
primordial power spectrum, which can manifest itself in the observable
large-scale structure and cosmic microwave background. The effect is predicted
to have almost scale-invariant form dominated by a quadrupole and may serve as
a non-trivial test of the inflationary scenario. Theoretical expectation of the
magnitude of this statistical anisotropy depends on the assumptions about the
physics in the trans-Planckian region of wavenumbers.",1002.4879v1
2010-02-27,The Nature of Primordial Fluctuations from Anisotropic Inflation,"We study the statistical nature of primordial fluctuations from an
anisotropic inflation which is realized by a vector field coupled to an
inflaton. We find a suitable gauge, which we call the canonical gauge, for
anisotropic inflation by generalizing the flat slicing gauge in conventional
isotropic inflation. Using the canonical gauge, we reveal the structure of the
couplings between curvature perturbations, vector waves, and gravitational
waves. We identify two sources of anisotropy, i.e. the anisotropy due to the
anisotropic expansion of the universe and that due to the anisotropic couplings
among variables. It turns out that the latter effect is dominant. Since the
coupling between the curvature perturbations and vector waves is the strongest
one, the statistical anisotropy in the curvature perturbations is larger than
that in gravitational waves. We find the cross correlation between the
curvature perturbations and gravitational waves which never occurs in
conventional inflation. We also find the linear polarization of gravitational
waves. Finally, we discuss cosmological implication of our results.",1003.0056v2
2010-03-11,Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind,"Correlations are studied between the power density of transverse waves having
frequencies between $0.01$ and $1$ normalized to the proton gyrofrequency in
the plasma frame and the ratio of the perpendicular and parallel temperature of
the protons. The wave power spectrum is evaluated from high-resolution 3D
magnetic field vector components, and the ion temperatures are derived from the
velocity distribution functions as measured in fast solar wind during the
Helios-2 primary mission at radial distances from the Sun between 0.3~AU and
0.9~AU. From our statistical analysis, we obtain a striking correlation between
the increases in the proton temperature ratio and enhancements in the wave
power spectrum. Near the Sun the transverse part of the wave power is often
found to be by more than an order of magnitude higher than its longitudinal
counterpart. Also the measured ion temperature anisotropy appears to be limited
by the theoretical threshold value for the ion-cyclotron instability. This
suggests that high-frequency Alfv\'{e}n-cyclotron waves regulate the proton
temperature anisotropy.",1003.2299v2
2010-03-26,Anisotropic electron spin resonance of YbIr2Si2,"A series of electron spin resonance (ESR) experiments were performed on a
single crystal of the heavy fermion metal YbIr2Si2 to map out the anisotropy of
the ESR-intensity I_ESR which is governed by the microwave field component of
the g-factor. The temperature dependencies of I_ESR(T) and g(T) were measured
for different orientations and compared within the range 2.6K \le T \le 16K.
The analysis of the intensity dependence on the crystal orientation with
respect to both the direction of the microwave field and the static magnetic
field revealed remarkable features: The intensity variation with respect to the
direction of the microwave field was found to be one order of magnitude smaller
than expected from the g-factor anisotropy. Furthermore, we observed a weak
basal plane anisotropy of the ESR parameters which we interpret to be an
intrinsic sample property.",1003.5133v1
2010-03-30,Stability of a strongly anisotropic thin epitaxial film in a wetting interaction with elastic substrate,"The linear dispersion relation for longwave surface perturbations, as derived
by Levine et al. Phys. Rev. B 75, 205312 (2007) is extended to include a smooth
surface energy anisotropy function with a variable anisotropy strength (from
weak to strong, such that sharp corners and slightly curved facets occur on the
corresponding Wulff shape). Through detailed parametric studies it is shown
that a combination of a wetting interaction and strong anisotropy, and even a
wetting interaction alone results in complicated linear stability
characteristics of strained and unstrained films. PACS: 68.55.J, Morphology of
films; 81.15.Aa, Theory and models of film growth; 81.16.Dn, Self-assembly.",1003.5806v5
2010-04-06,Electron spin resonance in S=1/2 antiferromagnets at high temperature,"We study the electron spin resonance (ESR) of low-dimensional spin systems at
high temperature, and test the Kubo-Tomita theory of exchange narrowing. In
finite-size systems (molecular magnets), we found a double-peak resonance which
strongly differs from the usual Lorentzian. For infinite systems, we have
predictions for the linewidth and lineshape as a function of the anisotropy
strength. For this, we have used an interpolation between a non-perturbative
calculation of the memory function at short times (exact diagonalization) and
the hydrodynamic spin-diffusion at long times. We show that the
Dzyaloshinskii-Moriya anisotropies generally induce a much larger linewidth
than the exchange anisotropies in two dimensions, contrary to the
one-dimensional case.",1004.0839v1
2010-04-20,Electronic transport in an anisotropic Sierpinski gasket,"We present exact results on certain electronic properties of an anisotropic
Sierpinski gasket fractal. We use a tight binding Hamiltonian and work within
the formalism of a real space renormalization group (RSRG) method. The
anisotropy is introduced in the values of the nearest neighbor hopping
integrals. An extensive numerical examination of the two terminal transmission
spectrum and the flow of the hopping integrals under the RSRG iterations
strongly suggest that an anisotropic gasket is more conducting than its
isotropic counter part and that, even a minimal anisotropy in the hopping
integrals generate {\it continuous bands} of eigenstates in the spectrum for
finite Sierpinski gaskets of arbitrarily large size. We also discuss the effect
of a magnetic field threading the planar gasket on its transport properties and
calculate the persistent current in the system. The sensitivity of the
persistent current on the anisotropy and on the band filling is also discussed.",1004.3353v1
2010-04-23,Critical current scaling and anisotropy in oxypnictide superconductors,"Investigating the anisotropy of superconductors permits an access to
fundamental properties. Having succeeded in the fabrication of epitaxial
superconducting LaFeAs(O,F) thin films we performed an extensive study of
electrical transport properties. In face of multiband superconductivity we can
demonstrate that a Blatter scaling of the angular dependent critical current
densities can be adopted, although being originally developed for single band
superconductors. In contrast to single band superconductors the mass anisotropy
of LaFeAs(O,F) is temperature dependent. A very steep increase of the upper
critical field and the irreversibility field can be observed at temperatures
below 6K, indicating that the band with the smaller gap is in the dirty limit.
This temperature dependence can be theoretically described by two dominating
bands responsible for superconductivity. A pinning force scaling provides
insight into the prevalent pinning mechanism and can be specified in terms of
the Kramer model.",1004.4185v1
2010-04-24,Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001),"Magnetic anisotropies of Co-implanted ZnO (0001) films grown on
single-crystalline Al2O3 (11-20) substrates have been studied by ferromagnetic
resonance (FMR) technique for different cobalt implantation doses. The FMR data
show that the easy and hard axes have a periodicity of 60 degrees in the film
plane, in agreement with the hexagonal structure of the ZnO films. This
six-fold in-plane magnetic anisotropy, which is observed for the first time in
ZnO-based diluted magnetic semiconductors, is attributed to the substitution of
cobalt on Zn sites in the ZnO structure, and a clear indication for long range
ferromagnetic ordering between substitutional cobalt ions in the
single-crystalline ZnO films.",1004.4291v1
2010-05-12,Stripe antiferromagnetic correlations in LaFeAsO1-xFx probed by 75As NMR,"The anisotropy of the nuclear spin-lattice relaxation rate $1/T_{1}$ of
$^{75}$As was investigated in the iron-based superconductor
LaFeAs(O$_{1-x}$F$_{x}$) ($x = 0.07, 0.11$ and 0.14) as well as LaFeAsO. While
the temperature dependence of the normal-state $1/T_1T$ in the superconducting
(SC) $x = 0.07$ is different from that in the SC $x = 0.11$, their anisotropy
of $1/T_1$, $R \equiv (1/T_{1})_{H \parallel ab}/(1/T_{1})_{H \parallel c}$ in
the normal state is almost the same ($\simeq$ 1.5). The observed anisotropy is
ascribable to the presence of the local stripe correlations with $Q = (\pi, 0)$
or $(0, \pi)$. In contrast, $1/T_1$ is isotropic and $R$ is approximately 1 in
the overdoped $x = 0.14$ sample, where superconductivity is almost suppressed.
These results suggest that the presence of the local stripe correlations
originating from the nesting between hole and electron Fermi surfaces is linked
to high-$T_c$ superconductivity in iron pnictides.",1005.2013v2
2010-05-12,Striped-magnetic-order suppresses giant optical anisotropy and drives structural distortion in iron arsenide superconductors,"To examine the role of magnetism in superconductivity of iron-based
superconductors, we first present first-principles optical calculations on
three representative parent compounds: LaFeAsO, BaFe2As2 and LiFeAs. Both
nonmagnetic (NM) and spin-density wave (SDW) with striped antiferromagnetic
order are considered. Due to their layer structure, these compounds in NM
states show anomalously large optical anisotropy with a conductivity ratio
$\sigma_{zz}/\sigma{xx}$ as large as 313% in LaFeAsO and 530% in LiFeAs.
Interestingly the giant optical anisotropy is significantly suppressed by SDW.
On the other hand, the variable-cell-shape optimizations confirm that SDW does
drive an orthorhombic-distortion. The drive force is dependent on the local
magnetic moment on Fe sublattice, which is tuned by its bonding environment.
Based on these results, we discussed the delicate role of magnetism in
superconductivity.",1005.2121v2
2010-05-17,Confinement-induced resonance in quasi-one-dimensional systems under transversely anisotropic confinement,"We theoretically investigate the confinement-induced resonance for
quasi-one-dimensional quan- tum systems under transversely anisotropic
confinement, using a two-body s-wave scattering model in the zero-energy
collision limit. We predict a single resonance for any transverse anisotropy,
whose position shows a slight downshift with increasing anisotropy. We compare
our prediction with the recent experimental result by Haller et al. [Phys. Rev.
Lett. 104, 153203 (2010)], in which two resonances are observed in the presence
of transverse anisotropy. The discrepancy between theory and experiment remains
to be resolved.",1005.2794v2
2010-05-17,Measurement of the Anisotropy of Cosmic Ray Arrival Directions with IceCube,"We report the first observation of an anisotropy in the arrival direction of
cosmic rays with energies in the multi TeV region in the Southern sky using
data from the IceCube detector. Between June 2007 and March 2008, the
partially-deployed IceCube detector was operated in a configuration with 1320
digital optical sensors distributed over 22 strings at depths between 1450 and
2450 meters inside the Antarctic ice. IceCube is a neutrino detector, but the
data are dominated by a large background of cosmic ray muons. Therefore, the
background data are suitable for high-statistics studies of cosmic rays in the
Southern sky. The data include 4.3 billion muons produced by downgoing cosmic
ray interactions in the atmosphere; these events were reconstructed with a
median angular resolution of 3 degrees and a median energy of $\sim20$ TeV.
Their arrival direction distribution exhibits an anisotropy in right ascension
with a first harmonic amplitude of $(6.4\pm0.2 $stat$. \pm 0.8
$syst$.)\times10^{-4}$.",1005.2960v1
2010-05-27,Azimuthal anisotropy: transition from hydrodynamic flow to jet suppression,"Measured 2nd and 4th azimuthal anisotropy coefficients v_{2,4}(N_{part}),
p_T) are scaled with the initial eccentricity \varepsilon_{2,4}(N_{part}) of
the collision zone and studied as a function of the number of participants
N_{part} and the transverse momenta p_T. Scaling violations are observed for
$p_T \alt 3$ GeV/c, consistent with a $p_T^2$ dependence of viscous corrections
and a linear increase of the relaxation time with $p_T$. These empirical
viscous corrections to flow and the thermal distribution function at freeze-out
constrain estimates of the specific viscosity and the freeze-out temperature
for two different models for the initial collision geometry. The apparent
viscous corrections exhibit a sharp maximum for $p_T \agt 3$ GeV/c, suggesting
a breakdown of the hydrodynamic ansatz and the onset of a change from
flow-driven to suppression-driven anisotropy.",1005.4979v2
2010-06-14,"Tuning perpendicular magnetic anisotropy in (Ga,Mn)(As,P) by thermal annealing","We have investigated the effects of post growth low temperature annealing on
the magnetic, electrical and structural properties of
(Ga_0.94,Mn_0.06)(As_0.9,P_0.1) layers grown by molecular beam epitaxy. By
controlling the annealing time we are able to tune the magnetic anisotropy
between an easy axis in the plane for the as-grown samples, to an easy axis
perpendicular to the plane for fully annealed samples. The increase of the
carrier density, as a result of annealing, is found to be the primary reason
for the change in magnetic anisotropy, in qualitative agreement with
theoretical predictions.",1006.2644v1
2010-06-29,Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study,"Microstrip ferromagnetic resonance and Brillouin scattering are used to
provide a comparative determination of the magnetic parameters of thin
permalloy layers interfaced with a non-magnetic (Al2O3) or with an
antiferromagnetic oxide (NiO). It is shown that the perpendicular anisotropy is
monitored by an interfacial surface energy term which is practically
independent of the nature of the interface. In the investigated interval of
thicknesses (5-25 nm) the saturation magnetisation does not significantly
differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy
and exchange-bias anisotropy are also derived from this study of the dynamic
magnetic excitations and compared to our independent evaluations using
conventional magnetometry",1006.5598v1
2010-07-06,Dissipative Dynamics of Highly Anisotropic Systems,"In this paper we present a method to improve the description of 0+1
dimensional boost invariant dissipative dynamics in the presence of large
momentum-space anisotropies. We do this by reorganizing the canonical
hydrodynamic expansion of the distribution function around a momentum-space
anisotropic ansatz rather than an isotropic equilibrium one. At leading order
the result obtained is two coupled ordinary differential equations for the
momentum-space anisotropy and typical momentum of the degrees of freedom. We
show that this framework can reproduce both the ideal hydrodynamic and free
streaming limits. Additionally, we demonstrate that when linearized the
differential equations reduce to 2nd order Israel-Stewart viscous
hydrodynamics. Finally, we make quantitative comparisons of the evolution of
the pressure anisotropy within our approach and 2nd order viscous hydrodynamics
in both the strong and weak coupling limits.",1007.0889v3
2010-07-21,Exchange anisotropy pinning of a standing spin wave mode,"Standing spin waves in a thin film are used as sensitive probes of interface
pinning induced by an antiferromagnet through exchange anisotropy. Using
coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin
wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was
studied for a range of IrMn thicknesses. We show that pinning of the standing
mode can be used to amplify, relative to the fundamental resonance, frequency
shifts associated with exchange bias. The shifts provide a unique `fingerprint'
of the exchange bias and can be interpreted in terms of an effective
ferromagnetic film thickness and ferromagnet/antiferromagnet interface
anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic
Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in
the pinning fields. The pinning strength magnitude is found to grow with
cooling of the sample, while the effective ferromagnetic film thickness
simultaneously decreases. These results suggest that exchange bias involves
some deformation of magnetic order in the interface region.",1007.3577v1
2010-08-10,Magnetic anisotropy effects on quantum impurities in superconducting host,"We study the magnetic anisotropy effects on the localized sub-gap excitations
induced by quantum impurities coupled to a superconducting host. We establish
the ground-state phase diagrams for single-channel and two-channel high-spin
Kondo impurities; they unveil surprising complexity that results from the
(multi-stage) Kondo screening in competition with the superconducting
correlations and the magnetic anisotropy splitting of the spin multiplets. We
discuss the possibility of detecting the Zeeman splitting of the sub-gap
states, which would provide an interesting spectroscopic tool for studying the
magnetism on the single-atom level. We also study the problem of two impurities
coupled by the Heisenberg exchange interaction, and we follow the evolution of
the sub-gap states for both antiferromagnetic and ferromagnetic coupling. For
sufficiently strong antiferromagnetic coupling, the impurities bind into a
singlet state that is non-magnetic, thus the sub-gap states move to the edge of
the gap and can no longer be discerned. For ferromagnetic coupling, some
excited states remain present inside the gap.",1008.1734v2
2010-08-20,Morphological diagram of diffusion driven aggregate growth in plane: competition of anisotropy and adhesion,"Two-dimensional structures grown with Witten and Sander algorithm are
investigated. We analyze clusters grown off-lattice and clusters grown with
antenna method with $N_{fp}=3,4,5,6,7$ and 8 allowed growth directions. With
the help of variable probe particles technique we measure fractal dimension of
such clusters $D(N)$ as a function of their size $N$. We propose that in the
thermodynamic limit of infinite cluster size the aggregates grown with high
degree of anisotropy ($N_{fp}=3,4,5$) tend to have fractal dimension $D$ equal
to 3/2, while off-lattice aggregates and aggregates with lower anisotropy
($N_{fp}>6$) have $D \approx 1.710$. Noise-reduction procedure results in the
change of universality class for DLA. For high enough noise-reduction value
clusters with $N_{fp} \ge 6$ have fractal dimension going to $3/2$ when
$N\rightarrow\infty$.",1008.3449v1
2010-09-03,"Free energies, vacancy concentrations and density distribution anisotropies in hard--sphere crystals: A combined density functional and simulation study","We perform a comparative study of the free energies and the density
distributions in hard sphere crystals using Monte Carlo simulations and density
functional theory (employing Fundamental Measure functionals). Using a recently
introduced technique (Schilling and Schmid, J. Chem. Phys 131, 231102 (2009))
we obtain crystal free energies to a high precision. The free energies from
Fundamental Measure theory are in good agreement with the simulation results
and demonstrate the applicability of these functionals to the treatment of
other problems involving crystallization. The agreement between FMT and
simulations on the level of the free energies is also reflected in the density
distributions around single lattice sites. Overall, the peak widths and
anisotropy signs for different lattice directions agree, however, it is found
that Fundamental Measure theory gives slightly narrower peaks with more
anisotropy than seen in the simulations. Among the three types of Fundamental
Measure functionals studied, only the White Bear II functional (Hansen-Goos and
Roth, J. Phys.: Condens. Matter 18, 8413 (2006)) exhibits sensible results for
the equilibrium vacancy concentration and a physical behavior of the chemical
potential in crystals constrained by a fixed vacancy concentration.",1009.0613v1
2010-09-13,Lateral Confinement of Electrons in Vicinal N-polar AlGaN/GaN Heterostructure,"We studied orientation dependent transport in vicinal N-polar AlGaN/GaN
heterostructures. We observed significant anisotropy in the current carrying
charge parallel and perpendicular to the miscut direction. A quantitative
estimate of the charge anisotropy was made based on gated TLM and Hall
measurements. The formation of electro-statically confined one-dimensional
channels is hypothesized to explain charge anisotropy. A mathematical model was
used to verify that polarization charges distributed on miscut structure can
create lateral one-dimensional confinement in vicinal substrates. This
polarization-engineered electrostatic confinement observed is promising for new
research on low-dimensional physics and devices besides providing a template
for manufacturable one-dimensional devices.",1009.2537v1
2010-09-29,Transference of Transport Anisotropy to Composite Fermions,"When interacting two-dimensional electrons are placed in a large
perpendicular magnetic field, to minimize their energy, they capture an even
number of flux quanta and create new particles called composite fermions (CFs).
These complex electron-flux-bound states offer an elegant explanation for the
fractional quantum Hall effect. Furthermore, thanks to the flux attachment, the
effective field vanishes at a half-filled Landau level and CFs exhibit
Fermi-liquid-like properties, similar to their zero-field electron
counterparts. However, being solely influenced by interactions, CFs should
possess no memory whatever of the electron parameters. Here we address a
fundamental question: Does an anisotropy of the electron effective mass and
Fermi surface (FS) survive composite fermionization? We measure the resistance
of CFs in AlAs quantum wells where electrons occupy an elliptical FS with large
eccentricity and anisotropic effective mass. Similar to their electron
counterparts, CFs also exhibit anisotropic transport, suggesting an anisotropy
of CF effective mass and FS.",1009.5732v1
2010-10-04,Observation of mixed anisotropy in the critical susceptibility of an ultrathin magnetic film,"Measurements of the magnetic susceptibility of Fe/W(110) films with thickness
in the range of 1.6 to 2.4 ML Fe, show that in addition to the large response
along the easy axis associated with the Curie transition, there is a much
smaller, paramagnetic hard axis response that is not consistent with the 2D
anisotropic Heisenberg model used to describe homogeneous in-plane ferromagnets
with uniaxial anisotropy. The shape, amplitude, and peak temperature of the
hard axis susceptibility, as well as its dependence upon layer completion close
to 2.0 ML, indicate that inhomogeneities in the films create a system of mixed
anisotropy. A likely candidate for inhomogeneities that are magnetically
relevant in the critical region are the closed lines of step edges associated
with the incomplete layers. According to the Harris criterion, the existence of
magnetically relevant inhomogeneities may alter the critical properties of the
films from those of a 2D Ising model. Experiments in the recent literature are
discussed in this context.",1010.0657v2
2010-10-05,Large Scale Traces of Solar System Cold Dust on CMB Anisotropies,"We explore the microwave anisotropies at large angular scales produced by the
emission from cold and large dust grains, expected to exist in the outer parts
of the Solar System, using a simple toy model for this diuse emission. Its
amplitude is constrained in the Far-IR by the COBE data and is compatible with
simulations found in the literature. We analyze the templates derived after
subtracting our model from the WMAP ILC 7 yr maps and investigate on the
cosmological implications of such a possible foreground. The anomalies related
to the low quadrupole of the angular power spectrum, the two-point correlation
function, the parity and the excess of signal found in the ecliptic plane are
significantly alleviated. An impact of this foreground for some cosmological
parameters characterizing the spectrum of primordial density perturbations,
relevant for on-going and future CMB anisotropy experiments, is found.",1010.0830v2
2010-10-12,Atomistic spin-model based on a new spin-cluster expansion technique: Application to the IrMn3/Co interface,"In order to derive tensorial exchange interactions and local magnetic
anisotropies in itinerant magnetic systems, an approach combining the
Spin-Cluster Expansion with the Relativistic Disordered Local Moment scheme is
introduced. The theoretical background and computational aspects of the method
are described in detail. The exchange interactions and site resolved anisotropy
contributions for the IrMn3/Co(111) interface, a prototype for an exchange bias
system, are calculated including a large number of magnetic sites from both the
antiferromagnet and ferromagnet. Our calculations reveal that the coupling
between the two subsystems is fairly limited to the vicinity of the interface.
The magnetic anisotropy of the interface system is discussed, including effects
of the Dzyaloshinskii-Moriya interactions that appear due to symmetry breaking
at the interface.",1010.2375v1
2010-10-14,Theory of Orbital Nematicity in Underdoped Iron Arsenides,"Recent finding of an {\it unusual} in-plane resistivity anisotropy in the
underdoped 122-family at high temperature ($T$) suggests an orbital nematic
(ON) order, posing a challenge to extant theories. The {\it sign} of the
anisotropy contradicts expectations from weakly correlated as well as pure
spin-only nematic views. Here, we show how such an ON order with accompanying
structural distortion arises from {\it residual}, intersite and inter-orbital
two-body interactions in an incoherent ""bad metal"" close to Mottness.
Enhancement of orbital-selective incoherence is shown to be necessary for
understanding transport anisotropy. Our results suggest that ON order, with
subsequent antiferromagnetic order might be the {\it primary} competitor to
superconductivity in Fe arsenides.",1010.2940v1
2010-10-22,"Single-ion anisotropy, Dzyaloshinskii-Moriya interaction and negative magnetoresistance of the spin-1/2 pyrochlores R2V2O7","The electronic and magnetic properties of spin-1/2 pyrochlores R2V2O7 were
investigated on the basis of density-functional calculations. Contrary to the
common belief, the spin-1/2 V4+ ions are found to have a substantial easy-axis
single-ion anisotropy. The |D/J| ratio deduced from the magnon quantum Hall
effect of Lu2V2O7, where J is the nearest-neighbor spin exchange and D is the
Dzyaloshinskii-Moriya parameter, is much greater than the value estimated from
our calculations (i.e., 0.32 vs. 0.05). We show that this discrepancy is due to
the neglect of the single-ion anisotropy of the V4+ ions, and the negative
magnetoresistance observed for R2V2O7 arises from a new mechanism.",1010.4606v1
2010-10-22,"Investigation on Anharmonicity, Vibrational Anisotropy and Thermal Expansion of an Amorphous Ni$_{46}$Ti$_{54}$ Alloy Produced by Mechanical Alloying using Extended X-ray Absorption Fine Structure","A method to investigate anharmonicity, vibrational anisotropy and thermal
expansion using correlated mean-square relative displacements (MSRD) parallel
and perpendicular to the interatomic bonds obtained only from Extended X-ray
Absorption Fine Structure (EXAFS) analysis based on cumulant expansion is
suggested and applied to an amorphous Ni$_{46}$Ti$_{54}$ alloy produced by
mechanical alloying. From EXAFS measurements taken on Ni and Ti K edges at
several temperatures, the thermal behavior of $\text{MSRD}_\parallel$,
$\text{MSRD}_\perp$ and of the cumulants $C_1^*$, $C_2^*$ and $C_3^*$ of the
real distribution functions $\varrho_{ij}(r,T)$, and also the Einstein
temperatures and frequencies associated with parallel and perpendicular motion
were obtained, furnishing information about the anharmonicity of the
interatomic potential, vibrational anisotropy and the contribution of the
perpendicular motion to the total disorder and thermal expansion.",1010.4703v1
2010-10-26,Single domain to multi-domain transition due to in-plane magnetic anisotropy in phase separated (La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films,"Phase separated perovskite manganites have competing phases with different
crystal structures, magnetic and electronic properties. Hence, strain effects
play a critical role in determining the magnetic properties of manganite thin
films. Here we report the effect of anisotropic stress on the magnetic
properties of the phase separated manganite
(La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$. Thin films of
(La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ grown under anisotropic
in-plane stress on (110) NdGaO$_{3}$ substrates display in-plane mangetic
anisotropy and single domain to multidomain transition as a function of
temperature. Angle dependent magnetization measurements also show that the
magnetization reversal occurs mainly through the nucleation $&$ propagation
mechanism. By comparing the results with
(La$_{0.4}$Pr$_{0.6}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin films grown on (001)
SrLaGaO$_{4}$ substrates, we have confirmed that the magnetic anisotropy is
mainly due to substrate induced anisotropic stress. Our results suggest novel
avenues for storing magnetic information in nanoscale magnetic media.",1010.5482v1
2010-11-01,Optimization of artificial flockings by means of anisotropy measurements,"An effective procedure to determine the optimal parameters appearing in
artificial flockings is proposed in terms of optimization problems. We
numerically examine genetic algorithms (GAs) to determine the optimal set of
parameters such as the weights for three essential interactions in BOIDS by
Reynolds (1987) under `zero-collision' and `no-breaking-up' constraints. As a
fitness function (the energy function) to be maximized by the GA, we choose the
so-called the $\gamma$-value of anisotropy which can be observed empirically in
typical flocks of starling. We confirm that the GA successfully finds the
solution having a large $\gamma$-value leading-up to a strong anisotropy. The
numerical experience shows that the procedure might enable us to make more
realistic and efficient artificial flocking of starling even in our personal
computers. We also evaluate two distinct types of interactions in agents,
namely, metric and topological definitions of interactions. We confirmed that
the topological definition can explain the empirical evidence much better than
the metric definition does.",1011.0362v2
2010-11-12,Non-boost-invariant anisotropic dynamics,"We study the non-boost-invariant evolution of a quark-gluon plasma subject to
large early-time momentum-space anisotropies. Rather than using the canonical
hydrodynamical expansion of the distribution function around an isotropic
equilibrium state, we expand around a state which is anisotropic in momentum
space and parameterize this state in terms of three proper-time and
spatial-rapidity dependent parameters. Deviations from the Bjorken scaling
solutions are naturally taken into account by the time evolution of the
spatial-rapidity dependence of the anisotropic ansatz. As a result, we obtain
three coupled partial differential equations for the momentum-space anisotropy,
the typical momentum of the degrees of freedom, and the longitudinal flow.
Within this framework (0+1)-dimensional Bjorken expansion is obtained as an
asymptotic limit. Finally, we make quantitative comparisons of the temporal and
spatial-rapidity evolution of the dynamical parameters and resulting pressure
anisotropy in both the strong and weak coupling limits.",1011.3056v2
2010-11-17,Interaction anisotropy and random impurities effects on the critical behaviour of ferromagnets,"The theory of phase transitions is based on the consideration of ""idealized""
models, such as the Ising model: a system of magnetic moments living on a cubic
lattice and having only two accessible states. For simplicity the interaction
is supposed to be restricted to nearest--neighbour sites only. For these
models, statistical physics gives a detailed description of the behaviour of
various thermodynamic quantities in the vicinity of the transition temperature.
These findings are confirmed by the most precise experiments. On the other
hand, there exist other cases, where one must account for additional features,
such as anisotropy, defects, dilution or any effect that may affect the nature
and/or the range of the interaction. These features may have impact on the
order of the phase transition in the ideal model or smear it out. Here we
address two classes of models where the nature of the transition is altered by
the presence of anisotropy or dilution.",1011.3923v1
2010-11-24,Observation of the anisotropy in arrival direction of Cosmic Rays with IceCube,"The IceCube Neutrino Observatory is a kilometer-scale detector currently
under construction at the South Pole. In its final configuration the detector
will comprise 5160 Digital Optical Modules (DOMs) deployed on 86 strings
between 1.5-2.5 km deep within the ice. While still incomplete, the detector
has already recorded tens of billions of cosmic ray muons with a median energy
of 20 TeV. This large sample has been used to study the arrival direction
distribution of the cosmic rays. We report the observation of an anisotropy in
the cosmic rays arrival direction at two different angular scales. The observed
large scale anisotropy seems to be a continuation of similar structures
observed in the Northern Sky by several experiments. IceCube observes also
significant features on the angular scale of $20^{\circ} - 30^{\circ}$ that
might be part of the larger scale structure.",1011.5428v1
2010-12-17,Structural and magnetic properties of Co2MnSi thin films,"Co2MnSi (CMS) films of different thicknesses (20, 50 and 100 nm) were grown
by radio frequency (RF) sputtering on a-plane sapphire substrates. Our X-rays
diffraction study shows that, in all the samples, the cubic <110> CSM axis is
normal to the substrate and that there exist well defined preferential in-plane
orientations. Static and dynamic magnetic properties were investigated using
vibrating sample magnetometry (VSM) and micro-strip line ferromagnetic
resonance (MS-FMR), respectively. From the resonance measurements versus the
direction and the amplitude of an applied magnetic field we derive most of the
magnetic parameters: magnetization, gyromagnetic factor, exchange stiffness
coefficient and magnetic anisotropy terms. The in-plane anisotropy can be
described as resulting from the superposition of two terms showing a two-fold
and a four-fold symmetry without necessarily identical principal axes. The
observed behavior of the hysteresis loops is in agreement with this complex
form of the in-plane anisotropy",1012.3837v2
2010-12-21,Antiferromagnetic resonance in ferroborate NdFe$_3$(BO$_3$)$_4,"The AFMR spectra of the NdFe$_3$(BO$_3$)$_4$ crystal are measured in a wide
range of frequencies and temperatures. It is found that by the type of magnetic
anisotropy the compound is an ""easy-plane"" antiferromagnet with a weak
anisotropy in the basal plane. The effective magnetic parameters are
determined: anisotropy fields $H_{a1}$=1.14 kOe and $H_{a2}$=60 kOe and
magnetic excitation gaps $\Delta\nu_1$=101.9 GHz and $\Delta \nu_2$=23.8 GHz.
It is shown that commensurate-incommensurate phase transition causes a shift in
resonance field and a considerable change in absorption line width.
  At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low
microwave power levels are observed.",1012.4588v1
2011-02-01,Disentangle plume-induced anisotropy in the velocity field in buoyancy-driven turbulence,"We present a method of disentangling the anisotropies produced by the cliff
structures in turbulent velocity field and test it in the system of turbulent
Rayleigh-B\'{e}nard (RB) convection. It is found that in the RB system the
cliff structures in the velocity field are generated by thermal plumes. These
cliff structures induce asymmetry in the velocity increments, which leads us to
consider the plus and minus velocity structure functions (VSF). The plus
velocity increments exclude cliff structures, while the minus ones include
them. Our results show that the scaling exponents of the plus VSFs are in
excellent agreement with those predicted for homogeneous and isotropic
turbulence (HIT), whereas those of the minus VSFs exhibit significant
deviations from HIT expectations in places where thermal plumes abound. These
results demonstrate that plus and minus VSFs can be used to quantitatively
study the effect of cliff structures in the velocity field and to effectively
disentangle the associated anisotropies caused by these structures.",1102.0098v1
2011-02-04,An Asymptotic-Preserving method for highly anisotropic elliptic equations based on a micro-macro decomposition,"The concern of the present work is the introduction of a very efficient
Asymptotic Preserving scheme for the resolution of highly anisotropic diffusion
equations. The characteristic features of this scheme are the uniform
convergence with respect to the anisotropy parameter $0<\eps <<1$, the
applicability (on cartesian grids) to cases of non-uniform and non-aligned
anisotropy fields $b$ and the simple extension to the case of a non-constant
anisotropy intensity $1/\eps$. The mathematical approach and the numerical
scheme are different from those presented in the previous work [Degond et al.
(2010), arXiv:1008.3405v1] and its considerable advantages are pointed out.",1102.0904v1
2011-02-20,Electrostriction Effects During Defibrillation,"Background-The electric field applied to the heart during defibrillation
causes mechanical forces (electrostriction), and as a result the heart deforms.
This paper analyses the physical origin of the deformation, and how significant
it is. Methods-We represent the heart as an anisotropic cylinder. This simple
geometry allows us to obtain analytical solutions for the potential, current
density, charge, stress, and strain. Results-Charge induced on the heart
surface in the presence of the electric field results in forces that deform the
heart. In addition, the anisotropy of cardiac tissue creates a charge density
throughout the tissue volume, leading to body forces. These two forces cause
the tissue to deform in a complicated manner, with the anisotropy suppressing
radial displacements in favor of tangential ones. Quantitatively, the
deformation of the tissue is small, although it may be significant when using
some imaging techniques that require the measurement of small displacements.
Conclusions-The anisotropy of cardiac tissue produces qualitatively new
mechanical behavior during a strong, defibrillation-strength electric shock.",1102.4077v1
2011-03-05,Quantum entanglement and teleportation in quantum dot,"We study the thermal entanglement and quantum teleportation using quantum dot
as a resource. We first consider entanglement of the resource, and then focus
on the effects of different parameters on the teleportation fidelity under
different conditions. The critical temperature of disentanglement is obtained.
Based on Bell measurements in two subspaces, we find the anisotropy
measurements is optimal to the isotropy arising from the entangled eigenstates
of the system in the anisotropy subspace. In addition, it is shown that the
anisotropy transmission fidelity is very high and stable for quantum dot as
quantum channel when the parameters are adjusted. The possible applications of
quantum dot are expected in the quantum teleportation.",1103.1000v2
2011-03-06,"The Influence of Magnetic Anisotropy on the Kondo Effect and Spin-Polarized Transport through Magnetic Molecules, Adatoms and Quantum Dots","Transport properties in the Kondo regime of a nanosystem displaying uniaxial
magnetic anisotropy (such as a magnetic molecule, magnetic adatom or quantum
dot coupled to a localized magnetic moment) are analyzed theoretically. In
particular, the influence of spin-polarized transport through a local orbital
of the system and exchange coupling of conduction electrons to the system's
magnetic core on the Kondo effect is discussed. The numerical renormalization
group method is applied to calculate the spectral functions and linear
conductance in the case of the parallel and antiparallel configurations of the
electrodes' magnetic moments. It is shown that both the magnetic anisotropy as
well as the exchange coupling between electrons tunneling through the
conducting orbital and magnetic core play an important role in formation of the
Kondo resonance, leading generally to its suppression. Specific transport
properties of such a system appear also as a nontrivial behavior of tunnel
magnetoresistance. It is also shown that the Kondo effect can be restored by an
external magnetic field in both the parallel and antiparallel magnetic
configurations.",1103.1128v2
2011-03-08,Effects of Anisotropy in QED3 from Dyson-Schwinger equations in a box,"We investigate the effect of anisotropies in the fermion velocities of 2+1
dimensional QED on the critical number N_f^c of fermions for dynamical mass
generation. Our framework are the Dyson-Schwinger equations for the gauge boson
and fermion propagators formulated in a finite volume. In contrast to previous
Dyson-Schwinger studies we do not rely on an expansion in small anisotropies
but keep the full velocity dependence of fermion equations intact. As result we
find sizable variations of N_f^c away from the isotropic point in agreement
with other approaches. We discuss the relevance of our findings for models of
high-T_c superconductors.",1103.1578v2
2011-03-25,Temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites,"The temperature dependence of core loss in cobalt substituted Ni-Zn-Cu
ferrites was investigated. Co2+ ions are known to lead to a compensation of the
magneto-crystalline anisotropy in Ni-Zn ferrites, at a temperature depending on
the cobalt content and the Ni/Zn ratio. We observed similar behaviour in
Ni-Zn-Cu and it was found that the core loss goes through a minimum around this
magneto-crystalline anisotropy compensation. Moreover, the anisotropy induced
by the cobalt allowed a strong decrease of core loss, a ferrite having a core
loss of 350 mW/cm3 at 80 ^\circ C was then developed (measured at 1.5 MHz and
25 mT). This result represents an improvement of a factor 4 compared to the
state of art Ni-Zn ferrites.",1103.5021v1
2011-03-31,Anisotropic Inflation with Non-Abelian Gauge Kinetic Function,"We study an anisotropic inflation model with a gauge kinetic function for a
non-abelian gauge field. We find that, in contrast to abelian models, the
anisotropy can be either a prolate or an oblate type, which could lead to a
different prediction from abelian models for the statistical anisotropy in the
power spectrum of cosmological fluctuations. During a reheating phase, we find
chaotic behaviour of the non-abelian gauge field which is caused by the
nonlinear self-coupling of the gauge field. We compute a Lyapunov exponent of
the chaos which turns out to be uncorrelated with the anisotropy.",1103.6164v2
2011-04-07,Electron g-Factor Anisotropy in Symmetric (110)-oriented GaAs Quantum Wells,"We demonstrate by spin quantum beat spectroscopy that in undoped symmetric
(110)-oriented GaAs/AlGaAs single quantum wells even a symmetric spatial
envelope wavefunction gives rise to an asymmetric in-plane electron
Land\'e-g-factor. The anisotropy is neither a direct consequence of the
asymmetric in-plane Dresselhaus splitting nor of the asymmetric Zeeman
splitting of the hole bands but is a pure higher order effect that exists as
well for diamond type lattices. The measurements for various well widths are
very well described within 14 x 14 band k.p theory and illustrate that the
electron spin is an excellent meter variable to map out the internal -otherwise
hidden- symmetries in two dimensional systems. Fourth order perturbation theory
yields an analytical expression for the strength of the g-factor anisotropy,
providing a qualitative understanding of the observed effects.",1104.1360v1
2011-04-11,The effects of strong temperature anisotropy on the kinetic structure of collisionless slow shocks and reconnection exhausts. Part II: Theory,"Simulations of collisionless oblique propagating slow shocks have revealed
the existence of a transition associated with a critical temperature anisotropy
epsilon=1-mu_0(P_parallel-P_perpendicular)/ B^2 = 0.25 (Liu, Drake and Swisdak
(2011)). An explanation for this phenomenon is proposed here based on
anisotropic fluid theory, in particular the Anisotropic Derivative
Nonlinear-Schrodinger-Burgers equation, with an intuitive model of the energy
closure for the downstream counter-streaming ions. The anisotropy value of 0.25
is significant because it is closely related to the degeneracy point of the
slow and intermediate modes, and corresponds to the lower bound of the coplanar
to non-coplanar transition that occurs inside a compound slow shock
(SS)/rotational discontinuity (RD) wave. This work implies that it is a pair of
compound SS/RD waves that bound the outflows in magnetic reconnection, instead
of a pair of switch-off slow shocks as in Petschek's model. This fact might
explain the rareness of in-situ observations of
Petschek-reconnection-associated switch-off slow shocks.",1104.2055v1
2011-04-17,On the theory of microwave absorption by the spin-1/2 Heisenberg-Ising magnet,"We analyze the problem of microwave absorption by the Heisenberg-Ising magnet
in terms of shifted moments of the imaginary part of the dynamical
susceptibility. When both, the Zeeman field and the wave vector of the incident
microwave, are parallel to the anisotropy axis, the first four moments
determine the shift of the resonance frequency and the line width in a
situation where the frequency is varied for fixed Zeeman field. For the
one-dimensional model we can calculate the moments exactly. This provides exact
data for the resonance shift and the line width at arbitrary temperatures and
magnetic fields. In current ESR experiments the Zeeman field is varied for
fixed frequency. We show how in this situation the moments give perturbative
results for the resonance shift and for the integrated intensity at small
anisotropy as well as an explicit formula connecting the line width with the
anisotropy parameter in the high-temperature limit.",1104.3298v1
2011-05-25,Anisotropy of zero-resistance states in InN films under an in-plane magnetic filed,"We report low temperature current-voltage measurements on n-type InN films
grown by molecular beam epitaxy. The zero-resistance state with a large
critical current around 1 mA has been observed at 0.3 K. Under in-plane field
configuration, the zero-resistance state shows a large anisotropy in critical
current for B parallel and perpendicular to applied current. The ratio of
critical current between B parallel and perpendicular to the applied current
can be up to 2.5, when B = 0.15T. The anisotropy is explained by the vortex
flow in the context of type II superconductivity. We have thus established an
important aspect of the phenomenology of superconductivity in an otherwise
typical narrow gap semiconductor.",1105.5150v1
2011-05-31,g-Factor anisotropy of hole quantum wires induced by the Rashba interaction,"We present calculations of the g factors for the lower conductance steps of
3D hole quantum wires. Our results prove that the anisotropy with magnetic
field orientation, relative to the wire, originates in the Rashba spin-orbit
coupling. We also analyze the relevance of the deformation, as the wire evolves
from 3D towards a flat 2D geometry. For high enough wire deformations, the
perpendicular g factors are greatly quenched by the Rashba interaction. On the
contrary, parallel g factors are rather insensistive to the Rashba interaction,
resulting in a high g factor anisotropy. For low deformations we find a more
irregular behavior which hints at a sample dependent scenario.",1105.6278v2
2011-06-05,Thermal-assisted Anisotropy and Thermal-driven Instability in the Superfluidity state of Two-Species Polar Fermi Gas,"We study the superfluid state of two-species heteronuclear Fermi gases with
isotropic contact and anisotropic long-range dipolar interactions. By
explicitly taking account of Fock exchange contribution, we derive
self-consistent equations describing the pairing states in the system.
Exploiting the symmetry of the system, we developed an efficient way of solving
the self-consistent equations by exploiting the symmetries. We find that the
temperature tends to increase the anisotropy of the pairing state, which is
rather counterintuitive. We study the anisotropic properties of the system by
examining the angular dependence of the number density distribution, the
excitation spectrum and the pair correlation function. The competing effects of
the contact interaction and the dipolar interaction upon the anisotropy are
revealed. We derive and compute the superfluid mass density $\rho_{ij}$ for the
system. Astonishingly, we find that $\rho_{zz}$ becomes negative above some
certain temperature $T^*$($T<T_c$), signaling some instability of the system.
This suggests that the elusive FFLO state may be observed in experiments, due
to an anisotropic state with a spontaneously generated superflow.",1106.0891v1
2011-06-06,Quantum Spin Hall Insulators with Interactions and Lattice Anisotropy,"We investigate the interplay between spin-orbit coupling and
electron-electron interactions on the honeycomb lattice combining the cellular
dynamical mean-field theory and its real space extension with analytical
approaches. We provide a thorough analysis of the phase diagram and temperature
effects at weak spin-orbit coupling. We systematically discuss the stability of
the quantum spin Hall phase toward interactions and lattice anisotropy
resulting in the plaquette-honeycomb model. We also show the evolution of the
helical edge states characteristic of quantum spin Hall insulators as a
function of Hubbard interaction and anisotropy. At very weak spin-orbit
coupling and intermediate electron-electron interactions, we substantiate the
existence of a quantum spin liquid phase.",1106.0943v2
2011-06-08,"In-plane electronic anisotropy of underdoped ""122"" Fe-arsenide superconductors revealed by measurements of detwinned single crystals","The parent phases of the Fe-arsenide superconductors harbor an
antiferromagnetic ground state. Significantly, the N\'eel transition is either
preceded or accompanied by a structural transition that breaks the four fold
symmetry of the high-temperature lattice. Borrowing language from the field of
soft condensed matter physics, this broken discrete rotational symmetry is
widely referred to as an Ising nematic phase transition. Understanding the
origin of this effect is a key component of a complete theoretical description
of the occurrence of superconductivity in this family of compounds, motivating
both theoretical and experimental investigation of the nematic transition and
the associated in-plane anisotropy. Here we review recent experimental progress
in determining the intrinsic in-plane electronic anisotropy as revealed by
resistivity, reflectivity and ARPES measurements of detwinned single crystals
of underdoped Fe arsenide superconductors in the ""122"" family of compounds.",1106.1675v1
2011-06-22,Tunable Magnonic Frequency and Damping in [Co/Pd]8 Multilayers with Variable Co Layer Thickness,"We report the experimental observation of collective picosecond magnetization
dynamics in [Co/Pd]8 multilayers with perpendicular magnetic anisotropy. The
precession frequency shows large and systematic variation from about 5 GHz to
about 90 GHz with the decrease in the Co layer thickness from 1.0 nm to 0.22 nm
due to the linear increase in the perpendicular magnetic anisotropy. The
damping coefficient 'alpha' is found to be inversely proportional to the Co
layer thickness and a linear relation between the perpendicular magnetic
anisotropy and 'alpha' is established. We discuss the possible reasons behind
the enhanced damping as the d-d hybridization at the interface and spin
pumping. These observations are significant for the applications of these
materials in spintronics and magnonic crystals.",1106.4491v1
2011-06-23,Direct measurements of anisotropic energy transfers in a rotating turbulence experiment,"We investigate experimentally the influence of a background rotation on the
energy transfers in decaying grid turbulence. The anisotropic energy flux
density, ${\bf F} ({\bf r}) = < \delta {\bf u}\,(\delta {\bf u})^2 >$, where
$\delta {\bf u}$ is the vector velocity increment over separation ${\bf r}$, is
determined for the first time using Particle Image Velocimetry. We show that
rotation induces an anisotropy of the energy flux $\nabla \cdot {\bf F}$, which
leads to an anisotropy growth of the energy distribution $E({\bf r}) = <
(\delta {\bf u})^2 >$, in agreement with the K\'arm\'an-Howarth-Monin equation.
Surprisingly, our results prove that this anisotropy growth is essentially
driven by a nearly radial, but orientation-dependent, energy flux density ${\bf
F} ({\bf r})$.",1106.4683v1
2011-06-29,Non-Gaussianities in the Cosmological Perturbation Spectrum due to Primordial Anisotropy,"We investigate possible signatures of a pre-inflationary anisotropic phase in
two-point and three-point correlation functions of the curvature perturbation
for high-momentum modes which exit the horizon after isotropization. In this
momentum regime, the early time dynamics admits a WKB description and the late
time dynamics can be described in terms of a non-Bunch Davies vacuum state
which encodes the information of initial anisotropy in the background
spacetime. We compute the bi-spectrum for curvature perturbation in a canonical
single-field action with and without higher derivative operators. We show that
the bi-spectrum at late times, in either case, is enhanced for a flattened
triangle configuration as well as a squeezed triangle configuration and compute
the corresponding $f_{NL}$ parameters. The angular dependence and the
particular momentum dependence of the $f_{NL}$ parameter appear as distinctive
features of background anisotropy at early times.",1106.5840v3
2011-07-07,Measurement of elliptic and higher order flow from ATLAS experiment at the LHC,"We present a differential measurement of the azimuthal anisotropy of charged
hadron production in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$=2.76 TeV.
This azimuthal anisotropy is expanded into a Fourier series in azimuthal angle,
where the coefficient for each term, $v_n$, characterizes the magnitude of the
anisotropy at a particular angular scale. We extract $v_2-v_6$ via a discrete
Fourier analysis of the two-particle $\Delta\phi-\Delta\eta$ correlation with a
large $\Delta\eta$ gap ($|\Delta\eta|>2$), and via an event plane method based
on the Forward Calorimeter. Significant $v_2-v_6$ values are observed over a
broad range in $\pT$, $\eta$ and centrality, and they are found to be
consistent between the two methods in the transverse momentum region $\pT<3-4$
GeV. This suggests that the measured $v_2-v_6$ obtained from two-particle
correlations at low $\pT$ with a large $\Delta\eta$ gap are consistent with the
collective response of the system to the initial state geometry fluctuations,
and is not the result of jet fragmentation or resonance decay.",1107.1468v2
2011-08-04,Qualitative difference between the angular anisotropy parameters in fast electron scattering and photoionization,"It is demonstrated for the first time that in spite of well known big
similarities between atomic ionization by photons and fast electrons, a
qualitative difference exists in angular anisotropy parameters of electrons
knocked out in these processes. The difference is disclosed here and attributed
to distinction between normal (transverse) and virtual (longitudinal) photons.
Formulas are derived for dipole and non-dipole angular anisotropy parameters in
fast electronatom scattering. The ratio of quadrupole-to-dipole matrix elements
is determined by the parameter \omega R/v << 1 where \omega is the transferred
in collision energy, R is the ionized shell radius and v is the speed of
projectile. This factor can be much bigger than in the case of photoionization,
where one has the speed of light c that is much bigger than v . We illustrate
general formulas by concrete results for outer s-subshells of noble gas atoms
Ar and Xe. Even for very small transferred momentum q, in the so-called optical
limit, the deviation from photoionization case is prominent and instructive.",1108.1013v1
2011-08-10,Magnetic-field-induced nonlocal effects on the vortex interactions in twin-free YBa2Cu3O7,"The vortex lattice (VL) in the high-kappa superconductor YBa2Cu3O7, at 2 K
and with the magnetic field parallel to the crystal c-axis, undergoes a
sequence of transitions between different structures as a function of applied
magnetic field. However, from structural studies alone, it is not possible to
determine precisely the system anisotropy that governs the transitions between
different structures. To address this question, here we report new small-angle
neutron scattering measurements of both the VL structure at higher
temperatures, and the field- and temperature-dependence of the VL form factor.
Our measurements demonstrate how the influence of anisotropy on the VL, which
in theory can be parameterized as nonlocal corrections, becomes progressively
important with increasing magnetic field, and suppressed by increasing the
temperature towards Tc. The data indicate that nonlocality due to different
anisotropies play important roles in determining the VL properties.",1108.2176v1
2011-08-31,Optical Conductivity Anisotropy in the Undoped Three-Orbital Hubbard Model for the Pnictides,"The resistivity anisotropy unveiled in the study of detwinned single crystals
of the undoped 122 pnictides is here studied using the two-dimensional
three-orbital Hubbard model in the mean-field approximation. Calculating the
Drude weight in the x and y directions at zero temperature for a Q=(\pi,0)
magnetically ordered state, the conductance along the antiferromagnetic
direction is shown to be larger than along the ferromagnetic direction. This
effect is caused by the suppression of the d_{yz} orbital at the Fermi surface,
but additional insight based on the momentum dependence of the transitions
induced by the current operator is provided. It is shown that the effective
suppression of the inter-orbital hopping d_{xy} and d_{yz} along the y
direction is the main cause of the anisotropy.",1109.0012v1
2011-09-12,Single-ion anisotropy in Haldane chains and form factor of the O(3) nonlinear sigma model,"We consider spin-1 Haldane chains with single-ion anisotropy, which exists in
known Haldane chain materials. We develop a perturbation theory in terms of
anisotropy, where magnon-magnon interaction is important even in the low
temperature limit. The exact two-particle form factor in the O(3) nonlinear
sigma model leads to quantitative predictions on several dynamical properties
including dynamical structure factor and electron spin resonance frequency
shift. These agree very well with numerical results, and with experimental data
on the Haldane chain material Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(PF$_6$).",1109.2607v2
2011-09-13,CMB Anomalies from Imperfect Dark Energy: Confrontation with the Data,"We test anisotropic dark energy models with the 7-year WMAP temperature
observations data. In the presence of imperfect sources, due to large-scale
gradients or anisotropies in the dark energy field, the CMB sky will be
distorted anisotropically on its way to us by the ISW effect. The signal
covariance matrix then becomes nondiagonal for small multipoles, but at $\ell
\gtrsim 20$ the anisotropy is negligible. We parametrize possible violations of
rotational invariance in the late universe by the magnitude of a
post-Friedmannian deviation from isotropy and its scale dependence. This allows
to obtain hints on possible imperfect nature of dark energy and the large-angle
anomalous features in the CMB. A robust statistical analysis, subjected to
various tests and consistency checks, is performed to compare the predicted
correlations with those obtained from the satellite-measured CMB full sky maps.
The preferred axis point towards $(l,b) = (168^\circ, -31^\circ)$ and the
amplitude of the anisotropy is $\varpi_0 = (0.51\pm 0.94)$ (1$\sigma$ deviation
quoted). The best-fit model has a steep blue anisotropic spectrum
($n_{\mathrm{de}} = 3.1\pm1.5$).",1109.2778v1
2011-09-14,Rise of azimuthal anisotropies as a signature of the Quark-Gluon-Plasma in relativistic heavy-ion collisions,"The azimuthal anisotropies of the collective transverse flow of hadrons are
investigated in a large range of heavy-ion collision energy within the
Parton-Hadron-String Dynamics (PHSD) microscopic transport approach which
incorporates explicit partonic degrees of freedom in terms of strongly
interacting quasiparticles (quarks and gluons) in line with an
equation-of-state from lattice QCD as well as dynamical hadronization and
hadronic dynamics in the final reaction phase. The experimentally observed
increase of the elliptic flow $v_2$ with bombarding energy is successfully
described in terms of the PHSD approach in contrast to a variety of other
kinetic models based on hadronic interactions. The analysis of higher-order
harmonics $v_3$ and $v_4$ shows a similar tendency of growing deviations
between partonic and purely hadronic models with increasing bombarding energy.
This signals that the excitation functions of azimuthal anisotropies provide a
sensitive probe for the underling degrees of freedom excited in heavy-ion
collisions.",1109.3039v2
2011-09-26,Symmetric and antisymmetric exchange anisotropies in quasi-one-dimensional CuSe$_2$O$_5$ as revealed by ESR,"We present an electron spin resonance (ESR) study of single-crystalline spin
chain-system CuSe$_2$O$_5$ in the frequency range between 9 GHz and 450 GHz. In
a wide temperature range above the N\'{e}el temperature $T_N=17$ K we observe
strong and anisotropic frequency dependence of a resonance linewidth. Although
sizeable interchain interaction $J_{IC}\approx 0.1 J$ ($J$ is the intrachain
interaction) is present in this system, the ESR results agree well with the
Oshikawa-Affleck theory for one-dimensional $S=1/2$ Heisenberg antiferromagnet.
This theory is used to extract the anisotropies present in CuSe$_2$O$_5$. We
find that the symmetric anisotropic exchange $J_c=(0.04 \pm 0.01) \:J$ and the
antisymmetric Dzyaloshinskii-Moriya (DM) interaction $D=(0.05\pm 0.01)\:J$ are
very similar in size in this system. Staggered-field susceptibility induced by
the presence of the DM interaction is witnessed in the macroscopic
susceptibility anisotropy.",1109.5597v2
2011-09-29,Anisotropic modules over artinian principal ideal rings,"Let V be a finite-dimensional vector space over a field k and let W be a
1-dimensional k-vector space. Let < , >: V x V \to W be a symmetric bilinear
form. Then < , > is called anisotropic if for all nonzero v \in V we have <v,v>
\neq 0. Motivated by a problem in algebraic number theory, we come up with a
generalization of the concept of anisotropy to symmetric bilinear forms on
finitely generated modules over artinian principal ideal rings. We will give
many equivalent definitions of this concept of anisotropy. One of the
definitions shows that one can check if a form is anisotropic by checking if
certain forms on vector spaces are anisotropic. We will also discuss the
concept of quasi-anisotropy of a symmetric bilinear form, which has no useful
vector space analogue. Finally we will discuss the radical root of a symmetric
bilinear form, which doesn't have a useful vector space analogue either. All
three concepts have applications in algebraic number theory.",1109.6483v1
2011-09-30,Anisotropy and the integral closure,"Let K be a number field and let A be an order in K. The trace map from K to Q
induces a non-degenerate symmetric bilinear form <,>: B x B \to Q/Z where B is
a certain finite abelian group of size \Delta(A). In this article we discuss
how one can obtain information about \mathcal{O}_K by purely looking at this
symmetric bilinear form. The concepts of anisotropy and quasi-anisotropy, as
defined in another article by the author, turn out to be very useful. We will
for example show that under certain assumptions one can obtain \mathcal{O}_K
directly from <,>.
  In this article we will work in a more general setting than we have discussed
above. We consider orders over Dedekind domains.",1109.6733v1
2011-10-13,Incorporating Kinetic Physics into a Two-Fluid Solar-Wind Model with Temperature Anisotropy and Low-Frequency Alfven-Wave Turbulence,"We develop a 1D solar-wind model that includes separate energy equations for
the electrons and protons, proton temperature anisotropy, collisional and
collisionless heat flux, and an analytical treatment of low-frequency,
reflection-driven, Alfven-wave turbulence. To partition the turbulent heating
between electron heating, parallel proton heating, and perpendicular proton
heating, we employ results from the theories of linear wave damping and
nonlinear stochastic heating. We account for mirror and oblique firehose
instabilities by increasing the proton pitch-angle scattering rate when the
proton temperature anisotropy exceeds the threshold for either instability. We
numerically integrate the equations of the model forward in time until a steady
state is reached, focusing on two fast-solar-wind-like solutions. These
solutions are consistent with a number of observations, supporting the idea
that Alfven-wave turbulence plays an important role in the origin of the solar
wind.",1110.3029v2
2011-10-13,Anisotropy in BaFe2Se3 single crystals with double chains of FeSe tetrahedra,"We studied the anisotropy in physical properties of Ba1.00(4)Fe1.9(1)Se3.1(1)
single crystals. BaFe2Se3 is a semiconductor below 300 K. Magnetization
measurements show that there is a crossover from short-range antiferromagnetic
(AFM) correlations at room temperature to a long-range AFM order with TN = 255
K. The anisotropy of magnetization is consistent with the previous neutron
results. This crossover is supported by the heat-capacity measurement, where
the phase-transition peak is absent at 255 K. The superconducting transition at
about 10 K is likely due to the small amount of beta-FeSe impurities.",1110.3039v3
2011-10-18,Polarization properties of excitonic qu-bits in single self-assembled quantum dots,"We investigate polarization properties of neutral exciton emission in single
self-assembled InAs/GaAs quantum dots. The in-plane shape and strain anisotropy
strongly couple the heavy and light hole states and lead to large optical
anisotropy with non-orthogonal linearly polarized states misaligned with
respect to the crystallographic axes. Owing to a waveguiding experimental
configuration, luminescence polarization along the growth axis has been
observed revealing the presence of shear components of the deformation tensor
out of the growth plane. Resonant luminescence experiments allowed determining
the oscillator strength ratio of the two exciton eigenstates. Valence band
mixing governs this ratio and can be very different from dot to dot, however
the polarization anisotropy axis is quite fixed inside a scanned area of one
\mum^{2} and indicates that the in-plane deformation direction to which it is
related has a correlation length of the order of magnitude of one \mum^{2}.",1110.4042v1
2011-10-19,Small scale anisotropy in turbulent shearless mixing,"The generation of small-scale anisotropy in turbulent shearless mixing is
numerically investigated. Data from direct numerical simulations at Taylor
Reynolds' numbers between 45 and 150 show that there is not only a significant
departure of the longitudinal velocity derivative moments from the values found
in homogeneous and isotropic turbulence, but that the variation of skewness has
an opposite sign for the components across the mixing layer and parallel to it.
The anisotropy induced by the presence of a kinetic energy gradient has a very
different pattern from the one generated by an homogeneous shear. The
transversal derivative moments in the mixing are in fact found to be very
small, which highlights that smallness of the transversal moments is not a
sufficient condition for isotropy.",1110.4328v1
2011-10-24,"Magnetoresistance of 2D and 3D Electron Gas in LaAlO3/SrTiO3 Heterostructures: Influence of Magnetic Ordering, Interface Scattering and Dimensionality","Magnetoresistance (MR) anisotropy in LaAlO3/SrTiO3 (LAO/STO) interfaces is
compared between samples prepared in high oxygen partial pressure (PO2) of 10-4
mbar exhibiting quasi-two-dimensional (quasi-2D) electron gas and low PO2 of
10-6 mbar exhibiting 3D conductivity. While MR of an order of magnitude larger
was observed in low PO2 samples compared to those of high PO2 samples, large MR
anisotropies were observed in both cases. The MR with the out-of-plane field is
always larger compared to the MR with in-plane field suggesting lower
dissipation of electrons from interface versus defect scattering. The quasi-2D
interfaces show a negative MR at low temperatures while the 3D interfaces show
positive MR for all temperatures. Furthermore, the angle relationship of MR
anisotropy for these two different cases and temperature dependence of in-plane
MR are also presented. Our study demonstrates that MR can be used to
distinguish the dimensionality of the charge transport and various (defect,
magnetic center, and interface boundary) scattering processes in this system.",1110.5290v1
2011-10-24,Anisotropy of upper critical fields and thermally-activated flux flow of quenched KxFe2-ySe2 single crystals,"We report the anisotropy of the upper critical fields mu0Hc2(T) and
thermally-activated flux flow (TAFF) behavior of quenched KxFe2-ySe2. Even
though the post-annealing and quenching process enhances the superconducting
volume fraction, it has a minor effect on the upper critical fields for H//c
and H//ab. Analysis of the angular-dependence of resistivity rho_ab(theta,H)
indicates that it follows the scaling law based on the anisotropic
Ginzburg-Landau (GL) theory and the anisotropy Gamma(T) increases with
decreasing temperature with Gamma(T) ~ 3.6 at 27 K. The resistivity of quenched
sample exhibits an Arrhenius TAFF behavior for both field directions. Field
dependence of thermally activated energy U0(H) implies that the collective flux
creep is dominant in high fields and point defects are the main pinning source
in this regime.",1110.5316v1
2011-11-03,Effect of tensile stress on the in-plane resistivity anisotropy in BaFe2As2,"The effect of uniaxial tensile stress and the resultant strain on the
structural/magnetic transition in the parent compound of the iron arsenide
superconductor, BaFe$_2$As$_2$, is characterized by temperature-dependent
electrical resistivity, x-ray diffraction and quantitative polarized light
imaging. We show that strain induces a measurable uniaxial structural
distortion above the first-order magnetic transition and significantly smears
the structural transition. This response is different from that found in
another parent compound, SrFe$_2$As$_2$, where the coupled structural and
magnetic transitions are strongly first order. This difference in the
structural responses explains the in-plain resistivity anisotropy above the
transition in BaFe$_2$As$_2$. This conclusion is supported by the
Ginzburg-Landau - type phenomenological model for the effect of the uniaxial
strain on the resistivity anisotropy.",1111.0997v1
2011-11-07,Observation of anisotropic diffusion of light in compacted granular porous materials,"It is known that compaction of granular matter can lead to anisotropic
mechanical properties. Recent work has confirmed the link to pore space
anisotropy, but the relation between compression, mechanical properties and
material microstructure remains poorly understood and new diagnostic tools are
needed. By studying the temporal and spatial characteristics of short optical
pulses diffusively transmitted through compacted granular materials, we show
that powder compaction can also give rise to strongly anisotropic diffusion of
light. Investigating technologically important materials such as
microcrystalline cellulose, lactose and calcium phosphate, we report increasing
optical anisotropy with compaction force and radial diffusion constants being
up to 1.7 times the longitudinal. This open new and attractive routes to
material characterization and investigation of compression-induced structural
anisotropy. In addition, by revealing inadequacy of isotropic diffusion models,
our observations also have important implications for quantitative spectroscopy
of powder compacts (e.g., pharmaceutical tablets).",1111.1700v2
2011-12-05,Orbital upper critical field and its anisotropy of clean one- and two-band superconductors,"The Helfand-Werthamer (HW) scheme\cite{HW} of evaluating the orbital upper
critical field is generalized to anisotropic superconductors in general, and to
two-band clean materials, in particular. Our formal procedure differs from
those in the literature; it reproduces not only the isotropic HW limit, but
also the results of calculations for the two-band superconducting
MgB$_2$\cite{MMK,DS} along with the existing data on $H_{c2}(T)$ and its
anisotropy $\gamma(T)=H_{c2,ab}(T)/H_{c2,c}(T)$ ($a,c$ are the principal
directions of a uniaxial crystal). Using rotational ellipsoids as model Fermi
surfaces we apply the formalism developed to study $\gamma(T)$ for a few
different anisotropies of the Fermi surface and of the order parameters. We
find that even for a single band d-wave order parameter $\gamma(T)$ decreases
on warming, however, relatively weakly. For order parameters of the form $
\Delta(k_z) = \Delta_0(1+\eta\cos k_za)$,\cite{Xu} according to our simulations
$\gamma(T)$ may either increase or decrease on warming even for a single band
depending on the sign of $\eta$. Hence, the common belief that the multi-band
Fermi surface is responsible for the temperature variation of $\gamma$ is
proven incorrect.",1112.0996v2
2011-12-06,Analyzing flow anisotropies with excursion sets in relativistic heavy-ion collisions,"We show that flow anisotropies in relativistic heavy-ion collisions can be
analyzed using a certain technique of shape analysis of excursion sets recently
proposed by us for CMBR fluctuations to investigate anisotropic expansion
history of the universe. The technique analyzes shapes (sizes) of patches above
(below) certain threshold value for transverse energy/particle number (the
excursion sets) as a function of the azimuthal angle and rapidity. Modeling
flow by imparting extra anisotropic momentum to the momentum distribution of
particles from HIJING, we compare the resulting distributions for excursion
sets at two different azimuthal angles. Angles with maximum difference in the
two distributions identify the event plane, and the magnitude of difference in
the two distributions relates to the magnitude of momentum anisotropy, i.e.
elliptic flow.",1112.1177v1
2011-12-08,Effect of the anisotropy on the glory structure of molecule-molecule scattering cross sections,"Total (elastic + rotationally inelastic) integral cross sections are computed
for O$_2(^3\Sigma_g^-)$-O$_2(^3\Sigma_g^-)$ using a recent ab initio potential
energy surface. The sampled velocity range allows us a thorough comparison of
the glory interference pattern observed in molecular beam experiments. The
computed cross sections are about 10% smaller than the measured ones, however,
a remarkable agreement in the velocity positions of the glory extrema is
achieved. By comparing with models where the anisotropy of the interaction is
reduced or removed, it is found that the glory pattern is very sensitive to the
anisotropy, especially the positions of the glory extrema.",1112.1925v1
2011-12-16,Cosmic ray anisotropy studies with the Stockholm Educational Air Shower array,"The Stockholm Educational Air Shower Array (SEASA) project has established a
network of GPS time-synchronised scintillator detector stations at high-schools
in the Stockholm region. The primary aim of this project is outreach. A part of
the network comprises a dense cluster of detector stations located at AlbaNova
University Centre. This cluster is being used to study the cosmic ray
anisotropy around the knee. Each station consists of three scintillator
detectors in a triangular geometry which allows multiple timing measurements as
the shower front sweeps over the station. The timing resolution of the system
has been determined and the angular resolution has been studied using Monte
Carlo simulations and is compared to data. The potential of this system to
study small and large scale cosmic ray anisotropies is discussed.",1112.3902v1
2011-12-29,Ordering of anisotropic polarizable polymer chains on the full many-body level,"We study the effect of dielectric anisotropy of polymers on their equilibrium
ordering within mean-field theory but with a formalism that takes into account
the full n-body nature of van der Waals forces. Dielectric anisotropy within
polymers is to be expected as the electronic properties of the polymer will
typically be different along the polymer than across its cross section. It is
therefore physically intuitive that larger charge fluctuations can be induced
along the chain than perpendicular to it. We show that this dielectric
anisotropy leads to n-body interactions which can induce an isotropic--nematic
transition. The two body and three body components of the full van der Waals
interaction are extracted and it is shown how the two body term behaves like
the phenomenological self-aligning-pairwise nematic interaction. At the three
body interaction level we see that the nematic phase that is energetically
favorable is discotic, however on the full n-body interaction level we find
that the normal axial nematic phase is always the stable ordered phase. The
n-body nature of our approach also shows that the key parameter driving the
nematic-isotropic transition is the bare persistence length of the polymer
chain.",1112.6278v1
2011-12-29,Anisotropic Ginzburg-Landau and Lawrence-Doniach Models for Layered Ultracold Fermi Gases,"We study the anisotropic Ginzburg-Landau and Lawrence-Doniach models
describing a layered superfluid ultracold Fermi gas in optical lattices. We
derive the coefficients of the anisotropic Ginzburg-Landau and the mass tensor
as a function of anisotropy, filling and interaction, showing that near the
unitary limit the effective anisotropy of the masses is significantly reduced.
The anisotropy parameter is shown to vary in realistic setups in a wide range
of values. We also derive the Lawrence-Doniach model - often used to describe
the 2D-3D dimensional crossover in layered superconductors - for a layered
ultracold Fermi gas, obtaining a relation between the interlayer Josephson
couplings and the Ginzburg-Landau masses. Comparing to the Ginzburg-Landau
description, we find that the region of validity of the Lawrence-Doniach model
is near the unitary limit.",1112.6429v2
2012-01-07,Anisotropic Fast-Marching on cartesian grids using Lattice Basis Reduction,"We introduce a modification of the Fast Marching Algorithm, which solves the
generalized eikonal equation associated to an arbitrary continuous riemannian
metric, on a two or three dimensional domain. The algorithm has a logarithmic
complexity in the maximum anisotropy ratio of the riemannian metric, which
allows to handle extreme anisotropies for a reduced numerical cost. We prove
the consistence of the algorithm, and illustrate its efficiency by numerical
experiments. The algorithm relies on the computation at each grid point of a
special system of coordinates: a reduced basis of the cartesian grid, with
respect to the symmetric positive definite matrix encoding the desired
anisotropy at this point.",1201.1546v3
2011-11-11,Observations of Large Scale Sidereal Anisotropy in 1 and 11 TeV cosmic rays from the MINOS experiment,"The MINOS Near and Far Detectors are two large, functionally-identical,
steel-scintillating sampling calorimeters located at depths of 220 mwe and 2100
mwe respectively. The detectors observe the muon component of hadronic showers
produced from cosmic ray interactions with nuclei in the earth's atmosphere.
From the arrival direction of these muons, the anisotropy in arrival direction
of the cosmic ray primaries can be determined. The MINOS Near and Far Detector
have observed anisotropy on the order of 0.1% at 1 and 11 TeV respectively. The
amplitude and phase of the first harmonic at 1 TeV are
8.2$\pm$1.7(stat.)$\times 10^{-4}$ and (8.9$\pm$12.1(stat.))$^{\circ}$, and at
11 TeV are 3.8$\pm$0.5(stat.)$\times 10^{-4}$ and
(27.2$\pm$7.2(stat.))$^{\circ}$.",1201.2621v1
2012-01-16,Testing Yukawa-like potentials from f(R)-gravity in elliptical galaxies,"We present the first analysis of extended stellar kinematics of elliptical
galaxies where a Yukawa--like correction to the Newtonian gravitational
potential derived from f(R)-gravity is considered as an alternative to dark
matter. In this framework, we model long-slit data and planetary nebulae data
out to 7 Re of three galaxies with either decreasing or flat dispersion
profiles. We use the corrected Newtonian potential in a dispersion-kurtosis
Jeans analysis to account for the mass-anisotropy degeneracy. We find that
these modified potentials are able to fit nicely all three elliptical galaxies
and the anisotropy distribution is consistent with that estimated if a dark
halo is considered. The parameter which measures the ""strength"" of the
Yukawa-like correction is, on average, smaller than the one found previously in
spiral galaxies and correlates both with the scale length of the Yukawa-like
term and the orbital anisotropy.",1201.3363v1
2012-01-31,Phase-space consistency of stellar dynamical models determined by separable augmented densities,"Assuming the separable augmented density, it is always possible to construct
a distribution function of a spherical population with any given density and
anisotropy. We consider under what conditions the distribution constructed as
such is in fact non-negative everywhere in the accessible phase-space. We first
generalize known necessary conditions on the augmented density using fractional
calculus. The condition on the radius part R(r^2) (whose logarithmic derivative
is the anisotropy parameter) is equivalent to the complete monotonicity of
R(1/w)/w. The condition on the potential part on the other hand is given by its
derivative up to any order not greater than (3/2-beta) being non-negative where
beta is the central anisotropy parameter. We also derive a specialized
inversion formula for the distribution from the separable augmented density,
which leads to sufficient conditions on separable augmented densities for the
non-negativity of the distribution. The last generalizes the similar condition
derived earlier for the generalized Cuddeford system to arbitrary separable
systems.",1202.0004v1
2012-02-20,Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides,"The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity $\rho_{a}$ across the long
orthorhombic axis $a_{O}$ - along which the spins couple antiferromagnetically
below the magnetic transition temperature - is smaller than the resistivity
$\rho_{b}$ of the short orthorhombic axis $b_{O}$, i. e. $\rho_{a}<\rho_{b}$.
Here we report that in the hole-doped compounds
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$, as the doping level increases, the
resistivity anisotropy initially becomes vanishingly small, and eventually
changes sign for sufficiently large doping, i. e. $\rho_{b}<\rho_{a}$. This
observation is in agreement with a recent theoretical prediction that considers
the anisotropic scattering of electrons by spin-fluctuations in the
orthorhombic/nematic state.",1202.4430v2
2012-02-21,Refining the Spin Hamiltonian in the Spin-1/2 Kagome Lattice Antiferromagnet ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ using Single Crystals,"We report thermodynamic measurements of the S=1/2 kagome lattice
antiferromagnet ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$, a promising candidate system with
a spin-liquid ground state. Using single crystal samples, the magnetic
susceptibility both perpendicular and parallel to the kagome plane has been
measured. A small, temperature-dependent anisotropy has been observed, where
$\chi_{z}/ \chi_{p} > 1$ at high temperatures and $\chi_{z}/ \chi_{p} < 1$ at
low temperatures. Fits of the high-temperature data to a Curie-Weiss model also
reveal an anisotropy. By comparing with theoretical calculations, the presence
of a small easy-axis exchange anisotropy can be deduced as the primary
perturbation to the dominant Heisenberg nearest neighbor interaction. These
results have great bearing on the interpretation of theoretical calculations
based on the kagome Heisenberg antiferromagnet model to the experiments on
ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$.",1202.4729v2
2012-03-02,A common solution to the cosmic ray anisotropy and gradient problems,"Multichannel Cosmic Ray (CR) spectra and the large scale CR anisotropy can
hardly be made compatible in the framework of conventional isotropic and
homogeneous propagation models. These models also have problems explaining the
longitude distribution and the radial emissivity gradient of the $\gamma$-ray
galactic interstellar emission. We argue here that accounting for a well
physically motivated correlation between the CR escape time and the spatially
dependent magnetic turbulence power can naturally solve both problems. Indeed,
by exploiting this correlation we find propagation models that fit a wide set
of CR primary and secondary spectra, and consistently reproduce the CR
anisotropy in the energy range $10^2 - 10^4 \GeV$ and the $\gamma$-ray
longitude distribution recently measured by Fermi-LAT.",1203.0570v2
2012-03-05,In-plane and Out-of-plane Plasma Resonances in Optimally Doped La1.84Sr0.16CuO4,"We addressed the inconsistency between the electron mass anisotropy ratios
determined by the far-infrared experiments and DC conductivity measurements. By
eliminating possible sources of error and increasing the sensitivity and
resolution in the far-infrared reflectivity measurement on the single
crystalline and on the polycrystalline La1.84Sr0.16CuO4, we have unambiguously
identified that the source of the mass anisotropy problem is in the estimation
of the free electron density involved in the charge transport and
superconductivity. In this study we found that only 2.8 % of the total
doping-induced charge density is itinerant at optimal doping. Our result not
only resolves the mass anisotropy puzzle but also points to a novel electronic
structure formed by the rest of the electrons that sets the stage for the high
temperature superconductivity.",1203.0963v1
2012-03-08,An Effective Medium Approach to Electron Waves: Graphene Superlattices,"We develop an effective medium approach to characterize the propagation of
matter waves in periodic structures, such as graphene or semiconductor
superlattices. It is proven that the time evolution of the states that are not
more localized in space than the characteristic period of the structure can be
described exactly through an effective Hamiltonian, and that the electronic
band structure of the system can be exactly determined from the effective
Hamiltonian. As an illustration of the application of the method, we
characterize the mesoscopic response of graphene superlattices. It is shown
that these structures may be described using simply two effective parameters: a
dispersive potential, and an anisotropy tensor that characterizes the
pseudospin. Our model predicts that a graphene superlattice characterized by an
indefinite anisotropy tensor - such that the eigenvalues of the tensor have
opposite signs - may permit the perfect tunneling of all the stationary states
with a specific value of the energy when it is paired with a dual graphene
superlattice with positive definite anisotropy tensor.",1203.1902v2
2012-03-15,A study of the anisotropy associated with dipole asymmetry in heavy ion collisions,"The anisotropy associated with the initial dipole asymmetry in heavy ion
collisions is studied via the two-particle relative azimuthal azimuthal angle
(\Delta\phi=\phi^a-\phi^b) correlations, within a multi-phase transport model.
For a broad selection of centrality, transverse momenta (pT^{a,b}) and
pseudorapidity (\eta^{a,b}), a fitting method is used to decompose the
anisotropy into a rapidity-even component, characterized by the Fourier
coefficient v1, and a global momentum conservation component. The extracted v1
values are negative for pT<=0.7-0.9 GeV, reach a maximum at 2-3 GeV, and
decreases at higher pT. The v1 values vary weakly with \eta and centrality, but
increases with collision energy and parton cross-section. The extracted global
momentum conservation component is found to depend on \Delta\eta= \eta^a-\eta^b
for \Delta\eta<3.",1203.3410v3
2012-03-16,Scaling patterns for azimuthal anisotropy in Pb+Pb collisions at Root_s = 2.76 TeV: Further constraints on transport coefficients,"Azimuthal anisotropy measurements for charged hadrons, characterized by the
second order Fourier coefficient $v_2$, are used to investigate the path length
($L$) and transverse momentum ($p_T$) dependent jet quenching patterns of the
QCD medium produced in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$\,TeV. $v_2$
shows a linear decrease as $1/\sqrt{p_T}$ and a linear increase with the medium
path length difference ($\Delta L$) in- and out of the $\Psi_2$ event plane.
These patterns compliment a prior observation of the scaling of jet quenching
($R_{\rm AA}$) measurements. Together, they suggest that radiative parton
energy loss is a dominant mechanism for jet suppression, and $v_2$ stems from
the difference in the parton propagation length $\Delta L$.An estimate of the
transport coefficient $\hat{q}$, gives a value comparable to that obtained in a
prior study of the scaling properties of $R_{\rm AA}$. These results suggest
that high-$p_T$ azimuthal anisotropy measurements provide strong constraints
for delineating the mechanism(s) for parton energy loss, as well as for
reliable extraction of $\hat{q}$.",1203.3605v1
2012-03-16,Shapes and Probabilities of Galaxy Clusters II: Comparisons with observations,"We identify low redshift clusters and groups in the Sloan Digital Sky Survey
(SDSS) and estimate their kinetic and correlation potential energies. We
compare the distribution of these energies to the predictions by Yang and
Saslaw (2012) and in the process estimate a measure of an average 3-dimensional
velocity and spatial anisotropy of a sample of clusters. We find that the
inferred velocity anisotropy is correlated with the inferred spatial
anisotropy. We also find that the general shape of the energy distribution
agrees with theory over a wide range of scales from small groups to
superclusters once the uncertainties and fluctuations in the estimated energies
are included.",1203.3823v2
2012-04-05,Dynamical magnetic anisotropy and quantum phase transitions in a vibrating spin-1 molecular junction,"We study the electronic transport through a spin-1 molecule in which
mechanical stretching produces a magnetic anisotropy. In this type of device, a
vibron mode along the stretching axis will couple naturally to the molecular
spin. We consider a single molecular vibrational mode and find that the
electron-vibron interaction induces an effective correction to the magnetic
anisotropy that shifts the ground state of the device toward a non-Fermi liquid
phase. A transition into a Fermi liquid phase could then be achieved, by means
of mechanical stretching, passing through an underscreened spin-1 Kondo regime.
We present numerical renormalization group results for the differential
conductance, the spectral density, and the magnetic susceptibility across the
transition.",1204.1108v2
2012-04-23,Broken degeneracies: the rotation curve and velocity anisotropy of the Milky Way halo,"We use distant Blue Horizontal Branch stars with Galactocentric distances 16
< r/kpc < 48 as kinematic tracers of the Milky Way dark halo. We model the
tracer density as an oblate, power-law embedded within a spherical power-law
potential. Using a distribution function method, we estimate the overall
power-law potential and the velocity anisotropy of the halo tracers. We measure
the slope of the potential to be gamma ~ 0.4 and the overall mass within 50 kpc
is ~ 4 x 10^11 M_sol. The tracer velocity anisotropy is radially biased with
beta ~ 0.5, which is in good agreement with local solar neighbourhood studies.
Our results provide an accurate outer circular velocity profile for the Milky
Way and suggest a relatively high concentration dark matter halo (c_vir ~ 20).",1204.5189v2
2012-04-25,Susceptibility anisotropy in an iron arsenide superconductor revealed by x-ray diffraction in pulsed magnetic fields,"In addition to unconventional high-Tc superconductivity, the iron arsenides
exhibit strong magnetoelastic coupling and a notable electronic anisotropy
within the a-b plane. We relate these properties by studying underdoped
Ba(Fe{1-x}Co{x})2As2 by x-ray diffraction in pulsed magnetic fields up to 27.5
Tesla. We exploit magnetic detwinning effects to demonstrate anisotropy in the
in-plane susceptibility, which develops at the structural phase transition
despite the absence of magnetic order. The degree of detwinning increases
smoothly with decreasing temperature, and a single- domain condition is
realized over a range of field and temperature. At low temperatures we observe
an activated behavior, with a large hysteretic remnant effect. Detwinning was
not observed within the superconducting phase for accessible magnetic fields.",1204.5693v1
2012-05-07,Random field and random anisotropy O(N) spin systems with a free surface,"We study the surface scaling behavior of a semi-infinite $d$-dimensional O(N)
spin system in the presence of quenched random field and random anisotropy
disorders. It is known that above the lower critical dimension
$d_{\mathrm{lc}}=4$ the infinite models undergo a paramagnetic-ferromagnetic
transition for $N>N_c$ ($N_c=2.835$ for random field and $N_c=9.441$ for random
anisotropy). For $N<N_c$ and $d<d_{\mathrm{lc}}$ there exists a
quasi-long-range ordered phase with zero order parameter and a power-law decay
of spin correlations. Using functional renormalization group we derive the
surface scaling laws which describe the ordinary surface transition for
$d>d_{\mathrm{lc}}$ and the long-range behavior of spin correlations near the
surface in the quasi-long-range ordered phase for $d<d_{\mathrm{lc}}$. The
corresponding surface exponents are calculated to one-loop order. The obtained
results can be applied to the surface scaling of periodic elastic systems in
disordered media and amorphous magnets.",1205.1338v1
2012-05-21,Unilateral interactions in granular packings: A model for the anisotropy modulus,"Unilateral interparticle interactions have an effect on the elastic response
of granular materials due to the opening and closing of contacts during
quasi-static shear deformations. A simplified model is presented, for which
constitutive relations can be derived. For biaxial deformations the elastic
behavior in this model involves three independent elastic moduli: bulk, shear,
and anisotropy modulus. The bulk and the shear modulus, when scaled by the
contact density, are independent of the deformation. However, the magnitude of
the anisotropy modulus is proportional to the ratio between shear and
volumetric strain. Sufficiently far from the jamming transition, when
corrections due to non-affine motion become weak, the theoretical predictions
are qualitatively in agreement with simulation results.",1205.4593v1
2012-06-04,Anisotropy of spin relaxation and transverse transport in metals,"Using first principles methods we explore the anisotropy of the spin
relaxation and transverse transport properties in bulk metals with respect to
the direction of the spin quantization axis in paramagnets or of the
spontaneous magnetization in ferromagnets. Owing to the presence of the
spin-orbit interaction the orbital and spin character of the Bloch states
depends sensitively on the orientation of the spins relative to the crystal
axes. This leads to drastic changes in quantities which rely on interband
mixing induced by the spin-orbit interaction. The anisotropy is particularly
striking for quantities which exhibit spiky and irregular distribution in the
Brillouin zone, such as the spin-mixing parameter or the Berry curvature of the
electronic states. We demonstrate this for three cases: (i) the Elliott-Yafet
spin-relaxation mechanism in paramagnets with structural inversion symmetry;
(ii) the intrinsic anomalous Hall effect in ferromagnets; and (iii) the spin
Hall effect in paramagnets. We discuss the consequences of the pronounced
anisotropic behavior displayed by these properties for spin-polarized transport
applications.",1206.0589v1
2012-06-28,Giant birefringence in optical antenna arrays with widely tailorable optical anisotropy,"The manipulation of light by conventional optical components such as a
lenses, prisms and wave plates involves engineering of the wavefront as it
propagates through an optically-thick medium. A new class of ultra-flat optical
components with high functionality can be designed by introducing abrupt phase
shifts into the optical path, utilizing the resonant response of arrays of
scatters with deeply-subwavelength thickness. As an application of this
concept, we report a theoretical and experimental study of birefringent arrays
of two-dimensional (V- and Y-shaped) optical antennas which support two
orthogonal charge-oscillation modes and serve as broadband, anisotropic optical
elements that can be used to locally tailor the amplitude, phase, and
polarization of light. The degree of optical anisotropy can be designed by
controlling the interference between the light scattered by the antenna modes;
in particular, we observe a striking effect in which the anisotropy disappears
as a result of destructive interference. These properties are captured by a
simple, physical model in which the antenna modes are treated as independent,
orthogonally-oriented harmonic oscillators.",1206.6792v1
2012-07-06,Two-band superconductivity featuring different anisotropies in the ternary iron silicide Lu$_{2}$Fe$_{3}$Si$_{5}$,"We report detailed studies of the upper critical field and low-temperature
specific heat in the two-gap superconductor Lu$_{2}$Fe$_{3}$Si$_{5}$. The
anisotropy of the upper critical field suggests that the active band is
quasi-one-dimensional. Low-temperature specific heat in magnetic fields reveals
that the virtual $H_{c2}$ in the passive band is almost isotropic. These
results strongly indicate that the two bands have two different anisotropies,
similar to the typical two-gap superconductor MgB$_{2}$, and their interplay
may be essential to the two-gap superconductivity in Lu$_{2}$Fe$_{3}$Si$_{5}$.",1207.1502v1
2012-07-17,Multicomponent Skyrmion lattices and their excitations,"We study quantum Hall ferromagnets with a finite density topologically
charged spin textures in the presence of internal degrees of freedom such as
spin, valley, or layer indices, so that the system is parametrised by a
$d$-component complex spinor field. In the absence of anisotropies, we find
formation of a hexagonal Skyrmion lattice which completely breaks the
underlying SU(d) symmetry. The ground state charge density modulation, which
inevitably exists in these lattices, vanishes exponentially in $d$. We compute
analytically the complete low-lying excitation spectrum, which separates into
$d^{2}-1$ gapless acoustic magnetic modes and a magnetophonon. We discuss the
role of effective mass anisotropy for SU(3)-valley Skyrmions relevant for
experiments with AlAs quantum wells. Here, we find a transition, which breaks a
six-fold rotational symmetry of a triangular lattice, followed by a formation
of a square lattice at large values of anisotropy strength.",1207.4021v1
2012-07-27,Evidence for a cos(4\varphi) Modulation of the Superconducting Energy Gap of Optimally Doped FeTe_{0.6}Se_{0.4} Single Crystals Using Laser Angle-Resolved Photoemission Spectroscopy,"We study the superconducting(SC)-gap anisotropy of the \Gamma-centered hole
Fermi surface in optimally doped FeTe_{0.6}Se_{0.4} (T_c = 14.5 K), using
laser-excited angle-resolved photoemission spectroscopy (ARPES). We observe
sharp superconducting coherence peaks at T = 2.5 K. In contrast to earlier
ARPES studies but consistent with thermodynamic results, the momentum
dependence shows a \cos(4\varphi) modulation of the SC-gap anisotropy. The
observed SC-gap anisotropy strongly indicates that the pairing interaction is
not a conventional phonon-mediated isotropic one. Instead, the results suggest
the importance of second-nearest-neighbor electronic interactions between the
iron sites in the framework of s_\pm-wave superconductivity.",1207.6571v3
2012-08-13,Quarkonium dissociation by anisotropy,"We compute the screening length for quarkonium mesons moving through an
anisotropic, strongly coupled N=4 super Yang-Mills plasma by means of its
gravity dual. We present the results for arbitrary velocities and orientations
of the mesons, as well as for arbitrary values of the anisotropy. The
anisotropic screening length can be larger or smaller than the isotropic one,
and this depends on whether the comparison is made at equal temperatures or at
equal entropy densities. For generic motion we find that: (i) mesons dissociate
above a certain critical value of the anisotropy, even at zero temperature;
(ii) there is a limiting velocity for mesons in the plasma, even at zero
temperature; (iii) in the ultra-relativistic limit the screening length scales
as $(1-v^2)^\epsilon$ with \epsilon =1/2, in contrast with the isotropic result
\epsilon =1/4.",1208.2672v2
2012-08-17,Interface induced perpendicular magnetic anisotropy in Co/CoO/Co thin film structure: An in-situ MOKE investigation,"Co /CoO/Co polycrystalline film was grown on Si (001) substrate and magnetic
properties have been investigated using in-situ magneto-optic Kerr effect
during growth of the sample. Magnetic anisotropy with easy axis perpendicular
to the film surface has been observed in top Co layer, whereas bottom layer was
found to be soft with in-plane magnetization without any influence of top
layer. Ex-situ in-plane and out-of-plane diffraction measurements revealed that
the growth of Co on oxidized interface takes place with preferential
orientation of c-axis perpendicular to the film plane, which results in the
observed perpendicular magnetic anisotropy. Texturing of the c-axis is expected
to be a result of minimization of the interface energy due to hybridization
between Co and oxygen at the interface.",1208.3673v1
2012-09-06,Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface,"We investigate the bismuth (111) surface by means of time and angle resolved
photoelectron spectroscopy. The parallel detection of the surface states below
and above the Fermi level reveals a giant anisotropy of the Spin-Orbit (SO)
spitting. These strong deviations from the Rashba-like coupling cannot be
treated in $\textbf{k}\cdot \textbf{p}$ perturbation theory. Instead, first
principle calculations could accurately reproduce the experimental dispersion
of the electronic states. Our analysis shows that the giant anisotropy of the
SO splitting is due to a large out-of plane buckling of the spin and orbital
texture.",1209.1219v2
2012-09-10,Strong anisotropy in two-dimensional surfaces with generic scale invariance: Gaussian and related models,"Among systems that display generic scale invariance, those whose asymptotic
properties are anisotropic in space (strong anisotropy, SA) have received a
relatively smaller attention, specially in the context of kinetic roughening
for two-dimensional surfaces. This is in contrast with their experimental
ubiquity, e.g. in the context of thin film production by diverse techniques.
Based on exact results for integrable (linear) cases, here we formulate a SA
Ansatz that, albeit equivalent to existing ones borrowed from equilibrium
critical phenomena, is more naturally adapted to the type of observables that
are measured in experiments on the dynamics of thin films, such as one and
two-dimensional height structure factors. We test our Ansatz on a paradigmatic
nonlinear stochastic equation displaying strong anisotropy like the Hwa-Kardar
equation [Phys. Rev. Lett. 62, 1813 (1989)], that was initially proposed to
describe the interface dynamics of running sand piles. A very important role to
elucidate its SA properties is played by an accurate (Gaussian) approximation
through a non-local linear equation that shares the same asymptotic properties.",1209.1968v3
2012-09-11,Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy,"Stripe domains are studied in perpendicular magnetic anisotropy films
nanostructured with a periodic thickness modulation that induces the lateral
modulation of both stripe periods and inplane magnetization. The resulting
system is the 2D equivalent of a strained superlattice with properties
controlled by interfacial misfit strain within the magnetic stripe structure
and shape anisotropy. This allows us to observe, experimentally for the first
time, the continuous structural transformation of a grain boundary in this 2D
magnetic crystal in the whole angular range. The magnetization reversal process
can be tailored through the effect of misfit strain due to the coupling between
disclinations in the magnetic stripe pattern and domain walls in the in-plane
magnetization configuration.",1209.2281v1
2012-09-20,Interface Induced Anisotropy and nematic glass/gel state in Jammed Aqueous Laponite Suspensions,"Aqueous suspensions of Laponite, a system composed of disk-like
nanoparticles, are found to develop optical birefringence over several days,
well after the suspensions solidified due to jamming. The optical anisotropy is
particularly enhanced near the air Laponite suspension interface over
length-scales of several millimetres, which is beyond five orders of magnitude
larger than the particle length scale, suggestive of large scale ordering
influenced by the interface. The orientational order increases with time and is
always greater for higher concentration of salt, higher concentration of
Laponite and higher temperature of the suspension. While weakly birefringent,
Laponite suspensions covered by paraffin oil do not show any enhancement in the
optical anisotropy near the interface compared to that in the bulk. We suggest
that the expedited structure formation near the air interface propagating
progressively inside the sample is responsible for the observed behaviour. We
discuss the observed nematic ordering in the context of glasslike and gellike
microstructure associated with aqueous Laponite suspensions.",1209.4507v1
2012-09-22,Origin of perpendicular magneto-crystalline anisotropy in L10-FeNi under tetragonal distortion,"We investigated the origin of perpendicular magneto-crystalline anisotropy
(MCA) in L10 ordered FeNi alloy using first-principles density-functional
calculations. We found that the perpendicular MCA of L10-FeNi arises
predominantly from the constituent Fe atoms, which is consistent with recent
measurements of the anisotropy of the Fe orbital magnetic moment of L10-FeNi by
x-ray magnetic circular dichroism. Analysis of the second-order perturbation of
the spin-orbit interaction indicates that spin-flip excitations between the
occupied majority-spin and unoccupied minority-spin bands make a considerable
contribution to the perpendicular MCA as does the spin-conservation term in the
minority-spin bands. Furthermore, the MCA energy increases as the in-plane
lattice parameter decreases (increasing the axial ratio c/a). The increase in
the MCA energy can be attributed to further enhancement of the spin-flip term
due to modulation of the Fe d(xy) and d(x2-y2) orbital components around the
Fermi level under the compressive in-plane distortion.",1209.5003v2
2012-10-01,The distinct in-plane resistivity anisotropy in the nematic states of detwinned NaFeAs and FeTe single crystals: evidences for Hund's rule metal,"The in-plane resistivity anisotropy has been studied with the Montgomery
method on two detwinned parent compounds of the iron-based superconductors,
NaFeAs and FeTe. For NaFeAs, the resistivity in the antiferromagnetic (AFM)
direction is smaller than that in the ferromagnetic (FM) direction, similar to
that observed in BaFe2As2 before. While for FeTe, the resistivity in the AFM
direction is larger than that in the FM direction. We show that these two
opposite resistivity anisotropy behaviors could be attributed to the strong
Hund's rule coupling effects: while the iron pnictides are in the itinerant
regime, where the Hund's rule coupling causes strong reconstruction and
nematicity of the electronic structure; the FeTe is in the localized regime,
where Hund's rule coupling makes hopping along the FM direction easier than
along the AFMdirection, similar to the colossal magnetoresistance observed in
some manganites.",1210.0397v1
2012-10-03,Magnetic anisotropy energy of disordered tetragonal Fe-Co systems from ab initio alloy theory,"We present results of systematic fully relativistic first-principles
calculations of the uniaxial magnetic anisotropy energy (MAE) of a disordered
and partially ordered tetragonal Fe-Co alloy using the coherent potential
approximation (CPA). This alloy has recently become a promising system for thin
ferromagnetic films with a perpendicular magnetic anisotropy. We find that
existing theoretical approaches to homogeneous random bulk Fe-Co alloys, based
on a simple virtual crystal approximation (VCA), overestimate the maximum MAE
values obtained in the CPA by a factor of four. This pronounced difference is
ascribed to the strong disorder in the minority spin channel of real alloys,
which is neglected in the VCA and which leads to a broadening of the d-like
eigenstates at the Fermi energy and to the reduction of the MAE. The ordered
Fe-Co alloys with a maximum L1_0-like atomic long-range order can exhibit high
values of the MAE, which, however, get dramatically reduced by small
perturbations of the perfect order.",1210.1028v2
2012-10-15,Ground state properties and excitation spectrum of a two dimensional gas of bosonic dipoles,"We present a quantum Monte Carlo study of two-dimensional dipolar Bose gases
in the limit of zero temperature. The analysis is mainly focused on the
anisotropy effects induced in the homogeneous gas when the polarization angle
with respect to the plane is changed. We restrict our study to the regime where
the dipolar interaction is strictly repulsive, although the strength of the
pair repulsion depends on the vector interparticle distance. Our results show
that the effect of the anisotropy in the energy per particle scales with the
gas parameter at low densities as expected, and that this scaling is preserved
for all polarization angles even at the largest densities considered here. We
also evaluate the excitation spectrum of the dipolar Bose gas in the context of
the Feynman approximation and compare the results obtained with the Bogoliubov
ones. As expected, we find that these two approximations agree at very low
densities, while they start to deviate from each other as the density
increases. For the largest densities studied, we observe a significant
influence of the anisotropy of the dipole-dipole interaction in the excitation
spectrum.",1210.3969v1
2012-10-22,Accelerating the switching of logical units by anisotropy driven magnetization dynamics,"In this work the magnetization dynamics of clusters supported on non-magnetic
substrates is shown to exhibit an unprecedented complex response when subjected
to external magnetic fields. The field-driven magnetization reversal of small
Co clusters deposited on a Cu(111) surface has been studied by means of
first-principles calculations and atomistic spin dynamics simulations. For
applied fields ranging from 1 Tesla to 10 Tesla, we observe a coherent
magnetization reversal with switching times in the range of several tenths of
picoseconds to several nanoseconds, depending on the field strength. We find a
non-monotonous dependence of the switching times with respect to the strength
of the applied field, which we prove to have its origin in the complex magnetic
anisotropy landscape of these low dimensional systems. This effect is shown to
be stable for temperatures around 10 K, and is possible to realize over a range
of exchange interactions and anisotropy landscapes. Possible experimental
routes to achieve this unique switching behaviour are discussed.",1210.5836v1
2012-10-22,Spin polarization anisotropy in a narrow spin-orbit-coupled nanowire quantum dot,"One and two-electron systems confined in a single and coupled quantum dots
defined within a nanowire with a finite radius are studied in the context of
spin-orbit coupling effects. Anisotropy of the spin-orbit interaction is
discussed in terms of the system geometry and orientation of the external
magnetic field vector. We find that there are easy and hard spin polarization
axes and in the quantum dot with strong lateral confinement electron spin
becomes well defined in spite of the presence of spin-orbit coupling. We
present an analytical solution for the one-dimensional limit and study its
validity for nanowires of finite radii by comparing the results with a full
three-dimensional calculation. The results are also confronted with the recent
measurements of the effective Lande factor and avoided crossing width
anisotropy in InSb nanowire quantum dots [S. Nadj-Perge et al., Phys. Rev.
Lett. 108, 166801 (2012)].",1210.5901v3
2012-10-31,Probing Dark Energy Anisotropy,"Wide area cosmological surveys enable investigation of whether dark energy
properties are the same in different directions on the sky. Cosmic microwave
background observations strongly restrict any dynamical effects from
anisotropy, in an integrated sense. For more local constraints we compute
limits from simulated distance measurements for various distributions of survey
fields in a Bianchi I anisotropic universe. We then consider the effects of
fitting for line of sight properties where isotropic dynamics is assumed
(testing the accuracy through simulations) and compare sensitivities of
observational probes for anisotropies, from astrophysical systematics as well
as dark energy. We also point out some interesting features of anisotropic
expansion in Bianchi I cosmology.",1210.8221v2
2012-11-06,Anisotropies and Homogeneities of Superconducting Properties in Iron-Platinum-Arsenide Ca10(Pt3As8)(Fe1.79Pt0.21As2)5,"We report a study on the anisotropy of superconducting properties in single
crystalline Ca10(Pt4-{\delta}As8)(Fe1.79Pt0.21As2)5 with Tc ~13.6 K. Under a
field of 5 Oe, the sample reaches fully-diamagnetic state at ~10 K for H//c,
and ~8 K for H//ab, indicating the presence of slight inhomogeneities. The
magnetization measurements reveal fish-tail effect in the hysteresis loop for
both H//c and H//ab. Averaged critical current densities at low magnetic fields
along the c-axis and ab-plane Jc(H//c) and Jc(H//ab) at 5 K are estimated to be
0.9*10^5 and 0.7*10^5 A/cm2, respectively. Resistive transitions under magnetic
field show broadening, which is consistent with a relatively large anisotropy
of upper critical field. Magneto-optical images reveal homogenous current flow
within the ab-plane.",1211.1221v2
2012-11-27,The extended Lawrence-Doniach model: the temperature evolution of the in-plane magnetic field anisotropy,"Using the quasi-classical formalism we provide the description of the
temperature and field-direction dependence of the in-plane upper critical field
in layered superconductors, taking into account the interlayer Josephson
coupling and the paramagnetic spin splitting. We generalize the
Lawrence-Doniach model for the case of high magnetic fields and show that the
re-entrant superconductivity is naturally described by our formalism when
neglecting the Pauli pair breaking effect. We demonstrate that in layered
superconductors the in-plane anisotropy of the onset of superconductivity
exhibits four different\ temperature regimes: from the Ginzburg-Landau type in
the vicinity of the critical temperature $T_{c0}$ with anisotropies of
coherence lengths, up to the FFLO type induced by the strong interference
between the modulation vector and the orbital effect. Our results are in
agreement with the experimental measurements of the field-angle dependence of
the superconducting onset temperature of the organic compound (TMTSF)$_{2}
$ClO$_{4}$.",1211.6262v1
2012-12-05,Event-by-event distributions of azimuthal asymmetries in ultrarelativistic heavy-ion collisions,"Relativistic dissipative fluid dynamics is a common tool to describe the
space-time evolution of the strongly interacting matter created in
ultrarelativistic heavy-ion collisions. For a proper comparison to experimental
data, fluid-dynamical calculations have to be performed on an event-by-event
basis. Therefore, fluid dynamics should be able to reproduce, not only the
event-averaged momentum anisotropies, $<v_{n}>$, but also their distributions.
In this paper, we investigate the event-by-event distributions of the
initial-state and momentum anisotropies $\epsilon_n$ and $v_n$, and their
correlations. We demonstrate that the event-by-event distributions of relative
$v_n$ fluctuations are almost equal to the event-by-event distributions of
corresponding $\epsilon_n$ fluctuations, allowing experimental determination of
the relative anisotropy fluctuations of the initial state. Furthermore, the
correlation $c(v_2,v_4)$ turns out to be sensitive to the viscosity of the
fluid providing an additional constraint to the properties of the strongly
interacting matter.",1212.1008v1
2012-12-12,Dissociation of quarkonium in an anisotropic hot QCD medium,"We have investigated the properties of quarkonium states in an anisotropic
hot QCD medium by correcting the full Cornell potential, not the Coulomb term
alone as usually done in the literature, with a dielectric function from the
hard-loop resummed gluon propagator. We have found that in-medium modification
in anisotropic medium causes less screening than in isotropic medium. In the
short distance limit, potential does not show any medium dependence whereas in
the long-distance limit, it reduces to the Coulomb potential with a dynamically
screened color charge. In addition, anisotropy in momentum space introduces a
characteristic angular dependence in the potential and as a result, quarkonium
states in anisotropic medium are more tightly bound than in isotropic medium.
In particular, quark pairs aligned in the direction of anisotropy are more
bound than perpendicular to the direction of anisotropy.",1212.2803v3
2012-12-21,Critical properties of a spin-1 triangular lattice Ising antiferromagnet,"We employ Monte Carlo simulations in order to investigate critical behavior
of a geometrically frustrated spin-1 Ising antiferromagnet on a triangular
lattice in the presence of a single-ion anisotropy. It has been previously
found that long-range order can exist in the isotropic system with a spin
larger than some critical value estimated as 11/2. We show that the presence of
the single-ion anisotropy can lead to a partial long-range order in the
low-temperature region even below this critical value, namely for the spin 1,
within a certain range of the anisotropy strength. At higher temperatures we
identify another phase of the Berezinsky-Kosterlitz-Thouless type and using a
finite-size scaling analysis evaluate the correlation decay exponent. We also
study densities of various local spin patterns in the respective phases.",1212.5488v1
2013-01-07,Curvature Perturbations in Anisotropic Inflation with Symmetry Breaking,"We study curvature perturbations in the anisotropic inflationary model with a
complex scalar field charged under a $U(1)$ gauge field in Bianchi I universe.
Due to Abelian Higgs mechanism, the gauge field receives an additional
longitudinal mode. We verify that the dominant contributions into statistical
anisotropies come from matter fields perturbations and one can neglect the
contributions from the metric perturbations. It is shown that the contribution
of longitudinal mode into the statistical anisotropy power spectrum, though
exponentially small, has an opposite sign compared to the corresponding
contribution from the transverse mode. We obtain an upper bound on gauge
coupling in order to satisfy the observational constraints on curvature
perturbations anisotropy.",1301.1219v3
2013-01-17,Low field anisotropic colossal magnetoresistance in $Sm_{0.53} Sr_{0.47} Mn O_3$ thin films,"SSMO5347 thin films (thicknesses ~200 nm) were deposited by on-axis dc
magnetron sputtering on the single crystal LSAT (001) substrates. These films
are oriented along the out of plane c-direction. The ferromagnetic and
insulator-metal transition occurs at 96 K and 91 K, respectively. The
magnetization easy axis is observed to lie in the plane of the film while the
magnetic hard axis is found to be along the normal to this. The
magnetotransport of the SSMO films, which was measured as a function of angle
(theta) between the magnetic field (H) and plane of the film, shows colossal
anisotropy. Magnetoresistance (MR) decreases drastically as theta increases
from 0 degree (H//easy axis) to 90 degree (H//hard axis). The out-of-plane
anisotropic MR (AMR) is as high as 88 % at H=3.6 kOe and 78 K. The colossal
anisotropy has been explained in terms of the magnetic anisotropies at play and
the magnetic domain motion in applied magnetic field.",1301.4048v1
2013-01-23,Comparative study of tight-binding and ab initio electronic structure calculations focused on magnetic anisotropy in ordered CoPt alloy,"An empirical multiorbital (spd) tight binding (TB) model including magnetism
and spin-orbit coupling is applied to calculations of magnetic anisotropy
energy (MAE) in CoPt L1_0 structure. A realistic Slater-Koster parametrisation
for single-element transition metals is adapted for the ordered binary alloy.
Spin magnetic moment and density of states are calculated using a
full-potential linearized augmented plane-wave (LAPW) ab initio method and our
TB code with different variants of the interatomic parameters. Detailed mutual
comparison of this data allows for determination of a subset of the compound TB
parameters tuning of which improves the agreement of the TB and LAPW results.
MAE calculated as a function of band filling using the refined parameters is in
broad agreement with ab initio data for all valence states and in quantitative
agreement with ab initio and experimental data for the natural band filling.
Our work provides a practical basis for further studies of relativistic
magnetotransport anisotropies by means of local Green's function formalism
which is directly compatible with our TB approach.",1301.5369v1
2013-01-31,Effects of Transverse Magnetic Anisotropy on Current-Induced Spin Switching,"Spin-polarized transport through bistable magnetic adatoms or single-molecule
magnets (SMMs), which exhibit both uniaxial and transverse magnetic anisotropy,
is considered theoretically. The main focus is on the impact of transverse
anisotropy on transport characteristics and the adatom's/SMM's spin. In
particular, we analyze the role of quantum tunneling of magnetization (QTM) in
the mechanism of the current-induced spin switching, and show that the QTM
phenomenon becomes revealed as resonant peaks in the average values of the
molecule's spin and in the charge current. These features appear at some
resonant fields and are observable when at least one of the electrodes is
ferromagnetic. We also show that the conductance generally depends on the
relative orientation of the average adatom's/SMM's spin and electrode's
magnetic moment. This spin-valve like magnetoresistance effect can be used to
control spin switching of the adatom's/SMM's spin.",1302.1074v1
2013-02-07,Ferromagnetic Exchange Anisotropy from Antiferromagnetic Superexchange in the Mixed 3d-5d Transition-Metal Compound Sr3CuIrO6,"We report a combined experimental and theoretical study of the unusual
ferromagnetism in the one-dimensional copper-iridium oxide Sr$_3$CuIrO$_6$.
Utilizing Ir $L_3$ edge resonant inelastic x-ray scattering, we reveal a large
gap magnetic excitation spectrum. We find that it is caused by an unusual
exchange anisotropy generating mechanism, namely, strong ferromagnetic
anisotropy arising from antiferromagnetic superexchange, driven by the
alternating strong and weak spin-orbit coupling on the $5d$ Ir and 3d Cu
magnetic ions, respectively. From symmetry consideration, this novel mechanism
is generally present in systems with edge-sharing Cu$^{2+}$O$_4$ plaquettes and
Ir$^{4+}$O$_6$ octahedra. Our results point to unusual magnetic behavior to be
expected in mixed 3d-5d transition-metal compounds via exchange pathways that
are absent in pure 3d or 5d compounds.",1302.1818v2
2013-02-12,Direction dependence of the power spectrum and its effect on the Cosmic Microwave Background Radiation,"We study several anisotropic inflationary models and their implications for
the observed violation of statistical isotropy in the CMBR data. In two of
these models the anisotropy decays very quickly during the inflationary phase
of expansion. We explicitly show that these models lead to violation of
isotropy only for low l CMBR modes. Our primary aim is to fit the observed
alignment of l=2,3 multipoles to the theoretical models. We use two measures,
based on the power tensor, which contains information about the alignment of
each multipole, to quantify the anisotropy in data. One of the measures uses
the dispersion in eigenvalues of the power tensor. We also define another
measure which tests the overall correlation between two different multipoles.
We perturbatively compute these measures of anisotropy and fix the theoretical
parameters by making a best fit to l=2,3 multipoles. We show that some of the
models studied are able to consistently explain the observed violation of
statistical isotropy.",1302.2706v1
2013-02-13,Local mechanical response in semiflexible polymer networks subjected to an axisymmetric prestress,"Analytical and numerical calculations are presented for the mechanical
response of fiber networks in a state of axisymmetric prestress, in the limit
where geometric non-linearities such as fiber rotation are negligible. This
allows us to focus on the anisotropy deriving purely from the non-linear
force-extension curves of individual fibers. The number of independent elastic
coefficients for isotropic, axisymmetric and fully anisotropic networks are
enumerated, before deriving expressions for the response to a locally applied
force that can be tested against e.g. microrheology experiments. Localised
forces can generate anisotropy away from the point of application, so numerical
integration of non-linear continuum equations is employed to determine the
stress field, and induced mechanical anisotropy, at points located directly
behind and in front of a force monopole. Results are presented for the wormlike
chain model in normalised forms, allowing them to be easily mapped to a range
of systems. Finally, the relevance of these findings to naturally occurring
systems and directions for future investigation are discussed.",1302.3049v2
2013-02-15,A fingerprint of surface-tension anisotropy in the free-energy cost of nucleation,"We focus on the Gibbs free energy $\Delta G$ for nucleating a droplet of the
stable phase (e.g. solid) inside the metastable parent phase (e.g. liquid),
close to the first-order transition temperature. This quantity is central to
the theory of homogeneous nucleation, since it superintends the nucleation
rate. We recently introduced a field theory describing the dependence of
$\Delta G$ on the droplet volume $V$, taking into account besides the
microscopic fuzziness of the droplet-parent interface, also small fluctuations
around the spherical shape whose effect, assuming isotropy, was found to be a
characteristic logarithmic term. Here we extend this theory, introducing the
effect of anisotropy in the surface tension, and show that in the limit of
strong anisotropy $\Delta G(V)$ once more develops a term logarithmic on $V$,
now with a prefactor of opposite sign with respect to the isotropic case. Based
on this result, we argue that the geometrical shape that large solid nuclei
mostly prefer could be inferred from the prefactor of the logarithmic term in
the droplet free energy, as determined from the optimization of its
near-coexistence profile.",1302.3712v1
2013-02-16,Magnetic state of pyrochlore Cd2Os2O7 emerging from strong competition of ligand distortions and longer-range crystalline anisotropy,"By many-body quantum-chemical calculations, we investigate the role of two
structural effects - local ligand distortions and the anisotropic Cd-ion
coordination - on the magnetic state of Cd2Os2O7, a spin S=3/2 pyrochlore. We
find that these effects strongly compete, rendering the magnetic interactions
and ordering crucially depend on these geometrical features. Without trigonal
distortions a large easy-plane magnetic anisotropy develops. Their presence,
however, reverses the sign of the zero-field splitting and causes a large
easy-axis anisotropy (D = -6.8 meV), which in conjunction with the
antiferromagnetic exchange interaction (J = 6.4 meV) stabilizes an
all-in/all-out magnetic order. The competition uncovered here is a generic
feature of pyrochlore magnets.",1302.3989v1
2013-02-20,Anisotropy of the Superconducting State in Sr2RuO4,"Despite intense studies the exact nature of the order parameter in
superconducting Sr2RuO4 remains unresolved. We have used small-angle neutron
scattering to study the vortex lattice in Sr2RuO4 with the field applied close
to the basal plane, taking advantage of the transverse magnetization. We
measured the intrinsic superconducting anisotropy between the c axis and the
Ru-O basal plane (~60), which greatly exceeds the upper critical field
anisotropy (~20). Our result imposes significant constraints on possible models
of triplet pairing in Sr2RuO4 and raises questions concerning the direction of
the zero spin projection axis.",1302.4810v3
2013-02-20,The chromo-Weibel instability in an expanding background,"In this proceedings contribution we review recent calculations of the
dynamics of the chromo-Weibel instability in the quark gluon plasma. This
instability is present in gauge theories with a one-particle distribution
function which is momentum-space anisotropic in the local rest frame. The
conditions necessary for triggering this instability can be present already in
the color-glass-condensate initial state or dynamically generated by the rapid
longitudinal expansion of the matter created in a heavy-ion collision. Using
the hard-loop framework we study the case that the one-particle distribution
function possesses an arbitrary initial momentum anisotropy that increases in
time due to longitudinal free streaming. The resulting three-dimensional
dynamical equations for the chromofield evolution are solved numerically. We
find that there is regeneration of the longitudinal pressure due to unstable
plasma modes; nevertheless, the system seems to maintain a high-degree of
momentum-space anisotropy. Despite this anisotropy, we find that there is rapid
longitudinal thermalization of the plasma due to the non-linear mode couplings
inherent in the unstable evolution.",1302.5098v1
2013-02-22,Mixing of blackbodies: Increasing our view of inflation to 17 e-folds with spectral distortions from Silk damping,"Silk damping in the early Universe, before and during recombination, erases
anisotropies in the cosmic microwave background (CMB) on small scales. This
power, which disappears from anisotropies, appears in the monopole as y-type,
i-type and \mu-type distortions. The observation of the CMB spectral
distortions will thus make available to us the information about the primordial
power spectrum on scales corresponding to the comoving wavenumbers $8< k < 10^4
Mpc^{-1}$ increasing our total view of inflation, when combined with CMB
anisotropies, to span 17 e-folds. These distortions can be understood simply as
mixing of blackbodies of different temperatures and the subsequent
comptonization of the resulting distortions.",1302.5633v1
2013-02-28,Anisotropy in the cosmic radiation at TeV energy,"In recent years very important results were obtained from cosmic ray
experiments about the arrival direction distribution of primaries in the TeV
energy range. As most of these particles are charged nuclei, they are deflected
by the magnetic field they pass through before reaching the Earth surface, the
effect of the Lorentz force being inversely proportional to the particle
energy. As far as the local interstellar medium is known, the gyroradius of a
10 TeV proton is expected to be only 100 a.u., small enough to make the arrival
direction distribution isotropic. Since 1930s a ""large scale""
(90{\deg}-120{\deg}) anisotropy is known to exist, generally interpreted as the
combined effect of sources far away and magnetic fields nearby. Nonetheless, in
the last decade experiments like Tibet-ASg, Milagro, ARGO-YBJ and IceCube
discovered structures as wide as 10{\deg}-30{\deg} all over the sky at ~ 10 TeV
energy, what is unexplainable within the standard model of cosmic rays. In this
paper a review of the most recent experimental results about cosmic ray
anisotropy is given, together with the status of the art of theoretical efforts
aimed at interpreting them within the current cosmic-ray paradigma.",1302.7184v1
2013-03-05,Constraining the Anisotropic Expansion of Universe,"We study the possibly existing anisotropy in the accelerating expansion
universe with the Union2 Type Ia supernovae data and Gamma-ray burst data. We
construct a direction-dependent dark energy model and constrain the anisotropy
direction and strength of modulation. We find that the maximum anisotropic
deviation direction is $(l,\,b)=(126^{\circ},\,13^{\circ})$ (or equivalently
$(l,\,b)=(306^{\circ},\,-13^{\circ})$), and the current anisotropy level is
$g_0=0.030_{+0.010}^{-0.030}$ ($1\sigma$ confidence level with Union2 data).
Our results do not show strong evidence for the anisotropic dark energy model.
We also discuss potential methods that may distinguish the peculiar velocity
field from the anisotropic dark energy model.",1303.0961v4
2013-03-09,Dark Matter implications of Fermi-LAT measurement of anisotropies in the diffuse gamma-ray background,"The detailed origin of the diffuse gamma-ray background is still unknown.
However, the contribution of unresolved sources is expected to induce
small-scale anisotropies in this emission, which may provide a way to identify
and constrain the properties of its contributors. Recent studies have predicted
the contributions to the angular power spectrum (APS) from extragalactic and
galactic dark matter (DM) annihilation or decay. The Fermi-LAT collaboration
reported detection of angular power with a significance larger than $3\sigma$
in the energy range from 1 GeV to 10 GeV on 22 months of data [Ackermann et al.
2012]. For these preliminary results the already published Fermi-LAT APS
measurements [Ackermann et al. 2012] are compared to the accurate predictions
for DM anisotropies from state-of-the-art cosmological simulations as presented
in [Fornasa et al. 2013] to derive constraints on different DM candidates.",1303.2154v1
2013-03-13,Electric control of a $\{Fe_4\}$ single-molecule magnet in a single-electron transistor,"Using first-principles methods we study theoretically the properties of an
individual $\{Fe_4\}$ single-molecule magnet (SMM) attached to metallic leads
in a single-electron transistor geometry. We show that the conductive leads do
not affect the spin ordering and magnetic anisotropy of the neutral SMM. On the
other hand, the leads have a strong effect on the anisotropy of the charged
states of the molecule, which are probed in Coulomb blockade transport.
Furthermore, we demonstrate that an external electric potential, modeling a
gate electrode, can be used to manipulate the magnetic properties of the
system. For a charged molecule, by localizing the extra charge with the gate
voltage closer to the magnetic core, the anisotropy magnitude and spin ordering
converges to the values found for the isolated $\{Fe_4\}$ SMM. We compare these
findings with the results of recent quantum transport experiments in
three-terminal devices.",1303.3283v1
2013-03-21,Tuning magnetic anisotropy in (001) oriented L10 (Fe1-xCux)55Pt45 films,"We have achieved (001) oriented L10 (Fe1-xCux)55Pt45 thin films, with
magnetic anisotropy up to 3.6x10^7 erg/cm^3, using atomic-scale multilayer
sputtering and post annealing at 400 {\deg}C for 10 seconds. By fixing the Pt
concentration, structure and magnetic properties are systematically tuned by
the Cu addition. Increasing Cu content results in an increase in the tetragonal
distortion of the L10 phase, significant changes to the film microstructure,
and lowering of the saturation magnetization and anisotropy. The relatively
convenient synthesis conditions, along with the tunable magnetic properties,
make such materials highly desirable for future magnetic recording
technologies.",1303.5208v1
2013-03-21,Spin dynamics of two bosons in an optical lattice site: a role of anharmonicity and anisotropy of the trapping potential,"We study a spin dynamics of two magnetic Chromium atoms trapped in a single
site of a deep optical lattice in a resonant magnetic field. Dipole-dipole
interactions couple spin degrees of freedom of the two particles to their
motion in the site. The motion is quantized, therefore a trap geometry combined
with two-body contact s-wave interactions influence a spin dynamics through the
energy spectrum of the two atom system. Anharmonicity and anisotropy of the
site results in a `fine' structure of two body eigenenergies. The structure can
be easily resolved by a weak magnetic dipole-dipole interactions. As an example
we examine the effect of anharmonicity and anisotropy of the binding potential
on the Einstein-de Haas effect. We show that the weak dipolar interactions
provide a perfect tool for a precision spectroscopy of the energy spectrum of
the interacting few particle system.",1303.5232v2
2013-04-07,Thermodynamic properties of a diluted Heisenberg ferromagnet with interaction anisotropy -- magnetocaloric point of view,"The thermodynamics of a site-diluted ferromagnetic Heisenberg model for spin
$S=1/2$ with interaction anisotropy in spin space is investigated. The study is
aimed at presenting the magnetocaloric properties of such a model, including
the entropy and temperature changes in magnetization/demagnetization processes,
generalized Gr\""uneisen ratio as well as the quantities characterizing the
efficiency of magnetic cooling cycles. The results are obtained using Pair
Approximation (PA) method and extensively compared with the Molecular Field
Approximation (MFA) calculations. The importance of interaction anisotropy and
site-dilution is discussed. The inadequacy of the MFA approach (even on the
qualitative level) is found for selected quantities, while PA provides the
results which are consistent with the experimentally observed behaviour.",1304.2034v1
2013-04-09,Anisotropies in the Gravitational Wave Background from Preheating,"We investigate the anisotropies in the gravitational wave (GW) background
produced at preheating after inflation. Using lattice field theory simulations
of a massless preheating model, we show that the GW amplitude depends
sensitively on the value of the decay product field chi coupled to the inflaton
phi, with the only requisite that chi is light during inflation. We find a
strong anisotropy in the amplitude of the GW background on large angular
scales, the details of which strongly depend on the reheating dynamics. We
expect similar conclusions for a wide class of inflationary models with light
scalar fields. If future direct detection GW experiments are capable of
detecting the GW produced by preheating, they should also be able to detect
this effect. This could eventually provide a powerful way to distinguish
between different inflationary and preheating scenarios.",1304.2657v1
2013-04-19,Anisotropic Heisenberg Model in Thin Film Geometry,"The effect of the anisotropy in the exchange interaction on the phase
diagrams and magnetization behavior of the Heisenberg thin film has been
investigated with effective field formulation in a two spin cluster using the
decoupling approximation. Phase diagrams and magnetization behaviors have been
obtained for several different cases, by grouping the systems in accordance
with, whether the surfaces/interior of the film have anisotropic exchange
interaction or not. Particular attention has been paid on the evolution of the
special point coordinate with the anisotropy in the exchange interaction. It
has been concluded that for increasing ratio of the anisotropies in the
exchange interaction between the surface and interior of the film, special
point disappears at a special value of this ratio.",1304.5552v1
2013-04-21,Uniaxial pressure effect on structural and magnetic phase transitions in NaFeAs and its comparison with as-grown and annealed BaFe$_2$As$_2$,"We use neutron scattering to study the effect of uniaxial pressure on the
tetragonal-to-orthorhombic structural ($T_s$) and
paramagnetic-to-antiferromagnetic ($T_N$) phase transitions in NaFeAs and
compare the outcome with similar measurements on as-grown and annealed
BaFe$_2$As$_2$. In previous work on as-grown BaFe$_2$As$_2$, uniaxial pressure
necessary to detwin the sample was found to induce a significant increase in
zero pressure $T_N$ and $T_s$. However, we find that similar uniaxial pressure
used to detwin NaFeAs and annealed BaFe$_2$As$_2$ has a very small effect on
their $T_N$ and $T_s$.Since transport measurements on these samples still
reveal resistivity anisotropy above $T_N$ and $T_s$, we conclude that such
anisotropy cannot be due to uniaxial strain induced $T_N$ and $T_s$ shifts, but
must arise from intrinsic electronic anisotropy in these materials.",1304.5794v1
2013-04-23,Interfacial tuning of perpendicular magnetic anisotropy and spin magnetic moment in CoFe/Pd multilayers,"We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4nm/Pd t]6
(t = 1.0-2.0 nm) multilayers fabricated by DC sputtering in a ultrahigh vacuum
chamber. Saturation magnetization, $M_s$, and uniaxial anisotropy, $K_u$, of
the multilayers decrease with increasing the spacing thickness, with a $M_s$ of
155 emu/cc and a $K_u$ of 1.14$\times 10^5$ J/m$^3$ at a spacing thickness of t
= 2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism
measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe
film decrease as function of Pd thickness, indicating the major contribution of
surface/interfacial magnetism to the magnetic properties of the film.",1304.6156v2
2013-04-25,Exploring a New Class of Non-stationary Spatial Gaussian Random Fields with Varying Local Anisotropy,"Gaussian random fields (GRFs) constitute an important part of spatial
modelling, but can be computationally infeasible for general covariance
structures. An efficient approach is to specify GRFs via stochastic partial
differential equations (SPDEs) and derive Gaussian Markov random field (GMRF)
approximations of the solutions. We consider the construction of a class of
non-stationary GRFs with varying local anisotropy, where the local anisotropy
is introduced by allowing the coefficients in the SPDE to vary with position.
This is done by using a form of diffusion equation driven by Gaussian white
noise with a spatially varying diffusion matrix. This allows for the
introduction of parameters that control the GRF by parametrizing the diffusion
matrix. These parameters and the GRF may be considered to be part of a
hierarchical model and the parameters estimated in a Bayesian framework. The
results show that the use of an SPDE with non-constant coefficients is a
promising way of creating non-stationary spatial GMRFs that allow for physical
interpretability of the parameters, although there are several remaining
challenges that would need to be solved before these models can be put to
general practical use.",1304.6949v2
2013-04-27,Rotation of Triangular Vortex Lattice in the Two-Band Superconductor MgB2,"To identify the contributions of the multiband nature and the anisotropy of a
microscopic electronic structure to a macroscopic vortex lattice morphology, we
develop a method based on the Eilenberger theory near Hc2 combined with the
first-principles band calculation to estimate the stable vortex lattice
configuration. For a typical two-band superconductor MgB2, successive
transitions of vortex lattice orientation that have been observed recently by
small angle neutron scattering [Das, et al.: Phys. Rev. Lett. 108 (2012)
167001] are explained by the characteristic field-dependence of twoband
superconductivity and the competition of sixfold anisotropy between the sigma-
and pi-bands. The reentrant transition at low temperature reflects the Fermi
velocity anisotropy of the sigma-band.",1304.7314v1
2013-05-13,Anisotropy of Cosmic Acceleration,"In this paper, we study the anisotropy of cosmic acceleration by dividing the
Union2 Type Ia supernova dataset into 12 subsets according to their positions
in Galactic coordinate system. In each region, we derive the deceleration
parameter $q_0$ as the diagnostic to quantify the anisotropy level in the
corresponding direction, and construct $q_0$ anisotropic maps by combining
these $q_0$ values. In addition to the monopole component, we find the
significant dipole effect in the $q_0$-maps with the amplitude
$A_1=0.466^{+0.255}_{-0.205}$, which deviates from zero at more than 2-$\sigma$
level. The direction of the best-fit dipole is ($\theta=108.8^{\circ}$,
$\phi=187.0^{\circ}$) in Galactic system. Interesting enough, we find the
direction of this dipole is nearly perpendicular to the CMB kinematic dipole,
and the angle between them is $95.7^{\circ}$. The perpendicular relation is
anomalous at the 1-in-10 level.",1305.2701v2
2013-05-15,Anisotropy of flow in stochastically generated porous media,"Models of porous media are often applied to relatively small systems, which
leads not only to system-size-dependent results, but also to phenomena that
would be absent in larger systems. Here we investigate one such finite-size
effect: anisotropy of the permeability tensor. We show that a non-zero angle
between the external body force and macroscopic flux vector exists in
three-dimensional periodic models of sizes commonly used in computer
simulations and propose a criterion, based on the system size to the grain size
ratio, for this phenomenon to be relevant or negligible. The finite-size
anisotropy of the porous matrix induces a pressure gradient perpendicular to
the axis of a porous duct and we analyze how this effect scales with the system
and grain sizes.",1305.3426v1
2013-05-24,Two Photon Correlation in Anisotropic Quark-gluon plasma (aQGP),"The only way to obtain the space-time structure of heavy ion collision is
through the study of two-particle momentum correlations. Thus we have studied
the intensity correlation for the photons having fixed transverse momentum of
one of the photons ($k_{1T}$= 2 GeV) in anisotropic Quark Gluon Plasma (aQGP)
to have an idea about emission zone in presence of initial momentum anisotropy.
The {\em free streaming interpolating} model with fixed initial condition has
been used for the space-time evolution for most central collision at RHIC
energy. The variation of Bose-Einstein correlation function (BECF), $C_2$, for
two identical photons as a function of $q_{out}$, $q_{side}$ and $q_{long}$ is
evaluated. We have restricted our analysis only to QGP phase to know the effect
of anisotropy on the correlation function and HBT radii extracted. It is
observed that the longitudinal dimension of the reaction zone is mostly
affected due to the presence of momentum space anisotropy.",1305.5702v2
2013-05-26,Giant magnetic anisotropy of transition-metal dimers on defected graphene,"Continuous miniaturization of magnetic units in spintronics and quantum
computing devices inspires efforts to search for magnetic nanostructures with
large magnetic anisotropy energy (MAE). Typical nanostructures including
molecular magnets, magnetic nanoclusters and magnetic nanowires have MAEs of a
few meV so their blocking temperature is mostly lower than 50 K. In this work,
we demonstrated the feasibility of achieving giant MAE in systems with
transition metal dimers on defected and decorated graphene, based on density
functional theory calculations. In particular, either a Pt-Ir dimer on a single
vacancy or an Os-Ru dimer on a nitrogen-decorated divacancy possesses an MAE
larger than 60 meV and high structural stability. Interestingly, their magnetic
anisotropy can be conveniently manipulated by using external electric field.
These features make them good candidates for the use in room temperature
spintronics and quantum computing devices.",1305.5978v4
2013-06-05,A Dynamical Signature of Multiple Stellar Populations in 47 Tucanae,"Based on the width of its main sequence, and an actual observed split when
viewed through particular filters, it is widely accepted that 47 Tucanae
contains multiple stellar populations. In this contribution, we divide the
main-sequence of 47 Tuc into four color groups, which presumably represent
stars of various chemical compositions. The kinematic properties of each of
these groups is explored via proper-motions, and a strong signal emerges of
differing proper-motion anisotropies with differing main-sequence color; the
bluest main-sequence stars exhibit the largest proper-motion anisotropy which
becomes undetectable for the reddest stars. In addition, the bluest stars are
also the most centrally concentrated. A simiilar analysis for SMC stars, which
are located in the background of 47 Tuc on our frames, yields none of the
anisotropy exhibited by the 47 Tuc stars. We discuss implications of these
results for possible formation scenarios of the various populations.",1306.1226v1
2013-06-12,The Imaginary Part of the Static Potential in Strongly Coupled Anisotropic Plasma,"Using the gauge/gravity duality we study the imaginary part of the static
potential associated to the thermal width in finite temperature strongly
coupled anisotropic plasma. We firstly derive the potential for a generic
anisotropic background. Then we apply our formulas to a theory where the
anisotropy has been generated by a space dependent axion term. We find that
using our method there exist a peculiar turning point in the imaginary part of
the potential, similar to the one appearing in the real part. The presence of
anisotropy leads to decrease of the imaginary potential, where larger decrease
happens along the anisotropic direction when the temperature is kept fixed.
When the entropy density is fixed, increase happens along the parallel
direction while along the transverse plane we observe a decrease. To estimate
the thermal width we use an approximate extrapolation beyond the turning point
and we find a decrease in presence of the anisotropy, independently of the
comparison scheme used.",1306.2929v2
2013-06-18,"Orbital-selective superconductivity, gap anisotropy and spin resonance excitations in a multiorbital t-J1-J2 model for iron pnictides","We study the orbital-dependent superconducting pairing in a five-orbital
t-J1-J2 model for iron pnictides. Depending on the orbital selectivity of
electron correlations and the orbital characters along the Fermi surface, the
superconducting gap in an A_{1g} pairing state may exhibit anisotropy. This
anisotropy varies with the degree of J1-J2 magnetic frustration. We have also
calculated the dynamical spin susceptibility in the superconducting state. The
frequency dependence of the susceptibility at the antiferromagnetic wavevector
(\pi,0) shows a resonance, whose width is enhanced by the orbital dependence of
the superconducting gap; when the latter is sufficiently strong, the resonance
peak may be split into two. We discuss the implications of our results on the
recent angle-resolved photoemission and neutron-scattering measurements in
several superconducting iron pnictides.",1306.4184v1
2013-07-09,Electrical anisotropy of heteroepitaxial InSb/GaAs layers,"We report on study of electrical and structural properties of InSb/GaAs(001)
heteroepitaxial layers in [110] and [1-10] crystallographic directions. Strong
anisotropy of electron transport parameters measured at a low magnetic field
has been found, whereas the electrical transport through the InSb bulk layer
studied by Shubnikov-de Haas oscillations is shown to be independent of the
crystallographic directions. The low-field electrical anisotropy of the InSb
films appears to be governed by two competitive anisotropic effects: influence
of spontaneously formed In nanoclusters inhomogeneously distributed within the
InSb layers and conductivity through the near-interface layer with high
anisotropic density of extended defects.",1307.2368v1
2013-07-24,The TeV Cosmic-Ray Anisotropy from Local Dark Matter Annihilation,"Several experiments have reported regions in the TeV sky with an excess of
cosmic rays. Here we consider the possibility that the excess cosmic rays are
coming from dark matter annihilation in nearby subhalos. We provide motivation
for dark matter as the source of the excess and show that dark matter
annihilations can naturally produce the cosmic ray anisotropy without the need
for exotic dark matter models. We show that viable dark matter explanations of
the cosmic ray excess are consistent with current measurements of antiprotons,
positrons, and gamma-rays. Additionally, we show that the dark matter
interpretation of the observed anisotropy predicts detections in several cosmic
ray channels by the next generation of experiments.",1307.6537v1
2013-08-09,Relativistic and thermal effects on the magnon spectrum of a ferromagnetic monolayer,"A spin model including magnetic anisotropy terms and Dzyaloshinsky-Moriya
interactions is studied for the case of a ferromagnetic monolayer with C2v
symmetry like Fe/W(110). Using the quasiclassical stochastic
Landau-Lifshitz-Gilbert equations, the magnon spectrum of the system is derived
using linear response theory. The Dzyaloshinsky-Moriya interaction leads to
asymmetry in the spectrum, while the anisotropy terms induce a gap. It is shown
that in the presence of lattice defects, both the Dzyaloshinsky-Moriya
interactions and the two-site anisotropy lead to a softening of the magnon
energies. Two methods are developed to investigate the magnon spectrum at
finite temperatures. The theoretical results are compared to atomistic spin
dynamics simulations and a good agreement is found between them.",1308.2082v2
2013-08-27,Upper Critical Fields and Anisotropy of Ca1-xLaxFe2As2 Single Crystals,"Superconductivity of Ca1-xLaxFe2As2 single crystals with various doping level
were investigated via electromagnetic measurements for out-plane (H//c) and
in-plane (H//ab) directions. Obvious double superconducting transitions, which
can survive in magnetic fields up to several Tesla, were observed in the
medium-doped (x = 0.13) sample. Two kinds of distinct Hc2 phase diagrams were
established for the low superconducting phase with Tc lower than 15 K and the
high superconducting phase with Tc of over 40 K, respectively. Both the two
kinds of phase diagrams exist in the medium-doped sample. Unusual upward
curvature near Tc was observed in Hc2 phase diagrams and analyzed in detail.
Temperature dependences of anisotropy for different doping concentrations were
obtained and compared. Both superconducting phases manifest extremely large
anisotropies, which may originate from the interface or intercalation
superconductivity.",1308.5734v1
2013-08-31,Quantum Phase Diagram of the Triangular-Lattice XXZ Model in a Magnetic Field,"The triangular lattice of S=1/2 spins with XXZ anisotropy is a ubiquitous
model for various frustrated systems in different contexts. We determine the
quantum phase diagram of the model in the plane of the anisotropy parameter and
the magnetic field by means of a large-size cluster mean-field method with a
scaling scheme. We find that quantum fluctuations break up the nontrivial
continuous degeneracy into two first-order phase transitions. In between the
two transition boundaries, the degeneracy lifting results in the emergence of a
new coplanar phase not predicted in the classical counterpart of the model. We
suggest that the quantum phase transition to the nonclassical coplanar state
can be observed in triangular-lattice antiferromagnets with large easy-plane
anisotropy or in the corresponding optical-lattice systems.",1309.0086v3
2013-09-02,Oblique MHD shocks: space-like and time-like,"Shock waves constitute discontinuities in matter which are relevant in
studying the plasma behaviour in astrophysical scenarios and in heavy-ion
collision. They can produce conical emission in relativistic collisions and are
also thought to be the mechanism behind the acceleration of energetic particles
in active galactic nuclei and gamma ray bursts. The shocks are mostly
hydrodynamic shocks. In a magnetic background they become magnetohydrodynamic
(MHD) shocks. For that reason we study the space-like and time-like shock
discontinuity in a magnetic plasma. The shocks induce a phase transition in the
plasma, here assuming a transition from hadron to quarks. The MHD conservation
conditions are derived across the shock. The conservation conditions are solved
for downstream velocities and flow angles for given upstream variables. The
shock conditions are solved at different baryon densities. For the space-like
shocks the anisotropy in the downstream velocity arises due to the magnetic
field. The downstream velocity vector always points downward with respect to
the shock normal. With the increase in density the anisotropy is somewhat
reduced. The magnetic field has effectively no effect on time-like shocks. The
slight anisotropy in the downstream flow velocities is caused by the boosting
that brings the quantities from the fluid frame to normal incidence (NI) frame.",1309.0397v1
2013-09-03,Phase diagram and water-like anomalies in core-softened shoulder-dumbbells system,"Using molecular dynamics we studied the role of the anisotropy on the phase
boundary and on the anomalous behavior of 250 dimeric particles interacting by
a core-softened potential. This study led us to an unexpected result: the
introduction of a rather small anisotropy, quantified by the distance between
the particles inside each dimer, leads to the increase of the size of the
regions in the pressure-temperature phase diagram of anomalies when compared to
the isotropic monomeric case. However, as the anisotropy increases beyond a
threshold the anomalous regions shrinks. We found that this behavior can be
understood by decoupling the translational and non-translational kinetic energy
components into different translational and non-translational temperatures.",1309.0843v1
2013-09-12,One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6,"Using inelastic neutron scattering, we have observed a quasi-one-dimensional
dispersive magnetic excitation in the frustrated triangular-lattice spin-2
chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
characterized by a large zone-center spin gap of ~27 meV, which we attribute to
the large single-ion anisotropy, and disperses along the chain direction with a
bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
measurable dispersion was found. With increasing temperature, the magnon
dispersion shifts towards lower energies, yet persists up to at least 150 K,
indicating that the ferromagnetic intrachain correlations survive up to 6 times
higher temperatures than the long-range interchain antiferromagnetic order. The
magnon dispersion can be well described within the predictions of linear
spin-wave theory for a system of weakly coupled ferromagnetic chains with large
single-ion anisotropy, enabling the direct quantitative determination of the
magnetic exchange and anisotropy parameters.",1309.3222v2
2013-09-12,Multiple scattering Sunyaev-Zeldovich signal II: relativistic effects,"We study the multiple scattering Sunyaev-Zeldovich (SZ) signature, extending
our previous analysis to high-temperature clusters. We consistently treat the
anisotropy of the ambient radiation field caused by the first scattering and
also consider lowest order kinematic terms. We show that due to temperature
corrections monopole through octupole anisotropy of the singly scattered SZ
signal attain different spectra in the second scattering. The difference
becomes more pronounced at high temperature, and thus could be used to
constrain individual line of sight moments of the electron density and
temperature profiles. While very challenging from the observational point of
view, this further extends the list of possible SZ observables that will be
important for 3D cluster-profile reconstruction, possibly helping to break
geometric degeneracies caused by projection effects. We also briefly discuss
the scattering of primordial CMB anisotropies by SZ clusters.",1309.3274v2
2013-10-04,Designing a robustly metallic noncenstrosymmetric ruthenate oxide with large thermopower anisotropy,"The existence of approximately 30 noncentrosymmetric metals (NCSM) suggests a
contraindication between crystal structures without inversion symmetry and
metallic behavior. Those containing oxygen are especially scarce. Here we
propose and demonstrate a design framework to remedy this property disparity
and accelerate NCSM-oxide discovery: The primary ingredient relies on the
removal of inversion symmetry through displacements of atoms whose electronic
degrees of freedom are decoupled from the states at the Fermi level. Density
functional theory calculations validate this crystal--chemistry strategy, and
we predict a new polar ruthenate exhibiting robust metallicity. We demonstrate
that the electronic structure is unaffected by the inclusion of spin-orbit
interactions (SOI), and that cation ordered SrCaRu$_2$O$_6$ exhibits a large
thermopower anisotropy ($\left|\Delta\mathcal{S}_\perp\right|\sim6.3 \mu
\textrm{V K}^{-1}$ at 300 K) derived from its polar structure. Our findings
provide chemical and structural selection guidelines to aid in the search of
new NCS metals with enhanced thermopower anisotropy.",1310.1148v2
2013-10-06,Magnetization Properties and Vortex Phase Diagram in CuxTiSe2 Single Crystals,"We have investigated the magnetization properties and flux dynamics of
superconducting Cu$_x$TiSe$_2$ single crystals within wide range of copper
concentrations. We find that the superconducting anisotropy is low and
independent on copper concentration ($\gamma\sim1.7$), except in the case of
strongly underdoped samples ($x\leq0.06$) that show a gradual increase in
anisotropy to $\gamma\sim1.9$. The vortex phase diagram in this material is
characterized by broad region of vortex liquid phase that is unusual for such
low-$T_c$ superconductor with low anisotropy. Below the irreversibility line
the vortex solid state supports relatively low critical current densities as
compared to the depairing current limit ($J_c/J_0\sim10^{-7}$). All this points
out that local fluctuations in copper concentration have little effect on bulk
pinning properties in this system.",1310.1613v1
2013-10-12,Edge Modes in the Intermediate-D and Large-D Phases of the S=2 Quantum Spin Chain with XXZ and On-Site Anisotropies,"We investigate the edge modes at T=0 in the intermediate-D (ID) phase and the
large-D (LD) phase of the S=2 quantum spin chain with the XXZ anisotropy and
the generalized on-site anisotropies by use of the DMRG. There exists a gapless
edge mode in the ID phase, while no gapless edge mode in the LD phase. These
results are consistent with the physical pictures of these phases. We also show
the ground-state phase diagrams obtained by use of the exact diagonalization
and the level spectroscopy analysis.",1310.3385v1
2013-10-15,CMB distortion anisotropies due to the decay of primordial magnetic fields,"We investigate the power spectrum of the distortion of Cosmic Microwave
Background (CMB) due to the decay of the primordial magnetic fields. It is
known that there are two-types of the CMB distortions, so-called \mu- and
y-types and we find that the signal of the y-type distortion becomes larger
than that of the \mu-type one. We also discuss cross power spectra between the
CMB distortions and the CMB temperature anisotropy, which are naturally
generated due to the existence of the primordial magnetic fields. We find that
such cross power spectra have small amplitudes compared with the auto-power
spectra of the CMB distortions because of the Silk damping effect of the
temperature anisotropy. We also investigate the possibility of detecting such
signal in the future CMB experiments, including not only absolutely calibrated
experiments such as PIXIE but also relatively calibrated experiments such as
LiteBIRD and CMBpol.",1310.3886v1
2013-10-22,Thermal conductivity of anisotropic spin - 1/2 two leg ladder:Green's function approach,"We study the thermal transport of a spin-1/2 two leg antiferromagnetic ladder
in the direction of legs. The possible effect of spin-orbit coupling and
crystalline electric field are investigated in terms of anisotropies in the
Heisenberg interactions on both leg and rung couplings. The original spin
ladder is mapped to a bosonic model via a bond-operator transformation where an
infinite hard-core repulsion is imposed to constrain one boson occupation per
site. The Green's function approach is applied to obtain the energy spectrum of
quasi-particle excitations responsible for thermal transport. The thermal
conductivity is found to be monotonically decreasing with temperature due to
increased scattering among triplet excitations at higher temperatures. A tiny
dependence of thermal transport on the anisotropy in the leg direction at low
temperatures is observed in contrast to the strong one on the anisotropy along
the rung direction, due to the direct effect of the triplet density. Our
results reach asymptotically the ballistic regime of the spin - 1/2 Heisenberg
chain and compare favorably well with exact diagonalization data.",1310.5943v1
2013-11-04,Anisotropic g factor in InAs self-assembled quantum dots,"We investigate the wave functions, spectrum, and g-factor anisotropy of
low-energy electrons confined to self-assembled, pyramidal InAs quantum dots
(QDs) subject to external magnetic and electric fields. We present the
construction of trial wave functions for a pyramidal geometry with hard-wall
confinement. We explicitly find the ground and first excited states and show
the associated probability distributions and energies. Subsequently, we use
these wave functions and 8-band $k\cdot p$ theory to derive a Hamiltonian
describing the QD states close to the valence band edge. Using a perturbative
approach, we find an effective conduction band Hamiltonian describing
low-energy electronic states in the QD. From this, we further extract the
magnetic field dependent eigenenergies and associated g factors. We examine the
g factors regarding anisotropy and behavior under small electric fields. In
particular, we find strong anisotropies, with the specific shape depending
strongly on the considered QD level. Our results are in good agreement with
recent measurements [Takahashi et al., Phys. Rev. B 87, 161302 (2013)] and
support the possibility to control a spin qubit by means of g-tensor
modulation.",1311.0908v2
2013-11-05,The isotropy problem of Sub-ankle Ultra-high energy cosmic rays,"We study the time dependent propagation of sub-ankle ultra-high energy cosmic
rays (UHECRs) originating from point-like Galactic sources. We show that drift
in the Galactic magnetic field (GMF) may play an important role in the
propagation of UHECRs and their measured anisotropy, particularly when the
transport is anisotropic. To fully account for the discreteness of UHECR
sources in space and time, a Monte Carlo method is used to randomly place
sources in the Galaxy. The low anisotropy measured by Auger is not generally
characteristic of the theoretical models, given that the sources are
distributed in proportion to the star formation rate, but it can possibly be
understood as a) intermittency effects due to the discrete nature of the
sources or, with extreme parameters, b) a cancellation of drift current along a
current sheet with the outward radial diffusive flux. We conclude that it is
possible to interpret the Galactic sub-ankle CR flux as being due entirely to
intermittent discrete Galactic sources distributed in proportion to star
formation, but only with probability of roughly 35 percent, of which the
spectrum is in accord with observations about 30 percent of the time.
  An alternative explanation for the low anisotropy may be that they are mostly
extragalactic and/or heavy.",1311.1208v1
2013-11-08,Curvature effects in statics and dynamics of a thin magnetic shell,"Equations of the magnetization dynamics are derived for an arbitrary curved
2D surface. General static solutions are obtained in the limit of a strong
anisotropy of both signs (easy-surface and easy-normal cases). It is shown that
the effect of the curvature can be treated as appearance of an effective
magnetic field which is aligned along the surface normal for the case of
easy-surface anisotropy and it is tangential to the surface for the case of
easy-normal anisotropy. In general, the existence of such a field denies the
solutions strictly tangential as well as strictly normal to the surface. As an
example we consider static equilibrium solutions and linear dynamics for a cone
surface magnetization.",1311.2026v2
2013-11-12,Magnetic Coupling and Single-Ion Anisotropy in Surface-Supported Mn-based Metal-Organic Networks,"The electronic and magnetic properties of Mn coordinated to
1,2,4,5-tetracyanobenzene (TCNB) in the Mn-TCNB 2D metal-ligand networks have
been investigated by combining scanning tunneling microscopy and X-ray magnetic
circular dichroism (XMCD) performed at low temperature (3 K). When formed on
Au(111) and Ag(111) substrates the Mn-TCNB networks display similar geometric
structures. Magnetization curves reveal ferromagnetic (FM) coupling of the Mn
sites with similar single-ion anisotropy energies, but different coupling
constants. Low-temperature XMCD spectra show that the local environment of the
Mn centers differs appreciably for the two substrates. Multiplet structure
calculations were used to derive the corresponding ligand field parameters
confirming an in-plane uniaxial anisotropy. The observed interatomic coupling
is discussed in terms of superexchange as well as substrate-mediated magnetic
interactions.",1311.2775v3
2013-11-25,Target-skyrmions and skyrmion clusters in nanowires of chiral magnets,"In bulk non-centrosymmetric magnets the chiral Dzyaloshinskii-Moriya exchange
stabilizes tubular skyrmions with a reversed magnetization in their centers.
While the double-twist is favorable in the center of a skyrmion, it gives rise
to an excess of the energy density at the outskirt. Therefore, magnetic
anisotropies are required to make skyrmions more favorable than the conical
spiral state in bulk materials. Using Monte Carlo simulations, we show that in
magnetic nanowires unusual skyrmions with a doubly twisted core and a number of
concentric helicoidal undulations (target-skyrmions) are thermodynamically
stable even in absence of single-ion anisotropies. Such skyrmions are free of
magnetic charges and, since the angle describing the direction of magnetization
at the surface depends on the radius of the nanowire and an applied magnetic
field, they carry a non-integer skyrmion charge s > 1. This state competes with
clusters of spatially separated s=1 skyrmions. For very small radii, the
target-skyrmion transforms into a skyrmion with s < 1, that resembles the
vortex-like state stabilized by surface-induced anisotropies.",1311.6283v1
2013-11-28,Direct Measurement of Competing Quantum Effects on the Kinetic Energy of Heavy Water upon Melting,"Even at room temperature, quantum mechanics plays a major role in determining
the quantitative behaviour of light nuclei, changing significantly the values
of physical properties such as the heat capacity. However, other observables
appear to be only weakly affected by nuclear quantum effects (NQEs): for
instance, the melting temperatures of light and heavy water differ by less than
4 K. Recent theoretical work has attributed this to a competition between intra
and inter molecular NQEs, which can be separated by computing the anisotropy of
the quantum kinetic energy tensor. The principal values of this tensor change
in opposite directions when ice melts, leading to a very small net quantum
mechanical effect on the melting point. This paper presents the first direct
experimental observation of this phenomenon, achieved by measuring the
deuterium momentum distributions n(p) in heavy water and ice using Deep
Inelastic Neutron Scattering (DINS), and resolving their anisotropy. Results
from the experiments, supplemented by a theoretical analysis, show that the
anisotropy of the quantum kinetic energy tensor can also be captured for
heavier atoms such as oxygen.",1311.7247v1
2013-12-04,Non-Gaussianity of the Cosmic Infrared Background anisotropies I : Diagrammatic formalism and application to the angular bispectrum,"We present the first halo model based description of the Cosmic Infrared
Background (CIB) non-Gaussianity (NG) that is fully parametric. To this end, we
introduce, for the first time, a diagrammatic method to compute high order
polyspectra of the 3D galaxy density field. It allows an easy derivation and
visualisation of the different terms of the polyspectrum. We apply this
framework to the power spectrum and bispectrum, and we show how to project them
on the celestial sphere in the purpose of the application to the CIB angular
anisotropies. Furthermore, we show how to take into account the particular case
of the shot noise terms in that framework. Eventually, we compute the CIB
angular bispectrum at 857 GHz and study its scale and configuration
dependencies, as well as its variations with the halo occupation distribution
parameters. Compared to a previously proposed empirical prescription, such
physically motivated model is required to describe fully the CIB anisotropies
bispectrum. Finally, we compare the CIB bispectrum with the bispectra of other
signals potentially present at microwave frequencies, which hints that
detection of CIB NG should be possible above 220 GHz.",1312.1251v1
2013-12-20,Anisotropy of excitation and relaxation of photogenerated Dirac electrons in graphene,"We investigate the polarization dependence of the carrier excitation and
relaxation in epitaxial multilayer graphene. Degenerate pump-probe experiments
with a temporal resolution of 30 fs are performed for different rotation angles
of the pump-pulse polarization with respect to the polarization of the probe
pulse. A pronounced dependence of the pump-induced transmission on this angle
is found. It reflects a strong anisotropy of the pump-induced occupation of
photogenerated carriers in momentum space even though the band structure is
isotropic. Within 150 fs after excitation an isotropic carrier distribution is
established. Our observations imply the predominant role of collinear
scattering preserving the initially optically generated anisotropy in the
carrier distribution. The experiments are well described by microscopic time-,
momentum, and angle-resolved modelling, which allows us to unambiguously
identify non-collinear carrier-phonon scattering to be the main relaxation
mechanism giving rise to an isotropic distribution in the first hundred fs
after optical excitation.",1312.5860v1
2013-12-30,Cosmic-ray diffusion in collisionless plasmas including pressure anisotropy,"Using a hybrid kinetic magnetohydrodynamic formalism incorporating the
effects of pressure anisotropy, we simulate the evolution of a turbulent
collisionless plasma in six different models covering the sub/super-sonic and
sub/super-Alfv\'enic regimes. Based on the power spectrum of the simulated
magnetic field, we compute the particle diffusion coefficients for protons with
kinetic energy in the $50-500$ MeV range, and compare them to those obtained
within standard magnetohydrodynamics. Our results show that the differences in
the statistical properties of the magnetic field, generated by pressure
anisotropy and its associated kinetic instabilities, have an appreciable impact
on the diffusion coefficients of energetic protons. Moreover, the values of the
diffusion coefficients that we obtain within each of the six models considered
vary significantly.",1312.7822v1
2013-12-31,Dissociation of Quarkonium in a Complex Potential,"We have studied the quasi-free dissociation of quarkonia through a complex
potential which is obtained by correcting both the perturbative and
nonperturbative terms of the $Q \bar Q$ potential at T=0 through the dielectric
function in real-time formalism. The presence of confining nonperturbative term
even above the transition temperature makes the real-part of the potential more
stronger and thus makes the quarkonia more bound and also enhances the
(magnitude) imaginary-part which, in turn contributes more to the thermal
width, compared to the medium-contribution of the perturbative term alone.
These cumulative observations result the quarkonia to dissociate at higher
temperatures. Finally we extend our calculation to a medium, exhibiting local
momentum anisotropy, by calculating the leading anisotropic corrections to the
propagators in Keldysh representation. The presence of anisotropy makes the
real-part of the potential stronger but the imaginary-part is weakened
slightly. However, since the medium corrections to the imaginary-part is a
small perturbation to the vacuum part, overall the anisotropy makes the
dissociation temperatures higher, compared to isotropic medium.",1401.0172v2
2014-01-27,Edge states in 2D lattices with hopping anisotropy and Chebyshev polynomials,"Analytic technique based on Chebyshev polynomials is developed for studying
two-dimensional lattice ribbons with hopping anisotropy. In particular, the
tight-binding models on square and triangle lattice ribbons are investigated
with anisotropic nearest neighbouring hoppings. For special values of hopping
parameters the square lattice becomes topologically equivalent to a honeycomb
one either with zigzag or armchair edges. In those cases as well as for
triangle lattices we perform the exact analytic diagonalization of
tight-binding Hamiltonians in terms of Chebyshev polynomials. Deep inside the
edge state subband the wave functions exhibit exponential spatial damping which
turns into power-law damping at edge-bulk transition point. It is shown that
strong hopping anisotropy crashes down edge states, and the corresponding
critical conditions are found.",1401.6770v2
2014-02-27,Azimuthal Anisotropy Measurements by STAR,"The recent study of centrality and transverse momentum ($p_{T}$) dependence
of inclusive charged hardron elliptic anisotropy ($v_{2}$) at midrapidity
($|\eta|<1.0$) in Au+Au collision at $\sqrt{s_{NN}} =$ 7.7, 11.5, 19.6, 27, and
39 GeV in STAR Beam Energy Scan program is presented. We show that the observed
increase of inclusive $v_{2}$ is mainly due to the average $p_{T}$ increase
with energy. In Au+Au 200 GeV collisions, the triangular anisotropy ($v_{3}$)
measurements highly depend on measurment methods; $v_{3}$ is strongly dependent
on $\Delta\eta$. The difference between two- and four-particle cumulants
$v_{2}\lbrace{2}\rbrace$ and $v_{2}\lbrace{4}\rbrace$ for Au+Au and Cu+Cu
collision at $\sqrt{s_{NN}} = $ 62.4 and 200 GeV is used to explore flow
fluctuations. Furthermore, by exploiting the symmetry of average flow in
pseudorapidity $\eta$ about mid-rapidty, the $\Delta\eta$-dependent and
independent components are seperated using $v_{2}\lbrace2\rbrace$ and
$v_{2}\lbrace{4}\rbrace$.",1402.6982v1
2014-03-03,Azimuthal anisotropies of reconstructed jets in Pb+Pb collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV in a multiphase transport model,"Azimuthal anisotropies of reconstructed jets [$v_{n}^{jet} (n=2, 3)$] have
been investigated in Pb+Pb collisions at the center of mass energy
$\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV within a framework of a multiphase transport
(AMPT) model. The $v_{2}^{jet}$ is in good agreement with the recent ATLAS
data. However, the $v_{3}^{jet}$ shows a smaller magnitude than $v_{2}^{jet}$,
and approaches zero at a larger transverse momentum. It is attributed to the
path-length dependence in which the jet energy loss fraction depends on the
azimuthal angles with respect to different orders of event planes. The ratio
$v_{n}^{jet}/\varepsilon_{n}$ increases from peripheral to noncentral
collisions, and $v_{n}^{jet}$ increases with the initial spatial asymmetry
($\varepsilon_{n}$) for a given centrality bin. These behaviors indicate that
the $v_{n}^{jet}$ is produced by the strong interactions between jet and the
partonic medium with different initial geometry shapes. Therefore, azimuthal
anisotropies of reconstructed jet are proposed as a good probe to study the
initial spatial fluctuations, which are expected to provide constraints on the
path-length dependence of jet quenching models.",1403.0328v2
2014-03-11,Piezo-Voltage Manipulation of the Magnetization and Magnetic Reversal in Thin Fe Film,"We carefully investigated the in-plane magnetic reversal and corresponding
magnetic domain structures in Fe/GaAs/piezo-transducer heterostructure using
longitudinal magneto-optical Kerr microscopy. The coexistence of the <100>
cubic magnetic anisotropy and uniaxial magnetic anisotropy was observed in our
Fe thin film grown on GaAs. The induced deformation along [110] orientation can
effectively manipulate the magnetic reversal with magnetic field applied along
magnetic uniaxial hard [110] axes. The control of two-jump magnetization
switching to one-jump magnetization switching during the magnetic reversal was
achieved by piezo-voltages with magnetic field applied in [100] direction. The
additional uniaxial anisotropy induced by piezo-voltages at -75 /75V are
-1.400/1400 J/m3 .",1403.2469v1
2014-03-11,Relating the inhomogeneous power spectrum to the CMB hemispherical anisotropy,"We relate the observed hemispherical anisotropy in the cosmic microwave
radiation data to an inhomogeneous power spectrum model. The hemispherical
anisotropy can be parameterized in terms of the dipole modulation model. This
model leads to correlations between spherical harmonic coefficients
corresponding to multipoles, l and l+1. We extract the $l$ dependence of the
dipole modulation amplitude, A, by making a fit to the WMAP and PLANCK CMBR
data. We propose an inhomogeneous power spectrum model and show that it also
leads to correlations between multipoles, l and l+1. The model parameters are
determined by making a fit to the data. The spectral index of the inhomogeneous
power spectrum is found to be consistent with zero.",1403.2567v4
2014-03-19,Coexistence of bunching and meandering instability in simulated growth of 4H-SiC(0001) surface,"Bunching and meandering instability of steps at the 4H-SiC(0001) surface is
studied by the kinetic Monte Carlo simulation method. Change in the character
of step instability is analyzed for different rates of particle jumps towards
step. In the experiment effective value of jump rates can be controlled by
impurities or other growth conditions. An anisotropy of jump barriers at the
step influences the character of surface structure formed in the process of
crystal growth. Depending on the growth parameters different surface patterns
are found. We show phase diagrams of surface patterns as a function of
temperature and crystal growth rate for two different choices of step kinetics
anisotropy. Jump rates which effectively model high inverse Schwoebel barrier
(ISB) at steps lead either to regular, four-multistep or bunched structure. For
weak anisotropy at higher temperatures or for lower crystal growth rates
meanders and mounds are formed, but on coming towards lower temperatures and
higher rates we observe bunch and meander coexistence. These results show that
interplay between simple dynamical mechanisms induced by the asymmetry of the
step kinetics and step movement assisted by the step edge diffusion are
responsible for different types of surface morphology.",1403.4846v2
2014-03-25,Spin waves in the anisotropic fcc kagome antiferromagnet,"Spin wave calculations demonstrate that the macroscopic continuous degeneracy
associated with the two-dimensional kagome Heisenberg spin lattice persists in
the case of the stacked fcc structure giving rise to zero energy modes in three
dimensions. The addition of an effective local cubic anisotropy is shown to
remove this continuous degeneracy and introduce a gap in the spectrum as well
as modify the inelastic scattering function $S({\bf q},\omega)$. This scenario
supports earlier Monte Carlo simulations which indicate that the phase
transition to long range $q=0$ magnetic order is driven to be discontinuous by
critical fluctuations associated with the large degeneracy in the absence of
anisotropy, but becomes continuous with the addition of anisotropy. The results
are relevant to Ir-Mn alloys which are widely used in the magnetic storage
industry in thin film form as the antiferromagnetic pinning layer in spin-valve
structures.",1403.6352v1
2014-03-29,Strong out-of-plane magnetic anisotropy of Fe adatoms on Bi$_2$Te$_3$,"The electronic and magnetic properties of individual Fe atoms adsorbed on the
surface of the topological insulator Bi$_2$Te$_3$(111) are investigated.
Scanning tunneling microscopy and spectroscopy prove the existence of two
distinct types of Fe species, while our first-principles calculations assign
them to Fe adatoms in the hcp and fcc hollow sites. The combination of x-ray
magnetic circular dichroism measurements and angular dependent magnetization
curves reveals out-of-plane anisotropies for both species with anisotropy
constants of $K_{\text{fcc}} = (10 \pm 4)$ meV/atom and $K_{\text{hcp}} = (8
\pm 4)$ meV/atom. These values are well in line with the results of
calculations.",1403.7621v1
2014-04-02,Multiple Andreev Reflections Spectroscopy of Superconducting LiFeAs Single Crystals: Anisotropy and Temperature Behavior of the Order Parameters,"The superconducting state of LiFeAs single crystals with the maximum critical
temperature $T_c\,\approx\,17\,K$ in the 111 family has been studied in detail
by multiple Andreev reflections (MAR) spectroscopy implemented by the
break-junction technique. The three superconducting gaps, $\Delta_{\Gamma}\,=
(5.1-6.5)\,meV$, $\Delta_L\,= (3.8-4.8)\,meV$, and $\Delta_S\,= (0.9-1.9)\,meV$
(at $T\,<<\,T_c$), as well as their temperature dependences, have been directly
determined in a tunneling experiment with these samples. The anisotropy degrees
of the order parameters in the k-space have been estimated as $<\,8$%,
$\approx12$%, and $\approx20$%, respectively. Andreev spectra have been fitted
within the extended Kummel-Gunsenheimer-Nikolsky model with allowance for
anisotropy. The relative electron-boson coupling constants in LiFeAs have been
determined by approximating the ${\Delta}(T)$ dependences by the system of the
two-band Moskalenko and Suhl equations. It has been shown that the densities of
states in bands forming ${\Delta}_{\Gamma}$ and ${\Delta}_L$ are approximately
the same, intraband pairing dominates in this case, and the interband coupling
constants are related as
${\lambda}_{{\Gamma}L}\,\approx\,{\lambda}_{L{\Gamma}}\,<<
{\lambda}_{S{\Gamma}},\,{\lambda}_{SL}$.",1404.0517v1
2014-04-07,Directional pinning and anisotropy in YBa2Cu3O7-x with BaZrO3 nanorods: intrinsic and nanorods-induced anisotropy,"We present a study of the anisotropic vortex parameters as obtained from
measurements of the microwave complex resistivity in the vortex state with a
tilted applied magnetic field in YBa2Cu3O7-x thin films with BaZrO3 nanorods.
We present the angular dependence of the vortex viscosity $\eta$, the pinning
constant k_p and the upper limit for the creep factor \chi_M. We show that the
directional effect of the nanorods is absent in \eta, which is dictated by the
mass anisotropy \gamma. By contrast, pinning-mediated properties are strongly
affected by the nanorods. It is significant that the pinning and creep affected
by the nanorods is detectable also at our very high operating frequency, which
implies very short-range displacements of the vortices from their equilibrium
position.",1404.1670v1
2014-04-15,A second-order spin-flop transition in collinear two-sublattice antiferromagnets,"Identifying the nature of a spin-flop (SFO) transition, first- or
second-order (FO or SO), remains a major challenge in condensed-matter physics
due to the technically undistinguishable effect of misalignment between
applied-field direction and the relevant antiferromagnetic (AFM) easy axis. A
classical SFO transition is believed to be of FO in character. Here a
mean-field theoretical calculation endowed with AFM exchange interaction
(\emph{J}), easy axis anisotropy ($\gamma$), uniaxial single-ion exchange
anisotropy (\emph{D}), and Zeeman coupling to a magnetic field parallel to the
easy axis unambiguously reveals that a SO SFO transition indeed exists by
virtue of its relatively lower free energy. Their equilibrium phase conditions
are found to be: $D \geq 0$ (FO); $-\frac{1}{2} \gamma < D < 0$ (SO). Compared
numerically to the associated AFM and spin-flip phases, the deduced SO SFO
transition results from a negative single-ion anisotropy which is restricted to
a certain range by the anisotropic exchange interaction",1404.3914v1
2014-04-16,Momentum anisotropy in nuclear collisions from quantum mechanics,"We point out that the intrinsic relationship between space and momentum in
quantum physics through the uncertainty principle has potential implications
for momentum anisotropy in heavy-ion collisions. Using a harmonic oscillator
potential we calculate the elliptic anisotropy and find it to be sizeable
compared to elliptic flow measurements in nuclear collisions. Our results
question the validity of the completely hydrodynamic interpretation of
anisotropic flow data, and highlight the importance of including quantum
physics in hydrodynamic calculations which has largely been neglected so far.",1404.4119v2
2014-05-06,Polarization of Direct Photons from Gluon Anisotropy in Ultrarelativistic Heavy Ion Collisions,"We show how anisotropy in momentum of the gluon distribution in
ultrarelativistic heavy ion collisions gives rise to polarization of direct
photons produced via gluon-quark Compton scattering, as well as by
quark-antiquark annihilation into a gluon-photon pair. We estimate the
polarization asymmetry from the Compton process within a toy model where the
polarized photons are produced from thermal gluons scattered by heavy-quark
scattering centers moving with Bjorken boost-invariant flow, and find that it
could be as large as 10%. We conclude that polarization measurements of
directly produced photons can shed light on gluon pressure anisotropy in the
early stages of collisions.",1405.1376v2
2014-05-09,Phase diagram of two-dimensional hard ellipses,"We report the phase diagram of two-dimensional hard ellipses as obtained from
replica exchange Monte Carlo simulations. The replica exchange is implemented
by expanding the isobaric ensemble in pressure. The phase diagram shows four
regions: isotropic, nematic, plastic, and solid (letting aside the hexatic
phase at the isotropic-plastic two-step transition [PRL 107, 155704 (2011)]).
At low anisotropies, the isotropic fluid turns into a plastic phase which in
turn yields a solid for increasing pressure (area fraction). Intermediate
anisotropies lead to a single first order transition (isotropic-solid).
Finally, large anisotropies yield an isotropic-nematic transition at low
pressures and a high-pressure nematic-solid transition. We obtain continuous
isotropic-nematic transitions. For the transitions involving quasi-long-range
positional ordering, i. e. isotropic-plastic, isotropic-solid, and
nematic-solid, we observe bimodal probability density functions. This supports
first order transition scenarios.",1405.2236v1
2014-05-14,Magnetic anisotropy of spin tetramer system SeCuO$_3$ studied by torque magnetometry and ESR spectroscopy,"We present an experimental study of macroscopic and microscopic magnetic
anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and
ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature
observed from torque magnetometry agrees reasonably well with the rotation of
the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$
tensor is temperature independent, while macroscopic magnetic axes continue to
rotate. Additionally, the susceptibility anisotropy has a temperature
dependence which cannot be reconciled with the isotropic Heisenberg model of
interactions between spins. ESR linewidth analysis shows that anisotropic
exchange interaction must be present in SeCuO$_3$. These findings strongly
support the presence of anisotropic exchange interactions in the Hamiltonian of
the studied system. Below $T_N=8$~K, the system enters a long - range
antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$
direction. Small but significant rotation of magnetic axes is also observed in
the antiferromagnetically ordered state suggesting strong spin-lattice coupling
in this system.",1405.3389v2
2014-05-16,Grid induced noise and entropy growth in 3d particle-in-cell simulation of high intensity beams,"The numerical noise inherent to particle-in-cell simulation of 3D high
intensity bunched beams is studied with the TRACEWIN code and compared with an
analytical model by Struckmeier. The latter assumes that entropy growth can be
related to Markov type stochastic processes due to temperature anisotropy and
the artificial collisions caused by using macro-particles and calculating the
space charge effect. The resulting noise can lead to growth of the
six-dimensional rms emittance and a suitably defined rms entropy. We confirm
the dependence of this growth on the bunch temperature anisotropy as predicted
by Struckmeier. However,we also find an apparently modified mechanism of noise
generation by the non-Liouvillean effect of the Poisson solver grid, which
exists in periodic focusing systems even in the complete absence of temperature
anisotropy. Our findings are applicable in particular to high current linac
simulation, where they can provide guidance to estimate noise effects and help
finding an effective balance between the number of simulation particles and the
grid resolution.",1405.4153v1
2014-06-04,Magnetic hard-axis ordering near ferromagnetic quantum criticality,"We investigate the interplay of quantum fluctuations and magnetic
anisotropies in metallic ferromagnets. Our central result is that fluctuations
close to a quantum critical point can drive the moments to point along a
magnetic hard axis. As a proof of concept, we show this behavior explicitly for
a generic two-band model with local Coulomb and Hund's interactions, and a
spin-orbit-induced easy plane anisotropy. The phase diagram is calculated
within the fermionic quantum order-by-disorder approach, which is based on a
self-consistent free energy expansion around a magnetically ordered state with
unspecified orientation. Quantum fluctuations render the transition of the
easy-plane ferromagnet first-order below a tricritical point. At even lower
temperatures, directionally dependent transverse fluctuations dominate the
magnetic anisotropy and the moments flip to lie along the magnetic hard axis.
We discuss our findings in the context of recent experiments that show this
unusual ordering along the magnetic hard direction.",1406.1173v2
2014-06-05,Skyrmion fractionalization and merons in chiral magnets with easy-plane anisotropy,"We study the equilibrium phase diagram of ultrathin chiral magnets with
easy-plane anisotropy $A$. The vast triangular skyrmion lattice phase that is
stabilized by an external magnetic field evolves continuously as a function of
increasing $A$ into a regime in which nearest-neighbor skyrmions start
overlapping with each other. This overlap leads to a continuous reduction of
the skyrmion number from its quantized value $Q=1$ and to the emergence of
antivortices at the center of the triangles formed by nearest-neighbor
skyrmions. The antivortices also carry a small ""skyrmion number"" $Q_A \ll 1$
that grows as a function of increasing $A$. The system undergoes a first order
phase transition into a square vortex-antivortex lattice at a critical value of
$A$. Finally, a canted ferromagnetic state becomes stable through another first
order transition for a large enough anisotropy $A$. Interestingly enough, this
first order transition is accompanied by {\it metastable} meron solutions.",1406.1422v3
2014-06-20,Dependence of the Cosmic Microwave Background Lensing Power Spectrum on the Matter Density,"The anisotropies in the cosmic microwave background (CMB) provide our best
laboratory for testing models of the formation and evolution of large-scale
structure. The rich features in the cosmic microwave background anisotropy
spectrum, in combination with highly precise observations and theoretical
predictions, also allow us to simultaneously constrain a number of cosmological
parameters. As observations have progressed, measurements at smaller angular
scales have provided increasing leverage. These smaller angular scales provide
sensitive measures of the matter density through the effect of gravitational
lensing. In this work we provide an analytic explanation of the manner in which
the lensing of CMB anisotropies depends on the matter density, finding that the
dominant effect comes from the shape of the matter power spectrum set by the
decay of small-scale potentials between horizon crossing and matter-radiation
equality.",1406.5459v2
2014-06-26,Growth and angular dependent resistivity of Nb2Pd0.73S5.7 superconducting single crystals fiber,"We report the growth of Nb2Pd0.73S5.7 superconducting single crystal fibers
via slow cooling solid state reaction method. Superconducting transition
temperature (Tc ~ 6.5K) is confirmed from magnetization and transport
measurements. A comparative study is performed for determination of
superconducting anisotropy, {\Gamma}, via conventional method (by taking ration
of two superconducting parameters) and scaling approach method. Scaling
approach, defined within the framework of the Ginzburg-Landau theory is applied
to the angular dependent resistivity measurements to estimate the anisotropy.
The value of {\Gamma} close to Tc from scaling approach is found to be ~ 2.5
that is slight higher compare to conventional approach (~2.2). Further,
variation of anisotropy with temperature suggests that it is a type of
multi-band superconductor.",1406.6790v2
2014-06-29,Azimuthal anisotropy in U+U collisions at STAR,"The azimuthal anisotropy of particle production is commonly used in
high-energy nuclear collisions to study the early evolution of the expanding
system. The prolate shape of uranium nuclei makes it possible to study how the
geometry of the colliding nuclei affects final state anisotropies. It also
provides a unique opportunity to understand how entropy is produced in heavy
ion collisions. In this paper, the two- and four- particle cumulant $v_2$
($v_{2}\{2\}$ and $v_{2}\{4\}$) from U+U collisions at $\sqrt{s_{NN}}$ = 193
GeV and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for inclusive charged
hadrons will be presented. The STAR Zero Degree Calorimeters are used to select
very central collisions. Differences were observed between the multiplicity
dependence of $v_{2}\{2\}$ for most central Au+Au and U+U collisions. The
multiplicity dependence of $v_{2}\{2\}$ in central collisions were compared to
Monte Carlo Glauber model predictions and it was seen that this model cannot
explain the present results.",1406.7522v1
2014-07-01,Emergent defect states as a source of resistivity anisotropy in the nematic phase of iron pnictides,"We consider the role of potential scatterers in the nematic phase of Fe-based
superconductors above the transition temperature to the (pi,0) magnetic state
but below the orthorhombic structural transition. The anisotropic spin
fluctuations in this region can be frozen by disorder, to create elongated
magnetic droplets whose anisotropy grows as the magnetic transition is
approached. Such states act as strong anisotropic defect potentials which
scatter with much higher probability perpendicular to their length than
parallel, although the actual crystal symmetry breaking is tiny. We calculate
the scattering potentials, relaxation rates, and conductivity in this region,
and show that such emergent defect states are essential for the transport
anisotropy observed in experiments.",1407.0117v1
2014-07-10,Effects of cosmic strings with delayed scaling on CMB anisotropy,"The network of cosmic strings generated in a phase transition during
inflation enters the scaling regime later than that of usual strings. If it
occurs after the recombination, temperature anisotropies of the cosmic
microwave background (CMB) at high multipole moments are significantly reduced.
In this paper, we study such effects qualitatively and show that the constraint
on the cosmic string tension from the CMB temperature anisotropies and B-mode
polarizations can be relaxed. It is shown to be difficult to explain the recent
BICEP2 and POLARBEAR results in terms of signals induced by cosmic strings
alone even if we take into account the delayed scaling. However, the
inflationary tensor-to-scalar ratio required to explain the observed B-mode
signals can be slightly reduced to be consistent with the Planck constraint.",1407.2951v2
2014-07-11,A 4-fold-symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy and tunnel magnetoresistance,"An unusual crystallographic orientation of hexagonal Ru with a 4-fold
symmetry emerging in epitaxial MgO/Ru/Co2FeAl/MgO heterostructures is reported,
in which an approximately Ru(02-23) growth attributes to the lattice matching
among MgO, Ru, and Co2FeAl. Perpendicular magnetic anisotropy of the
Co2FeAl/MgO interface is substantially enhanced as compared with those with a
Cr(001) layer. The MTJs incorporating this structure gave rise to the largest
tunnel magnetoresistance for perpendicular MTJs using low damping Heusler
alloys. The 4-fold-symmetry hexagonal Ru arises from an epitaxial growth with
an unprecedentedly high crystal index, opening a unique pathway for the
development of perpendicular anisotropy films of cubic and tetragonal
ferromagnetic alloys.",1407.3160v2
2014-07-21,Mapping the Integrated Sachs-Wolfe Effect,"On large scales, the anisotropies in the cosmic microwave background (CMB)
reflect not only the primordial field but also the energy gain when photons
traverse decaying gravitational potentials of large scales structure, the
Integrated Sachs-Wolfe (ISW) effect. Decomposing the anisotropy signal into a
primordial piece and an ISW component is more urgent than ever as cosmologists
strive to understand the Universe on the largest of scales. Here we present a
likelihood technique for extracting the ISW signal from measurements of the
CMB, the distribution of galaxies, and maps of gravitational lensing. We test
this technique first to simulated data and then we apply it to the combination
of temperature anisotropies, the lensing map made by the Planck satellite, and
the NVSS galaxy survey. We also show projections for upcoming surveys.",1407.5623v2
2014-08-02,Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on Kapton,"Bending effect on the magnetic anisotropy in 20 nm Co$_{2}$FeAl Heusler thin
film grown on Kapton\textregistered{} has been studied by ferromagnetic
resonance and glued on curved sample carrier with various radii. The results
reported in this letter show that the magnetic anisotropy is drastically
changed in this system by bending the thin films. This effect is attributed to
the interfacial strain transmission from the substrate to the film and to the
magnetoelastic behavior of the Co$_{2}$FeAl film. Moreover two approaches to
determine the in-plane magnetostriction coefficient of the film, leading to a
value that is close to $\lambda^{CFA}=14\times10^{-6}$, have been proposed.",1408.0379v1
2014-08-05,Azimuthal Anisotropy Distributions in High-Energy Collisions,"Elliptic flow in ultrarelativistic heavy-ion collisions results from the
hydrodynamic response to the spatial anisotropy of the initial density profile.
A long-standing problem in the interpretation of flow data is that
uncertainties in the initial anisotropy are mingled with uncertainties in the
response. We argue that the non-Gaussianity of flow fluctuations in small
systems can be used to disentangle the initial state from the response. We
apply this method to recent measurements of anisotropic flow in Pb+Pb and p+Pb
collisions at the LHC. The response coefficient is found to decrease mildly as
the system becomes smaller. This mild decrease is consistent with a low value
of the ratio of viscosity over entropy.",1408.0921v3
2014-08-09,CMB statistical anisotropies of classical and quantum origins,"We examine the impact of different anisotropic relics on inflation, in
particular the predictions on the density perturbations. These relics can be
the source of the large scale anomalies in the cosmic microwave background.
There are two different types of background relics, one from the matter sector
and the other purely from the metric. Although the angular-dependence of the
statistical anisotropy in both cases are degenerate, the scale-dependence are
observationally distinctive. In addition, we demonstrate that non-Bunch-Davies
vacuum states can extend the statistical anisotropy to much shorter scales, and
leave a scale-dependence that is insensitive to the different backgrounds but
sensitive to the initial quantum state.",1408.2096v1
2014-08-12,Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain,"The perpendicular magnetic anisotropy K$_e$$_f$$_f$, magnetization reversal,
and field-driven domain wall velocity in the creep regime are modified in
Pt/Co(0.85-1.0 nm)/Pt thin films by strain applied via piezoelectric
transducers. K$_e$$_f$$_f$, measured by the extraordinary Hall effect, is
reduced by 10 kJ/m$^3$ by tensile strain out-of-plane {\epsilon}$_z$ = 9 x
10-4, independently of the film thickness, indicating a dominant volume
contribution to the magnetostriction. The same strain reduces the coercive
field by 2-4 Oe, and increases the domain wall velocity measured by wide-field
Kerr microscopy by 30-100 %, with larger changes observed for thicker Co
layers. We consider how strain-induced changes in the perpendicular magnetic
anisotropy can modify the coercive field and domain wall velocity.",1408.2664v2
2014-08-12,Nematic spin correlations in the tetragonal state of uniaxial strained BaFe2-xNixAs2,"Understanding the microscopic origins of electronic phases in high-transition
temperature (high-Tc) superconductors is important for elucidating the
mechanism of superconductivity. In the paramagnetic tetragonal phase of
BaFe2-xTxAs2 (where T is Co or Ni) iron pnictides, an in-plane resistivity
anisotropy has been observed. Here we use inelastic neutron scattering to show
that low-energy spin excitations in these materials change from four-fold
symmetric to two-fold symmetric at temperatures corresponding to the onset of
the in-plane resistivity anisotropy. Because resistivity and spin excitation
anisotropies both vanish near optimal superconductivity, we conclude that they
are likely intimately connected.",1408.2756v1
2014-08-13,p-wave Superfluidity by Spin-Nematic Fermi Surface Deformation,"We study attractively interacting fermions on a square lattice with
dispersion relations exhibiting strong spin-dependent anisotropy. The resulting
Fermi surface mismatch suppresses the s-wave BCS-type instability, clearing the
way for unconventional types of order. Unbiased sampling of the Feynman
diagrammatic series using Diagrammatic Monte Carlo methods reveals a rich phase
diagram in the regime of intermediate coupling strength. Instead of a proposed
Cooper-pair Bose metal phase [A. E. Feiguin and M. P. A. Fisher, Phys. Rev.
Lett. 103, 025303 (2009)] we find an incommensurate density wave at strong
anisotropy and two different p-wave superfluid states with unconventional
symmetry at intermediate anisotropy.",1408.3119v2
2014-08-18,Ground-State Phases of Anisotropic Mixed Diamond Chains with Spins 1 and 1/2,"The ground-state phases of anisotropic mixed diamond chains with spins 1 and
1/2 are investigated. Both single-site and exchange anisotropies are
considered. We find the phases consisting of an array of uncorrelated spin-1
clusters separated by singlet dimers. Except in the simplest case where the
cluster consists of a single $S=1$ spin, this type of ground state breaks the
translational symmetry spontaneously. Although the mechanism leading to this
type of ground state is the same as that in the isotropic case, it is
nonmagnetic or paramagnetic depending on the competition between two types of
anisotropy. We also find the N\'eel, period-doubled N\'eel, Haldane, and
large-$D$ phases, where the ground state is a single spin cluster of infinite
size equivalent to the spin-1 Heisenberg chain with alternating anisotropies.
The ground-state phase diagrams are determined for typical sets of parameters
by numerical analysis. In various limiting cases, the ground-state phase
diagrams are determined analytically. The low-temperature behaviors of magnetic
susceptibility and entropy are investigated to distinguish each phase by
observable quantities. The relationship of the present model with the
anisotropic rung-alternating ladder with spin-1/2 is also discussed.",1408.3890v2
2014-08-27,Chiral Magnetic Effect in the Anisotropic Quark-Gluon Plasma,"An anisotropic thermal plasma phase of a strongly coupled gauge theory can be
holographically modelled by an anisotropic AdS black hole. The temperature and
anisotropy parameter of the AdS black hole background of interest [1] is
specified by the location of the horizon and the value of the Dilaton field at
the horizon. Interestingly, for the first time, we obtain two functions for the
values of the horizon and Dilaton field in terms of the temperature and
anisotropy parameter. Then by introducing a number of spinning probe D7-branes
in the anisotropic background, we compute the value of the chiral magnetic
effect (CME). We observe that in the isotropic and anisotropic plasma the value
of the CME is equal for the massless quarks. However, at fixed temperature,
raising the anisotropy in the system will increase the value of the CME for the
massive quarks.",1408.6361v2
2014-08-30,Anisotropic resistivity of the monolayer graphene in the trigonal warping and connected Fermi curve regimes,"In the present study, the anisotropic resistivity of the monolayer graphene
has been obtained in semiclassical regime beyond the Dirac point approximation.
In particular, detailed investigations were made on the dependence of
conductivity on the Fermi energy. At low energies, in the vicinity of the Dirac
points, band energy of the monolayer graphene is isotropic at the Fermi level.
Meanwhile, at the intermediate Fermi energies anisotropic effects such as
trigonal warping is expected to be the origin of the anisotropic resistivity.
However, besides the band anisotropy there also exists an other source of
anisotropic resistivity which was introduced by scattering matrix. At high
energies it was shown that the band anisotropy is less effective than the
anisotropy generated by the scattering matrix. It was also shown that there
exist two distinct regimes of anisotropic resistivity corresponding the
trigonal warping and connected Fermi curve at intermediate and high energies
respectively.",1409.0130v1
2014-09-03,Strong Thermal Transport Anisotropy and Strain Modulation in Single-Layer Phosphorene,"Using first-principles calculations and non-equilibrium Green's function
method, we investigate the ballistic thermal transport in single-layer
phosphorene. A significant crystallographic orientation dependence of thermal
conductance is observed, with room temperature thermal conductance along zigzag
direction being 40 percent higher than that along armchair direction.
Furthermore, we find that the thermal conductance anisotropy with the
orientation can be tuned by applying strain. In particular, the zigzag-oriented
thermal conductance is enhanced when a zigzag-oriented strain is applied but
decreases when an armchair-oriented strain is applied; whereas the
armchair-oriented thermal conductance always decreases when either a zigzag- or
an armchair-oriented strain is applied. The present work suggests that the
remarkable thermal transport anisotropy and its strain-modulated effect in
single-layer phosphorene may be used for thermal management in
phosphorene-based electronics and optoelectronic devices.",1409.0974v1
2014-09-04,Dimensional cross-over of the bandgap transition in quasi-two-dimensional MoS2,"The anisotropy of the electronic transition is an important physical property
not only determining the materials' optical property, but also revealing the
underlying character of the electronic states involved. Here we used
momentum-resolved electron energy-loss spectroscopy to study the evolution of
the anisotropy of the electronic transition involving the low energy valence
electrons in the free-standing MoS2 systems as the layer thickness was reduced
to monolayer. We used the orientation and the spectral-density analysis to show
that indirect to direct band-gap transition is accompanied by a three- to
two-dimensional anisotropy cross-over. The result provides a logical
explanation for the large sensitivity of indirect transition to the change of
thickness compared with that for direct transition. By tracking the energy of
indirect transition, we also revealed the asymmetric response of the valence
band and conduction band to the quantum confinement effect. Our results have
implication for future optoelectronic applications of atomic thin MoS2.",1409.1409v1
2014-09-08,Anisotropy of spin-orbit induced electron spin relaxation in [001] and [111] grown GaAs quantum dots,"We report a systematic study of the spin relaxation anisotropy between single
electron Zeeman sublevels in cuboidal GaAs quantum dots (QDs). The QDs are
subject to an in-plane magnetic field. As the field orientation varies, the
relaxation rate oscillates periodically, showing ``magic'' angles where the
relaxation rate is suppressed by several orders of magnitude. This behavior is
found in QDs with different shapes, heights, crystallographic orientations and
external fields. The origin of these angles can be traced back to the
symmetries of the spin admixing terms of the Hamiltonian. In [001] grown QDs,
the suppression angles are different for Rashba and Dresselhaus spin-orbit
terms. By contrast, in [111] grown QDs they are the same, which should
facilitate a thorough suppression of spin-orbit induced relaxation. Our results
evidence that cubic Dresselhaus terms play a critical role in determining the
spin relaxation anisotropy even in quasi-2D QDs.",1409.2392v1
2014-09-09,Micro-strip ferromagnetic resonance study of strain-induced anisotropy in amorphous FeCuNbSiB film on flexible substrate,"The magnetic anisotropy of a FeCuNbSiB (Finemet) film deposited on Kapton has
been studied by micro-strip ferromagnetic resonance technique. We have shown
that the flexibility of the substrate allows a good transmission of elastic
strains generated by a piezoelectric actuator. Following the resonance field
angular dependence, we also demonstrate the possibility of controlling the
magnetic anisotropy of the film by applying relatively small voltages to the
actuator. Moreover, a suitable model taking into account the effective elastic
strains measured by digital image correlation and the effective elastic
coefficients measured by Brillouin light scattering, allowed to deduce the
magnetostrictive coefficient. This latter was found to be positive
$(\lambda=16\times10^{-6}$) and consistent with the usually reported values for
bulk amorphous FeCuNbSiB.",1409.2845v1
2014-09-29,Self-Gravitating Relativistic Models of Fermions with Anisotropy and Cutoff Energy in their Distribution Function,"In this paper we study the equilibrium configurations of anisotropic
self-gravitating fermions, by extending to general relativity the solutions
obtained in a previous paper. This treatment also generalizes to anisotropic
systems the relativistic self-gravitating Fermi gas model, by considering
different degrees of anisotropy. We discuss some important characteristics of
the models and the obtained density profiles, and generalize the relation
between the anisotropy and the mass of particles in the relativistic regime.
These relativistic models may also be applied to the study of superdense
neutron stars with anisotropic pressure or super-Chandrasekhar white dwarfs
generated by the presence of a magnetic field.",1409.8124v4
2014-10-23,The Effects of Rayleigh Scattering on the CMB and Cosmic Structure,"During and after recombination, in addition to Thomson scattering with free
electrons, photons also coupled to neutral hydrogen and helium atoms through
Rayleigh scattering. This coupling influences both CMB anisotropies and the
distribution of matter in the Universe. The frequency-dependence of the
Rayleigh cross section breaks the thermal nature of CMB temperature and
polarization anisotropies and effectively doubles the number of variables
needed to describe CMB intensity and polarization statistics, while the
additional atomic coupling changes the matter distribution and the lensing of
the CMB. We introduce a new method to capture the effects of Rayleigh
scattering on cosmological power spectra. Rayleigh scattering modifies CMB
temperature and polarization anisotropies at the $\sim\!1 \%$ level at $353
{\rm GHz}$ (scaling $\propto \nu^4$), and modifies matter correlations by as
much as $\sim\!0.3\%$. We show the Rayleigh signal, especially the
cross-spectra between the thermal (Rayleigh) E-polarization and Rayleigh
(thermal) intensity signal, may be detectable with future CMB missions even in
the presence of foregrounds, and how this new information might help to better
constrain the cosmological parameters.",1410.6484v1
2014-11-10,Effect of anisotropy on HBT radii using leptonpair interferometry,"The effect of initial state momentum-space anisotropy on invariant mass
dependence of HBT radii extracted from the leptonpair interferometry is
presented here. We have studied the Bose-Einstein Correlation Function (BECF)
for two identical virtual photons decaying to leptonpairs at most central
collision of LHC energy having fixed transverse momentum of one of the virtual
photons ($k_{1T}$= 2 GeV). The {\em free streaming interpolating} model with
fixed initial condition has been used for the evolution in anisotropic Quark
Gluon Plasma (aQGP) and the relativistic (1+2)d hydrodynamics model with
cylindrical symmetry and longitudinal boost invariance has been used for both
isotropic Quark Gluon Plasma (iQGP) and hadronic phases. We found a significant
change in the spatial and temporal dimension of the evolving system in presence
of initial state momentum-space anisotropy.",1411.2322v1
2014-11-14,Photo-induced magnetization enhancement in two-dimensional weakly anisotropic Heisenberg magnets,"By comparing the photo-induced magnetization dynamics in simple layered
systems we show how light-induced modifications of the magnetic anisotropy
directly enhance the magnetization. It is observed that the spin precession in
(CH3NH3)2CuCl4, initiated by a light pulse, increases in amplitude at the
critical temperature TC. The phenomenon is related to the dependence of the
critical temperature on the axial magnetic anisotropy. The present results
underline the possibility and the importance of the optical modifications of
the anisotropy, opening new paths toward the control of the magnetization state
for ultrafast memories.",1411.3918v1
2014-11-21,Holographic renormalization and anisotropic black branes in higher curvature gravity,"We consider five-dimensional AdS-axion-dilaton gravity with a Gauss-Bonnet
term and find a solution of the equations of motion which corresponds to a
black brane exhibiting a spatial anisotropy, with the source of the anisotropy
being an axion field linear in one of the horizon coordinates. Our solution is
static, regular everywhere on and outside the horizon, and asymptotically AdS.
It is analytic and valid in a small anisotropy expansion, but fully
non-perturbative in the Gauss-Bonnet coupling. We discuss various features of
this solution and use it as a gravity dual to a strongly coupled anisotropic
plasma with two independent central charges, $a\neq c$. In the limit of small
Gauss-Bonnet coupling, we carry out holographic renormalization of the system
using (a recursive variant of) the Hamilton-Jacobi method and derive a generic
expression for the boundary stress tensor, which we later specialize to our
solution. Finally, we compute the shear viscosity to entropy ratios and
conductivities of this anisotropic plasma.",1411.5964v2
2014-12-04,CMB anisotropies generated by a stochastic background of primordial magnetic fields with non-zero helicity,"We consider the impact of a stochastic background of primordial magnetic
fields with non-vanishing helicity on CMB anisotropies in temperature and
polarization. We compute the exact expressions for the scalar, vector and
tensor part of the energy-momentum tensor including the helical contribution,
by assuming a power-law dependence for the spectra and a comoving cutoff which
mimics the damping due to viscosity. We also compute the parity-odd correlator
between the helical and non-helical contribution which generate the TB and EB
cross-correlation in the CMB pattern. We finally show the impact of including
the helical term on the power spectra of CMB anisotropies up to multipoles with
ell ~ O(10^3)$.",1412.1836v2
2014-12-10,Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene,"The room temperature carrier mobility in atomically thin 2D materials is
usually far below the intrinsic limit imposed by phonon scattering as a result
of scattering by remote charged impurities in its environment. We simulate the
charged impurity-limited carrier mobility $\mu$ in bare and encapsulated
monolayer phosphorene. We find a significant temperature dependence in the
carrier mobilities ($\mu \propto T^{-\gamma}$) that results from the
temperature variability of the charge screening and varies with the crystal
orientation. The anisotropy in the effective mass leads to an anisotropic
carrier mobility, with the mobility in the armchair direction about one order
of magnitude larger than in the zigzag direction. In particular, this mobility
anisotropy is enhanced at low temperatures and high carrier densities. Under
encapsulation with a high-$\kappa$ overlayer, the mobility increases by up to
an order of magnitude although its temperature dependence and its anisotropy
are reduced.",1412.3211v1
2014-12-10,Shape-sensitive Pauli blockade in a bent carbon nanotube,"Motivated by a recent experiment [F. Pei et al., Nat. Nanotech. 7, 630
(2012)], we theoretically study the Pauli blockade transport effect in a double
quantum dot embedded in a bent carbon nanotube. We establish a model for Pauli
blockade, taking into account the strong g-factor anisotropy that is linked to
the local orientation of the nanotube axis in each quantum dot. We provide a
set of conditions under which our model is approximately mapped to the
spin-blockade model of Jouravlev and Nazarov [O. N. Jouravlev and Y. V.
Nazarov, Phys. Rev. Lett. 96, 176804 (2006)]. The results we obtain for the
magnetic anisotropy of the leakage current, together with their qualitative
geometrical explanation, provide a possible interpretation of previously
unexplained experimental results. Furthermore, we find that in a certain
parameter range, the leakage current becomes highly sensitive to the shape of
the tube, and this sensitivity increases with increasing g-factor anisotropy.
This mutual dependence of the electron transport and the tube shape allows for
mechanical control of the leakage current, and for characterization of the tube
shape via measuring the leakage current.",1412.3232v2
2014-12-16,High order cumulants of the azimuthal anisotropy in the dilute-dense limit: Connected graphs,"We analytically compute higher order cumulants of the azimuthal anisotropy,
$c_2\{2m\}$, and corresponding $v_2\{2m\}$ at high transverse momentum in the
dilute-dense limit. The dense target is considered in the framework of the
McLerran-Venugopolan model. The absolute values of the harmonics $v_2\{2m\}$ of
the azimuthal anisotropy are approximately equal, $|v_2\{2m\}| \approx
|v_2\{2m'\}| $, for large $m$ and $m'$. However, the harmonics with order
$2m=4n$ are complex. We argue that this is a generic property of connected
graphs, which remains true in the dense-dense limit.",1412.5191v2
2014-12-22,Surface sensitivity of the spin Seebeck effect,"We have investigated the influence of the interface quality on the spin
Seebeck effect (SSE) of the bilayer system yttrium iron garnet (YIG) - platinum
(Pt). The magnitude and shape of the SSE is strongly influenced by mechanical
treatment of the YIG single crystal surface. We observe that the saturation
magnetic field H_{sat} for the SSE signal increases from 55.3 mT to 72.8 mT
with mechanical treatment. The change in the magnitude of H_{sat} can be
attributed to the presence of a perpendicular magnetic anisotropy due to the
treatment induced surface strain or shape anisotropy in the Pt/YIG system. Our
results show that the SSE is a powerful tool to investigate magnetic anisotropy
at the interface.",1412.7712v1
2014-12-30,Reversible control of Co magnetism by voltage induced oxidation,"We demonstrate that magnetic properties of ultra-thin Co films adjacent to
Gd2O3 gate oxides can be directly manipulated by voltage. The Co films can be
reversibly changed from an optimally-oxidized state with a strong perpendicular
magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy,
or to an oxidized state with nearly zero magnetization, depending on the
polarity and time duration of the applied electric fields. Consequently, an
unprecedentedly large change of magnetic anisotropy energy up to 0.73 erg/cm2
has been realized in a nonvolatile manner using gate voltages of only a few
volts. These results open a new route to achieve ultra-low energy magnetization
manipulation in spintronic devices.",1412.8668v1
2015-01-18,Physics of the cosmic microwave background anisotropy,"Observations of the cosmic microwave background (CMB), especially of its
frequency spectrum and its anisotropies, both in temperature and in
polarization, have played a key role in the development of modern cosmology and
our understanding of the very early universe. We review the underlying physics
of the CMB and how the primordial temperature and polarization anisotropies
were imprinted. Possibilities for distinguishing competing cosmological models
are emphasized. The current status of CMB experiments and experimental
techniques with an emphasis toward future observations, particularly in
polarization, is reviewed. The physics of foreground emissions, especially of
polarized dust, is discussed in detail, since this area is likely to become
crucial for measurements of the B modes of the CMB polarization at ever greater
sensitivity.",1501.04288v1
2015-02-19,Anisotropic parton escape is the dominant source of azimuthal anisotropy in transport models,"We trace the development of elliptic anisotropy ($v_2$) via parton-parton
collision history in two transport models. The parton $v_2$ is studied as a
function of the number of collisions of each parton in Au+Au and $d$+Au
collisions at $\sqrt{s_{_{\rm NN}}}=200$ GeV. It is found that the majority of
$v_2$ comes from the anisotropic escape probability of partons, with no
fundamental difference at low and high transverse momenta. The contribution to
$v_2$ from hydrodynamic-type collective flow is found to be small. Only when
the parton-parton cross-section is set unrealistically large does this
contribution start to take over. Our findings challenge the current paradigm
emerged from hydrodynamic comparisons to anisotropy data.",1502.05572v4
2015-02-23,The Casimir force between parallel plates separated by anisotropic media,"The Casimir force between two parallel plates separated by anisotropic media
is investigated. We theoretically calculate the Casimir force between two
parallel plates when the interspace between the plates is filled with
anisotropic media. Our result shows that the anisotropy of the material between
the plates can significantly affect the Casimir force, especially the direction
of the force. If ignoring the anisotropy of the in-between material makes the
force to be repulsive (attractive), by contrast, taking the anisotropy into
account may produce an extra attractive (repulsive) force. The physical
explanation for this phenomenon is also discussed.",1502.06335v2
2015-02-23,Anisotropic Friedel oscillations inside the domain wall,"The influence of the non-collinear magnetic configuration on Friedel is
investigated theoretically. Specifically the influence of the magnetic
configuration on the induced electric charge in a N\'{e}el type domain wall
(DW) has been obtained. The well-known Levy and Zhang eigenstates for a linear
DW have been employed. Then the dielectric function of this magnetic system has
been obtained within the random phase approximation. Results of the current
work demonstrated that magnetic configuration of the system manifests itself in
the electric properties such as induced charge distribution. Meanwhile the
anisotropy of the induced charge distribution in the real space provides a
measurable way for the determination of the DW orientation. In addition
anisotropy of the dielectric function in k-space arises as a result of the
anisotropy of the magnetic configuration. Therefore the orientation of the
magnetic DW could also be captured by full optical measurements.",1502.06421v1
2015-03-09,Quantized electronic fine structure with large anisotropy in ferromagnetic Fe films,"We report on the spectroscopic observation of a quantized electronic fine
structure near the Fermi energy in thin Fe films grown on W(110). The quantum
well states are detected down to binding energies of $\sim$10 meV by
angle-resolved photoelectron spectroscopy. The band dispersion of these states
is found to feature a pronounced anisotropy within the surface plane: It is
free-electron like along the $\bar{\Gamma \rm{H}}$-direction while it becomes
heavy along $\bar{\Gamma \rm{N}}$. Density functional theory calculations
identify the observed states to have both majority and minority spin character
and indicate that the large anisotropy can be dependent on the number of
Fe-layers and coupling to the substrate.",1503.02440v1
2015-03-12,Anisotropic particle production and azimuthal correlations in high-energy pA collisions,"We summarize some recent ideas relating to anisotropic particle production in
high-energy collisions. Anisotropic gluon distributions lead to anisotropies of
the single-particle azimuthal distribution and hence to disconnected
contributions to multi-particle cumulants. When these dominate, the
four-particle elliptic anisotropy $c_2\{4\}$ changes sign. On the other hand,
connected diagrams for $m$-particle cumulants are found to quickly saturate
with increasing $m$, a ``coherence'' quite unlike conventional ``non-flow''
contributions such as decays. Finally, we perform a first exploratory
phenomenological analysis in order to estimate the amplitude ${\cal A}$ of the
$\cos(2\varphi)$ anisotropy of the gluon distribution at small $x$, and we
provide a qualitative prediction for the elliptic asymmetry from three-particle
correlations, $c_2\{3\}$.",1503.03897v1
2015-03-31,Imprint of Inhomogeneous and Anisotropic Primordial Power Spectrum on CMB Polarization,"We consider an inhomogeneous model and independently an anisotropic model of
primordial power spectrum in order to describe the observed hemispherical
anisotropy in Cosmic Microwave Background Radiation. This anisotropy can be
parametrized in terms of the dipole modulation model of the temperature field.
Both the models lead to correlations between spherical harmonic coefficients
corresponding to multipoles, l and l \pm 1. We obtain the model parameters by
making a fit to TT correlations in CMBR data. Using these parameters we predict
the signature of our models for correlations among different multipoles for the
case of the TE and EE modes. These predictions can be used to test whether the
observed hemispherical anisotropy can be correctly described in terms of a
primordial power spectrum. Furthermore these may also allow us to distinguish
between an inhomogeneous and an anisotropic model.",1503.08997v2
2015-04-01,Impact of the modulation doping layer on the ν=5/2 anisotropy,"We have carried out a systematic study of the tilted magnetic field induced
anisotropy at the Landau level filling factor \nu=5/2 in a series of high
quality GaAs quantum wells, where the setback distance (d) between the
modulation doping layer and the GaAs quantum well is varied from 33 to 164 nm.
We have observed that in the sample of the smallest d electronic transport is
anisotropic when the in-plane magnetic field (B_{ip}) is parallel to the [1-10]
crystallographic direction, but remains more or less isotropic when B_{ip} //
[110]. In contrast, in the sample of largest d, electronic transport is
anisotropic in both crystallographic directions. Our results clearly show that
the modulation doping layer plays an important role in the tilted field induced
\nu=5/2 anisotropy.",1504.00338v1
2015-04-17,"Ab initio calculations of the structural, electronic and elastic properties of the MZN2 (M=Be, Mg; Z=C, Si) chalcopyrite semiconductors","Four ternary semiconductors with the chalcopyrite structure (BeCN2, BeSiN2,
MgCN2, and MgSiN2) were studied using the first principles methods. The
structural, electronic, optical and elastic properties were calculated. All
these materials were found to be the indirect band gap semiconductors, with the
calculated band gaps in the range from 3.46 eV to 3.88 eV. Comparison of the
degree of covalency/ionicity of the chemical bonds in these compounds was
performed. Anisotropy of the optical properties of these tetragonal crystals
was demonstrated by calculating the real and imaginary parts of the dielectric
function {\epsilon}. Anisotropy of the elastic properties of these materials
was analyzed by plotting the three-dimensional dependences of the Young moduli
and their two-dimensional cross-sections. It was also shown (at least,
qualitatively) that there exists a correlation between the optical and elastic
anisotropy: the most optically anisotropic MgSiN2 is also most elastically
anisotropic material in the considered group. High hardness (bulk moduli up to
300 GPa) together with large band gaps may lead to new potential applications
of these compounds.",1504.04440v1
2015-04-26,Speed of field driven domain walls in nanowires with large transverse magnetic anisotropy,"Recent analytical and numerical work on field driven domain wall propagation
in nanowires has shown that for large transverse anisotropy and sufficiently
large applied fields the Walker profile becomes unstable before the breakdown
field, giving way to a slower stationary domain wall. We perform an asymptotic
expansion of the Landau Lifshitz Gilbert equation for large transverse magnetic
anisotropy and show that the asymptotic dynamics reproduces this behavior. At
low applied field the speed increases linearly with the field and the profile
is the classic Landau profile. Beyond a critical value of the applied field the
domain wall slows down. The appearance of a slower domain wall profile in the
asymptotic dynamics is due to a transition from a pushed to a pulled front of a
reaction diffusion equation.",1504.06865v1
2015-05-11,Effects of anisotropy in simple lattice geometries on many-body properties of ultracold fermions in optical lattices,"We study the effects of anisotropic hopping amplitudes on quantum phases of
ultracold fermions in optical lattices described by the repulsive Fermi-Hubbard
model. In particular, using dynamical mean-field theory (DMFT) we investigate
the dimensional crossover between the isotropic square and the isotropic cubic
lattice. We analyze the phase transition from the antiferromagnetic to the
paramagnetic state and observe a significant change in the critical
temperature: Depending on the interaction strength, the anisotropy can lead to
both a suppression or increase. We also investigate the localization properties
of the system, such as the compressibility and double occupancy. Using the
local density approximation in combination with DMFT we conclude that density
profiles can be used to detect the mentioned anisotropy-driven transitions.",1505.02733v2
2015-05-14,Sensitivity of full-sky experiments to large scale cosmic ray anisotropies,"The two main advantages of space-based observation of extreme energy
($\gtrsim5\times10^{19}$ eV) cosmic rays (EECRs) over ground based
observatories are the increased field of view and the full-sky coverage with
nearly uniform systematics across the entire sky. The former guarantees
increased statistics, whereas the latter enables a clean partitioning of the
sky into spherical harmonics. The discovery of anisotropies would help to
identify the long sought origin of EECRs. We begin an investigation of the
reach of a full-sky space-based experiment such as EUSO to detect anisotropies
in the extreme-energy cosmic-ray sky compared to ground based partial-sky
experiments such as the Pierre Auger Observatory and Telescope Array. The
technique is explained here, and simulations for a Universe with just two
nonzero multipoles, monopole plus either dipole or quadrupole, are presented.
These simulations quantify the advantages of space-based, all-sky coverage.",1505.03922v1
2015-05-15,Manifestation of proton structure in the initial-state anisotropies in high-energy proton-proton collisions,"Ridge-like correlations in high-energy proton-proton collisions reported by
the CMS collaboration suggest a collective flow that resembles the one in
heavy-ion collisions. If the hydrodynamic description is valid then the effect
results from the initial anisotropy of the colliding matter which depends on
the structure of protons. Following recent theoretical developments, we propose
several phenomenological models of the proton structure and calculate the
anisotropy coefficients using the Monte Carlo Glauber model. Our estimates
suggest that the event multiplicity dependence allows one to discriminate
between different proton models.",1505.04155v4
2015-05-24,Gamma-ray bounds from EAS detectors and heavy decaying dark matter constraints,"The very high energy Galactic $\gamma$-ray sky is partially opaque in the
($0.1-10$) PeV energy range. In the light of the recently detected high energy
neutrino flux by IceCube, a comparable very high energy $\gamma$-ray flux is
expected in any scenario with a sizable Galactic contribution to the neutrino
flux. Here we elaborate on the peculiar energy and anisotropy features imposed
upon these very high energy $\gamma$-rays by the absorption on the cosmic
microwave background photons and Galactic interstellar light. As a notable
application of our considerations, we study the prospects of probing the
PeV-scale decaying DM scenario, proposed as a possible source of IceCube
neutrinos, by extensive air shower (EAS) cosmic ray experiments. In particular,
we show that anisotropy measurements at EAS experiments are already sensitive
to $\tau_{\rm DM}\sim {\cal O}(10^{27})$~s and future measurements, using
better gamma/hadron separation, can improve the limit significantly.",1505.06486v2
2015-05-26,Direction dependent thermal conductivity of monolayer phosphorene: parameterization of Stillinger-Weber potential and molecular dynamics study,"A Stillinger-Weber interatomic potential is parameterized for phosphorene. It
well reproduces the crystal structure, cohesive energy and phonon dispersion
predicted by first-principles calculations. The thermal conductivity of
phosphorene is further explored by equilibrium molecular dynamics simulations
adopting the optimal set of potential parameters. At room temperature, the
intrinsic thermal conductivities along zigzag and armchair directions are about
152.7 and 33.0 W/mK, respectively, with a large anisotropy ratio of five. The
remarkably directional dependence of thermal conductivity in phosphorene,
consistent with previous reports, is mainly due to the strong anisotropy of
phonon group velocities, and weak anisotropy of phonon lifetimes as revealed by
lattice dynamics calculations. Moreover, the effective phonon mean free paths
at zigzag and armchair directions are about 141.4 and 43.4nm, respectively.",1505.06871v1
2015-05-26,"Tunable electronic anisotropy in single-crystal A2Cr3As3 (A = K, Rb) quasi-one-dimensional superconductors","Single crystals of A2Cr3As3 (A = K, Rb) were successfully grown using a
self-flux method and studied via structural, transport and thermodynamic
measurement techniques. The superconducting state properties between the two
species are similar, with critical temperatures of 6.1 K and 4.8 K in K2Cr3As3
and Rb2Cr3As3, respectively. However, the emergence of a strong normal state
electronic anisotropy in Rb2Cr3As3 suggests a unique electronic tuning
parameter is coupled to the inter-chain spacing in the A2Cr3As3 structure,
which increases with alkali metal ionic size while the one-dimensional
[(Cr3As3)^{2-}]_{\infty} chain structure itself remains essentially unchanged.
Together with dramatic enhancements in both conductivity and magnetoresistance
(MR), the appearance of a strong anisotropy in the MR of Rb2Cr3As3 is
consistent with the proposed quasi-one-dimensional character of band structure
and its evolution with alkali metal species in this new family of
superconductors.",1505.07051v2
2015-06-02,Structure and Dynamics of Poly(methacrylic acid) and Its Interpolymer Complex Probed by Covalently Bound Rhodamine-123,"The dynamics and structural characteristics of polymethacrylic acid bound
rhodamine-123 (PMAAR123) and its interpolymer complex with
poly(vinylpyrrolidone) were investigated using single molecular fluorescence
studies. The time resolved fluorescence anisotropy decay of PMAA-R123 at
different pH exhibits an associated anisotropy decay behavior characteristic of
two different environments experienced by the fluorophore and decays with one
shorter and another longer lifetime components. The anisotropy decay retains
normal bi-exponential behavior under neutral pH. Fluorescence correlation
spectroscopic investigation reveals that the attached fluorophore undergoes
hydrolysis under basic condition which results in the release of the
fluorophore from the polymer backbone. Shrinkage in the hydrodynamic radius of
PMAA is observed on addition of the complementary polymer PVP which is
attributed to the formation compact solubilized nanoparticle like aggregates.
The size of particle further decreases on the addition of NaCl. The detailed
results show that these complexes have potential for use as drug-delivery
system under physiological conditions.",1506.01044v2
2015-06-18,Investigation of the Magnetic Model in Multiferroic NdFe$_{3}$(BO$_{3}$)$_{4}$ by Inelastic Neutron Scattering,"We performed inelastic neutron scattering measurements on single crystals of
NdFe$_{3}$($^{11}$BO$_{3}$)$_{4}$ to explore the magnetic excitations, to
establish the underlying Hamiltonian, and to reveal the detailed nature of
hybridization between the 4$f$ and 3$d$ magnetism. The observed spectra
exhibiting a couple of key features, i.e., anti-crossing of Nd- and
Fe-excitations and anisotropy gap at the antiferromagnetic zone center, are
explained by the magnetic model including spin interaction in the framework of
weakly-coupled Fe$^{3+}$ chains, interaction between the Fe$^{3+}$ and
Nd$^{3+}$ moments, and single-ion anisotropy derived from Nd$^{3+}$ crystal
field. The combination of the measurements and calculations reveals that the
hybridization between 4$f$ and 3$d$ magnetism propagates the local magnetic
anisotropy of the Nd$^{3+}$ ion to the Fe$^{3+}$ network, resulting in the bulk
structure of multiferroics.",1506.05569v2
2015-06-21,Quantum Phase Transition and Protected Ideal Transport in a Kondo Chain,"We study the low energy physics of a Kondo chain where electrons from a
one-dimensional band interact with magnetic moments via an anisotropic exchange
interaction. It is demonstrated that the anisotropy gives rise to two different
phases which are separated by a quantum phase transition. In the phase with
easy plane anisotropy, Z$_2$ symmetry between sectors with different helicity
of the electrons is broken. As a result, localization effects are suppressed
and the dc transport acquires (partial) symmetry protection. This effect is
similar to the protection of the edge transport in time-reversal invariant
topological insulators. The phase with easy axis anisotropy corresponds to the
Tomonaga-Luttinger liquid with a pronounced spin-charge separation. The slow
charge density wave modes have no protection against localizatioin.",1506.06368v2
2015-06-22,Event shape sorting,"We propose a novel method for sorting events of multiparticle production
according to the azimuthal anisotropy of their momentum distribution. Although
the method is quite general, we advocate its use in analysis of
ultra-relativistic heavy-ion collisions where large number of hadrons is
produced. The advantage of our method is that it can automatically sort out
samples of events with histograms that indicate similar distributions of
hadrons. It takes into account the whole measured histograms with all orders of
anisotropy instead of a specific observable (e.g. $v_2$, $v_3$, $q_2$). It can
be used for more exclusive experimental studies of flow anisotropies which are
then more easily compared to theoretical calculations. It may also be useful in
the construction of mixed-events background for correlation studies as it
allows to select events with similar momentum distribution.",1506.06776v2
2015-06-25,Impact of momentum-space anisotropy on heavy quark dynamics in a QGP medium,"Momentum space anisotropy present in the quark and gluon distribution
functions in relativistic heavy ion collisions induces Chromo-Weibel
instability in the hot QCD medium created therein. The impact of the
Chromo-Weibel instability on the dynamics of a heavy-quark (HQ) traversing in
the QGP medium is investigated within the framework of kinetic theory by
studying the momentum and temperature behavior of HQ drag and diffusion
coefficients. The physics of anisotropy is captured in an effective Vlasov term
in the transport equation. The effects of the instability are handled by making
a relation with the phenomenologically known jet quenching parameter in RHIC
and LHC. Interestingly, the presence of instability significantly affect the
temperature and momentum dependences of the HQ drag and diffusion coefficients.
These results may have appreciable impact on the experimental observables such
as, the nuclear suppression factor, $R_{AA}(p_T)$, and the elliptic flow,
$v_2(p_T)$, of heavy mesons in heavy ion collisions at RHIC and LHC energies
which is a matter of future investigation.",1506.07805v3
2015-07-06,Delta chain with anisotropic ferromagnetic and antiferromagnetic interactions,"We consider analytically and numerically an anisotropic spin-$\frac{1}{2}$
delta-chain (sawtooth chain) with nearest-neighbor ferromagnetic and
next-nearest-neighbor antiferromagnetic interactions. For certain values of the
interactions a lowest one-particle band becomes flat and there is a class of
localized-magnon eigenstates which form a ground state with a macroscopic
degeneracy. In this case the model depends on a single parameter which can be
chosen as the anisotropy of the exchange interactions. When this parameter
changes from zero to infinity the model interpolates between the
one-dimensional isotropic ferromagnet and the frustrated Ising model on the
delta-chain. It is shown that the low-temperature thermodynamic properties in
these limiting cases are governed by the specific structure of the excitation
spectrum. In particular, the specific heat has one or infinite number of
low-temperature maxima for the small or the large anisotropy parameter,
correspondingly. Numerical calculations of finite chains demonstrate that this
behavior is generic for definite values of the anisotropy parameter.",1507.01389v1
2015-07-07,Anisotropy of iron-platinum-arsenide Ca10(PtnAs8)(Fe2-xPtxAs2)5 single crystals,"The upper critical field Hc2 anisotropy of Ca10(PtnAs8)(Fe2-xPtxAs2)5 (n = 3,
4) single crystals with long FeAs interlayer distance (d) was studied by
angular dependent resistivity measurements. A scaling of the angular dependent
resistivity was realized for both single crystals using the anisotropic
Ginzburg-Landau (AGL) approach with an appropriate anisotropy parameter
{\gamma}. The AGL scaling parameter {\gamma} increases with decreasing
temperature and reaches a value of about 10 at 0.8Tc for both single crystals.
These values are much larger than those of other iron-based superconductors
(FeSCs). Remarkably, the values of {\gamma}2 show an almost linear increase
with the FeAs/FeSe interlayer distance d for FeSCs. Compared to cuprates, FeSCs
are less anisotropic, indicating that two dimensionality of the
superconductivity is intrinsically weak.",1507.01987v1
2015-07-20,Electronic nematic correlations in the stress free tetragonal state of BaFe$_{2-x}$Ni$_{x}$As$_{2}$,"We use transport and neutron scattering to study electronic, structural, and
magnetic properties of the electron-doped BaFe$_{2-x}$Ni$_x$As$_2$ iron
pnictides in the external stress free detwinned state. Using a specially
designed in-situ mechanical detwinning device, we demonstrate that the in-plane
resistivity anisotropy observed in the uniaxial strained tetragonal state of
BaFe$_{2-x}$Ni$_x$As$_2$ below a temperature $T^\ast$, previously identified as
a signature of the electronic nematic phase, is also present in the stress free
tetragonal phase below $T^{\ast\ast}$ ($<T^\ast$). By carrying out neutron
scattering measurements on BaFe$_2$As$_2$ and BaFe$_{1.97}$Ni$_{0.03}$As$_2$,
we argue that the resistivity anisotropy in the stress free tetragonal state of
iron pnictides arises from the magnetoelastic coupling associated with
antiferromagnetic order. These results thus indicate that the local lattice
distortion and nematic spin correlations are responsible for the resistivity
anisotropy in the tetragonal state of iron pnictides.",1507.05423v1
2015-07-23,Photon production from a non-equilibrium quark-gluon plasma,"We calculate leading-order medium photon yields from a quark-gluon plasma
using (3+1)-dimensional anisotropic hydrodynamics. Non-equilibrium corrections
to the photon rate are taken into account using a self-consistent modification
of the particle distribution functions and the corresponding anisotropic
hard-loop fermionic self-energies. We present predictions for the high-energy
photon spectrum and photon elliptic flow as a function of transverse momentum,
shear viscosity, and initial momentum-space anisotropy. Our findings indicate
that high-energy photon production is sensitive to the assumed level of initial
momentum-space anisotropy of the quark-gluon plasma. As a result, it may be
possible to experimentally constrain the early-time momentum-space anisotropy
of the quark-gluon plasma generated in relativistic heavy-ion collisions using
high-energy photon yields.",1507.06605v3
2015-08-05,Anisotropy of the acoustooptic figure of merit for LiNbO3 crystals. Isotropic diffraction,"We have developed the approach for analyzing of anisotropy of acoustooptic
figure of merit (AOFM) for lithium niobate crystals in the case of isotropic
acoustooptic (AO) diffraction. The working relations for the effective
elastooptic coefficients and the AOFM have been derived. We have found that,
under the conditions of isotropic AO diffraction, the maximum AOFM value for
LiNbO3 is equal tp 11.62x10-15s3/kg. It is peculiar for the geometry of AO
interaction of the shear acoustic wave propagating in the YZ plane (the
velocity 3994 m/s) with the optical wave polarized in the same plane. We have
demonstrated that the maximum AOFM values are achieved mainly due to essential
anisotropy and high values of the elastooptic coefficients of LiNbO3.",1508.01075v1
2015-08-10,Standardized compliance matrixes for general anisotropic materials and a simple measure of anisotropy degree based on shear-extension coupling coefficient,"The compliance matrix for a general anisotropic material is usually expressed
in an arbitrarily chosen coordinate system, which brings some confusion or
inconvenience in identifying independent elastic material constants and
comparing elastic properties between different materials. In this paper, a
unique stiffest orientation based standardized (STF-OS) compliance matrix is
established, and 18 independent elastic material constants are clearly shown.
During the searching process for stiffest orientation, it is interesting to
find from our theoretical analysis and an example that a material with
isotropic tensile stiffness does not definitely possess isotropic elasticity.
Therefore the ratio between the maximum and minimum tensile stiffnesses is not
a correct measure of anisotropy degree. Alternatively, a simple and correct
measure of anisotropy degree based on the maximum shear-extension coupling
coefficient in all orientations is proposed.",1508.02105v1
2015-08-10,Strain-Induced Magnetic Anisotropy in Epitaxial Thin Films of the Spinel CoCr$_2$O$_4$,"We show that the magnetic anisotropy in spinel-structure CoCr$_2$O$_4$ thin
films exhibits a strain dependence in which compressive strain induces an
out-of-plane magnetic easy axis and tensile strain an in-plane easy axis,
exactly opposite to the behavior reported for the related compound
CoFe$_2$O$_4$. We use density functional theory calculations within the LSDA+U
approximation to reproduce and explain the observed behavior. Using
second-order perturbation theory, we analyse the anisotropy tensor of the
Co$^{2+}$ ions in both octahedral and tetrahedral coordination, allowing us to
extend our results to spinels with general arrangements of Co$^{2+}$ ions.",1508.02165v1
2015-08-13,Survival rate of initial azimuthal anisotropy in a multi-phase transport model,"We investigate the survival rate of an initial momentum anisotropy
(${v}_2^{ini}$), not spatial anisotropy, to the final state in a multi-phase
transport (AMPT) model in Au+Au collisions at $\sqrt{s_{NN}}$=200~GeV. It is
found that both the final-state parton and charged hadron $v_2$ show a linear
dependence versus $v_2^{ini}\{\rm PP\}$ with respect to the participant plane
(PP). It is found that the slope of this linear dependence (referred to as the
survive rate) increases with transverse momentum ($p_T$), reaching~$\sim$100\%
at $p_T$$\sim$2.5 GeV/c for both parton and charged hadron. The survival rate
decreases with collision centrality and energy, indicating decreasing survival
rate with increasing interactions. It is further found that a $v_2^{ini}\{\rm
Rnd\}$ with respect to a random direction does not survive in $v_2\{\rm PP\}$
but in the two-particle cumulant $v_2\{2\}$. The dependence of $v_2\{2\}$ on
$v_2^{ini}\{\rm Rnd\}$ is quadratic rather than linear.",1508.03215v2
2015-09-09,Current helicity and magnetic field anisotropy in solar active regions,"The electric current helicity density $\displaystyle
\chi=\langle\epsilon_{ijk}b_i\frac{\partial b_k}{\partial x_j}\rangle$ contains
six terms, where $b_i$ are components of the magnetic field. Due to the
observational limitations, only four of the above six terms can be inferred
from solar photospheric vector magnetograms. By comparing the results for
simulation we distinguished the statistical difference of above six terms for
isotropic and anisotropic cases. We estimated the relative degree of anisotropy
for three typical active regions and found that it is of order 0.8 which means
the assumption of local isotropy for the observable current helicity density
terms is generally not satisfied for solar active regions. Upon studies of the
statistical properties of the anisotropy of magnetic field of solar active
regions with latitudes and with evolution in the solar cycle, we conclude that
the consistency of that assumption of local homogeneity and isotropy requires
further analysis in the light of our findings.",1509.02652v1
2015-09-14,Photon and dilepton production from a non-equilibrium quark-gluon plasma,"We calculate leading-order medium photon and dilepton yields from a
quark-gluon plasma using (3+1)-dimensional anisotropic hydrodynamics. In the
case of dileptons, at leading-order it is sufficient to take into account
non-equilibrium corrections to the rate through the use of anisotropic
distribution functions. In the case of photons, non-equilibrium corrections to
the rate are taken into account using a self-consistent modification of the
distribution functions and the corresponding anisotropic hard-loop quark
self-energies. We present predictions for the high-energy photon and dilepton
spectrum and the photon elliptic flow as a function of invariant mass,
transverse momentum, shear viscosity, and initial momentum-space anisotropy.
Our findings indicate that both high-energy photon and dilepton production are
sensitive to the assumed level of initial momentum-space anisotropy of the
quark-gluon plasma. In addition, we find that the photon elliptic flow depends
on the initial momentum-space anisotropy.",1509.04249v1
2015-09-24,Skyrmions in Chiral Magnets with Rashba and Dresselhaus Spin-Orbit Coupling,"Skyrmions are topological spin textures of interest for fundamental science
and applications. Previous theoretical studies have focused on systems with
broken bulk inversion symmetry, where skyrmions are stabilized by easy-axis
anisotropy. We investigate here systems that break surface inversion symmetry,
in addition to possible broken bulk inversion. This leads to two distinct
Dzyaloshinskii-Moriya (DM) terms with strengths $D_\perp$, arising from Rashba
spin-orbit coupling (SOC), and $D_\parallel$ from Dresselhaus SOC. We show that
skyrmions become progressively more stable with increasing
$D_\perp/D_\parallel$, extending into the regime of easy-plane anisotropy. We
find that the spin texture and topological charge density of skyrmions develops
nontrivial spatial structure, with quantized topological charge in a unit cell
given by a Chern number. Our results give a design principle for tuning Rashba
SOC and magnetic anisotropy to stabilize skyrmions in thin films, surfaces,
interfaces and bulk magnetic materials that break mirror symmetry.",1509.07508v2
2015-09-29,Coherent control of group index and magneto-optical anisotropy in a multilevel atomic vapor,"We study electromagnetically induced transparency (EIT) in a heated potassium
vapor cell, using a simple optical setup with a single free-running diode laser
and an acousto-optic modulator. Despite the fact that the Doppler width is
comparable to the ground state hyperfine splitting, transparency windows with
deeply sub-natural line widths and large group indices are obtained. A
longitudinal magnetic field is used to split the EIT feature and induce
magnetooptical anisotropy. Using the beat note between co-propagating coupling
and probe beams, we perform a heterodyne measurement of the circular dichroism
(and therefore birefringence) of the EIT medium. The observed spectra reveal
that lin-par-lin polarizations lead to greater anisotropy than lin-perp-lin. A
simplified analytical model encompassing sixteen Zeeman states and eighteen
\Lamda\ subsytems reproduces the experimental observations.",1509.08776v4
2015-09-30,The origin of anisotropy and high density of states in the electronic structure of Cr$_2$GeC by means of polarized soft X-ray spectroscopy and ab initio calculations,"The anisotropy in the electronic structure of the inherently nanolaminated
ternary phase Cr$_{2}$GeC is investigated by bulk-sensitive and element
selective soft x-ray absorption/emission spectroscopy. The angle-resolved
absorption/emission measurements reveal differences between the in-plane and
out-of-plane bonding at the (0001) interfaces of Cr$_{2}$GeC. The Cr $L_{2,3}$,
C $K$, and Ge $M_{1}$, $M_{2,3}$ emission spectra are interpreted with
first-principles density-functional theory (DFT) including core-to-valence
dipole transition matrix elements. For the Ge $4s$ states, the x-ray emission
measurements reveal two orders of magnitude higher intensity at the Fermi level
than DFT within the General Gradient Approximation (GGA) predicts. We provide
direct evidence of anisotropy in the electronic structure and the orbital
occupation that should affect the thermal expansion coefficient and transport
properties. As shown in this work, hybridization and redistribution of
intensity from the shallow $3d$ core levels to the $4s$ valence band explain
the large Ge density of states at the Fermi level.",1509.09190v1
2015-10-03,Engineering spin-orbit torque in Co/Pt multilayers with perpendicular magnetic anisotropy,"To address thermal stability issues for spintronic devices with a reduced
size, we investigate spin-orbit torque in Co/Pt multilayers with strong
perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from
the global imbalance of the spin currents from the top and bottom interfaces
for each Co layer. By inserting Ta or Cu layers to strengthen the top-down
asymmetry, the spin-orbit torque efficiency can be greatly modified without
compromised perpendicular magnetic anisotropy. Above all, the efficiency builds
up as the number of layers increases, realizing robust thermal stability and
high spin-orbit-torque efficiency simultaneously in the multilayers structure.",1510.00836v1
2015-10-05,On the upper limits for dipole anisotropies in cosmic-ray positrons,"The excess of cosmic-ray positrons in the energy range from 10 GeV to few
hundred GeV reported by PAMELA and AMS experiments is not consistent with a
pure secondary origin and requires the introduction of a source term. The
presence of anisotropies in the positron arrival directions would be a
distinctive signature of their origin. Current measurements are consistent with
isotropy and limits to a dipole anisotropy have been established. In this note,
we review the mathematical basis of this analysis and provide a general bound
to the dipole upper limits achievable from a given sample of events. The
published experimental limits are confronted with this bound.",1510.01221v1
2015-10-06,Unveiling the Origin of the Basal-plane Antiferromagnetism in the Jeff=1/2 Mott Insulator Ba2IrO4: A Density Functional and Model Hamiltonian Study,"Based on the density functional theory and our new model Hamiltonian, we have
studied the basal-plane antiferromagnetism in the novel Jeff=1/2 Mott insulator
Ba2IrO4. By comparing the magnetic properties of the bulk Ba2IrO4 with those of
the single-layer Ba2IrO4, we demonstrate unambiguously that the basal-plane
antiferromagnetism is caused by the intralyer magnetic interactions rather than
by the previously proposed interlayer ones. In order to reveal the origin of
the basal-plane antiferromagnetism, we propose a new model Hamiltonian by
adding the single ion anisotropy and pseudo-quadrupole interactions into the
general bilinear pseudo-spin Hamiltonian. The obtained magnetic interaction
parameters indicate that the single ion anisotropy and pseudo-quadrupole
interactions are unexpectedly strong. Systematical Monte Carlo simulations
demonstrate that the basal-plane antiferromagnetism is caused by the isotropic
Heisenberg, bond-dependent Kitaev and pseudo-quadrupole interactions. Our
results show for the first time that the single ion anisotropy and
pseudo-quadrupole interaction can play significant roles in establishing the
exotic magnetism in the Jeff=1/2 Mott insulator.",1510.01451v1
2015-10-08,Explaining TeV Cosmic-Ray Anisotropies with Non-Diffusive Cosmic-Ray Propagation,"Constraining the behavior of cosmic ray data observed at Earth requires a
precise understanding of how the cosmic rays propagate in the interstellar
medium. The interstellar medium is not homogeneous; although turbulent magnetic
fields dominate over large scales, small coherent regions of magnetic field
exist on scales relevant to particle propagation in the nearby Galaxy. Guided
propagation through a coherent field is significantly different from random
particle diffusion and could be the explanation of spatial anisotropies in the
observed cosmic rays. We present a Monte Carlo code to propagate cosmic
particle through realistic magnetic field structures. We discuss the details of
the model as well as some preliminary studies which indicate that coherent
magnetic structures are important effects in local cosmic-ray propagation,
increasing the flux of cosmic rays by over two orders of magnitude at
anisotropic locations on the sky. The features induced by coherent magnetic
structure could be the cause of the observed TeV cosmic-ray anisotropy.",1510.02487v2
2015-10-29,Indirect switching of vortex polarity through magnetic dynamic coupling,"Magnetic vortex cores exhibit a gyrotropic motion, and may reach a critical
velocity, at which point they invert their z-component of the magnetization. We
performed micromagnetic simulations to describe this vortex core polarity
reversal in magnetic nanodisks presenting a perpendicular anisotropy. We found
that the critical velocity decreases with increasing perpendicular anisotropy,
therefore departing from a universal criterion, that relates this velocity only
to the exchange stiffness of the material. This leads to a critical velocity
inversely proportional to the vortex core radius. We have also shown that in a
pair of interacting disks, it is possible to switch the core vortex polarity
through a non-local excitation; exciting one disk by applying a rotating
magnetic field, one is able to switch the polarity of a neighbor disk, with a
larger perpendicular anisotropy.",1510.08783v1
2015-10-30,Density of states in gapped superconductors with pairing-potential impurities,"We study the density of states in disordered s-wave superconductors with a
small gap anisotropy. Disorder comes in the form of common nonmagnetic
scatterers and pairing-potential impurities, which interact with electrons via
an electric potential and a local distortion of the superconducting gap. A set
of equations for the quasiclassical Green functions is derived and solved.
Within one spin sector, pairing-potential impurities and weak spin-polarized
magnetic impurities have essentially the same effect on the density of states.
We show that if the gap is isotropic, an isolated impurity with suppressed
pairing supports an infinite number of Andreev states. With growing impurity
concentration, the energy-dependent density of states evolves from a sharp gap
edge with an impurity band below it to a smeared BCS singularity in the
so-called universal limit. If a gap anisotropy is present, the density of
states becomes sensitive to ordinary potential disorder, and the existence of
of Andreev states localized at pairing-potential impurities requires special
conditions. An unusual feature related to the anisotropy is a nonmonotonic
dependence of the gap edge smearing on impurity concentration.",1510.09172v1
2015-11-13,Cosmic ray transport and anisotropies to high energies,"A model is introduced, in which the irregularity spectrum of the Galactic
magnetic field beyond the dissipation length scale is first a Kolmogorov
spectrum $k^{-5/3}$ at small scales $\lambda \, = \, 2 \pi/k$ with $k$ the
wave-number, then a saturation spectrum $k^{-1}$, and finally a shock-dominated
spectrum $k^{-2}$ mostly in the halo/wind outside the Cosmic Ray disk. In an
isotropic approximation such a model is consistent with the Interstellar Medium
(ISM) data. With this model we discuss the Galactic Cosmic Ray (GCR) spectrum,
as well as the extragalactic Ultra High Energy Cosmic Rays (UHECRs), their
chemical abundances and anisotropies. UHECRs may include a proton component
from many radio galaxies integrated over vast distances, visible already below
3 EeV.",1511.04229v1
2015-11-23,Spin-orbit coupling controlled ground state in Sr$_2$ScOsO$_6$,"We report neutron scattering experiments which reveal a large spin gap in the
magnetic excitation spectrum of weakly-monoclinic double perovskite Sr2ScOsO6.
The spin gap is demonstrative of appreciable spin-orbit-induced anisotropy,
despite nominally orbitally-quenched 5d3 Os5+ ions. The system is successfully
modeled including nearest neighbor interactions in a Heisenberg Hamiltonian
with exchange anisotropy. We find that the presence of the spin-orbit-induced
anisotropy is essential for the realization of the type I antiferromagnetic
ground state. This demonstrates that physics beyond the LS or JJ coupling
limits plays an active role in determining the collective properties of 4d3 and
5d3 systems, and that theoretical treatments must include spin-orbit coupling.",1511.07486v3
2015-11-24,Magnetic domain walls in nanostrips of single-crystalline $\mathrm{Fe}_4\mathrm{N}(001)$ thin films with fourfold in-plane magnetic anisotropy,"We investigated head-to-head domain walls in nanostrips of epitaxial
$\mathrm{Fe}_4\mathrm{N}(001)$ thin films, displaying a fourfold magnetic
anisotropy. Magnetic force microscopy and micromagnetic simulations show that
the domain walls have specific properties, compared to soft magnetic materials.
In particular, strips aligned along a hard axis of magnetization are wrapped by
partial flux-closure concertina domains below a critical width, while
progressively transforming to zigzag walls for wider strips. Transverse walls
are favored upon initial application of a magnetic field transverse to the
strip, while transformation to a vortex walls is favored upon motion under a
longitudinal magnetic field. In all cases the magnetization texture of such
fourfold anisotropy domain walls exhibits narrow micro-domain walls, which may
give rise to peculiar spin-transfer features.",1511.07520v1
2015-12-02,Strain-activated structural anisotropy in BaFe2As2,"High-resolution single crystal neutron diffraction measurements are presented
probing the magnetostructural response to uniaxial pressure in the iron
pnictide parent system BaFe2As2. Scattering data reveal a strain-activated,
anisotropic broadening of nuclear Bragg reflections, which increases upon
cooling below the resolvable onset of global orthorhombicity. This anisotropy
in lattice coherence continues to diverge until a lower temperature scale---the
first-order onset of antiferromagnetism---is reached. Our data suggest that
antiferromagnetism and strong magnetoelastic coupling drive the
strain-activated lattice response in this material and that the development of
anisotropic lattice coherence under strain is the physical origin for the
anomalous nematic anisotropy in this compound.",1512.00782v2
2015-12-07,Exact results for model wave functions of anisotropic composite fermions in the fractional quantum Hall effect,"The microscopic wave functions of the composite fermion theory can
incorporate electron mass anisotropy by a trivial rescaling of the coordinates.
These wave functions are very likely adiabatically connected to the actual wave
functions of the anisotropic fractional quantum Hall states. We show in this
article that they possess the nice property that their energies can be
analytically related to the previously calculated energies for the isotropic
states through a universal scale factor, thus allowing an estimation of several
observables in the thermodynamic limit for all fractional quantum Hall states.
The rather weak dependence of the scale factor on the anisotropy provides
insight into why fractional quantum Hall effect and composite fermions are
quite robust to electron mass anisotropy. We discuss how better, though still
approximate, wave functions can be obtained by introducing a variational
parameter, following Haldane [Phys. Rev. Lett. {\bf 107}, 116801 (2011)], but
the resulting wave functions are not readily amenable to calculations. Our
considerations are also applicable, with minimal modification, to the case
where the dielectric function of the background material is anisotropic.",1512.01894v2
2015-12-07,Origin of the DC and AC conductivity anisotropy in iron-based superconductors: scattering rate versus spectral weight effects,"To shed light on the mechanism responsible for the in-plane resistivity
anisotropy in the nematic phase of the iron-based superconductors, we
investigate the impact of spin fluctuations on the anisotropic AC conductivity.
On the one hand, the scattering of electrons off magnetic fluctuations causes
an anisotropic scattering rate. On the other hand, the accompanying Fermi
velocity renormalization contributes to both the plasma frequency and the
scattering rate in antagonistic ways, giving rise to anisotropies in these
quantities that exactly cancel each other in the DC limit. As a result, the
effective scattering rate changes its sign as function of temperature, but the
DC conductivity retains the same sign, in agreement with recent experiments.",1512.02259v2
2015-12-08,Atomistic Simulation of frictional anisotropy on quasicrystal approximant surfaces,"Park {\it et al.} have reported eight times greater atomic-scale friction in
the periodic than in the quasiperiodic direction on the two-fold face of a
decagonal Al-Ni-Co quasicrystal. We present results of molecular-dynamics
simulations intended to elucidate mechanisms behind this giant frictional
anisotropy. Simulations of a bare atomic-force-microscope tip on several model
substrates and under a variety of conditions failed to reproduce experimental
results. On the other hand, including the experimental passivation of the tip
with chains of hexadecane thiol, we reproduce qualitatively the experimental
anisotropy in friction, finding evidence for entrainment of the organic chains
in surface furrows parallel to the periodic direction.",1512.02305v2
2015-12-14,Magnetic critical properties and basal-plane anisotropy of Sr$_2$IrO$_4$,"The anisotropic magnetic properties of Sr$_2$IrO$_4$ are investigated, using
longitudinal and torque magnetometry. The critical scaling across $T_c$ of the
longitudinal magnetization is the one expected for the 2D XY universality
class. Modeling the torque for a magnetic field in the basal-plane, and taking
into account all in-plane and out-of-plane magnetic couplings, we derive the
effective 4-fold anisotropy $K_4 \approx$ 1 10$^5$ erg mole$^{-1}$. Although
larger than for the cuprates, it is found too small to account for a
significant departure from the isotropic 2D XY model. The in-plane torque also
allows us to put an upper bound for the anisotropy of a field-induced shift of
the antiferromagnetic ordering temperature.",1512.04448v1
2015-12-30,Cross-field transport and pitch-angle anisotropy of solar energetic particles in MHD turbulence,"Recent modelling of solar energetic particles (SEPs) propagation through the
heliospheric turbulence, also discussed in this workshop, has investigated the
role of the pitch-angle scattering and the perpendicular transport in spreading
particles in heliolongitude, as shown by multi-spacecraft measurements (STEREO
A/B, ACE, SOHO, etc.) at 1 AU in various energy ranges. In some events the
first-order pitch-angle anisotropy of the particles distribution is
not-negligible. We calculate the average perpendicular displacement due to the
gradient/curvature drift in an inhomogeneous turbulence accounting for
pitch-angle dependence for two MHD turbulence models: (a) 3-D isotropic, (b)
anisotropic as conjectured by Goldreich-Sridhar. We find in both cases that the
drift scales as $(1-\mu^2)^2$ with the cosine of pitch-angle $\mu$, in contrast
with previous models for transport of SEPs. This result can impact the models
of propagation of SEPs through the heliosphere.",1512.08973v1
2016-01-05,Anisotropic parton escape is the dominant source of azimuthal anisotropy in transport models,"We trace the development of elliptic anisotropy (v2) via parton-parton
collision history in two transport models. The parton v2 is studied as a
function of the number of collisions of each parton in Au+Au and d+Au
collisions at sNN =200 GeV. It is found that the majority of v2 comes from the
anisotropic escape probability of partons, with no fundamental difference at
low and high transverse momenta. The contribution to v2 from hydrodynamic-type
collective flow is found to be small. Only when the parton-parton cross-section
is set unrealistically large does this contribution start to take over. Our
findings challenge the current paradigm emerged from hydrodynamic comparisons
to anisotropy data.",1601.00878v2
2016-01-10,"Interfacial Dzyaloshinskii-Moriya interaction, surface anisotropy energy,and spin pumping at spin orbit coupled Ir/Co interface","The interfacial Dzyaloshinskii-Moriya interaction (iDMI), surface anisotropy
energy, and spin pumping at the Ir/Co interface are experimentally investigated
by performing Brillouin light scattering. Contrary to previous reports, we
suggest that the sign of the iDMI at the Ir/Co interface is the same as in the
case of the Pt/Co interface. We also find that the magnitude of the iDMI energy
density is relatively smaller than in the case of the Pt/Co interface, despite
the large strong spin-orbit coupling (SOC) of Ir. The saturation magnetization
and the perpendicular magnetic anisotropy (PMA) energy are significantly
improved due to a strong SOC. Our findings suggest that an SOC in an Ir/Co
system behaves in different ways for iDMI and PMA. Finally, we determine the
spin pumping effect at the Ir/Co interface, and it increases the Gilbert
damping constant from 0.012 to 0.024 for 1.5 nmthick Co.",1601.02210v3
2016-01-12,Domain configurations in Co/Pd and L10-FePt nanowire arrays with perpendicular magnetic anisotropy,"Perpendicular magnetic anisotropy [Co/Pd]15 and L10-FePt nanowire arrays of
period 63 nm with linewidths 38 nm and 27 nm and film thickness 27 nm and 20 nm
respectively were fabricated using a self-assembled PS-b-PDMS diblock copolymer
film as a lithographic mask. The wires are predicted to support Neel walls in
the Co/Pd and Bloch walls in the FePt. Magnetostatic interactions from nearest
neighbor nanowires promote a ground state configuration consisting of
alternating up and down magnetization in adjacent wires. This was observed over
~75% of the Co/Pd wires after ac-demagnetization but was less prevalent in the
FePt because the ratio of interaction field to switching field was much
smaller. Interactions also led to correlations in the domain wall positions in
adjacent Co/Pd nanowires. The reversal process was characterized by nucleation
of reverse domains, followed at higher fields by propagation of the domains
along the nanowires. These narrow wires provide model system for exploring
domain wall structure and dynamics in perpendicular anisotropy systems.",1601.02735v1
2016-02-01,Higher order test of Lorentz invariance with an optical ring cavity,"We have developed an apparatus to search for the higher-order Lorentz
violation in photons by measuring the resonant frequency difference between two
counterpropagating directions of an asymmetric optical ring cavity. From the
year-long data taken between 2012 and 2013, we found no evidence for the light
speed anisotropy at the level of $\delta c/c \lesssim 10^{-15}$. Limits on the
dipole components of the anisotropy are improved by more than an order of
magnitude, and limits on the hexapole components are obtained for the first
time. An overview of our apparatus and the data analysis in the framework of
the spherical harmonics decomposition of anisotropy are presented. We also
present the status of the recent upgrade of the apparatus.",1602.00391v1
2016-02-03,Dynamic Error in Strain Induced Magnetization Reversal of Nanomagnets due to Incoherent Switching and Formation of Metastable States: A Size-dependent Study,"Modulation of stress anisotropy of magnetostrictive nanomagnets with strain
offers an extremely energy-efficient method of magnetization reversal. The
reversal process, however, is often incoherent and hence error-prone in the
presence of thermal noise at room temperature. Occurrence of incoherent
metastable states in the potential landscape of the nanomagnet can further
exacerbate the error. Stochastic micromagnetic simulations at room temperature
are used to understand and calculate energy dissipations and switching error
probabilities in this important magnetization switching methodology. We find
that these quantities have an intriguing dependence on nanomagnet size: small
nanomagnets perform better owing to the fact that they are more resilient to
the formation of metastable states and magnetization dynamics in them is more
coherent. However, for a fixed stress anisotropy energy density, smaller
nanomagnets will also have poorer resilience against thermal instability. Thus,
the challenge in straintronics is to maximize the stress anisotropy energy
density by developing materials and processes that yield the largest
magnetostriction.",1602.01491v2
2016-02-06,Testing the isotropy of the Hubble expansion,"We have used the Union2.1 SNIa compilation to search for possible Hubble
expansion anisotropies, dividing the sky in 9 solid angles containing roughly
the same number of SNIa, as well as in the two Galactic hemispheres. We
identified only one sky region, containing 82 SNIa (~15% of total sample with
$z>0.02$), that indeed appears to share a significantly different Hubble
expansion than the rest of the sample. However, this behavior appears to be
attributed to the joint ""erratic"" behavior of only three SNIa and not to an
anisotropic expansion. We also find that the northern and southern galactic
hemispheres have different cosmological parameter solutions but still not
significant enough to assert the detection of a Hubble expansion anisotropy. We
conclude that even a few outliers can have such an effect as to induce
artificial indications of anisotropies, when the number of analysed SNIa is
relatively small.",1602.02310v1
2016-02-15,Decoherence wave in magnetic systems and creation of Néel antiferromagnetic state by measurement,"The interplay between the singlet ground state of the antiferromagnetic
Heisenberg model and the experimentally measured N\'eel state of
antiferromagnets is studied. To verify the hypothesis [M. I. Katsnelson et al.,
Phys. Rev. B 63, 212404 (2001)] that the latter can be considered to be a
result of local measurements destroying the entanglement of the quantum ground
state, we have performed systematic simulations of the effects of von
Neumannmeasurements for the case of a one-dimensional antiferromagnetic
spin-1/2 system for various types and degrees of magnetic anisotropies. It is
found that in the ground state, a magnetization measurement can create
decoherence waves [M. I. Katsnelson et al. Phys. Rev. A 62, 022118 (2000)] in
the magnetic sublattices, and that a symmetry breaking anisotropy does not lead
to alignment of the spins in a particular direction. However, for an easy-axis
anisotropy of the same order magnitude as the exchange constant, a measurement
on the singlet ground state can create N\'eel-ordering in finite systems of
experimentally accessible size.",1602.04703v1
2016-02-20,Simultaneous Evidence for Pauli Paramagnetic Effects and Multiband Superconductivity in KFe$_2$As$_2$ by Small-Angle Neutron Scattering Studies of the Vortex Lattice,"We study the intrinsic anisotropy of the superconducting state in
KFe$_2$As$_2$, using small-angle neutron scattering to image the vortex lattice
as the applied magnetic field is rotated towards the FeAs crystalline planes.
The anisotropy is found to be strongly field dependent, indicating multiband
superconductivity. Furthermore, the high field anisotropy significantly exceeds
that of the upper critical field, providing further support for Pauli limiting
in KFe$_2$As$_2$ for field applied in the basal plane. The effect of Pauli
paramagnetism on the unpaired quasiparticles in the vortex cores is directly
evident from the ratio of scattered intensities due to the longitudinal and
transverse vortex lattice field modulation.",1602.06463v1
2016-02-24,Lattice Boltzmann simulations of 3D crystal growth: Numerical schemes for a phase-field model with anti-trapping current,"A lattice-Boltzmann (LB) scheme, based on the Bhatnagar-Gross-Krook (BGK)
collision rules is developed for a phase-field model of alloy solidification in
order to simulate the growth of dendrites. The solidification of a binary alloy
is considered, taking into account diffusive transport of heat and solute, as
well as the anisotropy of the solid-liquid interfacial free energy. The
anisotropic terms in the phase-field evolution equation, the phenomenological
anti-trapping current (introduced in the solute evolution equation to avoid
spurious solute trapping), and the variation of the solute diffusion
coefficient between phases, make it necessary to modify the equilibrium
distribution functions of the LB scheme with respect to the one used in the
standard method for the solution of advection-diffusion equations. The effects
of grid anisotropy are removed by using the lattices D3Q15 and D3Q19 instead of
D3Q7. The method is validated by direct comparison of the simulation results
with a numerical code that uses the finite-difference method. Simulations are
also carried out for two different anisotropy functions in order to demonstrate
the capability of the method to generate various crystal shapes.",1602.07483v1
2016-02-25,Nonequilibrium current-carrying steady states in the anisotropic $XY$ spin chain,"Out-of-equilibrium behavior is explored in the one-dimensional anisotropic
$XY$ model. Initially preparing the system in the isotropic $XX$ model with a
linearly varying magnetic field to create a domain-wall magnetization profile,
dynamics is generated by rapidly changing the exchange interaction anisotropy
and external magnetic field. Relaxation to a nonequilibrium steady state is
studied analytically at the critical transverse Ising point, where correlation
functions may be computed in closed form. For arbitrary values of anisotropy
and external field, an effective generalized Gibbs' ensemble is shown to
accurately describe observables in the long-time limit. Additionally, we find
spatial oscillations in the exponentially decaying, transverse spin-spin
correlation functions with wavelength set by the magnetization jump across the
initial domain wall. This wavelength depends only weakly on anisotropy and
magnetic field in contrast to the current, which is highly dependent on these
parameters.",1602.08027v2
2016-03-02,Voltage controlled core reversal of fixed magnetic skyrmions without a magnetic field,"Using micromagnetic simulations we demonstrate core reversal of a fixed
magnetic skyrmion by modulating the perpendicular magnetic anisotropy of a
nanomagnet with an electric field. We can switch reversibly between two
skyrmion states and two ferromagnetic states, i.e. skyrmion states with the
magnetization of the core pointing down/up and periphery pointing up/down, and
ferromagnetic states with magnetization pointing up/down, by sequential
increase and decrease of the perpendicular magnetic anisotropy. The switching
between these states is explained by the fact that the spin texture
corresponding to each of these stable states minimizes the sum of the magnetic
anisotropy, demagnetization, Dzyaloshinskii-Moriya interaction (DMI) and
exchange energies. This could lead to the possibility of energy efficient
nanomagnetic memory and logic devices implemented with fixed skyrmions without
using a magnetic field and without moving skyrmions with a current.",1603.00927v1
2016-03-03,Giant isotropic Nernst effect in an anisotropic Kondo semimetal,"The ""failed Kondo insulator"" CeNiSn has long been suspected to be a nodal
metal, with a node in the hybridization matrix elements. Here we carry out a
series of Nernst effect experiments to delineate whether the severely
anisotropic magnetotransport coefficients do indeed derive from a nodal metal
or can simply be explained by a highly anisotropic Fermi surface. Our
experiments reveal that despite an almost 20-fold anisotropy in the Hall
conductivity, the large Nernst signal is isotropic. Taken in conjunction with
the magnetotransport anisotropy, these results provide strong support for an
isotropic Fermi surface with a large anisotropy in quasiparticle mass derived
from a nodal hybridization.",1603.01258v1
2016-03-08,Gravitational Baryogenesis after Anisotropic Inflation,"The gravitational baryogensis may not generate a sufficient baryon asymmetry
in the standard thermal history of the Universe when we take into account the
gravitino problem. Hence it has been suggested that anisotropy of the Universe
can enhance the generation of the baryon asymmetry through the increase of the
time change of the Ricci scalar curvature. We study the gravitational
baryogenesis in the presence of anisotropy, which is produced at the end of an
anisotropic inflation. Although we confirm that the generated baryon asymmetry
is enhanced compared with the original isotropic cosmological model, taking
into account the constraint on the anisotropy by the recent CMB observations,
we find that it is still difficult to obtain the observed baryon asymmetry only
through the gravitational baryogenesis without suffering from the gravitino
problem.",1603.02403v2
2016-03-10,Stability and dynamics of anisotropically-tumbling chemotactic swimmers,"Micro-swimmers such as bacteria perform random walks known as run-and-tumbles
to move up chemo-attractant gradients and as a result aggregate with others. It
is also known that such micro-swimmers can self-organize into macroscopic
patterns due to interactions with neighboring cells through the fluidic
environment they live in. While the pattern formation resulting from
chemotactic and hydrodynamic interactions separately and together have been
previously investigated, the effect of the anisotropy in the tumbles of
micro-swimmers has been unexplored. Here we show through linear analysis and
full nonlinear simulations that the slight anisotropy in the individual swimmer
tumbles can alter the collective pattern formation in non-trivial ways. We show
that tumbling anisotropy diminishes the magnitude of the chemotactic aggregates
but may result in more such aggregation peaks.",1603.03249v3
2016-04-02,Ground-State Phase Diagram of the Bond-Alternating $S=2$ Quantum Spin Chain with the $XXZ$ and On-Site Anisotropies -- Symmetry Protected Topological Phase versus Trivial Phase,"We investigate the ground-state phase diagram of the bond-alternating $S=2$
quantum spin chain with the $XXZ$ and on-site anisotropies. For the on-site
anisotropies, in addition to the popular $D_2 \sum_j (S_j^z)^2$ term, we
consider the $D_4 \sum_j (S_j^z)^4$ term. Mainly we use the exact
diagonalization and the level spectroscopy analysis. We show that the Haldane
state, large-$D$ state and the Dimer2 state belong to the same trivial phase,
by finding the existence of adiabatic paths directly connecting these states
without the quantum phase transition. Similarly, we show that the
intermediate-$D$ state and the Dimer1 state belong to the same symmetry
protected topological phase.",1604.00452v1
2016-04-09,Anisotropy of in-plane hole g-factor in CdTe/ZnTe quantum dots,"Optical studies of a bright exciton provide only limited information about
the hole anisotropy in a quantum dot. In this work we present a universal
method to study heavy hole anisotropy using a dark exciton in a moderate
in-plane magnetic field. By analysis of the linear polarization of the dark
exciton photoluminescence we identify both isotropic and anisotropic
contributions to the hole g-factor. We employ this method for a number of
individual self-assembled CdTe/ZnTe quantum dots, demonstrating a variety of
behaviors of in-plane hole g-factor: from almost fully anisotropic to almost
isotropic. We conclude that, in general, both contributions play an important
role and neither contribution can be neglected.",1604.02591v1
2016-04-11,All-Optical Study of Tunable Ultrafast Spin Dynamics in [Co/Pd]-NiFe Systems: The Role of Spin-Twist Structure on Gilbert Damping,"We investigate optically induced ultrafast magnetization dynamics in [Co(0.5
nm)/Pd(1 nm)]x5/NiFe(t) exchange-spring samples with tilted perpendicular
magnetic anisotropy using a time-resolved magneto-optical Kerr effect
magnetometer. The competition between the out-of-plane anisotropy of the hard
layer, the in-plane anisotropy of the soft layer and the applied bias field
reorganizes the spins in the soft layer, which are modified further with the
variation in t. The spin-wave spectrum, the ultrafast demagnetization time, and
the extracted damping coefficient all depend on the spin distribution in the
soft layer, while the latter two also depend on the spin-orbit coupling between
the Co and Pd layers. The spin-wave spectra change from multimode to
single-mode as t increases. At the maximum field reached in this study, H=2.5
kOe, the damping shows a nonmonotonic dependence on t with a minimum at t=7.5
nm. For t<7.5 nm, intrinsic effects dominate, whereas for t>7.5 nm, extrinsic
effects govern the damping mechanisms.",1604.02998v1
2016-04-11,Edge anisotropy and the geometric perspective on flow networks,"Spatial networks have recently attracted great interest in various fields of
research. While the traditional network-theoretic viewpoint is commonly
restricted to their topological characteristics (often disregarding existing
spatial constraints), this work takes a geometric perspective, which considers
vertices and edges as objects in a metric space and quantifies the
corresponding spatial distribution and alignment. For this purpose, we
introduce the concept of edge anisotropy and define a class of measures
characterizing the spatial directedness of connections. Specifically, we
demonstrate that the local anisotropy of edges incident to a given vertex
provides useful information about the local geometry of geophysical flows based
on networks constructed from spatio-temporal data, which is complementary to
topological characteristics of the same flow networks. Taken both structural
and geometric viewpoints together can thus assist the identification of
underlying flow structures from observations of scalar variables.",1604.03100v1
2016-05-07,Order-by-disorder effects in antiferromagnets on face-centered cubic lattice,"We discuss the role of quantum fluctuations in Heisenberg antiferromagnets on
face-centered cubic lattice with small dipolar interaction in which the
next-nearest-neighbor exchange coupling dominates over the nearest-neighbor
one. It is well known that a collinear magnetic structure which contains (111)
ferromagnetic planes arranged antiferromagnetically along one of the space
diagonals of the cube is stabilized in this model via order-by-disorder
mechanism. On the mean-field level, the dipolar interaction forces spins to lie
within (111) planes. By considering 1/S - corrections to the ground state
energy, we demonstrate that quantum fluctuations lead to an anisotropy within
(111) planes favoring three equivalent directions for the staggered
magnetization (e.g., $[11\overline{2}]$, $[1\overline{2}1]$, and
$[\overline{2}11]$ directions for (111) plane). Such in-plane anisotropy was
obtained experimentally in related materials MnO, $\alpha$-MnS, $\alpha$-MnSe,
EuTe, and EuSe. We find that the order-by-disorder mechanism can contribute
significantly to the value of the in-plane anisotropy in EuTe. Magnon spectrum
is also derived in the first order in 1/S.",1605.02208v2
2016-05-12,Near isotropic behaviour of turbulent thermal convection,"We investigate the anisotropy in turbulent convection in a 3D box using
direct numerical simulation. We compute the anisotropic parameter $A =
u_\perp^{2}/(2u_{\parallel}^{2})$, where $u_{\perp}$ and $u_{\parallel}$ are
the components of velocity perpendicular and parallel to the buoyancy
direction, the shell and ring spectra, and shell-to-shell energy transfers. We
observe that the flow is nearly isotropic for the Prandtl number $\mathrm{Pr}
\approx 1$, but the anisotropy increases with the Prandtl number. For
$\mathrm{Pr}=\infty$, $A \approx 0.3$, thus anisotropy is not very significant
even in extreme cases. We also observe that $u_{\parallel}$ feeds energy to
$u_{\perp}$ via pressure. The computation of shell-to-shell energy transfers
reveals that the energy transfer in turbulent convection is local and forward,
similar to hydrodynamic turbulence. These results are consistent with the
Kolmogorov's spectrum observed by Kumar et al.~[Phys. Rev. E {\bf 90}, 023016
(2014)] for turbulent convection.",1605.03725v2
2016-05-20,Deciphering the Dipole Anisotropy of Galactic Cosmic Rays,"Recent measurements of the dipole anisotropy in the arrival directions of
Galactic cosmic rays (CRs) indicate a strong energy dependence of the dipole
amplitude and phase in the TeV-PeV range. We argue here that these observations
can be well understood within standard diffusion theory as a combined effect of
(i) one or more local sources at Galactic longitude 120deg < l < 300deg
dominating the CR gradient below 0.1-0.3 PeV, (ii) the presence of a strong
ordered magnetic field in our local environment, (iii) the relative motion of
the solar system, and (iv) the limited reconstruction capabilities of
ground-based observatories. We show that an excellent candidate of the local CR
source responsible for the dipole anisotropy at 1-100 TeV is the Vela supernova
remnant.",1605.06446v2
2016-05-26,Tensor Squeezed Limits and the Higuchi Bound,"We point out that tensor consistency relations-i.e. the behavior of
primordial correlation functions in the limit a tensor mode has a small
momentum-are more universal than scalar consistency relations. They hold in the
presence of multiple scalar fields and as long as anisotropies are diluted
exponentially fast. When de Sitter isometries are approximately respected
during inflation this is guaranteed by the Higuchi bound, which forbids the
existence of light particles with spin: De Sitter space can support scalar hair
but no curly hair. We discuss two indirect ways to look for the violation of
tensor con- sistency relations in observations, as a signature of models in
which inflation is not a strong isotropic attractor, such as solid inflation:
(a) Graviton exchange contribution to the scalar four-point function; (b)
Quadrupolar anisotropy of the scalar power spectrum due to super-horizon tensor
modes. This anisotropy has a well-defined statistics which can be distinguished
from cases in which the background has a privileged direction.",1605.08424v2
2016-06-08,Observing magnetic anisotropy in electronic transport through individual single-molecule magnets,"We review different electron transport methods to probe the magnetic
properties, such as the magnetic anisotropy, of an individual Fe4 SMM. The
different approaches comprise first and higher order transport through the
molecule. Gate spectroscopy, focusing on the charge degeneracy-point, is
presented as a robust technique to quantify the longitudinal magnetic
anisotropy of the SMM in different redox states. We provide statistics showing
the robustness and reproducibility of the different methods. In addition,
conductance measurements typically show high-energy excited states well beyond
the ground spin multiplet of SMM. Some of these excitations have their origin
in excited spin multiplets, others in vibrational modes of the molecule. The
interplay between vibrations, charge and spin may yield a new approach for spin
control.",1606.02572v1
2016-06-20,Tamm-Langmuir surface waves,"In this work we develop a theory of surface electromagnetic waves localized
at the interface of periodic metal-dielectric structures. We have shown that
the anisotropy of plasma frequency in metal layers lifts the degeneracy of
plasma oscillations and opens a series of photonic band gaps. This results in
appearance of surface waves with singular density of states - we refer to them
as Tamm-Langmuir waves. Such naming is natural since we have found that their
properties are very similar to the properties of both bulk Langmuir and surface
Tamm waves. Depending on the anisotropy parameters, Tamm-Langmuir waves can be
either forward or backward waves. Singular density of states and high
sensitivity of the dispersion to the anisotropy of the structure makes
Tamm-Langmuir waves very promising for potential applications in nanophotonics
and biosensing.",1606.05928v1
2016-07-18,Anisotropic composite fermions and fractional quantum Hall effect,"We study the role of anisotropy on the transport properties of composite
fermions near Landau level filling factor $\nu=1/2$ in two-dimensional holes
confined to a GaAs quantum well. By applying a parallel magnetic field, we tune
the composite fermion Fermi sea anisotropy and monitor the relative change of
the transport scattering time at $\nu=1/2$ along the principal directions.
Interpreted in a simple Drude model, our results suggest that the scattering
time is longer along the longitudinal direction of the composite fermion Fermi
sea. Furthermore, the measured energy gap for the fractional quantum Hall state
at $\nu=2/3$ decreases when anisotropy becomes significant. The decrease,
however, might partly stem from the charge distribution becoming bilayer-like
at very large parallel magnetic fields.",1607.05163v2
2016-07-21,Effect of annealing on the interfacial Dzyaloshinskii-Moriya interaction in Ta/CoFeB/MgO trilayers,"The interfacial Dzyaloshinskii-Moriya interaction (DMI) has been shown to
stabilize homochiral N\'eel-type domain walls in thin films with perpendicular
magnetic anisotropy and as a result permit them to be propagated by a spin Hall
torque. In this study, we demonstrate that in Ta/Co$_{20}$Fe$_{60}$B$_{20}$/MgO
the DMI may be influenced by annealing. We find that the DMI peaks at
$D=0.057\pm0.003$ mJ/m$^{2}$ at an annealing temperature of 230 $^{\circ}$C.
DMI fields were measured using a purely field-driven creep regime domain
expansion technique. The DMI field and the anisotropy field follow a similar
trend as a function of annealing temperature. We infer that the behavior of the
DMI and the anisotropy are related to interfacial crystal ordering and B
expulsion out of the CoFeB layer as the annealing temperature is increased.",1607.06405v1
2016-07-25,Amplification of the diamagnetic response in small Hubbard rings,"In this paper, we present a study of the electric transport properties of
small discrete rings with $3\leq N\leq 6$ sites and $N_{e}<2N$ electrons, which
can be seen as a simplified version of real aromatic molecules. In particular,
the ring with six sites and six electrons is our prototype of the benzene
molecule. It is already known that the Hubbard model itself cannot account for
the anisotropy of the diamagnetic susceptibility of the aromatic molecules,
which is observed when they are subjected to an external magnetic field
perpendicular to their basal plane. Therefore, we propose an extension of the
Hubbard model, with an ad hoc extra interaction term, with two adjustable
parameters. Our results show that this extension of the Hubbard model is able
to amplify the persistent currents established in the ground state of our rings
and, moreover, promotes an enhancement of the magnetic susceptibility
anisotropy depending on the tuning of the adjustable parameters. In particular,
for the prototype of the benzene molecule, we recover the order of magnitude of
the diamagnetic anisotropy measured for this molecule.",1607.07473v1
2016-07-29,An Asymptotic Preserving method for strongly anisotropic diffusion equations based on field line integration,"In magnetized plasma, the magnetic field confines the particles around the
field lines. The anisotropy intensity in the viscosity and heat conduction may
reach the order of $10^{12}$. When the boundary conditions are periodic or
Neumann, the strong diffusion leads to an ill-posed limiting problem. To remove
the ill-conditionedness in the highly anisotropic diffusion equations, we
introduce a simple but very efficient asymptotic preserving reformulation in
this paper. The key idea is that, instead of discretizing the Neumann boundary
conditions locally, we replace one of the Neumann boundary condition by the
integration of the original problem along the field line, the singular
$1/\epsilon$ terms can be replaced by $O(1)$ terms after the integration, so
that yields a well-posed problem. Small modifications to the original code are
required and no change of coordinates nor mesh adaptation are needed.
  Uniform convergence with respect to the anisotropy strength $1/\epsilon$ can
be observed numerically and the condition number does not scale with the
anisotropy.",1608.00541v1
2016-07-29,Mesostructure anisotropy of bacterial cellulose-polyacrylamide hydrogels as studied by spin-echo small-angle neutron scattering,"The submicron- and micron-scale structures of composite hydrogels based on
bacterial cellulose (BC) and polyacrylamide were studied by spin-echo
small-angle neutron scattering (SESANS). These hydrogels were synthesized via
free-radical polymerization of acrylamide carried out in pellicle of BC swollen
in the reaction solution. No neutron scattering was observed for the samples
swollen in heavy water to the equilibrium state, but a SESANS signal appeared
when TbCl$_{3}$ salt was added to the solvent. The SESANS dependences obtained
for these samples revealed the anisotropy of mesostructure for the hydrogels
under investigation. Density inhomogeneities on the characteristic scale of
11.5 $\pm$ 0.5 $\mu$m were detected in one specific orientation of the sample,
i.e. with growth plane of BC parallel to plane formed by neutron beam and
spin-echo length. The uniaxial anisotropy revealed agrees with the proposed
model, which attributes this behavior to the existence of the tunnel-like
oriented structures inside BC.",1608.00544v1
2016-08-03,Stiffer double-stranded DNA in two-dimensional confinement due to bending anisotropy,"Using analytical approach and Monte-Carlo (MC) simulations, we study the
elastic behaviour of the intrinsically twisted elastic ribbons with bending
anisotropy, such as double-stranded DNA (dsDNA), in two-dimensional (2D)
confinement. We show that, due to the bending anisotropy, the persistence
length of dsDNA in 2D conformations is always greater than 3D conformations.
This result is in consistence with the measured values for DNA persistence
length in 2D and 3D in equal biological conditions. We also show that in 2D, an
anisotropic, intrinsically twisted polymer exhibits an implicit twist-bend
coupling, which leads to the kink formations with a half helical turn
periodicity along the bent polymer.",1608.01347v2
2016-08-08,Anisotropy of the infrared-active phonon modes in the mono-domain state of tetragonal SrTiO3 (110),"With infrared and terahertz ellipsometry we investigated the anisotropy of
the infrared active phonon modes in SrTiO3 (110) single crystals in the
tetragonal state below the so-called antiferrodistortive transition at T* = 105
K. In particular, we show that the anisotropy of the oscillator strength of the
so-called R-mode, which becomes weakly infrared active below T*, is a valuable
indicator for the orientation of the structural domains. Our results reveal
that a mono-domain state with the tetragonal axis (c-axis) parallel to the
[001] direction can be created by applying a moderate uniaxial stress of about
2.3 MPa along the [1-10] direction (with a mechanical clamp). The resulting,
intrinsic splitting of the infrared-active phonon modes is reported.",1608.02329v1
2016-08-09,Lateral-drag Casimir forces induced by anisotropy,"We predict the existence of lateral drag forces near the flat surface of an
absorbing slab of an anisotropic material. The forces originate from the
fluctuations of the electromagnetic field, when the anisotropy axis of the
material forms a certain angle with the surface. In this situation, the spatial
spectra of the fluctuating electromagnetic fields becomes asymmetric, different
for positive and negative transverse wave vectors components. Differently from
the case of van der Waals interactions in which the forward-backward symmetry
is broken due to the particle movement or in quantum noncontact friction where
it is caused by the mutual motion of the bodies, in our case the lateral motion
results merely from the anisotropy of the slab. This new effect, of particular
significance in hyperbolic materials, could be used for the manipulation of
nanoparticles.",1608.03200v1
2016-08-29,"In-plane anisotropic magnetoresistance in antiferromagnetic Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ and Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$","Using the Kubo-Greenwood formalism the resistivity anisotropy for electron
doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, hole doped (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$
and isovalently doped Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ in their antiferromagnetic
state has been calculated in order to clarify the origin of this important
phenomenon. The results show good agreement with experiment for all cases
without considering impurity states extending over several unit cells or
temperature induced spin fluctuations. From this it is concluded that the
resistivity anisotropy at low temperatures is primarily caused by an in-plane
anisotropic magnetoresistance. Accounting for the band dispersion with respect
to $k_z$ is however mandatory to explain the results, showing the importance of
the three-dimensional character of the electronic structure for the iron
pnictides. Furthermore, it is shown that the counterintuitive sign of the
resistivity anisotropy is no fundamental property but just a peculiarity of the
anisotropic band structure.",1608.08077v1
2016-09-05,Anderson localization of ultracold atoms: Where is the mobility edge?,"Recent experiments on non-interacting ultra-cold atoms in correlated disorder
have yielded conflicting results regarding the so-called mobility edge, i.e.
the energy threshold separating Anderson localized from diffusive states. At
the same time, there are theoretical indications that the experimental data
overestimate the position of this critical energy, sometimes by a large amount.
The non-trivial effect of anisotropy in the spatial correlations of
experimental speckle potentials have been put forward as a possible cause for
such discrepancy. Using extensive numerical simulations we show that the effect
of anisotropy alone is not sufficient to explain the experimental data. In
particular, we find that, for not-too-strong anisotropy, realistic disorder
configurations are essentially identical to the isotropic case, modulo a simple
rescaling of the energies.",1609.01065v1
2016-10-12,Grain structure dependence of coercivity in thin films,"We investigated coercive fields of 200nm x 1200nm x 5nm rectangular
nanocrystalline thin films as a function of grain size D using finite elements
simulations. To this end, we created granular finite element models with grain
sizes ranging from 5nm to 60nm, and performed micromagnetic hysteresis
calculations along the y-axis (easy direction) as well as along the x-axis
(hard direction). We then used an extended Random Anisotropy model to interpret
the results and to illustrate the interplay of random anisotropy and shape
induced anisotropy, which is coherent on a much larger scale, in thin films.",1610.03630v3
2016-10-13,Spin wave surface states in one-dimensional planar magnonic crystals,"We have investigated surface spin wave states in one-dimensional planar
bi-component magnonic crystals, localized on the surfaces resulting from the
breaking of the periodic structure. The two systems have been considered: the
magnonic crystal with periodic changes of the anisotropy field in exchange
regime and the magnonic crystal composed of Fe and Ni stripes in dipolar regime
with exchange interactions included. We chose the symmetric unit cell for both
systems to implement the symmetry related criteria for existence of the surface
states. We investigated also the surface states induced by the presence of
perturbation of the surface areas of the magnonic crystals. We showed, that the
system with modulated anisotropy is a direct analog of the electronic crystal.
Therefore, the surface states in both systems have the same properties. For
surface states existing in magnonic crystals in dipolar regime we demonstrated
that spin waves preserve distinct differences to the electronic crystals, which
are due to long-range dynamic dipolar interactions. We found that tuning of the
strength of magnetization pinning resulting from the surface anisotropy or
dipolar effect is vitally important for existence of the surface states in
magnonic crystals.",1610.04083v1
2016-10-13,Nanoscale distribution of magnetic anisotropies in bimagnetic soft core-hard shell MnFe$_2$O$_4$@CoFe$_2$O$_4$ nanoparticles,"The nanoscale distribution of magnetic anisotropies was measured in
core@shell MnFe$_2$O$_4$@CoFe$_2$O$_4$ 7.0 nm particles using a combination of
element selective magnetic spectroscopies with different probing depths. As
this picture is not accessible by any other technique, emergent magnetic
properties were revealed. The coercive field is not constant in a whole
nanospinel. The very thin (0.5 nm) CoFe$_2$O$_4$ hard shell imposes a strong
magnetic anisotropy to the otherwise very soft MnFe$_2$O$_4$ core: a large
gradient in coercivity was measured inside the MnFe$_2$O$_4$ core with lower
values close to the interface region, while the inner core presents a
substantial coercive field (0.54 T) and a very high remnant magnetization (90%
of the magnetization at saturation).",1610.04263v2
2016-10-20,Local and long-range realizations of a spin-reorientation surface phase transition,"The spin reorientation transition of an ultrathin film from perpendicular to
in-plane magnetization is driven by a competition between dipole and anisotropy
energies. \textit{In situ} measurements of the magnetic susceptibility of Fe/2
ML Ni/W(110) films as a function of Fe coverage, made as the films are
deposited at constant temperature, show two clear peaks; one at the long-range
and one at the local realization of the transition. In the long-range
realization, the susceptibility probes the striped domain pattern that is
formed in response to the balance of energetics on a mesoscopic scale. Here the
reorientation transition occurs at a non-integer layer thickness. In the local
realization, the susceptibility probes the response of small islands with
in-plane anisotropy in the 3rd atomic Fe layer that are grown on the 2nd atomic
Fe layer, which has perpendicular anisotropy. It is a response to the local
finite-size, metastable energetics due to discrete steps in thickness. An
excellent quantitative description of the susceptibility data is obtained when
both local and long-range aspects of the spin reorientation transition are
included.",1610.06446v1
2016-10-26,Anisotropic permeability in deterministic lateral displacement arrays,"We uncover anisotropic permeability in microfluidic deterministic lateral
displacement (DLD) arrays. A DLD array can achieve high-resolution bimodal
size-based separation of microparticles, including bioparticles, such as cells.
For an application with a given separation size, correct device operation
requires that the flow remains at a fixed angle to the obstacle array. We
demonstrate via experiments and lattice-Boltzmann simulations that subtle array
design features cause anisotropic permeability. Anisotropic permeability
indicates the microfluidic array's intrinsic tendency to induce an undesired
lateral pressure gradient. This can cause an inclined flow and therefore local
changes in the critical separation size. Thus, particle trajectories can become
unpredictable and the device useless for the desired separation task.
Anisotropy becomes severe for arrays with unequal axial and lateral gaps
between obstacle posts and highly asymmetric post shapes. Furthermore, of the
two equivalent array layouts employed with the DLD, the rotated-square layout
does not display intrinsic anisotropy. We therefore recommend this layout over
the easier-to-implement parallelogram layout. We provide additional guidelines
for avoiding adverse effects of anisotropy on the DLD.",1610.08427v2
2016-10-27,Holographic Isotropisation in Gauss-Bonnet Gravity,"We study holographic isotropisation of homogeneous, strongly coupled,
non-Abelian plasmas in Gauss-Bonnet gravity with a negative cosmological
constant. We focus on small values of the Gauss-Bonnet coupling parameter
$\lambda_{GB}$ and linearise the equations of motion around a time-dependent
background solution with $\lambda_{GB}=0$. We numerically solve the linearised
equations and show that the entire time evolution of the pressure anisotropy
can be well approximated by the linear in $\lambda_{GB}$ corrections to the
quasinormal mode expansion, even in the cases of high anisotropy. We finally
show that, quite generally, the time evolution of the pressure anisotropy with
the Gauss-Bonnet term is approximately {\it shifted} with respect to the
evolution without it, with the sign of the shift being directly related to the
sign of the $\lambda_{GB}$ parameter. This suggests that finite coupling
corrections generically {\it increase} the isotropisation time of strongly
coupled plasmas.",1610.08987v2
2016-11-01,Shear softening of Earth's inner core indicated by its high Poisson's ratio and elastic anisotropy,"Earth's inner core exhibits an unusually high Poisson's ratio and noticeable
elastic anisotropy. The mechanisms responsible for these features are critical
for understanding the evolution of the Earth but remain unclear. This study
indicates that once the correct formula for the shear modulus is used, shear
softening can simultaneously explain the high Poisson's ratio and strong
anisotropy of the inner core. Body-centred-cubic (bcc) iron shows shear
instability at the pressures found in the inner-core and can be dynamically
stabilized by temperature and light elements. It is very likely that some
combinations of light elements stabilize the bcc iron alloy under inner-core
conditions. Such a bcc phase would exhibit significant shear softening and
match the geophysical constraints of the inner core. Identifying which light
elements and what concentrations of these elements stabilize the bcc phase will
provide critical information on the light elements of the inner core.",1611.00244v1
2016-11-09,Voltage control of magnetic anisotropy in epitaxial Ru/Co2FeAl/MgO heterostructures,"Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is
a key technology for achieving energy-efficiency electronic devices with
ultralow power consumption. Here, we report the first demonstration of the VCMA
effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial
perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel
junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an
effective voltage control on switching fields for the CFA free layer. A large
VCMA coefficient of 108 (139) fJ/Vm for the CFA film was achieved at room
temperature (4 K). The interfacial stability in the heterostructure was
confirmed by repeating measurements. Temperature dependences of both the
interfacial PMA and the VCMA effect were also investigated. It is found that
the temperature dependences follow power laws of the saturation magnetization
with an exponent of ~2. The significant VCMA effect observed in this work
indicates that the Ru/CFA/MgO heterostructure could be one of the promising
candidates for spintronic devices with voltage control.",1611.02827v1
2016-11-09,Anisotopic inflation with a non-abelian gauge field in Gauss-Bonnet gravity,"In presence of Gauss-Bonnet corrections, we study anisotropic inflation aided
by a massless $SU(2)$ gauge field where both the gauge field and the
Gauss-Bonnet term are non-minimally coupled to the inflaton. In this scenario,
under slow-roll approximations, the anisotropic inflation is realized as an
attractor solution with quadratic forms of inflaton potential and Gauss-Bonnet
coupling function. We show that the degree of anisotropy is proportional to the
additive combination of two slow-roll parameters of the theory. The anisotropy
may become either positive or negative similar to the non-Gauss-Bonnet
framework, a feature of the model for anisotropic inflation supported by a
non-abelian gauge field but the effect of Gauss-Bonnet term further enhances or
suppresses the generated anisotropy.",1611.03037v2
2016-11-10,Energy efficient and fast reversal of a fixed skyrmions with spin current assisted by voltage controlled magnetic anisotropy,"Recent work [1,2] suggests that ferromagnetic reversal with spin transfer
torque (STT) requires more current in a system in the presence of DMI than
switching a typical ferromagnet of the same dimensions and perpendicular
magnetic anisotropy (PMA). However, DMI promotes stabilization of skyrmions and
we report that when the perpendicular anisotropy is modulated (reduced) for
both the skyrmion and ferromagnet, it takes much smaller current to reverse the
fixed skyrmion than to reverse the ferromagnet in the same time, or the
skyrmion reverses much faster than the ferromagnet at similar levels of
current. We show with rigorous micromagnetic simulations and energy portraits
that the skyrmion switching proceeds along a different path at very low PMA
which results in a significant reduction in the spin current required or time
required for reversal. This can have potential for memory application where a
relatively simple modification of the standard STT-RAM to include a heavy metal
adjacent to the soft magnetic layer and with appropriate design of the tunnel
barrier can lead to energy efficient and fast magnetic memory device based on
the reversal of fixed skyrmions.",1611.03138v2
2016-12-07,General quadrupolar statistical anisotropy: Planck limits,"Several early Universe scenarios predict a direction-dependent spectrum of
primordial curvature perturbations. This translates into the violation of the
statistical isotropy of cosmic microwave background radiation. Previous
searches for statistical anisotropy mainly focussed on a quadrupolar
direction-dependence characterised by a single multipole vector and an overall
amplitude $g_*$. Generically, however, the quadrupole has a more complicated
geometry described by two multipole vectors and $g_*$. This is the subject of
the present work. In particular, we limit the amplitude $g_*$ for different
shapes of the quadrupole by making use of Planck 2015 maps. We also constrain
certain inflationary scenarios which predict this kind of more general
quadrupolar statistical anisotropy.",1612.02347v2
2016-12-07,Effect of anisotropy on generalized Chaplygin gas scalar field and its interaction with other dark energy models,"In this work, we establish a correspondence between the interacting
holographic, new agegraphic dark energy and generalized Chaplygin gas model in
Bianchi type I universe. In continue, we reconstruct the potential of the
scalar field which describes the generalized Chaplygin cosmology. Cosmological
solutions are obtained when the kinetic energy of the phantom field is order of
the anisotropy and dominates over the potential energy of the field. We
investigate observational constraints on the generalized Chaplygin gas,
holographic and new agegraphic dark energy models as the unification of dark
matter and dark energy, by using the latest observational data. To do this we
focus on observational determinations of the expansion history $H(z)$. It is
shown that the HDE model is better than the NADE and generalized Chaplygin gas
models in an anisotropic universe. Then, we calculate the evolution of density
perturbations in the linear regime for three models of dark energy and compare
the results $\Lambda$CDM model. Finally, the analysis shows that the increase
in anisotropy leads to more correspondence between the dark energy scalar field
model and observational data",1612.02453v1
2016-12-28,2D SnS: a phosphorene analogue with strong in-plane electronic anisotropy,"We study the anisotropic electronic properties of 2D SnS, an analogue of
phosphorene, grown by physical vapor transport. With transmission electron
microscope and polarized Raman spectroscopy, we identify the zigzag and
armchair directions of the as-grown 2D crystals. 2D SnS field-effect
transistors with a cross-Hall-bar structure are fabricated. They show heavily
hole-doped (~10$^{19}$ cm$^{-3}$) conductivity with strong in-plane anisotropy.
At room temperature the mobility along the zigzag direction exceeds 20
cm$^{2}$V$^{-1}$s$^{-1}$, which can be up to 1.7 times of that in the armchair
direction. This strong anisotropy is then explained by the effective-mass ratio
along the two directions and agrees well with previous theoretical predictions.
Temperature-dependent carrier density is used to find out the acceptor energy
level to be ~45 meV above the valence band maximum. This value matches with a
calculated defect level of 42 meV for Sn vacancies, indicating that Sn
deficiency is the main cause of the p-type conductivity.",1612.08896v1
2017-01-09,"Magnetic properties of ultra-thin 3d transition-metal binary alloys I: spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior","The structure and static magnetic properties - saturation magnetization,
perpendicular anisotropy, spectroscopic g-factor, and orbital magnetization -
of thin-film 3d transition metal alloys are determined over the full range of
alloy compositions via X-ray diffraction, magnetometry, and ferromagnetic
resonance measurements. We determine the interfacial perpendicular magnetic
anisotropy by use of samples sets with varying thickness for specific alloy
concentrations. The results agree with prior published data and theoretical
predictions. They provide a comprehensive compilation of the magnetic
properties of thin-film Ni-Co, Ni-Fe and Co-Fe alloys that goes well beyond the
often-cited Slater-Pauling dependence of magnetic moment on alloy
concentration.",1701.02177v1
2017-01-14,Strong perpendicular magnetic anisotropy energy density at Fe alloy/HfO2 interfaces,"We report on the perpendicular magnetic anisotropy (PMA) behavior of heavy
metal (HM)/ Fe alloy/MgO thin film heterostructures after an ultrathin HfO2
passivation layer is inserted between the Fe alloy and the MgO. This is
accomplished by depositing one to two atomic layers of Hf onto the Fe alloy
before the subsequent rf sputter deposition of the MgO layer. This Hf layer is
fully oxidized during the subsequent deposition of the MgO layer, as confirmed
by X-ray photoelectron spectroscopy measurements. As the result a strong
interfacial perpendicular anisotropy energy density can be achieved without any
post-fabrication annealing treatment, for example 1.7 erg/cm^2 for the
Ta/Fe60Co20B20/HfO2/MgO heterostructure. Depending on the HM, further
enhancements of the PMA can be realized by thermal annealing to at least 400C.
We show that ultra-thin HfO2 layers offer a range of options for enhancing the
magnetic properties of magnetic heterostructures for spintronics applications.",1701.03933v1
2017-01-24,Momentum anisotropy effects for quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature,"In the early stages of heavy-ion collisions, the hot QCD matter expands more
longitudinally than transversely. This imbalance causes the system to become
rapidly colder in the longitudinal direction and a local momentum anisotropy
appears. In this paper, we study the heavy-quarkonium spectrum in the presence
of a small plasma anisotropy. We work in the framework of pNRQCD at finite
temperature. We inspect arrangements of non-relativistic and thermal scales
complementary to those considered in the literature. In particular, we consider
temperatures larger and Debye masses smaller than the binding energy, which is
a temperature range relevant for presently running LHC experiments. In this
setting we compute the leading thermal corrections to the binding energy and
the thermal width induced by quarkonium gluo-dissociation.",1701.06956v1
2017-02-03,Significant reduction of critical currents in MRAM designs using dual free layer with perpendicular and in-plane anisotropy,"One essential feature in MRAM cells is the spin torque efficiency, which
describes the ratio of the critical switching current to the energy barrier.
Within this paper it is reported that the spin torque efficiency can be
improved by a factor of 3.2 by the use a of dual free layer device, which
consists of one layer with perpendicular crystalline anisotropy and a second
layer with in-plane crystalline anisotropy. Detailed simulations solving the
spin transport equations simultaneously with the micromagnetics equation were
performed in order to understand the origin of the switching current reduction
by a factor of 4 for the dual layer structure compared to a single layer
structure. The main reason could be attributed to an increased spin
accumulation within the free layer due to the dynamical tilting of the
magnetization within the in-plane region of the dual free layer.",1702.00996v2
2017-01-16,Dynamics of magnetic nano particles in a viscous fluid driven by rotating magnetic fields,"The rotational dynamics of magnetic nano particles in rotating magnetic
fields in the presence of thermal noise is studied both theoretically and by
performing numerical calculations. Kinetic equations for the dynamics of
particles with uniaxial magnetic anisotropy are studied and the phase lag
between the rotating magnetic moment and the driving field is obtained. It is
shown that for large enough anisotropy energy the magnetic moment is locked to
the anisotropy axis so that the particle behaves like a rotating magnetic
dipole. The corresponding rigid dipole model is analyzed both numerically by
solving the appropriate Fokker-Planck equation and analytically by applying an
effective field method. In the special case of a rotating magnetic field
applied analytic results are obtained in perfect agreement with numerical
results based on the Fokker-Planck equation. The analytic formulas derived are
not restricted to small magnetic fields or low frequencies and are therefore
important for applications. The illustrative numerical calculations presented
are performed for magnetic parameters typical for iron oxide.",1702.04673v1
2017-02-24,Giant perpendicular exchange bias with antiferromagnetic MnN,"We investigated an out-of-plane exchange bias system that is based on the
antiferromagnet MnN. Polycrystalline, highly textured film stacks of Ta / MnN /
CoFeB / MgO / Ta were grown on SiO$_x$ by (reactive) magnetron sputtering and
studied by x-ray diffraction and Kerr magnetometry. Nontrivial modifications of
the exchange bias and the perpendicular magnetic anisotropy were observed both
as functions of film thicknesses as well as field cooling temperatures. In
optimized film stacks, a giant perpendicular exchange bias of 3600 Oe and a
coercive field of 350 Oe were observed at room temperature. The effective
interfacial exchange energy is estimated to be $J_\mathrm{eff} = 0.24$ mJ/m$^2$
and the effective uniaxial anisotropy constant of the antiferromagnet is
$K_\mathrm{eff} = 24$ kJ/m$^3$. The maximum effective perpendicular anisotropy
field of the CoFeB layer is $H_\mathrm{ani} = 3400$ Oe. These values are larger
than any previously reported values. These results possibly open a route to
magnetically stable, exchange biased perpendicularly magnetized spin valves.",1702.07538v2
2017-02-26,Exploring the Optical States for Black Phosphorus: Anisotropy and Bandgap Tuning,"The dressed states arising from the interaction between electrons and holes,
and off-resonant electromagnetic radiation have been investigated for recently
fabricated gapped and anisotropic black phosphorus. Our calculations were
carried out for the low-energy electronic subbands near the $\Gamma$ point.
States for both linear and circular polarizations of the incoming radiation
have been computed. However, our principal emphasis is on linearly polarized
light with arbitrary polarization since this case has not been given much
attention for dressing fields imposed on anisotropic structures. We have
considered various cases for one- and few-layer phosphorus, including massless
Dirac fermions with tunable in-plane anisotropy. Initial Hamiltonian parameters
are renormalized in a largely different way compared to those for previously
reported for gapped Dirac structures and, most importantly, existing anisotropy
which could be modified in every direction.",1702.08058v1
2017-03-07,Anisotropy Driven Transition from Moore-Read State to Quantum Hall Stripes,"We investigate the nature of the quantum Hall liquid in a half-filled second
Landau level ($n=1$) as a function of band mass anisotropy using numerical
exact diagonalization (ED) and density matrix renormalization group (DMRG)
methods. We find increasing the mass anisotropy induces a quantum phase
transition from the Moore-Read state to a charge density wave state. By
analyzing the energy spectrum, guiding center structure factors and by adding
weak pinning potentials, we show that this charge density wave is a
uni-directional quantum Hall stripe, which has a periodicity of a few magnetic
lengths and survives in the thermodynamic limit. We find smooth profiles for
the guiding center occupation function that reveal the strong coupling nature
of the array of chiral Luttinger liquids residing at the stripe edges.",1703.02167v2
2017-03-13,Artificial control of the bias-voltage dependence of tunnelling anisotropic magnetoresistance using quantization in a single-crystal ferromagnet,"A major issue in the development of spintronic memory devices is the
reduction of the power consumption for the magnetization reversal. For this
purpose, the artificial control of the magnetic anisotropy of ferromagnetic
materials is of great importance. Here, we demonstrate the control of the
carrier-energy dependence of the magnetic anisotropy of the density of states
(DOS) using the quantum size effect in a single-crystal ferromagnetic material,
GaMnAs. We show that the mainly two-fold symmetry of the magnetic anisotropy of
DOS, which is attributed to the impurity band, is changed to a four-fold
symmetry by enhancing the quantum size effect in the valence band of the GaMnAs
quantum wells. By combination with the gate-electric field control technique,
our concept of the usage of the quantum size effect for the control of the
magnetism will pave the way for the ultra-low-power manipulation of
magnetization in future spintronic devices.",1703.04294v1
2017-03-16,Primordial anisotropies from cosmic strings during inflation,"In this work we study the imprints of a primordial cosmic string on
inflationary power spectrum. Cosmic string induces two distinct contributions
on curvature perturbations power spectrum. The first type of correction
respects the translation invariance while violating isotropy. This generates
quadrupolar statistical anisotropy in CMB maps which is constrained by the
Planck data. The second contribution breaks both homogeneity and isotropy,
generating a dipolar power asymmetry in variance of temperature fluctuations
with its amplitude falling on small scales. We show that the strongest
constraint on the tension of string is obtained from the quadrupolar anisotropy
and argue that the mass scale of underlying theory responsible for the
formation of string can not be much higher than the GUT scale. The predictions
of string for the diagonal and off-diagonal components of CMB angular power
spectrum are presented.",1703.05714v1
2017-03-19,Surface anisotropy of iron oxide nanoparticles and slabs from first principles : influence of coatings and ligands as a test of the Heisenberg model,"We performed ab initio computations of the magnetic properties of simple iron
oxide clusters and slabs. We considered an iron oxide cluster functionalized by
a molecule or glued to a gold cluster of the same size. We also considered a
magnetite slab coated by cobalt oxide or a mixture of iron oxide and cobalt
oxide. The changes in magnetic behavior were explored using constrained
magnetic calculations. A possible value for the surface anisotropy was
estimated from the fit of a classical Heisenberg model on ab initio results.
The value was found to be compatible with estimations obtained by other means,
or inferred from experimental results. The addition of a ligand, coating, or of
a metallic nanoparticle to the systems degraded the quality of the description
by the Heisenberg Hamiltonian. Proposing a change in the anisotropies allowing
for the proportion of each transition atom we could get a much better
description of the magnetism of series of hybrid cobalt and iron oxide systems.",1703.06414v1
2017-03-21,Hybrid straintronics and voltage-controlled-magnetic-anisotropy: Precessional switching of a perpendicular anisotropy magneto-tunneling junction without a magnetic field,"We propose an all-electric implementation of a precessionally switched
perpendicular magnetic anisotropy magneto-tunneling-junction (p-MTJ) based
toggle memory cell where data is written with
voltage-controlled-magnetic-anisotropy (VCMA) without requiring an in-plane
magnetic field. The soft layer of the MTJ is a two-phase
(magnetostrictive/piezoelectric) multiferroic which is electrically stressed to
produce an effective in-plane magnetic field around which the magnetization
precesses to complete a flip when the VCMA voltage pulse duration and the
stress duration are independently adjusted to obtain a high switching
probability. A two-terminal energy-efficient cell, that is compatible with
crossbar architecture and high cell density, is designed.",1703.07437v2
2017-03-22,Anisotropy of transport in bulk Rashba metals,"The recent experimental discovery of three-dimensional (3D) materials hosting
a strong Rashba spin-orbit coupling calls for the theoretical investigation of
their transport properties. Here we study the zero temperature dc conductivity
of a 3D Rashba metal in the presence of static diluted impurities. We show
that, at variance with the two-dimensional case, in 3D systems spin-orbit
coupling affects dc charge transport in all density regimes. We find in
particular that the effect of spin-orbit interaction strongly depends on the
direction of the current, and we show that this yields strongly anisotropic
transport characteristics. In the dominant spin-orbit coupling regime where
only the lowest band is occupied, the SO-induced conductivity anisotropy is
governed entirely by the anomalous component of the renormalized current. We
propose that measurements of the conductivity anisotropy in bulk Rashba metals
may give a direct experimental assessment of the spin-orbit strength.",1703.07701v2
2017-03-23,Theory of anomalous magnetotransport from mass anisotropy,"In underdoped YBa$_2$Cu$_3$O$_{6+x}$, there is evidence of a small Fermi
surface pocket subject to substantial mass enhancement in the doping regime $
0.12<p<0.16$. This mass enhancement may vary substantially over the Fermi
surface, due to ""hot spot"" or other relevant physics. We therefore examine the
magnetotransport of an electron-like Fermi pocket with large effective mass
anisotropy. Within the relaxation time approximation, we show that even for a
pocket with a fixed shape, the magnitude and sign of the Hall effect may change
as the mass anisotropy changes (except at very large, likely inaccessible
magnetic fields). We discuss implications for recent Hall measurements in near
optimally doped cuprates in high fields. In addition we identify a novel
intermediate asymptotic regime of magnetic field, characterized by B-linear
magnetoresistance. Similar phenomena should occur in a variety of other
experimental systems with anisotropic mass enhancement",1703.08187v2
2017-04-10,Patterned growth of crystalline Y$_{3}$Fe$_{5}$O$_{12}$ nanostructures with engineered magnetic shape anisotropy,"We demonstrate patterned growth of epitaxial yttrium iron garnet (YIG) thin
films using lithographically defined templates on gadolinium gallium garnet
(GGG) substrates. The fabricated YIG nanostructures yield the desired
crystallographic orientation, excellent surface morphology, and narrow
ferromagnetic resonance (FMR) linewidth (~ 4 Oe). Shape-induced magnetic
anisotropy is clearly observed in a patterned array of nanobars engineered to
exhibit the larger coercivity (40 Oe) compared with that of continuous films.
Both hysteresis loop and angle-dependent FMR spectra measurements indicate that
the easy axis aligns along the longitudinal direction of the nanobars, with an
effective anisotropy field of 195 Oe. Our work overcomes difficulties in
patterning YIG thin films and provides an effective means to control their
magnetic properties and magnetic bias conditions.",1704.03056v2
2017-04-04,Magnetic Dipole Interaction and Total Magnetic Energy of Lithium Ferrire Thin Films,"The total magnetic energy of Lithium ferrite thin films was determined using
the classical Heisenberg Hamiltonian. The short range magnetic dipole
interactions between spins within one unit cell and the interactions between
spins in two adjacent unit cells have been determined in order to find the
total magnetic energy of lithium ferrite films. Only the spin pairs with
separation less than cell constant have been taken into account to calculate
dipole interaction and spin exchange interaction. Theoretically several easy
and hard directions of lithium ferrite film were found for one set of energy
parameters included in our modified Heisenberg Hamiltonian. The dependence of
total magnetic energy of a lithium ferrite film on number of unit cells, spin
exchange interaction, dipole interaction, second order magnetic anisotropy,
fourth order magnetic anisotropy, internal applied magnetic field and stress
induced magnetic anisotropy has been explained in this manuscript.",1704.03314v1
2017-04-11,Can anisotropy in the galaxy distribution tell the bias?,"We use information entropy to analyze the anisotropy in the mock galaxy
catalogues from dark matter distribution and simulated biased galaxy
distributions from $\Lambda$CDM N-body simulation. We show that one can recover
the linear bias parameter of the simulated galaxy distributions by comparing
the radial, polar and azimuthal anisotropies in the simulated galaxy
distributions with that from the dark matter distribution. This method for
determination of the linear bias requires only $O(N)$ operations as compared to
$O(N^{2})$ or at least $O(N \log N)$ operations required for the methods based
on the two-point correlation function and the power spectrum. We apply this
method to determine the linear bias parameter for the galaxies in the 2MASS
Redshift Survey (2MRS) and find that the 2MRS galaxies in the $K_{s}$ band have
a linear bias of $\sim 1.3$.",1704.03405v1
2017-04-12,Predicting reaction coordinates in energy landscapes with diffusion anisotropy,"We consider a range of model potentials with metastable states undergoing
molecular dynamics coupled to a thermal bath in the high friction regime, and
consider how the optimal reaction coordinate depends on the diffusion
anisotropy. For this we use our recently proposed method 'Spectral gap
optimization of order parameters (SGOOP)' (Tiwary and Berne, Proc. Natl. Acad.
Sci. 113 2839 2016). We show how available information about dynamical
observables in addition to static information can be incorporated into SGOOP,
which can then be used to accurately determine the 'best' reaction coordinate
for arbitrary anisotropies. We compare our results with transmission
coefficient calculations and published benchmarks where applicable or available
respectively.",1704.03912v2
2017-04-13,Cardiac re-entry dynamics & self-termination in DT-MRI based model of Human Foetal Heart,"The effect of heart geometry and anisotropy on cardiac re-entry dynamics and
self-termination is studied here in anatomically realistic computer simulations
of human foetal heart. 20 weeks of gestational age human foetal heart isotropic
and anisotropic anatomy models from diffusion tensor MRI data sets are used in
the computer simulations. The fibre orientation angles of the heart were
obtained from the DT-MRI primary eigenvalues. In a spatially homogeneous
electrophysiological mono domain model with the DT-MRI based heart geometries,
we initiate simplified Fitz-Hugh-Nagumo kinetics cardiac re-entry at a
prescribed location in a 2D slice, and in the full 3D anatomy model. In a slice
of the heart, the MRI based fibre anisotropy changes the re-entry dynamics from
pinned to anatomical re-entry. In the full 3D MRI based model, the foetal heart
fibre anisotropy changes the re-entry dynamics from a persistent re-entry to
the re-entry self-termination.",1704.04208v2
2017-04-24,Probing non-linearity of higher order anisotropic flow in Pb--Pb collisions,"The second and the third order anisotropic flow, $V_{2}$ and $V_3$, are
determined by the corresponding initial spatial anisotropy coefficients,
$\varepsilon_{2}$ and $\varepsilon_{3}$, in the initial density distribution.
On the contrary, the higher order anisotropic flow $V_n$ ($n > 3$), in addition
to their dependence on the same order initial anisotropy coefficient
$\varepsilon_{n}$, have a significant contribution from lower order initial
anisotropy coefficients, which leads to mode-coupling effects. In this
contribution, we present the investigations on linear and non-linear modes in
higher order anisotropic flow ($V_{4}$, $V_{5}$ and $V_{6}$) in Pb--Pb
collisions at $\sqrt{s_{\rm NN}} =$ 2.76 TeV using the ALICE detector at the
Large Hadron Collider (LHC). A significant contribution from a non-linear mode
is observed. A new observable, the non-linear response coefficient, is measured
as well. The comparison to theoretical calculations provides crucial
information on dynamic of the created system especially at the freeze-out
conditions, which are poorly known from previous flow measurements.",1704.07070v1
2017-04-28,Strong anisotropy effect in iron-based superconductor CaFe$_{0.882}$Co$_{0.118}$AsF,"The anisotropy of the Fe-based superconductors is much smaller than that of
the cuprates and the theoretical calculations. A credible understanding for
this experimental fact is still lacking up to now. Here we experimentally study
the magnetic-field-angle dependence of electronic resistivity in the
superconducting phase of iron-based superconductor
CaFe$_{0.882}$Co$_{0.118}$AsF, and find the strongest anisotropy effect of the
upper critical field among the iron-based superconductors based on the
framework of Ginzburg-Landau theory. The evidences of energy band structure and
charge density distribution from electronic structure calculations demonstrate
that the observed strong anisotropic effect mainly comes from the strong ionic
bonding in between the ions of Ca$^{2+}$ and F$^-$, which weakens the
interlayer coupling between the layers of FeAs and CaF. This finding provides a
significant insight into the nature of experimentally observed strong
anisotropic effect of electronic resistivity, and also paves an avenue to
design exotic two dimensional artificial unconventional superconductors in
future.",1704.08791v1
2017-05-03,Single array of magnetic vortex disks uses in-plane anisotropy to create different logic gates,"Using micromagnetic simulation, we show that in-plane uniaxial magnetic
anisotropy (IPUA) can be used to obtain FAN-OUT, AND and OR gates in an array
of coupled disks with magnetic vortex configuration. First, we studied the
influence of the direction of application of the IPUA on the energy transfer
time ({\tau}) between two identical coupled nanodisks. We found that when the
direction of the IPUA is along the x axis the magnetic interaction increases,
allowing shorter values of {\tau}, while the IPUA along the y direction has the
opposite effect. The magnetic interactions between the nanodisks along x and y
directions (the coupling integrals) as a function of the uniaxial anisotropy
constant (K {\sigma} ) were obtained using a simple dipolar model. Next, we
demonstrated that choosing a suitable direction of application of the IPUA, it
is possible to create several different logic gates with a single array of
coupled nanodisks",1705.01232v1
2017-05-09,Extreme anisotropy and anomalous transport properties of heavily electron doped Lix(NH3)yFe2Se2 single crystals,"The missing hole packets near the Brillouin zone center render unique
electronic structures to the heavily electron doped FeSe-based superconductors
with Tc above 40 K. It challenges the existing scenario accounting for the
nature of superconductivity in the iron-based family. Yet, one hurdle that has
to be overcome is the materials complexity in the rather limited number of
compounds. Here we report the growth of heavily electron doped Li-NH3
intercalated FeSe single crystals that are free of such complexities and allow
access to the intrinsic superconducting properties. Our results show extremely
large electronic anisotropy in both normal and superconducting states.
Moreover, the anomalous transport properties appear in normal state, which are
believed related to the anisotropy of relaxation time and/or temperature
dependent electron carrier concentration. In view of the great chemical
flexibility of intercalants, our findings provide novel platform to
understanding of superconductivity origin of FeSe-related superconductors.",1705.03301v1
2017-05-11,Linear and non-linear flow mode in Pb-Pb collisions at $\sqrt{s_{\rm NN}} =$ 2.76 TeV,"The second and the third order anisotropic flow, $V_{2}$ and $V_3$, are
mostly determined by the corresponding initial spatial anisotropy coefficients,
$\varepsilon_{2}$ and $\varepsilon_{3}$, in the initial density distribution.
In addition to their dependence on the same order initial anisotropy
coefficient, higher order anisotropic flow, $V_n$ ($n > 3$), can also have a
significant contribution from lower order initial anisotropy coefficients,
which leads to mode-coupling effects. In this Letter we investigate the linear
and non-linear modes in higher order anisotropic flow $V_n$ for $n=4$, $5$, $6$
with the ALICE detector at the Large Hadron Collider. The measurements are done
for particles in the pseudorapidity range $|\eta| < 0.8$ and the transverse
momentum range $0.2 < p_{\rm T} < 5.0$ GeV/$c$ as a function of collision
centrality. The results are compared with theoretical calculations and provide
important constraints on the initial conditions, including initial spatial
geometry and its fluctuations, as well as the ratio of the shear viscosity to
entropy density of the produced system.",1705.04377v2
2017-05-13,"Tuning the perpendicular magnetic anisotropy, spin Hall switching current density and domain wall velocity by submonolayer insertion in Ta / CoFeB / MgO heterostructures","By submonolayer insertion of Au, Pt, or Pd into Ta / CoFeB / MgO / Ta
heterostructures we tune the perpendicular magnetic anisotropy and the coercive
field of the ferromagnetic layer. We demonstrate that this has a major
influence on the spin Hall switching current density and its dependence on the
external magnetic field. Despite a rather small effective spin Hall angle of
$\theta_\mathrm{SH} \approx -0.07$, we obtain switching current densities as
low as $2 \times 10^{10}$ A/m$^2$ with a 2 \AA{} Au interlayer. We find that
the Dzyaloshinskii-Moriya interaction parameter $D$ is reduced with Au or Pd
interlayers, and the perpendicular anisotropy field is reduced by an order of
magnitude with the Pd interlayer. The dependence of the switching current
density on the current pulse width is quantitatively explained with a domain
wall nucleation and propagation model. Interface engineering is thus found to
be a suitable route to tailor the current-induced magnetization switching
properties of magnetic heterostructures.",1705.04800v1
2017-05-16,Strong exchange anisotropy in YbMgGaO$_4$ from polarized neutron diffraction,"We measured the magnetic correlations in the triangular lattice spin-liquid
candidate material YbMgGaO$_4$ via polarized neutron diffraction. The extracted
in-plane and out-of-plane components of the magnetic structure factor show
clear anisotropy. We found that short-range correlations persist at the lowest
measured temperature of 52 mK and neutron scattering intensity is centered at
the $M$ middle-point of the hexagonal Brillouin-zone edge. Moreover, we found
pronounced spin anisotropy, with different correlation lengths for the in-plane
and out-of-plane spin components. When comparing to a self-consistent Gaussian
appoximation, our data clearly support a model with only first-neighbor
coupling and strongly anisotropic exchanges.",1705.05699v1
2017-05-23,The Sine-Gordon regime of the Landau-Lifshitz equation with a strong easy-plane anisotropy,"It is well-known that the dynamics of biaxial ferromagnets with a strong
easy-plane anisotropy is essentially governed by the Sine-Gordon equation. In
this paper, we provide a rigorous justification to this observation. More
precisely, we show the convergence of the solutions to the Landau-Lifshitz
equation for biaxial ferromagnets towards the solutions to the Sine-Gordon
equation in the regime of a strong easy-plane anisotropy. Moreover, we
establish the sharpness of our convergence result.
  This result holds for solutions to the Landau-Lifshitz equation in high order
Sobolev spaces. We first provide an alternative proof for local well-posedness
in this setting by introducing high order energy quantities with better
symmetrization properties. We then derive the convergence from the consistency
of the Landau-Lifshitz equation with the Sine-Gordon equation by using
well-tailored energy estimates. As a by-product, we also obtain a further
derivation of the free wave regime of the Landau-Lifshitz equation.",1705.08146v1
2017-06-05,Dynamic anisotropy in MHD turbulence induced by mean magnetic field,"In this paper, we study the development of anisotropy in strong MHD
turbulence in the presence of a large scale magnetic field B 0 by analyzing the
results of direct numerical simulations. Our results show that the developed
anisotropy among the different components of the velocity and magnetic field is
a direct outcome of the inverse cascade of energy of the perpendicular velocity
components u? and a forward cascade of the energy of the parallel component u k
. The inverse cascade develops for a strong B0, where the flow exhibits a
strong vortical structure by the suppression of fluctuations along the magnetic
field. Both the inverse and the forward cascade are examined in detail by
investigating the anisotropic energy spectra, the energy fluxes, and the shell
to shell energy transfers among different scales.",1706.01250v2
2017-06-06,Temperature scaling of the Dzyaloshinsky-Moriya interaction in the spin wave spectrum,"The temperature scaling of the micromagnetic Dzyaloshinsky-Moriya exchange
interaction is calculated for the whole range of temperature. We use Green's
function theory to derive the finite-temperature spin wave spectrum of
ferromagnetic systems described by a classical atomistic spin model
Hamiltonian. Within this model, we find universal expressions for the
temperature scaling not only of the Dzyaloshinsky-Moriya interaction but also
of the Heisenberg exchange stiffness and the single-ion anisotropy. In the
spirit of multiscale models, we establish a clear connection between the
atomistic interactions and the temperature-dependent coefficients in the spin
wave spectrum and in the micromagnetic free energy functional. We demonstrate
that the corrections to mean-field theory or the random phase approximation for
the temperature scaling of Dzyaloshinsky-Moriya and Heisenberg exchange
interactions assume very similar forms. In the presence of thermal fluctuations
and Dzyaloshinsky-Moriya interaction an anisotropy-like term emerges in the
spin wave spectrum which, at low temperature, increases with temperature, in
contrast to the decreasing single-ion anisotropy. We evaluate the accuracy of
the theoretical method by comparing it to the spin wave spectrum calculated
from Monte Carlo simulations.",1706.01684v1
2017-06-21,Unusual anisotropy of inplane field magnetoresistance in ultra-high mobility SiGe/Si/SiGe quantum wells,"We find an unusual anisotropy of the inplane field magnetoresistance in
ultra-high mobility SiGe/Si/SiGe quantum wells. The anisotropy depends on the
orientation between the inplane field, $B_\parallel$, and current, $I$,
relative to the crystallographic axes of the sample and is a consequence of the
intrinsic ridges on the quantum well surface. For the simplest orientations
between current and crystallographic axes, a method of recalculating the
magnetoresistance measured at $I\perp B_\parallel$ into the one measured at
$I\parallel B_\parallel$ is suggested and is shown to yield results that agree
with the experiment.",1706.06919v2
2017-06-28,Composite fermions in bands with N-fold rotational symmetry,"We study the effect of band anisotropy with discrete rotational symmetry
$C_N$ (where $N\ge 2$) in the quantum Hall regime of two-dimensional electron
systems. We focus on the composite Fermi liquid (CFL) at half filling of the
lowest Landau level. We find that the magnitude of anisotropy transferred to
the composite fermions decreases very rapidly with $N$. We demonstrate this by
performing density matrix normalization group calculations on the CFL, and
comparing the anisotropy of the composite fermion Fermi contour with that of
the (non-interacting) electron Fermi contour at zero magnetic field. We also
show that the effective interaction between the electrons after projecting into
a single Landau level is much less anisotropic than the band, a fact which does
not depend on filling and thus has implications for other quantum Hall states
as well. Our results confirm experimental observations on anisotropic bands
with warped Fermi contours, where the only detectable effect on the composite
Fermi contour is an elliptical distortion ($N = 2$).",1706.09470v1
2017-07-18,Pion transverse-momentum spectrum and elliptic anisotropy of partially coherent source,"In this letter, we study the pion momentum distribution of a coherent source
and investigate the influences of coherent emission on the pion
transverse-momentum ($p_T$) spectrum and elliptic anisotropy. With a partially
coherent source, constructed by a conventional viscous hydrodynamics model
(chaotic part) and a parameterized expanding coherent source model, we
reproduce the pion $p_T$ spectrum and elliptic anisotropy coefficient
$v_2(p_T)$ in the peripheral Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. It
is found that the influences of coherent emission on the pion $p_T$ spectrum
and $v_2(p_T)$ are related to the initial size and shape of the coherent
source, largely due to the interference effect. However, the effect of source
dynamical evolution on coherent emission is relatively small. The results of
the partially coherent source with 33% coherent emission and 67% chaotic
emission are consistent with the experimental measurements of the pion $p_T$
spectrum, $v_2(p_T)$, and especially four-pion Bose-Einstein correlations.",1707.05461v4
2017-07-25,The dipole anisotropy of WISE x SuperCOSMOS number counts,"We probe the isotropy of the Universe with the largest all-sky photometric
redshift dataset currently available, namely WISE~$\times$~SuperCOSMOS. We
search for dipole anisotropy of galaxy number counts in multiple redshift
shells within the $0.10 < z < 0.35$ range, for two subsamples drawn from the
same parent catalogue. Our results show that the dipole directions are in good
agreement with most of the previous analyses in the literature, and in most
redshift bins the dipole amplitudes are well consistent with $\Lambda$CDM-based
mocks in the cleanest sample of this catalogue. In the $z<0.15$ range, however,
we obtain a persistently large anisotropy in both subsamples of our dataset.
Overall, we report no significant evidence against the isotropy assumption in
this catalogue except for the lowest redshift ranges. The origin of the latter
discrepancy is unclear, and improved data may be needed to explain it.",1707.08091v4
2017-08-02,Implications of the Measured Angular Anisotropy at the Hidden Order Transition of URu2Si2,"The heavy fermion compound URu2Si2 continues to attract great interest due to
the long- unidentified nature of the hidden order that develops below 17.5K.
Here we discuss the implications of an angular survey of the linear and
nonlinear susceptibility of URu2Si2 in the vicinity of the hidden order
transition. While the anisotropic nature of spin fluctuations and
low-temperature quasiparticles was previously established, our recent results
suggest that the order parameter itself has intrinsic Ising anisotropy, and
that moreover this anisotropy extends far above the hidden order transition.
Consistency checks and subsequent questions for future experimental and
theoretical studies of hidden order are discussed.",1708.00589v1
2017-08-17,Enhanced superconductivity and anisotropy of FeTe0.6Se0.4 single crystals with Li-NH3 intercalation,"We report a systematic study of anisotropy resistivity, magnetoresistance and
Hall effect of Li0.32(NH3)yFe2Te1.2Se0.8 single crystals. When compared to the
parent compound FeTe0.6Se0.4, the Li-NH3 intercalation not only increases the
superconducting transition temperature, but also enhances the electronic
anisotropy in both normal and superconducting states. Moreover, in contrast to
the parent compound, the Hall coefficient RH becomes negative at low
temperature, indicating electron-type carriers are dominant due to Li doping.
On the other hand, the sign reverse of RH at high temperature and the failure
of scaling behavior of magnetoresistance imply that hole pockets may be still
crossing or just below the Fermi energy level, leading to the multiband
behavior in Li0.32(NH3)yFe2Te1.2Se0.8.",1708.05310v2
2017-08-19,Current induced multi-mode propagating spin waves in a spin transfer torque nano-contact with strong perpendicular magnetic anisotropy,"Current induced spin wave excitations in spin transfer torque nano-contacts
are known as a promising way to generate exchange-dominated spin waves at the
nano-scale. It has been shown that when these systems are magnetized in the
film plane, broken spatial symmetry of the field around the nano-contact
induced by the Oersted field opens the possibility for spin wave mode
co-existence including a non-linear self-localized spin-wave bullet and a
propagating mode. By means of micromagnetic simulations, here we show that in
systems with strong perpendicular magnetic anisotropy (PMA) in the free layer,
two propagating spin wave modes with different frequency and spatial
distribution can be excited simultaneously. Our results indicate that in-plane
magnetized spin transfer nano-contacts in PMA materials do not host a solitonic
self-localized spin-wave bullet, which is different from previous studies for
systems with in plane magnetic anisotropy. This feature renders them
interesting for nano-scale magnonic waveguides and crystals since magnon
transport can be configured by tuning the applied current.",1708.05886v1
2017-08-22,Ice-Templated W-Cu Composites with High Anisotropy,"Controlling anisotropy in self-assembled structures enables engineering of
materials with highly directional response. Here, we harness the anisotropic
growth of ice walls in a thermal gradient to assemble an anisotropic refractory
metal structure, which is then infiltrated with Cu to make a composite. Using
experiments and simulations, we demonstrate on the specific example of
tungsten-copper composites the effect of anisotropy on the electrical and
mechanical properties. The results are compared to isotropic tungsten-copper
composites fabricated by standard powder metallurgical methods. Our results
have the potential to fuel the development of more efficient materials, used in
electrical power grids and solar-thermal energy conversion systems. The method
presented here can be used with a variety of refractory metals and ceramics,
which fosters the opportunity to design and functionalize a vast class of new
anisotropic load-bearing hybrid metal composites with highly directional
properties.",1708.06801v1
2017-08-30,Current induced magnetization switching in PtCoCr structures with enhanced perpendicular magnetic anisotropy and spin-orbit torques,"Magnetic trilayers having large perpendicular magnetic anisotropy (PMA) and
high spin-orbit torques (SOTs) efficiency are the key to fabricate nonvolatile
magnetic memory and logic devices. In this work, PMA and SOTs are
systematically studied in Pt/Co/Cr stacks as a function of Cr thickness. An
enhanced perpendicular anisotropy field around 10189 Oe is obtained and is
related to the interface between Co and Cr layers. In addition, an effective
spin Hall angle up to 0.19 is observed due to the improved antidamping-like
torque by employing dissimilar metals Pt and Cr with opposite signs of spin
Hall angles on opposite sides of Co layer. Finally, we observed a nearly linear
dependence between spin Hall angle and longitudinal resistivity from their
temperature dependent properties, suggesting that the spin Hall effect may
arise from extrinsic skew scattering mechanism. Our results indicate that 3d
transition metal Cr with a large negative spin Hall angle could be used to
engineer the interfaces of trilayers to enhance PMA and SOTs.",1708.09174v1
2017-09-07,"Elastic, electronic, thermodynamic and transport properties of XOsSi (X=Nb, Ta) superconductors: A first-principles exploration","A first-principles calculation has been performed to study elastic,
electronic, thermodynamic, transport and superconducting properties of recently
reported osmium based two superconductors, XOsSi (X=Nb, Ta). We have calculated
elastic constants and elastic moduli of XOsSi for the first time. The
calculated values of bulk, Youngs, shear moduli are reasonably larger than the
average value obtained from the rule of mixtures of the constituents. NbOsSi
and TaOsSi both compounds are found to be relatively hard material, elastically
stable and ductile in nature. The obtained directional bulk modulus and shear
anisotropic factors indicate that both compounds have high elastic anisotropy.
The shear anisotropic factors show higher elastic anisotropy than the
percentage anisotropy in these compounds. The Debye temperature and bulk
modulus increases with pressure but decreases with temperature as usual for
metals. The magnetic susceptibility of TaOsSi follow the Curie law but NaOsSi
do not follow due to its delocalized magnetic moment and electronic specific
heat slightly deviates from the linear relationship with temperature. The
calculated band structures of XOsSi compounds show metallic nature. In both
cases d-orbitals have the dominating contribution to the total density of
states. The smaller electron-phonon coupling constant implies that XOsSi (X=Nb,
Ta) are weakly coupled superconductors.",1709.02173v1
2017-09-07,Interaction anisotropy and the KPZ to KPZQ transition in particle deposition at the edges of drying drops,"The deposition process at the edge of evaporating colloidal drops varies with
the shape of suspended particles. Experiments with prolate ellipsoidal
particles suggest that the spatiotemporal properties of the deposit depend
strongly on particle aspect ratio. As the aspect ratio increases, the particles
form less densely-packed deposits and the statistical behavior of the deposit
interface crosses over from the Kardar-Parisi-Zhang (KPZ) universality class to
another universality class which was suggested to be consistent with the KPZ
plus quenched disorder. Here, we numerically study the effect of particle
interaction anisotropy on deposit growth. In essence, we model the ellipsoids,
at the interface, as disk-like particles with two types of interaction patches
that correspond to specific features at the poles and equator of the ellipsoid.
The numerical results corroborate experimental observations and further suggest
that the deposition transition can stem from interparticle interaction
anisotropy. Possible extensions of our model to other systems are also
discussed.",1709.02350v1
2017-09-12,Evidence for short-range magnetic order in the nematic phase of FeSe from anisotropic in-plane magnetostriction and susceptibility measurements,"The nature of the nematic state in FeSe remains one of the major unsolved
mysteries in Fe- based superconductors. Both spin and orbital physics have been
invoked to explain the origin of this phase. Here we present experimental
evidence for frustrated, short-range magnetic order, as suggested by several
recent theoretical works, in the nematic state of FeSe. We use a combination of
magnetostriction, susceptibility and resistivity measurements to probe the
in-plane anisotropies of the nematic state and its associated fluctuations.
Despite the absence of long-range magnetic order in FeSe, we observe a sizable
in-plane magnetic susceptibility anisotropy, which is responsible for the
field-induced in-plane distortion inferred from magnetostriction measurements.
Further we demonstrate that all three anisotropies in FeSe are very similar to
those of BaFe2As2, which strongly suggests that the nematic phase in FeSe is
also of magnetic origin.",1709.03861v1
2017-09-18,Growth-Induced In-Plane Uniaxial Anisotropy in V$_{2}$O$_{3}$/Ni Films,"We report on a strain-induced and temperature dependent uniaxial anisotropy
in V$_{2}$O$_{3}$/Ni hybrid thin films, manifested through the interfacial
strain and sample microstructure, and its consequences on the angular dependent
magnetization reversal. X-ray diffraction and reciprocal space maps identify
the in-plane crystalline axes of the V$_{2}$O$_{3}$; atomic force and scanning
electron microscopy reveal oriented rips in the film microstructure.
Quasi-static magnetometry and dynamic ferromagnetic resonance measurements
identify a uniaxial magnetic easy axis along the rips. Comparison with films
grown on sapphire without rips shows a combined contribution from strain and
microstructure in the V$_{2}$O$_{3}$/Ni films. Magnetization reversal
characteristics captured by angular-dependent first order reversal curve
measurements indicate a strong domain wall pinning along the direction
orthogonal to the rips, inducing an angular-dependent change in the reversal
mechanism. The resultant anisotropy is tunable with temperature and is most
pronounced at room temperature, which is beneficial for potential device
applications.",1709.06100v1
2017-10-16,On the anisotropy in the arrival directions of ultra-high-energy cosmic rays,"We present results of elaborate four-dimensional simulations of the
propagation of ultra-high-energy cosmic rays (UHECR), which are based on a
realistic astrophysical scenario. The distribution of the arrival directions of
the UHECR is found to have a pronounced dipolar anisotropy and rather weak
higher-order contributions to the angular power spectrum. This finding agrees
well with the recent observation of a dipolar anisotropy for UHECR with arrival
energies above 8 EeV by the Pierre Auger Observatory and constitutes an
important prediction for other energy ranges and higher-order angular
contributions for which sufficient experimental data are not yet available.
Since our astrophysical scenario enables simulations that are completely
consistent with the available data, this scenario will be a very useful basis
for related future studies.",1710.05617v1
2017-10-21,Spin interferometry in anisotropic spin-orbit fields,"Electron spins in a two-dimensional electron gas (2DEG) can be manipulated by
spin-orbit (SO) fields originating from either Rashba or Dresselhaus
interactions with independent isotropic characteristics. Together, though, they
produce anisotropic SO fields with consequences on quantum transport through
spin interference. Here we study the transport properties of modelled
mesoscopic rings subject to Rashba and Dresselhaus [001] SO couplings in the
presence of an additional in-plane Zeeman field acting as a probe. By means of
1D and 2D quantum transport simulations we show that this setting presents
anisotropies in the quantum resistance as a function of the Zeeman field
direction. Moreover, the anisotropic resistance can be tuned by the Rashba
strength up to the point to invert its response to the Zeeman field. We also
find that a topological transition in the field texture that is associated with
a geometric phase switching is imprinted in the anisotropy pattern. We conclude
that resistance anisotropy measurements can reveal signatures of SO textures
and geometric phases in spin carriers.",1710.07810v2
2017-10-25,Spin-1 two-impurity Kondo problem on a lattice,"We present an extensive study of the two-impurity Kondo problem for spin-1
adatoms on square lattice using an exact canonical transformation to map the
problem onto an effective one-dimensional system that can be numerically solved
using the density matrix renormalization group method. We provide a simple
intuitive picture and identify the different regimes, depending on the distance
between the two impurities, Kondo coupling $J_K$, longitudinal anisotropy $D$,
and transverse anisotropy $E$. In the isotropic case, two impurities on
opposite(same) sublattices have a singlet(triplet) ground state. However, the
energy difference between the triplet ground state and the singlet excited
state is very small and we expect an effectively four-fold degenerate ground
state, i.e., two decoupled impurities. For large enough $J_K$ the impurities
are practically uncorrelated forming two independent underscreened states with
the conduction electrons, a clear non-perturbative effect. When the impurities
are entangled in an RKKY-like state, Kondo correlations persists and the two
effects coexist: the impurities are underscreened, and the dangling spin-$1/2$
degrees of freedom are responsible for the inter-impurity entanglement. We
analyze the effects of magnetic anisotropy in the development of
quasi-classical correlations.",1710.09473v1
2017-11-02,Resistivity scaling model for metals with conduction band anisotropy,"It is generally understood that the resistivity of metal thin films scales
with film thickness mainly due to grain boundary and boundary surface
scattering. Recently, several experiments and ab initio simulations have
demonstrated the impact of crystal orientation on resistivity scaling. The
crystal orientation cannot be captured by the commonly used resistivity scaling
models and a qualitative understanding of its impact is currently lacking. In
this work, we derive a resistivity scaling model that captures grain boundary
and boundary surface scattering as well as the anisotropy of the band
structure. The model is applied to Cu and Ru thin films, whose conduction bands
are (quasi-)isotropic and anisotropic respectively. After calibrating the
anisotropy with ab initio simulations, the resistivity scaling models are
compared to experimental resistivity data and a renormalization of the fitted
grain boundary reflection coefficient can be identified for textured Ru.",1711.00796v3
2017-11-03,THz-driven demagnetization with Perpendicular Magnetic Anisotropy: Towards ultrafast ballistic switching,"We study THz-driven spin dynamics in thin CoPt films with perpendicular
magnetic anisotropy. Femtosecond magneto-optical Kerr effect measurements show
that demagnetization amplitude of about $1\%$ can be achieved with a peak THz
electric field of $300$~kV/cm, and a corresponding peak magnetic field of
$0.1$~T. The effect is more than an order of magnitude larger than observed in
samples with easy-plane anisotropy irradiated with the same field strength. We
also utilize finite-element simulations to design a meta-material structure
that can enhance the THz magnetic field by more than an order of magnitude,
over an area of several tens of square micrometers. Magnetic fields exceeding
$1$~Tesla, generated in such meta-materials with the available laser-based THz
sources, are expected to produce full magnetization reversal via ultrafast
ballistic precession driven by the THz radiation. Our results demonstrate the
possibility of table-top ultrafast magnetization reversal induced by THz
radiation.",1711.01234v2
2017-11-07,Tuning electrical and optical anisotropy of a monolayer black phosphorus magnetic superlattice,"We investigate theoretically the effects of modulated periodic perpendicular
magnetic fields on the electronic states and optical absorption spectrum in a
monolayer black phosphorus (phosphorene). We demonstrate that different
phosphorene magnetic superlattice (PMS) orientations can give rise to distinct
energy spectra, i.e., tuning the intrinsic electronic anisotropy. The Rashba
spin-orbit coupling (RSOC) will develop a spin-splitting energy dispersion in
this phosphorene magnetic supperlattice. Anisotropic momentum-dependent carrier
distributions along/perpendicular to the magnetic strips are demonstrated, and
the manipulations of these exotic properties by tuning superlattice geometry,
magnetic field and the RSOC term (via an external electric field) are addressed
systematically. Accordingly, we find bright-to-dark transitions in the ground
state electron-hole pairs transition rate spectrum and PMS orientation
dependent anisotropic optical absorption spectrum. This feature offers us a
practical way to modulate the electronic anisotropy in phosphorene by magnetic
superlattice configurations and detect these modulation capability by using the
optical technique.",1711.02426v1
2017-11-07,Spin-Orbit Coupling and Magnetic Anisotropy in Iron-Based Superconductors,"We determine theoretically the effect of spin-orbit coupling on the magnetic
excitation spectrum of itinerant multi-orbital systems, with specific
application to iron-based superconductors. Our microscopic model includes a
realistic ten-band kinetic Hamiltonian, atomic spin-orbit coupling, and
multi-orbital Hubbard interactions. Our results highlight the remarkable
variability of the resulting magnetic anisotropy despite constant spin-orbit
coupling. At the same time, the magnetic anisotropy exhibits robust universal
behavior upon changes in the bandstructure corresponding to different materials
of iron-based superconductors. A natural explanation of the observed
universality emerges when considering optimal nesting as a resonance
phenomenon. Our theory is also of relevance to other itinerant system with
spin-orbit coupling and nesting tendencies in the bandstructure.",1711.02460v1
2017-11-15,Anisotropy of the Seebeck and Nernst coefficients in parent compounds of the iron-based superconductors,"In-plane longitudinal and transverse thermoelectric phenomena in two parent
compounds of iron-based superconductors are studied. Namely, the Seebeck (S)
and Nernst (n) coefficients were measured in the temperature range 10 - 300 K
for BaFe2As2 and CaFe2As2 single crystals that were detwinned in-situ. The
thermoelectric response shows sizeable anisotropy in the spin density wave
state (SDW) for both compounds, while some dissimilarities in the vicinity of
the SDW transition can be attributed to the different nature of the phase
change in BaFe2As2 and CaFe2As2. Temperature dependences of S and n can be
described within a two-band model that contains a contribution from highly
mobile, probably Dirac, electrons. The Dirac band seems to be rather isotropic,
whereas most of the anisotropy in the transport phenomena could be attributed
to ""regular"" hole-like charge carriers. We also observe that the off-diagonal
element of the Peltier tensor axy is not the same for the a and b orthorhombic
axes, which indicates that the widely used Mott formula is not applicable to
the SDW state of iron-based superconductors.",1711.05831v2
2017-11-17,Measuring anisotropic spin relaxation in graphene,"We compare different methods to measure the anisotropy of the spin-lifetime
in graphene. In addition to out-of-plane rotation of the ferromagnetic
electrodes and oblique spin precession, we present a Hanle experiment where the
electron spins precess around either a magnetic field perpendicular to the
graphene plane or around an in-plane field. In the latter case, electrons are
subject to both in-plane and out-of-plane spin relaxation. To fit the data, we
use a numerical simulation that can calculate precession with anisotropies in
the spin-lifetimes under magnetic fields in any direction. Our data show a
small, but distinct anisotropy that can be explained by the combined action of
isotropic mechanisms, such as relaxation by the contacts and resonant
scattering by magnetic impurities, and an anisotropic Rashba spin-orbit based
mechanism. We also assess potential sources of error in all three types of
experiment and conclude that the in-plane/out-of-plane Hanle method is most
reliable.",1711.06472v2
2017-11-28,Dendritic Growth of a Polymer on a 2D Mesoscale Square Lattice,"Dendritic growth patterns exhibiting four-fold anisotropy are observed when
polyethylene oxide undergoes phase segregation from a solution phase to a solid
phase. When this phase transition occurs on a substrate that has patterns of
cross-linked polyethylene oxide resist pillars made using electron beam
lithography, the polymer grows in between the patterns giving rise to dendritic
growth structures exhibiting eight-fold anisotropy. This paper presents these
experimental observations and explains the dendritic growth using principles of
minimization of free energy associated with phase change. Numerical simulations
are carried out using phase-field modeling, and the results are shown to
qualitatively match experimental observations. The simulations reveal that the
polymer assumes the anisotropy of the patterned lattice.",1711.10141v3
2017-12-04,Renormalization of single-ion magnetic anisotropy in the absence of Kondo effect,"Inelastic spin flip excitations associated with single-ion magnetic
anisotropy of quantum spins, can be strongly renormalized by Kondo exchange
coupling to the conduction electrons in the substrate, as shown recently for
the case of Co adatoms on CuN$_2$ islands. In this case differential
conductance spectra show zero-bias anomalies due to a Kondo effect of the
doubly degenerate ground state, and finite-bias step features due to spin flip
excitations. Here I consider spin-1 quantum magnets with positive uniaxial
anisotropy, where the ground state is non-degenerate and hence the Kondo effect
does not take place. Nevertheless the renormalization of inelastic spin
excitations due to exchange coupling by hybridization of the quantum spin with
the conduction electrons still takes place despite the complete absence of the
Kondo effect in the ground state. Additionally, I show that away from
particle-hole symmetry, charge fluctuations have a similar effect to Kondo
exchange coupling, leading to the renormalization of spin flip excitations.
However, in contrast to the renormalization by Kondo exchange, charge
fluctuations lead to asymmetric spectra, which for strong charge fluctuations
can mimic Fano behavior.",1712.01005v2
2017-12-05,A review on anisotropy analysis of spatial point patterns,"A spatial point pattern is called anisotropic if its spatial structure
depends on direction. Several methods for anisotropy analysis have been
introduced in the literature. In this paper, we give an overview of
nonparametric methods for anisotropy analysis of (stationary) point patterns in
$\mathbf{R}^2$ and $\mathbf{R}^3$. We discuss methods based on nearest
neighbour and second order summary statistics as well as spectral and wavelet
analysis. All techniques are illustrated on both a clustered and a regular
example. Finally, we discuss methods for testing for isotropy as well as for
estimating preferred directions in a point pattern.",1712.01634v2
2017-12-05,Magneto-elastic coupling in Fe-based superconductors,"We used polarization-resolved Raman scattering to study the magneto-elastic
coupling in the parent compounds of several families of Fe-based
superconductors (BaFe2As2, EuFe2As2, NaFeAs, LiFeAs, FeSe and LaFeAsO). We
observe an emergent Ag-symmetry As phonon mode in the XY scattering geometry
whose intensity is significantly enhanced below the magneto-structural
transition only for compounds showing magnetic ordering. We conclude that the
small lattice anisotropy is insufficient to induce the in-plane electronic
polarizability anisotropy necessary for the observed phonon intensity
enhancement, and interpret this enhancement below the Neel temperature in terms
of the anisotropy of the magnetic moment and magneto-elastic coupling. We
evidence a Fano line- shape in the XY scattering geometry resulting from a
strong coupling between the Ag (As) phonon mode and the B2g symmetry-like
electronic continuum. Strong electron-phonon coupling may be relevant to
superconductivity.",1712.01896v1
2017-12-05,Third order perturbed modified Heisenberg Hamiltonian of fcc structured ferromagnetic films with seventy spin layers,"Magnetic properties of fcc structured ferromagnetic films with the number of
spin layers up to seventy was described using third order perturbed Heisenberg
Hamiltonian. The variation of magnetic easy direction, magnetic energies in
easy and hard directions, magnetic anisotropy energy and the angle between easy
and hard directions was investigated by varying the number of spin layers. Spin
exchange interaction, magnetic dipole interaction, second and fourth order
magnetic anisotropies, in and out of plane applied magnetic fields,
demagnetization factor and stress induced anisotropy were considered in the
model. Because magnetic dipole interaction and demagnetization factor represent
microscopic and macroscopic properties of the sample, respectively, both these
terms were incorporated in our theoretical model. Although our model is a
semi-classical model, some discrete variations of angle of easy axis were
observed. Our theoretical data qualitatively agree with experimental data of Fe
and Ni ferromagnetic films.",1712.02636v1
2017-12-15,Inplane anisotropy of longitudinal thermal conductivities and weak localization of magnons in a disordered spiral magnet,"We demonstrate the inplane anisotropy of longitudinal thermal conductivities
and the weak localization of magnons in a disordered screw-type spiral magnet
on a square lattice. We consider a disordered spin system, described by a spin
Hamiltonian for the antiferromagnetic Heisenberg interaction and the
Dzyaloshinsky-Moriya interaction with the mean-field type potential of
impurities. We derive longitudinal thermal conductivities for the disordered
screw-type spiral magnet in the weak-localization regime by using the
linear-response theory with the linear-spin-wave approximation and performing
perturbation calculations. We show that the inplane longitudinal thermal
conductivities are anisotropic due to the Dzyaloshinsky-Moriya interaction.
This anisotropy may be useful for experimentally estimating the magnitude of a
ratio of the Dzyaloshinsky-Moriya interaction to the Heisenberg interaction. We
also show that the main correction term gives a logarithmic suppression with
the length scale due to the critical back scattering. This suggests that the
weak localization of magnons is ubiquitous for the disordered two-dimensional
magnets having global time-reversal symmetry. We finally discuss several
implications for further research.",1712.05575v2
2017-12-19,Measurements and atomistic theory of electron $g$ factor anisotropy for phosphorus donors in strained silicon,"This work reports the measurement of electron $g$ factor anisotropy ($|
\Delta g |$ = $| g_{001} - g_{1 \bar 1 0} |$) for phosphorous donor qubits in
strained silicon (sSi = Si/Si$_{1-x}$Ge$_x$) environments. Multi-million-atom
tight-binding simulations are performed to understand the measured decrease in
$| \Delta g |$ as a function of $x$, which is attributed to a reduction in the
interface-related anisotropy. For $x <$7\%, the variation in $| \Delta g |$ is
linear and can be described by $\eta_x x$, where $\eta_x \approx$1.62$\times$
10$^{-3}$. At $x$=20\%, the measured $| \Delta g |$ is 1.2 $\pm$ 0.04 $\times$
10$^{-3}$, which is in good agreement with the computed value of 1$\times
10^{-3}$. When strain and electric fields are applied simultaneously, the
strain effect is predicted to play a dominant role on $| \Delta g |$. Our
results provide useful insights on spin properties of sSi:P for spin qubits,
and more generally for devices in spintronics and valleytronics areas of
research.",1712.06765v2
2018-01-02,Parton self-energies for general momentum-space anisotropy,"We introduce an efficient general method for calculating the self-energies,
collective modes, and dispersion relations of quarks and gluons in a
momentum-anisotropic high-temperature quark-gluon plasma. The method introduced
is applicable to the most general classes of deformed anisotropic momentum
distributions and the resulting self-energies are expressed in terms of a
series of hypergeometric basis functions which are valid in the entire complex
phase-velocity plane. Comparing to direct numerical integration of the
self-energies, the proposed method is orders of magnitude faster and provides
results with similar or better accuracy. To extend previous studies and
demonstrate the application of the proposed method, we present numerical
results for the parton self-energies and dispersion relations of partonic
collective excitations for the case of an ellipsoidal momentum-space
anisotropy. Finally, we also present, for the first time, the gluon unstable
mode growth rate for the case of an ellipsoidal momentum-space anisotropy.",1801.00863v2
2018-01-03,Spin and mass superfluidity in ferromagnetic spin-1 Bose-Einstein condensate,"The paper investigates the coexistence and interplay of spin and mass
superfluidity in a ferromagnetic spin-1 Bose-Einstein condensate. Superfluidity
is possible only in the presence of uniaxial anisotropy (linear and quadratic
Zeeman effect). This follows from the topology of the order-parameter space
(vacuum manifold). According to the Landau criterion, the critical phase
gradients, both for mass and spin supercurrents, vanish at the phase transition
from the easy-plane to the easy-axis anisotropy. However, mass superfluidity is
still possible at the phase transition. This is because the Landau criterion
signals instability only with respect to nonsingular vortices with special
ratio between circulations of mass and spin currents. Phase slips produced by
these vortices are not sufficient for complete decay of supercurrents. Full
decay of supercurrents requires phase slips with vortices of another
topological class and larger energy. These phase slips are suppressed by
energetic barriers up to the upper critical velocity (gradient) exceeding the
Landau critical velocity. The upper critical velocity does not vanish nor has
any anomaly in the critical point at the phase transition from the easy-plane
to the easy-axis anisotropy.",1801.01099v2
2018-01-12,Relativistic anisotropic stars with the polytropic equation of state in general relativity,"Spherically symmetric relativistic stars with the polytropic equation of
state, which possess the local pressure anisotropy, are considered in the
context of general relativity. The modified Lane-Emden equations are derived
for the special ansatz for the anisotropy parameter $\Delta$ in the form of the
differential relation between $\Delta$ and the metric function $\nu$. The
analytical solutions of the obtained equations are found for incompressible
fluid stars. The dynamical stability of incompressible anisotropic fluid stars
against radial oscillations is studied.",1801.06958v2
2018-01-26,Enhancement of exchange bias in ferromagnetic/antiferromagnetic core-shell nanoparticles through ferromagnetic domain wall formation,"The spin configuration in the ferromagnetic part during the magnetization
reversal plays a crucial role in the exchange bias effect. Through Monte Carlo
simulation, the exchange bias effect in ferromagnetic-antiferromagnetic
core-shell nanoparticles is investigated. Magnetization reversals in the
ferromagnetic core were controlled between the coherent rotation and the domain
wall motion by modulating ferromagnetic domain wall width with parameters of
uniaxial anisotropy constant and exchange coupling strength. An anomalous
monotonic dependence of exchange bias on the uniaxial anisotropy constant is
found in systems with small exchange coupling, showing an obvious violation of
classic Meiklejohn-Bean model, while domain walls are found to form close to
the interface and propagate in the ferromagnetic core with larger uniaxial
anisotropy in both branches of the hysteresis. The asymmetric magnetization
reversal with the formation of a spherical domain wall dramatically reduces the
coercive field in the ascending branch, leading to the enhancement of the
exchange bias. The results provide another degree of freedom to optimize the
magnetic properties of magnetic nanoparticles for applications.",1801.08743v1
2018-01-31,Finite-temperature dynamic structure factor of the spin-1 XXZ chain with single-ion anisotropy,"Improving matrix-product state techniques based on the purification of the
density matrix, we are able to accurately calculate the finite-temperature
dynamic response of the infinite spin-1 XXZ chain with single-ion anisotropy in
the Haldane, large-$D$ and antiferromagnetic phases. Distinct thermally
activated scattering processes make a significant contribution to the spectral
weight in all cases. In the Haldane phase intraband magnon scattering is
prominent, and the onsite anisotropy causes the magnon to split into singlet
and doublet branches. In the large-$D$ phase response, the intraband signal is
separated from an exciton-antiexciton continuum. In the antiferromagnetic
phase, holons are the lowest-lying excitations, with a gap that closes at the
transition to the Haldane state. At finite temperatures, scattering between
domain-wall excitations becomes especially important and strongly enhances the
spectral weight for momentum transfer $\pi$.",1801.10572v2
2018-02-08,Direct observation of spin excitation anisotropy in the paramagnetic orthorhombic state of BaFe$_{2-x}$Ni$_x$As$_2$,"We use transport and inelastic neutron scattering measurements to investigate
single crystals of iron pnictide BaFe$_{2-x}$Ni$_{x}$As$_{2}$ ($x=0,0.03$),
which exhibit a tetragonal-to-orthorhombic structural transition at $T_s$ and
stripe antiferromagnetic order at $T_N$ ($T_s\geq T_N$).
  Using a tunable uniaxial pressure device, we detwin the crystals and study
their transport and spin excitation properties at antiferromagnetic wave vector
$S_1(1,0)$ and its 90$^\circ$ rotated wave vector $S_2(0,1)$ under different
pressure conditions. We find that uniaxial pressure necessary to detwin and
maintain single domain orthorhombic antiferromagnetic phase of
BaFe$_{2-x}$Ni$_{x}$As$_{2}$ induces resistivity and spin excitation anisotropy
at temperatures above zero pressure $T_s$. In uniaxial pressure-free detwinned
sample, spin excitation anisotropy between $S_1(1,0)$ and $S_2(0,1)$ first
appear in the paramagnetic orthorhombic phase below $T_s$. These results are
consistent with predictions of spin nematic theory, suggesting the absence of
structural or nematic phase transition above $T_s$ in iron pnictides.",1802.02713v1
2018-02-12,On effects of inhomogeneity on anisotropy in Backus average,"In general, the Backus average of an inhomogeneous stack of isotropic layers
is a transversely isotropic medium. Herein, we examine a relation between this
inhomogeneity and the strength of resulting anisotropy, and show that, in
general, they are proportional to one another. There is an important case,
however, in which the Backus average of isotropic layers results in an
isotropic -- as opposed to a transversely isotropic -- medium. We show that it
is a consequence of the same rigidity of layers, regardless of their
compressibility. Thus, in general, the strength of anisotropy of the Backus
average increases with the degree of inhomogeneity among layers, except for the
case in which all layers exhibit the same rigidity.",1802.04075v4
2018-02-16,Anisotropies in the stochastic gravitational-wave background: Formalism and the cosmic string case,"We develop a powerful analytical formalism for calculating the energy density
of the stochastic gravitational wave background, including a full description
of its anisotropies. This is completely general, and can be applied to any
astrophysical or cosmological source. As an example, we apply these tools to
the case of a network of Nambu-Goto cosmic strings. We find that the angular
spectrum of the anisotropies is relatively insensitive to the choice of model
for the string network, but very sensitive to the value of the string tension
$G\mu$.",1802.06046v4
2018-02-19,Static properties and current-induced dynamics of pinned $90$ degree magnetic domain walls under applied fields: an analytic approach,"Magnetic domain walls are pinned strongly by abrupt changes in magnetic
anisotropy. When driven into oscillation by a spin-polarized current, locally
pinned domain walls can be exploited as tunable sources of short-wavelength
spin waves. Here, we develop an analytical framework and discrete Heisenberg
model to describe the static and dynamic properties of pinned domain walls with
a head-to-tail magnetic structure. We focus on magnetic domain walls that are
pinned by 90$^\circ$ rotations of uniaxial magnetic anisotropy. Our model
captures the domain wall response to a spin-transfer torque that is exerted by
an electric current. Model predictions of the domain wall resonance frequency
and its evolution with magnetic anisotropy strength and external magnetic field
are compared to micromagnetic simulations.",1802.06741v3
2018-02-19,Borderline Magnetism: How Does Adding Magnesium to Paramagnetic CeCo$_3$ Make a 450 K Ferromagnet with Large Magnetic Anisotropy?,"A recent experimental study (Phys. Rev. Appl. 9, 024023, 2018) on
paramagnetic CeCo$_3$ finds that Magnesium alloying induces a ferromagnetic
transition with intrinsic properties large enough for permanent magnet
applications. Here we explain these surprising results \textit{via} a first
principles study of the electronic structure and magnetism of Magnesium-alloyed
CeCo$_3$. We find the origin of this Magnesium-induced ferromagnetic transition
to be Stoner physics - the substantial increase in the Fermi-level
density-of-states $N(E_F)$ with Mg alloying. Our calculations suggest that both
Ce and Co atoms are important for generating large magnetic anisotropy
suggesting the viability of Co-3$d$, and Ce-4$f$ interaction for the generation
of magnetic anisotropy in magnetic materials. These results offer a new route
to the discovery of ferromagnetic materials and provide fundamental insight
into the magnetic properties of these alloys",1802.06747v2
2018-02-21,Phonon mode softening and elastic properties of hafnium under pressure,"The effect of pressure on the zone-center optical phonon modes and the
elastic properties of hafnium has been studied by both experimental (Raman
scattering) and theoretical (DFT) approaches. It was found an anomaly
dependence of the phonon frequency of E$_{2g}$ mode in the pressure range from
0 to 67 GPa. The calculated electronic structure of hafnium shows significant
changes under pressure, which have a pronounced spatial anisotropy similar to
the anisotropy of the observed phonon properties. The dependencies of the
elastic properties on pressure including the components of the elasticity
tensor, bulk and shear modulus, Poisson ratio and Universal anisotropy index
obtained during the calculations has characteristic features indicating the
occurrence of the structural phase transition.",1802.07531v1
2018-02-25,Scaling Behavior of Anisotropy Relaxation in Deformed Polymers,"Drawing an analogy to the paradigm of quasi-elastic neutron scattering, we
present a general approach for quantitatively investigating the spatiotemporal
dependence of structural anisotropy relaxation in deformed polymers by using
small-angle neutron scattering. Experiments and non-equilibrium molecular
dynamics simulations on polymer melts over a wide range of molecular weights
reveal that their conformational relaxation at relatively high momentum
transfer $Q$ and short time can be described by a simple scaling law, with the
relaxation rate proportional to $Q$. This peculiar scaling behavior, which
cannot be derived from the classical Rouse and tube models, is indicative of a
surprisingly weak direct influence of entanglement on the microscopic mechanism
of single-chain anisotropy relaxation.",1802.09002v2
2018-02-26,Relationship between Magnetic Anisotropy Below Pseudogap Temperature and Short-Range Antiferromagnetic Order in High-Temperature Cuprate Superconductor,"The central issue in high-temperature cuprate superconductors is the
pseudogap state appearing below the pseudogap temperature $T^*$, which is well
above the superconducting transition temperature. In this study, we
theoretically investigate the rapid increase of the magnetic anisotropy below
the pseudogap temperature detected by the recent torque-magnetometry
measurements on YBa$_2$Cu$_3$O$_y$ [Y. Sato et al., Nat. Phys., 13, 1074
(2017)]. Applying the spin Green's function formalism including the
Dzyaloshinskii--Moriya interaction arising from the buckling of the CuO$_2$
plane, we obtain results that are in good agreement with the experiment and
find a scaling relationship. Our analysis suggests that the characteristic
temperature associated with the magnetic anisotropy, which coincides with
$T^*$, is not a phase transition temperature but a crossover temperature
associated with the short-range antiferromagnetic order.",1802.09163v2
2018-02-26,Elliptic flow from Coulomb interaction and low density elastic scattering,"In high energy heavy ion collisions and interacting cold atom systems, large
elliptic flow anisotropies have been observed. For the large opacity
($\rho\sigma L\sim 10^{3}$) of the latter hydrodynamics is a natural
consequence, but for the small opacity ($\rho\sigma L\sim 1$) of the former
hydrodynamic description is questionable. To shed light onto the situation, we
simulate the expansion of a low density Argon ion (or atom) system, initially
trapped in an elliptical region, under the Coulomb interaction (or elastic
scattering). Significant elliptic anisotropy is found in both cases, and the
anisotropy depends on the initial spatial eccentricity and the density of the
system. The results may provide insights into the physics of anisotropic flow
in high energy heavy ion collisions and its role in the study of quantum
chromodynamics.",1802.09595v1
2018-02-28,Voigt effect-based wide-field magneto-optical microscope integrated in a pump-probe experimental setup,"In this work we describe an experimental setup for spatially-resolved
pump-probe experiment with integrated wide-field magneto-optical (MO)
microscope. The MO microscope can be used to study ferromagnetic materials with
both perpendicular-to-plane and in-plane magnetic anisotropy via polar Kerr and
Voigt effects, respectively. The functionality of the Voigt effect-based
microscope was tested using an in-plane magnetized ferromagnetic semiconductor
(Ga,Mn)As. It was revealed that the presence of mechanical defects in the
(Ga,Mn)As epilayer alters significantly the magnetic anisotropy in their
proximity. The importance of MO experiments with simultaneous temporal and
spatial resolutions was demonstrated using (Ga,Mn)As sample attached to a
piezoelectric actuator, which produces a voltage-controlled strain. We observed
a considerably different behavior in different parts of the sample that enabled
us to identify sample parts where the epilayer magnetic anisotropy was
significantly modified by a presence of the piezostressor and where it was not.
Finally, we discuss the possible applicability of our experimental setup for
the research of compensated antiferromagnets, where only MO effects even in
magnetic moments are present.",1802.10534v1
2018-03-07,Anisotropic electronic transport and Rashba effect of the two-dimensional electron system in (110) SrTiO$_3$-based heterostructures,"The two-dimensional electron system in (110)Al$_2$O$_{3-\delta}$/SrTiO$_3$
heterostructures displays anisotropic electronic transport. Largest and lowest
conductivity and electron mobility $\mu$ are observed along the $[001]$ and
$[1\bar{1}0]$ direction, respectively. The anisotropy of the sheet resistance
and $\mu$ likewise leads to a distinct anisotropic normal magnetotransport (MR)
for T < 30K. However, at temperatures T<5K and magnetic field B<2T MR is
dominated by weak antilocalization.Despite the rather strong anisotropy of the
Fermi surfaces, the in-plane anisotropic magnetoresistance (AMR) displays
two-fold non-crystalline anisotropy. However, the AMR-amplitude is found to be
anisotropic with respect to the current direction, leading to a 60% larger AMR
amplitude for current I along the $[001]$ direction compared to I parallel to
$[1\bar{1}0]$. Tight binding calulations evidence an anisotropic Rashba-induced
band splitting with dominant linear k-dependence. In combination with
semiclassical Boltzmann theory the non-crystalline AMR is well described,
despite the anisotropic Fermi surface.",1803.02646v1
2018-03-12,Focused ion beam direct writing of magnetic patterns with controlled structural and magnetic properties,"Focused ion beam irradiation of metastable Fe$_{78}$Ni$_{22}$ thin films
grown on Cu(100) substrates is used to create ferromagnetic,
body-centered-cubic patterns embedded into paramagnetic, face-centered-cubic
surrounding. The structural and magnetic phase transformation can be controlled
by varying parameters of the transforming gallium ion beam. The focused ion
beam parameters as ion dose, number of scans, and scanning direction can be
used not only to control a degree of transformation, but also to change the
otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy
along specific crystallographic direction. This change is associated with a
preferred growth of specific crystallographic domains. The possibility to
create magnetic patterns with continuous magnetization transitions and at the
same time to create patterns with periodical changes in magnetic anisotropy
makes this system an ideal candidate for rapid prototyping of a large variety
of nanostructured samples. Namely spin-wave waveguides and magnonic crystals
can be easily combined into complex devices in a single fabrication step.",1803.04348v1
2018-03-28,Primordial Anisotropies in the Gravitational Wave Background from Cosmological Phase Transitions,"Phase transitions in the early universe can readily create an observable
stochastic gravitational wave background. We show that such a background
necessarily contains anisotropies analogous to those of the cosmic microwave
background (CMB) of photons, and that these too may be within reach of proposed
gravitational wave detectors. Correlations within the gravitational wave
anisotropies and their cross-correlations with the CMB can provide new insights
into the mechanism underlying primordial fluctuations, such as multi-field
inflation, as well as reveal the existence of non-standard ``hidden sectors"" of
particle physics in earlier eras.",1803.10780v2
2018-04-03,Raman Signatures of Broken Inversion Symmetry and In-plane Anisotropy in Type-II Weyl Semimetal Candidate TaIrTe4,"The layered ternary compound TaIrTe4 is an important candidate to host the
recently predicted type-II Weyl Fermions. However, a direct and definitive
proof of the absence of inversion symmetry in this material, a prerequisite for
the existence of Weyl Fermions, has so far remained evasive. Herein, an
unambiguous identification of the broken inversion symmetry in TaIrTe4 is
established using angle-resolved polarized Raman spectroscopy. Combining with
high-resolution transmission electron microscopy, we demonstrate an efficient
and nondestructive recipe to determine the exact crystallographic orientation
of TaIrTe4 crystals. Such technique could be extended to the fast
identification and characterization of other type-II Weyl Fermions candidates.
A surprisingly strong in-plane electrical anisotropy in TaIrTe4 thin flakes is
also revealed, up to 200% at 10K, which is the strongest known electrical
anisotropy for materials with comparable carrier density, notably in such good
metals as copper and silver.",1804.00797v1
2018-04-04,Emergence of topological Hall effect in half-metallic manganite thin films by tuning perpendicular magnetic anisotropy,"Magnetic materials hosting topological spin textures like magnetic skyrmion
exhibit nontrivial Hall effect, namely, topological Hall effect (THE). In this
study, we demonstrate the emergence of THE in thin films of half-metallic
perovskite manganites. To stabilize magnetic skyrmions, we control the
perpendicular magnetic anisotropy by imposing a compressive epitaxial strain as
well as by introducing a small Ru doping. When the perpendicular magnetic
anisotropy is tuned so that it is balanced with the magnetic dipolar
interaction, the film exhibits a sizable THE in a magnetization reversal
process. Real-space observations indicate the formation of skyrmions and some
of them have high topological charge number. The present result opens up the
possibility for novel functionalities that emerge under keen competition
between the skyrmion phase and other rich phases of perovskite manganites with
various orders in spin, charge, and orbital degrees of freedom.",1804.01425v2
2018-04-09,Dislocation-induced thermal transport anisotropy in single-crystal group-III nitride films,"Dislocations, one-dimensional lattice imperfections, are common to
technologically important materials such as III-V semiconductors, and adversely
affect heat dissipation in e.g., nitride-based high-power electronic devices.
For decades, conventional models based on nonlinear elasticity theory have
predicted this thermal resistance is only appreciable when heat flux is
perpendicular to the dislocations. However, this dislocation-induced
anisotropic thermal transport has yet to be seen experimentally. In this study,
we measure strong thermal transport anisotropy governed by highly oriented
threading dislocation arrays along the cross-plane direction in micron-thick,
single-crystal indium nitride (InN) films. We find that the cross-plane thermal
conductivity is more than tenfold higher than the in-plane thermal conductivity
at 80 K when the dislocation density is on the order of ~3x10^10 cm^-2. This
large anisotropy is not predicted by the conventional models. With enhanced
understanding of dislocation-phonon interactions, our results open new regimes
for tailoring anisotropic thermal transport with line defects, and will
facilitate novel methods for directed heat dissipation in thermal management of
diverse device applications.",1804.02825v1
2018-04-12,Anisotropic Superfluid Behavior of a Dipolar Bose-Einstein Condensate,"We present transport measurements on a dipolar superfluid using a
Bose-Einstein condensate of Dy-162 with strong magnetic dipole-dipole
interactions. By moving an attractive laser beam through the condensate we
observe an anisotropy in superfluid flow. This observation is compatible with
an anisotropic critical velocity for the breakdown of dissipationless flow,
which, in the spirit of the Landau criterion, can directly be connected to the
anisotropy of the underlying dipolar excitation spectrum. In addition, the
heating rate above this critical velocity reflects the same anisotropy. Our
observations are in excellent agreement with simulations based on the
Gross-Pitaevskii equation and highlight the effect of dipolar interactions on
macroscopic transport properties, rendering dissipation anisotropic.",1804.04552v2
2018-04-16,Simulation study of elliptic flow of charged hadrons produced in Au + Au collisions at the Facility for Antiproton and Ion Research,"Centrality and system geometry dependence of azimuthal anisotropy of charged
hadrons measured in terms of the elliptic flow parameter are investigated using
Au+Au event samples at incident beam energy $20$A GeV and $40$A GeV generated
by Ultrarelativistic Quantum Molecular Dynamics and A Multiphase Transport
models. The Monte Carlo Glauber model is employed to estimate the eccentricity
of the overlapping zone at an early stage of the collisions. Anisotropies
present both in the particle multiplicity distribution and in the kinetic
radial expansion are examined by using standard statistical and
phenomenological methods. In the context of upcoming Compressed Baryonic Matter
experiment to be held at the Facility for Antiproton and Ion Research, the
present set of simulated results provide us not only with an opportunity to
examine the expected collective behavior of hadronic matter at high baryon
density and moderate temperature environment, but when compared with similar
results obtained from Relativistic Heavy Ion Collider and Large Hadron Collider
experiments, they also allow us to investigate how anisotropy of hadronic
matter may differ or agree with its low baryon density and high temperature
counterpart.",1804.05564v1
2018-04-27,Size and shape of skyrmions for variable Dzyaloshinskii-Moriya interaction and uniaxial anisotropy,"We have performed micromagnetic simulations to study the formation of
skyrmions in ferromagnetic elements with different shapes having perpendicular
anisotropy. The strength of Dzyaloshinskii-Moriya interaction (D) and uniaxial
anisotropy (K) are varied to elucidate the regime in which skyrmion formation
can take place. It is found that for a certain combination of D and K skyrmion
formation does not happen. Further we also observed that for large D and small
K values, finite size effect dominates which in turn hinders formation of
typical N'eel (spherical) skyrmions. However the resulting magnetic phase is
skyrmionic in nature and has different shape. We also have found that the shape
of the magnetic nano element has a significant role in determining the final
magnetic state in addition to the competing D and K values.",1804.10548v1
2018-05-01,On anisotropy of the maximum attainable speed of low-mass particles,"We evaluated the emission of a low-mass particle in the system (atomic)
transition for the case when the particle Lorentz factor is $10^{18}$ and found
that the angular distribution of emission in the laboratory inertial system is
strongly affected by the directional variation of the maximum attainable speed
of the particle. We show that for a photon mass consistent with the
experimental limit, $m_{ph} \leq 10^{-18}$ eV, due to the experimentally known
absence of a significant anisotropy of the photon emission by an atom, the
anisotropy of the one-way speed of light, $\Delta c_1/c$, is $10^{-37}$ or
less. This is many orders of magnitude smaller than previously reported and the
limit becomes even stronger for the lower mass of the photon.",1805.00408v4
2018-05-07,Anatomy of interfacial spin-orbit coupling in Co/Pd multilayers using X-ray magnetic circular dichroism and first-principles calculations,"Element-specific orbital magnetic moments and their anisotropies in
perpendicularly magnetised Co/Pd multilayers are investigated using Co L-edge
and Pd M-edge angle-dependent x-ray magnetic circular dichroism. We show that
the orbital magnetic moments in Co are anisotropic, whereas those in Pd are
isotropic. The first-principles density-functional-theory calculations also
suggest that the Co/Pd interfacial orbital magnetic moments in Co are
anisotropic and contribute to the perpendicular magnetic anisotropy (PMA), and
that the isotropic ones in Pd manipulates the Co orbitals at the interface
through proximity effects. Orbital-resolved anatomy of Co/Pd interfaces reveals
that the orbital moment anisotropy in Co and spin-flipped transition related to
the magnetic dipoles in Pd are essential for the appearance of PMA.",1805.02416v1
2018-05-26,Ionic vs. van der Waals Layered Materials: Identification and Comparison of Elastic Anisotropy,"In this work, we expand the set of known layered compounds to include ionic
layered materials, which are well known for superconducting, thermoelectric,
and battery applications. Focusing on known ternary compounds from the ICSD, we
screen for ionic layered structures by expanding upon our previously developed
algorithm for identification of van der Waals (vdW) layered structures, thus
identifying over 1,500 ionic layered compounds. Since vdW layered structures
can be chemically mutated to form ionic layered structures, we have developed a
methodology to structurally link binary vdW to ternary ionic layered materials.
We perform an in-depth analysis of similarities and differences between these
two classes of layered systems and assess the interplay between layer geometry
and bond strength with a study of the elastic anisotropy. We observe a rich
variety of anisotropic behavior in which the layering direction alone is not a
simple predictor of elastic anisotropy. Our results enable discovery of new
layered materials through intercalation or de- intercalation of vdW or ionic
layered systems, respectively, as well as lay the groundwork for studies of
anisotropic transport phenomena such as sound propagation or lattice thermal
conductivity.",1805.10489v1
2018-06-07,Strong and Tunable Spin Lifetime Anisotropy in Dual-Gated Bilayer Graphene,"We report the discovery of a strong and tunable spin lifetime anisotropy with
excellent spin lifetimes up to 7.8 ns in dual-gated bilayer graphene.
Remarkably, this realizes the manipulation of spins in graphene by
electrically-controlled spin-orbit fields, which is unexpected due to
graphene's weak intrinsic spin-orbit coupling. We utilize both the in-plane
magnetic field Hanle precession and oblique Hanle precession measurements to
directly compare the lifetimes of out-of-plane vs. in-plane spins. We find that
near the charge neutrality point, the application of a perpendicular electric
field opens a band gap and generates an out-of-plane spin-orbit field that
stabilizes out-of-plane spins against spin relaxation, leading to a large spin
lifetime anisotropy. This intriguing behavior occurs because of the unique
spin-valley coupled band structure of bilayer graphene. Our results demonstrate
the potential for highly tunable spintronic devices based on dual-gated 2D
materials.",1806.02477v1
2018-06-14,Molecular ordering of nematic liquid crystals in tubular nanopores: Tailoring of optical anisotropy at the nanoscale by polymer pore-surface grafting,"The optical polarimetry technique is used to explore molecular ordering of
nematic liquid crystals 5FPFFPP3 embedded in parallel cylindrical channels of
alumina membranes with pore walls covered by a SE-1211 polymer film enhancing
normal anchoring. A chemical film deposition from organic solution apparently
results in inhomogeneous coverage with local islands on the channels walls.
Accordingly, a coexistence of differently ordered LC regions (nanodomains),
characterized by positive and negative anisotropy, results in a weak effective
(average) optical birefringence. Repeated polymer deposition reduces the size
of uncovered pore walls regions and thus leads to a strengthening of negative
optical anisotropy observed in the experiments.",1806.05630v2
2018-06-29,Finsler space-time can explain both parity asymmetry and power deficit seen in CMB temperature anisotropies,"We propose a framework of Finsler space-time to explain the observed parity
asymmetry and the power deficit in the low-$\ell$ ($2\leqslant \ell \leqslant
29$) multipole range of cosmic microwave background (CMB) temperature
anisotropies. In the $3+1$ dimensional space-time, the three-dimensional space
is described by a Randers-Finsler space, which is spatially irreversible,
inducing the parity asymmetry in the CMB angular power spectrum. We estimate
the constraints on the two parameters introduced by Finsler space-time via
analyzing the low-$\ell$ angular power spectrum in PLANCK 2015 CMB temperature
data. We see that the low-$\ell$ power suppression in the CMB temperature
anisotropies can also be resolved in this scenario. Our study shows that the
two low-$\ell$ anomalies, i.e., parity asymmetry and power deficit, may have a
common origin.",1806.11425v1
2018-07-13,Gilbert damping of high anisotropy Co/Pt multilayers,"Using broadband ferromagnetic resonance, we measure the damping parameter of
[Co(5 \r{A})/Pt(3 \r{A})]${\times 6}$ multilayers whose growth was optimized to
maximize the perpendicular anisotropy. Structural characterizations indicate
abrupt interfaces essentially free of intermixing despite the miscible
character of Co and Pt. Gilbert damping parameters as low as 0.021 can be
obtained despite a magneto-crystalline anisotropy as large as
$10^6~\textrm{J/m}^3$. The inhomogeneous broadening accounts for part of the
ferromagnetic resonance linewidth, indicating some structural disorder leading
to a equivalent 20 mT of inhomogenity of the effective field. The unexpectedly
relatively low damping factor indicates that the presence of the Pt heavy metal
within the multilayer may not be detrimental to the damping provided that
intermixing is avoided at the Co/Pt interfaces.",1807.04977v1
2018-07-18,Multi-band effects in in-plane resistivity anisotropy of strain-detwinned disordered Ba(Fe$_{1-x}$Ru$_{x}$)$_{2}$As$_{2}$,"In-plane resistivity anisotropy was measured in strain-detwinned as-grown and
partially annealed samples of isovalently-substituted
$\mathrm{Ba(Fe_{1-x}Ru_{x})_{2}As_{2}}$ ($0<x \leq 0.125$) and the results were
contrasted with previous reports on anneal samples with low residual
resistivity. In samples with high residual resistivity, detwinned with
application of strain, the difference of the two components of in-plane
resistivity in the orthorhombic phase, $\rho_a -\rho_b$, was found to obey
Matthiessen rule irrespective of sample composition, which is in stark contrast
with observations on annealed samples. Our findings are consistent with
two-band transport model in which contribution from high mobility carriers of
small pockets of the Fermi surface has negligible anisotropy of residual
resistivity and is eliminated by disorder. Our finding suggests that
magnetic/nematic order has dramatically different effect on different parts of
the Fermi surface. It predominantly affects inelastic scattering for small
pocket high mobility carriers and elastic impurity scattering for larger sheets
of the Fermi surface.",1807.07130v1
2018-09-03,Confinement-induced Resonance of Alkaline-earth-metal-like Atoms in Anisotropic Quasi-one-dimensional Traps,"We study the confinement-induced resonance (CIR) of $^{173}$Yb atoms near an
orbital Feshbach resonance in a quasi-one-dimensional tube with transversal
anisotropy. By solving the two-body scattering problem, we obtain the location
of CIR for various anisotropy ratio and magnetic field. Our results show that
the anisotropy of the trapping potential can serve as an additional knob to
tune the location of CIR. In particular, one can shift the location of CIR to
the region attainable in current experiment. We also study the energy spectrum
of the system and analyze the properties of CIR from the perspective of bound
states. We find that as the orbital Feshbach resonance acquires two nearly
degenerate scattering channels, which in general have different threshold
energies, CIR takes place when the closed channel bound state energy becomes
degenerate with one of the thresholds.",1809.00471v1
2018-09-13,Anisotropic hybridization in a new Kondo lattice compound CeCoInGa$_3$,"We report a detailed and comparative study of the single crystal CeCoInGa$_3$
in both experiment and theory. Resistivity measurements reveal the typical
behavior of Kondo lattice with the onset temperature of coherence, $T^*\approx
50\,$K. The magnetic specific heat can be well fitted using a spin-fluctuation
model at low temperatures, yielding a large Sommerfeld coefficient,
$\gamma\approx172\,$mJ/mol K$^2$ at 6 K, suggesting that this is a
heavy-fermion compound with a pronounced coherence effect. The magnetic
susceptibility exhibits a broad field-independent peak at $T_{\chi}$ and shows
an obvious anisotropy within the $bc$ plane, reflecting the anisotropy of the
coherence effect at high temperatures. These are compared with strongly
correlated calculations combining first-principles band structure calculations
and dynamical mean-field theory. Our results confirm the onset of coherence at
about 50 K and reveal a similar anisotropy in the hybridization gap, pointing
to a close connection between the hybridization strength of the low-temperature
Fermi-liquid state and the high-temperature coherence effect.",1809.04735v1
2018-10-10,Activity driven orientational order in active nematic liquid crystals on an anisotropic substrate,"We investigate the effect of an anisotropic substrate on the turbulent
dynamics of a simulated two dimensional active nematic. This is introduced as
an anisotropic friction and an effective anisotropic viscosity, with the
orientation of the anisotropy being defined by the substrate. In this system we
observe the emergence of global nematic order of topological defects that is
controlled by the degree of anisotropy in the viscosity and the magnitude of
the active stress. No global defect alignment is seen in passive liquid
crystals with anisotropic viscosity or friction confirming that ordering is
driven by the active stress. We then closely examine the active flow generated
by a single defect to show that the kinetic energy of the flow is orientation
dependent, resulting in a torque on the defect to align them with the
anisotropy in the substrate.",1810.04549v1
2018-10-12,Effectof biquadratic exchange on the phase diagram of a spin-1 transverse XY modelwith single-ion anisotropy,"The two-time Green function method is employed to explore the effect of the
biquadratic exchange interaction on the phase diagram of a $d$-dimensional
spin-1 transverse XY model with single-ion anisotropy close to the
magnetic-field-induced quantum critical point. We work at level of the
Anderson-Callen-decoupling-like framework for both easy-plane and easy-axis
single-ion anisotropy. The structure of the phase diagram is analyzed with
analytical estimates and numerical calculations by adopting Tyablikov-like
decouplings for the exchange higher order Green functions in the equation of
motion. For dominant bilinear short-range exchange interaction the structure of
the phase diagram close to the quantum critical point remains qualitatively the
same of that in absence of biquadratic interaction including reentrant critical
lines. When the biquadratic exchange becomes increasingly dominant its role
appears more effective and tends to reduce or destroy the reentrant character
of the critical lines.",1810.05505v1
2018-10-24,Nearly isotropic spin-pumping related Gilbert damping in Pt/Ni$_{81}$Fe$_{19}$/Pt,"A recent theory by Chen and Zhang [Phys. Rev. Lett. 114, 126602 (2015)]
predicts strongly anisotropic damping due to interfacial spin-orbit coupling in
ultrathin magnetic films. Interfacial Gilbert-type relaxation, due to the spin
pumping effect, is predicted to be significantly larger for magnetization
oriented parallel to compared with perpendicular to the film plane. Here, we
have measured the anisotropy in the Pt/Ni$_{81}$Fe$_{19}$/Pt system via
variable-frequency, swept-field ferromagnetic resonance (FMR). We find a very
small anisotropy of enhanced Gilbert damping with sign opposite to the
prediction from the Rashba effect at the FM/Pt interface. The results are
contrary to the predicted anisotropy and suggest that a mechanism separate from
Rashba spin-orbit coupling causes the rapid onset of spin-current absorption in
Pt.",1810.10595v4
2018-10-31,Angular momentum of fission fragments,"The strong deformation present immediately after scission has consequences
for the angular momentum population of the fragments as well as the angular
distribution of their decay radiation. We find that the usual spin-cutoff
parameterization describes very well the angular momentum distribution
associated with the deformation of the fragments at the scission point.
Depending on the deformation, its contribution can comparable to the thermal
contribution to the angular momentum of the newly formed fragments. The
$M$-distribution of the angular momentum is highly polarized and gives rise to
large anisotropies in the subsequent gamma cascade. We treat in detail a
typical gamma cascade in a daughter nucleus, following usual model assumptions
except for the anisotropy of the initial state. In principle, the observed
anisotropy can provide information on the relative amounts of deformation and
thermal energy present at the scission point.",1810.13429v1
2018-11-02,Ferromagnetic ordering of linearly coordinated Co ions in LiSr$_2$[CoN$_2$],"LiSr$_2$[CoN$_2$] single crystals were successfully grown out of Li-rich
flux. Temperature- and field-dependent measurements of the magnetization in the
range of $T = 2 - 300$ K and up to $\mu_{0}\textit{H} = 7$ T as well as
measurements of the heat capacity are presented. Ferromagnetic ordering emerges
below $T_C = 44$ K and comparatively large coercivity fields of $\mu_0H = 0.3$
T as well as pronounced anisotropy are observed upon cooling. Polycrystalline
samples of the Ca analog LiCa$_2$[CoN$_2$] were obtained and investigated in a
similar way. In both compounds Co manifests orbital contributions to the
magnetic moment and large single-ion anisotropy that is caused by second-order
Spin-orbit coupling. Quantum chemistry calculations reveal a magnetic
anisotropy energy of 7 meV, twice as large as the values reported for similar
Co $d^{8}$ systems.",1811.00867v1
2018-12-14,Anisotropic magnetic properties and giant rotating magnetocaloric effect in double-perovskite Tb2CoMnO6,"We investigated the anisotropy of the magnetic and magnetocaloric properties
of singlecrystalline double perovskite Tb2CoMnO6, which crystallizes in a
monoclinic P21/n structure. Due to dissimilar magnetic anisotropy, the
ferromagnetic order of the Co2+ and Mn4+ moments emerges along the c-axis at TC
= 100 K, and the larger Tb3+ moments align perpendicular to the c-axis, below
TTb = 15 K. The intricate temperature development of the metamagnetism along
the c-axis results in a large negative change in the magnetic entropy at low
temperature. On the other hand, the larger but almost reversible magnetization,
perpendicular to the c-axis, results in a small and positive entropy change.
This highly anisotropic magnetocaloric effect (MCE) leads to a giant rotational
MCE, estimated to be 20.8 J/kg K. Our findings, based on the magnetic
anisotropy in Tb2CoMnO6, enrich fundamental and applied research on magnetic
materials, considering the distinct magnetic characteristics of double
perovskites.",1812.05798v1
2018-12-28,Anisotropy in 2D Discrete Exterior Calculus,"We present a local formulation for 2D Discrete Exterior Calculus (DEC)
similar to that of the Finite Element Method (FEM), which allows a natural
treatment of material heterogeneity (element by element). It also allows us to
deduce, in a robust manner, anisotropic fluxes and the DEC discretization of
the pullback of 1-forms by the anisotropy tensor, i.e. we deduce how the
anisotropy tensor acts on primal 1-forms. Due to the local formulation, the
computational cost of DEC is similar to that of the Finite Element Method with
Linear interpolations functions (FEML). The numerical DEC solutions to the
anisotropic Poisson equation show numerical convergence, are very close to
those of FEML on fine meshes and are slightly better than those of FEML on
coarse meshes.",1812.11155v1
2019-01-03,Realization of Kondo chain in CeCo$_2$Ga$_8$,"We revisited the anisotropy of the heavy-fermion material CeCo$_2$Ga$_8$ by
measuring the electrical resistivity and magnetic susceptibility along all the
principal $\mathbf{a}$-, $\mathbf{b}$- and $\mathbf{c}$-axes. Resistivity along
$\mathbf{c}$-axis ($\rho_c$) shows clear Kondo coherence below about 17 K,
while both $\rho_{a}$ and $\rho_{b}$ remain incoherent down to 2 K. The
magnetic anisotropy is well understood within the theoretical frame of
crystalline electric field effect in combination with magnetic exchange
interactions. We found the anisotropy ratio of these magnetic exchange
interactions, $|J_{ex}^c/J_{ex}^{a,b}|$, reaches a large value of 4-5. We,
therefore, firmly demonstrate that CeCo$_2$Ga$_8$ is a quasi-one-dimensional
heavy-fermion compound both electrically and magnetically, and thus provide a
realistic example of \textit{Kondo chain}.",1901.00558v2
2019-01-07,Giant anisotropy of Gilbert damping in epitaxial CoFe films,"Tailoring Gilbert damping of metallic ferromagnetic thin films is one of the
central interests in spintronics applications. Here we report a giant Gilbert
damping anisotropy in epitaxial Co$_{50}$Fe$_{50}$ thin film with a
maximum-minimum damping ratio of 400 \%, determined by broadband spin-torque as
well as inductive ferromagnetic resonance. We conclude that the origin of this
damping anisotropy is the variation of the spin orbit coupling for different
magnetization orientations in the cubic lattice, which is further corroborate
from the magnitude of the anisotropic magnetoresistance in Co$_{50}$Fe$_{50}$.",1901.01941v1
2019-01-15,Effect of random anisotropy on NMR frequency shift in the polar phase of the superfluid 3He,"The orbital anisotropy induced in the superfluid 3He by nematic aerogel is,
generally speaking, spatially non-uniform. This anisotropy in its turn induces
spatial fluctuations of the order parameter. It is shown here that for the
polar phase these fluctuations decrease the overall amplitude of the order
parameter and the value of the frequency shift of the transverse NMR. Different
contributions to this effect are discussed and estimated. Their temperature
dependencies are discssed as well.",1901.05025v2
2019-01-18,Ballistic transport experiment detects Fermi surface anisotropy of graphene,"Monolayer graphene and bilayer graphene have strikingly different properties.
One such difference is the shape of the Fermi surface. Although anisotropic
band structures can be detected in optical measurements, they have so far been
difficult to detect in transport experiments on twodimensional materials. Here
we describe a ballistic transport experiment using high-quality graphene that
revealed Fermi surface anisotropy in the magnetoresistance. The shape of the
Fermi surface is closely related with the cyclotron orbit in real space.
Electron trajectories in samples with triangular lattices of holes depend on
the anisotropy of the Fermi surface. We found that this results in the
magnetoresistance which are dependent on crystallographic orientation of the
antidot lattice, which indicates the anisotropic Fermi surface of bilayer
graphene which is a trigonally-warped circle in shape. While in monolayer,
shape of magnetoresistance was approximately independent of the orientation of
antidot lattice, which indicates that the Fermi surface is a circle in shape.
The ballistic transport experiment is a new method of detecting anisotropic
electronic band structures in two-dimensional electron systems.",1901.06073v1
2019-02-02,Propagation of UHECRs in the local Universe and origin of cosmic magnetic fields,"We simulate the propagation of cosmic rays at ultra-high energies, $\gtrsim
10^{18}$ eV, in models of extragalactic magnetic fields in constrained
simulations of the local Universe. We investigate the impact of different
magneto-genesis scenarios, both, primordial and astrophysical, on the
propagation of cosmic rays. Our study shows that different scenarios of
magneto-genesis do not have a large impact on the anisotropy measurements. The
distribution of nearby sources causes anisotropy at very high energies,
independent of the magnetic field model. We compare our results to the dipole
signal measured by the Pierre Auger Observatory. All our models could reproduce
the observed dipole amplitude with a pure iron injection composition. This is
due to clustering of secondary nuclei in direction of nearby sources of heavy
nuclei. A light injection composition is disfavoured by the non-observation of
anisotropy at energies of 4 - 8 EeV.",1902.04408v1
2019-02-12,Characterization of spin wave propagation in (111) YIG thin films with large anisotropy,"We report on long-range spin wave (SW) propagation in nanometer-thick yttrium
iron garnet (YIG) film with an ultralow Gilbert damping. The knowledge of a
wavenumber value $|\vec{k}|$ is essential for designing SW devices. Although
determining the wavenumber $|\vec{k}|$ in experiments like Brillouin light
scattering spectroscopy is straightforward, quantifying the wavenumber in
all-electrical experiments has not been widely commented upon so far. We
analyze magnetostatic spin wave (SW) propagation in YIG films in order to
determine the SW wavenumber $|\vec{k}|$ excited by the coplanar waveguide. We
show that it is crucial to consider the influence of magnetic anisotropy fields
present in YIG thin films for precise determination of SW wavenumber. With the
proposed methods we find that experimentally derived values of $|\vec{k}|$ are
in perfect agreement with that obtained from electromagnetic simulation only if
anisotropy fields are included.",1902.04608v1
2019-02-25,Magic Numbers for the Photoelectron Anisotropy in Li-Doped Dimethyl Ether Clusters,"Photoelectron velocity map imaging of Li(CH$_3$OCH$_3$)$_n$ clusters (1
$\leq$ n $\leq$ 175) is used to search for magic numbers related to the
photoelectron anisotropy. Comparison with density functional calculations
reveals magic numbers at n=4, 5, and 6, resulting from the symmetric charge
distribution with high s-character of the highest occupied molecular orbital.
Since each of these three cluster sizes correspond to the completion of a first
coordination shell, they can be considered as 'isomeric motifs of the first
coordination shell'. Differences in the photoelectron anisotropy, the vertical
ionization energies and the enthalpies of vaporization between
Li(CH$_3$OCH$_3$)$_n$ and Na(CH$_3$OCH$_3$)$_n$ can be rationalized in terms of
differences in their solvation shells, atomic ionization energies,
polarizabilities, metal-oxygen bonds, ligand-ligand interactions, and by
cooperative effects.",1902.09575v1
2019-03-12,Neutron Diffraction Studies on Temperature Driven Crystallographic Anisotropy in FeVO4 Multiferroic: Evidence of Strong Magnetostructural Correlations,"We used temperature-dependent neutron diffraction measurements on FeVO4 to
understand the temperature driven anisotropy and observed that the maximum
change for a and b lattice parameters in conjunction with a large contraction
in angle \beta\ as a function of temperature. The least changes are observed
for the c lattice parameter and in \gamma\ angle. From these structural
parameters, it can be said that, FeVO4 exhibits large structural anisotropy
with lowering temperature. The large change in lattice parameters in magnetic
phases i.e. below 22 K explains the strong magnetostructural coupling in FeVO4.",1903.04913v1
2019-03-12,The tidal deformability of an anisotropic compact star: Implications of GW170817,"We use gravitational wave (GW) and electromagnetic (EM) observations of
GW170817 to constrain the extent of pressure anisotropy in it. While it is
quite likely that the pressure inside a neutron star is mostly isotropic,
certain physical processes or characteristics, such as phase transitions in
nuclear matter or the presence of strong magnetic fields, can introduce
pressure anisotropy. In this work, we show that anisotropic pressure in neutron
stars can reduce their tidal deformability substantially. For the
anisotropy-pressure model of Bowers and Liang and a couple of relativistic EOSs
-- DDH$\delta$ and GM1 -- we demonstrate that this reduction in spherical
neutron stars with masses in the range of 1 to 2 $M_\odot$ can be 23% to 46%.
This suggests that certain EOSs that are ruled out by GW170817 observations,
under assumptions of pressure isotropy, can become viable if the stars had a
significant enough anisotropic pressure component, but do not violate
causality. We also show how the inference of the star radius can be used to
rule out certain EOSs (such as GM1), even for high anisotropic pressure,
because their radii are larger than what the observations find.",1903.04956v1
2019-03-14,In-plane anisotropic faceting of ultralarge and thin single-crystalline colloidal SnS nanosheets,"The colloidal synthesis of large thin two-dimensional (2D) nanosheets is
fascinating but challenging, since the growth along the lateral and vertical
dimensions need to be controlled independently. In-plane anisotropy in 2D
nanosheets is attracting more attention as well. We present a new synthesis for
large colloidal single-crystalline SnS nanosheets with the thicknesses down to
7 nm and lateral sizes up to 8 um. The synthesis uses trioctylphosphine-S
(TOP-S) as sulfur source and oleic acid (with or without TOP) as ligands. Upon
adjusting the capping ligand amount, the growth direction can be switched
between anisotropic directions (armchair and zigzag) and isotropic directions
(""ladder"" directions), leading to an edge-morphology anisotropy. This is the
first report on solution-phase synthesis of large thin SnS NSs with tunable
edge faceting. Furthermore, electronic transport measurements show strong
dependency on the crystallographic directions confirming structural anisotropy.",1903.06062v1
2019-03-21,Magnetic and electrical anisotropy with correlation and orbital effects in dimerized honeycomb ruthenate Li$_2$RuO$_3$,"Li2RuO3 undergoes a structural transition at a relatively high temperature of
550 K with a distinct dimerization of Ru-Ru bonds on the otherwise isotropic
honeycomb lattice. It exhibits a unique herringbone dimerization pattern with a
largest ever reported value of the bond shrinkage of about ~ 0.5 \r{A}. Despite
extensive studies, both theoretical and experimental, however, its origin and
its effect on physical properties still remain to be understood. In this work,
using high quality single crystals we investigated the anisotropy of
resistivity ($\rho$) and magnetic susceptibility ($\chi$) to find a very clear
anisotropy: $\rho$$_c*$ > $\rho$$_b$ > $\rho$$_a$ and $\chi$$_b$ > $\chi$$_a$ >
$\chi$$_c*$. For possible theoretical interpretations, we carried out density
functional calculations to conclude that these anisotropic behavior is due to
the correlation effects combined with the unique orbital structure and the
dimerization of Ru 4d bands.",1903.08812v2
2019-04-01,An all-electron product-basis set: application to plasmon anisotropy in simple metals,"An efficient basis set for products of all-electron wave functions is
proposed, which comprises plane waves defined over the entire unit cell and
orbitals confined to small non-overlapping spheres. The size of the set and the
basis functions are, in principle, independent of the computational parameters
of the band structure method. The approach is implemented in the extended LAPW
method, and its properties and accuracy are discussed. The method is applied to
analyze the dielectric response of the simple metals Al, Na, Li, K, Rb, and Cs
with a focus on the origin of the anisotropy of the plasmon dispersion in Al
and Na. The anisotropy is traced to tiny structures of the one-particle
excitation spectra of Al and Na, and relevant experimental observations are
explained.",1904.00968v1
2019-04-08,Spectral anisotropies and intermittency of plasma turbulence at ion kinetic scales,"By means of three dimensional high-resolution hybrid simulations we study the
properties of the magnetic field spectral anisotropies near and beyond ion
kinetic scales. By using both a Fourier analysis and a local analysis based on
multi-point 2nd-order structure function techniques, we show that the
anisotropy observed is less than what expected by standard wave normal modes
turbulence theories although the non linear energy transfer is still in the
perpendicular direction, only advected in the parallel direction as expected
balancing the non-linear energy transfer time and the decorrelation time. Such
result can be explained by a phenomenological model based on the formation of
strong intermittent two-dimensional structures in the plane perpendicular to
the local mean field that have some prescribed aspect ratio eventually
depending on the scale. This model support the idea that small scales
structures, such as reconnecting current sheets, contribute significantly to
the formation of the turbulent cascade at kinetic scales.",1904.03903v2
2019-04-09,Large effect of the metal substrate on the magnetic anisotropy of Co on hexagonal Boron Nitride,"We combine x-ray absorption spectroscopy (XAS), x-ray magnetic circular
dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) data with first
principles density functional theory (DFT) calculations and a multiorbital many
body Hamiltonian approach to understand the electronic and magnetic properties
of Co atoms adsorbed on h-BN/Ru(0001) and h-BN/Ir(111). The XAS line shape
reveals, for both substrates, an electronic configuration close to $3d^8$,
corresponding to a spin $S = 1$. Magnetic field dependent XMCD data show large
(14 meV) out-of-plane anisotropy on h-BN/Ru(0001), while it is almost isotropic
(tens of $\mu$eV) on h-BN/Ir(111). XMLD data together with both DFT
calculations and the results of the multiorbital Hubbard model suggest that the
dissimilar magnetic anisotropy originates from different Co adsorption sites,
namely atop N on h-BN/Ru(0001) and 6-fold hollow on h-BN/Ir(111).",1904.04738v1
2019-04-16,Properties of the stochastic astrophysical gravitational wave background: astrophysical sources dependencies,"This article explores the properties (amplitude and shape) of the angular
power spectrum of the anisotropies of the astrophysical gravitational wave
background (AGWB) focusing on the signatures of the astrophysical models
describing sub-galactic physics. It demonstrates that while some parameters
have negligible impact others, and in particular the stellar evolution models,
the metallicity and the merger time delay distribution can result in relative
differences of order 40% in the angular power spectrum of anisotropies in both
the LIGO/Virgo and LISA frequency bands. It is also shown that the monopole and
the anisotropic components of the AGWB are complementary and sensitive to
different astrophysical parameters. It follows that AGWB anisotropies are a new
observable with the potential to provide new astrophysical information that can
not be accessed otherwise.",1904.07797v3
2019-04-19,Sub-terahertz ferrimagnetic spin-transfer torque oscillator,"A theory of magnetization dynamics in ferrimagnetic materials with
antiparallel aligned spin sub-lattices under action of spin-transfer torques
(STT) is developed. We consider magnetization dynamics in GdFeCo layers in two
cases of magnetic anisotropy: easy plane and easy axis. We demonstrate that,
(i) for the easy plane anisotropy the precession of the N\'{e}el vector is
conical and the cone angle depends on the STT strength and the value of spin
non-compensation, while the frequency of precession can reach sub-THz
frequencies; (ii) for the easy axis anisotropy two regimes are possible:
deterministic switching of the net magnetization and a conical sub-THz
precession depending on the STT strength.",1904.09341v1
2019-04-30,Dynamics of a magnetic skyrmionium in an anisotropy gradient,"Magnetic skyrmionium is a novel magnetization configuration with zero
skyrmion number, which is composed by two skyrmions with opposite skyrmion
number. Here, we study the dynamics of skyrmionium under an anisotropy
gradient. We find that the skyrmionium can be efficiently driven by an
anisotropy gradient with moving straightly along the direction of gradient. The
skyrmion Hall angle for skyrmionium is close to zero which is much smaller than
that of skyrmion. while the speed is much larger. We also demonstrate that the
skyrmionium motion depends on the damping cofficient, and the skyrmionium
stabilization in the motion can be modulated by narrowing the width of the
nanowire. Our work shows a efficient driven method for skyrmionium, which may
be promising in the application of skyrmionium based racetrack memory.",1904.13332v1
2019-05-06,Probing cosmic anisotropy with GW/FRB as upgraded standard sirens,"Recently it was shown that cosmic anisotropy can be well tested using either
standard siren measurement of luminosity distance $d_\mathrm{L}(z)$ from
gravitational-wave (GW) observation or dispersion measure ($\mathrm{DM}(z)$)
from fast radio burst (FRB). It was also observed that the combined measurement
of $d_\mathrm{L}(z)\cdot\mathrm{DM}(z)$ from the GW/FRB association system as
suggested in some of FRB models is more effective to constrain cosmological
parameters than $d_\mathrm{L}(z)$ or $\mathrm{DM}(z)$ separately due to its
independence from Hubble constant. In this paper, we will show both
theoretically and with simulation that, this upgraded sirens from combined
GW/FRB observations could test cosmic anisotropy with a double relative
sensitivity compared to the usual standard siren from GW observation alone.",1905.01803v2
2019-05-10,Long-wavelength emergent phonons in skyrmion crystals distorted by exchange anisotropy and tilted magnetic fields,"Skyrmion crystals (SkX) are periodic alignment of magnetic skyrmions, i.e., a
type of topologically protected spin textures. Compared with ordinary crystals,
they can be drastically deformed under anisotropic effects because they are
composed of field patterns whose deformation does not cause any bond-breaking.
This exotic ductility of SkX bring about great tunability of its collective
excitations called emergent phonons, which are vital for magnonics application.
The question is how to quantitatively determine the emergent phonons of
distorted SkX. Here we systematically study the long wavelength emergent
phonons of SkX distorted by (a) a negative exchange anisotropy, and (b) a
tilted magnetic field. In both cases, deformation and structural transitions of
SkX thoroughly influence the frequency, anisotropy of vibrational pattern and
dispersion relation, and coupling between lattice vibration and in-lattice
vibration for all modes. Tilted magnetic fields are very effective in tuning
the emergent phonons, such that all modes except the Goldstone mode can be
excited by AC magnetic fields when a tilted bias field is presented.",1905.03987v1
2019-05-08,Hidden Anisotropy in the Drude Conductivity of Charge Carriers with Dirac-Schrödinger Dynamics,"We show that the conductivity of a two-dimensional electron gas can be
intrinsically anisotropic despite isotropic Fermi surface, energy dispersion,
and disorder configuration. In the model we study, the anisotropy stems from
the interplay between Dirac and Schr\""odinger features combined in a special
two-band Hamiltonian describing the quasiparticles similar to the low-energy
excitations in phosphorene. As a result, even scalar isotropic disorder
scattering alters the nature of the carriers and results in anisotropic
transport. Solving the Boltzmann equation exactly for such carriers with
point-like random impurities we find a hidden knob to control the anisotropy
just by tuning either the Fermi energy or temperature. Our results are expected
to be generally applicable beyond the model studied here, and should stimulate
further search for the alternative ways to control electron transport in
advanced materials.",1905.04292v1
2019-05-20,Anisotropy engineering edge magnetism in zigzag honeycomb nanoribbons,"It have been demonstrated that the zigzag honeycomb nanoribbons exhibit an
intriguing edge magnetism. Here the effect of the anisotropy on the edge
magnetism in zigzag honeycomb nanoribbons is investigated by using two kinds of
large-scale quantum Monte Carlo simulations. The anisotropy in zigzag honeycomb
nanoribbons is characterized by the ratios of nearest-neighboring hopping
integrals $t_{1}$ in one direction and $t_{2}$ in another direction.
Considering the electron-electron correlation, it is shown that the edge
ferromagnetism could be enhanced greatly as $t_{2}/|t_{1}|$ increase from $1$
to $3$, which not only presenting the avenue for the control of this magnetism,
but also being useful for exploring further novel magnetism in new nano-scale
materials.",1905.08050v1
2019-05-20,Density jump as a function of magnetic field for collisionless shocks in pair plasmas: the perpendicular case,"In the absence of frequent binary collisions to isotropize the plasma, the
fulfillment of the magnetohydrodynamic (MHD) Rankine-Hugoniot jump conditions
by collisionless shocks is not trivial. In particular, the presence of an
external magnetic field can allow for stable anisotropies, implying some
departures from the isotropic MHD jumps. The functional dependence of such
anisotropies in terms of the field is yet to be determined. By hypothesizing a
kinetic history of the plasma through the shock front, we recently devised a
theory of the downstream anisotropy, hence of the density jump, in terms of the
field strength for a parallel shock [J. Plasma Phys. (2018), vol. 84,
905840604]. Here, we extend the analysis to the case of a perpendicular shock.
We still find that the field reduces the density jump, but the effect is less
pronounced than in the parallel case.",1905.08079v1
2019-05-28,Sensitivity of D meson azimuthal anisotropies to system size and nuclear structure,"Recent experimental data at the Large Hadron Collider (LHC) confirmed that
the soft sector azimuthal anisotropies in central XeXe collisions are sensitive
to deformations in the wave function of the Xenon nucleus. Additionally, the
CMS experiment found that D meson flow is slightly suppressed compared to other
particle species when considering quark number scaling in small systems of pPb
compared to PbPb. In this talk we used the D and B Mesons Modular (DAB-MOD)
code coupled to Trento+v-USPhydro to calculate the $R_{AA}$ and $v_n$'s of D
mesons using different energy loss models and Langevin techniques. Comparing D
mesons $R_{AA}$ and $v_n$ in PbPb to XeXe collisions it is found that in
central collisions D meson azimuthal anisotropies are sensitive to details in
the nuclear structure wave function of Xenon. Additionally, we find that in
mid-central collisions the smaller system size of XeXe suppresses D meson flow.",1905.12038v1
2019-06-01,"Theory of skyrmion, meron, anti-skyrmion and anti-meron in chiral magnets","We find closed-form solution of the Euler equation for a chiral magnet in
terms of a skyrmion or a meron depending on the relative strengths of magnetic
anisotropy and magnetic field. We show that the relevant length scales for
these solutions primarily depend on the strengths of Dzyaloshinskii-Moriya
interaction through its ratios, respectively, with magnetic field and magnetic
anisotropy. We thus unambiguously determine the parameter dependencies on the
radius of the topological structures particularly of the skyrmions, showing an
excellent agreement with experiments and first-principle studies. An
anisotropic Dzyaloshinskii-Moriya interaction suitable for thin films made with
$C_{nv}$ symmetric materials is found to stabilize anti-skyrmion and
anti-meron, which are prototypical for $D_{2d}$ symmetric systems, depending on
the degree of anisotropy. Based on these solutions, we obtain phase diagram by
comparing the energies of various collinear and non-collinear competing phases.",1906.00210v2
2019-06-03,Induced Charge Anisotropy: a Hidden Variable Affecting Ion Transport through Membranes,"The ability of semipermeable membranes to selectively impede the transport of
undesirable solutes is key to many applications. Yet, obtaining a systematic
understanding of how membrane structure affects selectivity remains elusive due
to the insufficient spatiotemporal resolution of existing experimental
techniques, and the inaccessibility of relevant solute transport timescales to
conventional molecular simulations. Here, we utilize jumpy forward-flux
sampling to probe the transport of sodium and chloride ions through a graphitic
membrane with sub-nm pores. We find chlorides to traverse the pore at rates
over two orders of magnitude faster than sodiums. We also identify two major
impediments to the transport of both ion types. In addition to the partial
dehydration of the leading ion, its traversal induces charge anisotropy at its
rear, which exerts a net restraining force on the ion. Charge anisotropy is
therefore a crucial hidden variable controlling the kinetics of ion transport
through nanopores.",1906.00853v2
2019-06-07,Shear-Induced Anisotropy in Rough Elastomer Contact,"True contact between randomly rough solids consists of myriad individual
micro-junctions. While their total area controls the adhesive friction force of
the interface, other macroscopic features, including viscoelastic friction,
wear, stiffness and electric resistance, also strongly depend on the size and
shape of individual micro-junctions. Here we show that, in rough elastomer
contacts, the shape of micro-junctions significantly varies as a function of
the shear force applied to the interface. This process leads to a growth of
anisotropy of the overall contact interface, which saturates in macroscopic
sliding regime. We show that smooth sphere/plane contacts have the same
shear-induced anisotropic behaviour as individual micro-junctions, with a
common scaling law over four orders of magnitude in initial area. We discuss
the physical origin of the observations in the light of a fracture-based
adhesive contact mechanics model, described in the companion article, which
captures the smooth sphere/plane measurements. Our results shed light on a
generic, overlooked source of anisotropy in rough elastic contacts, not taken
into account in current rough contact mechanics models.",1906.02947v1
2019-06-10,Formation of spiral ordering by magnetic field in frustrated anisotropic antiferromagnets,"We discuss theoretically phase transitions in frustrated antiferromagnets
with biaxial anisotropy or dipolar forces in magnetic field applied along the
easy axis at $T=0$. There are well-known sequences of phase transitions upon
the field increasing: the conventional spin-flop transition and the flop of the
spiral plane at strong and weak easy-axis anisotropy, respectively. We argue
that much less studied scenarios can appear at moderate anisotropy in which the
magnetic field induces transitions of the first order from the collinear state
to phases with spiral orderings. Critical fields of these transitions are
derived in the mean-field approximation and the necessary conditions are found
for the realization of these scenarios. We show that one of the considered
sequences of phase transitions was found in multiferroic MnWO$_4$ both
experimentally and numerically (in a relevant model) and our theory reproduces
quantitatively the numerical findings.",1906.03839v2
2019-06-12,Perfect control of photoelectron anisotropy for randomly oriented ensembles of molecules by XUV REMPI and polarization shaping,"We report two schemes to generate perfect anisotropy in the photoelectron
angular distribution of a randomly oriented ensemble of polyatomic molecules.
In order to exert full control over the anisotropy of photoelectron emission,
we exploit interferences between single-photon pathways and a manifold of
resonantly-enhanced two-photon pathways. These are shown to outperform
non-sequential $(\omega,2\omega)$ bichromatic phase control for the example of
CHFClBr molecules. We are able to optimize pulses that yield anisotropic
photoelectron emission thanks to a very efficient calculation of photoelectron
momentum distributions. This is accomplished by combining elements of quantum
chemistry, variational scattering theory, and time-dependent perturbation
theory.",1906.05207v1
2019-06-13,Thermal Creation of Skyrmions in Ferromagnetic Films with Perpendicular Anisotropy and Dzyaloshinskii-Moriya Interaction,"We study theoretically, via Monte Carlo simulations on lattices containing up
to 1000 x 1000 spins, thermal creation of skyrmion lattices in a 2D
ferromagnetic film with perpendicular magnetic anisotropy and
Dzyaloshinskii-Moriya interaction. At zero temperature, skyrmions only appear
in the magnetization process in the presence of static disorder. Thermal
fluctuations violate conservation of the topological charge and reduce the
effective magnetic anisotropy that tends to suppress skyrmions. In accordance
with recent experiments, we find that elevated temperatures assist the
formation of skyrmion structures. Once such a structure is formed, it can be
frozen into a regular skyrmion lattice by reducing the temperature. We
investigate topological properties of skyrmion structures and find the average
skyrmion size. Energies of domain and skyrmion states are computed. It is shown
that skyrmion lattices have lower energy than labyrinth domains within a narrow
field range.",1906.05952v1
2019-06-17,Searching for Fossil Fields in the Gravity Sector,"Evidence for the presence of extra fields during inflation may be found in
the anisotropies of the scalar and tensor spectra across a vast range of
scales. Indeed, beyond the single-field slow-roll paradigm, a long tensor mode
can modulate the power spectrum inducing a sizable quadrupolar anisotropy. We
investigate how this dynamics plays out for the tensor two-point correlator.
The resulting quadrupole stores information on squeezed tensor
non-Gaussianities, specifically those sourced by the extra field content and
responsible for the breaking of so-called consistency relations. We underscore
the potential of anisotropies as a probe of new physics: testable at CMB scales
through the detection of B-modes, they are accessible at smaller scales via
interferometers and pulsar timing arrays.",1906.07204v1
2019-06-19,Edge localization of spin waves in antidot multilayers with perpendicular magnetic anisotropy,"We study the spin-wave dynamics in nanoscale antidot lattices based on Co/Pd
multilayers with perpendicular magnetic anisotropy. Using time-resolved
magneto-optical Kerr effect measurements we demonstrate that the variation of
the antidot shape introduces significant change in the spin-wave spectra,
especially in the lower frequency range. By employing micromagnetic simulations
we show that additional peaks observed in the measured spectra are related to
narrow shell regions around the antidots, where the magnetic anisotropy is
reduced due to the Ga+ ion irradiation during the focused ion beam milling
process of the antidot fabrication. The results point at new possibilities for
exploitation of localized spin waves in out-of-plane magnetized thin films,
which are easily tunable and suitable for magnonics applications.",1906.08109v2
2019-06-20,Intrinsic origin of interfacial second-order magnetic anisotropy in ferromagnet/normal metal heterostructures,"Interfacial perpendicular magnetic anisotropy, which is characterized by the
first-order (K1) and second-order (K2) anisotropies, is the core phenomenon for
nonvolatile magnetic devices. A sizable K2 satisfying a specific condition
stabilizes the easy-cone state, where equilibrium magnetization forms at an
angle from the film normal. The easy-cone state offers intriguing possibilities
for advanced spintronic devices and unique spin textures, such as spin
superfluids and easy-cone domain walls. Experimental realization of the
easy-cone state requires understanding the origin of K2, thereby enhancing K2.
However, previously proposed origins of K2 cannot fully account for
experimental results. Here we show experimentally that K2 scales almost
linearly with the work-function difference between the Co and X layers in
Pt/Co/X heterostructures (X = Pd, Cu, Pt, Mo, Ru, W, and Ta), suggesting the
central role of the inversion asymmetry in K2. Our result provides a guideline
for enhancing K2 and realizing magnetic applications based on the easy-cone
state.",1906.08450v1
2019-06-20,Effects of spin-orbit coupling on the neutron spin resonance in iron-based superconductors,"The so-called neutron spin resonance consists of a prominent enhancement of
the magnetic response at a particular energy and momentum transfer upon
entering the superconducting state of unconventional superconductors. In the
case of iron-based superconductors, the neutron resonance has been extensively
studied experimentally, and a peculiar spin-space anisotropy has been
identified by polarized inelastic neutron scattering experiments. Here we
perform a theoretical study of the energy- and spin-resolved magnetic
susceptibility in the superconducting state with $ s_{+-} $-wave order
parameter, relevant to iron-pnictide and iron-chalcogenide superconductors. Our
model is based on a realistic bandstructure including spin-orbit coupling with
electronic Hubbard-Hund interactions included at the RPA level. Spin-orbit
coupling is taken into account both in the generation of spin-fluctuation
mediated pairing, as well as the numerical computation of the spin
susceptibility in the superconducting state. We find that spin-orbit coupling
and superconductivity in conjunction can reproduce the salient experimentally
observed features of the magnetic anisotropy of the neutron resonance. This
includes the possibility of a double resonance, the tendency for a $c$-axis
polarized resonance, and the existence of enhanced magnetic anisotropy upon
entering the superconducting phase.",1906.08566v1
2019-06-27,Extrinsic Spin-Orbit Coupling and Spin Relaxation in Phosphorene,"An effective Hamiltonian is derived to describe the conduction band of
monolayer black phosphorus (phosphorene) in the presence of spin-orbit coupling
and external electric field. Envelope function approximation along with
symmetry arguments and Lowdin partitioning are utilized to derive extrinsic
spin-orbit coupling. The resulting spin splitting appears in fourth order
perturbation terms and is shown to be linear in both the magnitude of the
external electric field and the strength of the atomic spin-orbit coupling,
similar to the Bychkov-Rashba expression but with an in-plane anisotropy. The
anisotropy depends on the coupling between conduction band and other bands both
close and distant in energy. The spin relaxation of conduction electrons is
then calculated within the Dyakonov-Perel mechanism where momentum scattering
randomizes the polarization of a spin ensemble. We show how the anisotropic
Fermi contour and the anisotropic extrinsic spin splitting contribute to the
anisotropy of spin-relaxation time. Scattering centers in the substrate are
considered to be charged impurities with screened Coulomb potential.",1906.11939v2
2019-06-28,"Influence of anisotropy, tilt and pairing of Weyl nodes: The Weyl semimetals TaAs, TaP, NbAs and NbP","By means of $ab \ initio$ band structure methods and model Hamiltonians we
investigate the electronic, spin and topological properties of four
monopnictides crystallizing in body centered tetragonal structure. We show that
the Weyl bands around a Weyl point W1 or W2 possess a strong anisotropy and
tilt of the accompanying Dirac cones. These effects are larger for W2 nodes
than for W1 ones. The node tilts and positions in energy space significantly
influence the density of states of single-particle Weyl excitations. The node
anisotropies destroy the conventional picture of (anti)parallel spin and wave
vector of a Weyl fermion. This also holds for the Berry curvature around a
node, while the monopole charges are independent as integrated quantities. The
pairing of the nodes strongly modify the spin texture and the Berry curvature
for wave vectors in between the two nodes. Spin components may change their
orientation. Integrals over planes perpendicular to the connection line yield
finite Zak phases and winding numbers for planes between the two nodes, thereby
indicating the topological character.",1906.12231v2
2019-06-30,Heavy ion anisotropies: a closer look at the angular power spectrum,"Anisotropies in the final state of heavy-ion collisions carry information on
the creation, expansion and evolution of the quark-gluon plasma. Currently,
there is an abundance of studies on azimuthal anisotropies in comparison to
longitudinal ones. The purpose of this work is to quantify angular $(\theta,
\phi)$ correlations to further the understanding of the full spatial 3-D
picture of emitted hadrons. Therefore, public ALICE data from Run 1 (2010) of
Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76\mathrm{~TeV}$ is analyzed through the
estimation of an angular power spectrum. Issues with $|\eta| < 0.9$ limitation
are tackled, as well as event multiplicity and detector efficiency. Firstly,
spectra are calculated for toy Monte Carlo samples. Secondly, heavy-ion data
spectra are presented for the full momentum phase space $0.15 < p_T <
100\mathrm{~GeV}$ and also separate intervals $p_T < 0.54\mathrm{~GeV}$ and
$p_T > 0.54\mathrm{~GeV}$. The latter reveal how different geometries dominate
at distinct scales and transverse momentum. Finally, the study submits
particles generated through the AMPT model to the same power spectrum analysis.
This comparison shows that in scales dominated by flow geometry, AMPT
qualitatively describes the data spectra, while the opposite is true for
smaller scales.",1907.00413v2
2019-07-24,Improved limits on a stochastic gravitational-wave background and its anisotropies from Advanced LIGO O1 and O2 runs,"We integrate the entire, publicly available, Advanced LIGO (ALIGO) data set
to obtain maximum-likelihood constraint maps of the Stochastic
Gravitational-Wave Background (SGWB). From these we derive limits on the energy
density of the stochastic background $\Omega_{\rm GW}$, and its anisotropy. We
find 95% confident limits $\Omega_{\rm GW} < 5.2\times 10^{-8}$ at $50$ Hz for
a spectral index $\alpha=2/3$ consistent with a stochastic background due to
inspiral events and $\Omega_{\rm GW} < 3.2\times 10^{-7}$ for a scale
(frequency) invariant spectrum. We also report upper limits on the angular
power spectra $C_\ell$ for three broadband integrations of the data. Finally we
present an estimate where we integrate the data into ten separate spectral bins
as a first attempt to carry out a model-independent estimate the SGWB and its
anisotropies.",1907.10329v1
2019-07-25,Splitting of antiferromagnetic resonance modes in the quasi-two-dimensional collinear antiferromagnet Cu(en)(H$_2$O)$_2$SO$_4$,"Low-temperature magnetic resonance study of the quasi-two-dimensional
antiferromagnet Cu(en)(H$_2$O)$_2$SO$_4$ (en = C$_2$H$_8$N$_2$) was performed
down to 0.45~K. This compound orders antiferromagnetically at 0.9K. The
analysis of the resonance data within the hydrodynamic approach allowed to
identify anisotropy axes and to estimate the anisotropy parameters for the
antiferromagnetic phase. Dipolar spin-spin coupling turns out to be the main
contribution to the anisotropy of the antiferromagnetic phase. The splitting of
the resonance modes and its non-monotonous dependency on the applied frequency
was observed below 0.6K in all three field orientations. Several models were
discussed to explain the origin of the nontrivial splitting and the existence
of inequivalent magnetic subsystems in Cu(en)(H$_2$O)$_2$SO$_4$ was chosen as
the most probable source.",1907.11140v2
2019-08-02,Origin of magnetic anisotropy in the spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$,"The $S=1/2$ spin ladder compound (C$_5$H$_{12}$N)$_2$CuBr$_4$ (BPCB) is
studied by means of high-resolution inelastic neutron scattering. In agreement
with previous studies we find a band of triplet excitations with a spin gap of
$\sim0.8$~meV and a bandwidth of $\sim0.6$~meV. In addition, we observe a
distinct splitting of the triplet band of $50(1)$~$\mu$eV or $40(2)$~$\mu$eV at
the band minimum or maximum, respectively. By comparison to a strong coupling
expansion calculation of the triplet dispersion for a spin ladder with
anisotropic exchange, weakly anisotropic leg interactions are identified as the
dominant source of magnetic anisotropy in BPCB. Based on these results, we
discuss the nature of magnetic exchange anisotropy in BPCB and in related
transition-metal insulators.",1908.00724v2
2019-08-14,Propagation of Gravitational Waves in Anisotropic Universe,"In this paper, we have considered a toy model of an anisotropic universe and
studied the propagation of gravitational waves in such a universe. The
consideration of this toy model simplifies the analysis and helps us to
illustrate the effects of anisotropy. Incorporating linear perturbations on
this anisotropic background, we have considered the synchronous, transverse,
traceless gauge conditions and evaluated the perturbations of the Ricci tensor.
The energy-momentum tensor is that of a perfect fluid, for which the Einstein's
field equations are determined in presence of perturbations. We arrive at the
set of linearised Einstein's equations explicitly and find solutions for
gravitational waves propagating along the direction of anisotropy. We also
study the propagation along a direction perpendicular to the direction of
anisotropy. Subsequently we have validated the assumption of the tracelessness
of the linear perturbations. Finally we determine the amount of tidal
acceleration caused by the propagation of gravitational waves in this
background spacetime.",1908.06743v1
2019-08-21,Designing Anisotropic Microstructures with Spectral Density Function,"Materials' microstructure strongly influences its performance and is thus a
critical aspect in design of functional materials. Previous efforts on
microstructure mediated design mostly assume isotropy, which is not ideal when
material performance is dependent on an underlying transport phenomenon. In
this article, we propose an anisotropic microstructure design strategy that
leverages Spectral Density Function (SDF) for rapid reconstruction of high
resolution, two phase, isotropic or anisotropic microstructures in 2D and 3D.
We demonstrate that SDF microstructure representation provides an intuitive
method for quantifying anisotropy through a dimensionless scalar variable
termed anisotropy index. The computational efficiency and low dimensional
microstructure representation enabled by our method is demonstrated through an
active layer design case study for Bulk Heterojunction Organic Photovoltaic
Cells (OPVCs). Results indicate that optimized design, exhibiting strong
anisotropy, outperforms isotropic active layer designs. Further, we show that
Cross-sectional Scanning Tunneling Microscopy and Spectroscopy (XSTM/S) is as
an effective tool for characterization of anisotropic microstructures.",1908.07661v1
2019-08-28,Impact of Strong Anisotropy on Phase Diagram of Superfluid $^3$He in Aerogels,"Recently, one analog of the Anderson's Theorem for the $s$-wave
superconductor has attracted much interest in the context of the $p$-wave polar
pairing state of superfluid $^3$He in a model aerogel in the limit of strong
uniaxial anisotropy. We discuss to what extent the theorem is satisfied in the
polar phase in real aerogels by examining the normal to polar transition
temperature $T_c$ and the low temperature behavior of the superfluid energy gap
under an anisotropy of a moderate strength and comparing the obtained results
with experimental data. The situation in which the Anderson's theorem clearly
breaks down is also discussed.",1908.10712v4
2019-09-06,Effect of Tantalum spacer thickness and deposition conditions on the properties of MgO/CoFeB/Ta/CoFeB/MgO free layers,"To get stable perpendicularly magnetized tunnel junctions at small device
dimensions, composite free layers that comprise two MgO/FeCoB interfaces as
sources of interface anisotropy are generally used. Proper cristallisation and
annealing robustness is typically ensured by the insertion of a spacer layer of
the early transition metal series within the FeCoB layer. We study the
influence of the spacer thickness and growth condition on the switching metrics
of tunnel junctions thermally annealed at 400$^\circ$C for the case of 1-4
\r{A} Ta spacers. Thick Ta spacer results in a large anisotropies indicative of
a better defined top FeCoB/MgO interface, but this is achieved at the
systematic expense of a stronger damping. For the best anisotropy-damping
compromise, junctions of diameter 22 nm can still be stable and spin-torque
switched. Coercivity and inhomogeneous linewidth broadening, likely arising
from roughness at the FeCoB/Ta interface, can be reduced if a sacrificial Mg
layer is inserted before the Ta spacer deposition.",1909.02741v1
2019-09-07,"Long-range order induced by random fields in two-dimensional O(n) models, and the Imry-Ma state","The influence of defects of the ""random local field"" type with an anisotropic
distribution of random fields on two-dimensional models with continuous
symmetry of the vector order parameter is considered. In the case of weak
anisotropy of random fields, with decreasing temperature there takes place a
smooth transition from the paramagnetic phase with dynamic fluctuations of the
order parameter to the Imry-Ma phase with static fluctuations caused by
fluctuations of the random field of defects. In the case of strong anisotropy
of random fields, defects lead to an effective decrease in the number of
components of the order parameter and the appearance of a phase transition to
an ordered state at finite temperature. It is shown that in the case of the
defect-free two-dimensional X-Y model, the appearance of an arbitrarily weak
anisotropy in the two-dimensional space of the order parameter completely
eliminates the appearance of the Berezinsky-Kosterlitz-Thouless phase and gives
rise to the phase with the long-range order.",1909.03264v1
2019-09-27,Gravitational Wave Anisotropies from Primordial Black Holes,"An observable stochastic background of gravitational waves is generated
whenever primordial black holes are created in the early universe thanks to a
small-scale enhancement of the curvature perturbation. We calculate the
anisotropies and non-Gaussianity of such stochastic gravitational waves
background which receive two contributions, the first at formation time and the
second due to propagation effects. The former contribution can be generated if
the distribution of the curvature perturbation is characterized by a local and
scale-invariant shape of non-Gaussianity. Under such an assumption, we conclude
that a sizeable magnitude of anisotropy and non-Gaussianity in the
gravitational waves would suggest that primordial black holes may not comply
the totality of the dark matter.",1909.12619v2
2019-09-30,Bianchi spacetimes as super-curvature modes around isotropic cosmologies,"A powerful result in theoretical cosmology states that a subset of
anisotropic Bianchi models can be seen as the homogeneous limit of (standard)
linear cosmological perturbations. Such models are precisely those leading to
Friedmann spacetimes in the limit of zero anisotropy. Building on previous
works, we give a comprehensive exposition of this result, and perform the
detailed identification between anisotropic degrees of freedom and their
corresponding scalar, vector, and tensor perturbations of standard perturbation
theory. In particular, we find that anisotropic models very close to open
(i.e., negatively curved) Friedmann spaces correspond to some type of
super-curvature perturbations. As a consequence, provided anisotropy is mild,
its effects on all types of cosmological observables can always be computed as
simple extensions of the standard techniques used in relativistic perturbation
theory around Friedmann models. This fact opens the possibility to consistently
constrain, for all cosmological observables, the presence of large scale
anisotropies on the top of the stochastic fluctuations.",1909.13688v1
2019-10-05,Resistivity anisotropy of quantum Hall stripe phases,"Quantum Hall stripe phases near half-integer filling factors $\nu \ge 9/2$
were predicted by Hartree-Fock (HF) theory and confirmed by discoveries of
giant resistance anisotropies in high-mobility two-dimensional electron gases.
A theory of such anisotropy was proposed by MacDonald and Fisher, although they
used parameters whose dependencies on the filling factor, electron density, and
mobility remained unspecified. Here, we fill this void by calculating the
hard-to-easy resistivity ratio as a function of these three variables.
Quantitative comparison with experiment yields very good agreement which we
view as evidence for the ""plain vanilla"" smectic stripe HF phases.",1910.02260v3
2019-10-07,Three-Dimensional Stability of Current Sheets Supported by Electron Pressure Anisotropy,"The stability of electron current sheets embedded within the reconnection
exhaust is studied with a 3D fully kinetic particle-in-cell simulation. The
electron current layers studied here form self-consistently in a reconnection
regime with a moderate guide field, are supported by electron pressure
anisotropy with the pressure component parallel to the magnetic field direction
larger than the perpendicular components, and extend well beyond electron
kinetic scales. In 3D, in addition to drift instabilities common to nearly all
reconnection exhausts, the regime considered also exhibits an electromagnetic
instability driven by the electron pressure anisotropy. While the fluctuations
modulate the current density on small scales, they do not break apart the
general structure of the extended electron current layers. The elongated
current sheets should therefore persist long enough to be observed both in
space observations and in laboratory experiments.",1910.02848v1
2019-10-07,The Role of Pressure Anisotropy in Cosmic Ray Hydrodynamics,"Cosmic ray propagation in the Milky Way and other galaxies is largely
diffusive, with mean free path determined primarily by pitch angle scattering
from hydromagnetic waves with wavelength of order the cosmic ray gyroradius. In
the theory of cosmic ray self confinement, the waves are generated by
instabilities driven by the cosmic rays themselves. The dominant instability is
due to bulk motion, or streaming, of the cosmic rays, parallel to the
background magnetic field B, and transfers cosmic ray momentum and energy to
the thermal gas as well as confining the cosmic rays. Classical arguments and
recent numerical simulations show that self confinement due to the streaming
instability breaks down unless the cosmic ray pressure and thermal gas density
gradients parallel to B are aligned, a condition which is unlikely to always be
satisfied We investigate an alternative mechanism for cosmic ray self
confinement and heating of thermal gas based on pressure anisotropy
instability. Although pressure anisotropy is demonstrably less effective than
streaming instability as a self confinement and heating mechanism on global
scales, it may be important on mesoscales, particularly near sites of cosmic
ray injection.",1910.03052v1
2019-10-10,Transition between dissipatively stabilized helical states,"We analyze a $XXZ$ spin-1/2 chain which is driven dissipatively at its
boundaries. The dissipative driving is modelled by Lindblad jump operators
which only act on both boundary spins. In the limit of large dissipation, we
find that the boundary spins are pinned to a certain value and at special
values of the interaction anisotropy, the steady states are formed by a rank-2
mixture of helical states with opposite winding numbers. Contrarily to previous
stabilization of topological states, these helical states are not protected by
a gap in the spectrum of the Lindbladian. By changing the anisotropy, the
transition between these steady states takes place via mixed states of higher
rank. In particular, crossing the value of zero anisotropy a totally mixed
state is found as the steady state. The transition between the different
winding numbers via mixed states can be seen in the light of the transitions
between different topological states in dissipatively driven systems. The
results are obtained developing a perturbation theory in the inverse
dissipative coupling strength and using the numerical exact diagonalization and
matrix product state methods.",1910.04501v1
2019-10-10,The synergy between CMB spectral distortions and anisotropies,"Spectral distortions and anisotropies of the CMB provide independent and
complementary probes to study energy injection processes in the early universe.
Here we discuss the synergy between these observables, and show the promising
future of spectral distortion missions to constrain both exotic and non-exotic
energy injections. We show that conventional probes such as Big Bang
Nucleosynthesis and CMB anisotropies can benefit from and even be surpassed by
future spectral distortion experiments. For this, we have implemented a unified
framework within the Boltzmann code CLASS to consistently treat the thermal
evolution of photons and baryons. Furthermore, we give an extensive and
pedagogical introduction into the topic of spectral distortions and energy
injections throughout the thermal history of the universe, highlighting some of
their unique features and potential as a novel probe for cosmology and particle
physics.",1910.04619v3
2019-10-10,A unified view of anisotropies in the astrophysical gravitational wave background,"In the literature different approaches have been proposed to compute the
anisotropies of the astrophysical gravitational wave background. The different
expressions derived, although starting from our work Cusin, Pitrou, Uzan,
Phys.Rev.D96, 103019 (2017) [1], seem to differ. This article compares the
various theoretical expressions proposed so far and provides a separate
derivation based on a Boltzmann approach. We show that all the theoretical
formula in the literature are equivalent and boil down to the one of Ref. [1]
when a proper matching of terms and integration by parts are performed. The
difference between the various predictions presented for anisotropies in a
cosmological context can only lie in the astrophysical modeling of sources, and
neither in the theory nor in the cosmological description of the large scale
structures. Finally we comment on the gauge invariance of expressions.",1910.04645v2
2019-10-15,"Rotational transition, domain formation, dislocations and defects in vortex systems with combined six- and 12-fold anisotropic interactions","We introduce a new model for a pairwise repulsive interaction potential of
vortices in a type-II superconductor, consisting of superimposed six- and
12-fold anisotropies. Using numerical simulations we study how the vortex
lattice configuration varies as the magnitudes of the two anisotropic
interaction terms change. A triangular lattice appears for all values, and
rotates through 30 degrees as the ratio of the six- and 12-fold anisotropy
amplitudes is varied. The transition causes the VL to split into domains that
have rotated clockwise or counter-clockwise, with domain boundaries that are
""decorated"" by dislocations consisting of five- and seven-fold coordinated
vortices. We also find intra-domain dislocations and defects, and characterize
them in terms of their energy cost. We discuss how this model could be
generalized to other particle-based systems with anisotropic interactions, such
as colloids, and consider the limit of very large anisotropy where it is
possible to create cluster crystal states.",1910.06885v2
2019-10-01,Magnetocaloric effect in molecular spin clusters and their assemblies: model exact and Monte Carlo studies,"We study the magnetocaloric effect (MCE) in spin clusters of six spins with
site spins $s=1$, $3/2$ and $2$ for different exchange anisotropies. We also
study MCE in an assembly of spin clusters, on a chain, a 2-D square lattice and
3-D cubic lattice with spin-dipolar interactions using a Monte Carlo method in
spin-1 systems. We compute the magnetic Gr\""uneisen parameter $\Gamma_H$, and
study its dependence on exchange anisotropy and spin-dipolar interaction. With
increase of exchange anisotropy the maxima in $\Gamma_H$, shifts to higher
magnetic fields and becomes a sharp singularity. The first maximum in
$\Gamma_H$ shifts to lower fields as we increase spin-dipolar interaction. The
behaviour of $\Gamma_H$ on applied magnetic field is also reflected in the
magnetic entropy of the systems. The first maximum in $\Gamma_H$ also shifts to
lower magnetic field strength as the magnitude of the site spin increases. We
also show the dependence of $\Gamma_H$ on dimensionality of the lattice for a
fixed lattice constant.",1910.07085v2
2019-10-31,Possibility of a continuous phase transition in random-anisotropy magnets with ageneric random-axis distribution,"We reconsider the problem of the critical behavior of a three-dimensional
$O(m)$ symmetric magnetic system in the presence of random anisotropy disorder
with a generic trimodal random axis distribution. By introducing $n$ replicas
to average over disorder it can be coarse-grained to a $\phi^{4}$-theory with
$m \times n$ component order parameter and five coupling constants taken in the
limit of $n \to 0$. Using a field theory approach we renormalize the model to
two-loop order and calculate the $\beta$-functions within the $\varepsilon$
expansion and directly in three dimensions. We analyze the corresponding
renormalization group flows with the help of the Pad\'e-Borel resummation
technique. We show that there is no stable fixed point accessible from physical
initial conditions whose existence was argued in the previous studies. This may
indicate an absence of a long-range ordered phase in the presence of random
anisotropy disorder with a generic random axis distribution.",1910.14461v2
2019-11-06,Surfing multiple conformation-property landscapes via machine learning: Designing magnetic anisotropy,"The advent of computational statistical disciplines, such as machine
learning, is leading to a paradigm shift in the way we conceive the design of
new compounds. Today computational science does not only provide a sound
understanding of experiments, but also can directly design the best compound
for specific applications. This approach, known as reverse engineering,
requires the construction of models able to efficiently predict continuous
structure-property maps. Here we show that reverse engineering can be used to
tune the magnetic properties of a single-ion molecular magnet in an automated
intelligent fashion. We design a machine learning model to predict both the
energy and magnetic properties as function of the chemical structure. Then, a
particle-swarm optimization algorithm is used to explore the conformational
landscapes in the search for new molecular structures leading to an enhanced
magnetic anisotropy. We find that a 5% change in one of the coordination angles
leads to a 50% increase in the anisotropy. Our approach paves the way for a
machine-learning-driven exploration of the chemical space of general classes of
magnetic materials. Most importantly, it can be applied to any
structure-property relation and offers an effective way to automatically
generate new materials with target properties starting from the knowledge of
previously synthesized ones.",1911.02263v1
2019-11-08,Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet,"Giant Gilbert damping anisotropy is identified as a signature of strong
Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb
lattice. The phenomenon originates in spin-orbit induced splitting of
conduction electron subbands that strongly suppresses certain spin-flip
processes. As a result, the spin-orbit interaction is shown to support an
undamped non-equilibrium dynamical mode that corresponds to an ultrafast
in-plane N\'eel vector precession and a constant perpendicular-to-the-plane
magnetization. The phenomenon is illustrated on the basis of a two dimensional
$s$-$d$ like model. Spin-orbit torques and conductivity are also computed
microscopically for this model. Unlike Gilbert damping these quantities are
shown to reveal only a weak anisotropy that is limited to the semiconductor
regime corresponding to the Fermi energy staying in a close vicinity of
antiferromagnetic gap.",1911.03408v1
2019-11-13,Perpendicular Magnetic Anisotropy in Conducting NiCo2O4 Films from Spin-Lattice Coupling,"High perpendicular magnetic anisotropy (PMA), a property needed for nanoscale
spintronic applications, is rare in oxide conductors. We report the observation
of a PMA up to 0.23 MJ/m3 in modestly strained epitaxial NiCo2O4 (NCO) films
which are room-temperature ferrimagnetic conductors. Spin-lattice coupling
manifested as magnetoelastic effect was found as the origin of the PMA. The
in-plane xx-yy states of Co on tetrahedral sites play crucial role in the
magnetic anisotropy and spin-lattice coupling with an energy scale of 1
meV/f.u. The elucidation of the microscopic origin paves a way for engineering
oxide conductors for PMA using metal/oxygen hybridizations.",1911.05322v1
2019-11-25,Spin-valve Josephson junctions with perpendicular magnetic anisotropy for cryogenic memory,"We demonstrate a Josephson junction with a weak link containing two
ferromagnets, with perpendicular magnetic anisotropy and independent switching
fields in which the critical current can be set by the mutual orientation of
the two layers. Such pseudospin-valve Josephson junctions are a candidate
cryogenic memory in an all superconducting computational scheme. Here, we use
Pt/Co/Pt/CoB/Pt as the weak link of the junction with $d_\text{Co} = 0.6$ nm,
$d_\text{CoB} = 0.3$ nm, and $d_\text{Pt} = 5$ nm and obtain a $60\%$ change in
the critical current for the two magnetization configurations of the
pseudospin-valve. Ferromagnets with perpendicular magnetic anisotropy have
advantages over magnetization in-plane systems which have been exclusively
considered to this point, as in principle the magnetization and magnetic
switching of layers in the junction should not affect the in-plane magnetic
flux.",1911.11051v2
2019-11-26,Enhanced anisotropy and study of magnetization reversal in Co/C60 bilayer thin film,"The interface between organic semiconductor [OSC]/ferromagnetic [FM] material
can exhibit ferromagnetism due to their orbital hybridization. Charge/spin
transfer may occur from FM to OSC layer leading to the formation of
`spinterface' i.e. the interface exhibiting a finite magnetic moment. In this
work, the magnetic properties of Co/C$_{60}$ bilayer thin film have been
studied to probe the interface between Co and C$_{60}$ layer. Polarized neutron
reflectivity [PNR] measurement indicates that the thickness and moment of the
spinterface are $\sim$ 2 $\pm$ 0.18 nm and 0.8 $\pm$ 0.2 $\mu_B$/cage,
respectively. The comparison of the magnetization reversal between the
Co/C$_{60}$ bilayer and the parent single layer Co thin film reveals that
spinterface modifies the domain microstructure. Further, the anisotropy of the
bilayer system shows a significant enhancement ($\sim$ two times) in comparison
to its single layer counterpart which is probably due to an additional
interfacial anisotropy arising from the orbital hybridization at the
Co/C$_{60}$ interface.",1911.11873v1
2019-12-06,Increased Curie temperature and enhanced perpendicular magneto anisotropy of Cr2Ge2Te6/NiO heterostructure,"Magnetism in two-dimensional van der Waals materials has received significant
attention recently. The Curie temperature reported for those materials,
however, has been so far remained relatively low. Here, we measure
magneto-optical Kerr effects (MOKE) under perpendicular magnetic field for van
der Waals ferromagnet Cr2Ge2Te6 as well as its heterostructure with
antiferromagnetic insulator NiO. We observe a notable increase in both Curie
temperature and magnetic perpendicular anisotropy in Cr2Ge2Te6/NiO
heterostructures compared to those in Cr2Ge2Te6. Measurements on the same
exfoliated Cr2Ge2Te6 flake (on a SiO2/Si substrate) before and after depositing
NiO show that the hysteresis loop can change into a square shape with larger
coercive field for Cr2Ge2Te6/NiO. The maximum Curie temperature (TC) observed
for Cr2Ge2Te6/NiO reaches ~120 K, is nearly twice the maximum TC ~ 60 K
reported for Cr2Ge2Te6 alone. Both enhanced perpendicular anisotropy and
increased Curie temperature are observed for Cr2Ge2Te6 flakes with a variety of
thicknesses ranging from ~5 nm to ~200 nm. The results indicate that magnetic
properties of two-dimensional van der Waals magnets can be engineered and
controlled by using the heterostructure interface with other materials.",1912.03147v1
2019-12-11,Implications for cosmology from Ground-based Cosmic Microwave Background observations,"Cosmic Microwave Background (CMB) anisotropy encodes a lot of information
about our Universe. In this paper we take the ground-based CMB observations
(GCMB), including the South Pole Telescope (SPT), SPTpol and the Atacama
Cosmology Telescope Polarimeter (ACTPol), as a new probe to the CMB anisotropy
independent of two satellite observations, i.e. Wilkinson Microwave Anisotropy
Probe (WMAP) and Planck. The combination of current GCMB data is consistent
with WMAP and Planck. In the spatially flat $\Lambda$CDM model, the Hubble
constant is $H_0=69.72\pm 1.63$ km/s/Mpc at $68\%$ confidence level (CL).
Combining with baryon acoustic oscillation (BAO) and the Pantheon sample of
Type Ia supernovae (SN), we find that $H_0=68.40\pm 0.58$ km/s/Mpc ($68\%$ CL)
in the spatially flat $\Lambda$CDM cosmology which has a tension with local
measurement given by Riess et al. in 2019 at $3.7\sigma$ level, and
$\Omega_k=-0.0013\pm 0.0039$ and $N_{\rm{eff}}=2.90\pm 0.41$ ($68\%$ CL) in the
extended cosmological models.",1912.05491v2
2019-12-17,Gapped $Z_2$ spin liquid in the breathing kagome Heisenberg antiferromagnet,"We investigate the spin-1/2 Heisenberg antiferromagnet on the kagome lattice
with breathing anisotropy (i.e. with weak and strong triangular units),
constructing an improved simplex Resonating Valence Bond (RVB) ansatz by
successive applications (up to three times) of local quantum gates which
implement a filtering operation on the bare nearest-neighbor RVB state. The
resulting Projected Entangled Pair State involves a small number of variational
parameters (only one at each level of application) and preserves full lattice
and spin-rotation symmetries. Despite its simple analytic form, the simplex RVB
provides very good variational energies at strong and even intermediate
breathing anisotropy. We show that it carries $Z_2$ topological order which
does not fade away under the first few applications of the quantum gates,
suggesting that the RVB topological spin liquid becomes a competing ground
state candidate for the kagome antiferromagnet at large breathing anisotropy.",1912.08284v1
2019-12-19,Origin of Magnetic Ordering in a Structurally-Perfect Quantum Kagome Antiferromagnet,"The ground state of the simple Heisenberg nearest-neighbor quantum kagome
antiferromagnetic model is a magnetically disordered spin liquid, yet various
perturbations may lead to fundamentally different states. Here we disclose the
origin of magnetic ordering in the structurally-perfect kagome material
YCu$_3$(OH)$_6$Cl$_3$, which is free of the widespread impurity problem. {\it
Ab-initio} calculations and modeling of its magnetic susceptibility reveal
that, similar to the archetypal case of herbertsmithite, the nearest-neighbor
exchange is by far the dominant isotropic interaction. Dzyaloshinskii-Moriya
(DM) magnetic anisotropy deduced from electron spin resonance and specific-heat
measurements is, however, significantly larger than in herbertsmithite. By
enhancing spin correlations within kagome planes, this anisotropy is essential
for magnetic ordering. Our study isolates the effect of DM anisotropy from
other perturbations and unambiguously confirms the theoretical phase diagram.",1912.09047v2
2020-01-06,Enhanced voltage-controlled magnetic anisotropy via magneto-elasticity in FePt/MgO(001),"The interplay between magneto-electricity (ME) and magneto-elasticity (MEL)
is studied in the context of voltage-controlled magnetic anisotropy (VCMA).
Strain plays more than a role of changing lattice constant but that of the
internal electric field in the heterostructure. As a prototype, FePt/MgO(001)
is visited, where the behavior of two interfaces are drastically different: one
exhibits switching the other does not. Whether an external electric field
($E_{ext}$) is present or not, we found VCMA coefficient larger than 1
pJ/V$\cdot$m, as a consequence of the rearrangement of $d$ orbitals with
$m=\pm1$ and $\pm2$ in response to an external electric field. In addition,
magneto-crystalline anisotropy (MA) is analyzed with strain taken into account,
where non-linear feature is presented only accountable by invoking second-order
MEL.",2001.01464v1
2020-01-21,High order magnon bound states in the quasi-one-dimensional antiferromagnet $α$-NaMnO$_2$,"Here we report on the formation of two and three magnon bound states in the
quasi-one-dimensional antiferromagnet $\alpha$-NaMnO$_2$, where the single-ion,
uniaxial anisotropy inherent to the Mn$^{3+}$ ions in this material provides a
binding mechanism capable of stabilizing higher order magnon bound states.
While such states have long remained elusive in studies of antiferromagnetic
chains, neutron scattering data presented here demonstrate that higher order
$n>2$ composite magnons exist, and, specifically, that a weak three-magnon
bound state is detected below the antiferromagnetic ordering transition of
NaMnO$_2$. We corroborate our findings with exact numerical simulations of a
one-dimensional Heisenberg chain with easy-axis anisotropy using matrix-product
state techniques, finding a good quantitative agreement with the experiment.
These results establish $\alpha$-NaMnO$_2$ as a unique platform for exploring
the dynamics of composite magnon states inherent to a classical
antiferromagnetic spin chain with Ising-like single ion anisotropy.",2001.07300v1
2020-01-28,Quantifying the Redshift Space Distortion of the Bispectrum I: Primordial Non-Gaussianity,"The anisotropy of the redshift space bispectrum contains a wealth of
cosmological information. This anisotropy depends on the orientation of three
vectors ${\bf k_1,k_2,k_3}$ with respect to the line of sight. Here we have
decomposed the redshift space bispectrum in spherical harmonics which
completely quantify this anisotropy. To illustrate this we consider linear
redshift space distortion of the bispectrum arising from primordial
non-Gaussianity. In the plane parallel approximation only the first four even
$\ell$ multipoles have non-zero values, and we present explicit analytical
expressions for all the non-zero multipoles {\it i.e.} upto $\ell=6,m=4$. The
ratio of the different multipole moments to the real space bispectrum depends
only on $\beta_1$ the linear redshift distortion parameter and the shape of the
triangle. Considering triangles of all possible shapes, we have studied how
this ratio depends on the shape of the triangle for $\beta_1=1$. We have also
studied the $\beta_1$ dependence for some of the extreme triangle shapes. If
measured in future, these multipole moments hold the potential of constraining
$\beta_1$. The results presented here are also important if one wishes to
constrain $f_{\text{NL}}$ using redshift surveys.",2001.10243v1
2020-01-29,Perpendicularly Magnetized Ni / Pt (001) Epitaxial Superlattice,"A perpendicularly magnetized ferromagnetic layer is an important building
block for recent/future highdensity spintronic memory applications. This paper
reports on the fabrication of perpendicularly magnetized Ni / Pt superlattices
and the characterization of their structures and magnetic properties. The
optimization of film growth conditions allowed us to grow epitaxial Ni / Pt
(001) superlattices on SrTiO$_{3}$ (001) single crystal substrates. We
investigated their structural parameters and magnetic properties as a function
of the Ni layer thickness, and obtained a high uniaxial magnetic anisotropy
energy of 1.9 x 10$^{6}$ erg/cm$^{3}$ for a [Ni (4.0 nm) / Pt (1.0 nm)]
superlattice. In order to elucidate the detailed mechanism on perpendicular
magnetic anisotropy for the Ni / Pt (001) superlattices, the experimental
results were compared with the first-principles calculations. It has been found
that the strain effect is a prime source of the emergence of perpendicular
magnetic anisotropy.",2001.11127v1
2020-01-30,Quantum approach to a Bianchi I singularity,"The approach of a quantum state to a cosmological singularity is studied
through the evolution of its moments in a simple version of a Bianchi I model.
In spite of the simplicity, the model exhibits several instructive and
unexpected features of the moments. They are investigated here both
analytically and numerically in an approximation in which anisotropy is assumed
to vary slowly, while numerical methods are also used to analyze the case of a
rapidly evolving anisotropy. Physical conclusions are drawn mainly regarding
two questions. First, quantum uncertainty of anisotropies does not necessarily
eliminate the existence of isotropic solutions, with potential implications for
the interpretation of minisuperspace truncations as well as structure-formation
scenarios in the early universe. Secondly, back-reaction of moments on basic
expectation values is found to delay the approach to the classical singularity.",2001.11488v2
2020-02-04,Deterministic control of an antiferromagnetic spin arrangement using ultrafast optical excitation,"A central prospect of antiferromagnetic spintronics is to exploit magnetic
properties that are unavailable with ferromagnets. However, this poses the
challenge of accessing such properties for readout and control. To this end,
light-induced manipulation of the transient ground state, e.g. by changing the
magnetic anisotropy potential, opens promising pathways towards ultrafast
deterministic control of antiferromagnetism. Here, we use this approach to
trigger a $\it{coherent}$ rotation of the entire long-range antiferromagnetic
spin arrangement about a crystalline axis in $GdRh_2Si_2$ and demonstrate
$\it{deterministic}$ control of this rotation upon ultrafast optical
excitation. Our observations can be explained by a displacive excitation of the
Gd spins$'$ local anisotropy potential by the optical excitation, allowing for
a full description of this transient magnetic anisotropy potential.",2002.01398v1
2020-02-17,Enhancement of magnetization plateaus in low dimensional spin systems,"We study the low-energy properties and, in particular, the magnetization
process of a spin-1/2 Heisenberg $J_1-J_2$ sawtooth and frustrated chain (also
known as zig-zag ladder) with a spatially anisotropic $g$-factor. We treat the
problem both analytically and numerically while keeping the $J_2/J_1$ ratio
generic. Numerically, we use complete and Lanczos diagonalization as well as
the infinite time-evolving block decimation (iTEBD) method. Analytically we
employ (non-)Abelian bosonization. Additionally for the sawtooth chain, we
provide an analytical description in terms of flat bands and localized magnons.
By considering a specific pattern for the $g$-factor anisotropy for both
models, we show that a small anisotropy significantly enhances a magnetization
plateau at half saturation. For the magnetization of the frustrated chain, we
show the destruction of the $1/3$ of the full saturation plateau in favor of
the creation of a plateau at half-saturation. For large anisotropies, the
existence of an additional plateau at zero magnetization is possible. Here and
at higher magnetic fields, the system is locked in the half-saturation plateau,
never reaching full saturation.",2002.07190v1
2020-02-19,Modeling the atomic structure in the vicinity of the spherical voids and calculation of void growth rate anisotropy in bcc iron and tungsten,"We study the influence of the atomic structure in the vicinity of voids on
their growth rate anisotropy. In the first part, we model the atomic structure
in the vicinity of nanovoids in Fe and W using the advanced Molecular Statics
method. In the second part, we use the earlier obtained equations that taking
the influence of elastic fields into account to calculate the shifting rate of
the void surface elements, and to evaluate the components of the strain tensor
we use the atomic structure modeling results from the first part. The
calculations are performed for voids of several sizes at certain
oversaturation's in a wide temperature range. The simulation results for the
mentioned metals with a bcc structure show that displacements of atoms located
along the crystallographic directions of the 100, 110, 111 types in the
vicinity of the voids are significantly different, and this anisotropy of atom
displacements leads to a reduction of spherical symmetry for the shifting rate
of the surface elements. As the result, the initially spherical void shape
becomes faceted.",2002.07943v1
2020-02-25,Three-dimensional phonon population anisotropy in silicon nanomembranes,"Nanoscale single-crystals possess modified phonon dispersions due to the
truncation of the crystal. The introduction of surfaces alters the population
of phonons relative to the bulk and introduces anisotropy arising from the
breaking of translational symmetry. Such modifications exist throughout the
Brillouin zone, even in structures with dimensions of several nanometers,
posing a challenge to the characterization of vibrational properties and
leading to uncertainty in predicting the thermal, optical, and electronic
properties of nanomaterials. Synchrotron x-ray thermal diffuse scattering
studies find that freestanding Si nanomembranes with thicknesses as large as 21
nm exhibit a higher scattering intensity per unit thickness than bulk silicon.
In addition, the anisotropy arising from the finite thickness of these
membranes produces particularly intense scattering along reciprocal-space
directions normal to the membrane surface compared to corresponding in-plane
directions. These results reveal the dimensions at which calculations of
materials properties and device characteristics based on bulk phonon
dispersions require consideration of the nanoscale size of the crystal.",2002.11196v1
2020-03-01,A Study of Geometry in Anisotropic Quantum Hall States by Principal Component Analysis,"In the presence of mass anisotropy, anisotropic interaction, or in-plane
magnetic field, quantum Hall droplets can exhibit shape deformation and
internal geometrical degree of freedom. We characterize the geometry of quantum
Hall states by principal component analysis, which is a statistical technique
that emphasizes variation in a dataset. We first test the method in an integer
quantum Hall droplet with dipole-dipole interaction in disk geometry. In the
subsequent application to fractional quantum Hall systems with anisotropic
Coulomb interaction in torus geometry, we demonstrate that the principal
component analysis can quantify the metric degree of freedom and predict the
collapse of a $\nu= 1/3$ state. We also calculate the metric response to
interaction anisotropy at filling fractions $\nu= 1/5$ and $2/5$ and show that
the response is roughly the same within the same Jain sequence, but can differ
at large anisotropy for different sequences.",2003.00456v1
2020-03-09,Measuring mechanical anisotropy of the cornea with Brillouin microscopy,"Load-bearing tissues are typically fortified by networks of protein fibers,
often with preferential orientations. This fiber structure imparts the tissues
with direction-dependent mechanical properties optimized to support specific
external loads. To accurately model and predict tissues' mechanical response,
it is essential to characterize the anisotropy on a microstructural scale.
Previously, it has been difficult to measure the mechanical properties of
intact tissues noninvasively. Here, we use Brillouin optical microscopy to
visualize and quantify the anisotropic mechanical properties of corneal tissues
at different length scales. We derive the stiffness tensor for a lamellar
network of collagen fibrils and use angle-resolved Brillouin measurements to
determine the longitudinal stiffness coefficients (longitudinal moduli)
describing the ex vivo porcine cornea as a transverse isotropic material.
Lastly, we observe significant mechanical anisotropy of the human cornea in
vivo, highlighting the potential for clinical applications of off-axis
Brillouin microscopy.",2003.04344v2
2020-03-17,Domain wall dynamics in stepped magnetic nanowire with perpendicular magnetic anisotropy,"Micromagnetic simulation is carried out to investigate the current-driven
domain wall (DW) in a nanowire with perpendicular magnetic anisotropy (PMA). A
stepped nanowire is proposed to pin DW and achieve high information storage
capacity based on multi-bit per cell scheme. The DW speed is found to increase
for thicker and narrower nanowires. For depinning DW from the stepped region,
the current density Jdep is investigated with emphasis on device geometry and
materials intrinsic properties. The Jdep could be analytically determined as a
function of the nanocontriction dimension and the thickness of the nanowire.
Furthermore, Jdep is found to exponential dependent on the anisotropy energy
and saturation magnetization, offering thus more flexibility in adjusting the
writing current for memory applications.",2003.07721v1
2020-03-27,Anisotropy-induced Extrinsic Chirality and Chiral Discrimination of Surface Plasmon Polaritons,"We present the characteristics of a simple waveguiding structure constructed
by anisotropic birefringent crystal-metal-chiral medium,
anisotropic-metal-chiral in short, and reveal the chiral-dependent dispersion
and propagation properties of the surface plasmon polaritons (SPPs). We
demonstrate its remarkable discrimination ability to the magnitude and sign of
both the real and imaginary part of the chirality parameter. The anisotropy
plays a key role in such performance and shows tuneable ability in enantiomeric
discrimination even when the chirality parameter is complex-valued. Most
importantly, the physical origin of chiral discrimination stems from the
extrinsic chirality of the system, which arises from the mutual orientation of
the SPPs and the optical axis. Moreover, we also clarify the fundamental
physics behind the chiral discriminating behaviour by associating the intrinsic
quantum spin Hall effect (QSHE) of the SPPs with the electromagnetic field
analysis. This structure does not rely on complicated fabrication but provides
the opportunity of on-chip surface-sensitive biosensing. We anticipate that our
work will stimulate intensive research to investigate the anisotropy-induced
chiral sensing techniques in plasmonic platforms.",2003.12453v1
2020-04-01,Voltage- and temperature-dependent rare-earth dopant contribution to the interfacial magnetic anisotropy,"The control of magnetic materials and devices by voltages without electric
currents holds the promise of power-saving nano-scale devices. Here we study
the temperature-dependent voltage control of the magnetic anisotropy caused by
rare-earth (RE) local moments at an interface between a magnetic metal and a
non-magnetic insulator, such as Co|(RE)|MgO. Based on a Stevens operator
representation of crystal and applied field effects, we find large dominantly
quadrupolar intrinsic and field-induced interface anisotropies at room
temperature. We suggest improved functionalities of transition metal tunnel
junctions by dusting their interfaces with rare earths.",2004.00320v2
2020-04-01,"Spin-transfer torque-driven motion, deformation, and instabilities of magnetic skyrmions at high currents","In chiral magnets, localized topological magnetic whirls, magnetic skyrmions,
can be moved by spin polarized electric currents. Upon increasing the current
strength, with prospects for high-speed skyrmion motion for spintronics
applications in mind, isolated skyrmions deform away from their typical
circular shape. We analyze the influence of spin-transfer torques on the shape
of a single skyrmion, including its stability upon adiabatically increasing the
strength of the applied electric current. For rather compact skyrmions at
uniaxial anisotropies well above the critical anisotropy for domain wall
formation, we find for high current densities that the skyrmion assumes a
non-circular shape with a tail, reminiscent of a shooting star. For larger and
hence softer skyrmions close to the critical anisotropy, in turn, we observe a
critical current density above which skyrmions become unstable. We show that
above a second critical current density the shooting star solution can be
recovered also for these skyrmions.",2004.00450v2
2020-04-09,Hysteresis-free magnetization reversal of exchange-coupled bilayers with finite magnetic anisotropy,"Exchange-coupled structures consisting of ferromagnetic and ferrimagnetic
layers become technologically more and more important. We show experimentally
the occurrence of completely reversible, hysteresis-free minor loops of [Co(0.2
nm)/Ni(0.4 nm)/Pt(0.6 nm)]$_N$ multilayers exchange-coupled to a 20 nm thick
ferrimagnetic Tb$_{28}$Co$_{14}$Fe$_{58}$ layer, acting as hard magnetic
pinning layer. Furthermore, we present detailed theoretical investigations by
means of micromagnetic simulations and most important a purely analytical
derivation for the condition of the occurrence of full reversibility in
magnetization reversal. Hysteresis-free loops always occur if a domain wall is
formed during the reversal of the ferromagnetic layer and generates an
intrinsic hard-axis bias field that overcomes the magnetic anisotropy field of
the ferromagnetic layer. The derived condition further reveals that the
magnetic anisotropy and the bulk exchange of both layers, as well as the
exchange coupling strength and the thickness of the ferromagnetic layer play an
important role for its reversibility.",2004.04419v1
2020-04-11,Chirality of the gravitational-wave background and pulsar-timing arrays,"We describe the signatures of a circularly polarized gravitational-wave
background on the timing residuals obtained with pulsar-timing arrays. Most
generally, the circular polarization will depend on the gravitational-wave
direction, and we describe this angular dependence in terms of spherical
harmonics. While the amplitude of the monopole (the overall chirality of the
gravitational-wave background) cannot be detected, measures of the anisotropy
are theoretically conceivable. We provide expressions for the minimum-variance
estimators for the circular-polarization anisotropy. We evaluate the smallest
detectable signal as a function of the signal-to-noise ratio with which the
isotropic GW signal is detected and the number of pulsars (assumed to be
roughly uniformly spread throughout the sky) in the survey. We find that the
overall dipole of the circular polarization and a few higher overall
multipoles, are detectable in a survey with $\gtrsim100$ pulsars if their
amplitude is close to maximal and once the isotropic signal is established with
a signal-to-noise ratio $\gtrsim400$. Even if the anisotropy can be
established, though, there will be limited information on its direction.
Similar arguments apply to astrometric searches for gravitational waves.",2004.05480v1
2020-04-14,Multimessenger Cosmology: correlating CMB and SGWB measurements,"Characterizing the physical properties of the stochastic gravitational waves
background (SGWB) is a key step towards identifying the nature of its possible
origin. We focus our analysis on SGWB anisotropies. The existence of a
non-trivial primordial scalar-tensor-tensor (STT) correlation in the squeezed
configuration may be inferred from the effect that a long wavelength scalar
mode has on the gravitational wave power spectrum: an anisotropic contribution.
Crucially, such contribution is correlated with temperature anisotropies in the
cosmic microwave background (CMB). We show that, for inflationary models that
generate suitably large STT non-Gaussianities, cross-correlating the CMB with
the stochastic background of gravitational waves is a very effective probe of
early universe physics. The resulting signal can be a smoking-gun for
primordial SGWB anisotropies.",2004.06619v2
2020-05-12,Anisotropic electrostatic screening of charged colloids in nematic solvents,"The physical behaviour of anisotropic charged colloids is determined by their
material dielectric anisotropy, affecting colloidal self-assembly, biological
function and even out-of-equilibrium behaviour. However, little is known about
anisotropic electrostatic screening, which underlies all electrostatic
effective interactions in such soft or biological materials. In this work, we
demonstrate anisotropic electrostatic screening for charged colloidal particles
in a nematic electrolyte. We show that material anisotropy behaves markedly
different from particle anisotropy: The electrostatic potential and pair
interactions decay with an anisotropic Debye screening length, contrasting the
constant screening length for isotropic electrolytes. Charged dumpling-shaped
near-spherical colloidal particles in a nematic medium are used as an
experimental model system to explore the effects of anisotropic screening,
demonstrating competing anisotropic elastic and electrostatic effective pair
interactions for colloidal surface charges tunable from neutral to high,
yielding particle-separated metastable states. Generally, our work contributes
to the understanding of electrostatic screening in nematic anisotropic media.",2005.05682v2
2020-05-13,Split Ga vacancies and the unusually strong anisotropy of positron annihilation spectra in $\boldsymbolβ$-Ga$_2$O$_3$,"We report a systematic first principles study on positron annihilation
parameters in the $\beta$-Ga$_2$O$_3$ lattice and Ga mono-vacancy defects
complemented with orientation-dependent experiments of the Doppler broadening
of the positron-electron annihilation. We find that both the
$\beta$-Ga$_2$O$_3$ lattice and the considered defects exhibit unusually strong
anisotropy in their Doppler broadening signals. This anisotropy is associated
with low symmetry of the $\beta$-Ga$_2$O$_3$ crystal structure that leads to
unusual kind of one-dimensional confinement of positrons even in the
delocalized state in the lattice. In particular, the split Ga vacancies
recently observed by scanning transmission electron microscopy produce
unusually anisotropic positron annihilation signals. We show that in
experiments, the positron annihilation signals in $\beta$-Ga$_2$O$_3$ samples
seem to be often dominated by split Ga vacancies.",2005.06283v2
2020-05-13,"Direct Imaging, Three-dimensional Interaction Spectroscopy, and Friction Anisotropy of Atomic-scale Ripples on MoS$_{2}$","Theory predicts that two-dimensional (2D) materials may only exist in the
presence of out-ofplane deformations on atomic length scales, frequently
referred to as ripples. While such ripples can be detected via electron
microscopy, their direct observation via surface-based techniques and
characterization in terms of interaction forces and energies remain limited,
preventing an unambiguous study of their effect on mechanical characteristics,
including but not limited to friction anisotropy. Here, we employ
high-resolution atomic force microscopy to demonstrate the presence of
atomic-scale ripples on supported samples of few-layer molybdenum disulfide
(MoS$_{2}$). Three-dimensional force / energy spectroscopy is utilized to study
the effect of ripples on the interaction landscape. Friction force microscopy
reveals multiple symmetries for friction anisotropy, explained by studying
rippled sample areas as a function of scan size. Our experiments contribute to
the continuing development of a rigorous understanding of the nanoscale
mechanics of 2D materials.",2005.06442v1
2020-05-16,Studies on binary mixtures of nematic liquid crystals made of strongly polar molecules with identical cores and antagonistic orientation of permanent dipoles,"We report experimental studies on optical (birefringence, $\Delta n$),
dielectric $(\Delta \varepsilon)$ and bend-splay elastic anisotropies ($\Delta
K=K_{33}-K_{11})$ of a few mixtures of two nematic liquid crystals, namely
CCH-7 and CCN-47, made of highly polar molecules with identical cores and
antagonistic orientation of permanent dipoles. In particular, the polar group
(-CN) attached to the bicyclohexane core of CCH-7 is oriented along the
longitudinal direction whereas, in CCN-47, it is oriented along the transverse
direction. We show that apart from the significant contribution to the optical
and dielectric anisotropies, the antagonistic orientation of strongly polar
groups plays a crucial role in determining the bend-splay elastic anisotropy.
The elastic properties are explained based on a model proposed by Priest,
considering the effect of intermolecular association and the resulting
length-to-width ratio of the molecules.",2005.07887v1
2020-05-21,Theories with limited extrinsic curvature and a nonsingular anisotropic universe,"We propose a class of theories that can limit scalars constructed from the
extrinsic curvature. Applied to cosmology, this framework allows us to control
not only the Hubble parameter but also anisotropies without the problem of
Ostrogradsky ghost, which is in sharp contrast to the case of limiting
spacetime curvature scalars. Our theory can be viewed as a generalization of
mimetic and cuscuton theories (thus clarifying their relation), which are known
to possess a structure that limits only the Hubble parameter on homogeneous and
isotropic backgrounds. As an application of our framework, we construct a model
where both anisotropies and the Hubble parameter are kept finite at any stage
in the evolution of the universe in the diagonal Bianchi type I setup. The
universe starts from a constant-anisotropy phase and recovers Einstein gravity
at low energies. We also show that the cosmological solution is stable against
a wide class of perturbation wavenumbers, though instabilities may remain for
arbitrary initial conditions.",2005.10844v2
2020-06-02,Intrinsically weak magnetic anisotropy of cerium in potential hard-magnetic intermetallics,"Cerium-based intermetallics are currently attracting much interest as a
possible alternative to existing high-performance magnets containing scarce
heavy rare-earth elements. However, the intrinsic magnetic properties of Ce in
these systems are poorly understood due to the difficulty of a quantitative
description of the Kondo effect, a many-body phenomenon where conduction
electrons screen out the Ce-4f moment. Here, we show that the Ce-4f shell in
Ce-Fe intermetallics is partially Kondo screened. The Kondo scale is
dramatically enhanced by nitrogen interstitials completely suppressing the
Ce-4f contribution to the magnetic anisotropy, in striking contrast to the
effect of nitrogenation in isostructural intermetallics containing other
rare-earth elements. We determine the full temperature dependence of the Ce-4f
single-ion anisotropy and show that even unscreened Ce-4f moments contribute
little to the room-temperature intrinsic magnetic hardness. Our study thus
establishes fundamental constraints on the potential of cerium-based permanent
magnet intermetallics.",2006.01792v2
2020-06-08,Time-dependent spintronic anisotropy in magnetic molecules,"We theoretically study the quench dynamics of induced anisotropy of a
large-spin magnetic molecule coupled to spin-polarized ferromagnetic leads. The
real-time evolution is calculated by means of the time-dependent density-matrix
numerical renormalization group method implemented within the matrix product
states framework, which takes into account all correlations in very accurate
manner. We determine the system's response to a quench in the spin-dependent
coupling to ferromagnetic leads. In particular, we focus on the transient
dynamics associated with crossing from the weak to the strong coupling regime,
where the Kondo correlations become important. The dynamics is examined by
calculating the time-dependent expectation values of the spin-quadrupole moment
and the associated spin operators. We identify the relevant time scales
describing the quench dynamics and determine the influence of the molecule's
effective exchange coupling and leads spin-polarization on the dynamical
behavior of the system. Furthermore, the generalization of our predictions for
large values of molecule's spin is considered. Finally, we analyze the effect
of finite temperature and show that it gives rise to a reduction of magnetic
anisotropy by strong suppression of the time-dependent spin-quadrupole moment
due to thermal fluctuations.",2006.04431v1
2020-06-15,Control of Spin Relaxation Anisotropy by Spin-Orbit-Coupled Diffusive Spin Motion,"Spatiotemporal spin dynamics under spin-orbit interaction is investigated in
a (001) GaAs two-dimensional electron gas using magneto-optical Kerr rotation
microscopy. Spin polarized electrons are diffused away from the excited
position, resulting in spin precession because of the diffusion-induced
spin-orbit field. Near the cancellation between spin-orbit field and external
magnetic field, the induced spin precession frequency depends nonlinearly on
the diffusion velocity, which is unexpected from the conventional linear
relation between the spin-orbit field and the electron velocity.This behavior
originates from an enhancement of the spin relaxation anisotropy by the
electron velocity perpendicular to the diffused direction. We demonstrate that
the spin relaxation anisotropy, which has been regarded as a material constant,
can be controlled via diffusive electron motion.",2006.08253v1
2020-06-15,Influence of $XY$ anisotropy on a magnetoelectric effect in spin-1/2 $XY$ chain in a transverse magnetic field,"A magnetoelectric effect according to Katsura-Nagaosa-Balatsky mechanism in
spin-1/2 $XY$ chain in transverse magnetic field is considered. A spatial
orientation of the electric field is chosen to provide an exact solution of the
model in terms of free spinless fermions. The simplest model of quantum spin
chain demonstrating a magnetoelectric effect, a zero temperature case of the
spin-1/2 $XX$ chain in a transverse magnetic field with
Katsura-Nagaosa-Balatsky mechanism, is considered. The model has the simplest
possible form of the magnetization, polarization and susceptibility functions,
depending on electric and magnetic fields in a most simple form. For the case
of arbitrary $XY$ anisotropy, a non-monotonous dependence of magnetization on
the $XY$ anisotropy parameter is figured out. This non-uniform behaviour is
governed by the critical point which is connected with the possibility to drive
the system gapless or gapped by the electric field. Singularities of the
magnetoelectric susceptibility at the critical value of system parameters are
shown.",2006.08525v3
2020-07-06,Quantum phase transitions in a spin-1 antiferromagnetic chain with long-range interactions and modulated single-ion anisotropy,"We study the phase diagram of spin-1 antiferromagnetic chain with isotropic
antiferromagnetic interactions decaying with a power-law $\propto r^{-\alpha}$
($\alpha\ge 1$) accompanied by modulated single-ion anisotropy. Employing the
techniques of the density-matrix renormalization group, effects of long-range
interactions and single-ion anisotropy on a variety of correlations are
investigated. In order to check the consistency, the fidelity susceptibilities
are evaluated across quantum phase transitions. The quantum critical points are
faithfully detected and orders of phase transitions are determined. The
correlation-length critical exponent is extracted from scaling functions of the
fidelity susceptibility. The presence of long-range interactions leads to
quantitative change of the phase boundaries and reduces the order of phase
transition under certain conditions. A direct first-order transition between
the periodic N\'eel phase and the large-$D$ phase occurs for slowly decaying
antiferromagnetic interactions.",2007.02878v1
2020-07-07,Investigation of in-plane anisotropy of c-axis magnetoresistance for BiCh2-based layered superconductor NdO0.7F0.3BiS2,"We have investigated the in-plane anisotropy of the c-axis magnetoresistance
(MR) in both superconducting and normal states of single crystals of
NdO0.7F0.3BiS2 under in-plane magnetic fields. In the superconducting states of
NdO0.7F0.3BiS2, four-fold-symmetric in-plane anisotropy of the c-axis MR was
observed below the superconducting transition temperature. Since the crystal
structure of NdO0.7F0.3BiS2 is tetragonal, the rotational symmetry in the
superconducting state is preserved in the present compound. This result is
clearly different from the previous report observed in LaO0.5F0.5BiSSe single
crystals, where the in-plane MR in the superconducting state shows two-fold
symmetry. On the other hand, in the normal states of NdO0.7F0.3BiS2, two-fold
symmetric MR with a small amplitude was observed. The possible origin of the
two-fold-symmetric behavior was discussed with the presence of local structural
disorder in the conducting plane of BiCh2-based compounds.",2007.03235v1
2020-07-14,Giant magnetic anisotropy energy and long coherence time of uranium substitution on defected Al2O3(0001),"Nanomagnets with giant magnetic anisotropy energy and long coherence time are
desired for various technological innovations such as quantum information
procession and storage. Based on the first-principles calculations and model
analyses, we demonstrate that a single uranium atom substituting Al on the
Al2O3(0001) surface may have high structural stability and large magnetic
anisotropy energy up to 48 meV per uranium atom. As the magnetization resides
in the localized f-shell and is not much involved in chemical bonding with
neighbors, long coherence time up to ~1.6 mS can be achieved for the quantum
spin states. These results suggest a new strategy for the search of ultrasmall
magnetic units for diverse applications in the quantum information era.",2007.07345v1
2020-07-24,Reversible vs. irreversible voltage manipulation of interfacial magnetic anisotropy in Pt/Co/oxide multilayers,"The perpendicular magnetic anisotropy at the Co/oxide interface in Pt/Co/MOx
(MOx = MgOx, AlOx, TbOx) was modified by an electric field using a 10 nm-thick
ZrO2 as a solid electrolyte. The large voltage-driven modification of
interfacial magnetic anisotropy and the non-volatility of the effect is
explained in terms of the migration of oxygen ions towards/away from the Co/MOx
interface. While the effect is reversible in Pt/Co/AlOx and Pt/Co/TbOx, where
the Co layer can be oxidised or reduced, in Pt/Co/MgOx the effect has been
found to be irreversible. We propose that these differences may be related to
the different nature of the ionic conduction within the MOx layers.",2007.12570v1
2020-07-24,Theroy of anisotropic plasmons,"We develop the complete theory for the collective plasmon modes of an
interacting electron system in the presence of explicit mass (or velocity)
anisotropy in the corresponding non-interacting situation, with the effective
Fermi velocity being different along different axes. Such effective mass
anisotropy is common in solid state materials (e.g., silicon or germanium),
where the Fermi surface is often not spherical. We find that the plasmon
dispersion itself develops significant anisotropy in such systems, and the
commonly used isotropic approximation of using a density of states or optical
effective mass does not work for the anisotropic system. We predict a
qualitatively new phenomenon in anisotropic systems with no corresponding
isotropic analog, where the plasmon mode along one direction decays into
electron-hole pairs through Landau damping while the mode remains undamped and
stable along a different directions",2007.12694v2
2020-08-03,Anisotropic skyrmion bubbles in ultra-thin epitaxial Au$_{0.67}$Pt$_{0.33}$/Co/W films,"We studied the symmetry of magnetic properties and the resulting magnetic
textures in ultra-thin epitaxial Au$_{0.67}$Pt$_{0.33}$/Co/W, a model system
exhibiting perpendicular magnetic anisotropy and interface
Dzyaloshinskii-Moriya interaction (DMI). As a peculiar feature, the
C$_\mathrm{2v}$ crystal symmetry induced by the Co/W interface results in an
additional uniaxial in-plane magnetic anisotropy in the cobalt layer.
Photoemission electron microscopy with magnetic sensitivity reveals the
formation of self-organized magnetic stripe domains oriented parallel to the
hard in-plane magnetization axis. We attribute this behavior to the lower
domain wall energy when oriented along this axis, where both the DMI and the
in-plane magnetic anisotropy favor a N\'{e}el domain wall configuration. The
anisotropic domain wall energy also leads to the formation of elliptical
skyrmion bubbles in a weak out-of-plane magnetic field.",2008.00717v1
2020-08-13,Isotropic or anisotropic screening in black phosphorous: can doping tip the balance?,"Black phosphorus (BP), a layered van der Waals (vdW) crystal, has unique
in-plane band anisotropy and many resulting anisotropy properties such as the
effective mass, electron mobility, optical absorption, thermal conductivity and
plasmonic dispersion. However, whether anisotropic or isotropic charge
screening exist in BP remains a controversial issue. Based on first-principles
calculations, we study the screening properties in both of single-layer and
bulk BP, especially concerning the role of doping. Without charge doping, the
single-layer and bulk-phase BP show slight anisotropic screening. Electron and
hole doping can increase the charge screening of BP and significantly change
the relative static dielectric tensor elements along two different in-plane
directions. We further study the charge density change induced by potassium (K)
adatom near the BP surface, under different levels of charge doping. The
calculated two-dimensional (2D) charge redistribution patterns also confirm
that doping can greatly affect the screening feature and tip the balance
between isotropic and anisotropic screening. We corroborate that screening in
BP exhibit slight intrinsic anisotropy and doping has significant influence on
its screening property.",2008.05761v1
2020-09-01,Great enhancement of Curie temperature and magnetic anisotropy in two-dimensional van der Waals magnetic semiconductor heterostructures,"In two-dimensional (2D) magnetic systems, large magnetic anisotropy is needed
to stabilize the magnetic order according to Mermin-Wagner theorem. Based on
density functional theory (DFT) calculations, we propose that the magnetic
anisotropic energy (MAE) of 2D ferromagnetic (FM) semiconductors can be
strongly enhanced in van der Waals heterostructures by attaching a nonmagnetic
semiconductor monolayer with large spin-orbit coupling. We studied
Cr2Ge2Te6/PtSe2 bilayer heterostructures, where each layer has been realized in
recent experiments. The DFT calculations show that the MAE of Cr2Ge2Te6/PtSe2
is enhanced by 70%, and the Curie temperature TC is increased far beyond room
temperature. A model Hamiltonian is suggested to analyze the DFT results,
showing that both the Dzyaloshinskii-Moriya interaction and the single-ion
anisotropy contribute to the enhancement of the MAE. Based on the superexchange
picture, we find that the decreased energy difference between 3d orbitals of Cr
and 5p orbitals of Te contributes partially to the increase of TC. Our present
work indicates a promising way to enhance the MAE and TC by constructing van
der Waals semiconductor heterostructures, which will inspire further studies on
the 2D magnetic semiconductor systems.",2009.00317v1
2020-09-11,Interplay between spatial anisotropy and further exchange interactions in the triangular Heisenberg model,"We investigate the interplay between spatial anisotropy and further exchange
interactions in the spin-$\frac{1}{2}$ Heisenberg antiferromagnetic model on a
triangular lattice. We use the Schwinger boson theory by including Gaussian
fluctuations above the mean-field approach. The phase diagram exhibits a strong
reduction of the long range collinear and incommensurate spirals regions with
respect to the mean-field ones. This reduction is accompanied by the emergence
of its short range order counterparts, leaving an ample room for $0$-flux and
nematic spin liquid regions. Remarkably, within the neighborhood of the
spatially isotropic line, there is a range where the spirals are so fragile
that only the commensurate $120^{\circ}$ N\'eel ones survive. The good
agreement with recent variational Monte Carlo predictions gives support to the
rich phase diagram induced by spatial anisotropy.",2009.05447v1
2020-09-14,Voltage-driven Magnetization Switching via Dirac Magnetic Anisotropy and Spin--orbit Torque in Topological-insulator-based Magnetic Heterostructures,"Electric-field control of magnetization dynamics is fundamentally and
technologically important for future spintronic devices. Here, based on
electric-field control of both magnetic anisotropy and spin--orbit torque, two
distinct methods are presented for switching the magnetization in topological
insulator (TI)/magnetic-TI hybrid systems. The magnetic anisotropy energy in
magnetic TIs is formulated analytically as a function of the Fermi energy, and
it is confirmed that the out-of-plane magnetization is always favored for the
partially occupied surface band. Also proposed is a transistor-like device with
the functionality of a nonvolatile magnetic memory that uses voltage-driven
writing and the (quantum) anomalous Hall effect for readout. For the
magnetization reversal, by using parameters of Cr-doped
Bi_{1-x}Sb_{x})_{2}Te_{3}, the estimated source-drain current density and gate
voltage are of the orders of $10^4$--$10^5$~A/cm$^2$ and 0.1~V, respectively,
below 20~K and the writing requires no external magnetic field. Also discussed
is the possibility of magnetization switching by the proposed method in
TI/ferromagnetic-insulator bilayers with the magnetic proximity effect.",2009.06187v1
2020-09-22,REPORT: Investigation on Curvilinear Anisotropy via Isogeometric Analysis (IGA),"The advent of multi-material additive manufacturing and automated composite
manufacturing has enabled the design of structures featuring complex
curvilinear anisotropy. To take advantage of the new design space, efficient
computational approaches are quintessential. In this study, we explored a new
NURBS-based Isogeometric Analysis (IGA) framework for the simulation of
curvilinear fiber composites and we compared it to standard Finite Element
Analysis (FEA). A plate featuring a semi-circular notch under tensile loading
with different fiber configurations served as a case study. We showed that,
thanks to the exact geometric representation and the enriched continuity
between elements, NURBS-based IGA outperforms classical FEA in terms of
computational efficiency, time-consumption, and estimation quality of field
variables for same number of degrees-of-freedom. To further demonstrate the use
of the IGA framework, we performed optimization studies aimed at identifying
the fiber paths minimizing stress concentration and Tsai-Wu failure index. The
model showed that curvilinear anisotropy can be effectively harnessed to reduce
the stress concentration of up to 82 % compared to unidirectional composites
without affecting the overall plate stiffness significantly.",2009.10230v3
2020-10-07,Large anisotropies of the stochastic gravitational wave background from cosmic domain walls,"We investigate the stochastic gravitational wave background (SGWB) from
cosmic domain walls (DWs) caused by quantum fluctuations of a light scalar
field $\phi$ during inflation. Perturbations of $\phi$ remain almost constant
after leaving the Hubble horizon. The probabilities of the two domains depend
on the averaged value of $\phi$ at each large scale region, leading to large
scale perturbations of DW energy density and large anisotropies in the SGWB. We
find that the angular power spectrum is scale-invariant and at least of the
order of $10^{-2}$, which is expected to be detected by future
gravitational-wave (GW) detectors. Since we have not detected primordial GWs
yet, anisotropies of the SGWB could help us to verify the rationality of
inflation and determine the energy scale of inflation.",2010.03225v1
2020-10-14,Interface-driven magnetic anisotropy in relaxed La$_{0.7}$Sr$_{0.3}$CrO$_3$/La$_{0.7}$Sr$_{0.3}$MnO$_3$ heterostructures on MgO,"We investigate the structural and magnetic properties of
La$_{0.7}$Sr$_{0.3}$CrO$_3$ (LSCO)/La$_{0.7}$Sr$_{0.3}$MnO$_3$(LSMO)
heterostructures grown on (001)-oriented MgO by molecular beam epitaxy. Due to
the large film-substrate lattice mismatch, strain relaxation is found to occur
within the first 2-3 unit cells (uc) of the film as evidenced by reflection
high energy electron diffraction and high-resolution synchrotron X-ray
reciprocal space mapping. We find that the presence of the LSCO spacer and
capping layers leads to ferromagnetism in ultra-thin LSMO layers with
thicknesses on the order of 2 uc with the magnetic easy axis oriented in the
film plane. Net magnetic moments of 1.4 and 2.4 $\mu_B$/Mn are measured for [2
uc LSCO/ 2 uc LSMO] and [2 uc LSCO/ 4 uc LSMO] superlattices, respectively by
SQUID magnetometry. The effective magnetic anisotropy of the relaxed [2 uc
LSCO/ 4 uc LSMO] heterostructure is found to be an order of magnitude higher
than bulk LSMO highlighting the critical role of interfacial magnetic exchange
interactions in tuning magnetic anisotropy at complex oxide interfaces.",2010.07180v1
2020-10-08,The anisotropy in the optical constants of quartz crystals for soft X-rays,"The refractive index of a y-cut SiO$_2$ crystal surface is reconstructed from
polarization dependent soft X-ray reflectometry measurements in the energy
range from 45 eV to 620 eV. Due to the anisotropy of the crystal structure in
the (100) and (001) directions, we observe a significant deviation of the
measured reflectance at the Si-L$_{2,3}$ and O-K absorption edges. The
anisotropy in the optical constants reconstructed from these data is also
confirmed by ab initio Bethe-Salpeter Equation calculations of the O-K edge.
This new experimental dataset expands the existing literature data for quartz
optical constants significantly, particularly in the near-edge regions.",2010.09436v1
2020-11-06,Gigantic magnetochiral anisotropy in the topological semimetal ZrTe5,"Topological materials with broken inversion symmetry can give rise to
nonreciprocal responses, such as the current rectification controlled by
magnetic fields via magnetochiral anisotropy. Bulk nonreciprocal responses
usually stem from relativistic corrections and are always very small. Here we
report our discovery that ZrTe5 crystals in proximity to a topological quantum
phase transition present gigantic magnetochiral anisotropy, which is the
largest ever observed to date. We argue that a very low carrier density,
inhomogeneities, and a torus-shaped Fermi surface induced by breaking of
inversion symmetry in a Dirac material are central to explain this
extraordinary property.",2011.03329v3
2020-11-13,Resolving Multiphoton Processes with High-Order Anisotropy Ultrafast X-ray Scattering,"We present first results on ultrafast X-ray scattering of strongly driven
molecular Iodine and analysis of high-order anisotropic components of the
scattering signal, up to four-photon absorption. We discuss the technical
details of retrieving high fidelity high-order anisotropy components, and
outline a method to analyze the scattering signal using Legendre decomposition.
We use simulated anisotropic scattering signals and Fourier analysis to map how
anisotropic dissociation motions can be extracted from the various Legendre
orders. We observe multitude dissociation and vibration motions simultaneously
arising from various multiphoton transitions. We use the anisotropy information
of the scattering signal to disentangle the different processes and assign
their dissociation velocities on the Angstrom and femtosecond scales de-novo.",2011.06761v3
2020-11-24,Temperature dependence of London penetration depth anisotropy in superconductors with anisotropic order parameters,"We study the effects of anisotropic order parameters on the temperature
dependence of London penetration depth anisotropy $\gamma_\lambda(T)$. After
MgB$_2$, this dependence is commonly attributed to distinct gaps on multi-band
Fermi surfaces in superconductors. We have found, however, that the anisotropy
parameter may depend on temperature also in one-band materials with anisotropic
order parameters $\Delta(T,k_F)$, a few such examples are given. We have found
also that for different order parameters, the temperature dependence of
$\Delta(T)/\Delta(0)$ can be represented with good accuracy by the
interpolation suggested by D. Einzel, J. Low Temp. Phys, {\bf 131}, 1 (2003),
which simplifies considerably the evaluation of $\gamma_\lambda(T)$. Of
particular interest is mixed order parameters of two symmetries for which
$\gamma_\lambda(T)$ may go through a maximum for a certain relative weight of
two phases. Also, for this case, we find that the ratio $\Delta_{max}(0)/T_c$
may exceed substantially the weak coupling limit of 1.76. It, however, does not
imply a strong coupling, rather it is due to significantly anisotropic angular
variation of $\Delta$.",2011.12412v1
2020-11-27,"Pinning, flux flow resistivity and anisotropy of Fe(Se,Te) thin films from microwave measurements through a bitonal dielectric resonator","We report on the anisotropy of the vortex motion surface impedance of a \fst
thin film grown on a CaF$_2$ substrate. The dependence on the magnetic field
intensity up to 1.2 T and direction, both parallel and perpendicular to the
sample $c$-axis, was explored at fixed temperature at two distinct frequencies,
$\sim16\;$GHz and $\sim27\;$GHz, by means of bitonal dielectric resonator. The
free flux flow resistivity $\rho_{ff}$ was obtained by exploiting standard
models for the high frequency dynamics, whereas the angle dependence was
studied in the framework of the well known and widely used
Blatter-Geshkenbein-Larkin (BGL) scaling theory for anistropic superconductors.
Excellent agreement with the scaling law prescription by the fluxon flux flow
resistivity was obtained. From the scaling analysis, a low-field mass
anisotropy $\sim1.8$ was obtained, well within the value ranges reported in
literature. The angular dependence of the pinning constant suggests that
pinning is dominated by random, isotropic point pins, consistently with
critical current density measurements.",2011.13819v1
2020-12-03,MoS$_2$ flake as a van der Waals homostructure: luminescence properties and optical anisotropy,"We investigated multilayer plates made by exfoliation from a high-quality
MoS$_2$ crystal and reveal that they represent a new object - van der Waals
homostructure consisting of a bulk core and a few detached monolayers on its
surface. This architecture comprising elements with different electron band
structure leads to specific luminescence, when the broad emission band from the
core is cut by the absorption peaks of strong exciton resonances in the surface
monolayers. The exfoliated flakes exhibit strong optical anisotropy. We have
observed a conversion of normally incident light polarization to $15\%$ in
transmission geometry. This background effect is due to fluctuations of the c
axis relative to the normal, whereas the pronounced resonance contribution is
explained by the polarization anisotropy of excitons localized in the stripes
of dissected surface monolayers.",2012.02032v2
2020-12-06,On anisotropy and inhomogeneity parameter estimation using traveltimes,"We consider an anisotropic inhomogeneous model to simulate measured
vertical-seismic-profile traveltimes. In this model, we assume that velocity
increases linearly with depth and anisotropy is the result of elliptical
velocity dependence. Using a series of sources in a line to a single receiver,
we minimize the least-squares residual between measured and modelled
traveltimes to estimate the anisotropy and inhomogeneity parameters of the
subsurface. To verify the approach, we construct synthetic traveltime data for
a one- and two-layer model and perform the traveltime inversion. We justify the
convergence-ensuring specifications and model-parameter restrictions that are
intrinsic to the parameter estimation. To determine the approach's
practicality, we assess the reliability of results under the influence of
noise. From this assessment, we discern the noise threshold for both models and
determine that the noise restriction is severely restrictive for increasing
model complexity. We estimate parameters, using the same methodology, for a
real-data case and conclude with a discussion of results.",2012.03393v1
2020-12-07,Cross-correlations as a Diagnostic Tool for Primordial Gravitational Waves,"We explore and corroborate, by working out explicit examples, the
effectiveness of cross-correlating stochastic gravitational wave background
anisotropies with CMB temperature fluctuations as a way to establish the
primordial nature of a given gravitational wave signal. We consider the case of
gravitational wave anisotropies induced by scalar-tensor-tensor primordial
non-Gaussianity. Our analysis spans anisotropies exhibiting different angular
behaviours, including a quadrupolar dependence. We calculate the expected
uncertainty on the non-linearity parameter $F_{\rm NL}$ obtained as a result of
cross-correlation measurements for several proposed experiments such as the
ground-based Einstein Telescope, Cosmic Explorer, and the space-based Big-Bang
Observer. As a benchmark for future survey planning, we also calculate the
theoretical, cosmic-variance-limited, error on the non-linearity parameter.",2012.03498v2
2020-12-07,Magnetic anisotropy from linear defect structures in correlated electron systems,"Correlated electron systems, particularly iron-based superconductors, are
extremely sensitive to strain, which inevitably occurs in the crystal growth
process. Built-in strain of this type has been proposed as a possible
explanation for experiments where nematic order has been observed at high
temperatures corresponding to the nominally tetragonal phase of iron-based
superconductors. Strain is assumed to produce linear defect structures, e.g.
dislocations, which are quite similar to O vacancy chainlets in the underdoped
cuprate superconductor YBCO. Here we investigate a simple microscopic model of
dislocations in the presence of electronic correlations, which create defect
states that can drive magnetic anisotropy of this kind, if spin orbit
interaction is present. We estimate the contribution of these dislocations to
magnetic anisotropy as detected by current torque magnetometry experiments in
both cuprates and Fe-based systems.",2012.03824v2
2020-12-15,Thermodynamically stable skyrmion lattice in tetragonal frustrated antiferromagnet with dipolar interaction,"Motivated by recent experimental results on GdRu$_2$Si$_2$ [Khanh, N.D.,
Nakajima, T., Yu, X. et al., \emph{Nat. Nanotechnol.} \textbf{15}, 444-449
(2020)], where nanometric square skyrmion lattice was observed, we propose
simple analytical mean-field description of the high-temperature part of the
phase diagram of centrosymmetric tetragonal frustrated antiferromagnets with
dipolar interaction in the external magnetic field. In the reciprocal space
dipolar forces provide momentum dependent biaxial anisotropy. It is shown that
in tetragonal lattice in the large part of the Brillouin zone for mutually
perpendicular modulation vectors in the $ab$ plane this anisotropy has mutually
perpendicular easy axes and collinear middle axes, what leads to double-Q
modulated spin structure stabilization. The latter turns out to be a square
skyrmion lattice in the large part of its stability region with the topological
charge $\pm 1$ per magnetic unit cell, which is determined by the frustrated
exchange coupling, and, thus, nanometer-sized. In the presence of additional
single-ion easy-axis anisotropy, easy and middle axes can be swapped, which
leads to different phase diagram. It is argued that the latter case is relevant
to GdRu$_2$Si$_2$.",2012.08422v1
2020-12-23,Effect of Fullerene on domain size and relaxation in a perpendicularly magnetized Pt/Co/C60/Pt system,"Buckminsterfullerene (C60) can exhibit ferromagnetism at the interface
(called as a spinterface) when it is placed next to a ferromagnet (FM).
Formation of such spinterface happens due to orbital hybridization and spin
polarized charge transfer at the interface. The spinterface can influence the
domain size and dynamics of the organic/ferromagnetic heterostructure. Here, we
have performed magnetic domain imaging and studied the relaxation dynamics in
Pt/Co/C60/Pt system with perpendicular anisotropy. We have compared the results
with its parent Pt/Co/Pt system. It is observed that presence of C60 in the
Pt/Co/Pt system increases the anisotropy and a decrease in the bubble domain
size. Further the switching time of Pt/Co/C60/Pt system is almost two times
faster than Pt/Co/Pt system. We have also performed the spin polarized density
functional theory (DFT) calculations to understand the underneath mechanism.
DFT results show formation of a spin polarized spinterface which leads to an
enhancement in anisotropy.",2012.12777v3
2020-12-28,A study on the effect of anisotropy under Finch-Skea geometry,"The popularity of the Finch-Skea ansatz to describe relativistic stellar
model have encouraged us to study the analytic solutions of the Einstein field
equation. We have presented a class of exact solutions to the field equations
after considering the corresponding two cases: (i) positive value of
anisotropic parameter, and (ii) absence of any anisotropy. Smooth matching of
the interior solutions with the Schwarzschild exterior solution helped us to
determine constants. The physical features of the solutions thus obtained have
been studied both graphically and numerically with the specific pulsar
$4U~1608-52$ (Mass = $1.57^{+0.30}_{-0.29}~M_\odot$ and radius = $9.8\pm
1.8~km$). The stability conditions for the model have also been discussed,
however the model is found to be stable for zero anisotropy.",2012.14085v2
2021-01-04,Reconstructing Patchy Reionization with Deep Learning,"The precision anticipated from next-generation cosmic microwave background
(CMB) surveys will create opportunities for characteristically new insights
into cosmology. Secondary anisotropies of the CMB will have an increased
importance in forthcoming surveys, due both to the cosmological information
they encode and the role they play in obscuring our view of the primary
fluctuations. Quadratic estimators have become the standard tools for
reconstructing the fields that distort the primary CMB and produce secondary
anisotropies. While successful for lensing reconstruction with current data,
quadratic estimators will be sub-optimal for the reconstruction of lensing and
other effects at the expected sensitivity of the upcoming CMB surveys. In this
paper we describe a convolutional neural network, ResUNet-CMB, that is capable
of the simultaneous reconstruction of two sources of secondary CMB
anisotropies, gravitational lensing and patchy reionization. We show that the
ResUNet-CMB network significantly outperforms the quadratic estimator at low
noise levels and is not subject to the lensing-induced bias on the patchy
reionization reconstruction that would be present with a straightforward
application of the quadratic estimator.",2101.01214v2
2021-01-27,Strong In-plane Anisotropy in the Electronic Properties of Doped Transition Metal Dichalcogenides exhibited in W1-xNbxS2,"In this work, we study the electronic properties of monolayer transition
metal dichalcogenide materials subjected to aliovalent doping, using Nb-doped
WS2 as an exemplar. Scanning transmission electron microscopy imaging of the
as-grown samples reveals an anisotropic Nb dopant distribution, prompting our
investigation of anisotropy in electronic properties. Through electronic
structure calculations on supercells representative of observed structures, we
confirm that local Nb-atom distributions are consistent with energetic
considerations, although kinetic processes occurring during sample growth must
be invoked to explain the overall symmetry-breaking. We perform effective
bandstructure and conductivity calculations on realistic models of the material
that demonstrate that a high level of anisotropy can be expected in electronic
properties including conductivity and mobility.",2101.11687v3
2021-02-05,Symmetry-Driven Spin-Wave Gap Modulation in Nanolayered SrRuO3/SrTiO3 Heterostructures: Implications for Spintronic Applications,"A strong correlation between magnetic interaction and topological symmetries
leads to unconventional magneto-transport behavior. Weyl fermions induce
topologically protected spin-momentum locking, which is closely related to
spin-wave gap formation in magnetic crystals. Ferromagnetic SrRuO3, regarded as
a strong candidate for Weyl semimetal, inherently possesses a nonzero spin-wave
gap owing to its strong magnetic anisotropy. In this paper, we propose a method
to control the spin-wave dynamics by nanolayer designing of the SrRuO3/SrTiO3
superlattices. In particular, the six-unit-cell-thick SrRuO3 layers within the
superlattices undergo a phase transition in crystalline symmetry from
orthorhombic to tetragonal, as the thickness of the SrTiO3 layers is modulated
with atomic-scale precision. Consequently, the magnetic anisotropy, anomalous
Hall conductivity, and spin-wave gap could be systematically manipulated. Such
customization of magnetic anisotropy via nanoscale heterostructuring offers a
novel control knob to tailor the magnon excitation energy for future spintronic
applications, including magnon waveguides and filters. Our nanolayer approach
unveils the important correlation between the tunable lattice degrees of
freedom and spin dynamics in topologically non-trivial magnetic materials.",2102.03008v1
2021-02-10,Measuring magnetization with rotation measures and velocity centroids in supersonic MHD turbulence,"The interstellar turbulence is magnetized and thus anisotropic. The
anisotropy of turbulent magnetic fields and velocities is imprinted in the
related observables, rotation measures (RMs), and velocity centroids (VCs).
This anisotropy provides valuable information on both the direction and
strength of the magnetic field. However, its measurement is difficult
especially in highly supersonic turbulence in cold interstellar phases due to
the distortions by isotropic density fluctuations. By using 3D simulations of
supersonic and sub-Alfv\'enic magnetohydrodynamic(MHD) turbulence, we find that
the problem can be alleviated when we selectively sample the volume-filling
low-density regions in supersonic MHD turbulence. Our results show that in
these low-density regions, the anisotropy of RM and VC fluctuations depends on
the Alfv\'enic Mach number as $\rm M_A^{-4/3}$. This anisotropy-$\rm M_A$
relation is theoretically expected for sub-Alfv 'enic MHD turbulence and
confirmed by our synthetic observations of $^{12}$CO emission. It provides a
new method for measuring the plane-of-the-sky magnetic fields in cold
interstellar phases.",2102.05647v1
2021-02-19,Revealing the intrinsic superconducting gap anisotropy in surface-neutralized BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$,"Alkaline-earth iron arsenide (122) is one of the most studied families of
iron-based superconductors, especially for angle-resolved photoemission
spectroscopy. While extensive photoemission results have been obtained, the
surface complexity of 122 caused by its charge-non-neutral surface is rarely
considered. Here, we show that the surface of 122 can be neutralized by
potassium deposition. In potassium-coated BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$,
the surface-induced spectral broadening is strongly suppressed, and hence the
coherent spectra that reflect the intrinsic bulk electronic state recover. This
enables the measuring of superconducting gap with unpreceded precision. The
result shows the existence of two pairing channels. While the gap anisotropy on
the outer hole/electron pockets can be well fitted using an s$_\pm$ gap
function, the gap anisotropy on the inner hole/electron shows a clear
deviation. Our results provide quantitative constraints for refining
theoretical models and also demonstrate an experimental method for revealing
the intrinsic electronic properties of 122 in future studies.",2102.09919v1
2021-02-22,Exact Critical Casimir Amplitude of Anisotropic Systems from Conformal Field Theory and Self-Similarity of Finite-Size Scaling Functions in $d\geq 2$ Dimensions,"The exact critical Casimir amplitude is derived for anisotropic systems
within the $d=2$ Ising universality class by combining conformal field theory
(CFT) with anisotropic $\varphi^4$ theory. Explicit results are presented for
the general anisotropic scalar $\varphi^4$ model and for the fully anisotropic
triangular-lattice Ising model in finite rectangular and infinite strip
geometries with periodic boundary conditions (PBC). These results demonstrate
the validity of multiparameter universality for confined anisotropic systems
and the nonuniversality of the critical Casimir amplitude. We find an
unexpected complex form of self-similarity of the anisotropy effects near the
instability where weak anisotropy breaks down. This can be traced back to the
property of modular invariance of isotropic CFT for $d=2$. More generally, for
$d>2$ we predict the existence of self-similar structures of the finite-size
scaling functions of $O(n)$-symmetric systems with planar anisotropies and PBC
both in the critical region for $ n \geq 1$ as well as in the
Goldstone-dominated low-temperature region for $ n \geq 2$.",2102.11214v2
2021-02-25,Magnetic anisotropy in Fe/U and Ni/U bilayers,"Magnetometry measurements of Fe/U and Ni/U bilayer systems reveal a
non-monotonic dependence of the magnetic anisotropy for U thicknesses in the
range 0 nm - 8 nm, with the Fe/U bilayers showing a more prominent effect as
compared to Ni/U. The stronger response for Fe/U is ascribed to the stronger
3d-5f hybridization of Fe and U. This non-monotonic behaviour is thought to
arise from quantum well states in the uranium overlayers. Estimating an
oscillation period from the non-monotonic data, and comparing it to Density
Functional Theory calculations, we find that wavevector matches to the
experimental data can be made to regions of high spectral density in (010) and
(100) cuts of the electronic structure of{\alpha}-U, consistent with the
measured texture in the films. Unexpectedly, there are also indications of
perpendicular magnetic anisotropy in a subset of Fe/U samples at relatively
large U thickness.",2102.12784v1
2021-02-26,Crossover from itinerant to localized states in the thermoelectric oxide [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$],"The layered cobaltite [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], often expressed as
the approximate formula Ca$_3$Co$_4$O$_9$, is a promising candidate for
efficient oxide thermoelectrics but an origin of its unusual thermoelectric
transport is still in debate. Here we investigate \textit{in-plane} anisotropy
of the transport properties in a broad temperature range to examine the
detailed conduction mechanism. The in-plane anisotropy between $a$ and $b$ axes
is clearly observed both in the resistivity and the thermopower, which is
qualitatively understood with a simple band structure of the triangular lattice
of Co ions derived from the angle-resolved photoemission spectroscopy
experiments. On the other hand, at high temperatures, the anisotropy becomes
smaller and the resistivity shows a temperature-independent behavior, both of
which indicate a hopping conduction of localized carriers. Thus the present
observations reveal a crossover from low-temperature itinerant to
high-temperature localized states, signifying both characters for the enhanced
thermopower.",2102.13250v1
2021-03-03,Skyrmion Logic Clocked via Voltage Controlled Magnetic Anisotropy,"Magnetic skyrmions are exciting candidates for energy-efficient computing due
to their non-volatility, detectability,and mobility. A recent proposal within
the paradigm of reversible computing enables large-scale circuits composed
ofdirectly-cascaded skyrmion logic gates, but it is limited by the
manufacturing difficulty and energy costs associated withthe use of notches for
skyrmion synchronization. To overcome these challenges, we therefore propose a
skyrmion logicsynchronized via modulation of voltage-controlled magnetic
anisotropy (VCMA). In addition to demonstrating theprinciple of VCMA
synchronization through micromagnetic simulations, we also quantify the impacts
of current den-sity, skyrmion velocity, and anisotropy barrier height on
skyrmion motion. Further micromagnetic results demonstratethe feasibility of
cascaded logic circuits in which VCMA synchronizers enable clocking and
pipelining, illustrating afeasible pathway toward energy-efficient large-scale
computing systems based on magnetic skyrmions.",2103.02724v2
2021-03-11,"Perpendicular magnetic anisotropy at Fe/Au(111) interface studied by Mössbauer, x-ray absorption, and photoemission spectroscopies","The origin of the interfacial perpendicular magnetic anisotropy (PMA) induced
in the ultrathin Fe layer on the Au(111) surface was examined using
synchrotron-radiation-based M\""{o}ssbauer spectroscopy (MS), X-ray magnetic
circular dichroism (XMCD), and angle-resolved photoemission spectroscopy
(ARPES). To probe the detailed interfacial electronic structure of orbital
hybridization between the Fe 3$d$ and Au 6$p$ bands, we detected the
interfacial proximity effect, which modulates the valence-band electronic
structure of Fe, resulting in PMA. MS and XMCD measurements were used to detect
the interfacial magnetic structure and anisotropy in orbital magnetic moments,
respectively. $In$-$situ$ ARPES also confirms the initial growth of Fe on large
spin-orbit coupled surface Shockley states under Au(111) modulated electronic
states in the vicinity of the Fermi level. This suggests that PMA in the
Fe/Au(111) interface originates from the cooperation effects among the spin,
orbital magnetic moments in Fe, and large spin-orbit coupling in Au. These
findings pave the way to develop interfacial PMA using $p$-$d$ hybridization
with a large spin-orbit interaction.",2103.06572v1
2021-03-23,Induced side-branching in smooth and faceted dendrites: theory and Phase-Field simulations,"The present work is devoted to the phenomenon of induced side branching
stemming from the disruption of free dendrite growth. Therein, we postulate
that the secondary branching instability can be triggered by the departure of
the morphology of the dendrite from its steady state shape. Thence, the
instability results from the thermodynamic trade-off between non monotonic
variations of interface temperature, surface energy, kinetic anisotropy and
interface velocity within the Gibbs Thomson equation. For purposes of
illustration, the toy model of capillary anisotropy modulation is prospected
both analytically and numerically by means of phase field simulations. It is
evidenced that side branching can befall both smooth and faceted dendrites, at
a normal angle from the front tip which is specific to the nature of the
capillary anisotropy shift applied.",2103.12400v1
2021-04-07,Anisotropic Turbulence in Position-Position-Velocity Space: Probing Three-Dimensional Magnetic Fields,"Direct measurements of three-dimensional magnetic fields in the interstellar
medium (ISM) are not achievable. However, the anisotropic nature of
magnetohydrodynamic (MHD) turbulence provides a novel way of tracing the
magnetic fields. Guided by the advanced understanding of turbulence's
anisotropy in the Position-Position-Velocity (PPV) space, we extend the
Structure-Function Analysis (SFA) to measure both the three-dimensional
magnetic field orientation and Alfven Mach number $M_A$, which provides the
information on magnetic field strength. Following the theoretical framework
developed in Kandel et al. (2016), we find that the anisotropy in a given
velocity channel is affected by the inclination angle between the 3D magnetic
field direction and the line-of-sight as well as media magnetization. We
analyze the synthetic PPV cubes generated by incompressible and compressible
MHD simulations. We confirm that the PPV channel's intensity fluctuations
measured in various position angles reveal plane-of-the-sky magnetic field
orientation. We show that by varying the channel width, the anisotropies of the
intensity fluctuations in PPV space can be used to simultaneously estimate both
magnetic field inclination angle and strength of total magnetic fields.",2104.02842v2
2021-04-07,Switchable Rashba Anisotropy in Two-dimensional Hybrid Organic-Inorganic Perovskite by Hybrid Improper Ferroelectricity,"Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are
introducing new directions in the 2D materials landscape. The coexistence of
ferroelectricity and spin-orbit interactions play a key role in their
optoelectronic properties. We perform a detailed study on a recently
synthesized ferroelectric 2D-HOIP, (AMP)PbI$_4$ (AMP =
4-aminomethyl-piperidinium). The calculated polarization and Rashba parameter
are in excellent agreement with experimental values. We report a striking new
effect, i.e., an extraordinarily large Rashba anisotropy that is tunable by
ferroelectric polarization: as polarization is reversed, not only the spin
texture chirality is inverted, but also the major and minor axes of the Rashba
anisotropy ellipse in k-space are interchanged - a pseudo rotation. A $k \cdot
p$ model Hamiltonian and symmetry-mode analysis reveal a quadrilinear coupling
between the cation-rotation modes responsible for the Rashba ellipse
pseudo-rotation, the framework rotation, and the polarization. These findings
may provide new avenues for spin-optoelectronic devices such as spin valves or
spin FETs.",2104.02970v1
2021-04-07,Analytical results for the low-temperature Drude weight of the XXZ spin chain,"The spin-$1/2$ XXZ chain is an integrable lattice model and parts of its spin
current can be protected by local conservation laws for anisotropies
$-1<\Delta<1$. In this case, the Drude weight $D(T)$ is non-zero at finite
temperatures $T$. Here we obtain analytical results for $D(T)$ at low
temperatures for zero external magnetic field and anisotropies
$\Delta=\cos(n\pi/m)$ with $n,m$ coprime integers, using the thermodynamic
Bethe ansatz. We show that to leading orders
$D(T)=D(0)-a(\Delta)T^{2K-2}-b_1(\Delta)T^2$ where $K$ is the Luttinger
parameter and the prefactor $a(\Delta)$, obtained in closed form, has a fractal
structure as function of anisotropy $\Delta$. The prefactor $b_1(\Delta)$, on
the other hand, does not have a fractal structure and can be obtained in a
standard field-theoretical approach. Including both temperature corrections, we
obtain an analytic result for the low-temperature asymptotics of the Drude
weight in the entire regime $-1<\Delta=\cos(n\pi/m)<1$.",2104.03266v1
2021-04-15,Dyakonov surface waves in dielectric crystals with negative anisotropy,"We report the prediction of a new type of Dyakonov surface waves that
propagate along the flat strip of the interface between two dielectrics with
negative anisotropy. It is shown that the surface waves condition is satisfied
for negatively anisotropic dielectrics due to specific boundaries of the strip
waveguide confined between two metallic plates. Such modes are studied by the
perturbation theory in the approximation of weak anisotropy. The existence of
Dyakonov surface waves in negative uniaxial crystals motivates us to reconsider
the list of materials suitable for their practical implementation. We believe
that this work opens a new unexplored research area in the field of surface
waves.",2104.07394v1
2021-04-22,Low Anisotropy Sense Retrofitting (LASeR) : Towards Isotropic and Sense Enriched Representations,"Contextual word representation models have shown massive improvements on a
multitude of NLP tasks, yet their word sense disambiguation capabilities remain
poorly explained. To address this gap, we assess whether contextual word
representations extracted from deep pretrained language models create
distinguishable representations for different senses of a given word. We
analyze the representation geometry and find that most layers of deep
pretrained language models create highly anisotropic representations, pointing
towards the existence of representation degeneration problem in contextual word
representations. After accounting for anisotropy, our study further reveals
that there is variability in sense learning capabilities across different
language models. Finally, we propose LASeR, a 'Low Anisotropy Sense
Retrofitting' approach that renders off-the-shelf representations isotropic and
semantically more meaningful, resolving the representation degeneration problem
as a post-processing step, and conducting sense-enrichment of contextualized
representations extracted from deep neural language models.",2104.10833v1
2021-04-27,Stability of Mn2RuxGa-based Multilayer Stacks,"Perpendicular heterostructures based on a ferrimagnetic Mn2RuxGa (MRG) layer
and a ferromagnetic Co/Pt multilayer were examined to understand the effects of
different spacer layers (V, Mo, Hf, HfOx and TiN) on the interfaces with the
magnetic electrodes, after annealing at 350 C. Loss of perpendicular anisotropy
in MRG is strongly correlated with a reduction in the substrate-induced
tetragonality due to relaxation of the crystal structure. In the absence of
diffusion, strain and chemical ordering within MRG are correlated. The limited
solubility of both Hf and Mo in MRG is a source of additional valence
electrons, which results in an increase in compensation temperature Tcomp. This
also stabilises perpendicular anisotropy, compensating for changes in strain
and defect density. The reduction in squareness of the MRG hysteresis loop
measured by anomalous Hall effect is <10 %, making it useful in active devices.
Furthermore, a CoPt3 phase with (2 2 0) texture in the perpendicular Co/Pt free
layer promoted by a Mo spacer layer is the only one that retains its
perpendicular anisotropy on annealing.",2104.13319v2
2021-05-25,Dynamics of particles with cubic magnetic anisotropy in a viscous liquid,"The specific absorption rate (SAR) of a dilute assembly of spherical iron
nanoparticles with cubic anisotropy distributed in a viscous liquid is
calculated using the solution of stochastic Landau - Lifshitz equation for unit
magnetization vector and stochastic equations for multiple particle directors
that specify the spatial orientation of the nanoparticle in a liquid. The
viscous and magnetic magnetization reversal modes of particles are revealed at
low and sufficiently high amplitudes of alternating magnetic field,
respectively. The SAR of iron nanoparticle assembly is shown to exceed
significantly that of iron oxide nanoparticles with uniaxial anisotropy at the
same amplitudes and frequencies of applied magnetic field. The linear response
theory is shown to be valid only at small magnetic field amplitudes, H0 < 50 -
70 Oe.",2105.11916v1
2021-05-27,Optimal control of anisotropic Allen-Cahn equations,"This paper aims at solving an optimal control problem governed by an
anisotropic Allen-Cahn equation numerically. Therefore we first prove the
Fr\'echet differentiability of an in time discretized parabolic control problem
under certain assumptions on the involved quasilinearity and formulate the
first order necessary conditions. As a next step, since the anisotropies are in
general not smooth enough, the convergence behavior of the optimal controls are
studied for a sequence of (smooth) approximations of the former quasilinear
term. In addition the simultaneous limit in the approximation and the time step
size is considered. For a class covering a large variety of anisotropies we
introduce a certain regularization and show the previously formulated
requirements. Finally, a trust region Newton solver is applied to various
anisotropies and configurations, and numerical evidence for mesh independent
behavior and convergence with respect to regularization is presented.",2105.13310v3
2021-05-27,Compact stellar model in presence of pressure anisotropy in modified Finch Skea spacetime,"A new model of anisotropic compact star is obtained in our present paper by
assuming the pressure anisotropy. The proposed model is singularity free. The
model is obtained by considering a physically reasonable choice for the metric
potential $g_{rr}$ which depends on a dimensionless parameter `n'. The effect
of $n$ is discussed numerically, analytically and through plotting. We have
concentrated a wide range for n ($10\leq n \leq 1000$) for drawing the profiles
of different physical parameters. The maximum allowable mass for different
values of $n$ have been obtained by M-R plot. We have checked that the
stability of the model is increased for larger value of $n$. For the viability
of the model we have considered two compact stars PSR J1614-2230 and EXO
1785-248. We have shown that the expressions for the anisotropy factor and the
metric component may serve as generating functions for uncharged stellar models
in the context of the general theory of relativity.",2106.01316v1
2021-06-07,Probing pre-Recombination Physics by the Cross-Correlation of Stochastic Gravitational Waves and CMB Anisotropies,"We study the effects of pre-recombination physics on the Stochastic
Gravitational Wave Background (SGWB) anisotropies induced by the propagation of
gravitons through the large-scale density perturbations and their
cross-correlation with Cosmic Microwave Background (CMB) temperature and E-mode
polarization ones. As examples of Early Universe extensions to the $\Lambda$CDM
model, we consider popular models featuring extra relativistic degrees of
freedom, a massless non-minimally coupled scalar field, and an Early Dark
Energy component. Assuming the detection of a SGWB, we perform a Fisher
analysis to assess in a quantitative way the capability of future gravitational
wave interferometers (GWIs) in conjunction with a future large-scale CMB
polarization experiment to constrain such variations. Our results show that the
cross-correlation of CMB and SGWB anisotropies will help tighten the
constraints obtained with CMB alone, with an improvement that significantly
depends on the specific model as well as the maximum angular resolution
$\ell_{\rm max}^{\rm GW}$ of the GWIs, their designed sensitivity, and the
amplitude $A_*$ of the monopole of the SGWB.",2106.03786v2
2021-06-10,Steering visible Dyakonov surface waves at the hyperbolic metasurface,"Dyakonov surface wave existing at the interface with anisotropy offers a
promising way of guiding light in two-dimension with almost no loss. However,
predicted decades ago, the experimental demonstration of the Dyakonov surface
wave seems always challenging for the weak anisotropic indices from the natural
materials. Here we experimentally demonstrated a Dyakonov surface wave mode
propagating in a hyperbolic metasurface at the visible frequency. Dyakonov
surface waves at the two surfaces of the metasurface can be supported
simultaneously by the hyperbolic anisotropy and form a Dyakonov typed mode with
low loss and a large allowed angle band. A detailed theoretical analysis and
numerical simulations prove that the electric field of such a surface wave mode
shows transverse spin, whose direction is determined by the orientations of the
hyperbolic anisotropy and surface normal, based on which we experimentally
observed the photonic spin Hall effect of the surface wave mode in our
metasurface.",2106.05699v1
2021-06-13,Morphology of an interacting three-dimensional trapped Bose-Einstein condensate from many-particle variance anisotropy,"The variance of the position operator is associated with how wide or narrow a
wave-packet is, the momentum variance is similarly correlated with the size of
a wave-packet in momentum space, and the angular-momentum variance quantifies
to what extent a wave-packet is non-spherically symmetric. We examine an
interacting three-dimensional trapped Bose-Einstein condensate at the limit of
an infinite number of particles, and investigate its position, momentum, and
angular-momentum anisotropies. Computing the variances of the three Cartesian
components of the position, momentum, and angular-momentum operators we present
simple scenarios where the anisotropy of a Bose-Einstein condensate is
different at the many-body and mean-field levels of theory, despite having the
same many-body and mean-field densities per particle. This suggests a way to
classify correlations via the morphology of 100\% condensed bosons in a
three-dimensional trap at the limit of an infinite number of particles.
Implications are briefly discussed.",2106.07001v1
2021-06-18,Exchange bias without directional anisotropy in Permalloy/CoO bilayers,"We utilize transverse ac susceptibility measurements to characterize magnetic
anisotropy in archetypal exchange-bias bilayers of ferromagnet Permalloy (Py)
and antiferromagnet CoO. Unidirectional anisotropy is observed for thin Py, but
becomes negligible at larger Py thicknesses, even though the directional
asymmetry of the magnetic hysteresis loop remains significant. Additional
magnetoelectronic measurements, magneto-optical imaging, as well as
micromagnetic simulations show that these surprising behaviors are likely
associated with asymmetry of spin flop distribution created in CoO during Py
magnetization reversal, which facilitates the rotation of the latter back into
its field-cooled direction. Our findings suggest new possibilities for
efficient realization of multistable nanomagnetic systems for neuromorphic
applications.",2106.09924v1
2021-06-20,Genuine tripartite entanglement as a probe of quantum phase transitions in a spin-1 Heisenberg chain with single-ion anisotropy,"We study the quantum phase transitions of spin-1 Heisenberg chains with an
easy-axis anisotropy $\Delta$ and a uniaxial single-ion anisotropy $D$ using a
multipartite entanglement approach. The genuine tripartite entanglement between
the spin blocks, measured by the tripartite qutrit hyperdeterminant, is
calculated within the quantum renormalization group method. Using this
approach, the phase boundaries between the topological Haldane, large-D and
anti-ferromagnetic N\'eel phases are determined in the half $\Delta-D$ plane
with $\Delta>0$. When the size of the spin blocks increases, the genuine
tripartite entanglement between the blocks exhibits a nonzero plateau in the
topological Haldane phase, and experiences abrupt drops at both the phase
boundaries between the Haldane--large-D and Haldane--N\'eel phases, which
justifies the usage of genuine multipartite entanglement as a probe of
topological phases in spin systems.",2106.10690v1
2021-07-05,Probing primordial black holes with anisotropies in stochastic gravitational-wave background,"Primordial black holes, if considered to constitute a significant fraction of
cold dark matter, trace the inhomogeneous large-scale structure of the
Universe. Consequently, the stochastic gravitational-wave background,
originating from incoherent superposition of unresolved signals emitted by
primordial black hole binaries, is expected to display anisotropies across the
sky. In this work, we investigate the angular correlations of such anisotropies
for the first time and demonstrate their difference from the analogous signal
produced by astrophysical black hole binaries. We carefully evaluate the
associated uncertainties due to shot-noise and cosmic variance, and demonstrate
that the studied signal in the low-frequency regime can be differentiated from
the signal of astrophysical origin. Our results are particularly promising in
the stellar mass-range, where the identification of the merger origin has been
particularly challenging.",2107.01935v3
2021-07-08,Emergence of Unconventional Interfacial Magnetic Phenomenon in Topological Insulator-Based Magnetic Heterostructures,"In a topological insulator (TI)/magnetic insulator (MI) hetero-structure,
large spin-orbit coupling of the TI and inversion symmetry breaking at the
interface could foster non-planar spin textures such as skyrmions at the
interface. This is observed as topological Hall effect in a conventional Hall
set-up. While this effect has been observed at the interface of TI/MI, where MI
beholds perpendicular magnetic anisotropy, non-trivial spin-textures that
develop in interfacial MI with in-plane magnetic anisotropy is under-reported.
In this work, we study Bi$_2$Te$_3$/EuS hetero-structure using planar Hall
effect (PHE). We observe planar topological Hall and spontaneous planar Hall
features that are characteristic of non-trivial in-plane spin textures at the
interface. We find that the latter is minimum when the current and magnetic
field directions are aligned parallel, and maximum when they are aligned
perpendicularly within the sample plane, which maybe attributed to the
underlying planar anisotropy of the spin-texture. These results demonstrate the
importance of PHE for sensitive detection and characterization of non-trivial
magnetic phase that has evaded exploration in the TI/MI interface.",2107.03596v2
2021-07-08,Self-consistently renormailzed spin-wave theory of layered ferromagnets on honeycomb lattice,"We develop a self-consistently renormalized spin-wave theory, within a
mean-field approximation, for the two-dimensional Heisenberg ferromagnet with
perpendicular easy-axis anisotropy on the honeycomb lattice, as well as its
few-layer and bulk extensions. In this method, the magnetization dependence on
temperature is found as the solution of the self-consistency equation.
Furthermore, we account for the physical difference of surface and bulk layers
by treating the layers as separate sublattices. Thus, the method can be readily
generalized to study various magnetic phenomena in a broad range of systems,
including those comprising magnetically inequivalent sublattices. Using our
theory, we calculate the temperature-dependent magnetization for two
chromium-based layered van der Waals insulating magnets, Cr$_2$Ge$_2$Te$_6$ and
CrI$_3$, employing various sets of Heisenberg exchange and single-ion
anisotropy values reported for these materials in the existing literature. As
expected, we observe a strong dimensionality effect where the ordering
temperature is reduced and its sensitivity on the anisotropy is enhanced with
the decrease of dimensionality.",2107.04085v1
2021-07-12,Origin of Perpendicular Magnetic Anisotropy in Yttrium Iron Garnet Thin Films Grown on Si (100),"We report the magnetic properties of yttrium iron garnet (YIG) thin films
grown by pulsed laser deposition technique. The films were deposited on Si
(100) substrates in the range of 15-50 nm thickness. Magnetic characterizations
were investigated by ferromagnetic resonance spectra. Perpendicular magnetic
easy axis was achieved up to 50 nm thickness. We observed that the
perpendicular anisotropy values decreased by increasing the film thickness. The
origin of the perpendicular magnetic anisotropy (PMA) was attributed to the
texture and the lattice distortion in the YIG thin films. We anticipate that
perpendicularly magnetized YIG thin films on Si substrates pave the way for a
cheaper and compatible fabrication process.",2107.05591v1
2021-07-23,Green's function formalism for nonlocal elliptical magnon transport,"We develop a non-equilibrium Green's function formalism to study magnonic
spin transport through a strongly anisotropic ferromagnetic insulator contacted
by metallic leads. We model the ferromagnetic insulator as a finite-sized
one-dimensional spin chain, with metallic contacts at the first and last sites
that inject and detect spin in the form of magnons. In the presence of
anisotropy, these ferromagnetic magnons become elliptically polarized, and spin
conservation is broken. We show that this gives rise to a novel parasitic spin
conductance, which becomes dominant at high anisotropy. Moreover, the spin
state of the ferromagnet becomes squeezed in the high-anisotropy regime. We
show that the squeezing may be globally reduced by the application of a local
spin bias.",2107.11072v2
2021-08-05,Triaxial magnetic anisotropy in the two-dimensional ferromagnetic semiconductor CrSBr,"Two-dimensional (2D) ferromagnets have recently drawn extensive attention,
and here we study the electronic structure and magnetic properties of the bulk
and monolayer of CrSBr, using first-principles calculations and Monte Carlo
simulations. Our results show that bulk CrSBr is a magnetic semiconductor and
has the easy magnetization b-axis, hard c-axis, and intermediate a-axis. Thus,
the experimental triaxial magnetic anisotropy (MA) is well reproduced here, and
it is identified to be the joint effects of spin-orbit coupling (SOC) and
magnetic dipole-dipole interaction. We find that bulk CrSBr has a strong
ferromagnetic (FM) intralayer coupling but a marginal interlayer one. We also
study CrSBr monolayer in detail and find that the intralayer FM exchange
persists and the shape anisotropy has a more pronounced contribution to the MA.
Using the parameters of the FM exchange and the triaxial MA, our Monte Carlo
simulations show that CrSBr monolayer has Curie temperature Tc = 175 K.
Moreover, we find that a uniaxial tensile (compressive) strain along the a (b)
axis would further increase the Tc.",2108.02418v2
2021-08-14,Voltage-controlled magnetism enabled by resistive switching,"The discovery of new mechanisms of controlling magnetic properties by
electric fields or currents furthers the fundamental understanding of magnetism
and has important implications for practical use. Here, we present a novel
approach of utilizing resistive switching to control magnetic anisotropy. We
study a ferromagnetic oxide that exhibits an electrically triggered
metal-to-insulator phase transition producing a volatile resistive switching.
This switching occurs in a characteristic spatial pattern: the formation of a
transverse insulating barrier inside a metallic matrix resulting in an unusual
ferromagnetic/paramagnetic/ferromagnetic configuration. We found that the
formation of this voltage-driven paramagnetic insulating barrier is accompanied
by the emergence of a strong uniaxial magnetic anisotropy that overpowers the
intrinsic material anisotropy. Our results demonstrate that resistive switching
is an effective tool for manipulating magnetic properties. Because resistive
switching can be induced in a very broad range of materials, our findings could
enable a new class of voltage-controlled magnetism systems.",2108.06445v1
2021-09-03,Effective Debye Screening Mass in an Anisotropic Quark Gluon Plasma,"Due to the rapid longitudinal expansion of the quark-gluon plasma created in
heavy-ion collisions, large local-rest-frame momentum-space anisotropies are
generated during the system's evolution. These momentum-space anisotropies
complicate the modeling of heavy-quarkonium dynamics in the quark-gluon plasma
due to the fact that the resulting inter-quark potentials are spatially
anisotropic, requiring real-time solution of the 3D Schr\""odinger equation.
Herein, we introduce a method for reducing anisotropic heavy-quark potentials
to isotropic ones by introducing an effective screening mass that depends on
the quantum numbers $l$ and $m$ of a given state. We demonstrate that, using
the resulting effective Debye screening masses, one can solve a 1D
Schr\""odinger equation and reproduce the full 3D results for the energies and
binding energies of low-lying heavy-quarkonium bound states to relatively high
accuracy. The resulting effective isotropic potential models could provide an
efficient method for including momentum-anisotropy effects in open quantum
system simulations of heavy-quarkonium dynamics in the quark-gluon plasma.",2109.01284v2
2021-09-03,Mechanisms of the in-plane magnetic anisotropy in superconducting NbSe2,"We present a unifying picture of the magnetic in-plane anisotropies of
two-dimensional superconductors based on transition metal dichalcogenides. The
symmetry considerations are first applied to constrain the form of the
conductivity tensor. We hence conclude that the two-fold periodicity of
transport distinct from the planar Hall related contributions requires a tensor
perturbation. At the same time, the six-fold periodic variation of the critical
field results from the Rashba spin-orbit coupling on a hexagonal lattice. We
have considered the effect of a weak tensor perturbation on the critical field,
gap function, and magneto-conductivity. The latter is studied using the
time-dependent Ginzburg-Landau phenomenology. The common origin of the two-fold
anisotropy in transport and thermodynamics properties is identified. The scheme
constructed here is applied to describe the existing theoretical scenarios from
a unified point of view. This allows us to single out the differences and
similarities between the suggested approaches.",2109.01505v1
2021-09-12,"Spin excitation spectra in helimagnetic states: proper-screw, cycloid, vortex crystal, and hedgehog lattice","We investigate the spin excitation spectra in chiral and polar magnets by the
linear spin-wave theory for an effective spin model with symmetric and
antisymmetric long-range interactions. In one dimension, we obtain the analytic
form of the dynamical spin structure factor for proper-screw and cycloidal
helical spin states with uniform twists, which shows a gapless mode with strong
intensity at the helical wave number. When introducing spin anisotropy in the
symmetric interactions, we numerically show that the stable spin spirals become
elliptically anisotropic with nonuniform twists and the spin excitation is
gapped. In higher dimensions, we find that similar anisotropy stabilizes
multiple-$Q$ spin states, such as vortex crystals and hedgehog lattices. We
show that the anisotropy in these states manifests itself in the dynamical spin
structure factor: a strong intensity in the transverse components to the wave
number appears only when the helical wave vector and the corresponding easy
axis are perpendicular to each other. Our findings could be useful not only to
identify the spin structure but also to deduce the stabilization mechanism by
inelastic neutron scattering measurements.",2109.05628v2
2021-09-16,Lone pair driven anisotropy in antimony chalcogenide semiconductors,"Antimony sulfide (Sb2S3) and selenide (Sb2Se3) have emerged as promising
earth-abundant alternatives among thin-film photovoltaic compounds. A
distinguishing feature of these materials is their anisotropic crystal
structures, which are composed of quasi-one-dimensional (1D) [Sb4X6]n ribbons.
The interaction between ribbons has been reported to be van der Waals (vdW) in
nature and Sb2X3 are thus commonly classified in the literature as 1D
semiconductors. However, based on first-principles calculations, here we show
that inter-ribbon interactions are present in Sb2X3 beyond the vdW regime. The
origin of the anisotropic structures is related to the stereochemical activity
of the Sb 5s lone pair according to electronic structure analysis. The impacts
of structural anisotropy on the electronic and optical properties are further
examined, including the presence of higher dimensional Fermi surfaces for
charge carrier transport. Our study provides guidelines for optimising the
performance of Sb2X3-based solar cells via device structuring based on the
underlying crystal anisotropy.",2109.08117v3
2021-09-16,Parameter estimation in an anisotropic expanding spacetime,"In this work, we investigate how the anisotropy affects the cosmological
parameters estimation. Here the anisotropy is incorporated as a small
gravitational disturbance. We calculate the Fisher information for both
cosmological parameters $\epsilon$ (expansion volume) and $\rho$ (expansion
rate), and we show that the anisotropy introduces oscillations in the Fisher
information spectrum. This implies that the estimation of the cosmological
parameters is sensible to the direction of the momentum $k$ of particles. In
addition, we observe that for small values of the momentum $k$ there is a
substantial difference between the Fisher information spectrum for the minimum
and conformal couplings.",2109.08252v1
2021-09-23,Anisotropy of the proton kinetic energy as a tool for capturing structural transition in nanoconfined H$_2$O,"The proton dynamics of a 2D water monolayer confined inside a graphene slit
pore is studied in Cartesian and molecular frames of reference using molecular
dynamics simulations. The vibrational density of states of the proton was
calculated versus temperature and was further used to deduce the mean kinetic
energy of the hydrogen atoms, Ke(H), in both frames of reference. The
directional components of Ke(H) are in good agreement with experimental
observations for bulk as well as nanoconfined water. Nonetheless, while in the
molecular frame of reference the effect of temperature on the anisotropy ratios
of Ke(H) (the ratio between its directional components) are practically
invariant between the 2D and 3D cases, those in the Cartesian frame of
reference reveal a rather notable reduction across 200K, indicating the
occurrence of an order-disorder transition. This result is further supported by
the calculated entropy and enthalpy of the confined water molecules. Overall it
is shown that Ke(H) anisotropy ratios may serve as a valuable order parameter
for detecting structural transformations in hydrogen bonds containing molecular
systems.",2109.11175v1
2021-09-27,Subdiffusive hydrodynamics of nearly-integrable anisotropic spin chains,"We address spin transport in the easy-axis Heisenberg spin chain subject to
integrability-breaking perturbations. We find that spin transport is
subdiffusive with dynamical exponent $z=4$ up to a timescale that is
parametrically long in the anisotropy. In the limit of infinite anisotropy,
transport is subdiffusive at all times; for large finite anisotropy, one
eventually recovers diffusion at late times, but with a diffusion constant
independent of the strength of the integrability breaking perturbation. We
provide numerical evidence for these findings, and explain them by adapting the
generalized hydrodynamics framework to nearly integrable dynamics. Our results
show that the diffusion constant of near-integrable interacting spin chains is
generically not perturbative in the integrability breaking strength.",2109.13251v2
2021-10-06,Nano-imaging of the edge-dependent optical polarization anisotropy of black phosphorus,"The electronic structure and functionality of 2D materials is highly
sensitive to structural morphology, opening the possibility for manipulating
material properties, but also making predictable and reproducible functionality
challenging. Black phosphorus (BP), a corrugated orthorhombic 2D material, has
in-plane optical absorption anisotropy critical for applications such as
directional photonics, plasmonics, and waveguides. Here, we use
polarization-dependent photoemission electron microscopy to visualize the
anisotropic optical absorption of BP with 54 nm spatial resolution. We find the
edges of BP flakes have a shift in their optical polarization anisotropy from
the flake interior due to the 1D confinement and symmetry reduction at flake
edges that alter the electronic charge distributions and transition dipole
moments of edge electronic states, confirmed with first-principles
calculations. These results uncover previously hidden modification of the
polarization-dependent absorbance at the edges of BP, highlighting the
opportunity for selective excitation of edge states of 2D materials with
polarized light.",2110.02430v3
2021-10-17,Semiclassical Boltzmann magnetotransport theory in anisotropic systems with a nonvanishing Berry curvature,"Understanding the transport behavior of an electronic system under the
influence of a magnetic field remains a key subject in condensed matter
physics. Particularly in topological materials, their nonvanishing Berry
curvature can lead to many interesting phenomena in magnetotransport owing to
the coupling between the magnetic field and Berry curvature. By fully
incorporating both the field-driven anisotropy and inherent anisotropy in the
band dispersion, we study the semiclassical Boltzmann magnetotransport theory
in topological materials with a nonvanishing Berry curvature. We show that as a
solution to the Boltzmann transport equation the effective mean-free-path
vector is given by the integral equation, including the effective velocity
arising from the coupling between the magnetic field, Berry curvature and
mobility. We also calculate the conductivity of Weyl semimetals with an
isotropic energy dispersion, and find that the coupling between the magnetic
field and Berry curvature induces anisotropy in the relaxation time, showing a
substantial deviation from the result obtained assuming a constant relaxation
time.",2110.08816v3
2021-10-31,Thermally induced all-optical ferromagnetic resonance in thin YIG films,"All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
damping or spin stiffness. In this work we demonstrate that the AO-FMR method
can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
layer (Au, Pt) is deposited on top of the film. Magnetization precession is
triggered by heating of the metallic layer with femtosecond laser pulses. The
heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
the quasi-equilibrium orientation of magnetization, which results in
precessional magnetization dynamics. The laser-induced magnetization precession
corresponds to a uniform (Kittel) magnon mode, with the precession frequency
determined by the magnetic anisotropy of the material as well as the external
magnetic field, and the damping time set by a Gilbert damping parameter. The
AO-FMR method thus enables measuring local magnetic properties, with spatial
resolution given only by the laser spot size.",2111.00586v1
2021-11-02,Interferometric weak value of polarization observable and differential Jones matrix algebra,"The quantification of simultaneously present weak polarization anisotropy
effects are of practical interest from polarimetric and metrological
perspective. Recently, in Phys. Rev. A 103, 053518, we experimentally
demonstrated a classical analog of post-selected quantum weak measurement
through optical interferometry to amplify all possible weak polarization
anisotropy effects individually. Here, we propose an extension of this
interferometric framework to quantify simultaneously present polarization
anisotropy effects. Moreover, a clear correspondence of differential Jones
matrix approach with the present scheme is indicated. The proposed scheme
enables the measurement of differential Jones matrices through characteristic
Stokes vector elements. Our proposal leads to a new class of polarimeter for
experimental detection of differential Jones matrix of non-depolarizing
anisotropic medium exhibiting simultaneous multiple polarimetric effects of
tiny magnitude.",2111.01642v2
2021-11-16,Synthesis and thermal expansion of chalcogenide MAX phase Hf2SeC,"Thermal expansion of MAX phases along different directions tended to be
different because of the anisotropy of hexagonal crystals. Herein, a new Hf2SeC
phase was synthesized and confirmed to be relatively isotropic, whose
coefficients of thermal expansion (CTEs) were determined to be 9.73 {\mu}K-1
and 10.18 {\mu}K-1 along a and c directions. The strong M-S bond endowed Hf2SC
and Zr2SC lower CTEs than Hf2SeC and Zr2SeC. A good relationship between the
thermal expansion anisotropy and the ratio of elastic stiffness constant c11
and c33 was established. This straightforward approximation could be used to
roughly predict the thermal expansion anisotropy of MAX phases.",2111.08257v1
2021-11-21,Electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in nematic liquid crystals,"We study electrophoretic mobility of metal-dielectric Janus particles with
dipolar director profile in two nematic liquid crystals (LCs) having same
(positive) conductivity anisotropy and opposite dielectric anisotropy. The
applied ac electric field is parallel and perpendicular to the director for the
positive and negative dielectric anisotropy LCs, respectively. The velocity of
the Janus particles in both LCs is significantly higher than that of the
non-Janus particles. We map the electroosmotic flow fields surrounding the
particles using microparticle image velocimetry ($\mu$-PIV) and show that the
flows on the metal hemisphere is stronger than that on the dielectric
hemisphere and the pumping of LC along the direction of motion of the Janus
particles is more than that of the non-Janus particles. For a given liquid
crystal, particles with asymmetric surface properties is useful for enhancing
their electrophoretic mobility and activity.",2111.10714v2
2021-11-26,Characterization of Anisotropic Gaussian Random Fields by Minkowski Tensors,"Gaussian random fields are among the most important models of amorphous
spatial structures and appear across length scales in a variety of physical,
biological, and geological applications, from composite materials to geospatial
data. Anisotropy in such systems can sensitively and comprehensively be
characterized by the so-called Minkowski tensors from integral geometry. Here,
we analytically calculate the expected Minkowski tensors of arbitrary rank for
the level sets of Gaussian random fields. The explicit expressions for
interfacial Minkowski tensors are confirmed in detailed simulations. We
demonstrate how the Minkowski tensors detect and characterize the anisotropy of
the level sets, and we clarify which shape information is contained in the
Minkowski tensors of different rank. Using an irreducible representation of the
Minkowski tensors in the Euclidean plane, we show that higher-rank tensors
indeed contain additional anisotropy information compared to a rank two tensor.
Surprisingly, we can nevertheless predict this information from the second-rank
tensor if we assume that the random field is Gaussian. This relation between
tensors of different rank is independent of the details of the model. It is,
therefore, useful for a null hypothesis test that detects non-Gaussianities in
anisotropic random fields.",2111.13349v1
2021-11-30,Dimension reduction induced anisotropic magnetic thermal conductivity in hematite nanowire,"The thermophysical properties near the magnetic phase transition point is of
great importance in the study of critical phenomenon. Low-dimensional materials
are suggested to hold different thermophysical properties comparing to their
bulk counterpart due to the dimension induced quantum confinement and
anisotropy. In this work, we measured the thermal conductivity of
$\alpha$-Fe$_2$O$_3$ nanowires along [110] direction (growing direction) with
temperature from 100K to 150K and found a dip of thermal conductivity near the
Morin temperature. We found the thermal conductivity near Morin temperature
varies with the angle between magnetic field and [110] direction of nanowire.
More specifically, an angular-dependent thermal conductivity is observed, due
to the magnetic field induced movement of magnetic domain wall. The angle
corresponding to the maximum of thermal conductivity varies near the Morin
transition temperature, due to the different magnetic easy axis as suggested by
our calculation based on magnetic anisotropy energy. This angular dependence of
thermal conductivity indicates that the easy axis of $\alpha$-Fe$_2$O$_3$
nanowires is different from bulk $\alpha$-Fe$_2$O$_3$ due to the geometric
anisotropy.",2111.15137v1
2021-12-02,Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite,"Perpendicular magnetic anisotropy (PMA) energy up to
$K_{\mathrm{u}}=6.1\pm0.8$ MJ m$^{-3}$ is demonstrated in this study by
inducing large lattice-distortion exceeding 3% at room temperature in
epitaxially distorted cobalt ferrite Co$ _{x} $Fe$ _{3-x} $O$ _{4} $ (x = 0.72)
(001) thin films. Although the thin film materials include no rare-earth
elements or noble metals, the observed $ K_{u} $ is larger than that of the
neodymium-iron-boron compounds for high-performance permanent magnets. The
large PMA is attributed to the significantly enhanced magneto-elastic effects,
which are pronounced in distorted films with epitaxial lattice structures upon
introducing a distortion control layer of composition Mg$ _{2-x} $Sn$_{1+x}$O$
_{4} $. Surprisingly, the induced $ K_{u} $ can be quantitatively explained in
terms of the agreement between the local crystal field of Co$ ^{2+} $ and the
phenomenological magneto-elastic model, indicating that the linear response of
induced $K_u$ is sufficiently valid even under lattice distortions as large as
3.2%. Controlling tetragonal lattice deformation using a non-magnetic spinel
layer for ferrites could be a promising protocol for developing materials with
large magnetic anisotropies.",2112.00916v1
2021-12-03,Inertial range magnetic fluctuation anisotropy observed from PSP first seven orbits,"Solar wind turbulence is anisotropic with respect to the mean magnetic field.
Anisotropy leads to ambiguity when interpreting in-situ turbulence observations
in the solar wind because an apparent change in the measurements could be due
either to the change of intrinsic turbulence properties or to a simple change
of the spacecraft sampling direction. We demonstrate the ambiguity using the
spectral index and magnetic compressibility in the inertial range observed by
the Parker Solar Probe during its first seven orbits ranging from 0.1 to 0.6
AU. To unravel the effects of the sampling direction, we assess whether the
wavevector anisotropy is consistent with a two-dimensional (2D) plus slab
turbulence transport model and determine the fraction of power in the 2D versus
slab component. Our results confirm that the 2D plus slab model is consistent
with the data and the power ratio between 2D and slab components depends on
radial distance, with the relative power in 2D fluctuations becoming smaller
closer to the Sun.",2112.01711v1
2021-12-08,Interplay of orientational order and roughness in simulated thin film growth of anisotropically interacting particles,"Roughness and orientational order in thin films of anisotropic particles are
investigated using kinetic Monte Carlo simulations on a cubic lattice.
Anisotropic next-neighbor interactions between the lattice particles were
chosen to mimic the effects of shape anisotropy in the interactions of disc- or
rod-like molecules with van-der-Waals attractions. Increasing anisotropy leads
first to a preferred orientation in the film (which is close to the
corresponding equilibrium transition) while the qualitative mode of roughness
evolution (known from isotropic systems) does not change. At strong
anisotropies, an effective step-edge (Ehrlich-Schwoebel) barrier appears and a
non-equilibrium roughening effect is found, accompanied by re-ordering in the
film which can be interpreted as the nucleation and growth of domains of
lying-down discs or rods. The information on order and roughness is combined
into a diagram of dynamic growth modes.",2112.04270v3
2021-12-09,Exchange-bias dependent diffusion rate of hydrogen discovered from evolution of hydrogen-induced noncollinear magnetic anisotropy in FePd thin films,"Hydrogenation-induced noncollinear magnetic anisotropy is observed from the
evolution of the magnetic domains in FePd alloy thin films using magneto-optic
Kerr effect (MOKE) microscopy. MOKE images reveal complicated competitions
between different magnetic anisotropies during hydrogen diffusion into the
film. An intriguing enhancement of the hydrogen diffusion rate due to the
presence of an initial exchange bias induced by a high magnet field is thereby
discovered, pointing to an additional scope of controllability of magnetic
metal hydrides as potential future hydrogen sensing and storage materials.",2112.05079v1
2021-12-09,Spectral Distortion Anisotropy from Inflation for Primordial Black Holes,"Single field inflationary models that seek to greatly enhance small scale
power in order to form primordial black holes predict both a squeezed
bispectrum that is enhanced by this small scale power and a potentially
detectable enhancement of CMB spectral distortions. Despite this combination,
spectral distortion anisotropy on CMB scales remains small since the squeezed
bispectrum represents an unobservable modulation of the scale rather than local
amplitude for the short wavelength acoustic power that dissipates and forms the
$\mu$ spectral distortion. The leading order amplitude effect comes from the
local modulation of acoustic dissipation at the beginning of the $\mu$ epoch at
the end of thermalization by a long wavelength mode that is correlated with CMB
anisotropy itself. Compensating factors from the suppression by the square of
the ratio the comoving horizon at thermalization to the smallest detectable
primary CMB scales ($\sim 0.0005$) and maximal allowed enhancement of $\mu$
($\sim 5000$) leaves a signal in the $\mu T$ cross spectrum that is still well
beyond the capabilities of PIXIE or LiteBIRD due to sensitivity and resolution
while remaining much larger than in single field slow roll inflation and
potentially observable.",2112.05190v1
2021-12-09,Electronic control and switching of entangled spin state using anisotropy and exchange in the three-particle paradigm,"We explore the control and switching of the entangled spin states of
multi-spin particle qubit coupled to an electron using a three-particle spin
model described by $S_i$ ($i=1,2,3$), in which $S_1=\tfrac{1}{2}$ is an
electron and $S_{2,3}$ can have any spin with both exchange coupling and
magnetic anisotropy. We derive a general formula for the existence of a
switching (DJ) resonance for any spin $S_{2,3}$. We further contrast the
entanglement switching mechanisms for the $S_{2,3}=\tfrac{1}{2}$ and
$S_{2,3}=1$ spin models. We find that while the onsite magnetic anisotropy in
the case of $S_{2,3}>\tfrac{1}{2}$ allows full control of their spin states via
interaction with $S_1$, in order to achieve acceptable control of a Bloch
vector within the $S_{2,3}=\tfrac{1}{2}$ model, additional mechanisms, such as
anisotropic exchange coupling, are required.",2112.05223v2
2021-12-14,Robust perpendicular magnetic anisotropy in Ce substituted yttrium iron garnet epitaxial thin films,"Cerium substituted yttrium iron garnet (Ce:YIG) epitaxial thin films are
prepared on gadolinium gallium garnet (GGG) substrate with pulsed laser
deposition (PLD). It is observed that the films grown on GGG(111) substrate
exhibit perpendicular magnetic anisotropy (PMA) as compared to films grown on
GGG(100) substrate. The developed PMA is confirmed from magneto-optical Kerr
effect, bulk magnetization and ferromagnetic resonance measurements. Further,
the magnetic bubble domains are observed in the films exhibiting PMA. The
observations are explained in terms of the growth direction of Ce:YIG films and
the interplay of various magnetic anisotropy terms. The observed PMA is found
to be tunable with thickness of the film and a remarkable temperature stability
of the PMA is observed in all the studied films of Ce:YIG deposited on GGG(111)
substrate.",2112.07264v1
2021-12-19,A New Picture of Cosmic String Evolution and Anisotropic Stochastic Gravitational-Wave Background,"We investigate the anisotropies of the stochastic gravitational-wave
background (SGWB) produced by cosmic strings associated with the spontaneous
U(1) symmetry breaking of Grand Unified Theory, which happens at the onset of
inflation. The string network evolution is determined by primordial
fluctuations and never reaches the scaling regime. The string loops are
inhomogeneously distributed in large scale regions, resulting in large
anisotropies in the SGWB. We find that the angular power spectrum of SGWB
anisotropies depends on frequency, which is testable in multiband observations
of GWs. In particular, GWs from the cosmic strings can appropriately interpret
the common-spectrum process reported by NANOGrav collaboration, and the angular
power spectrum in the nanohertz band,
$\mathtt{l}(\mathtt{l}+1)C_{\mathtt{l}}=5.6\times 10^{-2}$ at large scales, is
expected to be detectable by pulsar timing array experiments in the near
future.",2112.10131v1
2021-12-23,Visible Out-of-plane Polarized Luminescence and Electronic Resonance from Black Phosphorus,"Black Phosphorus (BP) is unique among layered materials owing to its
homonuclear lattice and strong structural anisotropy. While recent
investigations on few layers BP have extensively explored the in-plane (a,c)
anisotropy, much less attention has been given to the out-of-plane direction
(b). Here, the optical response from bulk BP is probed using
polarization-resolved photoluminescence (PL), photoluminescence excitation
(PLE) and resonant Raman scattering along the zigzag, out-of-plane, and
armchair directions. PL reveals an unexpected b-polarized emission occurring in
the visible at 1.75 eV, far above the fundamental gap (0.3 eV). PLE indicates
that this emission is generated through b-polarized excitation at 2.3 eV. The
same electronic resonance is observed in resonant Raman scans, where the
scattering efficiency of both Ag phonon modes is enhanced. These experimental
results are fully consistent with DFT calculations of the permittivity tensor
elements and demonstrate the remarkable extent to which the anisotropy
influences the optical properties and carrier dynamics in black phosphorus.",2112.12617v1
2021-12-28,$Λ$CDM cosmology with a quiescent anisotropy in a higher dimensional steady state universe,"In this work, which follows a series of studies on the higher-dimensional
steady state universe idea and prepared for Professor Tekin Dereli's
Festschrift, we show the influence of the dynamical internal (unobservable)
space on the evolution of the possible anisotropy of the external (observable)
space. We obtain mathematically exactly the same Friedmann equation of the
standard $\Lambda$CDM model for the external space, but with some remarkable
physical differences. In particular, the higher-dimensional negative
cosmological constant plays the role of the four-dimensional positive
cosmological constant and the expansion anisotropy, viz., the shear scalar, of
the external space mimics a negative cosmological constant; it would mimic a
stiff fluid when allowed on top of the standard $\Lambda$CDM model. This latter
feature gives us the opportunity to manipulate the CMB quadrupole temperature
fluctuation, suggesting a possible answer to the fact that its observed value
is lower than that predicted by the standard $\Lambda$CDM model.",2112.14259v1
2021-12-29,A unified theory of ferromagnetic quantum phase transitions in heavy fermion metals,"Motivated by the recent discovery of a continuous ferromagnetic quantum phase
transition in CeRh$_6$Ge$_4$ and its distinction from other U-based heavy
fermion metals such as UGe$_2$, we develop a unified explanation of their
different ground state properties based on an anisotropic ferromagnetic
Kondo-Heisenberg model. We employ an improved large-$N$ Schwinger boson
approach and predict a full phase diagram containing both a continuous
ferromagnetic quantum phase transition for large magnetic anisotropy and
first-order transitions for relatively small anisotropy. Our calculations
reveal three different ferromagnetic phases including a half-metallic spin
selective Kondo insulator with a constant magnetization. The Fermi surface
topologies are found to change abruptly between different phases, consistent
with that observed in UGe$_2$. At finite temperatures, we predict the
development of Kondo hybridization well above the ferromagnetic long-range
order and its relocalization near the phase transition, in good agreement with
band measurements in CeRh$_6$Ge$_4$. Our results highlight the importance of
magnetic anisotropy and provide a unified theory for understanding the
ferromagnetic quantum phase transitions in heavy fermion metals.",2112.14515v1
2021-12-30,ARGO-YBJ Observation of the Large-scale Anisotropy During the Solar Minimum between Cycles 23 and 24,"This paper reports on the measurement of the large-scale anisotropy in the
distribution of cosmic-ray arrival directions using the data collected by the
air shower detector ARGO-YBJ from 2008 January to 2009 December,during the
minimum of solar activity between cycles 23 and 24. In this period, more than
200 billion showers were recorded with energies between 1 and 30 TeV. The
observed two-dimensional distribution of cosmic rays is characterized by two
wide regions of excess and deficit, respectively, both of relative intensity
0.001 with respect to a uniform flux, superimposed on smaller size structures.
The harmonic analysis shows that the large-scale cosmic-ray relative intensity
as a function of R.A. can be described by the first and second terms of a
Fouries series. The high event statistics allow the study of the energy
dependence of the anistropy, showing that the amplitude increases with energy,
with a maximum intensity at 10 TeV, and then decreases while the phase slowly
shifts toward lower values of R.A. with increasing energy. The ARGO-YBJ data
provide accurate observations over more than a decade of energy around this
feature of the anisotropy spectrum.",2112.14891v1
2021-12-31,Random Anisotropy Magnet at Finite Temperature,"Abstract We present finite-temperature Monte Carlo studies of a 2D
random-anisotropy magnet on lattices containing one million spins. The
correlated spin-glass state predicted by analytical theories is reproduced in
simulations, as are the field-cooled and zero-field-cooled magnetization curves
observed in experiments. The orientations of lattice spins begin to freeze when
the temperature is lowered. The freezing transition is due to the energy
barriers generated by the random anisotropy rather than due to random
interactions in conventional spin-glasses. We describe freezing by introducing
the time-dependent spin-glass order parameter $q$ and the spin-melting time
$\tau_{M}$ defined via $q=\tau_{M}/t$ above freezing, where t is the time of
the experiment represented by the number of Monte Carlo steps.",2112.15269v1
2022-01-02,Percolation on spatial anisotropic networks,"Many realistic systems such as infrastructures are characterized by spatial
structure and anisotropic alignment. Here we propose and study a model for
dealing with such characteristics by introducing a parameter that controls the
strength of the anisotropy in the spatial network. This parameter is added to
an existing isotropic model used to describe networks under spatial
constraints, thus generalizing the spatial model to take into account both
spatial and anisotropic features. We study the resilience of such networks by
using a percolation process and find that anisotropy has a negative impact on a
network's robustness. In addition, our results suggest that the anisotropy in
this model does not affect the critical exponent of the correlation length,
$\nu$, which remains the same as the known $\nu$ in 2D isotropic lattices.",2201.00373v1
2021-12-29,Modifications of CMB spectrum by nonextensive statistical mechanics,"Cosmic microwave background radiation can supply us some most significant
parts of the information on the universe. Some researchers believe that The
gravitational system cannot be decribed by the standard statistical mechanics.
In this article we apply Tsallis nonextensive statistical mechanics to
investigate CMB spectrum and related cosmological processes. Based on recent
observational data we find that the nonextensive statistical mechanics can
modify the values of related physical quantites. Since the value of physical
quantites have changed, some processes, such as recombination, can be affected.
We have investigated the anisotropy of the CMB for two effects: the dipole
anisotropy of CMB and the Sunyaev-Zel'dovich effect. We find that the dipole
anisotropy of CMB cannot be modified by the nonextensive statistical mechanics.
However, the standard result of the Sunyaev-Zel'dovich effect should be
modified by nonextensive statistical mechanics. In principle, future work can
distinguish these effects.",2201.00758v1
2022-01-04,Benchmarking of different strategies to include anisotropy in a curvature-driven multi-phase-field model,"Two benchmark problems for quantitative assessment of anisotropic curvature
driving force in phase field method were developed and introduced. Both
benchmarks contained an anisotropically shrinking grain in homogeneous matrix.
The first benchmark was a shrinking Wulff shape and in the second, such
inclination dependence of the kinetic coefficient was added so that the
shrinkage was isotropic. In both cases the match to the expected shape was
quantified by means of Hausdorff distance and the shrinkage rate was
analytically expressed. Three different ways of interface energy anisotropy
inclusion in a multi-phase field model were compared. Because their performance
was comparable, they were tested in an additional benchmark problem, which
concerned direct measurement of equilibrium triple junction angles. Based on
this benchmark, only one of the three strategies to include anisotropy was
reliable in strongly anisotropic systems.",2201.00922v2
2022-01-10,"Elastic anisotropy of 1,3,5-Triamino-2,4,6-Trinitrobenzene as a function of temperature and pressure: A Molecular Dynamics study","The equation of state of the triclinic compound
1,3,5-triamino-2,4,6-trinitrobenzene (TATB) as well as its second-order
isothermal elastic tensor were computed through classical molecular dynamics
simulations under various temperature and pressure conditions. Hydrostatic
pressures similar to previous diamond anvil cell experiments were imposed
within the range [0, 66] GPa and temperatures chosen between 100 and 900 K in
conjunction with the most recent version of an all-atom fully-flexible molecule
force field. The isothermal elastic constants were computed using the
generalized Hooke's law by fitting Cauchy stress vs. linear strain curves.
Along isobaric pathways, TATB single crystal stiffness is found to undergo
linear softening, less pronounced at high pressure, while maintaining its
elastic anisotropy. On the other hand, along an isothermal pathways, a
non-linear increase is observed in the elastic constants with a significant
decrease in anisotropy. Towards a precise mesoscopic modeling of TATB single
crystal mechanical behavior, we provide ""ready to plug-in"" analytical
formulations of the P,V,T equation of state and pressure-temperature dependent
non-linear elasticity.",2201.03224v1
2022-01-24,Hund's coupling and electronic anisotropy in the spin-density wave state of iron pnictides,"In the multiband systems, Hund's coupling ($J$) plays a significant role in
the spin and charge excitations. We study the dependence of electronic
anisotropy on $J$ in terms of Drude-weight along different directions as well
as the orbital order in the four-fold symmetry broken spin-density wave state
of iron pnictides. A robust behavior of the Drude-weight anisotropy within a
small window around $J \sim 0.25U$ with $U$ as intraorbital Coulomb interaction
is described in terms of orbital-weight distribution along the reconstructed
Fermi surfaces. We also find that the ferro-orbital order increases with $J$ in
the widely accepted regime for the latter, which is explained as a consequence
of rising exchange field with an increase in magnetization.",2201.09808v1
2022-01-26,Magnetoconductance Anisotropies and Aharonov-Casher Phases,"The spin-orbit interaction is a key tool for manipulating and functionalizing
spin-dependent electron transport. However, the precise value of the spin-orbit
coupling constant is hard to determine and control. Here we propose a
measurement of the geometric (Aharonov-Casher) phase of the electron
wavefunction generated by the spin-orbit coupling as a means to deduce the
spin-orbit coupling strength in weak links. Unlike other proposed measurements
of geometric phases, which rely on interference, we show that the anisotropy of
the magnetoconductance, measured at different directions of an external
magnetic field,is determined by the geometric phase. Specifically we consider
weak links in which the Rashba interaction is caused by an external electric
field, but our method is expected to apply also for other forms of the
spin-orbit coupling. Measuring this magnetoconductance anisotropy thus allows
calibrating Rashba spintronic devices by an external electric field that tunes
the spin-orbit interaction.",2201.10845v2
2022-02-02,Photochemical Anisotropy and Direction-dependent Optical Absorption in Semiconductors,"Photochemical reactions on semiconductors are anisotropic, since they occur
with different rates on surfaces of different orientation. Understanding the
origin of this anisotropy is crucial to engineering more efficient
photocatalysts. In this work, we use hybrid density functional theory (DFT) to
identify the surfaces associated with the largest number of photo-generated
carriers in different semiconductors. For each material we create a spherical
heat map of the probability of optical transitions at different wave vectors.
These maps allow to identify the directions associated with the majority of the
photo-generated carriers and can thus be used to make predictions about the
most reactive surfaces for photochemical applications. Results indicate that it
is generally possible to correlate the heat maps with the anisotropy of the
bands observed in conventional band-structure plots, as previously suggested.
However, we also demonstrate that conventional bands-structure plots do not
always provide all the informations and that taking into account the
contribution of all possible transitions weighted by their transition dipole
moments is crucial to obtain a complete picture.",2202.01073v1
2022-02-02,Antiferromagnetic parametric resonance driven by voltage-controlled magnetic anisotropy,"Voltage controlled magnetic anisotropy (VCMA) is a low-energy alternative to
manipulate the ferromagnetic state, which has been recently considered also in
antiferromagnets (AFMs). Here, we theoretically demonstrate that VCMA can be
used to excite linear and parametric resonant modes in easy-axis AFMs with
perpendicular anisotropy, thus opening the way for an efficient electrical
control of the Neel vector, and for detection of high-frequency dynamics. Our
work leads to two key results: (i) VCMA parametric pumping experiences the
so-called exchange enhancement of the coupling efficiency and, thus, is 1-2
orders of magnitude more efficient than microwave magnetic fields or
spin-orbit-torques, and (ii) it also allows for zero-field parametric
resonance, which cannot be achieved by other parametric pumping mechanisms in
AFMs with out-of-plane easy axis. Therefore, we demonstrate that the VCMA
parametric pumping is the most promising method for coherent excitation and
manipulation of AFM order in perpendicular easy-axis AFMs.",2202.01156v1
2022-02-24,Resistivity anisotropy from the multiorbital Boltzmann equation in nematic FeSe,"We compute the resistivity anisotropy in the nematic phase of FeSe from the
static solution of the multiorbital Boltzmann equation. By introducing disorder
at the level of the microscopic multiorbital model we show that even elastic
scattering by localized impurities may lead to non-trivial anisotropic
renormalization of the electronic velocities, challenging the usual
understanding of transport based only on cold- and hot-spots effects. Our model
takes into account both the $xz/yz$ and the recently proposed $xy$ nematic
ordering. We show that the latter one has a crucial role in order to reproduce
the experimentally-measured anisotropy, providing a direct fingerprint of the
different nematic scenarios on the bulk transport property of FeSe.",2202.12070v2
2022-03-08,Topological phase transition in magnon bands in a honeycomb ferromagnet driven by sublattice symmetry breaking,"Ferromagnetic honeycomb systems are known to exhibit a magnonic topological
phase under the existence of the next-nearest neighbor Dzyaloshinskii-Moriya
interaction (DMI). Motivated by the recent progress in the sublattice-specific
control of magnetic anisotropy, we study the topological phase of magnon bands
of honeycomb ferromagnetic monolayer and bilayer with the sublattice symmetry
breaking due to the different anisotropy energy in the presence of the DMI. We
show that there is a topological phase transition between the topological
magnon insulator and the topologically trivial magnon phase driven by the
change of the relative size of the DMI and the anisotropy differences between
the sublattices. The magnon thermal Hall conductivity is proposed as an
experimental probe of the magnon topology.",2203.03845v1
2022-03-15,Standing spin wave excitation in Bi:YIG films via temperature induced anisotropy changes and magnetoacoustic coupling,"Based on micromagnetic simulations and experimental observations of the
magnetization and lattice dynamics following the direct optical excitation of
the magnetic insulator Bi:YIG or indirect excitation via an optically opaque
Pt/Cu double layer, we disentangle the dynamical effects of magnetic anisotropy
and magnetoelastic coupling. The strain and temperature of the lattice are
quantified via modeling ultrafast x-ray diffraction data. Measurements of the
time-resolved magneto-optical Kerr effect agree well with the magnetization
dynamics simulated according to the excitation via two mechanisms: The
magneto-acoustic coupling to the experimentally verified strain dynamics and
the ultrafast temperature-induced transient change in the magnetic anisotropy.
The numerical modeling proves that for direct excitation both mechanisms drive
the fundamental mode with opposite phase. The relative ratio of standing
spin-wave amplitudes of higher order modes indicates that both mechanisms are
substantially active.",2203.07851v1
2022-03-16,Testing the empirical relationship between Forbush decreases and cosmic ray diurnal anisotropy,"The abrupt aperiodic modulation of cosmic ray (CR) flux intensity, often
referred to as Forbush decrease (FD), plays a significant role in our
understanding of the Sun-Earth electrodynamics. Accurate and precise
determination of FD magnitude and timing are among the intractable problems in
FD-based analysis. FD identification is complicated by CR diurnal anisotropy.
CR anisotropy can increase or reduce the number and amplitude of FDs. It is
therefore important to remove its contributions from CR raw data before FD
identification. Recently, an attempt was made, using a combination of Fourier
transformed technique and FD-location machine to address this. Thus, two FD
catalogs and amplitude diurnal variation (ADV) were calculated from filtered
(FD1 and ADV) and raw (FD2) CR data. In the current work, we test the empirical
relationship between FD1, FD2, ADV, and solar-geophysical characteristics. Our
analysis shows that two types of magnetic fields-interplanetary (IMF) and
geomagnetic (Dst) govern the evolution of CR flux intensity reductions.",2203.08883v1
2022-03-18,Implications of phonon anisotropy on thermal conductivity of fluorite oxides,"Fluorite oxides are attractive ionic compounds for a range of applications
with critical thermal management requirements. In view of recent reports
alluding to anisotropic thermal conductivity in this face-centered cubic
crystalline systems, we perform a detailed analysis of the impact of
direction-dependent phonon group velocities and lifetimes on the thermal
transport of fluorite oxides. We demonstrate that the bulk thermal conductivity
of this class of materials remains isotropic despite notable anisotropy in
phonon lifetime and group velocity. However, breaking the symmetry of the
phonon lifetime under external stimuli including boundary scattering present in
nonequilibrium molecular dynamics simulations of finite size simulation cell
gives rise to apparent thermal conductivity anisotropy. We observe that for
accurate determination of thermal conductivity, it is important to consider
phonon properties not only along high symmetry directions commonly measured in
inelastic neutron or x-ray scattering experiments but also of those along lower
symmetry. Our results suggests that certain low symmetry directions have a
larger contribution to thermal conductivity compared to high symmetry ones.",2203.09923v2
2022-03-29,Continuous ferromagnetic quantum phase transition on an anisotropic Kondo lattice,"Motivated by the recent discovery of ferromagnetic quantum criticality in the
heavy fermion compound CeRh$_6$Ge$_4$, we develop a numerical algorithm of
infinite projected entangled pair states for the anisotropic ferromagnetic
Kondo-Heisenberg model in two dimensions and study the ferromagnetic quantum
phase transitions with varying magnetic and hopping anisotropy. Our
calculations reveal a continuous ferromagnetic quantum phase transition in the
large anisotropic region and first-order quantum phase transitions for smaller
anisotropy. Our results highlight the importance of magnetic anisotropy on
ferromagnetic quantum criticality in Kondo lattice systems and provide a
possible explanation for the experimental observation in CeRh$_6$Ge$_4$ with a
quasi-one-dimensional magnetic structure. Our work opens the avenue for future
studies of the rich Kondo lattice physics using state-of-the-art tensor network
approaches.",2203.15475v2
2022-03-30,Origin of Perpendicular Magnetic Anisotropy in Co$_x$Fe$_{3-x}$O$_{4+δ}$ Thin Films Studied by X-ray Magnetic Circular and Linear Dichroisms,"We investigate the element-specific spin and orbital states and their roles
on magnetic anisotropy in the Co-ferrite (Co$_x$Fe$_{3-x}$O$_{4+\delta}$ (001))
thin films which exhibit perpendicular magnetic anisotropy (PMA). The origin of
PMA in the low $x$ region ($x$ $<$ 1) can be mainly explained by the large
perpendicular orbital magnetic moments in the Co$^{2+}$ (3$d^7$) states
detected by X-ray magnetic circular and linear dichroisms (XMCD/XMLD). The XMLD
for a PMA film ($x=0.2$) with square hysteresis curve shows the oblate charge
distribution in the Co$^{2+}$ site, which is consistent with the change in
local nearest neighbor distance in Co detected by extended X-ray absorption
fine structure analysis. Our finding reveals that the microscopic origin of PMA
in Co-ferrite comes from the enhanced orbital magnetic moments along
out-of-plane [001] direction through in-plane charge distribution by tensile
strain, which adds the material functionalities in spinel ferrite thin films
from the viewpoint of strain and orbital magnetic moments.",2203.16061v1
2022-04-07,High-throughput computational discovery of 40 ultralow thermal conductivity and 20 highly anisotropic crystalline materials,"We performed ab-initio driven density functional theory-based high throughput
computations to search for materials with low thermal conductivity and high
thermal transport anisotropy. We shortlisted a pool of 429 stable ternary
semiconductors from the Materials Project and obtained phonon thermal
conductivity by solving the Boltzmann transport equation on 225 materials. We
found the lowest thermal conductivity of 0.16 W/m-K in SbRbK 2 and 40 materials
with a thermal conductivity lower than 1 W/m-K at 300 K. For anisotropic
thermal transport, we have identified six materials with anisotropy larger than
5 and 20 with thermal transport anisotropy higher than the largest reported
literature value.",2204.03628v2
2022-04-09,Learning hyperelastic anisotropy from data via a tensor basis neural network,"Anisotropy in the mechanical response of materials with microstructure is
common and yet is difficult to assess and model. To construct accurate response
models given only stress-strain data, we employ classical representation
theory, novel neural network layers, and L1 regularization. The proposed
tensor-basis neural network can discover both the type and orientation of the
anisotropy and provide an accurate model of the stress response. The method is
demonstrated with data from hyperelastic materials with off-axis transverse
isotropy and orthotropy, as well as materials with less well-defined symmetries
induced by fibers or spherical inclusions. Both plain feed-forward neural
networks and input-convex neural network formulations are developed and tested.
Using the latter, a polyconvex potential can be established, which, by
satisfying the growth condition can guarantee the existence of boundary value
problem solutions.",2204.04529v1
2022-04-11,Aharonov-Bohm oscillations in phosphorene quantum rings: mass anisotropy compensation by confinement potential,"We consider the Aharonov-Bohm (AB) effect on a confined electron ground state
in a quantum ring defined electrostatically within the phosphorene monolayer.
The strong anisotropy of effective masses in phosphorene quenches ground-state
oscillations for a circular ring because of interrupted persistent current
circulation around the ring. An elliptic deformation of the confinement
potential can compensate for the anisotropy of the effective masses and produce
ground-state parity transformations with the AB periodicity. Moreover, a
specific ratio of the semiaxes is determined for which the spectrum becomes
identical to that of a circular quantum ring and an isotropic effective mass.
We identify a generalized angular momentum operator which commutes with the
continuum Hamiltonian for the chosen ratio of the semi-axes that closes the
avoided crossings of energy levels for states of the same parity and spin.
Ground-state oscillations for the two-electron ground state are also discussed.",2204.05364v1
2022-05-03,"Carrier Doping Modulates 2D Intrinsic Ferromagnetic Mn2Ge2Te6 Monolayer High Curie Temperature, Large Magnetic Crystal Anisotropy","The Mn2Ge2Te6 shows intrinsic ferromagnetic (FM) order, with Curie
temperature (Tc) of 316 K. The FM order origins from superexchange interaction
between Mn and Te atoms. Mn2Ge2Te6 is half-metal (HM), and spin-\b{eta}
electron is a semiconductor with gap of 1.462 eV. Mn2Ge2Te6 tends in-plane
anisotropy (IPA), with magnetic anisotropy energy (MAE) of -13.2 meV/f.u.. The
Mn2Ge2Te6 shows good dynamical and thermal stability. Moreover, Mn2Ge2Te6
presents good ferromagnetic and half-metallic stability under charge doping.
The carriers doping could effectively tune magnetic and electronic properties.
Specifically, the magnetic moment, exchange parameter, and MAE could be
efficiently tuned. The total magnetic moment changes linearly with charges
doping. The exchange parameters could be controlled by the doping carriers. The
carriers doping could modulate MAE to -18.4 (+0.4 e), -0.85 (-1.6 e), 1.31
(-2.4 e) meV/f.u., by changing hybridization between Te atoms' py and pz
orbitals. Mn2Ge2Te6 with intrinsic ferromagnetism, high tunable MAE, good
stability of ferromagnetism and half-metallicity could help researchers to
investigate its wide application in the electronics and spintronics.",2205.01498v1
2022-05-18,Rectangular and square skyrmion crystals on a centrosymmetric square lattice with easy-axis anisotropy,"We report our theoretical results on the emergence of rectangular- and
square-shaped magnetic skyrmion crystals on a centrosymmetric square lattice
with magnetic anisotropy. By performing the simulated annealing for a
frustrated spin model with an easy-axis single-ion anisotropy on a square
lattice, we find that a competition of the interactions in momentum space gives
rise to the formation of two skyrmion crystals, where the skyrmion cores are
aligned in a rectangle- or square-lattice way. Especially, the interactions at
the higher harmonic wave vectors play an important role in stabilizing the
square/rectangular skyrmion crystals. Our results provide a reference to
explore further skyrmion-hosting materials in centrosymmetric tetragonal
systems.",2205.09236v1
2022-05-27,Fourfold anisotropic magnetoresistance of L1$_0$ FePt due to relaxation time anisotropy,"Experimental measurements show that the angular dependence of the anisotropic
magnetoresistance (AMR) in L1$_0$ ordered FePt epitaxial films on the current
orientation and magnetization direction is a superposition of the corresponding
dependences of twofold and fourfold symmetries. The twofold AMR exhibits a
strong dependence on the current orientation, whereas the fourfold term only
depends on the magnetization direction in the crystal and is independent of the
current orientation. First-principles calculations reveal that the fourfold AMR
arises from the relaxation time anisotropy due to the variation of the density
of states near the Fermi energy under rotation of the magnetization. This
relaxation time anisotropy is a universal property in ferromagnetic metals and
determines other anisotropic physical properties that are observable in
experiment.",2205.13767v1
2022-05-31,Anisotropy driven response of skyrmion lattice in MnSc$_2$S$_4$ to applied magnetic fields,"We theoretically and experimentally study the stability of the unconventional
fractional antiferromagnetic skyrmion lattice (AF-SkL) in Mn$_2$S$_4$ spinel
under magnetic fields applied along the $[$1-10$]$ crystal direction. By
performing numerical Monte Carlo simulations for the minimal effective spin
model that we proposed in Ref. [S. Gao, et al., Nature 586, 37-41 (2020)], we
show that the skyrmion lattice is aligned within the equivalent and symmetric
$[$1-11$]$ or $[$1-11$]$ planes, which are equally inclined to the applied
magnetic field. We attribute this behavior to the magnetic anisotropy of the
host material. Neutron single crystal diffraction presents a very good
agreement with the predictions of the effective model. It reveals that the
topological spin texture gets destabilized at low temperatures and moderate
magnetic fields and is replaced by a conical phase for B// $[$1-10$]$. The
present study elucidates the central role of the magnetic anisotropy in the
stabilization of antiferromagnetic skyrmionic states.",2205.15787v1
2022-07-02,Scaling Relations and Topological Quadruple Points in Light-matter Interactions with Anisotropy and Nonlinear Stark Coupling,"Universality is a common quality in different physical parameters that is
rooted in the deep nature of physical systems. Scaling relation is a typical
universality for critical phenomena around a quantum phase transition, while
topological classification provides another type of universality essentially
different from the critical universality. Both classes of universalities can be
present in a single-qubit system with light-matter interactions, as exhibiting
generally in the fundamental quantum Rabi model with anisotropy not only for
linear coupling but also for nonlinear Stark coupling (NSC). In low frequencies
different levels of scaling relations are demonstrated, holding for anisotropic
or/and NSCs, locally or globally. At finite frequencies such a critical
universality breaks down and diversity is dominant. However, common topological
feature of the ground state can be extracted from the node number, which yields
a topological class of universality amidst the critical diversity. Both
conventional and unconventional topological transitions emerge, with their
meeting, which never occurs in linear interaction, enabled by the nonlinear
coupling to form topological quadruple points which are found to be
spin-invariant points. Sensitivity analysis indicates that the NSC can be
another approach to manipulate topological transitions in addition to coupling
anisotropy.",2207.00904v1
2022-07-19,Spatially flat universes with isotropic tidal forces,"We investigate the dynamics of the spatially flat universes submitted to
isotropic tidal forces and adiabatic expansion under Einstein's equations.
Surprisingly, the tendency to a high Hubble anisotropy at late times starts to
appear as far as we assume the strong energy condition, a characteristic which
becomes dominant in the radiation era and even more stringent under a stiff
matter regime. We introduce the parameter b which measures the relative change
in the magnitudes of the Hubble anisotropy and the scale factor and use it to
show that the anisotropies must be kept small as long as we assume the Universe
has passed through an inflationary period, in accordance with the cosmic
no-hair theorem. Hence, we have a class of models that shows us a simple and
straightforward way the instability of the FLRW universes, the furtiveness of
the isotropy concept, and how they can still be consistent with the standard
model of Cosmology as far as we assume the occurrence of an inflationary early
period.",2207.09279v1
2022-08-11,Magneto-anisotropic weak antilocalization in near-surface quantum wells,"We investigate the effects of an in-plane magnetic field on the weak
antilocalization signature of near-surface quantum wells lacking bulk and
inversion symmetry. The measured magnetoconductivity exhibits a strong
anisotropy with respect to the direction of the in-plane magnetic field. The
two-fold symmetry of the observed magneto-anisotropy originates from the
competition between Rashba and Dresselhaus spin-orbit couplings. The high
sensitivity of the weak antilocalization to the spin texture produced by the
combined Zeeman and spin-orbit fields results in very large anisotropy ratios,
reaching 100%. Using a semiclassical universal model in quantitative agreement
with the experimental data, we uniquely determine the values of the Dresselhaus
and Rashba parameters as well as the effective in-plane g-factor of the
electrons. Understanding these parameters provides new prospects for novel
applications ranging from spintronics to topological quantum computing.",2208.06050v3
2022-08-21,Origin of anisotropic diffusion in Turing Patterns,"In this paper, we numerically study Turing patterns by the Finsler geometry
(FG) modeling technique on thermally fluctuating triangular lattices, which are
often used for modeling cell membranes or lipid membranes, focusing on the
origin of diffusion anisotropy. The FG modeling prescription allows us to
assume direction-dependent diffusion described by Laplacian. To implement such
diffusion anisotropy in the FG modeling, we need an internal degree of freedom
(IDF), which depends on direction and position and is controlled by some
external forces or stimuli. For such a direction-dependent IDF, we use velocity
directions corresponding to thermal fluctuations of the lattice vertices. We
find that anisotropic Turing patterns emerge in the direction along which
vertices fluctuate. In the simulations, direction-dependent diffusion
coefficients are unnecessary for input, and instead, the IDF aligns the
direction of vertex fluctuation along a direction implemented by external
stimuli. Our results and techniques provide insight into the origin of
diffusion anisotropy connected to Turing patterns.",2208.09977v1
2022-08-22,Gauge Theory Couplings on Anisotropic Lattices,"The advantage of simulating lattice field theory with quantum computers is
hamstrung by the limited resources that induce large errors from finite volume
and sizable lattice spacings. Previous work has shown how classical simulations
near the Hamiltonian limit can be used for setting the lattice spacings in
real-time through analytical continuation, thereby reducing errors in quantum
simulations. In this work, we derive perturbative relations between bare and
renormalized quantities in Euclidean spacetime at any anisotropy factor -- the
ratio of spatial to temporal lattice spacings -- and in any spatial dimension
for $U(N)$ and $SU(N)$. This reduces the required classical preprocessing for
quantum simulations. We find less than $10\%$ discrepancy between our
perturbative results and those from existing nonperturbative determinations of
the anisotropy for $SU(2)$ and $U(1)$ gauge theories. For the discrete groups
$\mathbb{Z}_{10}$, $\mathbb{Z}_{100}$ and $\mathbb{BI}$, we perform lattice
Monte Carlo simulations to extract anisotropy factors and observe similar
agreement with our perturbative results.",2208.10417v1
2022-08-23,Translational Symmetry Broken Magnetization Plateau of the $S=2$ Antiferromagnetic Chain with Anisotropies,"The magnetization plateau of the $S=2$ antiferromagnetic chain with
interaction and single-ion anisotropies is investigated using the numerical
diagonalization of finite-size clusters and some size scaling analyses. The
previous level spectroscopy analysis indicated that two different magnetization
plateau phases appear at half of the saturation magnetization. One is due to
the large-$D$ mechanism and the other is due to the Haldane one. In the present
study the phase diagram is extended to wider region of the anisotropies. As a
result we find another half magnetization plateau phase, where the
translational symmetry is spontaneously broken .",2208.10983v1
2022-09-01,"Uniaxial strain, topological band singularities and pairing symmetry changes in superconductors","Uniaxial strain affects pairing symmetry states in superconductors by
changing the lattice symmetry, and by altering Fermi surface topology. Here, we
present a systematic study of these effects within a one-band negative-U
Hubbard model for s, p and d-wave pairing states. We consider a general 2D
model that can be applied to superconductors under uniaxial strain, modelled
via hopping anisotropy, on a square lattice. The results presented here model
an in plane compression along the x-axis, which reduces the lattice symmetry
from a tetragonal to an orthorhombic crystal space group. The effects of
hopping anisotropy on the different types of gap pairings are explored. We show
that changes in Tc are tunable with hopping anisotropy and depend on the
orientation of the gap function in relation to the opening of the Fermi surface
during the Lifshitz transition. In comparing the model results to experimental
data for the case of Sr2RuO4 it is found that both the d + id and d + ig
pairings best describe the changes in Tc for the superconducting state in
regards to its response to small uniaxial strain.",2209.00300v1
2022-09-13,Anisotropic warm inflation,"Anisotropic inflation is a model succeeded in explaining statistical
anisotropy. Warm inflation is a model succeeded in providing a mechanism of
reheating during inflation. We study anisotropic warm inflation focusing on the
cosmic no-hair conjecture. In the anisotropic warm inflation, the condition for
making anisotropy survived is clarified. By assuming a constant value for the
dissipation ratio, we find exact solutions of power-law anisotropic warm
inflation, and investigate the phase space structure of general solutions. It
turns out that whether the anisotropy during inflation survives or not depends
on the competition of the potential that drive anisotropic inflation against
dissipation of an inflaton field. Anisotropic warm inflation will be realized
if the decaying process is not efficient.",2209.05776v2
2022-09-17,Temperature-driven changes in the Fermi surface of graphite,"We report on temperature-dependent size and anisotropy of the Fermi pockets
in graphite revealed by magnetotransport measurements. The magnetoresistances
obtained in fields along the c-axis obey an extended Kohler's rule, with the
carrier density following prediction of a temperature-dependent Fermi energy,
indicating a change in the Fermi pocket size with temperature. The
angle-dependent magnetoresistivities at a given temperature exhibit a scaling
behavior. The scaling factor that reflects the anisotropy of the Fermi surface
is also found to vary with temperature. Our results demonstrate that
temperature-driven changes in Fermi surface can be ubiquitous and need to be
considered in understanding the temperature-dependent carrier density and
magnetoresistance anisotropy in semimetals.",2209.08406v1
2022-09-20,Elastic anisotropy of lizardite at subduction zone conditions,"Subduction zones transport water into Earth's deep interior through slab
subduction. Serpentine minerals, the primary hydration product of ultramafic
peridotite, are abundant in most subduction zones. Characterization of their
high-temperature elasticity, particularly their anisotropy, will help us better
estimate the extent of mantle serpentinization and the Earth's deep water
cycle. Lizardite, the low-temperature polymorph of serpentine, is stable under
the P-T conditions of cold subduction slabs (< 260{\deg}C at 2 GPa), and its
high-temperature elasticity remains unknown. Here we report ab initio
elasticity and acoustic wave velocities of lizardite at P-T conditions of
subduction zones. Our static results agree with previous studies. Its
high-temperature velocities are much higher than previous experimental-based
lizardite estimates with chrysotile but closer to antigorite velocities. The
elastic anisotropy of lizardite is much larger than that of antigorite and
could better account for the observed large shear-wave splitting in some cold
slabs such as Tonga.",2209.09783v1
2022-09-22,Spin wave study of magnetic perpendicular surface anisotropy in single crystalline MgO$\text{/}$Fe$\text{/}$MgO films,"Broadband ferromagnetic resonance is measured in single crystalline Fe films
of varying thickness sandwiched between MgO layers. An exhaustive magnetic
characterization of the films (exchange constant, cubic, uniaxial and surface
anisotropies) is enabled by the study of the uniform and the first
perpendicular standing spin wave modes as a function of applied magnetic field
and film thickness. Additional measurements of non-reciprocal spin wave
propagation allow us to separate each of the two interface contributions to the
total surface anisotropy. The results are consistent with the model of a
quasi-bulk film interior and two magnetically different top and bottom
interfaces, a difference ascribed to different oxidation states.",2209.10906v2
2022-09-28,"One $μ$ to rule them all: CMB spectral distortions can probe domain walls, cosmic strings and low scale phase transitions","We present a new probe of purely gravitationally coupled sectors with large
anisotropies. These anisotropies are damped via gravitational interactions with
the baryon-photon fluid, which is heated up in the process. The injected heat
causes measurable distortions of the cosmic microwave background spectrum. We
give analytic estimates for the size of the distortions and outline how to
calculate them from first principles. These methods are applied to anisotropies
in the form of a domain wall/cosmic string network or caused by a first order
phase transition or scalar field dynamics. We find that this method can
potentially probe large regions of previously unconstrained parameter space and
is very much complementary to up-coming searches of gravitational waves caused
by such dark sectors.",2209.14313v2
2022-10-16,Phase transitions in 3-dimensional Dirac semi-metals using Schwinger-Dyson equations,"We study the semi-metal/insulator quantum phase transition in
three-dimensional Dirac semi-metals by solving a set of Schwinger-Dyson
equations. We study the effect of an anisotropic fermion velocity on the
critical coupling of the transition. We consider the influence of several
different approximations that are commonly used in the literature and show that
results for the critical coupling change considerably when some of these
approximations are relaxed. Most importantly, the nature of the dependence of
the critical coupling on the anisotropy depends strongly on the approximations
that are used for the photon polarization tensor. On the one hand, this means
that calculations that include full photon dynamics are necessary to answer
even the basic question of whether the critical coupling increases or decreases
with anisotropy. On the other hand, our results mean that it is possible that
anisotropy could provide a mechanism to promote dynamical gap generation in
realistic three-dimensional Dirac semi-metallic materials.",2210.08563v2
2022-10-21,Anisotropy and crystallite misalignment in textured superconductors,"A misalignment of anisotropic crystallites causes small values of anisotropy
and decreases the critical current density of textured polycrystalline
superconductors. To relate the crystallite misalignment and out-plane
anisotropy, the magnetic properties of the textured Bi2223 polycrystalline
superconductor were investigated. A distribution of orientation angles of
crystallites was determined using different data: scanning electron microscopy
images and hysteresis magnetization loops when an external magnetic field was
applied at different angles with respect to the texturing plane of the sample.
It was demonstrated that the standard deviation of the distribution and the
magnetic disorder angle of crystallites in textured samples can be determined
from the magnetization data in perpendicular directions. These data may be
either the irreversible magnetization measured for two different orientations
of the sample or the simultaneously measured magnetization projections parallel
and perpendicular to the magnetic field.",2210.11712v1
2022-10-30,"Interplay of symmetry-conserved tunneling, interfacial oxidation and perpendicular magnetic anisotropy in CoFeB/MgO-based junctions","The interfacial oxidation level and thermodynamic properties of the MgO-based
perpendicular magnetic tunneling junctions are investigated. The
symmetry-conserved tunneling effect depends sensitively on the MgO adatom
energy during the RF sputtering, as well as the thermal stability of the
structure during the post-growth thermal annealing. Two different failure modes
of the magnetoresistance are highlighted, involving with the decay of
perpendicular magnetic anisotropy and destruction of coherent tunneling
channels, respectively. Through the careful control of interfacial oxidation
level and proper selection of the heavy metal layers, both perpendicular
magnetic anisotropy and tunneling magnetoresistance of the junctions can be
increased.",2210.16734v1
2022-11-04,In-plane anisotropy of electrical transport in Y$_{0.85}$Tb$_{0.15}$Ba$_2$Cu$_3$O$_{7-x}$ films,"We fabricate high-quality c-axis oriented epitaxial YBa$_2$Cu$_3$O$_{7-x}$
films with 15% of yttrium atoms replaced by terbium (YTBCO) and study their
electrical properties. The Tb substitution reduces the charge carrier density
resulting in increased resistivity and decreased critical current density
compared to the pure YBa$_2$Cu$_3$O$_{7-x}$ films. The electrical properties of
the YTBCO films show an in-plane anisotropy in both the superconducting and
normal state providing evidence for the twin-free film. Unexpectedly, the
resistive transition of the bridges also demonstrates the in-plane anisotropy
that can be explained within the framework of Tinkham's model of the resistive
transition and the Berezinskii-Kosterlitz-Thouless (BKT) model depending on the
sample parameters. We consider YTBCO films to be a promising platform for both
the fundamental research on the BKT transition in the cuprate superconductors
and for the fabrication of devices with high kinetic inductance.",2211.02564v2
2022-11-15,A Tilt Instability in the Cosmological Principle,"We show that the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) framework has
an instability towards the growth of fluid flow anisotropies, even if the
Universe is accelerating. This flow (tilt) instability in the matter sector is
invisible to Cosmic No-Hair Theorem-like arguments, which typically only flag
shear anisotropies in the metric. We illustrate our claims in the setting of
``dipole cosmology'', the maximally Copernican generalization of FLRW that can
accommodate a flow. Simple models are sufficient to show that the cosmic flow
need not track the shear, even in the presence of a positive cosmological
constant. We also emphasize that the growth of the tilt hair is fairly generic
if the total equation of state $w(t) \rightarrow -1$ at late times (as it does
in standard cosmology), irrespective of the precise model of dark energy. The
generality of our theoretical result puts various recent observational claims
about late time anisotropies and cosmic dipoles in a new light.",2211.08093v2
2022-11-17,Large Primordial Fluctuations in Gravitational Waves from Phase Transitions,"It is well-known that first order phase transitions in the early universe can
be a powerful source of observable stochastic gravitational wave backgrounds.
Any such gravitational wave background must exhibit large-scale anisotropies at
least as large as those seen in the CMB $\sim 10^{-5}$, providing a valuable
new window onto the (inflationary) origins of primordial fluctuations. While
significantly larger fractional anisotropies are possible (for example, in
multi-field inflation) and would be easier to interpret, it has been argued
that these can only be consistent with CMB bounds if the gravitational wave
signal is correspondingly smaller. In this paper, we show that this argument,
which relies on assuming radiation dominance of the very early universe, can be
evaded if there is an era of early matter dominance of a certain robust type.
This allows large gravitational wave anisotropies to be consistent with
observable signals at proposed future gravitational wave detectors. Constraints
from the CMB on large scales, as well as primordial black hole and mini-cluster
formation on small scales, and secondary scalar-induced gravitational waves are
all taken into account.",2211.09301v1
2022-11-21,Magnetocaloric effect at the reorientation of the magnetization in ferromagnetic multilayers with perpendicular anisotropy,"We investigate the magnetocaloric effect obtained by the rotation of a
magnetic field applied to an exchange-coupled multilayer system composed of two
different ferromagnetic (FM) materials. We specifically consider a system in
which the two FMs have perpendicular uniaxial anisotropy axes and utilise
conditions which yield a reorientation of the total magnetization when
compensation between the anisotropies of the two layers occurs. We calculate
the consequent entropy change associated with the ""artificial"" reorientation.
By using known parameters from MnBi and Co we predict an entropy change of
$\Delta s = 0.34$ Jkg$^{-1}$K$^{-1}$ for perfect coupling. Lastly, we study the
behavior of the multilayer under a rotating magnetic field via a micromagnetic
model. When the layer thicknesses are of the order of the local domain wall
width, the magnetic field-induced entropy change can be obtained with magnetic
fields one order of magnitude lower than in the uncoupled case.",2211.11146v3
2022-11-21,Ferromagnetic frozen structures from the dipolar hard spheres fluid at moderate and small volume fractions,"We study the magnetic phase diagram of an ensemble of dipolar hard spheres
(DHS) with or without uniaxial anisotropy and frozen in position on a
disordered structure by tempered Monte Carlo simulations. The crucial point is
to consider an anisotropic structure, obtained from the liquid state of the
dipolar hard spheres fluid, frozen in its polarized state at low temperature.
The freezing inverse temperature $\beta_f$ determines the degree of anisotropy
of the structure which is quantified through a structural nematic order
parameter, $\lambda_s$. The case of the non zero uniaxial anisotropy is
considered only in its infinitely strong strength limit where the system
transforms in a dipolar Ising model (DIM). The important finding of this work
is that both the DHS and the DIM with a frozen structure build in this way
present a ferromagnetic phase at volume fractions below the threshold value
where the corresponding isotropic DHS systems exhibit a spin glass phase at low
temperature.",2211.11268v4
2022-11-29,Mechano-lithography: stress anisotropy driven nematic order in growing three-dimensional bacterial biofilms,"Living active collectives have evolved with remarkable self-patterning
ability to meet the physical and biological constraints for growth and
survival. However, how complex multicellular patterns emerge from a single
founder cell remains elusive. Here, by recourse to an agent-based model, we
track the three-dimensional (3D) morphodynamics and cell orientational order of
growing bacterial biofilms encased by agarose gels. Confined growth causes
spatiotemporally heterogeneous stress buildup in the biofilm. High hydrostatic
and low shear stresses at the core of the biofilm promote viscous-to-elastic
transition and randomize cell packing, whereas the opposite stress state near
the gel-cell interface drives nematic ordering with a time delay inherent to
shear stress relaxation. Overall, stress anisotropy spatiotemporally coincides
with nematic order in the confined biofilms, suggesting an
anisotropic-stress-driven ordering mechanism. The strong reciprocity between
stress anisotropy and cell ordering inspires innovative 3D mechano-lithography
of living active collectives for a variety of environmental and biomedical
applications.",2211.16354v1
2022-11-30,Supercurrent-induced Anomalous Thermal Hall Effect as a New Probe to Superconducting Gap Anisotropy,"Two-dimensional superconductors have been realized in various atomically thin
films such as the twisted bilayer graphene, some of which are anticipated to
involve unconventional pairing mechanism. Due to their low dimensionality,
experimental probes of the exact nature of superconductivity in these systems
have been limited. We propose, by applying a \emph{vertical} supercurrent to a
bilayer superconductor where the mirror symmetry is naturally broken by the
twisting, there will be anomalous thermal Hall effect induced by the
supercurrent that can serve as a sharp probe for the \emph{in-plane} anisotropy
of the superconducting gap function. This effect occurs in the \emph{absence}
of an external magnetic field and spontaneous breaking of the time-reversal
symmetry in the ground state. We derive explicit formulas for the induced
thermal Hall conductivity and show them to be significant in the examples of
twisted cuprates and twisted FeSe where monolayer superconductivity have
already been observed. Though technical challenges still exist, we propose this
to be a generic probe of the gap anisotropy in a twisted bilayer
superconductor.",2211.16651v2
2022-12-02,Anisotropic Van der Waals 2D GeAs Integrated on Silicon Four-Waveguide Crossing,"In-plane optical anisotropy plays a critical role in manipulating light in a
wide range of planner photonic devices. In this study, the strong anisotropy of
multilayer 2D GeAs is leveraged and utilized to validate the technical
feasibility of on-chip light management. A 2D GeAs is stamped into an
ultra-compact silicon waveguide four-way crossing optimized for operation in
the O-optical band. The measured optical transmission spectra indicated a
remarkable discrepancy between the in-plane crystal optical axes with an
attenuation ratio of ~ 3.5 (at 1330 nm). Additionally, the effect of GeAs
crystal orientation on the electro-optic transmission performance is
demonstrated on a straight waveguide. A notable 50 % reduction in responsivity
was recorded for devices constructed with cross direction compared to devices
with a crystal a-direction parallel to the light polarization. This
extraordinary optical anisotropy, combined with a high refractive index ~ 4 of
2D GeAs, opens possibilities for efficient on-chip light manipulation in
photonic devices.",2212.01154v1
2022-12-06,Spatially Homogeneous Universes with Late-Time Anisotropy,"The cosmological principle asserts that on sufficiently large scales the
Universe is homogeneous and isotropic on spatial slices. To deviate from this
principle requires a departure from the FLRW ansatz. In this paper we analyze
the cosmological evolution of two spatially homogeneous but anisotropic
universes, namely the spatially closed Kantowski-Sachs Universe and the open
axisymmetric Bianchi type III Universe. These models are characterized by two
scale factors and we study their evolution in universes with radiation, matter
and a cosmological constant. In all cases, the two scale factors evolve
differently and this anisotropy leads to a lensing effect in the propagation of
light. We derive explicit formulae for computing redshifts, angular diameter
distances and luminosity distances and discuss the predictions of these models
in relation to observations for type Ia supernovae and the CMB. We comment on
the possibility of explaining the observed luminosity distance plot for type Ia
supernovae within the context of cosmologies featuring late-time anisotropy and
a vanishing cosmological constant.",2212.03234v3
2023-01-16,Probing the Blue Axion with Cosmic Optical Background Anisotropies,"A radiative decaying Big Bang relic with a mass $m_a\simeq 5-25 \,\rm eV$,
which we dub ""blue axion"", can be probed with direct and indirect observations
of the cosmic optical background (COB). The strongest bounds on blue-axion cold
dark matter come from the Hubble Space Telescope (HST) measurements of COB
anisotropies at $606$~nm. We suggest that new HST measurements at higher
frequencies ($336$~nm and $438$~nm) can improve current constraints on the
lifetime up to one order of magnitude, and we show that also thermally produced
and hot relic blue axions can be competitively probed by COB anisotropies. We
exclude the simple interpretation of the excess in the diffuse COB detected by
the Long Range Reconnaissance Imager (LORRI) as photons produced by a decaying
hot relic. Finally, we comment on the reach of upcoming line intensity mapping
experiments, that could detect blue axions with a lifetime as large as
$10^{29}\,\rm s$ or $10^{27}\,\rm s$ for the cold dark matter and the hot relic
case, respectively.",2301.06560v2
2023-01-17,"Observation of field-induced single-ion magnetic anisotropy in a multiorbital Kondo alloy $\mathrm{(Lu,Yb)}\mathrm{Rh}_{2}\mathrm{Zn}_{20}$","We demonstrate field-induced single-ion magnetic anisotropy resulting from
the multiorbital Kondo effect on the diluted ytterbium alloy
$(\mathrm{Lu}_{1-x}\mathrm{Yb}_x)\mathrm{Rh}_2\mathrm{Zn}_{20}$. Single-ion
anisotropic metamagnetic behavior is revealed in low-temperature regions where
the local Fermi-liquid state is formed. Specific hea, low-field magnetic
susceptibility, and resistivity indicate reproduction of the ground-state
properties by the $\mathrm{SU}(N = 8)$ Kondo model with a relatively large
$c$-$f$ hybridization of $T_{\mathrm{K}} = 60.9 \ \mathrm{K}$. Dynamical
susceptibility measurements on $\mathrm{Yb}\mathrm{Rh}_2\mathrm{Zn}_{20}$
support realizing the multiorbital Kondo ground state in
$(\mathrm{Lu}_{1-x}\mathrm{Yb}_x)\mathrm{Rh}_2\mathrm{Zn}_{20}$. The single-ion
magnetic anisotropy becomes evident above $\sim5 \ \mathrm{T}$, which is lower
than the isotropic Kondo crossover field of 22.7 T, verifying blurred low-lying
crystal field states through the multiorbital Kondo effect.",2301.07038v3
2023-01-31,Validating dark energy models using polarised Sunyaev-Zel'dovich effect with large-angle CMB temperature and E-mode polarization anisotropies,"The tomography of the polarized Sunyaev-Zeldvich effect due to free electrons
of galaxy clusters can be used to constrain the nature of dark energy because
CMB quadrupoles at different redshifts as the polarization source are sensitive
to the integrated Sachs-Wolfe effect. Here we show that the low multipoles of
the temperature and E-mode polarization anisotropies from the all-sky CMB can
improve the constraint further through the correlation between them and the CMB
quadrupoles viewed from the galaxy clusters. Using a Monte-Carlo simulation, we
find that low multipoles of the temperature and E-mode polarization
anisotropies potentially improve the constraint on the equation of state of
dark energy parameter by $\sim 17$ percent.",2301.13676v1
2023-02-08,Scanning Reflectance Anisotropy Microscopy for Multi-Material Strain Mapping,"Strain-engineering of materials encompasses significant elastic deformation
and leads to breaking of the lattice symmetry and as a consequence to the
emergence of optical anisotropy. However, the capability to image and map local
strain fields by optical microscopy is currently limited to specific materials.
Here, we introduce a broadband scanning reflectance anisotropy microscope as a
phase-sensitive multi-material optical platform for strain mapping. The
microscope produces hyperspectral images with diffraction-limited sub-micron
resolution of the near-normal incidence ellipsometric response of the sample,
which is related to elastic strain by means of the elasto-optic effect. We
demonstrate cutting edge strain sensitivity using a variety of materials, such
as metasurfaces, semiconductors and metals. The versatility of the method to
study the breaking of the lattice symmetry by simple reflectance measurements
opens up the possibility to carry out non-destructive mechanical
characterization of multi-material components, such as wearable electronics and
optical semiconductor devices.",2302.04095v2
2023-02-11,Modelling the emergence of cosmic anisotropy from non-linear structures,"Astronomical observations suggest that the Universe may be anisotropic on the
largest scales. In order to model this situation, we develop a new approach to
cosmology that allows for large-scale anisotropy to emerge from the growth of
non-linear structure. This is achieved by decomposing all relevant fields with
respect to a preferred space-like direction, and then averaging the resulting
scalar quantities over spatial domains. Our approach allows us to derive a set
of large-scale effective field equations that govern the dynamics of any
emergent large-scale anisotropy, and which (up to back-reaction terms) take the
form of the field equations of the locally rotationally symmetric Bianchi
cosmologies. We apply our approach to the dust-filled Farnsworth solutions,
which are an interesting set of exact cosmological models that allow for both
anisotropic expansion and large-scale bulk flow.",2302.05715v2
2023-03-06,An upscaling based three parameter elastic anisotropy model,"Rock formations often exhibit transversely anisotropic elastic behavior due
to their layered structure. Such materials are characterized by five
independent elastic constants. In the context of petroleum applications, it is
often challenging to accurately measure all these elastic parameters. At the
same time, the effect of elastic anisotropy can be noticeable and therefore
there is a need to include it in some form. To fill the gap, this study
proposes a three parameter elastic anisotropy model. It captures the dominant
anisotropic behavior and yet has only three elastic constants that are
relatively easy to measure in laboratory. The approach is based on upscaling of
a periodically layered material characterized by equal height layers with
different Young's moduli and the same Poisson's ratio. The resultant upscaled
material is transversely isotropic and is also physically admissible. The
developed approach allows to effectively reconstruct or estimate the values of
the two remaining parameters needed for the transversely isotropic model.
Comparison between the reconstructed results and the measured values are
compared for several rock types.",2303.03236v1
2023-03-07,Jet polarisation in an anisotropic medium,"We study the evolution of an energetic jet which propagates in an anisotropic
quark-gluon plasma, as created in the intermediate stages of ultrarelativistic
heavy-ion collisions. We argue that the partons of the jet should acquire a
non-zero average polarisation proportional to the medium anisotropy. We first
observe that the medium anisotropy introduces a difference between the rates
for transverse momentum broadening along the two directions perpendicular to
the jet axis. In turn, this difference leads to a polarisation-dependent bias
in the BDMPS-Z rates for medium-induced gluon branching. Accordingly, the
daughter gluons in a branching process can carry net polarisation even if their
parent gluon was unpolarised. Using these splitting rates, we construct kinetic
equations which describe the production and transmission of polarisation via
multiple branching in an anisotropic medium. The solutions to these equations
show that polarisation is efficiently produced via quasi-democratic branchings,
but then it is rapidly washed out by the subsequent branchings, due to the
inability of soft gluons to keep trace of the polarisation of their parents.
Based on that, we conclude that a net polarisation for the jet should survive
in the final state if and only if the medium anisotropy is sizeable as the jet
escapes the medium.",2303.03914v1
2023-04-01,Itinerant ferromagnetism entrenched by the anisotropy of spin-orbit coupling in a dipolar Fermi gas,"We investigate the the itinerant ferromagnetism in a dipolar Fermi atomic
system with the anisotropic spin-orbit coupling (SOC),which is traditionally
explored with isotropic contact interaction.We first study the ferromagnetism
transition boundaries and the properties of the ground states through the
density and spin-flip distribution in momentum space, and we find that both the
anisotropy and the magnitude of the SOC play an important role in this process.
We propose a helpful scheme and a quantum control method which can be applied
to conquering the difficulties of previous experimental observation of
itinerant ferromagnetism. Our further study reveals that exotic Fermi surfaces
and an abnormal phase region can exist in this system by controlling the
anisotropy of SOC, which can provide constructive suggestions for the research
and the application of a dipolar Fermi gas. Furthermore, we also calculate the
ferromagnetism transition temperature and novel distributions in momentum space
at finite temperature beyond the ground states from the perspective of
experiment.",2304.00286v1
2023-04-03,Magnetic resonance in the quasi-2D square lattice easy-plane antiferromagnet Ba$_2$MnGe$_2$O$_7$,"We report results of a multi-frequency (0.8-60 GHz) electron spin resonance
study of the spin dynamics in the quasi-2D square lattice antiferromagnet
Ba$_2$MnGe$_2$O$_7$ both in antiferromagnetically ordered and paramagnetic
phases. We directly observe two zero-field gaps in the excitation spectrum of
the ordered phase, the larger one being due to easy-plane anisotropy, and the
smaller one indicates the presence of fourth-order in-plane anisotropy probably
related to the multiferroic properties of this compound. We observe effects of
hyperfine interaction on the electron spin resonance spectra in the
antiferromagnetically ordered state, which turns out to be comparable with
in-plane anisotropy. The hyperfine field strength is found from the observed
low-temperature electron spin resonance data. The spin dynamics of the
paramagnetic phase is characterized by strong broadening of the ESR absorption
line, which can be ascribed to the vortex dynamics of a 2D magnet.",2304.01280v1
2023-04-04,Exploring velocity-spreading factor and consequences through dynamic ray-tracing in general anisotropic media: A comprehensive tutorial,"In seismic imaging, understanding the relationship between
wavefront-propagation velocity and time-interval velocity is crucial for
achieving optimal resolution. However, this task becomes even more challenging
when considering anisotropic situations. To accurately account for the
influence of anisotropy on wavefronts, it is essential to have a solid grasp of
the underlying physics. Unfortunately, the anisotropy model that best describes
the medium is often unknown. To address this issue, we utilize paraxial-ray
theory in a ray-centered coordinate system to study the wavefront phenomenon.
This approach allows us to develop explicit expressions that describe the
physics of the problem. Using this theoretical framework, we can accurately
generalize the relationship between time-migration rays and Dix velocity by
incorporating the velocity-spreading factor for general anisotropic media. This
factor lets us determine the type of anisotropy present in the medium.
Moreover, the velocity-spreading factor provides valuable information for
various applications, including model building, time-imaging, and time-to-depth
conversion. Overall, the presented theoretical framework offers a comprehensive
understanding of wavefront propagation in anisotropic media, which can aid in
improving the knowledge of the phenomena that form seismic images.",2304.02069v1
2023-04-06,Production of Primordial Gravitational Waves in Teleparallel Gravity,"We study the production of primordial gravitational waves in the context of
extended teleparallel gravity models and compare them with those of general
relativity. Teleparallel gravity has been widely studied in the context of the
late universe but not much in the early universe. Two sources of primordial
gravitational waves are considered, vacuum fluctuations and tensor anisotropies
within two inflation-compatible backgrounds: a perfect de Sitter and a quasi de
Sitter background. We find that in the vacuum case with a perfect de Sitter
background, the gravitational waves propagation equation is the same as that of
general relativity, however, if the background is promoted to a quasi de Sitter
background, the propagation equations are different resulting in an important
difference on the tensor spectral index. When tensor anisotropies are included,
we compute the most general solution for gravitational waves in terms of a
retarded Green's function and analyze the contributions to the power spectrum
from these anisotropies. Finally, we investigate the energy density of these
gravitational waves.",2304.03067v2
2023-05-18,Azimuthal Anisotropy of Magnetic Fields in the Circumgalactic Medium Driven by Galactic Feedback Processes,"We use the TNG50 cosmological magnetohydrodynamical simulation of the
IllustrisTNG project to show that magnetic fields in the circumgalactic medium
(CGM) have significant angular structure. This azimuthal anisotropy at fixed
distance is driven by galactic feedback processes that launch strong outflows
into the halo, preferentially along the minor axes of galaxies. These
feedback-driven outflows entrain strong magnetic fields from the interstellar
medium, dragging fields originally amplified by small-scale dynamos into the
CGM. At the virial radius, $z=0$ galaxies with M$_\star \sim
10^{10}\,\rm{M_\odot}$ show the strongest anisotropy ($\sim 0.35$ dex). This
signal weakens with decreasing impact parameter, and is also present but weaker
for lower mass as well as higher mass galaxies. Creating mock Faraday rotation
measure (RM) sightlines through the simulated volume, we find that the angular
RM trend is qualitatively consistent with recent observational measurements. We
show that rich structure is present in the circumgalactic magnetic fields of
galaxies. However, TNG50 predicts small RM amplitudes in the CGM that make
detection difficult as a result of other contributions along the line of sight.",2305.11214v2
2023-05-24,Competing Uniaxial Anisotropies in Epitaxial Fe Thin Films Grown on InAs(001),"We report on the interplay of two uniaxial magnetic anisotropies in epitaxial
Fe thin films of varying thickness grown on InAs(001) as observed in
ferromagnetic resonance experiments. One anisotropy originates from the Fe/InAs
interface while the other originates from in-plane shear strain resulting from
the anisotropic relaxation of the Fe film. X-ray diffraction was used to
measure the in-plane lattice constants of the Fe films, confirming the
correlation between the onset of film relaxation and the corresponding shear
strain inferred from ferromagnetic resonance data. These results are relevant
for ongoing efforts to develop spintronic and quantum devices utilizing large
spin-orbit coupling in III-V semiconductors.",2305.14648v1
2023-05-25,Random-anisotropy mixed-spin Ising on a triangular lattice,"We have studied the mixed spin-1/2 and 1 Ising ferrimagnetic system with a
random anisotropy on a triangular lattice with three interpenetrating
sublattices $A$, $B$, and $C$. The spins on the sublattices are represented by
$\sigma_{A}$ (states $\pm1/2$), $\sigma_{B}$ (states $\pm1/2$), and $S_{C}$
(states $\pm1$, $0$). We have performed Monte Carlo simulations to obtain the
phase diagram temperature $k_{\text{B}}T/\left|J\right|$ versus the strength of
the random anisotropy $D/\left|J\right|$. The phase boundary between two
ferrimagnetic $FR_{1}$ and $FR_{2}$ phases at lower temperatures are always
first-order for $p<0.25$ and second-order phase transition between the
$FR_{1}$, $FR_{2}$ and the paramagnetic $P$ phases. On the other hand, for
values of $p\gtrapprox0.5$, the phase diagram presents only second-order phase
transition lines.",2305.15866v1
2023-06-03,Critical behaviours of anisotropic XY ferromagnet in the presence of random field,"The anisotropic XY ferromagnet has been studied by Monte Carlo simulation in
a three dimensional simple cubic lattice. The increase in critical temperature
(ferro-para transition) has been noticed with increasing the strength of
anisotropy. The effects of random fields (both with full circular symmetry and
in angular window) on the critical temperature are investigated systematically
in the anisotropic XY ferromagnet in three dimensions. Reduction in the
critical temperature of anisotropic XY ferromagnet has been observed in the
presence of random field. The compensating field (the required amount of field
which preserves the critical temperature for isotropic XY ferromagnet) has been
studied as a function of the strength of anisotropy. The compensating field was
found to depend linearly on the strength of anisotropy. We have also studied
the effects of random field confined in the angular window and observed the
reduction of the critical temperature with increase of the angular extension.
The critical behaviours are formalized by the usual finite size analysis and
the estimation of critical exponents for the susceptibility and the specific
heat. .",2306.02162v2
2023-06-13,Reduced energies for thin ferromagnetic films with perpendicular anisotropy,"We derive four reduced two-dimensional models that describe, at
  different spatial scales, the micromagnetics of ultrathin
  ferromagnetic materials of finite spatial extent featuring
  perpendicular magnetic anisotropy and interfacial
  Dzyaloshinskii-Moriya interaction. Starting with a microscopic model
  that regularizes the stray field near the material's lateral edges,
  we carry out an asymptotic analysis of the energy by means of
  $\Gamma$-convergence. Depending on the scaling assumptions on the
  size of the material domain vs. the strength of dipolar interaction,
  we obtain a hierarchy of the limit energies that exhibit
  progressively stronger stray field effects of the material
  edges. These limit energies feature, respectively, a renormalization
  of the out-of-plane anisotropy, an additional local boundary penalty
  term forcing out-of-plane alignment of the magnetization at the
  edge, a pinned magnetization at the edge, and, finally, a pinned
  magnetization and an additional field-like term that blows up at the
  edge, as the sample's lateral size is increased. The pinning of the
  magnetization at the edge restores the topological protection and
  enables the existence of magnetic skyrmions in bounded samples.",2306.07634v2
2023-06-13,How to cross an energy barrier at zero Kelvin without tunneling effect,"This paper deals with the broad class of magnetic systems having a single or
collective spin $S$ with an energy barrier, such as Rare-Earth elements and
their compounds, Single Molecule Magnets with uniaxial anisotropy and more
generally any other quantum system made of single or multiple objects with
discrete energy levels. Till now, the reversal of the magnetization of such
systems at zero Kelvin required to make use of quantum tunneling with a
significant transverse field or transverse anisotropy term, at resonance. Here,
we show that another very simple method exists. It simply consists in the
application of a particular sequence of electromagnetic radiations in the
ranges of optical or microwave frequencies, depending on the characteristics of
the system (spin and anisotropy values for magnetic systems). This produces
oscillations of the Rabi type that pass above the barrier, thus extending these
oscillations between the two energy wells. with mixtures of all the 2S+1
states. In addition to its basic character, this approach opens up new
directions of research in quantum information with possible breakthroughs in
the current use of multiple quantum bits.",2306.07729v2
2023-06-22,Collective modes of a collisional anisotropic quark-gluon plasma,"In this paper we consider the collective modes of a momentum-space
anisotropic quark-gluon plasma taking into account the effect of collisions
between the plasma constituents. Our analysis is carried out using a
collisional kernel of Bhatnagar-Gross-Krook form and extends prior analyses in
the literature by considering all possible angles of propagation of the gluonic
modes relative to the momentum-anisotropy axis. We extract both the stable and
unstable modes as a function of the collision rate and confirm prior findings
that gluonic unstable modes can be eliminated from the spectrum if the
collision rate is sufficiently large. In addition, we discuss the conditions
necessary for the existence of unstable modes and present evidence that
unstable mode growth rates are maximal for modes with momentum along the
anisotropy direction. Finally, we demonstrate that when there is a finite
collisional rate, gluonic unstable modes are absent from the spectrum at both
small and large momentum anisotropy. These results pave the way for
understanding the impact of collisions on a variety of non-equilibrium
quark-gluon plasma observables.",2306.12851v2
2023-07-09,Enhancement and anisotropy of electron Lande factor due to spin-orbit interaction in semiconductor nanowires,"We investigate the effective Lande factor in semiconductor nanowires with
strong Rashba spin-orbit coupling. Using the $\mathbf{k}\cdot\mathbf{p}$ theory
and the envelope function approach we derive a conduction band Hamiltonian
where the tensor $g^*$ is explicitly related to the spin-orbit coupling
constant $\alpha_R$. Our model includes orbital effects from the Rashba
spin-orbit term, leading to a significant enhancement of the effective Lande
factor which is naturally anisotropic. For nanowires based on the low-gap, high
spin-orbit coupled material InSb, we investigate the anisotropy of the
effective Lande factor with respect to the magnetic field direction, exposing a
twofold symmetry for the bottom gate architecture. The anisotropy results from
the competition between the localization of the envelope function and the spin
polarization of the electronic state, both determined by the magnetic field
direction.",2307.04265v2
2023-07-18,Tilted Spirals and Low Temperature Skyrmions in Cu2OSeO3,"The bulk helimagnet Cu2OSeO3 represents a unique example in the family of B20
cubic helimagnets exhibiting a tilted spiral and skyrmion phase at low
temperatures when the magnetic field is applied along the easy <001>
crystallographic direction. Here we present a systematic study of the stability
and ordering of these low temperature magnetic states. We focus our attention
on the temperature and field dependencies of the tilted spiral state that we
observe persisting up to above T =35 K, i.e. up to higher temperatures than
reported so far. We discuss these results in the frame of the phenomenological
theory introduced by Dzyaloshinskii in an attempt to reach a quantitative
description of the experimental findings. We find that the anisotropy
constants, which are the drivers behind the observed behaviour, exhibit a
pronounced temperature dependence. This explains the differences in the
behaviour observed at high temperatures (above T = 18 K), where the cubic
anisotropy is weak, and at low temperatures (below T = 18 K), where a strong
cubic anisotropy induces an abrupt appearance of the tilted spirals out of the
conical state and enhances the stability of skyrmions.",2307.09539v1
2023-07-19,Unraveling Cosmological Anisotropies within Stochastic Gravitational Wave Backgrounds,"Identifying the anisotropies in a cosmologically sourced stochastic
gravitational wave background (SGWB) would be of significance in shedding light
on the nature of primordial inhomogeneities. For example, if SGWB carries
isocurvature fluctuations, it would provide evidence for a multi-field
inflationary origin of these inhomogeneities. However, this is challenging in
practice due to finite detector sensitivity and also the presence of the
astrophysical foregrounds that can compete with the cosmological signal. In
this work, we explore the prospects for measuring cosmological SGWB
anisotropies in the presence of an astrophysical counterpart and detector
noise. To illustrate the main idea, we perform a Fisher analysis using a
well-motivated cosmological SGWB template corresponding to a first order phase
transition, and an astrophysical SGWB template corresponding to extra-galactic
binary mergers, and compute the uncertainty with which various parameters
characterizing the isotropic and anisotropic components can be extracted. We
also discuss some subtleties and caveats involving shot noise in the
astrophysical foreground. Overall, we show that upcoming experiments, e.g.,
LISA, Taiji, Einstein Telescope, Cosmic Explorer, and BBO, can all be effective
in discovering plausible anisotropic cosmological SGWBs.",2307.10360v1
2023-07-26,Highly Tunable Perpendicular Magnetic Anisotropy and Anisotropic Magnetoresistance in Ru-doped La0.67Sr0.33MnO3 Epitaxial Films,"As a prototypical half-metallic ferromagnet, La0.67Sr0.33MnO3 (LSMO) has been
extensively studied due to its versatile physical properties and great
potential in spintronic applications. However, the weak perpendicular magnetic
anisotropy (PMA) limits the controllability and detection of magnetism in LSMO,
thus hindering the realization of oxide-based spintronic devices with low
energy consumption and high integration level. Motivated by this challenge, we
develop an experimental approach to enhance the PMA of LSMO epitaxial films. By
cooperatively introducing 4d Ru doping and a moderate compressive strain, the
maximum uniaxial magnetic anisotropy in Ru-doped LSMO can reach 3.0 to 1E5 J/m3
at 10 K. Furthermore, we find a significant anisotropic magnetoresistance
effect in these Ru-doped LSMO films, which is dominated by the strong PMA. Our
findings offer an effective pathway to harness and detect the orientations of
magnetic moments in LSMO films, thus promoting the feasibility of oxide-based
spintronic devices, such as spin valves and magnetic tunnel junctions.",2307.13881v1
2023-07-28,Field-Free Switching in Symmetry Breaking Multilayers: The Critical Role of Interlayer Chiral Exchange,"It is crucial to realize field-free, deterministic, current-induced switching
in spin-orbit torque magnetic random-access memory (SOT-MRAM) with
perpendicular magnetic anisotropy (PMA). A tentative solution has emerged
recently, which employs the interlayer chiral exchange coupling or the
interlayer Dzyaloshinskii-Moriya interaction (i-DMI) to achieve symmetry
breaking. We hereby investigate the interlayer DMI in a Pt/Co multilayer system
with orthogonally magnetized layers, using repeatedly stacked [Pt/Co]n
structure with PMA, and a thick Co layer with in-plane magnetic anisotropy
(IMA). We clarify the origin and the direction of such symmetry breaking with
relation to the i-DMI effective field, and show a decreasing trend of the said
effective field magnitude to the stacking number (n). By comparing the
current-induced field-free switching behavior for both PMA and IMA layers, we
confirm the dominating role of i-DMI in such field-free switching, excluding
other possible mechanisms such as tilted-anisotropy and unconventional spin
currents that may have arisen from the symmetry breaking.",2307.15258v2
2023-07-31,Cosmological First-Order Vacuum Phase Transitions in an Expanding Anisotropic Universe,"We examine the anisotropy originated from a first-order vacuum phase
transitions through three-dimensional numerical simulations. We apply Bianchi
Type-I metric to our model that has one scalar field minimally coupled to the
gravity. We calculate the time evolution of the energy density for the shear
scalar and the directional Hubble parameters as well as the power spectra for
the scalar field and the gravitational radiation although there are a number of
caveats for the tensor perturbations in Bianchi Type-I universe. We run
simulations with different mass scales of the scalar field, therefore, in
addition to investigation of anisotropy via the shear scalar, we also determine
at which mass scale the phase transition completes successfully, hence,
neglecting the expansion of the Universe does not significantly affect the
results. Finally, we showed that such an event may contribute to the total
anisotropy depending on the mass scale of the scalar field and the initial
population of nucleated bubbles.",2307.16458v1
2023-08-04,Anisotropy of the spin Hall effect in a Dirac ferromagnet,"We study the intrinsic spin Hall effect of a Dirac Hamiltonian system with
ferromagnetic exchange coupling, a minimal model combining relativistic
spin-orbit interaction and ferromagnetism. The energy bands of the Dirac
Hamiltonian are split after introducing a Stoner-type ferromagnetic ordering
which breaks the spherical symmetry of pristine Dirac model. The totally
antisymmetric spin Hall conductivity (SHC) tensor becomes axially anisotropic
along the direction of external electric field. Interestingly, the anisotropy
does not vanish in the asymptotic limit of zero magnetization. We show that the
ferromagnetic ordering breaks the spin degeneracy of the eigenfunctions and
modifies the selection rules of the interband transitions for the intrinsic
spin Hall effect. The difference in the selection rule between the pristine and
the ferromagnetic Dirac phases causes the anisotropy of the SHC, resulting in a
discontinuity of the SHC as the magnetization, directed orthogonal to the
electric field, is reduced to zero in the ferromagnetic Dirac phase and enters
the pristine Dirac phase.",2308.02336v1
2023-08-22,Theory of defect-induced crystal field perturbations in rare earth magnets,"We present a theory describing the single-ion anisotropy of rare earth (RE)
magnets in the presence of point defects. Taking the RE-lean 1:12 magnet class
as a prototype, we use first-principles calculations to show how the
introduction of Ti substitutions into SmFe$_{12}$ perturbs the crystal field,
generating new coefficients due to the lower symmetry of the RE environment. We
then demonstrate that these perturbations can be described extremely
efficiently using a screened point charge model. We provide analytical
expressions for the anisotropy energy which can be straightforwardly
implemented in atomistic spin dynamics simulations, meaning that such
simulations can be carried out for an arbitrary arrangement of point defects.
The significant crystal field perturbations calculated here demonstrate that a
sample which is single-phase from a structural point of view can nonetheless
have a dramatically varying anisotropy profile at the atomistic level if there
is compositional disorder, which may influence localized magnetic objects like
domain walls or skyrmions.",2308.11303v1
2023-09-04,Anisotropic Seebeck coefficient of $\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$ in the incoherent regime,"Intuitive entropic interpretations of the thermoelectric effect in metals
predict an isotropic Seebeck coefficient at high temperatures in the incoherent
regime even in anisotropic metals since entropy is not directional.
$\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$ is an enigmatic material known for a
well characterised anisotropic normal state and unconventional
superconductivity. Recent ab-initio transport calculations of
$\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$ that include the effect of strong
electronic correlations predicted an enhanced high-temperature anisotropy of
the Seebeck coefficient at temperatures above 300 K, but experimental evidence
is missing. From measurements on clean $\mathrm{Sr}_2\mathrm{Ru}\mathrm{O}_4$
single crystals along both crystallographic directions, we find that the
Seebeck coefficient becomes increasingly isotropic upon heating towards room
temperature as generally expected. Above 300 K, however, $S$ acquires a new
anisotropy which rises up to the highest temperatures measured (750 K), in
qualitative agreement with calculations. This is a challenge to entropic
interpretations and highlights the lack of an intuitive framework to understand
the anisotropy of thermopower at high temperatures.",2309.01403v1
2023-09-04,On the anisotropies of the cosmological gravitational-wave background from pulsar timing array observations,"Significant evidence for a stochastic gravitational-wave background has
recently been reported by several Pulsar Timing Array observations. These
studies have shown that, in addition to astrophysical explanations based on
supermassive black hole binaries (SMBHBs), cosmological origins are considered
equally important sources for these signals. To further explore these
cosmological sources, in this study, we discuss the anisotropies in the
cosmological gravitational wave background (CGWB) in a model-independent way.
Taking the North American Nanohertz Observatory for Gravitational Waves
(NANOGrav) 15-year dataset as a benchmark, we estimate the angular power
spectra of the CGWB and their cross-correlations with cosmic microwave
background (CMB) fluctuations and weak gravitational lensing. We find that the
NANOGrav 15-year data implies suppressed Sachs-Wolf (SW) effects in the CGBW
spectrum, leading to a marginally negative cross-correlation with the CMB at
large scales. This procedure is applicable to signals introduced by different
early universe processes and is potentially useful for identifying unique
features about anisotropies of CGWB from future space-based interferometers and
astrometric measurements.",2309.01643v2
2023-09-07,Nonreciprocal phonon dichroism induced by Fermi pocket anisotropy in two-dimensional Dirac materials,"Electrons in two-dimensional (2D) Dirac materials carry local band geometric
quantities, such as the Berry curvature and orbital magnetic moments, which,
combined with electron-phonon coupling, may affect the phonon dynamics in an
unusual way. Here, we propose intrinsic nonreciprocal linear and circular
phonon dichroism in magnetic 2D Dirac materials, which originate from nonlocal
band geometric quantities of electrons and reduce to pure Fermi-surface
properties for acoustic phonons. We find that to acquire the nonreciprocity,
the Fermi pocket anisotropy rather than the chirality of electrons is crucial.
Two possible mechanisms of Fermi pocket anisotropy are suggested: (i) trigonal
warping and out-of-plane magnetization or (ii) Rashba spin-orbit interaction
and in-plane magnetization. As a concrete example, we predict appreciable and
tunable nonreciprocal phonon dichroism in 2H-MoTe 2 on a EuO substrate. Our
finding points to a different route towards electrical control of phonon
nonreciprocity for acoustoelectronics applications based on 2D quantum
materials.",2309.03540v1
2023-09-11,Anisotropic diffusion of radiation-induced self-interstitial clusters in HCP zirconium: a molecular dynamics and rate-theory assessment,"Under irradiation, Zr and Zr alloys undergo growth in the absence of applied
stress. This phenomenon is thought to be associated with the anisotropy of
diffusion of either or both radiation-induced point defects and defect
clusters. In this work, molecular dynamic simulations are used to study the
anisotropy of diffusion of self-interstitial atom clusters. Both
near-equilibrium clusters generated by aggregation of self-interstitial atoms
and cascade-induced clusters were considered. The cascade-induced clusters
display more anisotropy than their counterparts produced by aggregation. In
addition to 1-dimensional diffusing clusters, 2-dimensional diffusing clusters
were observed. Using our molecular dynamic simulations, the input parameters
for the ""self-interstitial atom cluster bias"" rate-theory model were estimated.
The radiation-induced growth strains predicted using this model are largely
consistent with experiments, but are highly sensitive to the choice of
interatomic interaction potential.",2309.05781v1
2023-09-16,Anisotropy of Antiferromagnetic Domains in a Spin-orbit Mott Insulator,"The temperature-dependent behavior of magnetic domains plays an essential
role in the magnetic properties of materials, leading to widespread
applications. However, experimental methods to access the three-dimensional
(3D) magnetic domain structures are very limited, especially for
antiferromagnets. Over the past decades, the spin-orbit Mott insulator iridate
$Sr_2IrO_4$ has attracted particular attention because of its interesting
magnetic structure and analogy to superconducting cuprates. Here, we apply
resonant x-ray magnetic Bragg coherent diffraction imaging to track the
real-space 3D evolution of antiferromagnetic ordering inside a $Sr_2IrO_4$
single crystal as a function of temperature, finding that the antiferromagnetic
domain shows anisotropic changes. The anisotropy of the domain shape reveals
the underlying anisotropy of the antiferromagnetic coupling strength within
$Sr_2IrO_4$. These results demonstrate the high potential significance of 3D
domain imaging in magnetism research.",2309.09091v1
2023-09-20,A comparative study on maximum mass and radius of compact star from Heintzmann geometry and TOV approach,"In this article a class of anisotropic compact star is analysed in Heintzmann
geometry. We have introduced the pressure anisotropy parameter ($\alpha$) and
solved Einstein field equations to obtain stellar model. We have considered
$g_{tt}$ component as proposed by Heintzmann and by solving Einstein field
equation, the $g_{rr}$ component is evaluated in presence of pressure
anisotropy. It is noted that for isotropic star ($\alpha=0$), the maximum mass
lies within the range $1.87-3.04~ M_{\odot}$ for radii ranges between $8-13$
Km. For anisotropic compact stars maximum mass increases with $\alpha$ and lies
within the range $1.99-3.23~ M_{\odot}$ for anisotropy parameter $\alpha=0.5$.
The physical viability of the model is examined by applying our model to study
the properties of few known compact objects. It is noted that all the stability
conditions are fulfilled in the proposed model. It is interesting to note that
maximum mass calculated from our model and from solving TOV equation are
approximately same and also the predicted radius of few newly observed pulsars
and companion star of GW events GW 190814 and GW 170817 from our model comply
with the estimated value of radius from observation.",2309.11468v1
2023-09-21,The influence of film thickness and uniaxial anisotropy on in-plane skyrmions: Numerical investigations of the phase space of chiral magnets,"The equilibrium phase space of magnetic textures in thin-films of cubic
chiral ferromagnets, including skyrmions, is explored as a function of in-plane
magnetic field strength, film thickness and uniaxial anisotropy. The interplay
between these system parameters is found to give rise to a phase space with a
rich structure, distinct from that of the nano-stripes that have been
previously studied. For certain values of the anisotropy, the range of
thicknesses supporting in-plane skyrmions and/or helicoids with an out-of-plane
propagation vector is found to be disconnected, suggesting a possible direction
for future experiments. We explain how this interesting phase space topology
arises due to the geometric confinement of the thin-film system, and identify
the optimal parameter ranges for future explorations of novel magnetic textures
such as the oblique spiral phase.",2309.12419v1
2023-10-04,Anisotropy of magnetized quark matter,"Strong transient magnetic fields are generated in non-central relativistic
heavy-ion collisions. These fields induce anisotropy within the strongly
interacting medium that, in principle, can affect the thermodynamic properties
of the medium. We use the Polaykov loop extended Nambu Jona-Lasinio (PNJL)
model to study the quark matter subjected to an external magnetic field at
vanishing baryon chemical potential. We have estimated the degree of anisotropy
in the speed of sound and isothermal compressibility within the magnetized
quark matter as a function of temperature and magnetic field. This study helps
us to understand the extent of directionality generated in the initial stages
of non-central collisions while giving us useful information about the system.",2310.02711v1
2023-10-06,Rock anisotropy promotes hydraulic fracture containment at depth,"We report laboratory experiments and numerical simulations demonstrating that
the anisotropic characteristics of rocks play a major role in the elongation of
hydraulic fractures propagating in a plane perpendicular to bedding. Transverse
anisotropy leads to larger hydraulic fracture extension in the
parallel-to-bedding/divider direction compared to the
perpendicular-to-bedding/arrester direction. This directly promotes vertical
containment of hydraulic fractures in most sedimentary basins worldwide even in
the absence of any favorable in-situ stress contrasts or other material
heterogeneities. More importantly, the ratio of the energy dissipated in fluid
viscous flow in the fracture to the energy dissipated in the creation of new
surfaces is found to play a critical role on fracture elongation, with
fracture-energy dominated hydraulic fractures being the most elongated while
the viscous dominated ones remain more circular. These results open the door to
a better engineering and control of hydraulic fractures containment at depth in
view of the competition between material anisotropy and injection parameters
(fluid viscosity and rate of injection).",2310.04374v1
2023-10-09,Spatial asymmetry of optically excited spin waves in anisotropic ferromagnetic film,"We analytically discuss and micromagnetically prove the ways to tune the
spatial asymmetry of the initial phase, amplitude, and wavevectors of
magnetostatic waves driven by ultrafast laser excitation. We consider that the
optical pulse heats a thin ferromagnetic metallic film and abruptly decreases
the saturation magnetization and the parameter of uniaxial anisotropy. The two
corresponding terms of laser-induced torque have different azimuthal
symmetries, with the 4-fold symmetry of the demagnetization-related term, and
the isotropic distribution of the anisotropy-related term. As a result, the
initial phase and amplitude of excited magnetostatic waves have a non-trivial
azimuthal distribution tunable with the angle between the external magnetic
field and anisotropy axis, and the laser spot diameter. Moreover, the variation
of these parameters tunes the distribution of wavevectors, resulting in
additional asymmetry between the spectral components of the waves propagating
in different directions.",2310.05895v1
2023-10-12,Effective potential engineering by emergent anisotropy in a tunable open-access microcavity,"Photonic spin-orbit (SO) coupling is an important physical mechanism leading
to numerous interesting phenomena in the systems of microcavity photons and
exciton-polaritons. We report the effect of SO coupling in a tunable
open-access microcavity embedded with anisotropic active media. The SO coupling
associated with the TE-TM splitting results in an emergent anisotropy, which
further leads to fine energy splittings allowing clear observation of the full
set of eigenstates, in sharp contrast with the isotropic situation which leads
to the isotropic eigenstates of spin vortices. We show that the photonic
potential can be engineered by playing with the relation between the emergent
anisotropy and the cavity ellipticity. All the experimental results are well
reproduced by the degenerate perturbation theory. Our results constitute a
significant extension to the research field of microcavity spinoptronics, with
potential applications in polarization control and optical property measurement
of photonic devices and materials.",2310.08024v1
2023-10-18,Giant Spin Transport Anisotropy in Magnetic Topological Insulators,"We report on exceptionally long spin transport and giant spin lifetime
anisotropy in the gapped surface states of three-dimensional (3D) magnetic
topological insulators (MTIs). We examine the properties of these states using
the Fu-Kane-Mele Hamiltonian in presence of a magnetic exchange field. The
corresponding spin textures of surface states, which are well reproduced by an
effective two-band model, hint at a considerable enhancement of the lifetime of
out-of-plane spins compared to in-plane spins. This is confirmed by large-scale
spin transport simulations for 3D MTIs with disorder. The energy dependence of
the spin lifetime anisotropy arises directly from the nontrivial spin texture
of the surface states, and is correlated with the onset of the quantum
anomalous Hall phase. Our findings suggest novel spin filtering capabilities of
the gapped surface MTI states, which could be explored by Hanle spin precession
measurements.",2310.12377v1
2023-10-24,Strain-driven switching between antiferromagnetic states in frustrated antiferromagnet UO2 probed by exchange bias effect,"Frustrated antiferromagnets offer a captivating platform to study the
intricate relationship of magnetic interactions, geometric constraints, and
emergent phenomena. By controlling spin orientations, these materials can be
tailored for applications in spintronics and quantum information processing.
The research focuses on the interplay of magnetic and exchange anisotropy
effects in artificial heterostructures based on a canonical frustrated
antiferromagnet, UO2. The potential to manipulate the spin directions in this
material and switch between distinct antiferromagnetic states is investigated
using substrate-induced strain. The phenomenon is probed using exchange bias
(EB) effects in stoichiometric UO2/Fe3O4 bilayers. By employing many-body
first-principles calculations magnetic configurations in the UO2 layers are
identified. Even a minor tetragonal distortion triggers a transition between
antiferromagnetic states of different symmetries, driven by a robust alteration
of single-ion anisotropy due to the distortion. Consequently, this change
influences the arrangement of magnetic moments at the UO2/Fe3O4 interface,
affecting the magnitude of exchange bias. The findings showcase how epitaxial
strain can effectively manipulate the antiferromagnetic states in frustrated
antiferromagnets by controlling single-site anisotropy.",2310.15696v1
2023-10-31,Highly Anisotropic Elastic Properties of Suspended Black Arsenic Nanoribbons,"Anisotropy, as an exotic degree of freedom, enables us to discover the
emergent two-dimensional (2D) layered nanomaterials with low in-plane symmetry
and to explore their outstanding properties and promising applications. 2D
black arsenic (b-As) with puckered structure has garnered increasing attention
these years owing to its extreme anisotropy with respect to the electrical,
thermal, and optical properties. However, the investigation on mechanical
properties of 2D b-As is still lacking, despite much effort on theoretical
simulations. Herein, we report the highly anisotropic elastic properties of
suspended b-As nanoribbons via atomic force microscope-based nanoindentation.
It was found that the extracted Young's modulus of b-As nanoribbons exhibits
remarkable anisotropy, which approximates to 72.2 +- 5.4 and 44.3 +- 1.4 GPa
along zigzag and armchair directions, respectively. The anisotropic ratio
reaches up to ~ 1.6. We expect that these results could lay a solid foundation
for the potential applications of 2D anisotropic nanomaterials in the
next-generation nanomechanics and optoelectronics.",2310.20164v1
2023-11-07,Classical spin models and basic magnetic interactions on 1/1-approximant crystals,"We study classical spin models on the 1/1 Tsai-type approximant lattice using
Monte Carlo and mean-field methods. Our aim is to understand whether the phase
diagram differences between Gd- and Tb-based approximants can be attributed to
anisotropy induced by the crystal-electric field. To address this question, we
treat Gd ions as Heisenberg spins and Tb ions as Ising spins. Additionally, we
consider the presence of the RKKY interaction to replicate the experimentally
observed correlation between magnetic properties and electron concentration.
Surprisingly, our findings show that the transition between ferromagnetic and
antiferromagnetic order remains unaltered by the anisotropy, even when
accounting for the dipole interaction. We conclude that a more comprehensive
model, extending beyond the free-electron gas RKKY interaction, is likely
required to fully understand the distinctions between Gd- and Tb-based
approximants. Our work represents a systematic exploration of the impact of
anisotropy on the ground-state properties of classical spin models in
quasicrystal approximants.",2311.03781v2
2023-11-07,Structural Transition and Magnetic Anisotropy in $α$-RuCl$_{3}$,"We report X-ray diffraction and magnetic susceptibility studies of the
structural phase transition in $\alpha$-RuCl$_{3}$. By utilizing a single
crystal sample with predominantly single twin domain, we show that
$\alpha$-RuCl$_{3}$ goes from high-temperature C2/m structure to a rhombohedral
structure with R$\bar{3}$ symmetry at low temperature. While the defining
feature of the structural transition is changing the stacking direction from
the monoclinic a-axis to the b-axis, bond-anisotropy disappears when the
structural change occurs, indicating that the local $C_3$ symmetry is restored
within the honeycomb layer. The symmetry change is corroborated by the
vanishing magnetic anisotropy in the low-temperature structure. Our study
demonstrates that magnetic interaction is extremely sensitive to structural
details in $\alpha$-RuCl$_{3}$, which could explain the sample dependence found
in this material.",2311.04000v1
2023-11-08,Giant anisotropy and Casimir phenomena: the case of carbon nanotube metasurfaces,"The Casimir interaction and torque are related phenomena originating from the
exchange of electromagnetic excitations between objects. While the Casimir
force exists between any types of objects, the materials or geometrical
anisotropy drives the emergence of the Casimir torque. Here both phenomena are
studied theoretically between dielectric films with immersed parallel single
wall carbon nanotubes in the dilute limit with their chirality and collective
electronic and optical response properties taken into account. It is found that
the Casimir interaction is dominated by thermal fluctuations at sub-micron
separations, while the torque is primarily determined by quantum mechanical
effects. This peculiar quantum vs. thermal separation is attributed to the
strong influence of reduced dimensionality and inherent anisotropy of the
materials. Our study suggests that nanostructured anisotropic materials can
serve as novel platforms to uncover new functionalities in ubiquitous Casimir
phenomena.",2311.05001v1
2023-11-13,Translational symmetry broken magnetization plateau of the S=1 antiferromagnetic Heisenberg chain with competing anisotropies,"We investigate the S=1 antiferromagnetic quantum spin chain with the exchange
and single-ion anisotropies in a magnetic field, using the numerical exact
diagonalization of finite-size clusters, the level spectroscopy analysis, and
the density matrix renormalization group (DMRG) method. It is found that a
translational symmetry broken magnetization plateau possibly appears at the
half of the saturation magnetization, when the anisotropies compete with each
other. The level spectroscopy analysis gives the phase diagram at half the
saturation magnetization. The DMRG calculation presents the magnetization
curves for some typical parameters and clarifies the spin structure in the
plateau phase.",2311.07123v1
2023-11-13,"Nematic superconductivity from selective orbital pairing in Ba(Fe1-xMx)2As2 (M = Co, Ni) single crystals","We use transport measurements to determine the in-plane anisotropy of the
upper critical field Hc2 in detwinned superconducting Ba(Fe1-xMx)2As2 (M = Co,
Ni) single crystals. In previous measurements on twinned single crystals, the
charge carrier doping dependence (x) of the upper critical field anisotropy for
fields along the inter-planar (c-axis) and in-plane field directions was found
to increase in the overdoped regime. For underdoped samples, which exhibit a
spin nematic phase below the tetragonal to orthorhombic structural transition
temperature Ts , we find that Hc2 along the a-axis is considerably lower than
that along the b-axis. The upper critical field anisotropy disappears in the
over-doped regime when the system becomes tetragonal. By combining these
results with inelastic neutron scattering studies of spin excitations, and
angle-resolved photoemission spectroscopy, we conclude that superconductivity
in under-doped iron pnictides is orbital selective - with a dominant
contribution from electrons with the dyz orbital character and being intimately
associated with spin excitations.",2311.07697v1
2023-11-19,Multicritical dissipative phase transitions in the anisotropic open quantum Rabi model,"We investigate the nonequilibrium steady state of the anisotropic open
quantum Rabi model, which exhibits first-order and second-order dissipative
phase transitions upon varying the degree of anisotropy between the coupling
strengths of rotating and counterrotating terms. Using both semiclassical and
quantum approaches, we find a rich phase diagram resulting from the interplay
between the anisotropy and the dissipation. First, there exists a bistable
phase where both the normal and superradiant phases are stable. Second, there
are multicritical points where the phase boundaries for the first- and
second-order phase transitions meet. We show that a new set of critical
exponents governs the scaling of the multicritical points. Finally, we discuss
the feasibility of observing the multicritical transitions and bistability
using a pair of trapped ions where the anisotropy can be tuned by the
controlling the intensity of the Raman transitions. Our study enlarges the
scope of critical phenomena that may occur in finite-component quantum systems,
which could be useful for the applications in the critical quantum sensing.",2311.11346v1
2023-11-24,Physics-Informed Tensor Basis Neural Network for Turbulence Closure Modeling,"Despite the increasing availability of high-performance computational
resources, Reynolds-Averaged Navier-Stokes (RANS) simulations remain the
workhorse for the analysis of turbulent flows in real-world applications.
Linear eddy viscosity models (LEVM), the most commonly employed model type,
cannot accurately predict complex states of turbulence. This work combines a
deep-neural-network-based, nonlinear eddy viscosity model with turbulence
realizability constraints as an inductive bias in order to yield improved
predictions of the anisotropy tensor. Using visualizations based on the
barycentric map, we show that the proposed machine learning method's anisotropy
tensor predictions offer a significant improvement over all LEVMs in
traditionally challenging cases with surface curvature and flow separation.
However, this improved anisotropy tensor does not, in general, yield improved
mean-velocity and pressure field predictions in comparison with the
best-performing LEVM.",2311.14576v1
2023-11-30,Dynamic Phase Transition in 2D Ising Systems: Effect of Anisotropy and Defects,"We investigate the dynamic phase transition in two-dimensional Ising models
whose equilibrium characteristics are influenced by either anisotropic
interactions or quenched defects. The presence of anisotropy reduces the
dynamical critical temperature, leading to the expected result that the
critical temperature approaches zero in the full-anisotropy limit. We show that
a comprehensive understanding of the dynamic behavior of systems with quenched
defects requires a generalized definition of the dynamic order parameter. By
doing so, we demonstrate that the inclusion of quenched defects lowers the
dynamic critical temperature as well, with a linear trend across the range of
defect fractions considered. We also explore if and how it is possible to
predict the dynamic behavior of specific magnetic systems with quenched
randomness. Various geometric quantities, such as a defect potential index, the
defect dipole moment, and the properties of the defect Delaunay triangulation,
prove useful for this purpose.",2312.00153v2
2023-12-04,Real-Space Visualization of Frequency-Dependent Anisotropy of Atomic Vibrations,"The underlying dielectric properties of materials, intertwined with
intriguing phenomena such as topological polariton modes and anisotropic
thermal conductivities, stem from the anisotropy in atomic vibrations.
Conventionally, X-ray diffraction techniques have been employed to estimate
thermal ellipsoids of distinct elements, albeit lacking the desired spatial and
energy resolutions. Here we introduce a novel approach utilizing the dark-field
monochromated electron energy-loss spectroscopy for momentum-selective
vibrational spectroscopy, enabling the cartographic delineation of variations
of phonon polarization vectors. By applying this technique to centrosymmetric
cubic-phase strontium titanate, we successfully discern two types of oxygen
atoms exhibiting contrasting vibrational anisotropies below and above 60 meV
due to their frequency-linked thermal ellipsoids. This method establishes a new
pathway to visualize phonon eigenvectors at specific crystalline sites for
diverse elements, thus delving into uncharted realms of dielectric, optical,
and thermal property investigations with unprecedented spatial resolutions.",2312.01694v1
2023-12-05,Gate-tunable graphene Josephson diode effect due to magnetochiral anisotropy,"Usually the magnetochiral anisotropy related Josephson diode effect is
assumed to be based on conventional two-dimensional electron gas, such as the
InAs quantum well. Here we propose a graphene-based Josephson junction as a
broadly gate-tunable platform for achieving nonreciprocal supercurrent within
the context of magnetochiral anisotropy. We show that the resulting
nonreciprocal supercurrents will exhibit a sign reversal when the graphene
switches from $n$-type doping to $p$-type doping. Particularly, the magnitude
of the nonreciprocity is highly sensitive to the electrostatic doping level of
graphene, enabling gate control of the diode efficiency from zero up to
approximately $40\%$. This giant gate-tunability stems from the chiral nature
of the pseudo-relativistic carriers in grapehe, allowing the graphene Josephson
diode emerges as a promising element for advanced superconducting circuits and
computation devices. Moreover, we have also obtained the so-called $0-\pi$-like
phase transitions in the current-phase relation, in coincidence with recent
experimental finding.",2312.02692v1
2023-12-05,Miniaturized Double-Wing Delta-E Effect Sensors,"Magnetoelastic composites are integral elements of sensors and actuators
utilizing magnetostriction for their functionality. Their sensitivity typically
scales with the saturation magnetostriction and inversely with magnetic
anisotropy. However, this makes the devices prone to minuscule residual
anisotropic stress from the fabrication process, impairing their performance
and reproducibility, hence limiting their suitability for arrays. This study
presents a shadow mask deposition technology combined with a free-free
magnetoelectric microresonator design intended to minimize residual stress and
inhomogeneity in the magnetoelastic layer. Resonators are experimentally and
theoretically analyzed regarding local stress anisotropy, magnetic anisotropy,
and the {\Delta}E effect in several resonance modes. Further, the sensitivity
is analyzed in the example of {\Delta}E-effect sensors. The results demonstrate
a device-to-device variation of the resonance frequency < 0.2 % with
sensitivities comparable with macroscopic {\Delta}E-effect sensors. The
reproducibility is drastically improved over previous magnetoelastic device
arrays. This development marks a step forward in the reproducibility and
homogeneity of magnetoelastic resonators and contributes to the feasibility of
large-scale, integrated sensor arrays.",2312.02903v1
2023-12-08,Dipolar coupled core-shell perpendicular shape anisotropy MTJ with enhanced write speed and reduced cross-talk,"The concept of Perpendicular Shape-Anisotropy Spin-Transfer-Torque Magnetic
Random-Access Memory tackles the downsize scalability limit of conventional
ultrathin magnetic tunnel junctions (MTJ) below sub-20 nm technological nodes.
This concept uses a thicker storage layer with a vertical aspect ratio,
enhancing the thermal stability factor thanks to the favorable contribution of
the shape anisotropy. However, the increased aspect ratio comes with an
increase in switching time under applied voltage and the cross-over to
non-uniform reversal mechanism at higher aspect ratio, limiting the gain in
scalability. Additionally, the larger volume of the magnetic cell significantly
increases the stray field acting on the neighboring devices compared to thin
MTJs. In this work, we propose the use of a dipolar-coupled core-shell system
as a storage layer. This improves both bottlenecks, as predicted by
micromagnetic simulations for magnetisation reversal, and a macrospin model to
estimate the stray field in a dense array.",2312.05245v1
2023-12-12,Constraining ultralight bosons in dwarf spheroidal galaxies with a radially varying anisotropy,"Axions, and axion-like particles, have come back into fashion in the last
decades as a possible solution to the galactic-scale crisis suffered by the
cold dark matter model. In the framework of the wave Dark Matter model, we have
carried out a Jeans Analysis on eight dwarf spheroidal galaxies that are
orbiting around the Milky Way, and we have constrained the boson mass.
Differently to a previous analysis, we adopted an anisotropy parameter that
varies with the distance from the centre of the galaxy to assess whether this
assumption would help to resolve, or at least alleviate, the well-known tension
with the value of the boson mass favoured by the cosmological analysis. Our
results indicate that, differently to what happens in ultra-faint dwarf
galaxies, such a tension cannot be lifted introducing a variable anisotropy
parameter, leaving as a possible solution the existence of additional axion or
axion-like particles with higher masses as naturally predicted in the Axiverse.",2312.07217v1
2023-12-13,Highly anisotropic lattices for Yang-Mills theory,"In this conference proceeding, we investigate the physical anisotropy in
terms of the temporal and spatial lattice spacings in relation to the bare
parameters of SU(2) pure gauge theory using Wilson gradient flow. Anisotropic
lattices have a wide range of applications, from thermodynamic calculations in
QCD to very recent real-time simulations using the complex Langevin method. We
find an almost linear relationship between the bare and renormalized
anisotropy. Using a parametrization that includes nonlinear effects and was
earlier proposed for SU(3) theory, we obtain a good description of the coupling
dependence of the anisotropy with only two fitting parameters. Our observation
of an approximately linear relationship and this parametrization should
strongly reduce the computational effort of anisotropic lattice calculations in
the future.",2312.08172v1
2024-01-18,Exploring the anisotropic HISQ (aHISQ) action,"The fate of heavy quarkonia states in quark-gluon plasma is encoded in the
temperature dependence of their spectral functions. Reconstruction of spectral
functions from Euclidean lattice correlators is an ill-posed problem. Despite a
variety of techniques developed recently, many questions remain unresolved. It
is known that the situation may be improved using anisotropic ensembles that
provide finer resolution in the temporal direction. To date, the effort focused
on Wilson fermions. We report on our first study with anisotropic improved
staggered quarks. To compute the spectrum of the anisotropic Highly Improved
Staggered Quarks (aHISQ) we generated a library of anisotropic pure gauge
ensembles. We discuss the gauge anisotropy tuning that is performed with the
Wilson and Symanzik gradient flow, as well as tuning of the strange quark mass
and quark anisotropy with aHISQ, using spectrum measurements on quenched
ensembles. Finally, we discuss the impact of anisotropy on pion taste
splittings for aHISQ.",2401.10049v1
2024-01-28,Constraints on an Anisotropic Universe,"We analyze the possibility of global anisotropy of the universe. We consider
an altered FLRW metric in which there are different scale factors along the 3
different axes of space. We construct the corresponding altered Friedmann
equations. We show that any initial anisotropies decrease into the future. At
late times, the difference in Hubble parameters changes as $1/\sqrt{t}$ in a
radiation dominated era and as $1/t$ in a matter dominated era. We use
constraints from Big Bang Nucleosynthesis and the Cosmic Microwave Background
to constrain the level of anisotropies at early times. We also examine how the
approach back in time to the singularity is radically altered; happening much
more abruptly, as a function of density, in an anisotropic universe. We also
mention improved bounds that can arise from measurements of primordial
gravitons, WIMPs, and neutrinos.",2401.15782v2
2024-02-29,Viscoelastic response and anisotropic hydrodynamics in Weyl semimetals,"We study viscoelastic response in Weyl semimetals with broken time-reversal
symmetry. Topology and anisotropy of the Fermi surface are manifested in the
viscoelasticity tensor of the electron fluid. In the dynamic (inter-band) part
of this tensor, the anisotropy leads to a qualitatively different, compared to
isotropic models, scaling with frequency and the Fermi energy. While components
of the viscosity tensor determined by the Fermi surface properties agree in the
Kubo and kinetic formalisms, the latter misses the anomalous Hall viscosity
determined by filled states below the Fermi surface. The anisotropy of the
dispersion relation is also manifested in the acceleration and relaxation terms
of the hydrodynamic equations.",2402.19304v1
2024-03-04,Elliptic anisotropy of open-charm hadron in p--Pb collisions at LHC energies from parton scatterings,"The elliptic azimuthal anisotropy coefficient ($v_{2}$) of open-charm hadron
at midrapidity ($|\eta<1|$) was studied in p--Pb collisions at
$\sqrt{s_{\mathrm{NN}}}=$ 8.16 TeV using a multi-phase transport model (AMPT).
By implementing an additional heavy quark--antiquark pair production trigger in
the AMPT, we obtained a simultaneously description of the $p_{\mathrm{T}}$
spectrum and $v_{2}$ of $D^{0}$ meson. Then the predictions for the $v_{2}$ of
charm hadrons including $D^{+}$, $D_{s}^{+}$ and $\Lambda_{c}^{+}$ in p--Pb
collisions are provided for the first time. We found that the $v_{2}$ of
open-charm hadron follows the number-of-constituent-quark (NCQ) scaling in
high-multiplicity p--Pb collisions, and is significantly affected by the parton
scattering process. These findings further demonstrate the importance of
partonic degrees of freedom in small collision systems for heavy flavors, and
provide referential value for future measurements of azimuthal anisotropy at
the LHC energies.",2403.01677v1
2024-03-08,Heavy quarkonium spectral function in an anisotropic background,"In this paper, we use a five-dimensional Einstein-dilaton-two-Maxwell
holographic QCD model to investigate the dissociation effects of $J/\Psi$ and
$\Upsilon(1S)$ states in an anisotropic medium by calculating their spectral
functions. First, we present the holographic quarkonium masses at zero
temperature via Physics-Informed Neural Networks. Then, at finite temperature,
we derive the spectral functions, representing heavy vector mesons as peaks,
and observe that with increasing anisotropy, temperature, chemical potential,
and warp factor, the peak height diminishes while its width expands, indicating
an accelerated dissociation process. Additionally, the results indicate the
anisotropy induces a stronger dissociation effect in the direction parallel to
the polarization compared to the perpendicular, revealing the anisotropy's
directional influence.",2403.04966v3
2024-03-09,Switching intrinsic magnetic skyrmions with controllable magnetic anisotropy in van der Waals multiferroic heterostructures,"Magnetic skyrmions, topologically nontrivial whirling spin textures at
nanometer scales, have emerged as potential information carriers for spintronic
devices. The ability to efficiently create and erase magnetic skyrmions is
vital yet challenging for such applications. Based on first-principles studies,
we find that switching between intrinsic magnetic skyrmion and high-temperature
ferromagnetic states can be achieved in two-dimensional van der Waals (vdW)
multiferroic heterostructure CrSeI/In2Te3 by reversing the ferroelectric
polarization of In2Te3. The core mechanism of this switching is traced to the
controllable magnetic anisotropy of CrSeI influenced by the ferroelectric
polarization of In2Te3. We propose a useful descriptor linking the presence of
magnetic skyrmions to magnetic parameters, and validate this connection through
studies of a variety of similar vdW multiferroic heterostructures. Our work
demonstrates that manipulating magnetic skyrmions via tunable magnetic
anisotropies in vdW multiferroic heterostructures represents a highly promising
and energy-efficient strategy for future development of spintronics.",2403.05747v1
2024-03-12,Bending Mechanics of Biomimetic Scale Plates,"We develop the fundamentals of nonlinear and anisotropic bending behavior of
biomimetic scale plates using a combination of analytical modeling, finite
element (FE) computations, and motivational experiments. The analytical
architecture-property relationships are derived for both synclastic and
anticlastic curvatures. The results show that, as the scales engage, both
synclastic and anticlastic deformations show non-linear scale contact
kinematics and cross-curvature sensitivity of moments resulting in strong
curvature-dependent elastic nonlinearity and emergent anisotropy. The
anisotropy of bending rigidities and their evolution with curvature are
affected by both the direction and magnitude of bending as well as scale
geometry parameters, and their distribution on the substrate. Like earlier
beam-like substrates, kinematic locked states were found to occur; however,
their existence and evolution are also strongly determined by scale geometry
and imposed cross-curvatures. This validated model helps us to quantify bending
response, locking behavior, and their geometric dependence, paving the way for
a deeper understanding of the nature of nonlinearity and anisotropy of these
systems.",2403.08026v1
2024-03-15,Agile and Safe Trajectory Planning for Quadruped Navigation with Motion Anisotropy Awareness,"Quadruped robots demonstrate robust and agile movements in various terrains;
however, their navigation autonomy is still insufficient. One of the challenges
is that the motion capabilities of the quadruped robot are anisotropic along
different directions, which significantly affects the safety of quadruped robot
navigation. This paper proposes a navigation framework that takes into account
the motion anisotropy of quadruped robots including kinodynamic trajectory
generation, nonlinear trajectory optimization, and nonlinear model predictive
control. In simulation and real robot tests, we demonstrate that our
motion-anisotropy-aware navigation framework could: (1) generate more efficient
trajectories and realize more agile quadruped navigation; (2) significantly
improve the navigation safety in challenging scenarios. The implementation is
realized as an open-source package at
https://github.com/ZWT006/agile_navigation.",2403.10101v1
1996-03-08,A Line of Sight Approach to Cosmic Microwave Background Anisotropies,"We present a new method for calculating linear cosmic microwave background
(CMB) anisotropy spectra based on integration over sources along the photon
past light cone. In this approach the temperature anisotropy is written as a
time integral over the product of a geometrical term and a source term. The
geometrical term is given by radial eigenfunctions which do not depend on the
particular cosmological model. The source term can be expressed in terms of
photon, baryon and metric perturbations, all of which can be calculated using a
small number of differential equations. This split clearly separates between
the dynamical and geometrical effects on the CMB anisotropies. More
importantly, it allows to significantly reduce the computational time compared
to standard methods. This is achieved because the source term, which depends on
the model and is generally the most time consuming part of calculation, is a
slowly varying function of wavelength and needs to be evaluated only in a small
number of points. The geometrical term, which oscillates much more rapidly than
the source term, does not depend on the particular model and can be precomputed
in advance. Standard methods that do not separate the two terms and require a
much higher number of evaluations. The new method leads to about two orders of
magnitude reduction in CPU time when compared to standard methods and typically
requires a few minutes on a workstation for a single model. The method should
be especially useful for accurate determinations of cosmological parameters
from CMB anisotropy and polarization measurements that will become possible
with the next generation of experiments. A programm implementing this method
can be obtained from the authors.",9603033v1
1999-09-01,Evolution of Multi-mass Globular Clusters in Galactic Tidal Field with the Effects of Velocity Anisotropy,"We study the evolution of globular clusters with mass spectra under the
influence of the steady Galactic tidal field, including the effects of velocity
anisotropy. Similar to single-mass models, velocity anisotropy develops as the
cluster evolves, but the degree of anisotropy is much smaller than isolated
clusters. Except for very early epochs of the cluster evolution, nearly all
mass components become tangentially anisotropic at the outer parts. We have
compared our results with multi-mass, King-Michie models. The isotropic King
model better fits to the Fokker-Planck results because of tangential
anisotropy. However, it is almost impossible to fit the computed density
profiles to the multi-mass King models for all mass components. Thus if one
attempts to derive global mass function based on the observed mass function in
limited radial range using multi-mass King models, one may get somewhat erratic
results, especially for low mass stars. We have examined how the mass function
changes in time. Specifically, we find that the power-law index of the mass
function decreases monotonically with the total mass of the cluster. This
appears to be consistent with the behaviour of the observed slopes of mass
functions for a limited number of clusters, although it is premature to compare
quantitatively because there are other mechanisms in contributing the
evaporation of stars from the clusters. The projected velocity profiles for
anisotropic models with the apocenter criterion for evaporation show
significant flattening toward the tidal radius compared to isotropic model or
anisotropic model with the energy criterion. Such a behaviour of velocity
profile appears to be consistent with the observed profiles of collapsed
cluster M15.",9909006v1
2001-03-06,The Anisotropy of the Ultra-High Energy Cosmic Rays,"Ultra-high energy cosmic rays (UHECRs) may originate from the decay of
massive relic particles in the dark halo of the Galaxy, or they may be produced
by supermassive black holes in the nuclei of nearby galaxies. The anisotropy in
the arrival directions is studied in four dark halo models (cusped, isothermal,
triaxial and tilted) and in four galaxy samples (galaxies intrinsically
brighter than Centaurus A within 50 and 100 Mpc, and brighter than M32 within
50 and 100 Mpc). In decaying dark matter models, the amplitude of the
anisotropy is controlled by the size of the Galactic halo, while the phase is
controlled by the shape. In the northern hemisphere, the amplitude is about 0.5
for cusped haloes, but falls to roughly 0.3 for isothermal haloes. The phase
points in the direction of the Galactic Centre, with deviations of up to 30
degrees possible for triaxial and tilted haloes. The effect of the halo of M31
is too weak to provide conclusive evidence for the decaying dark matter origin
of UHECRs. In extragalactic models, samples of galaxies brighter than Centaurus
A produce substantial anisotropies (roughly 1.8), much larger than the limits
set by the available data. If all galaxies brighter than M32 contribute, then
the anisotropy is more modest (roughly 0.5) and is directed toward mass
concentrations in the supergalactic plane, like the Virgo cluster. Predictions
are made for the southern hemisphere station of the Pierre Auger Observatory.
If the UHECRs have a Galactic origin, then the phase points towards the
Galactic Centre. If they have an extragalactic origin, then it points in the
rough direction of the Fornax cluster. This provides an unambiguous
discriminant and requires about 350-500 events at South Auger.",0103085v2
2002-05-22,The Anisotropy of the Microwave Background to l = 3500: Deep Field Observations with the Cosmic Background Imager,"We report measurements of anisotropy in the cosmic microwave background
radiation over the multipole range l ~ 200 - 3500 with the Cosmic Background
Imager based on deep observations of three fields. These results confirm the
drop in power with increasing l first reported in earlier measurements with
this instrument, and extend the observations of this decline in power out to l
\~ 2000. The decline in power is consistent with the predicted damping of
primary anisotropies. At larger multipoles, l = 2000 - 3500, the power is 3.1
sigma greater than standard models for intrinsic microwave background
anisotropy in this multipole range, and 3.5 sigma greater than zero. This
excess power is not consistent with expected levels of residual radio source
contamination but, for sigma_8 >~ 1, is consistent with predicted levels due to
a secondary Sunyaev-Zeldovich anisotropy. Further observations are necessary to
confirm the level of this excess and, if confirmed, determine its origin.",0205384v2
2003-09-11,Beyond the Damping Tail: Cross-Correlating the Kinetic Sunyaev-Zel'dovich Effect with Cosmic Shear,"Secondary anisotropies of the CMB have the potential to reveal intricate
details about the history of our universe between the present and recombination
epochs. However, because the CMB we observe is the projected sum of a multitude
of effects, the interpretation of small scale anisotropies by future high
resolution experiments will be marred by uncertainty and speculation without
the handles provided by other observations. In this paper we show that cross
correlating the CMB with an overlapping weak lensing survey will isolate the
elusive kinetic Sunyaev-Zel'dovich Effect from secondary anisotropies generated
at higher redshifts. We show that if upcoming high angular resolution CMB
experiments, like PLANCK/ACT/SPT, cover the same area of sky as current and
future weak lensing surveys, like CFTHLS/SNAP/LSST, the cross correlation of
cosmic shear with the kSZ effect will be detected with high signal to noise
ratio, increasing the potential science accessible to both sets of surveys. For
example, if ACT and a CFHTLS like survey were to overlap this cross-correlation
would be detected with a total signal to noise ratio greater than 220, reaching
1.8 per individual multipole around l \sim 5000. Furthermore, this
cross-correlation probes the three point coupling between the underlying dark
matter and the ""momentum"" of the ionized baryons in the densest regions of the
universe at intermediate redshifts. Similar to the tSZ power spectrum, its
strength is extremely sensitive to the power spectrum normalization parameter,
\sigma_8, scaling roughly as \sigma_8^7. It provides an effective mechanism to
isolate any component of anisotropy due to patchy reionization and rule out
primordial small scale anisotropy.",0309337v2
2004-08-20,Galactic foreground contribution to the BEAST CMB Anisotropy Maps,"We report limits on the Galactic foreground emission contribution to the
Background Emission Anisotropy Scanning Telescope (BEAST) Ka- and Q-band CMB
anisotropy maps. We estimate the contribution from the cross-correlations
between these maps and the foreground emission templates of an H${\alpha}$ map,
a de-striped version of the Haslam et al. 408 MHz map, and a combined 100
$\mu$m IRAS/DIRBE map. Our analysis samples the BEAST $\sim10^\circ$
declination band into 24 one-hour (RA) wide sectors with $\sim7900$ pixels
each, where we calculate: (a) the linear correlation coefficient between the
anisotropy maps and the templates; (b) the coupling constants between the
specific intensity units of the templates and the antenna temperature at the
BEAST frequencies and (c) the individual foreground contributions to the BEAST
anisotropy maps. The peak sector contributions of the contaminants in the
Ka-band are of 56.5% free-free with a coupling constant of $8.3\pm0.4$
$\mu$K/R, and 67.4% dust with $45.0\pm2.0$ $\mu$K/(MJy/sr). In the Q-band the
corresponding values are of 64.4% free-free with $4.1\pm0.2$ $\mu$K/R and 67.5%
dust with $24.0\pm1.0$ $\mu$K/(MJy/sr). Using a lower limit of 10% in the
relative uncertainty of the coupling constants, we can constrain the sector
contributions of each contaminant in both maps to $< 20$% in 21 (free-free), 19
(dust) and 22 (synchrotron) sectors. At this level, all these sectors are found
outside of the $\mid$b$\mid = 14.6^\circ$ region. By performing the same
correlation analysis as a function of Galactic scale height, we conclude that
the region within $b=\pm17.5^{\circ}$ should be removed from the BEAST maps for
CMB studies in order to keep individual Galactic contributions below $\sim 1$%
of the map's rms.",0408385v1
2004-10-06,Constraining the Primordial Magnetic Field from Cosmic Microwave Background Anisotropies at Higher Multipoles,"The cosmological magnetic field is one of the important physical quantities
which affect strongly the cosmic microwave background (CMB) power spectrum.
Recent CMB observations have been extended to higher multipoles $l\gtrsim$1000,
and they resultantly exhibit an excess power than the standard model prediction
in cosmological theory which best fits the Wilkinson Microwave Anisotropy Probe
(WMAP) data at lower multipoles $l\lesssim$900. We calculate the CMB
temperature anisotropies generated by the power-law magnetic field at the last
scattering surface (LSS) in order to remove the tension between theory and
observation at higher multipoles and also place an upper limit on primordial
magnetic field. In our present calculation we take account of the effect of
ionization ratio exactly without approximation. This effect is very crucial to
precisely estimate the effect of the magnetic field on CMB power spectrum. We
consider both effects of the scalar and vector modes of magnetic field on the
CMB anisotropies, where current data are known to be insensitive to the tensor
mode which we ignore in the present study. In order to constrain the primordial
magnetic field, we evaluate likelihood function of the WMAP data in a wide
range of parameters of the magnetic field strength $|\mathbf{B}|_\lambda$ and
the power-law spectral index $n$, along with six cosmological parameters in
flat Universe models, using the technique of the Markov Chain Monte Carlo(MCMC)
method. We find that the upper limit at $2\sigma$ C.L. turns out to be
$|\mathbf{B}_\lambda|\lesssim 3.9 $nG at 1 Mpc for any $n_B$ values, which is
obtained by comparing the calculated result including the Sunyaev-Zeldovich(SZ)
effect with recent WMAP data of the CMB anisotropies.",0410142v3
2004-12-08,"Anisotropies in the Neutrino Fluxes and Heating Profiles in Two-dimensional, Time-dependent, Multi-group Radiation Hydrodynamics Simulations of Rotating Core-Collapse Supernovae","Using the 2D multi-group, flux-limited diffusion version of the code
VULCAN/2D, that also incorporates rotation, we have calculated the collapse,
bounce, shock formation, and early post-bounce evolutionary phases of a
core-collapse supernova for a variety of initial rotation rates. This is the
first series of such multi-group calculations undertaken in supernova theory
with fully multi-D tools. We find that though rotation generates
pole-to-equator angular anisotropies in the neutrino radiation fields, the
magnitude of the asymmetries is not as large as previously estimated. Moreover,
we find that the radiation field is always more spherically symmetric than the
matter distribution, with its plumes and convective eddies. We present the
dependence of the angular anisotropy of the neutrino fields on neutrino
species, neutrino energy, and initial rotation rate. Only for our most rapidly
rotating model do we start to see qualitatively different hydrodynamics, but
for the lower rates consistent with the pre-collapse rotational profiles
derived in the literature the anisotropies, though interesting, are modest.
This does not mean that rotation does not play a key role in supernova
dynamics. The decrease in the effective gravity due to the centripetal effect
can be quite important. Rather, it means that when a realistic mapping between
initial and final rotational profiles and 2D multi-group
radiation-hydrodynamics are incorporated into collapse simulations the
anisotropy of the radiation fields may be only a secondary, not a pivotal
factor, in the supernova mechanism.",0412187v3
2006-01-16,Kinematical and Dynamical Modeling of Elliptical Galaxies,"Elements of kinematical and dynamical modeling of elliptical galaxies (Es)
are presented. In projection, NFW models resemble Sersic models, but with a
very narrow range of shapes (m=3+/-1). The total density profile of Es cannot
be NFW-like because the predicted local M/L and aperture velocity dispersion
within an effective radius (Re) are much lower than observed. Stars must then
dominate Es out to a few Re. Fitting an NFW model to the total density profile
of Sersic+NFW (stars+dark matter [DM]) Es results in very high concentration
parameters, as found by X-ray observers. Kinematical modeling of Es assuming an
isotropic NFW DM model underestimates M/L at the virial radius by a factor of
1.6 to 2.4, because dissipationless LCDM halos have slightly different density
profiles and slightly radial velocity anisotropy. In N-body+gas simulations of
Es as merger remnants of spirals embedded in DM halos, the slope of the DM
density profile is steeper when the initial spiral galaxies are gas-rich. The
Hansen & Moore (2006) relation between anisotropy and the slope of the density
profile breaks down for gas and DM, but the stars follow an analogous relation
with slightly less radial anisotropies for a given density slope. Using
kurtosis (h_4) to infer anisotropy in Es is dangerous, as h_4 is also sensitive
to small levels of rotation. The stationary Jeans equation provides accurate
masses out to 8 Re. The discrepancy between the modeling of Romanowsky et al.
(2003), indicating a dearth of DM in Es, and the simulations analyzed by Dekel
et al. (2005), which match the spectroscopic observations of Es, is partly due
to radial anisotropy and to observing oblate Es face-on. However, one of the 15
solutions to the orbit modeling of Romanowsky et al. is found to have an amount
and concentration of DM consistent with LCDM predictions.",0601345v1
2007-03-20,"The SAURON project -- X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/sigma,epsilon) diagram with integral-field stellar kinematics","We analyse the orbital distribution of E and S0 galaxies using SAURON
integral-field stellar kinematics. We construct the anisotropy
(V/sigma,epsilon) diagram, for the 48 E/S0 galaxies from the SAURON survey. For
a subsample of 24 galaxies consistent with axisymmetry, we use three-integral
axisymmetric Schwarzschild dynamical models to recover the detailed orbital
distribution and we find good agreement with the anisotropy derived from the
(V/sigma,epsilon) diagram. In the companion Paper IX we show that the
early-type galaxies can be subdivided into two classes of systems with or
without a significant amount of specific stellar angular momentum. Here we show
that the two classes have different distributions on the (V/sigma,epsilon)
diagram. The slow rotators are more common among the most massive systems and
are generally classified as E from photometry alone. Those in our sample tend
to be fairly round (epsilon<0.3), but can have significant kinematical
misalignments, indicating that as a class they are moderately triaxial, and
span a range of anisotropies (delta<0.3). The fast rotators are generally
fainter and are classified either E or S0. They can appear quite flattened
(epsilon<0.7), do not show significant kinematical misalignments (unless barred
or interacting), indicating they are nearly axisymmetric, and span an even
larger range of anisotropies (delta<0.5). These results are confirmed when we
extend our analysis to 18 additional E/S0 galaxies observed with SAURON. All
these results support the idea that fast rotators are nearly oblate and contain
disk-like components. The role of gas must have been important for their
formation. The slow rotators are weakly triaxial. Current collisionless merger
models seem unable to explain their detailed observed properties. (Abridged)",0703533v1
1993-03-25,Influence of cubic and dipolar anisotropies on the static and dynamic coexistence anomalies of the time-dependent Ginzburg-Landau models,"In isotropic systems below the transition temperature, the massless Goldstone
modes imply critical infrared singularities in the statics and dynamics along
the entire coexistence curve. We examine the important question whether these
coexistence anomalies are of relevance also in more realistic systems
displaying anisotropies. By applying a generalized renormalization scheme to
the time-dependent Ginzburg-Landau models, we treat two quite different but
characteristic cases, namely the influence of (i) weak cubic anisotropies, and
(ii) long-range dipolar interactions. In the presence of cubic terms, the
transverse excitations acquire a mass and thus one expects the theory to
approach an uncritical ""Gaussian"" regime in the limit ${\vec q} \rightarrow 0$
and $\omega \rightarrow 0$. Therefore, we first consider the one-component case
in order to show that our formalism also provides a consistent description of
the crossover into an asymptotically Gaussian theory. In the case of (weak)
cubic anisotropies, the fact that for $n < 4$ the fluctuations tend to restore
the $O(n)$-symmetry at the critical point proves to be most important, since
under these circumstances coexistence-type singularities may be found in an
intermediate wavenumber and frequency range. The dipolar interaction induces an
anisotropy in momentum space, which does not completely destroy the massless
character of the transverse fluctuations, but only effectively reduces the
number of Goldstone modes by one. Remarkably, similar to the isotropic case the
asymptotic theory can be treated exactly. For $n \geq 3$ we find coexistence
anomalies governed by the isotropic power laws. However, the amplitudes of the
respective scaling functions depend on the angle between order parameter and
external wavevector.",9303044v1
2008-03-07,Giant Uniaxial Anisotropy in the Magnetic and Transport Properties of CePd5Al2,"Electrical resistivity rho, magnetic susceptibility chi, magnetization M and
specific heat measurements are reported on a singlecrystalline sample of
CePd5Al2, showing successive antiferromagnetic orderings at T_N1=4.1 K and
T_N2=2.9 K. The temperature dependence of T_N1 shows a Kondo metal behavior
with large anisotropy, rho_c/rho_a=3.2 at 20 K, and opening of a superzone gap
along the tetragona c-direction below T_N1. Both T_N1 and T_N2 gradually
increase with applying pressure up to 2.5 GPa. The data of chi(T) and M(B) in
the paramagnetic state were analyzed using a crystalline electric field (CEF)
model. It led to a Kramers doublet ground state with wave functions consisting
primarily of |+-5/2>, whose energy level is isolated from the excited states by
230 and 300 K. This CEF effect gives rise to the large anisotropy in the
paramagnetic state. In the ordered state, the uniaxial magnetic anisotropy is
manifested as M_c/M_a=20 in B=5 T and at 1.9 K, and chi_c/chi_a=25 in B=0.1 T
and at 4 K. This huge uniaxial magnetic anisotropy in the antiferromagnetic
states can be interpreted in terms of isotropic magnetic interaction among the
Ce^{3+} moments governed by the strong CEF. In powder neutron diffraction
experiments, magnetic reflections were observed owing to the antiferromagnetic
ordered states below T_N1, however, no additional reflection was found below
T_N2.",0803.1078v3
2008-06-13,The Large Scale Cosmic-Ray Anisotropy as Observed with Milagro,"Results are presented of a harmonic analysis of the large scale cosmic-ray
anisotropy as observed by the Milagro observatory. We show a two-dimensional
display of the sidereal anisotropy pro jections in right ascension generated by
the fitting of three harmonics to 18 separate declination bands. The Milagro
observatory is a water Cherenkov detector located in the Jemez mountains near
Los Alamos, New Mexico. With a high duty cycle and large field-of-view, Milagro
is an excellent instrument for measuring this anisotropy with high sensitivity
at TeV energies. The analysis is conducted using a seven year data sample
consisting of more than 95 billion events, the largest such data set in
existence. We observe an anisotropy with a magnitude around 0.1% for cosmic
rays with a median energy of 6 TeV. The dominant feature is a deficit region of
depth (2.49 +/- 0.02 stat. +/- 0.09 sys.)x10^(-3) in the direction of the
Galactic North Pole centered at 189 degrees right ascension. We observe a
steady increase in the magnitude of the signal over seven years.",0806.2293v2
2008-10-03,Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations,"We investigate the spectral shape, the anisotropy of the wave vector
distributions and the anisotropy of the amplitudes of the magnetic fluctuations
in the Earth's magnetosheath within a broad range of frequencies. We present
the first observations of a Kolmogorov-like inertial range of Alfvenic
fluctuations in the magnetosheath flanks, below fci. In the vicinity of fci, a
spectral break is observed, like in solar wind turbulence. Above the break, the
energy of compressive and Alfvenic fluctuations generally follow a power law
with a spectral index between -3 and -2. Concerning the anisotropy of the wave
vector distribution, we observe a change in its nature in the vicinity of ion
characteristic scales: if at MHD scales there is no evidence for a dominance of
a slab (k||>kperp) or 2D (kperp>k||) turbulence, above the spectral break,
(f>fci, kc/wpi>1) the 2D turbulence dominates. This 2D turbulence is observed
in six selected one-hour intervals among which the average proton beta varies
from 0.8 to 9. It is observed for both the transverse and compressive magnetic
fluctuations, independently on the presence of linearly unstable modes at low
frequencies or Alfven vortices at the spectral break. We then analyse the
anisotropy of the magnetic fluctuations in a time dependent reference frame
based on the field B and the flow velocity V directions. Within the range of
the 2D turbulence, at scales [1,30]kc/wpi, and for any beta we find that the
magnetic fluctuations at a given frequency in the plane perpendicular to B have
more energy along the BxV direction. This non-gyrotropy of the fluctuations is
consistent with gyrotropic fluctuations at a given wave vector, with kperp>k||,
which suffer a different Doppler shift along and perpendicular to V in the
plane perpendicular to B.",0810.0675v1
2009-03-26,Gamma-ray background anisotropy from galactic dark matter substructure,"Dark matter annihilation in galactic substructure would imprint
characteristic angular signatures on the all-sky map of the diffuse gamma-ray
background. We study the gamma-ray background anisotropy due to the subhalos
and discuss detectability at Fermi Gamma-ray Space Telescope. We derive
analytic formulae that enable to directly compute the angular power spectrum,
given parameters of subhalos. As our fiducial subhalo models, we adopt M^{-1.9}
mass spectrum, subhalos radial distribution suppressed towards the galactic
center, and luminosity profile of each subhalo dominated by its smooth
component. We find that, for multipole regime corresponding to \theta <~ 5 deg,
the angular power spectrum is dominated by a noise-like term, with suppression
due to internal structure of relevant subhalos. If the mass spectrum extends
down to Earth-mass scale, then the subhalos would be detected in the anisotropy
with Fermi at angular scales of ~10 deg, if their contribution to the gamma-ray
background is larger than ~20%. If the minimum mass is around 10^4 M_{sun}, on
the other hand, the relevant angular scale for detection is ~1 deg, and the
anisotropy detection requires that the subhalo contribution to the gamma-ray
background intensity is only ~4%. These can be achieved with a modest boost for
particle physics parameters. We also find that the anisotropy analysis could be
a more sensitive probe for the subhalos than individual detection. We also
study dependence on model parameters, where we reach the similar conclusions
for all the models investigated. The analytic approach should be very useful
when Fermi data are analyzed and the obtained angular power spectrum is
interpreted in terms of subhalo models.",0903.4685v2
2010-02-21,A nonlinear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma,"Weakly collisional plasmas dynamically develop pressure anisotropies with
respect to the magnetic field. These anisotropies trigger plasma instabilities
at scales just above the ion Larmor radius \rho_i and much below the mean free
path \lambda_{mfp}. They have growth rates of a fraction of the ion cyclotron
frequency - much faster than either the global dynamics or local turbulence.
The instabilities dramatically modify the transport properties and, therefore,
the macroscopic dynamics of the plasma. Their nonlinear evolution drives
pressure anisotropies towards marginal stability, controlled by the plasma beta
\beta_i. Here this nonlinear evolution is worked out for the simplest
analytically tractable example - the parallel firehose instability. In the
nonlinear regime, both analytical theory and the numerical solution predict
secular growth of magnetic fluctuations. They develop a k^{-3} spectrum,
extending from scales somewhat larger than \rho_i to the maximum scale that
grows secularly with time (~t^{1/2}); the relative pressure anisotropy
(\pperp-\ppar)/\ppar tends to the marginal value -2/\beta_i. The marginal state
is achieved via changes in the magnetic field, not particle scattering. When a
parallel ion heat flux is present, the firehose mutates into the new
gyrothermal instability (GTI), which continues to exist up to firehose-stable
values of pressure anisotropy, which can be positive and are limited by the
heat flux. The nonlinear evolution of the GTI also features secular growth of
magnetic fluctuations, but the spectrum is eventually dominated by modes around
the scale ~\rho_i l_T/\lambda_{mfp}, where l_T is the scale of the parallel
temperature variation. Implications for momentum and heat transport are
speculated about. This study is motivated by the dynamics of galaxy cluster
plasmas.",1002.4017v2
2010-04-01,Simulations of the cosmic infrared and submillimeter background for future large surveys: II. Removing the low-redshift contribution to the anisotropies using stacking,"Herschel and Planck are surveying the sky at unprecedented angular scales and
sensitivities over large areas. But both experiments are limited by source
confusion in the submillimeter. The high confusion noise in particular
restricts the study of the clustering properties of the sources that dominate
the cosmic infrared background. At these wavelengths, it is more appropriate to
consider the statistics of the unresolved component. In particular, high
clustering will contribute in excess of Poisson noise in the power spectra of
CIB anisotropies. These power spectra contain contributions from sources at all
redshift. We show how the stacking technique can be used to separate the
different redshift contributions to the power spectra. We use simulations of
CIB representative of realistic Spitzer, Herschel, Planck, and SCUBA-2
observations. We stack the 24um sources in longer wavelengths maps to measure
mean colors per redshift and flux bins. The information retrieved on the mean
spectral energy distribution obtained with the stacking technique is then used
to clean the maps, in particular to remove the contribution of low-redshift
undetected sources to the anisotropies. Using the stacking, we measure the mean
flux of populations 4 to 6 times fainter than the total noise at 350um at
redshifts z=1 and z=2, respectively, and as faint as 6 to 10 times fainter than
the total noise at 850um at the same redshifts. In the deep Spitzer fields, the
detected 24um sources up to z~2 contribute significantly to the submillimeter
anisotropies. We show that the method provides excellent (using COSMOS 24um
data) to good (using SWIRE 24um data) removal of the z<2 (COSMOS) and z<1
(SWIRE) anisotropies. Using this cleaning method, we then hope to have a set of
large maps dominated by high redshift galaxies for galaxy evolution study
(e.g., clustering, luminosity density).",1004.0123v1
2010-07-25,Searching for a Cosmological Preferred Axis: Union2 Data Analysis and Comparison with Other Probes,"We review, compare and extend recent studies searching for evidence for a
preferred cosmological axis. We start from the Union2 SnIa dataset and use the
hemisphere comparison method to search for a preferred axis in the data. We
find that the hemisphere of maximum accelerating expansion rate is in the
direction $(l,b)=({309^\circ}^{+23^\circ}_{-3^\circ},
{18^\circ}^{+11^\circ}_{-10^\circ})$ ($\omm=0.19$) while the hemisphere of
minimum acceleration is in the opposite direction
$(l,b)=({129^\circ}^{+23^\circ}_{-3^\circ},{-18^\circ}^{+10^\circ}_{-11^\circ})$
($\omm=0.30$). The level of anisotropy is described by the normalized
difference of the best fit values of $\omm$ between the two hemispheres in the
context of \lcdm fits. We find a maximum anisotropy level in the Union2 data of
$\frac{\Delta \ommax}{\bomm}=0.43\pm 0.06$. Such a level does not necessarily
correspond to statistically significant anisotropy because it is reproduced by
about $30%$ of simulated isotropic data mimicking the best fit Union2 dataset.
However, when combined with the axes directions of other cosmological
observations (bulk velocity flow axis, three axes of CMB low multipole moments
and quasar optical polarization alignment axis), the statistical evidence for a
cosmological anisotropy increases dramatically. We estimate the probability
that the above independent six axes directions would be so close in the sky to
be less than $1%$. Thus either the relative coincidence of these six axes is a
very large statistical fluctuation or there is an underlying physical or
systematic reason that leads to their correlation.",1007.4347v3
2010-10-26,Generic role of the anisotropic surface free energy on the morphological evolution in a strained-heteroepitaxial solid droplet on a rigid substrate,"A systematic study based on the self-consistent dynamical simulations is
presented for the spontaneous evolution of an isolated thin solid droplet on a
rigid substrate, which is driven by the surface drift diffusion induced by the
anisotropic capillary forces (surface stiffness) and mismatch stresses. In this
work, we studied the affect of surface free energy anisotropies on the
development kinetics of the 'Stranski-Krastanow' island type morphology. The
anisotropic surface free energy and the surface stiffness were treated with
well accepted trigonometric functions. Although, various tilt angles and
anisotropy constants were considered during simulations, the main emphasis was
given on the effect of rotational symmetries associated with the surface
Helmholtz free energy topography in 2D space. Our computer simulations revealed
the formation of an extremely thin wetting layer during the development of the
bell-shaped Stranski-Krastanow island through the mass accumulation at the
central region of the droplet via surface drift-diffusion. In the strong
(anomalous) anisotropy constant domain, we demonstrated the existence of two
distinct morphological modes: i) the complete stability of the initial
Cosine-shaped droplet just above a certain anisotropy constant threshold level
by spontaneous slight readjustments of the base and the height of the cluster;
ii) the Frank-van der Merwe mode of thin film formation for very large values
of the anisotropy constant by the spreading and coalescence of the droplets
over the substrate surface. During the course of the simulations, we have
continuously tracked both the morphology (i.e., the peak height, the extension
of the wetting layer beyond the domain boundaries, and the triple junction
contact angle) and energetic (the global Helmholtz free energy changes
associated with the total strain and surface energy variations) of the system.",1010.5363v1
2012-01-04,"Anisotropy of the irreversibility field for Zr-doped $(Y,Gd)Ba_2Cu_3O_{7-x}$ thin films up to 45T","The anisotropic irreversibility field B$_{Irr}$ of two $YBa_2Cu_3O_{7-x}$
thin films doped with additional rare earth (RE)=(Gd,Y) and Zr and containing
strong correlated pins (splayed BaZrO$_{3}$ nanorods, and $RE_2O_3$
nanoprecipitates), has been measured over a very broad range up to 45T at
temperatures 56 K<T<$T_c$. We found that the experimental angular dependence of
$B_{Irr}(\theta)$ does not follow the mass anisotropy scaling
$B_{Irr}(\theta)=B_{Irr}(0)(cos^2\theta+\gamma^{-2}sin^2\theta)^{-1/2}$, where
$\gamma=(m_c/m_{ab})^{1/2}=5-6$ for the RE-doped $YBa_2Cu_3O_{7-x}$ (REBCO)
crystals, m$_{ab}$ and m$_{c}$ are the effective masses along the ab plane and
the c-axis, respectively, and $\theta$ is the angle between B and the c-axis.
For B parallel to the ab-planes and to the c-axis correlated pinning strongly
enhances B$_{Irr}$, while at intermediate angles, $B_{Irr}(\theta)$ follows the
scaling behavior
$B_{Irr}(\theta)\propto(cos^2\theta+\gamma_{RP}^2sin^2\theta)^{1/2}$ with the
effective anisotropy factor $\gamma_{RP}\approx3$ significantly smaller than
the mass anisotropy would suggest. In spite of the strong effects of c-axis
BaZrO$_{3}$ nanorods, we found even greater enhancements of B$_{Irr}$ for
fields along the ab-planes than for fields parallel to the c-axis, as well as
different temperature dependences of the correlated pinning contributions to
B$_{Irr}$ for B//ab and B//c. Our results show that the dense and strong pins,
which can now be incorporated into REBCO thin films in a controlled way, exert
major and diverse effects on the measured vortex pinning anisotropy and the
irreversibility field over wide ranges of B and T. In particular, we show that
the relative contribution of correlated pinning to B$_{Irr}$ for B//c increases
as the temperature increases due to the suppression of thermal fluctuations of
vortices by splayed distribution of BaZrO$_{3}$ nanorods.",1201.1020v1
2012-05-10,The Near-IR Background Intensity and Anisotropies During The Epoch of Reionization,"A fraction of the extragalactic near-infrared (near-IR) background light
involves redshifted photons from the ultraviolet (UV) emission from galaxies
present during reionization at redshifts above 6. The absolute intensity and
the anisotropies of the near-IR background provide an observational probe of
the first-light galaxies and their spatial distribution. We estimate the
extragalactic background light intensity during reionization by accounting for
the stellar and nebular emission from first-light galaxies. We require the UV
photon density from these galaxies to generate a reionization history that is
consistent with the optical depth to electron scattering from cosmic microwave
background measurements. We also require the bright-end luminosity function of
galaxies in our models to reproduce the measured Lyman drop-out luminosity
functions at redshifts of 6 to 8. The absolute intensity is about 0.1 to 0.3 nW
m$^{-2}$ sr$^{-1}$ at the peak of its spectrum at $\sim$ 1.1 $\mu$m. We also
discuss the anisotropy power spectrum of the near-IR background using a halo
model to describe the galaxy distribution. We compare our predictions for the
anisotropy power spectrum to existing measurements from deep near-IR imaging
data from {\it Spitzer}/IRAC, {\it Hubble}/NICMOS, and {\it AKARI}. The
predicted rms fluctuations at tens of arcminute angular scales are roughly an
order of magnitude smaller than the existing measurements. While strong
arguments have been made that the measured fluctuations do not have an origin
involving faint low-redshift galaxies, we find that the existing measurements
are also incompatible with an origin during the era of reionization. The
measured near-IR background anisotropies remain unexplained and could be
associated with an unidentified non-astrophysical origin.",1205.2316v3
2012-05-31,Effect of temperature anisotropy on various modes and instabilities for a magnetized non-relativistic bi-Maxwellian plasma,"Using kinetic theory for homogeneous collisionless magnetized plasmas, we
present an extended review of the plasma waves and instabilities and discuss
the anisotropic response of generalized relativistic dielectric tensor and
Onsager symmetry properties for arbitrary distribution functions. In general,
we observe that for such plasmas only those electromagnetic modes whose
magnetic field perturbations are perpendicular to the ambient magneticeld,
i.e.,B1 \perp B0, are effected by the anisotropy. However, in oblique
propagation all modes do show such anisotropic effects. Considering the
non-relativistic bi-Maxwellian distribution and studying the relevant
components of the general dielectric tensor under appropriate conditions, we
derive the dispersion relations for various modes and instabilities. We show
that only the electromagnetic R- and L- waves, those derived from them and the
O-mode are affected by thermal anisotropies, since they satisfy the required
condition B1\perpB0. By contrast, the perpendicularly propagating X-mode and
the modes derived from it (the pure transverse X-mode and Bernstein mode) show
no such effect. In general, we note that the thermal anisotropy modifies the
parallel propagating modes via the parallel acoustic effect, while it modifies
the perpendicular propagating modes via the Larmor-radius effect. In oblique
propagation for kinetic Alfven waves, the thermal anisotropy affects the
kinetic regime more than it affects the inertial regime. The generalized fast
mode exhibits two distinct acoustic effects, one in the direction parallel to
the ambient magnetic field and the other in the direction perpendicular to it.
In the fast-mode instability, the magneto-sonic wave causes suppression of the
firehose instability. We discuss all these propagation characteristics and
present graphic illustrations.",1205.6896v1
2013-05-17,A large anisotropy in the sky distribution of 3CRR quasars and other radio galaxies,"We report the presence of large anisotropies in the sky distributions of
powerful extended quasars as well as some other sub-classes of radio galaxies
in the 3CRR survey, the most reliable and most intensively studied complete
sample of strong steep-spectrum radio sources. The anisotropies lie about a
plane passing through the equinoxes and the north celestial pole. Out of a
total of 48 quasars in the sample, 33 of them lie in one half of the observed
sky and the remaining 15 in the other half. The probability that in a random
distribution of 3CRR quasars in the sky, statistical fluctuations could give
rise to an asymmetry in observed numbers up to this level is only $\sim 1\%$.
Also only about 1/4th of Fanaroff-Riley 1 (FR1) type of radio galaxies lie in
the first half of the observed sky and the remainder in the second half. If we
include all the observed asymmetries in the sky distributions of quasars and
radio galaxies in the 3CRR sample, the probability of their occurrence by a
chance combination reduces to $\sim 2 \times 10^{-5}$. Two pertinent but
disturbing questions that could be raised here are -- firstly why should there
be such large anisotropies present in the sky distribution of some of the
strongest and most distant discrete sources, implying inhomogeneities in the
universe at very large scales (covering a fraction of the universe)? Secondly
why should such anisotropies lie about a great circle decided purely by the
orientation of earth's rotation axis and/or the axis of its revolution around
the sun? Are these alignments a mere coincidence or do they imply that these
axes have a preferential placement in the larger scheme of things, implying an
apparent breakdown of the Copernican principle or its more generalization,
cosmological principle, upon which the standard cosmological model is based
upon?",1305.4134v2
2013-07-31,Analytical families of 2-component anisotropic polytropes and their relativistic extensions,"In this paper, we study a family of two-component anisotropic polytropes
which model a wide range of spherically symmetric astrophysical systems such as
early-type baryonic galaxies. This family is found to contain a large class of
models such as the hypervirial family (which satisfy the virial theorem
locally), the Plummer and Hernquist models and Navarro-Frenk-White (NFW)-like
models. The potential--density pair for these models are derived, as well as
their velocity dispersions and anisotropy parameters. The projected quantities
are computed and found to reduce to analytical expressions in some cases. The
first section of this paper presents an extension of the two-term anisotropic
polytropes to encompass a very wide range of potential-density pairs. In the
next section, we present the general relativistic extension of the
potential-density pair, and calculate the stress-energy tensor, the
relativistic anisotropy parameter, the velocity of circular orbits and the
angular momentum. Remarkably, for the case of the hypervirial family, the
relativistic pressure in the Newtonian limit and the relativistic anisotropy
parameter are found to coincide with the corresponding Newtonian expressions.
The weak, dominant and strong energy conditions are found to be satisfied only
for a certain range of the free parameters. We show that the relativistic
hypervirial family also has a finite total mass like its Newtonian counterpart.
In the first appendix, a relativistic extension of a different hypervirial
family of models is studied, and the relativistic anisotropy parameter is found
to coincide with the Newtonian one. Finally, we present a family of models
obtained from our distribution function that are similar to the
Ossipkov-Merritt models; by computing their anisotropy parameters, we show that
they model systems with isotropic cores and radially anisotropic exteriors.",1307.8433v2
2013-08-05,Environments of Extended Radio Sources in the ATLBS Survey,"We present a study of the environments of extended radio sources in the
Australia Telescope Low Brightness Survey (ATLBS). The radio sources were
selected from the Extended Source Sample (ATLBS-ESS), which is a well defined
sample containing the most extended of radio sources in the ATLBS sky survey
regions. The environments were analyzed using 4-m CTIO Blanco telescope
observations carried out for ATLBS fields in the SDSS ${\rm r}^{\prime}$ band.
We have estimated the properties of the environments using smoothed density
maps derived from galaxy catalogs constructed using these optical imaging data.
The angular distribution of galaxy density relative to the axes of the radio
sources has been quantified by defining anisotropy parameters that are
estimated using a new method presented here. Examining the anisotropy
parameters for a sub-sample of extended double radio sources that includes all
sources with pronounced asymmetry in lobe extents, we find good evidence for
environmental anisotropy being the dominant cause for lobe asymmetry in that
higher galaxy density occurs almost always on the side of the shorter lobe, and
this validates the usefulness of the method proposed and adopted here. The
environmental anisotropy parameters have been used to examine and compare the
environments of FRI and FRII radio sources in two redshift regimes ($z<0.5$ and
$z>0.5$). Wide-angle tail sources and Head-tail sources lie in the most
overdense environments. The Head-tail source environments (for the HT sources
in our sample) display dipolar anisotropy in that higher galaxy density appears
to lie in the direction of the tails. Excluding the Head-tail and Wide-angle
tail sources, subsamples of FRI and FRII sources from the ATLBS survey appear
to lie in similar moderately overdense environments, with no evidence for
redshift evolution in the regimes studied herein.",1308.0884v1
2013-11-05,"Mass, velocity anisotropy, and pseudo phase-space density profiles of Abell 2142","Aim: We aim to compute the mass and velocity anisotropy profiles of Abell
2142 and, from there, the pseudo phase--space density profile $Q(r)$ and the
density slope - velocity anisotropy $\beta - \gamma$ relation, and then to
compare them with theoretical expectations. Methods: The mass profiles were
obtained by using three techniques based on member galaxy kinematics, namely
the caustic method, the method of Dispersion - Kurtosis, and MAMPOSSt. Through
the inversion of the Jeans equation, it was possible to compute the velocity
anisotropy profiles. Results: The mass profiles, as well as the virial values
of mass and radius, computed with the different techniques agree with one
another and with the estimates coming from X-ray and weak lensing studies. A
concordance mass profile is obtained by averaging the lensing, X-ray, and
kinematics determinations. The cluster mass profile is well fitted by an NFW
profile with $c=4.0 \pm 0.5$. The population of red and blue galaxies appear to
have a different velocity anisotropy configuration, since red galaxies are
almost isotropic, while blue galaxies are radially anisotropic, with a weak
dependence on radius. The $Q(r)$ profile for the red galaxy population agrees
with the theoretical results found in cosmological simulations, suggesting that
any bias, relative to the dark matter particles, in velocity dispersion of the
red component is independent of radius. The $\beta - \gamma$ relation for red
galaxies matches the theoretical relation only in the inner region. The
deviations might be due to the use of galaxies as tracers of the gravitational
potential, unlike the non--collisional tracer used in the theoretical relation.",1311.1210v4
2013-11-23,The effects of structure anisotropy on lensing observables in an exact general relativistic setting for precision cosmology,"The study of relativistic, higher order and nonlinear effects has become
necessary in recent years in the pursuit of precision cosmology. We develop and
apply here a framework to study gravitational lensing in exact models in
general relativity that are not restricted to homogeneity and isotropy, and
where full nonlinearity and relativistic effects are included. We apply the
framework to a specific, anisotropic galaxy cluster model which is based on a
modified NFW halo density profile and described by the Szekeres metric. We
examine the effects of increasing levels of anisotropy in the galaxy cluster on
lensing observables like the convergence and shear for various lensing
geometries, finding a strong nonlinear response in both the convergence and
shear for rays passing through anisotropic regions of the cluster. Deviation
from the expected values in a spherically symmetric structure are asymmetric
with respect to path direction and thus will persist as a statistical effect
when averaged over some ensemble of such clusters. The resulting relative
difference in various geometries can be as large as approximately 2%, 8%, and
24% in the measure of convergence for levels of anisotropy of 5%, 10%, and 15%,
respectively, as a fraction of total cluster mass. For the total magnitude of
shear, the relative difference can grow near the center of the structure to be
as large as 15%, 32%, and 44% for the same levels of anisotropy, averaged over
the two extreme geometries. The convergence is impacted most strongly for rays
which pass in directions along the axis of maximum dipole anisotropy in the
structure, while the shear is most strongly impacted for rays which pass in
directions orthogonal to this axis, as expected. These effects due to
anisotropic structures will affect lensing measurements and must be fully
examined in an era of precision cosmology.",1311.5936v2
2014-02-13,Trend of the magnetic anisotropy for individual Mn dopants near the (110) GaAs surface,"Using a microscopic finite-cluster tight-binding model, we investigate the
trend of the magnetic anisotropy energy as a function of the cluster size for
an individual Mn impurity positioned in the vicinity of the (110) GaAs
surface,We present results of calculations for large cluster sizes, containing
approximately 104 atoms, which have not been investigated so far. Our
calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs
found to be non-zero in previous tight-binding calculations, is purely a finite
size effect, and it vanishes as the inverse cluster size. In contrast to this,
we find that the splitting of the three in-gap Mn acceptor energy levels
converges to a finite value in the limit of infinite cluster size. For a Mn in
bulk GaAs this feature is related to the nature of the mean-field treatment of
the coupling between the impurity and its nearest neighbors atoms. Moreover, we
calculate the trend of the anisotropy energy in the sublayers, as the Mn dopant
is moved away from the surface towards the center of the cluster. Here the use
of large cluster sizes allows us to position the impurity in deeper sublayers
below the surface, compared to previous calculations. In particular, we show
that the anisotropy energy increases up to the fifth sublayer and then
decreases as the impurity is moved further away from the surface, approaching
its bulk value. The present study provides important insight for experimental
control and manipulation of the electronic and magnetic properties of
individual Mn dopants at the semiconductor surface by means of advanced
scanning tunneling microscopy techniques.",1402.3069v2
2014-03-18,Suppressing the impact of a high tensor-to-scalar ratio on the temperature anisotropies,"The BICEP2 collaboration has reported a strong B mode signal in the CMB
polarization, which is well fit by a tensor-to-scalar ratio of r ~ 0.2. This is
greater than the upper limit r < 0.11 obtained from the temperature
anisotropies under the assumption of a constant scalar spectral index n_s. This
discrepancy can be reduced once the statistical error and the contamination
from polarized dust are accounted for. If however a large value for r will be
confirmed, it will need to be reconciled with the temperature anisotropies
data. The most advocated explanation involves a variation of n_s with scales
(denoted as running) that has a magnitude significantly greater than the
generic slow roll predictions. We instead study the possibility that the large
scale temperature anisotropies are not enhanced because of a suppression of the
scalar power at large scales. Such a situation can be achieved for instance by
a sudden change of the speed of the inflaton (by about 14 %), and we show that
it fits the temperature anisotropies and polarization data considerably better
than a constant running (its chi^2 improves by ~ 7.5 over that of the constant
running, at the cost of one more parameter). We also consider the possibility
that the large scale temperature fluctuations are suppressed by an
anti-correlation between tensor and scalar modes. Unfortunately, while such
effect does affect the temperature fluctuations at large scales, it does not
affect the temperature power spectrum and cannot, therefore, help in
reconciling a large value of r with the limits from temperature fluctuations.",1403.4596v4
2014-07-08,On the Observation of the Cosmic Ray Anisotropy below 10$^{15}$ eV,"The measurement of the anisotropy in the arrival direction of cosmic rays is
complementary to the study of their energy spectrum and chemical composition to
understand their origin and propagation. It is also a tool to probe the
structure of the magnetic fields through which cosmic rays travel. As cosmic
rays are mostly charged nuclei, their trajectories are deflected by the action
of galactic magnetic field they propagate through before reaching the Earth
atmosphere, so that their detection carries directional information only up to
distances as large as their gyro-radius. If cosmic rays below
$10^{15}{\rm\,eV}$ are considered and the local galactic magnetic field
($\sim3{\rm\,\mu G}$) is accounted for, gyro-radii are so short that isotropy
is expected. At most, a weak di-polar distribution may exist, reflecting the
contribution of the closest CR sources. However, a number of experiments
observed an energy-dependent \emph{""large scale""} anisotropy in the sidereal
time frame with an amplitude of about 10$^{-4}$ - 10$^{-3}$, revealing the
existence of two distinct broad regions: an excess distributed around
40$^{\circ}$ to 90$^{\circ}$ in Right Ascension (commonly referred to as
""tail.in"" excess) and a deficit (the ""loss cone"") around 150$^{\circ}$ to
240$^{\circ}$ in Right Ascension. In recent years the Milagro and ARGO-YBJ
collaborations reported the of a ""medium"" scale anisotropy inside the tail-in
region. The observation of such small features has been recently claimed by the
IceCube experiment also in the Southern hemisphere. So far, no theory of cosmic
rays in the Galaxy exists which is able to explain the origin of these
different anisotropies leaving the standard model of cosmic rays and that of
the galactic magnetic field unchanged at the same time.",1407.2144v1
2014-10-22,On the Anisotropic Nature of MRI-Driven Turbulence in Astrophysical Disks,"The magnetorotational instability is thought to play an important role in
enabling accretion in sufficiently ionized astrophysical disks. The rate at
which MRI-driven turbulence transports angular momentum is related to both the
strength of the amplitudes of the fluctuations on various scales and the degree
of anisotropy of the underlying turbulence. This has motivated several studies
of the distribution of turbulent power in spectral space. In this paper, we
investigate the anisotropic nature of MRI-driven turbulence using a
pseudo-spectral code and introduce novel ways to robustly characterize the
underlying turbulence. We show that the general flow properties vary in a
quasi-periodic way on timescales comparable to 10 inverse angular frequencies
motivating the temporal analysis of its anisotropy. We introduce a 3D tensor
invariant analysis to quantify and classify the evolution of the anisotropic
turbulent flow. This analysis shows a continuous high level of anisotropy, with
brief sporadic transitions towards two- and three-component isotropic turbulent
flow. This temporal-dependent anisotropy renders standard shell-average,
especially when used simultaneously with long temporal averages, inadequate for
characterizing MRI-driven turbulence. We propose an alternative way to extract
spectral information from the turbulent magnetized flow, whose anisotropic
character depends strongly on time. This consists of stacking 1D Fourier
spectra along three orthogonal directions that exhibit maximum anisotropy in
Fourier space. The resulting averaged spectra show that the power along each of
the three independent directions differs by several orders of magnitude over
most scales, except the largest ones. Our results suggest that a
first-principles theory to describe fully developed MRI-driven turbulence will
likely have to consider the anisotropic nature of the flow at a fundamental
level.",1410.6196v1
2014-11-11,Electron-vibron coupling effects on electron transport via a single-molecule magnet,"We investigate how the electron-vibron coupling influences electron transport
via an anisotropic magnetic molecule, such as a single-molecule magnet (SMM)
Fe$_4$, by using a model Hamiltonian with parameter values obtained from
density-functional theory (DFT). Magnetic anisotropy parameters, vibrational
energies, and electron-vibron coupling strengths of the Fe$_4$ are computed
using DFT. A giant spin model is applied to the Fe$_4$ with only two charge
states, specifically a neutral state with the total spin $S=5$ and a singly
charged state with $S=9/2$, which is consistent with our DFT result and
experiments on Fe$_4$ single-molecule transistors. In sequential electron
tunneling, we find that the magnetic anisotropy gives rise to new features in
conductance peaks arising from vibrational excitations. In particular, the peak
height shows a strong, unusual dependence on the direction as well as magnitude
of applied B field. The magnetic anisotropy also introduces vibrational
satellite peaks whose position and height are modified with the direction and
magnitude of applied B field. Furthermore, when multiple vibrational modes with
considerable electron-vibron coupling have energies close to one another, a
low-bias current is suppressed, independently of gate voltage and applied B
field, although that is not the case for a single mode with the similar
electron-vibron coupling. In the former case, the conductance peaks reveal a
stronger B-field dependence than in the latter case. The new features appear
because the magnetic anisotropy barrier is of the same order of magnitude as
the energies of vibrational modes with significant electron-vibron coupling.
Our findings clearly show the interesting interplay between magnetic anisotropy
and electron-vibron coupling in electron transport via the Fe$_4$. The similar
behavior can be observed in transport via other anisotropic magnetic molecules.",1411.2677v1
2014-12-15,Isotropy constraints on powerful sources of ultrahigh-energy cosmic rays at $10^{19}$ eV,"Anisotropy in the arrival direction distribution of ultrahigh-energy cosmic
rays (UHECRs) produced by powerful sources is numerically evaluated. We show
that, taking account of the Galactic magnetic field, nondetection of
significant anisotropy at $\approx 10^{19}$ eV at present and in future
experiments imposes general upper limits on UHECR proton luminosity of steady
sources as a function of source redshifts. The upper limits constrain the
existence of typical steady sources in the local universe and limit the local
density of $10^{19}$ eV UHECR sources to be $\gtrsim 10^{-3}$ Mpc$^{-3},$
assuming average intergalactic magnetic fields less than $10^{-9}$ G. This
isotropy, which is stronger than measured at the highest energies, may indicate
the transient generation of UHECRs. Our anisotropy calculations are applied for
extreme high-frequency-peaked BL Lac objects 1ES 0229+200, 1ES 1101-232, and
1ES 0347-121, to test the UHECR-induced cascade model, in which beamed UHECR
protons generate TeV radiation in transit from sources. While the
magnetic-field structure surrounding the sources affects the required absolute
cosmic-ray luminosity of the blazars, the magnetic-field structure surrounding
the Milky Way directly affects the observed anisotropy. If both of the magnetic
fields are weak enough, significant UHECR anisotropy from these blazars should
be detectable by the Pierre Auger Observatory unless the maximum energy of
UHECR protons is well below $10^{19}$ eV. Furthermore, if these are the sources
of UHECRs above $10^{19}$ eV, a local magnetic structure surrounding the Milky
Way is needed to explain the observed isotropy at $\sim 10^{19}$ eV, which may
be incompatible with large magnetic structures around all galaxies for the
UHECR-induced cascade model to work with reasonable jet powers.",1412.4716v3
2015-03-09,I-Love-Q anisotropically: Universal relations for compact stars with scalar pressure anisotropy,"Certain physical quantities that characterize neutron stars and quark stars
(e.g. their mass, spin angular momentum and quadrupole moment) are interrelated
in a way that is approximately insensitive to their internal structure. Such
approximately universal relations are useful to break degeneracies in data
analysis for future radio, X-ray and gravitational wave observations. Although
the pressure inside compact stars is most likely nearly isotropic, certain
scenarios have been put forth that suggest otherwise, for example due to phase
transitions. We here investigate whether pressure anisotropy affects the
approximate universal relations and whether it prevents their use in future
observations. We achieve this by numerically constructing slowly-rotating and
tidally-deformed, anisotropic, compact stars in General Relativity to third
order in spin. We find that anisotropy affects the universal relations only
weakly; the relations become less universal by a factor of 1.5-3 relative to
the isotropic case, but remain approximately universal to 10%. We succeed in
explaining this increase in variability as an increase in the eccentricity
variation of isodensity contours, which provides further support for the
emergent approximate symmetry explanation of universality. Anisotropy does not
affect the universal relations to a sufficient level to prevent their use in
gravitational wave astrophysics or in experimental relativity. We provide an
explicit example of the latter in dynamical Chern-Simons gravity. The increase
in variability of the universal relations due to pressure anisotropy could
affect their use in future X-ray observations. Given expected observational
uncertainties, however, the relations remain sufficiently universal for use in
such observations if the anisotropic modifications to the moment of inertia and
the quadrupole moment are less than 10% of their isotropic values.",1503.02726v2
2016-08-15,"Physical properties of single crystalline $R$Mg$_{2}$Cu$_{9}$ ($R$ = Y, Ce-Nd, Gd-Dy, Yb) and the search for in-plane magnetic anisotropy in hexagonal systems","Single crystals of $R$Mg$_{2}$Cu$_{9}$ ($R$=Y, Ce-Nd, Gd-Dy, Yb) were grown
using a high-temperature solution growth technique and were characterized by
measurements of room-temperature x-ray diffraction, temperature-dependent
specific heat and temperature-, field-dependent resistivity and anisotropic
magnetization. YMg$_{2}$Cu$_{9}$ is a non-local-moment-bearing metal with an
electronic specific heat coefficient, $\gamma \sim$ 15 mJ/mol K$^2$. Yb is
divalent and basically non-moment bearing in YbMg$_{2}$Cu$_{9}$. Ce is
trivalent in CeMg$_{2}$Cu$_{9}$ with two magnetic transitions being observed at
2.1 K and 1.5 K. PrMg$_{2}$Cu$_{9}$ does not exhibit any magnetic phase
transition down to 0.5 K. The other members being studied ($R$=Nd, Gd-Dy) all
exhibits antiferromagnetic transitions at low-temperatures ranging from 3.2 K
for NdMg$_{2}$Cu$_{9}$ to 11.9 K for TbMg$_{2}$Cu$_{9}$. Whereas
GdMg$_{2}$Cu$_{9}$ is isotropic in its paramagnetic state due to zero angular
momentum ($L$=0), all the other local-moment-bearing members manifest an
anisotropic, planar magnetization in their paramagnetic states. To further
study this planar anisotropy, detailed angular-dependent magnetization was
carried out on magnetically diluted (Y$_{0.99}$Tb$_{0.01}$)Mg$_{2}$Cu$_{9}$ and
(Y$_{0.99}$Dy$_{0.01}$)Mg$_{2}$Cu$_{9}$. Despite the strong, planar
magnetization anisotropy, the in-plane magnetic anisotropy is weak and
field-dependent. A set of crystal electric field parameters are proposed to
explain the observed magnetic anisotropy.",1608.04310v1
2017-05-16,A novel JEAnS analysis of the Fornax dwarf using evolutionary algorithms: mass follows light with signs of an off-centre merger,"Dwarf galaxies, among the most dark matter dominated structures of our
universe, are excellent test-beds for dark matter theories. Unfortunately, mass
modelling of these systems suffers from the well documented mass-velocity
anisotropy degeneracy. For the case of spherically symmetric systems, we
describe a method for non-parametric modelling of the radial and tangential
velocity moments. The method is a numerical velocity anisotropy ""inversion"",
with parametric mass models, where the radial velocity dispersion profile,
$\sigma_{\mathrm{rr}}^2$ is modeled as a B-spline, and the optimization is a
three step process that consists of: (i) an Evolutionary modelling to determine
the mass model form and the best B-spline basis to represent
$\sigma_{\mathrm{rr}}^2$; (ii) an optimization of the smoothing parameters;
(iii) a Markov chain Monte Carlo analysis to determine the physical parameters.
The mass-anisotropy degeneracy is reduced into mass model inference,
irrespective of kinematics. We test our method using synthetic data. Our
algorithm constructs the best kinematic profile and discriminates between
competing dark matter models. We apply our method to the Fornax dwarf
spheroidal galaxy. Using a King brightness profile and testing various dark
matter mass models, our model inference favours a simple mass-follows-light
system. We find that the anisotropy profile of Fornax is tangential ($\beta(r)
< 0$) and we estimate a total mass of $M_{\text{tot}} = 1.613
^{+0.050}_{-0.075} \times 10^8 \, \text{M}_{\odot}$, and a mass-to-light ratio
of $\Upsilon_V = 8.93 ^{+0.32}_{-0.47} \, (\text{M}_{\odot}/\text{L}_{\odot})$.
The algorithm we present is a robust and computationally inexpensive method for
non-parametric modelling of spherical clusters independent of the
mass-anisotropy degeneracy.",1705.05724v1
2017-08-13,PIC Simulations of Velocity-Space Instabilities in a Decreasing Magnetic Field: Viscosity and Thermal Conduction,"We use particle-in-cell (PIC) simulations of a collisionless, electron-ion
plasma with a decreasing background magnetic field, $B$, to study the effect of
velocity-space instabilities on the viscous heating and thermal conduction of
the plasma. If $B$ decreases, the adiabatic invariance of the magnetic moment
gives rise to pressure anisotropies with $p_{||,j} > p_{\perp,j}$ ($p_{||,j}$
and $p_{\perp,j}$ represent the pressure of species $j$ ($=i$ or $e$) parallel
and perpendicular to the magnetic field). Linear theory indicates that, for
sufficiently large anisotropies, different velocity-space instabilities can be
triggered. These instabilities, which grow on scales comparable to the electron
and ion Larmor radii, in principle have the ability to pitch-angle scatter the
particles, limiting the growth of the anisotropies. Our PIC simulations focus
on the nonlinear, saturated regime of the instabilities. This is done through
the permanent decrease of the magnetic field by an imposed shear in the plasma.
Our results show that, in the regime $2 \lesssim \beta_j \lesssim 20$ ($\beta_j
\equiv 8\pi p_j/B^2$), the saturated ion and electron pressure anisotropies are
controlled by the combined effect of the oblique ion firehose (OIF) and the
fast magnetosonic/whistler (FM/W) instabilities. These instabilities grow
preferentially on the ion Larmor radius scale, and make the ion and electron
pressure anisotropies nearly equal: $\Delta p_e/p_{||,e} \approx \Delta
p_i/p_{||,i}$ (where $\Delta p_j=p_{\perp,j} - p_{||,j}$). We also quantify the
thermal conduction of the plasma by directly calculating the mean free path of
electrons along the mean magnetic field, which we find strongly depends on
whether $B$ decreases or increases. Our results can be applied in studies of
low collisionality plasmas such as the solar wind, the intracluster medium, and
some accretion disks around black holes.",1708.03926v2
2017-10-05,Planck 2015 constraints on the non-flat XCDM inflation model,"We study Planck 2015 cosmic microwave background (CMB) anisotropy data using
the energy density inhomogeneity power spectrum generated by quantum
fluctuations during an early epoch of inflation in the non-flat XCDM model.
Here dark energy is parameterized using a fluid with a negative equation of
state parameter but with the speed of fluid acoustic inhomogeneities set to the
speed of light. We use this simple parameterization of dynamical dark energy,
that is relatively straightforward to use in a computation, in a first attempt
to gain some insight into how dark energy dynamics and non-zero spatial
curvature jointly affect the CMB anisotropy data constraints. Unlike earlier
analyses of non-flat models, we use a physically consistent power spectrum for
energy density inhomogeneities. We find that the Planck 2015 data in
conjunction with baryon acoustic oscillation measurements are reasonably well
fit by a closed XCDM model in which spatial curvature contributes a percent of
the current cosmological energy density budget. In this model, the measured
Hubble constant and non-relativistic matter density parameter are in good
agreement with values determined using most other data. Depending on parameter
values, the closed XCDM model has reduced power, relative to the tilted,
spatially-flat $\Lambda$CDM case, and appears to partially alleviate the low
multipole CMB temperature anisotropy deficit and can help partially reconcile
the CMB anisotropy and weak lensing $\sigma_8$ constraints, at the expense of
somewhat worsening the fit to higher multipole CMB temperature anisotropy data.
However, the closed XCDM inflation model does not seem to improve the agreement
much, if at all, compared to the closed $\Lambda$CDM inflation case, even
though it has one more free parameter. Our results are interesting but
tentative; a more thorough analysis is needed to properly gauge their
significance.",1710.03271v2
2017-10-09,Influence of classical anisotropy fields on the properties of Heisenberg antiferromagnets within unified molecular field theory,"A comprehensive study of the influence of classical anisotropy fields on the
magnetic properties of Heisenberg antiferromagnets within unified molecular
field theory versus temperature T, magnetic field H, and anisotropy field
parameter hA1 is presented for systems comprised of identical
crystallographically-equivalent local moments. The anisotropy field for
collinear z-axis antiferromagnetic (AFM) ordering is constructed so that it is
aligned in the direction of each ordered and/or field-induced thermal-average
moment with a magnitude proportional to the moment, whereas that for XY
anisotropy is defined to be in the direction of the projection of the moment
onto the xy plane, again with a magnitude proportional to the moment.
Properties studied include the zero-field Neel temperature TN, ordered moment,
heat capacity and anisotropic magnetic susceptibility of the AFM phase versus T
with moments aligned either along the z axis or in the xy plane. Also
determined are the high-field magnetization perpendicular to the axis or plane
of collinear or planar noncollinear AFM ordering, the high-field magnetization
along the z axis of a collinear z-axis AFM, spin-flop (SF), and paramagnetic
(PM) phases, and the free energies of these phases versus T, H, and hA1. Phase
diagrams at T = 0 in the Hz-hA1 plane and at T > 0 in the Hz-T plane are
constructed for spins S = 1/2. For hA1 = 0 the SF phase is stable at low field
and the PM phase at high field with no AFM phase present. As hA1 increases, the
phase diagram contains the AFM, SF and PM phases. Further increases in hA1 lead
to the disappearance of the SF phase and the appearance of a tricritical point
on the AFM-PM transition curve. Applications of the theory to extract hA1 from
experimental low-field magnetic susceptibility data and high-field
magnetization versus field isotherms for single crystals of AFMs are discussed.",1710.03750v1
2017-11-21,Thickness-dependence of the Dzyaloshinskii-Moriya interaction in Co2FeAl ultrathin films: effects of the annealing temperature and the heavy metal material,"Interfacial Dzyaloshinskii-Moriya interaction (iDMI) has been investigated in
Co2FeAl (CFA) ultrathin films of various thicknesses (0.8 nm<tCFA<2 nm) grown
on Si substrates, using Pt, W, Ir and MgO buffer or/and capping layers.
Vibrating sample magnetometry revealed that magnetization at saturation (Ms)
for the Pt and Ir buffered films is higher than the usual Ms of CFA due to the
proximity induced magnetization (PIM) in Ir and Pt, estimated to be 19% and
27%, respectively. The presence of PIM in these materials is confirmed using
x-ray resonant magnetic reflectivity. Moreover, while no PIM is induced in W,
higher PIM is obtained with Pt when it is used as buffer layer rather than
capping layer. Brillouin light scattering (BLS) in the Damon-Eshbach geometry
has been used to investigate iDMI constants and the perpendicular anisotropy
field versus the annealing temperature. The DMI sign has been found to be
negative for Pt/CFA and Ir/CFA while it is positive for W/CFA. The thickness
dependence of the effective iDMI constant for stacks involving Pt and W shows
the existence of two regimes similarly to that of the perpendicular anisotropy
constant due to the degradation of the interfaces as the CFA thickness
approaches the nanometer. The surface iDMI and anisotropy constants of each
stack have been determined for the thickest samples where a linear thickness
dependence of the effective iDMI constant and the effective magnetization has
been observed. The interface anisotropy and iDMI constants, investigated for
Pt/CFA/MgO system, showed different trends with the annealing temperature. The
decrease of iDMI constant with increasing annealing temperature is probably due
to the electronic structure changes at the interfaces, while the increase of
the interface anisotropy constant is coherent the interface quality and
disorder enhancement.",1711.07776v1
2017-12-05,Accurate estimation of microscopic diffusion anisotropy and its time dependence in the mouse brain,"Microscopic diffusion anisotropy ({\mu}A) has been recently gaining
increasing attention for its ability to decouple the average compartment
anisotropy from orientation dispersion. Advanced diffusion MRI sequences, such
as double diffusion encoding (DDE) and double oscillating diffusion encoding
(DODE) have been used for mapping {\mu}A. However, the time-dependence of
{\mu}A has not been investigated insofar, and furthermore, the accuracy of
{\mu}A estimation vis-\`a-vis different b-values was not assessed. Here, we
investigate both these concepts using theory, simulation, and experiments in
the mouse brain. In the first part, simulations and experimental results show
that the conventional estimation of microscopic anisotropy from the difference
of D(O)DE sequences with parallel and orthogonal gradient directions yields
values that highly depend on the choice of b-value. To mitigate this
undesirable bias, we propose a multi-shell approach that harnesses a polynomial
fit of the signal difference up to third order terms in b-value. In
simulations, this approach yields more accurate {\mu}A metrics, which are
similar to the ground truth values. The second part of this work uses the
proposed multi-shell method to estimate the time/frequency dependence of
{\mu}A. The data shows either an increase or no change in {\mu}A with frequency
depending on the region of interest, both in white and gray matter. When
comparing the experimental results with simulations, it emerges that simple
geometric models such as infinite cylinders with either negligible or finite
radii cannot replicate the measured trend, and more complex models, which, for
example, incorporate structure along the fibre direction are required. Thus,
measuring the time dependence of microscopic anisotropy can provide valuable
information for characterizing tissue microstructure.",1712.01954v2
2018-02-27,Extracting foreground-obscured $μ$-distortion anisotropies to constrain primordial non-Gaussianity,"Correlations between cosmic microwave background (CMB) temperature,
polarization and spectral distortion anisotropies can be used as a probe of
primordial non-Gaussianity. Here, we perform a reconstruction of
$\mu$-distortion anisotropies in the presence of Galactic and extragalactic
foregrounds, applying the so-called Constrained ILC component separation method
to simulations of proposed CMB space missions (PIXIE, LiteBIRD, CORE, PICO).
Our sky simulations include Galactic dust, Galactic synchrotron, Galactic
free-free, thermal Sunyaev-Zeldovich effect, as well as primary CMB temperature
and $\mu$-distortion anisotropies, the latter being added as correlated field.
The Constrained ILC method allows us to null the CMB temperature anisotropies
in the reconstructed $\mu$-map (and vice versa), in addition to mitigating the
contaminations from astrophysical foregrounds and instrumental noise. We
compute the cross-power spectrum between the reconstructed (CMB-free)
$\mu$-distortion map and the ($\mu$-free) CMB temperature map, after foreground
removal and component separation. Since the cross-power spectrum is
proportional to the primordial non-Gaussianity parameter, $f_{\rm NL}$, on
scales $k\simeq 740$ Mpc$^{-1}$, this allows us to derive $f_{\rm
NL}$-detection limits for the aforementioned future CMB experiments. Our
analysis shows that foregrounds degrade the theoretical detection limits (based
mostly on instrumental noise) by more than one order of magnitude, with PICO
standing the best chance at placing upper limits on scale-dependent
non-Gaussianity. We also discuss the dependence of the constraints on the
channel sensitivities and chosen bands. Like for $B$-mode polarization
measurements, extended coverage at frequencies $\nu\lesssim 40\,{\rm GHz}$ and
$\nu\gtrsim 400\,{\rm GHz}$ provides more leverage than increased channel
sensitivity.",1802.10101v2
2018-03-02,Multi-messenger constraints to the local emission of cosmic-ray electrons,"The data on the inclusive flux of cosmic positrons and electrons
($e^++e^{-}$) have been recently collected from GeV to tens of TeV energies by
several experiments with unprecedented precision. In addition, the Fermi-LAT
Collaboration has provided a new energy spectrum for the upper bounds on the
$e^++e^{-}$ dipole anisotropy. This observable can bring information on the
emission from local Galactic sources, notably measured with high precision at
radio frequencies. We develop a framework in which $e^-$ and $e^+$ measured at
Earth from GeV up to tens of TeV energies have a composite origin. A dedicated
analysis is deserved to Vela YZ and Cygnus Loop Supernova Remnants (SNRs), for
which we consider two different models for the injection of $e^-$. We
investigate the consistency of these models using the three physical
observables: the radio flux from Vela YZ and Cygnus Loop at all the available
frequencies, the $e^++e^-$ flux from five experiments from the GeV to tens of
TeV energy, the $e^++e^-$ dipole anisotropy upper limits from 50 GeV to about 1
TeV. We find that the radio flux for these nearby SNRs strongly constraints the
properties of the injection electron spectrum, partially compatible with the
looser constraints derived from the $e^+ + e^-$ flux data. We also perform a
multi-wavelength multi-messenger analysis by fitting simultaneously the radio
flux on Vela YZ and Cygnus Loop and the $e^+ + e^-$ flux, and checking the
outputs against the $e^+ + e^-$ dipole anisotropy data. Remarkably, we find a
model which is compatible with all the $e^++e^-$ flux data, the radio data for
Vela YZ and Cygnus Loop, and with the anisotropy upper bounds. We show the
severe constraints imposed by the most recent data on the $e^+ + e^-$ dipole
anisotropy.",1803.01009v3
2018-05-22,Exploring compensated isocurvature perturbations with CMB spectral distortion anisotropies,"We develop a linear perturbation theory for the spectral $y$-distortions of
the cosmic microwave background (CMB). The $y$-distortions generated during the
recombination epoch are usually negligible because the energy transfer due to
the Compton scattering is strongly suppressed at that time, but they can be
significant if there is a considerable amount of compensated isocurvature
perturbation (CIP), which is not tightly constrained from the present CMB
observations. The linear $y$-distortions explicitly depend on the baryon
density fluctuations, therefore $y$ anisotropies can completely resolve the
degeneracy between the baryon isocurvature perturbations and the cold dark
matter ones. This novel method is free from lensing contaminations that can
affect the previous approach to the CIPs based on the nonlinear modulation of
the CMB anisotropies. We compute the cross correlation functions of the
$y$-distortions with the CMB temperature and the $E$ mode polarization
anisotropies. They are sensitive to the correlated CIPs parameterized by
$f'\equiv\mathcal P_{\rm CIP\zeta}/\mathcal P_{\zeta \zeta}$ with $\mathcal
P_{\zeta \zeta}$ and $\mathcal P_{\rm CIP\zeta}$ being the auto correlation of
the adiabatic perturbations and the cross correlation between them and the
CIPs. We investigate how well the $y$ anisotropies will constrain $f'$ in
future observations such as those provided by a PIXIE-like and a PRISM-like
survey, LiteBIRD and a cosmic variance limited (CVL) survey, taking into
account the degradation in constraining power due to the presence of Sunyaev
Zel'dovich effect from galaxy clusters. For example, our forecasts show that it
is possible to achieve an upper limit of $f'< 2 \times 10^{5}$ at 68% C.L. with
LiteBIRD, and $f'<2\times 10^{4}$ with CVL observations.",1805.08773v3
2018-06-27,"Cosmic ray short burst observed with the Global Muon Detector Network (GMDN) on June 22, 2015","We analyze the short cosmic ray intensity increase (""cosmic ray burst"": CRB)
on June 22, 2015 utilizing a global network of muon detectors and derive the
global anisotropy of cosmic ray intensity and the density (i.e. the
omnidirectional intensity) with 10-minute time resolution. We find that the CRB
was caused by a local density maximum and an enhanced anisotropy of cosmic rays
both of which appeared in association with Earth's crossing of the heliospheric
current sheet (HCS). This enhanced anisotropy was normal to the HCS and
consistent with a diamagnetic drift arising from the spatial gradient of cosmic
ray density, which indicates that cosmic rays were drifting along the HCS from
the north of Earth. We also find a significant anisotropy along the HCS,
lasting a few hours after the HCS crossing, indicating that cosmic rays
penetrated into the inner heliosphere along the HCS. Based on the latest
geomagnetic field model, we quantitatively evaluate the reduction of the
geomagnetic cut-off rigidity and the variation of the asymptotic viewing
direction of cosmic rays due to a major geomagnetic storm which occurred during
the CRB and conclude that the CRB is not caused by the geomagnetic storm, but
by a rapid change in the cosmic ray anisotropy and density outside the
magnetosphere.",1806.10601v1
2018-08-27,Magic angle effects in a trigonal Mn(III)3 cluster: deconstruction of a single-molecule magnet,"We present angle-dependent high-frequency EPR studies on a single-crystal of
a trigonal Mn3 cluster with an unusual structure in which the local magnetic
easy-axes of the constituent Mn(III) ions are tilted significantly away from
the molecular C3 axis towards the magic-angle of 54.7 degrees, resulting in an
almost complete cancelation of the 2nd-order axial magnetic anisotropy
associated with the ferromagnetically coupled total spin ST = 6 ground state.
This contrasts the situation in many related Mn3 single-molecule magnets (SMMs)
that have been studied intensively in the past, for which the local MnIII
anisotropy tensors are reasonably parallel, resulting in substantial barriers
to magnetization relaxation (Ueff = 30 to 35 cm 1) and magnetization blocking
below about 2.5 K. The suppression of the 2nd-order anisotropy in the present
case results in a situation in which the zero-field splitting (ZFS) of the ST =
6 ground state is dominated by 4th- and higher-order interactions. This
provides a unique opportunity to study in depth how molecular geometry
influences these interactions that are responsible for quantum tunneling of
magnetization in high-symmetry SMMs. Angle-dependent EPR measurements provide a
full mapping of the molecular magneto-anisotropy. Meanwhile, irreducible tensor
operator (ITO) methods are employed in order to obtain analytic expressions
that directly relate molecular anisotropy to the microscopic physics, i.e., the
ZFS tensors associated with the individual MnIII ions, their orientations, and
the exchange coupling between the three spins. We find that the magic-angle
tilting leads to a massive compression of the ST = 6 ground state energy level
diagram and strong mixing between spin projection states. Although these
characteristics are antagonistic to SMM behavior, they provide important
insights into the physics of polynuclear molecular nanomagnets.",1808.08922v1
2018-09-04,Dynamics of cardiac re-entry in micro-CT and serial histological sections based models of mammalian hearts,"Cardiac re-entry regime of self-organised abnormal synchronisation underlie
dangerous arrhythmias and fatal fibrillation. Recent advances in the theory of
dissipative vortices, experimental studies, and anatomically realistic computer
simulations, elucidated the role of cardiac re-entry interaction with fine
anatomical features in the heart, and anatomy induced drift. The fact that
anatomy and structural anisotropy of the heart is consistent within a species
suggested its possible functional effect on spontaneous drift of cardiac
re-entry. A comparative study of the anatomy induced drift could be used in
order to predict evolution of atrial arrhythmia, and improve low-voltage
defibrillation protocols and ablation strategies. Here, in micro-CT based model
of rat pulmonary vein wall, and in sheep atria models based on high resolution
serial histological sections, we demonstrate effects of heart geometry and
anisotropy on cardiac re-entry anatomy induced drift, its pinning to
fluctuations of thickness in the layer. The data sets of sheep atria and rat
pulmonary vein wall are incorporated into the BeatBox High Performance
Computing simulation environment. Re-entry is initiated at prescribed locations
in the spatially homogeneous mono-domain models of cardiac tissue. Excitation
is described by FitzHugh-Nagumo kinetics. In the in-silico models, isotropic
and anisotropic conduction show specific anatomy effects and the interplay
between anatomy and anisotropy of the heart. The main objectives are to
demonstrate the functional role of the species hearts geometry and anisotropy
on cardiac re-entry anatomy induced drift. In case of the rat pulmonary vein
wall with ~90 degree transmural fibre rotation, it is shown that the joint
effect of the PV wall geometry and anisotropy turns a plane excitation wave
into a re-entry pinned to a small fluctuation of thickness in the wall.",1809.01186v1
2019-03-07,"Uniaxial anisotropy, intrinsic and extrinsic damping in Co$_{2}$FeSi Heusler alloy thin films","Ferromagnetic resonance (FMR) technique has been used to study the
magnetization relaxation processes and magnetic anisotropy in two different
series of the Co2FeSi (CFS) Heusler alloy thin films, deposited on the Si(111)
substrate by UHV sputtering. While the CFS films of fixed (50 nm) thickness,
deposited at different substrate temperatures (TS) ranging from room
temperature (RT) to 600^C, constitute the series-I, the CFS films with
thickness t varying from 12 nm to 100 nm and deposited at 550^C make up the
series-II. In series-I, the CFS films deposited at TS = RT and 200^C are
completely amorphous, the one at TS = 300^C is partially crystalline, and those
at TS equal 450^C, 550^C and 600^C are completely crystalline with B2 order. By
contrast, all the CFS films in series-II are in the fully-developed B2
crystalline state. Irrespective of the strength of disorder and film thickness,
angular variation of the resonance field in the film plane unambiguously
establishes the presence of global in-plane uniaxial anisotropy. Angular
variation of the linewidth in the film plane reveals that, in the CFS thin
films of varying thickness, a crossover from the in-plane local four-fold
symmetry (cubic anisotropy) to local two-fold symmetry (uniaxial anisotropy)
occurs as t exceeds 50 nm. Gilbert damping parameter {\alpha} decreases
monotonously from 0.047 to 0.0078 with decreasing disorder strength (increasing
TS) and jumps from 0.008 for the CFS film with t = 50 nm to 0.024 for the film
with t equal 75 nm. Such variations of {\alpha} with TS and t are understood in
terms of the changes in the total (spin-up and spin-down) density of states at
the Fermi level caused by the disorder and film thickness.",1903.02976v1
2019-08-19,Effects of magnetic anisotropy on spin and thermal transports in classical antiferromagnets on the square lattice,"Transport properties of the classical antiferromagnetic XXZ model on the
square lattice have been theoretically investigated, putting emphasis on how
the occurrence of a phase transition is reflected in spin and thermal
transports. As is well known, the anisotropy of the exchange interaction
$\Delta\equiv J_z/J_x$ plays a role to control the universality class of the
transition of the model, i.e., either a second-order transition at $T_N$ into a
magnetically ordered state or the Kosterlitz-Thouless (KT) transition at
$T_{KT}$, which respectively occur for the Ising-type ($\Delta >1$) and
$XY$-type ($\Delta <1$) anisotropies, while for the isotropic Heisenberg case
of $\Delta=1$, a phase transition does not occur at any finite temperature. It
is found by means of the hybrid Monte-Carlo and spin-dynamics simulations that
the spin current probes the difference in the ordering properties, while the
thermal current does not. For the $XY$-type anisotropy, the longitudinal
spin-current conductivity $\sigma^s_{xx}$ ($=\sigma^s_{yy}$) exhibits a
divergence at $T_{KT}$ of the exponential form, $\sigma^s_{xx} \propto
\exp\big[ B/\sqrt{T/T_{KT}-1 }\, \big]$ with $B={\cal O}(1)$, while for the
Ising-type anisotropy, the temperature dependence of $\sigma^s_{xx}$ is almost
monotonic without showing a clear anomaly at $T_{N}$ and such a monotonic
behavior is also the case in the Heisenberg-type spin system. The significant
enhancement of $\sigma^s_{xx}$ at $T_{KT}$ is found to be due to the
exponential rapid growth of the spin-current-relaxation time toward $T_{KT}$,
which can be understood as a manifestation of the topological nature of a
vortex whose lifetime is expected to get longer toward $T_{KT}$. Possible
experimental platforms for the spin-transport phenomena associated with the KT
topological transition are discussed.",1908.06630v1
2019-08-31,Spin-gapped magnets with weak anisotropies I: Constraints on the phase of the condensate wave function,"We study the thermodynamic properties of dimerized spin-gapped quantum
magnets with and without exchange anisotropy (EA) and Dzyaloshinsky and Moriya
(DM) anisotropies within the mean-field approximation (MFA). For this purpose
we obtain the thermodynamic potential $\Omega$ of a triplon gas taking into
account the strength of DM interaction up to second order. The minimization of
$\Omega$ with respect to self-energies $\Sigma_n$ and $\Sigma_{an}$ yields the
equation for $X_{1,2}=\Sigma_n\pm\Sigma_{an}-\mu$, which define the dispersion
of quasiparticles $E_k=\sqrt{\epsilon_k+X_1}\sqrt{\epsilon_k+X_2}$ where
$\epsilon_k$ is the bare dispersion of triplons. The minimization of $\Omega$
with respect to the magnitude $\rho_0$ and the phase $\Theta$ of triplon
condensate leads to coupled equations for $\rho_0$ and $\Theta$. We discuss the
restrictions on $\rho_0$ and $\Theta$ imposed by these equations for systems
with and without anisotropy. The requirement of dynamical stability conditions
$(X_1>0, X_2>0)$ in equilibrium, as well as the Hugenholtz-Pines theorem,
particularly for isotropic Bose condensate, impose certain conditions to the
physical solutions of these equations. It is shown that the phase angle of a
purely homogenous Bose-Einstein condensate (BEC) without any anisotropy may
only take values $\Theta=\pi n $ (n=0,$\pm 1,\pm 2$...) while that of BEC with
even a tiny DM interaction results in $\Theta=\pi/2+2\pi n$. In contrast to the
widely used Hartree-Fock-Popov approximation, which allows arbitrary phase
angle, our approach predicts that the phase angle may have only discrete
values, while the phase of the wave function of the whole system remains
arbitrary as expected. The consequences of this phase locking for interference
of two Bose condensates and to their possible Josephson junction is studied.",1909.00281v3
2019-10-03,Initial conditions of the universe: Decaying tensor modes,"Many models of the early universe predict that there should be primordial
tensor perturbations. These leave an imprint into the temperature and
polarisation anisotropies of the cosmic microwave background (CMB). The
differential equation describing the primordial tensor perturbations is a
second order differential equation and thus has two solutions. Canonically, the
decaying solution of this equation in radiation domination is dropped as it
diverges at early times and on superhorizon scales while it is then suppressed
at late times. Furthermore, if there is an inflationary phase prior to the
radiation domination phase, the amplitude of the decaying mode will also be
highly suppressed as it enters the radiation phase, thus its effect will be
negligible. In this study we remain agnostic to the early universe models
describing pre-radiation domination physics and allow this mode to be present
and see what effect it has on the CMB anisotropies. We find that the decaying
mode, if normalised at the same time on subhorizon scales as the growing mode
leaves an imprint on the CMB anisotropies that is identical to the growing
mode. Contrary to expectation, on large scales both modes are poorly
constrained for a scale invariant spectrum, and the apparent divergence of the
decaying mode does not lead to a divergent physical observable. Quantitatively,
the decaying mode can be more constrained both from temperature and
polarisation anisotropies. We use a model independent, non-parametric, approach
to constrain both of these primordial tensor perturbations using the
temperature and polarisation anisotropies. We find that both modes are best
constrained at the reionisation and recombination bumps and crucially, at the
reionisation bump the decaying mode can be distinguished from the growing mode.",1910.01416v1
2019-10-04,Giant perpendicular magnetic anisotropy in Ir/Co/Pt multilayers,"We have studied the magnetic properties of multilayers composed of
ferromagnetic metal Co and heavy metals with strong spin orbit coupling (Pt and
Ir). Multilayers with symmetric (ABA stacking) and asymmetric (ABC stacking)
structures are grown to study the effect of broken structural inversion
symmetry. We compare the perpendicular magnetic anisotropy (PMA) energy of
symmetric Pt/Co/Pt, Ir/Co/Ir multilayers and asymmetric Pt/Co/Ir, Ir/Co/Pt
multilayers. First, the interface contribution to the PMA is studied using the
Co layer thickness dependence of the effective PMA energy. Comparison of the
interfacial PMA between the Ir/Co/Pt, Pt/Co/Ir asymmetric structures and
Pt/Co/Pt, Ir/Co/Ir symmetric structures indicate that the broken structural
inversion symmetry induced PMA is small compared to the overall interfacial
PMA. Second, we find the magnetic anisotropy field is significantly increased
in multilayers when the ferromagnetic layers are antiferromagnetically coupled
via interlayer exchange coupling (IEC). Macrospin model calculations can
qualitatively account for the relation between the anisotropy field and the
IEC. Among the structures studied, IEC is the largest for the asymmetric
Ir/Co/Pt multilayers: the exchange coupling field exceeds 3 T and consequently,
the anisotropy field approaches 10 T. Third, comparing the asymmetric Ir/Co/Pt
and Pt/Co/Ir structures, we find the IEC and, to some extent, the interface PMA
are stronger for the former than the latter. X-ray magnetic circular dichroism
studies suggest that the proximity induced magnetization in Pt is larger for
the Ir/Co/Pt multilayers than the inverted structure, which may partly account
for the difference in the magnetic properties. These results show the intricate
relation between PMA, IEC and the proximity induced magnetization that can be
exploited to design artificial structures with unique magnetic characteristics.",1910.01777v2
2020-02-12,"Formation of a fast ""lane"" for positional transition in a microparticle-suspended nematic liquid crystal cell","In this paper, based on the numerical calculation of total energy utilizing
the Green's function method, we found that the external electric field applied
to a microparticle-suspended nematic liquid crystal cell, if reaching a
critical value, combined with its direction, surface anchoring feature and
molecular dielectric anisotropy, is possible to create an anisotropic ""bubble""
around the microparticle with a vertical fast ""lane"", in which the
microparticle can, driven by the asymmetric buoyant force, vertically move
swiftly from the cell's midplane to a new equilibrium position, triggering a
positional transition discovered by the author previously. Such a new
equilibrium position is decided via a competition between the buoyant force and
the effective force built upon the microparticle by the elastic energy gradient
along the ""lane"". The threshold value of external field, depends on thickness
$L$ and Frank elastic constant $K$ and slightly on the microparticle size and
density, in a Fr\'{e}edericksz-like manner, but by a factor. For a nematic
liquid crystal cell with planar surface alignment, a bistable equilibrium
structure for the transition is found when the direction of the applied
electric field is (a) perpendicular to the two plates of the cell with positive
molecular dielectric anisotropy, or (b) parallel to the two plates and the
anchoring direction of the cell with negative molecular dielectric anisotropy.
Except for the formation of a vertical fast ""lane"", when the electric field
applied is parallel to both the two plates and perpendicular to the anchoring
direction, the microparticle suspended in the nematic liquid crystal tends to
be trapped in the midplane, regardless of the sign of the molecular dielectric
anisotropy. Such phenomenon also occurs for negative molecular dielectric
anisotropy while the external is applied perpendicular to the two plates.",2002.05084v1
2020-04-10,Ion beam modification of magnetic tunnel junctions,"The impact of 400 keV $Ar^+$ ion irradiation on the magnetic and electrical
properties of in-plane magnetized magnetic tunnel junction (MTJ) stacks was
investigated by ferromagnetic resonance, vibrating sample magnetometry and
current-in-plane tunneling techniques. The irradiation-induced changes of the
magnetic anisotropy, coupling energies and tunnel magnetoresistance (TMR)
exhibited a correlated dependence on the ion fluence, which allowed us to
distinguish between two irradiation regimes. In the low-fluence regime, ${\Phi}
< 10^{14} cm^{-2}$, the parameters required for having a functioning MTJ were
preserved: the anisotropy of the FeCoB free layer (FL) was weakly modulated
following a small decrease in the saturation magnetization $M_S$; the TMR
decreased continuously; the interlayer exchange coupling (IEC) and the exchange
bias (EB) decreased slightly. In the high-fluence regime, ${\Phi} > 10^{14}
cm^{-2}$, the MTJ was rendered inoperative: the modulation of the FL anisotropy
was strong, caused by a strong decrease in $M_S$, ascribed to a high degree of
interface intermixing between the FL and the Ta capping; the EB and IEC were
also lost, likely due to intermixing of the layers composing the synthetic
antiferromagnet; and the TMR vanished due to the irradiation-induced
deterioration of the MgO barrier and MgO/FeCoB interfaces. We demonstrate that
the layers surrounding the FL play a decisive role in determining the trend of
the magnetic anisotropy evolution resulting from the irradiation, and that an
ion-fluence window exists where such a modulation of magnetic anisotropy can
occur, while not losing the TMR or the magnetic configuration of the MTJ.",2004.05025v1
2020-04-13,Intermittency and Ion Temperature-Anisotropy Instabilities: Simulation and Magnetosheath Observation,"Weakly collisional space plasmas are rarely in local thermal equilibrium and
often exhibit non-Maxwellian electron and ion velocity distributions that lead
to the growth of microinstabilities, that is, enhanced electric and magnetic
fields at relatively short wavelengths. These instabilities play an active role
in the evolution of space plasmas, as does ubiquitous broadband turbulence
induced by turbulent structures. This study compares certain properties of a
2.5 dimensional Particle-In-Cell (PIC) simulation for the forward cascade of
Alfvenic turbulence in a collisionless plasma against the same properties of
turbulence observed by the Magnetospheric Multiscale Mission spacecraft in the
terrestrial magnetosheath. The PIC
  simulation is of decaying turbulence which develops both coherent structures
and anisotropic ion velocity distributions with the potential to drive kinetic
scale instabilities. The uniform background magnetic field points perpendicular
to the plane of the simulation. Growth rates are computed from linear theory
using the ion temperature anisotropies and ion beta values for both the
simulation and the observations. Both the simulation and the observations show
that strong anisotropies and growth rates occur highly intermittently in the
plasma, and the simulation further shows that such anisotropies preferentially
occur near current sheets. This suggests that, though microinstabilities may
affect the plasma globally , they act locally and develop in response to
extreme temperature anisotropies generated by turbulent structures. Further
studies will be necessary to understand why there is an apparent correlation
between linear instability theory and strongly intermittent turbulence.",2004.06164v1
2020-06-03,Thermodynamics and magnetism in the 2D-3D crossover of the Hubbard model,"The realization of antiferromagnetic (AF) correlations in ultracold fermionic
atoms on an optical lattice is a significant achievement. Experiments have been
carried out in one, two, and three dimensions, and have also studied
anisotropic configurations with stronger tunneling in some lattice directions.
Such anisotropy is relevant to the physics of cuprate superconductors and other
strongly correlated materials. Moreover, this anisotropy might be harnessed to
enhance AF order. Here we numerically investigate, using Determinant Quantum
Monte Carlo, a simple realization of anisotropy in the 3D Hubbard model in
which the tunneling between planes, $t_\perp$, is unequal to the intraplane
tunneling $t$. This model interpolates between the three-dimensional isotropic
($t_\perp = t$) and two-dimensional ($t_\perp =0$) systems. We show that at
fixed interaction strength to tunneling ratio ($U/t$), anisotropy can enhance
the magnetic structure factor relative to both 2D and 3D results. However, this
enhancement occurs at interaction strengths below those for which the N\'eel
temperature $T_{\rm N\acute{e}el}$ is largest, in such a way that the structure
factor cannot be made to exceed its value in isotropic 3D systems at the
optimal $U/t$. We characterize the 2D-3D crossover in terms of the magnetic
structure factor, real space spin correlations, number of doubly-occupied
sites, and thermodynamic observables. An interesting implication of our results
stems from the entropy's dependence on anisotropy. As the system evolves from
3D to 2D, the entropy at a fixed temperature increases. Correspondingly, at
fixed entropy, the temperature will decrease going from 3D to 2D. This suggests
a cooling protocol in which the dimensionality is adiabatically changed from 3D
to 2D.",2006.02029v2
2020-09-17,Metastability in graded and step like variation of field and anisotropy of the Blume-Capel ferromagnet,"The metastable behaviour of two dimensional anisotropic Blume-Capel
ferromagnet, under the influence of graded and stepped like variations of
magnetic field, has been investigated by extensive Monte Carlo simulation using
Metropolis single spin flip algorithm. Starting from the initial perfectly
ordered state, reversal of magnetisation has been studied in presence of the
field. Metastable lifetime or the reversal time of magnetisation for the system
having uniform anisotropy and in the presence of both graded and stepped field
has been studied. Also the same has been explored for a {\it graded and stepped
anisotropic system} in presence of a uniform field. Finite size effect is
analyzed for the variation of reversal time with gradient of field ($G_h$) and
a scaling relation $\langle \tau \rangle \sim L^{-\beta} f(G_h L^\alpha)$ is
proposed. Spatial variation of density profile for the projection states (i.e.,
+1, 0 and -1) has also been studied at the moment of reversal of magnetisation.
The spatial variation of the number of spin flips per site is studied. Motion
of the interface (or domain wall) with the gradient of field and gradient of
anisotropy are investigated and are found to follow the hyperbolic tangent like
behaviours in both cases. Since, both the anisotropy and the applied field have
significant impact on the metastable lifetime, an interesting competitive
scenario is observed for a {\it graded anisotropic system in graded field} and
a {\it stepped anisotropic system in stepped field}. A line of marginal
competition has been found out for both the cases separating the regions of
field dominated reversal and anisotropy dominated reversal. The decay of the
metastable volume fraction was found to follow the Avrami's law. The mean
reversal time was observed to decrease monotonically across the phase boundary
of the ferro-para transition.",2009.08342v3
2020-10-26,Insights into searches for anisotropies in the nanohertz gravitational-wave background,"Within the next several years pulsar timing arrays (PTAs) are positioned to
detect the stochastic gravitational-wave background (GWB) likely produced by
the collection of inspiralling super-massive black holes binaries, and
potentially constrain some exotic physics. So far most of the pulsar timing
data analysis has focused on the monopole of the GWB, assuming it is perfectly
isotropic. The natural next step is to search for anisotropies in the GWB. In
this paper, we use the recently developed PTA Fisher matrix to gain insights
into optimal search strategies for GWB anisotropies. For concreteness, we apply
our results to EPTA data, using realistic noise characteristics of its pulsars.
We project the detectability of a GWB whose angular dependence is assumed to be
a linear combination of predetermined maps, such as spherical harmonics or
coarse pixels. We find that the GWB monopole is always statistically correlated
with these maps, implying a loss of sensitivity to the monopole when searching
simultaneously for anisotropies. We then derive the angular distributions of
the GWB intensity to which a PTA is most sensitive, and illustrate how one may
use these ""principal maps"" to approximately reconstruct the angular dependence
of the GWB. Since the principal maps are neither perfectly anisotropic nor
uncorrelated with the monopole, we also develop a frequentist criterion to
specifically search for anisotropies in the GWB without any prior knowledge
about their angular distribution. Lastly, we show how to recover existing EPTA
results with our Fisher formalism, and clarify their meaning. The tools
presented here will be valuable in guiding and optimizing the computationally
demanding analyses of pulsar timing data.",2010.13958v2
2021-04-06,Modulating Curie Temperature and Magnetic Anisotropy in Nanoscale Layered Cr_{2}Te_{3} Films: Implications for Room-Temperature Spintronics,"Nanoscale layered ferromagnets have demonstrated fascinating two-dimensional
magnetism down to atomic layers, providing a peculiar playground of spin orders
for investigating fundamental physics and spintronic applications. However,
strategy for growing films with designed magnetic properties is not well
established yet. Herein, we present a versatile method to control the Curie
temperature (T_{C}) and magnetic anisotropy during growth of ultrathin
Cr_{2}Te_{3} films. We demonstrate increase of the TC from 165 K to 310 K in
sync with magnetic anisotropy switching from an out-of-plane orientation to an
in-plane one, respectively, via controlling the Te source flux during film
growth, leading to different c-lattice parameters while preserving the
stoichiometries and thicknesses of the films. We attributed this modulation of
magnetic anisotropy to the switching of the orbital magnetic moment, using
X-ray magnetic circular dichroism analysis. We also inferred that different
c-lattice constants might be responsible for the magnetic anisotropy change,
supported by theoretical calculations. These findings emphasize the potential
of ultrathin Cr_{2}Te_{3} films as candidates for developing room-temperature
spintronics applications and similar growth strategies could be applicable to
fabricate other nanoscale layered magnetic compounds.",2104.02224v1
2021-05-22,Local origin of the strong field-space anisotropy in the magnetic phase diagrams of Ce$_{1-x}$La$_x$B$_6$ measured in a rotating magnetic field,"Cubic f-electron compounds commonly exhibit highly anisotropic magnetic phase
diagrams consisting of multiple long-range ordered phases. Field-driven
metamagnetic transitions between them may depend not only on the magnitude, but
also on the direction of the applied magnetic field. Examples of such behavior
are plentiful among rare-earth borides, such as RB$_6$ or RB$_{12}$ ($R$ = rare
earth). In this work, for example, we use torque magnetometry to measure
anisotropic field-angular phase diagrams of La-doped cerium hexaborides,
Ce$_{1-x}$La$_x$B$_6$ ($x$ = 0, 0.18, 0.28, 0.5). One expects that
field-directional anisotropy of phase transitions must be impossible to
understand without knowing the magnetic structures of the corresponding
competing phases and being able to evaluate their precise thermodynamic energy
balance. However, this task is usually beyond the reach of available
theoretical approaches, because the ordered phases can be noncollinear, possess
large magnetic unit cells, involve higher-order multipoles of 4f ions rather
than simple dipoles, or just lack sufficient microscopic characterization. Here
we demonstrate that the anisotropy under field rotation can be qualitatively
understood on a much more basic level of theory, just by considering the
crystal-electric-field scheme of a pair of rare-earth ions in the lattice,
coupled by a single nearest-neighbor exchange interaction. Transitions between
different crystal-field ground states, calculated using this minimal model for
the parent compound CeB6, possess field-directional anisotropy that strikingly
resembles the experimental phase diagrams. This implies that the anisotropy of
phase transitions is of local origin and is easier to describe than the ordered
phases themselves.",2105.10694v2
2021-09-02,Primordial tensor bispectra in $μ$-CMB cross-correlations,"Cross-correlations between Cosmic Microwave Background (CMB) temperature and
polarization anisotropies and $\mu$-spectral distortions have been considered
to measure (squeezed) primordial scalar bispectra in a range of scales
inaccessible to primary CMB bispectra. In this work we address whether it is
possible to constrain tensor non-Gaussianities with these cross-correlations.
We find that only primordial tensor bispectra with statistical anisotropies
leave distinct signatures, while isotropic tensor bispectra leave either
vanishing or highly suppressed signatures. We discuss how the angular
dependence of squeezed bispectra in terms of the short and long momenta
determine the non-zero cross-correlations. We also discuss how these
non-vanishing configurations are affected by the way in which primordial
bispectra transform under parity. By employing the so-called BipoSH formalism
to capture the observational effects of statistical anisotropies, we make
Fisher-forecasts to assess the detection prospects from $\mu T$, $\mu E$ and
$\mu B$ cross-correlations. Observing statistical anisotropies in squeezed
$\langle \gamma \gamma \gamma\rangle$ and $\langle \gamma \gamma \zeta\rangle$
bispectra is going to be challenging as the imprint of tensor perturbations on
$\mu$-distortions is subdominant to scalar perturbations, therefore requiring a
large, independent amplification of the effect of tensor perturbations in the
$\mu$-epoch. In absence of such a mechanism, statistical anisotropies in
squeezed $\langle \zeta \zeta \gamma\rangle$ bispectrum are the most relevant
sources of $\mu T$, $\mu E$ and $\mu B$ cross-correlations. In particular, we
point out that in anisotropic inflationary models where $\langle \zeta \zeta
\zeta \rangle$ leaves potentially observable signatures in $\mu T$ and $\mu E$,
the detection prospects of $\langle \zeta \zeta \gamma\rangle$ from $\mu B$ are
enhanced.",2109.01095v3
2021-11-30,Spin and valley ordering of fractional quantum Hall states in monolayer graphene,"We study spin and valley ordering in the quantum Hall fractions in monolayer
graphene at Landau level filling factors $\nu_G=-2+n/3$ $(n=2,4,5)$. We use
exact diagonalizations on the spherical as well as toroidal geometry by taking
into account the effect of realistic anisotropies that break the spin/valley
symmetry of the pure Coulomb interaction. We also use a variational method
based on eigenstates of the fully $SU(4)$ symmetric limit. For all the
fractions we study there are two-component states for which the competing
phases are generalizations of those occurring at neutrality $\nu_G=0$. They are
ferromagnetic, antiferromagnetic, charge-density wave and K\'ekul\'e phases,
depending on the values of Ising or XY anisotropies in valley space. The
varying spin-valley content of the states leads to ground state quantum numbers
that are different from the $\nu_G=0$ case. For filling factor $\nu_G=-2+5/3$
there is a parent state in the $SU(4)$ limit which has a flavor content
$(1,1/3,1/3,0)$ where the two components that are one-third filled form a
two-component singlet. The addition of anisotropies leads to the formation of
new states that have no counterpart at $\nu_G=0$. While some of them are
predicted by the variational approach, we find notably that negative Ising-like
valley anisotropy leads to the formation of a state which is a singlet in both
spin and valley space and lies beyond the reach of the variational method. Also
fully spin polarized two-component states at $\nu=-2+4/3$ and $\nu=-2+5/3$
display an emergent $SU(2)$ valley symmetry because they do not feel
point-contact anisotropies. We discuss implications for current experiments
concerning possible spin transitions.",2111.15453v1
2022-02-21,Anisotropy of the magnetic and transport properties in EuZn$_2$As$_2$,"Several recent studies have shown that the anisotropy in the magnetic
structure of \ECA\ plays a significant role in stabilizing the Weyl nodes. To
investigate the relationship between magnetic anisotropy and Weyl physics, we
present a comparative study between EuZn$_2$As$_2$ and EuCd$_2$As$_2$ that are
isostructural but with different magnetic anisotropy. We performed structural
analysis, electronic transport, and magnetization experiments on
millimeter-sized single crystals of EuZn$_2$As$_2$, and compared the results to
those of EuCd$_2$As$_2$. By combining the first principle calculations and
neutron diffraction experiment, we identify the magnetic ground state of
EuZn$_2$As$_2$ as A-type antiferromagnetic order with a transition temperature
($T_\mathrm{N}$ = 19.6 K) twice that of EuCd$_2$As$_2$. Like EuCd$_2$As$_2$,
the negative magnetoresistance of EuZn$_2$As$_2$ is observed after suppressing
the resistivity peak at $T_\mathrm{N}$ with increasing fields. However, the
anisotropy in both transport and magnetization are much reduced in
EuZn$_2$As$_2$. The difference could be ascribed to the weaker spin-orbit
coupling, more localized $d$-orbitals, and a larger contribution from the Eu
$s$-orbitals in the zinc compound, as suggested by the electronic band
calculations. The same band structure effect could be also responsible for the
observation of a smaller non-linear anomalous Hall effect in EuZn$_2$As$_2$
compared to EuCd$_2$As$_2$.",2202.09963v1
2022-08-31,A Heating Mechanism via Magnetic Pumping in the Intracluster Medium,"Turbulence driven by AGN activity, cluster mergers and galaxy motion
constitutes an attractive energy source for heating the intracluster medium
(ICM). How this energy dissipates into the ICM plasma remains unclear, given
its low collisionality and high magnetization (precluding viscous heating by
Coulomb processes). Kunz et al. 2011 proposed a viable heating mechanism based
on the anisotropy of the plasma pressure (gyroviscous heating) under ICM
conditions. The present paper builds upon that work and shows that particles
can be gyroviscously heated by large-scale turbulent fluctuations via magnetic
pumping. We study how the anisotropy evolves under a range of forcing
frequencies, what waves and instabilities are generated and demonstrate that
the particle distribution function acquires a high energy tail. For this, we
perform particle-in-cell simulations where we periodically vary the mean
magnetic field $\textbf{B}(t)$. When $\textbf{B}(t)$ grows (dwindles), a
pressure anisotropy $P_{\perp}>P_{\parallel}$ ($P_{\perp}< P_{\parallel}$)
builds up ($P_{\perp}$ and $P_{\parallel}$ are, respectively, the pressures
perpendicular and parallel to $\textbf{B}(t)$). These pressure anisotropies
excite mirror ($P_{\perp}>P_{\parallel}$) and oblique firehose
($P_{\parallel}>P_{\perp}$) instabilities, which trap and scatter the
particles, limiting the anisotropy and providing a channel to heat the plasma.
The efficiency of this mechanism depends on the frequency of the large-scale
turbulent fluctuations and the efficiency of the scattering the instabilities
provide in their nonlinear stage. We provide a simplified analytical heating
model that captures the phenomenology involved. Our results show that this
process can be relevant in dissipating and distributing turbulent energy at
kinetic scales in the ICM.",2209.00019v1
2022-09-26,On the scaling and anisotropy of two subranges in the inertial range of solar wind turbulence,"Intermittency and anisotropy are two important aspects of plasma turbulence,
which the solar wind provides a natural laboratory to investigate. However,
their forms and nature are still under debate, making it difficult to achieve a
consensus in the theoretical interpretation. Here, we perform higher-order
statistics for the observations in the fast solar wind at 1.48 au obtained by
Ulysses and in the slow solar wind at 0.17 au obtained by Parker Solar Probe
(PSP). We find that two subranges clearly exist in the inertial range and they
present distinct features with regard to the intermittency and anisotropy. The
subrange 1 with smaller scale has a multifractal scaling with the second index
$\xi(2) \sim 2/3$ and the subrange 2 with larger scale is also multifractal but
with $\xi(2) \sim 1/2$. The break between two subranges locates at the same
spatial scale for both Ulysses and PSP observations. Subrange 1 is multifractal
in the direction perpendicular to the local magnetic field with $\xi_{\perp}(2)
\sim 2/3$ and seems to be monoscaling in the parallel direction with
$\xi_{\parallel}(2) \sim 1$. Subrange 2 is multifractal in both parallel and
perpendicular directions with $\xi_{\perp}(2) \sim 1/2$ and $\xi_{\parallel}(2)
\sim 2/3$. Both subrange 1 and subrange 2 present power and wavevector
anisotropies. The distinct features of two subranges suggest that a transition
from weak to strong turbulence may occur and the spatial scale of the break may
not evolve with the solar wind expansion. These new results update our
knowledge of the inertial range and provide strong observational constraints on
the understanding of intermittency and anisotropy in solar wind turbulence.",2209.12409v1
2023-05-13,Temperature dependence of magnetic anisotropy and domain wall tuning in BaTiO3(111)/CoFeB multiferroics,"Artificial multiferroics consist of two types of ferroic materials, typically
a ferroelectric and ferromagnet, often coupled interfacially by
magnetostriction induced by the lattice elongations in the ferroelectric. In
BaTiO3 the magnitude of strain induced by these elongations is heavily
temperature dependent, varying greatly between each of the polar crystal phases
and exerting a huge influence over the properties of a coupled magnetic film.
Here we demonstrate that temperature, and thus strain, is an effective means of
controlling the magnetic anisotropy in BaTiO3(111)/CoFeB heterostructures. We
investigate the three polar phases of BaTiO3: tetragonal (T) at room
temperature, orthorhombic (O) below 280 K and rhombohedral (R) below 190 K,
across a total range of 77 K to 420 K. We find two distinct responses; a
step-like change in the anisotropy across the low-temperature phase
transitions, and a sharp high-temperature reduction around the ferroelectric
Curie temperature, measured from hard axis hysteresis loops. Using our
measurements of this anisotropy strength we are then able to show by
micromagnetic simulation the behaviour of all possible magnetic domain wall
states and determine their scaling as a function of temperature. The most
significant changes occur in the head-to-head domain wall states, with a
maximum change of 210 nm predicted across the entire range effectively doubling
the size of the domain wall as compared to room temperature. Notably, similar
changes are seen for both high and low temperatures which suggest different
routes for potential control of magnetic anisotropy and elastically pinned
magnetic domain walls.",2305.07879v1
2023-05-28,What can be learnt from UHECR anisotropies observations Paper II: intermediate-scale anisotropies,"Analysing the available data relative to the anisotropies of the
ultra-high-energy cosmic rays (UHECR) at intermediate angular scales, we
examine to what extent they can be used to constrain the origin of these
particles, and what could be gained from a new generation of observatories with
increased exposure. We simulate realistic UHECR sky maps for a wide range of
scenarios, with the assumption that the distribution of UHECR sources follows
that of matter in the Universe, also considering possible biases. We produce
numerous datasets on which we apply similar analyses as those recently used by
the Auger and TA collaborations. We find that: i) the investigated scenarios
can easily account for the significance of the anisotropies reported by Auger
and TA; ii) the direction in which the maximum flux excess is found in the
Auger data differs from where it is found in most of our simulations; iii) for
datasets simulated with the same astrophysical scenario, the significance with
which the isotropy hypothesis is rejected through the Auger likelihood analysis
can be largest either when ""all galaxies"" or when ""starburst"" galaxies are used
to model the signal, depending on which GMF model is used; iv) the study of the
energy evolution of the anisotropy patterns can provide new insight about the
origin of UHECRs; v) the direction in which the most significant flux excess is
found in the Auger dataset above 8 EeV appears to essentially disappear in the
dataset above 32 EeV; vi) this appears to be very uncommon in our simulations,
which could point to a failure of some generic assumption in the investigated
scenarios, such as the predominance of a unique type of sources in the flux
above the ankle, with essentially the same composition and spectrum; vii) a
meaningful measurement of their energy evolution, from 10 EeV to the highest
energies, will require a significant increase in statistics.",2305.17811v1
2023-06-01,Impact of magnetic anisotropy on the magnon Hanle effect in $α$-Fe$_2$O$_3$,"In easy-plane antiferromagnets, the nature of the elementary excitations of
the spin system is captured by the precession of the magnon pseudospin around
its equilibrium pseudofield, manifesting itself in the magnon Hanle effect.
Here, we investigate the impact of growth-induced changes in the magnetic
anisotropy on this effect in the antiferromagnetic insulator
$\alpha$-Fe$_2$O$_3$ (hematite). To this end, we compare the structural,
magnetic, and magnon-based spin transport properties of $\alpha$-Fe$_2$O$_3$
films with different thicknesses grown by pulsed laser deposition in molecular
and atomic oxygen atmospheres. While in films grown with molecular oxygen a
spin-reorientation transition (Morin transition) is absent down to $10\,$K, we
observe a Morin transition for those grown by atomic-oxygen-assisted
deposition, indicating a change in magnetic anisotropy. Interestingly, even for
a $19\,$nm thin $\alpha$-Fe$_2$O$_3$ film grown with atomic oxygen we still
detect a Morin transition at $125\,$K. We characterize the magnon Hanle effect
in these $\alpha$-Fe$_2$O$_3$ films via all-electrical magnon transport
measurements. The films grown with atomic oxygen show a markedly different
magnon spin signal from those grown in molecular oxygen atmospheres. Most
importantly, the maximum magnon Hanle signal is significantly enhanced and the
Hanle peak is shifted to lower magnetic field values for films grown with
atomic oxygen. These observations suggest a change of magnetic anisotropy for
$\alpha$-Fe$_2$O$_3$ films fabricated by atomic-oxygen-assisted deposition
resulting in an increased oxygen content in these films. Our findings provide
new insights into the possibility to fine-tune the magnetic anisotropy in
$\alpha$-Fe$_2$O$_3$ and thereby to engineer the magnon Hanle effect.",2306.00375v1
2023-09-01,f-mode oscillations of anisotropic neutron stars in full general relativity,"We investigate f-mode oscillations of static anisotropic stable neutron stars
within the framework of full general relativity. We present equations governing
unperturbed stellar structures and oscillations with an ansatz to account for
the anisotropy. We solve those equations for two different equations of states.
We see that, moderately anisotropic neutron stars with the tangential pressure
larger than the radial pressure can give more massive neutron stars than the
isotropic or very anisotropic ones. We find that the frequency of the f-mode
exhibits a linear relationship with the square root of the average density of
the stars and the slope of the fit depends on the anisotropic strength. For any
given value of the anisotropic strength, the frequency increases with the
increase of the mass of the neutron star, linearly for lower masses, and
rapidly at higher masses. However, this non-linear rise in the frequency with
the mass is not prominent when the radial pressure is larger than the
tangential pressure. For a fixed value of a small mass, higher anisotropy leads
to a larger value of the frequency, but when the fixed mass is above a
threshold value, higher anisotropy leads to a smaller value of the frequency.
The nature of the variation in the frequency with the change in the anisotropic
strength is similar for the two equations of state, but for a fixed mass and
the same amount of the anisotropy, the softer equations of state gives higher
frequency. We also find that the damping time of the f-mode oscillation
decreases as the mass of the neutron star increases for all values of the
anisotropic strength. For a fixed mass of the neutron star and for the same
amount of the anisotropy, the value of the damping time is lower for the softer
equation of state, but the nature of the variation in the damping time with the
change in the anisotropic strength is similar.",2309.00439v2
2023-10-02,Control of the magnetic anisotropy in multi-repeat Pt/Co/Al heterostructures using magneto-ionic gating,"Controlling magnetic properties through the application of an electric field
is a significant challenge in modern nanomagnetism. In this study, we
investigate the magneto-ionic control of magnetic anisotropy in the topmost Co
layer in Ta/Pt/[Co/Al/Pt]$_n$/Co/Al/AlO$_\text{x}$ multilayer stacks comprising
$n +1$ Co layers and its impact on the magnetic properties of the multilayers.
We demonstrate that the perpendicular magnetic anisotropy can be reversibly
quenched through gate-driven oxidation of the intermediary Al layer between Co
and AlO$_\text{x}$, enabling dynamic control of the magnetic layers
contributing to the out-of-plane remanence - varying between $n$ and $n +1$.
For multilayer configurations with $n = 2$ and $n = 4$, we observe reversible
and non-volatile additions of 1/3 and 1/5, respectively, to the anomalous Hall
effect amplitude based on the applied gate voltage. Magnetic imaging reveals
that the gate-induced spin-reorientation transition occurs through the
propagation of a single 90$^{\circ}$ magnetic domain wall separating the
perpendicular and in-plane anisotropy states. In the 5-repetition multilayer,
the modification leads to a doubling of the period of the magnetic domains at
remanence. These results demonstrate that the magneto-ionic control of the
anisotropy of a single magnetic layer can be used to control the magnetic
properties of coupled multilayer systems, extending beyond the gating effects
on a single magnetic layer.",2310.01623v1
2023-12-19,Magnetism of noncolinear amorphous DyCo3 and TbCo3 thin films,"The magnetization of amorphous DyCo3 and TbCo3 is studied by magnetometry,
anomalous Hall effect and magneto-optic Kerr effect to understand the
temperature-dependent magnetic structure. A square magnetic hysteresis loop
with perpendicular magnetic anisotropy and coercivity that reaches 3.5 T in the
vicinity of the compensation temperature is seen in thin films. An anhysteretic
soft component, seen in the magnetization of some films but not in their Hall
or Kerr loops is an artefact due to sputter-deposition on the sides of the
substrate. The temperature-dependence of the net rare earth moment from 4-300K
is deduced, using the cobalt moment in amorphous YxCo1-x. The single-ion
anisotropy of the quadrupole moments of the 4f atoms in the randomly-oriented
local electrostatic field gradient overcomes their exchange coupling to the
cobalt subnetwork, resulting in a sperimagnetic ground state where spins of the
noncollinear rare-earth subnetwork are modelled by a distribution of rare earth
moments within a cone whose axis is antiparallel to the ferromagnetic axis z of
the cobalt subnetwork. The reduced magnetization (Jz)/J at T=0 is calculated
from an atomic Hamiltonian as a function of the ratio of anisotropy to exchange
energy per rare-earth atom for a range of angles between the local anisotropy
axis and -z and then averaged over all directions in a hemisphere. The
experimental and calculated values of (J-z)/J are close to 0.7 at low
temperature for both Dy and Tb. On increasing temperature, the magnitude of the
rare earth moment and the local random anisotropy that creates the cone are
reduced; the cone closes and the structure approaches collinear ferrimagnetism
well above ambient temperature. An asymmetric spin flop of the exchange-coupled
subnetworks appears in the vicinity of the magnetization compensation
temperatures of 175K for amorphous Dy0.25Co0.75 and 200 K for amorphous TbCo3.",2312.12602v1
2013-07-22,"CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z=0.44 galaxy cluster MACS 1206.2-0847","We use an unprecedented data-set of about 600 redshifts for cluster members,
obtained as part of a VLT/VIMOS large programme, to constrain the mass profile
of the z=0.44 cluster MACS J1206.2-0847 over the radial range 0-5 Mpc (0-2.5
virial radii) using the MAMPOSSt and Caustic methods. We then add external
constraints from our previous gravitational lensing analysis. We invert the
Jeans equation to obtain the velocity-anisotropy profiles of cluster members.
With the mass-density and velocity-anisotropy profiles we then obtain the first
determination of a cluster pseudo-phase-space density profile. The kinematics
and lensing determinations of the cluster mass profile are in excellent
agreement. This is very well fitted by a NFW model with mass M200=(1.4 +- 0.2)
10^15 Msun and concentration c200=6 +- 1, only slightly higher than theoretical
expectations. Other mass profile models also provide acceptable fits to our
data, of (slightly) lower (Burkert, Hernquist, and Softened Isothermal Sphere)
or comparable (Einasto) quality than NFW. The velocity anisotropy profiles of
the passive and star-forming cluster members are similar, close to isotropic
near the center and increasingly radial outside. Passive cluster members follow
extremely well the theoretical expectations for the pseudo-phase-space density
profile and the relation between the slope of the mass-density profile and the
velocity anisotropy. Star-forming cluster members show marginal deviations from
theoretical expectations. This is the most accurate determination of a cluster
mass profile out to a radius of 5 Mpc, and the only determination of the
velocity-anisotropy and pseudo-phase-space density profiles of both passive and
star-forming galaxies for an individual cluster [abridged]",1307.5867v2
1993-05-29,Reionization and cosmic microwave background distortions: a complete treatment of second order Compton scattering,"The ionization history of the universe provides a major source of ambiguity
in constraining cosmological models using small angular scale microwave
background anisotropies. To clarify these issues, we consider a complete
treatment of Compton scattering to second order, an approach which may be
applicable to other astrophysical situations. We find that only the ${\cal O}
(v)$ Doppler effect, and the ${\cal O} (v\delta)$ Vishniac effect are important
for recent last scattering epochs; the ${\cal O} (v^2)$ Doppler effect is not
significant on any angular scale, and other higher-order effects are completely
negligible. However the ${\cal O}(v^2)$ effect does lead to \Cy\ distortions,
which although generally below current constraints, set an unavoidable minimum
level in reionization models. We consider the small-angle approximation for the
Vishniac effect in detail, and show several improvements over previous
treatments, particularly for low $\Omega_0$. For standard cold dark matter
models, the effect of reionization is to redistribute the anisotropies to
arcminute scales; late reionization leads to partially erased primary
fluctuations and a secondary contribution of comparable magnitude. Using recent
anisotropy limits from the ATCA experiment, we set new constraints on baryonic
dark matter models. Stronger constraints are imposed (in second order) upon
models with higher Hubble constant, steeper $n$, and higher density. These
limits depend on the specific ionization history assumed, but the factor gained
by lowering the ionization fraction is generally small, and may be tested by
currently-planned",9305038v1
1993-10-28,Analysis of Small Scale MBR Anisotropy in the Presence of Foreground Contamination,"Many of the current round of experiments searching for anisotropies in the
MBR are confronting the problem of how to disentangle the cosmic signal from
contamination due to galactic and intergalactic foreground sources. Here we
show how commonly used likelihood function techniques can be generalized to
account for foreground. Specifically we set some restrictions on the spectrum
of foreground contamination but allow the amplitude to vary arbitrarily. The
likelihood function thus generalized gives reasonable limits on the MBR
anisotropy which, in some cases, are not much less restrictive than what one
would get from more detailed modeling of the foreground. Furthermore, the
likelihood function is exactly the same as one would obtain by simply
projecting out foreground contamination and just looking at the reduced data
set. We apply this generalized analysis to the recent medium angle data sets of
ACME-HEMT and MAX. The resulting analysis constrains the one free parameter in
the standard cold dark matter theory to be Q=18_-5^+8 microK. This best fit
value, although in striking agreement with the normalization from COBE, is not
a very good fit, with an overall chi^2/ degree of freedom =208/168. We also
argue against three commonly used methods of dealing with foreground: (i)
ignoring it completely; (ii) subtracting off a best fit foreground and treating
the residuals as if uncontaminated; and (iii) culling data which appears to be
contaminated by foreground.",9310048v1
1993-12-24,Anisotropies of Cosmic Background Radiation from a Local Collapse,"We present an exact solution of the anisotropies of cosmic background
radiation (CBR) from a local collapse described by a spherical over-dense
region embedded in a flat universe, with the emphasis on the relationship
between the dipole $(\Delta {\sf T}/{\sf T})_d$ and the quadrupole $(\Delta
{\sf T}/{\sf T})_q$ anisotropy. This result has been used to examine the
kinematic quadrupole correction $(\Delta {\sf T}/{\sf T})_q=(\Delta {\sf
T}/{\sf T})_d^2/2$, which is usually applied to remove the contamination of the
quadrupole produced by local density inhomogeneities when finding the cosmic
amplitude of the quadrupole at the surface of last scattering. We have found
that the quadrupole of local collapse origin cannot always be approximately
described by the kinematic quadrupole. Our numerical result shows that the
difference between the kinematic and local quadrupoles depends on the size and
matter density in the peculiar field, and the position of the observer. For a
given dipole, the local quadrupole can be different from the kinematic
quadrupole by a factor as large as 3. Therefore, the kinematic quadrupole
correction remains an uncertain factor in the determination of the amplitude of
a cosmic quadrupole. Nevertheless, a preliminary analysis shows that this
uncertainty might not dramatically change the cosmological origin of the
COBE-DMR's quadrupole, unless a huge peculiar gravitational field is assumed.",9312057v1
1994-04-28,Measurements of Anisotropy in the Cosmic Microwave Background Radiation at Degree Angular Scales Near the Stars Sigma Hercules and Iota Draconis,"We present results from two four-frequency observations centered near the
stars Sigma Hercules and Iota Draconis during the fourth flight of the
Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 x
0.6-degree strips of the sky with 1.4-degree peak to peak sinusoidal chop in
all bands. The FWHM beam sizes were 0.55+/-0.05 degrees at 3.5 cm-1 and a
0.75+/-0.05 degrees at 6, 9, and 14 cm-1. Significant correlated structures
were observed at 3.5, 6 and 9 cm-1. The spectra of these signals are
inconsistent with thermal emission from known interstellar dust populations.
The extrapolated amplitudes of synchrotron and free-free emission are too small
to account for the amplitude of the observed structures. If the observed
structures are attributed to CMB anisotropy with a Gaussian autocorrelation
function and a coherence angle of 25', then the most probable values are
DT/TCMB = (3.1 +1.7-1.3) x 10^-5 for the Sigma Hercules scan, and DT/TCMB =
(3.3 +/- 1.1) x 10^-5 for the Iota Draconis scan (95% confidence upper and
lower limits). Finally a comparison of all six MAX scans is presented.",9404072v3
1994-11-08,The Anisotropy in the Cosmic Microwave Background At Degree Angular Scales,"We detect anisotropy in the cosmic microwave background (CMB) at degree
angular scales and confirm a previous detection reported by Wollack et al.
(1993). The root-mean-squared amplitude of the fluctuations is $44^{+13}_{-7}
\mu$K. This may be expressed as the square root of the angular power spectrum
in a band of multipoles between $l_{eff}=69^{+29}_{-22}$. We find $\delta T_l =
\sqrt{l(2l+1)<|a_l^m|^2>/4\pi} = 42^{+12}_{-7} \mu$K. The measured spectral
index of the fluctuations is consistent with zero, the value expected for the
CMB. The spectral index corresponding to Galactic free-free emission, the most
likely foreground contaminant, is rejected at approximately $3\sigma$.
  The analysis is based on three independent data sets. The first, taken in
1993, spans the 26 - 36 GHz frequency range with three frequency bands; the
second was taken with the same radiometer as the first but during an
independent observing campaign in 1994; and the third, also take in 1994, spans
the 36-46 GHz range in three bands. For each telescope position and radiometer
channel, the drifts in the instrument offset are $\le 4~\mu$K/day over a period
of one month. The dependence of the inferred anisotropy on the calibration and
data editing is addressed.",9411035v1
1994-12-07,Cosmic Background Anisotropies in CDM Cosmology,"Cosmic microwave background (CMB) anisotropies and density fluctuations are
calculated for flat cold dark matter (CDM) models with a wide range of
parameters, i.e., $\Omega_0, h$ and $\Omega_B$ for both standard recombination
and various epochs of reionization. Tables of the power spectrum of CMB
anisotropies in the form of $C_\ell$'s as a function of $\ell$ are presented.
Although the Harrison-Zeldovich initial spectrum is assumed in these tables, we
present simple approximations for obtaining the $C_\ell$'s corresponding to a
tilted spectrum from those with a Harrison-Zeldovich spectrum. The $\sigma_8$
values are obtained for the matter density spectrum, with $\sigma(10^\circ)$,
fixed $Q_{rms-PS}$ and COBE DMR 2 year normalizations. Simple modifications of
the fitting formula of the density transfer function which are applicable for
models with high baryon density are given. By using both numerical results and
these fitting formulae, we calculate the relation between $\sigma_8$ and
$Q_{rms-PS}$, and find good agreement. Velocity fields are also calculated.",9412025v2
1995-01-31,Simple Analytical Methods for Computing the Gravity-Wave Contribution to the Cosmic Background Radiation Anisotropy,"We present two simple analytical methods for computing the gravity wave
contribution to the cosmic background radiation (CBR) anisotropy in
inflationary models; one method uses a time-dependent transfer function, the
other method uses an approximate gravity-wave mode function which is a simple
combination of the lowest order spherical Bessel functions. We compare the CBR
anisotropy tensor multipole spectrum computed using our methods with the
previous result of the highly accurate numerical method, the ``Boltzmann''
method. Our time-dependent transfer function is more accurate than the
time-independent transfer function found by Turner, White, and Lidsey; however,
we find that the transfer function method is only good for $l \la 120$. Using
our approximate gravity-wave mode function, we obtain much better accuracy; the
tensor multipole spectrum we find differs by less than 2\% for $l \la 50$, less
than 10\% for $l \la 120$, and less than 20\% for $l \leq 300$ from the
``Boltzmann'' result. Our approximate graviton mode function should be quite
useful in studying tensor perturbations from inflationary models.",9501116v2
1995-08-18,MSAM1-94: Repeated Measurement of Medium-Scale Anisotropy in the Cosmic Microwave Background Radiation,"The second flight of the Medium Scale Anisotropy Measurement (MSAM1-94)
observed the same field as the first flight (MSAM1-92) to confirm our earlier
measurement of cosmic microwave background radiation (CMBR) anisotropy. This
instrument chops a 30\arcmin\ beam in a 3 position pattern with a throw of
$\pm40\arcmin$, and simultaneously measures single and double differenced sky
signals. We observe in four spectral channels centered at 5.6, 9.0, 16.5, and
22.5~\icm, providing sensitivity to the peak of the CMBR and to thermal
emission from interstellar dust. The dust component correlates well with the
\IRAS\ 100~\micron\ map. The CMBR observations in our double difference channel
correlate well with the earlier observations, but the single difference channel
shows some discrepancies. We obtain a detection of fluctuations in the MSAM1-94
dataset that match CMBR in our spectral bands of $\Delta T/T =
1.9^{+1.3}_{-0.7}\times 10^{-5}$ (90\% confidence interval, including
calibration uncertainty) for total rms Gaussian fluctuations with correlation
angle 0\fdg3, using the double difference demodulation.",9508087v1
1995-10-08,The Nonlinear Redshift Space Power Spectrum: Omega from Redshift Surveys,"We examine the anisotropies in the power spectrum by the mapping of real to
redshift space. Using the Zel'dovich approximation, we obtain an analytic
expression for the nonlinear redshift space power spectrum in the distant
observer limit. For a given unbiased galaxy distribution in redshift space, the
anisotropies in the power spectrum depend on the parameter $f(\Omega)\approx
\Omega^{0.6}$, where $\Omega$ is the density parameter. We quantify these
anisotropies by the ratio, $R$, of the quadrupole to monopole angular moments
of the power spectrum. In contrast to linear theory, the Zel'dovich
approximation predicts a decline in $R$ with decreasing scale. This departure
from linear theory is due to nonlinear dynamics and not a result of incoherent
random velocities. The rate of decline depends strongly on $\Omega$ and the
initial power spectrum. However, we find a {\it universal} relation between the
quantity $R/R_{lin}$ (where $R_{lin}$ the linear theory value of $R$) and the
dimensionless variable $k/k_{nl}$, where $k_{nl}$ is a wavenumber determined by
the scale of nonlinear structures. The universal relation is in good agreement
with a large N-body simulation. This universal relation greatly extends the
scales over which redshift distortions can be used as a probe of $\Omega$. A
preliminary application to the 1.2 Jy IRAS yields $\Omega\sim 0.4$ if IRAS
galaxies are unbiased.",9510049v1
1995-12-21,Implications of the Background Radiation for Cosmic Structure Formation,"The CMB is a remarkably distortionless blackbody, and this strongly
constrains the amount of energy that can have been injected at high redshift,
thereby limiting the role that hydrodynamical amplification can have played in
cosmic structure formation. The current data on primary anisotropies (those
calculated using linear response theory) provide very strong support for the
gravitational instability theory and encouraging support that the initial
fluctuation spectrum was not far off the scale invariant form that inflation
(and defect) models prefer. By itself, the (low resolution) 4-year DMR data
allow relatively precise \sigma_8 normalization factors for density fluctuation
spectra and rough information on the large scale slope of the anisotropy power,
thereby focusing our attention on a relatively narrow set of viable models.
Useful formulae relating the DMR bandpower to \sigma_8 and post-inflation
scalar and tensor power spectra measures are given. Smaller angle data are
consistent with these models, and will soon be powerful enough to strongly
select among the possibilities, although there remains much room for surprises.
In spite of foregrounds, future high resolution experiments should be able to
allow precise determination of many combinations of the cosmological parameters
that define large scale structure formation theories: mode
(adiabatic/isocurvature, gravity wave content), shape functions, amplitudes,
and various mean energy densities. Secondary anisotropies arising from
nonlinear structures will be invaluable probes of shorter-distance aspects of
structure formation theories.",9512142v2
1995-12-26,CMB Anisotropies and Theories of the Early Universe,"I present recent work aimed at showing how currently competing theories of
the early universe leave their imprint on the temperature anisotropies of the
CMB radiation. We consider the 3-point correlation function, as well as the
inherent theoretical uncertainties associated with it, for which we derive
explicit analytic formulae. We apply them in the study of non-Gaussian features
that arise on large scales in the framework of both inflationary and
topological defects models. For inflation, we develop a perturbative analysis
for the study of spatial correlations in the inflaton in the context of the
stochastic approach to inflation. We also include an analysis of a particular
geometry, the so-called `collapsed' 3-point function, in the case of post
recombination integrated effects, arising generically whenever the mildly non
linear growth of perturbations is taken into account. We also devote a part of
the thesis to the study of recently proposed analytic models of topological
defects, and implement them in the analysis of both the CMB excess kurtosis
(for cosmic strings) and the CMB collapsed 3-point function and skewness (for
textures). Lastly, we present a study of the CMB anisotropies on the degree
angular scale in the framework of the global texture scenario, and show the
relevant features that arise; among these, the Doppler peaks.",9512161v1
1996-04-01,The Signature of a Correlation between $>10^{19}{\rm eV}$ Cosmic Ray Sources and Large Scale Structure,"We analyze the anisotropy signature expected if the high energy (above
$10^{19}$eV) cosmic ray (CR) sources are extra-Galactic and trace the
distribution of luminous matter on large scales. We investigate the dependence
of the anisotropy on both the relative bias between the CR sources and the
galaxy distribution and on the (unknown) intrinsic CR source density. We find
that the expected anisotropy associated with the large scale structure (LSS)
should be detected once the number of CR events observed above $10^{19}{\rm
eV}$ is increased by a factor of $\sim10$. This would require $\sim30$
observation-years with existing experiments, but less then $1$ year with the
proposed $\sim5000\ {\rm km}^2$ Auger detectors. We find that the recently
reported concentration of the Haverah Park CR events towards the super-galactic
plane is not consistent with the known LSS. If real, the Haverah Park result
suggests that the CR sources are much more concentrated towards the
super-galactic plane than the known LSS. Our results are not sensitive to the
number density of CR sources. We show that once the number of detected events
is increased by a factor of $\sim10$, the number density would be strongly
constrained by considering the probability for having repeating sources.",9604005v1
1996-05-15,The Analytical Distribution Function of Anisotropic Hernquist+Hernquist Models,"The analytical phase-space distribution function (DF) of spherical
self--consistent galaxy (or cluster) models, embedded in a dark matter halo,
where both density distributions follow the Hernquist profile, with different
total masses and core radii (hereafter called HH models), is presented. The
concentration and the amount of the stellar and dark matter distributions are
described by four parameters: the mass and core radius of the {\it reference}
component, and two dimensionless parameters describing the mass and core radius
of the {\it halo} component. A variable amount of orbital anisotropy is allowed
in both components, following the widely used parameterization of
Osipkov-Merritt. An important case is obtained for a null core radius of the
halo, corresponding to the presence of a central black hole (BH). It is proved
that globally isotropic HH models are consistent for any mass ratio and core
radii ratio, even in the case of a central BH. In this last case the analytical
expression for a lower limit of the anisotropy radius of the host system as a
function of the BH mass is given. In the particular case of global isotropy the
stability of HH models is proved, and the stability of radially anisotropic HH
models is briefly discussed. The expression derived for the DF is useful for
understanding the relations between anisotropy, density shape and external
potential well in a consistent stellar system, and to produce initial
conditions for N-body simulations of two-component galaxies or galaxy clusters.",9605084v1
1996-05-17,Quantum fluctuations and CMB anisotropies in one-bubble open inflation models,"We first develop a method to calculate a complete set of mode functions which
describe the quantum fluctuations generated in one-bubble open inflation
models. We consider two classes of models. One is a single scalar field model
proposed by Bucher, Goldhaber and Turok and by us as an example of the open
inflation scinario, and the other is a two-field model such as the
``supernatural'' inflation proposed by Linde and Mezhlumian. In both cases we
assume the difference in the vacuum energy density between inside and outside
the bubble is negligible. There are two kinds of mode functions. One kind has
usual continuous spectrum and the other has discrete spectrum with
characteristic wavelengths exceeding the spatial curvature scale. The latter
can be further devided into two classes in terms of its origin. One is called
the de Sitter super-curvature mode, which arises due to the global spacetime
structure of de Sitter space, and the other is due to fluctuations of the
bubble wall. We calculate the spectrum of quantum fluctuations in these models
and evaluate the resulting large angular scale CMB anisotropies. We find there
are ranges of model parameters that are consistent with observed CMB
anisotropies.",9605103v1
1996-10-15,The Theoretical Agenda in CMB Research,"The terrain that theorists cover in this CMB golden age is described. We
ponder early universe physics in quest of the fluctuation generator. We extoll
the virtues of inflation and defects. We transport fields, matter and radiation
into the linear (primary anisotropies) and nonlinear (secondary anisotropies)
regimes. We validate our linear codes to deliver accurate predictions for
experimentalists to shoot at. We struggle at the computing edge to push our
nonlinear simulations from only illustrative to fully predictive. We are now
phenomenologists, optimizing statistical techniques for extracting truths and
their errors from current and future experiments. We begin to clean
foregrounds. We join CMB experimental teams. We combine the CMB with large
scale structure, galaxy and other cosmological observations in search of
current concordance. The brave use all topical data. Others carefully craft
their prior probabilities to downweight data sets. We are always unbiased. We
declare theories sick, dead, ugly. Sometimes we cure them, resurrect them,
rarely beautify them. Our goal is to understand how all cosmic structure we see
arose and what the Universe is made of, and to use this to discover the laws of
ultrahigh energy physics. Theorists are humble, without hubris.",9610119v1
1996-11-05,Signatures of Stellar Reionization of the Universe,"The high ionization level and universal metallicity (1% solar) of the
intergalactic gas at redshifts z<5 implies that nonlinear structure had started
to form in the universe at earlier times than we currently probe. In Cold Dark
Matter (CDM) cosmologies, the first generation of baryonic objects emerges at
redshifts z=10-50. Here we examine the observable consequences of the
possibility that an early generation of stars reionized the universe and
resulted in the observed metallicity of the Lyman-alpha forest. Forthcoming
microwave anisotropy experiments will be sensitive to the damping of
anisotropies caused by scattering off free electrons from the reionization
epoch. For a large range of CDM models with a Scalo stellar mass function, we
find that reionization occurs at a redshift z>10 and damps the amplitude of
anisotropies on angular scales <10 degrees by a detectable amount, of order
10-25%. However, reionization is substantially delayed if the initial stellar
mass function transformed most of the baryons into low mass stars. In this
case, the mass fraction of pre-galactic stars could be constrained from the
statistics of microlensing events in galactic halos or along lines of sight to
quasars. Deep infrared imaging with future space telescopes (such as SIRTF or
the Next Generation Space Telescope) will be able to detect bright star
clusters at z>5. The cumulative Bremsstrahlung emission from these star
clusters yields a measurable distortion to the spectrum of the microwave
background.",9611028v2
1997-02-21,An Upper Limit to Arcminute Scale Anisotropy in the Cosmic Microwave Background Radiation at 142 GHz,"We present limits to anisotropies in the cosmic microwave background
radiation (CMB) at angular scales of a few arcminutes. The observations were
made at a frequency of 142 GHz using a 6-element bolometer array (the
Sunyaev-Zel'dovich Infrared Experiment) at the Caltech Submillimeter
Observatory. Two patches of sky, each approximately 36'x4' and free of known
sources, were observed for a total of 6-8 hours each, resulting in
approximately 80 independent 1.7' full-width half-maximum pixels. Each pixel is
observed with both a dual-beam and a triple-beam chop, with a sensitivity per
pixel of 90-150 uK in each chop. These data have been analyzed using maximum
likelihood techniques by assuming a gaussian autocorrelation function for the
distribution of CMB fluctuations on the sky. We set an upper limit of Delta T/T
<= 2.1 x 10^{-5} (95% confidence) for a coherence angle to the fluctuations of
1.1. These limits are comparable to the best limits obtained from
centimeter-wavelength observations on similar angular scales but have the
advantage that the contribution from known point sources is negligible at these
frequencies. They are the most sensitive millimeter-wavelength limits for
coherence angles <= 3'. The results are also considered in the context of
secondary sources of anisotropy, specifically the Sunyaev-Zel'dovich effect
from galaxy clusters.",9702196v1
1997-04-24,Evidence for Brightness-Dependent Anisotropy of Gamma Ray Bursts and Its Galactic Intepretation,"We show that the brighter gamma-ray bursts (GRBs) in the BATSE 3B catalog
concentrate slightly toward the Galactic plane and center, suggesting that at
least some bursts originate within the Galaxy. To develop an interpretation of
this brightness-dependent anisotropy, we consider GRBs distributed in a thick
disk centered on the Galaxy. As an approximation to the true luminosity
distribution, we divide bursts into two distinct luminosity classes. Most
bursts originate from low-luminosity, nearby sources while the relatively few
high-luminosity sources trace the shape of the thick disk. We find that
characteristic disk dimensions as small as 20 kpc in thickness and 30 kpc in
radial extent can match the observed brightness-dependent anisotropy as well as
the number-flux distribution; these dimensions are smaller than previously
considered viable. For bursts distributed in a disk of these compact
dimensions, the low-luminosity sources must have peak powers of $\lapprox
5\times 10^{40}$ erg s$^{-1}$ and rate densities of $\gapprox 5\times 10^{-3}$
yr$^{-1}$ kpc$^{-3}$. The high-luminosity sources must have a peak luminosity
of $\simeq 10^{42}$ erg s$^{-1}$ but their rate density need be only 5% or less
than that of the low-luminosity sources. If the Andromeda Galaxy contained a
similar population of high-luminosity sources, their peak gamma-ray fluxes
would be less than $\sim 0.1$ s$^{-1}$ cm$^{-2}$, making their detection
problematic. Statistical analyses of the gamma-ray burst events obtained since
the compilation of the 3B catalog will determine whether the thick-disk
interpretation is preferred over the isotropic one.",9704244v1
1998-03-04,Moving Gravitational Lenses: imprints on the CMB,"With the new generation of instruments for Cosmic Microwave Background (CMB)
observations aiming at an accuracy level of a few percent in the measurement of
the angular power spectrum of the anisotropies, the study of the contributions
due to secondary effects has gained impetus. Furthermore, a reinvestigation of
the main secondary effects is crucial in order to predict and quantify their
effects on the CMB and the errors that they induce in the measurements. In this
paper, we investigate the contribution, to the CMB, of secondary anisotropies
induced by the transverse motions of clusters of galaxies. This effect is
similar to the Kaiser-Stebbins effect. In order to address this problem, we
model the gravitational potential well of an individual structure using the
Navarro, Frenk & White profile. We generalise the effect of one structure to a
population of objects predicted using the Press-Schechter formalism. We
simulate maps of these secondary fluctuations, compute the angular power
spectrum and derive the average contributions for three cosmological models. We
then investigate a simple method to separate this new contribution from the
primary anisotropies and from the main secondary effect, the Sunyaev-Zel'dovich
kinetic effect from the lensing clusters.",9803040v1
1998-04-04,Computing CMB Anisotropy in Compact Hyperbolic Spaces,"The measurements of CMB anisotropy have opened up a window for probing the
global topology of the universe on length scales comparable to and beyond the
Hubble radius. For compact topologies, the two main effects on the CMB are: (1)
the breaking of statistical isotropy in characteristic patterns determined by
the photon geodesic structure of the manifold and (2) an infrared cutoff in the
power spectrum of perturbations imposed by the finite spatial extent. We
present a completely general scheme using the regularized method of images for
calculating CMB anisotropy in models with nontrivial topology, and apply it to
the computationally challenging compact hyperbolic topologies. This new
technique eliminates the need for the difficult task of spatial eigenmode
decomposition on these spaces. We estimate a Bayesian probability for a
selection of models by confronting the theoretical pixel-pixel temperature
correlation function with the COBE-DMR data. Our results demonstrate that
strong constraints on compactness arise: if the universe is small compared to
the `horizon' size, correlations appear in the maps that are irreconcilable
with the observations. If the universe is of comparable size, the likelihood
function is very dependent upon orientation of the manifold wrt the sky. While
most orientations may be strongly ruled out, it sometimes happens that for a
specific orientation the predicted correlation patterns are preferred over the
conventional infinite models.",9804041v2
1998-05-24,"Brown Dwarfs, White Knights and Demons","This paper investigates the hypothesis that the lensing objects towards the
Large Magellanic Cloud (LMC) are brown dwarfs by analysing the effects of
velocity anisotropy on the inferred microlensing masses. To reduce the masses,
the transverse velocity of the lenses with respect to the microlensing tube
must be minimised. In the outer halo, radial anisotropy is best for doing this;
closer to the solar circle, azimuthal anisotropy is best. By using a constraint
on the total kinetic energy of the tracer population from the Jeans equations,
the microlensing mass is minimised over orientations of the velocity dispersion
tensor. This minimum mass is about a tenth of a solar mass, which lies above
the hydrogen burning limit. This demonstrates explicitly that populations of
brown dwarfs with smoothly decreasing densities and dynamically mixed velocity
distributions cannot be responsible for the microlensing events. Brown dwarfs
are no white knights! There is one caveat. If there are demons sitting on the
microlensing tube, they can drop brown dwarfs so as to reproduce the
microlensing data-set exactly. Such a distribution is not smooth and does not
give well-mixed velocities in phase space. It is a permissible solution only if
the outer halo is dynamically young and lumpy. In such a case, theorists cannot
rule out brown dwarfs. Only exorcists can!",9805304v1
1998-06-06,Study of Broad Scale Anisotropy of Cosmic Ray Arrival Directions from $2\times 10^{17} eV$ to $10^{20} eV$ from Fly's Eye Data,"We report results on the broad scale anisotropy of cosmic ray arrival
directions in the energy rage from $2 \times 10^{17} eV$ to $10^{20} eV$. The
data was taken by the Fly's Eye detector in both monocular and stereo modes of
operation. We look for dependence on galactic latitude or supergalactic
latitude by fitting the data to a Wdowczyk and Wolfendale plane enhancement
function and a N-S gradient functional form. We report a small but
statistically significant galactic plane enhancement in the energy range
between $2\times 10^{17}eV$ and $3.2 \times 10^{18} eV$. The probability that
this anisotropy is due to fluctuations of an isotropic distribution is less
than 0.06%. The most significant galactic plane enhancement factor $f_{E} =
0.104 \pm 0.036$ is in the energy range $0.4-1.0 \times 10^{18} eV$. No
statistically significant evidence for a N-S gradient is found. There is no
sign of significant deviation from isotropic background when the data is
analyzed in terms of supergalactic latitude distributions",9806096v1
1998-06-27,Observationally Determining the Properties of Dark Matter,"Determining the properties of the dark components of the universe remains one
of the outstanding challenges in cosmology. We explore how upcoming CMB
anisotropy measurements, galaxy power spectrum data, and supernova (SN)
distance measurements can observationally constrain their gravitational
properties with minimal assumptions on the theoretical side. SN observations
currently suggest the existence of dark matter with an exotic equation of state
p/rho < -1/3 that accelerates the expansion of the universe. When combined with
CMB anisotropy measurements, SN or galaxy survey data can in principle
determine the equation of state and density of this component separately,
regardless of their value, as long as the universe is spatially flat. Combining
these pairs creates a sharp consistency check. If p/rho > -1/2, then the
clustering behavior (sound speed) of the dark component can be determined so as
to test the scalar-field ``quintessence'' hypothesis. If the exotic matter
turns out instead to be simply a cosmological constant (p/rho = -1), the
combination of CMB and galaxy survey data should provide a significant
detection of the remaining dark matter, the neutrino background radiation
(NBR). The gross effect of its density or temperature on the expansion rate is
ill-constrained as it is can be mimicked by a change in the matter density.
However, anisotropies of the NBR break this degeneracy and should be detectable
by upcoming experiments.",9806362v1
1998-07-29,ARGO CMB Anisotropy Measurement Constraints on Open and Flat-Lambda CDM Cosmogonies,"We use data from the ARGO cosmic microwave background (CMB) anisotropy
experiment to constrain cosmogonies. We account for the ARGO beamwidth and
calibration uncertainties, and marginalize over the offset removed from the
data. Our derived amplitudes of the CMB anisotropy detected by the ARGO
experiment are smaller than those derived previously.
  We consider open and spatially-flat-Lambda cold dark matter cosmogonies, with
clustered-mass density parameter Omega_0 in the range 0.1-1, baryonic-mass
density parameter Omega_B in the range (0.005-0.029)h^{-2}, and age of the
universe t_0 in the range (10--20) Gyr. Marginalizing over all parameters but
Omega_0, the ARGO data favors an open (spatially-flat-Lambda) model with
Omega_0= 0.23 (0.1). However, these numerical values are model dependent.
  At the 2 sigma confidence level model normalizations deduced from the ARGO
data are consistent with those drawn from the UCSB South Pole 1994, MAX 4+5,
White Dish, and SuZIE data sets. The ARGO open model normalizations are also
consistent with those deduced from the DMR data. However, for most
spatially-flat-Lambda models the DMR normalizations are more than 2 sigma above
the ARGO ones.",9807298v1
1998-08-01,Implications of SCUBA observations for the Planck Surveyor,"We investigate the implications for the Planck Surveyor of the recent
sub-millimetre number counts obtained using the SCUBA camera. Since it observes
at the same frequency as one of the higher frequency science channels on
Planck, SCUBA can provide constraints on the point-source contribution to the
CMB angular power spectrum, which require no extrapolation in frequency. We
have calculated the two-point function of these sub-millimetre sources, using a
Poisson model normalized to the observed counts. While the current data are
uncertain, under reasonable assumptions the point-source contribution to the
anisotropy is comparable to the noise in the 353GHz channel. The clustering of
these sources is currently unknown, however if they cluster like the z~3
Lyman-break galaxies their signal would be larger than the primary anisotropy
signal on scales smaller than about 10 arcmin. We expect the intensity of these
sources to decrease for wavelengths longward of 850 microns. At the next lowest
Planck frequency, 217GHz, the contribution from both the clustered and Poisson
terms are dramatically reduced. Hence we do not expect these sources to
seriously affect Planck's main science goal, the determination of the
primordial anisotropy power spectrum. Rather, the potential determination of
the distribution of sub-mm sources is a further piece of cosmology that Planck
may be able to tackle.",9808003v3
1999-04-29,1+3 Covariant Cosmic Microwave Background anisotropies II: The almost - Friedmann Lemaitre model,"This is the second of a series of papers extending the 1+3 covariant and
gauge invariant treatment of kinetic theory to an examination of Cosmic
Microwave Background temperature anisotropies arising from inhomogeneities in
the early universe. The first paper dealt with algebraic issues.
  Here we derive the mode form of the integrated Boltzmann equations, first,
giving a covariant version of the standard derivation using the mode recursion
relations, second, demonstrating the link to the multipole divergence equations
and finally various analytic ways of solving the resulting equations are
discussed.
  A general integral form of solution is obtained for the equations with
Thomson scattering. The covariant Friedmann-Lemaitre multipole form of the
transport equations are found using the covariant and gauge-invariant
generalization of the Peebles and Yu expansion in Thompson scattering time. The
dispersion relations and damping scale are then obtained from the covariant
approach. The equations are integrated to give the covariant and
gauge-invariant equivalent of the canonical scalar sourced anisotropies.
  We carry out a simple treatment of the matter dominated free-streaming
projection, slow decoupling, and tight-coupling cases, with the aim both giving
a unified transparent derivation of this range of results and clarifying the
connection between the more usual approaches (for example that of Hu and
Sugiyama) and the treatment for scalar perturbations (for example the treatment
of Challinor and Lasenby).",9904408v2
1999-06-22,The origin and formation of cuspy density profiles through violent relaxation of stellar systems,"It is shown that the cuspy density distributions observed in the cores of
elliptical galaxies can be realized by dissipationless gravitational collapse.
The initial models consist of power-law density spheres such as $\rho\propto
r^{-1}$ with anisotropic velocity dispersions. Collapse simulations are carried
out by integrating the collisionless Boltzmann equation directly, on the
assumption of spherical symmetry. From the results obtained, the extent of
constant density cores, formed through violent relaxation, decreases as the
velocity anisotropy increases radially, and practically disappears for
extremely radially anisotropic models. As a result, the relaxed density
distributions become more cuspy with increasing radial velocity anisotropy. It
is thus concluded that the velocity anisotropy could be a key ingredient for
the formation of density cusps in a dissipationless collapse picture. The
velocity dispersions increase with radius in the cores according to the nearly
power-law density distributions. The power-law index, $n$, of the density
profiles, defined as $\rho\propto r^{-n}$, changes from $n\approx 2.1$ at
intermediate radii, to a shallower power than $n\approx 2.1$ toward the centre.
This density bend can be explained from our postulated local phase-space
constraint that the phase-space density accessible to the relaxed state is
determined at each radius by the maximum phase-space density of the initial
state.",9906354v1
1999-07-05,Mean magnetic field generation in sheared rotators,"A generalized mean magnetic field induction equation for differential
rotators is derived, including a compressibility, and the anisotropy induced on
the turbulent quantities from the mean magnetic field itself and a mean
velocity shear. Derivations of the mean field equations often do not emphasize
that there must be anisotropy and inhomogeneity in the turbulence for mean
field growth. The anisotropy from shear is the source of a term involving the
product of the mean velocity gradient and the cross-helicity correlation of the
isotropic parts of the fluctuating velocity and magnetic field,
$\lb{\bfv}\cdot{\bfb}\rb^{(0)}$. The full mean field equations are derived to
linear order in mean fields, but it is also shown that the cross-helicity term
survives to all orders in the velocity shear. This cross-helicity term can
obviate the need for a pre-existing seed mean magnetic field for mean field
growth: though a fluctuating seed field is necessary for a non-vanishing
cross-helicity, the term can produce linear (in time) mean field growth of the
toroidal field from zero mean field. After one vertical diffusion time, the
cross-helicity term becomes sub-dominant and dynamo exponential
amplification/sustenance of the mean field can subsequently ensue. The
cross-helicity term should produce odd symmetry in the mean magnetic field, in
contrast to the usually favored even modes of the dynamo amplification in
sheared discs. This may be important for the observed mean field geometries of
spiral galaxies. The strength of the mean seed field provided by the cross-
helicity depends linearly on the magnitude of the cross-helicity.",9907061v3
1999-08-26,Data Processing and Compression of Cosmic Microwave Background Anisotropies on Board the PLANCK Satellite,"We present a simple way of coding and compressing the data on board the
Planck instruments (HFI and LFI) to address the problem of the on board data
reduction. This is a critical issue in the Planck mission. The total
information that can be downloaded to Earth is severely limited by the
telemetry allocation. This limitation could reduce the amount of diagnostics
sent on the stability of the radiometers and, as a consequence, curb the final
sensitivity of the CMB anisotropy maps. Our proposal to address this problem
consists in taking differences of consecutive circles at a given sky pointing.
To a good approximation, these differences are independent of the external
signal, and are dominated by thermal (white) instrumental noise. Using
simulations and analytical predictions we show that high compression rates,
$c_r \simeq 10$, can be obtained with minor or zero loss of CMB sensitivity.
Possible effects of digital distortion are also analized. The proposed scheme
allows for flexibility to optimize the relation with other critical aspects of
the mission. Thus, this study constitutes an important step towards a more
realistic modeling of the final sensitivity of the CMB temperature anisotropy
maps.",9908289v1
2000-02-21,Properties of spherical galaxies and clusters with an NFW density profile,"Using the standard dynamical theory of spherical systems, we calculate the
properties of spherical galaxies and clusters whose density profiles obey the
universal form first obtained in high resolution cosmological N-body
simulations by Navarro, Frenk & White. We adopt three models for the internal
kinematics: isotropic velocities, constant anisotropy and increasingly radial
Osipkov-Merritt anisotropy. Analytical solutions are found for the radial
dependence of the mass, gravitational potential, velocity dispersion, energy
and virial ratio and we test their variability with the concentration parameter
describing the density profile and amount of velocity anisotropy. We also
compute structural parameters, such as half-mass radius, effective radius and
various measures of concentration. Finally, we derive projected quantities, the
surface mass density and line-of-sight as well as aperture velocity dispersion,
all of which can be directly applied in observational tests of current
scenarios of structure formation. On the mass scales of galaxies, if constant
mass-to-light is assumed, the NFW surface density profile is found to fit well
Hubble-Reynolds laws. It is also well fitted by Sersic R^(1/m) laws, for m ~ 3,
but in a much narrower range of m and with much larger effective radii than are
observed. Assuming in turn reasonable values of the effective radius, the mass
density profiles imply a mass-to-light ratio that increases outwards at all
radii.",0002395v2
2000-02-24,An Australia telescope survey for CMB anisotropies,"We have surveyed six distinct `empty fields' using the Australia Telescope
Compact Array in an ultra-compact configuration with the aim of imaging, with a
high brightness sensitivity, any arcmin-scale brightness-temperature
anisotropies in the background radio sky. The six well-separated regions were
observed at a frequency of 8.7 GHz and the survey regions were limited by the
ATCA primary beams which have a full width at half maximum of 6 arcmin at this
frequency; all fields were observed with a resolution of 2 arcmin and an rms
thermal noise of 24 microJy/beam. After subtracting foreground confusion
detected in higher resolution images of the fields, residual fluctuations in
Stokes I images are consistent with the expectations from thermal noise and
weaker (unidentified) foreground sources; the Stokes Q and U images are
consistent with expectations from thermal noise.
  Within the sensitivity of our observations, we have no reason to believe that
there are any Sunyaev-Zeldovich holes in the microwave sky surveyed. Assuming
Gaussian-form CMB anisotropy with a `flat' spectrum, we derive 95 per cent
confidence upper limits of Q_flat < 10--11 microK in polarized intensity and
Q_flat < 25 microK in total intensity. The ATCA filter function peaks at l=4700
and has half maximum values at l=3350 and 6050.",0002467v1
2000-04-28,A Flat Universe from High-Resolution Maps of the Cosmic Microwave Background Radiation,"The blackbody radiation left over from the Big Bang has been transformed by
the expansion of the Universe into the nearly isotropic 2.73K Cosmic Microwave
Background. Tiny inhomogeneities in the early Universe left their imprint on
the microwave background in the form of small anisotropies in its temperature.
These anisotropies contain information about basic cosmological parameters,
particularly the total energy density and curvature of the universe. Here we
report the first images of resolved structure in the microwave background
anisotropies over a significant part of the sky. Maps at four frequencies
clearly distinguish the microwave background from foreground emission. We
compute the angular power spectrum of the microwave background, and find a peak
at Legendre multipole $\ell_{peak}=(197 \pm 6)$, with an amplitude
$DT_{200}=(69 \pm 8)\mu K$. This is consistent with that expected for cold dark
matter models in a flat (euclidean) Universe, as favoured by standard
inflationary scenarios.",0004404v1
2000-05-22,Exhaustive Study of Cosmic Microwave Background Anisotropies in Quintessential Scenarios,"Recent high precision measurements of the CMB anisotropies performed by the
BOOMERanG and MAXIMA-1 experiments provide an unmatched set of data allowing to
probe different cosmological models. Among these scenarios, motivated by the
recent measurements of the luminosity distance versus redshift relation for
type Ia supernovae, is the quintessence hypothesis. It consists in assuming
that the acceleration of the Universe is due to a scalar field whose final
evolution is insensitive to the initial conditions. Within this framework we
investigate the cosmological perturbations for two well-motivated potentials:
the Ratra-Peebles and the SUGRA tracking potentials. We show that the solutions
of the perturbed equations possess an attractor and that, as a consequence, the
insensitivity to the initial conditions is preserved at the perturbed level.
Then, we study the predictions of these two models for structure formation and
CMB anisotropies and investigate the general features of the multipole moments
in the presence of quintessence. We also compare the CMB multipoles calculated
with the help of a full Boltzmann code with the BOOMERanG and MAXIMA-1 data. We
pay special attention to the location of the second peak and demonstrate that
it significantly differs from the location obtained in the cosmological
constant case. Finally, we argue that the SUGRA potential is compatible with
all the recent data with a standard values of the cosmological parameters. In
particular, it fits the MAXIMA-1 data better than a cosmological constant or
the Ratra-Peebles potential.",0005428v1
2000-07-13,Cyclotron Line Features from Near-Critical Fields II: on the Effect of Anisotropic Radiation Fields,"We assess the impact of radiation anisotropy on the line shapes that result
from relativistic magnetic Compton scattering in the low-density/high-field
regime. A Monte Carlo implementation of radiation transport allows for spatial
diffusion of photons in arbitrary geometries and accounts for relativistic
angular redistribution. The cross section includes natural line widths and
photon ""spawning"" from up to fourth harmonic photons. In our first paper we
noted that even if the photon injection is isotropic a strongly anisotropic
radiation field rapidly ensues. We now investigate the angular distribution of
cyclotron spectra emerging from an internally irradiated magnetized plasma with
a prescribed global geometry (either cylindrical or plane parallel) and the
effects of anisotropic photon injection on the line shapes. Varying the input
angular distribution permits a better understanding of the line formation
process in more realistic scenarios where the radiative mechanisms are
influenced by the intrinsic anisotropy of the field and by moderate
relativistic beaming. In general, the line features are most pronounced along
the directions of the anisotropic continuum injection and tend to be weakened
in other directions, relative to the line features resulting from an isotropic
continuum injection. We find that the enhancements at the line wings of the
fundamental, which appear prominantly in the case of isotropic continuum
injection, are strongly suppressed along the direction of anisotropy in the
case of beamed continuum injection, regardless of geometry or beaming pattern.",0007191v1
2000-08-02,Constraints on Cosmological Anisotropy out to z=1 from Supernovae Ia,"A combined sample of 79 high and low redshift supernovae Ia (SNe) is used to
set constraints on the degree of anisotropy in the Universe out to $z\simeq1$.
First we derive the global most probable values of matter density $\Omega_M $,
the cosmological constant $\Omega_\Lambda $, and the Hubble constant $H_0$, and
find them to be consistent with the published results from the two data sets of
Riess et al. 1998 (R98) and Perlmutter et al. 1999 (P99). We then examine the
Hubble diagram (HD, i.e., the luminosity-redshift relation) in different
directions on the sky by utilising spherical harmonic expansion. In particular,
via the analysis of the dipole anisotropy, we divide the sky into the two
hemispheres that yield the most discrepant of the three cosmological
parameters, and the scatter $\chi^2_{\rm HD}$ in each case. The most discrepant
values roughly move along the locus $-4\Omega_M +3 \Omega_{\Lambda} = 1$ (cf.
P99), but by no more than $\Delta \approx 2.5$ along this line. For a perfect
FRW universe, Monte Carlo realizations that mimic the current set of SNe yield
values higher than the measured $\Delta$ in $\sim 1/5$ of the cases. We discuss
implications for the validity of the Cosmological Principle, and possible
calibration problems in the SNe data sets.",0008041v1
2000-10-05,Planck LFI: Comparison Between Galaxy Straylight Contamination and other Systematic Effects,"The straylight contamination due to the Galactic emission (GSC, Galaxy
Straylight Contamination) entering at large angles from the antenna centre
direction may be one of the most critical sources of systematic effects in
observations of the cosmic microwave background (CMB) anisotropies by future
satellite missions like {\sc Planck} and MAP. We describe here different
methods to evaluate the impact of this effect and compare it with other
systematics of instrumental and astrophysical origin. The contributions within
few degrees from the beam centre dominate the GSC near the Galaxy plane. The
antenna sidelobes at intermediate and large angles from the beam centre
dominate the GSC at medium and high Galactic latitudes. We find a GSC peak at
$\sim 15\mu$K and a GSC angular power spectrum above that of the white noise
for multipoles $\ell \lsim 10$ albeit smaller than that of CMB anisotropies by
a factor larger than $\sim 10$. Although the GSC is largest at low Galactic
latitudes, the contamination produced by far pattern features at medium and
high Galactic latitudes, peaking at $\sim 4\mu$K, has to be carefully
investigated, because the combination of low amplitude of Galaxy emission in
those regions with the extremely good nominal {\sc Planck} sensitivity
naturally makes high Galactic latitude areas the targets for unprecedentedly
precise estimation of cosmological CMB anisotropy.",0010113v1
2000-12-28,Probing the dark energy: methods and strategies,"The presence of dark energy in the Universe is inferred directly from the
accelerated expansion of the Universe, and indirectly, from measurements of
cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3
of the critical density, is very smoothly distributed, and has large negative
pressure. Its nature is very much unknown. Most of its discernible consequences
follow from its effect on evolution of the expansion rate of the Universe,
which in turn affects the growth of density perturbations and the age of the
Universe, and can be probed by the classical kinematic cosmological tests.
Absent a compelling theoretical model (or even a class of models), we describe
the dark energy by an effective equation-of-state w=p_X/\rho_X which is allowed
to vary with time. We describe and compare different approaches for determining
w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies
and clusters, and CMB anisotropy, focusing particular attention on the use of a
sample of several thousand type Ia supernova with redshifts z\lesssim 1.7, as
might be gathered by the proposed SNAP satellite. Among other things, we derive
optimal strategies for constraining cosmological parameters using type Ia
supernovae. While in the near term CMB anisotropy will provide the first
measurements of w, supernovae and number counts appear to have the most
potential to probe dark energy.",0012510v1
2001-01-22,Polarization of the Cosmic Microwave Background from Non-Uniform Reionization,"We study the signal in the Cosmic Microwave Background (CMB) polarization
anisotropy resulting from patchy reionization. It is well known that the
primordial polarization of the CMB is very sensitive to the details of
reionization. Combining a semi-analytic model of galaxy formation, in which the
optical depth to the reionization epoch is in the range 0.014 to 0.048, with a
high resolution N-body simulation we find that reionization generates a peak
with amplitude 0.05~0.15 \mu K at large angular scales. The position of this
peak reveals the size of the horizon at reionization, whilst its amplitude is a
measure of the optical depth to reionization. On small scales, ionized patches
prior to full reionization create a second order polarization signal due to the
coupling of the free electron density fluctuation with the quadrupole moment of
the temperature anisotropy. Careful study reveals that the coupling generates
the same power spectra for electric and magnetic modes, whose amplitudes of
polarization anisotropies from this process are predicted to be ~10nK. The
amplitude depends strongly on the total baryon density $\Omega_b$ and on the
spatial correlations of the free electron density in the ionized regions, and
weakly on the fraction of ionizing photons able to escape their source galaxy,
$f_{esc}$. The first- and second-order signals are therefore sensitive to the
details of how the reionization occurred. Detection of these signals will place
important constraints on the reionization history of the Universe.",0101368v2
2001-03-09,Rayleigh Scattering and Microwave Background Fluctuations,"During the recombination epoch, cosmic background photons couple not only to
free electrons through Thompson scattering, but also to the neutral hydrogen
through Rayleigh scattering. This latter is ~2% effect for photons near the
peak of the photon energy distribution at z=800 and a ~0.2% effect at z=1100.
Including Rayleigh scattering in the calculation reduces Silk damping at fixed
redshift, alters the position of the surface of last scattering and alters the
propagation of acoustic waves. We estimate the amplitude of these effects. For
the Microwave Anisotropy Probe (MAP), Rayleigh scattering increases the
anisotropy spectrum by 0.1% at the most. For the highest frequencies of the
Planck Surveyor, the effects of Rayleigh scattering are much more dramatic
(decreasing the anisotropy spectrum by 3% at \nu~550GHz and l~1000). The
relative difference between the spectra of low and high frequencies is imposed
by an oscillation with a function of multipole l and the oscillation amplitude
is up to 0.5% between 100 and 550GHz. Rayleigh scattering also slows the
decoupling between radiation and matter, but the effect is undetectably small.",0103149v3
2001-03-12,Constraining the Properties of Dark Energy,"The presence of dark energy in the Universe is inferred directly from the
accelerated expansion of the Universe, and indirectly, from measurements of
cosmic microwave background (CMB) anisotropy. Dark energy contributes about 2/3
of the critical density, is very smoothly distributed, and has large negative
pressure. Its nature is very much unknown. Most of its discernible consequences
follow from its effect on evolution of the expansion rate of the Universe,
which in turn affects the growth of density perturbations and the age of the
Universe, and can be probed by the classical kinematic cosmological tests.
Absent a compelling theoretical model (or even a class of models), we describe
dark energy by an effective equation of state w=p_X/rho_X which is allowed to
vary with time. We describe and compare different approaches for determining
w(t), including magnitude-redshift (Hubble) diagram, number counts of galaxies
and clusters, and CMB anisotropy, focusing particular attention on the use of a
sample of several thousand type Ia supernova with redshifts z < 1.7, as might
be gathered by the proposed SNAP satellite. Among other things, we derive
optimal strategies for constraining cosmological parameters using type Ia
supernovae. While in the near term CMB anisotropy will provide the first
measurements of w, supernovae and number counts appear to have the most
potential to probe dark energy.",0103175v1
2001-05-23,Squared temperature-temperature power spectrum as a probe of the CMB bispectrum,"It is now well known that mode-coupling effects associated with certain
secondary effects generate higher order correlations in cosmic microwave
background (CMB) temperature anisotropies, beyond the two-point function. In
order to extract the non-Gaussian signal at the three-point level, we suggest a
two-point statistic in the form of an angular power spectrum involving
correlations between squared temperature and temperature anisotropies. This
power spectrum contains compressed information from the bispectrum and can be
easily measured in data with the same techniques that have been considered for
the measurement of the usual temperature-temperature anisotropy power spectrum.
We study the proposed power spectrum resulting from the non-Gaussian signal
generated by correlations involved with gravitational lensing angular
deflections in CMB and the Sunyave-Zel'dovich (SZ) effect due to large scale
pressure fluctuations. Using the Planck frequency cleaned CMB and SZ maps, the
CMB^2-SZ power spectrum provides a direct estimate of the cross-power between
lensing angular deflections and the SZ effect. Through an optimal filter
applied to the squared CMB map, the proposed statistic allows one to obtain all
information from the lensing-SZ bispectrum. The observational measurement of
the lensing-SZ cross-correlation is useful to understand the relation between
large scale structure pressure and dark matter fluctuations.",0105415v1
2001-09-25,Dark Matter in Dwarf Spheroidals I: Models,"This paper introduces a new two-parameter family of dwarf spheroidal (dSph)
galaxy models. The density distribution has a Plummer profile and falls like
the inverse fourth power of distance in projection, in agreement with the
star-count data. The first free parameter controls the velocity anisotropy, the
second controls the dark matter content. The dark matter distribution can be
varied from one extreme of mass-follows-light through a near-isothermal halo
with flat rotation curve to the other extreme of an extended dark halo with
harmonic core. This family of models is explored analytically in some detail --
the distribution functions, the intrinsic moments and the projected moments are
all calculated. For the nearby Galactic dSphs, samples of hundreds of discrete
radial velocities are becoming available. A technique is developed to extract
the anisotropy and dark matter content from such data sets by maximising the
likelihood function of the sample of radial velocities. This is constructed
from the distribution function and corrected for observational errors and the
effects of binaries. Tests on simulated data sets show that samples of 1000
discrete radial velocities are ample to break the degeneracy between mass and
anisotropy in the nearby dSphs. Interesting constraints can already be placed
on the distribution of the dark matter with samples of 160 radial velocities
(the size of the present-day data set for Draco).",0109451v2
2002-04-03,Weak Lensing of the CMB: Extraction of Lensing Information from the Trispectrum,"We discuss the four-point correlation function, or the trispectrum in Fourier
space, of CMB temperature and polarization anisotropies due to the weak
gravitational lensing effect by intervening large scale structure. We discuss
the squared temperature power spectrum as a probe of this trispectrum and, more
importantly, as an observational approach to extracting the power spectrum of
the deflection angle associated with the weak gravitational lensing effect on
the CMB. We extend previous discussions on the trispectrum and associated weak
lensing reconstruction from CMB data by calculating non-Gaussian noise
contributions, beyond the previously discussed dominant Gaussian noise.
Non-Gaussian noise contributions are generated by lensing itself and by the
correlation between the lensing effect and other foreground secondary
anisotropies in the CMB such as the Sunyaev-Zel'dovich (SZ) effect. When the SZ
effect is removed from temperature maps using its spectral dependence, we find
these additional non-Gaussian noise contributions to be an order of magnitude
lower than the dominant Gaussian noise. If the noise-bias due to the dominant
Gaussian part of the temperature squared power spectrum is removed, then these
additional non-Gaussian contributions provide the limiting noise level for the
lensing reconstruction. The temperature squared power spectrum allows a high
signal-to-noise extraction of the lensing deflections and a confusion-free
separation of the curl (or B-mode) polarization due to inflationary
gravitational waves from that due to lensed gradient (or E-mode) polarization.
The small angular scale temperature and polarization anisotropy measurements
provide a novel approach to weak lensing studies, complementing the approach
based on galaxy ellipticities.",0204068v1
2002-04-04,Large Scale Structure in an Era of Precision CMB Measurements,"The advent of high signal-to-noise cosmic microwave background (CMB)
anisotropy experiments now allow detailed studies on the statistics related to
temperature fluctuations. The existence of acoustic oscillations in the
anisotropy power spectrum is now established with the clear detection of the
first, and to a lesser confidence the second and the third, peak. Beyond the
acoustic peak structure associated with CMB photon temperature fluctuations, we
study the possibility for an observational detection of oscillations in the
large scale structure (LSS) matter power spectrum due to baryons. We also
suggest a new cosmological test using the angular power spectrum of dark matter
halos, or clusters of galaxies detected via wide-field surveys of the large
scale structure. The standard rulers of the proposed test involve overall shape
of the matter power spectrum and baryon oscillation peaks in projection. The
test allows a measurement of the angular diameter distance as a function of
redshift, similar to the distance to the last scattering surface from the first
acoustic peak in the temperature anisotropy power spectrum. The simultaneous
detection of oscillations in both photons and baryons will provide a strong,
and a necessary, confirmation of our understanding related to the physics
during the recombination era. The proposed studies can be carried out with a
combined analysis of CMB data from missions such as the MAP and the large scale
structure data from missions such as the DUET.",0204090v2
2002-04-15,Small Angular Scale CMB Anisotropies from CBI and BIMA: Early Universe or Local structures ?,"The advent of high resolution cosmic microwave background (CMB) experiments
now allows studies on the temperature fluctuations at scales corresponding to
few arcminutes and below. Though the reported excess power at $\ell \sim 2000 -
6000$ by CBI and BIMA is roughly consistent with a secondary contribution
resulting from the Sunyaev-Zeldovich effect, this requires a higher
normalization for the matter power spectrum than measured by other means. In
addition to a local red-shift contribution, another strong possibility for
anisotropies at very small scales involve non-standard aspects of inflationary
models. To distinguish between contributions from early universe and local
structures, including a potential point source contribution, and to understand
the extent to which structures at low red-shifts contribute to small scale
temperature anisotropies, it maybe necessary to perform a combined study
involving CMB and the large scale structure. We suggest a cross-correlation of
the temperature data with a map of the large scale structure, such as the
galaxy distribution. For next generation small angular scale CMB experiments,
multi-frequency observations may be a necessary aspect to allow an additional
possibility to distinguish between these different scenarios.",0204250v3
2003-01-06,"Compressible Magnetohydrodynamic Turbulence: mode coupling, scaling relations, anisotropy, new regime and astrophysical implications","We present numerical simulations and explore scalings and anisotropy of
compressible magnetohydrodynamic (MHD) turbulence. Our study covers both gas
pressure dominated (high beta) and magnetically dominated (low beta) plasmas at
different Mach numbers. In addition, we present results for superAlfvenic
turbulence and discuss in what way it is similar to the subAlfvenic turbulence.
We describe a technique of separating different magnetohydrodynamic (MHD) modes
(slow, fast and Alfven) and apply it to our simulations. We show that, for both
high and low beta cases, Alfven and slow modes reveal the Kolmogorov spectrum
(index=-5/3) and scale-dependent Goldreich-Sridhar anisotropy, while fast modes
exhibit spectrum with index=-3/2 and isotropy. We discuss the statistics of
density fluctuations arising from MHD turbulence at different regimes. Our
findings entail numerous astrophysical implications ranging from cosmic ray
propagation to gamma ray bursts and star formation. In particular, we show that
the rapid decay of turbulence reported by earlier researchers is not related to
compressibility and mode coupling in MHD turbulence. In addition, we show that
magnetic field enhancements and density enhancements are marginally correlated.
Addressing the density structure of partially ionized interstellar gas on AU
scales, we show that the new regime of MHD turbulence that we earlier reported
for incompressible flows persists for compressible turbulence and therefore may
provide an explanation for those mysterious structures.",0301062v3
2003-02-16,Anisotropies in the redshift-space correlations of galaxy groups and clusters II: Analysis of observational cluster samples,"We study the redshift space correlation function of galaxy clusters for
observational samples constructed in different surveys. We explore correlation
amplitudes, pairwise velocity distributions and bias factors. Systematics in
cluster identification procedures are the main source of biased estimates of
the correlation amplitude and inferred velocity dispersions. By comparing our
results with those of numerical simulations we explore the strong influence on
the clustering distortion pattern in redshift space from effects associated
with the cluster identification procedure from two dimensional surveys as is
the case of Abell and APM clusters. The identification of clusters in X-ray
surveys improves this situation, although there are still systematic effects
which are probably due to identification of optical sources in the
determination of cluster redshifts. These systematics are particularly strong
for the most luminous X-ray selected clusters in the Extended Bright Cluster
Survey, which exhibits very large anisotropies, comparable to those present in
the Abell catalogue. Our results demonstrate that forthcoming large redshift
surveys will be extremely important for the construction of new samples of
groups and clusters as well as improving the determination of optical and X-ray
selected cluster distances, essential for reliable analyses of the large scale
structure.",0302310v1
2003-02-18,Current constraints on Cosmological Parameters from Microwave Background Anisotropies,"We compare the latest observations of Cosmic Microwave Background (CMB)
Anisotropies with the theoretical predictions of the standard scenario of
structure formation. Assuming a primordial power spectrum of adiabatic
perturbations we found that the total energy density is constrained to be
$\Omega_{tot}=1.03\pm0.06$ while the energy density in baryon and Cold Dark
Matter (CDM) are $\Omega_bh^2=0.021\pm0.003$ and $\Omega_{cdm}h^2=0.12\pm0.02$,
(all at 68% C.L.) respectively. The primordial spectrum is consistent with
scale invariance, ($n_s=0.97\pm0.04$) and the age of the universe is
$t_0=14.6\pm0.9$ Gyrs. Adding informations from Large Scale Structure and
Supernovae, we found a strong evidence for a cosmological constant
$\Omega_{\Lambda}=0.70_{-0.05}^{+0.07}$ and a value of the Hubble parameter
$h=0.69\pm0.07$. Restricting this combined analysis to flat universes, we put
constraints on possible 'extensions' of the standard scenario. A gravity waves
contribution to the quadrupole anisotropy is limited to be $r \le 0.42$ (95%
c.l.). A constant equation of state for the dark energy component is bound to
be $w_Q \le -0.74$ (95% c.l.). We constrain the effective relativistic degrees
of freedom $N_\nu \leq 6.2$ and the neutrino chemical potential $-0.01 \leq
\xi_e \leq 0.18$ and $|\xi_{\mu,\tau}|\leq 2.3$ (massless neutrinos).",0302361v1
2003-03-02,Small-scale CMB polarization anisotropies due to tangled primordial magnetic fields,"Tangled, primordial cosmic magnetic fields create small rotational velocity
perturbations on the last scattering surface (LSS) of the cosmic microwave
background radiation (CMBR). Such perturbations can contribute significantly to
the CMBR temperature and polarization anisotropies at large l > 1000 or so,
like the excess power detected by the CBI experiment. The magnetic contribution
can be distinguished from most conventional signals, as they lead to CMBR
polarization dominated by the odd parity, B-type signal. Experiments like DASI
and WMAP have detected evidence for CMBR polarization at small l. Many
experiments will also probe the large $l$ regime. We therefore calculate the
polarization signals due to primordial magnetic fields, for different spectra
and different cosmological parameters. A scale-invariant spectrum of tangled
fields which redshifts to a present value B_{0}=3\times 10^{-9} Gauss, produces
B-type polarization anisotropies of order 0.3 - 0.4 micro Kelvin between l of
1000-5000. Larger signals result if the spectral index of magnetic tangles is
steeper, n>-3. The peak of the signal shifts to larger l for a lambda-dominated
universe, or if the baryon density is larger. The signal will also have
non-Gaussian statistics. We also predict the much smaller E-type polarization,
and T-E cross correlations for these models.",0303014v2
2003-09-12,Stellar Orbits and the Interstellar Gas Temperature in Elliptical Galaxies,"We draw attention to the close relationship between the anisotropy parameter
beta(r) for stellar orbits in elliptical galaxies and the temperature profile
T(r) of the hot interstellar gas. For nearly spherical galaxies the gas density
can be accurately determined from X-ray observations and the stellar luminosity
density can be accurately found from the optical surface brightness. The Jeans
equation and hydrostatic equilibrium establish a connection between beta(r) and
T(r) that must be consistent with the observed stellar velocity dispersion.
Purely optical observations of the bright elliptical galaxy NGC 4472 indicate
beta(r) < 0.35 within the effective radius. However, the X-ray gas temperature
profile T(r) for NGC 4472 requires significantly larger anisotropy, beta = 0.6
- 0.7, about twice the optical value. This strong preference for radial stellar
orbits must be understood in terms of the formation history of massive
elliptical galaxies. Conversely, if the smaller, optically determined
anisotropy is indeed correct, we are led to the important conclusion that the
temperature profile T(r) of the hot interstellar gas in NGC 4472 must differ
from that indicated by X-ray observations, or that the hot gas is not in
hydrostatic equilibrium.",0309367v1
2003-09-18,Sunyaev-Zel'dovich Effect by Multiple Sctattering : Numerical Solution of the Transfer Equations,"The radiative transfer equations for multiple inverse Compton scattering of
the Cosmic Microwave Background Radiation (CMBR) by the hot intra-cluster
electrons are solved numerically. The spherical isothermal and inhomogeneous
$\beta$ model has been considered for the electron distribution. The anisotropy
of the CMBR caused by scattering, known as thermal Sunyaev-Zel'dovich effect,
along the radial axis of the medium is compared with the analytical solution of
Kompaneets equation. The X-ray data of several clusters of galaxies at low
redshifts provide an estimation of the central electron density $n_0$ to be of
the order $10^{-3}$. It is found that for this value of $n_0$ the effect of
multiple scattering is negligible. The numerically calculated anisotropy along
the radial axis matches well with the analytical solution that describes single
scattering. The result incorporating multiple scattering is fitted with the
recent observation of Sunyaev-Zel'dovich effect in the cluster Abell 2163. It
is shown that if $n_0$ is greater by an order of magnitude, which could be
possible for cluster of galaxies at comparatively higher redshift, multiple
scattering would play a significant role at the Wien region of the anisotropy
spectrum. A fitting formula for the correction to the Sunyaev-Zel'dovich effect
due to multiple scattering is provided.",0309507v1
2003-09-29,Non-linear evolution of the cosmological background density field as diagnostic of the cosmological reionization,"We present constraints on the cosmological and reionization parameters based
on the cumulative mass function of the Ly-alpha systems.
  We find that the analysis of the cumulative mass function of the Ly-alpha
systems indicates a reionization redshift z_r=24.2\+-4 (68%CL) in agreement
with the value found on the basis of the WMAP anisotropy measurements, setting
constraints on the amplitude of the density contrast, sigma_8=0.91+-0.04
(68\CL), similar to those derived from the X-ray cluster temperature function.
  Our joint analysis of Ly-alpha cumulative mass function and WMAP anisotropy
measurements shows that the possible current identification of a running of the
slope, dn_s/dlnk \ne 0, at k_p=0.05Mpc^-1 (multipole l of about 700) is mainly
an effect of the existing degeneracy in the amplitude-slope plane at this
scale, the result being consistent with the absence of running, the other
constraints based on WMAP data remaining substantially unchanged.
  Finally, we evaluate the progress on the determination the considered
parameters achievable by using the final temperature anisotropy data from WMAP
and from the forthcoming Planck satellite that will significantly improve the
sensitivity and reliability of these results.
  This work has been done in the framework of the Planck LFI activities.",0309785v1
2003-11-21,Cross-Correlation Studies with CMB Polarization Maps,"The free-electron population during the reionized epoch rescatters CMB
temperature quadrupole and generates a now well-known polarization signal at
large angular scales. While this contribution has been detected in the
temperature-polarization cross power spectrum measured with WMAP data, due to
the large cosmic variance associated with anisotropy measurements at tens of
degree angular scales only limited information related to reionization, such as
the optical depth to electron scattering, can be extracted. The inhomogeneities
in the free-electron population lead to an additional secondary polarization
anisotropy contribution at arcminute scales. While the fluctuation amplitude,
relative to dominant primordial fluctuations, is small, we suggest that a
cross-correlation between arcminute scale CMB polarization data and a tracer
field of the high redshift universe, such as through fluctuations captured by
the 21 cm neutral Hydrogen background or those in the infrared background
related to first proto-galaxies, may allow one to study additional details
related to reionization. For this purpose, we discuss an optimized higher order
correlation measurement, in the form of a three-point function, including
information from large angular scale CMB temperature anisotropies in addition
to arcminute scale polarization signal related to inhomogeneous reionization.
We suggest that the proposed bispectrum can be measured with a substantial
signal-to-noise ratio and does not require all-sky maps of CMB polarization or
that of the tracer field. A measurement such as the one proposed may allow one
to establish the epoch when CMB polarization related to reionization is
generated and to address if the universe was reionized once or twice.",0311513v3
2003-12-23,The CMB Power Spectrum from the Background Emission Anisotropy Scanning Telescope (BEAST) Experiment,"The Background Emission Anisotropy Scanning Telescope (BEAST) is a 2.2m
off-axis telescope with an 8 element mixed Q (38-45GHz) and Ka (26-36GHz) band
focal plane, designed for balloon borne and ground based studies of the Cosmic
Microwave Background. Here we present the Cosmic Microwave Background (CMB)
angular power spectrum calculated from 682 hours of data observed with the
BEAST instrument. We use a binned pseudo-Cl estimator (the MASTER method). We
find results that are consistent with other determinations of the CMB
anisotropy for angular wavenumber l between 100 and 600. We also perform
cosmological parameter estimation. The BEAST data alone produces a good
constraint on Omega_k = 1-Omega_tot=-0.074 +/- 0.070, consistent with a flat
Universe. A joint parameter estimation analysis with a number of previous CMB
experiments produces results consistent with previous determinations.",0312610v1
2004-02-15,Extended Mosaic Observations with the Cosmic Background Imager,"Two years of microwave background observations with the Cosmic Background
Imager (CBI) have been combined to give a sensitive, high resolution angular
power spectrum over the range 400 < l < 3500. This power spectrum has been
referenced to a more accurate overall calibration derived from WMAP. The data
cover 90 deg^2 including three pointings targeted for deep observations. The
uncertainty on the l > 2000 power previously seen with the CBI is reduced.
Under the assumption that any signal in excess of the primary anisotropy is due
to a secondary Sunyaev-Zeldovich anisotropy in distant galaxy clusters we use
CBI, ACBAR, and BIMA data to place a constraint on the present-day rms mass
fluctuation sigma_8. We present the results of a cosmological parameter
analysis on the l < 2000 primary anisotropy data which show significant
improvements in the parameters as compared to WMAP alone, and we explore the
role of the small-scale cosmic microwave background data in breaking parameter
degeneracies.",0402359v2
2004-05-25,Cross Terms and Weak Frequency Dependent Signals in the CMB Sky,"In this paper, we study the amplification of weak frequency dependent signals
in the CMB sky due to their cross correlation to intrinsic anisotropies. In
particular, we center our attention on mechanisms generating some weak signal,
of peculiar spectral behaviour, such as resonant scattering in ionic, atomic or
molecular lines, thermal SZ effect or extragalactic foreground emissions, whose
typical amplitude (denoted by $\epsilon$) is sufficiently smaller than the
intrinsic CMB fluctuations. We find that all these effects involve either the
autocorrelation of anisotropies generated during recombination ($z_{rec}$) or
the cross-correlation of those anisotropies with fluctuations arising at some
later redshift $z_i$. The degree of this correlation can be computed under the
assumption that density fluctuations were generated as standard inflationary
models dictate and that they evolved in time according to linear theory. In
case that the weak signal is frequency dependent, we show that, by substracting
power spectra at different frequencies, it is possible to avoid the limit
associated to Cosmic Variance and unveil weaker terms linear in $\epsilon$. We
find that the correlation term shows a different spectral dependence than the
squared ($\propto \epsilon^2$) term considered usually, making its extraction
particularly straightforward for the thermal SZ effect. Furthermore, we find
that in most cases the correlation terms are particularly relevant at low
multipoles and must be taken into account when characterising the power
spectrum associated to weak signals in the large angular scales.",0405487v2
2004-06-03,CMB anisotropies from primordial inhomogeneous magnetic fields,"Primordial inhomogeneous magnetic fields of the right strength can leave a
signature on the CMB temperature anisotropy and polarization. Potentially
observable contributions to polarization B-modes are generated by vorticity and
gravitational waves sourced by the magnetic anisotropic stress. We compute the
corresponding CMB transfer functions in detail including the effect of
neutrinos. The shear rapidly causes the neutrino anisotropic stress to cancel
the stress from the magnetic field, suppressing the production of gravitational
waves and vorticity on super-horizon scales after neutrino decoupling. A
significant large scale signal from tensor modes can only be produced before
neutrino decoupling, and the actual amplitude is somewhat uncertain. Plausible
values suggest primordial nearly scale invariant fields of ~ 10^(-10)G today
may be observable from their large scale tensor anisotropy. They can be
distinguished from primordial gravitational waves by their non-Gaussianity.
Vector mode vorticity sources B-mode power on much smaller scales with a power
spectrum somewhat similar to that expected from weak lensing, suggesting
amplitudes ~ 10^(-9)G may be observable on small scales for a spectral index of
n ~ -2.9. In the appendix we review the covariant equations for computing the
vector and tensor CMB power spectra that we implement numerically.",0406096v2
2004-06-22,Dealing with systematics in cosmic shear studies: new results from the VIRMOS-Descart Survey,"We present a reanalysis of the VIRMOS-Descart weak lensing data, with a
particular focus on different corrections for the variation of the point spread
function anisotropy (PSF) across the CCDs. We show that the small scale
systematics can be minimised, and eventually suppressed, using the B mode
(curled shear component)measured in the corrected stars and galaxies. Updated
cosmological constraints are obtained, free of systematics caused by PSF
anisotropy. To facilitate general use of our results, we provide the two-points
statistics data points with their covariance matrices up to a scale of one
degree. For the normalisation of the mass power spectrum we obtain
sigma_8=(0.83\pm 0.07)(Omega_M/0.3)^(-0.49). The shape parameter Gamma was
marginalised over Gamma=[0.1,0.3] and the mean source redshift z_s over
[0.8,1.0]. The latter is consistent with recent photometric redshifts obtained
for the VIRMOS data and the preliminary spectroscopic redshifts from the
VIRMOS-VVDS survey. The quoted 68% contour level includes all identified
sources of error. We discuss the possible sources of residual contamination in
this result: the effect of the non-linear mass power spectrum and remaining
issues concerning the PSF correction. Our result is compared with the first
release of the Wilkinson Microwave Anisotropy Probe data. It is found that Cold
Dark Matter models with a power law primordial power spectrum and high matter
density Omega_M > 0.5 are excluded at 3-sigma.",0406468v1
2004-08-19,Gamma Ray Bursts: new rulers to measure the Universe,"The best measure of the Universe should be done using a standard ""ruler"" at
any redshift. Type Ia Supernovae (SN Ia) probe the universe up to z$\sim$1.5,
while the Cosmic Microwave Background (CMB) primary anisotropies concern
basically $z\sim$1000. Apparently, Gamma--Ray Bursts (GRBs) are all but
standard candles. However, their emission is collimated and the
collimation--corrected energy correlates tightly with the frequency at which
most of the radiation of the prompt is emitted, as found by Ghirlanda et al.
(2004). Through this correlation we can infer the burst energy accurately
enough to probe the intermediate redshift ($z<10$) Universe. Using the best
known 15 GRBs we find very encouraging results that emphasize the cosmological
GRB role. A combined fit with SN Ia yields $\Omega_{\rm M}=0.37\pm0.10$ and
$\Omega_{\Lambda}=0.87\pm 0.23$. Assuming in addition a flat Universe, the
parameters are constrained to be $\Omega_{\rm M}=0.29\pm0.04$ and
$\Omega_{\Lambda}=0.71\pm 0.05$. GRBs accomplish the role of ""missing link""
between SN Ia and CMB primary anisotropies. They can provide a new insight on
the cosmic effects of dark energy, complementary to the one supplied by CMB
secondary anisotropies through the Integrated Sachs Wolfe effect. The
unexpected Standard Candle cosmological role of GRBs motivates the most
optimistic hopes for what can be obtained when the GRB-dedicated satellite,
Swift, will be launched.",0408350v1
2005-02-02,Cosmological Constraints on the Very Low Frequency Gravitational-Wave Background,"While there are no strong observational constraints on the gravitational wave
background across six or more orders of magnitude between 10^{-16} Hz and
10^{-10} Hz and it is difficult to get a constraint below 10^{-12}Hz using
objects in our Galaxy, we suggest that the anisotropy pattern of time variation
of the redshift related to a sample of high redshift objects can be used to
constrain the gravitational wave background around 10^{-12} Hz. Useful
observations for the monitoring of an anisotropy signal in a global redshift
change include spectroscopic observations of the Ly-alpha forest in absorption
towards a sample of quasars, redshifted 21 cm line observations either in
absorption or emission towards a sample of neutral HI regions before or during
reionization, and high frequency (0.1 Hz to 1
  Hz) gravitational wave analysis of a sample of neutron star--neutron star
binaries detected with gravitational wave instruments such as the Decihertz
Interferometer Gravitational Wave Observatory (DECIGO). The low frequency
background can also be constrained by arcsecond-scale anisotropy observations
of the CMB. For reasonable observations in the future involving extragalactic
sources, we find best limits at the level of \Omega_{GW} < 10^{-5} at a
frequency around 10^{-12} Hz while the eventual ultimate limit one cannot beat
is \Omega_{GW} < 10^{-11}.",0502054v1
2005-02-21,The effect of long range gravitational perturbations on the first acoustic peak of the cosmic microwave background,"In the standard cosmological model, the temperature anisotropy of the cosmic
microwave background is interpreted as variation in the gravitational potential
at the point of emission, due to the emitter being embedded in a region ${\cal
C}$ of over- or under-density spanning the length (or size) scale $\lambda$ on
which the anisotropy is measured. If the Universe is inhomogeneous, however,
similar density contrasts of size $\lambda$ are also located everywhere
surrounding ${\cal C}$. Since they are superposition states of many independent
Fourier modes with no preferred direction, such primordial clumps and voids
should not be configured according to some prescribed spatial pattern. Rather,
they can randomly trade spaces with each other while preserving the
Harrison-Zeldovich character of the matter spectrum. The outcome is an {\it
extra} perturbation of the potential when averaged over length $\lambda$ at the
emitter, and consequently an additional anisotropy on the same scale, which has
apparently been overlooked. Unlike the conventional application of the
Sachs-Wolfe effect to the WMAP observations, this extra effect is {\it not}
scale independent over the $P(k) \sim k$ part of the matter spectrum, but
increases towards smaller lengths, as $\sqrt{k}$. The consequence is a
substantial revision of the currently advertised values of the key cosmological
parameters, {\it unless} one postulates a more rapid decrease in the
gravitational force with distance than that given by the inverse-square law.",0502430v2
2005-03-08,The influence of non-uniform reionization on the CMB,"We investigate the impact of spatial variations in the ionized fraction
during reionization on temperature anisotropies in the CMB. We combine
simulations of large scale structure to describe the underlying density field
with an analytic model based on extended Press-Schechter theory to track the
reionization process. We find that the power spectrum of the induced CMB
anisotropies depends sensitively on the character of the reionization epoch.
Models that differ in the extent of the ""patchy phase"" could be distinguished
by future experiments such as the Atacama Cosmology Telescope (ACT) and the
South Pole Telescope (SPT). In our models, the patchy signal peaks at $l\simeq
2000$, where it can be four times larger than the kinetic Sunyaev-Zel'dovich
(kSZ)/Ostriker-Vishniac (OV) signal ($\Delta T_{\rm tot} \simeq 2.6 \mu K$). On
scales beyond $l \simeq 4000$ the total Doppler signal is dominated by kSZ/OV,
but the patchy signal can contribute up to 30% to the power spectrum. The
effect of patchy reionization is largest on scales where the primordial CMB
anisotropies dominate. Ignoring this contribution could lead to significant
biases in the determination of cosmological parameters derived from CMB
temperature measurements. Improvements in the theoretical modeling of the
reionization epoch will become increasingly important to interpret the results
of upcoming experiments.",0503166v2
2005-05-14,Homeoidally striated density profiles: sequences of virial equilibrium configurations with constant anisotropy parameters,"The formulation of the tensor virial equations is generalized to unrelaxed
configurations, where virial equilibrium does not coincide with dynamical (or
hydrostatic) equilibrium. Further investigation is devoted to special classes
of homeoidally striated ellipsoids, defined as homeoidally striated, Jacobi
ellipsoids. In particular, virial equilibrium configurations with constant
anisotropy parameters are studied with more detail, including both flattened
and elongated, triaxial configurations, and the determination of the related
bifurcation points. The explicit expression of different rotation parameters is
also determined. An application is made to dark matter haloes hosting giant,
galaxies, with regard to assigned initial and final configuration, following
and generalizing to many respects a procedure conceived by Thuan & Gott (1975).
The dependence of the limiting axis ratios, below which no configuration is
allowed for the sequence under consideration, on the change in mass, total
energy, and angular momentum, during the evolution, is illustrated in some
representative situations. The dependence of axis ratios and rotation
parameters on an additional parameter, related to the initial conditions of the
density perturbation, is analysed in connection with a few special cases.
Within the range of Peebles (1969) rotation parameter, inferred from
high-resolution numerical simulations, the shape of dark matter haloes is
mainly decided by the amount of anisotropy in residual velocity distribution.
On the other hand, the contribution of rotation has only a minor effect on the
meridional plane, and no effect on the equatorial plane, as bifurcation points
occur for larger values of Peebles (1969) rotation parameter. To this respect,
dark matter haloes are found to resemble giant elliptical galaxies.",0505306v1
2005-07-11,Topological signatures in CMB temperature anisotropy maps,"We propose an alternative formalism to simulate CMB temperature maps in
$\Lambda$CDM universes with nontrivial spatial topologies. This formalism
avoids the need to explicitly compute the eigenmodes of the Laplacian operator
in the spatial sections. Instead, the covariance matrix of the coefficients of
the spherical harmonic decomposition of the temperature anisotropies is
expressed in terms of the elements of the covering group of the space. We
obtain a decomposition of the correlation matrix that isolates the topological
contribution to the CMB temperature anisotropies out of the simply connected
contribution. A further decomposition of the topological signature of the
correlation matrix for an arbitrary topology allows us to compute it in terms
of correlation matrices corresponding to simpler topologies, for which closed
quadrature formulae might be derived. We also use this decomposition to show
that CMB temperature maps of (not too large) multiply connected universes must
show ``patterns of alignment'', and propose a method to look for these
patterns, thus opening the door to the development of new methods for detecting
the topology of our Universe even when the injectivity radius of space is
slightly larger than the radius of the last scattering surface. We illustrate
all these features with the simplest examples, those of flat homogeneous
manifolds, i.e., tori, with special attention given to the cylinder, i.e.,
$T^1$ topology.",0507238v2
2005-09-05,Joint constraints on the lepton asymmetry of the Universe and neutrino mass from the Wilkinson Microwave Anisotropy Probe,"We use the Wilkinson Microwave Anisotropy Probe (WMAP) data on the spectrum
of cosmic microwave background anisotropies to put constraints on the present
amount of lepton asymmetry L, parameterized by the dimensionless chemical
potential (also called degeneracy parameter) xi and on the effective number of
relativistic particle species. We assume a flat cosmological model with three
thermally distributed neutrino species having all the same mass and chemical
potential, plus an additional amount of effectively massless exotic particle
species. The extra energy density associated to these species is parameterized
through an effective number of additional species DeltaN_oth$. We find that
0<|xi|<1.1 and correspondingly 0<|L|<0.9 at 2sigma, so that WMAP data alone
cannot firmly rule out scenarios with a large lepton number; moreover, a small
preference for this kind of scenarios is actually found. We also discuss the
effect of the asymmetry on the estimation of other parameters and in particular
of the neutrino mass. In the case of perfect lepton symmetry, we obtain the
standard results. When the amount of asymmetry is left free, we find \sum m_nu
< 3.6 eV at 2sigma. Finally we study how the determination of |L| is affected
by the assumptions on DeltaN_oth. We find that lower values of the extra energy
density allow for larger values of the lepton asymmetry, effectively ruling
out, at 2sigma level, lepton symmetric models with DeltaN_oth=0.",0509079v2
2005-10-09,PSF Anisotropy and Systematic Errors in Weak Lensing Surveys,"Given the basic parameters of a cosmic shear weak lensing survey, how well
can systematic errors due to anisotropy in the point spread function (PSF) be
corrected? The largest source of error in this correction to date has been the
interpolation of the PSF to the locations of the galaxies. To address this
error, we separate the PSF patterns into components that recur in multiple
exposures/pointings and those that vary randomly between different exposures
(such as those due to the atmosphere). In an earlier study we developed a
principal component approach to correct the recurring PSF patterns (Jarvis and
Jain 2004). In this paper we show how randomly varying PSF patterns can also be
circumvented in the measurement of shear correlations. For the two-point
correlation function this is done by simply using pairs of galaxy shapes
measured in different exposures. Combining the two techniques allows us to
tackle generic combinations of PSF anisotropy patterns. The second goal of this
paper is to give a formalism for quantifying residual systematic errors due to
PSF patterns. We show how the main PSF corrections improve with increasing
survey area (and thus can stay below the reduced statistical errors), and we
identify the residual errors which do not scale with survey area. Our formalism
can be applied both to planned lensing surveys to optimize instrumental and
survey parameters and to actual lensing data to quantify residual errors.",0510231v2
2005-11-24,A Cusp Slope -- Central Anisotropy Theorem,"For a wide class of self-gravitating systems, we show that if the density is
cusped like 1/r^{gamma} near the center, then the limiting value of the
anisotropy parameter beta = 1 - <v_T^2>/(2<v_r^2>) at the center may not be
greater than (gamma/2). Here, <v_r^2> and <v_T^2> are the radial and tangential
velocity second moments. This follows from the non-negativity of the phase
space density. We compare this theorem to other proposed relations between the
cusp slope and the central anisotropy to clarify their applicabilities and
underlying assumptions. The extension of this theorem to tracer populations in
an externally imposed potential is also derived. In particular, for stars
moving in the vicinity of a central black hole, this reduces to gamma >=
beta+(1/2), indicating that an isotropic system in Keplerian potential should
be cusped at least as steep as 1/r^{0.5}. Similar limits have been noticed
before for specific forms of the distribution function, but here we establish
this as a general result.",0511686v4
2006-02-15,High-Energy Activity in the Unusually Soft TeV Source HESS J1804-216 toward the Galactic Center,"In recent years, apparent anisotropies in the ~EeV cosmic ray (CR) flux
arriving at Earth from the general direction of the galactic center have been
reported from the analysis of AGASA and SUGAR data. The more recently
commissioned Auger Observatory has not confirmed these results. HESS has now
detected an unusually soft TeV source roughly coincident with the location of
the previously claimed CR anisotropy. In this paper, we develop a model for the
TeV emission from this object, consistent with observations at other
wavelengths, and examine the circumstances under which it might have
contributed to the $\sim$ EeV cosmic ray spectrum. We find that the supernova
remnant G8.7-0.1 can plausibly account for all the known radiative
characteristics of HESS J1804-216, but that it can accelerate cosmic rays only
up to an energy $\sim 10^5$ GeV. On the other hand, the pulsar (PSR J1803-2137)
embedded within this remnant can in principle inject EeV protons into the
surrounding medium, but it cannot account for the broadband spectrum of HESS
J1804-216. We therefore conclude that although G8.7-0.1 is probably the source
of TeV photons originating from this direction, there is no compelling
theoretical motivation for expecting a cosmic ray anisotropy at this location.
However, if G8.7-0.1 is indeed correctly identified with HESS J1804-216, it
should also produce a $\sim$ GeV flux detectable in a one-year all sky survey
by GLAST.",0602330v1
2006-03-16,The impacts of dark matter particle annihilation on recombination and the anisotropies of the cosmic microwave background,"The recombination history of the Universe provides a useful tool for
constraining the annihilation of dark matter particles. Even a small fraction
of dark matter particles annihilated during the cosmic dark age can provide
sufficient energy to affect the ionization state of the baryonic gas. Although
this effect is too small for neutralinos, lighter dark matter particle
candidates, e.g. with mass of 1-100 MeV, which was proposed recently to explain
the observed excess of positrons in the Galactic Center, may generate
observable differences in the cosmic microwave background (CMB) temperature and
polarization anisotropies. The annihilations at the era of recombination
affects mainly the CMB anisotropy at small angular scales (large $\ell$), and
is distinctively different from the effect of early reionization. We perform a
multi-parameter analysis of the CMB data, including the both the WMAP first
year and three year data, and the ACBAR, Boomerang, CBI, and VSA data. Assuming
that the observed excess of $e^+e^-$ pairs in the galactic center region is
produced by dark matter annihilation, and that a sizable fraction of the energy
produced in the annihilation is deposited in the baryonic gas during
recombination, we obtain a %95 dark matter mass limit of $M<8 \MeV$ with the
current data set.",0603425v3
2006-03-22,Small Scale Anisotropy Predictions for the Auger Observatory,"We study the small scale anisotropy signal expected at the Pierre Auger
Observatory in the next 1, 5, 10, and 15 years of operation, from sources of
ultra-high energy (UHE) protons. We numerically propagate UHE protons over
cosmological distances using an injection spectrum and normalization that fits
current data up to $\sim 10^{20}\eV$. We characterize possible sources of
ultra-high energy cosmic rays (UHECRs) by their mean density in the local
Universe, $\bar{\rho} = 10^{-r}$ Mpc$^{-3}$, with $r$ between 3 and 6.
  These densities span a wide range of extragalactic sites for UHECR sources,
from common to rare galaxies or even clusters of galaxies. We simulate 100
realizations for each model and calculate the two point correlation function
for events with energies above $4 \times 10^{19}\eV$ and above $10^{20}\eV$, as
specialized to the case of the Auger telescope. We find that for $r\ga 4$,
Auger should be able to detect small scale anisotropies in the near future.
Distinguishing between different source densities based on cosmic ray data
alone will be more challenging than detecting a departure from isotropy and is
likely to require larger statistics of events. Combining the angular
distribution studies with the spectral shape around the GZK feature will also
help distinguish between different source scenarios.",0603615v1
2006-04-04,"Robust Dark Energy Constraints from Supernovae, Galaxy Clustering, and Three-Year Wilkinson Microwave Anisotropy Probe Observations","Type Ia supernova (SN Ia), galaxy clustering, and cosmic microwave background
anisotropy (CMB) data provide complementary constraints on the nature of the
dark energy in the universe. We find that the three-year Wilkinson Microwave
Anisotropy Probe (WMAP) observations give a CMB shift parameter of R =
(\Omega_m H_0^2)^{1/2} \int_0^{z_{CMB}} dz'/H(z')= 1.70 \pm 0.03. Using this
new measured value of the CMB shift parameter, together with the baryon
acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey
(SDSS), and SN Ia data from the HST/GOODS program and the first year Supernova
Legacy Survey, we derive model-independent constraints on the dark energy
density rho_X(z) and the cosmic expansion rate H(z). We also derive constraints
on the dark energy equation of state w_X(z)=w_0+w'z (with cutoff at z=2) and
w_X(a)=w_0+(1-a)w_a.
  We find that current data provide slightly tighter constraints on rho_X(z)
and H(z) as free functions in redshift, and roughly a factor of two improvement
in constraining w_X(z). A cosmological constant remains consistent with data,
however, uncertainties remain large for model-independent constraints of dark
energy. Significant increase in the number of observed SNe Ia between redshifts
of 1 and 2, complemented by improved BAO and weak lensing cosmography
measurements (as expected from the JEDI mission concept for the Joint Dark
Energy Mission), will be required to dramatically tighten model-independent
dark energy constraints.",0604051v2
2006-12-12,Radial stability of a family of anisotropic Hernquist models with and without a supermassive black hole,"We present a method to investigate the radial stability of a spherical
anisotropic system that hosts a central supermassive black hole (SBH). Such
systems have never been tested before for stability, although high anisotropies
have been considered in the dynamical models that were used to estimate the
masses of the central putative supermassive black holes. A family of analytical
anisotropic spherical Hernquist models with and without a black hole were
investigated by means of N-body simulations. A clear trend emerges that the
supermassive black hole has a significant effect on the overall stability of
the system, i.e. an SBH with a mass of a few percent of the total mass of the
galaxy can prevent or reduce the bar instabilities in anisotropic systems. Its
mass not only determines the strength of the instability reduction, but also
the time in which this occurs. These effects are most significant for models
with strong radial anisotropies. Furthermore, our analysis shows that unstable
systems with similar SBH but with different anisotropy radii evolve
differently: highly radial systems become oblate, while more isotropic models
tend to form into prolate structures. In addition to this study, we also
present a Monte-Carlo algorithm to generate particles in spherical anisotropic
systems.",0612307v1
2007-03-19,Cosmic Microwave Background Anisotropies up to Second Order,"These lecture notes present the computation of the full system of Boltzmann
equations describing the evolution of the photon, baryon and cold dark matter
fluids up to second order in perturbation theory, as recently studied in
(Bartolo, Matarrese & Riotto 2006, 2007). These equations allow to follow the
time evolution of the cosmic microwave background anisotropies at all angular
scales from the early epoch, when the cosmological perturbations were
generated, to the present, through the recombination era. The inclusion of
second-order contributions is mandatory when one is interested in studying
possible deviations from Gaussianity of cosmological perturbations, either of
primordial (e.g. inflationary) origin or due to their subsequent evolution.
Most of the emphasis in these lectures notes will be given to the derivation of
the relevant equations for the study of cosmic microwave background
anisotropies and to their analytical solutions.",0703496v2
1999-07-13,Anomalous scaling of a passive scalar advected by the synthetic compressible flow,"The field theoretic renormalization group and operator product expansion are
applied to the problem of a passive scalar advected by the Gaussian
nonsolenoidal velocity field with finite correlation time, in the presence of
large-scale anisotropy. The energy spectrum of the velocity in the inertial
range has the form $E(k)\propto k^{1-\epsilon}$, and the correlation time at
the wavenumber $k$ scales as $k^{-2+\eta}$. It is shown that, depending on the
values of the exponents $\epsilon$ and $\eta$, the model exhibits various types
of inertial-range scaling regimes with nontrivial anomalous exponents. Explicit
asymptotic expressions for the structure functions and other correlation
functions are obtained; they are represented by superpositions of power laws
with nonuniversal amplitudes and universal (independent of the anisotropy)
anomalous exponents, calculated to the first order in $\epsilon$ and $\eta$ in
any space dimension. These anomalous exponents are determined by the critical
dimensions of tensor composite operators built of the scalar gradients, and
exhibit a kind of hierarchy related to the degree of anisotropy: the less is
the rank, the less is the dimension and, consequently, the more important is
the contribution to the inertial-range behavior. The leading terms of the even
(odd) structure functions are given by the scalar (vector) operators. The
anomalous exponents depend explicitly on the degree of compressibility.",9907018v1
1996-01-31,Instabilities in the Flux Line Lattice of Anisotropic Superconductors,"The stability of the flux line lattice has been investigated within
anisotropic London theory. This is the first full-scale investigation of
instabilities in the `chain' state. It has been found that the lattice is
stable at large fields, but that instabilities occur as the field is reduced.
The field at which these instabilities first arise, $b^*(\epsilon,\theta)$,
depends on the anisotropy $\epsilon$ and the angle $\theta$ at which the
lattice is tilted away from the $c$-axis. These instabilities initially occur
at wavevector $k^*(\epsilon,\theta)$, and the component of $k^*$ along the
average direction of the flux lines, $k_z$, is always finite. As the
instability occurs at finite $k_z$ the dependence of the cutoff on $k_z$ is
important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The
instabilities only occur for values of the anisotropy $\epsilon$ appropriate to
a material like BSCCO, and not for anisotropies more appropriate to YBCO. The
lower critical field $H_{c_1}(\phi)$ is calculated as a function of the angle
$\phi$ at which the applied field is tilted away from the crystal axis. The
presence of kinks in $H_{c_1}(\phi)$ is seen to be related to instabilities in
the equilibrium flux line structure.",9601154v2
1998-01-06,Quasi-Long-Range Order in Random-Anisotropy Heisenberg Models,"Monte Carlo simulations have been used to study a discretized Heisenberg
ferromagnet (FM) with random uniaxial single-site anisotropy on $L \times L
\times L$ simple cubic lattices, for $L$ up to 64. The spin variable on each
site is chosen from the twelve [110] directions. The random anisotropy has
infinite strength and a random direction on a fraction $x$ of the sites of the
lattice, and is zero on the remaining sites. In many respects the behavior of
this model is qualitatively similar to that of the corresponding random-field
model. Due to the discretization, for small $x$ at low temperature there is a
[110] FM phase. For $x>0$ there is an intermediate quasi-long-range ordered
(QLRO) phase between the paramagnet and the ferromagnet, which is characterized
by a $|k|^{-3}$ divergence of the magnetic structure factor S$(k)$ for small
$k$, but no true FM order. At the transition between the paramagnetic and QLRO
phases S$(k)$ diverges like $|k|^{-2}$. The limit of stability of the QLRO
phase is somewhat greater than $x=0.5$. For $x$ close to 1 the low temperature
form of S$(k)$ can be fit by a Lorentzian, with a correlation length estimated
to be $11 \pm 1$ at $x=1.0$ and $25 \pm 5$ at $x=0.75$.",9801033v1
1998-04-06,Scaling of a slope: the erosion of tilted landscapes,"We formulate a stochastic equation to model the erosion of a surface with
fixed inclination. Because the inclination imposes a preferred direction for
material transport, the problem is intrinsically anisotropic. At zeroth order,
the anisotropy manifests itself in a linear equation that predicts that the
prefactor of the surface height-height correlations depends on direction. The
first higher-order nonlinear contribution from the anisotropy is studied by
applying the dynamic renormalization group. Assuming an inhomogeneous
distribution of soil substrate that is modeled by a source of static noise, we
estimate the scaling exponents at first order in $\ep$-expansion. These
exponents also depend on direction. We compare these predictions with empirical
measurements made from real landscapes and find good agreement. We propose that
our anisotropic theory applies principally to small scales and that a
previously proposed isotropic theory applies principally to larger scales.
Lastly, by considering our model as a transport equation for a driven diffusive
system, we construct scaling arguments for the size distribution of erosion
``events'' or ``avalanches.'' We derive a relationship between the exponents
characterizing the surface anisotropy and the avalanche size distribution, and
indicate how this result may be used to interpret previous findings of
power-law size distributions in real submarine avalanches.",9804067v2
1998-07-28,Thermal Conductivity of the Accidental Degeneracy and Enlarged Symmetry Group Models for Superconducting UPt<sub>3</sub>,"We present theoretical calculations of the thermal conductivity for the
accidental degeneracy and enlarged symmetry group models that have been
proposed to explain the phase diagram of UPt3. The order parameters for these
models possess point nodes or cross nodes, reflecting the broken symmetries of
the ground state. These broken symmetries lead to robust predictions for the
ratio of the low-temperature thermal conductivity for heat flow along the c
axis and in the basal plane. The anisotropy of the heat current response at low
temperatures is determined by the phase space for scattering by impurities. The
measured anisotropy ratio, $\kappa_c/\kappa_b$, provides a strong constraint of
theoretical models for the ground state order parameter. The accidental
degeneracy and enlarged symmetry group models based on no spin-orbit coupling
do not account for the thermal conductivity of UPt3. The models for the order
parameter that fit the experimental data for the c and b directions of the heat
current are the 2D E1g and E2u models, for which the order parameters possess
line nodes in the ab-plane and point nodes along the c axis, and the A1g+E1g
model of Zhitomirsky and Ueda. This model spontaneously breaks rotational
symmetry in theab-plane below Tc2 and predicts a large anisotropy for the
$ab$-plane heat current.",9807370v1
1998-12-31,Effect of disorder on quantum phase transitions in anisotropic XY spin chains in a transverse field,"We present some exact results for the effect of disorder on the critical
properties of an anisotropic XY spin chain in a transverse field. The continuum
limit of the corresponding fermion model is taken and in various cases results
in a Dirac equation with a random mass. Exact analytic techniques can then be
used to evaluate the density of states and the localization length. In the
presence of disorder the ferromagnetic-paramagnetic or Ising transition of the
model is in the same universality class as the random transverse field Ising
model solved by Fisher using a real space renormalization group decimation
technique (RSRGDT). If there is only randomness in the anisotropy of the
magnetic exchange then the anisotropy transition (from a ferromagnet in the $x$
direction to a ferromagnet in the $y$ direction) is also in this universality
class. However, if there is randomness in the isotropic part of the exchange or
in the transverse field then in a non-zero transverse field the anisotropy
transition is destroyed by the disorder. We show that in the Griffiths' phase
near the Ising transition that the ground state energy has an essential
singularity. The results obtained for the dynamical critical exponent, the
typical correlation length, and the temperature dependence of the specific heat
near the Ising transition agree with the results of the RSRGDT and numerical
work.",9812430v1
1999-10-14,Effect of symmetry breaking perturbations in the one-dimensional SU(4) spin-orbital model,"We study the effect of symmetry breaking perturbations in the one-dimensional
SU(4) spin-orbital model. We allow the exchange in spin ($J_1$) and orbital
($J_2$) channel to be different and thus reduce the symmetry to SU(2) $\otimes$
SU(2). A magnetic field $h$ along the $S^z$ direction is also applied. Using
the formalism developped by Azaria et al we extend their analysis of the
isotropic $J_1=J_2$, h=0 case and obtain the low-energy effective theory near
the SU(4) point in the asymmetric case. An accurate analysis of the
renormalization group flow is presented with a particular emphasis on the
effect of the anisotropy. In zero magnetic field, we retrieve the same
qualitative low-energy physics than in the isotropic case. In particular, the
massless behavior found on the line $J_1=J_2>K/4$ extends in a large
anisotropic region. We discover though that the anisotropy plays its trick in
allowing non trivial scaling behaviors of the physical quantities. When a
magnetic field is present the effect of the anisotropy is striking. In addition
to the usual commensurate-incommensurate phase transition that occurs in the
spin sector of the theory, we find that the field may induce a second
transition of the KT type in the remaining degrees of freedom to which it does
not couple directly. In this sector, we find that the effective theory is that
of an SO(4) Gross-Neveu model with an h-dependent coupling that may change its
sign as h varies.",9910218v2
1999-12-28,Effects of microscopic strain distribution on Ga(1-x)In(x)As quantum wires grown by strain-induced lateral ordering,"Band Structures and optical matrix elements of quantum wires(QWR's) made of
short-period superlattices(SPS) with strain-induced lateral ordering(SILO) are
investigated theoretically via an effective bond-orbital model(EBOM) combined
with a valence-force field(VFF) model. Valence-band anistropy, band mixing, and
effects due to local strain distribution at the atomistic level are all taken
into account. In particular, Ga(1-x)In(x)As QWR's grown by SILO process are
considered. A VFF model is used to find the equilibrium atomic positions in the
SILO QWR structure by minimizing the lattice energy. The strain tensor at each
atomic(In or GA) site is then obtained and included in the calculations of
electronic states and optical peroperties. It is found that different local
arrangement of atoms leads to very different strain distribution, which in term
alters the optical properties. In particular, we found that the optical
anisotropy can be reversed due to the change in shear strain caused by the
inter-change of atomic positions. Good agreement with the existing experimental
data on band gap and optical anisotropy can be obtained when a 2D alloy
structure with lateral composition modulation in the InAs/GaAs interface planes
of the SPS is used. Our studies revealed the possibility of ""shear-strain
engineering"" in SILO QWR light-emitting devices to achieve desired optical
anisotropy.",9912468v3
2000-04-21,First-principles study of ferroelectric and antiferrodistortive instabilities in tetragonal SrTiO3,"We carry out first-principles density-functional calculations of the
antiferrodistortive (AFD) and ferroelectric (FE) soft-mode instabilities in
tetragonal SrTiO3, with the structural degrees of freedom treated in a
classical, zero-temperature framework. In particular, we use frozen-phonon
calculations to make a careful study of the anisotropy of the AFD and FE mode
frequencies in the tetragonal ground state, in which an R-point AFD soft phonon
has condensed. Because of the anharmonic couplings, the presence of this AFD
distortion substantially affects both the AFD and FE mode frequencies. The AFD
mode is found to be softer for rotations around a perpendicular axis (Eg mode)
than for rotations about the tetragonal axis (A1g mode), in agreement with
experimental results. The FE mode, on the other hand, is found to be softer
when polarized perpendicular to the tetragonal axis (Eu mode) than parallel to
it (A2u mode). The sign of this frequency splitting is consistent with the
experimentally reported anisotropy of the dielectric susceptibility and other
evidence. Finally, we present a discussion of the influence of various types of
structural distortions on the FE instability and its anisotropy.",0004372v1
2000-05-23,Systematic study of Ga$_{1-x}$In$_x$As self-assembled quantum wires with different interfacial strain relaxation,"A systematic theoretical study of the electronic and optical properties of
Ga$_{1-x}$In$_x$As self-assembled quantum-wires (QWR's) made of short-period
superlattices (SPS) with strain-induced lateral ordering is presented. The
theory is based on the effective bond-orbital model (EBOM) combined with a
valence-force field (VFF) model. Valence-band anisotropy, band mixing, and
effects due to local strain distribution at the atomistic level are all taken
into account. Several structure models with varying degrees of alloy mixing for
lateral modulation are considered. A valence force field model is used to find
the equilibrium atomic positions in the QWR structure by minimizing the lattice
energy. The strain tensor at each atomic (In or Ga) site is then obtained and
included in the calculation of electronic states and optical properties. It is
found that different local arrangement of atoms leads to very different strain
distribution, which in turn alters the optical properties. In particular, we
found that in model structures with thick capping layer the electron and hole
are confined in the Ga-rich region and the optical anisotropy can be reversed
due to the variation of lateral alloying mixing, while for model structures
with thin capping layer the electron and hole are confined in the In-rich
region, and the optical anisotropy is much less sensitive to the lateral alloy
mixing.",0005392v1
2001-09-04,"Fully relativistic calculation of magnetic properties of Fe, Co and Ni adclusters on Ag(100)","We present first principles calculations of the magnetic moments and magnetic
anisotropy energies of small Fe, Co and Ni clusters on top of a Ag(100) surface
as well as the exchange-coupling energy between two single adatoms of Fe or Co
on Ag(100). The calculations are performed fully relativistically using the
embedding technique within the Korringa-Kohn-Rostoker method. The magnetic
anisotropy and the exchange-coupling energies are calculated by means of the
force theorem. In the case of adatoms and dimers of iron and cobalt we obtain
enhanced spin moments and, especially, unusually large orbital moments, while
for nickel our calculations predict a complete absence of magnetism. For larger
clusters, the magnitudes of the local moments of the atoms in the center of the
cluster are very close to those calculated for the corresponding monolayers.
Similar to the orbital moments, the contributions of the individual atoms to
the magnetic anisotropy energy strongly depend on the position, hence, on the
local environment of a particular atom within a given cluster. We find strong
ferromagnetic coupling between two neighboring Fe or Co atoms and a rapid,
oscillatory decay of the exchange-coupling energy with increasing distance
between these two adatoms.",0109045v1
2002-03-06,c-Axis Transport and Resistivity Anisotropy of Lightly- to Moderately-Doped La_{2-x}Sr_{x}CuO_{4} Single Crystals: Implications on the Charge Transport Mechanism,"Both the in-plane and the out-of-plane resistivities (\rho_{ab} and \rho_{c})
are measured in high-quality La_{2-x}Sr_{x}CuO_{4} (LSCO) single crystals in
the lightly- to moderately-doped region, x = 0.01 to 0.10, and the resistivity
anisotropy is determined. In all the samples studied, the anisotropy ratio \rho
_{c}/\rho_{ab} quickly increases with decreasing temperature, although in
non-superconducting samples the strong localization effect causes \rho
_{c}/\rho_{ab} to decrease at low temperatures. Most notably, it is found that
\rho_{c}/\rho_{ab} at moderate temperatures (100 - 300 K) is almost completely
independent of doping in the non-superconducting regime (x = 0.01 to 0.05);
this indicates that the same charge confinement mechanism that renormalizes the
c-axis hopping rate is at work down to x = 0.01. It is discussed that this
striking x-independence of \rho_{c}/\rho_{ab} is consistent with the idea that
holes form a self-organized network of hole-rich regions, which also explains
the unusually metallic in-plane transport of the holes in the lightly-doped
region. Furthermore, the data for x > 0.05 suggest that the emergence of the
superconductivity is related to an increase in the c-axis coupling.",0203107v1
2002-03-12,Angular dependence of magnetoresistivity in c-oriented MgB2 thin film,"The anisotropy of MgB2 is still under debate: its value, strongly dependent
on the sample and on the measuring method, ranges between 1.2 and 13. In this
work we present our results on a MgB2 c-oriented superconducting thin film. To
evaluate the anisotropy, we followed two different approaches. Firstly,
magnetoresistivity was measured as a function of temperature at selected
magnetic fields applied both parallel and perpendicular to the c-axis;
secondly, we measured magnetoresistivity at selected temperatures and magnetic
fields, varying the angle q between the magnetic field and the c-axis. The
anisotropy estimated from the ratio between the upper critical fields parallel
and perpendicular to the c-axis and the one obtained in the framework of the
scaling approach within the anisotropic Ginzburg-Landau theory are different
but show a similar trend in the temperature dependence. The obtained results
are compared and discussed in the light of the two-band nature of MgB2. A
comparison between critical fields in thin films and single crystal is also
performed.",0203246v3
2002-05-15,Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ} single crystals for a wide range of hole doping,"To elucidate how the temperature dependence of the resistivity anisotropy of
the cuprate superconductors changes with hole doping, both the in-plane and the
out-of-plane resistivities (\rho_{ab} and \rho_{c}) are measured in a series of
high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} (BSLCO) single crystals for a
wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu,
p, of 0.03 - 0.18. The anisotropy ratio, \rho_{c}/\rho_{ab}, shows a systematic
increase with decreasing p at moderate temperatures, except for the most
underdoped composition where the localization effect enhances \rho_{ab} and
thus lowers \rho_{c}/\rho_{ab}. The exact p dependence of \rho_{c}/\rho_{ab} at
a fixed temperature is found to be quite peculiar, which is discussed to be due
to the effect of the pseudogap that causes \rho_{c}/\rho_{ab} to be
increasingly more enhanced as p is reduced. The pseudogap also causes a rapid
growth of \rho_{c}/\rho_{ab} with decreasing temperature, and, as a result, the
\rho_{c}/\rho_{ab} value almost reaches 10^6 in underdoped samples just above
T_c. Furthermore, it is found that the temperature dependence of \rho_{c} of
underdoped samples show two distinct temperature regions in the pseudogap
phase, which suggests that the divergence of \rho_{c} below the pseudogap
temperature is governed by two different mechanisms.",0205305v2
2002-09-16,"Correlation energy, quantum phase transition, and bias potential effects in quantum Hall bilayers at nu=1","We study the correlation energy, the effective anisotropy parameter, and
quantum fluctuations of the pseudospin magnetization in bilayer quantum Hall
systems at total filling factor nu=1 by means of exact diagonalizations of the
Hamiltonian in the spherical geometry. We compare exact diagonalization results
for the ground state energy with finite-size Hartree-Fock values. In the
ordered ground state phase at small layer separations the Hartree-Fock data
compare reasonably with the exact results. Above the critical layer separation,
however, the Hartree-Fock findings still predict an increase in the ground
state energy, while the exact ground state energy is in this regime independent
of the layer separation indicating the decoupling of layers and the loss of
spontaneous phase coherence between them. We also find accurate values for the
pseudospin anisotropy constant whose dependence of the layer separation
provides another very clear indication for the strong interlayer correlations
in the ordered phase and shows an inflection point at the phase boundary.
Finally we discuss the possibility of interlayer correlations in biased systems
even above the phase boundary for the balanced case. Certain features of our
data for the pseudospin anisotropy constant as well as for quantum fluctuations
of the pseudospin magnetization are not inconsistent with the occurence of this
effect. However, it appears to be rather weak at least in the limit of
vanishing tunneling amplitude.",0209349v2
2003-07-02,Specific Heat Study of the Magnetic Superconductor HoNi2B2C,"The complex magnetic transitions and superconductivity of HoNi2B2C were
studied via the dependence of the heat capacity on temperature and in-plane
field angle. We provide an extended, comprehensive magnetic phase diagram for B
// [100] and B // [110] based on the thermodynamic measurements. Three magnetic
transitions and the superconducting transition were clearly observed. The 5.2 K
transition (T_{N}) shows a hysteresis with temperature, indicating the first
order nature of the transition at B=0 T. The 6 K transition (T_{M}), namely the
onset of the long-range ordering, displays a dramatic in-plane anisotropy:
T_{M} increases with increasing magnetic field for B // [100] while it
decreases with increasing field for B // [110]. The anomalous anisotropy in
T_{M} indicates that the transition is related to the a-axis spiral structure.
The 5.5 K transition (T^{*}) shows similar behavior to the 5.2 K transition,
i.e., a small in-plane anisotropy and scaling with Ising model. This last
transition is ascribed to the change from a^{*} dominant phase to c^{*}
dominant phase.",0307041v4
2003-08-13,Effect of varying material anisotropy on critical current anistropy in vicinal YBa$_2$Cu$_3$O$_{7-δ}$ thin films,"The high $T_{c}$ cuprate superconductors are noted for their anisotropic
layered structure, certain of these materials indeed tend toward the limit of a
Lawrence-Doniach superconductor. However, YBa$_2$Cu$_3$O$_{7-\delta}$ has a
smaller anisotropy than would be expected from its interlayer spacing. This is
due to the cuprate chains in the structure. To investigate the influence of the
chain oxygen on transport properties critical current versus applied field
angle measurements were performed on fully oxygenated and de-oxygenated
YBa$_2$Cu$_3$O$_{7-\delta}$ thin films and optimally oxygenated
Y$_{0.75}$Ca$_{0.2}$Ba$_2$Cu$_3$O$_{7-\delta}$ thin films. The films were grown
on 10$^{\circ}$ mis-cut SrTiO$_3$ substrates to enable the intrinsic vortex
channelling effect to be observed. The form of the vortex channelling minimum
observed in field angle dependent critical current studies on the films was
seen to depend on film oxygenation. The vortex channelling effect is dependent
on a angular dependent cross-over to a string-pancake flux line lattice. The
results obtained appear to be consistent with the prediction of Blatter et al.
[Rev. Mod. Phys., 66 (4): 1125 (1994)] that increased superconducting
anisotropy leads to the kinked string-pancake lattice existing over a smaller
angular range.",0308246v1
2003-09-26,Magnetic phases and reorientation transitions in antiferromagnetically coupled multilayers,"In antiferromagnetically coupled superlattices grown on (001) faces of cubic
substrates, e.g. based on materials combinations as Co/Cu, Fe/Si, Co/Cr, or
Fe/Cr, the magnetic states evolve under competing influence of bilinear and
biquadratic exchange interactions, surface-enhanced four-fold in-plane
anisotropy, and specific finite-size effects. Using phenomenological
(micromagnetic) theory, a comprehensive survey of the magnetic states and
reorientation transitions has been carried out for multilayer systems with even
number of ferromagnetic sub-layers and magnetizations in the plane. In
two-layer systems (N=2) the phase diagrams in dependence on components of the
applied field in the plane include ``swallow-tail'' type regions of
(metastable) multistate co-existence and a number of continuous and
discontinuous reorientation transitions induced by radial and transversal
components of the applied field. In multilayers (N \ge 4) noncollinear states
are spatially inhomogeneous with magnetization varying across the multilayer
stack. For weak four-fold anisotropy the magnetic states under influence of an
applied field evolve by a complex continuous reorientation into the saturated
state. At higher anisotropy they transform into various inhomogeneous and
asymmetric structures. The discontinuous transitions between the magnetic
states in these two-layers and multilayers are characterized by broad ranges of
multi-phase coexistence of the (metastable) states and give rise to specific
transitional domain structures.",0309621v1
2004-04-10,Effects of anisotropy on a quantum Heisenberg spin glass in a three-dimensional hierarchical lattice,"We study the anisotropic Heisenberg spin-glass model in a three-dimensional
hierarchical lattice (designed to approximate the cubic lattice), within a
real-space renormalization-group approach. Two different initial probability
distributions for the exchange interaction ($J_{ij}$), Gaussian and uniform,
are used, with zero mean and width $\bar{J}$. The $(kT/\bar{J}) \times
\Delta_0$ phase diagram is obtained, where $T$ is the temperature, $\Delta_0$
is the first moment of the probability distribution for the uniaxial
anisotropy, and $k$ is the Boltzmann constant. For the Ising model
($\Delta_0=1$), there is a spin-glass phase at low temperatures (high
$\bar{J}$) and a paramagnetic phase at high temperatures (low $\bar{J}$). For
the isotropic Heisenberg model ($\Delta_0=0$), our results indicate no
spin-glass phase at finite temperatures. The transition temperature between the
spin-glass and paramagnetic phase decreases with $\Delta_0$, as expected, but
goes to zero at a finite value of the anisotropy parameter, namely $\Delta_0 =
\Delta_c \sim 0.59$. Our results indicate that the whole transition line,
between the paramagnetic and the spin-glass phases, for $\Delta_c \leq \Delta_0
< 1$, belongs to the same universality class as the transition for the Ising
spin glass.",0404251v2
2004-06-08,Decoupled two-dimensional superconductivity and continuous melting transitions in layered superconductors immersed in a parallel magnetic field,"Possible phases and the B-T phase diagram of interlayer Josephson vortices
induced by a magnetic field parallel to the superconducting layers are
investigated by Monte Carlo simulations based on the anisotropic, frustrated XY
model. While for low magnetic fields and small anisotropy parameters a single
first-order transition is observed similarly to the melting of Abrikosov (or
pancake) vortex lattice, an intermediate phase, characterized by decoupled,
two-dimensional (2D) quasi long-range crystalline order (QLRCO) and
superconductivity, is found at high magnetic fields and large anisotropy
parameters. Combining the simulation results with a symmetry argument, it is
revealed that this intermediate phase is of Kosterlitz-Thouless (KT) type, and
the melting of 2D quasi Josephson vortex lattices and suppression of
superconductivity is a KT transition. Evolution of the intermediate phase to
the low-temperature phase of 3D LRCO is second order and belongs to the 3D XY
universality class. The three phase boundaries merge at a multicritical point.
It is revealed that decoupling of the 3D Josephson vortex lattice into the 2D
phase is triggered by hops of Josephson flux lines across superconducting
layers activated by thermal fluctuations. The equilibrium phase diagram with
the KT phase at high magnetic fields and large anisotropy parameters is
consistent with the peculiar Lorentz-force-independent dissipation observed in
highly anisotropic high-Tc superconductor Bi2Sr2CaCu2O(8+y) by Iye et al.
(Physica 159C, 433 (1989)).",0406183v1
2004-12-13,Point Contact Spectroscopy of Superconducting Gap Anisotropy in Nickel Borocarbide Compound LuNi2B2C,"Point contacts are used to investigate the anisotropy of the superconducting
energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that
the experimental curves should be described assuming that the superconducting
gap is non-uniformly distributed over the Fermi surface. The largest and the
smallest gaps have been estimated by two-gap fitting models. It is found that
the largest contribution to the point-contact conductivity in the c direction
is made by a smaller gap and, in the ab plane by a larger gap. The deviation
from the one-gap BCS model is pronounced in the temperature dependence of the
gap in both directions. The temperature range, where the deviation occurs, is
for the c direction approximately 1.5 times more than in the ab plane. The
\Gamma parameter, allowing quantitatively estimate the gap anisotropy by
one-gap fitting, in c direction is also about 1.5 times greater than in the ab
plane. Since it is impossible to describe satisfactorily such gap distribution
either by the one- or two-gap models, a continuous, dual-maxima model of gap
distribution over the Fermi surface should be used to describe
superconductivity in this material.",0412325v1
2005-03-24,Fast magnetization switching of Stoner particles: A nonlinear dynamics picture,"The magnetization reversal of Stoner particles is investigated from the point
of view of nonlinear dynamics within the Landau-Lifshitz-Gilbert formulation.
The following results are obtained. 1) We clarify that the so-called
Stoner-Wohlfarth (SW) limit becomes exact when damping constant is infinitely
large. Under the limit, the magnetization moves along the steepest energy
descent path. The minimal switching field is the one at which there is only one
stable fixed point in the system. 2) For a given magnetic anisotropy, there is
a critical value for the damping constant, above which the minimal switching
field is the same as that of the SW-limit. 3) We illustrate how fixed points
and their basins change under a field along different directions. This change
explains well why a non-parallel field gives a smaller minimal switching field
and a short switching time. 4) The field of a ballistic magnetization reversal
should be along certain direction window in the presence of energy dissipation.
The width of the window depends on both of the damping constant and the
magnetic anisotropy. The upper and lower bounds of the direction window
increase with the damping constant. The window width oscillates with the
damping constant for a given magnetic anisotropy. It is zero for both zero and
infinite damping. Thus, the perpendicular field configuration widely employed
in the current experiments is not the best one since the damping constant in a
real system is far from zero.",0503594v1
2005-04-19,Thermodynamics of S>=1 ferromagnetic Heisenberg chains with uniaxial single-ion anisotropy,"The thermodynamic properties of S>=1 ferromagnetic chains with an easy-axis
single-ion anisotropy are investigated at arbitrary temperatures by both a
Green-function approach, based on a decoupling of three-spin operator products,
and by exact diagonalizations of chains with up to N=12 sites using periodic
boundary conditions. A good agreement between the results of both approaches is
found. For the S=1 chain, the temperature dependence of the specific heat
reveals two maxima, if the ratio of the anisotropy energy D and the exchange
energy J exceeds a characteristic value, D/J >7.4, and only one maximum for D/J
<7.4. This is in contrast to previous exact diagonalization data for comparably
small chains (N <= 7) using open boundary conditions. Comparing the theory with
experiments on di-bromo Ni complexes the fit to the specific heat yields
concrete values for D and J which are used to make predictions for the
temperature dependences of the spin-wave spectrum, the correlation length, and
the transverse magnetic susceptibility.",0504481v2
2005-12-21,Magnetic Anisotropy of Isolated Cobalt Nanoplatelets,"Motivated in part by experiments performed by M.H. Pan et al. (nanoletters,
v.5, p 83, 2005), we have undertaken a theoretical study of the the magnetic
properties of two-monolayer thick Co nanoplatelets with an equilateral
triangular shape. The analysis is carried out using a microscopic Slater-Koster
tight-binding model with atomic exchange and spin-orbit interactions designed
to realistically capture the salient magnetic features of large nanoclusters
containing up to 350 atoms. Two different truncations of the FCC lattice are
studied, in which the nanoplatelet surface is aligned parallel to the FCC (111)
and (001)crystal planes respectively. We find that the higher coordination
number in the (111) truncated crystal is more likely to reproduce the
perpendicular easy direction found in experiment. Qualitatively, the most
important parameter governing the anisotropy of the model is found to be the
value of the intra-atomic exchange integral J. If we set the value of J near
the bulk value in order to reproduce the experimentally observed magnitude of
the magnetic moments, we find both quasi-easy-planes and perpendicular easy
directions. At larger values of J we find that the easy-axis of magnetization
is perpendicular to the surface, and the value of the magnetic anisotropy
energy per atom is larger. The possible role of hybridization with substrate
surface states in the experimental systems is discussed.",0512523v2
2006-02-07,Magnetic excitations and their anisotropy in YBCO: slave-boson mean-field analysis of bilayer t-J model,"We perform a comprehensive analysis of the dynamical magnetic susceptibility
\chi(q,\omega) in the slave-boson mean-field scheme of the bilayer t-J model.
In the d-wave pairing state, the strongest magnetic spectral weight appears at
q=Q=(pi,pi) and \omega=\omega_{Q}^{res}, and spreads into a diamond-shaped
shell around Q in q space for \omega<\omega_{Q}^{res}. This weight is due to a
collective mode, namely a particle-hole bound state, which has a downward
\omega versus q dispersion around Q. Within the high intensity shell, the
incommensurate (IC) signals at q=(pi,pi\pm 2pi\eta) and (pi\pm 2pi\eta,pi) tend
to be stronger than the diagonal incommensurate (DIC) signals at q=(pi\pm
2pi\eta',pi\pm 2pi\eta'), especially for a large hole density \delta. For
\omega \ll \omega_{Q}^{res} the IC signals completely disappear and the weight
remains only around the DIC positions. For \omega > \omega_{Q}^{res} strong
signals of Im\chi(q,\omega) tracing an upward dispersion are found and
interpreted as an overdamped collective mode near \omega_{Q}^{res}. In the
normal state, Im\chi(q,\omega) has a broad peak at q=Q. That is, the IC and DIC
signals appear only in the d-wave pairing state. We also study effects of a
small orthorhombic anisotropy, which is intrinsic in untwinned YBCO crystals.
Because of electron-electron correlations favoring d-wave shaped Fermi surface
deformations (dFSD), we expect an enhanced anisotropy of magnetic excitation
spectra. This effect is particularly pronounced for low \delta and at
relatively high temperature. The present theory provides a rather detailed
microscopic explanation of the most salient properties of magnetic excitations
observed in YBCO.",0602189v1
2006-02-16,"Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy","The ferromagnetism of a thin GaMnAs layer with a perpendicular easy
anisotropy axis is investigated by means of several techniques, that yield a
consistent set of data on the magnetic properties and the domain structure of
this diluted ferromagnetic semiconductor. The magnetic layer was grown under
tensile strain on a relaxed GaInAs buffer layer using a procedure that limits
the density of threading dislocations. Magnetometry, magneto-transport and
polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality
of this layer, in particular through its high Curie temperature (130 K) and
well-defined magnetic anisotropy. We show that magnetization reversal is
initiated from a limited number of nucleation centers and develops by easy
domain wall propagation. Furthermore, MOKE microscopy allowed us to
characterize in detail the magnetic domain structure. In particular we show
that domain shape and wall motion are very sensitive to some defects, which
prevents a periodic arrangement of the domains. We ascribed these defects to
threading dislocations emerging in the magnetic layer, inherent to the growth
mode on a relaxed buffer.",0602388v2
2006-09-26,Competing impurities and reentrant magnetism in La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) revisited. The role of the Dzyaloshinskii-Moriya and XY anisotropies,"We study the order-from-disorder transition and reentrant magnetism in
La(2-x)Sr(x)Cu(1-z)Zn(z)O(4) within the framework of a long-wavelength
nonlinear sigma model that properly incorporates the Dzyaloshinskii-Moriya and
XY anisotropies. Doping with nonmagnetic impurities, such as Zn, is considered
according to classical percolation theory, whereas the effect of Sr, which
introduces charge carriers into the CuO(2) planes, is described as a dipolar
frustration of the antiferromagnetic order. We calculate several magnetic,
thermodynamic, and spectral properties of the system, such as the
antiferromagnetic order parameter, the Neel temperature, the spin-stiffness,
and the anisotropy gaps, as well as their evolution with both Zn and Sr doping.
We explain the nonmonotonic and reentrant behavior experimentally observed for
T_N by Hucker et al. in Phys. Rev. B 59, R725 (1999), as resulting from the
reduction, due to the nonmagnetic impurities, of the dipolar frustration
induced by the charge carriers (order-from-disorder). Furthermore, we find a
similar nonmonotonic and reentrant behavior for all the other observables
studied. Most remarkably, our results show that while for x=2% and z=0 the
Dzyaloshinskii-Moriya gap \Delta_{DM}=0, for z=15% it is approximately
\Delta_{DM} = 7.5 cm^(-1). The later is larger than the lowest low-frequency
cutoff for Raman spectroscopy (~ 5 cm^(-1)), and could thus be observed in
one-magnon Raman scattering.",0609653v1
2007-01-22,Influence of Point-like Disorder on the Guiding of Vortices and the Hall Effect in a Washboard Planar Pinning Potential,"Explicit current-dependent expressions for anisotropic longitudinal and
transverse nonlinear magnetoresistivities are represented and analyzed on the
basis of a Fokker-Planck approach for two-dimensional single-vortex dynamics in
a washboard pinning potential in the presence of point-like disorder. Graphical
analysis of the resistive responses is presented both in the current-angle
coordinates and in the rotating current scheme. The model describes nonlinear
anisotropy effects caused by the competition of point-like (isotropic) and
anisotropic pinning. Nonlinear guiding effects are discussed and the critical
current anisotropy is analyzed. Gradually increasing the magnitude of isotropic
pinning force this theory predicts a gradual decrease of the anisotropy of the
magnetoresistivities. The physics of transition from the new scaling relations
for anisotropic Hall resistance in the absence of point-like pins to the
well-known scaling relations for the point-like disorder is elucidated. This is
discussed in terms of a gradual isotropizaton of the guided vortex motion,
which is responsible for the existence in a washboard pinning potential of new
(with respect to magnetic field reversal) Hall voltages. It is shown that
whereas the Hall conductivity is not changed by pinning, the Hall resistivity
can change its sign in some current-angle range due to presence of the
competition between i- and a-pins.",0701530v1
2007-03-05,Rotator and extender ferroelectrics: Importance of the shear coefficient to the piezoelectric properties of domain-engineered crystals and ceramics,"The importance of a high shear coefficient d15 (or d24) to the piezoelectric
properties of domain-engineered and polycrystalline ferroelectrics is
discussed. The extent of polarization rotation, as a mechanism of piezoelectric
response, is directly correlated to the shear coefficient. The terms ""rotator""
and ""extender"" are introduced to distinguish the contrasting behaviors of
crystals such as 4mm BaTiO3 and PbTiO3. In ""rotator"" ferroelectrics, where d15
is high relative to the longitudinal coefficient d33, polarization rotation is
the dominant mechanism of piezoelectric response; the maximum longitudinal
piezoelectric response is found away from the polar axis. In ""extender""
ferroelectrics, d15 is low and the collinear effect dominates; the maximum
piezoelectric response is found along the polar axis. A variety of 3m, mm2 and
4mm ferroelectrics, with various crystal structures based on oxygen octahedra,
are classified in this way. It is shown that the largest piezoelectric
anisotropies d15/d33 are always found in 3m crystals; this is a result of the
intrinsic electrostrictive anisotropy of the constituent oxygen octahedra.
Finally, for a given symmetry, the piezoelectric anisotropy increases close to
ferroelectric-ferroelectric phase transitions; this includes morphotropic phase
boundaries and temperature induced polymorphic transitions.",0703121v1
2007-03-13,Online Supplementary Material: Low temperature vortex liquid in $\rm La_{2-x}Sr_xCuO_4$,"We report here the supplementary material for Ref. [1]. Using torque
magnetometry, we measured the magnetization anisotropy of 7 crystals of $\rm
La_{2-x}Sr_xCuO_4$ (LSCO). In optimally-doped cuprates, the bulk susceptibility
is dominated by the paramagnetic van-Vleck orbital term $\chi_{orb}$ which has
a significant anisotropy ($\chi^{orb}_c>\chi^{orb}_{ab}$) that changes weakly
with $T$ (subscripts $c$ and ${ab}$ identify quantities measured with $\bf
H||c$ and $\bf H\perp c$, respectively). Moreover, in the lightly-doped regime,
the paramagnetic spin susceptibilities $\chi^s_c$ and $\chi^s_{ab}$ become
significantly large below the interval 40-60 K. However, the spin
susceptibility is very nearly isotropic (except below 10 K where its anisotropy
becomes measurable). Against the large orbital and spin terms, the weak
diamagnetic signal is very difficult to resolve using standard bulk
magnetometry in lightly-doped cuprates. By contrast, torque magnetometry
selectively detects the orbital diamagnetism generated by supercurrents
confined to the CuO$_2$ layers while ignoring the large spin contribution when
it is isotropic. The orbital van-Vleck contribution is also detected, but as a
``background'' that is $H$-linear to intense fields and only mildly $T$
dependent.",0703348v1
2007-03-28,Stability of Biaxial Nematic Phase for Systems with Variable Molecular Shape Anisotropy,"We study the influence of fluctuations in molecular shape on the stability of
the biaxial nematic phase by generalizing the mean field model of Mulder and
Ruijgrok [Physica A {\bf 113}, 145 (1982)]. We limit ourselves to the case when
the molecular shape anisotropy, represented by the alignment tensor, is a
random variable of an annealed type. A prototype of such behavior can be found
in lyotropic systems - a mixture of potassium laurate, 1-decanol, and $D_2O$,
where distribution of the micellar shape adjusts to actual equilibrium
conditions. Further examples of materials with the biaxial nematic phase, where
molecular shape is subject to fluctuations, are thermotropic materials composed
of flexible trimeric- or tetrapod-like molecular units. Our calculations show
that the Gaussian equilibrium distribution of the variables describing
molecular shape (dispersion force) anisotropy gives rise to new classes of the
phase diagrams, absent in the original model. Depending on properties of the
shape fluctuations, the stability of the biaxial nematic phase can be either
enhanced or depressed, relative to the uniaxial nematic phases. In the former
case the splitting of the Landau point into two triple points with a direct
phase transition line from isotropic to biaxial phase is observed.",0703736v2
2000-01-20,Locally Anisotropic Kinetic Processes and Thermodynamics in Curved Spaces,"The kinetic theory is formulated with respect to anholonomic frames of
reference on curved spacetimes. By using the concept of nonlinear connection we
develop an approach to modelling locally anisotropic kinetic processes and, in
corresponding limits, the relativistic non-equilibrium thermodynamics with
local anisotropy. This lead to a unified formulation of the kinetic equations
on (pseudo) Riemannian spaces and in various higher dimensional models of
Kaluza-Klein type and/or generalized Lagrange and Finsler spaces. The
transition rate considered for the locally anisotropic transport equations is
related to the differential cross section and spacetime parameters of
anisotropy. The equations of states for pressure and energy in locally
anisotropic thermodynamics are derived. The obtained general expressions for
heat conductivity, shear and volume viscosity coefficients are applied to
determine the transport coefficients of cosmic fluids in spacetimes with
generic local anisotropy. We emphasize that such locally anisotropic structures
are induced also in general relativity if we are modelling physical processes
with respect to frames with mixed sets of holonomic and anholonomic basis
vectors which naturally admits an associated nonlinear connection structure.",0001060v3
2005-03-01,Primordial magnetic seed field amplification by gravitational waves,"Using second-order gauge-invariant perturbation theory, a self-consistent
framework describing the non-linear coupling between gravitational waves and a
large-scale homogeneous magnetic field is presented. It is shown how this
coupling may be used to amplify seed magnetic fields to strengths needed to
support the galactic dynamo. In situations where the gravitational wave
background is described by an `almost' Friedmann-Lema{\^i}tre-Robertson-Walker
(FLRW) cosmology we find that the magnitude of the original magnetic field is
amplified by an amount proportional to the magnitude of the gravitational wave
induced shear anisotropy and the square of the field's initial co-moving scale.
We apply this mechanism to the case where the seed field and gravitational wave
background are produced during inflation and find that the magnitude of the
gravitational boost depends significantly on the manner in which the estimate
of the shear anisotropy at the end of inflation is calculated. Assuming a seed
field of $10^{-34}$ $\rm{G}$ spanning a comoving scale of about $10 \rm{kpc}$
today, the shear anisotropy at the end of inflation must be at least as large
as $10^{-40}$ in order to obtain a generated magnetic field of the same order
of magnitude as the original seed. Moreover, contrasting the weak field
approximation to our gauge-invariant approach, we find that while both methods
agree in the limit of high conductivity, their corresponding solutions are
otherwise only compatible in the limit of infinitely long-wavelength
gravitational waves.",0503006v2
2003-02-28,Two flavors of dynamical quarks on anisotropic lattices,"We report on our study of two-flavor full QCD on anisotropic lattices using
$O(a)$-improved Wilson quarks coupled with an RG-improved glue. The bare gauge
and quark anisotropies corresponding to the renormalized anisotropy
$\xi=a_s/a_t = 2$ are determined as functions of $\beta$ and $\kappa$, which
covers the region of spatial lattice spacings $a_s\approx 0.28$--0.16 fm and
$m_{PS}/m_V\approx 0.6$--0.9. The calibrations of the bare anisotropies are
performed with the Wilson loop and the meson dispersion relation at 4 lattice
cutoffs and 5--6 quark masses. Using the calibration results we calculate the
meson mass spectrum and the Sommer scale $r_0$. We confirm that the values of
$r_0$ calculated for the calibration using pseudo scalar and vector meson
energy momentum dispersion relation coincide in the continuum limit within
errors. This work serves to lay ground toward studies of heavy quark systems
and thermodynamics of QCD including the extraction of the equation of state in
the continuum limit using Wilson-type quark actions.",0302024v2
1993-03-19,Post-COBE predictions for Inflationary Gravity Wave and Density Perturbation spectra,"We assess the relative contribution to the COBE - measured microwave
anisotropy arising both from relic gravity waves as well as primordial density
perturbations originating during inflation. We show that the gravity wave
contribution to the CMBR anisotropy depends sensitively upon $n$ -- the
primordial spectral index ($\dk^2 \propto k^n$), increasing as $n$ deviates
from a Harrison - Zeldovich spectrum (n = 1). As a result, for $n < 0.84$ the
contribution from gravity waves towards $\delta T/ T $ is greater than the
corresponding contribution from density perturbations, whereas for $n > 0.84$
the reverse is true. ($ n = 0.84$ corresponds to an expansion index $p = 13.5$
in models with power-law inflation $a \propto t^p$. ) Our results show that for
a scale-invariant Harrison-Zeldovich spectrum generated by chaotic inflation,
gravity waves contribute approximately $24\%$ to the CMBR anisotropy measured
by COBE. Applying our results to the cold dark matter scenario for galaxy
formation, we find that in general CDM models with tilted power spectra ($n <
1$), require the biasing parameter to be greater than unity, on scales of
$16h_{50}^{-1} Mpc$. We also obtain an expression for the COBE - normalised
amplitude and spectrum of the stochastic gravity wave background and compare it
with the sensitivity of planned laser-interferometer gravity wave detectors.",9303285v1
1999-09-17,Microwave background anisotropies and large scale structure constraints on isocurvature modes in a two-field model of inflation,"In this paper we study the isocurvature mode contribution to the cosmic
microwave background anisotropies and the large scale structure power spectrum,
for a two-field model of inflation proposed by Linde and Mukhanov. We provide
constraints on the parameters of the model by comparing its predictions with
observations of the microwave background anisotropies, large scale structure
data on the galaxy power spectrum, and the number density of nearby galaxy
clusters. We find that such models are consistent with observations for a
narrow range of parameters. As our main result, we find that only a very small
isocurvature component is allowed, $\al \le 0.006$, for any underlying
Friedmann model. Furthermore, we give the expected resolution with which the
model parameters will be determined from future satellite missions like MAP and
Planck, for a fiducial flat $\Lambda$CDM model. We find that Planck mission
will be able to detect such small contributions, especially if polarization
information is included. The isocurvature spectral index $\niso$ will also be
determined with better than 8% precision.",9909420v2
2003-08-07,On the origin of the large scale structures of the universe,"We revise the statistical properties of the primordial cosmological density
anisotropies that, at the time of matter radiation equality, seeded the
gravitational development of large scale structures in the, otherwise,
homogeneous and isotropic Friedmann-Robertson-Walker flat universe. Our
analysis shows that random fluctuations of the density field at the same
instant of equality and with comoving wavelength shorter than the causal
horizon at that time can naturally account, when globally constrained to
conserve the total mass (energy) of the system, for the observed scale
invariance of the anisotropies over cosmologically large comoving volumes.
Statistical systems with similar features are generically known as glass-like
or lattice-like. Obviously, these conclusions conflict with the widely accepted
understanding of the primordial structures reported in the literature, which
requires an epoch of inflationary cosmology to precede the standard expansion
of the universe. The origin of the conflict must be found in the widespread,
but unjustified, claim that scale invariant mass (energy) anisotropies at the
instant of equality over comoving volumes of cosmological size, larger than the
causal horizon at the time, must be generated by fluctuations in the density
field with comparably large comoving wavelength.",0308078v5
2004-08-27,Progress in Anisotropic Plasma Physics,"In 1959 Weibel demonstrated that when a QED plasma has a temperature
anisotropy there exist unstable transverse magnetic excitations which grow
exponentially fast. In this paper we will review how to determine the growth
rates for these unstable modes in the weak-coupling and ultrarelativistic
limits in which the collective behavior is describable in terms are so-called
""hard-loops"". We will show that in this limit QCD is subject to instabilities
which are analogous to the Weibel instability in QED. The presence of such
instabilities dominates the early time evolution of a highly anisotropic
plasma; however, at longer times it is expected that these instabilities will
saturate (condense). I will discuss how the presence of non-linear interactions
between the gluons complicates the determination of the saturated state. In
order to discuss this I present the generalization of the Braaten-Pisarski
isotropic hard-thermal-loop effective action to a system with a temperature
anisotropy in the parton distribution functions. The resulting hard-loop
effective action can be used to determine the time and energy scales associated
with the possible saturation (condensation) of the gluonic modes. We will also
discuss the effects of anisotropies on observables, in particular on the heavy
quark energy loss.",0408314v2
1998-06-12,Limit on suppression of ionization in metastable neon traps due to long-range anisotropy,"This paper investigates the possibility of suppressing the ionization rate in
a magnetostatic trap of metastable neon atoms by spin-polarizing the atoms.
Suppression of the ionization is critical for the possibility of reaching
Bose-Einstein condensation with such atoms. We estimate the relevant long-range
interactions for the system, consisting of electric quadrupole-quadrupole and
dipole-induced dipole terms, and develop short-range potentials based on the
Na_2 singlet and triplet potentials. The auto-ionization widths of the system
are also calculated. With these ingredients we calculate the ionization rate
for spin-polarized and for spin-isotropic samples, caused by anisotropy of the
long-range interactions. We find that spin-polarization may allow for four
orders of magnitude suppression of the ionization rate for Ne. The results
depend sensitively on a precise knowledge of the interaction potentials,
however, pointing out the need for experimental input. The same model gives a
suppression ratio close to unity for metastable xenon in accordance with
experimental results, due to a much increased anisotropy in this case.",9806018v1
2004-04-22,Small scale structure of homogeneous turbulent shear flow,"The structure of homogeneous turbulent shear flow is studied using data
generated by Direct Numerical Simulations (DNS) and a linear analysis for both
compressible and incompressible cases. At large values of the mean shear rate,
the Rapid Distortion Theory (RDT) limit is approached. Analytical solutions are
found for the inviscid compressible RDT equations at long times. The RDT
equations are also solved numerically for both inviscid and viscous cases. The
RDT solutions, confirmed by the DNS results, show that the even order
transverse derivative moments of the dilatational and solenoidal velocity
fields are anisotropic, with the dilatational motions more anisotropic than
their solenoidal counterparts. The results obtained for the incompressible case
are similar to those obtained for the solenoidal motions in the compressible
case. The DNS results also indicate an increase in the anisotropy of the even
order transverse derivative moments with the order of the moment, in agreement
with the RDT predictions. Although the anisotropy decreases with Reynolds
number, it is likely that for higher even order moments it will persist at
large values of the Reynolds number, in contrast with the postulate of local
isotropy. The RDT solutions also predict that the normalized odd order
transverse derivative moments of the solenoidal velocity for the compressible
case and of the velocity for the incompressible case should approach a constant
different than zero at large times. This prediction is supported by the DNS
data. For higher odd order normalized moments, the RDT analysis suggests that
the anisotropy may persist at large values of the Reynolds number, in agreement
with the existent experimental data.",0404108v1
2006-11-27,Generando entrelazamiento en cadenas XY - (Generating entanglement in XY chains),"Se estudia en este trabajo la capacidad de generar entrelazamiento de una
cadena de espines con acoplamiento de Heisenberg XY y un campo magnetico
uniforme a partir de un estado inicial en el que los espines estan
completamente alineados. Se encuentra que la capacidad de generar estados
entrelazados no muestra un comportamiento monotono con el campo presentando, en
cambio, plateaus y resonancias. Tambien se muestra que, a pesar de que la
anisotropia es necesaria para que se generen estados entrelazados, una mayor
anisotropia no implica necesariamente mejores condiciones para generar
entrelazamiento que sirva para usarse en una computadora cuantica. Inclusive,
se observa que, se genera una cantidad finita de entrelazamiento en el limite
de pequena anisotropia.
  (The maximum entanglement reached by an initially fully aligned state
evolving in a XY Heisenberg spin chain placed in a uniform transverse magnetic
field is studied. It is shown that the capacity to create entangled states
(both of one qubit with the rest of the chain and pairwise between two adjacent
qubits) is not a monotonous function of the magnetic field: it presents
plateaus and resonances. It is also shown that, though anisotropy in the
interaction is necessary for entanglement generation, the best conditions for
generating entanglement that may be suitable for use in quantum computation is
not that of biggest anisotropy. Moreover finite amounts of entanglement are
generated in the small anisotropy limit.)",0611258v1
2007-04-11,Anisotropy and Magnetic Field Effects on the Genuine Multipartite Entanglement of Multi-Qubit Heisenberg {\it XY} Chains,"It has been shown that, for the two-qubit Heisenberg XY model, anisotropy and
magnetic field may together be used to produce entanglement for any finite
temperature by adjusting the external magnetic field beyond some finite
critical strength. This interesting result arises from an analysis employing
the Wootters concurrence, a computable measure of entanglement for two-qubit
states. Recently, Mintert {\em et al.} proposed generalizations of Wootters
concurrence for multipartite states. These MKB concurrences possess a
mathematical property that enables one to understand the origin of this
characteristic behavior. Here, we first study the effect of anisotropy and
magnetic field on the multipartite thermal entanglement of a four-qubit
Heisenberg XY chain using the MKB concurrences. We show that this model
exhibits characteristic behavior similar to that of the two-qubit model. In
addition, we show that this can again be understood using the same mathematical
property. Next, we show that the six-qubit Heisenberg XY chain possesses
properties necessary for it to have the characteristic behavior too. Most
importantly, it is possible to directly measure the multipartite MKB
concurrences of pure states. This may provide an experimental verification of
our conjecture that for a Heisenberg XY chain of any even number of qubits, it
is always possible to obtain non-zero genuine multipartite entanglement at any
finite temperature by applying a sufficiently large magnetic field.",0704.1368v2
2007-04-19,On Larkin-Imry-Ma State of 3He-A in Aerogel,"Superfluid 3He-A shares the properties of spin nematic and chiral orbital
ferromagnet. Its order parameter is characterized by two vectors d and l. This
doubly anisotropic superfluid, when it is confined in aerogel, represents the
most interesting example of a system with continuous symmetry in the presence
of random anisotropy disorder. We discuss the Larkin-Imry-Ma state, which is
characterized by the short-range orientational order of the vector l, while the
long-range orientational order is destroyed by the collective action of the
randomly oriented aerogel strings. On the other hand, sufficiently large
regular anisotropy produced either by the deformation of the aerogel or by
applied superflow suppresses the Larkin-Imry-Ma effect leading to the uniform
orientation of the vector l. This interplay of regular and random anisotropy
allows us to study many different effects.",0704.2484v10
2007-04-23,What it takes to measure a fundamental difference between dark matter and baryons: the halo velocity anisotropy,"Numerous ongoing experiments aim at detecting WIMP dark matter particles from
the galactic halo directly through WIMP-nucleon interactions. Once such a
detection is established a confirmation of the galactic origin of the signal is
needed. This requires a direction-sensitive detector. We show that such a
detector can measure the velocity anisotropy beta of the galactic halo.
Cosmological N-body simulations predict the dark matter anisotropy to be
nonzero, beta~0.2. Baryonic matter has beta=0 and therefore a detection of a
nonzero beta would be strong proof of the fundamental difference between dark
and baryonic matter. We estimate the sensitivity for various detector
configurations using Monte Carlo methods and we show that the strongest signal
is found in the relatively few high recoil energy events. Measuring beta to the
precision of ~0.03 will require detecting more than 10^4 WIMP events with
nuclear recoil energies greater than 100 keV for a WIMP mass of 100 GeV and a
32S target. This number corresponds to ~10^6 events at all energies. We discuss
variations with respect to input parameters and we show that our method is
robust to the presence of backgrounds and discuss the possible improved
sensitivity for an energy-sensitive detector.",0704.2909v3
2007-04-25,Revisiting the effect of nearby supernova remnants on local cosmic rays,"In an earlier paper, the effect of the nearby known supernova remnants (SNRs)
on the local cosmic-rays (CRs) was studied, considering different possible
forms of the particle injection time. The present work is a continuation of the
previous work, but assumes a more realistic model of CR propagation in the
Galaxy. The previous work assumed an unbounded three-dimensional diffusion
region, whereas the present one considers a flat cylindrical disc bounded in
both the radial and vertical directions. The study has found that the effect of
the vertical halo boundary $H$ on the local SNR contribution to the observed CR
anisotropy is negligible as long as $H\gtrsim 2kpc$. Considering the values of
the halo height $H\gtrsim 2kpc$ obtained by different authors, the present work
suggests that the study of the effect of local sources on the CR anisotropy can
be carried out without having much information on $H$ and hence, using the much
simpler three-dimentional unbounded solution. Finally, the present work
discusses about the possibility of explaining the observed anisotropy below the
knee by a single dominant source with properly chosen source parameters, and
claims that the source may be an \textit{undetected} old SNR with a
characteristic age of $\sim 1.5\times 10^5 yr$ located at a distance of $\sim
0.57 kpc$ from the Sun.",0704.3336v2
2007-07-05,Theory of cosmological perturbations in an anisotropic universe,"This article describes the theory of cosmological perturbations around a
homogeneous and anisotropic universe of the Bianchi I type. Starting from a
general parameterisation of the perturbed spacetime a la Bardeen, a complete
set of gauge invariant variables is constructed. Three physical degrees of
freedom are identified and it is shown that, in the case where matter is
described by a scalar field, they generalize the Mukhanov-Sasaki variables. In
order to show that they are canonical variables, the action for the
cosmological perturbations at second order is derived. Two major physical
imprints of the primordial anisotropy are identified: (1) a scalar-tensor
``see-saw'' mechanism arising from the fact that scalar, vector and tensor
modes do not decouple and (2) an explicit dependence of the statistical
properties of the density perturbations and gravity waves on the wave-vector
instead of its norm. This analysis extends, but also sheds some light on, the
quantization procedure that was developed under the assumption of a
Friedmann-Lemaitre background spacetime, and allows to investigate the
robustness of the predictions of the standard inflationary scenario with
respect to the hypothesis on the symmetries of the background spacetime. These
effects of a primordial anisotropy may be related to some anomalies of the
cosmic microwave background anisotropies on large angular scales.",0707.0736v1
2007-07-12,Superorbital variability of X-ray and radio emission of Cyg X-1. I. Emission anisotropy of precessing sources,"We study theoretical interpretations of the 150-d (superorbital) modulation
observed in X-ray and radio emission of Cyg X-1 in the framework of models
connecting this phenomenon to precession. Precession changes the orientation of
the emission source (either disc or jet) relative to the observer. This leads
to emission modulation due to an anisotropic emission pattern of the source or
orientation-dependent amount of absorbing medium along the line of sight or
both. We consider, in particular, anisotropy patterns of blackbody-type
emission, thermal Comptonization in slab geometry, jet/outflow beaming, and
absorption in a coronal-type medium above the disc. We then fit these models to
the data from the RXTE/ASM, CGRO/BATSE, and the Ryle and Green Bank radio
telescopes, and find relatively small best-fit angles between the precession
and orbital planes, ~10-20 degrees. The thermal Comptonization model for the
X-ray emission explains well the observed decrease of the variability amplitude
from 1 to 300 keV as a result of a reduced anisotropy of the emission due to
multiple scatterings. Our modeling also yield the jet bulk velocity of
~(0.3-0.5)c, which is in agreement with the previous constraint from the lack
of an observed counterjet and lack of short-term X-ray/radio correlations.",0707.1880v1
2007-08-07,Systematic {\it ab initio} study of the magnetic and electronic properties of all 3d transition metal linear and zigzag nanowires,"It is found that all the zigzag chains except the nonmagnetic (NM) Ni and
antiferromagnetic (AF) Fe chains which form a twisted two-legger ladder, look
like a corner-sharing triangle ribbon, and have a lower total energy than the
corresponding linear chains. All the 3d transition metals in both linear and
zigzag structures have a stable or metastable ferromagnetic (FM) state. The
electronic spin-polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co and
Ni linear chains is close to 90% or above. In the zigzag structure, the AF
state is more stable than the FM state only in the Cr chain. It is found that
the shape anisotropy energy may be comparable to the electronic one and always
prefers the axial magnetization in both the linear and zigzag structures. In
the zigzag chains, there is also a pronounced shape anisotropy in the plane
perpendicular to the chain axis. Remarkably, the axial magnetic anisotropy in
the FM Ni linear chain is gigantic, being ~12 meV/atom. Interestingly, there is
a spin-reorientation transition in the FM Fe and Co linear chains when the
chains are compressed or elongated. Large orbital magnetic moment is found in
the FM Fe, Co and Ni linear chains.",0708.0973v1
2007-10-02,SAURON's Challenge for the Major Merger Scenario of Elliptical Galaxy Formation,"The intrinsic anisotropy delta and flattening epsilon of simulated merger
remnants is compared with elliptical galaxies that have been observed by the
SAURON collaboration, and that were analysed using axisymmetric Schwarzschild
models. Collisionless binary mergers of stellar disks and disk mergers with an
additional isothermal gas component, neglecting star formation cannot reproduce
the observed trend delta = 0.55 epsilon (SAURON relationship). An excellent fit
of the SAURON relationship for flattened ellipticals with epsilon >= 0.25 is
however found for merger simulations of disks with gas fractions >= 20%,
including star formation and stellar energy feedback. Massive black hole
feedback does not strongly affect this result. Subsequent dry merging of merger
remnants however does not generate the slowly-rotating SAURON ellipticals which
are characterized by low ellipticities epsilon < 0.25 and low anisotropies.
This indicates that at least some ellipticals on the red galaxy sequence did
not form by binary mergers of disks or early-type galaxies. We show that
stellar spheroids resulting from multiple, hierarchical mergers of
star-bursting subunits in a cosmological context are in excellent agreement
with the low ellipticities and anisotropies of the slowly rotating SAURON
ellipticals and their observed trend of delta with epsilon. The numerical
simulations indicate that the SAURON relation might be a result of strong
violent relaxation and phase mixing of multiple, kinematically cold stellar
subunits with the angular momentum of the system determining its location on
the relation.",0710.0663v1
2007-10-12,Magnetism and effect of anisotropy with one dimensional monatomic chain of cobalt by a Monte Carlo simulation,"The magnetic properties of the one dimensional (1D) monatomic chain of Co
reported in a previous experimental work are investigated by a classical Monte
Carlo simulation based on the anisotropic Heisenberg model. In our simulation,
the effect of the on-site uniaxial anisotropy, Ku, on each individual Co atom
and the nearest neighbour exchange interaction, J, are accounted for. The
normalized coercivity HC(T)/HC(TCL) is found to show a universal behaviour,
HC(T)/HC(TCL) = h0(e^{TB/T}-e) in the temperature interval, TCL < T < TBCal,
arising from the thermal activation effect. In the above expression, h0 is a
constant, TBCal is the blocking temperature determined by the calculation, and
TCL is the temperature above which the classical Monte Carlo simulation gives a
good description on the investigated system. The present simulation has
reproduced the experimental features, including the temperature dependent
coercivity, HC(T), and the angular dependence of the remanent magnetization,
MR(phi,theta), upon the relative orientation (phi,theta) of the applied field
H. In addition, the calculation reveals that the ferromagnetic-like open
hysteresis loop is a result of a slow dynamical process at T < TBCal. The
dependence of the dynamical TBCal on the field sweeping rate R, the on-site
anisotropy constant Ku, and the number of atoms in the atomic chain, N, has
been investigated in detail.",0710.2381v1
2007-10-23,Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background,"The extragalactic cosmic gamma-ray background (CGB) is an interesting channel
to look for signatures of dark matter annihilation. In particular, besides the
imprint in the energy spectrum, peculiar anisotropy patterns are expected
compared to the case of a pure astrophysical origin of the CGB. We take into
account the uncertainties in the dark matter clustering properties on
sub-galactic scales, deriving two possible anisotropy scenarios. A clear dark
matter angular signature is achieved when the annihilation signal receives only
a moderate contribution from sub-galactic clumps and/or cuspy haloes.
Experimentally, if galactic foregrounds systematics are efficiently kept under
control, the angular differences are detectable with the forthcoming GLAST
observatory, provided that the annihilation signal contributes to the CGB for a
fraction >10-20%. If, instead, sub-galactic structures have a more prominent
role, the astrophysical and dark matter anisotropies become degenerate,
correspondingly diluting the DM signature. As complementary observables we also
introduce the cross-correlation between surveys of galaxies and the CGB and the
cross-correlation between different energy bands of the CGB and we find that
they provide a further sensitive tool to detect the dark matter angular
signatures.",0710.4136v2
2007-11-12,Cosmic microwave anisotropies from BPS semilocal strings,"We present the first ever calculation of cosmic microwave background CMB
anisotropy power spectra from semilocal cosmic strings, obtained via
simulations of a classical field theory. Semilocal strings are a type of
non-topological defect arising in some models of inflation motivated by
fundamental physics, and are thought to relax the constraints on the symmetry
breaking scale as compared to models with (topological) cosmic strings. We
derive constraints on the model parameters, including the string tension
parameter mu, from fits to cosmological data, and find that in this regard BPS
semilocal strings resemble global textures more than topological strings. The
observed microwave anisotropy at l = 10 is reproduced if Gmu = 5.3x10^{-6} (G
is Newton's constant). However as with other defects the spectral shape does
not match observations, and in models with inflationary perturbations plus
semilocal strings the 95% confidence level upper bound is Gmu<2.0x10^{-6} when
CMB data, Hubble Key Project and Big Bang Nucleosynthesis data are used (c.f.
Gmu<0.9x10^{-6} for cosmic strings). We additionally carry out a Bayesian model
comparison of several models with and without defects, showing models with
defects are neither conclusively favoured nor disfavoured at present.",0711.1842v2
2007-11-12,Cosmic Covariance and the Low Quadrupole Anisotropy of the Wilkinson Microwave Anisotropy Probe (WMAP) Data,"The quadrupole power of cosmic microwave background (CMB) temperature
anisotropies seen in the WMAP data is puzzlingly low. In this paper we
demonstrate that Minimum Variance Optimization (MVO), a technique used by many
authors (including the WMAP science team) to separate the CMB from
contaminating foregrounds, has the effect of forcing the extracted CMB map to
have zero statistical correlation with the foreground emission. Over an
ensemble of universes the true CMB and foreground are indeed expected to be
uncorrelated, but any particular sky pattern (such as the one we happen to
observe) will generate non-zero measured correlations simply by chance. We call
this effect ""cosmic covariance"" and it is a possible source of bias in the CMB
maps cleaned using the MVO technique. We show that the presence of cosmic
covariance is expected to artificially suppress the variance of the Internal
Linear Combination (ILC) map obtained via MVO. It also propagates into the
multipole expansion of the ILC map, generating a quadrupole deficit with more
than 90% confidence. Since we do not know the CMB and the foregrounds a priori,
there is therefore an unknown contribution to the uncertainty in the measured
quadrupole power, over and above the usual cosmic variance contribution. Using
the MVO on a series of Monte Carlo simulations that assume Gaussian CMB
fluctuations, we estimate that the real quadrupole power of the CMB lies in the
range [305.16,400.40] microKelvin^2 (at the 1-sigma level).",0711.1860v1
2008-01-17,Thermodynamic quantum crtical behavior in the anisotropic Kondo necklace model,"The Ising-like anisotropy parameter $\delta$ in the Kondo necklace model is
analyzed using the bond-operator method at zero and finite temperatures for
arbitrary $d$ dimensions. A decoupling scheme on the double time Green's
functions is used to find the dispersion relation for the excitations of the
system. At zero temperature and in the paramagnetic side of the phase diagram,
we determine the spin gap exponent $\nu z\approx0.5$ in three dimensions and
anisotropy between $0\leq\delta\leq1$, a result consistent with the dynamic
exponent $z=1$ for the Gaussian character of the bond-operator treatment. At
low but finite temperatures, in the antiferromagnetic phase, the line of Neel
transitions is calculated for $\delta\ll1$ and $\delta\approx1$. For $d>2$ it
is only re-normalized by the anisotropy parameter and varies with the distance
to the quantum critical point QCP $|g|$ as, $T_N \propto |g|^{\psi}$ where the
shift exponent $\psi=1/(d-1)$. Nevertheless, in two dimensions, long range
magnetic order occurs only at T=0 for any $\delta$. In the paramagnetic phase,
we find a power law temperature dependence on the specific heat at the
\textit{quantum liquid trajectory} $J/t=(J/t)_{c}$, $T\to0$. It behaves as
$C_{V}\propto T^{d}$ for $\delta\leq 1$ and $\delta\approx1$, in concordance
with the scaling theory for $z=1$.",0801.2792v1
2008-01-29,Searching for a Correlation Between Cosmic-Ray Sources Above 10^{19} eV and Large-Scale Structure,"We study the anisotropy signature which is expected if the sources of ultra
high energy, >10^{19} eV, cosmic-rays (UHECRs) are extragalactic and trace the
large scale distribution of luminous matter. Using the PSCz galaxy catalog as a
tracer of the large scale structure (LSS), we derive the expected all sky
angular distribution of the UHECR intensity. We define a statistic, that
measures the correlation between the predicted and observed UHECR arrival
direction distributions, and show that it is more sensitive to the expected
anisotropy signature than the power spectrum and the two point correlation
function. The distribution of the correlation statistic is not sensitive to the
unknown redshift evolution of UHECR source density and to the unknown strength
and structure of inter-galactic magnetic fields. We show, using this statistic,
that recently published >5.7x10^{19} eV Auger data are inconsistent with
isotropy at ~98% CL, and consistent with a source distribution that traces LSS,
with some preference to a source distribution that is biased with respect to
the galaxy distribution. The anisotropy signature should be detectable also at
lower energy, >4x10^{19} eV. A few fold increase of the Auger exposure is
likely to increase the significance to >99% CL, but not to >99.9% CL (unless
the UHECR source density is comparable or larger than that of galaxies). In
order to distinguish between different bias models, the systematic uncertainty
in the absolute energy calibration of the experiments should be reduced to well
below the current ~25%.",0801.4516v2
2008-04-01,"A Cosmic Ray Positron Anisotropy due to Two Middle-Aged, Nearby Pulsars?","Geminga and B0656+14 are the closest pulsars with characteristic ages in the
ran ge of 100 kyr to 1 Myr. They both have spindown powers of the order 3e34
erg/s at present. The winds of these pulsars had most probably powered pulsar
wind nebulae (PWNe) that broke up less than about 100 kyr after the birth of
the pulsars. Assuming that leptonic particles accelerated by the pulsars were
confined in th e PWNe and were released into the interstellar medium (ISM) on
breakup of the PW Ne, we show that, depending on the pulsar parameters, both
pulsars make a non-ne gligible contribution to the local cosmic ray (CR)
positron spectrum, and they m ay be the main contributors above several GeV.
The relatively small angular dist ance between Geminga and B0656+14 thus
implies an anisotropy in the local CR po sitron flux at these energies. We
calculate the contribution of these pulsars to the locally observed CR electr
on and positron spectra depending on the pulsar birth period and the magnitude
o f the local CR diffusion coefficient. We further give an estimate of the
expecte d anisotropy in the local CR positron flux. Our calculations show that
within the framework of our model, the local CR posit ron spectrum imposes
constraints on pulsar parameters for Geminga and B0656+14, notably the pulsar
period at birth, and also the local interstellar diffusion co efficient for CR
leptons.",0804.0220v1
2008-04-26,"Spatial Periodicity of Galaxy Number Counts, CMB Anisotropy, and SNIa Hubble Diagram Based on the Universe Accompanied by a Non-Minimally Coupled Scalar Field","We have succeeded in establishing a cosmological model with a non-minimally
coupled scalar field $\phi$ that can account not only for the spatial
periodicity or the {\it picket-fence structure} exhibited by the galaxy $N$-$z$
relation of the 2dF survey but also for the spatial power spectrum of the
cosmic microwave background radiation (CMB) temperature anisotropy observed by
the WMAP satellite. The Hubble diagram of our model also compares well with the
observation of Type Ia supernovae. The scalar field of our model universe
starts from an extremely small value at around the nucleosynthesis epoch,
remains in that state for sufficiently long periods, allowing sufficient time
for the CMB temperature anisotropy to form, and then starts to grow in
magnitude at the redshift $z$ of $\sim 1$, followed by a damping oscillation
which is required to reproduce the observed picket-fence structure of the
$N$-$z$ relation. To realize such behavior of the scalar field, we have found
it necessary to introduce a new form of potential $V(\phi)\propto
\phi^2\exp(-q\phi^2)$, with $q$ being a constant. Through this parameter $q$,
we can control the epoch at which the scalar field starts growing.",0804.4240v1
2008-05-28,Effect of anisotropy on the ground-state magnetic ordering of the spin-one quantum $J_{1}^{XXZ}$--$J_{2}^{XXZ}$ model on the square lattice,"We study the zero-temperature phase diagram of the
$J_{1}^{XXZ}$--$J_{2}^{XXZ}$ Heisenberg model for spin-1 particles on an
infinite square lattice interacting via nearest-neighbour ($J_1 \equiv 1$) and
next-nearest-neighbour ($J_2 > 0$) bonds. Both bonds have the same $XXZ$-type
anisotropy in spin space. The effects on the quasiclassical N\'{e}el-ordered
and collinear stripe-ordered states of varying the anisotropy parameter
$\Delta$ is investigated using the coupled cluster method carried out to high
orders. By contrast with the spin-1/2 case studied previously, we predict no
intermediate disordered phase between the N\'{e}el and collinear stripe phases,
for any value of the frustration $J_2/J_1$, for either the $z$-aligned ($\Delta
> 1$) or $xy$-planar-aligned ($0 \leq \Delta < 1$) states. The quantum phase
transition is determined to be first-order for all values of $J_2/J_1$ and
$\Delta$. The position of the phase boundary $J_{2}^{c}(\Delta)$ is determined
accurately. It is observed to deviate most from its classical position $J_2^c =
{1/2}$ (for all values of $\Delta > 0$) at the Heisenberg isotropic point
($\Delta = 1$), where $J_{2}^{c}(1) = 0.55 \pm 0.01$. By contrast, at the XY
isotropic point ($\Delta = 0$), we find $J_{2}^{c}(0) = 0.50 \pm 0.01$. In the
Ising limit ($\Delta \to \infty$) $J_2^c \to 0.5$ as expected.",0805.4388v2
2008-05-29,Pre-equilibrium dilepton production from an anisotropic quark-gluon plasma,"We calculate leading-order dilepton yields from a quark-gluon plasma which
has a time-dependent anisotropy in momentum space. Such anisotropies can arise
during the earliest stages of quark-gluon plasma evolution due to the rapid
longitudinal expansion of the created matter. Two phenomenological models for
the proper time dependence of the parton hard momentum scale, p_hard, and the
plasma anisotropy parameter, xi, are constructed which describe the transition
of the plasma from its initial non-equilibrium state to an isotropic
thermalized state. The first model constructed interpolates between 1+1
dimensional free streaming at early times and 1+1 dimensional ideal
hydrodynamical expansion at late times. In the second model we include the
effect of collisional broadening of the parton distribution functions in the
early-time pre-equilibrium stage of plasma evolution. We find for both cases
that for fixed initial conditions high-energy dilepton production is enhanced
by pre-equilibrium emission. When the models are constrained to fixed final
pion multiplicity the dependence of the resulting spectra on the assumed plasma
isotropization time is reduced. Using our most realistic
collisionally-broadened model we find that high-transverse momentum dilepton
production would be enhanced by at most 40% at the Relativistic Heavy Ion
Collider and 50% at CERN Large Hadron Collider if one assumes an
isotropization/thermalization time of 2 fm/c. Given sufficiently precise
experimental data this enhancement could be used to determine the plasma
isotropization time experimentally.",0805.4552v2
2008-06-10,Impact of Point Source Clustering on Cosmological Parameters with CMB Anisotropies,"The faint radio point sources that are unresolved in cosmic microwave
background (CMB) anisotropy maps are likely to be a biased tracer of the
large-scale structure dark matter distribution. While the shot-noise
contribution to the angular power spectrum of unresolved radio point sources is
included either when optimally constructing the CMB angular power spectrum, as
with WMAP data, or when extracting cosmological parameters, we suggest that
clustering part of the point source power spectrum should also be included.
This is especially necessary at high frequencies above 150 GHz, where the
clustering of far-IR sources is expected to dominate the shot-noise level of
the angular power spectrum at tens of arcminute angular scales of both radio
and sub-mm sources. We make an estimate of source clustering of unresolved
radio sources in both WMAP and ACBAR, and marginalize over the amplitude of
source clustering in each CMB data set when model fitting for cosmological
parameters. For the combination of WMAP 5-year data and ACBAR, we find that the
spectral index changes from the value of $0.963 \pm 0.014$ to $0.959 \pm 0.014$
(at 68% c.l.) when the clustering power spectrum of point sources is included
in model fits. While we find that the differences are marginal with and without
source clustering in current data, it may be necessary to account for source
clustering with future datasets such as Planck, especially to properly model
fit anisotropies at arcminute angular scales. If clustering is not accounted
and point sources are modeled with a shot-noise only out to $l \sim 2000$, the
spectral index will be biased by about 1.5$\sigma$.",0806.1742v1
2008-06-15,Magnetic interactions of cold atoms with anisotropic conductors,"We analyze atom-surface magnetic interactions on atom chips where the
magnetic trapping potentials are produced by current carrying wires made of
electrically anisotropic materials. We discuss a theory for time dependent
fluctuations of the magnetic potential, arising from thermal noise originating
from the surface. It is shown that using materials with a large electrical
anisotropy results in a considerable reduction of heating and decoherence rates
of ultra-cold atoms trapped near the surface, of up to several orders of
magnitude. The trap loss rate due to spin flips is expected to be significantly
reduced upon cooling the surface to low temperatures. In addition, the
electrical anisotropy significantly suppresses the amplitude of static spatial
potential corrugations due to current scattering within imperfect wires. Also
the shape of the corrugation pattern depends on the electrical anisotropy: the
preferred angle of the scattered current wave fronts can be varied over a wide
range. Materials, fabrication, and experimental issues are discussed, and
specific candidate materials are suggested.",0806.2427v2
2008-06-15,Anisotropy in the electrical resistivity and susceptibility of superconducting BaFe$_{2}$As$_{2}$ single crystals,"Sizable single crystals of $BaFe_2As_2$ have been grown with self-flux
method. The crystals are plate-like with c-axis perpendicular to the plane. The
size can be as large as 3 x 5 x 0.2 $mm^3$. The resistivity anisotropy
($\rho_c/\rho_{ab}$) is as large as about 150, and independent of temperature.
The transport in ab plane and along c-axis direction shares the same scattering
mechanism. In contrast to the magnetic behavior of polycrystalline samples, no
Curie-Weiss behavior are observed, a temperature linear dependent
susceptibility occurs above spin-density-wave (SDW) transition. The
susceptibility behavior is very similar to that of antiferromagnetic SDW
chromium. Magnetic behavior of single crystal definitely gives evidence for
existence of local moment except for the contribution to susceptibility from
itinerant electrons. A resistivity minimum strongly dependent on magnetic field
is observed. A log(1/T) divergency, similar to that of the underdoped cuprates,
happens at low temperature. Here we first present intrinsic transport and
magnetic properties, and their anisotropy from high quality single crystal.",0806.2452v2
2008-06-26,Different resistivity response to spin density wave and superconductivity at 20 K in $Ca_{1-x}Na_xFe_2As_2$,"We report that intrinsic transport and magnetic properties, and their
anisotropy from high quality single crystal $CaFe_2As_2$. The resistivity
anisotropy ($\rho_c/\rho_{ab}$) is $\sim 50 $, and less than 150 of
$BaFe_2As_2$, which arises from the strong coupling along c-axis due to an
apparent contraction of about 0.13 nm compared to $BaFe_2As_2$. Temperature
independent anisotropy indicates that the transport in ab plane and along
c-axis direction shares the same scattering mechanism. In sharp contrast to the
case of parent compounds $ROFeAs$ (R=rare earth) and $MFe_2As_2$ (M=Ba and Sr),
spin-density-wave (SDW) ordering (or structural transition) leads to a steep
increase of resistivity in $CaFe_2As_2$. Such different resistivity response to
SDW ordering is helpful to understand the role played by SDW ordering in
Fe-based high-$T_c$ superconductors. The susceptibility behavior is very
similar to that observed in single crystal $BaFe_2As_2$. A linear temperature
dependent susceptibility occurs above SDW transition of about 165 K. Partial
substitution of Na for Ca suppresses the SWD ordering (anomaly in resistivity)
and induces occurrence of superconductivity at $\sim 20$ K.",0806.4279v1
2008-08-14,Measurement of the dark matter velocity anisotropy in galaxy clusters,"The internal dynamics of a dark matter structure may have the remarkable
property that the local temperature in the structure depends on direction. This
is parametrized by the velocity anisotropy beta which must be zero for relaxed
collisional structures, but has been shown to be non-zero in numerical
simulations of dark matter structures. Here we present a method to infer the
radial profile of the velocity anisotropy of the dark matter halo in a galaxy
cluster from X-ray observables of the intracluster gas. This non-parametric
method is based on a universal relation between the dark matter temperature and
the gas temperature which is confirmed through numerical simulations. We apply
this method to observational data and we find that beta is significantly
different from zero at intermediate radii. Thus we find a strong indication
that dark matter is effectively collisionless on the dynamical time-scale of
clusters, which implies an upper limit on the self-interaction cross-section
per unit mass sigma/m < 1 cm2/g. Our results may provide an independent way to
determine the stellar mass density in the central regions of a relaxed cluster,
as well as a test of whether a cluster is in fact relaxed.",0808.2049v1
2008-09-05,Anomalous CMB north-south asymmetry,"Several accurate analyses have revealed a statistically significant
North-South ecliptic asymmetry in the large-angle correlations strength of the
Cosmic Microwave Background (CMB) radiation temperature field data from the
Wilkinson Microwave Anisotropy Probe (WMAP). This asymmetry is inconsistent
with the statistical isotropy expected in the concordance cosmological model
LCDM. It has been suggested that a possible cause-effect relationship exists
between this large-angle anisotropy and the anomalous CMB quadrupole-octopole
planes alignment. In turn, this later phenomenon (or both) would be a
consequence of one or more of the following undesired effects in CMB data: a
systematic error in the data processing or in the instrument characterization,
residual foregrounds, and large-angle correlations induced by the incomplete
sky CMB data (cut-sky masks are needed to reject Galactic foregrounds). Here,
it is proved that the North-South (NS) asymmetry is unrelated to the quadrupole
(l=2) and the octopole (l=3) properties because we find, at high confidence
levels, such large-angle anisotropy in three- and five-year WMAP CMB maps
containing only the multipole components 4 <= l <= 10. The statistical
significance depends on both, the CMB map analyzed as well as the cut-sky mask
applied to exclude foregrounds. The significance level of the NS-asymmetry is
less in five-year WMAP data with KQ75 (> 90% CL) than it is in three-year data
with Kp0 (> 96% CL). Additionally, robustness tests show that the statistical
significance of the NS-asymmetry is affected by the use of the KQ85 and KQ75
masks in five-year single-frequency WMAP CMB maps, whereas it is insensitive
with respect to application of the Kp2 and Kp0 masks in three-year
single-frequency WMAP CMB maps.",0809.0934v1
2008-09-10,Extremely Anisotropic Scintillations,"A small number of quasars exhibit interstellar scintillation on time-scales
less than an hour; their scintillation patterns are all known to be
anisotropic. Here we consider a totally anisotropic model in which the
scintillation pattern is effectively one-dimensional. For the persistent rapid
scintillators J1819+3845 and PKS1257-326 we show that this model offers a good
description of the two-station time-delay measurements and the annual cycle in
the scintillation time-scale. Generalising the model to finite anisotropy
yields a better match to the data but the improvement is not significant and
the two additional parameters which are required to describe this model are not
justified by the existing data. The extreme anisotropy we infer for the
scintillation patterns must be attributed to the scattering medium rather than
a highly elongated source. For J1819+3845 the totally anisotropic model
predicts that the particular radio flux variations seen between mid July and
late August should repeat between late August and mid November, and then again
between mid November and late December as the Earth twice changes its direction
of motion across the scintillation pattern. If this effect can be observed then
the minor-axis velocity component of the screen and the orientation of that
axis can both be precisely determined. In reality the axis ratio is finite,
albeit large, and spatial decorrelation of the flux pattern along the major
axis may be observable via differences in the pairwise fluxes within this
overlap region; in this case we can also constrain both the major-axis velocity
component of the screen and the magnitude of the anisotropy.",0809.1694v1
2008-09-18,Azimuthal anisotropy and fundamental symmetries in QCD matter at RHIC,"A study of collective behavior in heavy ion collisions provides one of the
most sensitive and promising probes for investigation of possible formation of
new extreme state of strong interacting matter and elucidating its properties.
Systematic of experimental results for final state azimuthal anisotropy is
presented for heavy ion interactions at RHIC. Experimental data for azimuthal
anisotropy indicate that the final state strongly interacting matter under
extreme conditions behaves as near-ideal liquid rather, than ideal gas of
quarks and gluons. The strong quenching of jets and the dramatic modification
of jet-like azimuthal correlations, observed in ${Au+Au}$ collisions, are
evidences of the extreme energy loss of partons traversing matter which
contains a large density of color charges. For the first time, dependence of
the jet suppression on orientation of a jet with respect to the reaction plane
is found at RHIC experimentally. The model of compound collective flow and
corresponding analytic approach are discussed. The possible violations of
$\cal{P}$ and $\cal{CP}$ symmetries of strong interactions in heavy ion
collisions at different initial energies are considered. Thus, now the fact is
established firmly, that extremely hot and dense matter created in relativistic
heavy ion collisions at RHIC differs dramatically from everything that was
observed and investigated before.",0809.3130v1
2008-10-20,The CMBR ISW and HI 21-cm Cross-correlation Angular Power Spectrum,"The late-time growth of large scale structures (LSS) is imprinted in the CMBR
anisotropy through the Integrated Sachs Wolfe (ISW) effect. This is perceived
to be a very important observational probe of dark energy. Future observations
of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI)
distribution hold the potential of probing the LSS over a large redshift range.
We have investigated the possibility of detecting the ISW through
cross-correlations between the CMBR anisotropies and redshifted 21-cm
observations. Assuming that the HI traces the dark matter, we find that the
ISW-HI cross-correlation angular power spectrum at an angular multipole l is
proportional to the dark matter power spectrum evaluated at the comoving wave
number l/r, where r is the comoving distance to the redshift from which the HI
signal originated. The amplitude of the cross-correlation signal depends on
parameters related to the HI distribution and the growth of cosmological
perturbations. However the cross-correlation is extremely weak as compared to
the CMBR anisotropies and the predicted HI signal. As a consequence the
cross-correlation signal is smaller than the cosmic variance, and a
statistically significant detection is not very likely.",0810.3649v2
2008-10-23,Collective Phenomena in the Non-Equilibrium Quark-Gluon Plasma,"In this work we study the non-equilibrium dynamics of a quark-gluon plasma,
as created in heavy-ion collisions. We investigate how big of a role plasma
instabilities can play in the isotropization and equilibration of a quark-gluon
plasma. In particular, we determine, among other things, how much collisions
between the particles can reduce the growth rate of unstable modes. This is
done both in a model calculation using the hard-loop approximation, as well as
in a real-time lattice simulation combining both classical Yang-Mills-fields as
well as inter-particle collisions. The new extended version of the simulation
is also used to investigate jet transport in isotropic media, leading to a
cutoff-independent result for the transport coefficient q-hat. The precise
determination of such transport coefficients is essential, since they can
provide important information about the medium created in heavy-ion collisions.
In anisotropic media, the effect of instabilities on jet transport is studied,
leading to a possible explanation for the experimental observation that
high-energy jets traversing the plasma perpendicular to the beam axis
experience much stronger broadening in rapidity than in azimuth. The
investigation of collective modes in the hard-loop limit is extended to
fermionic modes, which are shown to be all stable. Finally, we study the
possibility of using high energy photon production as a tool to experimentally
determine the anisotropy of the created system. Knowledge of the degree of
local momentum-space anisotropy reached in a heavy-ion collision is essential
for the study of instabilities and their role for isotropization and
thermalization, because their growth rate depends strongly on the anisotropy",0810.4306v1
2008-11-03,Compensation-dependent in-plane magnetization reversal processes in Ga1-xMnxP1-ySy,"We report the effect of dilute alloying of the anion sublattice with S on the
in-plane uniaxial magnetic anisotropy and magnetization reversal process in
Ga1-xMnxP as measured by both ferromagnetic resonance (FMR) and superconducting
quantum interference device (SQUID) magnetometry. At T=5K, raising the S
concentration increases the uniaxial magnetic anisotropy between in-plane <011>
directions while decreasing the magnitude of the (negative) cubic anisotropy
field. Simulation of the SQUID magnetometry indicates that the energy required
for the nucleation and growth of domain walls decreases with increasing y.
These combined effects have a marked influence on the shape of the
field-dependent magnetization curves; while the direction remains the easy axis
in the plane of the film, the field dependence of the magnetization develops
double hysteresis loops in the [011] direction as the S concentration increases
similar to those observed for perpendicular magnetization reversal in lightly
doped Ga1-xMnxAs. The incidence of double hysteresis loops is explained with a
simple model whereby magnetization reversal occurs by a combination of coherent
spin rotation and noncoherent spin switching, which is consistent with both FMR
and magnetometry experiments. The evolution of magnetic properties with S
concentration is attributed to compensation of Mn acceptors by S donors, which
results in a lowering of the concentration of holes that mediate
ferromagnetism.",0811.0385v1
2009-01-28,Spin canting in a Dy-based Single-Chain Magnet with dominant next-nearest neighbor antiferromagnetic interactions,"We investigate theoretically and experimentally the static magnetic
properties of single crystals of the molecular-based Single-Chain Magnet (SCM)
of formula [Dy(hfac)$_{3}$NIT(C$_{6}$H$_{4}$OPh)]$_{\infty}$ comprising
alternating Dy$^{3+}$ and organic radicals. A peculiar inversion between maxima
and minima in the angular dependence of the magnetic molar susceptibility
$\chi_{M}$ occurs on increasing temperature. Using information regarding the
monomeric building block as well as an {\it ab initio} estimation of the
magnetic anisotropy of the Dy$^{3+}$ ion, this anisotropy-inversion phenomenon
can be assigned to weak one-dimensional ferromagnetism along the chain axis.
This indicates that antiferromagnetic next-nearest-neighbor interactions
between Dy$^{3+}$ ions dominate, despite the large Dy-Dy separation, over the
nearest-neighbor interactions between the radicals and the Dy$^{3+}$ ions.
Measurements of the field dependence of the magnetization, both along and
perpendicularly to the chain, and of the angular dependence of $\chi_{M}$ in a
strong magnetic field confirm such an interpretation. Transfer matrix
simulations of the experimental measurements are performed using a classical
one-dimensional spin model with antiferromagnetic Heisenberg exchange
interaction and non-collinear uniaxial single-ion anisotropies favoring a
canted antiferromagnetic spin arrangement, with a net magnetic moment along the
chain axis. The fine agreement obtained with experimental data provides
estimates of the Hamiltonian parameters, essential for further study of the
dynamics of rare-earths based molecular chains.",0901.4409v1
2009-02-04,Spin dynamics of frustrated easy-axis triangular antiferromagnet 2H-AgNiO2 explored by inelastic neutron scattering,"We report inelastic neutron scattering measurements of the spin dynamics in
the layered hexagonal magnet 2H-AgNiO2 which has stacked triangular layers of
antiferromagnetically-coupled Ni2+ spins (S=1) ordered in a collinear
alternating stripe pattern. We observe a broad band of magnetic excitations
above a small gap of 1.8 meV and extending up to 7.5 meV, indicating strongly
dispersive excitations. The measured dispersions of the boundaries of the
powder-averaged spectrum can be quantitatively explained by a linear spin-wave
dispersion for triangular layers with antiferromagnetic nearest- and weak
next-nearest neighbor couplings, a strong easy-axis anisotropy and additional
weak inter-layer couplings. The resulting dispersion relation has global minima
not at magnetic Bragg wavevectors but at symmetry-related soft points and we
attribute this anomalous feature to the strong competition between the
easy-axis anisotropy and the frustrated antiferromagnetic couplings. We have
also calculated the quantum corrections to the dispersion relation to order 1/S
in spin-wave theory by extending the work of Chubukov and Jolicoeur [Phys. Rev.
B v46, 11137 (1992)] and find that the presence of easy-axis anisotropy
significantly reduces the quantum renormalizations predicted for the isotropic
model.",0902.0676v1
2009-02-04,Optical Anisotropy of Schwarzschild Metric within Equivalent Medium Framework,"It is has been long known that the curved space in the presence of
gravitation can be described as a non-homogeneous anisotropic medium in flat
geometry with different constitutive equations. In this article, we show that
the eigenpolarizations of such medium can be exactly solved, leading to a
pseudo-isotropic description of curved vacuum with two refractive index
eigenvalues having opposite signs, which correspond to forward and backward
travel in time. We conclude that for a rotating universe, time-reversal
symmetry is broken. We also demonstrate the applicability of this method to
Schwarzschild metric and derive exact forms of refractive index. We derive the
subtle optical anisotropy of space around a spherically symmetric, non-rotating
and uncharged blackhole in the form of an elegant closed form expression, and
show that the refractive index in such a pseudo-isotropic system would be a
function of coordinates as well as the direction of propagation. Corrections
arising from such anisotropy in the bending of light are shown and a simplified
system of equations for ray-tracing in the equivalent medium of Schwarzschild
metric is found.",0902.0728v7
2009-02-05,Anisotropic clustering of inertial particles in homogeneous shear flow,"Recently, clustering of inertial particles in turbulence has been thoroughly
analyzed for statistically homogeneous isotropic flows. Phenomenologically,
spatial homogeneity of particles configurations is broken by the advection of a
range of eddies determined by the Stokes relaxation time of the particles which
results in a multi-scale distribution of local concentrations and voids. Much
less is known concerning anisotropic flows. Here, by addressing direct
numerical simulations (DNS) of a statistically steady particle-laden
homogeneous shear flow, we provide evidence that the mean shear preferentially
orients particle patterns. By imprinting anisotropy on large scales velocity
fluctuations, the shear indirectly affects the geometry of the clusters.
Quantitative evaluation is provided by a purposely designed tool, the angular
distribution function of particle pairs (ADF), which allows to address the
anisotropy content of particles aggregates on a scale by scale basis. The data
provide evidence that, depending on the Stokes relaxation time of the
particles, anisotropic clustering may occur even in the range of scales where
the carrier phase velocity field is already recovering isotropy. The strength
of the singularity in the anisotropic component of the ADF quantifies the level
of fine scale anisotropy, which may even reach values of more than 30%
direction-dependent variation in the probability to find two close-by particles
at viscous scale separation.",0902.0893v1
2009-02-15,Sudden Critical Current Drops Induced in S/F Structures,"In the search for new physical properties of S/F structures, we have found
that the superconductor critical current can be controlled by the domain state
of the neighboring ferromagnet. The superconductor is a thin wire of thickness
d_{s} ~ 2 xi_{S}. Nb/Co and Nb/Py (Permalloy Ni_{80}Fe_{20}) bilayer structures
were grown with a significant magnetic anisotropy. Critical current
measurements of Nb/Co structures with ferromagnet thickness d_{F} > 30nm show
sudden drops in two very defined steps when the measurements are made along the
hard axes direction (i.e. current track parallel to hard anisotropy axes
direction). These drops disappear when they are made along the easy axis
direction or when the ferromagnet thickness is below 30nm. The drops are
accompanied by vortex flux flow. In addition magnetorestistance measurements
close to Tc show a sharp increase near saturation fields of the ferromagnet.
Similar results are reproduced in Nb/Py bilayer structure with the ferromagnet
thickness d_{F} ~ 50nm along the easy anisotropy axes. These results are
explained as being due to spontaneous vortex formation and flow induced by
Bloch domain walls of the ferromagnet underneath. We argue these Bloch domain
walls produce a 2D vortex-antivortex lattice structure.",0902.2572v2
2009-03-13,2D XY Behavior observed in quasi-2D quantum Heisenberg antiferromagnets,"The magnetic properties of a new family of molecular-based quasi-two
dimension $S=1/2$ Heisenberg antiferromagnets are reported. Three compounds,
($Cu(pz)_2(ClO_4)_2$, $Cu(pz)_2(BF_4)_2$, and $[Cu(pz)_2(NO_3)](PF_6)$) contain
similar planes of Cu$^{2+}$ ions linked into magnetically square lattices by
bridging pyrazine molecules (pz = $C_4H_4N_2$). The anions provide charge
balance as well as isolation between the layers. Single crystal measurements of
susceptibility and magnetization, as well as muon spin relaxation studies,
reveal low ratios of N\'{e}el temperatures to exchange strengths ($4.25 / 17.5
= 0.243$, $3.80/15.3=0.248$, and $3.05/10.8=0.282$, respectively) while the
ratio of the anisotropy fields $H_A$ (kOe) to the saturation field
$H_\mathrm{SAT}$ (kOe) are small ($2.6/490 = 5.3\times10^{-3}$,
$2.4/430=5.5\times10^{-3}$, and $0.07/300=2.3\times10^{-4}$, respectively),
demonstrating close approximations to a 2D Heisenberg model. The
susceptibilities of ClO$_4$ and BF$_4$ show evidence of an exchange anisotropy
crossover (Heisenberg to $XY$) at low temperatures; their ordering transitions
are primarily driven by the $XY$ behavior with the ultimate 3D transition
appearing parasitically. The PF$_6$ compound remains Heisenberg-like at all
temperatures, with its transition to the N\'{e}el state due to the interlayer
interactions. Effects of field-induced anisotropy have been observed.",0903.2470v1
2009-03-18,Approximate Analytic Spectra of Reionized CMB Anisotropies and Polarization generated by Relic Gravitational Waves,"We present an approximate, analytical calculation of the reionized spectra
$C_l^{XX}$ of cosmic microwave background radiation (CMB) anisotropies and
polarizations generated by relic gravitational waves (RGWs). Three simple
models of reionization are explored, whose visibility functions are fitted by
gaussian type of functions as approximations. We have derived the analytical
polarization $\beta_l$ and temperature anisotropies $\alpha_l$, both consisting
of two terms proportional to RGWs at the decoupling and at the reionization as
well. The explicit dependence of $\beta_l$ and $\alpha_l$ upon the reionization
time $\eta_r$, the duration $\Delta\eta_r$, and the optical depth $\kappa_r$
are demonstrated. Moreover, $\beta_l$ and $\alpha_l$ contain $\kappa_r$ in
different coefficients, and the polarization spectra $C_l^{EE}$ are $C_l^{BB}$
are more sensitive probes of reionization than $C_l^{TT}$. These results
facilitate examination of the reionization effects, in particular, the
degeneracies of $\kappa_r$ with the normalization amplitude and with the
initial spectral index of RGWs. It is also found that reionization also causes
a $\kappa_r$-dependent shift $\Delta l\sim 20$ of the zero multipole $l_0$ of
$C_l^{TE}$, an effect that should be included in order to detect the traces of
RGWs. Compared with numerical results, the analytical $C_l^{XX}$ as
approximation have the limitation. For the primary peaks in the range $l\simeq
(30, 600)$, the error is $\le 3%$ in three models. In the range $l < 20$ for
the reionization bumps, the error is $\le 15%$ for $C_l^{EE}$ and $C_l^{BB}$ in
the two extended reionization models, and $C_l^{TT}$ and $C_l^{TE}$ have much
larger departures for $l<10$. The bumps in the sudden reionization model are
too low.",0903.3159v2
2009-04-08,Anisotropy of the upper critical field in a Co-doped BaFe2As2 single crystal,"The temperature dependence of the upper critical magnetic field (Hc2) in a
BaFe1.84Co0.16As2 single crystal was determined via resistivity, for the
inter-plane (H^ab) and in-plane (H//ab) directions in pulsed and static
magnetic fields of up to 60 T. Suppressing superconductivity in a pulsed
magnetic field at 3He temperatures permits us to construct an H-T phase diagram
from quantitative Hc2(0) values and determine its behavior in low temperatures.
Hc2(0) with H//ab (Hc2//(0)) and H^ab (Hc2^(0)) are ~ 55 T and 50 T
respectively. These values are ~ 1.2 - 1.4 times larger than the weak-coupling
Pauli paramagnetic limit (Hp = 1.84 Tc), indicating that enhanced paramagnetic
limiting is essential and this superconductor is unconventional. While Hc2//ab
is saturated at low temperature, Hc2 with H^ab (Hc2^) exhibits almost linear
temperature dependence towards T = 0 K which results in reduced anisotropy of
Hc2 in low temperature. The anisotropy of Hc2 was ~ 3.4 near Tc, and decreases
rapidly with lower temperatures reaching ~ 1.1 at T = 0.7 K.",0904.1418v3
2009-04-16,Significant foreground unrelated non-acoustic anisotropy on the one degree scale in WMAP 5-year observations,"The spectral variation of the cosmic microwave background (CMB) as observed
by WMAP was tested using foreground reduced WMAP5 data, by producing
subtraction maps at the 1$^\circ$ angular resolution between the two
cosmological bands of V and W, for masked sky areas that avoid the Galactic
disk. The resulting $V-W$ map revealed a non-acoustic signal over and above the
WMAP5 pixel noise, with two main properties. Firstly, it possesses quadrupole
power at the $\approx$ 1 $\mu K$ level which may be attributed to foreground
residuals. Second, it fluctuates also at all values of $\ell >$ 2, especially
on the $1^\circ$ scale ($200 \lesssim \ell \lesssim 300$). The behavior is {\it
random and symmetrical} about zero temperature with a r.m.s. amplitude of
$\approx$ 7 $\mu K$, or 10 % of the maximum CMB anisotropy, which would require
a `cosmic conspiracy' among the foreground components if it is a consequence of
their existences. Both anomalies must be properly diagnosed and corrected if
`precision cosmology' is the claim. The second anomaly is, however, more
interesting because it opens the question on whether the CMB anisotropy
genuinely represents primordial density seeds.",0904.2513v3
2009-05-15,The contribution of the kinematic Sunyaev-Zel'dovich Effect from the Warm Hot Intergalactic Medium to the Five-Year WMAP Data,"We study the contribution of the kinematic Sunyaev-Zel'dovich (kSZ) effect,
generated by the warm-hot intergalactic medium (WHIM), to the cosmic microwave
background (CMB) temperature anisotropies in the Five-Year Wilkinson Microwave
Anisotropy Probe (WMAP) data. We explore the concordance LambdaCDM cosmological
model, with and without this kSZ contribution, using a Markov chain Monte Carlo
algorithm. Our model requires a single extra parameter to describe this new
component. Our results show that the inclusion of the kSZ signal improves the
fit to the data without significantly altering the best-fit cosmological
parameters except Obh^2. The improvement is localized at the l>500 multipoles.
For the best-fit model, this extra component peaks at l~450 with an amplitude
of 129 muK^2, and represents 3.1% of the total power measured by the Wilkinson
Microwave Anisotropy Probe. Nevertheless, at the 2-sigma level a null kSZ
contribution is still compatible with the data. Part of the detected signal
could arise from unmasked point sources and/or Poissonianly distributed
foreground residuals. A statistically more significant detection requires the
wider frequency coverage and angular resolution of the forthcoming Planck
mission.",0905.2582v2
2009-05-27,A Three-Point Cosmic Ray Anisotropy Method,"The two-point angular correlation function is a traditional method used to
search for deviations from expectations of isotropy. In this paper we develop
and explore a statistically descriptive three-point method with the intended
application being the search for deviations from isotropy in the highest energy
cosmic rays. We compare the sensitivity of a two-point method and a
""shape-strength"" method for a variety of Monte-Carlo simulated anisotropic
signals. Studies are done with anisotropic source signals diluted by an
isotropic background. Type I and II errors for rejecting the hypothesis of
isotropic cosmic ray arrival directions are evaluated for four different event
sample sizes: 27, 40, 60 and 80 events, consistent with near term data
expectations from the Pierre Auger Observatory. In all cases the ability to
reject the isotropic hypothesis improves with event size and with the fraction
of anisotropic signal. While ~40 event data sets should be sufficient for
reliable identification of anisotropy in cases of rather extreme (highly
anisotropic) data, much larger data sets are suggested for reliable
identification of more subtle anisotropies. The shape-strength method
consistently performs better than the two point method and can be easily
adapted to an arbitrary experimental exposure on the celestial sphere.",0905.4488v2
2009-06-13,Angular momentum transfer and the size - mass relation in early - type galaxies,"Early - type galaxies (ETGs) define a narrow strip in the size - mass plane
because of the observed correlation between the effective radius $R_{eff}$ and
the total stellar mass $M_{\star}$. When expressed in logarithmic units, a
linear relation, $\log{R_{eff}} \propto \gamma \log{M_{\star}}$, is indeed
observationally found, but the slope $\gamma$ deviates from the canonical
$\gamma = 1/2$ value which can be naively predicted for a spherically symmetric
isotropic system. We propose here that a transfer of angular momentum to the
stellar component induces an anisotropy in the velocity space thus leading to a
modified distribution function (DF). Assuming an Osipkov - Merritt like
anisotropic DF, we derive an analytic relation between the slope $\gamma$ of
the size - mass relation and the slope $\alpha$ of the angular momentum term in
the DF. With this simple model, we are then able to recover the observed
$\gamma$ value provided $\alpha$ is suitably set. It turns out that an
anisotropy profile which is tangential inside $\sim 0.6 r_a$ and radial
outside, with $r_a$ the anisotropy radius, is able to reproduce the observed
size - mass relation observed for massive ($M_{\star} \ge 2 \times 10^{10} \
h^{-1} {\rm M}_{\odot}$) elliptical galaxies.",0906.2457v1
2009-06-24,Anisotropic Fermi liquid theory of the ultra cold fermionic polar molecules: Landau parameters and collective modes,"We study the Fermi liquid properties of the cold atomic dipolar Fermi gases
with the explicit dipolar anisotropy using perturbative approaches. Due to the
explicit dipolar anisotropy, Fermi surfaces exhibit distortions of the
$d_{r^2-3z^2}$-type in three dimensions and of the $d_{x^2-y^2}$-type in two
dimensions. The fermion self-energy, effective mass, and Fermi velocity develop
the same anisotropy at the Hartree-Fock level proportional to the interaction
strength. The Landau interaction parameters in the isotropic Fermi liquids
become the tri-diagonal Landau interaction matrices in the dipolar Fermi
liquids which renormalize thermodynamic susceptibilities. With large dipolar
interaction strength, the Fermi surface collapses along directions
perpendicular to the dipole orientation. The dynamic collective zero sound
modes exhibit an anisotropic dispersion with the largest sound velocity
propagating along the polar directions. Similarly, the longitudinal p-wave
channel spin mode becomes a propagating mode with an anisotropic dispersion in
multi-component dipolar systems.",0906.4403v5
2009-06-29,J/psi azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon,"The J/$\psi$ azimuthal distribution relative to the reaction plane has been
measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various
physical mechanisms related to charmonium dissociation in the medium created in
the heavy ion collision are expected to introduce an anisotropy in the
azimuthal distribution of the observed J/$\psi$ mesons at SPS energies. Hence,
the measurement of J/$\psi$ elliptic anisotropy, quantified by the Fourier
coefficient v$_2$ of the J/$\psi$ azimuthal distribution relative to the
reaction plane, is an important tool to constrain theoretical models aimed at
explaining the anomalous J/$\psi$ suppression observed in Pb-Pb collisions. We
present the measured J/$\psi$ yields in different bins of azimuthal angle
relative to the reaction plane, as well as the resulting values of the Fourier
coefficient v$_{2}$ as a function of the collision centrality and of the
J/$\psi$ transverse momentum. The reaction plane has been estimated from the
azimuthal distribution of the neutral transverse energy detected in an
electromagnetic calorimeter. The analysis has been performed on a data sample
of about 100 000 events, distributed in five centrality or p$_{\rm T}$
sub-samples. The extracted v$_{2}$ values are significantly larger than zero
for non-central collisions and are seen to increase with p$_{\rm T}$.",0906.5376v2
2009-07-15,Transport properties and the anisotropy of Ba_{1-x}K_xFe_2As_2 single crystals in normal and superconducting states,"The transport and superconducting properties of Ba_{1-x}K_xFe_2As_2 single
crystals with T_c = 31 K were studied. Both in-plane and out-of plane
resistivity was measured by modified Montgomery method. The in-plane
resistivity for all studied samples, obtained in the course of the same
synthesis, is almost the same, unlike to the out-of plane resistivity, which
differ considerably. We have found that the resistivity anisotropy
\gamma=\rho_c /\rho_{ab} is almost temperature independent and lies in the
range 10-30 for different samples. This, probably, indicates on the extrinsic
nature of high out-of-plane resistivity, which may appear due to the presence
of the flat defects along Fe-As layers in the samples. This statement is
supported by comparatively small effective mass anisotropy, obtained from the
upper critical field measurements, and from the observation of the so-called
""Friedel transition"", which indicates on the existence of some disorder in the
samples in c-direction.",0907.2598v1
2009-08-30,On the anisotropy barrier reduction in fast relaxing Mn12 single-molecule magnets,"A novel angle-swept high-frequency EPR (HFEPR) technique is described that
enables in-situ alignment of single-crystal samples containing low-symmetry
magnetic species such as single-molecule magnets (SMMs). This cavity-based
method involves recording spectra at fixed frequency and field, while sweeping
the field orientation. The method is applied to the study of a low-symmetry
Jahn-Teller variant of the spin S = 10 Mn12 SMMs (e.g. Mn12-acetate). The
low-symmetry complex is also an SMM, but with a significantly reduced barrier
to magnetization reversal (Ueff ~ 43 K) and, hence, faster relaxation at low
temperature in comparison with the high-symmetry species. Mn12 complexes that
crystallize in lower symmetry structures exhibit a tendency for one or more of
the Mn(III) Jahn-Teller axes to be abnormally oriented, which is believed to be
the cause of the faster relaxation. An extensive HFEPR study of
[Mn12O12(O2CCH2But)16(H2O)4].CH2Cl2.MeNO2 is presented in order to examine the
influence of the abnormally oriented Jahn-Teller axis on the effective barrier.
The reduction in the axial anisotropy, D, is found to be insufficient to
account for the nearly 40% reduction in Ueff. However, the reduced symmetry of
the Mn12 core gives rise to a very significant 2nd order transverse anisotropy,
E ~ D/6. This, in turn, causes a significant mixing of spin projection states
well below the top of the classical barrier. Thus, magnetic quantum tunneling
is the dominant factor contributing to the barrier reduction in fast relaxing
Mn12 SMMs.",0908.4434v1
2009-09-24,Assembly bias and the dynamical structure of dark matter halos,"Based on the Millennium Simulation we examine assembly bias for the halo
properties: shape, triaxiality, concentration, spin, shape of the velocity
ellipsoid and velocity anisotropy. For consistency we determine all these
properties using the same set of particles, namely all gravitationally
self-bound particles belonging to the most massive sub-structure of a given
friends-of-friends halo. We confirm that near-spherical and high-spin halos
show enhanced clustering. The opposite is true for strongly aspherical and
low-spin halos. Further, below the typical collapse mass, M*, more concentrated
halos show stronger clustering whereas less concentrated halos are less
clustered which is reversed for masses above M*. Going beyond earlier work we
show that: (1) oblate halos are more strongly clustered than prolate ones; (2)
the dependence of clustering on the shape of the velocity ellipsoid coincides
with that of the real-space shape, although the signal is stronger; (3) halos
with weak velocity anisotropy are more clustered, whereas radially anisotropic
halos are more weakly clustered; (4) for all highly clustered subsets we find
systematically less radially biased velocity anisotropy profiles. These
findings indicate that the velocity structure of halos is tightly correlated
with environment.",0909.4302v2
2009-10-09,Quasi-Chemical and Structural Analysis of Polarizable Anion Hydration,"Quasi-chemical theory is utilized to analyze the roles of solute polarization
and size in determining the structure and thermodynamics of bulk anion
hydration for the Hofmeister series Cl$^-$, Br$^-$, and I$^-$. Excellent
agreement with experiment is obtained for whole salt hydration free energies
using the polarizable AMOEBA force field. The quasi-chemical approach exactly
partitions the solvation free energy into inner-shell, outer-shell packing, and
outer-shell long-ranged contributions by means of a hard-sphere condition.
Small conditioning radii, even well inside the first maximum of the
ion-water(oxygen) radial distribution function, result in Gaussian behavior for
the long-ranged contribution that dominates the ion hydration free energy. The
spatial partitioning allows for a mean-field treatment of the long-ranged
contribution, leading to a natural division into first-order electrostatic,
induction, and van der Waals terms. The induction piece exhibits the strongest
ion polarizability dependence, while the larger-magnitude first-order
electrostatic piece yields an opposing but weaker polarizability dependence. In
addition, a structural analysis is performed to examine the solvation
anisotropy around the anions. As opposed to the hydration free energies, the
solvation anisotropy depends more on ion polarizability than on ion size:
increased polarizability leads to increased anisotropy. The water dipole
moments near the ion are similar in magnitude to bulk water, while the ion
dipole moments are found to be significantly larger than those observed in
quantum mechanical studies. Possible impacts of the observed over-polarization
of the ions on simulated anion surface segregation are discussed.",0910.1786v2
2009-10-19,Fermi surface topology and magneto-quantum oscillations for under-doped YBCO with hopping anisotropy,"We investigate a chiral d-density wave (CDDW) mean field Hamiltonian in
momentum space, which also includes the in-plane hopping anisotropy parameter
e, for the under-doped YBCO to explore the possibility of quantum oscillations
(QO) in the specific heat in the presence of a changing magnetic field (B). The
inclusion is motivated by the experimental signature of nematic order found in
cuprates in neutron scattering experiments of Hinkov et al. (see Ref.[10]). We
obtain the Fermi surface topologies, without and with magnetic field
background, including the elastic scattering by impurities in the investigation
within t-matrix approximation framework. The topologies are found to be
distinct from the Fermi arc picture: we find that the minimally gapped portion
of Fermi surface forms closed loops (hole pockets) and not arcs. However, some
k-points of the electron pockets are found to be associated with the negative
density of state values (see Ref.[28]) when B and e are zero; for non-zero B
and e slightly positive these pockets acquire positive DOS values. The latter
thus seems to justify the inclusion of the hopping anisotropy in the
Hamiltonian. We relate these findings to QO in specific heat. We show that the
origin of the main frequency of the oscillations is the electron pocket of the
Fermi surface at a magnetic field B equal to 50 T.",0910.3464v1
2009-11-02,"Kinematics of Milky Way Satellites: Mass Estimates, Rotation Limits, and Proper Motions","In the past several years high resolution kinematic data sets from Milky Way
satellite galaxies have confirmed earlier indications that these systems are
dark matter dominated objects. Further understanding of what these galaxies
reveal about cosmology and the small scale structure of dark matter relies in
large part on a more detailed interpretation of their internal kinematics. This
article discusses a likelihood formalism that extracts important quantities
from the kinematic data, including the amplitude of rotation, proper motion,
and the mass distribution. In the simplest model the projected error on the
rotational amplitude is shown to be $\sim 0.5 $ km s$^{-1}$ with $\sim 10^3$
stars from either classical or ultra-faint satellites. The galaxy Sculptor is
analyzed for the presence of a rotational signal; no significant detection of
rotation is found, and given this result limits are derived on the Sculptor
proper motion. A criteria for model selection is discussed that determines the
parameters required to describe the dark matter halo density profiles and the
stellar velocity anisotropy. Applied to four data sets with a wide range of
velocities, the likelihood is found to be more sensitive to variations in the
slope of the dark matter density profile than variations in the velocity
anisotropy. Models with variable radial velocity anisotropy are shown to be
preferred relative to those in which this quantity is constant at all radii in
the galaxy.",0911.0220v1
2009-11-06,Cosmological hydrogen recombination: The effect of extremely high-n states,"Calculations of cosmological hydrogen recombination are vital for the
extraction of cosmological parameters from cosmic microwave background (CMB)
observations, and for imposing constraints to inflation and re-ionization. The
Planck} mission and future experiments will make high precision measurements of
CMB anisotropies at angular scales as small as l~2500, necessitating a
calculation of recombination with fractional accuracy of ~10^{-3}. Recent work
on recombination includes two-photon transitions from high excitation states
and many radiative transfer effects. Modern recombination calculations
separately follow angular momentum sublevels of the hydrogen atom to accurately
treat non-equilibrium effects at late times (z<900). The inclusion of extremely
high-n (n>100) states of hydrogen is then computationally challenging,
preventing until now a determination of the maximum n needed to predict CMB
anisotropy spectra with sufficient accuracy for Planck. Here, results from a
new multi-level-atom code (RecSparse) are presented. For the first time,
`forbidden' quadrupole transitions of hydrogen are included, but shown to be
negligible. RecSparse is designed to quickly calculate recombination histories
including extremely high-n states in hydrogen. Histories for a sequence of
values as high as n_max=250 are computed, keeping track of all angular momentum
sublevels and energy shells of the hydrogen atom separately. Use of an
insufficiently high n_max value (e.g., n_max=64) leads to errors (e.g., 1.8
sigma for Planck) in the predicted CMB power spectrum. Extrapolating errors,
the resulting CMB anisotropy spectra are converged to 0.5 sigma at
Fisher-matrix level for n_max=128, in the purely radiative case.",0911.1359v2
2009-11-23,Magnetic anisotropy determination and magnetic hyperthermia properties of small Fe nanoparticles in the superparamagnetic regime,"We report on the magnetic and hyperthermia properties of iron nanoparticles
synthesized by organometallic chemistry. They are 5.5 nm in diameter and
display a saturation magnetization close to the bulk one. Magnetic properties
are dominated by the contribution of aggregates of nanoparticles with respect
to individual isolated nanoparticles. Alternative susceptibility measurements
are been performed on a low interacting system obtained after eliminating the
aggregates by centrifugation. A quantitative analysis using the Gittleman s
model allow a determination of the effective anisotropy Keff = 1.3 * 10^5
J.m^{-3}, more than two times the magnetocristalline value of bulk iron.
Hyperthermia measurements are performed on agglomerates of nanoparticles at a
magnetic field up to 66 mT and at frequencies in the range 5-300 kHz. Maximum
measured SAR is 280 W/g at 300 kHz and 66 mT. Specific absorption rate (SAR)
displays a square dependence with the magnetic field below 30 mT but deviates
from this power law at higher value. SAR is linear with the applied frequency
for mu_0H=19 mT. The deviations from the linear response theory are discussed.
A refined estimation of the optimal size of iron nanoparticles for hyperthermia
applications is provided using the determined effective anisotropy value.",0911.4413v1
2009-11-25,A Scaling Relation of the Evolving Tidal Fields in a LCDM Cosmology,"We report the finding of a scaling relation among the cosmic-web anisotropy
parameter $A$, the linear density rms fluctuation sigma(r) and the linear
growth factor D(z). Using the tidal field derived from the Millennium
Simulation on 512^{3} grids at z=0, 2, 5 and 127, we calculate the largest
eigenvalues $\lambda$ of the local tidal tensor at each grid resolution and
measure its distance-averaged two-point correlation function, xi_{lambda}, as a
function of the cosines of polar angles cos(theta) in the local principal axis
frame. We show that xi_{lambda} is quite anisotropic, increasing toward the
directions of minimal matter compression, and that the anisotropy of
xi_{lambda} increases as the redshift, z, decreases and as the upper distance
cutoff r_{c} decreases. Fitting the numerical results to an analytic fitting
model \xi_{\lambda}(\cos\theta)\propto (1+A\cos^{n}\theta)^{-1}, it is found
that the best fit value of A, dubbed the cosmic-web anisotropy parameter,
varies systematically with sigma(r_{c}) and D(z), allowing us to determine the
simple empiral scaling relation A(r_{c},z)=0.8, D^{0.76}(z), sigma (r_{c})$.",0911.4755v2
2010-02-10,Power and spectral index anisotropy of the entire inertial range of turbulence in the fast solar wind,"We measure the power and spectral index anisotropy of high speed solar wind
turbulence from scales larger than the outer scale down to the ion gyroscale,
thus covering the entire inertial range. We show that the power and spectral
indices at the outer scale of turbulence are approximately isotropic. The
turbulent cascade causes the power anisotropy at smaller scales manifested by
anisotropic scalings of the spectrum: close to k^{-5/3} across and k^{-2} along
the local magnetic field, consistent with a critically balanced Alfvenic
turbulence. By using data at different radial distances from the Sun, we show
that the width of the inertial range does not change with heliocentric distance
and explain this by calculating the radial dependence of the ratio of the outer
scale to the ion gyroscale. At the smallest scales of the inertial range, close
to the ion gyroscale, we find an enhancement of power parallel to the magnetic
field direction coincident with a decrease in the perpendicular power. This is
most likely related to energy injection by ion kinetic modes such as the
firehose instability and also marks the beginning of the dissipation range of
solar wind turbulence.",1002.2096v1
2010-03-13,"A thermally stable heating mechanism for the intracluster medium: turbulence, magnetic fields and plasma instabilities","We consider the problem of self-regulated heating and cooling in galaxy
clusters and the implications for cluster magnetic fields and turbulence.
Viscous heating of a weakly collisional magnetised plasma is regulated by the
pressure anisotropy with respect to the local direction of the magnetic field.
The intracluster medium is a high-beta plasma, where pressure anisotropies
caused by the turbulent stresses and the consequent local changes in the
magnetic field will trigger very fast microscale instabilities. We argue that
the net effect of these instabilities will be to pin the pressure anisotropies
at a marginal level, controlled by the plasma beta parameter. This gives rise
to local heating rates that turn out to be comparable to the radiative cooling
rates. Furthermore, we show that a balance between this heating and
Bremsstrahlung cooling is thermally stable, unlike the often conjectured
balance between cooling and thermal conduction. Given a sufficient (and
probably self-regulating) supply of turbulent power, this provides a physical
mechanism for mitigating cooling flows and preventing cluster core collapse.
For observed density and temperature profiles, the assumed balance of viscous
heating and radiative cooling allows us to predict magnetic-field strengths,
turbulent velocities and turbulence scales as functions of distance from the
centre. Specific predictions and comparisons with observations are given for
several different clusters. Our predictions can be further tested by future
observations of cluster magnetic fields and turbulent velocities.",1003.2719v2
2010-03-16,Mass modification of itinerant carriers in RKKY oscillations induced by finite range exchange interactions,"We investigate the Ruderman-Kittel-Kasuya-Yosida oscillations of the
itinerant carrier spin density in a system where those oscillations appear only
due to a finite distribution of a localized spin. The system represents a
half-infinite one-dimensional quantum wire with a magnetic impurity located at
its edge. In contrast to the conventional model of a point-like exchange
interaction the itinerant carrier spin density oscillations in this system
exist. We {\it analytically} demonstrate that when the radius of the exchange
interaction is less than the wave length of the itinerant carriers living on
the Fermi surface, the long range behavior of the oscillations is identical to
the one taking place in the zero radius limit of the same exchange interaction
but for an infinite one-dimensional quantum wire where, in comparison with the
original half-infinite system, the mass of the itinerant carriers is {\it
strongly} modified by the exchange interaction radius. On the basis of our
analysis we make a suggestion on directionality of surface
Ruderman-Kittel-Kasuya-Yosida interaction shown in recent experiments: we
believe that in general the anisotropy of the Ruderman-Kittel-Kasuya-Yosida
interaction could result not only from the anisotropy of the {\it Fermi
surface} of itinerant carriers but also from the anisotropy of the {\it spin
carrying atomic orbitals} of magnetic impurities.",1003.3140v2
2010-03-22,Complexity and anisotropy in host morphology make populations safer against epidemic outbreaks,"One of the challenges in epidemiology is to account for the complex
morphological structure of hosts such as plant roots, crop fields, farms,
cells, animal habitats and social networks, when the transmission of infection
occurs between contiguous hosts. Morphological complexity brings an inherent
heterogeneity in populations and affects the dynamics of pathogen spread in
such systems. We have analysed the influence of realistically complex host
morphology on the threshold for invasion and epidemic outbreak in an SIR
(susceptible-infected-recovered) epidemiological model. We show that disorder
expressed in the host morphology and anisotropy reduces the probability of
epidemic outbreak and thus makes the system more resistant to epidemic
outbreaks. We obtain general analytical estimates for minimally safe bounds for
an invasion threshold and then illustrate their validity by considering an
example of host data for branching hosts (salamander retinal ganglion cells).
Several spatial arrangements of hosts with different degrees of heterogeneity
have been considered in order to analyse separately the role of shape
complexity and anisotropy in the host population. The estimates for invasion
threshold are linked to morphological characteristics of the hosts that can be
used for determining the threshold for invasion in practical applications.",1003.4239v1
2010-03-29,Effective field theory for Sp(N) antiferromagnets and its phase structure,"In this paper, we study quantum Sp(N) antiferromagnetic (AF) Heisenberg
models in two dimensions (2D) by using the Schwinger-boson representation and
the path-integral methods. An effective field theory, which is an extension of
CP^{N-1} model in (2+1)D, is derived and its phase structure is studied by the
1/N-expansion. We introduce a spatial anisotropy in the exchange couplings and
show that the effective coupling constant in the CP^{N-1} model is an
increasing function of the anisotropy. For the SU(N) AF Heisenberg model, which
is a specific case of the Sp(N) model, we found that phase transition from the
ordered ""N\'eel state"" to paramagnetic phase takes place as the anisotropy is
increased. In the vicinity of the SU(N) symmetric point, this phase structure
is retained. However as a parameter that controls explicit breaking of the
SU(N) symmetry is increased, a new phase, which is similar to the spiral-spin
phase with a nematic order in frustrated SU(2) spin systems, appears. It is
shown that at that phase transition point, a local SU(2) gauge symmetry with
composite SU(2) gauge field appears in the low-energy sector. It is another
example of symmetry-enhancement phenomenon at low energies. We also introduce a
lattice gauge-theoretical model, which is a counterpart of the effective field
theory, and study its phase structure by means of the Monte-Carlo simulations.",1003.5412v1
2010-04-12,Anisotropic Anomalous Diffusion assessed in the human brain by scalar invariant indices,"A new method to investigate anomalous diffusion in human brain is proposed.
The method has been inspired by both the stretched-exponential model proposed
by Hall and Barrick (HB) and DTI. Quantities extracted using HB method were
able to discriminate different cerebral tissues on the basis of their
complexity, expressed by the stretching exponent gamma and of the anisotropy of
gamma across different directions. Nevertheless, these quantities were not
defined as scalar invariants like mean diffusivity and fractional anisotropy,
which are eigenvalues of the diffusion tensor. We hypotesize instead that the
signal may be espressed as a simple stretched-exponential only along the
principal axes of diffusion, while in a generic direction the signal is modeled
as a combination of three different stretched-exponentials. In this way, we
derived indices to quantify both the tissue anomalous diffusion and its
anisotropy, independently of the reference frame of the experiment. We tested
and compare our new method with DTI and HB approaches applying them to 10
healty subjects brain at 3T. Our experimental results show that our parameters
are highly correlated to intrinsic local geometry when compared to HB indices.
Moreover, they offer a different kind of contrast when compared to DTI outputs.
Specifically, our indices show a higher capability to discriminate among
different areas of the corpus callosum, which are known to be associated to
different axonal densities.",1004.2001v1
2010-04-29,Non-gaussianity and Statistical Anisotropy in Cosmological Inflationary Models,"We study the statistical descriptors for some cosmological inflationary
models that allow us to get large levels of non-gaussianity and violations of
statistical isotropy. Basically, we study two different class of models: a
model that include only scalar field perturbations, specifically a subclass of
small-field slow-roll models of inflation with canonical kinetic terms, and
models that admit both vector and scalar field perturbations. We study the
former to show that it is possible to attain very high, including observable,
values for the levels of non-gaussianity f_{NL} and \tao_{NL} in the bispectrum
B_\zeta and trispectrum T_\zeta of the primordial curvature perturbation \zeta
respectively. Such a result is obtained by taking care of loop corrections in
the spectrum P_\zeta, the bispectrum B_\zeta and the trispectrum T_\zeta .
Sizeable values for f_{NL} and \tao_{NL} arise even if \zeta is generated
during inflation. For the latter we study the spectrum P_\zeta, bispectrum
B_\zeta and trispectrum $T_\zeta of the primordial curvature perturbation when
\zeta is generated by scalar and vector field perturbations. The tree-level and
one-loop contributions from vector field perturbations are worked out
considering the possibility that the one-loop contributions may be dominant
over the tree level terms. The levels of non-gaussianity f_{NL} and \tao_{NL},
are calculated and related to the level of statistical anisotropy in the power
spectrum, g_\zeta . For very small amounts of statistical anisotropy in the
power spectrum, the levels of non-gaussianity may be very high, in some cases
exceeding the current observational limit.",1004.5363v1
2010-05-20,A new test for the Galactic formation and evolution -- prediction for the orbital eccentricity distribution of the halo stars,"We present theoretical calculations for the differential distribution of
stellar orbital eccentricity in a galaxy halo, assuming that the stars
constitute a spherical, collisionless system in dynamical equilibrium with a
dark matter halo. In order to define the eccentricity e of a halo star for
given energy E and angular momentum L, we adopt two types of gravitational
potential, such as an isochrone potential and a Navarro-Frenk-White potential,
that could form two ends covering in-between any realistic potential of dark
matter halo. Based on a distribution function of the form f(E,L) that allows
constant anisotropy in velocity dispersions characterized by a parameter \beta,
we find that the eccentricity distribution is a monotonically increasing
function of e for the case of highly radially anisotropic velocity dispersions
(\beta > 0.6), while showing a hump-like shape for the cases from radial
through tangential velocity anisotropy (\beta < 0.6). We also find that when
the velocity anisotropy agrees with that observed for the Milky Way halo stars
(\beta = 0.5-0.7), a nearly linear eccentricity distribution of N(e) \alpha e
results at e < 0.7, largely independent of the potential adopted. Our
theoretical eccentricity distribution would be a vital tool of examining how
far out in the halo the dynamical equilibrium has been achieved, through
comparison with kinematics of halo stars sampled at greater distances. Given
that large surveys of the SEGUE and Gaia projects would be in progress, we
discuss how our results would serve as a new guide in exploring the formation
and evolution of the Milky Way halo.",1005.3685v1
2010-05-28,Limits on light-speed anisotropies from Compton scattering of high-energy electrons,"The possibility of anisotropies in the speed of light relative to the
limiting speed of electrons is considered. The absence of sidereal variations
in the energy of Compton-edge photons at the ESRF's GRAAL facility constrains
such anisotropies representing the first non-threshold collision-kinematics
study of Lorentz violation. When interpreted within the minimal Standard-Model
Extension, this result yields the two-sided limit of 1.6 x 10^{-14} at 95%
confidence level on a combination of the parity-violating photon and electron
coefficients kappa_{o+} and c. This new constraint provides an improvement over
previous bounds by one order of magnitude.",1005.5230v2
2010-06-22,Loop algorithm for classical Heisenberg models with spin-ice type degeneracy,"In many frustrated Ising models, a single-spin flip dynamics is frozen out at
low temperatures compared to the dominant interaction energy scale because of
the discrete ""multiple valley"" structure of degenerate ground-state manifold.
This makes it difficult to study low-temperature physics of these frustrated
systems by using Monte Carlo simulation with the standard single-spin flip
algorithm. A typical example is the so-called spin ice model, frustrated
ferromagnets on the pyrochlore lattice. The difficulty can be avoided by a
global-flip algorithm, the loop algorithm, that enables to sample over the
entire discrete manifold and to investigate low-temperature properties. We
extend the loop algorithm to Heisenberg spin systems with strong easy-axis
anisotropy in which the ground-state manifold is continuous but still retains
the spin-ice type degeneracy. We examine different ways of loop flips and
compare their efficiency. The extended loop algorithm is applied to the
following two models, a Heisenberg antiferromagnet with easy-axis anisotropy
along the z axis, and a Heisenberg spin ice model with the local <111>
easy-axis anisotropy. For both models, we demonstrate high efficiency of our
loop algorithm by revealing the low-temperature properties which were hard to
access by the standard single-spin flip algorithm. For the former model, we
examine the possibility of order-from-disorder and critically check its
absence. For the latter model, we elucidate a gas-liquid-solid transition,
namely, crossover or phase transition among paramagnet, spin-ice liquid, and
ferromagnetically-ordered ice-rule state.",1006.4300v2
2010-06-30,Broadband Fizeau Interferometers for Astrophysics,"Measurements of the 2.7 K cosmic microwave background (CMB) radiation now
provide the most stringent constraints on cosmological models. The power
spectra of the temperature anisotropies and the $E$-mode polarization of the
CMB are explained well by the inflationary paradigm. The next generation of CMB
experiments aim at providing the most direct evidence for inflation through the
detection of $B$-modes in the CMB polarization, presumed to have been caused by
gravitational waves generated during the inflationary epoch around $10^{-34}$s.
The $B$-mode polarization signals are very small ($\leq$10$^{-8}$K) compared
with the temperature anisotropies ($\sim 10^{-4}$K). Systematic effects in CMB
telescopes can cause leakage from temperature anisotropy into polarization.
Bolometric interferometry (BI) is a novel approach to measuring this small
signal with lower leakage. If BI can be made to work over wide bandwidth
($\sim20-30\%$) it can provide similar sensitivity to imagers. Subdividing the
frequency passband of a Fizeau interferometer would mitigate the problem of
`fringe smearing.' Furthermore, the approach should allow simultaneous
measurements in image space and visibility space. For subdividing the frequency
passsband (`sub-band splitting' henceforth), we write an expression for the
output from every baseline at every detector in the focal plane as a sum of
visibilities in different frequency sub-bands. For operating the interferometer
simultaneously as an imager, we write the output as two integrals over the sky
and the focal plane, with all the phase differences accounted for.}{The
sub-band splitting method described here is general and can be applied to
broad-band Fizeau interferometers across the electromagnetic spectrum.
Applications to CMB measurements and to long-baseline optical interferometry
are promising.",1006.5936v1
2010-07-23,Nonspherical similarity solutions for dark halo formation,"We carry out fully 3-dimensional simulations of evolution from self-similar,
spherically symmetric linear perturbations of a Cold Dark Matter dominated
Einstein-de Sitter universe. As a result of the radial orbit instability, the
haloes which grow from such initial conditions are triaxial with major-to-minor
axis ratios of order 3:1. They nevertheless grow approximately self-similarly
in time. In all cases they have power-law density profiles and near-constant
velocity anisotropy in their inner regions. Both the power-law index and the
value of the velocity anisotropy depend on the similarity index of the initial
conditions, the former as expected from simple scaling arguments. Halo
structure is thus not ""universal"" but remembers the initial conditions. On
larger scales the density and anisotropy profiles show two characteristic
scales, corresponding to particles at first pericentre and at first apocentre
after infall. They are well approximated by the NFW model only for one value of
the similarity index. In contrast, at all radii within the outer caustic the
pseudo phase-space density can be fit by a single power law with an index which
depends only very weakly on the similarity index of the initial conditions.
This behaviour is very similar to that found for haloes formed from LCDM
initial conditions and so can be considered approximately universal.",1007.4195v1
2010-07-28,Small anisotropy of the lower critical field and $s_\pm$-wave two-gap feature in single crystal LiFeAs,"The in- and out-of-plane lower critical fields and magnetic penetration
depths for LiFeAs were examined. The anisotropy ratio $\gamma_{H_{c1}}(0)$ is
smaller than the expected theoretical value, and increased slightly with
increasing temperature from 0.6$T_c$ to $T_c$. This small degree of anisotropy
was numerically confirmed by considering electron correlation effect. The
temperature dependence of the penetration depths followed a power
law($\sim$$T^n$) below 0.3$T_c$, with $n$$>$3.5 for both $\lambda_{ab}$ and
$\lambda_c$. Based on theoretical studies of iron-based superconductors, these
results suggest that the superconductivity of LiFeAs can be represented by an
extended $s_\pm$-wave due to weak impurity scattering effect. And the
magnitudes of the two gaps were also evaluted by fitting the superfluid density
for both the in- and out-of-plane to the two-gap model. The estimated values
for the two gaps are consistent with the results of angle resolved
photoemission spectroscopy and specific heat experiments.",1007.4906v2
2010-08-03,CMB observations in LTB universes: Part II: the kSZ effect in an LTB universe,"We study the kinematic Sunyaev-Zel'dovich (kSZ) effect in a
Lem\^itre-Tolman-Bondi (LTB) universe model whose distance-redshift relation
agrees with that of the concordance $\Lambda$CDM model at redshifts
$z\lesssim2$. This LTB universe model has a void with size comparable to the
Hubble horizon scale. We first determine the decoupling epoch in this LTB
universe model by an approximate analytical condition under a few simplified
assumptions on the physical quantities at that epoch. Then we calculate the
cosmic microwave background (CMB) anisotropy observed in the rest frame of
clusters of galaxies which are assumed to be at rest in the spatial comoving
coordinates of the LTB universe model. We find that the obtained temperature
anisotropies are dominated by dipole, although there may exist higher
multi-poles in general. We may interpret this dipole anisotropy as the drift
velocity of a cluster of galaxies relative to the CMB rest frame. Hence it
gives rise to the kSZ effect. We calculate this effect and compare it with
observational data. We find that if we assume the conventional adiabatic
perturbation scenario at the time of decoupling, the drift velocity of clusters
of galaxies becomes unacceptably large. Conversely, this observational
constraint may be relaxed by introducing a non-adiabatic (i.e., primordially
isocurvature) component of inhomogeneities at the time of decoupling. However,
our result indicates that the necessary isocurvature perturbation amplitude is
very large.",1008.0469v2
2010-08-17,On the interactions of transverse ion-cyclotron waves with ions in solar wind plasma,"We show the evidence of ion-cyclotron dissipation mechanism in solar wind
plasma using Helios data. From our statistical analysis we found that the wave
power of high-frequency transverse waves (having frequencies between 0.01 and 1
normalized to the proton gyrofrequency in the plasma frame) correlates with
both, the proton temperature anisotropy, $T_{\perp}/T_{\parallel}$, and the
normalized differential speed, $V_{\alpha p}/V_A$, between alpha particles and
protons. Furthermore, when this speed stays below 0.5, then the alpha-particle
temperature anisotropy correlate positively with the relative power of the
transverse waves. However, if $V_{\alpha p}/V_A$ is larger than 0.6, then the
alpha-particle temperature anisotropy tends to decrease towards values below
unity, despite the presence of transverse waves with relatively large
amplitudes. For small relative wave amplitude, it is found that alpha particles
can even be heated more strongly than protons when the alpha-to-electron
density ratio nearly or below 0.01. Our findings are in good agreement with
predictions of kinetic theory for the resonant interaction of ions with
Alfv\'en-cyclotron waves and for the resulting wave dissipation. Also, the
study suggests that the turbulence could lead to the generation of parallel
Alfven cyclotron waves.",1008.2893v3
2010-11-10,Large scale anisotropies on halo infall,"We perform a statistical analysis of the peculiar velocity field around dark
matter haloes in numerical simulations. We examine different properties of the
infall of material onto haloes and its relation to central halo shapes and the
shape of the large scale surrounding regions (LSSR). We find that the amplitude
of the infall velocity field along the halo shape minor axis is larger than
that along the major axis. This is consistent for general triaxial haloes, and
for both prolate and oblate systems. We also report a strong anisotropy of the
velocity field along the principal axes of the LSSR. The infall velocity field
around dark matter haloes reaches a maximum value along the direction of the
minor axis of the LSSR, whereas along the direction of its major axis, it
exhibits the smallest velocities. We also analyse the dependence of the matter
velocity field on the local environment. The amplitude of the infall velocity
at high local density regions is larger than at low local density regions. The
velocity field tends to be more laminar along the direction towards the minor
axis of the LSSR, where the mean ratio between flow velocity and velocity
dispersion is of order unity and nearly constant up to scales of 15 Mpc/h. We
also detect anisotropies in the outflowing component of the velocity field,
showing a maximum amplitude along the surrounding LSSR major axis.",1011.2494v1
2010-11-16,Nematic spin fluid in the tetragonal phase of BaFe2As2,"Magnetic interactions are generally believed to play a key role in mediating
electron pairing for superconductivity in iron arsenides; yet their character
is only partially understood. Experimentally, the antiferromagnetic (AF)
transition is always preceded by or coincident with a tetragonal to
orthorhombic structural distortion. Although it has been suggested that this
lattice distortion is driven by an electronic nematic phase, where a
spontaneously generated electronic liquid crystal state breaks the C4
rotational symmetry of the paramagnetic state, experimental evidence for
electronic anisotropy has been either in the low-temperature orthorhombic phase
or the tetragonal phase under uniaxial pressure that breaks this symmetry. Here
we use inelastic neutron scattering to demonstrate the presence of a large
in-plane spin anisotropy above TN in the unstressed tetragonal phase of
BaFe2As2. In the low-temperature orthorhombic phase, we find highly anisotropic
spin waves with a large damping along the AF a-axis direction. On warming the
system to the paramagnetic tetragonal phase, the low-energy spin waves evolve
into quasi-elastic excitations, while the anisotropic spin excitations near the
zone boundary persist. These results strongly suggest that the spin nematicity
we find in the tetragonal phase of BaFe2As2 is the source of the electronic and
orbital anisotropy observed above TN by other probes, and has profound
consequences for the physics of these materials.",1011.3771v1
2010-11-22,Microwave Emission from the Edgeworth-Kuiper Belt and the Asteroid Belt Constrained from WMAP,"Objects in the Edgeworth-Kuiper belt and the main asteroid belt should emit
microwaves that may give rise to extra anisotropy signals in the multipole of
the cosmic microwave background (CMB) experiment. Constraints are derived from
the absence of positive detection of such anisotropies for ell < 50, giving the
total mass of Edgeworth-Kuiper belt objects to be smaller than 0.2 earth mass.
This limit is consistent with the mass extrapolated from the observable
population with the size of a > 15 km, assuming that the small-object
population follows the power law in size dN/da ~ a^{-q} with the canonical
index expected for collisional equilibrium, q ~ 3.5, with which 23% of the mass
is ascribed to objects smaller than are observationally accessible down to
grains. A similar argument applied to the main asteroid belt indicates that the
grain population should not increase faster than q ~ 3.6 towards smaller radii,
if it follows the power law continued to observed asteroids with larger radii.
It is underlined that both cases are at or only slightly above the limit that
can be physically significant, implying the importance of tightening further
the CMB anisotropy limit, which may be attained with the observation at higher
radio frequencies.",1011.4796v2
2010-11-30,"Haldane, Large-D and Intermediate-D States in an S=2 Quantum Spin Chain with On-Site and XXZ Anisotropies","Using mainly numerical methods, we investigate the ground-state phase diagram
of the S=2 quantum spin chain described by $H = \sum_j (S_j^x S_{j+1}^x + S_j^y
S_{j+1}^y + \Delta S_j^z S_{j+1}^z) + D \sum_j (S_j^z)^2$, where $\Delta$
denotes the $XXZ$ anisotropy parameter of the nearest-neighbor interactions and
$D$ the on-site anisotropy parameter. We restrict ourselves to the case with
$\Delta \ge 0$ and $D \ge 0$ for simplicity. Each of the phase boundary lines
is determined by the level spectroscopy or the phenomenological renormalization
analysis of numerical results of exact-diagonalization calculations. The
resulting phase diagram on the $\Delta$-$D$ plane consists of four phases; the
XY 1 phase, the Haldane/large-$D$ phase, the intermediate-$D$ phase and the
N\'eel phase. The remarkable natures of the phase diagram are: (1) the Haldane
state and the large-$D$ state belong to the same phase; (2) there exists the
intermediate-$D$ phase which was predicted by Oshikawa in 1992; (3) the shape
of the phase diagram on the $\Delta$-$D$ plane is different from that believed
so far. We note that this is the first report of the observation of the
intermediate-$D$ phase.",1011.6568v2
2010-11-30,Effects of anisotropic winds on massive stars evolution,"Whenever stars are rotating very fast (Omega/Omega_crit > 0.7, with
Omega_crit the Keplerian angular velocity of the star accounting for its
deformation) radiative stellar winds are enhanced in polar regions. This
theoretical prediction is now confirmed by interferometric observations of fast
rotating stars.} Polar winds remove less angular momentum than spherical winds
and thus allow the star to keep more angular momentum. We quantitatively assess
the importance of this effect.
  First we use a semi-analytical approach to estimate the variation of the
angular momentum loss when the rotation parameter increases. Then we compute
complete 9 MSun stellar models at very high angular velocities (starting on the
ZAMS with Omega/Omega_crit = 0.8 and reaching the critical velocity during the
Main Sequence) with and without radiative wind anisotropies.
  When wind anisotropies are accounted for, the angular momentum loss rate is
reduced by less than 4% for Omega/Omega_crit < 0.9 with respect to the case of
spherical winds. The reduction amounts to at most 30% when the star is rotating
near the critical velocity. These values result from two counteracting effects:
on the one hand polar winds reduce the loss of angular momentum, on the other
hand, surface deformations imply that the mass which is lost at high
co-latitude is lost at a larger distance from the rotational axis and thus
removes more angular momentum.
  In contrast with previous studies, which neglected surface deformations, we
show that the radiative wind anisotropies have a relatively modest effect on
the evolution of the angular momentum content of fast rotating stars.",1011.6581v2
2010-12-23,Turbulence in collisionless plasmas: statistical analysis from numerical simulations with pressure anisotropy,"In the past years we have experienced an increasing interest in understanding
of the physical properties of collisionless plasmas, mostly because of the
large number of astrophysical environments, e.g. the intracluster medium (ICM),
containing magnetic fields which are strong enough to be coupled with the
ionized gas and characterized by densities sufficiently low to prevent the
pressure isotropization with respect to the magnetic line direction. Under
these conditions a new class of kinetic instabilities arises, such as firehose
and mirror ones, which were extensively studied in the literature. Their role
in the turbulence evolution and cascade process in the presence of pressure
anisotropy, however, is still unclear. In this work we present the first
statistical analysis of turbulence in collisionless plasmas using three
dimensional double isothermal magnetohydrodynamical with the
Chew-Goldberger-Low closure (CGL-MHD) numerical simulations. We study models
with different initial conditions to account for the firehose and mirror
instabilities and to obtain different turbulent regimes. We study the
probability distribution functions, spectra, structure functions and anisotropy
of density and velocity fluctuations. The results indicate that in some cases
the instabilities significantly modifies the statistical properties of
turbulence and even though preliminary and restricted to very specific
conditions, show that the physical properties of turbulence in collisionless
plasmas, as those found in the ICM, may be very different from what has been
largely believed. Implications can range from interchange of energies to cosmic
rays acceleration.",1012.5125v1
2011-01-31,Nuclear modification factor in an anisotropic {\em Quark-Gluon-Plasma},"We calculate the nuclear modification factor ($R_{AA}$) of light hadrons by
taking into account the initial state momentum anisotropy of the quark gluon
plasma (QGP) expected to be formed in relativistic heavy ion collisions. Such
an anisotropy can result from the initial rapid longitudinal expansion of the
matter. A phenomenological model for the space time evolution of the
anisotropic QGP is used to obtain the time dependence of the anisotropy
parameter $\xi$ and the hard momentum scale, $p_{\rm hard}$. The result is then
compared with the PHENIX experimental data to constrain the isotropization time
scale, $\tau_{\rm iso}$ for fixed initial conditions (FIC). It is shown that
the extracted value of $\tau_{\rm iso}$ lies in the range $0.5 \leq \tau_{\rm
iso} \leq 1.5$. However, using fixed final multiplicity (FFM) condition does
not lead to any firm conclusion about the extraction of the isotropization
time. The present calculation is also extended to contrast with the recent
measurement of nuclear modification factor by ALICE collaboration at
$\sqrt{s}=2.76$ TeV. It is argued that in the present approach, the extraction
of $\tau_{\rm iso}$ at this energy is uncertain and, therfore, refinement of
the model is necessary. The sensitivity of the results on the initial
conditions has been discussed. We also present the nuclear modification factor
at LHC energies with $\sqrt{s} = 5.5$ TeV.",1101.5855v2
2011-03-15,Nernst effect in the cuprate superconductor YBCO: Broken rotational and translational symmetries,"The Nernst coefficient of the cuprate superconductor YBa2Cu3Oy was recently
shown to become strongly anisotropic within the basal plane when cooled below
the pseudogap temperature T*, revealing that the pseudogap phase breaks the
four-fold rotational symmetry of the CuO2 planes. Here we report on the
evolution of this Nernst anisotropy at low temperature, once superconductivity
is suppressed by a magnetic field. We find that the anisotropy drops rapidly
below 80 K, to vanish in the T=0 limit. We show that this loss of anisotropy is
due to the emergence of a small high-mobility electron-like pocket in the Fermi
surface at low temperature, a reconstruction attributed to a low-temperature
state that breaks the translational symmetry of the CuO2 planes. We discuss the
sequence of broken symmetries - first rotational, then translational - in terms
of an electronic nematic-to-smectic transition such as could arise when
unidirectional spin or charge modulations order. We compare YBa2Cu3Oy with
iron-pnictide superconductors where the process of (unidirectional)
antiferromagnetic ordering gives rises to the same sequence of broken
symmetries.",1103.3044v1
2011-04-19,The Primordial Curvature Perturbation from Vector Fields of General non-Abelian Groups,"We consider the generation of primordial curvature perturbation by general
non-Abelian vector fields without committing to a particular group.
Self-interactions of non-Abelian fields make the field perturbation
non-Gaussian. We calculate the bispectrum of the field perturbation using the
in-in formalism at tree level. The bispectrum is dominated by the classical
evolution of fields outside the horizon. In view of this we show that the
dominant contribution can be obtained from the homogeneous classical equation
of motion. Then we calculate the power spectrum of the curvature perturbation.
The anisotropy in spectrum is suppressed by the number of fields. This makes it
possible for vector fields to be responsible for the total curvature
perturbation in the Universe without violating observational bounds on
statistical anisotropy. The bispectrum of the curvature perturbation is also
anisotropic. Finally we give an example of the end-of-inflation scenario in
which the curvature perturbation is generated by vector gauge fields through
varying gauge coupling constant(s), which in covariant derivatives couples the
Higgs field to the vector fields. We find that reasonably large gauge groups
may result in the observable anisotropy in the power spectrum of the curvature
perturbation.",1104.3629v2
2011-04-28,Anisotropy in the Interaction of Ultracold Dysprosium,"The nature of the interaction between ultracold atoms with a large orbital
and spin angular momentum has attracted considerable attention. It was
suggested that such interactions can lead to the realization of exotic states
of highly correlated matter. Here, we report on a theoretical study of the
competing anisotropic dispersion, magnetic dipole-dipole, and electric
quadrupole-quadrupole forces between two dysprosium atoms. Each dysprosium atom
has an orbital angular momentum L=6 and magnetic moment $\mu=10\mu_B$. We show
that the dispersion coefficients of the ground state adiabatic potentials lie
between 1865 a.u. and 1890 a.u., creating a non-negligible anisotropy with a
spread of 25 a.u. and that the electric quadrupole-quadrupole interaction is
weak compared to the other interactions. We also find that for interatomic
separations $R< 50\,a_0$ both the anisotropic dispersion and magnetic
dipole-dipole potential are larger than the atomic Zeeman splittings for
external magnetic fields of order 10 G to 100 G. At these separations spin
exchange can occur. We finish by describing two scattering models for inelastic
spin exchange. A universal scattering theory is used to model loss due to the
anisotropy in the dispersion and a distorted-wave-Born theory is used to model
losses from the magnetic dipole-dipole interaction for the $^{164}$Dy isotope.
These models find loss rates that are the same order of magnitude as the
experimental value.",1104.5411v1
2011-07-18,Quasi-static magnetohydrodynamic turbulence at high Reynolds number,"We analyse the anisotropy of homogeneous turbulence in an electrically
conducting fluid submitted to a uniform magnetic field, for low magnetic
Reynolds number, in the quasi- static approximation. We interpret disagreeing
previous predictions between linearized theory and simulations: in the linear
limit, the kinetic energy of transverse velocity components, normal to the
magnetic field, decays faster than the kinetic energy of the axial component,
along the magnetic field (Moffatt (1967)); whereas many numerical studies
predict a final state characterised by dominant energy of transverse velocity
components. We investigate the corresponding nonlinear phenomenon using Direct
Numerical Simulations of freely-decaying turbulence, and a two-point
statistical spectral closure based on the Eddy Damped Quasi-Normal Markovian
model. The transition from the three-dimensional turbulent flow to a
""two-and-a-half-dimensional"" flow (Montgomery & Turner (1982)) is a result of
the combined effects of short-time linear Joule dissipation and longer time
nonlinear creation of polarisation anisotropy. It is this combination of linear
and nonlinear effects which explains the disagreement between predictions from
linearized theory and results from numerical simulations. The transition is
characterized by the elongation of turbulent structures along the applied
magnetic field, and by the strong anisotropy of directional two-point
correlation spectra, in agreement with experimental evidence. Inertial
equatorial transfers in both DNS and the model are presented to describe in
detail the most important equilibrium dynamics. Spectral scalings are
maintained in high Reynolds number turbulence attainable only with the EDQNM
model, which also provides simplified modelling of the asymptotic state of
quasi-static MHD turbulence.",1107.3435v1
2011-08-25,3D simulations of gyrosynchrotron emission from mildly anisotropic nonuniform electron distributions in symmetric magnetic loops,"Microwave emission of solar flares is formed primarily by incoherent
gyrosynchrotron radiation generated by accelerated electrons in coronal
magnetic loops. The resulting emission depends on many factors, including
pitch-angle distribution of the emitting electrons and the source geometry. In
this work, we perform systematic simulations of solar microwave emission using
recently developed tools (GS Simulator and fast gyrosynchrotron codes) capable
of simulating maps of radio brightness and polarization as well as spatially
resolved emission spectra. A 3D model of a symmetric dipole magnetic loop is
used. We compare the emission from isotropic and anisotropic (of loss-cone
type) electron distributions. We also investigate effects caused by
inhomogeneous distribution of the emitting particles along the loop. It is
found that effect of the adopted moderate electron anisotropy is the most
pronounced near the footpoints and it also depends strongly on the loop
orientation. Concentration of the emitting particles at the loop top results in
a corresponding spatial shift of the radio brightness peak, thus reducing
effects of the anisotropy. The high-frequency (around 50 GHz) emission spectral
index is specified mainly by the energy spectrum of the emitting electrons;
however, at intermediate frequencies (around 10-20 GHz), the spectrum shape is
strongly dependent on the electron anisotropy, spatial distribution, and
magnetic field nonuniformity. The implications of the obtained results for the
diagnostics of the energetic electrons in solar flares are discussed.",1108.5150v1
2011-09-30,Power Anisotropy in the Magnetic Field Power Spectral Tensor of Solar Wind Turbulence,"We observe the anisotropy of the power spectral tensor of magnetic field
fluctuations in the fast solar wind for the first time. In heliocentric RTN
coordinates the power in each element of the tensor has a unique dependence on
the angle between the magnetic field and velocity of the solar wind (\theta)
and the angle of the vector in the plane perpendicular to the velocity (\phi).
We derive the geometrical effect of the high speed flow of the solar wind past
the spacecraft on the power spectrum in the frame of the plasma P(k) to arrive
at the observed power spectrum P(f,\theta,\phi) based on a scalar field
description of turbulence theory. This allows us to predict the variation in
the \phi direction and compare it to the data. We then transform the
observations from RTN coordinates to magnetic-field-aligned coordinates. The
observed reduced power spectral tensor matches the theoretical predictions we
derive in both RTN and field-aligned coordinates which means that the local
magnetic field we calculate with wavelet envelope functions is an accurate
representation of the physical axis of symmetry for the turbulence and implies
that on average the turbulence is axi-symmetric. We also show that we can
separate the dominant toroidal component of the turbulence from the smaller but
significant poloidal component and that these have different power anisotropy.
We also conclude that the magnetic helicity is anisotropic and mostly
two-dimensional, arising from wavevectors largely confined to the plane
perpendicular to B.",1109.6877v2
2011-10-14,Collective Flow Measurements from the PHENIX Experiment,"Recent collective flow measurements including higher moment event anisotropy
from the PHENIX experiment are presented, and the particle type, beam energy
dependence and the relation with jet modification are discussed. The measured
higher order event anisotropy with event plane defined at forward rapidities
and the long range correlation with large $\eta$ gaps are both consistent with
initial geometrical fluctuation of the participating nuclei. In 200 GeV Au+Au
collisions, higher order event anisotropy, especially simultaneous description
of v$_2$ and v$_3$, is found to give an additional constraining power on
initial geometrical condition and viscosity in the hydrodynamic calculations.
v$_2$, v$_3$ and v$_4$ are almost unchanged down to the lower colliding energy
at 39 GeV in Au+Au. The measured two particle correlation with subtraction of
the measured v$_n$ parameters shows a significant effect on the shape and yield
in the associate particle $\Delta\phi$ distribution with respect to the
azimuthal direction of trigger particles. However some medium responses from
jet suppression or jet modification seems to be observed. Direct photon v$_2$
has been measured in 200 GeV Au+Au collisions. The measured v$_2$ is found to
be small at high p$_{\rm T}$ as expected from non-suppressed direct photon
R$_{\rm AA}$ $\simeq$ 1, which can be understood as being dominated by prompt
photons from initial hard scattering. On the other hand, at lower p$_{\rm T}$
$<$ 4 GeV/c it is found to be significantly larger than zero, which is
comparable to other hadron v$_2$, where thermal photons are observed.",1110.3223v1
2011-12-29,Anisotropy in the electronic structure of V2GeC investigated by soft x-ray emission spectroscopy and first-principles theory,"The anisotropy of the electronic structure of ternary nanolaminate V2GeC is
investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured
polarization-dependent emission spectra of V L2,3, C K, Ge M1 and Ge M2,3 in
V2GeC are compared to those from monocarbide VC and pure Ge. The experimental
emission spectra are interpreted with calculated spectra using ab initio
density-functional theory including dipole transition matrix elements.
Different types of covalent chemical bond regions are revealed; V 3d - C 2p
bonding at -3.8 eV, Ge 4p - C 2p bonding at -6 eV and Ge 4p - C 2s interaction
mediated via the V 3d orbitals at -11 eV below the Fermi level. We find that
the anisotropic effects are high for the 4p valence states and the shallow 3d
core levels of Ge, while relatively small anisotropy is detected for the V 3d
states. The macroscopic properties of the V2GeC nanolaminate result from the
chemical bonds with the anisotropic pattern as shown in this work.",1112.6287v1
2012-01-16,Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at sqrt(s[NN]) = 2.76 TeV,"Measurements from the CMS experiment at the LHC of dihadron correlations for
charged particles produced in PbPb collisions at a nucleon-nucleon
centre-of-mass energy of 2.76 TeV are presented. The results are reported as a
function of the particle transverse momenta (pt) and collision centrality over
a broad range in relative pseudorapidity [Delta(eta)] and the full range of
relative azimuthal angle [Delta(phi)]. The observed two-dimensional correlation
structure in Delta(eta) and Delta(phi) is characterised by a narrow peak at
(Delta(eta), Delta(phi)) approximately (0, 0) from jet-like correlations and a
long-range structure that persists up to at least |Delta(eta)| = 4. An
enhancement of the magnitude of the short-range jet peak is observed with
increasing centrality, especially for particles of pt around 1-2 GeV/c. The
long-range azimuthal dihadron correlations are extensively studied using a
Fourier decomposition analysis. The extracted Fourier coefficients are found to
factorise into a product of single-particle azimuthal anisotropies up to pt
approximately 3-3.5 GeV/c for at least one particle from each pair, except for
the second-order harmonics in the most central PbPb events. Various orders of
the single-particle azimuthal anisotropy harmonics are extracted for associated
particle pt of 1-3 GeV/c, as a function of the trigger particle pt up to 20
GeV/c and over the full centrality range.",1201.3158v2
2012-01-16,Azimuthal anisotropies for Au+Au collisions in the parton-hadron transient energy range,"The azimuthal anisotropies of the collective transverse flow of charged
hadrons are investigated in a wide range of heavy-ion collision energies within
the microscopic parton-hadron-string dynamics (PHSD) transport approach which
incorporates explicit partonic degrees of freedom in terms of strongly
interacting quasiparticles (quarks and gluons) in line with an equation of
state from lattice QCD as well as the dynamical hadronization and hadronic
collision dynamics in the final reaction phase. The experimentally observed
increase of the elliptic flow $v_2$ of charged hadrons with collision energy is
successfully described in terms of the PHSD approach. The PHSD scaling
properties of various collective observables are confronted with experimental
data as well as with hydrodynamic predictions. The analysis of higher-order
harmonics $v_3$ and $v_4$ in the azimuthal angular distribution shows a similar
tendency of growing deviations between partonic and purely hadronic models with
increasing collision energy. This demonstrates that the excitation functions of
azimuthal anisotropies reflect the increasing role of quark-gluon degrees of
freedom in the early phase of relativistic heavy-ion collisions. Furthermore,
the specific variation of the ratio $v_4/(v_2)^2$ with respect to bombarding
energy, centrality and transverse momentum is found to provide valuable
information on the underlying dynamics.",1201.3320v2
2012-01-31,Explorations into the inertial and integral scales of homogeneous axisymmetric turbulence,"A flow generator is described in which homogeneous axisymmetric turbulent air
flows with varying and fully controllable degrees of anisotropy, including the
much studied isotropic case, are generated by the combined agitations produced
by 32 acoustic mixers focusing at the center of the system. The axisymmetric
turbulence in a central volume of the size of the inertial scale is shown to
have negligible mean and shear. The Taylor Reynolds number is about 480.
  The influence of large scale anisotropy on the turbulence is examined from
three aspects, namely the velocity structure functions, the velocity
correlation functions, and the integral lengths. The directional dependence of
two different second order transverse structure functions, in which one of them
has separations stretched along the axis of symmetry of the turbulence and the
other one normal to it, is studied. It is shown that the inertial range scaling
exponents, determined using the extended-self-similarity procedure, and the
Kolmogorov constants of the two structure functions are unaffected by the
direction in which the structure functions are measured.
  Finally, it is found that, except in the isotropic case, the second order
transverse velocity correlation functions deviate from each other at the large
scale with increasing anisotropy. A self-similarity argument similar to one
found in the study of critical phenomena is proposed. It is shown that the
argument leads to a power-law relationship between the large scale velocity
fluctuation and the correlation length, with an exponent that depends on the
inertial range scaling exponent of the turbulence. The data collapse predicted
by the self-similarity hypothesis is verified. It is demonstrated that the
value of the power-law exponent is consistent with the value of the inertial
range scaling exponent.",1201.6412v1
2012-04-30,Analytic Spectra of CMB Anisotropies and Polarization Generated by Scalar Perturbations in Synchronous Gauge,"We present a detailed analytical calculation of CMB temperature anisotropies
\alpha_k and polarization \beta_k generated by scalar metric perturbations in
synchronous gauge, parallel to our previous work with RGW as a generating
source. This is realized primarily by an analytic time-integration of
Boltzmann's equation, yielding the closed forms of \alpha_k and \beta_k.
Approximations, such as the tight-coupling approximation for photons a prior to
the recombination and the long wavelength limit for scalar perturbations are
used. The residual gauge modes in scalar perturbations are analyzed and a
proper joining condition of scalar perturbations at the radiation-matter
equality is chosen, ensuring the continuity of energy perturbation.
  The resulting analytic expressions of the multipole moments of polarization
a^E_l, and of temperature anisotropies a^T_l are explicit functions of the
scalar perturbations, recombination time, recombination width, photon free
streaming damping factor, baryon fraction, initial amplitude, primordial scalar
spectral index, and the running index. These results show that a longer
recombination width yields higher amplitudes of polarization on large scales
and more damping on small scales, and that a late recombination time shifts the
peaks of C^{XX'}_l to larger angular scales.
  The analytic spectra C^{XX'}_l agree with the numerical ones and with those
observed by WMAP on large scales (l \lesssim 500), but deviate considerably
from the numerical results on smaller scales, showing the limitations of our
approximate analytic calculations. Several possible improvements are pointed
out for further studies.",1204.6683v1
2012-05-21,Orbit-based dynamical models of the Sculptor dSph galaxy,"We have developed spherically symmetric dynamical models of dwarf spheroidal
galaxies using Schwarzschild's orbit superposition method. This type of
modelling yields constraints both on the total mass distribution (e.g. enclosed
mass and scale radius) as well as on the orbital structure of the system (e.g.
velocity anisotropy). This method is thus less prone to biases introduced by
assumptions in comparison to the more commonly used Jeans modelling, and it
allows us to derive the dark matter content in a robust way. Here we present
our results for the Sculptor dwarf spheroidal galaxy, after testing our methods
on mock data sets. We fit both the second and fourth velocity moment profile to
break the mass-anisotropy degeneracy. For an NFW dark matter halo profile, we
find that the mass of Sculptor within 1 kpc is M_1kpc = 1.03 \pm 0.07 x 10^8
Msol, and that its velocity anisotropy profile is tangentially biased and
nearly constant with radius. The preferred concentration (c ~ 15) is low for
its dark matter mass but consistent within the scatter found in N-body
cosmological simulations. When we let the value of the central logarithmic
slope \alpha{} vary, we find that the best-fit model has \alpha{} = 0, although
an NFW cusp or shallower is consistent at 1 \sigma{} confidence level. On the
other hand, very cuspy density profiles with logarithmic central slopes
\alpha{} < -1.5 are strongly disfavoured for Sculptor.",1205.4712v2
2012-06-08,Weak Spin Fluctuation with Finite Wave Vector and Superconducting Gap Symmetry in KxFe2-ySe2: 77Se Nuclear Magnetic Resonance,"We report $^{77}$Se-nuclear magnetic resonance (NMR) results down to
sufficiently low temperatures under magnetic fields parallel to both the
$ab$-plane and the c-axis in a paramagnetic/superconducting (PM/SC) phase of
K$_x$Fe$_{2-y}$Se$_2$. The observation of anisotropy in the orbital part of the
Knight shift results in the anisotropy of its spin part increasing on
approaching the transition temperature. The anisotropy of the Korringa relation
suggests the presence of the weak spin fluctuations with a finite wave vector
$\bm{q}$, which induce the magnetic fluctuations along the ab-plane at the Se
site. Such fluctuations do not correspond to the stripe $(\pi,0)$ correlation
of the Fe moment observed in many Fe-based superconductors, and are not
contradictory to weak $(\pi,\pi)$ correlations. The nuclear spin-lattice
relaxation rate $1/T_1$ shows a field-independent $T_1T \sim const.$ behavior
at low temperatures for $H \parallel ab$, which is attributed to the nonzero
density of states at the Fermi level and can be explained by the sign-changing
order parameter even for nodeless gaps. The temperature dependence of $1/T_1$
is reproduced well by nodeless models with two isotropic gaps or a single
anisotropic gap. The obtained gap magnitude in the isotropic two-gap model is
comparable to those obtained in the angle-resolved photoemission spectroscopy
experiments.",1206.1756v2
2012-06-09,Deflection of Light and Shapiro Delay: An Equivalent Medium Theory Approach,"We discuss the deflection of light and Shapiro delay under the influence of
gravity as described by Schwarzschild metric. We obtain an exact expression
based on the coordinate velocity, as first set forth by Einstein, and present a
discussion on the effect of velocity anisotropy. We conclude that the
anisotropy in the coordinate velocity, as the velocity apparent to a distant
observer, gives rise to a third order error in the deflection angle, so that
the practical astronomical observations from gravitational lensing data remain
inconclusive on the anisotropy. However, measurement of Shapiro delay provides
a fairly convenient way to determine whether the spacetime is optically
anisotropic for a distant observer or not. We calculate the Shapiro delay for a
round trip path between Earth and Venus and observe excellent agreement to two
experimentally reported values measured during a time span of six months in
1967, without any need to extra fitting parameters. This is while the expected
delay obtained from an isotropic light velocity as described by Einstein's
model suffers from much larger errors under similar conditions. This article
illustrates the usefulness of the equivalent medium theory in understanding of
general theory of relativity.",1206.1947v1
2012-06-28,Measuring D_A and H at z=0.35 from the SDSS DR7 LRGs using baryon acoustic oscillations,"We present measurements of the angular diameter distance D_A(z) and the
Hubble parameter H(z) at z=0.35 using the anisotropy of the baryon acoustic
oscillation (BAO) signal measured in the galaxy clustering distribution of the
Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Luminous Red Galaxies
(LRG) sample. Our work is the first to apply density-field reconstruction to an
anisotropic analysis of the acoustic peak. Reconstruction partially removes the
effects of non-linear evolution and redshift-space distortions in order to
sharpen the acoustic signal. We present the theoretical framework behind the
anisotropic BAO signal and give a detailed account of the fitting model we use
to extract this signal from the data. Our method focuses only on the acoustic
peak anisotropy, rather than the more model-dependent anisotropic information
from the broadband power. We test the robustness of our analysis methods on 160
LasDamas DR7 mock catalogues and find that our models are unbiased at the ~0.2%
level in measuring the BAO anisotropy. After reconstruction we measure
D_A(z=0.35)=1050+/-38 Mpc and H(z=0.35)=84.4+/-7.0 km/s/Mpc assuming a sound
horizon of r_s=152.76 Mpc. Note that these measurements are correlated with a
correlation coefficient of 0.58. This represents a factor of 1.4 improvement in
the error on D_A relative to the pre-reconstruction case; a factor of 1.2
improvement is seen for H.",1206.6732v2
2012-07-06,Physical properties underlying observed kinematics of satellite galaxies,"We study the kinematics of satellites around isolated galaxies selected from
the Sloan Digital Sky Survey (SDSS) spectroscopic catalog. Using a model of the
phase-space density previously measured for the halos of LCDM dark matter
cosmological simulations, we determine the properties of the halo mass
distribution and the orbital anisotropy of the satellites as a function of the
colour-based morphological type and the stellar mass of the central host
galaxy. We place constraints on the halo mass and the concentration parameter
of dark matter and the satellite number density profiles. We obtain a
concentration-mass relation for galactic dark matter haloes that is consistent
with predictions of a standard LCDM cosmological model. At given halo or
stellar mass, red galaxies have more concentrated halos than their blue
counterparts. The fraction of dark matter within a few effective radii is
minimal for 11.25<log M_star<11.5. The number density profile of the satellites
appears to be shallower than of dark matter, with the scale radius typically 60
per cent larger than of dark matter. The orbital anisotropy around red hosts
exhibits a mild excess of radial motions, in agreement with the typical
anisotropy profiles found in cosmological simulations, whereas blue galaxies
are found to be consistent with an isotropic velocity distribution. Our new
constraints on the halo masses of galaxies are used to provide analytic
approximations of the halo-to-stellar mass relation for red and blue galaxies.",1207.1647v3
2012-07-11,Anomalous Workfunction Anisotropy in Ternary Acetylides,"Anomalous anisotropy of workfunction values in ternary alkali metal
transition metal acetylides is reported. Workfunction values of some
characteristic surfaces in these emerging semiconducting materials may differ
by more than $\approx$ 2 eV as predicted by Density Functional Theory
calculations. This large anisotropy is a consequence of the relative
orientation of rod-like [MC$_{2}$]$_{\infty}$ negatively charged polymeric
subunits and the surfaces, with M being a transition metal or metalloid element
and C$_{2}$ refers to the acetylide ion C$_{2}^{2-}$, with the rods embedded
into an alkali cation matrix. It is shown that the conversion of the seasoned
Cs$_{2}$Te photo-emissive material to ternary acetylide Cs$_{2}$TeC$_{2}$
results in substantial reduction of its $\approx$ 3 eV workfunction down to
1.71-2.44 eV on the Cs$_{2}$TeC$_{2}$(010) surface while its high quantum yield
is preserved. Similar low workfunction values are predicted for other ternary
acetylides as well, allowing for a broad range of applications from improved
electron- and light-sources to solar cells, field emission displays, detectors
and scanners.",1207.2512v1
2012-08-16,High superconducting anisotropy and weak vortex pinning in Co doped LaFeAsO,"Here, we present an electrical transport study in single crystals of
LaFe$_{0.92}$Co$_{0.08}$AsO ($T_c \simeq 9.1$ K) under high magnetic fields. In
contrast to most of the previously reported Fe based superconductors, and
despite its relatively low $T_c$, LaFe$_{1-x}$Co$_x$AsO shows a superconducting
anisotropy which is comparable to those seen for instance in the cuprates or
$\gamma_H = H_{c2}^{ab}/H_{c2}^{c} = m_c/m_{ab} \simeq 9$, where $m_c/m_{ab}$
is the effective mass anisotropy. Although, in the present case and as in all
Fe based superconductors, $\gamma \rightarrow 1$ as $T \rightarrow 0$. Under
the application of an external field, we also observe a remarkable broadening
of the superconducting transition particularly for fields applied along the
inter-planar direction. Both observations indicate that the low dimensionality
of LaFe$_{1-x}$Co$_x$AsO is likely to lead to a more complex vortex
phase-diagram when compared to the other Fe arsenides and consequently, to a
pronounced dissipation associated with the movement of vortices in a possible
vortex liquid phase. When compared to, for instance, F-doped compounds
pertaining to same family, we obtain rather small activation energies for the
motion of vortices. This suggests that the disorder introduced by doping
LaFeAsO with F is more effective in pinning the vortices than alloying it with
Co.",1208.3435v1
2012-08-30,"High-pressure flux growth, structural, and superconducting properties of LnFeAsO (Ln = Pr, Nd, Sm) single crystals","Single crystals of the LnFeAsO (Ln1111, Ln = Pr, Nd, and Sm) family with
lateral dimensions up to 1 mm were grown from NaAs and KAs flux at high
pressure. The crystals are of good structural quality and become
superconducting when O is partially substituted by F (PrFeAsO1-xFx and
NdFeAsO1-xFx) or when Fe is substituted by Co (SmFe1-xCoxAsO). From
magnetization measurements, we estimate the temperature dependence and
anisotropy of the upper critical field and the critical current density of
underdoped PrFeAsO0.7F0.3 crystal with Tc = 25 K. Single crystals of
SmFe1-xCoxAsO with maximal Tc up to 16.3 K for x = 0.08 were grown for the
first time. From transport and magnetic measurements we estimate the critical
fields and their anisotropy, and find these superconducting properties to be
quite comparable to the ones in SmFeAsO1-xFx with a much higher Tc of = 50 K.
The magnetically measured critical current densities are as high as 109 A/m2 at
2 K up to 7 T, with indication of the usual fishtail effect. The upper critical
field estimated from resistivity measurements is anisotropic with slopes of
-8.7 T/K (H // ab-plane) and -1.7 T/K (H // c-axis). This anisotropy (= 5) is
similar to that in other Ln1111 crystals with various higher Tc s.",1208.6207v2
2012-10-07,Tailoring Magnetism of Perpendicularly Magnetized MnxGa Epitaxial Films on GaAs for Practical Applications,"MnxGa films with high perpendicular anisotropy, coercivity and energy product
have great application potential in ultrahigh-density perpendicular recording,
permanent magnets, spin-transfer-torque memory and oscillators,
magneto-resistance sensors and ferromagnetic metal/semiconductor
heterostructure devices. Here we present a comprehensive diagram of effective
magnetism-tailoring of perpendicularly magnetized MnxGa films grown on III-V
semiconductor GaAs by using molecular-beam epitaxy for the first time, by
systematically investigating the wide-range composition and detailed
post-growth annealing effects. We show that the (001)-orientated MnxGa films
with L10 or D022 ordering could be crystallized on GaAs in a very wide
composition range from x=0.76 to 2.6. L10-ordered MnxGa films show robust
magnetization, high remanent ratio, giant perpendicular anisotropy, high
intrinsic and extrinsic coercivity, and large energy product, which make this
kind of material favorable for perpendicular magnetic recording,
high-performance spintronic devices and permanent magnet applications. In
contrast, D022-ordered films exhibit lower perpendicular anisotropy and weaker
magnetism. Post-growth annealing MnxGa films studies reveal high
thermal-stability up to 450 oC, and effective tailoring of magnetic properties
can be realized by prolonging annealing at 450 oC. These results would be
helpful for understanding this kind of material and designing new spintronic
devices for specific practical applications.",1210.2062v3
2012-10-11,Anisotropic universe with anisotropic sources,"We analyze the state space of a Bianchi-I universe with anisotropic sources.
Here we consider an extended state space which includes null geodesics in this
background. The evolution equations for all the state observables are derived.
Dynamical systems approach is used to study the evolution of these equations.
The asymptotic stable fixed points for all the evolution equations are found.
We also check our analytic results with numerical analysis of these dynamical
equations. The evolution of the state observables are studied both in cosmic
time and using a dimensionless time variable. Then we repeat the same analysis
with a more realistic scenario, adding the isotropic (dust like dark) matter
and a cosmological constant (dark energy) to our anisotropic sources, to study
their co-evolution. The universe now approaches a de~Sitter space
asymptotically dominated by the cosmological constant. The cosmic microwave
background anisotropy maps due to shear are also generated in this scenario,
assuming that the universe contains anisotropic matter along with the usual
(dark) matter and vacuum (dark) energy since decoupling. We find that they
contribute dominantly to the CMB quadrupole. We also constrain the current
level of anisotropy and also search for any cosmic preferred axis present in
the data. We use the Union~2 Supernovae data to this extent. An anisotropy axis
close to the mirror symmetry axis seen in the cosmic microwave background data
from Planck probe is found.",1210.3159v3
2012-10-11,The anisotropic power spectrum and bispectrum in the f(phi) F^2 mechanism,"A suitable coupling of the inflaton phi to a vector kinetic term F^2 gives
frozen and scale invariant vector perturbations. We compute the cosmological
perturbations zeta that result from such coupling by taking into account the
classical vector field that unavoidably gets generated at large scales during
inflation. This generically results in a too anisotropic power spectrum of
zeta. Specifically, the anisotropy exceeds the 1% level (10% level) if
inflation lasted ~5 e-folds (~50 e-folds) more than the minimal amount required
to produce the CMB modes. This conclusion applies, among others, to the
application of this mechanism for magnetogenesis, for anisotropic inflation,
and for the generation of anisotropic perturbations at the end of inflation
through a waterfall field coupled to the vector (in this case, the unavoidable
contribution that we obtain is effective all throughout inflation, and it is
independent of the waterfall field). For a tuned duration of inflation, a 1%
(10%) anisotropy in the power spectrum corresponds to an anisotropic bispectrum
which is enhanced like the local one in the squeezed limit, and with an
effective local f_{NL} ~3 (~30). More in general, a significant anisotropy of
the perturbations may be a natural outcome of all models that sustain higher
than 0 spin fields during inflation.",1210.3257v1
2012-10-30,Large Stark Effect for Li Donor Spins in Si,"We study the effect of a static electric field on lithium donor spins in
silicon. The anisotropy of the effective mass leads to the anisotropy of the
quadratic Stark susceptibility, which we determined using the Dalgarno-Lewis
exact summation method. The theory is asymptotically exact in the field domain
below Li-donor ionization threshold, relevant to the Stark-tuning electron spin
resonance experiments. To obtain the generalized Stark susceptibilities at
arbitrary fields, we propose a new variational wave function which reproduces
the exact results in the low-field limit. With the calculated susceptibilities
at hand, we are able to predict and analyze several important physical effects.
First, we observe that the energy level shifts due to the quadratic Stark
effect for Li donors in Si are equivalent to, and can be mapped onto, those
produced by an external stress.
  Second, we demonstrate that the Stark effect anisotropy, combined with the
unique valley-orbit splitting of a Li donor in Si, spin-orbit interaction and
specially tuned external stress, may lead to a very strong modulation of the
donor spin $g$-factor by the electric field. Third, we investigate the
influence of random strains on the $g$-factor shifts and quantify the random
strain limits and requirements to Si material purity necessary to observe the
$g$-factor Stark shifts experimentally. Finally, we discuss possible
implications of our results for quantum information processing with Li spin
qubits in Si.",1210.8164v1
2012-11-30,An anisotropic-Alfvenic-turbulence-based solar wind model with proton temperature anisotropy,"How the solar wind is accelerated to its supersonic speed is intimately
related to how it is heated. Mechanisms based on ion-cyclotron resonance have
been successful in explaining a large number of observations, those concerning
the significant ion temperature anisotropy above coronal holes in particular.
However, they suffer from the inconsistency with turbulence theory which says
that the turbulent cascade in a low-beta medium like the solar corona should
proceed in the perpendicular rather than the parallel direction, meaning that
there is little energy in the ion gyro-frequency range for ions to absorb via
ion-cyclotron resonance. Recently a mechanism based on the interaction between
the solar wind particles and the anisotropic turbulence has been proposed,
where the perpendicular proton energy addition is via the stochastic heating
(Chandran et al. 2011). We extend this promising mechanism by properly
accounting for the effect of proton temperature anisotropy on the propagation
of Alfven waves, for the radiative losses of electron energy, and for the field
line curvature that naturally accompanies solar winds in the corona. While this
mechanism was shown in previous studies to apply to the polar fast solar wind,
we demonstrate here for the first time that it applies also to the slow wind
flowing along field lines bordering streamer helmets.",1211.7136v1
2012-12-12,"Holographic quark-antiquark potential in hot, anisotropic Yang-Mills plasma","Using the gauge/gravity duality we calculate the heavy quark-antiquark
potential in a hot, anisotropic and strongly coupled Yang-Mills plasma in
(3+1)-dimensions. As the anisotropic medium we take a deformed version of
\mathcal{N} = 4 super Yang-Mills theory at finite temperature following a
recent work where the dual type IIB supergravity solution is also proposed. We
turn on a small value of the anisotropy parameter, for which the gravity dual
is known analytically (perturbatively), and compute the velocity-dependent
quark-antiquark interaction potential when the pair is moving through the
plasma with a velocity v. By setting v = 0 we recover the static
quark-antiquark potential. We numerically study how the potential is modified
in the presence of anisotropy. We further show numerically how the
quark-antiquark separation (both in the static and the velocity-dependent case)
and hence, the screening length gets modified by anisotropy. We discuss various
cases depending upon the direction of the dipole and the direction of its
propagation and make a comparative study of these cases. We are also able to
obtain an analytical expression for the screening length of the dipole moving
in a hot, anisotropic plasma in a special case.",1212.2769v2
2012-12-18,Interplay of anisotropies of momentum distribution and mean field in heavy-ion collisions,"Two important parametrizations of momentum-dependent nucleonic fields,
proposed for the simulations of central heavy-ion collisions, one by Gale et
al. and the other by Welke et al., suffer from practical limitations. The first
gives rise to mean fields isotropic in momentum, even when underlying momentum
distributions are anisotropic, making descriptions of early nonequilibrium
stages of collisions unrealistic. The second parametrization gives rise to
anisotropic mean fields, but is computationally expensive, because the mean
field has to be computed separately for every location of a nucleon in phase
space, through folding. Here we construct a parametrization of the nucleonic
mean field that yields an anisotropic mean field for an anisotropic momentum
distribution and is inexpensive computationally. To demonstrate the versatility
of our parametrization, we take the case of results from the parametrization by
Welke et al. and attempt to approximate them. In arriving at a suitable
anisotropic mean-field potential, we draw, on one hand, from the idea behind
the parametrization of Gale et al., of a separable expansion of the potential
energy, and, on the other, from the idea of a parallel expansion of the energy
and mean field in anisotropy. We show that using our novel parametrization we
can qualitatively and partially quantitatively reproduce the features of the
mean-field parametrization of Welke et al.. This opens up the possibility of
exploring the effects of mean-field anisotropy in collisions, without the
penalty of computational cost behind the folding parametrization.",1212.4460v3
2012-12-19,Metallicity Bias in the Kinematics of the Milky Way Stellar Halo,"Here we study the metallicity bias in the velocity dispersions, the derived
quantity called anisotropy and the mean azimuthal velocity profiles of the
Milky Way stellar halo using Blue Horizontal Branch (BHB) stars taken from
SDSS/SEGUE survey. The comparatively metal-rich sample ([Fe/H]>-2) has prograde
motion and is found to have an offset of 40 km/s in the mean azimuthal velocity
with respect to a metal-poor sample ([Fe/H]<=-2) which has retrograde motion.
The difference in rotation between the most metal-poor and most metal-rich
population was found to be around 65 km/s. For galactocentric distances r<16
kpc, an offset in velocity dispersion profiles and anisotropy can also be seen.
In the inner regions, the metal-poor population is in average tangential orbit;
however, anisotropy is found to decrease monotonically with radius independent
of metallicity. Beyond r = 16 kpc, both the metal-rich and the metal-poor
samples are found to have tangential motion. The metallicity bias in the
kinematics of the halo stars qualitatively supports the co-existence of at
least two-components in the halo having different formation history e.g.
in-situ formation and formation by accretion.",1212.4576v2
2013-01-21,Importance of both spin and orbital fluctuations in BaFe2(As1-xPx)2 : Evidence from superconducting gap anisotropy,"In the iron pnictide superconductors, two distinct unconventional mechanisms
of superconductivity have been put forth: One is mediated by spin fluctuations
leading to the s+- state with sign change of superconducting gap between the
hole and electron bands, and the other is orbital fluctuations which favor the
s++ state without sign reversal. Here we report direct observation of peculiar
momentum-dependent anisotropy in the superconducting gap from angle-resolved
photoemission spectroscopy (ARPES) in BaFe2(As1-xPx)2 (Tc=30 K). The large
anisotropy found only in the electron Fermi surface (FS) and the nearly
isotropic gap on the entire hole FSs are together consistent with modified s+-
gap with nodal loops, which can be theoretically reproduced by considering both
spin and orbital fluctuations whose competition generates the gap modulation.
This indicates that these two fluctuations are nearly equally important to the
high-Tc superconductivity in this system.",1301.4818v1
2013-01-28,The contribution of the Warm-Hot Intergalactic Medium to the CMB anisotropies via the Sunyaev-Zeldovich effect,"Cosmological hydrodynamical simulations predict that a large fraction of all
baryons reside within mildly non-linear structures with temperatures in the
range $10^{5}-10^{7}$K. As the gas is highly ionized, it could be detected by
the temperature anisotropies generated on the Cosmic Microwave Background
radiation. We refine our previous estimates of the thermal Sunyaev-Zeldovich
effect by introducing a non-polytropic equation of state to model the
temperature distribution of the shock heated gas derived from
temperature-density phase diagrams of different hydrodynamical simulations.
Depending on the specific model, the Comptonization parameter varies in the
range $10^{-7}\le y_c \le 2\times 10^{-6}$, compatible with the FIRAS upper
limit. This amplitude is in agreement with a simple toy model constructed to
estimate the average effect induced by filaments of ionized gas. Using the
log-normal probability density function we calculate the correlation function
and the power spectrum of the temperature anisotropies generated by the WHIM
filaments. For a wide range of the parameter space, the maximum amplitude of
the radiation power spectrum is $(\ell+1)\ell C_{\ell}/2\pi =0.7-70(\mu K)^2$
at $\ell \approx 200-500$. This amplitude scales with baryon density, Hubble
constant and the amplitude of the matter power spectrum $\sigma_8$ as
$[(\ell+1)\ell C_\ell]_{\mathrm{max}}/2\pi \propto \sigma_8^{2.6}(\Omega_b
h)^2$. Since the thermal Sunyaev-Zeldovich effect has a specific frequency
dependence, we analyze the possibility of detecting this component with the
forthcoming Planck data.",1301.6546v1
2013-02-04,Radial evolution of the wave-vector anisotropy of solar wind turbulence between 0.3 and 1 AU,"We present observations of the power spectral anisotropy in wave-vector space
of solar wind turbulence, and study how it evolves in interplanetary space with
increasing heliocentric distance. For this purpose we use magnetic field
measurements made by the Helios-2 spacecraft at three positions between 0.29
and 0.9 AU. To derive the power spectral density (PSD) in $(k_\parallel,
k_\bot)$-space based on single-satellite measurements is a challenging task not
yet accomplished previously. Here we derive the spectrum
$\rm{PSD}_{\rm{2D}}$($\rm{k}_\parallel$, $\rm{k}_\bot$) from the spatial
correlation function $\rm{CF}_{\rm{2D}}(r_\parallel, r_\bot)$ by a
transformation according to the projection-slice theorem. We find the so
constructed PSDs to be distributed in k-space mainly along a ridge that is more
inclined toward the $\rm{k}_\bot$ than $\rm{k}_\parallel$ axis, a new result
which probably indicates preferential cascading of turbulent energy along the
$\rm{k}_\bot$ direction. Furthermore, this ridge of the distribution is found
to gradually get closer to the $\rm{k}_\bot$ axis, as the outer scale length of
the turbulence becomes larger while the solar wind flows further away from the
Sun. In the vicinity of the $\rm{k}_\parallel$ axis, there appears a minor
spectral component that probably corresponds to quasi-parallel Alfv\'enic
fluctuations. Their relative contribution to the total spectral density tends
to decrease with radial distance. These findings suggest that solar wind
turbulence undergoes an anisotropic cascade transporting most of its magnetic
energy towards larger $\rm{k}_\bot$, and that the anisotropy in the inertial
range is radially developing further at scales that are relatively far from the
ever increasing outer scale.",1302.0699v1
2013-02-05,Loop Quantum Cosmology of Bianchi I Model in $\barμ$ and $\barμ'$ Schemes with Higher Order Holonomy Corrections,"The detailed formulation of loop quantum cosmology with higher order holonomy
corrections has been constructed recently in the homogeneous and isotropic
spacetime, yet it is important to extend the higher order holonomy corrections
to include the effects of anisotropy which typically grow during the collapsing
phase. In this paper we investigate the Bianchi I model in $\bar{\mu}'$ scheme
which truly captures the regularization of the Hamiltonian constraint. To
compare with the earlier works and provide a comparison with the $\bar{\mu}'$
scheme, we also investigate the $\bar{\mu}$ scheme although it has many
disadvantages. First we construct the effective dynamics with higher order
holonomy corrections in a massless scalar field, then we extend it to the
inclusion of arbitrary matter. Besides that, we also analyze the behavior of
the anisotropy during the evolution of the universe. We find that in the
$\bar{\mu}'$ scheme, the singularity is never approached and the quantum bounce
is generic as in the isotropic case, regardless of the order of the holonomy
corrections. Some differences in the bouncing phase of the two schemes are also
found out. It is also shown that in the two schemes the behavior of the
anisotropy is not the same before and after the bounce.",1302.1014v2
2013-03-08,Measurement of Cosmic Ray Spectrum and Anisotropy with the ARGO-YBJ experiment,"The combined measurement of the cosmic ray (CR) energy spectrum and
anisotropy in their arrival direction distribution needs the knowledge of the
elemental composition of the radiation to discriminate between different origin
and propagation models. Important information on the CR mass composition can be
obtained studying the EAS muon content through the measurement of the CR rate
at different zenith angles.
  In this paper we report on the observation of the anisotropy of galactic CRs
at different angular scales with the ARGO-YBJ experiment. We report also on the
study of the primary CR rate for different zenith angles. The light component
(p+He) has been selected and its energy spectrum measured in the energy range
(5 - 200) TeV for quasi-vertical events. With this analysis for the first time
a ground-based measurement of the CR spectrum overlaps data obtained with
direct methods for more than one energy decade, thus providing a solid
anchorage to the CR spectrum measurements carried out by EAS arrays in the knee
region.
  Finally, a preliminary study of the non-attenuated shower component at a
zenith angle $\theta >$ 70$^{\circ}$ (through the observation of the so-called
horizantal air showers) is presented.",1303.2049v1
2013-03-22,The signature of the Warm Hot Intergalactic Medium in WMAP and the forthcoming PLANCK data,"We compute the cross-correlation between the Warm-Hot Intergalactic Medium
and maps of Cosmic Microwave Background temperature anisotropies using a
log-normal probability density function to describe the weakly non-linear
matter density field. We search for this contribution in the data measured by
the Wilkinson Microwave Anisotropy Probe. We use a template of projected matter
density reconstructed from the Two-Micron All-Sky Redshift Survey as a tracer
of the electron distribution. The spatial distribution of filaments is modeled
using the recently developed Augmented Lagrangian Perturbation Theory. On the
scales considered here, the reconstructed density field is very well described
by the assumed log-normal distribution function. We predict that the
cross-correlation will have an amplitude of $0.03-0.3\mu$K. The measured value
is close to $1.5\mu$K, compatible with random alignments between structure in
the template and in the temperature anisotropy data. Using the W1 Differencing
Assembly to remove this systematic gives a residual correlation dominated by
Galactic foregrounds. Planck could detect the Warm-Hot Medium if it is well
traced by the density field reconstructed from galaxy surveys. The 217GHz
channel will allow to eliminate spurious contributions and its large frequency
coverage can show the sign change from the Rayleigh-Jeans to the Wien part of
the spectrum, characteristic of the thermal Sunyaev-Zeldovich effect.",1303.5623v2
2013-04-04,Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications,"The performance of magnetic nanoparticles is intimately entwined with their
structure, mean size and magnetic anisotropy. Besides, ensembles offer a unique
way of engineering the magnetic response by modifying the strength of the
dipolar interactions between particles. Here we report on an experimental and
theoretical analysis of magnetic hyperthermia, a rapidly developing technique
in medical research and oncology. Experimentally, we demonstrate that
single-domain cubic iron oxide particles resembling bacterial magnetosomes have
superior magnetic heating efficiency compared to spherical particles of similar
sizes. Monte Carlo simulations at the atomic level corroborate the larger
anisotropy of the cubic particles in comparison with the spherical ones, thus
evidencing the beneficial role of surface anisotropy in the improved heating
power. Moreover we establish a quantitative link between the particle
assembling, the interactions and the heating properties. This knowledge opens
new perspectives for improved hyperthermia, an alternative to conventional
cancer therapies.",1304.1298v1
2013-05-03,Multiplicity and transverse-momentum dependence of two- and four-particle correlations in pPb and PbPb collisions,"Measurements of two- and four-particle angular correlations for charged
particles emitted in pPb collisions are presented over a wide range in
pseudorapidity and full azimuth. The data, corresponding to an integrated
luminosity of approximately 31 inverse nanobarns, were collected during the
2013 LHC pPb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV by the
CMS experiment. The results are compared to 2.76 TeV semi-peripheral PbPb
collision data, collected during the 2011 PbPb run, covering a similar range of
particle multiplicities. The observed correlations are characterized by the
near-side (abs(Delta(phi)~0) associated pair yields and the azimuthal
anisotropy Fourier harmonics (v[n]). The second-order (v[2]) and third-order
(v[3]) anisotropy harmonics are extracted using the two-particle azimuthal
correlation technique. A four-particle correlation method is also applied to
obtain the value of v[2] and further explore the multi-particle nature of the
correlations. Both associated pair yields and anisotropy harmonics are studied
as a function of particle multiplicity and transverse momentum. The associated
pair yields, the four-particle v[2], and the v[3] become apparent at about the
same multiplicity. A remarkable similarity in the v[3] signal as a function of
multiplicity is observed between the pPb and PbPb systems. Predictions based on
the color glass condensate and hydrodynamic models are compared to the
experimental results.",1305.0609v3
2013-05-03,"Co2 FeAl thin films grown on MgO substrates: Correlation between static, dynamic and structural properties","Co2FeAl (CFA) thin films with thickness varying from 10 nm to 115 nm have
been deposited on MgO(001) substrates by magnetron sputtering and then capped
by Ta or Cr layer. X-rays diffraction (XRD) revealed that the cubic $[001]$ CFA
axis is normal to the substrate and that all the CFA films exhibit full
epitaxial growth. The chemical order varies from the $B2$ phase to the $A2$
phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and
vibrating sample magnetometer measurements show that, depending on the field
orientation, one or two-step switchings occur. Moreover, the films present a
quadratic MOKE signal increasing with the CFA thickness, due to the increasing
chemical order. Ferromagnetic resonance, MOKE transverse bias initial inverse
susceptibility and torque (TBIIST) measurements reveal that the in-plane
anisotropy results from the superposition of a uniaxial and of a fourfold
symmetry term. The fourfold anisotropy is in accord with the crystal structure
of the samples and is correlated to the biaxial strain and to the chemical
order present in the films. In addition, a large negative perpendicular
uniaxial anisotropy is observed. Frequency and angular dependences of the FMR
linewidth show two magnon scattering and mosaicity contributions, which depend
on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.",1305.0714v1
2013-05-16,Effect of doping on the magnetostructural ordered phase of iron arsenides: A comparative study of the resistivity anisotropy in the doped BaFe$_2$As$_2$ with doping into three different sites,"In order to unravel a role of doping in the iron-based superconductors, we
investigated the in-plane resistivity for BaFe$_2$As$_2$ doped at either of the
three different lattice sites, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,
BaFe$_2$(As$_{1-x}$P$_x$)$_2$, and Ba$_{1-x}$K$_x$Fe$_2$As$_2$, focusing on the
doping effect in the low-temperature antiferromagnetic/orthorhombic (AFO)
phase. A major role of doping in the high-temperature paramagnetic/tetragonal
(PT) phase is known to change the Fermi surface by supplying charge carriers or
by exerting chemical pressure. In the AFO phase, we found a clear correlation
between the magnitude of residual resistivity and resistivity anisotropy. This
indicates that the resistivity anisotropy originates from the anisotropic
impurity scattering from dopant atoms. The magnitude of residual resistivity is
also found to be a parameter controlling the suppression rate of AFO ordering
temperature $T_s$. Therefore, the dominant role of doping in the AFO phase is
to introduce disorder to the system, distinct from that in the PT phase.",1305.3744v1
2013-06-28,A unified solution to the anisotropy and gradient problems,"The Fermi-LAT collaboration recently confirmed a discrepancy between the
observed longitudinal profile of gamma-ray diffuse emission from the Galaxy and
that computed with numerical codes assuming that Cosmic Rays (CRs) are produced
by Galactic supernova remnants; the accurate Fermi-LAT measurements make this
anomaly hardly explainable in terms of conventional diffusion schemes.
Moreover, experimental data from both Muon detector and Extensive Air Shower
experiments about the large scale dipole anisotropy of CRs can hardly be
compatible with model predictions within the framework of conventional
isotropic and homogeneous propagation. We argue that, accounting for a well
physically motivated correlation between the CR escape time and the spatially
dependent magnetic turbulence power, it is possible to solve both problems at
the same time in a very natural way. Indeed, by exploiting this correlation, we
find propagation models that fit a wide set of CR primary and secondary
spectra, and consistently reproduce the CR anisotropy in the energy range 100
GeV - 10 TeV and the gamma-ray longitude distribution recently measured by
Fermi-LAT.",1306.6849v1
2013-07-04,Approximation methods in Loop Quantum Cosmology: From Gowdy cosmologies to inhomogeneous models in Friedmann-Robertson-Walker geometries,"We develop approximation methods in the hybrid quantization of the Gowdy
model with linear polarization and a massless scalar field, for the case of
three-torus spatial topology. The loop quantization of the homogeneous
gravitational sector of the Gowdy model (according to the improved dynamics
prescription) and the presence of inhomogeneities lead to a very complicated
Hamiltonian constraint. Therefore, the extraction of physical results calls for
the introduction of well justified approximations. We first show how to
approximate the homogeneous part of the Hamiltonian constraint, corresponding
to Bianchi I geometries, as if it described a Friedmann-Robertson-Walker (FRW)
model corrected with anisotropies. This approximation is valid in the
high-energy sector of the FRW geometry (concerning its contribution to the
constraint) and for anisotropy profiles that are sufficiently smooth. In
addition, for certain families of states associated to regimes of physical
interest, with negligible effects of the anisotropies and small
inhomogeneities, one can approximate the Hamiltonian constraint of the
inhomogeneous system by that of an FRW geometry with a relatively simple matter
content, and then obtain its solutions.",1307.1420v2
2013-07-29,Feebly Self-Interacting Cold Dark Matter: New theory for the Core-Halo structure in GLSB Galaxies,"We explore the low energy cosmological dynamics of feebly self-interacting
cold dark matter and propose a new simple explanation for the rotation curves
of the core-halo model in massive LSB (Low Surface brightness)galaxies. We
argue in favor of the truly collisionless nature of cold dark matter,which is
feebly,self-interacting at small scales between epochs of equality and
recombination.For this, we assume a model, wherein strongly coupled
baryon-radiation plasma ejects out of small regions of concentrated cold dark
matter without losing its equilibrium. We use the Merscerskii equation i.e. the
variable mass formalism of classical dynamics.We obtain new results relating
the oscillations in the CMB anisotropy to the ejection velocity of the
baryon-radiation plasma,which can be useful tool for numerical work for
exploring the second peak of CMB. Based on this model, we discuss the growth of
perturbations in such a feebly self-interacting,cold dark matter both in the
Jeans theory and in the expanding universe using Newton's theory.We obtain an
expression for the growth of fractional perturbations in cold dark matter,which
reduce to the standard result of perturbation theory for late recombination
epochs. We see the effect of the average of the perturbations in the cold dark
matter potential on the cosmic microwave background temperature anisotropy that
originated at redshifts between equality and recombination i.e. 1100 < z <
z_{eq}. Also we obtain an expression for the Sachs-Wolfe effect,i.e. the CMB
temperature anisotropy at decoupling in terms of the average of the
perturbations in cold dark matter potential.",1307.7469v2
2013-08-24,Spin-chain magnetism and uniform Dzyaloshinsky-Moriya anisotropy in BaV$_3$O$_8$,"We report on the microscopic magnetic model of a spin-1/2 magnet
BaV$_3$O$_8$. In contrast to earlier phenomenological analysis, our
density-functional band-structure calculations combined with quantum
Monte-Carlo simulations establish a relatively simple and non-frustrated model
of weakly coupled spin chains with the intrachain coupling of $J\sim$ 38 K and
the Neel temperature of $T_N\sim$ 6 K, both in excellent agreement with the
experiment. The intrachain coupling between the spin-1/2 V$^{+4}$ ions takes
place via two contiguous V$^{+5}$O$_4$ tetrahedra forming an extended
superexchange pathway with the V$^{+4}$--V$^{+4}$ distance of 7.44 A.
Surprisingly, this pathway is preferred over shorter V$^{+4}$--V$^{+4}$
connections, owing to peculiarities in the interacting orbitals of the magnetic
V$^{+4}$ ions and V$^{+5}$ ions that are non-magnetic, but feature low-lying
$3d$ states contributing to the superexchange process. We also note that the
crystal structure of BaV$_3$O$_8$ supports the long-sought uniform arrangement
of Dzyaloshinsky-Moriya (DM) couplings on a spin-1/2 chain. While our
calculations yield only a weak DM anisotropy in BaV$_3$O$_8$, the crystal
structure of this compound provides a suitable framework for the search of spin
chains with the uniform DM anisotropy in other compounds of the vanadate
family.",1308.5305v2
2013-09-26,Reionization on Large Scales IV: Predictions for the 21 cm signal incorporating the light cone effect,"We present predictions for the 21 cm brightness temperature power spectrum
during the Epoch of Reionization (EoR). We discuss the implications of the
""light cone"" effect, which incorporates evolution of the neutral hydrogen
fraction and 21 cm brightness temperature along the line of sight. Using a
novel method calibrated against radiation-hydrodynamic simulations, we model
the neutral hydrogen density field and 21 cm signal in large volumes ($L = 2$
Gpc/$h$). The inclusion of the light cone effect leads to a relative decrease
of about 50% in the 21 cm power spectrum on all scales. We also find that the
effect is more prominent at the midpoint of reionization and later. The light
cone effect also can introduce an anisotropy along the line of sight. By
decomposing the 3D power spectrum into components perpendicular to and along
the line of sight, we find that in our fiducial reionization model, there is no
significant anisotropy. However, parallel modes can contribute up to 40% more
power for shorter reionization scenarios. The scales on which the light cone
effect is relevant are comparable to scales where one measures the baryon
acoustic oscillation. We argue that due to its large comoving scale and
introduction of anisotropy, the light cone effect is important when considering
redshift space distortions and future application to the Alcock-Paczynski test
for the determination of cosmological parameters.",1309.7056v3
2013-09-28,Synthetic Multiferroic Interconnects for Magnetic Logic Circuits,"In this work, we consider the possibility of using synthetic multiferroics
comprising piezoelectric and magnetostrictive materials as an interconnect for
nano magnetic logic circuits. The proposed interconnect resembles a parallel
plate capacitor filled with a piezoelectric, where one of the plates is made of
a magnetoelastic material. The operation of the interconnect is based on the
effect of stress-mediated anisotropy modulation, where an electric field
applied across the piezoelectric material produces stress, which, in turn,
affects the anisotropy field in the magnetostrictive material. We present the
results of numerical modeling illustrating signal propagation through the
interconnect. The model combines electric and magnetic parts, where the
electric part describes the distribution of an electric field through the
piezoelectric and the magnetic part describes the change of magnetization in
the magnetoelastic layer. The model is based on the Landau-Lifshitz-Gilbert
equation with the electric field dependent anisotropy term included. The
utilization of the electro-magnetic coupling makes it possible to amplify
magnetic signal during its propagation via energy conversion from the electric
to magnetic domains. Potentially, synthetic multiferroic interconnects can be
implemented in a variety of spin-based devices ensuring reliable and low-energy
consuming data transmission. According to the estimates, the group velocity of
magnetic signals may be up to 100 km/s with energy dissipation less than aJ per
bit per 100nm. The fundamental limits and practical shortcoming of the proposed
approach are also discussed.",1309.7399v1
2013-09-29,Magnetic Properties of Two-dimensional Nanodots: Ground State and Phase Transition,"We study the effect of perpendicular single-ion anisotropy,
$-As_{\text{z}}^2$, on the ground-state structure and finite-temperature
properties of a two-dimensional magnetic nanodot in presence of a dipolar
interaction of strength $D$. By a simulated annealing Monte Carlo method, we
show that in the ground state a vortex core perpendicular to the nanodot plane
emerges already in the range of moderate anisotropy values above a certain
threshold level. In the giant-anisotropy regime the vortex structure is
superseded by a stripe domain structure with stripes of alternate domains
perpendicular to the surface of the sample. We have also observed an
intermediate stage between the vortex and stripe structures, with satellite
regions of tilted nonzero perpendicular magnetization around the core. At
finite temperatures, at small $A$, we show by Monte Carlo simulations that
there is a transition from the the in-plane vortex phase to the disordered
phase characterized by a peak in the specific heat and the vanishing vortex
order parameter. At stronger $A$, we observe a discontinuous transition with a
large latent heat from the in-plane vortex phase to perpendicular stripe
ordering phase before a total disordering at higher temperatures. In the regime
of perpendicular stripe domains, namely with giant $A$, there is no phase
transition at finite $T$: the stripe domains are progressively disordered with
increasing $T$. Finite-size effects are shown and discussed.",1309.7631v1
2013-10-01,Field Induced Magnetic Ordering and Single-ion Anisotropy in the Quasi-1D Haldane Chain Compound SrNi2V2O8: A Single Crystal investigation,"Field-induced magnetic ordering in the Haldane chain compound
SrNi$_{2}$V$_{2}$O$_{8}$ and effect of anisotropy have been investigated using
single crystals. Static susceptibility, inelastic neutron scattering,
high-field magnetization, and low temperature heat-capacity studies confirm a
non-magnetic spin-singlet ground state and a gap between the singlet ground
state and triplet excited states. The intra-chain exchange interaction is
estimated to be $J \sim 8.9{\pm}$0.1 meV. Splitting of the dispersions into two
modes with minimum energies 1.57 and 2.58 meV confirms the existence of
single-ion anisotropy $D(S^z){^2}$. The value of {\it D} is estimated to be
$-0.51{\pm}0.01$ meV and the easy axis is found to be along the
crystallographic {\it c}-axis. Field-induced magnetic ordering has been found
with two critical fields [$\mu_0H_c^{\perp c} = 12.0{\pm}$0.2 T and
$\mu_0H_c^{\parallel c} = 20.8{\pm}$0.5 T at 4.2 K]. Field-induced
three-dimensional magnetic ordering above the critical fields is evident from
the heat-capacity, susceptibility, and high-field magnetization study. The
Phase diagram in the {\it H-T} plane has been obtained from the high-field
magnetization. The observed results are discussed in the light of theoretical
predictions as well as earlier experimental reports on Haldane chain compounds.",1310.0221v1
2013-10-17,Wake in anisotropic Quark-Gluon Plasma,"We calculate the wake in charge density and the wake potential due to the
passage of a fast parton in an anisotropic quark gluon plasma(AQGP). For the
sake of simplicity small $\xi$(anisotropic parameter) limit has been
considered. When the velocity($v$) of the jet is parallel to the anisotropy
direction(${\hat n}$) and remains below the phase velocity($v_p$), the wake in
induced charge density shows a little oscillatory behavior in AQGP, contrary to
the isotropic case. With the jet velocity greater than the phase velocity, the
oscillatory behavior increases with $\xi$. Also for $v>v_p$ one observes a
clear modification of the cone-like structure in presence of anisotropy. For
the parallel direction in the backward region, the depth of the wake potential
decreases with the increase of $\xi$ for $v<v_p$ and the potential becomes
modified Coulomb-like for higher values of $\xi$. In the forward region, the
potential remains modified Coulomb-like with the change in magnitude for
nonzero $\xi$, for both $v>v_p$ and $v<v_p$. In the perpendicular direction,
the wake potential is symmetric in the forward and backward regions. With the
increase of $\xi$, the depth of negative minimum is moving away from the origin
irrespective of the jet velocity. On the other hand when the jet velocity is
perpendicular to the anisotropy direction, we find significant changes in the
case of both wake charge density and potential in comparison to the isotropic
case.",1310.4657v1
2014-01-22,The Ellipsoidal Universe in the Planck Satellite Era,"Recent Planck data confirm that the cosmic microwave background displays the
quadru-pole power suppression together with large scale anomalies. Progressing
from previous results, that focused on the quadrupole anomaly, we strengthen
the proposal that the slightly anisotropic ellipsoidal universe may account for
these anomalies. We solved at large scales the Boltzmann equation for the
photon distribution functions by taking into account both the effects of the
inflation produced primordial scalar perturbations and the anisotropy of the
geometry in the ellipsoidal universe. We showed that the low quadrupole
temperature correlations allowed us to fix the eccentricity at decoupling,
$e_{\rm dec} \, = \, (0.86 \, \pm \, 0.14) \, 10^{-2}$, and to constraint the
direction of the symmetry axis. We found that the anisotropy of the geometry of
the universe contributes only to the large scale temperature anisotropies
without affecting the higher multipoles of the angular power spectrum.
Moreover, we showed that the ellipsoidal geometry of the universe induces
sizable polarization signal at large scales without invoking the reionization
scenario. We explicitly evaluated the quadrupole TE and EE correlations. We
found an average large scale polarization $\Delta T_{pol} \, = \, (1.20 \, \pm
\, 0.38) \; \mu K $. We point out that great care is needed in the experimental
determination of the large-scale polarization correlations since the average
temperature polarization could be misinterpreted as foreground emission
leading, thereby, to a considerable underestimate of the cosmic microwave
background polarization signal.",1401.5627v3
2014-02-17,A review of two-band superconductivity: materials and effects on the thermodynamic and reversible mixed-state properties,"Two-band superconductivity has become an important topic over the last ten
years. Extensive experimental and theoretical studies started with MgB2 and are
now focused on the iron-based and other new superconductors. In this review, I
describe how important thermodynamic, reversible mixed-state, and other
superconducting properties are changed by two-band and, for comparison, by
other effects such as anisotropy in a single-band material or an energy gap
structure different from the conventional s-wave symmetry. The work consists of
three main parts, in which I review (i) theoretical models and what they
predict for experimentally accessible properties in the two-band and other
scenarios, (ii) experimental methods applied for investigating superconducting
properties and the results obtained in potential two-band materials, and (iii)
materials, for which two- or multi-band superconductivity has been suggested.
It is shown that two-band effects appear in most of the analyzed properties and
that they can be quite significant but usually fade away as interband
interactions increase. Anisotropy often leads to similar modifications in
single-band superconductors, which is why the distinction of two-band and
anisotropy effects is usually difficult, particularly when the temperature
dependence of the quantities is examined. In contrast, the field dependent
effects are more often different and thus more often allow a reliable
distinction between the models.",1402.3956v1
2014-02-27,Enhanced Stability of Skyrmions in Two-Dimensional Chiral Magnets with Rashba Spin-Orbit Coupling,"Recent developments have led to an explosion of activity on skyrmions in
three-dimensional (3D) chiral magnets. Experiments have directly probed these
topological spin textures, revealed their nontrivial properties, and led to
suggestions for novel applications. However, in 3D the skyrmion crystal phase
is observed only in a narrow region of the temperature-field phase diagram. We
show here, using a general analysis based on symmetry, that skyrmions are much
more readily stabilized in two-dimensional (2D) systems with Rashba spin-orbit
coupling. This enhanced stability arises from the competition between field and
easy-plane magnetic anisotropy and results in a nontrivial structure in the
topological charge density in the core of the skyrmions. We further show that,
in a variety of microscopic models for magnetic exchange, the required
easy-plane anisotropy naturally arises from the same spin-orbit coupling that
is responsible for the chiral Dzyaloshinskii-Moriya interactions. Our results
are of particular interest for 2D materials like thin films, surfaces, and
oxide interfaces, where broken surface-inversion symmetry and Rashba spin-orbit
coupling naturally lead to chiral exchange and easy-plane compass anisotropy.
Our theory gives a clear direction for experimental studies of 2D magnetic
materials to stabilize skyrmions over a large range of magnetic fields down to
T=0.",1402.7082v2
2014-03-03,Pressure-induced ferromagnetism with strong Ising-type anisotropy in YbCu$_2$Si$_2$,"We report dc magnetic measurements on YbCu$_2$Si$_2$ at pressures above 10
GPa using a miniature ceramic anvil cell. YbCu$_2$Si$_2$ shows a
pressure-induced transition from the non-magnetic to a magnetic phase at 8 GPa.
We find a spontaneous dc magnetization in the pressure-induced phase above 9.4
GPa. The pressure dependence of the ferromagnetic transition temperature T_C
and the spontaneous magnetic moment m_0 at 2.0 K have been determined. The
value of m_0 in the present macroscopic measurement is less than half of that
determined via Mossbauer experiment. The difference may be attributed to
spatial phase separation between the ferromagnetic and paramagnetic phases.
This separation suggests that the pressure-induced phase boundary between the
paramagnetic and ferromagnetic states is of first order. Further, we have
studied the magnetic anisotropy in the pressure-induced ferromagnetic state.
The effect of pressure on the magnetization with magnetic field along the
magnetic easy $c$-axis is much larger than for field along the hard $a$-axis in
the tetragonal structure. The pressure-induced phase has strong Ising-type
uniaxial anisotropy, consistent with the two crystal electric field (CEF)
models proposed for YbCu$_2$Si$_2$.",1403.0290v2
2014-03-19,"Erosion of Globular Cluster Systems: The Influence of Radial Anisotropy, Central Black Holes and Dynamical Friction","We present the adaptable MUESLI code for investigating dynamics and erosion
processes of globular clusters (GCs) in galaxies. MUESLI follows the orbits of
individual clusters and applies internal and external dissolution processes to
them. Orbit integration is based on the self-consistent field method in
combination with a time-transformed leapfrog scheme, allowing us to handle
velocity-dependent forces like triaxial dynamical friction. In a first
application, the erosion of globular cluster systems (GCSs) in elliptical
galaxies is investigated. Observations show that massive ellipticals have rich,
radially extended GCSs, while some compact dwarf ellipticals contain no GCs at
all. For several representative examples, spanning the full mass scale of
observed elliptical galaxies, we quantify the influence of radial anisotropy,
galactic density profiles, SMBHs, and dynamical friction on the GC erosion
rate. We find that GC number density profiles are centrally flattened in less
than a Hubble time, naturally explaining observed cored GC distributions. The
erosion rate depends primarily on a galaxy's mass, half-mass radius and radial
anisotropy. The fraction of eroded GCs is nearly 100% in compact, M 32 like
galaxies and lowest in extended and massive galaxies. Finally, we uncover the
existence of a violent tidal disruption dominated phase which is important for
the rapid build-up of halo stars.",1403.4946v1
2014-04-22,Results from the Wilkinson Microwave Anisotropy Probe,"The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of
temperature and polarization over the entire sky in five microwave frequency
bands. These full-sky maps were used to obtain measurements of temperature and
polarization anisotropy of the cosmic microwave background with the
unprecedented accuracy and precision. The analysis of two-point correlation
functions of temperature and polarization data gives determinations of the
fundamental cosmological parameters such as the age and composition of the
universe, as well as the key parameters describing the physics of inflation,
which is further constrained by three-point correlation functions. WMAP
observations alone reduced the flat $\Lambda$ cold dark matter ($\Lambda$CDM)
cosmological model (six) parameter volume by a factor of >68,000 compared with
pre-WMAP measurements. The WMAP observations (sometimes in combination with
other astrophysical probes) convincingly show the existence of non-baryonic
dark matter, the cosmic neutrino background, flatness of spatial geometry of
the universe, a deviation from a scale-invariant spectrum of initial scalar
fluctuations, and that the current universe is undergoing an accelerated
expansion. The WMAP observations provide the strongest ever support for
inflation; namely, the structures we see in the universe originate from quantum
fluctuations generated during inflation.",1404.5415v2
2014-04-22,Order-by-disorder and spin-orbital liquids in a distorted Heisenberg-Kitaev model,"The microscopic modeling of spin-orbit entangled $j=1/2$ Mott insulators such
as the layered hexagonal Iridates Na$_2$IrO$_3$ and Li$_2$IrO$_3$ has spurred
an interest in the physics of Heisenberg-Kitaev models. Here we explore the
effect of lattice distortions on the formation of the collective spin-orbital
states which include not only conventionally ordered phases but also gapped and
gapless spin-orbital liquids. In particular, we demonstrate that in the
presence of spatial anisotropies of the exchange couplings conventionally
ordered states are formed through an order-by-disorder selection which is not
only sensitive to the type of exchange anisotropy but also to the relative
strength of the Heisenberg and Kitaev couplings. The spin-orbital liquid phases
of the Kitaev limit -- a gapless phase in the vicinity of spatially isotropic
couplings and a gapped Z$_2$ phase for a dominant spatial anisotropy of the
exchange couplings -- show vastly different sensitivities to the inclusion of a
Heisenberg exchange. While the gapless phase is remarkably stable, the gapped
Z$_2$ phase quickly breaks down in what might be a rather unconventional phase
transition driven by the simultaneous condensation of its elementary
excitations.",1404.5490v2
2014-06-10,Resolving the mass--anisotropy degeneracy of the spherically symmetric Jeans equation II: optimum smoothing and model validation,"The spherical Jeans equation is widely used to estimate the mass content of a
stellar systems with apparent spherical symmetry. However, this method suffers
from a degeneracy between the assumed mass density and the kinematic anisotropy
profile, $\beta(r)$. In a previous work, we laid the theoretical foundations
for an algorithm that combines smoothing B-splines with equations from dynamics
to remove this degeneracy. Specifically, our method reconstructs a unique
kinematic profile of $\sigma_{rr}^2$ and $\sigma_{tt}^2$ for an assumed free
functional form of the potential and mass density $(\Phi,\rho)$ and given a set
of observed line-of-sight velocity dispersion measurements, $\sigma_{los}^2$.
In Paper I (submitted to MNRAS: MN-14-0101-MJ) we demonstrated the efficiency
of our algorithm with a very simple example and we commented on the need for
optimum smoothing of the B-spline representation; this is in order to avoid
unphysical variational behaviour when we have large uncertainty in our data. In
the current contribution we present a process of finding the optimum smoothing
for a given data set by using information of the behaviour from known ideal
theoretical models. Markov Chain Monte Carlo methods are used to explore the
degeneracy in the dynamical modelling process. We validate our model through
applications to synthetic data for systems with constant or variable
mass-to-light ratio $\Upsilon$. In all cases we recover excellent fits of
theoretical functions to observables and unique solutions. Our algorithm is a
robust method for the removal of the mass-anisotropy degeneracy of the
spherically symmetric Jeans equation for an assumed functional form of the mass
density.",1406.2546v1
2014-08-12,Thermal Conduction in Single-Layer Black Phosphorus: Highly Anisotropic?,"The single-layer black phosphorus is characteristic for its puckered
structure, which has leaded to highly anisotropy in its optical, electronic,
and mechanical properties. We report, using the non-equilibrium Green's
function approach and the first-principles method, that the anisotropy in the
thermal conduction is very weak in the single-layer black phosphorus -- the
difference between two in-plane directions is less than 4%. Our phonon
calculations disclose that the two in-plane acoustic phonon branches have lower
group velocities in the direction perpendicular to the pucker, as the black
phosphorus is softer in this direction, leading to a weakening effect for the
thermal conductance in the perpendicular direction. However, the out-of-plane
acoustic phonon branch behaviors abnormally; i.e., the group velocity of this
phonon branch is higher in the perpendicular direction, although the
single-layer black phosphorus is softer in this direction. The abnormal
behavior of the out-of-plane phonon branch is closely related to the highly
anisotropic Poisson's ratio in the single-layer black phosphorus. As a result
of the counteraction between the in-plane phonon modes and the out-of-plane
phonon mode, the thermal conductance in the perpendicular direction is weaker
than the parallel direction, but the anisotropy is pretty small.",1408.2622v2
2014-08-18,Constraining topological defects with temperature and polarization anisotropies,"We analyse the possible contribution of topological defects to cosmic
microwave anisotropies, both temperature and polarisation. We allow for the
presence of both inflationary scalars and tensors, and of polarised dust
foregrounds that may contribute to or dominate the B-mode polarisation signal.
We confirm and quantify our previous statements that topological defects on
their own are a poor fit to the B-mode signal. However, adding topological
defects to a models with a tensor component or a dust component improves the
fit around $\ell=200$. Fitting simultaneously to both temperature and
polarisation data, we find that textures fit almost as well as tensors
($\Delta\chi^2 = 2.0$), while Abelian Higgs strings are ruled out as the sole
source of the B-mode signal at low $\ell$. The 95% confidence upper limits on
models combining defects and dust are $G\mu < 2.7\times 10^{-7}$ (Abelian Higgs
strings), $G\mu < 9.8\times 10^{-7}$ (semilocal strings) and $G\mu < 7.3\times
10^{-7}$ (textures), a small reduction on the $Planck$ bounds. The most
economical fit overall is obtained by the standard $\Lambda$CDM model with a
polarised dust component.",1408.4126v2
2014-09-02,Switching of Perpendicularly Polarized Nanomagnets with Spin Orbit Torque without an External Magnetic Field by Engineering a Tilted Anisotropy,"Spin orbit torque (SOT) provides an efficient way of generating spin current
that promises to significantly reduce the current required for switching
nanomagnets. However, an in-plane current generated SOT cannot
deterministically switch a perpendicularly polarized magnet due to symmetry
reasons. On the other hand, perpendicularly polarized magnets are preferred
over in-plane magnets for high-density data storage applications due to their
significantly larger thermal stability in ultra-scaled dimensions. Here we show
that it is possible switch a perpendicularly polarized magnet by SOT without
needing an external magnetic field. This is accomplished by engineering an
anisotropy in the magnets such that the magnetic easy axis slightly tilts away
from the film-normal. Such a tilted anisotropy breaks the symmetry of the
problem and makes it possible to switch the magnet deterministically. Using a
simple Ta/CoFeB/MgO/Ta heterostructure, we demonstrate reversible switching of
the magnetization by reversing the polarity of the applied current. This
demonstration presents a new approach for controlling nanomagnets with spin
orbit torque.",1409.0620v3
2014-09-02,The Fortuitous Latitude of the Pierre Auger Observatory and Telescope Array for Reconstructing the Quadrupole Moment,"Determining anisotropies in the arrival directions of cosmic rays at the
highest energy is an important task in astrophysics. It is common and useful to
partition the sky into spherical harmonics as a measure of anisotropy. The two
lowest nontrivial spherical harmonics, the dipole and the quadrupole, are of
particular interest, since these distributions encapsulate a dominant single
source and a plane of sources, as well as offering relatively high statistics.
The best experiments for the detection of ultra high energy cosmic rays
currently are all ground-based, with highly nonuniform exposures on the sky
resulting from the fixed experimental locations on the earth. This nonuniform
exposure increases the complexity and error in inferring anisotropies. It turns
out that there is an optimal latitude for an experiment at which nonuniform
exposure does not diminish the inference of the quadrupole moment. We derive
the optimal latitude, and find that (presumably by a fortuitous coincidence)
this optimal latitude runs through the largest cosmic ray experiment, Pierre
Auger Observatory (PAO) in the Southern Hemisphere, and close to the largest
cosmic ray experiment in the Northern Hemisphere, Telescope Array (TA).
Consequently, assuming a quadrupole distribution, PAO and TA can reconstruct
the cosmic ray quadrupole distribution to a high precision, without concern for
their partial sky exposure.",1409.0883v2
2014-09-10,Magnetohydrodynamic normal mode analysis of plasma with equilibrium pressure anisotropy,"In this work, we generalise linear magnetohydrodynamic (MHD) stability theory
to include equilibrium pressure anisotropy in the fluid part of the analysis. A
novel 'single-adiabatic' (SA) fluid closure is presented which is complementary
to the usual 'double-adiabatic' (CGL) model and has the advantage of naturally
reproducing exactly the MHD spectrum in the isotropic limit. As with MHD and
CGL, the SA model neglects the anisotropic perturbed pressure and thus loses
non-local fast-particle stabilisation present in the kinetic approach. Another
interesting aspect of this new approach is that the stabilising terms appear
naturally as separate viscous corrections leaving the isotropic SA closure
unchanged. After verifying the self-consistency of the SA model, we re-derive
the projected linear MHD set of equations required for stability analysis of
tokamaks in the MISHKA code. The cylindrical wave equation is derived
analytically as done previously in the spectral theory of MHD and clear
predictions are made for the modification to fast-magnetosonic and slow ion
sound speeds due to equilibrium anisotropy.",1409.2980v1
2014-09-12,Naturally large tensor-to-scalar ratio in inflation,"Recently, BICEP2 measurements of the cosmic microwave background (CMB)
$B$-mode polarization at degree angular scales has indicated the presence of
tensor modes with a high tensor-to-scalar ratio of $r=0.2$ when assuming nearly
scale-invariant tensor and scalar spectra, although the signal may be
contaminated by dust emission as implied by the recent {\em Planck}
polarization data. This result is in conflict with the {\em Planck} best-fit
Lambda Cold Dark Model with $r<0.11$. Due to the fact that inflaton has to be
interacting with other fields so as to convert its potential energy into
radiation to reheat the Universe, the interacting inflaton may result in a
suppression of the scalar spectrum at large scales. This suppression has been
used to explain the observed low quadrupole in the CMB anisotropy. In this
paper, we show that a combination of the tensor modes measured by BICEP2 and
the large-scale suppressed scalar modes contributes to the CMB anisotropy in
such a way that the resultant CMB anisotropy and polarization power spectra are
consistent with both {\em Planck} and BICEP2 data. We also project our findings
to cases in which $r$ may become reduced in future CMB polarization
measurements.",1409.3661v2
2014-10-24,Probing the epoch of pre-reionization by cross-correlating cosmic microwave and infrared background anisotropies,"The epoch of first star formation and the state of the intergalactic medium
(IGM) at that time are not directly observable with current telescopes. The
radiation from those early sources is now part of the Cosmic Infrared
Background (CIB) and, as these sources ionize the gas around them, the IGM
plasma would produce faint temperature anisotropies in the Cosmic Microwave
Background (CMB) via the thermal Sunyaev-Zeldovich (TSZ) effect. While these
TSZ anisotropies are too faint to be detected, we show that the
cross-correlation of maps of source-subtracted CIB fluctuations from {\it
Euclid}, with suitably constructed microwave maps at different frequencies can
probe the physical state of the gas during reionization and test/constrain
models of the early CIB sources. We identify the frequency-combined
CMB-subtracted microwave maps from space and ground-based instruments to show
that they can be cross-correlated with the forthcoming all-sky {\it Euclid} CIB
maps to detect the cross-power at scales $\sim 5'-60'$ with the signal/noise of
up to $S/N\sim 4-8$ depending on the contribution to the Thomson optical depth
during those pre-reionization epochs ($\Delta \tau\simeq 0.05$) and the
temperature of IGM (up to $\sim10^4$K). Such a measurement would offer a new
window to explore emergence and physical properties of these first light
sources.",1410.6619v2
2014-11-05,On the Origin of Near-Infrared Extragalactic Background Light Anisotropy,"Extragalactic background light (EBL) anisotropy traces variations in the
total production of photons over cosmic history, and may contain faint,
extended components missed in galaxy point source surveys. Infrared EBL
fluctuations have been attributed to primordial galaxies and black holes at the
epoch of reionization (EOR), or alternately, intra-halo light (IHL) from stars
tidally stripped from their parent galaxies at low redshift. We report new EBL
anisotropy measurements from a specialized sounding rocket experiment at 1.1
and 1.6 micrometers. The observed fluctuations exceed the amplitude from known
galaxy populations, are inconsistent with EOR galaxies and black holes, and are
largely explained by IHL emission. The measured fluctuations are associated
with an EBL intensity that is comparable to the background from known galaxies
measured through number counts, and therefore a substantial contribution to the
energy contained in photons in the cosmos.",1411.1411v1
2014-11-11,Effect of magnetic anisotropy on spin-dependent thermoelectric effects in nanoscopic systems,"Conventional and spin-related thermoelectric effects in electronic transport
through a nanoscopic system exhibiting magnetic anisotropy $-$with both
uniaxial and transverse components$-$ are studied theoretically in the linear
response regime. In particular, a magnetic tunnel junction with a large-spin
impurity $-$either a magnetic atom or a magnetic molecule$-$ embedded in the
barrier is considered as an example. Owing to magnetic interaction with the
impurity, conduction electrons traversing the junction can scatter on the
impurity, which effectively can lead to angular momentum and energy exchange
between the electrons and the impurity. As we show, such processes have a
profound effect on the thermoelectric response of the system. Specifically, we
present a detailed analysis of charge, spin and thermal conductance, together
with the Seebeck and spin Seebeck coefficients (thermopowers). Since the
scattering mechanism also involves processes when electrons are inelastically
scattered back to the same electrode, one can expect the flow of spin and
energy also in the absence of charge transport through the junction. This, in
turn, results in a finite spin thermopower, and the magnetic anisotropy plays a
key role for this effect to occur.",1411.2741v2
2014-11-20,Anisotropic inflation reexamined: upper bound on broken rotational invariance during inflation,"The presence of a light vector field coupled to a scalar field during
inflation makes a distinct prediction: the observed correlation functions of
the cosmic microwave background (CMB) become statistically anisotropic. We
study the implications of the current bound on statistical anisotropy derived
from the Planck 2013 CMB temperature data for such a model. The previous
calculations based on the attractor solution indicate that the magnitude of
anisotropy in the power spectrum is proportional to $N^2$, where $N$ is the
number of $e$-folds of inflation counted from the end of inflation. In this
paper, we show that the attractor solution is not compatible with the current
bound, and derive new predictions using another branch of anisotropic
inflation. In addition, we improve upon the calculation of the mode function of
perturbations by including the leading-order slow-roll corrections. We find
that the anisotropy is roughly proportional to
$[2(\varepsilon_H+4\eta_H)/3-4(c-1)]^{-2}$, where $\varepsilon_H$ and $\eta_H$
are the usual slow-roll parameters and $c$ is the parameter in the model,
regardless of the form of potential of an inflaton field. The bound from Planck
implies that breaking of rotational invariance during inflation (characterized
by the background homogeneous shear divided by the Hubble rate) is limited to
be less than ${\cal O}(10^{-9})$. This bound is many orders of magnitude
smaller than the amplitude of breaking of time translation invariance, which is
observed to be ${\cal O}(10^{-2})$.",1411.5489v2
2014-11-30,An experimental test of the viscous anisotropy hypothesis for partially molten rocks,"Chemical differentiation of rocky planets occurs by melt segregation away
from the region of melting. The mechanics of this process, however, are complex
and incompletely understood. In partially molten rocks undergoing shear
deformation, melt pockets between grains align coherently in the stress field;
it has been hypothesized that this anisotropy in microstructure creates an
anisotropy in the viscosity of the aggregate. With the inclusion of anisotropic
viscosity, continuum, two-phase-flow models reproduce the emergence and angle
of melt-enriched bands that form in laboratory experiments. In the same
theoretical context, these models also predict sample-scale melt migration due
to a gradient in shear stress. Under torsional deformation, melt is expected to
segregate radially inward. Here we present new torsional deformation
experiments on partially molten rocks that test this prediction.
Microstructural analyses of the distribution of melt and solid reveal a radial
gradient in melt fraction, with more melt toward the centre of the cylinder.
The extent of this radial melt segregation grows with progressive strain,
consistent with theory. The agreement between theoretical prediction and
experimental observation provides a validation of this theory, which is
critical to understanding the large-scale geodynamic and geochemical evolution
of Earth.",1412.0203v1
2014-12-11,Cosmological constraints from the redshift dependence of the Alcock-Paczynski test: galaxy density gradient field,"We propose a method based on the redshift dependence of the Alcock-Paczynski
(AP) test to measure the expansion history of the Universe. It uses the
isotropy of the galaxy density gradient field to constrain cosmological
parameters. If the density parameter $\Omega_m$ or the dark energy equation of
state $w$ are incorrectly chosen, the gradient field appears to be anisotropic
with the degree of anisotropy varying with redshift. We use this effect to
constrain the cosmological parameters governing the expansion history of the
Universe. Although redshift-space distortions (RSD) induced by galaxy peculiar
velocities also produce anisotropies in the gradient field, these effects are
close to uniform in magnitude over a large range of redshift. This makes the
redshift variation of the gradient field anisotropy relatively insensitive to
the RSD. By testing the method on mock surveys drawn from the Horizon Run 3
cosmological N-body simulations, we demonstrate that the cosmological
parameters can be estimated without bias. Our method is complementary to the
baryon acoustic oscillation or topology methods as it depends on $D_AH$, the
product of the angular diameter distance and the Hubble parameter.",1412.3564v3
2014-12-12,Anisotropic Superconducting Gap and Elongated Vortices with Caroli-De-Gennes-Matricon States in the New Superconductor Ta4Pd3Te16,"The superconducting state is formed by the condensation of a large number of
Cooper pairs. The normal state electronic properties can give significant
influence on the superconducting state. For usual type-II superconductors, the
vortices are cylinder like with a round cross-section. For many two dimensional
superconductors, such as Cuprates, 2H-NbSe$_2$ etc., albeit the in-plane
anisotropy, the vortices generally have a round shape. In this paper we report
results based on the scanning tunneling microscopy/spectroscopy measurements on
a newly discovered superconductor Ta$_4$Pd$_3$Te$_{16}$. The chain like
conducting channels of PdTe$_2$ in Ta$_4$Pd$_3$Te$_{16}$ make a significant
anisotropy of the in-plane Fermi velocity. We suggest at least one anisotropic
superconducting gap with gap minima or possible node exists in this multiband
system. In addition, elongated vortices are observed with an anisotropy of
$\xi_{\parallel b}/\xi_{\perp b}\approx 2.5$. Clear Caroli-de-Gennes-Matricon
states are also observed within the vortex cores. Our results will initiate the
study on the elongated vortices and superconducting mechanism in the new
superconductor Ta$_4$Pd$_3$Te$_{16}$.",1412.3993v1
2015-02-03,Transitions to valence-bond solid order in a honeycomb lattice antiferromagnet,"We use Quantum Monte-Carlo methods to study the ground state phase diagram of
a S=1/2 honeycomb lattice magnet in which a nearest-neighbor antiferromagnetic
exchange J (favoring N\'eel order) competes with two different multi-spin
interaction terms: a six-spin interaction Q_3 that favors columnar valence-bond
solid (VBS) order, and a four-spin interaction Q_2 that favors staggered VBS
order. For Q_3 ~ Q_2 >> J, we establish that the competition between the two
different VBS orders stabilizes N\'eel order in a large swathe of the phase
diagram even when J is the smallest energy-scale in the Hamiltonian. When Q_3
>> (Q_2,J) (Q_2 >> (Q_3,J)), this model exhibits at zero temperature phase
transition from the N\'eel state to a columnar (staggered) VBS state. We
establish that the N\'eel-columnar VBS transition is continuous for all values
of Q_2, and that critical properties along the entire phase boundary are
well-characterized by critical exponents and amplitudes of the non-compact CP^1
(NCCP^1) theory of deconfined criticality, similar to what is observed on a
square lattice. However, a surprising three-fold anisotropy of the phase of the
VBS order parameter at criticality, whose presence was recently noted at the
Q_2=0 deconfined critical point, is seen to persist all along this phase
boundary. We use a classical analogy to explore this by studying the critical
point of a three-dimensional XY model with a four-fold anisotropy field which
is known to be weakly irrelevant at the three-dimensional XY critical point. In
this case, we again find that the critical anisotropy appears to saturate to a
nonzero value over the range of sizes accessible to our simulations.",1502.01035v1
2015-03-25,Anisotropy of Thermal Conductivity of Free-Standing Reduced Graphene Oxide Films Annealed at High Temperature,"We investigated thermal conductivity of free-standing reduced graphene oxide
films subjected to a high-temperature treatment of up to 1000 C. It was found
that the high-temperature annealing dramatically increased the in-plane thermal
conductivity, K, of the films from 3 W/mK to 61 W/mK at room temperature. The
cross-plane thermal conductivity, Kc, revealed an interesting opposite trend of
decreasing to a very small value of 0.09 W/mK in the reduced graphene oxide
films annealed at 1000 C. The obtained films demonstrated an exceptionally
strong anisotropy of the thermal conductivity, K/Kc ~ 675, which is
substantially larger even than in the high-quality graphite. The electrical
resistivity of the annealed films reduced to 1 - 19 Ohms/sq. The observed
modifications of the in-plane and cross-plane thermal conductivity components
resulting in an unusual K/Kc anisotropy were explained theoretically. The
theoretical analysis suggests that K can reach as high as ~500 W/mK with the
increase in the sp2 domain size and further reduction of the oxygen content.
The strongly anisotropic heat conduction properties of these films can be
useful for applications in thermal management.",1503.07239v1
2015-05-05,Elastic anisotropy and Poisson's ratio of solid helium under pressure,"The elastic moduli, elastic anisotropy coefficients, sound velocities and
Poisson's ratio of hcp solid helium have been calculated using density
functional theory in generalized gradient approximation (up to $30$ TPa), and
pair+triple semi-empirical potentials (up to 100 GPa). Zero-point vibrations
have been treated in the Debye approximation assuming $^4$He isotope (we
exclude the quantum-crystal region at very low pressures from consideration).
Both methods give a reasonable agreement with the available experimental data.
Our calculations predict significant elastic anisotropy of helium ($\triangle P
\approx 1.14$, $\triangle S_1 \approx 1.7$, $\triangle S_2 \approx 0.93$ at low
pressures). Under terapascal pressures helium becomes more elastically
isotropic. At the metallization point there is a sharp feature in the elastic
modulus $C_S$, which is the stiffness with respect to the isochoric change of
the $c/a$ ratio. This is connected with the previously obtained sharp minimum
of the $c/a$ ratio at the metallization point.
  Our calculations confirm the previously measured decrease of the Poisson's
ratio with increasing pressure. This is not a quantum effect, as the same sign
of the pressure effect was obtained when we disregarded zero-point vibrations.
At TPa pressures Poisson's ratio reaches the value of $0.31$ at the theoretical
metallization point ($V_{mol}=0.228$ cm$^3$/mol, $p=17.48$ TPa) and $0.29$ at
30 TPa. For $p=0$ we predict a Poisson's ratio of $0.38$ which is in excellent
agreement with the low-$p$-low-$T$ experimental data.",1505.00927v3
2015-05-06,Anisotropy of the solar network magnetic field around the average supergranule,"Supergranules in the quiet Sun are outlined by a web-like structure of
enhanced magnetic field strength, the so-called magnetic network. We aim to map
the magnetic network field around the average supergranule near disk center. We
use observations of the line-of-sight component of the magnetic field from the
Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory
(SDO). The average supergranule is constructed by coaligning and averaging over
3000 individual supergranules. We determine the positions of the supergranules
with an image segmentation algorithm that we apply on maps of the horizontal
flow divergence measured using time-distance helioseismology. In the center of
the average supergranule the magnetic (intranetwork) field is weaker by about
2.2 Gauss than the background value (3.5 Gauss), whereas it is enhanced in the
surrounding ring of horizontal inflows (by about 0.6 Gauss on average). We find
that this network field is significantly stronger west (prograde) of the
average supergranule than in the east (by about 0.3 Gauss). With time-distance
helioseismology, we find a similar anisotropy. The observed anisotropy of the
magnetic field adds to the mysterious dynamical properties of solar
supergranulation.",1505.01427v2
2015-05-11,Biases in the determination of dynamical parameters of star clusters: today and in the Gaia era,"The structural and dynamical properties of star clusters are generally
derived by means of the comparison between steady-state analytic models and the
available observables. With the aim of studying the biases of this approach, we
fitted different analytic models to simulated observations obtained from a
suite of direct N-body simulations of star clusters in different stages of
their evolution and under different levels of tidal stress to derive mass, mass
function and degree of anisotropy. We find that masses can be
under/over-estimated up to 50% depending on the degree of relaxation reached by
the cluster, the available range of observed masses and distances of radial
velocity measures from the cluster center and the strength of the tidal field.
The mass function slope appears to be better constrainable and less sensitive
to model inadequacies unless strongly dynamically evolved clusters and a
non-optimal location of the measured luminosity function are considered. The
degree and the characteristics of the anisotropy developed in the N-body
simulations are not adequately reproduced by popular analytic models and can be
detected only if accurate proper motions are available. We show how to reduce
the uncertainties in the mass, mass-function and anisotropy estimation and
provide predictions for the improvements expected when Gaia proper motions will
be available in the near future.",1505.02598v1
2015-05-21,Radially anisotropic systems with $r^{-α}$ forces: equilibrium states,"We continue the study of collisionless systems governed by additive
$r^{-\alpha}$ interparticle forces by focusing on the influence of the force
exponent $\alpha$ on radial orbital anisotropy. In this preparatory work we
construct the radially anisotropic Osipkov-Merritt phase-space distribution
functions for self-consistent spherical Hernquist models with $r^{-\alpha}$
forces and $1\leq\alpha<3$. The resulting systems are isotropic at the center
and increasingly dominated by radial orbits at radii larger than the anisotropy
radius $r_a$. For radially anisotropic models we determine the minimum value of
the anisotropy radius $r_{ac}$ as a function of $\alpha$ for phase-space
consistency (such that the phase-space distribution function is nowhere
negative for $r_a\geq r_{ac}$). We find that $r_{ac}$ decreases for decreasing
$\alpha$, and that the amount of kinetic energy that can be stored in the
radial direction relative to that stored in the tangential directions for
marginally consistent models increases for decreasing $\alpha$. In particular,
we find that isotropic systems are consistent in the explored range of
$\alpha$. By means of direct $N$-body simulations we finally verify that the
isotropic systems are also stable.",1505.05713v1
2015-05-27,Full-Wave Algorithm to Model Effects of Bedding Slopes on the Response of Subsurface Electromagnetic Geophysical Sensors near Unconformities,"We propose a full-wave pseudo-analytical numerical electromagnetic (EM)
algorithm to model subsurface induction sensors, traversing planar-layered
geological formations of arbitrary EM material anisotropy and loss, which are
used, for example, in the exploration of hydrocarbon reserves. Unlike past
pseudo-analytical planar-layered modeling algorithms that impose parallelism
between the formation's bed junctions however, our method involves judicious
employment of Transformation Optics techniques to address challenges related to
modeling relative slope (i.e., tilting) between said junctions (including
arbitrary azimuth orientation of each junction). The algorithm exhibits this
flexibility, both with respect to loss and anisotropy in the formation layers
as well as junction tilting, via employing special planar slabs that coat each
""flattened"" (i.e., originally tilted) planar interface, locally redirecting the
incident wave within the coating slabs to cause wave fronts to interact with
the flattened interfaces as if they were still tilted with a specific,
user-defined orientation. Moreover, since the coating layers are homogeneous
rather than exhibiting continuous material variation, a minimal number of these
layers must be inserted and hence reduces added simulation time and
computational expense. As said coating layers are not reflectionless however,
they do induce artificial field scattering that corrupts legitimate field
signatures due to the (effective) interface tilting. Numerical results, for two
half-spaces separated by a tilted interface, quantify error trends versus
material and sensor characteristics. We finally exhibit responses of sensors
traversing three-layered media, where we vary the anisotropy, loss, and
relative tilting of the formations and explore the sensitivity of the sensor's
complex-valued measurements.",1505.07407v2
2015-06-12,Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures,"Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts
extensive attentions due to its non-volatility, high density and low power
consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel
junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well
as a large value of perpendicular magnetic anisotropy (PMA). It has been
experimentally proven that a capping layer coating on CoFeB layer is essential
to obtain a strong PMA. However, the physical mechanism of such effect remains
unclear. In this paper, we investigate the origin of the PMA in
MgO/CoFe/metallic capping layer structures by using a first-principles
computation scheme. The trend of PMA variation with different capping materials
agrees well with experimental results. We find that interfacial PMA in the
three-layer structures comes from both the MgO/CoFe and CoFe/capping layer
interfaces, which can be analyzed separately. Furthermore, the PMAs in the
CoFe/capping layer interfaces are analyzed through resolving the magnetic
anisotropy energy by layer and orbital. The variation of PMA with different
capping materials is attributed to the different hybridizations of both d and p
orbitals via spin-orbital coupling. This work can significantly benefit the
research and development of nanoscale STT-MRAM.",1506.04078v4
2015-06-15,Spin-Induced Polarizations and Non-Reciprocal Directional Dichroism of Multiferroic BiFeO$_3$,"A microscopic model for the room-temperature multiferroic BiFeO$_3$ that
includes two Dzyaloshinskii-Moriya interactions and single-ion anisotropy along
the ferroelectric polarization predicts both the zero-field spectroscopic modes
as well as their splitting and evolution in a magnetic field. Due to
simultaneously broken time-reversal and spatial-inversion symmetries, the
absorption of light changes as the magnetic field or the direction of light
propagation is reversed. We discuss three physical mechanisms that may
contribute to this absorption asymmetry known as non-reciprocal directional
dichroism: the spin current, magnetostriction, and single-ion anisotropy. We
conclude that the non-reciprocal directional dichroism in \BF is dominated by
the spin-current polarization and is insensitive to the magnetostriction and
easy-axis anisotropy. With three independent spin-current parameters, our model
accurately describes the non-reciprocal directional dichroism observed for
magnetic field along $[1,-1,0]$. Since some modes are almost transparent to
light traveling in one direction but opaque for light traveling in the opposite
direction, BiFeO$_3$ can be used as a room-temperature optical diode at certain
frequencies in the GHz to THz range. Our work demonstrates that an analysis of
the non-reciprocal directional dichroism spectra based on an effective spin
model supplemented by first-principles calculations can produce a quantitative
microscopic theory of the magnetoelectric couplings in multiferroic materials.",1506.04595v2
2015-06-17,Stellar Velocity Dispersion and Anisotropy of the Milky Way Inner Halo,"We measure the three components of velocity dispersion,
$\sigma_{R},\sigma_{\theta},\sigma_{\phi}$, for stars within 6 < R < 30 kpc of
the Milky Way using a new radial velocity sample from the MMT telescope. We
combine our measurements with previously published data so that we can more
finely sample the stellar halo. We use a maximum likelihood statistical method
for estimating mean velocities, dispersions, and covariances assuming only that
velocities are normally distributed. The alignment of the velocity ellipsoid is
consistent with a spherically symmetric gravitational potential. From the
spherical Jeans equation, the mass of the Milky Way is M(<12 kpc) =
$1.3\times10^{11}$ M$_{\odot}$ with an uncertainty of 40%. We also find a
region of discontinuity, 15 < R < 25 kpc, where the estimated velocity
dispersions and anisotropies diverge from their anticipated values, confirming
at high significance the break observed by others. We argue that this break in
anisotropy is physically explained by coherent stellar velocity structure in
the halo, such as the Sgr stream. To significantly improve our understanding of
halo kinematics will require combining radial velocities with future Gaia
proper motions.",1506.05369v2
2015-06-21,Fast magnetic field amplification in the early Universe: growth of collisionless plasma instabilities in turbulent media,"In this work we report a numerical study of the cosmic magnetic field
amplification due to collisionless plasma instabilities. The collisionless
magnetohydrodynamic equations derived account for the pressure anisotropy that
leads, in specific conditions, to the firehose and mirror instabilities. We
study the time evolution of seed fields in turbulence under the influence of
such instabilities. An approximate analytical time evolution of magnetic field
is provided. The numerical simulations and the analytical predictions are
compared. We found that i) amplification of magnetic field was efficient in
firehose unstable turbulent regimes, but not in the mirror unstable models, ii)
the growth rate of the magnetic energy density is much faster than the
turbulent dynamo, iii) the efficient amplification occurs at small scales. The
analytical prediction for the correlation between the growth timescales with
pressure anisotropy ratio is confirmed by the numerical simulations. These
results reinforce the idea that pressure anisotropies - driven naturally in a
turbulent collisionless medium, e.g. the intergalactic medium -, could
efficiently amplify the magnetic field in the early Universe
(post-recombination era), previous to the collapse of the first large-scale
gravitational structures. This mechanism, though fast for the small scale
fields ($\sim$kpc scales), is however unable to provide relatively strong
magnetic fields at large scales. Other mechanisms that were not accounted here
(e.g., collisional turbulence once instabilities are quenched, velocity shear,
or gravitationally induced inflows of gas into galaxies and clusters) could
operate afterwards to build up large scale coherent field structures in the
long time evolution.",1506.06398v1
2015-06-23,Breakdown of long-wavelength magnons in cubic antiferromagnets with dipolar forces at small temperature,"Using $1/S$ expansion, we discuss the magnon spectrum of Heisenberg
antiferromagnet (AF) on a simple cubic lattice with small dipolar interaction
at small temperature $T\ll T_N$, where $T_N$ is the Neel temperature. Similar
to 3D and 2D ferromagnets, quantum and thermal fluctuations renormalize greatly
the bare gapless spectrum leading to a gap $\Delta\sim \omega_0$, where
$\omega_0$ is the characteristic dipolar energy. This gap is accompanied by
anisotropic corrections to the free energy which make the cube edges easy
directions for the staggered magnetization (dipolar anisotropy). In accordance
with previous results, we find that dipolar forces split the magnon spectrum
into two branches. This splitting makes possible two types of processes which
lead to a considerable enhance of the damping compared to the Heisenberg AF: a
magnon decay into two other magnons and a confluence of two magnons. It is
found that magnons are well defined quasiparticles in quantum AF. We
demonstrate however that a small fraction of long-wavelength magnons can be
overdamped in AFs with $S\gg1$ and in quantum AFs with a single-ion anisotropy
competing with the dipolar anisotropy. Particular materials are pointed out
which can be suitable for experimental observation of this long-wavelength
magnons breakdown that contradicts expectation of the quasiparticle concept.",1506.06989v2
2015-06-25,The importance of XY anisotropy in Sr2IrO4 revealed by magnetic critical scattering experiments,"The magnetic critical scattering in Sr$_2$IrO$_4$ has been characterized
using X-ray resonant magnetic scattering (XRMS) both below and above the 3D
antiferromagnetic ordering temperature, T$_{\text{N}}$. The order parameter
critical exponent below T$_{\text{N}}$ is found to be \beta=0.195(4), in the
range of the 2D XYh$_4$ universality class. Over an extended temperature range
above T$_{\text{N}}$, the amplitude and correlation length of the intrinsic
critical fluctuations are well described by the 2D Heisenberg model with XY
anisotropy. This contrasts with an earlier study of the critical scattering
over a more limited range of temperature which found agreement with the theory
of the isotropic 2D Heisenberg quantum antiferromagnet, developed to describe
the critical fluctuations of the conventional Mott insulator La$_2$CuO$_4$ and
related systems. Our study therefore establishes the importance of XY
anisotropy in the low-energy effective Hamiltonian of Sr$_2$IrO$_4$, the
prototypical spin-orbit Mott insulator.",1506.07720v1
2015-07-15,Self-consistent triaxial models,"We present self-consistent triaxial stellar systems that have analytic
distribution functions (DFs) expressed in terms of the actions. These provide
triaxial density profiles with cores or cusps at the centre. They are the first
self-consistent triaxial models with analytic DFs suitable for modelling giant
ellipticals and dark haloes. Specifically, we study triaxial models that
reproduce the Hernquist profile from Williams & Evans (2015), as well as
flattened isochrones of the form proposed by Binney (2014). We explore the
kinematics and orbital structure of these models in some detail. The models
typically become more radially anisotropic on moving outwards, have velocity
ellipsoids aligned in Cartesian coordinates in the centre and aligned in
spherical polar coordinates in the outer parts.
  In projection, the ellipticity of the isophotes and the position angle of the
major axis of our models generally changes with radius. So, a natural
application is to elliptical galaxies that exhibit isophote twisting. As
triaxial St\""ackel models do not show isophote twists, our DFs are the first to
generate mass density distributions that do exhibit this phenomenon, typically
with a gradient of $\approx 10^\circ$/effective radius, which is comparable to
the data.
  Triaxiality is a natural consequence of models that are susceptible to the
radial orbit instability. We show how a family of spherical models with
anisotropy profiles that transition from isotropic at the centre to radially
anisotropic becomes unstable when the outer anisotropy is made sufficiently
radial. Models with a larger outer anisotropy can be constructed but are found
to be triaxial. We argue that the onset of the radial orbit instability can be
identified with the transition point when adiabatic relaxation yields strongly
triaxial rather than weakly spherical endpoints.",1507.04129v1
2015-07-16,"Importance of Fermi Surface Topology for In-Plane Resistivity Anisotropy in Hole- and Electron-Doped Ba(Fe$_{1-x}$TM$_{x}$)$_2$As$_2$ (TM=Cr, Mn and Co)","The in-plane anisotropy of resistivity has been investigated for
Ba(Fe$_{1-x}$TM$_{x}$)$_2$As$_2$ (TM-Ba122, TM$=$Cr, Mn, and Co) where the
substitution sites are the same but the doped carriers are different for
different TM elements. The Hall coefficient measurements indicated that hole
carriers are effectively doped by Cr substitution but not by Mn substitution.
It has been found that the resistivity difference $\Delta\rho=\rho_{\rm
b}-\rho_{\rm a}$ in the antiferromagnetic-orthorhombic (AFO) phase of Cr-Ba122
is initially positive but it turns to negative with increasing Cr content,
whereas the positive $\Delta\rho$ monotonically increases with Mn substitution
in Mn-Ba122. In the paramagnetic-tetragonal phase, $\Delta\rho$ is always
positive, but it decreases with substitution in Cr-Ba122, in contrast to the
electron-doped case. These results demonstrate that the resistivity anisotropy
exhibits electron-hole asymmetry in both AFO and nematic phases and that it
depends on the Fermi surface topology whether the carrier scattering results in
a positive or negative $\Delta\rho$.",1507.04519v2
2015-07-27,Constraints on the Early and Late Integrated Sachs-Wolfe effects from Planck 2015 Cosmic Microwave Background Anisotropies angular power spectra,"The Integrated Sachs-Wolfe (ISW) effect predicts additional anisotropies in
the Cosmic Microwave Background due to time variation of the gravitational
potential when the expansion of the universe is not matter dominated. The ISW
effect is therefore expected in the early universe, due to the presence of
relativistic particles at recombination, and in the late universe, when dark
energy starts to dominate the expansion. Deviations from the standard picture
can be parameterized by $A_{e\text{ISW}}$ and $A_{l\text{ISW}}$, which rescale
the overall amplitude of the early and late ISW effects. Analyzing the most
recent CMB temperature spectra from the Planck 2015 release, we detect the
presence of the early ISW at high significance with $A_{e\mathrm{ISW}} =
1.06\pm0.04$ at 68% CL and an upper limit for the late ISW of
$A_{l\mathrm{ISW}} < 1.1$ at 95% CL. The inclusion of the recent polarization
data from the Planck experiment results in $A_{e\mathrm{ISW}} = 0.999\pm0.028$
at 68% CL, in better agreement with the value $A_{e\mathrm{ISW}} = 1$ of a
standard cosmology. When considering the recent detections of the late ISW
coming from correlations between CMB temperature anisotropies and weak lensing,
a value of $A_{l\mathrm{ISW}}=0.85\pm0.21$ is predicted at 68% CL, showing a
$4\sigma$ evidence. We discuss the stability of our result in the case of an
extra relativistic energy component parametrized by the effective neutrino
number $N_\mathrm{eff}$ and of a CMB lensing amplitude $A_\mathrm{L}$.",1507.07586v2
2015-07-28,Structural properties of non-spherical dark halos in Milky Way and Andromeda dwarf spheroidal galaxies,"We investigate the non-spherical density structure of dark halos of the dwarf
spheroidal (dSph) galaxies in the Milky Way and Andromeda galaxies based on
revised axisymmetric mass models from our previous work. The models we adopt
here fully take into account velocity anisotropy of tracer stars confined
within a flattened dark halo. Applying our models to the available kinematic
data of the 12 bright dSphs, we find that these galaxies associate with, in
general, elongated dark halos, even considering the effect of this velocity
anisotropy of stars. We also find that the best-fit parameters, especially for
the shapes of dark halos and velocity anisotropy, are susceptible to both the
availability of velocity data in the outer regions and the effect of the lack
of sample stars in each spatial bin. Thus, to obtain more realistic limits on
dark halo structures, we require photometric and kinematic data over much
larger areas in the dSphs than previously explored. The results obtained from
the currently available data suggest that the shapes of dark halos in the dSphs
are more elongated than those of $\Lambda$CDM subhalos. This mismatch needs to
be solved by theory including baryon components and the associated feedback to
dark halos as well as by further observational limits in larger areas of dSphs.
It is also found that more diffuse dark halos may have undergone consecutive
star formation history, thereby implying that dark-halo structure plays an
important role in star formation activity.",1507.07620v2
2015-08-11,Haloes light and dark: dynamical models of the stellar halo and constraints on the mass of the Galaxy,"We develop a flexible set of action-based distribution functions (DFs) for
stellar haloes. The DFs have five free parameters, controlling the inner and
outer density slope, break radius, flattening and anisotropy respectively. The
DFs generate flattened stellar haloes with a rapidly varying logarithmic slope
in density, as well as a spherically aligned velocity ellipsoid with a long
axis that points towards the Galactic centre - all attributes possessed by the
stellar halo of the Milky Way. We use our action-based distribution function to
model the blue horizontal branch stars extracted from the Sloan Digital Sky
Survey as stellar halo tracers in a spherical Galactic potential. As the
selection function is hard to model, we fix the density law from earlier
studies and solve for the anisotropy and gravitational potential parameters.
Our best fit model has a velocity anisotropy that becomes more radially
anisotropic on moving outwards. It changes from $\beta \approx 0.4$ at
Galactocentric radius of 15 kpc to $\approx 0.7$ at 60 kpc. This is a gentler
increase than is typically found in simulations of stellar haloes built from
the mutiple accretion of smaller systems. We find the potential corresponds to
an almost flat rotation curve with amplitude of $\approx 200$ kms$^{-1}$ at
these distances. This implies an enclosed mass of $\approx 4.5 \times 10^{11}
M_\odot$ within a spherical shell of radius 50 kpc.",1508.02584v2
2015-08-11,Donor Wavefunctions in Si Gauged by STM Images,"The triumph of effective mass theory in describing the energy spectrum of
dopants does not guarantee that the model wavefunctions will withstand an
experimental test. Such wavefunctions have recently been probed by scanning
tunneling spectroscopy, revealing localized patterns of resonantly enhanced
tunneling currents. We show that the shape of the conducting splotches resemble
a cut through Kohn-Luttinger (KL) hydrogenic envelopes, which modulate the
interfering Bloch states of conduction electrons. All the non-monotonic
features of the current profile are consistent with the charge density
fluctuations observed between successive {001} atomic planes, including a
counterintuitive reduction of the symmetry - a heritage of the lowered point
group symmetry at these planes. A model-independent analysis of the diffraction
figure constrains the value of the electron wavevector to $k_0 = (0.82 \pm
0.03)(2\pi/a_{Si})$. Unlike prior measurements, averaged over a sizeable
density of electrons, this estimate is obtained directly from isolated
electrons. We further investigate the model-specific anisotropy of the wave
function envelope, related to the effective mass anisotropy. This anisotropy
appears in the KL variational wave function envelope as the ratio between Bohr
radii b=a. We demonstrate that the central cell corrected estimates for this
ratio are encouragingly accurate, leading to the conclusion that the KL theory
is a valid model not only for energies but for wavefunctions as well.",1508.02772v1
2015-08-18,"Determination of the blocking temperature of magnetic nanoparticles: The good, the bad and the ugly","In a magnetization vs. temperature (M vs. T) experiment, the blocking region
of a magnetic nanoparticle (MNP) assembly is the interval of T values were the
system begins to respond to an applied magnetic field H when heating the sample
from the lower reachable temperature. The location of this region is determined
by the anisotropy energy barrier depending on the applied field H, the volume
V, the magnetic anisotropy constant K of the MNPs and the observing time of the
technique. In the general case of a polysized sample, a representative blocking
temperature value $T_B$ can be estimated from ZFC-FC experiments as a way to
determine the effective anisotropy constant.
  In this work, a numerical solved Stoner-Wolfharth two level model with
thermal agitation is used to simulate ZFC-FC curves of monosized and polysized
samples and to determine the best method for obtaining a representative $T_B$
value of polysized samples. The results corroborate a technique based on the T
derivative of the difference between ZFC and FC curves proposed by Micha et
al(the good) and demonstrate its relation with two alternative methods: the ZFC
maximum (the bad) and inflection point (the ugly). The derivative method is
then applied to experimental data, obtaining the $T_B$ distribution of a
polysized $Fe_3O_4$ MNP sample suspended in hexane with an excellent agreement
with TEM characterization.",1508.04413v1
2015-09-15,Domain-resolved room-temperature magneto-electric coupling in manganite-titanate heterostructures,"We present a model artificial multiferroic system consisting of a
(011)-oriented ferroelectric Pb(Mg,Nb,Ti)O$_3$ substrate intimately coupled to
a ferromagnetic (La,Sr)MnO$_3$ film through epitaxial strain and converse
piezoelectric effects. Electric field pulse sequences of less than 6 kV/cm were
shown to induce large reversible and bistable remanent strains in the manganite
film. Magnetic hysteresis loops demonstrate that the changes in strain states
result in significant changes in magnetic anisotropy from a highly anisotropic
two-fold magnetic symmetry to a more isotropic one. Such changes in magnetic
anisotropy are reversible upon multiple cycles and are stable at zero applied
electric field, and are accompanied by large changes in resistivity. We
directly image the change between the two-fold and isotropic magnetic
configurations at the scale of a single ferromagnetic domain using X-ray
photoemission electron microscopy as a function of applied electric field
pulses. Imaging the domain reversal process as a function of electric field
shows that the energy barrier for magnetization reversal is drastically
lowered, by up to 70% as determined from free energy calculations, through the
anisotropic strain change generated by the ferroelectric substrate. Thus, an
electric field pulse can be used to 'set' and 'reset' the magnetic anisotropy
orientation and resistive state in the film, as well as lowering the coercive
field required to reverse magnetization, showing a promising route towards
electric-field manipulation of multifunctional nanostructures at room
temperature.",1509.04775v1
2015-09-23,Anisotropic hyperfine interactions in FeP studied by 57Fe Mossbauer spectroscopy and 31P NMR,"We report results of 57Fe Mossbauer and 31P NMR studies of a phosphide FeP
powder sample performed in a wide temperature range including the point (TN ~
120 K) of magnetic phase transitions. The 57Fe Mossbauer spectra at low
temperatures T < TN consist of very diffuse Zeeman pattern with line
broadenings and sizeable spectral asymmetry. It was shown that the change of
the observed spectral shape is consistent with the transition into the space
modulated helicoidal magnetic structure. Analysis of the experimental spectra
was carried out assuming the anisotropy of the magnetic hyperfine field Hhf at
the 57Fe nuclei when the Fe3+ magnetic moment rotates with respect to the
principal axis of the electric field gradient (EFG) tensor. The obtained large
temperature independent anharmonicity parameter m ~ 0.96 of the helicoidal spin
structure results from easy-axis anisotropy in the plane of the iron spin
rotation. It was assumed that the very low maximal value of Hhf(11K) ~ 36 kOe
and its high anisotropy delta_Hanis(11K) ~ 30 kOe can be attributed to the
stabilization of iron cations in the low-spin state (SFe = 1/2). The 31P NMR
measurements demonstrate an extremely broad linewidth reflecting the spatial
distribution of the transferred internal magnetic fields of the Fe3+ ions onto
P sites in the magnetically ordered state.",1509.06953v2
2015-10-07,Large scale CMB anomalies from thawing cosmic strings,"Cosmic strings formed during inflation are expected to be either diluted over
super-Hubble distances, i.e., invisible today, or to have crossed our past
light cone very recently. We discuss the latter situation in which a few
strings imprint their signature in the Cosmic Microwave Background (CMB)
Anisotropies after recombination. Being almost frozen in the Hubble flow, these
strings are quasi static and evade almost all of the previously derived
constraints on their tension while being able to source large scale
anisotropies in the CMB sky. Using a local variance estimator on thousand of
numerically simulated Nambu-Goto all sky maps, we compute the expected signal
and show that it can mimic a dipole modulation at large angular scales while
being negligible at small angles. Interestingly, such a scenario generically
produces one cold spot from the thawing of a cosmic string loop. Mixed with
anisotropies of inflationary origin, we find that a few strings of tension GU =
O(1) x 10^(-6) match the amplitude of the dipole modulation reported in the
Planck satellite measurements and could be at the origin of other large scale
anomalies.",1510.01916v2
2015-11-14,Anisotropies of gravitational-wave standard sirens as a new cosmological probe without redshift information,"Gravitational waves (GWs) from compact binary stars at cosmological distances
are promising and powerful cosmological probes, referred to as the GW standard
sirens. With future GW detectors, we will be able to precisely measure source
luminosity distances out to a redshift $z\sim5$. To extract cosmological
information, previously proposed cosmological studies using the GW standard
sirens rely on source redshift information obtained through an extensive
electromagnetic follow-up campaign. However, the redshift identification is
typically time consuming and rather challenging. Here, we propose a novel
method for cosmology with the GW standard sirens free from the redshift
measurements. Utilizing the anisotropies of the number density and luminosity
distances of compact binaries originated from the large-scale structure, we
show that, once GW observations will be well established in the future, (i)
these anisotropies can be measured even at very high redshifts ($z\geq 2$),
where the identification of the electromagnetic counterpart is difficult, (ii)
the expected constraints on the primordial non-Gaussianity with the Einstein
Telescope would be comparable to or even better than the other large-scale
structure probes at the same epoch, and (iii) the cross-correlation with other
cosmological observations is found to have high-statistical significance,
providing additional cosmological information at very high redshifts.",1511.04638v2
2015-11-18,Nonadiabatic bounce and an inflationary phase in the quantum mixmaster universe,"Following our previous paper, Bergeron et al, Smooth quantum dynamics of the
mixmaster universe, Phys. Rev. D 92, 061302(R) (2015), concerning the
quantization of the vacuum Bianchi IX model and the Born-Huang-Oppenheimer
framework, we present a further analysis of the dynamical properties of the
model. Consistently with the deep quantum regime, we implement the harmonic
approximation of the anisotropy potential. We thus obtain manageable dynamical
equations. We study the quantum anisotropic oscillations during the bouncing
phase of the universe. Neglecting the backreaction from transitions between
quantum anisotropy states we obtain analytical results. In particular, we
identify a parameter which is associated with dynamical properties of the
quantum model and describes a sort of phase transition. Once the parameter
exceeds its critical value, the Born-Huang-Oppenheimer approximation breaks
down. The application of the present result to a simple model of the Universe
indicates that the parameter indeed exceeds its critical value and that there
takes place a huge production of anisotropy at the bounce. This in turn must
lead to a sustained phase of accelerated expansion, an inflationary phase. The
quantitative inclusion of backreaction shall be examined in a follow-up paper
based on the vibronic approach.",1511.05790v2
2016-01-06,Galaxy structure from multiple tracers: II. M87 from parsec to megaparsec scales,"Following a number of conflicting studies of M87's mass profile, we undertake
a dynamical analysis of multiple tracer populations to constrain its mass over
a large radius range. We combine stellar kinematics in the central regions with
the dynamics of 612 globular clusters out to 200 kpc and satellite galaxies
extending to scales comparable with the virial radius. Using a spherical Jeans
analysis, we are able to disentangle the mass contributions from the dark and
baryonic components and set constraints on the structure of each. Assuming
isotropy, we explore four different models for the dark matter halo and find
that a centrally-cored dark matter distribution is preferred. We infer a
stellar mass-to-light ratio $\Upsilon_{\star,v} = 6.9 \pm 0.1$ -- consistent
with a Salpeter-like IMF -- and a core radius $r_c = 67 \pm 20$ kpc. We then
introduce anisotropy and find that, while the halo remains clearly cored, the
radial stellar anisotropy has a strong impact on both $\Upsilon_{\star,v}$ and
the core's radius; here we find $\Upsilon_{\star,v} = 3.50_{-0.36}^{+0.32}$ --
consistent with a Chabrier-like IMF -- and $r_c = 19.00_{-8.34}^{+8.38}$ kpc.
Thus the presence of a core at the centre of the dark halo is robust against
anisotropy assumptions, while the stellar mass and core size are not. We are
able to reconcile previously discrepant studies by showing that modelling the
globular cluster data alone leads to the very different inference of a
super-NFW cusp, thus highlighting the value of multiple-population modelling,
and we point to the possible role of M87's AGN and the cluster environment in
forming the central dark matter core.",1601.01323v1
2016-01-23,Spectral imaging of galaxy clusters with Planck,"The Sunyaev-Zeldovich (SZ) effect is a promising tool for detecting the
presence of hot gas out to the galaxy cluster peripheries. We developed a
spectral imaging algorithm dedicated to the SZ observations of nearby galaxy
clusters with Planck, with the aim of revealing gas density anisotropies
related to the filamentary accretion of materials, or pressure discontinuities
induced by the propagation of shock fronts. To optimize an unavoidable
trade-off between angular resolution and precision of the SZ flux measurements,
the algorithm performs a multiscale analysis of the SZ maps as well as of other
extended components, such as the cosmic microwave background (CMB) anisotropies
and the Galactic thermal dust. The demixing of the SZ signal is tackled through
kernel weighted likelihood maximizations. The CMB anisotropies are further
analyzed through a wavelet analysis, while the Galactic foregrounds and SZ maps
are analyzed via a curvelet analysis that best preserves their anisotropic
details. The algorithm performance has been tested against mock observations of
galaxy clusters obtained by simulating the Planck High Frequency Instrument and
by pointing a few characteristic positions in the sky. These tests suggest that
Planck should easily allow us to detect filaments in the cluster peripheries
and detect large-scale shocks in colliding galaxy clusters that feature
favorable geometry.",1601.06323v1
2016-02-01,Derivation of anisotropic dissipative fluid dynamics from the Boltzmann equation,"Fluid-dynamical equations of motion can be derived from the Boltzmann
equation in terms of an expansion around a single-particle distribution
function which is in local thermodynamical equilibrium, i.e., isotropic in
momentum space in the rest frame of a fluid element. However, in situations
where the single-particle distribution function is highly anisotropic in
momentum space, such as the initial stage of heavy-ion collisions at
relativistic energies, such an expansion is bound to break down. Nevertheless,
one can still derive a fluid-dynamical theory, called anisotropic dissipative
fluid dynamics, in terms of an expansion around a single-particle distribution
function, $\hat{f}_{0\bf k}$, which incorporates (at least parts of) the
momentum anisotropy via a suitable parametrization. We construct such an
expansion in terms of polynomials in energy and momentum in the direction of
the anisotropy and of irreducible tensors in the two-dimensional momentum
subspace orthogonal to both the fluid velocity and the direction of the
anisotropy. From the Boltzmann equation we then derive the set of equations of
motion for the irreducible moments of the deviation of the single-particle
distribution function from $\hat{f}_{0\bf k}$. Truncating this set via the
14-moment approximation, we obtain the equations of motion of anisotropic
dissipative fluid dynamics.",1602.00573v2
2016-02-16,Theoretical study on the anisotropic electronic structure of antiferromagnetic BaFe$_2$As$_2$ and Co-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ seen by angle-resolved photoemission,"By means of one-step model calculations the strong in-plane anisotropy seen
in angle-resolved photoemission of the well-known iron pnictide prototype
compounds BaFe$_2$As$_2$ and Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ in their
low-temperature antiferromagnetic phases is investigated. The
fully-relativistic calculations are based on the Korringa-Kohn-Rostoker-Green
function approach combined with the coherent potential approximation alloy
theory to account for the disorder induced by Co substitution on Fe sites in a
reliable way. The results of the calculations can be compared directly to
experimental spectra of detwinned single crystals. One finds very good
agreement with experiment and can reveal all features of the electronic
structure contributing to the in-plane anisotropy. In particular the local
density approximation can capture most of the correlation effects for the
investigated system without the need for more advanced techniques. In addition,
the evolution of the anisotropy for increasing Co concentration $x$ in
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ can be tracked almost continuously. The results
are also used to discuss surface effects and it is possible to identify clear
signatures to conclude about different types of surface termination.",1602.05027v1
2016-02-24,Effects of low anisotropy on interacting holographic and new agegraphic scalar fields models of dark energy,"A spatially homogeneous and anisotropic Bianchi type I universe is studied
with the interacting holographic and new agegraphic scalar fields models of
dark energy.
  Given, the framework of the anisotropic model, both the dynamics and
potential of these scalar field models according to the evolutionary behavior
of both dark energy models are reconstructed. We also investigate the
cosmological evolution of interacting dark energy models, and compare it with
observational data and schematic diagram.
  In order to do so, we focus on observational determinations of the expansion
history $H(z)$. Next, we evaluate effects of anisotropy on various topics, such
as evolution of the growth of perturbations in the linear regime, statefinder
diagnostic, Sandage-Loeb (SL) test and distance modulus from holographic and
new agegraphic dark energy models and compare the results with standard FRW and
$\Lambda$CDM and $w$CDM models.
  Our numerical result show the effects of the interaction and anisotropy on
the evolutionary behavior the new agegraphic scalar field models",1602.07683v6
2016-03-02,Incommensurate--commensurate transitions in the mono-axial chiral helimagnet driven by the magnetic field,"The zero temperature phase diagram of the mono-axial chiral helimagnet in the
magnetic field plane formed by the components parallel and perpendicular to the
helical axis is thoroughly analyzed. The nature of the transition to the
commensurate state depends on the angle between the field and the helical axis.
For field directions close to the directions parallel or perpendicular to the
helical axis the transition is continuous, while for intermediate angles the
transition is discontinuous and the incommensurate and commensurate states
coexist on the transition line. The continuous and discontinuous transition
lines are separated by two tricritical points with specific singular behaviour.
The location of the continuous and discontinuous lines and of the tricritical
points depend strongly on the easy-plane anisotropy, the effect of which is
analyzed. For large anisotropy the conical approximation locates the transition
line very accurately, although it does not predict the continuous transitions
nor the tricitical behaviour. It is shown that for large anisotropy, as in
CrNb3S6, the form of the transition line is universal, that is, independent of
the sample, and obeys a simple equation. The position of the tricritical
points, which is not universal, is theoretically estimated for a sample of
CrNb3S6",1603.00755v1
2016-03-09,Primordial Magnetic Field Via Weibel Instability In The Quark Gluon Plasma Phase,"The origin of the observed large scale magnetic fields in the Universe is a
mystery. The seed of these magnetic fields has been attributed to physical
process in the early universe. In this work we provide a mechanism for the
generation of a primordial magnetic field in the early universe via the Weibel
instability in the quark gluon plasma. The Weibel instability occurs in the
plasma if there is an anisotropy in the particle distribution function of the
particles. In early universe, the velocity anisotropy required for Weibel
instability to operate is generated in the quark gluon plasma by the collapse
of closed $Z(3)$ domain walls that arise in the deconfined phase of the QCD
(above $T\sim 200$ MeV). Such large domains can arise in the context of certain
low energy scale inflationary models. The closed domains undergo supersonic
collapse and the velocity anisotropy is generated in the shocks produced in the
wake of the collapsing domain walls. This results in a two stream Weibel
instability in the ultra-relativistic quark gluon plasma. The instability in
turn generates strong magnetic fields in the plasma. We find that the field
strengths generated can be comparable to the equipartition energy density at
the QCD scale which is of the order of $10^{18}$ G.",1603.02852v2
2016-03-14,Rotational symmetry breaking in the topological superconductor Sr$_x$Bi$_2$Se$_3$ probed by upper-critical field experiments,"Recently it was demonstrated that Sr intercalation provides a new route to
induce superconductivity in the topological insulator Bi$_2$Se$_3$. Topological
superconductors are predicted to be unconventional, with mixed even and odd
parity Cooper pairs states. An adequate probe to test for unconventional
superconductivity is the upper critical field, $B_{c2}$. For a standard BCS
layered superconductor $B_{c2}$ shows an anisotropy when the magnetic field is
applied parallel and perpendicular to the layers, but is isotropic when the
field is rotated in the plane of the layers. Here we report measurements of the
upper critical field of superconducting Sr$_x$Bi$_2$Se$_3$ crystals ($T_c =
3.0$~K). Surprisingly, field-angle dependent magnetotransport measurements
reveal a large anisotropy of $B_{c2}$ when the magnet field is rotated in the
basal plane. The large two-fold anisotropy, while six-fold is anticipated,
cannot be explained with the Ginzburg-Landau anisotropic effective mass model
or flux flow induced by the Lorentz force. The rotational symmetry breaking of
$B_{c2}$ indicates unconventional superconductivity with an odd-parity
polarized triplet Cooper pair state ($\Delta_4$-pairing) recently proposed for
rhombohedral topological superconductors, or might have a structural nature,
such as self-organized stripe ordering of Sr atoms.",1603.04197v1
2016-03-21,NMR signal for particles diffusing under potentials: From path integrals and numerical methods to a new model of diffusion anisotropy,"We study the influence of diffusion on NMR experiments when the molecules
undergo random motion under the influence of a force field, and place special
emphasis on parabolic (Hookean) potentials. To this end, the problem is studied
using path integral methods. Explicit relationships are derived for commonly
employed gradient waveforms involving pulsed and oscillating gradients. The
Bloch-Torrey equation, describing the temporal evolution of magnetization, is
modified by incorporating potentials. A general solution to this equation is
obtained for the case of parabolic potential by adopting the multiple
correlation function (MCF) formalism, which has been used in the past to
quantify the effects of restricted diffusion. Both analytical and MCF results
were found to be in agreement with random walk simulations. A multi-dimensional
formulation of the problem is introduced that leads to a new characterization
of diffusion anisotropy. Unlike for the case of traditional methods that employ
a diffusion tensor, anisotropy originates from the tensorial force constant,
and bulk diffusivity is retained in the formulation. Our findings suggest that
some features of the NMR signal that have traditionally been attributed to
restricted diffusion are accommodated by the Hookean model. Under certain
conditions, the formalism can be envisioned to provide a viable approximation
to the mathematically more challenging restricted diffusion problems.",1603.06373v1
2016-04-06,Universal behavior of dense clusters of magnetic nanoparticles,"A detailed numerical simulation of quasistatic hysteresis loops of dense
clusters of interacting magnetic nanoparticles is carried out. Both clusters of
magnetically soft and magnetically hard nanoparticles are considered. The
clusters are characterized by an average particle diameter D, the cluster
radius Rc, the particle saturation magnetization Ms, and the uniaxial
anisotropy constant K. The number of particles in the cluster varies between Np
= 30 - 120. The particle centers are randomly distributed within the cluster,
their easy anisotropy axes being randomly oriented. It is shown that a rare
assembly of identical random clusters of magnetic nanoparticles can be
characterized by two dimensionless parameters: 1) the relative strength of
magneto-dipole interaction, K/Ms^2, and the average particle concentration
within the cluster, {\eta} = VNp/Vc. Here V is the nanoparticle volume, and Vc
is the volume of the cluster, respectively. In the strong interaction limit,
Ms*{\eta}/Ha >> 1, where Ha = 2K/Ms is the anisotropy field, the ultimate
hysteresis loops of dilute assemblies of clusters have been constructed. In the
variables (M/Ms, H/Ms) these hysteresis loops depend only on the particle
volume fraction {\eta}. In the weak interaction limit, Ms*{\eta}/Ha << 1, the
assembly hysteresis loops in the variables (M/Ms, H/Ha) are close to the
standard Stoner-Wohlfarth hysteresis loop.",1604.01705v1
2016-04-18,Anisotropic magnetization relaxation in ferromagnetic multilayers with variable interlayer exchange coupling,"The FMR linewidth and its anisotropy in F$_1$/f/F$_2$/AF multilayers, where
spacer f has a low Curie point compared to the strongly ferromagnetic F$_1$ and
F$_2$, is investigated. The role of the interlayer exchange coupling in
magnetization relaxation is determined experimentally by varying the thickness
of the spacer. It is shown that stronger interlayer coupling via thinner
spacers enhances the microwave energy exchange between the outer ferromagnetic
layers, with the magnetization of F$_2$ exchange-dragged by the resonance
precession in F$_1$. A weaker mirror effect is also observed: the magnetization
of F$_1$ can be exchange-dragged by the precession in F$_2$, which leads to
anti-damping and narrower FMR linewidths. A theory is developed to model the
measured data, which allows separating various contributions to the magnetic
relaxation in the system. Key physical parameters, such as the interlayer
coupling constant, in-plane anisotropy of the FMR linewidth, dispersion of the
magnetic anisotropy fields are quantified. These results should be useful for
designing high-speed magnetic nanodevices based on thermally-assisted
switching.",1604.05145v1
2016-04-19,Firehose constraints for the solar wind suprathermal electrons,"The indefinite increase of temperature predicted by the solar wind expansion
in the direction parallel to the interplanetary magnetic field is already
notorious for not being confirmed by the observations. In hot and dilute
plasmas from space particle-particle collisions are not efficient in
constraining large deviations from isotropy, but the resulting firehose
instability provides in this case plausible limitations for the temperature
anisotropy of the thermal (core) populations of both the electron and proton
species. The present paper takes into discussion the suprathermal (halo)
electrons, which are ubiquitous in the solar wind. Less dense but hotter than
the core, suprathermals may be highly anisotropic and susceptible to the
firehose instability. The main features of the instability are here derived
from a first-order theory for conditions specific to the suprathermal electrons
in the solar wind and terrestrial magnetospheres. Unveiled here, new regimes of
the electron firehose instability may be exclusively controlled by the
suprathermals. The instability is found to be systematically stimulated by the
suprathermal electrons, with thresholds that approach the limits of the
temperature anisotropy reported by the observations. These results represent
new and valuable evidences for the implication of the firehose instability in
the relaxation of the temperature anisotropy in space plasmas.",1604.05628v1
2016-04-20,Dipolar matter-wave solitons in two-dimensional anisotropic discrete lattices,"We numerically demonstrate two-dimensional (2D) matter-wave solitons in the
disk-shaped dipolar Bose-Einstein condensates (BECs) trapped in strongly
anisotropic optical lattices (OLs) in a disk's plane. The considered OLs are
square lattices which can be formed by interfering two pairs of plane waves
with different intensities. The hopping rates of the condensates between two
adjacent lattices in the orthogonal directions are different, which gives rise
to a linearly anisotropic system. We find that when the polarized orientation
of the dipoles is parallel to disk's plane with the same direction, the
combined effects of the linearly anisotropy and the nonlocal nonlinear
anisotropy strongly influence the formations, as well as the dynamics of the
lattice solitons. Particularly, the isotropy-pattern solitons (IPSs) are found
when these combined effects reach a balance. Motion, collision and rotation of
the IPSs are also studied in detail by means of systematic simulations. We
further find that these IPSs can move freely in the 2D anisotropic discrete
system, hence giving rise to an anisotropic effective mass. Four types of
collisions between the IPSs are identified. By rotating an external magnetic
field up to a critical angular velocity, the IPSs can still remain localized
and play as a breather. Finally, the influences from the combined effects
between the linear and the nonlocal nonlinear anisotropy with consideration of
the contact/local nonlinearity are discussed too.",1604.05798v2
2016-04-25,Origin of the mass splitting of azimuthal anisotropies in a multi-phase transport model,"Both hydrodynamics-based models and a multi-phase transport (AMPT) model can
reproduce the mass splitting of azimuthal anisotropy ($v_n$) at low transverse
momentum ($p_{\perp}$) as observed in heavy ion collisions. In the AMPT model,
however, $v_n$ is mainly generated by the parton escape mechanism, not by the
hydrodynamic flow. In this study we provide detailed results on the mass
splitting of $v_n$ in this transport model, including $v_2$ and $v_3$ of
various hadron species in d+Au and Au+Au collisions at the Relativistic Heavy
Ion Collider and p+Pb collisions at the Large Hadron Collider. We show that the
mass splitting of hadron $v_2$ and $v_3$ in AMPT first arises from the
kinematics in the quark coalescence hadronization process, and then, more
dominantly, comes from hadronic rescatterings, even though the contribution
from the latter to the overall charged hadron $v_n$ is small. We further show
that there is no qualitative difference between heavy ion collisions and
small-system collisions or between elliptic ($v_2$) and triangular ($v_3$)
anisotropies. Our studies thus demonstrate that the mass splitting of $v_2$ and
$v_3$ at low-$p_{\perp}$ is not a unique signature of hydrodynamic collective
flow but can be the interplay of several physics effects.",1604.07387v3
2016-05-04,The Influence of Temperature Anisotropies in Controlling the Development of Magnetospheric Substorms,"Ion anisotropies can affect a host of processes within the magnetosphere,
from modifying the growth rate of various instabilities to the energization and
mass transport within the magnetosphere. Global multi-fluid simulations using a
full treatment of the pressure tensor are used to evaluate the influence of
temperature anisotropies on the magnetospheric dynamics for an idealized
substorm. The simulations are able to resolve the development of conics over
the polar cap which eventually turn into beams in the lobes. Entry of this
plasma, particularly heavy ions with high Tparallel, leads to a faster
reconnection rate, additional turbulence within the reconnection region, and
the substorm onset time occurs approximately 5 min earlier relative to
isotropic simulations. The anisotropic treatment yields much more intense
auroral currents on the nightside associated with onset and a faster expansion
phase of the substorm. The plasma entering into the current sheet experiences
stronger heating in the anisotropic simulations, which increases plasma
transport into the equatorial dayside. Hence, the convection of the
plasmasphere towards the dayside magnetosphere during the growth phase is
accompanied by a relative increase in Tparallel. This leads to a very distinct
temperature profile on the dayside. The injection of the energetic particles
from the substorm leads to an overall increase Tperpendicular on the dayside,
but only O+ reaches sufficient energies for the bulk of these ions to be able
to cross noon local time during the expansion phase to participate in the
formation of symmetric ring current. The net effect from these processes is to
decrease the cross-polar cap potential, modify the timing of the development of
reconnection and the development of the auroral currents and enhance the
injection of energetic particles into the inner magnetosphere.",1605.01399v1
2016-05-07,Giant interfacial perpendicular magnetic anisotropy in MgO/CoFe/capping layer structures,"Magnetic tunnel junction (MTJ) based on CoFeB/MgO/CoFeB structures is of
great interest due to its application in the spin-transfer-torque magnetic
random access memory (STT-MRAM). Large interfacial perpendicular magnetic
anisotropy (PMA) is required to achieve high thermal stability. Here we use
first-principles calculations to investigate the magnetic anisotropy energy
(MAE) of MgO/CoFe/capping layer structures, where the capping materials include
5d metals Hf, Ta, Re, Os, Ir, Pt, Au and 6p metals Tl, Pb, Bi. We demonstrate
that it is feasible to enhance PMA by using proper capping materials.
Relatively large PMA is found in the structures with capping materials of Hf,
Ta, Os, Ir and Pb. More importantly, the MgO/CoFe/Bi structure gives rise to
giant PMA (6.09 mJ/m2), which is about three times larger than that of the
MgO/CoFe/Ta structure. The origin of the MAE is elucidated by examining the
contributions to MAE from each atomic layer and orbital. These findings provide
a comprehensive understanding of the PMA and point towards the possibility to
achieve advanced-node STT-MRAM with high thermal stability.",1605.02247v5
2016-05-17,Classical Monte Carlo study for antiferro quadrupole orders in a diamond lattice,"We investigate antiferro quadrupole orders in a diamond lattice under
magnetic fields by Monte Carlo simulations for two types of classical effective
models. One is an XY model with Z_3 anisotropy, and the other is a
two-component phi^4 model with a third-order anisotropy. We confirm that the
universality class of the zero-field transition is that for the
three-dimensional XY model. Magnetic field corresponds to a Z_3 field in the
effective model, and under this field, we find that collinear and canted
antiferro-quadrupole orders compete. Each phase is characterized by symmetry
breaking in the sector of (sublattice Z_2)x(reflection Z_2 for the order
parameter). When Z_3 anisotropy and magnetic field vary, it turns out that this
system is a good playground for various multicritical points; bicritical and
tetracritical points emerge in a finite field. Another important finding is
about the scaling of parasitic ferro quadrupole order at the zero-field
critical point. This is the secondary order parameter induced by the primary
antiferro order, and its critical exponent beta'=0.815 clearly differs from the
expected value that is twice the value for the primary order parameter. The
corresponding correlation length exponent is also different, nu'=0.597(12). We
also discuss relation of the present effective quadrupole models with the
3-state Potts model as well as implication to undertanding of orbital orders in
Pr-based 1-2-20 compounds.",1605.05175v2
2016-05-18,Structural and magnetic properties of FeMn$_x$ ($x=$1...6) chains supported on Cu$_2$N / Cu (100),"Heterogeneous atomic magnetic chains are built by atom manipulation on a
Cu$_2$N/Cu (100) substrate. Their magnetic properties are studied and
rationalized by a combined scanning tunneling microscopy (STM) and density
functional theory (DFT) work completed by model Hamiltonian studies. The chains
are built using Fe and Mn atoms ontop of the Cu atoms along the N rows of the
Cu$_2$N surface. Here, we present results for FeMn$_x$ ($x$=1...6) chains
emphasizing the evolution of the geometrical, electronic, and magnetic
properties with chain size. By fitting our results to a Heisenberg Hamiltonian
we have studied the exchange-coupling matrix elements $J$ for different chains.
For the shorter chains, $x \leq 2$, we have included spin-orbit effects in the
DFT calculations, extracting the magnetic anisotropy energy. Our results are
also fitted to a simple anisotropic spin Hamiltonian and we have extracted
values for the longitudinal-anisotropy $D$ and transversal-anisotropy $E$
constants. These parameters together with the values for $J$ allow us to
compute the magnetic excitation energies of the system and to compare them with
the experimental data.",1605.05464v1
2016-05-19,Extreme-value statistics from Lagrangian convex hull analysis for homogeneous turbulent Boussinesq convection and MHD convection,"We investigate the utility of the convex hull of many Lagrangian tracers to
analyze transport properties of turbulent flows with different anisotropy. In
direct numerical simulations of statistically homogeneous and stationary
Navier-Stokes turbulence, neutral fluid Boussinesq convection, and MHD
Boussinesq convection a comparison with Lagrangian pair dispersion shows that
convex hull statistics capture the asymptotic dispersive behavior of a large
group of passive tracer particles. Moreover, convex hull analysis provides
additional information on the sub-ensemble of tracers that on average disperse
most efficiently in the form of extreme value statistics and flow anisotropy
via the geometric properties of the convex hulls. We use the convex hull
surface geometry to examine the anisotropy that occurs in turbulent convection.
Applying extreme value theory, we show that the maximal square extensions of
convex hull vertices are well described by a classic extreme value
distribution, the Gumbel distribution. During turbulent convection,
intermittent convective plumes grow and accelerate the dispersion of Lagrangian
tracers. Convex hull analysis yields information that supplements standard
Lagrangian analysis of coherent turbulent structures and their influence on the
global statistics of the flow.",1605.05983v4
2016-05-21,Mott Transitions and Staggered Orders in the Three-component Fermionic System: Variational Cluster Approach,"The variational cluster approximation is used to study the ground-state
properties and single-particle spectra of the three-component fermionic Hubbard
model defined on the two-dimensional square lattice at half filling. First, we
show that either a paired Mott state or color-selective Mott state is realized
in the paramagnetic system, depending on the anisotropy in the interaction
strengths, except around the SU(3) symmetric point, where a paramagnetic
metallic state is maintained. Then, by introducing Weiss fields to observe
spontaneous symmetry breakings, we show that either a color-density-wave state
or color-selective antiferromagnetic state is realized depending on the
interaction anisotropy and that the first-order phase transition between these
two states occurs at the SU(3) point. We moreover show that these staggered
orders originate from the gain in potential energy (or Slater mechanism) near
the SU(3) point but originate from the gain in kinetic energy (or Mott
mechanism) when the interaction anisotropy is strong. The staggered orders near
the SU(3) point disappear when the next-nearest-neighbor hopping parameters are
introduced, indicating that these orders are fragile, protected only by the
Fermi surface nesting.",1605.06648v1
2016-05-23,Collisionless Isotropization of the Solar-Wind Protons by Compressive Fluctuations and Plasma Instabilities,"Compressive fluctuations are a minor yet significant component of
astrophysical plasma turbulence. In the solar wind, long-wavelength compressive
slow-mode fluctuations lead to changes in $\beta_{\parallel \mathrm p}\equiv
8\pi n_{\mathrm p}k_{\mathrm B}T_{\parallel \mathrm p}/B^2$ and in $R_{\mathrm
p}\equiv T_{\perp \mathrm p}/T_{\parallel \mathrm p}$, where $T_{\perp \mathrm
p}$ and $T_{\parallel \mathrm p}$ are the perpendicular and parallel
temperatures of the protons, $B$ is the magnetic field strength, and
$n_{\mathrm p}$ is the proton density. If the amplitude of the compressive
fluctuations is large enough, $R_{\mathrm p}$ crosses one or more instability
thresholds for anisotropy-driven microinstabilities. The enhanced field
fluctuations from these microinstabilities scatter the protons so as to reduce
the anisotropy of the pressure tensor. We propose that this scattering drives
the average value of $R_{\mathrm p}$ away from the marginal stability boundary
until the fluctuating value of $R_{\mathrm p}$ stops crossing the boundary. We
model this ""fluctuating-anisotropy effect"" using linear Vlasov--Maxwell theory
to describe the large-scale compressive fluctuations. We argue that this effect
can explain why, in the nearly collisionless solar wind, the average value of
$R_{\mathrm p}$ is close to unity.",1605.07143v2
2016-05-30,Suppressed magnetic circular dichroism and valley-selective magneto-absorption due to the effective mass anisotropy in bismuth,"We have measured the far-infrared reflectivity and Kerr angle spectra on a
high-quality crystal of pure semimetallic bismuth as a function of magnetic
field, from which we extract the conductivity for left- and right handed
circular polarisations. The high spectral resolution allows us to separate the
intraband Landau level transitions for electrons and holes. The hole transition
exhibits 100% magnetic circular dichroism, it appears only for one polarisation
as expected for a circular cyclotron orbit. However the dichroism for electron
transitions is reduced to only $13\pm 1$%, which is quantitatively explained by
the large effective mass anisotropy of the electron pockets of the Fermi
surface. This observation is a signature of the mismatch between the metric
experienced by the photons and the electrons. It allows for a contactless
measurement of the effective mass anisotropy and provides a direction towards
valley polarised magneto-optical pumping with elliptically polarised light.",1605.09224v2
2016-06-16,"Magnetic Properties from the Viewpoints of Electronic Hamiltonian: Spin Exchange Parameters, Spin Orientation and Spin-Half Misconception","In this chapter we review the quantitative and qualitative aspects of
describing the properties of magnetic solids on the basis of electronic
Hamiltonian. We show that a spin Hamiltonian approach becomes consistent with
an electronic Hamiltonian approach if the spin lattice and its associated spin
exchange parameters, to be used for the spin Hamiltonian, are determined by the
energy-mapping analysis based on DFT calculations. The preferred spin
orientation (i.e., the magnetic anisotropy) of a magnetic ion is not predicted
by a spin Hamiltonian because it does not include the orbital degree of freedom
explicitly. In contrast, the magnetic anisotropy is readily predicted by
electronic structure theories employing both orbital and spin degrees of
freedom, if one takes into consideration the spin-orbit coupling (SOC). It was
shown that the preferred spin orientation of a magnetic ion can be predicted
and understood in terms of the HOMO-LUMO interactions of the magnetic ion by
taking SOC as perturbation. A spin Hamiltonian gives rise to the spin-half
misconception, namely, the blind belief that spin-half magnetic ions do not
possess magnetic anisotropy that arise from SOC. This misconception is a direct
consequence from the limitedness of a spin Hamiltonian that it lacks the
orbital degree of freedom. We show that the magnetic properties of 5d ion
oxides are better explained by the LS-coupling than by the jj-coupling scheme
of SOC, that the spin-orbital entanglement of 5d ions is not as strong as has
been assumed.",1606.05220v1
2016-06-21,Is there evidence for anomalous dipole anisotropy in the large-scale structure?,"We probe the anisotropy of the large-scale structure (LSS) with the
WISE-2MASS catalogue. This analysis is performed by a directional comparison of
the galaxy number counts through the entire celestial sphere once systematic
effects, such as star-galaxy separation and foregrounds contamination, are
properly taken into account. We find a maximal hemispherical asymmetry whose
dipolar component is $A = 0.0507 \pm 0.0014$ toward the $(l,b) =
(323^{\circ},-5^{\circ})$ direction, whose result is consistent with previous
estimations of our proper motion in low and intermediate redshifts, as those
carried out with Type Ia Supernovae and similar LSS catalogues. Furthermore,
this dipole amplitude is statistically consistent ($p$-value = $0.061$) with
mock catalogues simulated according to the expected $\Lambda$CDM matter density
fluctuations, in addition to observational biases such as the incomplete
celestial coverage and anisotropic sky exposure. Our results suggest,
therefore, that there is no strong evidence for anomalous anisotropy in the
LSS, given the limitations and systematics of current data, in the concordance
model scenario.",1606.06751v3
2016-06-25,Observation of Optical and Electrical In-plane Anisotropy in High-mobility Few-layer ZrTe5,"Transition metal pentatelluride ZrTe5 is a versatile material in
condensed-matter physics and has been intensively studied since the 1980s. The
most fascinating feature of ZrTe5 is that it is a 3D Dirac semimetal which has
linear energy dispersion in all three dimensions in momentum space.
Structure-wise, ZrTe5 is a layered material held together by weak interlayer
van der Waals force. The combination of its unique band structure and 2D atomic
structure provides a fertile ground for more potential exotic physical
phenomena in ZrTe5 related to 3D Dirac semimentals. However the physical
properties of its few-layer form have yet to be thoroughly explored. Here we
report strong optical and electrical in-plane anisotropy of mechanically
exfoliated few-layer ZrTe5. Raman spectroscopy shows significant intensity
change with sample orientations, and the behavior of angle-resolved phonon
modes at the gamma point is explained by theoretical calculation. DC
conductance measurement indicates a 50% of difference along different in-plane
directions. The diminishing of resistivity anomaly in few-layer samples
indicates the evolution of band structure with reduced thickness.
Low-temperature Hall experiment sheds lights on more intrinsic anisotropic
electrical transport, with hole mobility of 3,000 and 1,500 cm2/Vs along a-axis
and c-axis respectively. Pronounced quantum oscillations in magneto-resistance
are observed at low temperatures with highest electron mobility up to 44,000
cm2/Vs.",1606.07960v2
2016-07-03,Lattice Defects and the Mechanical Anisotropy of Borophene,"Using density functional theory combined with a semi-empirical van der Waals
dispersion correction, we have investigated the stability of lattice defects
including boron vacancy, substitutional and interstitial X (X=H, C, B, N, O)
and $\Sigma$5 tilt grain boundaries in borophene and their influence on the
anisotropic mechanical properties of this two-dimensional system. The pristine
borophene has significant in-plane Young's moduli and Poisson's ratio
anisotropy due to its strong and highly coordinated B-B bonds. The
concentration of B vacancy and $\Sigma$5 grain boundary could be rather high
given that their formation energies are as low as 0.10 eV and 0.06 eV/$\AA$
respectively. In addition, our results also suggest that borophene can react
easily with H$_2$, O$_2$ and N$_2$ when exposed to these molecules. We find
that the mechanical properties of borophene are remarkably degraded by these
defects. The anisotropy in Poisson's ratio, however, can be tuned by some of
them. Furthermore, the adsorbed H or substitutional C may induce remarkably
negative Poisson's ratio in borophene, and the substitutional C or N can
significantly increase the Poisson's ratio by contrast.",1607.00642v4
2016-07-29,Searching for Cosmic Strings in CMB Anisotropy Maps using Wavelets and Curvelets,"We use wavelet and curvelet transforms to extract signals of cosmic strings
from cosmic microwave background (CMB) temperature anisotropy maps, and to
study the limits on the cosmic string tension which various ongoing CMB
temperature anisotropy experiments will be able to achieve. We construct sky
maps with size and angular resolution corresponding to various experiments.
These maps contain the signals of a scaling solution of long string segments
with a given string tension $G \mu$, the contribution of the dominant Gaussian
primordial cosmological fluctuations, and pixel by pixel white noise with an
amplitude corresponding to the instrumental noise of the various experiments.
In the case that we include white noise, we find that the curvelets are more
powerful than wavelets. For maps with Planck specification, we obtain bounds on
the string tension comparable to what was obtained by the Planck collaboration.
Experiments with better angular resolution such as the South Pole Telescope
third generation (SPT-3G) survey will be able to yield stronger limits. For
maps with a specification of SPT-3G we find that string signals will be visible
down to a string tension of $G \mu = 1.4 \times 10^{-7}$.",1608.00004v2
2016-08-09,Compensated ferrimagnetic tetragonal Heusler thin films for antiferromagnetic spintronics,"In recent years, antiferromagnetic spintronics has received much attention
since ideal antiferromagnets do not produce stray fields and are much more
stable to external magnetic fields compared to materials with net
magnetization. Akin to antiferromagnets, compensated ferrimagnets have zero net
magnetization but have the potential for large spin-polarization and strong out
of plane magnetic anisotropy, and, hence, are ideal candidates for high density
memory applications. Here, we demonstrate that a fully compensated magnetic
state with a tunable magnetic anisotropy is realized in Mn-Pt-Ga based
tetragonal Heusler thin films. Furthermore, we show that a bilayer formed from
a fully compensated and a partially compensated Mn-Pt-Ga layer, exhibits a
large interfacial exchange bias up to room temperature. The present work
establishes a novel design principle for spintronic devices that are formed
from materials with similar elemental compositions and nearly identical crystal
and electronic structures. Such devices are of significant practical value due
to their improved properties such as thermal stability. The flexible nature of
Heusler materials to achieve tunable magnetizations, and anisotropies within
closely matched materials provides a new direction to the growing field of
antiferromagnetic spintronics.",1608.02887v1
2016-08-29,Sub-micrometer yttrium iron garnet LPE films with low ferromagnetic resonance losses,"Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG)
films with thicknesses of ~100 nm and surface roughnesses as low as 0.3 nm have
been grown as a basic material for spin-wave propagation experiments in
microstructured waveguides. The continuously strained films exhibit nearly
perfect crystallinity without significant mosaicity and with effective lattice
misfits of delta a(perpendicular)/a(substrate) ~10-4 and below. The
film/substrate interface is extremely sharp without broad interdiffusion layer
formation. All LPE films exhibit a nearly bulk-like saturation magnetization of
(1800+-20) Gs and an `easy cone' anisotropy type with extremely small in-plane
coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy
with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No
significant out-of-plane anisotropy is observed, but a weak dependence of the
effective magnetization on the lattice misfit is detected. The narrowest
ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is
the lowest value reported so far for YIG films of 100 nm thicknesses and below.
The Gilbert damping coefficient for investigated LPE films is estimated to be
close to 1 x 10-4.",1608.08043v1
2016-08-29,Detecting 3D vegetation structure with the Galileo space probe: Can a distant probe detect vegetation structure on Earth?,"Sagan et al. (1993) used the Galileo space probe data and first principles to
find evidence of life on Earth. Here we ask whether Sagan et al. (1993) could
also have detected whether life on Earth had three-dimensional structure, based
on the Galileo space probe data. We reanalyse the data from this probe to see
if structured vegetation could have been detected in regions with abundant
photosynthetic pigments through the anisotropy of reflected shortwave
radiation. We compare changing brightness of the Amazon forest (a region where
Sagan et al. (1993) noted a red edge in the reflectance spectrum, indicative of
photosynthesis) as the planet rotates to a common model of reflectance
anisotropy and found measured increase of surface reflectance of 0.019 versus a
0.007 predicted from only anisotropic effects. We hypothesize the difference
was due to minor cloud contamination. However, the Galileo dataset had only a
small change in phase angle (sun-satellite position) which reduced the observed
anisotropy signal and we demonstrate that theoretically if the probe had a
variable phase angle between 0-20, there would have been a much larger
predicted change in surface reflectance of 0.06 and under such a scenario
three-dimensional vegetation structure on Earth could possibly have been
detected. These results suggest that anisotropic effects may be useful to help
determine whether exoplanets have three-dimensional vegetation structure in the
future but that further comparisons between empirical and theoretical results
are first necessary.",1608.08125v1
2016-09-28,Beyond the Maltese cross: geometry of turbulence between 0.2 and 1 AU,"The spectral anisotropy of turbulent structures has been measured in the
solar wind since 1990, relying on the assumption of axisymmetry about the mean
magnetic field, B0. However, several works indicate that this hypothesis might
be partially wrong, thus raising two questions: (i) is it correct to interpret
measurements at 1 AU (the so-called Maltese cross) in term of a sum of slab and
2D turbulence? (ii) what information is really contained in the Maltese cross?
  We solve direct numerical simulations of the MHD equations including the
transverse stretching exerted by the solar wind flow and study the genuine 3D
anisotropy of turbulence as well as that one resulting from the assumption of
axisymmetry about B0. We show that the evolution of the turbulent spectrum from
0.2 to 1 AU depends strongly on its initial anisotropy. An axisymmetric
spectrum with respect to B0 keeps its axisymmetry, i.e., resists stretching
perpendicular to radial, while an isotropic spectrum becomes essentially
axisymmetric with respect to the radial direction.
  We conclude that close to the Sun, slow-wind turbulence has a spectrum that
is axisymmetric around B0 and the measured 2D component at 1 AU describes the
real shape of turbulent structures. On the contrary, fast-wind turbulence has a
more isotropic spectrum at the source and becomes radially symmetric at 1 AU.
Such structure is hidden by the symmetrization applied to the data that instead
returns a slab geometry.",1609.09094v1
2016-09-30,Antiferromagnetic THz-frequency Josephson-like Oscillator Driven by Spin Current,"The development of compact and tunable room temperature sources of coherent
THz-frequency signals would open a way for numerous new applications. The
existing approaches to THz-frequency generation based on superconductor
Josephson junctions (JJ), free electron lasers, and quantum cascades require
cryogenic temperatures or/and complex setups, preventing the miniaturization
and wide use of these devices. We demonstrate theoretically that a bi-layer of
a heavy metal (Pt) and a bi-axial antiferromagnetic (AFM) dielectric (NiO) can
be a source of a coherent THz signal. A spin-current flowing from a
DC-current-driven Pt layer and polarized along the hard AFM anisotropy axis
excites a non-uniform in time precession of magnetizations sublattices in the
AFM, due to the presence of a weak easy-plane AFM anisotropy. The frequency of
the AFM oscillations varies in the range of 0.1-2.0 THz with the driving
current in the Pt layer from $10^8\text{A}/\text{cm}^2$ to
$10^9\text{A}/\text{cm}^2$. The THz-frequency signal from the AFM with the
amplitude exceeding 1 V/cm is picked up by the inverse spin-Hall effect in Pt.
The operation of a room-temperature AFM THz-frequency oscillator is similar to
that of a cryogenic JJ oscillator, with the energy of the easy-plane magnetic
anisotropy playing the role of the Josephson energy.",1609.09866v1
2016-11-28,Atomistic simulation of finite temperature magnetism of nanoparticles: application to cobalt clusters on Au(111),"We developed a technique to determine suitable spin models for small embedded
clusters of arbitrary geometry by combining the spin-cluster expansion with the
relativistic disordered local moment scheme. We present results for uncovered
and covered hexagonal Co clusters on Au(111) surface, and use classical Monte
Carlo simulations to study the temperature dependent properties of the systems.
To test the new method we compare the calculated spin-model parameters of the
uncovered clusters with those of a Co monolayer deposited on Au(111). In
general, the isotropic and DM interactions are larger between atoms at the
perimeter than at the center of the clusters. For Co clusters covered by Au,
both the contribution to the magnetic anisotropy and the easy axis direction of
the perimeter atoms differ from those of the inner atoms due to reduced
symmetry. We investigate the spin reversals of the covered clusters with
perpendicular magnetic anisotropy and by measuring the magnetization variance
in the easy direction we suggest a technique to determine the blocking
temperature of superparamagnetic particles. We also determine the N\'eel
relaxation time from the Monte Carlo simulations and find that it satisfies the
N\'eel--Arrhenius law with an energy barrier close to the magnetic anisotropy
energy of the clusters.",1611.09199v2
2016-12-17,"Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm$_4$Fe$_2$As$_2$Te$_{1-x}$O$_{4-y}$F$y$","We present a detailed study of the electrical transport properties of a
recently discovered iron-based superconductor:
Sm$_4$Fe$_2$As$_2$Te$_{0.72}$O$_{2.8}$F$_{1.2}$. We followed the temperature
dependence of the upper critical field by resistivity measurement of single
crystals in magnetic fields up to 16 T, oriented along the two main
crystallographic directions. This material exhibits a zero-temperature upper
critical field of 90 T and 65 T parallel and perpendicular to the Fe$_2$As$_2$
planes, respectively. An unprecedented superconducting magnetic anisotropy
$\gamma_H=H_{c2}^{ab}/H_{c2}^c \sim 14$ is observed near Tc, and it decreases
at lower temperatures as expected in multiband superconductors. Direct
measurement of the electronic anisotropy was performed on microfabricated
samples, showing a value of $\rho_c/\rho_{ab}(300K) \sim 5$ that raises up to
19 near Tc. Finally, we have studied the pressure and temperature dependence of
the in-plane resistivity. The critical temperature decreases linearly upon
application of hydrostatic pressure (up to 2 GPa) similarly to overdoped
cuprate superconductors. The resistivity shows saturation at high temperatures,
suggesting that the material approaches the Mott-Ioffe-Regel limit for metallic
conduction. Indeed, we have successfully modelled the resistivity in the normal
state with a parallel resistor model that is widely accepted for this state.
All the measured quantities suggest strong pressure dependence of the density
of states.",1612.05792v1
2016-12-21,"Spin Pumping, Dissipation, and Direct and Alternating Inverse Spin Hall Effects in Magnetic Insulator-Normal Metal Bilayers","We theoretically consider the spin-wave mode- and wavelength-dependent
enhancement of the Gilbert damping in magnetic insulator--normal metal bilayers
due to spin pumping as well as the enhancement's relation to direct and
alternating inverse spin Hall voltages in the normal metal. In the
long-wavelength limit, including long-range dipole interactions, the ratio of
the enhancement for transverse volume modes to that of the macrospin mode is
equal to two. With an out-of-plane magnetization, this ratio decreases with
both an increasing surface anisotropic energy and mode number. If the surface
anisotropy induces a surface state, the enhancement can be an order of
magnitude larger than for to the macrospin. With an in-plane magnetization, the
induced dissipation enhancement can be understood by mapping the anisotropy
parameter to the out-of-plane case with anisotropy. For shorter wavelengths, we
compute the enhancement numerically and find good agreement with the analytical
results in the applicable limits. We also compute the induced direct- and
alternating-current inverse spin Hall voltages and relate these to the magnetic
energy stored in the ferromagnet. Because the magnitude of the direct spin Hall
voltage is a measure of spin dissipation, it is directly proportional to the
enhancement of Gilbert damping. The alternating spin Hall voltage exhibits a
similar in-plane wave-number dependence, and we demonstrate that it is greatest
for surface-localized modes.",1612.07020v2
2016-12-21,CMB-lensing beyond the leading order: temperature and polarization anisotropies,"We investigate the weak lensing corrections to the CMB temperature and
polarization anisotropies. We consider all the effects beyond the leading
order: post-Born corrections, LSS corrections and, for the polarization
anisotropies, the correction due to the rotation of the polarization direction
between the emission at the source and the detection at the observer. We show
that the full next-to-leading order correction to the B-mode polarization is
not negligible on small scales and is dominated by the contribution from the
rotation, this is a new effect not taken in account in previous works.
Considering vanishing primordial gravitational waves, the B-mode correction due
to rotation is comparable to cosmic variance for $\ell \gtrsim 3500$, in
contrast to all other spectra where the corrections are always below that
threshold for a single multipole. Moreover, the sum of all the effects is
larger than cosmic variance at high multipoles, showing that higher-order
lensing corrections to B-mode polarization are in principle detectable.",1612.07263v3
2017-01-14,Crossovers due to anisotropy and disorder in quantum critical fluctuations,"Scaling relations are used to study cross-overs, due to anisotropic spin
interactions or single ion anisotropy, and due to disorder, in the
thermodynamics and correlation functions near quantum-critical transitions. The
principal results are simple with a wide range of applications. The region of
attraction to the stable anisotropic fixed point in the quantum-critical region
is exponentially enhanced by the dynamical critical exponent $z$ compared to
the region of attraction to the fixed point in the quantum disordered region.
The result implies that, even for small anisotropy, the region of attraction to
the stable incommensurate Ising or planar metallic anti-ferromagnetic critical
points, which belong to the universality class of the XY model with $z \to
\infty$, covers the entire quantum-critical region. In crossovers due to
disorder, the instability of the pure fixed point in the quantum disordered
region is exponentially enhanced by $z$ compared to that in the
quantum-critical region. This result suggests that for some classes of disorder
and for large enough $z$, one may find singularities in the correlations as a
function of frequency and temperature down to very low temperatures even though
the correlation length in space remains short range.",1701.03853v3
2017-01-24,"Helical paths, gravitaxis, and separation phenomena for mass-anisotropic self-propelling colloids: experiment versus theory","The self-propulsion mechanism of active colloidal particles often generates
not only translational but also rotational motion. For particles with an
anisotropic mass density under gravity, the motion is usually influenced by a
downwards oriented force and an aligning torque. Here we study the trajectories
of self-propelled bottom-heavy Janus particles in three spatial dimensions both
in experiments and by theory. For a sufficiently large mass anisotropy, the
particles typically move along helical trajectories whose axis is oriented
either parallel or antiparallel to the direction of gravity (i.e., they show
gravitaxis). In contrast, if the mass anisotropy is small and rotational
diffusion is dominant, gravitational alignment of the trajectories is not
possible. Furthermore, the trajectories depend on the angular self-propulsion
velocity of the particles. If this component of the active motion is strong and
rotates the direction of translational self-propulsion of the particles, their
trajectories have many loops, whereas elongated swimming paths occur if the
angular self-propulsion is weak. We show that the observed gravitational
alignment mechanism and the dependence of the trajectory shape on the angular
self-propulsion can be used to separate active colloidal particles with respect
to their mass anisotropy and angular self-propulsion, respectively.",1701.06824v2
2017-01-02,Ferromagnetic films with three to twenty spin layers as described using second order perturbed Heisenberg Hamiltonian,"Modified second order perturbed Heisenberg Hamiltonian was employed to
describe the magnetic properties of ferromagnetic films with three to twenty
spin layers for the first time. Previously, the solution of second order
perturbed Heisenberg Hamiltonian was found for ferromagnetic films with two to
five layers under some assumptions by us. In this report, the exact solution is
presented without any assumptions by calculating the pseudo inverse of matrix
C. All eight magnetic parameters such as spin exchange interaction, second
order magnetic anisotropy, fourth order magnetic anisotropy, stress induced
magnetic anisotropy, demagnetization factor, in plane magnetic field, out of
plane magnetic field and magnetic dipole interaction were taken into account.
The easy and hard directions were found using 3-D and 2-D plots of total
magnetic energy versus these magnetic parameters. Angle between easy and hard
directions was nearly 107 degrees in many cases. The magnetic easy axis
gradually rotates from out of plane to in plane direction by indicating a
preferred in plane orientation of magnetic easy axis for films with higher
number of spin layers. These theoretical results agree with some experimental
research data of ferromagnetic thin films.",1701.07780v1
2017-02-09,Modification of microstructure and micromagnetic properties in Gd-Fe thin films by rapid thermal processing,"Impact of rapid thermal processing (RTP) on microstructure and magnetic
properties of Gd-Fe thin films have been investigated with a special emphasis
to magnetic microstructure. 100 nm thick amorphous Gd-Fe film shows elongated
stripe domains with characteristic feature size of 122 nm, which signifies the
development of perpendicular magnetic anisotropy (PMA) in this system. RTP at
550^oC for different time intervals viz. 5, 10, 15, 20 minutes induces the
crystallization of Fe over the amorphous Gd-Fe matrix. Cross-sectional imaging
with transmission electron microscope reveals the presence of Fe nanocrystal
and the reacted film-substrate interface, which has also been verified by
Rutherford backscattering spectrometry. With increasing RTP time, the
characteristic size and the threshold height of the topographic feature
increases. While the magnetic contrast drops down for the processed films, the
increasing threshold height of the nanocrystalline grains results a topography
dominated mixed phase in the magnetic force microscopy images. The
magnetization measurements clearly indicate a re-orientation of the
magnetization direction from perpendicular to the plane of the surface. To
unravel the effect of anisotropy modification on domain structure, 3D
micromagnetic simulations have been performed, which showed that with 50%
reduction of original anisotropy, the magnetization tries to orient in the
plane of the surface, whereas an in-plane (along xz plane) tilt angle of 30^o
has been estimated to be the threshold for the decrease in perpendicular
component of magnetization in the investigated Gd-Fe thin film system.",1702.02987v2
2017-02-23,Measurement of Anisotropy and Search for UHECR Sources,"Ultra-high energy cosmic rays (UHECRs) are particles, likely protons and/or
nuclei, with energies up to $10^{20}$ eV that are observed through the giant
air showers they produce in the atmosphere. These particles carry the
information on the most extreme phenomena in the Universe. At these energies,
even charged particles could be magnetically rigid enough to keep track of, or
even point directly to, the original positions of their sources on the sky. The
discovery of anisotropy of UHECRs would thus signify opening of an entirely new
window onto the Universe. With the construction and operation of the new
generation of cosmic ray experiments -- the Pierre Auger Observatory in the
Southern hemisphere and the Telescope Array in the Northern one -- the study of
these particles, the most energetic ever detected, has experienced a jump in
statistics as well as in the data quality, allowing for a much better
sensitivity in searching for their sources. In this review, we summarize the
searches for anisotropies and the efforts to identify the sources of UHECRs
which have been carried out using these new data.",1702.07209v1
2017-02-27,Far-from-equilibrium initial conditions probed by a nonlocal observable,"Using the gauge/gravity duality, we investigate the evolution of an
out-of-equilibrium strongly-coupled plasma from the viewpoint of the two-point
function of scalar gauge-invariant operators with large conformal dimension.
This system is out of equilibrium due to the presence of anisotropy and/or a
massive scalar field. Considering various functions for the initial anisotropy
and scalar field, we conclude that the effect of the anisotropy on the
evolution of the two-point function is considerably more than the effect of the
scalar field. We also show that the ordering of the equilibration time of the
one-point function for the non-probe scalar field and the correlation function
between two points with a fixed separation can be reversed by changing the
initial configuration of the plasma, when the system is out of the equilibrium
due to the presence of at least two different sources like our problem. In
addition, we find the equilibration time of the two-point function to be
linearly increasing with respect to the separation of the two points with a
fixed slope, regardless of the initial configuration that we start with.
Finally we observe that, for larger separations the geodesic connecting two
points on the boundary crosses the event horizon after it has reached its final
equilibrium value, meaning that the two-point function can probe behind the
event horizon.",1702.08482v2
2017-04-11,Uniaxial strain control of spin-polarization in multicomponent nematic order of BaFe$_{2}$As$_{2}$,"The iron-based high temperature superconductors exhibit a rich phase diagram
reflecting a complex interplay between spin, lattice, and orbital degrees of
freedom [1-4]. The nematic state observed in many of these compounds epitomizes
this complexity, by entangling a real-space anisotropy in the spin fluctuation
spectrum with ferro-orbital order and an orthorhombic lattice distortion [5-7].
A more subtle and much less explored facet of the interplay between these
degrees of freedom arises from the sizable spin-orbit coupling present in these
systems, which translates anisotropies in real space into anisotropies in spin
space. Here, we present a new technique enabling nuclear magnetic resonance
under precise tunable strain control, which reveals that upon application of a
tetragonal symmetry-breaking strain field, the magnetic fluctuation spectrum in
the paramagnetic phase of BaFe$_{2}$As$_{2}$ also acquires an anisotropic
response in spin-space. Our results unveil a hitherto uncharted internal spin
structure of the nematic order parameter, indicating that similar to liquid
crystals, electronic nematic materials may offer a novel route to
magneto-mechanical control.",1704.03566v1
2017-04-21,Strain-gradient-induced magnetic anisotropy in straight-stripe mixed-phase bismuth ferrites: An insight into flexomagnetic phenomenon,"Implementation of antiferromagnetic compounds as active elements in
spintronics has been hindered by their insensitive nature against external
perturbations which causes difficulties in switching among different
antiferromagnetic spin configurations. Electrically-controllable strain
gradient can become a key parameter to tune the antiferromagnetic states of
multiferroic materials. We have discovered a correlation between an
electrically-written straight-stripe mixed-phase boundary and an in-plane
antiferromagnetic spin axis in highly-elongated La-5%-doped BiFeO$_{3}$ thin
films by performing polarization-dependent photoemission electron microscopy in
conjunction with cluster model calculations. Model Hamiltonian calculation for
the single-ion anisotropy including the spin-orbit interaction has been
performed to figure out the physical origin of the link between the strain
gradient present in the mixed phase area and its antiferromagnetic spin axis.
Our findings enable estimation of the strain-gradient-induced magnetic
anisotropy energy per Fe ion at around 5$\times$10$^{-12}$ eV m, and provide a
new pathway towards an electric-field-induced 90$^{\circ}$ rotation of
antiferromagnetic spin axis at room temperature by flexomagnetism.",1704.06627v1
2017-05-05,Extragalactic Sources and Propagation of UHECRs,"With the publicly available astrophysical simulation framework for
propagating extraterrestrial UHE particles, CRPropa 3, it is now possible to
study realistic UHECR source scenarios including deflections in Galactic and
extragalactic magnetic fields in an efficient way. Here we discuss three recent
studies that have already been done in that direction. The first one
investigates what can be expected in the case of maximum allowed intergalactic
magnetic fields. Here is shown that, even if voids contain strong magnetic
fields, deflections of protons with energies $\gtrsim 60 \; \text{EeV}$ from
nearby sources might be small enough to allow for UHECR astronomy. The second
study looks into several scenarios with a smaller magnetization focusing on
large-scale anisotropies. Here is shown that the local source distribution can
have a more significant effect on the large-scale anisotropy than the EGMF
model. A significant dipole component could, for instance, be explained by a
dominant source within 5 Mpc distance. The third study looks into whether
UHECRs can come from local radio galaxies. If this is the case it is difficult
to reproduce the observed low level of anisotropy. Therefore is concluded that
the magnetic field strength in voids in the EGMF model used here is too low
and/or there are additional sources of UHECRs that were not taken into account
in these simulations.",1705.02293v1
2017-05-15,Unconventional magnetic anisotropy in one-dimentional Rashba system realized by adsorbing Gd atom on zigzag graphene nanoribbons,"The Rashba effect, a spin splitting in electronic band structure, attracts
much attention for the potential applications in spintronics with no
requirement of external magnetic field. Realizing one-dimensional (1D) Rashba
system is a big challenge due to the difficulties of growing high-quality
heavy-metal nanowires or introducing strong spin-orbit coupling (SOC) and
broken inversion symmetry in flexible materials. Here, based on
first-principles calculations, we propose a pathway to realize the Rashba
spin-split by adsorbing Gd atom on zigzag graphene nanoribbons (Gd-ZGNR) and
further investigate the magnetic anisotropy energy (MAE). Perpendicular MAE and
unconventional MAE contributions in k-space are found in the self-assembled
Gd-ZGNR system, which present a remarkable Rashba effect (the estimated
strength is 1.89 eV {\AA}) attributed to strong SOC (~65.6 meV) and the
asymmetric adsorption site at the nanoribbons edge. Moreover, first-order MAE
is connected to the intrinsic Rashba effect beyond the traditional second-order
MAE, which is confirmed based on the analysis of electronic structures
perturbed with SOC in comparison with metastable Gd-ZGNR at central symmetric
adsorption site. The dependence of first-order MAE as well as Rashba effect of
Gd-ZGNRs on the ribbon width are also examined. This work offers new
perspective to achieve 1D Rashba system and provides fundamental understanding
on the magnetic anisotropy, which would be of great significance for searching
Majorana fermions and promoting the potential applications in spintronics.",1705.05121v2
2017-05-22,Time-of-flight elastic and inelastic neutron scattering studies on the localized $4d$ electron layered perovskite La$_5$Mo$_4$O$_{16}$,"The magnetic structure and spin-wave excitations in the quasi-square-lattice
layered perovskite compound La$_5$Mo$_4$O$_{16}$ were studied by a combination
of neutron diffraction and inelastic neutron scattering techniques using
polycrystalline sample. Neutron powder diffraction refinement revealed that the
magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic
stacking along the $c$ axis where the magnetic propagation vector is
$\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are
estimated to be $0.54(2)\mu_\text{B}$ for Mo$^{5+}$ ($4d^1$) ions and
$1.07(3)\mu_\text{B}$ for Mo$^{4+}$ ($4d^2$) ions at 4 K, which are about half
of the expected values. The inelastic neutron scattering results display strong
easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit
interaction in Mo ions evidenced by the spin gap at the magnetic zone center.
The model Hamiltonian consisting of in-plane anisotropic exchange interactions,
the interlayer exchange interaction, and easy-axis single-ion anisotropy can
explain our inelastic neutron scattering data well. Strong Ising-like
anisotropy and weak interlayer coupling compared with the intralayer exchange
interaction can explain both the high-temperature magnetoresistance and
long-time magnetization decay recently observed in La$_5$Mo$_4$O$_{16}$.",1705.07916v1
2017-06-05,How important is non-ideal physics in simulations of sub-Eddington accretion onto spinning black holes?,"Black holes with accretion rates well below the Eddington rate are expected
to be surrounded by low-density, hot, geometrically thick accretion disks. This
includes the two black holes being imaged at sub-horizon resolution by the
Event Horizon Telescope. In these disks, the mean free path for Coulomb
interactions between charged particles is large, and the accreting matter is a
nearly collisionless plasma. Despite this, numerical simulations have so far
modeled these accretion flows using ideal magnetohydrodynamics. Here, we
present the first global, general relativistic, 3D simulations of accretion
flows onto a Kerr black hole including the non-ideal effects most likely to
affect the dynamics of the disk: the anisotropy between the pressure parallel
and perpendicular to the magnetic field, and the heat flux along magnetic field
lines. We show that for both standard and magnetically arrested disks, the
pressure anisotropy is comparable to the magnetic pressure, while the heat flux
remains dynamically unimportant. Despite this large pressure anisotropy,
however, the time-averaged structure of the accretion flow is strikingly
similar to that found in simulations treating the plasma as an ideal fluid. We
argue that these similarities are largely due to the interchangeability of the
viscous and magnetic shear stresses as long as the magnetic pressure is small
compared to the gas pressure, and to the sub-dominant role of pressure/viscous
effects in magnetically arrested disks. We conclude by highlighting outstanding
questions in modeling the dynamics of low collisionality accretion flows.",1706.01533v1
2017-06-14,Behavior of the Universe anisotropy in a big-bounce cosmology,"We investigate the classical and quantum behavior of a Bianchi I model in the
presence of a stiff matter contribution when the Vilenkin interpretation of the
wave function of the Universe is taken into account. We study its evolution in
the so-called polymer representation of quantum mechanics, in order to
characterize the modifications that a discrete nature in the isotropic variable
of the Universe induces on the morphology of the cosmological singularity. We
demonstrate that in such a model the Big-Bang singularity is removed at a
semiclassical level in favor of a Big-Bounce when a lattice on the isotropic
variable is considered. Furthermore, the analysis of the mean values on the
quantum degrees of freedom, \textit{i.e} the variables $\beta_{+},\beta_{-}$ in
the Misner picture, and the investigation on the evolution of the wave packets
show how the typical diverging behavior associated to the anisotropies of the
Universe in proximity of the initial singularity disappears in our polymer
modified scheme. Indeed, the anisotropies remain finite across the Big-Bounce
and they assume a value that depends on the initial conditions fixed far from
the turning point. Finally, we demonstrate that the proposed scenario can be
extended, with a suitable choice of the configuration parameters, to the
Bianchi IX cosmology and therefore it can be regarded as a paradigm for the
generic cosmological model.",1706.04361v1
2017-06-23,Magnetic properties of quasi-two-dimensional $S$ = 1/2 Heisenberg antiferromagnet with distorted square lattice,"We successfully synthesize single crystals of the verdazyl radical
$\alpha$-2,3,5-Cl$_3$-V. $Ab$ $initio$ molecular orbital calculations indicate
that the two dominant antiferromagnetic interactions, $J_{\rm{1}}$ and
$J_{\rm{2}}$ ($\alpha =J_{\rm{2}}/J_{\rm{1}}\simeq 0.56$), form an $S$ = 1/2
distorted square lattice. We explain the magnetic properties based on the $S$ =
1/2 square lattice Heisenberg antiferromagnet using the quantum Monte Carlo
method, and examine the effects of the lattice distortion and the interplane
interaction contribution. In the low-temperature regions below 6.4 K, we
observe anisotropic magnetic behavior accompanied by a phase transition to a
magnetically ordered state. The electron spin resonance signals exhibit
anisotropic behavior in the temperature dependence of the resonance field and
the linewidth. We explain the frequency dependence of the resonance fields in
the ordered phase using a mean-field approximation with out-of-plane easy-axis
anisotropy, which causes a spin-flop phase transition at approximately 0.4 T
for the field perpendicular to the plane. Furthermore, the anisotropic dipole
field provides supporting information regarding the presence of the easy-axis
anisotropy. These results demonstrate that the lattice distortion, anisotropy,
and interplane interaction of this model are sufficiently small that they do
not affect the intrinsic behavior of the $S$ = 1 / 2 square lattice Heisenberg
antiferromagnet.",1706.07546v1
2017-07-11,Interface Dzyaloshinskii-Moriya interaction in the interlayer exchange antiferromagnetic coupled Pt/CoFeB/Ru/CoFeB systems,"Interfacial Dzyaloshinskii-Moriya interaction (iDMI) in interlayer exchange
coupled (IEC) Pt/Co$_{20}$Fe$_{60}$B$_{20}$(1.12
nm)/Ru/Co$_{20}$Fe$_{60}$B$_{20}$(1.12 nm) systems have been studied
theoretically and experimentally. Vibrating sample magnetometer has been used
to measure their magnetization at saturation and their interlayer exchange
coupling constants. These latter are found to be of an antiferromagnetic nature
for the investigated Ru range thickness (0.5-1 nm). Their dynamic magnetic
properties were studied using Brillouin light scattering (BLS) technique. The
BLS measurements reveal pronounced non-reciprocal spin waves propagation. In
contrast to the calculations for symmetrical IEC CoFeB layers, this
experimental nonreciprocity is Ru thickness and thus coupling strength
dependent. Therefore, to explain the experimental behaviour, a theoretical
model based on the perpendicular interface anisotropy difference between the
bottom and top CoFeB layers has been developed. We show that the Ru thickness
dependence of the spin wave non-reciprocity is well reproduced by considering a
constant iDMI and different perpendicular interfacial anisotropy fields between
the top and bottom CoFeB layers. This anisotropy difference has been confirmed
by the investigation of the CoFeB thickness dependence of effective
magnetization of Pt/CoFeB/Ru and Ru/CoFeB/MgO individual layers, where a linear
behaviour has been observed.",1707.03427v1
2017-07-14,Symmetry-broken dissipative exchange flows in thin-film ferromagnets with in-plane anisotropy,"Planar ferromagnetic channels have been shown to theoretically support a
long-range ordered and coherently precessing state where the balance between
local spin injection at one edge and damping along the channel establishes a
dissipative exchange flow, sometimes referred to as a spin superfluid. However,
realistic materials exhibit in-plane anisotropy, which breaks the axial
symmetry assumed in current theoretical models. Here, we study dissipative
exchange flows in a ferromagnet with in-plane anisotropy from a dispersive
hydrodynamic perspective. Through the analysis of a boundary value problem for
a damped sine-Gordon equation, dissipative exchange flows in a ferromagnetic
channel can be excited above a spin current threshold that depends on material
parameters and the length of the channel. Symmetry-broken dissipative exchange
flows display harmonic overtones that redshift the fundamental precessional
frequency and lead to a reduced spin pumping efficiency when compared to their
symmetric counterpart. Micromagnetic simulations are used to verify that the
analytical results are qualitatively accurate, even in the presence of nonlocal
dipole fields. Simulations also confirm that dissipative exchange flows can be
driven by spin transfer torque in a finite-sized region. These results
delineate the important material parameters that must be optimized for the
excitation of dissipative exchange flows in realistic systems.",1707.04664v3
2017-07-19,Engineering elliptical spin-excitations by complex anisotropy fields in Fe adatoms and dimers on Cu(111),"We investigate the dynamics of Fe adatoms and dimers deposited on the Cu(111)
metallic surface in the presence of spin-orbit coupling, within time-dependent
density functional theory. The \textit{ab initio} results provide
material-dependent parameters that can be used in semiclassical approaches,
which are used for insightful interpretations of the excitation modes. By
manipulating the surroundings of the magnetic elements, we show that elliptical
precessional motion may be induced through the modification of the magnetic
anisotropy energy. We also demonstrate how different kinds of spin precession
are realized, considering the symmetry of the magnetic anisotropy energy, the
ferro- or antiferromagnetic nature of the exchange coupling between the
impurities, and the strength of the magnetic damping. In particular, the normal
modes of a dimer depend on the initial magnetic configuration, changing
drastically by going from a ferromagnetic metastable state to the
antiferromagnetic ground state. By taking into account the effect of the
damping into their resonant frequencies, we reveal that an important
contribution arises for strongly biaxial systems and specially for the
antiferromagnetic dimers with large exchange couplings. Counter intuitively,
our results indicate that the magnetic damping influences the quantum
fluctuations by decreasing the zero-point energy of the system.",1707.06087v2
2017-07-26,Stabilizing isolated skyrmions at low magnetic fields exploiting vanishing magnetic anisotropy,"Skyrmions are topologically protected non-collinear magnetic structures.
Their stability and dynamics, arising from their topological character, have
made them ideal information carriers e.g. in racetrack memories. The success of
such a memory critically depends on the ability to stabilize and manipulate
skyrmions at low magnetic fields. The driving force for skyrmion formation is
the non-collinear Dzyaloshinskii-Moriya exchange interaction (DMI) originating
from spin-orbit coupling (SOC). It competes with both the nearest neighbour
Heisenberg exchange interaction and the magnetic anisotropy, which favour
collinear states. While skyrmion lattices might evolve at vanishing magnetic
fields, the formation of isolated skyrmions in ultra-thin films so far required
the application of an external field which can be as high as several T. Here,
we show that isolated skyrmions in a monolayer (ML) of Co epitaxially grown on
a Ru(0001) substrate can be stabilized at magnetic fields as low as 100 mT.
Even though SOC is weak in the 4d element Ru, a homochiral spin spiral ground
state and isolated skyrmions could be detected and laterally resolved using a
combination of tunneling and anisotropic tunneling magnetoresistance effect in
spin-sensitive scanning tunneling microscopy (STM). Density functional theory
(DFT) calculations confirm these chiral magnetic textures, even though the
stabilizing DMI interaction is weak. We find that the key factor is the absence
of magnetocristalline anisotropy in this system which enables non-collinear
states to evolve in spite of weak SOC, opening up a wide choice of materials
beyond 5d elements.",1707.08519v1
2017-08-23,Principal-component analysis of two-particle azimuthal correlations in PbPb and pPb collisions at CMS,"For the first time a principle-component analysis is used to separate out
different orthogonal modes of the two-particle correlation matrix from heavy
ion collisions. The analysis uses data from sqrt(s[NN]) = 2.76 TeV PbPb and
sqrt(s[NN]) = 5.02 TeV pPb collisions collected by the CMS experiment at the
LHC. Two-particle azimuthal correlations have been extensively used to study
hydrodynamic flow in heavy ion collisions. Recently it has been shown that the
expected factorization of two-particle results into a product of the
constituent single-particle anisotropies is broken. The new information
provided by these modes may shed light on the breakdown of flow factorization
in heavy ion collisions. The first two modes (""leading"" and ""subleading"") of
two-particle correlations are presented for elliptical and triangular
anisotropies in PbPb and pPb collisions as a function of pt over a wide range
of event activity. The leading mode is found to be essentially equivalent to
the anisotropy harmonic previously extracted from two-particle correlation
methods. The subleading mode represents a new experimental observable and is
shown to account for a large fraction of the factorization breaking recently
observed at high transverse momentum. The principle-component analysis
technique has also been applied to multiplicity fluctuations. These also show a
subleading mode. The connection of these new results to previous studies of
factorization is discussed.",1708.07113v2
2017-08-29,Thermal diffusivity and butterfly velocity in anisotropic Q-Lattice models,"By using a holographic method we study a relation between the thermal
diffusivity ($D_T$) and two quantum chaotic properties, Lyapunov time
($\tau_L$) and butterfly velocity ($v_B$) in strongly correlated systems. It
has been shown that $D_T/(v_B^2 \tau_L)$ is universal in some holographic
models as well as condensed matter systems including the Sachdev-Ye-Kitaev
(SYK) models. We investigate to what extent this relation is universal in the
Q-lattice models with infrared (IR) scaling geometry, focusing on the effect of
spatial anisotropy. Indeed it was shown that $\mathcal{E}_i :=
D_{T,i}/(v_{B,i}^2 \tau_L)$ ($i=x,y$) is determined only by some scaling
exponents of the IR metric in the low temperature limit regardless of the
matter fields and ultraviolet data. Inspired by this observation, in this work,
we find the concrete expressions for $\mathcal{E}_i$ in terms of the critical
dynamical exponents $z_i$ in each direction. By analyzing the IR scaling
geometry we identify the allowed scaling parameter regimes, which enable us to
compute the allowed range of $\mathcal{E}_i$. We find the lower bound of
$\mathcal{E}_i$ is always $1/2$, which is not affected by anisotropy, contrary
to the $\eta/s$ case. However, there may be an upper bound determined by
anisotropy.",1708.08822v2
2017-09-06,Room-temperature superparamagnetism due to giant magnetic anisotropy in Mo$_{S}$ defected single-layer MoS$_{2}$,"Room-temperature superparamagnetism due to a large magnetic anisotropy energy
(MAE) of a single atom magnet has always been a prerequisite for nanoscale
magnetic devices. Realization of two dimensional (2D) materials such as
single-layer (SL) MoS$_{2}$, has provided new platforms for exploring magnetic
effects, which is important for both fundamental research and for industrial
applications. Here, we use density functional theory (DFT) to show that the
antisite defect (Mo$_{S}$) in SL MoS$_{2}$ is magnetic in nature with a
magnetic moment of $\mu$ of $\sim$ 2$\mu_{B}$ and, remarkably, exhibits an
exceptionally large atomic scale
MAE$=\varepsilon_{\parallel}-\varepsilon_{\perp}$ of $\sim$500 meV. Our
calculations reveal that this giant anisotropy is the joint effect of strong
crystal field and significant spin-orbit coupling (SOC). In addition, the
magnetic moment $\mu$ can be tuned between 1$\mu_{B}$ and 3$\mu_{B}$ by varying
the Fermi energy $\varepsilon_{F}$, which can be achieved either by changing
the gate voltage or by chemical doping. We also show that MAE can be raised to
$\sim$1 eV with n-type doping of the MoS$_{2}$:Mo$_{S}$ sample. Our systematic
investigations deepen our understanding of spin-related phenomena in SL
MoS$_{2}$ and could provide a route to nanoscale spintronic devices.",1709.01653v1
2017-09-13,Effects of spatial curvature and anisotropy on the asymptotic regimes in Einstein-Gauss-Bonnet gravity,"In this paper we address two important issues which could affect reaching the
exponential and Kasner asymptotes in Einstein-Gauss-Bonnet cosmologies --
spatial curvature and anisotropy in both three- and extra-dimensional
subspaces. In the first part of the paper we consider cosmological evolution of
spaces being the product of two isotropic and spatially curved subspaces. It is
demonstrated that the dynamics in $D=2$ (the number of extra dimensions) and $D
\geqslant 3$ is different. It was already known that for the $\Lambda$-term
case there is a regime with ""stabilization"" of extra dimensions, where the
expansion rate of the three-dimensional subspace as well as the scale factor
(the ""size"") associated with extra dimensions reach constant value. This regime
is achieved if the curvature of the extra dimensions is negative. We
demonstrate that it take place only if the number of extra dimensions is $D
\geqslant 3$. In the second part of the paper we study the influence of initial
anisotropy. Our study reveals that the transition from Gauss-Bonnet Kasner
regime to anisotropic exponential expansion (with expanding three and
contracting extra dimensions) is stable with respect to breaking the symmetry
within both three- and extra-dimensional subspaces. However, the details of the
dynamics in $D=2$ and $D \geqslant 3$ are different. Combining the two
described affects allows us to construct a scenario in $D \geqslant 3$, where
isotropisation of outer and inner subspaces is reached dynamically from rather
general anisotropic initial conditions.",1709.04258v1
2017-09-15,"Angular dependence of vortex instability in a layered superconductor: the case study of Fe(Se,Te) material","Anisotropy effects on flux pinning and flux flow are strongly effective in
cuprate as well as iron-based superconductors due to their intrinsically
layered crystallographic structure. However $\textrm{Fe(Se,Te)}$ thin films
grown on $\textrm{CaF}_2$ substrate result less anisotropic with respect to all
the other iron based superconductors. We present the first study on the angular
dependence of the flux flow instability, which occurs in the flux flow regime
as a current driven transition to the normal state at the instability point
($I^*$,$V^*$) in the current-voltage characteristics. The voltage jumps are
systematically investigated as a function of the temperature, the external
magnetic field, and the angle between the field and the $\textrm{Fe(Se,Te)}$
film. The scaling procedure based on the anisotropic Ginzburg-Landau approach
is successfully applied to the observed angular dependence of the critical
voltage $V^*$. Anyway, we find out that $\textrm{Fe(Se,Te)}$ represents the
case study of a layered material characterized by a weak anisotropy of its
static superconducting properties, but with an increased anisotropy in its
vortex dynamics due to the predominant perpendicular component of the external
applied magnetic field. Indeed, $I^*$ shows less sensitivity to angle
variations, thus being promising for high field applications.",1709.05089v3
2017-09-22,Micromagnetic study of skyrmion stability in confined magnetic structures with perpendicular anisotropy,"Skyrmions are emerging topological spin structures that are potentially
revolutionary for future data storage and spintronics applications. The
existence and stability of skyrmions in magnetic materials is usually
associated to the presence of the Dzyaloshinskii-Moriya interaction (DMI) in
bulk magnets or in magnetic thin films lacking inversion symmetry. While some
methods have already been proposed to generate isolated skyrmions in thin films
with DMI, a thorough study of the conditions under which the skyrmions will
remain stable in order to be manipulated in an integrated spintronic device are
still an open problem. The stability of such structures is believed to be a
result of ideal combinations of perpendicular magnetic anisotropy (PMA), DMI
and the interplay between geometry and magnetostatics. In the present work we
show some micromagnetic results supporting previous experimental observations
of magnetic skyrmions in spin-valve stacks with a wide range of DMI values.
Using micromagnetic simulations of cobalt-based disks, we obtain the magnetic
ground state configuration for several values of PMA, DMI and geometric
parameters. Skyrmion numbers, corresponding to the topological charge, are
calculated in all cases and confirm the occurrence of isolated, stable, axially
symmetric skyrmions for several combinations of DMI and anisotropy constant.
The stability of the skyrmions in disks is then investigated under magnetic
field and spin-polarized current, in finite temperature, highlighting the
limits of applicability of these spin textures in spintronic devices.",1709.07559v1
2017-09-22,The build up of the correlation between halo spin and the large scale structure,"Both simulations and observations have confirmed that the spin of
haloes/galaxies is correlated with the large scale structure (LSS) with a mass
dependence such that the spin of low-mass haloes/galaxies tend to be parallel
with the LSS, while that of massive haloes/galaxies tend to be perpendicular
with the LSS. It is still unclear how this mass dependence is built up over
time. We use N-body simulations to trace the evolution of the halo spin-LSS
correlation and find that at early times the spin of all halo progenitors is
parallel with the LSS. As time goes on, mass collapsing around massive halo is
more isotropic, especially the recent mass accretion along the slowest
collapsing direction is significant and it brings the halo spin to be
perpendicular with the LSS. Adopting the $fractional$ $anisotropy$ (FA)
parameter to describe the degree of anisotropy of the large-scale environment,
we find that the spin-LSS correlation is a strong function of the environment
such that a higher FA (more anisotropic environment) leads to an aligned
signal, and a lower anisotropy leads to a misaligned signal. In general, our
results show that the spin-LSS correlation is a combined consequence of mass
flow and halo growth within the cosmic web. Our predicted environmental
dependence between spin and large-scale structure can be further tested using
galaxy surveys.",1709.07881v1
2017-10-02,Strong-Coupling Lattice QCD on Anisotropic Lattices,"Anisotropic lattice spacings are mandatory to reach the high temperatures
where chiral symmetry is restored in the strong coupling limit of lattice QCD.
Here, we propose a simple criterion for the nonperturbative renormalisation of
the anisotropy coupling in strongly-coupled SU($N$) or U($N$) lattice QCD with
massless staggered fermions. We then compute the renormalised anisotropy, and
the strong-coupling analogue of Karsch's coefficients (the running anisotropy),
for $N=3$. We achieve high precision by combining diagrammatic Monte Carlo and
multi-histogram reweighting techniques. We observe that the mean field
prediction in the continuous time limit captures the nonperturbative scaling,
but receives a large, previously neglected correction on the unit prefactor.
Using our nonperturbative prescription in place of the mean field result, we
observe large corrections of the same magnitude to the continuous time limit of
the static baryon mass, and of the location of the phase boundary associated
with chiral symmetry restoration. In particular, the phase boundary, evaluated
on different finite lattices, has a dramatically smaller dependence on the
lattice time extent. We also estimate, as a byproduct, the pion decay constant
and the chiral condensate of massless SU(3) QCD in the strong coupling limit at
zero temperature.",1710.00611v2
2017-10-03,Simulations of ultra-high Energy Cosmic Rays in the local Universe and the origin of Cosmic Magnetic Fields,"We simulate the propagation of cosmic rays at ultra-high energies, $\gtrsim
10^{18}$ eV, in models of extragalactic magnetic fields in constrained
simulations of the local Universe. We use constrained initial conditions with
the cosmological magnetohydrodynamics code {\sc ENZO}. The resulting models of
the distribution of magnetic fields in the local Universe are used in the
\crpropa code to simulate the propagation of ultra-high energy cosmic rays. We
investigate the impact of six different magneto-genesis scenarios, both
primordial and astrophysical, on the propagation of cosmic rays over
cosmological distances. Moreover, we study the influence of different source
distributions around the Milky Way. Our study shows that different scenarios of
magneto-genesis do not have a large impact on the anisotropy measurements of
ultra-high energy cosmic rays. However, at high energies above the GZK-limit,
there is anisotropy caused by the distribution of nearby sources, independent
of the magnetic field model. This provides a chance to identify cosmic ray
sources with future full-sky measurements and high number statistics at the
highest energies. Finally, we compare our results to the dipole signal measured
by the Pierre Auger Observatory. All our source models and magnetic field
models could reproduce the observed dipole amplitude with a pure iron injection
composition. Our results indicate that the dipole is observed due to clustering
of secondary nuclei in direction of nearby sources of heavy nuclei. A light
injection composition is disfavoured by the non-observation of anisotropy at
energies of $4-8 \rm\ EeV$.",1710.01353v2
2017-10-06,Anisotropies of the magnetic field fluctuations at kinetic scales in the solar wind : Cluster observations,"We present the first statistical study of the anisotropy of the magnetic
field turbulence in the solar wind between 1 and 200Hz, i.e. from proton to
sub-electron scales. We consider 93 10-minute intervals of Cluster/STAFF
measurements. We find that the fluctuations $\delta B_{\perp}^2$ are not
gyrotropic at a given frequency $f$, a property already observed at larger
scales ($\parallel$/$\perp$ mean parallel/perpendicular to the average magnetic
${\bf B_0}$). This non-gyrotropy gives indications on the angular distribution
of the wave vectors ${\bf k}$: at $f <$ 10Hz, we find that $k_{\perp}\gg
k_{\parallel}$, mainly in the fast wind; at $f >$ 10Hz, fluctuations with a
non-negligible $k_{\parallel}$ are also present. We then consider the
anisotropy ratio $\delta B_{\parallel}^2/\delta B_{\perp}^2$, which is a
measure of the magnetic compressibility of the fluctuations. This ratio, always
smaller than 1, increases with $f.$ It reaches a value showing that the
fluctuations are more or less isotropic at electron scales, for $f \geq 50$Hz.
From 1 to 15-20Hz, there is a strong correlation between the observed
compressibility and the one expected for the kinetic Alfv\'en waves (KAW),
which only depends on the total plasma $\beta$. For $f > $ 15-20Hz, the
observed compressibility is larger than expected for KAW; and it is stronger in
the slow wind: this could be an indication of the presence of a slow-ion
acoustic mode of fluctuations, which is more compressive and is favored by the
larger values of the electron to proton temperature ratio generally observed in
the slow wind.",1710.02341v1
2017-10-20,Electron Heating in Low Mach Number Perpendicular shocks. I. Heating Mechanism,"Recent X-ray observations of merger shocks in galaxy clusters have shown that
the post-shock plasma is two-temperature, with the protons hotter than the
electrons. By means of two-dimensional particle-in-cell simulations, we study
the physics of electron irreversible heating in perpendicular low Mach number
shocks, for a representative case with sonic Mach number of 3 and plasma beta
of 16. We find that two basic ingredients are needed for electron entropy
production: (i) an electron temperature anisotropy, induced by field
amplification coupled to adiabatic invariance; and (ii) a mechanism to break
the electron adiabatic invariance itself. In shocks, field amplification occurs
at two major sites: at the shock ramp, where density compression leads to an
increase of the frozen-in field; and farther downstream, where the shock-driven
proton temperature anisotropy generates strong proton cyclotron and mirror
modes. The electron temperature anisotropy induced by field amplification
exceeds the threshold of the electron whistler instability. The growth of
whistler waves breaks the electron adiabatic invariance, and allows for
efficient entropy production. We find that the electron heating efficiency
displays only a weak dependence on mass ratio (less than 30 percent drop, as we
increase the mass ratio from 49 up to 1600). We develop an analytical model of
electron irreversible heating and show that it is in excellent agreement with
our simulation results.",1710.07648v1
2017-10-20,Transverse instabilities of stripe domains in magnetic thin films with perpendicular magnetic anisotropy,"Stripe domains are narrow, elongated, reversed regions that exist in magnetic
materials with perpendicular magnetic anisotropy. Stripe domains appear as a
pair of domain walls that can exhibit topology with a nonzero chirality. Recent
experimental and numerical investigations identify an instability of stripe
domains in the long direction as a means of nucleating isolated magnetic
skyrmions. Here, the onset and nonlinear evolution of transverse instabilities
for a dynamic stripe domain known as the bion stripe are investigated. Both
non-topological and topological variants of the bion stripe are shown to
exhibit a long-wavelength transverse instability with different characteristic
features. In the former, small transverse variations in the stripe's width lead
to a neck instability that eventually pinches the non-topological stripe into a
chain of two-dimensional breathers composed of droplet soliton pairs. In the
latter case, small variations in the stripe's center results in a snake
instability whose topological structure leads to the nucleation of dynamic
magnetic skyrmions and antiskyrmions as well as perimeter-modulated droplets.
Quantitative, analytical predictions for both the early, linear evolution and
the long-time, nonlinear evolution are achieved using an averaged Lagrangian
approach that incorporates both exchange (dispersion) and anisotropy
(nonlinearity). The method of analysis is general and can be applied to other
filamentary structures.",1710.07718v1
2017-12-04,The Nature of Bonding in Bulk Tellurium Composed of One-Dimensional Helical Chains,"Bulk tellurium (Te) is composed of one-dimensional (1D) helical chains which
have been considered to be coupled by van der Waals (vdW) interactions.
However, based on first-principles density-functional theory calculations, we
here propose a different bonding nature between neighboring chains: i.e., the
helical chains made of normal covalent bonds are connected together by
coordinate covalent bonds. It is revealed that the lone pairs of electrons of
Te atom participate in forming coordinate covalent bonds between neighboring
chains. Therefore, each Te atom behaves as both electron donor to neighboring
chains and electron acceptor from neighboring chains. This ligand-metal-like
bonding nature in bulk Te results in the same order of bulk moduli along the
directions parallel and perpendicular to the chains, contrasting with the large
anisotropy of bulk moduli in vdW crystals. We further find that the electron
effective masses parallel and perpendicular to the chains are almost the same
each other, consistent with the observed nearly isotropic electrical
resistivity. It is thus demonstrated that the normal/coordinate covalent bonds
parallel/perpendicular to the chains in bulk Te lead to a minor anisotropy in
structural and transport properties, distinct from a strong anisotropy observed
in the typical two-dimensional (2D) vdW materials such as graphite and MoS$_2$.",1712.00894v1
2017-12-08,Superconducting and normal-state anisotropy of the doped topological insulator Sr$_{0.1}$Bi$_2$Se$_3$,"Sr$_x$Bi$_2$Se$_3$ and the related compounds Cu$_x$Bi$_2$Se$_3$ and
Nb$_x$Bi$_2$Se$_3$ have attracted considerable interest, as these materials may
be realizations of unconventional topological superconductors.
Superconductivity with T$_c$ ~ 3 K in Sr$_x$Bi$_2$Se$_3$ arises upon
intercalation of Sr into the layered topological insulator Bi$_2$Se$_3$. Here
we elucidate the anisotropy of the normal and superconducting state of
Sr$_{0.1}$Bi$_2$Se$_3$ with angular dependent magnetotransport and
thermodynamic measurements. High resolution x-ray diffraction studies underline
the high crystalline quality of the samples. We demonstrate that the normal
state electronic and magnetic properties of Sr$_{0.1}$Bi$_2$Se$_3$ are
isotropic in the basal plane while we observe a large two-fold in-plane
anisotropy of the upper critical field in the superconducting state. Our
results support the recently proposed odd-parity nematic state characterized by
a nodal gap of $E_u$ symmetry in Sr$_x$Bi$_2$Se$_3$.",1712.03215v1
2017-12-09,Periodic chiral magnetic domains in single-crystal nickel nanowires,"We report on experimental and computational investigations of the domain
structure of ~0.2 x 0.2 x 8 {\mu}m single-crystal Ni nanowires (NWs). The Ni
NWs were grown by a thermal chemical vapor deposition technique that results in
highly-oriented single-crystal structures on amorphous SiOx coated Si
substrates. Magnetoresistance measurements of the Ni NWs suggest the average
magnetization points largely off the NW long axis at zero field. X-ray
photoemission electron microscopy images show a well-defined periodic
magnetization pattern along the surface of the nanowires with a period of
{\lambda} = 250 nm. Finite element micromagnetic simulations reveal that an
oscillatory magnetization configuration with a period closely matching
experimental observation ({\lambda} = 240 nm) is obtainable at remanence. This
magnetization configuration involves a periodic array of alternating chirality
vortex domains distributed along the length of the NW. Vortex formation is
attributable to the cubic anisotropy of the single crystal Ni NW system and its
reduced structural dimensions. The periodic alternating chirality vortex state
is a topologically protected metastable state, analogous to an array of
360{\deg} domain walls in a thin strip. Simulations show that other remanent
states are also possible, depending on the field history. Effects of material
properties and strain on the vortex pattern are investigated. It is shown that
at reduced cubic anisotropy vortices are no longer stable, while negative
uniaxial anisotropy and magnetoelastic effects in the presence of compressive
biaxial strain contribute to vortex formation.",1712.03387v1
2017-12-04,Planck 2015 constraints on the non-flat $φ$CDM inflation model,"We perform Markov chain Monte Carlo analyses to put constraints on the
non-flat $\phi$CDM inflation model using Planck 2015 cosmic microwave
background (CMB) anisotropy data and baryon acoustic oscillation distance
measurements. The $\phi$CDM model is a consistent dynamical dark energy model
in which the currently accelerating cosmological expansion is powered by a
scalar field $\phi$ slowly rolling down an inverse power-law potential energy
density. We also use a physically consistent power spectrum for energy density
inhomogeneities in this non-flat model. We find that, like the
closed-$\Lambda$CDM and closed-XCDM models, the closed-$\phi$CDM model provides
a better fit to the lower multipole region of the CMB temperature anisotropy
data compared to that provided by the tilted flat-$\Lambda$CDM model. Also,
like the other closed models, this model reduces the tension between the Planck
and the weak lensing $\sigma_8$ constraints. However, the higher multipole
region of the CMB temperature anisotropy data are better fit by the tilted
flat-$\Lambda$CDM model than by the closed models.",1712.08617v2
2018-01-09,Epitaxial Heusler Superlattice Co2MnAl/Fe2MnAl with Perpendicular Magnetic Anisotropy and Termination-Dependent Half-Metallicity,"Single-crystal Heusler atomic-scale superlattices that have been predicted to
exhibit perpendicular magnetic anisotropy and half-metallicity have been
successfully grown by molecular beam epitaxy. Superlattices consisting of
full-Heusler Co$_2$MnAl and Fe$_2$MnAl with one to three unit cell periodicity
were grown on GaAs (001), MgO (001), and Cr (001)/MgO (001). Electron energy
loss spectroscopy maps confirmed clearly segregated epitaxial Heusler layers
with high cobalt or high iron concentrations for samples grown near room
temperature on GaAs (001). Superlattice structures grown with an excess of
aluminum had significantly lower thin film shape anisotropy and resulted in an
out-of-plane spin reorientation transition at temperatures below 200 K for
samples grown on GaAs (001). Synchrotron-based spin resolved photoemission
spectroscopy found that the superlattice structure improves the Fermi level
spin polarization near the X point in the bulk Brillouin zone. Stoichiometric
Co$_2$MnAl terminated superlattice grown on MgO (001) had a spin polarization
of 95%, while a pure Co$_2$MnAl film had a spin polarization of only 65%.",1801.02787v1
2018-01-20,"Generalized coupled mode formalism in reciprocal waveguides with gain/loss, anisotropy or bianisotropy","In anisotropic or bianisotropic waveguides, the standard coupled mode theory
fails due to the broken link between the forward and backward propagating
modes, which together form the dual mode sets that are crucial in constructing
couple mode equations. We generalize the coupled mode theory by treating the
forward and backward propagating modes on the same footing via a generalized
eigenvalue problem that is exactly equivalent to the waveguide Hamiltonian. The
generalized eigenvalue problem is fully characterized by two operators, i.e.,
$( \bar{\bm{L}},\bar{\bm{B}})$, wherein $\bar{\bm{L}}$ is a self-adjoint
differential operator, while $\bar{\bm{B}}$ is a constant antisymmetric
operator. From the properties of $\bar{\bm{L}}$ and $\bar{\bm{B}}$, we
establish the relation between the dual mode sets that are essential in
constructing coupled mode equations in terms of forward and backward
propagating modes. By perturbation, the generalized coupled mode equation can
be derived in a natural way. Our generalized coupled mode formalism can be used
to study the mode coupling in waveguides that may contain gain/loss, anisotropy
or bianisotropy. We further illustrate how the generalized coupled theory can
be used to study the modal coupling in anisotropy and bianisotropy waveguides
through a few concrete examples.",1801.06673v1
2018-01-29,Magnetism of a Co monolayer on Pt(111) capped by overlayers of $5d$ elements: a spin-model study,"Using first-principles calculations, we study the magnetic properties of a Co
monolayer on a Pt(111) surface with a capping monolayer of selected $5d$
elements (Re, Os, Ir, Pt and Au). First we determine the tensorial exchange
interactions and magnetic anisotropies characterizing the Co monolayer for all
considered systems. We find a close relationship between the magnetic moment of
the Co atoms and the nearest-neighbor isotropic exchange interaction, which is
attributed to the electronic hybridization between the Co and the capping
layers, in spirit of the Stoner picture of ferromagnetism. The
Dzyaloshinskii-Moriya interaction is decreased for all overlayers compared to
the uncapped Co/Pt(111) system, while even the sign of the
Dzyaloshinskii-Moriya interaction changes in case of the Ir overlayer. We
conclude that the variation of the Dzyaloshinskii-Moriya interaction is well
correlated with the change of the magnetic anisotropy energy and of the orbital
moment anisotropy. The unique influence of the Ir overlayer on the
Dzyaloshinskii-Moriya interaction is traced by scaling the strength of the
spin--orbit coupling of the Ir atoms in Ir/Co/Pt(111) and by changing the Ir
concentration in the Au$_{1-x}$Ir$_{x}$/Co/Pt(111) system. Our spin dynamics
simulations indicate that the magnetic ground state of Re/Co/Pt(111) thin film
is a spin spiral with a tilted normal vector, while the other systems are
ferromagnetic.",1801.09426v1
2018-02-09,Co-formation of the Galactic disc and the stellar halo,"Using a large sample of Main Sequence stars with 7-D measurements supplied by
Gaia and SDSS, we study the kinematic properties of the local (within ~10 kpc
from the Sun) stellar halo. We demonstrate that the halo's velocity ellipsoid
evolves strongly with metallicity. At the low [Fe/H] end, the orbital
anisotropy (the amount of motion in the radial direction compared to the
tangential one) is mildly radial with 0.2<beta<0.4. However, for stars with
[Fe/H]>-1.7 we measure extreme values of beta~0.9. Across the metallicity range
considered, i.e. -3<[Fe/H]<-1, the stellar halo's spin is minimal, at the level
of 20<v_theta (km/s) <30. Using a suite of cosmological zoom-in simulations of
halo formation, we deduce that the observed acute anisotropy is inconsistent
with the continuous accretion of dwarf satellites. Instead, we argue, the
stellar debris in the inner halo were deposited in a major accretion event by a
satellite with Mvir>10^10 Msun around the epoch of the Galactic disc formation,
i.e. between 8 and 11 Gyr ago. The radical halo anisotropy is the result of the
dramatic radialisation of the massive progenitor's orbit, amplified by the
action of the growing disc.",1802.03414v1
2018-02-16,Interplay of phase boundary anisotropy and electro-autocatalytic surface reactions on the lithium intercalation dynamics in Li$_X$FePO$_4$ platelet-like nanoparticles,"Experiments on single crystal Li$_X$FePO$_4$ (LFP) nanoparticles indicate
rich nonequilibrium phase behavior, such as suppression of phase separation at
high lithiation rates, striped patterns of coherent phase boundaries,
nucleation by binarysolid surface wetting and intercalation waves. These
observations have been successfully predicted (prior to the experiments) by 1D
depth-averaged phase-field models, which neglect any subsurface phase
separation. In this paper, using an electro-chemo-mechanical phase-field model,
we investigate the coherent non-equilibrium subsurface phase morphologies that
develop in the $ab$- plane of platelet-like single-crystal platelet-like
Li$_X$FePO$_4$ nanoparticles. Finite element simulations are performed for 2D
plane-stress conditions in the $ab$- plane, and validated by 3D simulations,
showing similar results. We show that the anisotropy of the interfacial tension
tensor, coupled with electroautocatalytic surface intercalation reactions,
plays a crucial role in determining the subsurface phase morphology. With
isotropic interfacial tension, subsurface phase separation is observed,
independent of the reaction kinetics, but for strong anisotropy, phase
separation is controlled by surface reactions, as assumed in 1D models.
Moreover, the driven intercalation reaction suppresses phase separation during
lithiation, while enhancing it during delithiation, by electro-autocatalysis,
in quantitative agreement with {\it in operando} imaging experiments in
single-crystalline nanoparticles, given measured reaction rate constants.",1802.05847v1
2018-03-02,Broadband spectroscopy of thermodynamic magnetization fluctuations through a ferromagnetic spin-reorientation transition,"We use scanning optical magnetometry to study the broadband frequency spectra
of spontaneous magnetization fluctuations, or ""magnetization noise"", in an
archetypal ferromagnetic film that can be smoothly tuned through a spin
reorientation transition (SRT). The SRT is achieved by laterally varying the
magnetic anisotropy across an ultrathin Pt/Co/Pt trilayer, from the
perpendicular to in-plane direction, via graded Ar$^+$ irradiation. In regions
exhibiting perpendicular anisotropy, the power spectrum of the magnetization
noise, $S(\nu)$, exhibits a remarkably robust $\nu^{-3/2}$ power law over
frequencies $\nu$ from 1~kHz to 1~MHz. As the SRT region is traversed, however,
$S(\nu)$ spectra develop a steadily-increasing critical frequency, $\nu_0$,
below which the noise power is spectrally flat, indicating an evolving
low-frequency cutoff for magnetization fluctuations. The magnetization noise
depends strongly on applied in- and out-of-plane magnetic fields, revealing
local anisotropies and also a field-induced emergence of fluctuations in
otherwise stable ferromagnetic films. Finally, we demonstrate that higher-order
correlators can be computed from the noise. These results highlight broadband
spectroscopy of thermodynamic fluctuations as a powerful tool to characterize
the interplay between thermal and magnetic energy scales, and as a means of
characterizing phase transitions in ferromagnets.",1803.00962v1
2018-03-07,Highly thermally stable sub-20nm magnetic random-access memory based on perpendicular shape anisotropy,"A new approach to increase the downsize scalability of perpendicular STT-MRAM
is presented. It consists in significantly increasing the thickness of the
storage layer in out-of-plane magnetized tunnel junctions (pMTJ) as compared to
conventional pMTJ in order to induce a perpendicular shape anisotropy (PSA) in
this layer. This PSA is obtained by depositing a thick ferromagnetic (FM) layer
on top of an MgO/FeCoB based magnetic tunnel junction (MTJ) so that the
thickness of the storage layer becomes of the order or larger than the diameter
of the MTJ pillar. In contrast to conventional spin transfer torque magnetic
random access memory (STT-MRAM) wherein the demagnetizing energy opposes the
interfacial perpendicular magnetic anisotropy (iPMA), in these novel memory
cells, both PSA and iPMA contributions favor out-of-plane orientation of the
storage layer magnetization. Using thicker storage layers in these PSA-STT-MRAM
has several advantages. Thanks to the PSA, very high and easily tunable thermal
stability factors can be achieved, even down to sub-10 nm diameters. Moreover,
low damping material can be used for the thick FM material thus leading to a
reduction of the write current. The paper describes this new PSA-STT-MRAM
concept, practical realization of such memory arrays, magnetic characterization
demonstrating thermal stability factor above 200 for MTJs as small as 8nm in
diameter and possibility to maintain thermal stability factor above 60 down to
4nm diameter.",1803.02663v1
2018-03-13,Spatial Distribution of Globular Clusters in the Galaxy,"The Milky Way's satellite galaxies and Globular Clusters (GCs) are known to
exhibit an anisotropic spatial distribution. We examine in detail this
anisotropy by the means of the inertia tensor. We estimate the statistical
significance of the results by repeating this analysis for random catalogues
which use the radial distribution of the real sample. Our method reproduces the
well-known planar structure in the distribution of the satellite galaxies. We
show that for GCs several anisotropic structures are observed. The GCs at small
distances, $2<R<10$ kpc, show a structure coplanar with the Galactic plane. At
smaller and larger distances the whole sample of GCs shows quite weak
anisotropy. Nevertheless, at largest distances the orientation of the structure
is close to that of the satellite galaxies, i.e. perpendicular to the Galactic
plane. We estimate the probability of random realization for this structure of
1.7%. The Bulge-Disk GCs show a clear disk-like structure lying within the
galactic disk. The Old Halo GCs show two structures: a well pronounced polar
elongated structure at $R<3$ kpc which is perpendicular to the galactic plane,
and a less pronounced disk-like structure coplanar with the galactic disk at
$6<R<20$ kpc. The Young Halo GCs do not show significant anisotropy.",1803.04770v1
2018-03-31,Understanding current-driven dynamics of magnetic Néel walls in heavy metal/ferromagnetic metal/oxide trilayers,"We consider analytically current-driven dynamics of magnetic N\'{e}el walls
in heavy metal/ferromagnetic metal/oxide trilayers where strong spin-orbit
coupling and interfacial Dzyaloshinskii-Moriya interaction (i-DMI) coexist. We
show that field-like spin-orbit torque (FL-SOT) with effective field along
$\mathbf{n}\times\hat{\mathbf{J}}$ ($\mathbf{n}$ being the interface normal and
$\hat{\mathbf{J}}$ being the charge current direction) and i-DMI induced torque
can both lead to Walker breakdown suppression meanwhile leaving the wall
mobility (velocity versus current density) unchanged. However, i-DMI itself can
not induce the ""universal absence of Walker breakdown"" (UAWB) while FL-SOT
exceeding a certain threshold can. Finitely-enlarged Walker limits before UAWB
are theoretically calculated and well explain existing data. In addition,
change in wall mobility and even its sign-inversion can be understood only if
the anti-damping-like (ADL) SOT is appended. For N\'{e}el walls in
ferromagnetic-metal layer with both perpendicular and in-plane anisotropies, we
have calculated the respective modifications of wall mobility under the
coexistence of spin-transfer torque, SOTs and i-DMI. Analytics shows that in
trilayers with perpendicular anisotropy strong enough spin Hall angle and
appropriate sign of i-DMI parameter can lead to sign-inversion in wall mobility
even under small enough current density, while in those with in-plane
anisotropy this only occurs for current density in a specific range.",1804.00127v4
2018-04-03,Influence of Exchange Scattering on Superfluid He-3 states in Nematic Aerogel,"The superfluid state in bulk liquid $^3$He is realized in the form of A or B
phases. Uniaxially anisotropic aerogel (nafen) stabilizes transition from the
normal to the polar superfluid state which on further cooling transitions to
the axipolar orbital glass state (Phys. Rev. Lett. {\bf 115}, 165304 (2015)).
This is the case in nafen aerogel preplated by several atomic layers of $^4$He.
When pure liquid $^3$He fills the same nafen aerogel a solid-like layer of
$^3$He atoms coats the aerogel structure. The polar state is not formed anymore
and a phase transition occurs directly to the axipolar phase (Phys. Rev. Lett.
{\bf 120}, 075301 (2018). The substitution of $^4$He by $^3$He atoms at the
aerogel surface changes the potential and adds the exchange scattering of
quasiparticles on the aerogel strands. A calculation shows that both of these
effects can decrease the degree of anisotropy of scattering and suppress the
polar phase formation. The derived anisotropy of the spin diffusion coefficient
in globally anisotropic aerogel is determined by the same parameter which
controls the polar state emergence which allows one to check the effect of
anisotropy change for different types of covering.",1804.01073v3
2018-04-25,Determination of the spin-lifetime anisotropy in graphene using oblique spin precession,"We determine the spin-lifetime anisotropy of spin-polarized carriers in
graphene. In contrast to prior approaches, our method does not require large
out-of-plane magnetic fields and thus it is reliable for both low- and
high-carrier densities. We first determine the in-plane spin lifetime by
conventional spin precession measurements with magnetic fields perpendicular to
the graphene plane. Then, to evaluate the out-of-plane spin lifetime, we
implement spin precession measurements under oblique magnetic fields that
generate an out-of-plane spin population. We find that the spin-lifetime
anisotropy of graphene on silicon oxide is independent of carrier density and
temperature down to 150 K, and much weaker than previously reported. Indeed,
within the experimental uncertainty, the spin relaxation is isotropic.
Altogether with the gate dependence of the spin lifetime, this indicates that
the spin relaxation is driven by magnetic impurities or random spin-orbit or
gauge fields.",1804.09556v1
2018-04-30,Statistical anisotropies in temperature and polarization fluctuations from a scale-dependent trispectrum,"We study statistical anisotropies generated in the observed two-point
function of the cosmic microwave background (CMB) fluctuations if the
primordial statistics are non-Gaussian. Focusing on the dipole modulations of
the anisotropies, we find that the hemispherical power asymmetry observed in
the CMB temperature fluctuations can be modeled by a local-type trispectrum
with amplitude $\tau_{\rm NL}(k_p=0.05~{\rm Mpc}^{-1}) \approx 2 \times 10^4$
and a large red tilt $n\approx -0.68$. We numerically evaluate the non-Gaussian
covariance of the modulation estimators for both temperature and E-mode
polarization fluctuations and discuss the prospects of constraining the model
using Planck satellite data. We then discuss other effects of the
scale-dependent trispectrum that could be used to distinguish this scenario
from other explanations of the power asymmetry: higher-order modulations of the
two-point function and the non-Gaussian angular power spectrum covariance. As
an important consequence of the non-Gaussian power spectrum covariance, we
discuss how the CMB-inferred spectral index of primordial scalar fluctuations
can be significantly biased in the presence of a scale-dependent local-type
trispectrum.",1805.00037v2
2018-05-01,Diagonal Nematicity in the Pseudogap Phase of HgBa$_2$CuO$_{4+δ}$,"The pseudogap phenomenon in cuprates is the most mysterious puzzle in the
research of high-temperature superconductivity. In particular, whether the
pseudogap is associated with a crossover or phase transition has been a
long-standing controversial issue. The tetragonal cuprate
HgBa$_2$CuO$_{4+\delta}$, with only one CuO$_2$ layer per primitive cell, is an
ideal system to tackle this puzzle. Here, we measure the anisotropy of magnetic
susceptibility within the CuO$_2$ plane with exceptionally high-precision
magnetic torque experiments. Our key finding is that a distinct two-fold
in-plane anisotropy sets in below the pseudogap temperature $T^*$, which
provides thermodynamic evidence for a nematic phase transition with broken
four-fold symmetry. Most surprisingly, the nematic director orients along the
diagonal direction of the CuO$_2$ square lattice, in sharp contrast to the bond
nematicity reported in various iron-based superconductors and double-layer
YBa$_2$Cu$_3$O$_{6+\delta}$, where the anisotropy axis is along the Fe-Fe and
Cu-O-Cu directions, respectively. Another remarkable feature is that the
enhancement of the diagonal nematicity with decreasing temperature is
suppressed around the temperature at which short-range charge-density-wave
(CDW) formation occurs. This is in stark contrast to
YBa$_2$Cu$_3$O$_{6+\delta}$, where the bond nematicity is not influenced by the
CDW. Our result suggests a competing relationship between diagonal nematic and
CDW order in HgBa$_2$CuO$_{4+\delta}$.",1805.00276v1
2018-05-12,Dissociation of heavy quarkonia in an anisotropic hot QCD medium in a Quasi-Particle Model,"The present article is the follow up work of, Phys.\ Rev.\ D {\bf 94}, 094006
(2016), where we have extended the study of quarkonia dissociation in
(momentum) anisotropic hot QCD medium. As evident by the experimentally
observed collective flow at RHIC and LHC, the momentum anisotropy is present at
almost all the stages after the collision and therefore, it is important to
include its effects in the analysis. Employing the in-medium (corrected)
potential while considering the anisotropy (both oblate and prolate cases) in
the medium, the thermal widths and the binding energies of the heavy quarkonia
states (s-wave charmonia and s-wave bottomonia specifically, for radial quantum
numbers n = 1 and 2) have been determined. The hot QCD medium effects have been
included employing a quasi-particle description. The presence of anisotropy has
modified the potential and then the thermal widths and the binding energies of
these states in a significant manner. The results show a quite visible shift in
the values of dissociation temperatures as compared to the isotropic case.
Further, the hot QCD medium interaction effects suppress the dissociation
temperature as compared to the case where we consider the medium as a
non-interacting ultra-relativistic gas of quarks (anti-quarks) and gluons.",1805.04763v1
2018-05-21,Baryons under Strong Magnetic Fields or in Theories with Space-dependent $θ$-term,"Baryonic states are sufficiently complex to reveal physics that is hidden in
the mesonic bound states. Using gauge/gravity correspondence we study
analytically and numerically baryons in theories with space-dependent
$\theta$-term, or theories under strong magnetic fields. Such holographic
studies on baryons are accommodated in a generic analytic framework we develop
for anisotropic theories, where their qualitative features are common
irrespective of the source that triggers the anisotropy. We find that the
distribution of the quarks forming the state, depends on the angle between the
baryon and the anisotropic direction. Its shape is increasingly elliptic with
respect to the strength of the field sourcing the anisotropy, counterbalancing
the broken rotational invariance on the gluonic degrees of freedom. Strikingly,
the baryons dissociate in stages with a process that depends on the proximity
of the quarks to the anisotropic direction, where certain quark pairs abandon
the bound state first, followed by the closest pairs to them as the temperature
increases. This observation may also serve as a way to identify the nature of
certain exotic states. Finally, we investigate holographic baryons with
decreased number of quarks and explain why in theories under consideration the
presence of anisotropy does not modify the universal stability condition in
contrast to the usual trend.",1805.08245v2
2018-05-22,Structural properties and anisotropic electronic transport in SrIrO3 films,"Perovskite SrIrO3 (SIO) films epitaxially deposited with a thickness of about
60 nm on various substrate materials display nearly strain-relieved state.
Films grown on orthorhombic (110) DyScO3 (DSO) are found to display untwinned
bulk-like orthorhombic structure. However, film deposition on cubic (001)
SrTiO3 induces a twinned growth of SIO. Resistance measurements on the SIO
films reveal only weak temperature dependence, where the resistance R increases
with decreasing temperature T. Hall measurements show dominant electron-like
transport throughout the temperature range from 2 K to 300 K. At 2 K, the
electron concentration and resistivity for SIO on STO amount to ne = 1.4*10^20
cm-3 and 1 mohmcm. Interestingly, the film resistance of untwinned SIO on DSO
along the [1-10] and the [001] direction differs by up to 25% indicating
pronounced anisotropic electronic transport. The anisotropy of the resistance
increases with decreasing T and displays a distinct maximum around 86 K. The
specific T-dependence is similar to that of the structural anisotropy
sqrt(a2+b2)/c of bulk SIO. Therefore, anisotropic electronic transport in SIO
is very likely induced by the orthorhombic distortion. Consequently, for
twinned SIO films on STO anisotropy vanishes nearly completely. The
experimental results show that structural changes are very likely responsible
for the observed anisotropic electronic transport. The strong sensitivity of
the electronic transport in SIO films may be explained in terms of the narrow
electron-like bands in SIO caused by spin-orbit-coupling and orthorhombic
distortion.",1805.08473v2
2018-06-05,Bilayer Kitaev models: Phase diagrams and novel phases,"Kitaev's honeycomb-lattice spin-$1/2$ model has become a paradigmatic example
for $\mathbb{Z}_2$ quantum spin liquids, both gapped and gapless. Here we study
the fate of these spin-liquid phases in differently stacked bilayer versions of
the Kitaev model. Increasing the ratio between the inter-layer Heisenberg
coupling $J_\perp$ and the intra-layer Kitaev couplings $K^{x,y,z}$ destroys
the topological spin liquid in favor of a paramagnetic dimer phase. We study
phase diagrams as a function of $J_\perp/K$ and Kitaev coupling anisotropies
using Majorana-fermion mean-field theory, and we employ different expansion
techniques in the limits of small and large $J_\perp/K$. For strongly
anisotropic Kitaev couplings, we derive effective models for the different
layer stackings which we use to discuss the quantum phase transition out of the
Kitaev phase. We find that the phase diagrams depend sensitively on the nature
of the stacking and anisotropy strength. While in some stackings and at strong
anisotropies we find a single transition between the Kitaev and dimer phases,
other stackings are more involved: Most importantly, we prove the existence of
two novel macro-spin phases which can be understood in terms of Ising chains
which can be either coupled ferromagnetically or remain degenerate, thus
realizing a classical spin liquid. In addition, our results suggest the
existence of a flux phase with spontaneous inter-layer coherence.",1806.01852v2
2018-06-13,Evolution from Ferromagnetism to Antiferromagnetism in Yb(Rh1-xCox)2Si2,"Yb(Rh1-xCox)2Si2 is a model system to address two challenging problems in the
field of strongly correlated electron systems: The first is the intriguing
competition between ferromagnetic (FM) and antiferromagnetic (AFM) order when
approaching a magnetic quantum critical point (QCP). The second is the
occurrence of magnetic order along a very hard crystalline electric field (CEF)
direction, i.e. along the one with the smallest available magnetic moment.
Here, we present a detailed study of the evolution of the magnetic order in
this system from a FM state with moments along the very hard c direction at x =
0.27 towards the yet unknown magnetic state at x = 0. We first observe a
transition towards an AFM canted state with decreasing x and then to a pure AFM
state. This confirms that the QCP in YbRh2Si2 is AFM, but the phase diagram is
very similar to those observed in some inherently FM systems like NbFe2 and
CeRuPO, which suggests that the basic underlying instability might be FM.
Despite the huge CEF anisotropy the ordered moment retains a component along
the c-axis also in the AFM state. The huge CEF anisotropy in Yb(Rh1-xCox)2Si2
excludes that this hard-axis ordering originates from a competing exchange
anisotropy as often proposed for other heavy-fermion systems. Instead, it
points to an order-by-disorder based mechanism.",1806.05088v2
2018-06-29,Certain developments on the equilibrium of magnetized plasmas,"Recent results will be presented on steady states of magnetically confined
plasmas obtained by conventional and Hamiltonian methods. The presentation
consists of three parts. The first one concerns the derivation of a generalized
Grad-Shafranov equation describing helically symmetric equilibria with pressure
anisotropy and incompressible plasma flow of arbitrary direction with
application to straight-stellarator configurations [1]. The impact of pressure
anisotropy and flow on the equilibrium characteristics is also examined. In the
second part the axisymmetric equilibrium code HELENA is extended for pressure
anisotropy and flow parallel to the magnetic field and ITER-pertinent
equilibria are constructed. In the third part the Hamiltonian formulation of
helically symmetric plasmas is established within the framework of extended
MHD, a simplified two-fluid model including Hall-ion and electron-inertia
contributions [2,3]. Four families of Casimir invariants are obtained and they
are used to construct Energy-Casimir variational principles for deriving
generalized extended MHD equilibrium equations with arbitrary flow. The system
is then cast into the form of Grad-Shafranov-Bernoulli equations. In addition,
an example of an incompressible double-Beltrami equilibrium will be presented
in connection with a straight-stellarator configuration.",1806.11343v2
2018-07-04,Towards a Generalized Hydrodynamics description of Rényi entropies in integrable systems,"We investigate the steady-state R\'enyi entanglement entropies after a quench
from a piecewise homogeneous initial state in integrable models. In the quench
protocol two macroscopically different chains (leads) are joined together at
the initial time, and the subsequent dynamics is studied. We study the
entropies of a finite subsystem at the interface between the two leads. The
density of R\'enyi entropies coincides with that of the entropies of the
Generalized Gibbs Ensemble (GGE) that describes the interface between the
chains. By combining the Generalized Hydrodynamics (GHD) treatment of the
quench with the Bethe ansatz approach for the R\'enyi entropies, we provide
exact results for quenches from several initial states in the anisotropic
Heisenberg chain (XXZ chain), although the approach is applicable, in
principle, to any low-entangled initial state and any integrable model. An
interesting protocol that we consider is the expansion quench, in which one of
the two leads is prepared in the vacuum of the model excitations. An intriguing
feature is that for moderately large anisotropy the transport of bound-state is
not allowed. Moreover, we show that there is a `critical' anisotropy, above
which bound-state transport is permitted. This is reflected in the steady-state
entropies, which for large enough anisotropy do not contain information about
the bound states. Finally, we benchmark our results against time-dependent
Density Matrix Renormalization Group (tDMRG) simulations.",1807.01800v2
2018-07-19,Magnetization nutation induced by surface effects in nanomagnets,"We investigate the magnetization dynamics of ferromagnetic nanoparticles in
the atomistic approach taking account of surface anisotropy and the spin
misalignment it causes. We demonstrate that such inhomogeneous spin
configurations induce nutation in the dynamics of the particle's magnetization.
More precisely, in addition to the ordinary precessional motion with frequency
$f_{p}\sim10\,{\rm GHz}$, we find that the dynamics of the net magnetic moment
exhibits two more resonance peaks with frequencies $f_{c}$ and $f_{n}$ which
are higher than the frequency $f_{p} : f_{c}=4\times f_{p}\sim40\,{\rm GHz}$ is
related with the oscillations of the particle's magnetic moment between the
minima of the effective potential induced by weak surface anisotropy. On the
other hand, the much higher frequency $f_{n}\sim1\,{\rm THz}$ is attributed to
the magnetization fluctuations at the atomic level driven by exchange
interaction. We have compared our results on nutation induced by surface
effects with those rendered by the macroscopic approach based on the
Landau-Lifshitz-Gilbert equation augmented by an inertial term (proportional to
the second-order time derivative of the macroscopic moment) with a
phenomenological coefficient. The good agreement between the two models have
allowed us to estimate the latter coefficient in terms of the atomistic
parameters such as the surface anisotropy constant. We have thus proposed a new
origin for the magnetization nutations as being induced by surface effects and
have interpreted the corresponding resonance peaks and their frequencies.",1807.07392v1
2018-07-20,Schwarzschild dynamical model of the Fornax dwarf spheroidal galaxy,"We present a full dynamical model of the Fornax dwarf spheroidal galaxy
obtained with the spherically symmetric Schwarzschild orbit superposition
method applied to the largest kinematic data set presently available. We
modelled the total mass content of the dwarf with the mass-to-light ratio
$\Upsilon$ varying with radius and found that Fornax is with high probability
embedded in a massive and extended dark matter halo. We estimated the total
mass contained within 1$\,$kpc to be $M(<1\,$kpc$)=1.25^{+0.06}_{-0.13} \times
10^8\,$M$_{\odot}$. The data are consistent with the constant mass-to-light
ratio, i.e. the mass-follows-light model, only at 3$\sigma$ level, but still
require a high value of $\Upsilon \approx 11.2\,$M$_{\odot}/$L$_{\odot}$. Our
results are in general agreement with previous estimates of the dynamical mass
profile of Fornax. As the Schwarzschild method does not require any assumptions
on the orbital anisotropy of the stars, we obtained a profile of the anisotropy
parameter $\beta$ as an output of our modelling. The derived anisotropy is
close to zero in the centre of the galaxy and decreases with radius, but
remains consistent with isotropic orbits at all radii at 1$\sigma$ confidence
level.",1807.07852v2
2018-07-26,Modeling anisotropic magnetized White Dwarfs with $γ$ metric,"The effect of magnetic fields in the Equations of State (EoS) of compact
objects is the splitting of the pressure in two components, one parallel and
the other perpendicular to the magnetic field. This anisotropy suggests the
necessity of using structure equations considering the axial symmetry of the
magnetized system. In this work, we consider an axially symmetric metric in
spherical coordinates, the $\gamma$-metric, and construct a system of equations
to describe the structure of spheroidal compact objects. In addition, we
connect the geometrical parameter $\gamma$ linked to the spheroid's radii, with
the source of the anisotropy. So, the model relates the shape of the compact
object to the physics that determines the properties of the composing matter.
To illustrate how our structure equations work, we obtain the mass-radii
solutions for magnetized White Dwarfs. Our results show that the main effect of
the magnetic field anisotropy in White Dwarfs structure is to cause a
deformation of these objects. Since this effect is only relevant at low
densities, it does not affect the maximum values of magnetized White Dwarf's
masses, which remain under Chandrasekhar limit.",1807.09943v3
2018-08-04,The magnetic exchange parameters and anisotropy of the quasi-two dimensional antiferromagnet NiPS$_3$,"Neutron inelastic scattering has been used to measure the magnetic
excitations in powdered NiPS$_3$, a quasi-two dimensional antiferromagnet with
spin $S = 1$ on a honeycomb lattice. The spectra show clear, dispersive magnons
with a $\sim 7$ meV gap at the Brillouin zone center. The data were fitted
using a Heisenberg Hamiltonian with a single-ion anisotropy assuming no
magnetic exchange between the honeycomb planes. Magnetic exchange interactions
up to the third intraplanar nearest-neighbour were required. The fits show
robustly that NiPS$_3$ has an easy axis anisotropy with $\Delta = 0.3$ meV and
that the third nearest-neighbour has a strong antiferromagnetic exchange of
$J_3 = -6.90$ meV. The data can be fitted reasonably well with either $J_1 < 0$
or $J_1 > 0$, however the best quantitative agreement with high-resolution data
indicate that the nearest-neighbour interaction is ferromagnetic with $J_1 =
1.9$ meV and that the second nearest-neighbour exchange is small and
antiferromagnetic with $J_2 = -0.1$ meV. The dispersion has a minimum in the
Brillouin zone corner that is slightly larger than that at the Brillouin zone
center, indicating that the magnetic structure of NiPS$_3$ is close to being
unstable.",1808.01480v1
2018-08-12,Measurement of the azimuthal anisotropy of charged particles produced in $\sqrt{s_\mathrm{NN}} = 5.02$ TeV Pb+Pb collisions with the ATLAS detector,"Measurements of the azimuthal anisotropy in lead-lead collisions at
$\sqrt{s_\mathrm{NN}} = 5.02$ TeV are presented using a data sample
corresponding to 0.49 $\mathrm{nb}^{-1}$ integrated luminosity collected by the
ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is
enhanced by triggers for ""ultra-central"" collisions, providing an opportunity
to perform detailed study of flow harmonics in the regime where the initial
state is dominated by fluctuations. The anisotropy of the charged-particle
azimuthal angle distributions is characterized by the Fourier coefficients,
$v_{2}-v_{7}$, which are measured using the two-particle correlation,
scalar-product and event-plane methods. The goal of the paper is to provide
measurements of the differential as well as integrated flow harmonics $v_{n}$
over wide ranges of the transverse momentum, 0.5 $<p_{\mathrm{T}}<$ 60 GeV, the
pseudorapidity, $|\eta|<$ 2.5, and the collision centrality $0-80$%. Results
from different methods are compared and discussed in the context of previous
and recent measurements in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 2.76$
TeV and 5.02 TeV. In particular, the shape of the $p_{\mathrm{T}}$ dependence
of elliptic or triangular flow harmonics is observed to be very similar at
different centralities after scaling the $v_{n}$ and $p_{\mathrm{T}}$ values by
constant factors over the centrality interval $0-60$% and the $p_{\mathrm{T}}$
range $0.5 < p_{\mathrm{T}} < 5$ GeV.",1808.03951v2
2018-08-20,Breaking properties of neutron star crust,"The strength of neutron star crust is crucial for modelling magnetar flares,
pulsar glitches and gravitational wave emission. We aim to shed some light on
this problem by analysing uniaxial stretch deformation (elongation and
contraction) of perfect body-centered cubic Coulomb crystals, paying special
attention to the inherent anisotropy of this process. Our analysis is based on
the semi-analytical approach of Baiko and Kozhberov (2017), which, for any
uniform deformation, allows one to calculate, in fully non-linear regime,
critical deformation parameters beyond which the lattice loses its dynamic
stability. We determine critical strain, pressure anisotropy and deformation
energy for any stretch direction with respect to the crystallographic axes.
These quantities are shown to be strongly anisotropic: they vary by a factor of
almost 10 depending on the orientation of the deformation axis. For
polycrystalline crust, we argue that the maximum strain for the stretch
deformation sustainable elastically is 0.04. It is lower than the breaking
strain of 0.1 obtained in molecular dynamic simulations of a shear deformation
by Horowitz and Kadau (2009). The maximum pressure anisotropy of
polycrystalline matter is estimated to be in the range from 0.005 to 0.014
$nZ^2e^2/a$, where $n$ is the ion number density, $Ze$ is the ion charge, and
$a$ is the ion-sphere radius. We discuss possible mechanisms of plastic motion
and formation of large crystallites in neutron star crust as well as analyse
energy release associated with breaking of such crystallites in the context of
magnetic field evolution and magnetar flaring activity.",1808.06415v1
2018-09-03,Dynamics of a simple model microswimmer in an anisotropic fluid: implications for alignment behavior and active transport in a nematic liquid crystal,"Several recent experiments investigate the orientational and transport
behavior of self-driven bacteria and colloidal particles in nematic liquid
crystals. Correspondingly, we study theoretically the dynamics of a minimal
model microswimmer in a uniaxially anisotropic fluid. As a first step, the
hydrodynamic Green's function providing the resulting fluid flow in response to
a localized force acting on the anisotropic fluid is derived analytically. On
this basis, the behavior of both puller- and pusher-type microswimmers in the
anisotropic fluid is analyzed. Depending on the propulsion mechanism and the
relative magnitude of different involved viscosities, we find alignment of the
swimmers parallel or perpendicular to the anisotropy axis. Particularly, also
an oblique alignment is identified under certain circumstances. The observed
swimmer reorientation results from the hydrodynamic coupling between the
self-induced fluid flow and the anisotropy of the surrounding fluid, which
distorts the self-generated flow field. We support parts of our results by a
simplified linear stability analysis. Our theoretical predictions are in
qualitative agreement with recent experimental observations on swimming
bacteria in nematic liquid crystals. They support the objective of utilizing
the, possibly switchable, anisotropy of a host fluid to guide individual
microswimmers and active particles along a requested path, enabling controlled
active transport.",1809.01531v1
2018-09-12,Strong Anisotropy in Liquid Water upon Librational Excitation using Terahertz Laser Fields,"Tracking the excitation of water molecules in the homogeneous liquid is
challenging due to the ultrafast dissipation of rotational excitation energy
through the hydrogen-bonded network. Here we demonstrate strong transient
anisotropy of liquid water through librational excitation using single-color
pump-probe experiments at 12.3 THz. We deduce a third order response of chi^3
exceeding previously reported values in the optical range by three orders of
magnitude. Using a theory that replaces the nonlinear response with a material
response property amenable to molecular dynamics simulation, we show that the
rotationally damped motion of water molecules in the librational band is
resonantly driven at this frequency, which could explain the enhancement of the
anisotropy in the liquid by the external Terahertz field. By addition of salt
(MgSO4), the hydration water is instead dominated by the local electric field
of the ions, resulting in reduction of water molecules that can be dynamically
perturbed by THz pulses.",1809.04261v3
2018-09-21,Minimal Paths for Tubular Structure Segmentation with Coherence Penalty and Adaptive Anisotropy,"The minimal path method has proven to be particularly useful and efficient in
tubular structure segmentation applications. In this paper, we propose a new
minimal path model associated with a dynamic Riemannian metric embedded with an
appearance feature coherence penalty and an adaptive anisotropy enhancement
term. The features that characterize the appearance and anisotropy properties
of a tubular structure are extracted through the associated orientation score.
The proposed dynamic Riemannian metric is updated in the course of the geodesic
distance computation carried out by the efficient single-pass fast marching
method. Compared to state-of-the-art minimal path models, the proposed minimal
path model is able to extract the desired tubular structures from a complicated
vessel tree structure. In addition, we propose an efficient prior path-based
method to search for vessel radius value at each centerline position of the
target. Finally, we perform the numerical experiments on both synthetic and
real images. The quantitive validation is carried out on retinal vessel images.
The results indicate that the proposed model indeed achieves a promising
performance.",1809.07987v4
2018-09-24,"Strain-tunable magnetic anisotropy in monolayer CrCl$_3$, CrBr$_3$, and CrI$_3$","Recent observation of intrinsic ferromagnetism in two-dimensional (2D)
CrI$_3$ is associated with the large magnetic anisotropy due to strong
spin-orbit coupling (SOC) of I. Magnetic anisotropy energy (MAE) defines the
stability of magnetization in a specific direction with respect to the crystal
lattice and is an important parameter for nanoscale applications. In this work
we apply the density functional theory to study the strain dependence of MAE in
2D monolayer chromium trihalides CrX$_3$ (with X = Cl, Br, and I). Detailed
calculations of their energetics, atomic structures and electronic structures
under the influence of a biaxial strain $\varepsilon$ have been carried out. It
is found that all three compounds exhibit ferromagnetic ordering at the ground
state (with $\varepsilon$=0) and upon applying a compressive strain, phase
transition to antiferromagnetic state occurs. Unlike in CrCl$_3$ and CrBr$_3$,
the electronic band gap in CrI$_3$ increases when a tensile strain is applied.
The MAE also exhibits a strain dependence in the chromium trihalides: it
increases when a compressive strain is applied in CrI$_3$, while an opposite
trend is observed in the other two compounds. In particular, the MAE of CrI$_3$
can be increased by 47\% with a compressive strain of $\varepsilon$ = 5\%.",1809.08725v1
2018-10-22,Anisotropic Charge Distribution Induced by Spin Polarization in La$_{0.6}$Sr$_{0.4}$MnO$_{3}$ Thin Films Studied by X-ray Magnetic Linear Dichroism,"Magnetic anisotropy of epitaxially grown thin films is affected by the strain
from the substrates due to a combined effect of distorted electronic structure
and spin-orbit interaction (SOI). As an inverse process, one expects an
anisotropy of the electronic structure induced by magnetization in the presence
of SOI. We have studied the charge-density anisotropy induced by magnetization
in thin films of the ferromagnetic metal La$_{1-x}$Sr$_{x}$MnO$_3$ via x-ray
magnetic linear dichroism (XMLD). XMLD measurements on thin films with various
thicknesses have shown that the XMLD intensity is proportional to the square of
the ferromagnetic moment. Using the XMLD sum rule and cluster-model
calculation, it has been shown that more Mn 3$d$ electrons are distributed in
orbitals elongated along the direction parallel to the spin polarization than
in orbitals elongated in the direction perpendicular to it. The cluster-model
calculation has shown that the effect of tensile strain from the SrTiO$_3$
substrate on the XMLD spectra is also consistent with the observed XMLD
spectral line shapes.",1810.09077v1
2018-10-27,Fast determination of coarse grained cell anisotropy and size in epithelial tissue images using Fourier transform,"Mechanical strain and stress play a major role in biological processes such
as wound healing or morphogenesis. To assess this role quantitatively, fixed or
live images of tissues are acquired at a cellular precision in large fields of
views. To exploit these data, large numbers of cells have to be analyzed to
extract cell shape anisotropy and cell size. Most frequently, this is performed
through detailed individual cell contour determination, using so-called
segmentation computer programs, complemented if necessary by manual detection
and error corrections. However, a coarse grained and faster technique can be
recommended in at least three situations. First, when detailed information on
individual cell contours is not required, for instance in studies which require
only coarse-grained average information on cell anisotropy. Second, as an
exploratory step to determine whether full segmentation can be potentially
useful. Third, when segmentation is too difficult, for instance due to poor
image quality or too large a cell number. We developed a user-friendly, Fourier
transform-based image analysis pipeline. It is fast (typically $10^4$ cells per
minute with a current laptop computer) and suitable for time, space or ensemble
averages. We validate it on one set of artificial images and on two sets of
fully segmented images, one from a Drosophila pupa and the other from a chicken
embryo; the pipeline results are robust. Perspectives include \textit{in vitro}
tissues, non-biological cellular patterns such as foams, and $xyz$ stacks.",1810.11652v3
2018-11-14,Giant anisotropy in superconducting single crystals of CsCa$_2$Fe$_4$As$_4$F$_2$,"CsCa$_2$Fe$_4$As$_4$F$_2$ is a newly discovered iron-based superconductor
with $T_\mathrm{c}\sim$ 30 K containing double Fe$_2$As$_2$ layers that are
separated by insulating Ca$_2$F$_2$ spacer layers. Here we report the transport
and magnetization measurements on CsCa$_2$Fe$_4$As$_4$F$_2$ single crystals
grown for the first time using the self flux of CsAs. We observed a huge
resistivity anisotropy $\rho_c(T)/\rho_{ab}(T)$, which increases with
decreasing temperature, from 750 at 300 K to 3150 at 32 K. The $\rho_c(T)$ data
exhibit a non-metallic behavior above $\sim$140 K, suggesting an incoherent
electronic state at high temperatures due to the dimension crossover. The
superconducting onset transition temperature in $\rho_{ab}$ is 0.7 K higher
than that in $\rho_c$, suggesting two-dimensional (2D) superconducting
fluctuations. The lower and upper critical fields also show an exceptional
anisotropy among iron-based superconductors. The $H_{c1}^\bot(T)$ data are well
fitted using the model with two $s$-wave-like superconducting gaps,
$\Delta_1(0)=6.75$ meV and $\Delta_2(0)=2.32$ meV. The inter-plane coherence
length $\xi_c(0)$ is $3.6$ \AA, remarkably smaller than the distance between
conducting layers (8.6 \AA), consolidating the 2D nature in the title material.",1811.05706v1
2018-11-19,Cosmologically viable generalized Einstein-Aether theories,"We investigate generalized Einstein-Aether theories that are compatible with
the Planck Cosmic Microwave Background (CMB) temperature anisotropy,
polarisation, and lensing data. For a given dark energy equation of state,
$w_{\rm de}$, we formulate a designer approach and we investigate their impact
on the CMB temperature anisotropy and matter power spectra. We use the Equation
of State approach to parametrize the perturbations and find that this approach
is particularly useful in identifying the most suitable and numerically
efficient parameters to explore in a Markov chain Monte Carlo (MCMC) analysis.
We find the data constrains models with $w_{\rm de} = -1$ to be compatible with
$\Lambda$CDM. For $w_{\rm de} \not= -1$ models, which avoid the gravitational
waves constraint through the entropy perturbation, we constrain $w_{\rm de}$ to
be $w_{\rm de } = -1.06^{+0.08}_{-0.03}$ (CMB) and $w_{\rm de }
=-1.04^{+0.05}_{-0.02}$ (CMB+Lensing) at $68\%$C.L., and find that these models
can be different from $\Lambda$CDM and still be compatible with the data. We
also find that these models can ameliorate some anomalies in $\Lambda$CDM when
confronted with data, such as the low-$\ell$ and high-$k$ power in the CMB
temperature anisotropy and matter power spectra respectively, but not
simultaneously. We also investigate the anomalous lensing amplitude, quantified
by $A_{\rm lens}$, and find that that for $w_{\rm de} = -1$ models, $A_{\rm
lens} = 1.15^{+0.07}_{-0.08}$ (CMB) and $A_{\rm lens} = 1.12\pm0.05$
(CMB+Lensing) at $68\%$C.L. $\sim$ 2$\sigma$ larger than expected, similar to
previous analyses of $\Lambda$CDM.",1811.07805v1
2018-12-10,Influence of strain and chemical substitution on the magnetic anisotropy of antiferromagnetic Cr$_2$O$_3$: an ab-initio study,"The influence of the mechanical strain and chemical substitution on the
magnetic anisotropy energy (MAE) of Cr$_2$O$_3$ is studied using
first-principles calculations. Dzyaloshinskii-Moriya interaction contributes
substantially to MAE by inducing spin canting when the antiferromagnetic order
parameter is not aligned with the hexagonal axis. Nearly cubic crystal field
results in a very small MAE in pure Cr$_2$O$_3$ at zero strain, which is
incorrectly predicted to be negative (in-plane) on account of spin canting. The
MAE is strongly modified by epitaxial strain, which tunes the crystal-field
splitting of the $t_{2g}$ triplet. The contribution from magnetic dipolar
interaction is very small at any strain. The effects of cation (Al, Ti, V, Co,
Fe, Nb, Zr, Mo) and anion (B) substitutions on MAE are examined. Al increases
MAE thanks to the local lattice deformation. In contrast, the electronic
configuration of V and Nb strongly promotes easy-plane anisotropy, while other
transition-metal dopants have only a moderate effect on MAE. Substitution of
oxygen by boron, which has been reported to increase the N\'eel temperature,
has a weak effect on MAE, whose sign depends on the charge state of B. The
electric field applied along the (0001) axis has a weak second-order effect on
the MAE.",1812.04060v1
2018-12-12,Quasilinear Consequences of Turbulent Ion Heating by Magnetic Moment Breaking,"The fast solar wind emerging from coronal holes is likely heated and
accelerated by the dissipation of magnetohydrodynamic turbulence, but the
specific kinetic mechanism resulting in the perpendicular ion heating required
by observations is not understood. A promising mechanism has been proposed by
Chandran et al. (2010), which in this paper we call ""magnetic moment breaking""
(MMB). As currently formulated, MMB dissipation operates only on the ion
perpendicular motion, and does not influence their parallel temperature. Thus,
the MMB mechanism acting by itself produces coronal hole proton distributions
that are unstable to the ion-cyclotron anisotropy instability. This quasilinear
instability is expected to operate faster than the nonlinear turbulent cascade,
scattering ions into the parallel direction and generating
quasi-parallel-propagating ion-cyclotron (IC) waves. To investigate the
consequences of this instability on the MMB-heated protons, we construct a
homogeneous model for protons with coronal hole properties. Using a simplified
version of the resonant cyclotron interaction, we heat the protons by the MMB
process and instantaneously scatter them to lower anisotropy while
self-consistently generating parallel-propagating IC waves. We present several
illustrative cases, finding that the extreme anisotropies implied by the MMB
mechanism are limited to reasonable values, but the distinctive shape of the
proton distribution derived by Klein & Chandran (2016) is not maintained. We
also find that these combined processes can result in somewhat higher particle
energization than the MMB heating alone. These quasilinear consequences should
follow from any kinetic mechanism that primarily increases the perpendicular
ion temperature in a collisionless plasma.",1812.05021v1
2018-12-19,Interfacial Spin-Orbit Coupling: New Platform for Superconducting Spintronics,"Spin-orbit coupling (SOC) is a key interaction in spintronics, allowing an
electrical control of spin or magnetization and, vice versa, a magnetic control
of electrical current. However, recent advances have revealed much broader
implications of SOC that is also central to the design of topological states,
including topological insulators, skyrmions, and Majorana fermions, or to
overcome the exclusion of two-dimensional ferro-magnetism expected from the
Mermin-Wagner theorem. SOC and the resulting emergent interfacial spin-orbit
fields are simply realized in junctions through structural inversion asymmetry,
while the anisotropy in magnetoresistance (MR) allows for their experimental
detection. Surprisingly, we demonstrate that an all-epitaxial
ferromagnet/MgO/metal junction with only a negligible MR anisotropy undergoes a
remarkable transformation below the superconducting transition temperature of
the metal. The superconducting junction has a three orders of magnitude higher
MR anisotropy and supports the formation of spin-triplet superconductivity,
crucial for superconducting spintronics, and topologically-protected quantum
computing. Our findings call for revisiting the role of SOC in other systems
which, even when it seems negligible in the normal state, could have a profound
influence on the superconducting response.",1812.08090v2
2018-12-26,Discretized dynamics of exchange spin wave bulk and edge modes in honeycomb nanoribbons with armchair edge boundaries,"We develop a field theory to study the dynamics of long wavelength exchange
spin wave excitations on honeycomb nanoribbons characterized by armchair edge
boundaries and the N\'eel antiferromagnetic ordering state. Appropriate
boundary conditions are established by requiring that the bulk and edge spins
precess with the same frequency for any given spin wave eigenmode in these
systems. A set of characteristic boundary equations, common for bulk and edge
spin wave modes, are hence derived. The equations of motion for the spin
dynamics are then solved to determine the propagating and evanescent exchange
spin wave modes. We prove in general that the bulk spin wave dynamics is
discretized due to the finite width of the nanoribbon. For an isotropic
magnetic nanoribbon, the Dirac cone is reduced to a single linear dispersion
curve due to this discretization. The number and wavelengths of allowed bulk
modes for isotropic and anisotropic nanoribbons are determined from the derived
characteristic boundary equations. As witnessed by our numerical results for
different examples it is shown that the characteristics of these modes depend
on the width of the nanoribbon and its antiferromagnetic anisotropy. Further,
anisotropic nanoribbons, even those with the slightest anisotropy, present
evanescent modes with non-linear dispersion relations. The spatial variation of
the amplitudes of the evanescent exchange spin waves across the finite widths
of the nanoribbons, is found to be strongly dependent on the system magnetic
anisotropy and its width. The developed theoretical approach is general and can
be applied for nanoribbons with all types of boundary edges.",1812.10204v2
2018-12-31,Systematic Control of Strain-Induced Perpendicular Magnetic Anisotropy in Epitaxial Europium and Terbium Iron Garnets Thin Films,"We show tunable strain-induced perpendicular magnetic anisotropy (PMA) over a
wide range of thicknesses in epitaxial ferrimagnetic insulator Eu3Fe5O12 (EuIG)
and Tb3Fe5O12 (TbIG) thin films grown by pulsed-laser deposition on Gd3Ga5O12
with (001) and (111) orientations, respectively. The PMA field is determined by
measuring the induced anomalous Hall loops in Pt deposited on the garnet films.
Due to positive magnetostriction constants, compressive in-plane strain induces
a PMA field as large as 32.9 kOe for 4 nm thick EuIG and 66.7 kOe for 5 nm
thick TbIG at 300 K, and relaxes extremely slowly as the garnet film thickness
increases. In bilayers consisting of Pt and EuIG or Pt and TbIG, robust PMA is
revealed by squared anomalous Hall hysteresis loops in Pt, the magnitude of
which appears to be only related to the net magnetic moment of iron
sublattices. Furthermore, the magnetostriction constant is found to be
2.7x10^(-5) for EuIG and 1.35x10^(-5) for TbIG, comparable with the values for
bulk crystals. Our results demonstrate a general approach of tailoring magnetic
anisotropy of rare earth iron garnets by utilizing modulated strain via
epitaxial growth.",1812.11688v1
2019-01-17,Improved fibre dispersion estimation using b-tensor encoding,"Measuring fibre dispersion in white matter with diffusion magnetic resonance
imaging (MRI) is limited by an inherent degeneracy between fibre dispersion and
microscopic diffusion anisotropy (i.e., the diffusion anisotropy expected for a
single fibre orientation). This means that estimates of fibre dispersion rely
on strong assumptions, such as constant microscopic anisotropy throughout the
white matter or specific biophysical models. Here we present a simple approach
for resolving this degeneracy using measurements that combine linear
(conventional) and spherical tensor diffusion encoding.
  To test the accuracy of the fibre dispersion when our microstructural model
is only an approximation of the true tissue structure, we simulate
multi-compartment data and fit this with a single-compartment model. For such
overly simplistic tissue assumptions, we show that the bias in fibre dispersion
is greatly reduced ($\sim$5x) for single-shell linear and spherical tensor
encoding data compared with single-shell or multi-shell conventional data. In
in-vivo data we find a consistent estimate of fibre dispersion as we reduce the
b-value from 3 to 1.5 ms/$\mu$m$^2$, increase the repetition time, increase the
echo time, or increase the diffusion time. We conclude that the addition of
spherical tensor encoded data to conventional linear tensor encoding data
greatly reduces the sensitivity of the estimated fibre dispersion to the model
assumptions of the tissue microstructure.",1901.05820v2
2019-01-25,Dielectric Resonator Method For Determining Gap Symmetry Of Superconductors Through Anisotropic Nonlinear Meissner Effect,"We present a new measurement method which can be used to image gap nodal
structure of superconductors whose pairing symmetry is under debate. This
technique utilizes a high quality factor microwave resonance involving the
sample of interest. While supporting a circularly symmetric standing wave
current pattern, the sample is perturbed by a scanned laser beam, creating a
photoresponse that was previously shown to reveal the superconducting gap
anisotropy. Simulation and the measurement of the photoresponse of an
unpatterned Nb film show less than 8\% anisotropy, as expected for a
superconductor with nearly isotropic energy gap along with expected systematic
uncertainty. On the other hand, measurement of a YBa$_2$Cu$_3$O$_{7-\delta}$
thin film shows a clear 4-fold symmetric image with $\mathtt{\sim}12.5$\%
anisotropy, indicating the well-known 4-fold symmetric $d_{x^2-y^2}$ gap nodal
structure in the $ab$-plane. The deduced gap nodal structure can be further
cross-checked by low temperature surface impedance data, which is
simultaneously measured. The important advantage of the presented method over
the previous spiral resonator method is that it does not require a complicated
lithographic patterning process which limits one from testing various kinds of
materials due to photoresponse arising from patterning defects. This advantage
of the presented technique, and the ability to measure unpatterned samples such
as planar thin films and single crystals, enables one to survey the pairing
symmetry of a wide variety of unconventional superconductors.",1901.08762v2
2019-01-29,Initial state description of azimuthally collimated long range correlations in ultrarelativistic light-heavy ion collisions,"It was argued in arXiv:1805.09342 and arXiv:1807.00825 that the systematics
of the azimuthal anisotropy coefficients $v_{2,3}$ measured in
ultrarelativistic light-heavy ion collisions at RHIC and the LHC can be
described in an initial state dilute-dense Color Glass Condensate (CGC)
framework. We elaborate here on the discussion in these papers and provide
further novel results that strengthen their conclusions. The underlying
mathematical framework and numerical techniques employed are very similar to
those in the CGC based IP-Glasma model used previously as initial conditions
for heavy-ion collisions. The uncertainties in theory/data comparisons for
small systems are discussed, with unknowns that are specific to the model
distinguished from those that are generic to all models. We present analytical
arguments that demonstrate that quantum interference effects such as Bose
enhancement and Hanbury-Brown-Twiss correlations of gluons, as well as coherent
multiple scattering of gluons in the projectile off color domains in the
target, are enhanced in rare events. The quantum origins of the large
anisotropies in small systems are corroborated by numerical results for
deuteron-gold collisions that show that large anisotropies in rare
configurations can occur when the nucleons in the projectile overlap
significantly. This is at variance with the classical intuition of
hydrodynamical models. We also comment on the consequences of ignoring the
many-body color charge correlations of gluons in models that only consider
geometrical fluctuations in the energy density.",1901.10506v1
2019-01-31,Fundamental Spin Interactions Underlying the Magnetic Anisotropy in the Kitaev Ferromagnet CrI$_3$,"We lay the foundation for determining the microscopic spin interactions in
two-dimensional (2D) ferromagnets by combining angle-dependent ferromagnetic
resonance (FMR) experiments on high quality CrI$_3$ single crystals with
theoretical modeling based on symmetries. We discover that the Kitaev
interaction is the strongest in this material with $K \sim -5.2$ meV, 25 times
larger than the Heisenberg exchange $J \sim -0.2$ meV, and responsible for
opening the $\sim$5 meV gap at the Dirac points in the spin-wave dispersion.
Furthermore, we find that the symmetric off-diagonal anisotropy $\Gamma \sim
-67.5$ $\mu$eV, though small, is crucial for opening a $\sim$0.3 meV gap in the
magnon spectrum at the zone center and stabilizing ferromagnetism in the 2D
limit. The high resolution of the FMR data further reveals a $\mu$eV-scale
quadrupolar contribution to the $S=3/2$ magnetism. Our identification of the
underlying exchange anisotropies opens paths toward 2D ferromagnets with higher
$T_\text{C}$ as well as magnetically frustrated quantum spin liquids based on
Kitaev physics.",1902.00077v2
2019-02-06,Phase boundary anisotropy and its effects on the maze-to-lamellar transition in a directionally solidified Al-Al2Cu eutectic,"Solid-solid phase boundary anisotropy is a key factor controlling the
selection and evolution of non-faceted eutectic patterns during directional
solidification. This is most remarkably observed during the so-called
maze-to-lamellar transition. By using serial sectioning, we followed the
spatio-temporal evolution of a maze pattern over long times in a large Al-Al2Cu
eutectic grain with known crystal orientation of the Al and Al2Cu phases, hence
known crystal orientation relationship (OR). The corresponding phase boundary
energy anisotropy ($\gamma$-plot) was also known, as being previously estimated
from molecular-dynamics computations. The experimental observations reveal the
time-scale of the maze-to-lamellar transition and shed light on the processes
involved in the gradual alignment of the phase boundaries to one distinct
energy minimum which nearly corresponds to one distinct plane from the family
$\{120\}^{\rm{Al}} //\{110\}^{\rm{Al2Cu}}$. This particular plane is selected
due to a crystallographic bias induced by a small disorientation of the
crystals relative to the perfect OR. The symmetry of the OR is thus slightly
broken, which promotes lamellar alignment. Finally, the maze-to-lamellar
transition leaves behind a network of fault lines inherited from the phase
boundary alignment process. In the maze pattern, the fault lines align along
the corners of the Wulff shape, thus allowing us to propose a link between the
pattern defects and missing orientations in the Wulff shape",1902.02210v1
2019-02-06,Anisotropy induced vortex lattice rearrangement in CaKFe$_4$As$_4$,"The magnetic penetration depth anisotropy
$\gamma_\lambda=\lambda_{c}/\lambda_{ab}$ ($\lambda_{ab}$ and $\lambda_{c}$ are
the in-plane and the out-of-plane components of the magnetic penetration depth)
in a CaKFe$_4$As$_4$ single crystal sample (the critical temperature $T_{\rm
c}\simeq 35$ K) was studied by means of muon-spin rotation ($\mu$SR).
$\gamma_\lambda$ is almost temperature independent for $T\lesssim 20$ K
($\gamma_\lambda\simeq 1.9$) and it reaches $\simeq 3.0$ by approaching $T_{\rm
c}$. The change of $\gamma_\lambda$ induces the corresponding rearrangement of
the flux line lattice (FLL), which is clearly detected via enhanced distortions
of the FLL $\mu$SR response. Comparison of $\gamma_\lambda$ with the anisotropy
of the upper critical field ($\gamma_{H_{\rm c2}}$) studied in Phys. Rev B {\bf
94}, 064501 (2016), reveals that $\gamma_\lambda$ is systematically higher than
$\gamma_{H_{\rm c2}}$ at low-temperatures and approaches $\gamma_{H_{\rm c2}}$
for $T \rightarrow T_{\rm c}$. The anisotropic properties of $\lambda$ are
explained by the multi-gap nature of superconductivity in CaKFe$_4$As$_4$ and
are caused by anisotropic contributions of various bands to the in-plane and
the out-of-plane components of the superfluid density.",1902.02268v1
2019-02-10,Cosmic Anisotropy and Fast Radio Bursts,"In the recent years, the field of fast radio bursts (FRBs) is thriving and
growing rapidly. It is of interest to study cosmology by using FRBs with known
redshifts. In the present work, we try to test the possible cosmic anisotropy
with the simulated FRBs. In particular, we only consider the possible dipole in
FRBs, rather than the cosmic anisotropy in general, while the analysis is only
concerned with finding the rough number of necessary data points to distinguish
a dipole from a monopole structure through simulations. Noting that there is no
a large sample of actual data of FRBs with known redshifts by now, simulations
are necessary to this end. We find that at least 2800, 190, 100 FRBs are
competent to find the cosmic dipole with amplitude 0.01, 0.03, 0.05,
respectively. Unfortunately, even 10000 FRBs are not competent to find the tiny
cosmic dipole with amplitude of ${\cal O}(10^{-3})$. On the other hand, at
least 20 FRBs with known redshifts are competent to find the cosmic dipole with
amplitude 0.1. We expect that such a big cosmic dipole could be ruled out by
using only a few tens of FRBs with known redshifts in the near future.",1902.03580v3
2019-02-14,Calculating temperature-dependent properties of Nd$_2$Fe$_{14}$B permanent magnets by atomistic spin model simulations,"Temperature-dependent magnetic properties of Nd$_2$Fe$_{14}$B permanent
magnets, i.e., saturation magnetization $M_\text{s}(T)$, effective magnetic
anisotropy constants $K_i^\text{eff}(T)$ ($i=1,2,3$), domain wall width
$\delta_w(T)$, and exchange stiffness constant $A_\text{e}(T)$, are calculated
by using \textit{ab-initio} informed atomistic spin model simulations. We
construct the atomistic spin model Hamiltonian for Nd$_2$Fe$_{14}$B by using
the Heisenberg exchange of Fe$-$Fe and Fe$-$Nd atomic pairs, the uniaxial
single-ion anisotropy of Fe atoms, and the crystal-field energy of Nd ions
which is approximately expanded into an energy formula featured by second,
fourth, and sixth-order phenomenological anisotropy constants. After applying a
temperature rescaling strategy, we show that the calculated Curie temperature,
spin-reorientation phenomenon, $M_\text{s}(T)$, $\delta_w(T)$, and
$K_i^\text{eff}(T)$ agree well with the experimental results. $A_\text{e}(T)$
is estimated through a general continuum description of the domain wall profile
by mapping atomistic magnetic moments to the macroscopic magnetization.
$A_\text{e}$ is found to decrease more slowly than $K_1^\text{eff}$ with
increasing temperature, and approximately scale with normalized magnetization
as $A_\text{e}(T) \sim m^{1.2}$. This work provokes a scale bridge between
\textit{ab-initio} calculations and temperature-dependent micromagnetic
simulations of Nd-Fe-B permanent magnets.",1902.05636v2
2019-02-25,Mapping the stability of stellar rotating spheres via linear response theory,"Rotation is ubiquitous in the Universe, and recent kinematic surveys have
shown that early type galaxies and globular clusters are no exception. Yet the
linear response of spheroidal rotating stellar systems has seldom been studied.
This paper takes a step in this direction by considering the behaviour of
spherically symmetric systems with differential rotation. Specifically, the
stability of several sequences of Plummer spheres is investigated, in which the
total angular momentum, as well as the degree and flavour of anisotropy in the
velocity space are varied. To that end, the response matrix method is
customised to spherical rotating equilibria. The shapes, pattern speeds and
growth rates of the systems' unstable modes are computed. Detailed comparisons
to appropriate N-body measurements are also presented. The marginal stability
boundary is charted in the parameter space of velocity anisotropy and rotation
rate. When rotation is introduced, two sequences of growing modes are
identified corresponding to radially and tangentially-biased anisotropic
spheres respectively. For radially anisotropic spheres, growing modes occur on
two intersecting surfaces (in the parameter space of anisotropy and rotation),
which correspond to fast and slow modes, depending on the net rotation rate.
Generalised, approximate stability criteria are finally presented.",1902.09299v1
2019-02-25,Strong anisotropy in the mixed antiferromagnetic system Mn$_{1-x}$Fe$_{x}$PSe$_3$,"We report the magnetic phase diagram of Mn$_{1-x}$Fe$_{x}$PSe$_3$ which
represents a random magnet system of two antiferromagnetic systems with mixed
spin, mixed spin anisotropies, mixed nearest neighbor magnetic interactions and
mixed periodicities in their respective antiferromagnetic structure. Bulk
samples of Mn$_{1-x}$Fe$_{x}$PSe$_3$ have been prepared and characterized phase
pure by powder X-ray and neutron diffraction and X-ray fluorescence. Nature and
extent of magnetically ordered state has been established using powder neutron
diffraction, dc magnetic susceptibility and heat capacity. Long-range magnetic
ordering exists between $x = 0.0$ and 0.25 (MnPSe$_3$-type) and between $x =
0.875$ and $1$ (FePSe$_3$-type). A short-range magnetic order with existence of
both MnPSe$_3$- and FePSe$_3$-type nano-clusters has been established between
$x = 0.25$ and $0.875$. Irreversibility in dc magnetization measurements, also
characterized by isothermal and thermoremanent magnetization measurements
suggest similarities to magnetic nanoparticles where uncompensated surface
spins result in a non-zero TRM and IRM response, further reinforcing existence
of magnetic nano-clusters or domains. A spin glass state, observed in analogous
Mn$_{1-x}$Fe$_x$PS$_3$, has been ruled out and formation of nano-clusters
exhibiting both ordering types results from unusually high anisotropy values.
The effect of ligand contributions to the spin-orbit interactions has been
suggested as a possible explanation for high $D$ values in these compounds.",1902.09655v2
2019-02-27,Phenomenology of $^{63}$Cu nuclear relaxation in cuprate superconductors,"Nuclear relaxation is an important thermodynamic probe of electronic
excitations, in particular in conducting and superconducting systems. Here, an
empirical phenomenology based on all available literature data for planar Cu in
hole-doped cuprates is developed. It is found that most of the seemingly
different relaxation rates among the systems are due to a temperature
independent anisotropy that affects the mostly measured $1/T_{1\parallel}$, the
rate with an external magnetic field along the crystal $c$-axis, while
$1/T_{1\perp}$ is largely independent on doping and material above the critical
temperature of superconductivity ($T_c$). This includes very strongly overdoped
systems that show Fermi liquid behavior and obey the Korringa law. Below $T_c$
the relaxation rates are similar, as well, if plotted against the reduced
temperature $T/T_c$. Thus, planar Cu nuclear relaxation is governed by a
simple, dominant mechanism that couples the nuclei with varying anisotropy to a
rather ubiquitous bath of electronic excitations that appear Fermi liquid-like
irrespective of doping and family. In particular, there is no significant
enhancement of the relaxation due to electronic spin fluctuations, different
from earlier conclusions. Only the La$_{2-x}$Sr$_x$CuO$_4$ family appears to be
an outlier as additional relaxation is present, however, the anisotropy remains
temperature independent. Also systems with very low doping levels, for which
there is a lack of data, may behave differently.",1902.10625v2
2019-03-19,Axon diameters and myelin content modulate microscopic fractional anisotropy at short diffusion times in fixed rat spinal cord,"Mapping tissue microstructure accurately and noninvasively is one of the
frontiers of biomedical imaging. Diffusion Magnetic Resonance Imaging (MRI) is
at the forefront of such efforts, as it is capable of reporting on microscopic
structures orders of magnitude smaller than the voxel size by probing
restricted diffusion. Double Diffusion Encoding (DDE) and Double Oscillating
Diffusion Encoding (DODE) in particular, are highly promising for their ability
to report on microscopic fractional anisotropy ({\mu}FA), a measure of the pore
anisotropy in its own eigenframe, irrespective of orientation distribution.
However, the underlying correlates of {\mu}FA have insofar not been studied.
Here, we extract {\mu}FA from DDE and DODE measurements at ultrahigh magnetic
field of 16.4T in the aim to probe fixed rat spinal cord microstructure. We
further endeavor to correlate {\mu}FA with Myelin Water Fraction (MWF) derived
from multiexponential T2 relaxometry, as well as with literature-based
spatially varying axonal diameters. In addition, a simple new method is
presented for extracting unbiased {\mu}FA from three measurements at different
b-values. Our findings reveal strong anticorrelations between {\mu}FA (derived
from DODE) and axon diameter in the distinct spinal cord tracts; a moderate
correlation was also observed between {\mu}FA derived from DODE and MWF. These
findings suggest that axonal membranes strongly modulate {\mu}FA, which - owing
to its robustness towards orientation dispersion effects - reflects axon
diameter much better than its typical FA counterpart. The {\mu}FA exhibited
modulations when measured via oscillating or blocked gradients, suggesting
selective probing of different parallel path lengths and providing insight into
how those modulate {\mu}FA metrics. Our findings thus shed light into the
underlying microstructural correlates of {\mu}FA and are (...)",1903.10377v1
2019-03-27,Field-free spin-orbit-torque switching of perpendicular magnetization aided by uniaxial shape anisotropy,"It has been demonstrated that the switching of perpendicular magnetization
can be achieved with spin orbit torque (SOT) at an ultrafast speed and low
energy consumption. However, to make the switching deterministic, an
undesirable magnetic field or unconventional device geometry is required to
break the structure inverse symmetry. Here we propose a novel scheme for
SOT-induced field-free deterministic switching of perpendicular magnetization.
The proposed scheme can be implemented in a simple magnetic tunnel junction
(MTJ) /heavy-metal system, without the need of complicated device structure.
The perpendicular-anisotropy MTJ is patterned into elliptical shape and
misaligned with the axis of the heavy metal, so that the uniaxial shape
anisotropy aids the magnetization switching. Furthermore, unlike the
conventional switching scheme where the switched final magnetization state is
dependent on the direction of the applied current, in our scheme the bipolar
switching is implemented by choosing different current paths, which offers a
new freedom for developing novel spintronics memories or logic devices. Through
the macrospin simulation, we show that a wide operation window of the applied
current pulse can be obtained in the proposed scheme. The precise control of
pulse amplitude or pulse duration is not required. The influences of key
parameters such as damping constant and field-like torque strength are
discussed as well.",1903.11487v1
2019-04-15,Anisotropic upper critical field of pristine and proton-irradiated single crystals of the magnetically ordered superconductor RbEuFe$_4$As$_4$,"We present a study of the upper critical field, H$_{c2}$, of pristine and
proton-irradiated RbEuFe$_4$As$_4$ crystals in pulsed magnetic fields of up to
65 T. The data for H$_{c2}$ reveal pronounced downwards curvature, particularly
for the in-plane field orientation, and a superconducting anisotropy that
decreases with decreasing temperature. These features are indicative of Pauli
paramagnetic limiting. For the interpretation of these data, we use a model of
a clean single-band superconductor with an open Fermi surface in the shape of a
warped cylinder, which includes strong paramagnetic limiting. Fits to the data
reveal that the in-plane upper critical field is Pauli paramagnetic limited,
while the out-of-plane upper critical field is orbitally limited and that the
orbital and paramagnetic fields have opposite anisotropies. A consequence of
this particular combination is the unusual inversion of the anisotropy,
$H_{c2}^{ab} < H_{c2}^c$, of the irradiated sample at temperatures below 10 K.
The fits also yield an in-plane Maki parameter, $\alpha_M^{110} \approx$ 2.6,
exceeding the critical value for the formation of the
Fulde-Ferrell-Larkin-Ovchinnikov state. Nevertheless, the current measurements
did not reveal direct evidence for the occurrence of this state.",1904.07203v2
2019-04-19,Secondary CMB temperature anisotropies from magnetic reheating,"Spatially fluctuating primordial magnetic fields (PMFs) inhomogeneously
reheat the Universe when they dissipate deep inside the horizon before
recombination. Such an energy injection turns into an additional photon
temperature perturbation. We investigate secondary cosmic microwave background
(CMB) temperature anisotropies originated from this mechanism, which we call
{\it inhomogeneous magnetic reheating}. We find that it can bring us
information about non-linear coupling between PMFs and primordial curvature
perturbations parametrized by $b_{\rm NL}$, which should be important for
probing the generation mechanism of PMFs. In fact, by using current CMB
observations, we obtain an upper bound on the non-linear parameter as $\log
(b_{\rm NL} (B_{\lambda}/{\rm nG})^2) \lesssim {-36.5n_{B} - 94.0}$ with
$B_{\lambda}$ and $n_{\rm B}$ being a magnetic field amplitude smoothed over
$\lambda=1\; {\rm Mpc}$ scale and a spectral index of the PMF power spectrum,
respectively. Our constraints are far stronger than a previous forecast based
on the future CMB spectral distortion anisotropy measurements because
inhomogeneous magnetic reheating covers a much wider range of scales, i.e.,
$1\; {\rm Mpc}^{-1} \lesssim k\lesssim 10^{15}\; {\rm Mpc}^{-1}$.",1904.09121v2
2019-04-30,Tunable ferromagnetic resonance in coupled trilayers with crossed in-plane and perpendicular magnetic anisotropies,"A novel approach to tune the ferromagnetic resonance frequency of a soft
magnetic Ni$_{80}$Fe$_{20}$ (Permalloy = Py) film with in-plane magnetic
anisotropy (IMA) based on the controlled coupling to a hard magnetic
NdCo$_\text{x}$ film with perpendicular magnetic anisotropy (PMA) through a
non-magnetic Al spacer is studied. Using transverse magneto-optical Kerr effect
(TMOKE), alternating gradient magnetometry (AGM) as well as vector network
analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both
Co concentration and Al spacer thickness on the static and dynamic magnetic
properties of the coupled IMA/PMA system is investigated. Compared to a single
Py film, two striking effects of the coupling between IMA and PMA layers can be
observed in their FMR spectra. First, there is a significant increase in the
zero-field resonance frequency from 1.3 GHz up to 6.6 GHz, and second, an
additional frequency hysteresis occurs at low magnetic fields applied along the
hard axis. The maximum frequency difference between the frequency branches for
increasing and decreasing magnetic field is as high as 1 GHz, corresponding to
a tunability of about 20% at external fields of typically less than $\pm$70 mT.
The origin of the observed features in the FMR spectra is discussed by means of
magnetization reversal curves.",1904.13275v1
2019-05-02,Impact of single atomic defects and vacancies on the magnetic anisotropy energy of CoPt thin films,"The impact of surface vacancies and single adatoms on the magnetic properties
of tetragonal {\bf{L1}$_{0}$} CoPt thin films is investigated from first
principles. We consider Co and Fe single adatoms deposited on a Pt-terminated
thin film while a Pt adatom is assumed to be supported by a Co-terminated film.
The vacancy is injected in the top-surface layer of the films with both types
of termination. After finding the most stable location of the defects, we
discuss their magnetic properties tight to those of the substrate and
investigate the magnetic crystalline anisotropy energy (MAE). Previous
simulations [Brahimi et al. J. Phys.: Condens. Matter. \textbf{28}, 496002
(2016)] predicted a large out-of-plane surface MAE for the Pt-terminated CoPt
films (4 meV per f.u.) in contrast to in-plane surface MAE for Co-terminated
films (-1 meV per f.u.). Here, we find that the surface MAE is significantly
modified upon the presence of the atomic defects. All investigated defects
induce an in-plane MAE, which is large enough for Fe adatom and Pt vacancy to
switch the surface MAE from out-of-plane to in-plane for the Pt-terminated
films. Interestingly, among the investigated defects Pt vacancy has the largest
effect on the MAE in contrast to Co vacancy, which induced the smallest but
still significant effect. This behavior is explained in terms of the orbital
moment anisotropy of the thin films.",1905.00674v1
2019-05-03,Toggle Spin-Orbit Torque MRAM with Perpendicular Magnetic Anisotropy,"Spin-orbit torque (SOT) is a promising switching mechanism for magnetic
random-access memory (MRAM) as a result of the potential for improved switching
speed and energy-efficiency. It is of particular interest to develop an
SOT-MRAM device with perpendicular magnetic anisotropy (PMA) in order to
leverage the greater density and thermal stability achievable with PMA as
opposed to in-plane magnetic anisotropy. However, the orthogonality between SOT
and PMA prevents deterministic directional switching without an additional
device component that breaks the symmetry, such as an external magnetic field
or complex physical structure; not only do these components complicate
fabrication, they also are not robust to variations in fabrication and applied
switching current. This letter therefore proposes a simple SOT-MRAM structure
with PMA in which deterministic toggle switching is achieved without requiring
additional device components. Furthermore, this toggle PMA SOT-MRAM is shown to
be far more robust than previous approaches for directional PMA SOT-MRAM, with
greater than 50% tolerance to applied switching current magnitude. This letter
describes the physical structure and toggle switching mechanism, provides
micromagnetic simulations demonstrating its feasibility, and evaluates the
robustness and tolerance to material parameters to guide the fabrication of
optimized devices that will jumpstart the third generation of MRAM.",1905.01125v1
2019-05-13,Parallel-propagating Fluctuations at Proton-kinetic Scales in the Solar Wind are Dominated by Kinetic Instabilities,"We use magnetic helicity to characterise solar wind fluctuations at
proton-kinetic scales from Wind observations. For the first time, we separate
the contributions to helicity from fluctuations propagating at angles
quasi-parallel and oblique to the local mean magnetic field, $\mathbf{B}_0$. We
find that the helicity of quasi-parallel fluctuations is consistent with
Alfv\'en-ion cyclotron and fast magnetosonic-whistler modes driven by proton
temperature anisotropy instabilities and the presence of a relative drift
between $\alpha$-particles and protons. We also find that the helicity of
oblique fluctuations has little dependence on proton temperature anisotropy and
is consistent with fluctuations from the anisotropic turbulent cascade. Our
results show that parallel-propagating fluctuations at proton-kinetic scales in
the solar wind are dominated by proton temperature anisotropy instabilities and
not the turbulent cascade. We also provide evidence that the behaviour of
fluctuations at these scales is independent of the origin and macroscopic
properties of the solar wind.",1905.04951v2
2019-05-20,Micromagnetic Modelling of the Heat Assisted Switching Process in high Anisotropy FePt Granular Thin Films,"The dynamic process of assisted magnetic switchins has been simulated to
investigate the associated physics. The model uses a Voronoi construction to
determine the physical structure of the nano granular thin film recording
media; and the Landau-Lifshitz-Bloch (LLB) equation is solved to evolve the
magnetic system in time. The reduction of the magnetization is determined over
a range of peak system temperatures and for a number of anisotropy values. The
results show that the HAMR process is not simply magnetization reversal over a
thermally reduced energy barrier. To achieve full magnetization reversal (for
all anisotropies investigated) an applied field strength of at least 6kOe is
required and the peak system temperature must reach at least the Curie point
(Tc). When heated to Tc the magnetization associated with each grain is
destroyed, which invokes the non-precessional linear reversal mode. Reversing
the magnetization through this linear reversal mode is favourable, as the
reversal time is two orders of magnitude smaller than that associated with
precession. Under these conditions, as the temperature decreases to ambient,
the magnetization recovers in the direction of the applied field, completing
the reversal process. Also the model produces results which are consistent with
the concept of thermal writability; when heating the media to Tc, the smaller
grains require a larger field strength to reverse the magnetization.",1905.08134v1
2019-05-21,Anisotropic spin fluctuations in detwinned FeSe,"Superconductivity in FeSe emerges from a nematic phase that breaks four-fold
rotational symmetry in the iron plane. This phase may arise from orbital
ordering, spin fluctuations, or hidden magnetic quadrupolar order. Here we use
inelastic neutron scattering on a mosaic of single crystals of FeSe detwinned
by mounting on a BaFe2As2 substrate to demonstrate that spin excitations are
most intense at the antiferromagnetic wave vectors QAF = (1, 0) at low energies
E = 6-11 meV in the normal state. This two-fold (C2) anisotropy is reduced at
lower energies 3-5 meV, indicating a gapped four-fold (C4) mode. In the
superconducting state, however, the strong nematic anisotropy is again
reflected in the spin resonance (E = 3.7 meV) at QAF with incommensurate
scattering around 5-6 meV. Our results highlight the extreme electronic
anisotropy of the nematic phase of FeSe and are consistent with a highly
anisotropic superconducting gap driven by spin fluctuations.",1905.08399v1
2019-05-21,Orbital-flop Induced Magnetoresistance Anisotropy in Rare Earth Monopnictide CeSb,"The charge and spin of the electrons in solids have been extensively
exploited in electronic devices and in the development of spintronics. Another
attribute of electrons - their orbital nature - is attracting growing interest
for understanding exotic phenomena and in creating the next-generation of
quantum devices such as orbital qubits. Here, we report on orbital-flop induced
magnetoresistance anisotropy in CeSb. In the low temperature high
magnetic-field driven ferromagnetic state, a series of additional minima appear
in the angle-dependent magnetoresistance. These minima arise from the
anisotropic magnetization originating from orbital-flops and from the enhanced
electron scattering from magnetic multidomains formed around the first-order
orbital-flop transition. The measured magnetization anisotropy can be accounted
for with a phenomenological model involving orbital-flops and a spin-valve-like
structure is used to demonstrate the viable utilization of orbital-flop
phenomenon. Our results showcase a contribution of orbital behavior in the
emergence of intriguing phenomena.",1905.08682v1
2019-05-22,Whistler wave generation by halo electrons in the solar wind,"We present an analysis of simultaneous particle and field measurements from
the ARTEMIS spacecraft which demonstrate that quasi-parallel whistler waves in
the solar wind can be generated locally by a bulk flow of halo electrons
(whistler heat flux instability). ARTEMIS observes quasi-parallel whistler
waves in the frequency range $\sim 0.05 - 0.2 f_{ce}$ simultaneously with
electron velocity distribution functions that are a combination of
counter-streaming core and halo populations. A linear stability analysis shows
that the plasma is stable when there are no whistler waves, and unstable in the
presence of whistler waves. In the latter case, the stability analysis shows
that the whistler wave growth time is from a few to ten seconds at frequencies
and wavenumbers that match the observations. The observations clearly
demonstrate that the temperature anisotropy of halo electrons crucially affects
the heat flux instability onset: a slight anisotropy
$T_{\parallel}/T_{\perp}>1$ may quench the instability, while a slight
anisotropy $T_{\parallel} / T_{\perp}<1$ may significantly increase the growth
rate. These results demonstrate that heat flux inhibition is strongly dependent
on the microscopic plasma properties.",1905.08954v1
2019-05-28,Galactic Cosmic-Ray Anisotropies: Voyager 1 in the Local Interstellar Medium,"Since crossing the heliopause on August 25, 2012, Voyager 1 observed
reductions in galactic cosmic ray count rates caused by a time-varying
depletion of particles with pitch angles near 90-deg, while intensities of
particles with other pitch angles remain unchanged. Between late 2012 and
mid-2017, three large-scale events occurred, lasting from ~100 to ~630 days.
Omnidirectional and directional high-energy data from Voyager 1's Cosmic Ray
Subsystem are used to report cosmic ray intensity variations. Omnidirectional
(greater than ~20 MeV) proton-dominated measurements show up to a 3.8%
intensity reduction. Bi-directional (greater than ~70 MeV) proton-dominated
measurements taken from various spacecraft orientations provide insight about
the depletion region's spatial properties. We characterize the anisotropy as a
""notch"" in an otherwise uniform pitch-angle distribution of varying depth and
width centered about 90 degrees in pitch angle space. The notch averages 22-deg
wide and 15% deep - signifying a depletion region that is broad and shallow.
There are indications that the anisotropy is formed by a combination of
magnetic trapping and cooling downstream of solar-induced transient
disturbances in a region that is also likely influenced by the highly
compressed fields near the heliopause.",1905.11990v1
2019-06-07,Anisotropy-temperature phase diagram for the two-dimensional dipolar Heisenberg model with and without magnetic field,"We investigate phase transitions in the two-dimensional dipolar Heisenberg
model with uniaxial anisotropy with a specific ratio between the exchange and
dipolar constants, $\delta=1$. We obtain the $\eta$--$T$ (anisotropy vs.
temperature) phase diagrams for typical values of magnetic field by a Monte
Carlo method with an $O(N)$ algorithm. We find that at lower fields, the
$\eta$--$T$ phase diagram consists of the planar ferromagnetic (F),
(perpendicular) stripe-ordered (SO), and paramagnetic (P) phases, and is
characterized by the triple point. In the SO phase realized at larger $\eta$
and smaller $T$, the SO pattern changes depending on the field. On the other
hand, we find that at higher fields, the SO phase does not exist, while the
planer F phase robustly remains. We study the properties of the phase
boundaries by employing finite-size-scaling analyses. We find that the slope of
the spin-reorientation-transition line is positive with and without field,
i.e., $\frac{d\eta}{dT}>0$, which implies that the planar F phase changes to
the SO phase with lowering temperature. In the phase diagrams we observe a
characteristic shape of the P--planer F phase-transition line, whose maximum
point of $\eta$ is located at an intermediate temperature. This structure leads
to the temperature-induced reentrant transition associated with P and planar F
phases, which appears in successive phase transitions with lowering
temperature: P $\rightarrow$ planar F $\rightarrow$ P $\rightarrow$ SO phase at
lower fields and P $\rightarrow$ planar F $\rightarrow$ P phases at higher
fields.",1906.02954v1
2019-06-28,Mapping different skyrmion phases in double wedges of Ta/FeCoB(tFeCoB)/Ta(tTa)Ox,"Skyrmions are chiral magnetic textures that have immense potential for
applications in spintronic devices. However, their formation is quite
challenging and necessitates a subtle balance of the magnetic interactions at
play. Here, we study Ta/FeCoB/TaOx trilayer using crossed double wedges i.e.
thickness gradients of FeCoB and of top Ta, which is subsequently oxidized
leading to an oxidation gradient. This enabled us to observe micron-sized
skyrmions in the vicinity of different transition regions of the sample: from
perpendicular magnetic anisotropy to paramagnetic phase and also from
perpendicular to in-plane magnetic anisotropy. These observations can be
explained by the isolated bubble model taking into account the different energy
contributions at play namely anisotropy, exchange, Dzyaloshinskii-Moriya,
dipolar and Zeeman. We also qualitatively compare the current-induced motion of
skyrmions obtained in different transition regions. Our study not only provides
an effective means to form skyrmions by tuning the interfacial magnetic
properties but also highlights the differences pertaining to the skyrmions
observed in different transition zones, which is extremely crucial for any
envisaged application.",1906.12271v2
2019-07-02,"In-plane to perpendicular magnetic anisotropy switching in heavily-Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature","We report switching of magnetic anisotropy (MA) from in-plane to
perpendicular with increasing the thickness d of a (001)-oriented
ferromagnetic-semiconductor (FMS) (Ga0.7,Fe0.3)Sb layer with a high Curie
temperature (Tc > 320 K), using ferromagnetic resonance at room temperature. We
show that the total MA energy (E) along the [001] direction changes its sign
from positive (in-plane) to negative (perpendicular) with increasing d above an
effective critical value \mathrm{d}_\mathrm{C}^\mathrm{*}\ ~ 42 nm. We reveal
that (Ga,Fe)Sb has two-fold symmetry in the film plane. Meanwhile, in the plane
perpendicular to the film including the in-plane [110] axis, the two-fold
symmetry with the easy magnetization axis along [110] changes to four-fold
symmetry with easy magnetization axis along <001> with increasing d. This
peculiar behavior is different from that of (Ga,Mn)As, in which only the
in-plane MA depends on the film thickness and has four-fold symmetry due to its
dominant cubic anisotropy along the <100> axes. This work provides an important
guide for controlling the easy magnetization axis of high-Tc FMS (Ga,Fe)Sb for
room-temperature device applications.",1907.01188v1
2019-08-02,Magnetic and superconducting anisotropy in Ni-doped RbEuFe$_4$As$_4$ single crystals,"We investigate the effect of Ni doping on the Fe-site in single crystals of
the magnetic superconductor RbEuFe$_4$As$_4$ for doping concentrations of up to
4%. A clear suppression in the superconducting transition temperature is
observed in specific heat, resistivity and magnetization measurements. Upon
Ni-doping, the resistivity curves shift up in a parallel fashion indicating a
strong increase of the residual resistivity due to scattering by charged dopand
atoms while the shape of the curve and thus the electronic structure appears
largely unchanged. The observed step $\Delta C/T_c$ at the superconducting
transition decreases strongly for increasing Ni doping in agreement with
expectations based on a model of multi-band superconductivity and strong
inter-band pairing. The upper critical field slopes are reduced upon Ni doping
for in- as well as out-of-plane fields leading to a small reduction in the
superconducting anisotropy. The specific heat measurements of the magnetic
transition reveal the same BKT behavior close to the transition temperature
$T_m$ for all doping levels. The transition temperature is essentially
unchanged upon doping. The in to out-of-plane anisotropy of Eu-magnetism
observed at small magnetic fields is unaltered as compared to the undoped
compound. All of these observations indicate a decoupling of the Eu magnetism
from superconductivity and essentially no influence of Ni doping on the Eu
magnetism in this compound.",1908.00773v1
2019-08-07,A nano-carbon route to rare earth free permanent magnetism,"High coercivity magnets are an important resource for renewable energy,
electric vehicles and memory technologies. Most hard magnetic materials
incorporate rare-earths such as neodymium and samarium, but the concerns about
the environmental impact and supply stability of these materials is prompting
research into alternatives. Here, we present a hybrid bilayer of cobalt and the
nano-carbon molecule C60 which exhibits significantly enhanced coercivity with
minimal reduction in magnetisation. We demonstrate how this anisotropy
enhancing effect cannot be described by existing models of molecule-metal
magnetic interfaces. We outline a new form of magnetic anisotropy, arising from
asymmetric magneto-electric coupling in the metal-molecule interface. Because
this phenomenon arises from pi-d hybrid orbitals, we propose calling this
effect pi-anisotropy. While the critical temperature of this effect is
currently limited by the rotational degree of freedom of the chosen molecule,
C60, we describe how surface functionalisation would allow for the design of
room-temperature, carbon based hard magnetic films.",1908.02544v3
2019-08-15,CMB sky for an off-center observer in a local void I: framework for forecasts,"The Universe is not perfectly homogeneous, the large scale structure forms
overdense regions and voids. In this paper, we consider the possibility that we
occupy a special position in our Universe, close to the center of a local
underdense region that we model as an LTB void embedded in a homogeneous and
isotropic Universe. The CMB sky measured by an off-center observer in this void
is not statistically isotropic. In addition to the non-stochastic CMB
anisotropies due to the geometry of the model, we also observe a lensing-like
distortion of the CMB anisotropies. In this article, we propose a framework to
forecast the precision with which we can measure the amplitude of the
lensing-like deformation of the CMB temperature anisotropies. For illustrative
purposes, we apply this method to a couple of large-scale void models differing
over the matter density profile and we show that the CMB temperature data from
the Planck satellite is potentially capable to detect the effect for the large
voids chosen here. A companion paper will be dedicated to a systematic
exploration of different realistic void models.",1908.05484v2
2019-08-22,Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites,"An in-depth analysis of Zn/Al doped nickel ferrites grown by reactive
magnetron sputtering is relevant due to their promising characteristics for
applications in spintronics. The material is insulating and ferromagnetic at
room temperature with an additional low magnetic damping. By studying the
complex interplay between strain and cation distribution their impact on the
magnetic properties, i.e. anisotropy, damping and g-factor is unravelled. In
particular, a strong influence of the lattice site occupation of
Ni$^{2+}_{\text{Td}}$ and cation coordination of Fe$^{2+}_{\text{Oh}}$ on the
intrinsic damping is found. Furthermore, the critical role of the incorporation
of Zn$^{2+}$ and Al$^{3+}$ is evidenced by comparison with a sample of altered
composition. Especially, the dopant Zn$^{2+}$ is evidenced as a tuning factor
for Ni$^{2+}_{\text{Td}}$ and therefore unquenched orbital moments directly
controlling the g-factor. A strain-independent reduction of the magnetic
anisotropy and damping by adapting the cation distribution is demonstrated.",1908.08257v3
2019-08-28,A Method for Dimensionally Adaptive Sparse Trigonometric Interpolation of Periodic Functions,"We present a method for dimensionally adaptive sparse trigonometric
interpolation of multidimensional periodic functions belonging to a smoothness
class of finite order. This method targets applications where periodicity must
be preserved and the precise anisotropy is not known a priori. To the authors'
knowledge, this is the first instance of a dimensionally adaptive sparse
interpolation algorithm that uses a trigonometric interpolation basis. The
motivating application behind this work is the adaptive approximation of a
multi-input model for a molecular potential energy surface (PES) where each
input represents an angle of rotation. Our method is based on an anisotropic
quasi-optimal estimate for the decay rate of the Fourier coefficients of the
model; a least-squares fit to the coefficients of the interpolant is used to
estimate the anisotropy. Thus, our adaptive approximation strategy begins with
a coarse isotropic interpolant, which is gradually refined using the estimated
anisotropic rates. The procedure takes several iterations where ever-more
accurate interpolants are used to generate ever-improving anisotropy rates. We
present several numerical examples of our algorithm where the adaptive
procedure successfully recovers the theoretical ""best"" convergence rate,
including an application to a periodic PES approximation. An open-source
implementation of our algorithm resides in the Tasmanian UQ library developed
at Oak Ridge National Laboratory.",1908.10672v2
2019-09-17,Aniotropy of in-plane g-factor of electrons in HgTe quantum wells,"The results of experimental studies of the Shubnikov-de Haas (SdH) efect in
the (013)-HgTe/Hg$_{1-x}$Cd$_x$Te quantum wells (QWs) of electron type of
conductivity both with normal and inverted energy spectrum are reported.
Comprehensive analysis of the SdH oscillations measured for the different
orientations of magnetic field relative to the quantum well plane and
crystallographic exes allows us to investigate the anisotropy of the Zeeman
effect. For the QWs with inverted spectrum, it has been shown that the ratio of
the spin splitting to the orbital one is strongly dependent not only on the
orientation of the magnetic field relative to the QW plane but also on the
orientation of the in-plane magnetic field component relative to
crystallographic axes laying in the QW plane that implies the strong anisotropy
of in-plane g-factor. In the QW with normal spectrum, this ratio strongly
depends on the angle between the magnetic field and the normal to the QW plane
and reveals a very slight anisotropy in the QW plane. To interpret the data,
the Landau levels in the tilted magnetic field are calculated within the
framework of four-band \emph{kP} model. It is shown that the experimental
results can be quantitatively described only with taking into account the
interface inversion asymmetry.",1909.07611v1
2019-09-17,Single spin resonance driven by electric modulation of the g factor anisotropy,"We address the problem of electronic and nuclear spin resonance of an
individual atom on a surface driven by a scanning tunnelling microscope.
Several mechanisms have been proposed so far, some of them based on the
modulation of exchange and crystal field associated to a piezoelectric
displacement of the adatom driven by the RF tip electric field. Here we
consider a new mechanism, where the piezoelectric displacement modulates the g
factor anisotropy, leading both to electronic and nuclear spin flip
transitions. We discuss thoroughly the cases of Ti-H (S = 1/2) and Fe (S = 2)
on MgO, relevant for recent experiments. We model the system using two
approaches. First, an analytical model that includes crystal field, spin orbit
coupling and hyperfine interactions. Second, we carry out density functional
based calculations. We find that the modulation of the anisotropy of the g
tensor due to the piezoelectric displacement of the atom is an additional
mechanism for STM based single spin resonance, that would be effective in S =
1/2 adatoms with large spin orbit coupling. In the case of Ti-H on MgO, we
predict a modulation spin resonance frequency driven by the DC electric field
of the tip.",1909.07942v1
2019-09-19,Energy-based analysis and anisotropic spectral distribution of internal gravity waves in strongly stratified turbulence,"Stratified turbulence shows scale- and direction-dependent anisotropy and the
coexistence of weak turbulence of internal gravity waves and strong turbulence
of eddies. Straightforward application of standard analyses developed in
isotropic turbulence sometimes masks important aspects of the anisotropic
turbulence. To capture detailed structures of the energy distribution in the
wave-number space, it is indispensable to examine the energy distribution with
non-integrated spectra by fixing the codimensional wave-number component or in
the two-dimensional domain spanned by both the horizontal and vertical wave
numbers. Indices which separate the range of the anisotropic weak-wave
turbulence in the wave-number space are proposed based on the decomposed
energies. In addition, the dominance of the waves in the range is also verified
by the small frequency deviation from the linear dispersion relation. In the
wave-dominant range, the linear wave periods given by the linear dispersion
relation are smaller than approximately one third of the eddy-turnover time.
The linear wave periods reflect the anisotropy of the system, while the
isotropic Brunt-V\""ais\""al\""a period is used to evaluate the Ozmidov wave
number, which is necessarily isotropic. It is found that the time scales in
consideration of the anisotropy of the flow field must be appropriately
selected to obtain the critical wave number separating the weak-wave
turbulence.",1909.08779v1
2019-09-27,Magnetic Guinier law,"Small-angle scattering of x-rays and neutrons is a routine method for the
determination of nanoparticle sizes. The so-called Guinier law represents the
low-q approximation for the small-angle scattering curve from an assembly of
particles. The Guinier law has originally been derived for nonmagnetic
particle-matrix-type systems, and it is successfully employed for the
estimation of particle sizes in various scientific domains (e.g., soft matter
physics, biology, colloidal chemistry, materials science). An important
prerequisite for it to apply is the presence of a discontinuous interface
separating particles and matrix. Here, we introduce the Guinier law for the
case of magnetic small-angle neutron scattering (SANS) and experimentally
demonstrate its applicability for the example of nanocrystalline cobalt. It is
well-known that the magnetic microstructure of nanocrystalline ferromagnets is
highly nonuniform on the nanometer length scale and characterized by a spectrum
of continuously varying long-wavelength magnetization fluctuations, i.e., these
systems do not manifest sharp interfaces in their magnetization profile. The
magnetic Guinier radius depends on the applied magnetic field, on the magnetic
interactions (exchange, magnetostatics), and on the magnetic anisotropy-field
radius, which characterizes the size over which the magnetic anisotropy field
is coherently aligned into the same direction. In contrast to the nonmagnetic
conventional Guinier law, the magnetic version can be applied to fully dense
random-anisotropy-type ferromagnets.",1909.12687v2
2019-10-02,Whistler instability stimulated by the suprathermal electrons present in space plasmas,"In the absence of efficient collisions, deviations from thermal equilibrium
of plasma particle distributions are controlled by the self-generated
instabilities. The whistler instability is a notorious example, usually
responsible for the regulation of electron temperature anisotropy $A =
T_{\perp}/T_\parallel>$ (with $\perp, \parallel$ respective to the magnetic
field direction) observed in space plasmas, e.g., solar wind and planetary
magnetospheres. Suprathermal electrons present in these environments change the
plasma dispersion and stability properties, with expected consequences on the
kinetic instabilities and the resulting fluctuations, which, in turn, scatter
the electrons and reduce their anisotropy. In order to capture these mutual
effects we use a quasilinear kinetic approach and PIC simulations, which
provide a comprehensive characterization of the whistler instability under the
influence of suprathermal electrons. Analysis is performed for a large variety
of plasma conditions, ranging from low-beta plasmas encountered in outer corona
or planetary magnetospheres to a high-beta solar wind characteristic to large
heliospheric distances. Enhanced by the suprathermal electrons, whistler
fluctuations stimulate the relaxation of temperature anisotropy, and this
influence of suprathermals increases with plasma beta parameter.",1910.01506v1
2019-10-04,Spin fluctuation anisotropy as a probe of orbital-selective hole-electron quasiparticle excitations in detwinned Ba(Fe1-xCox)2As2,"We use inelastic neutron scattering to study spin excitation anisotropy in
mechanically detwinned Ba(Fe1-xCox)2As2 with x = 0.048 and 0.054. Both samples
exhibit a tetragonal-to-orthorhombic structural transition at Ts, a collinear
static antiferromagnetic (AF) order at wave vector Q1 = QAF = (1, 0) below the
Neel temperature TN, and superconductivity below Tc (Ts > TN > Tc). In the high
temperature paramagnetic tetragonal phase (T > Ts), spin excitations centered
at Q1 and Q2 = (0, 1) are gapless and have four-fold (C4) rotational symmetry.
On cooling to below TN but above Tc, spin excitations become highly
anisotropic, developing a gap at Q2 but still are gapless at Q1. Upon entering
into the superconducting state, a neutron spin resonance appears at Q1 with no
magnetic scattering at Q2. By comparing these results with those from angle
resolved photoemission spectroscopy experiments, we conclude that the
anisotropic shift of the dyz and dxz bands in detwinned Ba(Fe1-xCox)2As2 below
Ts is associated with the spin excitation anisotropy, and the
superconductivity-induced resonance arises from the electron-hole Fermi surface
nesting of quasiparticles with the dyz orbital characters.",1910.01871v1
2019-10-06,Ground-State Phase Diagram of an Anisotropic S=1 Ferromagnetic-Antiferromagnetic Bond-Alternating Chain,"By using mainly numerical methods, we investigate the ground-state phase
diagram (GSPD) of an $S=1$ ferromagnetic-antiferromagnetic bond-alternating
chain with the $XXZ$ and the on-site anisotropies. This system can be mapped
onto an anisotropic spin-2 chain when the ferromagnetic interaction is much
stronger than the antiferromagnetic interaction. Since there are many quantum
parameters in this system, we numerically obtained the GSPD on the plane of the
magnitude of the antiferromagnetic coupling versus its $XXZ$ anisotropy, by use
of the exact diagonalization, the level spectroscopy as well as the
phenomenological renormalization group. The obtained GSPD consists of six
phases. They are the $XY$1, the large-$D$ (LD), the intermediate-$D$ (ID), the
Haldane (H), the spin-1 singlet dimer (SD), and the N\'eel phases. Among them,
the LD, the H, and the SD phases are the trivial phases, while the ID phase is
the symmetry-protected topological phase. The former three are smoothly
connected without any quantum phase transitions. It is also emphasized that the
ID phase appears in a wider region compared with the case of the GSPD of the
anisotropic spin-2 chain with the $XXZ$ and the on-site anisotropies. We also
compare the obtained GSPD with the result of the perturbation theory.",1910.02456v1
2019-10-11,Magnetization governed magnetoresistance anisotropy in topological semimetal CeBi,"Magnetic topological semimetals, the latest member of topological quantum
materials, are attracting extensive attention as they may lead to
topologically-driven spintronics. Currently, magnetotransport investigations on
these materials are focused on anomalous Hall effect. Here, we report on the
magnetoresistance anisotropy of topological semimetal CeBi, which has tunable
magnetic structures arising from localized Ce 4f electrons and exhibits both
negative and positive magnetoresistances, depending on the temperature. We
found that the angle dependence of the negative magnetoresistance, regardless
of its large variation with the magnitude of the magnetic field and with
temperature, is solely dictated by the field-induced magnetization that is
orientated along a primary crystalline axis and flops under the influence of a
rotating magnetic field. The results reveal the strong interaction between
conduction electrons and magnetization in CeBi. They also indicate that
magnetoresistance anisotropy can be used to uncover the magnetic behavior and
the correlation between transport phenomena and magnetism in magnetic
topological semimetals.",1910.05247v1
2019-10-19,Anomalies in the switching dynamics of C-type antiferromagnets and antiferromagnetic nanowires,"Antiferromagnets (AFMs) are widely believed to be superior than ferromagnets
in spintronics because of their high stability due to the vanishingly small
stray field. It is thus expected that the order parameter of AFM should always
align along the easy-axis of the crystalline anisotropy. In contrast to this
conventional wisdom, we find that the AFM order parameter switches away from
the easy-axis below a critical anisotropy strength when an AFM is properly
tailored into a nano-structure. The switching time first decreases and then
increases with the damping. Above the critical anisotropy, the AFM order
parameter is stable and precesses under a microwave excitation. However, the
absorption peak is not at resonance frequency even for magnetic damping as low
as 0.01. To resolve these anomalies, we first ascertain the hidden role of
dipolar interaction that reconstructs the energy landscape of the nano-system
and propose a model of damped non-linear pendulum to explain the switching
behavior. In this framework, the second anomaly appears when an AFM is close to
the boundary between underdamped and overdamped phases, where the observed
absorption lineshape has small quality factor and thus is not reliable any
longer. Our results should be significant to extract the magnetic parameters
through resonance techniques.",1910.08668v1
2019-10-31,Magnetoplasmons in monolayer black phosphorus structures,"Two-dimensional materials supporting deep-subwavelength plasmonic modes can
also exhibit strong magneto-optical responses. Here, we theoretically
investigate magnetoplasmons (MPs) in monolayer black phosphorus (BP) structures
under moderate static magnetic fields. We consider three different structures,
namely, a continuous BP monolayer, an edge formed by a semi-infinite sheet, and
finally, a triangular wedge configuration. Each of these structures shows
strongly anisotropic magneto-optical responses induced both by the external
magnetic field and by the intrinsic anisotropy of the BP lattice. Starting from
the magneto-optical conductivity of a single-layer of BP, we derive the
dispersion relation of the MPs in the considered geometries, using a
combination of analytical, semi-analytical, and numerical methods. We fully
characterize the MP dispersions and the properties of the corresponding field
distributions, and we show that these structures sustain strongly anisotropic
subwavelength modes that are highly tunable. Our results demonstrate that MPs
in monolayer BP, with its inherent lattice anisotropy as well as magnetically
induced anisotropy, hold potential for tunable anisotropic materials operating
below the diffraction limit, thereby paving the way for tailored nanophotonic
devices at the nanoscale.",1910.14577v1
2019-11-11,Determining the phase diagram of atomically thin layered antiferromagnet CrCl$_3$,"Changes in the spin configuration of atomically-thin, magnetic van-der-Waals
multilayers can cause drastic modifications in their opto-electronic
properties. Conversely, the opto-electronic response of these systems provides
information about the magnetic state, very difficult to obtain otherwise. Here
we show that in CrCl$_3$ multilayers, the dependence of the tunnelling
conductance on applied magnetic field ($H$), temperature ($T$), and number of
layers ($N$) tracks the evolution of the magnetic state, enabling the magnetic
phase diagram of these systems to be determined experimentally. Besides a
high-field spin-flip transition occurring for all thicknesses, the in-plane
magnetoconductance exhibits an even-odd effect due to a low-field spin-flop
transition. If the layer number $N$ is even, the transition occurs at $\mu_0 H
\sim 0$ T due to the very small in-plane magnetic anisotropy, whereas for odd
$N$ the net magnetization of the uncompensated layer causes the transition to
occur at finite $H$. Through a quantitative analysis of the phenomena, we
determine the interlayer exchange coupling as well as the staggered
magnetization, and show that in CrCl$_3$ shape anisotropy dominates. Our
results reveal the rich behaviour of atomically-thin layered antiferromagnets
with weak magnetic anisotropy.",1911.04376v1
2019-11-12,Morphology of CMB fields -- effect of weak gravitational lensing,"We study the morphology of the cosmic microwave background temperature and
polarization fields using the shape and alignment parameters, $\beta$ and
$\alpha$, that are constructed from the contour Minkowski tensor. The primary
goal of our paper is to understand the effect of weak gravitational lensing on
the morphology of the CMB fields. In order to isolate different physical
effects that can be potentially confused with the effect of lensing, we first
study the effect of varying the cosmology on $\alpha$ and $\beta$, and show
that they are relatively insensitive to variation of cosmological parameters.
Next we analyze the signatures of hemispherical anisotropy, and show that
information of such anisotropy in $\alpha$ gets washed out at small angular
scales and become pronounced only at large angular scales. For $\beta$ we find
characteristic distortions which vary with the field threshold. We then study
the effect of weak gravitational lensing using simulations of lensed
temperature and $E$ and $B$ modes. We quantify the distortion induced in the
fields across different angular scales. We find that lensing makes structures
of all fields increasingly more anisotropic as we probe down to smaller scales.
We find distinct behaviour of morphological distortions as a function of
threshold for the different fields. The effect is small for temperature and $E$
mode, while it is significantly large for $B$ mode. Further, we find that
lensing does not induce statistical anisotropy, as expected from the isotropic
distribution of large scale structure of matter. We expect that the results
obtained in this work will provide insights on the reconstruction of the
lensing potential.",1911.04740v1
2019-11-18,Revisiting the role of intermittent heat transport towards Reynolds stress anisotropy in convective turbulence,"Thermal plumes are the energy containing eddy motions that carry heat and
momentum in a convective boundary layer. The detailed understanding of their
structure is of fundamental interest for a range of applications, from
wall-bounded engineering flows to quantifying surface-atmosphere flux
exchanges. We address the aspect of Reynolds stress anisotropy associated with
the intermittent nature of heat transport in thermal plumes by performing an
invariant analysis of the Reynolds stress tensor in an unstable atmospheric
surface layer flow, using a field-experimental dataset. Given the intermittent
and asymmetric nature of the turbulent heat flux, we formulate this problem in
an event-based framework. In this approach, we provide structural descriptions
of warm-updraft and cold-downdraft events and investigate the degree of
isotropy of the Reynolds stress tensor within these events of different sizes.
We discover that only a subset of these events are associated with the least
anisotropic turbulence in highly-convective conditions. Additionally,
intermittent large heat flux events are found to contribute substantially to
turbulence anisotropy under unstable stratification. Moreover, we find that the
sizes related to the maximum value of the degree of isotropy do not correspond
to the peak positions of the heat flux distributions. This is because, the
vertical velocity fluctuations pertaining to the sizes associated with the
maximum heat flux, transport significant amount of streamwise momentum. A
preliminary investigation shows that the sizes of the least anisotropic events
probably scale with a mixed-length scale ($z^{0.5}\lambda^{0.5}$, where $z$ is
the measurement height and $\lambda$ is the large-eddy length scale).",1911.07822v3
2019-11-28,Continuous Histograms for Anisotropy of 2D Symmetric Piece-wise Linear Tensor Fields,"The analysis of contours of scalar fields plays an important role in
visualization. For example the contour tree and contour statistics can be used
as a means for interaction and filtering or as signatures. In the context of
tensor field analysis, such methods are also interesting for the analysis of
derived scalar invariants. While there are standard algorithms to compute and
analyze contours, they are not directly applicable to tensor invariants when
using component-wise tensor interpolation. In this chapter we present an
accurate derivation of the contour spectrum for invariants with quadratic
behavior computed from two-dimensional piece-wise linear tensor fields. For
this work, we are mostly motivated by a consistent treatment of the anisotropy
field, which plays an important role as stability measure for tensor field
topology. We show that it is possible to derive an analytical expression for
the distribution of the invariant values in this setting, which is exemplary
given for the anisotropy in all details. Our derivation is based on a
topological sub-division of the mesh in triangles that exhibit a monotonic
behavior. This triangulation can also directly be used to compute the accurate
contour tree with standard algorithms. We compare the results to a na\""ive
approach based on linear interpolation on the original mesh or the subdivision.",1912.00739v1
2019-12-09,An anisotropic interaction model with collision avoidance,"In this article an anisotropic interaction model avoiding collisions is
proposed. Starting point is a general isotropic interacting particle system, as
used for swarming or follower-leader dynamics. An anisotropy is induced by
rotation of the force vector resulting from the interaction of two agents. In
this way the anisotropy is leading to a smooth evasion behaviour. In fact, the
proposed model generalizes the standard models, and compensates their drawback
of not being able to avoid collisions. Moreover, the model allows for formal
passage to the limit 'number of particles to infinity', leading to a mesoscopic
description in the mean-field sense. Possible applications are autonomous
traffic, swarming or pedestrian motion. Here, we focus on the latter, as the
model is validated numerically using two scenarios in pedestrian dynamics. The
first one investigates the pattern formation in a channel, where two groups of
pedestrians are walking in opposite directions. The second experiment considers
a crossing with one group walking from left to right and the other one from
bottom to top. The well-known pattern of lanes in the channel and travelling
waves at the crossing can be reproduced with the help of this anisotropic model
at both, the microscopic and the mesoscopic level. In addition, the
'right-before-left' and 'left-before-right' rule appear intrinsically for
different anisotropy parameters.",1912.04234v2
2019-12-24,Dark matter with excitable levels,"This paper explores the possibility that dark matter particles are objects
with a set of excitable levels, as for a string or drum. A change in excitation
is associated with the absorption or emission of a photon, and the probability
of such a change is dependent on the ambient photon energy density. Particle
mass comes entirely from excitations. Such dark matter with excitable levels,
or DMWEL, particles have a distribution of masses which freezes out to its
present-day form during the early universe. In the particular model considered,
consistency with Planck CMB anisotropy observations implies a cautious lower
bound on the energy of the first excitable level of 2 to 200 eV for a set of
reference parameters. While laboratory detection looks to require a
considerable increase in the power of controlled light-sources, it might be
possible in the near future to detect or constrain DMWEL further through
improved anisotropy observations, closer determination of the CMB's maximum
deviation from a blackbody shape, or from gravitational probes of the dark
matter power spectrum. For certain parameters near to the boundary of the
region allowed by CMB anisotropies, DMWEL dark matter is cold, but with a
cut-off halo mass many orders of magnitude greater than that typical for WIMP
cold dark matter.",1912.11453v3
2019-12-27,Anisotropy screening in Horndeski cosmologies,"We consider anisotropic cosmologies in a particular shift-symmetric Horndeski
theory containing the $G^{\mu\nu}\partial_\mu\phi \partial_\nu\phi$ coupling,
where $G^{\mu\nu}$ is the Einstein tensor. This theory admits stable in the
future self-accelerating cosmologies whose tensor perturbations propagate with
the velocity very close to the speed of light such that the theory agrees with
the gravity wave observations. Surprisingly, we find that the anisotropies
within the Bianchi I homogeneous spacetime model are screened at early time by
the scalar charge, whereas at late times they are damped in the usual way.
Therefore, contrary to what one would normally expect, the early state of the
universe in the theory cannot be anisotropic and (locally) homogeneous in the
absence of spatial curvature. The early universe cannot be isotropic either,
because it should then be unstable with respect to inhomogeneous perturbations.
As a result, the early universe should be inhomogeneous. At the same time, we
find that in the spatially curved Bianchi IX case the anisotropies can be
strong at early times even in the presence of a scalar charge.",1912.12320v2
2019-12-30,Cross-Correlation of Far-Infrared Background Anisotropies and CMB Lensing from Herschel and Planck satellites,"The cosmic infrared background (CIB) anisotropies and cosmic microwave
background (CMB) lensing are powerful measurements for exploring the
cosmological and astrophysical problems. In this work, we measure the
auto-correlation power spectrum of the CIB anisotropies in the Herschel-SPIRE
HerMES Large Mode Survey (HeLMS) field, and the cross power spectrum with the
CMB lensing measurements from the Planck satellite. The HeLMS field covers more
than 270 deg^2, which is much larger than the previous analysis. We use the
Herschel Level 1 time stream data to merge the CIB maps at 250, 350, and 500 um
bands, and mask the areas where the flux is greater than 3-sigma (~50 mJy/beam)
or no measured data. We obtain the final CIB power spectra at 100<ell<20000 by
considering several effects, such as beam function, mode coupling, transfer
function, and so on. We also calculate the theoretical CIB auto- and
cross-power spectra of CIB and CMB lensing by assuming that the CIB emissivity
follows Gaussian distribution in redshift. We find that, for the CIB auto power
spectra, we obtain the signal to noise ratio (SNR) of 15.9, 15.7, and 15.3 at
250, 350, and 500 um, and for the CIBxCMB lensing power spectra, SNR of 7.5,
7.0, and 6.2 at 250, 350, and 500 um, respectively. Comparing to previous
works, the constraints on the relevant CIB parameters are improved by factors
of 2~5 in this study.",1912.12840v2
2019-12-31,Noncoplanar ferrimagnetism and local crystalline-electric-field anisotropy in the quasicrystal approximant Au$_{70}$Si$_{17}$Tb$_{13}$,"Neutron scattering experiments have been performed to elucidate magnetic
properties of the quasicrystal approximant Au$_{70}$Si$_{17}$Tb$_{13}$,
consisting of icosahedral spin clusters in a body-centered-cubic lattice. Bulk
magnetic measurements performed on the single crystalline sample unambiguously
confirm long-range ordering at $T_{\rm C} = 11.6 \pm 1$ K. In contrast to the
simple ferromagnetic response in the bulk measurements, single crystal neutron
diffraction confirms a formation of intriguing non-collinear and non-coplanar
magnetic order. The magnetic moment direction was found to be nearly tangential
to the icosahedral cluster surface in the local mirror plane, which is quite
similar to that recently found in the antiferromagnetic quasicrystal
approximant Au$_{72}$Al$_{14}$Tb$_{14}$. Inelastic neutron scattering on the
powdered sample exhibits a very broad peak centered at $\hbar \omega \simeq 4$
meV. The observed inelastic spectrum was explained by the
crystalline-electric-field model taking account of the chemical disorder at the
fractional Au/Si sites. The resulting averaged anisotropy axis for the
crystalline-electric-field ground state is consistent with the ordered moment
direction determined in the magnetic structure analysis, confirming that the
non-coplanar magnetic order is stabilized by the local uniaxial anisotropy.",1912.13180v1
2020-01-09,Role of longitudinal fluctuations in L$1_0$ FePt,"L$1_0$ FePt is a technologically important material for a range of novel data
storage applications. In the ordered FePt structure the normally non-magnetic
Pt ion acquires a magnetic moment, which depends on the local field originating
from the neighboring Fe atoms. In this work a model of FePt is constructed,
where the induced Pt moment is simulated by using combined longitudinal and
rotational spin dynamics. The model is parameterized to include a linear
variation of the moment with the exchange field, so that at the Pt site the
magnetic moment depends on the Fe ordering. The Curie temperature of FePt is
calculated and agrees well with similar models that incorporate the Pt dynamics
through an effective Fe-only Hamiltonian. By computing the dynamic correlation
function the anisotropy field and the Gilbert damping are extracted over a
range of temperatures. The anisotropy exhibits a power-law dependence with
temperature with exponent $n\approx2.1$. This agrees well with what observed
experimentally and it is obtained without including a two-ion anisotropy term
as in other approaches. Our work shows that incorporating longitudinal
fluctuations into spin dynamics calculations is crucial for understanding the
properties of materials with induced moments.",2001.03074v1
2020-01-13,Virial models and Anisotropy of Velocity Dispersion in e-galaxies,"A tensor virial approach is used to construct detailed models of 22 flattened
ellipticals. The models are combined with the new observational data: extended
surface brightness distributions, the profiles of isophotes flattening and
their twisting, the rotation curves and the velocity dispersion profiles. A key
feature of these models is a rigorous consideration of the influence of the
spatial shape of galaxies (oblate spheroid or triaxial ellipsoid) on the
dynamics, as well as the structure of the internal density layers in these
systems. For each galaxy the ratio of the rotational energy to the potential
energy was found. Comparing this ratio with the observed it is concluded that
the majority of these systems cannot have isotropic velocity dispersion
tensors. The anisotropy parameter limited to the interval 0.0-0.224. A
correlation was found between and flattening of the outer regions for giant
E-galaxies. Our results are compared with the results of other researchers. It
was found that for small fast rotators our values \b{eta} are in good agreement
with those, obtained in the ATLAS project. However, for giant E-galaxies, our
models provide better agreement with observations, than axisymmetric JAM
models. In addition, our velocity dispersion anisotropy results are in
satisfactory agreement with the results of high resolution cosmological
simulations in the Illustris project",2001.04094v1
2020-02-06,"Effects of transition-metal spacers on the spin-orbit torques, spin Hall magnetoresistance, and magnetic anisotropy of Pt/Co bilayers","We studied the effect of inserting 0.5 nm-thick spacer layers (Ti, V, Cr, Mo,
W) at the Pt/Co interface on the spin-orbit torques, Hall effect,
magnetoresistance, saturation magnetization, and magnetic anisotropy. We find
that the damping-like spin-orbit torque decreases substantially for all samples
with a spacer layer compared to the reference Pt/Co bilayer, consistently with
the opposite sign of the atomic spin-orbit coupling constant of the spacer
elements relative to Pt. The reduction of the damping-like torque is monotonic
with atomic number for the isoelectronic 3d, 4d, and 5d elements, with the
exception of V that has a stronger effect than Cr. The field-like spin-orbit
torque almost vanishes for all spacer layers irrespective of their composition,
suggesting that this torque predominantly originates at the Pt/Co interface.
The anomalous Hall effect, magnetoresistance, and saturation magnetization are
also all reduced substantially, whereas the sheet resistance is increased in
the presence of the spacer layer. Finally, we evidence a correlation between
the amplitude of the spin-orbit torques, the spin Hall-like magnetoresistance,
and the perpendicular magnetic anisotropy. These results highlight the
significant influence of ultrathin spacer layers on the magnetotransport
properties of heavy metal/ferromagnetic systems.",2002.02162v1
2020-02-10,Joule-Thomson Expansion of Regular Bardeen AdS Black Hole Surrounded by Static Anisotropic Quintessence Field,"In the present paper, we investigate the required anisotropy of an exact
regular Bardeen black hole characterized by its mass $M$, the nonlinear
parameter $g$, the quintessence field parameter $a$ in anti-de sitter spacetime
with a static quintessence matter field. We also show that the relative
pressure anisotropy, equation of state and the pressure depends on radial
coordinate, reflecting the required anisotropy for Bardeen black hole in the
quintessence background.
  Next, we analyze the Joule-Thompson ($JT$) expansion of the black hole
spacetime. Treating the cosmological constant as thermodynamic pressure $P$ and
its conjugate quantity as thermodynamic volume $V$ we derive the equation of
state connecting Hawking temperature and various black hole parameters. We
study the $JT$ expansion in the regular Bardeen AdS black holes in the
quintessence background through the analysis of inversion temperature and
isenthalpic curves. We derive the $JT$ coefficient $\mu$, and use them to plot
the inversion and isenthalpic curves. We discuss the effect of quintessence
parameter $a$ and $\omega_q$ on the $JT$ coefficient and inversion temperature,
especially with the case of $\omega_q=-1$ and $\omega_q=-\frac{1}{3}$. Our
analysis shows that quintessence dark energy affects the inversion point
$(T_i,P_i)$ .",2002.03634v1
2020-03-19,Anisotropy of the Upper Critical Field in the Heavy-Fermion Superconductor UTe2 under Pressure,"We studied the anisotropy of the superconducting upper critical field $H_{\rm
c2}$ in the heavy-fermion superconductor UTe$_2$ under hydrostatic pressure by
magnetoresistivity measurements. In agreement with previous experiments we
confirm that superconductivity disappears near a critical pressure $p_{\rm c}
\approx 1.5$~GPa, and a magnetically ordered state appears. The unusual $H_{\rm
c2}(T)$ at low temperatures for $H \parallel a$ suggests that the multiple
superconducting phases which appear under pressure have quite different $H_{\rm
c2}$. For a field applied along the hard magnetization $b$ axis $H_{\rm c2}
(0)$ is glued to the metamagnetic transition $H_{\rm m}$ which is suppressed
near $p_{\rm c}$. The suppression of $H_{\rm m}$ with pressure follows the
decrease of temperature $T_{\chi}^{\rm max}$, at the maximum in the
susceptibility along $b$. The strong reinforcement of $H_{\rm c2}$ at ambient
pressure for $H \parallel b$ above 16~T is rapidly suppressed under pressure
due to the increase of $T_{\rm sc}$ and the decrease of $H_{\rm m}$. The change
in the hierarchy of the anisotropy of $H_{\rm c2}(0)$ on approaching $p_{\rm
c}$ points out that the $c$ axis becomes the hard magnetization axis.",2003.08728v1
2020-03-28,Bianchi I metric solutions with nonminimally coupled Einstein-Maxwell gravity theory,"By using Bianchi I type of homogenous and anisotropic background metric
having cylindrical symmetry in $x$ direction of a local cartesian coordinates
system, we solve metric field equations for a non-minimally coupled
Einstein-Maxwell gravity. To do so we choose long wavelength EM waves where
spatial dependence of the waves are negligible at the expansion duration.
Motivation of this work is study directional effects of the EM vector potential
on anisotropy trajectory of the space time expansion scale factor. This problem
is checked just for de Sitter inflationary epoch because of its importance in
the expansion of the universe. By applying the dynamical system approach we
investigate stability nature of the cosmic system in two different cases: (a)
direction of the EM vector potential is parallel to $x$ direction of the
spacetime and (b) it is perpendicular to $x$ direction. We obtained at stable
critical points for some of obtained inflationary solutions the EM waves behave
as dark energy in cases $a$ and $b$ where the anisotropy is negligible by
expanding of the universe while there are some stable critical points with
inflationary stable solutions in case $b$ for which the EM waves behave as
baryonic visible matter with non-vanishing anisotropy.",2003.14216v4
2020-03-31,Magnetic properties of Co/Ni-based multilayers with Pd and Pt insertion layers,"In this study, the influence of Pd and Pt insertion layers in Co/Ni
multilayers (MLs) on their magnetic properties, e.g. magnetic anisotropies,
saturation magnetization, coercivity, magnetic domain size, and Curie
temperature, is investigated. We compare three series of [Co/Ni/X]N ML systems
(X = Pd, Pt, no insertion layer), varying the individual Co layer thickness as
well as the repetition number N. All three systems behave very similarly for
the different Co layer thicknesses. For all systems, a maximum effective
magnetic anisotropy was achieved for MLs with a Co layer thickness between 0.15
nm and 0.25 nm. The transition from an out-of-plane to an in-plane system
occurs at about 0.4 nm of Co. While [Co(0.2 nm)/Ni(0.4 nm)]N MLs change their
preferred easy magnetization axis from out-of-plane to in-plane after 6 bilayer
repetitions, insertion of Pd and Pt results in an extension of this transition
beyond 15 repetitions. The maximum effective magnetic anisotropy was more than
doubled from 105 kJ/m3 for [Co/Ni]3 to 275 and 186 kJ/m3 for Pt and Pd,
respectively. Furthermore, the insertion layers strongly reduce the initial
saturation magnetization of 1100 kA/m of Co/Ni MLs and lower the Curie
temperature from 720 to around 500 K",2003.14306v1
2020-04-07,Laser-induced magnetization precession in individual magnetoelastic domains of a multiferroic CoFeB/BaTiO$_3$ composite,"Using a magneto-optical pump-probe technique with micrometer spatial
resolution we show that magnetization precession can be launched in individual
magnetic domains imprinted in a Co$_{40}$Fe$_{40}$B$_{20}$ (CoFeB) layer by
elastic coupling to ferroelectric domains in a BaTiO$_{3}$ substrate. The
dependence of the precession parameters on external magnetic field strength and
orientation reveal that by laser-induced ultrafast partial quenching of the
magnetoelastic coupling parameter of CoFeB by $\approx$27% along with 10%
ultrafast demagnetization trigger the magnetization precession. The relation
between the laser-induced reduction of the magnetoelastic coupling and the
demagnetization is approximated by the $n(n+1)/2$-law with n$\approx$2. This
correspondence confirms the thermal origin of the laser-induced anisotropy
change. Based on the analysis and modeling of the excited precession we find
signatures of laser-induced precessional switching, which occurs when the
magnetic field is applied along the hard magnetization axis and its value is
close to the effective magnetoelastic anisotropy field. The precession
excitation process in an individual magnetoelastic domain is found to be
unaffected by neighboring domains. This makes laser-induced changes of
magnetoelastic anisotropy a promising tool for driving magnetization dynamics
and switching in composite multiferroics with spatial selectivity.",2004.03566v5
2020-04-14,"On the Elastic Anisotropy of the Entropy-Stabilized Oxide (Mg, Co, Ni, Cu, Zn)O","In this paper, we study the elastic properties of the entropy-stabilized
oxide (Mg, Co, Ni, Cu, Zn)O, using experimental and first principles
techniques. Our measurements of the indentation modulus on grains with a wide
range of crystallographic orientations of the entropy-stabilized oxide revealed
a high degree of elastic isotropy at ambient conditions. First principles
calculations predict mild elastic anisotropy for the paramagnetic structure,
which decreases when the system is considered to be non-magnetic. When the
antiferromagnetic state of CoO, CuO and NiO is accounted for in the
calculations, a slight increase in the elastic anisotropy is observed,
suggesting a coupling between magnetic ordering and the orientation dependent
elastic properties. Furthermore, an examination of the local structure reveals
that the isotropy is favored through local ionic distortions of Cu and Zn - due
to their tendency to form tenorite and wurtzite phases. The relationships
between the elastic properties of the multicomponent oxide and those of its
constituent binary oxides are reviewed. These insights open up new avenues for
controlling isotropy for technological applications through tuning composition
and structure in the entropy-stabilized oxide or the high entropy compounds in
general.",2004.06613v1
2020-04-23,Temperature-dependent Magnetic Transitions in CoCrPt-Ru-CoCrPt Synthetic Ferrimagnets,"The magnetic orientations and switching fields of a CoCrPt-Ru-CoCrPt
synthetic ferrimagnet with perpendicular magnetic anisotropy have been studied
in the temperature range from 2 K to 300 K. It was found that two sets of
magnetic transitions occur in the CoCrPt-Ru-CoCrPt ferrimagnet across this
temperature range. The first set exhibits three magnetic transitions in the 50
K - 370 K range, whereas the second involves only two transitions in the 2 K
and 50 K range. The observed magnetic hysteresis curves of the synthetic
ferrimagnet are explained using the energy diagram technique framework
pioneered by Koplak et al. [1] which accurately describes the competition
between interlayer exchange coupling energy, Zeeman energy, and anisotropy
energy in the system. In this work we expand the framework to include synthetic
ferrimagnets (SFMs) comprising higher perpendicular magnetic anisotropy
materials and large (4X) interlayer exchange coupling energies which are
promising for the development of ultrafast (ps) magnetic switching free layers
in MTJ structures. Furthermore, we apply the analysis to predict SFM magnetic
hysteresis curves in a temperature regime that includes temperature extrema
that a synthetic ferrimagnet would be expected to reliably operate at, were it
to be utilized as a free layer in a memory or sensor spintronic device.",2004.11406v2
2020-05-07,Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy,"Prototypical three-dimensional (3D) topological Dirac semimetals (DSMs), such
as Cd$_3$As$_2$ and Na$_3$Bi, contain electrons that obey a linear
momentum-energy dispersion with different Fermi velocities along the three
orthogonal momentum dimensions. Despite being extensively studied in recent
years, the inherent \emph{Fermi velocity anisotropy} has often been neglected
in the theoretical and numerical studies of 3D DSMs. Although this omission
does not qualitatively alter the physics of light-driven massless
quasiparticles in 3D DSMs, it does \emph{quantitatively} change the optical
coefficients which can lead to nontrivial implications in terms of
nanophotonics and plasmonics applications. Here we study the linear optical
response of 3D DSMs for general Fermi velocity values along each direction.
Although the signature conductivity-frequency scaling, $\sigma(\omega) \propto
\omega$, of 3D Dirac fermion is well-protected from Fermi velocity anisotropy,
the linear optical response exhibits strong linear dichroism as captured by the
\emph{universal} extinction ratio scaling law, $\Lambda_{ij} = (v_i/v_j)^2$
(where $i\neq j$ denotes the three spatial coordinates $x,y,z$, and $v_i$ is
the $i$-direction Fermi velocity), which is independent of frequency,
temperature, doping, and carrier scattering lifetime. For Cd$_3$As$_2$ and
Na$_3$Bi$_3$, an exceptionally strong extinction ratio larger than 15 and
covering broad terahertz window is revealed. Our findings shed new light on the
role of Fermi velocity anisotropy in the optical response of Dirac semimetals
and open up novel polarization-sensitive functionalities, such as
photodetection and light modulation.",2005.03363v1
2020-05-18,"Effects of filling, strain, and electric field on the Néel vector in antiferromagnetic CrSb","CrSb is a layered antiferromagnet (AFM) with perpendicular magnetic
anisotropy, a high N\'{e}el temperature, and large spin-orbit coupling (SOC),
which makes it interesting for AFM spintronic applications. To elucidate the
various mechanisms of N\'{e}el vector control, the effects of strain, band
filling, and electric field on the magnetic anisotropy energy (MAE) of bulk and
thin-film CrSb are determined and analysed using density functional theory. The
MAE of the bulk crystal is large (1.2 meV per unit cell). Due to the
significant ionic nature of the Cr-Sb bond, finite slabs are strongly affected
by end termination. Truncation of the bulk crystal to a thin film with one
surface terminated with Cr and the other surface terminated with Sb breaks
inversion symmetry, creates a large charge dipole and average electric field
across the film, and breaks spin degeneracy, such that the thin film becomes a
ferrimagnet. The MAE is reduced such that its sign can be switched with
realistic strain, and the large SOC gives rise to an intrinsic voltage
controlled magnetic anisotropy (VCMA). A slab terminated on both faces with Cr
remains a compensated AFM, but with the compensation occurring nonlocally
between mirror symmetric Cr pairs. In-plane alignment of the moments is
preferred, the magnitude of the MAE remains large, similar to that of the bulk,
and it is relatively insensitive to filling.",2005.08412v5
2020-05-18,On problematic case of product approximation in Backus average,"Elastic anisotropy might be a combined effect of the intrinsic anisotropy and
the anisotropy induced by thin-layering. The Backus average, a useful
mathematical tool, allows us to describe such an effect quantitatively. The
results are meaningful only if the underlying physical assumptions are obeyed,
such as static equilibrium of the material. We focus on the only mathematical
assumption of the Backus average, namely, product approximation. It states that
the average of the product of a varying function with nearly-constant function
is approximately equal to the product of the averages of those functions. We
discuss particular, problematic case for which the aforementioned assumption is
inaccurate. Further, we focus on the seismological context. We examine
numerically if the inaccuracy affects the wave propagation in a homogenous
medium -- obtained using the Backus average -- equivalent to thin layers. We
take into consideration various material symmetries, including orthotropic,
cubic, and others. We show that the problematic case of product approximation
is strictly related to the negative Poisson's ratio of constituent layers.
Therefore, we discuss the laboratory and well-log cases in which such a ratio
has been noticed. Upon thorough literature review, it occurs that examples of
so-called auxetic materials (media that have negative Poisson's ratio) are not
extremely rare exceptions as thought previously. The investigation and
derivation of Poisson's ratio for materials exhibiting symmetry classes up to
monoclinic become a significant part of this paper. Except for the main
objectives, we also show that the averaging of cubic layers results in an
equivalent medium with tetragonal (not cubic) symmetry. Additionally, we
present concise formulations of stability conditions for low symmetry classes,
such as trigonal, orthotropic, and monoclinic.",2005.08677v2
2020-05-25,Optimal Boltzmann hierarchies with non-vanishing spatial curvature,"Within cosmological perturbation theory, the cosmic microwave background
anisotropies are usually computed from a Boltzmann hierarchy coupled to the
perturbed Einstein equations. In this setup, one set of multipoles describes
the temperature anisotropies, while two other sets, of electric and magnetic
types, describe the polarization anisotropies. In order to reduce the number of
multipoles types needed for polarization, and thus to speed up the numerical
resolution, an optimal hierarchy has been proposed in the literature for
Einstein-Boltzmann codes. However, it has been recently shown that the
separability between directional and orbital eigenfunctions employed in the
optimal hierarchy is not correct in the presence of spatial curvature. We
investigate how the assumption of separability affects the optimal hierarchy,
and show that it introduces relative errors of order $\Omega_K$ with respect to
the full hierarchy. Despite of that, we show that the optimal hierarchy still
gives extremely good results for temperature and polarization angular spectra,
with relative errors that are much smaller than cosmic variance even for
curvatures as large as $|\Omega_K|=0.1$. Still, we find that the polarization
angular spectra from tensor perturbations are significantly altered when using
the optimal hierarchy, leading to errors that are typically of order $50
|\Omega_K| \%$ on that component.",2005.12119v1
2020-05-29,Long-distance spin-transport across the Morin phase transition up to room temperature in ultra-low damping single crystals of the antiferromagnet α-Fe2O3,"Antiferromagnetic materials can host spin-waves with polarizations ranging
from circular to linear depending on their magnetic anisotropies. Until now,
only easy-axis anisotropy antiferromagnets with circularly polarized spin-waves
were reported to carry spin-information over long distances of micrometers. In
this article, we report long-distance spin-transport in the easy-plane canted
antiferromagnetic phase of hematite and at room temperature, where the linearly
polarized magnons are not intuitively expected to carry spin. We demonstrate
that the spin-transport signal decreases continuously through the easy-axis to
easy-plane Morin transition, and persists in the easy-plane phase through
current induced pairs of linearly polarized magnons with dephasing lengths in
the micrometer range. We explain the long transport distance as a result of the
low magnetic damping, which we measure to be below 0.0001 as in the best
ferromagnets. All of this together demonstrates that long-distance transport
can be achieved across a range of anisotropies and temperatures, up to room
temperature, highlighting the promising potential of this insulating
antiferromagnet for magnon-based devices.",2005.14414v5
2020-05-29,Direction-sensitive magnetophotonic surface crystal,"Nanometer-thin rare-earth-transition metal (RE-TM) alloys with precisely
controlled compositions and out-of-plane magnetic anisotropy are currently in
the focus for ultrafast magnetophotonic applications. However, achieving
lateral nanoscale dimensions, crucial for potential device downscaling, while
maintaining designable optomagnetic functionality and out-of-plane magnetic
anisotropy is extremely challenging. Here we integrate nanosized
Tb$_{18}$Co$_{82}$ ferrimagnetic alloys, having strong out-of-plane magnetic
anisotropy, within a gold plasmonic nanoantenna array to design
micrometer-scale a magnetophotonic crystal that exhibit abrupt and narrow
magneto-optical spectral features that are both magnetic field and light
incidence direction controlled. The narrow Fano-type resonance arises through
the interference of the individual nanoantenna's surface plasmons and a
Rayleigh anomaly of the whole nanoantenna array, in both optical and
magneto-optical spectra, which we demonstrate and explain using Maxwell-theory
simulations. This robust magnetophotonic crystal opens the way for conceptually
new high-resolution light incidence direction sensors, as well as for building
blocks for plasmon-assisted all-optical magnetization switching in
ferrimagnetic RE-TM alloys.",2005.14478v3
2020-06-10,Study of magnetic interface and its effect in Fe/NiFe bilayers of alternating order,"We present a comprehensive study on the magnetization reversal in Fe/NiFe
bilayer system by alternating the order of the magnetic layers. All the samples
show growth-induced uniaxial magnetic anisotropy due to oblique angle
deposition technique. Strong interfacial exchange coupling between the Fe and
NiFe layers leads to the single-phase hysteresis loops in the bilayer system.
The strength of coupling being dependent on the interface changes upon
alternating the order of magnetic layers. The magnetic parameters such as
coercivity HC, and anisotropy field HK become almost doubled when NiFe layer is
grown over the Fe layers. This enhancement in the magnetic parameters is
primarily dependent on the increase of the thickness and magnetic moment of
Fe-NiFe interfacial layer as revealed from the polarized neutron reectivity
(PNR) data of the bilayer samples. The difference in the thickness and
magnetization of the Fe-NiFe interfacial layer indicates the modification of
the microstructure by alternating the order of the magnetic layers of the
bilayers. The interfacial magnetic moment increased by almost 18 % when NiFe
layer is grown over the Fe layer. In spite of the different values of
anisotropy fields and modified interfacial exchange coupling, the Gilbert
damping constant values of the ferromagnetic bilayers remain similar to single
NiFe layer.",2006.05756v1
2020-06-25,Perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction at an oxide/ferromagnetic metal interface,"We report on the study of both perpendicular magnetic anisotropy (PMA) and
Dzyaloshinskii-Moriya interaction (DMI) at an oxide/ferromagnetic metal (FM)
interface, i.e. BaTiO3 (BTO)/CoFeB. Thanks to the functional properties of the
BTO film and the capability to precisely control its growth, we are able to
distinguish the dominant role of the oxide termination (TiO2 vs BaO), from the
moderate effect of ferroelectric polarization in the BTO film, on the PMA and
DMI at the oxide/FM interface. We find that the interfacial magnetic anisotropy
energy of the BaO-BTO/CoFeB structure is two times larger than that of the
TiO2-BTO/CoFeB, while the DMI of the TiO2-BTO/CoFeB interface is larger. We
explain the observed phenomena by first-principles calculations, which ascribe
them to the different electronic states around the Fermi level at the
oxide/ferromagnetic metal interfaces and the different spin-flip processes.
This study paves the way for further investigation of the PMA and DMI at
various oxide/FM structures and thus their applications in the promising field
of energy-efficient devices.",2006.14268v1
2020-07-12,Anisotropic Kondo screening induced by spin-orbit coupling in quantum wires,"Using the numerical renormalization group (NRG) method we study a magnetic
impurity coupled to a quantum wire with Rashba and Dresselhaus spin-orbit
coupling (SOC) in an external magnetic field. We consider the low-filling
regime with the Fermi energy close to the bottom of the band and report the
results for local static and dynamic properties in the Kondo regime. In the
absence of the field, local impurity properties remain isotropic in spin space
despite the SOC-induced magnetic anisotropy of the conduction band. In the
presence of the field, clear fingerprints of anisotropy are revealed through
the strong field-direction dependence of the impurity spin polarization and
spectra, in particular of the Kondo peak height. The detailed behavior depends
on the relative magnitudes of the impurity and band $g$-factors. For the case
of impurity $g$-factor somewhat lower than the band $g$-factor, the maximal
Kondo peak suppression is found for field oriented along the effective SOC
field axis, while for a field perpendicular to this direction we observe a
compensation effect (``revival of the Kondo peak''): the SOC counteracts the
Kondo peak splitting effects of the local Zeeman field. We demonstrate that the
SOC-induced anisotropy, measurable by tunneling spectroscopy techniques, can
help to determine the ratio of Rashba and Dresselhaus SOC strengths in the
wire.",2007.06044v1
2020-07-21,Gamma-ray and radio background constraints on cosmic rays in Milky Way circumgalactic medium,"We study the interaction of cosmic rays (CRs) with the diffuse circumgalactic
gas of Milky Way (MW) galaxy that results in hadronic $\gamma-$ray emission and
radio synchrotron emission. We aim to constrain the CR population in our
circumgalactic medium (CGM) with the help of observed isotropic $\gamma$-ray
background (IGRB), its anisotropy and radio continuum. We modify different
models of CGM gas in hydrostatic equilibrium discussed in literature by
including a cosmic ray population, parametrized by $\eta \equiv P_{\rm
CR}/P_{\rm th}$. For the simplest isothermal model, while the IGRB intensity
allows $\eta \lesssim 3$, the anisotropy resulting from the Solar system's
off-center position in MW rules out all values of $\eta$. For the precipitation
model, in which the cooling of the CGM gas is regulated with an optimum ratio
of cooling time to free-fall time,while the observed IGRB intensity allows
$\eta \lesssim 230$, the observed anisotropy allows only very large values of
$\eta$, of order $\gtrsim 100$. The radio continuum limits $\eta \lesssim 400$
for precipitation model and does not constrain isothermal model, however these
constraints are mitigated by synchrotron loss time being comparable to CR
diffusion time scales. These bounds are relevant for current numerical
simulations that indicate a significant CR population in CGM of galaxies of MW
mass.",2007.11015v2
2020-08-02,Tailoring Magnetism in Self-intercalated Cr1+δTe2 Epitaxial Films,"Magnetic transition metal dichalcogenide (TMD) films have recently emerged as
promising candidates to host novel magnetic phases relevant to next-generation
spintronic devices. However, systematic control of the magnetization
orientation, or anisotropy, and its thermal stability, characterized by Curie
temperature (Tc) remains to be achieved in such films. Here we present
self-intercalated epitaxial Cr1+{\delta}Te2 films as a platform for achieving
systematic/smooth magnetic tailoring in TMD films. Using a molecular beam
epitaxy (MBE) based technique, we have realized epitaxial Cr1+{\delta}Te2 films
with smoothly tunable over a wide range (0.33-0.82), while maintaining
NiAs-type crystal structure. With increasing {\delta}, we found monotonic
enhancement of Tc from 160 to 350 K, and the rotation of magnetic anisotropy
from out-of-plane to in-plane easy axis configuration for fixed film thickness.
Contributions from conventional dipolar and orbital moment terms are
insufficient to explain the observed evolution of magnetic behavior with
{\delta}. Instead, ab initio calculations suggest that the emergence of
antiferromagnetic interactions with {\delta}, and its interplay with
conventional ferromagnetism, may play a key role in the observed trends. To our
knowledge, this constitutes the first demonstration of tunable Tc and magnetic
anisotropy across room temperature in TMD films, and paves the way for
engineering novel magnetic phases for spintronic applications.",2008.00381v1
2020-08-18,Probing solar flare accelerated electron distributions with prospective X-ray polarimetry missions,"Solar flare electron acceleration is an extremely efficient process, but the
method of acceleration is not well constrained. Two of the essential
diagnostics: electron anisotropy (velocity angle to the guiding magnetic field)
and the high energy cutoff (highest energy electrons produced by the
acceleration conditions: mechanism, spatial extent, time), are important
quantities that can help to constrain electron acceleration at the Sun but both
are poorly determined. Here, using electron and X-ray transport simulations
that account for both collisional and non-collisional transport processes such
as turbulent scattering, and X-ray albedo, we show that X-ray polarization can
be used to constrain the anisotropy of the accelerated electron distribution
and the most energetic accelerated electrons together. Moreover, we show that
prospective missions, e.g. CubeSat missions without imaging information, can be
used alongside such simulations to determine these parameters. We conclude that
a fuller understanding of flare acceleration processes will come from missions
capable of both X-ray flux and polarization spectral measurements together.
Although imaging polarimetry is highly desired, we demonstrate that
spectro-polarimeters without imaging can also provide strong constraints on
electron anisotropy and the high energy cutoff.",2008.07849v2
2020-08-27,Study of Transverse Spherocity and Azimuthal Anisotropy in Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV using A Multi-Phase Transport Model,"Transverse spherocity is an event shape observable having a very unique
capability to separate the events based on their geometrical shapes. Recent
results from experiments at the LHC suggest that transverse spherocity is an
important event classifier in small collision systems. In this work, we use
transverse spherocity for the first time in heavy-ion collisions and perform an
extensive study on azimuthal anisotropy of charged particles produced in Pb-Pb
collisions at $\sqrt{s_{\rm{NN}}} = 5.02$ TeV using A Multi-Phase Transport
Model (AMPT). The azimuthal anisotropy is estimated using the 2-particle
correlation method, which suppresses the non-flow effects significantly with an
appropriate pseudorapidity gap of particle pairs. The results from AMPT are
compared with estimations from PYTHIA8 (Angantyr) model and it is found that
with the chosen pseudorapidity gap the residual non-flow effects become
negligible. We found that the high spherocity events have nearly zero elliptic
flow while low spherocity events contribute significantly to elliptic flow of
spherocity-integrated events. Our studies indicate that using transverse
spherocity in heavy-ion collisions, one can enhance and/or suppress the
collective effects.",2008.13616v2
2020-09-03,First-principles study on structure and anisotropy of high N-atom density layer in 4H-SiC,"A nitridation annealing process is well employed to reduce interface trap
states that degrade the channel mobility of 4H-SiC/SiO${}_2$
metal-oxide-semiconductor field-effect transistor. In recent experiments, the
existence of high N-atom density layers at the annealed interface is reported
and their concentrations are known to be anisotropic in the crystal planes.
Until now, the role of atomic structure and the electronic states surrounding
the N atoms incorporated by the nitridation annealing process on the origin of
anisotropy is not well understood. In this work, we propose a simplified
atomic-scale model structure of 4H-SiC with the a high N-atom density layer
($\sim 10^{15}~\mathrm{atom}/\mathrm{cm}^2$), which is of the order of the
experimental observation. We use bulk 4H-SiC as host crystal and consider
several sets of the atomic configurations of the N-atom incorporated structure
at the quasi cubic-($k$-) and hexagonal-($h$-)sites on $a$-, $m$-, and
Si-(C-)planes. Based on the density functional theory calculations, we
investigate the influence of the energy stability on the distribution
directions. Although our bulk model is simplified compared to the realistic
interface structures, we confirm significant difference among models and
observe that the incorporation of N atoms on the $a$-face is stable.
Furthermore, from the analysis of the electronic states, we suggest that this
anisotropy of the formation energy originates from the change of the
coordinating number due to the difference in geometric configurations of the
N-atom incorporated structures.",2009.01627v4
2020-09-14,Screening anisotropy via energy-momentum squared gravity: $Λ$CDM model with hidden anisotropy,"We construct a generalization of the standard $\Lambda$CDM model, wherein we
simultaneously replace the spatially flat Robertson-Walker metric with its
simplest anisotropic generalization (LRS Bianchi I metric), and couple the cold
dark matter to the gravity in accordance with the energy-momentum squared
gravity (EMSG) of the form $f(T_{\mu\nu}T^{\mu\nu})\propto
T_{\mu\nu}T^{\mu\nu}$. These two modifications -- namely, two new stiff
fluid-like terms of different nature -- can mutually cancel out, i.e., the
shear scalar can be screened completely, and reproduce mathematically exactly
the same Friedmann equation of the standard $\Lambda$CDM model. This evades the
BBN limits on the anisotropy, and thereby provides an opportunity to manipulate
the cosmic microwave background quadrupole temperature fluctuation at the
desired amount. We further discuss the consequences of the model on the very
early times and far future of the Universe. This study presents also an example
of that the EMSG of the form $f(T_{\mu\nu}T^{\mu\nu})\propto
T_{\mu\nu}T^{\mu\nu}$, as well as similar type other constructions, is not
necessarily relevant only to very early Universe but may even be considered in
the context of a major problem of the current cosmology related to the
present-day Universe, the so-called $H_0$ problem.",2009.06517v2
2020-09-22,Magnon-mediated spin currents in Tm3Fe5O12/Pt with perpendicular magnetic anisotropy,"The control of pure spin currents carried by magnons in magnetic insulator
(MI) garnet films with a robust perpendicular magnetic anisotropy (PMA) is of
great interest to spintronic technology as they can be used to carry, transport
and process information. Garnet films with PMA present labyrinth domain
magnetic structures that enrich the magnetization dynamics, and could be
employed in more efficient wave-based logic and memory computing devices. In
MI/NM bilayers, where NM being a normal metal providing a strong spin-orbit
coupling, the PMA benefits the spin-orbit torque (SOT) driven magnetization's
switching by lowering the needed current and rendering the process faster,
crucial for developing magnetic random-access memories (SOT-MRAM). In this
work, we investigated the magnetic anisotropies in thulium iron garnet (TIG)
films with PMA via ferromagnetic resonance measurements, followed by the
excitation and detection of magnon-mediated pure spin currents in TIG/Pt driven
by microwaves and heat currents. TIG films presented a Gilbert damping constant
{\alpha}~0.01, with resonance fields above 3.5 kOe and half linewidths broader
than 60 Oe, at 300 K and 9.5 GHz. The spin-to-charge current conversion through
TIG/Pt was observed as a micro-voltage generated at the edges of the Pt film.
The obtained spin Seebeck coefficient was 0.54 {\mu}V/K, confirming also the
high interfacial spin transparency.",2009.10299v1
2020-09-27,Effects of spatially-varying substrate anchoring on instabilities and dewetting of thin Nematic Liquid Crystal films,"Partially wetting nematic liquid crystal (NLC) films on substrates are
unstable to dewetting-type instabilities due to destablizing solid/NLC
interaction forces. These instabilities are modified by the nematic nature of
the films, which influences the effective solid/NLC interaction. In this work,
we focus on the influence of imposed substrate anchoring on the instability
development. The analysis is carried out within a long-wave formulation based
on the Leslie-Ericksen description of NLC films. Linear stability analysis of
the resulting equations shows that some features of the instability, such as
emerging wavelengths, may not be influenced by the imposed substrate anchoring.
Going further into the nonlinear regime, considered via large-scale GPU-based
simulations, shows however that nonlinear effects may play an important role,
in particular in the case of strong substrate anchoring anisotropy. Our
simulations show that instability of the film develops in two stages: the first
stage involves formation of ridges that are perpendicular to the local
anchoring direction; and the second involves breakup of these ridges and
formation of drops, whose final distribution is influenced by the anisotropy
imposed by the substrate. Finally, we show that imposing more complex substrate
anisotropy patterns allows us to reach basic understanding of the influence of
substrate-imposed defects in director orientation on the instability evolution.",2009.12946v1
2020-11-02,Compact stellar model in Tolman space-time in presence of pressure anisotropy,"In this paper, we develop a new relativistic compact stellar model for a
spherically symmetric anisotropic matter distribution. The model has been
obtained through generating a new class of solutions by invoking the Tolman
{\em ansatz} for one of the metric potentials $g_{rr}$ and a physically
reasonable selective profile of radial pressure. We have matched our obtained
interior solution to the Schwarzschild exterior spacetime over the bounding
surface of the compact star. These matching conditions together with the
condition of vanishing the radial pressure across the boundary of the star have
been utilized to determine the model parameters. We have shown that the central
pressure of the star depends on the parameter $p_0$. We have estimated the
range of $p_0$ by using the recent data of compact stars 4U 1608-52 and Vela
X-1. The effect of $p_0$ on different physical parameters e.g., pressure
anisotropy, the subliminal velocity of sound, relativistic adiabatic index etc.
have also been discussed. The developed model of the compact star is
elaborately discussed both analytically and graphically to justify that it
satisfies all the criteria demanded a realistic star. From our analysis, we
have shown that the effect of anisotropy becomes small for higher values of
$p_0$. The mass-radius (M-R) relationship which indicates the maximum mass
admissible for observed pulsars for a given surface density has also been
investigated in our model. Moreover, the variation of radius and mass with
central density has been shown which allow us to estimate central density for a
given radius (or mass) of a compact star.",2011.00856v2
2020-11-23,Primordial non-Gaussianity from the Effects of the Standard Model Higgs during Reheating after Inflation,"We propose a new way of studying the Higgs potential at extremely high
energies. The Standard Model (SM) Higgs boson, as a light spectator field
during inflation in the early Universe, can acquire large field values from its
quantum fluctuations which vary among different causal (Hubble) patches. Such a
space dependence of the Higgs after the end of inflation leads to
space-dependent SM particle masses and hence variable efficiency of reheating,
when the inflaton decays to Higgsed SM particles. Inhomogeneous reheating
results in (observable) temperature anisotropies. Further, the resulting
temperature anisotropy spectrum acquires a significant non-Gaussian component,
which is constrained by $\textit{Planck}$ observations of the Cosmic Microwave
Background (CMB) and potentially detectable in next-generation experiments.
Constraints on this non-Gaussian signal largely exclude the possibility of the
observed temperature anisotropies arising primarily from Higgs effects. Hence,
in principle, observational searches for non-Gaussianity in the CMB can be used
to constrain the dynamics of the Higgs boson at very high (inflationary)
energies.",2011.11649v3
2020-11-25,No Stagnation Region Before the Heliopause at Voyager 1? Inferences From New Voyager 2 Results,"We present anisotropy results for anomalous cosmic-ray (ACR) protons in the
energy range $\sim$0.5-35 MeV from Cosmic Ray Subsytem (CRS) data collected
during calibration roll maneuvers for the magnetometer instrument when Voyager
2 (V2) was in the inner heliosheath. We use a new technique to derive for the
first time the radial component of the anisotropy vector from CRS data. We find
that the CRS-derived radial solar wind speeds, when converted from the radial
components of the anisotropy vectors via the Compton-Getting (C-G) effect,
generally agree with those similarly-derived speeds from the Low-Energy Charged
Particle experiment using 28-43 keV data. However, they often differ
significantly from the radial solar wind speeds measured directly by the Plasma
Science (PLS) instrument. There are both periods when the C-G-derived radial
solar wind speeds are significantly higher than those measured by PLS and times
when they are significantly lower. The differences are not expected nor
explained, but it appears that after a few years in the heliosheath the V2
radial solar wind speeds derived from the C-G method underestimate the true
speeds as the spacecraft approaches the heliopause. We discuss the implications
of this observation for the stagnation region reported along the Voyager 1
trajectory as it approached the heliopause inferred using the C-G method.",2011.12926v1
2021-01-09,Dipolar Interaction and Sample Shape Effects on the Hysteresis Properties of 2d Array of Magnetic Nanoparticles,"We study the ground state and magnetic hysteresis properties of 2$d$ arrays
($L^{}_x\times L^{}_y$) of dipolar interacting magnetic nanoparticles (MNPs) by
performing micromagnetic simulations. Our primary interest is to understand the
effect of sample shape, $\Theta$- the ratio of the dipolar strength to the
anisotropy strength, and the direction of the applied field $\vec{H} =
H_{o}\hat{e}^{}_H$ on the ground state and the magnetic hysteresis in an array
of MNPs. To study the effect of shape of the sample, we have varied the aspect
ratio $A^{}_r=L^{}_y/L^{}_x$ which in turn, is found to induce shape anisotropy
in the system. Our main observations are: (a) When the dipolar interaction is
strong $(\Theta>1)$, the ground state morphology has in-plane ordering of
magnetic moments. (b) The ground state morphology has randomly oriented
magnetic moments which is robust with respect to system sizes and $A^{}_r$ for
weakly interacting MNPs ($\Theta<1$). (c) Micromagnetic simulations suggests
that the dipolar interaction decreases the coercive field $H^{}_c$. (d) The
remanence magnetization $M^{}_r$ is found to be strongly dependent not only on
the strength of dipolar interaction but also on the shape of the sample. (e)
Due to anisotropic nature of dipolar interaction, a strong effect of shape
anisotropy is observed when the field is applied along longer axis of the
sample. The dipolar interaction in such a case induces an effective
ferromagnetic coupling when the aspect ratio is very large. These results are
of vital importance in high-density recording systems, magneto-impedance
sensors, etc.",2101.03356v1
2021-01-15,Tunable spin-flop transition in artificial ferrimagnets,"Spin-flop transition (SFT) consists in a jump-like reversal of
antiferromagnetic magnetic moments into a non-collinear state when the magnetic
field increases above the critical value. Potentially the SFT can be utilized
in many applications of a rapidly developing antiferromagnetic spintronics.
However, the difficulty of using them in conventional antiferromagnets lies in
(a) too large switching magnetic fields (b) the need for presence of a magnetic
anisotropy, and (c) requirement to apply magnetic field along the correspondent
anisotropy axis. In this work we propose to use artificial ferrimagnets in
which the spin-flop transition occurs without anisotropy and the transition
field can be lowered by adjusting exchange coupling in the structure. This is
proved by experiment on artificial Fe-Gd ferrimagnets where usage of Pd spacers
allowed us to suppress the transition field by two orders of magnitude.",2101.06155v2
2021-01-17,Experimental determination of the magnetic interactions of frustrated Cairo pentagon lattice materials,"We present inelastic neutron scattering measurements of the Cairo pentagon
lattice magnets Bi$_2$Fe$_4$O$_9$ and Bi$_4$Fe$_5$O$_{13}$F, supported by high
field magnetisation measurements of Bi$_2$Fe$_4$O$_9$. Using linear spin wave
theory and mean field analyses we determine the spin exchange interactions and
single-ion anisotropy in these materials. The Cairo lattice is geometrically
frustrated and consists of two inequivalent magnetic sites, both occupied by
Fe$^{3+}$ ions and connected by two competing nearest neighbour interactions.
We found that one of these interactions, coupling nearest neighbour spins on
the three-fold symmetric sites, is extremely strong and antiferromagnetic.
These strongly coupled dimers are then weakly coupled to a framework formed
from spins occupying the other inequivalent site. In addition we found that the
Fe$^{3+}$ $S=5/2$ spins have a non-negligible single-ion anisotropy, which
manifests as a spin anisotropy gap in the neutron spectrum and a spin-flop
transition in high field magnetisation measurements.",2101.06786v1
2021-01-18,Giant Transport Anisotropy in ReS$_2$ Revealed via Nanoscale Conducting Path Control,"The low in-plane symmetry in layered 1T'-ReS$_2$ results in strong band
anisotropy, while its manifestation in the electronic properties is challenging
to resolve due to the lack of effective approaches for controlling the local
current path. In this work, we reveal the giant transport anisotropy in
monolayer to four-layer ReS$_2$ by creating directional conducting paths via
nanoscale ferroelectric control. By reversing the polarization of a
ferroelectric polymer top layer, we induce conductivity switching ratio of
>1.5x10$^8$ in the ReS$_2$ channel at 300 K. Characterizing the domain-defined
conducting nanowires in an insulating background shows that the conductivity
ratio between the directions along and perpendicular to the Re-chain can exceed
5.5x10$^4$. Theoretical modeling points to the band origin of the transport
anomaly, and further reveals the emergence of a flat band in few-layer ReS$_2$.
Our work paves the path for implementing the highly anisotropic 2D materials
for designing novel collective phenomena and electron lensing applications.",2101.07379v2
2021-02-15,Controlling Domain-Wall Nucleation in Ta/CoFeB/MgO Nanomagnets via Local Ga+ Ion Irradiation,"Comprehensive control of the domain wall nucleation process is crucial for
spin-based emerging technologies ranging from random-access and storage-class
memories over domain-wall logic concepts to nanomagnetic logic. In this work,
focused Ga+ ion-irradiation is investigated as an effective means to control
domain-wall nucleation in Ta/CoFeB/MgO nanostructures. We show that analogously
to He+ irradiation, it is not only possible to reduce the perpendicular
magnetic anisotropy but also to increase it significantly, enabling new,
bidirectional manipulation schemes. First, the irradiation effects are assessed
on film level, sketching an overview of the dose-dependent changes in the
magnetic energy landscape. Subsequent time-domain nucleation characteristics of
irradiated nanostructures reveal substantial increases in the anisotropy fields
but surprisingly small effects on the measured energy barriers, indicating
shrinking nucleation volumes. Spatial control of the domain wall nucleation
point is achieved by employing focused irradiation of pre-irradiated magnets,
with the diameter of the introduced circular defect controlling the coercivity.
Special attention is given to the nucleation mechanisms, changing from a
Stoner-Wohlfarth particle's coherent rotation to depinning from an anisotropy
gradient. Dynamic micromagnetic simulations and related measurements are used
in addition to model and analyze this depinning-dominated magnetization
reversal.",2102.07540v1
2021-02-17,Optimization of epitaxial graphene growth for quantum metrology,"(See the complete abstract within the thesis in both English and German
versions)
  In this thesis, the process conditions of the epitaxial graphene growth
through a socalled polymer-assisted sublimation growth method are minutely
investigated. Atomic force microscopy (AFM) is used to show that the previously
neglected flow-rate of the argon process gas has a significant influence on the
morphology of the SiC substrate and atop carbon layers. The results can be well
explained using a simple model for the thermodynamic conditions at the layer
adjacent to the surface. The resulting control option of step-bunching on the
sub-nanometer scales is used to produce the ultra-flat, monolayer graphene
layers without the bilayer inclusions that exhibit the vanishing of the
resistance anisotropy. The comparison of four-point and scanning tunneling
potentiometry measurements shows that the remaining small anisotropy represents
the ultimate limit, which is given solely by the remaining resistances at the
SiC terrace steps. ... The precise control of step-bunching using the Ar flow
also enables the preparation of periodic non-identical SiC surfaces under the
graphene layer. Based on the work function measurements by Kelvin-Probe force
microscopy and X-ray photoemission electron microscopy, it is shown for the
first time that there is a doping variation in graphene, induced by a proximity
effect of the different near-surface SiC stacks. The comparison of the AFM and
low-energy electron microscopy measurements have enabled the exact assignment
of the SiC stacks, and the examinations have led to an improved understanding
of the surface restructuring in the framework of a step-flow mode. ...",2102.08691v1
2021-02-22,Spirals and skyrmions in antiferromagnetic triangular lattices,"We study realizations of spirals and skyrmions in two-dimensional
antiferromagnets with a triangular lattice on an inversion-symmetry-breaking
substrate. As a possible material realization, we investigate the adsorption of
transition-metal atoms (Cr, Mn, Fe, or Co) on a monolayer of MoS$_2$, WS$_2$,
or WSe$_2$ and obtain the exchange, anisotropy, and Dzyaloshinskii-Moriya
interaction parameters using first-principles calculations. Using energy
minimization and parallel-tempering Monte-Carlo simulations, we determine the
magnetic phase diagrams for a wide range of interaction parameters. We find
that skyrmion lattices can appear even with weak Dzyaloshinskii-Moriya
interactions, but their stability is hindered by magnetic anisotropy. However,
a weak easy plane magnetic anisotropy can be beneficial for stabilizing the
skyrmion phase. Our results suggest that Cr$/$MoS$_2$, Fe$/$MoS$_2$, and
Fe$/$WSe$_2$ interfaces can host spin spirals formed from the 120$^{\circ}$
antiferromagnetic states. Our results further suggests that for other
interfaces, such as Fe$/$MoS$_2$, the Dzyaloshinskii-Moriya interaction is
strong enough to drive the system into a three-sublattice skyrmion lattice in
the presence of experimentally feasible external magnetic field.",2102.11246v1
2021-02-23,Phenomenological study of the anisotropic quark matter in the 2-flavor Nambu-Jona-Lasinio model,"With the two flavor Nambu-Jona-Lasinio (NJL) model we carry out a
phenomenological study on the chiral phase structure, mesonic properties and
transport properties in a momentum-space anisotropic quark matter. To calculate
transport coefficients we have utilized the kinetic theory in the relaxation
time approximation, where the momentum anisotropy is embedded in the estimation
of both distribution function and the relaxation time. It is shown that an
increase of the anisotropy parameter $\xi$ may results in a catalysis of chiral
symmetry breaking. The critical endpoint (CEP) is shifted to smaller
temperatures and larger quark chemical potentials as $\xi $ increases, the
impact of momentum anisotropy on temperature of CEP is almost the same as that
on the quark chemical potential of CEP. The meson masses and the associated
decay widths also exhibit a significant $\xi$ dependence. It is observed that
the temperature behavior of scaled shear viscosity $\eta/T^3$ and scaled
electrical conductivity $\sigma_{el}/T$ exhibit a similar dip structure, with
the minima of both $\eta/T^3$ and $\sigma_{el}/T$ shifting toward higher
temperatures with increasing $\xi$. Furthermore, we demonstrate that the
Seebeck coefficient $S$ decreases when temperature goes up and its sign is
positive, indicating the dominant carriers for converting the temperature
gradient to the electric field are up-quarks. The Seebeck coefficient $S$ is
significantly enhanced with a large $\xi$ for the temperature below the
critical temperature.",2102.11792v3
2021-03-08,Anisotropic turbulent transport with horizontal shear in stellar radiative zones,"Context. Turbulent transport in stellar radiative zones is a key ingredient
of stellar evolution theory, but the anisotropy of the transport due to the
stable stratification and the rotation of these regions is poorly understood.
The assumption of shellular rotation, which is a cornerstone of the so-called
rotational mixing, relies on an efficient horizontal transport. However, this
transport is included in many stellar evolution codes through phenomenological
models that have never been tested.
  Aims. We investigate the impact of horizontal shear on the anisotropy of
turbulent transport.
  Methods. We used a relaxation approximation (also known as {\tau}
approximation) to describe the anisotropising effect of stratification,
rotation, and shear on a background turbulent flow by computing velocity
correlations.
  Results. We obtain new theoretical scalings for velocity correlations that
include the effect of horizontal shear. These scalings show an enhancement of
turbulent motions, which would lead to a more efficient transport of chemicals
and angular momentum, in better agreement with helio- and asteroseismic
observations of rotation in the whole Hertzsprung-Russell diagram. Moreover, we
propose a new choice for the non-linear time used in the relaxation
approximation, which characterises the source of the turbulence.
  Conclusions. For the first time, we describe the effect of stratification,
rotation, and vertical and horizontal shear on the anisotropy of turbulent
transport in stellar radiative zones. The new prescriptions need to be
implemented in stellar evolution calculations. To do so, it may be necessary to
implement non-diffusive transport.",2103.05473v1
2021-03-17,Large Orbital Magnetic Moment and Strong Perpendicular Magnetic Anisotropy in Heavily Intercalated Fe$_{x}$TiS$_2$,"Titanium disulfide TiS$_2$, which is a member of the layered transition-metal
dichalcogenides with the 1T-CdI$_2$-type crystal structure, is known to exhibit
a wide variety of magnetism through intercalating various kinds of
transition-metal atoms of different concentrations. Among them, Fe-intercalated
titanium disulfide Fe$_x$TiS$_2$ is known to be ferromagnetic with strong
perpendicular magnetic anisotropy (PMA) and large coercive fields
($H_\text{c}$). In order to study the microscopic origin of the magnetism of
this compound, we have performed X-ray absorption spectroscopy (XAS) and X-ray
magnetic circular dichroism (XMCD) measurements on single crystals of heavily
intercalated Fe$_x$TiS$_2$ ($x\sim0.5$). The grown single crystals showed a
strong PMA with a large $H_\text{c}$ of $\mu_0H_\text{c} \simeq 1.0\ \text{T}$.
XAS and XMCD spectra showed that Fe is fully in the valence states of 2+ and
that Ti is in an itinerant electronic state, indicating electron transfer from
the intercalated Fe atoms to the host TiS$_2$ bands. The Fe$^{2+}$ ions were
shown to have a large orbital magnetic moment of $\simeq 0.59\
\mu_\text{B}\text{/Fe}$, to which, combined with the spin-orbit interaction and
the trigonal crystal field, we attribute the strong magnetic anisotropy of
Fe$_x$TiS$_2$.",2103.09538v2
2021-03-30,Positive magnetoresistance and chiral anomaly in exfoliated type-II Weyl semimetal $T_\mathrm{d}$-WTe$_{2}$,"Layered van der Waals semimetallic $T_\mathrm{d}$-WTe$_{2}$, exhibiting
intriguing properties which include non-saturating extreme positive
magnetoresistance (MR) and tunable chiral anomaly, has emerged as model
topological type-II Weyl semimetal system. Here, $\sim$45 nm thick mechanically
exfoliated flakes of $T_\mathrm{d}$-WTe$_{2}$ are studied $via$ atomic force
microscopy, Raman spectroscopy, low-$T$/high-$\mu_{0}H$ magnetotransport
measurements and optical reflectivity. The contribution of anisotropy of the
Fermi liquid state to the origin of the large positive transverse
$\mathrm{MR}_\perp$ and the signature of chiral anomaly of the type-II Weyl
fermions are reported. The samples are found to be stable in air and no
oxidation or degradation of the electronic properties are observed. A
transverse $\mathrm{MR}_\perp$ $\sim$1200\,\% and an average carrier mobility
of $5000$\, cm$^{2}$V$^{-1}$s$^{-1}$ at $T=5\,\mathrm{K}$ for an applied
perpendicular field $\mu_{0}H_{\perp} = 7\,\mathrm{T}$ are established. The
system follows a Fermi liquid model for $T\leq50\,\mathrm{K}$ and the
anisotropy of the Fermi surface is concluded to be at the origin of the
observed positive MR. The anisotropy of the electronic behaviour is also
confirmed by optical reflectivity measurements. The relative orientation of the
crystal axes and of the applied electric and magnetic fields is proven to give
rise to the observed chiral anomaly in the in-plane magnetotransport.",2103.16326v1
2021-04-10,Thermal buckling of thin injection-molded FRP plates with fiber orientation varying over the thickness,"The different thermo-elastic properties of glass fibers and polymer matrices
can generate residual thermal stresses in injection-molded fiber-reinforced
plastic (FRP) objects. During cooling from mold to room temperature, these
stresses can be relaxed by large deformations resulting from an instability of
the unwarped configuration (i.e., buckling). This article investigates the
thermal buckling of thin FRP disks via an analytical formulation based on the
Foppl-von Karman theory. Expanding on our previous work, cylindrical orthotropy
with material parameters varying over the disk thickness is assumed in order to
account for thickness dependency of the glass fiber orientation distribution. A
disk parameter generalizing the thermal anisotropy ratio for homogeneous
orthotropic disks is introduced and its relation with the occurrence and
periodicity of buckling is discussed. This is done for a skin-coreskin model,
for which the core-to-total thickness ratio is defined. For fiber orientation
distributions typical of injection-molded disks, it is found that there exists
a value of the thickness ratio for which no buckling occurs. It is also
demonstrated that the periodicity of the first buckling mode is described by
the generalized thermal anisotropy ratio, thus extending the results obtained
for a homogeneous fiber orientation distribution. Improvements in the accuracy
of the predictions for experimental data available in the literature when using
the skin-core-skin model are shown. Finally, we study the relation between
buckling temperature and disk thickness and propose an expression for the
dependence of the normalized buckling temperature on the thermal anisotropy
ratio. Results of FEM simulations are used to validate the proposed expression,
proving its applicability and accuracy.",2104.04735v1
2021-04-25,Topological quantum phase transition in the magnetic semimetal HoSb,"Magnetic topological semimetals, a novel state of quantum matter with
nontrivial band topology, have emerged as a new frontier in physics and
materials science. An external stimulus like temperature or magnetic field
could be expected to alter their spin states and thus the Fermi surface
anisotropies and topological features. Here, we perform the angular
magnetoresistance measurements and electronic band structure calculations to
reveal the evolution of HoSb's Fermi surface anisotropies and topological
nature in different magnetic states. The angular magnetoresistance results
manifest that its Fermi surface anisotropy is robust in the paramagnetic state
but is significantly modulated in the antiferromagnetic and ferromagnetic
states. More interestingly, a transition from the trivial (nontrivial) to
nontrivial (trivial) topological electronic phase is observed when HoSb
undergoes a magnetic transition from the paramagnetic (antiferromagnetic) to
antiferromagnetic (ferromagnetic) state induced by temperature (applied
magnetic field). Our studying suggests that HoSb provides an archetype platform
to study the correlations between magnetism and topological states of matter.",2104.12054v1
2021-05-06,Quantum Oscillation of Thermally Activated Conductivity in a Monolayer WTe$_2$-like Excitonic Insulator,"Recently, quantum oscillation of the resistance in insulating monolayer
WTe$_2$ was reported. An explanation in terms of gap modulation in the
hybridized Landau levels of an excitonic insulator was also proposed by one of
us. However, the previous picture of gap modulation in the Landau levels
spectrum was built on a pair of well nested electron and hole Fermi surfaces,
while the monolayer WTe$_2$ has one hole and two electron Fermi pockets with
relative anisotropy. Here we demonstrate that for system like monolayer
WTe$_2$, the excitonic insulating state arising from the coupled one hole and
two electron pockets possesses a finite region in interaction parameter space
that shows gap modulation in a magnetic field. In this region, the thermally
activated conductivity displays the $1/B$ periodic oscillation and it can
further develop into discrete peaks at low temperature, in agreement with the
experimental observation. We show that the relative anisotropy of the bands is
a key parameter and the qunatum oscillations decrease rapidly if the anisotropy
increases further than the realistic value for monolayer WTe$_2$.",2105.02411v2
2021-05-13,Effect of magnetic anisotropy relaxation on laser-induced magnetization precession in thin galfenol films,"The rate and pathways of relaxation of a magnetic medium to its equilibrium
following excitation with intense and short laser pulses are the key
ingredients of ultrafast optical control of spins. Here we study experimentally
the evolution of the magnetization and magnetic anisotropy of thin films of a
ferromagnetic metal galfenol (Fe$_{0.81}$Ga$_{0.19}$) resulting from excitation
with a femtosecond laser pulse. From the temporal evolution of the hysteresis
loops we deduce that the magnetization $M_S$ and magnetic anisotropy parameters
$K$ recover within a nanosecond, and the ratio between $K$ and $M_S$ satisfies
the thermal equilibrium's power law in the whole time range spanning from a few
picoseconds to 3 nanoseconds. We further use the experimentally obtained
relaxation times of $M_S$ and $K$ to analyze the laser-induced precession and
demonstrate how they contribute to its frequency evolution at the nanosecond
timescale.",2105.06385v4
2021-05-15,ElATools: A tool for analyzing anisotropic elastic properties of the 2D and 3D materials,"We introduce a computational method and a user-friendly code with a
terminal-based graphical user interface (GUI), named ElATools, developed to
analyze mechanical and anisotropic elastic properties. ElATools enables facile
analysis of the second-order elastic stiffness tensor of two-dimensional (2D)
and three-dimensional (3D) crystal systems. It computes and displays the main
mechanical properties including the bulk modulus, Young's modulus, shear
modulus, hardness, p-wave modulus, universal anisotropy index, Chung-Buessem
anisotropy index, log-Euclidean anisotropy parameter, Cauchy pressures,
Poisson's ratio, and Pugh's ratio, using three averaging schemes of Voigt,
Reuss, and Hill. It includes an online and offline database from the Materials
Project with more than 13,000 elastic stiffness constants for 3D materials. The
program supports output files of the well-known computational codes IRelast,
IRelast2D, ElaStic, and AELAS. Four types of plotting and visualization tools
are integrated to conveniently interface with GNUPLOT, XMGRACE, view3dscene,
and plotly libraries, offering immediate post-processing of the results. It can
efficiently identify anomalous mechanical properties, such as negative linear
compressibility, negative Poisson's ratio, and highly-anisotropic elastic
modulus in 2D and 3D materials, which are central properties to design and
develop high-performance nanoscale electromechanical devices. Six case studies
on selected material systems, namely, ZnAu$_2$ (CN)$_4$, CrB$_2$,
$\delta$-phosphorene, Pd$_2$O$_6$Se$_2$ monolayer, and GaAs, and a hypothetical
set of systems with cubic symmetry are presented to demonstrate the descriptive
and predictive capabilities of ElATools.",2105.07279v3
2021-05-20,Restoring isotropy in a three-dimensional lattice model: The Ising universality class,"We study a generalized Blume-Capel model on the simple cubic lattice. In
addition to the nearest neighbor coupling there is a next to next to nearest
neighbor coupling. In order to quantify spatial anisotropy, we determine the
correlation length in the high temperature phase of the model for three
different directions. It turns out that the spatial anisotropy depends very
little on the dilution parameter $D$ of the model and is essentially determined
by the ratio of the nearest neighbor and the next to next to nearest neighbor
coupling. This ratio is tuned such that the leading contribution to the spatial
anisotropy is eliminated. Next we perform a finite size scaling (FSS) study to
tune $D$ such that also the leading correction to scaling is eliminated. Based
on this FSS study, we determine the critical exponents $\nu=0.62998(5)$ and
$\eta=0.036284(40)$, which are in nice agreement with the more accurate results
obtained by using the conformal bootstrap method. Furthermore we provide
accurate results for fixed point values of dimensionless quantities such as the
Binder cumulant and for the critical couplings. These results provide the
groundwork for broader studies of universal properties of the three-dimensional
Ising universality class.",2105.09781v2
2021-05-27,Delineating corneal elastic anisotropy in a porcine model using non-contact optical coherence elastography and ex vivo mechanical tests,"Objective: To compare non-contact acoustic micro-tapping optical coherence
elastography (AuT-OCE) with destructive mechanical tests to confirm corneal
elastic anisotropy.
  Design: Ex vivo, laboratory study with non-contact AuT-OCE followed by
mechanical rheometry and extensometry.
  Subjects: Inflated cornea of whole-globe porcine eyes.
  Methods: A non-contact transducer was used to launch mechanical waves in the
cornea that were imaged with phase-sensitive OCT at physiologically relevant
pressures. Reconstruction of both Young's modulus (E) and out-of-plane shear
modulus (G) in the cornea from experimental data was performed using a model of
a nearly incompressible transversally isotropic (NITI) medium. Samples were
then excised and parallel plate rheometry was performed to measure the shear
modulus G. Corneal samples were then subjected to strip extensomety to measure
the Young's modulus.
  Main Outcome Measures: Strong corneal anisotropy was confirmed with both
AuT-OCE and mechanical tests, with the Young's and shear moduli differing by
over an order of magnitude. These results show that AuT-OCE can quantify both
moduli with a non-contact, non-invasive, clinically translatable technique.",2105.13140v1
2021-06-04,Optical read-out of the Néel vector in metallic antiferromagnet Mn$_{2}$Au,"Metallic antiferromagnets with broken inversion symmetry on the two
sublattices, strong spin-orbit coupling and high N\'{e}el temperatures offer
new opportunities for applications in spintronics. Especially Mn$_{2}$Au, with
high N\'{e}el temperature and conductivity, is particularly interesting for
real-world applications. Here, manipulation of the orientation of the staggered
magnetization,\textit{\ i.e.} the N\'{e}el vector, by current pulses has been
recently demonstrated, with the read-out limited to studies of anisotropic
magnetoresistance or X-ray magnetic linear dichroism. Here, we report on the
in-plane reflectivity anisotropy of Mn$_{2}$Au (001) films, which were N\'{e}el
vector aligned in pulsed magnetic fields. In the near-infrared, the anisotropy
is $\approx$ 0.6\%, with higher reflectivity for the light polarized along the
N\'{e}el vector. The observed magnetic linear dichroism is about four times
larger than the anisotropic magnetoresistance. This suggests the dichroism in
Mn$_{2}$Au is a result of the strong spin-orbit interactions giving rise to
anisotropy of interband optical transitions, in-line with recent studies of
electronic band-structure. The considerable magnetic linear dichroism in the
near-infrared could be used for ultrafast optical read-out of the N\'{e}el
vector in Mn$_{2}$Au.",2106.02729v2
2021-06-27,A new low-beta regime for unstable proton firehose modes in bi-Kappa distributed plasmas,"In the solar wind plasma an excess of kinetic temperature along the
background magnetic field stimulates proton firehose modes to grow if the
parallel plasma beta parameter is sufficiently high, i.e., $\beta_{p
\parallel}\gtrsim 1$. This instability can prevent the expansion-driven
anisotropy from increasing indefinitely, and explain the observations.
Moreover, such kinetic instabilities are expected to be even more effective in
the presence of suprathermal Kappa-distributed populations, which are
ubiquitous in the solar wind, are less affected by collisions than the core
population, but contribute with an additional free energy. In this work we use
both linear and extended quasi-linear (QL) frameworks to characterize the
unstable periodic proton firehose modes (propagating parallel to the magnetic
field) under the influence of suprathermal protons. Linear theory predicts a
systematic stimulation of the instability, suprathermals amplifying the growth
rates and decreasing the instability thresholds to lower anisotropies and lower
plasma betas ($\beta_{p \parallel}<1$). In perfect agreement with these
results, the QL approach reveals a significant enhancement of the resulting
electromagnetic fluctuations up to the saturation with a stronger back reaction
on protons, leading also to a faster and more efficient relaxation of the
temperature anisotropy.",2106.14291v1
2021-07-06,Relativistic aspects of orbital and magnetic anisotropies in the chemical bonding and structure of lanthanide molecules,"The electronic structure of magnetic lanthanide atoms is fascinating from a
fundamental perspective. They have electrons in a submerged open 4f shell lying
beneath a filled 6s shell with strong relativistic correlations leading to a
large magnetic moment and large electronic orbital angular momentum. This large
angular momentum leads to strong anisotropies, i. e. orientation dependencies,
in their mutual interactions. The long-ranged molecular anisotropies are
crucial for proposals to use ultracold lanthanide atoms in spin-based quantum
computers, the realization of exotic states in correlated matter, and the
simulation of orbitronics found in magnetic technologies. Short-ranged
interactions and bond formation among these atomic species have thus far not
been well characterized. Efficient relativistic computations are required.
Here, for the first time we theoretically determine the electronic and
ro-vibrational states of heavy homonuclear lanthanide Er2 and Tm2 molecules by
applying state-of-the-art relativistic methods. In spite of the complexity of
their internal structure, we were able to obtain reliable spin-orbit and
correlation-induced splittings between the 91 Er2 and 36 Tm2 electronic
potentials dissociating to two ground-state atoms. A tensor analysis allows us
to expand the potentials between the atoms in terms of a sum of seven spin-spin
tensor operators simplifying future research. The strengths of the tensor
operators as functions of atom separation are presented and relationships among
the strengths, derived from the dispersive long-range interactions, are
explained. Finally, low-lying spectroscopically relevant ro-vibrational energy
levels are computed with coupled-channels calculations and analyzed.",2107.02676v1
2021-07-08,"Unconventional thermal and magnetic-field-driven changes of a bipartite entanglement of a mixed spin-(1/2,$S$) Heisenberg dimer with an uniaxial single-ion anisotropy","The concept of negativity is adapted in order to explore the quantum and
thermal entanglement of the mixed spin-(1/2,$S$) Heisenberg dimers in presence
of an external magnetic field. The mutual interplay between the spin size $S$,
XXZ exchange and uniaxial single-ion anisotropy is thoroughly examined with a
goal to tune the degree and thermal stability of the pairwise entanglement. It
turns out that the antiferromagnetic spin-(1/2,$S$) Heisenberg dimers exhibit
higher degree of entanglement and higher threshold temperature in comparison
with their ferromagnetic counterparts when assuming the same set of model
parameters. The increasing spin magnitude $S$ accompanied with an easy-plane
uniaxial single-ion anisotropy can enhance not only the thermal stability but
simultaneously the degree of entanglement. It is additionally shown that the
further enhancement of a bipartite entanglement can be achieved in the mixed
spin-(1/2,$S$) Heisenberg dimers, involving half-odd-integer spins $S$. Under
this condition the thermal negativity saturates at low-enough temperatures in
its maximal value regardless of the magnitude of half-odd-integer spin $S$. The
magnetic field induces consecutive discontinuous phase transitions in the mixed
spin-(1/2,$S$) Heisenberg dimers with $S\!>\!1$, which are manifested in a
surprising oscillating magnetic-field dependence of the negativity observed at
low enough temperature.",2107.05628v2
2021-07-19,MoP$_3$SiO$_{11}$: a $4d^3$ honeycomb antiferromagnet with disconnected octahedra,"We report the crystal structure and magnetic behavior of the $4d^3$
spin-$\frac32$ silicophosphate MoP$_3$SiO$_{11}$ studied by high-resolution
synchrotron x-ray diffraction, neutron diffraction, thermodynamic measurements,
and ab initio band-structure calculations. Our data revise the crystallographic
symmetry of this compound and establish its rhombohedral space group ($R\bar
3c$) along with the geometrically perfect honeycomb lattice of the Mo$^{3+}$
ions residing in disconnected MoO$_6$ octahedra. Long-range antiferromagnetic
order with the propagation vector $\mathbf k=0$ observed below $T_N=6.8$ K is a
combined effect of the nearest-neighbor in-plane exchange coupling $J\simeq
2.6$ K, easy-plane single-ion anisotropy $D\simeq 2.2 $ K, and a weak
interlayer coupling $J_c\simeq 0.8$ K. The 12% reduction in the ordered
magnetic moment of the Mo$^{3+}$ ions and the magnon gap of $\Delta\simeq 7$ K
induced by the single-ion anisotropy further illustrate the impact of
spin-orbit coupling on the magnetism. Our analysis puts forward single-ion
anisotropy as an important ingredient of $4d^3$ honeycomb antiferromagnets
despite their nominally quenched orbital moment.",2107.08618v2
2021-07-23,Intermixing Induced Anisotropy Variations in CoB-based Chiral Multilayer Films,"We examine the atomic intermixing phenomenon in three distinct amorphous
CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO
- which are shown to stabilise room-temperature chiral magnetic textures.
Intermixing occurs predominantly between adjacent metallic layers. Notably, it
is stack-order dependent, and particularly extensive when Ir sits atop CoB.
Intermixing induced variations in magnetic properties are ascribed to the
formation of magnetic dead layer arising from CoIr alloying in the metallic
stacks. It also produces systematic variations in saturation magnetization, by
as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness
for the transition from perpendicular to in-plane magnetic anisotropy differs
by more than 2x across the stacks. Finally, with thermal annealing treatment
over moderate temperatures of 150-300 degree Celsius, the magnetic anisotropy
increases monotonically across all stacks, coupled with discernibly larger Hc
for the metallic stacks. These are attributed to thermally induced CoPt
alloying and MgO crystallization in the metallic and oxide stacks,
respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its
amorphous nature after annealing. Our results set the stage for harnessing the
collective attributes of amorphous CoB-based material platforms and associated
annealing processes for modulating magnetic interactions, enabling the tuning
of chiral magnetic texture properties in ambient conditions.",2107.11034v1
2021-07-23,Observation of Cosmic Ray Anisotropy with Nine Years of IceCube Data,"The IceCube Observatory has collected over 577 billion cosmic-ray induced
muon events in its final configuration from May 2011 to May 2020. We used this
data set to provide an unprecedented statistically accurate map of the cosmic
ray arrival direction distribution in the TeV-PeV energy range scale in the
Southern Hemisphere. Such an increase in event statistics makes it possible to
extend the sensitivity to anisotropies at higher cosmic ray energies and
smaller angular scales. It will also facilitate a more detailed assessment of
the observatory stability over both short- and long-time scales. This will
enable us to study the time variability of the cosmic ray anisotropy on a
yearly-base and over the entire data sample period covering most of the solar
cycle 24. We present the preliminary results from the study with the extended
event sample.",2107.11454v1
2021-08-03,"Adaptive critical balance and firehose instability in an expanding, turbulent, collisionless plasma","Using hybrid-kinetic particle-in-cell simulation, we study the evolution of
an expanding, collisionless, magnetized plasma in which strong Alfv\'enic
turbulence is persistently driven. Temperature anisotropy generated
adiabatically by the plasma expansion (and consequent decrease in the mean
magnetic-field strength) gradually reduces the effective elasticity of the
field lines, causing reductions in the linear frequency and residual energy of
the Alfv\'{e}nic fluctuations. In response, these fluctuations modify their
interactions and spatial anisotropy to maintain a scale-by-scale ""critical
balance"" between their characteristic linear and nonlinear frequencies.
Eventually the plasma becomes unstable to kinetic firehose instabilities, which
excite rapidly growing magnetic fluctuations at ion-Larmor scales. The
consequent pitch-angle scattering of particles maintains the temperature
anisotropy near marginal stability, even as the turbulent plasma continues to
expand. The resulting evolution of parallel and perpendicular temperatures does
not satisfy double-adiabatic conservation laws, but is described accurately by
a simple model that includes anomalous scattering. Our results have
implications for understanding the complex interplay between macro- and
micro-scale physics in various hot, dilute, astrophysical plasmas, and offer
predictions concerning power spectra, residual energy, ion-Larmor-scale
spectral breaks, and non-Maxwellian features in ion distribution functions that
may be tested by measurements taken in high-beta regions of the solar wind.",2108.01491v2
2021-08-04,Anisotropic turbulence in relativistic plasmas,"Signs of turbulence have been observed at the relativistic heavy ion
collision at high collision energies. We study the signatures of turbulence in
this system and find that there are significant departures from isotropic
turbulence in the initial stages of the collision. Since the anisotropic
fluctuations are sub leading to the isotropic fluctuations, the Kolmogorov
spectrum can usually be obtained even for the initial stages. However, the
energy spectrum and the temperature fluctuations indicate deviations from
isotropic turbulence. Since a strong momentum anisotropy exists between the
transverse and the longitudinal plane, we study the energy density spectrum in
these two planes. The geometrical anisotropy is reflected in the anisotropic
turbulence generated in the rotating plasma and we find that the scaling
exponent is different in the two planes. We find that the scaling exponents in
the longitudinal plane are independent of centrality while the scaling exponent
in the transverse plane depends on the centrality range. We also obtain the
temperature spectrum in the initial stages. The spectrum deviates from the
Gaussian spectra expected for an isotropic turbulence. All these seem to
indicate that the large scale momentum anisotropy persists in the smaller
length scales for the relativistic heavy ion collisions.",2108.01847v2
2021-08-10,Composition Sensitivity (for the Cosmic Ray Anisotropy with SWGO),"A number of cosmic-ray observatories have measured a change in both phase and
amplitude of the dipole component in the distribution of cosmic-ray arrival
directions above a primary energy of 100 TeV. We focus on probing the
cosmic-ray dipole and multipole evolution in the energy region of mutli TeV to
beyond PeV with a future large-area gamma-ray observatory, such as the Southern
Wide-field Gamma-ray Observatory (SWGO). The ability to discriminate between
different mass groups is essential to understand the origin of this evolution.
Through a consideration of the energy and mass resolution for cosmic-ray
detection by such an observatory, we estimate its separation power for
decomposing the full-particle anisotropy into mass groups. In particular, we
explore the feasibility of probing the dipole evolution with rigidity with
SWGO. In this way, we demonstrate the great potential that this instrument
offers for providing a deeper understanding of the origin of the cosmic-ray
anisotropy.",2108.04609v1
2021-08-10,The orbital effect on the anomalous magnetism and evolution in La$_x$Y$_{1-x}$VO$_3$($0\le x \le 0.2$) single crystals,"The orbital effect on the anomalous magnetism and evolution of low La-doping
single crystals, La$_x$Y$_{1-x}$VO$_{3}$ (x = 0, 0.1, and 0.2), has been
investigated by applying the X-ray diffraction, specific heat, magnetization
and Raman scattering techniques. The larger nearest-neighbor (NN) exchange
interaction along c-axis stabilizes the fluctuant G-type orbital ordering
(G-OO) which favors the exotic C-type antiferromagnetic order (C-AF). It is
found that the NN exchange interaction in ab plane is anisotropy relating to
the in plane magnetic anisotropy, which becomes smaller in high La-doped
sample. Most interestingly, with increasing the La$^{3+}$ content the orbital
fluctuation and hybridization are decreased which stabilizes the C-OO phase and
destabilizes the G-OO phase. Meanwhile, the diamagnetism in the exotic C-AF
phase becomes weak and the possible mechanism relates to the change of the
competition between the single-ion magnetic anisotropy and the
Dzyaloshinsky-Moriya (DM) interaction with increasing x. Finally, the strong
spin-orbital coupling has been observed at temperature just above T$_N$ in
La$_{0.2}$Y$_{0.8}$VO$_{3}$ and a short range spin-orbital correlation is
suggested.",2108.04648v1
2021-08-17,Probing small-scale baryon and dark matter isocurvature perturbations with cosmic microwave background anisotropies,"The Universe's initial conditions, in particular baryon and cold dark matter
(CDM) isocurvature perturbations, are poorly constrained on sub-Mpc scales. In
this paper, we develop a new formalism to compute the effect of small-scale
baryon perturbations on the mean free-electron abundance, thus on cosmic
microwave background (CMB) anisotropies. Our framework can accommodate
perturbations with arbitrary time and scale dependence. We apply this formalism
to four different combinations of baryon and CDM isocurvature modes, and use
Planck CMB-anisotropy data to probe their initial amplitude. We find that
Planck data is consistent with no small-scale isocurvature perturbations, and
that this additional ingredient does not help alleviate the Hubble tension. We
set upper bounds to the dimensionless initial power spectrum
$\Delta_{\mathcal{I}}^2(k)$ of these isocurvature modes at comoving wavenumbers
$1~\textrm{Mpc}^{-1} \le k \le 10^3$ Mpc$^{-1}$, for several parameterizations.
For a scale-invariant power spectrum, our 95% confidence-level limits on
$\Delta_{\mathcal{I}}^2$ are 0.023 for pure baryon isocurvature, 0.099 for pure
CDM isocurvature, 0.026 for compensated baryon-CDM perturbations, and 0.009 for
joint baryon-CDM isocurvature perturbations. Using a Fisher analysis
generalized to non-analytic parameter dependence, we forecast that a CMB
Stage-4 experiment would be able to probe small-scale isocurvature
perturbations with initial power 3 to 10 times smaller than Planck limits. The
formalism introduced in this work is very general and can be used more widely
to probe any physical processes or initial conditions sourcing small-scale
baryon perturbations.",2108.07798v1
2021-08-24,Direct Calculation of the Eddy Viscosity Operator in Turbulent Channel Flow at Re$_τ$=180,"This study aims to quantify how turbulence in a channel flow mixes momentum
in the mean sense. We applied the macroscopic forcing method (Mani and Park,
Physical Review Fluids, 2021, p.054607) to direct numerical simulation (DNS) of
a turbulent channel flow at Re_tau=180 using two different forcing strategies
that are designed to separately assess the anisotropy and nonlocality of
momentum mixing. In the first strategy, the leading term of the Kramers-Moyal
expansion of the eddy viscosity is quantified, revealing all 81 tensorial
coefficients that essentially characterize the local-limit eddy viscosity. The
results indicate: (1) the eddy viscosity has significant anisotropy, (2)
Reynolds stresses are generated by both the mean strain rate and mean rotation
rate tensors associated with the momentum field, and (3) the local-limit eddy
viscosity generates asymmetric Reynolds stress tensors. In the second strategy,
the eddy viscosity is quantified as an integration kernel revealing the
nonlocal influence of the mean momentum gradient at each wall-normal coordinate
on all nine components of the Reynolds stresses over the channel width. Our
results indicate that while the shear component of the Reynolds stress is
reasonably controlled by the local mean gradients, other components of the
Reynolds stress are highly nonlocal. These results provide an understanding of
anisotropy and nonlocality requirements for closure modeling of momentum
transport in wall-bounded turbulent flows.",2108.10898v3
2021-08-31,Using in-plane anisotropy to engineer Janus monolayers of rhenium dichalcogenides,"The new class of Janus two-dimensional (2D) transition-metal dichalcogenides
with two different interfaces are currently gaining increasing attention due to
their distinct properties different from the typical 2D materials. Here, we
show that in-plane anisotropy of a 2D atomic crystal, like ReS$_{2}$ or
ReSe$_{2}$, allows formation of a large number of inequivalent Janus
monolayers. We use first-principles calculations to investigate the structural
stability of 29 distinct ReX$_{2-x}$Y$_{x}$ ($\mathrm{X,Y \in \{S,Se\}}$)
structures, which can be obtained by selective exchange of exposed chalcogens
in a ReX$_{2}$ monolayer. We also examine the electronic properties and work
function of the most stable Janus monolayers and show that the large number of
inequivalent structures provides a way to engineer spin-orbit splitting of the
electronic bands. We find that the breaking of inversion symmetry leads to
sizable spin splittings and spontaneous diople moments than are larger than
those in other Janus dichalcogenides. Moreover, our caluclations suggest that
the work function of the Janus monolayers can be tuned by varying the content
of the substituting chalcogen. Our work demonstrates that in-plane anisotropy
provides additional flexibility in sub-layer engineering of 2D atomic crystals.",2109.00071v2
2021-09-02,Spin-$S$ impurities with XXZ anisotropy in a spin-1/2 Heisenberg chain,"We study the effect of anisotropy of spin-$S$ impurities on an
antiferromagnetic SU(2) Heisenberg chain. The magnetic impurities are assumed
to have an XXZ-type anisotropic exchange with its neighboring sites. First,
using density-matrix renormalization group technique. we examine spin-spin
correlation function, instability of N\'eel order, and local spin
susceptibility in the presence of a single spin-$S$ impurity. Based on the
results, we find that the types of spin-$S$ impurities are classified into two
groups: $\rm(\hspace{.18em}i\hspace{.18em})$ nonmagnetic and $S=1$ impurities
enhance only short-range antiferromagnetic correlation and
$\rm(\hspace{.08em}ii\hspace{.08em})$ $S=1/2$ and $S>1$ impurities can, in
contrast, stabilize a long-range N\'eel order in the disordered SU(2)
Heisenberg chain. Then, we focus on the case of $S=1/2$ impurity as a
representative of $\rm(\hspace{.08em}ii\hspace{.08em})$ and investigate the
evolution of some experimentally observable quantities such as magnetization,
specific heat, and magnetic susceptibility, as a function of concentration and
XXZ anisotropy strength of the impurity. We confirm that the N\'eel order is
induced in the bulk spin chain in the presence of finite amount of easy-axis
XXZ $S=1/2$ impurities. Furthermore, we recover some of the aforementioned
features using cluster mean-field theory, which allows us to present results on
experimentally accessible quantities at finite temperatures. Interestingly, in
the presence of uniform magnetic field, the total magnetization exhibits a
pseudo-gap behavior for low values of applied field. We also discuss the
dependence of NMR spectrum on various XXZ impurities and identify that the spin
state of Co impurity in SrCu$_{0.99}$Co$_{0.01}$O$_2$ is $S = 3/2$.",2109.00777v1
2021-09-05,Cooperative control of perpendicular magnetic anisotropy via crystal structure and orientation in single-crystal flexible SrRuO3 membranes,"Flexible magnetic materials with robust and controllable perpendicular
magnetic anisotropy (PMA) are highly desirable for developing flexible
high-performance spintronic devices. However, it is still challenge to
fabricate PMA films through current techniques of direct deposition on
polymers. Here, we report a facile method for synthesizing single-crystal
freestanding SrRuO3 (SRO) membranes with controlled crystal structure and
orientation using water-soluble Ca3-xSrxAl2O6 sacrificial layers. Through
cooperative effect of crystal structure and orientation engineering, flexible
SrRuO3 membranes reveal highly tunable magnetic anisotropy from in-plane to
our-of-plane with a remarkable PMA energy of 7.34*106 erg/cm3. Based on the
first-principles calculations, it reveals that the underlying mechanism of PMA
modulation is intimately correlated with structure-controlled Ru 4d-orbital
occupation, as well as the spin-orbital matrix element differences, dependent
on the crystal orientation. In addition, there are no obvious changes of the
magnetism after 10,000 bending cycles, indicating an excellent magnetism
reliability in the prepared films. This work provides a feasible approach to
prepare the flexible oxide films with strong and controllable PMA.",2109.02061v1
2021-09-16,Influence of Heliolatitudinal Anisotropy of Solar FUV/EUV Emissions on Lyman-alpha Helioglow: SOHO/SWAN Observations and WawHelioGlow Modeling,"Observations of the Sun's surface suggest a nonuniform radiated flux as
related to the presence of bright active regions and darker coronal holes. The
variations of the FUV/EUV source radiation can be expected to affect the
Lyman-alpha backscatter glow measured by spaceborne instruments. In particular,
inferring the heliolatitudinal structure of the solar wind from helioglow
variations in the sky can be quite challenging if the heliolatitudinal
structure of the solar FUV/EUV radiation is not properly included in the
modeling of the heliospheric glow. We present results of analysis of the
heliolatitudinal structure of the solar Lyman-alpha radiation as inferred from
comparison of SOHO/SWAN satellite observations of the helioglow intensity with
modeling results obtained from the recently-developed WawHelioGlow model. We
find that in addition to time-dependent heliolatitudinal anisotropy of the
solar wind, also time-dependent heliolatitudinal variations of the intensity of
the solar Lyman-alpha and photoionizing emissions must be taken into account to
reproduce the observed helioglow modulation in the sky. We present a particular
latitudinal and temporal dependence of the solar Lyman-alpha flux obtained as a
result of our analysis. We analyze also differences between polar-equatorial
anisotropies close to the solar surface and seen by an observer located far
from the Sun. We discuss the implications of these findings for the
interpretation of heliospheric-glow observations.",2109.08095v1
2021-10-06,Exploring the possible origin of spin reorientation transition in NdCrO$_3$,"Spin reorientation transitions and other related magnetic phenomena, which
owe their origin to the complex interplay between multiple magnetic
sublattices, have long attracted scientific attention both from the perspective
of fundamental curiosity and technological applications. In this study,
combining first principles calculations together with finite temperature Monte
Carlo simulations, we explore the possible origins of reorientation transition
of Cr spins in NdCrO$_3$. We construct a NdCrO$_3$ specific magnetic model,
consisting of symmetric superexchange interactions between magnetic ions, as
well as their magnetic anisotropy. We show that the observed spin reorientation
in NdCrO$_3$, arises out of a delicate balance between Nd$-$Cr magnetic
exchange interactions, single ion anisotropy of Nd spins, and single ion
anisotropy of Cr spins. Moreover, though our model does not take into
consideration the effect of anti-symmetric and anisotropic-symmetric magnetic
exchanges, the qualitative as well as quantitative agreement of the
theoretically derived and the experimentally observed spin-reorientation
transition in NdCrO$_3$, confirms the merit of our proposed microscopic model.
Our results also propose a hitherto unobserved collective magnetic ordering in
Nd sublattice, which is challenging to detect as it is an extreme low
temperature phenomena, therefore calls for further investigations.",2110.02532v1
2021-10-10,The influence of structural variations on the constitutive response and strain variations in thin fibrous materials,"The stochastic variations in the structural properties of thin fiber networks
govern to a great extent their mechanical performance. To assess the influence
of local structural variability on the local strain and mechanical response of
the network, we propose a multiscale approach combining modeling, numerical
simulation and experimental measurements. Based on micro-mechanical fiber
network simulations, a continuum model describing the response at the mesoscale
level is first developed. Experimentally measured spatial fields of thickness,
density, fiber orientation and anisotropy are thereafter used as input to a
macroscale finite-element model. The latter is used to simulate the impact of
spatial variability of each of the studied structural properties. In addition,
this work brings novelty by including the influence of the drying condition
during the production process on the fiber properties. The proposed approach is
experimentally validated by comparison to measured strain fields and uniaxial
responses. The results suggest that the spatial variability in density presents
the highest impact on the local strain field followed by thickness and fiber
orientation. Meanwhile, for the mechanical response, the fiber orientation
angle with respect to the drying restraints is the key influencer and its
contribution to the anisotropy of the mechanical properties is greater than the
contribution of the fiber anisotropy developed during the fiber sheet-making.",2110.04897v1
2021-10-13,Electric-field control of magnetic anisotropies: applications to Kitaev spin liquids and topological spin textures,"Magnetic anisotropies often originate from the spin-orbit coupling and
determine magnetic ordering patterns. We develop a microscopic theory for DC
electric-field controls of magnetic anisotropies in magnetic Mott insulators
and discuss its applications to Kitaev materials and topological spin textures.
Throughout this paper, we take a microscopic approach based on Hubbard-like
lattice models, tight-binding models with on-site interactions. We derive a
low-energy spin Hamiltonian from a fourth-order perturbation expansion of the
Hubbard-like model. We show in the presence of a strong intra-atomic spin-orbit
coupling that DC electric fields add non-Kitaev interactions such as a
Dzyaloshinskii-Moriya interaction and an off-diagonal $\Gamma'$ interaction to
the Kitaev-Heisenberg model and can induce a topological quantum phase
transition between Majorana Chern insulating phases. We also investigate the
inter-atomic Rashba spin-orbit coupling and its effects on topological spin
textures. DC electric fields turn out to create and annihilate magnetic
skyrmions, hedgehogs, and chiral solitons. We propose several methods of
creating topological spin textures with external electromagnetic fields. Our
theory clarifies that the strong but feasible electric field can control Kitaev
spin liquids and topological spin textures.",2110.06503v4
2021-10-24,Isotropic finite-difference approximations for phase-field simulations of polycrystalline alloy solidification,"Phase-field models of microstructural pattern formation during alloy
solidification are commonly solved numerically using the finite-difference
method, which is ideally suited to carry out computationally efficient
simulations on massively parallel computer architectures such as Graphic
Processing Units. However, one known drawback of this method is that the
discretization of differential terms involving spatial derivatives introduces a
spurious lattice anisotropy that can influence the solid-liquid interface
dynamics. We find that this influence is significant for the case of
polycrystalline dendritic solidification, where the crystal axes of different
grains do not generally coincide with the reference axes of the
finite-difference lattice. In particular, we find that with the commonly used
finite-difference implementation of the quantitative phase-field model of
binary alloy solidification, both the operating state of the dendrite tip and
the dendrite growth orientation are strongly affected by the lattice
anisotropy. To circumvent this problem, we use known methods in both real and
Fourier space to derive finite-difference approximations of leading
differential terms in 2D and 3D that are isotropic at order $h^2$ of the
lattice spacing $h$. Importantly, those terms include the divergence of the
anti-trapping current that is found to have a critical influence on pattern
selection. The 2D and 3D discretizations use an approximated form of the
anti-trapping current that facilitates the Fourier-space derivation of the
associated isotropic differential operator at $O(h^2)$, but we also derive a 2D
discretization of the standard form of this current. Finally, we present 2D and
3D phase-field simulations of alloy solidification, showing that the isotropic
finite-difference implementations can dramatically reduce spurious lattice
anisotropy effects.",2110.12448v1
2021-10-27,Size-dependent enhancement of passive microwave rectification in magnetic tunnel junctions with perpendicular magnetic anisotropy,"Spintronic rf detectors were demonstrated, recently, for energy harvesting
and wireless communication at low input power. Here we report on the
optimization of the rectified output dc voltage using magnetic tunnel junctions
(MTJ) with strong perpendicular anisotropy (PMA) of both the polarizing and the
free layer. The magnetization of the polarizing layer is fixed out of plane,
while the free layer thickness is adjusted so that its magnetization
orientation changes from in plane to out of plane. The rectification dc output
voltage lies in the mV range for moderate rf powers, with a signal to noise
ratio of 10 to 100 for Prf = -25dBm. It shows a strong dependence on the
dimensions of the MTJ: it increases by a factor of 5 to 6 when reducing the
diameter from 150nm to 20nm. This enhancement can be doubled when reducing the
FL thickness from 1.8nm to 1.6nm. This dimensional enhancement is attributed to
the change of the effective anisotropy of the excited free layer, and the MTJ
resistance. The results are of interest for the design of spintronic based rf
detectors with optimized sensitivity.",2110.14501v1
2021-11-08,Detectability of the cross-correlation between CMB lensing and stochastic GW background from compact object mergers,"The anisotropies of the Stochastic Gravitational-Wave Background (SGWB)
produced by merging compact binaries constitute a possible new probe of the
Large-Scale Structure (LSS). However, the significant shot noise contribution
caused by the discreteness of the GW sources and the poor angular resolution of
the instruments hamper the detection of the intrinsic anisotropies induced by
the LSS. In this work, we investigate the potential of cross-correlating
forthcoming high precision measurements of the SGWB energy density and the
Cosmic Microwave Background (CMB) lensing convergence to mitigate the effect of
shot noise. Combining a detailed model of stellar and galactic astrophysics
with a novel framework to distribute the GW emitters in the sky, we compute the
auto- and cross-correlation power spectra for the two cosmic fields, evaluate
the shot noise contribution and predict the signal-to-noise ratio. The results
of our analysis show that the SGWB energy density correlates significantly with
the CMB lensing convergence and that the cross-correlation between these two
cosmic fields reduces the impact of instrumental and shot noise. Unfortunately,
the S/N is not high enough to detect the intrinsic SGWB anisotropies.
Nevertheless, a network composed of both present and future generation GW
interferometers, operating for at least 10 yrs, should be able to measure the
shot noise contribution.",2111.04757v2
2021-11-11,Current-induced superconducting anisotropy of Sr$\mathsf{_2}$RuO$\mathsf{_4}$,"In the unconventional superconductor Sr$\mathsf{_2}$RuO$\mathsf{_4}$, unusual
first-order superconducting transition has been observed in the low-temperature
and high-field region, accompanied by a four-fold anisotropy of the in-plane
upper critical magnetic field $H_{c2}$. The origin of such unusual $H_{c2}$
behavior should be closely linked to the debated superconducting symmetry of
this oxide. Here, toward clarification of the unusual $H_{c2}$ behavior, we
performed the resistivity measurements capable of switching in-plane current
directions as well as precisely controlling the field directions. Our results
reveal that resistive $H_{c2}$ under the in-plane current exhibits an
additional two-fold anisotropy. By systematically analyzing $H_{c2}$ data taken
under various current directions, we succeeded in separating the two-fold
$H_{c2}$ component into the one originating from applied current and the other
originating from certain imperfection in the sample. The former component,
attributable to vortex flow effect, is weakened at low temperatures where
$H_{c2}$ is substantially suppressed. The latter component is enhanced in the
first order transition region, possibly reflecting a change in the nature of
the superconducting state under high magnetic field.",2111.06097v1
2021-11-22,Magnetization Reversal in Two-dimensional Ensemble of Nanoparticles with Positional Defects,"We study relaxation behaviour in the two-dimensional assembly of magnetic
nanoparticles (MNPs) with aligned anisotropy axes and positional defects. The
anisotropy axes orientation and disorder strength is changed by varying
$\alpha$ and $\Delta$, respectively. The magnetization decay does not depend on
the aspect ratio $A^{}_r$ of the system and $\Delta$ for small dipolar
interaction strength $h^{}_d=0.2$. Remarkably, the magnetization decays rapidly
for considerable $h^{}_d$ with negligible $\Delta$ and $A_r=1.0$. The dipolar
interaction of enough strength promotes antiferromagnetic coupling in square
ensembles of MNPs. There is a prolonged magnetization decay for large $\Delta$
because of enhancement in ferromagnetic coupling. Notably, magnetization
relaxes slowly for $\alpha<\alpha^\star$ even with moderate $h^{}_d$ and a
significant $A^{}_r$. Interestingly, the slowing down of the magnetic
relaxation shifts to a lower $\alpha^{\star}$ with $h^{}_d=1.0$. The
magnetization ceases to relax for $\alpha\leq60^\circ$ and $h^{}_d\leq0.6$ due
to large shape anisotropy with $A^{}_r=400.0$. Remarkably, a majority of the
magnetic moment reverses its direction by $180^\circ$ for $\alpha>60^\circ$ and
large $h^{}_d$, resulting in the negative magnetization. The effective N\'eel
relaxation time $\tau^{}_N$ also depends strongly on these parameters.
$\tau^{}_N$ depends weakly on $\alpha$ and $\Delta$ for $h^{}_d\leq0.2$,
irrespective of $A^{}_r$. On the other hand, $\tau^{}_N$ decreases with
$\alpha$ for significant $h^{}_d$ provided $\alpha$ is greater than $45^\circ$
because of antiferromagnetic coupling dominance. In a highly anisotropic
system, there is an enhancement in $\tau^{}_N$ with $\alpha$ ($\leq30^\circ$)
even with moderate $h^{}_d$. While for $\alpha>30^\circ$, $\tau^{}_N$ decreases
with $\alpha$. These observations are useful in novel materials, spintronics
based applications, etc.",2111.11034v1
2021-11-23,ChebLieNet: Invariant Spectral Graph NNs Turned Equivariant by Riemannian Geometry on Lie Groups,"We introduce ChebLieNet, a group-equivariant method on (anisotropic)
manifolds. Surfing on the success of graph- and group-based neural networks, we
take advantage of the recent developments in the geometric deep learning field
to derive a new approach to exploit any anisotropies in data. Via discrete
approximations of Lie groups, we develop a graph neural network made of
anisotropic convolutional layers (Chebyshev convolutions), spatial pooling and
unpooling layers, and global pooling layers. Group equivariance is achieved via
equivariant and invariant operators on graphs with anisotropic left-invariant
Riemannian distance-based affinities encoded on the edges. Thanks to its simple
form, the Riemannian metric can model any anisotropies, both in the spatial and
orientation domains. This control on anisotropies of the Riemannian metrics
allows to balance equivariance (anisotropic metric) against invariance
(isotropic metric) of the graph convolution layers. Hence we open the doors to
a better understanding of anisotropic properties. Furthermore, we empirically
prove the existence of (data-dependent) sweet spots for anisotropic parameters
on CIFAR10. This crucial result is evidence of the benefice we could get by
exploiting anisotropic properties in data. We also evaluate the scalability of
this approach on STL10 (image data) and ClimateNet (spherical data), showing
its remarkable adaptability to diverse tasks.",2111.12139v1
2021-11-23,The CMB Dipole: Eppur Si Muove,"The largest temperature anisotropy in the cosmic microwave background (CMB)
is the dipole. The simplest interpretation of the dipole is that it is due to
our motion with respect to the rest frame of the CMB. As well as creating the
$\ell$=1 mode of the CMB sky, this motion affects all astrophysical
observations by modulating and aberrating sources across the sky. It can be
seen in galaxy clustering, and in principle its time derivative through a
dipole-shaped acceleration pattern in quasar positions. Additionally, the
dipole modulates the CMB temperature anisotropies with the same frequency
dependence as the thermal Sunyaev-Zeldovich (tSZ) effect and so these modulated
CMB anisotropies can be extracted from the tSZ maps produced by Planck.
Unfortunately, this measurement cannot determine if the dipole is due to our
motion, but it does provide an independent measure of the dipole and a
validation of the y maps. This measurement, and a description of the
first-order terms of the CMB dipole, are outlined here.",2111.12186v1
2021-11-24,Effect of chemical disorder on the magnetic anisotropy in L$1_0$ FeNi from first principles calculations,"We use first principles calculations to investigate how deviations from
perfect chemical order affect the magneto-crystalline anisotropy energy (MAE)
in L$1_0$ FeNi. We first analyze the local chemical environment of the Fe atoms
in various partially ordered configurations, using the orbital magnetic moment
anisotropy (OMA) as proxy for a local contribution to the MAE. We are able to
identify a specific nearest neighbor configuration and use this ""favorable
environment"" to successfully design various structures with MAE higher than the
perfectly ordered system. However, a systematic analysis of the correlation
between local environment and OMA using smooth overlap of atomic positions
(SOAP), indicates only a partial correlation, which exists only if the
deviation from full chemical order is not too large, whereas in general no such
correlation can be identified even using up to third nearest neighbors. Guided
by the observation that the identified ""favorable environment"" implies an
Fe-rich composition, we investigate the effect of randomly inserting additional
Fe into the nominal Ni planes of the perfectly ordered structure. We find that
the MAE increases with Fe content, at least up to 62.5% Fe. Thus, our study
shows that the perfectly ordered case is not the one with highest MAE and that
an increased MAE can be obtained for slightly Fe-rich compositions.",2111.12492v3
2021-11-25,Manifestation of the anisotropic properties of the molecular J-aggregate shell in optical spectra of plexcitonic nanoparticles,"The theoretical studies of light absorption and scattering spectra of the
plexcitonic two-layer triangular nanoprisms and three-layer nanospheres are
reported. The optical properties of such metal-organic core--shell and
core--double-shell nanostructures were previously explained within the
framework of pure isotropic models for describing their outer excitonic shell.
In this work, we show that the anisotropy of the excitonic shell permittivity
can drastically affect the optical spectra of such hybrid nanostructures. This
fact is confirmed by directly comparing our theory with some available
experimental data, which cannot be treated using conventional isotropic shell
models. We have analyzed the influence of the shell anisotropy on the optical
spectra and proposed a type of hybrid nanostructure that seems most convenient
for experimental observation of the effects associated with the anisotropy of
the excitonic shell. A strong dependence of the anisotropic properties of the
J-aggregate shell on the material of the intermediate spacer layer is
demonstrated. This allows proposing a new way to effectively control the
optical properties of metal-organic nanostructures by selecting the spacer
material. Our results extend the understanding of physical effects in optics of
plexcitonic nanostructures to more complex systems with the anisotropic and
multi-excitonic properties of their molecular aggregate shell.",2111.13126v1
2021-11-26,Open quantum dynamics theory for a complex subenvironment system with a quantum thermostat: Application to a spin heat bath,"Complex environments, such as molecular matrices and biological material,
play a fundamental role in many important dynamic processes in condensed
phases. Because it is extremely difficult to conduct full quantum dynamics
simulations on such environments due to their many degrees of freedom, here we
treat in detail the environment only around the main system of interest (the
subenvironment), while the other degrees of freedom needed to maintain the
equilibrium temperature are described by a simple harmonic bath, which we call
a quantum thermostat. The noise generated by the subenvironment is spatially
non-local and non-Gaussian and cannot be characterized by the
fluctuation-dissipation theorem. We describe this model by simulating the
dynamics of a two-level system (TLS) that interacts with a subenvironment
consisting of a one-dimensional $XXZ$ spin chain. The hierarchical
Schr\""odinger equations of motion are employed to describe the quantum
thermostat, allowing time-irreversible simulations of the dynamics at arbitrary
temperature. To see the effects of a quantum phase transition of the
subenvironment, we investigate the decoherence and relaxation processes of the
TLS at zero and finite temperatures for various values of the spin anisotropy.
We observed the decoherence of the TLS at finite temperature, even when the
anisotropy of the $XXZ$ model is enormous. We also found that the population
relaxation dynamics of the TLS changed in a complex manner with the change of
the anisotropy and the ferromagnetic or antiferromagnetic orders of the spins.",2111.13277v1
2021-11-27,Effect of Rashba and Dresselhaus spin-orbit coupling on supercurrent rectification and magnetochiral anisotropy of ballistic Josephson junctions,"Simultaneous breaking of inversion- and time-reversal symmetry in Josephson
junction leads to a possible violation of the $I(\varphi)=-I(-\varphi)$
equality for the current-phase relation. This is known as anomalous Josephson
effect and it produces a phase shift $\varphi_0$ in sinusoidal current-phase
relations. In ballistic Josephson junctions with non-sinusoidal current phase
relation the observed phenomenology is much richer, including the supercurrent
diode effect and the magnetochiral anisotropy of Josephson inductance. In this
work, we present measurements of both effects on arrays of Josephson junctions
defined on epitaxial Al/InAs heterostructures. We show that the orientation of
the current with respect to the lattice affects the magnetochiral anisotropy,
possibly as the result of a finite Dresselhaus component. In addition, we show
that the two-fold symmetry of the Josephson inductance reflects in the
activation energy for phase slips.",2111.13983v2
2021-11-29,Single-pulse all-optical switching in amorphous Dy$_x$Co$_{1-x}\text{ }$ and Tb$_x$Co$_{1-x}$,"Repeated uniform switching of the magnetization of thin films of
ferrimagnetic amorphous Gd$_{x}$(FeCo)$_{1-x}$ in response to single fast laser
pulses is well established. Here we report unusual toggle switching in thin
films of sperimagnetic amorphous Dy$_x$Co$_{1-x}$ and Tb$_x$Co$_{1-x}$ with
$\it{x} \simeq$ 0.25 irradiated with single 200 fs pulses of 800 nm laser
light. The samples have strong local random anisotropy due to the non-S state
rare earth. The compensation temperature of the films is $\le$ 180 K and their
Curie temperature is $\simeq$ 500 K. They are mostly switched by the first
pulse, and subsequent pulses lead to partial re-switching of a decreasing
amount of the irradiated area, with a granular structure of submicron regions
of switched and unswitched material. Individual switched domains about 700 nm
in size are observed around the edge of the irradiated spots where the fluence
is at the threshold for switching. Results are discussed in terms of a random
anisotropy model where the ratio of local anisotropy to exchange is temperature
dependent and close to the threshold for strong pinning.",2111.14587v1
2021-11-30,SIRIUS Project. IV. The formation history of the Orion Nebula Cluster driven by clump mergers,"The Orion Nebula Cluster (ONC) is an excellent example for understanding the
formation of star clusters. Recent studies have shown that ONC has three
distinct age populations and anisotropy in velocity dispersions, which are key
characteristics for understanding the formation history of the ONC. In this
study, we perform a smoothed-particle hydrodynamics/$N$-body simulation of star
cluster formation from a turbulent molecular cloud. In this simulation, stellar
orbits are integrated using a high-order integrator without gravitational
softening; therefore, we can follow the collisional evolution of star clusters.
We find that hierarchical formation causes episodic star formation that is
observed in the ONC. In our simulation, star clusters evolve due to mergers of
subclumps. The mergers bring cold gas with the clumps into the forming cluster.
This enhances the star formation in the cluster centre. The dense cold gas in
the cluster centre continues to form stars until the latest time. This explains
the compact distribution of the youngest stars observed in the ONC. Subclump
mergers also contribute to the anisotropy in the velocity dispersions and the
formation of runaway stars. However, the anisotropy disappears within 0.5 Myr.
The virial ratio of the cluster also increases after a merger due to the
runaways. These results suggest that the ONC recently experienced a clump
merger. We predict that most runaways originated from the ONC have already been
found, but walkaways have not.",2111.15154v2
2021-12-03,Bianchi IX gravitational collapse of matter inhomogeneities,"We investigate a model of gravitational collapse of matter inhomogeneities
where the latter are modelled as Bianchi type IX (BIX) spacetimes. We found
that this model contains, as limiting cases, both the standard spherical
collapse model and the Zeldovich solution for a 1-dimensional perturbation. We
study how these models are affected by small anisotropic perturbations within
the BIX potential. For the spherical collapse case, we found that the model is
equivalent to a closed FLRW Universe filled with matter and two perfect fluids
representing the anisotropic contributions. From the linear evolution up to the
turnaround, the anisotropies effectively shift the value of the FLRW spatial
curvature, because the fluids have effective Equation of State (EoS) parameters
$w \approx -1/3$. Then we estimate the impact of such anisotropies on the
number density of haloes using the Press-Schechter formalism. If a fluid
description of the anisotropies is still valid after virialization, the
averaged over time EoS parameters are $w\approx 1/3$. Using this and demanding
hydrostatic equilibrium, we find a relation between the mass $M$, the average
radius $R$ and the pressure $p$ of the virialized final structure. When we
consider perturbations of the Zeldovich solution, our qualitative analysis
suggests that the so called \textit{pancakes} exhibit oscillatory behavior, as
would be expected in the case of a vacuum BIX spacetime.",2112.01869v2
2021-12-06,A Novel Full-Polarization SAR Images Ship Detector Based on the Scattering Mechanisms and the Wave Polarization Anisotropy,"Synthetic aperture radar (SAR) is considered being a good option for earth
observation with its unique advantages. In this paper, we proposed an adaptive
ship detector using full-polarization SAR images. First, by thoroughly
investigating the scattering characteristics between ships and their
background, and the wave polarization anisotropy, a novel ship detector is
proposed by jointing the two characteristics, named Scattering-Anisotropy joint
(joint-SA). Based on the theoretical analysis, we showed that the joint-SA is
an effective physical quantity to show the difference between the ship and its
background, and thus joint-SA can be used for ship detection of
full-polarization image data. Second, the generalized Gamma distribution was
used to characterize the joint-SA statistics of sea clutter with a large range
of homogeneity. As a result, an adaptive constant false alarm rate (CFAR)
method was implemented based on the joint-SA. Finally, RADARSAT-2 and GF-3 data
in C-band and ALOS data in L-band are used for verification. We tested on five
datasets, and the experimental results verify the correctness and superiority
of the constant false alarm rate (CFAR) method based on the joint-SA. In
addition, the experimental results also showed that the signal-clutter ratio
(SCR) of the proposed ship detector joint-SA (33.17 dB, 35.98 dB, 57.25 dB) is
better than that of DBSP (8.92 dB, 3.43 dB, 25.40 dB) and RsDVH (17.28 dB,
11.17 dB, 54.55 dB). More importantly, the proposed detector joint-SA has
higher detection accuracy and a lower false alarm rate.",2112.02965v2
2021-12-09,Nonlinear optical imaging of in-plane anisotropy in two-dimensional SnS,"Two-dimensional (2D) tin(II) sulfide (SnS) crystals belong to a class of
orthorhombic semiconducting materials that are lately attracting significant
interest, given their remarkable properties, such as in-plane anisotropic
optical and electronic response, multiferroic nature and lack of inversion
symmetry. The 2D SnS crystals exhibit anisotropic response along the in-plane
armchair (AC) and zigzag (ZZ) crystallographic directions, offering an
additional degree of freedom in manipulating their behavior. Therefore,
calculating the AC/ZZ directions is important in characterizing the 2D SnS
crystals. In this work, we take advantage of the lack of inversion symmetry of
the 2D SnS crystal, that produces second harmonic generation (SHG), to perform
polarization-resolved SHG (P-SHG) nonlinear imaging of the in-plane anisotropy.
We fit the P-SHG experimental data with a nonlinear optics model, that allows
us to calculate the AC/ZZ orientation from every point of the 2D crystal and to
map with high-resolution the AC/ZZ direction of several 2D SnS flakes belonging
in the same field of view. It is found that the P-SHG intensity polar patterns
are associated with the crystallographic axes of the flakes and with the
relative strength of the second order nonlinear susceptibility tensor in
different directions. Therefore, our method provides quantitative information
of the optical in-plane anisotropy of orthorhombic 2D crystals, offering great
promise for performance characterization during device operation in the
emerging optoelectronic applications of such crystals.",2112.04853v1
2021-12-10,Low-energy excitations and magnetic anisotropy of the layered van der Waals antiferromagnet Ni$_2$P$_2$S$_6$,"The quasi-two-dimensional antiferromagnet Ni$_2$P$_2$S$_6$ belongs to the
family of magnetic van der Waals compounds that provides a rich material base
for the realization of fundamental models of quantum magnetism in low
dimensions. Here, we report high-frequency/high-magnetic field electron spin
resonance measurements on single crystals of Ni$_2$P$_2$S$_6$. The results
enable one to reliably determine the positive, ""easy""-plane type of the single
ion anisotropy of the Ni$^{2+}$ ions with the upper limit of its magnitude
$\lesssim 0.7$ meV. The resonance response reveals strongly anisotropic spin
fluctuations setting in shortly above the N\'eel temperature $T_{\rm N} = 158$
K and extending in the antiferromagnetically ordered state down to low
temperatures. There, a low-energy magnon excitation gapped from the ground
state by only $\sim 1$ meV was found. This magnon mode may explain unusual low
temperature relaxation processes observed in a latest nuclear magnetic
resonance experiments and together with the estimate of the single ion
anisotropy they should enable setting up a realistic spin model for an accurate
description of magnetic properties of Ni$_2$P$_2$S$_6$.",2112.05699v3
2021-12-20,"Refined modelling of the radio SZ signal: kinematic terms, relativistic temperature corrections and anisotropies in the radio background","A significant cosmological radio background will inevitably lead to a radio
Sunyaev-Zeldovich (SZ) effect. In the simplest limit, the combined signal from
the scattered radio and cosmic microwave background exhibits a null at around
$\nu \simeq 735$ MHz. Here, we show that kinematic and relativistic temperature
corrections to this radio SZ signal are easily calculable. We treat both the
cluster and observer motion, and the scattering of anisotropies in the radio
background, highlighting how the spectrum of the radio SZ effect is affected in
each case. Although relativistic temperature corrections only enter at the
level of a few percent, our expressions allow high-precision modelling of these
terms. By measuring the SZ signal around the radio null, one is in principle
able to place constraints on the properties of a cosmological radio background.
A combination with standard SZ measurements from large cluster samples could
provide a promising avenue towards breaking degeneracies between different
contributions. Stacking analyses can reduce the effect of kinematic corrections
and dipolar anisotropies in the radio background, thereby providing a way to
constrain the redshift dependence of the average radio background. Our
qualitative discussion is meant to give an analytic understanding of the
various effects and also motivate further studies with the aim to obtain
quantitative forecasts of their observability. At this stage, a detection of
the corrections seems rather futuristic, but the advent of large SZ and X-ray
cluster samples could drastically improve our ability to disentangle various
effects.",2112.10666v2
2021-12-23,DyOCl: a rare-earth based two-dimensional van der Waals material with strong magnetic anisotropy,"Comparing with the widely known transitional metal based van der Waals (vdW)
materials, rare-earth based ones are rarely explored in the research of
intrinsic two-dimensional (2D) magnetism. In this work, we report the physical
properties of DyOCl, a rare-earth based vdW magnetic insulator with direct band
gap of $\sim 5.72~eV$. The magnetic order of bulk DyOCl is determined by
neutron scattering as the $A$-type antiferromagnetic structure below the
N\'{e}el temperature $T_N=10~$K. The large magnetic moment near 10.1 $ \mu_{B}
$/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At
$2~K$, a moderate magnetic field ($\sim 2~T$) applied along the easy axis
generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state.
Density functional theory calculations reveal an extremely large magnetic
anisotropy energy ($-5850~\mu eV/Dy$) for DyOCl, indicating the great
potentials to realize magnetism in 2D limit. Furthermore, the mechanical
exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated.
Our findings suggest DyOCl is a promising material playground to investigate 2D
$f$-electron magnetism and spintronic applications at the nanoscale.",2112.12556v1
2021-12-27,The incompressible energy cascade rate in anisotropic solar wind turbulence,"Context. The presence of a magnetic guide field induces several types of
anisotropy in solar wind turbulence. The energy cascade rate between scales in
the inertial range depends strongly on the direction of this magnetic guide
field, splitting the energy cascade according to the parallel and perpendicular
directions with respect to magnetic guide field. Aims. Using more than two
years of Parker Solar Probe (PSP) observations, the isotropy and anisotropy
energy cascade rates are investigated. The variance and normalized fluctuation
ratios, the kinetic and magnetic energies, and the normalized cross-helicity
and residual energy are studied. The connection between the heliocentric
distance, the local temperature of the plasma, and the energy cascade
components is made. Methods. Using exact relations for fully developed
incompressible magnetohydrodynamic (MHD) turbulence, the incompressible energy
cascade rate is computed. In particular, using the isotropy and 2D and slab
assumptions, the isotropic, perpendicular, and parallel energy cascade rate
components are estimated. Results. The variance anisotropy ratios, for both
velocity and magnetic fields, do not exhibit a dependence with respect to the
heliocentric distance $r$ between 0.2 and 0.8 au. While the velocity normalized
fluctuation ratio shows a dependence with $r$, the magnetic normalized
fluctuation ratio does not. A strong correlation between the isotropic and
anisotropic energy cascade rates and the temperature is found. A clear
dominance of the perpendicular cascades over the parallel cascades as PSP
approaches the Sun is observed. A dominant 2D cascade and/or geometry over the
slab component in slow solar wind turbulence in the largest MHD scales is
observed.",2112.13748v3
2022-01-01,Multiple stellar populations in Schwarzschild modeling and the application to the Fornax dwarf,"Dwarf spheroidal (dSph) galaxies are believed to be strongly dark matter
dominated and thus are considered perfect objects to study dark matter
distribution and test theories of structure formation. They possess resolved,
multiple stellar populations that offer new possibilities for modeling. A
promising tool for the dynamical modeling of these objects is the Schwarzschild
orbit superposition method. In this work we extend our previous implementation
of the scheme to include more than one population of stars and a more general
form of the mass-to-light ratio function. We tested the improved approach on a
nearly spherical, gas-free galaxy formed in the cosmological context from the
Illustris simulation. We modeled the binned velocity moments for stars split
into two populations by metallicity and demonstrate that in spite of larger
sampling errors the increased number of constraints leads to significantly
tighter confidence regions on the recovered density and velocity anisotropy
profiles. We then applied the method to the Fornax dSph galaxy with stars
similarly divided into two populations. In comparison with our earlier work, we
find the anisotropy parameter to be slightly increasing, rather than
decreasing, with radius and more strongly constrained. We are also able to
infer anisotropy for each stellar population separately and find them to be
significantly different.",2201.00151v1
2022-01-19,Effects of anisotropy and disorder on the superconducting properties of Niobium,"We report results for the superconducting transition temperature and
anisotropic energy gap for pure Niobium based on Eliashberg's equations and
electron and phonon band structures computed from density functional theory.
The electronic band structure is used to construct the Fermi surface and
calculate the Fermi velocity at each point on the Fermi surface.The phonon
bands are in excellent agreement with inelastic neutron scattering data. The
corresponding phonon density of states and electron-phonon coupling define the
electron-phonon spectral function, $\alpha^2F({\bf p},{\bf p}';\omega)$, and
the corresponding electron-phonon pairing interaction, which is the basis for
computing the superconducting properties. The electron-phonon spectral function
is good agreement with existing tunneling spectroscopy data except for the
spectral weight of the longitudinal phonon peak at
$\hbar\omega_{\text{LO}}=23\,\mbox{meV}$. We obtain an electron-phonon coupling
constant of $\lambda=1.057$, renormalized Coulomb interaction,
$\mu^{\star}=0.218$ and transition temperature $T_c=9.33\,\mbox{K}$. The
corresponding strong-coupling gap at $T=0$ is modestly enhanced,
$\Delta_0=1.55\,\mbox{meV}$, compared to the weak-coupling BCS value
$\Delta_0^{\text{wc}}=1.78\,k_{\mbox{b}}\,T_c= 1.43\,\mbox{meV}$. The
superconducting gap function exhibits substantial anisotropy on the Fermi
surface. We analyze the distribution of gap anisotropy and compute the
suppression of the superconducting transition temperature using a
self-consistent T-matrix theory for quasiparticle-impurity scattering to
describe Niobium doped with non-magnetic impurities. We compare these results
with experimental results on Niobium SRF cavities doped with Nitrogen
impurities.",2201.07403v2
2022-01-23,Valley-polarized quantum anomalous Hall insulator in monolayer $\mathrm{RuBr_2}$,"Coexistence of intrinsic ferrovalley (FV) and nontrivial band topology
attracts intensive interest both for its fundamental physics and for its
potential applications, namely valley-polarized quantum anomalous Hall
insulator (VQAHI). Here, based on first-principles calculations by using
generalized gradient approximation plus $U$ (GGA+$U$) approach, the VQAHI
induced by electronic correlation or strain can occur in monolayer
$\mathrm{RuBr_2}$. For perpendicular magnetic anisotropy (PMA), the ferrovalley
(FV) to half-valley-metal (HVM) to quantum anomalous Hall (QAH) to HVM to FV
transitions can be driven by increasing electron correlation $U$. However,
there are no special QAH states and valley polarization for in-plane magnetic
anisotropy. By calculating actual magnetic anisotropy energy (MAE), the VQAHI
indeed can exist between two HVM states due to PMA, a unit Chern number/a
chiral edge state and spontaneous valley polarization. The increasing $U$ can
induce VQAHI, which can be explained by sign-reversible Berry curvature or band
inversion between $d_{xy}$/$d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Even though
the real $U$ falls outside the range, the VQAHI can be achieved by strain.
Taking $U$$=$2.25 eV as a concrete case, the monolayer $\mathrm{RuBr_2}$ can
change from a common ferromagentic (FM) semiconductor to VQAHI under about
0.985 compressive strain. It is noted that the edge states of VQAHI are
chiral-spin-valley locking, which can achieve complete spin and valley
polarizations for low-dissipation electronics devices. Both energy band gap and
valley splitting of VQAHI in monolayer $\mathrm{RuBr_2}$ are higher than the
thermal energy of room temperature (25 meV), which is key at room temperature
for device applications.",2201.09258v1
2022-02-04,Three-axis torque investigation of interfacial exchange coupling in a NiFe/CoO bilayer micromagnetic disk,"Micrometer diameter bilayers of NiFe (permalloy, Py) and cobalt oxide (CoO)
deposited on nanomechanical resonators were used to investigate exchange bias
effects. The mechanical compliances of two resonator axes were enhanced by
severing one torsion arm, resulting in a unique three-axis resonator that
responds resonantly to torques generated by a three-axis RF field. Our
technique permits simultaneous measurement of three orthogonal torque
components. Measurements of the anisotropies associated with interfacial
exchange coupling effects have been made. At cryogenic temperatures,
observations of shifted linear hysteresis loops confirmed the presence of
exchange bias from the Py/CoO interface. An in-plane rotating DC bias field was
used to probe in-plane anisotropies through the out-of-plane torque. Training
effects in the rotational hysteresis data were observed and showed that
features due to interfacial coupling did not diminish irrespective of
substantial training of the unidirectional anisotropy. The data from the
rotational hysteresis loops were fit with parameters from a macrospin solution
to the Landau-Lifshitz-Gilbert equation. Each parameter of the exchange bias
model accounts for specific features of the rotational loop.",2202.02386v1
2022-02-11,Interaction between interface and massive states in multivalley topological heterostructures,"Topological interface states in multivalley systems are studied to unravel
their valley sensitivity. For this purpose, multivalley IV-VI topological
crystalline insulator (TCI) heterostructures are explored using magneto-optical
Landau level spectroscopy up to 34 teslas. We characterize the topological
interface states emerging from the distinct L-valleys in Pb1-xSnxSe multi
quantum wells grown along the [111] direction. It is shown that the shape of
the 2D Fermi surfaces of topological interface states residing at the
TCI/trivial insulator interfaces are strongly affected by the valley anisotropy
of topologically trivial Pb1-yEuySe barriers. This phenomenon is shown to be
due to the deep penetration of the topological interface states into the
barriers. For the valleys tilted with respect to the confinement direction, a
significant interaction between topological states and the conventional massive
quantum well states is observed, evidenced by the resulting large
anti-crossings between Landau levels. These are theoretically well-described by
a k.p model that takes into account tilt and anisotropy of the valleys in two
dimensions. Therefore, our work provides a precise characterization of the
topological interface state valley splitting, as well as an accurate
determination of the anisotropy of their Dirac cone dispersion.",2202.05640v1
2022-02-24,"Explaining the UHECR spectrum, composition and large-scale anisotropies with radio galaxies","Radio galaxies are promising candidates as the sources of ultrahigh energy
cosmic rays (UHECRs). In this work, we examine if the stringent constraints
imposed by the dipole and quadropole anisotropies as well as the UHECR spectrum
and composition allow that radio galaxies are the dominant extragalactic cosmic
ray sources. In order to calculate the UHECR flux emitted by individual radio
galaxies, we constrain their properties using information from the radio-CR
correlation and a dynamical evolution model. In addition to the UHECR flux from
individual, local sources, we include the diffuse flux emitted by the bulk of
non-local radio galaxies based on their radio luminosity distribution.
Analyzing the source parameters within a range around their expected
properties, we finally determine the configurations of local sources describing
well the UHECR spectrum, composition and large-scale anisotropies. We obtain a
good description of all data even in the case that we include only a small
number of local sources. In particular, we find that scenarios where few
sources like Fornax A and Virgo A dominate the flux above the ankle, while
low-luminosity radio galaxies contribute an isotropic background dominating
below the ankle, provide a good fit to the data.",2202.11942v2
2022-02-28,Large perpendicular magnetic anisotropy of transition metal dimers driven by polarization switching of two-dimensional ferroelectric In2Se3 substrate,"Large perpendicular magnetic anisotropy (MA) is highly desirable for
realizing atomic-scale magnetic data storage which represents the ultimate
limit of the density of magnetic recording. In this work, we studied the MA of
transition metal dimers Co-Os, Co-Co and Os-Os adsorbed on two-dimensional
ferroelectric In2Se3 (In2Se3-CoOs, In2Se3-OsCo, In2Se3-CoCo and In2Se3-OsOs) by
first-principles calculations. It is found that the Co-Os dimer in In2Se3-CoOs
has large total perpendicular magnetic anisotropy energy (MAE) of ~ 40 meV. In
particular, the MAE arising from Os atom is up to ~ 60 meV. The large MAE is
attributed to the high spin-orbit coupling constant and the onefold
coordination of Os atom. In addition, the MA of the dimers can be tuned by the
polarization reversal of In2Se3. When the polarization is upward, the easy-axis
directions of MA in In2Se3-OsCo, In2Se3-CoCo and In2Se3-OsOs are all in-plane,
while the directions become perpendicular as the polarization is switched to
downward. For the In2Se3-CoOs, switching polarization from upward to downward
enhance the perpendicular MA from ~ 20 meV to ~ 40 meV. Based on the
second-order perturbation theory, we confirm that the exchange splitting of
dxy/dx2-y2 and dxz/dyz orbitals as well as the occupation of dz2 orbital at the
vicinity of Fermi level play important roles in the changes of MA with the
reversal of FE polarization of In2Se3.",2202.13726v1
2022-03-08,Can Chameleon fields be the source of both the dark energy dipole and the CMB dipole?,"Recent research shows that the local group is moving toward (l,b)=(276,30)
relative to the cosmic background radiation at a speed of about $600 kms^{-1}$
which is known as the cosmic background radiation dipole. The exact cause of
this movement is still unknown. Areas with high mass densities such as galactic
superclusters seem to be one of the causes of this flow. There are several
methods for simulating the motion of local clusters, one of which is the bulk
flow. The bulk current can be seen as a mass movement of a large part of the
universe. This anisotropy at the local scale seems to have the same origin as
the anisotropy at the larger scale. In this paper, anisotropies on both small
and large scales were investigated using chameleon fields. The data used are
Type Ia supernovae (Pantheon catalog for a total of 1,048 supernovae in
redshift (0.15<z<2.3)). The results showed that on a smaller scale (less than
150 MPa) the direction of motion of the local group galaxies is the same as the
direction of the bulk, and on larger scales, the direction of the bulk current
is the same as the direction of the current of dark energy dipole.",2203.03983v1
2022-03-08,Early dynamical evolution of rotating star clusters in a tidal field,"In order to explore how the early internal rotational properties of star
clusters are affected by the external potential of their host galaxies, we have
run a suite of $N$-body simulations following the early dynamical evolution and
violent relaxation of rotating star clusters embedded in a tidal field. Our
study focuses on models for which the cluster's rotation axis has a generic
orientation relative to the torque of the tidal field. The interaction between
the violent relaxation process, angular momentum of the cluster, and the
external torque creates a complex kinematic structure within the cluster, most
prominently a radial variation in the position of the rotation axis along both
the polar and azimuthal directions. We also examine the cluster's velocity
dispersion anisotropy and show that the projected anisotropy may be affected by
the variation of the rotation axis directions within the cluster; the
combination of projection effects and the complex kinematical features may
result in the measurement of tangential anisotropy in the cluster's inner
regions. We also characterize the structural properties of our clusters as a
function of their initial rotation and virial ratio and find that clusters may
develop a triaxial morphology and a radial variation of the minor axis not
necessarily aligned with the rotation axis. Finally, we examine the long-term
evolution of these complex kinematic features.",2203.04330v1
2022-03-24,Simulating realistic screening clouds around quantum impurities: role of spatial anisotropy and disorder,"Dynamical quantum impurities in metals induce electronic correlations in real
space that are difficult to simulate due to their multi-scale nature, so that
only s-wave scattering in clean metallic hosts has been investigated so far.
However, screening clouds should show anisotropy due to lack of full rotational
invariance in two- and three-dimensional lattices, while inherent disorder will
also induce spatial inhomogeneities. To tackle these challenges, we present an
efficient and robust algorithm based on the recursive generation of natural
orbitals defined as eigenvectors of the truncated single-particle density
matrix. This method provides well-converged many-body wave functions on
lattices with up to tens of thousands of sites, bypassing some limitations of
other approaches. The algorithm is put to the test by investigating the charge
screening cloud around an interacting resonant level, both on clean and
disordered lattices, achieving accurate spatial resolution from short to long
distances. We thus demonstrate strong anisotropy of spatial correlations around
an adatom in the half-filled square lattice. Taking advantage of the efficiency
of the algorithm, we further compute the disorder-induced distribution of Kondo
temperatures over several thousands of random realizations, at the same time
gaining access to the full spatial profile of the screening cloud in each
sample. While the charge screening cloud is typically shortened due to the
polarization of the impurity by the disorder potential, we surprisingly find
that rare disorder configurations preserve the long range nature of Kondo
correlations in the electronic bath.",2203.13041v1
2022-03-25,"Optical constants of several multilayer transition metal dichalcogenides measured by spectroscopic ellipsometry in the 300-1700 nm range: high-index, anisotropy, and hyperbolicity","Transition metal dichalcogenides (TMDs) attract significant attention due to
their exceptional optical and excitonic properties. It was understood already
in the 1960s, and recently rediscovered, that many TMDs possess high refractive
index and optical anisotropy, which make them attractive for nanophotonic
applications. However, accurate analysis and predictions of nanooptical
phenomena require knowledge of dielectric constants along both in- and
out-of-plane directions and over a broad spectral range -- information, which
is often inaccessible or incomplete. Here, we present an experimental study of
optical constants from several exfoliated TMD multilayers obtained using
spectroscopic ellipsometry in the broad range of 300--1700 nm. The specific
materials studied include semiconducting WS$_2$, WSe$_2$, MoS$_2$, MoSe$_2$,
MoTe$_2$, as well as, in-plane anisotropic ReS$_2$, WTe$_2$, and metallic
TaS$_2$, TaSe$_2$, and NbSe$_2$. The extracted parameters demonstrate
high-index ($n$ up till $\approx 4.84$ for MoTe$_2$), significant anisotropy
($n_{\parallel}-n_{\perp} \approx 1.54$ for MoTe$_2$), and low absorption in
the near infrared region. Moreover, metallic TMDs show potential for combined
plasmonic-dielectric behavior and hyperbolicity, as their plasma frequency
occurs at around $\sim$1000--1300 nm depending on the material. The knowledge
of optical constants of these materials opens new experimental and
computational possibilities for further development of all-TMD nanophotonics.",2203.13793v1
2022-03-31,Anomalous Hall Effect and Perpendicular Magnetic Anisotropy in Ultrathin Ferrimagnetic NiCo$_2$O$_4$ Films,"The inverse spinel ferrimagnetic NiCo$_2$O$_4$ possesses high magnetic Curie
temperature $T_C$, high spin polarization, and strain-tunable magnetic
anisotropy. Understanding the thickness scaling limit of these intriguing
magnetic properties in NiCo$_2$O$_4$ thin films is critical for their
implementation in nanoscale spintronic applications. In this work, we report
the unconventional magnetotransport properties of epitaxial (001) NiCo$_2$O$_4$
films on MgAl$_2$O$_4$ substrates in the ultrathin limit. Anomalous Hall effect
measurements reveal strong perpendicular magnetic anisotropy for films down to
1.5 unit cell (1.2 nm), while $T_C$ for 3 unit cell and thicker films remains
above 300 K. The sign change in the anomalous Hall conductivity ($\sigma_{xy}$)
and its scaling relation with the longitudinal conductivity ($\sigma_{xx}$) can
be attributed to the competing effects between impurity scattering and band
intrinsic Berry curvature, with the latter vanishing upon the thickness driven
metal-insulator transition. Our study reveals the critical role of film
thickness in tuning the relative strength of charge correlation, Berry phase
effect, spin orbit interaction, and impurity scattering, providing important
material information for designing scalable epitaxial magnetic tunnel junctions
and sensing devices using NiCo$_2$O$_4$.",2204.00133v2
2022-03-29,A single Long Short-Term Memory network for enhancing the prediction of path-dependent plasticity with material heterogeneity and anisotropy,"This study presents the applicability of conventional deep recurrent neural
networks (RNN) to predict path-dependent plasticity associated with material
heterogeneity and anisotropy. Although the architecture of RNN possesses
inductive biases toward information over time, it is still challenging to learn
the path-dependent material behavior as a function of the loading path
considering the change from elastic to elastoplastic regimes. Our attempt is to
develop a simple machine-learning-based model that can replicate elastoplastic
behaviors considering material heterogeneity and anisotropy. The basic
Long-Short Term Memory Unit (LSTM) is adopted for the modeling of plasticity in
the two-dimensional space by enhancing the inductive bias toward the past
information through manipulating input variables. Our results find that a
single LSTM based model can capture the J2 plasticity responses under both
monotonic and arbitrary loading paths provided the material heterogeneity. The
proposed neural network architecture is then used to model elastoplastic
responses of a two-dimensional transversely anisotropic material associated
with computational homogenization (FE2). It is also found that a single LSTM
model can be used to accurately and effectively capture the path-dependent
responses of heterogeneous and anisotropic microstructures under arbitrary
mechanical loading conditions.",2204.01466v2
2022-04-10,Giant magnetic in-plane anisotropy and competing instabilities in Na3Co2SbO6,"We report magnetometry data obtained on twin-free single crystals of
Na3Co2SbO6, which is considered a candidate material for realizing the Kitaev
honeycomb model for quantum spin liquids. Contrary to a common belief that such
materials can be modeled with the symmetries of an ideal honeycomb lattice, our
data reveal a pronounced two-fold symmetry and in-plane anisotropy of over
200%, despite the honeycomb layer's tiny orthorhombic distortion of less than
0.2%. We further use magnetic neutron diffraction to elucidate a rich variety
of field-induced phases observed in the magnetometry. These phases manifest
themselves in the paramagnetic state as diffuse scattering signals associated
with competing ferro- and antiferromagnetic instabilities, consistent with a
theory that also predicts a quantum spin liquid phase nearby. Our results call
for theoretical understanding of the observed in-plane anisotropy, and render
Na3Co2SbO6 a promising ground for finding exotic quantum phases by targeted
external tuning.",2204.04593v2
2022-04-12,The Annual Cycle in Scintillation Timescale of PMN J1726+0639,"We discovered rapid intra-day variability in radio source PMN J1726+0639 at
GHz frequencies, during a survey to search for such variability with the
Australia Telescope Compact Array. Follow-up observations were conducted over
two years and revealed a clear, repeating annual cycle in the rate, or
characteristic timescale, of variability, showing that the observed variations
can be attributed to scintillations from interstellar plasma inhomogeneities.
The strong annual cycle includes an apparent ""standstill"" in April and another
in September. We fit kinematic models to the data, allowing for finite
anisotropy in the scintillation pattern. The cycle implies a very high degree
of anisotropy, with an axial ratio of at least 13:1, and the fit is consistent
with a purely one-dimensional scintillation pattern. The position angle of the
anisotropy, and the transverse velocity component are tightly constrained. The
parameters are inconsistent with expectations from a previously proposed model
of scattering associated with plasma filaments radially oriented around hot
stars. We note that evidence for a foreground interstellar cloud causing
anomalous Ca II absorption towards the nearby star Rasalhague ($\alpha$ Oph)
has been previously reported, and we speculate that the interstellar
scintillation of PMN 1726+0639 might be associated with this nearby cloud.",2204.05847v1
2022-04-13,Long-term evolution of multimass rotating star clusters,"We investigate the long-term dynamical evolution of the internal kinematics
of multimass rotating star clusters. We have performed a set of N-body
simulations to follow the internal evolution of clusters with different degrees
of initial rotation and have explored the evolution of the rotational velocity,
the degree of energy equipartition, and anisotropy in the velocity
distribution. Our simulations show that: 1) as the cluster evolves, the
rotational velocity develops a dependence on the stellar mass with more massive
stars characterised by a more rapid rotation and a peak in the rotation curve
closer to the cluster centre than low-mass stars; 2) the degree of energy
equipartition in the cluster's intermediate and outer regions depends on the
component of the velocity dispersion measured; for more rapidly rotating
clusters, the evolution towards energy equipartition is more rapid in the
direction of the rotational velocity; 3) the anisotropy in the velocity
distribution is stronger for massive stars; 4) both the degree of mass
segregation and energy equipartition are characterised by spatial anisotropy;
they have a dependence on both $R$ and $z$, correlated with the flattening in
the spatial variation of the cluster's density and velocity dispersion, as
shown by 2D maps of the mass segregation and energy equipartition on the
($R$-$z$) meridional plane.",2204.06578v1
2022-04-20,Varied magnetic phases in a van der Waals easy-plane antiferromagnet revealed by nitrogen-vacancy center microscopy,"Interest in van der Waals materials often stems from a desire to miniaturise
existing technologies by exploiting their intrinsic layered structure to create
near atomically-thin components that do not suffer from surface defects. One
appealing property is easily-switchable yet robust magnetic order, a quality
only sparsely demonstrated in the case of in-plane anisotropy. In this work, we
use widefield nitrogen-vacancy (NV) center magnetic imaging to measure the
properties of individual flakes of CuCrP$_2$S$_6$, a multiferroic van der Waals
magnet known to exhibit weak easy-plane anisotropy in the bulk. We chart the
crossover between in-plane ferromagnetism in thin flakes down to the trilayer,
and the bulk behaviour dominated by a low-field spin-flop transition. Further,
by exploiting the directional dependence of NV center magnetometry, we are able
to observe an instance of a predominantly out-of-plane ferromagetic phase near
zero field, in contradiction with expectation and previous experiments on the
bulk material. We attribute this to the presence of surface anisotropies
arising from the sample preparation process or exposure to the ambient
environment, which is expected to have more general implications for a broader
class of weakly anisotropic van der Waals magnets.",2204.09277v1
2022-04-25,Reduced effective magnetization and damping by slowly-relaxing impurities in strained $γ$-$\mathrm{Fe_2O_3}$ thin films,"We study the static and dynamic magnetic properties of epitaxially strained
$\gamma$-$\mathrm{Fe_2O_3}$ (maghemite) thin films grown via pulsed-laser
deposition on MgO substrates by SQUID magnetometry and cryogenic broadband
ferromagnetic resonance experiments. SQUID magnetometry measurements reveal
hysteretic magnetization curves for magnetic fields applied both in- and out of
the sample plane. From the magnetization dynamics of our thin films, we find a
small negative effective magnetization in agreement with a strain induced
perpendicular magnetic anisotropy. Moreover, we observe a non-linear evolution
of the ferromagnetic resonance-linewidth as function of the microwave frequency
and explain this finding with a model based on slowly relaxing impurities, the
so-called slow relaxor model. By investigating the magnetization dynamics in
our maghemite thin films as a function of frequency and temperature, we can
isolate the temperature dependent contribution of the slowly relaxing
impurities to the resonance linewidth and, in particular, observe a sign change
in the effective magnetization. This finding provides evidence for a transition
of the magnetic anisotropy from a perpendicular easy axis to an easy in-plane
anisotropy for reduced temperatures.",2204.11498v1
2022-04-28,Delocalization of dark and bright excitons in flat-band materials and the optical properties of V$_2$O$_5$,"The simplest picture of excitons in materials with atomic-like localization
of electrons is that of Frenkel excitons, where electrons and holes stay close
together, which is associated with a large binding energy. Here, using the
example of the layered oxide V$_2$O$_5$ , we show how localized charge-transfer
excitations combine to form excitons that also have a huge binding energy but,
at the same time, a large electron-hole distance, and we explain this seemingly
contradictory finding. The anisotropy of the exciton delocalization is
determined by the local anisotropy of the structure, whereas the exciton
extends orthogonally to the chains formed by the crystal structure. Moreover,
we show that the bright exciton goes together with a dark exciton of even
larger binding energy and more pronounced anisotropy. These findings are
obtained by combining first principles many-body perturbation theory
calculations, ellipsometry experiments, and tight binding modelling, leading to
very good agreement and a consistent picture. Our explanation is general and
can be extended to other materials.",2204.13580v2
2022-05-08,Tuning the magnetic anisotropy and topological phase with electronic correlation in single-layer H-FeBr$_2$,"Electronic correlation can strongly influence the electronic properties of
two-dimensional (2D) materials with open d- or f-orbitals. Herein, by taking
single-layer (SL) H-FeBr$_2$ as a representative of the SL H-FeX$_2$ (X=Cl, Br,
I) family, we investigated the electronic correlation effects in the magnetic
anisotropy and electronic topology of such a system based on first-principles
calculations with DFT+\textit{U} approach. Our result is that the magnetic
anisotropy energy (MAE) of SL H-FeBr$_2$ shows a non-monotonic evolution
behaviour with increasing electronic correlation strength, which is mainly due
to the competition between different element-resolved MAEs of Fe and Br.
Further investigations show that the evolution of element-resolved MAE arises
from the variation of the spin-orbital coupling (SOC) interaction between
different orbitals in each atom. Moreover, tuning the strength of the
electronic correlation can drive the occurrence of band inversions, causing the
system to undergoes multiple topological phase transitions, resulting in a
quantum anomalous valley Hall (QAVH) effect. These exotic properties are
universal for the SL H-FeX$_2$ (X = Cl, Br, I) family. Our work sheds light on
the role of electronic correlation effects in tuning magnetic and electronic
structures in the SL H-FeX$_2$ (X = Cl, Br, I) family, which could guide
advances in the development of new spintronics and valleytronics devices based
on these materials.",2205.03764v1
2022-05-11,No nematicity at the onset temperature of the pseudogap phase in the cuprate superconductor YBCO,"Electronic nematicity is the spontaneous loss of rotational symmetry in a
metal, without breaking translational symmetry. In the cuprate superconductors,
there is experimental evidence for nematicity, but its origin remains unclear.
Here we investigate the onset of nematicity in the transport of charge by means
of electric and thermoelectric measurements in underdoped YBa$_{\rm 2}$Cu$_{\rm
3}$O$_{\rm y}$, performed by passing the current (electrical or thermal) first
along the $a$ axis then the $b$ axis of the orthorhombic structure in the same
crystal, with a hole doping $p = 0.12$. Upon cooling, we observe no additional
in-plane anisotropy -- beyond the background anisotropy due to the CuO chains
-- in either the resistivity $\rho$ or the Seebeck coefficient $S$ as the
temperature $T^{\star}$~for the onset of the pseudogap phase is crossed. We
conclude that the pseudogap phase of cuprates is not nematic. However, at
temperatures much lower than $T^{\star}$, a strong additional anisotropy is
observed, most clearly in the Peltier coefficient $\alpha = S / \rho$. We
interpret it as nematicity associated with the development of charge order.",2205.05233v2
2022-05-12,Revisiting the Ulysses electron data with a triple fit of velocity distributions,"Given their uniqueness, the Ulysses data can still provide us with valuable
new clues about the properties of plasma populations in the solar wind, and,
especially, about their variations with heliographic coordinates. We revisit
the electron data reported by by the SWOOPS instrument on-board of the Ulysses
spacecraft between 1990 to early 2008. These observations reveal velocity
distributions out of thermal equilibrium, with anisotropies (e.g., parallel
drifts or/and different temperatures, parallel and perpendicular to the
background magnetic field), and quasi-thermal and suprathermal populations with
different properties. We apply a 2D nonlinear least square fitting procedure,
using the Levenberg-Marquardt algorithm, to simultaneously fit the velocity
electron data (up to a few keV) with a triple model combining three distinct
populations: the more central quasi-thermal core and suprathermal halo, and a
second suprathermal population consisting mainly of the electron strahl (or
beaming population with a major field-aligned drift). The recently introduced
$\kappa$-cookbook is used to describe each component with the following
anisotropic distribution functions (recipes): Maxwellian, regularized kappa-,
and generalized kappa-distributions. The temperature anisotropy quantified by
the best fits is considered as a case study of the main parameters
characterizing electron populations. By comparison to the core, both
suprathermal populations exhibit higher temperature anisotropies, which
slightly increase with the energy of electrons.",2205.05911v1
2022-05-14,Strain effects on topological and valley properties of Janus monolayer $\mathrm{VSiGeN_4}$,"Strain is an effective method to tune the electronic properties of
two-dimension (2D) materials, and can induce novel phase transition. Recently,
2D $\mathrm{MA_2Z_4}$ family materials are of interest because of their
emerging topological, magnetic and superconducting properties. Here, we
investigate the impact of strain effects ($a/a_0$:0.96$\sim$1.04) on the
physical properties of Janus monolayer $\mathrm{VSiGeN_4}$ as a derivative of
$\mathrm{VSi_2N_4}$ or $\mathrm{VGe_2N_4}$, which possesses dynamical,
mechanical and thermal stabilities. For out-of-plane magnetic anisotropy, with
increasing strain, $\mathrm{VSiGeN_4}$ undergoes transition between ferrovalley
semiconductor (FVS), half-valley-metal (HVM), valley-polarized quantum
anomalous Hall insulator (VQAHI), HVM and FVS. These imply twice topological
phase transitions, which are related with sign-reversible Berry curvature and
band inversion between $d_{xy}$+$d_{x^2-y^2}$ and $d_{z^2}$ orbitals for K or
-K valley. The band inversion also leads to transformation of valley splitting
strength between valence and conduction bands. However, for in-plane magnetic
anisotropy, no special quantum anomalous Hall (QAH) states and valley
polarization exist within the considered strain range. The actual magnetic
anisotropy energy (MAE) shows no special QAH and HVM states in monolayer
$\mathrm{VSiGeN_4}$. Fortunately, these can be easily achieved by external
magnetic field, which adjusts the easy magnetization axis of
$\mathrm{VSiGeN_4}$ from in-plane one to out-of-plane one. Our findings shed
light on how strain can be employed to engineer the electronic states of
$\mathrm{VSiGeN_4}$, which may open new perspectives for multifunctional
quantum devices in valleytronics and spintronics.",2205.07012v2
2022-05-16,Induced gravitational waves from statistically anisotropic scalar perturbations,"Scalar-induced gravitational waves (SIGWs) are attracting growing attention
for probing extremely short-scale scalar perturbations via gravitational wave
measurements. In this paper, we investigate the SIGWs from statistically
anisotropic scalar perturbations, which are motivated in inflationary scenarios
in the presence of, e.g., a vector field. While the ensemble average of the
SIGW energy spectrum is isotropic for the standard statistically isotropic
scalar perturbations, the statistical anisotropy in the source introduces the
multipole moments of the differential SIGW energy spectrum. We consider
quadrupole anisotropy in the scalar power spectrum and show that the SIGW
spectrum has anisotropies up to $\ell=4$. We present generic formulas of the
multipole moments and then apply them to the delta-function-like and log-normal
source spectra. We find analytic expressions for the former case and show that
the infrared scalings of the multipole moments are the same as the isotropic
SIGWs. Interestingly, the monopole has an additional local minimum in the
high-$k$ tail, a key feature to distinguish from the isotropic SIGWs. The
latter log-normal case is analytic for the narrow-peak source, and we perform
the numerical calculation for the broad peak. As one expects, the multipole
moments become broader with increasing source width. Our results are helpful to
test the isotropy of primordial density perturbations at extremely small scales
through SIGWs.",2205.07810v2
2022-06-01,Possible unconventional order parameter in single crystals of SrPt$_3$P superconductor,"Anisotropic properties of single crystals of SrPt$_{3}$P were studied using
London penetration depth and electrical resistivity measurements. The upper
critical field, $H_{c2}(T)$, was determined from four-probe electrical
resistivity measurements for three orthogonal directions of a magnetic field
with respect to the crystal. The London penetration depth, $\lambda(T)$, was
determined from the magnetic susceptibility of the Meissner-London state
measured using a tunnel-diode resonator technique. Whereas $H_{c2}(T)$ and the
normal-state $\rho(T)$ are practically identical for all three magnetic field
orientations, the London penetration depth shows significant unidirectional
anisotropy. The low-temperature $\lambda(T)$ is exponentially attenuated when a
small excitation radiofrequency magnetic field, $H_{rf}$, is applied along the
$c""-$direction, in which case screening currents flow in the $a""b""-$ plane,
while for the other two orientations, $H_{rf}\parallel a""$ and $H_{rf}\parallel
b""$, the London penetration depth shows a much weaker, $\lambda(T)\sim T^{2}$,
variation. Such unusual and contrasting behavior of the two anisotropies,
$\gamma_{H}\left(T\right)=H_{c2,ab}/H_{c2,c}=\xi_{ab}/\xi_{c}$ and
$\gamma_{\lambda}\left(T\right)=\lambda_{c}/\lambda_{ab}$, imposes significant
constraints on the possible order parameter. Although our measurements are
insufficient to derive conclusively the superconducting gap anisotropy,
qualitatively, order parameter with two point nodes and a modulation in the
perpendicular direction is consistent with the experimental observations.",2206.00584v1
2022-06-14,Quantitative assessment of perturbation theory-based lattice thermal conductivity models using quasi-continuum approximation,"The impact of dispersion relations, anisotropy, and Brillouin zone structure
on intrinsic phonon scattering rates has been assessed within the harmonic
approximation-perturbation theory approach for lattice dynamics. Anisotropic
nonlinear elastic continuum has been considered with various levels of
representation of phonon dispersion and Brillouin zone shape, and with
Gr\""uneisen parameter used as an average measure of crystal anharmonicity. In
addition, thermal conductivity prediction of different models for the treatment
of the off-diagonal elements of phonon collision operator are compared. For a
model system, argon, with a relatively high anisotropy ratio, the results show
that accounting for anisotropy is critical for accurate determination of
available phase space for 3-phonon scattering and scattering rates. Moreover,
widely spread approximations such as isotropic continuum and Single Mode
Relaxation Time are found unreliable, even for cubic systems. The success of
these approximations is demonstrated to be a direct result of error
cancellations. By benchmarking against our iterative solution of Boltzmann
Transport Equation, which achieves excellent agreement with experimental
thermal conductivity data for solid argon (2-80 K), we show the essential
importance of considering coupling terms of phonon scattering kernel at phonon
mode level, and not in a statistical average sense as, for example, Callaway
model does. Moreover, our results manifest the role played by coherent phonon
scattering near the melting temperature, in agreement with molecular dynamics
findings, which serves as an evidence for the crossover between heat diffusion
mediated by particle-like phonons (incoherent scattering) and wave-like heat
propagation due to phonon coherent scattering. Furthermore, sensitivity of
conductivity prediction to phonon spectrum is revealed to change over
temperature.",2206.06634v1
2022-07-05,"Prediction of High Curie Temperature, Large Magnetic Crystal Anisotropy in 2D Ferromagnetic Co$_2$Ge$_2$Te$_6$ Monolayer and Multilayer","The Co$_2$Ge$_2$Te$_6$ shows intrinsic ferromagnetic (FM) order, which
origins from superexchange interaction between Co and Te atoms, with higher
Curie temperature ($T_c$) of 161 K. Co$_2$Ge$_2$Te$_6$ monolayer (ML) is
half-metal (HM), and spin-$\beta$ electron is a semiconductor with gap of 1.311
eV. Co$_2$Ge$_2$Te$_6$ ML tends in-plane anisotropy (IPA), with magnetic
anisotropy energy (MAE) of -10.2 meV/f.u.. Co$_2$Ge$_2$Te$_6$ ML shows good
dynamical and thermal stability. Most interestingly, bilayers present
ferromagnetic half-metallicity independent of the stacking orders. Notley, the
multilayers ($N\ge 6$) present ferromagnetic HM, while the magnetoelectronic
properties are related with the stacking patterns in thinner multilayers.
Moreover, the magnetoelectronic properties are dependent on the stacking orders
of bulk. The magnetic order with multilayers is determined by the super-super
exchange and weak van der Waals (vdW) interaction. Co$_2$Ge$_2$Te$_6$ with
intrinsic ferromagnetism, good stability of ferromagnetism and half-metallicity
could help researchers to investigate its wide application in the spintronics.",2207.02024v1
2022-07-15,The magnetic dynamics of NiPS$_3$,"Neutron spectroscopy measurements have been performed on single crystals of
the antiferromagnetic van der Waals compound NiPS$_3$. Linear spin wave theory
using a Heisenberg Hamiltonian with single-ion anisotropies has been applied to
determine the magnetic exchange parameters and the nature of the anisotropy.
The analysis reveals that NiPS$_3$ is less two-dimensional than its sister
compounds, with a relatively large ferromagnetic exchange of $J^{\prime} =
-0.3$ meV between the layered \emph{ab} planes. In-plane magnetic exchange
interactions up to the third nearest-neighbour were required to fit the data.
The nearest-neighbour exchange was ferromagnetic with $J_1 = -2.6$ meV, the
second neighbour was antiferromagnetic and small with $J_2 = 0.2$ meV, and the
dominant antiferromagnetic third neighbour exchange was $J_3 = 13.5$ meV. The
anisotropy was shown to be largely XY-like with a small uniaxial component,
leading to the appearance of two low-energy spin wave modes in the spin wave
spectrum at the Brillouin zone centre. The analysis could reproduce the spin
wave energies, however there are discrepancies with the calculated neutron
intensities hinting at more exotic phenomena.",2207.07448v2
2022-07-27,p x n-Type Transverse Thermoelectrics in a Type-II Weyl Semimetal TaIrTe4,"p x n-type materials refer to materials with a p-type Seebeck coefficient in
one direction and a n-type coefficient in the orthogonal direction. This type
of materials allows for a transverse thermoelectric response, which is highly
desirable for energy applications. Here, we report the observation of p x
n-type behavior in TaIrTe4, a type-II Weyl semimetal, with an in-plane
thermopower anisotropy S$_{xx}$-S$_{yy}$ reaches a maximum value 40${\mu}$V/K
at 200K. Intriguingly. we found that such a p x n-type behavior is absent in
the similar compound NbIrTe4. The presence and absence of p x n-type behavior
in these two materials are consistent with density functional theory
calculations, which further predict that the thermopower anisotropy in both
compounds can be enhanced up to 130${\mu}$V/K by electron doping. Such a strong
thermopower anisotropy originates from the presence of both p-type and n-type
carriers, each with high mobility in one direction. These results suggest that
although type-II Weyl semimetal phase does not guarantee the existence of p x
n-type behavior, its unique band structure provides the ingredient to engineer
and optimize this phenomenon.",2207.13687v1
2022-07-28,Model form uncertainty quantification of Reynolds-averaged Navier-Stokes modeling of flows over a SD7003 airfoil,"It is well known that the Boussinesq turbulent viscosity hypothesis can yield
inaccurate predictions when complex f low features are involved, e.g.
laminar-turbulent transition. The focus of the study is to explore the
capability of a physics-based uncertainty quantification (UQ) approach to
quantify the model-form uncertainty in Reynolds-averaged Naiver-Stokes (RANS)
simulations of laminar-turbulent transitional flows over an Selig-Donovan (SD)
7003 airfoil. This methodology perturbs the modeled Reynolds stress tensor in
the momentum equations; perturbations are injected into the amplitude,
eigenvalues and eigenvectors of the anisotropy Reynolds stress tensor undergone
an eigen-decomposition. In this study, our analyses focus upon the amplitude
perturbation. We observed a monotonic behavior of the magnitude of the
predicted uncertainty bounds for different quantities of interest. High-order
regressions based on the turbulence kinetic energy discrepancies are used to
develop a novel switch marker function Mk to introduce perturbations in a
non-uniform manner over different regions of the domain based upon prior
knowledge of the limitations of the model. Importantly, the compound effect of
Mk and eigenvalue perturbations show a synergy behavior, e.g., dramatically
increased uncertainty bounds to account for the discrepancy in the RANS
prediction; and the Mk function effectively avoids over-perturbation to the
amplitude of the anisotropy Reynolds stress tensor. In this context, regression
based amplitude perturbation of the anisotropy Reynolds stress tensor makes a
new contribution to the RANS UQ methodology in the simulations of the airfoil
transitional flows, which shows very encouraging results.",2207.14376v1
2022-08-01,Hot spots along the Fermi contour of high-$T_c$ cuprates analyzed by $s$-$d$ exchange interaction,"We perform a thorough theoretical study of the electron properties of a
generic CuO$_2$ plane in the framework of Shubin-Kondo-Zener $s$-$d$ exchange
interaction that simultaneously describes the correlation between $T_c$ and the
Cu4$s$ energy. To this end, we apply the Pokrovsky theory [J. Exp. Theor. Phys.
13, 447-450 (1961)] for anisotropic gap BCS superconductors. It takes into
account the thermodynamic fluctuations of the electric field in the dielectric
direction perpendicular to the conducting layers. We microscopically derive a
multiplicatively separable kernel able to describe the scattering rate in the
momentum space, as well as the superconducting gap anisotropy within the BCS
theory. These findings may be traced back to the fact that both the Fermi
liquid and the BCS reductions lead to one and the same reduced Hamiltonian
involving a separable interaction, such that a strong electron scattering
corresponds to a strong superconducting gap and vice versa. Moreover, the
superconducting gap and the scattering rate vanish simultaneously along the
diagonals of the Brillouin zone. We would like to stress that our theoretical
study reproduces the phenomenological analysis of other authors aiming at
describing Angle Resolved Photoemission Spectroscopy measurements. Within
standard approximations one and the same $s$-$d$ exchange Hamiltonian describes
gap anisotropy of the superconducting phase and the anisotropy of scattering
rate of charge carriers in the normal phase.",2208.00936v1
2022-08-08,Study of Asymmetric Magnetization Reversal and Exchange Bias in FePt(L10)/FeCo/CoO/FeCo Magnetic Multilayer,"The effect of the saturation field on the magnetization reversal of
FePt(L10)/FeCo/CoO/FeCo multilayer (ML) has been investigated to understand the
origin of asymmetric magnetization reversal and its correlation with exchange
bias (EB). In the ML structure, the bottom FeCo layer is coupled to the hard
FePt(L10) layer, and the top FeCo layer is comparatively free due to the
relatively more distance from it. The ML has been deposited under UHV
conditions and characterized at each stage of growth using magneto-optical Kerr
effect and x-ray reflectivity techniques. Magnetization reversal is further
studied through domain imaging using the Kerr microscopy technique. The
experimental findings reveal that ML exhibits asymmetrical magnetization
reversal for a certain range of azimuthal angles for both 1.5kOe and 50kOe
saturation fields; however, this angular range of asymmetry decreases with the
increase in the saturation field. Furthermore, EB was absent at the low
saturation field, whereas, EB, in addition to asymmetry, is observed at the
large saturation field. The origin of asymmetry is attributed to
non-collinearity between magnetic anisotropy axes of both FeCo layers. It
results from the proximity effect through short-range Heisenberg exchange
interaction via the CoO barrier layer. On the other hand, EB arises due to
unidirectional anisotropy induced in the FePt layer due to the high saturation
field. It is further proposed that asymmetry would disappear when
unidirectional anisotropy is strong enough to align both the FeCo layers in the
saturation direction leading to loss of the non-collinearity between them.",2208.04038v1
2022-08-25,Biases to primordial non-Gaussianity measurements from CMB secondary anisotropies,"Our view of the last-scattering surface in the cosmic microwave background
(CMB) is obscured by secondary anisotropies, sourced by scattering,
extragalactic emission and gravitational processes between recombination and
observation. Whilst it is established that non-Gaussianity from the correlation
between the integrated-Sachs-Wolfe (ISW) effect and gravitational lensing can
significantly bias primordial non-Gaussianity (PNG) searches, recent work by
Hill (2018) has suggested that other combinations of secondary anisotropies can
also produce significant biases. Building on that work, we use the WebSky and
Sehgal et al.(2010) simulations to perform an extensive examination of possible
biases to PNG measurements for the local, equilateral and orthogonal shapes.
For a Planck-like CMB experiment, without foreground cleaning, we find
significant biases from cosmic infrared background (CIB)-lensing and thermal
Sunyaev-Zel'dovich (tSZ)-lensing bispectra for the local and orthogonal
templates, and from CIB and tSZ bispectra for the equilateral template. For
future experiments, such as the Simons Observatory, biases from correlations
between the ISW effect and the tSZ and CIB will also become important. Finally
we investigate whether foreground-cleaning techniques are able to suppress
these biases sufficiently. We find that the majority of these biases are
effectively suppressed by the internal-linear-combination method and the total
bias to Planck-like and SO-like experiments is less than the $1\,\sigma$
statistical error. However, the small total bias arises from the cancellation
of several $1\,\sigma$ biases for Planck-like experiments and $2\,\sigma$
biases for SO-like. As this cancellation is likely sensitive to the precise
modelling, to ensure robustness against these biases explicit removal methods
should be used, likely at the cost of decreased constraining power.",2208.12270v1
2022-08-30,A study of Dipolar Signal in distant Quasars with various observables,"We study the signal of anisotropy in AGNs/quasars of CatWISE2020 catalogue
using different observables. It has been reported earlier that this data shows
a strong signal of dipole anisotropy in the source number counts. We test this
claim using two independent data analysis procedures and find our number count
dipole consistent with the earlier results. In addition to number counts, we
test for the anisotropy signal in two other observables -- mean spectral index
$\bar{\alpha}$ and mean flux density $\bar{B}$. We find a dipole signal of
considerable strength both in the mean spectral index and the mean flux
density. The dipole in mean flux density points towards the galactic center and
becomes very weak after imposing a flux cut to remove sources with flux greater
than 1 mJy. This can be attributed to the presence of some bright sources. The
signal in mean spectral index, however, is relatively stable as a function of
both flux and galactic cuts. The dipole in this observable points roughly
opposite to the galactic center and hence most likely arises due to galactic
bias. Hence, the signal in both the mean spectral index and mean flux density
appears to be consistent with isotropy.",2208.14397v1
2022-09-13,Investigating the role of partonic and hadronic dynamics in mass splitting of elliptic anisotropy in p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV,"The mass ordering of $v_{2}^{hadron}$ is regarded as one of the key
signatures of collective behaviour in ultra relativistic heavy ion collisions.
This observation has been found to be in compliance with the hydrodynamical
response of a strongly interacting system to the initial spatial anisotropy.
Flow co-efficients measured with identified particles in p-Pb/d-Au collisions
have shown similar mass-splitting of $v_{2}^{hadron}$ indicating towards the
presence of collective dynamics in small collision systems. Arguably, small
size in the overlap geometry of such colliding systems may not be suitable for
hydrodynamical treatment that demands an early thermalization. Studies based on
a multi phase transport model suggests that elliptic or triangular anisotropy
is primarily due to escape mechanism of partons rather than hydro like
collectivity and mass ordering of $v_{2}^{hadron}$ can be generated from
coalescence dynamics as implemented in string melting version of AMPT even when
parton azimuthal directions are randomized. In this work, studies have been
performed on p-Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV using AMPT model
which has been found to explain the elliptic and traingular flow in such a
system where escape mechanism is the dominant source of flow generation. We
report that the mass splitting of $v_{2}^{hadron}$ can originate independently
both at the partonic and hadronic level in the string melting version of the
AMPT model.",2209.06166v1
2022-09-16,Probing the Galactic halo with RR Lyrae stars $-$ III. The chemical and kinematic properties of the stellar halo,"Based on a large spectroscopic sample of $\sim$ 4,300 RR Lyrae stars with
metallicity, systemic radial velocity and distance measurements, we present a
detailed analysis of the chemical and kinematic properties of the Galactic
halo. Using this sample, the metallicity distribution function (MDF) as a
function of $r$ and the velocity anisotropy parameter $\beta$ profiles (for
different metallicity populations) are derived for the stellar halo. Both the
chemical and kinematic results suggest that the Galactic halo is composed of
two distinct parts, the inner halo and outer halo. The cutoff radius ($\sim$ 30
kpc) is similar to the previous break radius found in the density distribution
of the stellar halo. We find that the inner part is dominated by a metal-rich
population with extremely radial anisotropy ($\beta \sim 0.9$). These features
are in accordance with those of ``{\it Gaia}-Enceladus-Sausage'' (GES) and we
attribute this inner halo component as being dominantly composed of stars
deposited from this ancient merged satellite. We find that GES probably has a
slightly negative metallicity gradient. The metal-poor populations in the inner
halo are characterized as a long-tail in MDF with an anisotropy of $\beta \sim
0.5$, which is similar to that of the outer part. The MDF for the outer halo is
very broad with several weak peaks and the value of $\beta$ is around 0.5 for
all metallicities.",2209.07885v1
2022-10-11,Wave-optics limit of the stochastic gravitational wave background,"The stochastic gravitational wave background (SGWB) is a rich resource of
cosmological information, encoded both in its source statistics and
anisotropies induced by propagation effects. We provide a theoretical
description of it, without employing theoretical tools which rely on the
geometric optics limit. Our formalism is based on the so-called {\it classical
matter approximation} and it is able to capture wave-optics effects, such as
interference and diffraction. We show that the interaction between the
gravitational waves and the cosmic structures along the line-of-sight produce
observable scalar and vector polarization modes, on top of modulating the
tensorial ones. We build the two point correlation function describing the
statistics of the SGWB, and introduce the intensity and gravitational Stokes
parameters for all its components. In the case of an unpolarized, Gaussian and
statistically homogeneous SGWB, we show that the interaction with matter
modulates its intensity and does not generate a net difference between left-
and right- helicity tensor and vector modes, as expected. We demonstrate that,
in order to produce $Q_T$- and $U_T$- tensor polarization modes the background
must posses an hexadecapole anisotropy, while a quandrupole anisotropy can
source the vector $Q_V$- and $U_V$- Stokes parameters.",2210.05718v2
2022-10-15,Azimuthal anisotropy of dijet events in PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV,"The path-length dependent parton energy loss within the dense partonic medium
created in lead-lead collisions at a nucleon-nucleon center-of-mass energy of
$\sqrt{s_\mathrm{NN}}$ = 5.02 TeV is studied by determining the azimuthal
anisotropies for dijets with high transverse momentum. The data were collected
by the CMS experiment in 2018 and correspond to an integrated luminosity of
1.69 nb$^{-1}$. For events containing back-to-back jets, correlations in
relative azimuthal angle and pseudorapidity ($\eta$) between jets and hadrons,
and between two hadrons, are constructed. The anisotropies are expressed as the
Fourier expansion coefficients $v_n$, $n = $ 2-4 of these azimuthal
distributions. The dijet $v_n$ values are extracted from long-range (1.5 $\lt$
$\vert\Delta\eta\vert$ $\lt$ 2.5) components of these correlations, which
suppresses the background contributions from jet fragmentation processes.
Positive dijet $v_2$ values are observed which increase from central to more
peripheral events, while the $v_3$ and $v_4$ values are consistent with zero
within experimental uncertainties.",2210.08325v2
2022-10-18,In-plane electronic anisotropy revealed by interlayer resistivity measurements on the iron-based superconductor parent compound CaFeAsF,"Both cuprates and iron-based superconductors demonstrate nematicity, defined
as the spontaneous breaking of rotational symmetry in electron systems. The
nematic state can play a role in the high-transition-temperature
superconductivity of these compounds. However, the microscopic mechanism
responsible for the transport anisotropy in iron-based compounds remains
debatable. Here, we investigate the electronic anisotropy of CaFeAsF by
measuring its interlayer resistivity under magnetic fields with varying field
directions. Counterintuitively, the interlayer resistivity was larger in the
longitudinal configuration ($B \parallel I \parallel c$) than in the transverse
one ($B \perp I \parallel c$). The interlayer resistivity exhibited a so-called
coherence peak under in-plane fields and was highly anisotropic with respect to
the in-plane field direction. At $T$ = 4 K and $B$ = 14 T, the
magnetoresistance $\Delta\rho/\rho_0$ was seven times larger in the $B
\parallel b_o$ than in the $B \parallel a_o$ configuration. Our theoretical
calculations of the conductivity based on the first-principles electronic band
structure qualitatively reproduced the above observations but underestimated
the magnitudes of the observed features. The proposed methodology can be a
powerful tool for probing the nematic electronic state in various materials.",2210.09533v2
2022-10-24,Studying the properties of compressible MHD turbulence by synchrotron fluctuation statistics,"We study the observable properties of compressible MHD turbulence covering
different turbulence regimes, based on synthetic synchrotron observations
arising from 3D MHD numerical simulations. Using the synchrotron emissivity and
intensity, we first explore how the cosmic ray spectral indices affect the
measurements of turbulence properties by employing normalized correlation
functions. We then study how the anisotropy of synchrotron total and
polarization intensities arising from three fundamental MHD modes vary with the
viewing angle, i.e., the angle between the mean magnetic field and the line of
sight. We employ the ratio of quadrupole moment to the monopole one (QM) for
this purpose. Our numerical results demonstrate that: (1) the two-point
correlation function of synchrotron statistics for the arbitrary cosmic ray
spectral index is related to the special case of magnetic field index
$\gamma=2$ in agreement with the analytical formulae provided by Lazarian \&
Pogosyan (2012); (2) the anisotropy of synchrotron total and polarization
intensities arising from Alfv\'en and slow modes increases with the increase of
the viewing angle, while that of fast mode remains almost unchanged with the
viewing angle; (3) the analytical formulae of synchrotron intensities for
studying turbulence can be applied to describing statistics of polarization
intensities, and the QM can be successfully used to recover turbulence
anisotropy. This study validates Lazarian \& Pogosyan's analytical approach and
opens a way to study turbulence from observations.",2210.13615v1
2022-10-30,Synchrotron Firehose Instability,"We demonstrate using linear theory and particle-in-cell (PIC) simulations
that a synchrotron-cooling collisionless plasma acquires pressure anisotropy
and, if the plasma beta is sufficiently high, becomes unstable to the firehose
instability, in a process that we dub the synchrotron firehose instability
(SFHI). The SFHI channels free energy from the pressure anisotropy of the
radiating, relativistic electrons (and/or positrons) into small-amplitude,
kinetic-scale magnetic-field fluctuations, which pitch-angle scatter the
particles and bring the plasma to a near-thermal state of marginal instability.
The PIC simulations reveal a nonlinear cyclic evolution of firehose bursts
interspersed by periods of stable cooling. We compare the SFHI for
electron-positron and electron-ion plasmas. As a byproduct of the growing
electron-firehose magnetic field fluctuations, magnetized ions gain a pressure
anisotropy opposite to that of the electrons. If these ions are
relativistically hot, we find that they also experience cooling due to
collisionless thermal coupling with the electrons, which we argue is mediated
by a secondary ion-cyclotron instability. We suggest that the SFHI may be
activated in a number of astrophysical scenarios, such as within ejecta from
black-hole accretion flows and relativistic jets, where the redistribution of
energetic electrons from low to high pitch angles may cause transient bursts of
radiation.",2210.16891v1
2022-11-07,Anisotropic gravitational waves induced by hypermagnetic fields during the electroweak phase transition epoch,"We study the anisotropies of gravitational waves induced by weak
hypermagnetic fields which are randomly distributed and oriented during the
electroweak phase transition in the early universe. The theory setup of this
study is the standard model plus a real singlet scalar field, which can produce
the needed strongly first order electroweak phase transition. Then we
investigate how the hypermagnetic fields can convert to magnetic fields and we
compute the departure of energy difference between the symmetric phase and the
broken phase when the magnetic fields are turned on. It is found that the
presence of the hypermagnetic fields can increase the Euclidean action, thus
can decrease nucleation temperature, which can lead to a supercool plasma. We
point out that the hypermagnetic field can enhance the gravitational wave
production from a first order electroweak phase transition and the
inhomogeneity of primordial hypermagnetic field can lead to anisotropies of
gravitational waves. By examining three well-motivated distribution of
hypermagnetic fields, we calculate the corresponding angular power spectra of
stochastic gravitational wave background and find they can be significantly
larger than the contributions of the Sachs-Wolfe effects and integrated
Sachs-Wolfe effects. Our results show that the anisotropies of gravitational
wave could provide a novel probe to the primordial hypermagnetic field in the
electroweak phase transition epoch.",2211.03368v2
2022-11-18,Model-independent search for anisotropies in stochastic gravitational-wave backgrounds and application to LIGO-Virgo's first three observing Runs,"A stochastic gravitational-wave (GW) background consists of a large number of
weak, independent and uncorrelated events of astrophysical or cosmological
origin. The GW power on the sky is assumed to contain anisotropies on top of an
isotropic component, i.e., the angular monopole. Complementary to the
LIGO--Virgo--KAGRA (LVK) searches, we develop an efficient analysis pipeline to
compute the maximum-likelihood anisotropic sky maps in stochastic backgrounds
directly in the sky pixel domain using data folded over one sidereal day. We
invert the full pixel-pixel correlation matrix in map-making of the GW sky, up
to an optimal eigenmode cutoff decided systematically using simulations. In
addition to modeled mapping, we implement a model-independent method to probe
spectral shapes of stochastic backgrounds. Using data from LIGO--Virgo's first
three observing runs, we obtain upper limits on anisotropies as well as the
isotropic monopole as a limiting case, consistent with the LVK results. We also
set constraints on the spectral shape of the stochastic background using this
novel model-independent method.",2211.10010v3
2022-11-30,CMB temperature trispectrum from accreting primordial black holes,"It is known that Primordial Black Holes (PBHs) can leave an imprint on Cosmic
Microwave Background (CMB) anisotropy power spectra, due to their
accretion-powered injection of energy into the recombining plasma. Here we
study a qualitatively new CMB observable sourced by accreting PBHs: the
temperature trispectrum or connected 4-point function. This non-Gaussian
signature is due to the strong spatial modulation of the PBH accretion
luminosity, thus ionization perturbations, by large-scale supersonic relative
velocities between PBHs and the accreted baryons. We first derive a
factorizable quadratic transfer function for free-electron fraction
inhomogeneities induced by accreting PBHs. We then compute the perturbation to
the CMB temperature anisotropy due to a general modification of recombination,
and apply our results to accreting PBHs. We calculate a new contribution to the
temperature power spectrum due to the spatial fluctuations of the ionization
perturbation induced by accreting PBHs, going beyond past studies which only
accounted for its homogeneous part. While these contributions are formally
comparable, we find the new part to be subdominant, due to the poor correlation
of the perturbed temperature field with the standard CMB anisotropy. For the
first time, we compute the temperature trispectrum due to accreting PBHs. This
trispectrum is weakly correlated with the local-type primordial non-Gaussianity
trispectrum, hence constraints on the latter do not lead to competitive bounds
on accreting PBHs. We also forecast Planck's sensitivity to the temperature
trispectrum sourced by accreting PBHs. Excitingly, we find it to be more
sensitive to PBHs under $\sim 10^3 M_{\odot}$ than current temperature-only
power spectrum constraints. This result motivates our future work extending
this study to temperature and polarization trispectra induced by
inhomogeneously-accreting PBHs.",2212.00075v1
2022-12-07,Effects of surfactants on bubble-induced turbulence,"We use experiments to explore the effect of surfactants on bubble-induced
turbulence (BIT) at different scales, considering how the bubbles affect the
flow kinetic energy, anisotropy and extreme events. To this end,
high-resolution Particle Shadow Velocimetry measurements are carried out in a
bubble column in which the flow is generated by bubble swarms rising in water
for two different bubble diameters ($3$ mm $\&$ $4$ mm) and moderate gas volume
fractions ($0.5\%\sim1.3\%$). To contaminate the flow, different amounts of
1-Pentanol were added to the flow, leading to different bubble shapes and
surface boundary conditions. The results reveal that with increasing surfactant
concentration, the BIT generated increases in strength, even though bubbles of
a given size rise more slowly with surfactants. We also find that the level of
anisotropy in the flow is enhanced with increasing surfactant concentration for
bubbles of the same size, and that for the same surfactant concentration,
smaller bubbles generate stronger anisotropy in the flow. Concerning the
intermittency quantified by the normalized probability density functions of the
fluid velocity increments, our results indicate that extreme values in the
velocity increments become more probable with decreasing surfactant
concentration for cases with smaller bubbles and low gas void fraction, while
the effect of the surfactant is much weaker for cases with larger bubble and
higher void fractions.",2212.03620v1
2022-12-08,Detection of Dipole Modulation in CMB Temperature Anisotropy Maps from WMAP and Planck using Artificial Intelligence,"Breakdown of rotational invariance of the primordial power spectrum manifests
in the statistical anisotropy of the observed Cosmic Microwave Background (CMB)
radiation. Hemispherical power asymmetry in the CMB may be caused due to a
dipolar modulation, indicating the presence of a preferred direction.
Appropriately re-scaled local variance maps of the CMB temperature anisotropy
data effectively encapsulate this dipolar pattern. As a first-of-its-kind
method, we train Artificial Neural Networks (ANNs) with such local variances as
input features to distinguish statistically isotropic CMB maps from dipole
modulated ones. Our trained ANNs are able to predict components of the
amplitude times the unit vector of the preferred direction for mixed sets of
modulated and unmodulated maps, with goodness of fit ($R^2$) scores $>0.97$ for
full sky, and $>0.96$ for partial sky coverage. On all observed
foreground-cleaned CMB maps, the ANNs detect the dipolar modulation signal with
overall consistent values of amplitudes and directions. This detection is
significant at $97.21\%-99.38\%$ C.L. for all full sky maps, and at
$98.34\%-100\%$ C.L. for all partial sky maps. Robustness of the signal holds
across full and partial skies, various foreground cleaning methods, inpainting
algorithms, instruments and all the different periods of observation for Planck
and WMAP satellites. The significant and robust detection of the signal, in
addition to the consistency of values of amplitude and directions, as found
independent of any pre-existing methods, further mitigates the criticisms of
look-elsewhere effects and a posteriori inferences for the preferred dipole
direction in the CMB.",2212.04438v2
2022-12-19,Anisotropic correlation functions as tracers of central galaxy alignments in simulations,"Motivated by observational results, we use IllustrisTNG hydrodynamical
numerical simulations to study the alignment of the central galaxies in groups
with the surrounding structures. This approach allows us to analyse galaxy and
group properties not available in observations. To perform this analysis, we
use a modified version of the two-point cross-correlation function and a
measure of the angle between the semi-major axes of the central galaxies and
the larger structures. Overall, our results reproduce observational ones, as we
find large-scale anisotropy, which is dominated by the red central galaxies. In
addition, the latter is noticeably more aligned with their group than the blue
ones. In contrast to the observations, we find a strong dependence of the
anisotropy on the central galaxy with mass, probably associated with the
inability of observational methods to determine them. This result allows us to
link the alignment to the process of halo assembly and the well-known
dependence of halo anisotropy on mass. When we include the dark matter
distribution in our analysis, we conclude that the galaxy alignment found in
simulations (and observations) can be explained by a combination of physical
processes at different scales: the central galaxy aligns with the dark matter
halo it inhabits, and this, in turn, aligns with the surrounding structures at
large scales.",2212.09781v2
2022-12-21,Adiabatic preparation of fractional Chern insulators from an effective thin-torus limit,"We explore the quasi one-dimensional (thin torus, or TT) limit of fractional
Chern insulators (FCIs) as a starting point for their adiabatic preparation in
quantum simulators. Our approach is based on tuning the hopping amplitude in
one direction as an experimentally amenable knob to dynamically change the
effective aspect ratio of the system. Similar to the TT limit of fractional
quantum Hall (FQH) systems in the continuum, we find that the hopping-induced
TT limit adiabatically connects the FCI state to a trivial charge density wave
(CDW) ground state. This adiabatic path may be harnessed for state preparation
schemes relying on the initialization of a CDW state followed by the adiabatic
decrease of a hopping anisotropy. Our findings are based on the calculation of
the excitation gap in a number of FCI models, both on a lattice and consisting
of coupled wires. By analytical calculation of the gap in the limit of strongly
anisotropic hopping, we show that its scaling is compatible with the
preparation of large size FCIs for sufficiently large hopping anisotropy. Our
numerical simulations in the framework of exact diagonalization explore the
full anisotropy range to corroborate these results.",2212.11294v2
2022-12-20,Anisotropic electron transport in the nuclear pasta phase,"The presence of nuclear pasta is expected to modify the transport properties
in the mantle of neutron stars. The non-spherical geometry of the pasta nuclear
clusters leads to anisotropies in the collision frequencies, impacting the
thermal and electrical conductivity. We derive analytical expressions for the
anisotropic collision frequencies using the Boltzmann equation in the
relaxation time approximation. The average parallel, perpendicular and Hall
electrical conductivities are computed in the high-temperature regime above
crustal melting, considering incoherent elastic electron-pasta scattering and
randomly oriented pasta structures. Numerical values are obtained at different
densities and temperatures by using the IUFSU parametrization of the non-linear
Walecka model to determine the crustal structure. We find that the anisotropy
of the collision frequencies grows with the length of the pasta structures and,
independently of the magnetic field, the presence of rod and slab phases
decreases the conductivity by more than one order of magnitude. Our numerical
results indicate that, even if the pasta structures might survive above the
crustal melting point, no strong anisotropies are to be expected in the
conduction properties in this temperature regime, even in the presence of a
very high magnetic field.",2212.11817v3
2022-12-30,Selection rules for ultrafast laser excitation and detection of spin correlations dynamics in a cubic antiferromagnet,"Exchange interactions determine the correlations between microscopic spins in
magnetic materials. Probing the dynamics of these spin correlations on
ultrashort length and time scales is, however rather challenging, since it
requires simultaneously high spatial and high temporal resolution. Recent
experimental demonstrations of laser-driven two-magnon modes - zone-edge
excitations in antiferromagnets governed by exchange coupling - posed questions
about the microscopic nature of the observed spin dynamics, the mechanism
underlying its excitation, and their macroscopic manifestation enabling
detection. Here, on the basis of a simple microscopic model, we derive the
selection rules for cubic systems that describe the polarization of pump and
probe pulses required to excite and detect dynamics of nearest-neighbor spin
correlations, and can be employed to isolate such dynamics from other magnetic
excitations and magneto-optical effects. We show that laser-driven spin
correlations contribute to optical anisotropy of the antiferromagnet even in
the absence of spin-orbit coupling. In addition, we highlight the role of
subleading anisotropy in the spin system and demonstrate that the dynamics of
the antiferromagnetic order parameter occurs only in next-to-leading order,
determined by the smallness of the magnetic anisotropy as compared to the
isotropic exchange interactions in the system. We expect that our results will
stimulate and support further studies of magnetic correlations on the shortest
length and time scale.",2212.14698v2
2023-01-07,"Single crystal growths and magnetic properties of hexagonal polar semimetals RAuGe (R = Y, Gd-Tm, and Lu)","We study structural and magnetic properties of rare-earth based semimetals
RAuGe (R = Y, Gd-Tm, and Lu) using flux-grown single crystals. These compounds
belong to the noncentrosymmetric polar space group P63mc. We confirm the
systematic structural evolution at room temperature as a function of ionic
radius of rare earths to clarify the isopointal crossover between two polar
structures: three-dimensional LiGaGe-type and quasi-two-dimensional
NdPtSb-type. Magnetism shows a characteristic anisotropy in reasonable
agreement with the crystal electric field (CEF) theory; the easy-plane-type
anisotropy for R = Tb and Dy turns into the Ising-type anisotropy for R = Er
and Tm. We evaluate the CEF parameters based on the Stevens operators to
reasonably reproduce the temperature dependence of magnetic susceptibilities
and specific heat for RAuGe (R = Tb-Tm). The estimated energy scale of the
Ising gap (~ 11 meV) in TmAuGe is consistent with an excitation observed in an
inelastic neutron scattering experiment. These findings suggest an opportunity
for interplay between conduction electrons and nontrivial spin structures in
the family of magnetic polar semimetals RAuGe.",2301.02794v1
2023-01-09,"Radial pulsations, moment of inertia and tidal deformability of dark energy stars","We construct dark energy stars with Chaplygin-type equation of state (EoS) in
the presence of anisotropic pressure within the framework of Einstein gravity.
From the classification established by Iyer et al. [Class. Quantum Grav. 2, 219
(1985)], we discuss the possible existence of isotropic dark energy stars as
compact objects. However, there is the possibility of constructing
ultra-compact stars for sufficiently large anisotropies. We investigate the
stellar stability against radial oscillations, and we also determine the moment
of inertia and tidal deformability of these stars. We find that the usual
static criterion for radial stability $dM/d\rho_c >0$ still holds for dark
energy stars since the squared frequency of the fundamental pulsation mode
vanishes at the critical central density corresponding to the maximum-mass
configuration. The dependence of the tidal Love number on the anisotropy
parameter $\alpha$ is also examined. We show that the surface gravitational
redshift, moment of inertia and dimensionless tidal deformability undergo
significant changes due to anisotropic pressure, primarily in the high-mass
region. Furthermore, in light of the detection of gravitational waves GW190814,
we explore the possibility of describing the secondary component of such event
as a stable dark energy star in the presence of anisotropy.",2301.03504v1
2023-01-12,Debiasing Standard Siren Inference of the Hubble Constant with Marginal Neural Ratio Estimation,"Gravitational wave (GW) standard sirens may resolve the Hubble tension,
provided that standard siren inference of $H_0$ is free from systematic biases.
However, standard sirens from binary neutron star (BNS) mergers suffer from two
sources of systematic bias, one arising from the anisotropy of GW emission, and
the other from the anisotropy of electromagnetic (EM) emission from the
kilonova. For an observed sample of BNS mergers, the traditional Bayesian
approach to debiasing involves the direct computation of the detection
likelihood. This is infeasible for large samples of detected BNS merger due to
the high dimensionality of the parameter space governing merger detection. In
this study, we bypass this computation by fitting the Hubble constant to
forward simulations of the observed GW and EM data under a simulation-based
inference (SBI) framework using marginal neural ratio estimation. A key
innovation of our method is the inclusion of BNS mergers which were only
detected in GW, which allows for estimation of the bias introduced by EM
anisotropy. Our method corrects for $\sim$90$\%$ of the bias in the inferred
value of $H_0$ when telescope follow-up observations of BNS mergers have
extensive tiling of the merger localization region, using known telescope
sensitivities and assuming a model of kilonova emission. Our SBI-based method
thus enables a debiased inference of the Hubble constant of BNS mergers,
including both mergers with detected EM counterparts and those without.",2301.05241v1
2023-01-22,Responses of quark-antiquark interaction and heavy quark dynamics to magnetic field,"We study how a magnetic field induced by colliding nuclei influences both
heavy quark (HQ) potential and HQ momentum diffusion coefficients beyond the
lowest Landau level approximation. By means of real-time hard thermal loop
resummed technique combined with dimension two gluon condensate, the effective
gluon propagator describing both perturbative and nonperturbative QCD nature at
finite temperature and magnetic field are obtained. We find that HQ momentum
diffusion coefficients in magnetized QCD medium become anisotropic, and with
increasing temperature, the higher Landau levels become significant, which
leads to the reduction of the anisotropic ratio ($>$ 1) and even overturn the
behavior ($<$ 1) at high temperature. The nonperturbative (perturbative)
contribution of HQ momentum diffusion coefficient in the low (high) temperature
is dominant. And the anisotropy feature of the real part of the potential is
essentially encoded in angular dependent Coulomb coupling and string tension.
Whereas, the imaginary part of the potential from quark-loop in this work
displays a significant anisotropy even though using the angular-independent
Coulomb coupling and string tension. Furthermore, we study the magnetic
response of viscous quark matter, which is manifested in the non-equilibrium
distribution function of (anti-)quark by solving Boltzmann equation within the
relaxation time approximation. We find the anisotropy ratio is almost
insensitive to the magnetized bulk viscosity, although HQ momentum diffusion
coefficient and HQ potential itself have visible changes.",2301.09110v1
2023-02-01,First measurements of periodicities and anisotropies of cosmic ray flux observed with a water-Cherenkov detector at the Marambio Antarctic base,"A new water-Cherenkov radiation detector, located at the Argentine Marambio
Antarctic Base (64.24S-56.62W), has been monitoring the variability of galactic
cosmic ray (GCR) flux since 2019. One of the main aims is to provide
experimental data necessary to study interplanetary transport of GCRs during
transient events at different space/time scales. In this paper we present the
detector and analyze observations made during one full year. After the analysis
and correction of the GCR flux variability due to the atmospheric conditions
(pressure and temperature), a study of the periodicities is performed in order
to analyze modulations due to heliospheric phenomena. We can observe two
periods: (a) 1 day, associated with the Earth's rotation combined with the
spatial anisotropy of the GCR flux; and (b) $\sim$ 30 days due to solar impact
of stable solar structures combined with the rotation of the Sun. From a
superposed epoch analysis, and considering the geomagnetic effects, the mean
diurnal amplitude is $\sim$ 0.08% and the maximum flux is observed in $\sim$ 15
hr local time (LT) direction in the interplanetary space. In such a way, we
determine the capability of Neurus to observe anisotropies and other
interplanetary modulations on the GCR flux arriving at the Earth.",2302.00322v1
2023-02-05,The role of spatial curvature in constraining the Universe anisotropies across a Big Bounce,"We study the implementation of Polymer Quantum Mechanics (PQM) to a system
decomposed into a quasi-classical background and a small quantum subsystem,
according to the original Vilenkin proposal. We develop the whole formalism in
the momentum representation that is the only viable in the continuum limit of
the polymer paradigm and we generalize the fundamental equations of the
original Vilenkin analysis in the considered context. Then, we provide a
Minisuperspace application of the theory, first considering a Bianchi I
cosmology and then extending the analysis to a Bianchi IX model in the limit of
small anisotropies. In both these cases, the quasi-classical background is
identified with an isotropic bouncing Universe whereas the small quantum
subsystem contains the anisotropic degrees of freedom. When the Big Bounce
scenario is considered, we obtain that in the Bianchi I model the anisotropies
standard deviation is regular at $t=0$ but still increases indefinitely,
whereas in the presence of the harmonic Bianchi IX potential such same quantity
is bounded and oscillate around a constant value. As a consequence, we
demonstrate that the picture of a semiclassical isotropic Bounce can be
extended to more general cosmological settings if the spatial curvature becomes
relevant when the anisotropic degrees of freedom are still small quantum
variables.",2302.02469v2
2023-02-24,Dielectric tunability of magnetic properties in orthorhombic ferromagnetic monolayer CrSBr,"Monolayer CrSBr is a recently discovered semiconducting spin-3/2 ferromagnet
with a Curie temperature around 146 K. Unlike many other known two-dimensional
(2D) magnets, CrSBr has an orthorhombic lattice, giving rise, for instance, to
spatial anisotropy of the magnetic excitations within the 2D plane. Theoretical
description of CrSBr within a spin Hamiltonian approach turns out to be
nontrivial due to the triaxial magnetic anisotropy as well as due to magnetic
dipolar interactions, comparable to spin-orbit effects in CrSBr. Here, we
employ a Green's function formalism combined with first-principles calculations
to systematically study the magnetic properties of monolayer CrSBr in different
regimes of surrounding dielectric screening. We find that the magnetic
anisotropy and thermodynamical properties of CrSBr depend significantly on the
Coulomb interaction and its external screening. In the free-standing limit, the
system turns out to be close to an easy-plane magnet, whose long-range ordering
is partially suppressed. On the contrary, in the regime of large external
screening, monolayer CrSBr behaves like an easy-axis ferromagnet with more
stable magnetic ordering. Despite being relatively large, the magnetic dipolar
interactions have only little effect on the magnetic properties. Our findings
suggests that 2D CrSBr is suitable platform for studying the effects of
substrate screening on magnetic ordering in low dimensions.",2302.12672v1
2023-03-08,First-principles study of enhancement of perpendicular magnetic anisotropy obtained by inserting an ultrathin LiF layer at an Fe/MgO interface,"Perpendicular magnetic anisotropy (PMA) is a key property of magnetoresistive
random access memory (MRAM). To increase areal density of MRAM it is important
to find a way to enhance the PMA. Recently a strong enhancement of the PMA by
inserting an ultrathin LiF layer at an Fe/MgO interface was reported [T. Nozaki
et al., NPG Asia Materials (2022) 14: 5]. To understand the origin of the
observed enhancement of the PMA we perform first-principles calculations of
magetocrystalline anisotropy energy (MAE) of the following four kind of
multilayer structures: Fe/MgO, Fe/LiF/MgO, Fe/FeO/MgO, and Fe/FeF/LiF/MgO. We
find that the MAEs of the Fe/LiF/MgO and the Fe/FeF/LiF/MgO structures are
almost the same as that of the Fe/MgO structure, while the MAE of the
Fe/FeO/MgO structure is less than a half of that of the Fe/MgO structure. The
results show that the major origin of the enhancement of the PMA obtained by
inserting an ultrathin LiF layer at an Fe/MgO interface is the suppression of
the mixing of Fe and O atoms at the interface. We also find that the in-plane
Fe-F coupling gives a positive contribution to the MAE while the in-plane Fe-O
coupling gives a negative contribution. The results are useful for designing of
high-PMA materials.",2303.04382v1
2023-03-08,Effect of massive graviton on dark energy star structure,"The presence of massive gravitons in the field of massive gravity is
considered as an important factor in investigating the structure of compact
objects. Hence, we are encouraged to study the dark energy star structure in
the Vegh's massive gravity. We consider that the equation of state governing
the inner spacetime of the star is the extended Chaplygin gas, and then using
this equation of state, we numerically solve the Tolman-Oppenheimer-Volkoff
(TOV) equation in massive gravity. In the following, assuming different values
of free parameters defined in massive gravity, we calculate the properties of
dark energy star such as radial pressure, transverse pressure, anisotropy
parameter, and other characteristics. Then, after obtaining the maximum mass
and its corresponding radius, we compute redshift and compactness. The obtained
results show that for this model of dark energy star, the maximum mass and its
corresponding radius depend on the massive gravity's free parameters and
anisotropy parameter. These results are consistent with the observational data,
and cover the lower mass gap. We also demonstrate that all energy conditions
are satisfied for this model, and in the presence of anisotropy, the dark
energy star is potentially unstable.",2303.04813v2
2023-03-10,Anisotropic LRS-BI Universe with $f(Q)$ gravity theory,"The possible anisotropic nature in the early phases of the Universe is one of
the interesting aspects of study in cosmology. We investigate the evolution of
the Universe in terms of few cosmological parameters considering an anisotropic
locally rotationally symmetric (LRS) Bianchi type-I spacetime (LRS-BI) under
the $f(Q)$ gravity of symmetric teleparallel theory equivalent to the GR
(STEGR). In this study we consider two $f(Q)$ gravity models, viz., $f(Q) =
-\,(Q+2\Lambda)$, a simple model with the cosmological constant $\Lambda$ and
the power law model, $f(Q) = -\, \alpha Q^n$ with two constant parameters
$\alpha$ and $n$. Considering a proportionality relation between the
directional Hubble parameters with a proportionality constant parameter
$\lambda$ we find a significant contribution of the anisotropic factor in the
evolution of the early Universe for both models. The power law model shows the
more dominating effect of anisotropy in comparison to the simple model
depending on model parameters, especially on the parameter $n$. The power law
model also shows some possible effects of anisotropy on the Universe's
evolution in the near future. In addition, both models confirm that the
anisotropy does not obtain any appreciable signature in the current stage of
the Universe. From our analysis we also set rough constraints on our model
parameters as $0.5 \le \lambda \le 1.25$, $0.75 \le \alpha \le 1.5$ and $0.95
\le n \le 1.05$.",2303.05905v1
2023-03-26,The effect of the magnetically dead layer on the magnetization and the magnetic anisotropy of the dextran coated magnetite nanoparticles,"We present a study on the magnetic behavior of dextran-coated magnetite
nanoparticles (DM NPs) with sizes between 3 and 19 nm, synthesized by
hydrothermal-assisted co-precipitation method. The decrease of saturation
magnetization ($M_s$) with decreasing particle size has been modeled by
assuming the existence of a spin-disordered layer at the particle surface,
which is magnetically dead. Based on this core-shell model and taking into
account the weight contribution of the non-magnetic coating layer (dextran) to
the whole magnetization, the dead layer thickness ($t$) and saturation
magnetization $M_s$ of the magnetic cores in our samples were estimated to be
$t = 6.8~\mathrm{\AA}$ and $M_s = 98.8~\mathrm{emu/g}$, respectively. The data
of $M_s$ were analyzed using a law of approach to saturation, indicating an
increase in effective magnetic anisotropy ($K_{eff}$) with decreasing particle
size as expected from the increased surface/volume ratio in small MNPs. The
obtained $K_{eff}$ values were successfully modeled by including an extra
contribution of dipolar interactions due to the formation of chain-like
clusters of MNPs. The surface magnetic anisotropy ($K_s$) was estimated to be
about $K_s = 1.04\times10^5~\mathrm{J/m^3}$. Our method provides a simple and
accurate way to obtain the $M_s$ core values in surface-disordered MNPs, a
relevant parameter required for magnetic modeling in many applications.",2303.14654v1
2023-03-27,Terahertz probing of anisotropic conductivity and morphology of CuMnAs epitaxial thin films,"Antiferromagnetic CuMnAs thin films have attracted attention since the
discovery of the manipulation of their magnetic structure via electrical,
optical, and terahertz pulses of electric fields, enabling convenient
approaches to the switching between magnetoresistive states of the film for the
information storage. However, the magnetic structure and, thus, the efficiency
of the manipulation can be affected by the film morphology and growth defects.
In this study, we investigate the properties of CuMnAs thin films by probing
the defect-related uniaxial anisotropy of electric conductivity by contact-free
terahertz transmission spectroscopy. We show that the terahertz measurements
conveniently detect the conductivity anisotropy, that are consistent with
conventional DC Hall-bar measurements. Moreover, the terahertz technique allows
for considerably finer determination of anisotropy axes and it is less
sensitive to the local film degradation. Thanks to the averaging over a large
detection area, the THz probing also allows for an analysis of strongly
non-uniform thin films. Using scanning near-field terahertz and electron
microscopies, we relate the observed anisotropic conductivity of CuMnAs to the
elongation and orientation of growth defects, which influence the local
microscopic conductivity. We also demonstrate control over the morphology of
defects by using vicinal substrates.",2303.15268v1
2023-03-30,Data-driven approach for modeling Reynolds stress tensor with invariance preservation,"The present study represents a data-driven turbulent model with Galilean
invariance preservation based on machine learning algorithm. The fully
connected neural network (FCNN) and tensor basis neural network (TBNN) [Ling et
al. (2016)] are established. The models are trained based on five kinds of flow
cases with Reynolds Averaged Navier-Stokes (RANS) and high-fidelity data. The
mappings between two invariant sets, mean strain rate tensor and mean rotation
rate tensor as well as additional consideration of invariants of turbulent
kinetic energy gradients, and the Reynolds stress anisotropy tensor are
trained. The prediction of the Reynolds stress anisotropy tensor is treated as
user's defined RANS turbulent model with a modified turbulent kinetic energy
transport equation. The results show that both FCNN and TBNN models can provide
more accurate predictions of the anisotropy tensor and turbulent state in
square duct flow and periodic flow cases compared to the RANS model. The
machine learning based turbulent model with turbulent kinetic energy gradient
related invariants can improve the prediction precision compared with only mean
strain rate tensor and mean rotation rate tensor based models. The TBNN model
is able to predict a better flow velocity profile compared with FCNN model due
to a prior physical knowledge.",2303.17178v2
2023-04-03,Nonrelativistic and nonmagnetic control of terahertz charge currents via electrical anisotropy in RuO2 and IrO2,"Precise and ultrafast control over photo-induced charge currents across
nanoscale interfaces could lead to important applications in energy harvesting,
ultrafast electronics, and coherent terahertz sources. Recent studies have
shown that several relativistic mechanisms, including inverse spin-Hall effect,
inverse Rashba-Edelstein effect and inverse spin-orbit-torque effect, can
convert longitudinally injected spin-polarized currents from magnetic materials
to transverse charge currents, thereby harnessing these currents for terahertz
generation. However, these mechanisms typically require external magnetic
fields and suffer from low spin-polarization rates and low efficiencies of
relativistic spin-to-charge conversion. In this work, we present a novel
nonrelativistic and nonmagnetic mechanism that directly utilizes the
photo-excited high-density charge currents across the interface. We demonstrate
that the electrical anisotropy of conductive oxides RuO2 and IrO2 can
effectively deflect injected charge currents to the transverse direction,
resulting in efficient and broadband terahertz radiation. Importantly, this new
mechanism has the potential to offer much higher conversion efficiency compared
to previous methods, as conductive materials with large electrical anisotropy
are readily available, whereas further increasing the spin-Hall angle of
heavy-metal materials would be challenging. Our new findings offer exciting
possibilities for directly utilizing these photo-excited high-density currents
across metallic interfaces for ultrafast electronics and terahertz
spectroscopy.",2304.00692v1
2023-04-03,Correlated order at the tipping point in the kagome metal CsV$_3$Sb$_5$,"Spontaneously broken symmetries are at the heart of many phenomena of quantum
matter and physics more generally. However, determining the exact symmetries
broken can be challenging due to imperfections such as strain, in particular
when multiple electronic orders form complex interactions. This is exemplified
by charge order in some kagome systems, which are speculated to show nematicity
and flux order from orbital currents. We fabricated highly symmetric samples of
a member of this family, CsV$_3$Sb$_5$, and measured their transport
properties. We find the absence of measurable anisotropy at any temperature in
the unperturbed material, however, a striking in-plane transport anisotropy
appears when either weak magnetic fields or strains are present. A symmetry
analysis indicates that a perpendicular magnetic field can indeed lead to
in-plane anisotropy by inducing a flux order coexisting with more conventional
bond order. Our results provide a unifying picture for the controversial charge
order in kagome metals and highlight the need for microscopic materials control
in the identification of broken symmetries.",2304.00972v1
2023-04-05,Effective model for superconductivity in magic-angle graphene,"We carry out large-scale quantum Monte Carlo simulations of a candidate field
theory for the onset of superconductivity in magic-angle twisted bilayer
graphene. The correlated insulating state at charge neutrality spontaneously
breaks U(1) Moir\'e valley symmetry. Owing to the topological nature of the
bands, skyrmion defects of the order parameter carry charge $2e$ and condense
upon doping. In our calculations we encode the U(1) symmetry by an internal
degree of freedom such that it is not broken upon lattice regularization.
Furthermore, the skyrmion carries the same charge. The nature of the
doping-induced phase transitions depends on the strength of the easy-plane
anisotropy that reduces the SU(2) valley symmetry to U(1) $\times \mathbb{Z}_2
$. For large anisotropy, we observe two distinct transitions separated by phase
coexistence. While the insulator to superconducting transition is of mean-field
character, the U(1) transition is consistent with three-dimensional XY
criticality. Hence, the coupling between the gapless charge excitations of the
superconducting phase and the XY order parameter is irrelevant. At small
anisotropy, we observe a first-order transition characterized by phase
separation.",2304.02428v2
2023-04-25,Role of effective mass anisotropy in realizing a hybrid nodal-line fermion state,"Understanding the role of lattice geometry in shaping topological states and
their properties is of fundamental importance to condensed matter and device
physics. Here we demonstrate how an anisotropic crystal lattice drives a
topological hybrid nodal line in transition metal tetraphosphides $Tm$P$_4$
($Tm$ = Transition metal). $Tm$P$_4$ constitutes a unique class of black
phosphorus materials formed by intercalating transition metal ions between the
phosphorus layers without destroying the characteristic anisotropic band
structure of the black phosphorous. Based on the first-principles calculations
and $k \cdot p$ theory, we show that $Tm$P$_4$ harbor a single hybrid nodal
line formed between oppositely-oriented anisotropic $Tm~d$ and P states
unhinged from the high-symmetry planes. The nodal line consists of both type-I
and type-II nodal band crossings whose nature and location are determined by
the effective-mass anisotropies of the intersecting bands. We further discuss a
possible topological phase transition to exemplify the formation of the hybrid
nodal line state in $Tm$P$_4$. Our results offer a comprehensive study for
understanding the interplay between structural motifs-driven mass anisotropies
and topology in anisotropic lattice materials to realize hybrid semimetal
states.",2304.13086v3
2023-04-28,"Noncollinear magnetic order, in-plane anisotropy, and magnetoelectric coupling in a pyroelectric honeycomb antiferromagnet Ni$_{2}$Mo$_{3}$O$_{8}$","Ni$_{2}$Mo$_{3}$O$_{8}$ is a pyroelectric honeycomb antiferromagnet
exhibiting peculiar changes of its electric polarization at magnetic
transitions. Ni$_{2}$Mo$_{3}$O$_{8}$ stands out from the isostructural magnetic
compounds, showing an anomalously low magnetic transition temperature and
unique magnetic anisotropy. We determine the magnetic structure of
Ni$_{2}$Mo$_{3}$O$_{8}$ utilizing high-resolution powder and single-crystal
neutron diffraction. A noncollinear stripy antiferromagnetic order is found in
the honeycomb planes. The magnetic space group is \textit{P$_C$na}2$_1$. The
in-plane magnetic connection is of the stripy type both for the $ab$-plane and
the $c$-axis spin components. This is a simpler connection than the one
proposed previously. The ferromagnetic interlayer order of the $c$-axis spin
components in our model is also distinct. The magnetic anisotropy of
Ni$_{2}$Mo$_{3}$O$_{8}$ is characterized by orientation-dependent magnetic
susceptibility measurements on a single crystal, consistent with neutron
diffraction analysis. The local magnetoelectric tensor analysis using our
magnetic models provides new insights into its magnetoelectric coupling and
polarization. Thus, our results deliver essential information for understanding
both the unusual magnetoelectric properties of Ni$_{2}$Mo$_{3}$O$_{8}$ and the
prospects for observation of exotic nonreciprocal, Hall, and magnonic effects
characteristic to this compound family.",2304.14641v2
2023-04-29,"Structural, electronic, and magnetic properties of CrTe2","Two-dimensional chromium ditelluride (CrTe2) is a promising ferromagnetic
layered material that exhibits long-range ferromagnetic ordering in the
monolayer limit. The formation energies of the different possible structural
phases (1T, 1H, 2H) calculated from density functional theory (DFT) show that
the 1T phase is the ground state, and the energetic transition barriers between
the phases, calculated by the nudged elastic band method, are large, on the
order of 0.5 eV. The self-consistent Hubbard $U$ correction parameters are
calculated for all the phases of CrTe$_2$. The calculated magnetic moment of
1T-CrTe$_2$ with $\geq 2$ layers lies in the plane, whereas the magnetic moment
of a monolayer is out-of-plane. Band filling and tensile bi-axial strain cause
the magnetic moment of a monolayer to switch from out-of-plane to in-plane, and
compressive bi-axial strain in a bilayer causes the magnetic moment to switch
from in-plane to out-of-plane. The magnetic anisotropy is shown to originate
from the large spin orbit coupling (SOC) of the Te atoms and the anisotropy of
the exchange coupling constants $J_{xy}$ and $J_z$ in an XXZ type Hamiltonian.
Renormalized spin wave theory using experimental values for the magnetic
anisotropy energy and Curie temperatures provides a range of values for the
nearest neighbor exchange coupling.",2305.00168v1
2023-05-27,A 3D Numerical Study of Anisotropies in Supernova Remnants,"We develop a suite of 3D hydrodynamic models of supernova remnants (SNRs)
expanding against the circumstellar medium (CSM). We study the Rayleigh-Taylor
Instability (RTI) forming at the expansion interface by calculating an angular
power spectrum for each of these models. The power spectra of young SNRs is
seen to exhibit a dominant angular mode, which is a diagnostic of their ejecta
density profile as found by previous studies. The steep scaling of power at
smaller modes and the time evolution of the spectra is indicative of absence of
a turbulent cascade. Instead, as the time evolution of the spectra suggests,
they may be governed by an angular mode dependent net growth rate. We also
study the impact of anisotropies in the ejecta as well as in the CSM on the
power spectra of velocity and density. We confirm that perturbations in the
density field (whether imposed on the ejecta or the CSM) do not influence the
anisotropy of the remnant significantly unless they have a very large amplitude
and form large-scale coherent structures. In any case, these clumps can only
affect structures on large angular scales. The power spectra on small angular
scales is completely independent of the initial clumpiness and only governed by
the growth and saturation of the Rayleigh-Taylor instability.",2305.17324v2
2023-06-05,Random sequential adsorption of aligned rectangles with two discrete orientations: Finite-size scaling effects,"We study saturated packings produced according to random sequential
adsorption (RSA) protocol built of identical rectangles deposited on a flat,
continuous plane. An aspect ratio of rectangles is defined as the
length-to-width ratio, $f=l/w$. The rectangles have a fixed unit area (i.e., $l
\times w=1$), and therefore, their shape is defined by the value of $f$
($l=\sqrt{f}$ and $w=1/\sqrt{f}$). The rectangles are allowed to align either
vertically or horizontally with equal probability. The particles are deposited
on a flat square substrate of side length $L$ (measured in units of particle
length, $L \in [20, 1000]$) and periodic boundary conditions are applied along
both directions. The finite-size scaling effects are characterized by a scaled
anisotropy defined as $\alpha = l/L = \sqrt{f}/L$. We showed that the
properties of such packings strongly depend on the value of aspect ratio $f$
and the most significant scaling effects are observed for relatively long
rectangles when $l\ge L/2$ (i.e. $\alpha \ge 0.5$). It is especially visible
for the mean packing fraction as a function of the scaled anisotropy $\alpha$.
The kinetics of packing growth for low to moderate rectangle anisotropy is to
be governed by $\ln t/t$ law, where $t$ is proportional to the number of RSA
iterations, which is the same as in the case of RSA of parallel squares. We
also analyzed global orientational ordering in such packings and properties of
domains consisting of a set of neighboring rectangles of the same orientation,
and the probability that such domain forms a percolation.",2306.03259v1
2023-06-14,Interfering Josephson diode effect and magnetochiral anisotropy in Ta2Pd3Te5 asymmetric edge interferometer,"Edge states of topological systems have attracted great interest due to their
robustness and linear dispersions. Here a superconducting-proximitized edge
interferometer is engineered on a second-order topological insulator Ta2Pd3Te5
with asymmetric edges to realize the interfering Josephson diode effect (JDE),
which hosts many advantages, such as the high efficiency as much as 73% at tiny
applied field 8.4 mT an ultra-low switching power around picowatt, and a giant
interfering magnetochiral anisotropy with a coefficient $\gamma$ = 1.2 $\times
10^9$ T$^{-1}$A$^{-1}$ - three orders of magnitude larger than the reported
record. As an important element to induce such JDE, the second-order harmonic
in the current-phase relation is also experimentally confirmed by half Shapiro
steps. This edge interferometer offers a novel and effective method to enhance
the overall performance of JDE and magnetochiral anisotropy, and boosts great
potential application for future superconducting quantum devices.",2306.08478v1
2023-07-17,Nematic spin correlations pervading the phase diagram of FeSe$_{1-x}$S$_{x}$,"We use resonant inelastic X-ray scattering (RIXS) at the Fe-L$_3$ edge to
study the spin excitations of uniaxial-strained and unstrained
FeSe$_{1-x}$S$_{x}$ ($0\leq x\leq0.21$) samples. The measurements on unstrained
samples reveal dispersive spin excitations in all doping levels, which show
only minor doping dependence in energy dispersion, lifetime, and intensity,
indicating that high-energy spin excitations are only marginally affected by
sulfur doping. RIXS measurements on uniaxial-strained samples reveal that the
high-energy spin-excitation anisotropy observed previously in FeSe is also
present in the doping range $0< x\leq0.21$ of FeSe$_{1-x}$S$_{x}$. The
spin-excitation anisotropy persists to a high temperature up to $T>200$ K in
$x=0.18$ and reaches a maximum around the nematic quantum critical doping
($x_c\approx0.17$). Since the spin-excitation anisotropy directly reflects the
existence of nematic spin correlations, our results indicate that high-energy
nematic spin correlations pervade the regime of nematicity in the phase diagram
and are enhanced by the nematic quantum criticality. These results emphasize
the essential role of spin fluctuations in driving electronic nematicity and
open the door for uniaxial strain tuning of spin excitations in quantum
materials hosting strong magnetoelastic coupling and electronic nematicity.",2307.08181v1
2023-08-01,Self-consistent dynamical models with a finite extent -- III. Truncated power-law spheres,"Fully analytical dynamical models usually have an infinite extent, while real
star clusters, galaxies, and dark matter haloes have a finite extent. The
standard method for generating dynamical models with a finite extent consists
of taking a model with an infinite extent and applying a truncation in binding
energy. This method, however, cannot be used to generate models with a pre-set
analytical mass density profile. We investigate the self-consistency and
dynamical properties of a family of power-law spheres with a general tangential
Cuddeford (TC) orbital structure. By varying the density power-law slope
$\gamma$ and the central anisotropy $\beta_0$, these models cover a wide
parameter space in density and anisotropy profiles. We explicitly calculate the
phase-space distribution function for various parameter combinations, and
interpret our results in terms of the energy distribution of bound orbits. We
find that truncated power-law spheres can be supported by a TC orbital
structure if and only if $\gamma \geqslant 2\beta_0$, which means that the
central density slope-anisotropy inequality is both a sufficient and a
necessary condition for this family. We provide closed expressions for
structural and dynamical properties such as the radial and tangential velocity
dispersion profiles, which can be compared against more complex numerical
modelling results. This work significantly adds to the available suite of
self-consistent dynamical models with a finite extent and an analytical
description.",2308.00366v1
2023-08-16,Multiple antiferromagnetic phases and magnetic anisotropy in exfoliated CrBr$_3$ multilayers,"In twisted two-dimensional (2D) magnets, the stacking dependence of the
magnetic exchange interaction can lead to regions of ferromagnetic and
antiferromagnetic interlayer order, separated by non-collinear, skyrmion-like
spin textures. Recent experimental searches for these textures have focused on
CrI$_3$, known to exhibit either ferromagnetic or antiferromagnetic interlayer
order, depending on layer stacking. However, the very strong uniaxial
anisotropy of CrI$_3$ disfavors smooth non-collinear phases in twisted
bilayers. Here, we report the experimental observation of three distinct
magnetic phases -- one ferromagnetic and two antiferromagnetic -- in exfoliated
CrBr$_3$ multilayers, and reveal that the uniaxial anisotropy is significantly
smaller than in CrI$_3$. These results are obtained by magnetoconductance
measurements on CrBr$_3$ tunnel barriers and Raman spectroscopy, in conjunction
with density functional theory calculations, which enable us to identify the
stackings responsible for the different interlayer magnetic couplings. The
detection of all locally stable magnetic states predicted to exist in CrBr$_3$
and the excellent agreement found between theory and experiments, provide
complete information on the stacking-dependent interlayer exchange energy and
establish twisted bilayer CrBr$_3$ as an ideal system to deterministically
create non-collinear magnetic phases.",2308.08355v1
2023-09-02,An Isotropic Discretization with Semi-implicit Approach for Phase Field Model of Alloy Solidification,"Quantitative phase field models have been extensively used to study the
solidification behavior of alloys under different conditions. However, a
longstanding challenge of phase field models is the directional bias caused by
the discretization-induced lattice effects. In particular, widely used
discretization methods may introduce significant spurious anisotropy for
simulations of polycrystalline solidification. In this paper, we demonstrate a
feasible 2D discretization strategy utilizing a hexagonal mesh to reduce the
lattice-induced anisotropy of the phase field model. The leading differential
terms of the 2D discretization methods are analyzed by using known methods in
Fourier space. Using Taylor expansion of discrete Fourier Transform up to sixth
order, we found that the proposed discretization strategy is more accurate and
isotropic than other methods, including the isotropic discretization recently
proposed by Ji et al.[1]. Additionally, the proposed 2D discretization method
can be easily incorporated into a semi-implicit algorithm to solve phase field
equations, thereby greatly reducing time step constraints and improving
computational efficiency compared to explicit approaches. To prove the accuracy
and efficiency of the proposed isotropic discretization with semi-implicit
algorithm, 2D simulations of alloy solidification with different discretization
schemes were performed and compared. We show that the proposed discretization
using a hexagonal mesh can drastically reduce grid-induced anisotropy compared
to conventional methods.",2309.00836v1
2023-09-29,"Magnetism, transport and atomic structure of amorphous binary YxCo1-x alloys","Sputtered thin films of binary YxCo1-x with 0 < x < 0.54 and thickness 15 nm
are investigated to help understand the ferromagnetism of cobalt in amorphous
rare-earth cobalt alloys. The magnetic moment per cobalt falls to zero at x0 =
0.50, where the appearance of magnetism is marked by a para-process with a
dimensionless susceptibility of up to 0.015. All films are magnetically soft,
with densities that fall between those of crystalline Y-Co intermetallic
compounds and the density of a relaxed 10,000-atom binary random close-packed
model of hard spheres with an Y:Co volume ratio of 3:1, where the packing
fractions for all films lies in a narrow range around 0.633 and Co is
coordinated by 3.2 Co and 3.2 Y atoms at x = 0.5. All films with x < 0.4
exhibit in-plane shape anisotropy that is about six times as great as an
intrinsic perpendicular component. Average cobalt spin and orbital moments
obtained by X-ray magnetic circular dichroism were 1.31 and 0.32 Bohr
magnetons, respectively for amorphous Y0.25Co0.75. Strong local anisotropy is
associated with the large cobalt orbital moment, but there is little influence
of anisotropy on the ferromagnetic order because of exchange averaging. The
Hall effect and magnetoresistance are modelled in terms of effective uniform
rotation of the magnetization, with spontaneous and band contributions.
Amorphous YxCo1-x is contrasted with amorphous YxFe1-x, which exhibits random
noncollinear magnetic order that is very sensitive to the film density.",2309.16996v1
2023-10-04,Numerical modeling of hydrogel scaffold anisotropy during extrusion-based 3D printing for tissue engineering,"Extrusion-based 3D printing is a recent and widely used tissue engineering
tool that provides precise 3D control of bioinks to create organ-size
biomaterial-based objects composed of hierarchically organized cellularized
scaffolds. The internal organization of scaffold constituents should mimic the
structural anisotropy of targeted tissue to stimulate proliferative cellular
behavior during 3D cell culture. Both the choice of polymers constituting the
bioink and the topological properties during the extrusion process greatly
influence the structural anisotropy and cellular response of tissue engineering
constructs. The bioink used in our study was a hydrogel made of three
constituents: fibrinogen, alginate and gelatin. These components provide
biocompatibility, printability and conservation of 3D shape after printing. The
topological properties in flowing polymers are dictated by macromolecule
conformation i.e. their orientation and degree of stretch. In this study, we
used the micro-macro approach to describe the orientation state of hydrogel
macromolecules during the extrusion process, offering a two-scale description
of fluid behavior. The goal of our study was to use the Fokker-Planck equation,
which describes the evolution of probability distribution function over time,
to represent the real state of the constituent population in the representative
elementary volume within a hydrogel during extrusion-based 3D printing. Our
data suggest that for a tubular nozzle syringe, constituent orientation is
driven by a high shear rate, which overcomes the fluid rheological behavior.
Also, the interaction coefficient, which represents the microscopic interaction
between fluid particles overcomes hydrogel behavior for constituent orientation
in the prediction model.",2310.02734v2
2023-10-11,Constraining Bianchi-I universe with Pantheon SNIa data,"We study the Bianchi-I cosmological model motivated by signals of statistical
isotropy violation seen in cosmic microwave background (CMB) observations and
others. To that end, we consider various kinds of anisotropic matter that
source anisotropy in our model, specifically cosmic strings, magnetic fields,
domain walls and Lorentz violation generated magnetic fields. These anisotropic
matter sources, taking one at a time, are studied for their co-evolution with
standard model (isotropic) sources viz., dust-like (dark/normal) matter and
dark energy modelled as cosmological constant. We constrain the Hubble
parameter, density fractions of anisotropic matter, isotropic cold dark matter
(CDM) and dark energy ($\Lambda$) in a Bianchi-I universe with planar symmetry
i.e., with a global ellipsoidal geometry, and try to find signatures of a
cosmic preferred axis if any. Pantheon Type Ia Supernova (SNIa) data is used in
our study to obtain constraints on cosmological parameters of this model. In
our analysis, we found a cosmic axis of anisotropy using SN1e data.
Interestingly this preferred axis lies in the same direction, broadly, as some
other cosmic anisotropy axes reported in the literature such as the CMB
hemispherical power asymmetry, etc., with some of anisotropic sources
considered. We also found a non-zero evidence for cosmic shear and eccentricity
for our universe with those sources. To be more conclusive, we require more
SNIa host galaxy data for tighter constraints on distance and absolute
magnitude calibration which we hope will be available from the future JWST
observations and other surveys.",2310.07661v1
2023-10-11,On the anisotropic distribution of clusters in the local Universe,"In his 2021 lecture to the Canadian Association of Physicists Congress,
P.J.E. Peebles pointed out that the brightest extra-galactic radio sources tend
to be aligned with the plane of the de Vaucouleur Local Supercluster up to
redshifts of $z=0.02$ ($d_{\rm MW}\approx 85~\rm{Mpc}$). He then asked whether
such an alignment of clusters is anomalous in the standard $\Lambda$CDM
framework. In this letter, we employ an alternative, absolute orientation
agnostic, measure of the anisotropy based on the inertia tensor axis ratio of
these brightest sources and use a large cosmological simulation from the
FLAMINGO suite to measure how common such an alignment of structures is. We
find that only 3.5% of randomly selected regions display an anisotropy of their
clusters more extreme than the one found in the local Universe's radio data.
This sets the region around the Milky Way as a $1.85\sigma$ outlier. Varying
the selection parameters of the objects in the catalogue, we find that the
clusters in the local Universe are never more than $2\sigma$ away from the
simulations' prediction for the same selection. We thus conclude that the
reported anisotropy, whilst note-worthy, is not in tension with the
$\Lambda$CDM paradigm.",2310.07866v2
2023-10-23,A multiple time scale approach for anisotropic inertial wave turbulence,"Wave turbulence is the study of the long-time statistical behaviour of
equations describing a set of weakly non-linear interacting waves. Such a
theory, which has a natural asymptotic closure, allows us to probe the nature
of turbulence more deeply than the exact Kolmogorov laws by rigorously proving
the direction of the cascade and the existence of an inertial range, predicting
stationary spectra for conserved quantities, or evaluating the Kolmogorov
constant. An emblematic example is given by fast rotating fluids for which a
wave turbulence theory has been derived by Galtier (2003). This work involves
nontrivial analytical developments for a problem that is anisotropic by nature.
We propose here a new path for the derivation of the kinetic equation by using
the anisotropy at the beginning of the analysis. We show that the helicity
basis is not necessary to obtain the wave amplitude equation for the canonical
variables that involve a combination of poloidal and toroidal fields. The
multiple time scale method adapted to this anisotropic problem is then used to
derive the kinetic equation which is the same as the original work when
anisotropy is eventually taken into account. This result proves the
commutativity between asymptotic closure and anisotropy. In addition, the
multiple time scale method informs us that the kinetic equation can be derived
without imposing restrictions on the probability distribution of the wave
amplitude such as quasi-Gaussianity, or on the phase such as random phase
approximation which naturally occurs dynamically.",2310.14640v1
2023-10-26,Honing cross-correlation tools for inference on ultra-high-energy cosmic-ray composition,"The chemical composition of the highest-energy cosmic rays, namely the atomic
number $Z$ of rays with energies $E\gg1~\text{EeV}$, remains to date largely
unknown. Some information on the composition can be inferred from the
deflections that charged ultra-high-energy cosmic rays experience while they
traverse intervening magnetic fields. Indeed, such deflections distort and
suppress the original anisotropy in the cosmic rays arrival directions; thus, a
measure of the anisotropy is also a measurement of the deflections, which in
turn informs us on the chemical composition. In this work, we show that, by
quantifying ultra-high-energy cosmic ray anisotropies through the angular,
harmonic cross-correlation between cosmic rays and galaxies, we are able to
exclude iron fractions $f_{\rm Fe}\leq{\cal O}(10\%)$ on a fiducial hydrogen
map at $2\sigma$ level, and even smaller fractions in the reverse case of
hydrogen on an iron map, going below $f_{\rm H}\lesssim10\%$ when we mask the
Galactic Centre up to latitudes of $40\,\text{deg}$. This is an improvement of
a factor of a few compared to our previous method, and is mostly ascribable to
a new test statistics which is sensitive to each harmonic multipole
individually. Our method can be applied to real data as an independent test of
the recent claim that current cosmic-ray data can not be reproduced by any
existing model of the Galactic magnetic field, as well as an additional handle
to compare any realistic, competing, data-driven composition models.",2310.17699v2
2023-11-17,In plane quantification of in vivo muscle elastic anisotropy factor by steered ultrasound pushing beams,"Skeletal muscles are organized into distinct layers and exhibit anisotropic
characteristics across various scales. Assessing the arrangement of skeletal
muscles may provide valuable biomarkers for diagnosing muscle related
pathologies and evaluating the efficacy of clinical interventions. In this
study, we propose a novel ultrafast ultrasound sequence constituted of steered
pushing beams was proposed for ultrasound elastography applications in
transverse isotropic muscle. Based on the propagation of the shear wave
vertical mode, it is possible to fit the experimental results to retrieve in
the same imaging plane, the shear modulus parallel to fibers as well as the
elastic anisotropy factor. The technique was demonstrated in vitro in phantoms
and ex vivo in fusiform beef muscles. At last, the technique was applied in
vivo on fusiform muscles (biceps braachi) and mono-penate muscles
(gastrocnemius medialis) during stretching and contraction. This novel sequence
provides access to new structural and mechanical biomarkers of muscle tissue,
including the elastic anisotropy factor, within the same imaging plane.
Additionally, it enables the investigation of multiples parameters during
muscle active and passive length changes.",2311.10620v1
2023-11-27,Spin order dependent skyrmion stabilization in MnFeCoGe hexagonal magnets,"Topological magnetic skyrmions in centrosymmetric systems exhibit a higher
degrees of freedom in their helicity, hence possess a great potential in the
advanced spintronics including skyrmion based quantum computation. However, the
centrosymmetric magnets also display non-topological trivial bubbles along with
the topological skyrmions. Hence it is utmost priority to investigate the
impact of different magnetic ground states and their underlying interactions on
the stabilization of magnetic skyrmions in cetrosymmetric magnets. Here, we
present a combined theoretical and experimental study on the role of
non-collinear magnetic ground state on the skyrmion stabilization in a series
of exchange frustrated non-collinear ferromagnetic system MnFe1-xCoxGe. With
the help of neutron diffraction (ND) and Lorentz transmission electron
microscopy (LTEM) studies, we show that hexagonal skyrmions lattice emerges as
a stable field driven state only when the underlying magnetic ground state is
collinear with easy-axis anisotropy. In contrast, non-topological type-II
bubbles are found to be stable state in the case of non-collinear magnetic
ordering with partial in-plane anisotropy. Furthermore, we also find that the
skyrmions transform to the non-topological bubbles when the system undergoes a
spin reorientation transition from the easy-axis to easy-cone ferromagnetic
phase. Our results categorically establish the significant role of in-plane
magnetic moment/anisotropy that hinders the stability of skyrmion both in the
case of collinear and non-collinear magnets. Thus, the present study offers a
wide range of opportunities to manipulate the stability of dipolar skyrmions by
changing the intrinsic characteristics of the materials.",2311.15823v1
2023-12-04,Optical anisotropy and nonlinearity in deep ultraviolet fluorooxoborates,"Optical anisotropy and nonlinearity are two tantalizingly important and
enticing properties of an optical crystal. Combining these two features will
have a miraculous effect. The up conversion can extend solid state laser
sources to the ultraviolet and deep ultraviolet (DUV) ranges through harmonic
generation and for down conversion needed for quantum information technology,
but only a few suitable materials are known as the medium because of the
combination of properties that are required. These include suitable band gaps,
moderate optical anisotropy for phase matching and strong nonlinear optical
(NLO) response. Fluorooxoborates are a new ideal platform for this effect in
DUV. Here we demonstrate that fluorooxoborate is the optimal framework for DUV
NLO material and show that the significance of the incorporation of fluorine in
borates. The NLO performance of fluorooxoborates is strongly improved in terms
of local crystal structure and distribution of electronic states. Importantly,
the role of fluorine is to control the structure, while maintaining high band
gaps but does not directly provide large contributions to birefringence and the
second harmonic generation as the conventional assumptions. This is a
consequence of the microscopic electron distribution and the energy position of
the fluorine states well below the valence band maxima. Based on our
understandings, we constructed two artificial structure and they all behave as
anticipated.",2312.01890v3
2023-12-05,Accurate Machine Learning Predictions of Coercivity in High-Performance Permanent Magnets,"Increased demand for high-performance permanent magnets in the electric
vehicle and wind turbine industries has prompted the search for cost-effective
alternatives. Nevertheless, the discovery of new magnetic materials with the
desired intrinsic and extrinsic permanent magnet properties presents a
significant challenge. Traditional density functional theory (DFT) accurately
predicts intrinsic permanent magnet properties such as magnetic moments,
magneto-crystalline anisotropy constants, and exchange interactions. However,
it cannot compute extrinsic macroscopic properties, such as coercivity ($H_c$),
which are influenced by factors like microscopic defects and internal grain
structures. Although micromagnetic simulation helps compute $H_c$, it
overestimates the values almost by an order of magnitude due to Brown's
paradox. To circumvent these limitations, we employ machine learning (ML)
methods in an extensive database obtained from experiments, DFT calculations,
and micromagnetic modeling. Our novel ML approach is computationally much
faster than the micromagnetic simulation program, the mumax$^3$. We
successfully utilize it to predict $H_c$ values for materials like cerium-doped
$\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$, and subsequently compare the
predicted values with experimental results. Remarkably, our ML model accurately
identifies uniaxial magnetic anisotropy as the primary contributor to $H_c$.
With DFT calculations, we predict the Nd-site dependent magnetic anisotropy
behavior in $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$, confirming $4f$-site
planar and $4g$-site uniaxial to crystalline $c$-direction in good agreement
with experiment. The Green's function atomic sphere approximation calculated a
Curie temperature ($T_{\rm C}$) for $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$
that also agrees well with experiment.",2312.02475v3
2023-12-05,Observable imprints of primordial gravitational waves on the temperature anisotropies of the Cosmic Microwave Background,"We examine the contribution of tensor modes, in addition to the dominant
scalar ones, on the temperature anisotropies of the cosmic microwave background
(CMB). To this end, we analyze in detail the temperature two-point angular
correlation function $C(\theta)$ from the Planck 2018 dataset, focusing on
large angles ($\theta \gtrsim 120^{\circ}$) corresponding to small $\ell$
multipoles. A hierarchical set of infrared cutoffs are naturally introduced to
the scalar and tensor power spectra of the CMB by invoking an extra
Kaluza-Klein dimension compactifying at about the GUT scale between the Planck
epoch and the start of inflation. We associate this set of lower scalar and
tensor cutoffs with the parity of the multipole expansion of the $C(\theta)$
function. By fitting the Planck 2018 data we compute the multipole coefficients
thereby reproducing the well-known odd-parity preference in angular
correlations seen by all three satellite missions COBE, WMAP and Planck. Our
fits improve significantly once tensor modes are included in the analysis,
hence providing a hint of the imprints of primordial gravitational waves on the
temperature correlations observed in the CMB today. To conclude we suggest a
relationship between, on the one hand, the lack of (positive) large-angle
correlations and the odd-parity dominance in the CMB and, on the other hand,
the effect of primordial gravitational waves on the CMB temperature
anisotropies.",2312.02740v1
2023-12-07,Effects of planetary day-night temperature gradients on He 1083 nm transit spectra,"A notable fraction of helium observations probing the evaporating atmospheres
of short-period gas giants at 1083~nm exhibit a blueshift during transit, which
might be indicative of a day-to-night side flow. In this study, we explore the
gas dynamic effects of day-to-night temperature contrasts on the escaping
atmosphere of a tidally locked planet. Using a combination of 3D hydrodynamic
simulations and radiative transfer post-processing, we modeled the transmission
spectra of the metastable helium triplet. Our key findings are as follows: (1)
Increasing the day-night anisotropy leads to a narrowing of the helium line and
an increase in the blueshift of the line centroid of a few km~s$^{-1}$. (2) The
velocity shift of the line depends on the line-forming altitude, with higher
planetary mass-loss rates causing the line to form at higher altitudes,
resulting in a more pronounced velocity shift. (3) A critical point of
day-night anisotropy comes about when the blueshift saturates, due to turbulent
flows generated by outflow material falling back onto the planet's night side.
(4) A strong stellar wind and the presence of turbulent flows may induce time
variations in the velocity shift. Assuming that the day-night temperature
gradient is the main cause of the observed blueshifts in the He-1083~nm
triplet, the correlation between the velocity shift and day-night anisotropy
provides an opportunity to constrain the temperature gradient of the
line-forming region.",2312.04682v2
2023-12-25,Exploration of the two-dimensional Ising magnetic materials in the triangular prismatic crystal field,"Magnetic anisotropy is essential for stabilizing two-dimensional (2D)
magnetism, which has significant applications in spintronics and the
advancement of fundamental physics. In this work, we examine the electronic
structure and magnetic properties of triangular prismatic MSi$_2$N$_4$ (M = V,
Cr) monolayers, using crystal field theory, spin-orbital state analyses, and
density functional calculations. Our results reveal that the pristine
VSi$_2$N$_4$ monolayer exhibits magnetism with a V$^{4+}$ 3$d^1$ $S$ = 1/2
charge-spin state within the triangular prismatic crystal field. However, the
strong $d$ orbital hybridization between adjacent V$^{4+}$ ions disrupts the
$d$ orbital splitting in this crystal field, resulting in a relatively small
in-plane magnetic anisotropy of approximately 2 $\mu$eV per V atom.In contrast,
the pristine CrSi$_2$N$_4$ monolayer is nonmagnetic, characterized by the
Cr$^{4+}$ 3$d^2$ $S$ = 0 state. Upon substituting nonmagnetic Cr$^{4+}$ with
Si$^{4+}$, Cr$_\frac{1}{3}$Si$_\frac{8}{3}$N$_4$ transforms into an
antiferromagnetic insulator with Cr$^{4+}$ 3$d^2$ $S$ = 1 state, featuring a
large orbital moment of -1.06 $\mu_{\rm B}$ oriented along the $z$-axis and
huge perpendicular magnetic anisotropy of 18.63 meV per Cr atom. These findings
highlight the potential for further exploration of 2D Ising magnetic materials
within a unique triangular prismatic crystal field.",2312.15625v1
2023-12-29,Anisotropy-driven topological quantum phase transition in magnetic impurities,"A few years ago, a topological quantum phase transition (TQPT) has been found
in Anderson and Kondo 2-channel spin-1 impurity models that include a hard-axis
anisotropy term $DS_z^2$ with $D > 0$. The most remarkable manifestation of the
TQPT is a jump in the spectral density of localized electrons, at the Fermi
level, from very high to very low values as $D$ is increased. If the two
conduction channels are equivalent, the transition takes place at the critical
anisotropy $D_c \sim 2.5\; T_K$, where $T_K$ is the Kondo temperature for
$D=0$. This jump might be important to develop a molecular transistor. The jump
is due to a corresponding one in the Luttinger integral, which has a
topological non-trivial value $\pi/2$ for $D > D_c$. Here, we review the main
results for the spectral density and highlight the significance of the theory
for the interpretation of measurements conducted on magnetic atoms or molecules
on metallic surfaces. In these experiments, where $D$ is held constant, the
energy scale $T_K$ is manipulated by some parameters. The resulting variation
gives rise to a differential conductance $dI/dV$, measured by
scanning-tunneling spectroscopy, which is consistent with a TQPT at an
intermediate value of $T_K$. We also show that the theory can be extended to
integer spin $S>1$ and two-impurity systems. This is also probably true for
half-integer spin and non-equivalent channels in some cases.",2312.17702v1
2023-12-31,CMB lensing from early-formed dark matter halos,"Some theoretical models for the early universe predict a spike-type
enhancement in the primordial power spectrum on a small scale, which would
result in forming early-formed dark matter halos (EFHs). In this work, we study
the CMB lensing effect, considering the existence of EFHs, and investigate the
potential to probe the EFHs and the primordial perturbations on scales smaller
than $1\mathrm{Mpc}$. We numerically calculate the angular power spectrum of
the lensing potential and the lensed CMB anisotropy of temperature, E-mode, and
B-mode polarization, including the nonlinear effects of EFHs. We find the
possibility that the lensed CMB temperature anisotropy is significantly
enhanced on small scales, $\ell>1000$, and could be tested by component
decomposition of observed signals through multi-frequency observations. Through
the calculation with different models of the spiky-type power spectrum, we
demonstrate that the accurate measurements of the CMB lensing effect would
provide insight into the abundance of EFHs within the limited mass range around
$10^{12}M_\odot$ and the primordial power spectrum on the limited scales around
$k\sim 1\mathrm{Mpc}^{-1}$. In particular, we find that the existence of such
EFHs can amplify the lensed anisotropy of CMB B-mode polarization even on large
scales, $\ell <100$, as the overall enhancement by $\sim 10 \%$ level compared
to the standard structure formation model without EFHs. Therefore, future CMB
measurements such as the LiteBIRD satellite can probe the existence of the EFHs
and the spike-type primordial power spectrum through the precise measurement of
the large-scale CMB B-mode polarization.",2401.00407v1
2023-12-31,Giant Optical Anisotropy in 2D Metal-Organic Chalcogenates,"Optical anisotropy is a fundamental attribute of some crystalline materials
and is quantified via birefringence. A birefringent crystal not only gives rise
to asymmetrical light propagation but also attenuation along two distinct
polarizations, a phenomenon called linear dichroism (LD). Two-dimensional (2D)
layered materials with high in- and out-of-plane anisotropy have garnered
interest in this regard. Mithrene, a 2D metal-organic chalcogenate (MOCHA)
compound, exhibits strong excitonic resonances due to its naturally occurring
multi-quantum well (MQW) structure and in-plane anisotropic response in the
blue wavelength (~400-500 nm) regime. The MQW structure and the large
refractive indices of mithrene allow the hybridization of the excitons with
photons to form self-hybridized exciton-polaritons in mithrene crystals with
appropriate thicknesses. Here, we report the giant birefringence (~1.01) and
tunable in-plane anisotropic response of mithrene, which stem from its low
symmetry crystal structure and unique excitonic properties. We show that the LD
in mithrene can be tuned by leveraging the anisotropic exciton-polariton
formation via the cavity coupling effect exhibiting giant in-plane LD (~77.1%)
at room temperature. Our results indicate that mithrene is an ideal polaritonic
birefringent material for polarization-sensitive nanophotonic applications in
the short wavelength regime.",2401.00590v2
2024-01-22,Atomistic calculation of the f0 attempt frequency in Fe3O4 magnetite nanoparticles,"The Arrhenius law predicts the transition time between equilibrium states in
physical systems due to thermal activation, with broad applications in material
science, magnetic hyperthermia and paleomagnetism where it is used to estimate
the transition time and thermal stability of assemblies of magnetic
nanoparticles. Magnetite is a material of great importance in paleomagnetic
studies and magnetic hyperthermia but existing estimates of the attempt
frequency $f_0$ vary by several orders of magnitude in the range $10^7-10^{13}$
Hz, leading to significant uncertainty in their relaxation rate. Here we
present a dynamical method enabling full parameterization of the
Arrhenius-N\'eel law using atomistic spin dynamics. We determine the
temperature and volume dependence of the attempt frequency of magnetite
nanoparticles with cubic anisotropy and find a value of $f_0 = 0.562 \pm 0.059$
GHz at room temperature. For particles with enhanced anisotropy we find a
significant increase in the attempt frequency and a strong temperature
dependence suggesting an important role of anisotropy. The method is applicable
to a wide range of dynamical systems where different states can be clearly
identified and enables robust estimates of domain state stabilities, with
particular importance in the rapidly developing field of micromagnetic analysis
of paleomagnetic recordings where samples can be numerically reconstructed to
provide a better understanding of geomagnetic recording fidelity over
geological time scales.",2401.12080v1
2024-01-23,Splitting Instability in Superalloys: A Phase-Field Study,"Precipitation-strengthened alloys, such as Ni-base, Co-base and Fe-base
superalloys, show the development of dendrite-like precipitates in the solid
state during aging at near-$\gamma^{\prime}$ solvus temperatures. These
features arise out of a diffusive instability wherein, due to the point effect
of diffusion, morphological perturbations over a growing sphere/cylinder are
unstable. These dendrite-like perturbations exhibit anisotropic growth
resulting from anisotropy in interfacial/elastic energies. Further,
microstructures in these alloys also exhibit ""split"" morphologies wherein
dendritic precipitates fragment beyond a critical size, giving rise to a
regular octet or quartet pattern of near-equal-sized precipitates separated by
thin matrix channels. The mechanism of formation of such morphologies has
remained a subject of intense investigation, and multiple theories have been
proposed to explain their occurrence. Here, we developed a phase-field model
incorporating anisotropy in elastic and interfacial energies to investigate the
evolution of these split microstructures during growth and coarsening of
dendritic $\gamma^{\prime}$ precipitates. Our principal finding is that the
reduction in elastic energy density drives the development of split morphology,
albeit a concomitant increase in the surface energy density. We also find that
factors such as supersaturation, elastic misfit, degree of elastic anisotropy
and interfacial energy strongly modulate the formation of these
microstructures. We analyze our simulation results in the light of classical
theories of elastic stress effects on coarsening and prove that negative
elastic interaction energy leads to the stability of split precipitates.",2401.13151v1
2024-01-26,Observing Kinematic Anisotropies of the Stochastic Background with LISA,"We propose a diagnostic tool for future analyses of stochastic gravitational
wave background signals of extra-galactic origin in LISA data. Next-generation
gravitational wave detectors hold the capability to track unresolved
gravitational waves bundled into a stochastic background. This composite
background contains cosmological and astrophysical contributions, the
exploration of which offers promising avenues for groundbreaking new insights
into very early universe cosmology as well as late-time structure formation. In
this article, we develop a full end-to-end pipeline for the extraction of
extra-galactic signals, based on kinematic anisotropies arising from the
galactic motion, via full-time-domain simulations of LISA's response to the
gravitational wave anisotropic sky. Employing a Markov-Chain-Monte-Carlo
map-making scheme, multipoles up to $\ell=2$ are recovered for scale-free
spectra that support an interpretation as signals originating from cosmic
strings in the case of a high signal-to-noise ratio. We demonstrate that our
analysis is consistently beating cosmic variance and is robust against
statistical and systematic errors. The impact of instrumental noise on the
extraction of kinematic anisotropies is investigated, and we establish a
detection threshold of $\Omega_{GW}\gtrsim 5\times 10^{-8}$ in the presence of
instrument-induced noise. Potential avenues for improvement in our methodology
are highlighted.",2401.14849v1
2024-01-29,Accurate detection of diffusion anisotropy from an individual short particle trajectory,"In parallel with advances in microscale imaging techniques, the fields of
biology and materials science have focused on precisely extracting particle
properties based on their diffusion behavior. Although the majority of
real-world particles exhibit anisotropy, their behavior has been studied less
than that of isotropic particles. In this study, we introduce a new method for
estimating the diffusion coefficients of individual anisotropic particles using
short-trajectory data on the basis of a maximum likelihood framework.
Traditional estimation techniques often use mean-squared displacement (MSD)
values or other statistical measures that inherently remove angular
information. Instead, we treated the angle as a latent variable and used belief
propagation to estimate it while maximizing the likelihood using the
expectation-maximization algorithm. Compared to conventional methods, this
approach facilitates better estimation of shorter trajectories and faster
rotations, as confirmed by numerical simulations and experimental data
involving bacteria and quantum rods. Additionally, we performed an analytical
investigation of the limits of detectability of anisotropy and provided
guidelines for the experimental design. In addition to serving as a powerful
tool for analyzing complex systems, the proposed method will pave the way for
applying maximum likelihood methods to more complex diffusion phenomena.",2401.15909v1
2024-02-05,Measuring jet energy loss fluctuations in the quark-gluon plasma via multiparticle correlations,"The quark-gluon plasma (QGP) is a high temperature state of matter produced
in the collisions of two nuclei at relativistic energies. The properties of
this matter at short distance scales are probed using jets with high transverse
momentum ($p_T$) resulting from quarks and gluons scattered with large momentum
transfer in the earliest stages of the collisions. The Fourier harmonics for
anisotropies in the high transverse momentum particle yield, $v_n(p_T)$,
indicate the path length dependence of jet energy loss within the QGP. We
present a framework to build off of measurements of jet energy loss using
$v_n(p_T)$ by characterizing fluctuations in jet energy loss that are currently
not constrained experimentally. In this paper, we utilize a set of multivariate
moments and cumulants as new experimental observables to measure event-by-event
fluctuations in the azimuthal anisotropies of rare probes, and compare them to
the azimuthal anisotropies of soft particles. Ultimately, these fluctuations
can be used to quantify the magnitude and fluctuations of event-by-event jet
energy loss. We relate these quantities to existing multivariate cumulant
observables, highlight their unique properties, and validate their
sensitivities with a Monte Carlo simulation.",2402.03512v1
2024-02-15,Understanding and tuning magnetism in layered Ising-type antiferromagnet FePSe3 for potential 2D magnet,"Recent development in two-dimensional (2D) magnetic materials have motivated
the search for new van der Waals magnetic materials, especially Ising-type
magnets with strong magnetic anisotropy. Fe-based MPX3 (M = transition metal, X
= chalcogen) compounds such as FePS3 and FePSe3 both exhibit an Ising-type
magnetic order, but FePSe3 receives much less attention compared to FePS3. This
work focuses on establishing the strategy to engineer magnetic anisotropy and
exchange interactions in this less-explored compound. Through chalcogen and
metal substitutions, the magnetic anisotropy is found to be immune against S
substitution for Se whereas tunable only with heavy Mn substitution for Fe. In
particular, Mn substitution leads to a continuous rotation of magnetic moments
from the out-of-plane direction towards in-plane. Furthermore, the magnetic
ordering temperature displays non-monotonic doping dependence for both
chalcogen and metal substitutions but due to different mechanisms. These
findings provide deeper insight into the Ising-type magnetism in this important
van der Waals material, shedding light on the study of other Ising-type
magnetic systems as well as discovering novel 2D magnets for potential
applications in spintronics.",2402.10155v1
2024-02-17,Anisotropic induced polarization modeling with neural networks and effective medium theory,"Accurately interpreting induced polarization (IP) data that reflects the
inherent anisotropy of the Earth's crust requires anisotropic IP models. The
Generalized Effective Medium Theory of Induced Polarization (GEMTIP) model
effectively simulates the IP signatures of rocks containing polarizable
minerals. A pivotal element of the GEMTIP model is calculating the
depolarization tensor elements, an intensive task for anisotropic rocks because
one must numerically solve six parametric integrals for each mineral inclusion.
This study aims to streamline anisotropic IP simulations by extending the
GEMTIP framework and introducing a machine learning approach to estimate the
depolarization tensors. The theoretical contributions of this research are
two-fold: (1) we augment the GEMTIP model to encompass anisotropic background
conductivity and triaxial ellipsoidal inclusions, and (2) we reformulate the
depolarization integrals to normalize their input and output variables,
facilitating their estimation by neural networks. Validation against analytical
solutions for spherical and spheroidal inclusions corroborates the accuracy of
the neural network. Analyzing the neural network model, we find that the
relationship between chargeability and polarizable inclusion content is
increasingly uncertain for increasingly anisotropic rocks. A similar
observation applies to the relationship between critical frequency and host
rock conductivity. Moreover, the depolarization tensors are, on average, 56 %
sensitive to inclusion anisotropy and 44 % sensitive to host rock conductivity
anisotropy. Remarkably, our neural network drastically accelerates GEMTIP
simulations--up to 100,000 times faster than numerical integration--without
substantially sacrificing accuracy. This advancement is promising for efficient
rock-scale IP modeling in complex and anisotropic geological settings.",2402.11313v1
2024-02-21,Isotropic and anisotropic neutron star structure in 4D Einstein Gauss Bonnet Gravity,"With regard to the coupling constant and the strong magnetic field of neutron
stars, we have studied these stars in the 4D Einstein Gauss Bonnet (4D EGB)
gravity model in order to grasp a better understanding of these objects. In
this paper, we have shown that the neutron star properties are considerably
affected by the coupling constant and magnetic field. We have found that as a
consequence of the strong magnetic field and the coupling constant, the maximum
mass and radius of a neutron star are increasing functions of the coupling
constant, while Schwarzschild radius, compactness, surface gravitational
redshift, and Kretschmann scalar are decreasing functions. Additionally, our
study has shown that the physical properties of a magnetized neutron star are
greatly influenced not only by the strong magnetic field, but also by the
anisotropy. Moreover, we have shown that to obtain the hydrostatic equilibrium
configuration of the magnetized material, both the local anisotropy effect and
the anisotropy due to the magnetic field should be considered. Finally, we have
found that in the anisotropic magnetized neutron stars, the maximum mass and
radius do not always increase with increasing the internal magnetic field.",2402.14038v1
2024-02-22,On the origin of the above-room-temperature magnetism in the 2D van der Waals ferromagnet Fe$_3$GaTe$_2$,"Recent advancements in 2D magnetic materials have attracted a growing
interest driven by their unique properties and potential applications in
spintronic devices. However, the scarcity of systems that exhibit magnetism at
room-temperature has limited their practical implementation into functional
devices. In this work we focus on the recently synthetised van der Waals (vdW)
ferromagnet Fe$_3$GaTe$_2$, which exhibits above-room-temperature magnetism
(T$_{\mathrm{c}}$ = 350-380 K) and strong perpendicular magnetic anisotropy.
Through first-principles calculations, we examine the magnetic properties of
Fe$_3$GaTe$_2$ and compare them with the widely known Fe$_3$GeTe$_2$
ferromagnet. Our calculations unveil the complex microscopic mechanisms
governing their magnetic behaviour, emphasizing the pivotal role of the
ferromagnetic in-plane exchange interactions in the stabilization of the
elevated T$_{\mathrm{c}}$ in Fe$_3$GaTe$_2$. Additionally, we predict the
stability, strong perpendicular anisotropy and high T$_{\mathrm{c}}$ of
single-layer Fe$_3$GaTe$_2$. We also demonstrate the potential of strain
engineering and electrostatic doping to modulate its magnetic exchange
interactions and anisotropy. Our results incentivise the isolation of the
monolayer and pave the way for the future optimization of Fe$_3$GaTe$_2$ in
magnetic and spintronic nanodevices.",2402.14618v1
2024-02-24,Collective excitations in two-dimensional harmonically trapped quantum droplets,"The collective excitation modes in quantum droplets trapped in a
two-dimensional harmonic potential in the context of symmetric weakly
interacting binary bosonic mixtures are studied. By utilizing the linearization
technique, the time-dependent extended Gross-Pitaevskii equation, and a
sum-rule approach with a variational approximation, the ground state properties
and collective excitations of such a two-dimensional quantum system are
investigated for various system parameters. We present comprehensive analysis
and calculations on the effect of the confinement strength and anisotropy of
the trapping potential, the number of atoms in the droplet, and the collective
excitation modes. The radius of the droplet, as well as the chemical potential,
is non-monotonically related to the number of atoms in the droplet, and the
confinement tends to shift the minimum values towards the ideal gas limit. The
excitation frequency peaks, which are prominent in a self-bounded droplet,
become less pronounced and smoother when subjected to a strong trapping
potential. The sum-rule approach fails to reproduce the breathing mode
frequency for a moderate number of atoms in a weak trapping potential, however,
works perfectly well in a strong confinement. It was found that the anisotropy
in the trap eliminates the degeneracy between the quadrupole and scissors modes
that occurs in an isotropic trap, causing the frequencies of these two modes to
immediately diverge from each other for any degree of anisotropy. These
findings provide valuable insights into the unique characteristics and behavior
of quantum droplets, offering potential implications for future research and
applications in the dynamic behaviors of intriguing quantum droplets.",2402.15811v1
2024-02-29,Pressure-induced optical anisotropy of HfS$_2$,"The effect of pressure on Raman scattering (RS) in the bulk HfS$_2$ is
investigated under hydrostatic and non-hydrostatic conditions. The RS lineshape
does not change significantly in the hydrostatic regime, showing a systematic
blueshift of the spectral features. In a non-hydrostatic environment, seven
peaks emerge in the spectrum ($P$=7 GPa) dominating the lineshape up to
$P$=10.5 GPa. The change in the RS lineshape manifests a pressure-induced phase
transition in HfS$_2$. The simultaneous observation of both low-pressure (LP)
and high-pressure (HP) related RS peaks suggests the corresponding coexistence
of two different phases over a large pressure range. We found that the
HP-related phase is metastable, persisting during the decompression cycle down
to $P$=1.2 GPa with the LP-related features finally recovering at even lower
pressures. The angle-resolved polarized RS (ARPRS) performed under $P$=7.4 GPa
revealed a strong in-plane anisotropy of both the LP-related A$_{1g}$ mode and
the HP peaks. The anisotropy is related to the possible distortion of the
structure induced by the non-hydrostatic component of the pressure. We describe
the obtained results by the influence of the non-hydrostatic pressure on the
observed phase transition. We interpret our results in terms of a distorted
$Pnma$ phase as a possible HP induced structure of HfS$_2$.",2402.19040v1
2024-03-01,Equilibrium Model with Anisotropy for Model-Based Reconstruction in Magnetic Particle Imaging,"Magnetic particle imaging is a tracer-based tomographic imaging technique
that allows the concentration of magnetic nanoparticles to be determined with
high spatio-temporal resolution. To reconstruct an image of the tracer
concentration, the magnetization dynamics of the particles must be accurately
modeled. A popular ensemble model is based on solving the Fokker-Plank
equation, taking into account either Brownian or N\'eel dynamics. The
disadvantage of this model is that it is computationally expensive due to an
underlying stiff differential equation. A simplified model is the equilibrium
model, which can be evaluated directly but in most relevant cases it suffers
from a non-negligible modeling error. In the present work, we investigate an
extended version of the equilibrium model that can account for particle
anisotropy. We show that this model can be expressed as a series of Bessel
functions, which can be truncated based on a predefined accuracy, leading to
very short computation times, which are about three orders of magnitude lower
than equivalent Fokker-Planck computation times. We investigate the accuracy of
the model for 2D Lissajous MPI sequences and show that the difference between
the Fokker-Planck and the equilibrium model with anisotropy is sufficiently
small so that the latter model can be used for image reconstruction on
experimental data with only marginal loss of image quality, even compared to a
system matrix-based reconstruction.",2403.00602v1
2024-03-06,The role of interfacial interactions and oxygen vacancies in tuning magnetic anisotropy in LaCrO$_{3}$/LaMnO$_{3}$ heterostructures,"The interplay of lattice, electronic, and spin degrees of freedom at
epitaxial complex oxide interfaces provides a route to tune their magnetic
ground states. Unraveling the competing contributions is critical for tuning
their functional properties. We investigate the relationship between magnetic
ordering and magnetic anisotropy and the lattice symmetry, oxygen content, and
film thickness in compressively strained LaMnO$_3$/LaCrO$_3$ superlattices.
Mn-O-Cr antiferromagnetic superexchange interactions across the heterointerface
resulting in a net ferrimagnetic magnetic structure. Bulk magnetometry
measurements reveal isotropic in-plane magnetism for as-grown oxygen-deficient
thinner thin samples due to equal fractions of orthorhombic a+a-c-, and a-a+c-
twin domains. As the superlattice thickness is increased, in-plane magnetic
anisotropy emerges as the fraction of the a+a-c- domain increases. On annealing
in oxygen, the suppression of oxygen vacancies results in a contraction of the
lattice volume, and an orthorhombic to rhombohedral transition leads to
isotropic magnetism independent of the film thickness. The complex interactions
are investigated using high-resolution synchrotron diffraction and X-ray
absorption spectroscopy. These results highlight the role of the evolution of
structural domains with film thickness, interfacial spin interactions, and
oxygen-vacancy-induced structural phase transitions in tuning the magnetic
properties of complex oxide heterostructures.",2403.03764v1
2024-03-18,Measurement of anisotropies in Supernova Remnant observations and their interpretation using numerical models,"Supernova remnants (SNRs) exhibit varying degrees of anisotropy, which have
been extensively modeled using numerical methods. We implement a technique to
measure anisotropies in SNRs by calculating power spectra from their
high-resolution images. To test this technique, we develop 3D hydrodynamical
models of supernova remnants and generate synthetic x-ray images from them.
Power spectra extracted from both the 3D models and the synthetic images
exhibit the same dominant angular scale, which separates large scale features
from small scale features due to hydrodynamic instabilities. The angular power
spectrum at small length scales during relatively early times is too steep to
be consistent with Kolmogorov turbulence, but it transitions to Kolmogorov
turbulence at late times. As an example of how this technique can be applied to
observations, we extract a power spectrum from a \textit{Chandra} observation
of Tycho's SNR and compare with our models. Our predicted power spectrum picks
out the angular scale of Tycho's fleece-like structures and also agrees with
the small-scale power seen in Tycho. We use this to extract an estimate for the
density of the circumstellar gas ($n \sim 0.28/\mathrm{cm^3}$), consistent with
previous measurements of this density by other means. The power spectrum also
provides an estimate of the density profile of the outermost ejecta. Moreover,
we observe additional power at large scales which may provide important clues
about the explosion mechanism itself.",2403.12264v1
2024-03-24,"Aggregate Frequency Width, Nuclear Hyperfine Coupling and Jahn-Teller Effect of $Cu^{2+}$ Impurity Ion ESR in $SrLaAlO_4$ Dielectric Resonator at $20$ Millikelvin","The impurity paramagnetic ion, $Cu^{2+}$ substitutes $Al$ in the $SrLaAlO_4$
single crystal lattice, this results in a $CuO_6$ elongated octahedron, the
resulting measured g-factors shows four-fold axes variation condition. The
aggregate frequency width of the electron spin resonance with the required
minimum level of impurity concentration has been evaluated in single crystal
$SrLaAlO_4$ at $20$ millikelvin. Measured parallel hyperfine constants,
$A_{\scriptscriptstyle\parallel Cu}$, were determined to be
$-155.7\times10^{-4}~cm^{-1},~ -163.0\times10^{-4}~cm^{-1},~
-178.3\times10^{-4}~cm^{-1} $ and$~-211.1\times10^{-4}~cm^{-1}$ at
$9.072~GHz~(WGH_{4,1,1})$ for the nuclear magnetic quantum number
$M_I=+\frac{3}{2},+\frac{1}{2},-\frac{1}{2}$,~and$-\frac{3}{2}$ respectively.
The anisotropy of the hyperfine structure reveals a characteristics of static
Jahn-Teller effect. The second-order-anisotropy-term, $\sim
(\frac{spin-orbit~coupling}{10D_q})^2$, is significant and can not be
disregarded, with the local strain dominating over the observed
Zeeman-anisotropy-energy difference. The Bohr electron magneton,
$\beta=9.23\times 10^{-24} JT^{-1}$, (within $-0.43\%$ so-called experimental
error) has been found using the measured spin-Hamiltonian parameters. Measured
nuclear dipolar hyperfine structure parameter
$P_{\scriptscriptstyle\parallel}=12.3\times10^{-4}~cm^{-1}$ shows that the mean
inverse third power of the electron distance from the nucleus is $\langle
r^{-3}_q\rangle\simeq 5.23$ a.u. for $Cu^{2+}$ ion in the substituted $Al^{3+}$
ion site assuming nuclear electric quadruple moment $Q=-0.211$ barn.",2403.16315v1
1993-05-07,Statistics of N-body Simulations I. Equal Masess Before Core Collapse,"We study the dynamical evolution of idealised stellar systems by averaging
results from many $N$-body simulations, each having modest numbers of stars.
For isolated systems with stars of uniform mass, we discuss aspects of
evolution up to the point of core collapse: relaxation and its $N$-dependence,
the evolution of the density profile, the development of the velocity
dispersion and anisotropy, and the rate of stellar escape.",9305008v1
1993-09-29,Blue perturbation spectra from inflation,"We investigate inflationary models leading to density perturbations with a
spectral index $n>1$ (``blue spectra""). These perturbation spectra may be
useful to simultaneously account for both the amount of ultra large-scale power
required to fit cosmic microwave background anisotropies, such as those
measured by COBE, and that required to give bulk motions and structures on the
$\sim 50~h^{-1}$ Mpc scale.",9309054v1
1994-08-01,Polarization-Temperature Correlations in the Microwave Background,"The polarization of the CMB offers a potentially valuable probe of the
physics of the early universe, specifically of the velocity of the
photon-baryon fluid on the last scattering surface. Here we discuss
qualitatively the correlations that arise between the temperature anisotropies
and polarization of the CMB and how they might be observed.",9408001v1
1994-08-05,BIMA observations of possible microwave background sources,"We present sensitive upper limits on the 90 GHz flux of known radio and
infrared sources in regions associated with possible cosmic microwave
background fluctuations at 0.5--1 degree scales. Specifically we look at the
MAX GUM region and the region of strongest fluctuation in the MSAM scan. None
of the known sources can account for the levels of anisotropy seen.",9408021v1
1994-10-27,A First Map of the CMB at 0.5Deg Resolution,"We use a Maximum Entropy technique to reconstruct a map of the microwave sky
near the star Gamma Ursae Minoris, based on data from flights 2, 3 and 4 of the
Millimeter-wave Anisotropy eXperiment (MAX).",9410088v1
1995-07-10,The COBRAS/SAMBA CMB Project,"COBRAS/SAMBA is a second generation satelitte dedicated to mapping at high
resolution and sensitivity the anisotropies of the Cosmic Microwave Background
(CMB). This mission is in the assessment study phase (A) at ESA, with a
decision expected mid 1996, for a launch around 2003.",9507032v1
1995-08-01,The Open Universe Grishchuk-Zel'dovich Effect,"The Grishchuk--Zel'dovich effect is the contribution to the microwave
background anisotropy from an extremely large scale adiabatic density
perturbation, on the standard hypothesis that this perturbation is a typical
realization of a homogeneous Gaussian random field. We analyze this effect in
open universes, corresponding to density parameter $\Omega_0<1$ with no
cosmological constant, and concentrate on the recently discussed
super-curvature modes. The effect is present in all of the low multipoles of
the anisotropy, in contrast with the $\Omega_0=1$ case where only the
quadrupole receives a contribution. However, for no value of $\Omega_0$ can a
very large scale perturbation generate a spectrum capable of matching
observations across a wide range of multipoles. We evaluate the magnitude of
the effect coming from a given wavenumber as a function of the magnitude of the
density perturbation, conveniently specified by the mean-square curvature
perturbation. From the absence of the effect at the observed level, we find
that for $0.25\leq\Omega_0\leq 0.8$, a curvature perturbation of order unity is
permitted only for inverse wavenumbers more than one thousand times the size of
the observable universe. As $\Omega_0$ tends to one, the constraint weakens to
the flat space result that the inverse wavenumber be more than a hundred times
the size of the observable universe, whereas for $\Omega_0 < 0.25$ it becomes
stronger. We explain the physical meaning of these results, by relating them to
the correlation length of the perturbation. Finally, in an Appendix we consider
the dipole anisotropy and show that it always leads to weaker constraints.",9508003v2
1995-10-05,Metric Perturbations from Quantum Tunneling in Open Inflation,"We study the effect that quantum fluctuations produced during the nucleation
of a single-bubble open inflationary universe have on the amplitude of
temperature anisotropies in the microwave background. We compute the instanton
action for the quantum tunneling between the false and true vacua in open
inflation models and show that the amplitude of quantum fluctuations of the
bubble wall is very sensitive to the gravitational effects of the true vacuum.
We study the spectrum of quantum fluctuations of the bubble wall and confirm
that there is only an inhomogeneous ($k^2 = -3$) discrete mode associated with
transverse traceless fluctuations of the bubble wall. This super-curvature mode
could in principle distort the anisotropy of the microwave background. We
compute the amplitude of the gauge invariant metric perturbations induced by
the bubble wall fluctuations on a comoving hypersurface, and calculate the
induced amplitude of temperature fluctuations in the microwave background, for
arbitrary values of $\Omega_0$. We find that in the limit $\Omega_0\simeq 1$,
the quadrupole dominates the angular power spectrum, like in the usual
Grishchuk-Zel'dovich effect. The resulting bounds on the amplitude of quantum
fluctuations of the bubble wall from the absence of such an effect in the
observed microwave background anisotropies are quite strong. We also study the
contribution from a discrete long wavelength super-curvature mode ($k^2 \simeq
2m^2/3H^2$) that appears in the spectrum of open de Sitter vacuum fluctuations.
We constrain the parameters of the models of open inflation so that these modes
do not distort the observed temperature anisotropy.",9510029v4
1996-02-27,UCSB South Pole 1994 CMB anisotropy measurement constraints on open and flat-Lambda CDM cosmogonies,"We develop methods to account for experimental and observational
uncertainties in likelihood analyses of data from cosmic microwave background
(CMB) anisotropy experiments and apply them to an analysis of the UCSB South
Pole 1994 (SP94) experiment. Observationally motivated open and spatially-flat
$\Lambda$, cold dark matter cosmogonies are considered. Among the models we
consider, the full SP94 data set is most consistent with $\Omega_0 \sim
0.1-0.2$ open models and less so with old $(t_0 \gap 15 - 16 Gyr)$, high baryon
density $(\Omega_B \gap 0.0175 h^{-2})$, low density ($\Omega_0 \sim 0.2 -
0.4), flat-$\Lambda$ models. The SP94 data do not rule out any of the models we
consider at the $2\sigma$ level. The SP94 experiment is most sensitive to
anisotropies on a somewhat larger, model-dependent, angular scale than the
scale at which the window function peaks. For establishing the significance of
a detection of CMB anisotropy we derive limits using the highest posterior
density (HPD) prescription, since it yields smaller lower limits. Since HPD
limits lead to tighter constraints on the CMB amplitude, they also provide for
greater discrimination between models. Model normalizations deduced from the
SP94 data subsets are mostly consistent with those deduced from the two-year
COBE-DMR data, although the Ka-band data prefer a normalization $\sim 1\sigma$
lower than do the Q-band data, the Q and Ka + Q data favour a slightly higher
normalization for the $\Omega_0 = 0.1$ open model than does the DMR, and the Ka
and Ka + Q data prefer a somewhat lower normalization for the older, higher
$\Omega_B$, low-density $\Lambda$ models than does the DMR.",9602141v2
1996-06-09,Open universes from bubbles: an introduction and update,"An introduction to models of open universes originating from bubbles,
including a summary of recent theoretical results for the power spectrum. To
appear in the proceedings of the XXXIth Moriond meeting, ""Microwave Background
Anisotropies.""",9606052v2
1996-09-03,Ω_0 and λ_0 from galaxy and quasar clustering: cosmic virial theorem and cosmological redshift-space distortion,"I discuss two cosmological tests to determine the cosmological density
parameter \Omega_0 the cosmological constant \lambda_0, which make use of the
anisotropy of the two-point correlation functions due to the peculiar velocity
field and the cosmological redshift-space distortion.",9609014v1
1996-09-15,The MAX and MAXIMA Experiments,"We summarize the performance of the MAX experiment during its 5 years of
operation and present a compilation of the results to date. We describe MAXIMA,
a balloon borne experiment employing an array of detectors in the focal plane,
that will provide sensitive measurements of the power spectrum between l~60 and
l~650.",9609098v1
1997-02-19,Non-Gaussian Spectra in the Cosmic Microwave Background,"We propose a set of new statistics which can be extracted out of the angular
distribution of the Fourier transform of the temperature anisotropies in the
small field limit. They quantify generic non-Gaussian structure and complement
the power spectrum in characterizing the sampled distribution function of a
data set (contribution to the 18th Texas Symposium Proceedings)",9702164v1
1997-02-22,The Maxima and Boomerang Experiments,"MAXIMA and BOOMERanG are balloon borne experiments designed to map the cosmic
microwave background anisotropy power spectrum from l=10 to l=900 with high
resolution. Here we describe the program of observations, the experiments,
their capabilities, and their expected performance.",9702200v1
1997-03-31,Topological defects and open inflation,"Topological defects can naturally be formed soon after bubble nucleation in
the open inflation scenario. The defects are not completely diluted away by the
subsequent period of inflation in the bubble interior and can produce
observable large-scale microwave background anisotropies. Superheavy strings
and monopoles attached to the strings can act as gravitational lenses with
angular separation between the images of up to an arc minute.",9703201v1
1997-05-30,On the rotation of the universe,"We point on a different possible explanation of the observations reported
recently by Nodland and Ralston, PRL 78 (1997) 3043 [astro-ph/9704196]. The
dipole anisotropy of the polarization of radiation from the distant radio
sources can be caused by the global cosmic rotation. This explanation is of
purely geometric origin and is completely within the conventional physics.",9705243v1
1997-10-13,Breaking the degeneracy between anisotropy and mass: The dark halo of the E0 galaxy NGC 6703,"(abridged) We have measured line-of-sight velocity profiles (VPs) in the E0
galaxy NGC 6703 out to 2.6 R_e. From these data we constrain the mass
distribution and the anisotropy of the stellar orbits in this galaxy.
  We have developed a non-parametric technique to determine the DF f(E,L^2)
directly from the kinematic data. From Monte Carlo tests using the spatial
extent, sampling, and error bars of the NGC 6703 data we find that smooth
underlying DFs can be recovered to an rms accuracy of 12%, and the anisotropy
parameter beta(r) to an accuracy of 0.1, in a given potential. An
asymptotically constant halo circular velocity v_0 can be determined with an
accuracy of +- \lta 50km/s.
  For NGC 6703 we determine the true circular velocity at 2.6 R_e to be 250 +-
40km/s at 95% c.l., corresponding to a total mass in NGC 6703 inside 78'' (13.5
h_50^-1 kpc), of 1.6-2.6 x 10^11 h_50^-1 Msun. No model without dark matter
will fit the data; however, a maximum stellar mass model in which the luminous
component provides nearly all the mass in the centre does. In such a model, the
total luminous mass inside 78'' is 9 x 10^10 Msun and the integrated
M/L_B=5.3-10, corresponding to a rise from the center by at least a factor of
1.6.
  The anisotropy of the stellar distribution function in NGC 6703 changes from
near-isotropic at the centre to slightly radially anisotropic (beta=0.3-0.4 at
30'', beta=0.2-0.4 at 60'') and is not well-constrained at the outer edge of
the data.
  Our results suggest that also elliptical galaxies begin to be dominated by
dark matter at radii of \sim 10kpc.",9710129v1
1997-11-08,The Cosmic Background Radiation,"We summarise the current status of cosmic microwave background spectrum and
anisotropy measurements, and their theoretical interpretation. This is the
update of the mini-review for the 1997 web-version of the Review of Particle
Properties.",9711069v1
1997-11-27,Textures and Cosmic Microwave Background non-Gaussian Signatures,"We report briefly on a recent analysis of the texture-induced CMB radiation
three-point correlation function of temperature anisotropies as predicted by an
analytical model. We specialize our analysis to both large-scales (e.g., for
COBE-DMR, where we compare our prediction with the actual four-year data) and
intermediate-scales. We show how the latter case puts strong constraints on the
model parameters.",9711343v1
1998-01-15,Inflation and the cosmic microwave background,"I give a status report and outlook concerning the use of the cosmic microwave
background anisotropies to constrain the inflationary cosmology, and stress its
crucial role as an underlying paradigm for the estimation of cosmological
parameters.",9801148v1
1998-03-06,Generation of Gravitational Waves and Scalar Perturbations in Inflation with Effective $Λ$-term and T/S Story,"We argue that gravitational wave contribution to the cosmic microwave
background anisotropy at angular scale $\sim 10^0$ may exceed 50% for some
models of hybrid inflation producing standard cosmology with the density
perturbation slope $n \simeq 1$.",9803064v1
1998-03-13,Inflation and the microwave background,"I discuss the interplay between inflation and microwave background
anisotropies, stressing in particular the accuracy with which inflation
predictions need to be made, and the importance of inflation as an underlying
paradigm for cosmological parameter estimation.",9803152v1
1998-03-18,Anisotropy of CMB & Cosmological Model,"In this brief review I will touch upon the main points and thends of
observational and theoretical cosmology, that influence and change today our
understanding of the Universe.",9803212v1
1998-04-17,CMB anisotropies on circular scans,"We address the problem of map-making with data from the Planck Surveyor High
Frequency Instrument, with an emphasis on the understanding and modelling of
instrumental effects, and in particular that of sidelobe straylight. We propose
a map-making method which takes advantage of the very special properties of the
Planck scanning strategy along circular scans.",9804180v1
1998-07-31,Reconstructing the Primordial Power Spectrum,"Cosmological models predict transfer functions by which primordial density
perturbations develop into CMB anisotropy and Large-Scale Structure. We use the
current set of observations to reconstruct the primordial power spectrum for
standard CDM, CDM with a cosmological constant, open CDM, and standard CDM with
a high baryon content.",9807328v1
1998-11-11,Cosmic microwave background: polarization and temperature anisotropies from symmetric structures,"I consider the case of anisotropies in the Cosmic Microwave Background (CMB)
from one single ordered perturbation source, or seed, existing well before
decoupling between matter and radiation. Such structures could have been left
by high energy symmetries breaking in the early universe.
  I focus on the cases of spherical and cylindrical symmetry of the seed. I
give general analytic expressions for the polarization and temperature linear
perturbations, factoring out of the Fourier integral the dependence on the
photon propagation direction and on the geometric coordinates describing the
seed. I show how the CMB perturbations manifestly reflect the symmetries of
their seeds. CMB anisotropies are obtained with a line of sight integration.
  This treatment highlights the undulatory properties of the CMB. I show with
numerical examples how the polarization and temperature perturbations propagate
beyond the size of their seeds, reaching the CMB sound horizon at the time
considered. Just like the waves from a pebble thrown in a pond, CMB anisotropy
from a seed intersecting the last scattering surface appears as a series of
temperature and polarization waves surrounding the seed, extending on the scale
of the CMB sound horizon at decoupling, roughly $1^{o}$ in the sky. Each wave
is characterized by its own value of the CMB perturbation, with the same mean
amplitude of the signal coming from the seed interior.
  These waves could allow to distinguish relics from high energy processes of
the early universe from point-like astrophysical sources, because of their
angular extension and amplitude. Also, the marked analogy between polarization
and temperature signals offers cross correlation possibilities for the future
Planck Surveyor observations.",9811176v3
1998-11-24,Perturbations in Quintessential Inflation,"Recently Peebles and Vilenkin proposed and quantitatively analyzed the
fascinating idea that a substantial fraction of the present cosmic energy
density could reside in the vacuum potential energy of the scalar field
responsible for inflation (quintessential inflation). Here we compute the
signature of this model in the cosmic microwave background polarization and
temperature anisotropies and in the large scale structure.",9811385v1
1999-03-15,Anisotropies in the CMB,"The ten's of micro-Kelvin variations in the temperature of the cosmic
microwave background (CMB) radiation across the sky encode a wealth of
information about the Universe. The full-sky, high-resolution maps of the CMB
that will be made in the next decade should determine cosmological parameters
to unprecedented precision and sharply test inflation and other theories of the
early Universe.",9903232v1
1999-07-22,Constraints on the Cosmological Parameters using CMB observations,"This paper covers several techniques of intercomparison of Cosmic Microwave
Background (CMB) anisotropy experiments and models of structure formation. It
presents the constraints on several cosmological parameters using current CMB
observations.",9907312v1
1999-08-17,The 2-10 keV XRB dipole and its cosmological implications,"The hard X-ray (>2 keV) emission of the local and distant Universe as
observed with the HEAO1-A2 experiment is reconsidered in the context of large
scale cosmic structure. Using all-sky X-ray samples of AGN and galaxy clusters
we remove the dominant local X-ray flux from within a redshift of ~ 0.02. We
evaluate the dipolar and higher order harmonic structure in 4 X-ray colours.
The estimated dipole anisotropy of the unresolved flux appears to be consistent
with a combination of the Compton-Getting effect due to the Local Group motion
(dipole amplitude Delta = 0.0042) and remaining large scale structure (0.0023
<~ Delta <~ 0.0085), in good agreement with the expectations of Cold Dark
Matter models. The observed anisotropy does however also suggest a
non-negligible Galactic contribution which is more complex than current, simple
models of >2 keV Galactic X-ray emission. Comparison of the soft and hard
colour maps with a harmonic analysis of the 1.5 keV ROSAT all-sky data
qualitatively suggests that at least a third of the faint, unresolved ~ 18 deg
scale structure in the HEAO1-A2 data may be Galactic in origin. However, the
effect on measured flux dipoles is small (<~3%).
  We derive an expression for dipole anisotropy and acceleration and
demonstrate how the dipole anisotropy of the distant X-ray frame can constrain
the amplitude of bulk motions of the universe. From observed bulk motions over
a local ~ 50 Mpc/h radius volume we determine 0.14 <~ Omega^0.6/b_x(0) <~ 0.59.",9908187v2
1999-11-30,Effects of inflationary bubbles on the polarization and temperature anisotropies of the cosmic microwave background,"We predict the imprint of linear bubbly perturbations on the polarization and
temperature anisotropies of the cosmic microwave background (CMB).
  We analytically model a bubbly density perturbation at the beginning of the
radiation dominated era and we apply the linear theory of cosmological
perturbations to compute its time evolution. At decoupling, it uniquely signs
the CMB polarization and temperature anisotropy sky. During evolution the
perturbation propagates beyond the size of the bubble and reaches the CMB sound
horizon at the time considered. Therefore, its signal appears as a series of
concentric rings, each characterized by its own amplitude and sign, on the
scale of 1^{o} on the sky, even if the real seed size is much smaller.
Polarization and temperature rings are strictly correlated. As expected for
linear perturbations with size L and density contrast \delta at decoupling,
\delta T/T is roughly \delta (L/H^{-1})^{2}; the polarization is about 10% of
the temperature anisotropy.
  We predict the impact of a distribution of bubbles on the CMB polarization
and temperature power spectra. Considering models containing both CDM Gaussian
and bubbly non-Gaussian fluctuations, we simulate and analyze 10^{o} x 10^{o}
sky patches with angular resolution of about 3.5^{'}. The CMB power associated
with the bubbles is entirely on sub-degree angular scales (200<= l<=1000), that
will be explored by the forthcoming high resolution CMB experiments with the
percent precision. Depending on the parameters of the bubbly distribution we
find extra-power with respect to the ordinary CDM Gaussian fluctuations; we
infer simple analytical scalings of the power induced by bubbly perturbations
and we constrain our parameters with the existing data.",9911530v1
2000-01-25,Stellar Dynamics in the Galactic centre: Proper Motions and Anisotropy,"We report a new analysis of stellar dynamics in the Galactic centre, based on
improved sky and LOS velocities for >100 stars within a few arcsec of SgrA*.
Overall the motions do not deviate strongly from isotropy. For 32 stars with
all 3 components determined the absolute, LOS and sky velocities agree well, as
for a spherical cluster. The projected radial and tangential motions of all 104
pm stars are also consistent with overall isotropy. However, the projected
velocities of the young, early type stars have a strong radial dependence. Most
of the bright HeI stars 1-10"" from SgrA* are on tangential orbits. This
anisotropy of the HeI stars and most of the brighter IRS16 complex members is
largely caused by a CW and counter-rotating, coherent rotation pattern. The
overall rotation of the young star cluster probably is a remnant of the angular
momentum in the cloud these stars formed from. The fainter, fast stars within
\~1"" of SgrA* appear to be largely moving on radial or very elliptical orbits.
We have not detected nonlinear motion for any of them. Most of the SgrA*
cluster members also are on CW orbits. Spectroscopy shows them to be early type
stars. We propose that the SgrA* cluster stars are those members of the early
type cluster with small angular momentum which can plunge to the vicinity of
SgrA*. Our anisotropy-independent estimate of the Sun-GC distance is 7.8-8.2
kpc (+/- 0.9 kpc). We include velocity anisotropy in estimating the central
mass distribution. We confirm previous conclusions that a compact central mass
concentration is present and dominates the potential from 0.01-1 pc. The
central mass ranges from 2.6-3.3E6 M_sun. (abridged)",0001428v1
2000-03-22,The best unbiased estimator for the CMB angular bispectrum,"For those angular multipoles where cosmic variance is an issue,
non-Gaussianities in the Cosmic Microwave Background (CMB) anisotropies will be
hard to detect. Here, we construct explicitly the best unbiased estimator for
the CMB angular bispectrum.",0003335v1
2000-03-23,Cosmological Strucure Formation with Topological Defects,"Structure formation with topological defects is described. The main
differences from inflationary models are highlighted. The results are compared
with recent observations. It is concluded that all the defect models studied so
far are in disagreement with recent observations of CMB anisotropies.
Furthermore, present observations do not support 'decoherence', a generic
feature of structure formation from topological defects.",0003363v1
2000-06-28,Bayesian Methods for Cosmological Parameter Estimation from Cosmic Microwave Background Measurements,"We present a strategy for a statistically rigorous Bayesian approach to the
problem of determining cosmological parameters from the results of observations
of anisotropies in the cosmic microwave radiation background. We propose the
application of Markov chain Monte Carlo methods, specifically the
Metropolis-Hastings algorithm, to estimate the parameters. A complete
statistical analysis is presented, with the Metropolis-Hastings algorithm
described in detail.",0006401v1
2000-12-01,$Λ$-Inflation and CMBR Anisotropy,"We argue that a $\Lambda$-inflation model can ensure large relative
contribution of cosmic gravity waves into the $\Delta T/T$ at COBE scale
preserving at the same time a near scale-invariant spectrum of cosmological
density perturbations favored by observational data ($n_S\simeq 1$). High
efficiency of these models to meet observational tests is discussed.",0012014v1
2001-03-13,Quintessence and the first Doppler peak,"By using a tracking quintessence model we obtain that the position of the
first Doppler peak in the spectrum of CMB anisotropies only depends on the
topology of the universe, $\Omega_k$, for any value of the ratio
$\Omega_{\Lambda}/\Omega_M$, so that such a dependence is perfectly valid in
the range suggested by supernova observations.",0103194v1
2001-08-03,"Toward a Measurement of the Cosmological Geometry at z~2: Predicting Lyman-alpha Forest Correlation in Three Dimensions, and the Potential of Future Data Sets","The correlation between Lyman-alpha absorption in the spectra of quasar pairs
can be used to measure the transverse distance scale at z~2, which is sensitive
to the cosmological constant (Omega_Lambda) or other forms of vacuum energy.
Using Hydro-PM simulations, I compute the three-dimensional power spectrum of
the Lyman-alpha forest flux, P_F(k,mu), from which the redshift-space
anisotropy of the correlation can be obtained. I find that box size ~40 Mpc/h
and resolution ~40 Kpc/h are necessary for convergence of the calculations to
<5% on all relevant scales, although somewhat poorer resolution can be used for
large scales. I compute directly the linear theory bias parameters of the
Lyman-alpha forest, potentially allowing simulation results to be extended to
arbitrarily large scales. I investigate the dependence of P_F(k,mu) on the
primordial power spectrum, the temperature-density relation of the gas, and the
mean flux decrement, finding that the redshift-space anisotropy is relatively
insensitive to these parameters. A table of results is provided for different
parameter variations. I investigate the constraint that can be obtained on
Omega_Lambda using quasars from a large survey. Assuming 13 (theta/1')^2 pairs
at separation <theta, and including separations <10', a measurement to <5% can
be made if simulations can predict the redshift-space anisotropy with <5%
accuracy, or to <10% if the anisotropy must be measured from the data. The
Sloan Digital Sky Survey (SDSS) will obtain spectra for a factor ~5 fewer pairs
than this, so followup observations of fainter pair candidates will be
necessary. I discuss the requirements on spectral resolution and
signal-to-noise ratio (SDSS-quality spectra are sufficient).",0108064v1
2001-09-12,Separation of instrumental and astrophysical foregrounds for mapping CMB anisotropies,"We address the extended problem of component separation for CMB applications
when a mixture of both astrophysical and instrumental components are present in
the observations, and show how standard methods can be adapted to handle this
more complex inversion problem.",0109187v1
2001-11-27,CMB: The ultimate test for theoretical models aiming at describing the very early universe,"In this talk, I will illustrate how one can use the cosmic microwave
background anisotropy measurements, in order to test theoretical models aiming
at describing the early universe.",0111501v1
2002-04-16,Cosmology Rounding the Cape,"A survey is made of the present observational status on cosmological
parameters from microwave background anisotropies. I then move to some
non-standard aspect of parameter extraction like quintessence, extra-background
of relativistic particles and variations in fundamental constants.",0204262v1
2002-05-10,Ultrahigh energy cosmic rays from dark matter annihilation,"Annihilation of clumped superheavy dark matter provides an interesting
explanation for the origin of ultrahigh energy cosmic rays.
  The predicted anisotropy signal provides a unique signature for this
scenario.",0205158v1
2002-09-26,"CMB Anisotropy Constraints on Flat-Lambda and Open CDM Cosmogonies from DMR, UCSB South Pole, Python, ARGO, MAX, White Dish, OVRO, and SuZIE Data","We use joint likelihood analyses of combinations of fifteen cosmic microwave
background (CMB) anisotropy data sets from the DMR, UCSB South Pole 1994,
Python I--III, ARGO, MAX 4 and 5, White Dish, OVRO, and SuZIE experiments to
constrain cosmogonies. We consider open and spatially-flat-Lambda cold dark
matter cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the
range 0.1--1, baryonic-mass density parameter Omega_B in the range
(0.005--0.029) h^{-2}, and age of the universe t_0 in the range (10--20) Gyr.
  Marginalizing over all parameters but Omega_0, the data favor Omega_0 \simeq
0.9--1 (0.4--0.6) flat-Lambda (open) models. The range in deduced Omega_0
values is partially a consequence of the different combinations of
smaller-angular-scale CMB anisotropy data sets used in the analyses, but more
significantly a consequence of whether the DMR quadrupole moment is accounted
for or ignored in the analysis. For both flat-Lambda and open models, after
marginalizing over all other parameters, a lower Omega_B h^2 \simeq
0.005--0.009 is favored. This is also marginally at odds with estimates from
more recent CMB anisotropy data and some estimates from standard
nucleosynthesis theory and observed light element abundances. For both sets of
models a younger universe with t_0 \simeq 12--15 Gyr is favored, consistent
with other recent non-CMB indicators. We emphasize that since we consider only
a small number of data sets, these results are tentative. More importantly, the
analyses here do not rule out the currently favored flat-Lambda model with
Omega_0 \sim 0.3, nor the larger Omega_B h^2 values favored by some other data.",0209567v1
2003-01-10,The Microwave Anisotropy Probe (MAP) Mission,"The purpose of the MAP mission is to determine the geometry, content, and
evolution of the universe via a 13 arcmin full-width-half-max (FWHM) resolution
full sky map of the temperature anisotropy of the cosmic microwave background
radiation with uncorrelated pixel noise, minimal systematic errors,
multifrequency observations, and accurate calibration. These attributes were
key factors in the success of NASA's Cosmic Background Explorer (COBE) mission,
which made a 7 degree FWHM resolution full sky map, discovered temperature
anisotropy, and characterized the fluctuations with two parameters, a power
spectral index and a primordial amplitude. Following COBE considerable progress
has been made in higher resolution measurements of the temperature anisotropy.
With 45 times the sensitivity and 33 times the angular resolution of the COBE
mission, MAP will vastly extend our knowledge of cosmology. MAP will measure
the physics of the photon-baryon fluid at recombination. From this, MAP
measurements will constrain models of structure formation, the geometry of the
universe, and inflation. In this paper we present a pre-launch overview of the
design and characteristics of the MAP mission. This information will be
necessary for a full understanding of the MAP data and results, and will also
be of interest to scientists involved in the design of future cosmic microwave
background experiments and/or space science missions.",0301158v1
2003-05-22,Scaling properties of the cosmic background plasma and radiation,"Scaling properties of the cosmic microwave background (CMB) radiation are
studied using satellite (COBE-DMR maps), balloon-borne and ground-based
(combined QMASK map) data. Quantitative consistency is found between the
multiscaling properties of the COBE-DMR and QMASK CMB maps. Surprisingly, it is
found that the observed CMB temperature multiscaling resembles quantitatively
the multiscaling properties of fluid turbulence, that indicates primordial
plasma turbulence as an origin of the CMB temperature space anisotropy.",0305433v1
2003-05-30,The CAPMAP Instrument and its First Season,"I describe here the new CAPMAP (Cosmic Anisotropy Polarization MAPer)
instrument, which performed its first season of observing between February and
April 2003 from the Crawford Hill 7-meter antenna in NJ. CAPMAP is based on the
design for the PIQUE instrument, but has better sensitivity and superior
angular resolution.",0306002v1
2003-07-31,An update on Archeops: flights and data products,"Archeops is a balloon-borne instrument dedicated to measuring CMB temperature
anisotropies at high resolution over a large fraction of sky. We present the
Archeops flights and data products, Archeops results, and the future use of
Archeops data for multi-experiment data analysis.",0307550v1
2003-07-31,"The Transverse Proximity Effect: A Probe to the Environment, Anisotropy, and Megayear Variability of QSOs","The transverse proximity effect is the expected decrease in the strength of
the Lya forest absorption in a QSO spectrum when another QSO lying close to the
line of sight enhances the photoionization rate above that due to the average
cosmic ionizing background. We select three QSOs from the Early Data Release of
the Sloan Digital Sky Survey that have nearby foreground QSOs, with proper line
of sight tangential separations of 0.50, 0.82, and 1.10 h^{-1} Mpc. We estimate
that the ionizing flux from the foreground QSO should increase the
photoionization rate by a factor (94, 13, 13) in these three cases, which would
be clearly detectable in the first QSO and marginally so in the other two. We
do not detect the transverse proximity effect. Three possible explanations are
provided: an increase of the gas density in the vicinity of QSOs, time
variability, and anisotropy of the QSO emission. We find that the increase of
gas density near QSOs can be important if they are located in the most massive
halos present at high redshift, but is not enough to fully explain the absence
of the transverse proximity effect. Anisotropy requires an unrealistically
small opening angle of the QSO emission. Variability demands that the
luminosity of the QSO with the largest predicted effect was much lower 10^6
years ago, whereas the transverse proximity effect observed in the HeII Lya
absorption in QSO 0302-003 by Jakobsen et al. (2003) implies a lifetime longer
than 10^7 years. A combination of all three effects may better explain the lack
of Lya absorption reduction. A larger sample of QSO pairs may be used to
diagnose the environment, anisotropy and lifetime distribution of QSOs.",0307563v2
2003-10-17,Multipole Vectors--a new representation of the CMB sky and evidence for statistical anisotropy or non-Gaussianity at 2<=l<=8,"We propose a novel representation of cosmic microwave anisotropy maps, where
each multipole order l is represented by l unit vectors pointing in directions
on the sky and an overall magnitude. These ""multipole vectors and scalars""
transform as vectors under rotations. Like the usual spherical harmonics,
multipole vectors form an irreducible representation of the proper rotation
group SO(3). However, they are related to the familiar spherical harmonic
coefficients, alm, in a nonlinear way, and are therefore sensitive to different
aspects of the CMB anisotropy. Nevertheless, it is straightforward to determine
the multipole vectors for a given CMB map and we present an algorithm to
compute them. Using the WMAP full-sky maps, we perform several tests of the
hypothesis that the CMB anisotropy is statistically isotropic and Gaussian
random. We find that the result from comparing the oriented area of planes
defined by these vectors between multipole pairs 2<=l1!=l2<=8 is inconsistent
with the isotropic Gaussian hypothesis at the 99.4% level for the ILC map and
at 98.9% level for the cleaned map of Tegmark et al. A particular correlation
is suggested between the l=3 and l=8 multipoles, as well as several other
pairs. This effect is entirely different from the now familiar planarity and
alignment of the quadrupole and octupole: while the aforementioned is fairly
unlikely, the multipole vectors indicate correlations not expected in Gaussian
random skies that make them unusually likely. The result persists after
accounting for pixel noise and after assuming a residual 10% dust contamination
in the cleaned WMAP map. While the definitive analysis of these results will
require more work, we hope that multipole vectors will become a valuable tool
for various cosmological tests, in particular those of cosmic isotropy.",0310511v2
2004-01-07,An updated nuclear reaction network for BBN,"The key Standard-Physics inputs of the Big Bang Nucleosynthesis (BBN) are the
light nuclei reaction rates. Both the network and the nuclear rates have been
recently reanalyzed and updated, and cosmological and New-Physics constraints
(taking into account the WMAP Cosmic Microwave Background anisotropies
measurement) obtained with a new code are presented.",0401072v1
2004-03-31,Gradient measure and extended self-similarity of the cosmic microwave background anisotropy,"Using the WMAP cosmic microwave background data it is shown that collisions
between Alfven wave packets and the cascades generated by these collisions (the
Iroshnikov model) can determine the photon temperature fluctuations for
arcminute scales on the last scattering surface.",0403702v2
2004-04-27,Pre-inflation models and WMAP data,"The effect of pre-inflation physics on the power spectrum of scalar
perturbations is estimated and there is a possibility that the pre-inflation
physics explains the Wilkinson Microwave Anisotropy Probe data if the length of
inflation is near 60 e-folds. Considering various pre-inflation models with
radiation-dominated or matter-dominated periods before inflation, the power
spectrum of curvature perturbations for large scales is calculated, and the
spectral index and running spectral index are derived.",0404519v1
2004-05-02,Low-order multipole maps of CMB anisotropy derived from WMAP,"Recent analyses of the WMAP data have suggested that the low-order multipoles
of the CMB anisotropy distribution show cosmologically interesting and
unexpected morphologies and amplitudes. In this paper, we apply a power
equalization (PE) filter to the high-latitude WMAP data in order to reconstruct
these low-l multipoles free from the largest Galactic foreground modelling
uncertainties in the Galactic plane. The characteristic spatial distributions
of the modes of order l=2,3,4,5 have been determined as a function of
frequency, sky coverage and two methods for foreground correction: using the
template fitting results of Bennett et al. (2003) and by a simple linear
projection scheme assuming the spectral dependence of the foreground
components. Our analyses suggest that the K and Ka frequency bands remain
significantly contaminated by residual foreground emission for the WMAP Kp2
mask. However, the l=3,4,5 multipole maps for the Q, V and W channels indicate
that, after foreground cleaning, these multipoles are dominated by the CMB
anisotropy component. We confirm the Tegmark et al. (2003) result that the
octopole does indeed show structure in which its hot and cold spots are centred
on a single plane in the sky, and show further that this is very stable with
respect to the applied mask and foreground correction. The estimated quadrupole
is much less stable showing non-negligible dependence on the Galactic
foreground correction. Including these uncertainties is likely to weaken the
statistical significance of the claimed alignment between the quadrupole and
octopole. Nevertheless, these anisotropy patterns are also present for in
COBE-DMR data, and are unlikely to be associated with instrumental systematic
artifacts.",0405007v3
2004-10-26,Inflation: Where Do We Stand?,"In this short review, the predictions of inflation are presented and compared
to the most recent measurements of the Cosmic Microwave Background (CMB)
anisotropy. It is argued that inflation is compatible with these observations
but that these ones are not yet accurate enough to probe the details of the
scenario.",0410629v1
2004-11-02,High Redshift Intergalactic Medium: Probes and Physical Models,"Recent years have seen major advances in understanding the state of the
intergalactic medium (IGM) at high redshift. Some aspects of this understanding
are reviewed here. In particular, we discuss: (1) Different probes of IGM like
Gunn-Peterson test, CMBR anisotropies, and neutral hydrogen emission from
reionization, and (2) some models of reionization of the universe.",0411050v1
2004-12-16,Can one hear the shape of the Universe?,"It is shown that the recent observations of NASA's explorer mission
""Wilkinson Microwave Anisotropy Probe"" (WMAP) hint that our Universe may
possess a non-trivial topology. As an example we discuss the Picard space which
is stretched out into an infinitely long horn but with finite volume.",0412407v1
2005-08-18,Going Nonlinear with Dark Energy Cosmologies,"We propose an efficient method for generating high accuracy (~1%) nonlinear
power spectra for grids of dark energy cosmologies. Our prescription for
matching matter growth automatically matches the main features of the cosmic
microwave background anisotropy power spectrum, thus naturally including ``CMB
priors''.",0508401v1
2005-11-25,Mass distribution in nearby Abell clusters,"We study the mass distribution in six nearby (z<0.06) relaxed Abell clusters
of galaxies A0262, A0496, A1060, A2199, A3158 and A3558. Given the dominance of
dark matter in galaxy clusters we approximate their total density distribution
by the NFW formula characterized by virial mass and concentration. We also
assume that the anisotropy of galactic orbits is reasonably well described by a
constant and that galaxy distribution traces that of the total density. Using
the velocity and position data for 120-420 galaxies per cluster we calculate,
after removal of interlopers, the profiles of the lowest-order even velocity
moments, dispersion and kurtosis. We then reproduce the velocity moments by
jointly fitting the moments to the solutions of the Jeans equations. Including
the kurtosis in the analysis allows us to break the degeneracy between the mass
distribution and anisotropy and constrain the anisotropy as well as the virial
mass and concentration. The method is tested in detail on mock data extracted
from N-body simulations of dark matter haloes. We find that the best-fitting
galactic orbits are remarkably close to isotropic in most clusters. Using the
fitted pairs of mass and concentration parameters for the six clusters we
conclude that the trend of decreasing concentration for higher masses found in
cosmological N-body simulations is consistent with the data. By scaling the
individual cluster data by mass we combine them to create a composite cluster
with 1465 galaxies and perform a similar analysis on such sample. The estimated
concentration parameter then lies in the range 1.5 < c < 14 and the anisotropy
parameter in the range -1.1 < \beta < 0.5 at the 95 percent confidence level.",0511723v2
2005-12-08,Anisotropy of the cosmic gamma-ray background from dark matter annihilation,"High-energy photons from dark matter annihilation contribute to the cosmic
gamma-ray background (CGB). Since dark matter particles are weakly interacting,
annihilation can happen only in high density regions such as dark matter halos.
The precise shape of the energy spectrum of CGB depends on the nature of dark
matter particles, as well as the cosmological evolution of dark matter halos.
In order to discriminate between the signals from dark matter annihilation and
other astrophysical sources, however, the information from the energy spectrum
may not be sufficient. We show that dark matter annihilation also produces a
characteristic anisotropy of the CGB, which provides a powerful tool for
testing the origin. We develop the formalism based on a halo model approach to
calculate the three-dimensional power spectrum of dark matter clumping, which
determines the power spectrum of annihilation signals. We show that the
sensitivity of future gamma-ray detectors such as GLAST should allow us to
measure the angular power spectrum of CGB anisotropy, if dark matter particles
are supersymmetric neutralinos and they account for most of the observed mean
intensity of CGB in GeV region. On the other hand, if dark matter has a
relatively small mass, and accounts for most of the CGB in MeV region, then the
future Advanced Compton Telescope should be able to measure the anisotropy in
MeV region. As the intensity of photons from annihilation is proportional to
the density squared, we show that the predicted shape of the angular power
spectrum of gamma rays from dark matter annihilation is different from that due
to other astrophysical sources such as blazars. Therefore, the angular power
spectrum of the CGB provides a smoking-gun signature of dark matter
annihilation.",0512217v2
2006-05-26,Cosmological and Astrophysical Parameter Measurements with 21-cm Anisotropies During the Era of Reionization,"We study the prospects for extracting cosmological and astrophysical
parameters from the low radio frequency 21-cm background due to the spin-flip
transition of neutral Hydrogen during and prior to the reionization of the
Universe. We make use of the angular power spectrum of 21-cm anisotropies,
which exists due to inhomogeneities in the neutral Hydrogen density field, the
gas temperature field, the gas velocity field, and the spatial distribution of
the Lyman-$\alpha$ intensity field associated with first luminous sources that
emit UV photons. We extract parameters that describe both the underlying mass
power spectrum and the global cosmology, as well as a set of simplified
astrophysical parameters that connect fluctuations in the dark matter to those
that govern 21-cm fluctuations. We also marginalize over a model for the
foregrounds at low radio frequencies. In this general description, we find
large degeneracies between cosmological parameters and the astrophysical
parameters, though such degeneracies are reduced when strong assumptions are
made with respect to the spin temperature relative to the CMB temperature or
when complicated sources of anisotropy in the brightness temperature are
ignored. Some of the degeneracies between cosmological and astrophysical
parameters are broken when 21-cm anisotropy measurements are combined with
information from the CMB, such as the temperature and the polarization
measurements with Planck. While the overall improvement on the cosmological
parameter estimates is not significant when measurements from first-generation
interferometers are combined with Planck, such a combination can measure
astrophysical parameters such as the ionization fraction in several redshift
bins with reasonable accuracy.",0605677v3
2006-10-31,Open questions with ultra-high energy cosmic rays,"We briefly discuss three aspects related to the origin of ultra-high energy
cosmic rays (UHECRs) namely: 1) particle acceleration in astrophysical sources;
2) transition to an extragalactic origin; 3) spectrum and anisotropies at the
highest energies.",0610951v1
2006-11-07,Improved Measurements of the CMB Power Spectrum with ACBAR,"We report improved measurements of temperature anisotropies in the cosmic
microwave background (CMB) radiation made with the Arcminute Cosmology
Bolometer Array Receiver (ACBAR). In this paper, we use a new analysis
technique and include 30% more data from the 2001 and 2002 observing seasons
than the first release to derive a new set of band-power measurements with
significantly smaller uncertainties. The planet-based calibration used
previously has been replaced by comparing the flux of RCW38 as measured by
ACBAR and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR.
The resulting power spectrum is consistent with the theoretical predictions for
a spatially flat, dark energy dominated LCDM cosmology including the effects of
gravitational lensing. Despite the exponential damping on small angular scales,
the primary CMB fluctuations are detected with a signal-to-noise ratio of
greater than 4 up to multipoles of l=2000. This increase in the precision of
the fine-scale CMB power spectrum leads to only a modest decrease in the
uncertainties on the parameters of the standard cosmological model. At high
angular resolution, secondary anisotropies are predicted to be a significant
contribution to the measured anisotropy. A joint analysis of the ACBAR results
at 150 GHz and the CBI results at 30 GHz in the multipole range 2000 < l < 3000
shows that the power, reported by CBI in excess of the predicted primary
anisotropy, has a frequency spectrum consistent with the thermal
Sunyaev-Zel'dovich effect and inconsistent with primary CMB. The results
reported here are derived from a subset of the total ACBAR data set; the final
ACBAR power spectrum at 150 GHz will include 3.7 times more effective
integration time and 6.5 times more sky coverage than is used here.",0611198v1
1993-08-01,Variational bound for the energy of two-dimensional quantum antiferromagnet,"We obtain the variational upper bound for the ground- state energy of
two-dimensional antiferromagnetic Heisenberg model on a square lattice at
arbitrary value of the anisotropy parameter using the two-dimensional
generalization of Jordan-Wigner transformation. Our result can be considered as
an upper bound for the perturbation theory series about the Ising limit.",9307067v1
1995-04-24,An Upsilon Point in a Spin Model,"We present analytic evidence for the occurrence of an upsilon point, an
infinite checkerboard structure of modulated phases, in the ground state of a
spin model. The structure of the upsilon point is studied by calculating
interface--interface interactions using an expansion in inverse spin
anisotropy.",9504093v1
1995-06-29,Theory of Nuclear Magnetic Relaxation in Haldane Gap Antiferromagnets,"A theory of Nuclear Magnetic Resonance (NMR) is developed for integer-spin,
one-dimensional antiferromagnets, which exhibit the Haldane gap. We consider
free boson, free fermion and non-linear sigma model approaches, all of which
give similar results. Detailed anisotropy and magnetic field dependence is
calculated and compared with experiment.",9506137v3
1995-10-01,Ultrasound attenuation in gap-anisotropic systems,"Transverse ultrasound attenuation provides a weakly-coupled probe of momentum
current correlations in electronic systems. We develop a simple theory for the
interpretation of transverse ultrasound attenuation coefficients in systems
with nodal gap anisotropy. Applying this theory we show how ultrasound can
delineate between extended-s and d-wave scenarios for the cuprate
superconductors.",9509177v2
1996-10-01,Generalized London free energy for high-$T_c$ vortex lattices,"We generalize the London free energy to include four-fold anisotropies which
could arise from d-wave pairing or other sources in a tetragonal material. We
use this simple model to study vortex lattice structure and discuss neutron
scattering, STM, Bitter decoration and $\mu$SR experiments.",9610006v1
1996-10-30,Fermi Surface of the 2D Hubbard Model at Weak Coupling,"We calculate the interaction-induced deformation of the Fermi surface in the
two-dimensional Hubbard model within second order perturbation theory. Close to
half-filling, interactions enhance anisotropies of the Fermi surface, but they
never modify the topology of the Fermi surface in the weak coupling regime.",9610216v2
1996-12-03,The Critical Temperature of an Anisotropic Superconductor in the Presence of a Homogeneous Magnetic Field and Impurities,"The effect of a homogeneous magnetic field and nonmagnetic impurities on the
critical temperature of an anisotropic superconductor has been investigated.
The role of these pair-breakers in relation to the anisotropy of the order
parameter is clarified.",9612030v1
1997-03-12,Only Fermi-Liquids are Metals,"Any singular deviation from Landau Fermi-liquid theory appears to lead, for
arbitrarily small concentration of impurities coupling to a non-conserved
quantity, to a vanishing density of states at the chemical potential and
infinite resistivity as temperature approaches zero. Applications to
copper-oxide metals including the temperature dependence of the anisotropy in
resistivity, and to other cases of non Fermi-liquids are discussed.",9703122v1
1997-09-13,Spin-density Wave in Ising-coupled Antiferromagnetic Chains,"The effect of anisotropy in the nearest-neighbor spin interactions that
couple $N\geq 2$ consecutive spin-1/2 antiferromagnetic chains is studied
theoretically by considering the limit where the coupling is purely of the
Ising type. An analysis based on the equivalent Luttinger model reveals that
the groundstate is an Ising antiferromagnet in general.",9709153v1
1998-02-04,Exact Correlation Amplitude for the S=1/2 Heisenberg Antiferromagnetic Chain,"The exact amplitude for the asymptotic correlation function in the S=1/2
Heisenberg antiferromagnetic chain is determined: <S^a_0 S^b_r> goes to (-1)^r
delta^{ab}(ln r)^{1/2}/[(2 pi)^{3/2}r]. The behaviour of the correlation
functions for small xxz anisotropy and the form of finite-size corrections to
the correlation function are also analysed.",9802045v2
1998-07-14,Non-equilibrium critical behavior of O(n)-symmetric systems: Effect of reversible mode-coupling terms and dynamical anisotropy,"Phase transitions in non-equilibrium steady states of O(n)-symmetric models
with reversible mode couplings are studied using dynamic field theory and the
renormalization group. The systems are driven out of equilibrium by dynamical
anisotropy in the noise for the conserved quantities, i.e., by constraining
their diffusive dynamics to be at different temperatures T^\par and T^\perp in
d_\par- and d_\perp-dimensional subspaces, respectively. In the case of the
Sasv'ari-Schwabl-Sz'epfalusy (SSS) model for planar ferro- and isotropic
antiferromagnets, we assume a dynamical anisotropy in the noise for the
non-critical conserved quantities that are dynamically coupled to the
non-conserved order parameter. We find the equilibrium fixed point (with
isotropic noise) to be stable with respect to these non-equilibrium
perturbations, and the familiar equilibrium exponents therefore describe the
asymptotic static and dynamic critical behavior. Novel critical features are
only found in extreme limits, where the ratio of the effective noise
temperatures T^\par/T^\perp is either zero or infinite. On the other hand, for
model J for isotropic ferromagnets with a conserved order parameter, the
dynamical noise anisotropy induces effective long-range elastic forces, which
lead to a softening only of the d_\perp-dimensional sector in wavevector space
with lower noise temperature T^\perp < T^\par. The ensuing static and dynamic
critical behavior is described by power laws of a hitherto unidentified
universality class, which, however, is not accessible by perturbational means
for d_\par \geq 1. We obtain formal expressions for the novel critical
exponents in a double expansion about the static and dynamic upper critical
dimensions and d_\par, i.e., about the equilibrium theory.",9807207v2
1998-10-21,Competition of Ferromagnetic and Antiferromagnetic Order in the Spin-1/2 XXZ Chain at Finite Temperature,"An analytical study is presented of the crossover in the gapless attractive
XXZ chain from antiferromagnetic to ferromagnetic behaviour at low to high
temperature, respectively. In particular, an analytic formula for the crossover
in the long distance asymptotics and explicit results for the nearest-neighbour
longitudinal correlation are obtained. We also provide results for the specific
heat and magnetic susceptibility for various anisotropies.",9810278v1
1999-01-08,Solidity of viscous liquids II: Anisotropic flow events,"Recent findings on the displacements in the surroundings of isotropic flow
events in viscous liquids [Phys. Rev. E, to appear Feb. 1999] are generalized
to the anisotropic case. Also, it is shown that a flow event is characterized
by a dimensionless number reflecting the degree of anisotropy.",9901061v1
1999-10-14,Magnetic field induced directional localization in a 2D rectangular lattice,"We study the effect of a perpendicular uniform magnetic field on the
dissipative conductivity of a rectangular lattice with anisotropic hopping,
$t_x\neq t_y $. We show that the magnetic field may enhance dramatically the
directional anisotropy in the conductivity. The effect is a measurable physical
realization of Aubry's duality in Harper systems.",9910209v1
1999-12-07,Impurity Scattering in f-wave Superconductor UPt_3,"We study theoretically the effect of impurity scattering in f-wave (or
E_{2u}) superconductors. The quasi-particle density of states of f-wave
superconductor is very similar to the one for d-wave superconductor as in
hole-doped high T_c cuprates. Also in spite of anisotropy in Delta(k), both the
normalized superfluid density and the thermal conductivity is completely
isotropic.",9912124v1
2000-02-28,The puzzle of 90 degree reorientation in the vortex lattice of borocarbide superconductors,"We explain 90 degree reorientation in the vortex lattice of borocarbide
superconductors on the basis of a phenomenological extension of the nonlocal
London model that takes full account of the symmetry of the system. We propose
microscopic mechanisms that could generate the correction terms and point out
the important role of the superconducting gap anisotropy.",0002431v1
2000-04-24,Vector lattice model for stresses in granular materials,"A vector lattice model for stresses in granular materials is proposed. A two
dimensional pile built by pouring from a point is constructed numerically
according to this model. Remarkably, the pile violates the Mohr Coulomb
stability criterion for granular matter, probably because of the inherent
anisotropy of such poured piles. The numerical results are also compared to the
earlier continuum FPA model and the (scalar) lattice $q$-model.",0004399v1
2000-05-13,Restoration of Macroscopic Isotropy on $(d+1)$-Simplex Fractal Conductor Networks,"Restoration of macroscopic isotropy has been investigated in (d+1)-simplex
fractal conductor networks via exact real space renormalization group
transformations. Using some theorems of fixed point theory, it has been shown
very rigoroursly that the macroscopic conductivity becomes isotropic for large
scales and anisotropy vanishes with a scaling exponent which is computed
exactly for arbitrary values of d and decimation numbers b=2,3,4 and
  5.",0005227v1
2001-01-04,Finite Size Scaling of the 2D Six-Clock model,"We investigate the isotropic-anisotropic phase transition of the
two-dimensional XY model with six-fold anisotropy, using Monte Carlo
renormalization group method. The result indicates difficulty of observing
asymptotic critical behavior in Monte Carlo simulations, owing to the marginal
flow at the fixed point.",0101035v1
2001-01-04,Coulomb effects in dynamics of polar lattices,"Zone-center phonon frequencies of polar lattices are calculated for uniaxial
crystals from the symmetry arguments. Long-range Coulomb forces and crystal
anisotropy are explicitly taken into account. Free-carrier contributions into a
dielectric constant are included. The angular dispersion of optical-phonon
modes is compared with data for hexagonal 6H-SiC politype.",0101050v1
2002-01-16,A Model for Granular Texture with Steric Exclusion,"We propose a new method to characterize the geometrical texture of a granular
packing at the particle scale including the steric hindrance effect. This
method is based on the assumption of a maximum disorder (entropy) compatible
both with strain-induced anisotropy of the contact network and steric
exclusions. We show that the predicted statistics for the local configurations
is in a fairly agreement with our numerical data.",0201275v1
2002-03-03,Symmetry Properties of Anisotropic Superfluids,"A system of equations is developed for a fluid with non-abelian local gauge
symmetry. Anisotropy is introduced by requiring that the symmetry breaking
preserves a restricted local gauge symmetry about a given direction in the
gauge parameter space. A set of equations is proposed for the 3He-A system.
Topological quantization conditions are discussed.",0203045v1
2002-04-01,Ground-State Phase Diagram of Frustrated Anisotropic Quantum Spin Chains,"Recent studies on the frustrated quantum spin chains with easy-plane
anisotropy are reviewed. We are particularly interested in novel ""chiral""
phases characterized by the spontaneous breaking of the parity symmetry. The
ground-state phase diagrams of the chains are discussed.",0204022v1
2002-05-13,Critical behavior of vector models with cubic symmetry,"We report on some results concerning the effects of cubic anisotropy and
quenched uncorrelated impurities on multicomponent spin models. The analysis of
the six-loop three-dimensional series provides an accurate description of the
renormalization-group flow.",0205251v1
2002-10-24,Competing interactions in the XYZ model,"We study the interplay between a XY anisotropy $\gamma$, exchange modulations
and an external magnetic field along the z direction in the XYZ chain using
bosonization and Lanczos diagonalization techniques. We find an Ising critical
line in the space of couplings which occur due to competing relevant
perturbations which are present. More general situations are also discussed.",0210546v1
2003-03-19,A new class of nodal stationary states in 2D Heisenberg ferromagnet,"A new class of nodal topological excitations in a two-dimensional Heisenberg
model is studied. The solutions correspond to a nodal singular point of the
gradient field of the azimuthal angle. An analytical solution found for the
isotropic case. An effect of in-plane exchange anisotropy is studied
numerically. It results in solutions which are analogues of the conventional
out-of-plane solitons in the two-dimensional magnets.",0303388v1
2003-04-18,Superradiation from Crystals of High-Spin Molecular Nanomagnets,"Phenomenological theory of superradiation from crystals of high-spin
molecules is suggested. We show that radiation friction can cause a
superradiation pulse and investigate the role of magnetic anisotropy, external
magnetic field and dipole-dipole interactions. Depending on the contribution of
all these factors at low temperature, several regimes of magnetization of
crystal sample are described. Very fast switch of magnetization's direction for
some sets of parameters is predicted.",0304424v1
2003-07-17,Local density of states induced by anisotropic impurity scattering in a d-wave superconductor,"We study a single impurity effect on the local density of states in a d-wave
superconductor accounting for the momentum-dependent impurity potential. We
show that the anisotropy of the scattering potential can alter significantly
the spatial dependence of the quasiparticle density of states in the vicinity
of the impurity.",0307427v1
2003-09-28,Liquid Crystals in Electric Field,"We present a general theory of electric field effects in liquid crystals
where the dielectric tensor depends on the orientation order. As applications,
we examine (i) the director fluctuations in nematic states in electric field
for arbitrary strength of the dielectric anisotropy and (ii) deformation of the
nematic order around a charged particle. Some predictions are made for these
effects.",0309643v1
2004-03-31,1D Exciton Spectroscopy of Semiconductor Nanorods,"We have theoretically shown that optical properties of semiconductor nanorods
are controlled by 1D excitons. The theory, which takes into account anisotropy
of spacial and dielectric confinement, describes size dependence of interband
optical transitions, exciton binding energies. We have demonstrated that the
fine structure of the ground exciton state explains the linear polarization of
photoluminescence. Our results are in good agreement with the measurements in
CdSe nanorods.",0403768v1
2004-04-14,On the theory of pseudogap anisotropy in the cuprate superconductors,"We show by means of the theory of the order parameter phase fluctuations that
the temperature of ""closing"" (or ""opening"") of the gap (and pseudogap) in the
electron spectra of superconductors with anisotropic order parameter takes
place within a finite temperature range. Every Fourier-component of the order
parameter has its own critical temperature.",0404335v3
2004-05-18,Multichannel field-effect spin barrier selector,"We have studied spin carrier dynamics under full spin-orbit coupling. The
anisotropy of dispersions for independent circular spinor polarizations is
explored as a possible vertical multichannel voltage controlled spin-filter.
Small voltage variations are found to select the current polarizations in a
resonant tunneling geometry.",0405418v1
2004-05-29,Anomalous interaction between vortices and nanomagnets,"We study a thin film system consisting of a superconducting and a magnetic
film, where the superconductor contains a vortex and the magnetic film a
nanomagnet. We find that if the magnetic film has planar anisotropy, the vortex
induces a magnetization distribution, and its interaction with the nanomagnet
crosses over from attractive to repulsive at short distances.",0405690v1
2004-09-27,Electronic Structure and Magnetic Properties of Solids,"We review basic computational techniques for simulations of various magnetic
properties of solids. Several applications to compute magnetic anisotropy
energy, spin wave spectra, magnetic susceptibilities and temperature dependent
magnetisations for a number of real systems are presented for illustrative
purposes.",0409704v1
2004-10-06,Superconductivity of Magnesium Diboride: Theoretical Aspects,"In this work we review our present understanding of superconductivity in
Magnesium Diboride from the theoretical perspective as it evolves from band
structure calculations. Particular emphasis is placed on two gap
superconductivity. Some of its peculiar consequences are discussed, in
particular upper critical field anisotropy and microwave conductivity.",0410158v1
2004-12-15,Elastic medium confined in a column versus the Janssen experiment,"We compute the stresses in an elastic medium confined in a vertical column,
when the material is at the Coulomb threshold everywhere at the walls.
Simulations are performed in 2 dimensions using a spring lattice, and in 3
dimensions, using Finite Element Method. The results are compared to the
Janssen model and to experimental results for a granular material. The
necessity to consider elastic anisotropy to render qualitatively the
experimental findings is discussed.",0412400v1
2005-03-02,Quantum shape effects on Zeeman splittings in semiconductor nanostructures,"We develop a general method to calculate Zeeman splittings of electrons and
holes in semiconductor nanostructures within the tight-binding framework. The
calculation is carried out in the electron-hole picture and is extensible to
the excitonic calculation by including the electron-hole Coulomb interaction.
The method is suitable for the investigation of quantum shape effects and the
anisotropy of the g-factors. Numerical results for CdSe and CdTe nanostructures
are presented.",0503042v1
2005-03-14,Carbon-doped high mobility two-dimensional hole gases on (110) faced GaAs,"Carbon-doped high mobility two-dimensional hole gases grown on (110) oriented
GaAs substrates have been grown with hole mobilities exceeding 10^6 cm^2/Vs in
single heterojunction GaAs/AlGaAs structures. At these high mobilities, a
pronounced mobility anisotropy has been observed. Rashba induced spin-splitting
in these asymmetric structures has been found to be independent on the
transport direction.",0503323v1
2005-04-28,To the theory of interaction between electron and nuclear systems,"Coupled electron-nuclear oscillations in antiferromagnetics with anisotropy
of ""light plane"" type in the strong external magnetic field are under
consideration. The new mode \epsilon_{2k} of these coupled oscillations is
obtained for antiferromagnetic systems by using ""u-v""-Bogolubov?s unitary
transformations. The dynamic shift of the frequency of nuclear magnetic
resonance concerned with this mode is obtained.",0504759v1
2006-02-21,Magnetic-induced phonon anisotropy in ZnCr$_2$O$_4$ from first principles,"We have studied the influence of magnetic order on the optical phonons of the
geometrically frustrated spinel ZnCr$_2$O$_4$ from first-principles. By mapping
the first-principles phonon calculations onto a Heisenberg-like model, we
developed a method to calculate exchange derivatives and subsequently the
spin-phonon couping parameter from first-principles. All calculations were
performed within LSDA+U.",0602503v1
2006-08-22,Simulation of stress-impedance effects in low magnetostrictive films,"A theoretical study of stress-impedance effect based on the solution of
Landau-Lifsitz-Gilbert equation has been carried out. The results show that
stress impedance effects depend largely on several extrinsic (external bias
field, external frequency) and intrinsic (orientation and magnitude of uniaxial
anisotropy, damping) parameters.",0608488v1
2006-10-09,On the occurrence of Kosterlitz-Thouless behavior in cuprate superconductors,"The observation of the characteristic Kosterlitz-Thouless behavior requires
the attaintment of the two dimensional limit where the correlation-length
anisotropy, gamma=gsiab/gsic, diverges. Our findings strongly suggest that the
failure of several experiments on films and single crystals to observe any
trace of KT-behavior is attributable either to inhomogeneities or doping by
means of chemical substitution.",0610230v1
2007-02-06,Finite-size effects for anisotropic bootstrap percolation: logarithmic corrections,"In this note we analyze an anisotropic, two-dimensional bootstrap percolation
model introduced by Gravner and Griffeath. We present upper and lower bounds on
the finite-size effects. We discuss the similarities with the semi-oriented
model introduced by Duarte.",0702145v1
1993-04-14,Relic Gravitational Waves and Limits on Inflation,"It is shown that only a narrow class of inflationary models can possibly
agree with the available observational data on the anisotropy of the cosmic
microwave background radiation (CMBR). These models may be governed by
``matter'' with the effective equation of state $-1.2 <p/ \epsilon < -0.6$
which includes the De-Sitter case $p/ \epsilon = -1$.",9304018v1
1995-11-15,Quadrupole anisotropy from photon quantum effects,"We consider quantum effects of an electromagnetic field in a
radiation-dominated almost FRW spacetime. The dominant non-local quantum
correction to the photon distribution is a quadrupole moment, corresponding to
an effective anisotropic pressure in the energy-momentum tensor.",9511044v1
1997-04-16,Constraints on Space-Time Torsion from Hughes-Drever Experiments,"The coupling of space-time torsion to the Dirac equation leads to effects on
the energy levels of atoms which can be tested by Hughes-Drever type
experiments. Reanalysis of these experiments carried out for testing the
anisotropy of mass and anomalous spin couplings can lead to the till now
tightest constraint on the axial torsion by $K \leq 1.5 . 10^{-15} m^{-1}$.",9704047v1
1999-12-20,Anisotropic 'hairs' in string cosmology,"In this letter we investigate whether the isotropy problem is naturally
solved in inflationary cosmologies inspired by string theory, so called
pre-big-bang cosmologies. We find that, in contrast to what happens in the more
common 'potential inflation' models, initial anisotropies do not decay during
pre-big-bang inflation.",9912081v1
2000-01-20,Stochastic Processes and Thermodynamics on Curved Spaces,"Our approach views the thermodynamics and kinetics in general relativity and
extended gravitational theories (with generic local anisotropy) from the
perspective of the theory of stochastic differential equations on curved
spaces.
  Nonequilibrium and irreversible processes in black hole thermodynamics are
considered. The paper summarizes the author's contribution to Journees
Relativistes 99 (12--17 September 1999), Weimar, Germany.",0001057v1
2002-03-24,A Geometric Anisotropic Model of Space-Time Based on Finsler Metric,"In this work we study an anisotropic model of general relativity based on the
framework of Finsler geometry. The observed anisotropy of the microwave
background radiation is incorporated in the Finslerian structure of space-time.
We also examine the electromagnetic (e.m.) field equations in our space. As a
result a modified wave equation of e.m. waves yields.",0203083v1
2002-07-24,Finslerian Extension of Lorentz Transformations and First-Order Censorship Theorem,"Granted the post-Lorentzian relativistic kinematic transformations are
described in the Finslerian framework, the uniformity between the actual light
velocity anisotropy change and the anisotropic deformation of measuring rods
can be the reason proper for the null results of the Michelson-Morley-type
experiments at the first-order level.",0207089v1
2000-10-17,Can One Study Heavy Meson Semileptonic Decays on Coarse Anisotropic Lattices ?,"Exploratory studies of heavy meson semileptonic decays on coarse lattices
using Symanzik improved glue, NRQCD heavy and D234 light quarks are discussed.
Comparisons are made between calculations on anisotropic and isotropic
lattices. We find evidence that having an anisotropy helps in extracting better
signals at higher momenta.",0010029v1
2001-10-26,Relativistic bottomonium spectrum from anisotropic lattices,"We report on our results from a fully relativistic simulation of the quenched
bottomonium spectrum. Using an anisotropic formulation of Lattice QCD, we were
able to retain a very fine resolution into the temporal direction for a range
of different lattice spacings. At fixed renormalized anisotropy we study the
scaling properties of the spectrum and compare our results with
non-relativistic calculations.",0110207v1
2001-12-03,Asymptotic freedom with discrete spin variables?,"We study the critical behaviour of the 2d dodecahedron spin model and
investigate the conjecture that the discrete model describes the same continuum
theory as the O(3) non-linear sigma model. In particular, we found that the
anisotropy of the magnetization A(z) measured in a fixed physical volume
decreases with increasing correlation length, at least up to \xi \approx 1000.",0112003v1
2003-09-16,Brane World Moduli and the CMB,"The evolution of moduli fields, which naturally appear in higher dimensional
models such as brane worlds, and their effects on the anisotropies of the
cosmological microwave background radiation is discussed.",0309181v1
2003-09-19,Status of observational cosmology and inflation,"We review the latest developments in the determination of the cosmological
parameters from the measurement of the Cosmic Microwave Background Radiation
(CMBR) anisotropies and of the Large Scale Structure (LSS) of the Universe. We
comment finally on the implications for the primordial spectrum and the
consequences for inflationary models.",0309238v1
2004-07-09,Modern Cosmology,"I review in these lectures our present understanding of the origin and
evolution of the universe, making emphasis on the most recent observations of
the acceleration of the universe, the precise measurements of the microwave
background anisotropies, and the formation of structure like galaxies and
clusters of galaxies from tiny primodial fluctuations generated during
inflation.",0407111v1
2001-11-26,Integrable XYZ Model with Staggered Anisotropy Parameter,"We apply to the XYZ model the technique of construction of integrable models
with staggered parameters, presented recently for the XXZ case. The solution of
modified Yang-Baxter equations is found and the corresponding integrable
zig-zag ladder Hamiltonian is calculated. The result is coinciding with the XXZ
case in the appropriate limit.",0111233v1
2002-01-17,Emptiness formation probability of the XXZ spin-1/2 Heisenberg chain at Delta=1/2,"Using a multiple integral representation for the correlation functions, we
compute the emptiness formation probability of the XXZ spin-1/2 Heisenberg
chain at anisotropy Delta=1/2. We prove it is expressed in term of the number
of alternating sign matrices.",0201134v1
2002-10-09,Multi-leg integrable ladder models,"We construct integrable spin chains with inhomogeneous periodic disposition
of the anisotropy parameter. The periodicity holds for both auxiliary (space)
and quantum (time) directions. The integrability of the model is based on a set
of coupled Yang-Baxter equations. This construction yields P-leg integrable
ladder Hamiltonians. We analyse the corresponding quantum group symmetry.",0210087v1
2005-03-21,Super-horizon Perturbations and CMBA,"We provided a gedanken experiment and argued that since observers inside a
given Hubble volume could not detect the super horizon perturbation modes as
real perturbations, these modes could only affect the average value of the
cosmic microwave background (CMB), but not its anisotropy properties (CMBA) in
that Hubble volume.",0503154v1
2001-10-26,Locating anisotropies in electrical impedance tomography,"In this article, we consider the problem of finding the support of an
inhomogenous possibly anisotropic inclusion in a background of constant
electric conductivity from the electrical impedance tomography data at the
boundary of a bounded body. The article discusses the linear sampling method
applied to this problem. A practical algorithm for solving this problem is
suggested.",0110299v1
2006-05-09,Measuring Large Scale Space Perception in Literary Texts,"The center and radius of perception associated with a written text are
defined, and algorithms for their computation are presented. Indicators for
anisotropy in large scale space perception are introduced. The relevance of
these notions for the analysis of literary and historical records is briefly
discussed and illustrated with an example taken from medieval historiography.",0605224v1
2006-05-18,Adaptive multiscale detection of filamentary structures in a background of uniform random points,"We are given a set of $n$ points that might be uniformly distributed in the
unit square $[0,1]^2$. We wish to test whether the set, although mostly
consisting of uniformly scattered points, also contains a small fraction of
points sampled from some (a priori unknown) curve with $C^{\alpha}$-norm
bounded by $\beta$. An asymptotic detection threshold exists in this problem;
for a constant $T_-(\alpha,\beta)>0$, if the number of points sampled from the
curve is smaller than $T_-(\alpha,\beta)n^{1/(1+\alpha)}$, reliable detection
is not possible for large $n$. We describe a multiscale significant-runs
algorithm that can reliably detect concentration of data near a smooth curve,
without knowing the smoothness information $\alpha$ or $\beta$ in advance,
provided that the number of points on the curve exceeds
$T_*(\alpha,\beta)n^{1/(1+\alpha)}$. This algorithm therefore has an optimal
detection threshold, up to a factor $T_*/T_-$. At the heart of our approach is
an analysis of the data by counting membership in multiscale multianisotropic
strips. The strips will have area $2/n$ and exhibit a variety of lengths,
orientations and anisotropies. The strips are partitioned into anisotropy
classes; each class is organized as a directed graph whose vertices all are
strips of the same anisotropy and whose edges link such strips to their ``good
continuations.'' The point-cloud data are reduced to counts that measure
membership in strips. Each anisotropy graph is reduced to a subgraph that
consist of strips with significant counts. The algorithm rejects $\mathbf{H}_0$
whenever some such subgraph contains a path that connects many consecutive
significant counts.",0605513v1
2002-01-11,Symmetric Periodic Solutions of the Anisotropic Manev Problem,"We consider the Manev Potential in an anisotropic space, i.e., such that the
force acts differently in each direction. Using a generalization of the
  Poincare' continuation method we study the existence of periodic solutions
for weak anisotropy. In particular we find that the symmetric periodic orbits
of the Manev system are perturbed to periodic orbits in the anisotropic
problem.",0201018v1
2002-12-18,Tip Oscillation of Dendritic Patterns in a Phase Field Model,"We study dendritic growth numerically with a phase field model. Tip
oscillation and regular side-branching are observed in a parameter region where
the anisotropies of the surface tension and the kinetic effect compete. The
transition from a needle pattern to a dendritic pattern is conjectured to be a
supercritical Hopf bifurcation.",0212040v1
2002-11-27,"Correlations, Fluctuations, and Flow Measurements from the STAR Experiment","New measurements of short-range and long-range two-particle correlations,
azimuthal anisotropy, and event-by-event fluctuations from the STAR experiment
for sqrt{s_{NN}}= 130 and 200 GeV Au+Au collisions are summarized. Striking
evidence is presented for large, non-statistical fluctuations in mean
transverse momentum. Descriptions of the data in terms of phenomenological
source function models are also presented.",0211030v1
2004-03-12,Azimuthal anisotropy: the higher harmonics,"We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.",0403019v1
1994-02-22,Fission fragment orientation and gamma ray emission anisotropy,"Experimental data on angular distributions of gamma rays emitted from binary
and ternary spontaneous fission of $^{252}{\rm Cf}$ are analyzed. Their
difference indicates that the alignment of fragments is higher in ternary
fission than in binary one. The consequences of possible relation between the
mechanism of ternary fission and the excitation of collective modes during the
saddle-to-scission stage are discussed.",9402024v1
1996-11-19,Transverse Radial Expansion and Directed Flow,"The effects of an interplay of radial expansion of the thermalized system
created in a heavy ion collision and directed flow are discussed. It is shown
that the study of azimuthal anisotropy of particle distribution as a function
of rapidity and transverse momentum could reveal important information on both
radial and directed flow.",9611038v1
2005-04-26,"Spin correlations in the reaction ""pi \vec D --> \vecΣΘ^+"" and the parity of Theta^+","We analyze two types of spin observables in the reaction $\pi \vec
D\to\vec\Sigma\Theta^+$ near the threshold. One concerns the spin-transfer
coefficients $K_x^x$ and $K_z^z$. The second one is the deuteron spin
anisotropy. These observables are sensitive to the $\Theta^+$ parity and can be
used as a tool for the $\Theta^+$ parity determination.",0504073v1
1995-04-20,Dynamic Domain Walls in Strongly Driven Ferromagnets,"A multiple-time scaling analysis of the dissipative, transversely driven
Landau-Lifshitz equation in presence of exchange, shape demagnetisation and
week anisotropy fields is performed for a dynamic domain state. Stationary
solutions of the resulting equations explain the spatiotemporal structure of
the walls and are in agreement with previous simulations.",9504004v1
1996-07-29,Numerical Simulation of Three-Dimensional Dendritic Growth,"Dendritic crystal growth in a pure undercooled melt is simulated
quantitatively in three dimensions using a phase-field approach. The full
non-axisymmetric morphology of the steady-state dendrite tip and $\sigma^*$ are
determined as a function of anisotropy for a crystal with a cubic symmetry.
Results are compared to experiment and used to critically test solvability
theory.",9607005v1
1997-09-25,Excitons with anisotropic effective mass,"We present a simple analytic scheme for calculating the binding energy of
excitons in semiconductors that takes full account of the existing anisotropy
in the effective mass, as a complement to the qualitative treatment in most
textbooks. Results obtained for excitons in gallium nitride form the basis for
a discussion of the accuracy of this approach.",9709036v1
2001-01-07,Quantum Evolution Supergenerator of Superparamagnetic System in Discrete Orientation Model,"The supergenerator of superparamagnetic system quantum evolution is
investigated in discrete orientation model (DOM). It is shown that the
generator is J-self-adjoint one at the case of potential drift field agreed
upon magnetic anisotropy of the sample investigated. Perturbation theory is
used for spectral analysis. The qualitative dependence of resonance absorption
spectrum on the relation between quantum and stochastic parameters is
demonstrated.",0101043v1
2001-04-19,The universal potential fluctuations,"It is assumed the existence of the universal potential fluctuations valid for
all scales in the universe which follow the fractal law $\delta_U=(\Delta
r/r)^2$. The value of the universal potential fluctuations is determined from
the data on anisotropy of the cosmic microwave background on degree scales. It
is suggested to test the existence of the universal potential fluctuations in
the laboratory experiment.",0104057v1
2002-09-12,Dipolar relaxation of cold sodium atoms in a magnetic field,"A quantum mechanical close coupling theory of spin relaxation in the
stretched hyperfine level of sodium is presented. We calculate the dipolar
relaxation rate of magnetically trapped cold sodium atoms in the magnetic
field. The influence of shape resonances and the anisotropy of the dipolar
interaction on the collision dynamics are explored. We examine the sensitivity
of the calculated cross sections on the choice of asymptotic atomic state
basis.",0209052v2
2003-11-14,Two dimensional modulational instability in photorefractive media,"We study theoretically and experimentally the modulational instability of
broad optical beams in photorefractive nonlinear media. We demonstrate the
impact of the anisotropy of the nonlinearity on the growth rate of periodic
perturbations. Our findings are confirmed by experimental measurements in a
strontium barium niobate photorefractive crystal.",0311070v1
2005-01-13,Terahertz pulse generation via optical rectification in photonic crystal microcavities,"Using a 3D fully-vectorial nonlinear time-domain analysis we numerically
investigate the generation of terahertz radiation by pumping a photonic crystal
microcavity out of resonance. High quality factors and a quadratic
susceptibility lead to few-cycle terahertz pulses via optical rectification.
Material dispersion as well as linear and nonlinear anisotropy is fully
accounted for.",0501065v1
2004-10-26,Lattice tube model of proteins,"We present a new lattice model for proteins that incorporates a tube-like
anisotropy by introducing a preference for mutually parallel alignments in the
conformations. The model is demonstrated to capture many aspects of real
proteins.",0410031v1
2005-05-10,Creation of Stable Multipartite Entangled States in Spin Chains with Defects,"We show how defects in a spin chain described by the XXZ model may be used to
generate entangled states, such as Bell and W states, and how to maintain them
with high fidelity. In the presence of several excitations, we also discuss how
the anisotropy of the system may be combined with defects to effectively assist
in the creation of the desired states.",0505072v1
2007-04-09,Sensitivity of solar off-limb line profiles to electron density stratification and the velocity distribution anisotropy,"The effect of the electron density stratification on the intensity profiles
of the H I Ly-$\alpha$ line and the O VI and Mg X doublets formed in solar
coronal holes is investigated. We employ an analytical 2-D model of the large
scale coronal magnetic field that provides a good representation of the corona
at the minimum of solar activity. We use the mass-flux conservation equation to
determine the outflow speed of the solar wind at any location in the solar
corona and take into account the integration along the line of sight (LOS). The
main assumption we make is that no anisotropy in the kinetic temperature of the
coronal species is considered. We find that at distances greater than 1 Rsun
from the solar surface the widths of the emitted lines of O VI and Mg X are
sensitive to the details of the adopted electron density stratification.
However, Ly-$\alpha$, which is a pure radiative line, is hardly affected. The
calculated total intensities of Ly-$\alpha$ and the O VI doublet depend to a
lesser degree on the density stratification and are comparable to the observed
ones for most of the considered density models. The widths of the observed
profiles of Ly-$\alpha$ and Mg X are well reproduced by most of the considered
electron density stratifications, while for the O VI doublet only few
stratifications give satisfying results. The densities deduced from SOHO data
result in O VI profiles whose widths and intensity ratio are relatively close
to the values observed by UVCS although only isotropic velocity distributions
are employed. These density profiles also reproduce the other considered
observables with good accuracy. Thus the need for a strong anisotropy of the
velocity distribution (i.e. a temperature anisotropy) is not so clear cut as
previous investigations of UVCS data suggested. ...",0704.1127v1
2007-04-25,Anisotropic Locations of Satellite Galaxies: Clues to the Orientations of Galaxies within their Dark Matter Halos,"We investigate the locations of the satellites of relatively isolated host
galaxies in the Sloan Digital Sky Survey and the Millennium Run simulation.
Provided we use two distinct prescriptions to embed luminous galaxies within
the simulated dark matter halos (ellipticals share the shapes of their halos,
while disks have angular momenta that are aligned with the net angular momenta
of their halos), we find a fair agreement between observation and theory.
Averaged over scales r_p \le 500 kpc, the satellites of red, high-mass hosts
with low star formation rates are found preferentially near the major axes of
their hosts. In contrast, the satellites of blue, low-mass hosts with low star
formation rates show little to no anisotropy when averaged over the same scale.
The difference between the locations of the satellites of red and blue hosts
cannot be explained by the effects of interlopers in the data. Instead, it is
caused primarily by marked differences in the dependence of the mean satellite
location, <\phi>, on the projected distance at which the satellites are found.
We also find that the locations of red, high-mass satellites with low star
formation rates show considerably more anisotropy than do the locations of
blue, low--mass satellites with high star formation rates. There are two
contributors to this result. First, the blue satellites have only recently
arrived within their hosts' halos, while the red satellites arrived in the far
distant past. Second, the sample of blue satellites is heavily contaminated by
interlopers, which suppresses the measured anisotropy compared to the intrinsic
anisotropy.",0704.3441v3
2007-05-07,Can We Detect the Anisotropic Shapes of Quasar HII Regions During Reionization Through The Small-Scale Redshifted 21cm Power Spectrum?,"Light travel time delays distort the apparent shapes of HII regions
surrounding bright quasars during early stages of cosmic reionization.
Individual HII regions may remain undetectable in forthcoming redshifted 21 cm
experiments. However, the systematic deformation along the line of sight may be
detectable statistically, either by stacking tomographic 21cm images of quasars
identified, for example, by JWST, or as small-scale anisotropy in the
three-dimensional 21cm power spectrum. Here we consider the detectability of
this effect. The anisotropy is largest when HII regions are large and expand
rapidly, and we find that if bright quasars contributed to the early stages of
reionization, then they can produce significant anisotropy, on scales
comparable to the typical sizes of HII regions of the bright quasars (approx.
30 Mpc and below). The effect therefore cannot be ignored when analyzing future
21cm power spectra on small scales. If 10 percent of the volume of the IGM at
redshift z=10 is ionized by quasars with typical ionizing luminosity of S= 5 x
10^{56} photons/second, the distortions can enhance by more than 10 percent the
21cm power spectrum in the radial (redshift) direction, relative to the
transverse directions. The level of this anisotropy exceeds that due to
redshift-space distortion, and has the opposite sign. We show that on-going
experiments such as MWA should be able to detect this effect. A detection would
reveal the presence of bright quasars, and shed light on the ionizing yield and
age of the ionizing sources, and the distribution and small-scale clumping of
neutral intergalactic gas in their vicinity.",0705.0981v2
2007-05-25,Exact Activation Energy of Magnetic Single Domain Particles,"I present the exact analytical expression for the activation energy as a
function of externally applied magnetic fields for a single--domain magnetic
particle with uniaxial anisotropy (Stoner--Wohlfahrt model), and investigate
the scaling behavior of the activation energy close to the switching boundary.",0705.3761v1
2007-07-31,Functional relations from the Yang-Baxter algebra: Eigenvalues of the XXZ model with non-diagonal twisted and open boundary conditions,"In this work we consider a functional method in the theory of exactly
solvable models based on the Yang-Baxter algebra. Using this method we derive
the eigenvalues of the XXZ model with non-diagonal twisted and open boundary
conditions for general values of the anisotropy and boundary parameters.",0708.0009v1
2007-10-02,Reply to 'Difficulty in the Fermi-Liquid-Based Theory for the In-Plane Magnetic Anisotropy in Untwinned High-$T_c$ Superconductors',A Reply to the Comment by Hou-Jun Zhao and Jun Li,0710.0473v1
2007-10-12,Probing the Origin of the Large-angle CMB Anomalies,"It has been argued that the large-angle cosmic microwave background
anisotropy has anomalies at 3-sigma level. We review various proposed ideas to
explain the origin of the anomalies and discuss how we can constrain the
proposed models using future observational data.",0710.2404v1
2007-10-23,Anisotropic Magnification Distortion of the 3D Galaxy Correlation: II. Fourier and Redshift Space,"In paper I of this series we discuss how magnification bias distorts the 3D
correlation function by enhancing the observed correlation in the line-of-sight
(LOS) orientation, especially on large scales. This lensing anisotropy is
distinctive, making it possible to separately measure the galaxy-galaxy,
galaxy-magnification {\it and} magnification-magnification correlations. Here
we extend the discussion to the power spectrum and also to redshift space. In
real space, pairs oriented close to the LOS direction are not protected against
nonlinearity even if the pair separation is large; this is because nonlinear
fluctuations can enter through gravitational lensing at a small transverse
separation (or i.e. impact parameter). The situation in Fourier space is
different: by focusing on a small wavenumber $k$, as is usually done, linearity
is guaranteed because both the LOS and transverse wavenumbers must be small.
This is why magnification distortion of the galaxy correlation appears less
severe in Fourier space. Nonetheless, the effect is non-negligible, especially
for the transverse Fourier modes, and should be taken into account in
interpreting precision measurements of the galaxy power spectrum, for instance
those that focus on the baryon oscillations. The lensing induced anisotropy of
the power spectrum has a shape that is distinct from the more well known
redshift space anisotropies due to peculiar motions and the Alcock-Paczynski
effect. The lensing anisotropy is highly localized in Fourier space while
redshift space distortions are more spread out. This means that one could
separate the magnification bias component in real observations, implying that
potentially it is possible to perform a gravitational lensing measurement
without measuring galaxy shapes.",0710.4191v3
2007-11-08,Super-horizon fluctuations and acoustic oscillations in relativistic heavy-ion collisions,"We focus on the initial state spatial anisotropies, originating at the
thermalization stage, for central collisions in relativistic heavy-ion
collisions. We propose that a plot of the root mean square values of the flow
coefficients $\sqrt{\bar {v_n^2}} \equiv v_n^{rms}$, calculated in a lab fixed
coordinate system, for a large range of $n$, from 1 to about 30, can give
non-trivial information about the initial stages of the system and its
evolution. We also argue that for all wavelengths $\lambda$ of the anisotropy
(at the surface of the plasma region) much larger than the acoustic horizon
size $H_s^{fr}$ at the freezeout stage, the resulting values of $v_n^{rms}$
should be suppressed by a factor of order $2H_s^{fr}/\lambda$. With initial
flow being zero, we discuss the possibility that the resulting flow could show
imprints of coherent oscillations in the plot of $v_n^{rms}$ for sub-horizon
modes. For gold-gold collision at 200 GeV, these features are expected to occur
for n $\ge$ 5, with $n < 4$ modes showing supression. This has strong
similarities with the physics of the anisotropies of the cosmic microwave
background radiation (CMBR) resulting from inflationary density fluctuations in
the universe. It seems possible that the statistical fluctuations due to finite
multiplicity may not be able to mask such features in the flow data, or, at
least a non-trivial overall shape of the plot of $v_n^{rms}$ may be inferred.
In that case, the successes of analysis of CMBR anisotropy power spectrum to
get cosmological parameters can be applied for relativistic heavy-ion
collisions to learn about various relevant parameters at the early stages of
the evolving system.",0711.1323v2
2007-11-15,Fast magnetization in counterstreaming plasmas with temperature anisotropies,"Counterstreaming plasmas exhibits an electromagnetic unstable mode of
filamentation type, which is responsible for the magnetization of plasma
system. It is shown that filamentation instability becomes significantly faster
when plasma is hotter in the streaming direction. This is relevant for
astrophysical sources, where strong magnetic fields are expected to exist and
explain the nothermal emission observed.",0711.2385v1
2008-01-26,Diversity of critical behavior within a universality class,"We study spatial anisotropy effects on the bulk and finite-size critical
behavior of the O$(n)$ symmetric anisotropic $\phi^4$ lattice model with
periodic boundary conditions in a $d$-dimensional hypercubic geometry above, at
and below $T_c$. The absence of two-scale factor universality is discussed for
the bulk order-parameter correlation function, the bulk scattering intensity,
and for several universal bulk amplitude relations. For the confined system,
renormalization-group theory within the minimal subtraction scheme at fixed
dimension $d$ for $2<d<4$ is employed. For the case of cubic symmetry and for
$n=1$ our perturbation approach yields excellent agreement with the Monte Carlo
(MC) data for the finite-size amplitude of the free energy of the
three-dimensional Ising model at $T_c$ by Mon [Phys. Rev. Lett. {\bf 54}, 2671
(1985)]. Below $T_c$ a minimum of the scaling function of the excess free
energy is found. We predict a measurable dependence of this minimum on the
anisotropy parameters. The relative anisotropy effect on the free energy is
predicted to be significantly larger than that on the Binder cumulant. Our
theory agrees quantitatively with the non-monotonic dependence of the Binder
cumulant on the ferromagnetic next-nearest neighbor (NNN) coupling of the
two-dimensional Ising model found by MC simulations of Selke and Shchur [J.
Phys. {\bf A 38}, L739 (2005)]. Our theory also predicts a non-monotonic
dependence for small values of the {\it antiferromagnetic} NNN coupling and the
existence of a Lifschitz point at a larger value of this coupling. The
nonuniversal anisotropy effects in the finite-size scaling regime are predicted
to satisfy a kind of restricted universality. The tails of the large-$L$
behavior at $T \neq T_c$ violate both finite-size scaling and universality.",0801.4096v2
2008-02-15,The AUGER experiment - status and results,"The Auger experiment was designed to study the high-energy cosmic rays by
measuring the properties of the showers produced in the atmosphere. The
Southern Auger Observatory has taken data since January 2004. Results on mass
composition, energy spectrum and anisotropy of the arrival directions are
presented. The most important result is the recent observation of correlations
with nearby extragalactic objects.",0802.2214v1
2008-03-11,Entanglement and Berry Phase in Two Interacting Qubits,"Entanglement and Berry phase are investigated in two interacting qubit
systems. The XXZ spin interaction model with a slowly rotating magnetic field
is employed for the interaction between the two qubits. We show how the
anisotropy of interaction reveals unique relations between the Berry phases and
the entanglements for the eigenstates of the system.",0803.1524v1
2008-06-09,The Doppler shift due to WMAP's spin mimics anisotropies in the cosmic microwave background,"This paper has been withdrawn because its ideas have been incorporated into
arXiv:0905.3971 and explained much better there.",0806.1508v2
2008-06-16,Thermal transport in the anisotropic Heisenberg chain with S = 1/2 and nearest-neighbor interactions,"The purpose of this note is to connect early work on thermal transport in
spin-1/2 Heisenberg chains with uniaxial exchange anisotropy and
nearest-neighbor interactions that was based on a moment analysis of the
Fourier transform of the energy density correlation function with subsequent
studies that make use of thermal current correlation functions.",0806.2670v1
2008-07-29,Wormhole geometry from real feasible matter sources,"We provide a prescription of real feasible sources that supply fuel to
construct a traversable wormhole. A class of exact solutions for
Einstein-Maxwell field equations describing wormhole with an anisotropic matter
distribution has been presented. The anisotropy plays a crucial role for the
existence of the spacetime comprising wormhole geometry.",0807.4596v1
2008-11-03,Imprints of microcausality violation on the cosmic microwave background,"We consider a modification of the Heisenberg algebra with the non-vanishing
commutator of scalar field operators. We then identify the scalar field with
the second quantized inflaton fluctuation and calculate effects of
microcausality violation on the temperature anisotropy of cosmic microwave
background radiation.",0811.0242v1
2008-11-04,Anomalous scaling and anisotropy in models of passively advected vector fields,"The small and large scale problem of various passive vector models with
anisotropic forcing is considered by solving exactly the equation for the pair
correlation function. Emphasis is placed in the phenomena of anomalous scaling
and the possible breakdown of isotropic dominance in the inertial range.",0811.0510v2
2008-11-11,Simulating weak lensing on CMB maps,"We present a fast, arbitrarily accurate method to simulate the effect of
gravitational lensing of the Cosmic Microwave Background anisotropies and
polarization fields by large scale structures. We demonstrate the efficiency
and accuracy of the method and exhibit their dependence on the algorithm
parameters.",0811.1677v1
2008-12-08,Equations of electromagnetism in some special anisotropic spaces,"We show that anisotropy of the space naturally leads to new terms in the
expression of Lorentz force, as well as in the expressions of currents.",0812.1513v1
2008-12-11,Lorentz Violation and Alpha-Decay,"Relating the effective Lorentz violation coefficients for composite particles
to the coefficients for their constituent fields is a challenging problem. We
calculate the Lorentz violation coefficients relevant to the dynamics of an
alpha-particle in terms of proton and neutron coefficients. The alpha-particle
coefficients would lead to anisotropies in the alpha-decays of nuclei, and
because the decay process involves quantum tunneling, the effects of any
Lorentz violations could be exponentially enhanced.",0812.2236v1
2008-12-28,The variation of the electromagnetic coupling and quintessence,"The properties of quintessence are examined through the study of the
variation of the electromagnetic coupling. We consider two simple quintessence
models with a modified exponential potential and study the parameter space
constraints derived from the existing observational bounds on the variation of
the fine structure constant and the most recent Wilkinson Microwave Anisotropy
Probe observations.",0812.4827v1
2009-02-14,Electronic structure of BaCu$_2$As$_2$ and SrCu$_2$As$_2$: sp-band metals,"The electronic structures of ThCr$_2$Si$_2$ structure BaCu$_2$As$_2$ and
SrCu$_2$As$_2$ are investigated using density functional calculations. The Cu
$d$ orbitals are located at 3 eV and higher binding energy, and are therefore
chemically inert with little contribution near the Fermi energy. These
materials are moderate density of states, sp-band metals with large Fermi
surfaces and low anisotropy.",0902.2502v1
2009-03-25,Isotropic superconducting state and high critical currents in Fe1+yTe1-xSx single crystals,"We report single crystal growth and a study of superconducting properties in
Fe_{1+y}Te_{1-x}S_{x}. We demonstrate the smallest upper critical field
anisotropy, gamma=H_{c2}^{//c}/H_{c2}^{//a}, among all iron based
superconductors, the value of gamma reaches 1.05 at T=0.65T_{C} for
Fe_{1.09}Te_{0.89}S_{0.11}, while still maintaining large values of upper
critical field.",0903.4430v2
2009-03-30,Anisotropic Evolution Driven by Kinetic Term,"We present a simple model where anisotropic evolution is driven by kinetic
term in extra dimensions. By introducing a canonical or a ghost kinetic term,
the possibility of anisotropy is studied.",0903.5118v2
2009-04-27,Constraints on the High-l Power Spectrum of Millimeter-wave Anisotropies from APEX-SZ,"We present measurements of the angular power spectrum of millimeter wave
anisotropies with the APEX-SZ instrument. APEX-SZ has mapped 0.8 square degrees
of sky at a frequency of 150 GHz with an angular resolution of 1'. These new
measurements significantly improve the constraints on anisotropy power at 150
GHz over the range of angular multipoles 3000 < l < 10,000, limiting the total
astronomical signal in a flat band power to be less than 105 microK^2 at 95%
CL. We expect both submillimeter-bright, dusty galaxies and to a lesser extent
secondary CMB anisotropies from the Sunyaev-Zel'dovich effect (SZE) to
significantly contribute to the observed power. Subtracting the SZE power
spectrum expected for sigma_8=0.8 and masking bright sources, the best fit
value for the remaining power is C_l = 1.1^{+0.9}_{-0.8} x 10^{-5} micro K^2
(1.7^{+1.4}_{-1.3} Jy^2 sr^{-1}). This agrees well with model predictions for
power due to submillimeter-bright, dusty galaxies. Comparing this power to the
power detected by BLAST at 600 GHz, we find the frequency dependence of the
source fluxes to be S_nu ~ nu^{2.6^{+0.4}_{-0.2}} if both experiments measure
the same population of sources. Simultaneously fitting for the amplitude of the
SZE power spectrum and a Poisson distributed point source population, we place
an upper limit on the matter fluctuation amplitude of sigma_8 < 1.18 at 95%
confidence.",0904.3939v2
2009-04-28,"Density profile, velocity anisotropy and line-of-sight external convergence of SLACS gravitational lenses","Data from 58 strong-lensing events surveyed by the Sloan Lens ACS Survey are
used to estimate the projected galaxy mass inside their Einstein radii by two
independent methods: stellar dynamics and strong gravitational lensing. We
perform a joint analysis of these two estimates inside models with up to three
degrees of freedom with respect to the lens density profile, stellar velocity
anisotropy, and line-of-sight (LOS) external convergence, which incorporates
the effect of the large-scale structure on strong lensing. A Bayesian analysis
is employed to estimate the model parameters, evaluate their significance and
compare models. We find that the data favor Jaffe's light profile over
Hernquist's, but that any particular choice between these two does not change
the qualitative conclusions with respect to the features of the system that we
investigate. The density profile is compatible with an isothermal, being
sightly steeper and having an uncertainty in the logarithmic slope of the order
of 5% in models that take into account a prior ignorance on anisotropy and
external convergence. We identify a considerable degeneracy between the density
profile slope and the anisotropy parameter, which largely increases the
uncertainties in the estimates of these parameters, but we encounter no
evidence in favor of an anisotropic velocity distribution on average for the
whole sample. An LOS external convergence following a prior probability
distribution given by cosmology has a small effect on the estimation of the
lens density profile, but can increase the dispersion of its value by nearly
40%.",0904.4381v4
2009-06-02,Patterned and Disordered Continuous Abelian Sandpile Model,"We study critical properties of the continuous Abelian sandpile model with
anisotropies in toppling rules that produce ordered patterns on it. Also we
consider the continuous directed sandpile model perturbed by a weak quenched
randomness and study critical behavior of the model using perturbative
conformal field theory and show the model has a new random fixed point.",0906.0459v1
2009-08-10,Tunnel magnetoresistance of magnetic junctions with cubic symmetry of the layers,"A tunnel magnetic junction is considered with magnetic hard and magnetic soft
layers of cubic symmetry. The magnetic switching is analyzed of the layers by a
magnetic field perpendicular to the initial magnetizations. In such a
situation, an additional peak of the TMR ratio appears at the magnetic field
value lower substantially than the anisotropy energy of the soft layer.",0908.1278v1
2009-09-09,Non-Gaussianity in WMAP Data Due to the Correlation of CMB Lensing Potential with Secondary Anisotropies,"We measure the skewness power spectrum of the Cosmic Microwave Background
(CMB) anisotropies optimized for a detection of the secondary bispectrum
generated by the correlation of the CMB lensing potential with integrated
Sachs-Wolfe effect and the Sunyaev-Zel'dovich effect. The covariance of our
measurements is generated by Monte-Carlo simulations of Gaussian CMB fields
with noise properties consistent with Wilkinson Microwave Anisotropy Probe
(WMAP) 5-year data. When interpreting multi-frequency measurements we also take
into account the confusion resulting from unresolved radio point sources. We
analyze Q, V and W-band WMAP 5-year raw and foreground-cleaned maps using the
KQ75 mask out to l_max=600. We find no significant evidence for a non-zero
non-Gaussian signal from the lensing-secondary correlation in all three bands
and we constrain the overall amplitude of the cross power spectrum between CMB
lensing potential and the sum of SZ and ISW fluctuations to be 0.42 \pm 0.86
and 1.19 \pm 0.86 in combined V and W-band raw and foreground-cleaned maps
provided by the WMAP team, respectively. The point source amplitude at the
bispectrum level measured with this skewness power spectrum is higher than
previous measurements of point source non-Gaussianity. We also consider an
analysis where we also account for the primordial non-Gaussianity in addition
to lensing-secondary bispectrum and point sources. The focus of this paper is
on secondary anisotropies. Consequently the estimator is not optimised for
primordial non-Gaussianity and the limit we find on local non-Gaussianity from
the foreground-cleaned V+W maps is f_NL = -13 \pm 62, when marginalized over
point sources and lensing-ISW/SZ constributions to the total bispectrum.",0909.1837v1
2009-09-15,The transport coefficient $\hat{q}$ in an anisotropic plasma,"We investigate the jet quenching parameter in the case of a fast moving quark
in an anisotropic plasma. In the leading log approximation, strong indications
are found that the transport coefficient increases with increasing anisotropy.
Implications for the phenomenology at RHIC are discussed.",0909.2794v1
2009-09-16,Matrix Product States and Quantum Phase Transitions,"We have developed a new approach based on matrix product representations of
ground states to study Quantum Phase Transitions (QPT). As confirmation of the
power of our approach we have analytically analyzed the XXZ spin-one chain with
uniaxial single-ion-type anisotropy and our results compare favourably with
previous numerical studies. In addition, our description lets to know which
part of parameters space of the Hamiltonian is most likely to be exactly
solvable.",0909.2928v1
2009-10-16,Constraints on f_nl and g_nl from the analysis of the N-pdf of the CMB large scale anisotropies,"[Abridged] In this paper we explore a local non-linear perturbative model up
to third order as a general characterization of the CMB anisotropies. We focus
our analysis in large scale anisotropies. At these angular scales, the
non-Gaussian description proposed in this work defaults (under certain
conditions) to an approximated local form of the weak non-linear coupling
inflationary model. In particular, quadratic and cubic terms are governed by
the non-linear coupling parameters f_nl and g_nl, respectively. The extension
proposed in this paper allows us to directly constrain these non-linear
parameters. Applying the proposed methodology to WMAP 5-yr data, we obtain -5.6
x 10^5 < g_nl < 6.4 x 10^5, at 95% CL. This result is in agreement with
previous findings obtained for equivalent non-Gaussian models and with
different non-Gaussian estimators. A model selection test is performed,
indicating that a Gaussian model is preferred to the non-Gaussian scenario.
When comparing different non-Gaussian models, we observe that a pure f_nl model
is the most favoured case, and that a pure g_nl model is more likely than a
general non-Gaussian scenario. Finally, we have analyzed the WMAP data in two
independent hemispheres, in particular the ones defined by the dipolar pattern
found by Hoftuft et al. 2009. We show that, whereas g_nl is still compatible
with zero for both hemispheres, it is not the case for f_nl (with a p-value
0.04). However, if anisotropy of the data is assumed, the distance between the
likelihood distributions for each hemisphere is larger than expected from
Gaussian and anisotropic simulations, also for g_nl (with a p-value of 0.001 in
the case of this parameter). This result is an extra evidence for the CMB
asymmetries previously reported in WMAP data.",0910.3196v2
2009-12-08,Magnetofluid dynamics of magnetized cosmic plasma: firehose and gyrothermal instabilities,"Both global dynamics and turbulence in magnetized weakly collisional cosmic
plasmas are described by general magnetofluid equations that contain pressure
anisotropies and heat fluxes that must be calculated from microscopic plasma
kinetic theory. It is shown that even without a detailed calculation of the
pressure anisotropy or the heat fluxes, one finds the macroscale dynamics to be
generically unstable to microscale Alfvenically polarized fluctuations. Two
instabilities are considered in detail: the parallel firehose instability
(including the finite-Larmor-radius effects that determine the fastest growing
mode) and the gyrothermal instability (GTI). The latter is a new result - it is
shown that a parallel ion heat flux destabilizes Alfvenically polarized
fluctuations even in the absence of the negative pressure anisotropy required
for the firehose. The main conclusion is that both pressure anisotropies and
heat fluxes trigger plasma microinstabilities and, therefore, their values will
likely be set by the nonlinear evolution of these instabilities. Ideas for
understanding this nonlinear evolution are discussed. It is argued that cosmic
plasmas will generically be ""three-scale systems,"" comprising global dynamics,
mesoscale turbulence and microscale plasma fluctuations. The astrophysical
example of cool cores of galaxy clusters is considered and it is noted that
observations point to turbulence in clusters being in a marginal state with
respect to plasma microinstabilities and so it is the plasma microphysics that
is likely to set the heating and conduction properties of the intracluster
medium. In particular, a lower bound on the scale of temperature fluctuations
implied by the GTI is derived.",0912.1359v2
2009-12-08,A dipole anisotropy of galaxy distribution: Does the CMB rest-frame exist in the local universe?,"The peculiar motion of the Earth causes a dipole anisotropy modulation in the
distant galaxy distribution due to the aberration effect. However, the
amplitude and angular direction of the effect is not necessarily the same as
those of the cosmic microwave background (CMB) dipole anisotropy due to the
growth of cosmic structures. In other words exploring the aberration effect may
give us a clue to the horizon-scale physics perhaps related to the cosmic
acceleration. In this paper we develop a method to explore the dipole angular
modulation from the pixelized galaxy data on the sky properly taking into
account the covariances due to the shot noise and the intrinsic galaxy
clustering contamination as well as the partial sky coverage. We applied the
method to the galaxy catalogs constructed from the Sloan Digital Sky Survey
(SDSS) Data Release 6 data. After constructing the four galaxy catalogs that
are different in the ranges of magnitudes and photometric redshifts to study
possible systematics, we found that the most robust sample against systematics
indicates no dipole anisotropy in the galaxy distribution. This finding is
consistent with the expectation from the concordance Lambda-dominated cold dark
matter model. Finally we argue that an almost full-sky galaxy survey such as
LSST may allow for a significant detection of the aberration effect of the CMB
dipole having the precision of constraining the angular direction to ~ 20
degrees in radius. Assuming a hypothetical LSST galaxy survey, we find that
this method can confirm or reject the result implied from a stacked analysis of
the kinetic Sunyaev-Zel'dovich effect of X-ray luminous clusters in Kashlinsky
et al. (2008,2009) if the implied cosmic bulk flow is not extended out to the
horizon.",0912.1460v2
2010-01-18,Nearest-neighbor coupling asymmetry in the generation of cluster states,"We demonstrate that charge-qubit cluster state generation by capacitive
coupling is anisotropic. Specifically, horizontal vs vertical nearest-neighbor
inter-qubit coupling differs in a rectangular lattice. We show how to
ameliorate this anisotropy by applying potential biases to the array of double
dots.",1001.2877v2
2010-04-22,Collisionless reconnection: Mechanism of self-ignition in thin current sheets,"The spontaneous onset of magnetic reconnection in thin collisionless current
sheets is shown to result from a thermal-anisotropy driven magnetic
Weibel-mode, generating seed-magnetic field {\sf X}-points in the centre of the
current layer.",1004.3992v1
2010-06-29,Magnetostatics of synthetic ferrimagnet elements,"We calculate the magnetostatic energy of synthetic ferrimagnet (SyF)
elements, consisting of two thin ferromagnetic layers coupled
antiferromagnetically through RKKY coupling. We calculate exact formulas as
well as approximate yet accurate ones, which can be used to easily derive
energy barriers and anisotropy fields of SyF. These can be used to evaluate
coercivity, thermal stability and other useful quantities.",1006.5531v2
2010-09-01,Entanglement in a Time-Dependent Coupled XY Spin Chain in an External Magnetic Field,"We consider an infinite one dimensional anisotropic XY spin chain with a
nearest neighbor time-dependent Heisenberg coupling J(t) between the spins in
presence of a time-dependent magnetic field h(t). We discuss a general solution
for the system and present an exact solution for particular choice of J and h
of practical interest. We investigate the dynamics of entanglement for
different degrees of anisotropy of the system and at both zero and finite
temperatures. We find that the time evolution of entanglement in the system
show non-ergodic and critical behavior at zero and finite temperatures and
different degrees of anisotropy. The asymptotic behavior of entanglement at the
infinite time limit at zero temperature and constant J and h depends only the
parameter lambda=J/h rather than the individual values of J and h for all
degrees of anisotropy but changes for nonzero temperature. Furthermore, the
asymptotic behavior is very sensitive to the initial values of J and h and for
particular choices we may create finite asymptotic entanglement regardless of
the final values of J and h. The persistence of quantum effects in the system
as it evolves and as the temperature is raised is studied by monitoring the
entanglement. We find that the quantum effects dominates within certain regions
of the kT-lambda space that vary significantly depending on the degree of the
anisotropy of the system. Particularly, the quantum effects in the Ising model
case persists in the vicinity of both its critical phase transition point and
zero temperature as it evolves in time. Moreover, the interplay between the
different system parameters to tune and control the entanglement evolution is
explored.",1009.0648v3
2010-10-01,Implications of the Cosmic Ray Electron Spectrum and Anisotropy measured with Fermi-LAT,"The Fermi Large Area Telescope (LAT) collaboration recently released the
updated results of the measurement of the cosmic ray electron (CRE) spectrum
and published its first constraints on the CRE anisotropy. With respect to the
previous Fermi-LAT results, the CRE spectrum measurement was extended down from
20 to 7 GeV, thus providing a better lever arm to discriminate theoretical
models. Here we show that the new data strengthen the evidence for the presence
of two distinct electron and positron spectral components. Furthermore, we show
that under such hypothesis most relevant CRE and positron data sets are
remarkably well reproduced. Consistent fits of cosmic-ray nuclei and antiproton
data, which are crucial to validate the adopted propagation setup(s) and to fix
the solar modulation potential, are obtained for the Kraichnan and
plain-diffusion propagation setups, while the Kolmogorov one is disfavored. We
then confirm that nearby pulsars are viable source candidates of the required
$e^\pm$ extra-component. In that case, we show that the predicted CRE
anisotropy is compatible with Fermi-LAT constraints and that a positive
detection should be at hand of that observatory. Models assuming that only
nearby supernova remnants contribute to the high energy tail of the observed
CRE spectrum are in contrast with anisotropy limits.",1010.0174v2
2010-10-19,Anisotropic Function Spaces and Elliptic Boundary Value Problems,"In this paper, we study anisotropic Bessel potential and Besov spaces, where
the anisotropy measures the extra amount of regularity in certain directions.
Some basic properties of these spaces are established along with applications
to elliptic boundary value problems.",1010.4046v2
2010-10-30,Symmetry breaking orbital anisotropy on detwinned Ba(Fe1-xCox)2As2 above the spin density wave transition,"Nematicity, defined as broken rotational symmetry, has recently been observed
in competing phases proximate to the superconducting phase in the cuprate high
temperature superconductors. Similarly, the new iron-based high temperature
superconductors exhibit a tetragonal to orthorhombic structural transition
(i.e. a broken C4 symmetry) that either precedes or is coincident with a
collinear spin density wave (SDW) transition in undoped parent compounds, and
superconductivity arises when both transitions are suppressed via doping.
Evidence for strong in-plane anisotropy in the SDW state in this family of
compounds has been reported by neutron scattering, scanning tunneling
microscopy, and transport measurements. Here we present an angle resolved
photoemission spectroscopy study of detwinned single crystals of a
representative family of electron-doped iron-arsenide superconductors,
Ba(Fe1-xCox)2As2 in the underdoped region. The crystals were detwinned via
application of in-plane uniaxial stress, enabling measurements of single domain
electronic structure in the orthorhombic state. At low temperatures, our
results clearly demonstrate an in-plane electronic anisotropy characterized by
a large energy splitting of two orthogonal bands with dominant dxz and dyz
character, which is consistent with anisotropy observed by other probes. For
compositions x>0, for which the structural transition (TS) precedes the
magnetic transition (TSDW), an anisotropic splitting is observed to develop
above TSDW, indicating that it is specifically associated with TS. For
unstressed crystals, the band splitting is observed close to TS, whereas for
stressed crystals the splitting is observed to considerably higher
temperatures, revealing the presence of a surprisingly large in-plane nematic
susceptibility in the electronic structure.",1011.0050v2
2010-11-22,Electrodynamic Response of the Charge Ordering Phase: Dielectric and Optical Studies of alpha-(BEDT-TTF)2I3,"We report on the anisotropic response, the charge and lattice dynamics of
normal and charge-ordered phases with horizontal stripes in single crystals of
the organic conductor alpha-(BEDT-TTF)2I3 determined by dc resistivity,
dielectric and optical spectroscopy. An overdamped Drude response and a small
conductivity anisotropy observed in optics is consistent with a weakly
temperature dependent dc conductivity and anisotropy at high temperatures. The
splitting of the molecular vibrations nu27(Bu) evidences the abrupt onset of
static charge order below TCO=136 K. The drop of optical conductivity measured
within the ab plane of the crystal is characterized by an isotropic gap that
opens of approximately 75 meV with several phonons becoming pronounced below.
Conversely, the dc conductivity anisotropy rises steeply, attaining at 50 K a
value 25 times larger than at high temperatures. The dielectric response within
this plane reveals two broad relaxation modes of strength Deltaepsilon_LD ~=
5000 and Deltaepsilon_SD ~= 400, centered at 1 kHz < f_LD < 100 MHz and f_SD ~=
1 MHz. The anisotropy of the large-mode (LD) mean relaxation time closely
follows the temperature behavior of the respective dc conductivity ratio. We
argue that this phason-like excitation is best described as a long-wavelength
excitation of a 2kF bond-charge density wave expected theoretically for layered
quarter-filled electronic systems with horizontal stripes. Conversely, based on
the theoretically expected ferroelectric-like nature of the charge-ordered
phase, we associate the small-mode (SD) relaxation with the motion of
domain-wall pairs, created at the interface between two types of domains, along
the a and b axes. We also consider other possible theoretical interpretations
and discuss their limitations.",1011.4912v2
2011-01-01,Gravimagnetic shock waves in the anisotropic plasma,"The relativistic magnetohydrodynamic equations for the anisotropic
magnetoactive plasma are obtained and accurately integrated in the plane
gravitational wave metrics. The dependence of the induction mechanism of the
gravimagnetic shock waves on the degree of the magnetoactive plasma anisotropy
is analyzed.",1101.0374v1
2011-04-05,Explicit constructions of operator scaling Gaussian fields,"We propose an explicit way to generate a large class of Operator scaling
Gaussian random fields (OSGRF). Such fields are anisotropic generalizations of
selfsimilar fields. More specifically, we are able to construct any Gaussian
field belonging to this class with given Hurst index and exponent. Our
construction provides - for simulations of texture as well as for detection of
anisotropies in an image - a large class of models with controlled anisotropic
geometries and structures.",1104.0774v1
2011-06-08,On a proof of the collapse conjecture for a diagonal Bianchi type-IX vacuum space-time,"It is given a simple proof of the collapse conjecture for a diagonal Bianchi
type-IX vacuum space-time. It is shown that the codimension of the infinity
stable attractor, restricted to the anisotropy plane, is not zero, thus proving
that ""escape along a channel"" is impossible.",1106.1534v1
2011-06-15,Role of d-wave pairing in $A15$ superconductors,"We argue that the recent Raman spectroscopy observation of a sharp mode in
s-wave superconducting V$_3$Si is due to a competing d-wave pairing state. We
present microscopic arguments for the origin of this d-wave order. We further
argue that the d-wave order explains the observed shrinking of the vortex core
structure at anomalously low magnetic fields and the large anisotropy observed
in the upper critical field.",1106.2931v1
2011-06-29,STAR Highlights,"We report selected results from STAR collaboration at RHIC, focusing on
jet-hadron and jet-like correlations, quarkonium suppression and collectivity,
di-electron spectrum in both p+p and Au+Au, and higher moments of net-protons
as well as azimuthal anisotropy from RHIC Beam Energy Scan program.",1106.6021v1
2011-07-15,Studying the stochasticity in astrophysical signals,"The efficiency of the Kolmogorov-Arnold technique for the astrophysical
signals is studied modeling sequences with both random and regular properties.
This technique has been applied to the study of the structures in cosmic
microwave background maps obtained by the Wilkinson Microwave Anisotropy Probe.",1107.3091v1
2011-08-02,Cosmic ray acceleration at oblique shocks,"We show that the diffusion approximation breaks down for particle
acceleration at oblique shocks with velocities typical of young supernova
remnants. Higher order anisotropies flatten the spectral index at
quasi-parallel shocks and steepen the spectral index at quasi-perpendicular
shocks. We compare the theory with observed spectral indices.",1108.0582v1
2011-09-07,Planar approximation for spin transfer systems with application to tilted polarizer devices,"Planar spin-transfer devices with dominating easy-plane anisotropy can be
described by an effective one-dimensional equation for the in-plane angle. Such
a description provides an intuitive qualitative understanding of the magnetic
dynamics. We give a detailed derivation of the effective planar equation and
use it to describe magnetic switching in devices with tilted polarizer.",1109.1331v1
2011-09-07,Planar approximation for the frequencies of spin transfer oscillators,"A large class of spin transfer oscillators use the free layer with a strong
easy plane anisotropy, which forces its magnetization to move close to the
plane. We show that in this situation the effective planar approximation
provides a fast and accurate way of calculating the oscillator frequency.",1109.1335v1
2011-10-10,Vortex structures of a two-component BEC for large anisotropies,"We calculate the vortex structures of an elongated two-component
Bose-Einstein condensate. We study how these structures depend on the
intra-component and inter-component interaction strengths. We present analytic
and numeric results respectively at weak and strong interactions; finding
lattices with different interlocking geometries: triangular, square,
rectangular and double-core.",1110.2135v1
2011-11-11,The IceCube Neutrino Observatory III: Cosmic Rays,"Cosmic rays and related measurements: IceTop overview; IceTop calibration;
Cosmic ray composition; Air shower measurements; Studies of cosmic ray muons;
Studies of PeV gamma rays; Cosmic ray anisotropy; Forbush decrease; Submitted
papers to the 32nd International Cosmic Ray Conference, Beijing 2011.",1111.2735v2
2011-12-07,Sixteen-state magnetic memory based on the extraordinary Hall effect,"We report on a proof-of-concept study of split-cell magnetic storage in which
multi-bit magnetic memory cells are composed of several multilevel
ferromagnetic dots with perpendicular magnetic anisotropy. Extraordinary Hall
effect is used for reading the data. Feasibility of the approach is supported
by realization of four-, eight- and sixteen- state cells.",1112.1624v1
2011-12-29,Apart Cen A are UHECR mostly heavy radioactive and galactic nuclei?,"Earliest AUGER UHECR anisotropy correlated with AGN within a GZK Universe
almost fade away. Recent UHECR mass compositions did show a negligible nucleon
composition and an UHECR nuclei (light or heavy) signature. The absence of
UHECR events toward the Virgo cluster, an unique spread clustering of events
around Cen-A, our nearest AGN, suggested a He-like nuclei as the main
extragalactic UHECR component from Cen A, coexisting with Auger and HIRES
composition. Because the light nuclei fragility such He UHECR cannot arrive
from Virgo. Multiplet at twenty EeV along Cen A recently discovered by Auger
confirm this interpretation to be indebt to fragments (D;He3; p) that had to
reach us along the same UHECR. Remaining majority of UHECR clustering are
partially correlated with a gamma noise at (1-3 MeV) in Comptel sky, linked to
Al 26 galactic radioactive map as well as to a few TeV gamma anisotropy maps;
rare UHECR triplet are overlapping on Vela TeV anisotropy. Therefore UHECR
might be also (or mostly) heavy radioactive galactic nuclei as Ni55, Ni56, Ni57
and Co57 bent from the sources whose gamma and beta radioactivity and decay in
flight is boosted (by Lorentz factor near a billion), leading to TeV correlated
sky anisotropy. Galactic UHECR signals inside the inner center maybe suppressed
by Lorentz bending forces. More clustering around external galactic plane is
expected. Magellanic Cloud and Magellanic Stream may also rise in UHECR maps
(as well as in multiplet). Future UHECR clustering might be observed around Cas
A and Cygnus by T.A. The UHECR spectra cut off may be just the imprint of a
galactic confinement and-or a spectroscopic heavy composition decrease step.",1112.6388v2
2012-01-16,Particles Flux of Ultrahigh Energy from a Galactic Plane,"Arrival directions of particles were analyzed according to the arrays of
extensive air showers (EAS) data. A new method of sources search and anisotropy
of arrival directions particles is suggested. There was found the particles
flux of ultrahigh energy from the galactic plane that exceeds the expected
number of particles in the case of isotropy more than 4\sigma and 5\sigma.",1201.3143v1
2012-01-31,On the absorption of microwaves by the one-dimensional spin-1/2 Heisenberg-Ising magnet,"We analyze the absorption of microwaves by the Heisenberg-Ising chain
combining exact calculations, based on the integrability of the model, with
numerical calculations. Within linear response theory the absorbed intensity is
determined by the imaginary part of the dynamical susceptibility. The moments
of the normalized intensity can be used to define the shift of the resonance
frequency induced by the interactions and the line width independently of the
shape of the spectral line. These moments can be calculated exactly as
functions of temperature and strength of an external magnetic field, as long as
the field is directed along the symmetry axis of the chain. This allows us to
discuss the line width and the resonance shift for a given magnetic field in
the full range of possible anisotropy parameters. For the interpretation of
these data we need a qualitative knowledge of the line shape which we obtain
from fully numerical calculations for finite chains. Exact analytical results
on the line shape are out of reach of current theories. From our numerical work
we could extract, however, an empirical parameter-free model of the line shape
at high temperatures which is extremely accurate over a wide range of
anisotropy parameters and is exact at the free fermion point and at the
isotropic point. Another prediction of the line shape can be made in the
zero-temperature and zero magnetic field limit, where the sufficiently
anisotropic model shows strong absorption. For anisotropy parameters in the
massive phase we derive the exact two-spinon contribution to the spectral line.
From the intensity sum rule it can be estimated that this contribution accounts
for more than 80% of the spectral weight if the anisotropy parameter is
moderately above its value at the isotropic point.",1201.6523v1
2012-03-09,Material Laws and Numerical Methods in Applied Superconductivity,"Contents Preface I Electromagnetism of type II superconductors 1 General
Statements Of The Critical State 1.1 The CS In The Maxwell Equations Formalism
1.2 The CS Regime And The MQS Limit 2 Variational Theory for CS Problems 2.1
General Principles Of The Variational Method 2.2 The Material Law: SCs with
magnetic anisotropy 2.2.1 Onto the 1D Critical States 2.2.2 Towards The 3D
Critical States 3 Computational Method Conclusions I References I II Critical
State Problems:Effects & Applications 4 Type-II SCs With Intrinsic Magnetic
Anisotropy 4.1 3D variational statement in slab geometry 4.2 Isotropic
predictions in -3D- configurations 4.3 T-states in -3D- configurations 4.4
CT-states in -3D- configurations 4.5 Smooth critical states in -3D-
configurations Appendix I Critical angle gradient in -3D- configurations 5 The
Longitudinal Transport Problem 5.1 Simplified analytical models and beyond
5.1.1 The simplest analytical model 5.1.2 The SDCST statement and the BM's
approach 5.2 Magnetic anisotropy and the uncommon effects 5.2.1 Extremal case:
The T-states model 5.2.2 Material laws with magnetic anisotropy: CT\chi -
models 6 Electromagnetism For Superconducting Wires 6.1 Theoretical framework
and general considerations 6.2 SC wires subjected to isolated external sources
6.2.1 Wires with an injected AC transport current 6.2.2 Wires under an external
AC magnetic flux 6.2.3 Ultimate considerations on the AC losses 6.3 SC wires
under simultaneous AC excitations (B_{0},I_{tr}) 6.3.1 Synchronous excitations
6.3.2 Asynchronous excitations Conclusions II References II Supplementary
Material II III Microscopical aspects also analyzed 7 E-Ph Theory And The Nodal
Kink Effect In HTSC 8 Is it necessary to go beyond the E-Ph mode? Conclusions
III References III Supplementary Material III IV Addenda",1203.2159v1
2012-03-14,Measurement of the azimuthal anisotropy for charged particle production in sqrt(s_NN) = 2.76 TeV lead-lead collisions with the ATLAS detector,"Differential measurements of charged particle azimuthal anisotropy are
presented for lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS
detector at the LHC, based on an integrated luminosity of approximately 8
mb^-1. This anisotropy is characterized via a Fourier expansion of the
distribution of charged particles in azimuthal angle (phi), with the
coefficients v_n denoting the magnitude of the anisotropy. Significant v_2-v_6
values are obtained as a function of transverse momentum (0.5<pT<20 GeV),
pseudorapidity (|eta|<2.5) and centrality using an event plane method. The v_n
values for n>=3 are found to vary weakly with both eta and centrality, and
their pT dependencies are found to follow an approximate scaling relation,
v_n^{1/n}(pT) \propto v_2^{1/2}(pT). A Fourier analysis of the charged particle
pair distribution in relative azimuthal angle (Dphi=phi_a-phi_b) is performed
to extract the coefficients v_{n,n}=<cos (n Dphi)>. For pairs of charged
particles with a large pseudorapidity gap (|Deta=eta_a-eta_b|>2) and one
particle with pT<3 GeV, the v_{2,2}-v_{6,6} values are found to factorize as
v_{n,n}(pT^a,pT^b) ~ v_n(pT^a)v_n(pT^b) in central and mid-central events. Such
factorization suggests that these values of v_{2,2}-v_{6,6} are primarily due
to the response of the created matter to the fluctuations in the geometry of
the initial state. A detailed study shows that the v_{1,1}(pT^a,pT^b) data are
consistent with the combined contributions from a rapidity-even v_1 and global
momentum conservation. A two-component fit is used to extract the v_1
contribution. The extracted v_1 is observed to cross zero at pT\sim1.0 GeV,
reaches a maximum at 4-5 GeV with a value comparable to that for v_3, and
decreases at higher pT.",1203.3087v3
2012-04-20,Interplay between Kondo tunneling and Rashba precession,"The influence of Thomas - Rashba precession on the physics of Kondo tunneling
through quantum dots is analyzed. It is shown that this precession is relevant
only at finite magnetic fields. Thomas - Rashba precession results in peculiar
anisotropy of the effective g-factor and initiates dephasing of the Kondo
tunneling amplitude at low temperature, that is strongly dependent on the
magnetic field.",1204.4695v1
2012-06-06,A Conditional Luminosity Function Model of the Cosmic Far-Infrared Background Anisotropy Power Spectrum,"The cosmic far-infrared background (CFIRB) is expected to be generated by
faint, dusty star-forming galaxies during the peak epoch of galaxy formation.
The anisotropy power spectrum of the CFIRB captures the spatial distribution of
these galaxies in dark matter halos and the spatial distribution of dark matter
halos in the large-scale structure. Existing halo models of CFIRB anisotropy
power spectrum are either incomplete or lead to halo model parameters that are
inconsistent with the galaxy distribution selected at other wavelengths. Here
we present a conditional luminosity function approach to describe the far-IR
bright galaxies. We model the 250 um luminosity function and its evolution with
redshift and model-fit the CFIRB power spectrum at 250 um measured by the
Herschel Space Observatory. We introduce a redshift dependent duty-cycle
parameter so that we are able to estimate the typical duration of the dusty
star formation process in the dark matter halos as a function of redshifts. We
find the duty cycle of galaxies contributing to the far-IR background is 0.3 to
0.5 with a dusty star-formation phase lasting for \sim0.3-1.6 Gyrs. This result
confirms the general expectation that the far-IR background is dominated by
star-forming galaxies in an extended phases, not bright starbursts that are
driven by galaxy mergers and last \sim10-100 Myrs. The halo occupation number
for satellite galaxies has a power-law slope that is close to unity over 0<z<4.
We find that the minimum halo mass for dusty, star-forming galaxies with
L_250>10^{10} L_Sun is 2\times10^{11}M_Sun and 3\times 10^{10}M_Sun at z=1 and
2, respectively. Integrating over the galaxy population with L_250>10^{9}
L_Sun, we find that the cosmic density of dust residing in the dusty,
star-forming galaxies responsible for the background anisotropies
\Omega_{dust}\sim3\times10^{-6} to 2\times10^{-5}.",1206.1324v2
2012-06-19,Constraints on the shapes of galaxy dark matter haloes from weak gravitational lensing,"We study the shapes of galaxy dark matter haloes by measuring the anisotropy
of the weak gravitational lensing signal around galaxies in the second
Red-sequence Cluster Survey (RCS2). We determine the average shear anisotropy
within the virial radius for three lens samples: all galaxies with
19<m_r'<21.5, and the `red' and `blue' samples, whose lensing signals are
dominated by massive low-redshift early-type and late-type galaxies,
respectively. To study the environmental dependence of the lensing signal, we
separate each lens sample into an isolated and clustered part and analyse them
separately. We also measure the azimuthal dependence of the distribution of
physically associated galaxies around the lens samples. We find that these
satellites preferentially reside near the major axis of the lenses, and
constrain the angle between the major axis of the lens and the average location
of the satellites to <theta>=43.7 deg +/- 0.3 deg for the `all' lenses,
<theta>=41.7 deg +/- 0.5 deg for the `red' lenses and <theta>=42.0 deg +/- 1.4
deg for the `blue' lenses. For the `all' sample, we find that the anisotropy of
the galaxy-mass cross-correlation function <f-f_45>=0.23 +/- 0.12, providing
weak support for the view that the average galaxy is embedded in, and
preferentially aligned with, a triaxial dark matter halo. Assuming an
elliptical Navarro-Frenk-White (NFW) profile, we find that the ratio of the
dark matter halo ellipticity and the galaxy ellipticity
f_h=e_h/e_g=1.50+1.03-1.01, which for a mean lens ellipticity of 0.25
corresponds to a projected halo ellipticity of e_h=0.38+0.26-0.25 if the halo
and the lens are perfectly aligned. For isolated galaxies of the `all' sample,
the average shear anisotropy increases to <f-f_45>=0.51+0.26-0.25 and
f_h=4.73+2.17-2.05, whilst for clustered galaxies the signal is consistent with
zero. (abridged)",1206.4304v1
2012-07-06,Analytical Solutions to the Mass-Anisotropy Degeneracy with Higher Order Jeans Analysis: A General Method,"The Jeans analysis is often used to infer the total density of a system by
relating the velocity moments of an observable tracer population to the
underlying gravitational potential. This technique has recently been applied in
the search for Dark Matter in objects such as dwarf spheroidal galaxies where
the presence of Dark Matter is inferred via stellar velocities. A precise
account of the density is needed to constrain the expected gamma ray flux from
DM self-annihilation and to distinguish between cold and warm dark matter
models. Unfortunately the traditional method of fitting the second order Jeans
equation to the tracer dispersion suffers from an unbreakable degeneracy of
solutions due to the unknown velocity anisotropy of the projected system. To
tackle this degeneracy one can appeal to higher moments of the Jeans equation.
By introducing an analog to the Binney anisotropy parameter at fourth order,
beta' we create a framework that encompasses all solutions to the fourth order
Jeans equations rather than those in the literature that impose unnecessary
correlations between anisotropy of second and fourth order moments. The
condition beta' = f(beta) ensures that the degeneracy is lifted and we
interpret the separable augmented density system as the order-independent case
beta'= beta. For a generic choice of beta' we present the line of sight
projection of the fourth moment and how it could be incorporated into a joint
likelihood analysis of the dispersion and kurtosis. Having presented the
mathematical framework, we then use it to develop a statistical method for the
purpose of placing constraints on dark matter density parameters from discrete
velocity data. The method is tested on simulated dwarf spheroidal data sets
leading to results which motivate study of real dwarf spheroidal data sets.",1207.1709v3
2012-09-04,Heavy-Flavour Production in Pb-Pb collisions at the LHC with ALICE,"Results on open heavy-flavour production in Pb-Pb collisions at sqrt{s_NN} =
2.76 TeV measured with ALICE at the LHC are presented. The nuclear modification
factors, extracted in three different channels, show a strong suppression in
central collisions. The measured D-meson azimuthal anisotropy indicates a
non-zero v2, which is similar to the one of charged hadrons.",1209.0630v1
2012-09-25,Cosmic Ray Physics with the IceCube Observatory,"The IceCube Neutrino Observatory with its 1-km^3 in-ice detector and the
1-km^2 surface detector (IceTop) constitutes a three-dimensional cosmic ray
detector well suited for general cosmic ray physics. Various measurements of
cosmic ray properties, such as energy spectra, mass composition and
anisotropies, have been obtained from analyses of air showers at the surface
and/or atmospheric muons in the ice.",1209.5610v1
2012-10-29,Orientation Sensitive Terahertz Resonances Observed in Protein Crystals,"A method is presented for measuring anisotropic THz response for small
crystals, Crystal Anisotropy Terahertz Microscopy (CATM). Sucrose CATM
measurements find the expected anisotropic phonon resonances. CATM measurements
of protein crystals find the expected broadband water absorption is suppressed
and strong orientation and hydration dependent resonant features.",1210.7531v1
2012-12-12,"Comment on the ""Excess ellipticity of hot and cold spots WMAP data?"" by Berntsen, E. and Hansen, F.K","The recent paper by Berntsen and Hansen devoted to the analysis of
elliptic-ity of anisotropies in CMB maps, distorts some statements of previous
studies, misses relevant papers, along with superficial comparison of the
results (in part of definitions, the role of noise, angular resolution, model
parameters).",1212.2718v1
2013-01-21,The anisotropic distribution of the interacting electrons,"The distribution function for a system of interacting electrons in metals is
multivalent in a certain region of wave vectors. One solution among many is
isotropic. For other solutions the distribution of electrons over the wave
vectors is anisotropic. In the simplest case, the anisotropy arises as a result
of the repulsion between electrons in states with the wave vectors $\bf k$ and
$-\hh\bf k$.",1301.4711v1
2013-01-30,Anisotropic branes,"We present a class of anisotropic brane configurations which shows BKL
oscillations near their cosmological singularities. Near horizon limits of
these solutions represent Kasner space embedded in AdS background. Dynamical
probe branes in these geometries inherit anisotropies from the background.
Amusingly, for a probe M5 brane, we find that there exists a parameter region
where three of its world-volume directions expand while the rest contract.",1301.7194v1
2013-02-19,TASI Lectures on Cosmological Perturbations,"We present a self-contained summary of the theory of linear cosmological
perturbations. We emphasize the effect of the six parameters of the minimal
cosmological model, first, on the spectrum of Cosmic Microwave Background
temperature anisotropies, and second, on the linear matter power spectrum. We
briefly review at the end the possible impact of a few non-minimal dark matter
and dark energy models.",1302.4640v1
2013-02-20,The Velocity Anisotropy of Distant Milky Way Halo Stars from Hubble Space Telescope Proper Motions,"Based on long baseline (5-7 years) multi-epoch HST/ACS photometry, used
previously to measure the proper motion of M31, we present the proper motions
(PMs) of 13 main-sequence Milky Way halo stars. The sample lies at an average
distance of r ~24 kpc from the Galactic center, with a root-mean-square spread
of 6 kpc. At this distance, the median PM accuracy is 5 km/s. We devise a
maximum likelihood routine to determine the tangential velocity ellipsoid of
the stellar halo. The velocity second moments in the directions of the Galactic
(l,b) system are < vl^2 >^{1/2} = 123 (+29, -23) km/s, and < vb^2 >^{1/2} = 83
(+24, -16) km/s. We combine these results with the known line-of-sight second
moment, < vlos^2 >^{1/2} = 105 \pm 5$ km/s, at this < r > to study the velocity
anisotropy of the halo. We find approximate isotropy between the radial and
tangential velocity distributions, with anisotropy parameter beta = 0.0 (+0.2,
-0.4). Our results suggest that the stellar halo velocity anisotropy out to r ~
30 kpc is less radially biased than solar neighborhood measurements. This is
opposite to what is expected from violent relaxation, and may indicate the
presence of a shell-type structure at r ~ 24 kpc. With additional multi-epoch
HST data, the method presented here has the ability to measure the transverse
kinematics of the halo for more stars, and to larger distances. This can yield
new improved constraints on the stellar halo formation mechanism, and the mass
of the Milky Way.",1302.5111v1
2013-03-18,Chaotic inflation in supergravity and cosmic string production,"We describe a simple model of chaotic inflation in supergravity where one can
easily tune not only the basic cosmological parameters such as n_{s}, r, and
f_NL, but also a possible (subdominant) cosmic string contribution to the CMB
anisotropy.",1303.4435v1
2013-03-25,Morphogenesis of defects and tactoids during isotropic-nematic phase transition in self-assembled lyotropic chromonic liquid crystals,"We explore the structure of nuclei and topological defects in the first-order
phase transition between the nematic (N) and isotropic (I) phases in lyotropic
chromonic liquid crystals (LCLCs). The LCLCs are formed by self-assembled
molecular aggregates of various lengths and show a broad biphasic region. The
defects emerge as a result of two mechanisms. 1) Surface anisotropy mechanism
that endows each N nucleus (tactoid) with topological defects thanks to
preferential (tangential) orientation of the director at the closed I-N
interface, and 2) Kibble mechanism with defects forming when differently
oriented N tactoids merge with each other. Different scenarios of phase
transition involve positive (N-in-I) and negative (I-in-N) tactoids with
non-trivial topology of the director field and also multiply connected
tactoids-in-tactoids configurations. The closed I-N interface limiting a
tactoid shows a certain number of cusps; the lips of the interface on the
opposite sides of the cusp make an angle different from pi. The N side of each
cusp contains a point defect-boojum. The number of cusps shows how many times
the director becomes perpendicular to the I-N interface when one
circumnavigates the closed boundary of the tactoid. We derive conservation laws
that connect the number of cusps c to the topological strength m of defects in
the N part of the simply-connected and multiply-connected tactoids. We
demonstrate how the elastic anisotropy of the N phase results in non-circular
shape of the disclination cores. A generalized Wulff construction is used to
derive the shape of I and N tactoids as the function of I-N interfacial tension
anisotropy in the frozen director field of various topological charges m. The
complex shapes and structures of tactoids and topological defects demonstrate
an important role of surface anisotropy in morphogenesis of phase transitions
in liquid crystals.",1303.6239v1
2013-03-29,On the Depolarization Factors for Anisotropic Ellipsoids in Anisotropic Media,"A definition of depolarization factors for anisotropic ellipsoid in an
anisotropic medium is considered. The expressions for these factors are
derived, which generalize some results known for special cases, and differences
from the usual depolarization factors for ellipsoid in isotropic medium are
described. The concept of ""reduced"" ellipsoid, allowing visually describe the
effect of the medium anisotropy on depolarization is also introduced.",1303.7341v1
2013-04-02,Cosmological anisotropy from non-comoving dark matter and dark energy,"We consider a cosmological model in which the two major fluid components of
the Universe, dark energy and dark matter, flow with distinct four-velocities.
This cosmological configuration is equivalent to a single anisotropic fluid,
expanding with a four-velocity that is an appropriate combination of the two
fluid four-velocities. The energy density of the single cosmological fluid is
larger than the sum of the energy densities of the two perfect fluids, i.e.,
dark energy and dark matter, respectively, and contains a correction term due
to the anisotropy generated by the differences in the four-velocities.
Furthermore, the gravitational field equations of the two-fluid anisotropic
cosmological model are obtained for a Bianchi type I geometry. By assuming that
the non-comoving motion of the dark energy and dark matter induces small
perturbations in the homogeneous and isotropic
Friedmann-Lemaitre-Robertson-Walker type cosmological background, and that the
anisotropy parameter is small, the equations of the cosmological perturbations
due to the non-comoving nature of the two major components are obtained. The
time evolution of the metric perturbations is explicitly obtained for the cases
of the exponential and power law background cosmological expansion. Therefore,
if there is a slight difference between the four-velocities of the dark energy
and dark matter, the Universe would acquire some anisotropic characteristics,
and its geometry will deviate from the standard FLRW one. In fact, the recent
Planck results show that the presence of an intrinsic large scale anisotropy in
the Universe cannot be excluded {\it a priori}, so that the model presented in
this work can be considered as a plausible and viable working hypothesis.",1304.0757v3
2013-05-13,ALICE status and plans,"The ALICE experiment has been running successfully since 2010 and made an
impressive progress towards understanding of hot and dense QCD matter produced
in heavy ion collisions at LHC energies. Recent results on identified particle
spectra, azimuthal anisotropy, heavy flavour and quarkonium production in Pb-Pb
collisions at sqrt(s_NN) = 2.76 TeV are presented. First results on p-Pb
collisions and ALICE upgrade plans are briefly reviewed.",1305.2804v1
2013-05-21,Transport of spin-anisotropy without spin currents,"We revisit the transport of spin-degrees of freedom across an electrically
and thermally biased tunnel junction between two ferromagnets with
non-collinear magnetizations. Besides the well-known charge and spin currents
we show that a non-zero spin-quadrupole current flows between the ferromagnets.
This tensor-valued current describes the non-equilibrium transport of
spin-anisotropy relating to both local and non-local multi-particle spin
correlations of the circuit. This quadratic spin-anisotropy, quantified in
terms of the spin-quadrupole moment, is fundamentally a two-electron quantity.
In spin-valves with an embedded quantum dot such currents have been shown to
result in a quadrupole accumulation that affects the measurable quantum dot
spin and charge dynamics. The spin-valve model studied here allows fundamental
questions about spin-quadrupole storage and transport to be worked out in
detail, while ignoring the detection by a quantum dot. This physical
understanding of this particular device is of importance for more complex
devices where spin-quadrupole transport can be detected. We demonstrate that,
as far as storage and transport are concerned, the spin anisotropy is only
partly determined by the spin polarization. In fact, for a thermally biased
spin-valve the charge- and spin-current may vanish, while a pure exchange
spin-quadrupole current remains, which appears as a fundamental consequence of
Pauli's principle. We extend the real-time diagrammatic approach to efficiently
calculate the average of multi-particle spin-observables, in particular the
spin-quadrupole current. Although the paper addresses only leading order and
spin-conserving tunneling we formulate the technique for arbitrary order in an
arbitrary, spin-dependent tunnel coupling in a way that lends itself to
extension to quantum-dot spin-valve structures.",1305.4843v1
2013-05-24,Magnetic field amplification and evolution in turbulent collisionless MHD: an application to the ICM,"The amplification and maintenance of the observed magnetic fields in the ICM
are usually attributed to the turbulent dynamo action. This is generally
derived employing a collisional MHD model. However, in the ICM the ion mean
free path between collisions is of the order of the dynamical scales, thus
requiring a collisionless MHD description. Unlike collisional MHD simulations,
our study uses an anisotropic plasma pressure with respect to the direction of
the local magnetic field, which brings the plasma within a parameter space
where collisionless instabilities should take place. Within the adopted model
these instabilities are contained at bay through the relaxation term of the
pressure anisotropy which simulates the feedback of the mirror and firehose
instabilities. This relaxation acts to get the plasma distribution function
consistent with the empirical studies of collisionless plasmas. Our 3D
numerical simulations of forced transonic turbulence motivated by modeling of
the turbulent ICM are performed for different initial values of the magnetic
field intensity, and different relaxation rates of the pressure anisotropy. We
found that in the high beta plasma regime corresponding to the ICM conditions,
a fast anisotropy relaxation rate gives results which are similar to the
collisional-MHD model as far as the statistical properties of the turbulence
are concerned. Also, the amplification of seed magnetic fields due to the
turbulent dynamo action is similar to the collisional-MHD model. Our
simulations that do not employ the anisotropy relaxation deviate significantly
from the collisional-MHD results, and show more power at the small-scale
fluctuations of both density and velocity representing the results of the
instabilities. For these simulations the large scale fluctuations in the
magnetic field are mostly suppressed and the turbulent dynamo fails in
amplifying seed magnetic fields.",1305.5654v1
2013-06-23,Searching For Anisotropic Gravitational-wave Backgrounds Using Pulsar Timing Arrays,"We present the results of simulated injections testing the first Bayesian
search-pipeline capable of investigating the angular-structure of a
gravitational-wave (GW) background influencing pulsar signals. A stochastic
background of GWs from the incoherent superposition of many inspiraling
supermassive black hole binaries at nHz frequencies is likely to be the
dominant GW signal detectable by pulsar timing arrays (PTAs). Even though one
might expect a background composed of a high-redshift cosmological population
of sources to be fairly isotropic, deviations from isotropy may be indicative
of local GW hotspots or some form of continuous anisotropy in the
angular-distribution of GW-power. A GWB induces time-of-arrival deviations in
pulsar signals which are correlated between separated pulsars. In an isotropic
background this cross-correlation follows a distinctive relationship, known as
the Hellings and Downs curve, that depends only on the angular separation of
the pulsars. If the background is anisotropic, the cross-correlation is
different, but predictable, and also depends on the absolute position of the
pulsars. By simulating datasets containing GWBs with various anisotropic
configurations, we have explored the prospects for constraining anisotropy
using near future data. We find that at moderate to high signal to noise ratio
the assumption of isotropy is no longer an appropriate description of the
simulated background. Furthermore, we can recover the nature of the injected
anisotropy in a Bayesian parameter-estimation search, and propose a prior on
the anisotropy search-space motivated by the physicality of the implied
distribution of sources.",1306.5395v2
2013-08-20,Super-intense highly anisotropic optical transitions in anisotropic quantum dots,"Coulomb interaction among electrons is found to have profound effects on the
electronic properties of anisotropic quantum dots in a perpendicular external
magnetic field, and in the presence of the Rashba spin-orbit interaction. This
is more evident in optical transitions, which we find in this system to be
highly anisotropic and super-intense, in particular, for large values of the
anisotropy parameter.",1308.4369v1
2013-10-22,Overview of ALICE results,"Selected ALICE results on the global event properties, particle spectra,
azimuthal anisotropy, heavy flavour and quarkonium production in Pb-Pb
collisions at sqrt(s_NN) = 2.76 TeV are presented. First results on p-Pb
collisions at sqrt(s_NN) = 5.02 TeV are briefly reviewed.",1310.5819v1
2014-01-02,Low temperature ordering in easy-axis $S=1$ kagome and triangular lattice antiferromagnets,"A brief review is provided of earlier work on the low temperature phases of
$S=1$ kagome and triangular lattice antiferromagnets in which there is
sufficiently strongly single-ion anisotropy $D$ that dominates over the
antiferromagnetic exchange $J$.",1401.0371v1
2014-01-07,"The SLUGGS Survey: Breaking degeneracies between dark matter, anisotropy and the IMF using globular cluster subpopulations in the giant elliptical NGC 5846","We study the mass and anisotropy distribution of the giant elliptical galaxy
NGC 5846 using stars, as well as the red and blue globular cluster (GC)
subpopulations. We break degeneracies in the dynamical models by taking
advantage of the different phase space distributions of the two GC
subpopulations to unambiguously constrain the mass of the galaxy and the
anisotropy of the GC system. Red GCs show the same spatial distribution and
behaviour as the starlight, whereas blue GCs have a shallower density profile,
a larger velocity dispersion and a lower kurtosis, all of which suggest a
different orbital distribution. We use a dispersion-kurtosis Jeans analysis and
find that the solutions of separate analyses for the two GC subpopulations
overlap in the halo parameter space. The solution converges on a massive dark
matter halo, consistent with expectations from $\Lambda$CDM and WMAP7 cosmology
in terms of virial mass ($\log M_{DM} \sim13.3 M_{sun}$) and concentration
($c_{vir}\sim8$). This is the first such analysis that solves the dynamics of
the different GC subpopulations in a self-consistent manner. Our method
improves the uncertainties on the halo parameter determination by a factor of
two and opens new avenues for the use of elliptical galaxy dynamics as tests of
predictions from cosmological simulations. The implied stellar mass-to-light
ratio derived from the dynamical modelling is fully consistent with a Salpeter
initial mass function (IMF) and rules out a bottom light IMF. The different GC
subpopulations show markedly distinct orbital distributions at large radii,
with red GCs having an anisotropy parameter $\beta\sim0.4$ outside $\sim3R_e$,
and the blue GCs having $\beta\sim0.15$ at the same radii, while centrally
($\sim1R_e$) they are both isotropic. We discuss the implications of our
findings within the two-phase formation scenario for early-type galaxies.",1401.1501v1
2014-01-17,Dynamical Models of Elliptical Galaxies -- I. Simple Methods,"We study dynamical models for elliptical galaxies, deriving the projected
kinematic profiles in a form that is valid for general surface-brightness
profiles and (spherical) total mass profiles, without the need for any explicit
deprojection. We then show that an almost flat rotation curve, combined with
modest velocity anisotropy, is already sufficient to recover the kinematic
profiles of nearby ellipticals. As an application, we provide two different
sets of mass estimators for elliptical galaxies, based on either the velocity
dispersion at a specific location near the effective radius, or the
aperture-averaged velocity dispersion. In the large aperture (virial) limit,
mass estimators are naturally independent of anisotropy. The spherical mass
enclosed within the effective radius $R_{\rm e}$ can be estimated as $2.4
R_{\rm e} \langle \sigma^{2}_{\rm p} \rangle/ G$, where $\langle \sigma^2_{\rm
p} \rangle$ is the average of the squared velocity dispersion over a finite
aperture. This formula does not depend on assumptions such as
mass-follows-light, and is a compromise between the cases of small and large
apertures sizes. Its general agreement with results from other methods in the
literature makes it a reliable means to infer masses in the absence of detailed
kinematic information. If on the other hand the velocity dispersion profile is
available, tight mass estimates can be found that are independent of the
mass-model and anisotropy profile (within $\approx$ 10% accuracy). Explicit
formulae are given for small anisotropy, large radii and/or power-law total
densities. Motivated by recent observational claims, we also discuss the issue
of weak homology of elliptical galaxies, emphasizing the interplay between
morphology and orbital structure.",1401.4462v2
2014-01-30,CMB statistical anisotropy from noncommutative gravitational waves,"Primordial statistical anisotropy is a key indicator to investigate early
Universe models and has been probed by the cosmic microwave background (CMB)
anisotropies. In this paper, we examine tensor-mode CMB fluctuations generated
from anisotropic gravitational waves, parametrised by $P_h({\bf k}) =
P_h^{(0)}(k) [ 1 + \sum_{LM} f_L(k) g_{LM} Y_{LM} (\hat{\bf k}) ]$, where
$P_h^{(0)}(k)$ is the usual scale-invariant power spectrum. Such anisotropic
tensor fluctuations may arise from an inflationary model with noncommutativity
of fields. It is verified that in this model, an isotropic component and a
quadrupole asymmetry with $f_0(k) = f_2(k) \propto k^{-2}$ are created and
hence highly red-tilted off-diagonal components arise in the CMB power spectra,
namely $\ell_2 = \ell_1 \pm 2$ in $TT$, $TE$, $EE$ and $BB$, and $\ell_2 =
\ell_1 \pm 1$ in $TB$ and $EB$. We find that B-mode polarisation is more
sensitive to such signals than temperature and E-mode polarisation due to the
smallness of large-scale cosmic variance and we can potentially measure $g_{00}
= 30$ and $g_{2M} = 58$ at 68% CL in a cosmic-variance-limited experiment. Such
a level of signal may be measured in a PRISM like experiment, while the
instrumental noise contaminates it in the $Planck$ experiment. These results
imply that it is impossible to measure the noncommutative parameter if it is
small enough for the perturbative treatment to be valid. Our formalism and
methodology for dealing with the CMB tensor statistical anisotropy are general
and straightforwardly applicable to other early Universe models.",1401.7936v2
2014-03-20,Weak solutions of the Stochastic Landau-Lifschitz Equations with non-zero anisotrophy energy,"We study a Stochastic Landau-Lifschitz Equation with non-zero anisotrophy
energy and multidimensional noise. The existence and some regularities of weak
solution have been proved.",1403.5220v2
2014-05-08,Azimuthal anisotropy of D meson production in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV,"The production of the prompt charmed mesons $D^0$, $D^+$ and $D^{*+}$
relative to the reaction plane was measured in Pb-Pb collisions at a
centre-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\rm NN}} =
2.76$ TeV with the ALICE detector at the LHC. D mesons were reconstructed via
their hadronic decays at central rapidity in the transverse momentum ($p_{\rm
T}$) interval of 2-16 GeV/$c$. The azimuthal anisotropy is quantified in terms
of the second coefficient $v_2$ in a Fourier expansion of the D meson azimuthal
distribution, and in terms of the nuclear modification factor $R_{\rm AA}$,
measured in the direction of the reaction plane and orthogonal to it. The $v_2$
coefficient was measured with three different methods and in three centrality
classes in the interval 0-50%. A positive $v_2$ is observed in mid-central
collisions (30-50% centrality class), with an mean value of
$0.204_{-0.036}^{+0.099}$ (tot.unc.) in the interval $2 < p_{\rm T} < 6$
GeV/$c$, which decreases towards more central collisions (10-30% and 0-10%
classes). The positive $v_2$ is also reflected in the nuclear modification
factor, which shows a stronger suppression in the direction orthogonal to the
reaction plane for mid-central collisions. The measurements are compared to
theoretical calculations of charm quark transport and energy loss in
high-density strongly-interacting matter at high temperature. The models that
include substantial elastic interactions with an expanding medium provide a
good description of the observed anisotropy. However, they are challenged to
simultaneously describe the strong suppression of high-$p_{\rm T}$ yield of D
mesons in central collisions and their azimuthal anisotropy in non-central
collisions.",1405.2001v2
2014-08-14,Utilizing wind in spatial covariance,"This work develops a covariance function which allows for a stronger spatial
correlation for pairs of points in the direction of a vector such as wind and
weaker for pairs which are perpendicular to it. It derives a simple covariance
function by stretching the space along the wind axes (upwind and across wind
axes). It is shown that this covariance function is anisotropy in the original
space and the functions is explicitly calculated.",1408.3174v1
2014-09-05,Simulations for a next-generation UHECR observatory,"We explore the potential of a future, ultra-high energy cosmic ray (UHECR)
experiment, that is able to overcome the limitation of low statistics, to
detect anisotropy in the arrival directions of UHECRs. We concentrate on the
lower energy range of future instruments (E > 50 EeV), where, if the UHECR
source number density is not too low, the sources should be numerous enough to
imprint a clustering pattern in the sky, and thus possibly in the UHECR arrival
directions. Under these limits, the anisotropy signal should be dominated by
the clustering of astrophysical sources per-se in the large-scale structures,
and not the clustering of events around individual sources. We study the
potential for a statistical discrimination between different astrophysical
models which we parametrise by the number density of UHECR sources, the
possible bias of the UHECR accelerators with respect to the galaxy
distribution, and the unknown fraction of UHECRs that have been deflected by
large angles. We demonstrate that an order-of-magnitude increase in statistics
would allow to discriminate between a variety of astrophysical models, provided
that a sub-sample of light elements can be extracted, and that it represents at
least ~70% of the overall flux, sensitive to the UHECR source number density.
Even without knowledge of the composition, an anisotropy at the 99.7% level
should be detectable when the number of detected events exceeds 2000 beyond 50
EeV, as long as the composition is proton dominated, and the number density of
UHECR sources is relatively high. If the UHECR sources are strongly biased
relative to the galaxy distribution, as are for example galaxy clusters, an
anisotropy at the 99.7% should be detectable once the number of detected events
exceeds 1000, if the fraction of protons at the highest energies is ~60% or
higher.",1409.1925v2
2014-10-31,Anisotropic flow from hard partons in ultra-relativistic nuclear collisions,"Anisotropies of hadronic distribution in nuclear collisions are used for
determination of properties of the nuclear matter. At the LHC it is important
to account for the contribution to the flow due to momentum transferred from
hard partons to the quark-gluon plasma.",1410.8711v1
2014-12-02,Collective modes in anisotropic double layer systems,"We study collective modes in anisotropic double layer systems. To this end,
we derive a zero-$T$ dynamic polarization function for a conductor with a
paraboloidal dispersion. Following this, we demonstrate the dependence of the
plasmonic modes on the relative orientation, doping, and system anisotropy.",1412.0811v1
2014-12-19,"Monotonicity formulae and classification results for singular, degenerate, anisotropic PDEs","We consider possibly degenerate and singular elliptic equations in a possibly
anisotropic medium.
  We obtain monotonicity results for the energy density, rigidity results for
the solutions and classification results for the
singularity/degeneracy/anisotropy allowed.
  As far as we know, these results are new even in the case of non-singular and
non-degenerate anisotropic equations.",1412.6561v1
2015-02-16,Anisotropy of third-order structure functions in MHD turbulence,"The measure of the third-order structure function, Y, is employed in the
solar wind to compute the cascade rate of turbulence. In the absence of a mean
field B0=0, Y is expected to be isotropic (radial) and independent of the
direction of increments, so its measure yields directly the cascade rate. For
turbulence with mean field, as in the solar wind, Y is expected to become more
two dimensional (2D), that is, to have larger perpendicular components, loosing
the above simple symmetry. To get the cascade rate one should compute the flux
of Y, which is not feasible with single-spacecraft data, thus measurements rely
upon assumptions about the unknown symmetry. We use direct numerical
simulations (DNS) of magneto-hydrodynamic (MHD) turbulence to characterize the
anisotropy of Y. We find that for strong guide field B0=5 the degree of
two-dimensionalization depends on the relative importance of shear and pseudo
polarizations (the two components of an Alfv\'en mode in incompressible MHD).
The anisotropy also shows up in the inertial range. The more Y is 2D, the more
the inertial range extent differs along parallel and perpendicular directions.
We finally test the two methods employed in observations and find that the
so-obtained cascade rate may depend on the angle between B0 and the direction
of increments. Both methods yield a vanishing cascade rate along the parallel
direction, contrary to observations, suggesting a weaker anisotropy of solar
wind turbulence compared to our DNS. This could be due to a weaker mean field
and/or to solar wind expansion.",1502.04705v2
2015-03-16,The benchmark black hole in NGC 4258: dynamical models from high-resolution two-dimensional stellar kinematics,"NGC 4258 is the galaxy with the most accurate (maser-based) determination for
the mass of the supermassive black hole (SMBH) in its nucleus. In this work we
present a two-dimensional mapping of the stellar kinematics in the inner 3.0 x
3.0 arcsec = 100 x 100 pc of NGC 4258 using adaptative-optics observations
obtained with the Near-Infrared Integral Field Spectrograph of the GEMINI North
telescope at a 0.11 arcsec (4 pc) angular resolution. The observations resolve
the radius of influence of the SMBH, revealing an abrupt increase in the
stellar velocity dispersion within 10 pc from the nucleus, consistent with the
presence of a SMBH there. Assuming that the galaxy nucleus is in a steady state
and that the velocity dispersion ellipsoid is aligned with a cylindrical
coordinate system, we constructed a Jeans anisotropic dynamical model to fit
the observed kinematics distribution. Our dynamical model assumes that the
galaxy has axial symmetry and is constructed using the multi-gaussian expansion
method to parametrize the observed surface brightness distribution. The Jeans
dynamical model has three free parameters: the mass of the central SMBH, the
mass-luminosity ratio of the galaxy and the anisotropy of the velocity
distribution. We test two types of models: one with constant velocity
anisotropy, and another with variable anisotropy. The model that best
reproduces the observed kinematics was obtained considering that the galaxy has
radially varying anisotropy, being the best-fitting parameters with 3$\sigma$
significance $M_\bullet=4.8^{+0.8}_{-0.9}\times 10^7\,{\rm M_\odot}$ and
$\Gamma_k = 4.1^{+0.4}_{-0.5}$. This value for the mass of the SMBH is just 25
per cent larger than that of the maser determination and 50 per cent larger
that a previous stellar dynamical determination obtained via Schwarzschild
models.",1503.04540v2
2015-04-30,Mass Models of Dwarf Spheroidal Galaxies with Variable Stellar Anisotropy. I. Jeans Analysis,"Using a flexible galactic model with variable stellar velocity anisotropy, I
apply the classical Jeans mass modeling approach to the five dwarf spheroidal
galaxies with the largest homogeneous datasets of stellar line-of-sight
velocities (between 330 and 2500 stars per galaxy) -- Carina, Fornax, Leo~I,
Sculptor, and Sextans. I carry out an exhaustive model parameter search,
assigning absolute probabilities to each parameter combination. My main finding
is that there is a well defined radius (unique for each galaxy) where the Jeans
analysis constraints on the enclosed mass are tightest, and are much better
than the constraints at previously suggested radii (e.g. 300~pc). For Carina,
Fornax, Leo~I, Sculptor, and Sextans the enclosed DM mass is $0.94 \pm 0.20$
(at 410~pc), $7.1 \pm 0.9$ (at 925~pc), $1.75 \pm 0.20$ (at 390~pc), $2.59 \pm
0.42$ (at 435~pc), and $2.3 \pm 0.9$ (at 1035~pc), respectively (two-sigma
uncertainties; in $10^7$~M$_\odot$ units). Local DM density has the tightest
constraints at smaller (and also unique for each galaxy) radii. The largest
central DM density constraint is for Sculptor: $\rho_0\gtrsim
0.09$~$M_\odot$~pc$^{-3}$ (at two-sigma level). I show that the DM density
logarithmic slope is totally unconstrained by the Jeans analysis at all the
radii probed by the data (and not just at the center, as was demonstrated
before). Stellar velocity anisotropy has only very weak constraints. In
particular, pure central tangential anisotropy is ruled out at better than two
sigma level for three dwarfs, and the data are consistent with the global
stellar velocity isotropy for all the five galaxies.",1504.08273v1
2015-06-11,Primordial Gravitational Waves Measurements and Anisotropies of CMB Polarization Rotation,"Searching for the signal of primordial gravitational waves in the B-modes
(BB) power spectrum is one of the key scientific aims of the cosmic microwave
background (CMB) polarization experiments. However, this could be easily
contaminated by several foreground issues, such as the thermal dust emission.
In this paper we study another mechanism, the cosmic birefringence, which can
be introduced by a CPT-violating interaction between CMB photons and an
external scalar field. Such kind of interaction could give rise to the rotation
of the linear polarization state of CMB photons, and consequently induce the
CMB BB power spectrum, which could mimic the signal of primordial gravitational
waves at large scales. With the recent polarization data of BICEP2 and the
joint analysis data of BICEP2/Keck Array and Planck, we perform a global
fitting analysis on constraining the tensor-to-scalar ratio $r$ by considering
the polarization rotation angle which can be separated into a background
isotropic part and a small anisotropic part. Since the data of BICEP2 and Keck
Array experiments have already been corrected by using the ""self-calibration""
method, here we mainly focus on the effects from the anisotropies of CMB
polarization rotation angle. We find that including the anisotropies in the
analysis could slightly weaken the constraints on $r$, when using current CMB
polarization measurements. We also simulate the mock CMB data with the
BICEP3-like sensitivity. Very interestingly, we find that if the effects of the
anisotropic polarization rotation angle can not be taken into account properly
in the analysis, the constraints on $r$ will be dramatically biased. This
implies that we need to break the degeneracy between the anisotropies of the
CMB polarization rotation angle and the CMB primordial tensor perturbations, in
order to measure the signal of primordial gravitational waves accurately.",1506.03526v1
2015-06-24,A soft ellipsoid potential for biaxial molecules : Modeling and computer simulation,"A soft ellipsoid contact potential model for a pair of biaxial ellipsoidal
molecules is proposed which considers the configuration dependent energy
anisotropy explicitly along with their geometrical aspects. We performed
Molecular Dynamics simulation study to generate both biaxial smectic and
nematic phases using this new potential.",1506.07319v1
2015-07-06,Novel method to obtain the anisotropic parameter of microcells,"In this paper we present a technique to measure the anisotropy parameter a
suspension of microscopic particles. To estimate this parameter we use an
integrating sphere as light collector, as well as a powder sample spherical
particles of TiO$ _2 $ with an average diameter $ a = 0.25 \ \mu $m. The
results for the sample of TiO$ _2$ are consistent with Mie calculations.",1507.01528v1
2015-08-26,Current and field driven domain wall motion under influence of the Dzyaloshinsky-Moriya interaction,"A complete analytical description of the dynamics of current and field driven
transverse domain walls under the influence of the Dzyaloshinsky-Moriya
interaction using the $\phi - q$ model will be given. Five different scenarios
will be observed where the Dzyaloshinsky-Moriya vector is either parallel or
perpendicular to the easy axis anisotropy of the system and a direct reversal
respectively precessional motion will be assumed.",1508.06372v1
2015-09-09,On a sidereal time variation of the Lorentz force,"We consider a search for a sidereal time variation of the beam trajectory in
the cyclotron motion in a static magnetic field. The combination of two beams
moving in opposite directions could allow a test of the radius stability with
sensitivity approaching $10^{-10}$. Such a level of variation of the Lorentz
force, if it exists, would require a speed of light anisotropy on the level of
$10^{-18}$.",1509.02754v1
2015-10-03,Measurement of D-meson production in Pb-Pb collisions at the LHC with ALICE,"The measurement of D-meson production in heavy-ion collisions at LHC energy
provides insights into the mechanisms of interaction of charm quarks in the hot
and dense medium formed in these collisions. ALICE results on the D-meson
nuclear modification factor and azimuthal anisotropy in Pb-Pb collisions at
$\sqrt{s_{\rm NN}}=2.76$ TeV are presented.",1510.00825v1
2015-10-21,Photon thermal Hall effect,"A near-field thermal Hall effect (i.e.Righi-Leduc effect) in networks of
magneto-optical particles placed in a constant magnetic field is predicted.
This many-body effect is related to a symmetry breaking in the system induced
by the magnetic field which gives rise to preferential channels for the
heat-transport by near-field interaction thanks to the particles anisotropy
tuning.",1510.06103v2
2015-11-05,Anisotropic Inflation and Cosmological Observations,"Recent observations opened up a new window on the inflationary model
building. As it was firstly reported by the WMAP data, there may be some
indications of statistical anisotropy on the CMB map, although the statistical
significance of these findings are under debate. Motivated by these
observations, people begun considering new inflationary models which may lead
to statistical anisotropy. The simplest possible way to construct anisotropic
inflation is to introduce vector fields. During the course of this thesis, we
study models of anisotropic inflation and their observational implications such
as power spectrum, bispectrum etc. Firstly we build a new model, which contains
the gauge field which breaks the conformal invariance while preserving the
gauge invariance. We show that in these kind of models, there can be an
attractor phase in the evolution of the system when the back-reaction of the
gauge field becomes important in the evolution of the inflaton field. We then
study the cosmological perturbation theory in these kind of models. More
specifically, we calculate the anisotropic corrections due to the presence of
the vector field. We then generalize the separate universe formalism to our
anisotropic set up and use it in some specific examples of anisotropic
inflation. Finally, we connect the primordial anisotropies to the specific
examples and to CMB observations. We calculate the TT, TE, TB, EB and BB
correlation in the model of charged scalar field model and look for the unique
signatures that the anisotropic inflation can have on the CMB map. Any future
detection of these statistical anisotropies would rule out the isotropic FRW
models.",1511.01683v1
2015-12-23,Differential cosmic expansion and the Hubble flow anisotropy,"The Universe on scales $10-100~h^{-1}$ Mpc is dominated by a cosmic web of
voids, filaments, sheets and knots of galaxy clusters. These structures
participate differently in the global expansion of the Universe: from
non-expanding clusters to the above average expansion rate of voids. In this
paper we characterize Hubble expansion anisotropies in the COMPOSITE sample of
4534 galaxies and clusters. We concentrate on the dipole and quadrupole in the
rest frame of the Local Group. These both have statistically significant
amplitudes. These anisotropies, and their redshift dependence, cannot be
explained solely by a boost of the Local Group in the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) model which expands isotropically
in the rest frame of the cosmic microwave background (CMB) radiation. We
simulate the local expansion of the Universe with inhomogeneous Szekeres
models, which match the standard FLRW model on $> 100~h^{-1}$ Mpc scales but
exhibit nonkinematic relativistic differential expansion on small scales. We
restrict models to be consistent with observed CMB temperature anisotropies,
while simultaneously fitting the redshift variation of the Hubble expansion
dipole. We include features to account for both the Local Void and the ""Great
Attractor"". While this naturally accounts for the Hubble expansion and CMB
dipoles, the simulated quadrupoles are smaller than observed. Further
refinement to incorporate additional structures may improve this. This would
enable a test of the hypothesis that some large angle CMB anomalies result from
failing to treat the relativistic differential expansion of the background
geometry, a natural feature of solutions to Einstein's equations not included
in the current standard model of cosmology.",1512.07364v3
2015-12-26,"Pressure-anisotropy-driven microturbulence and magnetic-field evolution in shearing, collisionless plasma","The nonlinear state of a high-beta collisionless plasma is investigated when
an imposed linear shear amplifies or diminishes a uniform magnetic field,
driving pressure anisotropies and hence firehose/mirror instabilities. The
evolution of the resulting microscale turbulence is considered when the shear
is switched off or reversed after one shear time (mimicking local behaviour of
a macroscopic flow), so a new macroscale configuration is superimposed on the
microscale state left behind by the previous one. There is a threshold value of
plasma beta: when $\beta\ll\Omega/S$ (ion cyclotron frequency/shear rate), the
emergence of firehose/mirror fluctuations driven unstable by shear and their
disappearance when the shear is removed/reversed are quasi-instantaneous
compared to the shear time, viz., the decay time of these fluctuations is
$\sim\beta/\Omega \ll 1/S$ (this result follows from the free decay of the
fluctuations being constrained by the same marginal-stability thresholds as
their growth). In contrast, when $\beta\gtrsim\Omega/S$ (""ultra-high"" beta),
the old microscale state can only be removed on the shear timescale. In this
regime, driven firehose fluctuations grow secularly to order-unity amplitudes,
compensating for the decay of the mean field and so pinning pressure anisotropy
at marginal stability with no appreciable scattering of particles---which is
unlike what happens at moderate $\beta$. When the shear reverses, the shearing
away of this firehose turbulence compensates for the increase in the mean field
and thus prevents growth of the pressure anisotropy, stopping the system from
going mirror-unstable. Therefore, at ultra-high beta, the system stays close to
the firehose threshold, the mirror instability is largely suppressed, while the
mean magnetic energy barely changes at all. Implications for plasma dynamo and
thus the origin of cosmic magnetism are discussed.",1512.08131v1
2016-01-19,Dilepton production rate in a hot and magnetized quark-gluon plasma,"The differential multiplicity of dileptons in a hot and magnetized
quark-gluon plasma, $\Delta_{B}\equiv dN_{B}/d^{4}xd^{4}q$, is derived from
first principles. The constant magnetic field $B$ is assumed to be aligned in a
fixed spatial direction. It is shown that the anisotropy induced by the $B$
field is mainly reflected in the general structure of photon spectral density
function. This is related to the imaginary part of the vacuum polarization
tensor, $\mbox{Im}[\Pi^{\mu\nu}]$, which is derived in a first order
perturbative approximation. As expected, the final analytical expression for
$\Delta_{B}$ includes a trace over the product of a photonic part,
$\mbox{Im}[\Pi^{\mu\nu}]$, and a leptonic part, ${\cal{L}}_{\mu\nu}$. It is
shown that $\Delta_{B}$ consists of two parts, $\Delta_{B}^{\|}$ and
$\Delta_{B}^{\perp}$, arising from the components $(\mu,\nu)=(\|,\|)$ and
$(\mu,\nu)=(\perp,\perp)$ of $\mbox{Im}[\Pi^{\mu\nu}]$ and
${\cal{L}}_{\mu\nu}$. Here, the transverse and longitudinal directions are
defined with respect to the direction of the $B$ field. Combining
$\Delta_{B}^{\|}$ and $\Delta_{B}^{\perp}$, a novel anisotropy factor $\nu_{B}$
is introduced. Using the final analytical expression of $\Delta_{B}$, the
possible interplay between the temperature $T$ and the magnetic field strength
$eB$ on the ratio $\Delta_{B}/\Delta_{0}$ and $\nu_{B}$ is numerically studied.
Here, $\Delta_{0}$ is the Born approximated dilepton multiplicity in the
absence of external magnetic fields. It is, in particular, shown that for each
fixed $T$ and $B$, in the vicinity of certain threshold energies,
$\Delta_{B}\gg \Delta_{0}$ and $\Delta_{B}^{\perp}\gg \Delta_{B}^{\|}$. The
latter anisotropy may be interpreted as one of the microscopic sources of the
macroscopic anisotropies, reflecting themselves, e.g., in the elliptic
asymmetry factor $v_{2}$ of dileptons.",1601.04887v3
2016-02-01,Numerical Modelling of Disordered Magnetic Systems: La2-xSrxCoO4,"Magnetic properties of La2-xSrxCoO4 have been modelled using McPhase for
different doping levels x. Footprints of different interactions, such as local
single ion anisotropy and variations in the exchange interactions have been
identified in the profile of the diffuse elastic neutron scattering cross
section. The role of quantum fluctuations in the formation of the hourglass
spectrum is discussed.",1602.00507v3
2016-02-09,Excitonic terahertz absorption in semiconductors with effective-mass anisotropies,"A microscopic approach is developed to compute the excitonic properties and
the corresponding terahertz response for semiconductors characterized by
anisotropic effective masses. The approach is illustrated for the example of
germanium where it is shown that the anisotropic electron mass in the L-valley
leads to two distinct terahertz absorption resonances separated by 0.8 meV.",1602.02972v1
2016-02-08,PIC Simulations of the Effect of Velocity Space Instabilities on Electron Viscosity and Thermal Conduction,"In low-collisionality plasmas, velocity-space instabilities are a key
mechanism providing an effective collisionality for the plasma. We use
particle-in-cell (PIC) simulations to study the interplay between electron and
ion-scale velocity-space instabilities and their effect on electron pressure
anisotropy, viscous heating, and thermal conduction. The adiabatic invariance
of the magnetic moment in low-collisionality plasmas leads to pressure
anisotropy, $p_{\perp,j} > p_{||,j}$, if the magnetic field $\vec{B}$ is
amplified ($p_{\perp,j}$ and $p_{||,j}$ denote the pressure of species $j$
[electron, ion] perpendicular and parallel to $\vec{B}$). If the resulting
anisotropy is large enough, it can in turn trigger small-scale plasma
instabilities. Our PIC simulations explore the nonlinear regime of the mirror,
ion-cyclotron, and electron whistler instabilities, through continuous
amplification of the magnetic field $|\vec{B}|$ by an imposed shear in the
plasma. In the regime $1 \lesssim \beta_j \lesssim 20$ ($\beta_j \equiv 8\pi
p_j/|\vec{B}|^2$), the saturated electron pressure anisotropy, $\Delta
p_e/p_{||,e}$, is determined mainly by the (electron-lengthscale) whistler
marginal stability condition, with a modest factor of $\sim 1.5-2$ decrease due
to the trapping of electrons by the mirrors. We explicitly calculate the mean
free path of the electrons and ions along the mean magnetic field and provide a
simple physical prescription for the mean free path and thermal conductivity in
low-collisionality $\beta_j \gtrsim 1$ plasmas. Our results imply that
velocity-space instabilities likely decrease the thermal conductivity of plasma
in the outer parts of massive, hot, galaxy clusters. We also discuss the
implications of our results for electron heating and thermal conduction in
low-collisionality accretion flows onto black holes, including Sgr A* in the
Galactic Center.",1602.03126v2
2016-03-11,Modeling SNR Cassiopeia A from the Supernova Explosion to its Current Age: The role of post-explosion anisotropies of ejecta,"The remnants of core-collapse supernovae (SNe) have complex morphologies that
may reflect asymmetries and structures developed during the progenitor SN
explosion. Here we investigate how the morphology of the SNR Cassiopeia A (Cas
A) reflects the characteristics of the progenitor SN with the aim to derive the
energies and masses of the post-explosion anisotropies responsible for the
observed spatial distribution of Fe and Si/S. We model the evolution of Cas A
from the immediate aftermath of the progenitor SN to the three-dimensional
interaction of the remnant with the surrounding medium. The post-explosion
structure of the ejecta is described by small-scale clumping of material and
larger-scale anisotropies. The hydrodynamic multi-species simulations consider
an appropriate post-explosion isotopic composition of the ejecta. The observed
average expansion rate and shock velocities can be well reproduced by models
with ejecta mass $M_{\rm ej}\approx 4M_{\odot}$ and explosion energy $E_{\rm
SN}\approx 2.3\times 10^{51}$ erg. The post-explosion anisotropies (pistons)
reproduce the observed distributions of Fe and Si/S if they had a total mass of
$\approx 0.25\,M_{\odot}$ and a total kinetic energy of $\approx 1.5\times
10^{50}$ erg. The pistons produce a spatial inversion of ejecta layers at the
epoch of Cas A, leading to the Si/S-rich ejecta physically interior to the
Fe-rich ejecta. The pistons are also responsible for the development of bright
rings of Si/S-rich material which form at the intersection between the reverse
shock and the material accumulated around the pistons during their propagation.
Our result supports the idea that the bulk of asymmetries observed in Cas A are
intrinsic to the explosion.",1603.03690v1
2016-04-14,Sobolev and Lipschitz regularity for local minimizers of widely degenerate anisotropic functionals,"We prove higher differentiability of bounded local minimizers to some widely
degenerate functionals, verifying superquadratic anisotropic growth conditions.
In the two dimensional case, we prove that local minimizers to a model
functional are locally Lipschitz continuous functions, without any restriction
on the anisotropy.",1604.04189v1
2015-09-24,Spectral Anisotropy of Elsässer Variables in Two Dimensional Wave-vector Space as Observed in the Fast Solar Wind Turbulence,"Intensive studies have been conducted to understand the anisotropy of solar
wind turbulence. However, the anisotropy of Els\""asser variables
($\textbf{Z}^\pm$) in 2D wave-vector space has yet to be investigated. Here we
first verify the transformation based on the projection-slice theorem between
the power spectral density PSD$_{2D}(k_\parallel,k_\perp )$ and the spatial
correlation function CF$_{2D} (r_\parallel,r_\perp )$. Based on the application
of the transformation to the magnetic field and the particle measurements from
the WIND spacecraft, we investigate the spectral anisotropy of Els\""asser
variables ($\textbf{Z}^\pm$), and the distribution of residual energy E$_{R}$,
Alfv\'en ratio R$_{A}$ and Els\""asser ratio R$_{E}$ in the
$(k_\parallel,k_\perp)$ space. The spectra PSD$_{2D}(k_\parallel,k_\perp )$ of
$\textbf{B}$, $\textbf{V}$, and $\textbf{Z}_{major}$ (the larger of
$\textbf{Z}^\pm$) show a similar pattern that PSD$_{2D}(k_\parallel,k_\perp )$
is mainly distributed along a ridge inclined toward the $k_\perp$ axis. This is
probably the signature of the oblique Alfv\'enic fluctuations propagating
outwardly. Unlike those of $\textbf{B}$, $\textbf{V}$, and
$\textbf{Z}_{major}$, the spectrum PSD$_{2D}(k_\parallel,k_\perp )$ of
$\textbf{Z}_{minor}$ is distributed mainly along the $k_\perp$ axis. Close to
the $k_\perp$ axis, $\left| {E}_{R}\right|$ becomes larger while R$_{A}$
becomes smaller, suggesting that the dominance of magnetic energy over kinetic
energy becomes more significant at small $k_\parallel$. R$_{E}$ is larger at
small $k_\parallel$, implying that PSD$_{2D}(k_\parallel,k_\perp )$ of
$\textbf{Z}_{minor}$ is more concentrated along the $k_\perp$ direction as
compared to that of $\textbf{Z}_{major}$. The residual energy condensate at
small $k_\parallel$ is consistent with simulation results in which E$_{R}$ is
spontaneously generated by Alfv\'en wave interaction.",1604.07760v1
2016-04-28,"Highly-anisotropic exchange interactions of $j_{\rm eff}=1/2$ iridium moments on the fcc lattice in La$_2B$IrO$_6$ ($B$ $=$ Mg, Zn)","We have performed inelastic neutron scattering (INS) experiments to
investigate the magnetic excitations in the weakly distorted
face-centered-cubic (fcc) iridate double perovskites La$_2$ZnIrO$_6$ and
La$_2$MgIrO$_6$, which are characterized by A-type antiferromagnetic ground
states. The powder inelastic neutron scattering data on these geometrically
frustrated $j_{\rm eff}=1/2$ Mott insulators provide clear evidence for gapped
spin wave excitations with very weak dispersion. The INS results and
thermodynamic data on these materials can be reproduced by conventional
Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable
second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange
interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only
arise from the weak crystal distortions away from the ideal fcc limit. This may
suggest that even weak distortions in $j_{\rm eff}=1/2$ Mott insulators might
lead to strong exchange anisotropies. More tantalizingly, however, we find an
alternative viable explanation of the INS results in terms of spin models with
a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the
highly-directional Kitaev interaction is a type of exchange anisotropy which is
symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon
gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev
couplings generated by the symmetry-lowering due to lattice distortions, can
pin the order and enhance the magnon gap. Our findings highlight how even
conventional magnetic orders in heavy transition metal oxides may be driven by
highly-directional exchange interactions rooted in strong spin-orbit coupling.",1604.08431v1
2016-06-12,Relativistic calculations of angular dependent photoemission time delay,"Angular dependence of photoemission time delay for the valence $np_{3/2}$ and
$np_{1/2}$ subshells of Ar, Kr and Xe is studied in the dipole relativistic
random phase approximation. Strong angular anisotropy of the time delay is
reproduced near respective Cooper minima while the spin-orbit splitting affects
the time delay near threshold.",1606.03780v1
2016-07-06,Chirality of topological gap solitons in bosonic dimer chains,"We study gap solitons which appear in the topological gap of 1D bosonic dimer
chains within the mean-field approximation. We find that such solitons have a
non-trivial texture of the sublattice pseudospin. We reveal their chiral nature
by demonstrating the anisotropy of their behavior in presence of a localized
energy potential.",1607.01805v2
2016-07-10,Eutectic colony formation in systems with interfacial energy anisotropy: A phase field study,"Instability of a binary eutectic solidification front to morphological
perturbations due to rejection of a ternary impurity leads to the formation of
eutectic colonies. Whereas, the instability dynamics and the resultant mi-
crostructural features are reasonably well understood for isotropic systems,
several experimental observations point to the existence of colonies in systems
with anisotropic interfaces. In this study, we extend the un- derstanding of
eutectic colonies to anisotropic systems, where only certain orientations of
the solid-liquid or solid-solid interfaces are thermodynamically stable.
Through phase field simulations in 2D and 3D, we have systematically probed the
colony formation dynamics and the resulting microstructures, as functions of
the pulling velocity and the relative orientation of the equilibrium interfaces
with that of the imposed tempera- ture gradient. We find that in 2D, stabler
finger spacings are selected with an increase in the magnitude of anisotropy
introduced, either in the solid-liquid or in the solid-solid interface. The
fingers have a well-defined orientation for the case of anisotropy in the
solid-liquid interface, with no fixed orientations for the lamellae
constituting the colony. For the case where anisotropy exists in the
solid-solid interface, the lamellae tend to orient themselves along the
direction of the imposed temperature gradient, with tilted solid-liquid
interfaces from the horizontal. The 3D simulations reveal existence of eutectic
spirals which might become tilted under certain orientations of the equilibrium
interfaces. Our simulations are able to explain several key features observed
in our experimantal studies of solidification in Ni-Al-Zr alloy.",1607.02722v3
2016-08-25,The angular power spectrum of the diffuse gamma-ray emission as measured by the Fermi Large Area Telescope and constraints on its Dark Matter interpretation,"The isotropic gamma-ray background arises from the contribution of unresolved
sources, including members of confirmed source classes and proposed gamma-ray
emitters such as the radiation induced by dark matter annihilation and decay.
Clues about the properties of the contributing sources are imprinted in the
anisotropy characteristics of the gamma-ray background. We use 81 months of
Pass 7 Reprocessed data from the Fermi Large Area Telescope to perform a
measurement of the anisotropy angular power spectrum of the gamma-ray
background. We analyze energies between 0.5 and 500 GeV, extending the range
considered in the previous measurement based on 22 months of data. We also
compute, for the first time, the cross-correlation angular power spectrum
between different energy bins. We find that the derived angular spectra are
compatible with being Poissonian, i.e. constant in multipole. Moreover, the
energy dependence of the anisotropy suggests that the signal is due to two
populations of sources, contributing, respectively, below and above 2 GeV.
Finally, using data from state-of-the-art numerical simulations to model the
dark matter distribution, we constrain the contribution from dark matter
annihilation and decay in Galactic and extragalactic structures to the measured
anisotropy. These constraints are competitive with those that can be derived
from the average intensity of the isotropic gamma-ray background. Data are
available at https://www-glast.stanford.edu/pub_data/552.",1608.07289v2
2016-08-29,"A discrete chemo-dynamical model of the giant elliptical galaxy NGC 5846: dark matter fraction, internal rotation and velocity anisotropy out to six effective radii","We construct a suite of discrete chemo-dynamical models of the giant
elliptical galaxy NGC 5846. These models are a powerful tool to constrain both
the mass distribution and internal dynamics of multiple tracer populations. We
use Jeans models to simultaneously fit stellar kinematics within the effective
radius $R_{\rm e}$, planetary nebula (PN) radial velocities out to $3\, R_{\rm
e}$, and globular cluster (GC) radial velocities and colours out to $6\,R_{\rm
e}$. The best-fitting model is a cored DM halo which contributes $\sim 10\%$ of
the total mass within $1\,R_{\rm e}$, and $67\% \pm 10\%$ within $6\,R_{\rm
e}$, although a cusped DM halo is also acceptable. The red GCs exhibit mild
rotation with $v_{\rm max}/\sigma_0 \sim 0.3$ in the region $R > \,R_{\rm e}$,
aligned with but counter-rotating to the stars in the inner parts, while the
blue GCs and PNe kinematics are consistent with no rotation. The red GCs are
tangentially anisotropic, the blue GCs are mildly radially anisotropic, and the
PNe vary from radially to tangentially anisotropic from the inner to the outer
region. This is confirmed by general made-to-measure models. The tangential
anisotropy of the red GCs in the inner regions could stem from the preferential
destruction of red GCs on more radial orbits, while their outer tangential
anisotropy -- similar to the PNe in this region -- has no good explanation. The
mild radial anisotropy of the blue GCs is consistent with an accretion
scenario.",1608.08238v1
2016-09-06,Numerical study of optimal partitioning problems in relation to an anisotropic perimeter,"We present a ${\Gamma}$-convergence approximation for the total anisotropic
length of a partition. This theoretical result gives rise to a numerical method
which allows the study of minimal partitions with respect to different
anisotropies. We also give a numerical framework for the study of isoperimetric
problems with density.",1609.01467v1
2016-11-04,Second-harmonic generation as probe for structural and electronic properties of buried GaP/Si(001) interfaces,"Optical second-harmonic generation is demonstrated to be a sensitive probe of
the buried interface between the lattice matched semiconductors gallium
phosphide and silicon with (001) orientation. Rotational anisotropy
measurements of SHG from GaP/Si show a strong isotropic component of the
response not present for pure Si(001) or GaP(001). The strength of the
overlaying anisotropic response directly correlates with the quality of the
interface as determined by atomically resolved scanning transmission electron
microscopy.Optical second-harmonic generation is demonstrated to be a sensitive
probe of the buried interface between the lattice matched semiconductors
gallium phosphide and silicon with (001) orientation. Rotational anisotropy
measurements of SHG from GaP/Si show a strong isotropic component of the
response not present for pure Si(001) or GaP(001). The strength of the
overlaying anisotropic response directly correlates with the quality of the
interface as determined by atomically resolved scanning transmission electron
microscopy. Systematic comparison of samples fabricated with different growth
modes in metal organic vapor phase epitaxy reveals that the anisotropy for
different polarization combinations can be used as a selective fingerprint for
the occurrence of anti-phase domains and twins. This all-optical technique can
be applied as an {\it in-situ} and non-invasive monitor even during growth.
Systematic comparison of samples fabricated with different growth modes in
metal organic vapor phase epitaxy reveals that the anisotropy for different
polarization combinations can be used as a selective fingerprint for the
occurrence of anti-phase domains and twins. This all-optical technique can be
applied as an {\it in-situ} and non-invasive monitor even during growth.",1611.01307v2
2016-11-10,Anisotropic inflation with a non-minimally coupled electromagnetic field to gravity,"We consider the non-minimal model of gravity in $Y(R) F^2$-form. We
investigate a particular case of the model, for which the higher order
derivatives are eliminated but the scalar curvature $R$ is kept to be dynamical
via the constraint $Y_RF_{mn}F^{mn} =-\frac{2}{\kappa^2}$. The effective fluid
obtained can be represented by interacting electromagnetic field and vacuum
depending on $Y(R)$, namely, the energy density of the vacuum tracks $R$ while
energy density of the conventional electromagnetic field is dynamically scaled
with the factor $\frac{Y(R)}{2}$. We give exact solutions for anisotropic
inflation by assuming the volume scale factor of the Universe exhibits a
power-law expansion. The directional scale factors do not necessarily exhibit
power-law expansion, which would give rise to a constant expansion anisotropy,
but expand non-trivially and give rise to a non-monotonically evolving
expansion anisotropy that eventually converges to a non-zero constant. Relying
on this fact, we discuss the anisotropic e-fold during the inflation by
considering observed scale invariance in CMB and demanding the Universe to
undergo the same amount of e-folds in all directions. We calculate the residual
expansion anisotropy at the end of inflation, though as a result of
non-monotonic behaviour of expansion anisotropy all the axes of the Universe
undergo the same of amount of e-folds by the end of inflation. We also discuss
the generation of the modified electromagnetic field during the first few
e-folds of the inflation and its persistence against to the vacuum till end of
inflation.",1611.03393v4
2016-11-11,Statistics of Reconnection-Driven Turbulence,"Magnetic reconnection is a process that changes magnetic field topology in
highly conducting fluids. Within the standard Sweet-Parker model, this process
would be too slow to explain observations (e.g. solar flares). In reality, the
process must be ubiquitous as astrophysical fluids are magnetized and motions
of fluid elements necessarily entail crossing of magnetic frozen-in field lines
and magnetic reconnection. In the presence of turbulence, the reconnection is
independent of microscopic plasma properties, and may be much faster than
previously thought, as proposed in Lazarian & Vishniac (1999) and tested in
Kowal et al. (2009, 2012). However, the considered turbulence in the
Lazarian-Vishniac model was imposed externally. In this work we consider
reconnection-driven magnetized turbulence in realistic three-dimensional
geometry initiated by stochastic noise. We demonstrate through numerical
simulations that the stochastic reconnection is able to self-generate
turbulence through interactions between its outflows. We analyze the
statistical properties of velocity fluctuations using power spectra and
anisotropy scaling, which demonstrates that the reconnection produces
Kolmogorov-like turbulence, compatible with Goldreich-Sridhar (1995) model.
Anisotropy statistics are, however, strongly affected by the dynamics of
reconnection outflows. Once the broad turbulent region is formed, the typical
anisotropy scaling $l_\parallel \propto l_\perp^{2/3}$ is formed, especially
for high resolution models, were the broader range of scales is available. The
decay of reconnection outflows to turbulent-like fluctuations, characterized by
different anisotropy scalings, strongly depends on $\beta$ plasma. Moreover,
the estimated reconnection rates are weakly dependent on the resolution,
suggesting that no external processes are required to make reconnection fast.",1611.03914v2
2016-11-25,Alignment of galaxies relative to their local environment in SDSS-DR8,"We study the alignment of galaxies relative to their local environment in
SDSS-DR8 and, using these data, we discuss evolution scenarios for different
types of galaxies. We defined a vector field of the direction of anisotropy of
the local environment of galaxies. We summed the unit direction vectors of all
close neighbours of a given galaxy in a particular way to estimate this field.
We found the alignment angles between the spin axes of disc galaxies, or the
minor axes of elliptical galaxies, and the direction of anisotropy. The
distributions of cosines of these angles are compared to the random
distributions to analyse the alignment of galaxies. Sab galaxies show
perpendicular alignment relative to the direction of anisotropy in a sparse
environment, for single galaxies and galaxies of low luminosity. Most of the
parallel alignment of Scd galaxies comes from dense regions, from 2...3 member
groups and from galaxies with low luminosity. The perpendicular alignment of S0
galaxies does not depend strongly on environmental density nor luminosity; it
is detected for single and 2...3 member group galaxies, and for main galaxies
of 4...10 member groups. The perpendicular alignment of elliptical galaxies is
clearly detected for single galaxies and for members of < 11 member groups; the
alignment increases with environmental density and luminosity. We confirm the
existence of fossil tidally induced alignment of Sab galaxies at low z. The
alignment of Scd galaxies can be explained via the infall of matter to
filaments. S0 galaxies may have encountered relatively massive mergers along
the direction of anisotropy. Major mergers along this direction can explain the
alignment of elliptical galaxies. Less massive, but repeated mergers are
possibly responsible for the formation of elliptical galaxies in sparser areas
and for less luminous elliptical galaxies.",1611.08378v1
2016-12-23,Cosmic-Ray Anisotropies: A Review,"Important observational results have been recently reported on the angular
distributions of cosmic rays (CRs) at all energies, calling into question the
perception of CRs a decade ago. These results together with their in-progress
interpretations are summarized in this short overview paper, following the
contribution presented at the XXV European Cosmic Ray Symposium.",1612.08002v1
2017-01-09,Orthogonal involutions and totally singular quadratic forms in characteristic two,"We associate to every central simple algebra with involution of orthogonal
type in characteristic two a totally singular quadratic form which reflects
certain anisotropy properties of the involution. It is shown that this
quadratic form can be used to classify totally decomposable algebras with
orthogonal involution. Also, using this form, a criterion is obtained for an
orthogonal involution on a split algebra to be conjugated to the transpose
involution.",1701.02169v1
2017-01-13,Anisotropy in finite continuum percolation: Threshold estimation by Minkowski functionals,"We examine the interplay between anisotropy and percolation, i.e., the
spontaneous formation of a system spanning cluster in an anisotropic model. We
simulate an extension of a benchmark model of continuum percolation, the
Boolean model, which is formed by overlapping grains. Here we introduce an
orientation bias of the grains that controls the degree of anisotropy of the
generated patterns. We analyze in the Euclidean plane the percolation
thresholds above which percolating clusters in $x$- and in $y$-direction
emerge. Only in finite systems, distinct differences between effective
percolation thresholds for different directions appear. If extrapolated to
infinite system sizes, these differences vanish independent of the details of
the model. In the infinite system, the uniqueness of the percolating cluster
guarantees a unique percolation threshold. While percolation is isotropic even
for anisotropic processes, the value of the percolation threshold depends on
the model parameters, which we explore by simulating a score of models with
varying degree of anisotropy. To which precision can we predict the percolation
threshold without simulations? We discuss analytic formulas for approximations
(based on the excluded area or the Euler characteristic) and compare them to
our simulation results. Empirical parameters from similar systems allow for
accurate predictions of the percolation thresholds (with deviations of $<5\%$
in our examples), but even without any empirical parameters, the explicit
approximations from integral geometry provide, at least for the systems studied
here, lower bounds that capture well the qualitative dependence of the
percolation threshold on the system parameters (with deviations of
$5\%$--$30\%$). As an outlook, we suggest further candidates for explicit and
geometric approximations based on second moments of the so-called Minkowski
functionals.",1701.03729v1
2017-01-19,Influence of uniaxial single-ion anisotropy on the magnetic and thermal properties of Heisenberg antiferromagnets within unified molecular field theory,"The influence of uniaxial single-ion anisotropy -DSz^2 on the magnetic and
thermal properties of Heisenberg antiferromagnets (AFMs) is investigated. The
uniaxial anisotropy is treated exactly and the Heisenberg interactions are
treated within unified molecular field theory (MFT) [Phys. Rev. B 91, 064427
(1915)], where thermodynamic variables are expressed in terms of directly
measurable parameters. The properties of collinear AFMs with ordering along the
z axis (D > 0) in applied fields Hz = 0 are calculated versus D and temperature
T. The high-field average magnetization per spin muz(Hz,D,T) is found, and the
critical field Hc(D,T) is derived at which the second-order AFM to PM phase
transition occurs. The magnetic properties of the spin-flop (SF) phase are
calculated, including the zero-field properties TN(D) and mu(D,T). The
high-field muz(Hz,D,T) is determined, together with the associated spin-flop
field HSF(D,T) at which a second-order SF to PM phase transition occurs. The
free energies of the AFM, SF and PM phases are derived from which Hz-T phase
diagrams are constructed. For a certain combination of parameters we find a
topologically distinct phase diagram where a spin-flop bubble occurs at finite
Hz and T. Also calculated are properties arising from a perpendicular magnetic
field. In addition to the above results for D > 0, some properties with D < 0
are determined. In order to compare the properties of the above spin systems
with those of noninteracting systems with DSz^2 uniaxial anisotropy with either
sign of D, an Appendix is included in which results for the thermal and
magnetic properties of such noninteracting spin systems are provided.",1701.05416v1
2017-01-26,Seed Layer Impact on Structural and Magnetic Properties of [Co/Ni] Multilayers with Perpendicular Magnetic Anisotropy,"[Co/Ni] multilayers with perpendicular magnetic anisotropy (PMA) have been
researched and applied in various spintronic applications. Typically the seed
layer material is studied to provide the desired face-centered cubic
(\textit{fcc}) texture to the [Co/Ni] to obtain PMA. The integration of [Co/Ni]
in back-end-of-line (BEOL) processes also requires the PMA to survive
post-annealing. In this paper, the impact of NiCr, Pt, Ru, and Ta seed layers
on the structural and magnetic properties of [Co(0.3 nm)/Ni(0.6 nm)]
multilayers is investigated before and after annealing. The multilayers were
deposited \textit{in-situ} on different seeds via physical vapor deposition at
room temperature. The as-deposited [Co/Ni] films show the required
\textit{fcc}(111) texture on all seeds, but PMA is only observed on Pt and Ru.
In-plane magnetic anisotropy (IMA) is obtained on NiCr and Ta seeds, which is
attributed to strain-induced PMA loss. PMA is maintained on all seeds after
post-annealing up to 400$^{\circ}$C. The largest effective perpendicular
anisotropy energy ($K_U^{\mathrm{eff}}\approx 2\times10^5$J/m$^3$) after
annealing is achieved on NiCr seed. The evolution of PMA upon annealing cannot
be explained by further crystallization during annealing or strain-induced PMA,
nor can the observed magnetization loss and the increased damping after
annealing. Here we identify the diffusion of the non-magnetic materials from
the seed into [Co/Ni] as the major driver of the changes in the magnetic
properties. By selecting the seed and post-annealing temperature, the [Co/Ni]
can be tuned in a broad range for both PMA and damping.",1701.07713v1
2017-02-25,Viscosity for Anisotropic Reissner Nordström Blackbranes,"We investigate the behavior of shear viscosity in the presence of small
anisotropy and a finite chemical potential. First, we construct an anisotropic
Reissner Nordstr{\""o}m blackbrane in 5 dimensions in a simple Einstein-Maxwell
theory with a small linear dilaton. This solution is characterized by three
mass scales : anisotropy $\rho$, temperature T and chemical potential $\mu$. We
find this solution upto second order in the dilaton anisotropy parameter
$\rho$. This blackbrane solution corresponds to an anisotropic phase where the
anisotropy is small compared to the temperature and chemical potential. We find
that in this anisotropic phase, some components of the anisotropic shear
viscosity tensor, which are spin one with respect to the residual symmetry
after breaking rotational invariance, violates the KSS bound (${\eta \over
s}\ge {1 \over 4 \pi} $) proposed by Kovtun, Son and Starinets. We identify the
regions of the parameter space where these violations are significant. We carry
out a similar analysis in 4 dimensions and find similar violation of the KSS
bound for the spin one components to demonstrate the generality of the result.
Our results are particularly relevant in the context of strongly coupled
systems found in nature. We also provide an intuitive understanding of the
results using dimensional reduction and a Boltzmann calculation in a weakly
coupled version of a similar system. The Boltzmann analysis performed in a
system of weakly interacting particles in a linear potential also shows that
components of the viscosity tensor may be reduced. It is intriguing that the
Boltzmann analysis also predicts the corrections to be negative and that too in
a manner similar to the anisotropic strongly coupled theories with smooth
gravity duals.",1702.07874v4
2017-04-05,"Structure, site-specific magnetism and magneto-transport properties of epitaxial D0$_{22}$ Mn$_2$Fe$_x$Ga thin films","Ferrimagnetic Mn$_2$Fe$_x$Ga $(0.26 \leq x \leq 1.12)$ thin films have been
characterised by X-ray diffraction, SQUID magnetometry, X-ray absorption
spectroscopy, X-ray magnetic circular dichroism and M\""{o}ssbauer spectroscopy
with the aim of determining the structure and site-specific magnetism of this
tetragonal, D0$_{22}$-structure Heusler compound. High-quality epitaxial films
with low RMS surface roughness ($\sim 0.6$ nm) are grown by magnetron
co-sputtering. The tetragonal distortion induces strong perpendicular magnetic
anisotropy along the $c$-axis with a typical coercive field $\mu_0 H\sim 0.8$ T
and an anisotropy field ranging from $6$ to $8$ T. Upon increasing the Fe
content $x$, substantial uniaxial anisotropy, $K_\mathrm{u} \geq 1.0$ MJ/m$^3$
can be maintained over the full $x$ range, while the magnetisation of the
compound is reduced from $400$ to $280$ kA/m. The total magnetisation is almost
entirely given by the sum of the spin moments originating from the
ferrimagnetic Mn and Fe sublattices, with the latter being coupled
ferromagnetically to one of the former. The orbital magnetic moments are
practically quenched, and have negligible contributions to the magnetisation.
The films with $x=0.73$ exhibit a high anomalous Hall angle of $2.5$ % and a
high Fermi-level spin polarisation, above $51$ %, as measured by point contact
Andreev reflection. The Fe-substituted Mn$_2$Ga films are highly tunable with a
unique combination of high anisotropy, low magnetisation, appreciable spin
polarisation and low surface roughness, making them very strong candidates for
thermally-stable spin-transfer-torque switching nanomagnets with lateral
dimensions down to $10$ nm.",1704.01326v1
2017-04-19,Anisotropic magnetic interactions and spin dynamics in the spin-chain compound Cu(py)$_2$Br$_2$: An experimental and theoretical study,"We compare theoretical results for electron spin resonance (ESR) properties
of the Heisenberg-Ising Hamiltonian with ESR experiments on the
quasi-one-dimensional magnet Cu(py)$_2$Br$_2$ (CPB). Our measurements were
performed over a wide frequency and temperature range giving insight into spin
dynamics, spin structure, and magnetic anisotropy of this compound. By
analyzing the angular dependence of ESR parameters (resonance shift and
linewidth) at room temperature we show that the two weakly coupled inequivalent
spin chain types inside the compound are well described by Heisenberg-Ising
chains with their magnetic anisotropy axes perpendicular to the chain direction
and almost perpendicular to each other. We further determine the full
$g$-tensor from these data. In addition, the angular dependence of the
linewidth at high temperatures gives us access to the exponent of the algebraic
decay of a dynamical correlation function of the isotropic Heisenberg chain.
From the temperature dependence of static susceptibilities we extract the
strength of the exchange coupling ($J/k_B = 52.0\,\text{K}$) and the anisotropy
parameter ($\delta\approx -0.02$) of the model Hamiltonian. An independent
compatible value of $\delta$ is obtained by comparing the exact prediction for
the resonance shift at low temperatures with high-frequency ESR data recorded
at $4\,\text{K}$. The spin structure in the ordered state implied by the two
(almost) perpendicular anisotropy axes is in accordance with the propagation
vector determined from neutron scattering experiments. In addition to undoped
samples we study the impact of partial substitution of Br by Cl ions on spin
dynamics. From the dependence of the ESR linewidth on doping level we infer an
effective decoupling of the anisotropic component $J\delta$ from the isotropic
exchange $J$ in these systems.",1704.05705v2
2017-06-16,Thermodynamic evidence for nematic phase transition at the onset of pseudogap in YBa$_2$Cu$_3$O$_y$,"A central issue in the quest to understand the superconductivity in cuprates
is the nature and origin of the pseudogap state, which harbours anomalous
electronic states such as Fermi arc, charge density wave (CDW), and $d$-wave
superconductivity. A fundamentally important, but long-standing controversial
problem has been whether the pseudogap state is a distinct thermodynamic phase
characterized by broken symmetries below the onset temperature $T^*$.
Electronic nematicity, a fourfold ($C_4$) rotational symmetry breaking, has
emerged as a key feature inside the pseudogap regime, but the presence or
absence of a nematic phase transition and its relationship to the pseudogap
remain unresolved. Here we report thermodynamic measurements of magnetic torque
in the underdoped regime of orthorhombic YBa$_2$Cu$_3$O$_y$ with a field
rotating in the CuO$_2$ plane, which allow us to quantify magnetic anisotropy
with exceptionally high precision. Upon entering the pseudogap regime, the
in-plane anisotropy of magnetic susceptibility increases after exhibiting a
distinct kink at $T^*$. Our doping dependence analysis reveals that this
anisotropy is preserved below $T^*$ even in the limit where the effect of
orthorhombicity is eliminated. In addition, the excess in-plane anisotropy data
show a remarkable scaling behaviour with respect to $T/T^*$ in a wide doping
range. These results provide thermodynamic evidence that the pseudogap onset is
associated with a second-order nematic phase transition, which is distinct from
the CDW transition that accompanies translational symmetry breaking. This
suggests that nematic fluctuations near the pseudogap phase boundary have a
potential link to the strange metallic behaviour in the normal state, out of
which high-$T_c$ superconductivity emerges.",1706.05214v1
2017-06-19,Surface Waves on the Interface Between Hyperbolic Material and Topological Insulator. 1,"Propagation of the surface waves on the interface between an uniaxial
hyperbolic material and an isotopical topological insulator is studied. The
cases of the anisotropy axes is normal to interface or one is coplanar to
interface are discussed. The dispersion relations are derived and analyzed. The
conditions of the existence of the surface waves are established.",1706.05951v1
2017-07-06,Distortions of the Cosmic Microwave Background through cooling lines during the epoch of Reionization,"By using N-body hydrodynamical cosmological simulations in which the
chemistry of major metals and molecules is consistently solved for, we study
the interaction of metallic fine-structure lines with the CMB. Our analysis
shows that the collisional induced emissions in the OI 145 $\mu$m and CII 158
$\mu$m lines during reionization introduce a distortion of the CMB spectrum at
low frequencies ($\nu < 300$ GHz) with amplitudes up to $\Delta
I_{\nu}/B_{\nu}(T_{\rm CMB})\sim 10^{-8}$-$10^{-7}$, i.e., at the $\sim 0.1$
percent level of FIRAS upper limits. Shorter wavelength fine-structure
transitions (OI 63 $\mu$m, FeII 26 $\mu$m, and SiII 35 $\mu$m) typically sample
the reionization epoch at higher observing frequencies ($\nu > 400$ GHz). This
corresponds to the Wien tail of the CMB spectrum and the distortion level
induced by those lines may be as high as $\Delta I_{\nu}/B_{\nu}(T_{\rm
CMB})\sim 10^{-4}$. The angular anisotropy produced by these lines should be
more relevant at higher frequencies: while practically negligible at $\nu=145
$GHz, signatures from CII 158 $\mu$m and OI 145 $\mu$m should amount to 1%-5%
of the anisotropy power measured at $l \sim 5000$ and $\nu=220 $GHz by the ACT
and SPT collaborations (after assuming $\Delta \nu_{\rm obs}/\nu_{\rm
obs}\simeq 0.005$ for the line observations). Our simulations show that
anisotropy maps from different lines (e.g., OI 145 $\mu$m and CII 158 $\mu$m)
at the same redshift show a very high degree ($>0.8$) of spatial correlation,
allowing for the use of observations at different frequencies to unveil the
same snapshot of the reionization epoch. Finally, our simulations demonstrate
that line-emission anisotropies extracted in narrow frequency/redshift shells
are practically uncorrelated in frequency space, thus enabling standard methods
for removal of foregrounds that vary smoothly in frequency, just as in HI 21 cm
studies.",1707.01910v1
2017-07-25,Reconstruction of the remote dipole and quadrupole fields from the kinetic Sunyaev Zel'dovich and polarized Sunyaev Zel'dovich effects,"The kinetic Sunyaev Zel'dovich (kSZ) and polarized Sunyaev Zel'dovich (pSZ)
effects are temperature and polarization anisotropies induced by the scattering
of CMB photons from structure in the post-reionization Universe. In the case of
the kSZ effect, small angular scale anisotropies in the optical depth are
modulated by the cosmic microwave background (CMB) dipole field, i.e. the CMB
dipole observed at each spacetime point, which is sourced by the primordial
dipole and especially the local peculiar velocity. In the case of the pSZ
effect, similar small-scale anisotropies are modulated by the CMB quadrupole
field, which receives contributions from both scalar and tensor modes.
Statistical anisotropies in the cross correlations of CMB temperature and
polarization with tracers of the inhomogeneous distribution of electrons
provide a means of isolating and reconstructing the dipole and quadrupole
fields. In this paper, we present a set of unbiased minimum variance quadratic
estimators for the reconstruction of the dipole and quadrupole fields, and
forecast the ability of future CMB experiments and large scale structure
surveys to perform this reconstruction. Consistent with previous work, we find
that a high fidelity reconstruction of the dipole and quadrupole fields over a
variety of scales is indeed possible, and demonstrate the sensitivity of the
pSZ effect to primordial tensor modes. Using a principle component analysis, we
estimate how many independent modes could be accessed in such a reconstruction.
We also comment on a few first applications of a detection of the dipole and
quadrupole fields, including a reconstruction of the primordial contribution to
our locally observed CMB dipole, a test of statistical homogeneity on large
scales from the first modes of the quadrupole field, and a reconstruction
technique for the primordial potential on the largest scales.",1707.08129v2
2017-07-29,Radiation Reaction in a Lorentz-Violating Electrodynamics,"We study radiation reaction in a Lorentz violating electrodynamics [1]. We
explore the possible modification whatsoever present in the radiation reaction
force experienced by an accelerating charge in the modified Maxwell theory.
However it turns out that radiation reaction receives no change due to Lorentz
violation whereas electromagnetic mass manifests anisotropy.",1707.09522v1
2017-10-26,Non-London electrodynamics in a multiband London model: anisotropy-induced non-localities and multiple magnetic field penetration lengths,"The London model describes strongly type-2 superconductors as massive vector
field theories, where the magnetic field decays exponentially at the length
scale of the London penetration length. This also holds for isotropic
multi-band extensions, where the presence of multiple bands merely renormalises
the London penetration length. We show that, by contrast, the magnetic
properties of anisotropic multi-band London models are not this simple, and the
anisotropy leads to the inter-band phase differences becoming coupled to the
magnetic field. This results in the magnetic field in such systems having N+1
penetration lengths, where N is the number of field components or bands. That
is, in a given direction, the magnetic field decay is described by N+1 modes
with different amplitudes and different decay length scales. For certain
anisotropies we obtain magnetic modes with complex masses. That means that
magnetic field decay is not described by a monotonic exponential increment set
by a real penetration length but instead is oscillating. Some of the
penetration lengths are shown to diverge away from the superconducting phase
transition when the mass of the phase-difference mode vanishes. Finally the
anisotropy-driven hybridization of the London mode with the Leggett modes can
provide an effectively non-local magnetic response in the nominally local
London model. Focusing on the two-component model, we discuss the magnetic
field inversion that results from the effective non-locality, both near the
surface of the superconductor and around vortices. In the regime where the
magnetic field decay becomes non-monotonic, the multiband London superconductor
is shown to form weakly-bound states of vortices.",1710.09907v3
2017-11-30,Inverse Prism based on Temporal Discontinuity and Spatial Dispersion,"We introduce the concept of the inverse prism as the dual of the conventional
prism and deduce from this duality an implementation of it based on temporal
discontinuity and spatial dispersion provided by anisotropy. Moreover, we show
that this inverse prism exhibits the following three unique properties:
chromatic refraction birefringence, ordinary-monochromatic and extraordinary-
polychromatic temporal refraction, and linear-to-Lissajous polarization
transformation.",1711.11204v2
2018-01-25,Voltage Control of Uni-directional Anisotropy in Ferromagnet-Multiferroic System,"Demonstration of ultra-low energy switching mechanisms is an imperative for
continued improvements in computing devices. Ferroelectric (FE) and
multiferroic (MF) orders and their manipulation promises an ideal combination
of state variables to reach atto-Joule range for logic and memory (i.e., ~ 30X
lower switching energy than nanoelectronics). In BiFeO3 the coupling between
the antiferromagnetic (AFM) and FE orders is robust at room temperature,
scalable in voltage, stabilized by the FE order, and can be integrated into a
fabrication process for a beyond-CMOS era. The presence of the AFM order and a
canted magnetic moment in this system causes exchange interaction with a
ferromagnet such as CoFe or LSMO. While previous work has shown that exchange
coupling (uniaxial anisotropy) can be controlled with an electric field,
several puzzling issues remain. Perhaps the most intriguing among them is that
the BiFeO3-CoFe bilayer did not demonstrate any electrically controlled
directional anisotropy, i.e., an exchange bias, which is a potential mechanism
for 180o magnetic reversal and is independent of switching kinetics. However,
what is needed/preferred for logic and memory is a magneto-electric mechanism
that works analogous to an applied field, i.e a uni-directional anisotropy that
is voltage modulated. Here, we present the evidence of electrical control of
exchange bias of a laterally scaled spin valve that is exchange-coupled to
BiFeO3 at room temperature. We show that the exchange bias in this bilayer is
thermally robust, electrically controlled and reversible. We anticipate that
magneto-electricity at such scaled dimensions provides a powerful pathway for
computing beyond the modern nanoelectronics transistors by enabling a new class
of non-volatile, ultra-low energy computing elements.",1801.08280v1
2018-02-13,Prospects for next generation Cosmic Microwave Background experiments,"In this lecture, after a synthetic review of measurements of CMB temperature
anisotropies and of their cosmological implications, the theoretical background
of CMB polarization is summarized and the concepts of the main experiments that
are ongoing or are being planned are briefly described.",1802.04753v1
2018-03-16,Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation,"The Magnetospheric Multiscale (MMS) mission has observed electron whistler
waves at the center and at the edges of magnetic holes in the dayside
magnetosheath. The magnetic holes are nonlinear mirror structures since their
magnitude is anti-correlated with particle density. In this article, we examine
the growth mechanisms of these whistler waves and their interaction with the
host magnetic hole. In the observations, as magnetic holes develop and get
deeper, an electron population gets trapped and develops a temperature
anisotropy favorable for whistler waves to be generated. In addition, the
decrease in magnetic field magnitude and the increase in density reduces the
electron resonance energy, which promotes the electron cyclotron resonance. To
investigate this process, we used an expanding box particle-in-cell simulations
to produce the mirror instability, which then evolves into magnetic holes. The
simulation shows that whistler waves can be generated at the center and edges
of magnetic holes, which reproduces the primary features of the MMS
observations. The simulation shows that the electron temperature anisotropy
develops in the center of the magnetic hole once the mirror instability reaches
its nonlinear stage of evolution. The plasma is then unstable to whistler waves
at the minimum of the magnetic field structures. In the saturation regime of
mirror instability, when magnetic holes are developed, the electron temperature
anisotropy appears at the edges of the holes and electron distributions become
more isotropic at the magnetic field minimum. At the edges, the expansion of
magnetic holes decelerates the electrons which leads to temperature
anisotropies.",1803.06399v1
2018-06-11,Spectral Conditions for Equivalence of Gaussian Random Fields with Stationary Increments,"This paper studies the problem of equivalence of Gaussian measures induced by
Gaussian random fields (GRFs) with stationary increments and proves a
sufficient condition for the equivalence in terms of the behavior of the
spectral measures at infinity. The main results extend those of Stein (2004),
Van Zanten (2007, 2008) and are applicable to a rich family of nonstationary
space-time models with possible anisotropy behavior.",1806.04181v1
2018-07-11,Viscous hydrodynamics for nonconformal anisotropic fluids,"A new formulation of (3+1)-dimensional anisotropic hydrodynamics is presented
that accounts nonperturbatively for the large longitudinal-transverse pressure
anisotropy and bulk viscous pressure in heavy-ion collisions. The
initialization of the anisotropic hydrodynamic stage is discussed, and a
comparison to standard viscous hydrodynamics for (0+1)- dimensional Bjorken
expansion is presented.",1807.04223v1
2018-10-04,The Anisotropies and Origins of Ultrahigh Energy Cosmic Rays,"IceCube detects more than 100,000 neutrinos per year in the GeV- to
PeV-energy range. Among those, we have isolated a flux of high-energy cosmic
neutrinos. I will discuss the instrument, the analysis of the data, the
significance of the discovery of cosmic neutrinos, and the recent
multi-messenger observation of a flaring TeV blazar in coincidence with the
IceCube neutrino alert IC170922.",1810.02484v1
2018-11-01,3-omega method for thermal properties of thin film multilayers,"Short review on the different models for the electro-thermal 3-omega method.
We present the deduction of the fundamental relation between the 3-omega
voltage with the temperature rise to determine the thermal conductivity. The
usage of the anisotropy of the films allows a smooth transition between 1D and
2D models. A comparison between the multilayer methods and analytical solutions
are presented.",1811.00571v1
2018-11-20,Results from the Pierre Auger Observatory,"I describe some of the results on ultrahigh-energy cosmic rays that have been
obtained with the Pierre Auger Observatory. These include measurements of the
spectrum, composition and anisotropies. Possible astrophysical scenarios that
account for these results are discussed.",1811.08260v1
2019-01-01,Comments on the chemical and kinetic equilibration in heavy ion collisions,"I argue that perturbative scattering of quarks and gluons are incompatible
with lattice and heavy ion data on QGP properties. The non-perturbative
mechanisms for quasiparticle rescattering and quark production are briefly
discussed, as well as experiments needed to measure matter anisotropy and quark
density at early stages of the collisions.",1901.00178v1
2019-01-02,Magnetization reorientation due to the superconducting transition in heavy-metal heterostructures,"Recent theoretical and experimental work has demonstrated how the
superconducting critical temperature ($T_c$) can be modified by rotating the
magnetization of a single homogeneous ferromagnet proximity-coupled to the
superconducting layer. This occurs when the superconductor and ferromagnet are
separated by a thin heavy normal metal that provides an enhanced interfacial
Rashba spin-orbit interaction. We consider the reciprocal effect: magnetization
reorientation driven by the superconducting phase transition. We solve the
tight-binding Bogoliubov-de Gennes equations on a lattice self-consistently and
find that the relative angle between the spin-orbit field and the magnetization
gives rise to a contribution in the free energy even in the normal state due to
band-structure effects. For temperatures below $T_c$, superconductivity gives
rise to a competing contribution. By lowering the temperature, in addition to
reorientation of the favored magnetization direction from in-plane to
out-of-plane, a $\pi/4$ in-plane rotation for thicker ferromagnetic layers is
possible. Furthermore, computation of $T_c$ of the structure in the ballistic
limit shows a dependence on the in-plane orientation of the magnetization, in
contrast to our previous result on the diffusive limit. This finding is
relevant with respect to thin-film heterostructures since these are likely to
be in the ballistic regime of transport. Finally, we discuss the experimental
feasibility of observing the magnetic anisotropy induced by the superconducting
transition when other magnetic anisotropies, such as the shape anisotropy for a
ferromagnetic film, are taken into account. Our work suggests that the
superconducting condensation energy in principle can trigger a reorientation of
the magnetization of a thin-film ferromagnet upon lowering the temperature
below $T_c$, in particular for ferromagnets with weak magnetic anisotropies.",1901.00501v3
2019-02-25,Creation Mechanism of Devil's Staircase Surface and Unstable and Stable Periodic Orbit in the Anisotropic Kepler Problem,"A long-standing question in two dimensional Anisotropic Kepler Problem (AKP)
concerns with the uniqueness of an unstable periodic orbit (PO) for a given
binary code (modulo symmetry equivalence). In this paper, a finite level ($N$)
surface defined by the binary coding of the orbit is considered over the
initial value domain $D_0$. It is proved that a tiling of $D_0$ by base ribbons
of the surface steps is proper; the surface height increases monotonously when
ribbons are traversed from left to right. The mechanism of level $N+1$ tiling
creation from $N$ one is clarified. Two cases are possible depending on the
code and the anisotropy. (A) Every ribbon shrinks to a line at $N \rightarrow
\infty$. Here the uniqueness holds. (B) When future (F) and past (P) ribbon
become tangent each other, they escape from shrinking, Then, the initial values
of a stable PO ($S$) and an unstable PO ($U$) sharing the same code co-exist
inside the overlap of F and P non-shrinking ribbons. This case corresponds to
Broucke's PO. At high anisotropy, it is only case (A), but with decreasing
anisotropy, bifurcation $U(R) \rightarrow S(R) +U'(NR)$ occurs, along with the
emergence of a non-shrinking ribbon. (Here $R$ and $NR$ are short for
self-retracing and non-retracing PO respectively). We conjecture that case (B)
occurs only for odd rank, $Y$-symmetric POs from a classification based on
topology and symmetry. We report two applications. First, the classification is
applied successfully to the successive bifurcation (above bifurcation is
followed by $S(R) \rightarrow S'(R) +S''(NR)$) of a high-rank PO ($n=15$).
Second, enhancing sensitivity to co-existence of S and U POs by ribbon tiling,
we examine high anisotropy region. A new symmetry type PO ($O$ type) is found
and, at $\gamma =0.2$, all POs are unstable and unique. 13648 POs at rank 10
verifies that Gutzwiller's action formula amazingly works.",1902.09275v1
2019-02-25,Modeling Nearly Spherical Pure-Bulge Galaxies with a Stellar Mass-to-Light Ratio Gradient under the $Λ$CDM and MOND Paradigms: II. The Orbital Anisotropy of Slow Rotators within the Effective Radius,"We investigate the anisotropy of the stellar velocity dispersions within the
effective radius, $R_{\rm e}$, in 24 ATLAS$^{\rm 3D}$ pure-bulge galaxies, 16
of which are kinematic slow rotators (SRs). We allow the spherical anisotropy
parameter $\beta$ to be radially varying and allow a radial gradient in the
stellar mass-to-light ratio ($M_\star/L$) through the parameter $K$ introduced
earlier. The median anisotropy for SRs depends on $K$ as follows:
$\langle\beta_{\rm m}\rangle = a + b K$ with $a=0.19\pm 0.05$, $b=-0.13\pm
0.07$ ($\Lambda$CDM) or $a=0.21\pm 0.05$, $b=-0.26\pm 0.08$ (MOND), where
$\beta_{\rm m}$ refers to the radially averaged quantity. Under the
$\Lambda$CDM paradigm this scaling is tied to a scaling of $\langle f_{\rm
DM}\rangle = (0.16\pm 0.03) +(0.31\pm 0.06) K$, where $f_{\rm DM}$ refers to
the DM fraction within a sphere of $r=R_{\rm e}$. For $K=0$ (constant
$M_\star/L$), we obtain radially biased results with $\langle\beta_{\rm
m}\rangle \approx 0.2$ consistent with previous results. However, marginalizing
over $0 < K < 1.5$ yields $\langle\beta_{\rm m}\rangle = 0.06 ^{+0.11}_{-0.14}$
with $\langle f_{\rm DM}\rangle = 0.35 \pm 0.08$: isotropy is preferred. This
isotropy hides the fact that $\beta_{\rm m}$ is correlated with kinematic
features such as counter rotating cores (CRCs), kinematically distinct cores
(KDCs), and low-level velocities (LVs): SRs with LVs are likely to be radially
biased while SRs with CRCs are likely to be tangentially biased, and SRs with
KDCs are intermediate. Existing cosmological simulations allow us to understand
these results qualitatively in terms of their dynamical structures and
formation histories although there exist quantitative tensions. More realistic
cosmological simulations, particularly allowing for $M_\star/L$ gradients, may
be required to better understand SRs.",1902.09350v1
2019-03-19,Magnetic properties and domain structure of ultrathin yttrium iron garnet/Pt bilayers,"We report on the structure, magnetization, magnetic anisotropy, and domain
morphology of ultrathin yttrium iron garnet (YIG)/Pt films with thickness
ranging from 3 to 90 nm. We find that the saturation magnetization is close to
the bulk value in the thickest films and decreases towards low thickness with a
strong reduction below 10 nm. We characterize the magnetic anisotropy by
measuring the transverse spin Hall magnetoresistance as a function of applied
field. Our results reveal strong easy plane anisotropy fields of the order of
50-100 mT, which add to the demagnetizing field, as well as weaker in-plane
uniaxial anisotropy ranging from 10 to 100 $\mu$T. The in-plane easy axis
direction changes with thickness, but presents also significant fluctuations
among samples with the same thickness grown on the same substrate. X-ray
photoelectron emission microscopy reveals the formation of zigzag magnetic
domains in YIG films thicker than 10 nm, which have dimensions larger than
several 100 $\mu$m and are separated by achiral N\'{e}el-type domain walls.
Smaller domains characterized by interspersed elongated features are found in
YIG films thinner than 10 nm.",1903.08285v1
2019-05-01,Signals for Lorentz violation in gravitational waves,"Lorentz violations in gravitational waves are investigated. Plane-wave
solutions for arbitrary gauge-invariant violations in linearized gravity are
constructed. Signatures of Lorentz violation include dispersion, birefringence,
and anisotropies. Modifications to waves from coalescing compact binaries and
to strain signals in gravitational-wave detectors are derived.",1905.00409v1
2019-05-14,Influence of transverse field on the spin-3/2 Blume-Capel model on rectangular lattice,"Transverse field effect on thermodynamic properties of the spin-3/2
Blume-Capel model on rectangular lattice in which the interactions in
perpendicular directions differ in signs is studied within the mean field
approximation. Phase diagrams in the (transverse field, temperature) plane are
constructed for various values of single-ion anisotropy.",1905.05852v1
2019-06-26,Strong electrical magneto-chiral anisotropy in tellurium,"We report the experimental observation of strong electrical magneto-chiral
anistropy (eMChA) in trigonal tellurium (t-Te) crystals. We introduce the
tensorial character of the effect and determine several tensor elements and we
propose a novel intrinsic bandstructure-based mechanism for eMChA which gives a
reasonable description of the principal results.",1906.10994v1
2019-07-10,"Quantum Hall Skyrmions at $ν=0,\pm 1$ in monolayer graphene","Monolayer graphene under a strong perpendicular field exhibit quantum Hall
ferromagnetism with spontaneously broken spin and valley symmetry. The
approximate SU(4) spin/valley symmetry is broken by small lattice scale effects
in the central Landau level corresponding to filling factors $\nu=0,\pm 1$.
Notably the ground state at $\nu=0$ is believed to be a canted
antiferromagnetic (AF) or a ferromagnetic (F) state depending on the component
of the magnetic field parallel to the layer and the strength of small
anisotropies. We study the skyrmions for the filling factors $\nu=\pm 1,0$ by
using exact diagonalizations on the spherical geometry. If we neglect
anisotropies we confirm the validity of the standard skyrmion picture
generalized to four degrees of freedom. For filling factor $\nu=- 1$ the hole
skyrmion is an infinite-size valley skyrmion with full spin polarization
because it does not feel the anisotropies. The electron skyrmion is also always
of infinite size. In the F phase it is always fully polarized while in the AF
phase it undergoes continuous magnetization under increasing Zeeman energy. In
the case of $\nu=0$ the skyrmion is always maximally localized in space both in
F and AF phase. In the F phase it is fully polarized while in the AF it has
also progressive magnetization with Zeeman energy. The magnetization process is
unrelated to the spatial profile of the skyrmions contrary to the SU(2) case.
In all cases the skyrmion physics is dominated by the competition between
anisotropies and Zeeman effect but not directly by the Coulomb interactions,
breaking universal scaling with the ratio Zeeman to Coulomb energy.",1907.04612v2
2019-10-07,Spin Nematic Liquids of the $S=1$ Spin Ladder in Magnetic Field,"The magnetization process of the $S=1$ spin ladder system is investigated
using the numerical exact diagonalization of finite-size clusters. The
field-induced spin nematic liquid phase was predicted to appear by our previous
work. Several ground-state phase diagrams in the plane of the single-ion
anisotropy and the external magnetic field are obtained in the present study.",1910.02582v1
2019-11-13,Charged Polytropic Models on Finch-Skea Spacetime,"The static, charged, spherically symmetric matter distribution have been
studied by considering polytropic equation of state. Two polytropic indices
have been considered for study. The plots of density, radial pressure,
tangential pressure, anisotropy and causality condition indicates the models
are suitable to describe the relativistic polytropes.",1911.05325v1
2019-12-11,Robust cycloid crossover driven by anisotropy in the skyrmion host GaV$_\mathbf{4}$S$_\mathbf{8}$,"We report on the anomalous magnetization dynamics of the
cycloidally-modulated spin textures under the influence of uniaxial anisotropy
in multiferroic $\mathrm{GaV_4S_8}$. The temperature and field dependence of
the linear ac susceptibility [$\chi_{1\omega}^{\prime}(T,H)$], ac magnetic loss
[$\chi_{1\omega}^{\prime\prime}(T,H)$], and nonlinear ac magnetic response
[$M_{3\omega}(T,H)$] are examined across the magnetic phase diagram in the
frequency range $f = 10-10000$ Hz. According to recent theory, skyrmion
vortices under axial crystal symmetry are confined along specific orientations,
resulting in enhanced robustness against oblique magnetic fields and altered
spin dynamics. We characterize the magnetic response of each spin texture and
find that the dynamic rigidity of the N\'eel skyrmion lattice appears enhanced
compared to Bloch-type skyrmions in cubic systems, even in the multidomain
state. Anomalous $M_{3\omega}$ and strong dissipation emerge over the same
phase regime where strong variations in the cycloid pitch were observed on
lowering temperature in recent small-angle neutron scattering experiments
[White et al., Phys. Rev. B 97, 020401(R) (2018)]. Here, we show that strong
anisotropy also drives an extended crossover of the zero-field cycloid texture
in $\mathrm{GaV_4S_8}$. The frequency dependence of these dynamic signatures is
consistent with that of a robust anharmonic spin texture exhibiting a
correlated domain arrangement. The results underpin the essential role of
magnetic anisotropy in enhancing the rigidity of topological spin textures for
diverse applications.",1912.05367v2
2020-01-26,"Neutron Induced Fission Fragment Angular Distributions, Anisotropy, and Linear Momentum Transfer Measured with the NIFFTE Fission Time Projection Chamber","The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE)
collaboration has performed measurements with a fission time projection chamber
(fissionTPC) to study the fission process by reconstructing full
three-dimensional tracks of fission fragments and other ionizing radiation. The
amount of linear momentum imparted to the fissioning nucleus by the incident
neutron can be inferred by measuring the opening angle between the fission
fragments. Using this measured linear momentum, fission fragment angular
distributions can be converted to the center-of-mass frame for anisotropy
measurements. Angular anisotropy is an important experimental observable for
understanding the quantum mechanical state of the fissioning nucleus and vital
to determining detection efficiency for cross section measurements. Neutron
linear momentum transfer to fissioning $^{235}$U, $^{238}$U, and $^{239}$Pu and
fission fragment angular anisotropy of $^{235}$U and $^{238}$U as a function of
neutron energies in the range 130 keV--250 MeV are presented.",2001.09381v1
2020-03-12,Holographic Entanglement Entropy in Anisotropic Background with Confinement-Deconfinement Phase Transition,"We discuss a general five-dimensional completely anisotropic holographic
model with three different spatial scale factors, characterized by a Van der
Waals-like phase transition between small and large black holes. A peculiar
feature of the model is the relation between anisotropy of the background and
anisotropy of the colliding heavy ions geometry. We calculate the holographic
entanglement entropy (HEE) of the slab-shaped region, the orientation of which
relatively to the beams line and the impact parameter is characterized by the
Euler angles. We study the dependences of the HEE and its density on the
thermodynamic (temperature, chemical potential) and geometric (parameters of
anisotropy, thickness, and orientation of entangled regions) parameters. As a
particular case the model with two equal transversal scaling factors is
considered. This model is supported by the dilaton and two Maxwell fields. In
this case we discuss the HEE and its density in detail: interesting features of
this model are jumps of the entanglement entropy and its density near the line
of the small/large black hole phase transition. These jumps depend on the
anisotropy parameter, chemical potential, and orientation. We also discuss
different definitions and behavior of c-functions in this model. The c-function
calculated in the Einstein frame decreases while increasing $\ell$ for all
$\ell$ in the isotropic case (in regions of $(\mu,T)$-plane far away from the
line of the phase transition). We find the non-monotonicity of the c-functions
for several anisotropic configurations, which however does not contradict with
any of the existing c-theorems since they all base on Lorentz invariance.",2003.05847v2
2020-04-07,Probing cosmic isotropy with a new X-ray galaxy cluster sample through the $L_{\text{X}}-T$ scaling relation,"The isotropy of the late Universe is an assumption greatly used in astronomy.
However, many studies have recently reported deviations from isotropy with a
definitive conclusion yet to be made. New, independent methods to robustly test
the cosmic isotropy are of crucial importance. In this work, we investigate the
directional behavior of the X-ray luminosity-temperature ($L_X-T$) relation of
galaxy clusters. A tight correlation exists between the luminosity and
temperature of the X-ray-emitting intracluster medium. While the measured
luminosity depends on the underlying cosmology, the temperature can be
determined without any cosmological assumptions. By exploiting this property
one can effectively test the isotropy of cosmological parameters over the full
extragalactic sky. Here, we used 313 homogeneously selected X-ray galaxy
clusters from the MCXC catalog and obtained core-excised temperatures for all
of them. We find that the behavior of the $L_X-T$ relation heavily depends on
the direction of the sky. Strong anisotropies are detected at a $\sim 4\sigma$
level toward $(l,b)\sim (280^{\circ}, -20^{\circ})$. Several X-ray and
cluster-related effects that could potentially explain these anisotropies were
examined, but none did so. Interestingly, two other available cluster samples
appear to have a similar behavior throughout the sky, while being fully
independent of each other and our sample. Performing a joint analysis of the
three samples, the final anisotropy is further intensified ($\sim 5\sigma$),
toward $(l,b)\sim (303^{\circ}, -27^{\circ})$, which is in good agreement with
other cosmological probes. This result demonstrates that X-ray galaxy cluster
studies that assume perfect isotropy can produce strongly biased results
whether the underlying reason is cosmological or related to X-rays. The
identification of the exact nature of these anisotropies is therefore crucial.",2004.03305v1
2020-04-08,High-order crystal field and rare-earth magnetism in RECo5 intermetallics,"Crystal-field (CF) effects on the rare-earth (RE) ions in ferrimagnetic
intermetallics NdCo$_5$ and TbCo$_5$ are evaluated using an ab initio density
functional + dynamical mean-field theory approach in conjunction with a
quasi-atomic approximation for on-site electronic correlations on the localized
4$f$ shell. The study reveals an important role of the high-order sectoral
harmonic component of the CF in the magnetism of RECo$_5$ intermetallics. An
unexpectedly large value is computed in the both systems for the corresponding
crystal-field parameter (CFP) $A_6^6 \langle r^6 \rangle$, far beyond what one
would expect from only electrostatic contributions. It allows solving the
enigma of the non-saturation of zero-temperature Nd magnetic moments in
NdCo$_5$ along its easy axis in the Co exchange field. This unsaturated state
had been previously found out from magnetization distribution probed by
polarised neutron elastic scattering but had so far remained theoretically
unexplained. The easy plane magnetic anisotropy of Nd in NdCo$_5$ is strongly
enhanced by the large value of $A_6^6\langle r^6 \rangle$. Counter-intuitively,
the polar dependence of anisotropy energy within the easy plane remains rather
small. The easy plane magnetic anisotropy of Nd is reinforced up to high
temperatures, which is explained through $J$-mixing effects. The calculated ab
initio anisotropy constants of NdCo$_5$ and their temperature dependence are in
quantitative agreement with experiment. Unlike NdCo$_5$, the $A_6^6 \langle r^6
\rangle$ CFP has negligible effects on the Tb magnetism in TbCo$_5$ suggesting
that its impact on the RE magnetism is ion-specific across the RECo$_5$ series.
The origin of its large value is the hybridization of RE and Co states in a
hexagonally coordinated local environment of the RE ion in RECo$_5$
intermetallics.",2004.03945v1
2020-05-11,Quantum dynamics of the corner of the Bianchi IX model in WKB approximation,"In this paper we analyse the Bianchi IX Universe dynamics within the corner
region associated to the potential term which the spatial curvature induces in
the Minisuperspace. The study is done in the vacuum and in the presence of a
massless scalar field $\phi$ and a cosmological constant term $\Lambda$. We
investigate the dynamics in terms of WKB scenario for which the isotropic
Misner variables (the volume) and one of the two anisotropic ones (and $\phi$
when present) are treated on a semi-classical level, while the remaining
anisotropy degree of freedom, the one trapped in the corner, is described on a
pure quantum level. The quantum dynamics always reduces to the one of a
time-dependent Schr\""{o}edinger equation for a harmonic potential with a time
dependent frequency. The vacuum case is treated in the limits of a collpasing
and an expanding Universe, while the dynamics in presence of $\phi$ and
$\Lambda$ is studied for $t \rightarrow \infty $. In both analysis the quantum
dynamics of the anisotropy variable is associated to a decaying standard
deviation of its probability density, corresponding to a suppression of the
quantum anisotropy associated. In the vacuum case, the corner configuration
becomes an attractor for the dynamics and the evolution resembles that one of a
Taub cosmology in the limit of a non-singular initial Universe. This suggests
that if the Bianchi dynamics enters enough the potential corner then the
initial singularity is removed and a Taub picture emerges. The case when $\phi$
is present well mimics the De-Sitter phase of an inflationary Universe. Here we
show that both the classical and quantum anisotropies are exponentially
suppressed, so that the resulting dynamics corresponds to an isotropic closed
Robertson-Walker geometry.",2005.05337v2
2020-06-12,Anisotropy of random motions of gas in Messier 33,"(Abridged) We study the properties of anisotropic and axisymmetric velocity
ellipsoids from maps of the gas velocity dispersion in nearby galaxies. This
data allow us to measure the azimuthal-to-radial axis ratio of gas velocity
ellipsoids, which is a useful tool to study the structure of gaseous orbits in
the disk. We also present the first estimates of perturbations in gas velocity
dispersion maps by applying an alternative model that considers isotropic and
asymmetric random motions. High-quality velocity dispersion maps of the atomic
medium at various angular resolutions of the nearby spiral galaxy Messier 33,
are used to test the anisotropic and isotropic velocity models. The velocity
dispersions of hundreds of individual molecular clouds are also analyzed. The
HI velocity dispersion of M33 is systematically larger along the minor axis,
and lower along the major axis. Isotropy is only possible if asymmetric motions
are considered. Fourier transforms of the HI velocity dispersions reveal a
bisymmetric mode which is mostly stronger than other asymmetric motions and
aligned with the minor axis of the galaxy. Within the anisotropic and
axisymmetric velocity model, the stronger bisymmetry is explained by a radial
component that is larger than the azimuthal component of the ellipsoid of
random motions, thus by gaseous orbits that are dominantly radial. The
azimuthal anisotropy parameter is not strongly dependent on the choice of the
vertical dispersion. The velocity anisotropy parameter of the molecular clouds
is observed highly scattered. Perturbations such as HI spiral-like arms could
be at the origin of the gas velocity anisotropy in M33. Further work is
necessary to assess whether anisotropic velocity ellispsoids can also be
invoked to explain the asymmetric gas random motions of other galaxies.",2006.07274v1
2020-08-31,A gradient Discretisation Method For Anisotropic Reaction Diffusion Models with applications to the dynamics of brain tumours,"A gradient discretisation method (GDM), Gradient schemes, Convergence
analysis, Existence of weak solutions, Anisotropic reaction diffusion models,
Dirichlet and Neumann boundary conditions, Non conforming finite element
methods, Finite volume schemes, Hybrid mixed mimetic (HMM) method,
Crouzeix--Raviart scheme, Brain tumour dynamics, Fractional anisotropy.",2009.00139v1
2020-09-07,Unconventional U(1) to $\mathbf{Z_q}$ cross-over in quantum and classical ${\bf q}$-state clock models,"We consider two-dimensional $q$-state quantum clock models with quantum
fluctuations connecting states with clock transitions with different choices
for matrix elements. We study the quantum phase transitions in these models
using quantum Monte Carlo simulations, with the aim of characterizing the
cross-over from emergent U(1) symmetry at the transition (for $q \ge 4$) to
$Z_q$ symmetry of the ordered state. We also study classical three-dimensional
clock models with spatial anisotropy corresponding to the space-time anisotropy
of the quantum systems. The U(1) to ${Z_q}$ symmetry cross-over in all these
systems is governed by a dangerously irrelevant operator. We specifically study
$q=5$ and $q=6$ models with different forms of the quantum fluctuations and
different anisotropies in the classical models. We find the expected classical
XY critical exponents and scaling dimensions $y_q$ of the clock fields.
However, the initial weak violation of the U(1) symmetry in the ordered phase,
characterized by a $Z_q$ symmetric order parameter $\phi_q$, scales in an
unexpected way. As a function of the system size $L$, close to the critical
temperature $\phi_q \propto L^p$, where the known value of the exponent is
$p=2$ in the classical isotropic clock model. In contrast, for strongly
anisotropic classical models and the quantum models we find $p=3$. For weakly
anisotropic classical models we observe a cross-over from $p=2$ to $p=3$
scaling. The exponent $p$ directly impacts the exponent $\nu'$ governing the
divergence of the U(1) to $Z_q$ cross-over length scale $\xi'$ in the
thermodynamic limit, according to the relationship $\nu'=\nu(1+|y_q|/p)$, where
$\nu$ is the conventional correlation length exponent. We present a
phenomenological argument based on an anomalous renormalization of the clock
field in the presence of anisotropy, possibly as a consequence of topological
(vortex) line defects.",2009.03249v3
2020-10-05,An estimate for the anisotropic maximum curvature in the planar case,"We fix a Finsler norm $F$ and, using the anisotropic curvature flow, we prove
that the anisotropic maximum curvature $k^F_{\max}$ of a smooth Jordan curve is
such that $ k^F_{\max}(\gamma)\geq \sqrt{\kappa/A}$ , where $A$ is the area
enclosed by $\gamma$ and $\kappa$ the area of the unitary Wulff shape
associated to the anisotropy $F$.",2010.01871v1
2020-10-13,Tailoring interface mixing and magnetic properties in (111) Permalloy/Pt multilayers,"We present deposition and characterization of multilayers consisting of 20
repetitions of 15 $\r{A}$ thick permalloy Ni$_{80}$Fe$_{20}$ at. \% (Py) and 5
$\r{A}$ Pt. The samples were prepared by two different sputter deposition
methods, namely dc magnetron sputtering (dcMS) and high power impulse magnetron
sputtering (HiPIMS), that represent low and moderate ionized flux fraction of
the film forming material, respectively, for deposition of the Py layers. The
effect of substrate roughness, working gas pressure and sputter power on the
in-plane uniaxial magnetic anisotropy of the films are studied. The multilayers
were characterized by X-ray reflectivity and diffraction, and by
magneto-optical Kerr effect (MOKE). It is shown that HiPIMS deposition produces
multilayers with unique surface roughness regardless of the substrate surface
roughness. Multilayers prepared by both dcMS and HiPIMS deposition present a
strong (111) texture normal to the film plane. The results show that utilizing
HiPIMS for deposition of the Py layer leads to a minimum interface mixing
between individual layers compared to dcMS deposition performed at sputter
power. This is associated with the smooth surface of Py deposited by HiPIMS.
However, this sharp interface results in higher coercivity and an opening in
the hard axis hysteresis loops while multilayers with intermixing present well
defined in-plane uniaxial anisotropy i.e. a linear hard axis. Comparison with
Py/Cu and Py/CuPt multilayers, prepared under identical conditions using
HiPIMS, suggests that poor in-plane uniaxial anisotropy is obtained in the
Py/Pt case, caused by the inverse magnetostriction arising from the large
lattice mismatch between Py and Pt. The Py/Pt multilayers that exhibit
interface mixing have a more relaxed interface and thus presents negligible
inverse magnetostriction and have better defined anisotropy.",2010.06104v3
2021-01-19,Phase diagram of the anisotropic triangular lattice Hubbard model,"In a recent study [Phys. Rev. X 10, 021042 (2020)], we showed using
large-scale density matrix renormalization group (DMRG) simulations on infinite
cylinders that the triangular lattice Hubbard model has a chiral spin liquid
phase. In this work, we introduce hopping anisotropy in the model, making one
of the three distinct bonds on the lattice stronger or weaker compared with the
other two. We implement the anisotropy in two inequivalent ways, one which
respects the mirror symmetry of the cylinder and one which breaks this
symmetry. In the full range of anisotropy, from the square lattice to weakly
coupled one-dimensional chains, we find a variety of phases. Near the isotropic
limit we find the three phases identified in our previous work: metal, chiral
spin liquid, and 120$^\circ$ spiral order; we note that a recent paper suggests
the apparently metallic phase may actually be a Luther-Emery liquid, which
would also be in agreement with our results. When one bond is weakened by a
relatively small amount, the ground state quickly becomes the square lattice
N\'{e}el order. When one bond is strengthened, the story is much less clear,
with the phases that we find depending on the orientation of the anisotropy and
on the cylinder circumference. While our work is to our knowledge the first
DMRG study of the anisotropic triangular lattice Hubbard model, the overall
phase diagram we find is broadly consistent with that found previously using
other methods, such as variational Monte Carlo and dynamical mean field theory.",2101.07454v3
2021-02-24,Neutrino-Antineutrino Asymmetry From The Space-time Noncommutativity,"A new mechanism having as an origin the space-time noncommutativity has been
shown to generate anisotropy and axial-like interaction giving rise to a
leptonic asymmetry for fermionic particles propagating in a curved
noncommutative $FRW$ universe. As a by-product, for ultra-relativistic
particles like neutrinos, an analytical expression of this asymmetry is derived
explicitly. Constraints and bounds from the cosmological parameters are also
discussed.",2102.12214v1
2021-03-02,Tunneling in an anisotropic cubic Dirac semi-metal,"Motivated by a recent first principles prediction of an anisotropic cubic
Dirac semi-metal in a real material Tl(TeMo)$_3$, we study the behavior of
electrons tunneling through a potential barrier in such systems. To clearly
investigate effects from different contributions to the Hamiltonian we study
the model in various limits. First, in the limit of a very thin material where
the linearly dispersive $z$-direction is frozen out at zero momentum and the
dispersion in the $x$-$y$ plane is rotationally symmetric. In this limit we
find a Klein tunneling reminiscent of what is observed in single layer graphene
and linearly dispersive Dirac semi-metals. Second, an increase in thickness of
the material leads to the possibility of a non-zero momentum eigenvalue $k_z$
that acts as an effective mass term in the Hamiltonian. We find that these lead
to a suppression of Klein tunneling. Third, the inclusion of an anisotropy
parameter $\lambda\neq 1$ leads to a breaking of rotational invariance.
Furthermore, we observed that for different values of incident angle $\theta$
and anisotropy parameter $\lambda$ the Hamiltonian supports different numbers
of modes propagating to infinity. We display this effect in form of a diagram
that is similar to a phase diagram of a distant detector. Fourth, we consider
coexistence of both anisotropy and non-zero $k_z$ but do not find any effect
that is unique to the interplay between non-zero momentum $k_z$ and anisotropy
parameter $\lambda$. Last, we studied the case of a barrier that was placed in
the linearly dispersive direction and found Klein tunneling $T-1\propto
\theta^6+\mathcal{O}(\theta^8)$ that is enhanced when compared to the Klein
tunneling in linear Dirac semi-metals or graphene where $T-1\propto
\theta^2+\mathcal{O}(\theta^4)$.",2103.01807v3
2021-03-08,"The effects of Vadasz term, anisotropy and rotation on bi-disperse convection","The onset of thermal convection in a uniformly rotating and horizontally
isotropic bi-disperse porous medium, taking into account the Vadasz term, is
investigated. Via linear instability analysis, it has been proven that the
Vadasz term allows the onset of convection via an oscillatory state but does
not affect convection via a stationary motion.",2103.04939v1
2021-03-11,Shock Waves in Relativistic Anisotropic Hydrodynamics,"Shock wave solutions in anisotropic relativistic hydrodynamics are
considered. A new phenomenon of anisotropy-related angular deflection of the
incident flow by the shock wave front is described. Patterns of velocity and
momentum transformation by the shock wave front are described.",2103.06745v2
2021-03-25,Cosmological implications of the anisotropy of ten galaxy cluster scaling relations,"The hypothesis that the late Universe is isotropic and homogeneous is adopted
by most cosmological studies. The expansion rate $H_0$ is thought to be
spatially constant, while bulk flows are often presumed to be negligible
compared to the Hubble expansion, even at local scales. Their effects on the
redshift-distance conversion are hence usually ignored. Any deviation from this
consensus can strongly bias the results of such studies and thus the importance
of testing these assumptions cannot be understated. Scaling relations of galaxy
clusters can be effectively used for that. In previous works, we observed
strong anisotropies in cluster scaling relations, whose origins remain
ambiguous. By measuring many different cluster properties, several scaling
relations with different sensitivities can be built. Nearly independent tests
of cosmic isotropy and bulk flows are then feasible. We make use of up to 570
clusters with measured properties at X-ray, microwave, and infrared
wavelengths, to construct 10 different cluster scaling relations (five of them
presented for the first time) and test the isotropy of the local Universe.
Through rigorous tests, we ensure that our analysis is not prone to generally
known systematic biases and X-ray absorption issues. By combining all available
information, we detect an apparent $9\%$ spatial variation in the local $H_0$
between $(l,b)\sim
({280^{\circ}}^{+35^{\circ}}_{-35^{\circ}},{-15^{\circ}}^{+20^{\circ}}_{-20^{\circ}})$
and the rest of the sky. The observed anisotropy has a nearly dipole form.
Using Monte Carlo simulations, we assess the statistical significance of the
anisotropy to be $>5\sigma$. This result could also be attributed to a $\sim
900$ km/s bulk flow which seems to extend out to at least $\sim 500$ Mpc. These
two effects are indistinguishable until more high$-z$ clusters are observed by
future all-sky surveys, such as eROSITA.",2103.13904v1
2021-05-04,Resampling Methods for Detecting Anisotropic Correlation Structure,"This paper proposes parametric and non-parametric hypothesis testing
algorithms for detecting anisotropy -- rotational variance of the covariance
function in random fields. Both algorithms are based on resampling mechanisms,
which enable avoiding relying on asymptotic assumptions, as is common in
previous algorithms. The algorithms' performance is illustrated numerically in
simulation experiments and on real datasets representing a variety of potential
challenges.",2105.01654v2
2021-05-19,Dynamical analysis of clusters of galaxies from cosmological simulations,"Studies of cluster mass and velocity anisotropy profiles are useful tests of
dark matter models, and of the assembly history of clusters of galaxies. These
studies might be affected by unknown systematics caused by projection effects.
We aim at testing observational methods for the determination of mass and
velocity anisotropy profiles of clusters of galaxies. Particularly, we focus on
the MAMPOSSt technique (Mamon et al. 2013).
  We use results from two semi-analytic models of galaxy formation coupled with
high-resolution N-body cosmological simulations, the catalog of De Lucia &
Blaizot (2007) and the FIRE catalog based on the new GAlaxy Evolution and
Assembly model.
  We test the reliability of the Jeans equation in recovering the true mass
profile when full projected phase-space information is available. We examine
the reliability of the MAMPOSSt method in estimating the true mass and velocity
anisotropy profiles of the simulated halos when only projected phase-space
information is available, as in observations.
  The spherical Jeans equation provides a reliable tool for the determination
of cluster mass profiles, also for subsamples of tracers separated by galaxy
color. Results are equally good for prolate and oblate clusters. Using only
projected phase-space information, MAMPOSSt provides estimates of the mass
profile with a standard deviation of 35-69 %, and a negative bias of 7-17 %,
nearly independent of radius, and that we attribute to the presence of
interlopers in the projected samples. The bias changes sign, that is, the mass
is over-estimated, for prolate clusters with their major axis aligned along the
line-of-sight. MAMPOSSt measures the velocity anisotropy profiles accurately in
the inner cluster regions, with a slight overestimate in the outer regions,
both for the whole sample of observationally-identified cluster members and
separately for red and blue galaxies.",2105.09126v1
2021-07-26,Graphical translators for anisotropic and crystalline mean curvature flow,"In this paper we discuss existence, uniqueness and some properties of a class
of solitons to the anisotropic mean curvature flow, i.e., graphical
translators, either in the plane or under an assumption of cylindrical symmetry
on the anisotropy and the mobility. In these cases, the equation becomes an
ordinary differential equation, and this allows to find explicitly the
translators and describe their main features.",2107.12082v1
2021-08-12,Optical anisotropies of asymmetric double GaAs (001) Quantum Wells,"In the present work, we were able to identify and characterize a new source
of in-plane optical anisotropies (IOAs) occurring in asymmetric DQWs; namely a
reduction of the symmetry from $D_{2d}$ to $C_{2v}$ as imposed by asymmetry
along the growth direction. We report on reflectance anisotropy spectroscopy
(RAS) of double GaAs quantum wells (DQWs) structures coupled by a thin ($<2$
nm) tunneling barrier. Two groups of DQWs systems were studied: one where both
QWs have the same thickness (symmetric DQW) and another one where they have
different thicknesses (asymmetric DQW). RAS measures the IOAs arising from the
intermixing of the heavy- and light- holes in the valence band when the
symmetry of the DQW system is lowered from $D_{2d}$ to $C_{2v}$. If the DQW is
symmetric, residual IOAs stem from the asymmetry of the QW interfaces; for
instance, associated to Ga segregation into the AlGaAs layer during the
epitaxial growth process. In the case of an asymmetric DQW with QWs with
different thicknesses, the AlGaAs layers (that are sources of anisotropies) are
not distributed symmetrically at both sides of the tunneling barrier. Thus, the
system losses its inversion symmetry yielding an increase of the RAS strength.
The RAS line shapes were compared with reflectance spectra in order to assess
the heavy- and light- hole mixing induced by the symmetry breakdown. The
energies of the optical transitions were calculated by numerically solving the
one-dimensional Schr\""odinger equation using a finite-differences method. Our
results are useful for interpretation of the transitions occurring in both,
symmetric and asymmetric DQWs.",2108.05920v1
2021-08-26,Elastic and electro-optical properties of flexible fluorinated dimers with negative dielectric anisotropy,"We report the synthesis and the temperature dependencies of optical,
dielectric, and elastic properties of four homologous dimeric mesogens in the
uniaxial nematic (N) phase.",2108.11855v1
2021-12-11,Various Applications of Transition Metal Dichalcogenides,"TMDs have recently been spotlighted due to their original features. Firstly,
they have layered structures with Van der Waals interactions. Secondly, they
have different phases, affecting a degree of anisotropy. Finally, they have
excellent carrier mobilities. In this review, based on these characteristics,
this journal shows how TMDs can be applied in a wide variety of industries. The
main applications that will be treated is biomedical and electronic
applications.",2112.05919v1
2022-01-21,Probing Anisotropies of the Stochastic Gravitational Wave Background with LISA,"We investigate the sensitivity of the Laser Interferometer Space Antenna
(LISA) to the anisotropies of the Stochastic Gravitational Wave Background
(SGWB). We first discuss the main astrophysical and cosmological sources of
SGWB which are characterized by anisotropies in the GW energy density, and we
build a Signal-to-Noise estimator to quantify the sensitivity of LISA to
different multipoles. We then perform a Fisher matrix analysis of the prospects
of detectability of anisotropic features with LISA for individual multipoles,
focusing on a SGWB with a power-law frequency profile. We compute the noise
angular spectrum taking into account the specific scan strategy of the LISA
detector. We analyze the case of the kinematic dipole and quadrupole generated
by Doppler boosting an isotropic SGWB. We find that $\beta\, \Omega_{\rm
GW}\sim 2\times 10^{-11}$ is required to observe a dipolar signal with LISA.
The detector response to the quadrupole has a factor $\sim 10^3 \,\beta$
relative to that of the dipole. The characterization of the anisotropies, both
from a theoretical perspective and from a map-making point of view, allows us
to extract information that can be used to understand the origin of the SGWB,
and to discriminate among distinct superimposed SGWB sources.",2201.08782v1
2022-02-15,On the robustness of the velocity anisotropy parameter in probing the stellar kinematics in Milky Way like galaxies: Take away from TNG50 simulation,"We analyze the velocity anisotropy of stars in real and energy space for a
sample of Milky Way-like galaxies in the TNG50 simulation. We employ different
selection criteria, including spatial, kinematic and metallicity cuts, and make
three halo classes ($\mathcal{A}$-$\mathcal{C}$) which show mild-to-strong
sensitivity to different selections. The above classes cover 48%, 16% and 36%
of halos, respectively. We analyze the $\beta$ radial profiles and divide them
into either monotonically increasing radial profiles or ones with peaks and
troughs. We demonstrate that halos with monotonically increasing $\beta$
profiles are mostly from class $\mathcal{A}$, whilst those with peaks/troughs
are part of classes $\mathcal{B}$-$\mathcal{C}$. This means that care must be
taken as the observationally reported peaks/troughs might be a consequence of
different selection criteria. We infer the anisotropy parameter $\beta$ energy
space and compare that against the $\beta$ radial profile. It is seen that 65%
of halos with very mild sensitivity to different selections in real space, are
those for which the $\beta$ radial and energy profiles are closely related.
Consequently, we propose that comparing the $\beta$ radial and energy profiles
might be a novel way to examine the sensitivity to different selection criteria
and thus examining the robustness of the anisotropy parameter in tracing
stellar kinematics. We compare simulated $\beta$ radial profiles against
various observations and demonstrate that, in most cases, the model diversity
is comparable with the error bars from different observations, meaning that the
TNG50 models are in good overall agreement with observations.",2202.07162v3
2022-03-28,Holographic $\mathrm{QCD}_{3}$ and Chern-Simons theory from anisotropic supergravity,"Based on the gauge-gravity duality, we study the three-dimensional QCD
($\mathrm{QCD}_{3}$) and Chern-Simons theory by constructing the anisotropic
black D3-brane solution in IIB supergravity. The deformed bulk geometry is
obtained by performing a double Wick rotation and dimension reduction which
becomes an anisotropic bubble configuration exhibiting confinement in the dual
theory. And its anisotropy also reduces to a Chern-Simons term due to the
presence of the dissolved D7-branes or the axion field in bulk. Using the
bubble geometry, we investigate the the ground-state energy density, quark
potential, entanglement entropy and the baryon vertex according to the standard
methods in the AdS/CFT dictionary. Our calculation shows that the ground-state
energy illustrates degenerate to the Chern-Simons coupling coefficient which is
in agreement with the properties of the gauge Chern-Simons theory. The behavior
of the quark tension, entanglement entropy and the embedding of the baryon
vertex further implies strong anisotropy may destroy the confinement.
Afterwards, we additionally introduce various D7-branes as flavor and
Chern-Simons branes to include the fundamental matter and effective
Chern-Simons level in the dual theory. By counting their orientation, we
finally obtain the associated topological phase in the dual theory and the
critical mass for the phase transition. Interestingly the formula of the
critical mass reveals the flavor symmetry, which may relate to the chiral
symmetry, would be restored if the anisotropy increases greatly. As all of the
analysis is consistent with characteristics of quark-gluon plasma, we therefore
believe our framework provides a remarkable way to understand the features of
Chern-Simons theory, the strong coupled nuclear matter and its deconfinement
condition with anisotropy.",2203.14489v3
2022-04-05,"Angle-resolved polarized Raman spectroscopy for distinguishing stage-I graphite intercalation compounds with Thorium, Uranium and Plutonium","Graphite intercalation compounds (GICs) with the geometrical anisotropy and
strong electron-phonon coupling are in full swing and have shown their great
potential for applications in nanodevices. I selected representative three
elements in actinide group with valence electron arrangement: Thorium (Th)
([Rn]6d27s2), Uranium (U) ([Rn]5f36d17s2), Plutonium (Pu) ([Rn]5f67s2). I
calculated their phonon spectra and demonstrated the atomic-scale
microstructure identification of actinide graphite intercalation compounds by
angle-resolved polarized Raman spectroscopy.",2204.01967v1
2022-05-31,Non-Gaussianity constraints from Planck spectral distortion cross-correlations,"Primordial non-Gaussianity can source $\mu$-distortion anisotropies that are
correlated with the large-scale temperature and polarization signals of the
cosmic microwave background (CMB). A measurement of $\mu T$ and $\mu E$
correlations can therefore be used to constrain it on wavelengths of
perturbations not directly probed by the standard CMB anisotropies. In this
work, we carry out a first rigorous search for $\mu$-type spectral distortion
anisotropies with \Planck data, applying the well-tested constrained ILC
component-separation method combined with the needlet framework. We reconstruct
a $\mu$ map from \Planck data, which we then correlate with the CMB
anisotropies to derive constraints on the amplitude $\fNL$ of the local form
bispectrum, specifically on the highly squeezed configurations with effective
wavenumbers $k_s \simeq \SI{740}{Mpc^{-1}}$ and $k_L \simeq
\SI{0.05}{Mpc^{-1}}$. We improve previously estimated constraints by more than
an order of magnitude. This enhancement is owing to the fact that for the first
time we are able to use the full multipole information by carefully controlling
biases and systematic effects in the final analysis. We also for the first time
incorporate constraints from measurements of $\mu E$ correlations, which
further tighten the limits. A combination of the derived \Planck $\mu T$ and
$\mu E$ power spectra yields $|\fNL| \lesssim 6800$ (95\% c.l.) on this highly
squeezed bispectrum. This is only $\simeq 3$ times weaker than the anticipated
constraint from \LiteBIRD alone. We show that a combination of \LiteBIRD with
\Planck will improve the expected future constraint by $\simeq 20\%$ over
\LiteBIRD alone. These limits can be used to constrain multi-field inflation
models and primordial black hole formation scenarios, thus providing a
promising novel avenue forward in CMB cosmology.",2205.15971v1
2022-06-21,Electron-driven instabilities in the solar wind,"The electrons are an essential particle species in the solar wind. They often
exhibit non-equilibrium features in their velocity distribution function. These
include temperature anisotropies, tails (kurtosis), and reflectional
asymmetries (skewness), which contribute a significant heat flux to the solar
wind. If these non-equilibrium features are sufficiently strong, they drive
kinetic micro-instabilities. We develop a semi-graphical framework based on the
equations of quasi-linear theory to describe electron-driven instabilities in
the solar wind. We apply our framework to resonant instabilities driven by
temperature anisotropies. These include the electron whistler anisotropy
instability and the propagating electron firehose instability. We then describe
resonant instabilities driven by reflectional asymmetries in the electron
distribution function. These include the electron/ion-acoustic, kinetic
Alfv\'en heat-flux, Langmuir, electron-beam, electron/ion-cyclotron,
electron/electron-acoustic, whistler heat-flux, oblique
fast-magnetosonic/whistler, lower-hybrid fan, and electron-deficit whistler
instability. We briefly comment on non-resonant instabilities driven by
electron temperature anisotropies such as the mirror-mode and the
non-propagating firehose instability. We conclude our review with a list of
open research topics in the field of electron-driven instabilities in the solar
wind.",2206.10403v1
2022-08-04,Boltzmann equations for astrophysical Stochastic Gravitational Wave Backgrounds scattering off of massive objects,"This work presents a set of coupled Boltzmann equations describing the
intensity and polarisation Stokes parameters of the SGWB. Collision terms,
which account for gravitational Compton scattering off of massive objects, are
also included. This set resembles that for the CMB Stokes parameters, but the
different spin nature of the gravitational radiation and the physics involved
in the scattering process determine crucial differences. In this case, due to
the Rutherford angular dependence of the cross section, all the SGWB intensity
multipoles of order $\ell$ are scattered out, producing outgoing intensity
anisotropies of any order $\ell$ if they are present in the incoming radiation.
On the other hand, SGWB linear polarisation modes can be expanded in a basis of
spherical harmonics with $m=\pm 4$ and $\ell\ge 4$. This means that SGWB
polarisation modes can be generated from unpolarised anisotropic radiation only
with $m=\pm 4$, therefore requiring at least a hexadecapole anisotropy
($\ell\ge 4$) in the incoming intensity. Assuming a simplified toy model, we
solve analytically the set of coupled Boltzmann equations to get explicit
expressions for the intensity and polarisation angular power spectra. We
confirm the contribution of the gravitational Compton scattering to the SGWB
anisoptropies is extremely small for collisions with compact objects in the
frequency range of current and upcoming surveys. The system of coupled
Boltzmann equations presented here provides a way to an accurate estimate of
the total amount of anisotropies generated by multiple SGWB scattering
processes off of massive objects, as well as the interplay between polarisation
and intensity, during the GW propagation across the LSS of the universe. These
results will be useful for the full treatment of the astrophysical SWGB
anisotropies in view of upcoming gravitational waves observatories.",2208.02800v3
2022-08-30,Reynolds Stress Anisotropy Tensor Predictions for Turbulent Channel Flow using Neural Networks,"The Reynolds-Averaged Navier-Stokes (RANS) approach remains a backbone for
turbulence modeling due to its high cost-effectiveness. Its accuracy is largely
based on a reliable Reynolds stress anisotropy tensor closure model. There has
been an amount of work aiming at improving traditional closure models, while
they are still not satisfactory to some complex flow configurations. In recent
years, advances in computing power have opened up a new way to address this
problem: the machine-learning-assisted turbulence modeling. In this paper, we
employ neural networks to fully predict the Reynolds stress anisotropy tensor
of turbulent channel flows at different friction Reynolds numbers, for both
interpolation and extrapolation scenarios. Several generic neural networks of
Multi-Layer Perceptron (MLP) type are trained with different input feature
combinations to acquire a complete grasp of the role of each parameter. The
best performance is yielded by the model with the dimensionless mean streamwise
velocity gradient $\alpha$, the dimensionless wall distance $y^+$ and the
friction Reynolds number $\mathrm{Re}_\tau$ as inputs. A deeper theoretical
insight into the Tensor Basis Neural Network (TBNN) clarifies some remaining
ambiguities found in the literature concerning its application of Pope's
general eddy viscosity model. We emphasize the sensitivity of the TBNN on the
constant tensor $\textbf{T}^{*(0)}$ upon the turbulent channel flow data set,
and newly propose a generalized $\textbf{T}^{*(0)}$, which considerably
enhances its performance. Through comparison between the MLP and the augmented
TBNN model with both $\{\alpha, y^+, \mathrm{Re}_\tau\}$ as input set, it is
concluded that the former outperforms the latter and provides excellent
interpolation and extrapolation predictions of the Reynolds stress anisotropy
tensor in the specific case of turbulent channel flow.",2208.14301v1
2022-09-13,"Large amplitude bidirectional anisotropy of cosmic-ray intensity observed with world-wide networks of ground-based neutron monitors and muon detectors in November, 2021","We analyze the cosmic-ray variations during a significant Forbush decrease
observed with world-wide networks of ground-based neutron monitors and muon
detectors during November 3-5, 2021. Utilizing the difference between primary
cosmic-ray rigidities monitored by neutron monitors and muon detectors, we
deduce the rigidity spectra of the cosmic-ray density (or omnidirectional
intensity) and the first- and second-order anisotropies separately, for each
hour of data. A clear two-step decrease is seen in the cosmic-ray density with
the first $\sim2\%$ decrease after the interplanetary shock arrival followed by
the second $\sim5\%$ decrease inside the magnetic flux rope (MFR) at 15 GV.
Most strikingly, a large bidirectional streaming along the magnetic field is
observed in the MFR with a peak amplitude of $\sim5\%$ at 15 GV which is
comparable to the total density decrease inside the MFR. The bidirectional
streaming could be explained by adiabatic deceleration and/or focusing in the
expanding MFR, which have stronger effects for pitch angles near 90$^\circ$, or
by selective entry of GCRs along a leg of the MFR. The peak anisotropy and
density depression in the flux rope both decrease with increasing rigidity. The
spectra vary dynamically indicating that the temporal variations of density and
anisotropy appear different in neutron monitor and muon detector data.",2209.05743v1
2022-10-25,Cosmic ray anisotropy study by means of detection of muon bundles,"In this work, we use muon bundles which are formed in extensive air showers
and detected at the ground level as a tool for searching anisotropy of high
energy cosmic rays. Such choice is explained by the penetrating ability of
muons which allows them to retain the direction of primary particles with a
good accuracy. In 2012-2022, we performed long-term muon bundle detection with
the coordinate-tracking detector DECOR, which is a part of the Experimental
complex NEVOD (MEPhI, Moscow). To search for the cosmic rays anisotropy, the
muon bundles arriving at zenith angles in the range from 15 to 75 degrees in
the local coordinate system are used. During the entire period of data taking,
about 14 million of such events have been accumulated. In this paper, we
describe some methods developed in the Experimental complex NEVOD and
implemented in our research, including: the method for compensating the
influence of meteorological conditions on the intensity of muon bundles at the
Earth's surface, the method for accounting the design features of the detector
and the inhomogeneity of the detection efficiency for different directions, as
well as the method for estimating primary energies of cosmic rays. Here we
present the results of the search for the dipole anisotropy of cosmic rays with
energies in the PeV region and also compare them with the results obtained at
the other scientific facilities.",2210.13916v1
2022-10-27,Modelling shock-like injections of solar energetic particles with 3D test particle simulations,"Solar Energetic Particle (SEP) acceleration and injection into interplanetary
space during gradual SEP events is thought to take place at Coronal Mass
Ejection (CME)-driven shocks. Features of measured intensity profiles at 1 au
have been attributed to properties of the radial and longitudinal/latitudinal
injections at the shock. Focussed transport models are typically used to model
acceleration at a CME-shock and subsequent propagation. Test particle
simulations are an alternative approach but so far they have been carried out
only with instantaneous injection near the Sun. We develop the first temporally
extended shock-like injection for our 3D test particle code and investigate how
the spatial features of injection affect SEP intensity and anisotropy profiles
for observers at 0.3 and 1.0 au. We conduct simulations of a monoenergetic
population of 5 MeV protons considering three different radial injection
functions and two longitudinal/latitudinal injection functions. We consider a
range of scattering conditions with scattering mean free path values ranging
from 0.1-1.0 au, and determine intensity and anisotropy profiles at six
observers at different longitudinal locations. We find that the radial,
longitudinal and latitudinal injection functions play a relatively minor role
in shaping the SEP intensity profiles. The dependence of profiles on the value
of the scattering mean free path is also weak, unlike what is found from 1D
focussed transport models. Spatial factors, such as the time of
observer-shock-connection/disconnection and time of shock passage have a much
stronger influence on SEP intensities and anisotropies. Persistent anisotropies
until shock passage are seen in our simulations. Comparing instantaneous and
shock-like injections, we find that the link between duration of injection and
of the SEP event is very weak, unlike what is commonly assumed.",2210.15587v2
2022-11-30,Vortex-bound solitons in topological superfluid $^3$He,"The different superfluid phases of $^3$He are described by $p$-wave order
parameters that include anisotropy axes both in the orbital and spin spaces.
The anisotropy axes characterize the broken symmetries in these macroscopically
coherent quantum many-body systems. The systems' free energy has several
degenerate minima for certain orientations of the anisotropy axes. As a result,
spatial variation of the order parameter between two such regions, settled in
different energy minima, forms a topological soliton. Such solitons can
terminate in the bulk liquid, where the termination line forms a vortex with
trapped circulation of mass and spin superfluid currents. Here we discuss
possible soliton-vortex structures based on the symmetry and topology arguments
and focus on the three structures observed in experiments: solitons bounded by
spin-mass vortices in the B phase, solitons bounded by half-quantum vortices in
the polar and polar-distorted A phases, and the composite defect formed by a
half-quantum vortex, soliton and the Kibble-Lazarides-Shafi wall in the
polar-distorted B phase. The observations are based on nuclear magnetic
resonance (NMR) techniques and are of three types: first, solitons can form a
potential well for trapped spin waves, observed as an extra peak in the NMR
spectrum at shifted frequency; second, they can increase the relaxation rate of
the NMR spin precession; lastly, the soliton can present the boundary
conditions for the anisotropy axes in bulk, modifying the bulk NMR signal.
Owing to solitons' prominent NMR signatures and the ability to manipulate their
structure with external magnetic field, solitons have become an important tool
for probing and controlling the structure and dynamics of superfluid $^3$He, in
particular half-quantum vortices with core-bound Majorana modes.",2211.17117v2
2022-12-19,"Quantum Magnetic Properties, Entanglement for Antiferromagnetic Spin 1 and 3/2 Cluster Models","Entanglement, magnetization and magnetic susceptibility for 1D
antiferromagnetic spin 1 and spin 3/2 Heisenberg XXX model with
Dzyaloshinskii-Moriya interaction, single-ion anisotropy and external magnetic
field on the finite chain are obtained.",2212.09403v2
2022-12-27,Potential signature of a quadrupolar Hubble expansion in Pantheon+ supernovae,"The assumption of isotropy -- that the Universe looks the same in all
directions on large scales -- is fundamental to the standard cosmological
model. This model forms the building blocks of essentially all of our
cosmological knowledge to date. It is therefore critical to empirically test in
which regimes its core assumptions hold. Anisotropies in the cosmic expansion
are expected on small scales due to nonlinear structures in the late Universe,
however, the extent to which these anisotropies might impact our low-redshift
observations remains to be fully tested. In this paper, we use fully general
relativistic simulations to calculate the expected local anisotropic expansion
and identify the dominant multipoles in cosmological parameters to be the
quadrupole in the Hubble parameter and the dipole in the deceleration
parameter. We constrain these multipoles simultaneously in the new Pantheon+
supernova compilation. The fiducial analysis is done in the rest frame of the
CMB with peculiar velocity corrections. Under the fiducial range of redshifts
in the Hubble flow sample, we find a $\sim 2\sigma$ deviation from isotropy. We
constrain the eigenvalues of the quadrupole in the Hubble parameter to be
$\lambda_1 =0.021\pm{ 0.011}$ and $ {\lambda_2= 3.15\times 10^{-5}}\pm 0.012$
and place a $1\sigma$ upper limit on its amplitude of $2.88\%$. We find no
significant dipole in the deceleration parameter, finding constraints of
$q_{\rm dip} = 4.5^{+1.9}_{-5.4}$. However, in the rest frame of the CMB
without corrections, we find $ q_{ \rm dip} = 9.6^{+4.0}_{-6.9}$, a $>2\sigma$
positive amplitude. We also investigate the impact of these anisotropies on the
Hubble tension. We find a maximal shift of $0.30$ km s$^{-1}$ Mpc$^{-1}$ in the
monopole of the Hubble parameter and conclude that local anisotropies are
unlikely to fully explain the observed tension.",2212.13569v1
2023-01-10,On the evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere,"We analyze a merged Parker Solar Probe ($PSP$) and Solar Orbiter ($SO$)
dataset covering heliocentric distances $13 \ R_{\odot} \lesssim R \lesssim
220$ $R_{\odot}$ to investigate the radial evolution of power and
spectral-index anisotropy in the wavevector space of solar wind turbulence. Our
results show that anisotropic signatures of turbulence display a distinct
radial evolution when fast, $V_{sw} \geq ~ 400 ~km ~s^{-1}$, and slow, $V_{sw}
\leq ~ 400 ~km ~s^{-1}$, wind streams are considered. The anisotropic
properties of slow wind in Earth orbit are consistent with a ``critically
balanced'' cascade, but both spectral-index anisotropy and power anisotropy
diminish with decreasing heliographic distance. Fast streams are observed to
roughly retain their near-Sun anisotropic properties, with the observed
spectral index and power anisotropies being more consistent with a
``dynamically aligned'' type of cascade, though the lack of extended fast-wind
intervals makes it difficult to accurately measure the anisotropic scaling. A
high-resolution analysis during the first perihelion of PSP confirms the
presence of two sub-ranges within the inertial range, which may be associated
with the transition from weak to strong turbulence. The transition occurs at
$\kappa d_{i} \approx 6 \times 10^{-2}$, and signifies a shift from -5/3 to -2
and -3/2 to -1.57 scaling in parallel and perpendicular spectra, respectively.
Our results provide strong observational constraints for anisotropic theories
of MHD turbulence in the solar wind.",2301.03896v4
2022-12-09,Anisotropy of Cosmic Rays and Chaotic Trajectories in the Heliosphere,"As cosmic rays (CRs) propagate in the Galaxy, they can be affected by
magnetic structures that temporarily trap them and cause their trajectories to
display chaotic behavior, therefore modifying the simple diffusion scenario.
When CRs arrive at the Earth, they do so anisotropically. These chaotic effects
can be a fundamental contributor to this anisotropy. Accordingly, this requires
a comprehensive description of chaos in trapping conditions since assessing
their repercussions on the CR arrival directions is necessary. This study
utilizes a new method described in L\'opez-Barquero and Desiati (2021) to
characterize chaotic trajectories in bound systems. This method is based on the
Finite-Time Lyapunov Exponent (FTLE), a quantity that determines the levels of
chaos based on the trajectories' divergence rate. The FTLE is useful since it
adapts to trapping conditions in magnetic structures or even propagating media
changes. Here, we explore the effects that chaos and trapping can have on the
TeV CR anisotropy. Concretely, we apply this method to study the behavior of
CRs entering the heliosphere. Specifically, how the distinct heliospheric
structures and CR impinging directions from the ISM can affect chaos levels.
The heliosphere has an intrinsic directionality that affects CRs differently
depending on where they enter it. This feature causes preferential directions
from which particles tend to be more chaotic than others. This eventually
translates into changes in the arrival maps which are not uniformly
distributed. Instead, we expect sectors in the map to change separately from
others, creating a time variation that could be detected. Consequently, this
result points to the idea that time-variability in the maps is essential to
understanding the CR anisotropy's overall processes.",2301.10065v1
2023-02-09,Minimal entropy production in the presence of anisotropic fluctuations,"Anisotropy in temperature, chemical potential, or ion concentration, provides
the fuel that feeds dynamical processes that sustain life. At the same time,
anisotropy is a root cause of incurred losses manifested as entropy production.
In this work we consider a rudimentary model of an overdamped stochastic
thermodynamic system in an anisotropic temperature heat bath, and study minimum
entropy production when driving the system between thermodynamic states in
finite time. While entropy production in isotropic temperature environments can
be expressed in terms of the length (in the Wasserstein-2 metric) traversed by
the thermodynamic state of the system, anisotropy complicates substantially the
mechanism of entropy production since, besides dissipation, seepage of energy
between ambient anisotropic heat sources by way of the system dynamics is often
a major contributing factor. A key result of the paper is to show that in the
presence of anisotropy, minimization of entropy production can once again be
expressed via a modified Optimal Mass Transport (OMT) problem. However, in
contrast to the isotropic situation that leads to a classical OMT problem and a
Wasserstein length, entropy production may not be identically zero when the
thermodynamic state remains unchanged (unless one has control over
non-conservative forces); this is due to the fact that maintaining a
Non-Equilibrium Steady-State (NESS) incurs an intrinsic entropic cost that can
be traced back to a seepage of heat between heat baths. As alluded to, NESSs
represent hallmarks of life, since living matter by necessity operates far from
equilibrium. Therefore, the question studied herein, to characterize minimal
entropy production in anisotropic environments, appears of central importance
in biological processes and on how such processes may have evolved to optimize
for available usage of resources.",2302.04401v1
2023-02-17,Quasi-classical Langmuir wave collapse in a magnetic field,"The anisotropy due to a magnetic field is shown to result in significant
changes in Langmuir collapse. Using a variational approach, the quasi-classical
collapse phenomenon is investigated analytically.
  A hierarchy of quasi-classical collapses is determined, along with the
structure of a field in the proximity of a stationary singularity that is
sustained by the continuous absorption of wave energy from a wave packet.",2302.08972v1
2023-04-07,Linear stability analysis of non-isothermal plane Couette flow in an anisotropic and inhomogeneous porous layer underlying a fluid layer,"This paper carries out a linear stability analysis of a plane Couette flow in
a porous layer underlying a fluid layer where the porous layer is anisotropic
and inhomogeneous. The plane Couette flow is induced due to the uniform
movement of the upper plate and convection arises due to the maintenance of the
temperature difference between the upper plate and the lower plate. The fluid
considered is Newtonian and incompressible. Darcy model is used to narrate the
flow in the porous layer and at the interface, the Beavers-Joseph condition is
used. The Chebyshev collocation method is used to solve the generalized
eigenvalue problem. Here, the effect of anisotropy and inhomogeneity of the
porous medium, along with the ratio of the thickness of fluid to porous layer,
i.e., depth ratio $(\hat{d})$, Reynolds number $(Re)$ and Darcy number
$(\delta)$ are studied. The analysis is carried out majorly for water; however,
the impact of anisotropy and inhomogeneity on different fluids by varying
Prandtl number ($Pr$) is also studied. Depending on the value of parameters,
the unimodal (porous mode or fluid mode), bimodal (porous mode and fluid mode)
and also trimodal (porous mode, fluid mode and porous mode) nature of the
neutral curve is obtained. The increasing value of the inhomogeneity parameter,
depth ratio or decreasing value of the anisotropy parameter, Reynolds number,
Prandtl number and Darcy number raises the system instability. For
$\delta=0.002$, $Pr=6.9$ and $Re=10$, dominating nature of porous mode is
always observed for $\hat{d}<0.07$, and fluid mode for $\hat{d}>0.21$
irrespective of anisotropy and inhomogeneity parameter. With the help of energy
budget analysis, the types of instability are categorized and also the types of
mode obtained from linear stability analysis are verified. Secondary flow
patterns are also visualized to understand the flow dynamics.",2304.03499v1
2023-04-26,Some aspects of anisotropic curvature flow of planar partitions,"We consider the geometric evolution of a network in the plane, flowing by
anisotropic curvature. We discuss local existence of a classical solution in
the presence of several smooth anisotropies. Next, we discuss some aspects of
the polycrystalline case.",2304.13454v1
2023-04-30,Inverse source problem for the Boltzmann equation in cosmology,"We study the inverse problem of recovering primordial perturbations from
anisotropies of Cosmic Microwave Background (CMB) using the kinetic model.
Mathematically, the problem in concern is the inverse source problem for the
linear Boltzmann equation with measurements on some Cauchy surface. We obtain
two stable determination results for generic absorption coefficients and
scattering kernels.",2305.00560v1
2023-05-21,Small-amplitude Compressible Magnetohydrodynamic Turbulence Modulated by Collisionless Damping in Earth's Magnetosheath: Observation Matches Theory,"Plasma turbulence is a ubiquitous dynamical process that transfers energy
across many spatial and temporal scales and affects energetic particle
transport. Recent advances in the understanding of compressible
magnetohydrodynamic (MHD) turbulence demonstrate the important role of damping
in shaping energy distributions on small scales, yet its observational evidence
is still lacking. This study provides the first observational evidence of
substantial collisionless damping (CD) modulation on small-amplitude
compressible MHD turbulence cascade in Earth's magnetosheath using four Cluster
spacecraft. Based on an improved compressible MHD decomposition algorithm,
turbulence is decomposed into three eigenmodes: incompressible Alfv\'en modes,
and compressible slow and fast (magnetosonic) modes. Our observations
demonstrate that CD enhances the anisotropy of compressible MHD modes because
CD has a strong dependence on wave propagation angle. The wavenumber
distributions of slow modes are mainly stretched perpendicular to the
background magnetic field ($\mathbf{B_0}$) and weakly modulated by CD. In
contrast, fast modes are subjected to a more significant CD modulation. Fast
modes exhibit a weak, scale-independent anisotropy above the CD truncation
scale. Below the CD truncation scale, the anisotropy of fast modes enhances as
wavenumbers increase. As a result, fast mode fractions in the total energy of
compressible modes decrease with the increase of perpendicular wavenumber (to
$\mathbf{B_0}$) or wave propagation angle. Our findings reveal how the
turbulence cascade is shaped by CD and its consequences to anisotropies in the
space environment.",2305.12507v3
2023-06-07,Emergent Magnetic Phases and Piezomagnetic Effects in Mn$_x$Ni$_{1-x}$F$_2$ Thin Film Alloys,"The effect of random competing single-ion anisotropies in antiferromagnets
was studied using epitaxial Mn$_x$Ni$_{1-x}$F$_2$ antiferromagnetic thin film
alloys grown via molecular beam epitaxy. The crystal structure of this material
is tetragonal for all values of $x$, and the Mn sites have a magnetic easy axis
single-ion anisotropy while the Ni sites have an easy plane anisotropy
perpendicular to the Mn easy axis. Crystallographic and magnetization
measurements demonstrated that the thin film alloys were homogeneously mixed
and did not phase-separate into their constituent parts. Pure MnF$_2$ thin
films epitaxially grown on MgF$_2$ exhibited compressive strain along all three
crystallographic axes which resulted in piezomagnetic effects. The
piezomagnetism disappeared if the film was grown on a (MnNi)F$_2$ graded buffer
layer. A mean-field theory fit to the transition temperature as a function of
the Mn concentration $x$, which takes into account piezomagnetic effects, gave
a magnetic exchange constant between Mn and Ni ions of $J_{\text{MnNi}} = 0.305
\pm 0.003$~meV. Mean-field theory calculations also predicted the existence of
an oblique antiferromagnetic phase in the Mn$_x$Ni$_{1-x}$F$_2$ alloy which
agreed with the experimental data. A magnetic phase diagram for
Mn$_x$Ni$_{1-x}$F$_2$ thin film alloys was constructed and showed evidence for
the existence of two unique magnetic phases, in addition to the ordinary
antiferromagnetic and paramagnetic phases: an oblique antiferromagnetic phase,
and an emergent magnetic phase proposed to be either a magnetic glassy phase or
a helical phase. The phase diagram is quantitatively different from that of
Fe$_x$Ni$_{1-x}$F$_2$ because of the much larger single-ion anisotropy of
Fe$^{2+}$ compared to Mn$^{2+}$.",2306.04809v2
2023-07-06,"Chaos, Cosmic Ray Anisotropy, and the Heliosphere","After more than a century of discovering cosmic rays, a comprehensive
description of their origin, propagation, and composition still eludes us. One
of the difficulties is that these particles interact with magnetic fields;
therefore, their directional information is distorted as they travel. In
addition, as cosmic rays (CRs) propagate in the Galaxy, they can be affected by
magnetic structures that temporarily trap them and cause their trajectories to
display chaotic behavior, therefore modifying the simple diffusion scenario.
Here, we examine the effects of chaos and trapping on the TeV CR anisotropy.
Concretely, we develop a new method to study the chaotic behavior of CRs. This
work is based on the heliospheric effects since they can be remarkably
significant for this anisotropy. Specifically, how the distinct heliospheric
structures can affect chaos levels. We model the heliosphere as a coherent
magnetic structure given by a static magnetic bottle and the presence of
temporal magnetic perturbations. This configuration is used to describe the
draping of the local interstellar magnetic field lines around the heliosphere
and the effects of magnetic field reversals induced by the solar cycles. In
this work, we explore the possibility that particle trajectories may develop
chaotic behavior while traversing and being temporarily trapped in this
heliospheric-inspired toy model and its potential consequences on the CR
arrival distribution. It was found that the level of chaos in a trajectory is
linked to the time the particles remain trapped in the system. This relation is
described by a power law that could prove to be inherently characteristic of
the system. Also, the arrival distribution maps show areas where the different
chaotic behaviors are present, which can constitute a source of
time-variability in the CR maps and can prove critical in understanding the
anisotropy on Earth.",2307.05515v1
2023-07-25,Interplay Between Anisotropy- and Skewness-driven Whistler Instabilities in the Solar Wind under the Core-Strahlo model,"Temperature anisotropy and field-aligned skewness are commonly observed
non-thermal features in electron velocity distributions in the solar wind.
These characteristics can act as a source of free energy to destabilize
different electromagnetic wave modes, which may alter the plasma state through
wave-particle interactions. Previous theoretical studies have mainly focused on
analyzing these non-thermal features and self-generated instabilities
individually. However, to obtain a more accurate and realistic understanding of
kinetic processes in the solar wind, it is necessary to examine the interplay
between these two energy sources. By means of linear kinetic theory, in this
paper we investigate the excitation of the parallel-propagating whistler mode,
when it is destabilized by electron populations exhibiting both temperature
anisotropy and field-aligned strahl or skewness. To describe the solar wind
electrons, we adopt the Core-Strahlo model as an alternative approach. This
model offers the advantage of representing the suprathermal features of halo
and strahl electrons, using a single skew-Kappa distribution already known as
the strahlo population. Our findings show that when the electron strahlo
exhibits an intrinsic temperature anisotropy, this suprathermal population
becomes a stronger and more efficient source of free energy for destabilizing
the whistler mode. This suggests a greater involvement of the anisotropic
strahlo in processes conditioned by wave-particle interactions. Present results
also suggest that the contribution of core anisotropy can be safely disregarded
when assessing the importance of instabilities driven by the suprathermal
population. This allows for a focused study, particularly regarding the
regulation of electron heat flux in the solar wind.",2307.13630v1
2023-09-15,"A comparative ab-initio investigation of the physical properties of cubic Laves phase compounds XBi$_2$ (X = K, Rb)","In this study, we looked into a number of physical properties of
alkali-bismuth compounds KBi$_2$ and RbBi$_2$ in the cubic Laves phase using
the density functional theory (DFT). The structural, elastic, anisotropy
indices, hardness, thermo-physical parameters, electronic band structure, and
optoelectronic properties have been explored. Most of the results presented in
this work are novel in nature.",2309.08307v1
2023-10-18,Testing the cosmological principle with the Pantheon+ sample and the region-fitting method,"The cosmological principle is fundamental to the standard cosmological model.
It assumes that the Universe is homogeneous and isotropic on very large scales.
As the basic assumption, it must stand the test of various observations. In
this work, using the region fitting (RF) method, we mapped the all-sky
distribution of cosmological parameters ($\Omega_{m}$ and $H_{0}$) and find
that the distribution significantly deviates from isotropy. A local matter
underdensity region exists toward (${308.4^{\circ}}$$_{-48.7}^{+47.6}$,
${-18.2^{\circ}}$$_{-28.8}^{+21.1}$) as well as a preferred direction of the
cosmic anisotropy (${313.4^{\circ}}$$_{-18.2}^{+19.6}$,
${-16.8^{\circ}}$$_{-10.7}^{+11.1}$) in galactic coordinates. Similar
directions may imply that local matter density might be responsible for the
anisotropy of the accelerated expansion of the Universe. Results of statistical
isotropy analyses including Isotropy and Isotropy with real-data positions (RP)
show high confidence levels. For the local matter underdensity, the statistical
significances are 2.78$\sigma$ (isotropy) and 2.34$\sigma$ (isotropy RP). For
the cosmic anisotropy, the statistical significances are 3.96$\sigma$
(isotropy) and 3.15$\sigma$ (isotropy RP). The comparison of these two kinds of
statistical isotropy analyses suggests that inhomogeneous spatial distribution
of real sample can increase the deviation from isotropy. The similar results
and findings are also found from reanalyses of the low-redshift sample (lp+)
and the lower screening angle ($\theta_\mathrm{max}$ = 60$^{\circ}$), but with
a slight decrease in statistical significance. Overall, our results provide
clear indications for a possible cosmic anisotropy. This possibility must be
taken seriously. Further testing is needed to better understand this signal.",2310.11727v2
2023-10-18,Spacecraft Charging of the Morazán MRZ-SAT Satellite in Low Earth Orbit: Initial Results on the Influence of Energetic Electron Anisotropy on Differential Charging,"The advent of the modular CubeSat satellite architecture has heralded a
revolution in satellite missions, drastically lowering the technical and
financial barriers to space. Surface charging resulting from energetic electron
poses a direct risk to satellites in space, causing electric arcing and
breakdowns. This risk is exacerbated for small technology demonstration
CubeSats that are less resilient than larger satellites. An upcoming CubeSat
launch is the first CubeSat project originating from Honduras, the Moraz\'an
satellite (MRZ-SAT), due to launch in 2024. This will carry earth observational
payloads to detect natural disasters. This study conducts simulations using the
Electro-Magnetic Spacecraft Environment Simulator code to study absolute and
differential charging of the MRZ-SAT cube-sat in Low Earth Orbit (LEO). The
MRZ-SAT hosts four antennas, an architecture which lends itself well to
studying and understanding differential charging in LEO. The MRZ-SAT was first
simulated in a typical benign ionospheric plasma environment. Here the antenna
located in the ambient plasma wake displayed the maximum charging up to --0.9
V, 0.24 V biased to the main cube. An energetic electron population was then
included and the wake antenna subsequently charged to greater values of --2.73
V, now 1.56 V biased to the main cube. The anisotropy of the energetic
electrons was then varied, and this differential charging trend appeared
exacerbated with anisotropies of 0.5 to 0.05 inducing absolute wake antenna
voltages up to --4.5 V and differential voltage biases 50 and 100 \% greater
than when an isotropic population was considered. This study highlights the
importance of electron anisotropy in LEO to surface charging and identifies
this property in the energetic electron distribution functions as inducing
potentially greater risks to satellites of electrical arcing and breakdown.",2310.11803v1
2024-01-25,Few-magnon excitations in a frustrated spin-$S$ ferromagnetic chain with single-ion anisotropy,"We study few-magnon excitations in a finite-size spin-$S$ chain with
ferromagnetic nearest-neighbor (NN) interaction $J>0$ and antiferromagnetic
next-nearest-neighbor (NNN) interaction $J'<0$, in the presence of the
single-ion (SI) anisotropy $D$. We first reveal the condition for the emergence
of zero-excitation-energy states. In the isotropic case with $\Delta=\Delta'=1$
($\Delta$ and $\Delta'$ are the corresponding anisotropy parameters), a
threshold of $J/|J'|$ above which the ground state is ferromagnetic is
determined by exact diagonalization for short chains up to $12$ sites. Using a
set of exact two-magnon Bloch states, we then map the two-magnon problem to a
single-particle one on an effective open chain with both NN and NNN hoppings.
The whole two-magnon excitation spectrum is calculated for large systems and
the commensurate-incommensurate transition in the lowest-lying mode is found to
exhibit different behaviors between $S=1/2$ and higher spins due to the
interplay of the SI anisotropy and the NNN interaction. For the commensurate
momentum $k=-\pi$, the effective lattice is decoupled into two NN open chains
that can be exactly solved via a plane-wave ansatz. Based on this, we
analytically identify in the $\Delta'-D/|J'|$ plane the regions supporting the
SI or NNN exchange two-magnon bound states near the edge of the band. In
particular, we prove that there always exists a lower-lying NN exchange
two-magnon bound state near the band edge for arbitrary $S\geq 1/2$. Finally,
we numerically calculate the $n$-magnon spectra for $S=1/2$ with $n\leq5$ by
using a spin-operator matrix element method. The corresponding $n$-magnon
commensurate instability regions are determined for finite chains and
consistent results with prior literature are observed.",2401.14101v2
2024-03-05,Anomalous continuum scattering and higher-order van Hove singularity in the strongly anisotropic S = 1/2 triangular lattice antiferromagnet,"The S = 1/2 triangular lattice antiferromagnet (TLAF) stands out as a
paradigmatic example of frustrated quantum magnetism. An ongoing challenge
involves understanding the influence of exchange anisotropy on the collective
behavior within such systems. Using inelastic neutron scattering (INS) and
advanced calculation techniques, we have studied the low and high temperature
spin dynamics of Ba2La2CoTe2O12 (BLCTO): a Co2+-based Jeff = 1/2 TLAF that
exhibits 120 deg order below TN = 3.26 K. The spin Hamiltonian was determined
by fitting the energy-resolved paramagnetic excitations measured at T > TN,
revealing an exceptionally strong easy-plane XXZ exchange anisotropy. Below TN,
the excitation spectrum exhibits a high energy continuum having a larger
spectral weight than the single-magnon modes. Combined with advanced
theoretical calculations of magnetic excitations based on magnons and spinons,
this observation suggests a scenario characterized by a spinon confinement
length that markedly exceeds the lattice spacing. We conjecture that this
phenomenon arises due to the proximity to a quantum melting point, which
persists even in the presence of strong easy-plane XXZ anisotropy. Finally, we
highlight characteristic flat features in the excitation spectrum, which are
connected to higher-order van Hove singularities in the magnon dispersion and
are directly induced by easy-plane XXZ anisotropy. Our results provide a rare
experimental insight into the nature of highly anisotropic S = 1/2 TLAFs
between the Heisenberg and XY limits.",2403.03210v1
1992-08-27,"COBE, Gravitational Waves, Inflation and Extended Inflation","We analyse the implications for inflationary models of the cosmic microwave
background (cmb) anisotropy measured by COBE. Vacuum fluctuations during
inflation generate an adiabatic density perturbation, and also gravitational
waves. The ratio of these two contributions to the cmb anisotropy is given for
an arbitrary slow-roll inflaton potential. Results from the IRAS/QDOT and
POTENT galaxy surveys are used to normalise the spectrum of the density
perturbation on the scale $20h^{-1}\Mpc$, so that the COBE measurement on the
scale $10^3h^{-1}\Mpc$ provides a lower bound on the spectral index $n$. For
`power law' and `extended' inflation, gravitational waves are significant and
the bound is $n>0.84$ at the $2$-sigma level. For `natural' inflation,
gravitational waves are negligible and the constraint is weakened to $n>0.70$,
at best marginally consistent with a recent proposal for explaining the excess
clustering observed in the APM galaxy survey. Many versions of extended
inflation, including those based on the Brans--Dicke theory, are ruled out,
because they require $n\lsim 0.75$ in order that bubbles formed at the end of
inflation should not be observed now in the cmb.",9208007v2
1993-01-07,Microwave Anisotropies in the Light of COBE,"The recent COBE measurement of anisotropies in the cosmic microwave
background and the recent South Pole experiment of Gaier {\it et al.} offer an
excellent opportunity to probe cosmological theories. We test a class of
theories in which the Universe today is flat and matter dominated, and
primordial perturbations are adiabatic parameterized by an index $n$. In this
class of theories the predicted signal in the South Pole experiment depends not
only on $n$, but also on the Hubble constant and the baryon density. For $n=1$
a large region of this parameter space is ruled out, but there is still a
window open which satisfies constraints coming from COBE, measurements of the
age of the Universe, the South Pole experiment, and big bang nucleosynthesis.
Using the central values of the Hubble constant and baryon density favored by
nucleosynthesis and age measurements, we find that, even if the COBE
normalization drops by $1\sigma$, $n > 1.2$ is ruled out.",9301002v1
1993-06-30,Tensor Perturbations in Inflationary Models as a Probe of Cosmology,"In principle, the tensor metric (gravity-wave) perturbations that arise in
inflationary models can, beyond probing the underlying inflationary model,
provide information about the Universe: ionization history, presence of a
cosmological constant, and epoch of matter-radiation equality. Because tensor
perturbations give rise to anisotropy of the cosmic background radiation (CBR)
solely through the Sachs-Wolfe effect we are able to calculate analytically the
variance of the multipole moments of this part of the CBR temperature
anisotropy. In so doing, we carefully take account of the contribution of
tensor perturbations that entered the Hubble radius during both the
matter-dominated and radiation-dominated epoch by means of a transfer function.
The striking feature in the spectrum of multipole amplitudes is a dramatic fall
off for $l\ga \sqrt{1+\zl}$, where $\zl$ is the red shift of the
last-scattering surface. ...",9306029v1
1993-11-02,Microwave Background Anisotropies in Primeval Isocurvature Baryon Models: Constraints on the Cosmological Parameters,"We have performed the most comprehensive predictions of the temperature
fluctuations \dtt in the primeval isocurvature baryon models to see whether or
not the models are consistent with the recent data on the cosmic microwave
background anisotropies. More specifically, we computed the \dtt corresponding
to the experimental set-up by the South-Pole and the Owens Valley experiments
as well as the COBE satellite. The amplitudes of the predicted \dtt are
normalized by means of the COBE 10$^\circ$ data. The resulting constraints on
the models are presented on $n - \Omega_b$ plane in the case of
$\lambda_0=1-\Omega_b$ (flat models) and $\lambda_0=0$ (open models), where $n$
is the primordial spectral index of entropy fluctuations and $\Omega_b$ is the
present baryon density parameter.
  Our results imply that the PIB models cannot be reconciled with the current
observations for any reasonable set of cosmological parameters.",9311012v1
1993-11-15,The Spatial Correlation Function from an X--ray Selected Sample of Abell Clusters,"We present here the Spatial Two--Point Correlation Function for a complete
sample of 67 X--ray selected Abell clusters of galaxies. We find a correlation
length of $16.1\pm3.4\mpc$ with no significant clustering beyond
$\simeq40\mpc$. This is the lowest uncorrected value for the correlation length
ever derived from the Abell catalogue of clusters. In addition, we have
investigated the anisotropy of the correlation function between the radial and
transverse directions. This can be characterised by the magnitude of pair--wise
cluster peculiar velocities such anisotropy predicts, which we find to be
$\simeq800{\rm km\,s^{-1}}$ for our sample. Again, this is the lowest
uncorrected value ever seen for the Abell catalogue. We therefore, no longer
need to invoke high cluster peculiar velocities or line of sight clustering to
understand the correlation function as derived from an Abell sample of
clusters. Furthermore, our result is consistent with recently published
correlation functions computed from automated selections of optical and X--ray
clusters. Therefore, we are now approaching a coherent picture for the form of
the cluster spatial correlation function which will be used to place confident
constraints on theories of galaxy formation.",9311033v1
1993-12-03,The Angular Bispectrum of The Cosmic Microwave Background,"COBE has provided us with a whole-sky map of the CBR anisotropies. However,
even if the noise level is negligible when the four year COBE data are
available, the cosmic variance will prevent us from obtaining information about
the Gaussian nature of the primordial fluctuations. This important issue is
addressed here by studying the angular bispectrum of the cosmic microwave
background anisotropies. A general form of the angular bispectrum is given and
the cosmic variance of the angular bispectrum for Gaussian fluctuations is
calculated. The advantage of using the angular bispectrum is that one can
choose to use the multipole moments which minimize the cosmic variance term.
The non-Gaussian signals in most physically motivated non-Gaussian models are
small compared with cosmic variance. Unless the amplitudes are large, the
non-Gaussian signals are only detectable in the COBE data in those models where
the angular bispectrum is flat or increases with increasing multipole moment.",9312004v2
1993-12-17,Anisotropy in the Angular Broadening of Sgr A$^*$ at the Galactic Center,"We present the results of a $\lambda$20 cm VLA observation of the compact
Galactic center radio source Sgr A$^*$. The scatter-broadened image is
elongated in the East-West direction, with an axial ratio of 0.6$\pm$0.05 and a
position angle of 87$^0\pm$3$^0$. A similar shape and orientation has been
found previously at shorter wavelengths using VLBI and VLBA. Both the major and
minor axes follow the $\lambda^2$ law appropriate for scattering by turbulence
in the intervening medium. Assuming that the anisotropy is caused by a magnetic
field permeating the scattering medium, we argue that the scattering occurs
within extended HII regions lying in the central 100 pc of the Galaxy. The
magnetic field in this region must be poloidal, organized and is estimated to
have a strength of at least 30 to 100 $\mu$Gauss.",9312040v1
1993-12-23,Dipole Anisotropy in the COBE DMR First-Year Sky Maps,"We present a determination of the cosmic microwave background dipole
amplitude and direction from the COBE Differential Microwave Radiometers (DMR)
first year of data. Data from the six DMR channels are consistent with a
Doppler-shifted Planck function of dipole amplitude Delta T = 3.365 +/-0.027 mK
toward direction (l,b) = (264.4 +/- 0.3 deg, 48.4 +/- 0.5 deg). The implied
velocity of the Local Group with respect to the CMB rest frame is 627 +/- 22
km/s toward (l,b) = (276 +/- 3 deg, 30 +/- 3 deg). DMR has also mapped the
dipole anisotropy resulting from the Earth's orbital motion about the Solar
system barycenter, yielding a measurement of the monopole CMB temperature at
31.5, 53, and 90 GHz, to be 2.75 +/- 0.05 K.",9312056v1
1994-01-11,Observational Constraints on the Spectral Index,"We address the possibility of bounding the spectral index $n$ of primordial
density fluctuations, using both the cosmic microwave background (cmb)
anisotropy and data on galaxies and clusters. Each piece of galaxy and cluster
data is reduced to a value of $\sigma(R)$ (the linearly evolved {\em rms}
density contrast with top hat smoothing on scale $R$) which allows data on
different scales to be readily compared. As a preliminary application, we
normalise the spectrum using the ten degree variance of the COBE data, and then
compare the prediction with a limited sample of low energy data, for the MDM
model with various values of $n$, $\Omega_\nu$ and $h$. With $h=.5$, the data
constrain the spectral index to the range $0.7\lsim n \lsim 1.2$. If
gravitational waves contribute to the cmb anisotropy with relative strength
$R=6(1-n)$ (as in some models of inflation), the lower limit on $n$ is
increased to about $0.85$. The uncertainty in $h$ widens this band by about
$0.1$ at either end.",9401014v2
1994-01-11,Angular Power Spectrum of the Microwave Background Anisotropy seen by the COBE Differential Microwave Radiometer,"The angular power spectrum estimator developed by Peebles (1973) and Hauser &
Peebles (1973) has been modified and applied to the 2 year maps produced by the
COBE DMR. The power spectrum of the real sky has been compared to the power
spectra of a large number of simulated random skies produced with noise equal
to the observed noise and primordial density fluctuation power spectra of power
law form, with $P(k) \propto k^n$. Within the limited range of spatial scales
covered by the COBE DMR, corresponding to spherical harmonic indices $3 \leq
\ell \lsim 30$, the best fitting value of the spectral index is $n =
1.25^{+0.4}_{-0.45}$ with the Harrison-Zeldovich value $n = 1$ approximately
0.5$\sigma$ below the best fit. For $3 \leq \ell \lsim 19$, the best fit is $n
= 1.46^{+0.39}_{-0.44}$. Comparing the COBE DMR $\Delta T/T$ at small $\ell$ to
the $\Delta T/T$ at $\ell \approx 50$ from degree scale anisotropy experiments
gives a smaller range of acceptable spectral indices which includes $n = 1$.",9401015v2
1994-02-11,Is a Massive Tau Neutrino Just What Cold Dark Matter Needs?,"The cold dark matter (CDM) scenario for structure formation in the Universe
is very attractive and has many successes; however, when its spectrum of
density perturbations is normalized to the COBE anisotropy measurement the
level of inhomogeneity predicted on small scales is too large. This can be
remedied by a tau neutrino of mass $1\MeV - 10\MeV$ and lifetime $0.1\sec -
100\sec$ whose decay products include electron neutrinos because it allows the
total energy density in relativistic particles to be doubled without
interfering with nucleosynthesis. The anisotropies predicted on the degree
scale for ``$\tau$CDM'' are larger than standard CDM. Experiments at $e^\pm$
colliders may be able to probe such a mass range.",9402028v1
1994-04-07,The Amplitude and Spectral Index of the Large Angular Scale Anisotropy in the Cosmic Microwave Background Radiation,"In many cosmological models, the large angular scale anisotropy in the cosmic
microwave background is parameterized by a spectral index, $n$, and a
quadrupolar amplitude, $Q$. For a Peebles-Harrison-Zel'dovich spectrum, $n=1$.
Using data from the Far Infra-Red Survey (FIRS) and a new statistical measure,
a contour plot of the likelihood for cosmological models for which $-1 < n < 3$
and $0 \le Q \le 50~\mu{\rm K}$ is obtained. We find that the likelihood is
maximum at $(n, Q) = (1.0, 19 uK)$. For constant $n$ the likelihood falls to
half its maximum at $Q \approx 14 uK$ and $25 uK$ and for constant $Q$ the
likelihood falls to half its maximum at $n \approx 0.5$ and $1.4$. Regardless
of $Q$, the likelihood is always less than half its maximum for $n < -0.4$ and
for $n > 2.2$, as it is for $Q < 8 uK$ and $Q > 44$.",9404009v1
1994-05-12,Black Hole Relics and Inflation: Limits on Blue Perturbation Spectra,"Blue primordial power spectra have spectral index $n>1$ and arise naturally
in the recently proposed hybrid inflationary scenario. An observational upper
limit on {\em n} is derived by normalizing the spectrum at the quadrupole scale
and considering the possible overproduction of Planck mass relics formed in the
final stage of primordial black hole evaporation. In the inflationary Universe
with the maximum reheating temperature compatible with the observed quadrupole
anisotropy, the upper limit is $n=1.4$, but it is slightly weaker for lower
reheat temperatures. This limit applies over 57 decades of mass and is
therefore insensitive to cosmic variance and any gravitational wave
contribution to the quadrupole anisotropy. It is also independent of the dark
matter content of the Universe and therefore the bias parameter. In some
circumstances, there may be an extended dust-like phase between the end of
inflation and reheating. In this case, primordial black holes form more
abundantly and the upper limit is $n=1.3$.",9405027v1
1994-06-14,Polarization and Anisotropy of the Microwave Sky,"We study the polarization-polarization and polarization-temperature
correlations in standard adiabatic scenarios for structure formation.
Temperature anisotropies due to gravitational potential wells and oscillations
in the photon-baryon-electron fluid on the surface of last scattering are each
associated with a correlated polarization pattern. While the `correlated part'
of the polarization has an r.m.s. of only a third of the total signal, it may
still be measurable by mapping a large area on the sky. We calculate the
expected signal to noise ratio for various measures of the polarization in a
hypothetical mapping experiment such as those now being planned.",9406046v2
1994-08-12,CMB Maps at 0.5 degree Resolution I: Full-Sky Simulations and Basic Results,"We have simulated full-sky maps of the Cosmic Microwave Background (CMB)
anisotropy expected from Cold Dark Matter (CDM) models at 0.5 and 1.0 degree
angular resolution. Statistical properties of the maps are presented as a
function of sky coverage, angular resolution, and instrument noise, and the
implications of these results for observability of the Doppler peak are
discussed. The rms fluctuations in a map are not a particularly robust probe of
the existence of a Doppler peak, however, a full correlation analysis can
provide reasonable sensitivity. We find that sensitivity to the Doppler peak
depends primarily on the fraction of sky covered, and only secondarily on the
angular resolution and noise level. Color plates and one-dimensional scans of
the maps are presented to visually illustrate the anisotropies.",9408037v1
1994-09-13,Optimizing Observing Patterns in Cosmic Microwave Background Radiation Anisotropy Experiments,"We consider several factors concerning the design of observing strategies in
Cosmic Microwave Background (CMB) anisotropy experiments. First we consider the
number of independent points on the sky one should observe given a fixed
observing time. Given an assumed level of sky temperature fluctuations,
$\sigma_{sky}$ and the presence of instrumental noise $s$ in units of K
s$^{-1/2}$ and a total observing time $t_{obs}$, we find there is an optimum
number of points in the sky to maximize the confidence level of a detection.
This number is a function of the signal to noise ratio $R^2 = \sigma_{sky}^2
t_{obs}/s^2$. We verify this analytical result with a monte carlo simulation,
which also includes the correlation between different positions in the sky.
Furthermore, using an $n=1$ spectrum of Gaussian fluctuations, we show that
arranging the observing patterns along a (great) circle, a raster scan, or a
randomized pattern yields results which are indistinguishable in Monte carlos.",9409031v1
1994-12-05,"Cosmological Inflation, Microwave Background Anisotropies and Large Scale Structure of the Universe","Cosmological inflation provides the simplest and most promising mechanism for
generating fluctuations for structure formation. Using powerful Hamilton-Jacobi
methods, I will describe (1) how to compute density fluctuations and cosmic
microwave anisotropies arising from inflation, and (2) improvements of the
Zel'dovich approximation describing gravitational collapse. I compare these
results with the latest cosmological observations.",9412012v2
1994-12-07,Degree Scale Anisotropy: Current Status,"The Cosmic Background Radiation gives us one of the few probes into the
density perturbations in the early universe that should later lead to the
formation of structure we now observe. Recent advances in degree scale
anisotropy measurements have allowed us to begin critically testing
cosmological models. Combined with the larger scale measurements from COBE we
are now able to directly compare data and theory. These measurements promise
future progress in understanding structure formation. Because of the extreme
sensitivities needed (1-10 ppm) and the difficulties of foreground sources,
these measurements require not only technological advances in detector and
measurement techniques, but multi spectral measurements and careful attention
to low level systematic errors. This field is advancing rapidly and is in a
true discovery mode. Our own group has been involved in a series of eleven
experiments over the last six years using the ACME (Advanced Cosmic Microwave
Explorer) payload which has made measurements at angular scales from 0.3 to 3
degrees and over a wavelength range from 1 to 10 mm. The recent data from these
and other measurements will be reviewed as well as some of the challenges and
potential involved in these and future measurements.",9412021v1
1994-12-09,No Very Large Scale Structure in an Open Universe,"We study the effects of negative spatial curvature on the statistics of
inhomogeneities in open cosmological models. In particular we examine the
suppression of large-separation correlations in density and gravitational
potential fluctuations and the resulting suppression of large-angle
correlations in the anisotropy of the microwave background radiation. We obtain
an expression which gives the {\it minimum} amount of suppression of
correlations for any statistical distribution described by a ``power
spectrum''. This minimum suppression requires that the correlations fall off
exponentially above the curvature scale. To the extent that the observed
correlations in the temperature anisotropy extend to large angular scales, one
can set a lower bound to the radius of curvature and hence on $\Omega_0$.",9412031v1
1995-01-10,COBE Constraints on Baryon Isocurvature Models,"We consider Bayesian constraints on standard isocurvature baryon models from
the slope and normalization of the anisotropy power spectrum detected by the
COBE DMR experiment in their two year maps. In conjunction with either the
amplitude of matter fluctuations $\sigma_8$ {\it or} its slope, all open models
are ruled out at greater than 95\% confidence, whereas cosmological constant
$\Lambda$ dominated models are constrained to be highly ionized. By including
the COBE FIRAS 95\% confidence upper limit on spectral distortion, we further
reduce the available parameter space for $\Lambda$ models by excluding these
highly ionized models. These constraints define a single class of barely viable
standard models which makes definite and testable predictions for degree scale
anisotropies and large scale structure.",9501034v1
1995-01-17,Velocity profiles of Osipkov-Merritt models,"A simple algorithm is presented for the calculation of the projected
line-of-sight velocity profiles (VPs) of non-rotating anisotropic spherical
stellar dynamical models with a phase-space distribution function of the
Osipkov-Merritt type. The velocity distribution in these models is isotropic
inside the anisotropy radius r_a and becomes increasingly radially biased at
larger radii. VP shape parameters are presented for a family of models in which
the luminous mass density has an r^{-gamma} power-law cusp at small radii and
an r^{-4} power-law fall-off at large radii. Self-consistent models and models
in which the luminous matter is embedded in a dark halo are discussed. The
effects of changes in the cusp slope gamma and in the anisotropy radius r_a are
documented, and the area in the (gamma,r_a)-plane that contains physical models
is delineated. The shapes of the VPs of the models show a considerable (and
observable) variation with projected galactocentric radius. These models will
be useful for interpreting the data on the VP shapes of elliptical galaxies
that are now becoming available.",9501054v1
1995-01-31,Large Angle CMB Anisotropy in an Open Universe in the One-Bubble Inflationary Scenario,"We consider an alternative scenario of inflation which can account for a
spatially open universe. It is similar to the old inflation in which the bubble
nucleation occurs in the sea of false vacuum, but differs from it in that the
second slow rollover inflation occurs inside a nucleated bubble. Hence our
observable universe is entirely contained in one nucleated bubble. The
significance of the scenario is that apart from a variance due to model
parameters it gives us a definite prediction on the spectrum of the primordial
density perturbations, hence is observationally testable. Here we investigate
the spectrum of CMB anisotropies on large angular scales. We find that the
contribution from peculiar modes which never appear in the usual harmonic
analysis is significant in the case $\Omega_0\lesssim0.1$.",9501109v1
1995-04-12,Parallel Linear General Relativity and CMB Anisotropies,"We have developed a code which links scalar-mode fluctuations in the early
universe with those observable at the present time by integrating the coupled,
linearized, Einstein, Boltzmann, and fluid equations in a perturbed flat
Robertson-Walker spacetime. The results are useful both for calculations of the
cosmic microwave background anisotropy and the linear power spectrum of matter
fluctuations. This paper introduces the serial and parallel codes, presents
timing results, and gives sample output in graphical and animated form.
  This is a latex version containing most of an HTML-format technical paper
submitted for Supercomputing '95. The preferred method of viewing is to point
your WWW client to http://arcturus.mit.edu/SC95/",9504040v1
1995-04-20,CBR Anisotropy and the Running of the Scalar Spectral Index,"Accurate ($\lesssim 1\% $) predictions for the anisotropy of the Cosmic
Background Radiation (CBR) are essential for using future high-resolution
($\lesssim 1^\circ$) CBR maps to test cosmological models. In many inflationary
models the variation (``running'') of the spectral index of the spectrum of
density perturbations is a significant effect and leads to changes of around
1\% to 10\% in the CBR power spectrum. We propose a general method for taking
running into account which uses the derivative of the spectral index ($dn/d\ln
k$). Conversely, high-resolution CBR maps may be able to determine $dn/d\ln k$,
giving important information about the inflationary potential.",9504071v2
1995-07-12,Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions. I. Pre-Collapse Evolution,"The evolution of a spherical single-mass star cluster is followed in detail
up to core collapse by numerically solving the orbit-averaged two-dimensional
Fokker-Planck equation in energy-angular momentum space. Velocity anisotropy is
allowed in the two-dimensional Fokker-Planck model. Using improved numerical
codes, the evolution has been followed until the central density increased by a
factor of $10^{14}$ with high numerical accuracy. The numerical results clearly
show self-similar evolution of the core during the late stages of the core
collapse. When Plummer's model is chosen as the initial condition, the collapse
time is about 17.6 times the initial half-mass relaxation time. This is longer
than the collapse time for the isotropic model by about 13%. As the result of
strong relaxation in the core, the halo becomes to be dominated by radial
orbits. The degree of anisotropy monotonically increases as the radius
increases.",9507040v1
1995-08-26,Wandering in the Background: A CMB Explorer,"We develop and examine the principles governing the formation of distortions
in the cosmic microwave background. Distortions in the frequency or spectral
distribution of the background probe the thermal history of the universe
whereas those in the angular temperature distribution probe its dynamics and
geometry. Stressing model independent results, we show how the microwave
background can be used to extract information on the mass density, vacuum
density, baryon content, radiation content, expansion rate and some aspects of
structure formation in the universe. To address these issues, we systematically
develop relativistic kinetic and perturbation theory addressing issues such as
fluctuation representation, or gauge, normal mode analysis in an open geometry,
and second order effects. Through analytic and numerical results, we construct
anisotropies in a critical, open, or cosmological constant universe with
adiabatic and/or isocurvature initial conditions allowing for possible early
reionization. We find that anisotropy formation is a simple process governed by
the Compton scattering of photons and electrons and their gravitational
coupling to the other particle species in the universe.",9508126v2
1995-08-31,Why Not Consider Closed Universes?,"We consider structure formation and CMB anisotropies in a closed universe,
both with and without a cosmological constant. The CMB angular power spectrum
and the matter transfer function are presented, along with a discussion of
their relative normalization. This represents the first full numerical
evolution of density perturbations and anisotropies in a spherical geometry. We
extend the likelihood function vs. Omega from the COBE 2-year data to Omega>=1.
For large Omega the presence of a very steep rise in the spectrum towards low
ell allows us to put an upper limit of Omega<=1.5 (95%CL) for primordial
spectra with n<=1. This compares favorably with existing limits on Omega. We
show that there are a range of closed models which are consistent with
observational constraints while being even older than the currently popular
flat models with a cosmological constant. Future constraints from degree scale
CMB data may soon probe this region of parameter space. A derivation of the
perturbed Einstein, fluid and Boltzmann equations for open and closed
geometries is presented in an appendix.",9508157v1
1995-10-13,Looking for $Λ$ with the Rees-Sciama Effect,"In models with a cosmological constant, a significant component of the large
scale cosmic microwave background (CMB) anisotropy is produced at rather low
redshifts, z < 1. In these models, the gravitational potential perturbations
begin to evolve at late times. Photons passing through these time varying
potentials aquire frequency shifts, an effect first noted by Rees and Sciama.
Since the gravitational potential is associated with matter at observable
redshifts, the local matter density (or some tracer thereof) is correlated with
the CMB anisotropy on the sky. We outline the optimal method of measuring this
correlation, and discuss the prospects for using an X-ray/COBE comparison to
detect a cosmological constant.",9510072v1
1995-10-19,Microlensing rates from self-consistent galactic models,"We study different models of dark matter distribution for the halo of our
galaxy. In particular, we consider Eddington and King-Michie models, which
[C[C, which include anisotropy in the velocity space, and compute in a
self-consistent way the amount of dark matter present in the halo. Assuming
that the dark matter is in form of MACHOs, we find for each model the expected
number of microlensing events and their average time duration for an experiment
monitoring stars in the LMC. The main effect of including anisotropy is to
reduce the microlensing rate by about 30% and to increase, but only slightly,
the mean event duration as compared to the standard halo model. Consideration
of different luminous models for the visible part of the galaxy also induce
variations in the microlensing results by roughly the same amount as mentioned
above. The main uncertainty, in order to be able to discriminate between
different dark matter distributions and to estimate the fraction of it in form
of MACHOs is due to the poor knowledge of the rotation velocity at large
galactocentric distances.",9510099v1
1995-12-20,A Fast and Accurate Algorithm for Computing Tensor CBR Anisotropy,"Inflation gives rise to a nearly scale-invariant spectrum of tensor
perturbations (gravitational waves), their contribution to the Cosmic
Background Radiation (CBR) anisotropy depends upon the present cosmological
parameters as well as inflationary parameters. The analysis of a
sampling-variance-limited CBR map offers the most promising means of detecting
tensor perturbations, but will require evaluation of the predicted multipole
spectrum for a very large number of cosmological parameter sets. We present
accurate polynomial formulae for computing the predicted variance of the
multipole moments in terms of the cosmological parameters $\Omega_\Lambda$,
$\Omega_0h^2$, $\Omega_B h^2$, $N_{\nu}$, and the power-law index $n_T$ which
are accurate to about 1\% for $l\le 50$ and to better than 3\% for $50< l \le
100$ (as compared to the numerical results of a Boltzmann code).",9512140v1
1995-12-22,Dependence of Inflationary Reconstruction upon Cosmological Parameters,"The inflationary potential and its derivatives determine the spectrum of
scalar and tensor metric perturbations that arise from quantum fluctuations
during inflation. The CBR anisotropy offers a promising means of determining
the spectra of metric perturbations and thereby a means of constraining the
inflationary potential. The relation between the metric perturbations and CBR
anisotropy depends upon cosmological parameters -- most notably the possibility
of a cosmological constant. Motivated by some observational evidence for a
cosmological constant (large-scale structure, cluster-baryon fraction,
measurements of the Hubble constant and age of the Universe) we derive the
reconstruction equations and consistency relation to second order in the
presence of a cosmological constant. We also clarify previous notation and
discuss alternative schemes for reconstruction.",9512155v1
1996-01-12,RMS Anisotropy in the COBE-DMR Four-Year Sky Maps,"The sky-RMS is the simplest model-independent characterization of a
cosmological anisotropy signal. The RMS temperature fluctuations determined
from the $COBE$-DMR four-year sky maps are frequency independent, consistent
with the hypothesis that they are cosmological in origin, with a typical
amplitude at 7 degrees of ~ 35 \pm\ 2 uK and at 10 degrees of ~29 \pm\ 1 uK. A
joint analysis of the 7 deg and 10 deg ""cross""-RMS derived from the data in
both Galactic and Ecliptic coordinates is used to determine the RMS quadrupole
normalization, $Q_{rms-PS}$, for a scale-invariant Harrison-Zel'dovich power
law model. The difference in the inferred normalizations either including or
excluding the quadrupole is a consequence of the sensitivity of the method to
the Galaxy contaminated observed sky quadrupole. Whilst there are variations
depending on the data selection, all results are consistent with an inferred
\qrms\ normalization of ~18 \pm\ 2 uK.",9601065v1
1996-01-19,The Tilt of the Fundamental Plane of Elliptical Galaxies: I. Dynamical and Structural Effects,"In this paper we explore several structural and dynamical effects on the
projected velocity dispersion as possible causes of the fundamental plane (FP)
tilt of elliptical galaxies. Specifically, we determine the size of the
systematic trend along the FP in the orbital radial anisotropy, in the dark
matter (DM) content and distribution relative to the bright matter, and in the
shape of the light profile that would be needed to produce the tilt, under the
assumption of a constant stellar mass to light ratio. Spherical, non rotating,
two--components models are constructed, where the light profiles resemble the
$R^{1/4}$ law. For the investigated models anisotropy cannot play a major role
in causing the tilt, while a systematic increase in the DM content and/or
concentration may formally produce it. Also a suitable variation of the shape
of the light profile can produce the desired effect, and there may be some
observational hints supporting this possibility. However, fine tuning is always
required in order to produce the tilt, while preserving the {\it tightness} of
the galaxies distribution about the FP.",9601100v1
1996-01-30,The Impact of the CMB on Large-Scale Structure,"The COBE detection of microwave anisotropies provides the best way of fixing
the amplitude of cosmological fluctuations on the largest scales. We discuss
the impact of this new, precise normalization and give fitting formulae for the
horizon-crossing amplitude as a function of \Omega_0 and n for both open and
flat cosmologies. We also discuss the relevant normalization (\sigma_8) at
galaxy-clustering scales. Already it is clear that the inferred \sigma_8 can be
unnaccepatably high for some of the simplest inflationary models, although many
minor variants give an adequate fit. Generic topological defect models appear
to fare rather badly, and it is unclear whether minor variants or improved
calculations will help much. The detection and mapping of structure in the CMB
anisotropy spectrum on smaller scales in the near future will enable us to
achieve much stronger constraints on models.",9601170v1
1996-02-07,Anisotropic Observations in Universes with Nonlinear Inhomogeneity,"We calculate the off--center observational relations in a spherically
symmetric dust universe that is inhomogeneous at small redshifts. In contrast
to the usual model, in which the CMBR dipole is interpreted as a Doppler effect
due to peculiar velocity, our model explores an alternative interpretation, in
which the CMBR dipole is non--Doppler, and the observer is comoving with the
mean matter flow. We do not assume a background frame relative to which
peculiar velocities are calculated. Our analysis is fully nonlinear and the
density contrast is not assumed to be small. We obtain exact expressions for
the Hubble and deceleration parameters, and find that both parameters have
quadrupole anisotropies, but no dipoles. A simple numerical procedure for
calculating the CMBR dipole anisotropy in our model is presented, and the
observed 0.1% dipole is shown to be reproducible with a reasonable choices of
parameters.",9602033v1
1996-02-08,Probing the dynamics of cluster-lenses,"We propose a new approach to study the dynamical implications of mass models
of clusters for the velocity structure of galaxies in the core. Strong and weak
lensing data are used to construct the total mass profile of the cluster, which
is used in conjunction with the optical galaxy data to solve in detail for the
nature of galaxy orbits and the velocity anisotropy in the central regions. We
also examine other observationally and physically motivated mass models,
specifically those obtained from X-ray observations and N-body simulations. The
aim of this analysis is to understand qualitatively the structure of the core
and test some of the key assumptions of the standard picture of cluster
formation regarding relaxation, virialization and equilibrium. This technique
is applied to the cluster Abell 2218, where we find evidence for an anisotropic
core, which we interpret to indicate the existence of a dynamically disturbed
central region. We find that the requirement of physically meaningful solutions
for the velocity anisotropy places stringent bounds on the slope of cluster
density profiles in the inner regions.",9602035v2
1996-04-11,Microwave Background Anisotropies Due to the Kinematic Sunyaev-Zel'dovich Effect of the Lyman-alpha Forest,"The Lyman-alpha absorption systems observed in the spectra of QSOs are likely
to possess bulk peculiar velocities. The free electrons in these systems
scatter the microwave background and distort its spectrum through the kinematic
Sunyaev-Zel'dovich effect. I calculate the temperature fluctuations of the
microwave sky due to variations in the number of Lyman-alpha systems along
different lines-of-sight throughout the universe. The known population of
absorbers out to z=5 introduces anisotropies on angular scales <1' with an rms
amplitude of order (DeltaT/T)= 10^{-6}*(Omega_Lya/0.05)*(v/400km/s), where
Omega_Lya is the cosmological density parameter of ionized gas in Lyman-alpha
absorption systems, and v is the rms line-of-sight peculiar velocity of these
systems at z=3. Detection of this signal will provide valuable information
about the cosmic velocity field and the gas content of Lyman-alpha absorption
systems at high redshifts.",9604060v1
1996-04-18,Structure Formation in Inflationary Cosmologies,"A brief account is given of large-scale structure modelling based on the
assumption that the initial perturbations arise from inflation. A recap is made
of the implications of inflation for large-scale structure; under the widely
applicable slow-roll paradigm inflation adds precisely two extra parameters to
the normal scenarios, which can be taken to be the tilt of the density
perturbation spectrum and the amplitude of gravitational waves. Some comments
are made about the {\it COBE} normalization. A short description is given of an
analysis combining cosmic microwave background anisotropy data and large-scale
structure data to constrain cosmological parameters, and the case of cold dark
matter models with a cosmological constant is used as a specific illustration.",9604105v1
1996-04-25,A Detection of Bright Features in the Microwave Background,"We report the characterization of bright, compact features in the cosmic
microwave background radiation (CMBR) detected during the June 1992 and June
1994 balloon flights of the Medium Scale Anisotropy Measurement (MSAM1-92 and
MSAM1-94, respectively). Spectral flux densities are determined for each
feature at 5.7, 9.3, and 16.5 cm$^{-1}$. No viable counterparts for these
features were found in source catalogs at 5 GHz or at 100 $\mu$m. The measured
spectrum of each feature is consistent with a temperature fluctuation in the
CMBR. The existence of these features is consistent with adiabatic fluctuation
models of anisotropy in the CMBR.",9604155v1
1996-08-08,Could a Local Group X-Ray Halo Affect the X-Ray and Microwave Backgrounds?,"Suto et al. (1996, astro-ph/9602061 and ApJ, 461, L33) have suggested that an
X-ray halo in the Local Group might explain both the observed low-energy excess
in the X-ray background and the quadrupole anisotropy in the cosmic microwave
background. Recent observations of poor groups of galaxies by the ROSAT PSPC
set reasonable limits on how extensive and dense such a halo could be. The poor
groups most similar to the Local Group do not have a detectable halo, and the
upper limits of these observations suggest that any Local Group halo would be
nearly two orders of magnitude too tenuous to produce the effects Suto et al.
(1996) discuss. In particular, the Sunyaev-Zel'dovich effect cannot contribute
significantly to the quadrupole anisotropy measured by COBE.",9608039v1
1996-10-21,Testing the effect of geodesic mixing with COBE data to Reveal the Curvature of the Universe,"When considering the statistical properties of a bundle of cosmic microwave
background (CMB) photons propagating through space, the effect of `mixing
geodesics' appears with a distinct signature that depends on the geometry of
space. In a Universe with negative curvature this effect is expected to produce
elongated anisotropy spots on CMB maps. We used COBE-DMR data to look for such
effect. Based on the analysis of a measure of eccentricity of hot spots it
appears that there is a clear indication of an excess eccentricity of hot spots
with respect to that expected from noise alone. This result must be interpreted
with caution as this effect can be due in part to galactic emission. If the
detected eccentricity of anisotropy spots can be attributed to the effect of
mixing it implies the negative curvature of the Universe and a value of $\Omega
< 1$.",9610152v1
1996-11-20,"Microlensing, or Galactic Twinkling","Microlensing has established itself as a powerful new method for the
detection of baryonic dark matter in the Galaxy. The theory of microlensing is
sketched and its similarity with the optical effect of twinkling is explained.
The bulk of the article presents a new analysis of the data-set on microlensing
towards the Large Magellanic Cloud. The extent, flattening and velocity
anisotropy of the Galactic halo are unknown. So, it is vital to analyse the
microlensing data-set with families of models that span the viable ranges of
these structural parameters. Also crucial is proper modelling of the dark
matter halo of the Large Magellanic Cloud. Despite all the unknowns, a robust
conclusion is that the Galactic and LMC haloes cannot be primarily built from
objects in the mass range 10^{-7} - 0.1 solar masses. The baryonic fraction of
the Galactic halo probably lies in the range 0.4 - 0.5. The mass of the
deflectors probably lies between 0.05 - 1.0 solar masses. Stronger claims
concerning the masses of the dark objects are unwarranted because the estimates
are sensitive to the uncertain velocity anisotropy.",9611161v1
1996-11-26,Results from CAT and prospects for the VSA,"We have produced an image of the microwave sky with 30' resolution in a 2
degree field using the Cosmic Anisotropy Telescope (CAT). Analysis of data
taken at three frequencies near 15 GHz indicates that most of the signal is due
to the CMB, with an equivalent broad-band power of Delta T/T = 1.9 +/- 0.5 x
10^{-5} at angular scales corresponding to multipoles l = 320-500, and Delta
T/T = 1.8 (+0.7 -0.5) x 10^{-5} at l = 500-680. We are now building a more
advanced instrument, the Very Small Array (VSA), which will cover the range l =
130-1800 with a sensitivity per resolution element of Delta T/T ~ 10^{-6}.",9611212v1
1996-12-11,Peaks in the Cosmic Microwave Background: flat versus open models,"We present properties of the peaks (maxima) of the CMB anisotropies expected
in flat and open CDM models. We obtain analytical expressions of several
topological descriptors: mean number of maxima and the probability distribution
of the gaussian curvature and the eccentricity of the peaks. These quantities
are calculated as functions of the radiation power spectrum, assuming a
gaussian distribution of temperature anisotropies. We present results for
angular resolutions ranging from 5' to 20' (antenna FWHM), scales that are
relevant for the MAP and COBRAS/SAMBA space missions and the ground-based
interferometer experiments. Our analysis also includes the effects of noise. We
find that the number of peaks can discriminate between standard CDM models, and
that the gaussian curvature distribution provides a useful test for these
various models, whereas the eccentricity distribution can not distinguish
between them.",9612114v1
1997-01-15,Limits to Global Rotation and Shear From the COBE DMR 4-Year Sky Maps,"Small departures from a homogeneous isotropic spacetime create observable
features in the large-scale anisotropy of the cosmic microwave background. We
cross-correlate the maps of the cosmic microwave background anisotropy from the
Cosmic Background Explorer (COBE) Differential Microwave Radiometers (DMR)
4-year data set with template maps from Bianchi VII_h cosmological models to
limit global rotation or shear in the early universe. On the largest scales,
spacetime is well described by the Friedmann-Robertson-Walker metric, with
departures from isotropy about each spatial point limited to shear sigma/H_0 <
10^{-9} and rotation omega/H_0 < 6 x 10^{-8} for 0.1 < Omega_0 < 1.",9701090v1
1997-02-12,Forecasting Cosmic Parameter Errors from Microwave Background Anisotropy Experiments,"Accurate measurements of the cosmic microwave background (CMB) anisotropies
with an angular resolution of a few arcminutes can be used to determine
fundamental cosmological parameters such as the densities of baryons, cold and
hot dark matter, and certain combinations of the cosmological constant and the
curvature of the Universe to percent-level precision. Assuming the true theory
is a variant of inflationary cold dark matter cosmologies, we calculate the
accuracy with which cosmological parameters can be determined by the next
generation of CMB satellites, MAP and Planck. We pay special attention to: (a)
the accuracy of the computed derivatives of the CMB power spectrum C_L; (b) the
number and choices of parameters; (c) the inclusion of prior knowledge of the
values of various parameters.",9702100v2
1997-02-23,On classical anisotropies in models of Open Inflation,"In the simplest model of open inflation there are two inflaton fields
decoupled from each other. One of them, the tunneling field, produces a first
stage of inflation which prepares the ground for the nucleation of a highly
symmetric bubble. The other, a free field, drives a second period of slow roll
inflation inside the bubble. However, the second field also evolves during the
first stage of inflation, which to some extent breaks the needed symmetry. We
show that this generates large supercurvature anisotropies which, together with
the results of Tanaka and Sasaki, rule out this class of simple models (unless,
of course, $\Omega_0$ is sufficiently close to one.) The problem does not arise
in modified models where the second field does not evolve in the first stage of
inflation.",9702201v2
1997-02-26,The Effect of Weak Gravitational Lensing on the Cosmic Microwave Background Anisotropy: Flat versus Open Universes,"We have studied the effect of gravitational lensing on the Cosmic Microwave
Background (CMB) anisotropy in flat and open universes. We develop a formalism
to calculate the changes on the radiation power spectrum induced by lensing in
the Newtonian and synchronous-comoving gauges. The previously considered
negligible contribution to the CMB radiation power spectrum of the anisotropic
term of the lensing correlation is shown to be appreciable. However,
considering the nonlinear evolution of the matter power spectrum produces only
slight differences on the results based on linear evolution. The general
conclusion for flat as well as open universes is that lensing slightly smoothes
the radiation power spectrum. For a given range of multipoles the effect of
lensing increases with Omega but for the same acoustic peak it decreases with
$\Omega$. The maximum contribution of lensing to the radiation power spectrum
for $l\leq 2000$ is $\sim$ 5% for $\Omega$ values in the range 0.1-1.",9702231v1
1997-03-28,Inflation: From Theory to Observation and Back,"Alan Guth introduced cosmologists to inflation at the 1980 Texas Symposium.
Since, inflation has had almost as much impact on cosmology as the big-bang
model itself. However, unlike the big-bang model, it has little observational
support. Hopefully, that situation is about to change as a variety and
abundance of data begin to test inflation in a significant way. The
observations that are putting inflation to test involve the formation of
structure in the Universe, especially measurements of the anisotropy of the
cosmic background radiation. The cold dark matter models of structure formation
motivated by inflation are holding up well as the observational tests become
sharper. In the next decade inflation will be tested even more significantly,
with more precise measurements of CBR anisotropy, the mean density of the
Universe, the Hubble constant, and the distribution of matter, as well as
sensitive searches for the nonbaryonic dark matter predicted to exist by
inflation. As an optimist I believe that we may be well on our way to a
standard cosmology that includes inflation and extends back to around 10^{-32}
sec, providing an important window on the earliest moments and fundamental
physics.",9703194v1
1997-04-09,Ribbons on the CBR Sky: A Powerful Test of a Baryon Symmetric Universe,"If the Universe consists of domains of matter and antimatter, annihilations
at domain interfaces leave a distinctive imprint on the Cosmic Background
Radiation (CBR) sky. The signature is anisotropies in the form of long, thin
ribbons of width $\theta_W\sim 0.1^\circ$, separated by angle $\theta_L\simeq
1^\circ(L/100h^{-1}{Mpc})$ where L is the characteristic domain size, and
y-distortion parameter $y \approx 10^{-6}$. Such a pattern could potentially be
detected by the high-resolution CBR anisotropy experiments planned for the next
decade, and such experiments may finally settle the question of whether or not
our Hubble volume is baryon symmetric.",9704070v2
1997-08-06,Cosmic Strings in an Open Universe: Quantitative Evolution and Observational Consequences,"The cosmic string scenario in an open universe is developed -- including the
equations of motion, a model of network evolution, the large angular scale CMB
temperature anisotropy, and the power spectrum of density fluctuations produced
by cosmic strings with dark matter. First we derive the equations of motion for
cosmic string in an open FRW space-time and construct a quantitative model of
the evolution of the gross features of a cosmic string network. Second, we
apply this model of network evolution to estimate the rms CMB temperature
anisotropy induced by cosmic strings, obtaining the normalization for the mass
per unit length $\mu$ as a function of $\Omega$. Third, we consider the effects
of the network evolution and normalization in an open universe on the large
scale structure formation scenarios with either cold or hot dark matter.",9708057v1
1997-08-13,A built-in scale in the initial spectrum of density perturbations: evidence from cluster and CMB data,"We calculate temperature anisotropies of the cosmic microwave background
(CMB) for several initial power spectra of density perturbations with a
built-in scale suggested by recent optical data on the spatial distribution of
rich clusters of galaxies. Using cosmological models with different values of
spectral index, baryon fraction, Hubble constant and cosmological constant, we
compare the calculated radiation power spectrum with the CMB temperature
anisotropies measured by the Saskatoon experiment. We show that spectra with a
sharp peak at 120 h^{-1} Mpc are in agreement with the Saskatoon data. The
combined evidence from cluster and CMB data favours the presence of a peak and
a subsequent break in the initial matter power spectrum. Such feature is
similar to the prediction of an inflationary model where an inflaton field is
evolving through a kink in the potential.",9708128v1
1997-09-03,On the Problem of Predicting Inflationary Perturbations,"We examine the theoretical foundations of standard methods for computing
density perturbations in inflationary models. We find that: (1) the time-delay
formalism (introduced by Guth and Pi, 1982) is only valid when inflation is
well-described by the de Sitter solution and the equation-of-state is nearly
unchanging; and, (2) the horizon-crossing/Bessel approximation extends to
non-exponential inflation, but only if the equation-of-state is changing
slowly. Integration of the gauge-invariant perturbation equations mode-by-mode
is the only method reliable for general models. For models with rapidly varying
equation-of-state, the correction leads to significantly different predictions
for the microwave background anisotropy. An important corollary is that methods
proposed for ""reconstruction"" of the inflaton potential from anisotropy data
are unreliable for general models.",9709032v1
1997-10-08,CMB anisotropy predictions for a model of double inflation,"We consider a double-inflationary model with two massive scalar fields
interacting only gravitationally in the context of a flat cold dark matter
(CDM) Universe. The cosmic microwave background (CMB) temperature anisotropies
produced in this theory are investigated in great details for a window of
parameters where the density fluctuation power spectrum P(k) is in good
agreement with observations. The first Doppler (``acoustic'') peak is a crucial
test for this model as well as for other models. For the ``standard'' values of
the cosmological parameters of CDM, our model is excluded if the height of the
Doppler peak is sensibly higher than about three times the Sachs-Wolfe plateau.",9710083v2
1997-10-16,Minkowski Functionals used in the Morphological Analysis of Cosmic Microwave Background Anisotropy Maps,"We present a novel approach to quantifying the morphology of Cosmic Microwave
Background (CMB) anisotropy maps. As morphological descriptors, we use shape
parameters known as Minkowski functionals. Using the mathematical framework
provided by the theory of integral geometry on arbitrary curved supports, we
point out the differences to their characterization and interpretation in the
case of flat space. With restrictions of real data -- such as pixelization and
incomplete sky coverage, to mention just a few -- in mind, we derive and test
unbiased estimators for all Minkowski functionals. Various examples, among them
the analysis of the four-year COBE DMR data, illustrate the application of our
method.",9710185v2
1997-10-30,Circular scans for CMB anisotropy observation and analysis,"A number of experiments for measuring anisotropies of the Cosmic Microwave
Background use scanning strategies in which temperature fluctuations are
measured along circular scans on the sky. It is possible, from a large number
of such intersecting circular scans, to build two-dimensional sky maps for
subsequent analysis. However, since instrumental effects --- especially the
excess low-frequency 1/f noise --- project onto such two-dimensional maps in a
non-trivial way, we discuss the analysis approach which focuses on information
contained in the individual circular scans. This natural way of looking at CMB
data from experiments scanning on the circles combines the advantages of
elegant simplicity of Fourier series for the computation of statistics useful
for constraining cosmological scenarios,and superior efficiency in analysing
and quantifying most of the crucial instrumental effects.",9710349v1
1998-01-24,Structure Formation with Generalized Dark Matter,"The next generation of cosmic microwave background (CMB) experiments, galaxy
surveys, and high-redshift observations can potentially determine the nature of
the dark matter observationally. With this in mind, we introduce a
phenomenological model for a generalized dark matter (GDM) component and
discuss its effect on large-scale structure and CMB anisotropies. Specifying
the gravitational influence of the otherwise non-interacting GDM requires not
merely a model for its equation of state but one for its full stress tensor.
  From consideration of symmetries, conservation laws, and gauge invariance, we
construct a simple but powerful 3 component parameterization of these stresses
that exposes the new phenomena produced by GDM. Limiting cases include: a
particle component (e.g. WIMPS, radiation or massive neutrinos), a cosmological
constant, and a scalar field component. Intermediate cases illustrate how the
clustering properties of the dark matter can be specified independently of its
equation of state. This freedom allows one to alter the amplitude and features
in the matter power spectrum relative to those of the CMB anisotropies while
leaving the background cosmology fixed. Conversely, observational constraints
on such properties can help determine the nature of the dark matter.",9801234v2
1998-01-28,Large-Scale Coherent Dipole Anisotropy ?,"We have reanalyzed and compared the dipoles of the 1.2 Jy and 0.6 Jy (QDOT)
IRAS galaxy samples. We find strong indications from both samples for (a)
significant contributions to the gravitational field that shapes the Local
Group motion from depths up to $\sim 170$ $h^{-1}$ Mpc and (b) a large-scale
coherence of the dipole anisotropy, indications provided mainly by the fact
that the differential dipoles of large equal volume shells are aligned with the
CMB dipole and exhibit significant dipole signals. The two IRAS dipoles are
indistinguishable within 50 $h^{-1}$ Mpc and beyond $\sim 130$ $h^{-1}$ Mpc
while the QDOT dipole, having a lower flux limit, continues growing with
respect to the 1.2 Jy sample up to $\sim 100$ $h^{-1}$ Mpc in agreement with
Rowan-Robinson et al (1990). The most probable cause of these deep dipole
contributions is the Shapley mass concentration.",9801271v1
1998-03-21,Evidence for non-Gaussianity in the COBE DMR Four Year Sky Maps,"We introduce and study the distribution of an estimator for the normalized
bispectrum of the Cosmic Microwave Background (CMB) anisotropy. We use it to
construct a goodness of fit statistic to test the coadded 53 and 90 GHz
COBE-DMR 4 year maps for non-Gaussianity. Our results indicate that Gaussianity
is ruled out at the confidence level in excess of 98%. This value is a lower
bound, given all the investigated systematics. The dominant non-Gaussian
contribution is found near the multipole of order $\ell=16$. Our attempts to
explain this effect as caused by the diffuse foreground emission from the
Galaxy have failed. We conclude that unless there exists a microwave foreground
emission which spatially correlates neither with the DIRBE nor Haslam maps, the
cosmological CMB anisotropy is genuinely non-Gaussian.",9803256v2
1998-03-23,Microwave Background Signals from Tangled Magnetic Fields,"An inhomogeneous cosmological magnetic field will create Alfven-wave modes
that induce a small rotational velocity perturbation on the last scattering
surface of the microwave background radiation. The Alfven-wave mode survives
Silk damping on much smaller scales than the compressional modes. This, in
combination with its rotational nature, ensures that there will be no sharp
cut-off in anisotropy on arc-minute scales. We estimate that a magnetic field
which redshifts to a present value of $3\times 10^{-9}$ Gauss produces
temperature anisotropies at the 10 micro Kelvin level at and below 10 arc-min
scales. A tangled magnetic field, which is large enough to influence the
formation of large scale structure is therefore potentially detectable by
future observations.",9803261v1
1998-05-04,The Impact of Inhomogeneous Reionization on Cosmic Microwave Background Anisotropy,"Hydrogen atoms in the Universe that initially formed at redshift z = 1100
were reionized at 5 < z < 60. It is likely that this transition proceeded
through a mixed phase of partial ionization. We develop an analytic approach to
calculating the effect on the cosmic microwave background (CMB) of Thomson
scattering off this inhomogeneous distribution of free electrons. We study two
models of the reionization process, one of which associates ionized patches
with overdense regions of the smoothed density field. We find the generated
anisotropy to have a power spectrum which peaks at angular scales corresponding
to the extent of the ionized regions, and has a width that reflects the
correlations between them. There is considerable uncertainty in the amplitude,
which depends on how efficiently collapsed objects can reionize the surrounding
medium. We calculate the effect of neglecting inhomogeneous reionization in the
determination of cosmological parameters from high resolution CMB maps and find
that it may be a significant source of systematic error.",9805012v2
1998-05-19,Australia Telescope Search for Cosmic Microwave Background Anisotropy,"We have made an 8.7 GHz image of a sky region with a resolution of 8 arcmin
and high brightness sensitivity using the Australia Telescope Compact Array
(ATCA). in an ultra compact configuration. The foreground discrete-source
confusion was estimated from observations with higher resolution at the same
frequency and in a scaled array at a lower frequency. Following the subtraction
of the foreground confusion, the field shows no features in excess of the
instrument noise. This limits the CMB anisotropy flat-band power to Q_flat <
23.6 microK with 95 per cent confidence; the ATCA filter function F_l in
multipole l-space peaks at l_eff = 4700 and has half maximum values at l = 3350
and 6050.",9805245v1
1998-05-22,Gravitational lensing of cosmic microwave background anisotropies and cosmological parameter estimation,"Gravitational lensing, caused by matter perturbations along the line-of-sight
to the last scattering surface, can modify the shape of the cosmic microwave
background (CMB) anisotropy power spectrum. We discuss the detectability of
lensing distortions to the temperature, polarisation and
temperature-polarisation cross-correlation power spectra and we analyse how
lensing might affect the estimation of cosmological parameters. For cold dark
matter-like models with present-day matter power spectra normalised to match
the abundances of rich clusters of galaxies, gravitational lensing causes
detectable distortions to cosmic variance limited CMB experiments sampling high
multipoles (l > 1000). Gravitational lensing of the CMB, although a small
effect, allows independent determinations of the curvature of the universe and
the cosmological constant, i.e. breaking the so-called geometrical degeneracy
in CMB parameter estimation discussed by Bond, Efstathiou and Tegmark (1997)
and Zaldarriaga, Spergel and Seljak (1997). Gravitational lensing of the CMB
temperature and polarisation patterns should be detectable by the Planck
Surveyor satellite leading to useful independent constraints on the
cosmological constant and spatial curvature.",9805294v2
1998-06-08,Cosmic strings in a universe with non-critical matter density,"In the light of recent work which suggests that structure formation by cosmic
strings in a critical matter density universe requires large biases, we discuss
the effects of reducing the matter density. Using a full linear
Einstein-Boltzmann solver, we com pute the cold dark matter density field and
the microwave background anisotropies/polarization in a flat universe with a
non-zero cosmological constant. We find that universes with
$\Omega_{\Lambda}=0.7-0.8$ give a good fit to the shape of the observed ga laxy
distribution, albeit with a bias of around 2. This has interesting implications
for the anisotropy and polarization of the microwave background. Finally, we
discuss the effects of relaxing the assumption that the universe is flat.",9806115v1
1998-06-08,Probing Unstable Massive Neutrinos with Current Cosmic Microwave Background Observations,"The pattern of anisotropies in the Cosmic Microwave Background depends upon
the masses and lifetimes of the three neutrino species. A neutrino species of
mass greater than 10 eV with lifetime between 10^{13} sec and 10^{17} sec
leaves a very distinct signature (due to the integrated Sachs-Wolfe effect):
the anisotropies at large angles are predicted to be comparable to those on
degree scales. Present data exclude such a possibility and hence this region of
parameter space. For $m_\nu \simeq 30$ eV, $\tau \simeq 10^{13}$ sec, we find
an interesting possibility: the Integrated Sachs Wolfe peak produced by the
decaying neutrino in low-$\Omega$ models mimics the acoustic peak expected in
an $\Omega = 1$ model.",9806116v1
1998-07-10,Cosmic Confusion: Degeneracies among Cosmological Parameters Derived from Measurements of Microwave Background Anisotropies,"In the near future, observations of the cosmic microwave background (CMB)
anisotropies will provide accurate determinations of many fundamental
cosmological parameters. In this paper, we analyse degeneracies among
cosmological parameters to illustrate some of the limitations inherent in CMB
parameter estimation. For simplicity, throughout our analysis we assume a cold
dark matter universe with power-law adiabatic scalar and tensor fluctuation
spectra. We show that most of the variance in cosmological parameter estimates
is contributed by a small number (two or three) principal components. An exact
likelihood analysis shows that the usual Fisher matrix approach can
significantly overestimate the errors on cosmological parameters. We show that
small correlated errors in estimates of the CMB power spectrum at levels well
below the cosmic variance limits, (caused, for example, by Galactic foregrounds
or scanning errors) can lead to significant biases in cosmological parameters.
Estimates of cosmological parameters can be improved very significantly by
applying theoretical restrictions to the tensor component and external
constraints derived from more conventional astronomical observations such as
measurements of he Hubble constant, Type 1a supernovae distances and
observations of galaxy clustering and peculiar velocities.",9807103v1
1998-08-06,Mapping the CMB I: the first flight of the QMAP experiment,"We report on the first flight of the balloon-borne QMAP experiment. The
experiment is designed to make a map of the cosmic microwave background
anisotropy on angular scales from 0.7 to several degrees. Using the map we
determine the angular power spectrum of the anisotropy in multipole bands from
l~40 to l~140. The results are consistent with the Saskatoon (SK) measurements.
The frequency spectral index (measured at low l) is consistent with that of CMB
and inconsistent with either Galactic synchrotron or free-free emission. The
instrument, measurement, analysis of the angular power spectrum, and possible
systematic errors are discussed.",9808043v1
1998-08-11,No Pulsar Kicks from Deformed Neutrinospheres,"In a supernova core, magnetic fields cause a directional variation of the
neutrino refractive index so that resonant flavor oscillations would lead to a
deformation of the ""neutrinosphere"" for, say, tau neutrinos. The associated
anisotropic neutrino emission was proposed as a possible origin of the observed
pulsar proper motions. We argue that this effect was vastly overestimated
because the variation of the temperature over the deformed neutrinosphere is
not an adequate measure for the anisotropy of neutrino emission. The neutrino
flux is generated inside the neutron star core and is transported through the
atmosphere at a constant luminosity, forcing the temperature gradient in the
atmosphere to adjust to the inflow of energy from below. Therefore, no emission
anisotropy is caused by a deformation of the neutrinosphere to lowest order. An
estimate of the higher-order corrections must take into account the modified
atmospheric temperature profile in response to the deformation of the
neutrinosphere and the corresponding feedback on the core. We go through this
exercise in the framework of a simplified model which can be solved
analytically.",9808099v2
1998-09-24,The Cosmic Microwave Background: Beyond the Power Spectrum,"Much recent work on the cosmic microwave background (CMB) has focussed on the
angular power spectrum of temperature anisotropies and particularly on the
recovery of cosmological parameters from acoustic peaks in the power spectrum.
However, there is more that can conceivably be done with CMB measurements. Here
I briefly survey a few such ideas: cross-correlation with other cosmic
backgrounds as a probe of the density of the Universe; CMB polarization as a
gravitational-wave detector; secondary anisotropies and the ionization history
of the Universe; tests of alternative-gravity theories; polarization, the
Sunyaev-Zeldovich effect, and cosmic variance; and tests for a neutrino mass.",9809320v1
1998-10-02,Computation of eigenmodes on a compact hyperbolic 3-space,"Measurements of cosmic microwave background (CMB) anisotropy are ideal
experiments for discovering the non-trivial global topology of the universe. To
evaluate the CMB anisotropy in multiply-connected compact cosmological models,
one needs to compute the eigenmodes of the Laplace-Beltrami operator. Using the
direct boundary element method, we numerically obtain the low-lying eigenmodes
on a compact hyperbolic 3-space called the Thurston manifold which is the
second smallest in the known compact hyperbolic 3-manifolds. The computed
eigenmodes are expanded in terms of eigenmodes on the unit three-dimensional
pseudosphere. We numerically find that the expansion coefficients behave as
Gaussian pseudo-random numbers for low-lying eigenmodes. The observed
gaussianity in the CMB fluctuations can partially be attributed to the Gaussian
pseudo-randomness of the expansion coefficients assuming that the Gaussian
pseudo-randomness is the universal property of the compact hyperbolic spaces.",9810034v3
1998-10-08,Microwave Background Anisotropies and Nonlinear Structures I. Improved Theoretical Models,"A new method is proposed for modelling spherically symmetric inhomogeneities
in the Universe. The inhomogeneities have finite size and are compensated, so
they do not exert any measurable gravitational force beyond their boundary. The
region exterior to the perturbation is represented by a
Friedmann-Robertson-Walker (FRW) Universe, which we use to study the anisotropy
in the cosmic microwave background (CMB) induced by the cluster. All
calculations are performed in a single, global coordinate system, with
nonlinear gravitational effects fully incorporated. An advantage of the gauge
choices employed here is that the resultant equations are essentially Newtonian
in form. Examination of the problem of specifying initial data shows that the
new model presented here has many advantages over `Swiss cheese' and other
models. Numerical implementation of the equations derived here is described in
a subsequent paper.",9810123v1
1998-10-09,Microwave background anisotropies and non-linear structures II. Numerical computations,"A new method for modelling spherically symmetric inhomogeneities is applied
to the formation of clusters in an expanding Universe. We impose simple initial
velocity and density perturbations of finite extent and we investigate the
subsequent evolution of the density field. Photon paths are also calculated,
allowing a detailed consideration of gravitational lensing effects and
microwave background anisotropies induced by the cluster. We apply the method
to modelling high-redshift clusters and, in particular, we consider the
reported microwave decrement observed towards the quasar pair PC1643+4631 A&B.
We also consider the effect on the primordial microwave background power
spectrum due to gravitational lensing by a population of massive high-redshift
clusters.",9810149v1
1998-10-20,Cosmic microwave background anisotropies seeded by coherent topological defects : a semi-analytic approach,"We consider a perfectly homogeneous, isotropic and spatially flat universe
which undergoes a sudden phase transition producing topological defects. We
assume that these defects form a coherent network which scales like the
background density during the radiation and matter dominated eras, and describe
them in terms of a few free functions. We carefully model the loss of scaling
invariance during the transition from radiation to matter dominated era. We
choose a simple set for the free functions, compute the microwave background
temperature anisotropies generated by such a network, and compare our results
to previous calculations.",9810313v2
1998-12-11,Constraints on Omega_Lambda and Omega_m from Distant Type 1a Supernovae and Cosmic Microwave Background Anisotropies,"We perform a combined likelihood analysis of the latest cosmic microwave
background anisotropy data and distant Type 1a Supernova data of Perlmutter
etal (1998a). Our analysis is restricted to cosmological models where structure
forms from adiabatic initial fluctuations characterised by a power-law spectrum
with negligible tensor component. Marginalizing over other parameters, our best
fit solution gives Omega_m = 0.25 (+0.18, -0.12) and Omega_Lambda = 0.63
(+0.17, -0.23) (95 % confidence errors) for the cosmic densities contributed by
matter and a cosmological constant respectively. The results therefore strongly
favour a nearly spatially flat Universe with a non-zero cosmological constant.",9812226v1
1998-12-15,Model-Independent Measurement of the Primordial Power Spectrum,"In inflationary models with minimal amount of gravity waves, the primordial
power spectrum of density fluctuations, $A_S^2(k)$, together with the basic
cosmological parameters, completely specify the predictions for the cosmic
microwave background (CMB) anisotropy and large scale structure. Here we show
how we can strongly constrain both $A_S^2(k)$ and the cosmological parameters
by combining the data from the Microwave Anisotropy Probe (MAP) and the galaxy
redshift survey from the Sloan Digital Sky Survey (SDSS). We allow $A_S^2(k)$
to be a free function, and thus probe features in the primordial power spectrum
on all scales. MAP and SDSS have scale-dependent measurement errors that
decrease in opposite directions on astrophysically interesting scales; they
complement each other and allow the measurement of the primordial power
spectrum independent of inflationary models, giving us valuable information on
physics in the early Universe, and providing clues to the correct inflationary
model.",9812291v1
1999-01-04,"CMB Anisotropy Constraints on Open and Flat-Lambda CDM Cosmogonies from UCSB South Pole, ARGO, MAX, White Dish, and SuZIE Data","We use combinations of ten small-scale cosmic microwave background anisotropy
data sets from the UCSB South Pole 1994, ARGO, MAX 4 and 5, White Dish and
SuZIE experiments to constrain cosmogonies. We consider open and
spatially-flat-Lambda cold dark matter cosmogonies. Marginalizing over all
parameters but $\Omega_0$, the combined data favors an Omega_0 simeq 1 for both
open and flat-Lambda models. Excluding the smallest angular scale SuZIE data,
an Omega_0 simeq 0.3 (1.0) open (flat-Lambda) model is favored. Considering
only multi-frequency data with error bars consistent with sample variance and
noise considerations, an Omega_0 simeq 0.1 (1) open (flat-Lambda) model is
favored. For both open and flat-$\Lambda$ models, after marginalizing over all
the other parameters, a lower Omega_B h^2 (sim 0.005) or younger (t_0 sim 10
Gyr) universe is favored. However, the data do not rule out other values of
Omega_0 in the flat-Lambda model and other values of Omega_B h^2 in both
models. (abriged)",9901014v1
1999-01-05,Limits on the gravity wave contribution to microwave anisotropies,"We present limits on the fraction of large angle microwave anisotropies which
could come from tensor perturbations. We use the COBE results as well as
smaller scale CMB observations, measurements of galaxy correlations, abundances
of galaxy clusters, and Lyman alpha absorption cloud statistics. Our aim is to
provide conservative limits on the tensor-to-scalar ratio for standard
inflationary models. For power-law inflation, for example, we find T/S<0.52 at
95% confidence, with a similar constraint for phi^p potentials. However, for
models with tensor amplitude unrelated to the scalar spectral index it is still
currently possible to have T/S>1.",9901028v2
1999-01-12,Observation of the east-west anisotropy of the atmospheric neutrino flux,"The east-west anisotropy, caused by the deflection of primary cosmic rays in
the Earth's magnetic field, is observed for the first time in the flux of
atmospheric neutrinos. Using a 45 kt-year exposure of the
  Super-Kamiokande detector, 552 e-like and 633 mu-like horizontally-going
events are selected in the momentum range between 400 and 3000 MeV/c.
  The azimuthal distribution of e-like and mu-like events agrees with the
expectation from atmospheric neutrino flux calculations that account for the
geomagnetic field, verifying that the geomagnetic field effects in the
production of atmospheric neutrinos in the GeV energy range are well
understood.",9901139v1
1999-01-27,Cosmic Microwave Background Anisotropies from Global Texture,"We investigate the global texture model of structure formation in cosmogonies
with non-zero cosmological constant for different values of the Hubble
parameter. We find that the absence of significant acoustic peaks and little
power on large scales are robust predictions of these models. However, from a
careful comparison with experiments we conclude that at present we cannot
safely reject the model on the grounds of published CMB anisotropy data.
  If bias is close to one on large scales, galaxy correlation data rules out
the models. New, very stringent constraints come from peculiar velocities.
  Investigating the large-N limit, we argue that our main conclusions apply to
all global O(N) models of structure formation.",9901377v1
1999-02-03,New CMB Power Spectrum Constraints from MSAMI,"We present new cosmic microwave background (CMB) anisotropy results from the
combined analysis of the three flights of the first Medium Scale Anisotropy
Measurement (MSAM1). This balloon-borne bolometric instrument measured about 10
square degrees of sky at half-degree resolution in 4 frequency bands from 5.2
icm to 20 icm with a high signal-to-noise ratio. Here we present an overview of
our analysis methods, compare the results from the three flights, derive new
constraints on the CMB power spectrum from the combined data and reduce the
data to total-power Wiener-filtered maps of the CMB. A key feature of this new
analysis is a determination of the amplitude of CMB fluctuations at $\ell \sim
400$. The analysis technique is described in a companion paper by Knox.",9902047v1
1999-02-22,Reionization of the Intergalactic Medium and its Effect on the CMB,"The bulk of the hydrogen in the universe transformed from neutral to ionized
somewhere in the redshift interval 5 < z < 40, most likely due to ionizing
photons produced by an early generation of stars or mini-quasars. The resulting
free electrons, interacting with the CMB photons via Thomson scattering, are a
mixed blessing, providing both a probe of the epoch of the first stars and a
contaminant to the pristine primary anisotropy. Here we review our current
knowledge of reionization with emphasis on inhomogeneities and describe the
possible connections to CMB anisotropy.",9902311v2
1999-03-05,Stability of rotating spherical stellar systems,"We study the stability of rotating collisionless self-gravitating spherical
systems by using high resolution N-body experiments on a Connection Machine
CM-5. We added rotation to Ossipkov-Merritt (hereafter OM) anisotropic
spherical systems by using two methods. The first method conserves the
anisotropy of the distribution function defined in the OM algorithm. The second
method distorts the systems in velocity space. We then show that the stability
of systems depends both on their anisotropy and on the value of the ratio
between the total kinetic energy and the rotational kinetic energy. We also
test the relevance of the stability parameters introduced by Perez et al.
(1996) for the case of rotating systems.",9903087v1
1999-03-09,Supercluster Magnetic Fields and Anisotropy of Cosmic Rays above 10**(19) eV,"We predict energy spectra and angular distributions of nucleons above
10**(19) eV that originate from sources distributed in the Local Supercluster,
which is also supposed to contain a large scale magnetic field of strength
between 0.05 and 0.5 micro Gauss. We show that this model can explain all
present-day features of ultra-high energy cosmic rays, at least for field
strengths close to 0.5 micro Gauss. The large-scale anisotropy and the
clustering predicted by this scenario will allow strong discrimination against
other models with next generation experiments.",9903124v1
1999-03-09,On Planck simulations: towards `2-nd order' analyses,"We simulate Planck observations by adopting a detailed model of the microwave
sky including monopole, dipole, anisotropies of the cosmic microwave background
(CMB) and galactic and extragalactic foregrounds. We estimate the impact of
main beam optical aberrations on CMB anisotropy measurements in presence of
extragalactic source fluctuations and we discuss the main implications for the
Planck telescope design. By analysing the dipole pattern, we quantify the
Planck performance in the determination of CMB spectral distortion parameters
in presence of foreground contaminations.",9903137v1
1999-03-11,Dark matter halos and the anisotropy of ultra-high energy cosmic rays,"Several explanations for the existence of Ultra High Energy Cosmic Rays
invoke the idea that they originate from the decay of massive particles created
in the reheating following inflation. It has been suggested that the decay
products can explain the observed isotropic flux of cosmic rays. We have
calculated the anisotropy expected for various models of the dark matter
distribution and find that at present data are too sparse above $4 \times
10^{19}$ eV to discriminate between different models. However we show that with
data from three years of operation of the southern section of the Pierre Auger
Observatory significant progress in testing the proposals will be made.",9903182v1
1999-03-18,The covariant perturbative approach to cosmic microwave background anisotropies,"The Ehlers-Ellis 1+3 formulation of covariant hydrodynamics, when
supplemented with covariant radiative transport theory, gives an exact,
physically transparent description of the physics of the cosmic microwave
background radiation (CMB). Linearisation around a Friedmann-Robertson-Walker
(FRW) universe provides a very direct and seamless route through to the linear,
gauge-invariant perturbation equations for scalar, vector and tensor modes in
an almost-FRW model. In this contribution we review covariant radiative
transport theory and its application to the perturbative method for calculating
and understanding the anisotropy of the CMB. Particular emphasis is placed on
the inclusion of polarization in a fully covariant manner. With this inclusion,
the covariant perturbative approach offers a complete description of linearised
CMB physics in an almost-FRW universe.",9903283v1
1999-04-18,Gravity waves goodbye,"The detection of a stochastic background of long-wavelength gravitational
waves (tensors) in the cosmic microwave background (CMB) anisotropy would be an
invaluable probe of the high energy physics of the early universe.
Unfortunately a combination of factors now makes such a detection seem
unlikely: the vast majority of the CMB signal appears to come from density
perturbations (scalars) - detailed fits to current observations indicate a
tensor-to-scalar quadrupole ratio of T/S < 0.5 for the simplest models; and on
the theoretical side the best-motivated inflationary models seem to require
very small T/S. Unfortunately CMB temperature anisotropies can only probe a
gravity wave signal down to T/S \sim 10% and optimistic assumptions about
polarization of the CMB only lower this another order of magnitude.",9904228v1
1999-05-08,A Measurement of the Angular Power Spectrum of the Microwave Background Made from the High Chilean Andes,"We report on a measurement of the angular spectrum of the anisotropy of the
microwave sky at 30 and 40 GHz between l=50 and l=200 over approximately 600
sq. deg. The data support a rise in the angular spectrum to a maximum with
$\delta T_l \approx 85 \mu$K at l=200. We also give a 2-sigma upper limit of
$\delta T_l < 122 \mu$K at l=432 at 144 GHz. These results come from the first
campaign of the Mobile Anisotropy Telescope (MAT) on Cerro Toco, Chile. To
assist in assessing the site, we present plots of the fluctuations in
atmospheric emission at 30 and 144 GHz.",9905100v3
1999-05-11,"Python I, II, and III CMB Anisotropy Measurement Constraints on Open and Flat-Lambda CDM Cosmogonies","We use Python I, II, and III cosmic microwave background anisotropy data to
constrain cosmogonies. We account for the Python beamwidth and calibration
uncertainties. We consider open and spatially-flat-Lambda cold dark matter
cosmogonies, with nonrelativistic-mass density parameter Omega_0 in the range
0.1--1, baryonic-mass density parameter Omega_B in the range (0.005--0.029)
h^{-2}, and age of the universe t_0 in the range (10--20) Gyr. Marginalizing
over all parameters but Omega_0, the combined Python data favors an open
(spatially-flat-Lambda) model with Omega_0 simeq 0.2 (0.1). At the 2 sigma
confidence level model normalizations deduced from the combined Python data are
mostly consistent with those drawn from the DMR, UCSB South Pole 1994, ARGO,
MAX 4 and 5, White Dish, and SuZIE data sets.",9905127v1
1999-05-19,UHECR Anisotropy and the Galactic Halo,"Several explanations for the existence of Ultra High Energy Cosmic Rays
(UHECR) invoke the idea that they originate from the decay of massive particles
created in the reheating following inflation. It has been suggested that the
decay products can explain the observed isotropic flux of UHECR. We have
calculated the anisotropy expected for various models of the dark matter
distribution and find that present data are too sparse above 4 x 10^19 eV to
discriminate between different models. However, after three years of operation
of the southern part of the Pierre Auger Observatory great progress in testing
the proposals is expected.",9905240v1
1999-05-20,Lensing-Induced Structure of Submillimeter Sources: Implications for the Microwave Background,"We consider the effect of lensing by galaxy clusters on the angular
distribution of submillimeter wavelength objects. While lensing does not change
the total flux and number counts of submillimeter sources, it can affect the
number counts and fluxes of flux-limited samples. Therefore imposing a flux cut
on point sources not only reduces the overall Poisson noise, but imprints the
correlations between lensing clusters on the unresolved flux distribution.
Using a simple model, we quantify the lensing anisotropy induced in
flux-limited samples and compare this to Poisson noise. We find that while the
level of induced anisotropies on the scale of the cluster angular correlation
length is comparable to Poisson noise for a slowly evolving cluster model, it
is negligible for more realistic models of cluster evolution. Thus the removal
of point sources is not expected to induce measurable structure in the
microwave or far-infrared backgrounds.",9905269v1
1999-05-26,Cosmic Microwave Background anisotropies and extra dimensions in String Cosmology,"A recently proposed mechanism for large-scale structure in string cosmology
--based on massless axionic seeds-- is further analyzed and extended to the
acoustic-peak region. Existence, structure, and normalization of the peaks turn
out to depend crucially on the overall evolution of extra dimensions during the
pre-big bang phase: conversely, precise cosmic microwave background anisotropy
data in the acoustic-peak region will provide, within the next decade, a window
on string-theory's extra dimensions before their eventual compactification.",9905327v3
1999-06-22,The roughness of the last scattering surface,"We propose an alternative analysis of the microwave background temperature
anisotropy maps that is based on the study of the roughness of natural
surfaces. We apply it to large angle anisotropies, such as those measured by
COBE-DMR. We show that for a large signal to noise experiment, the spectral
index can be determined independently of the normalization. We then analyze the
4 yr COBE map and find for a flat $\Omega=1$ universe, that the best-fitting
value for the spectral index is $n = 1.15^{+0.39}_{-0.34}$ and for the
amplitude $Q_{rms-PS}= 14.1^{+3.9}_{-3.5}\mu K$. For $n=1$, the best-fitting
normalization is $Q_{rms-PS}|_{n=1}= 16.2^{+1.4}_{-1.3}\mu K$.",9906345v1
1999-06-29,Microwave background anisotropies from gravitational waves: the 1+3 covariant approach,"We present a 1+3 covariant discussion of the contribution of gravitational
waves to the anisotropy of the CMB in an almost-Friedmann-Robertson-Walker
universe. Our discussion is based in the covariant approach to perturbations in
cosmology, which provides a physically transparent and gauge-invariant
methodology for CMB physics. Applying this approach to linearised gravitational
waves, we derive a closed set of covariant equations describing the evolution
of the shear and the Weyl tensor, and the angular multipoles of the CMB
intensity, valid for an arbitrary matter description and background spatial
curvature. A significant feature of the present approach is that the normal
mode expansion of the radiation distribution function, which arises naturally
here, preserves the simple quadrupolar nature of the anisotropic part of the
Thomson scattering source terms, and provides a direct characterisation of the
power in the CMB at a given angular multipole, as in the recently introduced
total angular momentum method. We provide the integral solution of the
multipole equations, and analytic solutions for the shear and the Weyl tensor,
for models with arbitrary spatial curvature. Numerical results for the CMB
power spectrum in open models are also presented.",9906474v2
1999-07-15,An Observational Test of Quantum Cosmology,"We compute the tensor CMB anisotropy power spectrum for singular and
non-singular instantons describing the beginning of an open universe according
to the Euclidean no boundary proposal. Singular instantons occur generically,
whereas non-singular instantons require more contrived scalar field potentials.
For the latter, we consider potentials in which a sharp feature, either
negative or positive, is added to a gently sloping potential. In the first case
one finds a nearly divergent contribution to the low multipole CMB anisotropy,
in conflict with the COBE observations. In the second case the divergence is
weaker, but matching the low multipoles forces the added feature to be large
and narrow. For singular instantons, there is a better match to the
observations, without any such contrivance. The distinction between singular
and nonsingular instantons disappears in the limit as the universe becomes
flat, but is still observable for densities as high as 0.7 of the critical
density.",9907212v2
1999-09-04,Constraints on structure formation models from Sunyaev-Zel'dovich Effect,"In the context of cold dark matter (CDM) cosmological models, we have
simulated images of the brightness temperature fluctuations in the cosmic
microwave background (CMB)sky owing to the Sunyaev Zel$^{\prime}$dovich (S-Z)
effect in a cosmological distribution of clusters. We compare the image
statistics with recent ATCA limits on arcmin-scale CMB anisotropy. The S-Z
effect produces a generically non-Gaussian field and we compute the variance in
the simulated temperature-anisotropy images, after convolution with the ATCA
beam pattern, for different cosmological models. All the models are normalised
to the 4-year {\it COBE} data. We find an increase in the simulated-sky
temperature variance with increase in the cosmological density parameter
$\Omega_0$. A comparison with the upper limits on the sky variance set by the
ATCA appears to rule out our closed-universe model: low-$\Omega_0$
open-universe models are preferred. The result is independent of any present
day observations of $\sigma_8$.",9909087v1
1999-09-07,Anisotropies of Cosmic Rays and Search for Intergalactic Cascades from the direction of the Highest Energetic Cosmic Ray Events with the HEGRA Scintillator Array,"Data taken with the HEGRA Scintillator Array have been used to search for
spatial anisotropies in the arrival directions of cosmic rays above 20 TeV. In
this paper results on the search for TeV gamma-ray emission from the Galactic
plane and the Gould belt are presented. Furthermore, a search for TeV gamma-ray
emission correlated with the arrival directions of cosmic rays with energies
well beyond the Greizen-Zatsepin-Kuzmin cutoff has been performed. Such a
correlation can be expected from sufficiently high energetic nuclei inducing
electromagnetic cascades on the diffuse intergalactic background radiation,
eventually producing TeV photons. Interestingly, the direction of the most
energetic event yields the highest excess with a chance probability of 1.8%.",9909125v1
1999-09-29,Analysis of CMB maps with 2D wavelets,"We consider the 2D wavelet transform with two scales to study sky maps of
temperature anisotropies in the cosmic microwave background radiation (CMB). We
apply this technique to simulated maps of small sky patches of size 12.8 \times
12.8 square degrees and 1.5' \times 1.5' pixels. The relation to the standard
approach, based on the cl's is established through the introduction of the
scalogram. We consider temperature fluctuations derived from standard, open and
flat-Lambda CDM models. We analyze CMB anisotropies maps plus uncorrelated
Gaussian noise (uniform and non-uniform) at idfferent S/N levels. We explore in
detail the denoising of such maps and compare the results with other techniques
already proposed in the literature. Wavelet methods provide a good
reconstruction of the image and power spectrum. Moreover, they are faster than
previously proposed methods.",9909497v1
1999-10-27,Lensing of the CMB: Non Gaussian aspects,"We study the generation of CMB anisotropies by gravitational lensing on small
angular scales. We show these fluctuations are not Gaussian. We prove that the
power spectrum of the tail of the CMB anisotropies on small angular scales
directly gives the power spectrum of the deflection angle. We show that the
generated power on small scales is correlated with the large scale gradient.
The cross correlation between large scale gradient and small scale power can be
used to test the hypothesis that the extra power is indeed generated by
lensing. We compute the three and four point function of the temperature in the
small angle limit. We relate the non-Gaussian aspects presented in this paper
as well as those in our previous studies of the lensing effects on large scales
to the three and four point functions. We interpret the statistics proposed in
terms of different configurations of the four point function and show how they
relate to the statistic that maximizes the S/N.",9910498v2
1999-11-03,Tensor Microwave Anisotropies from a Stochastic Magnetic Field,"We derive an expression for the angular power spectrum of cosmic microwave
background anisotropies due to gravity waves generated by a stochastic magnetic
field and compare the result with current observations; we take into account
the non-linear nature of the stress energy tensor of the magnetic field.
  For almost scale invariant spectra, the amplitude of the magnetic field at
galactic scales is constrained to be of order 10^{-9} Gauss. If we assume that
the magnetic field is damped below the Alfven damping scale, we find that its
amplitude at
  0.1 h^{-1}Mpc, B_\lambda, is constrained to be B_\lambda<7.9 x10^{-6} e^{3n}
Gauss, for n<-3/2, and B_\lambda<9.5x10^{-8} e^{0.37n} Gauss, for n>-3/2, where
n is the spectral index of the magnetic field and H_0=100h km s^{-1}Mpc^{-1} is
the Hubble constant today.",9911040v1
1999-11-19,MADCAP - The Microwave Anisotropy Dataset Computational Analysis Package,"Realizing the extraordinary scientific potential of the CMB requires precise
measurements of its tiny anisotropies over a significant fraction of the sky at
very high resolution. The analysis of the resulting datasets is a serious
computational challenge. Existing algorithms require terabytes of memory and
hundreds of years of CPU time. We must therefore both maximize our resources by
moving to supercomputers and minimize our requirements by algorithmic
development. Here we will outline the nature of the challenge, present our
current optimal algorithm, and discuss its implementation as the MADCAP
software package and application to data from the North American test flight of
the joint Italian-U.S. BOOMERanG experiment on the Cray T3E at NERSC and
CINECA.
  A documented beta-release of MADCAP is publicly available at
http://cfpa.berkeley.edu/~borrill/cmb/madcap.html",9911389v1
1999-11-22,Data Reduction and Analysis of the Python V Cosmic Microwave Background Anisotropy Experiment,"Observations of the microwave sky using the Python telescope in its fifth
season of operation at the Amundsen-Scott South Pole Station in Antarctica are
presented. The system consists of a 0.75 m off-axis telescope instrumented with
a HEMT amplifier-based radiometer having continuum sensitivity from 37-45 GHz
in two frequency bands. With a $0.91^{\circ} \times 1.02^{\circ} $ beam the
instrument fully sampled 598 deg$^2$ of sky, including fields measured during
the previous four seasons of Python observations. Interpreting the observed
fluctuations as anisotropy in the cosmic microwave background, we place
constraints on the angular power spectrum of fluctuations in eight multipole
bands up to $l \sim 260$. The observed spectrum is consistent with both the
COBE experiment and previous Python results. Total-power Wiener-filtered maps
of the CMB are also presented. There is no significant contamination from known
foregrounds. The results show a discernible rise in the angular power spectrum
from large ($l \sim 40$) to small ($l \sim 200$) angular scales.",9911419v1
1999-12-03,The mildly nonlinear imprint of structure on the CMB,"I outline some nonperturbative relativistic effects that arise from
gravitational corrections to the Boltzmann equations. These may be important
for the study of CMB temperature anisotropies, particularly their
interpretation. These terms are not included in the canonical treatment as they
arise from the exact equations. Here a weakly nonlinear investigation of these
effects is defined and investigated with an emphasis on a Rees-Sciama sourced
effect -- the imprint of structure evolution on the CMB. It is shown that
gravitational nonlinearity in the weakly nonlinear extension of almost-FLRW
temperature anisotropies leads to cancellation on small-scales when threading
in the Newtonian frame. In the general frame this cancellation does not occur.
In the context of a flat almost-FLRW CDM model I provide a heuristic argument
for a nonperturbative small scale correction, due to the Rees-Sciama effect, of
not more than $\Delta T/T \sim 10^{-6}-10^{-5}$ near $\ell \sim 100 - 300$. The
effect of mild gravitational nonlinearity could be more sophisticated than
previously expected.",9912072v2
2000-01-14,Electron Firehose instability and acceleration of electrons in solar flares,"An electron distribution with a temperature anisotropy T_par/T_perp > 1 can
lead to the Electron Firehose instability (Here par and perp denote directions
relative to the background magnetic field B_0). Since possible particle
acceleration mechanisms in solar flares exhibit a preference of energizing
particles in parallel direction, such an anisotropy is expected during the
impulsive phase of a flare. The properties of the excited waves and the
thresholds for instability are investigated by using linearized kinetic theory.
These thresholds were connected to the pre-flare plasma parameters by assuming
an acceleration model acting exclusively in parallel direction. For usually
assumed pre-flare plasma conditions the electrons become unstable during the
acceleration process and lefthand circularly polarized waves with frequencies
of about the proton gyrofrequency are excited at parallel propagation.
Indications have been found, that the largest growth rates occur at oblique
propagation and the according frequencies lie well above the proton
gyrofrequency.",0001262v1
2000-01-18,Weak Lensing of the CMB: A Harmonic Approach,"Weak lensing of CMB anisotropies and polarization for the power spectra and
higher order statistics can be handled directly in harmonic-space without
recourse to real-space correlation functions. For the power spectra, this
approach not only simplifies the calculations but is also readily generalized
from the usual flat-sky approximation to the exact all-sky form by replacing
Fourier harmonics with spherical harmonics. Counterintuitively, due to the
nonlinear nature of the effect, errors in the flat-sky approximation do not
improve on smaller scales. They remain at the 10% level through the acoustic
regime and are sufficiently large to merit adoption of the all-sky formalism.
For the bispectra, a cosmic variance limited detection of the correlation with
secondary anisotropies has an order of magnitude greater signal-to-noise for
combinations involving magnetic parity polarization than those involving the
temperature alone. Detection of these bispectra will however be severely noise
and foreground limited even with the Planck satellite, leaving room for
improvement with higher sensitivity experiments. We also provide a general
study of the correspondence between flat and all sky potentials, deflection
angles, convergence and shear for the power spectra and bispectra.",0001303v1
2000-02-27,Limits on Hot Intracluster Gas Contributions to the Tenerife Temperature Anisotropy Map,"We limit the contribution of the hot intracluster gas, by means of the
Sunyaev-Zel'dovich effect, to the temperature anisotropies measured by the
Tenerife experiment. The data is cross-correlated with maps generated from the
ACO cluster catalogue, the ROSAT PSPC catalogue of clusters of galaxies, a
catalogue of superclusters and the HEAO 1 A-1 map of X-ray sources. There is no
evidence of contamination by such sources at an rms level of $\sim 8\mu$K at
99% confidence level at $5^o$ angular resolution. We place an upper limit on
the mean Comptonization parameter of $ y \le 1.5\times 10^{-6}$ at the same
level of confidence. These limits are slightly more restrictive than those
previously found by a similar analysis on the COBE/DMR data and indicate that
most of the signal measured by Tenerife is cosmological.",0002497v1
2000-03-24,A Characteristic Scale on the Cosmic Microwave Sky,"The current suite of results from Cosmic Microwave Background anisotropy
experiments is fulfilling the promise of providing extraordinary levels of
discrimination between cosmological models. We calculate a binned anisotropy
power spectrum, which we tabulate, along with error bars and bin-to-bin
correlations, so that it can be easily used for constraining models. The
resulting power spectrum is flat at large angles, with a gradual rise to a
prominent peak at around 0.5 degrees and a decrease thereafter. This is
precisely the shape predicted by inflationary-inspired adiabatic models. Within
that class of cosmologies, this characteristic scale imprinted on the CMB sky
can be used to infer that the geometry of the Universe is very close to flat.
The next wave of CMB results should add fuel to the debate about whether or not
the Universe once inflated, as well as beginning in earnest the task of
measuring cosmological parameters.",0003393v1
2000-04-18,"Galaxy Cluster Baryon Fractions, Cluster Surveys and Cosmology","The properties of nearby galaxy clusters limit the range of cosmological
parameters consistent with our universe. We describe the limits which arise
from studies of the intracluster medium (ICM) mass fraction fICM and
consideration of the possible sources of systematic error:
Omega_M<0.44h_{50}^{-1/2} at 95% confidence. We emphasize that independent of
Type Ia supernovae (SNe Ia) observations, this cluster study, taken together
with published cosmic microwave background (CMB) anisotropy studies, indicates
a non-zero quintessence or dark energy component Omega_Q>0.
  We then discuss future galaxy cluster surveys which will probe the abundance
of galaxy clusters to intermediate and high redshift. We investigate the
sensitivity of these surveys to the cosmological density parameter Omega_M and
the equation of state parameter w of any quintessence component. In particular,
we show that cluster survey constraints from a proposed large solid angle X-ray
survey are comparable in precision and complementary in nature to constraints
expected from future CMB anisotropy and SNe Ia studies.",0004244v1
2000-05-11,Synchrotron Emission from Hot Accretion Flows and the Cosmic Microwave Background Anisotropy,"Current estimates of number counts of radio sources in the frequency range
where the most sensitive Cosmic Microwave Background (CMB) experiments are
carried out significantly under-represent sources with strongly inverted
spectra. Hot accretion flows around supermassive black holes in the nuclei of
nearby galaxies are expected to produce inverted radio spectra by thermal
synchrotron emission. We calculate the temperature fluctuations and power
spectra of these sources in the Planck Surveyor 30 GHz energy channel, where
their emission is expected to peak. We find that their potential contribution
is generally comparable to the instrumental noise, and approaches the CMB
anisotropy level at small angular scales. Forthcoming CMB missions, which will
provide a large statistical sample of inverted-spectra sources, will be crucial
for determining the distribution of hot accretion flows in nearby quiescent
galactic nuclei. Detection of these sources in different frequency channels
will help constrain their spectral characteristics, hence their physical
properties.",0005244v1
2000-05-17,Big Bang Leftovers in the Microwave: Cosmology with the Cosmic Microwave Background Radiation,"We combine detections of anisotropy in the Cosmic Microwave Background
radiation with observations of inhomogeneity in the large-scale distribution of
galaxies to test the predictions of models of cosmological structure formation.
This combination probes spatial scales varying by three orders of magnitude,
including a significant region where the two types of data overlap. We examine
Cold Dark Matter models with adiabatic density perturbations, isocurvature
models, and a topological defects model. We set upper limits on the neutrino
mass and find the primordial power spectrum needed to reconcile an apparent
disagreement between structure formation observations and direct observations
of cosmological parameters.
  Present and future observations of Cosmic Microwave Background anisotropy
suffer from foreground contamination. We develop detailed predictions for
microwave emission from radio and infrared-bright galaxies and the
Sunyaev-Zeldovich effect from clusters. We present realistic simulations of the
microwave sky, produced as part of the `WOMBAT Challenge' exercise, and
introduce a pixel-space method for subtracting foreground contamination which
can be tested on these simulations.",0005365v1
2000-06-27,Slow-roll inflation and CMB anisotropy data,"We emphasize that the estimation of cosmological parameters from cosmic
microwave background (CMB) anisotropy data, such as the recent high resolution
maps from BOOMERanG and MAXIMA-1, requires assumptions about the primordial
spectra. The latter are predicted from inflation. The physically best-motivated
scenario is that of slow-roll inflation. However, very often, the unphysical
power-law inflation scenario is (implicitly) assumed in the CMB data analysis.
We show that the predicted multipole moments differ significantly in both
cases. We identify several misconceptions present in the literature (and in the
way inflationary relations are often combined in popular numerical codes). For
example, we do not believe that, generically, inflation predicts the relation
n_S - 1 = n_T for the spectral indices of scalar and tensor perturbations or
that gravitational waves are negligible. We calculate the CMB multipole moments
for various values of the slow-roll parameters and demonstrate that an
important part of the space of parameters (n_S, n_T) has been overlooked in the
CMB data analysis so far.",0006392v2
2000-07-03,How accurately can we measure weak gravitational shear?,"With the recent detection of cosmic shear, the most challenging effect of
weak gravitational lensing has been observed. The main difficulties for this
detection were the need for a large amount of high quality data and the control
of systematics during the gravitational shear measurement process, in
particular those coming from the Point Spread Function anisotropy. In this
paper we perform detailed simulations with the state-of-the-art algorithm
developed by Kaiser, Squires and Broadhurst (KSB) to measure gravitational
shear. We show that for realistic PSF profiles the KSB algorithm can recover
any shear amplitude in the range $0.012 < |\gammavec |<0.32$ with a relative,
systematic error of $10-15%$. We give quantitative limits on the PSF correction
method as a function of shear strength, object size, signal-to-noise and PSF
anisotropy amplitude, and we provide an automatic procedure to get a reliable
object catalog for shear measurements out of the raw images.",0007021v2
2000-07-03,Internal Motions in Globular Clusters,"Observations of internal motions in globular clusters offer unique insights
into the dynamics of the clusters. We have recently developed methods of
high-precision astrometry with HST's WFPC2 camera, which allow us to measure
internal proper motions of individual stars. These new data open up many new
avenues for study of the clusters. Comparison of the dispersion of proper
motion with that of radial velocity offers what is potentially the best method
of measuring cluster distances, but reliable results will require dynamical
modeling of each cluster. Proper motions are much better able to measure
anisotropy of stellar motions than are radial velocities. In 47 Tucanae we have
measured thousands of proper motions near the center; their velocity
distribution is remarkably Gaussian. In two outer fields we have begun to study
anisotropy, which appears in the high velocities but not in the lower ones,
contrary to the spheroidal velocity distributions that have commonly been
assumed.",0007028v1
2000-07-14,Asymmetric Beams in Cosmic Microwave Background Anisotropy Experiments,"We propose a new formalism to handle asymmetric beams in the data analysis of
cosmic microwave background anisotropy experiments. For any beam shape, the
formalism finds the optimal circularly symmetric equivalent and is thus easily
adaptable to existing data analysis methods. We demonstrate certain key points
by using a simulated highly elliptic beam, and the beams and data of the
MAXIMA-1 experiment, where the asymmetry is mild. In particular, we show that
in both cases the formalism does not bias the angular power spectrum estimates.
We analyze the limitations of the formalism and find that it is well suited for
most practical situations.",0007212v2
2000-07-20,Time-Delay Effect on the cOsmic Background Radiation by Static Gravitational Potential of Clusters,"We present a quantitative analysis of the time-delay effect on the cosmic
background radiation (CBR) by static gravitational potential of galaxy
clusters. This is primarily motivated by growing observational evidence that
clusters have essentially experienced no-evolution since redshift $z\approx1$,
indicating that the contribution of a time-dependent potential to CBR
anisotropy discussed in literature could be rather small for the
dynamically-relaxed clusters. Using the softened isothermal sphere model and
the universal density profile for the mass distribution of rich clusters, we
calculate the CBR anisotropy by the time-delay effect and compare it with those
generated by the thermal and kinematic S-Z effects as well as by the transverse
motion of clusters. While it is unlikely that the time-delay effect is
detectable in the current S-Z measurement because of its small amplitude of
$10^{-6}$-$10^{-7}$ and its achromaticity, it nevertheless leads to an
uncertainty of $\sim10%$ in the measurement of the kinematic S-Z effect of
clusters. Future cosmological application of the peculiar velocity of clusters
to be measured through the S-Z effect should therefore take this uncertainty
into account.",0007299v1
2000-07-25,New Constraints on inflation from the Cosmic Microwave Background,"The recent data from the Boomerang and MAXIMA-1 balloon flights have marked
the beginning of the precision era of Cosmic Microwave Background anisotropy
(CMB) measurements. We investigate the observational constraints from the
current CMB anisotropy measurements on the simplest inflation models,
characterized by a single scalar field $\phi$, in the parameter space
consisting of scalar spectral index $n_S$ and tensor/scalar ratio $r$. If we
include constraints on the baryon density from big bang nucleosynthesis (BBN),
we show that the favored inflationary models have negligible tensor amplitude
and a ``red'' tilt, with a best fit of $n_S \simeq 0.93$, which is consistent
with the simplest ``small-field'' inflation models, but rules out large-field
models at the $1\sigma$ level. Without including BBN constraints, a broader
range of models are consistent with the data. The best fit (assuming negligible
reionization) is a scale-invariant spectrum, $n_S \simeq 1$, which includes
large-field and hybrid scenarios. Large-field models (such as chaotic and
power-law inflation) with tilt $n_S < 0.9$ are strongly disfavored in all
cases.",0007375v2
2000-07-31,Precision Cosmology and the Density of Baryons in the Universe,"Big-bang Nucleosynthesis (BBN) and Cosmic Microwave Background (CMB)
anisotropy measurements give independent, accurate measurements of the baryon
density and can test the framework of the standard cosmology. Early CMB data
are consistent with the longstanding conclusion from BBN that baryons
constitute a small fraction of matter in the Universe, but may indicate a
slightly higher value for the baryon density. We clarify precisely what the two
methods determine, and point out that differing values for the baryon density
can indicate either an inconsistency or physics beyond the standard models of
cosmology and particle physics. We discuss other signatures of the new physics
in CMB anisotropy.",0007454v2
2000-08-07,The Pseudo-$C_l$ method: Cosmic microwave background anisotropy power spectrum statistics for high precision cosmology,"As the era of high precision cosmology approaches, the empirically determined
power spectrum of the microwave background anisotropy $C_l$ will provide a
crucial test for cosmological theories. We present an exact semi-analytic
framework for the study of the ampling statistics of the $C_l$ resulting from
observations with partial sky coverage and anisotropic noise distributions.
This includes space-borne, air-borne and ground-based experiments. We apply
this theory to demonstrate its power for constructing fast but unbiased
approximate methods for the joint estimation of cosmological parameters.
Further applications, such as a test for possible non-Gaussianity of the
underlying theory and a ``poor man's power spectrum estimator'' are suggested.
An appendix derives recursion relations for the efficient computation of the
couplings between spherical harmonics on the cut sky.",0008111v1
2000-09-19,Cosmic Defects and CMB anisotropy,"Recent measurements of the cosmic microwave background (CMB) anisotropies by
BOOMERANG and MAXIMA collaborations have tightened the observational
constraints on theories of structure formation. They disagree with the
predictions of conventional topological defect models. Considering the fact
that topological defects are predicted by the majority of realistic particle
physics models, the exact nature of the constraints imposed by the recent data
on the population and the properties of the defects must be fully understood.
We show that the predictions of current cosmic string models can be brought
into a closer agreement with the observations by choosing a closed universe
with $\Omega=1.3$ and by including the effects of the small-scale structure and
radiation products of the strings. These alone, however, are not sufficient for
obtaining a good fit to the measured shape of the angular power spectrum. To
fit the data cosmic strings would either have to be correlated on large
(perhaps superhorizon) scales or would have to possess a higher degree of
coherence, i.e. be more ``time-correlated'.",0009307v1
2000-09-27,Implications for quintessence models from MAXIMA-1 and BOOMERANG-98,"Prompted by the recent MAXIMA-1 and BOOMERANG-98 measurements of the cosmic
microwave background (CMB) anisotropy power spectrum, and motivated by the
results from the observation of high-redshift Type Ia supernovae, we
investigate CMB anisotropies in quintessence models in order to characterize
the nature of the dark energy today. We perform a Bayesian likelihood analysis,
using the MAXIMA-1 and BOOMERANG-98 published bandpowers, in combination with
COBE/DMR, to explore the space of quintessence parameters: the quintessence
energy density \Omega_\phi and equation of state w_\phi. We restrict our
analysis to flat, scale-invariant, inflationary adiabatic models. We find that
this simple class of inflationary models, with a quintessence component
\Omega_\phi < ~0.7, -1 < = w_\phi < ~-0.5, is in good agreement with the data.
Within the assumptions of our analysis, pure quintessence models seem to be
slightly favored, although the simple cosmological constant scenario is
consistent with the data.",0009432v2
2000-10-17,"Statistical Power, the Bispectrum and the Search for Non-Gaussianity in the CMB Anisotropy","We use simulated maps of the cosmic microwave background anisotropy to
quantify the ability of different statistical tests to discriminate between
Gaussian and non-Gaussian models. Despite the central limit theorem on large
angular scales, both the genus and extrema correlation are able to discriminate
between Gaussian models and a semi-analytic texture model selected as a
physically motivated non-Gaussian model. When run on the COBE 4-year CMB maps,
both tests prefer the Gaussian model. Although the bispectrum has comparable
statistical power when computed on the full sky, once a Galactic cut is imposed
on the data the bispectrum loses the ability to discriminate between models.
Off-diagonal elements of the bispectrum are comparable to the diagonal elements
for the non-Gaussian texture model and must be included to obtain maximum
statistical power.",0010333v1
2000-10-30,A Limit on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales,"A ground-based polarimeter, PIQUE, operating at 90 GHz has set a new limit on
the magnitude of any polarized anisotropy in the cosmic microwave background.
The combination of the scan strategy and full width half maximum beam of 0.235
degrees gives broad window functions with average multipoles, l = 211+294-146
and l = 212+229-135 for the E- and B-mode window functions, respectively. A
joint likelihood analysis yields simultaneous 95% confidence level flat band
power limits of 14 and 13 microkelvin on the amplitudes of the E- and B-mode
angular power spectra, respectively. Assuming no B-modes, a 95% confidence
limit of 10 microkelvin is placed on the amplitude of the E-mode angular power
spectrum alone.",0010592v1
2000-12-13,Evidence for an inflationary phase transition from the LSS and CMB anisotropy data,"In the light of the recent Boomerang and Maxima observations of the CMB which
show an anomalously low second acoustic peak, we reexamine the prediction by
Adams et al (1997) that this would be the consequence of a 'step' in the
primordial spectrum induced by a spontaneous symmetry breaking phase transition
during primordial inflation. We demonstrate that a deviation from
scale-invariance around $k\sim0.1h$~Mpc$^{-1}$ can simultaneously explain both
the feature identified earlier in the APM galaxy power spectrum as well the
recent CMB anisotropy data, with a baryon density consistent with the BBN
value. Such a break also allows a good fit to the data on cluster abundances
even for a critical density matter-dominated universe with zero cosmological
constant.",0012284v1
2001-01-11,How to Avoid the Ambiguity in Applying the Copernican Principle for Cosmic Topology: Take the Observational Approach,"It is often stated that homogeneity and isotropy of the Universe are
assumptions of the almost Friedmann-Lema^itre (FL) model (the hot big bang
model), inspired from the Copernican Principle. However, only local homogeneity
and isotropy are required by the model: multiply connected almost FL models are
locally homogeneous and isotropic, but they can be globally anisotropic and/or
globally inhomogeneous. Toy models are used here to show how global anisotropy
and/or global inhomogeneity of an almost FL model could be shown directly in
observations. This approach may avoid having to make any assumptions regarding
global anisotropy and inhomogeneity.",0101191v1
2001-02-08,Early-universe constraints on a time-varying fine structure constant,"Higher-dimensional theories have the remarkable feature of predicting a time
(and hence redshift) dependence of the `fundamental' four dimensional constants
on cosmological timescales. In this paper we update the bounds on a possible
variation of the fine structure constant alpha at the time of BBN (z =10^10)
and CMB (z=10^3). Using the recently-released high-resolution CMB anisotropy
data and the latest estimates of primordial abundances of 4He and D, we do not
find evidence for a varying alpha at more than one-sigma level at either epoch.",0102144v4
2001-02-25,Probing the Evolution of Gas Mass Fraction with Sunyaev-Zel'dovich Effect,"Study of the primary anisotropies of the Cosmic Microwave Background (CMB)
can be used to determine the cosmological parameters to a very high precision.
The power spectrum of the secondary CMB anisotropies due to the thermal
Sunyaev-Zel'dovich Effect (SZE) by clusters of galaxies, can then be studied,
to constrain more cluster specific properties (like gas mass). We show the SZE
power spectrum from clusters to be a sensitive probe of any possible evolution
(or constancy) of the gas mass fraction. The position of the peak of the SZE
power spectrum is a strong discriminatory signature of different gas mass
fraction evolution models. For example, for a flat universe, there can be a
difference in the $l$ values (of the peak) of {\it as much as 3000} between a
constant gas mass fraction model and an evolutionary one. Moreover,
observational determination of power spectrum, from blank sky surveys, is
devoid of any selection effects that can possibly affect targeted X-ray or
radio studies of gas mass fractions in galaxy clusters.",0102430v1
2001-05-10,Cosmic Microwave Background Anisotropy with Cosine-Type Quintessence,"We study the Cosmic Microwave Background (CMB) anisotropies produced by
cosine-type quintessence models. In our analysis, effects of the adiabatic and
isocurvature fluctuations are both taken into account. For purely adiabatic
fluctuations with scale invariant spectrum, we obtain a stringent constraint on
the model parameters using the CMB data from COBE, BOOMERanG and MAXIMA.
Furthermore, it is shown that isocurvature fluctuations have significant
effects on the CMB angular power spectrum at low multipoles in some parameter
space, which may be detectable in future satellite experiments. Such a signal
may be used to test the cosine-type quintessence models.",0105161v2
2001-05-14,Understanding Cluster Gas Evolution and Fine-Scale CMB Anisotropy with Deep Sunyaev-Zel'dovich Effect Surveys,"We investigate the impact of gas evolution on the expected yields from deep
Sunyaev-Zel'dovich (SZ) effect surveys as well as on the expected SZ effect
contribution to fine scale anisotropy in the Cosmic Microwave Background. The
approximate yields from SZ effect surveys are remarkably insensitive to gas
evolution, even though the observable properties of the resulting clusters can
be markedly different. The CMB angular power spectrum at high multipoles due to
the SZ effect from clusters is quite sensitive to gas evolution. We show that
moderate resolution SZ effect imaging of clusters found in deep SZ effect
surveys should allow a good understanding of gas evolution in galaxy clusters,
independent of the details of the nature of the gas evolution. Such an
understanding will be necessary before precise cosmological constraints can be
set from yields of large cluster surveys.",0105229v1
2001-05-17,MASTER of the CMB Anisotropy Power Spectrum: A Fast Method for Statistical Analysis of Large and Complex CMB Data Sets,"We describe a fast and accurate method for estimation of the cosmic microwave
background (CMB) anisotropy angular power spectrum --- Monte Carlo Apodised
Spherical Transform EstimatoR. Originally devised for use in the interpretation
of the Boomerang experimental data, MASTER is both a computationally efficient
method suitable for use with the currently available CMB data sets (already
large in size, despite covering small fractions of the sky, and affected by
inhomogeneous and correlated noise), and a very promising application for the
analysis of very large future CMB satellite mission products.",0105302v1
2001-05-21,The lepton asymmetry: the last chance for a critical-density cosmology?,"We use a wide range of observations to constrain cosmological models
possessing a significant asymmetry in the lepton sector, which offer perhaps
the best chance of reconciling a critical-density Universe with current
observations. The simplest case, with massless neutrinos, fails to fit many
experimental data and does not lead to an acceptable model. If the neutrinos
have mass of order one electron-volt (which is favoured by some neutrino
observations), then models can be implemented which prove a good fit to
microwave anisotropies and large-scale structure data. However, taking into
account the latest microwave anisotropy results, especially those from
Boomerang, we show that the model can no longer accommodate the observed baryon
fraction in clusters. Together with the observed acceleration of the present
Universe, this puts considerable pressure on such critical-density models.",0105361v1
2001-05-23,Mapping the Dark Matter through the CMB Damping Tail,"The lensing of CMB photons by intervening large-scale structure leaves a
characteristic imprint on its arcminute-scale anisotropy that can be used to
map the dark matter distribution in projection on degree scales or ~100 Mpc/h
comoving. We introduce a new algorithm for mass reconstruction which optimally
utilizes information from the weak lensing of CMB anisotropies in the damping
tail. It can ultimately map individual degree scale mass structures with high
signal-to-noise. To achieve this limit an experiment must produce a high
signal-to-noise, foreground-free CMB map of arcminute scale resolution,
specifically with a FWHM beam of < 5' and a noise level of < 15 (10^-6-arcmin)
or 41 (uK-arcmin).",0105424v2
2001-06-08,"Archeops: A High Resolution, Large Sky Coverage Balloon Experiment for Mapping CMB Anisotropies","Archeops is a balloon-borne instrument dedicated to measuring cosmic
microwave background (CMB) temperature anisotropies at high angular resolution
(8 arcminutes) over a large fraction (25%) of the sky in the millimetre domain.
Based on Planck High Frequency Instrument (HFI) technology, cooled bolometers
(0.1 K) scan the sky in total power mode with large circles at constant
elevation. During the course of a 24-hour Arctic-night balloon flight, Archeops
will observe a complete annulus on the sky in four frequency bands centered at
143, 217, 353 and 545 GHz with an expected sensitivity to CMB fluctuations of
\~100muK for each of the 90 thousand 20 arcminute average pixels. We describe
the instrument and its performance obtained during a test flight from Trapani
(Sicily) to Spain in July 1999.",0106152v1
2001-07-18,Elliptical Beams in CMB Temperature and Polarization Anisotropy Experiments: An Analytic Approach,"We present an analytic approach to the estimation of beam asymmetry effects
in CMB temperature and linear polarization anisotropy experiments. We derive
via perturbative expansions simple and accurate results for the case of an
elliptical Gaussian window. Our results are applied to investigate the effect
of beam ellipticity in the estimation of full-sky polarization correlation
functions and the covariance matrix of power spectra. The relevance of this
effect is also discussed by forecasting errors including beam asymmetry for
current and future CMB experiments.",0107346v2
2001-08-03,WIMPS Are Stronger When They Stick Together,"Weakly interacting massive particles (WIMPs) remain the strongest candidates
for the dark matter in the Universe. If WIMPs are the dark matter, they will
form galactic halos according to the hierarchical clustering observed in N-body
simulations. Cold dark matter (CDM) simulations show that large dark matter
structures such as galactic and cluster halos are formed by the merging of many
smaller clumps of dark matter. Each clump or halo is characterized by a
centrally cusped density profile that can enhance the rate of WIMP annihilation
and make the annihilation products more easily detectable. Electrons and
positrons generated as decay products of WIMP annihilation emit synchrotron
radiation in the Galactic magnetic field. We study the synchrotron signature
from the clumps of dark matter in our Galactic halo. We find that the emission
in the radio and microwave region of the electromagnetic spectrum can be above
the CMB anisotropy level and should be detectable by CMB anisotropy
experiments. Depending on the density profile of dark matter clumps, hundreds
of clumps can have detectable fluxes and angular sizes.",0108060v1
2001-08-14,Neural Networks as a tool for parameter estimation in mega-pixel data sets,"We present a neural net algorithm for parameter estimation in the context of
large cosmological data sets. Cosmological data sets present a particular
challenge to pattern-recognition algorithms since the input patterns (galaxy
redshift surveys, maps of cosmic microwave background anisotropy) are not fixed
templates overlaid with random noise, but rather are random realizations whose
information content lies in the correlations between data points. We train a
``committee'' of neural nets to distinguish between Monte Carlo simulations at
fixed parameter values. Sampling the trained networks using additional Monte
Carlo simulations generated at intermediate parameter values allows accurate
interpolation to parameter values for which the networks were never trained.
The Monte Carlo samples automatically provide the probability distributions and
truth tables required for either a frequentist or Bayseian analysis of the one
observable sky. We demonstrate that neural networks provide unbiased parameter
estimation with comparable precision as maximum-likelihood algorithms but
significant computational savings. In the context of CMB anisotropies, the
computational cost for parameter estimation via neural networks scales as
$N^{3/2}$. The results are insensitive to the noise levels and sampling schemes
typical of large cosmological data sets and provide a desirable tool for the
new generation of large, complex data sets.",0108234v1
2001-08-31,"Big Bang Nucleosynthesis, Cosmic Microwave Background Anisotropies and Dark Energy","Over the last decade, cosmological observations have attained a level of
precision which allows for very detailed comparison with theoretical
predictions. We are beginning to learn the answers to some fundamental
questions, using information contained in Cosmic Microwave Background
Anisotropy (CMBA) data. In this talk, we briefly review some studies of the
current and prospected constraints imposed by CMBA measurements on the neutrino
physics and on the dark energy. As it was already announced by Scott (1999), we
present some possible ""new physics"" from the Cosmic Microwave Background.",0108515v2
2001-10-01,On the Global Anisotropy of Cosmic Ray Data above $4 \times 10^{19}eV$,"The distribution of arrival directions of ultra-high energy cosmic rays may
yield clues to their mysterious origin. We introduce a method of {\it invariant
statistics} to analyze cosmic ray data which eliminates coordinate-dependent
artifacts. When combined with maximum likelihood analysis, the method is
capable of quantifying deviations of the distribution from isotropy with high
reliability. We test our method against published AGASA events with energies
above $4 \times 10^{19}$ eV. Angular cuts from observational limitations are
taken into account. A model based on the Fisher distribution reveals the
rotation of the Earth with the axis $\hat n$ along the direction ($5^h 53.36^m,
85.78^{\circ}$) in $(RA,DEC)$ coordinates, which is within $5^{\circ}$ of the
equatorial north pole. Global anisotropy of the data, if any, hinges on finer
understanding of detector acceptance than what is available from the published
literature.",0110045v2
2001-10-18,Weak Lensing of the CMB: Power Spectrum Covariance,"We discuss the non-Gaussian contribution to the power spectrum covariance of
cosmic microwave background (CMB) anisotropies resulting through weak
gravitational lensing angular deflections and the correlation of deflections
with secondary sources of temperature fluctuations generated by the large scale
structure, such as the integrated Sachs-Wolfe effect and the Sunyave-Zel'dovich
effect. This additional contribution to the covariance of binned angular power
spectrum, beyond the well known cosmic variance and any associated instrumental
noise, results from a trispectrum, or a four point correlation function, in
temperature anisotropy data. With substantially wide bins in multipole space,
the resulting non-Gaussian contribution from lensing to the binned power
spectrum variance is insignificant out to multipoles of a few thousand and is
not likely to affect the cosmological parameter estimation through acoustic
peaks and the damping tail. The non-Gaussian contribution to covariance,
however, should be considered when interpreting binned CMB power spectrum
measurements at multipoles of a few thousand corresponding to angular scales of
few arcminutes and less.",0110415v1
2001-10-19,Galactic Foregrounds in OVRO and UCSB South Pole 1994 Cosmic Microwave Background Anisotropy Data,"We study Galactic emission foreground contamination of the OVRO and UCSB
South Pole 1994 cosmic microwave background (CMB) anisotropy data by
cross-correlating with templates of infrared dust emission and new high
resolution $H_{\alpha}$ data. $H_{\alpha}$ data provide rough upper limits on
the level of free-free emission in the data sets. The cross-correlation
analysis does not contradict a two component foreground emission hypothesis,
with the two dust-correlated components being free-free emission and spinning
dust emission.",0110457v2
2001-11-29,Cosmic Inversion: Reconstructing primordial spectrum from CMB anisotropy,"We investigate the possibility of reconstructing the initial spectrum of
density fluctuations from the cosmic microwave background (CMB) anisotropy. As
a first step toward this program, we consider a spatially flat, CDM dominated
universe. In this case, it is shown that, with a good accuracy, the initial
spectrum satisfies a first order differential equation with the source
determined by the CMB angular correlation function. The equation is found to
contain singularities arising from zeros of the acoustic oscillations in the
transfer functions. Nevertheless, we find these singularities are not fatal,
and the equation can be solved nicely. We test our method by considering simple
analytic forms for the transfer functions. We find the initial spectrum is
reproduced within 5% accuracy even for a spectrum that has a sharp spike.",0111549v1
2001-12-06,Cosmic String Signatures in the Cosmic Microwave Background Anisotropies,"We briefly review certain aspects of cosmic microwave background anisotropies
as generated in passive and active models of structure formation. We then focus
on cosmic strings based models and discuss their status in the light of current
high-resolution observations from the BOOMERanG, MAXIMA and DASI
collaborations. Upcoming megapixel experiments will have the potential to look
for non-Gaussian features in the CMB temperature maps with unprecedented
accuracy. We therefore devote the last part of this review to treat the
non-Gaussianity of the microwave background and present a method for
computation of the bispectrum from simulated string realizations.",0112145v1
2002-01-12,Cosmological Recombination of Lithium and its Effect on the Microwave Background Anisotropies,"The cosmological recombination history of lithium, produced during Big--Bang
nucleosynthesis, is presented using updated chemistry and cosmological
parameters consistent with recent cosmic microwave background (CMB)
measurements. For the popular set of cosmological parameters, about a fifth of
the lithium ions recombine into neutral atoms by a redshift $z\sim 400$. The
neutral lithium atoms scatter resonantly the CMB at 6708 \AA and distort its
intensity and polarization anisotropies at observed wavelengths around $\sim
300 \mu$m, as originally suggested by Loeb (2001). The modified anistropies
resulting from the lithium recombination history are calculated for a variety
of cosmological models and found to result primarily in a suppression of the
power spectrum amplitude. Significant modification of the power spectrum occurs
for models which assume a large primordial abundance of lithium. While
detection of the lithium signal might prove difficult, if offers the
possibility of inferring the lithium primordial abundance and is the only probe
proposed to date of the large-scale structure of the Universe for $z\sim
500-100$.",0201189v2
2002-02-26,Cosmic microwave background and large scale structure limits on the interaction between dark matter and baryons,"We study the effect on the cosmic microwave background (CMB) anisotropy and
large scale structure (LSS) power spectrum of a scattering interaction between
cold dark matter and baryons. This scattering alters the CMB anisotropy and LSS
spectrum through momentum transfer between the cold dark matter particles and
the baryons. We find that current CMB observations can put an upper limit on
the scattering cross section which is comparable with or slightly stronger than
previous disk heating constraints at masses greater than 1 GeV, and much
stronger at smaller masses. When large-scale structure constraints are added to
the CMB limits, our constraint is more stringent than this previous limit at
all masses. In particular, a dark matter-baryon scattering cross section
comparable to the ``Spergel-Steinhardt'' cross section is ruled out for dark
matter mass greater than 1 GeV.",0202496v2
2002-06-07,Newtonian motion as origin of anisotropy of the local velocity field of galaxies,"The origins of recently reported anisotropy of the local velocity field of
nearby galaxies (velocities < 500 km/s corresponding to the distance less than
8 Mpc) are studied. The exact solution of the Newtonian equation for the
expanding Universe is obtained. This solution allows us to separate the
Newtonian motion of nearby galaxies from the Hubble flow by the transition to
the conformal coordinates. The relation between the Hubble flow and the
Newtonian motion is established. We show that the anisotropic local velocity
field of nearby galaxies can be formed by such a Newtonian motion in the
expanding Universe, if at the moment of the capture of galaxies by the central
gravitational field.",0206114v6
2002-06-13,"Morphology of the Secondary CMB Anisotropies: the Key to ""Smoldering"" Reionization","We show how the morphological analysis of the maps of the secondary CMB
anisotropies can detect an extended period of ``smoldering'' reionization,
during which the universe remains partially ionized. Neither radio observations
of the redshifted 21cm line nor IR observations of the redshifted Lyman-alpha
forest will be able to detect such a period. The most sensitive to this kind of
non-gaussianity parameters are the number of regions in the excursion set, the
perimeter of the excursion set, and the genus of the largest (by area) region.
For example, if the universe reionized fully at z=6, but maintained about 1/3
mean ionized fraction since z=20, then a 2 arcmin map with 500x500 pixel
resolution and a signal-to-noise ratio S/N=1/2 allows to detect the
non-gaussianity due to reionization with better than 99% confidence level.",0206217v1
2002-06-16,Nonlinear Turbulent Magnetic Diffusion and Mean-Field Dynamo,"The nonlinear coefficients defining the mean electromotive force (i.e., the
nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, the
nonlinear kappa-tensor, etc.) are calculated for an anisotropic turbulence. A
particular case of an anisotropic background turbulence (i.e., the turbulence
with zero mean magnetic field) with one preferential direction is considered.
It is shown that the toroidal and poloidal magnetic fields have different
nonlinear turbulent magnetic diffusion coefficients. It is demonstrated that
even for a homogeneous turbulence there is a nonlinear effective velocity which
exhibits diamagnetic or paramagnetic properties depending on anisotropy of
turbulence and level of magnetic fluctuations in the background turbulence.
Analysis shows that an anisotropy of turbulence strongly affects the nonlinear
mean electromotive force. Two types of nonlinearities (algebraic and dynamic)
are also discussed. The algebraic nonlinearity implies a nonlinear dependence
of the mean electromotive force on the mean magnetic field. The dynamic
nonlinearity is determined by a differential equation for the magnetic part of
the alpha-effect. It is shown that for the alpha-Omega axisymmetric dynamo the
algebraic nonlinearity alone cannot saturate the dynamo generated mean magnetic
field while the combined effect of the algebraic and dynamic nonlinearities
limits the mean magnetic field growth. Astrophysical applications of the
obtained results are discussed.",0206261v1
2002-06-20,Sensitivity of the Cosmic Microwave Background Anisotropy to Initial Conditions in Quintessence Cosmology,"We analyze the evolution of energy density fluctuations in cosmological
scenarios with a mixture of cold dark matter and quintessence, in which the
quintessence field is modeled by a constant equation of state. We obtain
analytic expressions for the time evolution of the quintessence perturbations
in models with light fields. The fluctuations behave analogously to a driven
harmonic oscillator, where the driving term arises from the inhomogeneities in
the surrounding cosmological fluid. We demonstrate that the homogeneous
solution, determined by the initial conditions, is completely sub-dominant to
the inhomogeneous solution for physically realistic scenarios. Thus we show
that the cosmic microwave background anisotropy predicted for such models is
highly insensitive to the initial conditions in the quintessence field.",0206372v2
2002-08-06,Magnetic field amplification in CDM anisotropic collapse,"We use the Zel'dovich approximation to analyse the amplification of magnetic
fields in gravitational collapse of cold dark matter during the mildly
nonlinear regime, and identify two key features. First, the anisotropy of
collapse effectively eliminates one of the magnetic components, confining the
field in the pancake plane. Second, in agreement with recent numerical
simulations, we find that the shear anisotropy can amplify the magnetic field
well beyond the isotropic case. Our results suggest that the magnetic strengths
observed in spiral and disk galaxies today might have originated from seeds
considerably weaker than previous estimates.",0208126v2
2002-08-10,OVRO CMB Anisotropy Measurement Constraints on Flat-Lambda and Open CDM Cosmogonies,"We use Owens Valley Radio Observatory (OVRO) cosmic microwave background
(CMB) anisotropy data to constrain cosmological parameters. We account for the
OVRO beamwidth and calibration uncertainties, as well as the uncertainty
induced by the removal of non-CMB foreground contamination. We consider open
and spatially-flat-Lambda cold dark matter cosmogonies, with
nonrelativistic-mass density parameter Omega_0 in the range 0.1--1,
baryonic-mass density parameter Omega_B in the range (0.005--0.029)h^{-2}, and
age of the universe t_0 in the range (10--20) Gyr. Marginalizing over all
parameters but Omega_0, the OVRO data favors an open (spatially-flat-Lambda)
model with Omega_0 ~= 0.33 (0.1). At the 2 sigma confidence level model
normalizations deduced from the OVRO data are mostly consistent with those
deduced from the DMR, UCSB South Pole 1994, Python I-III, ARGO, MAX 4 and 5,
White Dish, and SuZIE data sets.",0208216v1
2002-08-30,The Far-Infrared Background Correlation with CMB Lensing,"The intervening large--scale structure distorts cosmic microwave background
(CMB) anisotropies via gravitational lensing. The same large--scale structure,
traced by dusty star--forming galaxies, also induces anisotropies in the
far--infrared background (FIRB). We investigate the resulting inter--dependence
of the FIRB and CMB with a halo model for the FIRB. In particular, we calculate
the cross--correlation between the lensing potential and the FIRB. The lensing
potential can be quadratically estimated from CMB temperature and/or
polarization maps. We show that the cross--correlation can be measured with
high signal--to--noise with data from the Planck Surveyor. We discuss how such
a measurement can be used to understand the nature of FIRB sources and their
relation to the distribution of dark matter.",0209001v1
2002-10-01,Missing Parameters in the CMB Physics,"The lecture is devoted to the comparison of a few models of cosmic
recombination kinetics with recent CMB anisotropy data and to corresponding
predictions for the upcoming PLANCK mission. The influence of additional
sources of ionized photons at the epoch of hydrogen recombination may restrict
our possibility to estimate the density of baryonic fraction of matter when
using PLANCK data. This new source of degeneracy of the cosmological parameters
which can be estimated from the CMB anisotropy data can mimic the distortion of
the CMB power spectrum for different models of baryonic matter. I would like to
point out that realistic values of the cosmological parameters can not be
obtained without PLANCK polarization data.",0210034v1
2002-10-29,The Inflationary Gravity Waves in light of recent Cosmic Microwave Background Anisotropies data,"One of the major predictions of inflation is the existence of a stochastic
background of cosmological gravitational waves (GW). These gravitational waves
can induce significant temperature anisotropies in the Cosmic Microwave
Background (CMB) on the angular scales recently probed by the Archeops
experiment. Here, we perform a combined analysis of Archeops together with
information from other CMB experiments and/or cosmological datasets, in order
to constrain the amplitude of the GW background. We find that, for a
scale-invariant GW background, the ratio of tensor/scalar perturbations at the
CMB quadrupole is now constrained to be $r \leq 0.43$ at 95% c.l., while the
bound on the spectral index of primordial density fluctuations is
$n_S=0.97_{-0.12}^{+0.10}$. We discuss the implications for future GW
detections through CMB polarization measurements.",0210606v3
2002-11-28,Cosmological Effects of a Class of Fluid Dark Energy Models,"We study the impact of a generalized Chaplygin gas as a candidate for dark
energy on CMB anisotropies. The generalized Chaplygin gas is a fluid component
with an exotic equation of state, $p = - A/\rho^\alpha$ (a polytropic gas with
negative constant and exponent). Such component interpolates in time between
dust and a cosmological constant, with an intermediate behaviour as $p=\alpha
\rho$. Perturbations of this fluid are stable on small scales, but behave in a
very different way with respect to standard quintessence. Moreover, a
generalized Chaplygin gas could also represent an archetypal example of a
phenomenological unified models of dark energy and dark matter. The results
presented here show how the CMB anisotropies induced by this class of models
differ from a $\Lambda$CDM model.",0211626v1
2002-12-11,Observational constraints on the curvaton model of inflation,"Simple curvaton models can generate a mixture of of correlated primordial
adiabatic and isocurvature perturbations. The baryon and cold dark matter
isocurvature modes differ only by an observationally null mode in which the two
perturbations almost exactly compensate, and therefore have proportional
effects at linear order. We discuss the CMB anisotropy in general mixed models,
and give a simple approximate analytic result for the large scale CMB
anisotropy. Working numerically we use the latest WMAP observations and a
variety of other data to constrain the curvaton model. We find that models with
an isocurvature contribution are not favored relative to simple purely
adiabatic models. However a significant primordial totally correlated baryon
isocurvature perturbation is not ruled out. Certain classes of curvaton model
are thereby ruled out, other classes predict enough non-Gaussianity to be
detectable by the Planck satellite. In the appendices we review the relevant
equations in the covariant formulation and give series solutions for the
radiation dominated era.",0212248v3
2002-12-28,Turbulent Magnetohydrodynamic Elasticity: I. Boussinesq-like Approximations for Steady Shear,"We re-examine the Boussinesq hypothesis of an effective turbulent viscosity
within the context of simple closure considerations for models of strong
magnetohydrodynamic turbulence. Reynolds-stress and turbulent Maxwell-stress
closure models will necessarily introduce a suite of transport coefficients,
all of which are to some degree model-dependent. One of the most important
coefficients is the relaxation time for the turbulent Maxwell stress, which
until recently has been relatively ignored. We discuss this relaxation within
the context of magnetohydrodynamic turbulence in steady high Reynolds-number,
high magnetic-Reynolds-number shearing flows. The relaxation time for the
turbulent Maxwell stress is not limited by the shear time scale, in contrast
with Reynolds-stress closure models for purely hydrodynamical turbulence. The
anisotropy of the turbulent stress tensor for magnetohydrodynamic turbulence,
even for the case of zero mean-field considered here, can therefore not be
neglected. This shear-generated anisotropy can be interpreted as being due to
an effective turbulent elasticity, in analogy to the Boussinesq turbulent
viscosity. We claim that this turbulent elasticity should be important for any
astrophysical problem in which the turbulent stress in quasi-steady shear has
been treated phenomenologically with an effective viscosity.",0212556v1
2003-01-02,"First Results From an X-ray, Weak Lensing, and Sunyaev-Zeldovich Effect Survey of Nearby Clusters: Abell 3266","As part of a combined Sunyaev-Zeldovich Effect (SZE), X-ray and weak lensing
survey of low redshift (z<0.1) X-ray clusters, we present SZE images of the
z=0.059 X-ray cluster Abell 3266 at three observing frequencies (150, 220, 275
GHz) and after the spectral subtraction of primary Cosmic Microwave Background
(CMB) anisotropies. These images were generated using the ACBAR bolometer array
operated on the Viper telescope at the South Pole. The multi-frequency data
from ACBAR should allow us to overcome one of the main obstacles facing the
analysis of SZE observations of nearby clusters, i.e. contamination from
primary Cosmic Microwave Background (CMB) anisotropies.",0301024v1
2003-01-17,Clues on the Evolution of Cluster Galaxies From The Analysis of Their Orbital Anisotropies,"We study the evolution of galaxies in clusters by the analysis of a sample of
about 3000 galaxies, members of 59 clusters from the ESO Nearby Abell Cluster
Survey (ENACS). We distinguish four cluster galaxy populations, based on their
radial and velocity distributions within the clusters. Using the class of
ellipticals and S0's (excluding the very bright ellipticals), we determine the
average cluster mass profile, that we compare with mass models available from
numerical simulations. We then use this cluster mass profile to solve for the
anisotropy profiles of the three other cluster galaxy populations, viz. the
very bright ellipticals, the early spirals, and the late spirals with the
emission-line galaxies. We discuss the implications of our findings for the
evolution of cluster galaxies.",0301343v1
2003-01-29,Galactic Foreground Constraints from the Python V Cosmic Microwave Background Anisotropy Data,"We constrain Galactic foreground contamination of the Python V cosmic
microwave background anisotropy data by cross correlating it with foreground
contaminant emission templates. To model foreground emission we use 100 and 12
$\mu$m dust emission templates and two point source templates based on the PMN
survey. The analysis takes account of inter-modulation correlations in 8
modulations of the data that are sensitive to a large range of angular scales
and also densely sample a large area of sky. As a consequence the analysis here
is highly constraining. We find little evidence for foreground contamination in
an analysis of the whole data set. However, there is indication that
foregrounds are present in the data from the larger-angular-scale modulations
of those Python V fields that overlap the region scanned earlier by the UCSB
South Pole 1994 experiment. This is an independent consistency cross-check of
findings from the South Pole 1994 data.",0301581v2
2003-02-02,Evidence for anisotropy in the distribution of short-lived gamma-ray bursts,"Measurements of the two-point angular correlation function w(\theta) for 407
short gamma-ray bursts collected in the Current BATSE Catalogue reveal a ~2
\sigma deviation from isotropy on angular scales \theta ~ 2-4 degrees. Such an
anisotropy is not observed in the distribution of long gamma-ray bursts and
hints to the presence of repeated bursts for up to ~13% of the sources under
exam. However, the available data cannot exclude the signal as due to the
presence of large-scale structure. Under this assumption, the amplitude of the
observed w(\theta) is compatible with those derived for different populations
of galaxies up to redshifts ~0.5, result that suggests short gamma-ray bursts
to be relatively local sources.",0302009v1
2003-02-03,Global Anisotropy Versus Small-Scale Fluctuations in Neutrino Flux in Core-Collapse Supernova Explosions,"Effects of small-scale fluctuations in the neutrino radiation on
core-collapse supernova explosions are examined. Through a parameter study with
a fixed radiation field of neutrinos, we find substantial differences between
the results of globally anisotropic neutrino radiation and those with
fluctuations. As the number of modes of fluctuations increases, the shock
positions, entropy distributions, and explosion energies approach those of
spherical explosion. We conclude that global anisotropy of the neutrino
radiation is the most effective mechanism of increasing the explosion energy
when the total neutrino luminosity is given. This supports the previous
statement on the explosion mechanism by Shimizu and coworkers.",0302015v5
2003-02-05,Cosmic ray spectrum and anisotropies from the knee to the second knee,"We consider the scenario in which the knee in the cosmic ray spectrum is due
to a change in the escape mechanism of cosmic rays from the Galaxy from one
dominated by transverse diffusion to one dominated by drifts. We show that this
scenario explains not only the changes in spectral slope at the knee and at the
second knee, but can also account for the main characteristics of the observed
energy dependent anisotropy amplitude and phase of first harmonic in the energy
range between $10^{15}$ and $10^{18}$ eV. This provides a useful handle to
distinguish this diffusion/drift model from other scenarios proposed to explain
the knee in the spectrum.",0302082v2
2003-02-05,Late reionizations of the Universe and their manifestation in the CMB data,"We investigate two sets of two-epoched reionization models and their
manifestation in the CMB anisotropy and polarization data of the recent WMAP
project and make some predictions for the future PLANCK missions. In the first
set of models, the universe was reionized twice, first at z~15 by population
III stars and then at z~6 by stars in large galaxies. In the second set of
models, the extra peak-like reionization at high redshifts z > 100 is induced
by the decay of unstable particles, followed by the standard picture of
reionization at z~6. We examine the general properties of these two-epoched
reionization models and their implication in the WMAP CMB temperature
anisotropy-polarization cross-correlation. We have shown that these models have
comparable likelihood values for the WMAP data and distinct characters which
can be tested with the Planck high sensitivities.",0302085v3
2003-02-25,Early Quintessence in Light of WMAP,"We examine the cosmic microwave background (CMB) anisotropy for signatures of
early quintessence dark energy -- a non-negligible quintessence energy density
during the recombination and structure formation eras. Only very recently does
the quintessence overtake the dark matter and push the expansion into
overdrive. Because the presence of early quintessence exerts an influence on
the clustering of dark matter and the baryon-photon fluid, we may expect to
find trace signals in the CMB and the mass fluctuation power spectrum. In
detail, we demonstrate that suppressed clustering power on small length-scales,
as suggested by the combined Wilkinson Microwave Anisotropy Probe (WMAP) / CMB
/ large scale structure data set, is characteristic of early quintessence. We
identify a set of concordant models, and map out directions for further
investigation of early quintessence.",0302505v2
2003-03-05,Spectral Properties of Compressible Magnetohydrodynamic Turbulence from Numerical Simulations,"We analyze the spectral properties of driven, supersonic compressible
magnetohydrodynamic (MHD) turbulence obtained via high-resolution numerical
experiments, for application to understanding the dynamics of giant molecular
clouds. Via angle-averaged power spectra, we characterize the transfer of
energy from the intermediate, driving scales down to smaller dissipative
scales, and also present evidence for inverse cascades that achieve
modal-equipartition levels on larger spatial scales. Investigating compressive
versus shear modes separately, we evaluate their relative total power, and find
that as the magnetic field strength decreases, (1) the shear fraction of the
total kinetic power decreases, and (2) slopes of power-law fits over the
inertial range steepen. To relate to previous work on incompressible MHD
turbulence, we present qualitative and quantitative measures of the
scale-dependent spectral anisotropy arising from the shear-Alfv\'{e}n cascade,
and show how these vary with changing mean magnetic field strength. Finally, we
propose a method for using anisotropy in velocity centroid maps as a diagnostic
of the mean magnetic field strength in observed cloud cores.",0303103v1
2003-03-10,Annual modulation in the scattering of J1819+3845: peculiar plasma velocity and anisotropy,"We present two years of monitoring observations of the extremely variable
quasar J1819+3845. We observe large yearly changes in the timescale of the
variations (from ~ 1 hour to ~ 10 hours at 5GHz). This annual effect can only
be explained if the variations are caused by a propagation effect, and thus
affected by the Earth's relative speed through the projected intensity pattern.
To account for this effect, the scattering plasma must have a transverse
velocity with respect to the local standard of rest.
  The velocity calculated from these observations is in good agreement with
that obtained from a two telescope delay experiment (Dennett-Thorpe & de Bruyn
2001). We also show that either the source itself is elongated, or that the
scattering plasma is anisotropic, with an axial ratio of >6:1. As the source is
extended on scales relevant to the scattering phenomenon, it seems plausible
that the anisotropy is due to the source itself, but this remains to be
investigated. From the scintillation characteristics we find that the
scattering material is a very strong, thin scatterer within ~ten parsecs. We
determine a source size at 5GHz of 100 to 900microarcsecs, and associated
brightness temperatures of 10^{10} to 10^{12}K.",0303201v1
2003-05-09,Full-Sky Search for Ultra High Energy Cosmic Ray Anisotropies,"Using data from the SUGAR and the AGASA experiments taken during a 10 yr
period with nearly uniform exposure to the entire sky, we search for
large-scale anisotropy patterns in the arrival directions of cosmic rays with
energies > 10^{19.6} eV. We determine the angular power spectrum from an
expansion in spherical harmonics for modes out to \ell=5. Based on available
statistics, we find no significant deviation from isotropy. We compare the
rather modest results which can be extracted from existing data samples with
the results that should be forthcoming as new full-sky observatories begin
operation.",0305158v3
2003-05-14,The shape of the CMB power spectrum,"The recent WMAP data represents a milestone in cosmology and helps constrain
cosmological parameters with unprecedented accuracy. In this work we combine
the WMAP data with previous CMB anisotropy measurements at smaller angular
scales to characterize the shape of the CMB anisotropy power spectrum. We carry
out a phenomenological analysis of the data. By allowing non-physical shapes of
the power spectrum we analyse high and low frequency experiments separately and
together. We find that WMAP dramatically constrains the power spectrum up to l
\~ 700. On smaller scales, the data show discrepancies that can be associated
with experimental systematics. If we combine all types of experiments, the
observable features in the power spectrum are in excellent agreement with the
WMAP cosmological parameter estimation. This work illustrates the advantages of
a model-independent approach to understanding experimental systematics that
might affect CMB observations.",0305254v1
2003-05-26,Small-scale CMB Temperature and Polarization Anisotropies due to Patchy Reionization,"We study contributions from inhomogeneous (patchy) reionization to arcminute
scale ($1000 < \ell < 10,000$) cosmic microwave background (CMB) anisotropies.
We show that inhomogeneities in the ionization fraction, rather than in the
mean density, dominate both the temperature and the polarization power spectra.
Depending on the ionization history and the clustering bias of the ionizing
sources, we find that rms temperature fluctuations range from 2 $\mu$K to 8
$\mu$K and the corresponding values for polarization are over two orders of
magnitude smaller. Reionization can significantly bias cosmological parameter
estimates and degrade gravitational lensing potential reconstruction from
temperature maps but not from polarization maps. We demonstrate that a simple
modeling of the reionization temperature power spectrum may be sufficient to
remove the parameter bias. The high-$\ell$ temperature power spectrum will
contain some limited information about the sources of reionization.",0305471v2
2003-06-01,Tests of Statistical Significance and Background Estimation in Gamma Ray Air Shower Experiments,"In this paper we discuss several methods of significance calculation and
point out the limits of their applicability. We then introduce a self
consistent scheme for source detection and discuss some of its properties. The
method allows incorporating background anisotropies by vetoing existing small
scale regions on the sky and compensating for known large scale anisotropies.
By giving an example using Milagro gamma ray observatory we demonstrate how the
method can be employed to relax the detector stability assumption. Two
practical implementations of the method are discussed. The method is universal
and can be used with any large field-of-view detector, where the object of
investigation, steady or transient, point or extended, traverses its field of
view.",0306015v1
2003-06-21,The Statistical Significance of the Low CMB Mulitipoles,"The Wilkinson Microwave Anisotropy Probe (WMAP) has measured lower amplitudes
for the temperature quadrupole and octopole anisotropies than expected in the
best fitting (concordance) Lambda-dominated cold dark matter cosmology. Some
authors have argued that this discrepancy may require new physics. Yet the
statistical significance of this result is not clear. Some authors have applied
frequentist arguments and claim that the discrepancy would occur by chance
about 1 time in 700 if the concordance model is correct. Other authors have
used Bayesian arguments to claim that the data show marginal evidence for new
physics. I investigate these confusing and apparently conflicting claims using
a frequentist analysis and a simplified Bayesian analysis. I conclude that the
WMAP results are consistent with the concordance Lambda CDM model.",0306431v3
2003-07-05,Large Scale Cosmic Microwave Background Anisotropies and Dark Energy,"In this note we investigate the effects of perturbations in a dark energy
component with a constant equation of state on large scale cosmic microwave
background anisotropies. The inclusion of perturbations increases the large
scale power. We investigate more speculative dark energy models with w<-1 and
find the opposite behaviour. Overall the inclusion of perturbations in the dark
energy component increases the degeneracies. We generalise the parameterization
of the dark energy fluctuations to allow for an arbitrary const ant sound
speeds and show how constraints from cosmic microwave background experiments
change if this is included. Combining cosmic microwave background with large
scale structure, Hubble parameter and Supernovae observations we obtain
w=-1.02+-0.16 (1 sigma) as a constraint on the equation of state, which is
almost independent of the sound speed chosen. With the presented analysis we
find no significant constraint on the constant speed of sound of the dark
energy component.",0307104v2
2003-07-31,Statistical isotropy of the Cosmic Microwave Background,"The breakdown of statistical homogeneity and isotropy of cosmic perturbations
is a generic feature of ultra large scale structure of the cosmos, in
particular, of non trivial cosmic topology. The statistical isotropy (SI) of
the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is
sensitive to this breakdown on the largest scales comparable to, and even
beyond the cosmic horizon. We propose a set of measures, $\kappa_\ell$
($\ell=1,2,3, ...$) which for non-zero values indicate and quantify statistical
isotropy violations in a CMB map. We numerically compute the predicted
$\kappa_\ell$ spectra for CMB anisotropy in flat torus universe models.
Characteristic signature of different models in the $\kappa_\ell$ spectrum are
noted.",0308002v1
2003-09-11,Optimized in-flight absolute calibration for extended CMB surveys,"Accurate measurements of the Cosmic Microwave Background (CMB) anisotropy
call for high precision and reliability of the in-flight calibration. For
extended surveys the CMB dipole provides an excellent calibration source at
frequencies lower than 200 GHz; however poorly known foreground emissions, such
as diffuse galactic components, complicate the signal and introduce a
systematic error in the calibration. We show that introducing a weight function
that takes into account the uncertainty in the a priori knowledge of the sky,
allows us to substantially improve the calibration accuracy with respect to
methods involving galactic latitude cuts. This new method is tested for
Planck-LFI radiometers at 30 and 100 GHz. On short time scales (less than 1
day) the absolute calibration of each channel can be recovered with an overall
1-2% accuracy. We also consider the effect of CMB anisotropy itself on the
calibration, and find that knowledge of the CMB pattern on large scales is
needed to keep the short-time scale calibration accuracy within 1%",0309317v1
2003-09-15,The MAXIMA Experiment: Latest Results and Consistency Tests,"The MAXIMA cosmic microwave background anisotropy experiment had a
significant impact on cosmology. Results from the program have played a
significant role in determining the geometry of the universe, given strong
supporting evidence to inflation, and, in combination with other astrophysical
data, showed that the universe is filled with dark matter and energy. We
present a subset of the internal consistency checks that were carried out on
the MAXIMA-1 data prior to their release, which demonstrate that systematics
errors were much smaller than statistical errors. We also discuss the MAXIMA-2
flight and data, compare the maps of MAXIMA-1 and -2 in areas where they
overlap and show that the two independent experiments confirm each other. All
of these results demonstrate that MAXIMA mapped the cosmic microwave background
anisotropy with high accuracy",0309409v1
2003-09-16,Polarization Measures And Nature Of Dark Energy,"Polarization measures, on wide angular scales, together with anisotropy data,
can fix DE parameters. Here we discuss the sensitivity needed to provide
significant limits. Our analysis puts in evidence that a class of models
predicts low correlation or anticorrelation between polarization and anisotropy
at low l. This class includes open models and models with DE due to a
Ratra--Peebles (RP) potential. Results on this point, given in a previous paper
of ours, are updated and partially corrected. We outline that, with the
sensitivity of experiments like SPOrt or WMAP, high values of Lambda (energy
scale in the RP potential) can be excluded. With the sensitivity expected for
PLANCK, the selection will extend to much lower Lambda's.",0309438v1
2003-09-25,Evolution of Second-Order Cosmological Perturbations and Non-Gaussianity,"We present a second-order gauge-invariant formalism to study the evolution of
curvature perturbations in a Friedmann-Robertson-Walker universe filled by
multiple interacting fluids. We apply such a general formalism to describe the
evolution of the second-order curvature perturbations in the standard
one-single field inflation, in the curvaton and in the inhomogeneous reheating
scenarios for the generation of the cosmological perturbations. Moreover, we
provide the exact expression for the second-order temperature anisotropies on
large scales, including second-order gravitational effects and extend the
well-known formula for the Sachs-Wolfe effect at linear order. Our findings
clarify what is the exact non-linearity parameter f_NL entering in the
determination of higher-order statistics such as the bispectrum of Cosmic
Microwave Background temperature anisotropies. Finally, we compute the level of
non-Gaussianity in each scenario for the creation of cosmological
perturbations.",0309692v3
2003-10-03,Current Status and Perspectives of Cosmic Microwave Background Observations,"Measurements of the cosmic microwave background (CMB) radiation provide a
unique opportunity for a direct study of the primordial cosmic plasma at
redshift z ~1000. The angular power spectra of temperature and polarisation
fluctuations are powerful observational objectives as they encode information
on fundamental cosmological parameters and on the physics of the early
universe. A large number of increasingly ambitious balloon-borne and
ground-based experiments have been carried out following the first detection of
CMB anisotropies by COBE-DMR, probing the angular power spectrum up to high
multipoles. The recent data from WMAP provide a new major step forward in
measurements percision. The ESA mission Planck Surveyor, to be launched in
2007, is the third-generation satellite devoted to CMB imaging. Planck is
expected to extract the full cosmological information from temperature
anisotropies and to open up new fronteers in the CMB field.",0310089v1
2003-10-06,Dust during the Reionization,"The possibility that population III stars have reionized the Universe at
redshifts greater than 6 has recently gained momentum with WMAP polarization
results. Here we analyse the role of early dust produced by these stars and
ejected into the intergalactic medium. We show that this dust, heated by the
radiation from the same population III stars, produces a submillimetre excess.
The electromagnetic spectrum of this excess could account for a significant
fraction of the FIRAS (Far Infrared Absolute Spectrophotometer) cosmic far
infrared background above 700 micron. This spectrum, a primary anisotropy
($\Delta T$) spectrum times the $\nu^2$ dust emissivity law, peaking in the
submillimetre domain around 750 micron, is generic and does not depend on other
detailed dust properties. Arcminute--scale anisotropies, coming from
inhomogeneities in this early dust, could be detected by future submillimetre
experiments such as Planck HFI.",0310135v2
2003-10-08,Radio Interferometers with wide bandwidths,"The Australia Telescope Compact Array and the Very Large Array are currently
being upgraded to operate with wide bandwidths; interferometers dedicated to
the measurement of cosmic microwave background anisotropies are being designed
with large instantaneous bandwidths for high sensitivity. Interferometers with
wide instantaneous bandwidths that do not operate with correlators capable of
decomposing the bands into narrow channels suffer from `bandwidth smearing'
effects in wide-field imaging. The formalism of mosaic imaging is extended here
to interferometers with finite bandwidths to examine the consequences for the
imaging of wide fields if very wide instantaneous bandwidths are used. The
formalism presented here provides an understanding of the signal processing
associated with wide-band interferometers: mosaicing may be viewed as
decomposing visibilities over wide observing bands and, thereby, avoiding
`bandwidth smearing' effects in wide-field imaging. In particular, the
formalism has implications for interferometer measurements of the angular power
spectrum of cosmic microwave background anisotropies: mosaic-mode observing
with wide-band radio interferometers decompose wide-band data and synthesize
narrow filters in multipole space.",0310240v1
2003-11-18,Anisotropy in the distribution of satellites around primary galaxies in the 2dFGRS: the Holmberg effect,"We have analysed a sample of satellite and primary galaxies in the 2dF galaxy
redshift survey. In our study we find a strong statistical evidence of the
Holmberg effect (that is a tendency for satellites to avoid regions along the
line defined by the primary plane) within 500 kpc of projected distance to the
primary. This effect is present only when we restrict to objects with radial
velocity relative to the primary $|\Delta v|<160$ km/s which correspond
approximately to the mean of the distribution. We explore the dependence of
this anisotropy on spectral type ($\eta$), colours, and luminosities of both
primaries and satellites, finding that objects with a low present-day star
formation rate present the most significant effect.",0311432v1
2003-12-04,Measuring the Small-Scale Power Spectrum of Cosmic Density Fluctuations Through 21 cm Tomography Prior to the Epoch of Structure Formation,"The thermal evolution of the cosmic gas decoupled from that of the cosmic
microwave background (CMB) at a redshift z~200. Afterwards and before the first
stars had formed, the cosmic neutral hydrogen absorbed the CMB flux at its
resonant 21cm spin-flip transition. We calculate the evolution of the spin
temperature for this transition and the resulting anisotropies that are
imprinted on the CMB sky due to linear density fluctuations during this epoch.
These anisotropies at an observed wavelength of 10.56[(1+z)/50] meters, contain
an amount of information that is orders of magnitude larger than any other
cosmological probe. Their detection, although challenging, could tightly
constrain any possible running of the spectral index from inflation (as
suggested by WMAP), small deviations from Gaussianity, or any significant
contribution from neutrinos or warm dark matter to the cosmic mass budget.",0312134v2
2004-01-05,S-Z Anisotropy & Cluster Counts: Consistent Selection of sigma_8 and the Temperature-Mass Relation,"The strong dependence of the mass variance parameter, sigma_8, on the adopted
cluster mass-temperature relation is explored. A recently compiled X-ray
cluster catalog and various mass-temperature relations are used to derive the
corresponding values of sigma_8. Calculations of the power spectrum of the CMB
anisotropy induced by the Sunyaev-Zeldovich effect and cluster number counts
are carried out in order to assess the need for a consistent choice of the
mass-temperature scaling and the parameter sigma_8. We find that the
consequences of inconsistent choice of the mass-temperature relation and
sigma_8 could be quite substantial, including a considerable mis-estimation of
the magnitude of the power spectrum and cluster number counts. Our results can
partly explain the large scatter between published estimates of the power
spectrum and number counts. We also show that the range of values of the
power-law index in the scaling C_l ~ sigma_8^[6-7] deduced in previous studies
is likely overestimated; we obtain a more moderate dependence, C_l ~
sigma_8^[4].",0401033v1
2004-01-09,Dynamical friction in flattened systems: A numerical test of Binney's approach,"We carry out a set of self-consistent N-body calculations to investigate how
important the velocity anisotropy in non-spherical dark-matter haloes is for
dynamical friction. For this purpose we allow satellite galaxies to orbit
within flattened and live dark-matter haloes (DMHs) with aspect-ratio q_h=0.6
and compare the resulting orbit evolution with a semi-analytic code. This code
solves the equation of motion of satellites orbiting within the same DMH and
implements, according to the dynamical friction model, either Chandrasekhar's
formula, which does not incorporate the velocity anisotropy, or Binney's
description of dynamical friction in anisotropic systems. In the numerical and
the two semi-analytic models the satellites are given different initial orbital
inclinations and orbital eccentricities.
  We find that Binney's approach successfully describes the overall satellite
decay and orbital inclination decrease for the whole set of orbits, with an
averaged discrepancy of less than 4 per cent in orbital radius during the first
3 orbits. If Chandrasekhar's expression is used instead, the discrepancy
increases to 20 per cent and no inclination decrease can be observed. Binney's
treatment therefore appears to provide a significantly improved treatment of
dynamical friction in anisotropic systems.",0401159v1
2004-02-28,Sensitivity of quintessence perturbations to initial conditions,"Gauge invariant quintessence perturbations in the quintessence and cold dark
matter (QCDM) model are investigated. For three cases of constant
equation-of-state (EOS) parameter, linear scalar field potential, and
supergravity scalar field potential, their perturbation evolutions have a
similar dependence on EOS parameter and scale, but they have different
sensitivity to the initial conditions due to the different shapes of the
quintessence potential. They have a minor effect on primary CMB anisotropies,
but change the secondary CMB effect in different ways. The first case is
insensitive to initial quintessence perturbations and only modifies the
Integrated Sachs-Wolfe (ISW) effect within a factor of 2. The other two cases
are sensitive to initial conditions at large scales and could affect the
secondary CMB anisotropies drastically depending on how smooth the initial
perturbations are. This makes it possible for future cosmological probes to
provide constraints on quintessence properties.",0403006v1
2004-03-02,Weak Lensing of the CMB by Large-Scale Structure,"Several recent papers have studied lensing of the CMB by large-scale
structures, which probes the projected matter distribution from $z=10^3$ to
$z\simeq 0$. This interest is motivated in part by upcoming high resolution,
high sensitivity CMB experiments, such as APEX/SZ, ACT, SPT or Planck, which
should be sensitive to lensing. In this paper we examine the reconstruction of
the large-scale dark matter distribution from lensed CMB temperature
anisotropies. We go beyond previous work in using numerical simulations to
include higher order, non-Gaussian effects and study how well the quadratic
estimator of \cite{Hu01a} is able to recover the input field. We also study
contamination by kinetic Sunyaev-Zel'dovich signals, which is spectrally
indistinguishable from lensed CMB anisotropies. We finish by estimating the
sensitivity of the previously cited experiments.",0403075v2
2004-03-06,WMAP Constraints on Decaying Cold Dark Matter,"We re-formulate cosmological perturbations in the decaying cold dark matter
model, and calculate cosmological microwave background (CMB) anisotropies. By
comparing our theoretical predictions with recent observational data from the
Wilkinson Microwave Anisotropy Probe(WMAP), we derive a new bound on the
abundance and lifetime of decaying dark matter particles. We show that the data
of WMAP alone do not prefer the decaying cold dark matter model: the lifetime
is constrained to \Gamma^{-1}> 123 Gyr at 68% C.L. (52 Gyr at 95.4% C.L.) when
cold dark matter consists only of such decaying particles. We also consider a
more general case in which cold dark matter consists of both stable and
decaying particles, and show that the constraint generalizes down to
\Omega_{DDM}h^2 < -0.5 (Gamma^{-1}/1 Gyr)^{-1}+0.12 for \Gamma^{-1} > 5 Gyr at
95.4% C.L.. These bounds are robust and widely applicable, because they are
derived only from gravitational effects and therefore do not rely on the
details of decay channels or decay products.",0403164v2
2004-03-10,LISA Measurement of Gravitational Wave Background Anisotropy: Hexadecapole Moment via a Correlation Analysis,"We discuss spatial fluctuations in the gravitational wave background arising
from unresolved Galactic binary sources, such as close white dwarf binaries,
due to the fact the galactic binary source distribution is anisotropic. We
introduce a correlation analysis of the two data streams of the Laser
Interferometer Space Antenna (LISA) to extract spherical harmonic coefficients,
in an independent manner, of the hexadecapole moment ($l=4$) related to the
projected two-dimensional density distribution of the binary source population.
The proposed technique complements and improves over previous suggestions in
the literature to measure the gravitational wave background anisotropy based on
the time modulation of data as LISA orbits around the Sun. Such techniques,
however, are restricted only to certain combinations of spherical harmonic
coefficients of the galaxy with no ability to separate them individually. With
LISA, $m=2,3$ and 4 coefficients of the hexadecapole ($l=4$) can be measured
with signal-to-noise ratios at the level of 10 and above in a certain
coordinate system. In addition to the hexadecapole coefficients, when combined
with the time modulation analysis, the correlation study can also be used, in
principle, to measure quadrupole coefficients of the binary distribution.",0403259v1
2004-04-20,Constraints On The Topology Of The Universe From The WMAP First-Year Sky Maps,"We compute the covariance expected between the spherical harmonic
coefficients $a_{\ell m}$ of the cosmic microwave temperature anisotropy if the
universe had a compact topology. For fundamental cell size smaller than the
distance to the decoupling surface, off-diagonal components carry more
information than the diagonal components (the power spectrum). We use a maximum
likelihood analysis to compare the Wilkinson Microwave Anisotropy Probe
first-year data to models with a cubic topology. The data are compatible with
finite flat topologies with fundamental domain $L > 1.2$ times the distance to
the decoupling surface at 95% confidence. The WMAP data show reduced power at
the quadrupole and octopole, but do not show the correlations expected for a
compact topology and are indistinguishable from infinite models.",0404400v1
2004-05-03,Constraining Born-Infeld models of dark energy with CMB anisotropies,"We study the CMB constraints on two Dark Energy models described by scalar
fields with different Lagrangians, namely a Klein-Gordon and a Born-Infeld
field. The speed of sound of field fluctuations are different in these two
theories, and therefore the predictions for CMB and structure formation are
different. Employing the WMAP data on CMB, we make a likelihood analysis on a
grid of theoretical models. We constrain the parameters of the models and
compute the probability distribution functions for the equation of state. We
show that the effect of the different sound speeds affects the low multipoles
of CMB anisotropies, but is at most marginal for the class of models studied
here.",0405041v1
2004-05-10,Primordial magnetic field and non-Gaussianity of the 1-year Wilkinson Microwave Anisotropy Probe (WMAP) data,"Alfven turbulence caused by statistically isotropic and homogeneous
primordial magnetic field induces correlations in the cosmic microwave
background anisotropies. The correlations are specifically between spherical
harmonic modes a_{l-1,m} and a_{l+1,m}. In this paper we approach this issue
from phase analysis of the CMB maps derived from the WMAP data sets. Using
circular statistics and return phase mapping we examine phase correlation of
\Delta l=2 for the primordial non-Gaussianity caused by the Alfven turbulence
at the epoch of recombination. Our analyses show that such specific features
from the power-law Alfven turbulence do not contribute significantly in the
phases of the maps and could not be a source of primordial non-Gaussianity of
the CMB.",0405181v2
2004-05-20,B polarization of the CMB from Faraday rotation,"We study the effect of Faraday rotation due to a homogeneous magnetic field
on the polarization of the cosmic microwave background (CMB). Scalar
fluctuations give rise only to parity-even E-type polarization of the CMB.
However in the presence of a magnetic field, a non-vanishing parity-odd B-type
polarization component is produced through Faraday rotation. We derive the
exact solution for the E and B modes generated by scalar perturbations
including the Faraday rotation effect of a uniform magnetic field, and evaluate
their cross-correlations with temperature anisotropies. We compute the angular
autocorrelation function of the B-modes in the limit that the Faraday rotation
is small. We find that primordial magnetic fields of present strength around
$B_0=10^{-9}$G rotate E-modes into B-modes with amplitude comparable to those
due to the weak gravitational lensing effect at frequencies around $\nu=30$
GHz. The strength of B-modes produced by Faraday rotation scales as
$B_0/\nu^2$. We evaluate also the depolarizing effect of Faraday rotation upon
the cross correlation between temperature anisotropy and E-type polarization.",0405396v4
2004-07-27,Theoretical uncertainty in baryon oscillations,"We discuss the systematic uncertainties in the recovery of dark energy
properties from the use of baryon acoustic oscillations as a standard ruler. We
demonstrate that while unknown relativistic components in the universe prior to
recombination would alter the sound speed, the inferences for dark energy from
low-redshift surveys are unchanged so long as the microwave background
anisotropies can measure the redshift of matter-radiation equality, which they
can do to sufficient accuracy. The mismeasurement of the radiation and matter
densities themselves (as opposed to their ratio) would manifest as an incorrect
prediction for the Hubble constant at low redshift. In addition, these
anomalies do produce subtle but detectable features in the microwave
anisotropies.",0407539v1
2004-07-30,An Unbiased Measurement of Ho through Cosmic Background Imager Observations of the Sunyaev-Zel'dovich Effect in Nearby Galaxy Clusters,"We present Ho results from Cosmic Background Imager (CBI) observations of the
Sunyaev-Zel'dovich Effect (SZE) in 7 galaxy clusters, A85, A399, A401, A478,
A754, A1651, and A2597. These observations are part of a program to study a
complete, volume-limited sample of low-redshift (z<0.1), X-ray selected
clusters. Our focus on nearby objects allows us to study a well-defined,
orientation unbiased sample, minimizing systematic errors due to cluster
asphericity. We use density models derived from ROSAT imaging data and
temperature measurements from ASCA and BeppoSAX spectral observations. We
quantify in detail sources of error in our derivation of Ho, including
calibration of the CBI data, density and temperature models from the X-ray
data, Cosmic Microwave Background (CMB) primary anisotropy fluctuations, and
residuals from radio point source subtraction. From these 7 clusters we obtain
a result of Ho = 67^{+30}_{-18}, ^{+15}_{-6} km/s/Mpc for an unweighted sample
average. The respective quoted errors are random and systematic uncertainties
at 68% confidence. The dominant source of error is confusion from intrinsic
anisotropy fluctuations.",0408005v1
2004-08-09,Multiple inflation and the WMAP 'glitches',"Observations of anisotropies in the cosmic microwave background by the
Wilkinson Microwave Anisotropy Probe suggest the possibility of oscillations in
the primordial density perturbation. Such deviations from the usually assumed
scale-free spectrum were predicted in the multiple inflation model wherein
`flat direction' fields undergo rapid phase transitions due to the breaking of
supersymmetry by the large vacuum energy driving inflation. This causes sudden
changes in the mass of the (gravitationally coupled) inflaton and interrupts
its slow roll. We calculate analytically the resulting modifications to the
density perturbation and demonstrate how the oscillations arise.",0408138v3
2004-08-18,Search for Small-Scale Anisotropy of Cosmic Rays above 10^19 eV with HiRes Stereo,"We present the results of a search for small-scale anisotropy in the
distribution of arrival directions of cosmic rays above 10^19 eV measured in
stereo by the High Resolution Fly's Eye (HiRes) experiment. Performing an
autocorrelation scan in energy and angular separation, we find that the
strongest correlation signal in the HiRes stereo data set recorded between
December 1999 and January 2004 is consistent with the null hypothesis of
isotropically distributed arrival directions. These results are compared to
previous claims of significant small-scale clustering in the AGASA data set.",0408343v1
2004-08-25,"The spectrum of particles accelerated in relativistic, collisionless shocks","We analytically study diffusive particle acceleration in relativistic,
collisionless shocks. We find a simple relation between the spectral index s
and the anisotropy of the momentum distribution along the shock front. Based on
this relation, we obtain s = (3beta_u - 2beta_u*beta_d^2 + beta_d^3) / (beta_u
- beta_d) for isotropic diffusion, where beta_u (beta_d) is the upstream
(downstream) fluid velocity normalized to the speed of light. This result is in
agreement with previous numerical determinations of s for all (beta_u,beta_d),
and yields s=38/9 in the ultra-relativistic limit. The spectrum-anisotropy
connection is useful for testing numerical studies and for constraining
non-isotropic diffusion results. It implies that the spectrum is highly
sensitive to the form of the diffusion function for particles travelling along
the shock front.",0408489v1
2004-08-30,Anisotropic Distribution of SDSS Satellite Galaxies: Planar (not Polar) Alignment,"The distribution of satellite galaxies relative to isolated host galaxies in
the Sloan Digital Sky Survey (SDSS) is investigated. Host-satellite systems are
selected using three different methods, yielding samples of ~3300, ~1600, and
\~950 satellites. In the plane of the sky, the distributions of all three
samples show highly significant deviations from circular symmetry (> 99.99%, >
99.99%, and 99.79% confidence levels, respectively), and the degree of
anisotropy is a strong function of the projected radius, r_p, at which the
satellites are found. For r_p < 100 kpc, the SDSS satellites are aligned
preferentially with the major axes of the hosts. This is in stark contrast to
the Holmberg effect, in which satellites are aligned with the minor axes of
host galaxies. The degree of anisotropy in the distribution of the SDSS
satellites decreases with r_p and is consistent with an isotropic distribution
at of order the 1-sigma level for 250 kpc < r_p < 500 kpc.",0408559v2
2004-09-06,The current status of observational cosmology,"Observational cosmology has indeed made very rapid progress in recent years.
The ability to quantify the universe has largely improved due to observational
constraints coming from structure formation. The transition to precision
cosmology has been spearheaded by measurements of the anisotropy in the cosmic
microwave background (CMB) over the past decade. Observations of the large
scale structure in the distribution of galaxies, high red-shift supernova, have
provided the required complementary information. We review the current status
of cosmological parameter estimates from joint analysis of CMB anisotropy and
large scale structure (LSS) data. We also sound a note of caution on
overstating the successes achieved thus far.",0409131v2
2004-09-15,The Search for Anisotropy in the Arrival Directions of Ultra-High Energy Cosmic Rays Observed by the High Resolution Fly's Eye Detector in Monocular Mode,"The High Resolution Fly's Eye HiRes-I detector has now been in operation in
monocular mode for over six years. During that time span, HiRes-I has
accumulated a larger exposure to Ultra-High Energy Cosmic Rays (UHECRs) above
10^19 eV than any other experiment built to date. This presents an
unprecedented opportunity to search for anisotropy in the arrival directions of
UHECRs. We present results of a search for dipole distributions oriented
towards major astrophysical landmarks and a search for small-scale clustering.
We conclude that the HiRes-I data set is, in fact, consistent with an isotropic
source model.",0409377v1
2004-09-15,First measurements of the polarization of the cosmic microwave background radiation at small angular scales from CAPMAP,"Polarization results from the Cosmic Anisotropy Polarization MAPper (CAPMAP)
experiment are reported. These are based upon 433 hours, after cuts, observing
a 2 square degree patch around the North Celestial Pole (NCP) with four 90 GHz
correlation polarimeters coupled to optics defining $4\arcmin$ beams. The
E-mode flat bandpower anisotropy within $\ell=940^{+330}_{-300}$ is measured as
66$^{+69}_{-29} \mu$K$^2$; the 95% Confidence level upper limit for B-mode
power within $\ell=1050^{+590}_{-520}$ is measured as 38 $\mu$K$^2$.",0409380v3
2004-09-30,Statistical Imprints of SZ Effects in the Cosmic Microwave Background,"We review several aspects of the Sunyaev-Zel'dovich (SZ) effect associated
with the large scale baryon distribution and its characteristic signatures in
the statistics of cosmic microwave background (CMB) anisotropies. We discuss
(1) the contributions to the angular power spectrum from the thermal and
kinetic SZ effects, (2) the effect of SZ non-Gaussianities on cosmological
parameter estimation, and (3) the SZ-induced CMB polarization towards galaxy
clusters. We also discuss the extent to which recent measurements of small
angular scale CMB anisotropy can be accounted for by SZ clusters and the
potential use of SZ polarization towards large samples of galaxy clusters as a
probe of dark energy parameters.",0410006v1
2004-10-11,CMB and foregrounds in WMAP first year data,"We perform a blind multi-component analysis of the WMAP 1 year foreground
cleaned maps using SMICA (Spectral Matching Independent Component Analysis). We
provide a new estimate of the CMB power spectrum as well as the amplitude of
the CMB anisotropies across frequency channels. We show that the CMB
anisotropies are compatible with temperature fluctuations as expected from the
standard paradigm. The analysis also allows us to identify and separate a weak
residual galactic emission present significantly in the Q-band outside of the
Kp2 mask limits, and mainly concentrated at low galactic latitudes. We produce
a map of this residual component by Wiener filtering using estimated
parameters. The level of contamination of CMB data by this component is
compatible with the WMAP team estimation of foreground residual contamination.
In addition, the multi-component analysis allows us to estimate jointly the
power spectrum of unresolved point source emission.",0410280v1
2004-11-10,On the Effects due to a Decaying Cosmological Fluctuation,"We present the initial conditions for a decaying cosmological perturbation
and study its signatures in the CMB anisotropies and matter power spectra. An
adiabatic decaying mode in presence of components which are not described as
perfect fluids (such as collisionless matter) decays slower than in a
perfect-fluid dominated universe and displays super-Hubble oscillations. By
including a correlated decaying mode with a red or a scale invariant spectrum,
the anisotropy pattern shows super-imposed oscillations before the first
Dopplear peak, while with a blue spectrum the amplitude of the secondary peaks
relative to the first one and the matter power spectrum can be altered. WMAP
first year data constrain the decaying to growing ratio of scale invariant
adiabatic fluctuations at the matter-radiation equality to less than 10%.",0411273v2
2004-11-15,The Planck Low Frequency Instrument,"Planck is the third generation of mm-wave instruments designed for space
observations of the cosmic microwave background (CMB) anisotropies within the
new Cosmic Vision 2020 ESA Science Program. Planck will map the whole sky with
unprecedented sensitivity, angular resolution, and frequency coverage, and it
likely leads us to the final comprehension of the CMB anisotropies. The Low
Frequency Instrument (LFI), operating in the 30-70 GHz range, is one of the two
instruments onboard Planck satellite, sharing the focal region of a 1.5 meter
off-axis dual reflector telescope together with the High Frequency Instrument
(HFI) operating at 100-857 GHz. We present LFI and discuss the major
instrumental systematic effects that could degrade the measurements and the
solutions adopted in the design and data analysis phase in order to adequately
reduce and control them.",0411412v1
2004-12-21,CMB lensing extraction and primordial non-Gaussianity,"The next generation of CMB experiments should get a better handle on
cosmological parameters by mapping the weak lensing deflection field, which is
separable from primary anisotropies thanks to the non-Gaussianity induced by
lensing. However, the generation of perturbations in the Early Universe also
produces a level of non-Gaussianity which is known to be small, but can
contribute to the anisotropy trispectrum at the same level as lensing. In this
work, we study whether the primordial non-Gaussianity can mask the lensing
statistics. We concentrate only on the ``temperature quadratic estimator'' of
lensing, which will be nearly optimal for the Planck satellite, and work in the
flat-sky approximation. We find that primordial non-Gaussianity contaminates
the deflection field estimator by roughly (0.1 f_NL)% at large angular scales,
which represents at most a 10% contribution, not sufficient to threaten lensing
extraction, but enough to be taken into account.",0412551v1
2004-12-22,Theoretical tools for CMB physics,"This review presents, in a self-consistent manner, those analytical tools
that are relevant for the analysis of the physics of CMB anisotropies generated
in different theoretical models of the early Universe. After introducing the
physical foundations of the Sachs-Wolfe effect, the origin and evolution of the
scalar, tensor and vector modes of the geometry is treated in both
gauge-invariant and gauge-dependent descriptions. Some of the recent progresses
in the theory of cosmological perturbations are scrutinized with particular
attention to their implications for the adiabatic and isocurvature paradigms,
whose description is reviewed both within conventional fluid approaches and
within the the Einstein-Boltzmann treatment. Open problems and theoretical
challenges for a unified theory of the early Universe are outlined in light of
their implications for the generation of large-scale anisotropies in the CMB
sky and in light of the generation of stochastic backgrounds of relic gravitons
between few Hz and the GHz.",0412601v3
2004-12-23,KASCADE: Astrophysical results and tests of hadronic interaction models,"KASCADE is a multi-detector setup to get redundant information on single air
shower basis. The information is used to perform multiparameter analyses to
solve the threefold problem of the reconstruction of (i)the unknown primary
energy, (ii) the primary mass, and (iii) to quantify the characteristics of the
hadronic interactions in the air-shower development. In this talk recent
results of the KASCADE data analyses are summarized concerning cosmic ray
anisotropy studies, determination of flux spectra for different primary mass
groups, and approaches to test hadronic interaction models. Neither large scale
anisotropies nor point sources were found in the KASCADE data set. The energy
spectra of the light element groups result in a knee-like bending and a
steepening above the knee. The topology of the individual knee positions shows
a dependency on the primary particle. Though no hadronic interaction model is
fully able to describe the multi-parameter data of KASCADE consistently, the
more recent models or improved versions of older models reproduce the data
better than few years ago.",0412610v1
2005-01-19,The first turbulent combustion,"The first turbulent combustion arises in a hot big bang cosmological model
Gibson (2004) where nonlinear exothermic turbulence permitted by quantum
mechanics, general relativity, multidimensional superstring theory, and fluid
mechanics cascades from Planck to strong force freeze out scales with gravity
balancing turbulent inertial-vortex forces. Interactions between Planck scale
spinning and non-spinning black holes produce high Reynolds number turbulence
and temperature mixing with huge Reynolds stresses driving the rapid inflation
of space. Kolmogorovian turbulent temperature patterns are fossilized as
strong-force exponential inflation stretches them beyond the scale of causal
connection ct where c is light speed and t is time. Fossil temperature
turbulence patterns seed nucleosynthesis, and then hydro-gravitational
structure formation in the plasma epoch, Gibson (1996, 2000). Evidence about
formation mechanisms is preserved by cosmic microwave background temperature
anisotropies. CMB spectra indicate hydro-gravitational fragmentation at
supercluster to galaxy masses in the primordial plasma with space stretched by
\~10^50. Bershadskii and Sreenivasan (2002, 2003) CMB multi-scaling
coefficients support a strong turbulence origin for the anisotropies prior to
the plasma epoch.",0501416v2
2005-02-21,Reionization History from Coupled CMB/21cm Line Data,"We study CMB secondary anisotropies produced by inhomogeneous reionization by
means of cosmological simulations coupled with the radiative transfer code
CRASH. The reionization history is consistent with the WMAP Thomson optical
depth determination. We find that the signal arising from this process
dominates over the primary CMB component for l > 4000 and reaches a maximum
amplitude of l(l+1)C_l/2\pi ~ 1.6 x 10^{-13} on arcmin scale, i.e. l as large
as several thousands. We then cross-correlate secondary CMB anisotropy maps
with neutral hydrogen 21cm line emission fluctuations obtained from the same
simulations. The two signals are highly anti-correlated on angular scales
corresponding to the typical size of HII regions (including overlapping) at the
21cm map redshift. We show how the CMB/21cm cross-correlation can be used to:
(a) study the nature of the reionization sources, (b) reconstruct the cosmic
reionization history, (c) infer the mean cosmic ionization level at any
redshift. We discuss the feasibility of the proposed experiment with
forthcoming facilities.",0502419v1
2005-02-25,Density scaling and anisotropy in supersonic MHD turbulence,"We study the statistics of density for supersonic turbulence in a medium with
magnetic pressure larger than the gaseous pressure. This study is motivated by
molecular cloud research. Our simulations exhibit clumpy density structures,
which contrast increases with the Mach number. At 10 Machs densities of some
clumps are three orders of magnitude higher than the mean density. These clumps
give rise to flat and approximately isotropic density spectrum corresponding to
the random distribution of clumps in space. We claim that the clumps originate
from our random, isotropic turbulence driving. When the contribution from those
clumps is suppressed by studying logarithm of density, the density statistics
exhibit scale-dependent anisotropy consistent with the models where density
structures arise from shearing by Alfv\'en waves. It is noteworthy that
originally such models were advocated for the case of low-Mach, nearly
incompressible turbulence.",0502547v1
2005-03-05,Signatures of Cosmic Strings in the Cosmic Microwave Background,"We report a search for signatures of cosmic strings in the the Cosmic
Microwave Background data from the Wilkinson Microwave Anisotropy Probe. We
used a digital filter designed to search for individual cosmic strings and
found no evidence for them in the WMAP CMB anisotropies to a level of $\Delta
T/T \sim 0.29$ mK. This corresponds to an absence of cosmic strings with $ G\mu
\ga 1.07 \times 10^{-5}$ for strings moving with velocity $v = c/\sqrt{2}$.
Unlike previous work, this limit does not depend on an assumed string
abundance. We have searched the WMAP data for evidence of a cosmic string
recently reported as the CSL-1 object, and found an ``edge'' with 2$\sigma$
significance. However, if this edge is real and produced by a cosmic string, it
would have to move at velocity $\ga$ 0.94c. We also present preliminary limits
on the CMB data that will be returned by the PLANCK satellite for comparison.
With the available information on the PLANCK satellite, we calculated that it
would be twice as sensitive to cosmic strings as WMAP.",0503120v1
2005-05-06,Large-Scale Sidereal Anisotropy of Galactic Cosmic-Ray Intensity Observed by the Tibet Air Shower Array,"We present the large-scale sidereal anisotropy ofgalactic cosmic-ray
intensity in the multi-TeV region observed with the Tibet-IIIair shower array
during the period from 1999 through 2003. The sidereal daily variation of
cosmic rays observed in this experiment shows an excess of relative intensity
around $4\sim7 $ hours local sidereal time, as well as a deficit around 12
hours local sidereal time. While the amplitude of the excess is not significant
when averaged over all declinations, the excess in individual declinaton bands
becomes larger and clearer as the viewing direction moves toward the south. The
maximum phase of the excess intensity changes from $\sim$7 at the northern
hemisphere to $\sim$4 hours at the equatorial region. We also show that both
the amplitude and the phase of the first harmonic vector of the daily variation
are remarkably independent of primary energy in the multi-TeV region. This is
the first result determining the energy and declination dependences of the full
24-hour profiles of the sidereal daily variation in the multi-TeV region with a
single air shower experiment.",0505114v1
2005-06-24,Large-Scale Anisotropy of EGRET Gamma Ray Sources,"In the course of its operation, the EGRET experiment detected high-energy
gamma ray sources at energies above 100 MeV over the whole sky. In this
communication, we search for large-scale anisotropy patterns among the
catalogued EGRET sources using an expansion in spherical harmonics, accounting
for EGRET's highly non-uniform exposure. We find significant excess in the
quadrupole and octopole moments. This is consistent with the hypothesis that,
in addition to the galactic plane, a second mid-latitude (5^{\circ} < |b| <
30^{\circ}) population, perhaps associated with the Gould belt, contributes to
the gamma ray flux above 100 MeV.",0506598v1
2005-08-05,Scalelengths in Dark Matter Halos,"We investigate a hypothesis regarding the origin of the scalelength in halos
formed in cosmological N-body simulations. This hypothesis can be viewed as an
extension of an earlier idea put forth by Merritt and Aguilar. Our findings
suggest that a phenomenon related to the radial orbit instability is present in
such halos and is responsible for density profile shapes. This instability sets
a scalelength at which the velocity dispersion distribution changes rapidly
from isotropic to radially anisotropic. This scalelength is reflected in the
density distribution as the radius at which the density profile changes slope.
We have tested the idea that radially dependent velocity dispersion anisotropy
leads to a break in density profile shape by manipulating the input of a
semi-analytic model to imitate the velocity structure imposed by the radial
orbit instability. Without such manipulation, halos formed are approximated by
single power-law density profiles and isotropic velocity distributions. Halos
formed with altered inputs display density distributions featuring scalelengths
and anisotropy profiles similar to those seen in cosmological N-body
simulations.",0508160v1
2005-08-30,Velocity moments of dark matter haloes,"Using cosmological N-body simulations we study the line-of-sight velocity
distribution of dark matter haloes focusing on the lowest-order even moments,
dispersion and kurtosis, and their application to estimate the mass profiles of
cosmological structures. For each of the ten massive haloes selected from the
simulation box we determine the virial mass, concentration and the anisotropy
parameter. In order to emulate observations from each halo we choose randomly
300 particles and project their velocities and positions along the line of
sight and on the surface of the sky, respectively. After removing interlopers
we calculate the profiles of the line-of-sight velocity moments and fit them
with the solutions of the Jeans equations. The estimates of virial mass,
concentration parameter and velocity anisotropy obtained in this way are in
good agreement with the values found from the full 3D analysis.",0508639v1
2005-09-12,Spontaneous Isotropy Breaking: A Mechanism for CMB Multipole Alignments,"We introduce a class of models in which statistical isotropy is broken
spontaneously in the CMB by a non-linear response to long-wavelength
fluctuations in a mediating field. These fluctuations appear as a gradient
locally and pick out a single preferred direction. The non-linear response
imprints this direction in a range of multipole moments. We consider two
manifestations of isotropy breaking: additive contributions and multiplicative
modulation of the intrinsic anisotropy. Since WMAP exhibits an alignment of
power deficits, an additive contribution is less likely to produce the observed
alignments than the usual isotropic fluctuations, a fact which we illustrate
with an explicit cosmological model of long-wavelength quintessence
fluctuations. This problem applies to other models involving foregrounds or
background anisotropy that seek to restore power to the CMB. Additive models
that account directly for the observed power exacerbate the low power of the
intrinsic fluctuations. Multiplicative models can overcome these difficulties.
We construct a proof of principle model that significantly improves the
likelihood and generates stronger alignments than WMAP in 30-45% of
realizations.",0509301v1
2005-09-15,Revisiting the (V/sigma)-epsilon anisotropy diagram of early-type galaxies using integral-field kinematics,"We use integral-field observation of the stellar kinematics obtained with
SAURON in combination with Schwarzschild dynamical models to revisit our
understanding of the classic (V/sigma)-epsilon anisotropy diagram of early-type
galaxies.",0509470v1
2005-09-25,Prediction of the Virgo axis anisotropy: CMB radiation illuminates the nature of things,"Recent findings of the anisotropy in the Cosmic Microwave Background (CMB)
radiation are confusing for standard cosmology. Remarkably, this fact has been
predicted several years ago in the framework of our model of the physical
world. Moreover, in exact agreement with our prediction the CMB has a preferred
direction towards the Virgo Cluster. The transpired structure of the CMB shows
workings of the suggested model of the physical world. Comprising the
information processes of Nature, this model presents a high-tech version of the
previous low-tech developments for mechanical ether and quantum vacuum. In the
current model, the phenomenon of Life turns up as a collective effect on the
""Internet of the Physical Universe"" using DNA structures for access codes. Most
convincingly, this construction points to a harmful analogy with so-called
""identity theft"" - improper manipulations with DNA of individual organisms can
destroy these organisms from a remote location without any physical contact.
Appearing incredible, such a possibility creates a superlative Experimentum
Crucis. In a broad sense, this surmised biological effect is intimately related
to the cosmological prediction of the structurization of the CMB, but it is
more compelling.",0509743v1
2005-10-14,Charting the New Frontier of the Cosmic Microwave Background Polarization,"The anisotropies of the cosmic microwave background are a gold mine for
cosmology and fundamental physics. ESA's Planck satellite should soon extract
all information from the temperature vein but will be limited concerning the
measurement of the degree of polarization of the anisotropies. This
polarization information allows new independent tests of the standard
cosmological paradigm, improves knowledge of cosmological parameters and last
but not least is the best window available for constraining the physics of the
very early universe, particularly the expected background of primordial
gravitational waves. But exploiting this vein will be a challenge, since the
sensitivity required is {\em at least} 10 times better than what Planck might
achieve at best, with the necessary matching level of control of all
systematics effects, both instrumental and astrophysical (foregrounds). We here
recall the cosmological context and the case for CMB polarization studies. We
also briefly introduce the SAMPAN project, a design study at CNES that aims at
detecting the primoridal gravitational wave background for a tensor to scalar
ratio T/S as small as 0.001.",0510423v1
2005-11-24,Distribution function of the dark matter,"There is good evidence from N-body simulations that the velocity distribution
in the outer parts of halos is radially anisotropic, with the kinetic energy in
the radial direction roughly equal to the sum of that in the two tangential
directions. We provide a simple algorithm to generate such cosmologically
important distribution functions. Introducing r_E(E), the radius of the largest
orbit of a particle with energy E, we show how to write down almost trivially a
distribution function of the form f(E,L)=g(r_E)/L for any spherical model --
including the NFW profile. We in addition give the generic form of the
distribution function for any model with a local density power-law index and
anisotropy parameter, and provide limiting forms appropriate for the central
parts and envelopes of dark matter halos. From those, we argue that, regardless
of the anisotropy, the density fall-off at large radii must evolve to 1/r^4 or
steeper ultimately.",0511687v2
2005-12-23,Local virial relation and velocity anisotropy in self-gravitating system,"We investigate the merging process in N-body self-gravitating system from the
viewpoints of the local virial relation which is the relation between the local
kinetic energy and the local potential. We compare both the density profile and
the phase space density profile in cosmological simulations with the critical
solutions of collisionless static state satisfying the local virial (LV)
relation. We got the results that the critical solution can explain the
characteristic density profile with the appropriate value of anisotropy
parameter $\beta \sim 0.5$. It can also explain the power law of the phase
space density profile in the outer part of a bound state. However, it fails in
explaining the central low temperature part which is connected to the scale
invariant phase space density. It can be well fitted to the critical solution
with the higher value of$\beta \sim 0.75$. These results indicate that the LV
relation is not compatible with the scale invariant phase space density in
cosmological simulation.",0512587v1
2006-01-16,Constraints on the coupled quintessence from cosmic microwave background anisotropy and matter power spectrum,"We discuss the evolution of linear perturbations in a quintessence model in
which the scalar field is non-minimally coupled to cold dark matter. We
consider the effects of this coupling on both cosmic microwave background
temperature anisotropies and matter perturbations. Due to the modification of
the scale of cold dark matter as $\rho_{c} = \rho_{c}^{(0)} a^{-3 + \xi}$, we
can shift the turnover in the matter power spectrum even without changing the
present energy densities of matter and radiation. This can be used to constrain
the strength of the coupling. We find that the phenomenology of this model is
consistent with current observations up to the coupling power $n_{c} \leq 0.01$
while adopting the current parameters measured by WMAP. Upcoming cosmic
microwave background observations continuing to focus on resolving the higher
peaks may put strong constraints on the strength of the coupling.",0601333v1
2006-01-25,Cosmic Microwave Background Polarization,"Cosmic microwave background (CMB) anisotropy is our richest source of
cosmological information; the standard cosmological model was largely
established thanks to study of the temperature anisotropies. By the end of the
decade, the Planck satellite will close this important chapter and move us
deeper into the new frontier of polarization measurements. Numerous
ground--based and balloon--borne experiments are already forging into this new
territory. Besides providing new and independent information on the primordial
density perturbations and cosmological parameters, polarization measurements
offer the potential to detect primordial gravity waves, constrain dark energy
and measure the neutrino mass scale. A vigorous experimental program is
underway worldwide and heading towards a new satellite mission dedicated to CMB
polarization.",0601576v3
2006-01-26,Small scale contributions to CMB: A coherent analysis,"We reanalyse Cosmic Microwave Background data from experiments probing both
large and small scales. We assume that measured anisotropies are due not only
to primary fluctuations but also, especially at small scales, to secondary
effects (namely the Sunyaev-Zel'dovich effect) and possible point source
contaminations. We first consider primary and secondary anisotropies only. For
the first time in such analyses, the cosmological dependence of secondary
fluctuations is fully taken into account. We show in that case that a higher
value of the normalisation $\sigma\_8$ is preferred, as found by previous
studies, but also higher values of the optical depth $\tau$ and power spectrum
index $n\_s$ are needed. In the second part of our analysis, we further include
possible contaminations from unresolved and unremoved point sources. Under
these considerations, we discuss the effects on the cosmological parameters. We
further obtain the best combination of relative contributions of the three
kinds of sources to the measured microwave power on small scales at each
frequency. Our method allows us to simultaneously obtain cosmological
parameters and explain the so-called small scale power excess in a consistent
way.",0601597v1
2006-02-06,Advanced Topics in Cosmology: A Pedagogical Introduction,"These lecture notes provide a concise, rapid and pedagogical introduction to
several advanced topics in contemporary cosmology. The discussion of thermal
history of the universe, linear perturbation theory, theory of CMBR temperature
anisotropies and the inflationary generation of perturbation are presented in a
manner accessible to someone who has done a first course in cosmology. The
discussion of dark energy is more research oriented and reflects the personal
bias of the author. Contents: (I) The cosmological paradigm and Friedmann model
(II) Thermal history of the universe (III) Structure formation and linear
perturbation theories (IV) Perturbations in dark matter and radiation (V)
Transfer function for matter perturbations (VI) Temperature anisotropies of
CMBR (VII) Generation of initial perturbations from inflation (VIII) The dark
energy.",0602117v1
2006-02-13,The shape of high order correlation functions in CMB anisotropy maps,"We present a phenomenological investigation of non-Gaussian effects that
could be seen on CMB temperature maps. Explicit expressions for the temperature
correlation functions are given for different types of primordial mode
couplings. We argue that a simplified description of the radial transfer
function for the temperature anisotropies allows to get insights into the
general properties of the bi and tri-spectra. The accuracy of these results is
explored together with the use of the small scale approximation to get explicit
expressions of high order spectra. The bi-spectrum is found to have alternate
signs for the successive acoustic peaks. Sign patterns for the trispectra are
more complicated and depend specifically on the type of metric couplings. Local
primordial couplings are found to give patterns that are different from those
expected from weak lensing effects.",0602276v1
2006-02-21,Long range correlation in cosmic microwave background radiation,"We investigate the statistical anisotropy and Gaussianity of temperature
fluctuations of Cosmic Microwave Background radiation (CMB) data from {\it
Wilkinson Microwave Anisotropy Probe} survey, using the multifractal detrended
fluctuation analysis, rescaled range and scaled windowed variance methods. The
multifractal detrended fluctuation analysis shows that CMB fluctuations has a
long range correlation function with a multifractal behavior. By comparing the
shuffled and surrogate series of CMB data, we conclude that the multifractality
nature of temperature fluctuation of CMB is mainly due to the long-range
correlations and the map is consistent with a Gaussian distribution.",0602461v2
2006-03-14,Global universe anisotropy probed by the alignment of structures in the cosmic microwave background,"We question the global universe isotropy by probing the alignment of local
structures in the cosmic microwave background (CMB) radiation. The original
method proposed relies on a steerable wavelet decomposition of the CMB signal
on the sphere. The analysis of the first-year WMAP data identifies a mean
preferred plane with a normal direction close to the CMB dipole axis, and a
mean preferred direction in this plane, very close to the ecliptic poles axis.
Previous statistical anisotropy results are thereby synthesized, but further
analyses are still required to establish their origin.",0603367v1
2006-03-23,"Probing Dynamics of Dark Energy with Supernova, Galaxy Clustering and the Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations","Using the Markov chain Monte Carlo (MCMC) method we perform a global analysis
constraining the dynamics of dark energy in light of the supernova (Riess
""Gold"" samples), galaxy clustering (SDSS 3D power spectra and SDSS lyman-\alpha
forest information) and the latest three-year Wilkinson Microwave Anisotropy
Probe (WMAP) observations. We have allowed the dark energy equation of state to
get across -1 and pay particular attention to the effects when incorrectly
neglecting dark energy perturbations. We find the parameter space of dynamical
dark energy is now well constrained and neglecting dark energy perturbations
will make the parameter space significantly smaller. Dynamical dark energy
model where the equation of state crosses -1 is mildly favored and the standard
\LambdaCDM model is still a good fit to the current data.",0603621v1
2006-04-06,On vector mode contribution to CMB temperature and polarization from local strings,"In a recent publication, we used the data from WMAP and SDSS to constrain the
primordial perturbations and to predict the B-mode polarization sourced by
cosmic string networks. We have been alerted by A. Slosar to the existence of
errors in the code we used to calculate the Cosmic Microwave Background
anisotropies from cosmic strings. Correcting the errors leads to a significant
increase in the vector mode contribution to the CMB temperature and
polarization anisotropies as well as an overall renormalization of the various
string spectra. In these notes we explain the nature of the errors and discuss
their implications for previously published constraints on cosmic strings based
on this code. The chief change in our results is that our derived limit for the
cosmic string tension is strengthened: G\mu < 1.8 (2.7) * 10^{-7} at 68 (95)%
confidence. We also note that the newly-enhanced vector mode contribution
produces a greatly-increased amplitude for B-mode polarization in the CMB which
could exceed the B-mode power produced by the lensing of primordial E-mode
polarization into B-mode polarization.",0604141v1
2006-04-06,"Amplified Doppler shift observed in diffraction images as function of the COBE ""ether drift"" direction","We report results on an ``one-way light path'' laser diffraction experiment
as a function of the laser beam alignment relative to the Earth's velocity
vector obtained by COBE measurements of the Doppler shift in the cosmic
microwave background radiation (CMBR). An amplified Doppler shift is observed
in the diffraction images, and the effect is compatible with a ``dipole'' speed
of light anisotropy due to Earth's motion relative to the ``CMBR rest frame'',
with an amplitude of $\delta c/\bar{c}=0.00123$. This amplitude coincides with
the value of the dipole temperature anisotropy $\delta T/\bar{T}=0.00123$ of
the CMBR obtained by COBE. Our results point out that it is not possible to
neglect the preferred frame imposed by the cosmology and they are well
described by the Ether Gauge Theory (an extension of the Lorentz's ether
theory) and it satisfies the cosmological time boundary condition.",0604145v1
2006-04-13,On the status of superheavy dark matter,"Superheavy particles are a natural candidate for the dark matter in the
universe and our galaxy, because they are produced generically during inflation
in cosmologically interesting amounts. The most attractive model for the origin
of superheavy dark matter (SHDM) is gravitational production at the end of
inflation. The observed cosmological density of dark matter determines the mass
of the SHDM particle as $m_X=$(a few)$\:\times 10^{13}$ GeV, promoting it to a
natural candidate for the source of the observed ultra-high energy cosmic rays
(UHECR). After a review of the theoretical aspects of SHDM, we up-date its
predictions for UHECR observations: no GZK cutoff, flat energy spectrum with
$dN/dE\approx 1/E^{1.9}$, photon dominance and galactic anisotropy. We analyze
the existing data and conclude that SDHM as explanation for the observed UHECRs
is at present disfavored but not yet excluded. We calculate the anisotropy
relevant for future Auger observations that should be the conclusive test for
this model. Finally, we emphasize that negative results of searches for SHDM in
UHECR do not disfavor SHDM as a dark matter candidate. Therefore, UHECRs
produced by SHDM decays and with the signatures as described should be searched
for in the future as subdominant effect.",0604311v1
2006-05-18,The Compton-Getting effect on ultra-high energy cosmic rays of cosmological origin,"Deviations from isotropy have been a key tool to identify the origin and the
primary type of cosmic rays at low energies. We suggest that the
Compton-Getting effect can play a similar role at ultra-high energies: If at
these energies the cosmic ray flux is dominated by sources at cosmological
distances, then the movement of the Sun relative to the cosmic microwave
background frame induces a dipole anisotropy at the 0.6% level. The energy
dependence and the orientation of this anisotropy provide important information
about the transition between galactic and extragalactic cosmic rays, the charge
of the cosmic ray primaries, the galactic magnetic field and, at the highest
energies, the energy-loss horizon of cosmic rays. A 3-sigma detection of this
effect requires around 10^6 events in the considered energy range and is thus
challenging but not impossible with present detectors. As a corollary we note
that the Compton-Getting effect allows one also to constrain the fraction of
the diffuse gamma-ray background emitted by sources at cosmological distance,
with promising detection possibilities for the GLAST satellite.",0605462v2
2006-07-04,Shear Recovery Accuracy in Weak Lensing Analysis with Elliptical Gauss-Laguerre Method,"We implement the Elliptical Gauss-Laguerre (EGL) galaxy-shape measurement
method proposed by Bernstein & Jarvis (2002) and quantify the shear recovery
accuracy in weak lensing analysis. This method uses a deconvolution fitting
scheme to remove the effects of the point-spread function (PSF). The test
simulates >10^7 noisy galaxy images convolved with anisotropic PSFs, and
attempts to recover an input shear. The tests are designed to be immune to
shape noise, selection biases, and crowding. The systematic error in shear
recovery is divided into two classes, calibration (multiplicative) and
additive, with the latter arising from PSF anisotropy. At S/N > 50, the
deconvolution method measures the galaxy shape and input shear to ~ 1%
multiplicative accuracy, and suppresses > 99% of the PSF anisotropy. These
systematic errors increase to ~ 4% for the worst conditions, with poorly
resolved galaxies at S/N ~ 20. The EGL weak lensing analysis has the best
demonstrated accuracy to date, sufficient for the next generation of weak
lensing surveys.",0607062v1
2006-07-08,Ellipticity in Cosmic Microwave Background as a Tracer of Large-Scale Universe,"Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data confirm the
ellipticity of anisotropies of Cosmic Microwave Background (CMB) maps, found
previously for Boomerang and WMAP 1-year high sensitivity maps. The low noise
level of the WMAP latter data enable also to show that, the ellipticity is a
property not described by the conventional cosmological model fitting the power
spectrum of CMB. As a large scale anomaly, the ellipticity characteristics are
consistent with the effect of geodesics mixing occurring in hyperbolic
Universe. Its relation to other large scale effects, i.e. to suppressed low
multipoles, as well as to dark energy if the latter is due to vacuum
fluctuations, is then an arising issue.",0607160v2
2006-07-12,Cosmology with CMB anisotropy,"Measurements of CMB anisotropy and, more recently, polarization have played a
very important role allowing precise determination of various parameters of the
`standard' cosmological model. The expectation of the paradigm of inflation and
the generic prediction of the simplest realization of inflationary scenario in
the early universe have also been established -- `acausally' correlated initial
perturbations in a flat, statistically isotropic universe, adiabatic nature of
primordial density perturbations. Direct evidence for gravitational instability
mechanism for structure formation from primordial perturbations has been
established. In the next decade, future experiments promise to strengthen these
deductions and uncover the remaining crucial signature of inflation -- the
primordial gravitational wave background.",0607255v1
2006-07-17,Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory,"Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius $A$. Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.",0607382v3
2006-07-26,Space-time Evolution and CMB Anisotropies from Quantum Gravity,"We propose an evolutional scenario of the universe which starts from quantum
states with conformal invariance, passing through the inflationary era, and
then makes transition to the conventional Einstein space-time. The space-time
dynamics is derived from the renormalizable higher-derivative quantum gravity
developed on the basis of a renormalizable conformal gravity in four
dimensions. Based on the linear perturbation theory in the inflationary
background, we simulate evolutions of gravitational scalar, vector and tensor
perturbations, and evaluate the spectra at the transition point located at the
beginning of the big bang. The obtained spectra cover the range of the
primordial spectra for explaining the tiny anisotropy in the homogeneous CMB.",0607586v3
2006-08-18,CMB Anomalies from Relic Anisotropy,"Most of the analysis of the Cosmic Microwave Background relies on the
assumption of statistical isotropy. However, given some recent evidence
pointing against isotropy, as for instance the observed alignment of different
multipoles on large scales, it is worth testing this assumption against the
increasing amount of available data. As a pivot model, we assume that the
spectrum of the primordial perturbations depends also on their directionality
(rather than just on the magnitude of their momentum, as in the standard case).
We explicitly compute the correlation matrix for the temperature anisotropies
in the simpler case in which there is a residual isotropy between two spatial
directions. As a concrete example, we consider a different initial expansion
rate along one direction, and the following isotropization which takes place
during inflation. Depending on the amount of inflation, this can lead to broken
statistical isotropy on the largest observable scales.",0608405v2
2006-08-23,Intracluster Medium through three years of WMAP,"Wilkinson Microwave Anisotropy Probe (WMAP) has provided us with the yet
highest resolution all-sky maps of the Cosmic Microwave Background. As a result
of thermal Sunyaev-Zel'dovich effect, clusters of galaxies are imprinted as
tiny, poorly resolved dips on top of primary CMB anisotropies in these maps.
Here, I describe different efforts to extract the physics of Intracluster
Medium (ICM) from the sea of primary CMB, through combining WMAP with
low-redshift galaxy or X-ray cluster surveys. This finally culminates at a mean
(universal) ICM pressure profile, which is for the first time directly
constrained from WMAP 3yr maps, and leads to interesting constraints on the ICM
baryonic budget.",0608503v1
2006-09-19,PAPPA: Primordial Anisotropy Polarization Pathfinder Array,"The Primordial Anisotropy Polarization Pathfinder Array (PAPPA) is a
balloon-based instrument to measure the polarization of the cosmic microwave
background and search for the signal from gravity waves excited during an
inflationary epoch in the early universe. PAPPA will survey a 20 x 20 deg patch
at the North Celestial Pole using 32 pixels in 3 passbands centered at 89, 212,
and 302 GHz. Each pixel uses MEMS switches in a superconducting microstrip
transmission line to combine the phase modulation techniques used in radio
astronomy with the sensitivity of transition-edge superconducting bolometers.
Each switched circuit modulates the incident polarization on a single detector,
allowing nearly instantaneous characterization of the Stokes I, Q, and U
parameters. We describe the instrument design and status.",0609546v1
2006-10-04,CMB Anisotropies at Second-Order II: Analytical Approach,"We provide an analytical approach to the second-order Cosmic Microwave
Background (CMB) anisotropies generated by the non-linear dynamics taking place
at last scattering. We study the acoustic oscillations of the photon-baryon
fluid in the tight coupling limit and we extend at second-order the Meszaros
effect. We allow for a generic set of initial conditions due to primordial
non-Gaussianity and we compute all the additional contributions arising at
recombination. Our results are useful to provide the full second-order
radiation transfer function at all scales necessary for establishing the level
of non-Gaussianity in the CMB.",0610110v2
2006-10-17,Cosmic microwave background limits on spatially homogeneous cosmological models with dark energy,"We investigate the effect of dark energy on the limits on the shear
anisotropy in spatially homogeneous Bianchi cosmological models obtained from
measurements of the temperature anisotropies in the cosmic microwave
background. We shall primarily assume that the dark energy is modelled by a
cosmological constant. In general, we find that there are tighter bounds on the
shear than in models with no cosmological constant, although the limits are
(Bianchi) model dependent. In addition, there are special spatially homogeneous
cosmological models whose rate of expansion is highly anisotropic, but whose
cosmic microwave background temperature is measured to be exactly isotropic at
one instant of time.",0610498v2
2006-11-08,Observational constraints on a decaying cosmological term,"We investigate the evolution of a universe with a decaying cosmological term
(vacuum energy) that is assumed to be a function of the scale factor. In this
model, while the cosmological term increases to the early universe, the
radiation energy density is lower than the model with the cosmological
""constant"". We find that the effects of the decaying cosmological term on the
expansion rate at the redshift z<2 is negligible.
  However, the decrease in the radiation density affects on the thermal history
of the universe; e.g. the photon decoupling occurs at higher $z$ compared to
the case of the standard \Lambda CDM model. As a consequence, a decaying
cosmological term affects on the cosmic microwave background anisotropy. We
show the angular power spectrum in D\Lambda CDM model and compare with the
Wilkinson Microwave Anisotropy Probe (WMAP) data.",0611258v2
2006-11-28,Constraining the Variation of G by Cosmic Microwave Background Anisotropies,"We use the Cosmic Microwave Background Anisotropies (CMBA) power spectra to
constrain the cosmological variation of gravitational constant G. It is found
that the sensitivity of CMBA to the variation of G is enhanced when G is
required to converge to its present value. The variations of G from the CMB
decoupling epoch z ~ 1000 to the present time are modelled by a step function
and a linear function of scale factor $a$ respectively, and the corresponding
95% confidence intervals for G/G_0 are [0.95, 1.05] and [0.89, 1.13], G_0 being
the present value. The CMBA constraint is unique in the sense that it entails
the range of redshift from z \approx 1000 to 0.",0611851v2
2007-02-06,"Primordial helium recombination III: Thomson scattering, isotope shifts, and cumulative results","Upcoming precision measurements of the temperature anisotropy of the cosmic
microwave background (CMB) at high multipoles will need to be complemented by a
more complete understanding of recombination, which determines the damping of
anisotropies on these scales. This is the third in a series of papers
describing an accurate theory of HeI and HeII recombination. Here we describe
the effect of Thomson scattering, the $^3$He isotope shift, the contribution of
rare decays, collisional processes, and peculiar motion. These effects are
found to be negligible: Thomson and $^3$He scattering modify the free electron
fraction $x_e$ at the level of several $\times 10^{-4}$. The uncertainty in the
$2^3P^o-1^1S$ rate is significant, and for conservative estimates gives
uncertainties in $x_e$ of order $10^{-3}$. We describe several convergence
tests for the atomic level code and its inputs, derive an overall $C_\ell$
error budget, and relate shifts in $x_e(z)$ to the changes in $C_\ell$, which
are at the level of 0.5% at $\ell =3000$. Finally, we summarize the main
corrections developed thus far. The remaining uncertainty from known effects is
$\sim 0.3%$ in $x_e$.",0702145v2
2007-02-13,On using the CMB shift parameter in tests of models of dark energy,"The so-called shift parameter is related to the position of the first
acoustic peak in the power spectrum anisotropies of the cosmic microwave
background (CMB) anisotropies. It is an often used quantity in simple tests of
dark energy models. However, the shift parameter is not directly measurable
from the cosmic microwave background, and its value is usually derived from the
data assuming a spatially flat cosmology with dark matter and a cosmological
constant. Our aim in this paper is to evaluate the effectiveness of the shift
parameter as a constraint on dark energy models, and the potential pitfalls in
using it as a test of non-standard models of dark energy. By comparing to full
CMB fits, we show that combining the shift parameter with the position of the
first acoustic peak in the CMB power spectrum improves the accuracy of the test
considerably.",0702343v1
2007-02-14,"Possible extensions of the standard cosmological model: anisotropy, rotation, and magnetic field","We show that the difference between the theoretically expected and measured
by WMAP amplitude of the quadrupole fluctuations of CMB can be related to the
impact of the anisotropic curvature of the homogeneous universe dominated by
the dark energy. In such universe the matter expansion becomes practically
isotropic just after the period of inflation and only at small redshifts the
anisotropic expansion is generated again by the small curvature $\Omega_K=1-
\Omega_m- \Omega_\Lambda \leq 10^{-4}$. For such models the possible deviations
from the parameters derived for the standard cosmological model are evidently
negligible but the correlations of large scale perturbations and distortions of
their Gaussianity are possible. Such models are also compatible with existence
of a homogeneous magnetic field and matter rotation which contribute to the low
$\ell$ anisotropy and can be considered as ``hidden parameters'' of the model.
Their influence can be observed as, for example, special correlations of small
scale fluctuations and the Faraday rotation of the CMB and radiation of the
farthest quasars. However, both the magnetic field and matter rotation require
also modifications of the simple models of isotropic inflation and they change
the evolutionary history of the early Universe.",0702381v2
2007-02-22,Temperature Anisotropy in a Shocked Plasma: Mirror-Mode Instabilities in the Heliosheath,"We show that temperature anisotropies induced at a shock can account for
interplanetary and planetary bow shock observations. Shocked plasma with
enhanced plasma beta is preferentially unstable to the mirror mode instability
downstream of a quasi-perpendicular shock and to the firehose instability
downstream of a quasi-parallel shock, consistent with magnetic fluctuations
observed downstream of a large variety of shocks. Our theoretical analysis of
the solar wind termination shock suggests that the magnetic holes observed by
Voyager 1 in the heliosheath are produced by the mirror mode instability. The
results are also of astrophysical interest, providing an energy source for
plasma heating.",0702599v1
2007-02-28,Looking for signs of Anisotropic Cosmological Expansion in the High-z Supernova data,"Several problematical epochs in cosmology, including the recent period of
structure formation (and acceleration), require us to understand cosmic
evolution during times when the basis of FRW expansion, the cosmological
principle, does not completely hold true. We consider that the breakdown of
isotropy and homogeneity at such times may be an important key towards
understanding cosmic evolution. To study this, we examine fluctuations in the
high-z supernova data to search for signs of large-scale anisotropy in the
Hubble expansion. Using a cosmological-model-independent statistical analysis,
we find mild evidence of real anisotropy in various circumstances. We consider
the significance of these results, and the importance of further searches for
violations of the cosmological principle.",0702730v1
2007-03-02,Dark-energy constraints with ALMA polarization measurements,"The Cosmic Microwave Background (CMB) physics can be used to constrain the
dark energy dynamics: B modes of the polarization of the diffuse CMB emission
as well as the polarized signal towards clusters of galaxies are sensitive to
the Hubble expansion rate and thus the dark energy abundance in the early stage
of cosmic acceleration. The first effect is sourced by gravitational lensing of
large scale cosmic structures, the second is due to scattering of the primary
CMB temperature anisotropy quadrupole by free electrons in cluster plasma. We
are investigating the capabilities of ALMA to detect these effects and
constrain the high-redshift dark energy abundance through measurements of
sub-arcminute CMB anisotropies.",0703050v1
1998-04-24,The Extraction of Anisotropic Contributions in Turbulent Flows,"We analyze turbulent velocity signals measured by two probes in the
atmosphere, both at the height of 35 meters but displaced by 40 cm nominally
orthogonal to the mean wind. Choosing a suitable coordinate system with respect
to that of the mean wind, we derive theoretical forms for second order
structure functions, and fit them to experimental data. We show that the effect
of flow anisotropy is small on the longitudinal component but significant on
the transverse component. The data provide an estimate of a universal exponent
from among a hierarchy that governs the decay of flow anisotropy with the
scale-size.",9804040v1
1999-09-29,Universality and saturation of intermittency in passive scalar turbulence,"The statistical properties of a scalar field advected by the non-intermittent
Navier-Stokes flow arising from a two-dimensional inverse energy cascade are
investigated. The universality properties of the scalar field are directly
probed by comparing the results obtained with two different types of injection
mechanisms. Scaling properties are shown to be universal, even though
anisotropies injected at large scales persist down to the smallest scales and
local isotropy is not fully restored. Scalar statistics is strongly
intermittent and scaling exponents saturate to a constant for sufficiently high
orders. This is observed also for the advection by a velocity field rapidly
changing in time, pointing to the genericity of the phenomenon. The persistence
of anisotropies and the saturation are both statistical signatures of the
ramp-and-cliff structures observed in the scalar field.",9909038v1
1993-05-13,Anisotropic Electron Coupling as a Phenomenological Model for High-Temperature Superconductors,"A three-dimensional weak coupling BCS model with an {\it anisotropic} pairing
interaction in momentum space is reported. It exhibits an anisotropic gap in
accord with recent experimental observations for high-$T_c$ oxides. The gap
ratio ${2 \Delta / k_B T_c }$ is calculated as function of the anisotropy ratio
of the electron pairing. It is found that the mean gap ratio decreases with
increasing anisotropy of the electron pairing, whereas the maximum gap ratio
increases. Assuming a unique strength of the effective electron interaction the
transition temperature turns out to be always larger than in the isotropic
case. The temperature dependence of the gap in the Cu-O plane and along the
c-axis of YBaCuO is presented.",9305009v1
1994-04-18,Temperature dependence of the superconducting gap anisotropy in Bi$_{2}$Sr$_{2}$Ca$_{1}$Cu$_{2}$O$_{8+x}$,"We present the first detailed data of the momentum-resolved, temperature
dependence of the superconducting gap of $Bi_{2}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$,
complemented by similar data on the intensity of the photoemission
superconducting condensate spectral area. The gap anisotropy between the
$\Gamma-\bar{M}$ and $\Gamma-X$ directions increases markedly with increasing
temperature, contrary to what happens for conventional anisotropic-gap
superconductors such as lead. Specifically, the size of the superconducting gap
along the $\Gamma-X$ direction decreases to values indistinguishable from zero
at temperatures for which the gap retains virtually full value along the
$\Gamma-\bar{M}$ direction.",9404056v1
1994-04-20,Gapless Phases in an s=1/2 Quantum Spin Chain with Bond Alternation,"The $S=1/2$ XXZ spin chain with the staggered XY anisotropy $$ H = J
\sum_{n}^{N} (S^{x}_{n} S^{x}_{n+1} + S^{y}_{n} S^{y}_{n+1} + \Delta S^{z}_{n}
S^{z}_{n+1}) - \delta \sum_{n}^{N} (-1)^{n} (S^{x}_{n} S^{x}_{n+1} - S^{y}_{n}
S^{y}_{n+1}) $$ is shown to possess gapless, Luttinger-liquid-like phases in a
wide range of its parameters: the XY-like phase and spin nematic phases, the
latter characterized by a two-spin order parameter breaking translational and
spin rotation symmetries. In the simplest, exactly solvable case $\Delta = 0$,
the spectrum remains gapless at arbitrary $J$ and $\delta$ and is described by
two massless Majorana (real) fermions with different velocities $v_{\pm} = |J
\pm \delta|$. At $|\delta| < J$ the staggered XY anisotropy does not influence
the ground state of the system (XY phase). At $|\delta| > J$, due to level
crossing, a spin nematic state is realized, with $\uparrow \uparrow \downarrow
\downarrow$ and $\uparrow \downarrow \downarrow \uparrow$ local symmetry of the
$xx$ and $yy$ spin correlations. The spin correlation functions are calculated
and the effect of thermally induced spin nematic ordering in the XY phase
(""order from disorder"") is discussed. The role of a finite $\Delta$ is studied
in the limiting cases $|\delta| \ll J$",9404063v1
1994-12-02,Fluctuations and Instabilities of Ferromagnetic Domain Wall pairs in an External Magnetic Field,"Soliton excitations and their stability in anisotropic quasi-1D ferromagnets
are analyzed analytically. In the presence of an external magnetic field, the
lowest lying topological excitations are shown to be either soliton-soliton or
soliton-antisoliton pairs. In ferromagnetic samples of macro- or mesoscopic
size, these configurations correspond to twisted or untwisted pairs of Bloch
walls. It is shown that the fluctuations around these configurations are
governed by the same set of operators. The soliton-antisoliton pair has exactly
one unstable mode and thus represents a critical nucleus for thermally
activated magnetization reversal in effectively one-dimensional systems. The
soliton-soliton pair is stable for small external fields but becomes unstable
for large magnetic fields. From the detailed expression of this instability
threshold and an analysis of nonlocal demagnetizing effects it is shown that
the relative chirality of domain walls can be detected experimentally in thin
ferromagnetic films. The static properties of the present model are equivalent
to those of a nonlinear sigma-model with anisotropies. In the limit of large
hard-axis anisotropy the model reduces to a double sine-Gordon model.",9412009v2
1995-03-12,Exact Solutions of Anisotropic Diffusion-Limited Reactions with Coagulation and Annihilation,"We report exact results for one-dimensional reaction-diffusion models A+A ->
inert, A+A -> A, and A+B -> inert, where in the latter case like particles
coagulate on encounters and move as clusters. Our study emphasized anisotropy
of hopping rates; no changes in universal properties were found, due to
anisotropy, in all three reactions. The method of solution employed mapping
onto a model of coagulating positive integer charges. The dynamical rules were
synchronous, cellular-automaton type. All the asymptotic large-time results for
particle densities were consistent, in the framework of universality, with
other model results with different dynamical rules, when available in the
literature.",9503064v1
1995-05-19,MAGNETISATION REVERSAL AND DOMAIN STRUCTURE IN THIN MAGNETIC FILMS: THEORY AND COMPUTER SIMULATION,"A model is introduced for the theoretical description of nanoscale magnetic
films with high perpendicular anisotropy. In the model the magnetic film is
described in terms of single domain magnetic grains, interacting via exchange
as well as via dipolar forces. Additionally, the model contains anisotropy
energy and a coupling to an external magnetic field. Disorder is taken into
account in order to describe realistic domain and domain wall structures.
Within this framework the dependence of the energy on the film thickness can be
discussed. The influence of a finite temperature as well as the dynamics can be
modeled by a Monte Carlo simulation. The results on the hysteresis loops, the
domain configurations, and the dynamics during the reversal process are in good
agreement with experimental findings.",9505084v1
1995-06-18,Magnetic anisotropies and general on--site Coulomb interactions in the cuprates,"This paper derives the anisotropic superexchange interactions from a Hubbard
model for excitations within the copper 3d band and the oxygen 2p band of the
undoped insulating cuprates. We extend the recent calculation of Yildirim et
al. [Phys. Rev. B {\bf VV}, pp, 1995] in order to include the most general
on--site Coulomb interactions (including those which involve more than two
orbitals) when two holes occupy the same site. Our general results apply when
the oxygen ions surrounding the copper ions form an octahedron which has
tetragonal symmetry (but may be rotated as in lanthanum cuprate). For the
tetragonal cuprates we obtain an easy--plane anisotropy in good agreement with
experimental values. We predict the magnitude of the small in--plane aniso",9506076v1
1995-11-20,Transverse Magnetoresistance of GaAs/AlGaAs Heterojunctions in the Presence of Parallel Magnetic Fields,"We have calculated the resistivity of a GaAs\slash AlGaAs heterojunction in
the presence of both an in--plane magnetic field and a weak perpendicular
component using a semiclassical Boltzmann transport theory. These calculations
take into account fully the distortion of the Fermi contour which is induced by
the parallel magnetic field. The scattering of electrons is assumed to be due
to remote ionized impurities. A positive magnetoresistance is found as a
function of the perpendicular component, in good qualitative agreement with
experimental observations. The main source of this effect is the strong
variation of the electronic scattering rate around the Fermi contour which is
associated with the variation in the mean distance of the electronic states
from the remote impurities. The magnitude of the positive magnetoresistance is
strongly correlated with the residual acceptor impurity density in the GaAs
layer. The carrier lifetime anisotropy also leads to an observable anisotropy
in the resistivity with respect to the angle between the current and the
direction of the in--plane magnetic field.",9511099v1
1995-11-29,Anisotropic optical response of the diamond (111)-2x1 surface,"The optical properties of the 2$\times$1 reconstruction of the diamond (111)
surface are investigated. The electronic structure and optical properties of
the surface are studied using a microscopic tight-binding approach. We
calculate the dielectric response describing the surface region and investigate
the origin of the electronic transitions involving surface and bulk states. A
large anisotropy in the surface dielectric response appears as a consequence of
the asymmetric reconstruction on the surface plane, which gives rise to the
zigzag Pandey chains. The results are presented in terms of the reflectance
anisotropy and electron energy loss spectra. While our results are in good
agreement with available experimental data, additional experiments are proposed
in order to unambiguously determine the surface electronic structure of this
interesting surface.",9511137v1
1996-02-21,Impurity scattering in highly anisotropic superconductors and interband sign reversal of the order parameter,"We discuss various mechanisms that can lead to interband sign reversal of the
order parameter in a multiband superconductor. In particular, we generalize
Abrikosov-Gor'kov solution of the problem of weakly coupled superconductor with
magnetic and nonmagnetic impurities on the case of arbitary order parameter
anisotropy, including extreme cases as $d-$pairing or interband sign reversal
of the order parameter, and show that interband scattering by magnetic
impurities can stabilize an interband sign-reversal state. We discuss a
possibility of such state in YBa$_2$Cu$_3$O$_7$ in the context of various
experiments: Josephson tunneling, neutron scattering, isotope effect
measurements.",9602118v1
1996-08-27,Valence band spectroscopy in V-grooved quantum wires,"We present a combined theoretical and experimental study of the anisotropy in
the optical absorption of V-shaped quantum wires. By means of realistic band
structure calculations for these structures, we show that detailed information
on the heavy- and light-hole states can be singled out from the anisotropy
spectra {\em independently of the electron confinement}, thus allowing accurate
valence band spectroscopy.",9608129v1
1996-09-17,On the gap structure of UPt$_3$: phases A and B,"We have used thermal conduction and transverse sound attenuation to probe the
anisotropy of the gap structure in two superconducting phases of UPt$_3$. For
the low-temperature phase B, transverse sound has in the past provided strong
evidence for a line node in the basal plane. Now, from the anisotropy of the
thermal conductivity we further establish the presence of a node along the
c-axis and provide information on its k-dependence. For the largely unexplored
high-temperature phase A, our study of the attenuation for two directions of
the polarization yields directional information on the quasiparticle spectrum,
and the first clear indication of a different gap structure in the two phases.",9609161v1
1996-09-28,Multifractal analysis of the metal-insulator transition in anisotropic systems,"We study the Anderson model of localization with anisotropic hopping in three
dimensions for weakly coupled chains and weakly coupled planes. The eigenstates
of the Hamiltonian, as computed by Lanczos diagonalization for systems of sizes
up to $48^3$, show multifractal behavior at the metal-insulator transition even
for strong anisotropy. The critical disorder strength $W_c$ determined from the
system size dependence of the singularity spectra is in a reasonable agreement
with a recent study using transfer matrix methods. But the respective spectrum
at $W_c$ deviates from the ``characteristic spectrum'' determined for the
isotropic system. This indicates a quantitative difference of the multifractal
properties of states of the anisotropic as compared to the isotropic system.
Further, we calculate the Kubo conductivity for given anisotropies by exact
diagonalization. Already for small system sizes of only $12^3$ sites we observe
a rapidly decreasing conductivity in the directions with reduced hopping if the
coupling becomes weaker.",9609276v1
1996-11-27,Micromagnetic Simulation of Nanoscale Films with Perpendicular Anisotropy,"A model is studied for the theoretical description of nanoscale magnetic
films with high perpendicular anisotropy. In the model the magnetic film is
described in terms of single domain magnetic grains with Ising-like behavior,
interacting via exchange as well as via dipolar forces. Additionally, the model
contains an energy barrier and a coupling to an external magnetic field.
Disorder is taken into account in order to describe realistic domain and domain
wall structures. The influence of a finite temperature as well as the dynamics
can be modeled by a Monte Carlo simulation.
  Many of the experimental findings can be investigated and at least partly
understood by the model introduced above. For thin films the magnetisation
reversal is driven by domain wall motion. The results for the field and
temperature dependence of the domain wall velocity suggest that for thin films
hysteresis can be described as a depinning transition of the domain walls
rounded by thermal activation for finite temperatures.",9611218v1
1996-12-18,Critical limit and anisotropy in the two-point correlation function of three-dimensional O(N) models,"In three-dimensional O(N) models, we investigate the low-momentum behavior of
the two-point Green's function G(x) in the critical region of the symmetric
phase. We consider physical systems whose criticality is characterized by a a
rotationally-invariant fixed point.
  In non rotationally-invariant physical systems with O(N)-invariant
interactions, the vanishing of anisotropy in approaching the
rotationally-invariant fixed point is described by a critical exponent rho,
which is universal and is related to the leading irrelevant operator breaking
rotational invariance. At N=infinity one finds rho=2. 1/N expansion and
strong-coupling calculations show that, for all values of N>=0, rho~2.
  Non-Gaussian corrections to the universal low-momentum behavior of G(x) are
evaluated, and found to be very small.",9612164v1
1996-12-31,Band structure and optical anisotropy in V-shaped and T-shaped semiconductor quantum wires,"We present a theoretical investigation of the electronic and optical
properties of V- and T-shaped quantum wires. Valence band mixing as well as
realistic sample geometries are fully included through an accurate and
efficient approach that is described here in detail. We investigate the
resulting valence band structure, which shows some significant peculiarities,
such as an anomalously large spin splitting in the lowest heavy hole subband of
T-shaped wires. For both classes of wires we obtain good agreement between
calculated optical absorption and recent experimental spectra, and we
demonstrate that the analysis of optical anisotropy can be used as an effective
tool to extract information on valence states, usually very difficult to obtain
otherwise.",9612251v1
1997-04-23,Anisotropy of zero-bias diffusive anomalies for different orientations of an external magnetic field,"We consider the influence of the electron-electron interaction on the
nonlinearity of the current-voltage characteristic of the tunnel junction at
low bias (diffusive anomaly) in the presence of the classical magnetic field.
We present the theory of a new phenomenon which manifests itself in the strong
anisotropy of a diffusive anomaly for different orientations of the magnetic
field with respect to the interface of the tunnel junction. The nonlinear
differential tunneling conductance has a universal magnetic field dependence,
so that only the magnetic field component perpendicular to the interface is
involved. In particular, when the magnetic field is parallel to the interface,
the I-V characteristic does not depend on the value of the magnetic field.",9704195v1
1997-05-09,The two-point correlation function of three-dimensional O(N) models: critical limit and anisotropy,"In three-dimensional O(N) models, we investigate the low-momentum behavior of
the two-point Green's function G(x) in the critical region of the symmetric
phase. We consider physical systems whose criticality is characterized by a
rotational-invariant fixed point. Several approaches are exploited, such as
strong-coupling expansion of lattice non-linear O(N) sigma models,
1/N-expansion, field-theoretical methods within the phi^4 continuum
formulation. In non-rotational invariant physical systems with O(N)-invariant
interactions, the vanishing of space-anisotropy approaching the
rotational-invariant fixed point is described by a critical exponent rho, which
is universal and is related to the leading irrelevant operator breaking
rotational invariance. At N=\infty one finds rho=2. We show that, for all
values of $N\geq 0$, $\rho\simeq 2$. Non-Gaussian corrections to the universal
low-momentum behavior of G(x) are evaluated, and found to be very small.",9705086v1
1997-06-15,Triangular Antiferromagnets,"In this article we review the effects of magnetic frustation in the stacked
triangular lattice. Frustration increases the degeneracy of the ground state,
giving rise to different physics. In particular it leads to unique phase
diagrams with multicritical points and novel critical phenomena. We describe
the confrontation of theory and experiment for a number of systems with
differing magnetic Hamiltonians; Heisenberg, Heisenberg with easy-axis
anisotropy, Heisenberg with easy-plane anisotropy, Ising and singlet ground
state. Interestingly each leads to different magnetic properties and phase
diagrams. We also describe the effects of ferromagnetic, rather than
antiferromagnetic, stacking and of small distortions of the triangular lattice.",9706153v2
1997-06-24,Ginzburg-Landau Expansion and the Slope of the Upper Critical Field in Superconductors with Anisotropic Normal Impurity Scattering,"Ginzburg-Landau expansion for superconductors with anisotropic $s-$ and
$d-$wave pairing is derived in the presence of anisotropic normal impurity
scattering which makes $d-$pairing state more stable under disordering. It is
demonstrated that the slope of the upper critical field $|dH_{c2}/dT|_{T_{c}}$
in superconductors with $d-$wave pairing has nonlinear dependence on disorder,
i.e. for the low anisotropic scattering rate it drops rather fast with
concentration of normal impurities, but as anisotropy of scattering increases
it features initial nonlinear growth, approaches a maximum and drops again,
vanishing at the critical impurity concentration. In superconductors with
anisotropic $s-$wave pairing $|dH_{c2}/dT|_{T_{c}}$ grows, approaching the
known asymptotic behavior, characteristic of usual isotropic case irrespective
to the scattering anisotropy.",9706240v2
1997-06-25,Domain Dynamics of Magnetic Films with Perpendicular Anisotropy,"We study the magnetic properties of nanoscale magnetic films with large
perpendicular anisotropy comparing polarization microscopy measurements on
Co_28Pt_72 alloy samples based on the magneto-optical Kerr effect with Monte
Carlo simulations of a corresponding micromagnetic model. We focus on the
understanding of the dynamics especially the temperature and field dependence
of the magnetisation reversal process. The experimental and simulational
results for hysteresis, the reversal mechanism, domain configurations during
the reversal, and the time dependence of the magnetisation are in very good
qualitative agreement. The results for the field and temperature dependence of
the domain wall velocity suggest that for thin films the hysteresis can be
described as a depinning transition of the domain walls rounded by thermal
activation for finite temperatures.",9706253v1
1997-09-01,Frequency shift and mode coupling in the nonlinear dynamics of a Bose condensed gas,"We investigate the behavior of large amplitude oscillations of a trapped
Bose-condensed gas of alkali atoms at zero temperature, by solving the
equations of hydrodynamics for collective modes. Due to the atom-atom
interaction, the equations of motion are nonlinear and give rise to significant
frequency shift and mode coupling. We provide analytic expressions for the
frequency shift, pointing out the crucial role played by the anisotropy of the
confining potential. For special values of the anisotropy parameter the mode
coupling is particularly strong and the frequency shift becomes large,
revealing a peculiar behavior of the Bose-condensed gas. Consequences on the
theory of collapse and revival of collective excitations are also discussed.",9709010v1
1997-11-18,Enhancement of Optical Nonlinearity Through Anisotropic Microstructures,"We investigate the polarization dependence of optical nonlinearity
enhancement for a uniaxial anisotropic composite of metal nanocrystals in a
dielectric host. Three cases are distinguished depending on whether the
polarization is parallel, perpendicular or unpolarized with respect to the axis
of anisotropy. For the parallel polarization, the results show that the 3D
results are qualitatively similar to the 2D case reported recently. For the
perpendicular polarization, the results are markedly different from the
parallel counterpart: In contrast to the absorption, the enhancement factor
actually increases with the anisotropy. Thus the separation of the absorption
and enhancement peaks becomes even more pronounced than the parallel
polarization case. These results indicate a strong polarization dependence of
the nonlinear optical response.",9711166v1
1997-12-19,On solitary waves in classical anisotropic Heisenberg chains with generalized boundary conditions,"We examine solitary waves in classical Heisenberg chains with an uniaxial
anisotropy and a parallel magnetic field in a continuum approach. The boundary
conditions commonly used are generalized to nonlinear spin wave states, which
themselves turn out to be stable only for an anisotropy of the easy-plane type.
In this case we obtain two different branches of one-soliton solutions which
can be mapped onto each other by a formal time inversion. Moreover, they show
some remarkable similarity to dark solitons of the Nonlinear Schr\""odinger
equation. Numerical simulations for the discrete Heisenberg chain show that
these solitary waves are highly, but not absolutely stable under interaction
with linear excitations and as well under scattering with each other. The
possible significance of these solitary waves in a phenomenological theory of
one-dimensional magnets is briefly addressed.",9712241v1
1998-01-09,Nonmonotonous Magnetic Field Dependence and Scaling of the Thermal Conductivity for Superconductors with Nodes of the Order Parameter,"We show that there is a new mechanism for nonmonotonous behavior of magnetic
field dependence of the electronic thermal conductivity of clean
superconductors with nodes of the order parameter on the Fermi surface. In
particular, for unitary scatterers the nonmonotony of relaxation time takes
place. Contribution from the intervortex space turns out to be essential for
this effect even at low temperatures. Our results are in a qualitative
agreement with recent experimental data for superconducting UPt_3. For
E_{2u}-type of pairing we find approximately the scaling of the thermal
conductivity in clean limit with a single parameter x=T/T_c\sqrt{B_{c2}/B} at
low fields and low temperatures, as well as weak low-temperature dependence of
the anisotropy ratio K_{zz}/K_{yy} in zero field. For E_{1g}-type of pairing
deviations from the scaling are more noticeable and the anisotropy ratio is
essentially temperature dependent.",9801076v1
1998-03-11,Effects of Fermi Surface Anisotropy on Unconventional Superconductivity in UPt_3,"We discuss the weak-coupling BCS theory of the heavy fermion superconductor
UPt_3, accounting for that system's anisotropic, multisheeted Fermi surface by
expanding the order parameter and pair potential in terms of appropriate basis
functions of the irreducible representations of the D_6h crystal point group.
Within a phenomenological model for the electronic structure of UPt_3 chosen to
capture the qualitative features of local density functional calculations and
de Haas-van Alphen measurements, we show how Fermi surface anisotropy can favor
pairing in certain symmetry classes, and influence the phase diagram of
unconventional superconductors. We also calculate the Ginzburg-Landau
coefficients, focussing on those coefficients relevant to current theories of
the UPt_3 phase diagram.",9803135v1
1998-04-06,The Phase Transition to a Square Vortex Lattice in Type-II Superconductors with Fourfold Anisotropy,"We investigate the stability of the square vortex lattice which has been
recently observed in experiments on the borocarbide family of superconductors.
Taking into account the tetragonal symmetry of these systems, we add fourfold
symmetric fourth-derivative terms to the Ginzburg-Landau(GL) free energy. At
$H_{c2}$ these terms may be treated perturbatively to lowest order to locate
the transition from a distorted hexagonal to a square vortex lattice. We also
solve for this phase boundary numerically in the strongly type-II limit,
finding large corrections to the lowest-order perturbative results. We
calculate the relative fourfold $H_{c2}$ anisotropy for field in the $xy$ plane
to be 4.5% at the temperature, $T_c^{\Box}$, where the transition occurs at
$H_{c2}$ for field along the $z$ axis. This is to be compared to the 3.6%
obtained in the perturbative calculation. Furthermore, we find that the phase
boundary in the $H-T$ phase diagram has positive slope near $H_{c2}$.",9804070v1
1998-04-15,Flux-Line Lattice Structures in Untwinned YBa2Cu3O,"A small angle neutron scattering study of the flux-line lattice in a large
single crystal of untwinned YBa2Cu3O is presented. In fields parallel to the
c-axis, diffraction spots are observed corresponding to four orientations of a
hexagonal lattice, distorted by the a-b anisotropy. A value for the anisotropy,
the penetration depth ratio, of 1.18(2) was obtained. The high quality of the
data is such that second order diffraction is observed, indicating a well
ordered FLL. With the field at 33 degrees to c a field dependent re-orientation
of the lattice is observed around 3T.",9804159v2
1998-10-09,Magnetic anisotropy and low-energy spin waves in the Dzyaloshinskii-Moriya spiral magnet Ba_2 Cu Ge_2 O_7,"New neutron diffraction and inelastic scattering experiments are used to
investigate in detail the field dependence of the magnetic structure and
low-energy spin wave spectrum of the Dzyaloshinskii-Moriya helimagnet Ba_2 Cu
Ge_2 O_7. The results suggest that the previously proposed model for the
magnetism of this compound (an ideal sinusoidal spin spiral, stabilized by
isotropic exchange and Dzyaloshinskii-Moriya interactions) needs to be refined.
Both new and previously published data can be quantitatively explained by
taking into account the Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) term, a
special magnetic anisotropy term that was predicted to always accompany
Dzyaloshinskii-Moriya interactions in insulators.",9810122v1
1998-10-13,Anisotropic in-plane thermal conductivity of single-crystal YBa_2Cu_4O_8,"We report measurements of the in-plane thermal conductivity ($\kappa$) of
YBa_2Cu_4O_8 (Y-124) single crystals in the temperature range $4K\leq T\leq
300K$ and compare them with previous results on YBa_2Cu_3O_{6+x} (Y-123). For
transport perpendicular to the CuO chains, $\kappa_a(300K)\simeq 10$W/mK, and
along the chains, $\kappa_b(300K)\simeq 40$W/mK. The temperature dependence of
$\kappa$ for both transport directions is much stronger than in
YBa_2Cu_3O_{6+x} (Y-123), indicative of substantially superior lattice heat
conduction in Y-124, and resulting in maximum values for $\kappa$ at $T\sim
20$K exceeding 200W/mK. The data imply a surprisingly large anisotropy in the
lattice conduction. $\kappa_a$ and $\kappa_b$ are enhanced in the
superconducting state as in other cuprates. The magnitude and anisotropy of the
enhancement are discussed and compared to those of Y-123.",9810152v1
1998-11-07,Normal-state resistivity anisotropy in underdoped RBa_2Cu_3O_{6+x} crystals,"We have revealed new features in the out-of-plane resistivity rho_c of
heavily underdoped RBa_2Cu_3O_{6+x} (R=Tm,Lu) single crystals, which give
evidence for two distinct mechanisms contributing the c-axis transport. We have
observed a crossover towards ""metal-like"" (d rho_c/d T > 0) behavior at the
temperature T_m which quickly increases with decreasing doping. The
""metal-like"" conductivity contribution dominates at T < T_m and provides a
saturation of the resistivity anisotropy, rho_c / rho_{ab}. The
antiferromagnetic ordering is found to block this ""metal-like"" part of the
c-axis conductivity and complete decoupling of CuO_2 planes, which may be the
reason of superconductivity disappearance.",9811104v1
1998-12-02,Strongly Anisotropic Transport in Higher Two-Dimensional Landau Levels,"Low-temperature, electronic transport in Landau levels N>1 of a
two-dimensional electron system is strongly anisotropic. At half-filling of
either spin level of each such Landau level the magnetoresistance either
collapses to form a deep minimum or is peaked in a sharp maximum, depending on
the in-plane current direction. Such anisotropies are absent in the N=0 and N=1
Landau level, which are dominated by the states of the fractional quantum Hall
effect. The transport anisotropies may be indicative of a new many particle
state, which forms exclusively in higher Landau levels.",9812025v1
1998-12-03,Critical properties and phase diagram of the quantum anisotropic XY spin chain in a random magnetic field: A density-matrix renormalization-group analysis,"The spin-1/2 quantum anisotropic XY spin chain in a transverse random
magnetic field parallel to the z axis is numerically studied by means of the
density-matrix renormalization group. The dependence of the spontaneous
magnetization and the energy gap on both the strength of the random magnetic
field and the factor of anisotropy is determined. The critical line for the
order-disorder phase transition is obtained and the resulting phase diagram is
drawn. Our results are compatible with the fact that models with different
factors of anisotropy fall within the same universality class as the quantum
Ising model in a transverse random field.",9812056v2
1998-12-16,Vortices with antiferromagnetic cores in the SO(5) theory of high temperature superconductivity,"We consider the problem of superconducting Ginzburg-Landau (G-L) vortices
with antiferromagnetic cores which arise in Zhang's SO(5) model of
antiferromagnetism (AF) and high temperature superconductivity (SC). This
problem was previously considered by Arovas et al. who constructed approximate
""variational"" solutions, in the large kappa limit, to estimate the domain of
stability of such vortices in the temperature-chemical potential phase diagram.
By solving the G-L equations numerically for general kappa, we show that the
amplitude of the antiferromagnetic component at the vortex core decreases to
zero continuously at a critical value of the AF-SC anisotropy (g~0.25) which is
essentially independent of kappa for large kappa. The magnetic field profile,
the vortex line energy and the value of the B-field at the center of the vortex
core, as functions of anisotropy are also presented.",9812283v2
1998-12-17,Spin wave analysis to the spatially-anisotropic Heisenberg antiferromagnet on triangular lattice,"We study the phase diagram at T=0 of the antiferromagnetic Heisenberg model
on the triangular lattice with spatially-anisotropic interactions. For values
of the anisotropy very close to J_alpha/J_beta=0.50, conventional spin wave
theory predicts that quantum fluctuations melt the classical structures, for
S=1/2. For the regime J_beta<J_alpha, it is shown that the incommensurate
spiral phases survive until J_beta/J_alpha=0.27, leaving a wide region where
the ground state is disordered. The existence of such nonmagnetic states
suggests the possibility of spin liquid behavior for intermediate values of the
anisotropy.",9812311v2
1998-12-22,Self-Consistent Second Order Perturbation Theory for the Hubbard Model in Two Dimensions,"We apply self-consistent second order perturbation theory (SCSOPT) with
respect to the on-site repulsive interaction U to study the Hubbard model in
two dimensions. We investigate single particle properties of the model over the
entire doping range at zero temperature. It is shown that as doping decreases
toward half-filling $\omega$-mass enhancement factor increases, while k-mass
enhancement factor decreases. The increase in $\omega$-mass enhancement factor
is larger than the decrease in k-mass enhancement factor, so that total-mass is
larger than that in the non-interacting case. When particle number density per
unit cell n is given by 0.64<n<1.0 interaction enhances anisotropy of the Fermi
surface, whereas at lower densities n<0.64 interaction suppresses anisotropy of
it. Due to the decrease in k-mass enhancement factor the density of states
(DOS) at the Fermi level is suppressed. It is possible to understand the
results within the framework of the weak coupling Fermi liquid theory.",9812358v1
1999-01-08,Anisotropy and magnetism of high temperature oxides superconductors,"Phonon or electron mediated weak BCS attraction is enough to have high
critical temperature if a van Hove anomaly is at work. This could apply to
electron doped compounds and also to compounds with CuO$_2$ planes overdoped in
holes, where $T_c$ decreases with increasing doping. If phonons dominate, it
should lead to an anisotropic but mainly $s$ superconductive gap, as observed
recently in overdoped LaSrCuO, and probably also in electron doped compounds.
If electrons dominate, a $d$ gap should develop as observed in a number of
cases. In the underdoped range, the observed decrease of $T_c$ with hole doping
can be related in all cases to the development of antiferromagnetic
fluctuations which produces a magnetic pseudogap, thus lowering the density of
states at the Fermi level. The observed mainly $d$ superconductive gap then can
be due to a prevalent superconductive coupling through antiferromagnetic
fluctuations; it could also possibly be attributed to the same phonon coupling
as in the overdoped range, now acting on Bloch functions scattered in the
magnetic pseudogap. More systematic studies of superconductive gap anisotropy
and of magnetic fluctuations would be in order.",9901065v2
1999-02-05,Phase transition between quantum and classical regimes for the escape rate of a biaxial spin system,"Employing the method of mapping the spin problem onto a particle one, we have
derived the particle Hamiltonian for a biaxial spin system with a transverse or
longitudinal magnetic field. Using the Hamiltonian and introducing the
parameter $p (\equiv (U_{max}-E)/(U_{max}-U_{min}))$ where $U_{max}$ (U_{min})
corresponds to the top (bottom) of the potential and $E$ is the energy of the
particle, we have studied the first- or second-order transition around the
crossover temperature between thermal and quantum regimes for the escape rate,
depending on the anisotropy constant and the external magnetic field. It is
shown that the phase boundary separating the first- and second-order transition
and its crossover temperature are greatly influenced by the transverse
anisotropy constant as well as the transverse or longitudinal magnetic field.",9902078v1
1999-02-10,Low Temperature Static and Dynamic Behavior of the Two-Dimensional Easy-Axis Heisenberg Model,"We apply the self-consistent harmonic approximation (SCHA) to study static
and dynamic properties of the two-dimensional classical Heisenberg model with
easy-axis anisotropy. The static properties obtained are magnetization and spin
wave energy as functions of temperature, and the critical temperature as a
function of the easy-axis anisotropy. We also calculate the dynamic correlation
functions using the SCHA renormalized spin wave energy. Our analytical results,
for both static properties and dynamic correlation functions, are compared to
numerical simulation data combining cluster-Monte Carlo algorithms and Spin
Dynamics. The comparison allows us to conclude that far below the transition
temperature, where the SCHA is valid, spin waves are responsible for all
relevant features observed in the numerical simulation data; topological
excitations do not seem to contribute appreciably. For temperatures closer to
the transition temperature, there are differences between the dynamic
correlation functions from SCHA theory and Spin Dynamics; these may be due to
the presence of domain walls and solitons.",9902149v1
1999-03-02,"Crystal Field, Magnetic Anisotropy and Excitations in Rare-Earth Hexaborides","We clarify the role of crystalline electric field (CEF) induced magnetic
anisotropy in the ground state and spin-wave spectrum of cubic rare-earth
materials with dominating isotropic magnetic exchange interactions. In
particular we study the hexaboride NdB_6 which is shown to exhibit strong
spin-quadrupolar coupling. The CEF scheme is analyzed and a non-collinear
magnetization response is found. The spin orientation in the
antiferromagnetically ordered ground-state is identified. Moreover, the spin
excitations are evaluated and in agreement with inelastic neutron scattering a
suppression of one of the two magnetic modes in the strong-coupling regime is
predicted.",9903039v1
1999-03-09,"Reply to Simon's Comment on ""Evidence for an Anisotropic State of Two-Dimensional Electrons in High Landau Levels""","We recently reported [PRL 82, 394 (1999)] large transport anisotropies in a
two-dimensional electron gas in high Landau levels. These observations were
made utilizing both square and Hall bar sample geometries. Simon recently
commented [cond-mat/9903086] that a classical calculation of the current flow
in the sample shows a magnification of an underlying anisotropy when using a
square sample. In this reply we present more recent data obtained with a very
high mobility sample, and reiterate that, with or without magnification, an
anisotropic state develops in high Landau levels at very low temperatures.",9903153v1
1999-05-04,"Quasiperiodicity, bistability and chaos in the Landau-Lifshitz equation","The dynamics of an individual magnetic moment is studied through the
Landau-Lifshitz equation with a periodic driving in the direction perpendicular
to the applied field. For fields lower than the anisotropy field and small
values of the perturbation amplitude we have observed the magnetic moment
bistability. At intermediate values we have found quasiperiodic bands
alternating with periodic motion. At even larger values a chaotic regime is
found. When the applied field is larger than the anisotropy one, the behavior
is periodic with quasiperiodic regions. Those appear periodically in the
amplitude of the oscillating field. Also, even for low values of the driving
force, the moment is not parallel to the applied field.",9905034v1
1999-06-04,Nematic phase of the two-dimensional electron gas in a magnetic field,"The two dimensional electron gas (2DEG) in moderate magnetic fields in
ultra-clean AlAs-GaAs heterojunctions exhibits transport anomalies suggestive
of a compressible, anisotropic metallic state. Using scaling arguments and
Monte Carlo simulations, we develop an order parameter theory of an electron
nematic phase. The observed temperature dependence of the resistivity
anisotropy behaves like the orientational order parameter if the transition to
the nematic state occurs at a finite temperature, $T_c \sim 65 mK$, and is
slightly rounded by a small background microscopic anisotropy. We propose a
light scattering experiment to measure the critical susceptibility.",9906064v2
1999-06-17,High Magnetic Field ESR in the Haldane Spin Chains NENP and NINO,"We present electron spin resonance experiments in the one-dimensional
antiferromagnetic S=1 spin chains NENP and NINO in pulsed magnetic fields up to
50T. The measured field dependence of the quantum energy gap for B||b is
analyzed using the exact diagonalization method and the density matrix
renormalization group method (DMRG). A staggered anisotropy term (-1)^i d(S_i^x
S_i^z + S_i^z S_i^x) was considered for the first time in addition to a
staggered field term (-1)^i S_i^x B_st. We show that the spin dynamics in high
magnetic fields strongly depends on the orthorhombic anisotropy E.",9906273v1
1999-07-14,Mid-infrared Hall effect in thin-film metals: Probing the Fermi surface anisotropy in Au and Cu,"A sensitive mid-infrared (MIR, 900-1100 cm-1, 112-136 meV) photo-elastic
polarization modulation technique is used to measure simultaneously Faraday
rotation and circular dichroism in thin metal films. These two quantities
determine the complex AC Hall conductivity. This novel technique is applied to
study Au and Cu thin films at temperatures down to 20 K and magnetic fields up
to 8 T. The Hall frequency is consistent with band theory predictions. We
report the first measurement of the MIR Hall scattering rate, which is
significantly lower than that derived from Drude analysis of zero magnetic
field MIR transmission measurements. This difference is qualitatively explained
in terms of the anisotropy of the Fermi surface in Au and Cu.",9907210v1
1999-07-28,Tight-binding Hamiltonians for Sr filled ruthenates: application to the gap anisotropy and Hall coefficient in Sr2RuO4,"Accurate orthogonal tight-binding Hamiltonians are constructed for
ferromagnetic SrRuO$_3$ and the layered perovskite superconductor,
Sr$_2$RuO$_4$ by fitting to all-electron full-potential local density band
structures obtained by the linearized augmented planewave method. These
Hamiltonians allow the band structure to be computed on very fine meshes in the
Brillouin zone at low cost, and additionally have analytic band velocities,
while retaining the accuracy of the full-potential electronic structure
calculations. This greatly facilitates calculation of transport and
superconducting parameters related to the fermiology. These features are
exploited to calculate the Hall coefficient and vortex lattice geometry for
Sr$_2$RuO$_4$ with fine integration meshes. We find the lower limit for the
interband order parameter anisotropy to be compatible with the observed square
geometry. We also find that the sign reversal of the Hall coefficient can be
explained in a conventional way if the bands are shifted by a few mRy so as to
match the experimental de Haas-van Alphen areas exactly, {\it and} the
temperature dependence of the relaxation time is strongly dependent on the band
character.",9907442v1
1999-08-02,Breakdown of the magnetization plateau of the S=1/2 ferromagnetic-ferromagnetic-antiferromagnetic trimerized spin chain with anisotropy,"We study the breakdown of the magnetization plateau at the magnetization
M=M_{S}/3 (M_{S} is the saturation magnetization) of the S=1/2 anisotropic spin
chain with ferromagnetic-ferromagnetic-antiferromagnetic interactions. We
consider the model with the isotropic ferromagnetic (trimer) coupling J_{F},
and anisotropic antiferromagnetic coupling (J_{x}=J_{y}=J_{AF} and J_{z}=\Delta
J_{AF}). For the limit of large \gamma\equiv J_{F}/J_{AF}, the model is
equivalent to the S=3/2 XXZ chain with the exchange anisotropy \Delta. There is
a phase transition between the plateau (small-\gamma) and the no-plateau
(large-\gamma) regions. This phase transition is of the
Berezinskii-Kosterlitz-Thouless type, and we determine the phase boundary from
the numerical diagonalization data. For \Delta=1, in particular, the phase
transition between the plateau and the no-plateau regions occurs at the point
\gamma_{c}=15.4.",9908027v2
1999-08-09,Magnetic subband structure of an electron on a triangular lattice,"The effects of anisotropic nearest-neighbor (NN) and isotropic
next-nearest-neighbor (NNN) hopping integrals on the magnetic subband structure
of an electron on a triangular lattice are studied within the tight-binding
approximation. A generalized Harper equation that includes both the NN and the
NNN hopping terms is first derived. Then, the effects of anisotropic NN hopping
integrals are examined and the results are compared in detail with those of an
existing literature [Phys. Rev. B {\bf 56}, 3787 (1997)]. It is found that the
hopping anisotropy generically leads to the occurrence of band broadening and
gap closing. The effects of isotropic NNN hopping integrals are next examined,
and it is found that introducing the NNN hopping integral changes considerably
the magnetic subband structure; band broadening, gap closing, gap reopening,
and band crossing occur depending on the strength of the isotropic NNN hopping
integral. Symmetries of the magnetic subband structures with and without both
the hopping anisotropy and the isotropic NNN hopping integrals are also
discussed.",9908120v1
1999-08-09,Critical Properties of Spin-1 Antiferromagnetic Heisenberg Chains with Bond Alternation and Uniaxial Single-Ion-Type Anisotropy,"One dimensional S=1 antiferromagnetic Heisenberg chains with bond alternation
and uniaxial single-ion-type anisotropy are studied by numerical exact
diagonalization of finite size systems. We calculate the ground state phase
diagram using the twisted boundary condition method for $D\geq 0$. The ground
states of this model contain the Haldane state, large-D state and the dimer
state. Using conformal field theory and the level spectroscopy method, we
calculate the D and $\delta$-dependence of the Luttinger liquid paraments K and
the critical exponent $\nu$ of the energy gap.",9908125v2
1999-08-09,"Magnetic anisotropy, first-order-like metamagnetic transitions and large negative magnetoresistance in the single crystal of Gd$_{2}$PdSi$_3$","Electrical resistivity ($\rho$), magnetoresistance (MR), magnetization,
thermopower and Hall effect measurements on the single crystal
Gd$_{2}$PdSi$_3$, crystallizing in an AlB$_2$-derived hexagonal structure are
reported. The well-defined minimum in $\rho$ at a temperature above N\'eel
temperature (T$_N$= 21 K) and large negative MR below $\sim$ 3T$_N$, reported
earlier for the polycrystals, are reproducible even in single crystals. Such
features are generally uncharacteristic of Gd alloys. In addition, we also
found interesting features in other data, e.g., two-step first-order-like
metamagnetic transitions for the magnetic field along [0001] direction. The
alloy exhibits anisotropy in all these properties, though Gd is a S-state ion.",9908128v1
1999-08-10,Pressure Dependence of the Irreversibility Line in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$:Role of Anisotropy in Flux-Line Formation,"One of the important problems of high-temperature superconductivity is to
understand and ultimately to control fluxoid motion. We present the results of
a new technique for measuring the pressure dependence of the transition to
superconductivity in a diamond anvil cell. By measuring the third harmonic of
the {\it ac} susceptibility, we determine the onset of irreversible flux
motion. This enables us to study the effects of pressure on flux motion. The
application of pressure changes interplanar spacing, and hence the interplanar
coupling, without significantly disturbing the intraplanar superconductivity.
Thus we are able to separate the effects of coupling from other properties that
might affect the flux motion. Our results directly show the relationship
between lattice spacing, effective- mass anisotropy, and the irreversibility
line in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$. Our results also demonstrate
that an application of 2.5 GPa pressure causes a dramatic increase in
interplanar coupling.",9908156v2
1999-08-12,Impurity-Induced Quasiparticle Transport and Universal Limit Wiedemann-Franz Violation in d-Wave Superconductors,"Due to the node structure of the gap in a d-wave superconductor, the presence
of impurities generates a finite density of quasiparticle excitations at zero
temperature. Since these impurity-induced quasiparticles are both generated and
scattered by impurities, prior calculations indicate a universal limit (\Omega
-> 0, T -> 0) where the transport coefficients obtain scattering-independent
values, depending only on the velocity anisotropy v_f/v_2. We improve upon
prior results, including the contributions of vertex corrections and Fermi
liquid corrections in our calculations of universal limit electrical, thermal,
and spin conductivity. We find that while vertex corrections modify electrical
conductivity and Fermi liquid corrections renormalize both electrical and spin
conductivity, only thermal conductivity maintains its universal value,
independent of impurity scattering or Fermi liquid interactions. Hence, low
temperature thermal conductivity measurements provide the most direct means of
obtaining the velocity anisotropy for high T_c cuprate superconductors.",9908182v3
1999-09-14,Energy-level statistics at the metal-insulator transition in anisotropic systems,"We study the three-dimensional Anderson model of localization with
anisotropic hopping, i.e. weakly coupled chains and weakly coupled planes. In
our extensive numerical study we identify and characterize the metal-insulator
transition using energy-level statistics. The values of the critical disorder
$W_c$ are consistent with results of previous studies, including the
transfer-matrix method and multifractal analysis of the wave functions. $W_c$
decreases from its isotropic value with a power law as a function of
anisotropy. Using high accuracy data for large system sizes we estimate the
critical exponent $\nu=1.45\pm0.2$. This is in agreement with its value in the
isotropic case and in other models of the orthogonal universality class. The
critical level statistics which is independent of the system size at the
transition changes from its isotropic form towards the Poisson statistics with
increasing anisotropy.",9909210v2
1999-09-17,Shape Effects of Finite-Size Scaling Functions for Anisotropic Three-Dimensional Ising Models,"The finite-size scaling functions for anisotropic three-dimensional Ising
models of size $L_1 \times L_1 \times aL_1$ ($a$: anisotropy parameter) are
studied by Monte Carlo simulations. We study the $a$ dependence of finite-size
scaling functions of the Binder parameter $g$ and the magnetization
distribution function $p(m)$. We have shown that the finite-size scaling
functions for $p(m)$ at the critical temperature change from a two-peak
structure to a single-peak one by increasing or decreasing $a$ from 1. We also
study the finite-size scaling near the critical temperature of the layered
square-lattice Ising model, when the systems have a large two-dimensional
anisotropy. We have found the three-dimensional and two-dimensional finite-size
scaling behavior depending on the parameter which is fixed; a unified view of
3D and 2D finite-size scaling behavior has been obtained for the anisotropic 3D
Ising models.",9909262v1
1999-10-21,Manifestations of the Charged Stripes in the Magnetoresistance of Heavily Underdoped YBa_2Cu_3O_{6+x},"We present a study of the in-plane and out-of-plane magnetoresistance (MR) in
heavily-underdoped, antiferromagnetic YBa_2Cu_3O_{6+x}, which reveals a variety
of striking features. The in-plane MR demonstrates a ""d-wave""-like anisotropy
upon rotating the magnetic field H within the ab plane. With decreasing
temperature below 20-25 K the system acquires memory: exposing a crystal to the
magnetic field results in a persistent in-plane resistivity anisotropy. The
overall features can be explained by assuming that the CuO_2 planes contain a
developed array of stripes accommodating the doped holes, and that the MR is
associated with the field-induced topological ordering of the stripes.",9910316v1
1999-11-01,A New Vortex Solution for Two-Component Nonlinear Schroedinger Equation in Anisotropic Optical Media,"A theoretical study is given of a new type of optical vortex in nonlinear
anisotropic media. This is realized as a special solution of the two-component
non-linear Schroedinger equation. The vortex is inherent in the spin texture
that is caused by an anisotropy of dielectric tensor, for which a role of spin
is played by the Stokes vector (or pseudo-spin). By using the effective
Lagrangian for the pseudo-spin field, we give an explicit form for the vortex
solution for the case of two types of optical anisotropy; that is, nonlinear
counterpart of birefringence giving rise to the Faraday and Cotton-Mouton
effects. We also examine the evolution equation of the new vortex with respect
to the propagation direction.",9910515v1
1999-11-14,Gap anisotropy in the angle-resolved photoemission spectroscopy of Bi_2Sr_2CaCu_2O_{8+δ},"The gap anisotropy in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ is revisited in the
framework of a d-wave scenario in view of the recent angle-resolved
photoemission experiment. Based on a tight-binding fit to the normal state
dispersion, a detail analysis on the effects of the inclusion of the next
harmonic in the d-wave has been presented. Significant effect has been observed
in the superconducting T$_c$. The density of states is linear at the nodes with
enhanced weight, caused by a marked increase in the low energy excitaions which
affect the thermodynamics considerably. The slope of the $\rho_s - T$ curve in
the low temperature regime increases and the specific heat reflects the
enhanced entropy at low temperatures. The leading edge of the ARPES energy
distribution curves have been calculated and found to shift towards higher
energy. The effect of scattering by non-magnetic impurities in this context is
also outlined.",9911209v1
1999-12-03,Torque magnetometry on single-crystal high temperature superconductors near the critical temperature: a scaling approach,"Angular-dependent magnetic torque measurements performed near the critical
temperature on single crystals of HgBa_{2}CuO_{4+y}, La_{2-x}Sr{x}CuO_{4}, and
YBa_{2}Cu_{3}O_{6.93} are scaled, following the 3D XY model, in order to
determine the scaling function dG^{\pm}(z)/dz which describes the universal
critical properties near T_{c}. A systematic shift of the scaling function with
increasing effective mass anisotropy \gamma = (m_{ab}*/m_{c}*)^{1/2} is
observed, which may be understood in terms of a 3D-2D crossover. Further
evidence for a 3D-2D crossover is found from temperature-dependent torque
measurements carried out in different magnetic fields at different field
orientations \delta, which show a quasi 2D ""crossing region'' (M*,T*). The
occurrence of this ""crossing phenomenon'' is explained in a phenomenological
way from the weak z dependence of the scaling function around a value z = z*.
The ""crossing'' temperature T* is found to be angular-dependent. Torque
measurements above T_{c} reveal that fluctuations are strongly enhanced in the
underdoped regime where the anisotropy is large, whereas they are less
important in the overdoped regime.",9912052v1
2000-01-04,Quantitative Description of Thermodynamics of Layered Magnets in a Wide Temperature Region,"The thermodynamics of layered antiferro- and ferromagnets with a weak
interlayer coupling and/or easy-axis anisotropy is investigated. A crossover
from an isotropic 2D-like to 3D Heisenberg (or 2D Ising) regime is discussed
within the renormalization group (RG) analysis. Analytical results for the the
(sublattice) magnetization and the ordering temperature are derived are
obtained in different regimes. Numerical calculations on the base of the
equations obtained yield a good agreement with experimental data on La2CuO4 and
layered perovskites. Corresponding results for the Kosterlitz-Thouless and
Curie (N\'eel) temperatures in the case of the easy-plane anisotropy are
derived.",0001032v1
2000-01-11,Theory of magnetic order in the three-dimensional spatially anisotropic Heisenberg model,"A spin-rotation-invariant Green's-function theory of long-range and
short-range order (SRO) in the $S=1/2$ antiferromagnetic Heisenberg model with
spatially anisotropic couplings on a simple cubic lattice is presented. The
staggered magnetization, the two-spin correlation functions, the correlation
leng spin-rotation-invariant Green's-function theory of long-range and
short-range order (SRO) in the $S=1/2$ antiferromagnetic Heisenberg model with
spatially anisotropic couplings on a simple cubic lattice is presented. The
staggered magnetization, the two-spin correlation functions, the correlation
lengths, and the static spin susceptibility are calculated self-consistently
over the whole temperature region, where the effects of spatial anisotropy are
explored. As compared with previous spin-wave approaches, the N\'{e}el
temperature is reduced by the improved description of SRO. The maximum in the
temperature dependence of the uniform static susceptibility is shifted with
anisotropy and is ascribed to the decrease of SRO with increasing temperature.
Comparing the theory with experimental data for the magnetization and
correlation length of La$_2$CuO$_4$, a good agreement in the temperature
dependences is obtained.",0001132v1
2000-01-27,Hall effect and conduction anisotropy in the organic conductor TMTSF2PF6,"Long missing basic experiments in the normal phase of the anisotropic
electron system of TMTSF2PF6 were performed. Both the Hall effect and the
ab'-plane conduction anisotropy are directly addressing the unconventional
electrical properties of this Bechgaard salt. We found that the dramatic
reduction of the carrier density deduced from recent optical data is not
reflected in an enhanced Hall-resistance. The pressure- and temperature
dependence of the b'-direction resitivity reveal isotropic relaxation time and
do not require explanations beyond the Fermi liquid theory. Our results allow a
coherent-diffusive transition in the interchain carrier propagation, however
the possible crossover to Luttinger liquid behavior is placed to an energy
scale above room temperature.",0001403v1
2000-01-27,Quasiparticle Spectrum of d-wave Superconductors in the Mixed State,"The quasiparticle spectrum of a two-dimensional d-wave superconductor in the
mixed state, H_{c1} << H << H_{c2}, is studied both analytically and
numerically using the linearized Bogoliubov-de Gennes equation. We consider
various values of the ""anisotropy ratio"" v_F/v_Delta for the quasiparticle
velocities at the Dirac points, and we examine the implications of symmetry.
For a Bravais lattice of vortices, we find there is always an isolated
energy-zero (Dirac point) at the center of the Brillouin zone, but for a
non-Bravais lattice with two vortices per unit cell there is generally an
energy gap. In both of these cases, the density of states should vanish at zero
energy, in contrast with the semiclassical prediction of a constant density of
states, though the latter may hold down to very low energies for large
anisotropy ratios. This result is closely related to the particle-hole symmetry
of the band structures in lattices with two vortices per unit cell. More
complicated non-Bravais vortex lattice configurations with at least four
vortices per unit cell can break the particle-hole symmetry of the linearized
energy spectrum and lead to a finite density of states at zero energy.",0001406v1
2000-02-04,Generalization properties of finite size polynomial Support Vector Machines,"The learning properties of finite size polynomial Support Vector Machines are
analyzed in the case of realizable classification tasks. The normalization of
the high order features acts as a squeezing factor, introducing a strong
anisotropy in the patterns distribution in feature space. As a function of the
training set size, the corresponding generalization error presents a crossover,
more or less abrupt depending on the distribution's anisotropy and on the task
to be learned, between a fast-decreasing and a slowly decreasing regime. This
behaviour corresponds to the stepwise decrease found by Dietrich et al.[Phys.
Rev. Lett. 82 (1999) 2975-2978] in the thermodynamic limit. The theoretical
results are in excellent agreement with the numerical simulations.",0002071v1
2000-02-08,Spin quantization axis dependent magnetic properties and x-ray magnetic circular dichroism of FePt and CoPt,"We have performed a theoretical study of the magnetic circular dichroism in
the x-ray absorption spectra (XMCD) of the equiatomic CoPt and FePt ordered
alloys as a function of the spin quantization axis. We found that the
magnetization axis is along the [001] direction and the magneto-crystalline
anisotropy energy (MCA) for the FePt compound is twice as large as that of the
CoPt compound in agreement with experiment. The band structure and the total
density of states confirm that all electronic states contribute to the MCA, and
not just the states at the vicinity of the Fermi level. The orbital magnetic
moments decrease with respect to the angle between the [001] axis and the spin
quantization axis, and are much larger for the CoPt compound. We show that the
orbital moment anisotropy is reflected in the XMCD signal.",0002110v1
2000-02-29,Impurity spin magnetization of thin Fe doped Au films,"In order to probe the influence of the surface-induced anisotropy on the
impurity spin magnetization, we measure the anomalous Hall effect in thin AuFe
films at magnetic fields up to 15 T. The observed suppression of the anomalous
Hall resistivity at low fields as well as the appearance of a minimum in the
differential Hall resistivity at higher fields can be explained by our
theoretical model which takes into account the influence of a polycrystalline
film structure on the surface-induced anisotropy. Our results imply that the
apparent discrepancy between different experimental results for the size
effects in dilute magnetic alloys can be linked to a different microstructure
of the samples.",0002467v1
2000-03-27,Quantum chiral phases in frustrated easy-plane spin chains,"The phase diagram of antiferromagnetic spin-S chain with XY-type anisotropy
and frustrating next-nearest-neighbor interaction is studied in the limit of
large integer S with the help of a field-theoretical approach. It is shown that
the existence of gapless and gapped chiral phases found in recent numerical
studies [M.Kaburagi et al., J. Phys. Soc. Jpn. vol.68, 3185 (1999), T.Hikihara
et al., J. Phys. Soc. Jpn. vol.69, 259 (2000)] is not specific for S=1, but is
rather a generic large-S feature. Estimates for the corresponding transition
boundaries are obtained, and a sketch of the typical phase diagram is
presented. It is also shown that frustration stabilizes the Haldane phase
against the variation of the anisotropy.",0003427v1
2000-03-27,Pseudospin Anisotropy Classification of Quantum Hall Ferromagnets,"Broken symmetry ground states with uniform electron density are common in
quantum Hall systems when two Landau levels simultaneously approach the
chemical potential at integer filling factor $\nu$. The close analogy between
these two-dimensional electron system states and conventional itinerant
electron ferromagnets can be emphasized by using a pseudospin label to
distinguish the two Landau levels. As in conventional ferromagnets, the
evolution of the system's state as external field parameters are varied is
expected to be sensitive to the dependence of ground state energy on pseudospin
orientation. We discuss the predictions of Hartree-Fock theory for the
dependence of the sign and magnitude of the pseudospin anisotropy energy on the
nature of the crossing Landau levels. We build up a classification scheme for
quantum Hall ferromagnets that applies for single layer and bilayer systems
with two aligned Landau levels distinguished by any combination of real-spin,
orbit-radius, or growth direction degree-of-freedom quantum numbers. The
possibility of in-situ tuning between easy-axis and easy-plane quantum Hall
ferromagnets is discussed for biased bilayer systems with total filling factors
$\nu=3$ or $\nu=4$. Detailed predictions are made for the bias dependence of
pseudospin reversal properties in $\nu=3$ bilayer systems.",0003430v1
2000-03-30,Reorientation of Anisotropy in a Square Well Quantum Hall Sample,"We have measured magnetotransport at half-filled high Landau levels in a
quantum well with two occupied electric subbands. We find resistivities that
are {\em isotropic} in perpendicular magnetic field but become strongly {\em
anisotropic} at $\nu$ = 9/2 and 11/2 on tilting the field. The anisotropy
appears at an in-plane field, $B_{ip} \sim$ 2.5T, with the easy-current
direction {\em parallel} to $B_{ip}$ but rotates by 90$^{\circ}$ at $B_{ip}
\sim$ 10T and points now in the same direction as in single-subband samples.
This complex behavior is in quantitative agreement with theoretical
calculations based on a unidirectional charge density wave state model.",0003483v1
2000-04-03,The effect of rare regions on a disordered itinerant quantum antiferromagnet with cubic anisotropy,"We study the quantum phase transition of an itinerant antiferromagnet with
cubic anisotropy in the presence of quenched disorder, paying particular
attention to the locally ordered spatial regions that form in the Griffiths
region. We derive an effective action where these rare regions are described in
terms of static annealed disorder. A one loop renormalization group analysis of
the effective action shows that for order parameter dimensions $p<4$ the rare
regions destroy the conventional critical behavior. For order parameter
dimensions $p>4$ the critical behavior is not influenced by the rare regions,
it is described by the conventional dirty cubic fixed point. We also discuss
the influence of the rare regions on the fluctuation-driven first-order
transition in this system.",0004013v1
2000-04-10,Magnetotransport study of the charged stripes in high-T_c cuprates,"We present a study of the in-plane and out-of-plane magnetoresistance (MR) in
heavily-underdoped, antiferromagnetic YBa_{2}Cu_{3}O_{6+x}, which reveals a
variety of striking features. The in-plane MR demonstrates a ""d-wave""-like
anisotropy upon rotating the magnetic field H within the ab plane. With
decreasing temperature below 20-25 K, the system acquires memory: exposing a
crystal to the magnetic field results in a persistent in-plane resistivity
anisotropy. The overall features can be explained by assuming that the CuO_2
planes contain a developed array of stripes accommodating the doped holes, and
that the MR is associated with the field-induced topological ordering of the
stripes.",0004135v1
2000-04-10,Combined Paramagnetic and Diamagnetic Response of YBCO,"It has been predicted that the zero frequency density of states of YBCO in
the superconducting phase can display interesting anisotropy effects when a
magnetic field is applied parallel to the copper-oxide planes, due to the
diamagnetic response of the quasi-particles. In this paper we incorporate
paramagnetism into the theory and show that it lessens the anisotropy and can
even eliminate it altogether. At the same time paramagnetism also changes the
scaling with the square root of the magnetic field first deduced by Volovik
leading to an experimentally testable prediction. We also map out the analytic
structure of the zero frequency density of states as a function of the
diamagnetic and paramagnetic energies. At certain critical magnetic field
values we predict kinks as we vary the magnetic field. However these probably
lie beyond currently accessible field strengths.",0004152v1
2000-05-12,Reflectivity Anisotropy Spectra of Cu- and Ag- (110) surfaces from {\it ab initio} theory,"We are able to disentagle the effects of the intraband and interband parts of
the bulk dielectric function on the bare dielectric anisotropy of the surface.
We show how the position, sign and amplitude of the structures observed in such
spectra depend on the above quantities. The lineshape of all the calculated
structures agree very well with the ones observed experimentally for samples
treated by suitable surface cleaning. In particular, we reproduce the observed
single peak structure of Ag at high energy, found to represent a state of the
clean surface different from the one giving the originally observed double peak
structure. This results is not reproduced by the 'local field' model.",0005209v1
2000-06-06,Influence of nonlocal electrodynamics on the anisotropic vortex pinning in $YNi_2B_2C$,"We have studied the pinning force density Fp of YNi_2B_2C superconductors for
various field orientations. We observe anisotropies both between the c-axis and
the basal plane and within the plane, that cannot be explained by usual mass
anisotropy. For magnetic field $H \parallel c$, the reorientation structural
transition in the vortex lattice due to nonlocality, which occurs at a field
$H_1 \sim 1kOe$, manifests itself as a kink in Fp(H). When $H \bot c$, Fp is
much larger and has a quite different H dependence, indicating that other
pinning mechanisms are present. In this case the signature of nonlocal effects
is the presence of a fourfold periodicity of Fp within the basal plane.",0006077v2
2000-06-08,Periodic forcing in viscous fingering of a nematic liquid crystal,"We study viscous fingering of an air-nematic interface in a radial Hele-Shaw
cell when periodically switching on and off an electric field, which reorients
the nematic and thus changes its viscosity, as well as the surface tension and
its anisotropy (mainly enforced by a single groove in the cell). We observe
undulations at the sides of the fingers which correlate with the switching
frequency and with tip oscillations which give maximal velocity to smallest
curvatures. These lateral undulations appear to be decoupled from spontaneous
(noise-induced) side branching. We conclude that the lateral undulations are
generated by successive relaxations between two limiting finger widths. The
change between these two selected pattern scales is mainly due to the change in
the anisotropy. This scenario is confirmed by numerical simulations in the
channel geometry, using a phase-field model for anisotropic viscous fingering.",0006131v3
2000-06-28,Chiral ordered phases in a frustrated S=1 chain with uniaxial single-ion-type anisotropy,"The ground-state phase transitions of a frustrated S=1 Heisenberg chain with
the uniaxial single-ion-type anisotropy and the frustrating
next-nearest-neighbor coupling are studied. For the system, it has been shown
that there are gapless and gapped chiral phases in which the chirality \kappa_l
= S^x_l S^y_{l+1} - S^y_l S^x_{l+1} exhibits a finite long-range order (LRO)
and the spin correlation decays either algebraically or exponentially. In this
study, the transitions between the Haldane and chiral phase and between the
large-D (LD) and chiral phase are investigated using the infinite-system
density-matrix renormalization group method. It is found that there exist two
types of gapped chiral phases, ""chiral Haldane"" and ""chiral LD"" phases, in
which the string LRO coexists with the chiral LRO and the string correlation
decays exponentially, respectively.",0006445v1
2000-07-18,Measuring anisotropic scattering in the cuprates,"A simple model of anisotropic scattering in a quasi two-dimensional metal is
studied. Its simplicity allows an analytic calculation of transport properties
using the Boltzmann equation and relaxation time approximation. We argue that
the c-axis magnetoresistance provides the key test of this model of transport.
We compare this model with experiments on overdoped Tl-2201 and find reasonable
agreement using only weak scattering anisotropy. We argue that optimally doped
Tl-2201 should show strong angular-dependent magnetoresistance within this
model and would provide a robust way of determining the in-plane scattering
anisotropy in the cuprates.",0007299v2
2000-08-02,"Confinement symmetry, mobility anisotropy, and metallic behavior in (311)A GaAs 2D holes","We study two dimensional hole systems confined to GaAs quantum wells grown on
the (311)A surface of GaAs substrates. Such samples exhibit an in-plane
mobility anisotropy. At constant 2D hole density, we vary the symmetry of the
quantum well potential and measure the temperature dependence of the
resistivity along two different current directions, in a regime where the
samples exhibit metallic behavior. The symmetry has a significant and
non-trivial effect on the metallic behavior. Moreover, differences between the
temperature-dependence of the resistivity along the two mobility directions
point to specific scattering mechanisms being important in the expression of
the metallic behavior.",0008041v1
2000-08-28,Josephson-Vortex-Glass Transition in Strong Fields,"A vortex-glass transition due to point disorder in layered superconductors is
studied for the case with an applied field {\it parallel} to the layers. Our
calculation of tilt responses indicates that, irrespective of the magnitude of
the field, the resulting glass phase, Josephson-vortex-glass (JG), should have
a transverse Meissner effect, as in a planar splayed glass phase, only for a
tilt perpendicular to the layers. Further, focusing on the high field (and/or
high anisotropy) region $B \sqrt{\Gamma} > \phi_0/d^2$, where $\Gamma$ is the
mass anisotropy in the Lawrence-Doniach model, the JG transition line
$T_{JG}(B)$ is shown to have a similar form to a $B$-$T$ line following from
the {\it disorder-free} Lindemann criterion and to decrease with increasing $B
\sqrt{\Gamma}$, in marked contrast to the disorder-free melting line {\it
insensitive to} $B \sqrt{\Gamma}$ in such the high field region. This
$T_{JG}(B)$ line seems to have been recently observed in a.c. susceptibility
and in-plane resistivity measurements in BSCCO and qualitatively explains a
field dependence at lower temperatures of previous BSCCO resistivity data
showing the so-called in-plane Lorentz force-free behavior.",0008397v1
2000-09-01,The Broad Brillouin Doublet and CP of Ktao_3 : Second Sound vs. Two-Phonon Difference Scattering,"Low-T Brillouin spectra of the incipient ferroelectric KTaO3 exhibit a broad
central peak (CP), and additional Brillouin doublets (BD), that can both be
related to phonon-density fluctuations. On the basis of new high-resolution
neutron data obtained of low-lying phonon branches, we analysed the
phonon-kinetics mechanisms that are possibly the origin of these unusual
features. Firstly, transverse acoustic (TA) phonons whose normal damping is
faster than the BD frequency can produce hydrodynamic second sound. Secondly,
two-phonon difference scattering from low damping thermal transverse phonons
contribute to the spectra with either a sharp or a broader doublet, depending
on the phonon group velocity and anisotropy of dispersion surfaces. The
position of the observed sharp doublet is consistent with both mechanisms, but
a comparison of the computed and experimental anisotropies favours the second
process.",0009011v1
2000-09-28,Magnetic qubits as hardware for quantum computers,"We propose two potential realisations for quantum bits based on nanometre
scale magnetic particles of large spin S and high anisotropy molecular
clusters. In case (1) the bit-value basis states |0> and |1> are the ground and
first excited spin states Sz = S and S-1, separated by an energy gap given by
the ferromagnetic resonance (FMR) frequency. In case (2), when there is
significant tunnelling through the anisotropy barrier, the qubit states
correspond to the symmetric, |0>, and antisymmetric, |1>, combinations of the
two-fold degenerate ground state Sz = +- S. In each case the temperature of
operation must be low compared to the energy gap, \Delta, between the states
|0> and |1>. The gap \Delta in case (2) can be controlled with an external
magnetic field perpendicular to the easy axis of the molecular cluster. The
states of different molecular clusters and magnetic particles may be entangled
by connecting them by superconducting lines with Josephson switches, leading to
the potential for quantum computing hardware.",0009432v1
2001-01-20,Ultrasound Attenuation in Sr$_2$RuO$_4$: an Angle-Resolved Study of the Superconducting Gap Function,"We present a study of the electronic ultrasound attenuation $\alpha$ in the
unconventional superconductor Sr$_2$RuO$_4$ . The power law behavior of
$\alpha$ at temperatures down to $T_c/30$ clearly indicates the presence of
nodes in the gap. In the normal state, we find an enormous anisotropy of
$\alpha$ in the basal plane of the tetragonal structure. In the superconducting
state, the temperature dependence of $\alpha$ also exhibits significant
anisotropy. We discuss these results in relation to possible gap functions.",0101319v2
2001-01-26,Highly Anisotropic Transport in the Integer Quantum Hall Effect,"At very large tilt of the magnetic (B) field with respect to the plane of a
two-dimensional electron system the transport in the integer quantum Hall
regime at $\nu$ = 4, 6, and 8 becomes strongly anisotropic. At these filling
factors the usual {\em deep minima} in the magneto-resistance occur for the
current flowing {\em perpendicular} to the in-plane B field direction but
develop into {\em strong maxima} for the current flowing {\em parallel} to the
in-plane B field. The origin of this anisotropy is unknown but resembles the
recently observed anisotropy at half-filled Landau levels.",0101416v1
2001-01-29,Phase transitions in two-dimensional anisotropic quantum magnets,"We consider quantum Heisenberg ferro- and antiferromagnets on the square
lattice with exchange anisotropy of easy-plane or easy-axis type. The
thermodynamics and the critical behaviour of the models are studied by the
pure-quantum self-consistent harmonic approximation, in order to evaluate the
spin and anisotropy dependence of the critical temperatures. Results for
thermodynamic quantities are reported and comparison with experimental and
numerical simulation data is made. The obtained results allow us to draw a
general picture of the subject and, in particular, to estimate the value of the
critical temperature for any model belonging to the considered class.",0101430v1
2001-02-21,Renormalization group and nonlinear susceptibilities of cubic ferromagnets at criticality,"For the three-dimensional cubic model, the nonlinear susceptibilities of the
fourth, sixth, and eighth orders are analyzed and the parameters \delta^(i)
characterizing their reduced anisotropy are evaluated at the cubic fixed point.
In the course of this study, the renormalized sextic coupling constants
entering the small-field equation of state are calculated in the four-loop
approximation and the universal values of these couplings are estimated by
means of the Pade-Borel-Leroy resummation of the series obtained. The
anisotropy parameters are found to be: \delta^(4) = 0.054 +/- 0.012, \delta^(6)
= 0.102 +/- 0.02, and \delta^(8) = 0.144 +/- 0.04, indicating that the
anisotropic (cubic) critical behavior predicted by the advanced higher-order
renormalization-group analysis should be, in principle, visible in physical and
computer experiments.",0102368v3
2001-03-01,The Hamiltonian of the V$_{15}$ Spin System from first-principles Density-Functional Calculations,"We report first-principles all-electron density-functional based studies of
the electronic structure, magnetic ordering and anisotropy for the V$_{15}$
molecular magnet. From these calculations, we determine a Heisenberg
Hamiltonian with four antiferromagnetic and one {\em ferromagnetic} coupling.
We perform direct diagonalization to determine the temperature dependence of
the susceptibility. This Hamiltonian reproduces the experimentally observed
spin $S$=1/2 ground state and low-lying $S$=3/2 excited state. A small
anisotropy term is necessary to account for the temperature independent part of
the magnetization curve.",0103031v2
2001-03-02,Competition Between Exchange and Anisotropy in a Pyrochlore Ferromagnet,"The Ising-like spin ice model, with a macroscopically degenerate ground
state, has been shown to be approximated by several real materials. Here we
investigate a model related to spin ice, in which the Ising spins are replaced
by classical Heisenberg spins. These populate a cubic pyrochlore lattice and
are coupled to nearest neighbours by a ferromagnetic exchange term J and to the
local <1,1,1> axes by a single-ion anisotropy term D. The near neighbour spin
ice model corresponds to the case D/J infinite. For finite D/J we find that the
macroscopic degeneracy of spin ice is broken and the ground state is
magnetically ordered into a four-sublattice structure. The transition to this
state is first-order for D/J > 5 and second-order for D/J < 5 with the two
regions separated by a tricritical point. We investigate the magnetic phase
diagram with an applied field along [1,0,0] and show that it can be considered
analogous to that of a ferroelectric.",0103051v1
2001-03-15,Phase Transition Of The Spin-One Square-Lattice Anisotropic Heisenberg Model,"The coupled cluster method (CCM) is applied to the spin-one anisotropic
Heisenberg antiferromagnet (HAF) on the square lattice at zero temperature
using a new high-order CCM ground-state formalism for general quantum spin
number ($s \ge 1/2$). The results presented constitute the first such
application of this new formalism, and they are shown to be among the most
accurate results for the ground-state energy and sublattice magnetisation of
this model as yet determined. We ``track'' the solution to the CCM equations at
a given level of approximation with respect to the anisotropy parameter,
$\Delta$, from the trivial Ising limit ($\Delta \to \infty$) down to a critical
value $\Delta_c$, at which point this solution terminates. This behaviour is
associated with a phase transition in the system, and hence a primary result of
these high-order CCM calculations is that they provide an accurate and unbiased
(i.e., {\it ab initio}) estimation of the position of the quantum phase
transition point as a function of the anisotropy parameter. Our result is,
namely, that this point occurs at (or slightly below) the isotropic Heisenberg
point at $\Delta=1$, for this model.",0103321v1
2001-03-16,Quantum Hall Stripe States in a Tilted Magnetic Field,"A strong anisotropy in the longitudinal resistivity of a 2D electron system
has been observed at half-filled high Landau levels. We report on detailed
Hartree-Fock calculations of the unidirectional charge density wave (UCDW)
orientation energy induced by a tilted magnetic field. We find that stripes can
orient both parallel or perpendicular to the in-plane field depending on the
sample parameters and field strength. The close agreement between complex
experimental data on different sample geometries and our theoretical results
strongly support the UCDW picture as the origin of the observed anisotropies in
high Landau levels.",0103339v1
2001-03-20,Fully dense MgB_2 superconductor textured by hot deformation,"Bulk textured MgB_2 material of nearly full density showing a weak c-axis
alignment of the hexagonal MgB_2 grains parallel to the pressure direction was
obtained by hot deformation of a stoichiometric MgB_2 pellet prepared by a
gas-solid reaction. The texture of the material was verified by comparing the
x-ray diffraction patterns of the hot deformed material with isotropic MgB_2
powder. A small, but distinct anisotropy of the upper critical field up to
Hc2^{a,b}/Hc2^{c}~1.2 depending on degree of texture was found by resistance
and susceptibility measurements. No anisotropy of the critical current density
determined from magnetization measurements was found for the textured material.",0103408v2
2001-04-05,Decoupling of the S=1/2 antiferromagnetic zig-zag ladder with anisotropy,"The spin-1/2 antiferromagnetic zig-zag ladder is studied by exact
diagonalization of small systems in the regime of weak inter-chain coupling. A
gapless phase with quasi long-range spiral correlations has been predicted to
occur in this regime if easy-plane (XY) anisotropy is present. We find in
general that the finite zig-zag ladder shows three phases: a gapless collinear
phase, a dimer phase and a spiral phase. We study the level crossings of the
spectrum,the dimer correlation function, the structure factor and the spin
stiffness within these phases, as well as at the transition points. As the
inter-chain coupling decreases we observe a transition in the anisotropic XY
case from a phase with a gap to a gapless phase that is best described by two
decoupled antiferromagnetic chains. The isotropic and the anisotropic XY cases
are found to be qualitatively the same, however, in the regime of weak
inter-chain coupling for the small systems studied here. We attribute this to a
finite-size effect in the isotropic zig-zag case that results from
exponentially diverging antiferromagnetic correlations in the weak-coupling
limit.",0104090v1
2001-04-10,Anomalous Superconducting Properties and Field Induced Magnetism in CeCoIn5,"In the heavy fermion superconductor CeCoIn5 (Tc=2.3K) the critical field is
large, anisotropic and displays hysteresis. The magnitude of the critical-field
anisotropy in the a-c plane can be as large as 70 kOe and depends on
orientation. Critical field measurements in the (110) plane suggest 2D
superconductivity, whereas conventional effective mass anisotropy is observed
in the (100) plane. Two distinct field-induced magnetic phases are observed: Ha
appears deep in the superconducting phase, while Hb intersects Hc2 at T=1.4 K
and extends well above Tc. These observations suggest the possible realization
of a direct transition from ferromagnetism to Fulde-Ferrel-Larkin-Ovchinnikov
superconductivity in CeCoIn5.",0104179v2
2001-04-20,Millikelvin magnetic relaxation measurements of alpha-Fe2O3 antiferromagnetic particles,"In this paper we report magnetic relaxation data for antiferromagnetic
alpha-Fe2O3 particles of 5 nm mean diameter in the temperature range 0.1 K to
25 K. The average spin value of these particles S=124 and the uniaxial
anisotropy constant D=1.6x10^-2 K have been estimated from the experimental
values of the blocking temperature and anisotropy field. The observed plateau
in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of
spin tunneling from the ground state Sz = S. However, the scaling M vs Tln(nu
t) is broken below 5 K, suggesting the occurrence of tunneling from excited
states below this temperature.",0104391v1
2001-04-24,Magnetothemopower study of quasi two-dimensional organic conductor $α$-(BEDT-TTF)$_2$KHg(SCN)$_4$,"We have used a low-frequency magneto-thermopower (MTEP) method to probe the
high magnetic field ground state behavior of
$\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ along all three principal crystallographic
axes at low temperatures. The thermopower tensor coefficients ($S_{xx}, S_{yx}$
and $S_{zz}$) have been measured to 30 T, beyond the anomalous low temperature,
field-induced transition at 22.5 T. We find a significant anisotropy in the
MTEP signal, and also observe large quantum oscillations associated with the de
Haas - van Alphen effect. The anisotropy indicates that the ground state
properties are clearly driven by mechanisms that occur along specific
directions for the in-plane electronic structure. Both transverse and
longitudinal magnetothermopower show asymptotic behavior in field, which can be
explained in terms of magnetic breakdown of compensated closed orbits.",0104447v1
2001-04-27,The Magnetic Susceptibility of Non-Interacting Nanoparticles,"We have calculated the low-field magnetic susceptibility $\chi$ of a system
consisting of non-interacting mono-dispersed nanoparticles using a classical
statistical approach. The model makes use of the assumption that the axes of
symmetry of all nanoparticles are aligned and oriented at a certain angle
$\psi$ with respect to the external magnetic field. An analytical expression
for the temperature dependence of the susceptibility $\chi(T)$ above the
blocking temperature is obtained. The derived expression is a generalization of
the Curie law for the case of anisotropic magnetic particles. We show that the
normalized susceptibility is a universal function of the ratio of the
temperature over the anisotropy constant for each angle $\psi$. In the case
that the easy-axis is perpendicular to the magnetic field the susceptibility
has a maximum. The temperature of the maximum allows one to determine the
anisotropy energy.",0104539v1
2001-06-08,Anisotropic Superconductivity in Epitaxial MgB2 Films,"High-quality epitaxial MgB2 thin films prepared by pulsed laser deposition
with Tc = 39 K offer the opportunity to study the anisotropy and robustness of
the superconducting state in magnetic fields. We measure the in-plane
electrical resistivity of the films in magnetic fields to 60T and estimate the
superconducting upper critical field Hc(0) = 24 +- 3 T for field oriented along
the c-axis, and Hab(0) = 30 +- 2 T for field in the plane of the film. We find
the zero-temperature coherence lengths xi_c(0) = 30 A and xi_ab(0) = 37 A to be
shorter than the calculated electronic mean free path l = 100 +- 50 A, which
places our films in the clean limit. The observation of such large upper
critical fields from clean limit samples, coupled with the relatively small
anisotropy, provides strong evidence of the viability of MgB2 as a
technologically important superconductor.",0106146v1
2001-06-27,"Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNi$_2$B$_2$C, YNi$_2$B$_2$C and MgB$_2$","The recently discovered intermetallic superconductor MgB2 appears to have a
highly anisotopic upper critical field with Hc2(max)/Hc2(min} = \gamma > 5. In
order to determine the temperature dependence of both Hc2(max) and Hc2(min) we
propose a method of extracting the superconducting anisotropy from the
magnetization M(H,T) of randomly oriented powder samples. The method is based
on two features in dM/dT the onset of diamagnetism at Tc(max), that is commonly
associated with Hc2, and a kink in dM/dT at a lower temperature Tc(min).
Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic Hc2
obtained from magneto-transport measurements on single crystals. Using this
method on four different types of MgB2 powder samples we are able to determine
Hc2(max)(T) and Hc2(min)(T) with \gamma \approx 6.",0106577v1
2001-07-02,Growth of c-oriented MgB2 thin films by Pulsed Laser Deposition: structural characterization and electronic anisotropy,"MgB2 thin films were deposited using Pulsed Laser Deposition (PLD) and
ex-situ annealing in Mg atmosphere. The films presented critical temperatures
up to 36K and turned out to be preferentially c-oriented both on Al2O3 (r-cut)
and MgO(100) substrates. Synchrotron analyses gave also some indications of in
plane texturing. The films exhibit very fine grain size (1200angstromin the
basal plane and 100angstrom along c-axis) but the general resistivity behavior
and the remarkable extension of the irreversible region confirm that the grains
boundaries are not barriers for supercurrents. Upper critical field
measurements with the magnetic field perpendicular and parallel with respect to
the film surface evidenced a field anisotropy ratio of 1.8. The Hc2 values are
considerably higher with respect to the bulk ones, namely when the field lies
in the basal plane, and the field-temperature phase diagram for the two
magnetic field orientations suggest the possibility of strongly enhancing the
pinning region by means of texturing.",0107031v1
2001-07-11,The Superconducting Gap in MgB_2: Electronic Raman Scattering Measurements of Single Crystals,"Polarisation-resolved Raman scattering measurements were performed on MgB_2
single crystals to determine the magnitude, symmetry and temperature dependence
of the superconducting gap. A single sharp peak due to Cooper pair breaking
appears in the electronic continuum below Tc, reaching an average maximum Raman
shift of 105 +/- 1 cm^{-1} (2 Delta(0) / k_{B}Tc = 3.96 +/- 0.09) and showing
up to 5 cm^{-1} anisotropy between polarised and depolarised spectra. The
temperature dependence of 2 Delta follows that predicted from BCS theory, while
the anisotropy decreases with decreasing temperature. It is concluded that the
Raman results are consistent with a slightly anisotropic s-wave gap in a
conventional BCS superconductor.",0107216v2
2001-07-23,Surface-induced magnetic anisotropy for impurity spins in granular AuFe films,"The theory of the surface-induced anisotropy is extended to the case of
granular films of dilute magnetic alloys. Since the surface-induced blocking of
a magnetic-impurity spin appears to be very sensitive to the specific
polycrystalline structure, we speculate that the apparent discrepancy between
the experimental results of different groups for the size dependence of the
Kondo resistivity can be linked to different microstructure of the samples. We
apply our model to calculate the magnetization of impurity spins in small AuFe
grains and to interpret the experimental data on the anomalous Hall effect in
thin Fe doped Au films.",0107460v1
2001-08-08,Magnetic anisotropy of the spin ice compound Dy2Ti2O7,"We report magnetization and ac susceptibility of single crystals of the spin
ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the charasteristic axes
[100] and [110] agree with the expected values for an effective ferromagnetic
nearest-neighbor Ising pyrochlore with local <111> anisotropy, where each
magnetic moment is constrained to obey the `ice-rule'. At high enough magnetic
fields along the [111] axis, the saturated moment exhibits a beaking of the
ice-rule; it agrees with the value expected for a three-in one-out spin
configuration. Assuming the realistic magnetic interaction between Dy ions
given by the dipolar spin ice model, we completely reproduce the results at 2 K
by Monte Carlo calculations. However, down to at least 60 mK, we have not found
any experimental evidence of the long-range magnetic ordering predicted by this
model to occur at around 180 mK. Instead, we confirm the spin freezing of the
system below 0.5 K.",0108129v1
2001-08-19,Critical thermodynamics of three-dimensional MN-component field model with cubic anisotropy from higher-loop εexpansion,"The critical thermodynamics of an $MN$-component field model with cubic
anisotropy relevant to the phase transitions in certain crystals with
complicated ordering is studied within the four-loop $\ve$ expansion using the
minimal subtraction scheme. Investigation of the global structure of RG flows
for the physically significant cases M=2, N=2 and M=2, N=3 shows that the model
has an anisotropic stable fixed point with new critical exponents. The critical
dimensionality of the order parameter is proved to be equal to
$N_c^C=1.445(20)$, that is exactly half its counterpart in the real hypercubic
model.",0108298v1
2001-08-27,Electron Spin Resonance in S=1/2 antiferromagnetic chains,"A systematic field-theory approach to Electron Spin Resonance (ESR) in the
$S=1/2$ quantum antiferromagnetic chain at low temperature $T$ (compared to the
exchange coupling $J$) is developed. In particular, effects of a transverse
staggered field $h$ and an exchange anisotropy (including a dipolar
interaction) $\delta$ on the ESR lineshape are discussed. In the lowest order
of perturbation theory, the linewidth is given as $\propto Jh^2/T^2$ and
$\propto (\delta/J)^2 T$, respectively. In the case of a transverse staggered
field, the perturbative expansion diverges at lower temperature;
non-perturbative effects at very low temperature are discussed using exact
results on the sine-Gordon field theory. We also compare our field-theory
results with the predictions of Kubo-Tomita theory for the high-temperature
regime, and discuss the crossover between the two regimes. It is argued that a
naive application of the standard Kubo-Tomita theory to the
Dzyaloshinskii-Moriya interaction gives an incorrect result. A rigorous and
exact identity on the polarization dependence is derived for certain class of
anisotropy, and compared with the field-theory results.",0108424v2
2001-08-30,Spin dynamics of Sr_14Cu_24O_41 two-leg ladder studied by Raman spectroscopy,"The two-magnon (2M) excitation at 3000 cm-1 in Sr_14Cu_24O_41 two-leg ladder
is studied by Raman scattering. A slight anisotropy of the superexchange
coupling J_{\perp}/J_{||} \approx 0.8 with J_{||} = 110 \pm 20 meV is proposed
from the analysis of the magnetic scattering. The resonant coupling across the
charge transfer gap increases the 2M intensity by orders of magnitude. The
anisotropy of Raman scattering is dependent upon the excitation energy. The 2M
relaxation is found to be correlated with the temperature dependent electronic
Raman continuum at low frequencies.",0108507v2
2001-09-26,Transport properties of c-oriented MgB2 thin films grown by Pulsed Laser Deposition,"The electronic anisotropy in MgB2, which arises from its layered crystal
structure is not completely clear until now. High quality c-oriented films
offer the opportunity of studying such property. MgB2 thin films were deposited
by using two methods both based on room temperature precursor deposition (by
Pulsed Laser Ablation) and ex-situ annealing in Mg atmosphere. The two methods
differ for the starting targets: stoichiometric MgB2 in one case and Boron in
the other. The two films presented in this paper are grown by means of the two
techniques on MgO substrates and are both c-oriented; they present TC values of
31.5 and 37.4 K respectively. Upper critical field measurements, up to 9T, with
the magnetic field in perpendicular and parallel directions in respect to the
film surface evidenced anisotropy ratios of 1.8 and 1.4 respectively. In this
paper we will discuss this remarkable and surprising difference also in
comparison with the literature data.",0109481v1
2001-09-28,Anisotropy in c-oriented MgB2 thin films grown by Pulsed Laser Deposition,"The electronic anisotropy in MgB2, is still a not completely clear topic;
high quality c-oriented films are suitable systems to investigate this
property. In this work we present our results on MgB2 superconducting thin
films grown on MgO and sapphire substrates. The films are deposited in high
vacuum, at room temperature, by Laser Ablation, starting from two different
targets: pure Boron and stoichiometric MgB2. In both cases, to obtain and
crystallize the superconducting phase, an ex-situ annealing in magnesium vapor
is needed. The films were characterized by Synchrotron radiation diffraction
measurements; the films turned out to be strongly c-oriented, with the c-axis
perpendicular to the film surface and an influence of the substrate on
crystallographic parameters is observed. Resisivity measurements with the
magnetic field perpendicular and parallel directions to the film surface
evidenced an anisotropic upper critical field behavior. The Hc2 ratios (h)
resulted in the range 1.2-1.8; this difference will be discussed also in
comparison with the literature data.",0109536v1
2001-11-30,Electron Paramagnetic Resonance Linewidths and Lineshapes for the Molecular Magnets Fe8 and Mn12,"We study theoretically Electron Paramagentic Resonance (EPR) linewidths for
single crystals of the molecular magnets Fe$_8$ and Mn$_{12}$ as functions of
energy eigenstates $M_s$, frequency, and temperature when a magnetic field
along the easy axis is swept at fixed excitation frequency. This work was
motivated by recent EPR experiments. To calculate the linewidths, we use
density-matrix equations, including dipolar interactions and distributions of
the uniaxial anisotropy parameter $D$ and the Land\'{e} $g$ factor. Our
calculated linewidths agree well with the experimental data. We also examine
the lineshapes of the EPR spectra due to local rotations of the magnetic
anisotropy axes caused by defects in samples. Our preliminary results predict
that this effect leads to asymmetry in the EPR spectra.",0111589v2
2002-02-08,Anisotropic Superconducting Properties of MgB2 Single Crystals,"In-plane electrical transport properties of MgB2 single crystals grown under
high pressure of 4-6 GPa and temperature of 1400-1700oC in Mg-B-N system have
been measured. For all specimens we found sharp superconducting transition
around 38.1-38.3K with transition width within 0.2-0.3K. Estimated resistivity
value at 40K is about 1 mkOhmcm and resistivity ratio R(273K)/R(40K) of about
4.9. Results of measurements in magnetic field up to 5.5T perpendicular to Mg
and B planes and up to 9T in parallel orientation show temperature dependent
anisotropy of the upper critical field with anisotropy ratio increasing from
2.2 close to Tc up to about 3 below 30K. Strong deviation of the angular
dependence of Hc2 from anisotropic mass model has been also found.",0202133v1
2002-03-06,Novel anisotropy in the superconducting gap structure of Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} probed by quasiparticle heat transport,"Since the nature of pairing interactions is manifested in the superconducting
gap symmetry, the exact gap structure, particularly any deviation from the
simple d_{x^2-y^2} symmetry, would help elucidating the pairing mechanism in
high-T_c cuprates. Anisotropic heat transport measurement in
Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta} (Bi-2212) reveals that the quasiparticle
populations are different for the two nodal directions and thus the gap
structure must be uniquely anisotropic, suggesting that pairing is governed by
interactions with a rather complicated anisotropy. Intriguingly, it is found
that the ""plateau"" in the magnetic-field dependence of the thermal conductivity
is observed only in the b-axis transport.",0203106v1
2002-03-07,The Onset of Anisotropic Transport of Two-Dimensional Electrons in High Landau Levels: An Isotropic-to-Nematic Liquid Crystal Phase Transition?,"The recently discovered anisotropy of the longitudinal resistance of
two-dimensional electrons near half filling of high Landau levels is found to
persist to much higher temperatures T when a large in-plane magnetic field B||
is applied. Under these conditions we find that the longitudinal resistivity
scales quasi-linearly with B||/T. These observations support the notion that
the onset of anisotropy at B||=0 does not reflect the spontaneous development
of charge density modulations but may instead signal an isotropic-to-nematic
liquid crystal phase transition.",0203174v1
2002-03-15,Superconducting Transition and Phase Diagram of Single Crystal MgB2,"The superconducting phase diagram of MgB2 was determined from magnetization,
magneto-transport and the first single-crystal specific heat measurements. A
zero-temperature in-plane coherence length of 8 nm is determined. The
superconducting anisotropy increases from a value around 2 near Tc to above 4.5
at 22 K. For H||c a pronounced peak effect in the critical current occurs at
the upper critical field. Evidence for a surface superconducting state is
presented for H||c which might account for the wide spread in reported values
of the anisotropy.",0203337v2
2002-03-27,"Transport critical current, anisotropy, irreversibility fields and exponential n factors in Fe sheathed MgB2 tapes","The influence of the initial MgB2 grain size on critical current density,
upper critical fields and irreversibility has been studied on Fe sheathed
monofilamentary MgB2 tapes prepared by the Powder-In-Tube technique. The effect
of the reduction of MgB2 grain size by ball milling was mainly to enhance both
the critical current density, jc, and the irreversibility field, while the
upper critical field remained unchanged. The anisotropy ratio of the upper
critical field between magnetic fields parallel and perpendicular the tape
surface was determined to 1.3, reflecting a deformation induced texture. A good
agreement has been found between resistive and inductive jc values, measured at
various temperatures. At 25K and 1 T, jc values close to 105 A/cm2 were
measured. The exponential n factor of the resistive transition was found to be
quite high at low fields, and decrease linearly from 60 at 4T to 10 at 8.5T.",0203551v1
2002-03-29,Anisotropic random resistor networks: a model for piezoresistive response of thick-film resistors,"A number of evidences suggests that thick-film resistors are close to a
metal-insulator transition and that tunneling processes between metallic grains
are the main source of resistance. We consider as a minimal model for
description of transport properties in thick-film resistors a percolative
resistor network, with conducting elements governed by tunneling. For both
oriented and randomly oriented networks, we show that the piezoresistive
response to an applied strain is model dependent when the system is far away
from the percolation thresold, while in the critical region it acquires
universal properties. In particular close to the metal-insulator transition,
the piezoresistive anisotropy show a power law behavior. Within this region,
there exists a simple and universal relation between the conductance and the
piezoresistive anisotropy, which could be experimentally tested by common
cantilever bar measurements of thick-film resistors.",0203612v1
2002-04-12,Anisotropic s-wave superconductivity: comparison with experiments on MgB2 single crystals,"The recently discovered superconductivity in MgB2 has captured world
attention due to its simple crystal structure and relatively high
superconducting transition temperature Tc=39K. It appears to be generally
accepted that it is phonon-mediated s-wave BCS-like superconductivity.
Surprisingly, the strongly temperature dependent anisotropy of the upper
critical field, observed experimentally in magnesium diboride single crystals,
is still lacking a consistent theoretical explanation. We propose a simple
single-gap anisotropic s-wave order parameter in order to compare its
implications with the prediction of a multi-gap isotropic s-wave model. The
quasiparticle density of states, thermodynamic properties, NMR spin-lattice
relaxation rate, optical conductivity, and Hc2 anisotropy have been analyzed
within this anisotropic s-wave model. We show that the present model can
capture many aspects of the unusual superconducting properties of MgB2
compound, though more experimental data appear to be necessary from single
crystal MgB2.",0204272v3
2002-04-12,Spatial dispersion in CaF$_2$ caused by the vicinity of an excitonic bound state,"The microscopic mechanism beyond the optical anisotropy of an ionic crystal
which occurs for short wavelengths is investigated. The electron-hole, two
particle propagator and its analytical behaviour close to the band edge of the
one particle continuum plays a major role for the mechanism of this optical
anisotropy. Especially for an ionic crystal the two particle bound state, the
exciton, is of special importance. In this way we argue that the so called
``intrinsic birefringence'' in CaF$_2$ is neither intrinsic to the material nor
it is birefringence. Instead it is spatial dispersion caused by the vicinity of
a dispersive optical absorption given by the excitonic bound state. We propose
a model which connects the bound state dispersion with the band structure and a
model potential for a screened coulomb interaction. Based on these
considerations we predict a wavelength dependence of the dielectric function
approaching close to the bound state level $\epsilon \sim (\lambda -
\lambda_0)^{-1}$, where $\lambda_0$ is the wavelength of the excitonic bound
state level.",0204282v1
2002-04-30,Quantum Monte Carlo simulation of thin magnetic films,"The stochastic series expansion quantum Monte Carlo method is used to study
thin ferromagnetic films, described by a Heisenberg model including local
anisotropies. The magnetization curve is calculated, and the results compared
to Schwinger boson and many-body Green's function calculations. A transverse
field is introduced in order to study the reorientation effect, in which the
magnetization changes from out-of-plane to in-plane. Since the approximate
theoretical approaches above differ significantly from each other, and the
Monte Carlo method is free of systematic errors, the calculation provides an
unbiased check of the approximate treatments. By studying quantum spin models
with local anisotropies, varying spin size, and a transverse field, we also
demonstrate the general applicability of the recent cluster-loop formulation of
the stochastic series expansion quantum Monte Carlo method.",0204629v1
2002-05-15,Competition between anisotropy and superconductivity in organic and cuprate superconductors,"We analyze the empirical correlation between the zero temperature penetration
depth $\lambda_{c}(0) $ and the corresponding normal state DC conductivity
$\sigma_{c}^{DC}$, measured slightly above the transition temperature $T_{c}$,
in different classes of quasi two-dimensional superconductors, including
cuprates and organics. For this purpose we invoke the scaling theory of quantum
and finite temperature critical phenomena. Important implications are:
Superconductivity in the organic and cuprate superconductors is a genuine three
dimensional (3D) phenomenon. The competition between anisotropy and
superconductivity destroys the latter in the 2D limit even in the ground state.
The data uncovers the flow to quantum criticality, including the 2D quantum
superconductor to insulator (2D-QSI) and the 3D quantum superconductor to
normal state (3D-QSN) transition. This flow gives a clear perspective of the
regimes where quantum fluctuations are essential and mean-field treatments
fail. Thus, a detailed account of the flow from mean-field to 2D-QSI
criticality in organics and the crossover from the 2D-QSI to the 3D-QSN
critical point in cuprates is a challenge for microscopic theories attempting
to solve the puzzle of superconductivity in these materials.",0205304v1
2002-05-17,Thermodynamic Properties of Weakly Anisotropic Disordered Magnetic Chains in the Large-S Limit,"we investigate the thermodynamic properties of weakly anisotropic disordered
magnetic chains where the nearest-neighbor Heisenberg exchange coupling is the
dominant spin-spin interaction. In addition to the exchange interaction, there
is single-ion anisotropy with the direction of the easy axis being the same for
all spins. The analysis is carried out in the limit S >> 1, where S denotes the
ionic spin, and in the temperature range T << JaveS, where Jave is the average
magnitude of the exchange interaction. It is assumed that the independent boson
picture is appropriate so that the thermodynamic properties of the chain are
those of a gas of weakly interacting magnons whose frequencies are obtained
from linearized equations of motion for the spins. The =+/-J model is studied
in detail with both random and non-random anisotropy. Particular emphasis is
placed on the existence",0205372v1
2002-05-27,Free fermion branches in some quantum spin models,"Extensive numerical analysis of the eigenspectra of the $SU_q(N)$ invariant
Perk-Schultz Hamiltonian shows some simple regularities for a significant part
of the eigenspectrum. Inspired by those results we have found two set of
solutions of the associated nested Bethe-ansatz equations. The first set is
obtained at a special value of the anisotropy ($q = \exp(i2\pi (N-1)/N)$) and
describes in particular the ground state and nearby excitations as a sum of
free-fermion quasienergies. The second set of solutions provides the energies
in the sectors whose number $n_i$ of particles of distinct species ($i =0,
>..., N-1$) are less or equal to the unity except for one of the species. For
this last set we obtain the eigenspectra of a free fermion model for arbitrary
values of the anisotropy.",0205567v1
2002-06-11,Anisotropy and large magnetoresistance in narrow gap semiconductor FeSb2,"A study of the anisotropy in magnetic, transport and magnetotransport
properties of FeSb2 has been made on large single crystals grown from Sb flux.
Magnetic susceptibility of FeSb2 shows diamagnetic to paramagnetic crossover
around 100K. Electrical transport along two axes is semiconducting whereas the
third axis exhibits a metal - semiconductor crossover at temperature Tmin which
is sensitive to current alignment and ranges between 40 and 80K. In H=70kOe
semiconducting transport is restored for T<300K, resulting in large
magnetoresistance [rho(70kOe)-rho(0)]/rho(0)=2200% in the crossover temperature
range",0206190v1
2002-06-13,Anisotropy of the Upper Critical Field and Critical Current in Single Crystal MgB$_2$,"We report on specific heat, high magnetic field transport and
$ac-$susceptibility measurements on magnesium diboride single crystals. The
upper critical field $H_{c2}$ for magnetic fields perpendicular and parallel to
the Mg and B planes is presented for the first time in the entire temperature
range. A very different temperature dependence has been observed in the two
directions which yields to a temperature dependent anisotropy with $\Gamma
\sim$ 5 at low temperatures and about 2 near $T_c$. A peak effect is observed
in susceptibility measurements for $H \sim $2 T parallel to the $c-$axis and
the critical current density presnts a sharp maximum for $H$ parallel to the
ab-plane.",0206231v2
2002-07-31,Transport anisotropy in biaxially strained La(2/3)Ca(1/3)MnO(3) thin films,"Due to the complex interplay of magnetic, structural, electronic, and orbital
degrees of freedom, biaxial strain is known to play an essential role in the
doped manganites. For coherently strained La(2/3)Ca(1/3)MnO(3) thin films grown
on SrTiO(3) substrates, we measured the magnetotransport properties both
parallel and perpendicular to the substrate and found an anomaly of the
electrical transport properties. Whereas metallic behavior is found within the
plane of biaxial strain, for transport perpendicular to this plane an
insulating behavior and non-linear current-voltage characteristics (IVCs) are
observed. The most natural explanation of this anisotropy is a strain induced
transition from an orbitally disordered ferromagnetic state to an orbitally
ordered state associated with antiferromagnetic stacking of ferromagnetic
manganese oxide planes.",0207730v1
2002-08-06,Spin order on pyrochlore lattices studied by the Self-Consistent Cluster Approach,"In this paper we present a study of magnetic order of quantum Heisenberg
spins on pyrochlore type lattices: a lattice of corner sharing tetrahedra. We
use the Cluster Variation Approximation with the tetrahedron as basic cluster.
We find that in case of anti-ferromagnetic nearest--neighbour exchange there is
no long--range spin order at any finite temperature for any spin s. For
ferromagnetic exchange and s=1/2 the spin system remains in a non-magnetic
phase for all temperatures, while for s > 1/2 there is a finite order
temperature. We derive the ground state phase diagram as a function of exchange
anisotropy and tetragonal anisotropy and find regions of re--entrant behaviour.
Magnetic fields can induce one or more magnetic transitions. Schottky--like
anomalies appear in the specific heat, with on top signs of re--entrant
behaviour. The limits of this Cluster Variation Approximations are discussed.",0208119v1
2002-08-07,Kinetics of photoinduced anisotropy in azopolymers: models and mechanisms,"We consider the effect of photoinduced optical anisotropy (POA) in
azopolymers. Using a unified approach to the kinetics of photo-reorientation we
discuss the assumptions underlying the known theoretical models of POA and
formulate a tractable phenomenological model in terms of angular redistribution
probabilities and order parameter correlation functions. The model takes into
account biaxiality effects and long term stability of POA in azopolymers. It
predicts that under certain conditions two different mechanisms,
photoorientation and photoselection, will dominate POA depending on the
wavelength of pumping light. By using available experimental data, we employ
the model to compute dependencies of principal absorption coefficients on the
illumination time. Our calculations clearly indicate the different regimes of
POA and the numerical results are found to be in good agreement with the
experimental data.",0208123v1
2002-09-04,More Evidence for a Distribution of Tunnel Splittings in Mn$_{12}$-acetate,"In magnetic fields applied parallel to the anisotropy axis, the magnetization
of Mn$_{12}$ has been measured in response to a field that is swept back and
forth across the resonances corresponding to steps $N=4,5,...9$. The fraction
of molecules remaining in the metastable well after each sweep through the
resonance is inconsistent with expectations for an ensemble of identical
molecules. The data are consistent instead with the presence of a broad
distribution of tunnel splittings. A very good fit is obtained for a Gaussian
distribution of the second-order anisotropy tunneling parameter $X_E=-\ln(\mid
E\mid/2D)$. We show that dipolar shuffling is a negligible effect which cannot
explain our data.",0209110v2
2002-09-10,Scattering of electrons by impurities within the framework of two band model of order parameter anisotropy,"The impurity concentration dependence of superconducting transition
temperature $T_c$ is studied within the framework of two band model of order
parameter anisotropy. Both intraband and interband electron scattering by
nonmagnetic and magnetic impurities are taken into account. It is demonstrated
that at various values of model parameters both types of impurity concentration
dependence of $T_c$ are possible: weak dependence typical of the model with
s-wave order parameter and strong suppression of $T_c$ by impurities with
critical impurity concentration at which $T_c=0$. It is found that in some
cases there is a possibility of a rise of critical temperature with increasing
impurity concentration. The obtained results are consistent with existing
experimental data for the high-temperature superconductors.",0209233v1
2002-09-12,Electron momentum density in yttrium,"A simultaneous analysis of high-resolution directional Compton profiles and
two-dimensional angular correlation of positron annihilation experimental data
has been performed by studying both a directional anisotropy of measured
spectra and reconstructed densities. The results were compared with theoretical
fully-relativistic augmented plane-wave calculations with and without including
correlation effects. Estimated symmetry selection rules have allowed us to
establish some values of Fermi momenta. Both experiments show exactly the same
shape of the anisotropy of the momentum densities, in agreement with the band
structure results. In the positron annihilation data electron-positron
correlations are not seen while in both experiments electron-electron
correlations are observed.",0209297v1
2002-09-17,Ground State Phase Diagram of S=1 XXZ Chains with Uniaxial Single-Ion-Type Anisotropy,"One dimensional S=1 XXZ chains with uniaxial single-ion-type anisotropy are
studied by numerical exact diagonalization of finite size systems. The
numerical data are analyzed using conformal field theory, the level
spectroscopy, phenomenological renormalization group and finite size scaling
method. We thus present the first quantitatively reliable ground state phase
diagram of this model. The ground states of this model contain the Haldane
phase, large-D phase, N\'{e}el phase, two XY phases and the ferromagnetic
phase. There are four different types of transitions between these phases: the
Brezinskii-Kosterlitz-Thouless type transitions, the Gaussian type transitions,
the Ising type transitions and the first order transitions. The location of
these critical lines are accurately determined.",0209403v1
2002-09-17,Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals,"Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.",0209404v1
2002-09-24,Low Temperature Static and Dynamic Behaviour of the Easy-Axis Heisenberg Antiferromagnet on the Kagome Lattice,"The antiferromagnetic Heisenberg model with easy-axis exchange anisotropy on
the Kagome lattice is studied by means of Monte Carlo simulations. From
equilibrium properties, we find that the values of the critical exponents
associated with the magnetization at the critical temperature $T_c$ vary with
the magnitude of the anisotropy. On the other hand, the spin-spin
autocorrelation functions have a stretched exponential behavior with a power
law divergence of the relaxation time at a glass-like temperature $T_g \sim
T_c$. From non-equilibrium dynamics at a fixed temperature below $T_g$, aging
effects are found which obey the same scaling laws as in spin glasses and
polymers.",0209568v2
2002-10-18,Field-Induced Transition in the S=1 Antiferromagnetic Chain with Single-Ion Anisotropy in a Transverse Magnetic Field,"The field-induced transition in one-dimensional S=1 Heisenberg
antiferromagnet with single-ion anisotropy in the presence of a transverse
magnetic field is obtained on the basis of the Schwinger boson mean-field
theory. The behaviors of the specific heat and susceptibility as functions of
temperature as well as the applied transverse field are explored, which are
found to be different from the results obtained under a longitudinal field. The
anomalies of the specific heat at low temperatures, which might be an
indicative of a field-induced transition from a Luttinger liquid phase to an
ordered phase, are explicitly uncovered under the transverse field. A schematic
phase diagram is proposed. The theoretical results are compared with
experimental observations.",0210394v1
2002-11-14,Magnetic relaxation and dipole-coupling-induced magnetization in nanostructured thin films during growth: A cluster Monte Carlo study,"For growing inhomogeneous thin films with an island nanostructure similar as
observed in experiment, we determine the nonequilibrium and equilibrium
remanent magnetization. The single-island magnetic anisotropy, the dipole
coupling, and the exchange interaction between magnetic islands are taken into
account within a micromagnetic model. A cluster Monte Carlo method is developed
which includes coherent magnetization changes of connected islands. This causes
a fast relaxation towards equilibrium for irregularly connected systems. We
analyse the transition from dipole coupled islands at low coverages to a
strongly connected ferromagnetic film at high coverages during film growth. For
coverages below the percolation threshold, the dipole interaction induces a
collective magnetic order with ordering temperatures of 1 - 10 K for the
assumed model parameters. Anisotropy causes blocking temperatures of 10 - 100 K
and thus pronounced nonequilibrium effects. The dipole coupling leads to a
somewhat slower magnetic relaxation.",0211290v2
2002-11-20,Nanoscale phase separation in $La_{0.7}Ca_{0.3}MnO_3$ films: evidence for the texture driven optical anisotropy,"The IR optical absorption (0.1-1.5 eV) in the $La_{0.7}Ca_{0.3}MnO_3$ films
on LAO substrate exhibits the drastic temperature evolution of the spectral
weight evidencing the insulator to metal transition. Single crystal films were
found to reveal strong linear dichroism with anomalous spectral oscillations
and fairly weak temperature dependence. Starting from the concept of phase
separation, we develop the effective medium model to account for these effects.
The optical anisotropy of the films is attributed to the texturization of the
ellipsoidal inclusions of the quasimetal phase caused by a mismatch of the film
and substrate and the twin texture of the latter.",0211430v1
2002-11-22,Linear and Second-order Optical Response of the III-V Mono-layer Superlattices,"We report the first fully self-consistent calculations of the nonlinear
optical properties of superlattices. The materials investigated are mono-layer
superlattices with GaP grown on the the top of InP, AlP and GaAs (110)
substrates. We use the full-potential linearized augmented plane wave method
within the generalized gradient approximation to obtain the frequency dependent
dielectric tensor and the second-harmonic-generation susceptibility. The effect
of lattice relaxations on the linear optical properties are studied. Our
calculations show that the major anisotropy in the optical properties is the
result of strain in GaP. This anisotropy is maximum for the superlattice with
maximum lattice mismatch between the constituent materials. In order to
differentiate the superlattice features from the bulk-like transitions an
improvement over the existing effective medium model is proposed. The
superlattice features are found to be more pronounced for the second-order than
the linear optical response indicating the need for full supercell calculations
in determining the correct second-order response.",0211512v2
2002-11-28,Investigation of surface critical behavior of semi-infinite systems with cubic anisotropy,"The critical behavior at the special surface transition and crossover
bevavior from special to ordinary surface transition in semi-infinite
n-component anisotropic cubic models are investigated by applying the field
theoretic approach directly in d=3 dimensions up to the two-loop approximation.
The crossover behavior for random semi-infinite Ising-like system, which is the
nontrivial particular case of the cubic model in the limit $n\to 0$, is also
investigated. The numerical estimates of the resulting two-loop series
expansions for the critical exponents of the special surface transition,
surface crossover critical exponent $\Phi$ and the surface critical exponents
of the layer, $\alpha_{1}$, and local specific heats, $\alpha_{11}$, are
computed by means of Pade and Pade-Borel resummation techniques. For $n<n_{c}$
the system belongs to the universality class of the isotropic n-component
model, while for $n>n_{c}$ the cubic fixed point is stable, where $n_{c}$ is
the marginal spin dimensionality of the cubic model. The obtained results
indicate that the surface critical behavior of semi-infinite systems with cubic
anisotropy is characterized by new set of surface critical exponents for
$n>n_{c}$.",0211654v1
2003-01-30,Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn12-acetate,"We present detailed angle-dependent single crystal electron paramagnetic
resonance (EPR) data for field rotations in the hard plane of the S=10 single
molecule magnet Mn12-acetate. A clear four-fold variation in the resonance
positions may be attributed to an intrinsic fourth order transverse anisotropy
(O44). Meanwhile, a four-fold variation of the EPR lineshapes confirms a
recently proposed model wherein disorder associated with the acetic acid of
crystallization induces a locally varying quadratic (rhombic) transverse
anisotropy (O22). These findings explain most aspects of the magnetic quantum
tunneling observed in Mn12-acetate.",0301599v2
2003-03-06,Anisotropy and Ising-like transition of the S=5/2 two-dimensional Heisenberg antiferromagnet Mn-formate di-Urea,"Recently reported measurements of specific heat on the compound Mn-formate
di-Urea (Mn-f-2U) by Takeda et al. [Phys. Rev. B 63, 024425 (2001)] are
considered. As a model to describe the overall thermodynamic behavior of such
compound, the easy-axis two-dimensional Heisenberg antiferromagnet is proposed
and studied by means of the 'pure quantum self-consistent harmonic
approximation' (PQSCHA). In particular it is shown that, when the temperature
decreases, the compound exhibits a crossover from 2D-Heisenberg to 2D-Ising
behavior, followed by a 2D-Ising-like phase transition, whose location allows
to get a reliable estimate of the easy-axis anisotropy driving the transition
itself. Below the critical temperature T_N=3.77 K, the specific heat is well
described by the two-dimensional easy-axis model down to a temperature T*=1.47
K where a T^3-law sets in, possibly marking a low-temperature crossover of
magnetic fluctuations from two to three dimensions.",0303119v1
2003-03-22,Photoinduced 3D orientational order in side chain liquid crystalline azopolymers,"We apply experimental technique based on the combination of methods dealing
with principal refractive indices and absorption coefficients to study the
photoinduced 3D orientational order in the films of liquid crystalline (LC)
azopolymers. The technique is used to identify 3D orientational configurations
of trans azobenzene chromophores and to characterize the degree of ordering in
terms of order parameters. We study two types of LC azopolymers which form
structures with preferred in-plane and out-of-plane alignment of
azochromophores, correspondingly. Using irradiation with the polarized light of
two different wavelengths we find that the kinetics of photoinduced anisotropy
can be dominated by either photo-reorientation or photoselection mechanisms
depending on the wavelength. We formulate the phenomenological model describing
the kinetics of photoinduced anisotropy in terms of the isomer concentrations
and the order parameter tensor. We present the numerical results for absorption
coefficients that are found to be in good agreement with the experimental data.
The model is also used to interpret the effect of changing the mechanism with
the wavelength of the pumping light.",0303488v1
2003-04-07,Transitions from small to large Fermi momenta in a one-dimensional Kondo lattice model,"We study a one-dimensional system that consists of an electron gas coupled to
a spin-1/2 chain by Kondo interaction away from half-filling. We show that
zero-temperature transitions between phases with ""small"" and ""large"" Fermi
momenta can be continuous. Such a continuous but Fermi-momentum-changing
transition arises in the presence of spin anisotropy, from a Luttinger liquid
with a small Fermi momentum to a Kondo-dimer phase with a large Fermi momentum.
We have also added a frustrating next-nearest-neighbor interaction in the spin
chain to show the possibility of a similar Fermi-momentum-changing transition,
between the Kondo phase and a spin-Peierls phase, in the spin isotropic case.
This transition, however, appears to involve a region in which the two phases
coexist.",0304129v3
2003-04-08,Fermi surface topology and vortex state in MgB2,"Based on a detailed modeling of the Fermi surface topology of MgB2 we
calculated the anisotropy of the upper critical field Bc2 within the two gap
model. The sigma-band is modeled as a distorted cylinder and the pi-band as a
half-torus, with parameters determined from bandstructure calculations. Our
results show that the unusual strong temperature dependence of the Bc2
anisotropy, that has been observed recently, can be understood due to the small
c-axis dispersion of the cylindrical Fermi surface sheets and the small
interband pairing interaction as obtained from bandstructure calculations. We
calculate the magnetic field dependence of the density of states within the
vortex state for field in c-axis direction and compare with recent measurements
of the specific heat on MgB2 single crystals.",0304194v1
2003-04-18,Detection of XY behaviour in weakly anisotropic quantum antiferromagnets on the square lattice,"We consider the Heisenberg antiferromagnet on the square lattice with S=1/2
and very weak easy-plane exchange anisotropy; by means of the quantum Monte
Carlo method, based on the continuous-time loop algorithm, we find that the
thermodynamics of the model is highly sensitive to the presence of tiny
anisotropies and is characterized by a crossover between isotropic and planar
behaviour. We discuss the mechanism underlying the crossover phenomenon and
show that it occurs at a temperature which is characteristic of the model. The
expected Berezinskii-Kosterlitz-Thouless transition is observed below the
crossover: a finite range of temperatures consequently opens for experimental
detection of non-critical 2D XY behaviour. Direct comparison is made with
uniform susceptibility data relative to the S=1/2 layered antiferromagnet
Sr2CuO2Cl2.",0304438v1
2003-04-25,Ising-like Spin Anisotropy and Competing Antiferromagnetic - Ferromagnetic Orders in GdBaCo_{2}O_{5.5} Single Crystals,"In RBaCo_{2}O_{5+x} compounds (R is rare earth), a
ferromagnetic-antiferromagnetic competition is accompanied by a giant
magnetoresistance. We study the magnetization of detwinned GdBaCo_{2}O_{5.5}
single crystals, and find a remarkable uniaxial anisotropy of Co^{3+} spins
which is tightly linked with the chain oxygen ordering in GdO_{0.5} planes.
Reflecting the underlying oxygen order, CoO_2 planes also develop a spin-state
order consisting of Co^{3+} ions in alternating rows of S=1 and S=0 states. The
magnetic structure appears to be composed of weakly coupled ferromagnetic
ladders with Ising-like moments, which gives a simple picture for
magnetotransport phenomena.",0304578v1
2003-05-06,Gigantic anisotropic uniaxial pressure effect on superconductivity within the CuO2 plane of La1.64Eu0.2Sr0.16CuO4 - strain control of stripe criticality,"The effect of uniaxial pressure on superconductivity was examined for a
high-Tc cuprate La1.64Eu0.2Sr0.16CuO4, which is located at the boundary between
the superconducting and stripe phases. We found remarkably large anisotropy of
the uniaxial pressure effect not only between the in-plane and out-of-plane
pressures but also within the CuO2-plane. When the pressure is applied along
the tetragonal [110] direction, we found the largest pressure effect ever
observed in cuprates, dTc/dP - 2.5 K/kbar, while the change of Tc was not
appreciable when applied along [100]. This substantial in-plane anisotropy is
attributed to an intimate link between the symmetry of the one-dimensional
stripes and that of the strain produced within the CuO2 plane.",0305111v1
2003-06-03,Phase separation effects in charge-ordered Pr0.5Ca0.5MnO3 thin film,"Compressed Pr0.5Ca0.5MnO3 films (250nm) deposited on LaAlO3 have been studied
by Electron Spin Resonance technique under high frequency and high magnetic
field. We show evidences for the presence of a ferromagnetic phase (FM)
embedded in the charge-order phase (CO), in form of thin layers which size
depends on the strength and orientation of the magnetic field (parallel or
perpendicular to the substrate plane). This FM phase presents an easy plane
magnetic anisotropy with an anisotropy constant 100 times bigger than typical
bulk values. When the magnetic field is applied perpendicular to the substrate
plane, the FM phase is strongly coupled to the CO phase whereas for the
parallel orientation it keeps an independent ferromagnetic resonance even when
the CO phase becomes antiferromagnetic.",0306075v1
2003-06-20,Anisotropic transport in the two-dimensional electron gas in the presence of spin-orbit coupling,"In a two-dimensional electron gas as realized by a semiconductor quantum
well, the presence of spin-orbit coupling of both the Rashba and Dresselhaus
type leads to anisotropic dispersion relations and Fermi contours. We study the
effect of this anisotropy on the electrical conductivity in the presence of
fixed impurity scatterers. The conductivity also shows in general an anisotropy
which can be tuned by varying the Rashba coefficient. This effect provides a
method of detecting and investigating spin-orbit coupling by measuring
spin-unpolarized electrical currents in the diffusive regime. Our approach is
based on an exact solution of the two-dimensional Boltzmann equation and
provides also a natural framework for investigating other transport effects
including the anomalous Hall effect.",0306528v2
2003-07-15,Relevance of space anisotropy in the critical behavior of m-axial Lifshitz points,"The critical behavior of $d$-dimensional systems with $n$-component order
parameter $\bm{\phi}$ is studied at an $m$-axial Lifshitz point where a
wave-vector instability occurs in an $m$-dimensional subspace ${\mathbb R}^m$
($m{>}1$). Field theoretic renormalization group techniques are exploited to
examine the effects of terms in the Hamiltonian that break the rotational
symmetry of the Euclidean group ${\mathbb E}(m)$. The framework for considering
general operators of second order in $\bm{\phi}$ and fourth order in the
derivatives $\partial_\alpha $ with respect to the Cartesian coordinates
$x_\alpha $ of ${\mathbb R}^m$ is presented. For the specific case of systems
with cubic anisotropy, the effects of having an additional term,
$\sum_{\alpha=1}^m(\partial_\alpha^2\bm{\phi})^2$, are investigated in an
$\epsilon$ expansion about the upper critical dimension $d^{*}(m)=4+m/2$. Its
associated crossover exponent is computed to order $\epsilon^2$ and found to be
positive, so that it is a \emph{relevant} perturbation on a model isotropic in
${\mathbb R}^m$.",0307355v2
2003-07-16,Anisotropies of the lower and upper critical fields in MgB$_2$ single crystals,"The temperature dependence of the London penetration depth ($\lambda$) and
coherence length ($\xi$) has been deduced from Hall probe magnetization
measurements in high quality MgB$_2$ single crystals in the two main
crystallographic directions. We show that, in contrast to conventional
superconductors, MgB$_2$ is characterized by two different anisotropy
parameters ($\Gamma_\lambda = \lambda_c/\lambda_{ab}$ and $\Gamma_\xi =
\xi_{ab}/\xi_c$) which strongly differ at low temperature and merge at $T_c $.
These results are in very good agreement with recent calculations in weakly
coupled two bands suprerconductors (Phys. Rev. B, 66, 020509(R) (2002).",0307388v1
2003-07-16,On $c=1$ critical phases in anisotropic spin-1 chains,"Quantum spin-1 chains may develop massless phases in presence of Ising-like
and single-ion anisotropies. We have studied c=1 critical phases by means of
both analytical techniques, including a mapping of the lattice Hamiltonian onto
an O(2) nonlinear sigma model, and a multi-target DMRG algorithm which allows
for accurate calculation of excited states. We find excellent quantitative
agreement with the theoretical predictions and conclude that a pure Gaussian
model, without any orbifold construction, describes correctly the low-energy
physics of these critical phases. This combined analysis indicates that the
multicritical point at large single-ion anisotropy does not belong to the same
universality class as the Takhtajan-Babujian Hamiltonian as claimed in the
past. A link between string-order correlation functions and twisting vertex
operators, along the c=1 line that ends at this point, is also suggested.",0307396v1
2003-07-23,Role of surface disorder on the magnetic properties and hysteresis of nanoparticles,"We present the results of Monte Carlo simulations of a model of a single
maghemite ferrimagnetic nanoparticle including radial surface anisotropy
distinct from that in the core with the aim to clarify what is its role on the
magnetization processes at low temperatures. The low temperature equilibrium
states are analized and compared to those of a ferromagnetic particle with the
same lattice structure. We have found that the formation of hedgehog-like
structures due to increased surface anisotropy is responsible for a change in
the reversal mechanism of the particles.",0307584v1
2003-07-23,Effect of crystalline disorder on magnetic switching in small magnetic cells,"I present a study of the influence of disorder in thin magnetic films on the
switching behavior of small magnetic cells of well defined shape and size. The
disorder considered arises from randomly oriented crystalline grains of
different shape, size, and crystalline orientation which gives rise to locally
fluctuating intrinsic anisotropy directions and strengths. The study comprises
a theoretical investigation of a disordered Stoner Wohlfarth model, as well as
micromagnetic simulations. I show that the fluctuations in the total anisotropy
and therefore in the switching fields are controlled by a single dimensionless
parameter. The theoretical findings are well confirmed by micromagnetic
simulations of many different samples",0307593v1
2003-07-29,Properties of low-lying excited manifolds in the Mn12 acetate,"Most experimental data on the single-molecule magnet Mn$_{12}$ acetate have
been successfully explained by the assumption that the Mn$_{12}$ acetate has an
effective ground-state spin of S=10. However, the effect of the low-lying
excited manifolds caused by interactions between Mn spins has not been well
understood. To investigate the features of the low-lying excited manifolds, the
intramolecular exchange interactions are calculated using density-functional
theory (DFT). With the calculated exchange parameters, the energy gap between
the S=10 ground-state and the first excited-state manifold is calculated by
diagonalization of the Heisenberg Hamiltonian. The upper limit on the energy
gap is about 40.5 K which is likely to be overestimated due to incomplete
treatment of the Coulomb potential within DFT. It is found that there are
several S=9 low-energy excited-state manifolds above the S=10 ground-state
manifold. The magnetic anisotropy barriers for the low-lying spin excitations
are calculated using DFT. Based on the calculations, it is found that the
anisotropy barriers for the low-lying excited manifolds are approximately the
same as that for the ground-state manifold, which is applicable to other
single-molecule magnets such as Mn$_4$.",0307707v1
2003-08-21,Magnetization plateau and quantum phase transitions in a spin-orbital model,"A spin-orbital chain with different Land\'e $g$ factors and one-ion
anisotropy is studied in the context of the thermodynamical Bethe ansatz. It is
found that there exists a magnetization plateau resulting from the different
Land\'e $g$ factors. Detailed phase diagram in the presence of an external
magnetic field is presented both numerically and analytically. For some values
of the anisotropy, the four-component system undergoes five consecutive quantum
phase transitions when the magnetic field varies. We also study the
magnetization in various cases, especially its behaviors in the vicinity of the
critical points. For the SU(4) spin-orbital model, explicit analytical
expressions for the critical fields are derived, with excellent accuracy
compared with numerics.",0308443v1
2003-09-24,Anomalous behavior of spin wave resonances in Ga_{1-x}Mn_{x}As thin films,"We report ferromagnetic and spin wave resonance absorption measurements on
high quality epitaxially grown Ga_{1-x}Mn_{x}As thin films. We find that these
films exhibit robust ferromagnetic long-range order, based on the fact that up
to seven resonances are detected at low temperatures, and the resonance
structure survives to temperatures close to the ferromagnetic transition. On
the other hand, we observe a spin wave dispersion which is linear in mode
number, in qualitative contrast with the quadratic dispersion expected for
homogeneous samples. We perform a detailed numerical analysis of the
experimental data and provide analytical calculations to demonstrate that such
a linear dispersion is incompatible with uniform magnetic parameters. Our
theoretical analysis of the ferromagnetic resonance data, combined with the
knowledge that strain-induced anisotropy is definitely present in these films,
suggests that a spatially dependent magnetic anisotropy is the most likely
reason behind the anomalous behavior observed.",0309566v2
2003-09-25,Three Dimensional Heisenberg Spin Glass Models with and without Random Anisotropy,"We reexamine the spin glass (SG) phase transition of the $\pm J$ Heisenberg
models with and without the random anisotropy $D$ in three dimensions ($d = 3$)
using complementary two methods, i.e., (i) the defect energy method and (ii)
the Monte Carlo method. We reveal that the conventional defect energy method is
not convincing and propose a new method which considers the stiffness of the
lattice itself. Using the method, we show that the stiffness exponent $\theta$
has a positive value ($\theta > 0$) even when $D = 0$. Considering the
stiffness at finite temperatures, we obtain the SG phase transition temperature
of $T_{\rm SG} \sim 0.19J$ for $D = 0$. On the other hand, a large scale MC
simulation shows that, in contrary to the previous results, a scaling plot of
the SG susceptibility $\chi_{\rm SG}$ for $D = 0$ is obtained using almost the
same transiton temperature of $T_{\rm SG} \sim 0.18J$. Hence we believe that
the SG phase transition occurs in the Heisenberg SG model in $d = 3$.",0309573v1
2003-10-07,Precessional switching of thin nanomagnets: analytical study,"We study analytically the precessional switching of the magnetization of a
thin macrospin. We analyze its response when subjected to an external field
along its in-plane hard axis. We derive the exact trajectories of the
magnetization. The switching versus non switching behavior is delimited by a
bifurcation trajectory, for applied fields equal to half of the effective
anisotropy field. A magnetization going through this bifurcation trajectory
passes exactly along the hard axis and exhibits a vanishing characteristic
frequency at that unstable point, which makes the trajectory noise sensitive.
Attempting to approach the related minimal cost in applied field makes the
magnetization final state unpredictable. We add finite damping in the model as
a perturbative, energy dissipation factor. For a large applied field, the
system switches several times back and forth. Several trajectories can be gone
through before the system has dissipated enough energy to converge to one
attracting equilibrium state. For some moderate fields, the system switches
only once by a relaxation dominated precessional switching. We show that the
associated switching field increases linearly with the damping parameter. The
slope scales with the square root of the effective anisotropy. Our simple
concluding expressions are useful to assess the potential application of
precessional switching in magnetic random access memories.",0310147v1
2003-10-08,Soft modes in the easy plane pyrochlore antiferromagnet,"Thermal fluctuations lift the high ground state degeneracy of the classical
nearest neighbour pyrochlore antiferromagnet, with easy plane anisotropy,
giving a first order phase transition to a long range ordered state. We show,
from spin wave analysis and numerical simulation, that even below this
transition a continuous manifold of states, of dimension N^{2/3} exist (N is
the number of degrees of freedom). As the temperature goes to zero a further
`order by disorder' selection is made from this manifold. The pyrochlore
antiferromagnet Er_2Ti_2O_7, is believed to have an easy plane anisotropy and
is reported to have the same magnetic structure. The latter is perhaps
surprising, given that the dipole interaction lifts the degeneracy of the
classical model in favour of a different structure. We interpret our results in
the light of these facts.",0310185v2
2003-10-15,Ultrafast Collective Dynamics in the Charge-Density-Wave Conductor K$_{0.3}$MoO$_{3}$,"Low-energy coherent charge-density wave excitations are investigated in blue
bronze (K$_{0.3}$MoO$_{3}$) and red bronze (K$_{0.33}$MoO$_{3}$) by femtosecond
pump-probe spectroscopy. A linear gapless, acoustic-like dispersion relation is
observed for the transverse phasons with a pronounced anisotropy in
K$_{0.33}$MoO$_{3}$. The amplitude mode exhibits a weak (optic-like) dispersion
relation with a frequency of 1.67 THz at 30 K. Our results show for the first
time that the time-resolved optical technique provides momentum resolution of
collective excitations in strongly correlated electron systems.Low-energy
coherent charge-density wave excitations are investigated in blue bronze
(K$_{0.3}$MoO$_{3}$) and red bronze (K$_{0.33}$MoO$_{3}$) by femtosecond
pump-probe spectroscopy. A linear gapless, acoustic-like dispersion relation is
observed for the transverse phasons with a pronounced anisotropy in
K$_{0.33}$MoO$_{3}$. The amplitude mode exhibits a weak (optic-like) dispersion
relation with a frequency of 1.67 THz at 30 K. Our results show for the first
time that the time-resolved optical technique provides momentum resolution of
collective excitations in strongly correlated electron systems.",0310357v1
2003-10-31,Varying critical percolation exponents on a multifractal support,"We study percolation as a critical phenomenon on a multifractal support. The
scaling exponents of the the infinite cluster size ($\beta$ exponent) and the
fractal dimension of the percolation cluster ($d_f$) are quantities that seem
do not depend on local anisotropies. These two quantities have the same value
as in the standard percolation in regular bidimensional lattices. On the other
side, the scaling of the correlation length ($\nu$ exponent) unfolds new
universality classes due to the local anisotropy of the critical percolation
cluster. We use two critical exponents $\nu$ according to the percolation
criterion for crossing the lattice in either direction or in both directions.
Moreover $\nu$ is related to a parameter that characterizes the stretching of
the blocks forming the tilling of the multifractal.",0310779v1
2003-11-06,Magnetic relaxation in terms of microscopic energy barriers in a model of dipolar interacting nanoparticles,"The magnetic relaxation and hysteresis of a system of single domain particles
with dipolar interactions are studied by Monte Carlo simulations. We model the
system by a chain of Heisenberg classical spins with randomly oriented
easy-axis and log-normal distribution of anisotropy constants interacting
through dipole-dipole interactions. Extending the so-called $T\ln(t/\tau_0)$
method to interacting systems, we show how to relate the simulated relaxation
curves to the effective energy barrier distributions responsible for the
long-time relaxation. We find that the relaxation law changes from
quasi-logarithmic to power-law when increasing the interaction strength. This
fact is shown to be due to the appearence of an increasing number of small
energy barriers caused by the reduction of the anisotropy energy barriers as
the local dipolar fields increase.",0311139v1
2003-11-25,Spin models with random anisotropy and reflection symmetry,"We study the critical behavior of a general class of cubic-symmetric spin
systems in which disorder preserves the reflection symmetry $s_a\to -s_a$,
$s_b\to s_b$ for $b\not= a$. This includes spin models in the presence of
random cubic-symmetric anisotropy with probability distribution vanishing
outside the lattice axes. Using nonperturbative arguments we show the existence
of a stable fixed point corresponding to the random-exchange Ising universality
class. The field-theoretical renormalization-group flow is investigated in the
framework of a fixed-dimension expansion in powers of appropriate quartic
couplings, computing the corresponding $\beta$-functions to five loops. This
analysis shows that the random Ising fixed point is the only stable fixed point
that is accessible from the relevant parameter region. Therefore, if the system
undergoes a continuous transition, it belongs to the random-exchange Ising
universality class. The approach to the asymptotic critical behavior is
controlled by scaling corrections with exponent $\Delta = - \alpha_r$, where
$\alpha_r\simeq -0.05$ is the specific-heat exponent of the random-exchange
Ising model.",0311576v1
2003-12-12,Surface critical behavior of semi-infinite systems with cubic anisotropy at the ordinary transition,"The critical behavior at the ordinary transition in semi-infinite n-component
anisotropic cubic models is investigated by applying the field theoretic
approach in d=3 dimensions up to the two-loop approximation. Numerical
estimates of the resulting two-loop series expansions for the critical
exponents of the ordinary transition are computed by means of Pade resummation
techniques. For $n<n_{c}$ the system belongs to the universality class of the
isotropic n-component model, while for $n>n_{c}$ the cubic fixed point becomes
stable, where $n_{c}<3$ is the marginal spin dimensionality of the cubic model.
The obtained results indicate that the surface critical behavior of the
semi-infinite systems with cubic anisotropy is characterized by a new set of
surface critical exponents for $n>n_{c}$.",0312320v1
2003-12-16,Anisotropic scaling in YBa2Cu3O7 crystals with columnar defects,"We explore the interplay between the mass anisotropy and the uniaxial pinning
of tilted columnar defects (CD) in a YBa2Cu3O7 single crystal. At high
temperatures T and fields H a sharp peak in the irreversible magnetization Mi
at the direction of the tracks signals the presence of the CD. At low T such a
peak is not observed, and the influence of the CD appears only as a
perturbation to the angular dependence due to the anisotropy. We show that at
low T and high H the uniaxial effects due to CD can be recovered by performing
an anisotropic rescaling. As expected, this scaling fails at low H.",0312405v1
2003-12-22,Anisotropic and Heterogeneous Polymerized Membranes,"In these lectures I discuss long-scale properties of fluctuating polymerized
membranes in the presence of network anisotropy and random heterogeneities.
Amazingly, even infinitesimal amount of these seemingly innocuous but
physically important ingredients in the membrane's internal structure leads to
a wealth of striking qualitatively new phenomena. Anisotropy leads to a
``tubule'' phase that is intermediate in its properties and location on the
phase diagram between previously discussed ``crumpled'' and ``flat'' phases. At
low temperature, network heterogeneity generates conformationally glassy
phases, with membrane normals exhibiting glass order analogous to spin-glasses.
The common thread to these distinct membrane phases is that they exhibit
universal anomalous elasticity, (singularly length-scale dependent elastic
moduli, universal Poisson ratio, etc.), driven by thermal fluctuations and/or
disorder and controlled by a nontrivial low-temperature fixed point.",0312567v1
2004-01-26,Strong-coupling theory of magnetic-exciton-mediated superconductivity in UPd$_2$Al$_3$,"There is compelling evidence from inelastic-neutron-scattering and tunneling
experiments that the heavy-fermion superconductor UPd$_2$Al$_3$ can be
understood as a dual system consisting of magnetic excitons, arising from
crystal-field-split U$^{4+}$ levels, coupled to delocalised f-electrons. We
have computed the superconducting transition temperature and the mass
renormalisation arising from a dual model with maximal spin anisotropy using a
strong-coupling approach. We find an instability to two possible
opposite-spin-pairing states with even- or odd-parity gap functions. Each has a
line node perpendicular to the c-direction, in agreement with NMR
relaxation-rate, specific-heat and thermal-conductivity measurements. In
addition, both have total spin component $S_z$=0, compatible with the
observation of a pronounced Knight shift and $H_{c2}$ Pauli limiting. For
parameter values appropriate to UPd$_2$Al$_3$, we determine the dependence of
the superconducting transition temperature $T_c$ on a phenomenological coupling
constant $g$ and we investigate the associated mass enhancement and its
anisotropy.",0401520v1
2004-01-29,Influence of Ising-anisotropy on the zero-temperature phase transition in the square lattice spin-1/2 J-J' model,"We use a variational mean-field like approach, the coupled cluster method
(CCM) and exact diagonalization to investigate the ground-state order-disorder
transition for the square lattice spin-half XXZ model with two different
nearest-neighbor couplings $J$ and $J'$. Increasing $J' > J$ the model shows in
the isotropic Heisenberg limit a second-order transition from semi-classical
N\'eel order to a quantum paramagnetic phase with enhanced local dimer
correlations on the $J'$ bonds at about $J'_{c} \sim 2.5 ... 3 J$. This
transition is driven by the quantum competition between $J'$ and $J$.
Increasing the anisotropy parameter $\Delta> 1$ we diminish the quantum
fluctuations and thus the degree of competition. As a result the transition
point $J'_{c}$ is shifted to larger values. We find indications for a linear
increase of $J'_{c}$ with $\Delta $, i.e. the transition disappears in the
Ising limit $\Delta \to \infty$.",0401604v3
2004-03-01,Anomalous Spin Dephasing in (110) GaAs Quantum Wells: Anisotropy and Intersubband Effects,"A strong anisotropy of electron spin decoherence is observed in GaAs/(AlGa)As
quantum wells grown on (110) oriented substrate. The spin lifetime of spins
perpendicular to the growth direction is about one order of magnitude shorter
compared to spins along (110). The spin lifetimes of both spin orientations
decrease monotonically above a temperature of 80 and 120 K, respectively. The
decrease is very surprising for spins along (110) direction and cannot be
explained by the usual Dyakonov Perel dephasing mechanism. A novel spin
dephasing mechanism is put forward that is based on scattering of electrons
between different quantum well subbands.",0403052v2
2004-03-09,Theory of nonlinear optical properties of phenyl-substituted polyacetylenes,"In this paper we present a theoretical study of the third-order nonlinear
optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the
third-harmonic-generation (THG) process. We study the aforesaid process in
PDPA's using both the independent electron Hueckel model, as well as
correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based
calculations were performed using various configuration interaction (CI)
methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the
quadruples-CI (QCI) methods, and the both longitudinal and the transverse
components of third-order susceptibilities were computed. The Hueckel model
calculations were performed on oligo-PDPA's containing up to fifty repeat
units, while correlated calculations were performed for oligomers containing up
to ten unit cells. At all levels of theory, the material exhibits highly
anisotropic nonlinear optical response, in keeping with its structural
anisotropy. We argue that the aforesaid anisotropy can be divided over two
natural energy scales: (a) the low-energy response is predominantly
longitudinal and is qualitatively similar to that of polyenes, while (b) the
high-energy response is mainly transverse, and is qualitatively similar to that
of trans-stilbene.",0403228v1
2004-03-10,Doublon Growth in Solidification,"We present experiments on the doublon growth morphology in directional
solidification. Samples used are succinonitrile with small amounts of
poly(ethylene oxide), acetone, or camphor as the solute. Doublons, or
symmetry-broken dendrites, are generic diffusion-limited growth structures
expected at large undercooling and low anisotropy. Low anisotropy growth is
achieved by selecting a grain near the $\{111\}$ plane leading to either
seaweed (dense branching morphology) or doublon growth depending on
experimental parameters. We find selection of doublons to be strongly dependent
on solute concentration and sample orientation. Doublons are selected at low
concentrations (low solutal undercooling) in contrast to the prediction of
doublons at large thermal undercooling in pure materials. Doublons also exhibit
preferred growth directions and changing the orientation of a specific
doublonic grain changes the character and stability of the doublons. We observe
transitions between seaweed and doublon growth with changes in concentration
and sample orientation.",0403279v2
2004-03-12,Consequences of spin-orbit coupling for the Bose-Einstein condensation of magnons,"In the first part we discuss how the BEC picture for magnons is modified by
anisotropies induced by spin-orbit coupling. In particular we focus on the
effects of antisymmetric spin interactions and/or a staggered component of the
$g$ (gyromagnetic) tensor. Such terms lead to a gapped quasiparticle spectrum
and a nonzero condensate density for all temperatures so that no phase
transition occurs. We contrast this to the effect of crystal field anisotropies
which are also induced by spin-orbit coupling. In the second part we study the
field-induced magnetic ordering in TlCuCl$_3$ on a quantitative level. We show
that the usual BEC picture does not allow for a good description of the
experimental magnetisation data and argue that antisymmetric spin interactions
and/or a staggered $g$ tensor component are still crucial, although both are
expected to be tiny in this compound due to crystal symmetries. Including this
type of interaction we obtain excellent agreement with experimental data.",0403311v2
2004-03-23,Intrinsic charge transport on the surface of organic semiconductors,"The novel technique based on air-gap transistor stamps enabled realization of
the intrinsic (not dominated by static disorder) transport of the
electric-field-induced charge carriers on the surface of rubrene crystals over
a wide temperature range. The signatures of the intrinsic transport are the
anisotropy of the carrier mobility, mu, and the growth of mu with cooling. The
anisotropy of mu vanishes in the activation regime at lower temperatures, where
the charge transport becomes dominated by shallow traps. The deep traps,
deliberately introduced into the crystal by X-ray radiation, increase the
field-effect threshold without affecting the mobility. These traps filled above
the field-effect threshold do not scatter the mobile polaronic carriers.",0403575v1
2004-04-02,Magnetic susceptibility study of hydrated and non-hydrated NaxCoO2-yH2O single crystals,"We have measured the magnetic susceptibility of single crystal samples of
non-hydrated NaxCoO2 (x ~ 0.75, 0.67, 0.5, and 0.3) and hydrated Na0.3CoO2-yH2O
(y ~ 0, 0.6, 1.3). Our measurements reveal considerable anisotropy between the
susceptibilities with H||c and H||ab. The derived anisotropic g-factor ratio
(g_ab/g_c) decreases significantly as the composition is changed from the
Curie-Weiss metal with x = 0.75 to the paramagnetic metal with x = 0.3. Fully
hydrated Na0.3CoO2-1.3H2O samples have a larger susceptibility than
non-hydrated Na0.3CoO2 samples, as well as a higher degree of anisotropy. In
addition, the fully hydrated compound contains a small additional fraction of
anisotropic localized spins.",0404061v3
2004-04-16,Momentum anisotropy of the scattering rate in cuprate superconductors,"We examine the momentum and energy dependence of the scattering rate of the
high temperature cuprate superconductors using angle resolved photoemission
spectroscopy. The scattering rate is of the form a + b*w. The inelastic
coefficient b is found to be isotropic. The elastic term, a, however, is found
to be highly anisotropic in the pseudogap phase of optimal doped samples, with
an anisotropy which correlates with that of the pseudogap. This can be
contrasted with heavily overdoped samples, which show an isotropic scattering
rate in the normal state.",0404385v1
2004-05-04,Islands in the Stream: Electromigration-Driven Shape Evolution with Crystal Anisotropy,"We consider the shape evolution of two-dimensional islands on a crystal
surface in the regime where mass transport is exclusively along the island
edge. A directed mass current due to surface electromigration causes the island
to migrate in the direction of the force. Stationary shapes in the presence of
an anisotropic edge mobility can be computed analytically when the capillary
effects of the line tension of the island edge are neglected, and conditions
for the existence of non-singular stationary shapes can be formulated. In
particular, we analyse the dependence of the direction of island migration on
the relative orientation of the electric field to the crystal anisotropy, and
we show that no stationary shapes exist when the number of symmetry axes is
odd. The full problem including line tension is solved by time-dependent
numerical integration of the sharp-interface model. In addition to stationary
shapes and shape instability leading to island breakup, we also find a regime
where the shape displays periodic oscillations.",0405068v1
2004-05-17,Internal state of granular assemblies near random close packing,"The structure of random sphere packings in mechanical equilibrium in
prescribed stress states, as studied by molecular dynamics simulations,
strongly depends on the assembling procedure. Frictionless packings in the
limit of low pressure are devoid of dilatancy, and consequently share the same
random close packing density, but exhibit fabric anisotropy related to stress
anisotropy. Efficient compaction methods can be viewed as routes to circumvent
the influence of friction. Simulations designed to resemble two such
procedures, lubrication and vibration (or ``tapping'') show that the resulting
granular structures differ, the less dense one having, remarkably, the larger
coordination number. Density, coordination number and fabric can thus vary
independently. Calculations of elastic moduli and comparisons with experimental
results suggest that measurable elastic properties provide information on those
important internal state variables.",0405358v1
2004-05-20,Influence of non-local exchange on RKKY interactions in III-V diluted magnetic semiconductors,"The RKKY interaction between substitutional Mn local moments in GaAs is both
spin-direction-dependent and spatially anisotropic. In this Letter we address
the strength of these anisotropies using a semi-phenomenological tight-binding
model which treats the hybridization between Mn d-orbitals and As p-orbitals
perturbatively and accounts realistically for the non-local exchange
interaction between their spins. We show that exchange non-locality,
valence-band spin-orbit coupling, and band-structure anisotropy all play a role
in determining the strength of both effects. We use these results to estimate
the degree of ground-state magnetization suppression due to frustrating
interactions between randomly located Mn ions.",0405484v2
2004-05-27,"Influence of gap structures to specific heat in oriented magnetic fields: Application to the orbital dependent superconductor, Sr$_2$RuO$_4$","We discuss influence of modulation of gap function and anisotropy of Fermi
velocity to field angle dependences of upper critical field, $H_{c2}$, and
specific heat, $C$, on the basis of the approximate analytic solution in the
quasiclassical formalism. Using 4-fold modulation of the gap function and the
Fermi velocity in the single-band model, we demonstrate field and temperature
dependence of oscillatory amplitude of $H_{c2}$ and $C$. We apply the method to
the effective two-band model to discuss the gap structure of Sr$_2$RuO$_4$,
focusing on recent field angle-resolved experiments. It is shown that the gap
structures with the intermediate magnitude of minima in $[100]$ direction for
$\gamma$ band, and tiny minima of gaps in $[110]$ directions for $\alpha$ and
$\beta$ bands give consistent behaviors with experiments. The interplay of the
above two gaps also explains the anomalous temperature dependence of in-plane
$H_{c2}$ anisotropy, where the opposite contribution from the passive
$\alpha\beta$ band is pronounced near $T_c$.",0405631v1
2004-06-29,"Aging, rejuvenation and memory phenomena in spin glasses","In this paper, we review several important features of the out-of-equilibrium
dynamics of spin glasses. Starting with the simplest experiments, we discuss
the scaling laws used to describe the isothermal aging observed in spin glasses
after a quench down to the low temperature phase. We report in particular new
results on the sub-aging behaviour of spin glasses. We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, from the point of view of both energy
landscape pictures and of real space pictures. We highlight the fact that both
approaches point out the necessity of hierarchical processes involved in aging.
Finally, we report an investigation of the effect of small temperature
variations on aging in spin glass samples with various anisotropies which
indicates that this hierarchy depends on the spin anisotropy.",0406721v2
2004-07-10,Anisotropy of the paramagnetic susceptibility in LaTiO$_{3}$: The electron-distribution picture in the ground state,"The energy-level scheme and wave functions of the titanium ions in
LaTiO$_{3}$ are calculated using crystal-field theory and spin-orbit coupling.
The theoretically derived temperature dependence and anisotropy of the magnetic
susceptibility agree well with experimental data obtained in an untwinned
single crystal. The refined fitting procedure reveals an almost isotropic
molecular field and a temperature dependence of the van Vleck susceptibility.
The charge distribution of the 3d--electron on the Ti positions and the
principle values of the quadrupole moments are derived and agree with NMR data
and recent measurements of orbital momentum $<l>$ and crystal-field splitting.
The low value of the ordered moment in the antiferromagnetic phase is
discussed.",0407264v1
2004-07-14,Motion of Contact Line of a Crystal Over the Edge of Solid Mask in Epitaxial Lateral Overgrowth,"Mathematical model that allows for direct tracking of the homoepitaxial
crystal growth out of the window etched in the solid, pre-deposited layer on
the substrate is described. The growth is governed by the normal (to the
crystal-vapor interface) flux from the vapor phase and by the interface
diffusion. The model accounts for possibly inhomogeneous energy of the mask
surface and for strong anisotropies of crystal-vapor interfacial energy and
kinetic mobility. Results demonstrate that the motion of the crystal-mask
contact line slows down abruptly as radius of curvature of the mask edge
approaches zero. Numerical procedure is suggested to overcome difficulties
associated with ill-posedness of the evolution problem for the interface with
strong energy anisotropy.
  Keywords: Thin films, epitaxy, MOCVD, surface diffusion, interface dynamics,
contact lines, rough surfaces, wetting, regularization of ill-posed evolution
problems.",0407362v1
2004-07-25,Triaxial Bright Solitons in Bose-Condensed Atomic Vapors,"The properties of triaxial bright solitons (TBSs) made of attractive
Bose-Einstein condensed atoms under transverse anisotropic harmonic confinement
are investigated by using a variational approach. We show that these metastable
TBSs change their shape from cigar-like to disc-like by increasing the
inter-atomic strength. Moreover, we find that the collective oscillations of a
TBS strongly depend on the anisotropy parameter of the external potential. We
calculate in detail the properties of TBS close to the collapse, which sets up
at a critical value of the inter-atomic strength. This critical strength is
maximal in the isotropic (axially symmetric) case and slightly reduces by
increasing the anisotropy. Finally, we investigate the formation of multiple
TBSs via modulational instability induced by a sudden change of the scattering
length from positive to negative.",0407653v1
2004-07-29,Magnetism of One-Dimensional Ni monoatomic chain on Au(110)-(1x2) surface,"Based on Density Functional Theory with no-collinear-magnetism formulations,
we have calculated magnetic anisotropy of supported Ni chains. Our results
indicate that the magnetic anisotropy is closely related to orbital quenching.
The easiest magnetized axis changes from parallel to perpendicular to the Ni
chains once they absorb on the surface. Our results for single absorbed 3d
transition metal atom show that the surface relaxation enhances the orbital
moments of left-end elements (Ti,V) and quenches the orbital moments of
right-end elements (Fe,Co,Ni) on the Au(110)-(1$\times$2) surface. This is
because Ti and V atom raise their position above the trough and Fe, Co, Ni atom
trap more deeply in the trough after the surface relaxation.",0407748v4
2004-07-29,Kondo Effect on Mesoscopic Scale (Review),"Following the discovery of the Kondo effect the bulk transport and magnetic
behavior of the dilute magnetic alloys have been successfully described. In the
last fifteen years new directions have been developed as the study of the
systems of reduced dimensions and the artificial atoms so called quantum dots.
In this review the first subject is reviewed starting with the scanning
tunneling microscope (STM) study of a single magnetic impurity. The next
subject is the reduction of the amplitude of the Kondo effect in samples of
reduced dimension which was explained by the surface magnetic anisotropy which
blocks the motion of the integer spin nearby the surface. The electron
dephasing and energy relaxation experiments are discussed with the possible
explanation including the surface anisotropy, where the situation in cases of
integer and half-integer spins is very different. Finally, the present
situation of the theory of dynamical structural defects is briefly presented
which may lead to two-channel Kondo behavior.",0407766v1
2004-08-12,Scattering of Carriers by Charged Dislocations in Semiconductors,"The scattering of carriers by charged dislocations in semiconductors is
studied within the framework of the linearized Boltzmann transport theory with
an emphasis on examining consequences of the extreme anisotropy of the
scattering potential. A new closed-form approximate expression for the carrier
mobility valid for all temperatures is proposed. The ratios of quantum and
transport scattering times are evaluated after averaging over the anisotropy in
the relaxation time. The value of the Hall scattering factor computed for
charged dislocation scattering indicates that there may be a factor of two
error in the experimental mobility estimates using the Hall data. An expression
for the resistivity tensor when the dislocations are tilted with respect to the
plane of transport is derived. Finally an expression for the isotropic
relaxation time is derived when the dislocations are located within the sample
with a uniform angular distribution.",0408256v2
2004-08-25,Thermal transport of the XXZ chain in a magnetic field,"We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic
fields where magnetothermal effects arise. Due to the integrability of this
model, all transport coefficients diverge, signaled by finite Drude weights.
Using exact diagonalization and mean-field theory, we analyze the temperature
and field dependence of the thermal Drude weight for various exchange
anisotropies under the condition of zero magnetization-current flow. First, we
find a strong magnetic field dependence of the Drude weight, including a
suppression of its magnitude with increasing field strength and a non-monotonic
field-dependence of the peak position. Second, for small exchange anisotropies
and magnetic fields in the massless as well as in the fully polarized regime
the mean-field approach is in excellent agreement with the exact
diagonalization data. Third, at the field-induced quantum critical line between
the para- and ferromagnetic region we propose a universal low-temperature
behavior of the thermal Drude weight.",0408529v2
2004-08-31,Influence of surface anisotropy on the hysteresis of magnetic nanoparticles,"We present the results of Monte Carlo simulations of the magnetic properties
of individual spherical nanoparticles with the aim to explain the role played
by surface anisotropy on their low temperature magnetization processes. Phase
diagrams for the equilibrium configurations have been obtained, showing a
change from quasi-uniform magnetization state to a state with hedgehog-like
structures at the surface as $k_S$ increases. Through the simulated hysteresis
loops and the analysis of spin configurations along them, we have identified a
change in the magnetization reversal mechanism from quasi-uniform rotation at
low $k_S$ values, to a non-uniform switching process at high $k_S$. Results for
the dependence of the coercive field and remanence on $k_S$ and particle size
are also reported.",0408678v1
2004-09-07,Spin Dynamics of Layered Triangular Antiferromagnets with Uniaxial Anisotropy,"The spin dynamics of the semiclassical Heisenberg model with uniaxial
anisotropy, on the layered triangular lattice with antiferromagnetic coupling
for both intralayer nearest neighbor interaction and interlayer interaction is
studied both in the ordered phase and in the paramagnetic phase, using the
Monte Carlo-molecular dynamics technique. The important quantities calculated
are the full dynamic structure function $S(\bf q, \omega)$, the chiral dynamic
structure function $S_{chi}(\omega)$, the static order parameter and some
thermodynamic quantities. Our results show the existence of propagating modes
corresponding to both $S(\bf q, \omega)$ and $S_{chi}(\omega)$ in the ordered
phase, supporting the recent conjectures. Our results for the static properties
show the magnetic ordering in each layer to be of coplanar 3-sublattice type
deviating from 120 degree structure. In the presence of magnetic trimerization
however, we find the 3-sublattice structure to be weakened alongwith the
tendency towards non-coplanarity of the spins.",0409151v1
2004-09-08,Electronic structure and magnetic anisotropy for nickel-based molecular magnets,"Recent magnetic measurements on tetra-nickel molecular magnets
[Ni(hmp)(ROH)Cl]$_4$, where R=CH$_3$, CH$_2$CH$_3$, or
(CH$_2$)$_2$C(CH$_3$)$_3$ and hmp$^-$ is the monoanion of
2-hydroxymethylpyridine, revealed a strong exchange bias prior to the external
magnetic field reversal as well as anomalies in electron paramagnetic resonance
peaks at low temperatures. To understand the exchange bias and observed
anomalies, we calculate the electronic structure and magnetic properties for
the Ni$_4$ molecules with the three different ligands, employing
density-functional theory. Considering the optimized structure with possible
collinear spin configurations, we determine a total spin of the lowest-energy
state to be S=0, which does not agree with experiment. We also calculate
magnetic anisotropy barriers for all three types of Ni$_4$ molecules to be in
the range of 4-6 K.",0409207v1
2004-09-13,Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds,"The ground state and thermodynamic properties of spin-1 and spin-3/2 chains
are investigated via exactly solved su(3) and su(4) models with physically
motivated chemical potential terms. The analysis involves the Thermodynamic
Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1
chain with large single-ion anisotropy, a gapped phase occurs which is
significantly different from the valence-bond-solid Haldane phase. The
theoretical curves for the magnetization, susceptibility and specific heat are
favourably compared with experimental data for a number of spin-1 chain
compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at
zero external magnetic field. A middle magnetization plateau can be triggered
by the single-ion anisotropy term. Overall, our results lend further weight to
the applicability of integrable models to the physics of low-dimensional
quantum spin systems. They also highlight the utility of the exact HTE method.",0409311v1
2004-09-16,Electronic state around vortex in a two-band superconductor,"Based on the quasiclassical theory, we investigate the vortex state in a
two-band superconductor with a small gap on a three dimensional Fermi surface
and a large gap on a quasi-two dimensional one, as in MgB_2. The field
dependence of zero-energy density of states is compared for fields parallel and
perpendicular to the ab plane, and the anisotropy of the vortex core shape is
discussed for a parallel field. The Fermi surface geometry of two-bands,
combining the effect of the normal-like electronic state on the small gap band
at high fields, produces characteristic behavior in the anisotropy of c- and
ab-directions.",0409413v1
2004-09-22,"Theory of anisotropic s-wave superconductivity with point-node like gap minima: analysis of (Y,Lu)Ni_2B_2C","Recent intensive experimental studies revealed that (Y,Lu)Ni$_2$B$_2$C is an
anisotropic s-wave superconductor. In addition, its gap function possesses deep
point minima, whose ratio of the gap anisotropy is more than 10. On the
theoretical side, however, it is nontrivial to understand the origin of such a
peculiar superconductivity. In the present paper, we propose a mechanism of the
s-wave superconductivity with deep gap minima, based on the theoretical model
where strong electron-phonon coupling as well as the moderate magnetic
fluctuations coexist. By analyzing the strong coupling Eliashberg equation, we
find that s-wave superconducting gap function owing to the electron-phonon
coupling becomes highly anisotropic as the magnetic fluctuations increases. The
set of model parameters for realizing the strong gap anisotropy in the present
model will be appropriate for (Y,Lu)Ni$_2$B$_2$C. According to the present
mechanism, (groups of) pair of gap minima appear at points on the Fermi surface
which are connected by the nesting vector ${\bf Q}$, in both cases of s-wave
superconductors and non s-wave ones. We briefly discuss other superconductors
with highly anisotropic gap function, e.g., PrOs$_{4}$Sb$_{12}$ and
Na$_{0.33}$CoO$_2$.",0409564v1
2004-10-21,"Temperature Dependent Magnetic Anisotropy in (Ga,Mn)As Layers","It is demonstrated by SQUID measurements that (Ga,Mn)As films can exhibit
perpendicular easy axis at low temperatures, even under compressive strain,
provided that the hole concentration is sufficiently low. In such films, the
easy axis assumes a standard in-plane orientation when the temperature is
raised towards the Curie temperature or the hole concentration is increased by
low temperature annealing. These findings are shown to corroborate
quantitatively the predictions of the mean-field Zener model for ferromagnetic
semiconductors. The in-plane anisotropy is also examined, and possible
mechanisms accounting for its character and magnitude are discussed.",0410549v1
2004-10-26,Momentum anisotropy of the scattering rate in cuprate superconductors,"We examine the momentum and energy dependence of the scattering rate of the
high temperature cuprate superconductors using angle resolved photoemission
spectroscopy. The scattering rate is of the form a + bw around the Fermi
surface for under and optimal doping. The inelastic coefficient ""b"" is found to
be isotropic. The elastic term, ""a"", however, is found to be highly anisotropic
for under and optimally doped samples, with an anisotropy which correlates with
that of the pseudogap. This is contrasted with heavily overdoped samples, which
show an isotropic scattering rate and an absence of the pseudogap above T_c. We
find this to be a generic property for both single and double layer compounds.",0410680v1
2004-12-09,Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy,"While magnetoresistance (MR) has generally been found to be symmetric in
applied field in non-magnetic or magnetic metals, we have observed
antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and
transport measurements show that the antisymmetric MR is due to the appearance
of domain walls that run perpendicular to both the magnetization and the
current, a geometry existing only in materials with perpendicular magnetic
anisotropy. As a result, the extraordinary Hall effect (EHE) gives rise to
circulating currents in the vicinity of the domain walls that contributes to
the MR. The antisymmetric MR and EHE have been quantitatively accounted for by
a theoretical model.",0412248v1
2004-12-17,Theoretical studies of the phase transition in the anisotropic 2-D square spin lattice,"The phase transition occurring in a square 2-D spin lattice governed by an
anisotropic Heisenberg Hamiltonian has been studied according to two recently
proposed methods. The first one, the Dressed Cluster Method, provides excellent
evaluations of the cohesive energy, the discontinuity of its derivative around
the critical (isotropic) value of the anisotropy parameter confirms the
first-order character of the phase transition. Nevertheless the method
introduces two distinct reference functions (either N\'eel or XY) which may in
principle force the discontinuity. The Real Space Renormalization Group with
Effective Interactions does not reach the same numerical accuracy but it does
not introduce a reference function and the phase transition appears
qualitatively as due to the existence of two domains, with specific fixed
points. The method confirms the dependence of the spin gap on the anisotropy
parameter occurring in the Heisenberg-Ising domain.",0412464v1
2005-01-05,Magnetic susceptibility of a CuO2 plane in the La2CuO4 system: I. RPA treatment of the Dzyaloshinskii-Moriya Interactions,"Motivated by recent experiments on undoped La2CuO4, which found pronounced
temperature-dependent anisotropies in the low-field magnetic susceptibility, we
have investigated a two-dimensional square lattice of S=1/2 spins that interact
via Heisenberg exchange plus the symmetric and anti-symmetric
Dzyaloshinskii-Moriya anisotropies. We describe the transition to a state with
long-ranged order, and find the spin-wave excitations, with a mean-field
theory, linear spin-wave analysis, and using Tyablikov's RPA decoupling scheme.
We find the different components of the susceptibility within all of these
approximations, both below and above the N'eel temperature, and obtain evidence
of strong quantum fluctuations and spin-wave interactions in a broad
temperature region near the transition.",0501086v1
2005-01-06,Ground State Properties of one-dimensional Antiferromagnetic Spin-1 Chain with Single-ion Anisotropy,"In this study, we have investigated ground state properties of
one-dimensional antiferromagnetic spin-1 chain with single-ion anisotropy at
very low temperatures using the Transfer Matrix method. Magnetic plateaus,
phase diagram, specific heat, susceptibility of the spin chain have been
evaluated numerically from the free energy. Results are in good agreement with
the experimental data for the spin-1 compounds
[Ni$_2$(Medpt)$_2$($\mu$-ox)(H$_2$O)$_2$](ClO$_4$)$_2$2H$_2$O,
[Ni$_{2}$(Medpt)$_{2}$($\mu$-ox)($\mu$-N$_{3}$)](ClO$_{4}$)0.5H$_{2}$O,
Ni(C$_2$H$_8$N$_2$)Ni(CN)$_4$ and Ni(C$_{10}$H$_8$N$_2$)$_2$Ni(CN)$_4$.H$_2$O.
However, spin-Peierls transition have not been observed in the temperature
dependence of specific heat and magnetic susceptibility.",0501111v2
2005-01-18,Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2,"We report measurements of the temperature dependent anisotropies
($\gamma_\lambda$ and $\gamma_\xi$) of both the London penetration depth
$\lambda$ and the upper critical field of MgB$_2$. Data for
$\gamma_\lambda=\lambda_c/\lambda_a$ was obtained from measurements of
$\lambda_{a}$ and $\lambda_c$ on a single crystal sample using a tunnel diode
oscillator technique. $\gamma_\xi=H_{c2}^{\parallel c}/H_{c2}^{\bot c}$ was
deduced from field dependent specific heat measurements on the same sample.
$\gamma_\lambda$ and $\gamma_\xi$ have opposite temperature dependencies, but
close to $T_c$ tend to a common value ($\gamma_\lambda\simeq
\gamma_\xi=1.75\pm0.05$). These results are in good agreement with theories
accounting for the two gap nature of MgB$_2$",0501415v2
2005-01-24,Metamagnetic phase transition of the antiferromagnetic Heisenberg icosahedron,"The observation of hysteresis effects in single molecule magnets like
Mn$_{12}$-acetate has initiated ideas of future applications in storage
technology. The appearance of a hysteresis loop in such compounds is an outcome
of their magnetic anisotropy. In this Letter we report that magnetic hysteresis
occurs in a spin system without any anisotropy, specifically, where spins
mounted on the vertices of an icosahedron are coupled by antiferromagnetic
isotropic nearest-neighbor Heisenberg interaction giving rise to geometric
frustration. At T=0 this system undergoes a first order metamagnetic phase
transition at a critical field $\Bcrit$ between two distinct families of ground
state configurations. The metastable phase of the system is characterized by a
temperature and field dependent survival probability distribution.",0501558v1
2005-02-24,Magnetic susceptibility anisotropies in a two-dimensional quantum Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions,"The magnetic and thermodynamic properties of the two-dimensional quantum
Heisenberg antiferromagnet that incorporates both a Dzyaloshinskii-Moriya and
pseudo-dipolar interactions are studied within the framework of a generalized
nonlinear sigma model (NLSM). We calculate the static uniform susceptibility
and sublattice magnetization as a function of temperature and we show that: i)
the magnetic-response is anisotropic and differs qualitatively from the
expected behavior of a conventional easy-axis QHAF; ii) the Neel second-order
phase transition becomes a crossover, for a magnetic field B perpendicular to
the CuO(2) layers. We provide a simple and clear explanation for all the
recently reported unusual magnetic anisotropies in the low-field susceptibility
of La(2)CuO(4), L. N. Lavrov et al., Phys. Rev. Lett. 87, 017007 (2001), and we
demonstrate explicitly why La(2)CuO(4) can not be classified as an ordinary
easy-axis antiferromagnet.",0502588v3
2005-03-01,Berry phase of magnons in textured ferromagnets,"We study the energy spectrum of magnons in a ferromagnet with topologically
nontrivial magnetization profile. In the case of inhomogeneous magnetization
corresponding to a metastable state of ferromagnet, the spin-wave equation of
motion acquires a gauge potential leading to a Berry phase for the magnons
propagating along a closed contour. The effect of magnetic anisotropy is
crucial for the Berry phase: we show that the anisotropy suppresses its
magnitude, which makes the Berry phase observable in some cases, similar to the
Aharonov-Bohm effect for electrons. For example, it can be observed in the
interference of spin waves propagating in mesoscopic rings. We discuss the
effect of domain walls on the interference in ferromagnetic rings, and propose
some experiments with a certain geometry of magnetization. We also show that
the nonvanishing average topological field acts on the magnons like a uniform
magnetic field on electrons. It leads to the quantization of the magnon
spectrum in the topological field.",0503013v1
2005-03-07,Experimental compaction of anisotropic granular media,"We report on experiments to measure the temporal and spatial evolution of
packing arrangements of anisotropic and weakly confined granular material,
using high-resolution $\gamma$-ray adsorption. In these experiments, the
particle configurations start from an initially disordered,
low-packing-fraction state and under vertical solicitations evolve to a dense
state. We find that the packing fraction evolution is slowed by the grain
anisotropy but, as for spherically shaped grains, can be well fitted by a
stretched exponential. For a given type of grains, the characteristic times of
relaxation and of convection are found to be of the same order of magnitude. On
the contrary compaction mechanisms in the media strongly depend on the grain
anisotropy.",0503151v1
2005-04-01,"Magnetoresistance Anomalies in (Ga,Mn)As Epilayers with Perpendicular Magnetic Anisotropy","We report the observation of anomalies in the longitudinal magnetoresistance
of tensile-strained (Ga,Mn)As epilayers with perpendicular magnetic anisotropy.
Magnetoresistance measurements carried out in the planar geometry (magnetic
field parallel to the current density) reveal ""spikes"" that are antisymmetric
with respect to the direction of the magnetic field. These anomalies always
occur during magnetization reversal, as indicated by a simultaneous change in
sign of the anomalous Hall effect. The data suggest that the antisymmetric
anomalies originate in anomalous Hall effect contributions to the longitudinal
resistance when domain walls are located between the voltage probes. This
interpretation is reinforced by carrying out angular sweeps of $\vec{H}$,
revealing an antisymmetric dependence on the helicity of the field sweep.",0504038v1
2005-04-18,Epitaxial self-organization: from surfaces to magnetic materials,"Self-organization of magnetic materials is an emerging and active field. An
overview of the use of self-organization for magnetic purposes is given, with a
view to illustrate aspects that cannot be covered by lithography. A first set
of issues concerns the quantitative study of low-dimensional magnetic phenomena
(1D and 0D). Such effects also occur in microstructured and
lithographically-patterned materials but cannot be studied in these because of
the complexity of such materials. This includes magnetic ordering, magnetic
anisotropy and superparamagnetism. A second set of issues concerns the
possibility to directly use self-organization in devices. Two sets of examples
are given: first, how superparamagnetism can be fought by fabricating thick
self-organized structures, and second, what new or improved functionalities can
be expected from self-organized magnetic systems, like the tailoring of
magnetic anisotropy or controlled dispersion of properties.",0504424v1
2005-05-12,Magnetic relaxation measurements of exchange biased (Pt/Co) multilayers with perpendicular anisotropy,"Magnetic relaxation measurements were carried out by magneto-optical Kerr
effect on exchange biased (Pt/Co)5/Pt/FeMn multilayers with perpendicular
anisotropy. In these films the coercivity and the exchange bias field vary with
Pt spacer thickness, and have a maximum for 0.2 nm. Hysteresis loops do not
reveal important differences between the reversal for ascending and descending
fields. Relaxation measurements were fitted using Fatuzzo's model, which
assumes that reversal occurs by domain nucleation and domain wall propagation.
For 2 nm thick Pt spacer (no exchange bias) the reversal is dominated by domain
wall propagation starting from a few nucleation centers. For 0.2 nm Pt spacer
(maximum exchange bias) the reversal is strongly dominated by nucleation, and
no differences between the behaviour of the ascending and descending branches
can be observed. For 0.4 nm Pt spacer (weaker exchange bias) the nucleation
density becomes less important, and the measurements reveal a much stronger
density of nucleation centers in the descending branch.",0505312v1
2005-05-26,Magnetic behavior of a spin-1 dimer: model system for homodinuclear nickel (II) complexes,"Magnetic behavior of a spin-1 Heisenberg dimer is analysed in dependence on
both uniaxial single-ion anisotropy and XXZ exchange anisotropy in a zero- as
well as non-zero longitudinal magnetic field. A complete set of eigenfunctions
and eigenvalues of the total Hamiltonian is presented together with an exact
analytical expression for the Gibbs free energy, longitudinal magnetization,
longitudinal and transverse susceptibility. The obtained theoretical results
are compared with the relevant experimental data of
[Ni2(Medpt)2(ox)(H2O)2](ClO4)2.2H2O (Medpt = methyl-bis(3-aminopropyl)amine).",0505636v2
2005-05-30,Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles,"We have studied the magnetic behavior of dextran-coated magnetite
(Fe$_3$O$_4$) nanoparticles with median particle size $\left<d\right>=8$ $nm$.
Magnetization curves and in-field M\""ossbauer spectroscopy measurements showed
that the magnetic moment $M_S$ of the particles was much smaller than the bulk
material. However, we found no evidence of magnetic irreversibility or
non-saturating behavior at high fields, usually associated to spin canting. The
values of magnetic anisotropy $K_{eff}$ from different techniques indicate that
surface or shape contributions are negligible. It is proposed that these
particles have bulk-like ferrimagnetic structure with ordered A and B
sublattices, but nearly compensated magnetic moments. The dependence of the
blocking temperature with frequency and applied fields, $T_B(H,\omega)$,
suggests that the observed non-monotonic behavior is governed by the strength
of interparticle interactions.",0505682v5
2005-06-20,Effects of trap anisotropy on impurity scattering regime in a Fermi gas,"We evaluate the low-lying oscillation modes and the ballistic expansion
properties of a harmonically trapped gas of fermionic K40 atoms containing
thermal Rb87 impurities as functions of the anisotropy of the trap. Numerical
results are obtained by solving the Vlasov-Landau equations for the one-body
phase-space distribution functions and are used to test simple scaling
Ansatzes. Starting from the gas in a weak impurity-scattering regime inside a
spherical trap, the time scales associated to motions in the axial and
azimuthal directions enter into competition as the trap is deformed to an
elongated cigar-like shape. This competition gives rise to coexistence of
collisionless and hydrodynamic behaviors in the low-lying surface modes of the
gas as well as to a dependence of the aspect ratio of the expanding cloud on
the collision time.",0506496v1
2005-07-26,55Mn NMR and magnetization studies of La0.67Sr0.33MnO3 thin films,"55Mn nuclear magnetic resonance and magnetization studies of the series of
La0.67Sr0.33MnO3 thin films have been performed at low temperature. Two
distinct lines were observed, at 322 MHz and 380 MHz, corresponding to two
different phases, the former located at the interface, with localized charges,
and the latter corresponding to the film bulk, with itinerant carriers (as it
was also found in Ca manganite films). The spin-echo amplitude was measured as
a function of a dc magnetic field applied either in the film plane or
perpendicular to it. The field dependence of both the main NMR signal intensity
and frequency shift is quite consistent with that calculated in a simple single
domain model. The best fit to the model shows that magnetization rotation
processes play a dominant role when the applied field exceeds the effective
anisotropy field. Distinctly different magnetic anisotropies are deduced from
the interface NMR signal.",0507598v1
2005-08-09,Disordered and ordered states of exactly solvable Ising-Heisenberg planar models with a spatial anisotropy,"Ground-state and finite-temperature properties of a special class of exactly
solvable Ising-Heisenberg planar models are examined using the generalized
decoration-iteration and star-triangle mapping transformations. The
investigated spin systems exhibit an interesting quantum behaviour manifested
in a remarkable geometric spin frustration, which appears notwithstanding the
purely ferromagnetic interactions of the considered model systems. This kind of
spin frustration originates from an easy-plane anisotropy in the XXZ Heisenberg
interaction between nearest-neighbouring spins that favours ferromagnetic
ordering of their transverse components, whereas their longitudinal components
are aligned antiferomagnetically.",0508224v2
2005-08-11,Magnetization self-organization in a single-domain ferromagnet subject to a spin current,"The Landau-Lifshitz equation for the magnetization dynamics of a
single-domain magnetic system is solved using the methods of self-organization.
The description takes into account the torque due to spin transfer. The
potential energy of the system includes the uniaxial and easy-plane
anisotropies, and the Zeeman energy due to an external magnetic field. The
equilibrium and stationary states are investigated as a function of the spin
current and external magnetic field. The presented bifurcation diagram allows
to determine the margins of a neutral stability mode of the equilibrium and
stationary states for different values of the easy-plane anisotropy constant.
Using the power spectral density method, the trajectory tracing, Hausdorff
dimension, and maximum Lyapunov exponent, the dynamics of the phase states in
an external magnetic field is demonstrated. The analytical transcendent
equations for switching between different equilibrium states are also obtained,
proving the importance of phase averaging.",0508280v1
2005-09-06,Conduction anisotropy and Hall effect in the organic conductor (TMTTF)2AsF6: evidence for Luttinger liquid and charge ordering,"We present the high-temperature (70 K < T < 300 K) resistivity anisotropy and
Hall effect measurements of the quasi-one-dimensional (1D) organic conductor
(TMTTF)2AsF6. The temperature variations of the resistivity are pronouncedly
different for the three different directions, with metallic-like at high
temperatures for the a-axis only. Above 220 K the Hall coefficient R_H is
constant, positive and strongly enhanced over the expected value; and the
corresponding carrier concentration is almost 100 times lower than calculated
for one hole/unit cell. Our results give evidence for the existence of a
high-temperature regime above 200 K where the 1D Luttinger liquid features
appear in the transport properties. Our measurements also give strong evidence
of charge ordering in (TMTTF)2AsF6. At the charge-ordering transition T_{CO}
\approx 100 K, R_H(T) abruptly changes its behavior, switches sign and rapidly
increases with further temperature decrease.",0509147v1
2005-09-15,Asymmetric magnetization reversal in the exchange bias system Fe/FeF_2 studied by MOKE,"The asymmetry of the magnetization reversal process in exchange biased
Fe/FeF$_2$ has been studied by magneto-optical Kerr effect. Qualitatively
different transverse magnetization loops are observed for different directions
of the cooling and the measuring field. These loops can be simulated by a
simple calculation of the total energy density which includes the relevant
magnetic anisotropies and coherent magnetization rotation only. Asymmetric
magnetization reversal is shown to originate from the unidirectional anisotropy
and may be observed if the external measuring field is not collinear with
either the exchange bias or the easy axis of the antiferromagnetic epitaxial
FeF$_2$(110) layer.",0509419v2
2005-09-19,Observation of field-dependent magnetic parameters in the magnetic molecule {Ni4Mo12},"We investigate the bulk magnetic, electron paramagnetic resonance, and
magneto-optical properties of {Ni4Mo12}, a magnetic molecule with
antiferromagnetically coupled tetrahedral {Ni4Mo12} in a diamagnetic molybdenum
matrix. The low-temperature magnetization exhibits steps at irregular field
intervals, a result that cannot be explained using a Heisenberg model even if
it is augmented by magnetic anisotropy and biquadratic terms. Allowing the
exchange and anisotropy parameters to depend on the magnetic field provides the
best fit to our data, suggesting that the molecular structure (and thus the
interactions between spins) may be changing with applied magnetic field.",0509476v2
2005-09-21,Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy,"We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer
system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer.
The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room
temperature which increases to 14.7% at 4.2K. The layers show clear separate
switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in
the NiMnSb layer leads to different switching characteristics depending on the
direction in which the magnetic field is applied, an effect which can be used
for sensor applications.",0509538v1
2005-09-29,"Modification of intergrain connectivity, upper critical field anisotropy, and critical current density in ion irradiated MgB2 films","We study the effect of 100 MeV Silicon and 200 MeV Gold ion irradiation on
the inter and intra grain properties of superconducting thin films of Magnesium
Diboride. Substantial decrease in inter-grain connectivity is observed,
depending on irradiation dose and type of ions used. We establish that
modification of sigma band scattering mechanism, and consequently the upper
critical field and anisotropy, depends on the size and directional properties
of the extrinsic defects. Post heavy ion irradiation, the upper critical field
shows enhancement at a defect density that is five orders of magnitude less
compared to neutron irradiation. The critical current density however is best
improved through light ion irradiation.",0509755v1
2005-10-13,Random field spin models beyond one loop: a mechanism for decreasing the lower critical dimension,"The functional RG for the random field and random anisotropy O(N)
sigma-models is studied to two loop. The ferromagnetic/disordered (F/D)
transition fixed point is found to next order in d=4+epsilon for N > N_c
(N_c=2.8347408 for random field, N_c=9.44121 for random anisotropy). For N <
N_c the lower critical dimension plunges below d=4: we find two fixed points,
one describing the quasi-ordered phase, the other is novel and describes the
F/D transition. The lower critical dimension can be obtained in an
(N_c-N)-expansion. The theory is also analyzed at large N and a glassy regime
is found.",0510344v3
2005-10-16,Spiral Spin Order and Transport Anisotropy in Underdoped Cuprates,"We discuss the spiral spin density wave model and its application to explain
properties of underdoped La$_{2-x}$Sr$_x$CuO$_4$. We argue that the spiral
picture is theoretically well justified in the context of the extended $t-J$
model, and then show that it can explain a number of observed features, such as
the location and symmetry of the incommensurate peaks in elastic neutron
scattering, as well as the in-plane resistivity anisotropy. A consistent
description of the low doping region (below 10% or so) emerges from the spiral
formulation, in which the holes show no tendency towards any type of charge
order and the physics is purely spin driven.",0510416v1
2005-10-24,Reduction of threshold current density for current-driven domain wall motion by shape control,"We investigated the aspect ratio (thickness/width) dependence of the
threshold current density required for the current-driven domain wall (DW)
motion for the Ni81Fe19 nanowires. It has been shown theoretically that the
threshold current density is proportional to the product of the hard-axis
magnetic anisotropy Kperp and the DW width lamda. (Phys. Rev. Lett. 92, 086601
(2004).) We show experimentally that Kperp can be controlled by the magnetic
shape anisotropy in the case of the Ni81Fe19 nanowires, and that the threshold
current density increases with an increase of Kperp*l. We succeeded to reduce
the threshold current density by half by the shape control.",0510619v2
2005-10-31,Generalized Mittag-Leffler functions in the theory of finite-size scaling for systems with strong anisotropy and/or long-range interaction,"The difficulties arising in the investigation of finite-size scaling in
$d$--dimensional O(n) systems with strong anisotropy and/or long-range
interaction, decaying with the interparticle distance $r$ as $r^{-d-\sigma}$
($0<\sigma\leq2$), are discussed. Some integral representations aiming at the
simplification of the investigations are presented for the classical and
quantum lattice sums that take place in the theory. Special attention is paid
to a more general form allowing to treat both cases on an equal footing and in
addition cases with strong anisotropic interactions and different geometries.
The analysis is simplified further by expressing this general form in terms of
a generalization of the Mittag-Leffler special functions. This turned out to be
very useful for the extraction of asymptotic finite-size behaviours of the
thermodynamic functions.",0510834v2
2005-11-11,"The open XXZ-chain: Bosonisation, Bethe ansatz and logarithmic corrections","We calculate the bulk and boundary parts of the free energy for an open
spin-1/2 XXZ-chain in the critical regime by bosonisation. We identify the
cutoff independent contributions and determine their amplitudes by comparing
with Bethe ansatz calculations at zero temperature T. For the bulk part of the
free energy we find agreement with Lukyanov's result [Nucl.Phys.B 522, 533
(1998)]. In the boundary part we obtain a cutoff independent term which is
linear in T and determines the temperature dependence of the boundary
susceptibility in the attractive regime for $T\ll 1$. We further show that at
particular anisotropies where contributions from irrelevant operators with
different scaling dimensions cross, logarithmic corrections appear. We give
explicit formulas for these terms at those anisotropies where they are most
important. We verify our results by comparing with extensive numerical
calculations based on a numerical solution of the T=0 Bethe ansatz equations,
the finite temperature Bethe ansatz equations in the quantum-transfer matrix
formalism, and the density-matrix renormalisation group applied to transfer
matrices.",0511272v1
2005-11-11,"Spin amplification, reading, and writing in transport through anisotropic magnetic molecules","Inelastic transport through a single magnetic molecule weakly coupled to
metallic leads is studied theoretically. We consider dynamical processes that
are relevant for writing, storing, and reading spin information in molecular
memory devices. Magnetic anisotropy is found to be crucial for slow spin
relaxation. In the presence of anisotropy we find giant spin amplification: The
spin accumulated in the leads if a bias voltage is applied to a molecule
prepared in a spin-polarized state can be made exponentially large in a
characteristic energy divided by temperature. For one ferromagnetic and one
paramagnetic lead the molecular spin can be reversed by applying a bias voltage
even in the absence of a magnetic field. We propose schemes for reading and
writing spin information based on our findings.",0511291v2
2005-11-15,Magnetism in reduced dimensions,"We propose a short overview of a few selected issues of magnetism in reduced
dimensions, which are the most relevant to set the background for more
specialized contributions to the present Special Issue. Magnetic anisotropy in
reduced dimensions is discussed, on a theoretical basis, then with experimental
reports and views from surface to single-atom anisotropy. Then conventional
magnetization states are reviewed, including macrospins, single domains,
multidomains, and domain walls in stripes. Dipolar coupling is examined for
lateral interactions in arrays, and for interlayer interactions in films and
dots. Finally thermally-assisted magnetization reversal and superparamagnetism
are presented. For each topic we sought a balance between well established
knowledge and recent developments.",0511362v1
2005-11-15,Measuring the Penetration Depth Anisotropy in MgB$_2$ using Small-Angle Neutron Scattering,"Using small-angle neutron scattering we have measured the misalignment
between an applied field of 4 kOe and the flux-line lattice in MgB$_2$, as the
field is rotated away from the c axis by an angle $\theta$. The measurements,
performed at 4.9 K, showed the vortices canting towards the c axis for all
field orientations. Using a two-band/two-gap model to calculate the
magnetization we are able to fit our results yielding a penetration depth
anisotropy, $\glam = 1.1 \pm 0.1$.",0511376v3
2005-12-22,Entanglement Entropy dynamics in Heisenberg chains,"By means of the time-dependent density matrix renormalization group algorithm
we study the zero-temperature dynamics of the Von Neumann entropy of a block of
spins in a Heisenberg chain after a sudden quench in the anisotropy parameter.
In the absence of any disorder the block entropy increases linearly with time
and then saturates. We analyze the velocity of propagation of the entanglement
as a function of the initial and final anisotropies and compare, wherever
possible, our results with those obtained by means of Conformal Field Theory.
In the disordered case we find a slower (logarithmic) evolution which may
signals the onset of entanglement localization.",0512586v2
2006-01-04,Pressure-Induced Zero-Gap Semiconducting State in Organic Conductor $α$-(BEDT-TTF)$_2$I$_3$ Salt,"We show a zero-gap semiconducting (ZGS) state in the quasi-two-dimensional
organic conductor $\alpha$-(BEDT-TTF)$_2$I$_3$ salt, which emerges under
uniaxial pressure along the a-axis (the stacking axis of the BEDT-TTF
molecule). The ZGS state is the state in which a Dirac cone with the band
spectrum of a linear dispersion exists around the Fermi point connecting an
unoccupied (electron) band with an occupied (hole) band. The spectrum exhibits
a large anisotropy in velocity, which depends on the direction from the Fermi
point. By varying the magnitude of several transfer energies of a tight-binding
model with four sites per unit cell, it is shown that the ZGS state exists in a
wide pressure range, and is attributable to the large anisotropy of the
transfer energies along the stacking axis.",0601068v3
2006-01-10,Linear polarization of the photoluminescence of quantum wells,"The degree and orientation of the magnetic-field induced linear polarization
of the photoluminescence from a wide range of heterostructures containing
(Cd,Mn)Te quantum wells between (Cd,Mn,Mg)Te barriers has been studied as a
function of detection photon energy, applied magnetic field strength and
orientation in the quantum well plane. A theoretical description of this effect
in terms of an in-plane deformation acting on the valence band states is
presented and is verified by comparison with the experimental data. We
attempted to identify clues to the microscopic origin of the valence band spin
anisotropy and to the mechanisms which actually determine the linear
polarization of the PL in the quantum wells subject to the in-plane magnetic
field. The conclusions of the present paper apply in full measure to
non-magnetic QWs as well as ensembles of disk-like QDs with shape and/or strain
anisotropy.",0601204v1
2006-01-12,Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells,"Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs
quantum wells are measured by means of Hanle effect. Three different spin
relaxation times for spins oriented along [110], [1-10] and [001]
crystallographic directions are extracted demonstrating anisotropy of
D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba
and Dresselhaus terms describing the spin-orbit coupling in semiconductor
quantum well structures. It is shown that the Rashba spin-orbit splitting is
about four times stronger than the Dresselhaus splitting in the studied
structure.",0601252v1
2006-01-18,Magnetic domain structure and dynamics in interacting ferromagnetic stacks with perpendicular anisotropy,"The time and field dependence of the magnetic domain structure at
magnetization reversal were investigated by Kerr microscopy in interacting
ferromagnetic Co/Pt multilayers with perpendicular anisotropy. Large local
inhomogeneous magnetostatic fields favor mirroring domain structures and domain
decoration by rings of opposite magnetization. The long range nature of these
magnetostatic interactions gives rise to ultra-slow dynamics even in zero
applied field, i.e. it affects the long time domain stability. Due to this
additionnal interaction field, the magnetization reversal under short magnetic
field pulses differs markedly from the well-known slow dynamic behavior.
Namely, in high field, the magnetization of the coupled harder layer has been
observed to reverse more rapidly by domain wall motion than the softer layer
alone.",0601401v1
2006-01-26,The high temperature expansion of the classical $XYZ$ chain,"We present the $\beta$-expansion of the Helmholtz free energy of the
classical $XYZ$ model, with a single-ion anisotropy term and in the presence of
an external magnetic field, up to order $\beta^{12}$. We compare our results to
the numerical solution of Joyce's [Phys. Rev. Lett. 19, 581 (1967)] expression
for the thermodynamics of the $XXZ$ classical model, with neither single-ion
anisotropy term nor external magnetic field. This comparison shows that the
derived analytical expansion is valid for intermediate temperatures such as
$kT/J_x \approx 0.5$. We show that the specific heat and magnetic
susceptibility of the spin-2 antiferromagnetic chain can be approximated by
their respective classical results, up to $kT/J \approx 0.8$, within an error
of 2.5%. In the absence of an external magnetic field, the ferromagnetic and
antiferromagnetic chains have the same classical Helmholtz free energy. We show
how this two types of media react to the presence of an external magnetic
field.",0601615v1
2006-02-26,Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB,"The temperature dependence of saturation and spin-flop fields for artificial
ferrimagnets (AFi) based on antiparallel coupled CoFeB/Ru/CoFeB trilayers has
been investigated in a temperature range between 80K and 600K. The results
presented in this paper are relevant for magnetic devices using this system,
e.g. magnetic-random access memory based on spin-flop switching. In good
accordance to the theory, the saturation field Hsat behaves like Hsat ~ H_0
(T/T_0)/sinh(T/T_0) with a characteristic temperature of T_0 = 150K. Within
this model, the Fermi velocity for the Ru layer is of the order of 10^5m/s,
therefore, explaining the strong variation of the coupling strength with the
temperature in Ru based AFi. Furthermore, a strong uniaxial anisotropy of K_u =
2x10^3 J/m^3 with a small angular distribution of the anisotropy axes is
observed for the AFi trilayers based on amorphous CoFeB alloys.",0602609v2
2006-04-05,Interparticle interaction and size effect in polymer coated magnetite nanoparticles,"Magnetization and Mossbauer studies have been performed on the polymer coated
magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in
the temperature dependence of magnetization (TM) is found to be inconsistent
with the particle size (DTEM). The effective magnetic anisotropy (Kan) is found
to increase with the decrease of DTEM, which is attributed to the increase of
surface anisotropy. The absence of coercivity and remanence of magnetization
noticed well above TM indicates the superparamagnetic behaviour, which has also
been observed in the temperature dependent Mossbauer results. The temperature
dependence of hyperfine field is found to follow similar dependence of
saturation magnetization for bulk magnetite.",0604119v2
2006-04-13,Charged inclusion in nematic liquid crystals,"We present a general theory of liquid crystals under inhomogeneous electric
field in a Ginzburg-Landau scheme. The molecular orientation can be deformed by
electric field when the dielectric tensor is orientation-dependent. We then
investigate the influence of a charged particle on the orientation order in a
nematic state. The director is aligned either along or perpendicular to the
local electric field around the charge, depending on the sign of the dielectric
anisotropy. The deformation becomes stronger with increasing the ratio $Ze/R$,
where $Ze$ is the charge and $R$ is the radius of the particle. Numerical
analysis shows the presence of defects around the particle for large $Ze/R$.
They are nanometer-scale defects for microscopic ions. If the dielectric
anisotropy is positive, a Saturn ring defect appears. If it is negative, a pair
of point defects appear apart from the particle surface, each being connected
to the surface by a disclination line segment.",0604334v1
2006-04-13,Signature of Fermi surface anisotropy in point contact conductance in the presence of defects,"In a previous paper (Avotina et al.,Phys. Rev. B Vol.71, 115430 (2005)) we
have shown that in principle it is possible to image the defect positions below
a metal surface by means of a scanning tunnelling microscope. The principle
relies on the interference of electron waves scattered on the defects, which
give rise to small but measurable conductance fluctuations. Whereas in that
work the band structure was assumed to be free-electron like, here we
investigate the effects of Fermi surface anisotropy. We demonstrate that the
amplitude and period of the conductance oscillations are determined by the
local geometry of the Fermi surface. The signal results from those points for
which the electron velocity is directed along the vector connecting the point
contact to the defect. For a general Fermi surface geometry the position of the
maximum amplitude of the conductance oscillations is not found for the tip
directly above the defect. We have determined optimal conditions for
determination of defect positions in metals with closed and open Fermi
surfaces.",0604344v1
2006-04-17,Angular Dependent Torque Measurements on CeCoIn$_5$ Single Crystals,"Angular dependent torque measurements were performed on single crystals of
CeCoIn$_5$, a heavy fermion superconductor ($T_{c0}$ = 2.3 K), in the
temperature, $T$, range 1.9 K $\leq T \leq $ 20 K and magnetic fields $H$ up to
14 T. A large paramagnetic effect is found in the normal state. Torque
measurements in the mixed state were also performed. The torque curves show
sharp hysteresis peaks at $\theta = 90^{o}$ ($\theta$ is the angle between $H$
and the $c-$axis of the crystal), a result of intrinsic pinning of vortices.
The anisotropy $\gamma \equiv \sqrt{m_{c}/m_{a}}$ in the mixed state was
determined from the reversible part of the vortex contribution to the torque
signal using Kogan's model [Phys. Rev. B \textbf{38}, 7049 (1988)]. The
anisotropy $\gamma$ decreases with increasing magnetic field and temperature.
The fact that $\gamma$ is not a constant points towards a multiband scenario in
this heavy fermion material.",0604399v1
2006-04-18,The gap exponent of XXZ model in a transverse field,"We have calculated numerically the gap exponent of the anisotropic Heisenberg
model in the presence of the transverse magnetic field. We have implemented the
modified Lanczos method to obtain the excited states of our model with the same
accuracy of the ground state. The coefficient of the leading term in the
perturbation expansion diverges in the thermodynamic limit (N --> infinity). We
have obtained the relation between this divergence and the scaling behaviour of
the energy gap. We have found that the opening of gap in the presence of
transverse field scales with a critical exponent which depends on the
anisotropy parameter (Delta). Our numerical results are in well agreement with
the field theoretical approach in the whole range of the anisotropy parameter,
-1 < Delta < 1.",0604405v1
2006-05-08,Mott glass in site-diluted S=1 antiferromagnets with single-ion anisotropy,"The interplay between site dilution and quantum fluctuations in S=1
Heisenberg antiferromagnets on the square lattice is investigated using quantum
Monte Carlo simulations. Quantum fluctuations are tuned by a single-ion
anisotropy D. In the clean limit, a sufficiently large D>D_c = 5.65(2) J forces
each spin into its m_S=0 state, and thus destabilizes antiferromagnetic order.
In the presence of site dilution, quantum fluctuations are found to destroy
N\'eel order before the percolation threshold of the lattice is reached, if D
exceeds a critical value D^* = 2.3(2) J. This mechanism opens up an extended
quantum-disordered Mott glass phase on the percolated lattice, characterized by
a gapless spectrum and vanishing uniform susceptibility.",0605200v1
2006-05-09,Superconducting Pairing Symmetries in Anisotropic Triangular Quantum Antiferromagnets,"Motivated by the recent discovery of a low temperature spin liquid phase in
layered organic compound $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ which becomes a
superconductor under pressure, we examine the phase transition of Mott
insulating and superconducting (SC) states in a Hubbard-Heisenberg model on an
anisotropic triangular lattice. We use a renormalized mean field theory to
study the Gutzwiller projected BCS wavefucntions. The half filled electron
system is a Mott insulator at large on-site repulsion $U$, and is a
superconductor at a moderate $U$. The symmetry of the SC state depends on the
anisotropy, and is gapful with $d_{x^2-y^2}+id_{xy}$ symmetry near the
isotropic limit and is gapless with $d_{x^2-y^2}$ symmetry at small anisotropy
ratio.",0605214v1
2006-05-10,Random anisotropy disorder in superfluid 3He-A in aerogel,"The anisotropic superfluid 3He-A in aerogel provides an interesting example
of a system with continuous symmetry in the presence of random anisotropy
disorder. Recent NMR experiments allow us to discuss two regimes of the
orientational disorder, which have different NMR properties. One of them, the
(s)-state, is identified as the pure Larkin-Imry-Ma state. The structure of
another state, the (f)-state, is not very clear: probably it is the
Larkin-Imry-Ma state contaminated by the network of the topological defects
pinned by aerogel.",0605276v8
2006-06-01,"Aluminium and carbon doped MgB2: band filling, band shift, and anisotropy loss","In this work the effect of Carbon and Aluminium doping on the multiband MgB2
superconductor is analyzed. Using the rigid band and virtual crystal
approximations (RBA and VCA), it was found that the main effect of doping on
the band structure is band filling and a relative band-shift. If this
band-shift is eliminated with an appropriate change of scale, then the RBA
provides a good description of the band structure as function of doping. With
this procedure both the inplane electrical conductivity of the C- and Al-doped
MgB2 and the superconducting critical temperature follow the same curve. The Tc
graph approximately follows the sigma-band density of states; the differences
between these two can be explained by loss of anisotropy which plays an
important role in these systems.",0606019v1
2006-06-03,Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers,"Quantum nanomagnets can show a field dependence of the relaxation time very
different from their classical counterparts, due to resonant tunneling via
excited states (near the anisotropy barrier top). The relaxation time then
shows minima at the resonant fields H_{n}=n D at which the levels at both sides
of the barrier become degenerate (D is the anisotropy constant). We showed that
in Mn12, near zero field, this yields a contribution to the nonlinear
susceptibility that makes it qualitatively different from the classical curves
[Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to
finite dc fields showing how the bias can trigger the system to display those
quantum nonlinear responses, near the resonant fields, while recovering an
classical-like behaviour for fields between them. The analysis of the
experiments is done with heuristic expressions derived from simple balance
equations and calculations with a Pauli-type quantum master equation.",0606091v1
2006-06-05,In-plane anisotropy of the electronic structure for the charge/orbital-ordered state in half-doped manganite with layered structure,"We report on the in-plane anisotropy of the electronic response in the
spin/charge/orbital ordered phase of a half-doped layered-structure manganite.
The optical conductivity spectra for a single domain of Eu$_{1/2}$%
Ca$_{3/2}$MnO$_{4}$ unambiguously show the anisotropic charge dynamics which
well corresponds to the theoretical calculation: the optical conductivity with
the polarization along the zigzag ferromagnetic chain direction exhibits a
smaller gap and a larger intensity at lower energies than that of the
perpendicular polarization mostly due to the charge/orbital ordering and the
associated quantum interference effect.",0606094v1
2006-06-19,Spin Diffusion in Trapped Gases: Anisotropy in Dipole and Quadrupole Modes,"Recent experiments in a mixture of two hyperfine states of trapped Bose gases
show behavior analogous to a spin-1/2 system, including transverse spin waves
and other familiar Leggett-Rice-type effects. We have derived the kinetic
equations applicable to these systems, including the spin dependence of
interparticle interactions in the collision integral, and have solved for
spin-wave frequencies and longitudinal and transverse diffusion constants in
the Boltzmann limit. We find that, while the transverse and longitudinal
collision times for trapped Fermi gases are identical, the Bose gas shows
unusual diffusion anisotropy in both dipole and quadrupole modes. Moreover, the
lack of spin isotropy in the interactions leads to the non-conservation of
transverse spin, which in turn has novel effects on the hydrodynamic modes.",0606490v1
2006-06-23,Dynamical spin chirality and spin anisotropy in gapped S=1/2 quantum systems,"We have studied the spin anisotropy in spin-singlet ground state compounds
and the magnetic chirality, as measured by inelastic polarized neutron
scattering techniques, in the chain-sublattice of Sr14Cu24O41. In-plane and out
of plane magnetic fluctuations are measured to be anisotropic and further
discussed in the light of the current hypothesis of spin-orbit coupling. We
show that under appropriate conditions of magnetic field and neutron
polarization, the \textit{trivial} magnetic chirality selects only one of the
Zeeman splitted triplet states for scattering and erases the other one that
posses opposite helicity. Our analysis pertains to previous studies on
dynamical magnetic chirality and chiral critical exponents, where the ground
state is chiral itself, the so-called \textit{non-trivial} dynamical magnetic
chirality. As it turns out, both \textit{trivial} and \textit{non-trivial}
dynamical magnetic chirality have identical selection rules for inelastic
polarized neutron scattering experiments and it is not at all evident that they
can be distinguished in a paramagnetic compound.",0606598v1
2006-06-26,Flux-flow resistivity anisotropy in the instability regime in the a-b plane of epitaxial YBCO thin films,"Measurements of the nonlinear flux-flow resistivity $\rho$ and the critical
vortex velocity $\rm v^*_\phi$ at high voltage bias close to the instability
regime predicted by Larkin and Ovchinnikov \cite{LO} are reported along the
node and antinode directions of the d-wave order parameter in the \textit{a-b}
plane of epitaxial $YBa_2Cu_3O_{7-\delta}$ films. In this pinning-free regime,
$\rho$ and $\rm v^*_\phi$ are found to be anisotropic with values in the node
direction larger on average by 10% than in the antinode direction. The
anisotropy of $\rho$ is almost independent of temperature and field. We
attribute the observed results to the anisotropic quasiparticle distribution on
the Fermi surface of $YBa_2Cu_3O_{7-\delta}$.",0606667v1
2006-06-27,Two-loop Functional Renormalization Group of the Random Field and Random Anisotropy O(N) Models,"We study by the perturbative Functional Renormalization Group (FRG) the
Random Field and Random Anisotropy O(N) models near $d=4$, the lower critical
dimension of ferromagnetism. The long-distance physics is controlled by
zero-temperature fixed points at which the renormalized effective action is
nonanalytic. We obtain the beta functions at 2-loop order, showing that despite
the nonanalytic character of the renormalized effective action, the theory is
perturbatively renormalizable at this order. The physical results obtained at
2-loop level, most notably concerning the breakdown of dimensional reduction at
the critical point and the stability of quasi-long range order in $d<4$, are
shown to fit into the picture predicted by our recent non-perturbative FRG
approach.",0606698v3
2006-06-28,Bounds on the shear load of cohesionless granular matter,"We characterize the force state of shear-loaded granular matter by relating
the macroscopic stress to statistical properties of the force network. The
purely repulsive nature of the interaction between grains naturally provides an
upper bound for the sustainable shear stress, which we analyze using an
optimization procedure inspired by the so-called force network ensemble. We
establish a relation between the maximum possible shear resistance and the
friction coefficient between individual grains, and find that anisotropies of
the contact network (or the fabric tensor) only have a subdominant effect.
These results can be considered the hyperstatic limit of the force network
ensemble and we discuss possible implications for real systems. Finally, we
argue how force anisotropies can be related quantitatively to experimental
measurements of the effective elastic constants.",0606747v2
2006-07-10,Auxetic properties and anisotropy of elastic material constants of 2D crystalline media,"Anisotropies of Young's modulus E, the shear modulus G, and Poisson's ratio
of all 2D symmetry systems are studied. Simple necessary and sufficient
conditions on their elastic compliances are derived to identify if any of these
crystals are completely auxetic, non-auxetic and auxetic. Particular attention
is paid to 2D crystals of quadratic symmetry. All mechanically stable quadratic
crystals are characterized by three parameters belonging to a prism with the
stability triangle in the base. Regions in the stability triangle in which
quadratic materials are completely auxetic, non-auxetic, and auxetic are
established. Examples of all types of auxetic properties of crystals of oblique
and rectangular symmetry are presented.",0607230v2
2006-07-11,Epitaxial growth of binary alloy nanostructures,"Stochastic growth of binary alloys on a weakly interacting substrate is
studied by kinetic Monte Carlo simulation. The underlying lattice model relates
to fcc alloys, and the kinetics are based on deposition, atomic migration with
bond-breaking processes and exchange processes mediated by nearest neighbor
hopping steps. We investigate the interrelation between surface processes and
the emerging nonequilibrium structure at and below the growing surface under
conditions where atoms in the bulk can be regarded as immobile. The parameters
of the model are adapted to CoPt_3 alloys. Growing nanoclusters exhibit an
anisotropic short range order, primarily caused by Pt segregation at the
surface. The overall structural anisotropy depends on both Pt surface
segregation and cluster shape, and can explain the perpendicular magnetic
anisotropy (PMA) recently measured in CoPt_3 nanoclusters on a van der Waals
substrate. The onset of L1_2 ordering in the cluster is induced by surface
processes. The same kinetic model is applied also to continuous thin films,
which in addition can exhibit a small bulk contribution to PMA.",0607284v1
2006-07-14,Anisotropic Zeeman splitting in ballistic one-dimensional hole systems,"We have studied the effect of an in-plane magnetic field B on a
one-dimensional hole system in the ballistic regime created by surface gate
confinement. We observed clearly the lifting of the spin degeneracy due to the
Zeeman effect on the one dimensional subbands for B applied parallel to the
channel. In contrast, no Zeeman splitting is detected for B applied
perpendicular to the channel, revealing an extreme anisotropy of the effective
Lande g-factor g*. We demonstrate that this anisotropy is a direct consequence
of the one-dimensional confinement on a system with strong spin-orbit coupling.",0607357v1
2006-07-17,Optical Anisotropy and Pinning of the Linear Polarization of Light in Semiconductor Microcavities,"We report a strong experimental evidence of the optical anisotropy in a
CdTe-based microcavity: the polarization of light is pinned to one of the
crystallographic axes independently on the polarization of the excitation. The
polarization degree depends strongly on the excitation power, reaching almost
100 % in the stimulated regime. The relaxation time of the polarization is
about 1 ns. We argue that all this is an effect of a splitting of the polariton
doublet at k=0. We consider different sources for the splitting and conclude
that the most likely one is optical birefringence in the mirrors and/or the
cavity.",0607420v1
2006-07-26,"Angle-dependent magnetotransport in cubic and tetragonal ferromagnets: Application to (001)- and (113)A-oriented (Ga,Mn)As","General expressions for the longitudinal and transverse resistivities of
single-crystalline cubic and tetragonal ferromagnets are derived from a series
expansion of the resistivity tensor with respect to the magnetization
orientation. They are applied to strained (Ga,Mn)As films, grown on (001)- and
(113)A-oriented GaAs substrates, where the resistivities are theoretically and
experimentally studied for magnetic fields rotated within various planes
parallel and perpendicular to the sample surface. We are able to model the
measured angular dependences of the resistivities within the framework of a
single ferromagnetic domain, calculating the field-dependent orientation of the
magnetization by numerically minimizing the free-enthalpy density.
Angle-dependent magnetotransport measurements are shown to be a powerful tool
for probing both anisotropic magnetoresistance and magnetic anisotropy. The
anisotropy parameters of the (Ga,Mn)As films inferred from the magnetotransport
measurements agree with those obtained by ferromagnetic resonance measurements
within a factor of two.",0607679v1
2006-08-10,Spin excitations in the antiferromagnet NaNiO2,"In NaNiO2, Ni3+ ions form a quasi two dimensional triangular lattice of S =
1=2 spins. The magnetic order observed below 20K has been described as an A
type antiferromagnet with ferro- magnetic layers weakly coupled
antiferromagnetically. We studied the magnetic excitations with the electron
spin resonance for frequencies 1-20 cm-1, in magnetic fields up to 14 T. The
bulk of the results are interpreted in terms of a phenomenological model
involving bi-axial anisotropy for the spins: a strong easy-plane term, and a
weaker anisotropy within the plane. The direction of the easy plane is
constrained by the collective Jahn-Teller distortion occurring in this material
at 480 K.",0608238v1
2006-08-14,Thermal relaxation of magnetic clusters in amorphous Hf_{57}Fe_{43} alloy,"The magnetization processes in binary magnetic/nonmagnetic amorphous alloy
Hf_{57}Fe_{43} are investigated by the detailed measurements of magnetic
hysteresis loops, temperature dependence of magnetization, relaxation of
magnetization and magnetic ac susceptibility, including a nonlinear term.
Blocking of magnetic moments at lower temperatures is accompanied with the slow
relaxation of magnetization and magnetic hysteresis loops. All of the observed
properties are explained with the superparamagnetic behaviour of the single
domain magnetic clusters inside the nonmagnetic host, their blocking by the
anisotropy barriers and thermal fluctuation over the barriers accompanied by
relaxation of magnetization. From magnetic viscosity analysis based on thermal
relaxation over the anisotropy barriers it is found out that magnetic clusters
occupy the characteristic volume from 25 up to 200 nm3 . The validity of the
superparamagnetic model of Hf_{57}Fe_{43} is based on the concentration of iron
in the Hf_{100-x}Fe_{43} system that is just below the threshold for the long
range magnetic ordering. This work throws more light on magnetic behaviour of
other amorphous alloys, too.",0608307v3
2006-08-30,Electrical conductivity of cellular Si/SiC ceramic composites prepared from plant precursors,"Electrical conductivity (sigma_dc) of the cellular Si/SiC ceramic composites
has been measured over a temperature range 25-1073 K while the thermoelectric
power (S) has been measured over 25-300 K. Remarkably, these cellular compounds
developed through biomimetic route - where the ceramic system grows within a
plant bio-template retaining the structural intricacies of the native templates
- are found to exhibit excellent mechanical, thermal, and electrical properties
quite comparable to or even better than those of the systems prepared through
conventional ceramic route. The electrical conductivity measured parallel
(sigma||) and perpendicular (sigma+) to the growth axes of the native plants,
depicts nearly temperature-independent anisotropy (sigma+/sigma||) of the order
\~2 while the thermoelectric power is nearly isotropic. The charge conduction
across the entire temperature range is found to follow closely the variable
range hopping (VRH) mechanism. The conductivity anisotropy appears to be driven
primarily by the unique microcellular morphology of the bio-templates which can
be exploited in many electrical applications.",0608668v1
2006-09-16,Insights into the Second Law of Thermodynamics from Anisotropic Gas-Surface Interactions,"Thermodynamic implications of anisotropic gas-surface interactions in a
closed molecular flow cavity are examined. Anisotropy at the microscopic scale,
such as might be caused by reduced-dimensionality surfaces, is shown to lead to
reversibility at the macroscopic scale. The possibility of a self-sustaining
nonequilibrium stationary state induced by surface anisotropy is demonstrated
that simultaneously satisfies flux balance, conservation of momentum, and
conservation of energy. Conversely, it is also shown that the second law of
thermodynamics prohibits anisotropic gas-surface interactions in ""equilibrium"",
even for reduced dimensionality surfaces. This is particularly startling
because reduced dimensionality surfaces are known to exhibit a plethora of
anisotropic properties. That gas-surface interactions would be excluded from
these anisotropic properties is completely counterintuitive from a causality
perspective. These results provide intriguing insights into the second law of
thermodynamics and its relation to gas-surface interaction physics.",0609398v1
2006-09-19,Lowest Landau-level description of a Bose-Einstein condensate in a rapidly rotating anisotropic trap,"A rapidly rotating Bose-Einstein condensate in a symmetric two-dimensional
trap can be described with the lowest Landau-level set of states. In this case,
the condensate wave function psi(x,y) is a Gaussian function of r^2 = x^2 +
y^2, multiplied by an analytic function P(z) of the single complex variable z=
x+ i y; the zeros of P(z) denote the positions of the vortices. Here, a similar
description is used for a rapidly rotating anisotropic two-dimensional trap
with arbitrary anisotropy (omega_x/omega_y le 1). The corresponding condensate
wave function psi(x,y) has the form of a complex anisotropic Gaussian with a
phase proportional to xy, multiplied by an analytic function P(zeta), where
zeta is proportional to x + i beta_- y and 0 le beta_- le 1 is a real parameter
that depends on the trap anisotropy and the rotation frequency. The zeros of
P(zeta) again fix the locations of the vortices. Within the set of lowest
Landau-level states at zero temperature, an anisotropic parabolic density
profile provides an absolute minimum for the energy, with the vortex density
decreasing slowly and anisotropically away from the trap center.",0609484v1
2006-10-16,Theoretical simulation of the anisotropic phases of antiferromagnetic thin films,"We simulate antiferromagnetic thin films. Dipole-dipole and antiferromagnetic
exchange interactions as well as uniaxial and quadrupolar anisotropies are
taken into account. Various phases unfold as the corresponding parameters, J, D
and C, as well as the temperature T and the number n of film layers vary. We
find (1) how the strength Delta_m of the anisotropy arising from dipole-dipole
interactions varies with the number of layers m away from the film's surface,
with J and with n; (2) a unified phase diagram for all n-layer films and bulk
systems; (3) a layer dependent spin reorientation (SR) phase in which spins
rotate continuously as T, D, C and n vary; (4) that the ratio of the SR to the
ordering temperature depends (approximately) on n only through (D+Delta/n)/C,
and hardly on J; (5) a phase transformation between two different magnetic
orderings, in which spin orientations may or may not change, for some values of
J, by varying n.",0610418v1
2006-10-17,Universal Anisotropy in Force Networks under Shear,"Scaling properties of patterns formed by large contact forces are studied as
a function of the applied shear stress, in two-dimensional static packings
generated from the force network ensemble. An anisotropic finite-size-scaling
analysis shows that the applied shear does not affect the universal scaling
properties of these patterns, but simply induces different length scales in the
principal directions of the macroscopic stress tensor. The ratio of these
length scales quantifies the anisotropy of the force networks, and is found not
to depend on the details of the underlying contact network, in contrast with
other properties such as the yield stress.",0610483v2
2006-10-23,Influence of external magnetic fields on growth of alloy nanoclusters,"Kinetic Monte Carlo simulations are performed to study the influence of
external magnetic fields on the growth of magnetic fcc binary alloy
nanoclusters with perpendicular magnetic anisotropy. The underlying kinetic
model is designed to describe essential structural and magnetic properties of
CoPt_3-type clusters grown on a weakly interacting substrate through molecular
beam epitaxy. The results suggest that perpendicular magnetic anisotropy can be
enhanced when the field is applied during growth. For equilibrium bulk systems
a significant shift of the onset temperature for L1_2 ordering is found, in
agreement with predictions from Landau theory. Stronger field induced effects
can be expected for magnetic fcc-alloys undergoing L1_0 ordering.",0610589v1
2006-10-24,Ferrimagnetic and Long Period Antiferromagnetic Phases in High Spin Heisenberg Chains with D-Modulation,"The ground state properties of the high spin Heisenberg chains with
alternating single site anisotropy are investigated by means of the numerical
exact daigonaization and DMRG method. It is found that the ferrimagnetic state
appears between the Haldane phase and period doubled N\'eel phase for the
integer spin chains. On the other hand, the transition from the
Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for
the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous
magnetization varies continuously with the modulation amplitude of the single
site anisotropy. Eventually, the magnetization is locked to fractional values
of the saturated magnetization. These fractional values satisfy the
Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to
reveal the physical nature of each state. In contrast to the case of
frustration induced ferrimagnetism, no incommensurate magnetic superstructure
is found.",0610660v1
2006-11-02,Order from Disorder in Graphene Quantum Hall Ferromagnet,"Valley-polarized quantum Hall states in graphene are described by a
Heisenberg O(3) ferromagnet model, with the ordering type controlled by the
strength and sign of valley anisotropy. A mechanism resulting from electron
coupling to strain-induced gauge field, giving leading contribution to the
anisotropy, is described in terms of an effective random magnetic field aligned
with the ferromagnet z axis. We argue that such random field stabilizes the XY
ferromagnet state, which is a coherent equal-weight mixture of the $K$ and $K'$
valley states. Other implications such as the Berezinskii-Kosterlitz-Thouless
ordering transition and topological defects with half-integer charge are
discussed.",0611062v1
2006-11-06,Universality class of isotropic on-lattice Eden clusters,"The shape of large on-lattice Eden clusters grown from a single seed is ruled
by the underlying lattice anisotropy. This is reflected on the linear growth
with time of the interface width ($w\sim t$), in contrast with the KPZ
universality class ($w\sim t^{1/3}$) observed when the Eden model is grown on
flat substrates. We propose an extended Eden model, in which the growth
probability has a power law dependence with the number of occupied nearest
neighbors. Large scale simulations ($N\gtrsim 4\times 10^9$ particles) were
used to determine the time evolution of $w$. We found that a suitable choice of
the power exponent removes the lattice-induced cluster anisotropy and provides
a growth exponent in very good agreement with the KPZ universality class. Also,
the present model corroborates the results found in off-lattice simulations, in
which the center of mass fluctuations are considered in the interface scaling
analysis.",0611160v1
2006-11-13,Anisotropic properties of the layered superconductor Cu0.07TiSe2,"The anisotropic superconducting properties of single crystals of Cu0.07TiSe2
were studied by measurements of magnetization and electrical resistivity. TC is
around 3.9 K, and the measured upper critical field (Hc2) values are ~1.25 T
and 0.8 T, for applied field parallel and perpendicular to the TiSe2 planes,
respectively. The anisotropy ratio gamma_anis = H^ab_c2 / H^c_c2 is close to
1.6 and nearly temperature independent. The lower critical field (Hc1) values
are much smaller (~ 32 Oe for H||ab and 17 Oe for H||c); demagnetizing
corrections for field perpendicular to the thin plate crystals are required for
the determination of H^c_c1. The anisotropy of the critical fields is described
well by the anisotropic Ginzburg-Landau (GL) theory, and the characteristic GL
parameters are determined and discussed.",0611310v1
2006-12-01,Antiferromagnetic Ising Model on Inverse Perovskite Lattice,"We study thermodynamic properties of an antiferromagnetic Ising model on the
inverse perovskite lattice by using Monte Carlo simulations. The lattice
structure is composed of corner-sharing octahedra and contains
three-dimensional geometrical frustration in terms of magnetic interactions.
The system with the nearest-neighbor interactions alone does not exhibit any
phase transition, leading to a degenerate ground state with large residual
entropy. The degeneracy is lifted by an external magnetic field or by an
anisotropy in the interactions. Depending on the anisotropy, they stabilize
either a 3D ferrimagnetic state or a partially-disordered antiferromagnetic
(PDAF) state with a dimensionality reduction to 2D. By the degeneracy-lifting
perturbations, all the transition temperatures of these different ordered
states continuously grow from zero, leaving an unusual zero-temperature
critical point at the unperturbed point. Such a zero-temperature
multicriticality is not observed in other frustrated structures such as
face-centered cubic and pyrochlore. The transition to the PDAF state is
represented by either the first- or second-order boundaries separated by
tricritical lines, whereas the PDAF phase shows 1/3 magnetization plateaus.",0612016v1
2006-12-03,General analysis of the complementary nature of coercivity enhancement and exchange bias in ferro-antiferromagnet (F-AF) exchange coupled systems,"Complementary nature of coercivity enhancement and exchange bias is
generalized from the layered systems to ferro-antiferromagnet (F-AF) exchange
coupled systems with arbitrary configurations and is proved based on the
coherent rotation of the F magnetization. In the proof, the effect of F-AF
coupling is absorbed into the anisotropy of the F part, resulting in an
arbitrary anisotropy for the F part. The proof starts from a general discussion
on the initial susceptibility of a single domain particle. Then the fundamental
correlation between the maximal initial susceptibility and the critical field
along an arbitrary easy direction of a single domain particle, at which the
magnetization becomes unstable, is discussed. Finally, the difference of the
initial switching field and the actual switching field along the arbitrarily
chosen easy direction is discussed.",0612062v1
2006-12-04,Interplane and intraplane heat transport in quasi two-dimensional nodal superconductors,"We analyze the behavior of the thermal conductivity in quasi-two dimensional
superconductors with line nodes. Motivated by measurements of the anisotropy
between the interplane and intraplane thermal transport in CeIrIn_5 we show
that a simple model of the open Fermi surface with vertical line nodes is
insufficient to describe the data. We propose two possible extensions of the
model taking into account a) additional modulation of the gap along the axial
direction of the open Fermi surface; and b) dependence of the interplane
tunneling on the direction of the in-plane momentum. We discuss the temperature
dependence of the thermal conductivity anisotropy and its low T limit in these
two models and compare the results with a model with a horizontal line of nodes
(``hybrid gap''). We discuss possible relevance of each model for the symmetry
of the order parameter in CeIrIn_5, and suggest further experiments aimed at
clarifying the shape of the superconducting gap.",0612094v1
2006-12-09,Field induced quantum phase transition in the anisotropic Kondo necklace model,"The anisotropic Kondo necklace model in 2D and 3D is treated as a genuine
model for magnetic to Kondo singlet quantum phase transitions in the heavy
fermion (HF) compounds. The variation of the quantum critical point (QCP) with
anisotropy parameters has been investigated previously in the zero field case
[1]. Here we extend the treatment to finite fields using a generalised bond
operator representation including all triplet states. The variation of critical
tc with external field H and the associated phase diagram is derived. The
influence of anisotropies and the different g-factors for localised and
itinerant spins on tc(H) is also investigated. It is found that three different
types of behaviour may appear: (i) Destruction of antiferromangetism and
appearance of a singlet state above a critical field. (ii) The inverese
behaviour, namely field induced antiferromagnetism out of the Kondo singlet
phase. (iii) Reentrance behaviour of the Kondo singlet phase as function of
field strength.",0612230v2
2007-01-04,Effect of the metal-to-wire ratio on the high-frequency magnetoimpedance of glass-coated CoFeBSi amorphous microwires,"High frequency [1-500 MHz] measurements of the magnetoimpedance (MI) of
glass-coated Co$_{69.4}$Fe$_{3.7}$B$_{15.9}$Si$_{11}$ microwires are carried
out with various metal-to-wire diameter ratios. A twin-peak, anhysteretic
behaviour is observed as a function of magnetic field. A maximum in the
normalized impedance, $\Delta Z$/$Z$, appears at different values of the
frequency $f$, 125, 140 and 85 MHz with the corresponding diameter ratio $p$ =
0.80, 0.55 and 0.32. We describe the measurement technique and interpret our
results with a thermodynamic model that leads to a clearer view of the effects
of $p$ on the maximum value of MI and the anisotropy field. The behavior of the
real and imaginary components of impedance is also investigated; they display a
resonance that becomes a function of the DC field $H_{DC}$ for values larger or
equal to $H_{K}$ the circumferential anisotropy field for each $p $ value.
These results are interpreted in terms of a rotation model of the outer shell
magnetization.",0701077v2
2007-01-04,Magnetic Susceptibility of the Kagome Antiferromagnet ZnCu3(OH)6Cl2,"We analyze the experimental data for the magnetic susceptibility of the
material ZnCu3(OH)6Cl2 in terms of the Kagome Lattice Heisenberg model (KLHM),
discussing possible role of impurity spins, dilution, exchange anisotropy, and
both out-of-plane and in-plane Dzyaloshinsky-Moriya (DM) anisotropies, with
explicit theoretical calculations using the Numerical Linked Cluster (NLC)
method and exact diagonalization (ED). The high-temperature experimental data
are well described by the pure Heisenberg model with J=170 K. We show that the
sudden upturn in the susceptibility around T=75 K is due to DM interactions. We
also observe that at intermediate temperatures, below T=J, our calculated
susceptibility for KLHM fits well with a power law T^{-0.25}.",0701087v3
2007-01-10,Brillouin scattering and molecular dynamics study of the elastic properties of Pb(Mg1/3Nb2/3)O3,"We report the complete set of elastic constants and the bulk modulus for
single crystal Pb(Mg1/3Nb2/3)O3 (PMN) at room temperature obtained from
Brillouin spectroscopy and molecular dynamics (MD) simulations. The bulk
modulus from Brillouin is found to be 103 GPa, in a good agreement with earlier
x-ray studies. We also derived the refractive index along all principal axes
and found PMN to be optically isotropic, with a refractive index of 2.52 +/-
0.02. PMN shows mechanical anisotropy with A=1.7. The MD simulations of PMN
using the random site model overestimate the elastic constants by 20-50 GPa and
the bulk modulus is 148 GPa, but the mechanical anisotropy matches the
Brillouin results of A = 1.7. We also determined the elastic constants for
various models of PMN and we find variation in the elastic constants based on
chemical ordering.",0701223v1
2007-01-11,Long-range correlated random field and random anisotropy O(N) models: A functional renormalization group study,"We study the long-distance behavior of the O(N) model in the presence of
random fields and random anisotropies correlated as ~1/x^{d-sigma} for large
separation x using the functional renormalization group. We compute the fixed
points and analyze their regions of stability within a double epsilon=d-4 and
sigma expansion. We find that the long-range disorder correlator remains
analytic but generates short-range disorder whose correlator develops the usual
cusp. This allows us to obtain the phase diagrams in (d,sigma,N) parameter
space and compute the critical exponents to first order in epsilon and sigma.
We show that the standard renormalization group methods with a finite number of
couplings used in previous studies of systems with long-range correlated random
fields fail to capture all critical properties. We argue that our results may
be relevant to the behavior of He-3A in aerogel.",0701256v3
2007-01-14,Sr1.5Ba0.5Zn2Fe12O22 Hexaferrites Ferromagnetic Resonance and Nonlinear Excitation for Magneto-Electric Devices,"A magneto electric (ME) effect was reported [1] for the insulator material of
helimagnetic hexaferrite of Sr1.5Ba0.5Zn2Fe12O22. In this study we are
interested in investigating this materials ferromagnetic resonance to define
its internal anisotropy fields. By using a vibrating sample magnetometer (VSM)
and ferromagnetic resonance (FMR) analysis we realized that this helical
hexaferrite has about -0.5 kOe exchange anisotropy field of HE. Also, by using
an alternative free energy model we derived this materials Polder tensor and
its ferromagnetic resonance condition. Meanwhile, we were able to show a
potential magneto electric coupling by nonlinear excitation of planar helical
hexaferrite, in which a magnetic nonlinear excitation is integrated into
dielectric permittivity.
  Index Terms, Ferrites, ferromagnetic resonances, and magnetic nonlinear
excitations.",0701309v2
2007-01-30,Magnetic Excitations in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl$_2$-4SC(NH$_2$)$_2$,"NiCl$_2$-4SC(NH$_2$)$_2$ (DTN) is a quantum S=1 chain system with strong
easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of
the spin degrees of freedom. ESR studies of magnetic excitations in DTN in
fields up to 25 T are presented. Based on analysis of the single-magnon
excitation mode in the high-field spin-polarized phase and previous
experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of
spin-Hamiltonian parameters is obtained. Our results yield $D=8.9$ K, $J_c=2.2$
K, and $J_{a,b}=0.18$ K for the anisotropy, intrachain, and interchain exchange
interactions, respectively. These values are used to calculate the
antiferromagnetic phase boundary, magnetization and the frequency-field
dependence of two-magnon bound-state excitations predicted by theory and
observed in DTN for the first time. Excellent quantitative agreement with
experimental data is obtained.",0701750v1
2007-02-27,Creep and flow regimes of magnetic domain wall motion in ultrathin Pt/Co/Pt films with perpendicular anisotropy,"We report on magnetic domain wall velocity measurements in ultrathin
Pt/Co(0.5-0.8 nm)/Pt films with perpendicular anisotropy over a large range of
applied magnetic fields. The complete velocity-field characteristics are
obtained, enabling an examination of the transition between thermally activated
creep and viscous flow: motion regimes predicted from general theories for
driven elastic interfaces in weakly disordered media. The dissipation limited
flow regime is found to be consistent with precessional domain wall motion,
analysis of which yields values for the damping parameter, $\alpha$.",0702654v2
2007-03-05,In-plane optical anisotropy due to conduction band electron wavefunctions,"Photoluminescence measurements were carried out on Be $\delta$-doped
  GaAs/Al$_{0.33}$Ga$_{0.67}$As heterostructure at 1.6 K in magnetic fields
($B$) up to 5 T. Luminescence originating from recombination of a
two-dimensional electron gas (2DEG) and photo excited holes localized on Be
acceptors was analyzed. The degree of circular polarization ($\gamma_C$) of the
luminescence from fully occupied Landau levels was determined as a function of
$B$ and the 2DEG concentration, $n_s$. At $B$ constant, $\gamma_C$ decreased
with the increase of $n_s$. Two mechanisms of the $\gamma_C(n_s)$ dependence
are discussed: a) the Stark effect on a photo excited hole bound to Be acceptor
and b) the in-plane anisotropy of the intensity of optical transitions. A
quantitative analysis shows that the influence of the Stark effect on
$\gamma_C$ is negligible in the present experiment. We propose that the
$\gamma_C(n_s)$ dependence results from the $C_{2v}$ symmetry of conduction
band electron wavefunctions and we give qualitative arguments supporting this
interpretation.",0703088v1
2007-03-19,Electron states in quantum rings with defects under axial or in-plane magnetic fields,"A comprehensive study of anisotropic quantum rings, QRs, subject to axial and
in-plane magnetic field, both aligned and transverse to the anisotropy
direction, is carried out. Elliptical QRs for a wide range of eccentricity
values and also perfectly circular QRs including one or more barriers
disturbing persistent QR current are considered. These models mimic anisotropic
geometry deformations and mass diffusion occuring in the QR fabrication
process. Symmetry considerations and simplified analytical models supply
physical insight into the obtained numerical results. Our study demonstrates
that, except for unusual extremely large eccentricities, QR geometry
deformations only appreciably influence a few low-lying states, while the
effect of barriers disturbing the QR persistent current is stronger and affects
all studied states to a similar extent. We also show that the response of the
electron states to in-plane magnetic fields provides accurate information on
the structural anisotropy.",0703484v1
2007-03-23,Transition-metal dimers and physical limits on magnetic anisotropy,"Recent advances in nanoscience have raised interest in the minimum bit size
required for classical information storage, i.e. for bistability with
suppressed quantum tunnelling and energy barriers that exceed ambient
temperatures. In the case of magnetic information storage much attention has
centred on molecular magnets[1] with bits consisting of ~ 100 atoms, magnetic
uniaxial anisotropy energy barriers ~ 50 K, and very slow relaxation at low
temperatures. In this article we draw attention to the remarkable magnetic
properties of some transition metal dimers which have energy barriers
approaching ~ 500 K with only two atoms. The spin dynamics of these ultra small
nanomagnets is strongly affected by a Berry phase which arises from
quasi-degeneracies at the electronic Highest Occupied Molecular Orbital (HOMO)
energy. In a giant spin-approximation, this Berry phase makes the effective
reversal barrier thicker. [1] Gatteschi, D., Sessoli, R. & Villain, J.
Molecular Nanomagnets. (Oxford, New York 2006).",0703607v2
2007-03-26,Exact results of the mixed-spin Ising model on a decorated square lattice with two different decorating spins of integer magnitudes,"The mixed-spin Ising model on a decorated square lattice with two different
decorating spins of the integer magnitudes S_B = 1 and S_C = 2 placed on
horizontal and vertical bonds of the lattice, respectively, is examined within
an exact analytical approach based on the generalized decoration-iteration
mapping transformation. Besides the ground-state analysis, finite-temperature
properties of the system are also investigated in detail. The most interesting
numerical result to emerge from our study relates to a striking critical
behaviour of the spontaneously ordered 'quasi-1D' spin system. It was found
that this quite remarkable spontaneous order arises when one sub-lattice of the
decorating spins (either S_B or S_C) tends towards their 'non-magnetic' spin
state S = 0 and the system becomes disordered only upon further single-ion
anisotropy strengthening. The effect of single-ion anisotropy upon the
temperature dependence of the total and sub-lattice magnetization is also
particularly investigated.",0703663v2
2007-03-28,Field-induced level crossings in spin clusters: Thermodynamics and magneto-elastic instability,"Quantum spin clusters with dominant antiferromagnetic Heisenberg exchange
interactions typically exhibit a sequence of field-induced level crossings in
the ground state as function of magnetic field. For fields near a level
crossing, the cluster can be approximated by a two-level Hamiltonian at low
temperatures. Perturbations, such as magnetic anisotropy or spin-phonon
coupling, sensitively affect the behavior at the level-crossing points. The
general two-level Hamiltonian of the spin system is derived in first-order
perturbation theory, and the thermodynamic functions magnetization, magnetic
torque, and magnetic specific heat are calculated. Then a magneto-elastic
coupling is introduced and the effective two-level Hamilitonian for the
spin-lattice system derived in the adiabatic approximation of the phonons. At
the level crossings the system becomes unconditionally unstable against lattice
distortions due to the effects of magnetic anisotropy. The resultant
magneto-elastic instabilities at the level crossings are discussed, as well as
the magnetic behavior.",0703747v1
1993-11-02,Graviton Mode Function in Inflationary Cosmology,"We consider the production of gravitons in an inflationary cosmology by
approximating each epoch of change in the equation of state as sudden, from
which a simple analytic graviton mode function has been derived. We use this
mode function to compute the graviton spectral energy density and the
tensor-induced cosmic microwave background anisotropy. The results are then
compared to the numerical calculations which incorporate a smooth
radiation-matter phase transition. We find that the sudden approximation is a
fairly good method. Besides, in determining the frequency range and amplitude
of the mode function, we introduce a pre-inflationary radiation-dominated epoch
and use a physically sensible regularization method.",9311002v3
1994-12-21,Photon rockets and gravitational radiation,"The absence of gravitational radiation in Kinnersley's ``photon rocket''
solution of Einstein's equations is clarified by studying the mathematically
well-defined problem of point-like photon rockets in Minkowski space (i.e.
massive particles emitting null fluid anisotro\-pically and accelerating
because of the recoil). We explicitly compute the (uniquely defined) {\it
linearized} retarded gravitational waves emitted by such objects, which are the
coherent superposition of the gravitational waves generated by the motion of
the massive point-like rocket and of those generated by the energy-momentum
distribution of the photon fluid. In the special case (corresponding to
Kinnersley's solution) where the anisotropy of the photon emission is purely
dipolar we find that the gravitational wave amplitude generated by the
energy-momentum of the photons exactly cancels the usual $1/r$ gravitational
wave amplitude generated by the accelerated motion of the rocket. More general
photon anisotropies would, however, generate genuine gravitational radiation at
infinity. Our explicit calculations show the compatibility between the
non-radiative character of Kinnersley's solution and the currently used
gravitational wave generation formalisms based on post-Minkowskian perturbation
theory.",9412063v1
1996-04-15,On compatibility of the Kaluza-Klein approach with the COBE experiment,"Contributions of primordial gravitational waves to the large-angular-scale
anisotropies of the cosmic microwave background radiation in multidimensional
cosmological models (Kaluza-Klein models) are studied. We derive limits on free
parameters of the models using results of the COBE experiment and other
astrophysical data. It is shown that in principle there is a room for
Kaluza-Klein models as possible candidates for the description of the Early
Universe. However, the obtained limits are very restrictive. Assuming that the
anisotropies are mostly due to gravitational waves, none of the concrete
models, analyzed in the article, satisfy them. On the other hand, if the
contribution of gravitational waves is very small then a string inspired model
is not ruled out.",9604031v1
1996-06-14,Anisotropy of fast-going processes in the Sun and new interaction in nature,"The processing of the galactic coordinates of 3543 solar flares with a
magnitude of 2 or more has shown that the distribution of these fast-going
processes on the surface of the ""nonrotating"" Sun is irregular and non-random
what testifies that in the near-Sun space an anisotropy takes place which
practically coincides with that predicted and obtained in laboratory
experiments and caused by existence of the intergalactic vector potential ${\bf
A_g}$.",9606033v1
1997-01-03,Semiclassical effects in black hole interiors,"First-order semiclassical perturbations to the Schwarzschild black hole
geometry are studied within the black hole interior. The source of the
perturbations is taken to be the vacuum stress-energy of quantized scalar,
spinor, and vector fields, evaluated using analytic approximations developed by
Page and others (for massless fields) and the DeWitt-Schwinger approximation
(for massive fields). Viewing the interior as an anisotropic collapsing
cosmology, we find that minimally or conformally coupled scalar fields, and
spinor fields, decrease the anisotropy as the singularity is approached, while
vector fields increase the anisotropy. In addition, we find that massless
fields of all spins, and massive vector fields, strengthen the singularity,
while massive scalar and spinor fields tend to slow the growth of curvature.",9701004v1
1997-01-16,Cosmological Limits on Slightly Skew Stresses,"We present an analysis of the cosmological evolution of matter sources with
small anisotropic pressures. This includes electric and magnetic fields,
collisionless relativistic particles, gravitons, antisymmetric axion fields in
low-energy string cosmologies, spatial curvature anisotropies, and stresses
arising from simple topological defects. We calculate their evolution during
the radiation and dust eras of an almost isotropic universe. In many
interesting cases the evolution displays a special critical behaviour created
by the non-linear evolution of the pressure and expansion anisotropies. The
isotropy of the microwave background is used to place strong limits of order
$\Omega _{a0}\leq 5\times 10^{-6}\Delta (1+z_{rec})^{-\Delta }$on the possible
contribution of these matter sources to the total density of the universe,
where $1\leq \Delta \leq 3$ characterises the anisotropic stress. The present
abundance of an anisotropic stress which becomes non-relativistic at a
characteristic low-energy scale is also calculated. We explain why the limits
obtained from primordial nucleosynthesis are generally weaker than those
imposed by the microwave background isotropy. The effect of inflation on these
stresses is also calculated.",9701038v1
1997-02-21,Chaos in Anisotropic Pre-Inflationary Universes,"We study the dynamics of anisotropic Bianchi type-IX models with matter and
cosmological constant. The models can be thought as describing the role of
anisotropy in the early stages of inflation. The concurrence of the
cosmological constant and anisotropy are sufficient to produce a chaotic
dynamics in the gravitational degrees of freedom, connected to the presence of
a critical point of saddle-center type in the phase space of the system. The
invariant character of chaos is guaranteed by the topology of the cylinders
emanating from unstable periodic orbits in the neighborhood of the
saddle-center. We discuss a possible mechanism for amplification of specific
wavelengths of inhomogeneous fluctuations in the models. A geometrical
interpretation is given for Wald's inequality in terms of invariant tori and
their destruction by increasing values of the cosmological constant.",9702044v1
1998-01-28,Lensing and caustic effects on cosmological distances,"We consider the changes which occur in cosmological distances due to the
combined effects of some null geodesics passing through low-density regions
while others pass through lensing-induced caustics. This combination of effects
increases observed areas corresponding to a given solid angle even when
averaged over large angular scales, through the additive effect of increases on
all scales, but particularly on micro-angular scales; however angular sizes
will not be significantly effected on large angular scales (when caustics
occur, area distances and angular-diameter distances no longer coincide). We
compare our results with other works on lensing, which claim there is no such
effect, and explain why the effect will indeed occur in the (realistic)
situation where caustics due to lensing are significant. Whether or not the
effect is significant for number counts depends on the associated angular
scales and on the distribution of inhomogeneities in the universe. It could
also possibly affect the spectrum of CBR anisotropies on small angular scales,
indeed caustics can induce a non-Gaussian signature into the CMB at small
scales and lead to stronger mixing of anisotropies than occurs in weak lensing.",9801092v1
1998-05-25,Speed of light on rotating platforms,"It is often taken for granted that on board a rotating disk it is possible to
operate a \QTR{it}{global}3+1 splitting of space-time, such that both lengths
and time intervals are \QTR{it}{uniquely} defined in terms of measurements
performed by real rods and real clocks at rest on the platform. This paper
shows that this assumption, although widespread and apparently trivial, leads
to an anisotropy of the velocity of two light beams travelling in opposite
directions along the rim of the disk; which in turn implies some recently
pointed out paradoxical consequences undermining the self-consistency of the
Special Theory of Relativity (SRT). A correct application of the SRT solves the
problem and recovers complete internal consistency for the theory. As an
immediate consequence, it is shown that the Sagnac effect only depends on the
non homogeneity of time on the platform and has nothing to do with any
anisotropy of the speed of light along the rim of the disk, contrary to an
incorrect but widely supported idea.",9805089v1
1999-12-23,Generation of the Scalar Field and Anisotropy at Quantum Creation of the Closed Universe,"The behaviour of the wave function of the Universe under the barrier for
anisotropic cosmological Bianchi type IX model with account of influence of the
scalar field is explored. In view of known difficulties with interpretation of
multidimensional wave functions the method of reduction of such problems to
one-dimensional is offered. For this purpose in frameworks of semiclassical
approach the system of characteristics equations relative to one variable is
written out. This system describe a bundle of the characteristics along which
the multidimensional problem is reduced to one-dimensional one that allows to
utillize the standard interpretation of the wave function as well as for usual
Schrodinger equation. The obtained results for Bianchi type IX model are
reduced to the following statement: the Universe tunnels through the barrier
from an isotropic state with zero initial value of the scalar field and appear
in classically allowed region with small anisotropy that is necessary for
providing of long-lived inflation for deriving the Universe such as ours.",9912098v1
2001-03-15,Locally Anisotropic Wormholes and Flux Tubes in 5D Gravity,"In this article we examine a class of wormhole and flux tube like solutions
to 5D vacuum Einstein equations. These solutions possess generic local
anisotropy, and their local isotropic limit is shown to be conformally
equivalent to the spherically symmetric 5D solutions of gr-qc/9807086. The
anisotropic solutions investigated here have two physically distinct
signatures: First, they can give rise to angular-dependent, anisotropic
``electromagnetic'' interactions. Second, they can result in a gravitational
running of the ``electric'' and ``magnetic'' charges of the solutions. This
gravitational running of the electromagnetic charges is linear rather than
logarithmic, and could thus serve as an indirect signal for the presence of
higher dimensions. The local anisotropy of these solutions is modeled using the
technique of anholonomic frames with respect to which the metrics are
diagonalized. If holonomic coordinates frames were used then such metrics would
have off-diagonal components.",0103058v3
2001-06-21,Anholonomic Frames and Thermodynamic Geometry of 3D Black Holes,"We study new classes three dimensional black hole solutions of Einstein
equations written in two holonomic and one anholonomic variables with respect
to anholonomic frames Thermodynamic properties of such (2+1)-black holes with
generic local anisotropy (having elliptitic horizons) are studied by applying
geometric methods. The corresponding thermodynamic systems are three
dimensional with entropy S being a hypersurface function on mass M, anisotropy
angle $\theta$ and eccentricity of elliptic deformations $\epsilon >.$
Two-dimensional curved thermodynamic geometries for locally anistropic deformed
black holes are constructed after integration on anisotropic parameter
$\theta$. Two approaches, the first one based on two-dimensional hypersurface
parametric geometry and the second one developed in a
Ruppeiner-Mrugala-Janyszek fashion, are analyzed. The thermodynamic curvatures
are computed and the critical points of curvature vanishing are defined.",0106069v3
2001-12-12,Spinors and Space-Time Anisotropy,"This is the first monograph on the geometry of anisotropic spinor spaces and
its applications in modern physics. The main subjects are the theory of gravity
and matter fields in spaces provided with off--diagonal metrics and associated
anholonomic frames and nonlinear connection structures, the algebra and
geometry of distinguished anisotropic Clifford and spinor spaces, their
extension to spaces of higher order anisotropy and the geometry of gravity and
gauge theories with anisotropic spinor variables. The book summarizes the
authors' results and can be also considered as a pedagogical survey on the
mentioned subjects.",0112028v3
2002-02-04,Anisotropic quantum cosmological models: a discrepancy between many-worlds and dBB interpretations,"In the isotropic quantum cosmological perfect fluid model, the initial
singularity can be avoided, while the classical behaviour is recovered
asymptotically. We verify if initial anisotropies can also be suppressed in a
quantum version of a classical anisotropic model where gravity is coupled to a
perfect fluid. Employing a Bianchi I cosmological model, we obtain a
""Schr\""odinger-like"" equation where the matter variables play de role of time.
This equation has a hyperbolic signature. It can be explicitly solved and a
wave packet is constructed. The expectation value of the scale factor,
evaluated in the spirit of the many-worlds interpretation, reveals an isotropic
Universe. On the other hand, the bohmian trajectories indicate the existence of
anisotropies. This is an example where the Bohm-de Broglie and the many-worlds
interpretations are not equivalent. It is argued that this inequivalence is due
to the hyperbolic structure of the ""Schr\""odinger-like"" equation.",0202009v1
2003-02-17,Galactic Potentials,"The information contained in galactic rotation curves is examined under a
minimal set of assumptions. If emission occurs from stable circular geodesic
orbits of a static spherically symmetric field, with information propagated to
us along null geodesics, observed rotation curves determine galactic potentials
without specific reference to any metric theory of gravity. Given the
potential, the gravitational mass can be obtained by way of an anisotropy
function of this field. The gravitational mass and anisotropy function can be
solved for simultaneously in a Newtonian limit without specifying any specific
source. This procedure, based on a minimal set of assumptions, puts very strong
constraints on any model of the ""dark matter"".",0302067v5
2003-04-11,Anisotropic brane cosmologies with exponential potentials,"We study Bianchi I type brane cosmologies with scalar matter self-interacting
through combinations of exponential potentials. Such models correspond in some
cases to inflationary universes. We discuss the conditions for accelerated
expansion to occur, and pay particular attention to the influence of extra
dimensions and anisotropy. Our results show that the associated effects evolve
in such a way that they become negligible in the late time limit, those related
to the anisotropy disappearing earlier. This study focuses mainly on single
field models, but we also consider a generalization yielding models with
multiple non-interacting fields and examine its features briefly. We conclude
that in the brane scenario, as happens in general relativity, an increase in
the number of fields assists inflation.",0304046v2
2004-11-10,On the Tensor/Scalar Ratio in Inflation with UV Cutoff,"Anisotropy of the cosmic microwave background radiation (CMB) originates from
both tensor and scalar perturbations. To study the characteristics of each of
these two kinds of perturbations, one has to determine the contribution of each
to the anisotropy of CMB. For example, the ratio of the power spectra of
tensor/scalar perturbations can be used to tighten bounds on the scalar
spectral index. We investigate here the implications for the tensor/scalar
ratio of the recent discovery (noted in astro-ph/0410139) that the introduction
of a minimal length cutoff in the structure of spacetime does not leave
boundary terms invariant. Such a cutoff introduces an ambiguity in the choice
of action for tensor and scalar perturbations, which in turn can affect this
ratio. We numerically solve for both tensor and scalar mode equations in a
near-de-sitter background and explicitly find the cutoff dependence of the
tensor/scalar ratio during inflation.",0411056v4
1998-04-17,Perturbative and non-perturbative studies of the SU(2)-Higgs model on lattices with asymmetric lattice spacings,"We present a calculation of the O(g^2,\lambda) perturbative corrections to
the coupling anisotropies of the SU(2)-Higgs model on lattices with asymmetric
lattice spacings. These corrections are obtained by a one-loop calculation
requiring the rotational invariance of the gauge and Higgs boson propagators in
the continuum limit. The coupling anisotropies are also determined from
numerical simulations of the model on appropriate lattices. The one-loop
perturbation theory and the simulation results agree with high accuracy. It is
demonstrated that rotational invariance is also restored for the static
potential determined from space-space and space-time Wilson loops.",9804026v2
1998-10-14,Anisotropic Improved Gauge Actions; --Perturbative and Numerical Studies --,"The $\Lambda$ parameter on the anisotropic lattice, the spatial and
temperature coupling constant $g_{\sigma}$, $g_{\tau}$ and their derivative
with respaect to the the anisotropy parameter $\xi$ are studied perturbatively
for the class of improved actions, which cover tree level Symanzik's, Iwasaki's
and QCDTARO's improved actions. The $\eta(=g_{\tau}/g_{\sigma})$ becomes less
than 1 for Iwasaki's and QCDTARO's action, which is confirmed nonperturbatively
by numerical simulations. Derivatives of the coupling constants with respect to
the anisotropy parameter, $\partial g_{\tau}/\partial \xi$ and $\partial
g_{\sigma}/\partial \xi$, change sign for those improved actions.",9810030v3
2000-10-28,Perfect Gauge Actions on Anisotropic Lattices,"On anisotropic lattices, where generally the lattice is rather coarse in
spatial directions, a parametrized classically perfect action could help
reducing lattice artifacts considerably. We investigate the possibility of
constructing such actions for SU(3) gauge theory. We present two different
methods to do so, either repeating the procedure used to create our newly
parametrized isotropic FP action, or performing one single step starting with
the isotropic result. The anisotropic action is parametrized using an ansatz
including anisotropically APE-like smeared (``fat'') links. The parametrized
classically perfect action with anisotropy $\xi=a_s/a_t=2$ is constructed and
the renormalized anisotropy is measured using the torelon dispersion relation.
It turns out that the renormalization is small.",0010057v1
2001-10-21,O(a) improved Wilson quark action on anisotropic lattice,"The $O(a)$ improved Wilson quark action on the anisotropic lattice is
investigated. We carry out numerical simulations in the quenched approximation
at three values of lattice spacing ($a_{\sigma}^{-1}=1$--2 GeV) with the
anisotropy $\xi=a_{\sigma}/a_{\tau}=4$, where $a_{\sigma}$ and $a_{\tau}$ are
the spatial and the temporal lattice spacings, respectively. Using the
dispersion relation of mesons, the bare anisotropy $\gamma_F$ in the quark
action is numerically tuned below the charm quark mass region with the
statistical accuracy of 1 % level. The systematic uncertainties in the
calibration are examined and found to be under control in the continuum limit.
Then we compute the light hadron masses and find that they are consistent with
the result of the UKQCD Collaboration on the isotropic lattice. The effect of
the uncertainty in the calibration on the hadron spectrum for physical quark
masses is also found to be under control.",0110176v1
2002-09-08,Heavy-light meson in anisotropic lattice QCD,"We examine whether the $O(a)$ improved quark action on anisotropic lattices
can be used as a framework for the heavy quark, which enables precision
computation of matrix elements of heavy-light mesons. To this end, it is
crucial to verify that a mass independent and nonperturbative tuning of the
parameters is possible. As a first step, we observe the dispersion relation of
heavy-light mesons on a quenched lattice using the action which is
nonperturbatively tuned only for the leading terms. On a lattice with the
spatial cutoff $a_\sigma^{-1} \simeq$ 1.6 GeV and the anisotropy $\xi=4$, the
relativity relation holds within 2% accuracy in the quark mass region $a_\sigma
m_Q \leq 1.2$ with the bare anisotropy parameter tuned for the massless quark.
We also apply the action to a calculation of heavy-light decay constants in the
charm quark mass region.",0209090v1
2003-01-30,Renormalization group improved action on anisotropic lattices,"We study a block spin transformation in the SU(3) lattice gauge theory on
anisotropic lattices to obtain Iwasaki's renormalization group improved action
for anisotropic cases. For the class of actions with plaquette and $1\times2$
rectangular terms, we determine the improvement parameters as functions of the
anisotropy $\xi= a_s/a_t$. We find that the program of improvement works well
also on anisotropic lattices. From a study of an indicator which estimates the
distance to the renormalized trajectory, we show that, for the range of the
anisotropy $\xi \approx 1$--4, the coupling parameters previously determined
for isotropic lattices improve the theory considerably.",0301029v2
2003-11-13,Improved gauge action on an anisotropic lattice II - Anisotropy parameter in the medium coupling region -,"The quantum correction of the anisotropy parameter, $\eta$, is calculated for
$\xi=2$ and 3 in the $\beta$ region where numerical simulations such as hadron
spectroscopy are currently carried out, for the improved actions composed of
plaquette and rectangular 6-link loops. The $\beta$ dependences of $\eta$ for
the renormalization group improved actions are quite different from those of
the standard and Symanzik actions. In Iwasaki and DBW2 actions, $\eta$ stays
almost constant in a wide range of $\beta$, which also differs from the
one-loop perturbative result, while in the case of Symanzik action, it
increases as $\beta$ decreases, which is qualitatively similar to the
perturbative result, but the slope is steeper. In the calculation of the $\eta$
parameter close to and in the confined phase, we have applied the link
integration method to suppress the fluctuation of the gauge fields. Some
technical details are summarized.",0311020v1
2004-07-21,QED in 2+1 Dimensions with Fermi and Gap Anisotropies,"QED in 2+1 dimensions has long been studied as a model field theory which
exhibits both asymptotic freedom and non-trivial IR behaviour. There is also a
trend towards viewing it as a candidate low energy effective theory for the
pseudogap phase of high temperature superconductors. One feature of these
theories is their lack of isotropy in the x and y directions (a common feature
of Dirac theories in condensed matter systems). A model motivated by this work
is outlined, and tentative evidence presented for chiral symmetry restoration
as the relative anisotropy is increased.",0407029v1
1992-06-18,The Implications of the COBE-DMR Results for Cosmic Strings,"We compare the anisotropies in the cosmic microwave background radiation
measured by the COBE experiment to the predictions of cosmic strings. We use an
analytic model for the $\Delta T/T$ power spectrum that is based on our
previous numerical simulations to show that the COBE results imply a value for
the string mass per unit length, $\mu$ under the assumption that cosmic strings
are the source of the measured anisotropy. We find $G\mu = 1.5\pm 0.5 \times
10^{-6}$ which is consistent with the value of $\mu$ thought to be required for
cosmic strings to seed galaxy formation.",9206233v1
1992-07-20,Inflation and Large Scale Structure Formation After COBE,"The simplest realizations of the new inflationary scenario typically give
rise to primordial density fluctuations which deviate logarithmically from the
scale free Harrison - Zeldovich spectrum. We consider a number of such examples
and, in each case we normalize the amplitude of the fluctuations with the
recent COBE measurement of the microwave background anisotropy. The predictions
for the bulk velocities as well as anisotropies on smaller (~1-2 degrees)
angular scales are compared with the Harrison-Zeldovich case. Deviations from
the latter range from a few to about 15 percent. We also estimate the redshift
beyond which the quasars would not be expected to be seen. The inflationary
quasar cutoff redshifts can vary by as much as 25\% from the Harrison-Zeldovich
case. We find that the inflationary scenario provides a good starting point for
a theory of large scale structure in the universe provided the dark matter is a
combination of cold plus (~10-30 \%) hot components.",9207247v1
1993-03-11,Peculiar Velocities and Microwave Background Anisotropopies from Cosmic Strings,"Using an analytic model we show that the predictions of the cosmic string
model for the peculiar velocities and the microwave background (MBR) anisotropy
depend on similar combinations of string evolution parameters. Normalizing from
the COBE detection of MBR anisotropy, and for certain reasonable values of
string network evolution parameters, we find that the magnitude of predicted
velocity flows is in good agreement with observations on small scales but is
inconsistent with observations on large scales ($ > 50 h^{-1}$Mpc). The Cosmic
Mach Number obtained from the cosmic string scenario is found to depend on a
single network evolution parameter and is consistent with observations on
scales $5h^{-1}$Mpc to $20h^{-1}$Mpc.",9303242v2
1994-07-21,Non-Zero Electric Charge of the Neutrino and the Solar Neutrino Problem,"It has recently been shown that the neutrino can have non-zero electric
charge in a number of gauge theories, including the Minimal Standard Model.
Assuming non-zero neutrino charge, we develop a new approach to the solar
neutrino problem. The key idea is that the charged neutrinos will be deflected
by the Lorentz force while they are crossing the solar magnetic fields. Such a
deflection will result in the anisotropy of the solar neutrino flux. Because of
this anisotropy, the solar neutrino flux registered on earth can be reduced as
compared to the Standard Solar Model prediction. The mechanism is purely
classical and does not require neutrino oscillations, spin-flip or neutrino
decay. We discuss qualitatively the consequences of our scenario for present
and future solar neutrino experiments as well as differences between our
mechanism and other proposed solutions.",9407346v1
1996-06-20,What would we learn by detecting a gravitational wave signal in the cosmic microwave background anisotropy?,"Inflation generates gravitational waves, which may be observable in the low
multipoles of the cosmic microwave background (cmb) anisotropy but only if the
inflaton field variation is at least of order the Planck scale. Such a large
variation would imply that the model of inflation cannot be part of an ordinary
extension of the standard model, and combined with the detection of the waves
it would also suggest that the inflaton field cannot be one of the superstring
moduli. Another implication of observable gravitational waves would be a
potential $V^{1/4}=2$ to $4\times 10^{16}\GeV$, which is orders of magnitude
bigger than is expected on the basis of particle theory. It might emerge in a
hybrid inflation model where most of the energy density comes from the Higgs
sector of a GUT, but only if both the vacuum expectation values {\em and the
masses } of the Higgs fields are of this order.",9606387v1
1996-10-22,$\eps$ expansion analysis of very weak first-order transitions in the cubic anisotropy model: Part I,"The cubic anisotropy model provides a simple example of a system with an
arbitrarily weak first-order phase transition. We present an analysis of this
model using $\eps$-expansion techniques with results up to
next-to-next-to-leading order in $\eps$. Specifically, we compute the relative
discontinuity of various physical quantities across the transition in the limit
that the transition becomes arbitrarily weakly first-order. This provides a
useful test-bed for the application of the $\eps$ expansion in weakly
first-order transitions.",9610447v2
1997-03-05,Cosmic Ray and Neutrino Tests of Special Relativity,"Searches for anisotropies due to Earth's motion relative to a preferred frame
-- modern versions of the Michelson-Morley experiment -- provide precise
verifications of special relativity. We describe other tests, independent of
this motion, that are or can become even more sensitive. The existence of
high-energy cosmic rays places strong constraints on Lorentz non-invariance.
Furthermore, if the maximum attainable speed of a particle depends on its
identity, then neutrinos, even if massless, may exhibit flavor oscillations.
Velocity differences far smaller than any previously probed can produce
characteristic effects at accelerators and solar neutrino experiments.",9703240v3
1997-10-07,Cosmological implications of neutrinos,"Massive neutrinos were the first proposed, and remain the most natural,
particle candidate for the dark matter. In the absence of firm laboratory
evidence for neutrino mass, considerations of the formation of large scale
structure in the universe provide a sensitive, albeit indirect, probe of this
possibility. Observations of galaxy clustering and large angle anisotropy in
the cosmic microwave background have been interpreted as requiring that
neutrinos provide about 20% of the critical density. However the need for such
`hot' dark matter is removed if the primordial spectrum of density fluctuations
is tilted below scale-invariance, as is often the case in physically realistic
inflationary models. This question will be resolved by forthcoming precision
measurements of microwave background anisotropy on small angular scales. This
data will also improve the nucleosynthesis bound on the number of neutrino
species and test whether decays of relic neutrinos could have ionized the
intergalactic medium.",9710273v2
1998-06-09,Constraints on pre-big bang models for seeding large-scale anisotropy by massive Kalb-Ramond axions,"We discuss the conditions under which pre-big bang models can fit the
observed large-scale anisotropy with a primordial spectrum of massive
(Kalb--Ramond) axion fluctuations.
  The primordial spectrum must be sufficiently flat at low frequency and
sufficiently steeper at high frequency. For a steep and/or long enough
high-frequency branch of the spectrum the bounds imposed by COBE's
normalization allow axion masses of the typical order for a
Peccei--Quinn--Weinberg--Wilczek axion. We provide a particular example in
which an appropriate axion spectrum is obtained from a class of backgrounds
satisfying the low-energy string cosmology equations.",9806327v1
1999-12-15,Cosmological measurement of neutrino mass in the presence of leptonic asymmetry,"We show that even the smallest neutrino mass consistent with the
Super--Kamiokande data is relevant for cosmological models of structure
formation and cosmic microwave background (CMB) anisotropies, provided that a
relic neutrino asymmetry exists. We calculate the precision with which a 0.07
eV neutrino mass could be extracted from CMB anisotropy and large-scale
structure data by the future Planck satellite and Sloan Digital Sky Survey. We
find that such a mass can be detected, assuming a large relic neutrino
asymmetry still allowed by current experimental data. This measurement of the
absolute value of the neutrino mass would be crucial for our understanding of
neutrino models.",9912363v2
2001-10-07,Effects of Cosmological Moduli Fields on Cosmic Microwave Background,"We discuss effects of cosmological moduli fields on the cosmic microwave
background (CMB). If a modulus field \phi once dominates the universe, the CMB
we observe today is from the decay of \phi and its anisotropy is affected by
the primordial fluctuation in the amplitude of the modulus field. Consequently,
constraints on the inflaton potential from the CMB anisotropy can be relaxed.
In particular, the scale of the inflation may be significantly lowered. In
addition, with the cosmological moduli fields, correlated mixture of adiabatic
and isocurvature fluctuations may be generated, which results in enhanced CMB
angular power spectrum at higher multipoles relative to that of lower ones.
Such an enhancement can be an evidence of the cosmological moduli fields, and
may be observed in future satellite experiments.",0110096v3
2002-10-29,Cosmic Microwave Background from Late-Decaying Scalar Condensations,"We study the cosmic microwave background (CMB) anisotropy in the scenario
with late-decaying scalar condensations which arise in many class of
cosmological scenarios based on supersymmetric models. With such a scalar
condensation \phi, the CMB radiation we observe today originates to \phi and
hence the CMB anisotropy is affected if \phi has a primordial fluctuation. In
particular, if all the components in the universe (i.e., radiation, baryon,
cold dark matter, and so on) are generated from the decay product of \phi, the
dominant source of the cosmic density perturbations can be the primordial
fluctuation of \phi, not the fluctuation of the inflaton field. In this case,
the constraints on the inflation models can be drastically relaxed. In other
case, the baryon or the CDM may not be from the decay product of \phi and
correlated mixture of the adiabatic and isocurvature fluctuations can be
generated. If so, the CMB angular power spectrum may not be the same as the
adiabatic result and the on-going MAP experiment may observe a deviation from
the prediction of the standard inflationary scenario.",0210392v1
2002-11-02,CMB Anisotropy from Baryogenesis by a Scalar Field,"We study the cosmic microwave background (CMB) anisotropy in the scenario
where the baryon asymmetry of the universe is generated from a condensation of
a scalar field. In such a scenario, the scalar condensation may acquire
fluctuation during the inflation which becomes a new source of the cosmic
density perturbations. In particular, the primordial fluctuation of the scalar
condensation may induce correlated mixture of the adiabatic and isocurvature
fluctuations. If the scalar condensation decays before it completely dominates
the universe, the CMB angular power spectrum may significantly deviate from the
conventional adiabatic result. Such a deviation may be observed in the on-going
MAP experiment.",0211019v1
2002-12-08,Constraints on pre-big bang parameter space from CMBR anisotropies,"The so-called curvaton mechanism --a way to convert isocurvature
perturbations into adiabatic ones-- is investigated both analytically and
numerically in a pre-big bang scenario where the role of the curvaton is played
by a sufficiently massive Kalb--Ramond axion of superstring theory. When
combined with observations of CMBR anisotropies at large and moderate angular
scales, the present analysis allows us to constrain quite considerably the
parameter space of the model: in particular, the initial displacement of the
axion from the minimum of its potential and the rate of evolution of the
compactification volume during pre-big bang inflation. The combination of
theoretical and experimental constraints favours a slightly blue spectrum of
scalar perturbations, and/or a value of the string scale in the vicinity of the
SUSY-GUT scale.",0212112v1
2003-04-14,Cosmic String from D-term Inflation and Curvaton,"We study effects of the cosmic string in the D-term inflation model on the
cosmic microwave background (CMB) anisotropy. In the D-term inflation model,
gauged cosmic string is usually formed, which may significantly affect the CMB
anisotropy. We see that its study imposes important constraint. In order to
realize the minimal model of D-term inflation, we see that the coupling
constant \lambda in the superpotential generating the inflaton potential should
be significantly small, \lambda \lesssim O(10^{-4}-10^{-5}). We also discuss
that a consistent scenario of the D-term inflation with \lambda \sim 1 can be
constructed by adopting the curvaton mechanism where the cosmic density
fluctuations are generated by a primordial fluctuation of a late-decaying
scalar field other than the inflaton.",0304126v1
2003-12-11,Quasiparticle description of the hot and dense quark-gluon plasma,"The collective modes of QCD at temperatures and densities above its
phase-transition are analyzed for isotropic systems as well as for systems
having an anisotropy in momentum-space using the HTL approximation. For
isotropic systems, results for the thermodynamic pressure and entropy at finite
densities based on a phenomenological description of lattice calculations at
vanishing densities are derived and compared to those following from different
methods. From the resulting equation of state the mass-radius relationship of
so-called quark-stars and other applications are investigated. It is shown that
systems with anisotropic momentum-space distributions contain unstable modes in
addition to the stable quasiparticle modes, which may be of great importance
for the dynamical evolution of an incompletely thermalized quark-gluon plasma.
Finally, the effects of the anisotropy on the collisional energy loss are
studied.",0312152v2
2004-03-20,Does the Low CMB Quadrupole Provide a New Cosmic Coincidence Problem ?,"We point out that the recent WMAP findings of a suppressed large scale power
in the Cosmic Microwave Background anisotropy power spectrum, if of
cosmological origin, make the case for a new cosmic coincidence problem.The
observed suppression of anisotropies at large angles requires an explanation
for why this suppression is occuring {\it only} for perturbation wavelengths of
the order of our present Hubble horizon. This is a very challenging task since
a consistent model for the emerging picture of the universe has to address any
cosmic coincidence and thus may reveal a deeper inter-relation with the dark
energy problem.",0403222v1
2005-05-30,From Primordial Quantum Fluctuations to the Anisotropies of the Cosmic Microwave Background Radiation,"These lecture notes cover mainly three connected topics. In the first part we
give a detailed treatment of cosmological perturbation theory. The second part
is devoted to cosmological inflation and the generation of primordial
fluctuations. In part three it will be shown how these initial perturbation
evolve and produce the temperature anisotropies of the cosmic microwave
background radiation. Comparing the theoretical prediction for the angular
power spectrum with the increasingly accurate observations provides important
cosmological information (cosmological parameters, initial conditions).",0505249v3
2005-05-31,Dynamics of Quark-Gluon-Plasma Instabilities in Discretized Hard-Loop Approximation,"Non-Abelian plasma instabilities have been proposed as a possible explanation
for fast isotropization of the quark-gluon plasma produced in relativistic
heavy-ion collisions. We study the real-time evolution of these instabilities
in non-Abelian plasmas with a momentum-space anisotropy using a hard-loop
effective theory that is discretized in the velocities of hard particles. We
extend our previous results on the evolution of the most unstable modes, which
are constant in directions transverse to the direction of anisotropy, from
gauge group SU(2) to SU(3). We also present first full 3+1-dimensional
simulation results based on velocity-discretized hard loops. In contrast to the
effectively 1+1-dimensional transversely constant modes we find subexponential
behaviour at late times.",0505261v3
2005-08-18,Azimuthal Asymmetry of Direct Photons in High Energy Nuclear Collisions,"We show that a sizeable azimuthal asymmetry, characterized by a coefficient
v_2, is to be expected for direct photons produced in non-central high energy
nuclear collisions. This signal is generated by photons radiated by jets
interacting with the surrounding hot plasma. The anisotropy is out of phase by
an angle $\pi/2$ with respect to that associated with the elliptic anisotropy
of hadrons, leading to negative values of v_2. Such an asymmetry, if observed,
could be a signature for the presence of a quark gluon plasma and would
establish the importance of jet-plasma interactions as a source of
electromagnetic radiation.",0508201v3
2006-03-03,A model of the effect of collisions on QCD plasma instabilities,"We study the effect of including a BGK collisional kernel on the collective
modes of a QCD plasma which has a hard-particle distribution function which is
anisotropic in momentum space. We calculate dispersion relations for both the
stable and unstable modes and show that the addition of hard particle
collisions slows the rate of growth of QCD plasma unstable modes. We also show
that for any anisotropy there is an upper limit on the collisional frequency
beyond which no instabilities exist. Estimating a realistic value for the
collisional frequency for alpha_s ~ 0.2 - 0.4 we find that for the
large-anisotropy case which is relevant for the initial state of matter
generated by free streaming in heavy-ion collisions that the collisional
frequency is below this critical value.",0603029v1
2006-06-28,Implications of cosmic strings with time-varying tension on CMB and large scale structure,"We investigate cosmological evolution and implications of cosmic strings with
time-dependent tension. We derive basic equations of time development of the
correlation length and the velocity of such strings, based on the one scale
model. Then, we find that, in the case where the tension depends on some power
of the cosmic time, cosmic strings with time-dependent tension goes into the
scaling solution if the power is lower than a critical value. We also discuss
cosmic microwave background anisotropy and matter power spectra produced by
these strings. The constraints on their tensions from the Wilkinson microwave
anisotropy probe (WMAP) three year data and Sloan digital sky survey (SDSS)
data are also given.",0606287v1
2006-07-20,Can a vector field be responsible for the curvature perturbation in the Universe?,"I investigate the possibility that the observed curvature perturbation is due
to a massive vector field. To avoid generating a large scale anisotropy the
vector field is not taken to be driving inflation. Instead it is assumed to
become important after inflation when it may dominate the Universe and imprint
its perturbation spectrum before its decay, as in the curvaton scenario. It is
found that, to generate a scale invariant spectrum of perturbations, the
mass-squared of the vector field has to be negative and comparable to the
Hubble scale during inflation. After inflation the mass-squared must become
positive so that the vector field engages into oscillations. It is shown that,
such an oscillating vector field behaves as pressureless matter and does not
lead to large scale anisotropy when it dominates the Universe. The possibilitiy
of realising this scenario in supergravity is also outlined.",0607229v2
1993-02-01,Spin-Anisotropy Commensurable Chains: Quantum Group Symmetries and N=2 SUSY,"In this paper we consider a class of the 2D integrable models. These models
are higher spin XXZ chains with an extra condition of the commensurability
between spin and anisotropy. The mathematics underlying this commensurability
is provided by the quantum groups with deformation parameter being an Nth root
of unity. Our discussion covers a range of topics including new integrable
deformations, thermodynamics, conformal behaviour, S-matrices and
magnetization. The emerging picture strongly depends on the N-parity. For the N
even case at the commensurable point, S-matrices factorize into N=2
supersymmetric Sine-Gordon matrix and an RSOS piece. The physics of the N odd
case is rather different. Here, the supersymmetry does not manifest itself and
the bootstrap hypothesis fails. Away from the commensurable point, we find an
unusual behaviour. The magnetization of our chains depends on the sign of the
external magnetic field.",9302001v1
1994-07-13,The Dynamical Correlation Function of the XXZ Model,"We perform a spectral decomposition of the dynamical correlation function of
the spin $1/2$ XXZ model into an infinite sum of products of form factors.
Beneath the four-particle threshold in momentum space the only non-zero
contributions to this sum are the two-particle term and the trivial vacuum
term. We calculate the two-particle term by making use of the integral
expressions for form factors provided recently by the Kyoto school. We evaluate
the necessary integrals by expanding to twelfth order in $q$. We show plots of
$S(w,k)$, for $k=0$ and $\pi$ at various values of the anisotropy parameter,
and for fixed anisotropy at various $k$ around $0$ and $\pi$.",9407062v1
2001-10-30,"Ellipsoidal, Cylindrical, Bipolar and Toroidal Wormholes in 5D Gravity","In this paper we construct and analyze new classes of wormhole and flux
tube-like solutions for the 5D vacuum Einstein equations. These 5D solutions
possess generic local anisotropy which gives rise to a gravitational running or
scaling of the Kaluza-Klein ``electric'' and ``magnetic'' charges of these
solutions. It is also shown that it is possible to self-consistently construct
these anisotropic solutions with various rotational 3D hypersurface geometries
(i.e. ellipsoidal, cylindrical, bipolar and toroidal). The local anisotropy of
these solutions is handled using the technique of anholonomic frames with their
associated nonlinear connection structures [vst]. Through the use of the
anholonomic frames the metrics are diagonalized, in contrast to holonomic
coordinate frames where the metrics would have off-diagonal components. In the
local isotropic limit these solutions are shown to be equivalent to spherically
symmetric 5D wormhole and flux tube solutions.",0110272v2
2002-04-08,Cosmic String Production Towards the End of Brane Inflation,"Towards the end of the brane inflationary epoch in the brane world, cosmic
strings (but not texture, domain walls or monopoles) are copiously produced
during brane collision. These cosmic strings are D$p$-branes with $(p-1)$
dimensions compactified. We elaborate on this prediction of the superstring
theory description of the brane world. Using the data on the temperature
anisotropy in the cosmic microwave background, we estimate the cosmic string
tension $\mu$ to be around $G \mu \simeq 10^{-7}$. This in turn implies that
the anisotropy in the cosmic microwave background comes mostly from inflation,
but with a component (of order 10%) from cosmic strings. This cosmic string
effect should also be observable in gravitational wave detectors and maybe even
pulsar timing measurements.
  Keywords : Inflation, Brane World, Superstring Theory, Cosmic String,
Cosmology",0204074v1
2002-05-06,Inflationary cosmology in the central region of String/M-theory moduli space,"The ""central"" region of moduli space of M- and string theories is where the
string coupling is about unity and the volume of compact dimensions is about
the string volume. Here we argue that in this region the non-perturbative
potential which is suggested by membrane instanton effects has the correct
scaling and shape to allow for enough slow-roll inflation, and to produce the
correct amplitude of CMB anisotropies. Thus, the well known theoretical
obstacles for achieving viable slow-roll inflation in the framework of
perturbative string theory are overcome. Limited knowledge of some generic
properties of the induced potential is sufficient to determine the simplest
type of consistent inflationary model and its predictions about the spectrum of
cosmic microwave background anisotropies: a red spectrum of scalar
perturbations, and negligible amount of tensor perturbations.",0205042v1
2002-07-18,Isotropization in Brane Gas Cosmology,"Brane Gas Cosmology (BGC) is an approach to unifying string theory and
cosmology in which matter is described by a gas of strings and branes in a
dilaton gravity background. The Universe is assumed to start out with all
spatial dimensions compact and small. It has previously been shown that in this
context, in the approximation of neglecting inhomogeneities and anisotropies,
there is a dynamical mechanism which allows only three spatial dimensions to
become large. However, previous studies do not lead to any conclusions
concerning the isotropy or anisotropy of these three large spatial dimensions.
Here, we generalize the equations of BGC to the anisotropic case, and find that
isotropization is a natural consequence of the dynamics.",0207168v3
2002-11-08,(Non)Commutative Finsler Geometry from String/M--theory,"We synthesize and extend the previous ideas about appearance of both
noncommutative and Finsler geometry in string theory with nonvanishing B--field
and/or anholonomic (super) frame structures \cite{vstring,vstr2,vnonc,vncf}.
There are investigated the limits to the Einstein gravity and string
generalizations containing locally anisotropic structures modeled by moving
frames. The relation of anholonomic frames and nonlinear connection geometry to
M--theory and possible noncommutative versions of locally anisotropic
supergravity and D--brane physics is discussed. We construct and analyze new
classes of exact solutions with noncommutative local anisotropy describing
anholonomically deformed black holes (black ellipsoids) in string gravity,
embedded Finsler--string two dimensional structures, solitonically moving black
holes in extra dimensions and wormholes with noncommutativity and anisotropy
induced from string theory.",0211068v3
2003-07-02,Primeval Corrections to the CMB Anisotropies,"We show that deviations of the quantum state of the inflaton from the thermal
vacuum of inflation may leave an imprint in the CMB anisotropies. The quantum
dynamics of the inflaton in such a state produces corrections to the
inflationary fluctuations, which may be observable. Because these effects
originate from IR physics below the Planck scale, they will dominate over any
trans-Planckian imprints in any theory which obeys decoupling. Inflation sweeps
away these initial deviations and forces its quantum state closer to the
thermal vacuum. We view this as the quantum version of the cosmic no-hair
theorem. Such imprints in the CMB may be a useful, independent test of the
duration of inflation, or of significant features in the inflaton potential
about 60 e-folds before inflation ended, instead of an unlikely discovery of
the signatures of quantum gravity. The absence of any such substructure would
suggest that inflation lasted uninterrupted much longer than ${\cal O}(100)$
e-folds.",0307016v3
2003-07-10,CMB anisotropies from vector perturbations in the bulk,"The vector perturbations induced on the brane by gravitational waves
propagating in the bulk are studied in a cosmological framework. Cosmic
expansion arises from the brane motion in a non-compact five-dimensional
anti-de Sitter spacetime. By solving the vector perturbation equations in the
bulk, for generic initial conditions, we find that they give rise to growing
modes on the brane in the Friedmann-Lema\^{\i}tre era. Among these modes, we
exhibit a class of normalizable perturbations, which are exponentially growing
with respect to conformal time on the brane. The presence of these modes is, at
least, strongly constrained by the current observations of the cosmic microwave
background (CMB). We estimate the anisotropies they induce in the CMB, and
derive quantitative constraints on the allowed amplitude of their primordial
spectrum. Our results provide stringent constraints for all braneworld models
with bulk inflation.",0307100v1
2003-12-28,A mechanism of the large-scale damping in the CMB anisotropy,"We present a mechanism through which a certain class of short-distance cutoff
affects the CMB anisotropies at large angular scales. Our analysis is performed
in two steps. The first is given in an intuitive way, using the property of the
inflationary universe that quantum fluctuations of an inflaton field become
classical after crossing the Hubble horizon. We give a condition for a cutoff
to yield a damping on large scales, and show that the holographic cutoff
introduced in the preceding paper (hep-th/0307029) does satisfy the condition.
The second analysis is carried out by setting an initial condition such that
each mode of inflaton starts as the vacuum fluctuation of the Hamiltonian when
being released from the constraint of cutoff. The first intuitive discussion is
then shown to be correct qualitatively.",0312298v7
2005-07-01,3+1 Approach to the Long Wavelength Iteration Scheme,"Large-scale inhomogeneities and anisotropies are modeled using the Long
Wavelength Iteration Scheme. In this scheme solutions are obtained as
expansions in spatial gradients, which are taken to be small. It is shown that
the choice of foliation for spacetime can make the iteration scheme more
effective in two respects: (i) the shift vector can be chosen so as to dilute
the effect of anisotropy on the late-time value of the extrinsic curvature of
the spacelike hypersurfaces of the foliation; and (ii) pure gauge solutions
present in a similar calculation using the synchronous gauge vanish when the
spacelike hypersurfaces have extrinsic curvature with constant trace. We
furthermore verify the main conclusion of the synchronous gauge calculation
which is large-scale inhomogeneity decays if the matter--considered to be that
of a perfect-fluid with a barotropic equation of state--violates the
strong-energy condition. Finally, we obtain the solution for the lapse function
and discuss its late-time behaviour. It is found that the lapse function is
well-behaved when the matter violates the strong energy condition.",0507015v1
2006-05-04,Scaling Dynamics of Domain Walls in the Cubic Anisotropy Model,"We have investigated the dynamics of domain walls in the cubic anisotropy
model. In this model a global O(N) symmetry is broken to a set of discrete
vacua either on the faces, or vertices of a (hyper)cube. We compute the scaling
exponents for $2\le N\le 7$ in two dimensions on grids of $2048^2$ points and
compare them to the fiducial model of $Z_2$ symmetry breaking. Since the model
allows for wall junctions lattice structures are locally stable and
modifications to the standard scaling law are possible. However, we find that
since there is no scale which sets the distance between walls, the walls appear
to evolve toward a self-similar regime with $L\sim t$.",0605057v1
2006-07-27,D-term inflation in non-minimal supergravity,"D-term inflation is one of the most interesting and versatile models of
inflation. It is possible to implement naturally D-term inflation within high
energy physics, as for example SUSY GUTs, SUGRA, or string theories. D-term
inflation avoids the $\eta$-problem, while in its standard form it always ends
with the formation of cosmic strings. Given the recent three-year WMAP data on
the cosmic microwave background temperature anisotropies, we examine whether
D-term inflation can be successfully implemented in non-minimal supergravity
theories. We show that for all our choices of K\""ahler potential, there exists
a parameter space for which the predictions of D-term inflation are in
agreement with the measurements. The cosmic string contribution on the measured
temperature anisotropies is always dominant, unless the superpotential coupling
constant is fine tuned; a result already obtained for D-term inflation within
minimal supergravity. In conclusion, cosmic strings and their r\^ole in the
angular power spectrum cannot be easily hidden by just considering a non-flat
K\""ahler geometry.",0607226v2
2006-11-07,Making a Universe,"For understanding the origin of anisotropies in the cosmic microwave
background, rules to construct a quantized universe is proposed based on the
dynamical triangulation method of the simplicial quantum gravity. A
$d$-dimensional universe having the topology $ D^d $ is created numerically in
terms of a simplicial manifold with $d$-simplices as the building blocks. The
space coordinates of a universe are identified on the boundary surface $
S^{d-1} $, and the time coordinate is defined along the direction perpendicular
to $ S^{d-1} $. Numerical simulations are made mainly for 2-dimensional
universes, and analyzed to examine appropriateness of the construction rules by
comparing to analytic results of the matrix model and the Liouville theory.
Furthermore, a simulation in 4-dimension is made, and the result suggests an
ability to analyze the observations on anisotropies by comparing to the scalar
curvature correlation of a $ S^2 $-surface formed as the last scattering
surface in the $ S^3 $ universe.",0611076v2
1998-12-18,Growth Rates in the Quaquaversal Tiling,"Conway and Radin's ""quaquaversal"" tiling of R^3 is known to exhibit
statistical rotational symmetry in the infinite volume limit. A finite patch,
however, cannot be perfectly isotropic, and we compute the rates at which the
anisotropy scales with size. In a sample of volume N, tiles appear in
O(N^{1/6}) distinct orientations. However, the orientations are not uniformly
populated. A small (O(N^{1/84})) set of these orientations account for the
majority of the tiles. Furthermore, these orientations are not uniformly
distributed on SO(3). Sample averages of functions on SO(3) seem to approach
their ergodic limits as N^{-1/336}. Since even macroscopic patches of a
quaquaversal tiling maintain noticable anisotropy, a hypothetical physical
quasicrystal whose structure was similar to the quaquaversal tiling could be
identified by anisotropic features of its electron diffraction pattern.",9812018v2
2001-03-20,Staggered Anisotropy Parameter Modification of the Anisotropic $t-J$ Model,"The anisotropic t-J model ($U_q(gl(2|1))$ Perk-Schultz model) with staggered
disposition of the anisotropy parameter along a chain is considered and the
corresponding ladder type integrable model is constructed. This is a
generalisation to spin-1 case of the staggered $XXZ$ spin-1/2 model considered
earlier. The corresponding Hamiltonian is calculated and, since it contains
next to nearest neighbour interaction terms, can be written in a zig-zag form.
The Algebraic Bethe Ansatz technique is applied and the eigenstates, along with
eigenvalues of the transfer matrix of the model are found.",0103027v3
2002-07-05,Scaling Exponents in Anisotropic Hydrodynamic Turbulence,"In anisotropic turbulence the correlation functions are decomposed in the
irreducible representations of the SO(3) symmetry group (with different
""angular momenta"" $\ell$). For different values of $\ell$ the second order
correlation function is characterized by different scaling exponents
$\zeta_2(\ell)$. In this paper we compute these scaling exponents in a Direct
Interaction Approximation (DIA). By linearizing the DIA equations in small
anisotropy we set up a linear operator and find its zero-modes in the inertial
interval of scales. Thus the scaling exponents in each $\ell$-sector follow
from solvability condition, and are not determined by dimensional analysis. The
main result of our calculation is that the scaling exponents $\zeta_2(\ell)$
form a strictly increasing spectrum at least until $\ell=6$, guaranteeing that
the effects of anisotropy decay as power laws when the scale of observation
diminishes. The results of our calculations are compared to available
experiments and simulations.",0207011v2
2005-01-01,Equatorial and related non-equilibrium states in magnetization dynamics of ferromagnets: Generalization of Suhl's spin-wave instabilities,"We investigate the nonlinear dynamics underlying the evolution of a 2-D
nanoscale ferromagnetic film with uniaxial anisotropy in the presence of
perpendicular pumping. Considering the associated Landau-Lifshitz spin
evolution equation with Gilbert damping together with Maxwell equation for the
demagnetization field, we study the dynamics in terms of the stereographic
variable. We identify several new fixed points for suitable choice of external
field in a rotating frame of reference. In particular, we identify explicit
equatorial and related fixed points of the spin vector in the plane transverse
to the anisotropy axis when the pumping frequency coincides with the amplitude
of the static parallel field. We then study the linear stability of these novel
fixed points under homogeneous and spin wave perturbations and obtain a
generalized Suhl's instability criterion, giving the condition for exponential
growth of P-modes under spin wave perturbations. Two parameter phase diagrams
(in terms of amplitudes of static parallel and oscillatory perpendicular
magnetic fields) for stability are obtained, which differ qualitatively from
those for the conventional ferromagnetic resonance near thermal equilibrium and
are amenable to experimental tests.",0501002v2
2006-07-28,Combined effects of small scale anisotropy and compressibility on anomalous scaling of a passive scalar,"Model of a passive scalar field advected by the compressible Gaussian
strongly anisotropic velocity field with the covariance $\propto
\delta(t-t^{\prime})|{\bf x}-{\bf x^{\prime}}|^{2\epsilon}$ is studied by using
the field theoretic renormalization group and the operator product expansion.
The inertial-range stability of the corresponding scaling regime is
established. The anomalous scaling of the single-time structure functions is
studied and the corresponding anomalous exponents are calculated. Their
dependence on the compressibility parameter and anisotropy parameters is
analyzed. It is shown that, as in the isotropic case, the presence of
compressibility leads to the decreasing of the critical dimensions of the
important composite operators, i.e., the anomalous scaling is more pronounced
in the compressible systems. All calculations are done to the first order in
$\epsilon$.",0607066v3
1997-09-15,Azimuthal Anisotropies as Stringent Test for Nuclear Transport Models,"Azimuthal distributions of charged particles and intermediate mass fragments
emitted in Au+Au collisions at 600AMeV have been measured using the FOPI
facility at GSI-Darmstadt. Data show a strong increase of the in-plane
azimuthal anisotropy ratio with the charge of the detected fragment.
Intermediate mass fragments are found to exhibit a strong momentum-space
alignment with respect of the reaction plane. The experimental results are
presented as a function of the polar center-of-mass angle and over a broad
range of impact parameters. They are compared to the predictions of the Isospin
Quantum Molecular Dynamics model using three different parametrisations of the
equation of state. We show that such highly accurate data provide stringent
test for microscopic transport models and can potentially constrain separately
the stiffness of the nuclear equation of state and the momentum dependence of
the nuclear interaction.",9709004v1
1999-03-15,Azimuthal Anisotropy of $η$ and $π^{0}$ Mesons in Heavy-Ion Collisions at 2 AGeV,"Azimuthal distributions of $\eta$ and $\pi^{0}$ mesons emitted at midrapidity
in collisions of 1.9 AGeV $^{58}$Ni+$^{58}$Ni and 2 AGeV $^{40}$Ca+$^{nat}$Ca
are studied as a function of the number of projectile-like spectator nucleons.
The observed anisotropy corresponds to a negative elliptic flow signal for
$\eta$ mesons, indicating a preferred emission perpendicular to the reaction
plane. The effect is smallest in peripheral Ni+Ni collisions. In contrast, for
$\pi^{0}$ mesons, elliptic flow is observed only in peripheral Ni+Ni
collisions, changing from positive to negative sign with increasing pion
transverse momentum.",9903008v1
1999-10-05,Elliptic flow of $η$ and $π^{0}$ Mesons in Heavy-Ion Collisions at 2 AGeV,"Azimuthal distributions of $\eta$ and $\pi^{0}$ mesons emitted at midrapidity
in collisions of 1.9 AGeV $^{58}$Ni+$^{58}$Ni and 2 AGeV $^{40}$Ca+$^{nat}$Ca
are studied as a function of the number of projectile-like spectator nucleons.
The observed anisotropy corresponds to a negative elliptic flow signal for
$\eta$ mesons, indicating a preferred emission perpendicular to the reaction
plane. In contrast, only small azimuthal anisotropies are observed for
$\pi^{0}$ mesons. This may indicate that $\eta$ mesons freeze out earlier from
the fire ball than pions.",9910002v1
2003-06-04,Particle-type dependence of azimuthal anisotropy and nuclear modification of particle production in Au+Au collisions at s(NN)**(1/2) = 200-GeV,"We present STAR measurements of the azimuthal anisotropy parameter $v_2$ and
the binary-collision scaled centrality ratio $R_{CP}$ for kaons and lambdas
($\Lambda+\bar{\Lambda}$) at mid-rapidity in Au+Au collisions at
$\sqrt{s_{_{NN}}}=200$ GeV. In combination, the $v_2$ and $R_{CP}$
particle-type dependencies contradict expectations from partonic energy loss
followed by standard fragmentation in vacuum. We establish $p_T \approx 5$
GeV/c as the value where the centrality dependent baryon enhancement ends. The
$K_S^0$ and $\Lambda+\bar{\Lambda}$ $v_2$ values are consistent with
expectations of constituent-quark-number scaling from models of hadron
fromation by parton coalescence or recombination.",0306007v3
2003-06-20,High-p_T charged particle azimuthal correlations at RHIC,"The analysis of two-particle azimuthal correlation function in p+p and Au+Au
collisions at s(NN)**(1/2) 200 GeV/c is presented. The mean jet fragmentation
transverse momentum <|mjTy|> and mean parton transverse momentum <|kTy|> are
inferred from p+p collisions. The analysis of Au+Au data, where elliptic flow
is a dominant source of two-particles correlation is also presented. We derive
the upper limit on partonic azimuthal anisotropy based on jet-quenching in a
Glauber model. We show that some new mechanism, generating the azimuthal
anisotropy observed in final state, is needed.",0306031v3
2003-09-22,Statistical Multifragmentation of Non-Spherical Expanding Sources in Central Heavy-Ion Collisions,"We study the anisotropy effects measured with INDRA at GSI in central
collisions of Xe+Sn at 50 A.MeV and Au+Au at 60, 80, 100 A.MeV incident energy.
The microcanonical multifragmentation model with non-spherical sources is used
to simulate an incomplete shape relaxation of the multifragmenting system. This
model is employed to interpret observed anisotropic distributions in the
fragment size and mean kinetic energy. The data can be well reproduced if an
expanding prolate source aligned along the beam direction is assumed. An either
non-Hubblean or non-isotropic radial expansion is required to describe the
fragment kinetic energies and their anisotropy. The qualitative similarity of
the results for the studied reactions suggests that the concept of a
longitudinally elongated freeze-out configuration is generally applicable for
central collisions of heavy systems. The deformation decreases slightly with
increasing beam energy.",0309016v2
2004-07-09,Azimuthal anisotropy and correlations at large transverse momenta in $p+p$ and Au+Au collisions at $\sqrt{s_{_{NN}}}$= 200 GeV,"Results on high transverse momentum charged particle emission with respect to
the reaction plane are presented for Au+Au collisions at $\sqrt{s_{_{NN}}}$=
200 GeV. Two- and four-particle correlations results are presented as well as a
comparison of azimuthal correlations in Au+Au collisions to those in $p+p$ at
the same energy. Elliptic anisotropy, $v_2$, is found to reach its maximum at
$p_t \sim 3$ GeV/c, then decrease slowly and remain significant up to
$p_t\approx 7$ -- 10 GeV/c. Stronger suppression is found in the back-to-back
high-$p_t$ particle correlations for particles emitted out-of-plane compared to
those emitted in-plane. The centrality dependence of $v_2$ at intermediate
$p_t$ is compared to simple models based on jet quenching.",0407007v3
2004-12-21,Semihard scattering unraveled from collective dynamics at $\sqrt{s}$=17 GeV,"We present a study of elliptic flow ($v_2$) and two-particle azimuthal
correlations of charged hadrons and high transverse momentum ($p_T$) pions
measured by the CERES experiment in Pb+Au collisions at $\sqrt{s}$~=~17 GeV.
Azimuthal anisotropy $v_2$ increases linearly with $p_T$ to a value of 10% at
$p_T$~=~1.5 GeV/$c$. Beyond this $p_T$ the slope decreases indicating a
possible saturation at high $p_T$. Two-pion azimuthal anisotropies ($p_T>$~1.2
GeV/$c$) exceed $v_2$ by about 60% in semicentral collisions and reveal
non-harmonic contributions at close ($\Delta\phi\approx0$) and back-to-back
($\Delta\phi\approx\pi$) angles that can be attributed to semihard processes.
While the close-angle peak remains unchanged, the back-to-back peak is
broadened and disappears in central collisions.",0412047v1
2005-02-04,Measurement of Single Electron Event Anisotropy in Au+Au Collisions at sqrt(s_NN) = 200 GeV,"The transverse momentum dependence of the azimuthal anisotropy parameter v_2,
the second harmonic of the azimuthal distribution, for electrons at
mid-rapidity (|eta| < 0.35) has been measured with the PHENIX detector in Au+Au
collisions at sqrt(s_NN) = 200 GeV. The measurement was made with respect to
the reaction plane defined at high rapidities (|eta| = 3.1 -- 3.9). From the
result we have measured the v_2 of electrons from heavy flavor decay after
subtraction of the v_2 of electrons from other sources such as photon
conversions and Dalitz decay from light neutral mesons. We observe a non-zero
single electron v_2 with a 90% confidence level in the intermediate p_T region.",0502009v1
2005-09-08,Single Electron Transverse Momentum and Azimuthal Anisotropy Distributions: Charm Hadron Production at RHIC,"Quantum Chromodynamics (QCD) is a basic gauge field theory to describe strong
interactions. Lattice QCD calculations predict a phase transition from hadronic
matter to a deconfined, locally thermalized Quark-Gluon Plasma (QGP) state at
high temperature and small baryon density. Plenty of exciting results from RHIC
experiments in the first three years have demonstrated that a hot dense matter
with strong collective motion which cannot be described with hadronic degrees
of freedom was created at RHIC. Charm quarks are believed to be mostly created
from initial gluon fusion in heavy ion collisions. Since they are massive,
charm hadrons are proposed to be ideal probes to study the early stage dynamics
in heavy ion collisions.
  We provide here an indirect measurement of charm semi-leptonic decay. Single
electron transverse momentum ($p_T$) distributions from 200 GeV \dAu, \pp
collisions and 62.4 GeV \AuAu collisions, and single electron azimuthal
anisotropy ($v_2$) from 62.4 GeV \AuAu collisions are presented. (Abridged)",0509011v1
2005-10-07,Azimuthal Anisotropy of Identified Hadrons in 200 GeV Au+Au Collisions,"The azimuthal anisotropy parameter v2 has been measured with high statistics
for identified hadrons in sqrt(s_NN) = 200 GeV Au+Au collisions with the STAR
experiment. At high transverse momentum (pT) a strong v2 for pi+ + pi- and p +
pbar is observed. In the intermediate pT region, number-of-constituent-quark
scaling was tested to high precision. A detailed comparison of v2 for the
multi-strange hadrons phi, Xi + anti-Xi, and Omega + anti-Omega with other
particle species substantiates the development of collectivity among partons in
the early phase of the collisions at RHIC.",0510026v1
2006-12-07,Polarization and relaxation of radon,"Investigations of the polarization and relaxation of $^{209}$Rn by spin
exchange with laser optically pumped rubidium are reported. On the order of one
million atoms per shot were collected in coated and uncoated glass cells.
Gamma-ray anisotropies were measured as a signal of the alignment (second order
moment of the polarization) resulting from the combination of polarization and
quadrupole relaxation at the cell walls. The temperature dependence over the
range 130$^\circ$C to 220$^\circ$C shows the anisotropies increasing with
increasing temperature as the ratio of the spin exchange polarization rate to
the wall relaxation rate increases faster than the rubidium polarization
decreases. Polarization relaxation rates for coated and uncoated cells are
presented. In addition, improved limits on the multipole mixing ratios of some
of the main gamma-ray transitions have been extracted. These results are
promising for electric dipole moment measurements of octupole-deformed
$^{223}$Rn and other isotopes, provided sufficient quantities of the rare
isotopes can be produced.",0612006v1
1998-11-03,Remnants of Initial Anisotropic High Energy Density Domains in Nucleus-Nucleus Collisions,"Anisotropic high energy density domains may be formed at early stages of
ultrarelativistic heavy ion collisions, e.g. due to phase transition dynamics
or non-equilibrium phenomena like (mini-)jets. Here we investigate hadronic
observables resulting from an initially created anisotropic high energy density
domain. Based on our studies using a transport model we find that the initial
anisotropies are reflected in the freeze-out multiplicity distribution of both
pions and kaons due to secondary hadronic rescattering. The anisotropy appears
to be stronger for particles at high transverse momenta. The overall kaon
multiplicity increases with large fluctuations of local energy densities, while
no change has been found in the pion multiplicity.",9811006v2
1999-06-24,The physics of the centrality dependence of elliptic flow,"The centrality dependence of elliptic flow and how it is related to the
physics of expansion of the system created in high energy nuclear collisions is
discussed. Since in the hydro limit the centrality dependence of elliptic flow
is mostly defined by the elliptic anisotropy of the overlapping region of the
colliding nuclei, and in the low density limit by the product of the elliptic
anisotropy and the multiplicity, we argue that the centrality dependence of
elliptic flow should be a good indicator of the degree of equilibration reached
in the reaction. Then we analyze experimental data obtained at AGS and SPS
energies. The observed difference in the centrality dependence of elliptic flow
could imply a transition from a hadronic to a partonic nature of the system
evolution. Finally we exploit the multiplicity dependence of elliptic flow to
make qualitative predictions for RHIC and LHC.",9906075v3
2000-07-27,New method for measuring azimuthal distributions in nucleus-nucleus collisions,"The methods currently used to measure azimuthal distributions of particles in
heavy ion collisions assume that all azimuthal correlations between particles
result from their correlation with the reaction plane. However, other
correlations exist, and it is safe to neglect them only if azimuthal
anisotropies are much larger than 1/sqrt(N), with N the total number of
particles emitted in the collision. This condition is not satisfied at
ultrarelativistic energies. We propose a new method, based on a cumulant
expansion of multiparticle azimuthal correlations, which allows to measure much
smaller values of azimuthal anisotropies, down to 1/N. It is simple to
implement and can be used to measure both integrated and differential flow.
Furthermore, this method automatically eliminates the major systematic errors,
which are due to azimuthal asymmetries in the detector acceptance.",0007063v3
2003-05-05,"High-$p_T$ Hadron Spectra, Azimuthal Anisotropy and Back-to-Back Correlations in High-energy Heavy-ion Collisions","The observed suppression of high-$p_T$ hadron spectra, finite azimuthal
anisotropy, disappearance of jet-like back-to-back correlations, and their
centrality dependence in $Au+Au$ collisions at RHIC are shown to be
quantitatively described by jet quenching within a pQCD parton model. The
difference between $h^{\pm}$ and $\pi^0$ suppression in intermediate $p_T$ is
consistent with the observed $(K+p)/\pi$ enhancement which should disappear at
$p_T>6$ GeV/$c$. The suppression of back-to-back correlations is shown to be
directly related to the medium modification of jet fragmentation functions(FF).",0305010v4
2004-11-25,Spin Alignment of Vector Mesons in Non-central A+A Collisions,"We discuss the consequence of global polarization of the produced quarks in
non-central heavy-ion collisions on the spin alignment of vector mesons. We
show that the alignment is quite different for different hadronization
scenarios. These results can be tested directly by measuring the vector mesons'
alignment through angular distributions of the decay products with respect to
the reaction plane. Such angular distributions will give rise to azimuthal
anisotropy $v_2$ of the decay products in the collision frame. Constraints
provided by the data on the azimuthal anisotropy of hadron spectra at RHIC
points to a quark recombination scenario of hadronization.",0411101v2
2005-05-12,Anisotropy of flow and the order of phase transition in relativistic heavy ion collisions,"Using a hydrodynamical model we study how the order of phase transition in
the equation of state of strongly interacting matter affects single particle
spectra, elliptic flow and higher order anisotropies in Au+Au collisions at
RHIC (sqrt{s_NN}=200 GeV energy). We find that the single particle spectra are
independent of the order of phase transition and that the fourth harmonic
v_4(p_T) shows only a weak dependence in the p_T region where hydrodynamics is
expected to work. The differential elliptic flow, v_2(p_T), of baryons shows
the strongest dependence on equation of state. Surprisingly the closest fit to
data was obtained when the equation of state had a strong first order phase
transition and a lattice inspired equation of state fits the data as badly as a
purely hadronic equation of state.",0505036v2
2005-11-28,Elliptic flow of thermal photons in relativistic nuclear collisions,"We predict the transverse momentum (pT) dependence of elliptic flow of
thermal photons for Au+Au collisions at the Relativistic Heavy Ion Collider. We
model the system hydrodynamically, assuming formation of a thermalized
quark-gluon plasma at some early time, followed by cooling through expansion,
hadronization and decoupling. Photons are emitted throughout the expansion
history. Contrary to hadron elliptic flow, which hydrodynamics predicts to
increase monotonically with pT, the elliptic flow of thermal photons is
predicted to first rise and then fall again as pT increases. Photon elliptic
flow at high pT is shown to reflect the quark momentum anisotropy at early
times when it is small, whereas at low pT it is controlled by the much larger
pion momentum anisotropy during the late hadronic emission stage. An
interesting structure is predicted at intermediate pT ~ 0.4 GeV/c where photon
elliptic flow reflects the momenta and the (compared to pions) reduced v2 of
heavy vector mesons in the late hadronic phase.",0511079v2
1998-09-20,Parametrically forced sine-Gordon equation and domain walls dynamics in ferromagnets,"A parametrically forced sine-Gordon equation with a fast periodic {\em
mean-zero} forcing is considered. It is shown that $\pi$-kinks represent a
class of solitary-wave solutions of the equation. This result is applied to
quasi-one-dimensional ferromagnets with an easy plane anisotropy, in a rapidly
oscillating magnetic field. In this case the $\pi$-kink solution we have
introduced corresponds to the uniform ``true'' domain wall motion, since the
magnetization directions on opposite sides of the wall are anti-parallel. In
contrast to previous work, no additional anisotropy is required to obtain a
true domain wall. Numerical simulations showed good qualitative agreement with
the theory.",9809008v1
2000-04-28,"The Exchange-correlation Hole of the Si Atom, A Quantum Monte Carlo Study","We have studied the exchange-correlation hole and pair correlation function
in the valence shell of the ground-state of the Si atom, using accurate
Slater-Jastrow wavefunctions and the Variational Monte Carlo method. The
exchange-correlation hole shows a number of interesting features caused by the
open shell structure of Si, including a marked transition from efficient to
poor screening behavior as a test majority-spin electron is moved from the
center of a valence 3p orbital onto the axis perpendicular to the occupied 3p
orbitals. This behavior results from the dramatic difference in the exchange
hole in the two cases, which is partially compensated by a corresponding
anisotropy in the correlation hole. In addition we observe an anisotropic
change in the spin density induced by Coulomb correlation, reducing the spatial
overlap between the different spin-components of the density and contributing
to the anisotropy of the correlation hole. In contrast to the longer range
features, we find that the ""on-top"" correlation hole is well described by
linear density functional theory, for a large range of local density and
magnetization.",0004073v1
2000-09-04,Test of Cosmic Spatial Isotropy for Polarized Electrons Using a Rotatable Torsion Balance,"To test the cosmic spatial isotropy, we use a rotatable torsion balance
carrying a transversely spin-polarized ferrimagnetic Dy_{6}Fe_{23} mass. With a
rotation period of one hour, the period of anisotropy signal is reduced from
one sidereal day by about 24 times, and hence the 1/f noise is greatly reduced.
Our present experimental results constrain the cosmic anisotropy Hamiltonian H
= C_{1} sigma_{1} + C_{2} sigma_{2} + C_{3} sigma_{3} (sigma_{3} is in the axis
of earth rotation) to (C_{1}^{2} +C_{2}^{2})^{1/2} = (1.8 +- 5.3) X 10^{-21} eV
and | C_{3} | = (1.2 +- 3.5) X 10^{-19} eV. This improves the previous limits
on (C_{1},C_{2}) by 120 times and C_{3} by a factor of 800.",0009012v1
2000-09-13,Average observed properties of the Earth's quasi-perpendicular and quasi-parallel bow shock,"We present a statistical analysis of 132 dayside (LT 0700-1700) bow shock
crossings of the AMPTE/IRM spacecraft. We perform a superposed epoch analysis
of plasma and magnetic field parameters as well as of low frequency magnetic
power spectra some minutes upstream and downstream of the bow shock by dividing
the events into categories depending on the angle between bow shock normal and
interplanetary magnetic field and on the plasma-beta, i.e., the ratio of plasma
to magnetic pressure.
  Downstream of the quasi-perpendicular low-beta (beta < 0.5) bow shock we find
a dominance of the left-hand polarized component at frequencies just below the
ion cyclotron frequency with amplitudes of about 3 nT. These waves are
identified as ion cyclotron waves which grow in a low-beta regime due to the
proton temperature anisotropy. We find a strong correlation of this anisotropy
with the intensity of the left-hand polarized component. Downstream of some
nearly perpendicular high-beta (beta > 1.0) crossings mirror waves are
identified. However, there are also cases where the conditions for mirror modes
are met downstream of the nearly perpendicular shock, but no mirror waves are
observed.",0009046v1
2001-01-29,An Atomic Linear Stark Shift Violating P But Not T Arising From the Electroweak Nuclear Anapole Moment,"We propose a direct method of detection of the nuclear anapole moment. It is
based on the existence of a linear Stark shift for alkali atoms in their ground
state perturbed by a quadrupolar interaction potential and a magnetic field.
This shift is proportional to the T-even pseudoscalar built from the
quadrupolar potential symmetry axis, the directions of the applied electric and
magnetic fields.It involves on the one hand the anisotropy of the hyperfine
interaction induced by the quadrupolar interaction and, on the other,the static
electric dipole moment arising from electroweak interactions inside the
nucleus. The case of ground state cesium atoms trapped in a uniaxial (hcp)
phase of solid helium-4 is examined. From an explicit evaluation of both the
hyperfine structure anisotropy and the static P-odd T-even dipole deduced from
recent empirical data about the cesium nuclear anapole moment, we predict the
Stark shift. It is three times the experimental upper bound to be set on the
T-odd Stark shift of free cesium atoms in order to improve the present limit on
the electron EDM.",0101098v1
2001-02-28,Experimental investigations of spatial distribution anisotropy of pulsed plasma generator radiation,"Results of experimental investigation of plasma luminous emittance
(integrated with respect to time and quartz transmission band spectrum) of a
pulsed plasma generator depending on its axis spatial position, are presented.
It is shown that the spatial distribution of plasma radiant intensity is of
clearly anisotropic character, that is, there exists a cone of the plasma
generator axial directions in which the radiation of plasma reaches its peak. A
possible explanation of the results obtained is given based on a hypothesis of
global anisotropy of space caused by the existence of a cosmological vectorial
potential $\bf{A}_g$. It is shown that the vector $\bf{A}_g$ has the following
coordinates in the second equatorial coordinate system: right ascension $\alpha
= 293^\circ \pm 10^\circ$, declination $\delta = 36^\circ \pm 10^\circ$. The
experimental results are in accordance with those of the earlier experiments on
determining the direction of $\bf{A}_g$.",0102090v1
2001-11-05,Evolution of induced axial magnetization in a two-component magnetized plasma,"In this paper, the evolution of the induced axial magnetization due to the
propagation of an electromagnetic (em) wave along the static background
magnetic field in a two-component plasma has been investigated using the Block
equation. The evolution process induces a strong magnetic anisotropy in the
plasma medium, depending nonlinearly on the incident wave amplitude. This
induced magnetic anisotropy can modify the dispersion relation of the incident
em wave, which has been obtained in this paper. In the low frequency Alfven
wave limit, this dispersion relation shows that the resulting phase velocity of
the incident wave depends on the square of the incident wave amplitude and on
the static background magnetic field of plasma. The analytical results are in
well agreement with the numerically estimated values in solar corona and
sunspots.",0111011v1
2002-04-18,Physical Properties of Iron in the Inner Core,"The Earth's inner core plays a vital role in the dynamics of our planet and
is itself strongly exposed to dynamic processes as evidenced by a complex
pattern of elastic structure. To gain deeper insight into the nature of these
processes we rely on a characterization of the physical properties of the inner
core which are governed by the material physics of its main constituent, iron.
Here we review recent research on structure and dynamics of the inner core,
focusing on advances in mineral physics. We will discuss results on core
composition, crystalline structure, temperature,and various aspects of
elasticity. Based on recent computational results, we will show that aggregate
seismic properties of the inner core can be explained by temperature and
compression effects on the elasticity of pure iron, and use single crystal
anisotropy to develop a speculative textural model of the inner core that can
explain major aspects of inner core anisotropy.",0204055v1
2002-12-20,Orbital magnetism in axially deformed sodium clusters: From scissors mode to dia-para magnetic anisotropy,"Low-energy orbital magnetic dipole excitations, known as scissors mode (SM),
are studied in alkali metal clusters. Subsequent dynamic and static effects are
explored. The treatment is based on a self-consistent microscopic approach
using the jellium approximation for the ionic background and the Kohn-Sham mean
field for the electrons. The microscopic origin of SM and its main features
(structure of the mode in light and medium clusters, separation into low- and
high-energy plasmons, coupling high-energy M1 scissors and E2 quadrupole
plasmons, contributions of shape isomers, etc) are discussed. The scissors M1
strength acquires large values with increasing cluster size. The mode is
responsible for the van Vleck paramagnetism of spin-saturated clusters. Quantum
shell effects induce a fragile interplay between Langevin diamagnetism and van
Vleck paramagnetism and lead to a remarkable dia-para anisotropy in magnetic
susceptibility of particular light clusters. Finally, several routes for
observing the SM experimentally are discussed.",0212084v1
2003-05-09,The particle-in-cell model for ab initio thermodynamics: implications for the elastic anisotropy of the Earth's inner core,"We assess the quantitative accuracy of the particle-in-cell (PIC)
approximation used in recent ab initio predictions of the thermodynamic
properties of hexagonal-close-packed iron at the conditions of the Earth's
inner core. The assessment is made by comparing PIC predictions for a range of
thermodynamic properties with the results of more exact calculations that avoid
the PIC approximation. It is shown that PIC gives very accurate results for
some properties, but that it gives an incorrect treatment of anharmonic lattice
vibrations. In addition, our assessment does not support recent PIC-based
predictions that the hexagonal c/a ratio increases strongly with increasing
temperature, and we point out that this casts doubt on a proposed
re-interpretation of the elastic anisotropy of the inner core.",0305033v2
2003-07-02,Oblique frozen modes in periodic layered media,"We study the classical scattering problem of a plane electromagnetic wave
incident on the surface of semi-infinite periodic stratified media
incorporating anisotropic dielectric layers with special oblique orientation of
the anisotropy axes. We demonstrate that an obliquely incident light, upon
entering the periodic slab, gets converted into an abnormal grazing mode with
huge amplitude and zero normal component of the group velocity. This mode
cannot be represented as a superposition of extended and evanescent
contributions. Instead, it is related to a general (non-Bloch) Floquet
eigenmode with the amplitude diverging linearly with the distance from the slab
boundary. Remarkably, the slab reflectivity in such a situation can be very
low, which means an almost 100% conversion of the incident light into the
axially frozen mode with the electromagnetic energy density exceeding that of
the incident wave by several orders of magnitude. The effect can be realized at
any desirable frequency, including optical and UV frequency range. The only
essential physical requirement is the presence of dielectric layers with proper
oblique orientation of the anisotropy axes. Some practical aspects of this
phenomenon are considered.",0307021v1
2004-09-21,The axial ratio of hcp iron at the conditions of the Earth's inner core,"We present ab initio calculations of the high-temperature axial c/a ratio of
hexagonal-close-packed (hcp) iron at Earth's core pressures, in order to help
interpret the observed seismic anisotropy of the inner core. The calculations
are based on density functional theory, which is known to predict the
properties of high-pressure iron with good accuracy. The temperature dependence
of c/a is determined by minimising the Helmholtz free energy at fixed volume
and temperature, with thermal contributions due to lattice vibrations
calculated using harmonic theory. Anharmonic corrections to the harmonic
predictions are estimated from calculations of the thermal average stress
obtained from ab initio molecular dynamics simulations of hcp iron at the
conditions of the inner core. We find a very gradual increase of axial ratio
with temperature. This increase is much smaller than found in earlier
calculations, but is in reasonable agreement with recent high-pressure,
high-temperature diffraction measurements. This result casts doubt on an
earlier interpretation of the seismic anisotropy of the inner core.",0409109v1
2004-10-19,Drift ordered short mean free path closure,"The complete short mean free path description of magnetized plasma in the
drift ordering has recently been derived. The results correct the previous
expressions for the ion pressure anisotropy (or parallel ion viscosity) and the
perpendicular ion viscosity - the ion gyro-viscosity is unchanged. In addition,
the electron problem is solved for the first time to obtain the electron
pressure anisotropy (parallel electron viscosity) and the electron
gyro-viscosity - the perpendicular electron viscosity is negligible. The
results have been used to obtain a reduced fluid description appropriate to the
edge of a tokamak. In addition, the complete description has been used to
evaluate the radial transport of toroidal angular momentum that determines the
radial electric field and flows in a tokamak.",0410154v1
2005-03-17,Relationship between acoustic body waves and in situ stresses around a borehole,"This paper shows that there are three types of shape of acoustic body waves
propagating inside competent and homogeneous formations penetrated by a
borehole : simple, double, and resonant. This fact is connected to the
modifications undergone by the area located around a well after drilling in
relation to in situ state of stress. There are overstressed and understressed
vertical cylindrical zones with ""bubble-shaped"" cross-sections, in which
acoustic body waves are supposed to reflect. The horizontal size and the shape
of the stress modified areas depend on the values of (K1+K2)/2 - with K1=SH/Sv
(the overburden pressure) and K2=Sh/Sv -, that is to say on the in situ
horizontal stress and the anisotropy of this stress. The calculation of the
velocities of the P and S double waves allows us to evaluate the radial
thicknesses of these stress modified areas. As their values are different
according to whether they result from P or S waves, we propose an explanation
based on their wavelengths. The comparisons with other works on the in situ
stress of the studied boreholes allow us to propose a method for evaluating the
horizontal stress and its anisotropy, thanks to the estimation of the value
(K1+K2)/2.",0503153v1
2006-06-10,Non-dipole angular anisotropy parameters of semi-filled shell atoms,"We present the results of calculations of outer shell non-dipole angular
anisotropy parameters for semi-filled shell atoms in the Hartree-Fock (HF)
one-electron approximation and with account of inter-electron correlations in
the frame of the Spin Polarized Random Phase Approximation with Exchange (SP
RPAE). We demonstrate for the first time that this characteristic of
photoionization process is essentially sensitive to the fact whether the
photoelectron has the same or opposite spin orientation to that of the
semi-filled shell.",0606093v2
2007-02-06,Force transmission in a packing of pentagonal particles,"We perform a detailed analysis of the contact force network in a dense
confined packing of pentagonal particles simulated by means of the contact
dynamics method. The effect of particle shape is evidenced by comparing the
data from pentagon packing and from a packing with identical characteristics
except for the circular shape of the particles. A counterintuitive finding of
this work is that, under steady shearing, the pentagon packing develops a lower
structural anisotropy than the disk packing. We show that this weakness is
compensated by a higher force anisotropy, leading to enhanced shear strength of
the pentagon packing. We revisit ""strong"" and ""weak"" force networks in the
pentagon packing, but our simulation data provide also evidence for a large
class of ""very weak"" forces carried mainly by vertex-to-edge contacts. The
strong force chains are mostly composed of edge-to-edge contacts with a marked
zig-zag aspect and a decreasing exponential probability distribution as in a
disk packing.",0702055v1
1999-03-12,A Possible Anisotropy in Blackbody Radiation Viewed through Non-uniform Gaseous Matter,"A non-local gauge symmetry of a complex scalar field, which can be trivially
extended to spinor fields, was demonstrated in a recent paper (Mod.Phys.Lett.
A13, 1265 (1998) ; hep-th/9902020). The corresponding covariant Lagrangian
density yielded a new, non-local Quantum Electrodynamics. In this letter we
show that as a consequence of this new QED, a blackbody radiation viewed
through gaseous matter appears to show a slight deviation from the Planck
formula, and propose an experimental test to check this effect. We also show
that a non-uniformity in this gaseous matter distribution leads to an
(apparent) spatial anisotropy in the blackbody radiation.",9903043v2
2003-09-25,Correlation Functions in Spin Chains and Information Theory,"Antiferromagnetic spin chains play an important role in condensed matter
physics and statistical mechanics. Recently XXX spin chain was discussed in
relation to the information theory. We consider here localizable entanglement,
introduced recently by F.Verstraete, M.Popp and J.I.Cirac. That is how much
entanglement can be localized on two spins on average by performing local
measurements on the other individual spins in a system of many interacting
spins. We consider the ground state in antiferromagnetic spin chains and study
localizable entanglement between two spins as a function of the distance. We
start with isotropic spin chain.
  Then we study effect of anisotropy and magnetic field. We conclude that
anisotropy increases localizable entanglement. We found an explicit dependence
of critical exponents in XXZ spin chain on magnetic field. We discovered that
the cases of high symmetry corresponds to high sensitivity of magnetic field.
We also calculated the concurrence before the measurement to illustrate that
the measurment raises the concurrence.",0309188v3
2003-12-03,Entanglement and Quantum Phases in the Anisotropic Ferromagnetic Heisenberg Chain in the Presence of Domain Walls,"We discuss entanglement in the spin-1/2 anisotropic ferromagnetic Heisenberg
chain in the presence of a boundary magnetic field generating domain walls. By
increasing the magnetic field, the model undergoes a first-order quantum phase
transition from a ferromagnetic to a kink-type phase, which is associated to a
jump in the content of entanglement available in the system. Above the critical
point, pairwise entanglement is shown to be non-vanishing and independent of
the boundary magnetic field for large chains. Based on this result, we provide
an analytical expression for the entanglement between arbitrary spins. Moreover
the effects of the quantum domains on the gapless region and for
antiferromagnetic anisotropy are numerically analysed. Finally multiparticle
entanglement properties are considered, from which we establish a
characterization of the critical anisotropy separating the gapless regime from
the kink-type phase.",0312039v3
2007-04-02,Huge magneto-crystalline anisotropy of x-ray linear dichroism observed on Co/FeMn bilayers,"We present an x-ray spectromicroscopic investigation of single-crystalline
magnetic FeMn/Co bilayers on Cu(001), using X-ray magnetic circular (XMCD) and
linear (XMLD) dichroism at the Co and Fe L3 absorption edges in combination
with photoelectron emission microscopy (PEEM). Using the magnetic coupling
between the ferromagnetic Co layer and the antiferromagnetic FeMn layer we are
able to produce magnetic domains with two different crystallographic
orientations of the magnetic easy axis within the same sample at the same time.
We find a huge difference in the XMLD contrast between the two types of
magnetic domains, which we discuss in terms of intrinsic magneto-crystalline
anisotropy of XMLD of the Co layer. We also demonstrate that due to the high
sensitivity of the method, the small number of induced ferromagnetic Fe moments
at the FeMn-Co interface is sufficient to obtain magnetic contrast from XMLD in
a metallic system.",0704.0182v1
2007-04-03,Possibility of Gapless Spin Liquid State by One-dimensionalization,"Motivated by the observation of a gapless spin liquid state in
$\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$, we analyze the anisotropic triangular
lattice $S=1/2$ Heisenberg model with the resonating valence bond mean-field
approximation. Paying attention to the small quasi-one-dimensional anisotropy
of the material, we take an approach from one-dimensional (1D) chains coupled
with frustrating zig-zag bonds. By calculating one-particle excitation spectra
changing anisotropy parameter $J'/J$ from the decoupled 1D chains to the
isotropic triangular lattice, we find almost gapless excitations in the wide
range from the 1D limit. This one-dimensionalization by frustration is
considered to be a candidate for the mechanism of the gapless spin liquid
state.",0704.0313v1
2007-04-04,Ising-like dynamics and frozen states in systems of ultrafine magnetic particles,"We use Monte-Carlo simulations to study aging phenomena and the occurence of
spinglass phases in systems of single-domain ferromagnetic nanoparticles under
the combined influence of dipolar interaction and anisotropy energy, for
different combinations of positional and orientational disorder. We find that
the magnetic moments oriente themselves preferably parallel to their anisotropy
axes and changes of the total magnetization are solely achieved by 180 degree
flips of the magnetic moments, as in Ising systems. Since the dipolar
interaction favorizes the formation of antiparallel chain-like structures,
antiparallel chain-like patterns are frozen in at low temperatures, leading to
aging phenomena characteristic for spin-glasses. Contrary to the intuition,
these aging effects are more pronounced in ordered than in disordered
structures.",0704.0580v1
2007-04-12,Green function theory versus Quantum Monte Carlo calculations for thin magnetic films,"In this work we compare numerically exact Quantum Monte Carlo (QMC)
calculations and Green function theory (GFT) calculations of thin ferromagnetic
films including second order anisotropies. Thereby we concentrate on easy plane
systems, i.e. systems for which the anisotropy favors a magnetization parallel
to the film plane. We discuss these systems in perpendicular external field,
i.e. B parallel to the film normal. GFT results are in good agreement with QMC
for high enough fields and temperatures. Below a critical field or a critical
temperature no collinear stable magnetization exists in GFT. On the other hand
QMC gives finite magnetization even below those critical values. This indicates
that there occurs a transition from non-collinear to collinear configurations
with increasing field or temperature. For slightly tilted external fields a
rotation of magnetization from out-of-plane to in-plane orientation is found
with decreasing temperature.",0704.1552v1
2007-04-23,CMB and LSS constraints on a single-field model of inflation,"A new inflationary scenario whose exponential potential $V(\Phi)$ has a
quadratic dependence on the field $\Phi$ in addition to the standard linear
term is confronted with the tree-year observations of the Wilkinson-Microwave
Anisotropy Probe and the Sloan Digital Sky Survey data. The number of e-folds
($N$), the ratio of tensor-to-scalar perturbations ($r$), the spectral scalar
index of the primordial power spectrum ($n_s$) and its running ($dn_s/d\ln k$)
depend on the dimensionless parameter $\alpha$ multiplying the quadratic term
in the potential. In the limit $\alpha \to 0$ all the results of the standard
exponential potential are fully recovered. For values of $\alpha \neq 0$, we
find that the model predictions are in good agreement with the current
observations of the Cosmic Microwave Background (CMB) anisotropies and
Large-Scale Structure (LSS) in the Universe.",0704.3043v1
2007-04-27,Cosmic Rays: The Second Knee and Beyond,"We conduct a review of experimental results on Ultra-High Energy Cosmic Rays
(UHECR's) including measurements of the features of the spectrum, the
composition of the primary particle flux and the search for anisotropy in event
arrival direction. We find that while there is a general consensus on the
features in the spectrum -- the Second Knee, the Ankle, and (to a lesser
extent) the GZK Cutoff -- there is little consensus on the composition of the
primaries that accompany these features. This lack of consensus on the
composition makes interpretation of the agreed upon features problematic. There
is also little direct evidence about potential sources of UHECRs, as early
reports of arrival direction anisotropies have not been confirmed in
independent measurements.",0704.3721v1
2007-05-03,Planar spin-transfer device with a dynamic polarizer,"In planar nano-magnetic devices magnetization direction is kept close to a
given plane by the large easy-plane magnetic anisotropy, for example by the
shape anisotropy in a thin film. In this case magnetization shows effectively
in-plane dynamics with only one angle required for its description. Moreover,
the motion can become overdamped even for small values of Gilbert damping. We
derive the equations of effective in-plane dynamics in the presence of
spin-transfer torques. The simplifications achieved in the overdamped regime
allow to study systems with several dynamic magnetic pieces (``free layers'').
A transition from a spin-transfer device with a static polarizer to a device
with two equivalent magnets is observed. When the size difference between the
magnets is less than critical, the device does not exhibit switching, but goes
directly into the ``windmill'' precession state.",0705.0406v1
2007-05-05,Damped Corrections to Inflationary Spectra from a Fluctuating Cutoff,"We reconsider trans-Planckian corrections to inflationary spectra by taking
into account a physical effect which has been overlooked and which could have
important consequences. We assume that the short length scale characterizing
the new physics is endowed with a finite width, the origin of which could be
found in quantum gravity. As a result, the leading corrections responsible for
superimposed osillations in the CMB temperature anisotropies are generically
damped by the blurring of the UV scale. To determine the observational
ramifications of this damping, we compare it to that which effectively occurs
when computing the angular power spectrum of temperature anisotropies. The
former gives an overall change of the oscillation amplitudes whereas the latter
depends on the angular scale. Therefore, in principle they could be
distinguished. In any case, the observation of superimposed oscillations would
place tight constraint on the variance of the UV cutoff.",0705.0747v1
2007-05-17,Predicting and Understanding Order of Heteroepitaxial Quantum Dots,"Heteroepitaxial self-assembled quantum dots (SAQDs) will allow breakthroughs
in electronics and optoelectronics. SAQDs are a result of Stranski-Krastanow
growth whereby a growing planar film becomes unstable after an initial wetting
layer is formed. Common systems are Ge$_{x}$Si$_{1-x}$/Si and
In$_{x}$Ga$_{1-x}$As/GaAs. For applications, SAQD arrays need to be ordered.
The role of crystal anisotropy, random initial conditions and thermal
fluctuations in influencing SAQD order during early stages of SAQD formation is
studied through a simple stochastic model of surface diffusion. Surface
diffusion is analyzed through a linear and perturbatively nonlinear analysis.
The role of crystal anisotropy in enhancing SAQD order is elucidated. It is
also found that SAQD order is enhanced when the deposited film is allowed to
evolve at heights near the critical wetting surface height that marks the onset
of non-planar film growth.",0705.2601v1
2007-05-18,Unconventional superconducting pairing by conventional phonons,"The common wisdom that the phonon mechanism of electron pairing in the
weak-coupling Bardeen-Cooper-Schrieffer (BCS) superconductors leads to
conventional s-wave Cooper pairs is revised. An inevitable anisotropy of sound
velocity in crystals makes the phonon-mediated attraction of electrons
non-local in space providing unconventional Cooper pairs with a nonzero orbital
momentum in a wide range of electron densities. As a result of this anisotropy
quasi-two dimensional charge carriers undergo a quantum phase transition from
an unconventional d-wave superconducting state to a conventional s-wave
superconductor with more carriers per unit cell. In the opposite
strong-coupling regime rotational symmetry breaking appears as a result of a
reduced Coulomb repulsion between unconventional bipolarons dismissing thereby
some constraints on unconventional pairing in the Bose-Einstein condensation
(BEC) limit. The conventional phonons, and not superexchange, are shown to be
responsible for the d-wave symmetry of cuprate superconductors, where the
on-site Coulomb repulsion is large.",0705.2697v2
2007-05-22,Spinon-holon interactions in an anisotropic t-J chain: a comprehensive study,"We consider a generalization of the one-dimensional t-J model with
anisotropic spin-spin interactions. We show that the anisotropy leads to an
effective attractive interaction between the spinon and holon excitations,
resulting in a localized bound state. Detailed quantitative analytic
predictions for the dependence of the binding energy on the anisotropy are
presented, and verified by precise numerical simulations. The binding energy is
found to interpolate smoothly between a finite value in the t-Jz limit and zero
in the isotropic limit, going to zero exponentially in the vicinity of the
latter. We identify changes in spinon dispersion as the primary factor for this
non-trivial behavior.",0705.3255v3
2007-05-23,Dust Distribution during Reionization,"The dust produced by the first generation of stars will be a foreground to
cosmic microwave background. In order to evaluate the effect of this early
dust, we calculate the power spectrum of the dust emission anisotropies and
compare it with the sensitivity limit of the Planck satellite. The spatial
distribution of the dust is estimated through the distribution of dark matter.
At small angular scales ($\ell \gtrsim 1000$) the dust signal is found to be
noticeable with the Planck detector for certain values of dust lifetime and
production rates. The dust signal is also compared to sensitivities of other
instruments. The early dust emission anisotropies are finally compared to those
of local dust and they are found to be similar in magnitude at mm wavelengths.",0705.3403v2
2007-06-04,CMB Constraint on Radion Evolution in the Brane World Scenario,"In many versions of brane model, the modulus field of extra dimensions, the
radion, could have cosmological evolution, which induces variation of the Higgs
vacuum expectation value, $<H>$, resulting in cosmological variation of the
electron mass $m_e$. The formation of Cosmic Microwave Background (CMB)
anisotropies is thus affected, causing changes both in the peaks positions and
amplitudes in the CMB power spectra. Using the three-year Wilkinson Microwave
Anisotropies Probe (WMAP) CMB data, with the Hubble parameter $H_0$ fixed to be
the Hubble Space Telescope (HST) result 72 km s$^{-1}$ Mpc$^{-1}$, we obtain a
constraint on $\rho$, the ratio of the value of $<H>$ at CMB recombination to
its present value, to be [0.97, 1.02].",0706.0391v2
2007-06-04,The shear viscosity of the non-commutative plasma,"We compute the shear viscosity of the non-commutative N=4 super Yang-Mills
quantum field theory at strong coupling using the dual supergravity background.
Special interest derives from the fact that the background presents an
intrinsic anisotropy in space through the distinction of commutative and
non-commutative directions. Despite this anisotropy the analysis exhibits the
ubiquitous result \eta/s = 1/4\pi for two different shear channels. In order to
derive this result, we show that the boundary energy momentum tensor must
couple to the open string metric. As a byproduct we compute the renormalised
holographic energy momentum tensor and show that it coincides with one in the
commutative theory.",0706.0411v2
2007-06-07,Meta-nematic transitions in a bilayer system: Application to the bilayer ruthenate,"It was suggested that the two consecutive metamagnetic transitions and the
large residual resistivity discovered in Sr$_3$Ru$_2$O$_7$ can be understood
via the nematic order and its domains in a single layer system. However, a
recently reported anisotropy between two longitudinal resistivities induced by
tilting the magnetic field away from the c-axis cannot be explained within the
single layer nematic picture. To fill the gap in our understanding within the
nematic order scenario, we investigate the effects of bilayer coupling and
in-plane magnetic field on the electronic nematic phases in a bilayer system.
We propose that the in-plane magnetic field in the bilayer system modifies the
energetics of the domain formation, since it breaks the degeneracy of two
different nematic orientations. Thus the system reveals a pure nematic phase
with a resistivity anisotropy in the presence of an in-plane magnetic field. In
addition to the nematic phase, the bilayer coupling opens a novel route to a
hidden nematic phase that preserves the x-y symmetry of the Fermi surfaces.",0706.1069v3
2007-06-19,Logarithmic growth law in the two-dimensional Ising spin glass state resulting from the electron doping in single-layered manganites,"The ac-susceptibility of the electron doped single-layered manganite
La$_{1.1}$Sr$_{0.9}$MnO$_4$ is analyzed in detail. A quasi two-dimensional
(2$D$) antiferromagnetic (AFM) order with Ising anisotropy is stabilized below
$T_N$ $\sim$ 80K. We show that below $T_N$, a rare 2$D$ spin-glass (SG)
correlation develops with the same Ising anisotropy as the AFM state. Using
simple scaling arguments of the droplet model, we derive a scaling form for the
ac-susceptibility data of a 2$D$ SG, which our experimental data follows fairly
well. Due to simplifications in this 2$D$ case, the proposed scaling form only
contains two unknown variables $\psi\nu$ and $\tau_0$. Hence, the logarithmic
growth law of the SG correlation predicted by the droplet model is convincingly
evidenced by the scaling of our experimental data. The origin and nature of
this 2$D$ SG state is also discussed.",0706.2691v1
2007-06-21,Super Heavy Dark Matter and UHECR Anisotropy at Low Energy,"Super Heavy quasi-stable particles are naturally produced in the early
universe and could represent a substantial fraction of the Dark Matter: the
so-called Super Heavy Dark Matter (SHDM). The decay of SHDM represents also a
possible source of Ultra High Energy Cosmic Rays (UHECR), with a reliably
calculated spectrum of the particles produced in the decay $(\propto
E^{-1.9})$. The SHDM model for the production of UHECR can explain
quantitatively only the excess of UHE events observed by AGASA. In the case of
an observed spectrum not showing the AGASA excess the SHDM model can provide
only a {\it subdominant} contribution to the UHECR flux. We discuss here the
basic features of SHDM for the production of a {\it subdominant} UHECR flux, we
refer our study to the possible signatures of the model at the Auger
observatory discussing in particular the expected chemical composition and
anisotropy.",0706.3196v2
2007-06-25,A coverage independent method to analyze large scale anisotropies,"The arrival time distribution of cosmic ray events is well suited to extract
information regarding sky anisotropies. For an experiment with nearly constant
exposure, the frequency resolution one can achieve is given by the inverse of
the time $T$ during which the data was recorded. For $T$ larger than one
calendar year the resolution becomes sufficient to resolve the sidereal and
diurnal frequencies. Using a Fourier expansion on a modified time parameter, we
show in this note that one can accurately extract sidereal modulations without
knowledge of the experimental coverage. This procedure also gives the full
frequency pattern of the event sample under studies which contains important
information about possible systematics entering in the sidereal analysis. We
also show how this method allows to correct for those systematics. Finally, we
show that a two dimensional analysis, in the form of the spherical harmonic
($Y_l^m$) decomposition, can be performed under the same conditions for all
$m\ne 0$.",0706.3705v1
2007-06-26,Cosmic Microwave Background Quadrupole and Ellipsoidal Universe,"Recent Wilkinson Microwave Anisotropy Probe (WMAP) data confirm the Cosmic
Microwave Background (CMB) quadrupole anomaly. We further elaborate our
previous proposal that the quadrupole power can be naturally suppressed in
axis-symmetric universes. In particular, we discuss in greater detail the CMB
quadrupole anisotropy and considerably improve our analysis. As a result, we
obtain tighter constraints on the direction of the axis of symmetry as well as
on the eccentricity at decoupling. We find that the quadrupole amplitude can be
brought in accordance with observations with an eccentricity at decoupling of
about 0.35 10^{-2}. Moreover, our determination of the direction of the
symmetry axis is in reasonable agreement with recent statistical analyses of
cleaned CMB temperature fluctuation maps obtained by means of improved internal
linear combination methods as Galactic foreground subtraction technique.",0706.3802v2
2007-06-27,Transmission des forces dans un milieu composé de grains non sphériques,"We perform a detailed analysis of the contact force network in a dense
confined packing of pentagonal particles simulated by means of the contact
dynamics method. The effect of particle shape is evidenced by comparing the
data from pentagon packing and from a packing with identical characteristics
except for the circular shape of the particles. A counterintuitive finding of
this work is that, under steady shearing, the pentagon packing develops a lower
structural anisotropy than the disk packing. We show that this weakness is
compensated by a higher force anisotropy, leading to enhanced shear strength of
the pentagon packing. We revisit ""strong"" and ""weak"" force networks in the
pentagon packing, but our simulation data provide also evidence for a large
class of ""very weak"" forces carried mainly by vertex-to-edge contacts. The
strong force chains are mostly composed of edge-to-edge contacts with a marked
zig-zag aspect and a decreasing exponential probability distribution as in a
disk packing.",0706.4007v1
2007-07-09,"CMB from the South Pole: Past, Present, and Future","South Pole Station offers a unique combination of high, dry, stable
conditions and well-developed support facilities. Over the past 20 years, a
sequence of increasingly sophisticated CMB experiments at Pole have built on
the experience of early pioneering efforts, producing a number of landmark
contributions to the field. Telescopes at the South Pole were among the first
to make repeated detections of degree-scale CMB temperature anisotropy and to
map out the harmonic structure of its acoustic peaks. More recent achievements
include the first detection of polarization of the CMB and the most precise
measurements of the temperature power spectrum at small angular scales. New CMB
telescopes at the South Pole are now making ultra-deep observations of the
large-scale polarization of the CMB and of its secondary temperature
anisotropies on arcminute scales. These two observing goals represent the
current frontiers of CMB research, focused on constraining Inflation and the
nature of Dark Energy. The South Pole now hosts an array of CMB observing
platforms covering a wide range of angular scales and supporting very long
integration times on the cleanest sky available, and thus should play an
increasing role in pushing these frontiers of CMB research.",0707.1075v1
2007-07-10,Polarization anisotropy in the optical properties of silicon ellipsoids,"A new real space quantum mechanical approach with local field effects
included is applied to the calculation of the optical properties of silicon
nanocrystals. Silicon ellipsoids are studied and the role of surface
polarization is discussed in details. In particular, surface polarization is
shown to be responsible for a strong optical anisotropy in silicon ellipsoids,
much more pronounced with respect to the case in which only quantum confinement
effects are considered. The static dielectric constant and the absorption
spectra are calculated, showing that the perpendicular and parallel components
have a very different dependence on the ellipsoid aspect ratio. Then, a
comparison with the classical dielectric model is performed, showing that the
model only works for large and regular structures, but it fails for thin
elongated ellipsoids.",0707.1499v1
2007-07-13,Nflation: observable predictions from the random matrix mass spectrum,"We carry out numerical investigations of the perturbations in Nflation models
where the mass spectrum is generated by random matrix theory. The
tensor-to-scalar ratio and non-gaussianity are already known to take the
single-field values, and so the density perturbation spectral index is the main
parameter of interest. We study several types of random field initial
conditions, and compute the spectral index as a function of mass spectrum
parameters. Comparison with microwave anisotropy data from the Wilkinson
Microwave Anisotropy Probe shows that the model is currently viable in the
majority of its parameter space.",0707.1982v2
2007-07-19,CMB temperature anisotropies from third order gravitational perturbations,"In this paper we present a complete computation of the Cosmic Microwave
Background (CMB) anisotropies up to third order from gravitational
perturbations accounting for scalar, vector and tensor perturbations. We then
specify our results to the large scale limit, providing the evolution of the
gravitational potentials in a flat universe filled with matter and cosmological
constant which characterizes the Integrated Sachs-Wolfe effect. As a byproduct
in the large scale approximation we are able to give non-perturbative solutions
for the photon geodesic equations. Our results are the first step to provide a
complete theoretical prediction for cubic non-linearities which are
particularly relevant for characterizing the level of non-Gaussianity in the
CMB through the detection of the four-point angular connected correlation
function (trispectrum). For this purpose we also allow for generic initial
conditions due to primordial non-Gaussianity.",0707.2894v2
2007-07-23,Dark matter annihilation near a black hole: plateau vs. weak cusp,"Dark matter annihilation in so-called ``spikes'' near black holes is believed
to be an important method of indirect dark matter detection. In the case of
circular particle orbits, the density profile of dark matter has a plateau at
small radii, the maximal density being limited by the annihilation
cross-section. However, in the general case of arbitrary velocity anisotropy
the situation is different. Particulary, for isotropic velocity distribution
the density profile cannot be shallower than r^{-1/2} in the very centre.
Indeed, a detailed study reveals that in many cases the term ``annihilation
plateau'' is misleading, as the density actually continues to rise towards
small radii and forms a weak cusp, rho ~ r^{-(beta+1/2)}, where beta is the
anisotropy coefficient. The annihilation flux, however, does not change much in
the latter case, if averaged over an area larger than the annihilation radius.",0707.3334v2
2007-07-27,Theory for Magnetic Anisotropy of Field-Induced Insulator-to-Metal Transition in Cubic Kondo Insulator YbB_{12},"Magnetization and energy gap of Kondo insulator YbB_{12} are calculated
theoretically based on the previously proposed tight-binding model composed of
Yb 5d$\epsilon$ and 4f $\Gamma_8$ orbitals. It is found that magnetization
curves are almost isotropic, naturally expected from the cubic symmetry, but
that the gap-closing field has an anisotropy: the gap closes faster for the
field in (100) direction than in (110) and (111) directions, in accord with the
experiments. This is qualitatively understood by considering the maximal
eigenvalues of the total angular momentum operators projected on each direction
of the magnetic field. But the numerical calculation based on the band model
yields better agreement with the experiment.",0707.4048v1
2007-07-28,"Magnetization and Magnetoscrition of van Vleck antiferromagnets with magnetic anisotropy of ""easy-plane"" type","The theoretical description of quantum phase transition, induced by the
external magnetic field, into antiferromagnetic state in the van Vleck -
singlet - magnet with a single-ion anisotropy of ""easy-plane"" type and ion spin
S=1 is proposed. It is shown that the spin polarization of the ground
non-degenerated state proves to be the order parameter of such a transition and
that the Landau thermodynamic approach can be employed for its (transition)
description. The magnetic properties which include the field behavior of the
magnetization and magnetic susceptibility of the antiferromagnetic phase in the
fields of different directions are studied. The peculiarities of induced
magnetostriction in van Vleck antiferromagnet, which as well as magnetization
has a singularity in the phase transition point, are investigated. An attempt
is made for qualitative comparison of results obtained with avaliable
experimental data.",0707.4227v1
2007-07-30,Tuning of ferromagnetism through anion substitution in Ga-Mn-pnictide ferromagnetic semiconductors,"We have synthesized Ga1-xMnxAs1-yPy and Ga1-xMnxP1-yNy by the combination of
ion implantation and pulsed-laser melting. We find that the incorporation of
isovalent impurities with smaller atomic radii leads to a realignment of the
magnetic easy axis in Ga1-xMnxP1-yNy/GaP and Ga1-xMnxAs1-yPy/GaAs thin films
from in-plane to out-of-plane. This tensile-strain-induced magnetic anisotropy
is reminiscent of that observed in Ga1-xMnxAs grown on larger lattice constant
(In,Ga)As buffer layers indicating that the role of strain in determining
magnetic anisotropy is fundamental to III-Mn-V materials. In addition, we
observe a decrease in the ferromagnetic Curie temperature in Ga1-xMnxAs1-yPy
with increasing y from 0 to 0.028. Such a decrease may result from localization
of holes as the P/As ratio on the Group V sublattice increases.",0707.4490v1
2007-08-07,Evidence for gap anisotropy in CaC6 from directional point-contact spectroscopy,"We present the first results of directional point-contact spectroscopy in
high quality CaC6 samples both along the ab plane and in the c-axis direction.
The superconducting order parameter \Delta(0), obtained by fitting the
Andreev-reflection (AR) conductance curves at temperatures down to 400 mK with
the single-band 3D Blonder-Tinkham-Klapwijk model, presents two different
distributions in the two directions of the main current injection, peaked at
1.35 and 1.71 meV, respectively. By ab-initio calculations of the AR
conductance spectra, we show that the experimental results are in good
agreement with the recent predictions of gap anisotropy in CaC6.",0708.0921v2
2007-08-13,Theoretical analysis of magnetic force microscopy contrast in multidomain states of magnetic superlattices with perpendicular anisotropy,"Recently synthesized magnetic multilayers with strong perpendicular
anisotropy exhibit unique magnetic properties including the formation of
specific multidomain states. In particular, antiferromagnetically coupled
multilayers own rich phase diagrams that include various multidomain ground
states. Analytical equations have been derived for the stray-field components
of these multidomain states in perpendicular multilayer systems. In particular,
closed expressions for stray fields in the case of ferromagnetic and
antiferromagnetic stripes are presented. The theoretical approach provides a
basis for the analysis of magnetic force microscopy (MFM) images from this
novel class of nanomagnetic systems. Peculiarities of the MFM contrast have
been calculated for realistic tip models. These characteristic features in the
MFM signals can be employed for the investigations of the different multidomain
modes. The obtained results are applied for the analysis of multidomain modes
that have been reported earlier in the literature from experiments on [Co/Cr]Ru
superlattices.",0708.1570v4
2007-08-16,Effective Spin-1/2 Description of Transverse-Field-Induced Random Fields in Dipolar Spin Glasses with Strong Single-Ion Anisotropy,"We present analytical and numerical evidence for the validity of an effective
S=1/2 approach to the description of random field generation in S>=1, and
especially in an S=1, dipolar spin glass models with strong uniaxial Ising
anisotropy and subject to weak external magnetic field Bx transverse to the
Ising direction. Explicitely Bx-dependent random fields are shown to naturally
emerge in the effective low-energy description of a microscopic S=1 toy model.
We discuss our results in relation to recent theoretical studies pertaining to
the topic of Bx-induced random fields in the LiHo$_x$Y$_{1-x}$F$_4$ magnetic
materials with the Ho$^{3+}$ Ising moments subject to a transverse field. We
show that the S_{eff}=1/2 approach is able to capture both the qualitative and
quantitative aspects of the physics at small Bx, giving results that agree with
those obtained using conventional second order perturbation theory.",0708.2286v1
2007-09-04,Rigorous Solution of the Spin-1 Quantum Ising Model with Single-ion Anisotropy,"We solve the spin-1 quantum Ising model with single-ion anisotropy by mapping
it onto a series of segmented spin-1/2 transverse Ising chains, separated by
the $S^z =0$ states called holes. A recursion formula is derived for the
partition function to simplify the summation of hole configurations. This
allows the thermodynamic quantities of this model to be rigorously determined
in the thermodynamic limit. The low temperature behavior is governed by the
interplay between the hole excitations and the fermionic excitations within
each spin-1/2 Ising segment. The quantum critical fluctuations around the Ising
critical point of the transverse Ising model are strongly suppressed by the
hole excitations.",0709.0337v3
2007-09-05,Strong Imbalanced Turbulence,"We consider stationary, forced, imbalanced, or cross-helical MHD Alfvenic
turbulence where the waves traveling in one direction have higher amplitudes
than the opposite waves. This paper is dedicated to so-called strong
turbulence, which cannot be treated perturbatively. Our main result is that the
anisotropy of the weak waves is stronger than the anisotropy of a strong waves.
We propose that critical balance, which was originally conceived as a causality
argument, has to be amended by what we call a propagation argument. This
revised formulation of critical balance is able to handle the imbalanced case
and reduces to old formulation in the balanced case. We also provide
phenomenological model of energy cascading and discuss possibility of
self-similar solutions in a realistic setup of driven turbulence.",0709.0554v2
2007-09-14,Influence of particle shape on shear stress in granular media,"We analyze the contact and force networks in a dense confined packing of
pentagonal particles simulated by means of the contact dynamics method. The
particle shape effect is evidenced by comparing the data from pentagon packing
and from a packing with identical characteristics except for the circular shape
of the particles. A surprising observation is that the pentagon packing
develops a lower structural anisotropy than the disk packing. We show in this
work that this weakness is compensated by a higher force anisotropy that leads
to enhanced shear strength of the pentagon packing. With the polygonal shape of
the particles, the strong force chains are mostly composed of edge-to-edge
contacts with a marked zig-zag aspect.",0709.2241v1
2007-09-18,Clustering properties of ultrahigh energy cosmic rays and the search for their astrophysical sources,"The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show
anisotropies on all scales, from just above the experimental angular resolution
up to medium scales and dipole anisotropies. We find that a global comparison
of the two-point auto-correlation function of the data with the one of
catalogues of potential sources is a powerful diagnostic tool. In particular,
this method is far less sensitive to unknown deflections in magnetic fields
than cross-correlation studies while keeping a strong discrimination power
among source candidates. We illustrate these advantages by considering ordinary
galaxies, gamma ray bursts and active galactic nuclei as possible sources.
Already the sparse publicly available data suggest that the sources of UHECRs
may be a strongly clustered sub-sample of galaxies or of active galactic
nuclei. We present forecasts for various cases of source distributions which
can be checked soon by the Pierre Auger Observatory.",0709.2712v2
2007-09-24,Nonlinear growth of firehose and mirror fluctuations in turbulent galaxy-cluster plasmas,"In turbulent high-beta astrophysical plasmas (exemplified by the galaxy
cluster plasmas), pressure-anisotropy-driven firehose and mirror fluctuations
grow nonlinearly to large amplitudes, dB/B ~ 1, on a timescale comparable to
the turnover time of the turbulent motions. The principle of their nonlinear
evolution is to generate secularly growing small-scale magnetic fluctuations
that on average cancel the temporal change in the large-scale magnetic field
responsible for the pressure anisotropies. The presence of small-scale magnetic
fluctuations may dramatically affect the transport properties and, thereby, the
large-scale dynamics of the high-beta astrophysical plasmas.",0709.3828v2
2007-09-30,Difficulty in the Fermi-Liquid-Based Theory for the In-Plane Magnetic Anisotropy in Untwinned High-T_c Superconductor,"Recently, Eremin and Manske [1] presented a oneband Fermi-liquid theory for
the in-plane magnetic anisotropy in untwinned high-Tc superconductor
YBa2Cu3O6:85 (YBCO). They claimed that they found good agreement with inelastic
neutron scattering (INS) spectra. In this Comment, we point out that their
conclusion on this important problem may be questionable due to an error in
logic about the orthorhombicity delta_0 characterizing the lattice structure of
YBCO. In Ref. [1], a single band at delta_0>0 is proved to be in accordance
with the angle resolved photoemission spectroscopy (ARPES) on untwinned YBCO.
But in their Erratum in PRL[3], they admit that delta_0= -0.03 was used to fit
the INS data. Hence publications [1,3] contain errors that we believe
invalidate their approach.",0710.0127v1
2007-10-10,CMB Anisotropies and Inflation from Non-Standard Spinors,"The apparent alignment of the cosmic microwave background multipoles on large
scales challenges the standard cosmological model. Scalar field inflation is
isotropic and cannot account for the observed alignment. We explore the
imprints, a non-standard spinor driven inflation would leave on the cosmic
microwave background anisotropies. We show it is natural to expect an
anisotropic inflationary expansion of the Universe which has the effect of
suppressing the low multipole amplitude of the primordial power spectrum, while
at the same time to provide the usual inflationary features.",0710.2003v4
2007-10-12,Slonczewski windmill with dissipation and asymmetry,"J. Slonczewski invented spin-transfer effect in layered systems in 1996.
Among his first predictions was the regime of ``windmill motion'' of a
perfectly symmetric spin valve where the magnetizations of the layers rotate in
a fixed plane keeping the angle between them constant. Since ``windmill'' was
predicted to happen in the case of zero magnetic anisotropy, while in most
experimental setups the anisotropy is significant, the phenomenon was not a
subject of much research. However, the behavior of the magnetically isotropic
device is related to the interesting question of current induced ferromagnetism
and is worth more attention. Here we study the windmill regime in the presence
of dissipation, exchange interaction, and layer asymmetry. It is shown that the
windmill rotation is almost always destroyed by those effects, except for a
single special value of electric current, determined by the parameters of the
device.",0710.2564v1
2007-10-17,Lensing Systematics from Space: Modeling PSF effects in the SNAP survey,"Anisotropy in the point spread function (PSF) contributes a systematic error
to weak lensing measurements. In this study we use a ray tracer that
incorporates all the optical elements of the SNAP telescope to estimate this
effect. Misalignments in the optics generates PSF anisotropy, which we
characterize by its ellipticity. The effect of three time varying effects:
thermal drift, guider jitter, and structural vibration on the PSF are estimated
for expected parameters of the SNAP telescope. Multiple realizations of a
thousand square degree mock survey are then generated to include the systematic
error pattern induced by these effects. We quantify their contribution to the
power spectrum of the lensing shear. We find that the dominant effect comes
from the thermal drift, which peaks at angular wavenumbers l ~ 10^3, but its
amplitude is over one order of magnitude smaller than the size of the expected
statistical error. While there are significant uncertainties in our modeling,
our study indicates that time-varying PSFs will contribute at a smaller level
than statistical errors in SNAP's weak lensing measurements.",0710.3355v1
2007-10-31,Direction-Dependent CMB Power Spectrum and Statistical Anisotropy from Noncommutative Geometry,"Modern cosmology has now emerged as a testing ground for theories beyond the
standard model of particle physics. In this paper, we consider quantum
fluctuations of the inflaton scalar field on certain noncommutative spacetimes
and look for noncommutative corrections in the cosmic microwave background
(CMB) radiation. Inhomogeneities in the distribution of large scale structure
and anisotropies in the CMB radiation can carry traces of noncommutativity of
the early universe. We show that its power spectrum becomes direction-dependent
when spacetime is noncommutative. (The effects due to noncommutativity can be
observed experimentally in the distribution of large scale structure of matter
as well.) Furthermore, we have shown that the probability distribution
determining the temperature fluctuations is not Gaussian for our noncommutative
spacetimes.",0710.5897v3
2007-11-10,Strong luminescence quantum efficiency enhancement near prolate metal nanoparticles: dipolar versus higher-order modes,"We present a theoretical study of the radiative and nonradiative decay rates
of an optical emitter in close proximity to a prolate-shaped metal
nanoparticle. We use the model developed by Gersten and Nitzan, that we correct
for radiative reaction and dynamic depolarization and extend for prolate
particle shapes. We show that prolate-shaped metal nanoparticles can lead to
much higher quantum efficiency enhancements than corresponding spherical
nanoparticles. For properly engineered emitter-nanoparticle geometries, quantum
efficiency enhancements from an initial value of 1% (in absence of the
nanoparticle) to 70% are feasible. We describe the anisotropy-induced
enhancement effects in terms of large field enhancements near the metal tips
that cause strong coupling to the (radiative) dipolar modes. For increasing
particle anisotropy, a strong spectral separation between radiative dipolar and
dark higher-order modes occurs, which leads to higher radiative efficiencies
for anisotropic particles. In addition, we demonstrate that for large (> 100
nm) nanoparticles, the influence of Ohmic losses on plasmon-enhanced
luminescence is substantially reduced, which implies that, if prolate shaped,
even lossy metals such as Al and Cu are suitable materials for optical
nano-antennas.",0711.1591v1
2007-11-13,Shape of Heteroepitaxial Island Determined by Asymmetric Detachment,"Square lattice gas models for heteroepitaxial growth are studied by means of
kinetic Monte Carlo simulations, in order to find a possible origin of
anisotropic island shape observed in growth experiments of long organic
molecules. When deposited molecules form clusters irreversibly at their
encounter during surface diffusion, islands grow in a ramified dendritic shape,
similar to DLA. Introduction of molecular detachment from edges makes islands
compact with smooth edges. Tilting of adsorbed long molecules or steps in a
vicinal substrate may induce orientation-dependence in the detachment rate of
edge molecules from an island. In simulations with orientation-dependent
detachment rates, a clear anisotropy in an island shape is observed. Shape
anisotropy on a vicinal substrate is enhanced as steps get dense, in agreement
to the experimental observation.",0711.1903v1
2007-11-20,A rotating hollow cone anisotropy of TeV emission from binary systems,"We show that TeV gamma-ray emission produced via interactions of high-energy
particles with anisotropic radiation field of a massive star in binary systems
should have a characteristic rotating hollow cone anisotropy pattern. The
hollow cone, whose axis is directed away from the massive star, rotates with
the period equal to the orbital period of the system. We note that the two
maxima pattern of the TeV energy band lightcurve of the gamma-ray loud binary
LS 5039 can be interpreted in terms of this rotating hollow cone model.
Adopting such an interpretation, we are able to constrain the geometry of the
system - either the inclination angle of the binary orbit, or the elevation of
the gamma-ray emission region above the orbital plane.",0711.3085v3
2007-11-30,The impact of going beyond the Maxwell distribution in direct dark matter detection rates,"We consider direct dark matter detection rates and investigate the difference
between a standard Maxwell-Boltzmann velocity distribution and a ""realistic""
distribution like the ones extracted from numerical N-body simulations. Sizable
differences are observed when such results are compared to the standard
Maxwell-Boltzmann distribution. For a light target both the total rate and the
annual modulation are reduced by ~25%. For a heavy target the total rate is
virtually unchanged, whereas the annual modulation is modified by up to 50%,
depending on the WIMP mass and detector energy threshold. We also consider the
effect of a possible velocity anisotropy, and the effect is found to be largest
for a light target For the realistic velocity distribution the anisotropy may
reduce the annual modulation, in contrast to the Maxwell-Boltzmann case.",0711.4895v1
2007-12-03,"Creep, recovery, and waves in a nonlinear fiber-reinforced viscoelastic solid","We present a constitutive model capturing some of the experimentally observed
features of soft biological tissues: nonlinear viscoelasticity, nonlinear
elastic anisotropy, and nonlinear viscous anisotropy. For this model we derive
the equation governing rectilinear shear motion in the plane of the fiber
reinforcement; it is a nonlinear partial differential equation for the shear
strain. Specializing the equation to the quasi-static processes of creep and
recovery, we find that usual (exponential-like) time growth and decay exist in
general, but that for certain ranges of values for the material parameters and
for the angle between the shearing direction and the fiber direction, some
anomalous behaviors emerge. These include persistence of a nonzero strain in
the recovery experiment, strain growth in recovery, strain decay in creep,
disappearance of the solution after a finite time, and similar odd
comportments. For the full dynamical equation of motion, we find kink
(traveling wave) solutions which cannot reach their assigned asymptotic limit.",0712.0229v1
2007-12-14,The effect of unbound stars on the mass modelling of the Fornax dwarf,"We discuss how different approaches to selecting member stars in kinematic
samples of dwarf spheroidal galaxies affect the estimates of their mass and
anisotropy of stellar orbits. We demonstrate that the selection of members is
an additional source of error compared to the usual uncertainties due to the
sampling of velocity moments. As an example we use the kinematic data set for
202 stars in the Fornax dwarf galaxy for which we model the velocity dispersion
profile and estimate the mass-to-light ratio and anisotropy assuming that mass
follows light. We also show that stronger constraints on these parameters can
be obtained if kurtosis of the velocity distribution is included in the
analysis. Using the Besancon model of the Milky Way we demonstrate that the
majority of contamination in Fornax probably comes from the Milky Way stars.",0712.2372v1
2007-12-23,Phase diagram of the one dimensional anisotropic Kondo-necklace model,"The one dimensional anisotropic Kondo-necklace model has been studied by
several methods. It is shown that a mean field approach fails to gain the
correct phase diagram for the Ising type anisotropy. We then applied the spin
wave theory which is justified for the anisotropic case. We have derived the
phase diagram between the antiferromagnetic long range order and the Kondo
singlet phases. We have found that the exchange interaction (J) between the
itinerant spins and local ones enhances the quantum fluctuations around the
classical long range antiferromagnetic order and finally destroy the ordered
phase at the critical value, J_c. Moreover, our results show that the onset of
anisotropy in the XY term of the itinerant interactions develops the
antiferromagnetic order for J<J_c. This is in agreement with the qualitative
feature which we expect from the symmetry of the anisotropic XY interaction. We
have justified our results by the numerical Lanczos method where the structure
factor at the antiferromagnetic wave vector diverges as the size of system goes
to infinity.",0712.3914v2
2007-12-24,Topological Defects in Spherical Nematics,"We study the organization of topological defects in a system of nematogens
confined to the two-dimensional sphere (S^2). We first perform Monte Carlo
simulations of a fluid system of hard rods (spherocylinders) living in the
tangent plane of S^2. The sphere is adiabatically compressed until we reach a
jammed nematic state with maximum packing density. The nematic state exhibits
four +1/2 disclinations arrayed on a great circle rather than at the vertices
of a regular tetrahedron. This arises from the high elastic anisotropy of the
system in which splay (K_1) is far softer than bending (K_3). We also introduce
and study a lattice nematic model on S^2 with tunable elastic constants and map
out the preferred defect locations as a function of elastic anisotropy. We
establish the existence of a one-parameter family of degenerate ground states
in the extreme splay-dominated limit K_1/K_3 -> 0. Thus the global defect
geometry is controllable by tuning the relative splay to bend modulus.",0712.4012v3
2008-01-02,Cosmic microwave background constraints on a decaying cosmological term related to the thermal evolution,"We constrain the thermal evolution of the universe with a decaying
cosmological term by using the method of the analysis for the Wilkinson
Microwave Anisotropy Probe (WMAP) observation data. The cosmological term is
assumed to be a function of the scale factor that increases toward the early
universe, and the radiation energy density is lower compared to that in the
model with the standard cosmological ""constant"" (LCDM). The decrease in the
radiation density affects the thermal history of the universe; e.g. the photon
decoupling occurs at higher-z compared to the case of the standard LCDM model.
As a consequence, a decaying cosmological term affects the cosmic microwave
background anisotropy. Thanks to the Markov-chain Monte Carlo method, we
compare the angular power spectrum in the decaying LCDM model with the CMB
data, and we get severe constraints on parameters of the model.",0801.0290v2
2008-01-03,High resolution 3D laser scanner measurements of a strike-slip fault quantify its morphological anisotropy at all scales,"The surface roughness of a recently exhumed strikeslip fault plane has been
measured by three independent 3D portable laser scanners. Digital elevation
models of several fault surface areas, from 1 m2 to 600 m2, have been measured
at a resolution ranging from 5 mm to 80 mm. Out of plane height fluctuations
are described by non-Gaussian distribution with exponential long range tails.
Statistical scaling analyses show that the striated fault surface exhibits
self-affine scaling invariance with a small but significant directional
morphological anisotropy that can be described by two scaling roughness
exponents, H1 = 0.7 in the direction of slip and H2 = 0.8 perpendicular to the
direction of slip.",0801.0544v1
2008-01-06,Evolution of Massive Blackhole Triples II -- The effect of the BH triples dynamics on the structure of the galactic nuclear,"In this paper, we investigate the structures of galaxies which either have or
have had three BHs using $N$-body simulations, and compare them with those of
galaxies with binary BHs. We found that the cusp region of a galaxy which have
(or had) triple BHs is significantly larger and less dense than that of a
galaxy with binary BHs of the same mass. Moreover, the size of the cusp region
depends strongly on the evolution history of triple BHs, while in the case of
binary BHs, the size of the cusp is determined by the mass of the BHs. In
galaxies which have (or had) three BHs, there is a region with significant
radial velocity anisotropy, while such a region is not observed in galaxies
with binary BH. These differences come from the fact that with triple BHs the
energy deposit to the central region of the galaxy can be much larger due to
multiple binary-single BH scatterings. Our result suggests that we can
discriminate between galaxies which experienced triple BH interactions with
those which did not, through the observable signatures such as the cusp size
and velocity anisotropy.",0801.0859v1
2008-01-14,"Azimuthal Anisotropy: Ridges, Recombination and Breaking of Quark Number Scaling","Azimuthal anisotropy is studied by taking into account the ridges created by
semi-hard scattering, which is sensitive to the initial spatial configuration
in non-central heavy-ion collisions. No rapid thermalization is required.
Although hydrodynamics is not used in this study, the validity of
hydrodynamical expansion is not excluded at later time after equilibration is
achieved. Phenomenological properties of the bulk and ridge behaviors are used
as inputs to determine the elliptic flow of pion and proton at low p_T. At
intermediate p_T the recombination of shower partons with thermal partons
becomes more important. The phi dependence arises from the variation of the
in-medium path length of the hard parton that generates the shower. The p_T
dependence of v_2 is therefore very different at intermediate p_T compared to
that at low p_T. Quark number scaling of v_2 is shown to be only approximately
valid at low p_T, but is broken at intermediate p_T, even though recombination
is the mechanism of hadronization in all p_T regions considered.",0801.2183v2
2008-01-24,"Spin-driven ferroelectricity and possible antiferroelectricity in triangular lattice antiferromagnets ACrO2 (A = Cu, Ag, Li, or Na)","Correlation between dielectric and magnetic properties was investigated on
the triangular lattice antiferromagnets ACrO2 (A= Cu, Ag, Li, or Na) showing
120-degree spiral spin structure with easy-axis anisotropy. For the A= Cu and
Ag compounds with delafossite structure, ferroelectric polarization emerges
upon the spiral spin order, implying the strong coupling between the
ferroelectricity and spiral spin structure. On the other hand, for the A = Li
and Na compounds with ordered rock salt structure, no polarization but only
clear anomalies in dielectric constant can be observed upon the spiral spin
order. The absence of polarization can be interpreted as the antiferroelectric
state induced by the alternate stacking of Cr3+ layer with opposite spin vector
chirality. These results imply that a vast range of trigonally stacked
triangular-lattice systems with 120-degree spin structure can be multiferroic,
irrespective of their magnetic anisotropy.",0801.3757v1
2008-01-28,GaMnAs-based hybrid multiferroic memory device,"A rapidly developing field of spintronics is based on the premise that
substituting charge with spin as a carrier of information can lead to new
devices with lower power consumption, non-volatility and high operational
speed. Despite efficient magnetization detection, magnetization manipulation is
primarily performed by current-generated local magnetic fields and is very
inefficient. Here we report a novel non-volatile hybrid multiferroic memory
cell with electrostatic control of magnetization based on strain-coupled GaMnAs
ferromagnetic semiconductor and a piezoelectric material. We use the
crystalline anisotropy of GaMnAs to store information in the orientation of the
magnetization along one of the two easy axes, which is monitored via transverse
anisotropic magnetoresistance. The magnetization orientation is switched by
applying voltage to the piezoelectric material and tuning magnetic anisotropy
of GaMnAs via the resulting stress field.",0801.4191v1
2008-01-28,Dynamical correlations in the spin-half two-channel Kondo model,"Dynamical correlations of various local operators are studied in the
spin-half two-channel Kondo (2CK) model in the presence of channel anisotropy
or external magnetic field. A conformal field theory-based scaling approach is
used to predict the analytic properties of various spectral functions in the
vicinity of the two-channel Kondo fixed point. These analytical results compare
well with highly accurate density matrix numerical renormalization group
results. The universal cross-over functions interpolating between
channel-anisotropy or magnetic field-induced Fermi liquid regimes and the
two-channel Kondo, non-Fermi liquid regimes are determined numerically. The
boundaries of the real 2CK scaling regime are found to be rather restricted,
and to depend both on the type of the perturbation and on the specific operator
whose correlation function is studied. In a small magnetic field, a universal
resonance is observed in the local fermion's spectral function. The dominant
superconducting instability appears in the composite superconducting channel.",0801.4272v1
2008-01-29,The Integrated Sachs-Wolfe Effect in Interacting Dark Energy Models,"Models with dark energy decaying into dark matter have been proposed in
Cosmology to solve the coincidence problem. We study the effect of such
coupling on the cosmic microwave background temperature anisotropies. The
interaction changes the rate of evolution of the metric potentials, the growth
rate of matter density perturbations and modifies the Integrated Sachs-Wolfe
component of cosmic microwave background temperature anisotropies, enhancing
the effect. Cross-correlation of galaxy catalogs with CMB maps provides a model
independent test to constrain the interaction. We particularize our analysis
for a specific interacting model and show that galaxy catalogs with median
redshifts $z_m=0.1-0.9$ can rule out models with an interaction parameter
strength of $c^2\simeq 0.1$ better than 99.95% confidence level. Values of
$c^2\le 0.01$ are compatible with the data and may account for the possible
discrepancy between the fraction of dark energy derived from WMAP 3yr data and
the fraction obtained from the ISW effect. Measuring the fraction of dark
energy by these two methods could provide evidence of an interaction.",0801.4517v2
2008-02-04,Effects of phonon interaction on the pairing in the high-T$c$ superconductors,"We study the effects of phonon interaction on the superconducting pairing in
the background of a d-wave gap, mediated by antiferromagnetic (AFM) spin
fluctuations, using coupled BCS gap equations. We found that phonon interaction
can induce a s-wave component to the d-wave gap in the (D+S) form with an
interaction anisotropy and in the (D+$i$S) form without anisotropy,
respectively. In either case, however, T$_c$ is not enhanced compared to the
pure d-wave pairing without phonon interaction. On the other hand, anisotropic
phonon interaction can dramatically enhance the d-wave pairing itself and
therefore T$_c$, together with the AFM spin fluctuation interaction. This
(D$_{AFM}$ + D$_{ph}$) type pairing exhibits strongly reduced isotope
coefficient despite the large enhancement of T$_c$ by phonon interaction.
Finally, we study the combined type of (D$_{AFM}$ + D$_{ph}$ +$i$S)) gap and
calculate the penetration depth and specific heat to be compared with the
experiments.",0802.0328v1
2008-02-05,Green's function theory for spin-1/2 ferromagnets with an easy-plane exchange anisotropy,"The many-body Green's function theory with the random-phase approximation is
applied to the study of easy-plane spin-1/2 ferromagnets in an in-plane
magnetic field. We demonstrate that the usual procedure, in which only the
three Green's functions $<< S_i^\mu;S_j^->>$ ($\mu=+,-,z$) are used, yields
unreasonable results in this case. Then the problem is discussed in more detail
by considering all combinations of Green's functions. We can derive one more
equation, which cannot be obtained by using only the set of the above three
Green's functions, and point out that the two equations contradict each other
if one demands that the identities of the spin operators are exactly satisfied.
We discuss the cause of the contradiction and attempt to improve the method in
a self consistent way. In our procedure, the effect of the anisotropy can be
appropriately taken into account, and the results are in good agreement with
the quantum Monte Carlo calculations.",0802.0559v2
2008-02-05,Cumulative effect of Weibel-type instabilities in counterstreaming plasmas with non-Maxwellian anisotropies,"Counterstreaming plasma structures are widely present in laboratory
experiments and astrophysical systems, and they are investigated either to
prevent unstable modes arising in beam-plasma experiments or to prove the
existence of large scale magnetic fields in astrophysical objects.
Filamentation instability arises in a counterstreaming plasma and is
responsible for the magnetization of the plasma. Filamentationally unstable
mode is described by assuming that each of the counterstreaming plasmas has an
isotropic Lorentzian (kappa) distribution. In this case, the filamentation
instability growth rate can reach a maximum value markedly larger than that for
a a plasma with a Maxwellian distribution function. This behaviour is opposite
to what was observed for the Weibel instability growth rate in a bi-kappa
plasma, which is always smaller than that obtained for a bi-Maxwellian plasma.
The approach is further generalized for a counterstreaming plasma with a
bi-kappa temperature anisotropy. In this case, the filamentation instability
growth rate is enhanced by the Weibel effect when the plasma is hotter in the
streaming direction, and the growth rate becomes even larger. These effects
improve significantly the efficiency of the magnetic field generation, and
provide further support for the potential role of the Weibel-type instabilities
in the fast magnetization scenarios.",0802.0570v1
2008-02-07,Large Scale Structure as a Probe of Gravitational Slip,"A new time-dependent, scale-independent parameter, \varpi, is employed in a
phenomenological model of the deviation from General Relativity in which the
Newtonian and longitudinal gravitational potentials slip apart on cosmological
scales as dark energy, assumed to be arising from a new theory of gravitation,
appears to dominate the universe. A comparison is presented between \varpi and
other parameterized post-Friedmannian models in the literature. The effect of
\varpi on the cosmic microwave background anisotropy spectrum, the growth of
large scale structure, the galaxy weak-lensing correlation function, and
cross-correlations of cosmic microwave background anisotropy with galaxy
clustering are illustrated. Cosmological models with conventional maximum
likelihood parameters are shown to find agreement with a narrow range of
gravitational slip.",0802.1068v1
2008-02-12,Giant orbital moments are responsible for the anisotropic magnetoresistance of atomic contacts,"We study here, both experimentally and theoretically, the anisotropy of
magnetoresistance in atomic contacts. Our measurements on iron break junctions
reveal an abrupt and hysteretic switch between two conductance levels when a
large applied field is continuously rotated. We show that this behaviour stems
from the coexistence of two metastable electronic states which result from the
anisotropy of electronic interactions responsible for the enhancement of
orbital magnetization. In both states giant orbital moments appear on the low
coordinated central atom in a realistic contact geometry. However they differ
by their orientation, parallel or perpendicular, with respect to the axis of
the contact. Our explanation is totally at variance with the usual model based
on the band structure of a monatomic linear chain, which we argue cannot be
applied to 3d ferromagnetic metals.",0802.1595v1
2008-02-12,Temperature dependent magnetization dynamics of magnetic nanoparticles,"Recent experimental and theoretical studies show that the switching behavior
of magnetic nanoparticles can be well controlled by external time-dependent
magnetic fields. In this work, we inspect theoretically the influence of the
temperature and the magnetic anisotropy on the spin-dynamics and the switching
properties of single domain magnetic nanoparticles (Stoner-particles). Our
theoretical tools are the Landau-Lifshitz-Gilbert equation extended as to deal
with finite temperatures within a Langevine framework. Physical quantities of
interest are the minimum field amplitudes required for switching and the
corresponding reversal times of the nanoparticle's magnetic moment. In
particular, we contrast the cases of static and time-dependent external fields
and analyze the influence of damping for a uniaxial and a cubic anisotropy.",0802.1740v1
2008-02-14,Strain dependence of the Mn anisotropy in ferromagnetic semiconductors observed by x-ray magnetic circular dichroism,"We demonstrate sensitivity of the Mn 3d valence states to strain in the
ferromagnetic semiconductors (Ga,Mn)As and (Al,Ga,Mn)As, using x-ray magnetic
circular dichroism (XMCD). The spectral shape of the Mn $L_{2,3}$ XMCD is
dependent on the orientation of the magnetization, and features with cubic and
uniaxial dependence are distinguished. Reversing the strain reverses the sign
of the uniaxial anisotropy of the Mn $L_3$ pre-peak which is ascribed to
transitions from the Mn 2p core level to p-d hybridized valence band hole
states. With increasing carrier localization, the $L_3$ pre-peak intensity
increases, indicating an increasing 3d character of the hybridized holes.",0802.2061v1
2008-02-18,Correlated Detection of sub-mHz Gravitational Waves by Two Optical-Fiber Interferometers,"Results from two optical-fiber gravitational-wave interferometric detectors
are reported. The detector design is very small, cheap and simple to build and
operate. Using two detectors has permitted various tests of the design
principles as well as demonstrating the first simultaneous detection of
correlated gravitational waves from detectors spatially separated by 1.1km. The
frequency spectrum of the detected gravitational waves is sub-mHz with a strain
spectral index a=-1.4 +/- 0.1. As well as characterising the wave effects the
detectors also show, from data collected over some 80 days in the latter part
of 2007, the dominant earth rotation effect and the earth orbit effect. The
detectors operate by exploiting light speed anisotropy in optical-fibers. The
data confirms previous observations of light speed anisotropy, earth rotation
and orbit effects, and gravitational waves.",0802.2406v1
2008-02-21,Damping by slow relaxing rare earth impurities in Ni80Fe20,"Doping NiFe by heavy rare earth atoms alters the magnetic relaxation
properties of this material drastically. We show that this effect can be well
explained by the slow relaxing impurity mechanism. This process is a
consequence of the anisotropy of the on site exchange interaction between the
4f magnetic moments and the conduction band. As expected from this model the
magnitude of the damping effect scales with the anisotropy of the exchange
interaction and increases by an order of magnitude at low temperatures. In
addition our measurements allow us to determine the relaxation time of the 4f
electrons as a function of temperature.",0802.3206v3
2008-02-28,Anisotropic modification of the effective hole $g$-factor by electrostatic confinement,"We investigate effects of lateral confinement on spin splitting of energy
levels in 2D hole gases grown on [311] GaAs. We found that lateral confinement
enhances anisotropy of spin splitting relative to the 2D gas for both confining
directions. Unexpectedly, the effective $g$-factor does not depend on the 1D
energy level number $N$ for $B\|[0\bar{1}1]$ while it has strong $N$-dependence
for $B\|[\bar{2}33]$. Apart from quantitative difference in the spin splitting
of energy levels for the two orthogonal confinement directions we also report
qualitative differences in the appearance of spin-split plateaus, with
non-quantized plateaus observed only for the confinement in $[0\bar{1}1]$
direction. In our samples we can clearly associate the difference with
anisotropy of spin-orbit interactions.",0802.4271v1
2008-03-02,Structural anisotropy of silica hydrogels prepared under magnetic field,"Birefringence measurements have been carried out on the Pb-doped silica
hydrogels prepared under various magnetic fields up to 5T. The silica gels
prepared at 5T were used as a medium of crystal growth of PbBr2, whose result
implied the structural anisotropy; an aligned array of crystallites was
obtained by transmission electron microscopy. While the samples prepared at 0,
1, and 3T have no birefringence, we found that the samples have negative
birefringence on the order of magnitude 10^-6 as if the direction of the
magnetic field is the optic axis of a uniaxal crystal. To the authors'
knowledge, the birefringent silica hydrogels were obtained by gelation under
magnetic field for the first time. Also, scanning microscopic light scattering
experiments have been performed. The results indicate that the characteristic
length distribution for birefringent samples is narrower than that for
non-birefringent ones.",0803.0114v2
2008-03-06,Variational method study of the spin-1 Ising model with biaxial crystal-field anisotropy,"The phase diagram of the spin-1 Ising model in the presence of a biaxial
crystal-field anisotropy is studied within the framework of a variational
approach, based on the Bogolyubov inequality for the free energy. We have
investigated the effects of a transverse crystal-field $D_{y}$ on the phase
diagram in the $T-D_{x}$ plane. Results obtained by using effective-field
theory (EFT) on the honeycomb (% $z=3$), square ($z=4$) and simple cubic
($z=6$) lattices ($z$ is the coordination number) show only continuous phase
transitions, while the variational approach presents first-order and continuous
phase transitions for $D_{y}=0$% . We have also used the EFT for larger values
of $z$ and we observe the presence of tricritical points in the phase diagrams,
for $z\geq 7$, in accordance with the variational approach results.",0803.0934v1
2008-03-31,Resolving Spacecraft Earth-Flyby Anomalies with Measured Light Speed Anisotropy,"Doppler shift observations of spacecraft, such as Galileo, NEAR, Cassini,
Rosetta and MESSENGER in earth flybys, have all revealed unexplained speed
`anomalies' - that the doppler-shift determined speeds are inconsistent with
expected speeds. Here it is shown that these speed anomalies are not real and
are actually the result of using an incorrect relationship between the observed
doppler shift and the speed of the spacecraft - a relationship based on the
assumption that the speed of light is isotropic in all frames, i.e. invariant.
Taking account of the repeatedly measured light-speed anisotropy the anomalies
are resolved. The Pioneer 10/11 anomalies are discussed, but not resolved. The
spacecraft observations demonstrate again that the speed of light is not
invariant, and is isotropic only with respect to a dynamical 3-space. The
existing doppler shift data also offers a resource to characterise a new form
of gravitational waves, the dynamical 3-space turbulence, that has also been
detected by other techniques.",0804.0039v4
2008-04-07,Fast rotating condensates in an asymmetric harmonic trap,"We investigate the effect of the anisotropy of a harmonic trap on the
behaviour of a fast rotating Bose-Einstein condensate. Fast rotation is reached
when the rotational velocity is close to the smallest trapping frequency,
thereby deconfining the condensate in the corresponding direction. A striking
new feature is the non-existence of visible vortices for the ground state. The
condensate can be described with the lowest Landau level set of states, but
using distorted complex coordinates. We find that the coarse grained atomic
density behaves like an inverted parabola with large radius in the deconfined
direction, and like a fixed Gaussian in the other direction. It has no visible
vortices, but invisible vortices which are needed to recover the mixed
Thomas-Fermi Gaussian profile. There is a regime of small anisotropy and
intermediate rotational velocity where the behaviour is similar to the
isotropic case: a hexagonal Abrikosov lattice of vortices, with an inverted
parabola profile.",0804.0971v3
2008-04-08,Transition metal dimers as potential molecular magnets: A challenge to computational chemistry,"Dimers are the smallest chemical objects that show magnetic anisotropy. We
focus on 3$d$ and 4$d$ transition metal dimers that have magnetic ground states
in most cases. Some of these magnetic dimers have a considerable barrier
against re-orientation of their magnetization, the so-called magnetic
anisotropy energy, MAE. The height of this barrier is important for
technological applications, as it determines, e.g., the stability of
information stored in magnetic memory devices. It can be estimated by means of
relativistic density functional calculations. Our approach is based on a
full-potential local-orbital method (FPLO) in a four-component Dirac-Kohn-Sham
implementation. Orbital polarization corrections to the local density
approximation are employed. They are discussed in the broader context of
orbital dependent density functionals. Ground state properties (spin
multiplicity, bond length, harmonic vibrational frequency, spin- and orbital
magnetic moment, and MAE) of the 3$d$ and 4$d$ transition metal dimers are
evaluated and compared with available experimental and theoretical data. We
find exceptionally high values of MAE, close to 0.2 eV, for four particular
dimers: Fe$_2$, Co$_2$, Ni$_2$, and Rh$_2$.",0804.1233v1
2008-04-16,Dilepton production as a measure of QGP thermalization time,"We discuss dilepton production from a quark-gluon plasma which has a
time-dependent anisotropy in momentum space. A phenomenological model for the
hard momentum scale, p_hard(tau) and the plasma anisotropy parameter, xi(tau),
is presented. The model interpolates between early-time 1+1 free streaming
behavior (tau << tau_iso) and late-time ideal 1+1 hydrodynamical behavior (tau
>> tau_iso). Using this model, we find that the dilepton rate arising from
electromagnetic annihilations of quarks in the kinematic range 3 <p_T< 8 GeV is
sensitive to the assumed isotropization time of the system, tau_iso. Therefore
high-energy dilepton production can be used to probe the degree of
momentum-space isotropy of a quark-gluon plasma produced in relativistic heavy
ion collisions and the time of onset of hydrodynamic expansion of the QGP.",0804.2618v1
2008-04-17,"Effective-medium theory for infinite-contrast, 2D-periodic, linear composites with strongly anisotropic matrix behavior: dilute limit and cross-over behavior","The overall behavior of a 2D lattice of voids embedded in an anisotropic
matrix is investigated in the limit of vanishing porosity f. An
effective-medium model (of the Hashin-Shtrikman type) which accounts for
elastic interactions between neighboring voids, is compared to Fast Fourier
Transform numerical solutions and, in the limits of infinite anisotropy, to
exact results. A cross-over between regular and singular dilute regimes is
found, driven by a characteristic length which depends on f and on the
anisotropy strength. The singular regime, where the leading dilute correction
to the elastic moduli is an O(f^{1/2}), is related to strain localization and
to change in character - from elliptic to hyperbolic - of the governing
equations.",0804.2817v1
2008-04-18,Dzyaloshinsky-Moriya Anisotropy in the Spin-1/2 Kagomé Compound ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$,"We report the determination of the Dzyaloshinsky-Moriya interaction, the
dominant magnetic anisotropy term in the \kagome spin-1/2 compound {\herbert}.
Based on the analysis of the high-temperature electron spin resonance (ESR)
spectra, we find its main component $|D_z|=15(1)$ K to be perpendicular to the
\kagome planes. Through the temperature dependent ESR line-width we observe a
building up of nearest-neighbor spin-spin correlations below $\sim$150 K.",0804.3107v2
2008-04-21,Anisotropic plasmons in a two-dimensional electron gas with spin-orbit interaction,"Spin-orbit coupling induced anisotropies of plasmon dynamics are investigated
in two-dimensional semiconductor structures. The interplay of the linear
Bychkov-Rashba and Dresselhaus spin-orbit interactions drastically affects the
plasmon spectrum: the dynamical structure factor exhibits variations over
several decades, prohibiting plasmon propagation in specific directions. While
this plasmon filtering makes the presence of spin-orbit coupling in plasmon
dynamics observable, it also offers a control tool for plasmonic devices.
Remarkably, if the strengths of the two interactions are equal, not only the
anisotropy, but all the traces of the linear spin-orbit coupling in the
collective response disappear.",0804.3366v3
2008-04-25,Evolution of the Kondo state of YbRh2Si2 probed by high field ESR,"An electron spin resonance (ESR) study of the heavy fermion compound YbRh2Si2
for fields up to ~ 8 T reveals a strongly anisotropic signal below the single
ion Kondo temperature T_K ~ 25 K. A remarkable similarity between the
T-dependence of the ESR parameters and that of the specific heat and the 29Si
nuclear magnetic resonance data gives evidence that the ESR response is given
by heavy fermions which are formed below T_K and that ESR properties are
determined by their field dependent mass and lifetime. The signal anisotropy,
otherwise typical for Yb{3+} ions, suggests that, owing to a strong
hybridization with conduction electrons at T < T_K, the magnetic anisotropy of
the 4f states is absorbed in the ESR of heavy quasiparticles. Tuning the Kondo
effect on the 4f states with magnetic fields ~ 2 - 8 T and temperature 2 - 25 K
yields a gradual change of the ESR g-factor and linewidth which reflects the
evolution of the Kondo state in this Kondo lattice system.",0804.4105v2
2008-05-06,Kleinberg navigation on anisotropic lattices,"We study the Kleinberg problem of navigation in Small World networks when the
underlying lattice is stretched along a preferred direction. Extensive
simulations confirm that maximally efficient navigation is attained when the
length $r$ of long-range links is taken from the distribution $P({\bf r})\sim
r^{-\alpha}$, when the exponent $\alpha$ is equal to 2, the dimension of the
underlying lattice, regardless of the amount of anisotropy, but only in the
limit of infinite lattice size, $L\to\infty$. For finite size lattices we find
an optimal $\alpha(L)$ that depends strongly on $L$. The convergence to
$\alpha=2$ as $L\to\infty$ shows interesting power-law dependence on the
anisotropy strength.",0805.0807v1
2008-05-09,New Anomalies in Cosmic Microwave Background Anisotropy: Violation of the Isotropic Gaussian Hypothesis in Low-$l$ Modes,"In the standard framework of cosmology, primordial density fluctuations are
assumed to have an isotropic Gaussian distribution. We search for deviations
from this assumption in the WMAP data for the low $l$ modes of Cosmic Microwave
Background Anisotropies (CMBA), by studying the directions of the z-axis that
maximize the $l=m$ modes and the resulting amplitudes of these modes. We find a
general alignment of the directions for $l=2$ to 10 modes to within 1/4 of the
northern hemisphere. This alignment can be regarded as a generalization of the
recently discovered alignment of the $l=2$ and 3 modes - the so-called `Axis of
Evil'. Furthermore, we find abnormally high (low) powers in the $l=m=6$, 12 -
17 ($l=m=5$) modes; the probabilities for having the anomalous amplitudes of
the $l=m=5$, 6, 17 modes are about 0.1%, 1% and 1% respectively according to
the Gaussian conjecture. The alignment and anomalous amplitudes for these low
$l$ modes are very robust against foreground contamination or different
cleaning strategies, suggesting a cosmological origin and possibly supporting a
non-standard inflation.",0805.1316v2
2008-05-12,Exchange coupled perpendicular media,"The potential of exchange spring bilayers and graded media is reviewed. An
analytical model for the optimization of graded media gives an optimal value of
the magnetic polarization of Js = 0.8 T. The optimum design allows for
thermally stable grains with grain diameters in the order of 3.3 nm, which
supports ultra high density up to 5 to 10 Tbit per inch2. The switching field
distribution is significantly reduced in bilayer media and graded media
compared to single phase media. For the graded media the switching field
distribution is reduced by about a factor of two. For bilayer media the minimum
switching field distribution is obtained for soft layer anisotropies about one
fifth of the hard layer anisotropy. The influence of precessional switching on
the reversal time and the reversal field is investigated in detail for magnetic
bilayers. Exchange spring bilayers can be reversed with field pulses of 20 ps.",0805.1674v1
2008-05-21,Exploring the order parameter symmetry of p-wave Fermi condensates,"We discuss the time-of-flight expansion of dilute p-wave Fermi condensates on
the BEC side of Feshbach resonances, as a way to extract information about the
order parameter symmetry for superfluidity. We show that the cloud profile is
in general sensitive to the interaction strength between fermions, the
magnitude and direction of external magnetic fields, and to the angular
momentum projection of the order parameter. In particular, due to the
anisotropic nature of p-wave interactions we show that the time-of-flight
expansion of a p-wave superfluid is anisotropic even if the superfluid is
confined to a completely isotropic trap, unlike the case of Bose or s-wave
Fermi condensates, which under the same circumstances expand isotropically.
Furthermore, we demonstrate that expanding p-wave superfluids released from
axially symmetric traps experience anisotropy inversions, where the aspect
ratio between the axial and radial directions change during expansion, while
the axial symmetry can also be lost reflecting the spatial anisotropy of the
underlying interaction.",0805.3315v1
2008-05-22,Repeated magnetic compensation behaviour in Nd0.75Gd0.25Rh3B2 alloy having hexagonal structure and planar anisotropy,"The results of dc and ac magnetization, electrical resistance and heat
capacity studies in an admixed rare earth alloy Nd0.75Gd0.25Rh3B2, which is
close to the zero magnetization limit, are reported. Novel observations include
the two antiferromagnetic like transitions, concomitant repeated/multiple
magnetic compensation behaviour and a characteristic oscillatory magnetic
response, with temperature dependence of magnetization at low fields crossing
the M = 0 axis thrice. The effective coercive field relating to the residual
remanence also has an oscillatory response, with two minima located close to
two zero-crossover temperatures. The unusual behavior in Nd0.75Gd0.25Rh3B2 is
conjectured to arise from its anisotropic hexagonal structure, with planar
anisotropy, resulting in a quasi one dimensional electronic structure and the
accentuated role of conduction electron polarization near the zero
magnetization limit.",0805.3412v2
2008-05-22,Cosmic Microwave Background Anisotropy from Nonlinear Structures in Accelerating Universes,"We study the cosmic microwave background (CMB) anisotropy due to spherically
symmetric nonlinear structures in flat universes with dust and a cosmological
constant. By modeling a time-evolving spherical compensated void/lump by
Lemaitre-Tolman-Bondi spacetimes, we numerically solve the null geodesic
equations with the Einstein equations. We find that a nonlinear void redshifts
the CMB photons that pass through it regardless of the distance to it. In
contrast, a nonlinear lump blueshifts (or redshifts) the CMB photons if it is
located near (or sufficiently far from) us. The present analysis
comprehensively covers previous works based on a thin-shell approximation and a
linear/second order perturbation method and the effects of shell thickness and
full nonlinearity. Our results indicate that, if quasi-linear and large
($>100$Mpc) voids/lumps would exist, they could be observed as cold or hot
spots with temperature variance $>10^{-5}$K in the CMB sky.",0805.3446v2
2008-05-27,System size and beam energy dependence of azimuthal anisotropy from PHENIX,"We present azimuthal anisotropy measurements in Au+Au and Cu+Cu collisions at
$\sqrt{s_{NN}}$ = 62.4 and 200 GeV. Comparison between reaction plane and
cumulant $v_2$ measurements in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV
show that non-flow contributions, originating mainly from jets, influence the
extracted $v_2$ for $p_T$ $\gtrsim$ 3.5 GeV/c. Number of constituent quark
(NCQ) scaling of $v_2$, when studied as a function of transverse kinetic energy
$KE_T$, is seen to hold for Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 and 200
GeV and for Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV for $KE_{T}$
$\lesssim$ 1 GeV/c. Differential hexadecupole flow $v_4$ seems to exhibit
scaling with integral $v_2$ for centrality $\le$ 40% as has been observed for
differential $v_2$.",0805.4039v1
2008-05-29,Band structure of ZnO from resonant x-ray emission spectroscopy,"Soft x-ray emission and absorption spectroscopy of the O K-edge are employed
to investigate the electronic structure of wurtzite ZnO(0001). A quasiparticle
band structure calculated within the GW approximation agrees well with the
data, most notably with the energetic location of the Zn3d - O2p hybridized
state and the anisotropy of the absorption spectra. Dispersion in the band
structure is mapped using the coherent k-selective part of the resonant x-ray
emission spectra. We show that a more extensive mapping of the bands is
possible in the case of crystalline anisotropy such as that found in ZnO.",0805.4641v3
2008-06-05,Anisotropy of superconducting single crystal SmFeAsO_(0.8)F_(0.2) studied by torque magnetometry,"Single crystals of the oxypnictide superconductor SmFeAsO_(0.8)F_(0.2) with
T_c=45(1) K were investigated by torque magnetometry. The crystals of mass~0.1
mug were grown by a high-pressure cubic anvil technique. The use of a
high-sensitive piezoresistive torque sensor made it possible to study the
anisotropic magnetic properties of these tiny crystals. The anisotropy
parameter was found to be field independent, but varies strongly with
temperature ranging from 8 at T=T_c to 23 at T=0.4T_c. This unusual behavior
signals unconventional superconductivity.",0806.1024v3
2008-06-07,Influence of quenched jets on di-hadron correlations,"A simple jet absorption model is used to study the influence of hadron pairs
produced by quenched jets, on di-hadron angular correlations at intermediate
transverse momentum ($p_T$). We demonstrate that such pairs can dominate both
the yield and the shape of angular correlations, and may account for the
similar properties between the near-side ""ridge"" and the away-side
""double-humped"" structure seen in recent data. These hadron pairs also show
azimuthal anisotropy which is sensitive to the emission angle of hadrons
relative to that of the jet. Measurement of this anisotropy may provide a
constraint for elucidating the production mechanism for near- and away-side
hadron pairs at intermediate $p_T$.",0806.1225v3
2008-06-12,Neutrino mass effects on vector and tensor CMB anisotropies in the presence of a primordial magnetic field,"If a primordial magnetic field (PMF) is present during photon decoupling and
afterward, a finite neutrino mass can affect all modes of the CMB. In this
work, we expand on earlier studies of the scalar mode effects by constructing
the vector and tensor mode equations in the presence of massive neutrinos and a
PMF. We compute the power spectrum of the various modes in an illustrative
example and find that the neutrino mass can significantly affect the vector and
tensor modes when a PMF exists, while the effects are negligible for no PMF.
The most prominent result of the present analysis is the behavior of the EE
component of the tensor mode at low multipoles. For massive neutrinos the EE
mode can become comparable to the observed primary anisotropy. Therefore, if
and when the EE mode power spectrum is measured at low multipoles the
possibility exists to place a strong constraint on the sum of the neutrino
masses.",0806.2018v1
2008-06-13,Topological defects in antiferromagnetically coupled multilayers with perpendicular anisotropy,"A rich variety of specific multidomain textures recently observed in
antiferromagnetically coupled multilayers with perpendicular anisotropy include
regular (equilibrium) multidomain states as well as different types of
topological magnetic defects. Within a phenomenological theory we have
classified and analyzed the possible magnetic defects in the antiferromagnetic
ground state and determine their structures. We have derived the optimal sizes
of the defects as functions of the antiferromagnetic exchange, the applied
magnetic field, and geometrical parameters of the multilayer. The calculated
magnetic phase diagrams show the existence regions for all types of magnetic
defects. Experimental investigations of the remanent states (observed after
different magnetic pre-history) in [Co/Pt]/Ru multilayers with wedged Co layers
reveal a corresponding succession of different magnetic defect domain types.",0806.2170v2
2008-06-22,Determination of the exchange anisotropy in perovskite antiferromagnets using powder inelastic neutron scattering,"A procedure is outlined for the determination of magnetic exchange constants
in anisotropic perovskite anitferromagnets using powder inelastic neutron
scattering. Spin wave densities-of-states are measured using time-of-flight
inelastic neutron scattering for LaMnO$_{3}$ ($A$-type antiferromagnet),
LaVO$_{3}$ ($C$-type), and LaFeO$_{3}$ ($G$-type) and compared to Heisenberg
model calculations. The anisotropy of in-plane ($J_{ab}$) and out-of-plane
($J_{c}$) exchange constants can be obtained from the data. The procedure
quickly determines the magnetic exchange interactions without the need for
single-crystal dispersion measurements and allows for rapid systematic studies
of the evolution of magnetism in perovskite systems.",0806.3576v1
2008-06-27,Statistical and systematical errors in cosmic microwave background maps,"Sky temperature map of the cosmic microwave background (CMB) is one of the
premier probes of cosmology. To minimize instrumentally induced systematic
errors, CMB anisotropy experiments measure temperature differences across the
sky using paires of horn antennas with a fixed separation angle, temperature
maps are recovered from temperature differences obtained in sky survey through
a map-making procedure. The instrument noise, inhomogeneities of the sky
coverage and sky temperature inevitably produce statistical and systematical
errors in recovered temperature maps. We show in this paper that
observation-dependent noise and systematic temperature distortion contained in
released Wilkinson Microwave Anisotropy Probe (WMAP) CMB maps are remarkable.
These errors can contribute to large-scale anomalies detected in WMAP maps and
distort the angular power spectrum as well. It is needed to remake temperature
maps from original WMAP differential data with modified map-making procedure to
avoid observation-dependent noise and systematic distortion in recovered maps.",0806.4493v1
2008-07-02,Numerical Studies of Quantum Hall Ferromagnetism in Two-Subband Systems,"We carry out a numerical study of the quantum Hall ferromagnetism in a
two-subband system using a set of experimental parameters in a recently
experiment [X. C. Zhang, I. Martin, and H. W. Jiang, Phys. Rev. B \textbf{74},
073301 (2006)]. Employing the self-consistence local density approximation for
growth direction wave function and the Hartree-Fock theory for the pseudospin
anisotropy energy, we are able to account for the easy-axis and easy-plane
quantum Hall ferromagnetism observed at total filling factor $\nu = 3$ and
$\nu= 4$, respectively. Our study provides some insight of how the anisotropy
energy, which highly depends upon the distribution of growth direction wave
functions, determines the symmetry of the quantum Hall ferromagnets.",0807.0297v1
2008-07-02,Cosmic microwave background bispectrum on small angular scales,"This article investigates the non-linear evolution of cosmological
perturbations on sub-Hubble scales in order to evaluate the unavoidable
deviations from Gaussianity that arise from the non-linear dynamics. It shows
that the dominant contribution to modes coupling in the cosmic microwave
background temperature anisotropies on small angular scales is driven by the
sub-Hubble non-linear evolution of the dark matter component. The perturbation
equations, involving in particular the first moments of the Boltzmann equation
for the photons, are integrated up to second order in perturbations. An
analytical analysis of the solutions gives a physical understanding of the
result as well as an estimation of its order of magnitude. This allows to
quantify the expected deviation from Gaussianity of the cosmic microwave
background temperature anisotropy and, in particular, to compute its bispectrum
on small angular scales. Restricting to equilateral configurations, we show
that the non-linear evolution accounts for a contribution that would be
equivalent to a constant primordial non-Gaussianity of order fNL~25 on scales
ranging approximately from l~1000 to l~3000.",0807.0341v2
2008-07-04,"Strain-Control of the magnetic anisotropy in (Ga,Mn)(As,P) ferromagnetic semiconductor layers","A small fraction of phosphorus (up to 10 %) was incorporated in ferromagnetic
(Ga,Mn)As epilayers grown on a GaAs substrate. P incorporation allows reducing
the epitaxial strain or even change its sign, resulting in strong modifications
of the magnetic anisotropy. In particular a reorientation of the easy axis
toward the growth direction is observed for high P concentration. It offers an
interesting alternative to the metamorphic approach, in particular for
magnetization reversal experiments where epitaxial defects stongly affect the
domain wall propagation.",0807.0748v1
2008-07-04,Polarization-Mixing in Optical Lattices with Uniaxial Anisotropy,"We study optical excitations of an ultracold gas in an optical lattice in the
Mott insulator case and with anisotropic properties. The anisotropy is induced
by an oriented transition dipole generated by optical pumping and external
static fields, and is of the type of uniaxial crystals. Within a cavity, the
electronic excitations and the cavity photons of both TE and TM polarizations
are coherently mixed to form two polariton branches. Also a photonic branch
appears which decouples from the electronic transitions. The photon
polarization mixing can be observed by linear optical spectra. For example, for
an incident field of TE polarization we obtain TE and TM transmitted and
reflected fields. Also we calculate the phase shift in the TE and TM
transmitted and reflected fields relative to the incident field phase, which
lead to polarization rotations.",0807.0761v1
2008-07-08,Semiclassical spin liquid state of easy axis Kagome antiferromagnets,"Motivated by recent experiments on Nd-langasite, we consider the effect of
strong easy axis single-ion anisotropy $D$ on $S > 3/2$ spins interacting with
antiferromagnetic exchange $J$ on the Kagome lattice. When $T \ll DS^2$, the
collinear low energy states selected by the anisotropy map on to configurations
of the classical Kagome lattice Ising antiferromagnet. However, the low
temperature limit is quite different from the cooperative Ising paramagnet that
obtains classically for $T \ll JS^2$. We find that sub-leading ${\mathcal
O}(J^3S/D^2)$ multi-spin interactions arising from the transverse quantum
dynamics result in a crossover from an intermediate temperature classical
cooperative Ising paramagnet to a semiclassical spin liquid with distinct
short-ranged correlations for $T \ll J^3S/D^2$.",0807.1163v1
2008-07-08,Revealing dark matter substructure with anisotropies in the diffuse gamma-ray background,"The majority of gamma-ray emission from Galactic dark matter annihilation is
likely to be detected as a contribution to the diffuse gamma-ray background. I
show that dark matter substructure in the halo of the Galaxy induces
characteristic anisotropies in the diffuse background that could be used to
determine the small-scale dark matter distribution. I calculate the angular
power spectrum of the emission from dark matter substructure for several models
of the subhalo population, and show that features in the power spectrum can be
used to infer the presence of substructure. The shape of the power spectrum is
largely unaffected by the subhalo radial distribution and mass function, and
for many scenarios I find that a measurement of the angular power spectrum by
Fermi will be able to constrain the abundance of substructure. An anti-biased
subhalo radial distribution is shown to produce emission that differs
significantly in intensity and large-scale angular dependence from that of a
subhalo distribution which traces the smooth dark matter halo, potentially
impacting the detectability of the dark matter signal for a variety of targets
and methods.",0807.1328v2
2008-07-09,"Molecular Beam Epitaxy grown (Ga,Mn)(As,P) with perpendicular to plane magnetic easy axis","We present an experimental investigation of the magnetic, electrical and
structural properties of Ga0.94Mn0.06As1-yPy layers grown by molecular beam
epitaxy on GaAs substrates for y less than or equal to 0.3. X-ray diffraction
measurements reveal that the layers are under tensile strain which gives rise
to a magnetic easy axis perpendicular to the plane of the layers. The strength
of the magnetic anisotropy and the coercive field increase as the phosphorous
concentration is increased. The resistivity of all samples shows metallic
behaviour with the resistivity increasing as y increases. These materials will
be useful for studies of micromagnetic phenomena requiring metallic
ferromagnetic material with perpendicular magnetic anisotropy.",0807.1469v1
2008-07-15,Constraints on Kinetically Modified Inflation from WMAP5,"Single field inflationary models with a non-minimal kinetic term (also called
k-inflationary models) can be characterised by the so-called sound flow
functions, which complete the usual Hubble flow hierarchy. These parameters
appear in the primordial power spectra of cosmological perturbations at leading
order and, therefore, affect the resulting Cosmic Microwave Background (CMB)
anisotropies. Using the fifth year Wilkinson Microwave Anisotropy Probe (WMAP5)
data, we derive the marginalised posterior probability distributions for both
the sound and Hubble flow parameters. In contrast to the standard situation,
these parameters remain separately unbounded, and notably there is no longer
any upper limit on epsilon_1, the first Hubble flow function. Only special
combinations of these parameters, corresponding to the spectral index and
tensor-to-scalar ratio observables, are actually constrained by the data. The
energy scale of k-inflation is nevertheless limited from above to Hinf/mpl <
6x10^(-6) at two-sigma level. Moreover, for the sub-class of Dirac-Born-Infeld
models, by considering the non-gaussianity bounds on the sound speed, we find a
weak limit epsilon_1 < 0.08 at 95% confidence level.",0807.2414v1
2008-07-17,Symmetry of standing waves generated by a point defect in epitaxial graphene,"Using scanning tunneling microscopy (STM) and Fourier Transform STM (FT-STM),
we have studied a point defect in an epitaxial graphene sample grown on silicon
carbide substrate. This analysis allows us to extract the quasiparticle energy
dispersion, and to give a first experimental proof of the validity of Fermi
liquid theory in graphene for a wide range of energies from -800 meV to +800
meV. We also find evidence of a strong threefold anisotropy in the standing
waves generated by the defect. We discuss possible relations between this
anisotropy, the chirality of the electrons, and the asymmetry between
graphene's two sublattices. All experimental measurements are compared and
related to theoretical T-matrix calculations.",0807.2813v1
2008-07-22,Exponential equilibration by slow cooling in the planar random-anisotropy magnet: experiments and simulations,"Neutron measurements of the equilibration of the staggered magnetization in
DyAs(0.35)V(0.65)O4 are compared with Monte Carlo simulations of spin dynamics
in a planar random-anisotropy magnet. The simulation results are in agreement
with striking observed relaxation phenomena: when cooled rapidly to a low
temperature no magnetic ordering is observed, but when cooled in small steps an
ordered magnetic moment appears which is found to equilibrate exponentially
with time at temperatures through and below the transition temperature. In
contrast to the freezing of spins in other random systems, the time scale of
the relaxation in this system does not increase significantly even at the
lowest temperatures.",0807.3536v1
2008-07-23,Large Scale Plane-Mirroring in the Cosmic Microwave Background WMAP5 Maps,"We continue investigation of the hidden plane-mirror symmetry in the
distribution of excursion sets in cosmic microwave background (CMB) temperature
anisotropy maps, previously noticed in the three-year data of the Wilkinson
microwave anisotropy probe (WMAP), using the WMAP 5 years maps. The symmetry is
shown to have higher significance, \chi^2 < 1.7, for low multipoles \ell < 5,
while disappearing at larger multipoles, \chi^2 > 3.5 for \ell > 10. The study
of the sum and difference maps of temperature inhomogeneity regions, along with
simulated maps, confirms its existence.The properties of these mirroring
symmetries are compatible with those produced by the Sachs-Wolfe effect in the
presence of an anomalously large component of horizon-size density
perturbations, independent of one of the spatial coordinates, and/or a
slab-like spatial topology of the Universe.",0807.3652v2
2008-07-23,Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass,"We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and
observed transport evidence of single anisotropic-mass valley occupancy for the
electrons in a 150 \AA wide QW. Our calculations of strain and quantum
confinement for these samples predict single anisotropic-mass valley occupancy
for well widths $W$ greater than 53 \AA. Below this, double-valley occupation
is predicted such that the longitudinal mass axes are collinear. We observed
mobility anisotropy in the electronic transport along the crystallographic
directions in the ratio of 2.8, attributed to the mass anisotropy as well as
anisotropic scattering of the electrons in the X-valley of AlAs.",0807.3763v1
2008-07-25,Caloric Determination of the Upper Critical Fields and Anisotropy of NdFeAsO1-xFx Single Crystals,"We present heat capacity measurements of the upper critical fields of
single-crystal NdFeAsO1-xFx. In zero-magnetic field a clear step in the heat
capacity is observed at Tc = 47K . In fields applied perpendicular to the
FeAs-layers the step broadens significantly whereas for the in-plane
orientation the field effects are small. This behavior is reminiscent of the
CuO2-high-Tc superconductors and is a manifestation of pronounced fluctuation
effects. Using an entropy conserving construction we determine the transition
temperatures in applied fields and the upper critical field slopes of dHc2,a =
-0.72 T/K and dHc2,ab = -3.1 T/K. Zero-temperature coherence lengths of xiab =
3.7 nm and xic = 0.9 nm and a modest superconducting anisotropy of gamma ~ 4
can be deduced in a single-band model.",0807.4196v1
2008-07-28,Determination of anisotropic Hc2 up to 60 T in (Ba0.55K0.45)Fe2As2 single crystals,"The radio frequency penetration depth was measured in the superconductor
(Ba$_{0.55}$K$_{0.45}$)Fe$_{2}$As$_{2}$ under pulsed magnetic fields extending
to 60 tesla and down to 14 K. Using these data we are able to infer a
$H_{c2}(T)$, $H-T$ phase diagram, for applied fields parallel and perpendicular
to the crystallographic c-axis. The upper critical field curvature is different
for the respective orientations but they each remain positive down to 14 K. The
upper critical field anisotropy is moderate, $\approx 3.5$ close to $T_c$, and
drops with the decrease of temperature, reaching $\approx 1.2$ at $14 K$. These
data and analysis indicate that (i) (Ba$_{0.55}$K$_{0.45}$)Fe$_{2}$As$_{2}$
anisotropy diminishes with temperature and has an unusual temperature
dependence, (ii) $H_{c2} (T=0)$ for this compound may easily approach fields of
75 tesla.",0807.4488v3
2008-07-30,LRS Bianchi Type I Models with Anisotropic Dark Energy and Constant Deceleration Parameter,"Locally rotationally symmetric (LRS) Bianchi Type I cosmological models are
examined in the presence of dynamically anisotropic dark energy and perfect
fluid. We assume that the dark energy (DE) is minimally interacting, has
dynamical energy density, anisotropic equation of state parameter (EoS). The
conservation of the energy-momentum tensor of the DE is assumed to consist of
two separately additive conserved parts. A special law is assumed for the
deviation from isotropic EoS, which is consistent with the assumption on the
conservation of the energy-momentum tensor of the DE. Exact solutions of
Einstein's field equations are obtained by assuming a special law of variation
for the mean Hubble parameter, which yields a constant value of the
deceleration parameter. Geometrical and kinematic properties of the models and
the behaviour of the anisotropy of the dark energy has been carried out. The
models give dynamically anisotropic expansion history for the universe that
allows to fine tune the isotropization of the Bianchi metric, hence the CMB
anisotropy.",0807.4867v2
2008-07-31,GaN/AlN Quantum Dots for Single Qubit Emitters,"We study theoretically the electronic properties of $c$-plane GaN/AlN quantum
dots (QDs) with focus on their potential as sources of single polarized photons
for future quantum communication systems. Within the framework of eight-band
k.p theory we calculate the optical interband transitions of the QDs and their
polarization properties. We show that an anisotropy of the QD confinement
potential in the basal plane (e.g. QD elongation or strain anisotropy) leads to
a pronounced linear polarization of the ground state and excited state
transitions. An externally applied uniaxial stress can be used to either induce
a linear polarization of the ground-state transition for emission of single
polarized photons or even to compensate the polarization induced by the
structural elongation.",0807.5024v2
2008-07-31,Wind anisotropy and stellar evolution,"Mass loss is a determinant factor which strongly affects the evolution and
the fate of massive stars. At low metallicity, stars are supposed to rotate
faster than at the solar one. This favors the existence of stars near the
critical velocity. In this rotation regime, the deformation of the stellar
surface becomes important, and wind anisotropy develops. Polar winds are
expected to be dominant for fast rotating hot stars.
  These polar winds allow the star to lose large quantities of mass and still
retain a high angular momentum, and they modifie the evolution of the surface
velocity and the final angular momentum kept in the star's core. We show here
how these winds affect the final stages of massive stars, according to our
knowledge about Gamma Ray Bursts. Computation of theoretical Gamma Ray Bursts
rate indicates that our models have too fast rotating cores, and that we need
to include an additional effect to spin them down. Magnetic fields in stars act
in this direction, and we show how they modify the evolution of massive star up
to the final stages.",0807.5061v1
2008-08-21,First Measurement of the J/psi Azimuthal Anisotropy in PHENIX at Forward Rapidity in Au+Au Collisions at sqrt s(NN) = 200 GeV,"The PHENIX experiment has shown that J/psis are suppressed in central Au+Au
collisions at a center of mass energy per nucleon-nucleon collision sqrt s(NN)
= 200 GeV, and that the suppression is larger at forward than at mid-rapidity.
Part of this difference may be explained by cold nuclear matter effects but the
most central collisions suggest that regeneration mechanisms could be at play.
In 2007, PHENIX collected almost four times more Au+Au collisions at this
energy than used for previous published results. Moreover, the addition of a
new reaction plane detector allows a much better analysis of the J/psi behavior
in the azimuthal plane. Since a large elliptic flow has been measured for open
charm, measuring J/psi azimuthal anisotropies may give a hint if J/psi are
recombined in the expanding matter. First PHENIX results of J/psi elliptic flow
as a function of transverse momentum at forward rapidity are presented in this
article. The analysis is detailed and results are compared to mid-rapidity
PHENIX preliminary results as well as to predictions.",0808.2925v2
2008-08-28,Suppression of forward dilepton production from an anisotropic quark-gluon plasma,"We calculate the rapidity dependence of leading-order medium dilepton yields
resulting from a quark-gluon plasma which has a local time-dependent anisotropy
in momentum space. We present a phenomenological model which includes temporal
evolution of the plasma anisotropy parameter, xi, and the hard momentum scale,
p_hard. Our model interpolates between 1+1 dimensional collisionally-broadened
expansion at early times and 1+1 dimensional ideal hydrodynamic expansion at
late times. Using our model, we find that at LHC energies, forward high-energy
medium dilepton production would be suppressed by up to a factor of 3 if one
assumes an isotropization/thermalization time of 2 fm/c. Therefore, it may be
possible to use forward dilepton yields to experimentally determine the time of
onset of locally isotropic hydrodynamic expansion of the quark-gluon plasma as
produced in ultrarelativistic heavy-ion collisions.",0808.3969v1
2008-09-04,The dynamical structure of dark matter halos with universal properties,"$N$-body simulations have unveiled several apparently universal properties of
dark matter halos, including a cusped density profile, a power-law pseudo
phase-space density $\rho/\sigma_r^3$, and a linear $\beta-\gamma$ relation
between the density slope and the velocity anisotropy. We present a family of
self-consistent phase-space distribution functions $F(E,L)$, based on the
Dehnen-McLaughlin Jeans models, that incorporate these universal properties
very accurately. These distribution functions, derived using a quadratic
programming technique, are analytical, positive and smooth over the entire
phase space and are able to generate four-parameter velocity anisotropy
profiles $\beta(r)$ with arbitrary asymptotic values $\beta_0$ and
$\beta_\infty$. We discuss the orbital structure of six radially anisotropic
systems in detail and argue that, apart from its use for generating initial
conditions for $N$-body studies, our dynamical modeling provides a valuable
complementary approach to understand the processes involved in the formation of
dark matter halos.",0809.0901v1
2008-09-15,Role of covalent Fe-As bonding in the magnetic moment formation and exchange mechanisms in iron-pnictide superconductors,"The electronic origin of the huge magnetostructural effect in layered Fe-As
compounds is elucidated using LiFeAs as a prototype. The crucial feature of
these materials is the strong covalent bonding between Fe and As, which tends
to suppress the exchange splitting. The bonding-antibonding splitting is very
sensitive to the distance between Fe and As nuclei. We argue that the fragile
interplay between bonding and magnetism is universal for this family of
compounds. The exchange interaction is analyzed in real space, along with its
correlation with covalency and doping. The range of interaction and itinerancy
increase as the Fe-As distance is decreased. Superexchange makes a large
antiferromagnetic contribution to the nearest-neighbor coupling, which develops
large anisotropy when the local moment is not too small. This anisotropy is
very sensitive to doping.",0809.2586v3
2008-09-17,Astrophysical Tests of Lorentz and CPT Violation with Photons,"A general framework for tests of Lorentz invariance with electromagnetic
waves is presented, allowing for operators of arbitrary mass dimension.
Signatures of Lorentz violations include vacuum birefringence, vacuum
dispersion, and anisotropies. Sensitive searches for violations using sources
such as active galaxies, gamma-ray bursts, and the cosmic microwave background
are discussed. Direction-dependent dispersion constraints are obtained on
operators of dimension 6 and 8 using gamma-ray bursts and the blazar Markarian
501. Stringent constraints on operators of dimension 3 are found using 5-year
data from the Wilkinson Microwave Anisotropy Probe. No evidence appears for
isotropic Lorentz violation, while some support at one sigma is found for
anisotropic violation.",0809.2846v2
2008-09-22,Tailoring the Magnetic Anisotropy in CoRh Nanoalloys: Experiment and Theory,"The magnetic moments and magnetic anisotropy energy (MAE) of CoRh alloy
nanoparticles are determined experimentally and theoretically. Non-trivial
correlations between chemical order, magnetic order and MAE are revealed. A
remarkable non-monotonous dependence of the MAE as a function of composition
and chemical order is observed that opens novel possibilities of tuning the
magnetic properties of nanoalloys. The observations are successfully compared
and analyzed with our electronic calculations. In this way we clearly
demonstrate that the induced 4d moments and the 3d-4d interfaces are the key
parameters controlling the magneto-anisotropic behavior.",0809.3638v1
2008-09-24,Systematic Distortion in Cosmic Microwave Background Maps,"To minimize instrumentally induced systematic errors, cosmic microwave
background (CMB) anisotropy experiments measure temperature differences across
the sky using paires of horn antennas, temperature map is recovered from
temperature differences obtained in sky survey through a map-making procedure.
To inspect and calibrate residual systematic errors in recovered temperature
maps is important as most previous studies of cosmology are based on these
maps. By analyzing pixel-ring couping and latitude dependence of CMB
temperatures, we find notable systematic deviation from CMB Gaussianity in
released Wilkinson Microwave Anisotropy Probe (WMAP) maps. The detected
deviation is hard to explain by any process in the early universe and can not
be ignored for a precision cosmology study.",0809.4160v2
2008-09-30,UHECR observations and lensing in the magnetic field of the Virgo cluster,"We discuss how lensing by magnetic fields in galaxy clusters affects
ultrahigh energy cosmic ray (UHECR) observations. As specific example, we use
Virgo together with the cluster magnetic fields obtained earlier in a
constrained simulation of structure formation including MHD processes. We find
that, if M87 is the single source of UHECRs from Virgo, the emitted flux is
strongly anisotropic in the most interesting energy range, (50-100)EeV, and
differs from the average value by a factor five or more for a significant
fraction of observers. Since magnetic lensing is energy dependent, the external
energy spectrum as seen by different observers varies strongly too. These
anisotropies are averaged out in the case that all active galactic nuclei in
Virgo emit UHECRs. In both cases, the anisotropies of the emitted UHECR flux
may introduce an important bias in the interpretation of UHECR data like, e.g.,
the determination of the source density n_s and the source energy spectrum of
UHECRs.",0809.5055v2
2008-10-01,Lorentz-violating contributions of the Carroll-Field-Jackiw model to the CMB anisotropy,"We study the finite temperature properties of the
Maxwell-Carroll-Field-Jackiw (MCFJ) electrodynamics for a purely spacelike
background. Starting from the associated finite temperature partition function,
a modified black body spectral distribution is obtained. We thus show that, if
the CMB radiation is described by this model, the spectrum presents an
anisotropic angular energy density distribution. We show, at leading order,
that the Lorentz-breaking contributions for the Planck's radiation law and for
the Stefan-Boltzmann's law are nonlinear in frequency and quadratic in
temperature, respectively. Using our results, we set up bounds for the
Lorentz-breaking parameter, and show that Lorentz violation in the context of
the MCFJ model is unable to yield the known CMB anisotropy (of 1 part in
$10^{5})$.",0810.0306v2
2008-10-03,"Small anisotropy, weak thermal fluctuations, and high field superconductivity in Co-doped iron pnictide Ba(Fe1-xCox)2As2","We performed high-field magnetotransport and magnetization measurements on a
single crystal of the 122-phase iron pnictide Ba(Fe1-xCox)2As2. Unlike the HTS
cuprates and 1111-phase oxypnictides, Ba(Fe1-xCox)2As2 showed practically no
broadening of the resistive transitions under magnetic fields up to 45 T. The
mass anisotropy gamma = Hc2ab/Hc2c deduced from the slopes of the upper
critical field dHc2ab/dT = 4.9T/K and dHc2c/dT = 2.5T/K decreases from ~2 near
Tc, to ~1.5 at lower temperatures. We observed the irreversibility field close
to Hc2, and a rather unusual symmetric volume pinning force curve Fp(H)
suggestive of strong pinning nano-structure.",0810.0699v2
2008-10-10,Fermi surface and order parameter driven vortex lattice structure transitions in twin-free YBa2Cu3O7,"We report on small-angle neutron scattering studies of the intrinsic vortex
lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8
T. Because of the suppressed pinning to twin-domain boundaries, a new distorted
hexagonal VL structure phase is stabilized at intermediate fields. It is
separated from a low-field hexagonal phase of different orientation and
distortion by a first-order transition at 2.0(2) T that is probably driven by
Fermi surface effects. We argue that another first-order transition at 6.7(2)
T, into a rhombic structure with a distortion of opposite sign, marks a
crossover from a regime where Fermi surface anisotropy is dominant, to one
where the VL structure and distortion is controlled by the order-parameter
anisotropy.",0810.1947v2
2008-10-14,Effective magnetic penetration depth in superconducting cylinders and spheres with highly anisotropic electrodynamics,"Effective magnetic penetration depth and microwave surface impedance are
derived for anisotropic layered superconductors in the shape of spheres and
long cylinders, where the external magnetic field is applied in the plane of
the highly conducting layers to induce out-of-plane screening currents. The
results are extended by analytic continuation to highly anisotropic conductors
and to lossy superconductors at high frequency. The electrodynamics for the
general case of a superconductor or metal with arbitrary anisotropy are
presented. The treatment is then specialized to layered materials with
unixaxial anisotropy, in which the penetration depth for currents flowing
perpendicular to the layers, lambda_c, is much greater than that for in-plane
currents, lambda_a. Exact solutions are found in the limit lambda_a goes to
zero, and are expected to provide an accurate representation of many
experiments on cuprates and other layered superconductors, particularly on
grain-aligned powders.",0810.2342v1
2008-10-14,Energetic selection of ordered states in a model of the Er2Ti2O7 frustrated pyrochlore XY antiferromagnet,"We consider the possibility that the discrete long-range ordered states of
Er2Ti2O7 are selected energetically at the mean field level as an alternative
scenario that suggests selection via thermal fluctuations. We show that nearest
neighbour exchange interactions alone are not sufficient for this purpose, but
that anisotropies arising from excited single ion crystal field states in
Er2Ti2O7, together with appropriate anisotropic exchange interactions, can
produce the required long range order. However, the effect of the single ion
anisotropies is rather weak so we expect thermal or quantum fluctuations, in
some guise, to be ultimately important in this material. We reproduce recent
experimental results for the variation of magnetic Bragg peak intensities as a
function of magnetic field.",0810.2483v2
2008-10-16,Dipolar interactions and thermal stability of two-dimensional nanoparticle arrays,"We show results of Monte Carlo simulations of an array of monodispersed
magnetic monodomain particles, in a square lattice with dipolar interactions
and perpendicular uniaxial anisotropy. We first show the equilibrium phase
diagram of the system, which shows three phases, superparamagnetic (SP),
out-of-plane antiferromagnetic and in-plane antiferromagnetic with a
reorientation transition between the last two. We then employ a recently
introduced time quantified Monte Carlo method to study the relaxation of
autocorrelations of the particle array for different ratios of dipolar to
anisotropy energies. In the non-interacting case we show that relaxation is
exponential in time with characteristic times obeying a classic result by
Brown. When dipolar interactions are switched on, the relaxation is very well
described by stretched exponential forms in the whole time window and in both
the SP and ordered phases. Relaxation times still obey a nearly Arrhenius
behaviour, with a single effective energy barrier that decreases as the dipolar
interaction increases, a result that must be interpreted within the dynamics
protocol. No signs of glassy behaviour were found, in agreement with the
absence of disorder in the model system.",0810.2940v1
2008-10-24,Spin Dynamics in the Magnetoelectric Effect LiCoPO$_4$ Compound,"Inelastic neutron scattering (INS) experiments were performed to investigate
the spin dynamics in magnetoelectric effect (ME) LiCoPO$_4$ single crystals.
Weak dispersion was detected in the magnetic excitation spectra along the three
principal crystallographic axes measured around the (0 1 0) magnetic
reflection. Analysis of the data using linear spin-wave theory indicate that
single-ion anisotropy in LiCoPO$_4$ is as important as the strongest
nearest-neighbor exchange coupling. Our results suggest that Co$^{2+}$
single-ion anisotropy plays an important role in the spin dynamics of
LiCoPO$_4$ and must be taken into account in understanding its physical
properties. High resolution INS measurements reveal an anomalous low energy
excitation that we hypothesize may be related to the magnetoelectric effect of
LiCoPO$_4$.",0810.4471v1
2008-10-27,Surface morphology and magnetic anisotropy of Fe/MgO(001) films deposited at oblique incidence,"We have studied surface morphology and magnetic properties of Fe/MgO(001)
films deposited at an angle varying between 0o and 60o with respect to the
surface normal and with azimuth along the Fe[010] or the Fe[110] direction. Due
to shadowing, elongated grains appear on the film surface for deposition at
sufficiently large angle. X-ray reflectivity reveals that, depending on the
azimuthal direction, films become either rougher or smoother for oblique
deposition. For deposition along Fe[010] the pronounced uniaxial magnetic
anisotropy (UMA) results in the occurrence of reversed two-step and of
three-step hysteresis loops. For deposition along Fe[110] the growth-induced
UMA is much weaker, causing a small rotation of the easy axes.",0810.4929v1
2008-10-31,"Anisotropy, Itineracy, and Magnetic Frustration in High-Tc Iron Pnictides","Using first-principle density functional theory calculations combined with
insight from a tight-binding representation, dynamical mean field theory, and
linear response theory, we have extensively investigated the electronic
structures and magnetic interactions of nine ferropnictides representing three
different structural classes. The calculated magnetic interactions are found to
be short-range, and the nearest ($J_{1a}$) and next-nearest ($J_{2}$) exchange
constants follow the universal trend of J_{1a}/2J_{2}\sim 1, despite their
itinerant origin and extreme sensitivity to the z-position of As. These results
bear on the discussion of itineracy versus magnetic frustration as the key
factor in stabilizing the superconducting ground state. The calculated spin
wave dispersions show strong magnetic anisotropy in the Fe plane, in contrast
to cuprates.",0811.0034v3
2008-11-03,The full contribution of a stochastic background of magnetic fields to CMB anisotropies,"We study the contribution of a stochastic background (SB) of primordial
magnetic fields (PMF) on the anisotropies in temperature and polarization of
the cosmic microwave background radiation (CMB). A SB of PMF modelled as a
fully inhomogeneous component induces non-gaussian scalar, vector and tensor
metric linear perturbations. We give the exact expressions for the Fourier
spectra of the relevant energy-momentum components of such SB, given a
power-law dependence parametrized by a spectral index $n_B$ for the magnetic
field power spectrum cut at a damping scale $k_D$. For all the values of $n_B$
considered here, the contribution to the CMB temperature pattern by such a SB
is dominated by the scalar contribution and then by the vector one at higher
multipoles. We also give an analytic estimate of the scalar contribution to the
CMB temperature pattern.",0811.0230v2
2008-11-06,The microscopic theory of the upper critical field Hc2 in two-band systems in the magnetic field directed parallel and perpendicular to the plane (ab). Application to MgB2,"The microscopic superconductivity theory in MgB2 systems in the magnetic
fields directed parallel and perpendicular to the plane (ab) is built. The two
energy bands of different dimensions overlapping on the Fermi surface
(two-dimensional sigma- band and three-dimensional pi-band) are taken into
account. The theory is built taking into account the weak dispersion of the
electron energy of sigma -band in z direction. The systems of equations for the
superconductive transition temperature Tc and the upper critical field Hc2(ab)
are obtained. The analytic solutions of the equations for Hc2^0(ab) are found
in the two temperature areas: nearby the zero temperature T<<Tc^0 and in the
vicinity of the superconductive transition temperature Tc^0-T<<Tc^0. The
temperature dependencies of the upper critical fields Hc2(ab) and Hc2(c) on the
temperature are built, and the anisotropy coefficient gammaH=Hc2^0(ab)/Hc2^0(c)
is determined. It is shown that the value of Hc2(ab) exceeds greatly the value
of Hc2(c) due to the system anisotropy (to small values of the average velocity
of electrons in the crystallographic axis direction).",0811.0897v1
2008-11-14,Superfluid $^3$He in globally isotropic random media,"Recent theoretical and experimental studies of superfluid $^3$He in aerogels
with a global anisotropy, e.g., due to an external stress, have definitely
shown that the A-like phase with an equal spin pairing (ESP) in such aerogel
samples is in the ABM (or, axial) pairing state. In this paper, the A-like
phase of superfluid $^3$He in globally {\it isotropic} aerogel is studied in
details by assuming a weakly disordered system in which singular topological
defects are absent. Through calculation of the free energy, a disordered ABM
state is found to be the best candidate of the pairing state of the globally
isotropic A-like phase. Further, it is found through a one-loop renormalization
group calculation that the coreless continuous vortices (or, vortex-skyrmions)
are irrelevant to the long-distance behavior of the disorder-induced textures,
and that the superfluidity is maintained in spite of lack of the conventional
off-diagonal long range order. Therefore, the globally isotropic A-like phase
at weak disorder is, like in the case with a global stretched anisotropy, a
superfluid glass with the ABM pairing.",0811.2292v2
2008-11-16,Anisotropy in spatial order-disorder transformations and the vortex lattice symmetry transition in $YNi_2B_2C$ and $LuNi_2B_2C$,"Explorations of the order-disorder transformation in vortex matter in single
crystals of tetragonal structured (c/a $\sim$3) borocarbide superconductors,
$YNi_2B_2C$ and $LuNi_2B_2C$, reveal that vortex arrays experience different
effective pinning in different crystallographic directions. We surmise that
correlation exists between the large anisotropy in effective pinning/disorder
and the differences in the (local) symmetry transition from rhombohedral to
(quasi) square vortex lattice(VL). For field along high symmetry directions,
like, c-axis and ab-basal plane, the VL symmetry is close to square and the
ordered state spans a large field interval. When the field is turned away from
the c-axis towards ab-plane, at intermediate angles, the region of ordered
state shrinks, in response to enhancement in effective pinning. At such
intermediate angles the symmetry of the VL would be far from ideal triangular
or square.",0811.2602v1
2008-11-17,Dynamics of Gas-Fluidized Granular Rods,"We study a quasi-two-dimensional monolayer of granular rods fluidized by a
spatially and temporally homogeneous upflow of air. By tracking the position
and orientation of the particles, we characterize the dynamics of the system
with sufficient resolution to observe ballistic motion at the shortest time
scales. Particle anisotropy gives rise to dynamical anisotropy and
superdiffusive dynamics parallel to the rod's long axis, causing the parallel
and perpendicular mean squared displacements to become diffusive on different
timescales. The distributions of free times and free paths between collisions
deviate from exponential behavior, underscoring the non-thermal character of
the particle motion. The dynamics show evidence of rotational-translational
coupling similar to that of an anisotropic Brownian particle. We model
rotational-translation coupling in the single-particle dynamics with a modified
Langevin model using non-thermal noise sources. This suggests a
phenomenological approach to thinking about collections of self-propelling
particles in terms of enhanced memory effects.",0811.2751v1
2008-11-19,Possible Verification of Tilted Anisotropic Dirac Cone in α-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance,"It is proposed that the presence of a tilted and anisotropic Dirac cone can
be verified using the interlayer magnetoresistance in the layered Dirac fermion
system, which is realized in quasi-two-dimensional organic compound
\alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic
Landau level wave functions and assuming local tunneling of electrons. It is
shown that the resistivity takes the maximum in the direction of the tilt if
anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is
described to determine the parameters of the tilt and anisotropy.",0811.3041v3
2008-11-28,On the non-Gaussianity from Recombination,"The non-linear effects operating at the recombination epoch generate a
non-Gaussian signal in the CMB anisotropies. Such a contribution is relevant
because it represents a major part of the second-order radiation transfer
function which must be determined in order to have a complete control of both
the primordial and non-primordial part of non-Gaussianity in the CMB
anisotropies. We provide an estimate of the level of non-Gaussianity in the CMB
arising from the recombination epoch which shows up mainly in the equilateral
configuration. We find that it causes a contamination to the possible
measurement of the equilateral primordial bispectrum shifting the minimum
detectable value of the non-Gaussian parameter f^equil_NL by Delta f^equil_NL=
O(10) for an experiment like Planck.",0811.4584v3
2008-11-28,Fast rotating Bose-Einstein condensates in an asymmetric trap,"We investigate the effect of the anisotropy of a harmonic trap on the
behaviour of a fast rotating Bose-Einstein condensate. This is done in the
framework of the 2D Gross-Pitaevskii equation and requires a symplectic
reduction of the quadratic form defining the energy. This reduction allows us
to simplify the energy on a Bargmann space and study the asymptotics of large
rotational velocity. We characterize two regimes of velocity and anisotropy; in
the first one where the behaviour is similar to the isotropic case, we
construct an upper bound: a hexagonal Abrikosov lattice of vortices, with an
inverted parabola profile. The second regime deals with very large velocities,
a case in which we prove that the ground state does not display vortices in the
bulk, with a 1D limiting problem. In that case, we show that the coarse grained
atomic density behaves like an inverted parabola with large radius in the
deconfined direction but keeps a fixed profile given by a Gaussian in the other
direction. The features of this second regime appear as new phenomena.",0811.4714v1
2008-12-02,U(1)-Symmetry breaking and violation of axial symmetry in TlCuCl3 and other insulating spin systems,"We describe the Bose-Einstein condensate of magnetic bosonic quasiparticles
in insulating spin systems using a phenomenological standard functional method
for T = 0. We show that results that are already known from advanced
computational techniques immediately follow. The inclusion of a perturbative
anisotropy term that violates the axial symmetry allows us to remarkably well
explain a number of experimental features of the dimerized spin-1/2 system
TlCuCl3. Based on an energetic argument we predict a general intrinsic
instability of an axially symmetric magnetic condensate towards a violation of
this symmetry, which leads to the spontaneous formation of an anisotropy gap in
the energy spectrum above the critical field. We, therefore, expect that a true
Goldstone mode in insulating spin systems, i.e., a strictly linear
energy-dispersion relation down to arbitrarily small excitations energies,
cannot be observed in any real material.",0812.0535v3
2008-12-04,Exchange bias and its phase reversal in the zero magnetization admixed rare earth intermetallics,"Exchange bias effect is an important attribute in several device
applications. Traditionally, it is discussed as a form of exchange anisotropy
at the interface between the ferromagnetic/antiferromagnetic layers of two
distinct systems. We report here on the magnetically ordered alloys possessing
the feature of unidirectional anisotropy, which reverses its sign across a
characteristic temperature. These are admixed rare earth intermetallics,
comprising two dissimilar rare earth (RE) ions, belonging to the two different
halves of the 4f-series and imbibing the notion of ferromagnetic coupling
between the spins of all 4f-rare earth ions and that of the conduction
electrons. Magnetic moments of dissimilar RE ions in such admixed alloys,
however, get antiferromagnetically coupled and they display magnetic
compensation feature such that the field induced reversal in the orientation of
the magnetic moments of dissimilar rare earth ions happens across the
compensation temperature (Tcomp). Above a threshold field, the conduction
electron polarization also reverses its sign across Tcomp, this is argued to
correlate with the observed phase reversal in the exchange bias field.",0812.0929v1
2008-12-08,Measuring the isotropization time of quark-gluon plasma from direct photons at energies available at the BNL Relativistic Heavy Ion Collider (RHIC),"We calculate transverse momentum distribution of direct photons from various
sources by taking into account the initial state momentum anisotropy of {\em
Quark-Gluon-Plasma} (QGP) and late stage transverse flow effects. The total
photon yield, calculated for various combinations of initial conditions,
transition temperatures, is then compared with the recent measurement of photon
transverse momentum distribution by the PHENIX collaboration. It is shown that
the presence of such an anisotropy can describe the PHENIX photon data better
than the isotropic case. We show that the isotropization time thus extracted
remains of the order of 1 fm/c and is almost insensitive to the initial
conditions used.",0812.1478v3
2008-12-08,High domain wall velocities induced by current in ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy,"Current-induced domain wall (DW) displacements in an array of ultrathin
Pt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly
observed by wide field Kerr microscopy. DWs in all wires in the array were
driven simultaneously and their displacement on the micrometer-scale was
controlled by the current pulse amplitude and duration. At the lower current
densities where DW displacements were observed (j less than or equal to 1.5 x
10^12 A/m^2), the DW motion obeys a creep law. At higher current density (j =
1.8 x 10^12 A/m^2), zero-field average DW velocities up to 130 +/- 10 m/s were
recorded.",0812.1515v2
2008-12-18,Interplay of anisotropy and frustration: triple transitions in a triangular-lattice antiferromagnet,"The classical Heisenberg antiferromagnet on a triangular lattice with the
single-ion anisotropy of the easy-axis type is theoretically investigated. The
mean-field phase diagram in an external magnetic field is constructed. Three
finite-temperature Berezinskii-Kosterlitz-Thouless transitions are found by the
Monte Carlo simulations in zero field. The two upper transitions are related to
the breaking of the discrete ${\mathbb Z}_{6}$ symmetry group, while the lowest
transition is associated with a quasi-long-range ordering of transverse
components. The intermediate collinear phase between first and second
transitions is the sliding phase predicted by J. V. Jos\'e {\it et al}. [Phys.
Rev. B {\bf 16}, 1217 (1977)].",0812.3574v2
2008-12-22,Observation of superspin glass state in magnetically textured ferrofluid (gamma-Fe2O3),"Magnetic properties in a magnetically textured ferrofluid made out of
interacting maghemite (gamma-Fe2O3) nanoparticles suspended in glycerin have
been investigated. Despite the loss of uniform distribution of anisotropy axes,
a superspin glass state exists at low temperature in a concentrated, textured
ferrofluid as in the case of its non-textured counterpart. The onset of
superspin glass state was verified from the sample's AC susceptibility. The
influence of the anisotropy axis orientation on the aging behavior in the
glassy states is also discussed.",0812.4282v2
2008-12-25,Band-power reconstruction of the primordial fluctuation spectrum by the maximum likelihood reconstruction method,"The primordial curvature fluctuation spectrum is reconstructed by the maximum
likelihood reconstruction method using the five-year Wilkinson Microwave
Anisotropy Probe data of the cosmic microwave background temperature
anisotropy. We apply the covariance matrix analysis and decompose the
reconstructed spectrum into statistically independent band-powers. The
prominent peak off a simple power-law spectrum found in our previous analysis
turn out to be a $3.3\sigma$ deviation. From the statistics of primordial
spectra reconstructed from mock observations, the probability that a primordial
spectrum including such excess is realized in a power-law model is estimated to
be about 2%.",0812.4585v2
2009-01-08,Angular distributions of leptons from J/psi's produced in 920 GeV fixed-target proton-nucleus collisions,"A study of the angular distributions of leptons from decays of J/psi's
produced in p-C and p-W collisions at sqrt{s}=41.6 GeV has been performed in
the Feynman-x region -0.34 < x_F < 0.14 and for transverse momentum up to 5.4
GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring
of the DESY laboratory. The results, based on a clean selection of 2.3 x 10^5
J/psi's reconstructed in both the e^+ e^- and mu^+ mu^- decay channels,
indicate that J/psi's are produced with longitudinal polarization. The
magnitude of the effect is maximal at low p_T. For p_T >1 GeV/c a significant
dependence on the reference frame is found: the polar anisotropy is more
pronounced in the Collins-Soper frame and almost vanishes in the helicity
frame, where, instead, a significant azimuthal anisotropy arises.",0901.1015v1
2009-01-10,Adiabatic dynamics in a spin-1 chain with uniaxial single-spin anisotropy,"We study the adiabatic quantum dynamics of an anisotropic spin-1 XY chain
across a second order quantum phase transition. The system is driven out of
equilibrium by performing a quench on the uniaxial single-spin anisotropy, that
is supposed to vary linearly in time. We show that, for sufficiently large
system sizes, the excess energy after the quench admits a non trivial scaling
behavior that is not predictable by standard Kibble-Zurek arguments for
isolated critical points or extended critical regions. This emerges from a
competing effect of many accessible low-lying excited states, inside the whole
continuous line of critical points.",0901.1384v3
2009-01-14,Quarkonium states in an anisotropic QCD plasma,"We consider quarkonium in a hot QCD plasma which, due to expansion and
non-zero viscosity, exhibits a local anisotropy in momentum space. At short
distances the heavy-quark potential is known at tree level from the
hard-thermal loop resummed gluon propagator in anisotropic perturbative QCD.
The potential at long distances is modeled as a QCD string which is screened at
the same scale as the Coulomb field. At asymptotic separation the potential
energy is non-zero and inversely proportional to the temperature. We obtain
numerical solutions of the three-dimensional Schroedinger equation for this
potential. We find that quarkonium binding is stronger at non-vanishing
viscosity and expansion rate, and that the anisotropy leads to polarization of
the P-wave states.",0901.1998v2
2009-01-15,Rogues' gallery: the full freedom of the Bianchi CMB anomalies,"Combining a recent derivation of the CMB evolution equations for homogeneous
but anisotropic (Bianchi) cosmologies with an account of the full linearized
dynamical freedoms available in such models, I calculate and discuss the
various temperature and polarisation anisotropy patterns which may be formed.
Certain anisotropies can be hidden in superhorizon modes at early times, thus
avoiding any constraints from nucleosynthesis while nevertheless producing
non-trivial redshift-zero temperature patterns in flat and open universes. The
results are likely to be more of pedagogical than observational interest, but
future work will assess whether such patterns can be matched to anomalies in
WMAP results.",0901.2122v2
2009-01-15,Two-gap superconductivity in Ba_1-xK_xFe_2As_2: A complementary study of the magnetic penetration depth by \muSR and ARPES,"We investigate the magnetic penetration depth \lambda in superconducting
Ba_1-xK_xFe_2As_2 (T_c\simeq32K) with muon-spin rotation (\muSR) and
angle-resolved photoemission (ARPES). Using \muSR, we find the
penetration-depth anisotropy \gamma_\lambda=\lambda_c/\lambda_{ab} and the
second-critical-field anisotropy \gamma_{H_c2} to show an opposite T-evolution
below T_c. This dichotomy resembles the situation in the two-gap superconductor
MgB_2. A two-gap scenario is also suggested by an inflection point in the
in-plane penetration depth \lambda_ab around 7K. The complementarity of \muSR
and ARPES allows us to pinpoint the values of the two gaps and to arrive to a
remarkable agreement between the two techniques concerning the full T-evolution
of \lambda_ab. This provides further support for the described scenario and
establishes ARPES as a tool to assess macroscopic properties of the
superconducting condensate.",0901.2329v2
2009-01-16,Prospects for sympathetic cooling of polar molecules: NH with alkali-metal and alkaline-earth atoms - a new hope,"We explore the potential energy surfaces for NH molecules interacting with
alkali-metal and alkaline-earth atoms using highly correlated ab-initio
electronic structure calculations. The surfaces for interaction with
alkali-metal atoms have deep wells dominated by covalent forces. The resulting
strong anisotropies will produce strongly inelastic collisions. The surfaces
for interaction with alkaline-earth atoms have shallower wells that are
dominated by induction and dispersion forces. For Be and Mg the anisotropy is
small compared to the rotational constant of NH, so that collisions will be
relatively weakly inelastic. Be and Mg are thus promising coolants for
sympathetic cooling of NH to the ultracold regime.",0901.2493v2
2009-01-19,Anisotropy probe of galactic and extra-galactic Dark Matter annihilations,"We study the flux and the angular power spectrum of gamma-rays produced by
Dark Matter (DM) annihilations in the Milky Way (MW) and in extra-galactic
halos. The annihilation signal receives contributions from: a) the smooth MW
halo, b) resolved and unresolved substructures in the MW, c) external DM halos
at all redshifts, including d) their substructures. Adopting a self-consistent
description of local and extra-galactic substructures, we show that the
annihilation flux from substructures in the MW dominates over all the other
components for angles larger than O(1) degrees from the Galactic Center, unless
an extreme prescription is adopted for the substructures concentration. We also
compute the angular power spectrum of gamma-ray anisotropies and find that, for
an optimistic choice of the particle physics parameters, an interesting
signature of DM annihilations could soon be discovered by the Fermi LAT
satellite at low multipoles, l<100, where the dominant contribution comes from
MW substructures with mass M>10^4 solar masses. For the substructures models we
have adopted, we find that the contribution of extra-galactic annihilations is
instead negligible at all scales.",0901.2921v1
2009-01-31,Hall Coefficient of Equilibrium Supercurrents Flowing inside Superconductors,"We study augmented quasiclassical equations of superconductivity with the
Lorentz force, which is missing from the standard Ginzburg-Landau and
Eilenberger equations. It is shown that the magnetic Lorentz force on
equilibrium supercurrents induces finite charge distribution and the resulting
electric field to balance the Lorentz force. An analytic expression is obtained
for the corresponding Hall coefficient of clean type-II superconductors with
simultaneously incorporating the Fermi-surface and gap anisotropies. It has the
same sign and magnitude at zero temperature as the normal state for an
arbitrary pairing, having no temperature dependence specifically for the s-wave
pairing. The gap anisotropy may bring a considerable temperature dependence in
the Hall coefficient and can lead to its sign change as a function of
temperature, as exemplified for a model d-wave pairing with a two-dimensional
Fermi surface. The sign change may be observed in some high-$T_{c}$
superconductors.",0902.0042v1
2009-02-03,Polarized wavelets and curvelets on the sphere,"The statistics of the temperature anisotropies in the primordial cosmic
microwave background radiation field provide a wealth of information for
cosmology and for estimating cosmological parameters. An even more acute
inference should stem from the study of maps of the polarization state of the
CMB radiation. Measuring the extremely weak CMB polarization signal requires
very sensitive instruments. The full-sky maps of both temperature and
polarization anisotropies of the CMB to be delivered by the upcoming Planck
Surveyor satellite experiment are hence being awaited with excitement.
Multiscale methods, such as isotropic wavelets, steerable wavelets, or
curvelets, have been proposed in the past to analyze the CMB temperature map.
In this paper, we contribute to enlarging the set of available transforms for
polarized data on the sphere. We describe a set of new multiscale
decompositions for polarized data on the sphere, including decimated and
undecimated Q-U or E-B wavelet transforms and Q-U or E-B curvelets. The
proposed transforms are invertible and so allow for applications in data
restoration and denoising.",0902.0574v1
2009-02-09,Evolution of Cosmological Perturbations in the Presence of Primordial Magnetic Fields,"Possible existence of the primordial magnetic fields has affected the
structure formation of the universe. In this paper it is shown that the initial
conditions for density perturbations with magnetic fields derived in previous
works are inconsistent with Einstein equations. We find that this inconsistency
arises due to the unwanted cancellation of contributions from the magnetic
fields and primordial radiations. A complete set of equations and consistent
initial conditions in the long wavelength limit are given with an explicit
derivation in the covariant approach with CDM frame, by newly taking into
account a non-relativistic matter contribution in the radiation dominated era.
By solving these equations numerically, we derive the angular spectrum of
cosmic microwave background anisotropies and the matter power spectrum with
magnetic fields. We find that the amplitude of the angular power spectrum of
CMB anisotropies can alter at most a order of magnitude at $l \lesssim 4000$
compared with the previous results in the literature.",0902.1367v2
2009-02-17,Inflationary Universe with Anisotropic Hair,"We study an inflationary scenario with a vector field coupled with an
inflaton field and show that the inflationary universe is endowed with
anisotropy for a wide range of coupling functions. This anisotropic inflation
is a tracking solution where the energy density of the vector field follows
that of the inflaton field irrespective of initial conditions. We find a
universal relation between the anisotropy and a slow-roll parameter of
inflation. Our finding has observational implications and gives a counter
example to the cosmic no-hair conjecture.",0902.2833v2
2009-02-24,Finite-Size Scaling Critical Behavior of Randomly Pinned Spin-Density Waves,"We have performed Monte Carlo studies of the 3D $XY$ model with random
uniaxial anisotropy, which is a model for randomly pinned spin-density waves.
We study $L \times L \times L$ simple cubic lattices, using $L$ values in the
range 16 to 64, and with random anisotropy strengths of $D / 2 J$ = 1, 2, 3, 6
and $\infty$. There is a well-defined finite temperature critical point, $T_c$,
for each these values of $D / 2 J$. We present results for the angle-averaged
magnetic structure factor, $S (k)$ at $T_c$ for $L = 64$. We also use
finite-size scaling analysis to study scaling functions for the critical
behavior of the specific heat, the magnetization and the longitudinal magnetic
susceptibility. Good data collapse of the scaling functions over a wide range
of $T$ is seen for $D / 2 J$ = 6 and $\infty$. For our finite values of $D / 2
J$ the scaled magnetization function increases with $L$ below $T_c$, and
appears to approach an $L$-independent limit for large $L$. This suggests that
the system is ferromagnetic below $T_c$.",0902.4049v2
2009-02-27,Monte Carlo Determination of the Low-Energy Constants of a Spin 1/2 Heisenberg Model with Spatial Anisotropy,"Motivated by the possible mechanism for the pinning of the electronic liquid
crystal direction in YBCO as proposed in \cite{Pardini08}, we use the first
principles Monte Carlo method to study the spin 1/2 Heisenberg model with
antiferromagnetic couplings $J_{1}$ and $J_{2}$ on the square lattice. The
corresponding low-energy constants, namely the spin stiffness $\rho_s$, the
staggered magnetization density ${\cal M}_s$, the spin wave velocity $c$, as
well as the ground state energy density $e_0$ are determined by fitting the
Monte Carlo data to the predictions of magnon chiral perturbation theory. In
particular, the spin stiffnesses $\rho_{s1}$ and $\rho_{s2}$ are investigated
as a function of the ratio $J_{2}/J_{1}$ of the couplings. Although we find a
good agreement between our results with those obtained by the series expansion
method in the weakly anisotropic regime, for strong anisotropy we observe
discrepancies.",0902.4861v3
2009-02-27,Superconductivity at 23 K and Low Anisotropy in Rb-Substituted BaFe_2As_2 Single Crystals,"Single crystals of Ba_{1-x}Rb_{x}Fe_2As_2 with x=0.05-0.1 have been grown
from Sn flux and are bulk superconductors with T_c up to 23 K. The crystal
structure was determined by X-ray diffraction analysis, and Sn is found to be
incorporated for 9% Ba, shifted by 1.1 Angstroem away from the Ba site towards
the (Fe_2As_2)-layers. The upper critical field deduced from resistance
measurements is anisotropic with slopes of 7.1(3) T/K (H || ab-plane) and
4.2(2) T/K (H || c-axis), sufficiently far below T_c. The extracted upper
critical field anisotropy of 3 close to T_c, is in good agreement with the
estimate from magnetic torque measurements. This indicates that the electronic
properties in the doped BaFe_2As_2 compound are significantly more isotropic
than those in the LnFeAsO family. The in-plane critical current density at 5 K
exceeds 10^6 A/cm^2, making Ba_{1-x}Rb_xFe_2As_2 a promising candidate for
technical applications.",0903.0004v2
2009-03-08,Spherical magnetic nanoparticles: magnetic structure and interparticle interaction,"The interaction between spherical magnetic nanoparticles is investigated from
micromagnetic simulations and ananlysed in terms of the leading dipolar
interaction energy between magnetic dipoles. We focus mainly on the case where
the particles present a vortex structure. In a first step the local magnetic
structure in the isolated particle is revisited. For particles bearing a
uniaxial magnetocrystaline anisotropy, it is shown that the vortex core
orientation relative to the easy axis depends on both the particle size and the
anisotropy constant. When the particles magnetization present a vortex
structure, it is shown that the polarization of the particles by the dipolar
field of the other one must be taken into account in the interaction. An
analytic form is deduced for the interaction which involves the vortex core
magnetization and the magnetic susceptibility which are obtained from the
magnetic properties of the isolated particle.",0903.1423v2
2009-03-09,Mangetic phase transition for three-dimensional Heisenberg weak random anisotropy model: Monte Carlo study,"Magnetic phase transition (MPT) to magnetic quasi-long-range order (QLRO)
phase in a three-dimensional Heisenberg weak (D/J=4) random anisotropy (RA)
model is investigated by Monte Carlo simulation. The isotropic and cubic
distributions of RA axes are considered for simple-cubic-lattice systems.
Finite-size scaling analysis shows that the critical couplings for the former
and latter are K_c= 0.70435(2) and K_c=0.70998(4), respectively. While the
critical exponent 1/\nu =1.40824(0) is the same for both cases. A second-order
MPT to the QLRO phase is therefore evidenced to be possible in favor with the
existence of the QLRO predicted by recent functional renormalization group
theories.",0903.1581v1
2009-03-09,"Thermal and Transport Behavior of Single Crystalline R2CoGa8 (R = Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) Compounds","The anisotropy in electrical transport and thermal behavior of single
crystalline R$_{2}$CoGa$_{8}$ series of compounds is presented. These compounds
crystallize in a tetragonal structure with space gropup P4/mmm. The nonmagnetic
counterparts of the series namely Y$_{2}$CoGa$_{8}$ and Lu$_{2}$CoGa$_{8}$show
a behavior consistent with the low density of states at the fermi level. In
Y$_{2}$CoGa$_{8}$, a possibility of charge density wave transition is observed
at $\approx$ 30 K. Gd$_{2}$CoGa$_{8}$ and Er$_{2}$CoGa$_{8}$ show a presence of
short range correlation above the magnetic ordering temperature of the
compound. In case of Gd$_{2}$CoGa$_{8}$, the magnetoresistance exhibits a
significant anisotropy for current parallel to {[}100{]} and {[}001{]}
directions. Compounds with other magnetic rare earths (R = Tb, Dy, Ho and Tm)
show the normal expected magnetic behavior whereas Dy$_{2}$CoGa$_{8}$ exhibits
the possibility of charge density wave (CDW) transition at approximately same
temperature as that of Y$_{2}$CoGa$_{8}$. The thermal property of these
compounds is analysed on the basis of crystalline electric field (CEF)
calculations.",0903.1607v1
2009-03-11,"Cosmological Alfvén waves in the recent CMB data, and the observational bound on the primordial vector perturbation","In the presence of the primordial magnetic field, initial vector (vorticity)
perturbations produce cosmological Alfven waves and leave imprints on cosmic
microwave background (CMB) temperature and polarization anisotropy. We have
investigated imprints of cosmological Alfven waves in CMB anisotropy. For data
constraints, we have used the power spectrum of the recent CMB observations,
and correlations estimated from WMAP Internal Linear Combination (ILC) maps.
Our analysis shows 3 sigma evidence of cosmological Alfven waves. Using the 3
sigma limit from our analysis and the Alfven velocity limit from the total
energy density constraint, we impose a lower bound on the amplitude of
primordial vector perturbation: 4*10^-12 at k_0=0.002/Mpc.",0903.1930v6
2009-03-11,Scaling of the fidelity susceptibility in a disordered quantum spin chain,"The phase diagram of a quantum XY spin chain with Gaussian-distributed random
anisotropies and transverse fields is investigated, with focus on the fidelity
susceptibility, a recently introduced quantum information theoretical measure.
Monitoring the finite-size scaling of the probability distribution of this
quantity as well as its average and typical values, we detect a
disorder-induced disappearance of criticality and the emergence of Griffiths
phases in this model. It is found that the fidelity susceptibility is not
self-averaging near the disorder-free quantum critical lines. At the Ising
critical point the fidelity susceptibility scales as a disorder-strength
independent stretched exponential of the system size, in contrast with the
quadratic scaling at the corresponding point in the disorder-free XY chain.
Along the line where the average anisotropy vanishes the fidelity
susceptibility appears to scale extensively, whereas in the disorder-free case
this point is quantum critical with quadratic finite-size scaling.",0903.2069v2
2009-03-14,Three-Qubit Ground State and Thermal Entanglement of $XXZ$ Model With Dzyaloshinskii-Moriya Interaction,"We have studied the symmetric and non-symmetric pairwise ground state and
thermal entanglement in three-qubit anisotropic Heisenberg (XXZ) and Ising in a
magnetic field models and in the presence of Dzyaloshinskii-Moriya (DM)
interaction. We have found that increasing of the DM interaction and magnetic
field can enhance and reduce the entanglement of system. We have shown that the
non-symmetric pairwise has higher value concurrence and critical temperature
(above which the entanglement vanishes) than the symmetric pairwise. For
negative anisotropy the non-symmetric entanglement is a monotonic function of
DM interaction while for positive anisotropy it has a maximum versus DM
parameter and vanishes for larger values of DM interaction. The conditions for
the existence of thermal entanglement are discussed in details. The most
remarkable result happens at zero temperature where 3-qubit ground state
entanglement of the system (in spite of 2-qubit counterpart) shows the
fingerprint of quantum phase transition for an infinite size system.",0903.2556v1
2009-03-19,Plane-mirroring anomaly in the cosmic microwave background maps,"The plane-mirror symmetry previously noticed in the Cosmic Microwave
Background (CMB) temperature anisotropy maps of Wilkinson Microwave Anisotropy
Probe is shown to possess certain anomalous properties. The degree of the
randomness determined by the Kolmogorov stochasticity parameter in the both
symmetry regions appears to have identical values which, however, essentially
differ from the corresponding values for other sky regions. If the mirroring
were of cosmological origin, this would imply either additional randomizing
properties in those directions of the Universe or their different line-of-sight
depth. This analysis also provides a way to test the hypothesis of a link
between the nature of dark energy and inhomogeneities.",0903.3273v1
2009-03-21,Anisotropic universal conductance fluctuations in disordered quantum wires with Rashba and Dresselhaus spin-orbit interaction and applied in-plane magnetic field,"We investigate the transport properties of narrow quantum wires realized in
disordered two-dimensional electron gases in the presence of k-linear Rashba
and Dresselhaus spin-orbit interaction (SOI), and an applied in-plane magnetic
field. Building on previous work [Scheid, et al., PRL 101, 266401 (2008)], we
find that in addition to the conductance, the universal conductance
fluctuations also feature anisotropy with respect to the magnetic field
direction. This anisotropy can be explained solely from the symmetries
exhibited by the Hamiltonian as well as the relative strengths of the Rashba
and Dresselhaus spin orbit interaction and thus can be utilized to detect this
ratio from purely electrical measurements.",0903.3656v1
2009-04-28,Scaling behavior of the crossover to short-stack regimes of Josephson vortex lattices in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ stacks,"We report the systematic investigations of the oscillation of the Josephson
vortex (JV) flow resistance in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$
micro-fabricated junctions with various geometries and superconducting
anisotropy parameters. As the applied magnetic field parallel to the $ab$-plane
is increased, oscillation with a period corresponding to a $\phi_0/2$ par
atomic Josephson junction changes to oscillation with a doubled period. This
crossover is scaled by both the junction length and the anisotropy parameter,
indicating that the bulk inductive coupling that favors the triangular JV
lattice is replaced with the surface deformation energy as the dominant
interaction for a JV lattice. These results suggest that the in-phase square JV
lattice is pronounced at a higher magnetic field in a smaller and more
anisotropic sample.",0904.4389v1
2009-04-28,Ising versus XY anisotropy in frustrated R$_{2}$Ti$_{2}$O$_7$ compounds as seen by polarized neutrons,"We studied the field induced magnetic order in R$_{2}$Ti$_{2}$O$_7$
pyrochlore compounds with either uniaxial (R=Ho, Tb) or planar (R=Er, Yb)
anisotropy, by polarized neutron diffraction. The determination of the local
susceptibility tensor \{$\chi_\parallel,\chi_\perp$\} provides a universal
description of the field induced structures in the paramagnetic phase (2-270
K), whatever the field value (1-7 T) and direction. Comparison of the thermal
variations of $\chi_\parallel$ and $\chi_\perp$ with calculations using the
rare earth crystal field shows that exchange and dipolar interactions must be
taken into account. We determine the molecular field tensor in each case and
show that it can be strongly anisotropic.",0904.4440v1
2009-04-30,Stabilization of Skyrmion textures by uniaxial distortions in noncentrosymmetric cubic helimagnets,"In cubic noncentrosymmetric ferromagnets uniaxial distortions suppress the
helical states and stabilize Skyrmion lattices in a broad range of
thermodynamical parameters. Using a phenomenological theory for modulated and
localized states in chiral magnets, the equilibrium parameters of the Skyrmion
and helical states are derived as functions of the applied magnetic field and
induced uniaxial anisotropy. These results show that due to a combined effect
of induced uniaxial anisotropy and an applied magnetic field Skyrmion lattices
can be formed as thermodynamically stable states in large intervals of magnetic
field and temperatures in cubic helimagnets, e.g., in intermetallic compounds
MnSi, FeGe, (Fe,Co)Si. We argue that this mechanism is responsible for the
formation of Skyrmion states recently observed in thin layers of
Fe_{0.5}Co_{0.5}Si [X.Z.Yu et al., Nature \textbf{465}(2010) 901].",0904.4842v2
2009-05-01,Maxwell and Kerr effects in solutions of macromolecules with dendrons in side groups,"Linear polymers with dendrons of first and second generations based on
L-aspargic acid are studied by the methods of flow birefringence and electric
birefringence. Optical, dipole, dynamic, and conformational properties of the
macromolecules, as well as contributions to their optical anisotropy due to
macroform and microform effects, are investigated. The polymers are found to
possess permanent electric dipole moments and undergo reorientation in external
electric and hydrodynamic fields according to large-scale rotation mechanism. A
significant growth in equilibrium rigidity, optical anisotropy, and dipole
moment of monomer units is observed when rigid benzamide fragments are
introduced into the dendrimers. The backbone conformation of second-generation
dendrimers containing such fragments is shown to be well described by
generalized wormlike chain model.",0905.0153v1
2009-05-11,Orbital-Ordering Induces Structural Phase Transition and the Resistivity Anomaly in Iron Pnictides,"We attribute the structural phase transition (SPT) in the parent compounds of
the iron pnictides to orbital ordering. Due to the anisotropy of the $d_{xz}$
and $d_{yz}$ orbitals in the $xy$ plane, a ferro-orbital ordering makes the
orthorhombic structure more energetically favorable, thus inducing the SPT. In
this orbital-ordered system, the sites with orbitals that do not order have
higher energies. Scattering of the itinerant electrons by these localized
two-level systems causes a resistivity anomaly upon the onset of the SPT. The
proposed orbital ordering also leads to the stripe-like anti-ferromagnetism and
anisotropy of the magnetic exchanges. This model is quantitatively consistent
with available experimental observations.",0905.1704v2
2009-05-21,Anisotropic dark energy and CMB anomalies,"We investigate the breaking of global statistical isotropy caused by a dark
energy component with an energy-momentum tensor which has point symmetry, that
could represent a cubic or hexagonal crystalline lattice. In such models
Gaussian, adiabatic initial conditions created during inflation can lead to
anisotropies in the cosmic microwave background whose spherical harmonic
coefficients are correlated, contrary to the standard assumption. We develop an
adaptation of the line of sight integration method that can be applied to
models where the background energy-momentum tensor is isotropic, but whose
linearized perturbations are anisotropic. We then show how this can be applied
to the cases of cubic and hexagonal symmetry. We compute quantities which show
that such models are indistinguishable from isotropic models even in the most
extreme parameter choices, in stark contrast to models with anisotropic initial
conditions based on inflation. The reason for this is that the dark energy
based models contribute to the CMB anistropy via the inegrated Sachs-Wolfe
effect, which is only relevent when the dark energy is dominant, that is, on
the very largest scales. For inflationary models, however, the anisotropy is
present on all scales.",0905.3403v1
2009-05-29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
magnitude larger than soft magnetic materials, such as pure iron (Fe) and
permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
FMR linewidth depends linearly on frequency for perpendicular applied fields
and increases significantly when the magnetization is rotated into the film
plane. Irradiation of the film with Helium ions decreases the PMA and the
distribution of PMA parameters. This leads to a great reduction of the FMR
linewidth for in-plane magnetization. These results suggest that fluctuations
in PMA lead to a large two magnon scattering contribution to the linewidth for
in-plane magnetization and establish that the Gilbert damping is enhanced in
such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
pure Fe).",0905.4779v2
2009-06-03,The imprint of the interaction between dark sectors in large scale cosmic microwave background anisotropies,"Dark energy interacting with dark matter is a promising model to solve the
cosmic coincidence problem. We study the signature of such interaction on large
scale cosmic microwave background (CMB) temperature anisotropies. Based on the
detail analysis in perturbation equations of dark energy and dark matter when
they are in interaction, we find that the large scale CMB, especially the late
Integrated Sachs Wolfe effect, is a useful tool to measure the coupling between
dark sectors. We also discuss the possibility to detect the coupling by
cross-correlating CMB maps with tracers of the large scale structure. We
finally perform the global fitting to constrain the coupling by using the CMB
power spectrum data together with other observational data. We find that in the
$1\sigma$ range, the constrained coupling between dark sectors can solve the
coincidence problem.",0906.0677v2
2009-06-04,Sensitivity of Ag/Al Interface Specific Resistances to Interfacial Intermixing,"We have measured an Ag/Al interface specific resistance, 2AR(Ag/Al)(111) =
1.4 fOhm-m^2, that is twice that predicted for a perfect interface, 50% larger
than for a 2 ML 50%-50% alloy, and even larger than our newly predicted 1.3
fOhmm^2 for a 4 ML 50%-50% alloy. Such a large value of 2ARAg/Al(111) confirms
a predicted sensitivity to interfacial disorder and suggests an interface
greater than or equal to 4 ML thick. From our calculations, a predicted
anisotropy ratio, 2AR(Ag/Al)(001)/2AR(Ag/Al)(111), of more then 4 for a perfect
interface, should be reduced to less than 2 for a 4 ML interface, making it
harder to detect any such anisotropy.",0906.0934v1
2009-06-12,Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3,"The integration of ferromagnetic and ferroelectric materials into hybrid
heterostructures yields multifunctional systems with improved or novel
functionality. We here report on the structural, electronic and magnetic
properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial
thin film onto ferroelectric BaTiO3. As a function of temperature, the
crystal-structure of BaTiO3 undergoes phase transitions, which induce
qualitative changes in the magnetic anisotropy of the ferromagnet. We observe
abrupt changes in the coercive field of up to 1.2T along with resistance
changes of up to 6.5%. These results are attributed to the high sensitivity of
the double perovskites to mechanical deformation.",0906.2276v1
2009-06-15,Subtlety of Determining the Critical Exponent $ν$ of the Spin-1/2 Heisenberg Model with a Spatially Staggered Anisotropy on the Honeycomb Lattice,"Puzzled by the indication of a new critical theory for the spin-1/2
Heisenberg model with a spatially staggered anisotropy on the square lattice as
suggested in \cite{Wenzel08}, we study a similar anisotropic spin-1/2
Heisenberg model on the honeycomb lattice. The critical point where the phase
transition occurs due to the dimerization as well as the critical exponent
$\nu$ are analyzed in great detail. Remarkly, using most of the available data
points in conjunction with the expected finite-size scaling ansatz with a
sub-leading correction indeed leads to a consistent $\nu = 0.691(2)$ with that
calculated in \cite{Wenzel08}. However by using the data with large number of
spins $N$, we obtain $\nu = 0.707(6)$ which agrees with the most accurate Monte
Carlo O(3) value $\nu = 0.7112(5)$ as well.",0906.2539v3
2009-06-15,Nonlocal Form of the Rapid Pressure-Strain Correlation in Turbulent Flows,"A new fundamentally-based formulation of nonlocal effects in the rapid
pressure-strain correlation in turbulent flows has been obtained. The resulting
explicit form for the rapid pressure-strain correlation accounts for nonlocal
effects produced by spatial variations in the mean-flow velocity gradients, and
is derived through Taylor expansion of the mean velocity gradients appearing in
the exact integral relation for the rapid pressure-strain correlation. The
integrals in the resulting series expansion are solved for high- and
low-Reynolds number forms of the longitudinal correlation function $f(r)$, and
the resulting nonlocal rapid pressure-strain correlation is expressed as an
infinite series in terms of Laplacians of the mean strain rate tensor. The new
formulation is used to obtain a nonlocal transport equation for the turbulence
anisotropy that is expected to provide improved predictions of the anisotropy
in strongly inhomogeneous flows.",0906.2755v1
2009-06-21,Magnetotransport properties in purple bronze Li$_{0.9}$Mo$_6$O$_{17}$ Single Crystal,"We have measured resistivity along the a, b and c axes of
Li$_{0.9}$Mo$_6$O$_{17}$ single crystal. The anisotropy $\rho$$_c$ / $\rho$$_a$
and $\rho$$_c$ / $\rho$$_b$ is given, confirming the quasi-one-dimensionality
of the compound. The sharp decrease in the anisotropy below a certain
temperature (T$_M$) indicates dimensional crossover. Superconductivity occurs
at 1.8 K well below $T_M$. Negative MRs are observed with magnetic field (H)
applied along b axis. This could be ascribed to suppression of energy gap
associated with CDW state. While large positive MR is observed with H
$\parallel$ c-axis. The MR data can be well fitted by a modified two-band model
which has been used in CDW compounds such as quasi-two-dimensional purple
bronzes A$_{0.9}$Mo$_6$O$_{17}$ (A = K, Na, Tl) and quasi-one-dimensional
conductor NbSe$_3$. The behavior of MR provides a strong evidence for the
existence of CDW instability in $Li_{0.9}Mo_6O_{17}$.",0906.3855v1
2009-06-26,The Role of Anisotropy in the Void Models without Dark Energy,"Void models provide a possible explanation of the ""accelerated expansion"" of
the Universe without dark energy. To make the conventional void models more
realistic, we allow the void, an underdense region around us, to be anisotropic
and consider an average of the distance-redshift relations over the solid angle
subtended at the observer. We first show that after taking the average of a
form of the optical scalar equation (distance equation), the effective distance
equation we obtain coincides with the one for the Lemaitre-Tolman-Bondi
universe with a Dyer-Roeder-like extension. We then numerically solve the
equation to compare with observational data of Type Ia supernovae. We find that
anisotropy allows smaller size of void and larger Omega_m.",0906.4857v1
2009-06-26,Density and kinematic cusps in M54 at the heart of the Sagittarius dwarf galaxy: evidence for a 10^4 M_sun Black Hole?,"We report the detection of a stellar density cusp and a velocity dispersion
increase in the center of the globular cluster M54, located at the center of
the Sagittarius dwarf galaxy (Sgr). The central line of sight velocity
dispersion is 20.2 +/- 0.7 km/s, decreasing to 16.4 +/- 0.4 km/s at 2.5"" (0.3
pc). Modeling the kinematics and surface density profiles as the sum of a King
model and a point-mass yields a black hole (BH) mass of ~ 9400 M_sun. However,
the observations can alternatively be explained if the cusp stars possess
moderate radial anisotropy. A Jeans analysis of the Sgr nucleus reveals a
strong tangential anisotropy, probably a relic from the formation of the
system.",0906.4894v1
2009-07-11,Large scale alignment anomalies of CMB anisotropies: a new test for residuals applied to WMAP 5yr maps,"We analyze the alignment of the low multipoles (quadrupole and octupole) of
various maps of the WMAP 5yr release: the CMB maps obtained with ILC and MCMC
methods, the CMB map in the V band after foreground reduction, and, for
comparison, the (not cleaned) V band map. We study how much this alignment is
polluted by residuals on the Galactic region. Among the considered maps, the
WMAP-ILC turns out to be the most clean map from the point of view of the
proposed test. This result has been found studying the redistribution (due to
the masking process) of each bin of the probability distribution functions of
the alignment estimators. By construction, our method, feasible through Monte
Carlo simulations, works for any possible mask adopted in the analysis of data
from current and forthcoming CMB anisotropy experiments and it can only exclude
that the considered map is clean.",0907.1949v1
2009-07-20,Liquid n-hexane condensed in silica nanochannels: A combined optical birefringence and vapor sorption isotherm study,"The optical birefringence of liquid n-hexane condensed in an array of
parallel silica channels of 7nm diameter and 400 micrometer length is studied
as a function of filling of the channels via the vapor phase. By an analysis
with the generalized Bruggeman effective medium equation we demonstrate that
such measurements are insensitive to the detailed geometrical (positional)
arrangement of the adsorbed liquid inside the channels. However, this technique
is particularly suitable to search for any optical anisotropies and thus
collective orientational order as a function of channel filling. Nevertheless,
no hints for such anisotropies are found in liquid n-hexane. The n-hexane
molecules in the silica nanochannels are totally orientationally disordered in
all condensation regimes, in particular in the film growth as well as in the
the capillary condensed regime. Thus, the peculiar molecular arrangement found
upon freezing of liquid n-hexane in nanochannel-confinement, where the
molecules are collectively aligned perpendicularly to the channels' long axes,
does not originate in any pre-alignment effects in the nanoconfined liquid due
to capillary nematization.",0907.3484v1
2009-07-20,A new collective phenomenon arising from spin anisotropic perturbations to a Heisenberg square lattice manifested in paramagnetic resonance experiments,"We report unexpected behaviour in a family of Cu spin- 1/2 systems, in which
an apparent gap in the low energy magneto-optical absorption spectrum opens at
low temperature. This previously unreported collective phenomenon arises at
temperatures where the energy of the dominant exchange interaction exceeds the
thermal energy. Simulations of the observed shifts in electron paramagnetic
resonance spectral weight, which include spin anisotropy, reproduce this
behavior yielding the magnitude of the spin anisotropy in these compounds.",0907.3514v2
2009-07-23,On Possible Variation in the Cosmological Baryon Fraction,"The fraction of matter that is in the form of baryons or dark matter could
have spatial fluctuations in the form of baryon-dark matter isocurvature
fluctuations. We use big bang nucleosynthesis calculations compared with
observed light element abundances as well as galaxy cluster gas fractions to
constrain cosmological variations in the baryon fraction. Light element
abundances constrain spatial variations to be less than 26-27%, while a sample
of ""relaxed"" galaxy clusters shows spatial variations in gas fractions less
than 8%. Larger spatial variations could cause differential screening of the
primary cosmic microwave background anisotropies, leading to asymmetries in the
fluctuations and ease some tension with the halo-star 7Li abundance.
Fluctuations within our allowed bounds can lead to ""B-mode"" CMB polarization
anisotropies at a non-negligible level.",0907.3919v2
2009-07-23,Quantum Phase Transition in Hall Conductivity on an Anisotropic Kagome Lattice,"We study the quantum Hall effect(QHE) on the Kagom\'{e} lattice with
anisotropy in one of the hopping integrals. We find a new type of QHE
characterized by the quantization rules for Hall conductivity
$\sigma_{xy}=2ne^{2}/h$ and Landau Levels $E(n)=\pm v_{F}\sqrt{(n+1/2)\hbar
Be}$ ($n$ is an integer), which is different from any known type. This phase
evolves from the QHE phase with $\sigma_{xy}=4(n+1/2)e^{2}/h$ and $E(n)=\pm
v_{F}\sqrt{2n\hbar Be}$ in the isotropic case, which is realized in a system
with massless Dirac fermions (such as in graphene). The phase transition does
not occur simultaneously in all Hall plateaus as usual but in sequence from low
to high energies, with the increase of hopping anisotropy.",0907.4023v1
2009-07-27,Electronic and phononic Raman scattering in detwinned YBa$_2$Cu$_3$O$_{6.95}$ and Y$_{0.85}$Ca$_{0.15}$Ba$_2$Cu$_3$O$_{6.95}$: s-wave admixture to the $d_{x^2-y^2}$-wave order parameter,"Inelastic light (Raman) scattering has been used to study electronic
excitations and phonon anomalies in detwinned, slightly overdoped
YBa$_2$Cu$_3$O$_{6.95}$ and moderately overdoped
Y$_{0.85}$Ca$_{0.15}$Ba$_2$Cu$_3$O$_{6.95}$ single crystals. In both samples
modifications of the electronic pair-breaking peaks when interchanging the a-
and b-axis were observed. The lineshapes of several phonon modes involving
plane and apical oxygen vibrations exhibit pronounced anisotropies with respect
to the incident and scattered light field configurations. Based on a
theoretical model that takes both electronic and phononic contributions to the
Raman spectra into account, we attribute the anisotropy of the
superconductivity-induced changes in the phonon lineshapes to a small s-wave
admixture to the $d_{x^2-y^2}$ pair wave-function. Our theory allows us to
disentangle the electronic Raman signal from the phononic part and to identify
corresponding interference terms. We argue that the Raman spectra are
consistent with an s-wave admixture with an upper limit of 20 percent.",0907.4587v1
2009-08-01,Magnetic solitons in frustrated ferromagnetic spin chain,"We study the classical anisotropic ferromagnetic spin chain with frustration.
The behavior of soliton and kink solutions in the vicinity of the ground state
phase transition from the ferromagnetic to the spiral phase is studied. The
dependence of the soliton energy on small anisotropy parameter is established
using scaling estimates and numerical minimization of the energy functional.
Conditions of the existence of the solitons are determined. It is shown that
solitons survive in the spiral phase though with some restrictions on their
size. A comparison of the energies of the classical solitons and the bound
magnon complexes in the quantum model shows the functional similarity between
them. The influence of the finite-size effects on the soliton states is studied
and it is shown that the localized solitons originate from the uniform state
when the system size exceeds some critical value depending on the anisotropy.",0908.0068v1
2009-08-04,Galaxy distribution and evolution around a sample of 2dF groups,"We study galaxy evolution and spatial patterns in the surroundings of a
sample of 2dF groups. Our aim is to find evidence of galaxy evolution and
clustering out to 10 times the virial radius of the groups and so redefine
their properties according to the spatial patterns in the fields and relate
them to galaxy evolution. Group members and interlopers were redefined after
the identification of gaps in the redshift distribution. We then used
exploratory spatial statistics based on the second moment of the Ripley
function to probe the anisotropy in the galaxy distribution around the groups.
We found an important anticorrelation between anisotropy and the fraction of
early-type galaxies in these fields. Our results illustrate how the dynamical
state of galaxy groups can be ascertained by the systematic study of their
neighborhoods.This is an important achievement, since the correct estimate of
the extent to which galaxies are affected by the group environment and follow
large-scale filamentary structure is relevant to understanding the process of
galaxy clustering and evolution in the Universe.",0908.0517v2
2009-08-06,Skymap for atmospheric muons at TeV energies measured in deep-sea neutrino telescope ANTARES,"Recently different experiments mention to have observed a large scale
cosmic-ray anisotropy at TeV energies, e.g. Milagro, Tibet and
Super-Kamiokande. For these energies the cosmic-rays are expected to be nearly
isotropic. Any measurements of cosmic-rays anisotropy could bring some
information about propagation and origin of cosmic-rays. Though the primary aim
of the ANTARES neutrino telescope is the detection of high energy cosmic
neutrinos, the detector measures mainly down-doing muons, which are decay
products of cosmic-rays collisions in the Earth's atmosphere. This proceeding
describes an anlaysis method for the first year measurement of down-going
atmospheric muons at TeV energies in the ANTARES experiment, when five out of
the final number of twelve lines were taking data.",0908.0858v1
2009-08-12,Detectability of the 21 cm-CMB cross-correlation from the EoR,"The 21-cm line fluctuations and the cosmic microwave background (CMB) are
powerful probes of the epoch of reionisation of the universe. We study the
potential of the cross-correlation between 21-cm line fluctuations and CMB
anisotropy to obtain further constraints on the reionisation history. We
compute analytically the 21-cm cross-correlation with the CMB temperature
anisotropy and polarisation, and we calculate the signal-to-noise (SN) ratio
for its detection with Planck together with LOFAR, MWA and SKA. We find, on the
one hand, that the 21-cm cross-correlation signal with CMB polarisation from
the instant reionisation can be detected with an SN ratio of $\sim 1$ for LOFAR
and $\sim 10$ for SKA. On the other hand, we confirm that the detection of the
21-cm cross-correlation with CMB polarisation is practically infeasible.",0908.1632v2
2009-08-17,Evolution of magnetic states in frustrated diamond lattice antiferromagnetic Co(Al1-xCox)2O4 spinels,"Using neutron powder diffraction and Monte-Carlo simulations we show that a
spin-liquid regime emerges at $all compositions in the diamond-lattice
antiferromagnets Co(Al1-xCox)2O4. This spin-liquid regime induced by
frustration due to the second-neighbour exchange coupling J2, is gradually
superseded by antiferromagnetic collinear long-range order (k=0) at low
temperatures. Upon substitution of Al3+ by Co3+ in the octahedral B-site the
temperature range occupied by the spin-liquid regime narrows and TN increases.
To explain the experimental observations we considered magnetic anisotropy D or
third-neighbour exchange coupling J3 as degeneracy-breaking perturbations. We
conclude that Co(Al1-xCox)2O4 is below the theoretical critical point
J2/J1=1/8, and that magnetic anisotropy assists in selecting a collinear
long-range ordered ground state, which becomes more stable with increasing x
due to a higher efficiency of O-Co3+-O as an interaction path compared to
O-Al3+-O.",0908.2318v2
2009-08-23,Upper critical fields and critical current density of BaFe2(As0.68P0.32)2 single crystal,"The transport properties, upper critical fields, superconducting anisotropy,
and critical current density in an iso-valent phosphorus-doped BaFe2As2 single
crystal close to optimum doping are investigated in this report. Temperature
dependent resistivity and susceptibility show a superconducting transition
temperature, Tc, just below 31 K both with sharp transitions. The upper
critical field parallel to the ab-plane, Hc2^ab, is above 77 Tesla while that
along the c-axis direction, Hc2^c, is just above 36 Tesla, yielding a low
superconducting anisotropy ratio ~ 2. The estimated inter-plane coherence
length based on the Ginzburg-Landau (G-L) theory indicates BaFe2(As0.68P0.32)2
is still above the point for a dimensional crossover inferring the
superconducting layers are not weakly-coupled in this system. The critical
current density at 5 K obtained from magnetization loops measurement show a
modest Jc as high as 10^5 A/cm2.",0908.3284v2
2009-08-27,"Soft x-ray magnetic circular dichroism of LaCoO$_{3}$, La$_{0.7}$Ce$_{0.3}$CoO$_{3}$, and La$_{0.7}$Sr$_{0.3}$CoO$_{3}$ films: Evidence for Co valency-dependent magnetism and magnetic anisotropy","Epitaxial thin films of undoped LaCoO$_{3}$\@, of electron-doped
La$_{0.7}$Ce$_{0.3}$CoO$_{3}$\@, and of hole-doped
La$_{0.7}$Sr$_{0.3}$CoO$_{3}$\@ exhibit ferromagnetic order with a transition
temperature $T_{\rm{C}}$ $\approx$ 85 K, 22 K, and 240 K, respectively. The
spin-state structure for these compounds was studied by soft x-ray magnetic
circular dichroism at the Co $L_{2,3}$ and O $K$ edges. It turns out that a
higher spin state of the Co$^{3+}$ ions is responsible for the magnetism in
LaCoO$_{3}$\@ while for La$_{0.7}$Ce$_{0.3}$CoO$_{3}$ the Co$^{3+}$ ions are in
a low-spin state and the ferromagnetism is predominantly determined by
Co$^{2+}$\@. For La$_{0.7}$Sr$_{0.3}$CoO$_{3}$\@, on the other hand, the
magnetism originates from higher spin states of Co$^{3+}$ and Co$^{4+}$\@.
Moreover, a strong magnetic anisotropy is observed for all systems.",0908.4015v1
2009-08-28,Polarization of bremsstrahlung at electron scattering in an anisotropic medium,"Bremsstrahlung from relativistic electrons is considered under conditions
when some transverse direction of momentum transfer is statistically preferred.
It is shown that in the dipole approximation all the medium anisotropy effects
can be accumulated into a special modulus-bound transverse vector, $\bm N$. To
exemplify a target with $N^2\sim1$, we calculate radiation from electron
incident at a small angle on an atomic row in oriented crystal. Radiation
intensity and polarization dependence on the emission angle and frequency for
constant $\bm N$ is investigated. Net polarization for the angle-integral
cross-section is evaluated, which appears to be proportional to $N^2/2$, and
decreases with the increase of the photon energy fraction. A prominent feature
of the radiation angular distribution is the existence of an angle at which the
radiation may be completely polarized, in spite of the target complete or
partial isotropy -- that owes to existence of an origin-centered tangential
circle for polarization in the fully differential radiation probability kernel.
Possibilities for utilizing various properties of the polarized bremsstrahlung
flux for preparation of polarized photon beams and for probing intrinsic
anisotropy of the medium are analyzed.",0908.4237v3
2009-08-31,Lorentz microscopy mapping for domain walls structure study in L1$_0$ FePd thin films,"Thin film alloys with perpendicular anisotropy were studied using Lorentz
Transmission Electron Microscopy (LTEM). This work focuses on the configuration
of domain walls and demonstrates the suitability and accuracy of LTEM for the
magnetic characterisation of perpendicular magnetic anisotropy materials. Thin
films of chemically ordered ($\unit{L1_0}$) FePd alloys were investigated by
micro-magnetic modelling and LTEM phase retrieval approach. The different
components of magnetization described by the modeling were studied on
experimental images and confirmed by LTEM contrast simulation. Furthermore,
quantitative measurements of magnetic induction inside the domain walls were
made by using an original method to separate the electrical and magnetical
contributions to the phase information. Irregularities were also observed along
the domain walls which could play a major role during the magnetization
processes.",0908.4463v1
2009-09-01,"Inflation, quantum fields, and CMB anisotropies","Inflationary cosmology has proved to be the most successful at predicting the
properties of the anisotropies observed in the cosmic microwave background
(CMB). In this essay we show that quantum field renormalization significantly
influences the generation of primordial perturbations and hence the expected
measurable imprint of cosmological inflation on the CMB. However, the new
predictions remain in agreement with observation, and in fact favor the
simplest forms of inflation. In the near future, observations of the influence
of gravitational waves from the early universe on the CMB will test our new
predictions.",0909.0026v1
2009-09-03,Thermalization through parton transport,"A radiative transport model is used to study kinetic equilibration during the
early stage of a relativistic heavy ion collision. The parton system is found
to be able to overcome expansion and move toward thermalization via parton
collisions. Scaling behaviors show up in both the pressure anisotropy and the
energy density evolutions. In particular, the pressure anisotropy evolution
shows an approximate alpha_s scaling when radiative processes are included. It
approaches an asymptotic time evolution on a time scale of 1 to 2 fm/c. The
energy density evolution shows an asymptotic time evolution that decreases
slower than the ideal hydro evolution. These observations indicate that partial
thermalization can be achieved and viscosity is important for the evolution
during the early longitudinal expansion stage of a relativistic heavy ion
collision.",0909.0780v1
2009-09-04,Magnetic anisotropy of singly Mn-doped InAs/GaAs quantum dots,"We report on the micro-photoluminescence spectroscopy of InAs/GaAs quantum
dots (QD) doped by a single Mn atom in a magnetic field either longitudinal or
perpendicular to the optical axis. In both cases the spectral features of
positive trion (X+) are found to split into strongly circularly polarized
components, an effect very surprising in a perpendicular magnetic field. The
field-induced splitting is ascribed to the transverse Zeeman splitting of the
neutral acceptor complex A0 issued by the Mn impurity, whereas the circular
optical selection rules result from the p-d exchange which acts as a very
strong longitudinal magnetic field inhibiting the spin mixing by the transverse
field of the QD heavy-hole ground state. A theoretical model of the spin
interactions which includes (i) the local strain anisotropy experienced by the
acceptor level and (ii) the anisotropic exchange due to the out-of-center Mn
position provides a very good agreement with our observations.",0909.0877v1
2009-09-19,The Impact of Secondary non-Gaussianities in the CMB on Cosmological Parameter Estimation,"We consider corrections to the underlying cosmology due to secondary
contributions from weak gravitational lensing, the integrated Sachs-Wolfe
effect, and the Sunyaev-Zel'dovich effect contained in the trispectrum. We
incorporate these additional contributions to the covariance of a binned
angular power spectrum of temperature anisotropies in the analysis of current
and prospective data sets. Although recent experiments such as ACBAR and CBI
are not particularly sensitive to these additional non-Gaussian effects, the
interpretation of Planck and CMBPol anisotropy spectra will require an
accounting of non-Gaussian covariance leading to a degradation in cosmological
parameter estimates by up to 20% and 30%, respectively.",0909.3515v3
2009-09-19,New Constraints on variations of the fine structure constant from CMB anisotropies,"We demonstrate that recent measurements of Cosmic Microwave Background
temperature and polarization anisotropy made by the ACBAR, QUAD and BICEP
experiments substantially improve the cosmological constraints on possible
variations of the fine structure constant in the early universe. This data,
combined with the five year observations from the WMAP mission yield the
constraint alpha/alpha_0 = 0.987 \pm 0.012 at 68% c.l.. The inclusion of the
new HST constraints on the Hubble constant further increases the accuracy to
alpha/alpha_0 = 1.001 \pm 0.007 at 68% c.l., bringing possible deviations from
the current value below the 1% level and improving previous constraints by a
factor 3.",0909.3584v1
2009-09-23,"Identified particle production, azimuthal anisotropy, and interferometry measurements in Au+Au collisions at $\sqrt{s_{NN}}$ = 9.2 GeV","We present the first measurements of identified hadron production, azimuthal
anisotropy, and pion interferometry from Au+Au collisions below the nominal
injection energy at the Relativistic Heavy-Ion Collider (RHIC) facility. The
data were collected using the large acceptance STAR detector at $\sqrt{s_{NN}}$
= 9.2 GeV from a test run of the collider in the year 2008. Midrapidity results
on multiplicity density (dN/dy) in rapidity (y), average transverse momentum
(<pT>), particle ratios, elliptic flow, and HBT radii are consistent with the
corresponding results at similar $\sqrt{s_{NN}}$ from fixed target experiments.
Directed flow measurements are presented for both midrapidity and forward
rapidity regions. Furthermore the collision centrality dependence of identified
particle dN/dy, <pT>, and particle ratios are discussed. These results also
demonstrate the readiness of the STAR detector to undertake the proposed QCD
critical point search and the exploration of the QCD phase diagram at RHIC.",0909.4131v2
2009-10-09,"Non-Euclidean statistics for covariance matrices, with applications to diffusion tensor imaging","The statistical analysis of covariance matrix data is considered and, in
particular, methodology is discussed which takes into account the non-Euclidean
nature of the space of positive semi-definite symmetric matrices. The main
motivation for the work is the analysis of diffusion tensors in medical image
analysis. The primary focus is on estimation of a mean covariance matrix and,
in particular, on the use of Procrustes size-and-shape space. Comparisons are
made with other estimation techniques, including using the matrix logarithm,
matrix square root and Cholesky decomposition. Applications to diffusion tensor
imaging are considered and, in particular, a new measure of fractional
anisotropy called Procrustes Anisotropy is discussed.",0910.1656v1
2009-10-12,Dirac-Born-Infeld and k-inflation: the CMB anisotropies from string theory,"Inflationary models within string theory exhibit unusual scalar field
dynamics involving non-minimal kinetic terms and generically referred to as
k-inflation. In this situation, the standard slow-roll approach used to
determine the behavior of the primordial cosmological perturbations cannot
longer be used. We present a generic method, based on the uniform
approximation, to analytically derive the primordial power spectra of scalar
and tensor perturbations. At leading order, the scalar spectral index, its
running and the tensor-to-scalar ratio are modified by the new dynamics. We
provide their new expression, correct previous results at next-to-leading order
and clarify the definition of what is the tensor-to-scalar ratio when the sound
horizon and Hubble radius are not the same. Finally, we discuss the constraints
the parameters encoding the non-minimal kinetic terms have to satisfy, such as
the sound speed and the energy scale of k-inflation, in view of the fifth year
Wilkinson Microwave Anisotropy Probe (WMAP5) data.",0910.2167v1
2009-10-16,Estimates of hadron azimuthal anisotropy from multiparton interactions in proton-proton collisions at sqrt(s) = 14 TeV,"We estimate the amount of collective ""elliptic flow"" expected at mid-rapidity
in proton-proton (p-p) collisions at the CERN Large Hadron Collider (LHC),
assuming that any possible azimuthal anisotropy of the produced hadrons with
respect to the plane of the reaction follows the same overlap-eccentricity and
particle-density scalings as found in high-energy heavy ion collisions. Using a
Glauber eikonal model, we compute the p-p eccentricities, transverse areas and
particle-multiplicities for various phenomenological parametrisations of the
proton spatial density. For realistic proton transverse profiles, we find
integrated elliptic flow v2 parameters below 3% in p-p collisions at sqrt(s) =
14 TeV.",0910.3029v3
2009-10-22,Consequences of the peculiar intrinsic properties of MgB2 on its macroscopic current flow,"The influence of two important features of magnesium diboride on the
macroscopic transport properties of polycrystalline MgB2 is discussed in the
framework of a percolation model. While two band superconductivity does not
have significant consequences in the field and temperature range of possible
power applications, the opposite is true for the anisotropy of the upper
critical field. The field dependence of the critical current densities strongly
increases and the macroscopic supercurrents disappear well below the apparent
upper critical field. The common scaling laws for the field dependence of the
volume pinning force are altered and Kramer's plot is no longer linear,
although grain boundary pinning dominates in nearly all polycrystalline MgB2
conductors. In contrast to the conventional superconductors NbTi and Nb3Sn, a
significant critical current anisotropy can be induced by the preparation
technique of MgB2 tapes.",0910.4316v1
2009-10-23,Morphological evolution of edge-hillocks on single crystal films having anisotropic drift-diffusion under the capillary and electromigration forces,"The morphological evolution of hillocks at the unpassivated sidewalls of the
single crystal metallic thin films is investigated via computer simulations by
using the free-moving boundary value problem. The effects of the
drift-diffusion anisotropy on the development of surface topographical
scenarios is fully explored under the action of electromigration and capillary
forces, utilizing numerous combination of the surface texture, the
drift-diffusion anisotropy and the direction of the applied electric field. The
present simulation studies yield very rich and technologically imported
information, in regards to the critical texture of the single crystal thin film
surfaces, and the intensity and the orientation of the applied electric field,
as far as the device reliability is concerned.",0910.4596v1
2009-10-27,Differences at low l in Planck's first light sky map of the cosmic microwave background from WMAP's and COBE's,"The recent release of the first light sky map of the cosmic microwave
background (CMB) from the Planck satellite provides an initial opportunity for
comparison with the WMAP and COBE sky maps and their reconstruction algorithms.
The precision of the match between Planck's and WMAP's anisotropies below
several degrees in size, which corresponds to spherical harmonics with high l,
provides confidence that the differences between the anisotropies at low l are
substantial. If the Planck first light sky map is taken as the gold standard,
the results seem to suggest the low l components of the WMAP map and a
considerable part of the COBE sky map have a similar reconstruction artefact.
As the Planck first light sky map covers only about 10% of the sky, any
conclusions drawn from this comparison are speculative but deserving of further
investigation.",0910.5102v3
2009-10-28,Quantum field theoretical study of an effective spin model in coupled optical cavity arrays,"Atoms trapped in microcavities and interacting through the exchange of
virtual photons can model an anisotropic Heisenberg spin-1/2 lattice.
  We do the quantum field theoretical study of such a system using the Abelian
bosonization method followed by the renormalization group analysis. We present
interesting physics due to the presence of exchange anisotropy. An infinite
order Kosterliz-Thouless-Berezinskii transition is replaced by second order XY
transition even an infinitesimal a small anisotropy in exchange coupling is
introduced. We predict a quantum phase transition between Mott insulating and
photonic superfluid phase due to detuning between the cavity and laser
frequency, a large detuning favours the photonic superfluid phase. We also do
the analysis of Jaynes and Cumming Hamiltonian to support results of quantum
field theoretical study.",0910.5341v1
2009-10-29,Anisotropic order parameter in Li-intercalated layered superconductor Li$_x$ZrNCl,"In this study, it is shown that in a layered nitride superconductor, i.e.,
LixZrNCl (0.07<=x<=0.21), the superconducting order parameter is highly
anisotropic in a sample with x=0.12, as inferred from both the temperature and
the magnetic field dependences of the muon depolarization rate (sigma_s,
proportional to the superfluid density). Moreover, the tendency of strong
anisotropy with an increase in x is indicated by the T dependence of sigma_s.
These observations are in good agreement with the recent theory that predicts
the development of anisotropy in a d+id' gap upon carrier filling to the bands
with disconnected Fermi surfaces on a honeycomb lattice.",0910.5557v2
2009-11-02,Inverse Spin-Galvanic Effect in a Topological-Insulator/Ferromagnet Interface,"When a ferromagnet is deposited on the surface of a topological insulator the
topologically protected surface state develops a gap and becomes a
2-dimensional quantum Hall liquid. We demonstrate that the Hall current in such
a liquid, induced by an external electric field, can have a large effect on the
magnetization dynamics of the ferromagnet by changing the effective anisotropy
field. This change is dissipationless and may be substantial even in weakly
spin-orbit coupled ferromagnets. We study the possibility of dissipationless
current-induced magnetization reversal in monolayer-thin, insulating
ferromagnets with a soft perpendicular anisotropy and discuss possible
applications of this effect.",0911.0106v1
2009-11-06,CMB temperature trispectrum of cosmic strings,"We provide an analytical expression for the trispectrum of the Cosmic
Microwave Background (CMB) temperature anisotropies induced by cosmic strings.
Our result is derived for the small angular scales under the assumption that
the temperature anisotropy is induced by the Gott-Kaiser-Stebbins effect. The
trispectrum is predicted to decay with a non-integer power-law exponent l^(-r)
with 6<r<7, depending on the string microstructure, and thus on the string
model. For Nambu-Goto strings, this exponent is related to the string mean
square velocity and the loop distribution function. We then explore two classes
of wavenumber configuration in Fourier space, the kite and trapezium
quadrilaterals. The trispectrum can be of any sign and appears to be strongly
enhanced for all squeezed quadrilaterals.",0911.1241v2
2009-11-12,An ac field probe for the magnetic ordering of magnets with random anisotropy,"A Monte Carlo simulation is carried out to investigate the magnetic ordering
in magnets with random anisotropy (RA). Our results show peculiar similarities
to recent experiments that the real part of ac susceptibility presents two
peaks for weak RA and only one for strong RA regardless of glassy critical
dynamics manifested for them. We demonstrate that the thermodynamic nature of
the low-temperature peak is a ferromagnetic-like dynamic phase transition to
quasi-long range order (QLRO) for the former. Our simulation, therefore, is
able to be incorporated with the experiments to help clarify the existence of
the QLRO theoretically predicted so far.",0911.2352v1
2009-11-19,Simple Types of Anisotropic Inflation,"We display some simple cosmological solutions of gravity theories with
quadratic Ricci curvature terms added to the Einstein-Hilbert lagrangian which
exhibit anisotropic inflation. The Hubble expansion rates are constant and
unequal in three orthogonal directions. We describe the evolution of the
simplest of these homogeneous and anisotropic cosmological models from its
natural initial state and evaluate the deviations they will create from
statistical isotropy in the fluctuations produced during a period of
anisotropic inflation. The anisotropic inflation is not a late-time attractor
in these models but the rate of approach to a final isotropic de Sitter state
is slow and is conducive to the creation of observable anisotropic statistical
effects in the microwave background. The statistical anisotropy would not be
scale invariant and the level of statistical anisotropy will grow with scale.",0911.3805v2
2009-11-23,Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6,"We report on high-field magnetization, specific-heat and electron spin
resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg
antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes
below TN = 4.38 K is described in the frame of the meanfield theory, confirming
a collinear magnetic structure with an easy-plane anisotropy. The obtained
results allowed us to determine the anisotropy/exchange interaction ratio, A/J
= 0.003, and the upper limit for the inter/intra-plane exchange-interaction
ratio, J'/J = 1/16. It is argued that despite the onset of 3D long-range
magnetic ordering the magnetic properties of this material (including
high-magnetic-field magnetization and non-monotonic field dependence of the
Neel temperature) are strongly affected by two-dimensional spin correlations.",0911.4402v1
2009-11-30,Frustrated local moment models for Fe-pnictide magnetism,"The low energy spin excitations of the Fe pnictide parent compounds have been
determined by inelastic neutron scattering and interpreted within the local
moment J_1a,b-J_2 Heisenberg model with orthorhombic symmetry. This has led to
alternative exchange models that strongly differ in the size of anisotropy.
Although the compounds are itinerant the localised spin model can explain basic
features of the excitations. The inherent frustration of this model leads to
quantum fluctuations and possible moment reduction. We investigate this
question in detail using spin wave approximation and partly exact
diagonalisation Lanczos calculations for finite clusters. We find that the
orthorhombic anisotropy stabilizes the columnar AF phase and its moment. For
the exchange models proposed from inelastic neutron scattering we can exclude a
strong influcence of frustration on the moment size. We also investigate
dependence of magnetisation and susceptibility on field and temperature.",0911.5664v2
2009-12-02,Dark Matter tested with satellites,"Recently, the distribution of velocity dispersion as far as 400kpc around red
isolated galaxies was derived from statistical studies of satellites in the
SDSS (Klypin & Prada 2009). This could help to constrain dark matter models at
intermediate scales. We compare the predictions of different DM distributions,
LCDM with NFW or cored profiles, and also modified gravity models, with
observations. It is shown how the freedom in the various parameters (radial
distribution of satellites, velocity anisotropy, external field effect),
prevents to disentangle the models, which all can give pretty good fits to the
data. In all cases, realistic radial variations of velocity anisotropy are used
for the satellites, and a constant stellar-mass to light ratio for the host
galaxies.",0912.0332v1
2009-12-03,C-axis critical current of a PrFeAsO0.7 single crystal,"The c-axis transport properties of a high-pressure synthesized PrFeAsO0.7
single crystal are studied using s-shaped junctions. Resistivity anisotropy of
about 120 detected at 50 K shows the presence of strong anisotropy in the
electronic states. The obtained critical current density for the c-axis of
2.9*10^5 A/cm^2 is two orders of magnitude larger than that in
Bi2Sr1.6La0.4CuO6+d. The appearance of a hysteresis in the current-voltage
curve below T_c is the manifestation of the intrinsic Josephson effect similar
to that in cuprate superconductors. The suppression of the critical
current-normal resistance (I_cR_n) product is explained by an inspecular
transport in s_pm-wave pair potential.",0912.0598v1
2009-12-06,The Correlation Functions of the XXZ Heisenberg Chain for Zero or Infinite Anisotropy and Random Walks of Vicious Walkers,"The XXZ Heisenberg chain is considered for two specific limits of the
anisotropy parameter: $\Dl\to 0$ and $\Dl\to -\infty$. The corresponding wave
functions are expressed by means of the symmetric Schur functions. Certain
expectation values and thermal correlation functions of the ferromagnetic
string operators are calculated over the base of N-particle Bethe states. The
thermal correlator of the ferromagnetic string is expressed through the
generating function of the lattice paths of random walks of vicious walkers. A
relationship between the expectation values obtained and the generating
functions of strict plane partitions in a box is discussed. Asymptotic estimate
of the thermal correlator of the ferromagnetic string is obtained in the limit
of zero temperature. It is shown that its amplitude is related to the number of
plane partitions.",0912.1138v2
2009-12-09,Dimensional phase transitions in small Yukawa clusters,"We investigate the one- to two-dimensional zigzag transition in clusters
consisting of a small number of particles interacting through a Yukawa (Debye)
potential and confined in a two-dimensional biharmonic potential well. Dusty
(complex) plasma clusters with $n \le 19$ monodisperse particles are
characterized experimentally for two different confining wells. The well
anisotropy is accurately measured, and the Debye shielding parameter is
determined from the longitudinal breathing frequency. Debye shielding is shown
to be important. A model for this system is used to predict equilibrium
particle configurations. The experiment and model exhibit excellent agreement.
The critical value of $n$ for the zigzag transition is found to be less than
that predicted for an unshielded Coulomb interaction. The zigzag transition is
shown to behave as a continuous phase transition from a one-dimensional to a
two-dimensional state, where the state variables are the number of particles,
the well anisotropy and the Debye shielding parameter. A universal critical
exponent for the zigzag transition is identified for transitions caused by
varying the Debye shielding parameter.",0912.1650v1
2009-12-09,Dual Behavior of Antiferromagnetic Uncompensated Spins in NiFe/IrMn Exchange Biased Bilayers,"We present a comprehensive study of the exchange bias effect in a model
system. Through numerical analysis of the exchange bias and coercive fields as
a function of the antiferromagnetic layer thickness we deduce the absolute
value of the averaged anisotropy constant of the antiferromagnet. We show that
the anisotropy of IrMn exhibits a finite size effect as a function of
thickness. The interfacial spin disorder involved in the data analysis is
further supported by the observation of the dual behavior of the interfacial
uncompensated spins. Utilizing soft x-ray resonant magnetic reflectometry we
have observed that the antiferromagnetic uncompensated spins are dominantly
frozen with nearly no rotating spins due to the chemical intermixing, which
correlates to the inferred mechanism for the exchange bias.",0912.1734v1
2009-12-16,Large anisotropy of spin-orbit interaction in a single InAs self-assembled quantum dot,"Anisotropy of spin-orbit interaction (SOI) is studied for a single uncapped
InAs self-assembled quantum dot (SAQD) holding just a few electrons. The SOI
energy is evaluated from anti-crossing or SOI induced hybridization between the
ground and excited states with opposite spins. The magnetic angular dependence
of the SOI energy falls on an absolute cosine function for azimuthal rotation,
and a cosine-like function for tilting rotation. The SOI energy is even
quenched at a specific rotation. These angular dependence compare well to
calculation of Rashba SOI in a two-dimensional harmonic potential.",0912.3088v1
2010-01-11,Multiscale autocorrelation function: a new approach to anisotropy studies,"We present a novel catalog-independent method, based on a scale dependent
approach, to detect anisotropy signatures in the arrival direction distribution
of the ultra highest energy cosmic rays (UHECR). The method provides a good
discrimination power for both large and small data sets, even in presence of
strong contaminating isotropic background. We present some applications to
simulated data sets of events corresponding to plausible scenarios for charged
particles detected by world-wide surface detector-based observatories, in the
last decades.",1001.1666v4
2010-01-13,Rotation of elliptic optical beam in anisotropic media,"We investigate the linear propagation of a paraxial optical beam in
anisotropic media. We start from the eigenmode solution of the plane wave in
the media, then subsequently derive the wave equation for the beam propagating
along a general direction except the optic axes. The wave equation has a term
containing the second mixed partial derivative which originates from the
anisotropy, and this term can result in the rotation of the beam spot. The
rotation effect is investigated by solving analytically the wave equation with
an initial elliptical Gaussian beam for both uniaxial and biaxial media. For
both media, it is found that there exists a specific direction, which is
dependent on anisotropy of the media, on the cross-section perpendicular to
propagation direction to determine the rotation of the beam spot. When the
major axis of the elliptical spot of the input beam is parallel to or
perpendicular to the specific direction, the beam spot will not rotate during
propagation, otherwise, it will rotate with the direction and the velocity
determined by input parameters of the beam.",1001.2061v2
2010-01-18,On the stability of the shear-free condition,"The evolution equation for the shear is reobtained for a spherically
symmetric anisotropic, viscous dissipative fluid distribution, which allows us
to investigate conditions for the stability of the shear-free condition. The
specific case of geodesic fluids is considered in detail, showing that the
shear-free condition, in this particular case, may be unstable, the departure
from the shear-free condition being controlled by the expansion scalar and a
single scalar function defined in terms of the anisotropy of the pressure, the
shear viscosity and the Weyl tensor or, alternatively, in terms of the
anisotropy of the pressure, the dissipative variables and the energy density
inhomogeneity.",1001.3020v1
2010-01-26,Observational Limits on Patchy Reionization: Implications for B-modes,"The recent detection of secondary CMB anisotropy by the South Pole Telescope
places a conservative bound on temperature fluctuations from the optical
depth-modulated Doppler effect of T_{3000} < sqrt{13} microK at multipoles
l~3000. This bound is the first empirical constraint on reionization optical
depth fluctuations at arcminute scales, tau_{3000} = 0.001 T_{3000}/microK,
implying that these fluctuations are no more than a few percent of the mean.
Optical depth modulation of the quadrupole source to polarization generates
B-modes that are correspondingly bounded as B_{3000} = 0.003 T_{3000}. The
maximal extrapolation to the l~100 gravitational wave regime yields B_{100} =
0.1 T_{3000} and remains in excess of gravitational lensing if the effective
comoving size of the ionizing regions is R > 80 Mpc. If patchy reionization is
responsible for much of the observed arcminute scale temperature fluctuations,
current bounds on B_{100} already require R < 200 Mpc and can be expected to
improve rapidly. Frequency separation of thermal Sunyaev-Zel'dovich
contributions to the measured secondary anisotropy would also substantially
improve the limits on optical depth fluctuations and B-modes from reionization.",1001.4803v1
2010-02-01,Vortex state in d-wave superconductors with strong paramagnetism: transport and specific heat anisotropy,"We analyse the combined effect of orbital and Pauli depairing on the
superconducting state, and apply the results to the heavy fermion CeCoIn$_5$.
We find that: a) standard extrapolation based on the slope of $H_{c2}(T)$ in
the vicinity of the transition temperature to T=0 does not always give accurate
values of the orbital upper critical field; b) critical value of the Maki
parameter, $\alpha$, that determines onset of the first order transition
depends on the Fermi surface shape and the symmetry of the gap, and is
$\alpha^*\approx 3$ for CeCoIn$_5$; c) the anisotropy of the thermodynamic and
transport coefficients in the low-temperature, low-field part of the phase
diagram is essentially insensitive to the Zeeman field and can be used to
determine the nodal directions in Pauli-limited superconductors. The latter
result confirms the finding of the $d_{x^2-y^2}$ order parameter CeCoIn$_5$.",1002.0330v1
2010-02-12,Anisotropy of Solar Wind Turbulence between Ion and Electron Scales,"The anisotropy of turbulence in the fast solar wind, between the ion and
electron gyroscales, is directly observed using a multispacecraft analysis
technique. Second order structure functions are calculated at different angles
to the local magnetic field, for magnetic fluctuations both perpendicular and
parallel to the mean field. In both components, the structure function value at
large angles to the field S_perp is greater than at small angles S_par: in the
perpendicular component S_perp/S_par = 5 +- 1 and in the parallel component
S_perp/S_par > 3, implying spatially anisotropic fluctuations, k_perp > k_par.
The spectral index of the perpendicular component is -2.6 at large angles and
-3 at small angles, in broad agreement with critically balanced whistler and
kinetic Alfven wave predictions. For the parallel component, however, it is
shallower than -1.9, which is considerably less steep than predicted for a
kinetic Alfven wave cascade.",1002.2539v2
2010-02-19,Confinement-Induced Resonances in Low-Dimensional Quantum Systems,"We report on the observation of confinement-induced resonances in strongly
interacting quantum-gas systems with tunable interactions for one- and
two-dimensional geometry. Atom-atom scattering is substantially modified when
the s-wave scattering length approaches the length scale associated with the
tight transversal confinement, leading to characteristic loss and heating
signatures. Upon introducing an anisotropy for the transversal confinement we
observe a splitting of the confinement-induced resonance. With increasing
anisotropy additional resonances appear. In the limit of a two-dimensional
system we find that one resonance persists.",1002.3795v2
2010-02-19,Highly sensitive frequency metrology for optical anisotropy measurements,"In this paper we present a novel apparatus aimed at measuring very small
birefringences and anisotropies, based on frequency metrology and not on
polarimetry as usual. In our experiment, a very high finesse resonant cavity is
used to convert the phase difference into a resonance frequency difference,
which can then be measured with very high accuracy. We describe the set-up and
present the results of experimental tests which exhibited a sensitivity dn ~ 2
x 10?18, allowing for the measurement of long-predicted magneto-electro-optical
effects in gases. Since the shotnoise limited sensitivity of our apparatus lies
well below the state-of-the-art sensitivity, frequency metrology appears as a
promising technique for small birefringence measurements.",1002.3812v1
2010-02-24,The entanglement dynamics of interacting qubits embedded in a spin environment with Dzyaloshinsky-Moriya term,"We investigate the entanglement dynamics of two interacting qubits in a spin
environment, which is described by an XY model with Dzyaloshinsky-Moriya (DM)
interaction. The competing effects of environmental noise and interqubit
coupling on entanglement generation for various system parameters are studied.
We find that the entanglement generation is suppressed remarkably in
weak-coupling region at quantum critical point (QCP). However, the suppression
of the entanglement generation at QCP can be compensated both by increasing the
DM interaction and by decreasing the anisotropy of the spin chain. Beyond the
weak-coupling region, there exist resonance peaks of concurrence when the
system-bath coupling equals to external magnetic field. We attribute the
presence of resonance peaks to the flat band of the self-Hamiltonian. These
peaks are highly sensitive to anisotropy parameter and DM interaction.",1002.4476v3
2010-02-26,Constraints on the SZ Power Spectrum on Degree Angular Scales in WMAP Data,"The Sunyaev-Zel'dovich (SZ) effect has a distinct spectral signature that
allows its separation from fluctuations in the cosmic microwave background
(CMB) and foregrounds. Using CMB anisotropies measured in Wilkinson Microwave
Anisotropy Probe's five-year maps, we constrain the SZ fluctuations at large,
degree angular scales corresponding to multipoles in the range from 10 to 400.
We provide upper bounds on SZ fluctuations at multipoles greater than 50, and
find evidence for a hemispherically asymmetric signal at ten degrees angular
scales. The amplitude of the detected signal cannot be easily explained with
the allowed number density and temperature of electrons in the Galactic halo.
We have failed to explain the excess signal as a residual from known Galactic
foregrounds or instrumental uncertainties such as 1/f-noise.",1002.4872v4
2010-03-02,Observable effects of anisotropic bubble nucleation,"Our universe may have formed via bubble nucleation in an eternally-inflating
background. Furthermore, the background may have a compact dimension--the
modulus of which tunnels out of a metastable minimum during bubble
nucleation--which subsequently grows to become one of our three large spatial
dimensions. Then the reduced symmetry of the background is equivalent to
anisotropic initial conditions in our bubble universe. We compute the
inflationary spectrum in such a scenario and, as a first step toward
understanding the effects of anisotropy, project it onto spherical harmonics.
The resulting spectrum exhibits anomalous multipole correlations, their
relative amplitude set by the present curvature parameter, which extend to
arbitrarily large multipole moments. This raises the possibility of future
detection, if slow-roll inflation does not last too long within our bubble. A
full understanding of the observational signal must account for the effects of
background anisotropy on photon free streaming, and is left to future work.",1003.0663v2
2010-03-04,Comparative study of transport and magnetic Jc in the polycrystalline iron-based superconductor NdFeAsO{0.88}F{0.12},"Polycrystalline NdFeAsO0.88F0.12 superconductors prepared by high pressure
(HP) and ambient pressure (AP) method were comparatively studied by
magnetization and transport measurements. Upper critical field (Hc2),
irreversibility field (Hirr) and the anisotropy parameter were estimated from
resistance transition curves. The broadening of transition width was observed,
and ascribed to both Hc2 anisotropy and superconductivity inhomogeneity of
samples. Magnetic hysteresis loops (MHLs) in low fields were measured to detect
the trace of weak-link behavior. The reclosed hysteresis loops in low fields
manifest that there are weak-links in both samples. Magnetization critical
current density Jcm were derived from MHLs. High-pressure synthesized sample
shows higher Jcm. However, by means of direct transport I-V measurements,
transport critical current density Jct was very low. The Jct values for two
samples are comparable. Large discrepancies between Jcm and Jct also indicate
that there are weak-links in both samples. The relative mechanism is discussed
in detail.",1003.0946v2
2010-03-05,Weak superconducting fluctuations and small anisotropy of the upper critical fields in an Fe1.05Te0.85Se0.15 single crystal,"We have investigated the temperature dependence of the resistive upper
critical fields ($\mu_{0}H_{\rm c2}(T)$) for an
Fe$_{1.05}$Te$_{0.85}$Se$_{0.15}$ single crystal, which exhibit
superconductivity at $T_{\rm c} \sim 14 K, in magnetic fields of up to 55 T.
Two-dimensional feature and superconducting fluctuations of the samples are
found to be weak, because the resistive broadening effect on applied magnetic
fields of up to 14 T is small. The Pauli paramagnetic effect is obviously
evidenced by the strong suppression of the $\mu_{0}H_{\rm c2}^{ab}(T)$ ($H
\parallel ab$) curve and nearly isotropic $\mu_{0}H_{\rm c2}(0) \approx 47 T is
seen for both $H \parallel ab$ and $H \parallel c$. This fact is almost
identical to the results of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ single crystals
reported previously. We have discussed that the small anisotropy of the upper
critical field at low temperatures in Fe$_{1+y}$(Te,Se) systems against the
variation of the Te/Se ratio.",1003.1171v3
2010-03-08,Anisotropic and quasipropagating spin excitations in superconducting Ba(Fe0.926Co0.074)2As2,"Inelastic neutron scattering from superconducting (SC)
Ba(Fe$_{0.926}$Co$_{0.074}$)$_2$As$_2$ reveals anisotropic and
quasi-two-dimensional (2D) magnetic excitations close to
\textbf{Q}$_{\texttt{AFM}}=({1}{2}/{1}{2})$ - the 2D antiferromagnetic (AFM)
wave-vector of the parent BaFe$_2$As$_2$ compound. The correlation length
anisotropy of these low energy fluctuations is consistent with spin nematic
correlations in the $J_1$-$J_2$ model with $J_1/J_2 \sim$ 1. The spin resonance
at $\sim$8.3 meV in the SC state displays the same anisotropy. The anisotropic
fluctuations experimentally evolve into two distinct maxima only along the
direction transverse to \textbf{Q}$_{\texttt{AFM}}$ above $\sim$80 meV
indicating unusual quasi-propagating excitations.",1003.1687v4
2010-03-09,Shear Viscosity in the Post-quasistatic Approximation,"We apply the post-quasi--static approximation, an iterative method for the
evolution of self-gravitating spheres of matter, to study the evolution of
anisotropic non-adiabatic radiating and dissipative distributions in General
Relativity. Dissipation is described by viscosity and free-streaming radiation,
assuming an equation of state to model anisotropy induced by the shear
viscosity. We match the interior solution, in non-comoving coordinates, with
the Vaidya exterior solution. Two simple models are presented, based on the
Schwarzschild and Tolman VI solutions, in the non--adiabatic and adiabatic
limit. In both cases the eventual collapse or expansion of the distribution is
mainly controlled by the anisotropy induced by the viscosity.",1003.1825v3
2010-03-10,Effects of excess Fe on upper critical field and magnetotransport in Fe1+y(Te1-xSx)z,"We have investigated the upper critical field anisotropy and magnetotransport
properties of Fe1.14(1)Te0.91(2)S0.09(2) single crystals in stable magnetic
fields up to 35 T. The results show that u0Hc2(T) along the c axis and in the
ab-plane exhibit saturation at low temperatures. The anisotropy of u0Hc2(T)
decreases with decreasing temperature, becoming nearly isotropic for T->0. Our
analysis indicates that the spin-paramagnetic pair-breaking with spin-orbital
scattering is responsible for the behavior of u0Hc2(T). Furthermore, from
analysis of the normal state properties, we show evidence that the excess Fe
acting as Kondo-type impurities is a key factor determining the normal and
superconducting state physical properties.",1003.2209v1
2010-03-11,Structural and Magnetic Properties of Nanosized Barium Hexaferrite Powders Obtained by Microemulsion Technique,"Thin hexagonal barium hexaferrite particles synthesized using the
microemulsion technique were studied. A water-in-oil reverse microemulsion
system with cetyltrimethylammonium bromide (CTAB) as a cationic surfactant,
n-butanol as a co-surfactant, n-hexanol as a continuous oil phase, and an
aqueous phase were used. The microstructural and magnetic properties were
investigated. The particles obtained were mono-domain with average particle
size 280 nm. The magnetic properties of the powder were investigated at 4.2 K
and at room temperature. The saturation magnetization was 48.86 emu/g and the
coercivity, 2.4 x 105 A/m at room temperature. The anisotropy field Ha and
magneto-crystalline anisotropy K1 were 1.4 x 106 A/m and 2.37 x 105 J/m3,
respectively.",1003.2276v1
2010-03-12,Tunable striped-patterns by lattice anisotropy and magnetic impurities in d-wave superconductors,"The pattern transition induced by lattice anisotropy (LA) and magnetic
impurities is computationally observed in near-optimally doped d-wave
superconductors (DSCs). For the single impurity case, a transition from the
checkerboard to stripe pattern can be induced even with a very weak LA.
Moreover, the modulation period of eight lattice constants (8$a$) in the spin
order coincides with neutron scattering data. For the two-impurity case, an
orientation transition from the longitudinal impurity-pinned stripe into the
transverse pattern is observed when the LA ratio reaches some critical value.
At the critical point, it is found that the structures around magnetic
impurities could restore checkerboard patterns. These results indicate that the
formation of stripes in DSCs might induced by various effects, and could be
tunable experimentally.",1003.3023v2
2010-03-23,Growth and Anisotropic Properties of RBa_2Cu_3O_x Single-Crystal Whiskers,"Single-crystal whiskers of RBa2Cu3Ox (R-123, R = Sm, Eu, Gd, Dy, Ho, Er, Tm,
Yb, and Y) were successfully grown from Sb- or Te-doped precursors with a
nominal composition of R1.5Ba2.75-3.00Cu3M0.5Ox (M: Sb,Te). The whiskers were
grown parallel to the ab-plane with the following typical dimensions: 2-8 mm in
length, 20-80 \mum in width, and 10-30 \mum in thickness. In the case of
rare-earth ions (R3+) with a small ionic radius (Dy, Ho, Er, Tm, Yb, and Y),
R-123 whiskers were grown from Te-doped precursors. The growths of Y-123 and
Ho-123 whiskers were confirmed using both Te-doped and Sb-doped precursors. On
the other hand, for rare-earth ions (R3+) with a large ionic radius (Sm, Eu,
and Gd), R-123 whiskers were grown only from Sb-doped precursors. Sb and Te
were not detected in the grown whiskers by electron probe microanalysis. The
anisotropies of R-123 single-crystal whiskers in the flux liquid state were
estimated to be 6.0-33 from the angular dependence of their resistivities under
various magnetic fields. The anisotropy increased with decreasing
superconducting transition temperature.",1003.4371v1
2010-03-24,Structural and magnetic evidence of confined strain fields in GaMnAs grown on ordered arrays of zero-dimensional nanostructures,"We prepared Ga0.95Mn0.05As films on top of periodic arrays of InAs quantum
dots. X-ray diffraction reveals periodically strained films, commensurate to
substrate's patterning. The dots produce a tensile strain in GaMnAs while
between the dots strain is compressive. Our experiments confirm that the
average tensile strain in the film increases with decreasing dots separation.
This trend in strain is accompanied by an increase of the out-of-plane
magnetization component familiar from the established relation between strain
and magnetic anisotropy in GaMnAs films. Our work provides a new route for
controlling magneto-crystalline anisotropies in GaMnAs on a nanometer scale.",1003.4768v1
2010-04-02,Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered potential,"We study the horizontal expansion of vertically confined ultra-cold atoms in
the presence of disorder. Vertical confinement allows us to realize a situation
with a few coupled harmonic oscillator quantum states. The disordered potential
is created by an optical speckle at an angle of 30{\deg} with respect to the
horizontal plane, resulting in an effective anisotropy of the correlation
lengths of a factor of 2 in that plane. We observe diffusion leading to
non-Gaussian density profiles. Diffusion coefficients, extracted from the
experimental results, show anisotropy and strong energy dependence, in
agreement with numerical calculations.",1004.0312v1
2010-04-05,Neutrino and axion hot dark matter bounds after WMAP-7,"We update cosmological hot dark matter constraints on neutrinos and hadronic
axions. Our most restrictive limits use 7-year data from the Wilkinson
Microwave Anisotropy Probe for the cosmic microwave background anisotropies,
the halo power spectrum (HPS) from the 7th data release of the Sloan Digital
Sky Survey, and the Hubble constant from Hubble Space Telescope observations.
We find 95% C.L. upper limits of \sum m_\nu<0.44 eV (no axions), m_a<0.91 eV
(assuming \sum m_\nu=0), and \sum m_\nu<0.41 eV and m_a<0.72 eV for two hot
dark matter components after marginalising over the respective other mass. CMB
data alone yield \sum m_\nu<1.19 eV (no axions), while for axions the HPS is
crucial for deriving m_a constraints. This difference can be traced to the fact
that for a given hot dark matter fraction axions are much more massive than
neutrinos.",1004.0695v2
2010-04-09,Perpendicular anisotropy of ultrathin epitaxial cobalt films on graphene,"Graphene is attractive for spintronics due to its long spin life time and
high mobility. So far only thick and polycrystalline slabs have been used as
ferromagnetic electrodes. We report the growth of flat, epitaxial ultrathin Co
films on graphene. These display perpendicular magnetic anisotropy in the
thickness range 0.5-1nm, which is confirmed by theory. PMA, epitaxy and
ultrathin thickness bring new perspectives for graphene-based spintronic
devices such as the zero-field control of an arbitrary magnetization direction,
band matching between electrodes and graphene, and interface effects such as
Rashba and electric field control of magnetism.",1004.1463v1
2010-04-16,Collective Diffusion of Colloidal Hard Rods in Smectic Liquid Crystals: Effect of Particle Anisotropy,"We study the layer-to-layer diffusion in smectic-A liquid crystals of
colloidal hard rods with different length-to-diameter ratios using computer
simulations. The layered arrangement of the smectic phase yields a hopping-type
diffusion due to the presence of permanent barriers and transient cages.
Remarkably, we detect stringlike clusters composed of inter-layer rods moving
cooperatively along the nematic director. Furthermore, we find that the
structural relaxation in equilibrium smectic phases shows interesting
similarities with that of out-of-equilibrium supercooled liquids, although
there the particles are kinetically trapped in transient rather than permanent
cages. Additionally, at fixed packing fraction we find that the barrier height
increases with increasing particle anisotropy, and hence the dynamics is more
heterogeneous and non-Gaussian for longer rods, yielding a lower diffusion
coefficient along the nematic director and smaller clusters of inter-layer
particles that move less cooperatively. At fixed barrier height, the dynamics
becomes more non-Gaussian and heterogeneous for longer rods that move more
collectively giving rise to a higher diffusion coefficient along the nematic
director.",1004.2897v1
2010-04-21,Missing Power vs low-l Alignments in the Cosmic Microwave Background: No Correlation in the Standard Cosmological Model,"On large angular scales (greater than about 60 degrees), the two-point
angular correlation function of the temperature of the cosmic microwave
background (CMB), as measured (outside of the plane of the Galaxy) by the
Wilkinson Microwave Anisotropy Probe, shows significantly lower large-angle
correlations than expected from the standard inflationary cosmological model.
Furthermore, when derived from the full CMB sky, the two lowest cosmologically
interesting multipoles, the quadrupole (l=2) and the octopole (l=3), are
unexpectedly aligned with each other. Using randomly generated full-sky and
cut-sky maps, we investigate whether these anomalies are correlated at a
statistically significant level. We conclusively demonstrate that, assuming
Gaussian random and statistically isotropic CMB anisotropies, there is no
statistically significant correlation between the missing power on large
angular scales in the CMB and the alignment of the l=2 and l=3 multipoles. The
chance to measure the sky with both such a lack of large-angle correlation and
such an alignment of the low multipoles is thus quantified to be below 10^{-6}.",1004.3784v1
2010-04-22,"Superconducting order parameter in nonmagnetic borocarbides RNi$_{2}$B$_{2}$C (R=Y, Lu) probed by point-contact Andreev reflection spectroscopy","We report on the measurements of the superconducting order parameter in the
nonmagnetic borocarbides LuNi$_2$B$_2$C and YNi$_2$B$_2$C. Andreev conductance
spectra are obtained from nanoscale metallic junctions on single crystal
surfaces prepared along three major crystallographic orientations: [001],
[110], and [100]. The gap values extracted by the single-gap
Blonder-Tinkham-Klapwijk model follow the BCS predictions as a function of
temperature and magnetic field and exhibit a small anisotropy. These
observations are robust and reproducible among all the measurements on two
different sets of LuNi$_2$B$_2$C crystals and one set of YNi$_2$B$_2$C
crystals. We suggest possible explanations for the small gap anisotropy based
on the recent detailed gap measurements by angle-resolved photoemission
spectroscopy and the tunneling cone effect. Our results provide a consistent
picture of the superconducting gap structure in these materials, addressing the
controversy particularly in the reported results of point-contact Andreev
reflection spectroscopy.",1004.3846v1
2010-04-26,Orbital Order and Spontaneous Orthorhombicity in Iron Pnictides,"A growing list of experiments show orthorhombic electronic anisotropy in the
iron pnictides, in some cases at temperatures well above the spin density wave
transition. These experiments include neutron scattering, resistivity and
magnetoresistance measurements, and a variety of spectroscopies. We explore the
idea that these anisotropies stem from a common underlying cause: orbital order
manifest in an unequal occupation of $d_{xz}$ and $d_{yz}$ orbitals, arising
from the coupled spin-orbital degrees of freedom. We emphasize the distinction
between the total orbital occupation (the integrated density of states), where
the order parameter may be small, and the orbital polarization near the Fermi
level which can be more pronounced. We also discuss light-polarization studies
of angle-resolved photoemission, and demonstrate how x-ray absorption linear
dichroism may be used as a method to detect an orbital order parameter.",1004.4611v2
2010-04-27,Anisotropic Pressures at Ultra-stiff Singularities and the Stability of Cyclic Universes,"We show that the inclusion of simple anisotropic pressures stops the
isotropic Friedmann universe being a stable attractor as an initial or final
singularity is approached when pressures can exceed the energy density. This
shows that the situation with isotropic pressures, studied earlier in the
context of cyclic and ekpyrotic cosmologies, is not generic, and Kasner-like
behaviour occurs when simple pressure anisotropies are present. We find all the
asymptotic behaviours and determine the dynamics when the anisotropic principal
pressures are proportional to the density. We expect distortions and
anisotropies to be significantly amplified through a simple cosmological bounce
in cyclic or ekpyrotic cosmologies when ultra-stiff pressures are present.",1004.4767v1
2010-04-30,Large-angle anomalies in the CMB,"We review the recently found large-scale anomalies in the maps of temperature
anisotropies in the cosmic microwave background. These include alignments of
the largest modes of CMB anisotropy with each other and with geometry and
direction of motion of the Solar System, and the unusually low power at these
largest scales. We discuss these findings in relation to expectation from
standard inflationary cosmology, their statistical significance, the tools to
study them, and the various attempts to explain them.",1004.5602v2
2010-05-02,CMB Constraints on a Stochastic Background of Primordial Magnetic Fields,"We constrain a stochastic background of primordial magnetic field (PMF) by
its contribution to the angular power spectrum of cosmic microwave background
anisotropies. We parametrize such stochastic background by a power-law spectrum
with index $n_B$ and by its Gaussian smoothed amplitude $B_\lambda$ on a
comoving length $\lambda$. We give an approximation for the spectra of the
relevant correlators of the energy-momentum of the stochastic background of PMF
for any $n_B$. By using the WMAP 7 year data in combination with ACBAR, BICEP
and QUAD we obtain the constraint $B_{1 {\rm Mpc}} < 5.0$ nG at 95% confidence
level for a stochastic background of non-helical PMF. We discuss the relative
importance of the scalar and vector contribution to CMB anisotropies in
obtaining these constraints. We then forecast {\sc Planck} capabilities in
constraining $B_{1 {\rm Mpc}}$.",1005.0148v2
2010-05-03,Collective spin mode in a multi-component system of coupled itinerant and localized electrons,"We study collective spin excitations of a magnetically ordered state in a
multi-component system composed of both itinerant electrons and local moments.
Here the induced spin-density-wave (SDW) ordering of itinerant electrons and
the collinear antiferromangetic (AF) ordering of local moments are locked
together via a Hund's rule coupling. We show that the Goldstone theorem still
holds at the RPA level with the gapless spin wave protected inside the small
SDW gap of itinerant electrons, which, however, is fragile in the presence of
ion-anisotropy. A gapped out-of-phase spin mode extending over a much wider
energy scale above the SDW gap is found to be more robust against the
ion-anisotropy, which is mainly contributed by the local moment fluctuations.
While the scattering between the Goldstone mode and itinerant electrons
diminishes within the SDW gap, the out-of-phase mode will strongly interact
with itinerant electrons and thus dominate the spin and charge dynamics in such
an ordered phase. Possible relevance of such a model to the iron-pnictides will
be also discussed.",1005.0421v1
2010-05-05,Structure-Sensitive Mechanism of Nanographene Failure,"The response of a nanographene sheet to external stresses is considered in
terms of a mechanochemical reaction. The quantum chemical realization of the
approach is based on a coordinate-of-reaction concept for the purpose of
introducing a mechanochemical internal coordinate (MIC) that specifies a
deformational mode. The related force of response is calculated as the energy
gradient along the MIC, while the atomic configuration is optimized over all of
the other coordinates under the MIC constant-pitch elongation. The approach is
applied to the benzene molecule and (5, 5) nanographene. A drastic anisotropy
in the microscopic behavior of both objects under elongation along a MIC has
been observed when the MIC is oriented either along or normally to the C-C
bonds chain. Both the anisotropy and high stiffness of the nanographene
originate at the response of the benzenoid unit to stress.",1005.0796v1
2010-05-05,Lensing reconstruction of cluster-mass cross-correlation with cosmic microwave background polarization,"We extend our maximum likelihood method for reconstructing the cluster-mass
cross-correlation from cosmic microwave background (CMB) temperature
anisotropies and develop new estimators that utilize six different quadratic
combinations of CMB temperature and polarization fields. Our maximum likelihood
estimators are constructed with delensed CMB temperature and polarization
fields by using an assumed model of the convergence field and they can be
iteratively applied to a set of clusters, approaching to the optimal condition
for the lensing reconstruction as the assumed initial model is refined. Using
smoothed particle hydrodynamics simulations, we create a catalog of realistic
clusters obtainable from the current Sunyaev-Zel'dovich (SZ) surveys, and we
demonstrate the ability of the maximum likelihood estimators to reconstruct the
cluster-mass cross-correlation from the massive clusters. The iTT temperature
estimator provides a signal-to-noise ratio of a factor 3 larger than the iEB
polarization estimator, unless the detector noise for measuring polarization
anisotropies is controlled under 3 microK.",1005.0847v2
2010-05-06,Anisotropic excitonic effects in the energy loss function of hexagonal boron nitride,"We demonstrate that the valence energy-loss function of hexagonal boron
nitride (hBN) displays a strong anisotropy in shape, excitation energy and
dispersion for momentum transfer q parallel or perpendicular to the hBN layers.
This is manifested by e.g. an energy shift of 0.7 eV that cannot be captured by
single-particle approaches and is a demonstration of a strong anisotropy in the
two-body electron-hole interaction. Furthermore, for in-plane directions of q
we observe a splitting of the -plasmon in the M direction that is absent in the
K direction and this can be traced back to band-structure effects.",1005.0930v1
2010-05-10,An attractor for dark matter structures,"Cosmological simulations of dark matter structures have identified a set of
universal profiles, and similar characteristics have been seen in
non-cosmological simulations. It has therefore been speculated whether these
profiles of collisionless systems relate to accretion and merger history, or if
there is an attractor for the dark matter systems. Here we identify such a
1-dimensional attractor in the 3-dimensional space spanned by the 2 radial
slopes of the density and velocity dispersion, and the velocity anisotropy.
This attractor effectively removes one degree of freedom from the Jeans
equation. It also allows us to speculate on a new fluid interpretation for the
Jeans equation, with an effective polytropic index for the dark matter
particles between 1/2 and 3/4. If this attractor solution holds for other
collisionless structures, then it may hold the key to break the mass-anisotropy
degeneracy, which presently prevents us from measuring the mass profiles in
dwarf galaxies uniquely.",1005.1643v1
2010-05-11,Magnetization vector in the reversible region of a highly anisotropic cuprate superconductor: anisotropy factor and the role of 2D vortex fluctuations,"By using a high quality Tl2Ba2Ca2Cu3O10 (Tl-2223) single crystal as an
example, the magnetization vector was probed in the reversible region of highly
anisotropic cuprate superconductors. For that, we have measured its components
along and transverse to the applied magnetic field for different crystal
orientations. The analysis shows that the angular dependence of the
perpendicular component of the magnetization vector follows the one predicted
by a London-like approach which includes a contribution associated with the
thermal fluctuations of the 2D vortex positions. For the Tl-2223 crystal
studied here, a lower bound for the anisotropy factor was estimated to be about
190.",1005.1777v1
2010-05-13,Pseudo-Dipole Signal Removal from WMAP Data,"It is discovered in our previous work that different observational
systematics, e.g., errors of antenna pointing directions, asynchronous between
the attitude and science data, can generate pseudo-dipole signal in full-sky
maps of the cosmic microwave background (CMB) anisotropy published by The
Wilkinson Microwave Anisotropy Probe (WMAP) team. Now the antenna sidelobe
response to the Doppler signal is found to be able to produce similar effect as
well. In this work, independent to the sources, we uniformly model the
pseudo-dipole signal and remove it from published WMAP7 CMB maps by model
fitting. The result demonstrates that most of the released WMAP CMB quadrupole
is artificial.",1005.2352v3
2010-05-18,Nematic liquid crystal dynamics under applied electric fields,"In this paper we investigate the dynamics of liquid crystal textures in a
two-dimensional nematic under applied electric fields, using numerical
simulations performed using a publicly available LIquid CRystal Algorithm
(LICRA) developed by the authors. We consider both positive and negative
dielectric anisotropies and two different possibilities for the orientation of
the electric field (parallel and perpendicular to the two-dimensional lattice).
We determine the effect of an applied electric field pulse on the evolution of
the characteristic length scale and other properties of the liquid crystal
texture network. In particular, we show that different types of defects are
produced after the electric field is switched on, depending on the orientation
of the electric field and the sign of the dielectric anisotropy.",1005.3083v1
2010-05-18,Determining Magnetic Nanoparticle Size Distributions from Thermomagnetic Measurements,"Thermomagnetic measurements are used to obtain the size distribution and
anisotropy of magnetic nanoparticles. An analytical transformation method is
described which utilizes temperature-dependent zero-field cooling (ZFC)
magnetization data to provide a quantitative measurement of the average
diameter and relative abundance of superparamagnetic nanoparticles. Applying
this method to self-assembled MnAs nanoparticles in MnAs-GaAs composite films
reveals a log-normal size distribution and reduced anisotropy for nanoparticles
compared to bulk materials. This analytical technique holds promise for rapid
assessment of the size distribution of an ensemble of superparamagnetic
nanoparticles.",1005.3252v2
2010-05-26,Cosmic strings and their induced non-Gaussianities in the cosmic microwave background,"Motivated by the fact that cosmological perturbations of inflationary quantum
origin were born Gaussian, the search for non-Gaussianities in the cosmic
microwave background (CMB) anisotropies is considered as the privileged probe
of non-linear physics in the early universe. Cosmic strings are active sources
of gravitational perturbations and incessantly produce non-Gaussian distortions
in the CMB. Even if, on the currently observed angular scales, they can only
contribute a small fraction of the CMB angular power spectrum, cosmic strings
could actually be the main source of its non-Gaussianities. In this article,
after having reviewed the basic cosmological properties of a string network, we
present the signatures Nambu-Goto cosmic strings would induce in various
observables ranging from the one-point function of the temperature anisotropies
to the bispectrum and trispectrum. It is shown that string imprints are
significantly different than those expected from the primordial type of
non-Gaussianity and could therefore be easily distinguished.",1005.4842v2
2010-06-07,"Theory of spin waves in ferromagnetic (Ga,Mn)As","The collective behavior of spins in a dilute magnetic semiconductor is
determined by their mutual interactions and influenced by the underlying
crystal structure. Hence, we begin with the atomic quantum-mechanical
description of this system using the proposed variational-perturbation
calculus, and then turn to the emerging macroscopic picture employing
phenomenological constants. Within this framework we study spin waves and
exchange stiffness in the p-d Zener model of (Ga,Mn)As, its thin layers and
bulk crystals described by the spds* tight-binding approximation. Analyzing the
anisotropic part of exchange, we find that the Dzyaloshinskii-Moriya
interaction may lead to the cycloidal spin arrangement and uniaxial in-plane
anisotropy in thin layers, resulting in a surface-like anisotropy in thicker
films. We also derive and discuss the spin-wave contribution to magnetization
and Curie temperature. Our theory reconstructs the values of stiffness
determined from the temperature dependence of magnetization, but reproduces
only partly those obtained from analyzing precession modes in (Ga,Mn)As thin
films.",1006.1271v4
2010-06-09,Electric Control of Multiple Domain Walls in Pt/Co/Pt Nanotrack with Perpendicular Magnetic Anisotropy,"Electric control of multiple domain walls (DWs) motion is demonstrated by
Pt/Co/Pt nanotracks with perpendicular magnetic anisotropy. Due to the weak
microstructural disorders with small DW propagation field, the purely
current-driven DW motion is achieved in the creep regime at current densities
less than 10^7 A/cm^2 at room temperature. It is confirmed that by use of a
scanning magneto-optical Kerr effect microscope, several DWs are simultaneously
and identically displaced by the same distance in the same direction. Utilizing
such DWs motion, we succeed to realize random bits writing and transferring as
a device prototype of four-bit shift registers.",1006.1726v1
2010-06-15,PIC Simulations of the Temperature Anisotropy-Driven Weibel Instability: Analyzing the perpendicular mode,"An instability driven by the thermal anisotropy of a single electron species
is investigated in a 2D particle-in-cell (PIC) simulation. This instability is
the one considered by Weibel and it differs from the beam driven filamentation
instability. A comparison of the simulation results with analytic theory
provides similar exponential growth rates of the magnetic field during the
linear growth phase of the instability. We observe in accordance with previous
works the growth of electric fields during the saturation phase of the
instability. Some components of this electric field are not accounted for by
the linearized theory. A single-fluid-based theory is used to determine the
source of this nonlinear electric field. It is demonstrated that the magnetic
stress tensor, which vanishes in a 1D geometry, is more important in this
2-dimensional model used here. The electric field grows to an amplitude, which
yields a force on the electrons that is comparable to the magnetic one. The
peak energy density of each magnetic field component in the simulation plane
agrees with previous estimates. Eddy currents develop, which let the amplitude
of the third magnetic field component grow, which is not observed in a 1D
simulation.",1006.3057v1
2010-06-16,Phase transformation in Si from semiconducting diamond to metallic beta-Sn phase in QMC and DFT under hydrostatic and anisotropic stress,"Silicon undergoes a phase transition from the semiconducting diamond phase to
the metallic beta-Sn phase under pressure. We use quantum Monte Carlo
calculations to predict the transformation pressure and compare the results to
density functional calculations employing the LDA, PBE, PW91, WC, AM05, PBEsol
and HSE06 exchange-correlation functionals. Diffusion Monte Carlo predicts a
transition pressure of 14.0 +- 1.0 GPa slightly above the experimentally
observed transition pressure range of 11.3 to 12.6 GPa. The HSE06 hybrid
functional predicts a transition pressure of 12.4 GPa in excellent agreement
with experiments. Exchange-correlation functionals using the local-density
approximation and generalized-gradient approximations result in transition
pressures ranging from 3.5 to 10.0 GPa, well below the experimental values. The
transition pressure is sensitive to stress anisotropy. Anisotropy in the stress
along any of the cubic axes of the diamond phase of silicon lowers the
equilibrium transition pressure and may explain the discrepancy between the
various experimental values as well as the small overestimate of the quantum
Monte Carlo transition pressure.",1006.3253v1
2010-06-21,Quarkonia in anisotropic hot QCD medium in a quasi-particle model,"The fate of heavy quarkonia states has been investigated in QCD at high
temperature when the plasma has a small momentum space anisotropy within a
quasi-particle model. A real time static potential has been obtained from a
Hard thermal loop expression for the gluon self-energy, by employing the
quasi-parton equilibrium distribution functions extracted from hot QCD
equations of state of $O(g^5)$ and $O(g^6\ln(1/g))$. Employing the potential,
quarkonia melting has been studied. It is found that the equations of state and
the momentum anisotropy cause significant modifications in the screening
properties of the plasma.",1006.3995v2
2010-06-21,"Coherent magnetization precession in ferromagnetic (Ga,Mn)As induced by picosecond acoustic pulses","We show that the magnetization of a thin ferromagnetic (Ga,Mn)As layer can be
modulated by picosecond acoustic pulses. In this approach a picosecond strain
pulse injected into the structure induces a tilt of the magnetization vector M,
followed by the precession of M around its equilibrium orientation. This effect
can be understood in terms of changes in magneto-crystalline anisotropy induced
by the pulse. A model where only one anisotropy constant is affected by the
strain pulse provides a good description of the observed time-dependent
response.",1006.4133v1
2010-06-24,Mott transition in the Hubbard model on the anisotropic kagomé lattice,"We investigate the Mott transition in the anisotropic kagom\'e lattice
Hubbard model using the cellular dynamical mean field theory combined with
continuous-time quantum Monte Carlo simulations. By calculating the double
occupancy and the density of states, we determine the interaction strength of
the first-order Mott transition and show that it becomes small as the
anisotropy increases. We also calculate the spin correlation functions and the
single-particle spectrum, and reveal that the quasiparticle and magnetic
properties change dramatically around the Mott transition; the spin
correlations are strongly enhanced and the quasiparticle bands are deformed. We
conclude that such dramatic changes are due to the enhancement of anisotropy
associated with the relaxation of frustration around the Mott transition.",1006.4784v2
2010-06-25,Epitaxial strain effects in the spinel ferrites CoFe2O4 and NiFe2O4 from first principles,"The inverse spinels CoFe2O4 and NiFe2O4, which have been of particular
interest over the past few years as building blocks of artificial multiferroic
heterostructures and as possible spin-filter materials, are investigated by
means of density functional theory calculations. We address the effect of
epitaxial strain on the magneto-crystalline anisotropy and show that, in
agreement with experimental observations, tensile strain favors perpendicular
anisotropy, whereas compressive strain favors in-plane orientation of the
magnetization. Our calculated magnetostriction constants $\lambda_{100}$ of
about -220 ppm for CoFe2O4 and -45 ppm for NiFe2O4 agree well with available
experimental data. We analyze the effect of different cation arrangements used
to represent the inverse spinel structure and show that both LSDA+U and GGA+U
allow for a good quantitative description of these materials. Our results open
the way for further computational investigations of spinel ferrites.",1006.5080v1
2010-07-01,Highly-anisotropic and strongly-dissipative hydrodynamics for early stages of relativistic heavy-ion collisions,"We introduce a new framework of highly-anisotropic hydrodynamics that
includes dissipation effects. Dissipation is defined by the form of the entropy
source that depends on the pressure anisotropy and vanishes for the isotropic
fluid. With a simple ansatz for the entropy source obeying general physical
requirements, we are led to a non-linear equation describing the time evolution
of the anisotropy in purely-longitudinal boost-invariant systems. Matter that
is initially highly anisotropic approaches naturally the regime of the perfect
fluid. Thus, the resulting evolution agrees with the expectations about the
behavior of matter produced at the early stages of relativistic heavy-ion
collisions. The equilibration is identified with the processes of entropy
production.",1007.0130v1
2010-07-06,Ferromagnetic phase of a uniaxial magnet with anisotropic biquadratic exchange,"The ferromagnetic phase (FMP) of a uniaxial magnet with the easy-plane
single-ion anisotropy (SIA) and the anisotropic biquadra\-tic exchange
interaction (BQEI) has been studied. The case $S=1$ for the site spin $S$ has
been considered. Expressions for two branches of the spin excitation spectrum
at finite temperatures $T$ have been obtained, and the conditions for spectral
mode stability have been determined. The spectral mode stability diagram in the
$T-h$ coordinates has been constructed. The diagram testifies that, under
certain conditions, the temperature decrease is accompanied by a violation of
the spectral mode stability followed, as the temperature decreases further, by
its restoration; i.e. the reentrance phenomenon is observed. The temperature of
the second-order phase transition (PT) from the FMP into the phase with
spontaneously broken symmetry has been demonstrated to depend considerably on
the BQEI anisotropy constant.",1007.0847v1
2010-07-06,"Past Galactic GRBs, and the origin and composition of ultrahigh-energy cosmic rays","Recent results from the Pierre Auger Observatory show energy dependent
chemical composition of ultrahigh-energy cosmic rays (UHECR) with a growing
fraction of heavy elements at high energies. This points to a non-negligible
contribution of the Galactic sources, such as past GRBs and other rare but
powerful stellar explosions in the Milky Way. The effects of diffusion in the
Galactic magnetic fields alter the observed composition and render the flux of
UHECR isotropic, up to a few per cent anisotropy in the direction of the
Galactic Center, as well as some small-scale anisotropy with ""hot spots"" due to
the locations of the most recent/closest bursts.",1007.0961v1
2010-07-07,Violation of Onsager Reciprocity in Underdoped Cuprates ?,"One of the canons of condensed matter physics is the Onsager Reciprocity
principle in systems in which the Hamiltonian commutes with the time-reversal
operator. Recent results of measurements of the Nernst coefficient in
underdoped YBa_2Cu_30_{6+x}, together with the measurements of the anisotropy
of conductivity and the inferred anisotropy of the thermopower, imply that this
principle is violated. The probable violation and its temperature dependence
are shown to be consistent with the Loop-current phase which has been directly
observed in other experiments. The violation is related directly to the
magneto-electric symmetry of such a phase in which an applied electric field
generates an effective magnetic field at right angle to it and to the order
parameter vector, and vice versa.",1007.1215v3
2010-07-12,Neutrino Astrophysics and Galactic Cosmic Ray Anisotropy in IceCube,"The IceCube Observatory is a kilometer-cube neutrino telescope under
construction at the South Pole and planned to be completed in early 2011. When
completed it will consist of 5,160 Digital Optical Modules (DOMs) which detect
Cherenkov radiation from the charged particles produced in neutrino
interactions and by cosmic ray initiated atmospheric showers. IceCube
construction is currently 90% complete. A selection of the most recent
scientific results are shown here. The measurement of the anisotropy in arrival
direction of galactic cosmic rays will also be presented and discussed.",1007.2621v2
2010-07-20,Evidence for Dynamically Important Magnetic Fields in Molecular Clouds,"Recent observational evidence that magnetic fields are dynamically important
in molecular clouds, compared to self-gravity and turbulence, is reviewed and
illustrated with data from the NGC 2024 region. One piece of evidence,
turbulence anisotropy, was found in the diffuse envelope of a cloud (Av~1;
Heyer et al. 2008); our data further suggests turbulence anisotropy in the
cloud (Av >7) and even near the cloud core (Av~100). The data also shows that
magnetic fields can channel gravitational contraction even for a region with
super-critical N(H2)/2Blos ratio (the ratio between the observed column density
and two times the line-of-sight observed field strength), a parameter which has
been widely used by observers to estimate core mass-to-flux ratios. Although
the mass-to-flux ratio is constant under the flux-freezing condition, we show
that N(H2)/2Blos grows with time if gravitational contraction is anisotropic
due to magnetic fields.",1007.3312v2
2010-07-20,Fractal Structure of Hastings-Levitov Patterns Restricted in a Sector Geometry,"A generalized form of the Hastings and Levitov (HL) algorithm for simulation
of diffusion-limited aggregation (DLA) restricted in a sector geometry is
studied. It is found that this generalization with uniform measure produces
""wedge-like"" fractal patterns in the physical space, whose fractal dimension
and anisotropy exponent depend significantly on the opening angle $\beta$ of
the sector. The morphological properties and the overall shape of the patterns
are analyzed by computing the angular two-point density correlation function of
the patterns. We also find that the fractal dimension of the patterns with
sinusoidal distributed measure depend weakly on $\beta$ with almost the same
dimension as the radial DLA cluster. The anisotropy exponent and the visual
appearance of the patterns in this case are shown to be compatible with those
of the advection-diffusion-limited aggregation (ADLA) clusters.",1007.3358v1
2010-07-23,Quantum Transport Through a Stretched Spin--1 Molecule,"We analyze the electronic transport through a model spin-1 molecule as a
function of temperature, magnetic field and bias voltage. We consider the
effect of magnetic anisotropy, which can be generated experimentally by
stretching the molecule. In the experimentally relevant regime the conductance
of the unstretched molecule reaches the unitary limit of the underscreened
spin- 1 Kondo effect at low temperatures. The magnetic anisotropy generates an
antiferromagnetic coupling between the remaining spin 1/2 and a singular
density of quasiparticles, producing a second Kondo effect and a reduced
conductance. The results explain recent measurements in spin-1 molecules
[Science 328 1370 (2010)].",1007.4214v2
2010-08-02,Temperature and bias voltage dependence of Co/Pd multilayer-based magnetic tunnel junctions with perpendicular magnetic anisotropy,"Temperature- and bias voltage-dependent transport measurements of magnetic
tunnel junctions (MTJs) with perpendicularly magnetized Co/Pd electrodes are
presented. Magnetization measurements of the Co/Pd multilayers are performed to
characterize the electrodes. The effects of the Co layer thickness in the Co/Pd
bilayers, the annealing temperature, the Co thickness at the MgO barrier
interface, and the number of bilayers on the tunneling magneto resistance (TMR)
effect are investigated. TMR-ratios of about 11 % at room temperature and 18.5
% at 13 K are measured and two well-defined switching fields are observed. The
results are compared to measurements of MTJs with Co-Fe-B electrodes and
in-plane anisotropy.",1008.0341v1
2010-08-10,Inverse Compton gamma-rays from Galactic dark matter annihilation: Anisotropy signatures,"High energy electrons and positrons from annihilating dark matter can imprint
unique angular anisotropies on the diffuse gamma-ray flux by inverse Compton
scattering off the interstellar radiation field. We develop a numerical tool to
compute gamma-ray emission from such electrons and positrons produced in the
smooth host halo and in substructure halos with masses down to 10^(-6)M_sun. We
show that the angular power spectrum from inverse Compton scattering is
exponentially suppressed below an angular scale determined by the diffusion
length of electrons and positrons. We also find that the total flux and the
shape of the angular power spectrum depends sensitively on the spatial
distribution of subhalos in the Milky Way. Finally, the contribution from the
smooth host halo component to the gamma-ray mean intensity is negligibly small
compared to subhalos.",1008.1801v3
2010-08-11,Theory for a dissipative droplet soliton excited by a spin torque nanocontact,"A novel type of solitary wave is predicted to form in spin torque oscillators
when the free layer has a sufficiently large perpendicular anisotropy. In this
structure, which is a dissipative version of the conservative droplet soliton
originally studied in 1977 by Ivanov and Kosevich, spin torque counteracts the
damping that would otherwise destroy the mode. Asymptotic methods are used to
derive conditions on perpendicular anisotropy strength and applied current
under which a dissipative droplet can be nucleated and sustained. Numerical
methods are used to confirm the stability of the droplet against various
perturbations that are likely in experiments, including tilting of the applied
field, non-zero spin torque asymmetry, and non-trivial Oersted fields. Under
certain conditions, the droplet experiences a drift instability in which it
propagates away from the nanocontact and is then destroyed by damping.",1008.1898v1
2010-08-11,Velocity Structure of Self-Similar Spherically Collapsed Halos,"Using a generalized self-similar secondary infall model, which accounts for
tidal torques acting on the halo, we analyze the velocity profiles of halos in
order to gain intuition for N-body simulation results. We analytically
calculate the asymptotic behavior of the internal radial and tangential kinetic
energy profiles in different radial regimes. We then numerically compute the
velocity anisotropy and pseudo-phase-space density profiles and compare them to
recent N-body simulations. For cosmological initial conditions, we find both
numerically and analytically that the anisotropy profile asymptotes at small
radii to a constant set by model parameters. It rises on intermediate scales as
the velocity dispersion becomes more radially dominated and then drops off at
radii larger than the virial radius where the radial velocity dispersion
vanishes in our model. The pseudo-phase-space density is universal on
intermediate and large scales. However, its asymptotic slope on small scales
depends on the halo mass and on how mass shells are torqued after turnaround.
The results largely confirm N-body simulations but show some differences that
are likely due to our assumption of a one-dimensional phase space manifold.",1008.1980v2
2010-08-13,Particle Systems arising from an anti-ferromagnetic Ising model,"We study a low temperature anisotropic anti-ferromagnetic 2D Ising model
through the guise of a certain dimer model. This model has a bijection with a
one-dimensional particle system equipped with creation and annihilation. In the
thermodynamic limit, we determine the explicit phase diagrams as functions of
temperature and anisotropy. Two values of the anisotropy are of particular
interest - the 'critical' value and the 'independent' value. At independence,
the particle system has the same distribution as the two colored noisy voter
model. Its limiting measure under a natural scaling window is the Continuum
Noisy Voter Model. At criticality, the distribution of particles on a given
horizontal line, is a Pfaffian point process whose kernel in the scaling window
can be written explicitly in terms of Bessel functions.",1008.2310v2
2010-08-16,On the Sensitivity of Partial Redistribution Scattering Polarization Profiles to Various Atmospheric Parameters,"This paper presents a detailed study of the scattering polarization profiles
formed under partial frequency redistribution (PRD) in two thermal models of
the solar atmosphere. Particular attention is given to understanding the
influence of several atmospheric parameters on the emergent fractional linear
polarization profiles. The shapes of these $Q/I$ profiles are interpreted in
terms of the anisotropy of the radiation field, which in turn depends on the
source function gradient that sets the angular variation of the specific
intensity. We define a suitable frequency integrated anisotropy factor for PRD
that can be directly related to the emergent linear polarization. We show that
complete frequency redistribution is a good approximation to model weak
resonance lines. We also show that the emergent linear polarization profiles
can be very sensitive to the thermal structure of the solar atmosphere and, in
particular, to spatial variations of the damping parameter.",1008.2585v1
2010-08-20,Destruction of chain-superconductivity in YBa_2Cu_4O_8 in a weak magnetic field,"We report measurements of the temperature dependent components of the
magnetic penetration depth {\lambda}(T) in single crystal samples of
YBa_2Cu_4O_8 using a radio frequency tunnel diode oscillator technique. We
observe a downturn in {\lambda}(T) at low temperatures for currents flowing
along the b and c axes but not along the a axis. The downturn in {\lambda}_b is
suppressed by a small dc field of ~0.25 T. This and the zero field anisotropy
of {\lambda}(T) likely result from proximity induced superconducting on the CuO
chains, however we also discuss the possibility that a significant part of the
anisotropy might originate from the CuO2 planes.",1008.3532v1
2010-08-31,General Solution of EM Wave Propagation in Anisotropic Media,"When anisotropy is involved, the wave equation becomes simultaneous partial
differential equations that are not easily solved. Moreover, when the
anisotropy occurs due to both permittivity and permeability, these equations
are insolvable without a numerical or an approximate method. The problem is
essentially due to the fact neither $\e$ nor $\m$ can be extracted from the
curl term, when they are in it. The terms $\na\times {\bf E}$ (or ${\bf H})$
and $\na\times \e{\bf E}$ (or $\;\m{\bf H})$ are practically independent
variables, and $\bf E$ and $\bf H$ are coupled to each other. However, if
Maxwell's equations are manipulated in a different way, new wave equations are
obtained. The obtained equations can be applied in anisotropic, as well as
isotropic, cases. In addition, $\bf E$ and $\bf H$ are decoupled in the new
equations, so the equations can be solved analytically by using tensor Green's
functions.",1008.5212v1
2010-09-01,Modeling mass independent of anisotropy,"By manipulating the spherical Jeans equation, Wolf et al. (2010) show that
the mass enclosed within the 3D deprojected half-light radius r_1/2 can be
determined with only mild assumptions about the spatial variation of the
stellar velocity dispersion anisotropy as long as the projected velocity
dispersion profile is fairly flat near the half-light radius, as is typically
observed. They find M_1/2 = 3 \sigma_los^2 r_1/2 / G ~ 4 \sigma_los^2 R_eff /
G, where \sigma_los^2 is the luminosity-weighted square of the line-of-sight
velocity dispersion and R_eff is the 2D projected half-light radius. This
finding can be used to show that all of the Milky Way dwarf spheroidal galaxies
(MW dSphs) are consistent with having formed within a halo of mass
approximately 3 x 10^9 M_sun assuming a LCDM cosmology. In addition, the
dynamical I-band mass-to-light ratio (M/L) vs. M_1/2 relation for
dispersion-supported galaxies follows a U-shape, with a broad minimum near M/L
~ 3 that spans dwarf elliptical galaxies to normal ellipticals, a steep rise to
M/L ~ 3,200 for ultra-faint dSphs, and a more shallow rise to M/L ~ 800 for
galaxy cluster spheroids.",1009.0295v1
2010-09-03,Anisotropy of Alfvénic Turbulence in the Solar Wind and Numerical Simulations,"We investigate the anisotropy of Alfv\'enic turbulence in the inertial range
of slow solar wind and in both driven and decaying reduced magnetohydrodynamic
simulations. A direct comparison is made by measuring the anisotropic
second-order structure functions in both data sets. In the solar wind, the
perpendicular spectral index of the magnetic field is close to -5/3. In the
forced simulation, it is close to -5/3 for the velocity and -3/2 for the
magnetic field. In the decaying simulation, it is -5/3 for both fields. The
spectral index becomes steeper at small angles to the local magnetic field
direction in all cases. We also show that when using the global rather than
local mean field, the anisotropic scaling of the simulations cannot always be
properly measured.",1009.0662v2
2010-09-07,Search for light-speed anisotropies using Compton scattering of high-energy electrons,"Based on the high sensitivity of Compton scattering off ultra relativistic
electrons, the possibility of anisotropies in the speed of light is
investigated. The result discussed in this contribution is based on the
gamma-ray beam of the ESRF's GRAAL facility (Grenoble, France) and the search
for sidereal variations in the energy of the Compton-edge photons. The absence
of oscillations yields the two-sided limit of 1.6 x 10^{-14} at 95 % confidence
level on a combination of photon and electron coefficients of the minimal
Standard Model Extension (mSME). This new constraint provides an improvement
over previous bounds by one order of magnitude.",1009.1299v1
2010-09-08,The decay of turbulence in rotating flows,"We present a parametric space study of the decay of turbulence in rotating
flows combining direct numerical simulations, large eddy simulations, and
phenomenological theory. Several cases are considered: (1) the effect of
varying the characteristic scale of the initial conditions when compared with
the size of the box, to mimic ""bounded"" and ""unbounded"" flows; (2) the effect
of helicity (correlation between the velocity and vorticity); (3) the effect of
Rossby and Reynolds numbers; and (4) the effect of anisotropy in the initial
conditions. Initial conditions include the Taylor-Green vortex, the
Arn'old-Beltrami-Childress flow, and random flows with large-scale energy
spectrum proportional to $k^4$. The decay laws obtained in the simulations for
the energy, helicity, and enstrophy in each case can be explained with
phenomenological arguments that separate the decay of two-dimensional from
three-dimensional modes, and that take into account the role of helicity and
rotation in slowing down the energy decay. The time evolution of the energy
spectrum and development of anisotropies in the simulations are also discussed.
Finally, the effect of rotation and helicity in the skewness and kurtosis of
the flow is considered.",1009.1595v2
2010-09-10,Electric Field Controlled Magnetic Anisotropy in a Single Molecule,"We have measured quantum transport through an individual Fe$_4$
single-molecule magnet embedded in a three-terminal device geometry. The
characteristic zero-field splittings of adjacent charge states and their
magnetic field evolution are observed in inelastic tunneling spectroscopy. We
demonstrate that the molecule retains its magnetic properties, and moreover,
that the magnetic anisotropy is significantly enhanced by reversible electron
addition / subtraction controlled with the gate voltage. Single-molecule
magnetism can thus be electrically controlled.",1009.2027v1
2010-09-13,Anisotropy of Imbalanced Alfvenic Turbulence in Fast Solar Wind,"We present the first measurement of the scale-dependent power anisotropy of
Elsasser variables in imbalanced fast solar wind turbulence. The dominant
Elsasser mode is isotropic at lower spacecraft frequencies but becomes
increasingly anisotropic at higher frequencies. The sub-dominant mode is
anisotropic throughout, but in a scale-independent way (at higher frequencies).
There are two distinct subranges exhibiting different scalings within what is
normally considered the inertial range. The low Alfven ratio and shallow
scaling of the sub-dominant Elsasser mode suggest an interpretation of the
observed discrepancy between the velocity and magnetic field scalings. The
total energy is dominated by the latter. These results do not appear to be
fully explained by any of the current theories of incompressible imbalanced MHD
turbulence.",1009.2427v2
2010-09-14,Diagnosing Timing Error in WMAP Data,"The Doppler dipole signal dominates the cosmic microwave background (CMB)
anisotropy maps obtained by the Wilkinson Microwave Anisotropy Probe (WMAP)
mission, and plays a key role throughout the data processing. Previously, we
discovered a timing asynchronism of -25.6ms between the timestamps of the
spacecraft attitude and radiometer output in the original raw WMAP time-ordered
data (TOD), which, if not corrected in following data processing, would
generate an artificial quadrupole component (l=2) in recovered CMB maps (Liu,
Xiong & Li 2010). Recently, Roukema (2010b) proves that there does exist a
timing-offset-induced error corresponding to about -25.6ms in the WMAP
calibrated TOD by studying the fluctuation variance per pixel in the
temperature map recovered from the TOD as a function of assumed timing-offset.
Here, we find evidence directly in the WMAP TOD for such an uncorrected timing
error, possibly occurred in calculating the Doppler dipole signal during the
WMAP team's TOD data processing. The amplitude is highly significant and is
consistent with previous work. We also show that the uncorrected timing-offset
can lead the WMAP CMB quadrupole to be substantially overestimated.",1009.2701v2
2010-09-22,Local symmetry and magnetic anisotropy in multiferroic MnWO4 and antiferromagnetic CoWO4 studied by soft x-ray absorption spectroscopy,"Soft x-ray absorption experiments on the transition metal L2,3 edge of
multiferroic MnWO4 and antiferromagnetic CoWO4 are presented. The observed
linear polarization dependence, analyzed by full-multiplet calculations, is
used to determine the ground state wave function of the magnetic Mn2+ and Co2+
ions. The impact of the local structure and the spin-orbit coupling on the
orbital moment is discussed in terms of the single-ion anisotropy. It is shown
that the orbital moment in CoWO4 is responsible for the collinear
antiferromagnetism, while the small size of spin-orbit coupling effects make
spiral magnetic order in MnWO4 possible, enabling the material to be
multiferroic.",1009.4338v1
2010-10-03,Cation-ordering effects in the single layered manganite La(2/3)Sr(4/3)MnO4,"We have synthesized epitaxial La(1-x)Sr(1+x)MnO4 (x=1/3) films as random
alloys and cation-ordered analogues to probe how cation order affects the
properties of a 2D manganite. The films show weak ferromagnetic ordering up to
130 K, although there is a dramatic difference in magnetic anisotropy depending
on the cation order. While all films exhibit similar gapped insulator behavior
above 130 K, there is a significant difference in the low temperature transport
mechanism depending on the cation order. Differences in magnetic anisotropy and
low temperature transport are consistent with differences in Mn 3d orbital
occupancies. Together this work suggests that cation ordering can significantly
alter the Mn 3d orbital ground state in these correlated electron systems.",1010.0372v2
2010-10-04,Improved Dark Energy Detection through the Polarization-assisted WMAP-NVSS ISW Correlation,"Integrated Sachs-Wolfe (ISW) effect can be estimated by cross-correlating
Cosmic Microwave Background (CMB) sky with tracers of the local matter
distribution. At late cosmic time, the dark energy induced decay of gravitation
potential generates a cross-correlation signal on large angular scales. The
dominant noise are the intrinsic CMB anisotropies from the inflationary epoch.
In this Letter we use CMB polarization to reduce this intrinsic noise. We
cross-correlate the microwave sky observed by Wilkinson Microwave Anisotropy
Probe (WMAP) with the radio source catalog compiled by NRAO VLA Sky Survey
(NVSS) to study the efficiency of the noise suppression . We find that the
error bars are reduced about 5-12 %, improving the statistical power.",1010.0578v1
2010-10-10,Anisotropy of Magnetoresistance Hysteresis around the $ν=2/3$ Quantum Hall State in Tilted Magnetic Field,"We present an anisotropy of the hysteretic transport around the spin
transition point at Landau level filling factor $\nu=2/3$ in tilted magnetic
field. When the direction of the in-plane component of the magnetic field
$B_{\parallel}$ is normal to the probe current $I$, a strong hysteretic
transport due to the current-induced nuclear spin polarization occurs. When
$B_{\parallel}$ is parallel to $I$, on the other hand, the hysteresis almost
disappears. We also demonstrate that the nuclear spin-lattice relaxation rate
$T_{1}^{-1}$ at the transition point increases with decreasing angle between
the directions of $B_{\parallel}$ and $I$. These results suggest that the
morphology of electron spin domains around $\nu =2/3$ is affected by the
current direction.",1010.1885v1
2010-10-15,Realizing bright matter-wave soliton collisions with controlled relative phase,"We propose a method to split the ground state of an attractively interacting
atomic Bose-Einstein condensate into two bright solitary waves with controlled
relative phase and velocity. We analyze the stability of these waves against
their subsequent re-collisions at the center of a cylindrically symmetric,
prolate harmonic trap as a function of relative phase, velocity, and trap
anisotropy. We show that the collisional stability is strongly dependent on
relative phase at low velocity, and we identify previously unobserved
oscillations in the collisional stability as a function of the trap anisotropy.
An experimental implementation of our method would determine the validity of
the mean field description of bright solitary waves, and could prove an
important step towards atom interferometry experiments involving bright
solitary waves.",1010.3219v2
2010-10-18,Significant elastic anisotropy in Ti$_{1-x}$Al$_x$N alloys,"Strong compositional-dependent elastic properties have been observed
theoretically and experimentally in Ti$_{1-x}$Al$_x$ N alloys. The elastic
constant, C$_{11}$, changes by more than 50% depending on the Al-content.
Increasing the Al-content weakens the average bond strength in the local
octahedral arrangements resulting in a more compliant material. On the other
hand, it enhances the directional (covalent) nature of the nearest neighbor
bonds that results in greater elastic anisotropy and higher sound velocities.
The strong dependence of the elastic properties on the Al-content offers new
insight into the detailed understanding of the spinodal decomposition and age
hardening in Ti$_{1-x}$Al$_x$N alloys.",1010.3678v1
2010-10-21,A model for vortex formation in magnetic nanodots,"We use Monte Carlo simulation to study the vortex nucleation on magnetic
nanodots at low temperature. In our simulations, we have considered a simple
microscopic two-dimensional anisotropic Heisenberg model with term to describe
the anisotropy due to the presence of the nanodot edge. We have considered the
thickness of the edge, which was not considered in previous works, introducing
a term that controls the energy associated to the edge. Our results clearly
show that the thickness of the edge has a considerable influence in the vortex
nucleation on magnetic nanodots. We have obtained the hysteresis curve for
several values of the surface anisotropy and skin depth parameter ($\xi$). The
results are in excellent agreement with experimental data.",1010.4541v1
2010-10-21,Van der Waals torque induced by external magnetic fields,"We present a method for inducing and controlling van der Waals torques
between two parallel slabs using a constant magnetic field. The torque is
calculated using the Barash theory of dispersive torques. In III-IV
semiconductors such as $InSb$, the effect of an external magnetic field is to
induce an optical anisotropy, in an otherwise isotropic material, that will in
turn induce a torque.
  The calculations of the torque are done in the Voigt configuration, with the
magnetic field parallel to the surface of the slabs. As a case study we
consider a slab made of calcite and a second slab made of $InSb$. In the
absence of magnetic field there is no torque. As the magnetic field increases,
the optical anisotropy of $InSb$ increases and the torque becomes different
from zero, increasing with the magnetic field. The resulting torque is of the
same order of magnitude as that calculated using permanent anisotropic
materials when the magnetic fields is close to 1 T.",1010.4553v1
2010-10-22,Thermally activated magnetization reversal in monoatomic magnetic chains on surfaces studied by classical atomistic spin-dynamics simulations,"We analyze the spontaneous magnetization reversal of supported monoatomic
chains of finite length due to thermal fluctuations via atomistic spin-dynamics
simulations. Our approach is based on the integration of the Landau-Lifshitz
equation of motion of a classical spin Hamiltonian at the presence of
stochastic forces. The associated magnetization lifetime is found to obey an
Arrhenius law with an activation barrier equal to the domain wall energy in the
chain. For chains longer than one domain-wall width, the reversal is initiated
by nucleation of a reversed magnetization domain primarily at the chain edge
followed by a subsequent propagation of the domain wall to the other edge in a
random-walk fashion. This results in a linear dependence of the lifetime on the
chain length, if the magnetization correlation length is not exceeded. We
studied chains of uniaxial and tri-axial anisotropy and found that a tri-axial
anisotropy leads to a reduction of the magnetization lifetime due to a higher
reversal attempt rate, even though the activation barrier is not changed.",1010.4730v2
2010-10-25,Quarkonium in a non-ideal hot QCD Plasma,"Substantial anisotropies should occur in the hot expanding QCD plasma
produced in relativistic heavy-ion collisions due to non-vanishing shear
viscosity. We discuss the form of the real-time, hard thermal loop resummed
propagator for static gluons in the presence of such anisotropies and the
consequences for quarkonium binding. It has been predicted that the propagator
develops an imaginary part due to Landau damping at high temperature. This
generates a much larger width of quarkonium states than the Appelquist-Politzer
vacuum estimate corresponding to decay into three gluons. We argue that this
might be observable in heavy-ion collisions as a suppression of the Upsilon(1S)
--> e+ e- process. Lastly, we consider the heavy quark (singlet) free energy
just above the deconfinement temperature. In the ""semi-QGP"", F(R) at distances
beyond 1/T is expected to be suppressed by 1/N as compared to an ideal plasma.",1010.5218v1
2010-10-25,Second Order Phase Transition in Anisotropic Lattice Gauge Theories with Extra Dimensions,"Field theories with extra dimensions live in a limbo. While their classical
solutions have been the subject of considerable study, their quantum aspects
are difficult to control. A special class of such theories are anisotropic
gauge theories. The anisotropy was originally introduced to localize chiral
fermions. Their continuum limit is of practical interest and it will be shown
that the anisotropy of the gauge couplings plays a crucial role in opening the
phase diagram of the theory to a new phase, that is separated from the others
by a second order phase transition. The mechanism behind this is generic for a
certain class of models, that can be studied with lattice techniques. This
leads to new perspectives for the study of quantum effects of extra dimensions.",1010.5281v1
2010-10-27,Orientation Effects on the Inner Region of Dusty Torus of Active Galactic Nuclei,"A sublimation process governs the innermost region of the dusty torus of
active galactic nuclei. However, the observed inner radius of the torus is
systematically smaller than the expected radius by a factor of ~ 1/3. We show
that the anisotropy of the emission from accretion disks resolves this conflict
naturally and quantitatively. An accretion disk emits lesser radiation in the
direction closer to its equatorial plane (i.e., to the torus). We find that the
anisotropy makes the torus inner region closer to the central black hole and
concave. Moreover, the innermost edge of the torus may connect with the
outermost edge of the disk continuously. Considering the anisotropic emission
of each clump in the torus, we calculate the near-infrared flux variation in
response to a UV flash. For an observer at the polar angle theta_obs = 25 deg,
the centroid of the time delay is found to be 37% of the delay expected in the
case of isotropic illumination, which explains the observed systematic
deviation.",1010.5799v1
2010-10-28,"Interplay of the Kondo Effect and Spin-Polarized Transport in Magnetic Molecules, Adatoms and Quantum Dots","We study the interplay of the Kondo effect and spin-polarized tunneling in a
class of systems exhibiting uniaxial magnetic anisotropy, such as magnetic
molecules, magnetic adatoms, or quantum dots coupled to a single localized
magnetic moment. Using the numerical renormalization group method we calculate
the spectral functions and linear conductance in the Kondo regime. We show that
the exchange coupling between conducting electrons and localized magnetic core
generally leads to suppression of the Kondo effect. We also predict a
nontrivial dependence of the tunnel magnetoresistance on the strength of
exchange coupling and on the anisotropy constant.",1010.6030v2
2010-11-01,Crossover phenomena involving the dense O($n$) phase,"We explore the properties of the low-temperature phase of the O($n$) loop
model in two dimensions by means of transfer-matrix calculations and
finite-size scaling. We determine the stability of this phase with respect to
several kinds of perturbations, including cubic anisotropy, attraction between
loop segments, double bonds and crossing bonds. In line with Coulomb gas
predictions, cubic anisotropy and crossing bonds are found to be relevant and
introduce crossover to different types of behavior. Whereas perturbations in
the form of loop-loop attractions and double bonds are irrelevant, sufficiently
strong perturbations of these types induce a phase transition of the Ising
type, at least in the cases investigated. This Ising transition leaves the
underlying universal low-temperature O($n$) behavior unaffected.",1011.0302v1
2010-11-01,Level crossings and zero-field splitting in the \{Cr$_8$\}-cubane spin-cluster by inelastic neutron scattering and magnetization studies,"Inelastic neutron scattering in variable magnetic field and high-field
magnetization measurements, at the milikelvin temperature range, were performed
to gain insight into the low-energy magnetic excitation spectrum and the
field-induced level crossings in the molecular spin cluster \{Cr$_8$\}-cubane.
These complementary techniques provide consistent estimates of the lowest
level-crossing field. The overall features of the experimental data are
explained using an isotropic Heisenberg model, based on three distinct exchange
interactions linking the eight Cr$^{\text{III}}$ paramagnetic centers (spins $s
= 3/2$), that is supplemented with a relatively large molecular magnetic
anisotropy term for the lowest S=1 multiplet. It is noted that the existence of
the anisotropy is clearly evident from the magnetic field dependence of the
excitations in the INS measurements, while the magnetization measurements are
not sensitive to its effects.",1011.0364v1
2010-11-01,"Magnetic phase diagram of spatially anisotropic, frustrated spin-1/2 Heisenberg antiferromagnet on a stacked square lattice","Magnetic phase diagram of a spatially anisotropic, frustrated spin-1/2
Heisenberg antiferromagnet on a stacked square lattice is investigated using
second-order spin-wave expansion. The effects of interlayer coupling and the
spatial anisotropy on the magnetic ordering of two ordered ground states are
explicitly studied. It is shown that with increase in next nearest neighbor
frustration the second-order corrections play a significant role in stabilizing
the magnetization. We obtain two ordered magnetic phases (Neel and stripe)
separated by a paramagnetic disordered phase. Within second-order spin-wave
expansion we find that the width of the disordered phase diminishes with
increase in the interlayer coupling or with decrease in spatial anisotropy but
it does not disappear. Our obtained phase diagram differs significantly from
the phase diagram obtained using linear spin-wave theory.",1011.0381v2
2010-11-08,Heavy Ion Initial Conditions and Correlations Between Higher Moments in the Spatial Anisotropy,"Fluctuations in the initial conditions for relativistic heavy ion collisions
are proving to be crucial to understanding final state flow and jet quenching
observables. The initial geometry has been parametrized in terms of moments in
the spatial anisotropy (i.e. $\epsilon_2, \epsilon_3, \epsilon_4,
\epsilon_5...$), and it has been stated in multiple published articles that the
vector directions of odd moments are uncorrelated with the even moments and the
reaction place angle. In this article, we demonstrate that this is incorrect
and that a substantial correlation exists between the even and odd moments in
peripheral Au+Au collisions. These correlations persist for all centralities,
though at a very small level for the 0-55% most central collisions.",1011.1853v2
2010-11-09,Structural change of vortex patterns in anisotropic Bose-Einstein condensates,"We study the changes in the spatial distribution of vortices in a rotating
Bose-Einstein condensate due to an increasing anisotropy of the trapping
potential. Once the rotational symmetry is broken, we find that the vortex
system undergoes a rich variety of structural changes, including the formation
of zig-zag and linear configurations. These spatial re-arrangements are well
signaled by the change in the behavior of the vortex-pattern eigenmodes against
the anisotropy parameter. The existence of such structural changes opens up
possibilities for the coherent exploitation of effective many-body systems
based on vortex patterns.",1011.2125v3
2010-11-13,Optical Dielectric Functions of III-V Semiconductors in Wurtzite Phase,"Optical properties of semiconductors can exhibit strong polarization
dependence due to crystalline anisotropy. A number of recent experiments have
shown that the photoluminescence intensity in free standing nanowires is
polarization dependent. One contribution to this effect is the anisotropy of
the dielectric function due to the fact that most nanowires crystalize in the
wurtzite form. While little is known experimentally about the band structures
wurtzite phase III-V semiconductors, we have previously predicted the bulk band
structure of nine III-V semiconductors in wurtzite phase.Here, we predict the
frequency dependent dielectric functions for nine non-Nitride wurtzite phase
III-V semiconductors (AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs and InSb).
Their complex dielectric functions are calculated in the dipole approximation
by evaluating the momentum matrix elements on a dense grid of special k-points
using empirical pseudopotential wave functions. Corrections to the momentum
matrix elements accounting for the missing core states are made using a scaling
factor which is determined by using the optical sum rules on the calculated
dielectric functions for the zincblende polytypes. The dielectric function is
calculated for polarizations perpendicular and parallel to the c-axis of the
crystal.",1011.3081v1
2010-11-25,First-principles investigation of the very large Perpendicular Magnetic Anisotropy at Fe|MgO Interfaces,"The perpendicular magnetic anisotropy (PMA) arising at the interface between
ferromagnetic transition metals and metallic oxides are investigated via
first-principles calculations. In this work very large values of PMA up to 3
erg/cm$^2$ at Fe$|$MgO interfaces are reported in agreement with recent
experiments. The origin of PMA is attributed to overlap between O-$p_z$ and
transition metal $d_{z^2}$ orbitals hybridized with $d_{xz(yz)}$ orbitals with
stronger spin-orbit coupling induced splitting around the Fermi level for
perpendicular magnetization orientation. Furthemore, it is shown that the PMA
value weakens in case of over- or underoxidation when oxygen $p_z$ and
transition metal $d_{z^2}$ orbitals overlap is strongly affected by disorder,
in agreement with experimental observations in magnetic tunnel junctions.",1011.5667v1
2010-12-03,Origin of In-Plane Anisotropy in Optical Conductivity for Antiferromagnetic Metallic Phase of Iron Pnictides,"We examine the optical conductivity in antiferromagnetic (AFM) iron pnictides
by mean-field calculation in a five-band Hubbard model. The calculated spectra
are well consistent with the in-plane anisotropy observed in the measurements,
where the optical conductivity along the direction with the AFM alignment of
neighboring spins is larger than that along the ferromagnetic (FM) direction in
the low-energy region; however, that along the FM direction becomes larger in
the higher-energy region. The difference between the two directions is
explained by taking account of orbital characters in both occupied and
unoccupied states as well as of the nature of Dirac-type linear dispersions
near the Fermi level.",1012.0670v2
2010-12-03,Measurement of anisotropies in the large-scale diffuse gamma-ray emission,"We have performed the first measurement of the angular power spectrum in the
large-scale diffuse emission at energies from 1-50 GeV. We compared results
from data and a simulated model in order to identify significant differences in
anisotropy properties. We found angular power above the photon noise level in
the data at multipoles greater than ~ 100 for energies 1< E <10 GeV. The excess
power in the data suggests a contribution from a point source population not
present in the model.",1012.0755v3
2010-12-05,Weak field magnetoresistance of narrow-gap semiconductor InSb,"The weak antilocalization effect of InSb film in perpendicular as well as
tilted magnetic field is investigated. It is found that the InSb film has
quasi-two-dimensional feature and the Nyquist mechanism dominates decoherence.
The two dimensionality is also verified further and the influence of roughness
effect and Zeeman effect on weak antilocalization effect is studied by
systematically investigating the anisotropy of weak field magnetoresistance
with respect to magnetic field. It is also found that the existence of in-plane
field can effectively suppress the weak antilocalization effect of InSb film
and the roughness effect plays an important role in the anisotropy.",1012.0968v1
2010-12-07,Jc Scaling and Anisotropies in Co-doped Ba-122 thin films,"We have successfully grown epitaxial, superconducting films of
Ba(Fe1-xCox)2As2 (Ba-122)with x ~ 0.1. The films grow without observable
correlated defects parallel to the c-axis, as confirmed by TEM. This is also
reflected in the absence of a caxis peak in Jc({\theta}). In contrast to
cuprate high-Tc superconductors such as YBa2Cu3O7-d or even Bi2Sr2Ca2Cu3O10-d,
the pnictides show a rather low anisotropic behavior in their Jc({\theta})
behavior as well as in their upper critical fields, Hc2. As a multiband
superconductor, Ba-122 exhibits a temperature dependent electronic mass
anisotropy.",1012.1523v1
2010-12-07,$π^{0}$ Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}=39-200$ GeV from PHENIX: Collision Energy and Path-Length Dependence of Jet-Quenching and the Role of Initial Geometry,"The azimuthal anisotropy of high $p_{T}$ particle production in heavy ion
collisions is a sensitive probe of the jet quenching mechanism. Recent PHENIX
measurements for Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV show a $\pi^{0}$
$v_{2}$ signal that exceeds the pQCD energy loss calculations up to $p_{T} \sim
10$ GeV/c, challenging the traditional perturbative picture of the energy loss
process. Here, we present an update and details of that measurement, as well as
new high $p_T$ measurements at $\sqrt{s_{NN}}=62$ and 39 GeV. These
measurements not only provide an important constraint for understanding the
path-length dependence of jet energy loss and the role of initial collision
geometry, but also allow a search for the onset of jet quenching as
$\sqrt{s_{NN}}$ is varied.",1012.1639v1
2010-12-13,Do Cosmological Perturbations Have Zero Mean?,"A central assumption in our analysis of cosmic structure is that cosmological
perturbations have zero ensemble mean. This property is one of the consequences
of statistically homogeneity, the invariance of correlation functions under
spatial translations. In this article we explore whether cosmological
perturbations indeed have zero mean, and thus test one aspect of statistical
homogeneity. We carry out a classical test of the zero mean hypothesis against
a class of alternatives in which perturbations have non-vanishing means, but
homogeneous and isotropic covariances. Apart from Gaussianity, our test does
not make any additional assumptions about the nature of the perturbations and
is thus rather generic and model-independent. The test statistic we employ is
essentially Student's t statistic, applied to appropriately masked,
foreground-cleaned cosmic microwave background anisotropy maps produced by the
WMAP mission. We find evidence for a non-zero mean in a particular range of
multipoles, but the evidence against the zero mean hypothesis goes away when we
correct for multiple testing. We also place constraints on the mean of the
temperature multipoles as a function of angular scale. On angular scales
smaller than four degrees, a non-zero mean has to be at least an order of
magnitude smaller than the standard deviation of the temperature anisotropies.",1012.2849v1
2010-12-15,Strong correlations and the anisotropy of acceptor states in insulating La(2-x)Sr(x)CuO(4),"We use the Green's function formalism to discuss the role of strong
correlations to the spatial structure of acceptor states doped into a
two-dimensional Mott-Hubbard antiferromagnetic insulator. When the scattering
between doped carriers, at the nesting wave vector ${\bf Q}=(\pi,\pi)$, is
strong enough to produce a momentum dependent scattering rate, $\Gamma_{\bf
k}$, the corresponding acceptor states become spatially anisotropic. As an
example, we calculate the spatial structure of an acceptor state bound to an
attractive two-dimensional Dirac delta potential, for a simple form of
$\Gamma_{\bf k}$. We then discuss the role of such spatial anisotropy for the
understanding of an apparent discrepancy between low temperature transport data
and photoemission spectra in lightly doped La(2-x)Sr(x)CuO(4).",1012.3302v1
2010-12-23,Confinement-induced Resonances in Quasi-one-dimensional Traps with Transverse Anisotropy,"We study atom-atom scattering in quasi-one-dimensional geometries with
transverse anisotropy. By assuming an s-wave pseudo-potential of contact
interaction, we show that the system would exhibit a single confinement-induced
resonance, where the scattering process degenerates to a total reflection as a
one-dimensional gas of impenetrable bosons. For a general form of interaction,
we present a formal calculation based on the two-channel model and conclude the
existence of only one confinement-induced resonance. Our findings are
inconsistent with a recent experiment by Haller et al. [Phys. Rev. Lett. 104,
153203 (2010)], where a splitting of confinement-induced resonances has been
observed in an anisotropic quasi-one-dimensional quantum gas of Cs atoms.",1012.5156v1
2010-12-27,Testing the Isotropy of the Universe with Type Ia Supernovae,"We analyze the magnitude-redshift data of type Ia supernovae included in the
Union and Union2 compilations in the framework of an anisotropic Bianchi type I
cosmological model and in the presence of a dark energy fluid with anisotropic
equation of state. We find that the amount of deviation from isotropy of the
equation of state of dark energy, the skewness \delta, and the present level of
anisotropy of the large-scale geometry of the Universe, the actual shear
\Sigma_0, are constrained in the ranges -0.16 < \delta < 0.12 and -0.012 <
\Sigma_0 < 0.012 (1\sigma C.L.) by Union2 data. Supernova data are then
compatible with a standard isotropic universe (\delta = \Sigma_0 = 0), but a
large level of anisotropy, both in the geometry of the Universe and in the
equation of state of dark energy, is allowed.",1012.5596v2
2010-12-29,Correspondence between HBT radii and the emission zone in non-central heavy ion collisions,"In non-central collisions between ultra-relativistic heavy ions, the
freeze-out distribution is anisotropic, and its major longitudinal axis may be
tilted away from the beam direction. The shape and orientation of this
distribution are particularly interesting, as they provide a snapshot of the
evolving source and reflect the space-time aspect of anisotropic flow.
Experimentally, this information is extracted by measuring pion HBT radii as a
function of angle with respect to the reaction plane. Existing formulae
relating the oscillations of the radii and the freezeout anisotropy are in
principle only valid for Gaussian sources with no collective flow. With a
realistic transport model of the collision, which generates flow and
non-Gaussian sources, we find that these formulae approximately reflect the
anisotropy of the freezeout distribution.",1012.5941v1
2011-01-03,Superconductivity at 32K and anisotropy in Tl0.58Rb0.42Fe1.72Se2 crystals,"Single crystals of Tl0.58Rb0.42Fe1.72Se2 are successfully grown with the
superconducting transition temperatures Tconset=32K and Tczero=31.4K. The Hall
coefficient exhibits a multi-band behavior, which is very similar to that of
all other Fe-based superconductors. We found that the susceptibility at the
normal state decreases with decreasing the temperature, indicating a strong
antiferromagnetic (AFM) spin fluctuation at the normal state, which might be
related to the superconductivity (SC). We also determined the upper critical
fields in ab-plane and along c-axis. The anisotropy of the superconductivity
determined by the ratio of Hc2ab and Hc2c is estimated to 5.0, which is larger
than that in (Ba,K)Fe2As2 and BaFe2-xCoxAs2, but smaller than that in cuprate
superconductors.",1101.0462v1
2011-01-06,Ordered moment in the anisotropic and frustrated square lattice Heisenberg model,"The two-dimensional frustrated next nearest neighbor Heisenberg model on the
square lattice is a prime example for a spin system where quantum fluctuations
can either destroy or stabilize magnetic order. The phase boundaries and
staggered moment dependence on the frustration ratio J_2/J_1 of the exchange
constants are fairly well understood both from approximate analytical and
numerical methods. In this work we use exact diagonalization for finite
clusters for an extensive investigation of the more general J_1a,b-J_2 model
which includes a spatial exchange anisotropy between next-neighbor spins. We
introduce a systematic way of tiling the square lattice and, for this low
symmetry model, define a controlled procedure for the finite size scaling that
is compatible with the possible magnetic phases. We obtain ground state
energies, structure factors and ordered moments and compare with the results of
spin wave calculations. We conclude that J_1a,b exchange anisotropy strongly
stabilizes the columnar antiferromagnetic phase for all frustration parameters,
in particular in the region of the spin nematic phase of the isotropic model.",1101.1181v2
2011-01-07,Competing phases in spin-1/2 J1-J2 chain with easy-plane anisotropy,"We summarize our theoretical findings on the ground-state phase diagram of
the spin-1/2 XXZ chain having competing nearest-neighbor (J1) and
antiferromagnetic next-nearest-neighbor (J2) couplings. Our study is mainly
concerned with the case of ferromagnetic J1, and the case of antiferromagnetic
J1 is briefly reviewed for comparison. The phase diagram contains a rich
variety of phases in the plane of J1/J2 versus the XXZ anisotropy Delta:
vector-chiral phases, N\'eel phases, several dimer phases, and
Tomonaga-Luttinger liquid phases. We discuss the vector-chiral order that
appears for a remarkably wide parameter space, successive N\'eel-dimer phase
transitions, and an emergent nonlocal string order in a narrow region of
ferromagnetic J1 side.",1101.1374v2
2011-01-07,Disorder effects at a nematic quantum critical point in d-wave cuprate superconductor,"A d-wave high temperature cuprate superconductor exhibits a nematic ordering
transition at zero temperature. Near the quantum critical point, the coupling
between gapless nodal quasiparticles and nematic order parameter fluctuation
can result in unusual behaviors, such as extreme anisotropy of fermion
velocities. We study the disorder effect on the nematic quantum critical
behavior and especially on the flow of fermion velocities. The disorders that
couple to nodal quasiparticles are divided into three types: random mass,
random gauge field, and random chemical potential. A renormalization group
analysis shows that random mass and random gauge field are both irrelevant and
thus do not change the fixed point of extreme velocity anisotropy. However, the
marginal interaction due to random chemical potential destroys this fixed point
and makes the nematic phase transition unstable.",1101.1551v3
2011-01-17,The upper critical field and its anisotropy in LiFeAs,"The upper critical field $\mu_0H_{c2}(T_c)$ of LiFeAs single crystals has
been determined by measuring the electrical resistivity using the facilities of
pulsed magnetic field at Los Alamos. We found that $\mu_0H_{c2}(T_c)$ of LiFeAs
shows a moderate anisotropy among the layered iron-based superconductors; its
anisotropic parameter $\gamma$ monotonically decreases with decreasing
temperature and approaches $\gamma\simeq 1.5$ as $T\rightarrow 0$. The upper
critical field reaches 15T ($H\parallel c$) and 24.2T ($H\parallel ab$) at
$T=$1.4K, which value is much smaller than other iron-based high $T_c$
superconductors. The temperature dependence of $\mu_0H_{c2}(T_c)$ can be
described by the Werthamer-Helfand-Hohenberg (WHH) method, showing orbitally
and (likely) spin-paramagnetically limited upper critical field for $H\parallel
c$ and $H\parallel ab$, respectively.",1101.3159v1
2011-01-20,Distortion of the ultrahigh energy cosmic ray flux from rare transient sources in inhomogeneous extragalactic magnetic fields,"Detecting and characterizing the anisotropy pattern of the arrival directions
of the highest energy cosmic rays are crucial steps towards the identification
of their sources. We discuss a possible distortion of the cosmic ray flux
induced by the anisotropic and inhomogeneous distribution of extragalactic
magnetic fields in cases where sources of ultrahigh energy cosmic rays are rare
transient phenomena, such as gamma-ray bursts and/or newly born magnetars. This
distortion does not involve an angular deflection but the modulation of the
flux related to the probability of seeing the source on an experiment lifetime.
To quantify this distortion, we construct sky maps of the arrival directions of
these highest energy cosmic rays for various magnetic field configurations and
appeal to statistical tests proposed in the literature. We conclude that this
distortion cannot affect present experiments but should be considered when
performing anisotropy studies with future large-scale experiments that record
as many as hundreds of events above 6x10^19 eV.",1101.3801v1
2011-01-24,Quarkonium states in a complex-valued potential,"We calculate quarkonium binding energies using a realistic complex-valued
potential for both an isotropic and anisotropic quark-gluon plasma. We
determine the disassociation temperatures of the ground and first excited
states considering both the real and imaginary parts of the binding energy. We
show that the effect of momentum-space anisotropy is smaller on the imaginary
part of the binding energy than on the real part of the binding energy. In the
case that one assumes an isotropic plasma, we find disassociation temperatures
for the J/psi, Upsilon and chi_b of 1.6 T_c, 2.8 T_c, and 1.5 T_c,
respectively. We find that a finite oblate momentum-space anisotropy increases
the disassociation temperature for all states considered and results in a
splitting of the p-wave states associated with the chi_b first excited state of
bottomonium.",1101.4651v4
2011-01-27,Transport in superlattices on single layer graphene,"We study transport in undoped graphene in the presence of a superlattice
potential both within a simple continuum model and using numerical
tight-binding calculations. The continuum model demonstrates that the
conductivity of the system is primarily impacted by the velocity anisotropy
that the Dirac points of graphene develop due to the potential. For
one-dimensional superlattice potentials, new Dirac points may be generated, and
the resulting conductivities can be approximately described by the anisotropic
conductivities associated with each Dirac point. Tight-binding calculations
demonstrate that this simple model is quantitatively correct for a single Dirac
point, and that it works qualitatively when there are multiple Dirac points.
Remarkably, for a two dimensional potential which may be very strong but
introduces no anisotropy in the Dirac point, the conductivity of the system
remains essentially the same as when no external potential is present.",1101.5270v1
2011-01-31,Estimation of isotropization time ($τ_{\rm iso}$) of QGP from direct photons,"We calculate transverse momentum distribution of direct photons from various
sources by taking into account the initial state momentum anisotropy of quark
gluon plasma (QGP). The total photon yield is then compared with the recent
measurement of photon transverse momentum distribution by the PHENIX
collaboration. It is also demonstrated that the presence of such an anisotropy
can describe the PHENIX photon data better than the isotropic case in the
present model. We show that the isotropization time thus extracted lies within
the range $1.5 \geq\tau_{\rm iso} \geq 0.5$ fm/c for the initial condition used
here.",1101.5857v1
2011-02-02,Effect of finite temperature and uniaxial anisotropy on the Casimir effect with three-dimensional topological insulators,"In this work we study the Casimir effect with three-dimensional topological
insulators including the effects of temperature and uniaxial anisotropy.
Although precise experimental values for the optical properties of these
materials are yet to be established, qualitative analysis is still possible. We
find qualitatively that the reported repulsive behavior and the equilibrium
point are robust features of the system, and are favored by low temperatures
and the enhancement of the optical response parallel to the optical axis. The
dependence of the equilibrium point with temperature and with the topological
magnetoelectric polarizability characteristic of three-dimensional topological
insulators is also discussed.",1102.0455v2
2011-02-04,Tuning of the spin-orbit interaction in a quantum dot by an in-plane magnetic field,"Using an exact diagonalization approach we show that one- and two-electron
InAs quantum dots exhibit avoided crossing in the energy spectra that are
induced by the spin-orbit coupling in the presence of an in-plane external
magnetic field. The width of the avoided crossings depends strongly on the
orientation of the magnetic field which reveals the intrinsic anisotropy of the
spin-orbit coupling interactions. We find that for specific orientations of the
magnetic field avoided crossings vanish. Value of this orientation can be used
to extract the ratio of the strength of Rashba and Dresselhaus interactions.
The spin-orbit anisotropy effects for various geometries and orientations of
the confinement potential are discussed. Our analysis explains the physics
behind the recent measurements performed on a gated self-assembled quantum dot
[S. Takahashi et al. Phys. Rev. Lett. 104, 246801 (2010)].",1102.1002v2
2011-02-22,Nodeless energy gaps of single-crystalline Ba0.68K0.32Fe2As2 as seen via 75As NMR,"We report $^{75}$As nuclear magnetic resonance studies on a very clean
hole-doped single-crystal Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ ($T_{\rm
{c}}=38.5$ K). The spin-lattice relaxation rate $1/T_{1}$ shows an exponential
decrease below $T \simeq 0.45 T_{\rm c}$ down to $T \simeq 0.11 T_{\rm c}$,
which indicates a fully opened energy gap. From the ratio $(T_{1})_{c} /
(T_{1})_{a}$, where $a$ and $c$ denote the crystal directions, we find that the
antiferromagnetic spin fluctuation is anisotropic in the spin space above
$T_{\rm c}$. The anisotropy decreases below $T_{\rm c}$ and disappears at $T
\rightarrow 0$. We argue that the anisotropy stems from spin-orbit coupling
whose effect vanishes when spin-singlet electron pairs form with a nodeless
gap.",1102.4417v2
2011-02-23,Rectification of spin currents in spin chains,"We study spin transport in nonitinerant one-dimensional quantum spin chains.
Motivated by possible applications in spintronics, we consider rectification
effects in both ferromagnetic and antiferromagnetic systems. We find that the
crucial ingredients in designing a system that displays a nonzero rectification
current are an anisotropy in the exchange interaction of the spin chain
combined with an offset magnetic field. For both ferromagnetic and
antiferromagnetic systems we can exploit the gap in the excitation spectrum
that is created by a bulk anisotropy to obtain a measurable rectification
effect at realistic magnetic fields. For antiferromagnetic systems we also find
that we can achieve a similar effect by introducing a magnetic impurity,
obtained by altering two neighboring bonds in the spin Hamiltonian.",1102.4801v2
2011-02-25,A large scale coherent magnetic field: interactions with free streaming particles and limits from the CMB,"We study a homogeneous and nearly-isotropic Universe permeated by a
homogeneous magnetic field. Together with an isotropic fluid, the homogeneous
magnetic field, which is the primary source of anisotropy, leads to a
plane-symmetric Bianchi I model of the Universe. However, when free-streaming
relativistic particles are present, they generate an anisotropic pressure which
counteracts the one from the magnetic field such that the Universe becomes
isotropized. We show that due to this effect, the CMB temperature anisotropy
from a homogeneous magnetic field is significantly suppressed if the the
neutrino masses are smaller than 0.3 eV.",1102.5235v1
2011-02-28,Anisotropic magnetotransport of superconducting and normal state in an electron-doped Nd_{1.85}Ce_{0.15}CuO_{4-δ} single crystal,"The anisotropic properties of an optimally doped
Nd_{1.85}Ce_{0.15}CuO_{4-\delta} single crystal have been studied both below
and above the critical temperature Tc via the resistivity measurement in
magnetic field H up to 12 T. By scaling the conductivity fluctuation around the
superconducting transition, the upper critical field H_{c2}(T) has been
determined for field parallel to the c-axis or to the basal ab-plane. The
anisotropy factor \gamma={H_c2||ab}/{H_c2||c} is estimated to be about 8. In
the normal state (50=<T=<180 K), the magnetoresistance (MR) basically follows
an H^2 dependence and for H||c it is almost 10 times larger than that for
H||ab. Comparing with hole-doped cuprates it suggests that the optimally doped
Nd_{1.85}Ce_{0.15}CuO_{4-\delta} cuprate superconductor has a moderate
anisotropy.",1102.5621v1
2011-03-01,The effects of strong temperature anisotropy on the kinetic structure of collisionless slow shocks and reconnection exhausts. Part I: PIC simulations,"A 2-D Riemann problem is designed to study the development and dynamics of
the slow shocks that are thought to form at the boundaries of reconnection
exhausts. Simulations are carried out for varying ratios of normal magnetic
field to the transverse upstream magnetic field (i.e., propagation angle with
respect to the upstream magnetic field). When the angle is sufficiently
oblique, the simulations reveal a large firehose-sense
(P_parallel>P_perpendicular) temperature anisotropy in the downstream region,
accompanied by a transition from a coplanar slow shock to a non-coplanar
rotational mode. In the downstream region the firehose stability parameter
epsilon=1-mu_0(P_parallel-P_perpendicular)/ B^2 tends to lock in to 0.25. This
balance arises from the competition between counterstreaming ions, which drives
epsilon down, and the scattering due to ion inertial scale waves, which are
driven unstable by the downstream rotational wave. At very oblique propagating
angles, 2-D turbulence also develops in the downstream region.",1103.0302v1
2011-03-02,Anomalous Hall effect in NiPt thin films,"We study Hall effect in sputtered NixPt1-x thin films with different Ni
concentrations. Temperature, magnetic field and angular dependencies are
analyzed and the phase diagram of NiPt thin films is obtained. It is found that
films with sub-critical Ni concentration exhibit cluster-glass behavior at low
temperatures with a perpendicular magnetic anisotropy below the freezing
temperature. Films with over-critical Ni concentration are ferromagnetic with
parallel anisotropy. At the critical concentration the state of the film is
strongly frustrated. Such films demonstrate canted magnetization with the easy
axis rotating as a function of temperature. The magnetism appears via
consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather
than a single second-order phase transition. But most remarkably, the
extraordinary Hall effect changes sign at the critical concentration. We
suggest that this is associated with a reconstruction of the electronic
structure of the alloy at the normal metal - ferromagnet quantum phase
transition.",1103.0367v2
2011-03-02,Anisotropic Hc2 of K0.8Fe1.76Se2 determined up to 60 T,"The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are
determined over a wide range of temperatures down to 1.5 K and magnetic fields
up to 60 T. Anisotropic initial slopes of Hc2 ~ -1.4 T/K and -4.6 T/K for
magnetic field applied along c-axis and ab-plane, respectively, were observed.
Whereas the c-axis Hc2|c(T) increases quasi-linearly with decreasing
temperature, the ab-plane Hc2|ab(T) shows a flattening, starting near 25 K
above 30 T. This leads to a non-monotonic temperature dependence of the
anisotropy parameter \gamma= Hc2|ab/Hc2|c. The anisotropy parameter is ~ 2 near
Tc ~ 32 K and rises to a maximum \gamma ~ 3.6 around 27 K. For lower
temperatures, \gamma decreases with T in a linear fashion, dropping to \gamma ~
2.5 by T ~ 18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and
(Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state
and proximity to an insulating state, the Hc2(T) curves are remarkably similar.",1103.0507v2
2011-03-03,Electron correlation induced small anisotropy in iron-based superconductors,"We have investigated the electron correlation effect on the electronic
structures and transport properties of the iron-based superconductors using the
density functional theory (DFT) and dynamical mean field theory (DMFT). By
considering the Fe 3d electron correlation using the DMFT, the bandwidth near
the Fermi level is substantially suppressed compared to the conventional DFT
calculation. Because of the different renormalization factors of each 3d
orbital, the DMFT gives considerably reduced electrical anisotropy compared to
the DFT results, which explains the unusually small anisotropic resistivity and
superconducting property observed in the iron-based superconductors. We suggest
that the electron correlation effect should be considered to explain the
anisotropic transport properties of the general d/f valence electron system.",1103.0678v2
2011-03-05,DDFT calibration and investigation of an anisotropic phase-field crystal model,"The anisotropic phase-field crystal model recently proposed and used by
Prieler et al. [J. Phys.: Condens. Matter 21, 464110 (2009)] is derived from
microscopic density functional theory for anisotropic particles with fixed
orientation. Further its morphology diagram is explored. In particular we
investigated the influence of anisotropy and undercooling on the process of
nucleation and microstructure formation from atomic to the microscale. To that
end numerical simulations were performed varying those dimensionless parameters
which represent anisotropy and undercooling in our anisotropic phase-field
crystal (APFC) model. The results from these numerical simulations are
summarized in terms of a morphology diagram of the stable state phase. These
stable phases are also investigated with respect to their kinetics and
characteristic morphological features.",1103.1068v1
2011-03-08,Upper critical field anisotropy in BaFe2-xCoxAs2 single crystals synthesized without flux,"The upper critical field was measured upto 12 T for three BaFe2-xCoxAs2
single crystals with estimated Co concentrations of x = 0.082, x = 0.117 and x
= 0.143. HC2 versus temperature was measured from temperature dependent
resistivity, for various applied magnetic fields, H || ab and H || c. The
[dHC2/dT]T=Tc, normalized with the corresponding TC, decreases with increasing
Co content, for both directions. The anisotropy {\gamma} defined as HC2 || ab /
HC2 || c shows a distinct increase with Co content, and its temperature
dependence shows a peak close to the TC. Magneto transport measurements, in the
spin density wave regions, showed significant negative MR for H || ab and
positive MR of H || c in the x = 0.082 sample. The implications of these
results are discussed.",1103.1476v1
2011-03-10,Forward-backward elliptic anisotropy correlation in parton cascade,"A potential experimental probe, forward-backward elliptic anisotropy
correlation ($C_{FB} $), has been proposed by Liao and Koch to distinguish the
jet and true elliptic flow contribution to the measured elliptic flow ($v_2$)
in relativistic heavy-ion collisions. Jet and flow fluctuation contribution to
elliptic flow is investigated within the framework of a multi-phase transport
model using the $C_{FB} $ probe. We found that the $C_{FB} $ correlation is
remarkably different and is about two times of that proposed by Liao and Koch.
It originates from the correlation between fluctuation of forward and backward
elliptic flow at low transverse momentum, which is mainly due to the initial
correlation between fluctuation of forward and backward eccentricity. This
results in an amendment of the $C_{FB}$ by a term related to the correlation
between fluctuation of forward and backward elliptic flow. Our results suggest
that a suitable rapidity gap for $C_{FB} $ correlation studies should be around
$\pm$ 3.5.",1103.2009v1
2011-03-25,Quantum Gravitational Contributions to the CMB Anisotropy Spectrum,"We derive the primordial power spectrum of density fluctuations in the
framework of quantum cosmology. For this purpose we perform a Born-Oppenheimer
approximation to the Wheeler-DeWitt equation for an inflationary universe with
a scalar field. In this way we first recover the scale-invariant power spectrum
that is found as an approximation in the simplest inflationary models. We then
obtain quantum gravitational corrections to this spectrum and discuss whether
they lead to measurable signatures in the CMB anisotropy spectrum. The
non-observation so far of such corrections translates into an upper bound on
the energy scale of inflation.",1103.4967v3
2011-03-31,"Cosmological observables, IR growth of fluctuations, and scale-dependent anisotropies","We extend semiclassical methods in inflationary cosmology that capture
leading IR corrections to correlators. Such large IR effects can be absorbed
into a coordinate change when examining sufficiently local observables, but not
when comparing observations at large separation in scales, such as seen by a
late-time observer. The analysis is facilitated by definition of a
scale-dependent metric and physical momentum. These assist definition of
""IR-safe"" observables seen by a post-inflationary observer, which are
contrasted to those based on the local geometry of the reheating surface. For
such observables, the observer's horizon provides an effective IR cutoff. IR
growth contributes to enhanced statistical inhomogeneities/anisotropies at
short scales, observation of which by a present day observer might be sought in
21 cm measurements. Such IR corrections are argued to grow large for a very
late-time observer.",1104.0002v2
2011-04-06,Improved tunneling magnetoresistance at low temperature in manganite junctions grown by molecular beam epitaxy,"We report resistance versus magnetic field measurements for a
La0.65Sr0.35MnO3/SrTiO3/La0.65Sr0.35MnO3 tunnel junction grown by
molecular-beam epitaxy, that show a large field window of extremely high
tunneling magnetoresistance (TMR) at low temperature. Scanning the in-plane
applied field orientation through 360^/circ, the TMR shows 4-fold symmetry,
i.e. biaxial anisotropy, aligned with the crystalline axes but not the junction
geometrical long axis. The TMR reaches ~ 1900% at 4K, corresponding to an
interfacial spin polarization of > 95% assuming identical interfaces. These
results show that uniaxial anisotropy is not necessary for large TMR, and lay
the groundwork for future improvements in TMR in manganite junctions.",1104.1072v1
2011-04-10,Interplay of orbital and spin ordering in the iron pnictides,"A number of recent experiments exhibit electronic anisotropy in the iron
pnictides, and there is a growing body of experimental evidence that its origin
is related to orbital ordering in Fe d_{xz} and d_{yz} orbitals. We examine
this problem in the parent compounds of the iron pnictides by a combination of
ab initio band theory calculations, phenomenological Ginzburg-Landau theory of
coupled orbital and magnetic order parameters, and a microscopic mean-field
study of the Kugel-Khomskii model. We find that orbital ordering is sufficient
to explain a number of key experimental observations, in particular a linear
correlation between the orthorhombic lattice distortion and the magnetic
ordered moment. We predict that orbital polarization should scale as a square
of magnetic moment close to T_N. Mediated by orbital polarization, the
effective spin-spin exchange interactions develop anisotropy in the ab-plane,
in accord with recent neutron scattering measurements.",1104.1747v1
2011-04-14,The Cosmic Linear Anisotropy Solving System (CLASS) II: Approximation schemes,"Boltzmann codes are used extensively by several groups for constraining
cosmological parameters with Cosmic Microwave Background and Large Scale
Structure data. This activity is computationally expensive, since a typical
project requires from 10'000 to 100'000 Boltzmann code executions. The newly
released code CLASS (Cosmic Linear Anisotropy Solving System) incorporates
improved approximation schemes leading to a simultaneous gain in speed and
precision. We describe here the three approximations used by CLASS for basic
LambdaCDM models, namely: a baryon-photon tight-coupling approximation which
can be set to first order, second order or to a compromise between the two; an
ultra-relativistic fluid approximation which had not been implemented in public
distributions before; and finally a radiation streaming approximation taking
reionisation into account.",1104.2933v3
2011-04-20,Static and dynamic properties of Single-Chain Magnets with sharp and broad domain walls,"We discuss time-quantified Monte-Carlo simulations on classical spin chains
with uniaxial anisotropy in relation to static calculations. Depending on the
thickness of domain walls, controlled by the relative strength of the exchange
and magnetic anisotropy energy, we found two distinct regimes in which both the
static and dynamic behavior are different. For broad domain walls, the
interplay between localized excitations and spin waves turns out to be crucial
at finite temperature. As a consequence, a different protocol should be
followed in the experimental characterization of slow-relaxing spin chains with
broad domain walls with respect to the usual Ising limit.",1104.4007v2
2011-04-28,The High-Redshift Neutral Hydrogen Signature of an Anisotropic Matter Power Spectrum,"An anisotropic power spectrum will have a clear signature in the 21cm
radiation from high-redshift hydrogen. We calculate the expected power spectrum
of the intensity fluctuations in neutral hydrogen from before the epoch of
reionization, and predict the accuracy to which future experiments could
constrain a quadrupole anisotropy in the power spectrum. We find that the
Square Kilometer Array will have marginal detection abilities for this signal
at z~17 if the process of reionization has not yet started; reionization could
enhance the detectability substantially. Pushing to higher redshifts and higher
sensitivity will allow highly precise (percent level) measurements of
anisotropy.",1104.5403v3
2011-04-29,Upper critical magnetic field in Ba_0.68K_0.32Fe_2As_2 and Ba(Fe_0.93Co_0.07)_2As_2,"We report measurements of the temperature dependence of the radio-frequency
magnetic penetration depth in Ba_0.68K_0.32Fe_2As_2 and
Ba(Fe_0.93Co_0.07)_2As_2 single crystals in pulsed magnetic fields up to 60 T.
From our data, we construct an H-T phase diagram for the inter-plane (H || c)
and in-plane (H || ab) directions for both compounds. For both field
orientations in Ba_0.68K_0.32Fe_2As_2, we find a concave curvature of the
Hc2(T) lines with decreasing anisotropy and saturation towards lower
temperature. Taking into account Pauli spin paramagnetism we can describe
Hc2(T) and its anisotropy. In contrast, we find that Pauli paramagnetic pair
breaking is not essential for Ba(Fe_0.93Co_0.07)_2As_2. For this electron-doped
compound, the data support a Hc2(T) dependence that can be described by the
Werthamer Helfand Hohenberg model for H || ab and a two-gap behavior for H ||
c.",1104.5619v1
2011-05-05,Antiferromagnet with two coupled antiferromagnetic sublattices in a magnetic field,"We discuss the magnon spectrum of an antiferromagnet (AF) in a magnetic field
$h$ consisting of two interpenetrating AF sublattices coupled by the exchange
interaction at T=0. One-ion easy-plane anisotropy is also taken into account.
We calculate using the 1/S expansion the gap in the spectrum which is a
manifestation of the order-by-disorder effect in this system and the optical
magnon mode splitting. Both of these phenomena originate from the
inter-sublattice interaction. We calculate also the gap value at $h\approx h_c$
in the leading order of the small parameter $(h_c-h)/h_c$ using the magnon
Bose-Einstein condensation treatment, where $h_c$ is the saturation field. By
comparing results obtained within these two approaches we conclude that the 1/S
expansion gives a qualitatively correct result at $h\sim h_c$ even at large
one-ion anisotropy but it overestimates the gap value. The application is
discussed of these results to the actively studied AF of the considered type
$\rm NiCl_2$-$\rm 4SC(NH_2)_2$ (DTN).",1105.1044v1
2011-05-05,Novel approach to description of quantum magnets with large singe-ion easy-plane anisotropy,"We introduce a new representation of an integer spin $S$ via bosonic
operators which is useful in describing the paramagnetic phase and transitions
to magnetically ordered phases in magnetic systems with large single-ion
easy-plane anisotropy $D$. Considering the exchange interaction between spins
as a perturbation and using the diagram technique we derive the elementary
excitation spectrum and the ground state energy in the third order of the
perturbation theory. In the special case of S=1 we obtain these expressions
also using simpler spin representations some of which were introduced before.
Comparison with results of previous numerical studies of 2D systems with S=1
demonstrates that our approach works better than other analytical methods
applied before for such systems. We apply our results for the elementary
excitation spectrum analysis obtained experimentally in $\rm NiCl_2$-$\rm
4SC(NH_2)_2$ (DTN). It is demonstrated that a set of model parameters (exchange
constants and $D$) which has been used for DTN so far describes badly the
experimentally obtained spectrum. A new set of parameters is proposed using
which we fit the spectrum and values of two critical fields of DTN.",1105.1077v1
2011-05-12,First-Order Phase Transition with Breaking of Lattice Rotation Symmetry in Continuous-Spin Model on Triangular Lattice,"Using a Monte Carlo method, we study the finite-temperature phase transition
in the two-dimensional classical Heisenberg model on a triangular lattice with
or without easy-plane anisotropy. The model takes account of competing
interactions: a ferromagnetic nearest-neighbor interaction $J_1$ and an
antiferromagnetic third nearest-neighbor interaction $J_3$. As a result, the
ground state is a spiral spin configuration for $-4 < J_1/J_3 < 0$. In this
structure, global spin rotation cannot compensate for the effect of 120-degree
lattice rotation, in contrast to the conventional 120-degree structure of the
nearest-neighbor interaction model. We find that this model exhibits a
first-order phase transition with breaking of the lattice rotation symmetry at
a finite temperature. The transition is characterized as a $Z_2$ vortex
dissociation in the isotropic case, whereas it can be viewed as a $Z$ vortex
dissociation in the anisotropic case. Remarkably, the latter is continuously
connected to the former as the magnitude of anisotropy decreases, in contrast
to the recent work by Misawa and Motome [J. Phys. Soc. Jpn. \textbf{79} (2010)
073001.] in which both the transitions were found to be continuous.",1105.2452v2
2011-05-22,The strong side of weak topological insulators,"Three-dimensional topological insulators are classified into ""strong"" (STI)
and ""weak"" (WTI) according to the nature of their surface states. While the
surface states of the STI are topologically protected from localization, this
does not hold for the WTI. In this work we show that the surface states of the
WTI are actually protected from any random perturbation that does not break
time-reversal symmetry, and does not close the bulk energy gap. Consequently,
the conductivity of metallic surfaces in the clean system remains finite even
in the presence of strong disorder of this type. In the weak disorder limit the
surfaces are found to be perfect metals, and strong surface disorder only acts
to push the metallic surfaces inwards. We find that the WTI differs from the
STI primarily in its anisotropy, and that the anisotropy is not a sign of its
weakness but rather of its richness.",1105.4351v2
2011-05-24,Effect of Polydispersity and Anisotropy in Colloidal and Protein Solutions: an Integral Equation Approach,"Application of integral equation theory to complex fluids is reviewed, with
particular emphasis to the effects of polydispersity and anisotropy on their
structural and thermodynamic properties. Both analytical and numerical
solutions of integral equations are discussed within the context of a set of
minimal potential models that have been widely used in the literature. While
other popular theoretical tools, such as numerical simulations and density
functional theory, are superior for quantitative and accurate predictions, we
argue that integral equation theory still provides, as in simple fluids, an
invaluable technique that is able to capture the main essential features of a
complex system, at a much lower computational cost. In addition, it can provide
a detailed description of the angular dependence in arbitrary frame, unlike
numerical simulations where this information is frequently hampered by
insufficient statistics. Applications to colloidal mixtures, globular proteins
and patchy colloids are discussed, within a unified framework.",1105.4723v1
2011-05-25,On the magnetization textures in NiPd nanostructures,"We have observed peculiar magnetization textures in Ni$_{80}$Pd$_{20}$
nanostructures using three different imaging techniques: magnetic force
microscopy, photoemission electron microscopy under polarized X-ray absorption,
and scanning electron microscopy with polarization analysis. The appearances of
diamond-like domains with strong lateral charges and of weak stripe structures
bring into evidence the presence of both a transverse and a perpendicular
anisotropy in these nanostrips. This anisotropy is seen to reinforce as
temperature decreases, as testified by a simplified domain structure at 150 K.
A thermal stress relaxation model is proposed to account for these
observations. Elastic calculations coupled to micromagnetic simulations support
qualitatively this model.",1105.4946v1
2011-05-27,Gluon dissociation of $J/ψ$ in anisotropic {\em Quark-Gluon-Plasma},"We calculate the gluon dissociation cross-section in an anisotropic quark
gluon plasma expected to be formed due relativistic nucleus-nucleus collisions.
The initial rapid longitudinal expansion of the system leads to momentum space
anisotropy due which the observables are affected in such a system. We show
that the thermally weighted cross-section of gluon dissociation undergoes
modification in anisotropic plasma leading to a decreased probability of
$J/\psi$ suppression both for RHIC and LHC energies. The dependence of the
cross section as well as the survival probability on the direction of
propagation of the charmonium with respect to the anisotropy axis are
presented. The sensitivity of the survival probability on the initial
conditions have also been demonstrated.",1105.5528v2
2011-05-31,Universal and non-universal amplitude ratios for scaling corrections on Ising strips,"We consider strips of Ising spins at criticality. For strips of width $N$
sites, subdominant (additive) finite-size corrections to scaling are assumed to
be of the form $a_k/N^k$ for the free energy, and $b_k/N^k$ for inverse
correlation length, with integer values of $k$. We investigate the set
$\{a_k,b_k\}$ ($k \geq 2$) by exact evaluation and numerical transfer-matrix
diagonalization techniques, and their changes upon varying anisotropy of
couplings, spin quantum number $S$, and (finite) interaction range, in all
cases for both periodic (PBC) and free (FBC) boundary conditions across the
strip. We find that the coefficient ratios $b_k/a_k$ remain constant upon
varying coupling anisotropy for $S=1/2$ and first-neighbor couplings, for both
PBC and FBC (albeit at distinct values in either case). Such universal behavior
is not maintained upon changes in $S$ or interaction range.",1105.6248v2
2011-06-01,Beyond the Standard cosmological model with CMB,"Measurements of CMB anisotropy and, more recently, polarization have played a
very important role in cosmology. Besides precise determination of various
parameters of the `standard' cosmological model, observations have also
established some important basic tenets that underlie models of cosmology and
structure formation in the universe -- `acausally' correlated, adiabatic,
primordial perturbations in a flat, statistically isotropic universe. These are
consistent with the expectation of the paradigm of inflation and the generic
prediction of the simplest realization of inflationary scenario in the early
universe. Further, gravitational instability is the established mechanism for
structure formation from these initial perturbations. Primordial perturbations
observed as the CMB anisotropy and polarization is the most compelling evidence
for new, possibly fundamental, physics in the early universe. The community is
now looking beyond the parameter estimation of the `standard' model, for
subtle, characteristic signatures of early universe physics.",1106.0106v1
2011-06-10,Non Axi-symmetric Anisotropy of Solar Wind Turbulence,"A key prediction of turbulence theories is frame-invariance, and in
magnetohydrodynamic (MHD) turbulence, axisymmetry of fluctuations with respect
to the background magnetic field. Paradoxically the power in fluctuations in
the turbulent solar wind are observed to be ordered with respect to the bulk
macroscopic flow as well as the background magnetic field. Here, non-
axisymmetry across the inertial and dissipation ranges is quantified using
in-situ observations from Cluster. The observed inertial range non- axisymmetry
is reproduced by a 'fly through' sampling of a Direct Numerical Simulation of
MHD turbulence. Furthermore, 'fly through' sampling of a linear superposition
of transverse waves with axisymmetric fluctuations generates the trend in non-
axisymmetry with power spectral exponent. The observed non-axisymmetric
anisotropy may thus simply arise as a sampling effect related to Taylor's
hypothesis and is not related to the plasma dynamics itself.",1106.2023v2
2011-06-14,Fine structure constant variation or spacetime anisotropy?,"Recent observations on the quasar absorption spectra supply evidence for the
variation of the fine structure constant $\alpha$. In this paper, we propose
another interpretation of the observational data on the quasar absorption
spectra: a scenario with spacetime inhomogeneity and anisotropy. Maybe the
spacetime is characterized by the Finsler geometry instead of the Riemann one.
The Finsler geometry admits fewer symmetries than the Riemann geometry does. We
investigate the Finslerian geodesic equations in the Randers spacetime (a
special Finsler spacetime). It is found that the cosmological redshift in this
spacetime deviates from the one in general relativity. The modification term to
the redshift could be generally revealed as a monopole plus dipole function of
spacetime locations and directions. We suggest that this modification
corresponds to the spatial monopole and dipole of $\alpha$ variation in the
quasar absorption spectra.",1106.2726v3
2011-06-16,Tunable multi-photon Rabi oscillations in an electronic spin system,"We report on multi-photon Rabi oscillations and controlled tuning of a
multi-level system at room temperature (S=5/2 for Mn2+:MgO) in and out of a
quasi-harmonic level configuration. The anisotropy is much smaller than the
Zeeman splittings, such as the six level scheme shows only a small deviation
from an equidistant diagram. This allows us to tune the spin dynamics by either
compensating the cubic anisotropy with a precise static field orientation, or
by microwave field intensity. Using the rotating frame approximation, the
experiments are very well explained by both an analytical model and a
generalized numerical model. The calculated multi-photon Rabi frequencies are
in excellent agreement with the experimental data.",1106.3365v1
2011-06-21,Probing Cosmic Acceleration by Using the SNLS3 SNIa Dataset,"We probe the cosmic acceleration by using the recently released SNLS3 sample
of 472 type Ia supernovae. Combining this type Ia supernovae dataset with the
cosmic microwave background anisotropy data from the Wilkinson Microwave
Anisotropy Probe 7-yr observations, the baryon acoustic oscillation results
from the Sloan Digital Sky Survey data release 7, and the Hubble constant
measurement from the Wide Field Camera 3 on the Hubble Space Telescope, we
measure the dark energy equation of state $w$ and the deceleration parameter
$q$ as functions of redshift by using the Chevallier-Polarski-Linder
parametrization. Our result is consistent with a cosmological constant at
1$\sigma$ confidence level, without evidence for the recent slowing down of the
cosmic acceleration. Furthermore, we consider three binned parametrizations
($w$ is piecewise constant in redshift $z$) based on different binning methods.
The similar results are obtained, i.e., the $\Lambda$CDM model is still nicely
compatible with current observations.",1106.4116v3
2011-06-27,Phase transitions and entanglement properties in spin-1 Heisenberg clusters with single-ion anisotropy,"The incipient quantum phase transitions of relevance to nonzero fluctuations
and entanglement in Heisenberg clusters are studied in this paper by exploiting
negativity as a measure in bipartite and frustrated spin-1 anisotropic
Heisenberg clusters with bilinear-biquadratic exchange, single-ion anisotropy
and magnetic field. Using the exact diagonalization technique, it is shown that
quantum critical points signaled by qualitative changes in behavior of
magnetization and particle number are ultimately related to microscopic
entanglement and collective excitations. The plateaus and peaks in spin and
particle susceptibilities define the conditions for a high/low-density quantum
entanglement and various ordered phases with different spin (particle)
concentrations.",1106.5378v1
2011-06-27,The Ising Limit of the XXZ Heisenberg Magnet and Certain Thermal Correlation Functions,"The spin-1/2 XXZ Heisenberg magnet is considered for the case of the
anisotropy parameter tending to infinity (so-called, Ising limit). A thermal
correlation function of the ferromagnetic string is calculated over the ground
state. The approach to the calculation of the correlation functions in the
limit of infinite anisotropy is based on the observation that the wave function
is expressed in terms of the symmetric Schur functions. It is demonstrated that
at low temperatures the amplitude of the asymptotical expression of this
correlation function is proportional to the squared numbers of strict boxed
plane partitions.",1106.5455v2
2011-06-29,Apparent temperature anisotropies due to wave activity in the solar wind,"The fast solar wind is a collisionless plasma permeated by plasma waves on
many different scales. A plasma wave represents the natural interplay between
the periodic changes of the electromagnetic field and the associated coherent
motions of the plasma particles. In this paper, a model velocity distribution
function is derived for a plasma in a single, coherent, large-amplitude wave.
This model allows one to study the kinetic effects of wave motions on particle
distributions. They are by in-situ spacecraft measured by counting, over a
certain sampling time, the particles coming from various directions and having
different energies. We compare our results with the measurements by the Helios
spacecraft, and thus find that by assuming high wave activity we are able to
explain key observed features of the measured distributions within the
framework of our model. We also address the recent discussions on nonresonant
wave--particle interactions and apparent heating. The applied time-averaging
procedure leads to an apparent ion temperature anisotropy which is connected
but not identical to the intrinsic temperature of the underlying distribution
function.",1106.5878v1
2011-06-29,Image denoising assessment using anisotropic stack filtering,"In this paper we propose a measure of anisotropy as a quality parameter to
estimate the amount of noise in noisy images. The anisotropy of an image can be
determined through a directional measure, using an appropriate statistical
distribution of the information contained in the image. This new measure is
achieved through a stack filtering paradigm. First, we define a local
directional entropy, based on the distribution of 0's and 1's in the
neigborhood of every pixel location of each stack level. Then the entropy
variation of this directional entropy is used to define an anisotropic measure.
The empirical results have shown that this measure can be regarded as an
excellent image noise indicator, which is particularly relevant for quality
assessment of denoising algorithms. The method has been evaluated with
artificial and real-world degraded images.",1106.5928v1
2011-07-01,Accurate determination of the Gaussian transition in spin-1 chains with single-ion anisotropy,"The Gaussian transition in the spin-one Heisenberg chain with single-ion
anisotropy is extremely difficult to treat, both analytically and numerically.
We introduce an improved DMRG procedure with strict error control, which we use
to access very large systems. By considering the bulk entropy, we determine the
Gaussian transition point to 4-digit accuracy, $D_{c}/J
  = 0.96845(8)$, resolving a long-standing debate in quantum magnetism. With
this value, we obtain high-precision data for the critical behavior of
quantities including the ground-state energy, gap, and transverse string-order
parameter, and for the critical exponent, $\nu = 1.472(2)$. Applying our
improved technique at $J_{z} = 0.5$ highlights essential differences in
critical behavior along the Gaussian transition line.",1107.0229v2
2011-07-02,Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations,"A common ploy to reduce the switching current and energy dissipation in
spin-transfer-torque driven magnetization switching of shape-anisotropic
single-domain nanomagnets is to employ magnets with low saturation
magnetization $M_s$ and high shape-anisotropy. The high shape-anisotropy
compensates for low $M_s$ to keep the static switching error rate constant.
However, this ploy increases the switching delay, its variance in the presence
of thermal noise, and the dynamic switching error rate. Using the stochastic
Landau-Lifshitz-Gilbert equation with a random torque emulating thermal noise,
we show that pumping some excess spin-polarized current into the nanomagnet
during switching will keep the mean switching delay and its variance constant
as we reduce $M_s$, while still reducing the energy dissipation significantly.",1107.0387v2
2011-07-06,Dynamical vs spectator models of (pseudo-)conformal Universe,"We discuss two versions of the conformal scenario for generating scalar
cosmological perturbations: a spectator version with a scalar field conformally
coupled to gravity and carrying negligible energy density, and a dynamical
version with a scalar field minimally coupled to gravity and dominating the
cosmological evolution. By making use of the Newtonian gauge, we show that (i)
no UV strong coupling scale is generated below $M_{Pl}$ due to mixing with
metric perturbations in the dynamical scenario, and (ii) the dynamical and
spectator models yield identical results to the leading non-linear order. We
argue that these results, which include potentially observable effects like
statistical anisotropy and non-Gaussianity, are characteristic of the entire
class of conformal models. As an example, we reproduce, within the dynamical
scenario and working in comoving gauge, our earlier result on the statistical
anisotropy, which was originally obtained within the spectator approach.",1107.1036v1
2011-07-11,Impairment of double exchange mechanism in electron transport of iron pnictides,"Double exchange mechanism is believed to favor transport along ferromagnetic
directions, the failure of which in explaining the unusual resistivity
anisotropy in iron pnictides is investigated. Several factors intrinsic to the
microscopic mechanism of transport in iron pnictides are identified and
analyzed, including the moderate Hund's coupling, low local moment, and
presence of two anisotropic degenerate orbitals xz and yz. In particular, the
substantial second neighbor hoppings are found to be decisive in giving results
opposite to the double exchange picture. In high temperature nonmagnetic phase,
orbital ordering is shown to give the right trend of resistivity anisotropy as
observed experimentally, advocating its essential role in electron transport of
iron pnictides.",1107.1952v1
2011-07-14,Statistical Anisotropy and the Vector Curvaton Paradigm,"The vector curvaton paradigm is reviewed. The mechanism allows a massive
vector boson field to contribute to or even generate the curvature perturbation
in the Universe. Contribution of vector bosons is likely to generate
statistical anisotropy in the spectrum and bispectrum of the curvature
perturbation, which will soon be probed observationally. Two specific models
for the generation of superhorizon spectra for the components of an Abelian
vector field are analysed. Emphasis is put on the observational signatures of
the models when the vector fields play the role of vector curvatons. If future
observations support the vector curvaton mechanism this will open a window into
the gauge field content of theories beyond the standard model.",1107.2779v2
2011-07-19,Spin-texture and magnetic anisotropy of Co adsorbed Bi$_2$Se$_3$ topological insulator surfaces,"Based upon first-principles methods, we investigate the magnetic anisotropy
and the spin-texture of Co adatoms embedded in the topmost Se network of the
topological insulator Bi$_2$Se$_3$ surface. We find the formation of
energetically stable magnetic moment perpendicular to the surface plane, S$_z$.
Our results for the pristine Bi$_2$Se$_3$ surface indicate the presence of
helical spin-texture not only in the massless surface Dirac states, but also
surface states resonant within the valence band present spin-texture. On the
other hand, upon the presence of Co adatoms we find that the out-of-plane
surface magnetism represents the dominant spin state (S$_z$), while the planar
spin components, S$_x$ and S$_y$, are almost suppressed.",1107.3810v1
2011-07-20,"Peculiar motions, accelerated expansion and the cosmological axis","Peculiar velocities change the expansion rate of any observer moving relative
to the smooth Hubble flow. As a result, observers in a galaxy like our Milky
Way can experience accelerated expansion within a globally decelerating
universe, even when the drift velocities are small. The effect is local, but
the affected scales can be large enough to give the false impression that the
whole cosmos has recently entered an accelerating phase. Generally, peculiar
velocities are also associated with dipole-like anisotropies, triggered by the
fact that they introduce a preferred spatial direction. This implies that
observers experiencing locally accelerated expansion, as a result of their own
drift motion, may also find that the acceleration is maximised in one direction
and minimised in the opposite. We argue that, typically, such a dipole
anisotropy should be relatively small and the axis should probably lie fairly
close to the one seen in the spectrum of the Cosmic Microwave Background.",1107.4045v3
2011-07-22,"Large spin-phonon coupling and magnetically-induced phonon anisotropy in Sr$M$O$_3$ perovskites ($M$=V,Cr,Mn,Fe,Co)","First-principles calculations reveal large zone-center spin-phonon coupling
and magnetically-driven phonon anisotropy in cubic perovskites Sr$M$O$_3$
($M$=V,Cr,Mn,Fe,Co). In particular, the frequency and splitting of the polar
Slater mode is found to depend strongly on magnetic ordering. The coupling is
parameterized in a crystal-structure-dependent Heisenberg model and its main
features seen to arise from the Goodenough-Kanamori rules. This coupling can be
expected to produce distinct low-energy alternative phases, resulting in a rich
variety of coupled magnetic, structural and electronic phase transitions driven
by temperature, stress, electric field and cation substitution.",1107.4405v1
2011-07-25,Thermalization in Weakly Coupled Nonabelian Plasmas,"We investigate how relativistic, nonabelian plasmas approach equilibrium in a
general context. Our treatment is entirely parametric and for small Yang-Mills
coupling $\alpha$. First we study isotropic systems with an initially
nonequilibrium momentum distribution. We consider both the case of initially
very high occupancy and initially very low occupancy. Then we consider systems
which are anisotropic. We consider both weak anisotropy and large anisotropy,
and allow the occupancy to be parametrically large or small. Writing the
typical momentum of an initial excitation as Q and the final temperature as T,
full equilibration occurs in a time t ~ \alpha^{-2}/T for T > Q, and t ~
\alpha^{-2} Q^{1/2} T^{-3/2} for T < Q, unless the initial system is
sufficiently anisotropic and T > \alpha^{2/3} Q, in which case equilibration
occurs somewhat faster, t ~ \alpha^{-13/7} Q^{5/7} T^{-12/7} (or \alpha^{-2}/T
if that is longer).",1107.5050v1
2011-07-27,Understanding anisotropy generated by fluctuations in heavy-ion collisions,"Event-by-event fluctuations are central to the current understanding of
ultrarelativistic heavy-ion collisions. In particular, fluctuations in the
geometry of the early-time collision system are responsible for new phenomena
such as triangular flow, which have solved important puzzles in existing data.
We propose a simple model where initial fluctuations stem from independent flux
tubes randomly distributed in the transverse plane. We calculate analytically
the moments of the initial anisotropies (dipole asymmetry, eccentricity,
triangularity), which are the sources of anisotropic flow, and their mutual
correlations. Our analytic results are in good agreement with calculations from
commonly-used Monte-Carlo codes, providing a simple understanding of the
fluctuations contained in these models. Any deviation from these results in
future experimental data would thus indicate the presence of non-trivial
correlations between the initial flux tubes and/or extra sources of
fluctuations that are not present in current models.",1107.5485v2
2011-07-27,The effects of plasma beta and anisotropy instabilities on the dynamics of reconnecting magnetic fields in the heliosheath,"The plasma {\beta} (the ratio of the plasma pressure to the magnetic
pressure) of a system can have a large effect on its dynamics as high {\beta}
enhances the effects of pressure anisotropies. We investigate the effects of
{\beta} in a system of stacked current sheets that break up into magnetic
islands due to magnetic reconnection. We find significant differences between
{\beta} < 1 and {\beta} > 1. At low {\beta} growing magnetic islands are
modestly elongated and become round as contraction releases magnetic stress and
reduces magnetic energy. At high {\beta} the increase of the parallel pressure
in contracting islands causes saturation of modestly elongated islands as
island cores approach the marginal firehose condition. Only highly elongated
islands reach finite size. The kinking associated with the Weibel and firehose
instabilities prevents full contraction of these islands, leading to a final
state of highly elongated islands in which further reconnection is suppressed.
The results are directly relevant to reconnection in the sectored region of the
heliosheath and possibly to saturation mechanisms of the magnetorotational
instability in accretion flows.",1107.5558v2
2011-08-01,Correlation energy of anisotropic quantum dots,"We study the $D$-dimensional high-density correlation energy $\Ec$ of the
singlet ground state of two electrons confined by a harmonic potential with
Coulombic repulsion. We allow the harmonic potential to be anisotropic, and
examine the behavior of $\Ec$ as a function of the anisotropy $\alpha^{-1}$. In
particular, we are interested in the limit where the anisotropy goes to
infinity ($\alpha\to0$) and the electrons are restricted to a lower-dimensional
space. We show that tuning the value of $\alpha$ from 0 to 1 allows a smooth
dimensional interpolation and we demonstrate that the usual model, in which a
quantum dot is treated as a two-dimensional system, is inappropriate. Finally,
we provide a simple function which reproduces the behavior of $\Ec$ over the
entire range of $\alpha$.",1108.0257v1
2011-08-05,Influence of strain on anisotropic thermoelectric transport of Bi$_2$Te$_3$ and Sb$_2$Te$_3$,"On the basis of detailed first-principles calculations and semi-classical
Boltzmann transport, the anisotropic thermoelectric transport properties of
Bi$_2$Te$_3$ and Sb$_2$Te$_3$ under strain were investigated. It was found that
due to compensation effects of the strain dependent thermopower and electrical
conductivity, the related powerfactor will decrease under applied in-plane
strain for Bi$_2$Te$_3, while being stable for Sb$_2$Te$_3$. A clear preference
for thermoelectric transport under hole-doping, as well as for the in-plane
transport direction was found for both tellurides. In contrast to the
electrical conductivity anisotropy, the anisotropy of the thermopower was
almost robust under applied strain. The assumption of an anisotropic relaxation
time for Bi$_2$Te$_3$ suggests, that already in the single crystalline system
strong anisotropic scattering effects should play a role.",1108.1304v2
2011-08-05,Role of Antisymmetric Exchange in Selecting Magnetic Chirality in Ba$_3$NbFe$_3$Si$_2$O$_{14}$,"We present electron spin resonance (ESR) investigation of the acentric
\FeLang, featuring a unique single-domain double-chiral magnetic ground state.
Combining simulations of the ESR line-width anisotropy and the
antiferromagnetic-resonance modes allows us to single out the
Dzyaloshinsky-Moriya (DM) interaction as the leading magnetic anisotropy term.
We demonstrate that the rather minute out-of-plane DM component $d_c=45$ mK is
responsible for selecting a unique ground state, which endures thermal
fluctuations up to astonishingly high temperatures.",1108.1390v2
2011-08-08,Anisotropy effects on Rashba and topological insulator spin polarized surface states: a unified phenomenological description,"Spin polarized two-dimensional electronic states have been previously
observed on metallic surface alloys with giant Rashba splitting and on the
surface of topological insulators. We study the surface band structure of these
systems, in a unified manner, by exploiting recent results of k.p theory. The
model suggests a different way to address the effect of anisotropy in Rashba
systems. Changes in the surface band structure of various Rashba compounds can
be captured by a single effective parameter which quantifies the competition
between the Rashba effect and the hexagonal warping of the constant energy
contours. The same model provides a unified phenomenological description of the
surface states belonging to materials with topologically trivial and
non-trivial band structures.",1108.1778v3
2011-08-10,Origin of Ultrahigh Energy Galactic Cosmic Rays: The Isotropy Problem,"We study the propagation of ultra-high-energy cosmic rays (UHECR) in the
Galaxy, concentrating on the energy range below the ankle in the spectrum at 4
EeV. A Monte-Carlo method, based on analytical solutions to the time-dependent
diffusion problem, is used to account for intermittency by placing sources at
random locations. Assuming a source population that scales with baryon mass
density or star formation (e.g. long GRB), we derive constraints arising from
intermittency and the observational limits on the composition and anisotropy.
It is shown that the composition and anisotropy at 1e18 eV are difficult to
reproduce and require that either a) the particle mean free path is much
smaller than a gyroradius, implying the escape time is very long, b) the
composition is heavier than suggested by recent Auger data, c) the
ultrahigh-energy sub-ankle component is mostly extragalactic, or d) we are
living in a rare lull in the ultrahigh-energy cosmic-ray production, and the
current ultrahigh-energy cosmic-ray intensity is far below the Galactic time
average. We therefore recommend a strong observational focus on determining the
UHECR composition around 1e18 eV.",1108.2135v2
2011-08-11,"Radiation pressure dominant acceleration: polarization and radiation reaction effects, and energy increase in three-dimensional simulations","Polarization and radiation reaction (RR) effects in the interaction of a
superintense laser pulse (I > 10^23 W/cm^2) with a thin plasma foil are
investigated with three dimensional particle-in-cell (PIC) simulations. For a
linearly polarized laser pulse, strong anisotropies such as the formation of
two high-energy clumps in the plane perpendicular to the propagation direction
and significant radiation reactions effects are observed. On the contrary,
neither anisotropies nor significant radiation reaction effects are observed
using circularly polarized laser pulses, for which the maximum ion energy
exceeds the value obtained in simulations of lower dimensionality. The
dynamical bending of the initially flat plasma foil leads to the self-formation
of a quasi-parabolic shell that focuses the impinging laser pulse strongly
increasing its energy and momentum densities.",1108.2372v3
2011-08-11,Entanglement Perturbation Theory for Infinite Quasi-1D Quantum Systems,"We develop Entanglement Perturbation Theory (EPT) for infinite Quasi-1D
quantum systems. The spin 1/2 Heisenberg chain with ferromagnetic nearest
neighbor (NN) and antiferromagnetic next nearest neighbor (NNN) interactions
with an easy-plane anisotropy is studied as a prototypical system. The obtained
accurate phase diagram is compared with a recent prediction
[Phys.Rev.B,81,094430(2010)] that dimer and Neel orders appear alternately as
the XXZ anisotropy Delta approaches the isotropic limit Delta=1. The first and
second transitions (across dimer, Neel, and dimer phases) are detected with
improved accuracy at Delta\approx 0.722 and 0.930. The third transition (from
dimer to Neel phases), previously predicted to be at Delta\approx 0.98, is not
detected at this Delta in our method, raising the possibility that the second
Neel phase is absent.",1108.2532v3
2011-08-13,Phononic Self energy effects and superconductivity in CaC$_6$,"We study the graphite intercalated compound CaC$_6$ by means of Eliashberg
theory, focusing on the anisotropy properties. An analysis of the
electron-phonon coupling is performed, and we define a minimal 6-band
anisotropy structure. Comparing with Superconducting Density Functional Theory
(SCDFT) the condition under which Eliashberg theory is able to reproduce the
SCDFT gap structure is determined, and we discuss the role of Coulomb
interactions. The Engelsberg-Schrieffer polaron structure is computed by
solving the Eliashberg equation on the Matsubara axis and analytically
continuing it to the full complex plane. This reveals the polaronic
quasiparticle bands anisotropic features as well as the interplay with
superconductivity.",1108.2800v2
2011-08-18,Large scale anisotropy due to pre-inflationary phase of cosmic evolution,"We show that perturbations generated during the anisotropic pre-inflationary
stage of cosmic evolution may affect cosmological observations today for a
certain range of parameters. Due to the anisotropic nature of the universe
during such early times, it might explain some of the observed signals of large
scale anisotropy. In particular we argue that the alignment of CMB quadrupole
and octopole may be explained by the Sachs-Wolfe effect due to the large scale
anisotropic modes from very early times of cosmological evolution. We also
comment on how the observed dipole modulation of CMB power may be explained
within this framework.",1108.3643v2
2011-08-22,Statistical Anisotropy from Vector Curvaton in D-brane Inflation,"We investigate the possibility of embedding the vector curvaton paradigm in
D-brane models of inflation in Type IIB string theory in a simple toy model.
The vector curvaton is identified with the U(1) gauge field that lives on the
world volume of a D3-brane, which may be stationary or undergoing general
motion in the internal space. The dilaton is considered as a spectator field
which modulates the evolution of the vector field. In this set up, the vector
curvaton is able to generate measurable statistical anisotropy in the spectrum
and bispectrum of the curvature perturbation assuming that the dilaton evolves
as e^(-\phi)\propto a^2 where a(t) is the scale factor. Our work constitutes a
first step towards exploring how such distinctive features may arise from the
presence of several light fields that naturally appear in string theory models
of cosmology.",1108.4424v3
2011-08-30,Molecular dynamics simulation for heat transport in thin diamond nanowires,"The phonon thermal conductivity in diamond nanowires (DNW) is studied by
molecular dynamics simulation. It is found that the thermal conductivity in
narrower DNW is lower and does not show obvious temperature dependence; a very
small value (about 2.0 W/m/K) of thermal conductivity is observed in
ultra-narrow DNW, which may be of potential applications in thermoelectric
devices. These two phenomena are probably due to the dominant surface effect
and phonon confinement effect in narrow DNW. Our simulation reveals a high
anisotropy in the heat transport of DNW. Specifically, the thermal conductivity
in DNW along [110] growth direction is about five times larger than that of
[100] and [111] growth directions. The anisotropy is believed to root in the
anisotropic group velocity for acoustic phonon modes in DNW along three
different growth directions.",1108.5812v1
2011-08-30,Direct measurement of the angular power spectrum of cosmic microwave background temperature anisotropies in the WMAP Data,"Angular power spectrum of the cosmic microwave background (CMB) temperature
anisotropies is one of the most important on characteristics of the Universe
such as its geometry and total density. Using flat sky approximation and
Fourier analysis, we estimate the angular power spectrum from an ensemble of
least foreground-contaminated square patches from WMAP W and V frequency band
map. This method circumvents the issue of foreground cleaning and that of
breaking orthogonality in spherical harmonic analysis due to masking out the
bright Galactic plane region, thereby rendering a direct measurement of the
angular power spectrum. We test and confirm Gaussian statistical characteristic
of the selected patches, from which the first and second acoustic peak of the
power spectrum are reproduced, and the third peak is clearly visible albeit
with some noise residual at the tail.",1108.5824v1
2011-09-06,Anisotropic magnetic deflagration in single crystals of Gd5Ge4,"Experimental evidence of the anisotropy of the magnetic deflagration
associated with the low-temperature first order antiferromagnetic (AFM) -->
ferromagnetic (FM) phase-transition in single crystals of Gd5Ge4 is reported.
The deflagrations have been induced by controlled pulses of surface acoustic
waves (SAW) allowing us to explore both the magnetic field and temperature
dependencies on the characteristic times of the phenomenon. The study was done
using samples with different geometries and configurations between the SAW
pulses and the direction of the applied magnetic field with respect to the
three main crystallographic directions of the samples. The effect of
temperature is nearly negligible, whereas observed strong magnetic field
dependence correlates with the magnetic anisotropy of the sample. Finally, the
role of the SAW pulses in both the ignition and formation of the deflagration
front was also studied, and we show that the thermal diffusivity of Gd5Ge4 must
be anisotropic, following \kappaa>\kappab>\kappac.",1109.1127v1
2011-09-07,"Spin wave theory study of neutron intensity, magnetic field, and anisotropy of Type IIA FCC antiferromagnet","We study the spin dynamics in a 3D quantum antiferromagnet on a face-centered
cubic (FCC) lattice. The effects of magnetic field, single-ion anisotropy, and
biquadratic interactions are investigated using linear spin wave theory with
spins in a canted basis about the Type IIA FCC antiferromagnetic ground state
structure which is known to be stable. We calculate the expected finite
frequency neutron scattering intensity and give qualitative criteria for
typical FCC materials MnO and CoO. The magnetization reduction due to quantum
zero point fluctuations is also analyzed.",1109.1350v3
2011-09-07,A theoretical analysis of inertia-like switching in magnets: applications to a synthetic antiferromagnet,"The magnetization dynamics of a synthetic antiferromagnet subject to a short
magnetic field pulse, has been studied by using a combination of
first-principles and atomistic spin dynamics simulations. We observe switching
phenomena on the time scale of tens of picoseconds, and inertia-like behavior
in the magnetization dynamics. We explain the latter in terms of a dynamic
redistribution of magnetic energy from the applied field pulse to other
possible energy terms, such as the exchange interaction and the magnetic
anisotropy, without invoking concepts such as inertia of an antiferromagnetic
vector. We also demonstrate that such dynamics can also be observed in a
ferromagnetic material where the incident field pulse pumps energy to the
magnetic anisotropy.",1109.1414v1
2011-09-09,Towards an experimental realization of affinely transformed linearized QED vacuum via inverse homogenization,"Within the framework of quantum electrodynamics (QED), vacuum is a nonlinear
medium which can be linearized for a rapidly time-varying electromagnetic field
with a small amplitude subjected to a magnetostatic field. The linearized QED
vacuum is a uniaxial dielectric-magnetic medium for which the degree of
anisotropy is exceedingly small. By implementing an affine transformation of
the spatial coordinates, the degree of anisotropy may become sufficiently large
as to be readily perceivable. The inverse Bruggeman formalism can be
implemented to specify a homogenized composite material (HCM) which is
electromagnetically equivalent to the affinely transformed QED vacuum. This HCM
can arise from remarkably simple component materials; for example, two
isotropic dielectric materials and two isotropic magnetic materials, randomly
distributed as oriented spheroidal particles.",1109.2125v1
2011-09-11,Quadrupole Approximation for Para-Positronium in Relativistic Schrödinger Theory,"The non-relativistic energy levels of para-positronium are calculated in the
quadrupole approximation of the interaction potential. This approximation
technique takes into account the anisotropy of the electrostatic
electron-positron interaction in the lowest order. The states due to different
values of the quantum number $(l_z)$ of angular momentum are found to be no
longer degenerate as is the case in the conventional theory. The physical
origin of this elimination of the conventional degeneracy may intuitively be
attributed to the state-dependent inertial \emph{broadening} of the rotating
charge clouds; the corresponding \emph{anisotropic} deformation (in the
quadrupole approximation) lowers then the negative electrostatic interaction
energy. The result of this influence of anisotropy is that the states with
$l_z=0$ adopt smaller binding energy whereas the states with maximal value of
$|l_z|$ (for fixed principal quantum number $n$) have the largest binding
energy within the angular momentum multiplet $(-|l_{z,\mathrm{max}}| \le l_z
\le |l_{z,\mathrm{max}}|)$. This yields a certain kind of electric
fine-structure splitting with the splitted RST levels being placed in a
relatively narrow band around the (highly degenerated) conventional levels.",1109.2331v1
2011-09-12,Three-Dimensional Structure of Solar Wind Turbulence,"We present a measurement of the scale-dependent, three-dimensional structure
of the magnetic field fluctuations in inertial range solar wind turbulence with
respect to a local, physically motivated coordinate system. The Alfvenic
fluctuations are three-dimensionally anisotropic, with the sense of this
anisotropy varying from large to small scales. At the outer scale, the magnetic
field correlations are longest in the local fluctuation direction, consistent
with Alfven waves. At the proton gyroscale, they are longest along the local
mean field direction and shortest in the direction perpendicular to the local
mean field and the local field fluctuation. The compressive fluctuations are
highly elongated along the local mean field direction, although axially
symmetric perpendicular to it. Their large anisotropy may explain why they are
not heavily damped in the solar wind.",1109.2558v2
2011-09-13,Elastodynamics of radially inhomogeneous spherically anisotropic elastic materials in the Stroh formalism,"A method is presented for solving elastodynamic problems in radially
inhomogeneous elastic materials with spherical anisotropy, i.e.\ materials such
that $c_{ijkl}= c_{ijkl}(r)$ in a spherical coordinate system
${r,\theta,\phi}$. The time harmonic displacement field $\mathbf{u}(r,\theta
,\phi)$ is expanded in a separation of variables form with dependence on
$\theta,\phi$ described by vector spherical harmonics with $r$-dependent
amplitudes. It is proved that such separation of variables solution is
generally possible only if the spherical anisotropy is restricted to transverse
isotropy with the principal axis in the radial direction, in which case the
amplitudes are determined by a first-order ordinary differential system.
Restricted forms of the displacement field, such as $\mathbf{u}(r,\theta)$,
admit this type of separation of variables solutions for certain lower material
symmetries. These results extend the Stroh formalism of elastodynamics in
rectangular and cylindrical systems to spherical coordinates.",1109.2865v1
2011-09-19,On the stability in weak topology of the set of global solutions to the Navier-Stokes equations,"Let $X$ be a suitable function space and let $\cG \subset X$ be the set of
divergence free vector fields generating a global, smooth solution to the
incompressible, homogeneous three dimensional Navier-Stokes equations. We prove
that a sequence of divergence free vector fields converging in the sense of
distributions to an element of $\cG$ belongs to $\cG$ if $n$ is large enough,
provided the convergence holds ""anisotropically"" in frequency space. Typically
that excludes self-similar type convergence. Anisotropy appears as an important
qualitative feature in the analysis of the Navier-Stokes equations; it is also
shown that initial data which does not belong to $\cG$ (hence which produces a
solution blowing up in finite time) cannot have a strong anisotropy in its
frequency support.",1109.4043v2
2011-09-21,Anisotropic critical magnetic fluctuations in the ferromagnetic superconductor UCoGe,"We report neutron scattering measurements of critical magnetic excitations in
the weakly ferromagnetic superconductor UCoGe. The strong non-Landau damping of
the excitations we observe, although unusual has been found in another related
ferromagnet, UGe2 at zero pressure. However, we also find there is a
significant anisotropy of the magnetic correlation length in UCoGe that
contrasts with an almost isotropic length for UGe2. The values of the magnetic
correlation length and damping are found to be compatible with
superconductivity on small Fermi surface pockets. The anisotropy may be
important to explain why UCoGe is a superconductor at zero pressure while UGe2
is not.",1109.4541v1
2011-09-22,Ground-state phases of ultracold bosons with Rashba-Dresselhaus spin-orbit coupling,"We study ultracold bosons in three dimensions with an anisotropic
Rashba-Dresselhaus spin-orbit coupling. We first carry out the exact summation
of ladder diagrams for the two-boson t-matrix at zero energy. Then, with the
t-matrix as the effective interaction, we find the ground-state phase diagrams
of bosons in mean field as a function of the spin-orbit coupling, the
anisotropy, and the scattering lengths between particles in the same and in
different pseudospin states. The resulting phase diagrams have much richer
structures than those obtained using mean-field couplings, exhibiting three
different phases: a plane-wave condensate, a striped condensate, and an
unstable phase. The differences between the present approach using the t-matrix
compared to using mean-field couplings is significant for large scattering
lengths, large spin-orbit-coupling strength, or small anisotropy.",1109.4954v2
2011-09-27,Counting hot/cold spots in quark-gluon plasma,"We study how local fluctuations in the initial states of relativistic
heavy-ion collisions manifest themselves in the correlations between different
orders of harmonic moments of the density profiles, particularly those
involving only odd harmonics which purely arise from initial state
fluctuations. We find the strengths of those correlations are sensitive to the
number of hot and cold spots in the initial states. Hydrodynamic evolution of
the fireball translates initial state geometric anisotropies as well as their
correlations into final state momentum anisotropies and correlations. We
conclude that the measurement of the correlations between different harmonic
moments of final state azimuthal distribution can be employed to quantify the
inhomogeneity of the initial density profiles such as the population of hot and
cold spots that are produced in high energy nuclear collisions.",1109.5961v3
2011-09-28,Anisotropic vortex lattice structures in the FeSe superconductor,"In the recent work by Song et al. [Science 332, 1410 (2011)], the scanning
tunneling spectroscopy experiment in the stoichiometric FeSe reveals evidence
for nodal superconductivity and strong anisotropy. The nodal structure can be
explained with the extended s-wave pairing structure with the mixture of the
$s_{x^2+y^2}$ and $s_{x^2y^2}$ pairing symmetries. We calculate the anisotropic
vortex structure by using the self-consistent Bogoliubov-de Gennes mean-field
theory. In considering the absence of magnetic ordering in the FeSe at the
ambient pressure, orbital ordering is introduced, which breaks the $C_4$
lattice symmetry down to $C_2$, to explain the anisotropy in the vortex
tunneling spectra.",1109.6116v3
2011-09-30,Entanglement Perturbation Theory for Antiferromagnetic Heisenberg Spin Chains,"A recently developed numerical method, entanglement perturbation theory
(EPT), is used to study the antiferromagnetic Heisenberg spin chains with
z-axis anisotropy $\lambda$ and magnetic field B. To demonstrate the accuracy,
we first apply EPT to the isotropic spin-1/2 antiferromagnetic Heisenberg
model, and find that EPT successfully reproduces the exact Bethe Ansatz results
for the ground state energy, the local magnetization, and the spin correlation
functions (Bethe ansatz result is available for the first 7 lattice
separations). In particular, EPT confirms for the first time the asymptotic
behavior of the spin correlation functions predicted by the conformal field
theory, which realizes only for lattice separations larger than 1000. Next,
turning on the z-axis anisotropy and the magnetic field, the 2-spin and 4-spin
correlation functions are calculated, and the results are compared with those
obtained by Bosonization and density matrix renormalization group methods.
Finally, for the spin-1 antiferromagnetic Heisenberg model, the ground state
phase diagram in $\lambda$ space is determined with help of the Roomany-Wyld RG
finite-size-scaling. The results are in good agreement with those obtained by
the level-spectroscopy method.",1109.6758v1
2011-09-30,Transport in Anisotropic Superfluids: A Holographic Description,"We study transport phenomena in p-wave superfluids in the context of
gauge/gravity duality. Due to the spacetime anisotropy of this system, the
tensorial structure of the transport coefficients is non-trivial in contrast to
the isotropic case. In particular, there is an additional shear mode which
leads to a non-universal value of the shear viscosity even in an Einstein
gravity setup. In this paper, we present a complete study of the helicity two
and helicity one fluctuation modes. In addition to the non-universal shear
viscosity, we also investigate the thermoelectric effect, i.e. the mixing of
electric and heat current. Moreover, we also find an additional effect due to
the anisotropy, the so-called flexoelectric effect.",1110.0007v2
2011-10-04,Weak lensing of CMB by cosmic (super-)strings,"We study the effect of weak lensing by cosmic (super-)strings on the
anisotropies of cosmic microwave background (CMB). In developing a method to
calculate the lensing convergence field due to strings, and thereby temperature
and polarization angular power spectra of CMB, we clarify how the nature of
strings, characterized by the intercommuting probability, can influence these
CMB anisotropies. Assuming that the power spectrum is dominated by
Poisson-distributed string segments, we find that the convergence spectrum
peaks at low multipoles and is mostly contributed from strings located at
relatively low redshifts. As the intercommuting probability decreases, the
spectra of the convergence and hence the lensed temperature and polarizations
are gained because the number density of string segments becomes larger. An
observationally important feature of the string-induced CMB polarizations is
that the string-lensed spectra decay more slowly on small scales compared with
primordial scalar perturbations from standard inflation.",1110.0556v3
2011-10-04,Low-temperature thermodynamics of the classical frustrated ferromagnetic chain in magnetic field,"Low-temperature magnetization curves of the classical frustrated
ferromagnetic chain in the external magnetic field near the transition point
between the ferromagnetic and the helical phases is studied. It is shown that
the calculation of the partition function in the scaling limit reduces to the
solution of the Schr\""{o}dinger equation of the special form for the quantum
particle. It is proposed that the magnetization of the classical model in the
ferromagnetic part of the phase diagram including the transition point defines
the universal scaling function which is valid for quantum model as well.
Explicit analytical formulae for the magnetization are given in the limiting
cases of low and high magnetic fields. The influence of the easy-axis
anisotropy on the magnetic properties of the model is studied. It is shown that
even small anisotropy essentially changes the behavior of the susceptibility in
the vicinity of the transition point.",1110.0771v2
2011-10-11,Deposition of general ellipsoidal particles,"We present a systematic overview of granular deposits composed of ellipsoidal
particles with different particle shapes and size polydispersities. We study
the density and anisotropy of such deposits as functions of size polydispersity
and two shape parameters that fully describe the shape of a general ellipsoid.
Our results show that, while shape influences significantly the macroscopic
properties of the deposits, polydispersity plays apparently a secondary role.
The density attains a maximum for a particular family of non-symmetrical
ellipsoids, larger than the density observed for prolate or oblate ellipsoids.
As for anisotropy measures, the contact forces show are increasingly preferred
along the vertical direction as the shape of the particles deviates for a
sphere. The deposits are constructed by means of an efficient molecular
dynamics method, where the contact forces are efficiently and accurately
computed. The main results are discussed in the light of applications for
porous media models and sedimentation processes.",1110.2792v1
2011-10-15,A Field-directional Specific Heat Study on the Gap Structure of Overdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$,"Low-temperature specific heat is measured on the overdoped
Ba(Fe_{1-x}Co_x)_2As_2 (x = 0.13) single crystal under magnetic fields along
three different directions. A clear anisotropy is observed on the field
dependent electronic specific heat coefficient {\gamma}(H). The value of
{\gamma}(H) is obviously larger with magnetic field along [001] (c-axis) than
that within the ab-plane of the crystal lattice, which cannot be attributed to
the effect by anisotropy of the upper critical field. Meanwhile, the data show
a rather small difference when the direction of the field is rotated from [100]
to [110] direction within the ab-plane. Our results suggest that a considerable
part of the line nodes is not excited to contribute to the quasiparticle
density of states by the field when the field is within the ab-plane. The
constraints on the topology of the gap nodes are discussed based on our
observations.",1110.3403v2
2011-10-17,Quadrupole oscillation in a dipolar Fermi gas: hydrodynamic vs collisionless regime,"The surface quadrupole mode of an harmonically trapped dipolar Fermi gas is
studied in both the hydrodynamic and collisionless regimes. The anisotropy and
long range effects of the dipolar force as well as the role of the trapping
geometry are explicitly investigated. In the hydrodynamic regime the frequency
is always slightly smaller than the $\sqrt{2}\omega_\perp$ value holding for
gases interacting with contact interactions. In the collisionless regime the
frequency can be either pretty smaller or larger than the non-interacting value
$2\omega_\perp$, depending on the cloud aspect ratio. Our results suggest that
the frequency of the surface quadrupole oscillation can provide a useful test
for studying, at very low temperatures, the transition between the normal and
the superfluid phase and, in the normal phase at higher temperatures, the
crossover between the collisional and collisionless regimes. The consequences
of the anisotropy of the dipolar force on the virial theorem are also
discussed.",1110.3670v1
2011-10-21,Schwarzschild models of the Sculptor dSph galaxy,"We have developed a spherically symmetric dynamical model of a dwarf
spheroidal galaxy using the Schwarzschild method. This type of modelling yields
constraints both on the total mass distribution (e.g. enclosed mass and scale
radius) as well as on the orbital structure of the system modelled (e.g.
velocity anisotropy). Therefore not only can we derive the dark matter content
of these systems, but also explore possible formation scenarios. Here we
present preliminary results for the Sculptor dSph. We find that the mass of
Sculptor within 1kpc is 8.5\times10^(7\pm0.05) M\odot, its anisotropy profile
is tangentially biased and slightly more isotropic near the center. For an NFW
profile, the preferred concentration (~15) is compatible with cosmological
models. Very cuspy density profiles (steeper than NFW) are strongly disfavoured
for Sculptor.",1110.4808v1
2011-11-01,Theory of quasiparticle vortex bound states in Fe-based superconductors: application to LiFeAs,"Spectroscopy of vortex bound states can provide valuable information on the
structure of the superconducting order parameter. Quasiparticle wavefunctions
are expected to leak out in the directions of gap minima or nodes, if they
exist, and scanning tunneling spectroscopy (STS) on these low-energy states
should probe the momentum dependence of the gap. Anisotropy can also arise from
band structure effects, however. We perform a quasiclassical calculation of the
density of states of a single vortex in an anisotropic superconductor, and show
that if the gap itself is not highly anisotropic, the Fermi surface anisotropy
dominates, preventing direct observation of superconducting gap features. This
serves as a cautionary message for the analysis of STS data on the vortex state
on Fe-based superconductors, in particular LiFeAs, which we treat explicitly.",1111.0126v1
2011-11-06,Continuous Time Monte Carlo for Lattice QCD in the Strong Coupling Limit,"We present results for lattice QCD with staggered fermions in the limit of
infinite gauge coupling, obtained from a worm-type Monte Carlo algorithm on a
discrete spatial lattice but with continuous Euclidean time. This is achieved
by sending both the anisotropy parameter $\gamma^2\simeq a/\at$ and the number
of time-slices $N_\tau$ to infinity, keeping the ratio $\gamma^2/N_\tau \simeq
aT$ fixed. In this limit, ambiguities arising from the anisotropy parameter
$\gamma$ are eliminated and discretization errors usually introduced by a
finite temporal lattice extent $\Nt$ are absent. The obvious gain is that no
continuum extrapolation $N_\tau \rightarrow \infty$ has to be carried out.
Moreover, the algorithm is faster and the sign problem disappears completely.
  As a first application, we determine the phase diagram as a function of
temperature and real and imaginary baryon chemical potential. We compare our
computations with those on lattices with discrete Euclidean time.
Discretization errors due to finite $\Nt$ in previous studies turn out to be
large at low temperatures.",1111.1434v1
2011-11-10,Highlights from Telescope Array,"The results from the first three years observation in Telescope Array are
reviewed. The energy spectrum, mass composition, and anisotropy in arrival
directions of ultra-high energy cosmic rays are discussed. The energy spectrum
of cosmic rays with energies above $10^{18}$ eV is determined using the data of
the fluorescence detectors, surface detectors, and with a hybrid shower
reconstruction technique using the both data. The ankle structure is clearly
found at $10^{18.7}$ eV. The second bending point is also identified, at which
the flux of cosmic rays begins to decrease and the spectral index changes from
$E^{-2.68}$ to $E^{-4.2}$. The study of shower development using the
fluorescence detector data shows that proton is dominant in cosmic rays above
$10^{18.2}$ eV. No apparent anisotropies in the arrival direction of cosmic
rays are found. I also present further experimental extensions which are being
developed at the Telescope Array site.",1111.2507v1
2011-11-15,Unconventional Anisotropic s-Wave Superconducting Gaps of LiFeAs Iron-Pnictide Superconductor,"We have performed high-resolution angle-resolved photoemission spectroscopy
on Fe-based superconductor LiFeAs (Tc = 18 K). We reveal multiple nodeless
superconducting (SC) gaps with 2D/kBTc ratios varying from 2.8 to 6.4,
depending on the Fermi surface (FS). We also succeeded in directly observing a
gap anisotropy along the FS with magnitude up to ~30 %. The anisotropy is
four-fold symmetric with an antiphase between the hole and electron FSs,
suggesting complex anisotropic interactions for the SC pairing. The observed
momentum dependence of the SC gap offers an excellent opportunity to
investigate the underlying pairing mechanism.",1111.3496v2
2011-11-16,On Wormhole Throats in $f(R)$ Gravity Theory,"We study the existence and properties of wormhole throats in modified $f(R)$
gravity theory. Specifically, we concentrate on the cases where the lapse is
not necessarily constant, and hence are not limited to the zero tidal force
scenarios. In the class of theories whose actions are generated by Lagrangians
of the form $f(R)=\sum \alpha_{n}\,R^{n}$ we find parameters which allow for
the existence of energy condition respecting throats, which do not exist in
Einstein gravity. We also consider the effect of the modified action on the
anisotropy of the models, and find that modified gravity can minimize the
amount of anisotropy required to support the existence of a throat. In both
these respects, the sector containing theories with positive $n$ is more
promising than the negative $n$ sector in comparison to Einstein gravity alone,
with large $n$ being most favorable",1111.3704v2
2011-11-26,Electronic reconstruction through the structural and magnetic transitions in detwinned NaFeAs,"We use angle-resolved photoemission spectroscopy to study twinned and
detwinned iron pnictide compound NaFeAs. Distinct signatures of electronic
reconstruction are observed to occur at the structural (TS) and magnetic (TSDW)
transitions. At TS, C4 rotational symmetry is broken in the form of an
anisotropic shift of the orthogonal dxz and dyz bands. The magnitude of this
orbital anisotropy rapidly develops to near completion upon approaching TSDW,
at which temperature band folding occurs via the antiferromagnetic ordering
wave vector. Interestingly, the anisotropic band shift onsetting at TS develops
in such a way to enhance the nesting conditions in the C2 symmetric state,
hence is intimately correlated with the long range collinear AFM order.
Furthermore, the similar behaviors of the electronic reconstruction in NaFeAs
and Ba(Fe1-xCox)2As2 suggests that this rapid development of large orbital
anisotropy between TS and TSDW is likely a general feature of the electronic
nematic phase in the iron pnictides, and the associated orbital fluctuations
may play an important role in determining the ground state properties.",1111.6134v1
2011-11-29,Theory of Spin Relaxation in Two-Electron Lateral Coupled Quantum Dots,"A global quantitative picture of the phonon-induced two-electron spin
relaxation in GaAs double quantum dots is presented using highly accurate
numerical calculations. Wide regimes of interdot coupling, magnetic field
magnitude and orientation, and detuning are explored in the presence of a
nuclear bath. Most important, the unusually strong magnetic anisotropy of the
singlet-triplet relaxation can be controlled by detuning switching the
principal anisotropy axes: a protected state becomes unprotected upon detuning,
and vice versa. It is also established that nuclear spins can dominate spin
relaxation for unpolarized triplets even at high magnetic fields, contrary to
common belief. These findings are central to designing quantum dots geometries
for spin-based quantum information processing with minimal environmental
impact.",1111.6724v3
2011-11-29,Anisotropy of Electrical Transport in Pnictide Superconductors Studied Using Monte Carlo Simulations of the Spin-Fermion Model,"The undoped three-orbital spin fermion model for the Fe-based superconductors
is studied via Monte Carlo techniques in two-dimensional clusters. At low
temperatures, the magnetic and one-particle spectral properties are in good
agreement with neutron and photoemission experiments. Our most important
results are the resistance vs. temperature curves that display all the features
experimentally observed in BaFe$_2$As$_2$ detwinned single crystals (under
uniaxial stress), including a low-temperature anisotropy between the two
directions followed by a peak at the magnetic ordering temperature, here
induced by short-range spin order and concomitant Fermi Surface orbital order.",1111.6994v4
2011-12-02,Two-dimensional arrays of superconducting strips as dc magnetic metamaterials,"We theoretically investigate the magnetic response of two-dimensional arrays
of superconducting strips, which are regarded as essential structures of dc
magnetic metamaterials. We analytically obtain local distributions of the
magnetic field for the ideal complete shielding state (i.e., $\Lambda/w\to 0$,
where $2w$ is the strip width, $\Lambda=\lambda^2/d$ is the Pearl length,
$\lambda$ is the London penetration depth, and $d$ is the strip thickness), and
derive effective permeability by averaging the local field distributions. We
also perform numerical calculations for a realistic case, taking finite
$\Lambda/w>0$ into account. We investigate two types of strip arrays: a
rectangular array and a hexagonal array. The resulting effective permeability
has large anisotropy that depends on the dimensions and arrangement of the
superconducting strips, and the hexagonal array is found to be more
advantageous for obtaining large anisotropy than the rectangular array.",1112.0372v1
2011-12-05,Quantum magnets with large single-ion easy-plane anisotropy in transverse magnetic field,"We discuss low-temperature properties of magnets with integer spin and large
single-ion easy-plane anisotropy $D$ in transverse magnetic field $h$.
Considering the exchange interaction between spins as a perturbation and using
the diagram technique we derive at $h\sim D$ in the first nonvanishing orders
of the perturbation theory thermal corrections to the elementary excitation
spectrum, magnetization and specific heat. An expression for the boundary
$h_{c1}(T)$ is found in the $h$-$T$ plane between the paramagnetic phase and
that with the long range magnetic order. The effective interaction is derived
between bosons near the quantum critical point $h_{c1}(0)$. The proposed theory
describes well experimental data obtained in $\rm NiCl_2$-$\rm 4SC(NH_2)_2$
(DTN).",1112.0833v1
2011-12-05,Magnetic anisotropy of elongated thin ferromagnetic nano-islands for artifical spin ice arrays,"The energetics of thin elongated ferromagnetic nano-islands is considered for
some different shapes, aspect ratios, and applied magnetic field directions.
These nano-island particles are important for artificial spin-ice materials.
For low temperature, the magnetic internal energy of an individual particle is
evaluated numerically as a function of the direction of a particle's net
magnetization. This leads to estimations of effective anisotropy constants for
(1) the easy axis along the particle's long direction, and (2) the hard axis
along the particle's thin direction. A spin relaxation algorithm together with
fast Fourier transform for the demagnetization field is used to solve the
micromagnetics problem for a thin system. The magnetic hysteresis is also
found. The results indicate some possibilities for controlling the equilibrium
and dynamics in spin-ice materials by using different island geometries.",1112.0913v2
2011-12-07,Exciton coherence lifetimes from electronic structure,"We model the coherent energy transfer of an electronic excitation within
covalently linked aromatic homodimers from first-principles, to answer whether
the usual models of the bath calculated via detailed electronic structure
calculations can reproduce the key dynamics. For these systems the timescales
of coherent transport are experimentally known from time-dependent polarization
anisotropy measurements, and so we can directly assess the whether current
techniques might be predictive for this phenomenon. Two choices of electronic
basis states are investigated, and their relative merits discussed regarding
the predictions of the perturbative model. The coupling of the electronic
degrees of freedom to the nuclear degrees of freedom is calculated rather than
assumed, and the fluorescence anisotropy decay is directly reproduced.
Surprisingly we find that although TDDFT absolute energies are routinely in
error by orders of magnitude more than the coupling energy, the coherent
transport properties of these dimers can be semi-quantitatively reproduced from
first-principles. The directions which must be pursued to yield predictive and
reliable prediction of coherent transport are suggested.",1112.1665v2
2011-12-09,Helium-4 Synthesis in an Anisotropic Universe,"We calculate the 4He abundance in a universe of Bianchi type I whose cosmic
anisotropy is dynamically generated by a fluid with anisotropic equation of
state. Requiring that the relative variation of mass fraction of 4He is less
than 4% with respect to the standard isotropic case to be consistent with
astrophysical data, we constrain the parameter of cosmic anisotropy, the shear
\Sigma, as |\Sigma(T_f)| < 0.4, where T_f is the freeze-out temperature of the
weak interactions that interconvert neutrons and protons. Anisotropic fluids,
whose energy density is subdominant with respect to the energy content of the
Universe during inflation and radiation era, generate much smaller shears at
the time of freeze-out and then do not appreciably affect the standard 4He
production. This is the case of anisotropic dark energy, and of a uniform
magnetic field with energy density much smaller than about 1.25 times the
energy density of neutrinos.",1112.2076v2
2011-12-17,Effect of temperature-dependent eta/s on flow anisotropies,"We investigate the effects of a temperature-dependent shear viscosity over
entropy density ratio eta/s on the flow anisotropy coefficients v_2 and v_4 in
ultrarelativistic heavy-ion collisions at RHIC and LHC. We find that v_4 is
more sensitive to the viscosity at low temperatures than v_2. At RHIC v_2 is
mostly affected by the viscosity around the phase transition, but the larger
the collision energy, the more the quark-gluon plasma viscosity affects v_2.",1112.4081v1
2011-12-21,Role of Interstitial Pinning in the Dynamical Phases of Vortices in Superconducting Films,"We analyze the vortex dynamics in superconducting thin films with a periodic
array of pinning centers. In particular, we study the effect of anisotropy for
a Kagom\'e pinning network when longitudinal and transverse transport currents
are applied. By solving the equations of motion for the vortex array
numerically at zero temperature we find different phases for the vortex
dynamics depending on the pinning and driving force. An unusual sequence of
peaks along and perpendicular to the main hexagonal lattice axes is observed
for the differential resistance reflecting the anisotropy of the transport
properties and the complex behavior of the vortex system. This behavior may be
understood in terms of interstitial pinning vacancies, which create channels of
vortices with different pinning strength.",1112.5001v1
2011-12-22,Magnetic structure of noncentrosymmetric perovskites PbVO3 and BiCoO3,"It is well known that if a crystal structure has no inversion symmetry, it
may allow for Dzyaloshinskii-Moriya magnetic interactions, operating between
different crystallographic unit cells, which in turn should lead to the
formation of long-periodic spin-spiral structures. Such a behavior is
anticipated for two simple perovskites PbVO3 and BiCoO3, crystallizing in the
noncentrosymmetric tetragonal P4mm structure. Nevertheless, we argue that in
reality PbVO3 and BiCoO3 should behave very differently. Due to the fundamental
Kramers degeneracy for the odd-electron systems, PbVO3 has no single-ion
anisotropy. Therefore, the ground state of PbVO3 will be indeed the spin spiral
with the period of about one hundred unit cells. However, the even-electron
BiCoO3 has a large single-ion anisotropy, which locks this system in the
collinear easy-axis C-type antiferromagnetic ground state. Our theoretical
analysis is based on the low-energy model, derived from the first-principles
electronic structure calculations.",1112.5219v1
2011-12-30,First-Order Reorientation of the Flux-Line Lattice in CaAlSi,"The flux line lattice in CaAlSi has been studied by small angle neutron
scattering. A well defined hexagonal flux line lattice is seen just above Hc1
in an applied field of only 54 Oe. A 30 degree reorientation of this vortex
lattice has been observed in a very low field of 200 Oe. This reorientation
transition appears to be of first-order and could be explained by non-local
effects. The magnetic field dependence of the form factor is well described by
a single penetration depth of 1496(1) angstroms and a single coherence length
of 307(1) angstroms at 2 K. At 1.5 K the penetration depth anisotropy is 2.7(1)
with the field applied perpendicular to the c axis and agrees with the
coherence length anisotropy determined from critical field measurements.",1201.0174v1
2012-01-12,The Oddly Quiet Universe: How the CMB challenges cosmology's standard model,"We discuss selected large-scale anomalies in the maps of temperature
anisotropies in the cosmic microwave background. Specfically, these include
alignments of the largest modes of CMB anisotropy with one another and with the
geometry and direction of motion of the Solar System, and the unexpected
absence of two-point angular corellations especially outside the region of the
sky most contaminated by the Galaxy. We discuss these findings in relation to
expectations from standard inflationary cosmology. This paper is adapted from a
talk given by one of us (GDS) at the SEENET-2011 meeting in August 2011 on the
Serbian bank of the Danube River.",1201.2459v1
2012-01-12,Universal behavior of the upper critical field in iron based superconductors,"The newly discovered iron-based high temperature superconductors have
demonstrated rich physical properties. Here we give a brief review on the
recent studies of the upper critical field and its anisotropy in a few typical
series of the iron-based superconductors (FeSCs). In spite of their characters
of a layered crystal structure, all the FeSCs possess an extremely large upper
critical field and a weak anisotropy of superconductivity, being unique among
the layered superconductors. These particular properties indicate potential
applications of the FeSCs in the future. Based on the experimental facts of the
FeSCs, we will discuss the possible mechanisms of pair breaking in high
magnetic fields and its restrictions on the theoretical analysis of the
superconducting pairing mechanisms.",1201.2548v1
2012-01-13,Cylindrically Symmetric Relativistic Fluids: A Study Based on Structure Scalars,"The full set of equations governing the structure and the evolution of
self--gravitating cylindrically symmetric dissipative fluids with anisotropic
stresses, is written down in terms of scalar quantities obtained from the
orthogonal splitting of the Riemann tensor (structure scalars), in the context
of general relativity. These scalars which have been shown previously (in the
spherically symmetric case) to be related to fundamental properties of the
fluid distribution, such as: energy density, energy density inhomogeneity,
local anisotropy of pressure, dissipative flux, active gravitational mass etc,
are shown here to play also a very important role in the dynamics of
cylindrically symmetric fluids. It is also shown that in the static case, all
possible solutions to Einstein equations may be expressed explicitly through
three of these scalars.",1201.2862v3
2012-01-18,Spectroscopy of spin-orbit quantum bits in indium antimonide nanowires,"Double quantum dot in the few-electron regime is achieved using local gating
in an InSb nanowire. The spectrum of two-electron eigenstates is investigated
using electric dipole spin resonance. Singlet-triplet level repulsion caused by
spin-orbit interaction is observed. The size and the anisotropy of
singlet-triplet repulsion are used to determine the magnitude and the
orientation of the spin-orbit effective field in an InSb nanowire double dot.
The obtained results are confirmed using spin blockade leakage current
anisotropy and transport spectroscopy of individual quantum dots.",1201.3707v2
2012-01-25,Inflation with Multi-Vector-Hair: The Fate of Anisotropy,"We study inflation with multiple vector fields. In the presence of
non-trivial couplings between the inflaton and the vector fields, it turns out
that no-hair conjecture does not hold and vector-hair appears. In the case of
uniform couplings, nevertheless, we find that the universe approaches an
isotropic final state after transient anisotropic inflationary phases. For
general couplings, we numerically show attractors are anisotropic inflation.
Even in these cases, it turns out that the inflation always tends to minimize
the anisotropy in the expansion of the universe.",1201.5309v2
2012-01-28,A cosmological concordance model with dynamical vacuum term,"We demonstrate that creation of dark-matter particles at a constant rate
implies the existence of a cosmological term that decays linearly with the
Hubble rate. We discuss the cosmological model that arises in this context and
test it against observations of the first acoustic peak in the cosmic microwave
background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type
Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the
distribution of large scale structures (LSS). We show that a good concordance
is obtained, albeit with a higher value of the present matter abundance than in
the \Lambda CDM model. We also comment on general features of the CMB
anisotropy spectrum and on the cosmic coincidence problem.",1201.5919v2
2012-01-30,"Exchange constants and spin waves of the orbital ordered, non-collinear spinel MnV$_2$O$_4$","We study the exchange constants of MnV$_2$O$_4$ using magnetic force theorem
and local spin density approximation of density functional theory supplemented
with a correction due to on-site Hubbard interaction U. We obtain the exchanges
for three different orbital orderings of the Vanadium atoms of the spinel. We
then map the exchange constants to a Heisenberg model with single-ion
anisotropy and solve for the spin-wave excitations in the non-collinear, low
temperature phase of the spinel. The single-ion anisotropy parameters are
obtained from an atomic multiplet exact-diagonalization program, taking into
effect the crystal-field splitting and the spin-orbit coupling. We find good
agreement between the spin waves of one of our orbital ordered setups with
previously reported experimental spin waves as determined by neutron
scattering. We can therefore determine the correct orbital order from various
proposals that exist in the literature.",1201.6375v2
2012-01-31,How well-proportioned are lens and prism spaces?,"The CMB anisotropies in spherical 3-spaces with a non-trivial topology are
analysed with a focus on lens and prism shaped fundamental cells. The
conjecture is tested that well proportioned spaces lead to a suppression of
large-scale anisotropies according to the observed cosmic microwave background
(CMB). The focus is put on lens spaces L(p,q) which are supposed to be oddly
proportioned. However, there are inhomogeneous lens spaces whose shape of the
Voronoi domain depends on the position of the observer within the manifold.
Such manifolds possess no fixed measure of well-proportioned and allow a
predestined test of the well-proportioned conjecture. Topologies having the
same Voronoi domain are shown to possess distinct CMB statistics which thus
provide a counter-example to the well-proportioned conjecture. The CMB
properties are analysed in terms of cyclic subgroups Z_p, and new point of view
for the superior behaviour of the Poincar\'e dodecahedron is found.",1201.6490v1
2012-02-06,Quantum phase transitions of 2-d dimerized spin-1/2 Heisenberg models with spatial anisotropy,"Motivated by the unexpected Monte Carlo results as well as the theoretical
proposal of a large correction to scaling for the critical theory of the 2-d
staggered-dimer spin-1/2 Heisenberg model on the square lattice, we study the
phase transitions induced by dimerization of several dimerized quantum
Heisenberg models with spatial anisotropy using first principles Monte Carlo
method. Remarkably, while our Monte Carlo data for all the models considered
here, including the herringbone- and ladder-dimer models on the square lattice,
are compatible with the recently proposed scenario of an enhanced correction to
scaling, we find it is likely that the enhanced correction to scaling manifests
itself as amplification of the nonuniversal prefactors appeared in the scaling
forms. In other words, our data are in consistence with the established
numerical values for the critical exponents, including the confluent exponent,
in the O(3) universality class. Convincing numerical evidence is provided to
support this proposed scenario.",1202.1057v2
2012-02-13,Cosmological parameters constraints from galaxy cluster mass function measurements in combination with other cosmological data,"We present the cosmological parameters constraints obtained from the
combination of galaxy cluster mass function measurements (Vikhlinin et al.,
2009a,b) with new cosmological data obtained during last three years: updated
measurements of cosmic microwave background anisotropy with Wilkinson Microwave
Anisotropy Probe (WMAP) observatory, and at smaller angular scales with South
Pole Telescope (SPT), new Hubble constant measurements, baryon acoustic
oscillations and supernovae Type Ia observations.
  New constraints on total neutrino mass and effective number of neutrino
species are obtained. In models with free number of massive neutrinos the
constraints on these parameters are notably less strong, and all considered
cosmological data are consistent with non-zero total neutrino mass \Sigma m_\nu
\approx 0.4 eV and larger than standard effective number of neutrino species,
N_eff \approx 4. These constraints are compared to the results of neutrino
oscillations searches at short baselines.
  The updated dark energy equation of state parameters constraints are
presented. We show that taking in account systematic uncertainties, current
cluster mass function data provide similarly powerful constraints on dark
energy equation of state, as compared to the constraints from supernovae Type
Ia observations.",1202.2889v1
2012-02-16,Transport and magnetic properties of La-doped CaFe$_2$As$_2$,"We measured the transport properties and susceptibility of single crystals
Ca$_{1-x}$La$_x$Fe$_2$As$_2$(x=0, 0.05, 0.1, 0.15, 0.19 and 0.25). Large
in-plane resistivity anisotropy similar to that in Co-doped 122 iron-pnictides
is observed although no transition metals were introduced in the FeAs-plane.
The in-plane resistivity anisotropy gradually increases with La doping below
T$_{SDW}$, being different from the hole-doped 122 superconductors. The
susceptibilities of the samples show that La doping leads to suppression of SDW
and induces a Curie-Weiss-like behavior at low temperature, which is much
stronger than the other 122 iron-based superconductors.",1202.3589v1
2012-02-21,Theoretical studies of 63Cu Knight shifts of the normal state of YBa2Cu3O7,"The 63Cu Knight shifts and g factors for the normal state of YBa2Cu3O7 in
tetragonal phase are theoretically studied in a uniform way from the high
(fourth-) order perturbation formulas of these parameters for a 3d9 ion under
tetragonally elongated octahedra. The calculations are quantitatively
correlated with the local structure of the Cu2+(2) site in YBa2Cu3O7. The
theoretical results show good agreement with the observed values, and the
improvements are achieved by adopting fewer adjustable parameters as compared
to the previous works. It is found that the significant anisotropy of the
Knight shifts is mainly attributed to the anisotropy of the g factors due to
the orbital interactions.",1202.4598v1
2012-02-23,Cross-correlation of WISE Galaxies with the Cosmic Microwave Background,"We estimated the cross-power spectra of a galaxy sample from the Wide-field
Infrared Survey Explorer (WISE) survey with the 7-year Wilkinson Microwave
Anisotropy Probe (WMAP) temperature anisotropy maps. A conservatively-selected
galaxy sample covers ~13000sq.deg, with a median redshift of z=0.15.
Cross-power spectra show correlations between the two data sets with no
discernible dependence on the WMAP Q, V and W frequency bands. We interpret
these results in terms of the the Integrated Sachs-Wolfe (ISW) effect: for the
|b|>20 deg sample at l=6-87, we measure the amplitude (normalized to be 1 for
vanilla LambdaCDM expectation) of the signal to be 3.4+-1.1, i.e., 3.1 sigma
detection. We discuss other possibilities, but at face value, the detection of
the linear ISW effect in a flat universe is caused by large scale decaying
potentials, a sign of accelerated expansion driven by Dark Energy.",1202.5306v1
2012-02-27,"Crystalline anisotropic magnetoresistance with two-fold and eight-fold symmetry in (In,Fe)As ferromagnetic semiconductor","We have investigated the anisotropic magnetoresistance (AMR) of (In,Fe)As
ferromagnetic semiconductor (FMS) layers grown on semi-insulating GaAs
substrates. In a 10 nm-thick (In,Fe)As layer which is insulating at low
temperature, we observed crystalline AMR with two-fold and eight-fold
symmetries. In a metallic 100 nm-thick (In,Fe)As layer with higher electron
concentration, only two-fold symmetric crystalline AMR was observed. Our
results demonstrate the macroscopic ferromagnetism in (In,Fe)As with magnetic
anisotropy that depends on the electron concentration. Non-crystalline AMR is
also observed in the 100 nm-thick layer, but its magnitude is as small as
10^-5, suggesting that there is no s-d scattering near the Fermi level of
(In,Fe)As. We propose the origin of the eight-fold symmetric crystalline
anisotropy in (In,Fe)As.",1202.5874v1
2012-03-01,Step bunching process induced by the flow of steps at the sublimated crystal surface,"Stepped GaN(0001) surface is studied by the kinetic Monte Carlo method and
compared with the model based on Burton-Carbera-Frank equations. Successive
stages of surface pattern evolution during high temperature sublimation process
are discussed. At low sublimation rates clear, well defined step bunches form.
The process happens in the absence or for very low Schwoebel barriers at the
ideal surface. Bunches of several steps are well separated, move slowly and are
rather stiff. Character of the process changes for more rapid sublimation
process where double step formations become dominant and together with meanders
and local bunches assemble into the less ordered surface pattern. Solution of
the analytic equations written for one dimensional system confirms that step
bunching is induced by the particle advection caused by step-flow anisotropy.
This anisotropy becomes important when due to the low Schwoebel barrier both
sides of step are symmetric. Simulations show that in the opposite limit of
very high Schwoebel barrier steps fracture and rough surface builds up.",1203.0194v1
2012-03-01,Revisiting Cosmic No-Hair Theorem for Inflationary Settings,"In this work we revisit Wald's cosmic no-hair theorem in the context of
accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing
anisotropic stress tensor and when the fluid energy momentum tensor is of the
form of a cosmological constant term plus a piece which does not respect strong
or dominant energy conditions. Such a fluid is the one appearing in
inflationary models. We show that for such a system anisotropy may grow, in
contrast to the cosmic no-hair conjecture. In particular, for a generic
inflationary model we show that there is an upper bound on the growth of
anisotropy. For slow-roll inflationary models our analysis can be refined
further and the upper bound is found to be of the order of slow-roll
parameters. We examine our general discussions and our extension of Wald's
theorem for three classes of slow-roll inflationary models, generic
multi-scalar field driven models, anisotropic models involving U(1) gauge
fields and the gauge-flation scenario.",1203.0219v2
2012-03-01,Parity Violating Statistical Anisotropy,"Particle production of an Abelian vector boson field with an axial coupling
is investigated. The conditions for the generation of scale invariant spectra
for the vector field transverse components are obtained. If the vector field
contributes to the curvature perturbation in the Universe, scale-invariant
particle production enables it to give rise to statistical anisotropy in the
spectrum and bispectrum of cosmological perturbations. The axial coupling
allows particle production to be parity violating, which in turn can generate
parity violating signatures in the bispectrum. The conditions for parity
violation are derived and the observational signatures are obtained in the
context of the vector curvaton paradigm. Two concrete examples are presented
based on realistic particle theory.",1203.0230v3
2012-03-02,Investigation of Optical Spin Transfer Torque in Ferromagnetic Semiconductor GaMnAs by Magneto-Optical Pump-and-Probe Method,"We report on magnetization precession induced in (Ga,Mn)As by an optical spin
transfer torque (OSTT). This phenomenon, which corresponds to a transfer of
angular momentum from optically-injected spin-polarized electrons to
magnetization, was predicted theoretically in 2004 and observed experimentally
by our group in 2012. In this paper we provide experimental details about the
observation of OSTT by a time-resolved pump-and-probe magneto-optical
technique. In particular, we show that the precession of magnetization due to
OSTT can be experimentally separated from that induced by the well known
magnetic-anisotropy-related mechanism in a hybrid structure
piezo-stressor/(Ga,Mn)As with an in situ electrical control of the magnetic
anisotropy. We also illustrate that OSTT is clearly apparent in the measured
dynamical magneto-optical signal in a large variety of (Ga,Mn)As samples with a
Mn concentration from 3% to 9%.",1203.0483v1
2012-03-12,Spin gating electrical current,"We use an aluminium single electron transistor with a magnetic gate to
directly quantify the chemical potential anisotropy of GaMnAs materials.
Uniaxial and cubic contributions to the chemical potential anisotropy are
determined from field rotation experiments. In performing magnetic field sweeps
we observe additional isotropic magnetic field dependence of the chemical
potential which shows a non-monotonic behavior. The observed effects are
explained by calculations based on the $\mathbf{k}\cdot\mathbf{p}$ kinetic
exchange model of ferromagnetism in GaMnAs. Our device inverts the conventional
approach for constructing spin transistors: instead of spin-transport
controlled by ordinary gates we spin-gate ordinary charge transport.",1203.2439v2
2012-03-19,A survey of lens spaces and large-scale CMB anisotropy,"The cosmic microwave background (CMB) anisotropy possesses the remarkable
property that its power is strongly suppressed on large angular scales. This
observational fact can naturally be explained by cosmological models with a
non-trivial topology. The paper focuses on lens spaces L(p,q) which are
realised by a tessellation of the spherical 3-space S^3 by cyclic deck groups
of order p<=72. The investigated cosmological parameter space covers the
interval Omega_tot \in [1.001,1.05]. Several spaces are found which have CMB
correlations on angular scales theta >= 60^\circ suppressed by a factor of two
compared to the simply connected S^3 space. The analysis is based on the S
statistics, and a comparison to the WMAP 7yr data is carried out. Although the
CMB suppression is less pronounced than in the Poincare dodecahedral space,
these lens spaces provide an alternative worth for follow-up studies.",1203.4086v2
2012-03-19,Anisotropy induced Feshbach resonances in a quantum dipolar gas of magnetic atoms,"We explore the anisotropic nature of Feshbach resonances in the collision
between ultracold magnetic submerged-shell dysprosium atoms, which can only
occur due to couplings to rotating bound states. This is in contrast to
well-studied alkali-metal atom collisions, where most Feshbach resonances are
hyperfine induced and due to rotation-less bound states. Our novel
first-principle coupled-channel calculation of the collisions between
open-4f-shell spin-polarized bosonic dysprosium reveals a striking correlation
between the anisotropy due to magnetic dipole-dipole and electrostatic
interactions and the Feshbach spectrum as a function of an external magnetic
field. Over a 20 mT magnetic field range we predict about a dozen Feshbach
resonances and show that the resonance locations are exquisitely sensitive to
the dysprosium isotope.",1203.4172v1
2012-03-22,Enhanced anisotropic spin fluctuations below tetragonal-to-orthorhombic transition in LaFeAs(O_{1-x}F_x) probed by ^{75}As and ^{139}La NMR,"$^{75}$As and $^{139}$La NMR results of LaFeAs(O$_{1-x}$F$_x$) ($x$=0, 0.025,
and 0.04) were reported. Upon F-doping, the tetragonal-to-orthorhombic
structural phase transition temperature $T_S$, antiferromagnetic transition
temperature $T_N$ and internal magnetic field $\mu_0H_{\rm int}$ are gradually
reduced for $x<0.04$. However, at $x=0.04$, $T_N$ is abruptly suppressed to be
30 K along with a tiny $\mu_0H_{\rm int}$, which is distinct from the
continuous disappearance of the ordered phases in the Ba122 systems of
Ba(Fe,Co)$_2$As$_2$ and BaFe$_2$(As,P)$_2$. The anisotropy of the spin-lattice
relaxation rate $T_1^{-1}$, $(T_1)^{-1}_{H\parallel ab}/(T_1)^{-1}_{H\parallel
c}$, in the paramagnetic phase of $x = 0$ and 0.025 is constant ($\sim 1.5$),
but increases abruptly below $T_S$ due to the enhancement of
$(T_1)^{-1}_{H\parallel ab}$ by the slowing down of magnetic fluctuations. This
indicates that the tetragonal-to-orthorhombic structural distortion enhances
the anisotropy in the spin space via magnetoelastic coupling and/or spin-orbit
interaction.",1203.4937v1
2012-03-22,Pair density waves and vortices in an elongated two-component Fermi gas,"We study the vortex structures of a two-component Fermi gas experiencing a
uniform effective magnetic field in an anisotropic trap that interpolates
between quasi-one dimensional (1D) and quasi-two dimensional (2D). At a fixed
chemical potential, reducing the anisotropy (or equivalently increasing the
attractive interactions or increasing the magnetic field) leads to
instabilities towards pair density waves, and vortex lattices. Reducing the
chemical potential stabilizes the system. We calculate the phase diagram, and
explore the density and pair density. The structures are similar to those
predicted for superfluid Bose gases. We further calculate the paired fraction,
showing how it depends on chemical potential and anisotropy.",1203.5120v1
2012-03-29,Superconducting critical field far above the Pauli limit in one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$,"The upper critical field $H_{c2}$ of purple bronze Li$_{0.9}$Mo$_6$O$_{17}$
is found to exhibit a large anisotropy, in quantitative agreement with that
expected from the observed electrical resistivity anisotropy. With the field
aligned along the most conducting axis, $H_{c2}$ increases monotonically with
decreasing temperature to a value five times larger than the estimated
paramagnetic pair-breaking field. Theories for the enhancement of $H_{c2}$
invoking spin-orbit scattering or strong-coupling superconductivity are shown
to be inadequate in explaining the observed behavior, suggesting that the
pairing state in Li$_{0.9}$Mo$_6$O$_{17}$ is unconventional and possibly
spin-triplet.",1203.6672v1
2012-04-01,Reconstruction of a Nonminimal Coupling Theory with Scale-invariant Power Spectrum,"A nonminimal coupling single scalar field theory, when transformed from
Jordan frame to Einstein frame, can act like a minimal coupling one. Making use
of this property, we investigate how a nonminimal coupling theory with
scale-invariant power spectrum could be reconstructed from its minimal coupling
counterpart, which can be applied in the early universe. Thanks to the coupling
to gravity, the equation of state of our universe for a scale-invariant power
spectrum can be relaxed, and the relation between the parameters in the action
can be obtained. This approach also provides a means to address the Big-Bang
puzzles and anisotropy problem in the nonminimal coupling model within Jordan
frame. Due to the equivalence between the two frames, one may be able to find
models that are free of the horizon, flatness, singularity as well as
anisotropy problems.",1204.0189v2
2012-04-02,A needlet ILC analysis of WMAP 9-year polarisation data: CMB polarisation power spectra,"We estimate Cosmic Microwave Background (CMB) polarisation power spectra, and
temperature-polarisation cross-spectra, from the 9-year data of the Wilkinson
Microwave Anisotropy Probe (WMAP). Foreground cleaning is implemented using
minimum variance linear combinations of the coefficients of needlet
decompositions of sky maps for all WMAP channels, to produce maps for CMB
temperature anisotropies (T-mode) and polarisation (E-mode and B-mode), for 9
different years of observation. The final power spectra are computed from
averages of all possible cross-year power spectra obtained using
foreground-cleaned maps for the different years. Our analysis technique yields
a measurement of the EE spectrum that is in excellent agreement with
theoretical expectations from the current cosmological model. By comparison,
the publicly available WMAP EE power spectrum is higher on average (and
significantly higher than the predicted EE spectrum from the current best fit)
at scales larger than about a degree, an excess that is not confirmed by our
analysis.",1204.0292v2
2012-04-10,In-plane magnetic field anisotropy of the FFLO state in layered superconductors,"There are strong experimental evidences of the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state formation in layered organic
superconductors in parallel magnetic field. We study theoretically the
interplay between the orbital effect and the FFLO modulation in this case and
demonstrate that the in-plane critical field anisotropy drastically changes at
the transition to the FFLO state. The very peculiar angular dependence of the
superconducting onset temperature which is predicted may serve for unambiguous
identification of the FFLO modulation. The obtained results permit us to
suggest the modulated phase stabilization as the origin of the magnetic-field
angle dependence of the onset of superconductivity experimentally observed in
(TMTSF)$_{2}$ClO$_{4}$ organic conductors.",1204.2287v1
2012-04-12,Highly-anisotropic hydrodynamics in 3+1 space-time dimensions,"Recently formulated model of highly-anisotropic and strongly dissipative
hydrodynamics is used in 3+1 dimensions to study behavior of matter produced in
ultra-relativistic heavy-ion collisions. We search for possible effects of the
initial high anisotropy of pressure on the final soft-hadronic observables. We
find that by appropriate adjustment of the initial energy density and/or the
initial pseudorapidity distributions, the effects of the initial anisotropy of
pressure may be easily compensated and the final hadronic observables become
insensitive to early dynamics. Our results indicate that the early
thermalization assumption is not necessary to describe hadronic data, in
particular, to reproduce the measured elliptic flow v_2. The complete
thermalization of matter (local equilibration) may take place only at the times
of about 1-2 fm/c, in agreement with the results of microscopic models.",1204.2624v1
2012-04-19,High intergrain critical current density in fine-grain (Ba0.6K0.4)Fe2As2 wires and bulks,"The K- and Co-doped BaFe2As2 (Ba-122) superconducting compounds are
potentially useful for applications because they have upper critical fields
(Hc2) of well over 50 T, Hc2 anisotropy Gamma < 2, and thin film critical
current densities exceeding 1 MAcm-2 at 4.2 K. However, thin-film bicrystals of
Co-doped Ba-122 clearly exhibit weak link behavior for [001] tilt
misorientations of more than about 5 degrees, suggesting that textured
substrates would be needed for applications, as in the cuprates. Here we
present a contrary and very much more positive result in which untextured
polycrystalline (Ba0.6K0.4)Fe2As2 bulks and round wires with high grain
boundary density have transport critical current densities well over 0.1 MAcm-2
(SF, 4.2 K), more than 10 times higher than that of any other ferropnictide
wire. The enhanced grain connectivity is ascribed to their much improved phase
purity and to the enhanced vortex stiffness of this low-anisotropy compound
(Gamma ~ 1-2) compared to YBa2Cu3O7-x (Gamma ~ 5).",1204.4426v3
2012-04-22,Scanning Tunneling Microscopy/Spectroscopy of Vortices in LiFeAs,"We investigate vortices in LiFeAs using scanning tunneling
microscopy/spectroscopy. Zero-field tunneling spectra show two superconducting
gaps without detectable spectral weight near the Fermi energy, evidencing
fully-gapped multi-band superconductivity. We image vortices in a wide field
range from 0.1 T to 11 T by mapping the tunneling conductance at the Fermi
energy. A quasi-hexagonal vortex lattice at low field contains domain
boundaries which consist of alternating vortices with unusual coordination
numbers of 5 and 7. With increasing field, the domain boundaries become
ill-defined, resulting in a uniformly disordered vortex matter. Tunneling
spectra taken at the vortex center are characterized by a sharp peak just below
the Fermi energy, apparently violating particlehole symmetry. The image of each
vortex shows energy-dependent 4-fold anisotropy which may be associated with
the anisotropy of the Fermi surface. The vortex radius shrinks with decreasing
temperature and becomes smaller than the coherence length estimated from the
upper critical field. This is direct evidence of the Kramer-Pesch effect
expected in a clean superconductor.",1204.4863v1
2012-04-26,Anisotropic flows from colour strings: Monte-Carlo simulations,"By direct Monte-Carlo simulations it is shown that the anisotropic flows can
be successfully described in the colour string picture with fusion and
percolation provided anisotropy of particle emission from the fused string is
taken into account. Quenching of produced particles in the strong colour field
of the string is the basic mechanism for this anisotropy. The concrete
realization of this mechanism is borrowed from the QED. Due to dependence of
this mechanism on the external field strength the found flows grow with energy,
with values for $v_2$ at LHC energies greater by ~15% than at RHIC energies.",1204.5829v2
2012-05-01,On geometry-dependent vortex stability and topological spin excitations on curved surfaces with cylindrical symmetry,"We study the Heisenberg Model on cylindrically symmetric curved surfaces. Two
kinds of excitations are considered. The first is given by the isotropic
regime, yielding the sine-Gordon equation and $\pi$-solitons are predicted. The
second one is given by the XY model, leading to a vortex turning around the
surface. Helical states are also considered, however, topological arguments can
not be used to ensure its stability. The energy and the anisotropy parameter
which stabilizes the vortex state are explicitly calculated for two surfaces:
catenoid and hyperboloid. The results show that the anisotropy and the vortex
energy depends on the underlying geometry.",1205.0287v5
2012-05-02,Enhanced magnetic anisotropy of Nickel nanosheet prepared in Na-4 mica,"Nanosheets of nickel with thickness equal to 0.6 nm have been grown within
the interlayer spaces of Na-4 mica. The sheets are made up of percolative
clusters of nanodisks. Magnetization characteristics indicate a
superparamagnetic behavior with a blocking temperature of 428 K.The magnetic
anisotropy constant as extracted from the coercivity data has been found to be
higher than that of bulk nickel by two orders of magnitude. This is ascribed to
a large aspect ratio of the nickel nanophase. The Bloch exponent is also found
to be considerably different from that of bulk nickel because of a size effect.
The Bloch Equation is still found to be valid for the two dimensional
structures.",1205.0405v1
2012-05-03,Interpreting Magnetic Variance Anisotropy Measurements in the Solar Wind,"The magnetic variance anisotropy ($\mathcal{A}_m$) of the solar wind has been
used widely as a method to identify the nature of solar wind turbulent
fluctuations; however, a thorough discussion of the meaning and interpretation
of the $\mathcal{A}_m$ has not appeared in the literature. This paper explores
the implications and limitations of using the $\mathcal{A}_m$ as a method for
constraining the solar wind fluctuation mode composition and presents a more
informative method for interpreting spacecraft data. The paper also compares
predictions of the $\mathcal{A}_m$ from linear theory to nonlinear turbulence
simulations and solar wind measurements. In both cases, linear theory compares
well and suggests the solar wind for the interval studied is dominantly
Alfv\'{e}nic in the inertial and dissipation ranges to scales $k \rho_i \simeq
5$.",1205.0749v1
2012-05-11,Cosmic Microwave and Infrared Backgrounds cross-correlation for ISW detection,"We investigate the cross-correlation between the cosmic infrared and
microwave backgrounds (CIB & CMB) anisotropies through the integrated
Sachs-Wolfe effect. We first describe the CIB anisotropies using a linearly
biased power spectrum, then derive the theoretical angular power spectrum of
the CMB-CIB cross-correlation for different instruments and frequencies. We
discuss the detectability of the ISW signal by performing a signal-to-noise
(SNR) analysis with our predicted spectra. The significances obtained range
from 6{\sigma} to 7{\sigma} in an ideal case, depending on the frequency ; in
realistic cases which account for the presence of noise including astrophysical
contaminants, the results span the range 2-5{\sigma}, depending strongly on the
major contribution to the noise term.",1205.2537v1
2012-05-16,"Piezoelectric strain induced variation of the magnetic anisotropy in a high Curie temperature (Ga,Mn)As sample","We show that effective electrical control of the magnetic properties in the
ferromagnetic semiconductor (Ga,Mn)As is possible using the strain induced by a
piezoelectric actuator even in the limit of high doping levels and high Curie
temperatures, where direct electric gating is not possible. We demonstrate very
large and reversible rotations of the magnetic easy axis. We compare the
results obtained from magneto-transport and SQUID magnetometry measurements,
extracting the dependence of the piezo-induced uniaxial magnetic anisotropy
constant upon strain in both cases and detailing the limitations encountered in
the latter approach.",1205.3725v1
2012-05-21,Charge Multiplicity Asymmetry Correlation Study Searching for Local Parity Violation at RHIC for STAR,"It has been suggested that local parity violation in QCD would lead to charge
separation of quarks by the Chiral Magnetic Effect (CME) in heavy ion
collisions. Charge separation could yield a dynamical charge multiplicity
asymmetry with respect to the reaction plane. In this talk, we report results
on charge multiplicity asymmetry correlations in $\sqrt{s_{NN}}$ = 200 GeV
Au+Au and d+Au collisions by the STAR experiment, as well as from the RHIC beam
energy scan. We found that the correlation results could not be explained by
CME alone. To gain further insights, we study our results as a function of the
measured azimuthal angle range as well as the event-by-event anisotropy
parameter $v_2$. The results indicate that the charge separation effect appears
to be in-plane rather than out-of-plane. We found that the charge separation
effect is proportional to the event-by-event $v_2$ and consistent with zero in
events with $v_2 \approx 0$. Our studies suggest that the charge separation
effect, within the statistical error, may be a net effect of event anisotropy
and correlated particle production. Possible upper limit on the CME imposed by
our data will be discussed.",1205.4638v1
2012-05-21,Probing Two Holographic Models of Strongly Coupled Anisotropic Plasma,"Quark-gluon plasma during its initial phase after its production in heavy-ion
collisions is expected to have substantial pressure anisotropies. In order to
model this situation by a strongly coupled N=4 super-Yang-Mills plasma with
fixed anisotropy by means of AdS/CFT duality, two models have been discussed in
the literature. Janik and Witaszczyk have considered a geometry involving a
comparatively benign naked singularity, while more recently Mateos and
Trancanelli have used a regular geometry involving a nontrivial axion field
dual to a parity-odd deformation of the gauge theory by a spatially varying
theta parameter. We study the (rather different) implications of these two
models on the heavy-quark potential as well as jet quenching and compare their
respective predictions with those of weakly coupled anisotropic plasmas.",1205.4684v2
2012-05-22,How to remedy the eta-problem of SUSY GUT hybrid inflation via vector backreaction,"It is shown that, in supergravity models of inflation where the gauge kinetic
function of a gauge field is modulated by the inflaton, we can obtain a new
inflationary attractor solution, in which the roll-over of the inflaton suffers
additional impedance due to the vector field backreaction. As a result,
directions of the scalar potential which, due to strong Kaehler corrections,
become too steep and curved to normally support slow-roll inflation can now
naturally do so. This solves the infamous eta-problem of inflation in
supergravity and also keeps the spectral index of the curvature perturbation
mildly red despite eta of order unity. This mechanism is applied to a model of
hybrid inflation in supergravity with a generic Kaehler potential. The spectral
index of the curvature perturbation is found to be 0.97 - 0.98, in excellent
agreement with data. The gauge field can act as vector curvaton generating
statistical anisotropy in the curvature perturbation. However, this anisotropy
could be possibly observable only if the gauge coupling constant is unnaturally
small.",1205.4830v1
2012-05-29,Spin excitations in K$_{2}$Fe$_{4+x}$Se$_{5}$: linear response approach,"Using \emph{ab initio} linear response techniques we calculate spin wave
spectra in K$_{2}$Fe$_{4+x}$Se$_{5}$, and find it to be in excellent agreement
with a recent experiment. The spectrum can be alternatively described rather
well by localized spin Hamiltonian restricted to first and second nearest
neighbor couplings. We confirm that exchange coupling between nearest neighbor
Fe magnetic moments is strongly anisotropic, and show directly that in the
ideal system this anisotropy has itinerant nature which can be imitated by
introducing higher order terms in effective localized spin Hamiltonian
(biquadratic coupling). In the real system, structural relaxation provides an
additional source of the exchange anisotropy of approximately the same
magnitude. The dependence of spin wave spectra on filling of Fe vacancy sites
is also discussed.",1205.6404v1
2012-05-30,Continuous Move From BTW to Manna Model,"In the present paper we consider the BTW model perturbed by random-direction
anisotropy with strength factor \epsilon ranging from 0 to 1 corresponding to
BTW and Manna model receptively and investigate the properties of the
statistical observables for various rates of anisotropy. By increasing the
\epsilon, we observe a cross-over taking place between these models. For small
length scales, the curves show properties similar to the BTW model whereas in
the Infra red limit the corresponding \kappa is nearly the same as the Manna
model. The observations confirm that this perturbation is relevant for the BTW
fixed point and the infra red limit of the perturbed model is described by the
Manna model. We also propose a differential equation whose solution properly
fits with the the Green's function obtained by the simulation. This can help us
to obtain the action of the perturbed model.",1205.6645v1
2012-05-30,Unified decoupling scheme for exchange and anisotropy contributions and temperature-dependent spectral properties of anisotropic spin systems,"We compute the temperature-dependent spin-wave spectrum and the magnetization
for a spin system using the unified decoupling procedure for the high-order
Green's functions for the exchange coupling and anisotropy, both in the
classical and quantum case. Our approach allows us to establish a clear
crossover between quantum-mechanical and classical methods by developing the
classical analog of the quantum Green's function technique. The results are
compared with the classical spectral density method and numerical modeling
based on the stochastic Landau-Lifshitz equation and the Monte Carlo technique.
As far as the critical temperature is concerned, there is a full agreement
between the classical Green's functions technique and the classical spectral
density method. However, the former method turns out to be more straightforward
and more convenient than the latter because it avoids any \emph{a priori}
assumptions about the system's spectral density. The temperature-dependent
exchange stiffness as a function of magnetization is investigated within
different approaches.",1205.6646v1
2012-05-30,Tunable Charge and Spin Seebeck Effects in Magnetic Molecular Junctions,"We study the charge and spin Seebeck effects in a spin-1 molecular junction
as a function of temperature (T), applied magnetic field (H), and magnetic
anisotropy (D) using Wilson's numerical renormalization group. A hard-axis
magnetic anisotropy produces a large enhancement of the charge Seebeck
coefficient Sc (\sim k_B/|e|) whose value only depends on the residual
interaction between quasiparticles in the low temperature Fermi-liquid regime.
In the underscreened spin-1 Kondo regime, the high sensitivity of the system to
magnetic fields makes it possible to observe a sizable value for the spin
Seebeck coefficient even for magnetic fields much smaller than the Kondo
temperature. Similar effects can be obtain in C60 junctions where the control
parameter is the gap between a singlet and a triplet molecular state.",1205.6759v1
2012-06-04,Electrostatically Controlled Magnetization Rotation in Ferromagnet-Topological Insulator Planar Structures,"An approach to the electrostatic control of $90^{\circ}$ magnetization
rotation in the hybrid structures composed of topological insulators (TIs) and
adjacent ferromagnetic insulators (FMI) is proposed and studied. The concept is
based on TI electron energy variation with in-plane to put-of plane FMI
magnetization turn. The calculations explicitly expose the effect of free
energy variability in the form of the electrically controlled uniaxial magnetic
anisotropy, which depends on proximate exchange interaction and TI surface
electron density. Combining with inherent anisotropy, the magnetization
rotation from in-plane to out-of-plane direction is shown to be realizable for
1.7~2.7 ns under the electrical variation of TI chemical potential in the range
$\pm$ 100 meV around Dirac point. When bias is withdrawn a small signal current
can target the out-of-plane magnetization instable state to the desirable
direction of in-plane easy axis, thus the structure can lay the foundation for
low energy nonvolatile memory prototype.",1206.0776v1
2012-06-05,Spin-Orbit Coupling in LaAlO$_3$/SrTiO$_3$ interfaces: Magnetism and Orbital Ordering,"The combination of Rashba spin-orbit coupling and electron correlations can
induce unusual phenomena in the metallic interface between SrTiO$_3$ and
LaAlO$_3$. We consider effects of Rashba spin-orbit coupling at this interface
in the context of the recent observation of anisotropic magnetism. Firstly, we
show how Rashba spin-orbit coupling in a system near a band-edge can account
for the observed magnetic anisotropy. Secondly, we investigate the coupling
between in-plane magnetic-moment anisotropy and nematicity in the form of an
orbital imbalance between d$_{xz}$ / d$_{yz}$ orbitals. We estimate this
coupling to be substantial in the low electron density regime. Such an orbital
ordering can affect magneto transport.",1206.1060v2
2012-06-06,Preliminary Investigation of the Frictional Response of Reptilian Shed Skin,"Developing deterministic surfaces relies on controlling the structure of the
rubbing interface so that not only the surface is of optimized topography, but
also is able to self-adjust its tribological behaviour according to the
evolution of sliding conditions. In seeking inspirations for such designs, many
engineers are turning toward the biological world to correlate surface
structure to functional behavior of bio-analogues. From a tribological point of
view, squamate reptiles offer diverse examples where surface texturing,
submicron and nano-scale features, achieve frictional regulation. In this
paper, we study the frictional response of shed skin obtained from a snake
(Python regius). The study employed a specially designed tribo-acoustic probe
capable of measuring the coefficient of friction and detecting the acoustical
behavior of the skin in vivo. The results confirm the anisotropy of the
frictional response of snakes. The coefficient of friction depends on the
direction of sliding: the value in forward motion is lower than that in the
backward direction. In addition it is shown that the anisotropy of the
frictional response may stem from profile asymmetry of the individual fibril
structures present within the ventral scales of the reptile",1206.1153v1
2012-06-07,Magnetic particle hyperthermia: Power losses under circularly polarized field in anisotropic nanoparticles,"The deterministic Landau-Lifshitz-Gilbert equation has been used to
investigate the nonlinear dynamics of magnetization and the specific loss power
in magnetic nanoparticles with uniaxial anisotropy driven by a rotating
magnetic field, generalizing the results obtained for the isotropic case found
in [P. F. de Chatel, I. Nandori, J. Hakl, S. Meszaros and K. Vad, J. Phys.:
Condens. Matter 21, 124202 (2009)]. As opposed to many applications of
magnetization reversal in single-domain ferromagnetic particles where losses
must be minimized, in this paper, we study the mechanisms of dissipation used
in cancer therapy by hyperthermia which requires the enhancement of energy
losses. We show that for circularly polarized field, the loss energy per cycle
is decreased by the anisotropy compared to the isotropic case when only
dynamical effects are taken into account. Thus, in this case, in the low
frequency limit, a better heating efficiency can be achieved for isotropic
nanoparticles. The possible role of thermal fluctuations is also discussed.
Results obtained are compared to experimental data.",1206.1544v2
2012-06-18,Thermoelectric transport in $\text{Bi}_2\text{Te}_3/\text{Sb}_2\text{Te}_3$ superlattices,"The thermoelectric transport properties of
$\text{Bi}_2\text{Te}_3/\text{Sb}_2\text{Te}_3$superlattices are analyzed on
the basis of first-principles calculations and semi-classical Boltzmann theory.
The anisotropy of the thermoelectric transport under electron and hole-doping
was studied in detail for different superlattice periods at changing
temperature and charge carrier concentrations. A clear preference for
thermoelectric transport under hole-doping, as well as for the in-plane
transport direction was found for all superlattice periods. At hole-doping the
electrical transport anisotropies remain bulk-like for all investigated
systems, while under electron-doping quantum confinement leads to strong
suppression of the cross-plane thermoelectric transport at several superlattice
periods. In addition, insights on the Lorenz function, the electronic
contribution to the thermal conductivity and the resulting figure of merit are
given.",1206.4078v1
2012-06-19,Anisotropic magnetoresistance of bulk carbon nanotube sheets,"We have measured the magnetoresistance of stretched sheets of carbon
nanotubes in temperatures ranging from 2 K to 300 K and in magnetic fields up
to 9 T, oriented either perpendicular or parallel to the plane of the sheets.
The samples have been partially aligned by post-fabrication stretching, such
that the direction of stretching was either parallel or perpendicular to the
direction of applied electric current. We have observed large differences
between the magnetoresistance measured under the two field orientations, most
pronounced at the lowest temperatures, highest fields, and for the
laterally-aligned sample. Treatment of the sheets with nitric acid affects this
anisotropy. We analyzed the results within the theoretical framework of weak
and strong localization and concluded that the anisotropy bears the mark of a
more unusual phenomenon, possibly magnetically-induced mechanical strain.",1206.4252v1
2012-06-20,Spin Hall Conductivity on the Anisotropic Triangular Lattice,"We present a detailed study of the spin Hall conductivity on a
two-dimensional triangular lattice in the presence of Rashba spin-orbit
coupling. In particular, we focus part of our attention on the effect of the
anisotropy of the nearest neighbor hopping amplitude. It is found that the
presence of anisotropy has drastic effects on the spin Hall conductivity,
especially in the hole doped regime where a significant increase or/and
reversed sign of the spin Hall conductivity has been obtained. We also provide
a systematic analysis of the numerical results in terms of Berry phases. The
changes of signs observed at particular density of carriers appear to be a
consequence of both Fermi surface topology and change of sign of electron
velocity. In addition, in contrast to the two-dimensional square lattice, it is
shown that the tight binding spin-orbit Hamiltonian should be derived carefully
from the continuous model on the triangular lattice.",1206.4537v1
2012-06-21,Late time anisotropy as an imprint of cosmological backreaction,"Backreaction effects of the large scale structure on the background dynamics
have been claimed to lead to a renormalization of the background dynamics that
may account for the late time acceleration of the cosmic expansion. This
article emphasizes that generically the averaged flow is locally anisotropic, a
property that can be related to observation. Focusing on perturbation theory,
the spatially averaged shear, that characterizes the anisotropy of the flow, is
computed. It is shown that this shear arising from backreaction differs from a
homogeneous shear: its time evolution is different and its amplitude is
completely determined by the cosmological parameters and the matter power
spectrum. It ranges within (2-37)% at a redshift of order 0.5 so that the
isotropy of the Hubble flow may allow to constrain the backreaction approach to
dark energy.",1206.4887v3
2012-06-21,Direct Observation of Massless Domain Wall Dynamics in Nanostripes with Perpendicular Magnetic Anisotropy,"Domain wall motion induced by nanosecond current pulses in nanostripes with
perpendicular magnetic anisotropy (Pt/Co/AlO$_x$) is shown to exhibit
negligible inertia. Time-resolved magnetic microscopy during current pulses
reveals that the domain walls start moving, with a constant speed, as soon as
the current reaches a constant amplitude, and no or little motion takes place
after the end of the pulse. The very low 'mass' of these domain walls is
attributed to the combination of their narrow width and high damping parameter
$\alpha$. Such a small inertia should allow accurate control of domain wall
motion, by tuning the duration and amplitude of the current pulses.",1206.4967v1
2012-06-26,Temperature dependence of electronic transport through molecular magnets in the Kondo regime,"The effects of finite temperature in transport through nanoscopic systems
exhibiting uniaxial magnetic anisotropy D, such as molecular magnets, adatoms,
or quantum dots side-coupled to a large spin are analyzed in the Kondo regime.
The linear-response conductance is calculated by means of the full
density-matrix numerical renormalization group method as a function of
temperature T, magnetic anisotropy D, and exchange coupling J between the
molecule's core spin and the orbital level. It is shown that such system
displays a two-stage Kondo effect as a function of temperature and a quantum
phase transition as a function of the exchange coupling J. Moreover, additional
peaks are found in the linear conductance for temperatures of the order of
T\sim|J| and T\simD. It is also shown that the conductance variation with T
remarkably depends on the sign of the exchange coupling J.",1206.6069v2
2012-06-27,Theoretical Analysis of Electronic and Magnetic Properties of NaV$_2$O$_4$: Crucial Role of the Orbital Degrees of Freedom,"Using realistic low-energy model with parameters derived from the
first-principles electronic structure calculation, we address the origin of the
quasi-one-dimensional behavior in orthorhombic NaV$_2$O$_4$, consisting of the
double chains of edge-sharing VO$_6$ octahedra. We argue that the geometrical
aspect alone does not explain the experimentally observed anisotropy of
electronic and magnetic properties of NaV$_2$O$_4$. Instead, we attribute the
unique behavior of NaV$_2$O$_4$ to one particular type of the orbital ordering,
which respects the orthorhombic $Pnma$ symmetry. This orbital ordering acts to
divide all $t_{2g}$ states into two types: the `localized' ones, which are
antisymmetric with respect to the mirror reflection $y \rightarrow -$$y$, and
the symmetric `delocalized' ones. Thus, NaV$_2$O$_4$ can be classified as the
double exchange system. The directional orientation of symmetric orbitals,
which form the metallic band, appears to be sufficient to explain both
quasi-one-dimensional character of interatomic magnetic interactions and the
anisotropy of electrical resistivity.",1206.6525v1
2012-06-28,Reentrant phase transitions and multicompensation points in the mixed-spin Ising ferrimagnet on a decorated Bethe lattice,"Mixed-spin Ising model on a decorated Bethe lattice is rigorously solved by
combining the decoration-iteration transformation with the method of exact
recursion relations. Exact results for critical lines, compensation
temperatures, total and sublattice magnetizations are obtained from a precise
mapping relationship with the corresponding spin-1/2 Ising model on a simple
(undecorated) Bethe lattice. The effect of next-nearest-neighbour interaction
and single-ion anisotropy on magnetic properties of the ferrimagnetic model is
investigated in particular. It is shown that the total magnetization may
exhibit multicompensation phenomenon and the critical temperature vs. the
single-ion anisotropy dependence basically changes with the coordination number
of the underlying Bethe lattice. The possibility of observing reentrant phase
transitions is related to a high enough coordination number of the underlying
Bethe lattice.",1206.6684v1
2012-07-04,D3/D7 Quark-Gluon Plasma with Magnetically Induced Anisotropy,"We study the effects of the temperature and of a magnetic field in the setup
of an intersection of D3/D7 branes, where a large number of D7 branes is
smeared in the transverse directions to allow for a perturbative solution in a
backreaction parameter. The magnetic field sources an anisotropy in the plasma,
and we investigate its physical consequences for the thermodynamics and energy
loss of particles probing the system. In particular we comment on the
stress-energy tensor of the plasma, the propagation of sound in the directions
parallel and orthogonal to the magnetic field, the drag force of a quark moving
through the medium and jet quenching.",1207.1047v2
2012-07-18,Cosmic Topology of Polyhedral Double-Action Manifolds,"A special class of non-trivial topologies of the spherical space S^3 is
investigated with respect to their cosmic microwave background (CMB)
anisotropies. The observed correlations of the anisotropies on the CMB sky
possess on large separation angles surprising low amplitudes which might be
naturally be explained by models of the Universe having a multiconnected
spatial space. We analysed in CQG 29(2012)215005 the CMB properties of prism
double-action manifolds that are generated by a binary dihedral group D^*_p and
a cyclic group Z_n up to a group order of 180. Here we extend the CMB analysis
to polyhedral double-action manifolds which are generated by the three binary
polyhedral groups (T^*, O^*, I^*) and a cyclic group Z_n up to a group order of
1000. There are 20 such polyhedral double-action manifolds. Some of them turn
out to have even lower CMB correlations on large angles than the Poincare
dodecahedron.",1207.4378v2
2012-08-06,Event-plane decorrelation over pseudo-rapidity and its effect on azimuthal anisotropy measurement in relativistic heavy-ion collisions,"Within A Multi-Phase Transport model, we investigate decorrelation of event
planes over pseudorapidity and its effect on azimuthal anisotropy measurements
in relativistic heavy-ion collisions. The decorrelation increases with
increasing {\eta} gap between particles used to reconstruct the event planes.
The third harmonic event planes are found even anticorrelated between forward
and backward rapidities, the source of which may root in the opposite
orientation of the collision geometry triangularities. The decorrelation may
call into question the anisotropic flow measurements with pseudorapidity gap
designed to reduce nonflow contributions, hence the hydrodynamic properties of
the quark-gluon plasma extracted from those measurements.",1208.1195v2
2012-08-07,Anisotropic electrical resistivity of LaFeAsO: evidence for electronic nematicity,"Single crystals of LaFeAsO were successfully grown out of KI flux.
Temperature dependent electrical resistivity was measured with current flow
along the basal plane, \rho_perpend(T), as well as with current flow along the
crystallographic c-axis, \rho_parallel(T), the latter one utilizing electron
beam lithography and argon ion beam milling. The anisotropy ratio was found to
lie between \rho_parallel/\rho_perpend = 20 - 200. The measurement of
\rho_perpend(T) was performed with current flow along the tetragonal [1 0 0]
direction and along the [1 1 0] direction and revealed a clear in-plane
anisotropy already at T \leq 175 K. This is significantly above the
orthorhombic distortion at T_0 = 147 K and indicates the formation of an
electron nematic phase. Magnetic susceptibility and electrical resistivity give
evidence for a change of the magnetic structure of the iron atoms from
antiferromagnetic to ferromagnetic arrangement along the c-axis at T^\ast = 11
K.",1208.1480v3
2012-08-09,Electron-like Fermi surface and in-plane anisotropy due to chain states in YBa$_2$Cu$_3$O$_{7-δ}$ superconductors,"We present magneto-transport calculations for YBa$_2$Cu$_3$O$_{7-\delta}$
(YBCO) materials to show that the electron-like metallic chain state gives both
the negative Hall effect and in-plane anisotropic large Nernst signal. We show
that the inevitable presence of the metallic 1D CuO chain layer lying between
the CuO2 bilayers in YBCO renders an electron-like Fermi surface in the doping
range as wide as p=0.05 to overdoping. With underdoping, a pseudogap opening in
the CuO2 state reduces its hole-carrier contribution, and therefore the net
electron-like quasiparticles dominate the transport properties, and a negative
Hall resistance commences. We also show that the observation of in-plane
anisotropy in the Nernst signal - which was taken as a definite evidence of the
electronic `nematic' pseudogap phase - is naturally explained by including the
`quasi-uniaxial' metallic chain state. Finally, we comment on how the chain
state can also lead to electron-like quantum oscillations.",1208.1979v1
2012-08-12,"UHECR bending, clustering and decaying feeding gamma anisotropy","Ultra High Cosmic Rays) made by He-like lightest nuclei might fit clustering
along Cen A. Moreover He like UHECR nuclei explain Virgo absence because the
light nuclei fragility and opacity above a few Mpc. We foresaw (2009) that
UHECR He from Cen-A AGN being fragile should partially fragment into
secondaries at tens EeV multiplet (D,He^{3},p) as the recent twin multiplet
discovered ones (AUGER-ICRC-2011), at 20 EeV along Cen A UHECR clustering. We
suggest that UHECR are also heavy radioactive galactic nuclei as Ni^{56},
Ni^{57} and Co^{57} widely bent (tens degree up to 100 degrees) by galactic
fields. UHECR radioactivity and decay in flight at hundreds keV is boosted (by
huge Lorentz factor (billion) leading to PeVs electrons and consequent
synchrotron TeVs gamma offering UHECR-TeV correlated sky anisotropy. Electron
and tau neutrinos secondaries at PeVs maybe the first signature of such
expected radioactive secondary tail.",1208.2471v1
2012-08-15,Vortex lock-in transition coinciding with the 3D to 2D crossover in YBa2Cu3O7,"A vortex lock-in transition was directly detected by torque magnetometry in
an overdoped YBa2Cu3O7 single crystal of low anisotropy (\approx 7). The
locked-in state was observed below the 3D to 2D crossover temperature Tcr = 76
K, independently of extrinsic pinning effects thanks to a high quality clean
crystal and the use of a vortex shaking technique. The shape of the torque
signal as a function of the angle between the applied magnetic field and the
crystallographic c-axis is in very good agreement with the model developped by
Feinberg and Ettouhami [Int. J. Mod. Phys. B 7, 2085 (1993)] for quasi-2D
superconductors, despite the low anisotropy of the material.",1208.3062v1
2012-08-15,Spin Triplet Supercurrent in Co/Ni Multilayer Josephson Junctions with Perpendicular Anisotropy,"We have measured spin-triplet supercurrent in Josephson junctions of the form
S/F'/F/F'/S, where S is superconducting Nb, F' is a thin Ni layer with in-plane
magnetization, and F is a Ni/[Co/Ni]n multilayer with out-of-plane
magnetization. The supercurrent in these junctions decays very slowly with
F-layer thickness, and is much larger than in similar junctions not containing
the two F' layers. Those two features are the characteristic signatures of
spin-triplet supercurrent, which is maximized by the orthogonality of the
magnetizations in the F and F' layers. Magnetic measurements confirm the
out-of-plane anisotropy of the Co/Ni multilayers. These samples have their
critical current optimized in the as-prepared state, which will be useful for
future applications.",1208.3118v1
2012-08-17,Non-volatile voltage control of magnetization and magnetic domain walls in magnetostrictive epitaxial thin films,"We demonstrate reproducible voltage induced non-volatile switching of the
magnetization in an epitaxial thin Fe81Ga19 film. Switching is induced at room
temperature and without the aid of an external magnetic field. This is achieved
by the modification of the magnetic anisotropy by mechanical strain induced by
a piezoelectric transducer attached to the layer. Epitaxial Fe81Ga19 is shown
to possess the favourable combination of cubic magnetic anisotropy and large
magnetostriction necessary to achieve this functionality with experimentally
accessible levels of strain. The switching of the magnetization proceeds by the
motion of magnetic domain walls, also controlled by the voltage induced strain.",1208.3567v1
2012-08-17,Percolation of linear $k$-mers on square lattice: from isotropic through partially ordered to completely aligned state,"Numerical simulations by means of Monte Carlo method and finite-size scaling
analysis have been performed to study the percolation behavior of linear
$k$-mers (also denoted in the literature as rigid rods, needles, sticks) on
two-dimensional square lattices $L \times L$ with periodic boundary conditions.
Percolation phenomena are investigated for anisotropic relaxation random
sequential adsorption of linear $k$-mers. Especially, effect of anisotropic
placement of the objects on the percolation threshold has been investigated.
Moreover, the behavior of percolation probability $R_L(p)$ that a lattice of
size $L$ percolates at concentration $p$ has been studied in details in
dependence on $k$, anisotropy and lattice size $L$. A nonmonotonic size
dependence for the percolation threshold has been confirmed in isotropic case.
We propose a fitting formula for percolation threshold $p_c =
a/k^{\alpha}+b\log_{10} k+ c$, where $a$, $b$, $c$, $\alpha$ are the fitting
parameters varying with anisotropy. We predict that for large $k$-mers
($k\gtrapprox 1.2\times10^4$) isotropic placed at the lattice, percolation
cannot occur even at jamming concentration.",1208.3602v1
2012-08-22,Anisotropy and effective dimensionality crossover of the fluctuation conductivity of hybrid superconductor/ferromagnet structures,"We study the fluctuation conductivity of a superconducting film, which is
placed to perpendicular non-uniform magnetic field with the amplitude $H_0$
induced by the ferromagnet with domain structure. The conductivity tensor is
shown to be essentially anisotropic. The magnitude of this anisotropy is
governed by the temperature and the typical width of magnetic domains $d$. For
$d\ll L_{H_0}=\sqrt{\Phi_0/H_0}$ the difference between diagonal fluctuation
conductivity components $\Delta\sigma_\parallel$ along the domain walls and
$\Delta\sigma_\perp$ across them has the order of $(d/L_{H_0})^4$. In the
opposite case for $d\gg L_{H_0}$ the fluctuation conductivity tensor reveals
effective dimensionality crossover from standard two-dimensional $(T-T_c)^{-1}$
behavior well above the critical temperature $T_c$ to the one-dimensional
$(T-T_c)^{-3/2}$ one close to $T_c$ for $\Delta\sigma_\parallel$ or to the
$(T-T_c)^{-1/2}$ dependence for $\Delta\sigma_\perp$. In the intermediate case
$d\approx L_{H_0}$ for a fixed temperature shift from $T_c$ the dependence
$\Delta\sigma_\parallel(H_0)$ is shown to have a minimum at $H_0\sim\Phi_0/d^2$
while $\Delta\sigma_\perp(H_0)$ is a monotonically increasing function.",1208.4562v2
2012-08-23,Angle-resolved photoemission studies of the superconducting gap symmetry in Fe-based superconductors,"The superconducting gap is the fundamental parameter that characterizes the
superconducting state, and its symmetry is a direct consequence of the
mechanism responsible for Cooper pairing. Here we discuss about angle-resolved
photoemission spectroscopy measurements of the superconducting gap in the
Fe-based high-temperature superconductors. We show that the superconducting gap
is Fermi surface dependent and nodeless with small anisotropy, or more
precisely, a function of momentum. We show that while this observation is
inconsistent with weak coupling approaches for superconductivity in these
materials, it is well supported by strong coupling models and global
superconducting gaps. We also suggest that the strong anisotropies measured by
other probes sensitive to the residual density of states are not related to the
pairing interaction itself, but rather emerge naturally from the smaller
lifetime of the superconducting Cooper pairs that is a direct consequence of
the momentum dependent interband scattering inherent to these materials.",1208.4717v1
2012-08-25,Spin dynamics of possible density wave states in the pseudogap phase of the high temperature superconductors,"In a recent inelastic neutron scattering experiment in the pseudogap state of
the high temperature superconductor $\mathrm{YBa_{2}Cu_{3}O_{6.6}}$ an unusual
`vertical' dispersion of the spin excitations with a large in-plane anisotropy
was observed. In this paper we discuss in detail the spin susceptibility of the
singlet $d$-density wave, the triplet $d$-density wave, as well as the more
common spin density wave orders with hopping anisotropies. From numerical
calculations within the framework of random phase approximation, we find nearly
vertical dispersion relations for spin excitations with anisotropic
incommensurability at low energy $\omega \le 90 meV$, which are reminiscent of
the experiments. At very high energy $\omega \ge 165 meV$, we also find
energy-dependent incommensurability. Although there are some important
difference between the three cases, unpolarized neutron measurements cannot
discriminate between these alternate possibilities; the vertical dispersion,
however, is a distinct feature of all three density wave states in contrast to
the superconducting state, which shows an hour-glass shape dispersion.",1208.5108v1
2012-08-28,Magnetic field sensor with voltage-tunable sensing properties,"We report on a magnetic field sensor based on CoFeB/MgO/CoFeB magnetic tunnel
junctions. By taking advantage of the perpendicular magnetic anisotropy of the
CoFeB/MgO interface, the magnetization of the sensing layer is tilted
out-of-plane which results in a linear response to in-plane magnetic fields.
The application of a bias voltage across the MgO tunnel barrier of the field
sensor affects the magnetic anisotropy and thereby its sensing properties. An
increase of the maximum sensitivity and simultaneous decrease of the magnetic
field operating range by a factor of two is measured. Based on these results,
we propose a voltage-tunable sensor design that allows for active control of
the sensitivity and the operating filed range with the strength and polarity of
the applied bias voltage.",1208.5588v1
2012-08-29,Electron spin resonance shifts in S=1 antiferromagnetic chains,"We discuss electron spin resonance (ESR) shifts in spin-1 Heisenberg
antiferromagnetic chains with a weak single-ion anisotropy based on several
effective field theories, the O(3) nonlinear sigma model (NLSM) in the Haldane
phase, free fermion theories around the lower and the upper critical fields. In
the O(3) NLSM, the single-ion anisotropy corresponds to a composite operator
which creates two magnons at the same time and position. Therefore, even inside
a parameter range where free magnon approximation is valid, we have to take
interactions among magnons into account. Though the O(3) NLSM is only valid in
the Haldane phase, an appropriate translation of Faddeev-Zamolodchikov
operators of the O(3) NLSM to fermion operators enables one to treat ESR shifts
near the lower critical field in a similar manner to discussions in Haldane
phase. We present that our theory gives quantitative agreements with recent ESR
experimental results on an spin-1 chain compounds NDMAP.",1208.6017v2
2012-09-04,Magnetic and nematic orderings in spin-1 antiferromagnets with single-ion anisotropy,"We study a spin-one Heisenberg model with exchange interaction, J, uniaxial
single-ion exchange anisotropy, D, and Zeeman coupling to a magnetic field, B,
parallel to the symmetry axis. We com- pute the (D/J,B/J) quantum phase diagram
for square and simple cubic lattices by combining an- alytical and Quantum
Monte Carlo approaches, and find a transition between XY-antiferromagnetic and
ferronematic phases that spontaneously break the U(1) symmetry of the model. In
the language of bosonic gases, this is a transition between a Bose-Einstein
condensate (BEC) of single bosons and a BEC of pairs. Our work opens up new
avenues for measuring this transition in real magnets.",1209.0688v3
2012-09-11,The role of pressure anisotropy in the turbulent intracluster medium,"In low-density plasma environments, such as the intracluster medium (ICM),
the Larmour frequency is much larger than the ion-ion collision frequency. In
such a case, the thermal pressure becomes anisotropic with respect to the
magnetic field orientation and the evolution of the turbulent gas is more
correctly described by a kinetic approach. A possible description of these
collisionless scenarios is given by the so-called kinetic magnetohydrodynamic
(KMHD) formalism, in which particles freely stream along the field lines, while
moving with the field lines in the perpendicular direction. In this way a
fluid-like behavior in the perpendicular plane is restored. In this work, we
study fast growing magnetic fluctuations in the smallest scales which operate
in the collisionless plasma that fills the ICM. In particular, we focus on the
impact of a particular evolution of the pressure anisotropy and its
implications for the turbulent dynamics of observables under the conditions
prevailing in the ICM. We present results from numerical simulations and
compare the results which those obtained using an MHD formalism.",1209.2302v1
2012-09-23,CMB Anisotropy Due to Filamentary Gas: Power Spectrum and Cosmological Parameter Bias,"Hot gas in filamentary structures induces CMB aniostropy through the SZ
effect. Guided by results from N-body simulations, we model the morphology and
gas properties of filamentary gas and determine the power spectrum of the
anisotropy. Our treatment suggests that power levels can be an appreciable
fraction of the cluster contribution at multipoles $\ell\lesssim 1500$. Its
spatially irregular morphology and larger characteristic angular scales can
help to distinguish this SZ signature from that of clusters. In addition to
intrinsic interest in this most extended SZ signal as a probe of filaments, its
impact on cosmological parameter estimation should also be assessed. We find
that filament `noise' can potentially bias determination of $A_s$, $n_s$, and
$w$ (the normalization of the primordial power spectrum, the scalar index, and
the dark energy equation of state parameter, respectively) by more than the
nominal statistical uncertainty in Planck SZ survey data. More generally, when
inferred from future optimal cosmic-variance-limited CMB experiments, we find
that virtually all parameters will be biased by more than the nominal
statistical uncertainty estimated for these next generation CMB experiments.",1209.5065v1
2012-09-27,Identifying the Magnetoelectric Modes of Multiferroic BiFeO$_3$,"We have identified three of the four magnetoelectric modes of multiferroic
BiFeO$_3$ measured using THz spectroscopy. Excellent agreement with the
observed peaks is obtained by including the effects of easy-axis anisotropy
along the direction of the electric polarization. By distorting the cycloidal
spin state, anisotropy splits the $\Psi_{\pm 1}$ mode into peaks at 20 and 21.5
cm$^{-1}$ and activates the lower $\Phi_{\pm 2}$ mode at 27 cm$^{-1}$ (T=200
K). An electromagnon is identified with the upper $\Psi_{\pm 1}$ mode at 21.5
cm$^{-1}$. Our results also explain recent Raman and inelastic
neutron-scattering measurements.",1209.6244v1
2012-09-28,Acoustic impedance and interface phonon scattering in Bi$_2$Te$_3$ and other semiconducting materials,"We present first principles calculations of the phonon dispersions of Bi2Te3
and discuss these in relation to the acoustic phonon interface scattering in
ceramics. The phonon dispersions show agreement with what is known from neutron
scattering for the optic modes. We find a difference between the generalized
gradient approximation and local density results for the acoustic branches.
This is a consequence of an artificial compression of the van der Waals bonded
gaps in the Bi2Te3 structure when using the generalized gradient approximation.
As a result local density approximation calculations provide a better
description of the phonon dispersions in Bi$_{2}$Te$_{3}$. A key characteristic
of the acoustic dispersions is the existence of a strong anisotropy in the
velocities. We develop a model for interface scattering in ceramics with
acoustic wave anisotropy and apply this to Bi2Te3 and compare with PbTe and
diamond.",1209.6555v1
2012-10-03,Event-by-event azimuthal anisotropy of jet quenching in relativistic heavy ion collisions,"In this paper we present with full details a systematic quantification, on an
even-by-event basis, of the hard probe response to the geometry and
fluctuations of the hot QCD matter created in heavy ion collisions at both the
Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The
azimuthal anisotropy of jet quenching is extracted and decomposed as harmonic
responses (for n=1,2,3,4,5,6) to the corresponding harmonics in the fluctuating
initial condition. We show that such jet response harmonics are sensitive to
the jet quenching models as well as to the bulk matter initial compositions. By
studying these for all centralities at both RHIC and LHC energies we put a
strong constraint on the path-length and medium-density dependence of jet
energy loss. We also examine the hard-soft di-hadron correlation arising from
the hard and soft sectors' responses to the common initial fluctuations. We
demonstrate that the experimentally observed ""hard-ridge"" can be explained this
way and that its dependence on the trigger-azimuthal-angle could also be
qualitatively understood.",1210.1245v2
2012-10-06,Bilayer Twisted Hubbard Model for Sr3Ir2O7,"We use the bilayer twisted Hubbard model to study the low energy electronic
structure of Sr3Ir2O7. Sr3Ir2O7 is suggested as a Mott insulator and described
by the bilayer twisted pseudospin-1/2 model. The bilayer twists in Sr3Ir2O7
bring the intrinsic anisotropy and the system is no longer SU(2) invariant. The
anisotropy selects an easy c-axis collinear antiferromagnetic magnetic
structure at low temperatures which breaks the discrete Ising symmetry. The
transverse spin excitations are gapped and the longitudinal one is weakly
dispersive. We implement the bond-operator mean field calculation to describe
the magnetic properties of the bilayer twisted pseudospin-1/2 model in good
agreement with experimental measurements in Sr3Ir2O7. The bilayer twisted
Hubbard model is believed to be the good zeroth approximation for the low
energy electronic structure of Sr3Ir2O7.",1210.1974v1
2012-10-10,An anisotropy preserving metric for DTI processing,"Statistical analysis of Diffusion Tensor Imaging (DTI) data requires a
computational framework that is both numerically tractable (to account for the
high dimensional nature of the data) and geometric (to account for the
nonlinear nature of diffusion tensors). Building upon earlier studies that have
shown that a Riemannian framework is appropriate to address these challenges,
the present paper proposes a novel metric and an accompanying computational
framework for DTI data processing. The proposed metric retains the geometry and
the computational tractability of earlier methods grounded in the affine
invariant metric. In addition, and in contrast to earlier methods, it provides
an interpolation method which preserves anisotropy, a central information
carried by diffusion tensor data.",1210.2826v1
2012-10-10,Magnetic Vortex with Skyrmionic Core in Thin Nanodisk of the Chiral Magnets,"A type of vortex spin texture with skyrmionic core and a series of circle
spin stripes was obtained in thin nanodisk of the chiral magnets with
Dzyaloshinskii-Moriya interaction and uniaxial anisotropy by means of
micromagnetic approach and Monte Carlo simulation. The size of skyrmionic core
can be modulated continuously by controlling the disk size. Moreover, in some
certain values of the disk size, this vortex state may be spontaneous ground
state even without the help of the external magnetic field and thermal
fluctuation. In addition, the uniaxial anisotropy is able to stabilize this
vortex spin texture. We anticipate that the present work will inspire further
experimental studies for exploring the spin structure.",1210.2862v2
2012-10-13,Large scale distribution of arrival directions of cosmic rays detected above $10^{18}$ eV at the Pierre Auger Observatory,"A thorough search for large scale anisotropies in the distribution of arrival
directions of cosmic rays detected above $10^{18}$ eV at the Pierre Auger
Observatory is presented. This search is performed as a function of both
declination and right ascension in several energy ranges above $10^{18}$ eV,
and reported in terms of dipolar and quadrupolar coefficients. Within the
systematic uncertainties, no significant deviation from isotropy is revealed.
Assuming that any cosmic ray anisotropy is dominated by dipole and quadrupole
moments in this energy range, upper limits on their amplitudes are derived.
These upper limits allow us to challenge an origin of cosmic rays above
$10^{18}$ eV from stationary galactic sources densely distributed in the
galactic disk and emitting predominantly light particles in all directions.",1210.3736v2
2012-10-17,The power-law spectra of energetic particles during multi-island magnetic reconnection,"Power-law distributions are a near universal feature of energetic particle
spectra in the heliosphere. Anomalous Cosmic Rays (ACRs), super-Alfv\'enic ions
in the solar wind and the hardest energetic electron spectra in flares all have
energy fluxes with power-laws that depend on energy $E$ approximately as
$E^{-1.5}$. We present a new model of particle acceleration in systems with a
bath of merging magnetic islands that self-consistently describes the
development of velocity-space anisotropy parallel and perpendicular to the
local magnetic field and includes the self-consistent feedback of pressure
anisotropy on the merging dynamics. By including pitch-angle scattering we
obtain an equation for the omni-directional particle distribution $f(v,t)$ that
is solved in closed form to reveal $v^{-5}$ (corresponding to an energy flux
varying as $E^{-1.5}$) as a near-universal solution as long as the
characteristic acceleration time is short compared with the characteristic loss
time. In such a state the total energy in the energetic particles reaches
parity with the remaining magnetic free energy. More generally, the resulting
transport equation can serve as the basis for calculating the distribution of
energetic particles resulting from reconnection in large-scale inhomogeneous
systems.",1210.4830v1
2012-10-18,Unstable dynamics of Yang-Mills fields at early times of heavy ion collisions,"The quark gluon plasma as produced in heavy ion collisions is exposed to
early anisotropies in momentum space due to its rapid expansion. Such
anisotropies can lead to non-abelian plasma instabilities, driven by unstable
gluonic modes that can grow exponentially fast. These plasma instabilities can
be simulated using a discretized version of gauge-covariant Boltzmann-Vlasov
and Yang-Mills equations. In the stationary case, a turbulent cascade forms in
the strong-field regime, which is associated with an approximately linear
growth of energy in collective fields. Early longitudinal expansion slows down
the growth of unstable modes, and the formation of soft gluonic fields depends
crucially on the initial conditions assumed.",1210.5150v1
2012-10-19,"Two-dimensional magnetism in kappa-(BEDT-TTF)2Cu[N(CN)2]Cl, a spin-1/2 Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interaction","Field-induced antiferromagnetic (AF) fluctuations and magnetization are
observed above the (zero-field) ordering temperature, T_N = 23 K by electron
spin resonance in kappa-(BEDT-TTF)_2Cu[N(CN)_2]Cl, a quasi two-dimensional
antiferromagnet with a large isotropic Heisenberg exchange interaction. The
Dzyaloshinskii-Moriya (DM) interaction is the main source of anisotropy, the
exchange anisotropy and the interlayer coupling are very weak. The AF
magnetization is induced by magnetic fields perpendicular to the DM vector;
parallel fields have no effect. The different orientation of the DM vectors and
the g factor tensors in adjacent layers allows the distinction between
interlayer and intralayer correlations. Magnetic fields induce the AF
magnetization independently in adjacent layers. We suggest that the phase
transition temperature, T_N is determined by intralayer interactions alone.",1210.5381v1
2012-10-19,Topological phases in ultracold polar-molecule quantum magnets,"We show how to use polar molecules in an optical lattice to engineer quantum
spin models with arbitrary spin S >= 1/2 and with interactions featuring a
direction-dependent spin anisotropy. This is achieved by encoding the effective
spin degrees of freedom in microwave-dressed rotational states of the molecules
and by coupling the spins through dipolar interactions. We demonstrate how one
of the experimentally most accessible anisotropies stabilizes symmetry
protected topological phases in spin ladders. Using the numerically exact
density matrix renormalization group method, we find that these interacting
phases -- previously studied only in the nearest-neighbor case -- survive in
the presence of long-range dipolar interactions. We also show how to use our
approach to realize the bilinear-biquadratic spin-1 and the Kitaev honeycomb
models. Experimental detection schemes and imperfections are discussed.",1210.5518v2
2012-10-22,CMB anisotropy science: a review,"The cosmic microwave background (CMB) provides us with our most direct
observational window to the early universe. Observations of the temperature and
polarization anisotropies in the CMB have played a critical role in defining
the now-standard cosmological model. In this contribution we review some of the
basics of CMB science, highlighting the role of observations made with
ground-based and balloon-borne Antarctic telescopes. Most of the ingredients of
the standard cosmological model are poorly understood in terms of fundamental
physics. We discuss how current and future CMB observations can address some of
these issues, focusing on two directly relevant for Antarctic programmes:
searching for gravitational waves from inflation via B-mode polarization, and
mapping dark matter through CMB lensing.",1210.6008v1
2012-10-26,Directional vortex pinning at microwave frequency in YBa$_{2}$Cu$_3$O$_{7-x}$ thin films with BaZrO$_3$ nanorods,"We investigate the effect of the anisotropy and of the directional pinning in
YBa$_2$Cu$_3$O$_{7-x}$ films grown by pulsed laser ablation from targets
containing BaZrO$_3$ at 5% mol. BaZrO$_3$ inclusions self-assemble to give
nanorods oriented along the c-axis, thus giving a preferential direction for
vortex pinning. The directionality of vortex response is studied at high ac
frequency with the complex microwave response at 48 GHz, as a function of the
applied field and of the angle $\theta$ between the field and the c-axis. The
complex microwave response does not exhibit any angular scaling, suggesting
that the structural anisotropy of YBa$_2$Cu$_3$O$_{7-x}$ is supplemented by at
least another preferred orientation. The pinning parameter $r$ shows evidence
of directional pinning, effective in a wide range of angles around the c-axis
(thus ascribed to BZO nanocolumns).",1210.7232v1
2012-10-28,Bottomonia in the Quark Gluon Plasma,"I review recent calculations of the suppression of bottomonium states in
heavy ion collisions. A non-relativistic potential is used which is complex
valued. This allows one to extract the binding energies and decay widths of the
ground and excited states of bottomonium as a function of the typical plasma
particle momentum and momentum-space anisotropy. The decay widths determined
are used as input and integrated over space-time taking into account the
dynamical evolution of the typical particle momentum and momentum-space
anisotropy. The suppression of Upsilon(1s), Upsilon(2s), Upsilon(3s), chi_b1,
and chi_b2 is obtained as a function of centrality, rapidity, and transverse
momentum. The obtained results are compared with data from the STAR and CMS
collaborations.",1210.7512v1
2012-10-30,Enhancement of Curie temperature due to the coupling between Fe itinerant electrons and Dy localized electrons in DyFe2Zn20,"The temperature dependence of magnetization and specific heat of the
ferromagnetic compound DyFe2Zn20 has been measured in detail in various
magnetic fields. We have observed anomalous magnetic behavior, i.e., a strong
anisotropy at 2 K, disappearance of this anisotropy between approximately 30 K
and T_c, and anomalous behavior of the specific heat in the magnetic fields
near 20 K. These anomalous phenomena have been analyzed based on the strong
exchange interaction between the Fe itinerant electrons and the Dy localized
electrons as well as the crystalline electric field, Zeeman energy, and an
usual exchange interaction between two Dy atoms. The higher T_c of DyFe2Zn20
compared with that of DyRu2Zn20 is caused by this exchange interaction between
the Fe and Dy atoms.",1210.7922v1
2012-11-01,Dynamics of Dark Matter in Baryon-Radiation Plasma: Perspectives using Meschersky equation,"With an aim to argue for the truly collisionless nature of cold dark matter
between epochs of equality and recombination, we assume a model, wherein
strongly coupled baryon-radiation plasma ejects out of small regions of
concentrated cold dark matter without losing its equilibrium. We use the
Meschersky equation to describe the dynamics of cold dark matter in the
presence of varying mass of strongly coupled baryon-radiation plasma. Based on
this model, we discuss the growth of perturbations in cold dark matter both in
the Jeans theory and in the expanding universe using Newton's theory. We see
the effect of the perturbations in the cold dark matter potential on the cosmic
microwave background anisotropy that originated at redshifts between equality
and recombination i.e. $1100 < z < z_{eq}$. Also we obtain an expression for
the Sachs-Wolfe effect, i.e. the CMB temperature anisotropy at decoupling in
terms of the perturbations in cold dark matter potential. We obtain similar
solutions both in the static and in the expanding universe, for epochs of
recombination. From this, we infer about the time scale when the dark energy
starts to dominate.",1211.0154v1
2012-11-01,Metric emerging to massive modes in quantum cosmological space-times,"We consider a massive quantum test Klein-Gordon field probing an isotropic
quantum cosmological space-time in the background. The result obtained is
surprising. It turns out, that despite the isotropy of the quantum
gravitational field, the semi-classical metric experienced by a mode of the K-G
field is non-isotropic. The anisotropy depends on the direction of the momentum
of the mode. Specifically, what we do is to derive a semi-classical space-time
which emerges to a mode of the field. The method amounts to a comparison
between QFT on a quantum background and QFT on a classical curved space-time,
giving rise to an emergent metric tensor. The components of the semi-classical
metric tensor are calculated from the equation of propagation of the quantum
K-G field in the test field approximation. The anisotropies are of a quantum
nature: they are proportional to Planck constant and ""dress"" the isotropic
classical space-time obtained in the classical limit.",1211.0161v2
2012-11-06,"Spin dynamics of hard-soft magnetic multi-layer systems: Effect of Exchange, Dipolar and Dzyaloshinski-Moriya interactions","We investigate the effect of coupling (intensity and nature), applied field,
and anisotropy on the spin dynamics of a multi-layer system composed of a hard
magnetic slab coupled to a soft magnetic slab through a nonmagnetic spacer. The
soft slab is modeled as a stack of several atomic layers while the hard layer,
of a different material, is either considered as a pinned macroscopic magnetic
moment or as an atomic multi-layer system. We compute the magnetization profile
and hysteresis loop of the multi-layer system by solving the Landau-Lifshitz
equations for the net magnetic moment of each (atomic) layer. We study the
competition between the intra-layer anisotropy and exchange interaction,
applied magnetic field, and the inter-slab exchange, dipolar or
Dzyaloshinski-Moriya interaction. Comparing the effects on the magnetization
profile of the three couplings shows that despite the strong effect of the
exchange coupling, the dipolar and Dzyaloshinski-Moriya interactions induce a
slight (but non negligible) deviation in either the polar or azimuthal
direction thus providing more degrees of freedom for adjusting the spin
configuration in the multi-layer system.",1211.1217v1
2012-11-09,Thermal photon production in a strongly coupled anisotropic plasma,"Photons produced in heavy ion collisions escape virtually unperturbed from
the surrounding medium, thus representing an excellent probe of the conditions
at the emission point. Using the gauge/gravity duality, we calculate the rate
of photon production in an anisotropic, strongly coupled N=4 plasma with Nf<<Nc
quark flavors. We consider arbitrary orientations of the photon momentum with
respect to the anisotropic direction, as well as arbitrary values of the
anisotropy. We present results for the correlation functions of two
electromagnetic currents and for the electric conductivity. These quantities
can be larger or smaller than the isotropic ones, depending on the direction of
propagation and polarization of the photons. The total production rate is
however always larger than the isotropic one, independently of the frequency,
direction of propagation, and value of the anisotropy.",1211.2199v2
2012-11-13,Lattice studies of magnetic phenomena in heavy-ion collisions,"We review some experimental consequences of the presence of superstrong
magnetic fields of order of the nuclear scale in noncentral heavy-ion
collisions. We present lattice estimates for the strength of the Chiral
Magnetic Effect (CME) for different quark flavours and argue that the
dependence of the anisotropy of the distribution of emitted hadrons on their
flavor content might be used as another experimental evidence of the CME.
Another possible effect of superstrong magnetic field might be the observed
abnormal enhancement of dilepton yield. We show that the presence of the
magnetic field leads to a specific anisotropy of the dilepton emission rate.",1211.3014v1
2012-11-13,Exploring the origin of the fine structures in the CMB temperature angular power spectrum,"The angular power spectrum of the cosmic microwave background (CMB)
temperature anisotropies is a good probe to look into the primordial density
fluctuations at large scales in the universe. Here we re-examine the angular
power spectrum of the Wilkinson Microwave Anisotropy Probe data, paying
particular attention to the fine structures (oscillations) at $\ell=100 \sim
150$ reported by several authors. Using Monte-Carlo simulations, we confirm
that the gap from the simple power law spectrum is a rare event, about
2.5--3$\sigma$, if these fine structures are generated by experimental noise
and the cosmic variance. Next, in order to investigate the origin of the
structures, we examine frequency and direction dependencies of the fine
structures by dividing the observed QUV frequency maps into four sky regions.
We find that the structures around $\ell \sim 120$ do not have significant
dependences either on frequencies or directions. For the structure around $\ell
\sim 140$, however, we find that the characteristic signature found in the all
sky power spectrum is attributed to the anomaly only in the South East region.",1211.3097v1
2012-11-14,CSL Wave Function Collapse Model as a Mechanism for the Emergence of Cosmological Asymmetries in Inflation,"As previously discussed in (D. Sudarsky, Int.J.Mod.Phys.D20:509-552, (2011);
[arXiv:0906.0315]), the inflationary account for the emergence of the seeds of
cosmic structure falls short of actually explaining the generation of
primordial anisotropies and inhomogeneities. This description starts from a
symmetric background, and invokes symmetric dynamics, so it cannot explain
asymmetries. To generate asymmetries, we present an application of the
Continuous Spontaneous Localization (CSL) model of wave function collapse (P.
Pearle, Phys. Rev. A 39, 2277, (1989); G. C. Ghirardi, P. Pearle and A. Rimini,
Phys. Rev. A42, 78 (1990)) in the context of inflation. This modification of
quantum dynamics introduces a stochastic non-unitary component to the evolution
of the inflaton field perturbations. This leads to passage from a homogeneous
and isotropic stage to another, where the quantum uncertainties in the initial
state of inflation transmute into the primordial inhomogeneities and
anisotropies. We examine requirements for, and show how to achieve,
compatibility with the precise observations of the cosmic microwave background
(CMB) radiation.",1211.3463v3
2012-11-28,Exploiting breakdown of the similarity relation for diffuse light transport: simultaneous retrieval of scattering anisotropy and diffusion constant,"As manifested in the similarity relation of diffuse light transport, it is
difficult to assess single scattering characteristics from multiply scattered
light. We take advantage of the limited validity of the diffusion approximation
of light transport and demonstrate, experimentally and numerically, that even
deep into the multiple scattering regime, time-resolved detection of
transmitted light allows simultaneous assessment of both single scattering
anisotropy and scattering mean free path, and therefore also macroscopic
parameters like the diffusion constant and the transport mean free path. This
is achieved via careful assessment of early light and matching against Monte
Carlo simulations of radiative transfer.",1211.6690v1
2012-11-29,A solution to the radiation pressure problem in the formation of massive stars,"We review our recent studies demonstrating that the radiation pressure
problem in the formation of massive stars can be circumvented via an anisotropy
of the thermal radiation field. Such an anisotropy naturally establishes with
the formation of a circumstellar disk. The required angular momentum transport
within the disk can be provided by developing gravitational torques. Radiative
Rayleigh-Taylor instabilities in the cavity regions - as previously suggested
in the literature - are not required and are shown to be not occurring in the
context of massive star formation.",1211.7064v1
2012-12-02,Manipulating the magnetic anisotropy of cobalt doped titanium dioxide by carrier accumulation,"Based on first-principles calculations, we predict that the magnetic
anisotropy energy (MAE) of Co-doped TiO$_2$ sensitively depends on carrier
accumulation. This magnetoelectric phenomenon provides a promising route to
directly manipulate the magnetization direction of diluted magnetic
semiconductor by external electric-fields. We calculate the band structures and
reveal the origin of carrier-dependent MAE in k-space. In fact, the carrier
accumulation shifts the Fermi energy and regulates the competing contributions
to MAE. The first-principles calculations provide a straightforward way to
design spintronics materials with electrically controllable spin direction.",1212.0175v3
2012-12-07,CMB interferometry,"Interferometry has been a very successful tool for measuring anisotropies in
the cosmic microwave background. Interferometers provided the first constraints
on CMB anisotropies on small angular scales (l~10000) in the 1980s and then in
the late 1990s and early 2000s made ground-breaking measurements of the CMB
power spectrum at intermediate and small angular scales covering the l-range
~100-4000. In 2002 the DASI made the first detection of CMB polarization which
remains a major goal for current and future CMB experiments. Interferometers
have also made major contributions to the detection and surveying of the
Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. In this short review I cover
the key aspects that made interferometry well-suited to CMB measurements and
summarise some of the central observations that have been made. I look to the
future and in particular to HI intensity mapping at high redshifts that could
make use of the advantages of interferometry.",1212.1729v1
2012-12-10,Interband Quasiparticle Scattering in Superconducting LiFeAs Reconciles Photoemission and Tunneling Measurements,"Several angle resolved photoemission spectroscopy (ARPES) studies reveal a
poorly nested Fermi surface of LiFeAs, far away from a spin density wave
instability, and clear-cut superconducting gap anisotropies. On the other hand
a very different, more nested Fermi surface and dissimilar gap anisotropies
have been obtained from quasiparticle interference (QPI) data, which were
interpreted as arising from intraband scattering within hole-like bands. Here
we show that this ARPES-QPI paradox is completely resolved by interband
scattering between the hole-like bands. The resolution follows from an
excellent agreement between experimental quasiparticle scattering data and
T-matrix QPI calculations (based on experimental band structure data), which
allows disentangling interband and intraband scattering processes.",1212.2009v2
2012-12-13,Material Targets for Scaling All Spin Logic,"All-spin logic devices are promising candidates to augment and complement
beyond-CMOS integrated circuit computing due to non-volatility, ultra-low
operating voltages, higher logical efficiency, and high density integration.
However, the path to reach lower energy-delay product performance compared to
CMOS transistors currently is not clear. We show that scaling and engineering
the nanoscale magnetic materials and interfaces is the key to realizing spin
logic devices that can surpass energy-delay performance of CMOS transistors.
With validated stochastic nano-magnetic and vector spin transport numerical
models, we derive the target material and interface properties for the
nanomagnets and channels. We identified promising new directions for material
engineering/discovery focusing on systematic scaling of magnetic anisotropy
(Hk) with saturation magnetization (Ms), use of perpendicular magnetic
anisotropy, and interface spin mixing conductance of ferromagnet/spin channel
interface (Gmix). We provide systematic targets for scaling spin logic
energy-delay product toward a 2 aJ.ns energy-delay product, comprehending the
stochastic noise for nanomagnets.",1212.3362v1
2012-12-14,Doping effect on thermoelectric properties of MoS$_2$,"We systematically study thermoelectric properties of layered MoS$_2$ by
doping, based on Boltzmann transport theory and first-principles calculations.
We obtain optimal doping region (around 10$^{19}$ cm$^{-3}$) by looking closely
to the temperature and doping level dependent thermopower, electrical
conductivity, power factor (PF) and ultimately figure of merit (ZT) coefficient
along in-plane and cross-plane directions. MoS$_2$ has a vanishingly small
anisotropy of thermopower but a big anisotropy of electrical conductivity and
electronic thermal conductivity in optimal doping region. $\kappa_e$ is
comparable to $\kappa_l$ in the plane while $\kappa_l$ dominates over
$\kappa_e$ across the plane. ZT can reach as high as 0.3 at around 700 K.
In-plane direction is demonstrated to be more preferable for thermoelectric
applications of MoS$_2$ by doping.",1212.3394v2
2012-12-17,Topological states in pyrochlore iridates: long-range anisotropy strongly competing with spin-orbit interaction,"In the search for topological phases in correlated electron systems,
iridium-based pyrochlores A2Ir2O7 -- materials with 5d transition-metal ions --
provide fertile grounds. Several novel topological states have been predicted
but the actual realization of such states is believed to critically depend on
the strength of local potentials arising from distortions of IrO6-cages. We
test this hypothesis by measuring with resonant x-ray scattering the electronic
level splittings in the A= Y, Eu systems, which we show to agree very well with
ab initio electronic structure calculations. We find, however, that not
distortions of IrO6-octahedra are the primary source for quenching the
spin-orbit interaction, but strong long-range lattice anisotropies, which
inevitably break the local cubic symmetry and will thereby be decisive in
determining the system's topological ground state.",1212.4009v2
2012-12-16,Dynamical 3-Space Gravitational Waves: Reverberation Effect,"Gravity theory missed a key dynamical process that became apparent only when
expressed in terms of a velocity field, instead of the Newtonian gravitational
acceleration field. This dynamical process involves an additional
self-interaction of the dynamical 3-space, and experimental data reveals that
its strength is set by the fine structure constant, implying a fundamental link
between gravity and quantum theory. The dynamical 3-space has been directly
detected in numerous light-speed anisotropy experiments. Quantum matter has
been shown to exhibit an acceleration caused by the time-dependence and
inhomogeneity of the 3-space flow, giving the first derivation of gravity from
a deeper theory, as a quantum wave refraction effect. EM radiation is also
refracted in a similar manner. The anisotropy experiments have all shown
3-space wave/turbulence effects, with the latest revealing the fractal
structure of 3-space. Here we report the prediction of a new effect, namely a
reverberation effect, when the gravitational waves propagate in the 3-space
inflow of a large mass. This effect arises from the non-linear dynamics of
3-space. These reverberations could offer an explanation for the Shnoll effect,
in which cosmological factors influence stochastic processes, such as
radioactive decay rates.",1212.4405v1
2012-12-19,Optical conductivity and Raman scattering of iron superconductors,"We discuss how to analyze the optical conductivity and Raman spectra of
multi-orbital systems using the velocity and the Raman vertices in a similar
way Raman vertices were used to disentangle nodal and antinodal regions in
cuprates. We apply this method to iron superconductors in the magnetic and
non-magnetic states, studied at the mean field level. We find that the
anisotropy in the optical conductivity at low frequencies reflects the
difference between the magnetic gaps at the X and Y electron pockets. Both gaps
are sampled by Raman spectroscopy. We also show that the Drude weight
anisotropy in the magnetic state is sensitive to small changes in the lattice
structure.",1212.4765v2
2012-12-31,Towards efficient and optimal analysis of CMB anisotropies on a masked sky,"Strong foreground contamination in high resolution CMB data requires masking
which introduces statistical anisotropies and renders a full maximum likelihood
analysis numerically intractable. Standard analysis methods like the pseudo-C_l
framework lead to information loss due to estimator suboptimalities. We set out
and validate a methodology for numerically efficient estimators for a masked
sky that recover nearly as much information as a full maximum likelihood
procedure. In addition to the standard pseudo-C_l statistic, the approach
introduces an augmented basis designed to account for the mode coupling due to
the masking of the sky. We motivate the choice of this basis by describing the
basic structure of the covariance matrix. We demonstrate that the augmented
estimator can achieve near-optimal results in the presence of a WMAP-realistic
mask.",1212.6945v2
2013-01-08,Interplay between interaction and chiral anomaly: Anisotropy in the electrical resistivity of interacting Weyl metals,"We predict that long-range interactions give rise to anisotropy in the
electrical resistivity of Weyl metals at low temperatures, where the electrical
resistivity becomes much reduced when electric fields are applied to the
direction of the momentum vector to connect two paired Weyl points. Performing
the renormalization group analysis, we find that the distance between two Weyl
points becomes enhanced logarithmically at low temperatures although the
coupling constant of such interactions vanishes inverse-logarithmically.
Considering the Adler-Bell-Jackiw anomaly, scattering between these two Weyl
points becomes suppressed to increase electrical conductivity in the
""longitudinal"" direction, counter-intuitive in the respect that interactions
are expected to reduce metallicity. We also propose that the anomalous
contribution in the Hall effect shows the logarithmic enhancement as a function
of temperature, originating from the fact that the anomalous Hall coefficient
turns out to be proportional to the distance between two paired Weyl points.
Correlations with topological constraints allow unexpected and exotic transport
properties.",1301.1436v2
2013-01-08,Phase diagram of the Anderson transition with atomic matter waves,"We realize experimentally a cold atom system equivalent to the 3D Anderson
model of disordered solids where the anisotropy can be controlled by adjusting
an experimentally accessible parameter. This allows us to study experimentally
the disorder vs anisotropy phase diagram of the Anderson metal-insulator
transition. Numerical and experimental data compare very well with each other
and a theoretical analysis based on the self-consistent theory of localization
correctly discribes the observed behavior, illustrating the flexibility of cold
atom experiments for the study of transport phenomena in complex quantum
systems.",1301.1615v1
2013-01-10,Magnetic structure and magnon dispersion in LaSrFeO$_4$,"We present elastic and inelastic neutron scattering data on LaSrFeO$_4$. We
confirm the known magnetic structure with the magnetic moments lying in the
tetragonal basal plane, but contrarily to previous reports our macroscopic and
neutron diffraction data do not reveal any additional magnetic phase transition
connected to a spin reorientation or to a redistribution of two irreducible
presentations. Our inelastic neutron scattering data reveals the magnon
dispersion along the main-symmetry directions [0 $\xi$ 0] and [$\xi$ -$\xi$ 0].
The dispersion can be explained within linear spin-wave theory yielding an
antiferromagnetic nearest-neighbour interaction parameter $J_{1}=7.4(1)$ meV
and a next-nearest neighbour interaction parameter $J_{2}=0.4(1)$ meV. The
dispersion is gapped with the out-of-plane anisotropy gap found at
$\Delta_{out}=5.26(2)$ meV, while evidence is present that the in-plane
anisotropy gap lies at lower energies, where it cannot be determined due to
limited instrument resolution.",1301.2106v1
2013-01-14,Impact of anisotropy on the noncritical squeezing properties of two-transverse-mode optical parametric oscillators,"In a series of articles we studied the quantum properties of a degenerate
optical parametric oscillator tuned to the first family of transverse modes at
the subharmonic. We found that, for a cavity having rotational symmetry respect
to the optical axis, a TEM$_{10}$ mode with an arbitrary orientation in the
transverse plane is emitted above threshold. We proved then that quantum noise
induces a random rotation of this bright TEM$_{10}$ mode in the transverse
plane, while the mode orthogonal to it, the so-called dark mode, has perfect
quadrature squeezing irrespective of the distance to threshold (noncritical
squeezing). This result was linked to the spontaneous rotational symmetry
breaking which occurs when the bright mode is generated, and here we analyze
how the squeezing of the dark mode is degraded when the cavity is not perfectly
symmetric. We will show that large levels of squeezing are still attainable for
reasonable values of this anisotropy, with the advantage that the orientation
of the bright and dark modes is basically fixed, a very attractive situation
from the experimental point of view.",1301.2849v1
2013-01-17,Anisotropic Zeeman splitting in p-type GaAs quantum point contacts,"Low-temperature electrical conductance spectroscopy measurements of quantum
point contacts implemented in p-type GaAs/AlGaAs heterostructures are used to
study the Zeeman splitting of 1D subbands for both in-plane and out-of-plane
magnetic field orientations. The resulting in-plane g-factors agree
qualitatively with those of previous experiments on quantum wires while the
quantitative differences can be understood in terms of the enhanced quasi-1D
confinement anisotropy. The influence of confinement potential on the
anisotropy is discussed and an estimate for the out-of-plane g-factor is
obtained which, in contrast to previous experiments, is closer to the
theoretical prediction.",1301.3992v1
2013-01-21,Quantum master equation for a system of identical particles,"We consider an open quantum many-particle system in which there are
dissipative processes. The evolution of this system is described by a kinetic
equation for the density matrix. From the equation describing a random Markov
process in this system, we obtain an equation for the single-particle
statistical operator. This equation describes the evolution of a system of
identical particles in a mean-field approximation. The equation for interacting
particles in thermodynamic equilibrium was obtained. The distribution function
of a system of interacting electrons in metals has multivalence in a certain
region of wave vectors. Among many solutions one is isotropic. Other solutions
have the anisotropy of the electron distribution over the wave vectors. The
anisotropy arises as a result of repulsion and attraction between electrons.",1301.4712v1
2013-01-23,Neutrino emissivity of anisotropic neutron superfluids,"We examine the influence of the anisotropy of the superfluid energy gap and
residual Fermi-liquid interactions in the triplet-correlated neutron liquid
onto neutrino energy losses through neutral weak currents. The neutrino-pair
emission caused by the pair breaking and formation processes and by the
spin-wave decays is considered for the case of the $^{3}P_{2}$ pairing in the
state with $m_{j}=0$. The simple analytical formulae are obtained. A comparison
with the previous results of the average-angle approach shows that the gap
anisotropy leads to quenching of the neutrino emissivity caused by the pair
recombination processes on about 15% and to substantial suppression of the
spin-wave decays. Residual particle-hole interactions increase the energy
losses in both the channels on about 5%.",1301.5439v1
2013-01-24,Optimal conditions for magnetization reversal of nanocluster assemblies with random properties,"Magnetization dynamics in the system of magnetic nanoclusters with randomly
distributed properties are studied by means of computer simulations. The main
attention is paid to the possibility of coherent magnetization reversal from a
strongly nonequilibrium state with a mean cluster magnetization directed
opposite to an external magnetic field. Magnetic nanoclusters are known to be
characterized by large magnetic anisotropy and strong dipole interactions. It
is also impossible to produce a number of nanoclusters with identical
properties. As a result, any realistic system of nanoclusters is composed of
the clusters with randomly varying anisotropies, effective spins, and dipole
interactions. Despite this randomness, it is possible to find conditions when
the cluster spins move coherently and display fast magnetization reversal due
to the feedback action of resonator. By analyzing the influence of different
cluster parameters, we find their optimal values providing fast magnetization
reversal.",1301.5789v1
2013-01-31,Anisotropic hydrodynamics -- basic concepts,"Due to the rapid longitudinal expansion of the quark-gluon plasma created in
relativistic heavy ion collisions, potentially large local rest frame
momentum-space anisotropies are generated. The magnitude of these
momentum-space anisotropies can be so large as to violate the central
assumption of canonical viscous hydrodynamical treatments which linearize
around an isotropic background. In order to better describe the early-time
dynamics of the quark gluon plasma, one can consider instead expanding around a
locally anisotropic background which results in a dynamical framework called
anisotropic hydrodynamics. In this proceedings contribution we review the basic
concepts of the anisotropic hydrodynamics framework presenting viewpoints from
both the phenomenological and microscopic points of view.",1301.7539v1
2013-01-31,Further details on the phase diagram of hard ellipsoids of revolution,"In recent work we revisited the phase diagram of hard ellipsoids of
revolution (spheroids) by means of replica exchange Monte Carlo simulations.
This was done by setting random initial configurations, and allows to confirm
the formation of sm2 crystal structures at high densities [Phys. Rev. E 75,
020402 (2007)] for large anisotropies and stretched-fcc for small anisotropies.
In this work we employed the same technique but setting the starting cells as
sm2 crystal structures having the maximum known packing density [Phys. Rev.
Lett. 92, 255506 (2004)]. This procedure yields a very rich behavior for
quasi-spherical oblates and prolates. These systems, from low to high
pressures, show the following phases: isotropic fluid, plastic solid,
stretched-fcc solid, and sm2 solid. The first three transitions are first
order, whereas the last one is a subtle, probably high order transition. This
picture is consistent with the fact of having the sm2 structure capable of
producing the maximally achievable density.",1301.7728v1
2013-02-01,"Spin relaxation and the Elliott-Yafet parameter in W(001) ultrathin films: surface states, anisotropy and oscillation effects","Using first-principles methods based on density-functional theory we
investigate the spin relaxation in W(001) ultrathin films. Within the framework
of the Elliott-Yafet theory we calculate the spin mixing of the Bloch states
and we explicitly consider spin-flip scattering off self-adatoms. We find an
oscillatory behavior of the spin-mixing parameter and relaxation rate as a
function of the film thickness, which we trace back tosurface-state properties.
We also analyze the Rashba effect experienced by the surface states and discuss
its influence on the spin relaxation. Finally we calculate the anisotropy of
the spin-relaxation rate with respect to the polarization direction of the
excited spin population relative to the crystallographic axes of thefilm. We
find that the spin-relaxation rate can increase by as much as 47% when the spin
polarization is directed out of plane, compared to the case when it is in
plane. Our calculations are based on the multiple-scattering formalism of the
Korringa-Kohn-Rostoker Green-function method.",1302.0140v1
2013-02-09,The effect of uniaxial pressure on the magnetic anisotropy of the Mn_{12}-Ac single-molecule magnet,"We study the effect of uniaxial pressure on the magnetic hysteresis loops of
the single-molecule magnet Mn_{12}-Ac. We find that the application of pressure
along the easy axis increases the fields at which quantum tunneling of
magnetization occurs. The observations are attributed to an increase in the
molecule's magnetic anisotropy constant D of 0.142(1)%/kbar. The increase in D
produces a small, but measurable increase in the effective energy barrier for
magnetization reversal. Density-functional theory calculations also predict an
increase in the barrier with applied pressure.",1302.2276v2
2013-02-17,Ab initio study of low-energy electronic collective excitations in bulk Pb: anisotropy and acoustic modes,"A theoretical study of the dynamical dielectric response of bulk lead at low
energies is presented. The calculations are performed with full inclusion of
the electron band structure calculated by means of a first-principles
pseudopotential approach. The effect of including the spin-orbit splittings in
the band structure is analyzed, together with dynamical exchange-correlation
and local-field effects. Excitations are studied in detail, showing the
presence at small momenta of acoustic-like dispersing excitations. The
character of these modes with sound-like dispersion depends on the direction of
the momentum transfer q. In general results show strong anisotropy effects on
the dielectric response of bulk Pb. Comparison with available optical
experimental data shows good agreement.",1302.4104v2
2013-02-19,Spin-flip hot spots in ultrathin films of monovalent metals: Enhancement and anisotropy of the Elliott-Yafet parameter,"In contrast to the long-known fact that spin-flip hot spots, i.e., special
\vc{k}-points on the Fermi surface showing a high spin-mixing parameter, do not
occur in the bulk of monovalent (noble and alkali) metals, we found them on the
surface Brillouin-zone boundary of ultrathin films of these metals.
Density-functional calculations within the Korringa-Kohn-Rostoker Green
function method for ultrathin (001) oriented Cu, Ag, and Au films of 10-layer
thickness show that the region around the hot spots can have a substantial
contribution, e.g.\ 52\% in Au(001), to the integrated spin-mixing parameter,
that could lead to a significant enhancement of the spin-relaxation rate or
spin-Hall angle in thin films. Owing to the appearance of spin-flip hot-spots,
a large anisotropy of the Elliott-Yafet parameter [50\% for Au(001)] is also
found in these systems. The findings are important for spintronics applications
in which noble-metals are frequently used and in which the dimensionality of
the sample is reduced.",1302.4671v2
2013-02-25,Anisotropic universes in the ghost-free bigravity,"We study Bianchi cosmologies in the ghost-free bigravity theory assuming both
metrics to be homogeneous and anisotropic, of the Bianchi class A, which
includes types I,II,VI$_0$,VII$_0$,VIII, and IX. We assume the universe to
contain a radiation and a non-relativistic matter, with the cosmological term
mimicked by the graviton mass. We find that, for generic initial values leading
to a late-time self-acceleration, the universe approaches a state with
non-vanishing anisotropies. The anisotropy contribution to the total energy
density decreases much slower than in General Relativity and shows the same
falloff rate as the energy of a non-relativistic matter. The solutions show a
singularity in the past, and in the Bianchi IX case the singularity is
approached via a sequence of Kasner-like steps, which is characteristic for a
chaotic behavior.",1302.6198v3
2013-02-26,Motion induced second order temperature and y-type anisotropies after the subtraction of linear dipole in the CMB maps,"y-type spectral distortions of the cosmic microwave background allow us to
detect clusters and groups of galaxies, filaments of hot gas and the
non-uniformities in the warm hot intergalactic medium. Several CMB experiments
(on small areas of sky) and theoretical groups (for full sky) have recently
published y-type distortion maps. We propose to search for two artificial hot
spots in such y-type maps resulting from the incomplete subtraction of the
effect of the motion induced dipole on the cosmic microwave background sky.
This dipole introduces, at second order, additional temperature and
y-distortion anisotropy on the sky of amplitude few \mu K which could
potentially be measured by Planck HFI and Pixie experiments and can be used as
a source of cross channel calibration by CMB experiments. This y-type
distortion is present in every pixel and is not the result of averaging the
whole sky. This distortion, calculated exactly from the known linear dipole,
can be subtracted from the final y-type maps, if desired.",1302.6571v1
2013-03-05,Strangelets and the TeV-PeV cosmic-ray anisotropies,"Several experiments (e.g., Milagro and IceCube) have reported the presence in
the sky of regions with significant excess in the arrival direction
distributions of Galactic cosmic rays in the TeV to PeV energy range. Here we
study the possibility that these hotspots are a manifestation of the peculiar
nature of these cosmic rays, and of the presence of molecular clouds near the
sources. We propose that stable quark matter lumps or so-called ""strangelets""
can be emitted in the course of the transition of a neutron star to a more
compact astrophysical object. A fraction of these massive particles would lose
their charge by spallation or electron capture in molecular clouds located in
the immediate neighborhood of their source, and propagate rectilinearly without
decaying further, hence inducing anisotropies of the order of the cloud size.
With reasonable astrophysical assumptions regarding the neutron star transition
rate, strangelet injection and neutralization rates, we can reproduce
successfully the observed hotspot characteristics and their distribution in the
sky.",1303.1186v1
2013-03-05,"Angle-Dependent Spin-Wave Resonance Spectroscopy of (Ga,Mn)As Films","A modeling approach for standing spin-wave resonances based on a
finite-difference formulation of the Landau-Lifshitz-Gilbert equation is
presented. In contrast to a previous study [Bihler et al., Phys. Rev. B 79,
045205 (2009)], this formalism accounts for elliptical magnetization precession
and magnetic properties arbitrarily varying across the layer thickness,
including the magnetic anisotropy parameters, the exchange stiffness, the
Gilbert damping, and the saturation magnetization. To demonstrate the
usefulness of our modeling approach, we experimentally study a set of (Ga,Mn)As
samples grown by low-temperature molecular-beam epitaxy by means of
electrochemical capacitance-voltage measurements and angle-dependent standing
spin-wave resonance spectroscopy. By applying our modeling approach, the angle
dependence of the spin-wave resonance data can be reproduced in a simulation
with one set of simulation parameters for all external field orientations. We
find that the approximately linear gradient in the out-of-plane magnetic
anisotropy is related to a linear gradient in the hole concentrations of the
samples.",1303.1192v1
2013-03-08,Interplay of inter-chain interactions and exchange anisotropy: Stability of multipolar states in quasi-1D quantum helimagnets,"We quantify the instability towards the formation of multipolar states in
coupled spin-1/2 chain systems with a frustrating J1-J2 exchange, in parameter
regimes that are of directly relevance to edge-shared cuprate spin-chain
compounds. Three representative types of inter-chain coupling and the presence
of uniaxial exchange anisotropy are considered. The magnetic phase diagrams are
determined by Density Matrix Renormalization Group calculations and completed
by exact analytic results for the nematic and dipolar phases. We establish that
the residual couplings strongly affect the pitch of spiral states and their
instability to multipolar phases. Our theoretical results bring to the fore
novel candidate materials close to quantum nematic/triatic ordering.",1303.1933v1
2013-03-10,Towards Anisotropy-Free and Non-Singular Bounce Cosmology with Scale-invariant Perturbations,"We investigate non-singular bounce realizations in the framework of
ghost-free generalized Galileon cosmology, which furthermore can be free of the
anisotropy problem. Considering an Ekpyrotic-like potential we can obtain a
total Equation-of-State (EoS) larger than one in the contracting phase, which
is necessary for the evolution to be stable against small anisotropic
fluctuations. Since such a large EoS forbids the Galileon field to generate the
desired form of perturbations, we additionally introduce the curvaton field
which can in general produce the observed nearly scale-invariant spectrum. In
particular, we provide approximate analytical and exact semi-analytical
expressions under which the bouncing scenario is consistent with observations.
Finally, the combined Galileon-curvaton system is free of the Big-Rip after the
bounce.",1303.2372v2
2013-03-12,Cosmic ray anisotropies to 5 PeV,"Several large cosmic ray (CR) detectors have recently provided data on the
arrival directions of CR, which taken together with previous data recorded over
many decades allow the amplitgude and phase of the first harmonic to be derived
with reasonable precision and up to higher energies. We find a high degree of
consistency amongst the various measurements. The new data indicate that at an
energy above ~0.1 PeV a change of the CR anisotropy sets in. The amplitude of
the first harmonic, which rises to 3 TeV, then diminishes and begins to rise
again. The direction of the phase also changes to the opposite one. A measure
of understanding follows from the use of two-dimensional maps of CR excesses
over the mean background. When the energy of CR approaches the PeV region, the
excess of CR moves from the Galactic Anti-Centre to the opposite direction of
the Galactic Centre. The possible role of such potential CR sources as the
supernovae Monogem Ring and Vela, which could help to explain some of the
observed results, is discussed.",1303.2889v1
2013-03-13,Crystalline symmetry and the melt-growth kinetics of solid-liquid interface,"One of the important factors governing the growth morphology of materials is
the interface kinetic coefficient \mu, which is the proportionality constant
between the velocity of solid-liquid interface and undercooling. We employ
Ginzburg-Landau (GL) free energy functional to derive an analytical expression
of kinetic coefficients. The anisotropy of kinetic coefficients naturally arise
from the broken symmetry at the solid-liquid interface for various crystalline
orientations. The analytical expression of kinetic coefficients is compared to
Mikheev-Chernov theory [J. Cryst. Growth 112, 591 (1991)] derived from
hydrodynamic equations. In addition, we use equilibrium density wave profiles
to evaluate kinetic coefficients and compare them with that from MD
simulations. Our results are in good agreement with Mikheev-Chernov theory and
MD simulations and shed lights on a possible origin of anisotropy of
interfacial kinetics.",1303.3111v2
2013-03-18,Frictional anisotropy of metal nanoparticles adsorbed on graphene,"Friction force acting on silver and nickel nanoparticles sheared on a
graphene sheet in different lateral directions is investigated using classical
molecular dynamics simulations. The results reveal the existence of frictional
anisotropy for both metals. In most cases, the maximum value of the friction
force is about two times larger than the minimum one. The form of dependencies
of instantaneous values of the friction force components on the corresponding
lateral components of the position of the centre of mass of the nanoislands
strongly depends on sliding direction, varying between the sawtooth and the
irregular one. A qualitative explanation of the results based on the ""patch""
model is proposed.",1303.4187v1
2013-03-19,Maximum Entropy deconvolution of Primordial Power Spectrum,"It is well known that CMB temperature anisotropies and polarization can be
used to probe the metric perturbations in the early universe. Presently, there
exist neither any observational detection of tensor modes of primordial metric
perturbations nor of primordial non-Gaussianity. In such a scenario, primordial
power spectrum of scalar metric perturbations is the only correlation function
of metric perturbations (presumably generated during inflation) whose effects
can be directly probed through various observations. To explore the possibility
of any deviations from the simplest picture of the era of cosmic inflation in
the early universe, it thus becomes extremely important to uncover the
amplitude and shape of this (only available) correlation sufficiently well. In
the present work, we attempt to reconstruct the primordial power spectrum of
scalar metric perturbations using the binned (uncorrelated) CMB temperature
anisotropies data using the Maximum Entropy Method (MEM) to solve the
corresponding inverse problem. Our analysis shows that, given the current CMB
data, there are no convincing reasons to believe that the primordial power
spectrum of scalar metric perturbations has any significant features.",1303.4747v1
2013-03-26,Study of the electronic nematic phase of Sr$_3$Ru$_2$O$_7$ with precise control of the applied magnetic field vector,"We report a study of the magnetoresistivity of high purity Sr$_3$Ru$_2$O$_7$,
in the vicinity of its electronic nematic phase. By employing a triple-axis
(9/1/1T) vector magnet, we were able to precisely tune both the magnitude and
direction of the in-plane component of the magnetic field (H$_\parallel$). We
report the dependence of the resistively determined anisotropy on H$_\parallel$
in the phase, as well as across the wider temperature-field region. Our
measurements reveal a high-temperature anisotropy which mimics the behaviour of
fluctuations from the underlying quantum critical point, and suggest the
existence of a more complicated phase diagram than previously reported.",1303.6459v1
2013-04-03,Adhesion and size dependent friction anisotropy in boron nitride nanotubes,"The frictional properties of individual multiwalled boron nitride nanotubes
(BN-NTs) synthesized by chemical vapor deposition (CVD) and deposited on a
silicon substrate are investigated using an atomic force microscope tip sliding
along (longitudinal sliding) and across (transverse sliding) the tube's
principal axis. Because of the tube transverse deformations during the tip
sliding, a larger friction coefficient is found for the transverse sliding as
compared to the longitudinal sliding. Here, we show that the friction
anisotropy in BN-NTs, defined as the ratio between transverse and longitudinal
friction forces per unit area, increases with the nanotube-substrate contact
area. Larger contact area denotes stronger surface adhesion, resulting in a
longitudinal friction coefficient closer to the value expected in absence of
transverse deformations. Compared to carbon nanotubes (C-NT), BN-NTs display a
friction coefficient in each sliding direction with intermediate values between
CVD and arc discharge C-NTs. CVD BN-NTs with improved tribological properties
and higher oxidation temperature might be a better candidate than CVD C-NTs for
applications in extreme environments.",1304.1013v1
2013-04-03,Magnetic topology and current channels in plasmas with toroidal current density inversions,"The equilibrium magnetic field inside axisymmetric plasmas with inversions on
the toroidal current density is studied. Structurally stable non-nested
magnetic surfaces are considered. For any inversion in the internal current
density the magnetic families define several positive current channels about a
central negative one. A general expression relating the positive and negative
currents is derived in terms of a topological anisotropy parameter. Next, an
analytical local solution for the poloidal magnetic flux is derived and shown
compatible with current hollow magnetic pitch measurements shown in the
literature. Finally, the analytical solution exhibits non-nested magnetic
families with positive anisotropy, indicating that the current inside the
positive channels have at least twice the magnitude of the central one.",1304.1029v1
2013-04-03,Loops and spurs: The angular power spectrum of the Galactic synchrotron background,"We present a new model of the diffuse Galactic synchrotron radiation,
concentrating on its angular anisotropies. While previous studies have focussed
on either the variation of the emissivity on large (kpc) scales, or on
fluctuations due to MHD turbulence in the interstellar medium, we unify these
approaches to match the angular power spectrum. We note that the usual
turbulence cascade calculation ignores spatial correlations at the injection
scale due to compression of the interstellar medium by old supernova remnants
-- the 'radio loops', only four of which are visible by eye in radio maps. This
new component naturally provides the otherwise missing power on intermediate
and small scales in the all-sky map at 408 MHz. Our model can enable more
reliable subtraction of the synchrotron foreground for studies of CMB
anisotropies (both in temperature and polarisation) or searches for dark matter
annihilation. We conclude with some remarks on the relevance to modelling of
the polarised foreground.",1304.1078v2
2013-04-09,Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi,"In this paper, we investigate the half-metallicity of Heusler alloys
Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance
measurements. It is found that, with the increase of Cr content x, the Fermi
level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of
conduction band, and a large half-metallic band gap of 0.75 eV is obtained for
x=0.75. We then successfully synthesized a series Heusler Fe2Co1-xCrxSi
polycrystalline ribbon samples. The results of X-ray diffraction indicate that
the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order
and the saturation magnetic moment follows half-metallic Slater-Pauling rule.
Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic
magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, 0.75) show a negative value
suggesting they are stable half-metallic ferromagnets.",1304.2602v1
2013-04-10,Newtonian polytropes for anisotropic matter: General framework and applications,"We set up the general formalism to model polytropic Newtonian stars with
anisotropic pressure. We obtain the corresponding Lane-Emden equation. A
heuristic model based on an ansatz to obtain anisotropic matter solutions from
known solutions for isotropic matter is adopted to illustrate the effects of
the pressure anisotropy on the structure of the star. In particular, we
calculate the Chandrasekhar mass for a white dwarf. It is clearly displayed how
the Chandrasekhar mass limit changes depending on the anisotropy. Prospective
astrophysical applications of the proposed approach are discussed.",1304.2824v2
2013-04-15,Field dependence of the Spin State and Spectroscopic Modes of Multiferroic BiFeO$_3$,"The spectroscopic modes of multiferroic BiFeO$_3$ provide detailed
information about the very small anisotropy and Dzyaloshinskii-Moriya (DM)
interactions responsible for the long-wavelength, distorted cycloid below $\TN
= 640$ K. A microscopic model that includes two DM interactions and easy-axis
anisotropy predicts both the zero-field spectroscopic modes as well as their
splitting and evolution in a magnetic field applied along a cubic axis. While
only six modes are optically active in zero field, all modes at the cycloidal
wavevector are activated by a magnetic field. The three magnetic domains of the
cycloid are degenerate in zero field but one domain has lower energy than the
other two in nonzero field. Measurements imply that the higher-energy domains
are depopulated above about 6 T and have a maximum critical field of 16 T,
below the critical field of 19 T for the lowest-energy domain. Despite the
excellent agreement with the measured spectroscopic frequencies, some
discrepancies with the measured spectroscopic intensities suggest that other
weak interactions may be missing from the model.",1304.4195v3
2013-04-22,Magnetic anisotropic energy gap and low energy spin wave excitation in antiferromagnetic block phase of K2Fe4Se5,"Neutron scattering experiments were performed to investigate magnetic order
and magnetic excitations in ternary iron chalcogenide K2Fe4Se5. The formation
of a superlattice structure below 580 K together with the decoupling between
the Fe-vacancy order-disorder transition and the antiferromagnetic order
transition appears to be a common feature in the A2Fe4Se5 family. The study of
spin dynamics of K2Fe4Se5 reveals two distinct energy gaps at the magnetic
Brillouin zone center, which indicates the presence of magnetic anisotropy and
the decrease of local symmetry due to electronic and orbital anisotropy. The
low-energy spin wave excitations of K2Fe4Se5 can be properly described by
linear spin wave theory within a Heisenberg model. Compared to iron pnictides,
K2Fe4Se5 exhibits a more two-dimensional magnetism as characterized by large
differences not only between out-of-plane and in-plane spin wave velocities,
but also between out-of-plane and in-plane exchange interactions.",1304.5950v1
2013-04-29,Completely flat bands and fully localized states on surfaces of anisotropic diamond-lattice models,"We discuss flat-band surface states on the (111) surface in the tight-binding
model with nearest-neighbor hopping on the diamond lattice, in analogy to the
flat-band edge states in graphene with a zigzag edge. The bulk band is gapless,
and the gap closes along a loop in the Brillouin zone. The verge of the
flat-band surface states is identical with this gap-closing loop projected onto
the surface plane. When anisotropies in the hopping integrals increase, the
bulk gap-closing points move and the distribution of the flat-band states
expands in the Brillouin zone. Then when the anisotropy is sufficiently large,
the surface flat bands cover the whole Brillouin zone. Because of the
completely flat bands, we can construct surface-state wavefunctions which are
localized in all the three directions.",1304.7592v3
2013-05-07,Micromagnetic modelling of anisotropic damping in ferromagnet,"We report a numerical implementation of the Landau-Lifshitz-Baryakhtar
theory, which dictates that the micromagnetic relaxation term obeys the
symmetry of the magnetic crystal, i. e. replacing the single intrinsic damping
constant with a tensor of corresponding symmetry. The effect of anisotropic
relaxation is studied in thin saturated ferromagnetic disk and ellipse with and
without uniaxial magneto-crystalline anisotropy. We investigate the angular
dependency of the linewidth of magnonic resonances with respect to the given
structure of the relaxation tensor. The simulations suggest that the anisotropy
of the magnonic linewidth is determined by only two factors: the projection of
the relaxation tensor onto the plane of precession and the ellipticity of the
later.",1305.1641v2
2013-05-15,Azimuthal Anisotropy from STAR Experiment,"We report the measurement of first (\textit{n} = 1) and higher
order(\textit{n} = 2-5) harmonic coefficients ($v_{n}$) of the azimuthal
anisotropy in the distribution of the particles produced in Au+Au collisions at
$\sqrt{s_{NN}}$ =200 GeV and U+U collisions at $\sqrt{s_{NN}}$ =193 GeV,
recorded with the STAR detector at RHIC. The differential measurement of
$(v_{n})$ is presented as a function of transverse momentum ($p_{T}$) and
centrality. We also present $v_{n}$ measurement in the ultra-central collisions
in U+U collisions. These data may provide strong constraints on the theoretical
models of the initial condition in heavy ion collisions and the transport
properties of the produced medium.",1305.3624v2
2013-05-23,Two-dimensional arrays of superconducting and soft magnetic strips as dc magnetic metamaterials,"We have theoretically investigated the magnetic response of two-dimensional
(2D) arrays of superconducting and soft magnetic strips, which are regarded as
models of dc magnetic metamaterials. The anisotropy of the macroscopic
permeabilities depends on whether the applied magnetic field is parallel to the
wide surface of the strips ($\mu_{\parallel}$) or perpendicular
($\mu_{\perp}$). For the 2D arrays of superconducting strips,
$0<\mu_{\perp}/\mu_0\ll \mu_{\parallel}/\mu_0\simeq 1$, whereas for the 2D
arrays of soft magnetic strips,
$\mu_{\parallel}/\mu_0\gg\mu_{\perp}/\mu_0\simeq 1$, where $\mu_0$ is the
vacuum permeability. We also demonstrate that strong anisotropy of the
macroscopic permeability can be obtained for hybrid arrays of superconducting
and soft magnetic strips, where $\mu_{\parallel}/\mu_0\gg 1\gg
\mu_{\perp}/\mu_0>0$.",1305.5318v1
2013-05-29,Enhanced interface perpendicular magnetic anisotropy in Ta|CoFeB|MgO using nitrogen doped Ta underlayers,"We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic
heterostructures are strongly influenced by doping the Ta underlayer with
nitrogen. In particular, the saturation magnetization drops upon doping the Ta
underlayer, suggesting that the doped underlayer acts as a boron diffusion
barrier. In addition, the thickness of the magnetic dead layer decreases with
increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy
increases to ~1.8 erg/cm2 when an optimum amount of nitrogen is introduced into
the Ta underlayer. These results show that nitrogen doped Ta serves as a good
underlayer for Spintronics applications including magnetic tunnel junctions and
domain wall devices.",1305.6660v1
2013-05-30,Evolution of ferromagnetic and spin-wave resonances with crystalline order in thin films of full-Heusler alloy Co2MnSi,"We report the evolution of magnetic moment as well as magnetic anisotropy
with crystalline order in Co$_2$MnSi thin films grown on $(100)$ MgO by pulsed
laser deposition. The films become more ordered as the annealing temperature
($T_A$) increases from 400 to 600 $^0$C. The extent of \emph{L}$2_1$ ordering
in the films annealed at 600 $^0$C is $\approx 96%$. The static magnetization
measurements by vibrating sample magnetometry shows a maximum moment of 4.95
$\mu_B$ per formula unit with low coercivity ($H_C$ $\approx$ 65 Oe) in the
films annealed at 600 $^0$C. A rigorous analysis of the azimuthal and polar
angle dependent ferromagnetic resonance (FMR) measured at several temperatures
allows determination of various anisotropy fields relevant to our system as a
function of $T_A$. Finally, we have evaluated the exchange stiffness constant
down to 100 K using spin wave modes in FMR spectra. We have also estimated the
exchange energies as well as stiffness constant by varying the lattice
parameter \emph{ab-initio} using the Korringa-Kohn-Rostoker method.",1305.7048v1
2013-06-07,Strong anisotropy in quasi-static magnetohydrodynamic turbulence for high interaction parameters,"We simulate forced quasi-static magnetohydrodynamic turbulence and
investigate the anisotropy, energy spectrum, and energy flux of the flow,
specially for large interaction parameters ($N$). We show that the angular
dependence of the energy spectrum is well quantified using Legendre
polynomials. For large $N$, the energy spectrum is exponential. Our direct
computation of energy flux reveals an inverse cascade of energy at low
wavenumbers, similar to that in two-dimensional turbulence. We observe the flow
be two-dimensional (2D) for moderate $N$ ($N \sim 20$), and two-dimensional
three-component (2D-3C) type for $N \ge 27$. In our forced simulation, the
transition from 2D to 2D-3C occurs at higher value of $N$ than Favier et al.,
[""On the two-dimensionalization of quasistatic magnetohydrodynamic turbulence,""
Phys. Fluids 22, 075104 (2010)] who employ decaying simulations.",1306.1611v2
2013-06-09,"First-principles calculations of the structural, electronic, optical and elastic properties of the CuYS2 semiconductor","Ternary semiconductor CuYS2 is studied by using the first-principles methods
in the density functional theory (DFT) framework. The structural, electronic,
optical and elastic properties were calculated at the ambient and elevated
hydrostatic pressures. The compound was shown to have an indirect band gap of
about 1.342/1.389 eV (in the generalized gradient and local density
approximations). The anisotropy of the optical properties was studied by
calculating the absorption spectra, dielectric function and index of refraction
for different polarizations. The anisotropy of the elastic properties was
visualized by plotting the three-dimensional dependence of the Young's moduli
on the direction in the crystal lattice. The obtained results, which are
reported for the first time to the best of the author's knowledge, can
facilitate assessment of possible applications of the title material.",1306.2063v1
2013-06-11,Localization at the Edge of 2D Topological Insulator by Kondo Impurities with Random Anisotropies,"We consider chiral electrons moving along the 1D helical edge of a 2D
topological insulator and interacting with a disordered chain of Kondo
impurities. Assuming the electron-spin couplings of random anisotropies, we map
this system to the problem of the pinning of the charge density wave by the
disordered potential. This mapping proves that arbitrary weak anisotropic
disorder in coupling of chiral electrons with spin impurities leads to the
Anderson localization of the edge states.",1306.2626v3
2013-06-18,Anisotropy in solid inflation,"In the model of solid / elastic inflation, inflation is driven by a source
that has the field theoretical description of a solid. To allow for prolonged
slow roll inflation, the solid needs to be extremely insensitive to the spatial
expansion. We point out that, because of this property, the solid is also
rather inefficient in erasing anisotropic deformations of the geometry. This
allows for a prolonged inflationary anisotropic solution, providing the first
example with standard gravity and scalar fields only which evades the
conditions of the so called cosmic no-hair conjecture. We compute the curvature
perturbations on the anisotropic solution, and the corresponding
phenomenological bound on the anisotropy. Finally, we discuss the analogy
between this model and the f (phi) F^2 model, which also allows for anisotropic
inflation thanks to a suitable coupling between the inflaton phi and a vector
field. We remark that the bispectrum of the curvature perturbations in solid
inflation is enhanced in the squeezed limit and presents a nontrivial angular
dependence, as had previously been found for the f (phi) F^2 model.",1306.4160v1
2013-06-21,Two-point correlation function of density perturbations in a large void universe,"We study the two-point correlation function of density perturbations in a
spherically symmetric void universe model which does not employ the Copernican
principle. First we solve perturbation equations in the inhomogeneous universe
model and obtain density fluctuations by using a method of non-linear
perturbation theory which was adopted in our previous paper. From the obtained
solutions, we calculate the two-point correlation function and show that it has
a local anisotropy at the off-center position differently from those in
homogeneous and isotropic universes. This anisotropy is caused by the tidal
force in the off-center region of the spherical void. Since no tidal force
exists in homogeneous and isotropic universes, we may test the inhomogeneous
universe by observing statistical distortion of the two-point galaxy
correlation function.",1306.5131v1
2013-06-21,Magnetic properties of a family of quinternary oxalates,"We report on the magnetic properties of four isomorphous compounds of a
family of quinternary oxalates down to 60 mK. In all these materials, the
magnetic FeII ions with a strong magneto-crystalline anisotropy form a
distorted kagome lattice, topologically equivalent to a perfect kagome one if
nearest-neighbor interactions only are considered. All the compounds order at
low temperature in an antiferromagnetic arrangement with magnetic moments at
120{\deg}. A remarkable magnetic behavior emerges below the N\'eel temperature
in three compounds (with inter-kagome-layer Zr, Sn, Fe but not with Al): the
spin anisotropy combined with a low exchange path network connectivity lead to
domain walls intersecting the kagome planes through strings of free spins.
These produce an unfamiliar slow spin dynamics in the ordered phase observed by
AC susceptibility, evolving from exchange-released spin-flips towards a
cooperative behavior on decreasing the temperature.",1306.5188v1
2013-06-21,Change of magnetic ground state by light electron-doping in CeOs2Al10,"The effect of Ir substitution for Os in CeOs2Al10, with an unusually high
Neel temperature of T~28.5K, has been studied by high-resolution neutron
diffraction and magnetization measurements. A small amount of Ir (~ 8%) results
in a pronounced change of the magnetic structure of the Ce-sublattice. The new
magnetic ground state is controlled by the single ion anisotropy and implies
antiferromagnetic arrangement of the Ce-moments along the a-axis, as expected
from the anisotropy of the paramagnetic susceptibility. The value of the
ordered moments, 0.92(1) mu_B, is substantially bigger than in the undoped
compound, whereas the transition temperature is reduced down to 21K. A
comparison of the observed phenomena with the recently studied CeRu1.9Rh0.1Al10
system, exhibiting similar behaviour [A. Kondo et al., J. Phys. Soc. Jpn. 82,
054709 (2013)], strongly suggests the electron doping as the main origin of the
ground state changes. This provides a new way of exploring the anomalous
magnetic properties of the Ce(Ru/Os)2Al10 compounds.",1306.5269v1
2013-06-24,Orientation of the Angular Momentum in Superfluid 3He-A in a Stretched Aerogel,"Superfluid 3He-A in a fully characterized stretched aerogel, used in previous
work [1], has been studied for parallel and perpendicular orientations of the
magnetic field relative to the anisotropy axis of the aerogel. Consistently, we
find that an equal spin pairing state (ESP) is stabilized down to the lowest
temperature. From our pulsed NMR frequency shifts as a function of temperature
and tip angle, the orientation of the orbital angular momentum l has been
determined. The aerogel anisotropy introduced by uniaxial stretching tends to
align l in the axial state parallel to the strain axis, confirming the theory
proposed by Sauls [2] and contrary to the prediction of Volovik [3] based on an
impurity calculation of Rainer and Vuorio [4].",1306.5783v1
2013-06-27,Proton Kinetic Effects in Vlasov and Solar Wind Turbulence,"Kinetic plasma processes have been investigated in the framework of solar
wind turbulence, employing Hybrid Vlasov-Maxwell (HVM) simulations. The
dependency of proton temperature anisotropy T_{\perp}/T_{\parallel} on the
parallel plasma beta \beta_{\parallel}, commonly observed in spacecraft data,
has been recovered using an ensemble of HVM simulations. By varying plasma
parameters, such as plasma beta and fluctuation level, the simulations explore
distinct regions of the parameter space given by T_{\perp}/T_{\parallel} and
\beta_{\parallel}, similar to solar wind sub-datasets. Moreover, both
simulation and solar wind data suggest that temperature anisotropy is not only
associated with magnetic intermittent events, but also with gradient-type
structures in the flow and in the density. This connection between
non-Maxwellian kinetic effects and various types of intermittency may be a key
point for understanding the complex nature of plasma turbulence.",1306.6455v1
2013-06-28,"The role of orbital order in the stabilization of the $(π,0)$ ordered magnetic state in a minimal two-band model for iron pnictides","Spin wave excitations and stability of the ($\pi,0$) ordered magnetic state
are investigated in a minimal two-band itinerant-electron model for iron
pnictides. Presence of hopping anisotropy generates a strong ferro-orbital
order in the $d_{xz}$ and $d_{yz}$ Fe orbitals. The orbital order sign is as
observed in experiments. The induced ferro-orbital order strongly enhances the
spin wave energy scale and stabilizes the magnetic state by optimizing the
strength of the emergent AF and F spin couplings through optimal band fillings
in the two orbitals. The calculated spin-wave dispersion is in quantitative
agreement with neutron scattering measurements. Finite inter-orbital Hund's
coupling is shown to further enhance the spin wave energies state by coupling
the two magnetic sub-systems. A more realistic two-band model with less hopping
anisotropy is also considered which yields not only the circular hole pockets,
also correct ferro-orbital order and emergent F spin coupling.",1306.6727v2
2013-07-03,Leaky mode analysis of luminescent thin films: the case of ZnO on sapphire,"Zinc oxide (ZnO) epitaxial thin films grown on c-sapphire substrates by
pulsed laser deposition were investigated using angle and polarization-resolved
photoluminescence spectroscopy. Side-emission spectra differed significantly
from surface-emission spectra in exhibiting dominant, narrow,
polarization-resolved peaks. These spectral features were attributed to leaky
substrate modes in the layers. Observations were first verified using
transmission calculations with non-adjustable parameters, which took into
account the dispersion, the anisotropy of the ZnO refractive index and the
dependence on film thickness. Results were consistent with Fabry-Perot-like
interference being the origin of the distinctive ZnO luminescence observed at
grazing incidence angles. A second analysis, based on the source terms method,
was used in order to retrieve the bulk emission properties, including the
wavelength-dependent quantum yield and the emission anisotropy. While ZnO thin
films were considered here, this analysis method can be extended to any
luminescent thin film of similar geometry, demonstrating the potential of leaky
mode analysis for probing passive and active material properties.",1307.0892v1
2013-07-10,New limits on the violation of local position invariance of gravity,"Within the parameterized post-Newtonian (PPN) formalism, there could be an
anisotropy of local gravity induced by an external matter distribution, even
for a fully conservative metric theory of gravity. It reflects the breakdown of
the local position invariance of gravity and, within the PPN formalism, is
characterized by the Whitehead parameter $\xi$. We present three different
kinds of observation, from the Solar system and radio pulsars, to constrain it.
The most stringent limit comes from recent results on the extremely stable
pulse profiles of solitary millisecond pulsars, that gives $|\hat \xi| < 3.9
\times 10^{-9}$ (95% CL), where the hat denotes the strong-field generalization
of $\xi$. This limit is six orders of magnitude more constraining than the
current best limit from superconducting gravimeter experiments. It can be
converted into an upper limit of $\sim 4 \times 10^{-16}$ on the spatial
anisotropy of the gravitational constant.",1307.2637v1
2013-07-17,Anisotropy-driven spin relaxation in germanium,"A unique spin depolarization mechanism, induced by the presence of g-factor
anisotropy and intervalley scattering, is revealed by spin transport
measurements on long-distance germanium devices in a longitudinal magnetic
field. The confluence of electron-phonon scattering (leading to Elliott-Yafet
spin flips) and this previously unobserved physics enables the extraction of
spin lifetime solely from spin-valve measurements, without spin precession, and
in a regime of substantial electric-field-generated carrier heating. We find
spin lifetimes in Ge up to several hundreds of ns at low temperature, far
beyond any other available experimental results.",1307.4745v3
2013-07-19,Pseudoscalar N-flation and axial coupling revisited,"We revisit the dynamics of the axial coupling between many N-flatons and an
Abelian gauge field, with special attention to its statistically anisotropic
signal. The anisotropic power spectrum of curvature perturbations associated to
the large wavelength modes of the gauge vector field is generally undetectable,
since the anisotropy is confined to small scales. If the gauge field is the
electromagnetic field, provided that the number of fields participating in the
exponential expansion is large, it could be possible to generate sizable large
scale magnetic fields. However, its spectrum is blue, and appreciable power on
large scales implies an overly strong field on smaller scales, incompatibly
with observations. Furthermore, the anisotropy is also markedly enhanced, and
might be at odds with the isotropic observed sky. These aspects further demand
that the scale of inflation is kept to a minimum.",1307.5215v3
2013-07-23,Anisotropic Infrared Response of Vanadium Dioxide Microcrystals,"Vanadium dioxide (VO2) undergoes a phase transition at a temperature of 340 K
between an insulating monoclinic M1 phase and a conducting rutile phase.
Accurate measurements of possible anisotropy of the electronic properties and
phonon features of VO2 in the insulating monoclinic M1 and metallic rutile
phases are a prerequisite for understanding the phase transition in this
correlated system. Recently, it has become possible to grow single domain
untwinned VO2 microcrystals which makes it possible to investigate the true
anisotropy of VO2. We performed polarized transmission infrared
micro-spectroscopy on these untwinned microcrystals in the spectral range
between 200 cm-1 and 6000 cm-1 and have obtained the anisotropic phonon
parameters and low frequency electronic properties in the insulating monoclinic
M1 and metallic rutile phases. We have also performed ab initio GGA+U total
energy calculations of phonon frequencies for both phases. We find our
measurements and calculations to be in good agreement.",1307.6022v1
2013-07-29,Current-induced spin wave excitation in Pt|YIG bilayer,"We develop a self-consistent theory for current-induced spin wave excitations
in normal metal-magnetic insulator bilayer systems, thereby establishing the
relation between spin wave excitation and the experimentally controlled
parameters. We fully take into account the complex spin wave spectrum including
dipolar interactions and surface anisotropy as well as the spin-pumping at the
interface. Our results focus on the mode-dependent power close to the critical
currents for spin wave excitation. The major findings are (a) the spin transfer
torque can excite different spin-wave modes simultaneously; (b) spin pumping
counterbalances spin-transfer torque and affects the surface modes more than
the bulk modes; (c) spin pumping inhibits high frequency spin-wave modes,
thereby redshifting the excitation spectrum. We can get agreement with
experiments on yttrium iron garnet|platinum bilayers by postulating the
existence of surface anisotropy modes.",1307.7607v2
2013-07-30,Evidence for exclusion of the possibility of $d$-wave superconducting-gap symmetry in Ba-doped KFe$_2$As$_2$,"We have investigated the superconducting(SC)-gap anisotropy for several
Ba-doped KFe$_2$As$_2$ samples using laser-based angle-resolved photoemission
spectroscopy. We show that the SC-gap anisotropy and node positions drastically
change with a small amount of Ba doping. Our results totally exclude a
possibility of $d$-wave symmetry and strongly suggest that both spin and
orbital fluctuations are important for the paring interaction in the Ba-doped
K122.",1307.7922v3
2013-07-31,"Cosmic ray Spectrum, Composition, and Anisotropy Measured with IceCube","Analysis of cosmic ray surface data collected with the IceTop array of
Cherenkov detectors at the South Pole provides an accurate measurement of the
cosmic ray spectrum and its features in the ""knee"" region up to energies of
about 1 EeV. IceTop is part of the IceCube Observatory that includes a deep-ice
cubic kilometer detector that registers signals of penetrating muons and other
particles. Surface and in-ice signals detected in coincidence provide clear
insights into the nuclear composition of cosmic rays. IceCube already measured
an increase of the average primary mass as a function of energy. We present
preliminary results on both IceTop-only and coincident event analyses.
Furthermore, we review the recent measurement of the cosmic ray anisotropy with
IceCube.",1307.8394v1
2013-08-02,Temperature-dependent exchange bias properties of polycrystalline PtxCo1-x/CoO bilayers,"Temperature and PtCo composition dependence of exchange bias in PtxCo1-x/CoO
bilayers is investigated. It is observed that exchange bias properties,
blocking temperature and magnetic anisotropy of the PtxCo1-x/CoO thin films are
strongly affected by the concentration of Pt at the common interface. A
detailed structural analysis of antiferromagnetic CoO has been done by x-ray
photoelectron spectroscopy (XPS). The XPS data revealed that CoO layer grows
with non-stoichiometric behavior which results in other cobalt oxide phases and
thus lowers blocking temperature for the exchange biased systems. Increase of
Pt concentration in PtCo layer strengths the exchange bias and thus decreases
training of the system. It also results in enhancement of growth-induced
uniaxial magnetic anisotropy and onset of exchange bias at higher temperatures.
The role of Pt concentration on the interfacial interactions between
ferromagnetic and antiferromagnetic layers, and the effect of
superstoichiometric CoO on blocking temperature are also discussed.",1308.0483v1
2013-08-09,Ground state phase diagram of the 2d Bose-Hubbard model with anisotropic hopping,"We compute the ground state phase diagram of the 2d Bose-Hubbard model with
anisotropic hopping using quantum Monte Carlo simulations, connecting the 1d to
the 2d system. We find that the tip of the lobe lies on a curve controlled by
the 1d limit over the full anisotropy range while the universality class is
always the same as in the isotropic 2d system. This behavior can be derived
analytically from the lowest RG equations and has a form typical for the
underlying Kosterlitz-Thouless transition in 1d. We also compute the phase
boundary of the Mott lobe for strong anisotropy and compare it to the 1d
system. Our calculations shed light on recent cold gas experiments monitoring
the dynamics of an expanding cloud.",1308.2229v2
2013-08-10,A longwave model for strongly anisotropic growth of a crystal step,"A continuum model for the dynamics of a single step with the strongly
anisotropic line energy is formulated and analyzed. The step grows by
attachment of adatoms from the lower terrace, onto which atoms adsorb from a
vapor phase or from a molecular beam, and the desorption is non-negligible (the
""one-sided"" model). Via a multi-scale expansion, we derived a longwave,
strongly nonlinear, and strongly anisotropic evolution PDE for the step
profile. Written in terms of the step slope, the PDE can be represented in the
form similar to a convective Cahn-Hilliard equation. We performed the linear
stability analysis and computed the nonlinear dynamics. Linear stability
depends on whether the stiffness is minimum or maximum in the direction of the
step growth. It also depends nontrivially on the combination of the anisotropy
strength parameter and the atomic flux from the terrace to the step.
Computations show formation and coarsening of a hill-and-valley structure
superimposed onto a large-wavelength profile, which independently coarsens.
Coarsening laws for the hill-and-valley structure are computed for two
principal orientations of a maximum step stiffness, the increasing anisotropy
strength, and the varying atomic flux.",1308.2308v1
2013-08-11,Proton Kinetic Effects and Turbulent Energy Cascade Rate in the Solar Wind,"The first observed connection between kinetic instabilities driven by proton
temperature anisotropy and estimated energy cascade rates in the turbulent
solar wind is reported using measurements from the Wind spacecraft at 1 AU. We
find enhanced cascade rates are concentrated along the boundaries of the
($\beta_{\parallel}$, $T_{\perp}/T_{\parallel}$)-plane, which includes regions
theoretically unstable to the mirror and firehose instabilities. A strong
correlation is observed between the estimated cascade rate and kinetic effects
such as temperature anisotropy and plasma heating, resulting in protons 5-6
times hotter and 70-90% more anisotropic than under typical isotropic plasma
conditions. These results offer new insights into kinetic processes in a
turbulent regime.",1308.2425v1
2013-08-13,Doping influence of spin dynamics and magnetoelectric effect in hexagonal Y$_{0.7}$Lu$_{0.3}$MnO$_{3}$,"We use inelastic neutron scattering to study spin waves and their correlation
with the magnetoelectric effect in Y$_{0.7}$Lu$_{0.3}$MnO$_3$. In the undoped
YMnO$_3$ and LuMnO$_3$, the Mn trimerization distortion has been suggested to
play a key role in determining the magnetic structure and the magnetoelectric
effect. In Y$_{0.7}$Lu$_{0.3}$MnO$_3$, we find a much smaller in-plane
(hexagonal $ab$-plane) single ion anisotropy gap that coincides with a weaker
in-plane dielectric anomaly at $T_N$. Since both the smaller in-plane
anisotropy gap and the weaker in-plane dielectric anomaly are coupled to a
weaker Mn trimerization distortion in Y$_{0.7}$Lu$_{0.3}$MnO$_3$ comparing to
YMnO$_3$ and LuMnO$_3$, we conclude that the Mn trimerization is responsible
for the magnetoelectric effect and multiferroic phenomenon in
Y$_{1-y}$Lu$_{y}$MnO$_{3}$.",1308.2908v1
2013-08-14,Nonperturbative analysis of the evolution of cosmological perturbations through a nonsingular bounce,"In bouncing cosmology, the primordial fluctuations are generated in a cosmic
contraction phase before the bounce into the current expansion phase. For a
nonsingular bounce, curvature and anisotropy grow rapidly during the bouncing
phase, raising questions about the reliability of perturbative analysis. In
this paper, we study the evolution of adiabatic perturbations in a nonsingular
bounce by nonperturbative methods including numerical simulations of the
nonsingular bounce and the covariant formalism for calculating nonlinear
perturbations. We show that the bounce is disrupted in regions of the universe
with significant inhomogeneity and anisotropy over the background energy
density, but is achieved in regions that are relatively homogeneous and
isotropic. Sufficiently small perturbations, consistent with observational
constraints, can pass through the nonsingular bounce with negligible alteration
from nonlinearity. We follow scale invariant perturbations generated in a
matter-like contraction phase through the bounce. Their amplitude in the
expansion phase is determined by the growing mode in the contraction phase, and
the scale invariance is well preserved across the bounce.",1308.3044v1
2013-08-20,Hole Spin Helix: Anomalous Spin Diffusion in Anisotropic Strained Hole Quantum Wells,"We obtain the spin-orbit interaction and spin-charge coupled transport
equations of a two-dimensional heavy hole gas under the influence of strain and
anisotropy. We show that a simple two-band Hamiltonian can be used to describe
the holes. In addition to the well-known cubic hole spin-orbit interaction,
anisotropy causes a Dresselhaus-like term, and strain causes a Rashba term. We
discover that strain can cause a shifting symmetry of the Fermi surfaces for
spin up and down holes. We predict an enhanced spin lifetime associated with a
spin helix standing wave similar to the Persistent Spin Helix which exists in
the two-dimensional electron gas with equal Rashba and Dresselhaus spin-orbit
interactions. These results may be useful both for spin-based experimental
determination of the Luttinger parameters of the valence band Hamiltonian and
for creating long-lived spin excitations.",1308.4248v3
2013-08-21,Thermal power spectrum in the CFT driven cosmology,"We present an overview of the recently suggested cosmological model driven by
conformal field theory (CFT) with the initial conditions in the form of the
microcanonical density matrix. In particular, we discuss the origin of
inflationary stage in this model and a novel feature -- the thermal nature of
the primordial power spectrum of the CMB anisotropy. The relevant effect of
""temperature of the relic temperature anisotropy"" can be responsible for a
thermal contribution to the red tilt of this spectrum, additional to its
conventional vacuum component. The amplification of this effect due to recently
established $a$-theorem in CFT is briefly discussed.",1308.4451v2
2013-08-22,Confined dissipative droplet solitons in spin-valve nanowires with perpendicular magnetic anisotropy,"Magnetic dissipative droplets are localized, strongly nonlinear dynamical
modes excited in nano-contact spin valves with perpendicular magnetic
anisotropy. These modes find potential application in nanoscale structures for
magnetic storage and computation, but dissipative droplet studies have so far
been limited to extended thin films. Here, numerical and asymptotic analyses
are used to demonstrate the existence and properties of novel solitons in
confined structures. As a nanowire's width is decreased with a nano-contact of
fixed size at its center, the observed modes undergo transitions from a fully
localized two-dimensional droplet into a two-dimensional droplet edge mode and
then a pulsating one-dimensional droplet. These solitons are interpreted as
dissipative versions of classical, conservative solitons, allowing for an
analytical description of the modes and the mechanisms of bifurcation. The
presented results open up new possibilities for the study of low-dimensional
solitons and droplet applications in nanostructures.",1308.4812v1
2013-08-27,Multiple scattering Sunyaev-Zeldovich signal I: lowest order effect,"Future high-resolution, high-sensitivity Sunyaev-Zeldovich (SZ) observations
of individual clusters will allow us to study the dynamical state of the intra
cluster medium (ICM). To exploit the full potential of this new observational
window, it is crucial to understand the different contributions to the total SZ
signal. Here, we investigate the signature caused by multiple scatterings at
lowest order of the electron temperature. Previous analytic discussions of this
problem used the isotropic scattering approximation (ISA), which even for the
simplest cluster geometries is rather rough. We take a step forward and
consistently treat the anisotropy of the ambient radiation field caused by the
first scattering. We show that the multiple scattering SZ signal directly
probes line of sight anisotropies of the ICM, thereby delivering a new set of
SZ observables which could be used for 3D cluster-profile reconstruction. The
multiple scattering signal should furthermore correlate spatially with the
cluster's X-ray and SZ polarization signals, an effect that could allow
enhancing the detectability of this contribution.",1308.5969v2
2013-08-28,Tunneling spectroscopy for probing orbital anisotropy in iron pnictides,"Using realistic multi-orbital tight-binding Hamiltonians and the T-matrix
formalism, we explore the effects of a non-magnetic impurity on the local
density of states in Fe-based compounds. We show that scanning tunneling
spectroscopy (STS) has very specific anisotropic signatures that track the
evolution of orbital splitting (OS) and antiferromagnetic gaps. Both
anisotropies exhibit two patterns that split in energy with decreasing
temperature, but for OS these two patterns map onto each other under 90 degree
rotation. STS experiments that observe these signatures should expose the
underlying magnetic and orbital order as a function of temperature across
various phase transitions.",1308.6248v2
2013-09-01,The orientation dependence of quasar spectral energy distributions,"We investigate the orientation dependence of the spectral energy
distributions in a sample of radio-loud quasars. Selected specifically to study
orientation issues, the sample contains 52 sources with redshifts in the range
0.16<z<1.4 and measurements of radio core dominance, a radio orientation
indicator. Measured properties include monochromatic luminosities at a range of
wavelengths between the infrared and X-rays, integrated infrared luminosity,
spectral slopes, and the covering fraction of the obscuring circumnuclear dust.
We estimate dust covering fraction assuming that the accretion disk emits
anisotropically and discuss the shortcomings and technical difficulties of this
calculation. Luminosities are found to depend on orientation, with face-on
sources factors of a 2-3 brighter than more edge-on sources, depending on
wavelength. The degree of anisotropy varies very little with wavelength such
that the overall shape of the spectral energy distribution does not vary
significantly with orientation. In the infrared, we do not observe a decrease
in anisotropy with increasing wavelength. The spectral slopes and estimates of
covering fraction are not significantly orientation dependent. We construct
composite spectral energy distributions as a function of radio core dominance
and find that these illustrate the results determined from the measured
properties.",1309.0182v1
2013-09-02,Recent progress in perpendicularly magnetized Mn-based binary alloy films,"In this article, we review the recent progress in growth, structural
characterization, magnetic properties and related spintronic devices of
tetragonal MnxGa and MnxAl thin films with perpendicular magnetic anisotropy.
In the first part of this review, we present a brief introduction to the
demands for perpendicularly magnetized materials in spintronics, magnetic
recording and permanent magnets applications, and the most promising candidates
of tetragonal MnxGa and MnxAl with strong perpendicular anisotropy. Then, in
the second and third parts, we focus on the recent progress of perpendicularly
magnetized MnxGa and MnxAl, respectively, including their lattice structures,
bulk synthesis, epitaxial growth, structural chracterizations, magnetic and
other spin-dependent properties, and spintronic devices like magnetic tunneling
junctions, spin valves and spin injector into semiconductors. Finally, we give
a summary and a perspective of these perpendicularly magnetized Mn-based binary
alloy films for future applications.",1309.0298v2
2013-09-02,Ground-state fidelity of the spin-1 Heisenberg chain with single ion anisotropy: quantum renormalization group and exact diagonalization approaches,"We study the phase diagram of the anisotropic spin-1 Heisenberg chain with
single ion anisotropy (D) using a ground-state fidelity approach. The
ground-state fidelity and its corresponding susceptibility are calculated
within the quantum renormalization group scheme where we obtained the
renormalization of fidelity preventing to calculate the ground state. Using
this approach, the phase boundaries between the antiferromagnetic N\'{e}el,
Haldane and large-D phases are obtained for the whole phase diagram, which
justifies the application of quantum renormalization group to trace the
symmetery protected topological phases. In addition, we present numerical exact
diagonalization (Lanczos) results in, which we employ a recently introduced
non-local order parameter to locate the transition from Haldane to large-D
phase accurately.",1309.0402v1
2013-09-04,Structural anisotropy of directionally dried colloids,"Aqueous colloidal dispersions of silica particles become anisotropic when
they are dried through evaporation. This anisotropy is generated by a uniaxial
strain of the liquid dispersions as they are compressed by the flow of water
toward a solidification front. Part of the strain produced by the compression
is relaxed, and part of it is stored and transferred to the solid. This stored
elastic strain has consequences for the properties of the solid, where it may
facilitate the growth of shear bands, and generate birefringence.",1309.1048v2
2013-09-05,Measurements of cosmic rays at the highest energies with the Pierre Auger Observatory,"This paper summarizes the status and the recent measurements from the Pierre
Auger Observatory. The energy spectrum is described and its features discussed.
We report searches for anisotropy of cosmic ray arrival directions on large
scales and through correlation with catalogues of celestial objects. We also
present the search for anisotropies in the data without the use of astronomical
catalogues. The first measurement of the proton-air cross section around
10^{18} eV is discussed. Finally, the mass composition is addressed with
measurements of the variation of the depth of shower maximum with energy and
with the muon density at ground.",1309.1249v1
2013-09-07,Anisotropy in Cosmic rays from internal transitions in neutron stars,"We discuss the possibility that some recently measured anisotropic cosmic ray
components in the TeV-PeV energy range may be an indication of the ejection of
a peculiar type of matter. We present a model where a neutron star internal
transition with nuclear deconfinement of the quark content takes place. This
catastrophic event may cause a mass ejection process seeding the insterstelar
medium with droplets of quark matter, so called nuclearites. Neutralization of
these droplets in molecular clouds may drive the anisotropy since
quasi-rectilinear trajectories are allowed. Complementary information from
current experimental settings on earth or magnetic spectrometers on the ISS may
shed light on this exotic form of matter.",1309.1852v1
2013-09-20,Nonlocal Granular Rheology: Role of Pressure and Anisotropy,"We probe the secondary rheology of granular media, by imposing a main flow
and immersing a vane-shaped probe into the slowly flowing granulate. The
secondary rheology is then the relation between the exerted torque T and
rotation rate \omega of our probe. In the absence of any main flow, the probe
experiences a clear yield-stress, whereas for any finite flow rate, the yield
stress disappears and the secondary rheology takes on the form of a double
exponential relation between \omega and T. This secondary rheology does not
only depend on the magnitude of T, but is anisotropic --- which we show by
varying the relative orientation of the probe and main flow. By studying the
depth dependence of the three characteristic torques that characterize the
secondary rheology, we show that for counter flow, the dominant contribution is
frictional like --- i.e., T and pressure are proportional for given \omega ---
whereas for co flow, the situation is more complex. Our experiments thus reveal
the crucial role of anisotropy for the rheology of granular media.",1309.5238v1
2013-09-21,Spin excitations of individual Fe atoms on Pt(111): impact of the site-dependent giant substrate polarization,"We demonstrate using inelastic scanning tunneling spectroscopy (ISTS) and
simulations based on density functional theory that the amplitude and sign of
the magnetic anisotropy energy for a single Fe atom adsorbed onto the Pt(111)
surface can be manipulated by modifying the adatom binding site. Since the
magnitude of the measured anisotropy is remarkably small, up to an order of
magnitude smaller than previously reported, electron-hole excitations are weak
and thus the spin-excitation exhibits long lived precessional lifetimes
compared to the values found for the same adatom on noble metal surfaces.",1309.5443v1
2013-09-17,Radical-pair model of magnetoreception with spin-orbit coupling,"The mechanism used by migratory birds to orientate themselves using the
geomagnetic field is still a mystery in many species. The radical pair
mechanism, in which very weak magnetic fields can influence certain types of
spin-dependent chemical reactions, leading to biologically observable signals,
has recently imposed itself as one of the most promising candidates for certain
species. This is thanks both to its extreme sensitivity and its capacity to
reproduce results from behavioral studies. Still, in order to gain a
directional sensitivity, an anisotropic mechanism is needed. Recent proposals
have explored the possibility that such an anisotropy is due to the
electron-nucleus hyperfine interaction. In this work we explore a different
possibility, in which the anisotropy is due to spin-orbit coupling between the
electron spin and its angular momentum. We will show how a
spin-orbit-coupling-based magnetic compass can have performances comparable
with the usually-studied nuclear-hyperfine based mechanism. Our results could
thus help researchers actively looking for candidate biological molecules which
may host magnetoreceptive functions, both to describe magnetoreception in birds
as well as to develop artificial chemical compass systems.",1309.5882v1
2013-09-25,Acausality and Nonunique Evolution in Generalized Teleparallel Gravity,"We show the existence of physical superluminal modes and acausality in the
Brans-Dicke type of extension of teleparallel gravity that includes F(T)
gravity and teleparallel dark energy as special cases. We derive the
characteristic hypersurface for the extra degrees of freedom in the theory,
thereby showing that the time evolution is not unique and closed causal curves
can appear. Furthermore, we present a concrete disastrous solution in Bianchi
type I spacetime, in which the anisotropy in expansion can be any function of
time, and thus anisotropy can emerge suddenly, a simple demonstration that the
theory is physically problematic.",1309.6461v2
2013-09-25,Generating Intrinsic Dipole Anisotropy in the Large Scale Structures,"There have been recent reports of unexpectedly large velocity dipole in the
NRAO VLA Sky Survey data. We investigate whether the excess in the NVSS dipole
reported can be of cosmological origin. We assume a long wavelength
inhomogeneous scalar perturbation of the form \alpha sin (\kappa z) and study
its effects on the matter density contrasts. Assuming an ideal fluid model we
calculate, in the linear regime, the contribution of the inhomogeneous mode to
the density contrast. We calculate the expected dipole in the LSS for two
cases, first assuming that the mode is still superhorizon everywhere, and
second assuming the mode is subhorizon, but has crossed the horizon deep in
matter domination and is subhorizon everywhere in the region of the survey
(NVSS). In both cases we find that such an inhomogeneous scalar perturbation is
sufficient to generate the reported values of dipole anisotropy in LSS. For the
superhorizon modes we find values which are consistent with both CMB and NVSS
results. We also predict signatures for the model which can be tested by future
observations.",1309.6547v2
2013-09-26,Anisotropic two-dimensional electron gas at SrTiO3(110) protected by its native overlayer,"Two dimensional electron gases (2DEGs) at a oxide heterostructures are
attracting considerable attention, as these might substitute conventional
semiconductors for novel electronic devices [1]. Here we present a minimal
set-up for such a 2DEG -the SrTiO3(110)-(4 x 1) surface, natively terminated
with one monolayer of chemically-inert titania. Oxygen vacancies induced by
synchrotron radiation migrate under- neath this overlayer, this leads to a
confining potential and electron doping such that a 2DEG develops. Our angular
resolved photoemission spectroscopy (ARPES) and theoretical results show that
confinement along (110) is strikingly different from a (001) crystal
orientation. In particular the quantized subbands show a surprising
""semi-heavy"" band, in contrast to the analogue in the bulk, and a high
electronic anisotropy. This anisotropy and even the effective mass of the (110)
2DEG is tunable by doping, offering a high flexibility to engineer the
properties of this system.",1309.7042v1
2013-09-29,Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2,"We report on a spin-polarized inelastic neutron scattering study of spin
waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct
excitation components are identified, with spins fluctuating along the c-axis,
perpendicular to the ordering direction in the ab-plane, and parallel to the
ordering direction. While the first two ""transverse"" components can be
described by a linear spin-wave theory with magnetic anisotropy and inter-layer
coupling, the third ""longitudinal"" component is generically incompatible with
the local moment picture. It points towards a contribution of itinerant
electrons to the magnetism already in the parent compound of this family of
Fe-based superconductors.",1309.7553v1
2013-09-30,"Robust Computation of Dipole Electromagnetic Fields in Arbitrarily-Anisotropic, Planar-Stratified Environments","We develop a general-purpose formulation, based on two-dimensional spectral
integrals, for computing electromagnetic fields produced by
arbitrarily-oriented dipoles in planar-stratified environments, where each
layer may exhibit arbitrary and independent anisotropy in both the (complex)
permittivity and permeability. Among the salient features of our formulation
are (1) computation of eigenmodes (characteristic plane waves) supported in
arbitrarily anisotropic media in a numerically robust fashion, (2)
implementation of an hp-adaptive refinement for the numerical integration to
evaluate the radiation and weakly-evanescent spectra contributions, and (3)
development of an adaptive extension of an integral convergence acceleration
technique to compute the strongly-evanescent spectrum contribution. While other
semianalytic techniques exist to solve this problem, none have full
applicability to media exhibiting arbitrary double anisotropies in each layer,
where one must account for the whole range of possible phenomena such as mode
coupling at interfaces and non-reciprocal mode propagation. Brute-force
numerical methods can tackle this problem but only at a much higher
computational cost. The present formulation provides an efficient and robust
technique for field computation in arbitrary planar-stratified environments. We
demonstrate the formulation for a number of problems related to geophysical
exploration.",1309.7952v1
2013-10-07,Double magnetic resonance and spin anisotropy in Fe-based superconductors due to static and fluctuating antiferromagnetic orders,"Motivated by recent neutron scattering experiments in Fe-based
superconductors, we study how the magnetic resonance in the superconducting
state is affected by the simultaneous presence of either static or fluctuating
magnetic orders using the random phase approximation. We find that for the
underdoped materials with coexisting superconducting and antiferromagnetic
orders, spin rotational symmetry is explicitly broken at the ordering momentum
$Q_1 = (\pi,0)$. Only the longitudinal susceptibility exhibits the resonance
mode, whereas a spin-wave Goldstone mode develops in the transverse component.
Meanwhile, at the frustrated momentum $Q_2 = (0,\pi)$, the susceptibility
becomes isotropic in spin space and the magnetic resonance exists for both
components. Furthermore, the resonance energies at $Q_1$ and $Q_2$ have
distinct scales, which provides a natural explanation for the recently observed
double resonance peaks. In addition, we show that near optimal doping the
existence of strong magnetic fluctuations, which are modeled here via a
Gaussian mode, can still induce the spin anisotropy in the magnetic
susceptibility.",1310.1657v2
2013-10-07,Isotropic Γ_6 Ground State in Caged Compound NdRu2Zn20,"The magnetic susceptibility $\chi$, the magnetization $M$, and the specific
heat $C$ were measured for the caged cubic compound NdRu$_2$Zn$_{20}$ at
temperatures down to 0.5 K in the magnetic field $H$ along the three
crystallographic principal axes, [100], [110], and [111]. The ferromagnetic
phase transition was observed at the Curie temperature $T_{\rm C}=1.9$ K in
both the temperature dependence of $\chi(T)$ and $C(T)$. Below $T_{\rm C}$, the
magnetization curves $M(H)$ show very weak magnetic anisotropy, and the $C(T)$
curves in the fields along the three principal axes show no magnetic anisotropy
both below and above $T_{\rm C}$. The easy direction of magnetization at 0.5 K
changes from the [111] direction in 0 T to the [110] diretion in 7 T. We
analyzed these characteristic behaviors theoretically taking into account the
crystalline-electric-field energy, the magnetic exchange interaction, and the
Zeeman energy. It was found that these features are originated from the
isotropic $\Gamma_6$ ground state mixing with the magnetic $\Gamma_8^{(1)}$
excited state. The temperature and the magnetic field dependences of $M(T,H)$
and $C(T,H)$ are quantitatively well analyzed by this theoretical calculation.",1310.1664v1
2013-10-09,Nematic Metal and Antiferromagnetic Insulator on Hexagonal Kagome Lattice,"Hexagonal Kagome lattice is a multiband system with a quadratic band crossing
point, in contrast with honeycomb lattice with linear band crossing point,
which has exotic correlated effect and can produce various novel quantum
states. Here we investigate the phase diagram of the fermions on the hexagonal
Kagome lattice as a function of interaction, temperature and lattice
anisotropy, by combining the cellular dynamical mean-field theory with the
continuous time quantum Monte Carlo method. For weak interaction, the quadratic
band-crossing point is broken to linear band crossing point and the system is
the semi-metal. With the increasing of the interaction, the system goes a first
order transition to antiferromagnetic Mott insulator at low temperature. Below
a critical temperature, due to the charge nematic fluctuation, a nematic metal
forms between the weak coupling semi-metal and strong correlated Mott
insulator. When the lattice anisotropy increases, the region of the nematic
metal is enlarged. Furthermore, we discuss how to detect these phases in real
experiments.",1310.2463v2
2013-10-17,Double neutron spin resonances and gap anisotropy in underdoped superconducting NaFe0.985Co0.015As,"We use inelastic neutron scattering to show that superconductivity in
electron-underdoped NaFe0.985Co0.015As induces a dispersive sharp resonance
near Er1 = 3:25 meV and a broad dis- persionless mode at Er2 = 6 meV. However,
similar measurements on overdoped superconducting NaFe0:955Co0:045As find only
a single sharp resonance at Er = 7 meV. We connect these results with the
observations of angle-resolved photoemission spectroscopy that the
superconducting gaps in the electron Fermi pockets are anisotropic in the
underdoped material but become isotropic in the overdoped case. Our analysis
indicates that both the double neutron spin resonances and gap anisotropy
originate from the orbital dependence of the superconducting pairing in the
iron pnic- tides. Our discovery also shows the importance of the inelastic
neutron scattering in detecting the multiorbital superconducting gap structures
of iron pnictides.",1310.4817v1
2013-10-17,Globular Cluster Scale Sizes in Giant Galaxies: The Case of M87 and the Role of Orbital Anisotropy and Tidal Filling,"We present new Hubble Space Telescope imaging of the outer regions of M87 in
order to study its globular cluster (GC) population out to large galactocentric
distances. We discuss particularly the relationship between GC effective radii
$r_h$ and projected galactocentric distance $R_{gc}$. The observations suggest
a shallow trend $r_h \propto R_{gc}^{0.14}$ out to $R_{gc} \sim 100$ kpc, in
agreement with studies of other giant elliptical galaxies. To theoretically
reproduce this relationship we simulate GC populations with various
distributions of orbits. For an isotropic distribution of cluster orbits we
find a steeper trend of $r_h \propto R_{gc}^{0.4}$. Instead we suggest that (a)
if the cluster system has an orbital anisotropy profile, where orbits become
preferentially radial with increasing galactocentric distance, AND (b) if
clusters become more tidally under-filling with galactocentric distance, the
observed relationship can be recovered. We also apply this approach to the red
and blue GC populations separately and predict that red clusters are
preferentially under-filling at large $R_{gc}$ and have a more isotropic
distribution of orbits than blue clusters.",1310.4834v1
2013-10-21,Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields,"The propagation of cosmic rays (CRs) in turbulent interstellar magnetic
fields is typically described as a spatial diffusion process. This formalism
predicts only a small deviation from an isotropic CR distribution in the form
of a dipole in the direction of the CR density gradient or relative background
flow. We show that the existence of a global CR dipole moment necessarily
generates a spectrum of higher multipole moments in the local CR distribution.
These ""anomalous"" anisotropies are a direct consequence of Liouville's theorem
in the presence of a local turbulent magnetic field. We show that the
predictions of this model are in excellent agreement with the observed power
spectrum of multi-TeV CRs.",1310.5712v2
2013-10-23,"Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning","We study the general problem of a manifold of interacting elastic lines whose
spatial correlations are strongly affected by the competition between random
and ordered pinning. This is done through magneto-transport experiments with
YBa2Cu3O7-d thin films that contain a periodic vortex pinning array created via
masked ion irradiation, in addition to the native random pinning. The strong
field-matching effects we observe suggest the prevalence of periodic pinning,
and indicate that at the matching field each vortex line is bound to an
artificial pinning site. However, the vortex-glass transition dimensionality,
quasi-2D instead of the usual 3D, evidences reduced vortex-glass correlations
along the vortex line. This is also supported by an unusual angular dependence
of the magneto-resistance, which greatly differs from that of Bose-glass
systems. A quantitative analysis of the angular magnetoresistance allows us to
link this behaviour to the enhancement of the system anisotropy, a collateral
effect of the ion irradiation.",1310.6165v1
2013-10-31,Ground-State Phase Diagram of S=2 Heisenberg Chains with Alternating Single-Site Anisotropy,"The ground-state phase diagram of $S=2$ antiferromagnetic Heisenberg chains
with coexisting uniform and alternating single-site anisotropies is
investigated by the numerical exact diagonalization and density matrix
renormalization group methods. We find the Haldane, large-$D$, N\'eel,
period-doubled N\'eel, gapless spin fluid, quantized and partial ferrimagnetic
phases. The Haldane phase is limited to the close neighborhood of the isotropic
point. Within numerical accuracy, the transition from the gapless spin-fluid
phase to the period-doubled N\'eel phase is a direct transition. Nevertheless,
the presence of a narrow spin-gap phase between these two phases is suggested
on the basis of the low-energy effective theory. The ferrimagnetic ground state
is present in a wide parameter range. This suggests the realization of
magnetized single-chain magnets with a uniform spin magnitude by controlling
the environment of each magnetic ion without introducing ferromagnetic
interactions.",1310.8586v2
2013-10-31,Measurement of higher-order harmonic azimuthal anisotropy in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV,"Measurements are presented by the CMS Collaboration at the Large Hadron
Collider (LHC) of the higher-order harmonic coefficients that describe the
azimuthal anisotropy of charged particles emitted in sqrt(s[NN]) = 2.76 TeV
PbPb collisions. Expressed in terms of the Fourier components of the azimuthal
distribution, the n = 3-6 harmonic coefficients are presented for charged
particles as a function of their transverse momentum (0.3 < pt < 8.0 GeV),
collision centrality (0-70%), and pseudorapidity (abs(eta) < 2.0). The data are
analyzed using the event plane, multiparticle cumulant, and Lee-Yang zeros
methods, which provide different sensitivities to initial-state fluctuations.
Taken together with earlier LHC measurements of elliptic flow (n = 2), the
results on higher-order harmonic coefficients develop a more complete picture
of the collective motion in high-energy heavy-ion collisions and shed light on
the properties of the produced medium.",1310.8651v2
2013-10-31,Two distinct spin liquid states in a layered cubic lattice,"We construct a family of short-range resonating-valence-bond wave functions
on a layered cubic lattice, allowing for a tunable anisotropy in the amplitudes
assigned to nearest-neighbour valence bonds along one axis. Monte Carlo
simulations reveal that four phases are stabilized over the full range of the
anisotropy parameter. They are separated from one another by a sequence of
continuous quantum phase transitions. An antiferromagnetic phase, centred on
the perfect isotropy point, intervenes between two distinct quantum spin liquid
states. One of them is continuously deformable to the two-dimensional U(1) spin
liquid, which is known to exhibit critical bond correlations. The other has
both spin and bond correlations that decay exponentially. The existence of this
second phase is proof that, contrary to expectations, neither a bipartite
lattice structure nor a conventional Marshall sign rule is an impediment to
realizing a fully gapped quantum spin liquid.",1311.0004v1
2013-11-03,Defect-induced conductivity anisotropy in MoS2 monolayers,"Various types of defects in MoS2 monolayers and their influence on the
electronic structure and transport properties have been studied using the
Density-Functional based Tight-Binding method in conjunction with the Green's
Function approach. Intrinsic defects in MoS2 monolayers significantly affect
their electronic properties. Even at low concentration they considerably alter
the quantum conductance. While the electron transport is practically isotropic
in pristine MoS2, strong anisotropy is observed in the presence of defects.
Localized mid-gap states are observed in semiconducting MoS2 that do not
contribute to the conductivity but direction-dependent scatter the current, and
that the conductivity is strongly reduced across line defects and selected
grain boundary models.",1311.0474v3
2013-11-06,Plan beta: Core or Cusp?,"The inner profile of Dark Matter (DM) halos remains one of the central
problems in small-scale cosmology. At present, the problem can not be resolved
in dwarf spheroidal galaxies due to a degeneracy between the DM profile and the
velocity anisotropy beta of the stellar population. We discuss a method which
can break the degeneracy by exploiting 3D positions and 1D line-of-sight (LOS)
velocities. With the full 3D spatial information, we can determine precisely
what fraction of each stars LOS motion is in the radial and tangential
direction. This enables us to infer the anisotropy parameter beta directly from
the data. The method is particularly effective if the galaxy is highly
anisotropic. Finally, we argue that such a test could be applied to Sagittarius
and potentially other dwarfs with RR Lyrae providing the necessary depth
information.",1311.1522v2
2013-11-13,Fokker-Planck approach to the theory of magnon-driven spin Seebeck effect,"Following the theoretical approach by Xiao et al [Phys. Rev. B 81, 214418
(2010)] to the spin Seebeck effect, we calculate the mean value of the total
spin current flowing through a normalmetal/ ferromagnet interface. The spin
current emitted from the ferromagnet to the normal metal is evaluated in the
framework of the Fokker-Planck approach for the stochastic
Landau-Lifshitz-Gilbert equation. We show that the total spin current depends
not only on the temperature difference between the electron and the magnon
baths, but also on the external magnetic field and magnetic anisotropy. Apart
from this, the spin current is shown to saturate with increasing magnon
temperature, and the saturation temperature increases with increasing magnetic
field and/or magnetic anisotropy.",1311.3117v1
2013-11-13,Cosmic Microwave Background temperature and polarization anisotropies from the large-N limit of global defects,"We determine the full C_l spectra and correlation functions of the
temperature and polarization anisotropies in the CMB, generated by a source
modeled by the large N limit of spontaneously broken global O(N)-theories. We
point out a problem in the standard approach of treating the radiation-matter
transition by interpolating the eigenvectors of the unequal-time correlators of
the source energy-momentum tensor. This affects the CMB predictions from all
type of cosmic defects. We propose a method to overcome this difficulty, and
find that in the large-N global model that we study, differences in the final
CMB power spectra amplitudes reach up to 25%, when compared to implementations
of the eigenvector interpolation technique. We discuss as well how to optimally
search for the contribution in the CMB from active sources such as cosmic
defects, in experiments like Planck, COrE and PRISM.",1311.3225v2
2013-11-14,Critical current anisotropy in Nd-1111 single crystals and the infuence of neutron irradiation,"We report on angle-resolved magnetization measurements on
NdFeAsO$_{0.65}$F$_{0.35}$ (Nd-1111) single crystals. The field dependence of
the critical current density, $J_c$, is non-monotonous in these crystals at all
orientations and temperatures due to the fishtail effect, which strongly
influences the angular dependence of $J_c$. The currents decrease as the field
is tilted from the crystallographic c-axis at low fields, but increase at high
fields. A peak occurs in the angular dependence of $J_c$ at intermediate
fields. The critical currents are significantly enhanced after irradiation with
fast neutrons and the fishtail disappears. The different current anisotropies
at low and high fields, however, persist. We discuss the data in the framework
of the anisotropic scaling approach and propose a transition from dominant
pinning by large defects of low density at low fields to pinning by small
defects of high density at high fields in the pristine crystal. Strong pinning
dominates at all fields after the irradiation, and the angular dependence of
$J_c$ can be described by anisotropic scaling only after an appropriate
extension to this pinning regime.",1311.3476v1
2013-11-14,Topology beyond the horizon: how far can it be probed?,"The standard cosmological model does not determine the spatial topology of
the universe. This article revisits the signature of a non-trivial topology on
the properties of the cosmic microwave background anisotropies. We show that
the correlation function of the coefficients of the expansion of the
temperature and polarization anisotropies in spherical harmonics, encodes a
topological signature that can be used to distinguish a multi-connected space
from an infinite space on sizes larger than the last scattering surface. The
effect of the instrumental noise and of a galactic cut are estimated. We thus
establish boundaries for the size of the biggest torus dintinguisable with
temperature and polarization CMB data. We also describe the imprint of the
spatial topology on the 3-point function and on non-Gaussianity.",1311.3509v2
2013-11-14,Nonequilibrium dynamics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic system with a time dependent oscillating magnetic field source,"Nonequilibrium phase transition properties of a mixed Ising ferrimagnetic
model consisting of spin-1/2 and spin-3/2 on a square lattice under the
existence of a time dependent oscillating magnetic field have been investigated
by making use of Monte Carlo simulations with single-spin flip Metropolis
algorithm. A complete picture of dynamic phase boundary and magnetization
profiles have been illustrated and the conditions of a dynamic compensation
behavior have been discussed in detail. According to our simulation results,
the considered system does not point out a dynamic compensation behavior, when
it only includes the nearest-neighbor interaction, single-ion anisotropy and an
oscillating magnetic field source. As the next-nearest-neighbor interaction
between the spins-1/2 takes into account and exceeds a characteristic value
which sensitively depends upon values of single-ion anisotropy and only of
amplitude of external magnetic field, a dynamic compensation behavior occurs in
the system. Finally, it is reported that it has not been found any evidence of
dynamically first-order phase transition between dynamically ordered and
disordered phases, which conflicts with the recently published molecular field
investigation, for a wide range of selected system parameters.",1311.3537v2
2013-11-15,Two-pulse field-free orientation reveals anisotropy of molecular shape resonance,"We report the observation of macroscopic field-free orientation, i.e. more
than 73 % of CO molecules pointing in the same direction. This is achieved
through an all-optical scheme operating at high particle densities
($>10^{17}$cm$^{-3}$) that combines a one-color ($\omega$) and a two-color
($\omega + 2\omega$) non-resonant femtosecond laser pulses. We show that the
achieved orientation solely relies on the hyperpolarizability interaction as
opposed to an ionization-depletion mechanism thus opening a wide range of
applications. The achieved strong orientation enables us to reveal the
molecular-frame anisotropies of the photorecombination amplitudes and phases
caused by a shape resonance. The resonance appears as a local maximum in the
even-harmonic emission around 28~eV. In contrast, the odd-harmonic emission is
suppressed in this spectral region through the combined effects of an
asymmetric photorecombination phase and a sub-cycle Stark effect, generic for
polar molecules, that we experimentally identify.",1311.3923v2
2013-11-16,Verification of Anisotropic s-Wave Superconducting Gap Structure in CeRu2 from Low-Temperature Field-Angle-Resolved Specific Heat Measurements,"The field-angle-resolved specific heat C(T,H,phi) of the f-electron
superconductor CeRu2 (Tc=6.3 K) has been measured at low temperatures down to
90 mK on two single crystals of slightly different qualities. We reveal that
the C(phi) oscillation in a rotating magnetic field, originating from the gap
anisotropy, diminishes at low temperatures below the characteristic field H*,
as expected for an anisotropic gap without nodes. We also observe the
suppression of H* by decreasing the gap anisotropy ratio $\Delta_{\rm
min}/\Delta_{\rm max}$, a behavior that has been predicted from a microscopic
theory for anisotropic s-wave superconductors. The present technique is
established as a powerful tool for investigating minimum-gap structures as well
as nodal structures.",1311.4050v1
2013-11-20,Relaxation after quantum quenches in the spin-1/2 Heisenberg XXZ chain,"We consider the time evolution after quantum quenches in the spin-1/2
Heisenberg XXZ quantum spin chain with Ising-like anisotropy. The time
evolution of short-distance spin-spin correlation functions is studied by
numerical tensor network techniques for a variety of initial states, including
N\'eel and Majumdar-Ghosh states and the ground state of the XXZ chain at large
values of the anisotropy. The various correlators appear to approach stationary
values, which are found to be in good agreement with the results of exact
calculations of stationary expectation values in appropriate generalized Gibbs
ensembles. In particular, our analysis shows how symmetries of the post-quench
Hamiltonian that are broken by particular initial states are restored at late
times.",1311.5216v2
2013-11-21,More on thermal probes of a strongly coupled anisotropic plasma,"We extend the analysis of 1211.2199, where the photon production rate of an
anisotropic strongly coupled plasma with Nf<<Nc massless quarks was considered.
We allow here for non-vanishing quark masses and study how these affect the
spectral densities and conductivities. We also compute another important probe
of the plasma, the dilepton production rate. We consider generic angles between
the anisotropic direction and the photon and dilepton wave vectors, as well as
arbitrary quark masses and arbitrary values of the anisotropy parameter.
Generically, the anisotropy increases the production rate of both photons and
dileptons, compared with an isotropic plasma at the same temperature.",1311.5513v3
2013-11-25,Anomalous Viscosity of the Quark-Gluon Plasma,"The shear viscosity of the quark-gluon plasma is predicted to be lower than
the collisional viscosity for weak coupling. The estimated ratio of the shear
viscosity to entropy density is rather close to the ratio calculated by N = 4
super Yang-Mills theory for strong coupling, which indicates that the
quark-gluon plasma might be strongly coupled. However, in presence of momentum
anisotropy, the Weibel instability can arise and drive the turbulent transport.
Shear viscosity can be lowered by enhanced collisionality due to turbulence,
but the decorrelation time and its relation to underlying dynamics and
color-magnetic fields have not been calculated self-consistently. In this
paper, we use resonance broadening theory for strong turbulence to calculate
the anomalous viscosity of the quark-gluon plasma for nonequilibrium. For
saturated Weibel instability, we estimate the scalings of the decorrelation
rate and viscosity and compare these with collisional transport. This
calculation yields an explicit connection between the underlying momentum space
anisotropy and the viscosity anomaly.",1311.6347v2
2013-11-26,Specific features of band structure and optical anisotropy of Cu2CdGeSe4 quaternary compounds,"The complex theoretical and experimental studies of the band structure and
the optical functions of the Cu2CdGeSe4 quaternary crystals are reported. The
benchmark band structure calculations were performed using the first-principles
methods. As a result, the structural, electronic, optical and elastic
properties of Cu2CdGeSe4 were calculated in the general gradient approximation
(GGA) and local density approximation (LDA). The calculated dielectric function
and optical absorption spectra exhibit some anisotropic behavior. Detailed
analysis of the band energy dispersion and the effective space charge density
helped in establishing the origin of the band structure anisotropy. All
calculated properties are compared with the experimental data. An additional
comparison with a similar crystal of Cu2CdGeSe4 allowed to reveal the role
played by the anions (S or Se) in formation of the optical properties of these
two materials.",1311.6753v1
2013-11-27,Higher harmonics of azimuthal anisotropy in relativistic heavy ion collisions in HYDJET++ model,"The LHC data on azimuthal anisotropy harmonics from PbPb collisions at
center-of-mass energy 2.76 TeV per nucleon pair are analyzed and interpreted in
the framework of the HYDJET++ model. The cross-talk of elliptic $v_2$ and
triangular $v_3$ flow in the model generates both even and odd harmonics of
higher order. Comparison with the experimental data shows that this mechanism
is able to reproduce the $p_{\rm T}$ and centrality dependencies of
quadrangular flow $v_4$, and also the basic trends for pentagonal $v_5$ and
hexagonal $v_6$ flows.",1311.7054v2
2013-11-30,Expansion of a Bose-Einstein Condensate with Vortices,"The expansion of Bose-Einstein condensates (BECs) is numerically studied.
Usually, the aspect ratio of a condensate is inverted due to the anisotropy of
the uncertainty principle. In turbulent BECs, however, the aspect ratio remains
constant. The reason for this phenomenon is still unknown, being a challenging
topic in the study of quantum turbulence. Here, the two-dimensional
Gross-Pitaevskii equation is solved and the time development of the aspect
ratio and of the radii of the condensates are calculated in the presence of
vortices. The results indicate that vortex pairs must be added to a condensate
in order to expand it while maintaining its aspect ratio. The anisotropy due to
the vortex pairs competes with that due to the uncertainty principle so that
the aspect ratio remains constant.",1312.0093v1
2013-12-02,Thermodynamic properties of LiCu$_{2}$O$_{2}$ multiferroic compound,"A spin model of quasi-one dimensional LiCu$_{2}$O$_{2}$ compound with ground
state of ellipsoidal helical structure in which the helical axis is along the
diagonal of CuO$_{4}$ squares has been adopted. By taking into account the
interchain coupling and exchange anisotropy, the exotic magnetic properties and
ferroelectricity induced by spiral spin order have been studied by performing
Monte Carlo simulation. The simulation results qualitatively reproduce the main
characters of ferroelectric and magnetic behaviors of LiCu$_{2}$O$_{2}$
compound and confirm the low-temperature incollinear spiral ordering.
Furthermore, by performing the calculations of spin structure factor, we
systematically investigate the effects of different exchange coupling on the
lower-temperature magnetic transition, and find that the spiral spin order
depends not only on the ratio of nearest and next-nearest neighbor inchain spin
coupling but also strongly on the exchange anisotropy.",1312.0293v1
2013-12-02,Numerical studies of Minimally Doubled Fermions,"We have performed the first numerical study of minimally doubled fermions of
the Karsten-Wilczek class in the quenched approximation. This requires fixing
the counterterms, which arise due to hypercubic symmetry breaking induced by
the Karsten-Wilczek term. Non-perturbative renormalisation criteria are
formulated after a detailed study of the parameter dependence of mesonic
observables. Minimisation of the mass anisotropy of the pseudoscalar ground
state fixes non-perturbative renormalisation conditions for the counterterm
coefficients. These anisotropies are mapped out by probing different euclidean
components of the transfer matrix through calculations of the pseudoscalar
ground state mass in different directions. The chiral behaviour of the
pseudoscalar ground state is studied with the tuned Karsten-Wilczek action for
multiple lattice spacings. Light pseudoscalar masses ($ M_{PS} \lesssim
250\,MeV $) were achieved in the quenched approximation without encountering
exceptional configurations. The presence of quenched chiral logarithms is
studied under the tentative assumption of Goldstone Boson-like behaviour.",1312.0488v2
2013-12-05,Diffusive motion of particles and dimers over anisotropic lattices,"Behavior of the mixture of particles and dimers moving with different jump
rates at reconstructed surfaces is described. Collective diffusion coefficient
is calculated by the variational approach. Anisotropy of the collective
particle motion is analyzed as a function of jump rates and local particle
density. Analytic expressions are compared with the results of Monte Carlo
simulations of diffusing particle and dimer mixture. Direction of driven
diffusive motion of the same system depends on the jump anisotropy and on the
value of driving force. Driven motion results in the particle and dimer
separation when the directions of their easy diffusion axes differ. It is shown
that in such case trapping sites concentrated at some surface areas act as
filters or barriers for particle and dimer mixtures.",1312.1592v2
2013-12-10,Spectrum splitting of bimagnon excitations in a spatially frustrated Heisenberg antiferromagnet revealed by resonant inelastic x-ray scattering,"We perform a comprehensive analysis of the bimagnon resonant inelastic x-ray
scattering (RIXS) intensity spectra of the spatially frustrated Jx-Jy-J2
Heisenberg model on a square lattice in both the antiferromagnetic and the
collinear antiferromagnetic phase. We study the model for strong frustration
and significant spatial anisotropy to highlight the key signatures of RIXS
spectrum splitting which may be experimentally discernible. Based on an
interacting spin wave theory study within the ladder approximation
Bethe-Salpeter scheme, we find the appearance of a robust two-peak structure
over a wide range of the transferred momenta in both magnetically ordered
phases. The unfrustrated model has a single-peak structure with a two-peak
splitting originating due to spatial anisotropy and frustrated interactions.
Our predicted two-peak structure from both magnetically ordered regime can be
realized in iron pnictides.",1312.2876v2
2013-12-12,Influence of the structure defects on the magnetic properties of the FePt/Fe bilayer,"Thin magnetic multilayered films containing FePt have attracted a lot of
attention recently due to their possible usage in ultra-high density magnetic
storage. Although structure defects play a dramatic role in the magnetization
process and influence magnetic properties in general this dependence haven't
been studied thoroughly. The main aim of this work was to perform theoretical
investigation of the magnetic properties of FePt and Fe/FePt thin films with
high coercivity with respect to the structure defects such as anisotropy
constant, magnetization saturation, exchange constant fluctuations and easy
axis deviation. For selected defect patterns the coercive field dependence on
layer thicknesses was analysed. Numerical study of the bilayer with hard
magnetic layer having the planar anisotropy was carried on using micromagnetic
calculations. Values of layers thickness have been found optimal for
perspective applications, the dependence of the hysteresis loop shape upon the
magnetization process has been shown and analysed.",1312.3541v1
2013-12-16,"Competing orders, competing anisotropies, and multicriticality: The case of Co-doped YbRh2Si2","Motivated by the unusual evolution of magnetic phases in stoichiometric and
Co-doped YbRh2Si2, we study Heisenberg models with competing ferromagnetic and
antiferromagnetic ordering combined with competing anisotropies in exchange
interactions and g factors. Utilizing large-scale classical Monte-Carlo
simulations, we analyze the ingredients required to obtain the characteristic
crossing point of uniform susceptibilities observed experimentally near the
ferromagnetic ordering of Yb(Rh0.73Co0.27)2Si2. The models possess
multicritical points, which we speculate to be relevant for the behavior of
clean as well as doped YbRh2Si2. We also make contact with experimental data on
YbNi4P2 where a similar susceptibility crossing has been observed.",1312.4539v1
2013-12-17,Reversal time of the magnetization of magnetic nanoparticles at very low damping,"The magnetization reversal time of ferromagnetic nanoparticles is
investigated in the very low damping regime. The energy-controlled diffusion
equation rooted in a generalization of the Kramers escape rate theory for point
Brownian particles in a potential to the magnetic relaxation of a macrospin,
yields the reversal time in closed integral form. The latter is calculated for
a nanomagnet with uniaxial anisotropy with a uniform field applied at an angle
to the easy axis and for a nanomagnet with biaxial anisotropy with the field
along the easy axis. The results completely agree with those yielded by
independent numerical and asymptotic methods.",1312.4904v3
2013-12-19,Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields,"Bulk motions of electrons along the line of sight induce secondary
temperature fluctuations in the post-decoupling, reionized universe. In the
presence of a magnetic field not only the scalar mode but also the vector mode
act as a source for the bulk motion. The resulting angular power spectrum of
temperature anisotropies of the cosmic microwave background is calculated
assuming a simple model of reionization.Contributions from the standard
adiabatic, curvature mode and a non helical magnetic field are included. The
contribution due to magnetic fields with field strengths of order nG and
negative magnetic spectral indices becomes important for multipoles larger than
$\ell \sim 10^4$.",1312.5630v2
2013-12-22,Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy,"We study the spectral characteristics of spin current nano-oscillators based
on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy.
By varying the applied magnetic field and current, both localized and
propagating spin wave modes of the oscillation are achieved. At small fields,
we observe an abrupt onset of the modulation sidebands. We use micromagnetic
simulations to identify this state as a dynamical magnetic skyrmion stabilized
in the active device region by spin current injection, whose current-induced
dynamics is accompanied by the gyrotropic motion of the core due to the skew
deflection. Our results demonstrate a practical route for controllable skyrmion
manipulation by spin current in magnetic thin films.",1312.6343v2
2013-12-23,Projection method and new formulation of leading-order anisotropic hydrodynamics,"The introduced earlier projection method for boost-invariant and
cylindrically symmetric systems is used to introduce a new formulation of
anisotropic hydrodynamics that allows for three substantially different values
of pressure acting locally in three different directions. Our considerations
are based on the Boltzmann kinetic equation with the collision term treated in
the relaxation time approximation and the momentum anisotropy is included
explicitly in the leading term of the distribution function. A novel feature of
our work is the complete analysis of the second moment of the Boltzmann
equation, in addition to the zeroth and first moments that have been analyzed
in earlier studies. We define the final equations of anisotropic hydrodynamics
in the leading order as a subset of the analyzed moment equations (and their
linear combinations) which agree with the Israel-Stewart theory in the case of
small pressure anisotropies.",1312.6614v1
2013-12-23,Effects of Electromagnetic Field on The Collapse and Expansion of Anisotropic Gravitating Source,"This paper is devoted to study the effects of electromagnetic on the collapse
and expansion of anisotropic gravitating source. For this purpose, we have
evaluated the generating solutions of Einstein-Maxwell field equations with
spherically symmetric anisotropic gravitating source. We found that a single
function generates the various anisotropic solutions. In this case every
generating function involves an arbitrary function of time which can be chosen
to fit several astrophysical time profiles. Two physical phenomenon occur, one
is gravitational collapse and other is the cosmological expanding solution. In
both cases electromagnetic field effects the anisotropy of the model. For
collapse the anisotropy is increased while for expansion it deceases from
maximum value to finite positive value. In case of collaps there exits two
horizons like in case of Reissner-Nordstr$\ddot{o}$m metric.",1312.6898v2
2014-01-01,Valleytronics on the Surface of Topological Crystalline Insulator: Elliptic Dichroism and Valley-Selective Optical Pumping,"The low-energy theory of the surface of the topological crystalline insulator
(TCI) is characterized by four Dirac cones anisotropic into the $x$ and $y$
directions. Recent experiments have shown that the band gap can be introduced
in these Dirac cones by crystal distortion by applying strain to the crystal
structure. The TCI surface provides us with a new way to valleytronics when
gaps are given to Dirac cones. Indeed the system has the Chern number and three
valley-Chern numbers. We investigate the optical absorption on the TCI surface.
It shows a strong elliptic dichroism though the four Dirac cones have the same
chiralities. Namely, it is found that the absorptions of the right- and
left-polarized light are different, depending on the sign of mass and the
location of the Dirac cones, owing to the anisotropy of the Dirac cone. By
measuring this elliptic dichroism it is possible to determine the anisotropy of
a Dirac cone experimentally.",1401.0273v2
2014-01-16,Absence of quasiclassical coherence in mean-field dynamics of bosons in a kinetically frustrated regime,"We study numerically the dynamics of bosons on a triangular lattice after
quenching both the on-site interactions and the external trapping potential to
negative values. In a similar situation on the square lattice, the dynamics can
be understood in terms of an effectively reversed Hamiltonian. On the
triangular lattice, however, the kinetic part of the reversed Hamiltonian is
frustrated and whether coherence can develop is an open question. The strength
of the frustration can be changed by tuning the ratio of the hopping rates
along different directions. We calculate time-of-flight images at different
times after the quench for different values of the hopping anisotropy. We
observe peaks at the maxima of the original non-interacting dispersion relation
both in the isotropic case and also in the rhombic limit of high hopping
anisotropy. For an intermediate value, however, no coherence develops up to the
longest simulation times. These results imply that experiments along similar
lines could study unconventional superfluidity of bosons and aspects of the
conjectured spin-liquid behavior in the hard-core limit.",1401.3966v2
2014-01-18,Enhancement of Perpendicular Magnetic Anisotropy and Transmission of Spin-Hall-Effect-Induced Spin Currents by a Hf Spacer Layer in W/Hf/CoFeB/MgO Layer,"We report that strong perpendicular magnetic anisotropy of the ferromagnetic
layer in a W/CoFeB/MgO multilayer structure can be established by inserting a
Hf layer as thin as 0.25 nm between the W and CoFeB layers. The Hf spacer also
allows transmission of spin currents generated by an in-plane charge current in
the W layer to apply strong spin torque on the CoFeB, thereby enabling
current-driven magnetic switching. The antidamping-like and field-like
components of the spin torque exerted on a 1 nm CoFeB layer are of comparable
magnitudes in this geometry. Both components originate from the spin Hall
effect in the underlying W layer.",1401.4617v1
2014-01-28,Phenomenological phase diagram of superfluid 3He in a stretched aerogel,"Highly anisotropic ""nematically ordered"" aerogel induces global uniaxial
anisotropy in superfluid 3He. The anisotropy lowers symmetry of 3He in aerogel
from spherical to axial. As a result instead of one transition temperature in
the state, characterized by the orbital moment l=1 there are two, corresponding
to projections l_z=o and l_z=\pm 1. The splitting of transition has a
pronounced effect on the phase diagram of superfluid 3He and on a structures of
appearing phases. Possible phase diagrams, obtained phenomenologically on a
basis of Landau expansion of thermodynamic potential in a vicinity of the
transition temperature are presented here. The order parameters, corresponding
to each phase and their temperature dependencies are found.",1401.7297v2
2014-01-31,Firehose and Mirror Instabilities in a Collisionless Shearing Plasma,"Hybrid-kinetic numerical simulations of firehose and mirror instabilities in
a collisionless plasma are performed in which pressure anisotropy is driven as
the magnetic field is changed by a persistent linear shear $S$. For a
decreasing field, it is found that mostly oblique firehose fluctuations grow at
ion Larmor scales and saturate with energies $\sim$$S^{1/2}$; the pressure
anisotropy is pinned at the stability threshold by particle scattering off
microscale fluctuations. In contrast, nonlinear mirror fluctuations are large
compared to the ion Larmor scale and grow secularly in time; marginality is
maintained by an increasing population of resonant particles trapped in
magnetic mirrors. After one shear time, saturated order-unity magnetic mirrors
are formed and particles scatter off their sharp edges. Both instabilities
drive sub-ion-Larmor--scale fluctuations, which appear to be
kinetic-Alfv\'{e}n-wave turbulence. Our results impact theories of momentum and
heat transport in astrophysical and space plasmas, in which the stretching of a
magnetic field by shear is a generic process.",1402.0010v2
2014-02-10,A search for small and medium scale anisotropy of cosmic rays above 1 PeV registered at the Tunka-133 array,"A search for anisotropy at different scales in the arrival directions of
cosmic rays with energies above 1 PeV is performed with data of the Tunka-133
array. A number of regions with angular sizes up to approximately 30 degrees
that deviate from the uniform background with a statistical significance
greater than three standard deviations are found using the shuffling technique
both in the complete data set and its subsets in different energy ranges. Some
regions with an excess of cosmic rays correlate with the distribution of
possible cosmic ray sources. A comparison of the results with a similar
analysis of the legacy data of the EAS MSU array is presented.",1402.2075v2
2014-02-10,Magnetic edge anisotropy in graphene-like honeycomb crystals,"The independent predictions of edge ferromagnetism and the Quantum Spin Hall
phase in graphene have inspired the quest of other two dimensional honeycomb
systems, such as silicene, germanene, stanene, iridiates, and organometallic
lattices, as well as artificial superlattices, all of them with electronic
properties analogous to those of graphene, but much larger spin orbit coupling.
Here we study the interplay of ferromagnetic order and spin orbit interactions
at the zigzag edges of these graphene-like systems. We find an in-plane
magnetic anisotropy that opens a gap in the otherwise conducting edge channels,
that should result in large changes of electronic properties upon rotation of
the magnetization.",1402.2235v2
2014-02-17,A case study of spin-$1$ Heisenberg model in a triangular lattice,"We study the spin-$1$ model in a triangular lattice in presence of a uniaxial
anisotropy field using a Cluster Mean-Field approach (CMF). The interplay
between antiferromagnetic exchange, lattice geometry and anisotropy forces
Gutzwiller mean-field approaches to fail in a certain region of the phase
diagram. There, the CMF yields two supersolid (SS) phases compatible with those
present in the spin-$1/2$ XXZ model onto which the spin-$1$ system maps.
Between these two SS phases, the three-sublattice order is broken and the
results of the CMF depend heavily on the geometry and size of the cluster. We
discuss the possible presence of a spin liquid in this region.",1402.4008v2
2014-02-18,Switching Properties in Magnetic Tunnel Junctions with Interfacial Perpendicular Anisotropy: Micromagnetic Study,"The role of universal memory can be successfully satisfied by magnetic tunnel
junctions (MTJs) where the writing mechanism is based on spin-transfer torque
(STT). An improvement in the switching properties (lower switching current
density maintaining the thermal stability) has been achieved in MTJs with
interfacial perpendicular anisotropy (IPA) at the interface between CoFeB and
MgO. In this paper, micromagnetic simulations point out the influence of IPA
and saturation magnetization (MS) on the properties of fast magnetization
reversal achieved in 5, 10 and 20 ns. Both cases of in-plane and out-of-plane
free layer are considered. In addition, the thermal effect is included for the
in-plane switching at 20 ns and a complete analysis of energy dissipation
during the switching is illustrated. This study can provide useful information
for the design of STT-based memories.",1402.4352v1
2014-02-23,Solution to the Inverse Wulff Problem by Means of the Enhanced Semidefinite Relaxation Method,"We propose a novel method of resolving the optimal anisotropy function. The
idea is to construct the optimal anisotropy function as a solution to the
inverse Wulff problem, i.e. as a minimizer for the anisoperimetric ratio for a
given Jordan curve in the plane. It leads to a nonconvex quadratic optimization
problem with linear matrix inequalities. In order to solve it we propose the
so-called enhanced semidefinite relaxation method which is based on a solution
to a convex semidefinite problem obtained by a semidefinite relaxation of the
original problem augmented by quadratic-linear constraints. We show that the
sequence of finite dimensional approximations of the optimal anisoperimetric
ratio converges to the optimal anisoperimetric ratio which is a solution to the
inverse Wulff problem. Several computational examples, including those
corresponding to boundaries of real snowflakes and discussion on the rate of
convergence of numerical method are also presented in this paper.",1402.5668v2
2014-02-28,Probing anisotropy in a new noncentrosymmetric superconductor BiPd,"Strength of Rashba type antisymmetric spin orbit coupling has the crucial
effect on superconducting and normal state properties in noncentrosymmetric
(NCS) superconductors. This can be seen on various anisotropic properties of
the system. For a system with lowered crystalline symmetry as in
noncentrosymmetric crystals, the superconducting pairing state can have
correlation to the normal state properties. In our earlier work we have shown
that alfa-BiPd which has a monoclinic (P_21) structure with the absence of the
centre of inversion exhibits bulk superconductivity at 3.8 K. In order to
understand the role of spin-orbit scattering, we have studied the anisotropic
properties of high quality single crystal (RRR 170) of NCS BiPd by measuring
magnetic susceptibility, electrical transport from 1.8 K to 300 K and
isothermal M_H loop (1.8 K to 3.8 K) in the superconducting state for <010> and
<100> crystallographic directions respectively. Moderate anisotropy up to 30 %
has been found in the electrical transport possibly indicating significant
Rashba type antisymmetric spin orbit coupling present in alfa-BiPd.",1402.7232v1
2014-03-16,Anisotropic intrinsic spin Hall effect in quantum wires,"We use numerical simulations to investigate the spin Hall effect in quantum
wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We
find that the intrinsic spin Hall effect is highly anisotropic with respect to
the orientation of the wire, and that the nature of this anisotropy depends
strongly on the electron density and the relative strengths of the Rashba and
Dresselhaus spin-orbit coupling. In particular, at low densities when only one
subband of the quantum wire is occupied, the spin Hall effect is strongest for
electron momentum along the $[\bar{1}10]$ axis, which is opposite than what is
expected for the purely 2D case. In addition, when more than one subband is
occupied, the strength and anisotropy of the spin Hall effect can vary greatly
over relatively small changes in electron density, which makes it difficult to
predict which wire orientation will maximize the strength of the spin Hall
effect. These results help to illuminate the role of quantum confinement in
spin-orbit-coupled systems, and can serve as a guide for future experimental
work on the use of quantum wires for spin-Hall-based spintronic applications.",1403.3936v1
2014-03-19,Is the anisotropy of the upper critical field of Sr$_2$RuO$_4$ consistent with a helical $p$-wave state?,"We calculate the angular and temperature $T$ dependencies of the upper
critical field $H_{c2}(\theta,\phi,T)$ for the $C_{4v}$ point group helical
$p$-wave states, assuming a single uniaxial ellipsoidal Fermi surface, Pauli
limiting, and strong spin-orbit coupling that locks the spin-triplet $\vec{\bf
d}$-vectors onto the layers. Good fits to the Sr$_2$RuO$_4$
$H_{c2,a}(\theta,T)$ data of Kittaka {\it et al.} [Phys. Rev. B {\bf 80},
174514 (2009)] are obtained. Helical states with $\vec{\bf d}(\vec{\bf
k})=k_x\vec{\bf x}-k_y\vec{\bf y}$ and $k_y\vec{\bf x}+k_x\vec{\bf y}$ (or
$k_x\vec{\bf x}+k_y\vec{\bf y}$ and $k_y\vec{\bf x}-k_x\vec{\bf y}$) produce
$H_{c2}(90^{\circ},\phi,T)$ that greatly exceed (or do not exhibit) the
four-fold azimuthal anisotropy magnitudes observed in Sr$_2$RuO$_4$ by Kittaka
{\it et al.} and by Mao {\it et al.} [Phys. Rev. Lett. {\bf 84}, 991 (2000)],
respectively.",1403.4715v1
2014-03-20,Spin susceptibility of two-dimensional transition metal dichalcogenides,"We have obtained analytical expressions for the q-dependent static spin
susceptibility of monolayer transition metal dichalcogenides, considering both
the electron-doped and hole-doped cases. Our results are applied to calculate
spin-related physical observables of monolayer MoS2, focusing especially on
in-plane/out-of-plane anisotropies. We find that the hole-mediated RKKY
exchange interaction for in-plane impurity-spin components decays with the
power law $R^{-5/2}$ as a function of distance $R$, which deviates from the
$R^{-2}$ power law normally exhibited by a two-dimensional Fermi liquid. In
contrast, the out-of-plane spin response shows the familiar $R^{-2}$ long-range
behavior. We also use the spin susceptibility to define a collective g-factor
for hole-doped MoS2 systems and discuss its density-dependent anisotropy.",1403.5021v3
2014-03-21,"Timescales, dynamical phase transitions and 3rd order phase transitions in the 1d anisotropic XY model","Recent research into time-integrated observables has revealed a special class
of states which cap- ture the singular features of the generating functions of
those observables, as estimated by full counting statistics (FCS). In this work
we extend the results of [Phys. Rev. B 87 184303 (2013)] to the 1d anisotropic
XY -model and find a set of FCS critical points associated with the
time-integrated transverse magnetization and anisotropy. We show dynamical
phase transitions (DPTs) as defined in [Phys. Rev. Lett. 110 135704 (2013)] do
not emerge on quenching the states associated with the time-integrated
anisotropy across FCS critical points. We also study the timescales required to
prepare the associated special states of the transverse magnetization using
appropriate Markovian baths and find they are independent of the number of
spins in the chain. However the probability to evolve to such a state decreases
drastically with increasing system size due to dissipation. Thus when preparing
such states it is preferable to use few body systems and to reach the
thermodynamic limit it is necessary to use an ancillary system in conjunction
with the Markovian baths.",1403.5515v1
2014-03-28,"The Glasma, Photons and the Implications of Anisotropy","We introduce distribution functions for quarks and gluons in the Glasma and
discuss how they satisfy various relationships of statistical physics. We use
these distributions to compute photon production in the early stages of heavy
ion collisions. Photon rates satisfy geometric scaling, that is, the emission
rate per unit area scales as a function of the saturation momenta divided by
the transverse momentum of the photon. Photon distributions from the Glasma are
steeper than those computed in the Thermalized Quark Gluon Plasma (TQGP). Both
the delayed equilibration of the Glasma and a possible anisotropy in the
pressure lead to slower expansion and mean times of photon emission of fixed
energy are increased. This delayed emission might allow for larger photon
elliptic flow.",1403.7462v1
2014-04-03,On the incorporation of cubic and hexagonal interfacial energy anisotropy in phase field models using higher order tensor terms,"In this paper, we show how to incorporate cubic and hexagonal anisotropies in
interfacial energies in phase field models; this incorporation is achieved by
including upto sixth rank tensor terms in the free energy expansion, assuming
that the free energy is only a function of coarse grained composition, its
gradient, curvature and aberration. We derive the number of non-zero and
independent components of these tensors. Further, by demanding that the
resultant interfacial energy is positive definite for inclusion of each of the
tensor terms individually, we identify the constraints imposed on the
independent components of these tensors. The existing results in the invariant
group theory literature can be used to simplify the process of construction of
some (but not all) of the higher order tensors. Finally, we derive the relevant
phase field evolution equations.",1404.0757v2
2014-04-03,Phases of triangular lattice antiferromagnet near saturation,"We consider 2D Heisenberg antiferromagnets on a triangular lattice with
spatially anisotropic interactions in a high magnetic field close to the
saturation. We show that this system possess rich phase diagram in
field/anisotropy plane due to competition between classical and quantum orders:
an incommensurate non-coplanar spiral state, which is favored classically, and
a commensurate co-planar state, which is stabilized by quantum fluctuations. We
show that the transformation between these two states is highly non-trivial and
involves two intermediate phases -- the phase with co-planar incommensurate
spin order and the one with non-coplanar double-${\bf Q}$ spiral order. The
transition between the two co-planar states is of commensurate- incommensurate
type, not accompanied by softening of spin-wave excitations. We show that a
different sequence of transitions holds in triangular antiferromagnets with
exchange anisotropy, such as Ba3CoSb2O9.",1404.1046v1
2014-04-04,Cosmological signatures of brane inflation,"Cosmology motivated by string theory has been studied extensively in the
recent literature. String theory is promising because it has interesting
features such as unifying gravity, electromagnetic, weak and strong nuclear
forces. However, even the energy scale of the experiments at the Large Hadron
Collider (~TeV) is too low to detect any strong evidence for string theory. The
energy scale of inflation can be above ~10^9 TeV. Therefore, it is expected to
find some signature of string theory in cosmology.
  String theory predicts ten space-time dimensions. In the brane world
scenario, our four dimensional Universe is confined onto the higher dimensional
object called the Brane in the ten dimensional space time. The
Dirac-Born-Infeld (DBI) inflation is based on this idea. DBI inflation predicts
a characteristic statistical feature in the Cosmic Microwave Background (CMB)
temperature anisotropies. In this thesis, we study the predictions of the DBI
inflation models on the CMB temperature anisotropies.",1404.1174v1
2014-04-07,Crystal structure and physical properties of EuPtIn$_{4}$ intermetallic antiferromagnet,"We report the synthesis of EuPtIn$_{4}$ single crystalline platelets by the
In-flux technique. This compound crystallizes in the orthorhombic Cmcm
structure with lattice parameters $a=4.542(1)$ \AA, $b=16.955(2)$ \AA$\,$ and
$c=7.389(1)$ \AA. Measurements of magnetic susceptibility, heat capacity,
electrical resistivity, and electron spin resonance (ESR) reveal that
EuPtIn$_{4}$ is a metallic Curie-Weiss paramagnet at high temperatures and
presents antiferromagnetic (AFM) ordering below $T_{N}=13.3$ K. In addition, we
observe a successive anomaly at $T^{*} = 12.6$ K and a spin-flop transition at
$H_{c} \sim 2.5$ T applied along the $ac$-plane. In the paramagnetic state, a
single Eu$^{2+}$ Dysonian ESR line with a Korringa relaxation rate of $b =
4.1(2)$ Oe/K is observed. Interestingly, even at high temperatures, both ESR
linewidth and electrical resistivity reveal a similar anisotropy. We discuss a
possible common microscopic origin for the observed anisotropy in these
physical quantities likely associated with an anisotropic magnetic interaction
between Eu$^{2+}$ 4$f$ electrons mediated by conduction electrons.",1404.1660v1
2014-04-10,Magnetic response of holographic Lifshitz superconductors:Vortex and Droplet solutions,"In this paper a holographic model of $s$-wave superconductor with anisotropic
Lifshitz scaling has been considered. In the presence of an external magnetic
field our holographic model exhibits both vortex and droplet solutions. Based
on analytic methods we have shown that the anisotropy has no effect on the
vortex and droplet solutions whereas it may affect the condensation. Our vortex
solution closely resembles the Ginzburg-Landau theory and a relation between
the upper critical magnetic field and superconducting coherence length has been
speculated from this comparison. Using Sturm-Liouville method, the effect of
anisotropy on the critical parameters in insulator/superconductor phase
transitions has been analyzed.",1404.2774v2
2014-04-11,Effective S=1/2 description of the S=1 chain with strong easy plane anisotropy,"We present a study of the one-dimensional S=1 antiferromagnetic spin chain
with large easy plane anisotropy, with special emphasis on field-induced
quantum phase transitions. Temperature and magnetic field dependence of
magnetization, specific heat, and thermal conductivity is presented using a
combination of numerical methods. In addition, the original S=1 model is mapped
into the low-energy effective S=1/2 XXZ Heisenberg chain, a model which is
exactly solvable using the Bethe ansatz technique. The effectiveness of the
mapping is explored, and we show that all considered quantities are in
qualitative, and in some cases quantitative, agreement. The thermal
conductivity of the considered S=1 model is found to be strongly influenced by
the underlying effective description. Furthermore, we elucidate the low-lying
electron spin resonance spectrum, based on a semi--analytical Bethe ansatz
calculation of the effective S=1/2 model.",1404.3064v2
2014-04-11,The Intrinsic Quasar Luminosity Function: Accounting for Accretion Disk Anisotropy,"Quasar luminosity functions are a fundamental probe of the growth and
evolution of supermassive black holes. Measuring the intrinsic luminosity
function is difficult in practice, due to a multitude of observational and
systematic effects. As sample sizes increase and measurement errors drop,
characterizing the systematic effects is becoming more important. It is well
known that the continuum emission from the accretion disk of quasars is
anisotropic --- in part due to its disk-like structure --- but current
luminosity function calculations effectively assume isotropy over the range of
unobscured lines of sight. Here, we provide the first steps in characterizing
the effect of random quasar orientations and simple models of anisotropy on
observed luminosity functions. We find that the effect of orientation is not
insignificant and exceeds other potential corrections such as those from
gravitational lensing of foreground structures. We argue that current
observational constraints may overestimate the intrinsic luminosity function by
as much as a factor of ~2 on the bright end. This has implications for models
of quasars and their role in the Universe, such as quasars' contribution to
cosmological backgrounds.",1404.3151v1
2014-04-13,Temporal and Spatial Turbulent Spectra of MHD Plasma and an Observation of Variance Anisotropy,"The nature of MHD turbulence is analyzed through both temporal and spatial
magnetic fluctuation spectra. A magnetically turbulent plasma is produced in
the MHD wind-tunnel configuration of the Swarthmore Spheromak Experiment (SSX).
The power of magnetic fluctuations is projected into directions perpendicular
and parallel to a local mean field; the ratio of these quantities shows the
presence of variance anisotropy which varies as a function of frequency.
Comparison amongst magnetic, velocity, and density spectra are also made,
demonstrating that the energy of the turbulence observed is primarily seeded by
magnetic fields created during plasma production. Direct spatial spectra are
constructed using multi-channel diagnostics and are used to compare to
frequency spectra converted to spatial scales using the Taylor Hypothesis.
Evidence for the observation of dissipation due to ion inertial length scale
physics is also discussed as well as the role laboratory experiment can play in
understanding turbulence typically studied in space settings such as the solar
wind. Finally, all turbulence results are shown to compare fairly well to a
Hall-MHD simulation of the experiment.",1404.3336v1
2014-04-14,The Hubble Expansion is Isotropic in the Epoch of Dark Energy,"The isotropy of the universal Hubble expansion is a fundamental tenet of
physical cosmology, but it has not been precisely tested during the current
epoch, when dark energy is dominant. Anisotropic expansion will produce a
shearing velocity field, causing objects to stream toward directions of faster
expansion and away from directions of slower expansion. This work tests the
basic cosmological assumption of isotropic expansion and thus the isotropy of
dark energy. The simplest anisotropy will manifest as a quadrupolar curl-free
proper motion vector field. We derive this theoretical signature using a
tri-axial expanding metric with a flat geometry (Bianchi I model), generalizing
and correcting previous work. We then employ the best current data, the Titov &
Lambert (2013) proper motion catalog of 429 objects, to measure the isotropy of
universal expansion. We demonstrate that the Hubble expansion is isotropic to
7% (1 $\sigma$), corresponding to streaming motions of 1 microarcsecond/yr, in
the best-constrained directions (-19% and +17% in the least-constrained
directions) and does not significantly deviate from isotropy in any direction.
The Gaia mission, which is expected to obtain proper motions for 500,000
quasars, will likely constrain the anisotropy below 1%.",1404.3735v1
2014-04-14,Magnetic field modulated Kondo effect in a single-magnetic-ion molecule,"We study numerically the low-temperature electronic transport properties of a
single-ion magnet with uniaxial and transverse spin anisotropies. We find clear
signatures of a Kondo effect caused by the presence of a transverse
(zero-field) anisotropy in the molecule. Upon applying a transverse magnetic
field to the single-ion magnet, we observe oscillations of the Kondo effect due
to the presence of diabolical (degeneracy) points of the energy spectrum of the
molecule caused by a geometrical phase interference effects similar to those
observed in the quantum tunneling of multi-ion molecular nanomagnets. The
field-induced lifting of the ground state degeneracy competes with the
interference modulation, resulting in some cases in a suppression of the Kondo
peak.",1404.3755v2
2014-04-15,Plasmons and screening in monolayer and multilayer black phosphorus,"Black phosphorus exhibits a high degree of band anisotropy. However, we found
that its in-plane static screening remains relatively isotropic for momenta
relevant to elastic long-range scattering processes. On the other hand, the
collective electronic excitations in the system exhibit a strong anisotropy.
Band non-parabolicity leads to a plasmon frequency which scales as $n^{\beta}$,
where $n$ is the carrier concentration, and $\beta<\tfrac{1}{2}$. Screening and
charge distribution in the out-of-plane direction are also studied using a
non-linear Thomas-Fermi model.",1404.4035v2
2014-04-18,Transport Properties of Dirac Ferromagnet,"We propose a model ferromagnet based on the Dirac Hamiltonian in three
spatial dimensions, and study its transport properties which include
anisotropic magnetoresistance (AMR) and anomalous Hall (AH) effect. This
relativistic extension allows two kinds of ferromagnetic order parameters,
denoted by $\bm{M}$ and $\bm{S}$, which are distinguished by the relative sign
between the positive- and negative-energy states (at zero momentum) and become
degenerate in the non-relativistic limit. Because of the relativistic coupling
between the spin and the orbital motion, both $\bm{M}$ and $\bm{S}$ induce
anisotropic deformations of the energy dispersion (and the Fermi surfaces) but
in mutually opposite ways. The AMR is determined primarily by the anisotropy of
the Fermi surface (group velocity), and secondarily by the anisotropy of the
damping; the latter becomes important for ${\bm M}=\pm{\bm S}$, where the Fermi
surfaces are isotropic. Even when the chemical potential lies in the gap, the
AH conductivity is found to take a finite non-quantized value, $\sigma_{ij} =
-(\alpha /3\pi^2 \hbar) \epsilon_{ijk} S_k $, where $\alpha$ is the (effective)
fine structure constant. This offers an example of Hall insulator in three
spatial dimensions.",1404.4741v2
2014-04-23,Meson Life Time in the Anisotropic Quark-Gluon Plasma,"In the hot (an)isotropic plasma the meson life time $\tau$ is defined as a
time scale after which the meson dissociates. According to the gauge/gravity
duality, this time can be identified with the inverse of the imaginary part of
the frequency of the quasinormal modes, $\omega_I$, in the (an)isotropic black
hole background. In the high temperature limit, we numerically show that at
fixed temperature(entropy density) the life time of the mesons
decreases(increases) as the anisotropy parameter raises. For general case, at
fixed temperature we introduce a polynomial function for $\omega_I$ and observe
that the meson life time decreases. Moreover, we realize that $(s/T^3)^6$,
where $s$ and $T$ are entropy density and temperature of the plasma
respectively, can be expressed as a function of anisotropy parameter over
temperature. Interestingly, this function is a Pad\'{e} approximant.",1404.5790v2
2014-04-26,"Fe clusters (Fe$_n$, n=1-6) chemisorbed on vacancy defects in graphene: Stability, spin-dipole moment and magnetic anisotropy","In this work, we have studied the chemical and magnetic interactions of
Fe$_n$ ; n=1-6 clusters with vacancy defects (monovacancy to correlated
vacancies with six missing C atoms) in a graphene sheet by ab-initio density
functional calculations combined with Hubbard U corrections for correlated Fe-
d electrons. It is found that the vacancy formation energies are lowered in the
presence of Fe, indicating an easier destruction of the graphene sheet. Due to
strong chemical interactions between Fe clusters and vacancies, a complex
distribution of magnetic moments appear on the distorted Fe clusters which
results in reduced averaged magnetic moments compared to the free clusters. In
addition to that, we have calculated spin-dipole moments and magnetic
anisotropy energies. The calculated spin-dipole moments arising from
anisotropic spin density distributions, vary between positive and negative
values, yielding increased or decreased effective moments. Depending on the
cluster geometry, the easy axis of magnetization of the Fe clusters shows
in-plane or out-of-plane behavior.",1404.6641v2
2014-04-27,Haldane-like antiferromagnetic spin chain in the large anisotropy limit,"We consider the one dimensional, periodic spin chain with $N$ sites, similar
to the one studied by Haldane \cite{hal}, however in the opposite limit of very
large anisotropy and small nearest neighbour, anti-ferromagnetic exchange
coupling between the spins, which are of large magnitude $s$. For a chain with
an even number of sites we show that actually the ground state is non
degenerate and given by a superposition of the two N\'eel states, due to
quantum spin tunnelling. With an odd number of sites, the N\'eel state must
necessarily contain a soliton. The position of the soliton is arbitrary thus
the ground state is $N$-fold degenerate. This set of states reorganizes into a
band. We show that this occurs at order $2s$ in perturbation theory. The ground
state is non-degenerate for integer spin, but degenerate for half-odd integer
spin as is required by Kramer's theorem \cite{kram}.",1404.6706v1
2014-04-28,Helical Inflation and Cosmic Strings,"Recent BICEP2 detection of low-multipole B-mode polarization anisotropy in
the cosmic microwave background radiation supports the inflationary universe
scenario and suggests a large inflaton field range. The latter feature can be
achieved with axion fields in the framework of string theory. We present such a
helical model which naturally becomes a model with a single cosine potential,
and which in turn reduces to the (quadratic) chaotic inflation model in the
super-Planckian limit. The slightly smaller tensor/scalar ratio $r$ of models
of this type provides a signature of the periodic nature of an axion potential.
We present a simple way to quantify this distinctive feature. As axions are
intimately related to strings/vortices and strings are ubiquitous in string
theory, we explore the possibility that cosmic strings may be contributing to
the B-mode polarization anisotropy observed.",1404.6988v3
2014-05-02,The Planck mission,"These lecture from the 100th Les Houches summer school on ""Post-planck
cosmology"" of July 2013 discuss some aspects of the Planck mission, whose prime
objective was a very accurate measurement of the temperature anisotropies of
the Cosmic Microwave Background (CMB). We announced our findings a few months
ago, on March 21$^{st}$, 2013. I describe some of the relevant steps we took to
obtain these results, sketching the measurement process, how we processed the
data to obtain full sky maps at 9 different frequencies, and how we extracted
the CMB temperature anisotropies map and angular power spectrum. I conclude by
describing some of the main cosmological implications of the statistical
characteristics of the CMB we found. Of course, this is a very much shortened
and somewhat biased view of the \Planck\ 2013 results, written with the hope
that it may lead some of the students to consult the original papers.",1405.0439v1
2014-05-07,Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of equilibrium,"We report on the observation of a large anisotropy in the rethermalization
dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our
system consists of an ultracold sample of strongly magnetic $^{167}$Er
fermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic
collisions arise purely from universal dipolar scattering. Based on
cross-dimensional rethermalization experiments, we observe a strong anisotropy
of the scattering, which manifests itself in a large angular dependence of the
thermal relaxation dynamics. Our result is in very good agreement with recent
theoretical predictions. Furthermore, we measure the rethermalization rate as a
function of temperature for different angles and find that the suppression of
collisions by Pauli blocking is not influenced by the dipole orientation.",1405.1537v2
2014-05-05,The CMB Derivatives of Planck's Beam Asymmetry,"We investigate the anisotropy in cosmic microwave background Planck maps due
to the coupling between its beam asymmetry and uneven scanning strategy.
Introducing a pixel space estimator based on the temperature gradients, we find
a highly significant (~20 \sigma) preference for these to point along ecliptic
latitudes. We examine the scale dependence, morphology and foreground
sensitivity of this anisotropy, as well as the capability of detailed Planck
simulations to reproduce the effect, which is crucial for its removal, as we
demonstrate in a search for the weak lensing signature of cosmic defects.",1405.1609v2
2014-05-08,Electro-optic switching of dielectrically negative nematic through nanosecond electric modification of order parameter (NEMOP),"We present experimental studies of nanosecond electric modification of the
order parameter (NEMOP) in a variety of nematic materials with negative
dielectric anisotropy. The study demonstrates that NEMOP enables a large
amplitude of fast (nanoseconds) electro-optic response with the field-induced
birefringence on the order of 0.01 and a figure of merit (FoM) on the order of
$10^4$ $\mu $m$^2/$s; the latter is orders of magnitude higher than the FoM of
the Frederiks effect traditionally used in electro-optic nematic devices. The
amplitude of the NEMOP response is generally stronger in nematics with larger
dielectric anisotropy and with higher natural (field-free) birefringence.",1405.2118v2
2014-05-14,"Dipole Polarizability of Alkali-Metal (Na, K, Rb) - Alkaline-Earth-Metal (Ca,Sr) Polar molecules - Prospects of Alignment","Electronic open-shell ground-state properties of selected alkali-metal (AM) -
alkaline-earth-metal (AEM) polar molecules are investigated. We determine
potential energy curves of the 2{\Sigma}+ ground state at the coupled-cluster
singles and doubles with partial triples (CCSD(T)) level of electron
correlation. Calculated spectroscopic constants for the isotopes (23Na, 39K,
85Rb) - (40Ca, 88Sr) are compared with available theoretical and experimental
results. The variation of the permanent dipole moment (PDM), average dipole
polarizability, and polarizability anisotropy with internuclear distance is
determined using finite-field perturbation theory at the CCSD(T) level. Owing
to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and
large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u.,
RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for
alignment and orientation in combined intense laser and external static
electric fields.",1405.3503v1
2014-05-15,Disentangling Soft and Hard Hadron Yields in PbPb Collisions at $\sqrt{s_{NN}}$ = 2.76 ATeV,"We demonstrate that charged pion spectra in central and peripheral PbPb
collisions at $\sqrt{s}$ = 2.76 ATeV obtained via perturbative quantum
chromodynamics improved parton model calculations [17] can be approximated by
the Tsallis distribution for transverse momenta $p_T \geq$ 4 GeV/c. Then, we
propose a model in which, hadrons produced in heavy-ion collisions stem either
from ""soft"" or ""hard"" processes, and are distributed according to the Tsallis
distribution in both types of yields. We describe transverse spectra as well as
azimuthal anisotropy ($v_2$) of charged hadrons stemming from various
centrality PbPb collisions at $\sqrt{s}$ = 2.76 ATeV [40,41,42] analytically.
In addition, we find that the anisotropy decreases for more central collisions.",1405.3963v2
2014-05-22,An Interacting Scenario for Dark Energy in Bianchi Type-I Universe,"We study the interaction between dark energy (DE) and dark matter (DM) in the
scope of anisotropic bianchi type I space-time. First we derive the general
form of the dark energy equation of state parameter (EoS) in both
non-interacting and interacting cases and then we examine it's future by
applying a hyperbolic scale factor. It is shown that in non-interacting case,
depending on the value of the anisotropy parameter $K$, the dark energy EoS
parameter is varying from phantom to quintessence whereas in interacting case
EoS parameter vary in quintessence region. However, in both cases the dark
energy EoS parameter $\omega^{de}$, ultimately (i. e at $z=-1$) tends to the
cosmological constant ($\omega^{de}=-1$). Moreover, we fixed the cosmological
bound on the anisotropy parameter $K$ by using the recent observational data of
Hubble parameter.",1405.5714v1
2014-05-27,Stability analysis of (a class of) anisotropic spacetimes,"We consider spherically symmetric spacetimes sourced by a fluid with pressure
anisotropy in the radial direction. We use gauge-invariant perturbation theory
to study the stability of this class of spacetimes under axial perturbations.
We apply our results to three diverse examples. Two examples arise as endpoints
of collapse of a ball of fluid --- one describes a well-behaved stellar
interior and the other has a naked singularity. We prove the stability of the
stellar interior both with respect to Dirichlet and quasinormal mode boundary
conditions on the perturbation. Surprisingly, the naked singularity is also
stable under axial perturbations. Lastly, we take the example of anisotropic
cosmology to show that in this case, the relevant perturbations are those in
which the direction of anisotropy is also perturbed.",1405.6821v2
2014-05-27,Stability of Multinode Dirac Semimetals against Strong Long-Range Correlations,"We study the stability of Dirac semimetals with $N$ nodes in three spatial
dimensions against strong $1/r$ Coulomb interactions. We particularly study the
cases of $N=4$ and $N=16$, where the $N=4$ Dirac semimetal is described by the
staggered fermions and the $N=16$ Dirac semimetal is described by the doubled
lattice fermions. We take into account the $1/r$ long-range Coulomb
interactions between the bulk electrons. Based on the U(1) lattice gauge
theory, we analyze the system from the strong coupling limit. It is shown that
the Dirac semimetals survive in the strong coupling limit when the out-of-plane
Fermi velocity anisotropy of the Dirac cones is weak, whereas they change to
Mott insulators when the anisotropy is strong. A Possible global phase diagram
of correlated multinode Dirac semimetals is presented. Implications of our
result to the stability of Weyl semimetals and three-dimensional topological
insulators are discussed.",1405.6932v2
2014-05-29,Reconfigurable anisotropy and functional transformations with VO$_{2}$-based metamaterial electric circuits,"We demonstrate an innovative multifunctional artificial material that
combines exotic metamaterial properties and the environmentally responsive
nature of phase change media. The tunable metamaterial is designed with the aid
of two interwoven coordinate-transformation equations and implemented with a
network of thin film resistors and vanadium dioxide ($VO_{2}$). The strong
temperature dependence of $VO_{2}$ electrical conductivity results in a
relevant modification of the resistor network behavior, and we provide
experimental evidence for a reconfigurable metamaterial electric circuit (MMEC)
that not only mimics a continuous medium but is also capable of responding to
thermal stimulation through dynamic variation of its spatial anisotropy. Upon
external temperature change the overall effective functionality of the material
switches between a ""truncated-cloak"" and ""concentrator"" for electric currents.
Possible applications may include adaptive matching resistor networks,
multifunctional electronic devices, and equivalent artificial materials in the
magnetic domain. Additionally, the proposed technology could also be relevant
for thermal management of integrated circuits",1405.7743v1
2014-06-11,Nonlinear valley and spin currents from Fermi pocket anisotropy in 2D crystals,"Controlled flow of spin and valley pseudospin is key to future electronics
exploiting these internal degrees of freedom of carriers. Here we discover a
universal possibility for generating spin and valley currents by electric bias
or temperature gradient only, which arises from the anisotropy of Fermi pockets
in crystalline solids. We find spin and valley currents to the second order in
the electric field, as well as their thermoelectric counterparts, i.e. the
nonlinear spin and valley Seebeck effects. These second-order nonlinear
responses allow two unprecedented possibilities to generate pure spin and
valley flows without net charge current: (i) by an AC bias; or (ii) by an
arbitrary inhomogeneous temperature distribution. As examples, we predict
appreciable nonlinear spin and valley currents in two-dimensional (2D) crystals
including graphene, monolayer and trilayer transition metal dichalcogenides,
and monolayer gallium selenide. Our finding points to a new route towards
electrical and thermal generations of spin and valley currents for spintronic
and valleytronic applications based on 2D quantum materials.",1406.2931v1
2014-06-19,Spin-Flop Phenomenon of Two-Dimensional Frustrated Antiferromagnets without Anisotropy in Spin Space,"Motivated by a recent finding of a spin-flop phenomenon in a system without
anisotropy in spin space reported in the S=1/2 Heisenberg antiferromagnet on
the square-kagome lattice, we study the S=1/2 Heisenberg antiferromagnets on
two other lattices composed of vertex-sharing triangles by the numerical
diagonalization method. One is a novel lattice including a shuriken shape with
four teeth; the other is the kagome lattice with
$\sqrt{3}\times\sqrt{3}$-structure distortion, which includes a shuriken shape
with six teeth. We find in the magnetization processes of these systems that a
magnetization jump accompanied by a spin-flop phenomenon occurs at the
higher-field-side edge of the magnetization plateau at one-third the height of
saturation. This finding indicates that the spin-flop phenomenon found in the
isotropic system on the square-kagome lattice is not an exceptional case.",1406.4964v1
2014-06-19,Broken symmetries in URu2Si2,"To resolve the nature of the hidden order below 17.5\,K in the heavy fermion
compound URu$_2$Si$_2$, identifying which symmetries are broken below the
hidden order transition is one of the most important steps. Several recent
experiments on the electronic structure have shown that the Fermi surface in
the hidden order phase is quite close to the result of band-structure
calculations within the framework of itinerant electron picture assuming the
antiferromagnetism. This provides strong evidence for the band folding along
the c-axis with the ordering vector of $(0\,0\,1)$, corresponding to broken
translational symmetry. In addition to this, there is growing evidence for
fourfold rotational symmetry breaking in the hidden-order phase from
measurements of the in-plane magnetic anisotropy and the effective mass
anisotropy in the electronic structure, as well as the orthorhombic lattice
distortion. This broken fourfold symmetry gives a stringent constraint that the
symmetry of the hidden order parameter should belong to the degenerate $E$-type
irreducible representation. We also discuss a possibility that time reversal
symmetry is also broken, which further narrows down the order parameter that
characterizes the hidden order.",1406.5043v1
2014-06-25,Probing the anisotropic expansion from supernovae and GRBs in a model-independent way,"In this paper, we study the anisotropic expansion of the universe using type
Ia supernovae Union 2.1 sample and 116 long gamma-ray bursts. The luminosity
distance is expanded with model-independent cosmographic parameters as a
function of $z/(1+z)$ directly. Thus the results are independent of cosmology
model. We find a dipolar anisotropy in the direction ($l=309.2^\circ \pm
15.8^\circ$, $b=-8.6^\circ \pm 10.5^\circ$) in galactic coordinates with a
significant evidence $97.29\%$ (more than $2~\sigma$). The magnitude is
$(1.37\pm 0.57) \times 10^{-3}$ for the dipole, and $(2.6\pm 2.1)\times
10^{-4}$ for the monopole, respectively. This dipolar anisotropy is more
significant at low redshift from the redshift tomography analysis. We also test
whether this preferred direction is caused by bulk flow motion or dark energy
dipolar scalar perturbation. We find that the direction and the amplitude of
the bulk flow in our results are approximately consistent with the bulk flow
surveys. Therefore, bulk flow motion may be the main reason for the anisotropic
expansion at low redshift, but the effect of dipolar distribution dark energy
can not be excluded, especially at high redshift.",1406.6448v1
2014-06-30,A Test for the Zero Mean Hypothesis in Cosmology,"One working hypothesis on which analyses of cosmological data are based is
the zero ensemble mean hypothesis, which is related to the statistical
homogeneity of cosmological perturbations. This hypothesis, however, should be
tested by observational data in the current era of precision cosmology. Herein,
we test the hypothesis by analyzing recent, foreground-reduced cosmic microwave
background (CMB) maps, combining the spherical harmonic coefficients of the
masked CMB temperature anisotropies in such a way that the combined variables
can be treated as statistically independent samples. We find evidence against
the zero mean hypothesis in two particular ranges of multipoles, with
significance levels of $2.5 \sigma$ and $3.1 \sigma$ in the multipole ranges of
$\ell \approx 61$-$86$ and $213$-$256$, respectively, for both the Planck and
Wilkinson Microwave Anisotropy Probe maps. The latter signal is consistent with
our previous result found by using brute-force Monte-Carlo simulations.
However, within the method employed in this paper we conclude that the zero
mean hypothesis is consistent with the current CMB data on the basis of
Stouffer's weighted Z statistics, which takes multiple testing into account.",1406.7613v3
2014-07-05,Nematic state stabilized by off-site Coulomb interaction in iron-based superconductors,"Using a variational Monte Carlo method, we investigate the nematic state in
iron-base superconductors based on a three-band Hubbard model. Our results
demonstrate that the nematic state, formed by introducing an anisotropic
hopping order into the projected wave function, can arise in the underdoped
regime when a realistic off-site Coulomb interaction $V$ is considered. {\color
{red} We demonstrate that the off-site Coulomb interaction $V$, which is
neglected so far in the analysis of iron-base superconductors, make a dominant
contribution to the stabilization of nematic state. We calculate the doping
dependencies of the anisotropic properties such as the unequal occupation of
$d_{xz}$ and $d_{yz}$ orbitals, anisotropies of kinetic energy and spin
correlations, and show that they are all suppressed upon electron doping, which
are consistent with the intrinsic anisotropies observed by optical spectrum
measurement and ARPES experiments.",1407.1411v1
2014-07-08,Anisotropy of the superconducting fluctuations in multiband superconductors: the case of LiFeAs,"Between the different families of pnictide multiband superconductors, LiFeAs
is probably one of the less understood. Indeed, despite the large amount of
experiments performed in the last few years on this material, no consensus has
been reached yet on the possible pairing mechanism at play in this system. Here
we focus on the precursor effects of superconductivity visible in the transport
experiments performed above Tc. By analyzing the superconducting fluctuations
in a layered multiband model appropriate for this material, we argue that the
strong two-dimensional character of the paraconductivity above Tc points
towards a significant modulation of the pairing interactions along the z
direction. We also discuss the peculiar differences between single-band and
multi-band superconductors for what concerns the anisotropy of the
superconducting-fluctuations effects above and below Tc.",1407.2187v2
2014-07-09,On the parallel spectrum in MHD Turbulence,"Anisotropy of MHD turbulence has been studied extensively for many years,
most prominently by measurements in the solar wind and high resolution
simulations. The spectrum parallel to the local magnetic field was observed to
be steeper than perpendicular spectrum, typically $k^{-2}$, consistent with the
widely accepted Goldreich-Sridhar (1995) model. In this Letter I looked deeper
into the nature of the relation between parallel and perpendicular spectra and
argue that this $k^{-2}$ scaling has the same origin as the $\omega^{-2}$
scaling of Lagrangian frequency spectrum in strong hydrodynamic turbulence.
This follows from the fact that Alfv\'en waves propagate along magnetic field
lines. It is now became clear that the observed anisotropy can be argued
without invocation of the ""critical balance"" argument and is more robust that
was previously thought. The relation between parallel (Lagrangian) and
perpendicular (Eulerian) spectra is inevitable consequence of strong turbulence
of Alfven waves, rather than a conjecture based on the uncertainty relation. I
tested this using high-resolution simulations of MHD turbulence, in particular
I verified that the cutoff of the parallel spectrum scales as Kolmogorov
timescale, not lengthscale.",1407.2613v2
2014-07-15,Interplay of anisotropy in shape and interactions in charged platelet suspensions,"Motivated by the intriguing phase behavior of charged colloidal platelets, we
investigate the structure and dynamics of charged repulsive disks by means of
Monte-Carlo simulations. The electrostatic interactions are taken into account
through an effective two-body potential, obtained within the non-linear
Poisson-Boltzmann formalism, which has the form of anisotropic screened Coulomb
potential. Recently, we showed that the original intrinsic anisotropy of the
electrostatic potential in competition with excluded volume effects leads to a
rich phase behavior that not only includes various liquid-crsytalline phases
but also predicts the existence of novel structures composed of alternating
nematic-antinematic sheets. Here, we examine the structural and dynamical
signatures of each of the observed structures for both translational and
rotational degrees of freedom. Finally, we discuss the influence of effective
charge value and our results in relation to experimental findings on charged
platelet suspensions.",1407.4166v2
2014-07-18,Evolution of shear zones in granular materials,"The evolution of wide shear zones (or shear bands) was investigated
experimentally and numerically for quasistatic dry granular flows in split
bottom shear cells. We compare the behavior of materials consisting of beads,
irregular grains (e.g. sand) and elongated particles. Shearing an initially
random sample, the zone width was found to significantly decrease in the first
stage of the process. The characteristic shear strain associated with this
decrease is about unity and it is systematically increasing with shape
anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g.
sand) and becomes elongated (pegs). The strongly decreasing tendency of the
zone width is followed by a slight increase which is more pronounced for rod
like particles than for grains with smaller shape anisotropy (beads or
irregular particles). The evolution of the zone width is connected to shear
induced density change and for nonspherical particles it also involves grain
reorientation effects. The final zone width is significantly smaller for
irregular grains than for spherical beads.",1407.4976v2
2014-07-20,Spintronic magnetic anisotropy,"An attractive feature of magnetic adatoms and molecules for nanoscale
applications is their superparamagnetism, the preferred alignment of their spin
along an easy axis preventing undesired spin reversal. The underlying magnetic
anisotropy barrier --a quadrupolar energy splitting-- is internally generated
by spin-orbit interaction and can nowadays be probed by electronic transport.
Here we predict that in a much broader class of quantum-dot systems with spin
larger than one-half, superparamagnetism may arise without spin-orbit
interaction: by attaching ferromagnets a spintronic exchange field of
quadrupolar nature is generated locally. It can be observed in conductance
measurements and surprisingly leads to enhanced spin filtering even in a state
with zero average spin. Analogously to the spintronic dipolar exchange field,
responsible for a local spin torque, the effect is susceptible to electric
control and increases with tunnel coupling as well as with spin polarization.",1407.5273v1
2014-07-23,Superconducting properties of novel BiSe$_{2}$-based layered LaO$_{1-x}$F$_{x}$BiSe$_{2}$ single crystals,"F-doped LaOBiSe$_{2}$ superconducting single crystals with typical size of
2$\times$4$\times$0.2 mm$^{3}$ are successfully grown by flux method and the
superconducting properties are studied. Both the superconducting transition
temperature and the shielding volume fraction are effectively improved with
fluorine doping. The LaO$_{0.48}$F$_{0.52}$BiSe$_{1.93}$ sample exhibits
zero-resistivity at 3.7 K, which is higher than that of the
LaO$_{0.5}$F$_{0.5}$BiSe$_{2}$ polycrystalline sample (2.4K). Bulk
superconductivity is confirmed by a clear specific-heat jump at the associated
temperature. The samples exhibit strong anisotropy and the anisotropy parameter
is about 30, as estimated by the upper critical field and effective mass model",1407.6114v1
2014-07-25,Anisotropic magnetoresistance of charge-density wave in $o$-TaS$_3$,"We report the magnetoresistance of a charge-density wave (CDW) in $o$-TaS$_3$
whiskers at 4.2 K under a magnetic field up to 5.2 T. An anisotropic negative
magnetoresistance is found in the nonlinear regime of current-voltage
characteristics. The angle dependence of the magnetoresistance, studied by
rotating the magnetic field upon the $c$-axis, exhibited a two-fold symmetry.
The magnetoresistance amplitude exhibits maxima when the field is parallel to
the $a$-axis, whereas it vanishes to the $b$-axis. The observed anisotropy may
come from difference in interchain coupling of adjacent CDWs along the $a$- and
$b$-axes. Comparison of the anisotropy to the scanning tunneling microscope
image of CDWs allows us to provide a simple picture to explain the
magnetoresistance in terms of delocalization of quantum interference of CDWs
extending over the $b$-$c$ plane.",1407.6795v2
2014-07-30,Influence of temperature dependent shear viscosity on elliptic flow at back- and forward rapidities in ultrarelativistic heavy-ion collisions,"We explore the influence of a temperature-dependent shear viscosity over
entropy density ratio $\eta/s$ on the azimuthal anisotropies v_2 and v_4 of
hadrons at various rapidities. We find that in Au+Au collisions at full RHIC
energy, $\sqrt{s_{NN}}=200$ GeV, the flow anisotropies are dominated by
hadronic viscosity at all rapidities, whereas in Pb+Pb collisions at the LHC
energy, $\sqrt{s_{NN}}=2760$ GeV, the flow coefficients are affected by the
viscosity both in the plasma and hadronic phases at midrapidity, but the
further away from midrapidity, the more dominant the hadronic viscosity is. We
find that the centrality and rapidity dependence of the elliptic and
quadrangular flows can help to distinguish different parametrizations of
$(\eta/s)(T)$. We also find that at midrapidity the flow harmonics are almost
independent of the decoupling criterion, but show some sensitivity to the
criterion at back- and forward rapidities.",1407.8152v2
2014-08-01,Optimization of indirect magnetoelectric effect in thin-film/substrate/piezoelectric-actuator heterostructure using polymer substrate,"Indirect magnetoelectric effect has been studied in
magnetostrictive-film/substrate/piezoelectric-actuator heterostructures. Two
different substrates have been employed: a flexible substrate (Young's modulus
of 4 GPa) and a rigid one (Young's modulus of 180 GPa). A clear optimization of
the indirect magnetoelectric coupling, studied by micro-strip ferromagnetic
resonance, has been highlighted when using the polymer substrate. However, in
contrast to the rigid substrate, the flexible substrate also leads to an a
priori undesirable and huge uniaxial anisotropy which seems to be related to a
non equibiaxial residual stress inside the magnetostrictive film. The strong
amplitude of this non equibiaxiallity is due to the large Young's modulus
mismatch between the polymer and the magnetostrictive film which leads to a
slight curvature along a given direction during the elaboration process and
thus to a large magnetoelastic anisotropy.",1408.0123v1
2014-08-04,Azimuthal elliptic anisotropy ($v_{_{2}}$) of high-$p_{_{T}}$ direct $γ$ in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV,"Preliminary results from the STAR collaboration for the azimuthal elliptic
anisotropy $(v_{_{2}})$ of high transverse momentum ($p_{_{T}}$) direct photons
($\gamma_{_{dir}}$) produced at mid-rapidity ($|\eta^{\gamma_{_{dir}}}|<1$) in
Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$~GeV are
presented, and compared to the measured $(v_{_{2}})$ of neutral pions
($\pi^{0}$) in the same kinematic range. The electromagnetic transverse shower
profile is used to distinguish $\pi^{0}$ from direct photons. The measured
$v_{_{2}}^{\gamma_{_{dir}}}(p_{_{T}})$ at high $p_{_{T}}$ ($8<
p_{_{T}}^{\gamma_{_{dir}}}<20$~GeV/$c$) is found to be smaller than that of
$\pi^{0}$ and consistent with zero when using the forward detectors in
determining the event plane.",1408.0576v2
2014-08-08,Effects of Lifshitz Transition on Charge Transport in Magnetic Phases of Fe-Based Superconductors,"The unusual temperature dependence of the resistivity and its in-plane
anisotropy observed in the Fe-based superconducting materials, particularly
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, has been a longstanding puzzle. Here we
consider the effect of impurity scattering on the temperature dependence of the
average resistivity within a simple two-band model of a dirty spin density wave
metal. The sharp drop in resistivity below the N\'eel temperature $T_N$ in the
parent compound can only be understood in terms of a Lifshitz transition
following Fermi surface reconstruction upon magnetic ordering. We show that the
observed resistivity anisotropy in this phase, arising from nematic defect
structures, is affected by the Lifshitz transition as well.",1408.1933v3
2014-08-11,Collective Expansion at the LHC: selected ALICE anisotropic flow measurements,"The collective expansion of matter created in collisions of heavy-ions,
ranging from collision energies of tens of MeV to a few TeV per nucleon pair,
proved to be one of the best probes to study the detailed properties of these
unknown states of matter. Collective expansion originates from the initial
pressure gradients in the created hot and dense matter. These pressure
gradients transform the initial spatial deformations and inhomogeneities of the
created matter into momentum anisotropies of the final state particle
production, which we call anisotropic flow. These momentum anisotropies are
experimentally characterised by so-called flow harmonics. In this paper I
review ALICE measurements of the flow harmonics at the CERN Large Hadron
Collider and discuss some of the open questions.",1408.2532v2
2014-08-15,Solution to the cosmic ray anisotropy problem,"In the standard diffusive picture for transport of cosmic rays (CRs), a
gradient in the CR density induces a typically small, dipolar anisotropy in
their arrival directions. This has been widely advertised as a tool for finding
nearby sources. However, the predicted dipole amplitude at TeV and PeV energies
exceeds the measured one by almost two orders of magnitude. Here, we critically
examine the validity of this prediction which is based on averaging over an
ensemble of turbulent magnetic fields. We focus (1) on the deviations of the
dipole in a particular random realisation from the ensemble average and (2) the
possibility of a misalignment between the regular magnetic field and the CR
gradient. We find that if the field direction and the gradient direction are
close to $\sim 90^\circ$, the dipole amplitude is considerably suppressed and
can be reconciled with observations, which sheds light on a long-standing
problem. Furthermore, we show that the dipole direction in general does not
coincide with the gradient direction, thus hampering the search for nearby
sources.",1408.3630v2
2014-08-22,Local variance asymmetries in Planck temperature anisotropy maps,"Recently, it was shown that local variance maps of temperature anisotropy are
simple and useful tools for the study of large scale hemispherical power
asymmetry. This was done by studying the distribution of dipoles of the local
variance maps. In this work, we extend the study of the dipolar asymmetry in
local variance maps using foreground cleaned Planck 143 GHz and 217 GHz data to
smaller scales. In doing so, we include the effect of the CMB Doppler dipole.
Further, we show that it is possible to use local variance maps to measure the
Doppler dipole in these Planck channel maps, after removing large scale
features (up to $l=600$), at a significance of about $3 \sigma$. At these small
scales, we do not find any power asymmetry in the direction of the anomalous
large scale power asymmetry beyond that expected from cosmic variance. At large
scales, we verify previous results i.e. the presence of hemispherical power
asymmetry at a significance of at least $3.3 \sigma$.",1408.5396v2
2014-08-25,The mechanics of anisotropic spring networks,"We construct and analyze a model for a disordered linear spring network with
anisotropy. The modeling is motivated by, for example, granular systems,
nematic elastomers, and ultimately cytoskeletal networks exhibiting some
underlying anisotropy. The model consists of a triangular lattice with two
different bond occupation probabilities, $p_x$ and $p_y$, for the linear
springs. We develop an effective medium theory (EMT) to describe the network
elasticity as a function of $p_x$ and $p_y$. We find that the onset of rigidity
in the EMT agrees with Maxwell constraint counting. We also find beyond linear
behavior in the shear and bulk modulus as a function of occupation probability
in the rigid phase for small strains, which differs from the isotropic case. We
compare our EMT with numerical simulations to find rather good agreement.
Finally, we discuss the implications of extending the reach of effective medium
theory as well as draw connections with prior work on both anisotropic and
isotropic spring networks.",1408.5910v2
2014-08-28,Anisotropy study of multiferroicity in the pyroxene NaFeGe$_2$O$_6$,"We present a study of the anisotropy of the dielectric, magnetic and
magnetoelastic properties of the multiferroic clinopyroxene NaFeGe$_2$O$_6$.
Pyroelectric currents, dielectric constants and magnetic susceptibilities as
well as the thermal expansion and the magnetostriction were examined on large
synthetic single crystals of NaFeGe$_2$O$_6$. The spontaneous electric
polarization detected below $T_{\rm C}\simeq 11.6$ K in an
antiferromagnetically ordered state ($T_{\rm N}\simeq 13$ K) is mainly lying
within the $ac$ plane with a small component along $b$, indicating a triclinic
symmetry of the multiferroic phase of NaFeGe$_2$O$_6$. The electric
polarization can be strongly modified by applying magnetic fields along
different directions. We derive detailed magnetic-field versus temperature
phase diagrams and identify three multiferroic low-temperature phases, which
are separated by a non-ferroelectric, antiferromagnetically ordered state from
the paramagnetic high-temperature phase.",1408.6772v3
2014-08-28,Channeling Effect in Polycrystalline Deuterium-Saturated CVD Diamond Target Bombarded by Deuterium Ion Beam,"At the ion accelerator HELIS at the LPI, the neutron yield is investigated in
DD reactions within a polycrystalline deuterium-saturated CVD diamond, during
an irradiation of its surface by a deuterium ion beam with the energy less than
30 keV. The measurements of the neutron flux in the beam direction are
performed in dependence on the target angle, \b{eta}, with respect to the beam
axis. These measurements are performed using a multichannel detector based on
He3 counters. A significant anisotropy in neutron yield is observed, it was
higher by a factor of 3 at \b{eta}=0 compared to that at \b{eta} = +-45{\deg}.
The possible reasons for the anisotropy, including ion channeling, are
discussed.",1408.7109v2
2014-09-01,The effects of a non-zero cosmological constant on the Veltmann models,"The Veltmann models, which include the Plummer and Hernquist models as
special cases, are studied in the presence of a cosmological constant.
Physically relevant quantities such as the velocity dispersion profiles and the
anisotropy parameter are computed through the use of the self-consistent
approach. The cutoff radii for these models and the mass contained within this
volume are also calculated. It is shown that the inclusion of a cosmological
constant leads to many observable quantities such as the surface density,
dispersion profiles and the anisotropy parameter becoming increasingly
modified. In some scenarios, they are easily distinguished from the case where
the cosmological constant is absent, as a result of their non-monotonic
behaviour. The effects of neighbouring gravitational systems on the central
system are also studied, and compared against the effects arising from the
cosmological constant. Consequently, it is suggested that the effects of a
cosmological constant can prove to be quite important when modelling dilute
collisionless systems.",1409.0581v1
2014-09-05,Influence of the Anisometry of Magnetic Particles on the Isotropic-Nematic Phase Transition,"The influence of the shape anisotropy of magnetic particles on the
isotropic-nematic phase transition was studied in ferronematics based on the
nematic liquid crystal 4-(trans-4-n-hexylcyclohexyl)-isothiocyanato-benzene
(6CHBT). The liquid crystal was doped with spherical or rod-like magnetic
particles of different size and volume concentrations. The phase transition
from isotropic to nematic phase was observed by polarizing microscope as well
as by capacitance measurements. The influence of the concentration and the
shape anisotropy of the magnetic particles on the isotropic-nematic phase
transition in liquid crystal is demonstrated. The results are in a good
agreement with recent theoretical predictions.",1409.1738v1
2014-09-06,Magnetochiral symmetry breaking in a Möbius ring,"We show that the interaction of the magnetic subsystem of a curved magnet
with the magnet curvature results in coupling of a topologically nontrivial
magnetization pattern and topology of the object. The mechanism of this
coupling is explored and illustrated by an example of ferromagnetic M\""obius
ring, where a topologically induced domain wall appears as a ground state in
case of strong easy-normal anisotropy. For the M\""obius geometry the
curvilinear form of the exchange interaction produces an additional effective
Dzyaloshinskii-like term which leads to the coupling of the magnetochirality of
the domain wall and chirality of the M\""obius ring. Two types of domain walls
are found, transversal and longitudinal, which are oriented across and along
the M\""obius ring, respectively. In both cases the effect of magnetochirality
symmetry breaking is established. The dependence of the ground state of the
M\""obius ring on its geometrical parameters and on the value of the easy-normal
anisotropy is explored numerically.",1409.2049v2
2014-09-10,Clustering Fossils in Solid Inflation,"In solid inflation the single field non-Gaussianity consistency condition is
violated. As a result, the long tensor perturbation induces observable
clustering fossils in the form of quardupole anisotropy in large scale
structure power spectrum. In this work we revisit the bispectrum analysis for
the scalar-scalar-scalar and tensor-scalar-scalar for the general parameter
space of solid. We consider the parameter space of the model in which the level
of non-Gaussianity generated is consistent with Planck constraints.
Specializing to this allowed range of model parameter, we calculate the
quadrupole anisotropy induced from the long tensor perturbations on the power
spectrum of scalar perturbations. We argue that imprints of clustering fossil
from primordial gravitational waves on large scale structures can be detected
from the future galaxy surveys.",1409.3004v1
2014-09-11,Spin Wave Emission in Field-Driven Domain Wall Motion,"A domain wall (DW) in a nanowire can propagate under a longitudinal magnetic
field by emitting spin waves (SWs). We numerically investigated the properties
of SWs emitted by the DW motion, such as frequency and wavenumber, and their
relation with the DW motion. For a wire with a low transverse anisotropy and in
a field above a critical value, a DW emits SWs to both sides (bow and stern),
while it oscillates and propagates at a low average speed. For a wire with a
high transverse anisotropy and in a weak field, the DW emits mostly stern
waves, while the DW distorts itself and DW center propagates forward like a
drill at a relative high speed.",1409.3286v2
2014-09-17,Birefringence of silica hydrogels prepared under high magnetic fields reinvestigated,"Birefringence is an indicator of structural anisotropy of materials. We
measured the birefringence of Pb(II)-doped silica hydrogels prepared under a
high magnetic field of various strengths. Because the silica is diamagnetic,
one does not expect the structural anisotropy induced by a magnetic field. In
previous work [Mori A, Kaito T, Furukawa H 2008 Mater. Lett. 62 3459-3461], we
prepared samples in cylindrical cells made of borosilicate glass and obtained a
preliminary result indicating a negative birefringence for samples prepared at
5T with the direction of the magnetic field being the optic axis. We have
measured the birefringence of Pn(II)-doped silica hydrogels prepared in square
cross-sectional cells made of quartz and reverted the previous conclusion.
Interestingly, the magnetic-influenced silica hydrogels measured have been
classified into four classes: two positive birefringent ones, no birefringent
one, and negative birefringent one. Proportionality between birefringence and
the strength of magnetic field is seen for the former two.",1409.4846v1
2014-09-27,Anisotropy of force distributions in sheared soft particle systems,"In this numerical study, measurements of the contact forces inside a periodic
two-dimensional sheared system of soft frictional particles are reported. The
distribution of normalized normal forces exhibits a gradual broadening with
increasing the pure shear deformation, leading to a slower decay for large
forces. The process however slows down and the distribution approaches an
invariant shape at high shear deformations. By introducing the joint
probability distribution in sheared configurations, it is shown that for a
fixed direction, the force distribution decays faster than exponentially even
in a sheared system. The overall broadening can be attributed to the averaging
over different directions in the presence of shear-induced stress anisotropy.
The distribution of normalized tangential forces almost preserves its shape for
arbitrary applied strain.",1409.7804v1
2014-09-30,Majorana Fermions in Ge/Si Hole Nanowires,"We consider Ge/Si core/shell nanowires with hole states coupled to an
$s$-wave superconductor in the presence of electric and magnetic fields. We
employ a microscopic model that takes into account material-specific details of
the band structure such as strong and electrically tunable Rashba-type
spin-orbit interaction and $g$ factor anisotropy for the holes. In addition,
the proximity-induced superconductivity Hamiltonian is derived starting from a
microscopic model. In the topological phase, the nanowires host Majorana
fermions with localization lengths that depend strongly on both the magnetic
and electric fields. We identify the optimal regime in terms of the directions
and magnitudes of the fields in which the Majorana fermions are the most
localized at the nanowire ends. In short nanowires, the Majorana fermions
hybridize and form a subgap fermion whose energy is split away from zero and
oscillates as a function of the applied fields. The period of these
oscillations could be used to measure the dependence of the spin-orbit
interaction on the applied electric field and the $g$ factor anisotropy.",1409.8645v2
2014-10-03,Thermophysical Properties of Lignocellulose: A Cell-scale Study down to 41K,"Thermal energy transport is of great importance in lignocellulose pyrolysis
for bio-fuels. The thermophysical properties of lignocellulose significantly
affect the overall properties of bio-composites and the related thermal
transport. In this work, cell-scale lignocellulose (mono-layer plant cells) is
prepared to characterize their thermal properties from room temperature down to
41 K. The thermal conductivities of cell-scale lignocellulose along different
directions show a little anisotropy due to the cell structure anisotropy. It is
found that with temperature going down, the volumetric specific heat of the
lignocellulose shows a slower decreasing trend against temperature than that of
microcrystalline cellulose, and its value is always higher than that of
microcrystalline cellulose. The thermal conductivity of lignocellulose
decreases with temperature from 243 K to 317 K due to increasing phonon-phonon
scatterings. From 41 K to 243 K, the thermal conductivity rises with
temperature and its change mainly depends on the heat capacity's change.",1410.0740v1
2014-10-20,Anisotropic inplane spin correlation in the parent and Co-doped BaFe2As2: a neutron scattering study,"Antiferromagnetic spin fluctuations were investigated in the normal states of
the parent ($x = 0$), under-doped ($x = 0.04$) and optimally-doped ($x = 0.06$)
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystals using inelastic neutron
scattering technique. For all the doping levels, quasi-two-dimensional
antiferromagnetic fluctuations were observed as a broad peak localized at ${\it
Q} = (1/2, 1/2, l)$. At lower energies, the peak shows an apparent anisotropy
in the $hk0$ plane; longitudinal peak widths are considerably smaller than
transverse widths. The anisotropy is larger for the higher doping level. These
results are consistent with the random phase approximation (RPA) calculations
taking account of the orbital character of the electronic bands, confirming
that the anisotropic nature of the spin fluctuations in the normal states is
mostly dominated by the nesting of Fermi surfaces. On the other hand, the
quasi-two-dimensional spin correlations grow much rapidly for decreasing
temperature in the $x = 0$ parent compound, compared to that expected for
nearly antiferromagnetic metals. This may be another sign of the unconventional
nature of the antiferromagnetic transition in BaFe$_2$As$_2$.",1410.5155v1
2014-10-23,On the origin of the electronic anisotropy in iron pnicitde superconductors,"We use polarization-resolved Raman spectroscopy to study the anisotropy of
the electronic characteristics of the iron-pnictide parent compounds
$A$Fe$_{2}$As$_{2}$ ($A$~=~Eu, Sr). We demonstrate that above the structural
phase transition at Ts the dynamical anisotropic properties of the 122
compounds are governed by the emergence of $xy$-symmetry critical collective
mode foretelling a condensation into a state with spontaneously broken
four-fold symmetry at a temperature $T^{*}$. However, the mode's critical
slowing down is intervened by a structural transition at Ts, about 80~K above
$T^{*}$, resulting in an anisotropic density wave state.",1410.6452v1
2014-10-24,Magnetic Excitations in the Spin-Spiral State of TbMnO$_3$ and DyMnO$_3$,"We calculate spectra of magnetic excitations in the spin-spiral state of
perovskite manganates. The spectra consist of several branches corresponding to
different polarizations and different ways of diffraction from the static
magnetic order. Goldstone modes and opening of gaps at zero and non-zero
energies due to the crystal field and the Dzyaloshinski-Moriya anisotropies are
discussed. Comparing results of the calculation with available experimental
data we determine values of effective exchange parameters and anisotropies. To
simplify the spin-wave calculation and to get a more clear physical insight in
the structure of excitations we use the {\sigma}-model-like effective field
theory to analyze the Heisenberg Hamiltonian and to derive the spectra.",1410.6598v1
2014-10-24,Anisotropic hydrodynamics for conformal Gubser flow,"We derive the equations of motion for a system undergoing boost-invariant
longitudinal and azimuthally-symmetric transverse ""Gubser flow"" using
leading-order anisotropic hydrodynamics. This is accomplished by assuming that
the one-particle distribution function is ellipsoidally-symmetric in the
momenta conjugate to the de Sitter coordinates used to parameterize the Gubser
flow. We then demonstrate that the SO(3)_q symmetry in de Sitter space further
constrains the anisotropy tensor to be of spheroidal form. The resulting system
of two coupled ordinary differential equations for the de Sitter-space momentum
scale and anisotropy parameter are solved numerically and compared to a
recently obtained exact solution of the relaxation-time-approximation Boltzmann
equation subject to the same flow. We show that anisotropic hydrodynamics
describes the spatio-temporal evolution of the system better than all currently
known dissipative hydrodynamics approaches. In addition, we prove that
anisotropic hydrodynamics gives the exact solution of the relaxation-time
approximation Boltzmann equation in the ideal, eta/s -> 0, and free-streaming,
eta/s -> infinity, limits.",1410.6790v2
2014-10-27,Relativistic anisotropic star and its maximum mass in higher dimensions,"We present a class of relativistic solutions of cold compact anisotropic
stars in hydrostatic equilibrium in the framework of higher dimensions using
spheroidal geometry. The solutions obtained with Vaidya-Tikekar metric are used
to construct stellar models of compact objects and studied their physical
features. The effects of anisotropy and extra dimensions on the global
properties namely, compactness, mass, radius, equation of state are determined
in higher dimensions in terms of the spheroidicity parameter ($\lambda$). It is
noted that for a given configuration, compactness of a star is found smaller in
higher dimensions compared to that in four space-time dimensions. It is also
noted that the maximum mass of compact objects increase with the increase of
space-time dimensions which however attains a maximum when $D=5$ for a large
($\lambda=100$), thereafter it decreases as one increases number of extra
dimensions. The effect of extra dimensions on anisotropy is also studied.",1410.7735v1
2014-11-02,Convergence of Space-Time Discrete Threshold Dynamics to Anisotropic Motion by Mean Curvature,"We analyze the continuum limit of a thresholding algorithm for motion by mean
curvature of one dimensional interfaces in various space-time discrete regimes.
The algorithm can be viewed as a time-splitting scheme for the Allen-Cahn
equation which is a typical model for the motion of materials phase boundaries.
Our results extend the existing statements which are applicable mostly in
semi-discrete (continuous in space and discrete in time) settings. The
motivations of this work are twofolds: to investigate the interaction between
multiple small parameters in nonlinear singularly perturbed problems, and to
understand the anisotropy in curvature for interfaces in spatially discrete
environments. In the current work, the small parameters are the the spatial and
temporal discretization step sizes $\triangle x = h$ and $\triangle t = \tau$.
We have identified the limiting description of the interfacial velocity in the
(i) sub-critical ($h \ll \tau$), (ii) critical ($h = O(\tau)$), and (iii)
super-critical ($h \gg \tau$) regimes. The first case gives the classical
isotropic motion by mean curvature, while the second produces intricate pinning
and de-pinning phenomena and anisotropy in the velocity function of the
interface. The last case produces no motion (complete pinning).",1411.0301v1
2014-11-10,Spin-dependent thermoelectric effects in transport through a nanoscopic junction involving spin impurity,"Conventional and spin-related thermoelectric effects in transport through a
magnetic tunnel junction with a large-spin impurity, such as a magnetic
molecule or atom, embedded into the corresponding barrier are studied
theoretically in the linear-response regime. The impurity is described by the
giant spin Hamiltonian, with both uniaxial and transverse magnetic anisotropy
taken into account. Owing to the presence of transverse component of magnetic
anisotropy, spin of a tunneling electron can be reversed during scattering on
the impurity, even in the low temperature regime. This reversal appears due to
exchange interaction of tunneling electrons with the magnetic impurity. We
calculate Seebeck and spin Seebeck coefficients, and analyze their dependence
on various parameters of the spin impurity and tunnel junction. In addition,
conventional and spin figures of merit, as well as the electronic contribution
to heat conductance are considered. We also show that pure spin current can be
driven by a spin bias applied to the junction with spin impurity, even if no
electron transfer between the electrodes can take place. The underlying
mechanism employs single-electrode tunneling processes (electrode-spin exchange
interaction) and the impurity as an intermediate reservoir of angular momentum.",1411.2375v1
2014-11-14,Femtosecond wavepacket interferometry using the rotational dynamics of a trapped cold molecular ion,"A Ramsey-type interferometer is suggested, employing a cold trapped ion and
two time-delayed off-resonant femtosecond laser pulses. The laser light couples
to the molecular polarization anisotropy, inducing rotational wavepacket
dynamics. An interferogram is obtained from the delay dependent populations of
the final field-free rotational states. Current experimental capabilities for
cooling and preparation of the initial state are found to yield an
interferogram visibility of more than 80\%. The interferograms can be used to
determine the polarizability anisotropy with an accuracy of about $\pm 2\%$,
respectively $\pm 5\%$, provided the uncertainty in the initial populations and
measurement errors are confined to within the same limits.",1411.3849v1
2014-11-17,The three-dimensional evolution of ion-scale current sheets: tearing and drift-kink instabilities in the presence of proton temperature anisotropy,"We present the first three-dimensional hybrid simulations of the evolution of
ion-scale current sheets, with an investigation of the role of temperature
anisotropy and associated kinetic instabilities on the growth of the tearing
instability and particle heating. We confirm the ability of the ion cyclotron
and firehose instabilities to enhance or suppress reconnection, respectively.
The simulations demonstrate the emergence of persistent three-dimensional
structures, including patchy reconnection sites and the fast growth of a
narrow-band drift-kink instability, which suppresses reconnection for thin
current sheets with weak guide fields. Potential observational signatures of
the three-dimensional evolution of solar wind current sheets are also
discussed. We conclude that kinetic instabilities, arising from non-Maxwellian
ion populations, are significant to the evolution of three-dimensional current
sheets, and two-dimensional studies of heating rates by reconnection may
therefore over-estimate the ability of thin, ion-scale current sheets to heat
the solar wind by reconnection.",1411.4422v1
2014-11-19,Universal domain wall dynamics under electric field in Ta/CoFeB/MgO devices with perpendicular anisotropy,"Electric field effects in ferromagnetic/oxide dielectric structures provide a
new route to control domain wall (DW) dynamics with low power dissipation.
However, electric field effects on DW velocities have only been observed so far
in the creep regime where DW velocities are low due to strong interactions with
pinning sites. Here, we show gate voltage modulation of DW velocities ranging
from the creep to the flow regime in Ta/Co40Fe40B20/MgO/TiO2 structures with
perpendicular magnetic anisotropy. We demonstrate a universal description of
the role of applied electric fields in the various pinning dependent regimes by
taking into account an effective magnetic field being linear with the electric
field. In addition, the electric field effect is found to change sign in the
Walker regime. Our work opens new opportunities for the study and optimization
of electric field effect at ferromagnetic metal/insulator interfaces.",1411.5267v2
2014-11-20,Residence time estimates for asymmetric simple exclusion dynamics on stripes,"The target of our study is to approximate numerically and, in some particular
physically relevant cases, also analytically, the residence time of particles
undergoing an asymmetric simple exclusion dynamics on a stripe. The source of
asymmetry is twofold: (i) the choice of boundary conditions (different
reservoir levels) and (ii) the strong anisotropy from a nonlinear drift with
prescribed directionality. We focus on the effect of the choice of anisotropy
in the flux on the asymptotic behavior of the residence time with respect to
the length of the stripe. The topic is relevant for situations occurring in
pedestrian flows or biological transport in crowded environments, where lateral
displacements of the particles occur predominantly affecting therefore in an
essentially way the efficiency of the overall transport mechanism.",1411.5490v2
2014-11-24,Anisotropy of the semi-classical gluon field of a large nucleus at high energy,"The McLerran-Venugopalan model describes a highly boosted hadron/nucleus as a
sheet of random color charges which source soft classical Weizs\""acker-Williams
gluon fields. We show that due to fluctuations, individual configurations are
azimuthally anisotropic. We present initial evidence that impact parameter
dependent small-x JIMWLK resummation preserves such anisotropies over several
units of rapidity. Finally, we compute the first four azimuthal Fourier
amplitudes of the S-matrix of a fundamental dipole in such background fields.",1411.6630v3
2014-11-26,(3+1)-dimensional framework for leading-order non conformal anisotropic hydrodynamics,"In this work I develop a new framework for anisotropic hydrodynamics that
generalizes the leading order of the hydrodynamic expansion to the full
(3+1)-dimensional anisotropic massive case. Following previous works, my
considerations are based on the Boltzmann kinetic equation with the collisional
term treated in the relaxation time approximation. The momentum anisotropy is
included explicitly in the leading term, allowing for a large difference
between the longitudinal and transverse pressures as well as for non trivial
transverse dynamics. Energy and momentum conservation is expressed by the first
moment of the Boltzmann equation. The system of equations is closed by using
the zeroth and second moments of the Boltzmann equation. The
close-to-equilibrium matching with second-order viscous hydrodynamics is
demonstrated. In particular, I show that the coupling between shear and bulk
pressure corrections, recently proved to be important for an accurate
description of momentum anisotropy and bulk viscous dynamics, does not vanish
in the close-to-equilibrium limit.",1411.7268v2
2014-11-27,New formulation of leading order anisotropic hydrodynamics,"Anisotropic hydrodynamics is a reorganization of the relativistic
hydrodynamics expansion, with the leading order already containing substantial
momentum-space anisotropies. The latter are a cause of concern in the
traditional viscous hydrodynamics, since large momentum anisotropies generated
in ultrarelativistic heavy-ion collisions are not consistent with the
hypothesis of small deviations from an isotropic background, i.e., from the
local equilibrium distribution.
  We discuss the leading order of the expansion, presenting a new formulation
for the (1+1)--dimensional case, namely, for the longitudinally boost invariant
and cylindrically symmetric flow. This new approach is consistent with the well
established framework of Israel and Stewart in the close to equilibrium limit
(where we expect viscous hydrodynamics to work well). If we consider the
(0+1)--dimensional case, that is, transversally homogeneous and longitudinally
boost invariant flow, {the new form of anisotropic hydrodynamics leads to
better agreement with known solutions} of the Boltzmann equation than the
previous formulations, especially when we consider finite mass particles.",1411.7615v1
2014-11-28,Cosmic ray propagation in the interstellar magnetic fields,"The propagation of TeV-PeV cosmic rays (CR) in our Galaxy can be described as
a diffusive process. We discuss here two effects, with important observational
consequences, that cannot be predicted by the diffusion approximation in its
usual form. First, we present an explanation for the CR anisotropies observed
at small angular scales on the sky. We show that the local magnetic field
configuration within a CR mean free path from Earth naturally results in CR
flux anisotropies at small and medium scales. Second, we point out that TeV-PeV
CRs should be expected to diffuse strongly anisotropically in the interstellar
medium on scales smaller than the maximum scale of spatial fluctuations of the
field, $\sim 100$ pc. This notably questions the usual assumptions on CR
diffusion around sources.",1411.7985v1
2014-12-02,Quantum Criticality in the 122 Iron Pnictide Superconductors Emerging from Orbital-Selective Mottness,"The twin issues of the nature of the normal state and competing order(s) in
the iron arsenides are central to understanding their unconventional, high-Tc
superconductivity. We use a combination of transport anisotropy measurements on
detwinned Sr(Fe(1-x)Co(x))2As2 single crystals and local density approximation
plus dynamical mean field theory (LDA + DMFT) calculations to revisit these
issues. The peculiar resistivity anisotropy and its evolution with x are
naturally interpreted in terms of an underlying orbital-selective Mott
transition (OSMT) that gaps out the dxz or dyz states. Further, we use a
Landau-Ginzburg approach using LDA + DMFT input to rationalize a wide range of
anomalies seen up to optimal doping, providing strong evidence for secondary
electronic nematic order. These findings suggest that strong dynamical
fluctuations linked to a marginal quantum-critical point associated with this
OSMT and a secondary electronic nematic order constitute an intrinsically
electronic pairing mechanism for superconductivity in Fe arsenides.",1412.1034v2
2014-12-05,Quantum metrology with non-equilibrium steady states of quantum spin chains,"We consider parameter estimations with probes being the boundary
driven/dissipated non- equilibrium steady states of XXZ spin 1/2 chains. The
parameters to be estimated are the dissipation coupling and the anisotropy of
the spin-spin interaction. In the weak coupling regime we compute the scaling
of the Fisher information, i.e. the inverse best sensitivity among all
estimators, with the number of spins. We find superlinear scalings and
transitions between the distinct, isotropic and anisotropic, phases. We also
look at the best relative error which decreases with the number of particles
faster than the shot-noise only for the estimation of anisotropy.",1412.1977v1
2014-12-07,Pressure-Induced Enhancement of the Magnetic Anisotropy in Mn(N(CN)$_{2}$)$_{2}$,"Using dc and ac magnetometry, the pressure dependence of the magnetization of
the three-dimensional antiferromagnetic coordination polymer
Mn(N(CN)$_{2}$)$_{2}$ was studied up to 12 kbar and down to 8K. The magnetic
transition temperature, $T_c$, increases dramatically with applied pressure
$(P)$, where a change from $T_c(P=\text{ambient}) = 16.0$ K to
$T_c(P=12.1$~kbar$) = 23.5$ K was observed. In addition, a marked difference in
the magnetic behavior is observed above and below 7.1 kbar. Specifically, for
$P<7.1$ kbar, the differences between the field-cooled and zero-field-cooled
(fc-zfc) magnetizations, the coercive field, and the remanent magnetization
decrease with increasing pressure. However, for $P>7.1$ kbar, the behavior is
inverted. Additionally, for $P>8.6$ kbar, minor hysteresis loops are observed.
All of these effects are evidence of the increase of the superexchange
interaction and the appearance of an enhanced exchange anisotropy with applied
pressure.",1412.2318v1
2014-12-11,Non-collinear Magnetic Configurations at Finite Temperature in Thin Films,"The finite-temperature magnetism of a monolayer on a bcc (110) surface was
examined using a model Hamiltonian containing ferromagnetic or
antiferromagnetic exchange interactions, Dzyaloshinsky-Moriya interactions and
easy-axis on-site anisotropy. We examined the competition between the collinear
ground state parallel to the easy axis and the spin spiral state in the plane
perpendicular to this axis preferred by the Dzyaloshinsky-Moriya interaction.
Using approximative methods to calculate the magnon spectrum at finite
temperatures, it was found that even if the ground state is collinear,
increasing the Dzyaloshinsky-Moriya interaction strongly decreases the critical
temperature where this collinear order disappears. Using atomistic spin
dynamics simulations it was found that at this critical temperature the system
transforms into the non-collinear state. Including external magnetic field
helps stabilising the ferromagnetic state. An effect due to the finite size of
the magnetic monolayer was included in the model by considering a different
value for the anisotropy at the edges of the monolayer. This effect was shown
to stabilize the spin spiral state by fixing the phase at the ends of the
stripe.",1412.3591v1
2014-12-14,Dielectric anisotropy in polar solvents under external fields,"We investigate dielectric saturation and increment in polar liquids under
external fields. We couple a previously introduced dipolar solvent model to a
uniform electric field and derive the electrostatic kernel of interacting
dipoles. This procedure allows an unambiguous definition of the liquid
dielectric permittivity embodying non-linear dielectric response and
correlation effects.We find that the presence of the external field results in
a dielectric anisotropy characterized by a two-component dielectric
permittivity tensor. The increase of the electric field amplifies the
permittivity component parallel to the field direction, i.e. dielectric
increment is observed along the field. However, the perpendicular component is
lowered below the physiological permittivity, indicating dielectric saturation
perpendicular to the field. By comparison with Molecular Dynamics simulations
from the literature, we show that the mean-field level dielectric response
theory underestimates dielectric saturation. The inclusion of dipolar
correlations at the weak-coupling level intensify the mean-field level
dielectric saturation and improves the agreement with simulation data at weak
electric fields. The correlation-corrected theory predicts as well the presence
of a metastable configuration corresponding to the antiparallel alignment of
dipoles with the field. This prediction can be verified by solvent-explicit
simulations where solvent molecules are expected to be trapped transiently in
this metastable state.",1412.4425v2
2014-12-16,Calculating thermal stability and attempt frequency of advanced recording structures without free parameters,"Ensuring a permanent increase of magnetic storage densities is one of the
main challenges in magnetic recording. Conventional approaches based on single
phase grains are not suitable to achieve this goal, because their grain volume
is limited due to the superparamagnetic limit. Grains with graded anisotropy
are the most promising candidates to overcome this limit, providing magnetic
memory bits with small volumes, low coercivity and high thermal stability at
the same time. Combining micromagnetic simulations with forward flux sampling
(FFS), a computational method for rare events that has been recently applied to
the magnetic nanostructures, we have determined thermal escape rates and
attempt frequencies of a graded media grain and two single phase grains of the
same geometry. We find that graded anisotropy can increase the thermal
stability of a grain by 12 orders of magnitudes from tens of milliseconds to
centuries without changing the coercive field.",1412.5057v1
2014-12-23,Anisotropic Thermal Conductivity in Single Crystal beta-Gallium Oxide,"The thermal conductivities of beta-Ga2O3 single crystals along four different
crystal directions were measured in the temperature range of 80-495K using the
time domain thermoreflectance (TDTR) method. A large anisotropy was found. At
room temperature, the [010] direction has the highest thermal conductivity of
27.0+/-2.0 W/mK, while that along the [100] direction has the lowest value of
10.9+/-1.0 W/mK. At high temperatures, the thermal conductivity follows a ~1/T
relationship characteristic of Umklapp phonon scattering, indicating
phonon-dominated heat transport in the \b{eta}-Ga2O3 crystal. The measured
experimental thermal conductivity is supported by first-principles calculations
which suggest that the anisotropy in thermal conductivity is due to the
differences of the speed of sound along different crystal directions.",1412.7472v1
2014-12-25,Full decoherence induced by local fields in open spin chains with strong boundary couplings,"We investigate an open $XYZ$ spin $1/2$ chain driven out of equilibrium by
boundary reservoirs targeting different spin orientations, aligned along the
principal axes of anisotropy. We show that by tuning local magnetic fields,
applied to spins at sites near the boundaries, one can change any
nonequilibrium steady state to a fully uncorrelated Gibbsian state at infinite
temperature. This phenomenon occurs for strong boundary coupling and on a
critical manifold in the space of the fields amplitudes. The structure of this
manifold depends on the anisotropy degree of the model and on the parity of the
chain size.",1412.7841v1
2014-12-29,Drag force of Anisotropic plasma at finite $U(1)$ chemical potential,"We perform the calculation of drag force acting on a massive quark moving
through an anisotropic ${\cal N}=4$ SU(N)= 4 SU(N) Super Yang-Mills plasma in
the presence of a U(1) chemical potential. We present the numerical results for
any value of anisotropy and arbitrary direction of the quark velocity with
respect to the direction of anisotropy. We find the effect of chemical
potential or charge density will enhance the drag force for the our charged
solution.",1412.8433v5
2015-01-05,Anisotropic flow generated by hard partons in medium,"Hard partons which are produced copiously in nuclear collisions at the LHC,
deposit most of their energy and momentum into the surrounding quark-gluon
plasma. We show that this generates streams in the plasma and contributes
importantly to flow anisotropies. With the help of event-by-event
three-dimensional perfect hydrodynamic simulations we calculate the observable
azimuthal anisotropies of hadronic distributions and show that the proposed
mechanism is capable of generating non-negligible part of the observed signal.
Hence, it must be taken into account in quantitative studies in which one tries
to extract the values of viscosities from the comparison of simulated results
with measured data.",1501.00788v1
2015-01-09,The ground-state phase diagram of the XXZ spin-s kagome antiferromagnet: A coupled-cluster study,"We use the coupled cluster method to high orders of approximation in order to
calculate the ground-state phase diagram of the XXZ spin-$s$ kagome
antiferromagnet with easy-plane anisotropy, i.e. the anisotropy parameter
$\Delta$ varies between $\Delta=1$ (isotropic Heisenberg model) and $\Delta=0$
($XY$ model). We find that for the extreme quantum case $s=1/2$ the ground
state is magnetically disordered in the entire region $0 \le \Delta \le 1$. For
$s=1$ the ground state is disordered for $0.818 < \Delta \le 1$, it exhibits
$\sqrt{3}\times\sqrt{3}$ magnetic long-range order for $0.281 < \Delta <0.818$,
and $q=0$ magnetic long-range order for $0 \le \Delta < 0.281$. We confirm the
recent result of Chernyshev and Zhitomirsky (Phys. Rev. Lett. 113, 237202
(2014)) that the selection of the ground state by quantum fluctuations is
different for small $\Delta$ ($XY$ limit) and for $\Delta$ close to one
(Heisenberg limit), i.e., $q=0$ magnetic order is favored over
$\sqrt{3}\times\sqrt{3}$ for $0\le \Delta <\Delta_c$ and vice versa for
$\Delta_c < \Delta \le 1$. We calculate $\Delta_c$ as a function of the spin
quantum number $s$.",1501.02146v1
2015-01-09,Spin Hall Switching of the Magnetization in Ta/TbFeCo Structures with Bulk Perpendicular Anisotropy,"Spin-orbit torques are studied in Ta/TbFeCo patterned structures with a bulk
perpendicular magnetic anisotropy (bulk-PMA) for the first time. The
current-induced magnetization switching is investigated in the presence of a
perpendicular, longitudinal, or transverse field. In order to rule out Joule
heating effect, switching of the magnetization is also demonstrated using
current pulses. It is found that the anti-damping torque correlated with spin
Hall effect is very strong, and a spin Hall angle of about 0.12 is obtained.
The field-like torque related with Rashba effect is negligible in this
structure suggesting that the interface play a significant role in Rashba-like
torque.",1501.02294v1
2015-01-14,Hydrodynamic spin fluctuations in the antiferromagnetic Heisenberg chain,"We study the finite temperature, low energy, long wave-length spectrum of the
dynamic structure factor of the spin-$1/2$ antiferromagnetic Heisenberg chain
in the presence of exchange anisotropy and external magnetic fields. Using
imaginary-time quantum Monte-Carlo we extract parameters, relevant to
characterize a {\it renormalized} Luttinger liquid. For small momentum our
results are consistent with a change from propagating spinon density waves to
spin diffusion, described by a finite-frequency spin-current relaxation rate.
Results for this relaxation rate as well as other Luttinger liquid parameters
are presented versus temperature, momentum, magnetic field, and anisotropy,
including finite-size analysis, and checks for anomalous diffusion. Our results
are consistent with exact diagonalization and Bethe Ansatz, where available,
and with corroborate findings of other previous studies using bosonization,
transfer matrix renormalization group, and quantum Monte-Carlo.",1501.03447v1
2015-01-17,Competition between Coulomb and Symmetry Potential in Semi-peripheral Heavy-ion Collisions,"The anisotropy of angular distributions of emitted nucleons and light charged
particles for the asymmetric reaction system, $^{40}$Ar+$^{197}$Au, at b=6fm
and $E_{beam}$=35, 50 and 100MeV/u, are investigated by using the Improved
Quantum Molecular Dynamics model. The competition between the symmetry
potential and Coulomb potential shows large impacts on the nucleons and light
charged particles emission in projectile and target region. As a result of this
competition, the angular distribution anisotropy of coalescence invariant
Y(n)/Y(p) ratio at forward regions shows sensitivity to the stiffness of
symmetry energy as well as the value of Y(n)/Y(p). This observable can be
further checked against experimental data to understand the reaction mechanism
and to extract information about the symmetry energy at subsaturation
densities.",1501.04178v1
2015-01-22,Azimuthal harmonics of color fields in a high energy nucleus,"Recent experimental results have revealed a surprisingly rich structure of
multiparticle azimuthal correlations in high energy proton-nucleus collisions.
Final state collective effects can be responsible for many of the observed
effects, but it has recently been argued that a part of these correlations are
present already in the wavefunctions of the colliding particles. We evaluate
the momentum space 2-particle cumulant azimuthal anisotropy coefficients
v_n{2}, n=2,3,4 from fundamental representation Wilson line distributions
describing the high energy nucleus. These would correspond to the flow
coefficients in very forward proton nucleus scattering. We find significant
differences beteen Wilson lines from the MV model and from JIMWLK evolution.
The magnitude and transverse momentum dependence of the v_n{2} values suggest
that the fluctuations present in the initial fields are a significant
contribution to the observed anisotropies.",1501.05505v2
2015-01-16,$v_2$ of charged hadrons in a`soft + hard' model for PbPb collisions at $\sqrt s$ = 2.76 ATeV,"We describe transverse spectra as well as azimuthal anisotropy ($v_2$) of
charged hadrons stemming from various centrality PbPb collisions at $\sqrt s$ =
2.76 ATeV analytically in a `soft + hard' model. In this model, we propose that
hadron yields produced in heavy-ion collisions are simply the sum of yields
stemming from jets (hard yields) and yields stemming from the Quark-Gluon
Plasma (soft yields). The hadron spectra in both types of yields are
approximated by the Tsallis distribution. It is found that the anisotropy
decreases for more central collisions.",1501.05959v1
2015-01-28,Two-body state with p-wave interaction in one-dimensional waveguides under transversely anisotropic confinement,"We theoretically study two atoms with $p$-wave interaction in a
one-dimensional waveguide, and investigate how the transverse anisotropy of the
confinement affects the two-body state, especially, the properties of the
resonance. For bound-state solution, we find there are totally three two-body
bound states due to the richness of the orbital magnetic quantum number of
$p$-wave interaction, while only one bound state is supported by $s$-wave
interaction. Two of them become nondegenerate due to the breaking of the
rotation symmetry under transversely anisotropic confinement. For scattering
solution, the effective one-dimensional scattering amplitude and scattering
length are derived. We find the position of the $p$-wave confinement-induced
resonance shifts apparently as the transverse anisotropy increases. In
addition, a two-channel mechanism for confinement-induced resonance in a
one-dimensional waveguide is generalized to $p$-wave interaction, which was
proposed only for $s$-wave interaction before. All our calculations are based
on the parameterization of the $^{40}$K atom experiments, and can be confirmed
in future experiments.",1501.06971v1
2015-01-29,Anisotropic critical-state model of type-II superconducting slabs,"We introduce a critical-state model incorporating the anisotropy of flux-line
pinning to analyze the critical states developing in an anisotropic biaxial
superconducting slab exposed to a uniform perpendicular magnetic field and to
two crossed in-plane magnetic fields which are applied successively. The theory
is an extension of the anisotropic collective pinning theory developed by
Mikitik and Brandt. The anisotropic flux-line pinning enters into the critical
states by generating the angular dependence of the critical current density and
by deviating the direction of the electric field from the current in the plane
perpendicular to the vortex line. We find that an enhanced in-plane anisotropy
moderates the gradients of the magnitudes of the magnetic field and the
electric field along the slab thickness, however increases the gradients of
their rotations.",1501.07355v2
2015-01-30,Microscopic properties of degradation-free capped GdN thin films studied by Electron Spin Resonance,"The microscopic magnetic properties of high-quality GdN thin films have been
investigated by electron spin resonance (ESR) and ferromagnetic resonance (FMR)
measurements. Detailed temperature dependence ESR measurements have shown the
existence of two ferromagnetic components at lower temperatures which was not
clear from the previous magnetization measurements. The temperature, where the
resonance shift occurs for the major ferromagnetic component, seems to be
consistent with the Curie temperature obtained from the previous magnetization
measurement. On the other hand, the divergence of line width is observed around
57 K for the minor ferromagnetic component. The magnetic anisotropies of GdN
thin films have been obtained by the analysis of FMR angular dependence
observed at 4.2 K. Combining the X-ray diffraction results, the correlation
between the magnetic anisotropies and the lattice constants is discussed.",1501.07672v1
2015-02-03,Anisotropy tuned magnetic order in pyrochlore iridates,"The magnetic behavior of polycrystalline samples of Er$_2$Ir$_2$O$_7$ and
Tb$_2$Ir$_2$O$_7$ pyrochlores is studied by magnetization measurements and
neutron diffraction. Both compounds undergo a magnetic transition at 140 and
130 K respectively, associated with an ordering of the Ir sublattice, signaled
by thermomagnetic hysteresis. In Tb$_2$Ir$_2$O$_7$, we show that the Ir
molecular field leads the Tb magnetic moments to order below 40 K in the
all-in/all-out magnetic arrangement. No sign of magnetic long range order on
the Er sublattice is evidenced in Er$_2$Ir$_2$O$_7$ down to 0.6 K where a spin
freezing is detected. These contrasting behaviors result from the competition
between the Ir molecular field and the different single-ion anisotropy of the
rare-earths on which it is acting. Additionally, this strongly supports the
all-in/all-out iridium magnetic order.",1502.00787v1
2015-02-05,Domain structure and perpendicular magnetic anisotropy in CoFe/Pd multilayers using off-axis electron holography,"Multilayers of Co90Fe10/Pd with different bilayer thicknesses, have been
deposited by dc-magnetron sputtering on thermally oxidized Si wafers.
Transmission electron microscopy showed that the highly textured crystalline
films had columnar structure, while scanning transmission electron microscopy
and atomic force microscopy respectively indicated some layer waviness and
surface roughness. The magnetic domain structure and perpendicular magnetic
anisotropy (PMA) of the Co90Fe10/Pd multilayers were investigated by off-axis
electron holography and magnetic force microscopy. The Co90Fe10 layer thickness
was the primary factor determining the magnetic domain size and the
perpendicular magnetization: both decreased as the thickness increased. The
strongest PMA was observed in the sample with the thinnest magnetic layer of
0.45 nm.",1502.01422v1
2015-02-06,Fast Magnetic Reconnection Due to Anisotropic Electron Pressure,"A new regime of fast magnetic reconnection with an out-of-plane (guide)
magnetic field is reported in which the key role is played by an electron
pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations
of state in the generalized Ohm's law, which even dominates the Hall term. A
description of the physical cause of this behavior is provided and
two-dimensional fluid simulations are used to confirm the results. The electron
pressure anisotropy causes the out-of-plane magnetic field to develop a
quadrupole structure of opposite polarity to the Hall magnetic field and gives
rise to dispersive waves. In addition to being important for understanding what
causes reconnection to be fast, this mechanism should dominate in plasmas with
low plasma beta and a high in-plane plasma beta with electron temperature
comparable to or larger than ion temperature, so it could be relevant in the
solar wind and some tokamaks.",1502.01781v1
2015-02-19,Characterization of spin relaxation anisotropy in Co using spin pumping,"Ferromagnets are believed to exhibit strongly anisotropic spin relaxation,
with relaxation lengths for spin longitudinal to magnetization significantly
longer than those for spin transverse to magnetization. Here we characterize
the anisotropy of spin relaxation in Co using the spin pumping contribution to
Gilbert damping in noncollinearly magnetized Py$_{1-x}$Cu$_{x}$/Cu/Co trilayer
structures. The static magnetization angle between Py$_{1-x}$Cu$_{x}$ and Co,
adjusted under field bias perpendicular to film planes, controls the
projections of longitudinal and transverse spin current pumped from
Py$_{1-x}$Cu$_{x}$ into Co. We find nearly isotropic absorption of pure spin
current in Co using this technique; fits to a diffusive transport model yield
the longitudinal spin relaxation length $< 2$ nm in Co. The longitudinal spin
relaxation lengths found are an order of magnitude smaller than those
determined by current-perpendicular-to-planes giant magnetoresistance
measurements, but comparable with transverse spin relaxation lengths in Co
determined by spin pumping.",1502.05687v3
2015-02-18,Entanglement entropy and fidelity susceptibility in the one-dimensional spin-1 XXZ chains with alternating single-site anisotropy,"We study the fidelity susceptibility in an antiferromagnetic spin-1 XXZ chain
numerically. By using the density-matrix renormalization group method, the
effects of the alternating single-site anisotropy $D$ on fidelity
susceptibility are investigated. Its relation with the quantum phase transition
is analyzed. It is found that the quantum phase transition from the Haldane
spin liquid to periodic N\'{e}el spin solid can be well characterized by the
fidelity. Finite size scaling of fidelity susceptibility shows a power-law
divergence at criticality, which indicates the quantum phase transition is of
second order. The results are confirmed by the second derivative of the
ground-state energy. We also study the relationship between the entanglement
entropy, the Schmidt gap and quantum phase transitions. Conclusions drawn from
these quantum information observables agree well with each other.",1502.05930v1
2015-02-23,Torsion induced effects in magnetic nanowires,"Magnetic helix wire is one of the most simple magnetic systems which manifest
properties of both curvature and torsion. There exist two equilibrium states in
the helix wire with easy-tangential anisotropy: a quasi-tangential
magnetization distribution in case of relatively small curvatures and torsions,
and an onion state in opposite case. In the last case the magnetization is
close to tangential one, deviations are caused by the torsion and curvature.
Possible equilibrium magnetization states in the helix magnet with different
anisotropy directions are studied theoretically. The torsion also essentially
influences the spin-wave dynamics, acting as an effective magnetic field.
Originated from the curvature induced effective Dzyaloshinskii interaction,
this magnetic field leads to the coupling between the helix chirality and the
magnetochirality, it breaks mirror symmetry in spin-wave spectrum. All
analytical predictions on magnetization statics an dynamics are well confirmed
by the direct spin lattice simulations.",1502.06482v3
2015-02-23,Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity,"The present article reviews recent experimental investigations of spin
dynamics in iron-based superconductors and their parent compounds by means of
inelastic neutron scattering. It mainly focuses on the most contemporary
developments in this field, pertaining to the observations of magnetic resonant
modes in new superconductors, spin anisotropy of low-energy magnetic
fluctuations that has now been observed in a wide range of chemical
compositions and doping levels, as well as their momentum-space anisotropy
incurred by the spin-nematic order. The implications of these new findings for
our understanding of the superconducting state, along with the remaining
unsettled challenges for neutron spectroscopy, are discussed.",1502.06570v1
2015-02-27,"Quantum oscillations, thermoelectric coefficients and the Fermi surface of semi-metallic WTe2","We present a study of angle-resolved quantum oscillations of electric and
thermoelectric transport coefficients in semi-metallic WTe$_{2}$, which has the
particularity of displaying a large B$^{2}$ magneto-resistance. The Fermi
surface consists of two pairs of electron-like and hole-like pockets of equal
volumes in a ""Russian doll"" structure. Carrier density, Fermi energy, mobility
and the mean-free-path of the system are quantified. An additional frequency is
observed above a threshold field and attributed to magnetic breakdown across
two orbits. In contrast to all other dilute metals, the Nernst signal remains
linear in magnetic field even in the high-field ($\omega_c\tau \gg 1$) regime.
Surprisingly, none of the pockets extend across the c-axis of the first
Brillouin zone, making the system a three-dimensional metal with moderate
anisotropy in Fermi velocity yet a large anisotropy in mean-free-path.",1502.07797v2
2015-03-01,"A combined first-principles and thermodynamic approach to M-Nitronyl Nitroxide (M=Co, Mn) spin helices","The properties of two molecular-based magnetic helices, composed of 3$d$
metal Co and Mn ions bridged by Nitronyl Nitroxide radicals, are investigated
by density functional calculations. Their peculiar and distinctive magnetic
behavior is here elucidated by a thorough description of their magnetic,
electronic, and anisotropy properties. Metal ions are antiferromagnetically
coupled with the radicals, leading to a ferrimagnetically ordered ground state.
A strong metal-radical exchange coupling is found, about 44 meV and 48 meV for
Co- and Mn-helices, respectively. The latter have also relevant
next-nearest-neighbor Mn-Mn antiferromagnetic interactions (of $\sim$ 6 meV).
Co-sites are characterized by non-collinear uniaxial anisotropies, whereas
Mn-sites are rather isotropic. A key result pertains to the Co-helix: the
microscopic picture resulting from density-functional calculations allows us to
propose a spin Hamiltonian of increased complexity with respect to the commonly
employed Ising Hamiltonian, suitable for the study of finite-temperature
behavior, and that seems to clarify the puzzling scenario of multiple
characteristic energy scales observed in experiments.",1503.00292v1
2015-03-06,Observation of Optical Solitons and Abnormal Modulation Instability in Liquid Crystals with Negative Dielectric Anisotropy,"We investigate theoretically and experimentally the optical beam propagation
in the nematic liquid crystal with negative dielectric anisotropy, which is
aligned homeotropically in a $80\mu m$-thickness planar cell in the presence of
an externally voltage. It is predicted that the nonlocal nonlinearity of liquid
crystal undergo an oscillatory response function with a negative nonlinear
refractive index coefficient. We found that the oscillatory nonlocal
nonlinearity can support stable bright solitons, which are observed in
experiment. We also found that abnormal modulation instability occurs with
infinity gain coefficient at a fixed spatial frequency, which is no depend on
the beam intensity. We observed the modulation instability in the liquid
crystal at a very low intensity ($0.26W/cm^2$), and the maximum gain frequency
were found kept unchange when beam power changes over 2-3 orders of magnitude.",1503.01953v1
2015-03-13,Magnetic interactions in iron superconductors: A review,"High temperature superconductivity in iron pnictides and chalcogenides
emerges when a magnetic phase is suppressed. The multi-orbital character and
the strength of correlations underlie this complex phenomenology, involving
magnetic softness and anisotropies, with Hund's coupling playing an important
role. We review here the different theoretical approaches used to describe the
magnetic interactions in these systems. We show that taking into account the
orbital degree of freedom allows us to unify in a single phase diagram the main
mechanisms proposed to explain the (\pi,0) order in iron pnictides: the
nesting-driven, the exchange between localized spins, and the Hund induced
magnetic state with orbital differentiation. Comparison of theoretical
estimates and experimental results helps locate the Fe superconductors in the
phase diagram. In addition, orbital physics is crucial to address the magnetic
softness, the doping dependent properties, and the anisotropies.",1503.04223v2
2015-03-19,Anomalous magnetization of $S$=2 ferromagnetic-antiferromagnetic alternating chain with Ising anisotropy,"We present the first experimental realization of an $S=2$
ferromagnetic-antiferromagnetic (F-AF) alternating chain in a new Mn-verdazyl
complex [Mn(hfac)$_2$]$\cdot$($o$-Py-V)
[hfac=1,1,1,5,5,5-hexafluoroacetylacetonate;
$o$-Py-V=3-(2-pyridyl)-1,5-diphenylverdazyl]. Through the $ab$ $initio$
molecular orbital calculation, magnetization, and ESR measurements, this
compound is confirmed to form an $S=2$ F-AF alternating chain with Ising
anisotropy below about 100 K. Furthermore, we find an anomalous change in
magnetization at 1/4 of the saturation value, which is probably a manifestation
of the quantum nature of the system.",1503.05633v1
2015-03-23,Quantum phase transition in the spin-anisotropic quantum spherical model,"Motivated by an analogy with the spin anisotropies in the quantum XY chain
and its reformulation in terms of spin-less Majorana fermions, its bosonic
analogue, the spin-anisotropic quantum spherical model, is introduced. The
exact solution of the model permits to analyse the influence of the
spin-anisotropy on the phase diagram and the universality of the critical
behaviour in a new way, since the interactions of the quantum spins and their
conjugate momenta create new effects. At zero temperature, a quantum critical
line is found, which is in the same universality class as the thermal phase
transition in the classical spherical model in $d+1$ dimensions. The location
of this quantum critical line shows a re-entrant quantum phase transition for
dimensions $1<d\lesssim 2.065$.",1503.06713v2
2015-03-30,Dynamical Evolution of Anisotropic Response in Black Phosphorus under Ultrafast Photoexcitation,"Black phosphorus has recently emerged as a promising material for high
performance electronic and optoelectronic device for its high mobility, tunable
mid-infrared bandgap and anisotropic electronic properties. Dynamical evolution
of photo excited carriers and its induced change of transient electronic
properties are critical for materials' high field performance, but remains to
be explored for black phosphorus. In this work, we perform angle resolved
transient reflection spectroscopy to study the dynamical evolution of
anisotropic properties of black phosphorus under photo excitation. We find that
the anisotropy of reflectivity is enhanced in the pump induced
quasi-equilibrium state, suggesting an extraordinary enhancement of the
anisotropy in dynamical conductivity in hot carrier dominated regime. These
results raise enormous possibilities of creating high field, angle sensitive
electronic, optoelectronic and remote sensing devices exploiting the dynamical
electronic anisotropic with black phosphorus.",1503.08524v1
2015-04-03,Ising exchange interaction in lanthanides and actinides,"The Ising exchange interaction is a limiting case of strong exchange
anisotropy and represents a key property of many magnetic materials. Here we
find necessary and sufficient conditions to achieve Ising exchange interaction
for metal sites with unquenched orbital moments. Contrary to current views, the
rules established here narrow much the range of lanthanide and actinide ions
which can exhibit Ising exchange interaction. It is shown that the arising
Ising interaction can be of two distinct types: (i) coaxial, with magnetic
moments directed along the anisotropy axes on the metal sites and (ii)
non-coaxial, with arbitrary orientation of one of magnetic moments. These
findings will contribute to purposeful design of lanthanide and actinide based
materials.",1504.00784v3
2015-04-08,Proximity effect between a topological insulator and a magnetic insulator with large perpendicular anisotropy,"We report that thin films of a prototype topological insulator,
Bi$_{2}$Se$_{3}$, can be epitaxially grown onto the (0001) surface of
BaFe$_{12}$O$_{19}$(BaM), a magnetic insulator with high Curie temperature and
large perpendicular anisotropy. In the Bi$_2$Se$_3$ thin films grown on
non-magnetic substrates, classic weak antilocalization (WAL) is manifested as
cusp-shaped positive magnetoresistance (MR) in perpendicular magnetic fields
and parabola-shaped positive MR in parallel fields, whereas in
Bi$_{2}$Se$_{3}$/BaM heterostructures the low field MR is parabola-shaped,
which is positive in perpendicular fields and negative in parallel fields. The
magnetic field and temperature dependence of the MR is explained as a
consequence of the suppression of WAL due to strong magnetic interactions at
the Bi$_{2}$Se$_{3}$/BaM interface.",1504.01922v1
2015-04-09,Disentangling inertial waves from eddy turbulence in a forced rotating turbulence experiment,"We present a spatio-temporal analysis of a statistically stationary rotating
turbulence experiment, aiming to extract a signature of inertial waves, and to
determine the scales and frequencies at which they can be detected. The
analysis uses two-point spatial correlations of the temporal Fourier transform
of velocity fields obtained from time-resolved stereoscopic particle image
velocimetry measurements in the rotating frame. We quantify the degree of
anisotropy of turbulence as a function of frequency and spatial scale. We show
that this space-time-dependent anisotropy is well described by the dispersion
relation of linear inertial waves at large scale, while smaller scales are
dominated by the sweeping of the waves by fluid motion at larger scales. This
sweeping effect is mostly due to the low-frequency quasi-two-dimensional
component of the turbulent flow, a prominent feature of our experiment which is
not accounted for by wave turbulence theory. These results question the
relevance of this theory for rotating turbulence at the moderate Rossby numbers
accessible in laboratory experiments, which are relevant to most geophysical
and astrophysical flows.",1504.02224v1
2015-04-14,Testing the isotropy of the Universe by using the JLA compilation of type-Ia supernovae,"We probe the possible anisotropy of the Universe by using the JLA compilation
of type-Ia supernovae. We apply the Markov Chain Monte Carlo (MCMC) method to
constrain the amplitude and direction of anisotropy in three cosmological
models. For the dipole-modulated $\Lambda$CDM model, the anisotropic amplitude
is consistent with zero at $68\%$ C.L., and has an upper bound
$A_D<1.98\times10^{-3}$ at $95\%$ C.L. Regardless of much larger uncertainty,
we find the dipole direction of JLA is amazingly opposite to that of Union2.
Similar results are found for the dipole-modulated $w$CDM and CPL models. Thus,
the Universe is still well consistent with the isotropy according to the JLA
compilation.",1504.03428v2
2015-04-15,The Anisotropic Line Correlation Function as a Probe of Anisotropies in Galaxy Surveys,"We propose an anisotropic generalisation of the line correlation function
(ALCF) to separate and quantify phase information in the large-scale structure
of galaxies. The line correlation function probes the strictly non-linear
regime of structure formation and since phase information drops out of the
power spectrum, the line correlation function provides a complementary tool to
commonly used techniques based on two-point statistics. Furthermore, it is
independent of linear bias as well as the Gaussian variance on the modulus of
the density field and thus may also prove to be advantageous compared to the
bispectrum or similar higher-order statistics for certain cases. For future
applications it is vital, though, to be able to account for observational
effects that cause anisotropies in the distribution of galaxies. Based on a
number of numerical studies, we find that our ALCF is well suited to accomplish
this task and we demonstrate how the Alcock-Paczynski effect and kinematical
redshift-space distortions can in principle be measured via the ALCF.",1504.04036v1
2015-04-21,Uniaxial anisotropy and low-temperature antiferromagnetism of Mn2BO4 single crystal,"The Mn2BO4 single crystals have been grown using the flux technique. The
careful study crystal structure and magnetic properties have been carried out.
The antiferromagnet transition at TN = 26 K has been traced through the dc
magnetization and specific heat temperature dependences. The magnetic uniaxial
anisotropy has been detected with easy axis of magnetization lying in ab-plane.
A reduction of the effective magnetic moment value is assigned to the
non-quenched orbital moment of Jahn-Teller Mn3+ ions. Based on the
superexchange interactions calculations the magnetic behavior is discussed.",1504.05870v1
2015-04-27,Two types of nematicity in the phase diagram of the cuprate superconductor YBa$_2$Cu$_3$O$_y$,"Nematicity has emerged as a key feature of cuprate superconductors, but its
link to other fundamental properties such as superconductivity, charge order
and the pseudogap remains unclear. Here we use measurements of transport
anisotropy in YBa$_2$Cu$_3$O$_y$ to distinguish two types of nematicity. The
first is associated with short-range charge-density-wave modulations in a
doping region near $p = 0.12$. It is detected in the Nernst coefficient, but
not in the resistivity. The second type prevails at lower doping, where there
are spin modulations but no charge modulations. In this case, the onset of
in-plane anisotropy - detected in both the Nernst coefficient and the
resistivity - follows a line in the temperature-doping phase diagram that
tracks the pseudogap energy. We discuss two possible scenarios for the latter
nematicity.",1504.06972v3
2015-04-27,FeCoCp3 Molecular Magnets as Spin Filters,"Metallorganic molecules have been proposed as excellent spin filters in
molecular spintronics because of the large spin-polarization of their
electronic structure. However, most of the studies involving spin transport,
have disregarded fundamental aspects such as the magnetic anisotropy of the
molecule and the excitation of spin-flip processes during electron transport.
Here, we study a molecule containing a Co and an Fe atoms stacked between three
cyclopentadienyl rings that presents a large magnetic anisotropy and a S=1.
These figures are superior to other molecules with the same transition metal,
and improves the spin-filtering capacities of the molecule. Non-equilibrium
Green's functions calculations based on density functional theory predict
excellent spin-filtering properties both in tunnel and contact transport
regimes. However, exciting the first magnetic state drastically reduces the
current's spin polarization. Furthermore, a difference of temperature between
electrodes leads to strong thermoelectric effects that also suppress spin
polarization. Our study shows that in-principle good molecular candidates for
spintronics need to be confronted with inelastic and thermoelectric effects.",1504.07282v1
2015-04-28,Monte-Carlo study of anisotropic scaling generated by disorder,"We analyze the critical properties of the three-dimensional Ising model with
linear parallel extended defects. Such a form of disorder produces two distinct
correlation lengths, a parallel correlation length $\xi_\parallel$ in the
direction along defects, and a perpendicular correlation length $\xi_\perp$ in
the direction perpendicular to the lines. Both $\xi_\parallel$ and $\xi_\perp$
diverge algebraically in the vicinity of the critical point, but the
corresponding critical exponents $\nu_\parallel$ and $\nu_\perp$ take different
values. This property is specific for anisotropic scaling and the ratio
$\nu_\parallel/\nu_\perp$ defines the anisotropy exponent $\theta$. Estimates
of quantitative characteristics of the critical behaviour for such systems were
only obtained up to now within the renormalization group approach. We report a
study of the anisotropic scaling in this system via Monte Carlo simulation of
the three-dimensional system with Ising spins and non-magnetic impurities
arranged into randomly distributed parallel lines. Several independent
estimates for the anisotropy exponent $\theta$ of the system are obtained, as
well as an estimate of the susceptibility exponent $\gamma$. Our results
corroborate the renormalization group predictions obtained earlier.",1504.07588v1
2015-05-09,Quantum Engineering of Spin and Anisotropy in Magnetic Molecular Junctions,"Single molecule magnets and single spin centers can be individually addressed
when coupled to contacts forming an electrical junction. In order to control
and engineer the magnetism of quantum devices, it is necessary to quantify how
the structural and chemical environment of the junction affects the spin
center. Metrics such as coordination number or symmetry provide a simple method
to quantify the local environment, but neglect the many-body interactions of an
impurity spin when coupled to contacts. Here, we utilize a highly corrugated
hexagonal boron nitride (h-BN) monolayer to mediate the coupling between a
cobalt spin in CoHx (x=1,2) complexes and the metal contact. While the hydrogen
atoms control the total effective spin, the corrugation is found to smoothly
tune the Kondo exchange interaction between the spin and the underlying metal.
Using scanning tunneling microscopy and spectroscopy together with numerical
simulations, we quantitatively demonstrate how the Kondo exchange interaction
mimics chemical tailoring and changes the magnetic anisotropy.",1505.02277v1
2015-05-12,Wave mechanics in media pinned at Bravais lattice points,"The propagation of waves through microstructured media with periodically
arranged inclusions has applications in many areas of physics and engineering,
stretching from photonic crystals through to seismic metamaterials. In the
high-frequency regime, modelling such behaviour is complicated by multiple
scattering of the resulting short waves between the inclusions. Our aim is to
develop an asymptotic theory for modelling systems with arbitrarily-shaped
inclusions located on general Bravais lattices. We then consider the limit of
point-like inclusions, the advantage being that exact solutions can be obtained
using Fourier methods, and go on to derive effective medium equations using
asymptotic analysis. This approach allows us to explore the underlying reasons
for dynamic anisotropy, localisation of waves, and other properties typical of
such systems, and in particular their dependence upon geometry. Solutions of
the effective medium equations are compared with the exact solutions, shedding
further light on the underlying physics. We focus on examples that exhibit
dynamic anisotropy as these demonstrate the capability of the asymptotic theory
to pick up detailed qualitative and quantitative features.",1505.02889v1
2015-05-20,Anisotropy Reversal of the Upper Critical Field at Low Temperatures and Spin-Locked Superconductivity in K2Cr3As3,"We report the first measurements of the anisotropic upper critical field
$H_{c2}(T)$ for K$_{2}$Cr$_{3}$As$_{3}$ single crystals up to 60 T and $T >
0.6$ K. Our results show that the upper critical field parallel to the Cr
chains, $H_{c2}^\parallel (T)$, exhibits a paramagnetically-limited behavior,
whereas the shape of the $H_{c2}^\perp (T)$ curve (perpendicular to the Cr
chains) has no evidence of paramagnetic effects. As a result, the curves
$H_{c2}^\perp (T)$ and $H_{c2}^\parallel(T)$ cross at $T\approx 4$ K, so that
the anisotropy parameter $\gamma_H(T)=H_{c2}^\perp/H_{c2}^\parallel (T)$
increases from $\gamma_H(T_c)\approx 0.35$ near $T_c$ to $\gamma_H(0)\approx
1.7$ at 0.6 K. This behavior of $H_{c2}^\|(T)$ is inconsistent with triplet
superconductivity but suggests a form of singlet superconductivity with the
electron spins locked onto the direction of Cr chains.",1505.05547v1
2015-05-21,"Competition of magneto-dipole, anisotropy and exchange interactions in composite multiferroics","We study the competition of magneto-dipole, anisotropy and exchange
interactions in composite three dimensional multiferroics. Using Monte Carlo
simulations we show that magneto-dipole interaction does not suppress the
ferromagnetic state caused by the interaction of the ferroelectric matrix and
magnetic subsystem. However, the presence of magneto-dipole interaction
influences the order-disorder transition: depending on the strength of
magneto-dipole interaction the transition from the ferromagnetic to the
superparamagnetic state is accompanied either by creation of vortices or
domains of opposite magnetization. We show that the temperature hysteresis loop
occurs due to non-monotonic behavior of exchange interaction versus
temperature. The origin of this hysteresis is related to the presence of stable
magnetic domains which are robust against thermal fluctuations.",1505.05605v1
2015-05-27,Torque magnetometry study of magnetically ordered state and spin reorientation in the quasi-one-dimensional $S=1/2$ Heisenberg antiferromagnet CuSb$_2$O$_6$,"We present an experimental study of macroscopic and microscopic magnetic
anisotropy of a spin tetramer system \cso using torque magnetometry and ESR
spectroscopy. Large rotation of macroscopic magnetic axes with temperature
observed from torque magnetometry agrees reasonably well with the rotation of
the $\mathbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\mathbf{g}$
tensor is temperature independent, while macroscopic magnetic axes continue to
rotate. Additionally, the susceptibility anisotropy has a temperature
dependence which cannot be reconciled with the isotropic Heisenberg model of
interactions between spins. ESR linewidth analysis shows that anisotropic
exchange interaction must be present in \csos. These findings strongly support
the presence of anisotropic exchange interactions in the Hamiltonian of the
studied system. Below $T_N=8$~K, the system enters a long - range
antiferromagnetically ordered state with easy axis along the $<\bar{1} 0 1>^*$
direction. Small but significant rotation of magnetic axes is also observed in
the antiferromagnetically ordered state suggesting strong spin-lattice coupling
in this system.",1505.07405v1
2015-05-28,Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal,"We explore the ferromagnetic quantum critical point in a three-dimensional
semimetallic system with upward- and downward-dispersing bands touching at the
Fermi level. Evaluating the static spin susceptibility to leading order in the
coupling between the fermions and the fluctuating ferromagnetic order
parameter, we find that the ferromagnetic quantum critical point is masked by
an incommensurate, longitudinal spin density wave phase. We first analyze an
idealized model which, despite having strong spin-orbit coupling, still
possesses O(3) rotational symmetry generated by the total angular momentum
operator. In this case, the direction of the incommensurate spin density wave
propagation can point anywhere, while the magnetic moment is aligned along the
direction of propagation. Including symmetry-allowed anisotropies in the
fermion dispersion and the coupling to the order parameter field, however, the
ordering wavevector instead breaks a discrete symmetry and aligns along either
the [111] or [100] direction, depending on the signs and magnitudes of these
two types of anisotropy.",1505.07685v1
2015-05-30,Large increase of the anisotropy factor in the overdoped region of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ as probed by fluctuation spectroscopy,"We study the diamagnetism induced by thermal fluctuations above the
superconducting transition of the iron pnictide Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$
with different doping levels. The measurements are performed with magnetic
fields up to 7 T applied in the two main crystal directions. These data provide
double information: first, they confirm at a quantitative level the
applicability to these materials of a 3D-anisotropic Ginzburg-Landau approach
valid in the finite field regime. Then, they allow to determine the
doping-level dependence of the in-plane coherence length and of the
superconducting anisotropy factor, $\gamma$. Our results provide a stringent
confirmation of the large increase of $\gamma$ with the doping level, as
recently proposed from magnetoresistivity measurements. The implications of the
applicability of the model used to a multiband superconductor are discussed.",1506.00170v1
2015-06-04,High Curie temperature and perpendicular magnetic anisotropy in homoepitaxial InMnAs films,"We have prepared the dilute magnetic semiconductor (DMS) InMnAs with
different Mn concentrations by ion implantation and pulsed laser melting. The
Curie temperature of the In1-xMnxAs epilayer depends on the Mn concentration x,
reaching 82 K for x=0.105. The substitution of Mn ions at the Indium sites
induces a compressive strain perpendicular to the InMnAs layer and a tensile
strain along the in-plane direction. This gives rise to a large perpendicular
magnetic anisotropy, which is often needed for the demonstration of electrical
control of magnetization and for spin-transfer-torque induced magnetization
reversal.",1506.01537v1
2015-06-05,The Shear Viscosity in Anisotropic Phases,"We construct anisotropic black brane solutions and analyse the behaviour of
some of their metric perturbations. These solutions correspond to field theory
duals in which rotational symmetry is broken due an externally applied,
spatially constant, force. We find, in several examples, that when the
anisotropy is sufficiently big compared to the temperature, some components of
the viscosity tensor can become very small in units of the entropy density,
parametrically violating the KSS bound. We obtain an expression relating these
components of the viscosity, in units of the entropy density, to a ratio of
metric components at the horizon of the black brane. This relation is generally
valid, as long as the forcing function is translationally invariant, and it
directly connects the parametric violation of the bound to the anisotropy in
the metric at the horizon. Our results suggest the possibility that such small
components of the viscosity tensor might also arise in anisotropic strongly
coupled fluids found in nature.",1506.01899v3
2015-06-09,On the Stability of (M theory) Stars against Collapse : Role of Anisotropic Pressures,"Unitarity of evolution in gravitational collapses implies existence of
macroscopic stable horizonless objects. With such objects in mind, we study the
effects of anisotropy of pressures on the stability of stars. We consider stars
in four or higher dimensions and also stars in M theory made up of
(intersecting) branes. Taking the stars to be static, spherically symmetric and
the equations of state to be linear, we study `singular solutions' and the
asymptotic perturbations around them. Oscillatory perturbations are likely to
imply instability. We find that non oscillatory perturbations, which may imply
stability, are possible if an appropriate amount of anisotropy is present. This
result suggests that it may be possible to have stable horizonless objects in
four or any higher dimensions, and that anisotropic pressures may play a
crucial role in ensuring their stability.",1506.02769v3
2015-06-09,Unitary evolution for a quantum Kantowski-Sachs cosmology,"It is shown that like Bianchi I, V and IX models, a Kantowski-Sachs
cosmological model also allows a unitary evolution on quantization. It has also
been shown that this unitarity is not at the expense of the anisotropy.
Non-unitarity, if there is any, cannot escape notice in this as the evolution
is studied against a properly oriented time parameter fixed by the evolution of
the fluid. Furthermore, we have constructed a wave-packet by superposing
different energy eigenstates, thereby establishing unitarity in a non-trivial
way, which is a stronger result than an energy eigenstate trivially giving time
independent probability density. For $\alpha\neq1$, we have proved that the
Hamiltonian upon suitable operator ordering admits a self-adjoint extension
under reasonable assumption, using a standard theorem. This consolidates the
recently shown fact that the problem of non-unitarity cannot be a generic
problem of anisotropy.",1506.02770v1
2015-06-17,"Temperature-dependent thermal conductivity and diffusivity of a Mg-doped insulating $β$-$\mathrm{Ga_2O_3}$ single crystal along [100], [010] and [001]","The monoclinic crystal structure of $\beta$-$\mathrm{Ga_2O_3}$ leads to
significant anisotropy of the thermal properties. The 2$\omega$-method is used
to measure the thermal diffusivity $D$ in [010] and [001] direction
respectively and to determine the thermal conductivity values $\lambda$ of the
[100], [010] and [001] direction from the same insulating Mg doped
$\beta$-$\mathrm{Ga_2O_3}$ single crystal. We detect a temperature independent
anisotropy factor of both the thermal diffusivity and conductivity values of
$D_{[010]}/D_{[001]}=\lambda_{[010]}/\lambda_{[001]}=1.4\pm 0.1$. The
temperature-dependence is in accord with phonon-phonon-Umklapp scattering
processes from 300 K down to 150 K. Below 150 K point-defect-scattering lowers
the estimated phonon-phonon-Umklapp-scattering values.",1506.05294v3
2015-06-23,Anisotropic matching principle for the hydrodynamics expansion,"Following the recent success of anisotropic hydrodynamics we propose a new,
general prescription for the hydrodynamics expansion around an anisotropic
background. The anisotropic distribution is fixing exactly the complete
energy-momentum tensor, just like the effective temperature is fixing the
proper energy density in the ordinary expansion around local equilibrium. This
means that momen- tum anisotropies are already included at the leading order,
allowing for large pressure anisotropies without the need of a next to leading
order treatment. The first moment of the Boltzmann equation (local
four-momentum conservation) provides the time evolution of the proper energy
density and the four velocity. Differently from previous prescriptions, the
dynamic equations for the pressure corrections are not derived from the zeroth
or second moment of the Boltzmann equation, but they are taken directly from
the exact evolution given by the Boltzmann equation. We check the effec-
tiveness of this new approach by matching with the exact solution of the
Boltzmann equation in the Bjorken limit with the collisional kernel treated in
relaxation time approximation, finding an unprecedented agreement.",1506.07164v1
2015-06-23,A new phase for the anisotropic N=4 super Yang-Mills plasma,"Black hole solutions of type IIB supergravity have been previously
constructed that describe the N=4 supersymmetric Yang-Mills plasma with an
anisotropic spatial deformation. The zero temperature limit of these black
holes approach a Lifshitz-like scaling solution in the infrared. We show that
these black holes become unstable at low temperature and we construct a new
class of black hole solutions which are thermodynamically preferred. The phase
transition is third order and incorporates a spontaneous breaking of the
$SO(6)$ global symmetry down to $SO(4)\times SO(2)$. The critical exponents for
the phase transition are given by $(\alpha,\beta,\gamma,\delta)=(-1,1,1,2)$
which differ from the standard mean-field exponents usually seen in holography.
At low temperatures the black holes approach a novel kind of scaling behaviour
in the far IR with spatial anisotropy and hyperscaling violation. We show that
the new ground states are thermal insulators in the direction of the
anisotropy.",1506.07176v2
2015-06-24,C-axis electrical resistivity of PrO$_{1-a}$F$_a$BiS$_2$ single crystals,"The high anisotropy in RO1-aFaBiS2 (R denotes a rare-earth element)
superconductors demonstrates their potential use as intrinsic Josephson
junctions, considering the weak coupling among BiS2-PrO(F)-BiS2
(superconducting-normal-superconducting) layers along the c-axis. We grew
PrO1-aFaBiS2 single crystals using CsCl/KCl flux. The superconducting
anisotropies of the grown single crystals were estimated to be approximately
40-50 from the effective mass model. The c-axis transport properties were
characterized using single-crystal s-shaped intrinsic Josephson junctions with
a focused ion beam. Along the c-axis, the crystals showed zero resistivity at
2.7 K and a critical current density of 1.33*10^3 A/cm2 at 2.0 K. The
current-voltage curve along the c-axis displayed hysteresis. The c-axis
transport measurements under a magnetic field parallel to the ab-plane revealed
a ""lock-in"" state due to the Josephson vortex flow, indicating that BiS2
superconductors are promising candidates for intrinsic Josephson junctions.",1506.07231v1
2015-06-25,Heavy quarkonia in strong magnetic fields,"We investigate the influence of a homogeneus and constant strong external
magnetic field on the heavy-meson spectrum. Quarkonium states $c\bar{c}$ and
$b\bar{b}$ are described within a non-relativistic framework and by means of a
suitable potential model based on the Cornell parametrization. In particular,
in this work we propose a model which takes into account the possible
anisotropies emerging at the level of the static quark-antiquark potential, as
observed in recent lattice studies. The investigation is perfomed both with and
without taking into account the anisotropy of the static potential, in order to
better clarify its effects",1506.07890v2
2015-06-26,Shapes for maximal coverage for two-dimensional random sequential adsorption,"The random sequential adsorption of various particle shapes is studied in
order to determine the influence of particle anisotropy on the saturated random
packing. For all tested particles there is an optimal level of anisotropy which
maximizes the saturated packing fraction. It is found that a concave shape
derived from a dimer of disks gives a packing fraction of 0.5833, which is
comparable to the maximum packing fraction of ellipsoids and spherocylinders
and higher than any other studied shape. Discussion why this shape is so
beneficial for random sequential adsorption is given.",1506.08164v2
2015-06-27,K*0(892) and phi(1020) resonance production at RHIC,"The measurement of resonance production in ultrarelativistic heavy-ion
collisions provides a glimpse of the hadronic medium properties and its
evolution at different stages. Resonances decaying into hadrons are used to
estimate the time span and hadronic interaction cross section in the hadronic
phase between chemical and kinetic freeze-out. Specifically, the comparison of
K*0(892) and phi(1020) resonances is interesting as the lifetimes of these
particles differ by about a factor of 10. Moreover, the nuclear modification
factor and azimuthal anisotropy measurements of mesonic resonances, which
measure parton energy loss in medium and reflect partonic collectivity, can
also probe particle-species and mass ordering.
  The K*0(892) and phi(1020) resonance production at mid-rapidity (|y|<0.5),
measured in high energy (Au+Au, Cu+Cu, d+Au and p+p) collisions at RHIC with
STAR experiment, reconstructed by their hadronic decay in Kpi and KK,
respectively, are discussed. Mesons' spectra, yields, mean transverse momentum,
nuclear modification factor, and azimuthal anisotropy are discussed as a
function of centrality and collision energy.",1506.08289v1
2015-06-30,Discrete Solitons and Vortices in Anisotropic Hexagonal and Honeycomb Lattices,"In the present work, we consider the self-focusing discrete nonlinear
Schrodinger equation on hexagonal and honeycomb lattice geometries. Our
emphasis is on the study of the effects of anisotropy, motivated by the
tunability afforded in recent optical and atomic physics experiments. We find
that important classes of solutions, such as the so-called discrete vortices,
undergo destabilizing bifurcations as the relevant anisotropy control parameter
is varied. We quantify these bifurcations by means of explicit analytical
calculations of the solutions, as well as of their spectral linearization
eigenvalues. Finally, we corroborate the relevant stability picture through
direct numerical computations. In the latter, we observe the prototypical
manifestation of these instabilities to be the spontaneous rearrangement of the
solution, for larger values of the coupling, into localized waveforms typically
centered over fewer sites than the original unstable structure. For weak
coupling, the instability appears to result in a robust breathing of the
relevant waveforms.",1506.08945v1
2015-07-01,Fading Features Found in the Kinematics of the Far-Reaching Milky Way Stellar Halo,"We test the long-term kinematical stability of a Galactic stellar halo model,
due to Kafle, et al. (2012), who study the kinematics of approximately 5000
blue horizontal branch (BHB) stars in the Sloan Digital Sky Survey (SDSS). The
velocity dispersion $\sigma$ and anisotropy parameter $\beta$ of the stars have
been determined as functions of Galactocentric radius, over the range
$6<R_\mathrm{GC} < 25$ kpc, and show a strong dip in the anisotropy profile at
$R_\mathrm{GC}\sim17$ kpc. By directly integrating orbits of particles in a 3-D
model of the Galactic potential with these characteristics, we show that the
$\sigma$ and $\beta$ profiles quickly evolve on a time scale of a
$\mathrm{few}\times10$ Myr whereas the density $\rho$ profile remains largely
unaffected. We suggest that the feature is therefore transient. The origin of
such features in the Galactic halo remains unclear.",1507.00351v1
2015-07-02,Microscale locomotion in a nematic liquid crystal,"Microorganisms often encounter anisotropy, for example in mucus and biofilms.
We study how anisotropy and elasticity of the ambient fluid affects the speed
of a swimming microorganism with a prescribed stroke. Motivated by recent
experiments on swimming bacteria in anisotropic environments, we extend a
classical model for swimming microorganisms, the Taylor swimming sheet,
actuated either by transverse or longitudinal traveling waves in a
three-dimensional nematic liquid crystal without twist. We calculate the
swimming speed and entrained volumetric flux as a function of the swimmer's
stroke properties as well as the elastic and rheological properties of the
liquid crystal. The behavior is quantitatively and qualitatively
well-approximated by a hexatic liquid crystal except in the cases of small
Ericksen number and in a nematic fluid with tumbling parameter near the
transition to a flow-aligning nematic, where anisotropic effects dominate. We
also propose a novel method of swimming or pumping in a nematic fluid by
passing a traveling wave of director oscillation along a rigid wall.",1507.00776v2
2015-07-03,Signal Improvement and Contrast Enhancement in Magnetic Resonance Imaging,"This thesis reports advances in magnetic resonance imaging (MRI), with the
ultimate goal of improving signal and contrast in biomedical applications. More
specifically, novel MRI pulse sequences have been designed to characterize
microstructure, enhance signal and contrast in tissue, and image functional
processes. In this thesis, rat brain and red bone marrow images are acquired
using iMQCs (intermolecular multiple quantum coherences) between intermediate
separated spins. As an important application, iMQCs images in different
directions can be used for anisotropy mapping and tissue microstructure
analysis. At the same time, the simulations prove that the dipolar field from
the overall shape only has small contributions to the experimental iMQC signal.
Besides magnitude of iMQCs, phase of iMQCs should be studied as well. The phase
anisotropy maps built by our method can clearly show susceptibility information
in rat brain. It may provide meaningful diagnostic information. To deeply study
susceptibility, the modified-crazed sequence is developed. Combining phase data
of modified-crazed images and phase data of iMQCs images is very promising to
construct microstructure maps. Obviously, the phase image in all above
techniques needs to be highly-contrasted and clear. To achieve the goal,
algorithm tools from Susceptibility-Weighted Imaging (SWI) and Susceptibility
Tensor Imaging (STI) stands out superb useful and creative in our system.",1507.01035v1
2015-07-09,Equilibrium structure and fluctuations of suspensions of colloidal dumbbells,"We investigate the structure and equilibrium linear-response dynamics of
suspensions of hard colloidal dumbbells using Brownian Dynamics computer
simulations. The focus lies on the dense fluid and plastic crystal states of
the colloids with investigated aspect (elongation-to-diameter) ratios varying
from the hard sphere limit up to 0.39, which is roughly the stability limit of
the plastic crystal phase. We find expected structural changes with larger
elongation with respect to the hard sphere reference case and very localized
orientational correlations, typically just involving next-neighbor couplings.
These relatively weak correlations are also reflected in only minor effects on
the translational and rotational diffusion coefficients for most of the
investigated elongations. However, the linear response shear viscosity exhibits
a dramatic increase at high packing fractions ($\phi\gtrsim 0.5$) beyond a
critical anisotropy factor of about $L^* \simeq 0.15$ which is surprising in
view of the relatively weak changes found before on the level of colloidal
self-dynamics. We suspect that even for the small investigated anisotropies,
newly occurring, collective rotational-translational couplings must be made
responsible for the slow time scales appearing in the plastic crystal.",1507.02533v1
2015-05-29,Anisotropic dark energy model with a hybrid scale factor,"Anisotropic dark energy model with dynamic pressure anisotropies along
different spatial directions is constructed at the backdrop of a spatially
homogeneous diagonal Bianchi type $V$ $(BV)$ space-time in the framework of
General Relativity. A time varying deceleration parameter generating a hybrid
scale factor is considered to simulate a cosmic transition from early
deceleration to late time acceleration. We found that the pressure anisotropies
along the $y-$ and $z-$ axes evolve dynamically and continue along with the
cosmic expansion without being subsided even at late times. The anisotropic
pressure along the $x-$axis becomes equal to the mean fluid pressure. At a late
phase of cosmic evolution, the model enters into a phantom region. From a state
finder diagnosis, it is found that the model overlaps with $\Lambda$CDM at late
phase of cosmic time.",1507.03515v2
2015-07-13,High temperature magnetic stabilization of cobalt nanoparticles by an antiferromagnetic proximity effect,"Thermal activation tends to destroy the magnetic stability of small magnetic
nanoparticles, with crucial implications in ultra-high density recording among
other applications. Here we demonstrate that low blocking temperature
ferromagnetic (FM) Co nanoparticles (TB<70 K) become magnetically stable above
400 K when embedded in a high N\'eel temperature antiferromagnetic (AFM) NiO
matrix. The origin of this remarkable TB enhancement is due to a magnetic
proximity effect between a thin CoO shell (with low N\'eel temperature, TN; and
high anisotropy, KAFM) surrounding the Co nanoparticles and the NiO matrix
(with high TN but low KAFM). This proximity effect yields an effective AFM with
an apparent TN beyond that of bulk CoO, and an enhanced anisotropy compared to
NiO. In turn, the Co core FM moment is stabilized against thermal fluctuations
via core-shell exchange-bias coupling, leading to the observed TB increase.
Mean-field calculations provide a semi-quantitative understanding of this
magnetic- proximity stabilization mechanism.",1507.03608v1
2015-07-16,Synchronization of particle motion in compressed two-dimensional plasma crystals,"The collective motion of dust particles during the mode-coupling induced
melting of a two-dimensional plasma crystal is explored in molecular dynamics
simulations. The crystal is compressed horizontally by an anisotropic
confinement. This compression leads to an asymmetric triggering of the
mode-coupling instability which is accompanied by alternating chains of
in-phase and anti-phase oscillating particles. A new order parameter is
proposed to quantify the synchronization with respect to different directions
of the crystal. Depending on the orientation of the confinement anisotropy,
mode-coupling instability and synchronized motion are observed in one or two
directions. Notably, the synchronization is found to be direction-dependent.
The good agreement with experiments suggests that the confinement anisotropy
can be used to explain the observed synchronization process.",1507.04480v1
2015-07-16,Global Existence of Weak Solutions for Compresssible Navier--Stokes Equations: Thermodynamically unstable pressure and anisotropic viscous stress tensor,"We prove global existence of appropriate weak solutions for the compressible
Navier--Stokes equations for more general stress tensor than those covered by
P.-L. Lions and E. Feireisl's theory. More precisely we focus on more general
pressure laws which are not thermodynamically stable; we are also able to
handle some anisotropy in the viscous stress tensor. To give answers to these
two longstanding problems, we revisit the classical compactness theory on the
density by obtaining precise quantitative regularity estimates: This requires a
more precise analysis of the structure of the equations combined to a novel
approach to the compactness of the continuity equation. These two cases open
the theory to important physical applications, for instance to describe solar
events (virial pressure law), geophysical flows (eddy viscosity) or biological
situations (anisotropy).",1507.04629v2
2015-07-16,Aspects of Anisotropic Fractional Quantum Hall Effect in Phosphorene,"We have analyzed the effects of the anisotropic energy bands of phosphorene
on magnetoroton branches for electrons and holes in the two Landau levels close
to the band edges. We have found that the fractional quantum Hall effect gap in
the lowest (highest) Landau level in conduction (valance) band is slightly
larger than that for conventional semiconductor systems and therefore
experimentally observable. We also found that the magnetoroton mode for both
electrons and holes consists of two branches with two minima due to the
anisotropy. Additionally, we show that due to the anisotropy, there is a second
mode with positive dispersion, well separated from the magnetoroton mode for
small wave vectors. These novel features of the collective mode can be observed
in resonant inelastic light scattering experiments.",1507.04709v1
2015-07-17,Fluctuations in slope parameter in event-by-event hydrodynamics and momentum anisotropy in heavy ion collisions,"In event by event hydrodynamic model, we have simulated 30-40\% Au+Au
collisions at RHIC and computed the slope parameter from the invariant pion
distribution. In each event, the slope parameter fluctuates azimuthally.
Fourier expansion coefficients $T_n$ for the slope parameter and the Fourier
expansion coefficients $v_n$ for the azimuthal distribution $\frac{dN}{d\phi}$
are found to be strongly correlated. Strong correlation between the two
expansion coefficients suggests that in addition to azimuthal distribution,
fluctuations in the slope parameter of the invariant distribution can as well
be used to study the final state momentum anisotropy in relativistic energy
heavy ion collisions. If measured experimentally, they can serve as additional
constraint for hydrodynamical modeling.",1507.04898v1
2015-07-20,Origin of the large anisotropic g-factor of holes in bismuth,"The ratio of the Zeeman splitting to the cyclotron energy ($M=\Delta E_{\rm
Z}/\hbar \omega_{\rm c}$) for hole-like carriers in bismuth has been quantified
with a great precision by many experiments performed during the past five
decades. It exceeds 2 when the magnetic field is along the trigonal axis and
vanishes in the perpendicular configuration. Theoretically, however, $M$ is
expected to be isotropic and equal to unity in a two-band Dirac model. We argue
that a solution to this half-a-century-old puzzle can be found by extending the
$k\cdot p$ theory to multiple bands. Our model not only gives a quantitative
account of magnitude and anisotropy of $M$ for hole-like carriers in bismuth,
but also explains its contrasting evolution with antimony doping pressure, both
probed by new experiments reported here. The present results have important
implications for the magnitude and anisotropy of $M$ in other systems with
strong spin-orbit coupling.",1507.05996v1
2015-07-22,Magnetic anisotropy induced by crystal distortion in Ge1-xMn xTe/PbTe//KCl (001) ferromagnetic semiconductor layers,"Ferromagnetic resonance (FMR) study of magnetic anisotropy is presented for
thin layers of IV-VI diluted magnetic semiconductor Ge1-xMn xTe with x=0.14
grown by molecular beam epitaxy (MBE) on KCl (001) substrate with a thin PbTe
buffer. Analysis of the angular dependence of the FMR resonant field reveals
that an easy magnetization axis is located near to the normal to the layer
plane and is controlled by two crystal distortions present in these
rhombohedral Ge1-xMnxTe layers: the ferroelectric distortion with the relative
shift of cation and anion sub-lattices along the [111] crystal direction and
the biaxial in-plane, compressive strain due to thermal mismatch.",1507.06124v1
2015-07-28,Effects of Dzyaloshinsky-Moriya Interaction on magnetism in Nanodisks,"We give a theoretical study on the magnetic properties of monolayer nanodisks
with both Heisenberg exchange and Dzyaloshinsky-Moriya (DM) interactions. In
particular, we survey the magnetic effects caused by anisotropy, external
magnetic field, and disk size when DM interaction is present by means of a new
quantum simulation method based on mean-field theory. This computational
approach finds that uniaxial anisotropy and transverse magnetic field enhances
the net magnetization as well as increases the transition temperature of the
vortex phase while preserving the chiralities of the nanodisks. Whereas, when
the strength of DM interaction is sufficiently strong for a given disk size,
magnetic domains appear within the circularly bounded region, which vanish and
gives in to a single vortex when a transverse magnetic field is applied. The
latter confirms the magnetic skyrmions induced by the magnetic field as
observed in the experiments.",1507.07715v1
2015-07-31,Elastic Properties of FeC and FeN Martensites,"Single crystal elastic constants of bcc iron and bct FeC and FeN alloys,
martensites, have been evaluated by ab initio calculations based on the density
functional theory. The energy of a strained crystal has been computed using the
supercell method at several values of the strain intensity, and the stiffness
coefficient has been determined from the slope of the energy versus square of
strain relation. Some of the third order elastic constants have also been
evaluated. The absolute magnitudes of the calculated values for bcc iron are in
fair agreement with experiment, including the third order constants, although
the computed elastic anisotropy is much weaker than measured. The tetragonally
distorted dilute FeC and FeN alloys exhibit lower stiffness than bcc iron,
particularly in the tensor component C33, while the elastic anisotropy is
virtually the same. Average values of elastic moduli for polycrystalline
aggregates are also computed. Youngs modulus and the rigidity modulus, as well
as the bulk modulus, are decreased by about 10 per cent by the addition of C or
N to 3.7 atomic per cent, which agrees with the experimental data for FeC
martensite.",1508.00521v1
2015-08-04,A Critical Analysis of the Feasibility of Pure Strain-Actuated Giant Magnetostrictive Nanoscale Memories,"Concepts for memories based on the manipulation of giant magnetostrictive
nanomagnets by stress pulses have garnered recent attention due to their
potential for ultra-low energy operation in the high storage density limit.
Here we discuss the feasibility of making such memories in light of the fact
that the Gilbert damping of such materials is typically quite high. We report
the results of numerical simulations for several classes of toggle precessional
and non-toggle dissipative magnetoelastic switching modes. Material candidates
for each of the several classes are analyzed and forms for the anisotropy
energy density and ranges of material parameters appropriate for each material
class are employed. Our study indicates that the Gilbert damping as well as the
anisotropy and demagnetization energies are all crucial for determining the
feasibility of magnetoelastic toggle-mode precessional switching schemes. The
roles of thermal stability and thermal fluctuations for stress-pulse switching
of giant magnetostrictive nanomagnets are also discussed in detail and are
shown to be important in the viability, design, and footprint of
magnetostrictive switching schemes.",1508.00629v2
2015-08-04,Scanning Kerr microscopy of current induced switching in Ta/CoFeB/MgO films with perpendicular magnetic anisotropy,"Ta/CoFeB/MgO trilayers with perpendicular magnetic anisotropy are expected to
play a key role in the next generation of current and electric field switched
memory and logic devices. In this study we use Kerr microscopy alongside
electrical transport measurement to gain insight into the underlying switching
mechanisms of such devices. We find switching to be a stochastic, domain wall
driven process, the speed of which is strongly dependent on the switching
current. Kerr imaging shows domain nucleation at the edge of the device which
modelling reveals is likely assisted by the perpendicular component of the
Oersted field. Further domain growth, leading to magnetisation reversal may be
assisted by spin torques.",1508.00833v2
2015-08-11,Stochastic Eternal Inflation in a Bianchi Type I Universe,"The phenomenon of stochastic eternal inflation is studied for a chaotic
inflation potential in a Bianchi Type I spacetime background. After deriving
the appropriate stochastic Klein-Gordon equation, we give details on the
conditions for eternal inflation. It is shown that for eternal inflation to
occur, the amount of anisotropy must be small. In fact, it is shown that
eternal inflation will only take place if the shear anisotropy variables take
on values within a small region of the interior of the Kasner circle. We then
calculate the probability of eternal inflation occurring based on techniques
from stochastic calculus.",1508.02670v6
2015-08-13,Anisotropic distributions in a multi-phase transport model,"With A Multi-Phase Transport (AMPT) model we investigate the relation between
the magnitude, fluctuations and correlations of the initial state spatial
anisotropy $\varepsilon_{n}$ and the final state anisotropic flow coefficients
$v_{n}$ in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=$ 200 GeV. It is found
that the relative eccentricity fluctuations in AMPT account for the observed
elliptic flow fluctuations, in agreement with measurements of the STAR
collaboration. In addition, the studies based on 2- and multi-particle
correlations and event-by-event distributions of the anisotropies suggest that
the Elliptic-Power function is a promising candidate of the underlying
probability density function of the event-by-event distributions of
$\varepsilon_{n}$ as well as $v_{n}$. Furthermore, the correlations between
different order symmetry planes and harmonics in the initial coordinate space
and final state momentum space are presented. Non-zero values of these
correlations have been observed. The comparison between our calculations and
data will, in the future, shed new insight into the nature of the fluctuations
of the Quark-Gluon Plasma produced in heavy ion collisions.",1508.03306v2
2015-08-17,Engineering the magnetic anisotropy of atomic-scale nanostructure under electric field,"Atomic-scale magnetic nanostructures are promising candidates for future
information processing devices. Utilizing external electric field to manipulate
their magnetic properties is an especially thrilling project. Here, by careful
identifying different contributions of each atomic orbital to the magnetic
anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is
possible to engineer both the MAE and the magnetic response to the electric
field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a
matrix, we propose several interesting iron nanostructures with dramatically
different magnetic properties. Such nanostructures could exhibit strong
magnetoelectric effect. Our work may open a new avenue to the artificial design
of electrically controlled magnetic devices.",1508.03917v1
2015-08-23,A study of the physical properties of single crystalline Fe5B2P,"Single crystals of Fe5B2P were grown by self-flux growth technique.
Structural and magnetic properties are studied. The Curie temperature of Fe5B2P
is determined to be 655$pm$2K. The saturation magnetization is determined to be
1.72 MuB/Fe at 2K. The temperature variation of the anisotropy constant K1 is
determined for the first time, reaching ~0.50 MJ/m3 at 2K, and it is comparable
to that of hard ferrites. The saturation magnetization is found to be larger
than the hard ferrites. The first principle calculations of saturation
magnetization and anisotropy constant are found to be consistent with the
experimental results.",1508.05629v1
2015-08-31,All electrical manipulation of magnetization dynamics in a ferromagnet by antiferromagnets with anisotropic spin Hall effects,"We investigate spin-orbit torques of metallic CuAu-I-type antiferromagnets
using spin-torque ferromagnetic resonance tuned by a dc-bias current. The
observed spin torques predominantly arise from diffusive transport of spin
current generated by the spin Hall effect. We find a growth-orientation
dependence of the spin torques by studying epitaxial samples, which may be
correlated to the anisotropy of the spin Hall effect. The observed anisotropy
is consistent with first-principles calculations on the intrinsic spin Hall
effect. Our work demonstrates large tunable spin-orbit effects in
magnetically-ordered materials.",1508.07906v2
2015-09-01,Elusive pure anapole excitation in homogenous spherical nanoparticles with radial anisotropy,"For homogenous isotropic dielectric nanospheres with incident plane waves,
Cartesian electric and toroidal dipoles can be tunned to cancel each other in
terms of far-field scattering, leading to the effective anopole excitation. At
the same time however, other multipoles such as magnetic dipoles with
comparable scattered power are simultanesouly excited, mixing with the anopole
and leading to a non-negligible total scattering cross section. Here we show
that for homogenous dielectric nanospheres, radial anisotropy can be employed
to significantly suppress the other multipole excitation, which at the same
time does not compromise the property of complete scattering cancallation
between Cartesian electric and toroidal dipoles. This enables an elusive pure
anopole excitation within radially anisotropic dielectric nanospheres, which
may shed new light to many scattering related fundamental researches and
applications.",1509.00119v1
2015-09-04,Computational up-scaling of anisotropic swelling and mechanical behavior of hierarchical cellular material,"The hygro-mechanical behavior of a hierarchical cellular material, i.e.
growth rings of softwood is investigated using a two-scale micro-mechanics
model based on a computational homogenization technique. The lower scale
considers the individual wood cells of varying geometry and dimensions.
Honeycomb unit cells with periodic boundary conditions are utilized to
calculate the mechanical properties and swelling coefficients of wood cells.
Using the cellular scale results, the anisotropy in mechanical and swelling
behavior of a growth ring in transverse directions is investigated. Predicted
results are found to be comparable to experimental data. It is found that the
orthotropic swelling properties of the cell wall in thin-walled earlywood cells
produce anisotropic swelling behavior while, in thick latewood cells, this
anisotropy vanishes. The proposed approach provides the ability to consider the
complex microstructure when predicting the effective mechanical and swelling
properties of softwood.",1509.01388v1
2015-09-07,Successively Thresholded Domain Boundary Roughening Driven by Pinning Centers and Missing Bonds: Hard-Spin Mean-Field Theory Applied to d=3 Ising Magnets,"Hard-spin mean-field theory has recently been applied to Ising magnets,
correctly yielding the absence and presence of an interface roughening
transition respectively in $d=2$ and $d=3$ dimensions and producing the
ordering-roughening phase diagram for isotropic and anisotropic systems. The
approach has now been extended to the effects of quenched random pinning
centers and missing bonds on the interface of isotropic and anisotropic Ising
models in $d=3$. We find that these frozen impurities cause domain boundary
roughening that exhibits consecutive thresholding transitions as a function
interaction of anisotropy. For both missing-bond and pinning-center impurities,
for moderately large values the anisotropy, the systems saturate to the
""solid-on-solid"" limit, exhibiting a single universal curve for the domain
boundary width as a function of impurity concentration.",1509.01910v2
2015-09-07,Giant exchange interaction in mixed lanthanides,"Combining strong magnetic anisotropy with strong exchange interaction is a
long standing goal in the design of quantum magnets. The lanthanide complexes,
while exhibiting a very strong ionic anisotropy, usually display a weak
exchange coupling, amounting to only a few wavenumbers. Recently, an
isostructural series of mixed Ln$^{3+}$-N$_2^{3-}$-Ln$^{3+}$ (Ln $=$ Gd, Tb,
Dy, Ho, Er) have been reported, in which the exchange splitting is estimated to
reach hundreds wavenumbers. The microscopic mechanism governing the unusual
exchange interaction in these compounds is revealed here by combining detailed
modeling with density-functional theory and {\it ab initio} calculations. We
find it to be basically kinetic and highly complex, involving non-negligible
contributions up to seventh power of total angular momentum of each lanthanide
site. The performed analysis also elucidates the origin of magnetization
blocking in these compounds. Contrary to general expectations the latter is not
always favored by strong exchange interaction.",1509.02206v4
2015-09-08,Magnetic and structural properties of ferromagnetic Fe5PB2 and Fe5SiB2 and effects of Co and Mn substitutions,"Crystallographic and magnetic properties of Fe5PB2, Fe4CoPB2, Fe4MnPB2,
Fe5SiB2, Fe4CoSiB2, and Fe4MnSiB2 are reported. All adopt the tetragonal Cr5B3
structure-type and are ferromagnetic at room temperature with easy axis of
magnetization along the c-axis. The spin reorientation in Fe5SiB2 is observed
as an anomaly in the magnetization near 170 K, and is suppressed by
substitution of Co or Mn for Fe. The silicides are found to generally have
larger magnetic moments than the phosphides, but the data suggests smaller
magnetic anisotropy in the silicides. Cobalt substitution reduces the Curie
temperatures by more than 100 K and ordered magnetic moments by 16-20%, while
manganese substitution has a much smaller effect. This suggests Mn moments
align ferromagnetically with the Fe and that Co does not have an ordered moment
in these structures. Anisotropic thermal expansion is observed in Fe5PB2 and
Fe5SiB2, with negative thermal expansion seen along the c-axis of Fe5SiB2.
First principles calculations of the magnetic properties of Fe5SiB2 and
Fe4MnSiB2 are reported. The results, including the magnetic moment and
anisotropy, and are in good agreement with experiment.",1509.02544v1
2015-09-10,Impact of anisotropy on the interaction of an atom with a one-dimensional nano-grating,"We study the interaction of an atom with a one-dimensional nano-grating
within the framework of macroscopic QED, with special emphasis on possible
anisotropic contributions. To this end, we first derive the scattering Green's
tensor of the grating by means of a Rayleigh expansion and discuss its symmetry
properties and asymptotes. We then determine the Casimir--Polder potential of
an atom with the grating. In particular, we find that strong anisotropy can
lead to a repulsive Casimir--Polder potential in the normal direction.",1509.03117v1
2015-09-15,Magnetization reversal of giant perpendicular magnetic anisotropy at the magnetic-phase transition in FeRh films on MgO,"Phenomena originated from spin-orbit interaction, such as magnetic anisotropy
(MA), Rashba-type interactions, or topological insulators, have drawn huge
attention for its intriguing physics. In particular, the search for a novel
antiferromagnetic material, with potentially large perpendicular MA (PMA), has
been becoming very intensive for next-generation high density memory
applications. Here, we propose that substitutions of transition metals Ru and
Ir, neighboring and same group elements in the periodic table, for the Rh site
in the vicinity of surface can induce a substantially large PMA, up to an order
of magnitude of 20 erg/cm2, in FeRh films on MgO. The main driving mechanism
for this huge PMA is the interplay between the dxy and dx2-y2 states of strong
spin-orbit 4d and 5d orbitals. Further investigations demonstrate that
magnetization direction of PMA undergoes a transition into an in-plane
magnetization at the antiferromagnetic-to-ferromagnetic phase transition, which
provides a viable route for achieving large and switchable PMA associated with
the magnetic-phase transition in antiferromagnetic spintronics.",1509.04361v2
2015-09-16,A spin dynamics approach to solitonics,"It is spatial dispersion which is exclusively responsible for the emergence
of exchange interaction and magnetic ordering. In contrast, magneto-crystalline
anisotropy present in any realistic material brings in a certain non-linearity
to the equation of motion. Unlike homogeneous ferromagnetic ordering a variety
of non-collinear ground state configurations emerge as a result of competition
among exchange, anisotropy, and dipole-dipole interaction. These particle-like
states, e.g. magnetic soliton, skyrmion, domain wall, form a spatially
localised clot of magnetic energy. In this paper we explore topologically
protected magnetic solitons that might potentially be applied for logical
operations and/or information storage in the rapidly advancing filed of
solitonics (and skyrmionics). An ability to easily create, address, and
manipulate such structures is among the prerequisite forming a basis of -onics
technology, and is investigated in detail here using numerical and analytical
tools.",1509.04860v2
2015-09-17,Antiferromagnetic Spin Wave Field-Effect Transistor,"In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates
that the spin wave modes must be doubly degenerate. Theses two modes,
distinguished by their opposite polarization and available only in
antiferromagnets, give rise to a novel degree of freedom to encode and process
information. We show that the spin wave polarization can be manipulated by an
electric field induced Dzyaloshinskii-Moriya interaction and magnetic
anisotropy. We propose a prototype spin wave field-effect transistor which
realizes a gate-tunable magnonic analog of the Faraday effect, and demonstrate
its application in THz signal modulation. Our findings open up the exciting
possibility of digital data processing utilizing antiferromagnetic spin waves
and enable the direct projection of optical computing concepts onto the
mesoscopic scale.",1509.05295v3
2015-09-20,Emergent formation of dynamic topographic patterns in electron beam induced etching,"Spontaneous formation of geometric patterns is a fascinating, ubiquitous
process that provides fundamental insights into the roles of symmetry breaking,
anisotropy and nonlinear interactions in emergent phenomena. Here we report
dynamic, highly ordered topographic patterns on the surface of diamond that
span multiple length scales and have a symmetry controlled by the chemical
species of a precursor gas used in electron beam induced etching (EBIE). This
behavior reveals an underlying etch rate anisotropy and an electron energy
transfer pathway that has been overlooked by existing EBIE theory. We present
an etch rate kinetics model that fully explains our results and is universally
applicable to EBIE. Our findings can be exploited for controlled wetting,
optical structuring and other emerging applications that require nano and
micro-scale surface texturing.",1509.05963v1
2015-09-22,The production of photons in relativistic heavy-ion collisions,"In this work it is shown that the use of a hydrodynamical model of heavy ion
collisions which incorporates recent developments, together with updated photon
emission rates greatly improves agreement with both ALICE and PHENIX
measurements of direct photons, supporting the idea that thermal photons are
the dominant source of direct photon momentum anisotropy. The event-by-event
hydrodynamical model uses IP-Glasma initial states and includes, for the first
time, both shear and bulk viscosities, along with second order couplings
between the two viscosities. The effect of both shear and bulk viscosities on
the photon rates is studied, and those transport coefficients are shown to have
measurable consequences on the photon momentum anisotropy.",1509.06738v3
2015-09-27,Perpendicular magnetic anisotropy and spin glass-like behavior in molecular beam epitaxy grown chromium telluride thin films,"Reflection high energy electron diffraction (RHEED), scanning tunneling
microscopy (STM), vibrating sample magnetometry and other physical property
measurements are used to investigate the structure, morphology, magnetic and
magneto-transport properties of (001)-oriented Cr$_2$Te$_3$ thin films grown on
Al$_2$O$_3$(0001) and Si(111)-(7$\times$7) surfaces by molecular beam epitaxy
(MBE). Streaky RHEED patterns indicate flat smooth film growth on both
substrates. STM studies show the hexagonal arrangements of surface atoms.
Determination of the lattice parameter from atomically resolved STM image is
consistent with the bulk crystal structures. Magnetic measurements show the
film is ferromagnetic having the Curie temperature of about 180 K, and a spin
glass-like behavior was observed below 35 K. Magneto-transport measurements
show the metallic nature of the film with a perpendicular magnetic anisotropy
along the $c$-axis.",1509.08140v1
2015-09-29,Field-free magnetization reversal by spin-Hall effect and exchange bias,"Magnetic random-access memory (MRAM) driven by spin-transfer torque (STT) is
a major contender for future memory applications. The energy dissipation
involved in writing remains problematic, even with the advent of more efficient
perpendicular magnetic anisotropy (PMA) devices. A promising alternative
switching mechanism employs spin-orbit torques and the spin-Hall effect (SHE)
in particular, but additional symmetry breaking is required to achieve
deterministic switching in PMA devices. Currently used methods rely on in-plane
magnetic fields or anisotropy gradients, which are not suitable for practical
applications. Here, we interface the magnetic layer with an anti-ferromagnetic
material. An in-plane exchange bias (EB) is created, and shown to enable
field-free SHE-driven magnetization reversal of a perpendicularly magnetized
Pt/Co/IrMn structure. Aside from the potential technological implications, our
experiment provides additional insight into the local spin structure at the
ferromagnetic/anti-ferromagnetic interface.",1509.08752v2
2015-09-30,Essential properties of the Difference Method for the Search of the Anisotropy of the Primary Cosmic Radiation,"The methodical properties of the original difference method for the search of
the anisotropy at the knee region of the primary cosmic radiation energy
spectrum are analyzed. The main feature of the suggested method is a study of
the difference in the EAS characteristics in different directions but not their
intensity. It is shown that the method is stable to the random experimental
errors and allows to separate the anomalies related to the laboratory
coordinate system from the anomalies in the celestial coordinates. The method
uses multiple scattering of the charge particles in the Galaxy magnetic fields
to study the whole celestial sphere including the regions outside of the line
of sight of the installation.",1509.09316v1
2015-10-01,Collectivity in Small QCD Systems,"Features of collectivity observed in high energy A+A collision systems at the
Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC)
imply a strongly coupled quark gluon plasma (QGP) that flows. One defining
feature of collectivity is long-range angular correlations which are
characterized experimentally by measuring the azimuthal anisotropy of particles
well separated in rapidity. Evidence indicating long-range angular correlations
include the appearance of the so-called near-side ""ridge"" in correlation
functions and $p_T$ dependent flow components ($v_N$). These features have been
well measured at RHIC for Au+Au collisions at $\sqrt{s_{NN}} $= 200 GeV and at
the LHC for Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. However, evidence
of collectivity has recently been observed at the LHC in p+p high multiplicity
collisions at $\sqrt{s_{NN}}$ = 7.0 TeV and p+Pb collisions at $\sqrt{s_{NN}}$
= 5.02 TeV and then at RHIC in d+Au and $3^He$+Au collisions at $\sqrt{s_{NN}}$
= 200 GeV. In this talk, we present the recent PHENIX results for d+Au and
$^3He$+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. Precise measurements of
anisotropy help distinguish between theoretical models based on relativistic
hydrodynamics or Color Glass Condensate (CGC). Comparisons of these
measurements to various theoretical models are shown.",1510.00435v1
2015-10-03,"Giant magnetic anisotropy of Co, Ru, and Os adatoms on MgO (001) surface","Large magnetic anisotropy energy (MAE) is desirable and critical for
nanoscale magnetic devices. Here, using ligand-field level diagrams and density
functional calculations, we well explain the very recent discovery [I. G. Rau
et al., Science 344, 988 (2014)] that an individual Co adatom on a MgO (001)
surface has a large MAE of more than 60 meV. More importantly, we predict that
a giant MAE up to 110 meV could be realized for Ru adatoms on MgO (001), and
even more for the Os adatoms (208 meV). This is a joint effect of the special
ligand field, orbital multiplet, and significant spin-orbit interaction, in the
intermediate-spin state of the Ru or Os adatoms on top of the surface oxygens.
The giant MAE could provide a route to atomic scale memory.",1510.00788v1
2015-10-07,"Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films","The half-metallic half-Heusler alloy NiMnSb is a promising candidate for
applications in spintronic devices due to its low magnetic damping and its rich
anisotropies. Here we use ferromagnetic resonance (FMR) measurements and
calculations from first principles to investigate how the composition of the
epitaxially grown NiMnSb influences the magnetodynamic properties of saturation
magnetization $M_S$, Gilbert damping $\alpha$, and exchange stiffness $A$.
$M_S$ and $A$ are shown to have a maximum for stoichiometric composition, while
the Gilbert damping is minimum. We find excellent quantitative agreement
between theory and experiment for $M_S$ and $\alpha$. The calculated $A$ shows
the same trend as the experimental data, but has a larger magnitude.
Additionally to the unique in-plane anisotropy of the material, these
tunabilities of the magnetodynamic properties can be taken advantage of when
employing NiMnSb films in magnonic devices.",1510.01894v1
2015-10-08,Recovering hidden signals of statistical anisotropy from a masked or partial CMB sky,"Any isotropy violating phenomena on cosmic microwave background (CMB) induces
off-diagonal correlations in the two-point function. These correlations
themselves can be used to estimate the underlying anisotropic signals. Masking
due to residual foregrounds, or availability of partial sky due to survey
limitation, are unavoidable circumstances in CMB studies. But, masking induces
additional correlations, and thus complicates the recovery of such signals. In
this work, we discuss a procedure based on bipolar spherical harmonic (BipoSH)
formalism to comprehensively addresses any spurious correlations induced by
masking and successfully recover hidden signals of anisotropy in observed CMB
maps. This method is generic, and can be applied to recover a variety of
isotropy violating phenomena. Here, we illustrate the procedure by recovering
the subtle Doppler boost signal from simulated boosted CMB skies, which has
become possible with the unprecedented full-sky sensitivity of PLANCK probe.",1510.02454v1
2015-10-15,Lipkin-Meshkov-Glick Model in a Quantum Otto Cycle,"Lipkin-Meshkov-Glick model of two anisotropically interacting spins in a
magnetic field is proposed as a working substance of a quantum Otto engine to
explore and exploit the anisotropy effects for the optimization of engine
operation. Three different cases for the adiabatic branches of the cycle have
been considered. In the first two cases, either the magnetic field or coupling
strength are changed; while in the third case, both the magnetic field and the
coupling strength are changed by the same ratio. The system parameters for
which the engine can operate similar to or dramatically different from the
engines of non-interacting spins or of coupled spins with Ising model or
isotropic XY model interactions are determined. In particular, the role of
anisotropy to enhance cooperative work, and to optimize maximum work with high
efficiency, as well as to operate the engine near the Carnot bound are
revealed.",1510.04495v3
2015-10-16,Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy,"We have studied the magnetic layer thickness dependence of the orbital
magnetic moment in magnetic heterostructures to identify contributions from
interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlO$_x$ and
Pt/Co/Pt, which possess significant interface contribution to the perpendicular
magnetic anisotropy, are studied as model systems. X-ray magnetic circular
dichroism spectroscopy is used to evaluate the relative orbital moment, i.e.
the ratio of the orbital to spin moments, of the magnetic elements constituting
the heterostructures. We find that the relative orbital moment of Co in
Pt/Co/Pt remains constant against its thickness whereas the moment increases
with decreasing Co layer thickness for Pt/Co/AlO$_x$, suggesting that a
non-zero interface orbital moment exists for the latter system. For
Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray
absorption spectra shows that a particular oxidized Co state in Pt/Co/AlO$_x$,
absent in other heterosturctures, may give rise to the interface orbital moment
in this system. These results show element specific contributions to the
interface orbital magnetic moments in ultrathin magnetic heterostructures.",1510.04756v1
2015-10-16,Ground-state phase diagram of an anisotropic S=1/2 ladder with alternating rung interactions,"Employing mainly numerical methods, we explore the ground-state phase diagram
of an anisotropic $S=1/2$ ladder, in which leg interactions are uniform and
isotropic, while rung interactions are alternating and have a common Ising-type
anisotropy. We determine the phase diagram in the case where $J_{\rm leg}=0.2$
(antiferromagnetic), $J_{\rm rung}=-1.0$ (ferromagnetic) and $|J_{\rm
rung}'|\!\leq\!1.0$, the first one being the magnitude of the leg interaction
and the second and third ones those of the rung interactions, which are
alternating. It is emphasized that the system has a frustration when $J_{\rm
rung}'$ is positive. We find that, in the frustrated region, the Haldane state
appears as the ground state even when the Ising character of rung interactions
is strong. This appearance of the Haldane phase is contrary to the ordinary
situation, and it is called the inversion phenomenon concerning the interaction
anisotropy. We also find that an incommensurate state becomes the ground state
in a portion of the Haldane phase region.",1510.04928v1
2015-10-19,Effect of magnetism on lattice dynamics in SrFe$_2$As$_2$ as seen via high resolution inelastic x-ray scattering,"Phonon spectra of detwinned {SrFe$_2$As$_2$} crystals, as measured by
inelastic x-ray scattering, show clear anisotropy accompanying the
magneto-structural transition at 200 K. We model the mode splitting using
magnetic DFT calculations, including a phenomenological reduction in
force-constant anisotropy that can be attributed to magnetic fluctuations. This
serves as a starting point for a general model of phonons in this material
applicable to both magnetic and non-magnetic phase. Using this model, the
measured splitting in the magnetic phase below $\it T_{N}$, and the measured
phonon linewidth, we set a lower bound on the mean magnetic fluctuation
frequency above $\it T_{N}$ at 210 K.",1510.05487v2
2015-10-23,Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet,"Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.",1510.06793v1
2015-10-26,Analytic theory for the switch from Bloch to Néel domain wall in nanowires with perpendicular anisotropy,"Rectangular nanowires may have domain walls nucleated and moved through them
to realize many devices. It has been shown that at a particular width and
thickness of a nanowire with perpendicular anisotropy, there is a switch from
the domain wall being of Bloch-type to it being of N\'eel-type. This critical
shape can be found through micromagnetics simulations, but here we present an
analytic calculation for the energies of both wall types involving two
iterations for the demagnetizing energy density. The expressions developed are
long, but have the advantage that by simply inputting material parameters for
the magnetic material, the critical shape can be found using a calculator in a
matter of seconds. We compare our results to those found using micromagnetics
and those found experimentally and the agreement is good.",1510.07673v1
2015-10-27,Extrinsic Spin Hall Effect from Anisotropic Rashba Spin-Orbit Coupling in Graphene,"We study the effect of anisotropy of the Rashba coupling on the extrinsic
spin Hall effect due to spin-orbit active adatoms on graphene. In addition to
the intrinsic spin-orbit coupling, a generalized anisotropic Rashba coupling
arising from the breakdown of both mirror and hexagonal symmetries of pristine
graphene is considered. We find that Rashba anisotropy can strongly modify the
dependence of the spin Hall angle on carrier concentration. Our model provides
a simple and general description of the skew scattering mechanism due to the
spin-orbit coupling that is induced by proximity to large adatom clusters.",1510.07771v1
2015-11-01,"Growth and characterization of R(O,F)BiS2 (R = La, Ce, Pr, Nd) superconducting single crystals","R(O,F)BiS2 (R: La, Ce, Pr, Nd) superconducting single crystals with different
F concentrations are grown using a CsCl/KCl flux. The obtained 1-2 mm-sized
single crystals have a plate-like shape and are cleavable along the ab-plane.
The crystal structure is tetragonal of space group P4/nmm (#129). The as-grown
single crystals exhibit superconductivity at around 3-5 K. The superconducting
transition temperature increases with decreasing the ionic radius of the R
element. The superconducting anisotropies of the R(O,F)BiS2 single crystals are
estimated to be 30-60 according to the effective mass model, whereas the
anisotropies for Ce(O,F)BiS2 single crystals are 13-21. The c-axis transport
measurements of a single crystal of Pr(O,F)BiS2 under a magnetic field parallel
to the ab-plane reveal a ""lock-in"" state attributed to the Josephson vortex
flow. Furthermore, the Ce(O,F)BiS2 single crystals exhibit a magnetic order at
the temperature range of 5-7 K that apparently coexist with superconductivity
below approximately 3 K.",1511.00219v1
2015-11-03,A hybrid method for anisotropic elliptic problems based on the coupling of an Asymptotic-Preserving method with the Asymptotic-Limit model,"This paper presents a hybrid numerical method to solve efficiently a class of
highly anisotropic elliptic problems. The anisotropy is aligned with one
coordinate-axis and its strength is described by a parameter $\eps \in (0,1]$,
which can largely vary in the study domain. Our hybrid model is based on
asymptotic techniques and couples (spatially) an Asymptotic-Preserving model
with its asymptotic Limit model, the latter being used in regions where the
anisotropy parameter $\eps$ is small. Adequate coupling conditions link the two
models. Aim of this hybrid procedure is to reduce the computational time for
problems where the region of small $\eps$-values extends over a significant
part of the domain, and this due to the reduced complexity of the limit model.",1511.00917v1
2015-11-05,Early-Matter-Like Dark Energy and the Cosmic Microwave Background,"Early-matter-like dark energy is defined as a dark energy component whose
equation of state approaches that of cold dark matter (CDM) at early times.
Such a component is an ingredient of unified dark matter (UDM) models, which
unify the cold dark matter and the cosmological constant of the LambdaCDM
concordance model into a single dark fluid. Power series expansions in
conformal time of the perturbations of the various components for a model with
early-matter-like dark energy are provided. They allow the calculation of the
cosmic microwave background (CMB) anisotropy from the primordial initial values
of the perturbations. For a phenomenological UDM model, which agrees with the
observations of the local Universe, the CMB anisotropy is computed and compared
with the CMB data. It is found that a match to the CMB observations is possible
if the so-called effective velocity of sound c_eff of the early-matter-like
dark energy component is very close to zero. The modifications on the CMB
temperature and polarization power spectra caused by varying the effective
velocity of sound are studied.",1511.01691v2
2015-11-09,Theoretical and experimental investigation of optical absorption anisotropy in $β$-Ga2O3,"The question of optical bandgap anisotropy in the monoclinic semiconductor
$\beta$-Ga2O3 was revisited by combining accurate optical absorption
measurements with theoretical analysis, performed using different advanced
computation methods. As expected, the bandgap edge of bulk $\beta$-Ga2O3 was
found to be a function of light polarization and crystal orientation, with the
lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6
eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The
theoretical analysis clearly indicates that the shift of the b onset is due to
a suppression of the transition matrix elements of the three top valence bands
at $\Gamma$ point.",1511.02601v1
2015-11-11,Dynamics of wave fronts and filaments in anisotropic cardiac tissue,"The heartbeat is mediated between cardiac cells by waves of electrical
depolarisation. During cardiac arrhythmias, electrical activity was found to be
organised in scroll waves which rotate around a dynamical filament curve. In
this thesis, a curved-space approach is used to mathematically capture
anisotropy of wave propagation. We derive for the first time the covariant laws
of motion for traveling wave fronts and scroll wave filaments in anisotropic
excitable media such as cardiac tissue. We show that locally varying anisotropy
yields non-zero Riemann tensor components, which may alter the stability of
scroll wave filaments. The instability of scroll wave filaments has been linked
to transition from ventricular tachycardia to fibrillation.",1511.03685v1
2015-11-17,Low-field behavior of an XY pyrochlore antiferromagnet: emergent clock anisotropies,"Using $\rm Er_2Ti_2O_7$ as a motivation, we investigate finite-field
properties of $XY$ pyrochlore antiferromagnets. In addition to a
fluctuation-induced six-fold anisotropy present in zero field, an external
magnetic field induces a combination of two-, three-, and six-fold clock terms
as a function of its orientation providing for a rich and controllable
magnetothermodynamics. For $\rm Er_2Ti_2O_7$, we predict a new phase transition
for ${\bf H}\parallel [001]$. Re-entrant transitions are also found for ${\bf
H}\parallel [111]$. We extend these results to the whole family the $XY$
pyrochlore antiferromagnets and show that presence and number of low-field
transitions for different orientations can be used for locating a given
material in the parameter space of anisotropic pyrochlores. Finite-temperature
classical Monte Carlo simulations serve to confirm and illustrate these
analytic predictions.",1511.05319v2
2015-11-24,Electronic and Magnetic Properties of single Fe atoms on a CuN Surface; Effects of Electron Correlations,"The electronic structure and magnetic properties of a single Fe adatom on a
CuN surface have been studied using density functional theory in the local spin
density approximation (LSDA), the LSDA+U approach and the local density
approximation plus dynamical mean-field theory (LDA+DMFT). The impurity problem
in LDA+DMFT is solved through exact diagonalization and in the Hubbard-I
approximation. The comparison of the one-particle spectral functions obtained
from LSDA, LSDA+U and LDA+DMFT show the importance of dynamical correlations
for the electronic structure of this system. Most importantly, we focused on
the magnetic anisotropy and found that neither LSDA, nor LSDA+U can explain the
measured, high values of the axial and transverse anisotropy parameters.
Instead, the spin excitation energies obtained from our LDA+DMFT approach with
exact diagonalization agree significantly better with experimental data. This
affirms the importance of treating fluctuating magnetic moments through a
realistic many-body treatment when describing this class of nano-magnetic
systems. Moreover, it facilitates insight to the role of the hybridization with
surrounding orbitals.",1511.07909v1
2015-11-27,Resonance spin-charge phenomena and mechanism of magnetoresistance anisotropy in manganite/metal bilayer structures,"The dc voltage generated under ferromagnetic resonance has been studied in
bilayer structures based on manganite thin epitaxial films La0.67Sr0.33MnO3
(LSMO) and non-magnetic metals (Au, Pt, and SrRuO3) in the temperature range up
to the Curie point. The effect is shown to be caused by two different
phenomena: (1) the resonance dc electromotive force related to anisotropic
magnetoresistance (AMR) in the manganite film and (2) pure spin current (spin
pumping) registered by means of the inverse spin Hall effect in normal metal.
The two phenomena were separated using the angular dependence of the effect,
the external magnetic field H0 being rotated in the film plane. It was found
that the AMR mechanism in the manganite films differs substantially from that
in traditional ferromagnetic metals being governed by the colossal
magnetoresistance together with the in-plane magnetic anisotropy. The spin
pumping effect registered in the bilayers was found to be much lower than that
reported for common ferromagnets; possible reasons are discussed.",1511.08664v1
2015-11-27,Multi-band superconductivity and large anisotropy in FeS crystals,"By using a hydrothermal method, we have successfully grown crystals of the
newly discovered superconductor FeS, which has an isostructure of the iron
based superconductor FeSe. The superconductivity appears at about 4.5K, as
revealed by both resistive and magnetization measurements. It is found that the
upper critical field is relatively low, with however an rather large anisotropy
$\Gamma=[(dH_{c2}^{ab}/dT)/(dH_{c2}^{c}/dT)]_{T_c}\approx5.8$. A huge
magnetoresistivity (290$\%$ at 9T and 10K, ${H}$ $\parallel$ c-axis) together
with a non-linear behavior of Hall resistivity vs. external field are observed.
A two-band model is applied to fit the magnetoresistance and non-linear
transverse resistivity, yielding the basic parameters of the electron and hole
bands.",1511.08716v2
2015-12-05,A new exact solution for anisotropic compact stars of embedding class one,"We have presented a new anisotropic solution of Einstein's field equations
for compact star models. The Einstein's field equations are solved by using the
class one condition \cite{1}. After that we constructed the physically valid
expression of anisotropy factor by the help of metric potentials and there
after we obtained the physical parameters like energy density, radial and
transverse pressure. These models parameters are well behaved inside the
compact star and satisfy all the required physical conditions. Also we observed
a very interesting result that all the physical parameters are depend on the
anisotropy factor. The present compact star models are quite compatible with
the observational astrophysical compact stellar objects like Her X-1, RXJ
1856-37, SAX J1808.4-3658(SS1), SAX J1808.4-3658(SS2)",1512.01667v2
2015-12-18,Exchange Bias and Bistable Magneto-Resistance States in Amorphous TbFeCo thin Films,"Amorphous TbFeCo thin films sputter deposited at room temperature on
thermally oxidized Si substrate are found to exhibit strong perpendicular
magnetic anisotropy (PMA). Atom probe tomography (APT), scanning transmission
electron microscopy (STEM), and energy dispersive spectroscopy (EDS) mapping
have revealed two nanoscale amorphous phases with different Tb atomic
percentages distributed within the amorphous film. Exchange bias accompanied by
bistable magneto-resistance states has been uncovered near room temperature by
magnetization and magneto-transport measurements. The exchange anisotropy
originates from the exchange interaction between the ferrimagnetic and
ferromagnetic components corresponding to the two amorphous phases. This study
provides a platform for exchange bias and magneto-resistance switching using
single-layer amorphous ferrimagnetic thin films that require no epitaxial
growth.",1512.06103v1
2015-12-22,Initial state azimuthal anisotropies in small collision systems,"Strong multiparticle azimuthal correlations have recently been observed in
high energy proton-nucleus collisions. While final state collective effects can
be responsible for many of the observations, the domain structure in the
classical color field of a high energy nucleus also naturally leads to such
correlations. We describe recent calculations of the momentum space 2-particle
cumulant azimuthal anisotropy coefficients v_n{2}, n=2,3,4 from fundamental
representation Wilson line distributions describing the high energy nucleus. We
find significant differences between Wilson lines from the MV model and from
JIMWLK evolution. We also discuss the relation of this calculation to earlier
work on the ridge correlation obtained in the ""glasma graph"" approximation, and
to the ""color electric field domain model.""",1512.07209v1
2015-12-23,Giant biquadratic interaction induced magnetic anisotropy in the iron-based superconductor AxFe2-ySe2,"The emergence of the electron-pocket only iron-based superconductor
AxFe2-ySe2 (A = alkali metal) challenges the Fermi-surface nesting picture
established in iron-pnictides. It was widely believed that magnetism is
correlated with the superconductivity in AxFe2-ySe2. Unfortunately, the highly
anisotropic exchange parameters and the disagreement between theoretical
calculations and experimental results triggered a fierce debate on the nature
of magnetism in AxFe2-ySe2. Here we find that the strong magnetic anisotropy is
from the anisotropic biquadratic interaction. In order to accurately obtain the
magnetic interaction parameters, we propose a universal method, which does not
need including other high energy configurations as did in conventional energy
mapping method. We show that our model successfully captures the magnetic
interactions in AxFe2-ySe2 and correctly predicts the spin wave spectrum, in
quantitative agreement with the experimental observation. These results suggest
that the local moment picture, including the biquadratic term, can describe
accurately the magnetic properties and spin excitations in AxFe2-ySe2, which
sheds new light on the future study of the high-Tc iron-based superconductors.",1512.07327v1
2015-12-23,Anisotropic hydrodynamics for conformal Gubser flow,"In this proceedings contribution, we review the exact solution of the
anisotropic hydrodynamics equations for a system subject to Gubser flow. For
this purpose, we use the leading-order anisotropic hydrodynamics equations
which assume that the distribution function is ellipsoidally symmetric in
local-rest-frame momentum. We then prove that the SO(3)_q symmetry in de Sitter
space constrains the anisotropy tensor to be of spheroidal form with only one
independent anisotropy parameter remaining. As a consequence, the exact
solution reduces to the problem of solving two coupled non-linear differential
equations. We show that, in the limit that the relaxation time goes to zero,
one obtains Gubser's ideal hydrodynamic solution and, in the limit that the
relaxation time goes to infinity, one obtains the exact free streaming solution
obtained originally by Denicol et al. For finite relaxation time, we solve the
equations numerically and compare to the exact solution of the
relaxation-time-approximation Boltzmann equation subject to Gubser flow. Using
this as our standard, we find that anisotropic hydrodynamics describes the
spatio-temporal evolution of the system better than all currently known
dissipative hydrodynamics approaches.",1512.07334v1
2015-12-23,J/$ψ$ polarization measurements in p+p collisions at $\sqrt{s}$ = 200 and 500 GeV with the STAR experiment,"In these proceedings, measurements of J/psi polarization in p+p collisions at
200 and 500 GeV via the dielectron decay channel at mid-rapidity with the STAR
experiment are discussed. At 200 GeV the polarization parameter,
$\lambda_{\theta}$, related to the polar anisotropy is obtained in the helicity
frame as a function of transverse momentum, 2 < $p_{T}$ < 6 GeV/c, and compared
to different model predictions. A new J/psi polarization measurement at 500 GeV
extends the previous analysis to a wide transverse momentum range of 5 <
$p_{T}$ < 16 GeV/c. Also, the polarization parameter related to the azimuthal
anisotropy, $\lambda_{\phi}$, is extracted in addition to $\lambda_{\theta}$,
in two reference frames: the helicity and Collins-Soper frames. This allows for
the frame invariant parameter calculation vs $p_{T}$ in these two frames.",1512.07405v1
2015-12-23,Low Energy Properties of the Kondo chain in the RKKY regime,"We study the Kondo chain in the regime of high spin concentration where the
low energy physics is dominated by the Ruderman-Kittel-Kasuya-Yosida (RKKY)
interaction. As has been recently shown (A. M. Tsvelik and O. M. Yevtushenko,
Phys. Rev. Lett 115, 216402 (2015)), this model has two phases with drastically
different transport properties depending on the anisotropy of the exchange
interaction. In particular, the helical symmetry of the fermions is
spontaneously broken when the anisotropy is of the easy plane type (EP). This
leads to a parametrical suppression of the localization effects. In the present
paper we substantially extend the previous theory, in particular, by analyzing
a competition of forward- and backward- scattering, including into the theory
short range electron interactions and calculating spin correlation functions.
We discuss applicability of our theory and possible experiments which could
support the theoretical findings.",1512.07495v1
2016-01-07,Primordial power spectra for scalar perturbations in loop quantum cosmology,"We provide the power spectrum of small scalar perturbations propagating in an
inflationary scenario within loop quantum cosmology. We consider the hybrid
quantization approach applied to a Friedmann--Robertson--Walker spacetime with
flat spatial sections coupled to a massive scalar field. We study the quantum
dynamics of scalar perturbations on an effective background within this hybrid
approach. We consider in our study adiabatic states of different orders. For
them, we find that the hybrid quantization is in good agreement with the
predictions of the dressed metric approach. We also propose an initial vacuum
state for the perturbations, and compute the primordial and the anisotropy
power spectrum in order to qualitatively compare with the current observations
of Planck mission. We find that our vacuum state is in good agreement with
them, showing a suppression of the power spectrum for large scale anisotropies.
We compare with other choices already studied in the literature.",1601.01716v3
2016-01-08,Current Control of Magnetic Anisotropy via Stress in a Ferromagnetic Metal Waveguide,"We demonstrate that in-plane charge current can effectively control the spin
precession resonance in an Al2O3/CoFeB/Ta heterostructure. Brillouin Light
Scattering (BLS) was used to detect the ferromagnetic resonance field under
microwave excitation of spin waves at fixed frequencies. The current control of
spin precession resonance originates from modification of the in-plane uniaxial
magnetic anisotropy field H_k, which changes symmetrically with respect to the
current direction. Numerical simulation suggests that the anisotropic stress
introduced by Joule heating plays an important role in controlling H_k. These
results provide new insights into current manipulation of magnetic properties
and have broad implications for spintronic devices.",1601.02048v1
2016-01-13,Investigation of Dosimetric Parameters of $^{192}$Ir MicroSelectron v2 HDR Brachytherapy Source Using EGSnrc Monte Carlo Code,"The $^{192}$Ir sources are widely used for high dose rate (HDR) brachytherapy
treatments. The aim of this study is to simulate $^{192}$Ir MicroSelectron v2
HDR brachytherapy source and calculate the air kerma strength, dose rate
constant, radial dose function and anisotropy function established in the
updated AAPM Task Group 43 protocol. The EGSnrc Monte Carlo (MC) code package
is used to calculate these dosimetric parameters, including dose contribution
from secondary electron source and also contribution of bremsstrahlung photons
to air kerma strength. The Air kerma strength, dose rate constant and radial
dose function while anisotropy functions for the distance greater than 0.5 cm
away from the source center are in good agreement with previous published
studies. Obtained value from MC simulation for air kerma strength is
$9.762\times 10^{-8} \textrm{UBq}^{-1}$and dose rate constant is $1.108\pm
0.13\%\textrm{cGyh}^{-1} \textrm{U}^{-1}$.",1601.03177v1
2016-01-14,Statistical anisotropy from inflationary magnetogenesis,"Provided the quantum fluctuations are amplified in the presence of a
classical gauge field configuration the resulting curvature perturbations
exhibit a mild statistical anisotropy which should be sufficiently weak not to
conflict with current observational data. The curvature power spectra induced
by weakly anisotropic initial states are computed here for the first time when
the electric and the magnetic gauge couplings evolve at different rates as it
happens, for instance, in the relativistic theory of van der Waals
interactions. After recovering the results valid for coincident gauge
couplings, the constraints imposed by the isotropy and the homogeneity of the
initial states are discussed. The obtained bounds turn out to be more stringent
than naively expected and cannot be ignored when discussing the underlying
magnetogenesis scenarios.",1601.03556v1
2016-01-20,Origin of the mass splitting of elliptic anisotropy in a multiphase transport model,"The mass splitting of elliptic anisotropy ($v_2$) at low transverse momentum
is considered as a hallmark of hydrodynamic collective flow. We investigate a
multiphase transport (AMPT) model where the $v_2$ is mainly generated by an
anisotropic escape mechanism, not of the hydrodynamic flow nature, and where
mass splitting is also observed. We demonstrate that the $v_2$ mass splitting
in AMPT is small right after hadronization (especially when resonance decays
are included); the mass splitting mainly comes from hadronic rescatterings,
even though their contribution to the overall charged hadron $v_2$ is small.
These findings are qualitatively the same as those from hybrid models that
combine hydrodynamics with a hadron cascade. We further show that there is no
qualitative difference between heavy ion collisions and small system
collisions. Our results indicate that the $v_2$ mass splitting is not a unique
signature of hydrodynamic collective flow and thus cannot distinguish whether
the elliptic flow is generated mainly from hydrodynamics or the anisotropic
parton escape.",1601.05390v2
2016-01-22,Determination of the Spin-Hall-Effect-Induced and the Wedged-Structure-Induced Spin Torque Efficiencies in Heterostructures with Perpendicular Magnetic Anisotropy,"We report that by measuring current-induced hysteresis loop shift versus
in-plane bias magnetic field, the spin Hall effect (SHE) contribution of the
current-induced effective field per current density, $\chi_{SHE}$, can be
estimated for Pt and Ta-based magnetic heterostructures with perpendicular
magnetic anisotropy (PMA). We apply this technique to a Pt-based sample with
its ferromagnetic (FM) layer being wedged-deposited and discover an extra
effective field contribution, $\chi_{Wedged}$, due to the asymmetric nature of
the deposited FM layer. We confirm the correlation between $\chi_{Wedged}$ and
the asymmetric depinning process in FM layer during magnetization switching by
magneto-optical Kerr (MOKE) microscopy. These results indicate the possibility
of engineering deterministic spin-orbit torque (SOT) switching by controlling
the symmetry of domain expansion through the materials growth process.",1601.05854v1
2016-01-27,Quasi-local conserved charges and spin transport in spin-$1$ integrable chains,"We consider the integrable one-dimensional spin-$1$ chain defined by the
Zamolodchikov-Fateev (ZF) Hamiltonian. The latter is parametrized, analogously
to the XXZ spin-$1/2$ model, by a continuous anisotropy parameter and at the
isotropic point coincides with the well-known spin-$1$ Babujian-Takhtajan
Hamiltonian. Following a procedure recently developed for the XXZ model, we
explicitly construct a continuous family of quasi-local conserved operators for
the periodic spin-$1$ ZF chain. Our construction is valid for a dense set of
commensurate values of the anisotropy parameter in the gapless regime where the
isotropic point is excluded. Using the Mazur inequality, we show that, as for
the XXZ model, these quasi-local charges are enough to prove that the
high-temperature spin Drude weight is non-vanishing in the thermodynamic limit,
thus establishing ballistic spin transport at high temperature.",1601.07289v3
2016-01-27,Dark Radiation and Inflationary Freedom after Planck 2015,"The simplest inflationary models predict a primordial power spectrum (PPS) of
the curvature fluctuations that can be described by a power-law function that
is nearly scale-invariant. It has been shown, however, that the low-multipole
spectrum of the CMB anisotropies may hint the presence of some features in the
shape of the scalar PPS, which could deviate from its canonical power-law form.
We study the possible degeneracies of this non-standard PPS with the neutrino
anisotropies, the neutrino masses, the effective number of relativistic species
and a sterile neutrino or a thermal axion mass. The limits on these additional
parameters are less constraining in a model with a non-standard PPS when only
including the temperature auto-correlation spectrum measurements in the data
analyses. The inclusion of the polarization spectra noticeably helps in
reducing the degeneracies, leading to results that typically show no deviation
from the $\Lambda$CDM model with a standard power-law PPS.",1601.07557v2
2016-01-28,Composition-tuned magneto-optical Kerr effect in L10-MnxGa films with giant perpendicular anisotropy,"We report the large polar magnetooptical Kerr effect in L10-MnxGa epitaxial
films with giant perpendicular magnetic anisotropy in a wide composition range.
The Kerr rotation was enhanced by a factor of up to 10 by decreasing Mn atomic
concentration, which most likely arises from the variation of the effective
spin-orbit coupling strength, compensation effect of magnetic moments at
different Mn atom sites, and overall strain. The Kerr ellipticity and the
magnitude of the complex Kerr angle is found to have more complex
composition-dependence that varies with the photon energy. These L10-MnxGa
films show large Kerr rotation of up to 0.10o, high reflectivity of 35%-55% in
a wide wavelength range of 400~850 nm, and giant magnetic anisotropic field of
up to 210 kOe, making them an interesting material system for emerging
spintronics and terahertz modulator applications.",1601.07939v4
2016-01-30,On the Chiral imbalance and Weibel Instabilities,"We study the chiral-imbalance and the Weibel instabilities in presence of the
quantum anomaly using the Berry-curvature modified kinetic equation. We argue
that in many realistic situations, e.g. relativistic heavy-ion collisions, both
the instabilities can occur simultaneously. The Weibel instability depends on
the momentum anisotropy parameter $\xi$ and the angle ($\theta_n$) between the
propagation vector and the anisotropy direction. It has maximum growth rate at
$\theta_n=0$ while $\theta_n=\pi/2$ corresponds to a damping. On the other hand
the pure chiral-imbalance instability occurs in an isotropic plasma and depends
on difference between the chiral chemical potentials of right and left-handed
particles. It is shown that when $\theta_n=0$, only for a very small values of
the anisotropic parameter $\xi\sim \xi_c$, growth rates of the both
instabilities are comparable. For the cases $\xi_c<\xi\ll1$, $\xi\approx 1$ or
$\xi \geq 1$ at $\theta_n=0$, the Weibel modes dominate over the
chiral-imbalance instability if $\mu_5/T\leq1$. However, when $\mu_5/T\geq1$,
it is possible to have dominance of the chiral-imbalance modes at certain
values of $\theta_n$ for an arbitrary $\xi$.",1602.00111v1
2016-02-04,Magnetic anisotropy of the single-crystalline ferromagnetic insulator Cr2Ge2Te6,"Cr2Ge2Te6 (CGT), a layered ferromagnetic insulator, has attracted a great
deal of interest recently owing to its potential for integration with Dirac
materials to realize the quantum anomalous Hall effect (QAHE) and to develop
novel spintronics devices. Here, we study the uniaxial magnetic anisotropy
energy of single-crystalline CGT and determine that the magnetic easy axis is
directed along the c-axis in its ferromagnetic phase. In addition, CGT is an
insulator below the Curie temperature. These properties make CGT a potentially
promising candidate substrate for integration with topological insulators for
the realization of the high-temperature QAHE.",1602.01556v1
2016-02-16,The dissipation tensor $\varepsilon_{ij}$ in wall turbulence,"The paper investigates the dissipation tensor $\varepsilon_{ij}$ in wall
turbulence. Available DNS data are examined to illustrate the differences in
the anisotropy of the dissipation tensor $\varepsilon_{ij}$ with respect to the
anisotropy of the Reynolds-stresses $r_{ij}$. The budgets of the transport
equations of the dissipation tensor $\varepsilon_{ij}$ are studied using novel
DNS data of low-Reynolds-number turbulent plane channel flow with spatial
resolution sufficiently fine to accurately determine the correlations of
products of 2-derivatives of fluctuating velocities $u_i'$ and pressure $p'$
which appear in various terms. Finally, the influence of the Reynolds number on
the diagonal components of $\varepsilon_{ij}$ ($\varepsilon_{xx}$,
$\varepsilon_{yy}$, $\varepsilon_{zz}$) and on the various terms in their
transport equations is studied using available DNS data of Vreman and Kuerten
(Phys. Fluids 26 (2014) 085103).",1602.05022v3
2016-02-19,Optical anisotropy of the Jeff = 1/2 Mott insulator Sr2IrO4,"We report the complex dielectric function along and perpendicular to the IrO2
planes in the layered perovskite Sr2IrO4 determined by spectroscopic
ellipsometry in the spectral range from 12 meV to 6 eV. Thin high quality
single crystals were stacked to measure the c-axis optical conductivity. In the
phonon response we identified 10 infrared-active modes polarized within the
basal plane and only four modes polarized along the c-axis, in full agreement
with first-principle lattice dynamics calculations. We also observed a strong
optical anisotropy in the near-infrared spectra arising from direct transitions
between Ir 5d t2g Jeff = 1/2 and Jeff = 3/2 bands, which transition probability
is highly suppressed for light polarized along the c-axis. The spectra are
analyzed and discussed in terms of relativistic LSDA+U band structure
calculations.",1602.06090v1
2016-02-19,Magnetic anisotropy of large floating-zone-grown single-crystals of SrRuO3,"SrRuO3 is a highly interesting material due to its anomalous-metal properties
related with ferromagnetism and its relevance as conductive perovskite layer or
substrate in heterostructure devices. We have used optical floating zone
technique in an infrared image furnace to grow large single crystals of SrRuO3
with volumes attaining several hundred mm3. Crystals obtained for optimized
growth parameters exhibit a high ferromagnetic Curie temperature of 165 K and a
low-temperature magnetization of 1.6 muB at a magnetic field of 6 T. The high
quality of the crystals is further documented by large residual resistance
ratios of 75 and by crystal structure and chemical analyzes. With these
crystals the magnetic anisotropy could be determined.",1602.06171v2
2016-02-22,Critical behaviour of anisotropic magnets with quenched disorder: replica symmetry breaking studied by operator product expansion,"We study critical behaviour of disordered magnets near four dimensions. We
consider the system with explicit cubic anisotropy and scalar disorder and that
with random direction of anisotropy axis. The quenched disorder is taken into
account by replica method. Using the method of operator product expansion, we
derive in the first order to $\epsilon$ approximation the renormalization group
equations taking into account possible replica symmetry breaking.",1602.06789v9
2016-02-23,Zero temperature non-plateau magnetization and magnetocaloric effect in an Ising-XYZ diamond chain structure,"Zero temperature non-plateau magnetization is a peculiar property of a
quantum spin chain and it sometimes appears due to different gyromagnetic
factors. In this study, we illustrate a quite unusual nonplateau magnetization
property driven by XY-anisotropy in an Ising-XYZ diamond chain. Two particles
with spin-1/2 are bonded by XYZ coupling and they are responsible for the
emergence of non-plateau magnetization. These two quantum operator spins are
bonded to two nodal Ising spins and this process is repeated infinitely to
yield a diamond chain structure. Due to the non-plateau magnetization property,
we focus our discussion on the magnetocaloric effect of this model by
presenting the isentropic curves and the Gruneisen parameters, as well as
showing the regions where the model exhibits an efficient magnetocaloric
effect. Due to the existence of two phases located very close to each other,
the strong XY-anisotropy exhibits a particular behavior with a magnetocaloric
effect, with a wider interval in the magnetic field, where the magnetocaloric
effect is efficient.",1602.07279v4
2016-02-25,Thermal simulation of magnetization reversals for size-distributed assemblies of core-shell exchange biased nanoparticles,"A temperature dependent coherent magnetization reversal model is proposed for
size-distributed assemblies of ferromagnetic nanoparticles and
ferromagnetic-antiferromagnetic core-shell nanoparticles. The nanoparticles are
assumed to be of uniaxial anisotropy and all aligned along their easy axis. The
thermal dependence is included by considering thermal fluctuations, implemented
via the N\'eel-Arrhenius theory. Thermal and angular dependence of
magnetization reversal loops, coercive field and exchange-bias field are
obtained, showing that F-AF size-distributed exchange-coupled nanoparticles
exhibit temperature-dependent asymmetric magnetization reversal. Also,
non-monotonic evolutions of He and Hc with T are demonstrated. The angular
dependence of Hc with T exhibits a complex behavior, with the presence of an
apex, whose position and amplitude are strongly T dependent. The angular
dependence of He with T exhibits complex behaviors, which depends on the AF
anisotropy and exchange coupling. The resulting angular behavior demonstrates
the key role of the size distribution and temperature in the magnetic response
of nanoparticles.",1602.07877v2
2016-02-25,Various Time-Scales of Relaxation,"Via gauge-gravity duality, relaxation of far-from-equilibrium initial states
in a strongly coupled gauge theory has been investigated. In the system we
consider in this paper there are two ways where the state under study can
deviate from its equilibrium: anisotropic pressure and time-dependent
expectation value of a scalar operator with \Delta=3. In the gravity theory,
this system corresponds to Einstein's general relativity with a non-trivial
metric, including the anisotropy function, coupled to a massive scalar matter
field. We study the effect of different initial configurations for scalar field
and anisotropy function on physical processes such as thermalization, i.e. time
evolution of event horizon, equilibration of the expectation value of scalar
operator and isotropization. We also discuss time ordering of these
time-scales.",1602.07903v2
2016-02-25,Dark matter component decaying after recombination: lensing constraints with Planck data,"It has been recently suggested~\cite{Berezhiani:2015yta} that emerging
tension between cosmological parameter values derived in high-redshift (CMB
anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can
be reconciled in a model which contains subdominant fraction of dark matter
decaying after recombination. We check the model against the CMB Planck data.
We find that lensing of the CMB anisotropies by the large-scale structure gives
strong extra constraints on this model, limiting the fraction as $F<8\%$ at
2\,$\sigma$ confidence level. However, investigating the combined data set of
CMB and conflicting low-$z$ measurements, we obtain that the model with
$F\approx2\!-\!5$\% exhibits better fit (by 1.5-3\,$\sigma$ depending on the
lensing priors) compared to that of the concordance $\Lambda$CDM cosmological
model.",1602.08121v2
2016-03-08,Searching for Cosmological Preferred Axis using cosmographic approach,"Recent released Planck data and other astronomical observations show that the
universe may be anisotropic on large scales. This hints a cosmological
privileged axis in our anisotropic expanding universe. This paper proceeds a
modified redshift in anisotropic cosmological model as $
1+\tilde{z}(t,\hat{\textbf{p}})=\frac{a(t_{0)}}{a(t)}(1-A(\hat{\textbf{n}}.\hat{\textbf{p}}))$
(where $A$ is the magnitude of anisotropy ,$\hat{\textbf{n}}$ is the direction
of privileged axis, and $\hat{\textbf{p}}$ is the direction of each SNe Ia
sample to galactic coordinates) along with anisotropic parameter
$\delta=\frac{A(\hat{\textbf{n}}.\hat{\textbf{p}})}{1+A(\hat{\textbf{n}}.\hat{\textbf{p}})}$.
The luminosity distance is expanded with model-independent cosmographic
parameters as a function of modified redshift $\tilde{z}$. As the
transformation matrix $M(n\times n)$ is obtained to convert the Taylor series
coefficients of isotropic luminosity distance to corresponding anisotropic
parameters. These results culminate the magnitude of anisotropy about $\mid
A\mid \simeq 10^{-3}$ and the direction of preferred axis as
$(l,b)=(297^{-34}_{+34},3^{-28}_{+28})$, which are consistent with other
studies in $1-\sigma$ confidence level.",1603.02659v2
2016-03-09,Evolution of perpendicular magnetized tunnel junctions upon annealing,"We study the evolution of perpendicularly magnetized tunnel junctions under
300 to 400 $^{\circ}$C annealing. The hysteresis loops do not evolve much
during annealing and they are not informative of the underlying structural
evolutions. These evolutions are better revealed by the frequencies of the
ferromagnetic resonance eigenmodes of the tunnel junction. Their modeling
provides the exchange couplings and the layers' anisotropies within the stack
which can serve as a diagnosis of the tunnel junction state after each
annealing step. The anisotropies of the two CoFeB-based parts and the two
Co/Pt-based parts of the tunnel junction decay at different rates during
annealing. The ferromagnet exchange coupling through the texture-breaking Ta
layer fails above 375$^{\circ}$C. The Ru spacer meant to promote a synthetic
antiferromagnet behavior is also insufficiently robust to annealing. Based on
these evolutions we propose optimization routes for the next generation tunnel
junctions.",1603.02824v1
2016-03-11,Measurement of the $B_{1g}$ and $B_{2g}$ components of the elastoresistivity tensor for tetragonal materials via transverse resistivity configurations,"The elastoresistivity tensor $m_{ij,kl}$ relates changes in resistivity to
strains experienced by a material. As a fourth-rank tensor, it contains
considerably more information about the material than the simpler (second-rank)
resistivity tensor; in particular, for a tetragonal material, the $B_{1g}$ and
$B_{2g}$ components of the elastoresistivity tensor ($m_{xx,xx}-m_{xx,yy}$ and
$2m_{xy,xy}$, respectively) can be related to its nematic susceptibility.
Previous experimental probes of this quantity have focused exclusively on
differential longitudinal elastoresistance measurements, which determine the
induced resistivity anisotropy arising from anisotropic in-plane strain based
on the difference of two longitudinal resistivity measurements. Here we
describe a complementary technique based on \textit{transverse}
elastoresistance measurements. This new approach is advantageous because it
directly determines the strain-induced resistivity anisotropy from a single
transverse measurement. To demonstrate the efficacy of this new experimental
protocol, we present transverse elastoresistance measurements of the
$2m_{xy,xy}$ elastoresistivity coefficient of BaFe$_2$As$_2$, a representative
iron-pnictide that has previously been characterized via differential
longitudinal elastoresistance measurements.",1603.03537v1
2016-03-11,Effects of anisotropy on interacting ghost dark energy in Brans-Dicke theories,"By interacting ghost dark energy (ghost DE) in the framework of Brans-Dicke
theory, a spatially homogeneous and anisotropic Bianchi type I Universe has
been studied. For this purpose, we use the squared sound speed $c_s^2$ whose
sign determines the stability of the model. As well as we probe observational
constraints on the ghost dark energy models as the unification of dark matter
and dark energy by using the latest observational data. In order to do so, we
focus on observational determinations of the Hubble expansion rate (namely, the
expansion history) $H(z)$. After that we evaluate the evolution of the growth
of perturbations in the linear regime for both ghost DE and Brans-Dicke theory
and compare the results with standard FRW and $\Lambda$CDM models. We display
the effects of the anisotropy on the evolutionary behavior the ghost DE models
where the growth rate is higher in this models. Eventually the growth factor
for the $\Lambda$CDM Universe will always fall behind the ghost DE models in an
anisotropic Universe",1603.03681v2
2016-03-15,"Interplay of Quantum Size Effect, Anisotropy and Surface Stress Shapes the Instability of Thin Metal Films","Morphological instability of a planar surface ([111], [011], or [001]) of an
ultra-thin metal film is studied in a parameter space formed by three major
effects (the quantum size effect, the surface energy anisotropy and the surface
stress) that influence a film dewetting. The analysis is based on the extended
Mullins equation, where the effects are cast as functions of the film
thickness. The formulation of the quantum size effect (Z. Zhang et al., PRL 80,
5381 (1998)) includes the oscillation of the surface energy with thickness
caused by electrons confinement. By systematically comparing the effects, their
contributions into the overall stability (or instability) is highlighted.",1603.04675v3
2016-03-15,Ordering in rolled-up single-walled ferromagnetic nanomembranes,"Magnetization of soft-ferromagnetic nano- and microtubes of nanometer-thin
walls (a single-widening rolled-up nanomembranes) is theoretically studied
using analytical and numerical approaches including different stress-induced
anisotropies. Within the analytical study, we consider magnetostatic effects
qualitatively, with an effective anisotropy, while they are fully treated in
the micromagnetic simulations (limited to the tubes of submicrometer diameters
however). Basic types of the periodic ordering have been established and their
presence in nanotubes of polycrystalline Permalloy and cobalt has been verified
within the simulations. The domain structure is basically determined by a
material-deposition-induced helical stress or a cooling-induced axial stress
via the volume magnetostriction while it is influenced by the distribution of
magnetic charges as well. Also, it is dependent on the initial state of the
magnetization process.",1603.04883v2
2016-03-16,Highly anisotropic and two-fold symmetric superconducting gap in nematically ordered FeSe$_{0.93}$S$_{0.07}$,"FeSe exhibits a novel ground state in which superconductivity coexists with a
nematic order in the absence of any long-range magnetic order. Here we report
an angle-resolved photoemission study on the superconducting gap structure in
the nematic state of FeSe$_{0.93}$S$_{0.07}$, without the complication caused
by Fermi surface reconstruction induced by magnetic order. We found that the
superconducting gap shows a pronounced 2-fold anisotropy around the elliptical
hole pocket near the Z point of the Brillouin zone, with gap minima at the
endpoints of its major axis, while no detectable gap was observed around the
zone center and zone corner. The large anisotropy and nodal gap distribution
demonstrate the substantial effects of the nematicity on the superconductivity,
and thus put strong constraints on the current theories.",1603.05219v1
2016-03-17,Anisotropic Ginzburg-Landau scaling of Hc2 and transport properties of 112-type Ca0.8La0.2Fe0.98Co0.02As2 single crystal,"High-quality single crystal of Ca0.8La0.2Fe0.98Co0.02As2 has been
successfully synthesized using a self-flux method. The magnetization
measurement reveals a second peak effect and high critical current density
exceeding 2*10^6 A/cm2 at 5 K(self-field). The upper critical field anisotropy
was systematically studied by measuring the electrical resistivity under
various magnetic fields and angles. The angle dependent magnetoresistance, by
choosing an appropriate anisotropy parameter within the framework of the
anisotropic Ginzburg Landau (AGL) theory, can be scaled onto one single curve.
In the normal state, the negative Hall coefficient shows strong but
nonmonotonic T-dependence through a minimum at 175 K. Moreover, it is shown
that the magnetoresistance apparently violates the semiclassical Kohler's rule
below 175 K but can be well scaled by the Hall angle instead. This suggests
either the change of carriers with T or the exotic anisotropic scattering in
the system.",1603.05392v1
2016-03-18,Electric-field dependent g-factor anisotropy in Ge-Si core-shell nanowire quantum dots,"We present angle-dependent measurements of the effective g-factor g* in a
Ge-Si core-shell nanowire quantum dot. g* is found to be maximum when the
magnetic field is pointing perpendicular to both the nanowire and the electric
field induced by local gates. Alignment of the magnetic field with the electric
field reduces g* significantly. g* is almost completely quenched when the
magnetic field is aligned with the nanowire axis. These findings confirm recent
calculations, where the obtained anisotropy is attributed to a Rashba-type
spin-orbit interaction induced by heavy-hole light-hole mixing. In principle,
this facilitates manipulation of spin-orbit qubits by means of a continuous
high-frequency electric field.",1603.05877v1
2016-03-21,Selection of direction of the ordered moments in Na$_2$IrO$_3$ and $α-$RuCl$_3$,"The magnetic orders in Na$_2$IrO$_3$ and $\alpha-$RuCl$_3$, honeycomb systems
with strong spin-orbit coupling and correlations, have been recently described
by models with the dominant Kitaev interactions. In this work we discuss how
the orientation of magnetic order parameter is selected in this class of
models. We show that while the order-by-disorder mechanism in the models with
solely Kitaev anisotropies always select cubic axes as easy axes for magnetic
ordering, the additional effect of other small bond-dependent anisotropies,
such as, e.g., $\Gamma$-terms, lead to a deviation of the order parameter from
the cubic directions. We show that both the zigzag ground state and the
face-diagonal orientation of magnetic moments in Na$_2$IrO$_3$ can be obtained
within the $J_1-K_1-J_2-K_2-J_3$ model in the presence of perturbatively small
$\Gamma$-terms. We also show that the zigzag phase found in the nearest
neighbor Kitaev-Heisenberg model, relevant for $\alpha-$RuCl$_3$, has some
stability against the $\Gamma$-term.",1603.06487v2
2016-03-24,Interplay of Coulomb interaction and spin-orbit coupling,"We employ the Gutzwiller variational approach to investigate the interplay of
Coulomb interaction and spin-orbit coupling in a three-orbital Hubbard model.
Already in the paramagnetic phase we find a substantial renormalization of the
spin-orbit coupling that enters the effective single-particle Hamiltonian for
the quasi-particles. Only close to half band-filling and for sizable Coulomb
interaction we observe clear signatures of Hund's atomic rules for spin,
orbital, and total angular momentum. For a finite local Hund's-rule exchange
interaction we find a ferromagnetically ordered state. The spin-orbit coupling
considerably reduces the size of the ordered moment, it generates a small
ordered orbital moment, and it induces a magnetic anisotropy. To investigate
the magnetic anisotropy energy, we use an external magnetic field that tilts
the magnetic moment away from the easy axis $(1,1,1)$.",1603.07544v3
2016-04-07,Angular distributions in $J/ψ\to p\bar{p}π^{0}(η)$ decays,"The differential decay rates of the processes $J/\psi\to p\bar{p}\pi^{0}$ and
$J/\psi\to p\bar{p}\eta$ close to the $p\bar{p}$ threshold are calculated with
the help of the $N\bar{N}$ optical potential. The same calculations are made
for the decays of $\psi(2S)$. We use the potential which has been suggested to
fit the cross sections of $N\bar{N}$ scattering together with $N\bar{N}$ and
six pion production in $e^{+}e^{-}$ annihilation close to the $p\bar{p}$
threshold. The $p\bar{p}$ invariant mass spectra is in agreement with the
available experimental data. The anisotropy of the angular distributions, which
appears due to the tensor forces in the $N\bar{N}$ interaction, is predicted
close to the $p\bar{p}$ threshold. This anisotropy is large enough to be
investigated experimentally. Such measurements would allow one to check the
accuracy of the model of $N\bar{N}$ interaction.",1604.01951v1
2016-04-04,Two-dimensional Hybrid Simulations of Kinetic Plasma Turbulence: Current and Vorticity vs Proton Temperature,"Proton temperature anisotropies between the directions parallel and
perpendicular to the mean magnetic field are usually observed in the solar wind
plasma. Here, we employ a high-resolution hybrid particle-in-cell simulation in
order to investigate the relation between spatial properties of the proton
temperature and the peaks in the current density and in the flow vorticity. Our
results indicate that, although regions where the proton temperature is
enhanced and temperature anisotropies are larger correspond approximately to
regions where many thin current sheets form, no firm quantitative evidence
supports the idea of a direct causality between the two phenomena. On the other
hand, quite a clear correlation between the behavior of the proton temperature
and the out-of-plane vorticity is obtained.",1604.03040v1
2016-04-21,Anisotropy and interaction effects of strongly strained SrIrO3 thin films,"Magneto-transport properties of SrIrO$_3$ thin films epitaxially grown on
SrTiO$_3$, using reactive RF sputtering, are investigated. A large anisotropy
between the in-plane and the out-of-plane resistivities is found, as well as a
signature of the substrate cubic to tetragonal transition. Both observations
result from the structural distortion associated to the epitaxial strain. The
low-temperature and field dependences of the Hall number are interpreted as due
to the contribution of Coulomb interactions to weak localization, evidencing
the strong correlations in this material. The introduction of a contribution
from magnetic scatters, in the analysis of magnetoconductance in the weakly
localized regime, is proposed as an alternative to an anomalously large
temperature dependence of the Land\'{e} coefficient.",1604.06390v2
2016-04-25,Non-Gaussian eccentricity fluctuations,"We study the fluctuations of the anisotropy of the energy density profile
created in a high-energy collision at the LHC. We show that the anisotropy in
harmonic $n$ has generic non-Gaussian fluctuations. We argue that these
non-Gaussianities have a universal character for small systems such as p+Pb
collisions, but not for large systems such as Pb+Pb collisions where they
depend on the underlying non-Gaussian statistics of the initial density
profile. We generalize expressions for the eccentricity cumulants
$\varepsilon_2\{4\}$ and $\varepsilon_3\{4\}$ previously obtained within the
independent-source model to a general fluctuating initial density profile.",1604.07230v2
2016-04-28,"Magnetization Saturation Process in the Magnonic Anti-dot Structures Based on (Ga,Mn)As: A Magnetometric Study","Applicability of dilute magnetic semiconductors (DMS) in electronic devices
relies upon the understanding and control of their magnetic anisotropy. This
paper explores one of the ways in engineering magnetic anisotropy in epitaxial
layers of DMS by forming them into magnonic structures. For this purpose the
canonical ferromagnetic DMS, namely (Ga,Mn)As, is employed. The anti-dot
systems based on (Ga,Mn)As layers of various thicknesses are fabricated with
focused ion beam apparatus and studied by means of microscopy as well as
magnetometry. The magnetometric data - collected along two nonequivalent
in-plane crystallographic directions of (Ga,Mn)As: [110] and [1-10] - shows the
effect of structuring on high-field magnetization process, whereas no
significant change of the width of hysteresis loop in anti-dot samples is
observed.",1604.08607v1
2016-04-29,Polarization-selective branching of stop gaps in three-dimensional photonic crystals,"We study the direction- and wavelength-dependent polarization anisotropy in
light scattering at the air-photonic crystal interface as a function of angle
of incidence for TE and TM polarized light. This is done using optical
reflectivity measurements at high-symmetry points in the Brillouin zone of a
three-dimensional photonic crystal with fcc symmetry. Polarized reflectivity
measurements indicate the presence of stop gap branching for TE polarization,
which is absent for TM polarization till the Brewster angle at K point. In
contrast, stop gap branching is present for both TE and TM polarizations at W
point due to the intricate mixing of crystal planes. This characteristic
behavior signifies the inevitable role of energy exchange in the stop gap
branching. The measured polarization anisotropy shows a prominent shift in the
Brewster angle for on-resonance wavelength as compared to the off-resonance
along both K and W points, and that, in accordance with theory. Our results
have implications in polarization-induced light scattering in sub-wavelength
photonic structures like plasmonic crystals, and meta-materials.",1604.08889v1
2016-05-04,Quantum domain walls induce incommensurate supersolid phase on the anisotropic triangular lattice,"We investigate the extended hard-core Bose-Hubbard model on the triangular
lattice as a function of spatial anisotropy with respect to both tunneling and
nearest-neighbor interaction strength. At half-filling the system can be tuned
from decoupled one-dimensional chains to a two-dimensional solid phase with
alternating density order by adjusting the anisotropic coupling. At
intermediate anisotropy, however, frustration effects dominate and an
incommensurate supersolid phase emerges, which is characterized by
incommensurate density order as well as an anisotropic superfluid density. We
demonstrate that this intermediate phase results from the proliferation of
topological defects in the form of quantum bosonic domain walls. Accordingly,
the structure factor has peaks at wave vectors, which are linearly related to
the number of domain walls in a finite system in agreement with extensive
quantum Monte Carlo simulations. We discuss possible connections with the
supersolid behavior in the high-temperature superconducting striped phase.",1605.01237v2
2016-05-08,Cage effect in supercooled molecular liquids: local anisotropies and collective solid-like response,"Both local geometry and collective, extended excitations drive the moves of a
particle in the cage of its neighbours in dense liquids. The strength of their
influence is investigated by Molecular Dynamics simulations of a supercooled
liquid of fully-flexible trimers with semirigid or rigid bonds. The rattling in
the cage is investigated on different length scales. First, the rattling
anisotropy due to local order is characterized by two order parameters sensing
the monomers succeeding or failing to escape from the cage. Then, the
collective response of the surroundings excited by the monomer-monomer
collisions is considered. The collective response is initially restricted to
the nearest neighbours of the colliding particle by a Voronoi analysis
revealing elastic contributions. Then, the long-range excitation of the
farthest neighbours is scrutinised by searching spatially-extended correlations
between the simultaneous fast displacements of the caged particle and the
surroundings. It is found that the longitudinal component has stronger spatial
modulation than the transverse one with wavelength of about one particle
diameter, in close resemblance with experimental findings on colloids. It is
concluded that the cage rattling is largely affected by solid-like extended
modes.",1605.02318v1
2016-05-11,Quasi-matter bounce and inflation in the light of the CSL model,"The Continuous Spontaneous Localization (CSL) model has been proposed as a
possible solution to the quantum measurement problem by modifying the
Schr\""{o}dinger equation. In this work, we apply the CSL model to two
cosmological models of the early Universe: the matter bounce scenario and slow
roll inflation. In particular, we focus on the generation of the classical
primordial inhomogeneities and anisotropies that arise from the dynamical
evolution, provided by the CSL mechanism, of the quantum state associated to
the quantum fields. In each case, we obtained a prediction for the shape and
the parameters characterizing the primordial spectra (scalar and tensor), i.e.
the amplitude, the spectral index and the tensor-to-scalar ratio. We found that
there exist CSL parameter values, allowed by other non-cosmological
experiments, for which our predictions for the angular power spectrum of the
CMB temperature anisotropy are consistent with the best fit canonical model to
the latest data released by the Planck Collaboration.",1605.03632v2
2016-05-14,Highly anisotropic electronic transport properties of monolayer and bilayer phosphorene from first principles,"The intrinsic carrier transport dynamics in phosphorene is theoretically
examined. Utilizing a density functional theory treatment, the low-field
mobility and the saturation velocity are characterized for both electrons and
holes in the monolayer and bilayer structures. The analysis clearly elucidates
the crystal orientation dependence manifested through the anisotropic band
structure and the carrier-phonon scattering rates. In the monolayer, the hole
mobility in the armchair direction is estimated to be approximately five times
larger than in the zigzag direction at room temperature (460 cm$^2$/Vs vs. 90
cm$^2$/Vs). The bilayer transport, on the other hand, exhibits a more modest
anisotropy with substantially higher mobilities (1610 cm$^2$/Vs and 760
cm$^2$/Vs, respectively). The calculations on the conduction-band electrons
indicate a comparable dependence while the characteristic values are generally
smaller by about a factor of two. The variation in the saturation velocity is
found to be less pronounced. With the anticipated superior performance and the
diminished anisotropy, few-layer phosphorene offers a promising opportunity
particularly in p-type applications.",1605.04377v1
2016-05-17,Quantum Spin Liquid in a Breathing Kagome Lattice,"Motivated by recent experiments on the vanadium oxyfluoride material DQVOF,
we examine possible spin liquid phases on a breathing kagome lattice of S=1/2
spins. By performing a projective symmetry group analysis, we determine the
possible phases for both fermionic and bosonic $\mathbb{Z}_2$ spin liquids on
this lattice, and establish the correspondence between the two. The nature of
the ground state of the Heisenberg model on the isotropic kagome lattice is a
hotly debated topic, with both $\mathbb{Z}_2$ and U(1) spin liquids argued to
be plausible ground states. Using variational Monte Carlo techniques, we show
that a gapped $\mathbb{Z}_2$ spin liquid emerges as the clear ground state in
the presence of this breathing anisotropy. Our results suggest that the
breathing anisotropy helps to stabilize this spin liquid ground state, which
may aid us in understanding the results of experiments and help to direct
future numerical studies on these systems.",1605.05322v1
2016-05-18,A Framework for FFT-based Homogenization on Anisotropic Lattices,"In order to take structural anisotropies of a given composite and different
shapes of its unit cell into account, we generalize the Basic Scheme in
Homogenization by Moulinec and Suquet to arbitrary sampling lattices and
tilings of the d-dimensional Euclidean space. Employing a Fourier transform on
arbitrary lattices, which generate sampling patterns in the unit cell of
interest, we derive a generalization of this scheme. In several cases, this
Fourier transform is of lower dimension than the space itself; for many
lattices it even reduces to a one-dimensional Fourier transform having the same
leading coefficient as the fastest Fourier transform implementation available.
We illustrate the generalized Basic Scheme on an anisotropic laminate and a
generalized ellipsoidal Hashin structure. For both we derive an analytical
solution to the elasticity problem, in two- and three dimensions, respectively.
We then illustrate the possibilities of choosing a pattern. Compared to
classical grids this introduces both a reduction of computation time and a
reduced error of the numerical method. It also allows for anisotropic
subsampling, i.e. choosing a sub lattice of a pixel or voxel grid based on
anisotropy information of the material at hand.",1605.05712v2
2016-05-25,Squeeze expulsion in grain size segregation,"Grain segregation occurs under various conditions, such as vibration, shear
and mixing. In the gravity-driven shear flow, size segregation is triggered by
the percolation of small particles through the opened voids (kinetic sieving),
and large particles are accumulated in the upper layer. One hypothesis for the
upward migration of large particles is the squeeze expulsion mechanism, which
remains yet ambiguous due to limited evidences from either physical or
numerical experiments. Here we show statistically how the percolation of small
particles facilitates the upward movement of large particles. We found that in
large particles, the mechanical anisotropy (strong force network) coincides
with the geometric anisotropy (contact network), which indicates squeeze, and
the connectivity of large particles is much higher when they are squeezed
through small particles. The presence of small particles filling the voids
hinders the downward movements and provides dynamic steps for the climbing
large particles. Furthermore, increasing the coefficient of friction promotes
rotation and empowers more large particles to reach the top layer, implying
that the climbing particles tend to rotate relative to their neighbors. Our
findings of the microstructure and movement pattern of individual particles add
new evidences to the mechanism of squeeze expulsion and provide new perspective
for the study of segregation.",1605.07994v1
2016-05-26,Handling magnetic anisotropy and dynamic magnetic response of ferromagnetic multilayers in flexible substrates,"We investigate the dynamic magnetic response of ferromagnetic flexible
NiFe/Ta and FeCuNbSiB/Ta multilayers under external stress. We explore the
possibility of handling magnetic anisotropy and dynamic magnetic response of
flexible magnetostrictive nanostructures. We quantify the sensitivity of the
multilayers under external stress by calculating the ratio $|\Delta
\textrm{MI}|/|\Delta \bar{\sigma}|$ and show that considerable values can be
reached by tuning the magnetic field, frequency, magnetostriction constant, and
external stress. The results reveal possibilities of application of flexible
magnetostrictive multilayers under external stress and place them as very
attractive candidates as element sensor for the development of sensitive smart
touch sensors.",1605.08193v2
2016-05-29,Universality of fractal to non-fractal morphological transitions in stochastic growth processes,"Stochastic growth processes give rise to diverse intricate structures
everywhere and across all scales in nature. Despite the seemingly unrelated
complex phenomena at their origin, the Laplacian growth theory has succeeded in
unifying their treatment under one framework, nonetheless, important aspects
regarding fractal to non-fractal morphological transitions, coming from the
competition between screening and anisotropy-driven forces, still lacks a
comprehensive description. Here we provide such unified description,
encompassing all the known characteristics for these transitions, as well as
new universal ones, through the statistical mix of basic models of
particle-aggregation and the introduction of a phenomenological physically
meaningful dimensionality function, that characterizes the fractality of a
symmetry-breaking process induced by a generalized anisotropy-driven force. We
also show that the generalized Laplacian growth (dielectric breakdown) model
belongs to this class. Moreover, our results provide important insights on the
dynamical origins of mono/multi-fractality in pattern formation, that generally
occur in far-from-equilibrium processes.",1605.08967v1
2016-05-31,Anisotropy-assisted non-scattering coherent absorption of surface plasmon-polaritons,"The ability to control propagation of electromagnetic guided modes lies at
the heart of integrated nanophotonics. Surface plasmon-polaritons are a class
of guided modes which can be employed in integrated optical systems. Here, we
present a theoretical design of a coherent surface plasmon absorber which can
perfectly harvest energy of coherently incident surface plasmons without
parasitic scattering into free space modes. Excitation of free space modes
which usually accompanies scattering of a surface plasmon by an interface
boundary is avoided due to specially tailored anisotropy of the absorber. The
concept of coherent SPP absorber is analyzed numerically for spatially
non-uniform and finite-size structures. We believe that our results will be
important for the development of integrated nanoplasmonic systems.",1606.00027v1
2016-06-02,"Bicollinear Antiferromagnetic Order, Monoclinic Distortion, and Reversed Resistivity Anisotropy in FeTe as a Result of Spin-Lattice Coupling","The bicollinear antiferromagnetic order experimentally observed in FeTe is
shown to be stabilized by the coupling $\tilde g_{12}$ between monoclinic
lattice distortions and the spin-nematic order parameter with $B_{\rm 2g}$
symmetry, within a three-orbital spin-fermion model studied with Monte Carlo
techniques. A finite but small value of $\tilde g_{12}$ is required, with a
concomitant lattice distortion compatible with experiments, and a
tetragonal-monoclinic transition strongly first order. Remarkably, the
bicollinear state found here displays a planar resistivity with the ""reversed""
puzzling anisotropy discovered in transport experiments.Orthorhombic
distortions are also incorporated and phase diagrams interpolating between
pnictides and chalcogenides are presented. We conclude that the spin-lattice
coupling discussed here is sufficient to explain the challenging properties of
FeTe.",1606.00904v1
2016-06-03,The effect of anisotropy on the absorption spectrum and the density of states of two-dimensional Frenkel exciton systems with Gaussian diagonal disorder,"On the optical absorption and the density of states of Frenkel exciton
systems on square, rectangular, and triangular lattices with nearest-neighbor
interactions and a Gaussian distribution of transition frequencies. The
analysis is based on an elliptic integral approach that gives results over the
entire spectrum. It is found that the absorption is weakly affected by the
anisotropy in contrast to the density of states where the effects can be much
stronger. The results for the square lattice are in good agreement with the
finite array calculations of Schreiber and Toyozawa. Our findings suggest that
the coherent potential approximation can be useful in interpreting the optical
properties of two-dimensional systems with dominant nearest-neighbor
interactions and Gaussian diagonal disorder where the optically excited states
are Frenkel excitons.",1606.01130v1
2016-06-03,Experimental demonstration of acoustic wave induced magnetization switching of dipole coupled magnetostrictive nanomagnets for ultralow power computing,"We report nanomagnetic switching with Acoustic Waves (AW) launched from
interdigitated electrodes that modulate the stress anisotropy of elliptical
cobalt nanoscale magnetostrictive magnets (340 nm x 270 nm x 12 nm) delineated
on 128 degree Y-cut lithium niobate. The dipole-coupled nanomagnet pairs are in
a single-domain state and are initially magnetized along the major axis of the
ellipse, with their magnetizations parallel to each other. The magnetizations
of nanomagnets having lower shape anisotropy are reversed upon acoustic wave
propagation. Thereafter, the magnetization of these nanomagnets remains in the
reversed state and demonstrate non-volatility. This executes a 'NOT' operation.
This proof of acoustic wave induced magnetic state reversal in dipole-coupled
nanomagnets implementing a 'NOT' gate operation could potentially lead to the
development of extremely energy-efficient nanomagnetic logic. Furthermore,
fabrication complexity is reduced immensely due to the absence of individual
contacts to the nanomagnets, leading to lower energy dissipation",1606.01303v1
2016-06-12,Probing primordial features with future galaxy surveys,"We study the capability of future measurements of the galaxy clustering power
spectrum to probe departures from a power-law spectrum for primordial
fluctuations. On considering the information from the galaxy clustering power
spectrum up to quasi-linear scales, i.e. $k<0.1$ h Mpc$^{-1}$, we present
forecasts for DESI, Euclid and SPHEREx in combination with CMB measurements. As
examples of departures in the primordial power spectrum from a simple
power-law, we consider four $Planck$ 2015 best-fits motivated by inflationary
models with different breaking of the slow-roll approximation. These four
representative models provide an improved fit to CMB temperature anisotropies,
although not at statistical significant level. As for other extensions in the
matter content of the simplest $\Lambda$CDM model, the complementarity of the
information in the resulting matter power spectrum expected from these galaxy
surveys and in the primordial power spectrum from CMB anisotropies can be
effective in constraining cosmological models. We find that the three galaxy
surveys can add significant information to CMB to better constrain the extra
parameters of the four models considered.",1606.03747v3
2016-06-20,Effective realization of random magnetic fields in compounds with large single-ion anisotropy,"We show that spin $S=1$ system with large and random single--ion anisotropy
can be at low energies mapped to a $S=1/2$ system with random magnetic fields.
This is for example realized in
\mbox{Ni(Cl$_{1-x}$Br$_{x}$)$_2$-4SC(NH$_2$)$_2$} compound (DTNX) and therefore
it represents a long sought realization of random local (on-site) magnetic
fields in antiferromagnetic systems. We support the mapping by numerical study
of $S=1$ and effective $S=1/2$ anisotropic Heisenberg chains and find excellent
agreement for static quantities and also for the spin conductivity. Such
systems can therefore be used to study the effects of local random magnetic
fields on transport properties.",1606.06013v2
2016-06-28,Zeeman splitting of conduction band in HgTe quantum wells near the Dirac point,"The Zeeman splitting of the conduction band in the HgTe quantum wells both
with normal and inverted spectrum has been studied experimentally in a wide
electron density range. The simultaneous analysis of the SdH oscillations in
low magnetic fields at different tilt angles and of the shape of the
oscillations in moderate magnetic fields gives a possibility to find the ratio
of the Zeeman splitting to the orbital one and anisotropy of g-factor. It is
shown that the ratios of the Zeeman splitting to the orbital one are close to
each other for both types of structures, with a normal and inverted spectrum
and they are close enough to the values calculated within kP method. In
contrast, the values of g-factor anisotropy in the structures with normal and
inverted spectra is strongly different and for both cases differs significantly
from the calculated ones. We believe that such disagreement with calculations
is a result of the interface inversion asymmetry in the HgTe quantum well,
which is not taken into account in the kP calculations.",1606.08614v2
2016-07-11,Heavy hole states in Germanium hut wires,"Hole spins have gained considerable interest in the past few years due to
their potential for fast electrically controlled qubits. Here, we study holes
confined in Ge hut wires, a so far unexplored type of nanostructure. Low
temperature magnetotransport measurements reveal a large anisotropy between the
in-plane and out-of-plane g-factors of up to 18. Numerical simulations verify
that this large anisotropy originates from a confined wave function which is of
heavy hole character. A light hole admixture of less than 1% is estimated for
the states of lowest energy, leading to a surprisingly large reduction of the
out-of-plane g-factors. However, this tiny light hole contribution does not
influence the spin lifetimes, which are expected to be very long, even in non
isotopically purified samples.",1607.02977v1
2016-07-19,Magnetic anisotropy in the Kitaev model systems Na2IrO3 and RuCl3,"We study the ordered moment direction in the extended Kitaev-Heisenberg model
relevant to honeycomb lattice magnets with strong spin-orbit coupling. We
utilize numerical diagonalization and analyze the exact cluster groundstates
using a particular set of spin coherent states, obtaining thereby quantum
corrections to the magnetic anisotropy beyond conventional perturbative
methods. It is found that the quantum fluctuations strongly modify the moment
direction obtained at a classical level, and are thus crucial for a precise
quantification of the interactions. The results show that the moment direction
is a sensitive probe of the model parameters in real materials. Focusing on the
experimentally relevant zigzag phases of the model, we analyze the currently
available neutron and resonant x-ray diffraction data on Na2IrO3 and RuCl3, and
discuss the parameter regimes plausible in these Kitaev-Heisenberg model
systems.",1607.05676v2
2016-08-12,NMR study of nematic spin fluctuations in a detwinned single crystal of underdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$,"We report the experimental details of how mechanical detwinning can be
implemented in tandem with high sensitivity nuclear magnetic resonance
measurements and use this setup to measure the in-plane anisotropy of the
spin-lattice relaxation rate in underdoped Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$
with $x=0.048$. The anisotropy reaches a maximum of 30\% at $T_{N}$, and the
recovery data reveal that the glassy behavior of the spin fluctuations present
in the twinned state persist in the fully detwinned crystal. A theoretical
model is presented to describe the spin-lattice relaxation rate in terms of
anisotropic nematic spin fluctuations.",1608.03899v1
2016-08-15,Anisotropic Hanle lineshape via anisotropic magnetothermoelectric phenomena,"We observe anisotropic Hanle lineshape with unequal in-plane and out-of-plane
non-local signals for spin precession measurements carried out on lateral
metallic spin valves with transparent interfaces. The conventional
interpretation for this anisotropy corresponds to unequal spin relaxation times
for in-plane and out-of-plane spin orientations as for the case of 2D materials
like graphene, but it is unexpected in a polycrystalline metallic channel.
Systematic measurements as a function of temperature and channel length,
combined with both analytical and numerical thermoelectric transport models,
demonstrate that the anisotropy in the Hanle lineshape is magneto-thermal in
origin, caused by the anisotropic modulation of the Peltier and Seebeck
coefficients of the ferromagnetic electrodes. Our results call for the
consideration of such magnetothermoelectric effects in the study of anisotropic
spin relaxation.",1608.04420v2
2016-08-16,Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains,"We investigate the spin-stripe mechanism responsible for the peculiar
nanometer modulation of the incommensurate magnetic order that emerges between
the vector-chiral and the spin-density-wave phase in the frustrated zigzag
spin-1/2 chain compound $\beta$-TeVO$_4$. A combination of magnetic-torque,
neutron-diffraction and spherical-neutron-polarimetry measurements is employed
to determine the complex magnetic structures of all three ordered phases. Based
on these results, we develop a simple phenomenological model, which exposes the
exchange anisotropy as the key ingredient for the spin-stripe formation in
frustrated spin systems.",1608.04495v2
2016-08-16,High anisotropy of fully hydrogenated borophene,"We have studied the mechanical properties and phonon dispersions of fully
hydrogenated borophene (borophane) under strains by first principles
calculations. Uniaxial tensile strains along the a- and b-direction,
respectively, and biaxial tensile strain have been considered. Our results show
that the mechanical properties and phonon stability of borophane are both
highly anisotropic. The ultimate tensile strain along the a-direction is only
0.12, but it can be as large as 0.30 along the b-direction. Compared to
borophene and other 2D materials (graphene, graphane, silicene, silicane, h-BN,
phosphorene and MoS2), borophane presents the most remarkable anisotropy in
in-plane ultimate strain, which is very important for strain engineering.
Furthermore, the phonon dispersions under the three applied strains indicate
that borophane can withstand up to 5% and 15% uniaxial tensile strain along the
a- and b-direction, respectively, and 9% biaxial tensile strain, indicating
that mechanical failure in borophane is likely to originate from phonon
instability.",1608.04788v2
2016-08-19,Quantized conductance and large g-factor anisotropy in InSb quantum point contacts,"Due to a strong spin-orbit interaction and a large Land\'e g-factor, InSb
plays an important role in research on Majorana fermions. To further explore
novel properties of Majorana fermions, hybrid devices based on quantum wells
are conceived as an alternative approach to nanowires. In this work, we report
a pronounced conductance quantization of quantum point contact devices in
InSb/InAlSb quantum wells. Using a rotating magnetic field, we observe a large
in-plane (|g1|=26) and out-of-plane (|g1|=52) g-factor anisotropy.
Additionally, we investigate crossings of subbands with opposite spins and
extract the electron effective mass from magnetic depopulation of
one-dimensional subbands.",1608.05478v1
2016-08-19,Progressive magnetic softening of ferromagnetic layers in multilayer ferromagnet-nonmagnet systems and the role of granularity,"We report a study of the structural and magnetic behavior of the topmost
magnetic layer in a ferromagnet-nonmagnet (Co-Au) multilayer system. Glancing
angle X-ray diffraction measurements performed on a series of multilayers
showed a gradually increasing degree of amorphization of the topmost magnetic
layer with increasing number of bilayers. Concurrently, the magnetic hardness
and magneto-crystalline anisotropy of the top Co layer were found to decrease,
as observed by magneto-optical Kerr effect measurements. This magnetic
softening has been discussed in the light of Herzer's random anisotropy model.
Micromagnetic simulations of the multilayer system also corroborated these
observations.",1608.05568v5
2016-08-23,Anisotropy-Induced Quantum Interference and Population Trapping Between Orthogonal Quantum Dot Exciton States in Semiconductor Cavity Systems,"We describe how quantum dot semiconductor cavity systems can be engineered to
realize anisotropy-induced dipole-dipole coupling between orthogonal dipole
states in a single quantum dot. Quantum dots in single-mode cavity structures
as well as photonic crystal waveguides coupled to spin states or linearly
polarized excitons are considered. We demonstrate pronounced dipole-dipole
coupling to control the radiative decay rate of excitons and form pure
entangled states in the long time limit. We investigate both field-free
entanglement evolution and coherently pumped exciton regimes, and show how a
double pumping scenario can completely eliminate the decay of coherent Rabi
oscillations and lead to population trapping. In the Mollow regime, we explore
the emitted spectra from the driven dipoles and show how a non-pumped dipole
can take on the form of a spectral triplet, quintuplet, or a singlet, which has
applications for producing subnatural linewidth single photons and more easily
accessing regimes of high-field quantum optics and cavity-QED.",1608.06650v3
2016-08-15,An approach to directly probe simultaneity,"The theory of special relativity derives from the Lorentz transformation. The
Lorentz transformation implies differential simultaneity and light speed
isotropy. Experiments to probe differential simultaneity should be able to
distinguish the Lorentz transformation from a kinematically-similar alternate
transformation that predicts absolute simultaneity, the absolute Lorentz
transformation. Here, we describe how published optical tests of light speed
isotropy/anisotropy cannot distinguish between the two transformations. We show
that the shared equations of the two transformations, from the perspective of
the ""stationary"" observer, are sufficient to predict null results in optical
resonator experiments and in tests of frequency changes in one-way light paths.
In an influential 1910 exposition on differential simultaneity, Comstock
described how a ""stationary"" observer would observe different clock readings
for spatially-separated ""moving"" clocks. The difference in clock readings is an
integral aspect of differential simultaneity. We derive the equation for the
difference in clock readings and show that it is equivalent to the Sagnac
correction that describes light speed anisotropies in satellite communications.
We describe an experimental strategy that can measure the differences in
spatially-separated clock times to allow a direct probe of the nature of
simultaneity.",1608.08516v1
2016-08-31,Tidal disruption rates in non-spherical galactic nuclei formed by galaxy mergers,"We explore the rates of tidal disruption events (TDEs) of stars by
supermassive black holes (SBHs) in galactic nuclei formed in mergers followed
by a formation and coalescence of a binary SBH. Such systems initially have a
deficit of stars on low-angular-momentum orbits caused by the slingshot process
during the binary SBH stage, which tends to reduce the flux of stars into the
SBH compared to the steady-state value. On the other hand, a newly formed
galactic nucleus has a non-spherical shape which enhances the mixing of stars
in angular momentum and thus the TDE rate. In galaxies with relatively low SBH
masses (<10^7 Msun), relaxation times are short enough to wash out the
anisotropy in initial conditions, and for more massive SBH the enhancement of
flux due to non-sphericity turns out to be more important than its suppression
due to initial anisotropy. Therefore, the present-day TDE rates generally
exceed conventional steady-state estimates based on a spherical isotropic
approximation. We thus conjecture that the lower observationally inferred TDE
rates compared to theoretical predictions cannot be attributed to the depletion
of low-angular-momentum stars by SBH binaries.",1609.00009v1
2016-09-07,Anisotropic dependence of tune-out wavelength near Dy 741-nm transition,"We report the first measurement of a tune-out wavelength for ground-state
bosonic Dy and linearly polarized light. The tune-out wavelength measured is
near the narrow-line 741-nm transition in $^{162}$Dy, and is the wavelength at
which the total Stark shift of the ground state vanishes. We find that it
strongly depends on the relative angle between the optical field and
quantization axis due to Dy's large tensor polarizability. This anisotropy
provides a wide, 22-GHz tunability of the tune-out frequency for linearly
polarized light, in contrast to Rb and Cs whose near-infrared tune-out
wavelengths do not exhibit large anisotropy. The measurements of the total
light shift are performed by measuring the contrast of multipulse Kapitza-Dirac
diffraction. The calculated wavelengths are within a few GHz of the measured
values using known Dy electronic transition data. The lack of hyperfine
structure in bosonic Dy implies that the tune-out wavelengths for the other
bosonic Dy isotopes should be related to this $^{162}$Dy measurement by the
known isotope shifts.",1609.02111v1
2016-09-12,Currentless reversal of Néel vector in antiferromagnets,"The bias driven perpendicular magnetic anisotropy is a magneto-electric
effect that can realize 90$^\circ$ magnetization rotation and even 180$% ^\circ
$ flip along the easy axis in the ferromagnets with a minimal energy
consumption. This study theoretically demonstrates a similar phenomenon of the
N\'{e}el vector reversal via a short electrical pulse that can mediate
perpendicular magnetic anisotropy in the antiferromagnets. The analysis based
on the dynamical equations as well as the micro-magnetic simulations reveals
the important role of the inertial behavior in the antiferromagnets that
facilitates the N\'{e}el vector to overcome the barrier between two free-energy
minima of the bistable states along the easy axis. In contrast to the
ferromagnets, this N\'{e}el vector reversal does not accompany angular moment
transfer to the environment, leading to acceleration in the dynamical response
by a few orders of magnitude. Further, a small switching energy requirement of
a few attojoules illustrates an added advantage of the phenomenon in low-power
spintronic applications.",1609.03454v2
2016-09-13,Spin-flop transition accompanied with changing the type of magnetic ordering,"We discuss theoretically rather rear example of spin-flop transition which is
accompanied with changing the type of magnetic ordering and which seemingly has
not been addressed yet. We demonstrate that changing the type of magnetic
ordering can manifest itself in antiferromagnetic (AF) resonance experiments as
an apparent peculiar switching of the anisotropy at the transition from the
easy-axis type to the easy-plane one. We argue that this kind of spin-flop
transition is observed recently by K.Yu. Povarov et al., Phys. Rev. B 87,
214402 (2013) in Cu(pz)$_2$(ClO$_4$)$_2$ (where pz denotes pyrazine), one of
the best realizations of spin-1/2 Heisenberg AFs on square lattice having a
very small anisotropy. We show that the magnetic ordering changes at the
spin-flop transition in this material in the direction perpendicular to AF
square planes. We examine the microscopic mechanism of such behavior in
Cu(pz)$_2$(ClO$_4$)$_2$ and find that dipolar forces and extremely small
exchange coupling between spins from neighboring planes are responsible for it.",1609.03702v2
2016-09-16,High-pressure study of the basal-plane anisotropy of the upper critical field of the topological superconductor SrxBi2Se3,"We report a high-pressure transport study of the upper-critical field,
$B_{c2}(T)$, of the topological superconductor Sr$_{0.15}$Bi$_2$Se$_3$ ($T_c =
3.0$ K). $B_{c2}(T)$ was measured for magnetic fields directed along two
orthogonal directions, $a$ and $a^*$, in the trigonal basal plane. While
superconductivity is rapidly suppressed at the critical pressure $p_c \sim 3.5$
GPa, the pronounced two-fold basal-plane anisotropy $B_{c2}^a/B_{c2}^{a^*} =
3.2$ at $T=0.3$ K, recently reported at ambient pressure (Pan et al., 2016), is
reinforced and attains a value of $\sim 5$ at the highest pressure (2.2 GPa).
The data reveal that the unconventional superconducting state with broken
rotational symmetry is robust under pressure.",1609.04945v1
2016-09-20,Anomalous Hall hysteresis in Tm3Fe5O12/Pt with strain-induced perpendicular magnetic anisotropy,"We demonstrate robust interface strain-induced perpendicular magnetic
anisotropy in atomically flat ferrimagnetic insulator Tm3Fe5O12 films grown
with pulsed laser deposition on substituted-Gd3Ga5O12 substrate which maximizes
the tensile strain at the interface. In bilayers consisting of Pt and TIG, we
observe large squared Hall hysteresis loops over a wide range of thicknesses of
Pt at room temperature. When a thin Cu layer is inserted between Pt and TIG,
the Hall hysteresis magnitude decays but stays finite as the thickness of Cu
increases up to 5 nm. However, if the Cu layer is placed atop Pt instead, the
Hall hysteresis magnitude is consistently larger than when the Cu layer with
the same thickness is inserted in between for all Cu thicknesses. These results
suggest that both the proximity-induced ferromagnetism and spin current
contribute to the anomalous Hall effect.",1609.06367v1
2016-09-27,First-principles studies of the Optical anisotropy of R3 space group chalcogenides crystal AX2MQ6,"In order to explain the reason that all the sythesised \ce{AX2MQ6}
chalcogenides compounds are phase-matching while isomorphic chalcogenides
compounds \ce{AX4M5Q12} are not phase-matched materials. The linear optical
property birefringence and non-linear optical property of $R3$ space group
crystals \ce{AX2MQ6} have been calculated to compare with \ce{AX4M5Q12}. Their
Electron Localization Function(ELF) was calculated to show that the acentricity
of the bonds on $sp^3$ hybridization \ce{Q^2-} ions is the main origin of
optical anisotropy. To quantificat the acentricity, a geometric parameter
dihedral angle between tetrahedral undersides and xy-planes was defined. We
find theoretically the birefringence depend on the defined geometric parameter
and ion radius. This relation between birefringence and structure resonalbly
explain the abnormal difference of birefringence of isostructural \ce{AX2MQ6}
and \ce{AX4M5Q12} and useful for exploring new phase-matching IR-NLO crystals.",1609.08243v3
2016-09-27,Inverted anisotropy in the in-plane dissipation of BSCCO tapes: preliminary results,"The electrical properties of superconducting tapes and coatings in the
direction transverse to the long dimension of the composite has been rarely
studied. However, transverse dissipation can eventually determine the behavior
of a transmission line in the case of failure due to the presence of
transversal cracks, and is also fundamental in the AC regime. In this paper we
present a preliminary experimental study of the electrical transport properties
along the transverse direction of BSCCO-metal tapes, and compare them with
those measured along the long axis of the material. In spite of the fact that
the tapes under study are not multi-filamentary, our experiments suggest that
there is a measurable anisotropy of the transport properties between the
longitudinal and transverse directions.",1609.08662v1
2016-09-30,Simultaneous control of the Dzyaloshinskii-Moriya interaction and magnetic anisotropy in nanomagnetic trilayers,"Magneto-optical Kerr effect (MOKE) microscopy measurements of magnetic bubble
domains demonstrate that Ar+ irradiation around 100 eV can tune the
Dzyaloshinskii-Moriya interaction (DMI) in Pt/Co/Pt trilayers. Varying the
irradiation energy and dose changes the DMI sign and magnitude separately from
the magnetic anisotropy, allowing tuning of the DMI while holding the coercive
field constant. This simultaneous control emphasizes the different physical
origins of these effects. To accurately measure the DMI, we propose and apply a
physical model for a poorly understood peak in domain wall velocity at zero
in-plane field. The ability to tune the DMI with the spatial resolution of the
Ar+ irradiation enables new fundamental investigations and technological
applications of chiral nanomagnetics.",1609.09790v2
2016-10-01,Pumping electrons in graphene to the $\mathbf{M}$-point in the Brillouin zone: The emergence of anisotropic plasmons,"We consider the existence of plasmons in a non-equilibrium situation where
electrons from the valence band of graphene are pumped to states in the
Brillouin zone around the $\mathbf{M}$-point by a high intensity UV
electromagnetic field. The resulting out-of-equilibrium electron gas is later
probed by a weak electromagnetic field of different frequency. We show that the
optical properties of the system and the dispersion of the plasmons are
strongly anisotropic, depending on the pumping radiation properties: its
intensity, polarization, and frequency. This anisotropy has its roots in the
saddle-like nature of the electronic dispersion relation around that particular
point in the Brillouin zone.
  It is found that despite the strong anisotropy, the dispersion of the
plasmons scales with the square root of the wave number but is characterized an
effective Fermi energy, which depends on the properties of the pumping
radiation. Our calculations go beyond the usual Dirac cone approximation taking
the full band structure of graphene into account. This is a necessary condition
for discussing plasmons at the $\mathbf{M}$-point in the Brillouin zone.",1610.00162v1
2016-10-03,The first moment of azimuthal anisotropy in nuclear collisions from AGS to LHC energies,"We review topics related to the first moment of azimuthal anisotropy ($v_1$),
commonly known as directed flow, focusing on both charged particles and
identified particles from heavy-ion collisions. Beam energies from the highest
available, at the CERN LHC, down to projectile kinetic energies per nucleon of
a few GeV per nucleon, as studied in experiments at the Brookhaven AGS, fall
within our scope. We focus on experimental measurements and on theoretical work
where direct comparisons with experiment have been emphasized. The physics
addressed or potentially addressed by this review topic includes the study of
Quark Gluon Plasma, and more generally, investigation of the Quantum
Chromodynamics phase diagram and the equation of state describing the
accessible phases.",1610.00646v1
2016-10-06,Flat bands and Dirac cones in breathing lattices,"In breathing pyrochlores and kagomes, couplings between neighbouring
tetrahedra and triangles are free to differ. Breathing lattices thus offer the
possibility to explore a different facet of the rich physics of these systems.
Here we consider nearest-neighbour classical Heisenberg interactions, both
ferromagnetic and antiferromagnetic, and study how the anisotropy of breathing
lattices modifies the mode spectrum of pyrochlore and kagome systems. The
nature and degeneracy of the flat bands are shown to be preserved for any value
of the anisotropy. These flat bands can coexist with Dirac nodes at the
$\Gamma$ point when the model becomes particle-hole symmetric. We also derive
the nature of the ground state for the breathing kagome lattice, which bears a
spontaneous chirality when neighbouring triangles are alternatively
ferromagnetic and antiferromagnetic.",1610.01748v1
2016-10-06,Spin-torque switching and control using chirped oscillating currents,"We propose to use oscillating spin currents with slowly varying frequency
(chirp) to manipulate and control the magnetization dynamics in a nanomagnet.
By recasting the Landau-Lifshitz-Slonczewski equation in a quantum-like
two-level formalism, we show that a chirped spin current polarized in the
direction normal to the anisotropy axis can induce a stable precession of the
magnetic moment at any angle (up to $90^\circ$) with respect to the anisotropy
axis. The drive current can be modest ($10^6\,\rm A/cm^2$ or lower) provided
the chirp rate is sufficiently slow. The induced precession is stable against
thermal noise, even for small nano-objects at room temperature. Complete
reversal of the magnetization can be achieved by adding a small external
magnetic field antiparallel to the easy axis. Alternatively, a combination of
chirped ac and dc currents with different polarization directions can also be
used to trigger the reversal.",1610.01819v2
2016-10-10,Interdiffusion in epitaxial ultrathin Co2FeAl/MgO heterostructures with interface-induced perpendicular magnetic anisotropy,"The structures of epitaxial ultrathin Co2FeAl/MgO(001) heterostructures
relating to the interface-induced perpendicular magnetic anisotropy (PMA) were
investigated using scanning transmission electron microscopy, energy dispersive
x-ray spectroscopy, and x-ray magnetic circular dichroism. We found that Al
atoms from the Co2FeAl layer significantly interdiffuse into MgO, forming an
Al-deficient Co-Fe-Al/Mg-Al-O structure near the Co2FeAl/MgO interface. This
atomic replacement may play an additional role for enhancing PMA, which is
consistent with the observed large perpendicular orbital magnetic moments of Fe
atoms at the interface. This work suggests that control of interdiffusion at
ferromanget/barrier interfaces is critical for designing an interface-induced
PMA system.",1610.03015v1
2016-10-10,Constraining quantum collapse inflationary models with CMB data,"The hypothesis of the self-induced collapse of the inflaton wave function was
proposed as responsible for the emergence of inhomogeneity and anisotropy at
all scales. This proposal was studied within an almost de Sitter space-time
approximation for the background, which led to a perfect scale-invariant power
spectrum, and also for a quasi-de Sitter background, which allows to
distinguish departures from the standard approach due to the inclusion of the
collapse hypothesis. In this work we perform a Bayesian model comparison for
two different choices of the self-induced collapse in a full quasi-de Sitter
expansion scenario. In particular, we analyze the possibility of detecting the
imprint of these collapse schemes at low multipoles of the anisotropy
temperature power spectrum of the Cosmic Microwave Background (CMB) using the
most recent data provided by the Planck Collaboration. Our results show that
one of the two collapse schemes analyzed provides the same Bayesian evidence of
the minimal standard cosmological model $\Lambda$CDM, while the other scenario
is weakly disfavoured with respect to the standard cosmology.",1610.03091v2
2016-10-10,TeV Cosmic-Ray Anisotropy from the Magnetic Field at the Heliospheric Boundary,"We performed numerical calculations to test the suggestion by Desiati &
Lazarian (2013) that the anisotropies of TeV cosmic rays may arise from their
interactions with the heliosphere. For this purpose, we used a magnetic field
model of the heliosphere and performed direct numerical calculations of
particle trajectories. Unlike earlier papers testing the idea, we did not
employ time-reversible techniques that are based on Liouville's theorem. We
showed numerically that for scattering by the heliosphere the conditions of
Liouville's theorem are not satisfied and the adiabatic approximation and
time-reversibility of the particle trajectories are not valid. Our results
indicate sensitivity to the magnetic structure of the heliospheric magnetic
field, and we expect that this will be useful for probing this structure in
future research.",1610.03097v1
2016-10-11,Strong anisotropy within a Heisenberg model in the J=1/2 insulating state of Sr2Ir0.8Ru0.2O4,"The dispersive magnetic excitations in Sr2IrO4 have previously been well
described within an isospin-1/2 Heisenberg model on a square lattice that
revealed parallels with La2CuO4. Here we investigate the inelastic spectra of
Sr2Ir0.8Ru0.2O4 with resonant inelastic x-ray scattering (RIXS) at the Ir
L3-edge. The results are well described using linear spin-wave theory within a
similar Heisenberg model applicable to Sr2IrO4, however the disorder induced by
the substitution of 20% Ir4+ ions for Ru4+ removes longer range exchange
interactions. A large spin-gap (40 meV) is measured indicating strong
anisotropy from spin-orbit coupling that is manifest due to the altered
magnetic structure in Sr2Ir0.8Ru0.2O4 with c-axis aligned moments compared to
the basal plane moments in the parent. Collectively the results indicate the
robustness of a Heisenberg model description even when the magnetic structure
is altered and the J=1/2 moments diluted.",1610.03399v1
2016-10-12,Thermal Anisotropy Enhanced by Phonon Size Effects in Nanoporous Materials,"While thermal anisotropicity is a desirable materials property for many
applications, including transverse thermoelectrics and thermal management in
electronic devices, it remains elusive in practical natural compounds. In this
work, we show how nanoporous materials with anisotropic pore lattices can be
used as a platform for inducing strong heat transport directionality in
isotropic materials. Using density functional theory and the phonon Boltzmann
transport equation, we calculate the phonon-size effects and thermal
conductivity of nanoporous silicon with different anisotropicpore lattices. Our
calculations predict a strong directionality in the thermal conductivity,
dictated by the difference in the pore-pore distances along the two Cartesian
axes. As the space between pores along the direction of the applied temperature
gradient represents the phonon bottleneck, an anisotropic pores lattice
distortion induces directionality in heat transport. Using Fourier's law, we
also compute diffusive heat transport for the same geometries obtaining
significantly smaller anisotropicity, revealing the crucial role of phonon-size
effects in tuning thermal transport directionality. Besides enhancing our
understanding of nanoscale heat transport, our results demonstrate the promise
of nanoporous materials for modulating anisotropy in thermal conductivity.",1610.03760v2
2016-10-17,Controlling energy transfer time between two coupled magnetic vortex-state disks,"The influence of the in-plane uniaxial anisotropy (IPUA) in the mutual energy
transfer time ($\tau$) between two identical coupled nanodisks was studied.
Using an analytical dipolar model we obtained the interactions between the
disks along x and y directions (the coupling integrals) as a function of the
uniaxial anisotropy constant (K$_{\sigma}$) and the distance. We find that the
IPUA increases the interaction between the disks allowing shorter energy
transfer times. For our range of K$_{\sigma}$ values we get a drop in the
values of $\tau$ of up to about 70$\%$. From the lagrangian of the system we
obtained the equations of motion and the coupling frequencies of the dynamic
system as a function of distance and K$_{\sigma}$. The coupling frequencies
were also obtained from micromagnetic simulations. Our results of the
simulations are in agreement with the analytical results.",1610.05109v1
2016-10-22,Giant nonreciprocal emission of spin waves in Ta/Py bilayers,"Spin waves are propagating disturbances in the magnetization of magnetic
materials. One of their interesting properties is the nonreciprocity,
exhibiting that their amplitude depends on the magnetization direction.
Nonreciprocity in spin waves is of great interest in both fundamental science
and applications, as it offers an extra knob to control the flow of waves for
the technological fields of logics and switch applications. We show a high
nonreciprocity in spin waves from Ta/Py bilayer systems with out-of-plane
magnetic fields. The nonreciprocity depends on the thickness of Ta underlayer
which is found to induce an interfacial anisotropy. The origin of observed high
nonreciprocity is twofold; different polarities of the in-plane magnetization
due to different angles of canted out-of-plane anisotropy and the spin pumping
effect at the Ta/Py interface. Our findings provide an opportunity to engineer
highly efficient nonreciprocal spin wave based applications such as
nonreciprocal microwave devices, magnonic logic gates, and information
transports.",1610.07023v1
2016-10-25,Anisotropy and memory during cage breaking events close to a wall,"The slow dynamics in a glassy hard-sphere system is dominated by cage
breaking events, i.e., rearrangements where a particle escapes from the cage
formed by its neighboring particles. We study such events for an overdamped
colloidal system by the means of Brownian dynamics simulations. While it is
difficult to relate cage breaking events to structural mean field results in
bulk, we show that the microscopic dynamics of particles close to a wall can be
related to the anisotropic two-particle density. In particular, we study
cage-breaking trajectories, mean forces on a tracked particle, and the impact
of the history of trajectories. Based on our simulation results, we further
construct two different one-particle random-walk models - one without and one
with memory incorporated - and find the local anisotropy and the
history-dependence of particles as crucial ingredients to describe the escape
from a cage. Finally, our detailed study of a rearrangement event close to a
wall not only reveals the memory effect of cages, but leads to a deeper insight
into the fundamental mechanisms of glassy dynamics.",1610.07846v1
2016-10-28,Anisotropic invariance and the distribution of quantum correlations,"We report the discovery of two new invariants for three-qubit states which,
similarly to the 3-tangle, are invariant under local unitary transformations
and permutations of the parties. These quantities have a direct interpretation
in terms of the anisotropy of pairwise spin correlations. Applications include
a universal ordering of pairwise quantum correlation measures for pure
three-qubit states; tradeoff relations for anisotropy, 3-tangle and Bell
nonlocality; strong monogamy relations for Bell inequalities,
Einstein-Podolsky-Rosen steering inequalities, geometric discord and fidelity
of remote state preparation (including results for arbitrary three-party
states); and a statistical and reference-frame-independent form of quantum
secret sharing.",1610.09302v3
2016-10-28,Uniform convergent scheme for strongly anisotropic diffusion equations with closed field lines,"In magnetized plasma, the magnetic field confines particles around field
lines. The ratio between the intensity of the parallel and perpendicular
viscosity or heat conduction may reach the order of $10^{12}$. When the
magnetic fields have closed field lines and form a ""magnetic island"", the
convergence order of most known schemes depends on the anisotropy strength. In
this paper, by integration of the original differential equation along each
closed field line, we introduce a simple but very efficient asymptotic
preserving reformulation, which yields uniform convergence with respect to the
anisotropy strength. Only slight modification to the original code is required
and neither change of coordinates nor mesh adaptation is needed. Numerical
examples demonstrating the performance of the new scheme are presented.",1610.09370v1
2016-10-31,Amplicification of Voltage Controlled Magnetic Anisotropy Effect with Negative Capacitance,"The high current density required by Magnetic Tunneling Junction (MTJ)
switching driven by Spin Transfer Torque (STT) effect leads to large power
consumption and severe reliability issues therefore hinder the timetable for
STT Magnetic Random Access Memory (STT-MRAM) to mass market. By utilizing
Voltage Controlled Magnetic Anisotropy (VCMA) effect, the MTJ can be switched
by voltage effect and is postulated to achieve ultra-low power (fJ). However,
the VCMA coefficient measured in experiments is far too small for MTJ dimension
below 100 nm. Here in this work, a novel approach for the amplification of VCMA
effect which borrow ideas from negative capacitance is proposed. The
feasibility of the proposal is proved by physical simulation and in-depth
analysis.",1610.09831v1
2016-10-31,Phenomenological predictions of 3+1d anisotropic hydrodynamics,"We make phenomenological predictions for particle spectra and elliptic flow
in heavy-ion collisions using 3+1d anisotropic hydrodynamics (aHydro) including
the effects of both shear and bulk viscosities. The dynamical equations
necessary are derived by taking moments of the Boltzmann equation allowing for
three distinct (diagonal) momentum-space anisotropy parameters. The formulation
is based on relaxation-time approximation for the collisional kernel and a
lattice-QCD-based equation of state. Evolving the system to late times, we
calculate particle production using THERMINATOR 2, modified to account for an
ellipsoidal distribution function. We obtain particle spectra for different
particle species such as pions, kaons, and protons, and elliptic flow $v_2$ as
a function of centrality, transverse momentum, and rapidity. In our model, we
have four free parameters, i.e. freeze-out temperature, initial central energy
density, initial momentum-space anisotropies, and shear viscosity to entropy
density ratio. Using a multidimensional fit to LHC experimental data, we make a
preliminary extraction of these parameters. We find reasonable agreement
between 3+1d aHydro and available experimental data for $\eta/s\sim 0.23$.",1610.10055v1
2016-11-02,Surface effects on ferromagnetic resonance in magnetic nanocubes,"We study the effect of surface anisotropy on the spectrum of spin-wave
excitations in a magnetic nanocluster and compute the corresponding absorbed
power. For this, we develop a general numerical method based on the (undamped)
Landau-Lifshitz equation, either linearized around the equilibrium state
leading to an eigenvalue problem or solved using a symplectic technique. For
box-shaped clusters, the numerical results are favorably compared to those of
the finite-size linear spin-wave theory. Our numerical method allows us to
disentangle the contributions of the core and surface spins to the spectral
weight and absorbed power. In regard to the recent developments in synthesis
and characterization of assemblies of well defined nano-elements, we study the
effects of free boundaries and surface anisotropy on the spin-wave spectrum in
iron nanocubes and give orders of magnitude of the expected spin-wave
resonances. For an 8 nm iron nanocube, we show that the absorbed power spectrum
should exhibit a low-energy peak around 10 GHz, typical of the uniform mode,
followed by other low-energy features that couple to the uniform mode but with
a stronger contribution from the surface. There are also high-frequency
exchange-mode peaks around 60 GHz.",1611.00614v1
2016-07-17,Effect of stress induced anisotropy and applied magnetic field on second order perturbed energy of thin ferromagnetic films,"All the simulations were carried out for sc(001) film with three (N=3)
layers. The effect of applied magnetic field and stress induced anisotropy on
energy of ultra-thin ferromagnetic films has been investigated using Heisenberg
Hamiltonian with second order perturbation. The energy becomes minimums at
certain values of angles, applied magnetic field and stress, by indicating that
film can be easily oriented in theses certain directions by applying particular
applied magnetic field or stress. For example, when applied magnetic field
perpendicular to film plane is 3.6, the film can be easily oriented along 0.97
and 2.65 radians directions. When in plane applied magnetic field is 3, energy
minimums can be detected at 1 and 2.6 radians. When applied stress is 2.7, film
can be easily oriented in 2.8 direction.",1611.02229v1
2016-11-08,Directional Anisotropy of Crack Propagation Along $Σ$3 Grain Boundary in BCC Fe,"Crack growth behaviour along the coherent twin boundary (CTB), i.e.,
$\Sigma$3{112} of BCC Fe is investigated using molecular dynamics (MD)
simulations. The growth of an atomistically sharp crack with {112}$<$110$>$
orientation has been examined along the two opposite $<$111$>$ directions of
CTB under mode-I loading at a constant strain rate. Separate MD simulations
were carried out with crack inserted in the left side, right side and middle of
the specimen model system. The results indicate that the crack grows
differently along the two opposite $<$111$>$ directions. In case of a crack
inserted in the left side, the crack grows in ductile manner, while it
propagates in semi-brittle manner in the case of crack inserted in the right
side. The directional dependence of crack growth along the CTB is also
confirmed by the stress-strain behaviour. This anisotropy in crack growth
behaviour has been attributed to the twinning-antitwinning asymmetry of
1/6$<$111$>$ partial dislocations on {112} planes.",1611.02458v1
2016-11-10,Total variation denoising in $l^1$ anisotropy,"We aim at constructing solutions to the minimizing problem for the variant of
Rudin-Osher-Fatemi denoising model with rectilinear anisotropy and to the
gradient flow of its underlying anisotropic total variation functional. We
consider a naturally defined class of functions piecewise constant on
rectangles (PCR). This class forms a strictly dense subset of the space of
functions of bounded variation with an anisotropic norm. The main result shows
that if the given noisy image is a PCR function, then solutions to both
considered problems also have this property. For PCR data the problem of
finding the solution is reduced to a finite algorithm. We discuss some
implications of this result, for instance we use it to prove that continuity is
preserved by both considered problems.",1611.03261v2
2016-11-10,Recent progress in astrophysical plasma turbulence from solar wind observations,"This paper summarises some of the recent progress that has been made in
understanding astrophysical plasma turbulence in the solar wind, from in situ
spacecraft observations. At large scales, where the turbulence is predominantly
Alfvenic, measurements of critical balance, residual energy, and 3D structure
are discussed, along with comparison to recent models of strong Alfvenic
turbulence. At these scales, a few percent of the energy is also in compressive
fluctuations, and their nature, anisotropy, and relation to the Alfvenic
component is described. In the small scale kinetic range, below the ion
gyroscale, the turbulence becomes predominantly kinetic Alfven in nature, and
measurements of the spectra, anisotropy, and intermittency of this turbulence
are discussed with respect to recent cascade models. One of the major remaining
questions is how the turbulent energy is dissipated, and some recent work on
this question, in addition to future space missions which will help to answer
it, are briefly discussed.",1611.03386v1
2016-11-14,A minimal empirical model for the cosmic far-infrared background anisotropies,"Cosmic far-infrared background (CFIRB) probes unresolved dusty star-forming
galaxies across cosmic time and is complementary to ultraviolet and optical
observations of galaxy evolution. In this work, we interpret the observed CFIRB
anisotropies using an empirical model based on resolved galaxies in ultraviolet
and optical surveys. Our model includes stellar mass functions, star-forming
main sequence, and dust attenuation. We find that the commonly used linear
Kennicutt relation between infrared luminosity and star formation rate
overproduces the observed CFIRB amplitudes. The observed CFIRB requires that
low-mass galaxies have lower infrared luminosities than expected from the
Kennicutt relation, implying that low-mass galaxies have lower dust content and
weaker dust attenuation. Our results demonstrate that CFIRB not only provides a
stringent consistency check for galaxy evolution models but also constrains the
dust content of low-mass galaxies.",1611.04517v2
2016-11-17,Recent results on collective effects in small systems from PHENIX at RHIC,"Collisions of simple systems, such as $p$+$p$, or $p$+Nucleus have been used
as benchmarks for our understanding of heavy ion collsions, since it was
assumed they would be free of the effects from hot nuclear matter.
  Recently long range correlations and anisotropies of momentum spectra have
been seen in such collisions, challenging this assumption. Such phenomena have
been understood to be the result of the collective motion, which can best be
described by hydrodynamics, whose initial conditions are set by the geometry of
the colliding systems, together with their fluctuations. This talk will discuss
the recent results from the PHENIX experiment at RHIC using a variety of
colliding species ($p$+Au, $d$+Au, $^{3}$He+Au) that give a better
understanding of the origin of the observed correlations and anisotropies, thus
providing insight as to whether a quark gluon plasma is formed in these simple
systems.",1611.05752v1
2016-11-17,On Escaping a Galaxy Cluster in an Accelerating Universe,"We derive the escape velocity profile for an Einasto density field in an
accelerating universe and demonstrate its physical viability by comparing
theoretical expectations to both light-cone data generated from N-body
simulations and archival data on 20 galaxy clusters. We demonstrate that the
projection function ($g(\beta )$) is deemed physically viable only for the
theoretical expectation that includes a cosmology-dependent term. Using
simulations, we show that the inferred velocity anisotropy is more than
6{\sigma} away from the expected value for the theoretical profile that ignores
the acceleration of the universe. In the archival data, we constrain the
average velocity anisotropy parameter of a sample of 20 clusters to be $\beta
={0.248}_{-0.360}^{+0.164}$ at the 68% confidence level. Lastly, we briefly
discuss how our analytic model may be used as a novel cosmological probe based
on galaxy clusters.",1611.05816v1
2016-11-18,Density dependent exciton dynamics and L valley anisotropy in germanium,"Optical pump-THz probe spectroscopy is used to investigate the exciton
formation dynamics and its intensity dependence in bulk Ge. Associated with the
intra-excitonic 1s-2p transition, the gradual build-up of an absorption peak
around 3.1 meV (0.75 THz) signifies the delayed exciton formation after optical
pump which is accelerated for higher excitation densities. Analyzing the
spectral shape of this THz absorption resonance, two distinct resonances are
found which are attributed to the mass-anisotropy of L valley electrons via a
microscopic theory.",1611.06117v1
2016-11-28,A test of local Lorentz invariance with Compton scattering asymmetry,"We report on a measurement of the constancy and anisotropy of the speed of
light relative to the electrons in photon-electron scattering. We used the
Compton scattering asymmetry measured by the new Compton polarimeter in Hall~C
at Jefferson Lab to test for deviations from unity of the vacuum refractive
index ($n$). For photon energies in the range of 9 - 46 MeV, we obtain a new
limit of $1-n < 1.4 \times 10^{-8}$. In addition, the absence of sidereal
variation over the six month period of the measurement constrains any
anisotropies in the speed of light. These constitute the first study of Lorentz
invariance using Compton asymmetry. Within the minimal standard model extension
framework, our result yield limits on the photon and electron coefficients
$\tilde{\kappa}_{0^+}^{YZ}, c_{TX}, \tilde{\kappa}_{0^+}^{ZX}$, and $c_{TY}$.
Although, these limits are several orders of magnitude larger than the current
best limits, they demonstrate the feasibility of using Compton asymmetry for
tests of Lorentz invariance. Future parity violating electron scattering
experiments at Jefferson Lab will use higher energy electrons enabling better
constraints.",1611.09173v1
2016-11-29,Domain wall profiles in Co/Ir$_n$/Pt(111) ultrathin films: influence of the Dzyaloshinskii-Moriya interaction,"We perform a study of domain walls in Co/Ir$_n$/Pt(111) (n = 0,1,...,6) films
by a combined approach of first-principles calculations and spin dynamics
simulations. We determine the tensorial exchange interactions and the magnetic
anisotropies for the Co overlayer in both FCC and HCP geometries, depending on
the number of Ir buffer layers. We find strong ferromagnetic nearest-neighbor
isotropic exchange interactions between the Co atoms and an out-of-plane
magnetic anisotropy for the films in FCC geometry. Our simulations show that
the magnetic domain walls are of N\'eel type, and their rotational sense
(chirality) is changed upon the insertion of an Ir buffer layer as compared to
the pristine Co/Pt(111) system. Our spin dynamics simulations indicate a
twisting of the spins with respect to the planar domain wall profile on the
triangular lattice. We discuss this domain wall twisting using symmetry
arguments and in terms of an appropriate micromagnetic continuum model
considering extra energy terms compared to the available literature.",1611.09518v1
2016-11-29,Observation of wavelength-dependent Brewster angle shift in 3D photonic crystals,"The interaction of polarized light with photonic crystals exhibit unique
features due to its sub-wavelength nature on the surface and the periodic
variation of refractive index in the depth of the crystals. Here, we present a
detailed study of polarization anisotropy in light scattering associated with
three-dimensional photonic crystals with face centered cubic symmetry over a
broad wavelength and angular range. The polarization anisotropy leads to a
shift in the conventional Brewster angle defined for a planar interface with
certain refractive index. The observed shift in Brewster angle strongly depends
on the index contrast and lattice constant. Polarization-dependent stop gap
measurements are performed on photonic crystals with different index contrast
and lattice constants. These measurements indicate unique stop gap branching at
high-symmetry points in the Brillouin zone of the photonic crystals. The
inherited stop gap branching is observed for TE polarization whereas that is
suppressed for TM polarization as a consequence of Brewster effect. Our results
have consequences in the polarized light-scattering from plasmonic structures
and dielectric meta-surfaces and are also useful in applications like
nano-scale polarization splitters and lasers.",1611.09693v1
2016-11-29,CoMET: Composite-Input Magnetoelectric-based Logic Technology,"This work proposes CoMET, a fast and energy-efficient spintronics device for
logic applications. An input voltage is applied to a ferroelectric (FE)
material, in contact with a composite structure - a ferromagnet (FM) with
in-plane magnetic anisotropy (IMA) placed on top of an intra-gate FM
interconnect with perpendicular magnetic anisotropy (PMA). Through the
magnetoelectric (ME) effect, the input voltage nucleates a domain wall (DW) at
the input end of the PMA-FM interconnect. An applied current then rapidly
propagates the DW towards the output FE structure, where the inverse-ME effect
generates an output voltage. This voltage is propagated to the input of the
next CoMET device using a novel circuit structure that enables efficient device
cascading. The material parameters for CoMET are optimized by systematically
exploring the impact of parameter choices on device performance. Simulations on
a 7nm CoMET device show fast, low-energy operation, with a delay/energy of
98ps/68aJ for INV and 135ps/85aJ for MAJ3.",1611.09714v3
2016-12-02,Mechanisms for strong anisotropy of in-plane g-factors in hole based quantum point contacts,"In-plane hole g-factors measured in quantum point contacts based on p-type
heterostructures strongly depend on the orientation of the magnetic field with
respect to the electric current. This effect, first reported a decade ago and
confirmed in a number of publications, has remained an open problem. In this
work, we present systematic experimental studies to disentangle different
mechanisms contributing to the effect and develop the theory which describes it
successfully. We show that there is a new mechanism for the anisotropy related
to the existence of an additional $B_+k_-^4\sigma_+$ effective Zeeman
interaction for holes, which is kinematically different from the standard
single Zeeman term $B_-k_-^2\sigma_+$ considered until now.",1612.00572v2
2016-12-02,FW/CADIS-$Ω$: An angle-informed hybrid method for deep-penetration radiation transport,"A new method for generating variance reduction parameters for strongly
anisotropic, deep-penetration radiation shielding studies is presented. This
method generates an alternate form of the adjoint scalar flux quantity,
$\phi^{\dagger}_{\Omega}$, which is used by both CADIS and FW-CADIS to generate
variance reduction parameters for local and global response functions,
respectively. The new method, called CADIS-$\Omega$, was implemented in the
Denovo/ADVANTG software suite, and results are presented for a concrete
labyrinth test problem. Results indicate that the flux generated by
CADIS-$\Omega$ incorporates localized angular anisotropies in the flux
effectively. CADIS-$\Omega$ outperformed CADIS in the test problem while
obtaining accurate results. This initial work indicates that CADIS-$\Omega$ may
be highly useful for shielding problems with strong angular anisotropies. A
future test plan to fully characterize the new method is proposed, which should
reveal more about the types of realistic problems for which the CADIS-$\Omega$
will be suited.",1612.00793v1
2016-12-03,Anisotropic magneto-transport and magnetic properties of low temperature phase of TaTe2,"TaTe2 is a quasi-2D charge density wave (CDW) compound with distorted-1T type
structure exhibiting double-zigzag chains. Here we report the Fermi surface
topology of low temperature phase of TaTe2 (LT-TaTe2) by anisotropic
magneto-transport and magnetic measurements on high-quality single crystals. An
anomalous large linear magnetoresistance up to 140% at 3 K in 9 T was observed,
suggesting the existence of a small Fermi pocket in Dirac cone state in quantum
transport models. Meanwhile, strong magnetic anisotropy was observed for B
(001) and B//(001). Angle-dependent magnetoresistance and de Hass-van Alphen
oscillations suggest the anisotropy of the normal Fermi surface and the small
Fermi pocket in Dirac cone state.",1612.00938v1
2016-12-05,Spatial Anisotropy in Nonrelativistic Holography,"We examine holographic theories where Lifshitz symmetry is broken with
spatial anisotropy. In particular, we focus on the conditions imposed by the
null energy condition, and demonstrate that it is possible to have unusual
anisotropic fixed points where a subset of the spatial dimensions have negative
scaling exponents. We also construct interpolating solutions between UV and IR
fixed points and show that there is essentially no restriction placed on the
endpoints of the flow once anisotropic scaling is allowed. As an example, we
demonstrate a flow from AdS to AdS with $c_{IR}>c_{UV}$ that is allowed by the
null energy condition since it proceeds through an intermediate
Lorentz-violating region. Finally, we examine the holographic Green's function
in anisotropic Lifshitz spacetimes.",1612.01557v2
2016-12-12,Polarization anisotropy of the emission from type-II quantum dots,"We study the polarization response of the emission from type-II GaAsSb capped
InAs quantum dots. The theoretical prediction based on the calculations of the
overlap integrals of the single-particle states obtained in the k.p framework
is given. This is verified experimentally by polarization resolved
photoluminescence measurements on samples with the type-II confinement. We show
that the polarization anisotropy might be utilized to find the vertical
position of the hole wavefunction and its orientation with respect to
crystallographic axes of the sample. A proposition for usage in the information
technology as a room temperature photonic gate operating at the communication
wavelengths as well as a simple model to estimate the energy of fine-structure
splitting for type-II GaAsSb capped InAs QDs are given.",1612.03585v1
2016-12-21,Magnetotransport studies of Superconducting Pr$_4$Fe$_2$As$_2$Te$_{1-x}$O$_4$,"We report a detailed study of the electrical transport properties of single
crystals of Pr$_4$Fe$_2$As$_2$Te$_{1-x}$O$_4$, a recently discovered iron-based
superconductor. Resistivity, Hall effect and magnetoresistance are measured in
a broad temperature range revealing the role of electrons as dominant charge
carriers. The significant temperature dependence of the Hall coefficient and
the violation of Kohler's law indicate multiband effects in this compound. The
upper critical field and the magnetic anisotropy are investigated in fields up
to 16 T, applied parallel and perpendicular to the crystallographic c-axis.
Hydrostatic pressure up to 2 GPa linearly increases the critical temperature
and the resistivity residual ratio. A simple two-band model is used to describe
the transport and magnetic properties of Pr$_4$Fe$_2$As$_2$Te$_{1-x}$O$_4$. The
model can successfully explain the strongly temperature dependent negative Hall
coefficient and the high magnetic anisotropy assuming that the mobility of
electrons is higher than that of holes.",1612.07090v1
2017-01-02,In-Plane Anisotropies of Polarized Raman Response and Electrical Conductivity in Layered Tin Selenide,"The group IV-VI compound SnSe, with an orthorhombic lattice structure, has
recently attracted particular interest due to its unexpectedly low thermal
conductivity and high power factor, showing great promise for thermoelectric
applications. SnSe displays intriguing anisotropic properties due to the
puckered low-symmetry in-plane lattice structure. Low-dimensional materials
have potential advantages in improving the efficiency of thermoelectric
conversion, due to the increased power factor and decreased thermal
conductivity. A complete study of the optical and electrical anisotropies of
SnSe nanostructures is a necessary prerequisite in taking advantage of the
material properties for high performance devices. Here, we synthesize the
single crystal SnSe nanoplates (NPs) by chemical vapor deposition. The angular
dependence of the polarized Raman spectra of SnSe NPs shows anomalous
anisotropic light-mater interaction. The angle-resolved charge transport of the
SnSe NPs expresses a strong anisotropic conductivity behavior. These studies
elucidate the anisotropic interactions which will be of use for future
ultrathin SnSe in electronic, thermoelectric and optoelectronic devices.",1701.00310v1
2017-01-05,Excitation and detection of short-waved spin waves in ultrathin Ta/CoFeB/MgO-layer system suitable for spin-orbit-torque magnonics,"We report on the excitation and detection of short-waved spin waves with wave
vectors up to about $40\,\mathrm{rad}\,\mu\mathrm{m}^{-1}$ in spin-wave
waveguides made from ultrathin, in-plane magnetized Co$_{8}$Fe$_{72}$B$_{20}$
(CoFeB). The CoFeB is incorporated in a layer stack of Ta/CoFeB/Mgo, a layer
system featuring large spin orbit torques and a large perpendicular magnetic
anisotropy constant. The short-waved spin waves are excited by nanometric
coplanar waveguides and are detected via spin rectification and microfocussed
Brillouin light scattering spectroscopy. We show that the large perpendicular
magnetic anisotropy benefits the spin-wave lifetime greatly, resulting in a
lifetime comparable to bulk systems without interfacial damping. The presented
results pave the way for the successful extension of magnonics to ultrathin
asymmetric layer stacks featuring large spin orbit torques.",1701.01399v1
2017-01-07,Measurement of $D^0$ Meson Production and Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV,"Due to the large masses, heavy-flavor quarks are dominantly produced in
initial hard scattering processes and experience the whole evolution of the
medium produced in heavy-ion collisions at RHIC energies. They are also
expected to thermalize slower than light-flavor quarks. Thus the measurement of
heavy quark production and azimuthal anisotropy can provide important insights
into the medium properties through their interactions with the medium.
  In these proceedings, we report measurements of $D^0$ production and elliptic
flow ($v_2$) via topological reconstruction using STAR's recently installed
Heavy Flavor Tracker (HFT). The new measurement of the nuclear modification
factor ($R_{AA}$) of $D^0$ mesons in central Au+Au collisions at
$\sqrt{s_{NN}}$ = 200 GeV confirms the strong suppression at high transverse
momenta ($p_{T}$) reported in the previous publication with much improved
precision. We also report the measurement of elliptic flow for $D^0$ mesons in
a wide transverse momentum range in 0-80% minimum-bias Au+Au collisions. The
$D^0$ elliptic flow is finite for $p_{T}$ $>$ 2 GeV/c and is systematically
below that of light hadrons in the same centrality interval. Furthermore,
several theoretical calculations are compared to both $R_{AA}$ and $v_2$
measurements, and the charm quark diffusion coefficient is inferred to be
between 2 and $\sim$12.",1701.01878v1
2017-01-11,a-b anisotropy of the intra-unit-cell magnetic order in $\rm YBa_2Cu_3O_{6.6}$,"Within the complex phase diagram of the hole-doped cuprates, seizing the
nature of the mysterious pseudo-gap phase is essential to unravel the
microscopic origin of high-temperature superconductivity. Below the pseudo-gap
temperature $\rm T^{\star}$, evidences for intra-unit-cell orders breaking the
4-fold rotation symmetry have been provided by neutron diffraction and scanning
tunneling spectroscopy. Using polarized neutron diffraction on a detwinned $\rm
YBa_2Cu_3O_{6.6}$ sample, we here report a distinct a-b anisotropy of the
intra-unit-cell magnetic structure factor below $\rm T^{\star}$, highlighting
that intra-unit-cell order in this material breaks the mirror symmetry of the
CuO$_2$ bilayers. This is likely to originate from a crisscrossed arrangement
of loop currents within the $\rm CuO_2$ bilayer, resulting in a bilayer mean
toroidal axis along the $\rm {\bf b}$ direction.",1701.02866v1
2017-01-11,Amplitude limits and nonlinear damping of shear-Alfvén waves in high-beta low-collisionality plasmas,"This work, which extends Squire et al. [ApJL, 830 L25 (2016)], explores the
effect of self-generated pressure anisotropy on linearly polarized
shear-Alfv\'en fluctuations in low-collisionality plasmas. Such anisotropies
lead to stringent limits on the amplitude of magnetic perturbations in
high-beta plasmas, above which a fluctuation can destabilize itself through the
parallel firehose instability. This causes the wave frequency to approach zero,
""interrupting"" the wave and stopping its oscillation. These effects are
explored in detail in the collisionless and weakly collisional ""Braginskii""
regime, for both standing and traveling waves. The focus is on simplified
models in one dimension, on scales much larger than the ion gyroradius. The
effect has interesting implications for the physics of magnetized turbulence in
the high-beta conditions that are prevalent in many astrophysical plasmas.",1701.03175v1
2017-01-13,Proton fire hose instabilities in the expanding solar wind,"Using two-dimensional hybrid expanding box simulations we study the
competition between the continuously driven parallel proton temperature
anisotropy and fire hose instabilities in collisionless homogeneous plasmas.
For quasi radial ambient magnetic field the expansion drives
$T_{\mathrm{p}\|}>T_{\mathrm{p}\perp}$ and the system becomes eventually
unstable with respect to the dominant parallel fire hose instability. This
instability is generally unable to counteract the induced anisotropization and
the system typically becomes unstable with respect to the oblique fire hose
instability later on. The oblique instability efficiently reduces the
anisotropy and the system rapidly stabilizes while a significant part of the
generated electromagnetic fluctuations is damped to protons. As long as the
magnetic field is in the quasi radial direction, this evolution repeats itself
and the electromagnetic fluctuations accumulate. For sufficiently oblique
magnetic field the expansion drives $T_{\mathrm{p}\perp}>T_{\mathrm{p}\|}$ and
brings the system to the stable region with respect to the fire hose
instabilities.",1701.03665v1
2017-01-18,Anisotropic Dzyaloshinskii-Moriya Interaction in ultra-thin epitaxial Au/Co/W(110),"We have used Brillouin Light Scattering spectroscopy to independently
determine the in-plane Magneto-Crystalline Anisotropy and the
Dzyaloshinskii-Moriya Interaction (DMI) in out-of-plane magnetized
Au/Co/W(110). We found that the DMI strength is 2-3 times larger along the
bcc$[\bar{1}10]$ than along the bcc$[001]$ direction. We use analytical
considerations to illustrate the relationship between the crystal symmetry of
the stack and the anisotropy of microscopic DMI. Such an anisotropic DMI is the
first step to realize isolated elliptical skyrmions or anti-skyrmions in thin
film systems with $C_{2v}$ symmetry.",1701.05062v2
2017-01-19,Linear Stability Analysis of a Levitated Nanomagnet in a Static Magnetic Field: Quantum Spin Stabilized Magnetic Levitation,"We theoretically study the levitation of a single magnetic domain nanosphere
in an external static magnetic field. We show that apart from the stability
provided by the mechanical rotation of the nanomagnet (as in the classical
Levitron), the quantum spin origin of its magnetization provides two additional
mechanisms to stably levitate the system. Despite of the Earnshaw theorem, such
stable phases are present even in the absence of mechanical rotation. For large
magnetic fields, the Larmor precession of the quantum magnetic moment
stabilizes the system in full analogy with magnetic trapping of a neutral atom.
For low magnetic fields, the magnetic anisotropy stabilizes the system via the
Einstein-de Haas effect. These results are obtained with a linear stability
analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy
in a Ioffe-Pritchard magnetic field.",1701.05410v3
2017-01-23,Understanding stability diagram of perpendicular magnetic tunnel junctions,"Perpendicular magnetic tunnel junctions (MTJ) with a bottom pinned reference
layer and a composite free layer (FL) are investigated. Different thicknesses
of the FL were tested to obtain an optimal balance between tunneling
magnetoresistance (TMR) ratio and perpendicular magnetic anisotropy. After
annealing at 400 $^\circ$C, the TMR ratio for 1.5 nm thick CoFeB sublayer
reached 180 % at room temperature and 280 % at 20 K with an MgO tunnel barrier
thickness corresponding to the resistance area product RA = 10
Ohm$\mathrm{\mu}$m$^2$. The voltage vs. magnetic field stability diagrams
measured in pillar-shaped MTJs with 130 nm diameter indicate the competition
between spin transfer torque (STT), voltage controlled magnetic anisotropy
(VCMA) and temperature effects in the switching process. An extended stability
phase diagram model that takes into account all three parameters and the
effective damping measured independently using broadband ferromagnetic
resonance technique enabled the determination of both STT and VCMA coefficients
that are responsible for the FL magnetization switching.",1701.06411v1
2017-01-26,Mechanism for nematic superconductivity in FeSe,"Despite its seemingly simple composition and structure, the pairing mechanism
of FeSe remains an open problem due to several striking phenomena. Among them
are nematic order without magnetic order, nodeless gap and unusual inelastic
neutron spectra with a broad continuum, and gap anisotropy consistent with
orbital selection of unknown origin. Here we propose a microscopic description
of a nematic quantum spin liquid that reproduces key features of neutron
spectra. We then study how the spin fluctuations of the local moments lead to
pairing within a spin-fermion model. We find the resulting superconducting
order parameter to be nodeless $s\pm d$-wave within each domain. Further we
show that orbital dependent Hund's coupling can readily capture observed gap
anisotropy. Our prediction calls for inelastic neutron scattering in a
detwinned sample.",1701.07813v2
2017-01-30,Quantum dynamics of a domain wall in a quasi one-dimensional $XXZ$ ferromagnet,"We derive an effective low-energy theory for a ferromagnetic $(2N+1)$-leg
spin-$\frac{1}{2}$ ladder with strong $XXZ$ anisotropy
$\left|J_{\parallel}^z\right|\ll \left|J_{\parallel}^{xy}\right|$, subject to a
kink-like non-uniform magnetic field $B_z(X)$ which induces a domain wall (DW).
Using Bosonization of the quantum spin operators, we show that the quantum
dynamics is dominated by a single one-dimensional mode, and is described by a
sine-Gordon model. The parameters of the effective model are explored as
functions of $N$, the easy-plane anisotropy
$\Delta=-J_{\parallel}^z/J_{\parallel}^{xy}$, and the strength and profile of
the transverse field $B_z(X)$. We find that at sufficiently strong and
asymmetric field, this mode may exhibit a quantum phase transition from a
Luttinger liquid to a spin-density-wave (SDW) ordered phase. As the effective
Luttinger parameter grows with the number of legs in the ladder ($N$), the SDW
phase progressively shrinks in size, recovering the gapless dynamics expected
in the two-dimensional limit $N\rightarrow\infty$.",1701.08556v1
2017-02-01,Anisotropic hydrodynamic turbulence in accretion disks,"Recently, the vertical shear instability (VSI) has become an attractive
purely hydrodynamic candidate for the anomalous angular momentum transport
required for weakly ionized accretion disks. In direct three-dimensional
numerical simulations of VSI turbulence in disks, a meridional circulation
pattern was observed that is opposite to the usual viscous flow behavior. Here,
we investigate whether this feature can possibly be explained by an anisotropy
of the VSI turbulence. Using three-dimensional hydrodynamical simulations, we
calculate the turbulent Reynolds stresses relevant for angular momentum
transport for a representative section of a disk.
  We find that the vertical stress is significantly stronger than the radial
stress. Using our results in viscous disk simulations with different viscosity
coefficients for the radial and vertical direction, we find good agreement with
the VSI turbulence for the stresses and meridional flow; this provides
additional evidence for the anisotropy. The results are important with respect
to the transport of small embedded particles in disks.",1702.00334v2
2017-02-02,Isotropization of two-dimensional hydrodynamic turbulence in the direct cascade,"We present results of numerical simulation of the direct cascade in
two-dimensional hydrodynamic turbulence (with spatial resolution up to $16384
\times 16384$). If at the earlier stage (at the time of order of the inverse
pumping growth rate $\tau\sim\Gamma_{max}^{-1}$), the turbulence develops
according to the same scenario as in the case of a freely decaying turbulence
\cite{KNNR-07, KKS}: quasi-singular distributions of di-vorticity are formed,
which in $k$-space correspond to jets, leading to a strong turbulence
anisotropy, then for times of the order of $10\tau$ turbulence becomes almost
isotropic. In particular, at these times any significant anisotropy in the
angular fluctuations for the energy spectrum (for a fixed $k$) is not visible,
while the probability distribution function of vorticity for large arguments
has the exponential tail with the exponent linearly dependent on vorticity, in
the agreement with the theoretical prediction \cite{FalkovichLebedev2011}.",1702.00738v1
2017-02-06,Temperature induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi$_{0.9}$Sm$_{0.1}$FeO$_3$ driven by $f$-$d$ induced magnetic anisotropy,"In multiferroic BiFeO$_3$ a cycloidal antiferromagnetic structure is coupled
to a large electric polarization at room temperature, giving rise to
magnetoelectric functionality that may be exploited in novel multiferroic-based
devices. In this paper, we demonstrate that by substituting samarium for 10% of
the bismuth ions the periodicity of the room temperature cycloid is increased,
and by cooling below $\sim15$ K the magnetic structure tends towards a simple
G-type antiferromagnet, which is fully established at 1.5 K. We show that this
transition results from $f-d$ exchange coupling, which induces a local
anisotropy on the iron magnetic moments that destroys the cycloidal order - a
result of general significance regarding the stability of non-collinear
magnetic structures in the presence of multiple magnetic sublattices.",1702.01635v1
2017-02-07,Magnetic domains in thin ferromagnetic films with strong perpendicular anisotropy,"We investigate the scaling of the ground state energy and optimal domain
patterns in thin ferromagnetic films with strong uniaxial anisotropy and the
easy axis perpendicular to the film plane. Starting from the full
three-dimensional micromagnetic model, we identify the critical scaling where
the transition from single domain to multidomain ground states such as bubble
or maze patterns occurs. Furthermore, we analyze the asymptotic behavior of the
energy in two regimes separated by a transition. In the single domain regime,
the energy $\Gamma$-converges towards a much simpler two-dimensional and local
model. In the second regime, we derive the scaling of the minimal energy and
deduce a scaling law for the typical domain size.",1702.01980v1
2017-02-09,Microscopic origin of ideal conductivity in integrable quantum models,"Non-ergodic dynamical systems display anomalous transport properties. A
prominent example are integrable quantum systems, whose exceptional property
are diverging DC conductivities. In this Letter, we explain the microscopic
origin of ideal conductivity by resorting to the thermodynamic particle content
of a system. Using group-theoretic arguments we rigorously resolve the
long-standing controversy regarding the nature of spin and charge Drude weights
in the absence of chemical potentials. In addition, by employing a hydrodynamic
description, we devise an efficient computational method to calculate exact
Drude weights from the stationary currents generated in an inhomogeneous quench
from bi-partitioned initial states. We exemplify the method on the anisotropic
Heisenberg model at finite temperatures for the entire range of anisotropies,
accessing regimes which are out of reach with other approaches. Quite
remarkably, spin Drude weight and asymptotic spin current rates reveal a
completely discontinuous (fractal) dependence on the anisotropy parameter.",1702.02930v2
2017-02-13,Cytoskeletal Anisotropy Controls Geometry and Forces of Adherent Cells,"We investigate the geometrical and mechanical properties of adherent cells
characterized by a highly anisotropic actin cytoskeleton. Using a combination
of theoretical work and experiments on micropillar arrays, we demonstrate that
the shape of the cell edge is accurately described by elliptical arcs, whose
eccentricity expresses the degree of anisotropy of the internal cell stresses.
This results in a spatially varying tension along the cell edge, that
significantly affects the traction forces exerted by the cell on the substrate.
Our work highlights the strong interplay between cell mechanics and geometry
and paves the way towards the reconstruction of cellular forces from
geometrical data.",1702.03916v2
2017-02-22,Universal scaling and critical exponents of the anisotropic quantum Rabi model,"We investigate first- and second-order quantum phase transitions of the
anisotropic quantum Rabi model, in which the rotating- and counter-rotating
terms are allowed to have different coupling strength. The model interpolates
between two known limits with distinct universal properties. Through a
combination of analytic and numerical approaches we extract the phase diagram,
scaling functions, and critical exponents, which allows us to establish that
the universality class at finite? anisotropy is the same as the isotropic
limit. We also reveal other interesting features, including a
superradiance-induced freezing of the effective mass and discontinuous scaling
functions in the Jaynes-Cummings limit. Our findings are relevant in a variety
of systems able to realize strong coupling between light and matter, such as
circuit QED setups where a finite anisotropy appears quite naturally.",1702.06641v1
2017-02-23,Spin-Orbit Coupling of Conduction Electrons in Magnetization Switching,"Strong magnetic field pulses associated with a relativistic electron bunch
can imprint switching patterns in magnetic thin films that have uniaxial
in-plane anisotropy. In experiments with Fe and FeCo alloy films the pattern
shape reveals an additional torque acting on magnetization during the short (in
the 100fs time scale) magnetic field pulse. The magnitude of the torque is as
high as 15% of the torque from the magnetic field. The torque symmetry is that
of a uniaxial anisotropy along the direction of the eddy current screening the
magnetic field. Spin-orbit interaction acting on the conduction electrons can
produce such a torque with the required symmetry and magnitude. The same
interaction causes the anomalous Hall current to be spin-polarized, exerting a
back reaction on magnetization direction. Such a mechanism may be at work in
all-optical laser switching of magnetic materials.",1702.07153v1
2017-02-27,Unusual enhancement of effective magnetic anisotropy with decreasing particle size in maghemite nanoparticles,"Experimental results and a model are presented to explain the observed
unusual enhancement of the effective magnetic anisotropy Keff with decreasing
particle size D from 15 nm to 2.5 nm in {\gamma}-Fe2O3 nanoparticles (NPs). The
samples include oleic acid-coated NPs with D = 2.5, 3.4, 6.3 and 7.0 nm
investigated here, with the results on other sizes taken from literature. Keff
is determined from the analysis of the frequency dependence of the blocking
temperature TB after considering the effects of interparticle interactions on
TB. The data of Keff vs. D is fit to the derived core-shell-based relation:
Keff = Kb + (6KS/D) +Ksh{[1-(2d/D)]^(-3) -1}, with Kb = 1.9 x10^5 ergs/cm^3 as
the bulk-like contribution of the core, KS = 0.035 ergs/cm^2 as the
contribution of the surface layer, and Ksh = 1.057 x10^4 ergs/cm^3 as the
contributions of spins in the shell of thickness d = 1.1 nm. This equation
represents an extension of the often-used Eq.: Keff = Kb + (6KS/D).
Significance of this new result is discussed.",1702.08378v1
2017-02-28,An a posteriori error analysis for a coupled continuum pipe-flow/Darcy model in Karst aquifers: anisotropic and isotropic discretizations,"This paper presents an a posteriori error analysis for a coupled continuum
pipe-flow/Darcy model in karst aquifers. We consider a unified anisotropic
finite element discretization (i.e. elements with very large aspect ratio). Our
analysis covers two-dimensional domains, conforming and nonconforming
discretizations as well as different elements. Many examples of finite elements
that are covered by analysis are presented. From the finite element solution,
the error estimators are constructed and based on the residual of model
equations. Lower and upper error bounds form the main result with minimal
assumptions on the elements. The lower error bound is uniform with respect to
the mesh anisotropy in the entire domain. The upper error bound depends on a
proper alignment of the anisotropy of the mesh which is a common feature of
anisotropic error estimation. In the special case of isotropic meshes, the
results simplify, and upper and lower error bounds hold unconditionally.",1702.08814v2
2017-03-15,Domain engineering of the metastable domains in the 4f-uniaxial-ferromagnet CeRu$_2$Ga$_2$B,"In search of novel, improved materials for magnetic data storage and
spintronic devices, compounds that allow a tailoring of magnetic domain shapes
and sizes are essential. Good candidates are materials with intrinsic
anisotropies or competing interactions, as they are prone to host various
domain phases that can be easily and precisely selected by external tuning
parameters such as temperature and magnetic field. Here, we utilize vector
magnetic fields to visualize directly the magnetic anisotropy in the uniaxial
ferromagnet CeRu$_2$Ga$_2$B. We demonstrate a feasible control both globally
and locally of domain shapes and sizes by the external field as well as a
smooth transition from single stripe to bubble domains, which opens the door to
future applications based on magnetic domain tailoring.",1703.05228v1
2017-03-21,Large anisotropic spin relaxation time of exciton bound to donor states in triple quantum wells,"We have studied the spin dynamics of a dense two-dimensional electron gas
confined in a GaAs/AlGaAs triple quantum well by using time-resolved Kerr
rotation and resonant spin amplification. Strong anisotropy of the spin
relaxation time up to a factor of 10 was found between the electron spins
oriented in-plane and out-of-plane when the excitation energy is tuned to an
exciton bound to neutral donor transition. We model this anisotropy using an
internal magnetic field and the inhomogeneity of the electron g-factor. The
data analysis allows us to determine the direction and magnitude of this
internal field in the range of a few mT for our studied structure, which
decreases with the sample temperature and optical power. The dependence of the
anisotropic spin relaxation was directly measured as a function of several
experimental parameters: excitation wavelength, sample temperature, pump-probe
time delay, and pump power.",1703.07156v2
2017-03-17,Mirror instability in the turbulent solar wind,"The relationship between a decaying strong turbulence and the mirror
instability in a slowly expanding plasma is investigated using two-dimensional
hybrid expanding box simulations. We impose an initial ambient magnetic field
perpendicular to the simulation box, and we start with a spectrum of
large-scale, linearly-polarized, random-phase Alfvenic fluctuations which have
energy equipartition between kinetic and magnetic fluctuations and vanishing
correlation between the two fields. A turbulent cascade rapidly develops,
magnetic field fluctuations exhibit a Kolmogorov-like power-law spectrum at
large scales and a steeper spectrum at sub-ion scales. The imposed expansion
(taking a strictly transverse ambient magnetic field) leads to generation of an
important perpendicular proton temperature anisotropy that eventually drives
the mirror instability. This instability generates large-amplitude,
nonpropagating, compressible, pressure-balanced magnetic structures in a form
of magnetic enhancements/humps that reduce the perpendicular temperature
anisotropy.",1703.07377v1
2017-03-24,Unconventional superconductivity in the BiS$_2$-based layered superconductor NdO$_{0.71}$F$_{0.29}$BiS$_2$,"We investigate the superconducting-gap anisotropy in one of the recently
discovered BiS$_2$-based superconductors, NdO$_{0.71}$F$_{0.29}$BiS$_2$ ($T_c$
$\sim$ 5 K), using laser-based angle-resolved photoemission spectroscopy.
Whereas the previously discovered high-$T_c$ superconductors such as copper
oxides and iron-based superconductors, which are believed to have
unconventional superconducting mechanisms, have $3d$ electrons in their
conduction bands, the conduction band of BiS$_2$-based superconductors mainly
consists of Bi 6$p$ electrons, and hence the conventional superconducting
mechanism might be expected. Contrary to this expectation, we observe a
strongly anisotropic superconducting gap. This result strongly suggests that
the pairing mechanism for NdO$_{0.71}$F$_{0.29}$BiS$_2$ is unconventional one
and we attribute the observed anisotropy to competitive or cooperative multiple
paring interactions.",1703.08379v1
2017-03-28,The influence of anti-site defects and stacking faults on the magneto crystalline anisotropy of FePt,"We present density functional theory (DFT) calculations of the magnetic
anisotropy energy (MAE) of FePt, which is of great interest for magnetic
recording applications. Our data, and the majority of previously calculated
results for perfectly ordered crystals, predict an MAE of $\sim 3.0$ meV per
formula unit, which is significantly larger than experimentally measured
values. Analyzing the effects of disorder by introducing stacking faults (SFs)
and anti site defects (ASDs) in varying concentrations we are able to reconcile
calculations with experimental data and show that even a low concentration of
ASDs are able to reduce the MAE of FePt considerably. Investigating the effect
of exact exchange and electron correlation within the adiabatic-connection
dissipation fluctuation theorem in the random phase approximation (ACDFT-RPA)
reveals a significantly smaller influence on the MAE. Thus the effect of
disorder, and more specifically ASDs, is the crucial factor in explaining the
deviation of common DFT calculations of FePt to experimental measurements.",1703.09559v1
2017-03-29,Magnon dispersion in Ca2RuO4: impact of spin-orbit coupling and oxygen moments,"The magnon dispersion of Ca$_2$RuO$_4$ has been studied by polarized and
unpolarized neutron scattering experiments on crystals containing 0, 1 and 10 %
of Ti. The entire dispersion of transverse magnons can be well described by a
conventional spin-wave model with interaction and anisotropy parameters that
agree with density functional theory calculations. Spin-orbit coupling strongly
influences the magnetic excitations, which is most visible in large energies of
the magnetic zone-center modes arising from magnetic anisotropy. We find
evidence for a low-lying additional mode that exhibits strongest scattering
intensity near the antiferromagnetic zone center. This extra signal can be
explained by a sizable magnetic moment of 0.11 Bohr magnetons on the apical
oxygens parallel to the Ru moment, which is found in the density functional
theory calculations. The energy and the signal strength of the additional
branch are well described by taking into account this oxygen moment with weak
ferromagnetic coupling between Ru and O moments.",1703.10017v1
2017-03-31,Temperature Dependence of the Anisotropy Field of L10 FePt near the Curie Temperature,"Near the Curie temperature the anisotropy field of magnetically uniaxial L10
FePt is expected to follow the scaling law $(1-T/Tc)^\beta$ where $T$ is the
temperature and $T_c$ the Curie temperature. In the literature $\beta$ values
between 0.36 and 0.65 have been reported. Based on recording measurements and
micromagnetic analysis, we show that only the values of $\beta$ near the low
end of the reported range are compatible with the data. We also conclude that
thermally activated magnetization reversal at temperatures near $T_c$ cannot be
ignored, even at time scales smaller than 1 ns. We demonstrate that thermally
activated magnetization reversal at temperatures close to $T_c$ is well
described by conventional theory with a frequency factor $f_0$ of the order of
$10^{12}$ Hz. It is reasoned that the unusually high value for $f_0$ is a
consequence of the temperature-induced reduction of the degree of alignment of
the micro-spins within the grains.",1703.10921v1
2017-04-01,Asymmetric isolated skyrmions in polar magnets with easy-plane anisotropy,"We introduce a new class of isolated magnetic skyrmions emerging within
tilted ferromagnetic phases of polar magnets with easy-plane anisotropy. The
asymmetric magnetic structure of these skyrmions is associated with an
intricate pattern of the energy density, which exhibits positive and negative
asymptotics with respect to the surrounding state with a ferromagnetic moment
tilted away from the polar axis. Correspondingly, the skyrmion-skyrmion
interaction has an anisotropic character and can be either attractive or
repulsive depending on the relative orientation of the skyrmion pair. We
investigate the stability of these novel asymmetric skyrmions against the
elliptical cone state and follow their transformation into axisymmetric
skyrmions, when the tilted ferromagnetic moment of the host phase is reduced.
Our theory gives clear directions for experimental studies of isolated
asymmetric skyrmions and their clusters embedded in tilted ferromagnetic
phases.",1704.00100v1
2017-04-05,Isotropic reconstruction of 3D fluorescence microscopy images using convolutional neural networks,"Fluorescence microscopy images usually show severe anisotropy in axial versus
lateral resolution. This hampers downstream processing, i.e. the automatic
extraction of quantitative biological data. While deconvolution methods and
other techniques to address this problem exist, they are either time consuming
to apply or limited in their ability to remove anisotropy. We propose a method
to recover isotropic resolution from readily acquired anisotropic data. We
achieve this using a convolutional neural network that is trained end-to-end
from the same anisotropic body of data we later apply the network to. The
network effectively learns to restore the full isotropic resolution by
restoring the image under a trained, sample specific image prior. We apply our
method to $3$ synthetic and $3$ real datasets and show that our results improve
on results from deconvolution and state-of-the-art super-resolution techniques.
Finally, we demonstrate that a standard 3D segmentation pipeline performs on
the output of our network with comparable accuracy as on the full isotropic
data.",1704.01510v1
2017-04-06,A critical study of the elastic properties and stability of Heusler compounds: Phase change and tetragonal $X_{2}YZ$ compounds,"In the present work, the elastic constants and derived properties of
tetragonal and cubic Heusler compounds were calculated using the high accuracy
of the full-potential linearized augmented plane wave (FPLAPW). To find the
criteria required for an accurate calculation, the consequences of increasing
the numbers of $k$-points and plane waves on the convergence of the calculated
elastic constants were explored. Once accurate elastic constants were
calculated, elastic anisotropies, sound velocities, Debye temperatures,
malleability, and other measurable physical properties were determined for the
studied systems. The elastic properties suggested metallic bonding with
intermediate malleability, between brittle and ductile, for the studied Heusler
compounds. To address the effect of off-stoichiometry on the mechanical
properties, the virtual crystal approximation (VCA) was used to calculate the
elastic constants. The results indicated that an extreme correlation exists
between the anisotropy ratio and the stoichiometry of the Heusler compounds,
especially in the case of Ni$_{2}$MnGa.",1704.01741v1
2017-04-10,Symmetry protected topological Luttinger liquids and the phase transition between them,"We show that a doped spin-1/2 ladder with antiferromagnetic intra-chain and
ferromagnetic inter-chain coupling is a symmetry protected topologically
non-trivial Luttinger liquid. Turning on a large easy-plane spin anisotropy
drives the system to a topologically-trivial Luttinger liquid. Both phases have
full spin gaps and exhibit power-law superconducting pair correlation. The
Cooper pair symmetry is singlet $d_{xy}$ in the non-trivial phase and triplet
$S_z=0$ in the trivial phase. The topologically non-trivial Luttinger liquid
exhibits gapless spin excitations in the presence of a boundary, and it has no
non-interacting or mean-field theory analog even when the fluctuating phase in
the charge sector is pinned. As a function of the strength of spin anisotropy
there is a topological phase transition upon which the spin gap closes. We
speculate these Luttinger liquids are relevant to the superconductivity in
metalized integer spin ladders or chains.",1704.02997v1
2017-04-18,Strong anisotropic optical conductivity in two dimensional puckered structures: The role of Rashba effect,"We calculate the optical conductivity of an anisotropic two-dimensional
system with Rashba spin-flip excitation within the Kubo formalism. We show that
the anisotropic Rashba effect caused by an external field changes significantly
the magnitude of the spin splitting. Furthermore, we obtain an analytical
expression for the longitudinal optical conductivity associated with inter-band
transitions as a function of the frequency for an arbitrary polarization angle.
We find that the diagonal components of the optical conductivity tensor are
direction-dependent and the spectrum of optical absorption is strongly
anisotropic with an absorption window. The height and width of this absorption
window are very sensitive to the system anisotropy. While the height of
absorption peak increases with increasing effective mass anisotropy ratio, the
peak intensity is larger when the light polarization is along the armchair
direction. Moreover, the absorption peak width becomes broader as the density
of state mass or Rashba interaction is enhanced. These features can be used to
determine parameters relevant for spintronics through the optical absorption
spectrum.",1704.05266v1
2017-04-19,Anisotropic features in the electronic structure of the two-dimensional transition metal trichalcogenide TiS$_3$: electron doping and plasmons,"Analysis of the band structure of TiS$_3$ single-layers suggests the
possibility of changing their physical behaviour by injecting electron
carriers. The anisotropy of the valence and conduction bands is explained in
terms of their complex orbital composition. The nature of the Fermi surface and
Lindhard response function for different doping concentrations is studied by
means of first-principles DFT calculations. It is suggested that for electron
doping levels $x$ (number of electrons per unit cell) $\sim$ 0.18-0.30$e^-$ the
system could exhibit incommensurate charge or spin modulations which, however,
would keep the metallic state whereas systems doped with smaller $x$ would be
2D metals without any electronic instability. The effect of spin-orbit coupling
in the band dispersion is analysed. The DFT effective masses are used to study
the plasmon spectrum from an effective low energy model. We find that this
material supports highly anisotropic plasmons, with opposite anisotropy for the
electron and hole bands.",1704.05824v1
2017-04-20,Anisotropy of the astrophysical gravitational wave background: analytic expression of the angular power spectrum and correlation with cosmological observations,"Unresolved and resolved sources of gravitational waves are at the origin of a
stochastic gravitational wave background. While the computation of its mean
density as a function of frequency in a homogeneous and isotropic universe is
standard lore, the computation of its anisotropies requires to understand the
coarse graining from local systems, to galactic scales and then to cosmology.
An expression of the gravitational wave energy density valid in any general
spacetime is derived. It is then specialized to a perturbed
Friedmann-Lema\^itre spacetime in order to determine the angular power spectrum
of this stochastic background as well as its correlation with other
cosmological probes, such as the galaxy number counts and weak lensing. Our
result for the angular power spectrum also provides an expression for the
variance of the gravitational wave background.",1704.06184v3
2017-04-20,Photon and dilepton observables: An experimental overview,"Dilepton and direct photon measurements in heavy ion collisions provide
access to the early stages of the collision. Dilepton continuum measurements at
SPS and RHIC show an excess consistent with broadening of the rho meson
spectral function as a result of hadronic interactions. Direct photon
measurements at RHIC and the LHC show an excess of low $p_{T}$ photons over the
expected yield. This excess has a large azimuthal anisotropy with respect to
the collision plane. Understanding the direct photon excess and its anisotropy
has become an outstanding question in the field of heavy ion physics. This
proceeding consists of a summary of new dilepton and direct photon experimental
results shown at the 2017 International Conference on Ultrarelativistic
Nucleus-Nucleus Collisions and presents them in the context of our current
understanding of these electromagentic probes.",1704.06307v3
2017-04-21,Magnetic anisotropy and valence states in La$_2$Co$_{1-x}$Mn$_{1+x}$O$_6$ ($x\approx 0.23$) thin films studied by X-ray absorption spectroscopy techniques,"X-ray absorption spectroscopy was used to determine the valence state in
La$_2$Co$_{1-x}$Mn$_{1+x}$O$_6$ ($x\approx 0.23$) thin films. We found that in
spite of the non-stoichiometry, Co is in a divalent state while Mn ions show a
mixed valence state. The relation of this finding with the magnetic properties
of the films is discussed. X-ray magnetic circular dichroism measurements prove
that magnetic anisotropy originates from Co spin-orbit coupling and it is
strain-dependent: a strong increase of the angular contribution to the magnetic
moment is found when in-plane (out-of-plane) and cell parameters get expanded
(compressed). This behavior is reproduced by first order perturbation theory
calculations.",1704.06411v1
2017-04-25,Distinguishing XY from Ising Electron Nematics,"At low temperatures in ultraclean GaAs-AlGaAs heterojunctions, high
fractional Landau levels break rotational symmetry, leading to increasingly
anisotropic transport properties as temperature is lowered below $\sim$150mK.
While the onset of transport anisotropy is well described by an XY model of an
electron nematic in the presence of a weak uniform symmetry-breaking term, the
low temperature behavior deviates significantly from this model. We find that
inclusion of interactions between the electron nematic and the underlying
crystalline lattice in the form of a 4-fold symmetry breaking term is
sufficient to describe the entire temperature dependence of the transport
anisotropy. This implies that the quantum Hall electron nematic is in the Ising
universality class. We propose new experimental tests that can distinguish
whether any two-dimensional electron nematic is in the XY or Ising universality
class.",1704.07527v1
2017-04-26,Transfer of magnetic order and anisotropy through epitaxial integration of 3$d$ and 4$f$ spin systems,"Resonant x-ray scattering at the Dy $M_5$ and Ni $L_3$ absorption edges was
used to probe the temperature and magnetic field dependence of magnetic order
in epitaxial LaNiO$_3$-DyScO$_3$ superlattices. For superlattices with 2 unit
cell thick LaNiO$_3$ layers, a commensurate spiral state develops in the Ni
spin system below 100 K. Upon cooling below $T_{ind} = 18$ K, Dy-Ni exchange
interactions across the LaNiO$_3$-DyScO$_3$ interfaces induce collinear
magnetic order of interfacial Dy moments as well as a reorientation of the Ni
spins to a direction dictated by the strong magneto-crystalline anisotropy of
Dy. This transition is reversible by an external magnetic field of 3 T.
Tailored exchange interactions between rare-earth and transition-metal ions
thus open up new perspectives for the manipulation of spin structures in
metal-oxide heterostructures and devices.",1704.07967v1
2017-04-28,Large magnetic anisotropy in quasi one-dimensional spin-1/2 fluoride antiferromagnets with a d(z2)1 ground state,"Hybrid density functional calculations are performed for a variety of systems
containing d9 ions (Cu2+, Ag2+), and exhibiting quasi-one-dimensional magnetic
properties. In particular we study fluorides containing these ions in a rarely
encountered compressed octahedral coordination which forces the unpaired
electron in the d(z2) orbital. We predict that such systems should exhibit
magnetic anisotropies surpassing that of Sr2CuO3 - one of the best realizations
of an one-dimensional system known to date. In particular we predict that the
inter-chain coupling in the Ag2+ containing [AgF][BF4] should be nearly five
orders of magnitude smaller than the intra-chain interaction. Our results
indicate that quasi-one-dimensional spin-1/2 systems containing chains with
spin sites in a d(z2)1 local ground state could constitute a versatile model
for testing modern theories of quantum many-body physics in the solid state.",1704.08902v1
2017-05-02,$z-$Weyl gravity in higher dimensions,"We consider higher dimensional gravity in which the four dimensional
spacetime and extra dimensions are not treated on an equal footing. The
anisotropy is implemented in the ADM decomposition of higher dimensional metric
by requiring the foliation preserving diffeomorphism invariance adapted to the
extra dimensions, thus keeping the general covariance only for the four
dimensional spacetime. The conformally invariant gravity can be constructed
with an extra (Weyl) scalar field and a real parameter $z$ which describes the
degree of anisotropy of conformal transformation between the spacetime and
extra dimensional metrics. In the zero mode effective 4D action, it reduces to
four-dimensional scalar-tensor theory coupled with nonlinear sigma model
described by extra dimensional metrics. There are no restrictions on the value
of $z$ at the classical level and possible applications to the cosmological
constant problem with a specific choice of $z$ is discussed.",1705.00866v2
2017-05-11,Spin Dynamics and Magnetoelectric Coupling Mechanism of Co4Nb2O9,"Neutron powder diffraction experiments reveal that Co4Nb2O9 forms a
noncollinear in-plane magnetic structure with Co2+ moments lying in the ab
plane. The spin-wave excitations of this magnet were measured by using
inelastic neutron scattering and soundly simulated by a dynamic model involving
nearest and next-nearest neighbour exchange interactions, in-plane anisotropy
and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of
Co4Nb2O9 is attributed to the large in-plane anisotropy while the
noncollinearity of the spin configuration is attributed to the
Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of
Co4Nb2O9 in fields can be explained by its special in-plane magnetic structure.",1705.04017v3
2017-05-24,Quantitative characterization of pore structure of several biochars with 3D imaging,"Pore space characteristics of biochars may vary depending on the used raw
material and processing technology. Pore structure has significant effects on
the water retention properties of biochar amended soils. In this work, several
biochars were characterized with three-dimensional imaging and image analysis.
X-ray computed microtomography was used to image biochars at resolution of 1.14
$\mu$m and the obtained images were analysed for porosity, pore-size
distribution, specific surface area and structural anisotropy. In addition,
random walk simulations were used to relate structural anisotropy to diffusive
transport. Image analysis showed that considerable part of the biochar volume
consist of pores in size range relevant to hydrological processes and storage
of plant available water. Porosity and pore-size distribution were found to
depend on the biochar type and the structural anisotopy analysis showed that
used raw material considerably affects the pore characteristics at micrometre
scale. Therefore attention should be paid to raw material selection and quality
in applications requiring optimized pore structure.",1705.08653v1
2017-05-29,"Contributions of Co and Fe orbitals to Perpendicular Magnetic Anisotropy of MgO/CoFeB Bilayers with Spin-Orbit-Torque-Related (Ta, W, IrMn, and Ti) Underlayers","We study the perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO
bilayers in contact with W, Ta, IrMn and Ti which has been suggested as the
spin-orbit-torque-related underlayers. The saturation magnetization of the
CoFeB depends on the underlayer materials due to formation of a dead-layer,
affecting PMA strength of each film. The x-ray magnetic circular dichroism
measurement reveals that the interfacial intermixing suppresses only the
perpendicular orbital moment of Fe, while the intermixing simultaneously
suppresses both the perpendicular and in-plane orbital moments of Co.",1705.10064v1
2017-05-29,Anisotropic electronic transport of the two-dimensional electron system in Al2O3/SrTiO3 heterostructures,"Transport measurements on the two dimensional electron system in Al2O3 SrTiO3
heterostructures indicate significant noncrystalline anisotropic behavior below
T = 30 K. Lattice dislocations in SrTiO3 and interfacial steps are suggested to
be the main sources for electronic anisotropy. Anisotropic defect scattering
likewise alters magnetoresistance at low temperature remarkably and influences
spin-orbit coupling significantly by the Elliot Yafet mechanism of spin
relaxation resulting in anisotropic weak localization. Applying a magnetic
field parallel to the interface results in an additional field induced
anisotropy of the conductance, which can be attributed to Rashba spin orbit
interaction. Compared to LaAlO3 SrTiO3, Rashba coupling seems to be reduced
indicating a weaker polarity in Al2O3 SrTiO3 heterostructures.",1705.10159v1
2017-05-30,Heteroepitaxial growth of tetragonal Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ (0 $\leqslant$ x $\leqslant$ 1.2) Heusler films with perpendicular magnetic anisotropy,"This work reports on the structural and magnetic properties of
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ Heusler films with different Fe content x (0
$\leqslant$ x $\leqslant$ 1.2). The films were deposited heteroepitaxially on
MgO single crystal substrates, by magnetron sputtering.
Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films with the thickness of 35 nm were
crystallized in tetragonal D0$_{22}$ structure with (001) preferred
orientation. Tunable magnetic properties were achieved by changing the Fe
content x. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ thins films exhibit high uniaxial
anisotropy Ku $\geqslant$ 1.4 MJ/m3, coercivity from 0.95 to 0.3 T and
saturation magnetization from 290 to 570 kA/m. The film with
Mn$_{1.6}$Fe$_{1.1}$Ga$_{1.3}$ composition shows high Ku of 1.47 MJ/m3 and
energy product ${(BH)_{max}}$ of 37 kJ/m3, at room temperature. These findings
demonstrate that Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films have promising properties
for mid-range permanent magnet and spintronic applications.",1705.10668v1
2017-06-02,Nonlinear anisotropic dielectric metasurfaces for ultrafast nanophotonics,"We report on the broadband transient optical response from anisotropic
nanobrick amorphous silicon particles, exhibiting Mie-type resonances. A
quantitative model is developed to identify and disentangle the three physical
processes that govern the ultrafast changes of the nanobrick optical
properties, namely two-photon absorption, free-carrier relaxation, and lattice
heating. We reveal a set of operating windows where ultrafast all-optical
modulation of transmission is achieved with full return to zero in 20 ps. This
is made possible due to the interplay between the competing nonlinear processes
and despite the slow (nanosecond) internal lattice dynamics. The observed
ultrafast switching behavior can be independently engineered for both or-
thogonal polarizations using the large anisotropy of nanobricks thus allowing
ultrafast anisotropy control. Our results categorically ascertain the potential
of all-dielectric resonant nanophotonics as a platform for ultrafast optical
devices, and reveal the pos- sibility for ultrafast polarization-multiplexed
displays and polarization rotators.",1706.00869v1
2017-06-07,Zero-point spin-fluctuations of single adatoms,"Stabilizing the magnetic signal of single adatoms is a crucial step towards
their successful usage in widespread technological applications such as
high-density magnetic data storage devices. The quantum mechanical nature of
these tiny objects, however, introduces intrinsic zero-point spin-fluctuations
that tend to destabilize the local magnetic moment of interest by dwindling the
magnetic anisotropy potential barrier even at absolute zero temperature. Here,
we elucidate the origins and quantify the effect of the fundamental ingredients
determining the magnitude of the fluctuations, namely the ($i$) local magnetic
moment, ($ii$) spin-orbit coupling and ($iii$) electron-hole Stoner
excitations. Based on a systematic first-principles study of 3d and 4d adatoms,
we demonstrate that the transverse contribution of the fluctuations is
comparable in size to the magnetic moment itself, leading to a remarkable
$\gtrsim$50$\%$ reduction of the magnetic anisotropy energy. Our analysis gives
rise to a comprehensible diagram relating the fluctuation magnitude to
characteristic features of adatoms, providing practical guidelines for
designing magnetically stable nanomagnets with minimal quantum fluctuations.",1706.02079v1
2017-06-09,Optical properties of an anisotropic hot QCD medium,"The present investigation involves explorations on the chromo-dielectric
properties of the hot QCD medium produced in relativistic heavy-ion collisions
in terms of refractive index. The isotropic/equilibrium modelling is done
within an effective quasi-particle model of hot QCD medium. The possibilities
of negative refraction in the medium are also explored in terms of the
Depine-Lakhtakia index. The anisotropic aspects of the hot QCD medium are
incorporated by introducing the anisotropy in a particular direction. That
makes the medium quite similar to uniaxial crystals, and hence we observe
phenomenon of birefringence ( two distinct refractive indices in the
anisotropic case). Interestingly, both anisotropy and medium effects play
significant roles in deciding the optical properties of the hot
QCD/Quark-Gluon-Plasma (QGP) medium.",1706.02995v2
2017-06-11,A new effective-field technique for the ferromagnetic spin-1 Blume-Capel model in a transverse crystal field,"A new approximating technique is developed so as to study the quantum
ferromagnetic spin-1 Blume-Capel model in the presence of a transverse crystal
field in the square lattice. Our proposal consists of approaching the spin
system by considering islands of finite clusters whose frontiers are surrounded
by non-interacting spins that are treated by the effective-field theory. The
resulting phase diagram is qualitatively correct, in contrast to most
effective-field treatments, in which the first-order line exhibits spurious
behavior by not being perpendicular to the anisotropy axis at low temperatures.
The effect of the transverse anisotropy is also verified by the presence of
quantum phase transitions. The possibility of using larger sizes constitutes an
advantage to other approaches where the implementation of larger sizes is
costly computationally.",1706.04071v1
2017-06-16,Observation of Various and Spontaneous Magnetic Skyrmionic Bubbles at Room-Temperature in a Frustrated Kagome Magnet with Uniaxial Magnetic Anisotropy,"Various and spontaneous magnetic skyrmionic bubbles are experimentally
observed for the first time, at room temperature in a frustrated kagome magnet
Fe3Sn2 with unixial magnetic anisotropy. The magnetization dynamics were
investigated using in-situ Lorentz transmission electron microscopy, revealing
that the transformation between different magnetic bubbles and domains are via
the motion of Bloch lines driven by applied external magnetic field. The
results demonstrate that Fe3Sn2 facilitates a unique magnetic control of
topological spin textures at room temperature, making it a promising candidate
for further skyrmion-based spintronic devices.",1706.05177v1
2017-06-16,Thermoelectric Band Engineering: The Role of Carrier Scattering,"Complex electronic band structures, with multiple valleys or bands at the
same or similar energies can be beneficial for thermoelectric performance, but
the advantages can be offset by inter-valley and inter-band scattering. In this
paper, we demonstrate how first-principles band structures coupled with
recently developed techniques for rigorous simulation of electron-phonon
scattering provide the capabilities to realistically assess the benefits and
trade-offs associated with these materials. We illustrate the approach using
n-type silicon as a model material and show that intervalley scattering is
strong. This example shows that the convergence of valleys and bands can
improve thermoelectric performance, but the magnitude of the improvement
depends sensitively on the relative strengths of intra- and inter-valley
electron scattering. Because anisotropy of the band structure also plays an
important role, a measure of the benefit of band anisotropy in the presence of
strong intervalley scattering is presented.",1706.05241v2
2017-06-20,Hidden peculiar magnetic anisotropy at the interface in a ferromagnetic perovskite-oxide heterostructure,"Understanding and controlling the interfacial magnetic properties of
ferromagnetic thin films are crucial for spintronic device applications.
However, using conventional magnetometry, it is difficult to detect them
separately from the bulk properties. Here, by utilizing tunneling anisotropic
magnetoresistance in a single-barrier heterostructure composed of
La0.6Sr0.4MnO3 (LSMO)/ LaAlO3 (LAO)/ Nb-doped SrTiO3 (001), we reveal the
presence of a peculiar strong two-fold magnetic anisotropy (MA) along the
[110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO.
This MA shows unknown behavior that the easy magnetization axis rotates by
90{\deg} at an energy of 0.2 eV below the Fermi level in LSMO. We attribute
this phenomenon to the transition between the eg and t2g bands at the LSMO
interface. Our finding and approach to understanding the energy dependence of
the MA demonstrate a new possibility of efficient control of the interfacial
magnetic properties by controlling the band structures of oxide
heterostructures.",1706.06300v1
2017-06-24,Above 400 K Robust Perpendicular Ferromagnetic Phase in a Topological Insulator,"The quantum anomalous Hall effect (QAHE) that emerges under broken
time-reversal symmetry in topological insulators (TI) exhibits many fascinating
physical properties for potential applications in nano-electronics and
spintronics. However, in transition-metal doped TI, the only experimentally
demonstrated QAHE system to date, the effect is lost at practically relevant
temperatures. This constraint is imposed by the relatively low Curie
temperature (Tc) and inherent spin disorder associated with the random magnetic
dopants. Here we demonstrate drastically enhanced Tc by exchange coupling TI to
Tm3Fe5O12, a high-Tc magnetic insulator with perpendicular magnetic anisotropy.
Signatures that the TI surface states acquire robust ferromagnetism are
revealed by distinct squared anomalous Hall hysteresis loops at 400 K.
Point-contact Andreev reflection spectroscopy confirms that the TI surface is
indeed spin-polarized. The greatly enhanced Tc, absence of spin disorder, and
perpendicular anisotropy are all essential to the occurrence of the QAHE at
high temperatures.",1706.07971v1
2017-06-24,The magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS$_3$,"The magnetic properties and magnetic structure are presented for CoPS$_3$, a
quasi-two-dimensional antiferromagnet on a honeycomb lattice with a N\'eel
temperature of $T_N \sim 120$ K. The compound is shown to have XY-like
anisotropy in its susceptibility, and the anisotropy is analysed to extract
crystal field parameters. For temperatures between 2 K and 300 K, no phase
transitions were observed in the field-dependent magnetization up to 10 Tesla.
Single-crystal neutron diffraction shows that the magnetic propagation vector
is {\bf{k}}= $\left[010\right]$ with the moments mostly along the $\mathbf{a}$
axis and with a small component along the $\mathbf{c}$ axis, which largely
verifies the previously-published magnetic structure for this compound. The
magnetic Bragg peak intensity decreases with increasing temperature as a power
law with exponent $2\beta = 0.60 \pm 0.01$ for $T > 0.9~T_N$.",1706.07989v1
2017-06-25,The static hard-loop gluon propagator to all orders in anisotropy,"We calculate the (semi-)static hard-loop self-energy and propagator using the
Keldysh formalism in a momentum-space anisotropic quark-gluon plasma. The
static retarded, advanced, and Feynman (symmetric) self-energies and
propagators are calculated to all orders in the momentum-space anisotropy
parameter $\xi$. For the retarded and advanced self-energies/propagators, we
present a concise derivation and comparison with previously-obtained results
and extend the calculation of the self-energies to next-to-leading order in the
gluon energy, $\omega$. For the Feynman self-energy/propagator, we present new
results which are accurate to all orders in $\xi$. We compare our exact results
with prior expressions for the Feynman self-energy/propagator which were
obtained using Taylor-expansions around an isotropic state. We show that,
unlike the Taylor-expanded results, the all-orders expression for the Feynman
propagator is free from infrared singularities. Finally, we discuss the
application of our results to the calculation of the imaginary-part of the
heavy-quark potential in an anisotropic quark-gluon plasma.",1706.08091v1
2017-06-26,Optically and electrically controllable adatom spin-orbital dynamics in transition metal dichalcogenides,"We analyze the interplay of spin-valley coupling, orbital physics and
magnetic anisotropy taking place at single magnetic atoms adsorbed on
semiconducting transition-metal dichalcogenides, MX$_2$ (M = Mo, W; X = S, Se).
Orbital selection rules turn out to govern the kinetic exchange coupling
between the adatom and charge carriers in the MX$_2$ and lead to highly
orbitally dependent spin-flip scattering rates, as we illustrate for the
example of transition metal adatoms with $d^9$ configuration. Our ab initio
calculations suggest that $d^9$ configurations are realizable by single Co, Rh,
or Ir adatoms on MoS$_2$, which additionally exhibit a sizable magnetic
anisotropy. We find that the interaction of the adatom with carriers in the
MX$_2$ allows to tune its behavior from a quantum regime with full Kondo
screening to a regime of ""Ising spintronics"" where its spin-orbital moment acts
as classical bit, which can be erased and written electronically and optically.",1706.08365v1
2017-06-27,Helical and skyrmion lattice phases in three-dimensional chiral magnets: Effect of anisotropic interactions,"In this work, we study the magnetic orders of the classical spin model with
the anisotropic exchange and Dzyaloshinskii-Moriya interactions in order to
understand the uniaxial stress effect in chiral magnets such as MnSi.
Variational zero temperature (T) calculated results demonstrate that various
helical orders can be developed depending on the magnitude of the interaction
anisotropy, consistent with the experimental observations at low T.
Furthermore, the creation and annihilation of the skyrmions by the uniaxial
pressure can be also qualitatively reproduced in our Monte Carlo simulations.
Thus, our work suggests that the interaction anisotropy tuned by applied
uniaxial stress may play an essential role in modulating the magnetic orders in
strained chiral magnets.",1706.08677v1
2017-06-27,Analytical and numerical $K_u - B$ phase diagrams for cobalt nanostructures: stability region for a Bloch skyrmion,"In this letter we calculate the energies corresponding to the different
magnetic phases present in a ferromagnetic cylinder by means of analytical
calculations. From the comparison of these energies, it is possible to
construct magnetic phase diagrams as a function of the uniaxial anisotropy of
the sample and the external magnetic field applied. As proof of concept, we
analyzed the magnetic phase diagrams for a cobalt dot of 240 nm in diameter and
70 nm in length, with an easy axis parallel to the dot axis, and with a
magnetic field applied towards or perpendicular to this axis. From these
diagrams we have obtained the stability regions for a Bloch skyrmion (Sk), a
vortex core (VC) and a ferromagnetic (F) configuration, which can point in any
$\psi$ direction. Our results provide a pathway to engineer the formation and
controllability of a skyrmion in a ferromagnetic dot to different anisotropy
constants and magnetic fields.",1706.08876v2
2017-06-28,Electric control of the edge magnetization in zigzag stanene nanoribbon,"There has been tremendous interest in manipulating electron and hole-spin
states in low-dimensional structures for electronic and spintronic
applications. We study the edge magnetic coupling and anisotropy in zigzag
stanene nanoribbons, by first-principles calculations. Taking into account
considerable spin-orbit coupling and ferromagnetism at each edge, zigzag
stanene nanoribbon is insulating and its band gap depends on the inter-edge
magnetic coupling and the magnetization direction. Especially for nanoribbon
edges with out-of-plane antiferromagnetic coupling, two non-degenerate valleys
of edge states emerge and the spin degeneracy is tunable by a transverse
electric field, which give full play to spin and valley degrees of freedom.
More importantly, both the magnetic order and anisotropy can be selectively
controlled by electron and hole doping, demonstrating a readily accessible
gate-induced modulation of magnetism. These intriguing features offer a
practical avenue for designing energy-efficient devices based on multiple
degrees of freedom of electron and magneto-electric couplings.",1706.09098v1
2017-06-28,Monte Carlo study of magnetic nanoparticles adsorbed on halloysite $Al_2Si_2O_5(OH)_4$ nanotubes,"We study properties of magnetic nanoparticles adsorbed on the halloysite
surface. For that a distinct magnetic Hamiltonian with random distribution of
spins on a cylindrical surface was solved by using a nonequilibrium Monte Carlo
method. The parameters for our simulations: anisotropy constant, nanoparticle
size distribution, saturated magnetization and geometrical parameters of the
halloysite template were taken from recent experiments. We calculate the
hysteresis loops and temperature dependence of the zero field cooling (ZFC)
susceptibility, which maximum determines the blocking temperature. It is shown
that the dipole-dipole interaction between nanoparticles moderately increases
the blocking temperature and weakly increases the coercive force. The obtained
hysteresis loops (e.g., the value of the coercive force) for Ni nanoparticles
are in reasonable agreement with the experimental data. We also discuss the
sensitivity of the hysteresis loops and ZFC susceptibilities to the change of
anisotropy and dipole-dipole interaction, as well as the 3d-shell occupation of
the metallic nanoparticles; in particular we predict larger coercive force for
Fe, than for Ni nanoparticles.",1706.09213v2
2017-06-30,Role of anisotropy in determining stability of electrodeposition at solid-solid interfaces,"We investigate the stability of electrodeposition at solid-solid interfaces
for materials exhibiting an anisotropic mechanical response. The stability of
electrodeposition or resistance to the formation of dendrites is studied within
a linear stability analysis. The deformation and stress equations are solved
using the Stroh formalism and faithfully recover the boundary conditions at the
interface. The stability parameter is used to quantify the stability of
different solid-solid interfaces incorporating the full anisotropy of the
elastic tensor of the two materials. Results show a high degree of variability
in the stability parameter depending on the crystallographic orientation of the
solids in contact, and point to opportunities for exploiting this effect in
developing Li metal anodes.",1707.00064v3
2017-07-03,Testing the anisotropy of the Universe with the distance duality relation,"The distance duality relation (DDR) is valid in Riemannian spacetime. The
astronomical data hint that the universe may have certain preferred direction.
If the universe is described by anisotropic cosmological models based on
Riemannian spacetime, then DDR still valid. If the anisotropy universe is
described by other models which are not based on Riemannian spacetime, then DDR
is violated. Thus, DDR could be used to test the validity of these anisotropic
cosmological models. In this paper, we perform anisotropic DDR parametrization
with the dipolar structures. The DDR is tested by comparing the luminosity
distance from type-Ia supernovae (Union 2.1 and JLA compilations) and the
angular diameter distance from strong gravitational lensing (SL) systems at the
same redshift. It is shown that, the DDR is valid with the Union2.1
compilation, while is violated more than 1$\sigma$ confidence level with the
JLA compilation. Additionally, we verify the statistical signification of our
method with Monte Carlo simulations. Due to the large uncertainty of available
data, no strong evidence is found to violate the DDR in the anisotropic models.",1707.00390v2
2017-06-22,"First-principles study of optical, elastic anisotropic and thermodynamic properties of TiN under high temperature and high pressure","The optical, elastic anisotropic and thermodynamic properties of TiN in the
NaCl (B1) structure are analyzed in detail in the temperature range from 0 to
2000 K and the pressure range from 0 to 20 GPa. From the calculated dielectric
constants, a first order isostructural phase transition between 29 and 30 GPa
is found for TiN. The absorption spectra exhibit high values ranging from the
far infrared region to the ultra-violet one. The anisotropy value of Young's
modulus of TiN is smaller than that of c-BN at 0 GPa and the anisotropy of TiN
clearly increases with an increase of pressure. The effects of pressure and
temperature on the bulk modulus, Gr\""uneisen parameter, Gibbs free energy, and
Debye temperature are significant. The Gr\""uneisen parameter of TiN is much
larger than that of c-BN. At temperatures below 1000 K, TiN's heat capacity is
much larger than that of c-BN.",1707.00676v1
2017-07-04,D-meson azimuthal anisotropy in mid-central Pb-Pb collisions at $\mathbf{\sqrt{s_{\rm NN}}=5.02}$ TeV,"The azimuthal anisotropy coefficient $v_2$ of prompt D$^0$, D$^+$, D$^{*+}$
and D$_s^+$ mesons was measured in mid-central (30-50% centrality class) Pb-Pb
collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}} =
5.02$ TeV, with the ALICE detector at the LHC. The D mesons were reconstructed
via their hadronic decays at mid-rapidity, $|y|<0.8$, in the transverse
momentum interval $1<p_{\rm T}<24$ GeV/$c$. The measured D-meson $v_2$ has
similar values as that of charged pions. The D$_s^+$ $v_2$, measured for the
first time, is found to be compatible with that of non-strange D mesons. The
measurements are compared with theoretical calculations of charm-quark
transport in a hydrodynamically expanding medium and have the potential to
constrain medium parameters.",1707.01005v2
2017-07-05,Magnetic Order in Laser-Irradiated Kagome Antiferromagnets,"Dispersionless ""zero energy mode'' is one of the hallmarks of frustrated
kagome antiferromagnets (KAFMs). It points to extensive classically degenerate
ground-states. The ""zero energy mode'' can be observed experimentally when
lifted to a flat mode at finite energy by a strong intrinsic magnetic
anisotropy. In this letter, we study the effects of irradiation of laser light
on the KAFMs. We adopt the magnon picture without loss of generality. It is
shown that circularly or linearly polarized light lifts the ""zero energy
mode'', stabilizes magnetic order, and induces energy gaps in the KAFMs. We
find that the circularly polarized light-induced anisotropies have similar
features as the intrinsic in-plane and out-of-plane Dzyaloshinskii-Moriya
interaction in KAFMs. The former stabilizes long-range magnetic order and the
latter induces spin canting out-of-plane with nonzero scalar spin chirality.
The Floquet thermal Hall effect shows that the synthetic magnetic excitation
modes in the case of circularly polarized light are topological, whereas those
of linearly polarized light are not.",1707.01502v3
2017-07-06,Strong angular dependent transmission ratio due to interplay between spin waves and the domain wall in perpendicular magnetic anisotropy materials,"Spin waves (SW) can induce rich domain wall (DW) motion in a
perpendicular-magnetic anisotropy nanostrip. In-plane magnetization tilt angle
resulting from the fluctuation of the effective field of the magnetization
response in the DW region plays an essential role in the dynamics of SW
interacting with a DW. We performed simulation and found that the transmission
ratio of the propagating SW across the DW depends strongly on the tilt angle in
the low-frequency regime. The material parameters and the geometrical
configuration can be fine-tuned for practical devices.",1707.01617v1
2017-07-17,Condensate of Massive Graviton and Dark Matter,"We study coherently oscillating massive gravitons in the ghost-free bigravity
theory. This coherent field can be interpreted as a condensate of the massive
gravitons. We first define the effective energy-momentum tensor of the coherent
massive gravitons in a curved spacetime. We then study the background dynamics
of the universe and the cosmic structure formation including the effects of the
coherent massive gravitons. We find that the condensate of the massive graviton
behaves as a dark matter component of the universe. From the geometrical point
of view the condensate is regarded as a spacetime anisotropy. Hence, in our
scenario, dark matter is originated from the tiny deformation of the spacetime.
We also discuss a production of the spacetime anisotropy and find that the
extragalactic magnetic field of a primordial origin can yield a sufficient
amount for dark matter.",1707.05003v2
2017-07-18,Discrimination of anisotropy in dark matter velocity distribution with directional detectors,"Directional detection of dark matter has sensitivity for both recoil energy
and direction of nuclear recoil. It opens the way to measure local velocity
distribution of dark matter. In this paper, we study possibility to
discriminate isotropic distribution and anisotropic one suggested by a N-body
simulation with directional detector. Numerical simulation is performed for two
cases according to the detectors, one corresponds to angular histogram and the
other is energy-angular distribution of the signals. We reveal that the
anisotropy of velocity distribution can be discriminated at 90% C.L. with
chi-squared test if O($10^4$) signals are obtained.",1707.05523v3
2017-07-25,Skyrmion mediated voltage controlled switching of ferromagnets for reliable and energy efficient 2-terminal memory,"We propose a two terminal nanomagnetic memory element based on magnetization
reversal of a perpendicularly magnetized nanomagnet employing a unipolar
voltage pulse that modifies the perpendicular anisotropy of the system. Our
work demonstrates that the presence of Dzyaloshinskii-Moriya Interaction (DMI)
can create alternative route for magnetization reversal that obviates the need
for utilizing precessional magnetization dynamics as well as a bias magnetic
field that are employed in traditional voltage control of magnetic anisotropy
(VCMA) based switching of perpendicular magnetization. We show with extensive
micromagnetic simulation, in the presence of thermal noise, that the proposed
skyrmion mediated VCMA switching mechanism is robust at room temperature
leading to extremely low error switching while also being potentially 1-2
orders of magnitude more energy efficient than state of the art spin transfer
torque (STT) based switching.",1707.07777v1
2017-07-27,Perfect diode in quantum spin chains,"We study the rectification of spin current in $XXZ$ chains segmented in two
parts, each with a different anisotropy parameter. Using exact diagonalization
and a matrix product states algorithm we find that a large rectification (of
the order of $10^4$) is attainable even using a short chain of $N=8$ spins,
when one half of the chain is gapless while the other has large enough
anisotropy. We present evidence of diffusive transport when the current is
driven in one direction and of a transition to an insulating behavior of the
system when driven in the opposite direction, leading to a perfect diode in the
thermodynamic limit. The above results are explained in terms of matching of
spectrum of magnon excitations between the two halves of the chain.",1707.08823v3
2017-08-06,On the limits of coercivity in permanent magnets,"The maximum coercivity that can be achieved for a given hard magnetic alloy
is estimated by computing the energy barrier for the nucleation of a reversed
domain in an idealized microstructure without any structural defects and
without any soft magnetic secondary phases. For
Sm$_{1-z}$Zr$_z$(Fe$_{1-y}$Co$_y$)$_{12-x}$Ti$_x$ based alloys, which are
considered an alternative to Nd$_2$Fe$_{14}$B magnets with lower rare-earth
content, the coercive field of a small magnetic cube is reduced to 60 percent
of the anisotropy field at room temperature and to 50 percent of the anisotropy
field at elevated temperature (473K). This decrease of the coercive field is
caused by misorientation, demagnetizing fields and thermal fluctuations.",1708.01880v1
2017-08-10,Klein-Gordon field from the XXZ Heisenberg model,"We examine the recently introduced idea of Spin-Field Correspondence focusing
on the example of the spin system described by the XXZ Heisenberg model with
external magnetic field. The Hamiltonian of the resulting nonlinear scalar
field theory is derived for arbitrary value of the anisotropy parameter
$\Delta$. We show that the linear scalar field theory is reconstructed in the
large spin limit. For $\Delta=1$ a non-relativistic scalar field theory
satisfying the Born reciprocity principle is recovered. As expected, for the
vanishing anisotropy parameter $\Delta \rightarrow 0$ the standard relativistic
Klein-Gordon field is obtained. Various aspects of the obtained class of the
scalar fields are studied, including the fate of the relativistic symmetries
and the properties of the emerging interaction terms. We show that, in a
certain limit, the so-called polymer quantisation of the field variables is
recovered. This and other discussed properties suggest a possible relevance of
the considered framework in the context of quantum gravity.",1708.03207v1
2017-08-14,Large Proximity-Induced Spin Lifetime Anisotropy in Transition Metal Dichalcogenide/Graphene Heterostructures,"Van-der-Waals heterostructures have become a paradigm for designing new
materials and devices, in which specific functionalities can be tailored by
combining the properties of the individual 2D layers. A single layer of
transition metal dichalcogenide (TMD) is an excellent complement to graphene
(Gr), since the high quality of charge and spin transport in Gr is enriched
with the large spin-orbit coupling of the TMD via proximity effect. The
controllable spin-valley coupling makes these heterostructures particularly
attractive for spintronic and opto-valleytronic applications. In this work, we
study spin precession in a monolayer MoSe2/Gr heterostructure and observe an
unconventional, dramatic modulation of the spin signal, showing one order of
magnitude longer lifetime of out-of-plane spins (40 ps) compared with that of
in-plane spins (3.5 ps). This demonstration of a large spin lifetime anisotropy
in TMD/Gr heterostructures, is a direct evidence of induced spin-valley
coupling in Gr and provides an accessible route for manipulation of spin
dynamics in Gr, interfaced with TMDs.",1708.04067v1
2017-08-14,Robustness of the semimetal state of Na3Bi and Cd3As2 against Coulomb interaction,"We study the excitonic semimetal-insulator quantum phase transition in
three-dimensional Dirac semimetal in which the fermion dispersion is strongly
anisotropic. After solving the Dyson-Schwinger equation for the excitonic gap,
we obtain a global phase diagram in the plane spanned by the parameter for
Coulomb interaction strength and the parameter for fermion velocity anisotropy.
We find that excitonic gap generation is promoted as the interaction becomes
stronger, but is suppressed if the anisotropy increases. Applying our results
to two realistic three-dimensional Dirac semimetals Na$_{3}$Bi and
Cd$_{3}$As$_{2}$, we establish that their exact zero-temperature ground state
is gapless semimetal, rather than excitonic insulator. Moreover, these two
materials are far from the excitonic quantum critical point, thus there should
not be any observable evidence for excitonic insulating behavior. This
conclusion is in general agreement with the existing experiments of Na$_{3}$Bi
and Cd$_{3}$As$_{2}$.",1708.04080v2
2017-08-15,Laser-written polarizing directional coupler with reduced interaction length,"Integrated optical devices are becoming a common tool in modern optical
science and engineering. This devices should be designed to allow for precise
control and manipulation of light. The femtosecond laser written (FSLW)
photonic chips have proven to cope with the most current demands of integrated
photonics. However, up to date the polarization degree of freedom has rarely
been exploited in experiments performed on the FSLW integrated platform. The
main obstacle is an intrinsically low anisotropy of laser written waveguides,
preventing the design of polarizing integrated devices with small footprint. In
this Letter we demonstrate the approach based on stress-induced anisotropy
allowing us to decrease the size of polarizing directional couplers fabricated
with the FSLW technology by almost an order of magnitude. We provide an
accurate account for the effects emerging in waveguides written in a close
proximity to each over.",1708.04450v1
2017-08-24,Delocalizing Entanglement of Anisotropic Black Branes,"We study the mutual information between pairs of regions on the two
asymptotic boundaries of maximally-extended anisotropic black-brane solutions.
This quantity characterizes the local pattern of entanglement of thermofield
double states which are dual to these geometries. We analyse the disruption of
the mutual information in anisotropic shock wave geometries and show that the
entanglement velocity plays an important role in this phenomenon. Besides that
we compute several chaos-related properties of this system, like the
entanglement velocity, the butterfly velocity and the scrambling time. We find
that the butterfly velocity and the entanglement velocity violate the upper
bounds proposed in 1311.1200 and 1612.00082, but remain bounded by their
corresponding values in the infrared effective theory.",1708.07243v3
2017-08-24,MgO thickness-induced spin reorientation transition in Co0.9Fe0.1/MgO/Co0.9Fe0.1 structure,"The magnetic anisotropy (MA) of Mo/Au/Co0.9Fe0.1/Au/MgO(0.7 - 3
nm)/Au/Co0.9Fe0.1/Au heterostructure has been investigated at room temperature
as a function of MgO layer thickness (tMgO). Our studies show that while the MA
of the top layer does not change its character upon variation of tMgO, the
uniaxial out-of-plane MA of the bottom one undergoes a spin reorientation
transition at tMgO of about 0.8 nm, switching to the regime where the
coexistence of in- and out-of-plane magnetization alignments is observed. The
magnitudes of the magnetic anisotropy constants have been determined from
ferromagnetic resonance and dc-magnetometry measurements. The origin of MA
evolution has been attributed to a presence of an interlayer exchange coupling
(IEC) between Co0.9Fe0.1 layers through the thin MgO film.",1708.07382v1
2017-08-29,Spin Dynamics in a Stripe-ordered Buckled Honeycomb Lattice Antiferromagnet Ba$_{2}$NiTeO$_{6}$,"We carried out inelastic neutron scattering experiments on a buckled
honeycomb lattice antiferromagnet Ba$_{2}$NiTeO$_{6}$ exhibiting a stripe
structure at a low temperature. Magnetic excitations are observed in the energy
range of $\hbar \omega \lesssim 10$ meV having an anisotropy gap of 2 meV at 2
K. We perform spin-wave calculations to identify the spin model. The obtained
microscopic parameters are consistent with the location of the stripe structure
in the classical phase diagram. Furthermore, the Weiss temperature
independently estimated from a bulk magnetic susceptibility is consistent with
the microscopic parameters. The results reveal that a competition between the
NN and NNN interactions that together with a relatively large single ion
magnetic anisotropy stabilize the stripe magnetic structure.",1708.08717v1
2017-09-03,Dynamics of the vortex line density in superfluid counterflow turbulence,"Describing superfluid turbulence at intermediate scales between the
inter-vortex distance and the macroscale requires an acceptable equation of
motion for the density of quantized vortex lines $\cal{L}$. The closure of such
an equation for superfluid inhomogeneous flows requires additional inputs
besides $\cal{L}$ and the normal and superfluid velocity fields. In this paper
we offer a minimal closure using one additional anisotropy parameter $I_{l0}$.
Using the example of counterflow superfluid turbulence we derive two coupled
closure equations for the vortex line density and the anisotropy parameter
$I_{l0}$ with an input of the normal and superfluid velocity fields. The
various closure assumptions and the predictions of the resulting theory are
tested against numerical simulations.",1709.00671v2
2017-09-04,Plum pudding random medium model of biological tissue toward remote microscopy from spectroscopic light scattering,"Biological tissue has a complex structure and exhibits rich spectroscopic
behavior. There is \emph{no} tissue model up to now able to account for the
observed spectroscopy of tissue light scattering and its anisotropy. Here we
present, \emph{for the first time}, a plum pudding random medium (PPRM) model
for biological tissue which succinctly describes tissue as a superposition of
distinctive scattering structures (plum) embedded inside a fractal continuous
medium of background refractive index fluctuation (pudding). PPRM faithfully
reproduces the wavelength dependence of tissue light scattering and attributes
the ""anomalous"" trend in the anisotropy to the plum and the powerlaw dependence
of the reduced scattering coefficient to the fractal scattering pudding. Most
importantly, PPRM opens up a novel venue of quantifying the tissue architecture
and microscopic structures on average from macroscopic probing of the bulk with
scattered light alone without tissue excision. We demonstrate this potential by
visualizing the fine microscopic structural alterations in breast tissue
(adipose, glandular, fibrocystic, fibroadenoma, and ductal carcinoma) deduced
from noncontact spectroscopic measurement.",1709.00795v1
2017-09-05,"Pinning, Rotation, and Metastability of BiFeO$_3$ Cycloidal Domains in a Magnetic Field","Earlier models for the room-temperature multiferroic BiFeO3 implicitly
assumed that a very strong anisotropy restricts the domain wavevectors q to the
three-fold symmetric axis normal to the static polarization P. However, recent
measurements demonstrate that the domain wavevectors rotate so that q rotates
within the hexagonal plane normal to P away from the field orientation m. We
show that the previously neglected three-fold anisotropy K3 restricts the
wavevectors to lie along the three-fold axis in zero field. For m along a
three-fold axis, the domain with q parallel to m remains metastable below Bc1 =
7 T. Due to the pinning of domains by non-magnetic impurities, the wavevectors
of the other two domains start to rotate away from m above 5.6 T, when the
component of the torque t = M x B along P exceeds a threshold value tpin. Since
t =0 when m is perpendicular to q, the wavevectors of those domains never
become completely perpendicular to the magnetic field. Our results explain
recent measurements of the critical field as a function of field orientation,
small-angle neutron scattering measurements of the wavevectors, as well as
spectroscopic measurements with m along a three-fold axis.",1709.01428v2
2017-09-12,Controllable transport of a skyrmion in a ferromagnetic narrow channel with voltage-controlled magnetic anisotropy,"Magnetic skyrmions have potential applications in next-generation spintronics
devices with ultralow energy consumption. In this work, the current-driven
skyrmion motion in a narrow ferromagnetic nanotrack with voltage-controlled
magnetic anisotropy (VCMA) is studied numerically. By utilizing the VCMA
effect, the transport of skyrmion can be unidirectional in the nanotrack,
leading to a one-way information channel. The trajectory of the skyrmion can
also be modulated by periodically located VCMA gates, which protects the
skyrmion from destruction by touching the track edge. In addition, the location
of the skyrmion can be controlled by adjusting the driving pulse length in the
presence of the VCMA effect. Our results provide guidelines for practical
realization of the skyrmion-based information channel, diode, and racetrack
memory.",1709.03733v1
2017-09-17,Detecting higher spin fields through statistical anisotropy in the CMB and galaxy power spectra,"Primordial inflation may represent the most powerful collider to test
high-energy physics models. In this paper we study the impact on the
inflationary power spectrum of the comoving curvature perturbation in the
specific model where massive higher spin fields are rendered effectively
massless during a de Sitter epoch through suitable couplings to the inflaton
field. In particular, we show that such fields with spin $s$ induce a
distinctive statistical anisotropic signal on the power spectrum, in such a way
that not only the usual $g_{2M}$-statistical anisotropy coefficients, but also
higher-order ones (i.e., $g_{4M}$, $g_{6M}$, $\cdots$, $g_{(2s-2)M}$ and
$g_{(2s) M}$) are nonvanishing. We examine their imprints in the cosmic
microwave background and galaxy power spectra. Our Fisher matrix forecasts
indicate that the detectability of $g_{LM}$ depends very weakly on $L$: all
coefficients could be detected in near future if their magnitudes are bigger
than about $10^{-3}$.",1709.05695v2
2017-09-21,Anisotropy effects on Baryogenesis in $f(R)$-Theories of Gravity,"We study the $f(R)$ theory of gravity in an anisotropic metric and its effect
on the baryon number to entropy ratio. The mechanism of gravitational
baryogenesis based on the CPT-violating gravitational interaction between
derivative of the Ricci scalar curvature and the baryon-number current is
investigated in the context of the $f(R)$ gravity. The gravitational
baryogenesis in the Bianchi type I universe is examined. We survey the effect
of anisotropy of the universe on the baryon asymmetry from point of view the
$f(R)$-theories of gravity and its effect on $n_{b}/s$ for radiation dominant
regime.",1709.06996v3
2017-09-26,Observation of correlated azimuthal anisotropy Fourier harmonics in pp and pPb collisions at the LHC,"The azimuthal anisotropy Fourier coefficients ($v_n$) in 8.16 TeV pPb data
are extracted via long-range two-particle correlations as a function of event
multiplicity and compared to corresponding results in pp and PbPb collisions.
Using a four-particle cumulant technique, $v_n$ correlations are measured for
the first time in pp and pPb collisions. The $v_2$ and $v_4$ coefficients are
found to be positively correlated in all collision systems. For high
multiplicity pPb collisions an anticorrelation of $v_2$ and $v_3$ is observed,
with a similar correlation strength as in PbPb data at the same multiplicity.
The new correlation results strengthen the case for a common origin of the
collectivity seen in pPb and PbPb collisions in the measured multiplicity
range.",1709.09189v2
2017-09-27,The influence of superparamagnetism on exchange anisotropy at CoO/[Co/Pd] interfaces,"Magnetic systems exhibiting exchange bias effect are being considered as
materials for applications in data storage devices, sensors and biomedicine. As
the size of new mag- netic devices is being continuously reduced, the influence
of thermally induced instabilities in magnetic order has to be taken into
account during their fabrication process. In this study we show the influence
of superparamagnetism on magnetic properties of exchange-biased [CoO/Co/Pd]10
multilayer. We find that the process of progressive thermal blocking of the
superparamagnetic clusters causes an unusually fast rise of the exchange
anisotropy field and coercivity, and promotes the easy axis switching to
out-of-plane direction.",1709.09399v1
2017-09-27,Anisotropic Particles Strengthen Granular Pillars under Compression,"We probe the effects of particle shape on the global and local behavior of a
two-dimensional granular pillar, acting as a proxy for a disordered solid,
under uniaxial compression. This geometry allows for direct measurement of
global material response, as well as tracking of all individual particle
trajectories. In general, drawing connections between local structure and local
dynamics can be challenging in amorphous materials due to lower precision of
atomic positions, so this study aims to elucidate such connections. We vary
local interactions by using three different particle shapes: discrete circular
grains (monomers), pairs of grains bonded together (dimers), and groups of
three bonded in a triangle (trimers). We find that dimers substantially
strengthen the pillar and the degree of this effect is determined by
orientational order in the initial condition. In addition, while the three
particle shapes form void regions at distinct rates, we find that anisotropies
in the local amorphous structure remain robust through the definition of a
metric that quantifies packing anisotropy. Finally, we highlight connections
between local deformation rates and local structure.",1709.09511v2
2017-09-28,Tailoring the exchange bias effect by in-plane magnetic anisotropy,"We report an unusual, non-monotonous dependence of the exchange bias on the
thickness of the ferromagnetic layer in a ferromagnet/antiferromagnet bilayer
system. We show that in epitaxial CoO/Fe(110) bilayers, the evolution of the Fe
magnetic anisotropy, which drives the thickness-induced in-plane
spin-reorientation process, controls the interfacial CoO spin directions in the
0-90 degrees range and, consequently, drastically modifies the magnitude of the
hysteresis loop shift and its dependence on the thickness of the Fe layer. Our
results present a new recipe for tailoring the exchange bias and
antiferromagnetic spin structure by utilizing the spin-reorientation process
that occurs in a ferromagnetic layer adjacent to an antiferromagnetic layer.",1709.09925v1
2017-09-20,Tailoring Magnetic Skyrmions by Geometric Confinement of Magnetic Structures,"Nanoscale magnetic skyrmions have interesting static and transport properties
that make them candidates for future spintronic devices. Control and
manipulation of the size and behavior of skyrmions is thus of crucial
importance. Using a Ginzburg-Landau approach, we show theoretically that
skyrmions and skyrmion lattices can be stabilized by a spatial modulation of
the uniaxial magnetic anisotropy in a thin film of centro-symmetric
ferromagnet. Remarkably, the skyrmion size is determined by the ratio of the
exchange length and the period of the spatial modulation of the anisotropy, at
variance with conventional skyrmions stabilized by dipolar and
Dzyaloshinskii--Moriya interactions (DMIs).",1710.00048v1
2017-10-03,Brownian Motion and Entropic Torque Driven Motion of Domain-Wall in Antiferromagnets,"We study the spin dynamics in antiferromagnetic nanowire under an applied
temperature gradient using micromagnetic simulations on a classical spin model
with a uniaxial anisotropy. The entropic torque driven domain-wall motion and
the Brownian motion are discussed in detail, and their competition determines
the antiferromagnetic wall motion towards the hotter or colder region.
Furthermore, the spin dynamics in an antiferromagnet can be well tuned by the
anisotropy and the temperature gradient. Thus, this paper not only strengthens
the main conclusions obtained in earlier works [Kim et al., Phys. Rev. B 92,
020402(R) (2015); Selzer et al., Phys. Rev. Lett. 117, 107201 (2016)], but more
importantly gives the concrete conditions under which these conclusions apply,
respectively. Our results may provide useful information on the
antiferromagnetic spintronics for future experiments and storage device design.",1710.01196v2
2017-10-09,Weak magnetic anisotropy in GdRh$_2$Si$_2$ studied by magnetic resonance,"The antiferromagnetically (AFM) ordered state of GdRh$_{2}$Si$_{2}$ which
consists of AFM-stacked ferromagnetic layers is investigated by magnetic
resonance spectroscopy. The almost isotropic Gd$^{3+}$ paramagnetic resonance
becomes anisotropic in the AFM ordered region below 107 K. The emerging
internal anisotropic exchange-fields are still small enough to allow an
investigation of their magnetization dynamics by using a standard
microwave-frequency magnetic resonance technique. We could characterize this
anisotropy in detail in the ferromagnetic layers of the excitation at 9 and 34
GHz. We derived a resonance condition for the AFM ordered phase to describe the
weak in-plane anisotropic behaviour in combination with a mean-field analysis.",1710.03079v1
2017-10-09,Confinement study of an SU(4) gauge theory with fermions in multiple representations,"We discuss the phase diagnostics used in our finite-temperature study of an
SU(4) gauge theory with dynamical fermions in both the fundamental and
two-index antisymmetric representations. Beyond the usual Polyakov loop
diagnostics of confinement, we employ several Wilson flow phase diagnostics.
The first, what we call the ""flow anisotropy"", is known in the literature: the
deconfinement transition introduces anisotropy between the spatial and temporal
directions, to which the flow is extremely sensitive. The second, the ""long
flow time Polyakov loop,"" is related but novel. While we do not claim to fully
understand this diagnostic, we have empirically found it to be useful as an
unusually sharp diagnostic of phase.",1710.03257v1
2017-10-10,Fully Kinetic Simulation of 3D Kinetic Alfven Turbulence,"We present results from a three-dimensional particle-in-cell simulation of
plasma turbulence, resembling the plasma conditions found at kinetic scales of
the solar wind. The spectral properties of the turbulence in the subion range
are consistent with theoretical expectations for kinetic Alfv\' en waves.
Furthermore, we calculate the local anisotropy, defined by the relation
$k_{\parallel}(k_{\perp})$, where $k_{\parallel}$ is a characteristic wave
number along the local mean magnetic field at perpendicular scale
$l_{\perp}\sim 1/k_{\perp}$. The subion range anisotropy is scale dependent
with $k_{\parallel}<k_{\perp}$ and the ratio of linear to nonlinear time scales
is of order unity, suggesting that the kinetic cascade is close to a state of
critical balance. Our results compare favorably against a number of \emph{in
situ} solar wind observations and demonstrate---from first principles---the
feasibility of plasma turbulence models based on a critically balanced cascade
of kinetic Alfv\' en waves.",1710.03581v2
2017-10-18,Cluster-glass phase in pyrochlore XY antiferromagnets with quenched disorder,"We study the impact of quenched disorder (random exchange couplings or site
dilution) on easy-plane pyrochlore antiferromagnets. In the clean system,
order-by-disorder selects a magnetically ordered state from a classically
degenerate manifold. In the presence of randomness, however, different orders
can be chosen locally depending on details of the disorder configuration. Using
a combination of analytical considerations and classical Monte-Carlo
simulations, we argue that any long-range-ordered magnetic state is destroyed
beyond a critical level of randomness where the system breaks into magnetic
domains due to random exchange anisotropies, becoming, therefore, a glass of
spin clusters, in accordance with the available experimental data. These random
anisotropies originate from off-diagonal exchange couplings in the microscopic
Hamiltonian, establishing their relevance to other magnets with strong
spin-orbit coupling.",1710.06658v2
2017-10-23,Manipulating Magnetic Moments by Superconducting Currents,"We show that the interaction between a superconducting order parameter and
the magnetic moment of an atomic cluster in a two-dimensional s-wave
superconductor with Rashba spin-orbit coupling generates magnetic anisotropy
that can be stronger or comparable to the magnetic anisotropy due to the
crystal field and the shape of the cluster. Transport current through the
superconductor produces the effective magnetic field acting on the cluster's
magnetic moment. The direction of the effective field depends on the direction
of the current, thus allowing one to manipulate the magnetic moment by the
superconducting current. Due to the large density of the superconducting
current this method of magnetization reversal can be more advantageous at low
temperatures than the spin-transfer torque method that requires a large
spin-polarized current through a normal metal.",1710.08157v1
2017-10-23,Magnetic anisotropy in antiferromagnetic hexagonal MnTe,"Antiferromagnetic hexagonal MnTe is a promising material for spintronic
devices relying on the control of antiferromagnetic domain orientations. Here
we report on neutron diffraction, magnetotransport, and magnetometry
experiments on semiconducting epitaxial MnTe thin films together with density
functional theory (DFT) calculations of the magnetic anisotropies.
  The easy axes of the magnetic moments within the hexagonal basal plane are
determined to be along $\left<1\bar100\right>$ directions. The spin-flop
transition and concomitant repopulation of domains in strong magnetic fields is
observed.
  Using epitaxially induced strain the onset of the spin-flop transition
changes from $\sim2$~T to $\sim0.5$~T for films grown on InP and SrF$_2$
substrates, respectively.",1710.08523v2
2017-10-25,Highlights from the Pierre Auger Observatory (ICRC17),"In this contribution we summarize the highlights from the Pierre Auger
Observatory presented at the 35th International Cosmic Ray Conference. We
discuss the update of the measurement of the energy spectrum of cosmic rays
over a wide range of energy ($10^{17.5}$ to above $10^{20}$ eV), studies of the
cosmic-ray mass composition with the fluorescence and surface detector of the
Observatory, the discovery of a large-scale anisotropy in the arrival direction
of cosmic rays above $8\times 10^{18}$ eV and indications of anisotropy at
intermediate angular scales above $4 \times 10^{19}$ eV. Moreover, we report on
tests of hadronic interactions beyond LHC energies, multi-messenger analyses
with neutral primaries and the progress of the upgrade of the Observatory,
AugerPrime, aimed at elucidating the origin of the observed flux suppression at
ultra-high energies.",1710.09478v1
2017-10-26,Dynamical spin accumulation in large-spin magnetic molecules,"The frequency-dependent transport through a nano-device containing a
large-spin magnetic molecule is studied theoretically in the Kondo regime.
Specifically, the effect of magnetic anisotropy on dynamical spin accumulation
is of primary interest. Such accumulation arises due to finite off-diagonal in
spin components of the dynamical conductance. Here, employing the Kubo
formalism and the numerical renormalization group (NRG) method, we demonstrate
that the dynamical transport properties strongly depend on magnetic
configuration of the device and intrinsic parameters of the molecule.
Specifically, the effect of dynamical spin accumulation is found to be greatly
affected by the type of magnetic anisotropy exhibited by the molecule, and it
develops for frequencies corresponding to the Kondo temperature. For the
parallel magnetic configuration of the device, the presence of dynamical spin
accumulation is conditioned by the interplay of ferromagnetic-lead-induced
exchange field and the Kondo correlations.",1710.09623v1
2017-10-27,Electron effective mass in Sn-doped monoclinic single crystal $β$-gallium oxide determined by mid-infrared optical Hall effect,"The isotropic average conduction band minimum electron effective mass in
Sn-doped monoclinic single crystal $\beta$-Ga$_2$O$_3$ is experimentally
determined by mid-infrared optical Hall effect to be $(0.284\pm0.013)m_{0}$
combining investigations on ($010$) and ($\bar{2}01$) surface cuts. This result
falls within the broad range of values predicted by theoretical calculations
for undoped $\beta$-Ga$_2$O$_3$. The result is also comparable to recent
density functional calculations using the
Gaussian-attenuation-Perdue-Burke-Ernzerhof hybrid density functional, which
predict an average effective mass of $0.267m_{0}$ (arXiv:1704.06711
[cond-mat.mtrl-sci]). Within our uncertainty limits we detect no anisotropy for
the electron effective mass, which is consistent with most previous theoretical
calculations. We discuss upper limits for possible anisotropy of the electron
effective mass parameter from our experimental uncertainty limits, and we
compare our findings with recent theoretical results.",1710.10094v1
2017-10-27,Evidence of thermal transport anisotropy in stable glasses of vapour deposited organic molecules,"Vapour-deposited organic glasses are currently in use in many optoelectronic
devices. Their operation temperature is limited by the glass transition
temperature of the organic layers and thermal management strategies become
increasingly important to improve the lifetime of the device. Here we report
the unusual finding that molecular orientation heavily influences heat flow
propagation in glassy films of small molecule organic semiconductors. The
thermal conductivity of vapour-deposited thin-film semiconductor glasses is
anisotropic and controlled by the deposition temperature. We compare our data
with extensive molecular dynamics simulations to disentangle the role of
density and molecular orientation on heat propagation. Simulations do support
the view that thermal transport along the backbone of the organic molecule is
strongly preferred with respect to the perpendicular direction. This is due to
the anisotropy of the molecular interaction strength that limit the transport
of atomic vibrations. This approach could be used in future developments to
implement small molecule glassy films in thermoelectric or other organic
electronic devices.",1710.10123v1
2017-10-29,Writing and storing information in an array of magnetic vortex nanodisks using their azimuthal modes,"The switching of a vortex core of a single disk in an array of a multilayer
system is investigated by micromagnetic simulation. We found that the
perpendicular uniaxial anisotropy (PUA) decreases the frequencies of the
azimuthal mode in disks with magnetic vortex configuration. We obtained a phase
diagram of magnetic field intensity vs. frequency of the azimuthal mode, as a
function of the value of perpendicular uniaxial anisotropy. We demonstrated
that rotating magnetic fields (CW and CCW) with frequency equal to azimuthal
modes can be used to switch the vortex core of single disks in a disk array.
This allows obtaining different memory states with a single array of nanodisks,
and therefore writing information through the application of rotating fields.",1710.10613v1
2017-10-31,Kink confinement in the antiferromagnetic XXZ spin-1/2 chain in a weak staggered magnetic field,"The Heisenberg XXZ spin-1/2 chain is considered in the massive
antiferromagnetic regime in the presence of a staggered longitudinal magnetic
field. The Hamiltonian of the model is characterised by the anisotropy
parameter $\Delta<-1$, and by the magnetic field strength h. At zero magnetic
field, the model is exactly solvable. In the thermodynamic limit, it has two
degenerate vacua and the kinks (which are also called spinons) interpolating
between these vacua, as elementary excitations. Application of the staggered
magnetic field breaks integrability of the model and induces the long-range
attractive potential between two adjacent kinks leading to their confinement
into the bound states. The energy spectra of the resulting two-kink bound
states are perturbatively calculated in the extreme anisotropic (Ising) limit
$\Delta\to-\infty$ to the first order in the inverse anisotropy constant
$|\Delta|^{-1}$, and also for generic values of $\Delta<-1$ to the first order
in the weak magnetic field h.",1710.11605v2
2017-11-06,Impact of domain anisotropy on the inverse cascade in geostrophic turbulent convection,"The effect of domain anisotropy on the inverse cascade occurring within the
geostrophic turbulence regime of rapidly rotating Rayleigh-B\'enard convection
(RRBC) is investigated. In periodic domains with square cross-section in the
horizontal a domain-filling dipole state is present. For rectangular periodic
domains a Kolmogorov-like flow consisting of a periodic array of alternating
unidirectional jets with embedded vortices is observed, together with an
underlying weak meandering transverse jet. Similar transitions occurring in
weakly dissipative two-dimensional flows driven by externally imposed small
amplitude noise as well as in classical hydrostatic geostrophic turbulence are
a consequence of inviscid conservation of energy and potential enstrophy and
can be understood using statistical mechanics considerations. RRBC represents
an important three-dimensional system with only one inviscid invariant that
nonetheless exhibits large-scale structures driven by intrinsically generated
fluctuations.",1711.01685v1
2017-11-07,Study on Effects of Dipole-dipole Interactions in Nd_2Fe_{14}B thin film Based on Stochastic Cut-off Method with New Efficient Algorithm,"We developed a new algorithm for the stochastic cutoff method, which is a
Monte Carlo method for long-range interacting systems. The present new
algorithm is efficient for complicated lattice structures, e.g., amorphous and
also materials with complicated unit cell structure. In addition, it has an
advantage in a high temperature region. With the present method, we
investigated an atomistic model of the permanent magnet Nd 2 Fe 14 B with
dipole-dipole interactions to study the effect of the anisotropy of the Fe ions
on the magnetization structure in the thin film system. It has revealed that
the anisotropy of the Fe ions plays an important role to maintain the uniaxial
magnetization structure at high temperatures.",1711.02284v2
2017-11-16,Testing the isotropy of the Universe with type Ia supernovae in a model-independent way,"In this paper, we study an anisotropic universe model with Bianchi-I metric
using Joint Light-curve Analysis (JLA) sample of type Ia supernovae (SNe Ia).
Because light-curve parameters of SNe Ia vary with different cosmological
models and SNe Ia samples, we fit the SNe Ia light-curve parameters and
cosmological parameters simultaneously employing Markov Chain Monte Carlo
method. Therefore, the results on the amount of deviation from isotropy of the
dark energy equation of state ($\delta$), and the level of anisotropy of the
large-scale geometry ($\Sigma_0$) at present, are totally model-independent.
The constraints on the skewness and cosmic shear are $-0.101<\delta<0.071$ and
$-0.007<\Sigma_0<0.008$. This result is consistent with a standard isotropic
universe ($\delta=\Sigma_0=0$). However, a moderate level of anisotropy in the
geometry of the Universe and the equation of state of dark energy, is allowed.
Besides, there is no obvious evidence for a preferred direction of anisotropic
axis in this model.",1711.05974v1
2017-11-19,Room-temperature observation and current control of skyrmions in Pt/Co/Os/Pt thin films,"We report the observation of room-temperature magnetic skyrmions in
Pt/Co/Os/Pt thin-film heterostructures and their response to electric currents.
The magnetic properties are extremely sensitive to inserting thin Os layers
between the Co-Pt interface resulting in reduced saturation magnetization,
magnetic anisotropy and Curie temperature. The observed skyrmions exist in a
narrow temperature, applied-field and layer-thickness range near the
spin-reorientation transition from perpendicular to in-plane magnetic
anisotropy. The skyrmions have an average diameter of 2.3{\mu}m and transport
measurements demonstrate these features can be displaced with current densities
as low as J = 2x10^4 A/cm^2 and display a skyrmion Hall effect.",1711.07101v1
2017-11-24,Heavy Quarks in Strongly Coupled Non-Conformal Plasmas with Anisotropy,"We analysis physical observables of heavy quarks in gravity models describing
strongly coupled non-conformal plasmas with anisotropy via the gauge/gravity
duality. The focus lies on the binding energy of static quark-antiquark $(q\bar
q$-)pairs, the maximum distance (screening distance) of a bound $q\bar q$-pair
and the drag force on uniformly moving quarks in the hot plasma. In order to
discover universal behavior in the observables, the computations are worked out
in a two parameter deformation of pure gravity in $AdS_5$ spacetime with a
black brane which is assumed to be dual to a respective two parameter
deformation of $\mathcal{N}$=\,4 supersymmetric Yang-Mills (SYM) theory at
temperature $T$. The deformation is designed to break isotropy and conformal
symmetry and is a solution to equations of motion of a gravity action.",1711.08943v2
2017-11-30,Domain Wall Motion Driven by Laplace Pressure in CoFeB-MgO Nanodots with Perpendicular Anisotropy,"We have studied the magnetization reversal of CoFeB-MgO nanodots with
perpendicular anisotropy for size ranging from w=400 nm to 1 {\mu}m. Contrary
to previous experiments, the switching field distribution is shifted toward
lower magnetic fields as the size of the elements is reduced with a mean
switching field varying as 1/w. We show that this mechanism can be explained by
the nucleation of a pinned magnetic domain wall (DW) at the edges of the
nanodots where damages are introduced by the patterning process. As the surface
tension (Laplace pressure) applied on the DW increases when reducing the size
of the nanodots, we demonstrate that the depinning field to reverse the entire
elements varies as 1/w. These results suggest that the presence of DWs has to
be considered in the switching process of nanoscale elements and open a path
toward scalable spintronic devices.",1711.11334v2
2017-12-01,Active control of thermomagnetic avalanches in superconducting Nb films with tunable anisotropy,"Active triggering and manipulation of ultrafast flux dynamics in
superconductors are demonstrated in films of Nb. Controlled amounts of magnetic
flux were injected from a point along the edge of a square sample, which at 2.5
K responds by nucleation of a thermomagnetic avalanche. Magneto-optical imaging
was used to show that when such films are cooled in the presence of in-plane
magnetic fields they become anisotropic, and the morphology of the avalanches
change systematically, both with the direction and magnitude of the field. The
images reveal that the avalanching dendrites consistently bend towards the
direction perpendicular to that of the in-plane field. The effect increases
with the field magnitude, and at 1.5 kOe the triggered avalanche becomes
quenched at the nucleation stage. The experimental results are explained based
on a theoretical model for thermomagnetic avalanche nucleation in
superconducting films, and by assuming that the frozen-in flux generates
in-plane anisotropy in the film thermal conductance. The results demonstrate
that applying in-plane magnetic fields to film superconductors can be a
versatile external tool for controlling their ultrafast flux dynamics.",1712.00300v1
2017-12-04,Directed Self-Assembly of Polarizable Ellipsoids in an External Electric Field,"The interplay between shape anisotropy and directed long-range interactions
enables the self-assembly of complex colloidal structures. As a recent
highlight, ellipsoidal particles polarized in an external electric field were
observed to associate into well-defined tubular structures. In this study, we
investigate systematically such directed self-assembly using Monte Carlo
simulations of a two-point-charge model of polarizable prolate ellipsoids. In
spite of its simplicity and computational efficiency, we demonstrate that the
model is capable of capturing the complex structures observed in experiments on
ellipsoidal colloids at low volume fractions. We show that, at sufficiently
high electric field strength, the anisotropy in shape and electrostatic
interactions causes a transition from 3-dimensional crystal structures observed
at low aspect ratios to 2-dimensional sheets and tubes at higher aspect ratios.
Our work thus illustrates the rich self-assembly behavior accessible when
exploiting the interplay between competing long- and short-range anisotropic
interactions in colloidal systems.",1712.01025v1
2017-10-14,Magnetocaloric Effect and Magnetic refrigeration: analytic and numeric study,"This work aims to present an analytical and numerical study of the
magnetocaloric effects (MCE) providing realistic proposals about materials that
should be chosen in the design of new refrigerator appliances around the room
temperature. Starting from a spin Hamiltonian including the exchange
interaction, the single-ion anisotropy and the applied magnetic field terms, we
have calculated the partition function at a given temperature and derived a set
of relevant physical quantities as magnetization, magnetic entropy and specific
heat and analyzed their behavior with atomic parameters as spin, exchange and
anisotropy. Using numerical programs that we developed by ourselves, we were
able to better elucidate the role of each microscopic parameter in order to
reinforce the relative cooling power (RCP) and give rise to optimal
performances of the refrigerant compound. This approach could be extended to
composite materials underscoring a giant MCE at room temperature.
  Key-words Magnetic refrigeration, Magnetocaloric Effect, Energy efficiency,
Spin Hamiltonian",1712.01096v1
2017-12-05,"Testing gravity on cosmological scales with cosmic shear, cosmic microwave background anisotropies, and redshift-space distortions","We use a range of cosmological data to constrain phenomenological
modifications to general relativity on cosmological scales, through
modifications to the Poisson and lensing equations. We include cosmic microwave
background anisotropy measurements from the Planck satellite, cosmic shear from
CFHTLenS and DES-SV, and redshift-space distortions from BOSS data release 12
and the 6dF galaxy survey. We find no evidence of departures from general
relativity, with the modified gravity parameters constrained to $\Sigma_0 =
0.05^{+0.05}_{-0.07}$ and $\mu_0 = -0.10^{+0.20}_{-0.16}$, where $\Sigma_0$ and
$\mu_0$ refer to deviations from general relativity today and are defined to be
zero in general relativity. We also forecast the sensitivity to those
parameters of the full five-year Dark Energy Survey and of an experiment like
the Large Synoptic Survey Telescope, showing a substantial expected improvement
in the constraint on $\Sigma_0$.",1712.01846v3
2017-12-06,Expectation of primordial gravity waves generated during inflation,"The inflationary paradigm is extremely successful regarding predictions of
temperature anisotropies in the CMB. However, inflation also makes predictions
for a CMB B-mode polarization, which has not been detected. Moreover, the
standard inflationary paradigm is unable to accommodate the evolution from the
initial state, which is assumed to be symmetric, into a non-symmetric
aftermath. In Phys. Rev. D 96, 101301(R), we show that the incorporation of an
element capable of explaining such a transition drastically changes the
prediction for the shape and size of the B-mode spectrum. In particular,
employing a realistic objective collapse model in a well-defined semiclassical
context, we find that, while predictions of temperature anisotropies are nor
altered (with respect to standard predictions), the B-mode spectrum gets
strongly suppressed--in accordance with observations. Here we present an
in-depth discussion of that analysis, together with the details of the
calculation.",1712.02435v2
2017-12-08,Cosmic anisotropy with Reduced Relativistic Gas,"The dynamics of cosmological anisotropies is investigated for Bianchi type I
universe filled by a relativistic matter represented by the reduced
relativistic gas model (RRG), with equation of state interpolating between
radiation and matter. Previously it was shown that the interpolation is
observed in the background cosmological solutions for homogeneous and isotropic
universe and also for the linear cosmological perturbations. We extend the
application of RRG to the Bianchi type I anisotropic model and find that the
solutions evolve to the isotropic universe with the pressureless matter
contents.",1712.03066v2
2017-12-19,Constraints on scattering of keV--TeV dark matter with protons in the early Universe,"We present the first cosmological constraint on dark matter scattering with
protons in the early Universe for the entire range of dark matter masses
between 1 keV and 1 TeV. This constraint is derived from the Planck
measurements of the cosmic microwave background (CMB) temperature and
polarization anisotropy, and the CMB lensing anisotropy. It improves upon
previous CMB constraints by many orders of magnitude, where limits are
available, and closes the gap in coverage for low-mass dark matter candidates.
We focus on two canonical interaction scenarios: spin-independent and
spin-dependent scattering with no velocity dependence. Our results exclude
(with 95% confidence) spin-independent interactions with cross sections greater
than $5.3 \times 10^{-27}$ cm$^2$ for 1 keV, $3.0 \times 10^{-26}$ cm$^2$ for 1
MeV, $1.7 \times 10^{-25}$ cm$^2$ for 1 GeV, and $1.6 \times 10^{-23}$ cm$^2$
for 1 TeV dark matter mass. Finally, we discuss the implications of this study
for dark matter physics and future observations.",1712.07133v2
2017-12-21,Persistent Homology and Non-Gaussianity,"In this paper, we introduce the topological persistence diagram as a
statistic for Cosmic Microwave Background (CMB) temperature anisotropy maps. A
central concept in `Topological Data Analysis' (TDA), the idea of persistence
is to represent a data set by a family of topological spaces. One then examines
how long topological features `persist' as the family of spaces is traversed.
We compute persistence diagrams for simulated CMB temperature anisotropy maps
featuring various levels of primordial non-Gaussianity of local type.
Postponing the analysis of observational effects, we show that persistence
diagrams are more sensitive to local non-Gaussianity than previous topological
statistics including the genus and Betti number curves, and can constrain
$\Delta f_{NL}^{\rm loc}= 35.8$ at the 68\% confidence level on the simulation
set, compared to $\Delta f_{NL}^{\rm loc}= 60.6$ for the Betti number curves.
Given the resolution of our simulations, we expect applying persistence
diagrams to observational data will give constraints competitive with those of
the Minkowski Functionals. This is the first in a series of papers where we
plan to apply TDA to different shapes of non-Gaussianity in the CMB and Large
Scale Structure.",1712.08159v1
2017-12-29,Nematic twist--bend phase in an external field,"Nematic twist--bend is the fifth nematic phase recognized in nature. This
phase exhibits spiral orientational order, thus it is a chiral structure and it
can be stabilized in systems composed of achiral molecules. The microscopic
origin of this spontaneous chiral symmetry breaking is to a large extent
unknown but phenomenologically it appears stabilized by assuming coupling
between steric polar and orientational orderings. Understanding of how external
fields affect the stability of this phase is of great intellectual interest and
of relevance to potential applications. Within mesoscopic Landau--de Gennes
theory we find that for compounds with positive anisotropy the helix unwinds to
a polar uniaxial nematic, however negative material anisotropy gives rise to a
rich sequence of new nematic phases obtained via mechanism of flattening the
conical spiral.",1801.00027v1
2018-01-04,Crystal growth and magnetic anisotropy in the spin-chain ruthenate Na$_2$RuO$_4$,"We report single crystal growth, electrical resistivity $\rho$, anisotropic
magnetic susceptibiltiy $\chi$, and heat capacity $C_p$ measurements on the
one-dimensional spin-chain ruthenate Na$_2$RuO$_4$. We observe variable range
hopping (VRH) behaviour in $\rho(T)$. The magnetic susceptibility with magnetic
field perpendicular ($\chi_\perp$) and parallel ($\chi_\parallel$) to the
spin-chains is reported. The magnetic properties are anisotropic with
$\chi_\perp > \chi_\parallel$ in the temperature range of measurements T
$\approx 2$ to $305$ K with $\chi_\perp / \chi_\parallel$ $\approx 1.4$ at
$305$ K. Analysis of the $\chi(T)$ data reveals an anisotropy in the $g$-factor
and Van-Vleck paramagnetic contribution. An anomaly in $\chi(T)$ and a
corresponding lambda-like anomaly in $C_p$ at $T_N = 37$ K confirms long-range
antiferromagnetic ordering. This temperature is an order of magnitude smaller
than the Weiss temperature $\theta \sim -250$ K and points to suppression of
long range magnetic order due to low dimensionality. However, we were unable to
get a satisfactory fit of the experimental $\chi(T)$ by an isolated
one-dimensional spin-chain model, suggesting the importance of inter-chain
interactions in Na$_2$RuO$_4$.",1801.01524v1
2018-01-09,First-principles investigation of elastic anomalies in niobium at high pressure and temperature,"Niobium does not show any structure transition up to very high pressures.
Nonetheless, by using density functional theory, we demonstrate in this work
that it exhibits striking softening in elastic moduli C44 and C' at a pressure
from 20 to 150 GPa. A novel anomaly softening in C44 from 275 to 400 GPa is
also predicted. The physics behind these two anomalies is elaborated by
electronic structure calculations, which revealed that they are actually
different, with the first one directly relates to an underlying rhombohedral
distortion whereas the latter originates in an electronic topological
transition. The large magnitude of the softening leads to a remarkable elastic
anisotropy in both the shear and the Young's moduli of Nb. Further
investigation shows that thermo-electrons have an important role on these
anomalies. This effect has not been noticed before. With increased electronic
temperature, it is found that all anomalies (both the elastic softening and
anisotropy) in Nb are gradually diminished, effectively giving rise to a
temperature-induced hardening phenomenon.",1801.02915v1
2018-01-09,Connecting CMB anisotropy and cold dark matter phenomenology via reheating,"Understanding the properties of dark matter has proved to be one of the most
challenging problems of particle phenomenology. In this paper, we have tried to
understand the phenomenology of dark matter in light of very well understood
properties of cosmic microwave background (CMB) anisotropy. To connect these
two, inflation and its subsequent evolution known as the reheating phase play
the important role. Following the previous analysis, we first established a
one-to-one correspondence between the CMB power spectrum and the reheating
temperature assuming the perturbative reheating scenario. Further by
incorporating a possible dark matter candidate through the radiation
annihilation process during reheating and the current value of dark matter
abundance, we constrain the dark matter parameter space through the
inflationary power spectrum for different inflationary models.",1801.03059v3
2018-01-17,Hartman effect for spin waves in exchange regime,"Hartman effect for spin waves tunnelling through a barrier in a thin magnetic
film is considered theoretically. The barrier is assumed to be created by a
locally increased magnetic anisotropy field. The considerations are focused on
a nanoscale system operating in the exchange-dominated regime. We derive the
formula for group delay $\tau_{gr}$ of spin wave package and show that
$\tau_{gr}$ saturates with increasing barrier width, which is a signature of
the Hartman effect predicted earlier for photonic and electronic systems. In
our calculations we consider the general boundary exchange conditions which
take into account different strength of exchange coupling between the barrier
and its surrounding. As a system suitable for experimental observation of the
Hartman effect we propose a CoFeB layer with perpendicular magnetic anisotropy
induced by a MgO overlayer.",1801.05876v3
2018-01-18,Excellent microwave and magnetic properties of La-Cu substituted Ba-hexaferrites prepared by ceramic process,"We demonstrate exceptional microwave magnetic performance of
crystallographycally textured barium hexaferrites prepared by conventional
ceramic method. Vibrating sample magnetometer (VSM) and rectangular cavity
perturbation measurements indicate that bulk Ba0.8La0.2Fe11.2Cu0.2O19 samples
exhibit a strong magnetic anisotropy field Ha of 14.6kOe, the highest remanent
magnetization of 3.96kGs, and the lowest ferromagnetic resonance (FMR)
linewidth of 401Oe with zero applied bias field at Q-band. Broadband
millimeter-wave transmittance measurements determined the complex permeability
and permittivity. The remanent magnetization, anisotropy field Ha, and
effective linewidth were also estimated based on Schlomann's theory of the
complex permeability. These calculated values are in good agreement with the
VSM and FMR measurements.",1801.05945v1
2018-01-21,Microwave fields driven domain wall motions in antiferromagnetic nanowires,"In this work, we study the microwave field driven antiferromagnetic domain
wall motion in an antiferromagnetic nanowire, using the numerical calculations
based on a classical Heisenberg spin model. We show that a proper combination
of a static magnetic field plus an oscillating field perpendicular to the
nanowire axis is sufficient to drive the domain wall propagation along the
nanowire with the axial magnetic anisotropy. More importantly, the drift
velocity at the resonance frequency is comparable to that induced by
temperature gradients, suggesting that microwave field can be a very promising
tool to control domain wall motions in antiferromagnetic nanostructures.
Furthermore, the dependences of resonance frequency and drift velocity on the
static and oscillating fields, the axial anisotropy, and the damping constant
are discussed in details. This work provides useful information for the spin
dynamics in antiferromagnetic nanostructures for spintronics applications.",1801.06748v1
2018-01-30,Critical behavior of two-dimensional intrinsically ferromagnetic semiconductor CrI3,"CrI3, which belongs to a rare category of two-dimensional (2D) ferromagnetic
semiconductors, is of great interest for spintronic device applications. Unlike
CrCl3 whose magnetism presents a 2D-Heisenberg behavior, CrI3 exhibits a larger
van der Waals gap, smaller cleavage energy, and stronger magnetic anisotropy
which could lead to a 3D magnetic characteristic. Hence, we investigate the
critical behavior of CrI3 in the vicinity of magnetic transition. We use the
modified Arrott plot and Kouvel-Fisher method, and conduct critical isotherm
analysis to estimate the critical exponents near the ferromagnetic phase
transition. This shows that the magnetism of CrI3 follows the crossover
behavior of a 3D-Ising model with mean field type interactions where the
critical exponents \b{eta}, {\gamma}, and {\delta} are 0.323, 0.835, and 3.585,
respectively, at the Curie temperature of 64 K. We propose the crossover
behavior can be attributed to the strong uniaxial anisotropy and inevitable
interlayer coupling. Our experiment demonstrates the applicability of crossover
behavior to a 2D ferromagnetic semiconductor.",1801.09878v1
2018-01-30,Anisotropic hydrodynamics with a scalar collisional kernel,"Prior studies of non-equilibrium dynamics using anisotropic hydrodynamics
have used the relativistic Anderson-Witting scattering kernel or some variant
thereof. In this paper, we make the first study of the impact of using a more
realistic scattering kernel. For this purpose, we consider a conformal system
undergoing transversally-homogenous and boost-invariant Bjorken expansion and
take the collisional kernel to be given by the leading order 2 <-> 2 scattering
kernel in scalar lambda phi^4. We consider both classical and quantum
statistics in order to assess the impact of Bose enhancement on the dynamics.
We also determine the anisotropic non-equilibrium attractor of a system subject
to this collisional kernel. We find that, when the near-equilibrium
relaxation-times in the Anderson-Witting and scalar collisional kernels are
matched, the scalar kernel results in a higher degree of momentum-space
anisotropy during the system's evolution, given the same initial conditions.
Additionally, we find that taking into account Bose enhancement further
increases the dynamically generated momentum-space anisotropy.",1801.10173v2
2018-01-31,Skyrmions formation due to unconventional magnetic modes in anisotropic multi-band superconductors,"Multiband superconductors have a sufficient number of degrees of freedom to
allow topological excitations characterized by Skyrmionic topological
invariants. In the most common, clean s-wave multiband, systems the interband
magnetic coupling favours composite vortex solutions, without a Skyrmionic
topological charge. It was discussed recently that certain kinds of
anisotropies lead to hybridisation of the interband phase difference (Leggett)
mode with magnetic modes, dramatically changing the hydromagnetostatics of the
system. Here we report this effect for a range of parameters that substantially
alter the nature of the topological excitations, leading to solutions
characterized by a nontrivial topological invariant, rather than the standard
composite vortex solutions. This invariant is not truly topologically conserved
but is energetically conserved, leading to a texture formed of bound
excitations in each band, namely fractional vortices, each carrying a fraction
of the flux quantum. We demonstrate that in this regime there is a rich
spectrum of Skyrmion solutions, with various topological charges, that are
robust with respect to changes of parameters of the system and present for a
wide range of anisotropies.",1801.10463v2
2018-01-26,Mean-field theory of differential rotation in density stratified turbulent convection,"A mean-field theory of differential rotation in a density stratified
turbulent convection has been developed. This theory is based on a combined
effect of the turbulent heat flux and anisotropy of turbulent convection on the
Reynolds stress. A coupled system of dynamical budget equations consisting in
the equations for the Reynolds stress, the entropy fluctuations and the
turbulent heat flux has been solved. To close the system of these equations,
the spectral tau approach which is valid for large Reynolds and Peclet numbers,
has been applied. The adopted model of the background turbulent convection
takes into account an increase of the turbulence anisotropy and a decrease of
the turbulent correlation time with the rotation rate. This theory yields the
radial profile of the differential rotation which is in agreement with that for
the solar differential rotation.",1801.10477v2
2018-02-08,Frustration and anisotropic exchange in ytterbium magnets with edge-shared octahedra,"We consider the structure of anisotropic exchange interactions in
ytterbium-based insulating rare-earth magnets built from edge-sharing
octahedra. We argue the features of trivalent ytterbium and this structural
configuration allow for a qualitative determination of the different
anisotropic exchange regimes that may manifest in such compounds. The validity
of such super-exchange calculations is tested through comparison to the
well-characterized breathing pyrochlore compound Ba$_3$Yb$_2$Zn$_5$O$_{11}$.
With this in hand, we then consider application to three-dimensional pyrochlore
spinels as well as two-dimensional honeycomb and triangular lattice systems
built from such edge-sharing octahedra. We find an extended regime of robust
emergent weak anisotropy with dominant antiferromagnetic Heisenberg
interactions as well as smaller regions with strong anisotropy. We discuss the
implications of our results for known compounds with the above structures, such
as the spinels AYb$_2$X$_4$ (A = Cd, Mg, X = S, Se), the triangular compound
YbMgGaO$_4$, which have recently emerged as promising candidates for observing
unconventional magnetic phenomena. Finally, we speculate on implications for
the R$_2$M$_2$O$_7$ pyrochlore compounds and some little studied honeycomb
ytterbium magnets.",1802.03024v1
2018-02-12,Easy-Plane Magnetic Strip as a Long Josephson Junction,"Spin-torque-biased magnetic dynamics in an easy-plane ferromagnet (EPF) is
theoretically studied in the presence of a weak in-plane anisotropy. While this
anisotropy spoils U(1) symmetry thereby quenching the conventional spin
superfluidity, we show that the system instead realizes a close analog of a
long Josephson junction (LJJ) model. The traditional magnetic-field and
electric-current controls of the latter map respectively onto the symmetric and
antisymmetric combinations of the out-of-plane spin torques applied at the ends
of the magnetic strip. This suggests an alternative route towards realizations
of superfluid-like transport phenomena in insulating magnetic systems. We study
spin-torque-biased phase diagram, providing an analytical solution for static
multidomain phases in the EPF. We adapt an existing self-consistency method for
the LJJ to develop an approximate solution for the EPF dynamics. The LJJ-EPF
mapping allows us to envision superconducting circuit functionality at elevated
temperatures. The results apply equally to antiferromagnets with suitable
effective free energy in terms of the N\'{e}el order instead of magnetization.",1802.04229v1
2018-02-14,Pathway towards programmable wave anisotropy in cellular metamaterials,"In this work, we provide a proof-of-concept experimental demonstration of the
wave control capabilities of cellular metamaterials endowed with populations of
tunable electromechanical resonators. Each independently tunable resonator
comprises a piezoelectric patch and a resistor-inductor shunt, and its resonant
frequency can be seamlessly re-programmed without interfering with the cellular
structure's default properties. We show that, by strategically placing the
resonators in the lattice domain and by deliberately activating only selected
subsets of them, chosen to conform to the directional features of the beamed
wave response, it is possible to override the inherent wave anisotropy of the
cellular medium. The outcome is the establishment of tunable spatial patterns
of energy distillation resulting in a non-symmetric correction of the
wavefields.",1802.04959v1
2018-02-16,Dual phase-space cascades in 3D hybrid-Vlasov-Maxwell turbulence,"To explain energy dissipation via turbulence in collisionless, magnetized
plasmas, the existence of a dual real- and velocity-space cascade of
ion-entropy fluctuations below the ion gyroradius has been proposed. Such a
dual cascade, predicted by the gyrokinetic theory, has previously been observed
in gyrokinetic simulations of two-dimensional, electrostatic turbulence. For
the first time we show evidence for a dual phase-space cascade of ion-entropy
fluctuations in a three-dimensional simulation of hybrid-kinetic,
electromagnetic turbulence. Some of the scalings observed in the energy spectra
are consistent with a generalized theory for the cascade that accounts for the
spectral anisotropy of critically balanced, intermittent, sub-ion-Larmor-scale
fluctuations. The observed velocity-space cascade is also anisotropic with
respect to the magnetic-field direction, with linear phase mixing along
magnetic-field lines proceeding mainly at spatial scales above the ion
gyroradius and nonlinear phase mixing across magnetic-field lines proceeding at
perpendicular scales below the ion gyroradius. Such phase-space anisotropy
could be sought in heliospheric and magnetospheric data of solar-wind
turbulence and has far-reaching implications for the dissipation of turbulence
in weakly collisional astrophysical plasmas.",1802.06133v2
2018-02-19,Azimuthal Anisotropies at High Momentum from Purely Non-Hydrodynamic Transport,"In the limit of short mean free path, relativistic kinetic theory gives rise
to hydrodynamics through a systematically improvable gradient expansion. In the
present work, a systematically improvable expansion in the opposite limit of
large mean free path is considered, describing the dynamics of particles which
are almost, but not quite, non-interacting. This non-hydrodynamic ""eremitic""
expansion does not break down for large gradients, and may be useful in
situations where a hydrodynamic treatment is not applicable. As applications,
azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions
at $\sqrt{s}=5.02$ TeV are calculated from the first order eremitic expansion
of kinetic theory in the relaxation time approximation.",1802.06804v3
2018-02-20,Diode-like asymmetric transmission in ultrathin hyperbolic epsilon-near-zero slabs: extreme anisotropy mimicking chirality,"We demonstrate that a strong asymmetric transmission for forward and backward
propagation of tilted circular polarized optical waves is supported by
ultrathin epsilon-near-zero hyperbolic slabs. We find that, remarkably, this
effect is solely triggered by anisotropy without resorting to any breaking of
reciprocity and chiral symmetries or spatial nonlocal effects. In addition, we
show that the asymmetric transmission undergoes a dramatic enhancement if the
slab is hyperbolic in the epsilon-near-zero regime. This happens since, close
to epsilon-near-zero point, the hyperbolic dispersion activates etalon
resonances where extraordinary waves accumulate propagation phase even though
the slab is ultrathin. The proposed strategy holds promise for realizing
ultra-compact and efficient polarization devices at different frequency bands.",1802.07017v1
2018-02-26,Quantum and Classical Phases of the Pyrochlore Heisenberg Model with Competing Interactions,"We investigate the quantum Heisenberg model on the pyrochlore lattice for a
generic spin $S$ in the presence of nearest-neighbor $J_{1}$ and
second-nearest-neighbor $J_{2}$ exchange interactions. By employing the
pseudofermion functional renormalization group method, we find, for $S=1/2$ and
$S=1$, an extended quantum-spin-liquid phase centered around $J_{2}=0$, which
is shown to be robust against the introduction of breathing anisotropy. The
effects of temperature, quantum fluctuations, breathing anisotropies, and a
$J_{2}$ coupling on the nature of the scattering profile, and the pinch points,
in particular, are studied. For the magnetic phases of the $J_{1}$-$J_{2}$
model, quantum fluctuations are shown to renormalize phase boundaries compared
to the classical model and to modify the ordering wave vectors of spiral
magnetic states, while no new magnetic orders are stabilized.",1802.09546v3
2018-02-28,Ultra-fast artificial neuron: generation of picosecond-duration spikes in a current-driven antiferromagnetic auto-oscillator,"We demonstrate analytically and numerically, that a thin film of an
antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being
driven by an external spin-transfer torque signal, can be used for the
generation of ultra-short ""Dirac-delta-like"" spikes. The duration of the
generated spikes is several picoseconds for typical AFM materials and is
determined by the in-plane magnetic anisotropy and the effective damping of the
AFM material. The generated output signal can consist of a single spike or a
discrete group of spikes (""bursting""), which depends on the repetition (clock)
rate, amplitude, and shape of the external control signal. The spike generation
occurs only when the amplitude of the control signal exceeds a certain
threshold, similar to the action of a biological neuron in response to an
external stimulus. The ""threshold"" behavior of the proposed AFM spike generator
makes possible its application not only in the traditional microwave signal
processing but also in the future neuromorphic signal processing circuits
working at clock frequencies of tens of gigahertz.",1802.10236v1
2018-02-28,Effect of exchange-correlation spin-torque on spin dynamics,"A recently proposed exchange-correlation functional (Dewhurst et al.
10.1021/acs.jctc.7b01049) with in density functional theory, which ensures that
the exchange-correlation magnetic field is source-free, is shown to give
non-zero internal spin-torque. This spin-torque is identically zero for all
conventional local and semi-local functionals. Extension of this source-free
functional to the time domain is used to study the effect of the internal
spin-torque on the laser induced spin-dynamics in bulk Co, Ni and interfaces of
these metals with Pt. It is shown that the internal spin-torque contribute
significantly to spin-dynamics only when the magneto crystalline anisotropy
energy is small, as in the case of cubic bulk materials. For surfaces or
interfaces, where the anisotropy energy is large, these torques are too small
to cause any significant precession of spins in early times ($<$ 100fs).
Further more it is shown that the spin-dynamics caused by the internal
spin-torque is slow compared to the inter-site spin transfer and spin-orbit
mediated spin-flips.",1802.10382v1
2018-03-01,Field-induced ordering in a random-bond quantum spin ladder compound with weak anisotropy,"The field induced quantum phase transitions in the disorder-free and
disordered samples of the spin ladder material (CH_3)_2CHNH_3Cu(Cl_{1-x}Br_x)_3
are studied using magnetic calorimetry and magnetic neutron diffraction on
single crystal samples. Drastically different critical indexes and correlation
lengths in the high field phase are found for two different orientations of the
applied field. It is argued that for a field applied along the crystallographic
c axis, as in previous studies [1], the transition is best described as an
Ising transition in random field and anisotropy, rather than as a magnetic Bose
Glass to Bose Condensate transition.
  [1] Tao Hong, A. Zheludev, H. Manaka, and L.- P. Regnault, Phys. Rev. B 81,
060410 (2010).",1803.00375v1
2018-03-05,Velocity-Space Cascade in Magnetized Plasmas: Numerical Simulations,"Plasma turbulence is studied via direct numerical simulations in a
two-dimensional spatial geometry. Using a hybrid Vlasov-Maxwell model, we
investigate the possibility of a velocity-space cascade. A novel theory of
space plasma turbulence has been recently proposed by Servidio {\it et al.}
[PRL, {\bf 119}, 205101 (2017)], supported by a three-dimensional Hermite
decomposition applied to spacecraft measurements, showing that velocity space
fluctuations of the ion velocity distribution follow a broad-band, power-law
Hermite spectrum $P(m)$, where $m$ is the Hermite index. We numerically explore
these mechanisms in a more magnetized regime. We find that (1) the plasma
reveals spectral anisotropy in velocity space, due to the presence of an
external magnetic field (analogous to spatial anisotropy of fluid and plasma
turbulence); (2) the distribution of energy follows the prediction $P(m)\sim
m^{-2}$, proposed in the above theoretical-observational work; and (3) the
velocity-space activity is intermittent in space, being enhanced close to
coherent structures such as the reconnecting current sheets produced by
turbulence. These results may be relevant to the nonlinear dynamics
weakly-collisional plasma in a wide variety of circumstances.",1803.01633v2
2018-03-12,Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence,"The circular polarization of the cosmic microwave background (CMB) is usually
taken to be zero since it is not generated by Thomson scattering. Here we
explore the actual level of circular polarization in the CMB generated by
conventional cosmological sources of birefringence. We consider two classes of
mechanisms for birefringence. One is alignment of the matter to produce an
anisotropic susceptibility tensor: the hydrogen spins can be aligned either by
density perturbations or CMB anisotropies themselves. The other is anisotropy
of the radiation field coupled to the non-linear response of the medium to
electromagnetic fields: this can occur either via photon-photon scattering
(non-linear response of the vacuum); atomic hyperpolarizability (non-linear
response of neutral atoms); or plasma delay (non-linear response of free
electrons). The strongest effect comes from photon-photon scattering from
recombination at a level of $\sim 10^{-14}$ K. Our results are consistent with
a negligible circular polarization of the CMB in comparison with the linear
polarization or the sensitivity of current and near-term experiments.",1803.04505v2
2018-03-13,Anisotropic susceptibilities in the honeycomb Kitaev system $α$-RuCl$_{3}$,"The magnetic insulator $\alpha$-RuCl$_{3}$ is a promising candidate to
realize Kitaev interactions on a quasi-2D honeycomb lattice. We perform
extensive susceptibility measurements on single crystals of
$\alpha$-RuCl$_{3}$, including angle-dependence of the in-plane longitudinal
and transverse susceptibilities, which reveal a unidirectional anisotropy
within the honeycomb plane. By comparing the experimental results to a
high-temperature expansion of a Kitaev-Heisenberg-$\Gamma$ spin Hamiltonian
with bond anisotropy, we find excellent agreement with the observed phase shift
and periodicity of the angle-resolved susceptibilities. Within this model, we
show that the pronounced difference between in-plane and out-of-plane
susceptibilities as well as the finite transverse susceptibility are rooted in
strong symmetric off-diagonal $\Gamma$ spin exchange. The $\Gamma$ couplings
and relationships between other terms in the model Hamiltonian are quantified
by extracting relevant Curie-Weiss intercepts from the experimental data.",1803.04871v1
2018-03-15,Magneto-elastic switching of magnetostrictive nanomagnets with in-plane shape anisotropy,"We theoretically study the effect of a material defect (material void) on
switching errors associated with magneto-elastic switching of magnetization in
elliptical magnetostrictive nanomagnets having in-plane magnetic anisotropy. We
find that the error probability increases significantly in the presence of the
defect, indicating that magneto-elastic switching is particularly vulnerable to
material imperfections. Curiously, there is a critical stress value that gives
the lowest error probability in both defect-free and defective nanomagnets. The
critical stress is much higher in defective nanomagnets than in defect-free
ones. Since it is more difficult to generate the critical stress in small
nanomagnets than in large nanomagnets (having the same energy barrier for
thermal stability), it would be a challenge to downscale magneto-elastically
switched nanomagnets in memory and other applications where reliable switching
is required. This is likely to be further exacerbated by the presence of
defects.",1803.05869v3
2018-03-16,Motion of vortices in ferromagnetic spin-1 BEC,"The paper investigates dynamics of nonsingular vortices in a ferromagnetic
spin-1 BEC, where spin and mass superfluidity coexist in the presence of
uniaxial anisotropy (linear and quadratic Zeeman effect). The analysis is based
on hydrodynamics following from the Gross-Pitaevskii theory. Cores of
nonsingular vortices are skyrmions with charge, which is tuned by uniaxial
anisotropy and can have any fractal value between 0 and 1. There are
circulations of mass and spin currents around these vortices. The results are
compared with the equation of vortex motion derived earlier in the
Landau-Lifshitz-Gilbert theory for magnetic vortices in easy-plane
ferromagnetic insulators. In the both cases the transverse gyrotropic force
(analog of the Magnus force in superfluid and classical hydrodynamics) is
proportional to the charge of skyrmions in vortex cores.",1803.06939v1
2018-03-30,"Azimuthal angle distributions of neutrons emitted from the $^9$Be($γ$,$n$) reaction with linearly polarized $γ$-rays","The electromagnetic transitions of $^9$Be with linearly polarized
$\gamma$-rays are calculated by using the $\alpha$~+~$\alpha$~+~$n$ three-body
model and the complex-scaled solutions of the Lippmann-Schwinger equation; the
azimuthal angle distributions of the emitted neutrons are investigated. We
calculate the anisotropy parameter as a function of the photon incident energy
$E_\gamma$, and discuss how sensitive the anisotropy parameter is to nuclear
structure and transition modes. The result suggests that the azimuthal angle
distribution of neutrons emitted from the $^9$Be($\gamma$,$n$) reaction with
the linearly polarized $\gamma$-rays is useful to identify the resonances in
the final states even if it is not clearly observed in the cross section.",1803.11327v1
2018-04-05,Derivation of a Ginzburg-Landau free energy density containing mixed gradient terms of a $p+ip$ superconductor with spin-orbit coupling,"A Ginzburg-Landau free energy for a superconducting chiral p-wave order
parameter is derived from a two-dimensional tight binding lattice model with
weak spin-orbit coupling included as a general symmetry-breaking field.
Superconductivity is accounted for by a BCS-type nearest neighbor opposite-spin
interaction where we project the potential onto the $p$-wave irreducible
representation of the square lattice symmetry group and assume this to be the
dominating order. The resulting free energy contains kinetic terms that mix
components of the order parameter as well as directional gradients --- so
called mixed gradient terms --- as a virtue of the symmetry of the order
parameter. Spin-orbit coupling and electron-hole anisotropy lead to additional
contributions to the coefficients of these terms, increasing the number of
necessary phenomenological parameters by one compared to previous work, and
leading to an increase in the coefficient measuring Fermi surface anisotropy
for Rashba spin-orbit coupling in the continuum limit.",1804.01808v1
2018-04-06,The lower symmetry electron-density distribution and the charge transport anisotropy in cubic dodecaboride LuB12,"High-quality single crystals of LuB12 are grown using the induction zone
melting method. The X-ray data are collected at temperatures 293, 135, 95, 50
K. The crystal structure of LuB12 can be refined with record low R-factor in
the cubic Fm-3m symmetry group despite reiterated observations of the cubic
symmetry distortions both in the unit-cell values and in the physical
properties. A peculiar computing strategy is developed to resolve this
contradiction. True symmetry of the electron-density distribution in LuB12 is
proved to be much lower than cubic as a result, which correlates very
accurately with anisotropy of transport properties of LuB12.",1804.02255v1
2018-04-06,Integer and Fractional Quantum Hall effect in Ultra-high Quality Few-layer Black Phosphorus Transistors,"As a high mobility two-dimensional semiconductor with strong structural and
electronic anisotropy, atomically thin black phosphorus (BP) provides a new
playground for investigating the quantum Hall (QH) effect, including
outstanding questions such as the functional dependence of Landau level (LL)
gaps on magnetic field B, and possible anisotropic fractional QH states. Using
encapsulating few-layer BP transistors with mobility up to 55,000 cm2/Vs, we
extract LL gaps over an exceptionally wide range of B for QH states at filling
factors {\nu}=-1 to -4, which are determined to be linear in B, thus resolving
a controversy raised by its anisotropy. Furthermore, a fractional QH state at
{\nu}~ -4/3 and an additional feature at -0.56+/- 0.1 are observed,
underscoring BP as a tunable 2D platform for exploring electron interactions.",1804.02427v1
2018-04-09,Microscopic origin of frictional rheology in dense suspensions: correlations in force space,"We develop a statistical framework for the rheology of dense, non-Brownian
suspensions, based on correlations in a space representing forces, which is
dual to position space. Working with the ensemble of steady state
configurations obtained from simulations of suspensions in two dimensions, we
find that the anisotropy of the pair correlation function in force space
changes with confining shear stress ($\sigma_{xy}$) and packing fraction
($\phi$). Using these microscopic correlations, we build a statistical theory
for the macroscopic friction coefficient: the anisotropy of the stress tensor,
$\mu = \sigma_{xy}/P$. We find that $\mu$ decreases (i) as $\phi$ is increased
and (ii) as $\sigma_{xy}$ is increased. Using a new constitutive relation
between $\mu$ and viscosity for dense suspensions that generalizes the
rate-independent one, we show that our theory predicts a Discontinuous Shear
Thickening (DST) flow diagram that is in good agreement with numerical
simulations, and the qualitative features of $\mu$ that lead to the generic
flow diagram of a DST fluid observed in experiments.",1804.03155v2
2018-04-12,Ballistic one-dimensional holes with strong g-factor anisotropy in germanium,"We report experimental evidence of ballistic hole transport in
one-dimensional quantum wires gate-defined in a strained SiGe/Ge/SiGe quantum
well. At zero magnetic field, we observe conductance plateaus at integer
multiples of 2e^2/h. At finite magnetic field, the splitting of these plateaus
by Zeeman effect reveals largely anisotropic g-factors, with absolute values
below 1 in the quantum-well plane, and exceeding 10 out of plane. This g-factor
anisotropy is consistent with a heavy-hole character of the propagating
valence-band states, in line with a predominant confinement in the growth
direction. Remarkably, we observe quantized ballistic conductance in device
channels up to 600 nm long. These findings mark an important step towards the
realization of novel devices for applications in quantum spintronics.",1804.04674v1
2018-04-16,Nematic Pairing from Orbital Selective Spin Fluctuations in FeSe,"FeSe is an intriguing iron-based superconductor. It presents an unusual
nematic state without magnetism and can be tuned to increase the critical
superconducting temperature. Recently it has been observed a noteworthy
anisotropy of the superconducting gaps. Its explanation is intimately related
to the understanding of the nematic transition itself. Here we show that the
spin-nematic scenario driven by orbital-selective spin-fluctuations provides a
simple scheme to understand both phenomena. The pairing mediated by anisotropic
spin modes is not only orbital selective but also nematic, leading to stronger
pair scattering across the hole and $X$ electron pocket. The delicate balance
between orbital ordering and nematic pairing points also to a marked $k_z$
dependence of the hole-gap anisotropy.",1804.05800v3
2018-04-16,Triple Exponential Relaxation Dynamics in a Metallacrown-Based {$Dy^{III}Cu^{II}_5$} 3d-4f Single-Molecule Magnet,"The interplay of strong single-ion anisotropy and magnetic interactions often
give rise to novel magnetic behavior and can provide additional routes for
controlling magnetization dynamics. However, novel effects arising from
interactions between lanthanide and transition-metal ions are nowadays rarely
observed. Herein, a {$Dy^{III}Cu^{II}_5$} 3d-4f single-molecule magnet (SMM) is
constructed as a rigid and planar [15-MC-5] metallacrown (MC), where the
$Dy^{III}$ ion is trapped in the central pseudo-$D_{5h}$ pocket. A strong axial
crystal field (CF) imbues the $Dy^{III}$ ion with large Ising-type magnetic
anisotropy, and we are able to observe and model the magnetic interactions
between the $Cu^{II}-Cu^{II}$ and $Dy^{III}-Cu^{II}$ pairs. Butterfly-shaped
magnetic hysteresis shows clear steps at $\pm$0.4 T, coincident with level
crossings in our model exchange Hamiltonian between the {$Cu^{II}_5$} and
$Dy^{III}$ spin systems. Most intriguingly, this air-stable SMM exhibits three
distinct regimes in its magnetic relaxation dynamics, all clearly displaying an
exponential dependence on temperature.",1804.05818v1
2018-04-16,Anisotropy of exchange stiffness based on atomic-scale magnetic properties in rare-earth permanent magnet Nd$_2$Fe$_{14}$B,"We examine the anisotropic properties of the exchange stiffness constant,
$\mathcal{A}$, for rare-earth permanent magnet, Nd$_2$Fe$_{14}$B, by connecting
analyses with two different scales of length, i.e., Monte Carlo (MC) method
with an atomistic spin model and Landau-Lifshitz-Gilbert (LLG) equation with a
continuous magnetic model. The atomistic MC simulations are performed on the
spin model of Nd$_2$Fe$_{14}$B constructed from ab-initio calculations, and the
LLG micromagnetics simulations are performed with the parameters obtained by
the MC simulations. We clarify that the amplitude and the thermal property of
$\mathcal{A}$ depend on the orientation in the crystal, which are attributed to
the layered structure of Nd atoms and weak exchange couplings between Nd and Fe
atoms. We also confirm that the anisotropy of $\mathcal{A}$ significantly
affects the threshold field for the magnetization reversal (coercivity) given
by the depinning process.",1804.05824v2
2018-04-17,Stringent Limit on Primordial Magnetic Fields from the Cosmic Microwave Background Radiation,"Primordial magnetic fields (PMFs), being present before the epoch of cosmic
recombination, induce small-scale baryonic density fluctuations. These
inhomogeneities lead to an inhomogeneous recombination process that alters the
peaks and heights of the large-scale anisotropies of the cosmic microwave
backround (CMB) radiation. Utilizing numerical compressible MHD calculations
and a Monte Carlo Markov chain analysis, which compares calculated CMB
anisotropies with those observed by the \textit{WMAP} and \textit{Planck}
satellites, we derive limits on the magnitude of putative PMFs. We find that
the {\it total} remaining present day field, integrated over all scales, cannot
exceed 47 pG for scale-invariant PMFs and 8.9 pG for PMFs with a violet
Batchelor spectrum at 95\% confidence level. These limits are more than one
order of magnitude more stringent than any prior stated limits on PMFs from the
CMB which have not accounted for this effect.",1804.06115v3
2018-04-18,Large perpendicular magnetic anisotropy in epitaxial Fe/MgAl2O4(001) heterostructures,"We investigated perpendicular magnetic anisotropy (PMA) and related
properties of epitaxial Fe (0.7 nm)/MgAl2O4(001) heterostructures prepared by
electron-beam evaporation. Using an optimized structure, we obtained a large
PMA energy ~1 MJ/m3 at room temperature, comparable to that in
ultrathin-Fe/MgO(001) heterostructures. Both the PMA energy and saturation
magnetization show weak temperature dependence, ensuring wide working
temperature in application. The effective magnetic damping constant of the 0.7
nm Fe layer was ~0.02 using time-resolved magneto-optical Kerr effect. This
study demonstrates capability of the Fe/MgAl2O4 heterostructure for
perpendicular magnetic tunnel junctions, as well as a good agreement with
theoretical predictions.",1804.06526v2
2018-04-22,Magnetic Droplet Soliton Nucleation in Oblique Fields,"We study the auto-oscillating magnetodynamics in orthogonal spin torque
nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic field
angle. In perpendicular fields and at OOP field angles down to approximately 50
degrees we observe the nucleation of a droplet. However, for field angles below
50 degrees, experiments indicate that the droplet gives way to propagating spin
waves, in agreement with our micromagnetic simulations. Theoretical
calculations show that the physical mechanism behind these observations is the
sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show
that the presence of a strong perpendicular magnetic anisotropy (PMA) free
layer in the system reverses the angular dependence of the SWN and dynamics in
STNOs with respect to the known behavior determined for the in-plane magnetic
anisotropy free layer. Our results are of fundamental interest in understanding
the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.",1804.08047v2
2018-04-22,Are homeostatic states stable? Dynamical stability in morphoelasticity,"Biological growth is often driven by mechanical cues, such as changes in
external pressure or tensile loading. Moreover, it is well known that many
living tissues actively maintain a preferred level of mechanical internal
stress, called the mechanical homeostasis. The tissue-level feedback mechanism
by which changes of the local mechanical stresses affect growth is called a
growth law within the theory of morphoelasticity, a theory for understanding
the coupling between mechanics and geometry in growing and evolving biological
materials. The goal of this article is to develop mathematical techniques to
analyze growth laws and to explore issues of heterogeneity and growth
stability. We discuss the growth dynamics of tubular structures, which are very
common in biology (e.g. arteries, plant stems, airways) and model the
homeostasis-driven growth dynamics of tubes which produces spatially
inhomogeneous residual stress. We show that the stability of the homeostatic
state depends nontrivially on the anisotropy of the growth response. The key
role of anisotropy may provide a foundation for experimental testing of
homeostasis-driven growth laws.",1804.08107v1
2018-04-26,Orbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms,"Laser cooled lanthanide atoms are ideal candidates with which to study strong
and unconventional quantum magnetism with exotic phases. Here, we use
state-of-the-art closed-coupling simulations to model quantum magnetism for
pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical
lattice. In contrast to the widely used single-channel Hubbard model
description of atoms and molecules in an optical lattice, we focus on the
single-site multi-channel spin evolution due to spin-dependent contact,
anisotropic van der Waals, and dipolar forces. This has allowed us to identify
the leading mechanism, orbital anisotropy, that governs molecular spin dynamics
among erbium atoms. The large magnetic moment and combined orbital angular
momentum of the 4f-shell electrons are responsible for these strong anisotropic
interactions and unconventional quantum magnetism. Multi-channel simulations of
magnetic Cr atoms under similar trapping conditions show that their
spin-evolution is controlled by spin-dependent contact interactions that are
distinct in nature from the orbital anisotropy in Er. The role of an external
magnetic field and the aspect ratio of the lattice site on spin dynamics is
also investigated.",1804.10102v1
2018-05-02,"Energy transport in a disordered spin chain with broken U(1) symmetry: Diffusion, subdiffusion, and many-body localization","We explore the physics of the disordered XYZ spin chain using two
complementary numerical techniques: exact diagonalization (ED) on chains of up
to 17 spins, and time-evolving block decimation (TEBD) on chains of up to 400
spins. Our principal findings are as follows. First, the clean XYZ spin chain
shows ballistic energy transport for all parameter values that we investigated.
Second, for weak disorder there is a stable diffusive region that persists up
to a critical disorder strength that depends on the XY anisotropy. Third, for
disorder strengths above this critical value energy transport becomes
increasingly subdiffusive. Fourth, the many-body localization transition moves
to significantly higher disorder strengths as the XY anisotropy is increased.
We discuss these results, and their relation to our current physical picture of
subdiffusion in the approach to many-body localization.",1805.01036v2
2018-05-10,"Lattice distortion effects on the frustrated spin-1 triangular-antiferromagnet A3NiNb2O9 (A = Ba, Sr and Ca)","In the geometrically frustrated materials with the low-dimensional and small
spin moment, the quantum fluctuation could interfere with the complicated
interplay of the spin, electron, lattice and orbital interactions, and host
exotic ground states such as nematic spin-state and chiral liquid phase. While
the quantum phases of the one-dimensional chain and S - 1/2 two-dimensional
triangular-lattice antiferromagnet (TLAF) had been more thoroughly investigated
by both theorists and experimentalists, the work on S = 1 TLAF has been
limited. We induced the lattice distortion into the TLAFs, A3NiNb2O9 (A = Ba,
Sr, and Ca) with S (Ni2+) = 1, and applied the thermodynamic, magnetic and
neutron scattering measurements. Although A3NiNb2O9 kept the non-collinear
120{\deg} antiferromagnetic phase as the ground state, the Ni2+-lattice changed
from the equilateral triangle (A = Ba) into isosceles triangle (A = Sr and Ca).
The inelastic neutron scattering data were simulated by the linear spin-wave
theory, and the competition between the single-ion anisotropy and the exchange
anisotropy from the distorted lattice was discussed.",1805.03986v1
2018-05-11,Azimuthal anisotropy of heavy-flavour decay electrons in p-Pb collisions at $ \sqrt{s_{\rm NN}}$ = 5.02 TeV,"Angular correlations between heavy-flavour decay electrons and charged
particles at mid-rapidity ($|\eta| < 0.8$) are measured in p-Pb collisions at
$\sqrt{s_{\rm NN}}$ = 5.02 TeV. The analysis is carried out for the 0-20%
(high) and 60-100% (low) multiplicity ranges. The jet contribution in the
correlation distribution from high-multiplicity events is removed by
subtracting the distribution from low-multiplicity events. An azimuthal
modulation remains after removing the jet contribution, similar to previous
observations in two-particle angular correlation measurements for light-flavour
hadrons. A Fourier decomposition of the modulation results in a positive
second-order coefficient ($v_{2}$) for heavy-flavour decay electrons in the
transverse momentum interval $1.5 < p_{\rm{T}} < 4$ GeV/$c$ in
high-multiplicity events, with a significance larger than $5\sigma$. The
results are compared with those of charged particles at mid-rapidity and of
inclusive muons at forward rapidity. The $v_2$ measurement of open
heavy-flavour particles at mid-rapidity in small collision systems could
provide crucial information to help interpret the anisotropies observed in such
systems.",1805.04367v2
2018-05-15,Bianchi I model as a prototype for a cyclical Universe,"We analyze the dynamics of the Bianchi I model in the presence of stiff
matter, an ultrarelativistic component and a small negative cosmological
constant. We quantize this model in the framework of the polymer quantum
mechanics, in order to introduce cut-off features in the minisuperspace
dynamics.
  We then apply to the polymer Wheeler-DeWitt equation, emerging from the Dirac
constraint, an adiabatic approximation a la Vilenkin, which treats the Universe
volume as a quasi-classical variable, becoming de facto the dynamical clock for
the pure quantum degrees of freedom, here identified in the Universe
anisotropies.
  The main issue of the present analysis consists of determining a cyclical
evolution for the Bianchi I model, oscillating between the Big-Bounce induced
by the cut-off physics and the turning point due to the small cosmological
constant. Furthermore, the mean value of the Universe anisotropy variables
remains finite during the whole evolution, including the phase across the
Big-Bounce. Such a feature, according to a suitable choice of the initial
conditions makes the present cosmological paradigm, a viable scenario for the
description of a possible primordial and late phases of the actual Universe.",1805.05666v1
2018-05-21,An upper limit on the strength of the extragalactic magnetic field from ultra-high-energy cosmic-ray anisotropy,"If ultra-high-energy cosmic rays originate from extragalactic sources, the
offsets of their arrival directions from these sources imply an upper limit on
the strength of the extragalactic magnetic field. The Pierre Auger
Collaboration has recently reported that anisotropy in the arrival directions
of cosmic rays is correlated with several types of extragalactic objects. If
these cosmic rays originate from these objects, they imply a limit on the
extragalactic magnetic field strength of B < 0.7-2.2 x 10^-9 (lambda_B / 1
Mpc)^-1/2 G for coherence lengths lambda_B < 100 Mpc and B < 0.7-2.2 x 10^-10 G
at larger scales. This is comparable to existing upper limits at lambda_B = 1
Mpc, and improves on them by a factor 4-12 at larger scales. The principal
source of uncertainty in our results is the unknown cosmic-ray composition.",1805.07995v2
2018-05-22,Spectral distortion anisotropies from single-field inflation,"Distortions of the Cosmic Microwave Background energy spectrum of the $\mu$
type are sensitive to the primordial power spectrum through the dissipation of
curvature perturbations on scales $k\simeq 50$ - $10^4\,\mathrm{Mpc}^{-1}$.
Their angular correlation with large-scale temperature anisotropies is then
sensitive to the squeezed limit of the primordial bispectrum. For inflationary
models obeying the single-field consistency relation, we show that the observed
$\mu T$ angular correlation that would correspond to the local shape vanishes
exactly. All leading non-primordial contributions, including all non-linear
production and projection effects, are of the ""equilateral shape"", namely
suppressed by $k^2/{\cal H}_f^2$, where ${\cal H}_f\simeq 10^{-1}\,{\rm
Mpc}^{-1}$ is the Hubble radius at the end of the $\mu$-era. Therefore, these
non-primordial contributions are orthogonal to a potential local primordial
signal (e.g. from multi-field inflation). Moreover, they are very small in
amplitude. Our results strengthen the position of $\mu$ distortions as the
ultimate probe of local primordial non-Gaussianity.",1805.08775v2
2018-05-23,Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling,"Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been
studied via inelastic neutron scattering. A simple Heisenberg model with a
single-ion anisotropy describes most features of the spin-wave dispersion
curves. However, there is shown to be a renormalization of the magnon energies
located at around 11 meV. Since both the magnon-magnon interaction and
magnon-phonon coupling can affect the renormalization in a noncollinear magnet,
we have accounted for both of these couplings by using a Heisenberg XXZ model
with 1=S expansions [1] and the Einstein site phonon model [13], respectively.
This quantitative analysis leads to the conclusion that the renormalization
effect primarily originates from the magnon-phonon coupling, while the
spontaneous magnon decay due to the magnon-magnon interaction is suppressed by
strong two-ion anisotropy.",1805.08919v1
2018-05-25,Quasiclassical theory of the spin-orbit magnetoresistance of three-dimensional Rashba metals,"The magnetoresistance of a three-dimensional Rashba material placed on top of
a ferromagnetic insulator is theoretically investigated. In addition to the
intrinsic Rashba spin-orbit interaction, we also consider extrinsic spin-orbit
coupling via side-jump and skew scattering, and the Elliott-Yafet spin
relaxation mechanism. The latter is anisotropic due to the mass anisotropy
which reflects the noncentrosymmetric crystal structure of three-dimensional
Rashba metals. A quasiclassical approach is employed to derive a set of coupled
spin-diffusion equations, which are supplemented by boundary conditions that
account for the spin-transfer torque at the interface of the bilayer. The
magnetoresistance is fully determined by the current-induced spin polarization,
i.e., it cannot in general be ascribed to a single (bulk) spin Hall angle. Our
theoretical results reproduce several features of the experiments, at least
qualitatively, and contain established phenomenological results in the relevant
limiting cases. In particular, the anisotropy of the Elliott-Yafet spin
relaxation mechanism plays a major role for the interpretation of the observed
magnetoresistance.",1805.10245v1
2018-05-29,Anisotropic Kondo pseudo-gap in URu2Si2,"A polarized electronic Raman scattering study reveals the emergence of
symmetry dependence in the electronic Raman response of single crystalline
URu$_{2}$Si$_{2}$ below the Kondo crossover scale $T_K\sim100K$. In particular,
the development of a coherent Kondo pseudo-gap predominantly in the E$_g$
channel highlights strong anisotropy in the Kondo physics in URu$_{2}$Si$_{2}$
that has previously been neglected in theoretical models of this system. A
calculation of the Raman vertices demonstrates that the strongest Raman vertex
does indeed develop within the E$_g$ channel for interband transitions and
reaches a maximum along the diagonals of the Brillouin zone, implying a
d-wave-like geometry for the Kondo pseudo-gap. Below the hidden order phase
transition at $T_{HO}= 17.5K$, the magnitude of the pseudo-gap is found to be
enhanced. Moreover, the anisotropy of the pseudo-gap is similar in form to that
proposed for the chiral d-wave (E$_g$) superconducting state that appears below
$T_c=1.5K$.",1805.11307v2
2018-06-01,Static Hopf Solitons and Knotted Emergent Fields in Solid-State Noncentrosymmetric Magnetic Nanostructures,"Two-dimensional topological solitons, commonly called Skyrmions, are
extensively studied in solid-state magnetic nanostructures and promise many
spintronics applications. However, three-dimensional topological solitons
dubbed hopfions have not been demonstrated as stable spatially localized
structures in solid-state magnetic materials. Here we model the existence of
such static solitons with different Hopf index values in noncentrosymmetric
solid magnetic nanostructures with a perpendicular interfacial magnetic
anisotropy. We show how this surface anisotropy, along with the
Dzyaloshinskii-Moriya interactions and the geometry of nanostructures,
stabilize hopfions. We demonstrate knots in emergent field lines and computer
simulate Lorentz transmission electron microscopy images of such solitonic
configurations to guide their experimental discovery in magnetic solids.",1806.00453v3
2018-06-02,Ultra-low damping insulating magnetic thin films get perpendicular,"A magnetic material combining low losses and large Perpendicular Magnetic
Anisotropy (PMA) is still a missing brick in the magnonic and spintronic
fields. We report here on the growth of ultrathin Bismuth doped
Y$_{3}$Fe$_{5}$O$_{12}$ (BiYIG) films on Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) and
substituted GGG (sGGG) (111) oriented substrates. A fine tuning of the PMA is
obtained using both epitaxial strain and growth induced anisotropies. Both
spontaneously in-plane and out-of-plane magnetized thin films can be
elaborated. Ferromagnetic Resonance (FMR) measurements demonstrate the high
dynamic quality of these BiYIG ultrathin films, PMA films with Gilbert damping
values as low as 3 10$^{-4}$ and FMR linewidth of 0.3 mT at 8 GHz are achieved
even for films that do not exceed 30 nm in thickness. Moreover, we measure
Inverse Spin Hall Effect (ISHE) on Pt/BiYIG stacks showing that the magnetic
insulator$'$s surface is transparent to spin current making it appealing for
spintronic applications.",1806.00658v1
2018-06-08,Geometry of flux attachment in anisotropic fractional quantum Hall states,"Fractional quantum Hall (FQH) states are known to possess an internal metric
degree of freedom that allows them to minimize their energy when contrasting
geometries are present in the problem (e.g., electron band mass and dielectric
tensor). We investigate the internal metric of several incompressible FQH
states by probing its response to band mass anisotropy using infinite DMRG
simulations on a cylinder geometry. We test and apply a method to extract the
internal metric of a FQH state from its guiding center structure factor. We
find that the response to band mass anisotropy is approximately the same for
states in the same Jain sequence, but changes substantially between different
sequences. We provide a theoretical explanation of the observed behavior of
primary states at filling $\nu = 1/m$ in terms of a minimal microscopic model
of flux attachment.",1806.03303v1
2018-06-11,Giant perpendicular magnetic anisotropy in Fe/III-V nitride thin films,"Large perpendicular magnetic anisotropy (PMA) in transition metal thin films
provides a pathway for enabling the intriguing physics of nanomagnetism and
developing broad spintronics applications. After decades of searches for
promising materials, the energy scale of PMA of transition metal thin films,
unfortunately, remains only about 1 meV. This limitation has become a major
bottleneck in the development of ultradense storage and memory devices. We
discovered unprecedented PMA in Fe thin-film growth on the $(000\bar{1})$
N-terminated surface of III-V nitrides from first-principles calculations. PMA
ranges from 24.1 meV/u.c. in Fe/BN to 53.7 meV/u.c. in Fe/InN.
Symmetry-protected degeneracy between $x^2-y^2$ and $xy$ orbitals and its lift
by the spin-orbit coupling play a dominant role. As a consequence, PMA in
Fe/III-V nitride thin films is dominated by first-order perturbation of the
spin-orbit coupling, instead of second-order in conventional transition
metal/oxide thin films. This game-changing scenario would also open a new field
of magnetism on transition metal/nitride interfaces.",1806.04162v1
2018-06-20,Magnetic field dependence of antiferromagnetic resonance in NiO,"We report on measurements of magnetic field and temperature dependence of
antiferromagnetic resonances in the prototypical antiferromagnet NiO. The
frequencies of the magnetic resonances in the vicinity of 1 THz have been
determined in the time-domain via time-resolved Faraday measurements after
selective excitation by narrow-band superradiant terahertz (THz) pulses at
temperatures down to 3K and in magnetic fields up to 10 T. The measurements
reveal two antiferromagnetic resonance modes, which can be distinguished by
their characteristic magnetic field dependencies. The nature of the two modes
is discussed by comparison to an eight-sublattice antiferromagnetic model,
which includes superexchange between the next-nearest-neighbor Ni spins,
magnetic dipolar interactions, cubic magneto-crystalline anisotropy, and Zeeman
interaction with the external magnetic field. Our study indicates that a
two-sublattice model is insufficient for the description of spin dynamics in
NiO, while the magnetic-dipolar interactions and magneto-crystalline anisotropy
play important roles.",1806.07968v1
2018-06-21,"Spin, orbital, Weyl and other glasses in topological superfluids","One of the most spectacular discoveries made in superfluid $^3$He confined in
a nanostructured material like aerogel or nafen was the observation of the
destruction of the long-range orientational order by a weak random anisotropy.
The quenched random anisotropy provided by the confining material strands
produces several different glass states resolved in NMR experiments in the
chiral superfluid $^3$He-A and in the time-reversal-invariant polar phase. The
smooth textures of spin and orbital order parameters in these glasses can be
characterized in terms of the randomly distributed topological charges, which
describe skyrmions, spin vortices and hopfions. In addition, in these skyrmion
glasses the momentum-space topological invariants are randomly distributed in
space. The Chern mosaic, Weyl glass, torsion glass and other exotic topological
sates are examples of close connections between the real-space and
momentum-space topologies in superfluid $^3$He phases in aerogel.",1806.08177v3
2018-06-25,Stripe order and magnetic anisotropy in the $S=1$ antiferromagnet BaMoP$_2$O$_8$,"Magnetic behavior of BaMoP$_2$O$_8$ with the spatially anisotropic triangular
arrangement of the $S=1$ Mo$^{4+}$ ions is explored using thermodynamic
measurements, neutron diffraction, and density-functional band-structure
calculations. A broad maximum in the magnetic susceptibility around 46\,K is
followed by the stripe antiferromagnetic order with the propagation vector
${\mathbf k}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ formed below $T_N\simeq 21$
K. This stripe phase is triggered by a pronounced one-dimensionality of the
spin lattice, where one of the in-plane couplings, $J_2\simeq 4.6$ meV, is much
stronger than its $J_1\simeq 0.4$ meV counterpart, and stabilized by the weak
easy-axis anisotropy. The ordered moment of 1.42(9) $\mu_B$ at 1.5 K is
significantly lower than the spin-only moment of 2 $\mu_B$ due to a combined
effect of quantum fluctuations and spin-orbit coupling.",1806.09314v2
2018-06-26,Oblique Klein tunneling in 8-Pmmn borophene p-n junctions,"The 8-\textit{Pmmn} borophene is one kind of new elemental monolayer, which
hosts anisotropic and tilted massless Dirac fermions (MDF). The planar
\textit{p-n} junction (PNJ) structure as the basic component of various novel
devices based on the monolayer material has attracted increasing attention.
Here, we analytically study the transport properties of anisotropic and tilted
MDF across 8-\textit{Pmmn} borophene PNJ. Similar to the isotropic MDF across
graphene junctions, perfect transmission exists but its direction departures
the normal direction of borophene PNJ induced by the anisotropy and tilt, i.e.,
oblique Klein tunneling. The oblique Klein tunneling does not depend on the
doping levels in \textit{N} and \textit{P} regions of PNJ as the normal Klein
tunneling but depends on the junction direction. Furthermore, we analytically
derive the special junction direction for the maximal difference between
perfect transmission direction and the normal direction of PNJ and clearly
distinguish the respective contribution of anisotropy and tilt underlying the
oblique Klein tunneling. In light of the rapid advances of experimental
technologies, we expect the oblique Klein tunneling to be observable in the
near future.",1806.09743v1
2018-06-29,Mapping Incoherent Gravitational Wave Backgrounds,"Given the recent detection of gravitational waves from individual sources it
is almost a certainty that some form of background of gravitational waves will
be detected in future. The most promising candidate for such a detection are
backgrounds made up of incoherent superposition of the signal of unresolved
astrophysical or, backgrounds sourced by earlier cosmological events. Such
backgrounds will also contain anisotropies about an average value. The
information contained in the background level and any anisotropies will be
extremely valuable as an astrophysical and cosmological probe. As such, the
ability to reconstruct sky maps of the signal will become important as the
sensitivity increases. We build and test a pixel--based, maximum--likelihood
Gravitational Wave Background (GWB) map-maker that uses the cross-correlation
of sets of generalised baselines as input. The resulting maps are a
representation of the GWB power, or strain ""intensity"" on the sky. We test the
algorithm by reconstructing known input maps with different baseline
configurations. We also apply the map-maker to a subset of the Advance LIGO
data.",1806.11360v1
2018-07-02,Systematics of azimuthal anisotropy harmonics in proton-nucleus collisions at the LHC from the Color Glass Condensate,"Simple power counting arguments in the dilute-dense framework of the Color
Glass Condensate (CGC) Effective Field Theory predict that even and odd
azimuthal anisotropy harmonics of two-particle correlations in proton-nucleus
collisions at the LHC will respectively satisfy v^2_{2n} ~ N_{ch}^0 and
v^2_{2n+1} ~ N_{ch}, where N_{ch} denotes the number of charged particles. We
show that these expectations are borne out qualitatively, and even
quantitatively, within systematic uncertainties, for v_2 and v_4 in comparisons
with data from the ATLAS collaboration. We also observe that ATLAS data for the
v_3 azimuthal harmonic are in excellent agreement with our qualitative
expectation; quantitative comparisons are numerically challenging at present.
The lessons from this study fully complement those gained by the recent
comparison of the CGC dilute-dense framework [arXiv:1805.09342] to data from
the PHENIX collaboration on small system collisions at RHIC.",1807.00825v1
2018-07-10,Magnetic anisotropy in HoIr$_2$Si$_2$ ($I4/mmm$),"Single crystals of HoIr$_2$Si$_2$ with the body-centered ThCr$_2$Si$_2$-type
structure ($I4/mmm$) were grown by Bridgman method from indium flux. Single
crystal structure determination yielded a Si-z position of 0.378(1) in the
structure. We excluded the presence of the high temperature phase with the
primitive CaBe$_2$Ge$_2$-type structure ($P 4/n m m$) by powder X-ray
diffraction. Magnetic measurements on the single crystals yield a Neel
temperature of $T_{\rm N}=22\,\rm K$. In the inverse magnetic susceptibility a
strong anisotropy with Weiss temperatures $\Theta_{W}^{001}=26\,\rm K$ and
$\Theta_{W}^{100}=-26\,\rm K$ occurs above $T_{\rm N}$. The effective magnetic
moment $\mu_{\rm eff}^{001}=10.64\mu_{B}$ and $\mu_{\rm
eff}^{100}=10.53\mu_{B}$ is close to the expected value for a free Ho$^{3+}$
ion, $\mu_{\rm eff}^{calc}=10.6\mu_{B}$. The field dependent magnetization
shows a step-like behaviour due to crystalline electric field effects.",1807.03657v1
2018-07-10,Photonic spin Hall effect in hyperbolic metamaterials at visible,"Photonic spin Hall effect in transmission is a transverse beam shift of the
out-coming beam depending on polarization of the in-coming beam. The effect can
be significantly enhanced by materials with high anisotropy. We report the
first experimental demonstration of the photonic spin Hall effect in a
multilayer hyperbolic metamaterial at visible wavelengths (wavelengths of 520
nm and 633 nm). The metamaterial is composed of alternating layers of gold and
alumina with deeply-subwavelength thicknesses, exhibiting extremely large
anisotropy. The angle resolved polarimetric measurements showed the shift of
165 $\mu m$ for the metamaterial of 176 nm in thickness. Additionally the
transverse beam shift is extremely sensitive to the variations of the incident
angle changing theoretically by 270 $\mu m$ with one milli-radian
($0.057^\circ$). These features can lead to minituarized spin Hall switches and
filters with high angular resolution.",1807.03689v1
2018-07-13,Features of the IP-Glasma,"We discuss differences between the IP-Glasma model and typical
wounded-nucleon model like initial conditions. We point out that the IP-Glasma
initial state is more compact in the transverse plane and produces a
significant initial flow, both of which contribute to an increased radial flow
in the subsequent hydrodynamic evolution. A larger bulk viscosity, compared to
calculations that use other initial state models, is required to compensate for
these effects and find agreement with experimental data. We further demonstrate
the importance of the initial momentum anisotropy of the glasma for anisotropy
measures in small collision systems such as p+Pb.",1807.05205v1
2018-07-16,Magnetic freezing transition in a CoO/Permalloy bilayer revealed by transverse ac susceptibility,"We utilize variable-temperature, variable-frequency magneto-optical
transverse magnetic susceptibility technique to study the static and dynamical
magnetic properties of a thin-film CoO/Permalloy bilayer. Our measurements
demonstrate that in the studied system, the directional asymmetry of the
hysteresis loop is associated mainly with the difference in the reversal
mechanisms between the two reversed states of magnetization stabilized by the
exchange-induced uniaxial anisotropy. The latter is found to be much larger
than the exchange-induced unidirectional anisotropy of the ferromagnet. We also
observe an abrupt variation of the frequency-dependent imaginary part of ac
susceptibility near the exchange bias blocking temperature, consistent with the
magnetic freezing transition inferred from the previous time-domain studies of
magnetic aging in similar systems. The developed measurement approach enables
precise characterization of the dynamical and static characteristics of
thin-film magnetic heterostructures that can find applications in
reconfigurable magnonic and neuromorphic circuits.",1807.05990v2
2018-07-17,Magnetic ordering with an XY-like anisotropy in the honeycomb lattice iridates ZnIrO$_3$ and MgIrO$_3$ synthesized via a metathesis reaction,"We have successfully synthesized the novel antiferromagnets with Ir$^{4+}$
honeycomb lattice ZnIrO$_3$ and MgIrO$_3$ and investigated their magnetic and
thermodynamic properties. The two iridates are isomorphic but exhibit
qualitatively different magnetic properties. ZnIrO$_3$ shows antiferromagnetic
ordering below 46.6 K, whereas MgIrO$_3$ displays weak ferromagnetic behavior
below 31.8 K owing to formation of a canted antiferromagnetic ordering. The
measurement of magnetic susceptibility with using an oriented powder sample
revealed the presence of an XY-like magnetic anisotropy and a tilting magnetic
structure which is possibly stabilized by the Kitaev interaction. Moreover,
magnetization curves of MgIrO3 and ZnIrO3 up to 60 T show different behaviors,
demonstrating that each magnetic ground state is different with each other. We
discuss the difference in the ground state between MgIrO$_3$ and ZnIrO$_3$ from
the viewpoint a magnetic model consisting of the Kitaev and
Dzyaloshinskii-Moriya interactions with the spin frustration effect on the
honeycomb lattice.",1807.06273v2
2018-07-17,Field-free spin-orbit torque switching from geometrical domain wall pinning,"Spin-orbit torques, which utilize spin currents arising from the spin-orbit
coupling, offer a novel method to electrically switch the magnetization with
perpendicular anisotropy. However, the necessity of an external magnetic field
to achieve a deterministic switching is an obstacle for realizing practical
spin-orbit torque devices with all-electric operation. Here, we report a
field-free spin-orbit torque switching by exploiting the domain wall motion in
an anti-notched microwire with perpendicular anisotropy, which exhibits
multi-domain states stabilized by the domain wall surface tension. The
combination of spin-orbit torque, Dzyaloshinskii-Moriya interaction, and domain
wall surface tension induced geometrical pinning allows a deterministic control
of the domain wall and offers a novel method to achieve a field-free spin-orbit
torque switching. Our work demonstrates the proof of concept of a perpendicular
memory cell which can be readily adopted in a three-terminal magnetic memory.",1807.06287v1
2018-07-17,Impact of further-range exchange and cubic anisotropy on magnetic excitations in the fcc kagome antiferromagnet IrMn3,"Exchange interactions up to fourth nearest neighbor are shown within a
classical local-moment Heisenberg approach to be important to model inelastic
neutron scattering data on the fcc kagome antiferromagnet IrMn$_3$. Spin wave
frequencies are calculated using the torque equation and the magnetic
scattering function, $S({\bf Q},\omega)$, is determined by a Green's function
method, as an extension of our previous work, LeBlanc et al, Phys. Rev. B 90,
144403 (2014). Results are compared with intensity contour data on powder
samples of ordered IrMn$_3$, where magnetic Mn ions occupy lattice sites of ABC
stacked kagome planes. Values of exchange parameters taken from DFT
calculations used in our model provide good agreement with the experimental
results only if further-neighbor exchange is included. Estimates of the
observed energy gap support the existence of strong cubic anisotropy predicted
by DFT calculations.",1807.06659v1
2018-07-18,New angles on standard force fields: towards a general approach for treating atomic-level anisotropy,"Nearly all standard force fields employ the 'sum-of-spheres' approximation,
which models intermolecular interactions purely in terms of interatomic
distances. Nonetheless, atoms in molecules can have significantly non-spherical
shapes, leading to interatomic interaction energies with strong orientation
dependencies. Neglecting this 'atomic-level anisotropy' can lead to significant
errors in predicting interaction energies. Herein we propose a simple,
transferable, and computationally-efficient model (MASTIFF) whereby
atomic-level orientation dependence can be incorporated into ab initio
intermolecular force fields. MASTIFF includes anisotropic exchange-repulsion,
charge penetration, and dispersion effects, in conjunction with a standard
treatment of anisotropic long-range (multipolar) electrostatics. To validate
our approach, we benchmark MASTIFF against various sum-of-spheres models over a
large library of intermolecular interactions between small organic molecules.
MASTIFF achieves quantitative accuracy with respect to both high-level
electronic structure theory and experiment, thus showing promise as a basis for
'next-generation' force field development.",1807.07096v1
2018-07-24,Finite element approximations for near-incompressible and near-inextensible transversely isotropic bodies,"This work comprises a detailed theoretical and computational study of the
boundary value problem for transversely isotropic linear elastic bodies.
General conditions for well-posedness are derived in terms of the material
parameters. The discrete form of the displacement problem is formulated for
conforming finite element approximations. The error estimate reveals that
anisotropy can play a role in minimizing or even eliminating locking behaviour,
for moderate values of the ratio of Young's moduli in the fibre and transverse
directions. In addition to the standard conforming approximation an alternative
formulation, involving under-integration of the volumetric and extensional
terms in the weak formulation, is considered. The latter is equivalent to
either a mixed or a perturbed Lagrangian formulation, analogously to the
well-known situation for the volumetric term. A set of numerical examples
confirms the locking-free behaviour in the near-incompressible limit of the
standard formulation with moderate anisotropy, with locking behaviour being
clearly evident in the case of near-inextensibility. On the other hand,
under-integration of the extensional term leads to extensional locking-free
behaviour, with convergence at superlinear rates.",1807.09168v2
2018-07-24,Mechanism of substrate-induced anisotropic growth of monolayer WS2 by kinetic Monte Carlo simulations,"Controlled anisotropic growth of two-dimensional materials provides an
approach for the synthesis of large single crystals and nanoribbons, which are
promising for applications as low-dimensional semiconductors and in
next-generation optoelectronic devices. In particular, the anisotropic growth
of transition metal dichalcogenides induced by the substrate is of great
interest due to its operability. To date, however, their substrate-induced
anisotropic growth is typically driven by the optimization of experimental
parameters without uncovering the fundamental mechanism. Here, the anisotropic
growth of monolayer tungsten disulfide on an ST-X quartz substrate is achieved
by chemical vapor deposition, and the mechanism of substrate-induced
anisotropic growth is examined by kinetic Monte Carlo simulations. These
results show that, besides the variation of substrate adsorption, the chalcogen
to metal (C/M) ratio is a major contributor to the large growth anisotropy and
the polarization of undergrowth and overgrowth; either perfect isotropy or high
anisotropy can be expected when the C/M ratio equals 2.0 by properly
controlling the linear relationship between gas flux and temperature.",1807.09323v2
2018-07-25,Hamiltonian theory for Quantum Hall systems in a tilted magnetic field: robustness of activation gaps,"We use the Hamiltonian theory developed by Shankar and Murthy to study a
quantum Hall system in a tilted magnetic field. With a finite width of the
system in the $z$ direction, the parallel component of the magnetic field
introduces anisotropy into the effective two-dimensional interactions. The
effects of such anisotropy can be effectively captured by the recently proposed
generalized pseudo-potentials. We find that the off-diagonal components of the
pseudo-potentials lead to mixing of composite fermions Landau levels, which is
a perturbation to the picture of $p$ filled Landau levels in composite-fermion
theory. By changing the internal geometry of the composite fermions, such a
perturbation can be minimized and one can find the corresponding activation
gaps for different tilting angles, and we calculate the associated optimal
metric. Our results show that the activation gap is remarkably robust against
the in-plane magnetic field in the lowest Landau level.",1807.09677v1
2018-07-24,Electromagnetic effect on anisotropic scalar field collapse in higher curvature gravity,"We consider a `Scalar-Maxwell-Einstein-Gauss-Bonnet' theory in four
dimension, where the scalar field couples non-minimally with the Gauss-Bonnet
(GB) term. This coupling with the scalar field ensures the non topological
character of the GB term. In such higher curvature scenario, we explore the
effect of electromagnetic field on scalar field collapse. Our results reveal
that the presence of a time dependent electromagnetic field requires an
anisotropy in the background spacetime geometry and such anisotropic spacetime
allows a collapsing solution for the scalar field. The singularity formed as a
result of the collapse is found to be a curvature singularity which may be
point like or line like depending on the strength of the anisotropy. We also
show that the singularity is always hidden from exterior by an apparent
horizon.",1807.10140v1
2018-08-10,Tunneling anomalous Hall effect in a ferroelectric tunnel junction,"We report on a theoretical study on the tunneling anomalous Hall effect
(TAHE) in a ferroelectric tunnel junction (FTJ), resulting from spin-orbit
coupling (SOC) in the ferroelectric barrier. For ferroelectric barriers with
large SOC, such as orthorhombic HfO2 and BiInO3, we predict values of the
tunneling anomalous Hall conductivity (TAHC) measurable experimentally. We
demonstrate strong anisotropy in TAHC depending on the type of SOC. For the SOC
with equal Rashba and Dresselhaus parameters, we predict the perfect anisotropy
with zero TAHC for certain magnetization orientations. The TAHC changes sign
with ferroelectric polarization reversal providing a new functionality of FTJs.
Conversely, measuring the TAHC as a function of magnetization orientation
offers an efficient way to quantify the type of SOC in the insulating barrier.
Our results provide a new insight into the TAHE and open avenues for potential
device applications.",1808.03583v2
2018-08-11,Walker solution for Dzyaloshinskii domain wall in ultrathin ferromagnetic films,"We analyze the electric current and magnetic field driven domain wall motion
in perpendicularly magnetized ultrathin ferromagnetic films in the presence of
interfacial Dzyaloshinskii-Moriya interaction and both out-of-plane and
in-plane uniaxial anisotropies. We obtain exact analytical Walker-type
solutions in the form of one-dimensional domain walls moving with constant
velocity due to both spin-transfer torques and out-of-plane magnetic field.
These solutions are embedded into a larger family of propagating solutions
found numerically. Within the considered model, we find the dependencies of the
domain wall velocity on the material parameters and demonstrate that adding
in-plane anisotropy may produce domain walls moving with velocities in excess
of 500 m/s in realistic materials under moderate fields and currents.",1808.03772v2
2018-08-11,Biaxial layering transition of hard rod-like particles in narrow slit-like pores,"The phase behavior of hard rectangular rods with length L and diameter D is
studied in a narrow slit-like pore using the Parsons-Lee density functional
theory. Using the restricted orientation approximation, we find strong
adsorption at the walls with planar ordering, second order uniaxial-biaxial
ordering transitions and first order layering transitions. The layering
transition takes place between two fluids having n and n+1 layers, where the
layer spacing is in the order of D. In the case of weak shape anisotropy
(L/D=3), the coexisting fluids can be either uniaxial or biaxial, while both
phases are found to be biaxial for L/D=6 and L/D=9. Interestingly, even two or
more layering transitions can be observed with increasing density at a given
shape anisotropy and pore width.",1808.03839v1
2018-08-12,Measurements and implications of cosmic ray anisotropies from TeV to trans-EeV energies,"Important observational results have been recently reported on the angular
distributions of cosmic rays at all energies, calling into question the
perception of cosmic rays a decade ago. These results together with their
in-progress interpretations are summarised in this review paper, covering both
large-scale and small-scale anisotropies from TeV energies to the highest ones.
While the magnetic field in the Galaxy has long been considered as an external
data imprinting a quasi-random walk to particles and thus shaping the angular
distributions of Galactic cosmic rays through the induced average density
gradient, the information encompassed in the angular distributions in the
TeV--PeV energy range appear today as a promising tool to infer some properties
of the local magnetic field environments. At the highest energies, the
extragalactic origin of the particles has been recently determined
observationally. While no discrete source of ultrahigh-energy cosmic rays has
been identified so far, the noose is tightening around nearby extragalactic
objects, and some prospects are discussed.",1808.03940v1
2018-08-16,Jamming and percolation properties of random sequential adsorption with relaxation,"The random sequential adsorption (RSA) model is a classical model in
Statistical Physics for adsorption on two-dimensional surfaces. Objects are
deposited sequentially at random and adsorb irreversibly on the landing site,
provided that they do not overlap any previously adsorbed object. The kinetics
of adsorption ceases when no more objects can be adsorbed (jamming state).
Here, we investigate the role of post-relaxation on the jamming state and
percolation properties of RSA of dimers on a two-dimensional lattice. We
consider that, if the deposited dimer partially overlaps with a previously
adsorbed one, a sequence of dimer displacements may occur to accommodate the
new dimer. The introduction of this simple relaxation dynamics leads to a more
dense jamming state than the one obtained with RSA without relaxation. We also
consider the anisotropic case, where one dimer orientation is favored over the
other, finding a non-monotonic dependence of the jamming coverage on the
strength of anisotropy. We find that the density of adsorbed dimers at which
percolation occurs is reduced with relaxation, but the value depends on the
strength of anisotropy.",1808.05637v1
2018-08-19,Quantized excitation spectra by magnon confinement in quasi-one-dimensional S=1 spin systems,"We apply the infinite time-evolving-block-decimation algorithm to calculate
the dynamical spin-structure factors of the quasi-one-dimensional (q1D) S=1
antiferromagnetic spin system with the single-ion anisotropy and the bond
alternation. We find that excitation continuum originating from magnons is
quantized, when the staggered field induced by the weak inter-chain interaction
is taken into account. The excitation energies of the quantized excitation
spectra are well explained by negative zeros of the Airy functions, when the
easy-axis anisotropy is strong and the ground state is located deep in the
N\'eel phase. This quantization of the magnon continuum is a counterpart of the
spinon confinement, which has been recently discussed in q1D S=1/2
antiferromagnets. We further show that, when the staggered field exists, the
quantized excitation spectra appear the phase boundary between the Haldane
phase and the N\'eel phase of the phase diagram without the staggered field.
However, the quantized excitation spectra disappear in the singlet dimer phase.",1808.06270v2
2018-08-27,Sign Reversal and Tunability of Exchange Bias in Nanoscale AuFe Alloy Film: A New Material for Spintronic Application,"We report here sign reversal and tunability of exchange bias in AuFe
cosputtered films of thickness about 63 nm. As deposited film exhibits exchange
bias effect at room temperature without external triggering field and its
magnitude increases gradually with decrease in temperature down to 5 K. Upon
irradiation with 100 MeV Au9+ ions at a fluence of 5*1013 ions/cm2, hysteresis
loop shifts completely from origin towards positive field side at room
temperature and reverses sign when temperature is reduced to 5 K as studied by
SQUID magnetometry. A well defined uniaxial magnetic anisotropy has been seen
by magneto optical Kerr effect (MOKE) in as deposited film as well as in
irradiated one. The results are explained on the basis of stress induced
magnetic anisotropy in thin films.",1808.08694v1
2018-08-30,Ground-state phase diagram of the $S = 1$ one-dimensional Kondo lattice model with a uniaxial anisotropy under transverse fields,"We study the effects of transverse magnetic fields on the $S=1$
one-dimensional Kondo lattice model with a uniaxial anisotropy using the
density matrix renormalization group. The model can be regarded as a simplified
one for analyzing the Ising ferromagnetic superconductor URhGe. We find various
phases such as ferromagnetic and antiferromagnetic phases, Kondo plateau (KP)
phases, Tomonaga-Luttinger liquids, and fully polarized phases. In the KP
phase, a pseudoplateau emerges in the magnetization due to strongly bound pairs
between the local and the conduction electron spins. This is why we call this
phase the Kondo plateau. At the critical field between the ferromagnetic and KP
phases, we find metamagnetic behavior in the magnetization curve. We discuss
various correlation functions and the Friedel oscillations in detail, and the
experimental data under transverse magnetic fields in URhGe are discussed on
the basis of the present results.",1808.10142v3
2018-09-04,Formation and Control of Twin Domains in the Pyrochlore Oxide Cd2Re2O7,"The successive phase transitions of the pyrochlore oxide Cd2Re2O7 are studied
by polarizing microscopy and magnetic susceptibility measurements. The
formation of twin domains is visualized in the polarizing images of a pristine
(111) crystal surface upon cooling through the cubic-to-tetragonal transition
at Ts1 ~ 200 K. Moreover, a dramatic change in the twinning pattern is observed
at Ts2 ~120 K, which suggests that the tetragonal c axis flips as the strain
changes its direction at the tetragonal-to-tetragonal transition. Magnetic
susceptibility measurements reveal significant domain alignment upon cooling
across Ts1 and Ts2 in a magnetic field of 7 T, which are due to ~10% anisotropy
in the magnetic susceptibility for the low-temperature phases. Interestingly,
the anisotropy is reversed at Ts2: \c{hi}c < \c{hi}a above Ts2 and vice versa
below Ts2.",1809.00771v2
2018-09-25,Effect of dispersity of particle length on the electrical conductivity of the two-dimensional systems,"By means of computer simulation, we examined effect of dispersity of filler
length on electrical conductivity of two-dimensional (2D) composites with
rod-like fillers. Continuous approach has been used. Highly conductive
zero-width rod-like particles were deposited uniformly with given anisotropy
onto a poorly conductive substrate. Length of particles varied according to the
lognormal distribution. Our simulation evidenced that slightly disordered
systems may have both the high figure of merit, i.e., both high electrical
conductivity and the optical transmission simultaneously, and the high
electrical anisotropy.",1809.09969v1
2018-09-26,Incipient and well-developed entropy plateaus in spin-S Kitaev models,"We present results on entropy and heat-capacity of the spin-S
honeycomb-lattice Kitaev models using high-temperature series expansions and
thermal pure quantum (TPQ) state methods. We study models with anisotropic
couplings $J_z=1\ge J_x=J_y$ for spin values 1/2, 1, 3/2, and 2. We show that
for $S>1/2$, any anisotropy leads to well developed plateaus in the entropy
function at an entropy value of $\frac{1}{2}\ln{2}$, independent of $S$.
However, in the absence of anisotropy, there is an incipient entropy plateau at
$S_{max}/2$, where $S_{max}$ is the infinite temperature entropy of the system.
We discuss possible underlying microscopic reasons for the origin and
implications of these entropy plateaus.",1809.10112v2
2018-09-27,Evolution of two-time correlations in dissipative quantum spin systems: aging and hierarchical dynamics,"We consider the evolution of two-time correlations in the quantum XXZ
spin-chain in contact with an environment causing dephasing. Extending
quasi-exact time-dependent matrix product state techniques to consider the
dynamics of two-time correlations within dissipative systems, we uncover the
full quantum behavior for these correlations along all spin directions.
Together with insights from adiabatic elimination and kinetic Monte Carlo, we
identify three dynamical regimes. For initial times, their evolution is
dominated by the system unitary dynamics and depends on the initial state and
the Hamiltonian parameters. For weak spin-spin interaction anisotropy, after
this initial dynamical regime, two-time correlations enter an algebraic scaling
regime signaling the breakdown of time-translation invariance and the emergence
of aging. For stronger interaction anisotropy, these correlations first go
through a stretched exponential regime before entering the algebraic one. Such
complex relaxation arises due to the competition between the proliferation
dynamics of energetically costly excitations and their motion. As a result,
dissipative heating dynamics of spin systems can be used to probe the entire
spectrum of the underlying Hamiltonian.",1809.10464v1
2018-10-04,Exotic criticality in the dimerized spin-1 $XXZ$ chain with single-ion anisotropy,"We consider the dimerized spin-1 $XXZ$ chain with single-ion anisotropy $D$.
In absence of an explicit dimerization there are three phases: a large-$D$, an
antiferromagnetically ordered and a Haldane phase. This phase structure
persists up to a critical dimerization, above which the Haldane phase
disappears. We show that for weak dimerization the phases are separated by
Gaussian and Ising quantum phase transitions. One of the Ising transitions
terminates in a critical point in the universality class of the dilute Ising
model. We comment on the relevance of our results to experiments on
quasi-one-dimensional anisotropic spin-1 quantum magnets.",1810.02195v3
2018-10-04,Fourier Domain Rotational Anisotropy Second Harmonic Generation,"We describe a novel scheme of detecting rotational anisotropy second harmonic
generation (RA-SHG) signals using a lock-in amplifier referenced to a fast
scanning RA-SHG apparatus. The method directly measures the $n^{th}$ harmonics
of the scanning frequency corresponding to SHG signal components of $C_n$
symmetry that appear in a Fourier series expansion of a general RA-SHG signal.
GaAs was used as a test sample allowing comparison of point-by-point averaging
with the lock-in based method. When divided by the $C_\infty$ signal component,
the lock-in detected data allowed for both self-referenced determination of
ratios of $C_n$ components of up to 1 part in 10$^4$ and significantly more
sensitive measurement of the relative amount of different $C_n$ components when
compared with conventional methods.",1810.02310v1
2018-10-10,An edge-based pressure stabilisation technique for finite elements on arbitrarily anisotropic meshes,"In this article, we analyse a stabilised equal-order finite element
approximation for the Stokes equations on anisotropic meshes. In particular, we
allow arbitrary anisotropies in a sub-domain, for example along the boundary of
the domain, with the only condition that a maximum angle is fulfilled in each
element.This discretisation is motivated by applications on moving domains as
arising e.g. in fluid-structure interaction or multiphase-flow problems. To
deal with the anisotropies, we define a modification of the original Continuous
Interior Penalty stabilisation approach. We show analytically the discrete
stability of the method and convergence of order ${\cal O}(h^{3/2})$ in the
energy norm and ${\cal O}(h^{5/2})$ in the $L^2$-norm of the velocities. We
present numerical examples for a linear Stokes problem and for a non-linear
fluid-structure interaction problem, that substantiate the analytical results
and show the capabilities of the approach.",1810.04766v1
2018-10-13,Noise in the helical edge channel anisotropically coupled to a local spin,"We calculate the frequency-dependent shot noise in the edge states of a
two-dimensional topological insulator coupled to a magnetic impurity with spin
$S=1/2$ of arbitrary anisotropy. If the anisotropy is absent, the noise is
purely thermal at low frequencies, but tends to the Poissonian noise of the
full current $I$ at high frequencies. If the interaction only flips the
impurity spin but conserves those of electrons, the noise at high voltages
$eV\gg T$ is frequency-independent. Both the noise and the backscattering
current $I_{bs}$ saturate at voltage-independent values. Finally, if the
Hamiltonian contains all types of non-spin-conserving scattering, the noise at
high voltages becomes frequency-dependent again. At low frequencies, its ratio
to $2eI_{bs}$ is larger than 1 and may reach 2 in the limit $I_{bs}\to 0$. At
high frequencies it tends to 1.",1810.05831v1
2018-10-22,Amplitude mode in the planar triangular antiferromagnet Na$_{0.9}$MnO$_2$,"Amplitude modes arising from symmetry breaking in materials are of broad
interest in condensed matter physics. These modes reflect an oscillation in the
amplitude of a complex order parameter, yet are typically unstable and decay
into oscillations of the order parameter's phase. This renders stable amplitude
modes rare, and exotic effects in quantum antiferromagnets have historically
provided a realm for their detection. Here we report an alternate route to
realizing amplitude modes in magnetic materials by demonstrating that an
antiferromagnet on a two-dimensional anisotropic triangular lattice
($\alpha$-Na$_{0.9}$MnO$_2$) exhibits a long-lived, coherent oscillation of its
staggered magnetization field. Our results show that geometric frustration of
Heisenberg spins with uniaxial single-ion anisotropy can renormalize the
interactions of a dense two-dimensional network of moments into largely
decoupled, one-dimensional chains that manifest a longitudinally polarized
bound state. This bound state is driven by the Ising-like anisotropy inherent
to the Mn$^{3+}$ ions of this compound.",1810.09518v1
2018-10-24,First analysis of GLE 72 event on 10 September 2017: Spectral and anisotropy characteristics,"Using neutron monitor and space-borne data we performed an analysis of the
second ground level enhancement of solar cycle 24, namely the event of 10
September 2017 (GLE 72) and derive the spectral and angular characteristics of
GLE particles. We employ new neutron monitor yield function and a recently
proposed model based on optimization procedure. The method consists of
simulation of particle propagation in a model magnetosphere in order to derive
the cut-off rigidity and neutron monitor asymptotic directions. Subsequently
the rigidity spectrum and anisotropy of GLE particles are obtained in their
dynamical evolution during the event on the basis of inverse problem solution.
The derived angular distribution and spectra are briefly discussed.",1810.10536v1
2018-10-31,Anisotropy of Dirac cones and van Hove singularity in an organic Dirac fermion system,"We propose an experimental method to examine the in-plane anisotropy of
electronic structure in layered conductors. In the method, we measure the
interlayer magnetoresistance as a function of in-plane magnetic field
orientation. We applied it to an organic Dirac fermion system a-(BEDT-TTF)2I3
to experimentally determine the orientation of the anisotropic Dirac cones. It
is concluded that the long axis of the elliptic constant-energy contours of the
Dirac cone is tilted by approximately -30 deg from the crystalline a-axis to
b-axis under hydrostatic pressures. Additionally, we observed a signature of
van Hove singularity (which is a saddle point of the band dispersion) at 30-40
K above or below the Dirac point. The ridgeline of the saddle point is
estimated as almost parallel to the crystalline b-axis.",1810.13079v1
2018-10-31,Reservoir computing with dipole-coupled nanomagnets,"The feasibility of reservoir computing based on dipole-coupled nanomagnets is
demonstrated using micro-magnetic simulations. The reservoir consists of an
2x10 array of nanomagnets. The static-magnetization directions of the
nanomagnets are used as reservoir states. To update these states, we change the
magnetization of one nanomagnet according to a single-bit-sequential signal. We
also change the uniaxial anisotropy of the other nanomagnets using a
voltage-induced magnetic-anisotropy change to enhance information flow,
storage, and linear/nonlinear calculations. Binary tasks with AND, OR, and XOR
operations were performed to evaluate the performance of the magnetic-array
reservoir. The reservoir-computing output matrix was found to be trainable to
perform AND, OR, and XOR operations with an input delay of up to three bits.",1810.13140v2
2018-10-31,Fast Reflective Optic-Based Rotational Anisotropy Nonlinear Harmonic Generation Spectrometer,"We present a novel Rotational Anisotropy Nonlinear Harmonic Generation
(RA-NHG) apparatus based primarily upon reflective optics. The data acquisition
scheme used here allows for fast accumulation of RA-NHG traces, mitigating low
frequency noise from laser drift, while permitting real-time adjustment of
acquired signals with significantly more data points per unit angle rotation of
the optics than other RA-NHG setups. We discuss the design and construction of
the optical and electronic components of the device and present example data
taken on a GaAs test sample at a variety of wavelengths. The RA-second harmonic
generation data for this sample show the expected four-fold rotational symmetry
across a broad range of wavelengths, while those for RA-third harmonic
generation exhibit evidence of cascaded nonlinear processes possible in
acentric crystal structures.",1811.01862v1
2018-11-06,Chiral-induced switching of antiferromagnet spins in a confined nanowire,"In the development of spin-based electronic devices, a particular challenge
is the manipulation of the magnetic state with high speed and low power
consumption. Although research has focused on the current-induced spin-orbit
torque based on strong spin-orbit coupling, the charge-based and the
torque-driven devices have fundamental limitations: Joule heating, phase
mismatching and overshooting. In this work, we investigate numerically and
theoretically alternative switching scenario of antiferromagnetic insulator in
one-dimensional confined nanowire sandwiched with two electrodes. As the
electric field could break inversion symmetry and induce Dzyaloshinskii-Moriya
interaction and pseudo-dipole anisotropy, the resulting spiral texture takes
symmetric or antisymmetric configuration due to additional coupling with the
crystalline anisotropy. Therefore, by competing two spiral states, we show that
the magnetization reversal of antiferromagnets is realized, which is valid in
ferromagnetic counterpart. Our finding provides promising opportunities to
realize the rapid and energy-efficient electrical manipulation of magnetization
for future spin-based electronic devices.",1811.02200v2
2018-11-08,"Comment on the article ""Anisotropies in the astrophysical gravitational-wave background: The impact of black hole distributions"" by A.C. Jenkins et al. [arXiv:1810.13435]","We investigate the discrepancy pointed out by Jenkins et al. in Ref. [1]
between the predictions of anisotropies of the astrophysical gravitational wave
(GW) background, derived using different methods in Cusin et al. [2] and in
Jenkins et al. [3]. We show that this discrepancy is not due to our treatment
of galaxy clustering, contrary to the claim made in Ref. [1] and we show that
our modeling of clustering gives results in very good agreement with
observations. Furthermore we show that the power law spectrum used in Refs. [1]
and [3] to describe galaxy clustering is incorrect on large scales and leads to
a different scaling of the multipoles $C_\ell$. Moreover, we also explain that
the analytic derivation of the gravitational wave background correlation
function in Refs. [1] and [3] is mathematically ill-defined and predicts an
amplitude of the angular power spectrum which depends on the (arbitrary) choice
of a non-physical cut-off.",1811.03582v2
2018-11-12,Thermopower in an anisotropic two-dimensional Weyl semimetal,"We investigate the generation of an electric current from a temperature
gradient in a two-dimensional Weyl semimetal with anisotropy, in both the
presence and absence of a quantizing magnetic field. We show that the
anisotropy leads to doping dependences of thermopower and thermal
conductivities which are different from those in isotropic Dirac materials.
Additionally, we find that a quantizing magnetic field in such systems leads to
an interesting magnetic field dependence of the longitudinal thermopower,
resulting in unsaturated thermoelectric coefficients. Thus the results
presented here will serve as a guide to achieving high thermopower and a
thermoelectric figure-of-merit in graphene-based materials, as well as organic
conductors such as $\alpha$-(BEDT-TTF)$_2$I$_3$.",1811.04952v6
2018-11-13,Spin-orbit torques acting upon a perpendicularly-magnetized Py layer,"We show that Py, a commonly-used soft ferromagnetic material with weak
anisotropy, can become perpendicularly-magnetized while depositing on Ta buffer
layer with Hf or Zr insertion layers (ILs) and MgO capping layer. By using two
different approaches, namely harmonic voltage measurement and hysteresis loop
shift measurement, the dampinglike spin-orbit torque (DL-SOT) efficiencies from
Ta/IL/Py/IL/MgO magnetic heterostructures with perpendicular magnetic
anisotropy are characterized. We find that though Ta has a significant spin
Hall effect, the DL-SOT efficiencies are small in systems with the Ta/Py
interface compared to that obtained from the control sample with the
traditional Ta/CoFeB interface. Our results indicate that the spin transparency
for the Ta/Py interface is much less than that for the Ta/CoFeB interface,
which might be related to the variation of spin mixing conductance for
different interfaces.",1811.05164v1
2018-10-31,Crack Path Selection in Orientationally Ordered Composites,"While cracks in isotropic homogeneous materials propagate straight,
perpendicularly to the tensile axis, cracks in natural and synthetic composites
deflect from a straight path, often increasing the toughness of the material.
Here we combine experiments and simulations to identify materials properties
that predict whether cracks propagate straight or kink on a macroscale larger
than the composite microstructure. Those properties include the anisotropy of
the fracture energy, which we vary several folds by increasing the volume
fraction of orientationally ordered alumina platelets inside a polymer matrix,
and a microstructure-dependent process zone size that is found to modulate the
additional stabilizing or destabilizing effect of the non-singular stress
acting parallel to the crack. Those properties predict the existence of an
anisotropy threshold for crack kinking and explain the surprisingly strong
dependence of this threshold on sample geometry and load distribution.",1811.05891v4
2018-11-15,Firehose instabilities triggered by the solar wind suprathermal electrons,"In collision-poor plasmas from space, e.g., solar wind, terrestrial
magnetospheres, kinetic instabilities are expected to play a major role in
constraining the temperature anisotropy of plasma particles, but a definitive
answer can be given only after ascertaining their properties in these
environments. Present study describes the full spectrum of electron firehose
instabilities in the presence of suprathermal electron populations which are
ubiquitous in space plasmas. Suprathermal electrons stimulate both the periodic
and aperiodic branches, remarkable being the effects shown by the aperiodic
mode propagating obliquely to the ambient magnetic field which markedly exceeds
the growth rates of the parallel (periodic) branch reported recently in Lazar
et al., (2017a, MNRAS 464, 564). Derived exclusively in terms of the plasma
parameters, the anisotropy thresholds of this instability are also lowered in
the presence of suprathermal electrons, predicting an enhanced effectiveness in
the solar wind conditions. These results may also be relevant in various other
astrophysical contexts where the firehose instabilities involve, e.g., solar
flares, sites of magnetic field reconnection, accretion flows or plasma jets
leading to shocks and co-rotating interactions in heliosphere, interstellar
medium and galaxy clusters.",1811.06320v1
2018-11-22,"E-by-e jet suppression, anisotropy, medium response and hard-soft tomography","The Linear Boltzmann Transport (LBT) model for jet propagation and
interaction in quark-gluon plasma (QGP) has been used to study jet quenching in
high-energy heavy-lion collisions. The suppression of single inclusive jet
production, medium modification of $\gamma$-jet correlation, jet profiles and
fragmentation functions as observed in experiments at Large Hadron Collider
(LHC) can be described well by LBT in which jet-induced medium response is
shown to play an essential role. In event-by-event simulations of jet quenching
within LBT, jet azimuthal anisotropies are found to correlate linearly with the
anisotropic flows of bulk hadrons from the underlying hydrodynamic events.",1811.08975v2
2018-11-22,BRDF Estimation of Complex Materials with Nested Learning,"The estimation of the optical properties of a material from RGB-images is an
important but extremely ill-posed problem in Computer Graphics. While recent
works have successfully approached this problem even from just a single
photograph, significant simplifications of the material model are assumed,
limiting the usability of such methods. The detection of complex material
properties such as anisotropy or Fresnel effect remains an unsolved challenge.
We propose a novel method that predicts the model parameters of an
artist-friendly, physically-based BRDF, from only two low-resolution shots of
the material. Thanks to a novel combination of deep neural networks in a nested
architecture, we are able to handle the ambiguities given by the
non-orthogonality and non-convexity of the parameter space. To train the
network, we generate a novel dataset of physically-based synthetic images. We
prove that our model can recover new properties like anisotropy, index of
refraction and a second reflectance color, for materials that have tinted
specular reflections or whose albedo changes at glancing angles.",1811.09131v1
2018-11-27,Layer dependent antiferromagnetism in the Sr4Ru3O10 ruthenate at the metamagnetic-like transition,"We have investigated the metamagnetic-like transition in the triple layer
ruthenate Sr4Ru3O10 by means of neutron diffraction from single crystals. The
magnetic structure of the compound appears to be determined in a complex way by
the two substructures of inequivalent ruthenium ions. At Tc=105K the system has
a sharp transition into a ferromagnetic state along the c-axis which is driven
by the ruthenium atoms in the central octahedra of the triple layers whereas
the substructure of the outer ruthenium atoms tend to align in the ab plane
achieving an antiferromagnetic order at the metamagnetic transition T*~50K.
Below T* the strong anisotropy along c prevails, the outer ruthenium tend to
align along the c-axis and the in-plane antiferromagnetic order disappears.
This finding confirms the delicate balance between antiferro and ferromagnetic
couplings in the (Sr,Ca)n+1RunO3n+1 family of compounds, and proves the layer
dependence of the magnetic anisotropy in Sr4Ru3O10.",1811.11065v3
2018-11-29,Magneto-immutable turbulence in weakly collisional plasmas,"We propose that pressure anisotropy causes weakly collisional turbulent
plasmas to self-organize so as to resist changes in magnetic-field strength. We
term this effect ""magneto-immutability"" by analogy with incompressibility
(resistance to changes in pressure). The effect is important when the pressure
anisotropy becomes comparable to the magnetic pressure, suggesting that in
collisionless, weakly magnetized (high-$\beta$) plasmas its dynamical relevance
is similar to that of incompressibility. Simulations of magnetized turbulence
using the weakly collisional Braginskii model show that magneto-immutable
turbulence is surprisingly similar, in most statistical measures, to critically
balanced MHD turbulence. However, in order to minimize magnetic-field
variation, the flow direction becomes more constrained than in MHD, and the
turbulence is more strongly dominated by magnetic energy (a nonzero ""residual
energy""). These effects represent key differences between pressure-anisotropic
and fluid turbulence, and should be observable in the $\beta\gtrsim1$ turbulent
solar wind.",1811.12421v2
2018-12-03,Magnetic excitations in the quasi-2D ferromagnet Fe3-xGeTe2 measured with inelastic neutron scattering,"Fe3-xGeTe2 is an itinerant ferromagnet composed of two-dimensional layers
weakly connected by van der Waals bonding that shows a variety of intriguing
phenomena. Inelastic neutron scattering measurements on bulk single crystals of
Fe2.75GeTe2 were performed to quantify the magnetic exchange interaction
energies and anisotropy. The observed inelastic excitations are indicative of
dominant in-plane correlations with negligible magnetic interactions between
the layers. A spin-gap of 3.9 meV is observed allowing a measure of the
magnetic anisotropy. As the excitations disperse to their maximum energy (~65
meV) they become highly damped, reflective of both the magnetic site occupancy
reduction of 25{\%} on one Fe sublattice and the itinerant interactions. A
minimal model is employed to describe the excitation spectra and extract
nearest neighbor magnetic exchange interaction values. The temperature
evolution of the excitations are probed and correlations shown to persist above
Tc, indicative of low dimensional magnetism.",1812.00519v1
2018-12-04,"Anisotropic thermal Sunyaev-Zel'dovich effect and the possibility of an independent measurement of the CMB dipole, quadrupole and octupole","We consider the effect of the cosmic microwave background (CMB) frequency
spectral distortions arising due to the Compton scattering of the anisotropic
radiation on Sunyaev-Zel'dovich (SZ) clusters. We derive the correction to the
thermal SZ effect due to the presence of multipoles with $\ell=1,2,3$ in the
anisotropy of the CMB radiation. We show that this effect gives us an
opportunity for an independent evaluation of the CMB dipole, quadrupole and
octupole angular anisotropy in our location using distorted signal from the
nearby galaxy clusters and to distinguish between the Sachs-Wolfe (SW) and the
Integrated Sachs-Wolfe (ISW) effects by combining such signals from distant and
nearby clusters. The future space mission 'Millimetron' will have unprecedented
sensitivity, which will make it possible to observe the spectral distortion we
are considering.",1812.01330v2
2018-12-05,Voltage-induced strain clocking of nanomagnets with perpendicular magnetic anisotropies,"Nanomagnetic logic (NML) has attracted attention during the last two decades
due to its promise of high energy efficiency combined with non-volatility. Data
transmission in NML relies on Bennett clocking through dipole interaction
between neighboring nanomagnetic bits. This paper uses a fully coupled finite
element model to simulate Bennett clocking based on strain-mediated
multiferroic system for Ni, CoFeB and Terfenol-D with perpendicular magnetic
anisotropies. Simulation results demonstrate that Terfenol-D system has the
highest energy efficiency, which is 2 orders of magnitude more efficient than
Ni and CoFeB. However, the high efficiency is associated with switching
incoherency due to its large magnetostriction coefficient. It is also suggested
that the CoFeB clocking system is slower and has lower bit-density than in Ni
or Terfenol-D systems due to its large dipole coupling. Moreover, we
demonstrate that the precessional perpendicular switching and the Bennett
clocking can be achieved using the same strain-mediated multiferroic
architecture with different voltage pulsing. This study opens new possibilities
to an all-spin in-memory computing system.",1812.02268v1
2018-12-06,Charge and Spin Transport Anisotropy in Nanopatterned Graphene,"Anisotropic electronic transport is a possible route towards nanoscale
circuitry design, particularly in two-dimensional materials. Proposals to
introduce such a feature in patterned graphene have to date relied on
large-scale structural inhomogeneities. Here we theoretically explore how a
random, yet homogeneous, distribution of zigzag-edged triangular perforations
can generate spatial anisotropies in both charge and spin transport.
Anisotropic electronic transport is found to persist under considerable
disordering of the perforation edges, suggesting its viability under realistic
experimental conditions. Furthermore, controlling the relative orientation of
perforations enables spin filtering of the transmitted electrons, resulting in
a half-metallic anisotropic transport regime. Our findings point towards a
co-integration of charge and spin control in a two-dimensional platform of
relevance for nanocircuit design. We further highlight how geometrical effects
allow finite samples to display finite transverse resistances, reminiscent of
Spin Hall effects, in the absence of any bulk fingerprints of such mechanisms,
and explore the underlying symmetries behind this behaviour.",1812.02429v1
2018-12-06,Kinetic theory of spin diffusion and superdiffusion in XXZ spin chains,"We address the nature of spin transport in the integrable XXZ spin chain,
focusing on the isotropic Heisenberg limit. We calculate the diffusion constant
using a kinetic picture based on generalized hydrodynamics combined with
Gaussian fluctuations: we find that it diverges, and show that a
self-consistent treatment of this divergence gives superdiffusion, with an
effective time-dependent diffusion constant that scales as $D(t) \sim t^{1/3}$.
This exponent had previously been observed in large-scale numerical
simulations, but had not been theoretically explained. We briefly discuss XXZ
models with easy-axis anisotropy $\Delta > 1$. Our method gives closed-form
expressions for the diffusion constant $D$ in the infinite-temperature limit
for all $\Delta > 1$. We find that $D$ saturates at large anisotropy, and
diverges as the Heisenberg limit is approached, as $D \sim (\Delta -
1)^{-1/2}$.",1812.02701v2
2018-12-10,Topologically nontrivial magnonic solitons,"The intrinsic non-linearities of the spin dynamics in condensed matter
systems give rise to a rich phenomenology that can be strongly affected by
topology. Here we study formation of magnonic solitons in the topologically
nontrivial bandgap of a spin lattice realization of the Haldane model, in both
static and dynamic (Floquet) regimes. We consider nonlinearities caused by
magnetic crystalline anisotropy and magnon-magnon interactions. We find soliton
formation power thresholds as a function of anisotropy coefficient and
interaction strength. We predict different classes of topological solitons for
the same topological class of the underlying lattice and explain it in terms of
a transition from a topologically nontrivial mass to a trivial one. Our
findings imply that a soliton can phase-separate, containing boundaries between
topologically trivial and non-trivial phases, which is associated with a
vanishing spin wave gap.",1812.03738v2
2018-12-10,Collectivity in pp from resummed interference effects?,"Azimuthal asymmetries $v_n$ in the soft transverse momentum spectra of
hadronic collisions can result as a consequence of quantum interference and
color flow which translates spatial anisotropies into momentum anisotropies via
multipole radiation patterns. Here, we analyze to what extent these effects
result in signal strengths $v_n\lbrace 2s\rbrace$ that can persist in higher
order $(2s)$ cumulants. In a simple model of soft multi-particle production
with quantum interference effects in which $m$ particles are emitted from $N$
sources and in which interference contributions appear naturally ordered in
inverse powers of the adjoint color trace, $1/(N_c^2-1)$, we provide the first
resummed calculation of all powers of $m^2/(N_c^2-1)$. This allows one to
determine all higher order flow cumulants $v_n\lbrace 2s\rbrace$ with the same
parametric accuracy. For a phenomenologically relevant range of $N$ sources
emitting $m$ particles, we find that the even flow coefficients $v_n\lbrace
2s\rbrace$ decrease very mildly with increasing cumulants. This provides a
proof of principle that non-vanishing higher order cumulants $v_n\lbrace
2s\rbrace$ can persist in systems that exhibit neither final state interactions
nor phenomena related to high (saturated) initial parton densities.",1812.04113v1
2018-12-17,Spin chirality fluctuation in two-dimensional ferromagnets with perpendicular anisotropy,"Non-coplanar spin textures with scalar spin chirality can generate effective
magnetic field that deflects the motion of charge carriers, resulting in
topological Hall effect (THE), a powerful probe of the ground state and
low-energy excitations of correlated systems. However, spin chirality
fluctuation in two-dimensional ferromagnets with perpendicular anisotropy has
not been considered in prior studies. Herein, we report direct evidence of
universal spin chirality fluctuation by probing the THE above the transition
temperatures in two different ferromagnetic ultra-thin films, SrRuO$_3$ and V
doped Sb$_2$Te$_3$. The temperature, magnetic field, thickness, and carrier
type dependences of the THE signal, along with our Monte-Carlo simulations,
unambiguously demonstrate that the spin chirality fluctuation is a universal
phenomenon in two-dimensional Ising ferromagnets. Our discovery opens a new
paradigm of exploring the spin chirality with topological Hall transport in
two-dimensional magnets and beyond",1812.07005v2
2018-12-18,Tilted Klein tunneling across atomically sharp interfaces,"Despite many similarities between electronics and optics, the hopping of the
electron on a discrete atomic lattice gives rise to energy band nonparabolicity
and anisotropy. The crucial influences of this effect on material properties
and its incorporation into the continuum model have received widespread
attention in the past half century. Here we predict the existence of a
different effect due to the hopping of the electron across an atomically sharp
interface. For a general lattice, its influence on transport could be equally
important as the energy band nonparabolicity/anisotropy, but cannot be
incorporated into the continuum model. On the honeycomb lattice of graphene, it
leads to the breakdown of the conventional Klein tunneling -- one of the exotic
phenomena of relativistic particles -- and the onset of tilted Klein tunneling.
This works identifies a unique feature of the discrete atomic lattice for
transport, which is relevant for ballistic electronic devices at high carrier
densities.",1812.07196v2
2018-12-19,Surface monolayers and magnetic field,"We study theoretically the magnetic properties of the surface monolayers with
the antiferromagnetic (AF) and ferromagnetic (FM) exchange interactions where
the Dzyaloshinskii-Moriya interaction (DMI) is a result of the mirror symmetry
breaking. To study the DMI helices in magnetic field a method is proposed. In
zero field the DMI gives rise a cycloid in both AF and FM cases. The cycloid
orientation is determined by the DMI induced in-plane anisotropy with the
symmetry of the layer lattice. As a result we have one, two and three chiral
domains in the rectangular, square and triangular lattices respectively. The
magnetic structure of the $M n/W(1 1 0)$ monolayer is explained. The
out-of-plane anisotropy may restore a collinear magnetic order. The chiral
domains are rotated by the in-plane field. In some field directions the spin
flops are predicted. In the out-of-plane field the chirality follows the field
direction. The length of the cycloid wave-vector decreases. In the
perpendicular field there is the spin flop to the corresponding collinear
state. A possibility of the layer electric polarization is discussed.",1812.07892v1
2019-01-07,"Heavily Fe-doped n-type ferromagnetic semiconductor (In,Fe)Sb with high Curie temperature and large magnetic anisotropy","We present high-temperature ferromagnetism and large magnetic anisotropy in
heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 -
35%) thin films grown by low-temperature molecular beam epitaxy. The
(In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and
band structure with single-phase ferromagnetism. The Curie temperature (TC) of
(In1-x,Fex)Sb reaches 390 K at x = 35%, which is significantly higher than room
temperature and the highest value so far reported in III-V based ferromagnetic
semiconductors. Moreover, large coercive force (HC = 160 Oe) and large remanent
magnetization (Mr/MS = 71%) have been observed for a (In1-x,Fex)Sb thin film
with x = 35%. Our results indicate that the n-type ferromagnetic semiconductor
(In1-x,Fex)Sb is very promising for spintronics devices operating at room
temperature.",1901.01996v1
2019-01-09,Six-loop $\varepsilon$ expansion study of three-dimensional $n$-vector model with cubic anisotropy,"The six-loop expansions of the renormalization-group functions of $\varphi^4$
$n$-vector model with cubic anisotropy are calculated within the minimal
subtraction (MS) scheme in $4 - \varepsilon$ dimensions. The $\varepsilon$
expansions for the cubic fixed point coordinates, critical exponents
corresponding to the cubic universality class and marginal order parameter
dimensionality $n_c$ separating different regimes of critical behavior are
presented. Since the $\varepsilon$ expansions are divergent numerical estimates
of the quantities of interest are obtained employing proper resummation
techniques. The numbers found are compared with their counterparts obtained
earlier within various field-theoretical approaches and by lattice
calculations. In particular, our analysis of $n_c$ strengthens the existing
arguments in favor of stability of the cubic fixed point in the physical case
$n = 3$.",1901.02754v3
2019-01-17,"Influences of interfacial oxidization on surface magnetic energy, magnetic damping and spin-orbit-torques in Pt / ferromagnet / capping structures","We investigate the effect of capping layer (CAP) on the interfacial magnetic
anisotropy energy density (K_S), magnetic damping ({\alpha}), and spin-orbit
torques (SOTs) in heavy-metal (Pt) / ferromagnet (Co or Py) / CAP (MgO/Ta,
HfOx, or TaN). At room temperature (RT) the CAP materials influence the
effective magnitude of K_S, which is associated with a formation of interfacial
magnetic oxides. The dynamical dissipation parameters of Co are considerably
influenced by the CAP (especially MgO) while those of Py are not. This is
possibly due to an extra magnetic damping via spin-pumping process across the
Co/CoO interface and incoherent magnon generation (spin fluctuation) in the
interfacial CoO. It is also observed that both anti-damping and field-like SOT
efficiencies vary marginally with the CAP in the thickness ranges we examined.
Our results reveal the crucial role of interfacial oxides on the perpendicular
magnetic anisotropy, magnetic damping, and SOTs.",1901.05777v1
2019-01-17,Waveguide propagation of light in polymer porous films filled with nematic liquid crystals,"We theoretically analyze the waveguide regime of light propagation in a
cylindrical pore of a polymer matrix filled with liquid crystals assuming that
the effective radial optical anisotropy is biaxial. From numerical analysis of
the dispersion relations, the waveguide modes are found to be sensitive to the
field-induced changes of the anisotropy. The electro-optic properties of the
polymer porous polyethylene terephthalate (PET) films filled with the nematic
liquid crystal 5CB are studied experimentally and the experimental results are
compared with the results of the theoretical investigation.",1901.05782v1
2019-01-21,Built-in Fluorescence Anisotropy: an in vivo Imaging Probe for bis-Retinoid Products in Retina,"Non-degradable fluorophores that accumulate as Lipofuscin in retinal pigment
epithelium (RPE) cells has been a major source of intrinsic biomarker for
quantifying the progression of several diseases, including age-related macular
degeneration, Stargardt disease and, more. Recent progression in quantifying
these diseases is entertained mostly by a few noninvasive imaging techniques,
relied either on the life-time of the retinoid-fluorophores or, their linear
and, non-linear absorption cross-sections. Apart from these intrinsic
properties, a native, excited state dipole-dipole interaction mediated typical
spectroscopic phenomenon that is excitation dependent emission-wavelength
shifting is observed from these bis-retinoid fluorophores. Here, we emphasize
the spectroscopic origin of this phenomenon and exploit one of its
associated-properties, that is built-in fluorescence anisotropy as a
noninvasive, in vivo imaging probe for bis-retinoid products in mouse eyes.",1901.08104v1
2019-01-28,Sedimentation of a suspension of rods: Monte Carlo simulation of a continuous two-dimensional problem,"The sedimentation of a two dimensional suspension containing rods was studied
by means of kinetic Monte Carlo (MC) simulations. An off-lattice model with
continuous positional and orientational degrees of freedom was considered. The
initial state before sedimentation was produced using a model of random
sequential adsorption. During such sedimentation, the rods undergo
translational and rotational Brownian motions. The MC simulations were run at
different initial number densities (the numbers of rods per unit area),
$\rho_i$, and sedimentation rates, $u$. For sediment films, the spatial
distributions of the rods, the order parameters and the electrical
conductivities were examined. Different types of sedimentation-driven
self-assembly and anisotropy of the electrical conductivity were revealed
inside the sediment films. This anisotropy can be finely regulated by changes
in the values of $\rho_i$ and $u$.",1901.09516v2
2018-12-12,Substrate induced magnetic anisotropies and magneto-optical response in YIG nanosized epitaxial films on NdGG(111),"Nanosized Y3Fe5O12 epitaxial films have been grown on Nd3Ga5O12 substrates
using laser molecular beam epitaxy method. Magneto-optical polar Kerr effect,
ferromagnetic resonance and spin wave propagation measurements show that the
stress-related anisotropy field has an opposite sign, compared to that in the
YIG/GGG systems. This leads to a considerable decrease of the effective
magnetization that opens a perspective to get YIG films with perpendicular
magnetization for utilizing forward volume spin waves. Longitudinal
magnetooptical Kerr effect magnetometry reveals a large contribution of
quadratic in magnetization terms into dielectric permittivity tensor at optical
frequencies. This effect strongly increases with temperature decrease and is
explained by magnetization of the interface Nd3+ ions that are exchange coupled
to the Fe3+ ions.",1901.10800v1
2019-01-30,Van Hove scenario of anisotropic transport in a two-dimensional spin-orbit coupled electron gas in an in-plane magnetic field,"We study electronic transport in two-dimensional spin-orbit coupled electron
gas subjected to an in-plane magnetic field. The interplay of the spin-orbit
interaction and the magnetic field leads to the Van Hove singularity of the
density of states and strong anisotropy of Fermi contours. We develop a method
that allows one to exactly calculate the nonequilibrium distribution function
for these conditions within the framework of the semiclassical Boltzmann
equation without using the scattering time approximation. The method is applied
to calculate the conductivity tensor and the tensor of spin polarization
induced by the electric field (Aronov-Lyanda-Geller-Edelstein effect). It is
found that both the conductivity and the spin polarization have a sharp
singularity as functions of the Fermi level or magnetic field, which occurs
when the Fermi level passes through the Van Hove singularity. In addition, the
transport anisotropy dramatically changes near the singularity.",1901.10823v1
2019-01-31,The Interplay of the Solar Wind Core and Suprathermal Electrons: A Quasilinear Approach for Firehose Instability,"In the solar wind an equipartition of kinetic energy densities can be easily
established between thermal and suprathermal electrons and the instability
conditions are markedly altered by the interplay of these two populations. The
new thresholds derived here for the periodic branch of firehose instability
shape the limits of temperature anisotropy reported by the observations for
both electron populations. This instability constraint is particularly
important for the suprathermal electrons which, by comparison to thermal
populations, are even less controlled by the particle-particle collisions. An
extended quasilinear approach of this instability confirms predictions from
linear theory and unveil the mutual effects of thermal and suprathermal
electrons in the relaxation of their temperature anisotropies and the
saturation of growing fluctuations.",1901.11406v1
2019-02-06,Barut-Girardello coherent states for anisotropic 2D-Dirac materials,"We construct the Barut-Girardello coherent states for charge carriers in
anisotropic 2D-Dirac materials immersed in a constant homogeneous magnetic
field which is orthogonal to the sample surface. For that purpose, we solve the
anisotropic Dirac equation and identify the appropriate arising and lowering
operators. Working in a Landau-like gauge, we explicitly construct nonlinear
coherent states as eigenstates of a generalized annihilation operator with
complex eigenvalues which depends on an arbitrary function $f$ of the number
operator. In order to describe the anisotropy effects on these states, we
obtain the Heisenberg uncertainty relation, the probability density, mean
energy value and occupation number distribution for three different functions
$f$. For the case in which the anisotropy is caused by uniaxial strain, we
obtain that when a stress is applied along the $x$-axis of the material
surface, the probability density for the nonlinear coherent states is smaller
compared to when the material is stressed along the orthogonal axis.",1902.01995v3
2019-02-07,Nanoscale optical and structural characterisation of silk,"Background: Nanoscale composition of silk defining its unique properties via
a hierarchical structural anisotropy has to be analysed at the highest spatial
resolution of tens-of-nanometers corresponding to the size of fibrils made of
b-sheets, which are the crystalline building blocks of silk. Results: Nanoscale
optical and structural properties of silk have been measured from 100-nm thick
longitudinal slices of silk fibers with ~10 nm resolution, the highest so far.
Optical sub-wavelength resolution in hyperspectral mapping of absorbance and
molecular orientation were carried out for comparison at IR wavelengths 2-10
micrometers using synchrotron radiation. Conclusion: Reliable distinction of
transmission changes by only 1-2% due to anisotropy of amide bands was obtained
from nano-thin slices of silk.",1902.02688v1
2019-02-08,A Microwave Oscillator Based on a Single Straintronic Magneto-tunneling Junction,"There is growing interest in exploring nanomagnetic devices as potential
replacements for electronic devices (e.g. transistors) in digital switching
circuits and systems. A special class of nanomagnetic devices are switched with
electrically generated mechanical strain leading to electrical control of
magnetism. Straintronic magneto-tunneling junctions (s-MTJ) belong to this
category. Their soft layers are composed of two-phase multiferroics comprising
a magnetostrictive layer elastically coupled to a piezoelectric layer. Here, we
show that a single straintronic magneto-tunneling junction with a passive
resistor can act as a microwave oscillator whose traditional implementation
would have required microwave operational amplifiers, capacitors and resistors.
This reduces device footprint and cost, while improving device reliability.
This is an analog application of magnetic devices where magnetic interactions
(interaction between the shape anisotropy, strain anisotropy, dipolar coupling
field and spin transfer torque in the soft layer of the s-MTJ) are exploited to
implement an oscillator with reduced footprint.",1902.03307v2
2019-02-13,Interacting non-Hermitian ultracold atoms in a harmonic trap: Two-body exact solution and high-order exceptional point,"We study interacting ultracold atoms in a three-dimensional (3D) harmonic
trap with spin-selective dissipations, which can be effectively described by
non-Hermitian parity-time ($\mathcal{PT}$) symmetric Hamiltonians. By solving
the non-Hermitian two-body problem of spin-1/2 (spin-1) bosons in a 3D harmonic
trap exactly, we find that the system can exhibit third-order (fifth-order)
exceptional point (EP) with ultra-sensitive cube-root (fifth-root) spectral
response due to interaction anisotropies in spin channels. We also present the
general principle for the creation of high-order EPs and their spectral
sensitivities with arbitrary particle number $N$ and arbitrary spin $s$.
Generally, with spin-independent interactions, the EP order of bosons can be as
high as $2Ns+1$, and the spectral response around EP can be as sensitive as
$\sim \epsilon^{1/(2ks+1)}$ under a $k$-body interaction anisotropy. Moreover,
we propose to detect the ultra-sensitive spectral response through the
probability dynamics of certain state. These results suggest a convenient route
towards more powerful sensor devices in spinor cold atomic systems.",1902.04769v3
2019-02-13,Numerical anisotropy study of a class of compact schemes,"We study the numerical anisotropy existent in compact difference schemes as
applied to hyperbolic partial differential equations, and propose an approach
to reduce this error and to improve the stability restrictions based on a
previous analysis applied to explicit schemes. A prefactorization of compact
schemes is applied to avoid the inversion of a large matrix when calculating
the derivatives at the next time level, and a predictor-corrector time marching
scheme is used to update the solution in time. A reduction of the isotropy
error is attained for large wave numbers and, most notably, the stability
restrictions associated with MacCormack time marching schemes are considerably
improved. Compared to conventional compact schemes of similar order of
accuracy, the multidimensional schemes employ larger stencils which would
presumably demand more processing time, but we show that the new stability
restrictions render the multidimensional schemes to be in fact more efficient,
while maintaining the same dispersion and dissipation characteristics of the
one dimensional schemes.",1902.05042v1
2019-02-21,Spin-orbit coupling and spin relaxation in phosphorene: Intrinsic versus extrinsic effects,"First-principles calculations of the essential spin-orbit and spin relaxation
properties of phosphorene are performed. Intrinsic spin-orbit coupling induces
spin mixing with the probability of $b^2 \approx 10^{-4}$, exhibiting a large
anisotropy, following the anisotropic crystalline structure of phosphorene. For
realistic values of the momentum relaxation times, the intrinsic
(Elliott--Yafet) spin relaxation times are hundreds of picoseconds to
nanoseconds. Applying a transverse electric field (simulating gating and
substrates) generates extrinsic $C_{2v}$ symmetric spin-orbit fields in
phosphorene, which activate the D'yakonov--Perel' mechanism for spin
relaxation. It is shown that this extrinsic spin relaxation also has a strong
anisotropy, and can dominate over the Elliott-Yafet one for strong enough
electric fields. Phosphorene on substrates can thus exhibit an interesting
interplay of both spin relaxation mechanisms, whose individual roles could be
deciphered using our results.",1902.07957v1
2019-02-22,Temperature-dependent Saturation of Weibel-type Instabilities in Counter-streaming Plasmas,"We present the first 2X2V continuum Vlasov-Maxwell simulations of
interpenetrating, unmagnetized plasmas to study the competition between
two-stream, Oblique, and filamentation modes in the weakly relativistic regime.
We find that after nonlinear saturation of the fastest-growing two-stream and
Oblique modes, the effective temperature anisotropy, which drives current
filament formation via the secular Weibel instability, has a strong dependence
on the internal temperature of the counter-streaming plasmas. The effective
temperature anisotropy is significantly more reduced in colder than in hotter
plasmas, leading to orders of magnitude lower magnetization for colder plasmas.
A strong dependence of the energy conversion efficiency of Weibel-type
instabilities on internal beam temperature has implications for determining
their contribution to the observed magnetization of many astrophysical and
laboratory plasmas.",1902.08672v1
2019-02-26,A new class of nonreciprocal spin waves on the edges of 2D antiferromagnetic honeycomb nanoribbons,"Antiferromagnetic two-dimensional (2D) materials are currently under
intensive theoretical and experimental investigations in view of their
potential applications in antiferromagnet-based magnonic and spintronic
devices. Recent experimental studies revealed the importance of magnetic
anisotropy and Dzyaloshinskii-Moriya interactions (DMI) on the ordered ground
state and the magnetic excitations in these materials. Here we present a robust
classical field theory approach to analyze the effect of magnetic anisotropy
and Dzyaloshinskii-Moriya interactions (DMI) on the edge and bulk spin waves in
2D antiferromagnetic nanoribbons. We predict the existence of a new class of
nonreciprocal edge spin waves characterized by opposite polarizations in
opposite directions. These novel edge spin waves are induced by the DMI and are
fundamentally different from conventional nonreciprocal spin waves for which
the polarization is independent of the propagation direction. Aside this
breakthrough in the field of antiferromagnetic spin waves, the study further
analysis the effect of the edges structure on the magnetic excitations. In
particular, we show that anisotropic bearded edges nanoribbons act as magnetic
topological insulators with exceptionally interesting potentials for
applications in magnonics.",1902.09704v3
2019-02-27,Cosmic ray acceleration to ultrahigh energy in radio galaxies,"The origin of ultrahigh energy cosmic rays (UHECRs) is an open question. In
this proceeding, we first review the general physical requirements that a
source must meet for acceleration to 10-100 EeV, including the consideration
that the shock is not highly relativistic. We show that shocks in the backflows
of radio galaxies can meet these requirements. We discuss a model in which
giant-lobed radio galaxies such as Centaurus A and Fornax A act as
slowly-leaking UHECR reservoirs, with the UHECRs being accelerated during a
more powerful past episode. We also show that Centaurus A, Fornax A and other
radio galaxies may explain the observed anisotropies in data from the Pierre
Auger Observatory, before examining some of the difficulties in associating
UHECR anisotropies with astrophysical sources.",1902.10382v1
2019-03-01,Modeling the non-trivial behavior of anisotropic beams: a simple Timoshenko beam with enhanced stress recovery and constitutive relations,"This paper analyzes the non-trivial influence of the material anisotropy on
the structural behavior of an anisotropic multilayer planar beam. Indeed,
analytical results available in literature are limited to homogeneous beams and
several aspects has not been addressed yet, impeding an in-depth understanding
of the mechanical response of anisotropic structural elements. This paper
proposes an effective recovery of stress distribution and an energetically
consistent evaluation of constitutive relations to be used within a planar
Timoshenko beam model. The resulting structural-analysis tool highlights the
following peculiarities of anisotropic beams: (i) the axial stress explicitly
depends on transversal internal force, which can weigh up to 30% on the maximal
magnitude of axial stress, and (ii) the anisotropy influences the beam
displacements more than standard shear deformation and even for extremely
slender beams. A rigorous comparison with analytical and accurate 2D Finite
Element solutions confirms the accuracy of the proposed approach that leads to
errors exceptionally greater than 5%.",1903.00200v1
2019-03-03,Dynamical mode coupling and coherence in spin Hall nano-oscillator with perpendicular magnetic anisotropy,"We experimentally study the dynamical modes excited by spin current in Spin
Hall nano-oscillators based on the Pt/[Co/Ni] multilayers with perpendicular
magnetic anisotropy. Both propagating spin wave and localized solitonic modes
of the oscillation are achieved and controlled by varying the applied magnetic
field and current. At room temperature, the generation linewidth broadening
associated with mode hopping was observed at currents close to the transition
between different modes and in the mode coexistence regimes. The mode hopping
was suppressed at cryogenic temperatures, confirming that the coupling between
modes is mediated by thermal magnons. We also demonstrate that coherent
single-mode oscillations with linewidth of 5 MHz can be achieved without
applying external magnetic field. Our results provide insight into the
mechanisms controlling the dynamical coherence in nanomagnetic oscillators, and
guidance for optimizing their applications in spin wave-based electronics.",1903.00822v1
2019-03-03,Goos-Hanchen Shift of a Spin-Wave Beam at the Interface Between Two Ferromagnets,"Spin waves are promising information carriers which can be used in modern
magnonic devices, characterized by higher performance and lower energy
consumption than presently used electronic circuits. However, before practical
application of spin waves, the efficient control over spin wave amplitude and
phase needs to be developed. We analyze analytically reflection and refraction
of the spin waves at the interface between two ferromagnetic materials. In the
model we consider the system consisting of two semi-infinite ferromagnetic
media, separated by the ultra-narrow interface region with the magnetic
anisotropy. We have found the Goos-Hanchen shift for spin waves in transmission
and reflection, and performed detailed investigations of its dependence on the
anisotropy at the interface and materials surrounding the interface. We have
demonstrated possibility of obtaining Goos-Hanchen shift of several wavelengths
in reflection for realistic material parameters. That proves the possibility
for change of the spin waves phase in ferromagnetic materials at subwavelength
distances, which can be regarded as a metasurface for magnonics.",1903.00861v1
2019-03-07,Effect of in-medium mass-shift on transverse-momentum spectrum and elliptic anisotropy of $φ$ meson,"We study the effect of in-medium mass-shift on transverse-momentum spectrum
and elliptic anisotropy of $\phi$ meson. It is found that the mass-shift
enhances the $\phi$ yields and suppresses the elliptic flow $v_2$ in large
momentum region, and the effects increase with the increasing mass-shift. The
effects are various for different sources and decrease with the increasing
expanding velocity. We further study the effects for parts of all $\phi$ meson
with mass-shift, and the effects decrease with the decreasing probability of
$\phi$ meson with mass-shift. Since the different mass-shift lead to different
transverse-momentum spectrum and $v_2$, our study may provide a way to restrict
the ranges of in-medium mass-shift of $\phi$ meson in high-energy heavy-ion
collisions.",1903.02997v3
2019-03-08,Intra- and inter-orbital correlated electron spin dynamics in $\rm Sr_2 Ir O_4$: spin-wave gap and spin-orbit exciton,"Transformation of Coulomb interaction terms to the pseudo-orbital basis
constituted by $J=1/2$ and $3/2$ states arising from spin-orbit coupling
provides a versatile tool. This formalism is applied to investigate magnetic
anisotropy effects on low-energy spin-wave excitations as well as high-energy
spin-orbit exciton modes in $\rm Sr_2 Ir O_4$. The Hund's coupling term
explictly yields easy-plane anisotropy, resulting in gapless (in-plane) and
gapped (out-of-plane) modes, in agreement with recent resonant inelastic x-ray
scattering (RIXS) measurements. The collective mode of inter-orbital,
spin-flip, particle-hole excitations with appropriate interaction strengths and
renormalized spin-orbit gap yields two well-defined propagating spin-orbit
exciton modes, with energy scale and dispersion in good agreement with RIXS
studies.",1903.03360v1
2019-03-11,Anisotropy Control in Photoelectron Spectra: A Coherent Two-Pulse Interference Strategy,"Coherence among rotational ion channels during photoionization is exploited
to control the anisotropy of the resulting photoelectron angular distributions
at specific photoelectron energies. The strategy refers to a robust and single
parameter control using two ultra-short light pulses delayed in time. The first
pulse prepares a superposition of a few ion rotational states, whereas the
second pulse serves as a probe that gives access to a control of the molecular
asymmetry parameter $\beta$ for individual rotational channels. This is
achieved by tuning the time delay between the pulses leading to channel
interferences that can be turned from constructive to destructive. The
illustrative example is the ionization of the $E(1\Sigma_{g}^{+})$ state of
Li$_{2}$. Quantum wave packet evolutions are conducted including both
electronic and nuclear degrees of freedom to reach angle-resolved photoelectron
spectra. A simple interference model based on coherent phase accumulation
during the field-free dynamics between the two pulses is precisely exploited to
control the photoelectron angular distributions from almost isotropic, to
marked anisotropic.",1903.04198v2
2019-03-11,Spin-glass state and reversed magnetic anisotropy induced by Cr doping in the Kitaev magnet $α$-RuCl$_3$,"Magnetic properties of the substitution series Ru$_{1-x}$Cr$_x$Cl$_3$ were
investigated to determine the evolution from the anisotropic Kitaev magnet
$\alpha$-RuCl$_3$ with $J_{\rm eff} = 1/2$ magnetic Ru$^{3+}$ ions to the
isotropic Heisenberg magnet CrCl$_3$ with $S = 3/2$ magnetic Cr$^{3+}$ ions.
Magnetization measurements on single crystals revealed a reversal of the
magnetic anisotropy under doping, which we argue to arise from the competition
between anisotropic Kitaev and off-diagonal interactions on the Ru-Ru links and
approximately isotropic Cr-Ru and isotropic Cr-Cr interactions. In addition,
combined magnetization, ac susceptibility and specific-heat measurements
clearly show the destabilization of the long-range magnetic order of
$\alpha$-RuCl$_3$ in favor of a spin-glass state of Ru$_{1-x}$Cr$_x$Cl$_3$ for
a low doping of $x\backsimeq0.1$. The corresponding freezing temperature as a
function of Cr content shows a broad maximum around $x\backsimeq0.45$.",1903.04248v3
2019-03-14,Black phosphorus nanodevices at terahertz frequencies: photodetectors and future challenges,"The discovery of graphene triggered a rapid rise of unexplored
two-dimensional materials and heterostructures having optoelectronic and
photonics properties that can be tailored on the nanoscale. Among these
materials, black phosphorus (BP) has attracted a remarkable interest thanks to
many favorable properties, such as high carrier mobility, in-plane anisotropy,
the possibility to alter its transport via electrical gating and direct
band-gap, that can be tuned by thickness from 0.3 eV (bulk crystalline) to 1.7
eV (single atomic layer). When integrated in a microscopic field effect
transistor (FET), a few-layer BP flake can detect Terahertz (THz) frequency
radiation. Remarkably, the in-plane crystalline anisotropy can be exploited to
tailor the mechanisms that dominate the photoresponse; a BP-based field effect
transistor can be engineered to act as a plasma-wave rectifier, a
thermoelectric sensor or a thermal bolometer. Here we present a review on
recent research on BP detectors operating from 0.26 THz to 3.4 THz with
particular emphasis on the underlying physical mechanisms and the future
challenges that are yet to be addressed for making BP the active core of stable
and reliable optical and electronic technologies.",1903.06198v1
2019-03-15,Shape of the quark gluon plasma droplet reflected in the high-p_T data,"We show, through analytic arguments, numerical calculations, and comparison
with experimental data, that the ratio of the high-p_T observables v_2/(1-R_AA)
reaches a well-defined saturation value at high p_T, and that this ratio
depends only on the spatial anisotropy of the quark gluon plasma (QGP) formed
in ultrarelativistic heavy-ion collisions. With expected future reduction of
experimental errors, the anisotropy extracted from experimental data will
further constrain the calculations of initial particle production in heavy-ion
collisions and thus test our understanding of QGP physics.",1903.06829v2
2019-03-19,H-T Phase Diagram of Rare-Earth -- Transition Metal Alloy in the Vicinity of the Compensation Point,"Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic
field and in the vicinity of the compensation temperature have so far been
explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for
ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic
rare-earth ion approximation and taking into account rare-earth (Gd) magnetic
anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice
is larger than that of the $d$-sublattice, the tricritical point can be at
higher temperature than the compensation point. The obtained phase diagram
explains the observed anomalous hysteresis loops as a result of high-field
magnetic phase transition, the order of which changes with temperature. It also
implies that in the vicinity of the magnetic compensation point the shape of
magnetic hysteresis loop is strongly temperature dependent.",1903.07941v1
2019-03-19,Quasilinear Approach of the Whistler Heat-Flux Instability in the Solar Wind,"The hot beaming (or strahl) electrons responsible for the main electron
heat-flux in the solar wind are believed to be self-regulated by the
electromagnetic beaming instabilities, also known as the heat-flux
instabilities. Here we report the first quasi-linear theoretical approach of
the whistler unstable branch able to characterize the long-term saturation of
the instability as well as the relaxation of the electron velocity
distributions. The instability saturation is not solely determined by the drift
velocities, which undergo only a minor relaxation, but mainly from a concurrent
interaction of electrons with whistlers that induces (opposite) temperature
anisotropies of the core and beam populations and reduces the effective
anisotropy. These results might be able to (i) explain the low intensity of the
whistler heat-flux fluctuations in the solar wind (although other explanations
remain possible and need further investigation), and (ii) confirm a reduced
effectiveness of these fluctuations in the relaxation and isotropization of the
electron strahl and in the regulation of the electron heat-flux.",1903.08005v1
2019-03-20,Hydrodynamic interactions and the diffusivity of spheroidal particles,"It is intuitive that the diffusivity of an isolated particle differs from
those in a monodisperse suspension, in which hydrodynamic interactions between
the particles are operative. Batchelor (1976,1983) calculated how hydrodynamic
interactions influenced the diffusivity of a dilute suspension of spherical
particles and Russel et al.(1991), and Brady (1994) treated non-dilute (higher
particle volume fraction) suspensions. Although most particles lack perfect
sphericity, little is known about the effects of hydrodynamic interactions on
the diffusivity of spheroidal particles, which are the simplest shapes that can
be used to model anisotropic particles. Here, we calculate the effects of
hydrodynamic interactions on the translational and rotational diffusivities of
spheroidal particles of arbitrary aspect ratio, in dilute monodisperse
suspensions. The origin of the hydrodynamic anisotropy is that found in the
stresslet field for the induced-dipole induced-dipole interaction. However, in
the dilute limit the anisotropy effects are at the level of a few percent.
These effects have influence in a vast range of settings, from partially frozen
colloidal suspensions to the dynamics of cytoplasm.",1903.08502v3
2019-03-22,WKB Approximation for the Polymer Quantization of the Taub Model,"We develop a suitable technical algorithm to implement a separation of the
Minisuperspace configurational variables into quasi-classical and purely
quantum degrees of freedom, in the framework of a Polymer quantum Mechanics
reformulation of the canonical dynamics. We then implement the obtained general
scheme to the specific case of a Taub Universe, in the presence of a free
massless scalar field. In particular, we identify the quasi-classical variables
in the Universe volume and a suitable function of the scalar field, while the
purely quantum degree of freedom corresponds to the Universe anisotropy. We
demonstrate that the Taub cosmology is associated to a cyclical Universe,
oscillating between a minimum and maximum volume turning points, respectively.
The pure quantum Universe anisotropy has always a finite value.",1903.09417v2
2019-03-24,Modeling Function-Valued Processes with Nonseparable and/or Nonstationary Covariance Structure,"We discuss a general Bayesian framework on modeling multidimensional
function-valued processes by using a Gaussian process or a heavy-tailed process
as a prior, enabling us to handle nonseparable and/or nonstationary covariance
structure. The nonstationarity is introduced by a convolution-based approach
through a varying anisotropy matrix, whose parameters vary along the input
space and are estimated via a local empirical Bayesian method. For the varying
matrix, we propose to use a spherical parametrization, leading to unconstrained
and interpretable parameters. The unconstrained nature allows the parameters to
be modeled as a nonparametric function of time, spatial location or other
covariates. The interpretation of the parameters is based on closed-form
expressions, providing valuable insights into nonseparable covariance
structures. Furthermore, to extract important information in data with complex
covariance structure, the Bayesian framework can decompose the function-valued
processes using the eigenvalues and eigensurfaces calculated from the estimated
covariance structure. The results are demonstrated by simulation studies and by
an application to wind intensity data. Supplementary materials for this article
are available online.",1903.09981v2
2019-03-27,Nonlinear Evolution of Ion Kinetic Instabilities in the Solar Wind,"In-situ observations of the solar wind (SW) plasma from 0.29 to 1AU show that
the protons and alpha particles are often non-Maxwellian, with evidence of
kinetic instabilities, temperature anisotropies, differential ion streaming,
and associated magnetic fluctuations spectra. The kinetic instabilities in the
SW multi-ion plasma can lead to preferential heating of alpha particles and the
dissipation of magnetic fluctuation energy, affecting the kinetic and global
properties of the SW. Using for the first time a three-dimensional hybrid
model, where ions are modeled as particle using the Particle-In-Cell (PIC)
method and electrons are treated as fluid, we study the onset, nonlinear
evolution and dissipation of ion kinetic instabilities. The
Alfven/ion-cyclotron, and the ion drift instabilities are modeled in the region
close to the Sun (~10R_s). Solar wind expansion is incorporated in the model.
The model produces self-consistent non-Maxwellian velocity distribution
functions (VDFs) of unstable ion populations, the associated temperature
anisotropies, and wave spectra for several typical SW instability cases in the
nonlinear growth and saturation stage of the instabilities. The 3D hybrid
modeling of the multi-ion SW plasma could be used to study the SW acceleration
region close to the Sun that will be explored by the Parker Solar Probe
mission.",1903.11343v1
2019-03-30,Anisotropic pressure induced by finite-size effects in SU(3) Yang-Mills theory,"We study the pressure anisotropy in anisotropic finite-size systems in SU(3)
Yang-Mills theory at nonzero temperature. Lattice simulations are performed on
lattices with anisotropic spatial volumes with periodic boundary conditions.
The energy-momentum tensor defined through the gradient flow is used for the
analysis of the stress tensor on the lattice. We find that a clear finite-size
effect in the pressure anisotropy is observed only at a significantly shorter
spatial extent compared with the free scalar theory, even when accounting for a
rather large mass in the latter.",1904.00241v2
2019-04-01,Experimental creation and annihilation of nonvolatile magnetic skyrmions using voltage control of magnetic anisotropy without an external magnetic field,"In this work, we utilize voltage controlled magnetic anisotropy (VCMA) to
manipulate magnetic skyrmions that are fixed in space. Memory devices based on
this strategy can potentially be of smaller footprint and better energy
efficiency than current-controlled motion-based skyrmionic devices. To
demonstrate VCMA induced manipulation of skyrmions, we fabricate
antiferromagnet/ferromagnet/oxide heterostructure films where skyrmions can be
stabilized without any external magnetic field due to the presence of exchange
bias. These isolated skyrmions were annihilated by applying a voltage pulse
that increased PMA. On the other hand, decreasing PMA promoted formation of
more skyrmions. Furthermore, skyrmions can be created from chiral domains by
increasing PMA of the system. To corroborate our experimental observations, we
performed micromagnetic simulation. The proposed method could potentially lead
to novel skyrmion-based memory devices.",1904.00701v1
2019-04-12,Antiferromagnetic Stacking of Ferromagnetic Layers and Doping Controlled Phase Competition in Ca$_{1-x}$Sr$_{x}$Co$_{2-y}$As$_{2}$,"In search of a quantum phase transition between the two-dimensional ($2$D)
ferromagnetism of CaCo$_{2-y}$As$_{2}$ and stripe-type antiferromagnetism in
SrCo$_{2}$As$_{2}$, we rather find evidence for $1$D magnetic frustration
between magnetic square Co layers. We present neutron diffraction data for
Ca$_{1-x}$Sr$_{x}$Co$_{2-y}$As$_{2}$ that reveal a sequence of $x$-dependent
magnetic transitions which involve different stacking of $2$D
ferromagnetically-aligned layers with different magnetic anisotropy. We explain
the $x$-dependent changes to the magnetic order by utilizing classical
analytical calculations of a $1$D Heisenberg model where single-ion magnetic
anisotropy and frustration of antiferromagnetic nearest- and next-nearest-layer
exchange are all composition dependent.",1904.06444v2
2019-04-17,Multifunctional 2D CuSe monolayer nanodevice,"In a very recent experimental work [Gao et al., 2018 Adv. Mater. 30,
1707055], a graphene-like CuSe monolayer was realized. Motivated by this
success, we performed first-principles calculations to investigate its
electronic transport and photoelectronic properties. We find that the CuSe ML
shows a strong electrical anisotropy, and its current-voltage (I-V) curves
along the zigzag and armchair directions are noticeably different. The CuSe ML
also displays a useful negative differential resistance (NDR) effect along the
both directions when the bias is beyond 1.0 V. Moreover, it has a large photon
absorption to orange light. Our study suggests that CuSe ML is a
multifunctional material and has various potential applications in
electrical-anisotropy-based, NDR-based, and even optical nanodevices.",1904.08047v1
2019-04-17,Action-based models for dwarf spheroidal galaxies and globular clusters,"A new family of self-consistent DF-based models of stellar systems is
explored. The stellar component of the models is described by a distribution
function (DF) depending on the action integrals, previously used to model the
Fornax dwarf spheroidal galaxy (dSph). The stellar component may cohabit with
either a dark halo, also described by a DF, or with a massive central black
hole. In all cases we solve for the model's self-consistent potential.
Focussing on spherically symmetric models, we show how the stellar observables
vary with the anisotropy prescribed by the DF, with the dominance and nature of
the dark halo, and with the mass of the black hole. We show that precise fits
to the observed surface brightness profiles of four globular clusters can be
obtained for a wide range of prescribed velocity anisotropies. We also obtain
precise fits to the observed projected densities of four dSphs. Finally, we
present a three-component model of the Scupltor dSph with distinct DFs for the
red and blue horizontal branch stars and the dark matter halo.",1904.08447v1
2019-04-24,Valley Anisotropy in Elastic Metamaterials,"Valley, as a new degree of freedom, raises the valleytronics in fundamental
and applied science. The elastic analogs of valley states have been proposed by
mimicking the symmetrical structure of either two-dimensional materials or
photonic valley crystals. However, the asymmetrical valley construction remains
unfulfilled. Here, we present the valley anisotropy by introducing asymmetrical
design into elastic metamaterials. The elastic valley metamaterials are
composed of bio-inspired hard spirals and soft materials. The anisotropic
topological nature of valley is verified by asymmetrical distribution of the
Berry curvature. We show the high tunability of the Berry curvature both in
magnitude and sign enabled by our anisotropic valley metamaterials. Finally, we
demonstrate the creation of valley topological insulators and show
topologically protected propagation of transverse elastic waves relying on
operating frequency. The proposed topological properties of elastic valley
metamaterials pave the way to better understanding the valley topology and to
creating a new type of topological insulators enabled by an additional valley
degree of freedom.",1904.11057v1
2019-05-09,Diffractive dijet production in impact parameter dependent saturation models,"We study coherent diffractive dijet production in electron-hadron and
electron-nucleus collisions within the dipole picture. We provide semi-analytic
results for the differential cross section and elliptic anisotropy in the angle
between dijet transverse momentum and hadron recoil momentum. We demonstrate
the direct relation between angular moments of the dipole amplitude in
coordinate space and angular moments of the diffractive dijet cross sections.
To perform explicit calculations we employ two different saturation models,
extended to include the target geometry. In the limit of large photon
virtuality or quark masses, we find fully analytic results that allow direct
insight into how the differential cross section and elliptic anisotropy depend
on the saturation scale, target geometry, and kinematic variables. We further
provide numerical results for more general kinematics in collisions at a future
electron-ion collider, and study the effects of approaching the saturated
regime on diffractive dijet observables.",1905.03763v2
2019-05-11,Anisotropic thermal expansion and thermomechanic properties of monolayer $β$-Te,"Recently, $\beta$-Te (atomically 2D tellurium) with rectangular crystal
structure has been synthesized successfully on highly oriented pyrolytic
graphite substrates by using molecular beam epitaxy. It has been found
possessing remarkable properties such as ultralow lattice thermal conductivity
and high thermoelectric efficiency. Based on the first-principles calculations,
we study the thermal expansion and thermomechanic properties of the
experimental phase monolayer $\beta$-Te, using quasiharmonic approach. It is
found $\beta$-Te shows large positive thermal expansion at elevated
temperature, while the linear thermal expansion coefficient is negative along a
direction at very low temperature. The linear thermal expansion coefficient
along b direction is 4.9*10$^{-5}$ K$^{-1}$ at 500 K, which is considerably
large in 2D materials. $\beta$-Te exhibits strong in-plane anisotropy,
including thermal expansion, 2D elastic moduli and Poisson's ratios. However,
the elastic moduli, Poisson's ratios and the in-plane anisotropy are weakened
with increasing temperature, and the variations are dominated by the
generalized mode Gr\""{u}neisen parameters.",1905.04481v1
2019-05-11,Primordial bouncing cosmology in the Deser-Woodard nonlocal gravity,"The Deser-Woodard (DW) nonlocal gravity model has been proposed in order to
describe the late-time acceleration of the universe without introducing dark
energy. In this paper we focus, however, on the early stage of the universe and
demonstrate how a primordial bounce in the vacuum spacetime can be realized in
the framework of the DW nonlocal model. We reconstruct the nonlocal distortion
function, which encodes all the modifications to the Einstein-Hilbert action,
in order to generate bouncing solutions to solve the initial singularity
problem. We show that the initial conditions can be chosen in such a way that
the distortion function and its first order derivative approach zero after the
bounce and the standard cosmological solution described by general relativity
is recovered afterwards. We also study the evolution of anisotropies near the
bounce. It turns out that the shear density defined by the anisotropy grows
towards the bounce, but due to the presence of nonlocal effects, it grows in a
milder manner compared with that in Einstein gravity.",1905.04557v2
2019-05-14,Phase diagrams of spin-3/2 Blume-Capel model on rectangular lattice under longitudinal magnetic field,"The spin-3/2 Blume-Capel model on a rectangular lattice with the
ferromagnetic bilinear short-range interaction $K^{\rm F}=K(1+x)$ in one
direction and the anti-ferromagnetic one $K^{\rm AF}=K(-1+x)$ in the
perpendicular direction under a longitudinal magnetic field and in the presence
of a single-ion anisotropy is investigated within the mean field approximation.
The quantity $x$ characterizes coupling between the interactions in the
perpendicular directions and its absolute value does not exceed unity. Basing
on the study of temperature dependencies of sublattice magnetizations the phase
diagrams in the ($x$, temperature) plane are constructed for different values
of the longitudinal magnetic field and the single-ion anisotropy. The global
phase diagram of the model demonstrates an unusual abundance.",1905.05674v1
2019-05-17,Anisotropy of electronic stopping power in graphite,"The rate of energy transfer from ion projectiles onto the electrons of a
solid target is hard to determine experimentally in the velocity regime between
the adiabatic limit and the Bragg peak. First-principles simulations have
lately offered relevant new insights and quantitative information for
prototypical homogeneous materials. Here we study the influence of structural
anisotropy on electronic stopping power with time-dependent density functional
theory simulations of a hydrogen projectile in graphite. The projectile
traveled at a range of angles and impact parameters for velocities between 0.1
and 1.4 a.u., and the electronic stopping power was calculated for each
simulation. After validation with average experimental data, the anisotropic
crystal structure was found to have a strong influence on the stopping power,
with a difference between simulations parallel and perpendicular to the
graphite plane of up to 25%, more anisotropic than expected based on previous
work. The velocity dependence at low velocity displays clear linear behavior in
general, except for projectiles traveling perpendicular to graphitic layers,
for which a threshold-like behavior is obtained. For projectiles traveling
along graphitic planes metallic behaviour is observed with a change of slope
when the projectile velocity reaches the Fermi velocity of the electrons.",1905.07200v2
2019-05-27,Bianchi models with a free massless scalar field: invariant sets and higher symmetries,"We scrutinize the overall structure of the space of cosmological models of
Bianchi type I-VII$_h$ that contain a free massless scalar field, with a
spatially homogeneous gradient $\nabla_\mu \varphi$ that generally breaks
isotropy, in addition to a standard perfect fluid. Specifically, state space is
written as a union of disjoint invariant sets, each corresponding to a
particular cosmological model that is classified with respect to the Bianchi
type and the matter content. Subsets corresponding to higher-symmetry models,
including all locally rotationally symmetric models and FLRW models, and models
with a shear-free normal congruence, are also derived and classified. For each
model the dimension ($d$) of the space of initial data is given, after fixing
the orientation of the orthonormal frame uniquely relative to matter
anisotropies and geometrical anisotropies.",1905.11456v2
2019-05-30,Interface moment dynamics and its contribution to spin-transfer torque switching process in magnetic tunnel junctions,"A practical problem for memory applications involving perpendicularly
magnetized magnetic tunnel junctions is the reliability of switching
characteristics at high-bias voltage. Often it has been observed that at
high-bias, additional error processes are present that cause a decrease in
switching probability upon further increase of bias voltage. We identify the
main cause of such error-rise process through examination of switching
statistics as a function of bias voltage and applied field, and the junction
switching dynamics in real time. These experiments show a coincidental onset of
error-rise and the presence of a new low-frequency microwave emission well
below that dictated by the anisotropy field. We show that in a few-macrospin
coupled numerical model, this is consistent with an interface region with
concentrated perpendicular anisotropy, and where the magnetic moment has
limited exchange coupling to the rest of the layers. These results point to the
important role high-frequency interface magnetic moment dynamics play in
determining the switching characteristics of these tunnel junction devices.",1905.13253v1
2019-06-05,Supersymmetric Landau-Ginzburg Tensor Models,"We study two dimensional $\mathcal{N} = (2, 2)$ Landau-Ginzburg models with
tensor valued superfields with the aim of constructing large central charge
superconformal field theories which are solvable using large $N$ techniques. We
demonstrate the viability of such constructions and motivate the study of
anisotropic tensor models. Such theories are a novel deformation of tensor
models where we break the continuous symmetries while preserving the large $N$
solvability. Specifically, we examine theories with superpotentials involving
tensor contractions chosen to pick out melonic diagrams. The anisotropy is
introduced by further biasing individual terms by different coefficients, all
of the same order, to retain large $N$ scaling. We carry out a detailed
analysis of the resulting low energy fixed point and comment on potential
applications to holography. Along the way we also examine gauged versions of
the models (with partial anisotropy) and find generically that such theories
have a non-compact Higgs branch of vacua.",1906.02163v2
2019-06-07,Shear-induced contact area anisotropy explained by a fracture mechanics model,"This paper gives a theoretical analysis for the fundamental problem of
anisotropy induced by shear forces onan adhesive contact, discussing the
experimental data of the companion Letter. We present a fracture mechanicsmodel
where two phenomenological mode-mixity functions are introduced to describe the
weak couplingbetween modes I and II or I and III, which changes the effective
toughness of the interface. The mode-mixityfunctions have been interpolated
using the data of a single experiment and then used to predict the behavior of
thewhole set of experimental observations. The model extends an idea by Johnson
and Greenwood, to solve purelymode I problems of adhesion in the presence of a
nonaxisymmetric Hertzian geometry, to the case of ellipticalcontacts sheared
along their major or minor axis. Equality between the stress intensity factors
and their criticalvalues is imposed solely at the major and minor axes. We
successfully validate our model against experimentaldata. The model predicts
that the punch geometry will affect both the shape and the overall decay of the
shearedcontact area.",1906.02957v1
2019-06-11,Phase-field material point method for dynamic brittle fracture with isotropic and anisotropic surface energy,"A novel phase field material point method is introduced for robust simulation
of dynamic fracture in elastic media considering the most general case of
anisotropic surface energy. Anisotropy is explicitly introduced through a
properly defined crack density functional. The particular case of impact driven
fracture is treated by employing a discrete field approach within the material
point method setting. In this, the equations of motion and phase field
governing equations are solved independently for each discrete field using a
predictor-corrector algorithm. Contact at the interface is resolved through
frictional contact conditions. The proposed method is verified using analytical
predictions. The influence of surface energy anisotropy and loading conditions
on the resulting crack paths is assessed through a set of benchmark problems.
Comparisons are made with the standard Phase Field Finite Element Method and
experimental observations.",1906.04740v1
2019-06-11,Effects of the magnetic field direction on the Tsallis statistic,"We extend the use of the Tsallis statistic to measure the differences in gas
dynamics relative to the mean magnetic field present from natural eddy-type
motions existing in magnetohydrodynamical (MHD) turbulence. The variation in
gas dynamics was estimated using the Tsallis parameters on the incremental
probability distribution function of the observables (intensity and velocity
centroid) obtained from compressible MHD simulations. We find that the Tsallis
statistic is susceptible to the anisotropy produce by the magnetic field, even
when anisotropy is percent the Tsallis statistic can be use to determine MHD
parameters such as the Sonic Mach number. We quantize the goodness of the
Tsallis parameters using the coefficient of determination to measure the
differences in the gas dynamics. These parameters also determine the level of
magnetization and compressibility of the medium. To further simulate realistic
spectroscopic observational data we introduced smoothing, noise, and cloud
boundaries to the MHD simulations.",1906.04821v1
2019-06-20,Relaxation dynamics and genuine properties of the solvated electron in neutral water clusters,"We have investigated the solvation dynamics and the genuine binding energy
and photoemission anisotropy of the solvated electron in neutral water clusters
with a combination of time-resolved photoelectron velocity map imaging and
electron scattering simulations. The dynamics was probed with a UV probe pulse
following above-band-gap excitation with a EUV pump pulse. The solvation
dynamics is completed within about 2 ps. Only a single band is observed in the
spectra, with no indication for isomers with distinct binding energies. Data
analysis with an electron scattering model reveals a genuine binding energy in
the range of 3.55-3.85 eV and a genuine anisotropy parameter in the range of
0.51-0.66 for the ground-state hydrated electron. All these observations
coincide with those for liquid bulk, which is rather unexpected for an average
cluster size of 300 molecules.",1906.08767v3
2019-07-03,Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba coupling,"Spin-transfer torques (STT), Gilbert damping (GD), and effective spin
renormalization (ESR) are investigated microscopically in a 2D Rashba
ferromagnet with spin-independent Gaussian white-noise disorder. Rashba
spin-orbit coupling induced anisotropy of these phenomena is thoroughly
analysed. For the case of two partly filled spin subbands, a remarkable
relation between the anisotropic STT, GD, and ESR is established. In the
absence of magnetic field and other torques on magnetization, this relation
corresponds to a current-induced motion of a magnetic texture with the
classical drift velocity of conduction electrons. Finally, we compute spin
susceptibility of the system and generalize the notion of spin-polarized
current.",1907.02041v3
2019-07-10,"Magneto-Crystalline Anisotropy of Fe, Co and Ni slabs from Density Functional Theory and Tight-Binding models","We report magneto-crystalline anisotropy (MCA) calculations of Fe, Co and Ni
slabs of various thicknesses and crystallographic orientations from two Density
Functional Theory codes based either on a plane wave or a local atomic basis
set expansion and a magnetic tight-binding method. We analyze the evolution of
the MCA with the number of layers of the slabs. The decomposition of MCA into
contributions of atomic sites helps understanding the oscillatory behaviour of
the MCA with the slab thickness and highlights the role of finite size effects.
We also identify some specific systems with enhanced MCA. A k-space as well as
a band-filling analysis show very rich features of the MCA that could be used
to tailor systems with enhanced magnetic properties. Finally this work can
serve as a benchmark for MCA calculations.",1907.04532v2
2019-07-11,Correlations between azimuthal anisotropy Fourier harmonics in PbPb collisions at $\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV in the HYDJET++ and AMPT models,"Correlations between azimuthal anisotropy Fourier harmonics $v_{n}$ ($n = 2,
3, 4$) are studied using the events from PbPb collisions at
$\sqrt{s_{_{\mathrm{NN}}}}=2.76$ TeV generated by the HYDJET++ and AMPT models,
and compared to the corresponding experimental results obtained by the ATLAS
Collaboration. The Fourier harmonics $v_{n}$ are measured over a wide
centrality range using the two-particle azimuthal correlation method. The
slopes of the $v_{2}$--$v_{3}$ correlation from both models are in a good
agreement with the ATLAS data. The HYDJET++ model predicts a stronger slope for
the $v_{2}$--$v_{4}$ and $v_{3}$--$v_{4}$ correlations than the ones
experimentally measured, while the results from the AMPT model are in a rather
good agreement with the experimental results. In contrast to the HYDJET++
predictions, the AMPT model predicts a boomerang-like shape in the structure of
the correlations as found in the experimental data.",1907.05450v2
2019-07-15,CMB constraints on ultra-light primordial black holes with extended mass distributions,"We examine the effects ultra-light primordial black holes (PBHs) have on the
anisotropies of the cosmic microwave background (CMB). PBHs in the mass range
of $10^{15}$ to $10^{17}$ g emit Hawking radiation in the early Universe,
modifying the standard recombination history. This leads to a damping of
small-scale temperature and polarisation anisotropies and enhances large-scale
polarisation fluctuations. As some models of inflation predict PBHs with a
range of masses, we investigate the impacts of extended mass distributions on
PBH abundance constraints. We model PBH energy injection using a ground-up
approach incorporating species-dependent deposition efficiencies. By allowing
the $\Lambda$CDM parameters to vary simultaneously with the PBH fraction and
mass, we show that exclusion bounds on the PBH fraction of DM $f_\text{PBH}$
are relaxed by up to an order of magnitude, compared to the case of fixed
$\Lambda$CDM parameters. We also give 95% exclusion regions for $f_\text{PBH}$
for a variety of mass distributions. In particular, for a uniform mass
distribution between $10^{15}$ and $10^{17}$ g, we find $f_\text{PBH} < 1.6
\times 10^{-5}$ when allowing $\Lambda$CDM parameters to vary.",1907.06485v1
2019-07-15,Estimating the angular power spectrum of the gravitational-wave background in the presence of shot noise,"There has been much recent interest in studying anisotropies in the
astrophysical gravitational-wave (GW) background, as these could provide us
with interesting new information about galaxy clustering and large-scale
structure. However, this information is obscured by shot noise, caused by the
finite number of GW sources that contribute to the background at any given
time. We develop a new method for estimating the angular spectrum of
anisotropies, based on the principle of combining statistically-independent
data segments. We show that this gives an unbiased estimate of the true,
astrophysical spectrum, removing the offset due to shot noise power, and that
in the limit of many data segments, it is the most efficient (i.e.
lowest-variance) estimator possible.",1907.06642v2
2019-07-19,"Manipulation of spin cluster qubits by electric-field induced modulation of exchange coupling, $g$-factor, and axial anisotropy","Electric fields are increasingly used for coherently manipulating spin states
in semiconductor and molecular systems. Here we discuss the spin manipulation
allowed by the modulation of the main parameters entering the Hamiltonians of
molecular spin clusters. In particular, we focus on transitions between states
that differ in terms of scalar quantities, such as the total- or the
partial-spin sums, but have vanishing expectation values of both the total- and
the single-spin projections. These conditions supposedly define subspaces that
are immune to the main decoherence mechanisms and that cannot be identified in
individual spins, where the total- and the partial-spin sums are fixed or
cannot be defined. We show that the desired transitions can in principle be
realized in systems as simple as a spin dimer, by modulating the g-factor, the
axial anisotropy, or, under suitable conditions, the exchange interaction.",1907.08391v2
2019-07-21,Elastic interactions of Fe adatoms on Cu(111) at the mesoscale,"An extended elastic eigenvector approach had earlier been developed to
interpret ab-initio calculations of adatom interactions. It shows oscillating
interactions as well as trio- and quarto (multisite) terms within clusters. It
is now applied to the interaction of Fe adatoms on Cu(111). The extended
approach differs from previous calculations by using a sharp cutoff -
generating oscillating interactions - and by taking into account interacting
dimers - generating strong anisotropies and multisite terms. Additional weak
anisotropy stems from the substrate and from the surface Brillouin zone shape.
This approach has 3 free parameters which have been fitted to first principles
interactions of Fe adatoms on Cu(111). Elastic adatom pair interactions and
dimer-dimer interactions at mesoscale separations show a reasonable good fit to
the first principles interactions. At smaller separations elastic interaction
values remain questionable. To enable a comparison with future first principle
calculations also dimer-monomer interactions are shown. Some conclusions on
initial adatom formation and diffusion are proposed and open questions are
formulated.",1907.08929v2
2019-07-21,Weibel-Mediated Shocks Propagating into Inhomogeneous Electron-Positron Plasmas,"The external forward shock emitting the gamma-ray burst (GRB) afterglow is
collisionless, and it is mediated by the Weibel instability which generates the
magnetic field. The GRB afterglow shows that the magnetic field in the large
downstream region is much stronger than the shock-compressed pre-shock field.
However, particle-in-cell (PIC) simulations of relativistic shocks propagating
into homogeneous media show that the Weibel generated field decays near the
shock front. Some GRB observations and theoretical studies suggest that the
preshock medium is inhomogeneous. We perform the PIC simulation of a
relativistic shock propagating into inhomogeneous plasma. It is found that the
post-shock magnetic field decays slowly compared with the homogeneous case.
Sound waves and entropy waves are also generated by the shock-wave interaction,
and temperature anisotropy is produced by the sound wave in the downstream
region. The free energy of the temperature anisotropy is large enough to
explain the observed field strength. Our results show that the upstream density
fluctuation has a significant effect in the downstream region of collisionless
shocks even if the wavelength of the upstream inhomogeneity is much larger than
the kinetic scale.",1907.08939v1
2019-07-24,Microsecond electro-optic switching of nematic liquid crystals with giant dielectric anisotropy,"Nematic liquid crystals exhibit a fast optical response when the applied
electric field modifies the degree of order but does not change the direction
of molecular orientation. The effect requires a relatively high electric field,
on the order of 10^8 V/m for a field induced birefringence change of 0.01. To
address this detrimental issue, this work explores electrically induced
modification of the order parameter in a material with a giant dielectric
anisotropy of +200. A relatively weak field 3X10^7 V/m causes a significant
change of birefringence, by about 0.04. Both switching on and off times are ~10
microseconds. The effect is called a microsecond electrically modified order
parameter (MEMOP) and can be used in electro-optical devices, such as fast
electro-optic shutters, phase modulators, and beam-steerers that require
microsecond response times.",1907.10227v1
2019-07-24,Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions,"We demonstrate field and current controlled magnetodynamics in nanocontact
spin-torque nano-oscillators (STNOs) based on orthogonal magnetic tunnel
junctions (MTJs). We systematically analyze the microwave properties (frequency
$f$, linewidth $\Delta f$, power $P$, and frequency tunability $df/dI$) with
their physical origins---perpendicular magnetic anisotropy (PMA), damping-like
and field-like spin transfer torque (STT), and voltage-controlled magnetic
anisotropy (VCMA). These devices present several advantageous characteristics:
high emission frequencies ($f> 20$ GHz), high frequency tunability
($df/dI=0.25$~GHz/mA), and zero-field operation ($f\sim 4$ GHz). Furthermore, a
detailed investigation of $f(H, I)$ reveals that $df/dI$ is mostly governed by
the large VCMA (287~fJ/(V$\cdot$m)), while STT plays a negligible role.",1907.10427v2
2019-07-24,"Crystal field splitting, local anisotropy, and low energy excitations in the quantum magnet YbCl$_3$","We study the correlated quantum magnet, YbCl$_3$, with neutron scattering,
magnetic susceptibility, and heat capacity measurements. The crystal field
Hamiltonian is determined through simultaneous refinements of the inelastic
neutron scattering and magnetization data. The ground state doublet is well
isolated from the other crystal field levels and results in an effective
spin-1/2 system with local easy plane anisotropy at low temperature. Cold
neutron spectroscopy shows low energy excitations that are consistent with
nearest neighbor antiferromagnetic correlations of reduced dimensionality.",1907.10627v1
2019-07-29,An improved interstitial-ice model for pure liquid water,"The main idea of the interstitial-ice model is that liquid water consists of
an intact hexagonal lattice with both vacant lattice positions and interstitial
water molecules. Narten, Danford and Levy derived the model parameters from the
X-ray diffraction patterns of liquid water. However, their results were
counter-intuitive: their model had almost no vacancies, the interstitial
concentration was temperature independent and the ice lattice was deformed
resulting in extra anisotropy. To overcome these problems, we refined the model
and derived the model parameters from the proton nuclear magnetic resonance
frequency of pure water. Without any extra anisotropy, a significant
concentration of vacancies was found (3.7% of the lattice positions at
0{\deg}C) and the concentration of both the vacancies and interstitials
increased quasi linear with temperature (0.05 M/{\deg}C). This improved model
successfully explains the thermodynamic data of water and is therefore a
promising candidate for a coherent and analytical water model.",1907.12479v3
2019-07-31,Experimental biases on the heliospheric contribution to the observed TeV cosmic ray anisotropy,"The arrival direction distribution of cosmic ray particles observed on Earth
is shaped by the cumulative effects of their galactic source locations and of
trajectory bending in the turbulent interstellar magnetic field. Coherent
magnetic structures are expected to disrupt particle trajectories and their
observed distribution, as well. The heliosphere, the large magnetic bubble
generated by the sweeping effect of solar wind on the local interstellar
plasma, strongly affects the TeV cosmic ray particles detected on Earth. By
unfolding the heliospheric influence on the observed anisotropy, it is possible
to determine the pitch angle distribution of cosmic rays in the interstellar
medium. This information makes it possible to study in detail the global
diffusion properties of TeV cosmic rays in the Galaxy. However, observational
blindness to key features of the cosmic ray arrival direction distribution may
lead to biases in the determination of the heliospheric influence and of the
interstellar CR distribution. Any inference of galactic TeV CR diffusion
properties must carefully account for local propagation phenomena and
observational limitations.",1908.00067v1
2019-08-05,Atomistic and mean-field estimates of effective stiffness tensor of nanocrystalline materials of cubic symmetry,"Anisotropic core-shell model of a nano-grained polycrystal, proposed recently
for nanocrystalline copper, is applied to estimate elastic effective properties
for a set of crystals of cubic symmetry. Materials selected for analysis differ
in the lattice geometry (face-centered cubic vs. body-centered cubic) as well
as the value of a Zener factor: a ratio of two shear moduli defining elastic
anisotropy of a cubic crystal. The predictions are verified by means of the
atomistic simulations. The dependence of the overall bulk and shear moduli on
the average grain diameter is analysed. In the mean-field approach the
thickness of the shell is specified by the \emph{cutoff radius} of a
corresponding atomistic potential, while the grain shell is isotropic and its
properties are identified by molecular simulations performed for very small
grains with approximately all atoms belonging to the grain boundary zone. It is
shown that the core-shell model provides predictions of satisfactory
qualitative and quantitative agreement with atomistic simulations. Performed
study indicates that the variation of the bulk and shear moduli with the grain
size changes qualitatively when the Zener anisotropy factor is smaller or
greater than one.",1908.01644v1
2019-08-07,Chaotic Effects on Cosmic Ray Anisotropy in a Heliosphere-inspired Model,"Cosmic rays propagate through the Galaxy and encounter systems that may trap
them temporarily, as well as magnetic field structures that induce chaotic
behavior on their trajectories. In particular, this is the case for particles
that propagate in the local interstellar medium and interact with the
heliospheric magnetic field before being detected on Earth. As a consequence,
the observed cosmic-ray arrival direction distribution is affected by the
heliosphere as long as their gyro-radius is smaller or comparable with the
heliospheric size, i.e. in the TeV energy range. The chaotic nature of those
cosmic-ray particle trajectories that are temporarily trapped inside the
heliosphere can be characterized using the Finite-Time Lyapunov Exponents.
Specifically, we will delve into the case of particles trapped in a
heliospheric-inspired toy model of a static magnetic bottle configuration and
the presence of temporal magnetic perturbations. In this work, we also suggest
that a time-variability could prove to be important in the understanding of the
TeV cosmic-ray anisotropy at Earth.",1908.02818v1
2019-08-14,Focusing Surface Acoustic Wave Microcavities on GaAs,"Focusing microcavities for surface acoustic waves (SAWs) produce highly
localized strain and piezoelectric fields that can dynamically control
excitations in nanostructures. Focusing transducers (FIDTs) that generate SAW
beams which match nanostructure dimensions require pattern correction due to
diffraction and wave velocity anisotropy. The anisotropy correction is normally
implemented by adding a quadratic term to the dependence of the wave velocity
on propagation angle. We show that SAW focusing to diffraction limited sizes in
GaAs requires corrections that more closely follow the group velocity
wavefront, which is not a quadratic function. Optical interferometric mapping
of the resultant SAW displacement field reveals tightly focused SAW beams on
GaAs with a minimal beam waist. An additional set of Gouy phase-corrected
passive fingers creates an acoustic microcavity in the focal region with small
volume and high quality factor. Our $\lambda_\mathrm{SAW} = 5.6~\mu$m FIDTs are
expected to scale well to the $\approx $ 500~nm wavelengths regime needed to
study strong coupling between vibrations and electrons in electrostatic GaAs
quantum dots.",1908.04980v3
2019-08-19,Isotropic charge screening of the anisotropic black phosphorus revealed by potassium adatoms,"Black phosphorus has attracted great research interest due to its numerous
applications in electronic devices, optoelectronic devices, energy storages and
so on. Compared with the majority of two-dimensional materials, black
phosphorus possesses a unique property, i.e. the strong in-plane anisotropy.
All the properties reported so far, including its effective mass, electron
mobility, light absorption, thermal conductivity and so on, have shown great
anisotropy in the basal plane. This property renders black phosphorus unique
applications not achievable with other two-dimensional materials. In this work,
however, we discover a remarkable isotropic behavior in the strongly
anisotropic black phosphorus, i.e. its electrostatic screening of point
charges. We use the tip-induced band bending of a scanning tunneling microscope
to map out the Coulomb field of ionized potassium adatoms on black phosphorus,
and reveal its isotropic charge screening. This discovery is important for
understanding electron scattering and transport in black phosphorus.",1908.06554v1
2019-08-20,Light diffusion in birefringent polycrystals and the IceCube ice anisotropy,"The IceCube Neutrino Observatory instruments about 1 km^3 of deep, glacial
ice at the geographic South Pole with 5160 photomultipliers to detect Cherenkov
light from charged relativistic particles. The experiment pursues a wide range
of scientific questions ranging from particle physics such as neutrino
oscillations to high-energy neutrino astronomy. Most of these efforts rely
heavily on an ever more precise understanding of the optical properties of the
instrumented ice. An unexpected light propagation effect, observed by the
experiment, is an anisotropic attenuation, which is aligned with the local flow
of the ice. The exact cause is still under investigation. In this contribution,
the micro-structure of ice as a birefringent polycrystal is explored as the
cause for this anisotropy.",1908.07608v1
2019-08-21,Effects of alpha-proton differential flow on proton temperature anisotropy instabilities in the solar wind: Wind observations,"Plasma kinetic waves and alpha-proton differential flow are two important
subjects on the topic of evolution of the solar wind. Based on the Wind data
during 2005-2015, this paper reports that the occurrence of electromagnetic
cyclotron waves (ECWs) near the proton cyclotron frequency significantly
depends on the direction of alpha-proton differential flow Vd. As Vd rotates
from anti-Sunward direction to Sunward direction, the occurrence rate of ECWs
as well as the percentage of left-handed (LH) polarized ECWs decreases
considerably. In particular, it is shown that the dominant polarization changes
from LH polarization to right-handed polarization during the rotation. The
investigation on proton and alpha particle parameters ordered by the direction
of Vd further illustrates that large kinetic energies of alpha-proton
differential flow correspond to high occurrence rates of ECWs. These results
are well consistent with theoretical predictions for effects of alpha-proton
differential flow on proton temperature anisotropy instabilities.",1908.07680v1
2019-08-22,Study of the velocity plateau of Dzyaloshinskii domain walls,"We study field-driven domain wall (DW) velocities in asymmetric multilayer
stacks with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya
interaction (DMI), both experimentally and by micromagnetic simulations. Using
magneto-optical Kerr microscopy under intense and nanoseconds-long fields, we
show that DWs in these films propagate at velocities up to hundreds of m/s and
that, instead of the expected decrease of velocity after the Walker field, a
long plateau with constant velocity is observed, before breakdown. Both the
maximum speed and the field extent of the velocity plateau strongly depend on
the values of the spontaneous magnetization and the DMI strength, as well as on
the magnetic anisotropy. Micromagnetic simulations reproduce these features in
sufficiently wide strips, even for perfect samples. A physical model explaining
the microscopic origin of the velocity plateau is proposed.",1908.08282v1
2019-08-24,Magnetic order and anisotropic interactions induced by mixing between the $J=1/2$ and $3/2$ sectors in spin-orbit coupled honeycomb-lattice compounds,"Novel magnetic ordering on the honeycomb lattice due to emergent weak
anisotropic interactions generated by the mixing between the $J=1/2$ sector and
the magnetically inactive 3/2 sector is investigated in a three-orbital
interacting electron model in the absence of Hund's coupling. Self-consistent
determination of magnetic order yields anisotropic N\'{e}el and zigzag orders
for different parameter regimes, highlighting the effect of the emergent
single-ion anisotropy. Study of magnon excitations shows extremely small magnon
energy scale compared to the hopping energy scale, and enhancement of
anisotropy effects for smaller spin-orbit coupling. These results account for
several features of the honeycomb lattice compounds such as $\rm Na_2 Ir O_3$
and $\rm Ru Cl_3$, where the leading order anisotropic interactions within the
magnetically active $J=1/2$ sector are completely quenched due to the
edge-sharing octahedra.",1908.09130v1
2019-08-27,A search for cosmological anisotropy using the Lyman alpha forest from SDSS quasar spectra,"The Cosmological Principle, the combined assumptions of cosmological isotropy
and homogeneity, underpins the standard model of Big Bang cosmology with which
we interpret astronomical observations. A new test of isotropy over the
redshift range $2<z<4$ and across large angular scales on the sky is presented.
We use the cosmological distribution of neutral hydrogen, as probed by the
Ly$\alpha$ forest seen towards distant quasars. The Sloan Digital Sky Survey
provides the largest dataset of quasar spectra available to date. We use
combined information from Data Releases 12 and 14 to select a sample of 142,661
quasars most suitable for this purpose. The scales covered by the data extend
beyond post-inflation causality scales, thus probing initial conditions in the
early universe. We identify significant spatially correlated systematic effects
that can emulate cosmological anisotropy. Once these systematics have been
accounted for, the data are found to be consistent with isotropy, providing an
important independent check on the standard model, consistent with results from
cosmic microwave background data.",1908.10301v1
2019-09-03,Single-site magnetic anisotropy governed by inter-layer cation charge imbalance in triangular-lattice AYbX$_2$,"The behavior in magnetic field of a paramagnetic center is characterized by
its $g$ tensor. An anisotropic form of the latter implies different kind of
response along different crystallographic directions. Here we shed light on the
anisotropy of the $g$ tensor of Yb$^{3+}$ 4$f^{13}$ ions in NaYbS$_2$ and
NaYbO$_2$, layered triangular-lattice materials suggested to host spin-liquid
ground states. Using quantum chemical calculations we show that, even if the
ligand-cage trigonal distortions are significant in these compounds, the
crucial role in realizing strongly anisotropic, `noncubic' $g$ factors is
played by inter-layer cation charge imbalance effects. The latter refer to the
asymmetry experienced by a given Yb center due to having higher ionic charges
at adjacent metal sites within the magnetic $ab$ layer, i.e., 3+ nearest
neighbors within the ab plane versus 1+ species between the magnetic layers.
According to our results, this should be a rather general feature of 4$f^{13}$
layered compounds: less inter-layer positive charge is associated with stronger
in-plane magnetic response.",1909.01224v1
2019-09-03,Polarization resolved radiation angular patterns of orientationally ordered nanorods,"We employ the transfer matrix approach combined with the Green's function
method to theoretically study polarization resolved far-field angular
distributions of photoluminescence from quantum nanorods (NRs) embedded in an
anisotropic polymer film. The emission and excitation properties of NRs are
described by the emission and excitation anisotropy tensors. These tensors and
the solution of the emission problem expressed in terms of the evolution
operators are used to derive the orientationally averaged coherency matrix of
the emitted wavefield. For the case of in-plane alignment and unpolarized
excitation, we estimate the emission anisotropy parameter and compute the
angular profiles for the photoluminescence polarization parameter such as the
degree of linear polarization, the Stokes parameter $s_1$, the ellipticity and
the polarization azimuth. We show that the alignment order parameter has a
profound effect on the angular profiles.",1909.01407v2
2019-09-04,Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector,"The elliptic flow of muons from the decay of charm and bottom hadrons is
measured in $pp$ collisions at $\sqrt{s}=13$ TeV using a data sample with an
integrated luminosity of 150 pb$^{-1}$ recorded by the ATLAS detector at the
LHC. The muons from heavy-flavor decay are separated from light-hadron decay
muons using momentum imbalance between the tracking and muon spectrometers. The
heavy-flavor decay muons are further separated into those from charm decay and
those from bottom decay using the distance-of-closest-approach to the collision
vertex. The measurement is performed for muons in the transverse momentum range
4-7 GeV and pseudorapidity range $|\eta|<2.4$. A significant non-zero elliptic
anisotropy coefficient $v_{2}$ is observed for muons from charm decays, while
the $v_{2}$ value for muons from bottom decays is consistent with zero within
uncertainties.",1909.01650v2
2019-09-04,Two-axis cavity optomechanical torque characterization of magnetic microstructures,"Significant new functionality is reported for torsion mechanical tools aimed
at full magnetic characterizations of both spin statics and dynamics in micro-
and nanostructures. Specifically, two orthogonal torque directions are
monitored and the results co-analyzed to separate magnetic moment and magnetic
susceptibility contributions to torque, as is desired for characterization of
anisotropic three-dimensional structures. The approach is demonstrated through
application to shape and microstructural disorder-induced magnetic anisotropies
in lithographically patterned permalloy, and will have utility for the
determination of important magnetic thin-film and multilayer properties
including interface anisotropy and exchange bias. The results reflect
remarkable sensitivity of the out-of-plane magnetic torque to the nature of
small edge domains perpendicular to the applied field direction, and also
contain tantalizing indications of direct coupling to spin dynamics at the
frequency of the mechanics.",1909.01949v1
2019-09-05,Large off diagonal exchange couplings and spin liquid states in $\mathbf{C_3}$ symmetric iridates,"Iridate oxides on a honeycomb lattice are considered promising candidates for
realization of quantum spin liquid states. We investigate the magnetic
couplings in a structural model for a honeycomb iridate K$_2$IrO$_3$, with
$C_3$ point group symmetry at the Ir sites, which is an end member of the
recently synthesized iridate family K$_x$Ir$_y$O$_2$. Using \textit{ab-initio}
quantum chemical methods, we elucidate the subtle relationship between the real
space symmetry and magnetic anisotropy and show that the higher point group
symmetry leads to high frustration with strong magnetic anisotropy driven by
the unusually large off-diagonal exchange couplings ($\Gamma$'s) as opposed to
other spin-liquid candidates considered so far. Consequently, large quantum
fluctuations imply lack of magnetic ordering consistent with the experiments.
Exact diagonalization calculations for the fully anisotropic $K$-$J$-$\Gamma$
Hamiltonian reveal the importance of the off-diagonal anisotropic exchange
couplings in stabilizing a spin liquid state and highlight an alternative route
to stabilize spin liquid states for ferromagnetic $K$.",1909.02277v1
2019-09-09,Neural Network Models for the Anisotropic Reynolds Stress Tensor in Turbulent Channel Flow,"Reynolds-averaged Navier-Stokes (RANS) equations are presently one of the
most popular models for simulating turbulence. Performing RANS simulation
requires additional modeling for the anisotropic Reynolds stress tensor, but
traditional Reynolds stress closure models lead to only partially reliable
predictions. Recently, data-driven turbulence models for the Reynolds
anisotropy tensor involving novel machine learning techniques have garnered
considerable attention and have been rapidly developed. Focusing on modeling
the Reynolds stress closure for the specific case of turbulent channel flow,
this paper proposes three modifications to a standard neural network to account
for the no-slip boundary condition of the anisotropy tensor, the Reynolds
number dependence, and spatial non-locality. The modified models are shown to
provide increased predicative accuracy compared to the standard neural network
when they are trained and tested on channel flow at different Reynolds numbers.
The best performance is yielded by the model combining the boundary condition
enforcement and Reynolds number injection. This model also outperforms the
Tensor Basis Neural Network (Ling et al., 2016) on the turbulent channel flow
dataset.",1909.03591v1
2019-09-11,Anomalous low-frequency conductivity in easy-plane XXZ spin chains,"In the easy-plane regime of XXZ spin chains, spin transport is ballistic,
with a Drude weight that has a discontinuous fractal dependence on the value of
the anisotropy $\Delta = \cos \pi \lambda$ at nonzero temperatures. We show
that this structure necessarily implies the divergence of the low-frequency
conductivity for generic irrational values of $\lambda$. Within the framework
of generalized hydrodynamics, we show that in the high-temperature limit the
low-frequency conductivity at a generic anisotropy scales as $\sigma(\omega)
\sim 1/\sqrt{\omega}$; anomalous response occurs because quasiparticles undergo
L\'evy flights. For rational values of $\lambda$, the divergence is cut off at
low frequencies and the corrections to ballistic spin transport are diffusive.
We also use our approach to recover that at the isotropic point $\Delta=1$,
spin transport is superdiffusive with $\sigma(\omega) \sim \omega^{-1/3}$. We
support our results with extensive numerical studies using matrix-product
operator methods.",1909.05263v1
2019-09-13,Tunable perpendicular exchange bias in oxide heterostructures,"The exchange bias effect is an essential component of magnetic memory and
spintronic devices. Whereas recent research has shown that anisotropies
perpendicular to the device plane provide superior stability against thermal
noise, it has proven remarkably difficult to realize perpendicular exchange
bias in thin-film structures. Here we demonstrate a strong perpendicular
exchange bias effect in heterostructures of the quasi-two-dimensional canted
antiferromagnet La$_2$CuO$_4$ and ferromagnetic (La,Sr)MnO$_3$ synthesized by
ozone-assisted molecular beam epitaxy. The magnitude of this effect can be
controlled via the doping level of the cuprate layers. Canted
antiferromagnetism of layered oxides is thus a new and potentially powerful
source of uniaxial anisotropy in magnetic devices.",1909.06152v1
2019-09-18,Anisotropy-induced photonic bound states in the continuum,"Bound states in the continuum (BICs) are radiationless localized states
embedded in the part of the parameter space that otherwise corresponds to
radiative modes. Many decades after their original prediction and early
observations in acoustic systems, such states have been demonstrated recently
in photonic structures with engineered geometries. Here, we put forward a
mechanism, based on waveguiding structures that contain anisotropic
birefringent materials, that affords the existence of BICs with fundamentally
new properties. In particular, anisotropy-induced BICs may exist in symmetric
as well as in asymmetric geometries; they form in tunable angular propagation
directions; their polarization may be pure transverse electric, pure transverse
magnetic or full vector with tunable polarization hybridity; and they may be
the only possible bound states of properly designed structures, and thus appear
as a discrete, isolated bound state embedded in a whole sea of radiative
states.",1909.08328v1
2019-09-19,Rashba-splitting of the Dirac points and the symmetry breaking in the strained artificial graphene,"The effect of Rashba spin-orbit interaction and anisotropic strain on the
electronic, optical and thermodynamic properties of artificial graphene-like
superlattice composed of InAs-GaAs quantum dots has been considered
theoretically. The electronic energy dispersions have been obtained using
Green's function formalism in combination with Fourier transformation to the
reciprocal space and an exact diagonalization technique. We have observed a
splitting of Dirac points and appearance of edditional Dirac-like points due to
the Rashba spin-orbit interaction. Breaking of the hexagonal symmetry of the
dispersion surfaces caused by the strain anisotropy is observed as well. It is
shown that both the spin-orbit interaction and strain anisotropy have a
qualitative impact on the measurable characteristics of the considered
structure and can be used as effective tools to control the performance of
devices based on artificial graphene.",1909.08935v1
2019-09-19,Cosmic Ray Small-Scale Anisotropies in Quasi-Linear Theory,"The distribution of arrival directions of cosmic rays is remarkably
isotropic, which is a consequence of their repeated scattering in magnetic
fields. Yet, high-statistics observatories like IceCube and HAWC have revealed
the presence of small-scale structures at levels of 1 part in 10,000 at
hundreds of TeV, which are not expected in typical diffusion models of cosmic
rays. We follow up on the suggestion that these small-scale anisotropies are a
result of cosmic ray streaming in a particular realisation of the turbulent
magnetic field within a few scattering lengths in our local Galactic
neighbourhood. So far, this hypothesis has been investigated mostly
numerically, by tracking test particles through turbulent magnetic fields. For
the first time, we present an analytical computation that through a
perturbative approach allows predicting the angular power spectrum of cosmic
ray arrival directions for a given model of turbulence. We illustrate this
method for a simple, isotropic turbulence model and we find remarkable
agreement with the results of numerical studies.",1909.09052v2
2019-09-20,Tuning entanglement by squeezing magnons in anisotropic magnets,"We theoretically study the entanglement between two arbitrary spins in a
magnetic material, where magnons naturally form a general squeezed coherent
state, in the presence of an applied magnetic field and axial anisotropies.
Employing concurrence as a measure of entanglement, we demonstrate that spins
are generally entangled in thermodynamic equilibrium, with the amount of
entanglement controlled by the external fields and anisotropies. As a result,
the magnetic medium can serve as a resource to store and process quantum
information. We, furthermore, show that the entanglement can jump
discontinuously when decreasing the applied magnetic field. This tunable
entanglement can be potentially used as an efficient switch in
quantum-information processing tasks.",1909.09653v2
2019-09-22,Angular x-ray cross-correlation analysis (AXCCA): Basic concepts and recent applications to soft matter and nanomaterials,"Angular x-ray cross-correlation analysis (AXCCA) is a technique which allows
quantitative measurement of the angular anisotropy of x-ray diffraction
patterns and provides insights into the orientational order in the system under
investigation. This method is based on the evaluation of the angular
cross-correlation function of the scattered intensity distribution on a
two-dimensional (2D) detector and further averaging over many diffraction
patterns for enhancement of the anisotropic signal. Over the last decade, AXCCA
was successfully used to study the anisotropy in various soft matter systems,
such as solutions of anisometric particles, liquid crystals, colloidal
crystals, superlattices composed by nanoparticles, etc. This review provides an
introduction to the technique and gives a survey of the recent experimental
work in which AXCCA in combination with micro- or nanofocused x-ray microscopy
was used to study the orientational order in various soft matter systems.",1909.09973v1
2019-09-14,The Phase Transition of Square Lattice Antiferromagnets at Finite Temperature,"The magnetic properties of the two-dimensional $J_{1}-J_{2}$ model with both
exchanges $J_{1}$ and $J_{2}$ being antiferromagnetic and a single-ion
anisotropy at nonzero temperature are investigated. As $J_{2}/J_{1}<1/2$
($>1/2$), only the N\'{e}el (collinear) state exists. When $J_{2}/J_{1}=1/2$,
both the N\'{e}el and collinear states can exist and have the same N\'{e}el
temperature. The calculated free energies show that there can occur a phase
transition between the two states below the N\'{e}el point when the single-ion
anisotropy is strong enough. It is a first-order transition at nonzero
temperature. It is possible that the doping in real materials can modify the
ratio of $J_{2}/J_{1}$ to reach $1/2$ so as to implement the phase transition.",1909.11537v1
2019-10-02,"Investigation of structural and elastic properties of monoclinic Ba$_2$P$_7$X (X $=$ Cl, Br, I) Zintl Salts compounds","Structural and elastic properties of Ba$_{2}$P$_{7}$X (X=Cl, Br, I) (Barium
Phosphide Halides) Zintl compounds have been investigated using the
pseudo-potential plane-wave (PP-PW) method based on the density functional
theory (DFT) within the generalized gradient approximation (GGA-PBESOL). The
calculated lattice constants and internal parameters are in a good agreement
with the experimental results reported in literature. In this paper, we present
an investigation of the relative changes of the structural parameters and
elastic constants as function of hydrostatic pressure. Isotropic elastic moduli
and their related properties for single-crystal and polycrystalline phase,
including the namely bulk modulus, shear modulus, Young's modulus, Poisson's
ratio, elastic anisotropy indexes, Pugh's indicator of brittle/ductile
behavior, elastic wave velocities and Debye temperature have been estimated
from $C_{ij}$ using Voigt, Russ and Hill approximations. Two different methods
have been used to study the elastic anisotropy of these compounds.",1910.00915v1
2019-10-08,A generalized Kasner transition for bouncing Bianchi I models in modified gravity theories,"We derive transition rules for Kasner exponents in bouncing Bianchi I models
with generic perfect fluid matter fields for a broad class of modified gravity
theories where cosmological singularities are resolved and replaced by a
non-singular bounce. This is a generalization of results obtained previously in
limiting curvature mimetic gravity and loop quantum cosmology. A geometric
interpretation is provided for the transition rule as a linear map in the
Kasner plane. We show that the general evolution of anisotropies in a Bianchi I
universe -- including during the bounce phase -- is equivalent to the motion of
a point particle on a sphere, where the sphere is the one-point
compactification of the Kasner plane. In addition, we study the evolution of
anisotropies in a large family of bouncing Bianchi I space-times. We also
present a novel explicit solution to the Einstein equations for a Bianchi I
universe with ekpyrotic matter with a constant equation of state $\omega=3$.",1910.03616v2
2019-10-11,The Optical Properties and Plasmonics of Anisotropic 2-Dimensional Materials,"In the fast growing two-dimensional (2D) materials family, anisotropic 2D
materials, with their intrinsic in-plane anisotropy, exhibit a great potential
in optoelectronics. One such typical material is black phosphorus (BP), with a
layer-dependent and highly tunable band gap. Such intrinsic anisotropy adds a
new degree of freedom to the excitation, detection and control of light.
Particularly, hyperbolic plasmons with hyperbolic q-space dispersion are
predicted to exist in BP films, where highly directional propagating polaritons
with divergent densities of states are hosted. Combined with a tunable
electronic structure, such natural hyperbolic surfaces may enable a series of
exotic applications in nanophotonics. In this review, the anisotropic optical
properties and plasmons (especially hyperbolic plasmons) of BP are discussed.
In addition, other possible 2D material candidates (especially anisotropic
layered semimetals) for hyperbolic plasmons are examined. This review may
stimulate further research interest in anisotropic 2D materials and fully
unleash their potential in flatland photonics.",1910.05007v1
2019-10-11,Spin-reversal energy barriers of 305 K for Fe$^{2+}$ $d^{6}$ ions with linear ligand coordination,"A remarkably large magnetic anisotropy energy of 305 K is computed by quantum
chemistry methods for divalent Fe$^{2+}$ $d^6$ substitutes at Li-ion sites with
$D_{6h}$ point-group symmetry within the solid-state matrix of Li$_3$N. This is
similar to values calculated by the same approach and confirmed experimentally
for linearly coordinated monovalent Fe$^{1+}$ $d^7$ species, among the largest
so far in the research area of single-molecule magnets. Our ab initio results
therefore mark a new exciting exploration path in the search for superior
single-molecule magnets, rooted in the $d_{xy}^{1.5} d_{x^2-y^2}^{1.5}
d_{z^2}^1 d_{yz}^1 d_{zx}^1$ configuration of $d^6$ transition-metal ions with
linear or quasilinear nearest-neighbor coordination. This $d^6$ axial
anisotropy may be kept robust even for symmetries lower than $D_{6h}$, provided
the ligand and farther-neighbor environment is engineered such that the
$d_{xy}^{1.5} d_{x^2-y^2}^{1.5} d_{z^2}^1 d_{yz}^1 d_{zx}^1$ - $d_{xy}^{1}
d_{x^2-y^2}^{1} d_{z^2}^2 d_{yz}^1 d_{zx}^1$ splitting remains large enough.",1910.05237v1
2019-10-15,Anisotropy of Cosmic Ray Fluxes Measured with the Alpha Magnetic Spectrometer on the ISS,"A measurement of the dipole anisotropy in galactic coordinates for different
charged cosmic rays has been performed with the Alpha Magnetic Spectrometer
(AMS) onboard the International Space Station (ISS). Results are presented for
the first 7.5 years of data taking for protons, Helium, Carbon and Oxygen, and
6.5 years for positrons and electrons. All the species are found to be
consistent with isotropy and upper limits to the dipole amplitude have been
computed. In particular, for energies above 16 GeV a limit of delta < 1.9% and
delta < 0.5% at the 95% C.I. is found for positrons and electrons respectively.
For rigidities above 200 GV a limit of delta < 0.38%, delta < 0.36%, delta <
1.9% and delta < 1.7% is obtained for protons, Helium, Carbon and Oxygen.",1910.06919v1
2019-10-17,MoB2:a new multifunctional transition metal diboride monolayer,"Several layered transition metal borides can now be realized by a simple and
general fabrication method [Fokwa et al.,Adv. Mater. 2018, 30,
1704181],inspiring our interest to transition metal borides monolayer. Here, we
predict a new two-dimensional (2D) transition metal diboride MoB2 monolayer
(ML) and study its intrinsic mechanical, thermal, electronic, and transport
properties. The MoB2 ML has isotropic mechanic properties along the zigzag and
armchair directions with a large Young's stiffness, and has an ultralow
room-temperature thermal conductivity. The Mo atoms dominate the metallic
nature of MoB2 ML. It shows an obvious electrical anisotropy and a
current-limiting behavior. Our findings suggest that MoB2 ML is a promising
multifunctional material used in ultrathin high-strength mechanical materials,
heat insulating materials, electrical-anisotropy-based materials, and current
limiters. It is helpful for the experimentalists to further prepare and utilize
the transition metal diboride 2D materials.",1910.07661v2
2019-10-17,Controllable splitting dynamics of a doubly quantized vortex in a rotating ring-shaped condensate,"We study the dynamics of a doubly quantized vortex (DQV), created by
releasing a ring-shaped Bose-Einstein condensate with quantized circulation
into harmonic potential traps. It is shown that a DQV can be generated and
exists stably in the middle of the ring-shaped condensate with the initial
circulation $s = 2$ after released into the rotationally symmetric trap
potential. For an asymmetric trap with a small degree of anisotropy the DQV
initially splits into two singly quantized vortices and revives again but
eventually evolves into two unit vortices due to the dynamic instability. For
the degree of anisotropy above a critical value, the DQV is extremely unstably
and decays rapidly into two singlet vortices. The geometry-dependent lifetime
of the DQV and vortex-induced excitations are also discussed intensively.",1910.07749v1
2019-10-18,Anisotropy-driven thermal conductivity switching and thermal hysteresis in a ferroelectric,"We present a theoretical proposal for the design of a thermal switch based on
the anisotropy of the thermal conductivity of PbTiO3 and of the possibility to
rotate the ferroelectric polarization with an external electric field. Our
calculations are based on an iterative solution of the phonon Boltzmann
Transport Equation and rely on interatomic force constants computed within an
efficient second-principles density functional theory scheme. We also
characterize the hysteresis cycle of the thermal conductivity in presence of an
applied electric field and show that the response time would be limited by
speed of the ferroelectric switch itself and thus can operate in the
high-frequency regime.",1910.08584v1
2019-10-21,Prospects of forming high-spin polar molecules from ultracold atoms,"We have investigated Feshbach resonances in collisions of high-spin atoms
such as Er and Dy with closed-shell atoms such as Sr and Yb, using
coupled-channel scattering and bound-state calculations. We consider both
low-anisotropy and high-anisotropy limits. In both regimes we find many
resonances with a wide variety of widths. The wider resonances are suitable for
tuning interatomic interactions, while some of the narrower resonances are
highly suitable for magnetoassociation to form high-spin molecules. These
molecules might be transferred to short-range states, where they would have
large magnetic moments and electric dipole moments that can be induced with
very low electric fields. The results offer the opportunity to study mixed
quantum gases where one species is dipolar and the other is not, and open up
important prospects for a new field of ultracold high-spin polar molecules.",1910.09641v4
2019-10-22,Atomistic picture of fluorescent probes with hydrocarbon tails in lipid bilayer membranes: an investigation of selective affinities and fluorescent anisotropies in different environmental phases,"By reverting to spectroscopy, changes in the biological environment of a
fluorescent probe can be monitored and the presence of various phases of the
surrounding lipid bilayer membranes can be detected. This study highlights the
important differences in orientation and location and therefore in efficiency
between the probes when they are used in fluorescence microscopy to screen
various lipid bilayer membrane phases. Dependent on the lipid composition, the
angle between the transition state dipole moments of both probes and the normal
to the membrane are found to deviate clearly from 90{\deg}. It is seen that the
DiI-C18(5) probe is located in the headgroup region of the SM:Chol mixture, in
close contact with water molecules. A fluorescence anisotropy study indicates
also that DiI-C18(5) gives rise to a distinctive behavior in the SM:Chol
membrane compared to the other considered membranes. The latter behavior has
not been seen for the studied BODIPY probe, which is located deeper in the
membrane.",1910.09827v1
2019-10-24,Electron spin resonance in spiral antiferromagnet linarite: theory and experiment,"We present combined experimental and theoretical investigation of the
low-frequency ESR dynamics in the ordered phases of magnetic mineral linarite.
This material consists of weakly coupled spin-1/2 chains of copper ions with
frustrated ferro- and antiferromagnetic interactions. In zero magnetic field,
linarite orders into a spiral structure and exhibits a peculiar magnetic phase
diagram sensitive to the field orientation. The resonance frequencies and their
field dependence are analyzed combining microscopic and macroscopic theoretical
approaches and precise values of magnetic anisotropy constants are obtained. We
conclude that possible realization of exotic multipolar quantum states in this
material is greatly influenced by the biaxial anisotropy.",1910.11056v1
2019-10-29,Steady one-dimensional domain wall motion in biaxial ferromagnets: mapping of the Landau-Lifshitz equation to the sine-Gordon equation,"Motivated by the difference between the dynamics of magnetization textures in
ferromagnets and antiferromagnets, the Landau-Lifshitz equation of motion is
explored. A typical one-dimensional domain wall in a bulk ferromagnet with
biaxial magnetic anisotropy is considered. In the framework of Walker-type of
solutions of steady-state ferromagnetic domain wall motion, the reduction of
the non-linear Landau-Lifshitz equation to a Lorentz-invariant sine-Gordon
equation typical for antiferromagnets is formally possible for velocities lower
than a critical velocity of the topological soliton. The velocity dependence of
the domain wall energy and the domain wall width are expressed in the
relativistic-like form in the limit of large ratio of the easy-plane/easy-axis
anisotropy constants. It is shown that the mapping of the Landau-Lifshitz
equation of motion to the sine-Gordon equation can be performed only by going
beyond the steady-motion Walker-type of solutions.",1910.13266v2
2019-10-29,Classical nucleation theory predicts the shape of the nucleus in homogeneous solidification,"Macroscopic models of nucleation provide powerful tools for understanding
activated phase transition processes. These models do not provide atomistic
insights and can thus sometime lack material-specific descriptions. Here we
provide a comprehensive framework for constructing a continuum picture from an
atomistic simulation of homogeneous nucleation. We use this framework to
determine the shape of the equilibrium solid nucleus that forms inside bulk
liquid for a Lennard-Jones potential. From this shape, we then extract the
anisotropy of the solid-liquid interfacial free energy, by performing a reverse
Wulff construction in the space of spherical harmonic expansions. We find that
the shape of the nucleus is nearly spherical and that its anisotropy can be
perfectly described using classical models.",1910.13481v2
2019-10-31,Quantum critical nematic fluctuations and spin excitation anisotropy in iron pnictides,"Quantum criticality in iron pnictides involves both the nematic and
antiferromagnetic degrees of freedom, but the relationship between the two
types of fluctuations has yet to be clarified. Here we study this problem in
the presence of a small external uniaxial potential, which breaks the
$C_4$-symmetry in the B$_{1g}$ sector. We establish an identity that connects
the spin excitation anisotropy, which is the difference of the dynamical spin
susceptibilities at $\vec{Q}_1=\left(\pi,0\right)$ and
$\vec{Q}_2=\left(0,\pi\right)$, with the dynamical magnetic susceptibility and
static nematic susceptibility. Using this identity, we introduce a scaling
procedure to determine the dynamical nematic susceptibility in the quantum
critical regime, and illustrate the procedure for the case of the optimally
Ni-doped BaFe$_2$As$_2$[Y. Song \textit{et al.}, Phys. Rev. B 92, 180504
(2015)]. The implications of our results for the overall physics of the
iron-based superconductors are discussed.",1910.14597v4
2019-11-04,Physics Beyond The Standard Model with Circular Polarization in the CMB and CMB-21cm Cross-Correlation,"Circular polarization is a relatively unexplored realm of CMB physics. Given
the substantial community effort towards building next generation CMB
polarization experiments, including those which will be sensitive to circular
polarization, it behooves theorists to understand the possible sources and
relevant physics of circular polarization, as encoded in the Stokes V
parameter. In this work we develop and derive the requisite formalism, namely
the Boltzmann hierarchy for V-mode scalar, vector, and tensor, anisotropies. We
derive the V-mode anisotropies induced by a general source term, and
demonstrate how existing proposals for the generation of V can be incorporated
as source terms in the Boltzmann hierarchy. A subset of these effects may be
correlated with 21cm intensity; we provide a worked example and derive an
estimator to extract this information from observations. We conclude by
computing the CMB TV cross-correlation generated by axions, and find a relation
between TV and VV spectra in axion models.",1911.01418v2
2019-11-11,Gap Anisotropy in Multiband Superconductors Based on Multiple Scattering Theory,"We implement the Bogoliubov-de Gennes (BdG) equation in a screened
Korringa-Kohn-Rostoker (KKR) method for solving, self-consistently, the
superconducting state for 3d crystals. This method combines the full complexity
of the underlying electronic structure and Fermi surface geometry with a simple
phenomenological parametrisation for the superconductivity. We apply this
theoretical framework to the known s-wave superconductors Nb, Pb, and MgB$_2$.
In these materials multiple distinct peaks at the gap in the density of states
were observed, showing significant gap anisotropy which is in good agreement
with experiment. Qualitatively, the results can be explained in terms of the
k-dependent Fermi velocities on the Fermi surface sheets exploiting concepts
from BCS theory.",1911.04163v1
2019-11-25,Fe$_{5-x}$Ge$_2$Te$_2$ -- A new exfoliable itinerant ferromagnet with high Curie temperature and large perpendicular magnetic anisotropy,"Layered van der Waals (vdW) crystals with intrinsic magnetic properties such
as high Curie temperature (TC) and large perpendicular magnetic anisotropy
(PMA) are key to the development and application of spintronic devices. The
ferromagnetic vdW metal Fe3-xGeTe2 (FGT) has gained prominence recently due to
its high TC (220 K) and strong PMA. Here, we introduce a new metallic vdW
ferromagnets, Fe5-xGe2Te2 or FG2T, which was successfully synthesized and fully
characterized. FG2T is a metal that orders ferromagnetically with a very sharp
transition at 250 K (bulk and single crystal thin flakes) and shows large PMA,
as found by both experimental and computational studies. This work enables
novel heterostructure devices with near room temperature capabilities by using
FG2T as spin injector.",1911.11259v1
2019-11-26,One-directional thermal transport in densely aligned single-wall carbon nanotube films,"Individual carbon nanotubes (CNTs) possess extremely high thermal
conductivities. However, the thermal conductivities and their anisotropy of
macroscopic assemblies of CNTs have so far remained small. Here, we report
results of directional thermal transport measurements on a nearly-perfectly
aligned CNT film fabricated via controlled vacuum filtration. We found the
thermal conductivity to be 43 +- 2.2 W m^-1 K^-1 with a record-high thermal
anisotropy of 500. From the temperature dependence of the thermal conductivity
and its agreement with the atomistic phonon transport calculation, we conclude
that the effect of intertube thermal resistance on heat conduction in the
alignment direction is negligible because of the large contact area between
CNTs. These observations thus represent ideal unidirectional thermal transport,
i.e., the thermal conductivity of the film is determined solely by that of
individual CNTs.",1911.11340v1
2019-11-27,Magnetic exchange interactions in monolayer CrI$_3$ from many-body wavefunction calculations,"The marked interplay between the crystalline, electronic, and magnetic
structure of atomically thin magnets has been regarded as the key feature for
designing next-generation magneto-optoelectronic devices. In this respect, a
detailed understanding of the microscopic interactions underlying the magnetic
responses of these crystals is of primary importance. Here, we combine model
Hamiltonians with multi-reference configuration interaction wavefunctions to
accurately determine the strength of the spin couplings in the prototypical
single-layer magnet CrI$_3$. Our calculations identify the (ferromagnetic)
Heisenberg exchange interaction $J = -1.44$ meV as the dominant term, being the
inter-site magnetic anisotropies substantially {weaker}. We also find that
single-layer CrI$_3$ features an out-of-plane easy axis ensuing from a
single-ion anisotropy $A = -0.10$ meV, and predict $g$-tensor in-plane
components $g_{xx} = g_{yy} = 1.90$ and out-of-plane component $g_{zz} = 1.92$.
In addition, we assess the performance of a dozen widely used density
functionals against our accurate correlated wavefunctions {calculations} and
available experimental data, thereby establishing reference results for future
first-principles investigations. Overall, our findings offer a firm theoretical
ground to experimental observations.",1911.12150v1
2019-12-02,On the interaction constant measurement of polarized fermions via sound wave spectra obtained from hydrodynamics with the pressure evolution equation,"Usually, hydrodynamic equations are restricted by the continuity and Euler
equations. However, the account of the higher moments of the distribution
function gives better description of the kinetic properties. Therefore, the
pressure tensor evolution equation (PTEE) is derived for spin polarized
degenerate fermions. Moreover, it is found that the pressure tensor enters the
interaction term generalizing the p-wave interaction in the Euler equation.
Hence, the PTEE allows to give a more accurate description of the interaction
in Euler equation. Next, the interaction is calculated for the PTEE. The
developed model is applied to the small amplitude bulk collective excitations
in homogeneous and trapped fermions in order to suggest the methods of
experimental measurement of the interaction constant of polarized fermions. It
is demonstrated that the anisotropy in the momentum space revealing in the
difference of the pressures in the anisotropy direction and the perpendicular
directions leads to a method of detection of the interaction constant.",1912.00843v1
2019-12-09,Anisotropies of galaxy ellipticity correlations in real and redshift space: angular dependence in linear tidal alignment model,"Investigating intrinsic alignments (IAs) of galaxy shapes is important not
only to constrain cosmological parameters unbiasedly from gravitational lensing
but also to extract cosmological information complimentary to galaxy clustering
analysis. We derive simple and useful formulas for the various IA statistics,
including the intrinsic ellipticity--ellipticity correlation, the gravitational
shear--intrinsic ellipticity correlation, and the velocity-intrinsic
ellipticity correlation functions. The angular dependence of each statistic is
explicitly given, namely the angle between the line-of-sight direction and the
separation vector of two points. It thus allows us to analyze anisotropies of
baryon acoustic oscillations encoded in the IA statistics, and we can extract
the maximum cosmological information using the Alcock-Pacyznski and
redshift-space distortion effects. We also provide these formulas for the
intrinsic ellipticities decomposed into E and B modes.",1912.04118v2
2019-12-16,"Discreteness effects, $N-$body chaos and the onset of radial-orbit instability","We study the stability of a family of spherical equilibrium models of
self-gravitating systems, the so-called $\gamma-$models with Osipkov-Merritt
velocity anisotropy, by means of $N-$body simulations. In particular, we
analyze the effect of self-consistent $N-$body chaos on the onset of
radial-orbit instability (ROI). We find that degree of chaoticity of the system
associated to its largest Lyapunov exponent $\Lambda_{\rm max}$ has no
appreciable relation with the stability of the model for fixed density profile
and different values of radial velocity anisotropy. However, by studying the
distribution of the Lyapunov exponents $\lambda_{\rm m}$ of the individual
particles in the single-particle phase space, we find that more anisotropic
systems have a larger fraction of orbits with larger $\lambda_{\rm m}$.",1912.07406v2
2019-12-19,Tuning Ginzburg-Landau theory to quantitatively study thin ferromagnetic materials,"Along with experiments, numerical simulations are key to gaining insight into
the underlying mechanisms governing domain wall motion in thin ferromagnetic
systems. However, a direct comparison between numerical simulation of model
systems and experimental results still represents a great challenge. Here, we
present a tuned Ginzburg-Landau model to quantitatively study the dynamics of
domain walls in quasi two-dimensional ferromagnetic systems with perpendicular
magnetic anisotropy. This model incorporates material and experimental
parameters and the micromagnetic prescription for thermal fluctuations,
allowing us to perform material-specific simulations and at the same time
recover universal features. We show that our model quantitatively reproduces
previous experimental velocity-field data in the archetypal perpendicular
magnetic anisotropy Pt/Co/Pt ultra-thin films in the three dynamical regimes of
domain wall motion (creep, depinning and flow). In addition, we present a
statistical analysis of the domain wall width parameter, showing that our model
can provide detailed nano-scale information while retaining the complex
behavior of a statistical disordered model.",1912.09392v2
2020-01-01,Pseudo-spin rotation symmetry breaking by Coulomb interaction terms in spin-orbit coupled systems,"By transforming from the pure-spin-orbital ($t_{\rm 2g}$) basis to the
spin-orbital entangled pseudo-spin-orbital basis, the pseudo-spin rotation
symmetry of the different Coulomb interaction terms is investigated under SU(2)
transformation in pseudo-spin space. While the Hubbard and density interaction
terms are invariant, the Hund's coupling and pair-hopping interaction terms
explicitly break pseudo-spin rotation symmetry systematically. The form of the
symmetry-breaking terms obtained from the transformation of the Coulomb
interaction terms accounts for the easy $x$-$y$ plane anisotropy and magnon gap
for the out-of-plane mode, highlighting the importance of mixing with the
nominally non-magnetic $J$=3/2 sector, and providing a physically transparent
approach for investigating magnetic ordering and anisotropy effects in
perovskite ($\rm Sr_2 Ir O_4$) and other $d^5$ pseudo-spin compounds.",2001.00190v2
2020-01-02,Emergence of Superconductivity in Doped Multiorbital Hubbard Chains,"We introduce a variational state for one-dimensional two-orbital Hubbard
models that intuitively explains the recent computational discovery of pairing
in these systems when hole doped. Our Ansatz is an optimized linear
superposition of Affleck-Kennedy-Lieb-Tasaki valence bond states, rendering the
combination a valence bond liquid dubbed Orbital Resonant Valence Bond. We show
that the undoped (one electron/orbital) quantum state of two sites coupled into
a global spin singlet is exactly written employing only spin-1/2 singlets
linking orbitals at nearest-neighbor sites. Generalizing to longer chains
defines our variational state visualized geometrically expressing our chain as
a two-leg ladder, with one orbital per leg. As in Anderson's resonating
valence-bond state, our undoped variational state contains preformed singlet
pairs that via doping become mobile leading to superconductivity. Doped real
materials with one-dimensional substructures, two near-degenerate orbitals, and
intermediate Hubbard U/W strengths -- W the carrier's bandwidth -- could
realize spin-singlet pairing if on-site anisotropies are small. If these
anisotropies are robust, spin-triplet pairing emerges.",2001.00589v2
2019-11-23,A limit on the anisotropy of the one-way maximum attainable speed of the electron,"We report here the first experimental result for the anisotropy of the
one-way maximum attainable speed of the electron, $\vec{\Delta c_{1,e}}$,
obtained via the study of a sidereal time dependence of a difference between
the electron and positron beam momenta in the CESR storage ring at Cornell
University. At 95 percent confidence, an upper limit for the component of
$\Delta \vec {c}_{1,e}/c$ perpendicular to Earth's rotational axis is found to
be $5.5 \times 10^{-15}$.",2001.00999v3
2020-01-04,Strain-mediated Symmetry Breaking Switch with Perpendicular Magnetic Anisotropy,"Magnetic switch with perpendicular magnetic anisotropy (PMA) is a promising
method for controlling magnetization in several applications like magnetic
tunnel junction and magnetic memory. However, incoherence happens during the
switch process and lower the switch frequency of the magnetic bits. Symmetry
broking can help solve this problem. Here, we present a field-free method for
the symmetry broking and then increase the switch speed of the magnetization. A
strain-mediated method with geometric asymmetry is presented here. In this
work, we build a finite element model that consists a 50 nanometer diameter
nanodisk with a varied thickness on the top of a 50 nanometer thick PZT
(Pby[ZrxTi1-x]O3) thin film. The results show a 66% faster switch than symmetry
PMA switching (0.85 nanosecond to 0.29 nanosecond) under same energy
consumption. Finally, we explore the mechanism of the symmetry broking of
varying thickness nanodot with calculating the energy profile.",2001.01018v2
2019-12-19,Heavy Ion Acceleration by Super-Alfvenic Waves,"A generation mechanism of super Alfv\'{e}nic (SPA) waves in multi-ion species
plasma is proposed and the associated heavy ion acceleration process is
discussed. The SPA waves are thought to play important roles in particle
acceleration since they have large wave electric field because of their high
phase velocity. It is demonstrated by using full particle-in-cell simulation
that large amplitude proton cyclotron waves, excited due to proton temperature
anisotropy, nonlinearly destabilize SPA waves through parametric decay
instability in a three component plasma composed of electrons, protons, and
$\alpha$ particles. At the same time, $\alpha$ cyclotron waves get excited via
another decay instability. A pre-accelerated $\alpha$ particle resonates
simultaneously with the two daughter waves, the SPA waves and the $\alpha$
cyclotron waves, and it is further accelerated perpendicular to the ambient
magnetic field. The process may work in astrophysical environments where
sufficiently large temperature anisotropy of lower mass ions occurs.",2001.02538v1
2020-01-08,Statistics of relative velocity for particles settling under gravity in a turbulent flow,"We study the joint probability distributions of separation, $R$, and radial
component of the relative velocity, $V_{\rm R}$, of particles settling under
gravity in a turbulent flow. We also obtain the moments of these distributions
and analyze their anisotropy using spherical harmonics. We find that the
qualitative nature of the joint distributions remains the same as no gravity
case. Distributions of $V_{\rm R}$ for fixed values of $R$ show a power-law
dependence on $V_{\rm R}$ for a range of $V_{\rm R}$, exponent of the power-law
depends on the gravity. Effects of gravity are also manifested in the following
ways: (a) moments of the distributions are anisotropic; the degree of
anisotropy depends on particle's Stokes number, but does not depend on $R$ for
small values of $R$. (b) mean velocity of collision between two particles is
decreased for particles having equal Stokes numbers but increased for particles
having different Stokes numbers. For the later, collision velocity is set by
the difference in their settling velocities.",2001.02724v1
2020-01-10,Partial quantum revivals of localized condensates in distorted lattices,"We report on a peculiar propagation of bosons loaded by a short
Laguerre-Gaussian pulse in a nearly flat band of a lattice potential. Taking a
system of exciton-polaritons in a kagome lattice as an example, we show that an
initially localized condensate propagates in a specific direction in space if
anisotropy is taken into account. This propagation consists of quantum jumps,
collapses, and revivals of the whole compact states, and it persists given any
direction of anisotropy. This property reveals its signatures in the
tight-binding model and, surprisingly, it is much more pronounced in a
continuous model. Quantum revivals are robust to the repulsive interaction and
finite lifetime of the particles. Since no magnetic field or spin-orbit
interaction is required, this system provides a new kind of easily
implementable optical logic.",2001.03317v1
2020-01-12,Imaging of Strain Driven Magnetic Domains and Strong Spin-Phonon Coupling in Epitaxial Thin Films of SrRuO3,"Epitaxial thin films of SrRuO3 with large strain disorder were grown using
pulsed laser deposition method which showed two distinct transition
temperatures in Magnetic measurements. For the first time, we present visual
evolution of magnetic domains across the two transitions using Magnetic force
microscopy on these films. The study clearly showed that the magnetic
anisotropy corresponding to the two transitions is different. It is observed
that the perpendicular magnetic anisotropy is dominating in films which results
in domain spin orientation preferably in out of plane direction. The Raman
studies showed that the lattice is highly influenced by the magnetic order. The
analysis of the phonon spectra around magnetic transition reveals the existence
of strong spin-phonon coupling and the calculations resulted in spin-phonon
coupling strength ({\lambda}) values of {\lambda} ~ 5 cm-1 and {\lambda} ~ 8.5
cm-1, for SrRuO3 films grown on LSAT and SrTiO3 single crystal substrates,
respectively.",2001.03901v1
2020-01-15,Anisotropic behavior of TiB2 nanoparticles reinforced 2024Al composites rolling sheet,"The in-plane anisotropy (IPA) of mechanical properties existed in plate
products is often undesired since it limits the industrial application and
increases the difficulty of material processing. It is thus one of the
important factors which requires strict control during the manufacture of
high-performance aluminum alloy plates. The anisotropic behavior of TiB2/2024Al
composite rolling sheet under different heat treatment is studied in this
article. T4 heat treated specimen shows good isotropy of yield strength and its
texture components are significantly weakened compared with traditional Al
alloys. The evolution of microstructures for T4 specimen was studied. The
submicron TiB2 particles increase the driving force of recrystallization during
rolling process and static recrystallization (SRX) is stimulated, thus induces
texture randomization. Anisotropic behavior of yield strength occurs in
specimen after T3 heat treatment. It is supposed that the difference in the
activation of slip system under different loading direction gives rise to this
anisotropy.",2001.05144v1
2020-01-16,On the linear stability of anisotropic pressure equilibria with field-aligned incompressible flow,"We derive a sufficient condition for the linear stability of plasma
equilibria with incompressible flow parallel to the magnetic field, $\bf B$,
constant mass density and anisotropic pressure such that the quantity
$\sigma_d= \mu_0(P_\parallel -P_\perp)/B^2$, where $P_\parallel$ ($P_\perp$) is
the pressure tensor element parallel (perpendicular) to $\bf B$, remains
constant. This condition is applicable to any steady state without geometrical
restriction. The condition, generalising the respective condition for MHD
equilibria with isotropic pressure and constant density derived in
Throumoulopoulos & Tasso (2007), involves physically interpretable terms
related to the magnetic shear, the flow shear and the variation of total
pressure perpendicular to the magnetic surfaces. On the basis of this condition
we prove that if a given equilibrium is linearly stable, then the ones
resulting from the application of Bogoyavlenskij symmetry transformations are
linearly stable too, provided that a parameter involved in those
transformations is positive. In addition, we examine the impact of pressure
anisotropy, flow, and torsion of a helical magnetic axis, for a specific class
of analytic equilibria. In this case we find that the pressure anisotropy and
the flow may have either stabilising or destabilising effects. Also, helical
configurations with small torsion and large pitch seem to have more favorable
stability properties.",2001.05750v1
2020-01-19,Gauge Corrections to Strong Coupling Lattice QCD on Anisotropic Lattices,"Lattice QCD with staggered fermions can be formulated in dual variables to
address the finite baryon density sign problem. In the past we have performed
simulations in the strong coupling regime, including leading order gauge
corrections. In order to vary the temperature for fixed $\beta$ it was
necessary to introduce a bare anisotropy. In this talk we will extend our work
to include results from a non-perturbative determination of the physical
anisotropy $a_\sigma$/$a_\tau = \xi(\gamma, \beta)$, which is necessary to
unambiguously locate the critical end point and the first order line of the
chiral transition.",2001.06797v1
2020-01-22,Effect of the interaction strength and anisotropy on the diffusio-phoresis of spherical colloids,"Gradients in temperature, concentration or electrostatic potential cannot
exert forces on a bulk fluid; they can, however, exert forces on a fluid in a
microscopic boundary layer surrounding a (nano)colloidal solute, resulting in
so-called phoretic flow. Here we present a simulation study of phoretic flow
around a spherical colloid held fixed in a concentration gradient. We show that
the resulting flow velocity depends non-monotonically on the strength of the
colloid-fluid interaction. The reason for this non-monotonic dependence is that
solute particles are effectively trapped in a shell around the colloid and
cannot contribute to diffusio-phoresis. We also observe that the flow depends
sensitively on the anisotropy of solute-colloid interaction.",2001.07959v1
2020-01-22,Holographic spontaneous anisotropy,"We construct a family of holographic duals to anisotropic states in a
strongly coupled gauge theory. On the field theory side the anisotropy is
generated by giving a vacuum expectation value to a dimension three operator.
We obtain our gravity duals by considering the geometry corresponding to the
intersection of D3- and D5- branes along 2+1 dimensions. Our backgrounds are
supersymmetric and solve the fully backreacted equations of motion of
ten-dimensional supergravity with smeared D5-brane sources. In all cases the
geometry flows to $AdS_{5}\times {\mathbb S}^5$ in the UV, signaling an
isotropic UV fixed point of the dual field theory. In the IR, depending on the
parameters of the solution, we find two possible behaviors: an isotropic fixed
point or a geometry with anisotropic Lifshitz-like scaling symmetry. We study
several properties of the solutions, including the entanglement entropy of
strips. We show that any natural extension of existing $c$-functions will
display non-monotonic behavior, conforming with the presence of new degrees of
freedom only at intermediate energy scales.",2001.08218v2
2020-01-22,On two phases inside the Bose condensation dome of Yb$_2$Si$_2$O$_7$,"Recent experimental data on Bose-Einstein Condensation (BEC) of magnons in
the spin-gap compound Yb$_2$Si$_2$O$_7$ revealed an asymmetric BEC dome
arXiv:1810.13096v2. We examine modifications to the Heisenberg model on a
breathing honeycomb lattice, showing that this physics can be explained by
competing forms of weak anisotropy. We employ a gamut of analytical and
numerical techniques to show that the anisotropy yields a field driven phase
transition from a state with broken Ising symmetry to a phase which breaks no
symmetries and crosses over to the polarized limit.",2001.08219v2
2020-01-23,Inelastic neutron scattering study of the anisotropic $S = 1$ spin chain [Ni(HF$_2$)(3-Clpyridine)$_4$]BF$_4$,"[Ni(HF$_2$)(3-Clpyridine)$_4$]BF$_4$ (NBCT) is a one-dimensional, $S = 1$
spin chain material that shows no magnetic neutron Bragg peaks down
temperatures of 0.1 K. Previous work identified NBCT to be in the Haldane phase
and near a quantum phase transition as a function of $D/J$ to the large-$D$
quantum paramagnet phase (QPM), where $D$ is the axial single-ion anisotropy
and $J$ is the intrachain superexchange. Herein, inelastic neutron scattering
results are presented on partially deuterated, $^{11}$B enriched NBCT
polycrystalline samples in zero magnetic field and down to temperatures of 0.3
K. Comparison to density matrix renormalization group calculations yields $D/J
= 1.51$ and a significant rhombic single-ion anisotropy $E$ ($E/D \approx
0.03$, $E/J \approx 0.05$). These $D$, $J$, and $E$ values place NBCT in the
large-$D$ QPM phase but precipitously near a quantum phase transition to a
long-range ordered phase.",2001.08555v1
2020-01-22,Regularity condition on the anisotropy induced by gravitational decoupling in the framework of MGD,"We use gravitational decoupling to establish a connection between the minimal
geometric deformation approach and the standard method for obtaining
anisotropic fluid solutions. Motivated by the relations that appear in the
framework of minimal geometric deformation, we give an anisotropy factor that
allows us to solve the quasi--Einstein equations associated to the decoupler
sector. We illustrate this by building an anisotropic extension of the well
known Tolman IV solution, providing in this way an exact and physically
acceptable solution that represents the behavior of compact objects. We show
that, in this way, it is not necessary to use the usual mimic constraint
conditions. Our solution is free from physical and geometrical singularities,
as expected. We have presented the main physical characteristics of our
solution both analytically and graphically and verified the viability of the
solution obtained by studying the usual criteria of physical acceptability.",2001.08573v2
2020-02-01,Estimation of Z-Thickness and XY-Anisotropy of Electron Microscopy Images using Gaussian Processes,"Serial section electron microscopy (ssEM) is a widely used technique for
obtaining volumetric information of biological tissues at nanometer scale.
However, accurate 3D reconstructions of identified cellular structures and
volumetric quantifications require precise estimates of section thickness and
anisotropy (or stretching) along the XY imaging plane. In fact, many image
processing algorithms simply assume isotropy within the imaging plane. To
ameliorate this problem, we present a method for estimating thickness and
stretching of electron microscopy sections using non-parametric Bayesian
regression of image statistics. We verify our thickness and stretching
estimates using direct measurements obtained by atomic force microscopy (AFM)
and show that our method has a lower estimation error compared to a recent
indirect thickness estimation method as well as a relative Z coordinate
estimation method. Furthermore, we have made the first dataset of ssSEM images
with directly measured section thickness values publicly available for the
evaluation of indirect thickness estimation methods.",2002.00228v2
2020-02-03,CMB and BBN constraints on evaporating primordial black holes revisited,"We derive new CMB anisotropy power spectrum and BBN constraints for
evaporating primordial black holes by explicitly solving the electromagnetic
particle cascades of emitted particles and the deposition of this emitted
energy to the background baryon-photon plasma. We show that the CMB
anisotropies can provide stronger constraints compared to BBN and CMB spectral
distortions on black holes with masses as small as $M_{\rm BH}=1.1\times
10^{13}$g, a slightly smaller mass than what has been considered in literature
until now. We also show that, with more up-to-date data on abundances of
deuterium and helium-3, BBN constraints are strengthened significantly.",2002.00898v2
2020-02-04,Localization anisotropy and complex geometry in two-dimensional insulators,"The localization tensor is a measure of distinguishability between insulators
and metals. This tensor is related to the quantum metric tensor associated with
the occupied bands in momentum space. In two dimensions and in the
thermodynamic limit, it defines a flat Riemannian metric over the twist-angle
space, topologically a torus, which endows this space with a complex structure,
described by a complex parameter $\tau$. It is shown that the latter is a
physical observable related to the anisotropy of the system. The quantity
$\tau$ and the Riemannian volume of the twist-angle space provide an invariant
way to parametrize the flat quantum metric obtained in the thermodynamic limit.
Moreover, if by changing the couplings of the theory, the system undergoes
quantum phase transitions in which the gap closes, the complex structure $\tau$
is still well defined, although the metric diverges (metallic state), and it is
fixed by the form of the Hamiltonian near the gap closing points. The
Riemannian volume is responsible for the divergence of the metric at the phase
transition.",2002.01312v2
2020-02-07,Model of damping and anisotropy at elevated temperatures: application to granular FePt films,"Understanding the damping mechanism in finite size systems and its dependence
on temperature is a critical step in the development of magnetic
nanotechnologies. In this work, nano-sized materials are modeled via atomistic
spin dynamics, the damping parameter being extracted from Ferromagnetic
Resonance (FMR) simulations applied for FePt systems, generally used for
heat-assisted magnetic recording media (HAMR). We find that the damping
increases rapidly close to Tc and the effect is enhanced with decreasing system
size, which is ascribed to scattering at the grain boundaries. Additionally,
FMR methods provide the temperature dependence of both damping and the
anisotropy, important for the development of HAMR. Semi-analytical calculations
show that, in the presence of a grain size distribution, the FMR linewidth can
decrease close to the Curie temperature due to a loss of inhomogeneous line
broadening. Although FePt has been used in this study, the results presented in
the current work are general and valid for any ferromagnetic material.",2002.02865v1
2020-02-07,Detecting the anisotropic astrophysical gravitational wave background in the presence of shot noise through cross-correlations,"The spatial and temporal discreteness of gravitational wave sources leads to
shot noise that may, in some regimes, swamp any attempts at measuring the
anisotropy of the gravitational wave background. Cross-correlating a
gravitational wave background map with a sufficiently dense galaxy survey can
alleviate this issue, and potentially recover some of the underlying properties
of the gravitational wave background. We quantify the shot noise level and we
explicitly show that cross-correlating the gravitational wave background and a
galaxy catalog improves the chances of a first detection of the background
anisotropy with a gravitational wave observatory operating in the frequency
range (10Hz,100Hz), given sufficient sensitivity.",2002.02888v1
2020-02-09,Probing Dark Matter with Future CMB Measurements,"Dark Matter (DM) annihilation and decay during the Dark Ages can affect the
cosmic ionization history and leave imprints in the Cosmic Microwave Background
(CMB) anisotropy spectra. CMB polarization anisotropy can be sensitive to such
energy injection at higher redshifts and help reducing degeneracy with
primordial spectral parameters in $\Lambda$CDM and astrophysical ionization
processes during reionization. In light of a number of upcoming CMB
polarization experiments, such as AdvACTPol, AliCPT, CLASS, Simons Observatory,
Simons Array, SPT-3G, we estimate their prospective sensitivity in probing dark
matter annihilation and decay signals. We find that future missions have 95\%
C.L. projected limits on DM decay and annihilation rates to orders of
$\Gamma_\chi (\tau_{\chi}^{-1}) \sim 10^{-27}{\rm{s}}^{-1}$ and $\left<\sigma v
\right>/m_{\chi} \sim 10^{-29}{\rm{cm^3s^{-1}GeV^{-1}}}$ respectively,
significantly improving the sensitivity to DM from current experimental bounds.",2002.03380v2
2020-02-11,Data Driven Finite Element Method: Theory and Applications,"A data driven finite element method (DDFEM) that accounts for more than two
material state variables has been presented in this work. DDFEM framework is
motivated from (1,2) and can account for multiple state variables, viz.
stresses, strains, strain rates, failure stress, material degradation, and
anisotropy which has not been used before. DDFEM is implemented in the context
of linear elements of a nonlinear elastic solid. The presented framework can be
used for variety of applications by directly using experimental data. This has
been demonstrated by using the DDFEM framework to predict deformation,
degradation and failure in diverse applications including nanomaterials and
biomaterials for the first time. DDFEM capability of predicting unknown and
unstructured dataset has also been shown by using Delaunay triangulation
strategy for scattered data having no structure or order. The framework is able
to capture the strain rate dependent deformation, material anisotropy, material
degradation, and failure which has not been presented in the past. The
predicted results show a very good agreement between data set taken from
literature and DDFEM predictions without requiring to formulate complex
constitutive models and avoiding tedious material parameter identification.",2002.04446v2
2020-02-20,Constraining dark photons and their connection to 21 cm cosmology with CMB data,"In the inhomogeneous Universe, the cosmological conversion of dark photons
into ordinary photons (and vice versa) may happen at a great number of
resonance redshifts. This alters the CMB observed energy spectrum and degree of
small-scale anisotropies. We utilize results from the EAGLE simulation to
obtain the conversion probability along random line-of-sights to quantify these
effects. We then apply our results to the case where dark photons are sourced
by dark matter decay and their high-redshift conversion into ordinary photons
modify the global 21 cm signal expected from the cosmic dawn era. Concretely,
we show that a significant portion of the parameter space for which a converted
population of photons in the Rayleigh-Jeans tail of the CMB explains the
absorption strength observed by EDGES, is ruled out from the brightness
temperature measurements of COBE/FIRAS and the CMB anisotropy measurements of
Planck and SPT.",2002.08942v2
2020-02-21,Determination of spin-orbit torque efficiencies in heterostructures with in-plane magnetic anisotropy,"It has been shown that the spin Hall effect from heavy transition metals can
generate sufficient spin-orbit torque and further produce current-induced
magnetization switching in the adjacent ferromagnetic layer. However, if the
ferromagnetic layer has in-plane magnetic anisotropy, probing such switching
phenomenon typically relies on tunneling magnetoresistance measurement of
nano-sized magnetic tunnel junctions, differential planar Hall voltage
measurement, or Kerr imaging approaches. We show that in magnetic
heterostructures with spin Hall metals, there exist current-induced in-plane
spin Hall effective fields and unidirectional magnetoresistance that will
modify their anisotropic magnetoresistance behavior. We also demonstrate that
by analyzing the response of anisotropic magnetoresistance under such
influences, one can directly and electrically probe magnetization switching
driven by the spin-orbit torque, even in micron-sized devices. This pump-probe
method allows for efficient and direct determination of key parameters from
spin-orbit torque switching events without lengthy device fabrication
processes.",2002.09104v1
2020-02-22,Molecular static simulation of edge dislocation core in bcc iron,"We simulate the dislocation core structure in bcc iron using the modified
Molecular Static method. A feature of this method is the application of an
iterative procedure in which the atomic structure in the vicinity of the defect
and the constants that determine the displacements of atoms immersed in the
elastic continuum are calculated in a self-consistent manner. Following the
mentioned approach, we develop a model for calculating the atomic structure of
edge dislocations, taking into account the anisotropy of the elastic medium
surrounding the main calculation cell. Anisotropy is taken into account by
introducing an explicit angular dependence for the parameters of the elastic
field created by the dislocation: magnitude of Burgers vector and Poisson's
ratio. Simulation is carried out for a split dislocation with Burgers vector
along [100]. The convergence of the iterative algorithm is shown and the
influence of the computational cell size on the results is considered.
Calculated results are: atomic structure of dislocation in bcc iron, angular
dependence of the parameters describing the elastic dislocation field at large
distances from the dislocation line, and the strain tensor components in the
entire simulation area.",2002.09601v2
2020-02-27,Anisotropic Nonequilibrium Lattice Dynamics of Black Phosphorus,"Black phosphorus has recently attracted significant attention for its highly
anisotropic properties. A variety of ultrafast optical spectroscopies has been
applied to probe the carrier response to photoexcitation, but the complementary
lattice response has remained unaddressed. Here we employ femtosecond electron
diffraction to explore how the structural anisotropy impacts the lattice
dynamics after photoexcitation. We observe two timescales in the lattice
response, which we attribute to electron-phonon and phonon-phonon
thermalization. Pronounced differences between armchair and zigzag directions
are observed, indicating a nonthermal state of the lattice lasting up to ~60
ps. This nonthermal state is characterized by a modified anisotropy of the
atomic vibrations compared to equilibrium. Our findings provide insights in
both electron-phonon as well as phonon-phonon coupling and bear direct
relevance for any application of black phosphorus in nonequilibrium conditions.",2002.12038v3
2020-03-04,Role of Anisotropy in Nonlinear Harmonic Generation Across TMD Monolayers,"Recent techniques have allowed transition metal dichalcogenides (TMD)
monolayers to be grown and adequately characterised. Of particular interest,
their nonlinear optical response presents many promising opportunities for
future nanophotonic devices and technology. The dispersion of the carriers is
trigonally-warped, leading to an anisotropic Fermi surface for low-lying
states. In this paper, the effects of such a deformation on the nonlinear
harmonic generation are studied by considering a tight-binding model expanded
up to third order in $\mathbf{k} \cdot \mathbf{p}$. By solving exactly the
free-carrier dynamics of the carriers when interacting with intense and
ultrashort pulses of light, we predict the photogenerated current in a
nonperturbative way and study its harmonic composition. We find frequency and
amplitude modulation of the nonlinear current in quadratic and cubic models.
Furthermore, we demonstrate anisotropy-induced modulation of the intensity of
higher-order harmonics and the existence of harmonic crossovers, depending on
the incident light polarisation. The methodology presented in this paper may be
applied to any general effective two-band model and offer a pathway to identify
signatures of electronic features in optical output.",2003.02332v1
2020-03-08,Voltage-Induced Inertial Domain Wall Motion in an Antiferromagnetic Nanowire,"Racetrack memory based on magnetic domain walls (DWs) motion exhibits
advantages of small volume and high reading speed. When compared to
current-induced DW motion, voltage-induced DW motion exhibits lower
dissipation. On the other hand, the DW in an antiferromagnet (AFM) moves at a
high velocity with weak stray field. In this work, the AFM DW motion induced by
a gradient of magnetic anisotropy energy under a voltage pulse has been
investigated in theory. The dynamics equation for the DW motion was derived.
The solution indicates that the DW velocity is higher than 100 m/s, and because
of inertia, the DW is able to keep moving at a speed of around 100 m/s for
several nano seconds after turning off the voltage in a period of pulse. The
mechanism for this DW inertia is explained based on the Lagrangian route. On
the other hand, a spin wave is emitted while the DW is moving, yet the DW is
still able to move at an ever increasing velocity with enlarging DW width. This
indicates energy loss from emission of spin wave is less than the energy gain
from the effective field of the gradient of anisotropy energy.",2003.03784v1
2020-03-10,Effect of magnons on the temperature dependence and anisotropy of spin-orbit torque,"We investigate the influence of magnons on the temperature-dependence and the
anisotropy of the spin-orbit torque (SOT). For this purpose we use 3rd order
perturbation theory in the framework of the Keldysh formalism in order to
derive suitable equations to compute the magnonic SOT. We find several
contributions to the magnonic SOT, which depend differently on the spin-wave
stiffness $\mathcal{A}$ and on the temperature $T$, with the dominating
contribution scaling like $T^{2}/\mathcal{A}^{2}$. Based on this formalism we
compute the magnonic SOT in the ferromagnetic Rashba model. For large Rashba
parameters the magnonic SOT is strongly anisotropic and for small quasiparticle
broadening it may become larger than the non-magnonic SOT.",2003.05028v3
2020-03-11,A comparison of two different mechanisms for deterministic spin orbit torque magnetization switching,"In this article we analyze by modeling two possible mechanisms for
magnetization switching using spin orbit torques, which have been reported to
cause field-free deterministic switching in experiments. Here we compare the
field-free magnetization switching due to a tilt of the anisotropy direction
against the use of an antiferromagnetic bias field. Simple results obtained
analytically show that a bias field not only causes the magnetization reversal
but also reduces the corresponding energy barrier. The critical current
required for magnetization switching is analyzed on the basis of a macrospin
model. It is shown that although the field-free deterministic switching caused
by a tilt of the anisotropy is more robust than the bias field in the
development of memory elements, a compromise between requirements has to be
adopted when selecting the parameters for specific applications.",2003.05468v1
2020-03-16,Dynamical spin excitations of topological Haldane gapped phase in the $S=1$ Heisenberg antiferromagnetic chain with single-ion anisotropy,"We study the dynamical spin excitations of the one-dimensional $S=1$
Heisenberg antiferromagnetic chain with single-ion anisotropy by using quantum
Monte Carlo simulations and stochastic analytic continuation of imaginary-time
correlation function. Using the transverse dynamic spin structure factor, we
observe the quantum phase transition with a critical point between the
topological Haldane gapped phase and the trivial phase. At the quantum critical
point, we find a broad continuum characterized by the Tomonaga-Luttinger liquid
similar to a $S=1/2$ Heisenberg antiferromagnetic chain. We further identify
that the elementary excitations are fractionalized spinons.",2003.07857v1
2020-03-28,Dynamic Skyrmion-Mediated Switching of Perpendicular MTJs: Scaling to 20 nm with Thermal Noise,"One method of creating and annihilating skyrmions in confined geometries is
to use Voltage-Controlled Magnetic Anisotropy (VCMA) [1, 2, 3]. Previous study
shows that robust voltage controlled ferromagnetic reversal from up to down
state in the soft layer of a perpendicular Magnetic Tunnel Junction (p-MTJ) can
be achieved by creating and subsequently annihilating an intermediate skyrmion
state [4] in the presence of room temperature thermal noise and anisotropy
variation across grains [4]. However, when scaling to 20 nm, thermal noise can
annihilate the skyrmions, for example, by randomly moving the core towards the
boundary of the nanostructure. In this work, we study three p-MTJs of different
dimensions, particularly lateral dimensions of 100nm, 50nm and 20 nm and
investigate the change in switching behavior as the dimension is decreased.
Particularly, our focus is to investigate to what extent skyrmion mediated
switching scheme can be employed below ~50nm lateral dimensions in the presence
of thermal perturbation.",2003.12904v1
2020-03-30,Spontaneous Rotation of Ferrimagnetism Driven by Antiferromagnetic Spin Canting,"Spin-reorientation phase transitions that involve the rotation of a
crystal$'$s magnetization have been well characterized in distorted-perovskite
oxides such as the orthoferrites. In these systems spin reorientation occurs
due to competing rare-earth and transition metal anisotropies coupled via
$f$-$d$ exchange. Here, we demonstrate an alternative paradigm for spin
reorientation in distorted perovskites. We show that the
$R_2\mathrm{CuMnMn_4O_{12}}$ (R = Y or Dy) triple A-site columnar-ordered
quadruple perovskites have three ordered magnetic phases and up to two
spin-reorientation phase transitions. Unlike the spin-reorientation phenomena
in other distorted perovskites, these transitions are independent of rare-earth
magnetism, but are instead driven by an instability towards antiferromagnetic
spin canting likely originating in frustrated Heisenberg exchange interactions,
and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.",2003.13774v1
2020-03-31,Strong in-plane anisotropy in the electronic structure of fixed-valence $β$-LuAlB$_4$,"The origin of intrinsic quantum criticality in the heavy-fermion
superconductor $\beta$-YbAlB$_4$ has been attributed to strong Yb valence
fluctuations and its peculiar crystal structure. Here, we assess these
contributions individually by studying the isostructural but fixed-valence
compound $\beta$-LuAlB$_4$. Quantum oscillation measurements and DFT
calculations reveal a Fermi surface markedly different from that of
$\beta$-YbAlB$_4$, consistent with a `large' Fermi surface there. We also find
an unexpected in-plane anisotropy of the electronic structure, in contrast to
the isotropic Kondo hybridization in $\beta$-YbAlB$_4$.",2003.14113v1
2020-04-02,Mechanical orientation of fine magnetic particles in powders by an external magnetic field: simulation-based optimization,"We present a numerical algorithm for predicting the optimal conditions for
the effective alignment of magnetic particles in dense powders during the
compactization process using an externally applied field. This task is
especially important for the permanent magnets development due to the fact that
alignment of anisotropy axes of nanocomposite grains increases both remanence
and coercivity of magnetic materials. In contrast to previously known methods
where magnetic moment of each particle was assumed to be 'fixed' with respect
to the particle itself, our approach takes into account the (field-dependent)
deviation of this moment from the particle anisotropy axis that occurs even for
magnetically 'hard' particles possessing a strong mechanical contact. We show,
that this deviation leads to the existence of the optimal value of the applied
field for which the particle orientation (or alignment) time is minimal. The
influence of the external pressure and internal mechanical friction on the
details of the compactization/orientation process is also studied.",2004.00868v1
2020-04-02,Interplay between shell structure and trap deformation in dipolar fermi gases,"Finite fermion systems are known to exhibit shell structure in the
weakly-interacting regime, as well known from atoms, nuclei, metallic clusters
or even quantum dots in two dimensions. All these systems have in common that
the particle interactions between electrons or nucleons are spatially
isotropic. Dipolar quantum systems as they have been realized with ultra-cold
gases, however, are governed by an intrinsic anisotropy of the two-body
interaction that depends on the orientation of the dipoles relative to each
other. Here we investigate how this interaction anisotropy modifies the shell
structure in a weakly interacting two-dimensional anisotropic harmonic trap.
Going beyond Hartree-Fock by applying the so-called ""importance-truncated""
configuration interaction (CI) method as well as quadratic CI with single- and
double-substitutions, we show how the magnetostriction in the system may be
counteracted upon by a deformation of the isotropic confinement, restoring the
symmetry.",2004.01006v1
2020-04-05,Optimal control of magnetization reversal in a monodomain particle by means of applied magnetic field,"A complete analytical solution to the optimal reversal of a macrospin with
easy-axis anisotropy is presented. Optimal control path minimizing the energy
cost of the reversal is identified and used to derive time-dependent direction
and amplitude of the optimal switching field. The minimum energy cost of the
reversal scales inversely with the switching time for fast switching, follows
an exponential asymptotics for slow switching and reaches the lower limit
proportional to the energy barrier between the target states and to the damping
parameter at infinitely long switching time. For a given switching time, the
energy cost is never smaller than that for a free macrospin. This limitation
can be bypassed by adding a hard anisotropy axis which activates the internal
torque in the desired switching direction, thereby significantly reducing the
energy cost. Comparison between the calculated optimal control path and minimum
energy path reveals that optimal control does not translate to the minimization
of the energy barrier, but signifies effective use of the system's internal
dynamics to aid the desired magnetic transition.",2004.02146v2
2020-04-05,Magnon spectrum and electron spin resonance in antiferromagnet with large single-ion easy plane anisotropy,"Motivated by recent experiments on quantum magnet
NiCl$_{2}$-4SC(NH$_{2}$)$_{2}$ (DTN) and its Br-doped counterpart DTNX we
propose a theoretical description of optical magnon branch in the
antiferromagnet with large single-ion anisotropy in the magnetically ordered
phase. In the framework of the 1/S expansion we derive analytical expressions
for optical magnon with $\mathbf{k}=0$ energy magnetic field dependence
$\Delta(h)$. It is shown that in the linear spin wave approximation $\Delta(h)$
is monotonic without extrema whereas first order in 1/S corrections makes it
drastically different function with a minimum near the center of magnetically
ordered phase. The latter behaviour was observed in ESR experiments. Moreover,
we show that $\Delta(h)$ has nontrivial dependence on the system parameters. It
solves the discrepancy between inelastic neutron scattering data where the
growth of interaction constants in DTNX with small Br concentration was
observed and ESR experiments showing almost unchanged $\Delta(h)$ in comparison
with pure DTN.",2004.02170v2
2020-04-05,Generalized phase-sensitivity of directional bond-breaking in laser-molecule interaction,"We establish a generalized picture of the phase-sensitivity of laser-induced
directional bond-breaking using the H$_2$ molecule as the example. We show that
the well-known proton ejection anisotropy measured with few-cycle pulses arises
as an amplitude-modulation of an intrinsic anisotropy that is sensitive to the
laser phase at the ionization time and determined by the molecule's electronic
structure. Our work furthermore reveals a strong electron-proton correlation
that may open up a new approach to experimentally accessing the laser-sub-cycle
intramolecular electron dynamics also in large molecules.",2004.02213v1
2020-04-15,Antisite disorder in the battery material LiFePO$_4$,"We report detailed magnetometry and high-frequency electron spin resonance
(HF-ESR) measurements which allow detailed investigation on Li-Fe antisite
disorder in single-crystalline LiFePO$_4$, i.e., exchange of Fe$^{2+}$- and
Li$^+$-ions. The data imply that magnetic moments of Fe$^{2+}$-ions at
Li-positions do not participate in long-range antiferromagnetic order in
LiFePO$_4$ but form quasi-free moments. Anisotropy axes of the magnetic moments
at antisite defects are attached to the main crystallographic directions. The
local character of these moments is confirmed by associated linear resonance
branches detected by HF-ESR studies. Magnetic anisotropy shows up in
significant zero-field splittings of $\Delta = 220(3)$~GHz, $\Delta'\sim50$~GHz
and a highly anisotropic $g$-factor, i.e., $g_\mathrm{a} = 1.4$, $g_\mathrm{b}
= 2.0$, and $g_\mathrm{c} = 6.3$. We demonstrate a general method to precisely
determine Fe-antisite disorder in LiFePO$_4$ from magnetic studies which
implies a density of paramagnetic Fe$^{2+}$-ions at Li-positions of 0.53\%.",2004.07091v1
2020-04-16,Exchange interaction of hole-spin qubits in double quantum dots in highly anisotropic semiconductors,"We study the exchange interaction between two hole-spin qubits in a double
quantum dot setup in a silicon nanowire in the presence of magnetic and
electric fields. Based on symmetry arguments we show that there exists an
effective spin that is conserved even in highly anisotropic semiconductors,
provided that the system has a twofold symmetry with respect to the direction
of the applied magnetic field. This finding facilitates the definition of qubit
basis states and simplifies the form of exchange interaction for two-qubit
gates in coupled quantum dots. If the magnetic field is applied along a generic
direction, cubic anisotropy terms act as an effective spin-orbit interaction
introducing novel exchange couplings even for an inversion symmetric setup.
Considering the example of a silicon nanowire double dot, we present the
relative strength of these anisotropic exchange interaction terms and calculate
the fidelity of the $\sqrt{\text{SWAP}}$ gate. Furthermore, we show that the
anisotropy-induced spin-orbit effects can be comparable to that of the direct
Rashba spin-orbit interaction for experimentally feasible electric field
strengths.",2004.07658v1
2020-04-20,Anomalous pressure dependence of the electronic transport and anisotropy in SrIrO3 films,"Iridate oxides display exotic physical properties that arise from the
interplay between a large spin-orbit coupling and electron correlations. Here,
we present a comprehensive study of the effects of hydrostatic pressure on the
electronic transport properties of SrIrO3 (SIO), a system that has recently
attracted a lot of attention as potential correlated Dirac semimetal. Our
investigations on untwinned thin films of SIO reveal that the electrical
resistivity of this material is intrinsically anisotropic and controlled by the
orthorhombic distortion of the perovskite unit cell. These effects provide
another evidence for the strong coupling between the electronic and lattice
degrees of freedom in this class of compounds. Upon increasing pressure, a
systematic increase of the transport anisotropies is observed. The anomalous
pressure-induced changes of the resistivity cannot be accounted for by the
pressure dependence of the density of the electron charge carriers, as inferred
from Hall effect measurements. Moreover, pressure-induced rotations of the IrO6
octahedra likely occur within the distorted perovskite unit cell and affect
electron mobility of this system.",2004.09116v1
2020-04-24,Observation of magnetic domains in uniaxial magnets via small-angle electron diffraction and Foucault imaging,"Observation of magnetic domains is important in understanding the magnetic
properties of magnetic materials and devices. In this study, we report that the
magnetic domains of M-type hexaferrites with uniaxial anisotropy can be
visualized via small-angle electron diffraction and Foucault imaging. The
position of the diffraction pattern spots has the same period as that of
magnetic domains in a Sc-substituted hexaferrite
(BaFe$_{12-x-\delta}$Sc$_x$Mg$_\delta$O$_{19}$). Conversely, the spots were
observed four times longer than the period of magnetic domains in hexaferrite
without substitution (BaFe$_{12}$O$_{19}$), demonstrating the long-range order
of the Bloch walls. When the specimen was tilted, the magnetic deflection
effect, as well as the periodic spots of magnetic domains, occurred. Thus, we
were able to visualize the magnetic domains with different magnetization
directions and domain orientations by selecting deflection spots. The results
indicate that the technique utilized in this study is useful in observing the
magnetic materials with uniaxial anisotropy.",2004.11589v1
2020-04-24,Spin-phonon interaction induces tunnel splitting in single-molecule magnets,"Quantum tunneling of the magnetization is a major obstacle to the use of
single-molecule magnets (SMMs) as basic constituents of next-generation storage
devices. In this context, phonons are often only considered (perturbatively) as
disturbances that promote the spin system to traverse the anisotropy barrier.
Here, we demonstrate the ability of phonons to induce a tunnel splitting of the
ground doublet which then reduces the required bistability due to Landau-Zener
tunneling of the magnetization. Harmful are those phonons that modify the spin
Hamiltonian so that its rotational symmetry about the field axis is destroyed.
In our calculations we treat spins and phonons on the same footing by
performing quantum calculations of a Hamiltonian where the single-anisotropy
tensors are coupled to harmonic oscillators.",2004.11735v1
2020-04-25,Dynamo action in sliding plates of anisotropic electrical conductivity,"With materials of anisotropic electrical conductivity, it is possible to
generate a dynamo with a simple velocity field, of the type precluded by
Cowling's theorems with isotropic materials. Following a previous study by
Ruderman and Ruzmaikin [1] who considered the dynamo effect induced by a
uniform shear flow, we determine the conditions for the dynamo threshold when a
solid plate is sliding over another one, both with anisotropic electrical
conductivity. We obtain numerical solutions for a general class of anisotropy
and obtain the conditions for the lowest magnetic Reynolds number, using a
collocation Chebyshev method. In a particular geometry of anisotropy and
wavenumber, we also derive an analytical solution, where the eigenvectors are
just combinations of four exponential functions. An explicit analytical
expression is obtained for the critical magnetic Reynold number. Above the
critical magnetic Reynold number, we have also derived an analytical expression
for the growth rate showing that this is a 'very fast' dynamo, extrapolating on
the 'slow' and 'fast' terminology introduced by Vainshtein and Zeldovich [2].",2004.12244v1
2020-04-29,High throughput computational screening for two-dimensional magnetic materials based on experimental databases of three-dimensional compounds,"We perform a computational screening for two-dimensional magnetic materials
based on experimental bulk compounds present in the Inorganic Crystal Structure
Database and Crystallography Open Database. A recently proposed geometric
descriptor is used to extract materials that are exfoliable into
two-dimensional derivatives and we find 85 ferromagnetic and 61
anti-ferromagnetic materials for which we obtain magnetic exchange and
anisotropy parameters using density functional theory. For the easy-axis
ferromagnetic insulators we calculate the Curie temperature based on classical
Monte Carlo simulations of anisotropic Heisenberg models. We find good
agreement with the experimentally reported Curie temperatures of known 2D
ferromagnets and identify 10 potentially exfoliable two-dimensional
ferromagnets that have not been reported previously. In addition, we find 18
easy-axis anti-ferromagnetic insulators with several compounds exhibiting very
strong exchange coupling and magnetic anisotropy.",2004.14460v1
2020-05-01,Detecting ultra-high energy cosmic ray anisotropies through cross-correlations,"We propose an observable for ultra-high energy cosmic ray (UHECR) physics:
the harmonic-space cross-correlation power spectrum between the arrival
directions of UHECRs and the large-scale cosmic structure mapped by galaxies.
This cross-correlation has not yet been considered in the literature, and it
permits a direct theoretical modelling of the main astrophysical components. We
describe the expected form of the cross-correlation and show how, if the
distribution of UHECR sources trace the large-scale cosmic structure, it could
be easier to detect with current data than the UHECR auto-correlation.
Moreover, the cross-correlation is more sensitive to UHECR anisotropies on
smaller angular scales, more robust to systematic uncertainties, and it could
be used to determine the redshift distribution of UHECR sources, making it a
valuable tool in determining their origins and properties.",2005.00244v2
2020-05-01,Pt and CoB trilayer Josephson $π$ junctions with perpendicular magnetic anisotropy,"We report on the electrical transport properties of Nb based Josephson
junctions with Pt/Co$_{68}$B$_{32}$/Pt ferromagnetic barriers. The barriers
exhibit perpendicular magnetic anisotropy, which has the main advantage for
potential applications over magnetisation in-plane systems of not affecting the
Fraunhofer response of the junction. In addition, we report that there is no
magnetic dead layer at the Pt/Co$_{68}$B$_{32}$ interfaces, allowing us to
study barriers with ultra-thin Co$_{68}$B$_{32}$. In the junctions, we observe
that the magnitude of the critical current oscillates with increasing thickness
of the Co$_{68}$B$_{32}$ strong ferromagnetic alloy layer. The oscillations are
attributed to the ground state phase difference across the junctions being
modified from zero to $\pi$. The multiple oscillations in the thickness range
$0.2~\leqslant~d_\text{CoB}~\leqslant~1.4$~nm suggests that we have access to
the first zero-$\pi$ and $\pi$-zero phase transitions. Our results fuel the
development of low-temperature memory devices based on ferromagnetic Josephson
junctions.",2005.00384v2
2020-05-07,Pressure-dependent Intermediate Magnetic Phase in Thin Fe$_3$GeTe$_2$ Flakes,"We investigated the evolution of ferromagnetism in layered Fe$_3$GeTe$_2$
flakes under different pressures and temperatures using in situ magnetic
circular dichroism (MCD) spectroscopy. We found that the rectangle shape of
hysteretic loop under an out-of-plane magnetic field sweep can sustain below 7
GPa. Above that pressure, an intermediate state appears at low temperature
region signaled by an 8-shaped skew hysteretic loop. Meanwhile, the coercive
field and Curie temperature decrease with increasing pressures, implying the
decrease of the exchange interaction and the magneto-crystalline anisotropy
under pressures. The intermediate phase has a labyrinthine domain structure,
which is attributed to the increase of ratio of exchange interaction to
magneto-crystalline anisotropy based on Jagla's theory. Moreover, our
calculation results reveal a weak structural transition around 6 GPa, which
leads to a drop of the magnetic momentum of Fe ions.",2005.03195v1
2020-05-07,Detecting quadrupole: a hidden source of magnetic anisotropy for Manganese alloys,"Mn-based alloys exhibit unique properties in the spintronics materials
possessing perpendicular magnetic anisotropy (PMA) beyond the Fe and Co-based
alloys. It is desired to figure out the quantum physics of PMA inherent to
Mn-based alloys, which have never been reported. Here, the origin of PMA in
ferrimagnetic Mn$_{3-{\delta}}$Ga ordered alloys is investigated to resolve
antiparallel-coupled Mn sites using x-ray magnetic circular and linear
dichroism (XMCD/XMLD) and a first-principles calculation. We found that the
contribution of orbital magnetic moments in PMA is small from XMCD and that the
finite quadrupole-like orbital distortion through spin-flipped electron hopping
is dominant from XMLD and theoretical calculations. These findings suggest that
the spin-flipped orbital quadrupole formations originate from the PMA in
Mn$_{3-{\delta}}$Ga and bring the paradigm shift in the researches of PMA
materials using x-ray magnetic spectroscopies.",2005.03249v1
2020-05-08,Staggered-flux state for rectangular-lattice spin 1/2 Heisenberg antiferromagnet,"We investigate the spin-1/2 Heisenberg model on a rectangular lattice, using
the Gutzwiller projected variational wave function known as the staggered flux
state. Using Monte Carlo techniques, the variational parameters and static
spin-structure factor for different coupling anisotropies $\gamma=J_y/J_x$ are
calculated. We observe a gradual evolution of the ground state energy towards a
value which is very close to the 1D estimate provided by the Bethe ansatz and a
good agreement between the finite size scaling of the energies. The spin-spin
correlation functions exhibit a power-law decay with varying exponents for
different anisotropies. Though the lack of N\'eel order makes the staggered
flux state energetically unfavorable in the symmetric case $\gamma=1$, it
appears to capture the essence of the system close to 1D. Hence we believe that
the staggered flux state provides an interesting starting point to explore the
crossover from quantum disordered chains to the N\'eel ordered 2D square
lattices.",2005.03928v1
2020-05-12,Ising superconductivity and magnetism in NbSe$_2$,"Recent studies on superconductivity in NbSe$_2$ have demonstrated a large
anisotropy in the superconducting critical field when the material is reduced
to a single monolayer. Motivated by this recent discovery, we use density
functional theory (DFT) calculations to quantitatively address the
superconducting properties of bulk and monolayer NbSe$_2$. We demonstrate that
NbSe$_2$ is close to a ferromagnetic instability, and analyze our results in
the context of experimental measurements of the spin susceptibility in
NbSe$_2$. We show how this magnetic instability, which is pronounced in a
single monolayer, can enable sizeable singlet-triplet mixing of the
superconducting order parameter, contrary to contemporary considerations of the
pairing symmetry in monolayer NbSe$_2$, and discuss approaches as to how this
degree of mixing can be addressed quantitatively within our DFT framework. Our
calculations also enable a quantitative description of the large anisotropy of
the superconducting critical field, using DFT calculations of monolayer
NbSe$_2$ in the normal state",2005.05497v3
2020-05-12,Anisometric mesoscale nuclear and magnetic texture in sintered Nd-Fe-B magnets,"By means of temperature and wavelength-dependent small-angle neutron
scattering (SANS) experiments on sintered isotropic and textured Nd-Fe-B
magnets we provide evidence for the existence of an anisometric structure in
the microstructure of the textured magnets. This conclusion is reached by
observing a characteristic cross-shaped angular anisotropy in the total
unpolarized SANS cross section at temperatures well above the Curie
temperature. Comparison of the experimental SANS data to a microstructural
model based on the superquadrics form factor allows us to estimate the shape
and lower bounds for the size of the structure. Subtraction of the scattering
cross section in the paramagnetic regime from data taken at room temperature
provides the magnetic SANS cross section. Surprisingly, the anisotropy of the
magnetic scattering is very similar to the nuclear SANS signal, suggesting that
the nuclear structure is decorated by the magnetic moments via spin-orbit
coupling. Based on the computation of the two-dimensional correlation function
we estimate lower bounds for the longitudinal and transversal magnetic
correlation lengths.",2005.05648v1
2020-05-14,Harmonic fine tuning and triaxial spatial anisotropy of dressed atomic spins,"The addition of a weak oscillating field modifying strongly dressed spins
enhances and enriches the system quantum dynamics. Through low-order harmonic
mixing the bichromatic driving generates additional rectified static field
acting on the spin system. The secondary field allows for a fine tuning of the
atomic response and produces effects not accessible with a single dressing
field, such as a spatial triaxial anisotropy of the spin coupling constants and
acceleration of the spin dynamics. This tuning-dressed configuration introduces
an extra handle for the system full engineering for quantum control
applications. Tuning amplitude, harmonic content, spatial orientation and phase
relation are control parameters. A theoretical analysis, based on perturbative
approach, is experimentally validated by applying a bichromatic radiofrequency
field to an optically pumped Cs atomic vapour. We measure the resonance shifts
produced by tuning fields up to the third harmonic.",2005.07279v3
2020-05-15,Examination of the four-fifths law for longitudinal third-order moments in incompressible magnetohydrodynamic turbulence in a periodic box,"The four-fifths law for third-order longitudinal moments is examined, by the
use of direct numerical simulation data on three-dimensional forced
incompressible magnetohydrodynamic (MHD) turbulence without a uniformly imposed
magnetic field in a periodic box. The magnetic Prandtl number is set to one,
and the number of grid points is $512^3$. A generalized
K\'arm\'an-Howarth-Kolmogorov equation for second-order velocity moments in
isotropic MHD turbulence is extended to anisotropic MHD turbulence by means of
a spherical average over the direction of $\textbf{r}$. Here, $\textbf{r}$ is a
separation vector. The viscous, forcing, anisotropy and nonstationary terms in
the generalized equation are quantified. It is found that the influence of the
anisotropic terms on the four-fifths law is negligible at small scales,
compared to that of the viscous term. However, the influence of the directional
anisotropy, which is measured by the departure of the third-order moments in a
particular direction of $\textbf{r}$ from the spherically averaged ones, on the
four-fifths law is suggested to be substantial, at least in the case studied
here.",2005.07358v2
2020-05-16,Imry-Ma phase in O(n) models for space dimensions higher than the lower critical dimensionality,"Systems with continuous symmetry of the vector order parameter containing
defects of the ""random local field"" or ""random local anisotropy"" types are
investigated. It is shown that the disordered Imry-Ma phase, in which the order
parameter follows the spatial fluctuations of the random field or random
anisotropy direction, can also occur in a coordinate space of dimension d
higher than the lower critical dimension dl = 4. For this, the hyperplanes of
dimension m < dl, must exist in the coordinate space in which there is a strong
exchange interaction between spins, and the interaction between spins belonging
to adjacent hyperplanes should not exceed a certain critical value.",2005.08091v2
2020-05-21,Strain and electric-field control of spin-spin interactions in monolayer CrI$_3$,"We investigate the impact of mechanical strains and a perpendicular electric
field on the electronic and magnetic ground-state properties of two-dimensional
monolayer CrI$_3$ using density functional theory. We propose a minimal spin
model Hamiltonian, consisting of symmetric isotropic exchange interactions,
magnetic anisotropy energy, and Dzyaloshinskii-Moriya (DM) interactions, to
capture most pertinent magnetic properties of the system. We compute the
mechanical strain and electric field dependence of various spin-spin
interactions. Our results show that both the amplitudes and signs of the
exchange interactions can be engineered by means of strain, while the electric
field affects only their amplitudes. However, strain and electric fields affect
both the directions and amplitudes of the DM vectors. The amplitude of the
magnetic anisotropy energy can also be substantially modified by an applied
strain. We show that in comparison with an electric field, strain can be more
efficiently used to manipulate the magnetic and electronic properties of the
system. Notably, such systematic tuning of the spin interactions is essential
for the engineering of room-temperature spintronic nanodevices.",2005.10520v1
2020-05-22,The soft-mode phonons mediated unconventional superconductivity in monolayer 1T'-WTe2,"Recent experiments have tuned the monolayer 1T'-WTe2 to be superconducting by
electrostatic gating. Here, we theoretically study the phonon-mediated
superconductivity in monolayer 1T'-WTe2 via charge doping. We reveal that the
emergence of soft-mode phonons with specific momentum is crucial to give rise
to the superconductivity in electron-doping regime, whereas no such soft-mode
phonons and no superconductivity emerge in hole-doping regime. We also find a
superconducting dome, which can be attributed to the change of Fermi surface
nesting condition as electron doping. By taking into account the experimentally
established strong anisotropy of temperature-dependent upper critical field
H_{c2} between the in-plane and out-of-plane directions, we show that the
superconducting state probably has the unconventional equal-spin-triplet
pairing in A_{u} channel of C_{2h} point group. Our studies provide a promising
understanding to the doping dependent superconductivity and strong anisotropy
of H_{c2} in monolayer 1T'-WTe2.",2005.11012v2
2020-05-25,Evidence for biquadratic exchange in the quasi-two-dimensional antiferromagnet FePS$_3$,"FePS$_3$ is a van der Waals compound with a honeycomb lattice that is a good
example of a two-dimensional antiferromagnet with Ising-like anisotropy.
Neutron spectroscopy data from FePS3 were previously analysed using a
straight-forward Heisenberg Hamiltonian with a single-ion anisotropy. The
analysis captured most of the elements of the data, however some significant
discrepancies remained. The discrepancies were most obvious at the Brillouin
zone boundaries. The data are subsequently reanalysed allowing for unequal
exchange between nominally equivalent nearest-neighbours, which resolves the
discrepancies. The source of the unequal exchange is attributed to a
biquadratic exchange term in the Hamiltonian which most probably arises from a
strong magnetolattice coupling. The new parameters show that there are features
consistent with Dirac magnon nodal lines along certain Brillouin zone
boundaries.",2005.12031v1
2020-05-26,"A Numerical Study on the Effects of Heterogeneity, Anisotropy, and Station Coverage on the Compensated Linear Vector Dipole Component of Deep Earthquake Moment Tensors","The moment tensors of a large portion of deep earthquakes show apparent
non-double-couple (non-DC) components. Previously, the observed apparent non-DC
values in deep earthquakes have been attributed to different mechanisms such as
complex source processes or complicated source medium structures. In this
paper, we focused on evaluating the second mechanism. We investigated the
effect of slab heterogeneity, supra-slab anisotropic structure, intra-slab
weakly anisotropic structure (e.g., the purported existence of the metastable
olivine wedge), and non-uniform station coverage, on the non-DC radiation
patterns of deep earthquakes using our 3-dimensional elastic finite-difference
modeling and full-waveform inversion of moment tensors. We found that these
investigated issues cannot cause the observed non-double-couple radiation
patterns and the in-situ structure with strong S-wave anisotropy near to the
earthquake focus is the simplest way to account for the apparent non-DC
components in the radiation patterns of deep earthquakes.",2005.12465v1
2020-05-27,Inducing anisotropies in Dirac fermions by periodic driving,"We consider the three-dimensional Hamiltonian for Bi$_2$Se$_3$, a
second-generation topological insulator, under the effect of a periodic drive
for both in-plane and out-of-plane fields. As it will be shown by means of
high-frequency expansions up to second order in the Floquet Hamiltonian, the
driving induces anisotropies in the Dirac cone and opens up a quasienergy gap
for in-plane elliptically polarized fields. Analytic expressions are obtained
for the renormalized velocities and the quasienergy gap. These expressions are
then compared to numerical calculations performed by discretizing the
Hamiltonian in a one-dimensional lattice and following a staggered fermion
approach, achieving a remarkable agreement. We believe our work may have an
impact on the transport properties of topological insulators.",2005.13351v1
2020-05-27,Crossover from Diffusive to Superfluid Transport in Frustrated Magnets,"We investigate the spin transport across the magnetic phase diagram of a
frustrated antiferromagnetic insulator and uncover a drastic modification of
the transport regime from spin diffusion to spin superfluidity. Adopting a
triangular lattice accounting for both nearest neighbor and next-nearest
neighbor exchange interactions with easy-plane anisotropy, we perform atomistic
spin simulations on a two-terminal configuration across the full magnetic phase
diagram. We found that as long as the ground state magnetic moments remain
in-plane, irrespective of whether the magnetic configuration is ferromagnetic,
collinear or non-collinear antiferromagnetic, the system exhibits spin
superfluid behavior with a device output that is independent on the value of
the exchange interactions. When the magnetic frustration is large enough to
compete with the easy-plane anisotropy and cant the magnetic moments out of the
plane, the spin transport progressively evolves towards the diffusive regime.
The robustness of spin superfluidity close to magnetic phase boundaries is
investigated and we uncover the possibility for {\em proximate} spin
superfluidity close to the ferromagnetic transition.",2005.13481v2
2020-06-11,Layering of magnetic nanoparticles at amorphous magnetic templates with perpendicular anisotropy,"We reveal the assembly of monodisperse magnetite nanoparticles of sizes 5 nm,
15 nm and 25 nm from dilute water-based ferrofluids onto an amorphous magnetic
template with out-of-plane anisotropy. From neutron reflectometry experiments
we extract density profiles and show that the particles self-assemble into
layers at the magnetic surface. The layers are extremely stable against
cleaning and rinsing of the substrate. The density of the layers is determined
by and increases with the remanent magnetic moment of the particles.",2006.06262v1
2020-06-12,Enhanced Stability of Antiferromagnetic Skyrmion during Its Motion by Anisotropic Dzyaloshinskii Moriya Interaction,"Searching for new methods to enhance the stability of antiferromagnetic (AFM)
skyrmion during its motion is an important issue for AFM spintronic devices.
Herein, the spin polarized current-induced dynamics of a distorted AFM skyrmion
is numerically studied, based on the Landau Lifshitz Gilbert simulations of the
model with an anisotropic Dzyaloshinskii Moriya (DM) interaction. It is
demonstrated that the DM interaction anisotropy induces the skyrmion
deformation, which suppresses the distortion during the motion and enhances the
stability of the skyrmion. Moreover, the effect of the DM interaction
anisotropy on the skyrmion velocity is investigated in detail, and the
simulated results are further explained by Thiele theory. This work unveils a
promising strategy to enhance the stability and the maximum velocity of AFM
skyrmion, benefiting future spintronic applications.",2006.06938v1
2020-06-14,Structural phase diagram of LaO1-xFxBiSSe: suppression of the structural phase transition by partial F substitutions,"We have investigated low-temperature crystal structure of BiCh2-based
compounds LaO1-xFxBiSSe (x = 0, 0.01, 0.02, 0.03, and 0.5), in which anomalous
two-fold-symmetric in-plane anisotropy of superconducting states has been
observed for x = 0.5. From synchrotron X-ray diffraction experiments, a
structural transition from tetragonal to monoclinic was observed for x = 0 and
0.01 at 340 and 240 K, respectively. For x = 0.03, a structural transition and
broadening of the diffraction peak were not observed down to 100 K. These facts
suggest that the structural transition could be suppressed by 3% F substitution
in LaO1-xFxBiSSe. Furthermore, the crystal structure for x = 0.5 at 4 K was
examined by low-temperature (laboratory) X-ray diffraction, which confirmed
that the tetragonal structure is maintained at 4 K for x = 0.5. Our results
suggest that the two-fold-symmetric in-plane anisotropy of superconducting
states observed for LaO0.5F0.5BiSSe was not originated from structural symmetry
lowering.",2006.07798v2
2020-06-17,Neural Anisotropy Directions,"In this work, we analyze the role of the network architecture in shaping the
inductive bias of deep classifiers. To that end, we start by focusing on a very
simple problem, i.e., classifying a class of linearly separable distributions,
and show that, depending on the direction of the discriminative feature of the
distribution, many state-of-the-art deep convolutional neural networks (CNNs)
have a surprisingly hard time solving this simple task. We then define as
neural anisotropy directions (NADs) the vectors that encapsulate the
directional inductive bias of an architecture. These vectors, which are
specific for each architecture and hence act as a signature, encode the
preference of a network to separate the input data based on some particular
features. We provide an efficient method to identify NADs for several CNN
architectures and thus reveal their directional inductive biases. Furthermore,
we show that, for the CIFAR-10 dataset, NADs characterize the features used by
CNNs to discriminate between different classes.",2006.09717v2
2020-06-19,Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co$_{88}$Tb$_{12}$ thin film with stripe domains,"We use time-resolved x-ray resonant magnetic scattering (tr-XRMS) at the Co
M$_{2,3}$- and Tb O$_1$-edges to study ultrafast demagnetization in an
amorphous Co$_{88}$Tb$_{12}$ alloy with stripe domains. Combining the
femtosecond temporal with nanometer spatial resolution of our experiment, we
demonstrate that the equilibrium spin texture of the thin film remains
unaltered by the optical pump-pulse on ultrashort timescales ($<$1 ps).
However, after $\simeq$ 4 ps, we observe the onset of a significant domain wall
broadening, which we attribute to a reduction of the uniaxial magnetic
anisotropy of the system, due to energy transfer to the lattice. Static
temperature dependent magnetometry measurements combined with analytical
modeling of the magnetic structure of the thin film corroborate this
interpretation.",2006.11246v1
2020-06-22,"Tunable Low-Loss Hyperbolic Plasmon Polaritons in a T$_{d}\,$-WTe$_2$ Single Layer","Natural hyperbolic two-dimensional systems are a fascinating class of
materials that could open alternative pathways to the manipulation of plasmon
propagation and light-matter interactions. Here, we present a comprehensive
study of the optical response in T$_d\,$-WTe$_2$ by means of density-functional
and many-body perturbation theories. We show how monolayer WTe$_2$ with
in-plane anisotropy sustains hyperbolic plasmon polaritons, which can be tuned
via chemical doping and strain. The latter is able to extend the hyperbolic
regime toward the near infrared with low losses. Moreover, with a moderate
strain, WTe$_2$ can even be switched between elliptic and hyperbolic regimes.
In addition, plasmons in WTe$_2$ are characterized by low losses owing to
electron-phonon scattering, which is responsible for the temperature dependence
of the plasmon line width. Interestingly, the temperature can also be utilized
to tune the in-plane anisotropy of the WTe$_2$ optical response.",2006.12257v3
2020-06-25,Spatial decomposition of magnetic anisotropy in magnets: application for doped Fe16N2,"We propose a scheme of decomposition of the total relativistic energy in
solids to intra- and interatomic contributions. The method is based on a
variation of the speed of light from its value in relativistic theory to
infinity (a non-relativistic limit). As an illustration of the method, we
tested such decomposition in the case of a spin-orbit interaction variation for
decomposition of the magnetic anisotropy energy (MAE) in CoPt. We further
studied the {\alpha}''-Fe16N2 magnet doped by Bi, Sb, Co and Pt atoms. It has
been found that the addition of Pt atoms can enhance the MAE by as large as
five times while Bi and Sb substitutions double the total MAE. Using the
proposed technique we demonstrate the spatial distribution of these
enhancements. Our studies also suggest that Sb, Pt and Co substitutions could
be synthesized by experiments.",2006.14665v2
2020-06-26,Initial fluctuations and power spectrum of flow anisotropies in relativistic heavy-ion collisions,"Flow has emerged as a crucial probe for the properties of the thermalized
medium produced in relativistic heavy-ion collisions. The evolution of initial
state fluctuations leaves imprints on the power spectrum of flow coefficients.
Therefore flow coefficients are a crucial probe of initial state fluctuations
arising from the parton distributions of the colliding nuclei. This has a very
strong correspondence with the physics of power spectrum of cosmic microwave
background radiation (CMBR) anisotropies which directly probes initial
inflationary fluctuations. Much work has been done to probe these interesting
interconnections, in particular, in developing techniques for the measurements
of higher flow coefficients. We present a short review of these developments.
The effect of initial magnetic field on these features will also be reviewed.
All this acquires special importance in view of upcoming electron-ion collider
which will directly probe initial parton distribution of the colliding nucleus.",2006.15177v2
2020-07-02,The Imprint of Relativistic Particles on the Anisotropies of the Stochastic Gravitational-Wave Background,"The Stochastic Gravitational-Wave Background (SGWB) is expected to be a key
observable for Gravitational-Wave (GW) interferometry. Its detection will open
a new window on early Universe cosmology, on the astrophysics of compact
objects and, as shown in this Letter, on the particle physics content of the
Universe. In this Letter we show that, besides their effects on the Cosmic
Microwave Background (CMB) and on Large Scale Structure (LSS), relativistic
particles in the early Universe leave a clear imprint on the anisotropies of
the SGWB. In particular we show that a change in the number of decoupled
relativistic particles shifts the angular power spectrum of the SGWB, as both
the Sachs-Wolfe (SW) and the Integrated Sachs-Wolfe (ISW) terms are affected.
Being very large-angle effects, these lead to new testable predictions for
future GW interferometers.",2007.01215v1
2020-07-03,A Vanishingly Small Vector Mass from Anisotropy of Higher Dimensional Spacetime,"We consider five-dimensional massive vector-gravity theory which is based on
the foliation preserving diffeomorphism and anisotropic conformal invariance.
It does not have an intrinsic scale and the only relevant parameter is the
anisotropic factor $z$ which characterizes the degree of anisotropy between the
four-dimensional spacetime and the extra dimension. We assume that physical
scale $M_*$ emerges as a consequence of spontaneous conformal symmetry breaking
of vacuum solution. It is demonstrated that a very small mass for the vector
particle compared to $M_*$ can be achieved with a relatively mild adjustment of
the parameter $z$. At the same time, it is also observed that the motion along
the extra dimension can be highly suppressed and the five-dimensional theory
can be effectively reduced to four-dimensional spacetime.",2007.01551v2
2020-07-06,Four-fold anisotropy of the parallel upper critical magnetic field in a pure layered d-wave superconductor at $T = 0$,"It is well known that a four-fold symmetry of the parallel upper critical
magnetic field disappears in the Ginzburg-Landau (GL) region in
quasi-two-dimensional (Q2D) $d$-wave superconductors. Therefore, it has been
accurately calculated so far as a correction to the GL results, which is valid
close to superconducting transition temperature and is expected to be stronger
at low temperatures. As to the case $T=0$, some approximated methods have been
used, which are good only for closed electron orbits and unappropriate for the
open orbits which exist in a parallel magnetic field in Q2D superconductors.
For the first time, we accurately calculate the four-fold anisotropy of the
parallel upper critical magnetic field in a pure Q2D $d$-wave superconductor at
$T=0$, where it has the highest possible value. Our results are applicable to
Q2D $d$-wave high-Tc and organic superconductors.",2007.03061v1
2020-07-07,Anisotropic Behavior of Excitons in Single Crystal α-SnS,"We investigate analytically the anisotropic dielectric properties of single
crystal {\alpha}-SnS near the fundamental absorption edge by considering atomic
orbitals. Most striking is the excitonic feature in the armchair- (b-) axis
direction, which is particularly prominent at low temperatures. To determine
the origin of this anisotropy, we perform first-principles calculations using
the GW0 Bethe-Salpeter equation (BSE) including the electron-hole interaction.
The results show that the anisotropic dielectric characteristics are a direct
result of the natural anisotropy of p orbitals. In particular, this dominant
excitonic feature originates from the py orbital at the saddle point in the
{\Gamma}-Y region.",2007.03449v1
2020-07-07,Anisotropy induced spin re-orientation in chemically-modulated amorphous ferrimagnetic films,"The ability to tune the competition between the in-plane and out-of-plane
orientation of magnetization provides a means to construct thermal sensors with
a sharp spin re-orientation transition at specific temperatures. We have
observed such a tuneable, temperature driven spin re-orientation in
structurally amorphous, ferrimagnetic rare earth-transition metal (RE-TM) alloy
thin films using scanning transmission X-ray microscopy (STXM) and magnetic
measurements. The nature of the spin re-orientation transition in FeGd can be
fully explained by a non-equilibrium, nanoscale modulation of the chemical
composition of the films. This modulation leads to a magnetic domain pattern of
nanoscale speckles superimposed on a background of in-plane domains that form
Laudau configurations in micron-scale patterned elements. It is this speckle
magnetic structure that gives rise to a sharp two step-reversal mechanism that
is temperature dependent. The possibility to balance competing anisotropies
through the temperature opens opportunities to create and manipulate
topological spin textures.",2007.03657v1
2020-07-12,"Large magnetic anisotropy energy and robust half-metallic ferromagnetism in 2D MnXSe$_4$ (X = As, Sb)","In recent years, intrinsic two-dimensional (2D) magnetism aroused great
interest because of its potential application in spintronic devices. However,
low Curie temperature (\emph{T}$_c$) and magnetic anisotropy energy (MAE) limit
its application prospects. Here, using first-principles calculations based on
density-functional theory (DFT), we predicted a series of stable MnXSe$_4$
(X=As, Sb) single-layer. The MAE of single-layer MnAsSe$_4$ and MnSbSe$_4$ was
648.76 and 808.95 ${\mu}$eV per Mn atom, respectively. Monte Carlo (MC)
simulations suggested the \emph{T}$_c$ of single-layer MnAsSe$_4$ and
MnSbSe$_4$ was 174 and 250 K, respectively. The energy band calculation with
hybrid Heyd-Scuseria-Ernzerhof (HSE06) function indicated the MnXSe$_4$ (X =
As, Sb) were ferromagnetic (FM) half-metallic. Also it had 100\%
spin-polarization ratio at the Fermi level. For MnAsSe$_4$ and MnSbSe$_4$, the
spin-gap were 1.59 and 1.48 eV, respectively. These excellent magnetic
properties render MnXSe$_4$ (X = As, Sb) promising candidate materials for 2D
spintronic applications.",2007.05951v1
2020-07-16,ENZ materials and Anisotropy: Enhancing Nonlinear Optical Interactions at the Nanoscale in Metal/Conducting-Oxide Multilayer Stacks,"Epsilon-near-zero materials are exceptional candidates for studying
electrodynamics and nonlinear optical processes at the nanoscale. We
demonstrate that by alternating a metal and a highly doped conducting-oxide,
the epsilon-near-zero regime may be accessed resulting in an anisotropic,
composite nanostructure that significantly enhances nonlinear interactions.
Using two independent and different computation techniques we show that the
structure can enhance the local field intensity by nearly two orders of
magnitudes, in large part due to the onset of the effective anisotropy. The
investigation of the multilayer nanostructure using a microscopic, hydrodynamic
approach also sheds light on the roles of two competing contributions that are
for the most part overlooked, but that can significantly modify linear and
nonlinear responses of the structure: nonlocal effects, which blueshift the
resulting resonance, and the hot electron nonlinearity, which redshifts the
plasma frequency as the effective mass of free electrons increases as a
function of incident power density. Finally, we show that, even in absence of
second order bulk nonlinearity, second order nonlinear processes are also
significantly enhanced by the layered structure.",2007.08312v1
2020-07-17,Partial local entropy and anisotropy in deep weight spaces,"We refine a recently-proposed class of local entropic loss functions by
restricting the smoothening regularization to only a subset of weights. The new
loss functions are referred to as partial local entropies. They can adapt to
the weight-space anisotropy, thus outperforming their isotropic counterparts.
We support the theoretical analysis with experiments on image classification
tasks performed with multi-layer, fully-connected and convolutional neural
networks. The present study suggests how to better exploit the anisotropic
nature of deep landscapes and provides direct probes of the shape of the minima
encountered by stochastic gradient descent algorithms. As a by-product, we
observe an asymptotic dynamical regime at late training times where the
temperature of all the layers obeys a common cooling behavior.",2007.09091v3
2020-07-20,Anisotropy fluctuation and correlation in central $α$-clustered $^{12}$C+$^{197}$Au collisions,"In the framework of a multi-phase transport model, fluctuation and
correlation of the azimuthal anisotropies in $^{12}$C+$^{197}$Au collisions at
$\sqrt{S_{NN}}$ = 200 GeV are explored. Properties of the initial eccentricity
and final harmonic flow fluctuation resulted from $^{12}$C+$^{197}$Au
collisions with Woods-Saxon configuration and triangular $\alpha$-clustering
configurations of $^{12}$C are investigated via scaled variance, skewness and
kurtosis. Comparisons are made between results from $\alpha$-clustered
configurations and Woods-Saxon configuration. The triangular flow fluctuation
is found to have particular sensitivity in distinguishing triangular
$\alpha$-clustering structure of $^{12}$C. Furthermore, correlations between
initial eccentricities and final flow harmonics are studied with strong
multiplicity dependence observed for the correlation functions.",2007.10063v1
2020-07-20,"Topology of many-body edge and extended quantum states in an open spin chain: 1/3--plateau, Kosterlitz-Thouless transition, and Luttinger liquid","Quantum many-body edge and extended magnon excitations from the 1/3 --
plateau of the anisotropic Heisenberg model on an open AB$_2$ chain in a
magnetic field $h$ are unveiled using the density matrix renormalization group
and exact diagonalization. By tuning both the anisotropy and $h$ in the rich
phase diagram, the edge states penetrate in the bulk, whose gap closes in a
symmetry-protected topological Kosterlitz-Thouless transition. Also, we witness
the squeezed chain effect, the breaking of the edge states degeneracy, and a
topological change of the excitations from gapped magnons with quadratic
long-wavelength dispersion to a linear spinon dispersion in the Luttinger
liquid gapless phase as the anisotropy $\lambda$ approaches the critical point
from the $\lambda>0$ side of the phase diagram.",2007.10414v1
2020-07-26,Optical Anisotropy in Tellurene and its Janus Allotropes -- A first principle Study,"Here, we present first principle study of structural, electronic, and optical
properties of pristine and janus tellurene allotropes using density functional
theory (DFT). The $\alpha$, $\beta$, $\delta$, and $\eta$ allotrope of pristine
tellurene exhibit indirect band gap while $\gamma$ and $\sigma$ allotropes are
metallic. The bandgap shows tunability in janus tellurene compared to pristine
tellurene. A metallic to semiconductor transition occurs in janus $\gamma$,
$\sigma$ and its allotropes. Dirac cone-like interesting feature has been
observed for pristine $\sigma$ tellurene which remains preserved with the
opening in energy gap for janus allotrope. In optical properties, imaginary
part dielectric function and electron energy loss spectra show a blue shift in
janus tellurene as compared to pristine form. Static dielectric constant is
tunable in janus tellurene. All allotropes of tellurene are optically active in
UV-Vis region with optical anisotropy in all three directions. We believe that
our findings will provide useful pointers in the experimental fabrication of
devices based on janus tellurene.",2007.13066v1
2020-07-28,Spin reorientation transition in an ultrathin Fe film on W(110) induced by Dzyaloshinsky-Moriya interactions,"Controlling the preferred direction of the magnetic moments is essential for
the design of spintronic devices based on ultrathin films and heterostructures.
As the film thickness or the temperature is increased, the easy anisotropy axis
is typically reoriented from an out-of-plane direction preferred by surface and
interface energy contributions to an in-plane alignment favored by the volume
anisotropy terms. We study the temperature-driven spin reorientation transition
in two atomic layers of Fe on W(110) using well-tempered metadynamics
simulations based on a spin model parametrized by ab initio calculations and
find that the transition only takes place in the presence of the
Dzyaloshinsky--Moriya interaction (DMI). This demonstrates that the chiral DMI
does not only differentiate between noncollinear spin structures of different
rotational senses, but it also influences the magnetic orientation of collinear
magnetic configurations.",2007.14116v2
2020-08-02,Small-scale Tests of Inflation,"We investigate small-scale signatures of the inflationary particle content.
We consider the case of a light spin-2 particle sourcing primordial
gravitational waves by employing an effective field theory description. Upon
allowing time-dependent sound speeds for the helicity modes, this setup
delivers a blue tensor spectrum detectable, for example, by upcoming laser
interferometers. Our focus is on the tensor non-Gaussianities that ensue from
this field configuration. After characterising the bispectrum amplitude and
shape-function at CMB scales, we move on to smaller scales where anisotropies
induced in the tensor power spectrum by long-short modes coupling become the
key handle on (squeezed) primordial non-Gaussianities. We identify the
parameter space generating percent level anisotropies at scales soon to be
probed by SKA and LISA.",2008.00452v2
2020-08-04,Skyrmions in twisted van der Waals magnets,"Magnetic skyrmions in 2D chiral magnets are in general stabilized by a
combination of Dzyaloshinskii-Moriya interaction and external magnetic field.
Here, we show that skyrmions can also be stabilized in twisted moir\'e
superlattices in the absence of an external magnetic field. Our setup consists
of a 2D ferromagnetic layer twisted on top of an antiferromagnetic substrate.
The coupling between the ferromagnetic layer and the substrate generates an
effective alternating exchange field. We find a large region of skyrmion
crystal phase when the length scales of the moir\'e periodicity and skyrmions
are compatible. Unlike chiral magnets under magnetic field, skyrmions in
moir\'e superlattices show enhanced stability for the easy-axis (Ising)
anisotropy which can be essential to realize skyrmions since most van der Waals
magnets possess easy-axis anisotropy.",2008.01294v2
2020-08-04,Chern insulator transitions with Wilson fermions on a hyperrectangular lattice,"A $U(1)$ gauge theory coupled to a Wilson fermion on a $2+1$ dimensional
cubic lattice is known to exhibit Chern insulator like topological transitions
as a function of the the ratio $M/R$ where $M$ is the fermion mass and $R$ is
the Wilson parameter. I show that, with $M$ and $R$ held fixed, a rectangular
lattice with anisotropic lattice spacing can exhibit distinct topological
phases as a function of the lattice anisotropy. As a consequence, a $2+1$
dimensional lattice theory without any domain wall in the fermion mass can
still exhibit chiral edge modes on a $1+1$ dimensional defect across which
lattice spacing changes abruptly. Likewise, a domain wall in the fermion mass
on a uniform rectangular lattice can exhibit discrete changes in the number and
chirality of zero modes as a function of lattice anisotropy. The construction
presented in this paper can be generalized to higher dimensional space-time
lattices.",2008.01743v3
2020-08-08,High-Frequency GaAs Optomechanical Bullseye Resonator,"The integration of optomechanics and optoelectronics in a single device opens
new possibilities for developing information technologies and exploring
fundamental phenomena. Gallium arsenide (GaAs) is a well-known material that
can bridge the gap between the functionalities of optomechanical devices and
optical gain media. Here, we experimentally demonstrate a high-frequency GaAs
optomechanical resonator with a ring-type bullseye geometry that is
unprecedented in this platform. We measured mechanical modes up to 3.4 GHz with
quality factors of 4000 (at 77 K) and optomechanical coupling rates up to 39
kHz at telecom wavelengths. Moreover, we investigated the material symmetry
break due to elastic anisotropy and its impact on the mechanical mode spectrum.
Finally, we assessed the temperature dependence of the mechanical losses and
demonstrated the efficiency and anisotropy resilience of the bullseye anchor
loss suppression, indicating that lower temperature operation may allow
mechanical quality factors over $10^4$. Such characteristics are valuable for
active optomechanics, coherent microwave-to-optics conversion via
piezo-mechanics and other implementations of high-frequency oscillators in
III-V materials.",2008.03429v2
2020-08-10,A Striped Electron Fluid on (111) KTaO$_3$,"A recent study has revealed that the low carrier density electron gas (2DEG)
induced at the interface of EuO and (111) KTaO$_3$ exhibits a broken symmetry
phase with a strong in-plane anisotropy of the resistivity. We present a
minimal tight binding model of this (111) 2DEG, including the large spin-orbit
coupling from the Ta ions, which reveals a hexagonal Fermi surface with a
highly enhanced 2$k_F$ electronic susceptibility. We argue that repulsive
electronic interactions, together with a ferromagnetic EuO substrate, favor a
magnetic stripe instability leading to a partially gapped Fermi surface. Such a
stripe state, or its vestigial nematicity, could explain the observed transport
anisotropy. We propose a $k\cdot p$ theory for the low energy $j=3/2$ states,
which captures the key results from our tight-binding study, and further
reveals the intertwined dipolar and octupolar modulations underlying this
magnetic stripe order. We conclude by speculating on the relation of this
stripe order to the superconductivity seen in this material.",2008.04337v1
2020-08-20,Anisotropic ultrafast spin/valley dynamics in WTe2 films,"WTe2 Weyl semimetal hosts the natural broken inversion symmetry and strong
spin orbit coupling, making it promising for exotic spin/valley dynamics within
a picosecond timescale. Here, we unveil an anisotropic ultrafast spin/valley
dynamics in centimeter-scale, single-crystalline Td-WTe2 films using a
femtosecond pump-probe technique at room temperature. We observe a transient
(~0.8 ps) intra-valley transition and a subsequent polarization duration (~5
ps) during the whole spin/valley relaxation process. Furthermore, the
relaxation exhibits the remarkable anisotropy of approximately six-fold and
two-fold symmetries due to the intrinsic anisotropy along the crystalline
orientation and the extrinsic matrix element effect, respectively. Our results
offer a prospect for the ultrafast manipulation of spin/valleytronics in
topological quantum materials for dissipationless high-speed spin/valleytronic
devices.",2008.08785v2
2020-08-21,"Growth and anisotropy evaluation of NbBiCh$_3$ (Ch = S, Se) misfit-layered superconducting single crystals","NbBiCh$_3$ (Ch = S, Se) misfit-layered superconducting single crystals were
successfully grown using a CsCl/KCl flux for the first time. The obtained
crystals had a well-developed habit parallel to the c-plane with a typical
width of 1-2 mm and thickness of 10-40 um. The superconducting transition
temperatures with zero resistivity of NbBiS$_3$ single crystals obtained from
the nominal composition of Nb0.9Bi1.2S3 was 0.31 K, and that value of the
NbBiSe$_3$ single crystals grown from the stoichiometry composition
(NbBiSe$_3$) was 2.3 K. Sharp decreases in electric resistivity and magnetic
susceptibility at approximately 3 K suggested a possible superconducting
transition temperature of NbBiSe$_3$. The normal-state anisotropy values of
grown NbBiS$_3$ and NbBiSe$_3$ single crystals were 2.2-2.4 and 1.5-1.6,
respectively.",2008.09322v1
2020-08-25,Anisotropy as a diagnostic test for distinct tensor network wavefunctions of integer and half-integer spin Kitaev quantum spin liquids,"Contrasting ground states of quantum magnets with the integer and
half-integer spin moments are the manifestation of many-body quantum
interference effects. In this work, we investigate the distinct nature of the
integer and half-integer spin quantum spin liquids in the framework of the
Kitaev's model on the honeycomb lattice. The models with arbitrary spin quantum
numbers are not exactly solvable in contrast to the well-known quantum spin
liquid solution of the spin-1/2 system. We use the tensor network wavefunctions
for the integer and half-integer spin quantum spin liquid states to unveil the
important difference between these states. We find that the distinct sign
structures of the tensor network wavefunction for the integer and half-integer
spin quantum spin liquids are responsible for completely different ground
states in the spatially anisotropic limit. Hence the spatial anisotropy would
be a useful diagnostic test for distinguishing these quantum spin liquid
states, both in the numerical computations and experiments on real materials.
We support this discovery via extensive numerics including the tensor network,
DMRG, and exact diagonalization computations.",2008.10792v1
2020-08-26,Revealing charge anisotropies in metal compounds via high-purity x-ray polarimetry,"Linear polarization analysis of hard x-rays is employed to probe electronic
anisotropies in metal-containing complexes with very high selectivity. We use
the pronounced linear dichroism of nuclear resonant x-ray scattering to
determine electric field gradients in an iron(II) containing compound as they
evolve during a temperature-dependent high-spin/low-spin phase transition. This
method constitutes a novel approach to analyze changes in the electronic
structure of metal-containing molecules as function of external parameters or
stimuli. The polarization selectivity of the technique allows us to monitor
defect concentrations of electronic valence states across phase transitions.
This opens new avenues to trace electronic changes and their precursors that
are connected to structural and electronic dynamics in the class of metal
compounds ranging from simple molecular solids to biological molecules.",2008.11820v1
2020-09-18,Schrödinger-type 2D coherent states of magnetized uniaxially strained graphene,"We revisit the uniaxially strained graphene immersed in a uniform homogeneous
magnetic field orthogonal to the layer in order to describe the time evolution
of coherent states build from a semi-classical model. We consider the symmetric
gauge vector potential to render the magnetic field, and we encode the tensile
and compression deformations on an anisotropy parameter $\zeta$. After solving
the Dirac-like equation with an anisotropic Fermi velocity, we define a set of
matrix ladder operators and construct electron coherent states as eigenstates
of a matrix annihilation operator with complex eigenvalues. Through the
corresponding probability density, we are able to study the anisotropy effects
on these states on the $xy$-plane as well as their time evolution. Our results
show clearly that the quasi-period of electron coherent states is affected by
the uniaxial strain.",2009.08587v1
2020-09-24,Phase diagram of multi-layer ferromagnet system with dipole-dipole interaction,"We investigate various magnetic configurations caused by the dipole-dipole
interaction (DDI) in the thin-film magnet with the perpendicular anisotropy
under the open boundary conditions. Two different approaches are simulated: one
starts from a random magnetic configuration and decreases temperatures
step-wisely; the other starts from the saturated out-of-plane ferromagnetic
state to evaluate its metastability. As typical patterns of magnetic
configuration, five typical configurations are found: an out-of-plane
ferromagnetic, in-plane ferromagnetic, vortex, multi-domain, and canted
multi-domain states. Notably, the canted multi-domain forms a concentric
magnetic-domain-pattern with an in-plane vortex structure, resulting from the
open boundary conditions. Concerning to the coercivity, a comparison of the
magnetic configurations in both processes reveals that the out-of-plane
ferromagnetic state exhibits metastability in the multi-domain state, while not
in the vortex state. We also confirm that the so-called Neel-cap
magnetic-domain-wall structure, which is originally discussed in the in-plane
anisotropy system, appears at the multi-domain state.",2009.11574v1
2020-09-24,Magnetic anisotropy and exchange paths for octa- and tetrahedrally coordinated Mn$^{2+}$ ions in the honeycomb multiferroic Mn$_2$Mo$_3$O$_8$,"We investigated the static and dynamic magnetic properties of the polar
ferrimagnet Mn$_2$Mo$_3$O$_8$ in three magnetically ordered phases via
magnetization, magnetic torque, and THz absorption spectroscopy measurements.
The observed magnetic field dependence of the spin-wave resonances, including
Brillouin zone-center and zone-boundary excitations, magnetization, and torque,
are well described by an extended two-sublattice antiferromagnetic classical
mean-field model. In this orbitally quenched system, the competing weak
easy-plane and easy-axis single-ion anisotropies of the two crystallographic
sites are determined from the model and assigned to the tetra- and octahedral
sites, respectively, by ab initio calculations.",2009.11683v1
2020-09-27,Theoretical study on the electric field effect on magnetism of Pd/Co/Pt thin films,"Based on first principles calculations we investigate the electronic and
magnetic properties of Pt layers in Pd$(001)$/Co/Pt thin film structures
exposed to an external electric field. Due to the Co underlayer, the surface Pt
layers have induced moments that are modified by an external electric field.
The field induced changes can be explained by the modified spin-dependent
orbital hybridization that varies non-linearly with the field strength. We
calculate the x-ray absorption and the x-ray magnetic circular dichroism
spectra for an applied external electric field and examine its impact on the
spectra in the Pt layer around the L$_{2}$ and L$_{3}$ edges. We also determine
the layer dependent magneto-crystalline anisotropy and show that the anisotropy
can be tuned easily in the different layers by the external electric field.",2009.12941v1
2020-09-30,Designing of Magnetic MAB Phases for Energy Applications,"Based on high-throughput density functional theory calculations, we performed
screening for stable magnetic MAB compounds and predicted potential strong
magnets for permanent magnet and magnetocaloric applications. The
thermodynamical, mechanical, and dynamical stabilities are systematically
evaluated, resulting in 21 unreported compounds on the convex hull, and 434
materials being metastable considering convex hull tolerance to be 100
meV/atom. Analysis based on the Hume-Rothery rules revealed that the valence
electron concentration and size factor difference are of significant importance
in determining the stability, with good correspondence with the local atomic
bonding. We found 71 compounds with the absolute value of magneto-crystalline
anisotropy energy above 1.0 MJ/m$^3$ and 23 compounds with a uniaxial
anisotropy greater than 0.4 MJ/m$^3$, which are potential gap magnets. Based on
the magnetic deformation proxy, 99 compounds were identified as potential
materials with interesting magnetocaloric performance.",2009.14543v1
2020-10-05,"Theoretical study of current-induced domain wall motion in magnetic nanotubes with azimuthal domains, including Œrsted field and spin-transfer torques","We report a theoretical overview of the magnetic domain wall behavior under
an electric current in infinitely-long nanotubes with azimuthal magnetization,
combining the $1$D analytic model and micromagnetic simulations. We highlight
effects that, besides spin-transfer torques already largely understood in flat
strips, arise specifically in the tubular geometry: the \OErsted field and
curvature-induced magnetic anisotropy resulting both from exchange and material
growth. Depending on both the geometry of the tube and the strength of the
azimuthal anisotropy, Bloch or N\'eel walls arise at rest, resulting in two
regimes of motion largely dominated by either spin-transfer torques or the
\OErsted field. We determine the Walker breakdown current in all cases, and
highlight the most suitable parameters to achieve high domain wall speed.",2010.01966v1
2020-10-13,Strong anisotropy of electron-phonon interaction in NbP probed by magnetoacoustic quantum oscillations,"In this study, we report on the observation of de Haas-van Alphen-type
quantum oscillations (QO) in the ultrasound velocity of NbP as well as `giant
QO' in the ultrasound attenuation in pulsed magnetic fields. The difference of
the QO amplitude for different acoustic modes reveals a strong anisotropy of
the effective deformation potential, which we estimate to be as high as
$9\,\mathrm{eV}$ for certain parts of the Fermi surface. Furthermore, the
natural filtering of QO frequencies and the tracing of the individual Landau
levels to the quantum limit allows for a more detailed investigation of the
Fermi surface of NbP as was previously achieved by means of analyzing QO
observed in magnetization or electrical resistivity.",2010.06530v2
2020-10-14,Fully anisotropic superconductivity with few Helmholtz Fermi-surface harmonics,"We present an alternative representation for the anisotropic Eliashberg
equations of superconductivity, whose numerical solution yields an efficiency
gain of several orders of magnitude with respect to the conventional
representation in momentum space. Our method is a practical realization of a
long-sought approach, whose essence is a linear transformation from regular
${\bf k}$ space to a set of orthonormal functions defined as the solutions of
the Helmholtz equation on the Fermi surface. In this way, all the anisotropy of
the problem can be described by a handful of coefficients with built-in
symmetry. We perform benchmark calculations on the gap anisotropy of MgB$_2$,
and reproduce previous results at a remarkably reduced computational cost.
Furthermore, we apply our methodology to efficiently determine the transition
temperature of the compressed YH$_6$ hydride, obtaining very good agreement
with recent experimental measurements. The simplification introduced by our
method enables the high-throughput exploration of superconducting materials
without having to resort to the isotropic approximation, and opens up
possibilities towards first principles calculations of more advanced theories
of superconductivity.",2010.06887v1
2020-10-16,Hyperfine Couplings as a Probe of Orbital Anisotropy in Heavy Fermion Materials,"The transferred hyperfine interaction between nuclear and electron spins in
an heavy fermion material depends on the hybridization between the $f$-electron
orbitals and those surrounding a distant nucleus. In CeMIn$_5$ (M=Rh, Ir, Co),
both the hyperfine coupling to the two indium sites as well as the crystalline
electric field at the Ce are strongly dependent on the transition metal. We
measure a series of CeRh$_{1-x}$Ir$_x$In$_5$ crystals and find that the
hyperfine coupling reflects the orbital anisotropy of the ground state Ce 4$f$
wavefunction. These findings provide direct proof that the localized to
itinerant transition is dominated by hybridization out of the Ce-In plane in
this system.",2010.08636v1
2020-10-21,Anisotropy in Dijet Production in Exclusive and Inclusive Processes,"We investigate the effect of soft gluon radiations on the azimuthal angle
correlation between the total and relative momenta of two jets in inclusive and
exclusive dijet processes. We show that the final state effect induces a
sizable $\cos(2\phi)$ anisotropy due to gluon emissions near the jet cones. The
phenomenological consequences of this observation are discussed for various
collider experiments, including diffractive processes in ultraperipheral $pA$
and $AA$ collisions, inclusive and diffractive dijet production at the EIC, and
inclusive dijet in $pp$ and $AA$ collisions at the LHC.",2010.10774v3
2020-10-21,Learning Integrodifferential Models for Image Denoising,"We introduce an integrodifferential extension of the edge-enhancing
anisotropic diffusion model for image denoising. By accumulating weighted
structural information on multiple scales, our model is the first to create
anisotropy through multiscale integration. It follows the philosophy of
combining the advantages of model-based and data-driven approaches within
compact, insightful, and mathematically well-founded models with improved
performance. We explore trained results of scale-adaptive weighting and
contrast parameters to obtain an explicit modelling by smooth functions. This
leads to a transparent model with only three parameters, without significantly
decreasing its denoising performance. Experiments demonstrate that it
outperforms its diffusion-based predecessors. We show that both multiscale
information and anisotropy are crucial for its success.",2010.10888v2
2020-10-22,Anomalous Quantum Oscillations in Spin-3/2 Topological Semimetal YPtBi,"The proposed high-spin superconductivity in the half-Heusler compounds
changes the landscape of superconductivity research. While superconducting
instability is possible only in systems with quantum mechanically coherent
quasiparticles, it has not been verified for any proposed high-spin Fermi
surfaces. Here we report an observation of anomalous Shubnikov-de Haas effect
in half-Heusler YPtBi, which is compatible with a coherent $j=3/2$ Fermi
surface. The quantum oscillation (QO) signal in cubic YPtBi manifests extreme
anisotropy upon rotation of the magnetic field from [100] to [110]
crystallographic direction where the QO signal drastically vanishes near [110].
This radical anisotropy for a cubic system cannot be explained by trivial
scenarios for QO involving effective mass or impurity scattering, but it is
naturally explained by the warping feature of the $j=3/2$ Fermi surface YPtBi.
Our results prove the high-spin nature of the quasiparticle in the half-Heusler
compounds, which makes the realization of the unprecedented high-spin
superconductivity more plausible.",2010.12085v2
2020-10-27,Demonstration of nanosecond operation in stochastic magnetic tunnel junctions,"Magnetic tunnel junctions operating in the superparamagnetic regime are
promising devices in the field of probabilistic computing, which is suitable
for applications like high-dimensional optimization or sampling problems.
Further, random number generation is of interest in the field of cryptography.
For such applications, a device's uncorrelated fluctuation time-scale can
determine the effective system speed. It has been theoretically proposed that a
magnetic tunnel junction designed to have only easy-plane anisotropy provides
fluctuation rates determined by its easy-plane anisotropy field, and can
perform on nanosecond or faster time-scale as measured by its
magnetoresistance's autocorrelation in time. Here we provide experimental
evidence of nanosecond scale fluctuations in a circular shaped easy-plane
magnetic tunnel junction, consistent with finite-temperature coupled macrospin
simulation results and prior theoretical expectations. We further assess the
degree of stochasticity of such signal.",2010.14393v1
2020-10-27,Wall-induced anisotropy effects on turbulent mixing in channel flow: A network-based analysis,"Turbulent mixing is studied in the Lagrangian framework with an approach
based on the complex network formalism. We consider the motion of passive,
noninertial particles inside a turbulent channel simulated at $Re_{\tau} =
950$. The time-dependent network is built to evaluate the transfer of tracers
between thin wall-parallel layers which partition the channel in the
wall-normal direction. By doing so, we are able to assess the spatial and
temporal complexities arising from turbulence dynamics and their influence on
the mixing process. This approach highlights the effects of small-scale
features of turbulent flow structures and also the larger scale effects
determined by wall-induced anisotropy. Complex networks, coupled to the
Lagrangian description of turbulence, are effective in providing novel insights
into inhomogeneous turbulence and mixing.",2010.14408v1
2020-10-30,"Spin-wave dispersion and exchange stiffness in Nd$_2$Fe$_{14}$B and $R$Fe$_{11}$Ti ($R$=Y, Nd, Sm) from first-principles calculations","We theoretically investigate spin-wave dispersion in rare-earth magnet
compounds by using first-principles calculations and a method we call the
reciprocal-space algorithm (RSA). The value of the calculated exchange
stiffness for Nd$_2$Fe$_{14}$B is within the range of reported experimental
values. We find that the exchange stiffness is considerably anisotropic when
only short-range exchange couplings are considered, whereas inclusion of
long-range couplings weakens the anisotropy. In contrast, $R$Fe$_{11}$Ti
($R$=Y, Nd, Sm) shows large anisotropy in the exchange stiffness.",2010.16022v3
2020-10-29,Crystal structures of dodecaborides: complexity in simplicity,"Analysis of the intriguing physical properties of the dodecaborides,
$R$B$_{12}$, requires accurate data on their crystal structure. We show that a
simple cubic model fits well with the atomic positions in the unit cell but
cannot explain the observed anisotropy in the physical properties. The
cooperative Jahn-Teller (JT) effect slightly violates the ideal metric of the
cubic lattice and the symmetry of the electron density distribution in the
lattice interstices. Theoretical models of the JT distortions of the boron
framework are presented. Their correspondence to the electron-density
distribution on the maps of Fourier syntheses obtained using x-ray data and
explaining the previously observed anisotropy of conductive properties is
demonstrated. The effect of boron isotope composition on the character of the
lattice distortions is shown. We also discuss the application of the Einstein
model for cations and the Debye model for the boron atoms to describe the
dynamics of the crystal lattice.",2010.16239v1
2020-11-02,Phase diagram of a three-dimensional dipolar model on a FCC lattice,"The magnetic phase diagram at zero external field of an ensemble of dipoles
with uniaxial anisotropy on a FCC lattice is investigated from tempered Monte
Carlo simulations. The uniaxial anisotropy is characterized by a random
distribution of easy axes and its magnitude $\lambda_u$ is the driving force of
disorder and consequently frustration. The phase diagram, separating the
paramagnetic, ferromagnetic, quasi long range ordered ferromagnetic and
spin-glass regions is thus considered in the temperature, $\lambda_u$ plane.
This system is aimed at modeling the magnetic phase diagram of supracrystals of
magnetic nanoparticles.",2011.00879v2
2020-11-04,Anisotropy and stratification effects in the dynamics of fast rotating compressible fluids,"The primary goal of this paper is to develop robust methods to handle two
ubiquitous features appearing in the modeling of geophysical flows: (i) the
anisotropy of the viscous stress tensor, (ii) stratification effects. We focus
on the barotropic Navier-Stokes equations with Coriolis and gravitational
forces. Two results are the main contributions of the paper. Firstly, we
establish a local well-posedness result for finite-energy solutions, via a
maximal regularity approach. This method allows us to circumvent the use of the
effective viscous flux, which plays a key role in the weak solutions theories
of Lions-Feireisl and Hoff, but seems to be restricted to isotropic viscous
stress tensors. Moreover, our approach is sturdy enough to take into account
non constant reference density states; this is crucial when dealing with
stratification effects. Secondly, we study the structure of the solutions to
the previous model in the regime when the Rossby, Mach and Froude numbers are
of the same order of magnitude. We prove an error estimate on the relative
entropy between actual solutions and their approximation by a large-scale
quasi-geostrophic flow supplemented with Ekman boundary layers. Our analysis
holds for a large class of barotropic pressure laws.",2011.02411v1
2020-11-06,Interface-driven electrical magnetochiral anisotropy in Pt/PtMnGa bilayers,"Nonreciprocal charge transport, which is frequently termed as electrical
magnetochiral anisotropy (EMCA) in chiral conductors, touches the most
important elements of modern condensed matter physics. Here, we have
investigated the EMCA in Pt/PtMnGa (PMG) bilayers with the assitance of
nonequilibrium fluctuation theorems. Large EMCA in the Pt/PMG bilayers can be
attributed to nonreciprocal response of an interface-driven chiral transport
channel. Due to the presence of large charge fluctuations for small current
region, higher order EMCA coefficients should be added and they are all
functions of current. A combination of asymmetrical electron scattering and
spin-dependent scattering furnish the PMG thickness dependent chiral transport
behaviors in Pt/PMG bilayers. The dramatically enhanced anomalous Hall angle of
PMG further demonstrates the modified surface state properties by strong
spin-orbit coupling.",2011.03244v3
2020-11-18,Towards a general quasi-linear approach for the instabilities of bi-Kappa plasmas. Whistler instability,"Kappa distributions are ubiquitous in space and astrophysical poorly
collisional plasmas, such as the solar wind, suggesting that microscopic and
macroscopic properties of these non-equilibrium plasmas are highly conditioned
by the wave-particle interactions. The present work addresses the evolution of
anisotropic bi-Kappa (or bi-$\kappa$-)distributions of electrons triggering
instabilities of electromagnetic electron-cyclotron (or whistler) modes. The
new quasi-linear approach proposed here includes time variations of the
$\kappa$ parameter during the relaxation of temperature anisotropy. Numerical
results show that $\kappa$ may increase for short interval of times at the
beginning, but then decreases towards a value lower than the initial one, while
the plasma beta and temperature anisotropy indicate a systematic relaxation.
Our results suggest that the electromagnetic turbulence plays an important role
on the suprathermalization of the plasma, ultimately lowering the parameter
$\kappa$. Even though the variation of $\kappa$ is in general negative ($\Delta
\kappa <0$) this variation seems to depend of the initial conditions of
anisotropic electrons, which can vary very much in the inner heliosphere.",2011.09108v2
2020-11-18,Nanoparticle size threshold for magnetic agglomeration and associated hyperthermia performance,"The likelihood of magnetic nanoparticles to agglomerate is usually estimated
through the ratio between magnetic dipole-dipole and thermal energies, thus
neglecting the fact that, depending on the magnitude of the magnetic anisotropy
constant ($K$), the particle moment may fluctuate internally and thus undermine
the agglomeration process. Based on the comparison between the involved
timescales, we study in this work how the threshold size for magnetic
agglomeration ($d_{aggl}$) varies depending on the $K$ value. Our results
suggest that small variations in $K$ -due to e.g. shape contribution-, might
shift $d_{aggl}$ by a few nm. A comparison with the usual
\textit{superparamagnetism} estimation is provided, as well as with the energy
competition approach. In addition, based on the key role of the anisotropy in
the hyperthermia performance, we also analyse the associated heating
capability, as non-agglomerated particles would be of high interest for the
application.",2011.09223v2
2020-11-22,Built-in Electric-Field-Control of Magnetic Coupling in van der Waals semiconductors,"Electrical control of magnetism in a two-dimensional (2D) semiconductor is of
great interest for emerging nanoscale low-dissipation spintronic devices. Here,
we propose a general approach of tuning magnetic coupling and anisotropy of a
van der Waals (vdW) 2D magnetic semiconductor via a built-in electric field
generated by the adsorption of superatomic ions. Using first-principles
calculations, we predict a significant enhancement of ferromagnetic (FM)
coupling and a great change of magnetic anisotropy in 2D semiconductors when
they are sandwiched between superatomic cations and anions. The magnetic
coupling is directly affected by the built-in electric field, which lifts the
energy levels of mediated ligands' orbitals and enhances the super-exchange
interactions. These findings will be of interest for ionic gating controlled
ferromagnets and magnetoelectronics based on vdW 2D semiconductors.",2011.10923v1
2020-11-24,Prospects of Future CMB Anisotropy Probes for Primordial Black Holes,"Cascade of particles injected as Hawking Radiation from Primordial Black
Holes (PBH) can potentially change the cosmic recombination history by ionizing
and heating the intergalactic medium, which results in altering the anisotropy
spectra of the Cosmic Microwave Background (CMB). In this paper, we study the
expected sensitivity of several future CMB experiments in constraining the
abundance of PBHs distributed in $10^{15}\sim10^{17}$ g mass window according
to four mass functions: the monochromatic, log-normal, power-law and critical
collapse models. Our result shows that future experiments, such as CMB-S4 and
PICO, can improve current {\it{Planck}} bounds by about two orders of
magnitudes. All regions in PBH parameter space that are allowed by current CMB
data, including monochromatically distributed PBHs with mass heavier than $4
\times 10^{16}$ grams, can be excluded by upcoming missions with high
significance.",2011.12244v2
2020-11-25,Antiferromagnetic magnon pseudospin: Dynamics and diffusive transport,"We formulate a theoretical description of antiferromagnetic magnons and their
transport in terms of an associated pseudospin. The need and strength of this
formulation emerges from the antiferromagnetic eigenmodes being formed from
superpositions of spin-up and -down magnons, depending on the material
anisotropies. Consequently, a description analogous to that of spin-1/2
electrons is demonstrated while accounting for the bosonic nature of the
antiferromagnetic eigenmodes. Introducing the concepts of a pseudospin chemical
potential together with a pseudofield and relating magnon spin to pseudospin
allows a consistent description of diffusive spin transport in
antiferromagnetic insulators with any given anisotropies and interactions.
Employing the formalism developed, we elucidate the general features of recent
non-local spin transport experiments in antiferromagnetic insulators hosting
magnons with different polarisations. The pseudospin formalism developed herein
is valid for any pair of coupled bosons and is likely to be useful in other
systems comprising interacting bosonic modes.",2011.12927v1
2020-11-26,Optically-induced frequency up-conversion of the ferromagnetic resonance in an ultrathin garnet,"We perform ultrafast pump-probe measurements on a nanometer-thick crystalline
Bi-doped yttrium iron garnet film with perpendicular magnetic anisotropy.
Tuning the photon energy of the pump laser pulses above and below the
material's bandgap, we trigger ultrafast optical and spin dynamics via both
one- and two-photon absorption. Contrary to the common scenario, the
optically-induced heating of the system induces an increase up to 20% of the
ferromagnetic resonance frequency. We explain this unexpected result in terms
of a photo-induced modification of the magnetic anisotropy, i.e. of the
effective field, identifying the necessary conditions to observe this effect.
Our results disclose the possibility to optically increase the magnetic
eigenfrequency in nanometer-thick magnets.",2011.13403v1
2020-12-02,Crystallographic Reconstruction Driven Modified Mechanical Properties in Anisotropic Rhenium Disulfides,"Atomic-scale investigation on mechanical behaviors is highly necessary to
fully understand the fracture mechanics especially of brittle materials, which
are determined by atomic-scale phenomena (e.g., lattice trapping). Here,
exfoliated anisotropic rhenium disulfide (ReS2) flakes are used to investigate
atomic-scale crack propagation depending on the propagation directions. While
the conventional strain-stress curves exhibit a strong anisotropy depending on
the cleavage direction of ReS2, but our experimental results show a reduced
cleavage anisotropy due to the lattice reconstruction in [100] cracking with
high resistance to fracture. In other words, [010] and [110] cracks with low
barriers to cleavage exhibit the ultimate sharpness of the crack tip without
plastic deformation, whereas [100] cracks drive lattice rotation on one side of
the crack, leading to a non-flat grain boundary formation. Finally,
crystallographic reconstruction associated with the high lattice randomness of
two-dimensional materials drives to a modified cleavage tendency, further
indicating the importance of atomic-scale studies for a complete understanding
of the mechanics.",2012.01045v1
2020-12-03,Constraining the initial stages of ultrarelativistic nuclear collisions,"It is frequently supposed that quark-gluon plasma created in heavy-ion
collisions undergoes free streaming at early times. We examine this issue based
on the assumption that a universal attractor dominates the dynamics already at
the earliest stages, which offers a way to connect the initial state with the
start of the hydrodynamic expansion in an approximate but conceptually
transparent fashion. We demonstrate that the centrality dependence of the
measured particle multiplicities can be used to quantitatively constrain the
pressure anisotropy and find that it strongly depends on the model of the
initial energy deposition. As an illustration, we compare three initial state
models and show that they predict rather different early-time values of the
pressure anisotropy. This strongly suggests that assuming free streaming prior
to hydrodynamization is not necessarily compatible with a generic initial state
model and that features of the pre-hydrodynamic flow need to be matched with
the model of the initial state.",2012.02184v3
2020-12-11,Anisotropies in Compressible MHD Turbulence: Probing Magnetic Fields and Measuring Magnetization,"Probing magnetic fields in the interstellar medium (ISM) is notoriously
challenging. Motivated by the modern theories of magnetohydrodynamic (MHD)
turbulence and turbulence anisotropy, we introduce the Structure-Function
Analysis (SFA) as a new approach to measure the magnetic field orientation and
estimate the magnetization. We analyze the statistics of turbulent velocities
in three-dimensional compressible MHD simulations through the second-order
structure functions in both local and global reference frames. In the
sub-Alfvenic turbulence with the magnetic energy larger than the turbulent
energy, the SFA of turbulent velocities measured in the directions
perpendicular and parallel to the magnetic field can be significantly
different. Their ratio has a power-law dependence on the Alfven Mach number
$M_A$, which is inversely proportional to the magnetic field strength. We
demonstrate that the anisotropic structure functions of turbulent velocities
can be used to estimate both the orientation and strength of magnetic fields.
With turbulent velocities measured using different tracers, our approach can be
generally applied to probing the magnetic fields in the multi-phase
interstellar medium.",2012.06039v2
2020-12-23,Interplay of crystal thickness and in-plane anisotropy and evolution of quasi-one dimensional electronic character in ReSe$_{2}$,"We study the valence band structure of ReSe$_{2}$ crystals with varying
thickness down to a single layer using nanoscale angle-resolved photoemission
spectroscopy and density functional theory. The width of the top valence band
in the direction perpendicular to the rhenium chains decreases with decreasing
number of layers, from 280 meV for the bulk to 61 meV for monolayer. This
demonstrates increase of in-plane anisotropy induced by changes in the
interlayer coupling and suggests progressively more one-dimensional character
of electronic states in few-layer rhenium dichalcogenides.",2012.12659v3
2020-12-23,Inertial effects on the Brownian gyrator,"The recent interest into the Brownian gyrator has been confined chiefly to
the analysis of Brownian dynamics both in theory and experiment despite the
applicability of general cases with definite mass. Considering mass explicitly
in the solution of the Fokker--Planck equation and Langevin dynamics
simulations, we investigate how inertia can change the dynamics and energetics
of the Brownian gyrator. In the Langevin model, the inertia reduces the
nonequilibrium effects by diminishing the declination of the probability
density function and the mean of a specific angular momentum, $j_\theta$, as a
measure of rotation. Another unique feature of the Langevin description is that
rotation is maximized at a particular anisotropy while the stability of the
rotation is minimized at a particular anisotropy or mass. Our results suggest
that the Langevin dynamics description of the Brownian gyrator is intrinsically
different from that with Brownian dynamics. In addition, $j_\theta$ is proven
to be essential and convenient for estimating stochastic energetics such as
heat currents and entropy production even in the underdamped regime.",2012.12713v2
2020-12-23,Electric manipulation of domain walls in magnetic Weyl semimetals via the axial anomaly,"We show how the axial (chiral) anomaly induces a spin torque on the
magnetization in magnetic Weyl semimetals. The anomaly produces an imbalance in
left- and right-handed chirality carriers when non-orthogonal electric and
magnetic fields are applied. Such imbalance generates a spin density which
exerts a torque on the magnetization, the strength of which can be controlled
by the intensity of the applied electric field. We show how this results in an
electric control of the chirality of domain walls, as well as in an improvement
of the domain wall dynamics, by delaying the onset of the Walker breakdown. The
measurement of the electric field mediated changes in the domain wall chirality
would constitute a direct proof of the axial anomaly. Additionally, we show how
quantum fluctuations of electronic Fermi arc states bound to the domain wall
naturally induce an effective magnetic anisotropy, allowing for high domain
wall velocities even if the intrinsic anisotropy of the magnetic Weyl semimetal
is small.",2012.12785v2
2020-12-28,Gravitational collapse of anisotropic stars,"We study the gravitational collapse of a spherically symmetric anisotropic
relativistic star within Einstein theory of gravity making use of one of our
recently developed collapsing stellar models [{\it Astrophys. Space Sci.}
{\bf361} 99 (2016)]. The final state of continual gravitational collapse of a
massive star under regular initial conditions is analyzed in terms of the
formation of black holes. To study the evolution of an anisotropic star
undergoing gravitational collapse, it is assumed that the dissipation process
happens in the form of radial heat-flux. The interior space-time is described
by static metric matched at the boundary with Vaidya metric that describes the
exterior to the radiating star. The initial static configuration is described
by the relativistic solution obtained by Paul and Deb [{\it Astrophys. Space
Sci.} {\bf354} 421 (2014)]. The impact of anisotropy on the dynamical
gravitational collapse of a massive star is studied. The relativistic causal
heat transport equation of the Maxwell-Cattaneo equation is utilized to show
the dependence of anisotropy on the temperature profile of the collapsing
system.",2012.14084v1
2020-12-30,RF signal detector and energy harvester based on a spin-torque diode with perpendicular magnetic anisotropy,"We demonstrate theoretically that in a spintronic diode (SD), having a free
magnetic layer with perpendicular magnetic anisotropy of the first and second
order and no external bias magnetic field, the out-of-plane regime of
magnetization precession can be excited by sufficiently large (exceeding a
certain threshold) RF signals with the frequencies <~250 MHz. We also show that
such a device can operate as a broadband energy harvester capable of converting
incident RF power into a DC power with the conversion efficiency of ~5%. The
developed analytical theory of the bias-free SD operation can be used for the
optimization of high-efficiency RF detectors and energy harvesters based on
SDs.",2012.15107v1
2020-12-30,"Anisotropic magnetic interactions in hexagonal AB-stacked kagome lattice structures: Applications to $\mathrm{Mn}_3\mathrm{X}$ ($\mathrm{X}$ = $\mathrm{Ge}$, $\mathrm{Sn}$, $\mathrm{Ga}$) compounds","$\mathrm{Mn}_3\mathrm{X}$ compounds in which the magnetic $\mathrm{Mn}$ atoms
form AB-stacked kagome lattices have received a tremendous amount of attention
since the observation of the anomalous Hall effect in
$\mathrm{Mn}_3\mathrm{Ge}$ and $\mathrm{Mn}_3\mathrm{Sn}$. Although the
magnetic ground state has been known for some time to be an inverse triangular
structure with an induced in-plane magnetic moment, there have been several
controversies about the minimal magnetic Hamiltonian. We present a general
symmetry-based model for these compounds that includes a previously unreported
interplane Dzyaloshinskii-Moriya interaction, as well as anisotropic exchange
interactions. The latter are shown to compete with the single-ion anisotropy
which strongly affects the ground state configurations and elementary spin-wave
excitations. Finally, we present the calculated elastic and inelastic neutron
scattering intensities and point to experimental assessment of the types of
magnetic anisotropy in these compounds that may be important.",2012.15280v2
2021-01-04,Spacing Homogenization in Lamellar Eutectic Arrays with Anisotropic Interphase Boundaries,"We analyze the effect of interphase boundary anisotropy on the dynamics of
lamellar eutectic solidification fronts, in the limit that the lamellar spacing
varies slowly along the envelope of the front. In the isotropic case, it is
known that the spacing obeys a diffusion equation, which can be obtained
theoretically by making two assumptions: (i) the lamellae always grow normal to
the large-scale envelope of the front, and (ii) the Jackson-Hunt law that links
lamellar spacing and front temperature remains locally valid. For anisotropic
boundaries, we replace hypothesis (i) by the symmetric pattern approximation,
which has recently been found to yield good predictions for lamellar growth
direction in presence of interphase anisotropy. We obtain a generalized
Jackson-Hunt law for tilted lamellae, and an evolution equation for the
envelope of the front. The latter contains a propagative term if the initial
lamellar array is tilted with respect to the direction of the temperature
gradient. However, the propagation velocity of the propagative wave modes are
found to be small, so that the dynamics of the front can be reasonably
described by a diffusion equation with a diffusion coefficient that is modified
with respect to the isotropic case.",2101.01040v1
2021-01-07,Giant interfacial induced Dzyaloshinskii-Moriya interaction in polycrystalline Co/Pt multilayers,"Multilayers of heavy metals and ferromagnets are the basis for the formation
of various structures with inhomogeneous chiral magnetic distributions. The
most informative method for studying magnetic states in such structures with a
high spatial resolution is Lorentz transmission electron microscopy (L-TEM).
Here, we report on the observation of chiral N\'eel domain walls by means of
L-TEM in Co/Pt multilayers with perpendicular magnetic anisotropy. We explain
the existence of chiral N\'eel internal structure due to the overcritical,
giant interfacial induced Dzyaloshinskii-Moriya interaction. Our results are
confirmed by micromagnetic modeling, which allows taking into account the
effect of local inhomogeneity of the magnetic anisotropy of polycrystalline
films on formation of spin textures.",2101.02460v1
2021-01-10,Crystallization of anisotropic colloids with a Yukawa potential,"Crystallization in a dense suspension of anisotropic spherical colloidal
particles with a Yukawa potential is numerically investigated in a
two-dimensional plane. It is found that a strong anisotropy can hinder the
particles from crystallizing, while a weak anisotropy but super-strong coupling
facilitates colloids to freeze into a hexagonal crystal. Different criterions
are employed to describe the phase transition, one can find that a competition
between anisotropic degree and coupling strength shall widened the transition
region in the phase diagram, where the heterogeneous structures coexist, which
render as a quasi-platform stretched across the probability distribution curve
of the local order parameter. Our study maybe helpful for the experiments
relating to the crystallizing behavior in statistical physics, materials
science and biophysical systems.",2101.03551v2
2021-01-17,Surface-Wave Propagation on Non-Hermitian Metasurfaces with Extreme Anisotropy,"Electromagnetic metasurfaces enable the advanced control of surface-wave
propagation by spatially tailoring the local surface reactance. Interestingly,
tailoring the surface resistance distribution in space provides new, largely
unexplored degrees of freedom. Here, we show that suitable spatial modulations
of the surface resistance between positive (i.e., loss) and negative (i.e.,
gain) values can induce peculiar dispersion effects, far beyond a mere
compensation. Taking inspiration from the parity-time symmetry concept in
quantum physics, we put forward and explore a class of non-Hermitian
metasurfaces that may exhibit extreme anisotropy mainly induced by the
gain-loss interplay. Via analytical modeling and full-wave numerical
simulations, we illustrate the associated phenomenon of surface-wave
canalization, explore nonlocal effects and possible departures from the ideal
conditions, and address the feasibility of the required constitutive
parameters. Our results suggest intriguing possibilities to dynamically
reconfigure the surface-wave propagation, and are of potential interest for
applications to imaging, sensing and communications.",2101.06641v1
2021-01-18,Manipulating the anisotropic phase separation in strained VO2 epitaxial films by nanoscale ion-implantation,"Manipulating the strain induced poly-domains and phase transition in
correlated oxide material are important for high performance devices
fabrication. Though the electronic transport in the strained oxide film at
macroscopic scales can be directly measured, the anisotropic electronic state
and the controllable phase separation cross the insulator-to-metal transition
within nanoscale size are still elusive. Here, we selected VO2 crystal film as
a prototypical oxide and achieved the manipulation of anisotropy electronic
phase separation via injecting He+ nanobeam into VO2 film at room temperature.
In addition, this nanoscale phase separation was directly visualized by
infrared near-field imaging measurements, showing the pronounced and unique
cR-axis dependent anisotropy on VO2 surface. Our results offered new insights
towards understanding the anisotropic nanoscale phase separation in strained
metal oxide films.",2101.07093v2
2021-01-22,New interpretation of the Extended Geometric Deformation in Isotropic Coordinates,"We study the particular case in which Extended Geometric Deformation does
consists of consecutive deformations of temporal and spatial components of the
metric, in Schwarzschild-like and isotropic coordinates. In the latter, we
present two inequivalent ways to perform this 2-steps GD. This was done in such
a way that the method may be applied to different seed solutions. As an
example, we use Tolman IV as seed solution, in order to obtain two inequivalent
physical solutions with anisotropy in the pressures in Schwarzschild-like
coordinates. In the isotropic sector, we obtained four different solutions with
anisotropy in the pressures that satisfy physical acceptability conditions,
using Gold III as seed solution.",2101.09148v4
2021-01-25,Formation of solid-state dendrites under the influence of coherency stresses: A diffuse interface approach,"In this paper, we have formulated a phase-field model based on the
grand-potential functional for the simulation of precipitate growth in the
presence of coherency stresses. In particular, we study the development of
dendrite-like patterns arising out of diffusive instabilities during the growth
of a precipitate in a supersaturated matrix. Here, we characterize the role of
elastic energy anisotropy and its strength on the selection of a dendrite tip
radius and velocity. We find that there is no selection of a unique tip shape
as observed in the case of solidification, and the selection constant
$\sigma^{*}=2d_0D/R_{tip}^{2}V_{tip}$ increases linearly with simulation time
for all the simulation conditions (where $R_{tip}$ and $V_{tip}$ are the tip
radius and velocity). Therefore, structures derived in solid-state in the
presence of elastic anisotropy may only be referred to as dendrite-like.",2101.09964v1
2021-01-26,Stabilizing current-driven steady flows of 180$^{\circ}$ domain walls in spin valves by interfacial Dzyaloshinskii-Moriya interaction,"Modulations of interfacial Dzyaloshinskii-Moriya interaction (iDMI) on
current-driven dynamics of 180$^{\circ}$ domain walls (180DWs) in long and
narrow spin valves (LNSVs) with heavy-metal caplayers are systematically
investigated. We focus on LNSVs with in-plane magnetic anisotropy in their free
layers. For planar-transverse polarizers (pinned layers of LNSVs), the Walker
breakdown can be postponed considerably (practical infinity) by iDMI. More
interestingly, the originally unstable traveling mode is also stabilized by
iDMI with high saturation velocity thus serves as fast carrier of information.
For parallel polarizers, the Walker limit is increased and the corresponding
modifications of iDMI to wall velocity in both steady and precessional flows of
180DWs are provided. For perpendicular polarizers, precessional flow of 180DWs
is absent due to the stability of stationary mode beyond the modified Walker
limit. For LNSVs with perpendicular magnetic anisotropy in their free layers,
similar results are obtained. Our findings open new possibilities for
developing magnetic nanodevices based on 180DW propagation with low energy
consumption and high robustness.",2101.10590v1
2021-01-29,Magnetization Reversal Mechanism in Exchange-Biased Spring-like Thin-Film Composite,"Development of modern spintronic devices requires materials exhibiting
specific magnetic effects. In this paper, we investigate a magnetization
reversal mechanism in a [Co/Pdx]7/CoO/[Co/Pdy]7 thin-film composite where an
antiferromagnet is sandwiched between a hard and a soft ferromagnets with
different coercivities. The antiferromagnet/ferromagnet interfaces give rise to
the exchange bias effect. The application of soft and hard ferromagnetic films
causes exchange-spring-like behavior while the choice of the Co/Pd multilayers
provides large out-of-plane magnetic anisotropy. We observed that the magnitude
and the sign of the exchange bias anisotropy field are related to the
arrangement of the magnetic moments in the antiferromagnetic layer. This
ordering is induced by the spin orientation present in neighboring
ferromagnetic films which is, in turn, dependent on the orientation and
strength of the external magnetic field.",2101.12495v1
2021-01-30,Cosmic-ray current-driven instabilities -- revisiting environmental conditions,"The growth of magneto-hydrodynamic fluctuations relevant to cosmic ray
confinement in and near their sources, and the effects of local plasma
conditions is revisited. We consider cases where cosmic rays penetrate a medium
which may contain a fraction of neutral particles, and explore the possible
effects of high-order cosmic-ray anisotropies. An algorithm for calculating the
dispersion relation for arbitrary distributions, and anisotropies is presented,
and a general solution for power-law cosmic-ray distributions is provided.
Implications for the resulting instabilities near to strong Galactic cosmic-ray
sources are discussed. We argue that cosmic-ray streaming in weakly ionised
plasmas eliminates the need for the existence of an evanescent band in the
dispersion relation, a conclusion which may be confirmed by gamma-ray
observations. The necessity for additional multi-scale numerical simulations is
highlighted, as understanding the non-linear behaviour is crucial.",2102.00334v1
2021-02-03,Parton collisional effect on the conversion of geometry eccentricities into momentum anisotropies in relativistic heavy-ion collisions,"We explore parton collisional effects on the conversion of geometry
eccentricities into azimuthal anisotropies in Pb+Pb collisions at
$\sqrt{s_{NN}}$ = 5.02 TeV using a multi-phase transport model. The initial
eccentricity $\varepsilon_{n}$ (n = 2,3) and flow harmonics $v_{n}$ (n = 2,3)
are investigated as a function of the number of parton collisions ($N_{coll}$)
during the source evolution of partonic phase. It is found that partonic
collisions leads to generate elliptic flow $v_{2}$ and triangular flow $v_{3}$
in Pb+Pb collisions. On the other hand, partonic collisions also result in an
evolution of the eccentricity of geometry. The collisional effect on the flow
conversion efficiency is therefore studied. We find that the partons with
larger $N_{coll}$ show a lower flow conversion efficiency, which reflect
differential behaviors with respect to $N_{coll}$. It provides an additional
insight into the dynamics of the space-momentum transformation during the QGP
evolution from a transport model point of view.",2102.01872v1
2021-02-05,Tip-induced domain protrusion in ferroelectric films with in-plane polarization,"Charge manipulation and fabrication of stable domain patterns in
ferroelectric materials by scanning probe microscopy open up broad avenues for
the development of tunable electronics. Harnessing the polarization energy and
electrostatic forces with specific geometry of the system enables producing the
nanoscale domains by-design. Along with that, domain engineering requires
mastery of underlying physical mechanisms that govern the domain formation.
Here, we present a theoretical description of the domain formation by a
scanning probe microscopy tip in a ferroelectric film with strong in-plane
anisotropy of polarization. We demonstrate that local charge injection produces
wedge-shaped domains that propagate along the anisotropy axis, whereas the
tip-written lines of charge generate a comb-like domain structure. The results
of our calculations agree with earlier experimental observations and allow for
the optimization of the targeted domain structures.",2102.03174v1
2021-02-07,Spinterface Induced Modification in Magnetic Properties in Co40Fe40B20/Fullerene Bilayers,"Organic semiconductor/ferromagnetic bilayer thin films can exhibit novel
properties due to the formation of the spinterface at the interface.
Buckminsterfullerene (C60) has been shown to exhibit ferromagnetism at the
interface when it is placed next to a ferromagnet (FM) such as Fe or Co.
Formation of spinterface occurs due to the orbital hybridization and spin
polarized charge transfer at the interface. In this work, we have demonstrated
that one can enhance the magnetic anisotropy of the low Gilbert damping alloy
CoFeB by introducing a C60 layer. We have shown that anisotropy increases by
increasing the thickness of C60 which might be a result of the formation of
spinterface. However, the magnetic domain structure remains same in the bilayer
samples as compared to the reference CoFeB film.",2102.03914v4
2021-02-08,"Axisymmetric dynamo action produced by differential rotation, with anisotropic electrical conductivity and anisotropic magnetic permeability","The effect on dynamo action of an anisotropic electrical conductivity
conjugated to an anisotropic magnetic permeability is considered. Not only is
the dynamo fully axisymmetric, but it requires only a simple differential
rotation, which twice challenges the well-established dynamo theory. Stability
analysis is conducted entirely analytically, leading to an explicit expression
of the dynamo threshold. The results show a competition between the anisotropy
of electrical conductivity and that of magnetic permeability, the dynamo effect
becoming impossible if the two anisotropies are identical. For isotropic
electrical conductivity, Cowling's neutral point argument does imply the
absence of an azimuthal component of current density, but does not prevent the
dynamo effect as long as the magnetic permeability is anisotropic.",2102.04343v1
2021-02-18,Two-dimensional easy-plane SU$(3)$ magnet with the transverse field: Anisotropy-driven multicriticality,"The two-dimensional easy-plane SU$(3)$ magnet subjected to the transverse
field was investigated with the exact-diagonalization method. So far, as to the
$XY$ model (namely, the easy-plane SU$(2)$ magnet), the transverse-field-driven
order-disorder phase boundary has been investigated with the
exact-diagonalization method, and it was claimed that the end-point singularity
(multicriticality) at the $XX$-symmetric point does not accord with
large-$N$-theory's prediction. Aiming to reconcile the discrepancy, we extend
the internal symmetry to the easy-plane SU$(3)$ with the anisotropy parameter
$\eta$, which interpolates the isotropic ($\eta=0$) and fully anisotropic
($\eta=1$) cases smoothly. As a preliminary survey, setting $\eta=1$, we
analyze the order-disorder phase transition through resorting to the fidelity
susceptibility $\chi_F$, which exhibits a pronounced signature for the
criticality. Thereby, with $\eta$ scaled carefully, the $\chi_F$ data are cast
into the crossover-scaling formula so as to determine the crossover exponent
$\phi$, which seems to reflect the extension of the internal symmetry group to
SU(3).",2102.09083v1
2021-02-18,"Voltage control of skyrmions: creation, annihilation and zero-magnetic field stablization","Voltage manipulation of skyrmions is a promising path towards low-energy
spintronic devices. Here, voltage effects on skyrmions in a GdOx/Gd/Co/Pt
heterostructure are observed experimentally. The results show that the skyrmion
density can be both enhanced and depleted by the application of an electric
field, along with the ability, at certain magnetic fields to completely switch
the skyrmion state on and off. Further, a zero magnetic field skyrmion state
can be stablized under a negative bias voltage using a defined voltage and
magnetic field sequence. The voltage effects measured here occur on a
few-second timescale, suggesting an origin in voltage-controlled magnetic
anisotropy rather than ionic effects. By investigating the skyrmion nucleation
rate as a function of temperature, we extract the energy barrier to skyrmion
nucleation in our sample. Further, micromagnetic simulations are used to
explore the effect of changing the anisotropy and Dzyaloshinskii-Moriya
interaction on skyrmion density. Our work demonstrates the control of skyrmions
by voltages, showing functionalities desirable for commercial devices.",2102.09178v1
2021-02-22,Robust formation of nanoscale magnetic skyrmions in easy-plane thin film multilayers with low damping,"We experimentally demonstrate the formation of room-temperature skyrmions
with radii of about 25\,nm in easy-plane anisotropy multilayers with
interfacial Dzyaloshinskii-Moriya interaction (DMI). We detect the formation of
individual magnetic skyrmions by magnetic force microscopy and find that the
skyrmions are stable in out-of-plane fields up to about 200 mT. We determine
the interlayer exchange coupling as well as the strength of the interfacial
DMI. Additionally, we investigate the dynamic microwave spin excitations by
broadband magnetic resonance spectroscopy. From the uniform Kittel mode we
determine the magnetic anisotropy and low damping $\alpha_{\mathrm{G}} < 0.04$.
We also find clear magnetic resonance signatures in the non-uniform (skyrmion)
state. Our findings demonstrate that skyrmions in easy-plane multilayers are
promising for spin-dynamical applications.",2102.11117v1
2021-02-23,A fully-kinetic model for orphan gamma-ray flares in blazars,"Blazars emit a highly-variable non-thermal spectrum. It is usually assumed
that the same non-thermal electrons are responsible for the IR-optical-UV
emission (via synchrotron) and the gamma-ray emission (via inverse Compton).
Hence, the light curves in the two bands should be correlated. Orphan gamma-ray
flares (i.e., lacking a luminous low-frequency counterpart) challenge our
theoretical understanding of blazars. By means of large-scale two-dimensional
radiative particle-in-cell simulations, we show that orphan gamma-ray flares
may be a self-consistent by-product of particle energization in turbulent
magnetically-dominated pair plasmas. The energized particles produce the
gamma-ray flare by inverse Compton scattering an external radiation field,
while the synchrotron luminosity is heavily suppressed since the particles are
accelerated nearly along the direction of the local magnetic field. The ratio
of inverse Compton to synchrotron luminosity is sensitive to the initial
strength of turbulent fluctuations (a larger degree of turbulent fluctuations
weakens the anisotropy of the energized particles, thus increasing the
synchrotron luminosity). Our results show that the anisotropy of the
non-thermal particle population is key to modeling the blazar emission.",2102.11770v1
2021-02-26,Effective anisotropy of periodic acoustic and elastic composites,"The propagation of acoustic or elastic waves in artificial crystals,
including the case of phononic and sonic crystals, is inherently anisotropic.
As is known from the theory of periodic composites, anisotropy is directly
dictated by the space group of the unit cell of the crystal and the rank of the
elastic tensor. Here, we examine effective velocities in the long wavelength
limit of periodic acoustic and elastic composites as a function of the
direction of propagation. We derive explicit and efficient formulas for
estimating the effective velocity surfaces, based on second-order perturbation
theory, generalizing the Christofell equation for elastic waves in solids. We
identify strongly anisotropic sonic crystals for scalar acoustic waves and
strongly anisotropic phononic crystals for vector elastic waves. Furthermore,
we observe that under specific conditions, quasi-longitudinal waves can be made
much slower than shear waves propagating in the same direction.",2102.13506v1
2021-02-27,Covalent 2D Cr$_2$Te$_3$ ferromagnet,"To broaden the scope of van der Waals 2D magnets, we report the synthesis and
magnetism of covalent 2D magnetic Cr$_2$Te$_3$ with a thickness down to
one-unit-cell. The 2D Cr$_2$Te$_3$ crystals exhibit robust ferromagnetism with
a Curie temperature of 180 K, a large perpendicular anisotropy of 7*105 J m-3,
and a high coercivity of ~ 4.6 kG at 20 K. First-principles calculations
further show a transition from canted to collinear ferromagnetism, a transition
from perpendicular to in-plane anisotropy, and emergent half-metallic behavior
in atomically-thin Cr$_2$Te$_3$, suggesting its potential application for
injecting carriers with high spin polarization into spintronic devices.",2103.00339v1
2021-03-01,Multi-Messenger Astrophysics with the Cosmic Neutrino Background,"The massive neutrinos of the Cosmic Neutrino Background (C$\nu$B) are
fundamental ingredients of the radiation-dominated early universe and are
important non-relativistic probes of the large-scale structure formation in the
late universe. The dominant source of anisotropies in the neutrino flux
distribution on the sky are highly amplified integrals of metric perturbations
encountered during the non-relativistic phase of the C$\nu$B. This paper
numerically compares the line-of-sight methods for computing C$\nu$B
anisotropies with the Einstein-Boltzmann hierarchy solutions in linear theory
for a range of neutrino masses. Angular power spectra are computed that are
relevant to a future polarized tritium target run of the PTOLEMY experiment.
Correlations between the C$\nu$B sky maps and galactic survey data are derived
using line-of-sight techniques and discussed in the context of multi-messenger
astrophysics.",2103.01274v3
2021-03-05,Rubbing and Drawing: Generic Ways to Improve the Thermoelectric Power Factor of Organic Semiconductors?,"Highly oriented polymer films can show considerable anisotropy in the
thermoelectric properties leading to power factors beyond those predicted by
the widely obeyed power law linking the thermopower $S$ and the electrical
conductivity $\sigma$ as $S\propto\sigma^{-1/4}$. This has led to encouraging
practical results with respect to the electrical conductivity, notwithstanding
that the conditions necessary to enhance $\sigma$ and $S$ simultaneously are
less clear. Here, kinetic Monte Carlo simulations are used to study the impact
of structural anisotropy on the thermoelectric properties of disordered organic
semiconductors. We find that stretching is a suitable strategy to improve the
conductivity along the direction of strain, while the effect on the power
factor depends on the morphology the polymer crystallizes. In general,
crystalline polymers show a simultaneous increase in $\sigma$ and $S$ which is
not the case for amorphous polymers. Moreover, we show that the trends
resulting from simulations based on variable-range hopping are in good
agreement with experiments and can describe the different functional
dependencies in the $S$ versus $\sigma$ behaviour of different directions.",2103.03814v1
2021-03-10,New insights into star cluster evolution towards energy equipartition,"We present the results of a study aimed at exploring the evolution towards
energy equipartition in star cluster models with different initial degrees of
anisotropy in the velocity distribution. Our study reveals a number of novel
aspects of the cluster dynamics and shows that the rate of evolution towards
energy equipartition (1) depends on the initial degree of radial velocity
anisotropy -- it is more rapid for more radially anisotropic systems; and (2)
differs for the radial and the tangential components of the velocity
dispersion. (3) The outermost regions of the initially isotropic system evolve
towards a state of `inverted' energy equipartition in which high-mass stars
have a larger velocity dispersion than low-mass stars -- this inversion
originates from the mass-dependence of the tangential velocity dispersion
whereas the radial velocity dispersion shows no anomaly. Our results add new
fundamental elements to the theoretical framework needed to interpret the
wealth of recent and upcoming observational studies of stellar kinematics in
globular clusters, and shed further light on the link between the clusters'
internal kinematics, their formation and evolutionary history.",2103.06272v1
2021-03-11,"Giant rectification in segmented, strongly interacting, spin chains despite the presence of perturbations","In Phys. Rev. Lett. 120, 200603 (2018), a segmented XXZ spin chain with zero
anisotropy in one half and a large anisotropy on the other half gave rise to a
spin current rectification which is perfect in the thermodynamic limit. Here we
extend the previous study to segmented chains with interacting integrable as
well as non-integrable halves, considering even cases in which no ballistic
transport can emerge in either half. We demonstrate that, also in this more
general case, it is possible to obtain giant rectification when the two
interacting half chains are sufficiently different. We also show that the
mechanism causing this effect is the emergence of an energy gap in the
excitation spectrum of the out-of-equilibrium insulating steady state in one of
the two biases. Finally we demonstrate that in the thermodynamic limit there is
no perfect rectification when each of the two half chains is interacting.",2103.06750v2
2021-03-14,Transverse spin dynamics in the anisotropic Heisenberg model realized with ultracold atoms,"In Heisenberg models with exchange anisotropy, transverse spin components are
not conserved and can decay not only by transport, but also by dephasing. Here
we utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin
chains, and observe fast, local spin decay controlled by the anisotropy.
Additionally, we directly observe an effective magnetic field created by
superexchange which causes an inhomogeneous decay mechanism due to variations
of lattice depth between chains, as well as dephasing within each chain due to
the twofold reduction of the effective magnetic field at the edges of the
chains and due to fluctuations of the effective magnetic field in the presence
of mobile holes. The latter is a new coupling mechanism between holes and
magnons. All these dephasing mechanisms, corroborated by extensive numerical
simulations, have not been observed before with ultracold atoms and illustrate
basic properties of the underlying Hubbard model.",2103.07866v1
2021-03-14,Relaxation of Thermal Capillary Waves for Nanoscale Liquid Films on Anisotropic-slip Substrates,"The relaxation dynamics of thermal capillary waves for nanoscale liquid films
on anisotropic-slip substrates are investigated, using both molecular dynamics
(MD) simulations and a Langevin model. The anisotropy of slip on substrates is
achieved using a specific lattice plane of a face-centred cubic lattice. This
surface's anisotropy breaks the simple scalar proportionality between slip
velocity and wall shear stress and requires the introduction of a
slip-coefficient tensor. The Langevin equation can describe both the growth of
capillary wave spectra and the relaxation of capillary wave correlations, with
the former providing a time scale for the surface to reach thermal equilibrium.
Temporal correlations of interfacial Fourier modes, measured at thermal
equilibrium in MD, demonstrate that (i) larger slip lengths lead to a faster
decay in wave correlations, and (ii) unlike on isotropic-slip substrates, the
time correlations of waves on anisotropic-slip substrates are wave-direction
dependent. These findings emerge naturally from the proposed Langevin equation,
which becomes wave-direction dependent, agrees well with MD results, and allows
to produce experimentally-verifiable predictions.",2103.07965v2
2021-03-15,"Magnetic phase diagram of $A_{2}$[FeCl$_{5}$(H$_{2}$O)] ($A$ = K, Rb, NH$_{4}$)","Erythrosiderites with the formula A2FeX5H2O, where A = Rb, K, and (NH4) and X
= Cl and Br are intriguing systems that possess various magnetic and electric
phases, as well as multiferroic phases in which magnetism and ferroelectricity
are coupled. In this report, we study the magnetic phase diagram of
erythrosiderites as a function of superexchange interactions. To this end, we
perform classical Monte Carlo simulations on magnetic Hamiltonians that contain
five different superexchange interactions with single-ion anisotropies. Our
phase diagram contains all magnetic ground states that have been experimentally
observed in these materials. We argue that the ground states can be explained
by varying the ratio of J4/J2. For J4/J2 > 0.95 a cycloidal spins structure is
stabilized as observed in (NH4)2FeCl5H2O and otherwise, a collinear spin
structure is stabilized as observed in (K,Rb)2FeCl5H2O. We also show that the
difference in the single-ion anisotropy along a- and c- axes is essential to
stabilize the intermediate state observed in (NH)2FeCl5H2O.",2103.08500v2
2021-03-16,A non-local fluid closure for modeling cyclotron resonance in collisionless magnetized plasmas,"A fluid description for collisionless magnetized plasmas that takes into
account the effect of cyclotron resonance has been developed. Following the
same approach as the Landau fluid closure, the heat flux components associated
with transverse electromagnetic fluctuations are approximated by a linear
combination of lower-order moments in wavenumber space. The closure
successfully reproduces the linear cyclotron resonance for electromagnetic
waves propagating parallel to the ambient magnetic field. In the presence of
finite temperature anisotropy, the model gives approximately correct prediction
for an instability destabilized via the cyclotron resonance. A nonlinear
simulation demonstrates the wave growth consistent with the linear theory
followed by the reduction of initial anisotropy, and finally, the saturation of
the instability. The isotropization may be understood in terms of quasi-linear
theory, which is developed within the framework of the fluid model but very
similar to its fully kinetic counterpart. The result indicates that both linear
and nonlinear collisionless plasma responses are approximately incorporated in
the fluid model.",2103.08880v1
2021-03-16,Stress-induced modification of gyration dynamics in stacked double-vortex structures studied by micromagnetic simulations,"In this paper, using micromagnetic simulations, we investigate the
stress-induced frequency tunability of double-vortex nano-oscillators
comprising magnetostrictive and non-magnetostrictive ferromagnetic layers
separated vertically by a non-magnetic spacer. We show that the the relative
orientations of the vortex core polarities $p_{1}$ and $p_{2}$ have a strong
impact on the eigen-frequencies of the dynamic modes. When the two vortices
with antiparallel polarities have different eigen-frequencies and the
magnetostatic coupling between them is sufficiently strong, the stress-induced
magnetoelastic anisotropy can lead to the single-frequency gyration mode of the
two vortex cores. Additionally, for the case of parallel polarities, we
demonstrate that for sufficiently strong magnetostatic coupling, the
magnetoelastic anisotropy leads to the coupled vortex gyration in the
stochastic regime and to the lateral separation of the vortex core
trajectories. These findings offer a fine control over gyration frequencies and
trajectories in vortex-based oscillators via adjustable elastic stress, which
can be easily generated and tuned electrically, mechanically or optically.",2103.08940v2
2021-03-16,"Experimental properties of continuously-forced, shear-driven, stratified turbulence. Part 2. Energetics, anisotropy, parameterisation","In this Part 2 we study further experimental properties of two-layer exchange
flows in a stratified inclined duct (SID), which are turbulent,
strongly-stratified, shear-driven, and continuously-forced. We analyse the same
state-of-the-art data sets using the same core shear layer methodology as in
Part 1, but we focus here on turbulent energetics and mixing statistics. The
detailed analysis of kinetic and scalar energy budgets reveals the specificity
and scalings of SID turbulence, while energy spectra provide insight into the
current strengths and limitations of our experimental data. The anisotropy of
the flow at different scales characterises the turbulent kinetic energy
production and dissipation mechanisms of Holmboe waves and turbulence. We then
assess standard mixing parameterisations models relying on uniform eddy
diffusivities, mixing lengths, flux parameters, buoyancy Reynolds numbers or
turbulent Froude numbers, and we compare representative values with the
stratified mixing literature. The dependence of these measures of mixing on
controllable flow parameters is also elucidated, providing asymptotic estimates
that may be extrapolated to more strongly turbulent flows, quantified by the
product of the tilt angle of the duct and the Reynolds number. These insights
may serve as benchmark for the future generation of experimental data with
superior spatio-temporal resolution required to probe increasingly vigorous
turbulence.",2103.09193v1
2021-03-23,A Scenario for a Singularity-free Generic Cosmological Solution,"We develop a scenario for the emergence of a non-singular generic
cosmological solution based on the a WKB characterization of one of the two
anisotropy degrees of freedom. We investigate the dynamics of the so-called
inhomogeneous mixmaster in the ""corner"" configuration and inferring that one of
the two anisotropic variables becomes small enough to explore the uncertainty
principle. Then, we apply a standard WKB approximation to the dynamics of the
Universe which has macroscopic volume, one macroscopic anisotropy and one
microscopic quantum degree of freedom. Our study demonstrates the possibility
that the Universe acquires a non-singular classical behavior, retaining the
quantum degree of freedom as a small oscillating ripple on a stationary
Universe. The role of the so-called ""fragmentation process"" is also taken into
account in outlining the generality of such a behavior in independent local
space regions.",2103.12473v2
2021-03-23,Anisotropic relativistic fluid spheres with a linear equation of state,"In this work, we present a class of relativistic and well-behaved solution to
Einstein's field equations for anisotropic matter distribution. We perform our
analysis by using the Buchdahl ansatz for the metric function grr. Three
different classes of new exact solution are found for anisotropy factor(delta).
We have analyzed our model with various physical aspects such as pressure
(radial as well as transverse), energy density, anisotropy factor, mass,
compactness parameter, adiabatic index(gamma) and surface redshift. A graphical
analysis of energy conditions, TOV equation and causality condition indicates
the model are well behaved. The physical acceptability of the model has
verified by considering compact objects with similar mass and radii, such as 4U
1820-30,Vela X-1, PSR J1614-2230, LMC X-4, SMC X-1, 4U 1538-52, Her X-1, Cyg
X-2, PSR B1913+16 and PSR J1903+327.",2103.12583v2
2021-03-24,Effective strain manipulation of the antiferromagnetic state of polycrystalline NiO,"As a candidate material for applications such as magnetic memory,
polycrystalline antiferromagnets offer the same robustness to external magnetic
fields, THz spin dynamics, and lack of stray field as their single crystalline
counterparts, but without the limitation of epitaxial growth and lattice
matched substrates. Here, we first report the detection of the average Neel
vector orientiation in polycrystalline NiO via spin Hall magnetoresistance
(SMR). Secondly, by applying strain through a piezo-electric substrate, we
reduce the critical magnetic field required to reach a saturation of the SMR
signal, indicating a change of the anisotropy. Our results are consistent with
polycrystalline NiO exhibiting a positive sign of the in-plane
magnetostriction. This method of anisotropy-tuning offers an energy efficient,
on-chip alternative to manipulate a polycrystalline antiferromagnets magnetic
state.",2103.13105v1
2021-03-25,Constraints on the initial state of PbPb collisions via measurements of Z boson yields and azimuthal anisotropy at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV,"The CMS experiment at the LHC has measured the differential cross sections of
Z bosons decaying to pairs of leptons, as functions of transverse momentum and
rapidity, in lead-lead collisions at a nucleon-nucleon center-of-mass energy of
5.02 TeV. The measured Z boson elliptic azimuthal anisotropy coefficient is
compatible with zero, showing that Z bosons do not experience significant
final-state interactions in the medium produced in the collision. Yields of Z
bosons are compared to Glauber model predictions and are found to deviate from
these expectations in peripheral collisions, indicating the presence of initial
collision geometry and centrality selection effects. The precision of the
measurement allows, for the first time, for a data-driven determination of the
nucleon-nucleon integrated luminosity as a function of lead-lead centrality,
thereby eliminating the need for its estimation based on a Glauber model.",2103.14089v2
2021-03-26,Conjectures on Hidden Onsager Algebra Symmetries in Interacting Quantum Lattice Models,"We conjecture the existence of hidden Onsager algebra symmetries in two
interacting quantum integrable lattice models, i.e. spin-1/2 XXZ model and
spin-1 Zamolodchikov-Fateev model at arbitrary root of unity values of the
anisotropy. The conjectures relate the Onsager generators to the conserved
charges obtained from semi-cyclic transfer matrices. The conjectures are
motivated by two examples which are spin-1/2 XX model and spin-1 U(1)-invariant
clock model. A novel construction of the semi-cyclic transfer matrices of
spin-1 Zamolodchikov-Fateev model at arbitrary root of unity value of the
anisotropy is carried out via transfer matrix fusion procedure.",2103.14569v5
2021-04-10,Spin-Hall nanooscillator based on an antiferromagnetic domain wall,"We propose here a high-frequency spin-Hall nano-oscillator based on a simple
magnetic texture, such as a domain wall, located in an antiferromagnet with
easy-axis anisotropy type. We show that the spin current, polarized along the
anisotropy axis, excites a conical precession of the N\'eel vector in such a
domain wall, which allows obtaining a robust ac output signal, -- contrary to
the planar precession in an uniform uniaxial antiferromagnet, where ac output
is hard to achieve. The frequency of the auto-oscillations is easily tunable by
the applied current up to the THz range, and the threshold current vanishes for
pure uniaxial antiferromagnet. By micro-magnetic simulations, we demonstrate
that the pinning of the domain wall is crucial for the oscillator design, which
can be achieved in nano-constriction layout of the free layer.",2104.04780v3
2021-04-13,Considerations towards quantitative X-ray and neutron tensor tomography: on the validity of linear approximations of dark-field anisotropy,"The validity of two approximative linear tensor models to be used for grating
based X-ray or neutron dark-field tensor tomography is investigated in a
simulation study. While the dark-field contrast originating from anisotropic
microscopic mass distributions has, in a previous study, been confirmed to be
in general a non-linear function of two orientations (optical axis and axis of
interferometer sensitivity), linear approximations with a reduced parameter
space (considering only one of the orientation dependencies) are highly
preferable with respect to tomographic volume reconstruction from projections.
By regarding isolated volume elements and systematically exploring the full
range of possible anisotropies, direct correspondences are drawn between the
respective tensors characterizing the complete model used for signal
synthesization and the reduced linear models used for reconstruction. The
tensors' dominant orientations are found to agree to a typical accuracy of
1{\deg}, with their eigenspectra exhibiting fuzzy, yet almost linear relations
among each other. Although modeling only either of two orientation dependencies
for the purpose of tensor reconstruction, the data acquisition scheme must
nevertheless adequately address both dependencies.",2104.06235v1
2021-04-13,Tryptophan-containing proteins as label-free nanothermometers,"There remains a need for techniques to monitor thermal processes at high
spatiotemporal resolution, with myriad potential applications in chemistry,
biology, and engineering. Measurement of temperature from nanoscale molecular
phenomena are particularly promising due to their general compatibility with
biological systems. Among these phenomena, fluorescence polarization anisotropy
is particularly attractive due to its high sensitivity to thermal and
photophysical information, and its general utility with a wide spectrum of
fluorophores. In this work, we propose that the measurement of the intrinsic
fluorescence polarization anisotropy of tryptophan can be used to measure
label-free temperature at the nanoscale in a variety of tryptophan-containing
proteins. We present a theoretical model of the temperature sensitivity of
fluorescence polarization in free tryptophan and tryptophan-containing
proteins, empirically explore these properties, and discuss the potential
development of proteins as thermal memory sensors.",2104.06409v1
2021-04-14,Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interactions,"We identify a mechanism for magnetic field generation in the interaction of
intense electromagnetic waves and underdense plasmas. We show that Raman
scattered plasma waves trap and heat the electrons preferentially in their
propagation direction, resulting in a temperature anisotropy. In the trail of
the laser pulse, we observe magnetic field growth which matches the Weibel
mechanism due to the temperature anisotropy. We discuss the role of the initial
electron temperature in our results. The predictions are confirmed with
multi-dimensional particle-in-cell simulations. We show how this configuration
is an experimental platform to study the long-time evolution of the Weibel
instability.",2104.06734v1
2021-04-15,Origins of anisotropic transport in electrically-switchable antiferromagnet $\mathrm{Fe_1/3NbS_2}$,"Recent experiments on the antiferromagnetic intercalated transition metal
dichalcogenide $\mathrm{Fe_{1/3}NbS_2}$ have demonstrated reversible
resistivity switching by application of orthogonal current pulses below its
magnetic ordering temperature, making $\mathrm{Fe_{1/3}NbS_2}$ promising for
spintronics applications. Here, we perform density functional theory
calculations with Hubbard U corrections of the magnetic order, electronic
structure, and transport properties of crystalline $\mathrm{Fe_{1/3}NbS_2}$,
clarifying the origin of the different resistance states. The two
experimentally proposed antiferromagnetic ground states, corresponding to
in-plane stripe and zigzag ordering, are computed to be nearly degenerate.
In-plane cross sections of the calculated Fermi surfaces are anisotropic for
both magnetic orderings, with the degree of anisotropy sensitive to the Hubbard
U value. The in-plane resistance, computed within the Kubo linear response
formalism using a constant relaxation time approximation, is also anisotropic,
supporting a hypothesis that the current-induced resistance changes are due to
a repopulating of AFM domains. Our calculations indicate that the transport
anisotropy of $\mathrm{Fe_{1/3}NbS_2}$ in the zigzag phase is reduced relative
to stripe, consistent with the relative magnitudes of resistivity changes in
experiment. Finally, our calculations reveal the likely directionality of the
current-domain response, specifically, which domains are energetically
stabilized for a given current direction.",2104.07591v1
2021-04-18,Acceptability Conditions and Relativistic Anisotropic Generalized Polytropes,"This paper explored the physical acceptability conditions for anisotropic
matter configurations in General Relativity. The study considered a generalized
polytropic equation of state $P=\kappa {\rho}^{\gamma}+\alpha \rho -\beta$ for
a heuristic anisotropy. We integrated the corresponding Lane-Emden equation for
several hundred models and found the parameter-space portion ensuring the
configurations' acceptability. Polytrope based on the total energy density are
more stable than those with baryonic density, and small positive local
anisotropies produce acceptable models. We also found that polytropic
configurations where tangential pressures are greater than radial ones are also
more acceptable. Finally, convective disturbances do not generate cracking
instabilities. Several models emerging from our simulations could represent
candidate of astrophysical compact objects.",2104.08923v4
2021-04-22,Impact of Fe$_{80}$B$_{20}$ insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions,"We explore the impact of Fe80B20 inserted at both
Co$_{20}$Fe$_{80}$B$_{20}$/MgO interfaces of dual-MgO free layers (FLs) in
bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30
min at 350 $^\circ$C and 400 $^\circ$C in a vacuum after film deposition.
Current-in-plane tunneling measurements are carried out to characterize
magnetotransport properties of the MTJs. Conventional magnetometry measurements
and ferromagnetic resonance are conducted to estimate the saturation
magnetization, the effective perpendicular anisotropy field and the Gilbert
damping of dual-MgO FLs as a function of the Fe$_{80}$B$_{20}$ thickness and
annealing temperatures. With ultrathin Fe$_{80}$B$_{20}$ (0.2 - 0.4 nm)
inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar
tunnel magneto-resistance (TMR) and low damping values. As Fe$_{80}$B$_{20}$
layer thickness further increases (0.6 - 1.2 nm), both TMR and PMA degrade, and
damping increases dramatically. This study demonstrates a novel approach to
tune properties of MTJ stacks with dual-MgO FLs up to 400 $^\circ$C annealing,
which enables MTJ stacks for various applications.",2104.10918v1
2021-04-26,A Theoretical Framework for the Electrochemical Characterization of Anisotropic Micro-Emulsions,"Micro emulsions (MEs) offer an exceptionally broad spectrum of applications
covering sensing, electrosynthesis, supercapacitors and redox-flow batteries.
Herein, we develop the theory for a sophisticated electrochemical
characterizion of MEs with a spatially and time-invariant anisotropy in the
diffusion domain by means of cyclic voltammerty (CV). By introducing spatially
dependent diffusion coefficients into Ficks' first law, we derive a modified
diffusion equation to simulate any inherent anisotropy of the ME under
investigation. Moreover, by formulating an extended second-order homogeneous
six-member square scheme for a kinetically controlled two-step two-electron
reaction we capture the intricate entanglement of chemical and electrochemical
equilibria. Our theoretical concept is finally validated by experimental CV
data for the ME based two-step redox reaction of methyl-viologen which paves
the way for a quantitative electrochemical characterization MEs.",2104.12342v1
2021-04-28,Method for critical current angular dependencies analysis of superconducting tapes,"Various applications of superconducting materials require accounting of
anisotropy of the current-carrying capacity relative to magnetic field
direction - Ic({\theta}). However, today there is no sufficiently comprehensive
model that takes into account the anisotropy, therefore the angular dependences
are usually not analysed, but only described using various mathematical
formulas. As a result, the fitting parameters have no physical meaning and it
is difficult to correlate the picture with the features of the microstructure.
In this paper, we propose a method for analysing the critical current angular
dependences based on the anisotropic pinning model. The applicability of this
model for conventional superconducting Nb-Ti tapes with one peak in the Ic
({\theta}) dependence is shown. The possibility of extending this model to
analyse the angular dependences of HTS materials is discussed.",2104.13596v1
2021-04-28,Anisotropic Landau-Lifshitz Model in Discrete Space-Time,"We construct an integrable lattice model of classical interacting spins in
discrete space-time, representing a discrete-time analogue of the lattice
Landau-Lifshitz ferromagnet with uniaxial anisotropy. As an application we use
this explicit discrete symplectic integration scheme to compute the spin Drude
weight and diffusion constant as functions of anisotropy and chemical
potential. We demonstrate qualitatively different behavior in the easy-axis and
the easy-plane regimes in the non-magnetized sector. Upon approaching the
isotropic point we also find an algebraic divergence of the diffusion constant,
signaling a crossover to spin superdiffusion.",2104.13863v3
2021-04-28,Thermal diffusivity and its lower bound in orthorhombic SnSe,"The orthorhombic monochalcogenide SnSe has attracted much attention in recent
years as a promising high-temperature thermoelectric material. We present a
study of its thermal conductivity and specific heat of SnSe between 2~K and
300~K and quantify its anisotropic thermal diffusivity, $D$. For both
crystallographic orientations, thermal diffusivity remains above the recently
identified Planckian limit ($D > v_s^2 \tau_P$, where $v_s$ is the sound
velocity and $\tau_P= \hbar/k_BT$) and its anisotropy in $D$ is set by the
anisotropy of $v_s$. Comparison with cubic members of the IV-VI family leads to
a consistent picture, where the diffusivity in all members of the family is set
by the product of v$_s$, $\tau_P$ and the 'melting' velocity derived from the
melting temperature.",2104.13994v2
2021-04-29,Nano-patterning of surfaces by ion sputtering: Numerical study of the anisotropic damped Kuramoto-Sivashinsky equation,"Nonlinear models for pattern evolution by ion beam sputtering on a material
surface present an ongoing opportunity for new numerical simulations. A
numerical analysis of the evolution of preexisting patterns is proposed to
investigate surface dynamics, based on a 2D anisotropic damped
Kuramoto-Sivashinsky equation, with periodic boundary conditions. A
finite-difference semi-implicit time splitting scheme is employed on the
discretization of the governing equation. Simulations were conducted with
realistic coefficients related to physical parameters (anisotropies, beam
orientation, diffusion). The stability of the numerical scheme is analyzed with
time step and grid spacing tests for the pattern evolution, and the Method of
Manufactured Solutions has been used to verify the proposed scheme. Ripples and
hexagonal patterns were obtained from a monomodal initial condition for certain
values of the damping coefficient, while spatiotemporal chaos appeared for
lower values. The anisotropy effects on pattern formation were studied, varying
the angle of incidence of the ion beam with respect to the irradiated surface.
Analytical discussions are based on linear and weakly nonlinear analysis.",2104.14104v1
2021-04-29,Directional Dependence of the Electronic and Transport Properties of 2D Monolayer Orthorhombic Diboron Dinitride (o-B2N2): DFT coupled with NEGF Study,"Tuning two dimensional nanomaterial's structural and electronic properties
has facilitated the new research paradigm in electronic device applications. In
this work, the first principles density functional theory based methods are
used to investigate the structural, electronic, and transport properties of an
orthorhombic diboron dinitride based polymorph. Interestingly, it depicts a low
band gap semiconducting nature with a robust anisotropic behaviour compared to
the hexagonal boron nitride, which is an insulator and isotropic. We can also
tune the structural and electronic properties of the semiconducting B2N2 based
structure through an external inplane mechanical strain. Further, by employing
the Landauer Buttiker approach, the electronic transmission function, and
electric current calculations reveal that the diboron dinitride based polymorph
shows a robust direction dependent anisotropy of the quantum transport
properties. We have demonstrated the direction dependence of the electric
current in two perpendicular directions, where we have observed an electric
current ratio of around 61.75 at 0.8 V. All these findings, such as directional
dependence anisotropy in transmission function, current voltage
characteristics, and bandgap tunning, suggest that the applicability of such
B2N2 based monolayer can be promising for futuristic electronic device
applications.",2104.14369v1
2021-04-29,Direct photons emission rate and electric conductivity in twice anisotropic QGP holographic model with first-order phase transition,"The electric conductivity and direct photons emission rate are considered in
the holographic theory with two types of anisotropy. The electric conductivity
is derived in two different ways, and their equivalence for the twice
anisotropic theory is shown. Numerical calculations of the electric
conductivity were done for Einstein-dilaton-three-Maxwell holographic model
[29]. The dependence of the conductivity on the temperature, the chemical
potential, the external magnetic field, and the spatial anisotropy of the
heavy-ions collision (HIC) is studied. The electric conductivity jumps near the
first-order phase transition are observed. This effect is similar to the jumps
of holographic entanglement that were studied previously.",2104.14582v3
2021-04-30,Control of stripe domain wall magnetization in perpendicular anisotropy multilayers,"We report on the controlled switching of domain wall (DW) magnetization in
aligned stripe domain structures, stabilized in [Co (0.44 nm)/Pt (0.7 nm)]$_X$
($X = 48$, 100, 150) multilayers with perpendicular magnetic anisotropy. The
switching process, induced by an external magnetic field, is monitored by
measuring the evolution of the in-plane magnetization. % We show that the
remanent in-plane magnetization originates from the polarization of the
Bloch-type DWs. With micromagnetic simulations, we reveal that the reversal of
the DW polarization is the result of the emergence and collapse of horizontal
Bloch lines within the DWs at particular strengths of the external magnetic
field, applied opposite to the DW polarization. Our findings are relevant for
DW-based magnonics and bubble skyrmion applications in magnetic multilayers.",2104.14934v1
2021-05-09,Sensing Strain-induced Symmetry Breaking by Reflectance Anisotropy Spectroscopy,"Intentional breaking of the lattice symmetry in solids is a key concept to
alter the properties of materials by modifying their electronic band structure.
However, the correlation of strain-induced effects and breaking of the lattice
symmetry is often indirect, resorting to vibrational spectroscopic techniques
such as Raman scattering. Here, we demonstrate that reflectance anisotropy
spectroscopy (RAS), which directly depends on the complex dielectric function,
enables the direct observation of electronic band structure modulation.
Studying the strain-induced symmetry breaking in copper, we show how uniaxial
strain lifts the degeneracy of states in the proximity of the both L and X
symmetry points, thus altering the matrix element for interband optical
transitions, directly observable in RAS. We corroborate our experimental
results by analysing the strain-induced changes in the electronic structure
based on ab-initio density functional theory calculations. The versatility to
study breaking of the lattice symmetry by simple reflectance measurements opens
up the possibility to gain a direct insight on the band-structure of other
strain-engineered materials, such as graphene and two-dimensional (2D)
transition metal dichalcogenides (TMDCs).",2105.03846v3
2021-05-10,Robust magnetic anisotropy of a monolayer of hexacoordinate Fe( ii ) complexes assembled on Cu(111),"The tris pyrazolyl borate ligand imposes a rigid scaffold around Fe( ii )
ensuring a robust magnetic anisotropy when the molecules assembled as
monolayers suffer from the dissymmetric environment of the substrate/vacuum
interface.",2105.04199v1
2021-05-11,Strength and energy consumption of inherently anisotropic rocks at failure,"Using a discrete-element approach and a bonding interaction law, we model and
test crushable inherently anisotropic structures reminiscent of the layering
found in sedimentary and metamorphic rocks. By systematically modifying the
level of inherent anisotropy, we characterize the evolution of the failure
strength of circular rock samples discretized using a modified Voronoi
tesselation under diametral point loading at different orientations relative to
the sample's layers. We characterize the failure strength, which can
dramatically increase as the loading becomes orthogonal to the rock layers. We
also describe the evolution of the macroscopic failure modes as a function of
the loading orientation and the energy consumption at fissuring. Our simulation
strategy let us conclude that the length of bonds between Voronoi cells
controls the energy being consumed in fissuring the rock sample, although
failure modes and strength are considerably changing. We end up this work
showing that the microstructure is largely afected by the level of inherent
anisotropy and loading orientation.",2105.05288v1
2021-05-14,Yu-Shiba-Rusinov states in real metals,"Theoretical descriptions of Yu-Shiba-Rusinov (YSR) states induced by magnetic
impurities inside the gap of a superconductor typically rely on a classical
spin model or are restricted to spin-1/2 quantum spins. These models fail to
account for important aspects of YSR states induced by transition-metal
impurities, including the effects of higher quantum spins coupled to several
conduction-electron channels, crystal or ligand-field effects, and magnetic
anisotropy. We introduce and explore a zero-bandwidth model, which incorporates
these aspects, is readily solved numerically, and analytically tractable in
several limiting cases. The principal simplification of the model is to neglect
Kondo renormalizations of the exchange couplings between impurity spin and
conduction electrons. Nevertheless, we find excellent correspondence in those
cases, in which we can compare our results to existing
numerical-renormalization-group calculations. We apply the model to obtain and
understand phase diagrams as a function of pairing strength and magnetic
anisotropy as well as subgap excitation spectra. The single-channel case is
most relevant for transition-metal impurities embedded into metallic
coordination complexes on superconducting substrates, while the multi-channel
case models transition-metal adatoms.",2105.06651v1
2021-05-16,Anatomy of inertial magnons in ferromagnets,"We analyze dispersion relations of magnons in ferromagnetic nanostructures
with uniaxial anisotropy taking into account inertial terms, i.e. magnetic
nutation. Inertial effects are parametrized by damping-independent parameter
$\beta$, which allows for an unambiguous discrimination of inertial effects
from Gilbert damping parameter $\alpha$. The analysis of magnon dispersion
relation shows its two branches are modified by the inertial effect, albeit in
different ways. The upper nutation branch starts at $\omega=1/ \beta$, the
lower branch coincides with FMR in the long-wavelength limit and deviates from
the zero-inertia parabolic dependence $\simeq\omega_{FMR}+Dk^2$ of the exchange
magnon. Taking a realistic experimental geometry of magnetic thin films,
nanowires and nanodiscs, magnon eigenfrequencies, eigenvectors and $Q$-factors
are found to depend on the shape anisotropy. The possibility of phase-matched
magneto-elastic excitation of nutation magnons is discussed and the condition
was found to depend on $\beta$, exchange stiffness $D$ and the acoustic
velocity.",2105.07376v1
2021-05-17,Contact force measurements and local anisotropy in ellipses and disks,"Experimental measurements of contact forces are limited to spheres and disks
in three and two dimensions, making the evaluation of the shape effect and
universality of force distributions and the comparison between experiments and
theories extremely difficult. Here we present precise measurements of vector
contact forces in photoelastic ellipses and disks subject to isotropic
compression and pure shear. We find the local, instead of the global, stress
ratio, control the width of the force distributions for forces larger than the
mean, regardless of the particle shape and preparation protocols. By taking
advantage of the anisotropic particle shape, we can determine the anisotropic
growth of contacts in ellipses subject to isotropic compression, revealing the
role of non-affine particle motions in homogenizing force distributions. Our
results uncover the role of local anisotropy in the statistical framework of
granular materials and open a new regime of exploring the role of particle
shape on the mechanical and dynamical properties of granular materials in
depth.",2105.07607v2
2021-05-19,"Rashba-type Dzyaloshinskii-Moriya interaction, perpendicular magnetic anisotropy and skyrmion states at 2D materials/Co interfaces","We report a significant Dzyaloshinskii-Moriya interaction (DMI) and
perpendicular magnetic anisotropy (PMA) at interfaces comprising hexagonal
boron nitride (h-BN) and Co. By comparing the behavior of these phenomena at
graphene/Co and h-BN/Co interfaces, it is found that the DMI in latter
increases as a function of Co thickness and beyond three monolayers stabilizes
with one order of magnitude larger values compared to those at graphene/Co,
where the DMI shows opposite decreasing behavior. At the same time, the PMA for
both systems shows similar trends with larger values for graphene/Co and no
significant variations for all thickness ranges of Co. Furthermore, using
micromagnetic simulations we demonstrate that such significant DMI and PMA
values remaining stable over large range of Co thickness give rise to formation
of skyrmions with small applied external fields in the range of 200-250 mT up
to 100 K temperatures. These findings open up further possibilities towards
integrating two-dimensional (2D) materials in spin-orbitronics devices.",2105.09015v1
2021-05-19,Structural and Morphological Effect of Ti underlayer on Pt/Co/Pt Magnetic Ultra-Thin Film,"Pt(x{\AA})/Co(5{\AA})/Pt(10{\AA}) trilayer films were deposited on naturally
oxidized Si(111) substrate to investigate Ti underlayer effect on PMA. A small
amount of Ti underlayer promoted the magnetic anisotropy to a perpendicular
direction for x=8{\AA} and 10{\AA}. Both GI XRD and STM results showed that the
Ti underlayer manipulated the growth of trilayer film. The Pt particles
preferably grow the neighborhood of the Ti cluster, giving rise to a relatively
smooth layer with a fiber texture fcc (111) structure. By contrast, the absence
of Ti underlayer leads to clustered, relatively rough, and randomly oriented
nano-crystalline growth. Differences in the growth mode, especially roughness,
also appeared as intensity loss in XPS spectra due to shadowing effects. Our
results indicate that a traceable amount of underlayer can change the magnetic
anisotropy of the film by manipulating film growth.",2105.09355v1
2021-04-25,Implementation of two-field inflation for cosmic linear anisotropy solving system,"We outline the modifications in the numerical Boltzmann code Cosmic Linear
Anisotropy Solving System (CLASS) in order to include extra inflationary
fields. The functioning of the code is first described, how and where
modifications are meant to be done are later explained. In the present study,
we focus on the modifications needed for the implementation of a two-field
inflationary model, with canonical kinetic terms and a polynomial potential
with no cross terms, presenting preliminary results for the effect of the
second field on the spectra. The adaptability of the code is exploited, making
use of the classes and structures of C and the generic Runge-Kutta integration
tool provided by the program.",2105.09747v1
2021-05-22,Spin Seebeck effect of correlated magnetic molecules,"In this paper we investigate the spin-resolved thermoelectric properties of
strongly correlated molecular junctions in the linear response regime. The
magnetic molecule is modeled by a single orbital level to which the molecular
core spin is attached by an exchange interaction. Using the numerical
renormalization group method we analyze the behavior of the (spin) Seebeck
effect, heat conductance and figure of merit for different model parameters of
the molecule. We show that the thermopower strongly depends on the strength and
type of the exchange interaction as well as the molecule's magnetic anisotropy.
When the molecule is coupled to ferromagnetic leads, the thermoelectric
properties reveal an interplay between the spin-resolved tunneling processes
and intrinsic magnetic properties of the molecule. Moreover, in the case of
finite spin accumulation in the leads, the system exhibits the spin Seebeck
effect. We demonstrate that a considerable spin Seebeck effect can develop when
the molecule exhibits an easy-plane magnetic anisotropy, while the sign of the
spin thermopower depends on the type and magnitude of the molecule's exchange
interaction.",2105.10713v1
2021-05-26,Antiferromagnetic magnons and local anisotropy: dynamical mean-field study,"We present a dynamical mean-field study of antiferromagnetic magnons in one-,
two- and three-orbital Hubbard model of square and bcc cubic lattice at
intermediate coupling strength. Weinvestigate the effect of anisotropy
introduced by an external magnetic field or single-ion anisotropy.For the
latter we tune continuously between the easy-axis and easy-plane models. We
also analyzea model with spin-orbit coupling in cubic site-symmetry setting.
The ordered states as well as themagnetic excitations are sensitive to even a
small breaking ofSU(2)symmetry of the model andfollow the expectations of
spin-wave theory as well as general symmetry considerations.",2105.12468v2
2021-05-27,Numerical method for the equilibrium configurations of a Maier-Saupe bulk potential in a Q-tensor model of an anisotropic nematic liquid crystal,"We present a numerical method, based on a tensor order parameter description
of a nematic phase, that allows fully anisotropic elasticity. Our method thus
extends the Landau-de Gennes $\mathbf{Q}$-tensor theory to anisotropic phases.
A microscopic model of the nematogen is introduced (the Maier-Saupe potential
in the case discussed in this paper), combined with a constraint on eigenvalue
bounds of $\mathbf{Q}$. This ensures a physically valid order parameter
$\mathbf{Q}$ (i.e., the eigenvalue bounds are maintained), while allowing for
more general gradient energy densities that can include cubic nonlinearities,
and therefore elastic anisotropy. We demonstrate the method in two specific two
dimensional examples in which the Landau-de Gennes model including elastic
anisotropy is known to fail, as well as in three dimensions for the cases of a
hedgehog point defect, a disclination line, and a disclination ring. The
details of the numerical implementation are also discussed.",2105.13317v1
2021-05-28,Strange star with Krori-Barua potential in presence of anisotropy,"In present paper a well-behaved new model of anisotropic compact star in
(3+1)-dimensional spacetime has been investigated in the background of
Einstein's general theory of relativity. The model has been developed by
choosing $g_rr$ component as Krori-Barua (KB) ansatz [Krori and Barua in J.
Phys. A, Math. Gen. 8:508, 1975]. The field equations have been solved by a
proper choice of the anisotropy factor which is physically reasonable and well
behaved inside the stellar interior. Interior spacetime has been matched
smoothly to the exterior Schwarzschild vacuum solution and it has also been
depicted graphically. Model is free from all types of singularities and is in
static equilibrium under different forces acting on the system. The stability
of the model has been tested with the help of various conditions available in
literature. The solution is compatible with observed masses and radii of a few
compact stars.",2105.15143v1
2021-06-01,Topological spin textures in chiral magnets on the honeycomb lattice with magnetic fields,"Topological spin textures, like skyrmions, have significant potential for
spintronics applications. The main purpose of this work is to study further the
topological spin textures on the discrete lattice with magnetic fields. In this
work, we study a classical rotated Heisenberg model with Dzyaloshinskii-Moriya
interaction, bond-dependent anisotropy and easy-axis anisotropy on the
honeycomb lattice via Monte Carlo simulations. We mainly focus on phase
diagrams with magnetic fields, especially on the non-trivial phases only
existing with fields. The results demonstrate the emergence of field-induced
incommensurate skyrmion superlattice including mixed skyrmion-bimeron states,
ferromagnetic star, vortex and z-vortex superlattice. We systematically analyze
structures of these topological spin textures through spin configurations,
structure factors, topological charge and vector chirality. We hope that our
results could be useful for the identification of topological phases
experimentally.",2106.00207v3
2021-06-01,CMB anisotropies and linear matter power spectrum in models with non-thermal neutrinos and primordial magnetic fields,"Angular power spectra of temperature anisotropies and polarization of the
cosmic microwave background (CMB) as well as the linear matter power spectra
are calculated for models with three light neutrinos with non-thermal
phase-space distributions in the presence of a primordial stochastic magnetic
field. The non-thermal phase-space distribution function is assumed to be the
sum of a Fermi-Dirac and a gaussian distribution. It is found that the known
effective description of the non-thermal model in terms of a twin thermal model
with extra relativistic degrees of freedom can also be extended to models
including a stochastic magnetic field. Numerical solutions are obtained for a
range of magnetic field parameters.",2106.00648v2
2021-06-04,Cross-correlating Astrophysical and Cosmological Gravitational Wave Backgrounds with the Cosmic Microwave Background,"General Relativity provides us with an extremely powerful tool to extract at
the same time astrophysical and cosmological information from the Stochastic
Gravitational Wave Backgrounds (SGWBs): the cross-correlation with other
cosmological tracers, since their anisotropies share a common origin and the
same perturbed geodesics. In this letter we explore the cross-correlation of
the cosmological and astrophysical SGWBs with Cosmic Microwave Background (CMB)
anisotropies, showing that future GW detectors, such as LISA or BBO, have the
ability to measure such cross-correlation signals. We also present, as a new
tool in this context, constrained realization maps of the SGWBs extracted from
the high-resolution CMB {\it Planck} maps. This technique allows, in the
low-noise regime, to faithfully reconstruct the expected SGWB map by starting
from CMB measurements.",2106.02591v2
2021-06-05,Heat rectification by two qubits coupled with Dzyaloshinskii-Moriya interaction,"We investigate heat rectification in a two-qubit system coupled via the
Dzyaloshinskii-Moriya (DM) interaction. We derive analytical expressions for
heat currents and thermal rectification and provide possible physical
mechanisms behind the observed results. We show that the anisotropy of DM
interaction in itself is insufficient for heat rectification, and some other
form of asymmetry is needed. We employ off-resonant qubits as the source of
this asymmetry. We find the regime of parameters for higher rectification
factors by examining the analytical expressions of rectification obtained from
a global master equation solution. In addition, it is shown that the direction
and quality of rectification can be controlled via various system parameters.
Furthermore, we compare the influence of different orientations of the DM field
anisotropy on the performance of heat rectification. Finally, we investigate
the possible interplay between quantum correlations and the performance of the
quantum thermal rectifier. We find that asymmetry in the coherences is a
fundamental resource for the performance of the quantum thermal rectifier.",2106.02891v3
2021-06-07,Crystal field effects in the zig-zag chain compound SrTm$_2$O$_4$,"The single ion properties of the zig-zag chain compound SrTm$_2$O$_4$ have
been investigated using heat capacity, magnetic susceptibility, magnetization,
inelastic neutron scattering, and polarized muon spectroscopy. Two crystal
field models are employed to estimate the single ion properties; a Density
Function Theory based model and an effective charge model based on the
Hutchings point charge model. The latter describes our experimental results
well. This model estimates an easy-axis anisotropy for one of the Tm$^{3+}$
sites and an easy-plane anisotropy for the second site. It also predicts a
mixed ground state with dominating $J = 0$ characteristics for both sites.
Additionally, muon spin rotation/relaxation ($\mu^+$SR) spectra reveal
oscillations, typically a sign of long-range magnetic order. However, the
temperature dependence of the precession frequency and the relaxation rates
indicate that the system is in an extended critical regime and the observed
relaxation is actually dynamic.",2106.03704v3
2021-06-09,A 2D front-tracking Lagrangian model for the modeling of anisotropic grain growth,"Grain growth is a well-known and complex phenomenon occurring during
annealing of all polycrystalline materials. Its numerical modeling is a complex
task when anisotropy sources such as grain orientation and grain boundary
inclination have to be taken into account. This article presents the
application of the front-tracking methodology ToRealMotion introduced in
previous works, to the context of anisotropic grain boundary motion at the
mesoscopic scale. The new formulation of boundary migration can take into
account any source of anisotropy both at grain boundaries as well as at
multiple junctions (MJs) (intersection point of three or more grain
boundaries). Special attention is given to the decomposition of high-order MJs
for which an algorithm is proposed based on local grain boundary energy
minimisation. Numerical tests are provided using highly heterogeneous
configurations, and comparisons with a recently developed Finite-Element
Level-Set (FE-LS) approach are given. Finally, the computational performance of
the model will be studied comparing the CPU-times obtained with the same model
but in an isotropic context.",2106.04892v2
2021-06-13,Theory of anisotropic superfluid He-4 counterflow turbulence,"We develop an analytic theory of strong anisotropy of the energy spectra in
the thermally-driven turbulent counterflow of superfluid He-4. The key
ingredients of the theory are the three-dimensional differential closure for
the vector of the energy flux and the anisotropy of the mutual friction force.
We suggest an approximate analytic solution of the resulting energy-rate
equation, which is fully supported by the numerical solution. The
two-dimensional energy spectrum is strongly confined in the direction of the
counterflow velocity. In agreement with the experiment, the energy spectra in
the direction orthogonal to the counterflow exhibit two scaling ranges: a
near-classical non-universal cascade-dominated range and a universal critical
regime at large wavenumbers. The theory predicts the dependence of various
details of the spectra and the transition to the universal critical regime on
the flow parameters.
  This article is a part of the theme issue 'Scaling the turbulence edifice'.",2106.07014v1
2021-06-15,Magnetic properties and phase diagrams of the ferrimagnetic triangular nanotube with core-shell structure: A Monte Carlo study,"Monte Carlo simulation has been employed to investigate the magnetic
properties and phase diagrams of ferrimagnetic mixed-spin (1/2, 1) triangular
Ising nanotube with core-shell structure. In particular, the effect of the
exchange couplings and the temperature on the magnetic and thermodynamic
properties, hysteresis loops as well as the compensation temperature have been
discussed in detail. Moreover, the effects of the single-ion anisotropy, as
well as external magnetic field, have been examined. The threshold values of
the exchange couplings and single-ion anisotropy have been found, determining
whether the system exhibits a compensation temperature. We have found that the
appearance of the compensation temperature is strongly linked with the system
parameters. Moreover, we have obtained the double and triple hysteresis loops
for certain physical parameters in the considered magnetic system.",2106.08397v1
2021-06-20,In-plane anisotropic quantum confinement effect in ultrasmall SnS sheets,"Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as
an attractive building block for electronic devices due to its highly
anisotropic response. Two-dimensional (2D) SnS has shown to exhibit in-plane
anisotropy in optical and electrical properties. However, the limitations in
growing ultrasmall structures of SnS hinder the experimental exploration of
anisotropic behavior in low dimension. Here, we present an elegant approach of
synthesizing highly crystalline nanometer-sized SnS sheets. Ultrasmall SnS
exhibits two distinct valleys along armchair and zig-zag directions due to
in-plane structural anisotropy like bulk SnS. We show that in such SnS
nanosheet dots, the band gaps corresponding to two valleys are increased due to
quantum confinement effect. We particularly observe that SnS quantum dots (QDs)
show excitation energy dependent photoluminescence (PL), which originates from
the two nondegenerate valleys. Our work may open up an avenue to show the
potential of SnS QDs for new functionalities in electronics and
optoelectronics.",2106.10763v1
2021-06-24,Redshift-space fluctuations in stochastic gravitational wave background,"We study the redshift-space fluctuations induced by a stochastic
gravitational wave background (SGWB) via the Sachs-Wolfe effect. The
redshift-space fluctuations can be encapsulated in a line-of-sight integral
that is useful for studying the imprint of short-wavelength gravitational waves
on the cosmic microwave background (CMB) anisotropy. We thus derive constraints
on the SGWB from small-scale CMB anisotropy measurements. Our results reproduce
the constraint on the short-wavelength SGWB, previously derived from the Planck
and BICEP/Keck array CMB data with a CMB Boltzmann numerical code. Furthermore,
we improve the constraint and extend it to shorter wavelengths by using the CMB
measurements made by the Atacama Cosmology Telescope and the South Pole
Telescope. Also, the integral provides us with a precise redshift fluctuation
correlation between a pair of pulsars in pulsar timing measurements, which
conveniently incorporates the effect of the pulsar term into a small-angle
correlation. We further discuss the observation of pulsar pairs in globular
clusters to look for this small-angle correlation.",2106.12843v3
2021-06-30,Confined Magnons,"Magnetic structures are known to possess magnon excitations confined to their
surfaces and interfaces, but these spatially localized modes are often not
resolved in spectroscopy experiments. We develop a theory to calculate the
confined magnon spectra and its associated spin scattering function, which is
the physical observable in neutron and electron scattering, and a proxy for
photon spectroscopy based on X-ray, Raman and THz sources. We show that extra
anisotropy at the surface or interface plays a key role in magnon confinement.
We obtain analytical expressions for the confinement length scale, and show
that it is qualitatively similar for ferromagnets and antiferromagnets in
dimension d>=2. For d=1 we find remarkable differences between ferromagnetic
and antiferromagnetic models. The theory indicates the presence of several
confined magnon resonances in addition to the usual magnons thought to explain
the excitations of magnetic nanostructures. Detecting these modes may elucidate
the impact of the interface on spin anisotropy and magnetic order.",2106.15771v2
2021-07-01,"Anisotropic Upper Critical Field, Seebeck and Nernst Coefficient in Nb0.20Bi2Se3 Topological Superconductor","We present the magneto-transport and the thermoelectric (Seebeck and Nernst
coefficient) studies of the Nb-doped Bi2Se3 topological superconductor. The
angle-dependent magnetoresistance study highlights the anisotropy in the upper
critical field (Hc2) with the anisotropy parameter Gamma ~1.2. We observed a
gradual decrease in low-temperature Hall resistivity on the application of
magnetic field like any conventional superconductor, instead of the finite Hall
resistivity which was linked to the chiral superconducting phase. The estimated
value of the carrier concentration (~ 10^19 cm-3) for Nb0.2Bi2Se3 is one order
larger than for Bi2Se3. Doping of Nb shows a significant decrease in the
Seebeck coefficient value and the estimated Fermi temperature of the
three-dimensional Fermi surface at the centre of Brillouin zone in the
zero-temperature limit enhances by ~4 times in comparison to pristine Bi2Se3.
We have observed a large value (~2.3 micro V K-1 T-1) of Nernst coefficient for
Bi2Se3 at room temperature which decreases with Nb doping ( ~0.5 micro V K-1
T-1).",2107.00432v1
2021-07-02,Deformation mechanisms of Mg-Ca-Zn alloys studied by means of micropillar compression tests,"The effect of Ca and Zn in solid solution on the critical resolved shear
stress (CRSS) of <a> basal slip, tensile twinning and <c+a> pyramidal slip in
Mg alloys has been measured through compression tests on single crystal
micropillars with different orientations. The solute atoms increased the CRSS
for basal slip to ~ 13.5 MPa, while the CRSS for pyramidal slip was lower than
85 MPa, reducing significantly the plastic anisotropy in comparison with pure
Mg. Moreover, the CRSSs for twin nucleation and growth were very similar (~ 37
MPa) and the large value of the CRSS for twin growth hindered the growth of
twins during thermo-mechanical processing. Finally, evidence of <a> prismatic
slip and cross-slip between basal and prismatic dislocations was found. It is
concluded that the reduction of plastic anisotropy, the activation of different
slip systems and cross-slip and the weak basal texture promoted by the large
CRSS for twin growth are responsible for the improved ductility and formability
of Mg-Ca-Zn alloys.",2107.00878v1
2021-07-08,Chiral domain wall dynamics in magnetic heterostructures with bulk Dzyaloshinskii-Moriya interactions,"In this work, dynamics of chiral domain walls in long and narrow magnetic
heterostructures based on non-centrosymmetric chiral magnets with bulk
Dzyaloshinskii-Moriya interactions (DMI) and perpendicular magnetic anisotropy
is systematically investigated. The driving forces can be out-of-plane magnetic
fields and in-plane currents, correspondingly both steady and precessional
flows are considered. Their dividing points (the Walker critical field and
current density) are obtained as functions of bulk DMI strength
($D_{\mathrm{b}}$) and the ratio ($\kappa$) of total (crystalline plus shape)
anisotropy in the hard axis over that in the easy one. When far beyond Walker
breakdown, the dependence curve of wall velocity on external in-plane bias
field takes parabolic shape around the compensation point where the total
in-plane field disappears. The center shift is determined by $D_{\mathrm{b}}$,
$\kappa$, and the wall's topological charge, thus can be used to measure the
bulk DMI strength in chiral magnets.",2107.03586v1
2021-07-10,The field-angle anisotropy of proximate Kitaev systems under an in-plane magnetic field,"We have investigated the field-angle behaviors of magnetic excitations under
an in-plane magnetic field for proximate Kitaev systems. By employing the exact
diagonalization method in conjunction with the linear spin wave theory, we have
demonstrated that the magnetic excitation gap in the polarized phase is
determined by the magnon excitation at $M$ points and has a strong anisotropy
with respect to the field direction in the vicinity of the critical field
limit. The specific heat from this magnon excitation bears qualitatively the
same anisotropic behaviors as expected one for the non-Abelian spin liquid
phase in the Kitaev model and experimentally observed one of the intermediate
phases in $\alpha$-RuCl$_3$.",2107.04785v2
2021-07-17,Magnetic anisotropy and critical behavior of the quaternary van der Waals ferromagnetic material $\bf CrGe_δSi_{1-δ}Te_3$,"Recently, two-dimensional ferromagnetism in the family of Chromium compounds
$\rm CrXTe_3 (X=Si, Ge)$ has attracted a broad research interest. Despite the
structural similarity in $\rm CrTe_6$ octahedra, the size effect of inserted Ge
or Si dimer contributes to significant differences in magnetism. Here, we
report a new quaternary van der Waals ferromagnetic material $\rm
CrGe_{\delta}Si_{1-\delta}Te_3$ synthesized by flux method. Ge substitution in
Si site results in the lattice expansion, further increasing the Curie
temperature and reducing the magnetic anisotropy. The critical behavior of $\rm
Cr_{0.96}Ge_{0.17}Si_{0.82}Te_3$ has been studied by specific heat as well as
magnetization measurements. And the extracted critical exponents are
self-consistent and well-obeying the scaling laws, which are closer to the 2D
Ising model with interaction decaying as $J(r)\approx r^{-3.44}$.",2107.08222v1
2021-07-17,Collective modes in anisotropic plasmas,"We study collective modes in anisotropic plasmas of quarks and gluons using a
quasi-particle picture and a hard loop approximation. We use a general class of
anisotropic distribution functions, and we consider chirally asymmetric
systems. We introduce a complete tensor basis to decompose the gluon
polarization tensor into a set of nine scalar functions. We derive and solve
the corresponding dispersion equations. Imaginary modes are particularly
important because of their potential influence on plasma dynamics. We explore
in detail their dependence on the chiral chemical potential and the parameters
that characterise the anisotropy of the system. We show that our generalized
distributions produce dispersion relations that are much richer in structure
than those obtained with a simple one parameter deformation of an isotropic
distribution. In addition, the size and domain of the imaginary solutions are
enhanced, relative to those obtained with a one parameter deformation. Finally,
we show that the influence of even a very small chiral chemical potential is
significantly magnified when anisotropy is present.",2107.08229v2
2021-07-23,Two-body Wigner molecularization in asymmetric quantum dot spin qubits,"Coulomb interactions strongly influence the spectrum and the wave functions
of few electrons or holes confined in a quantum dot. In particular, when the
confinement potential is not too strong, the Coulomb repulsion triggers the
formation of a correlated state, the Wigner molecule, where the particles tend
to split apart. We show that the anisotropy of the confinement potential
strongly enhances the molecularization process and affects the performances of
quantum-dot systems used as spin qubits. Relying on analytical and numerical
solutions of the two-particle problem -- both in a simplified single-band
approximation and in realistic setups -- we highlight the exponential
suppression of the singlet-triplet gap with increasing anisotropy. We compare
the molecularization effects in different semiconductor materials and discuss
how they specifically hamper Pauli spin blockade readout and reduce the
exchange interactions in two-qubit gates.",2107.11117v2
2021-07-23,Supershear surface waves reveal prestress and anisotropy of soft materials,"Surface waves play important roles in many fundamental and applied areas from
seismic detection to material characterizations. Supershear surface waves with
propagation speeds greater than bulk shear waves have recently been reported,
but their properties are not well understood. In this Letter, we describe
theoretical and experimental results on supershear surface waves in rubbery
materials. We find that supershear surface waves can be supported in
viscoelastic materials with no restriction on the shear quality factor.
Interestingly, the effect of prestress on the speed of the supershear surface
wave is opposite to that of the Rayleigh surface wave. Furthermore, anisotropy
of material affects the supershear wave much more strongly than the Rayleigh
surface wave. We offer heuristic interpretation as well as theoretical
verification of our experimental observations. Our work points to the potential
applications of supershear waves for characterizing the bulk mechanical
properties of soft solid from the free surface.",2107.11482v1
2021-07-29,Fine structure of the nonlinear Drude weights in the spin-1/2 XXZ chain,"We study nonlinear Drude weights (NLDWs) for the spin-1/2 XXZ chain in the
critical regime at zero temperature. The NLDWs are generalizations of the
linear Drude weight. Via the nonlinear extension of the Kohn formula, they can
be read off from higher-order finite-size corrections to the ground-state
energy in the presence of a $U(1)$ magnetic flux. The analysis of the
ground-state energy based on the Bethe ansatz reveals that the NLDWs exhibit
convergence, power-law, and logarithmic divergence, depending on the anisotropy
parameter $\Delta$. We determine the convergent and power-law divergent
regions, which depend on the order of the response $n$. Then, we examine the
behavior of the NLDWs at the boundary between the two regions and find that
they converge for $n=0, 1, 2$ $({\rm mod}~4)$, while they show logarithmic
divergence for $n=3$ $({\rm mod}~4)$. Furthermore, we identify particular
anisotropies $\Delta=\cos(\pi r/(r+1))$ ($r=1,2, 3,\ldots$) at which the NLDW
at any order $n$ converges to a finite value.",2107.13784v3
2021-07-31,Constant-roll $f(R)$ inflation compared with Cosmic Microwave Background anisotropies and swampland criteria,"Inflationary models derived from $f(R)$ gravity, where the scalaron rolls
down with a constant rate from the top to the minimum of the effective
potential, are considered. Specifically, we take into account three $f(R)$
models \textit{i.e.}\,Starobinsky $R^{2}$, $R^{2p}$ and the logarithmic
corrected models. We compare the inflationary parameters derived from the
models with the observational data of CMB anisotropies \textit{i.e.} the Planck
and Keck/array datasets in order to find observational constraints on the
parameters space. We find that although our $f(R)$ constant-roll models for
$\gamma=0$ show observationally acceptable values of $r$, they do not predict
favoured values of the spectral index. In particular, we have $n_{s}>1$ for the
Starobinsky $R^{2}$ and $R^{2p}$ models and $0.996<n_{s}<0.999$ for logarithmic
model. Finally, we study the models from the point of view of Weak Gravity
Conjecture adopting the swampland criteria.",2108.00175v2
2021-08-09,First-principles based simulations of electronic transmission in ReS$_{2}$/WSe$_{2}$ and ReS$_{2}$/MoSe$_{2}$ type-II vdW heterointerfaces,"Electronic transmission in monolayer ReS$_{2}$ and ReS$_{2}$ based van der
Waals (vdW) heterointerfaces are studied here. Since ReS$_{2}$/WSe$_{2}$ and
ReS$_{2}$/MoSe$_{2}$ type-II vdW heterostructures are suitable for near
infrared (NIR)/short-wave infrared (SWIR) photodetection, the role of
interlayer coupling at the heterointerfaces is examined in this work. Besides,
a detailed theoretical study is presented employing density functional theory
(DFT) and nonequilibrium Green's function (NEGF) combination to analyse the
transmission spectra of the two-port devices with ReS$_{2}$/WSe$_{2}$ and
ReS$_{2}$/MoSe$_{2}$ channels and compare the near-equilibrium conductance
values.Single layer distorted1T ReS$_{2}$ exhibits formation of parallel chains
of 'Re' - 'Re' bonds, leading to in-plane anisotropy. Owing to this structural
anisotropy, the charge carrier transport is very much orientation dependent in
ReS$_{2}$. Therefore, this work is further extended to investigate the role of
clusterized 'Re' atoms in electronic transmission.",2108.04341v1
2021-08-13,Model of the thermoelectric properties of anisotropic organic semiconductors,"A model of charge hopping transport that accounts for anisotropy of localized
states and Coulomb interaction between charges is proposed. For the anisotropic
localized states the degree of orientation relates exponentially to the ratio
of conductivities in parallel and perpendicular directions, while the ratio of
Seebeck coefficients stays nearly unaffected. However, the ratio of Seebeck
coefficients increases if Coulomb interaction is screened stronger in a
direction parallel to the predominant orientation of the localized states. This
implies two different physical mechanisms responsible for the anisotropy of
thermoelectric properties in the hopping regime: electronic state localization
for conductivities, and screening for Seebeck coefficients. This provides
explanation for recent experimental findings on tensile drawn and ribbed
polymer films.",2108.06097v2
2021-08-18,Magnetoelastic coupling enabled tunability of magnon spin current generation in 2D antiferromagnets,"We theoretically investigate the magnetoelastic coupling (MEC) and its effect
on magnon transport in two-dimensional antiferromagnets with a honeycomb
lattice. MEC coeffcient along with magnetic exchange parameters and spring
constants are computed for monolayers of transition metal trichalcogenides with
N\'eel order ($\text{MnPS}_3$ and $\text{VPS}_3$) and zigzag order
($\text{CrSiTe}_3$, $\text{NiPS}_3$ and $\text{NiPSe}_3$) by $ab$ $initio$
calculations. Using these parameters, we predict that the spin-Nernst
coefficient is significantly enhanced due to magnetoelastic coupling. Our study
shows that although Dzyaloshinskii-Moriya interaction can produce spin Nernst
effect in these materials, other mechanisms such as magnon-phonon coupling
should be taken into account. We also demonstrate that the magnetic anisotropy
is an important factor for control of magnon-phonon hybridization and
enhancement of the Berry curvature and thus the spin-Nernst coefficient. Our
results pave the way towards gate tunable spin current generation in 2D magnets
by SNE via electric field modulation of MEC and anisotropy.",2108.07999v1
2021-08-24,Engineering Purcell factor anisotropy for dark and bright excitons in two dimensional semiconductors,"Tightly bound dark excitons in atomically thin semiconductors can be used for
various optoelectronic applications including light storage and quantum
communication. Their optical accessibility is however limited due to their
out-of-plane transition dipole moment. We thus propose to strengthen the
coupling of dark excitons in two dimensional materials with out-of-plane
resonant modes of a cavity at room temperature, by engineering the anisotropy
in the Purcell factor. A silica micro-disk characterised by high confinement of
light in small modal volume, high Q-factor and free spectral range is used to
couple to the excitons in monolayer transition metal dichalcogenides. We show
numerically that the tapering of sidewalls of the micro-disk is an extremely
versatile route for achieving the selective coupling of whispering gallery
modes to light emitted from out-of-plane dipoles to the detriment of that from
in-plane ones for four representative monolayer transition metal
dichalcogenides.",2108.10680v1
2021-08-25,Pump-induced terahertz anisotropy in bilayer graphene,"We investigate the intraband nonlinear dynamics in doped bilayer graphene in
the presence of strong, linearly-polarized, in-plane terahertz fields. We
perform degenerate pump-probe experiments with 3.4 THz fields on doped bilayer
graphene at low temperature (12 K) and find that when the pump is co-polarized
with the probe beam, the differential pump-probe signal is almost double that
found in the cross-polarized case. We show that the origin of this pump-induced
anisotropy is the difference in the average electron effective mass in the
probe direction when carriers are displaced in k-space by the pump either
parallel or perpendicular to the direction of the probe polarization. We model
the system using both a simple semiclassical model and a Boltzmann equation
simulation of the electron dynamics with phenomenological scattering and find
good qualitative agreement with experimental results.",2108.11183v3
2021-09-01,Anisotropic Stars in 4D Einstein-Gauss-Bonnet Gravity,"The current trend concerning dense matter physics at sufficiently high
densities and low temperatures is expected to behave as a degenerate Fermi gas
of quarks forming Cooper pairs, namely a color superconductor, in the core of
compact objects. In this context, we study the anisotropy of quark stars (QSs)
assuming the internal composition to be comprised of homogeneous, charge
neutral 3-flavor interacting quark matter with $\mathcal{O}(m_s^4)$
corrections. Using the equation of state (EoS) with the
Tolmann-Oppenheimer-Volkoff (TOV) structure equations, we perform numerical
calculation for quark stars and determine the maximum mass-radius relation in
the context of $4D$ Einstein-Gauss-Bonnet (EGB) gravity. In particular, we
consider the effects of Gauss-Bonnet (GB) coupling constant on the diagrams
related to mass-radius $(M-R)$ relation and the mass-central mass density
$(M-\rho_c)$ relation of QSs. We pay particular attention to the influence of
the anisotropy in the equilibrium and stability of strange stars. We also study
the other properties of QSs related to compactness and binding energy.
Interestingly, our result provides circumstantial evidence in favor of
super-massive pulsars in $4D$ EGB gravity.",2109.00195v1
2021-09-06,Pitch Angle Anisotropy Controls Particle Acceleration and Cooling in Radiative Relativistic Plasma Turbulence,"Nature's most powerful high-energy sources are capable of accelerating
particles to high energy and radiate it away on extremely short timescales,
even shorter than the light crossing time of the system. It is yet unclear what
physical processes can produce such an efficient acceleration, despite the
copious radiative losses. By means of radiative particle-in-cell simulations,
we show that magnetically dominated turbulence in pair plasmas subject to
strong synchrotron cooling generates a nonthermal particle spectrum with a hard
power-law range (slope $p \sim 1$) within a few eddy turnover times. Low
pitch-angle particles can significantly exceed the nominal radiation-reaction
limit, before abruptly cooling down. The particle spectrum becomes even harder
($p < 1$) over time owing to particle cooling with an energy-dependent
pitch-angle anisotropy. The resulting synchrotron spectrum is hard ($\nu F_\nu
\propto \nu^s$ with $s \sim 1$). Our findings have important implications for
understanding the nonthermal emission from high-energy astrophysical sources,
most notably the prompt phase of gamma-ray bursts and gamma-ray flares from the
Crab nebula.",2109.02666v1
2021-09-09,Adjustable 3D magnetic configuration in ferrimagnetic multilayers with competing interactions visualized by soft X-ray vector tomography,"Soft X-ray magnetic vector tomography has been used to visualize with
unprecedented detail and solely from experimental data the 3D magnetic
configuration of a ferrimagnetic Gd12Co88/Nd17Co83/Gd24Co76 multilayer with
competing anisotropy, exchange and magnetostatic interactions at different
depths. The trilayer displays magnetic stripe domains, arranged in a chevron
pattern, which are imprinted from the central Nd17Co83 into the bottom Gd12Co88
layer with a distorted closure domain structure across the thickness. Near the
top Gd24Co76 layer, local exchange springs with out-of-plane magnetization
reversal, modulated ripple patterns and magnetic vortices and antivortices
across the thickness are observed. The detailed analysis of the magnetic
tomogram shows that the effective strength of the exchange spring at the
NdCo/GdCo interface can be finely tuned by GdxCo1-x composition and anisotropy
(determined by sample fabrication) and in-plane stripe orientation
(adjustable), demonstrating the capability of 3D magnetic visualization
techniques in magnetic engineering research.",2109.04064v1
2021-09-13,Pseudospin-Triplet Pairing in Iron-Chalcogenide Superconductors,"We study superconductivity of electron systems with both spin and
pseudospin-1/2 degrees of freedom. By solving linearized gap equations, we
derive a weak coupling criterion for the even-parity spin-singlet
pseudospin-triplet pairing. It can generally mix with the on-site s-wave
pairing since both of them belong to the same symmetry representation
($A_{1g}$) and their mixture could naturally give rise to anisotropic
intra-band pairing gap functions with or without nodes. This may directly
explain why some of the iron-chalcogenide superconductors are fully gapped
(e.g. FeSe thin film) and some have nodes (e.g. LaFePO and LiFeP). We also find
that the anisotropy of gap functions can be enhanced when the principal
rotation symmetry is spontaneously broken in the normal state such as
nematicity, and the energetic stabilization of pseudospin-triplet pairings
indicates the coexistence of nematicity and superconductivity. This could be
potentially applied to bulk FeSe, where gap anisotropy has been experimentally
observed.",2109.06039v4
2021-09-15,Turbulent magneto-genesis in a collisionless plasma,"We investigate an efficient mechanism for generating magnetic fields in
turbulent, collisionless plasmas. By using fully kinetic, particle-in-cell
simulations of an initially non-magnetized plasma, we inspect the genesis of
magnetization, in a nonlinear regime. The complex motion is initiated via a
Taylor-Green vortex, and the plasma locally develops strong electron
temperature anisotropy, due to the strain tensor of the turbulent flow.
Subsequently, in a domino effect, the anisotropy triggers a Weibel instability,
localized in space. In such active wave-particle interaction regions, the
magnetic field seed grows exponentially and spreads to larger scales due to the
interaction with the underlying stirring motion. Such a self-feeding process
might explain magneto-genesis in a variety of astrophysical plasmas, wherever
turbulence is present.",2109.07432v1
2021-09-16,Dynamics of microstructure anisotropy and rheology of soft jammed suspensions,"We explore the rheology predicted by a recently proposed constitutive model
for jammed suspensions of soft elastic particles derived from particle-level
dynamics [Cuny et al., Phys. Rev. Lett. 127, 218003 (2021)]. Our model predicts
that the orientation of the anisotropy of the microstructure, governed by an
interplay between advection and contact elasticity, plays a key role at
yielding and in flow. It generates normal stress differences contributing
significantly to the yield criterion and Trouton ratio. It gives rise to
non-trivial transients such as stress overshoots in step increases of shear
rate, residual stresses after flow cessation and power-law decay of the shear
rate in creep. Finally, it explains the collapse of storage modulus as measured
in parallel superposition for a yielded suspension.",2109.07786v2
2021-09-20,Random magnetic anisotropy in a new compound $\mbox{Sm}_2\mbox{Ag}\mbox{Si}_3$,"We report the experimental study on the structural and magnetic properties of
a new ternary intermetallic compound $\mathrm{Sm_2AgSi_3}$. The properties of
the sample were investigated in detail by X-ray diffraction, dc-magnetization,
and heat capacity measurements. The polycrystalline compound of
$\mathrm{Sm_2AgSi_3}$ crystallizes in the $\mathrm{ThSi_2}$-type tetragonal
structure (space group ${I_{4_1}/amd}$). The temperature-dependent
dc-magnetization and heat capacity results demonstrate that the compound
undergoes ferromagnetic behaviour with a Curie temperature ($T_C$) of 14 K. The
large coercive field in hysteresis loops and the thermomagnetic irreversibility
in the ferromagnetic region revealed that the compound exhibits a large
magnetic anisotropy. The magnitude of the applied field and the coercivity
obtained from the M-H loops corroborate with the thermomagnetic irreversibility
in the magnetization data. The magnetic contribution of the heat capacity
reveals a broad Schottky-type anomaly above $T_C$, due to the presence of the
crystal electric field effect of $\mathrm{Sm^{3+}}$ in $\mathrm{Sm_2AgSi_3}$.",2109.09608v1
2021-09-21,Analysis of the directionality on periodic materials,"There is an increasing interest in the study of metamaterials and periodic
materials across disciplines. These are anisotropic and their properties
present directionality. For example, the wave speed depends on the propagation
direction. Furthermore, they are heterogeneous, and their directionality
depends on their spectra. Common approaches to describe anisotropy have been
used in the large-wavelength approximation corresponding to static properties.
Here we present an anisotropy measure based on the dynamic behavior. It
receives dispersion surfaces from Bloch analyses and outputs a curve/surface
with bulk directionality encoded on it. We present results for elastodynamics,
but it is applicable to other phenomena.",2109.09893v4
2021-09-21,Influence of a spatial anisotropy on presence of the intermediate one-half magnetization plateau of a spin-1/2 Ising-Heisenberg branched chain,"A spin-1/2 Ising-Heisenberg branched chain constituted by regularly
alternating Ising spins and Heisenberg dimers involving an additional side
branching is exactly solved in a magnetic field by the transfer-matrix method.
The spin-1/2 Ising-Heisenberg branched chain involves two different Ising and
one Heisenberg coupling constants. The overall ground-state phase diagram is
formed by three different ground states emergent depending on a mutual
interplay between the magnetic field and three considered coupling constants:
the modulated quantum antiferromagnetic phase, the quantum ferrimagnetic phase,
and the classical ferromagnetic phase. It is shown that the interaction
anisotropy connected to two different Ising coupling constants substantially
influences a breakdown of the intermediate one-half magnetization plateau,
which represents a macroscopic manifestation of the quantum ferrimagnetic
phase.",2109.10026v1
2021-09-22,Zero Poisson' s Ratio and Suppressed Mechanical Anisotropy in BP/SnSe Van der Waals Heterostructure: A First-principles Study,"Black phosphorene and its analogs have attracted intensive attention due to
their unique puckered structures, anisotropic characteristics, and negative
Poisson's ratio. The van der Waals heterostructures assembly by stacking
different materials may show novel physical properties which the parent
materials don't possess. In this work, the first-principles calculations were
performed to study the mechanical properties of the BP/SnSe van der Waals
heterostructure. Interestingly, a near-zero Poisson's ratio vzx was found in
BP/SnSe heterostructure. In addition, compared to the parent materials BP and
SnSe with strong in-plane anisotropic mechanical properties, the BP/SnSe
heterostructure shows strongly suppressed anisotropy. Our findings suggest that
the vdW heterostructure could show quite different mechanical properties from
the parent materials and provide new opportunities for the mechanical
applications of the heterostructures.",2109.10494v1
2021-09-27,Magnetization tunable Weyl states in EuB6,"The interplay between magnetism and topological band structure offers
extraordinary opportunities to realize rich exotic magnetic topological phases
such as axion insulators, Weyl semimetals, and quantum anomalous Hall
insulators, which therefore has attracted fast growing research interest. The
rare-earth hexaborides EuB6 represents an interesting magnetic topological
phase with tunable magnetizations along different crystallographic directions,
while the correlation with the topological properties remains scarcely
explored. In this work, combining magnetotransport measurements and first
principles calculations, we demonstrate that EuB6 exhibits versatile magnetic
topological phases along different crystallographic directions, which tightly
correlate with the varied magnetizations. Moreover, by virtue of the weak
magneto-crystalline anisotropy and the relatively strong coupling between the
local magnetization and the conduction electrons, we show that the magnetic
ground state of the system can be directly probed by the anisotropy in the
magnetotransport properties. Our work thus introduces an excellent platform to
study the rich topological phases that are tunable by magnetic orders.",2109.12823v1
2021-10-03,Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics,"Through First-Principles real-time Density-Matrix (FPDM) dynamics
simulations, we investigate spin relaxation due to electron-phonon and
electron-impurity scatterings with spin-orbit coupling in two-dimensional Dirac
materials - silicene and germanene, at finite temperatures and under external
fields. We discussed the applicability of conventional descriptions of spin
relaxation mechanisms by Elliott-Yafet (EY) and D'yakonov-Perel' (DP) compared
to our FPDM method, which is determined by a complex interplay of intrinsic
spin-orbit coupling, external fields, and electron-phonon coupling strength,
beyond crystal symmetry. For example, the electric field dependence of spin
relaxation time is close to DP mechanism for silicene at room temperature, but
rather similar to EY mechanism for germanene. Due to its stronger spin-orbit
coupling strength and buckled structure in sharp contrast to graphene,
germanene has a giant spin lifetime anisotropy and spin valley locking effect
under nonzero Ez and relatively low temperature. More importantly, germanene
has extremely long spin lifetime (~100 ns at 50 K) and ultrahigh carrier
mobility, which makes it advantageous for spin-valleytronic applications.",2110.01128v1
2021-10-04,Anomalous temperature dependence of phonon pumping by ferromagnetic resonance in Co/Pd multilayers with perpendicular anisotropy,"We demonstrate the pumping of phonons by ferromagnetic resonance in a series
of [Co(0.8 nm)/Pd(1.5 nm)]$_n$ multilayers ($n =$ 6, 11, 15, and 20) with large
magnetostriction and perpendicular magnetic anisotropy. The effect is shown
using broadband ferromagnetic resonance over a range of temperatures (10 to 300
K), where a resonant damping enhancement is observed at frequencies
corresponding to standing wave phonons across the multilayer. The strength of
this effect is enhanced by approximately a factor of 4 at 10 K compared to room
temperature, which is anomalous in the sense that the temperature dependence of
the magnetostriction predicts an enhancement that is less than a factor of 2.
Lastly, we demonstrate that the damping enhancement is correlated with a shift
in the ferromagnetic resonance field as predicted quantitatively from linear
response theory.",2110.01714v1
2021-10-05,The impact of defects on excitations in two-dimensional bipartite uniaxial antiferromagnet insulators,"We address scatterings of spin waves off uncorrelated defects in
two-dimensional (2D) easy-axis antiferromagnet (AFM) insulators. Although an
onsite magnetic anisotropy leads gapped Goldstone modes, such that a long range
(AFM) order can be established in 2D, lattice imperfections tend to weaken, and
eventually destroy the magnetic ordering. Here, the impact of defects is
considered within two limits, single and multiple defects. Using Green's
function, we perform self consistent simulations to study magnon properties
such as density of states and lifetime of induced resonances. Our findings show
that repulsive defects decrease the magnon density of states while attractive
ones may enhance it. We provide a comprehensive analysis of how defects can
result in a reduction and even closing, the anisotropy induced gap, which
weakens the long range (AFM) order parameter in the 2D state. We conclude that
a small concentration of random defects can fill the gap of magnon spectrum.",2110.02045v3
2021-10-06,Current-Perpendicular-to-Plane Giant Magnetoresistance Effect in van der Waals Heterostructures,"Spin-dependent transport in a full van der Waals (vdW) giant
magnetoresistance (GMR) junctions with the structure of Fe3GeTe2/XTe2/Fe3GeTe2
(X = Pt, Pd) has been investigated by using first-principles calculations. The
ballistic conductance, magnetoresistance (MR) and resistance-area product (RA)
have been calculated in a current-perpendicular-to-plane (CPP) geometry. A
giant magnetoresistance of around 2000% and RA less than 0.3 {\Omega} {\mu}m2
have been found in the proposed vdW CPP GMR. In addition, the spin-orbit
coupling effect on transport and anisotropy magnetoresistance (AMR) has also
been investigated. The calculated AMR is found to be around 20% in
Fe3GeTe2/trilayer-PdTe2/Fe3GeTe2 CPP GMR. Both GMR and AMR in the proposed vdW
CPP GMR mainly originate from the bulk electronic structure properties of
Fe3GeTe2. This work demonstrates a vdW CPP GMR with superior advantages
including perpendicular magnetic anisotropy, large GMR, low RA as well as
sizable AMR may stimulate future experimental explorations and should be
appealing for their applications in spintronic devices including magnetic
sensor and memory.",2110.02535v1
2021-10-12,Primordial black hole formation for an anisotropic perfect fluid: Initial conditions and estimation of the threshold,"This work investigates the formation of primordial black holes within a
radiation fluid with an anisotropic pressure. We focus our attention on the
initial conditions describing cosmological perturbations in the super horizon
regime, using a covariant form of the equation of state in terms of pressure
and energy density gradients. The effect of the anisotropy is to modify the
initial shape of the cosmological perturbations with respect to the isotropic
case. Using the dependence of the threshold $\delta_\mathrm{c}$ for primordial
black holes with respect to the shape of cosmological perturbations, we
estimate here how the threshold is varying with respect to the amplitude of the
anisotropy. If this variation is large enough it could lead to a significant
variation of the abundance of PBHs.",2110.05982v4
2021-10-13,Generalized plasma waves in layered superconductors,"In a layered and strongly anisotropic superconductor the hybrid modes
provided by the propagation of electromagnetic waves in the matter identify two
well separate energy scales connected to the large in-plane plasma frequency
and to the soft out-of-plane Josephson plasmon. Despite the wide interest in
their detection and manipulation by means of different experimental protocols,
a unified description of plasma waves valid at arbitrary energy and momentum is
still lacking. Here we provide a complete description of generalized plasma
waves in a layered superconductors by taking advantage of their connection to
the gauge-invariant superconducting phase. We show that the anisotropy of the
superfluid response leads to two intertwined hybrid light-matter modes with
mixed longitudinal and transverse character, while a purely longitudinal
plasmon is only recovered for wavevectors larger than the crossover scale set
in by the plasma-frequencies anisotropy. Interestingly, below such scale both
modes appears with equal weight in the physical density response. Our results
open a promising perspective for plasmonic applications made possible by the
next-generation spectroscopic techniques able to combine sub-micron momentum
resolution with THz energy resolution.",2110.06772v1
2021-10-15,Effects of Quantum Pair Creation and Annihilation on a Classical Exclusion Process: the transverse XY model with TASEP,"We investigate how particle pair creation and annihilation, within the
quantum transverse XY model, affects the non-equilibrium steady state (NESS)
and Liouvillian gap of the stochastic Totally Asymmetric Exclusion Process
(TASEP). By utilising operator quantization we formulate a perturbative
description of the NESS. Furthermore, we estimate the Liouvillian gap by
exploiting a Majorana canonical basis as the basis of super-operators. In this
manner we show that the Liouvillian gap can remain finite in the thermodynamic
limit provided the XY model anisotropy parameter remains non-zero.
Additionally, we show that the character of the gap with respect to the
anisotropy parameter differs depending on the phase of the XY model. The change
of character corresponds to the quantum phase transition of the XY model.",2110.08283v1
2021-10-19,Ising and XY paramagnons in two-dimensional 2H-NbSe$_2$,"Paramagnons are the collective modes that govern the spin response of nearly
magnetic conductors. In some cases they mediate electron pairing leading to
superconductivity. This scenario may occur in 2H-NbSe$_2$ monolayers, that
feature spin-valley coupling on account of spin-orbit interactions and their
lack of inversion symmetry. Here we explore spin anisotropy of paramagnons both
for non-centrosymmetric Kane-Mele-Hubbard models for 2H-NbSe$_2$ monolayers
described with a DFT-derived tight-binding model. In the infinite wavelength
limit we find spatially uniform paramagnons with energies around $1$~meV that
feature a colossal off-plane uniaxial magnetic anisotropy, with quenched
transversal spin response. At finite wave vectors, longitudinal and transverse
channels reverse roles: XY fluctuations dominate within a significant portion
of the Brillouin zone. Our results show that 2H-NbSe$_2$ is close to a
Coulomb-driven in-plane (XY) spin density wave instability.",2110.09809v2
2021-10-28,Curved Magnetism in CrI$_3$,"Curved magnets attract considerable interest for their unusually rich phase
diagram, often encompassing exotic (e.g., topological or chiral) spin states.
Micromagnetic simulations are playing a central role in the theoretical
understanding of such phenomena; their predictive power, however, rests on the
availability of reliable model parameters to describe a given material or
nanostructure. Here we demonstrate how non-collinear-spin polarized
density-functional theory can be used to determine the flexomagnetic coupling
coefficients in real systems. By focusing on monolayer CrI$_3$, we find a
crossover as a function of curvature between a magnetization normal to the
surface to a cycloidal state, which we rationalize in terms of effective
anisotropy and Dzyaloshinskii-Moriya contributions to the magnetic energy. Our
results reveal an unexpectedly large impact of spin-orbit interactions on the
curvature-induced anisotropy, which we discuss in the context of existing
phenomenological models.",2110.15088v3
2021-10-29,Transport and spectral properties of the XX$+$XXZ diode and stability to dephasing,"We study the transport and spectral property of a segmented diode formed by
an XX $+$ XXZ spin chain. This system has been shown to become an ideal
rectifier for spin current for large enough anisotropy. Here we show numerical
evidence that the system in reverse bias has three different transport regimes
depending on the value of the anisotropy: ballistic, diffusive and insulating.
In forward bias we encounter two regimes, ballistic and diffusive. The system
in forward and reverse bias shows significantly different spectral properties,
with distribution of rapidities converging towards different functions. In the
presence of dephasing the system becomes diffusive, rectification is
significantly reduced, the relaxation gap increases and the spectral properties
in forward and reverse bias tend to converge. For large dephasing the
relaxation gap decreases again as a result of Quantum Zeno physics.",2110.15564v3
2021-11-05,Temperature-driven transition from skyrmion to bubble crystals in centrosymmetric itinerant magnets,"Interplay between itinerant electrons and localized spins in itinerant
magnets gives rise to a variety of noncoplanar multiple-$Q$ spin textures, such
as the skyrmion, hedgehog, meron, and vortex. We elucidate that another type of
multiple-$Q$ state consisting of collinear sinusoidal waves, a magnetic bubble
crystal, appears at finite temperatures in a centrosymmetric itinerant electron
system. The results are obtained for the classical Kondo lattice model with
easy-axis single-ion anisotropy on a triangular lattice by a large-scale
numerical simulation. We find that a finite-temperature topological phase
transition between the skyrmion crystal and the bubble crystal occurs by
changing the temperature. We obtain the minimal key ingredients for inducing
the finite-temperature transition by analyzing an effective spin model where it
is shown that the synergy between the multiple-spin interaction and magnetic
anisotropy plays a significant role.",2111.03202v1
2021-11-05,Transverse momentum broadening in real-time lattice simulations of the glasma,"The study of jets in heavy-ion collisions provides important information
about the interaction of partons with the medium that they traverse. The seeds
of jets are highly energetic partons, which are produced from hard scatterings
during the collision event. As such, they are affected by all different stages
of the medium's time evolution, including the glasma, which is the
pre-equilibrium precursor state of the quark-gluon plasma. Here we report on
our numerical lattice simulations of partons traversing the boost-invariant,
non-perturbative glasma as created at the early stages of collisions at RHIC
and LHC. We find that partons quickly accumulate transverse momentum up to the
saturation momentum during the glasma stage. Furthermore, we observe an
interesting anisotropy in transverse momentum broadening of partons with larger
broadening in the rapidity than in the azimuthal direction. Its origin can be
related to correlations among the longitudinal color-electric and
color-magnetic flux tubes in the initial state of the glasma. We compare these
observations to the semi-analytic results obtained by a weak-field
approximation, where we also find such an anisotropy in a parton's transverse
momentum broadening.",2111.03400v1
2021-11-11,$60^{\circ}$ and $120^{\circ}$ Domain Walls in Epitaxial BaTiO$_{3}$(111)/Co Multiferroic Heterostructures,"We report on domain pattern transfer from a ferroelectric
BaTiO$_{\mathrm{3}}$ substrate with a $(111)$-orientation of the surface to an
epitaxial Co film grown on a Pd buffer layer. Spatially modulated interfacial
strain transfer from ferroelectric/ferroelastic domains and inverse
magnetostriction in the ferromagnetic film induce stripe regions with a
modulation of the in-plane uniaxial magnetic anisotropy direction. Using
spin-polarized low energy electron microscopy, we observe the formation of two
distinct anisotropy configurations between stripe regions. Moreover, through
application of a magnetic field parallel or perpendicular to these stripes,
head-to-head or head-to-tail magnetization configurations are initialized. This
results in four distinct magnetic domain wall types associated with different
energies and widths, which in turn affects whether domain pattern transfer can
be achieved.",2111.06191v1
2021-11-11,Scale dependent anisotropy of electric field fluctuations in solar wind turbulence,"We study the variation of average powers and spectral indices of electric
field fluctuations with respect to the angle between average flow direction and
the mean magnetic field in solar wind turbulence. Cluster spacecraft data from
the years 2002 and 2007 are used for the present analysis. We perform a scale
dependent study with respect to the local mean magnetic field using wavelet
analysis technique. Prominent anisotropies are found for both the spectral
index and power levels of the electric power spectra. Similar to the magnetic
field fluctuations, the parallel (or antiparallel) electric fluctuation
spectrum is found to be steeper than the perpendicular spectrum. However the
parallel (or antiparallel) electric power is found to be greater than the
perpendicular one. Below 0.1 Hz, the slope of the parallel electric power
spectra deviates substantially from that of the total magnetic power spectra,
supporting the existence of Alfv\'enic turbulence.",2111.06280v1
2021-11-11,Elastic properties of Janus transition metal dichalcogenide nanotubes from first principles,"We calculate the elastic properties of Janus transition metal dichalcogenide
(TMD) nanotubes using first principles Kohn-Sham density functional theory
(DFT). Specifically, we perform electronic structure simulations that exploit
the cyclic and helical symmetry in the system to compute the Young's moduli,
Poisson's ratios, and torsional moduli for twenty-seven select armchair and
zigzag Janus TMD nanotubes at their equilibrium diameters. We find the
following trend in the moduli values: MSSe > MSTe > MSeTe, while their
anisotropy with respect to armchair and zigzag configurations has the following
ordering: MSTe > MSeTe > MSSe. This anisotropy and its ordering between the
different groups is confirmed by computing the shear modulus from the torsional
modulus using an isotropic elastic continuum model, and comparing it against
the value predicted from the isotropic relation featuring the Young's modulus
and Poisson's ratio. We also develop a model for the Young's and torsional
moduli of Janus TMD nanotubes based on linear regression.",2111.06446v4
2021-11-15,Dragging heavy quark in an anisotropic QCD medium beyond the static limit,"Heavy quark dynamics in an anisotropic QCD medium have been analyzed within
the Fokker-Planck approach. Heavy quark drag force and momentum diffusion
tensor have been decomposed by employing a general tensor basis for an
anisotropic medium. Depending upon the relative orientation of the direction of
the momentum anisotropy of the medium and heavy quark motion, two drag and four
diffusion coefficients have been estimated in the anisotropic QCD medium. The
relative significance of different components of drag and momentum diffusion
coefficients has been explored. The dependence of the angle between the
anisotropic vector and heavy quark motion to the drag and diffusion
coefficients has also been studied. Further, the energy loss of heavy quarks
due to the elastic collisional process in an anisotropic medium has been
studied. It is seen that the anisotropic contributions to heavy quark transport
coefficients and its collisional energy loss have a strong dependence on the
direction and strength of momentum anisotropy in the QCD medium.",2111.07563v1
2021-11-15,Determination of spin chirality using x-ray magnetic circular dichroism,"A 3-fold symmetric kagome lattice that has negative spin chirality can give a
non-zero x-ray magnetic circular dichroism (XMCD) signal, despite that the
total spin moment amounts to zero. This is explained by a hitherto unnoticed
rule for the rotational symmetry invariance of the XMCD signal. A necessary
condition is the existence of an anisotropic XMCD signal for the local magnetic
atom, which can arise from a spin anisotropy either in the ground state or the
final state. The angular dependence of the XMCD as a function of the beam
direction has an unusual behavior. The maximum dichroism is not aligned along
the spin direction, but depends on the relative orientation of the spin with
respect to the atomic orientation. Therefore, different geometries can result
in the same angular dependence, and the spin direction can only be determined
if the atomic orientation is known. The consequences for the x-ray
magneto-optical sum rules are given. The integrated XMCD signals are
proportional to the anisotropy in the orbital moment and the magnetic dipole
term, where the isotropic spin moment drops out.",2111.07690v1
2021-11-15,Model-free approach to the interpretation of restricted and anisotropic self-diffusion in magnetic resonance of biological tissues,"Magnetic resonance imaging (MRI) is the method of choice for noninvasive
studies of micrometer-scale structures in biological tissues via their effects
on the time/frequency-dependent (""restricted"") and anisotropic self-diffusion
of water. Traditional MRI relies on pulsed magnetic field gradients to encode
the signal with information about translational motion in the direction of the
gradient, which convolves fundamentally different aspects-such as bulk
diffusivity, restriction, anisotropy, and flow-into a single effective
observable lacking specificity to distinguish between biologically plausible
microstructural scenarios. To overcome this limitation, we introduce a formal
analogy between measuring rotational correlation functions and interaction
tensor anisotropies in nuclear magnetic resonance (NMR) spectroscopy and
investigating translational motion in MRI, which we utilize to convert data
acquisition and analysis strategies from NMR of rotational dynamics in
macromolecules to MRI of diffusion in biological tissues, yielding
model-independent quantitative metrics reporting on relevant microstructural
properties with unprecedented specificity. Our model-free approach advances the
state-of-the-art in microstructural MRI, thereby enabling new applications to
complex multi-component tissues prevalent in both tumors and healthy brain.",2111.07827v1
2021-11-16,Quantification of fracture roughness by change probabilities and Hurst exponents,"The objective of the current study is to utilize an innovative method called
'change probabilities' for describing fracture roughness. In order to detect
and visualize anisotropy of rock joint surfaces, the roughness of
one-dimensional profiles taken in different directions is quantified. The
central quantifiers, 'change probabilities', are based on counting monotone
changes in discretizations of a profile. These probabilities, which are usually
varying with the scale, can be reinterpreted as scale-dependent Hurst
exponents. For a large class of Gaussian stochastic processes change
probabilities are shown to be directly related to the classical Hurst exponent,
which generalizes a relationship known for fractional Brownian motion. While
being related to this classical roughness measure, the proposed method is more
generally applicable, increasing therefore the flexibility of modeling and
investigating surface profiles. In particular, it allows a quick and efficient
visualization and detection of roughness anisotropy and scale dependence of
roughness.",2111.08661v1
2021-11-17,Relativistic oblique shocks with ordered or random magnetic fields: tangential field governs,"Relativistic magnetohydrodynamic shocks are efficient particle accelerators,
often invoked in the models of gamma-ray bursts (GRBs) and shock-powered fast
radio bursts (FRBs). Most theoretical studies assume a perpendicular shock with
an ordered magnetic field perpendicular to the shock normal. However, the
degree of magnetization $\sigma$ and the magnetic field geometry in
shock-powered GRB/FRB scenarios are still poorly constrained by observations.
Analogous to the magnetization $\sigma$ associated with the total field
strength, we define a tangential magnetization $\sigma_\perp$ associated with
the tangential field component. We explore the jump conditions of magnetized
relativistic shocks, either with an ordered field of arbitrary inclination
angle or with a random field of arbitrary anisotropy. In either case, we find
that the jump conditions of relativistic shocks are governed by the tangential
magnetization $\sigma_\perp$ instead of the total magnetization $\sigma$,
insensitive to the inclination angles or the anisotropy of the pre-shock
magnetic field. The approximated analytical solution developed in this work
could serve as a quick check for numerical simulations and apply to theoretical
studies of GRBs/FRBs with a more general field geometry.",2111.09206v2
2021-11-22,Cycle deformation enabled controllable mechanical polarity of bulk metallic glasses,"Tuning anisotropy in bulk metallic glasses, ideally isotropic, is of
practical interest in optimizing properties and of fundamental interest in
understanding the amorphous structure and its instability. By employing the
quasi-elastic asymmetric mechanical cycling method, we effectively induce the
mechanical polarity of a model bulk metallic glass, without damaging the sample
or introducing significant annealing or rejuvenation effects. Moreover, the
polarized anelastic limit can be well controlled by regulating the amplitude of
mechanical cycling. Through the atomic-level analysis of nonaffine
displacement, we find that only plastic atomic rearranged events corresponding
to the training direction can be exhausted by asymmetric cycling and the
survived anelastic events dominate the directional anelastic limit. The
polarized distribution of local yield stress reveals that the mechanical
polarity is attributed to the plastic-event-healing induced asymmetry of local
potential energy surface, rather than frozen-in anelastic strain. Furthermore,
the healing of plastic events associated with the redistribution of local
residual stress indicates the origin of polarity induced by asymmetric cycling.
Our study is of fundamental importance, which furthers our understanding of the
mechanical deformation of metallic glasses and shed some light on the prospects
for improved properties through induced anisotropy.",2111.11164v1
2021-11-29,A prediction for anisotropies in the nearby Hubble flow,"We assess the dominant low-redshift anisotropic signatures in the
distance-redshift relation and redshift drift signals. We adopt
general-relativistic irrotational dust models allowing for gravitational
radiation -- the `quiet universe models' -- which are extensions of the silent
universe models. Using cosmological simulations evolved with numerical
relativity, we confirm that the quiet universe model is a good description on
scales larger than those of collapsing structures. With this result, we reduce
the number of degrees of freedom in the fully general luminosity distance and
redshift drift cosmographies by a factor of $\sim 2$ and $\sim 2.5$,
respectively, for the most simplified case. We predict a dominant dipolar
signature in the distance-redshift relation for low-redshift data, with
direction along the gradient of the large-scale density field. Further, we
predict a dominant quadrupole in the anisotropy of the redshift drift signal,
which is sourced by the electric Weyl curvature tensor. The signals we predict
in this work should be tested with present and near-future cosmological
surveys.",2111.14423v1
2021-11-30,First and second order magnetic anisotropy and damping of europium iron garnet under high strain,"Understanding and tailoring static and dynamic properties of magnetic
insulator thin films is important for spintronic device applications. Here, we
grow atomically flat epitaxial europium iron garnet (EuIG) thin films by pulsed
laser deposition on (111)-oriented garnet substrates with a range of lattice
parameters. By controlling the lattice mismatch between EuIG and the
substrates, we tune the strain in EuIG films from compressive to tensile
regime, which is characterized by X-ray diffraction. Using ferromagnetic
resonance, we find that in addition to the first-order perpendicular magnetic
anisotropy which depends linearly on the strain, there is a significant
second-order one that has a quadratic strain dependence. Inhomogeneous
linewidth of the ferromagnetic resonance increases notably with increasing
strain, while the Gilbert damping parameter remains nearly constant (~
2x10^-2). These results provide valuable insight into the spin dynamics in
ferrimagnetic insulators and useful guidance for material synthesis and
engineering of next-generation spintronics applications.",2111.15142v1
2021-12-07,On transverse momentum broadening in real-time lattice simulations of the glasma and in the weak-field limit,"In these proceedings, we report on our numerical lattice simulations of
partons traversing the boost-invariant, non-perturbative glasma as created at
the early stages of collisions at RHIC and LHC. Since these highly energetic
partons are produced from hard scatterings during heavy-ion collisions, they
are already affected by the first stage of the medium's time evolution, the
glasma, which is the pre-equilibrium precursor state of the quark-gluon plasma.
We find that partons quickly accumulate transverse momentum up to the
saturation momentum during the glasma stage. Moreover, we observe an
interesting anisotropy in transverse momentum broadening of partons with larger
broadening in the rapidity than in the azimuthal direction. Its origin can be
related to correlations among the longitudinal color-electric and
color-magnetic flux tubes in the initial state of the glasma. We compare these
observations to the semi-analytic results obtained by a weak-field
approximation, where we also find such an anisotropy in a parton's transverse
momentum broadening.",2112.03883v1
2021-12-09,Competition between isotropic and strongly anisotropic terms in the impact ionization rate of narrow- and middle-gap cubic semiconductors,"We report on the strong anisotropy of the inter-band process of impact
ionization in direct-gap cubic semiconductors with either weak or strong
spin-orbit coupling at low effective temperatures of electron distribution $T$,
and the crossover to isotropic behavior with increasing $T$. Such anisotropy is
related to specific mechanism of the impact ionization involving coupling of
the electron and heavy hole states $\it via$ remote bands, which is vanishing
for some high-symmetry propagation directions of an initial electron, namely
$\mathrm{[100]}$ and $\mathrm{[111]}$. At room temperature impact ionization
rate in narrow-gap semiconductors $\mathrm{InSb}$, $\mathrm{InAs}$,
$\mathrm{GaSb}$ and $\mathrm{In}_{0.53}\mathrm{Ga}_{0.47}\mathrm{As}$ is
isotropic while in middle-gap $\mathrm{InP}$, $\mathrm{GaAs}$ and
$\mathrm{CdTe}$ both terms are comparable. We propose simple and justified
analytic generalization of Keldysh formula for the impact ionization rate valid
for direct-gap semiconductors with $E_g$ up to $\mathrm{1.5}~\mathrm{eV}$,
which is suitable for incorporation into modelling software.",2112.05021v2
2021-12-11,Domain dependent Fermi arcs observed in a striped phase dichalcogenide,"Angle-resolved photoemission spectromicroscopy on IrTe2 reveals evolution of
mesoscopic striped domains across its first order phase transition at about 280
K. The striped texture of the domains is characterized by a herringbone
arrangement of the electronic anisotropy axes. Under further cooling down to 47
K, the striped domains evolve into trijunction domains with the electronic
anisotropy in three directions. Each domain harbors quasi one-dimensional
surface bands forming Fermi arcs with peculiar spin polarization. The Fermi arc
corresponds to an edge state of the two-dimensional bulk electronic states
truncated at the surface, indicating an interesting interplay between the
symmetry breaking and the surface electronic states.",2112.05930v1
2021-12-13,Induction of Large Magnetic Anisotropy Energy and Formation of Multiple Dirac States in SrIrO$_3$ Films: Role of correlation and spin-orbit coupling,"The 5$d$ transition metal oxides, in particular iridates, host novel
electronic and magnetic phases due to the interplay between onsite Coulomb
repulsion ($U$) and spin-orbit coupling (SOC). The reduced dimensionality
brings another degree of freedom to increase the functionality of these
systems. By taking the example of ultrathin films of SrIrO$_3$,theoretically,
we demonstrate that confinement led localization can introduce large magnetic
anisotropy energy (MAE) in the range 2-7 meV/Ir which is one to two orders
higher than that of the traditional MAE compounds formed out of transition
metals and their multilayers. Furthermore, in the weak correlation limit,
tailored terminations can yield multiple Dirac states across a large energy
window of 2 eV around the Fermi energy which is a rare phenomena in correlated
oxides and upon experimental realization it will give rise to unique transport
properties with excitation and doping.",2112.06813v2
2021-12-16,Dynamics of water and ethanol in graphene oxide,"We utilized the momentum transfer(Q)-dependence of Quasi-Elastic Neutron
Scattering (QENS) to reveal the dynamics of water and ethanol confined in
Graphene Oxide (GO) powder or membranes at different temperatures and in
different orientations. The dynamics was measured across different length and
time scales using several spectrometers. We found reduced diffusivities (up to
30\% in the case of water) and a depression of the transition temperatures.
While water showed near Arrhenius behavior with an almost bulk-like activation
barrier in a temperature range of 280-310 K, the diffusivity of ethanol showed
little temperature dependence. For both water and ethanol, we found evidence
for immobile and mobile fractions of the confined liquid. The mobile fraction
exhibited jump diffusion, with a jump length consistent with the expected
average spacing of hydroxide groups in the GO surfaces. From anisotropy
measurements, we found weak anisotropy in diffusion, with the surprising result
that diffusion was faster perpendicular to membrane than parallel to it.",2112.09235v1
2021-12-19,Heisenberg spins on an anisotropic triangular lattice: PdCrO2 under uniaxial stress,"When Heisenberg spins interact antiferromagnetically on a triangular lattice
and nearest-neighbor interactions dominate, the ground state is 120$^{\circ}$
antiferromagnetism. In this work, we probe the response of this state to
lifting the triangular symmetry, through investigation of the triangular
antiferromagnet PdCrO$_2$ under uniaxial stress by neutron diffraction and
resistivity measurements. The periodicity of the magnetic order is found to
change rapidly with applied stress; the rate of change indicates that the
magnetic anisotropy is roughly forty times the stress-induced bond length
anisotropy. At low stress, the incommensuration period becomes extremely long,
on the order of 1000 lattice spacings; no locking of the magnetism to
commensurate periodicity is detected. Separately, the magnetic structure is
found to undergo a first-order transition at a compressive stress of $\sim$0.4
GPa, at which the interlayer ordering switches from a double- to a single-q
structure.",2112.10215v1
2021-12-20,Anisotropies in Cosmological 21 cm Background by Oscillons/I-balls of Ultra-light Axion-like Particle,"Ultra-light axion-like particle (ULAP) with mass $m \sim 10^{-22}
~\mathrm{eV}$ has recently been attracting attention as a possible solution to
the small-scale crisis. ULAP forms quasi-stable objects called
oscillons/I-balls, which can survive up to a redshift $z \sim 10$ and affect
the structure formation on a scale $\sim \mathcal{O}(0.1)~\mathrm{Mpc}$ by
amplifying the density fluctuations. We study the effect of oscillons on 21~cm
anisotropies caused by neutral hydrogen in minihalos. It is found that this
effect can be observed in a wide mass range by future observations such as
Square Kilometer Array~(SKA) if the fraction of ULAP to the total dark matter
density is $\mathcal{O}(0.01 \text{--} 0.1)$.",2112.10464v1
2021-12-22,Effects of anisotropy on the transition to absolute instability in a porous medium heated from below,"The emerging instability of a forced throughflow in a fluid saturated
horizontal porous duct of rectangular cross section is investigated. The duct
is heated from below by assuming the horizontal boundaries to be at different
temperatures. Both the horizontal and the vertical boundaries are impermeable
and the basic flow is parallel to such boundaries. The porous medium is
anisotropic with different permeabilities in the vertical and horizontal
directions. The effect of the anisotropy on the onset of the buoyancy driven
modal instability and absolute instability is analysed. The parametric
conditions leading to the instability of the basic flow are determined by
employing an analytical dispersion relation. The different permeabilities in
the vertical and horizontal directions come out to play opposite roles in the
onset of modal instability and in the transition to absolute instability. It is
shown that an increasing vertical permeability has a destabilising effect,
while an increasing horizontal permeability has a stabilising effect.",2112.11733v2
2021-12-22,Anisotropic cosmic-ray diffusion in isotropic Kolmogorov turbulence,"Understanding the time scales for diffusive processes and their degree of
anisotropy is essential for modelling cosmic-ray transport in turbulent
magnetic fields. We show that the diffusion time scales are isotropic over a
large range of energy and turbulence levels, notwithstanding the high degree of
anisotropy exhibited by the components of the diffusion tensor for cases with
an ordered magnetic field component. The predictive power of the classical
scattering relation as a description for the relation between the parallel and
perpendicular diffusion coefficients is discussed and compared to numerical
simulations. Very good agreement for a large parameter space is found,
transforming classical scattering relation predictions into a computational
prescription for the perpendicular component. We discuss and compare these
findings and in particular the time scales to become diffusive with the time
scales that particles reside in astronomical environments, the so-called escape
time scales. The results show that, especially at high energies, the escape
times obtained from diffusion coefficients may exceed the time scales required
for diffusion. In these cases, the escape time cannot be determined by the
diffusion coefficients.",2112.11827v1
2021-12-23,Electric-field-induced parametric excitation of exchange magnons in a CoFeB/MgO junction,"Electric-field controlled magnetization dynamics is an important integrant in
low power spintronic devices. In this letter, we demonstrate electric-field
induced parametric excitation for CoFeB/MgO junctions by using interfacial
in-plane magnetic anisotropy. When the in-plane magnetic anisotropy and the
external magnetic field are parallel to each other, magnons are efficiently
excited by using electric-field induced parametric excitation. Its wavelength
and wavenumber are tuned by changing input power and frequency of the applied
voltage. A generalized phenomenological model is developed to explain the
underlying role of the electric-field torque. Electrical excitation with no
Joule heating offers a good opportunity for developing magnonic devices and
exploring various nonlinear dynamics in magnetic systems.",2112.12308v2
2021-12-28,Superfluid Spin Transistor,"We propose to use the Hall response of topological defects, such as merons
and antimerons, to spin currents in 2D magnetic insulator with in-plane
anisotropy for identification of the Berezinskii-Kosterlitz-Thouless (BKT)
transition in a transistor-like geometry. Our numerical results relying on a
combination of Monte Carlo and spin dynamics simulations show transition from
spin superfluidity to conventional spin transport, accompanied by the universal
jump of the spin stiffness and exponential growth of the transverse vorticity
current. We propose a superfluid spin transistor in which the spin and
vorticity currents are modulated by tuning the in-plane magnet across BKT
transition, e.g., by changing the exchange interaction, magnetic anisotropy, or
temperature.",2112.14241v2
2022-01-07,Spatial data modeling by means of Gibbs Markov random fields based on a generalized planar rotator model,"We introduce a Gibbs Markov random field for spatial data on Cartesian grids
which is based on the generalized planar rotator (GPR) model. The GPR model
generalizes the recently proposed modified planar rotator (MPR) model by
including in the Hamiltonian additional terms that better capture realistic
features of spatial data, such as smoothness, non-Gaussianity, and geometric
anisotropy. In particular, the GPR model includes up to infinite number of
higher-order harmonics with exponentially vanishing interaction strength,
directional dependence of the bilinear interaction term between nearest grid
neighbors, longer-distance neighbor interactions, and two types of an external
bias field. Hence, in contrast with the single-parameter MPR model, the GPR
model features five additional parameters: the number $n$ of higher-order terms
and the parameter $\alpha$ controlling their decay rate, the exchange
anisotropy parameter $J^{nn}$, the further-neighbor interaction coupling
$J^{fn}$, and the external field (bias) parameters $K$ (or $K'$). We present
numerical tests on various synthetic data which demonstrate the effects of the
respective terms on the model's prediction performance and we discuss these
results in connection with the data properties.",2201.02537v1
2022-01-11,Graphene Lattices with Embedded Transition-Metal Atoms and Tunable Magnetic Anisotropy Energy: Implications for Spintronic Devices,"Doping of the graphene lattice with transition metal atoms resulting in high
magnetic anisotropy energy (MAE) is an important goal of materials research
owing to its potential application in spintronics. In this article, by using
spin-polarized density functional theory including spin-orbit coupling, we
examined magnetic properties of graphene with vacancy defects, both bare and
nitrogen-decorated, and doped by Cr, Mn and Fe transition metal single atom
(TM-SA) and two different TM atoms simultaneously. [...] The computational
findings are supplemented by an atomic-resolution characterization of an
incidental Mn impurity bonded to four carbon atoms, whose localized spin
matches expectations as measured using core-level electron energy-loss
spectroscopy. Conducting TM-doped graphene with robust magnetic features offers
prospects for the design of graphene-based spintronic devices.",2201.03867v1
2022-01-17,Scanning nitrogen-vacancy center magnetometry in large in-plane magnetic fields,"Scanning magnetometry with nitrogen-vacancy (NV) centers in diamond has
emerged as a powerful microscopy for studying weak stray field patterns with
nanometer resolution. Due to the internal crystal anisotropy of the spin
defect, however, external bias fields -- critical for the study of magnetic
materials -- must be applied along specific spatial directions. In particular,
the most common diamond probes made from {100}-cut diamond only support fields
at an angle of $\theta = 55^\circ$ from the surface normal. In this paper, we
report fabrication of scanning diamond probes from {110}-cut diamond where the
spin anisotropy axis lies in the scan plane ($\theta=90^\circ$). We show that
these probes retain their sensitivity in large in-plane fields and demonstrate
scanning magnetometry of the domain pattern of Co-NiO films in applied fields
up to 40 mT. Our work extends scanning NV magnetometry to the important class
of materials that require large in-plane fields.",2201.06450v2
2022-01-18,Timing-residual power spectrum of a polarized stochastic gravitational-wave background in pulsar-timing-array observation,"We study the observation of stochastic gravitational-wave background (SGWB)
made by pulsar-timing arrays in the spherical harmonic space. Instead of using
the Shapiro time delay, we keep the Sachs-Wolfe line-of-sight integral for the
timing residual of an observed pulsar. We derive the power spectrum of the
timing residual, from which the overlap reduction functions and the bipolar
spherical harmonics coefficients are constructed for the SGWB intensity and
polarization anisotropies. We have reproduced the previous results, noting that
we have developed a fast algorithm for computing accurate overlap reduction
functions and the bipolar spherical harmonics coefficients for the
linear-polarization anisotropy are worked out for the first time. Our
harmonic-space method is useful for future pulsar-timing-array observation on a
few thousand pulsars and provides optimal estimators for testing the
statistical isotropy of the SGWB.",2201.06767v1
2022-01-19,Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2,"The 12442 compounds are a recently discovered family of iron-based
superconductors, that share several features with the cuprates due to their
strongly anisotropic structure, but are so far poorly understood. Here, we
report on the gap structure and anisotropy of RbCa2(Fe1-xNix)4As4F2 single
crystals, investigated by a combination of directional point-contact
Andreev-reflection spectroscopy and coplanar waveguide resonator measurements.
Two gaps were identified, with clear signatures of d-wave-like nodal structures
which persist upon Ni doping, well described by a two-band d-d state with
symmetry-imposed nodes. A large London penetration depth anisotropy was
revealed, weakly dependent on temperature and fully compatible with the d-d
model.",2201.07593v1
2022-01-21,Cavity Ferromagnetic Resonance Study of Acoustic and Optic excitations in Ru/Cr/Co and Ru/Co multilayers,"Two series of [Ru10/Cox)]12 and [Ru6/Cr3/Cox)]12 x=16-60 easy-plane
anisotropy multilayers (all thicknesses in {\AA}), prepared by sputter
deposition, are studied by cavity FMR. The acoustic modes are excited by
setting the RF field perpendicular to the saturating in-plane field. Their
resonance fields are in good agreement with the values predicted for acoustic
modes by macrospin models, using the interlayer RKKY exchange and anisotropy
fields derived by the magnetic measurements. The resonance fields of the modes
excited by setting the RF field parallel to the saturating field, are lower
than those expected for optical modes. This and could attributed to the
existence of hybridized mixed modes, according to results of micromagnetic
simulations which also show that the mode mixing is related to the
inhomogeneous magnetization profile along the multilayer thickness.",2201.08630v1
2022-01-26,Anisotropic compact star with a linear pressure-density relationship,"We present a model of compact astrophysical object under General Theory of
Relativity using the anisotropic extension of Tolman IV solution. The
anisotropy function, derived from the model, remains well behaved throughout
the interior of the star. The model satisfies several necessary conditions for
a physically realistic compact star. Physical viability of the model is
verified specifically by plugging in the estimated parameter values of the Low
Mass X-ray Binary (LMXB) candidate 4U 1608 - 52. Our stability analysis of this
star, by using various criteria for stability, provide satisfactory results. In
connection to anisotropy, we compute the Tidal Love Number (TLN) for the
compact stellar model and compare the calculated values with existing
literature.",2201.10772v1
2022-02-04,Influence of the triangular Mn-O breathing mode on the magnetic ordering in multiferroic hexagonal manganites,"We use a combination of symmetry analysis, phenomenological modelling and
first-principles density functional theory to explore the interplay between the
magnetic ground state and the detailed atomic structure in the hexagonal
rare-earth manganites. We find that the magnetic ordering is sensitive to a
breathing mode distortion of the Mn and O ions in the $ab$ plane, which is
described by the K\textsubscript{1} mode of the high-symmetry structure. Our
density functional calculations of the magnetic interactions indicate that this
mode particularly affects the single-ion anisotropy and the inter-planar
symmetric exchanges. By extracting the parameters of a magnetic model
Hamiltonian from our first-principles results, we develop a phase diagram to
describe the magnetic structure as a function of the anisotropy and exchange
interactions. This in turn allows us to explain the dependence of the magnetic
ground state on the identity of the rare-earth ion and on the
K\textsubscript{1} mode.",2202.02304v1
2022-02-07,DFT insights into the new Hf-based chalcogenide MAX phase Hf2SeC,"The physical characteristics of the novel chalcogenide MAX phase Hf2SeC have
been investigated using the DFT method. The obtained lattice constant and
elastic constants (Cij) are compared with previous results to check the
consistency of our setting parameters during calculations Moreover, the elastic
properties such as elastic constants, moduli, anisotropy, and hardness are also
compared with preexisting MAX phases of its kind. The checking of mechanical
stability has been done based on Cij in accordance with the previously stated
stability criteria. The reason for the higher hardness of Hf2SeC compared to
Hf2SC is explained using the density of states (DOS). The brittleness character
of Hf2SeC has been revealed using the Pugh ratio, Poisson ratio, and Cauchy
pressure. The electronic properties (band structure and charge density mapping)
of Hf2SeC are studied to disclose the metallic nature as well as bonding nature
within the titled chalcogenide. The anisotropy in both electronic conductivity
and mechanical properties is investigated. The temperature and pressure
dependence of volume, Gr\""uneisen parameter, Debye temperature, thermal
expansion coefficient (TEC), and specific heat at constant volume (Cv) are
explored. In addition, minimum thermal conductivity (Kmin) and melting point
(Tm) are studied to explore its suitability for high-temperature applications.",2202.03370v1
2022-02-07,Optically induced anisotropy in time-resolved scattering: Imaging molecular scale structure and dynamics in disordered media with experiment and theory,"Time-resolved scattering experiments enable imaging of materials at the
molecular scale with femtosecond time resolution. However, in disordered media
they provide access to just one radial dimension thus limiting the study of
orientational structure and dynamics. Here we introduce a rigorous and
practical theoretical framework for predicting and interpreting experiments
combining optically induced anisotropy and time-resolved scattering. Using
impulsive nuclear Raman and ultrafast X-ray scattering experiments of
chloroform and simulations, we demonstrate that this framework can accurately
predict and elucidate both the spatial and temporal features of these
experiments.",2202.03562v1
2022-02-05,Stochastic aspects of crack deflection and crack path prediction in short fiber reinforced polymer matrix composites,"Owing to the production process, short fiber reinforced composites exhibit a
pronounced anisotropy of both elastic properties and crack growth resistance.
In particular the latter issue has a major impact on crack deflection and
inevitably has to be taken into account for the sake of an accurate prediction
of crack paths. The perpendicular axes of transverse isotropy are associated
with the fiber orientations, whereupon a crack in transverse direction
encounters the largest fracture toughness. While the local mean fiber
orientations in polymer matrix composites are determined by the injection
molding process, their statistical fluctuations can approximately be described
in terms of Gaussian random field models. Furthermore, statistical variations
of the volume fraction of fibers and the fiber-matrix adhesion give rise to
stochasticity of the local ratio of fracture toughness anisotropy. Influencing
factors of prediction regions of crack paths obtained from finite element
simulations with an adapted J-integral deflection criterion are investigated,
just as stochastic aspects of bifurcation phenomena of crack deflection
observed under mode-I loading.",2202.06748v1
2022-02-15,Sharp phase-field modeling of isotropic solidification with a super efficient spatial resolution,"The numerical resolution efficiency of phase-field models is limited by grid
friction, grid anisotropy and pinning. The 1D sharp phase-field model
eliminates grid friction and pinning by a global restoration of Translational
Invariance (TI) in the discretized phase-field equation (Phys. Rev. Lett. 121,
025501, 2018). In 3D global TI restricts the beneficial modeling properties to
a finite number of fixed interface orientations. We propose an accurate scheme
to restore TI locally in the local interface normal direction. At
one-grid-point interface resolutions, the new model captures the formation of
isotropic seaweed structures without spurious dendritic selection by grid
anisotropy.",2202.07433v3
2022-02-15,Spin orbital reorientation transitions induced by magnetic field,"Here we report on a new effect similar to the spin reorientation transition
(SRT) that takes place at two magnetic fields of $B_{SORT1}$ and $B_{SORT2}$.
The effect is observed in the magnetization curves of small Mn$^{3+}$ magnetic
clusters in the wurtzite GaN (being in a paramagnetic state) calculated using
crystal field model approach. The obtained results suggest that the computed
magnetic anisotropy (MA) reverses its sign on increasing $B$ across $B_{SORT}$.
Detailed analysis show however that MA is unchanged for high magnetic fields.
We show that the observed effect arises from the interplay of the crystalline
environment and the spin-orbit coupling $\lambda \hat{\textbf{S}}
\hat{\textbf{L}}$, therefore we name it spin orbital reorientation transition
(SORT). The value of $B_{SORT1}$ depends on the crystal field model parameters
and the number of ions $N$ in a given cluster, whereas $B_{SORT2}$ is
controlled mostly by the magnitude of the spin-orbit coupling $\lambda$. The
explanation of SORT is given in terms of the spin $M_S$ and orbital momentum
$M_L$ contributions to the total magnetization $M = M_S + M_L$. The similar
effect should also be present in other materials with not completely quenched
(non zero) orbital angular momentum $L$, a uniaxial magnetic anisotropy and the
positive value of $\lambda$.",2202.07443v1
2022-03-01,Using the Energy probability distribution zeros to obtain the critical properties of the two-dimensional anisotropic Heisenberg model,"In this paper we present a Monte Carlo study of the critical behavior of the
easy axis anisotropic Heisenberg spin model in two dimensions. Based on the
partial knowledge of the zeros of the energy probability distribution we
determine with good precision the phase diagram of the model obtaining the
critical temperature and exponents for several values of the anisotropy. Our
results indicate that the model is in the Ising universality class for any
anisotropy.",2203.00419v2
2022-03-06,Entropy production in longitudinally expanding Yang-Mills field with use of Husimi function$-$semiclassical approximation,"We investigate the possible thermalization process of the highly occupied and
weakly coupled Yang-Mills fields expanding along the beam axis through an
evaluation of the entropy, particle number, and pressure anisotropy. The time
evolution of the system is calculated by solving the equation of motion for the
Wigner function in the semiclassical approximation with initial conditions
mimicking the glasma. For the evaluation of the entropy, we adopt the
Husimi-Wehrl (HW) entropy, which is obtained by using the Husimi function, a
positive semidefinite quantum distribution function given by smearing the
Wigner function. By numerical calculations at $g=0.1$ and $0.2$, the entropy
production is found to occur together with the particle creation in two
distinct stages: In the first stage, the particle number and the entropy at low
longitudinal momenta grow rapidly. In the second stage, the particle number and
the entropy of higher longitudinal momentum modes show slower increase. The
pressure anisotropy remains in our simulation and implies that the system is
still out-of-equilibrium.",2203.02859v3
2022-03-07,"Influence of Charge on Extended Decoupled Anisotropic Solutions in $f(\mathcal{R},\mathcal{T},\mathcal{R}_{λξ}\mathcal{T}^{λξ})$ Gravity","In this paper, we consider static self-gravitating spherical spacetime and
determine various anisotropic solutions through the extended gravitational
decoupling technique in
$f(\mathcal{R},\mathcal{T},\mathcal{R}_{\lambda\xi}\mathcal{T}^{\lambda\xi})$
gravity to analyze the influence of electromagnetic field on them. We construct
two different sets of modified field equations by employing the transformations
on both radial as well as temporal metric potentials. The first set symbolizes
the isotropic fluid distribution, thus we take Krori-Barua solution to deal
with it. The indefinite second sector comprises the influence of anisotropy. In
this regard, we apply some constraints to determine unknowns. Further, we
observe the impact of charge as well as decoupling parameter $\zeta$ on the
developed physical variables (such as energy density,~radial and tangential
pressures) and anisotropy. We also analyze other physical features of the
compact geometry like mass, compactness and redshift along with the energy
conditions. Eventually, we find that our both solutions show less stable
behavior for higher values of charge near the boundary in this gravity.",2203.03268v1
2022-03-11,Magnetic anisotropy energies and metal-insulator transitions in monolayers of $α$-RuCl$_3$ and OsCl$_3$ on graphene,"Transition metal thriclorides, with $4d$ or $5d$ electrons, are materials at
the forefront of recent studies about the interplay of spin-orbit coupling and
strong Coulomb interactions. Within our first-principles calculations
(DFT+$U$+SOC) we study the effects of graphene on the electronic and magnetic
properties of the monolayers of $\alpha$-RuCl$_3$ and OsCl$_3$. Despite the
spatially inhomogeneous $n$-type doping induced by graphene, we show that the
occupancy of the upper Hubbard bands of MLs of \rucl and OsCl$_3$ can be tuned
through external electric fields, and allows the control of (i) metal-insulator
transitions, and (ii) the magnetic easy-axis and anisotropy energies. Our
findings point towards the tunning of electronic and magnetic properties of
transition metal thriclorides monolayers by using graphene and external
electronic fields.",2203.06052v1
2022-03-21,Constraints of anisotropy on warm power-law inflation in light of Planck results,"In this article, we examine the effects of anisotropy on a model of canonical
warm inflation with the power-law potential. The results of this model are
compared to Planck satellite observational data. Using a conventional local
scalar fi?eld in the Bianchi type I metric, the slow-roll conditions and the
suitable regions, where the free parameters of the model show a good agreement
with Planck results, are investigated in detail. Following the usual
calculations for warm inflationary approaches, the early universe in two
different dissipative regimes, namely the weak dissipative and the strong
dissipative ones, is investigated. In this regard, the slow-roll parameters and
their observational indices in both regimes are obtained and finally, it is
shown that this model is in good agreement with observatio",2203.11165v1
2022-03-23,Holographic model for light quarks in anisotropic hot dense QGP with external magnetic field,"We present a five-dimensional twice anisotropic holographic model supported
by Einstein-dilaton-three-Maxwell action describing light quarks. The first of
the Maxwell fields provides finite chemical potential. The second Maxwell field
serves for anisotropy, characterizing spatial anisotropy of the QGP produced in
heavy-ion collisions (HIC). The third Maxwell field is related to a magnetic
field that appears in HIC. The dependence of the 5-dim black hole solution and
confinement/deconfinement phase diagram on this magnetic field is considered.
The effect of the inverse magnetic catalyses for light quarks phase diagram is
obtained. Positions of critical end points are found. We also study the
behavior of the conductivity for light quarks in both isotropic and anisotropic
cases and show that behaviour of the conductivity near critical points
essentially depend on quark masses, meanwhile at high temperature they are
similar.",2203.12539v2
2022-03-28,Quantum Yu-Shiba-Rusinov dimers,"Magnetic adatoms on a superconducting substrate undergo a quantum phase
transition as their exchange coupling to the conduction electrons increases.
For quantum spins, this transition is accompanied by screening of the adatom
spin. Here, we explore the consequences of this screening for the phase
diagrams and subgap excitation spectra of dimers of magnetic adatoms coupled by
hybridization of their Yu-Shiba-Rusinov states and spin-spin interactions. We
specifically account for higher spins, single-ion anisotropy,
Ruderman-Kittel-Kasuya-Yosida coupling, and Dzyaloshinsky-Moriya interactions
relevant in transition-metal and rare-earth systems. Our flexible approach
based on a zero-bandwidth approximation provides detailed physical insight and
is in excellent qualitative agreement with available numerical-renormalization
group calculations on monomers and dimers. Remarkably, we find that even in the
limit of large impurity spins or strong single-ion anisotropy, the phase
diagrams for dimers of quantum spins remain qualitatively distinct from phase
diagrams based on classical spins, highlighting the need for a theory of
quantum Yu-Shiba-Rusinov dimers.",2203.15011v1
2022-04-04,"Large-scale asymmetry in galaxy spin directions -- analysis of galaxies with spectra in DES, SDSS, and DESI Legacy Survey","Multiple previous studies using several different probes have shown
considerable evidence for the existence of cosmological-scale anisotropy and a
Hubble-scale axis. One of the probes that show such evidence is the
distribution of the directions toward which galaxies spin. The advantage of the
analysis of the distribution of galaxy spin directions compared to the CMB
anisotropy is that the ratio of galaxy spin directions is a relative
measurement, and therefore less sensitive to background contamination such as
Milky Way obstruction. Another advantage is that many spiral galaxies have
spectra, and therefore allow to analyze the location of such axis relative to
Earth. This paper shows an analysis of the distribution of the spin directions
of over 90K galaxies with spectra. That analysis is also compared to previous
analyses using the Earth-based SDSS, Pan-STARRS, and DESI Legacy Survey, as
well as space-based data collected by HST. The results show very good agreement
between the distribution patterns observed with the different telescopes. The
dipole or quadrupole axes formed by the spin directions of the galaxies with
spectra do not necessarily go directly through Earth.",2204.01192v1
2022-04-04,"Inter- to Intra-Layer Resistivity Anisotropy of NdFeAs(O,H) with Various Hydrogen Concentrations","With molecular beam epitaxy and topotactic chemical reaction, we prepared
NdFeAs(O,H) epitaxial thin films with various hydrogen concentrations on
5{\deg} vicinal cut MgO substrates. By measuring the resistivities along the
longitudinal and transversal directions, the ab plane and the c axis
resistivities (\{rho}_ab and \{rho}_c) were obtained. The resistivity
anisotropy {\gamma}_\{rho}=\{rho}_c \ \{rho}_ab of NdFeAs(O,H) with various
hydrogen concentrations was compared with that of NdFeAs(O,F). At the H
concentrations which led to superconducting transition temperatures Tc over 40
K, {\gamma}_\r{ho} recorded ~100-150 at 50 K. On the other hand, a low
{\gamma}_\{rho} value of 9 was observed with the mostly doped sample. The
exponent \{beta} of the ab plane resistivity obtained by fitting a power law
expression \{rho}_{ab}(T)=\{rho}_0+AT^\{beta} to the data was close to unity
down to low temperature in the vicinity where the second antiferromagnetic
phase locates, which may be related to the quantum critical point discussed at
the over-doped side of the phase diagram.",2204.01554v1
2022-04-09,The skyrmion bags in an anisotropy gradient,"Skyrmion bags as spin textures with arbitrary topological charge are expected
to be the carriers in racetrack memory. Here, we theoretically and numerically
investigated the dynamics of skyrmion bags in an anisotropy gradient. It is
found that, without the boundary potential, the dynamics of skyrmion bags are
dependent on the spin textures, and the velocity of skyrmionium with $Q = 0$ is
faster than other skyrmion bags. However, when the skyrmion bags move along the
boundary, the velocities of all skyrmion bags with different $Q$ are same. This
can be attributed to the same value of $u/\eta_{xx}$, where the $u$ and
$\eta_{xx}$ are the terms related to the magnetization distribution of skyrmion
bag. In addition, we theoretically derived the dynamics of skyrmion bags in the
two cases using the Thiele approach and discussed the scope of Thiele equation.
Within a certain range, the simulation results are in good agreement with the
analytically calculated results. Our findings provide an alternative way to
manipulate the racetrack memory based on the skyrmion bags.",2204.04439v2
2022-04-18,Cosmic microwave background spectral distortions from Rayleigh scattering at second order,"Cosmic microwave background (CMB) spectral distortion from Rayleigh
scattering is calculated for the first time in rigorous second-order
cosmological perturbation theory. The new spectral distortion is sensitive to
acoustic dissipation at $10^{-2}<k{\rm Mpc}/h<1$, which slightly extends the
scale constrained by the CMB anisotropies. The spectral shape is different from
either temperature perturbations or any other traditional spectral distortions
from Compton scattering, such as $y$ and $\mu$. The new spectral distortion is
not formed in the late Universe, unlike the thermal Sunyaev-Zel'dovich effect
degenerated with the primordial $y$ distortions since photons must be hot for
Rayleigh scattering. Therefore, ideal measurements can distinguish the signal
from the other effects and extract new information during recombination.
Assuming cosmological parameters consistent with the recent CMB anisotropy
measurements, we find the new spectral distortion is $6.5\times 10^{-3}$Jy/str,
which is one order of magnitude smaller than the currently proposed target
sensitivity range of voyage 2050.",2204.08177v1
2022-04-19,Role of shape anisotropy on thermal gradient-driven domain wall dynamics in magnetic nanowires,"We investigate the magnetic domain wall (DW) dynamics in uniaxial/biaxial
nanowires under a thermal gradient (TG). The findings reveal that the DW
propagates toward the hotter region in both nanowires. The main physics of such
observations is the magnonic angular momentum transfer to the DW. The hard
(shape) anisotropy exists in biaxial nanowire, which contributes an additional
torque, hence DW speed is larger than that in uniaxial nanowire. With lower
damping, the DW velocity is smaller and DW velocity increases with damping
which is opposite to usual expectation. To explain this, it is predicted that
there is a probability to form the standing spin-waves (which do not carry net
energy/momentum) together with travelling spin-waves if the propagation length
of thermally-generated spin-waves is larger than the nanowire length. For
larger-damping, DW decreases with damping since the magnon propagation length
decreases. Therefore, the above findings might be useful in realizing the
spintronic (racetrack memory) devices.",2204.09101v2
2022-04-21,Wurtzite quantum wires with strong spatial confinement: polarization anisotropies in single wire spectroscopy,"We report GaAs/AlGaAs nanowires in the one-dimensional (1D) quantum limit.
The ultrathin wurtzite GaAs cores between 20-40\,nm induce large confinement
energies of several tens of meV, allowing us to experimentally resolve up to
four well separated subband excitations in microphotoluminescence spectroscopy.
Our detailed experimental and theoretical polarization-resolved study reveals a
strong diameter-dependent anisotropy of these transitions: We demonstrate that
the polarization of the detected photoluminescence is governed by the symmetry
of the wurtzite 1D quantum wire subbands on the one hand, but also by the
dielectric mismatch of the wires with the surrounding material on the other
hand. The latter effect leads to a strong attenuation of perpendicularly
polarized light in thin dielectric wires, making the thickness of the AlGaAs
shell an important factor in the observed polarization behavior. Including the
dielectric mismatch to our k.p-based simulated polarization-resolved spectra of
purely wurtzite GaAs quantum wires, we find an excellent agreement between
experiment and theory.",2204.09991v1
2022-04-25,Ab-initio study of magneto-ionic mechanisms in ferromagnet/oxide multilayers,"The application of gate voltages in heavy metal/ferromagnet/Oxide multilayer
stacks has been identified as one possible candidate to manipulate their
anisotropy at will. However, this method has proven to show a wide variety of
behaviours in terms of reversibility, depending on the nature of the
metal/oxide interface and its degree of oxidation. In order to shed light on
the microscopic mechanism governing the complex magneto-ionic behaviour in
$\text{Ta/CoFeB/}\text{HfO}_2$, we perform ab-initio simulations on various
setups comprising $\text{Fe/O, Fe/HfO}_2$ interfaces with different oxygen atom
interfacial geometries. After the determination of the more stable interfacial
configurations, we calculate the magnetic anisotropy energy on the different
unit cell configurations and formulate a possible mechanism that well describes
the recent experimental observations in $\text{Ta/CoFeB/}\text{HfO}_2$.",2204.11699v1
2022-04-26,Cosmology from the kinetic polarized Sunyaev Zel'dovich effect,"The cosmic microwave background (CMB) photons that scatter off free electrons
in the large-scale structure induce a linear polarization pattern proportional
to the remote CMB temperature quadrupole observed in the electrons' rest frame.
The associated blackbody polarization anisotropies are known as the polarized
Sunyaev Zel'dovich (pSZ) effect. Relativistic corrections to the remote
quadrupole field give rise to a non-blackbody polarization anisotropy
proportional to the square of the transverse peculiar velocity field; this is
the kinetic polarized Sunyaev Zel'dovich (kpSZ) effect. In this paper, we
forecast the ability of future CMB and galaxy surveys to detect the kpSZ
effect, finding that a statistically significant detection is within the reach
of planned experiments. We further introduce a quadratic estimator for the
square of the peculiar velocity field based on a galaxy survey and CMB
polarization. Finally, we outline how the kpSZ effect is a probe of cosmic
birefringence and primordial non-Gaussianity, forecasting the reach of future
experiments.",2204.12503v2
2022-05-02,Pre-hydrodynamic evolution and its impact on quark-gluon plasma signatures,"State-of-the-art hydrodynamic models of heavy-ion collisions have
considerable theoretical model uncertainties in the description of the very
early pre-hydrodynamic stage. We add a new computational module,
K$_\mathrm{T}$Iso, that describes the pre-hydrodynamic evolution kinetically,
based on the relativistic Boltzmann equation with collisions treated in the
Isotropization Time Approximation. As a novelty, K$_\mathrm{T}$Iso allows for
the inclusion and evolution of initial-state momentum anisotropies. To maintain
computational efficiency K$_\mathrm{T}$Iso assumes strict longitudinal boost
invariance and allows collisions to isotropize only the transverse momenta. We
use it to explore the sensitivity of hadronic observables measured in
relativistic heavy-ion collisions to initial-state momentum anisotropies and
microscopic scattering during the pre-hydrodynamic stage.",2205.00964v2
2022-05-02,Anisotropic cosmic optical background bound for decaying dark matter in light of the LORRI anomaly,"Recently anomalous flux in the cosmic optical background (COB) has been
reported by the New Horizon observations. The COB flux is $16.37\pm 1.47\, \rm
nW m^{-2} sr^{-1}$, at the LORRI pivot wavelength of $0.608\,\rm \mu m$, which
is $\sim 4\sigma$ level above the expected flux from the Hubble Space Telescope
(HST) galaxy count. It would be great if this were a hint for the eV scale dark
matter decaying into photons. In this paper, we point out that such a decaying
dark matter model predicts a substantial amount of anisotropy in the COB flux,
which is accurately measured by the HST. The data of the HST excludes the decay
rate of the dominant cold dark matter larger than $10^{-24}$-$10^{-23}\,{\rm
s}^{-1}$ in the mass range of $5$-$20$eV. As a result, the decaying cold dark
matter explaining the COB excess is strongly disfavored by the anisotropy
bound. We discuss some loopholes: e.g. warm/hot dark matter or two-step decay
of the dark matter, to explain the COB excess.",2205.01079v2
2022-05-09,"Controlling magnetic exchange and anisotropy by non-magnetic ligand substitution in layered MPX3 (M = Ni, Mn; X = S, Se)","Recent discoveries in two-dimensional (2D) magnetism have intensified the
investigation of van der Waals (vdW) magnetic materials and further improved
our ability to tune their magnetic properties. Tunable magnetism has been
widely studied in antiferromagnetic metal thiophosphates MPX3. Substitution of
metal ions M has been adopted as an important technique to engineer the
magnetism in MPX3. In this work, we have studied the previously unexplored
chalcogen X substitutions in MPX3 (M = Mn/Ni; X = S/Se). We synthesized the
single crystals of MnPS3-xSex (0 < x < 3) and NiPS3-xSex (0 < x < 1.3) and
investigated the systematic evolution of the magnetism with varying x. Our
study reveals the effective tuning of magnetic interactions and anisotropies in
both MnPS3 and NiPS3 upon Se substitution. Such efficient engineering of the
magnetism provides a suitable platform to understand the low-dimensional
magnetism and develop future magnetic devices.",2205.04585v1
2022-05-13,The spatial distribution of satellites in galaxy clusters,"The planar distributions of satellite galaxies around the Milky Way and
Andromeda have been extensively studied as potential challenges to the standard
cosmological model. Using the Sloan Digital Sky Survey and the Millennium
simulation we extend such studies to the satellite galaxies of massive galaxy
clusters. We find that both observations and simulations of galaxy clusters
show an excess of anisotropic satellite distributions. On average, satellites
in clusters have a higher degree of anisotropy than their counterparts in
Milky-Way-mass hosts once we account for the difference in their radial
distributions. The normal vector of the plane of satellites is strongly aligned
with the host halo's minor axis, while the alignment with the large-scale
structure is weak. At fixed cluster mass, the degree of anisotropy is higher at
higher redshift. This reflects the highly anisotropic nature of satellites
accretion points, a feature that is partly erased by the subsequent orbital
evolution of the satellites. We also find that satellite galaxies are mostly
accreted singly so group accretion is not the explanation for the high
flattening of the planes of satellites.",2205.06767v1
2022-05-16,Fat-Tailed Variational Inference with Anisotropic Tail Adaptive Flows,"While fat-tailed densities commonly arise as posterior and marginal
distributions in robust models and scale mixtures, they present challenges when
Gaussian-based variational inference fails to capture tail decay accurately. We
first improve previous theory on tails of Lipschitz flows by quantifying how
the tails affect the rate of tail decay and by expanding the theory to
non-Lipschitz polynomial flows. Then, we develop an alternative theory for
multivariate tail parameters which is sensitive to tail-anisotropy. In doing
so, we unveil a fundamental problem which plagues many existing flow-based
methods: they can only model tail-isotropic distributions (i.e., distributions
having the same tail parameter in every direction). To mitigate this and enable
modeling of tail-anisotropic targets, we propose anisotropic tail-adaptive
flows (ATAF). Experimental results on both synthetic and real-world targets
confirm that ATAF is competitive with prior work while also exhibiting
appropriate tail-anisotropy.",2205.07918v1
2022-05-16,Surface Bound States in the Continuum in Dyakonov Structures,"Surface bound states in the continuum (SBICs) have been found to occur in
diverse settings, but so far always at the interface of non-homogeneous media,
such as discrete lattices or periodic systems. Here we show that they can also
exist at the interface of homogeneous media, resulting in unique SBICs.
Specifically, we found that, contrary to general belief, leaky Dyakonov states
exist at the interface between materials that exhibit opposite signs of
anisotropy. In addition, properly breaking the anisotropy-symmetry leads to the
formation of both guided states and also SBICs embedded within the continuum. A
direct implication of our finding is the possibility to create SBICs and
Dyakonov states in a whole new class of materials and metamaterials.",2205.07940v1
2022-05-24,Understanding temperature-dependent SU($3$) spin dynamics in the $S=1$ antiferromagnet Ba$_2$FeSi$_2$O$_7$,"Quantum magnets admit more than one classical limit and $N$-level systems
with strong single-ion anisotropy are expected to be described by a classical
approximation based on SU($N$) coherent states. Here we test this hypothesis by
modeling finite temperature inelastic neutron scattering (INS) data of the
effective spin-one antiferromagnet \bfso{}. The measured dynamic structure
factor is calculated with a generalized Landau-Lifshitz dynamics for SU($3$)
spins. Unlike the traditional classical limit based on SU($2$) coherent states,
the results obtained with classical SU($3$) spins are in good agreement with
the measured temperature-dependent spectrum. The SU($3$) approach developed
here provides a general framework to understand the broad class of materials
comprising weakly coupled antiferromagnetic dimers, trimers, or tetramers, and
magnets with strong single-ion anisotropy.",2205.11770v1
2022-05-25,Superconducting diode effect due to magnetochiral anisotropy in topological insulator and Rashba nanowires,"The critical current of a superconductor can depend on the direction of
current flow due to magnetochiral anisotropy when both inversion and
time-reversal symmetry are broken, an effect known as the superconducting (SC)
diode effect. Here, we consider one-dimensional (1D) systems in which
superconductivity is induced via the proximity effect. In both topological
insulator and Rashba nanowires, the SC diode effect due to a magnetic field
applied along the spin-polarization axis and perpendicular to the nanowire
provides a measure of inversion symmetry breaking in the presence of a
superconductor. Furthermore, a strong dependence of the SC diode effect on an
additional component of magnetic field applied parallel to the nanowire as well
as on the position of the chemical potential can be used to detect that a
device is in the region of parameter space where the phase transition to
topological superconductivity is expected to arise.",2205.12939v1
2022-05-28,Atomic-scale Deformation Process of Glasses Unveiled by Stress-induced Structural Anisotropy,"Experimentally resolving atomic-scale structural changes of a deformed glass
remains challenging owing to the disordered nature of glass structure. Here, we
show that the structural anisotropy emerges as a general hallmark for different
types of glasses (metallic glasses, oxide glass, amorphous selenium, and
polymer glass) after thermo-mechanical deformation, and it is highly correlates
with local nonaffine atomic displacements detected by the high-energy X-ray
diffraction technique. By analyzing the anisotropic pair density function, we
unveil the atomic-level mechanism responsible for the plastic flow, which
notably differs between metallic glasses and covalent glasses. The structural
rearrangements in metallic glasses are mediated through cutting and formation
of atomic bonds, which occurs in some localized inelastic regions embedded in
elastic matrix, whereas that of covalent glasses is mediated through the
rotation of atomic bonds or chains without bond length change, which occurs in
a less localized manner.",2205.14367v1
2022-05-31,Electrical measurement of the Spin Hall Effect isotropy in a ferromagnet,"The spin-dependent transport properties of paramagnetic metals are roughly
invariant under rotation. By contrast, in ferromagnetic materials the
magnetization breaks the rotational symmetry, and thus the spin Hall effect is
expected to become anisotropic. Here, using a specific design of lateral spin
valves, we measure electrically the spin Hall Effect anisotropy in NiCu and
NiPd, both in their ferromagnetic and paramagnetic phases. We show that the
appearance of the ferromagnetic order does not lead to a sizeable anisotropy of
the spin charge interconversion in these materials.",2205.15651v2
2022-06-01,Imprints of Anisotropy on the Power Spectrum in Matter Dominated Bouncing Universe as Background,"In this paper, we aim to investigate the effects of the anisotropy on the
scale-invariant power spectrum considering the matter-dominated collapsing
universe as background and look for the deviations from this scale invariance.
Having set up this background, we consider a massless scalar field and work out
the correlations, first by using the perturbative approach in which the
anisotropic background is approximated with an effective isotropic metric
represented by the metric of matter dominated collapsing universe, second by
directly solving the field equation numerically, and then obtain the power
spectrum for the range of modes which are of cosmological interest. Using both
techniques, we get an upper bound on the deviation in the power spectrum from
the scale invariance. We also work out the power spectrum for much smaller
modes and look at whether it is possible to explain the observed anomalies in
CMB via the matter bounce scenario.",2206.00656v2
2022-06-02,Hybrid iterative ensemble smoother for history matching of hierarchical models,"The choice of the prior model can have a large impact on the ability to
assimilate data. In standard applications of ensemble-based data assimilation,
all realizations in the initial ensemble are generated from the same covariance
matrix with the implicit assumption that this covariance is appropriate for the
problem. In a hierarchical approach, the parameters of the covariance function,
for example the variance, the orientation of the anisotropy and the ranges in
two principal directions, may all be uncertain. Thus, the hierarchical approach
is much more robust against model misspecification. In this paper, three
approaches to sampling from the posterior for hierarchical parameterizations
are discussed: an optimization-based sampling approach (RML), an iterative
ensemble smoother (IES), and a novel hybrid of the previous two approaches
(hybrid IES). The three approximate sampling methods are applied to a
linear-Gaussian inverse problem for which it is possible to compare results
with an exact ""marginal-then-conditional"" approach. Additionally, the IES and
the hybrid IES methods are tested on a two-dimensional flow problem with
uncertain anisotropy in the prior covariance. The standard IES method is shown
to perform poorly in the flow examples because of the poor representation of
the local sensitivity matrix by the ensemble-based method. The hybrid method,
however, samples well even with a relatively small ensemble size.",2206.01116v1
2022-06-12,Electronic and magnetic properties of intermetallic Kagome magnets $R$V$_6$Sn$_6$ ($R$ = Tb - Tm),"We present a systematic study of the structure, electronic, and magnetic
properties of a new branch of intermetalllic compounds, $R$V$_6$Sn$_6$ ($R$ =
Tb - Tm) by using X-ray diffraction, magnetic susceptibility, magnetization,
electrical transport, and heat-capacity measurements. These compounds feature a
combination of a non-magnetic vanadium kagome sublattice and a magnetic
rare-earth triangular sublattice that supports various spin anisotropies based
on different $R$ ions. We find magnetic orders for the $R$ = Tb, Dy, and Ho
compounds at 4.4, 3, 2.5 K, respectively, while no ordering is detected down to
0.4 K for the $R$ = Er and Tm compounds with easy-plane anisotropies.
Electronically, we found no superconductivity or charge ordering transition
down to 0.4 K for any member of this family, while all compounds exhibit
multi-band transport properties that originate from the band topology of the
vanadium kagome sublattice.",2206.05653v1
2022-06-15,Giant Rashba electrical control of magnetism in band models,"It is of considerable technological importance to achieve an electrical
control of magnetism of sufficient magnitude. To overcome the in-plane shape
anisotropy, needed is the electrical control of a perpendicular magnetic
anisotropy (PMA). It is known, within a free electron model, the Rashba
spin-orbit coupling provides such a control. Surprisingly, this same Rashba PMA
is enhanced by two to three orders of magnitude when a periodic potential is
added. Usually spin Berry phase physics reflects time dependent magnetic
fields. Here it is shown, within a time independent model, such physics arises
because the Rashba effective magnetic field has texture within the unit cell.
Predicted are electrical controllable band-structure gaps, linear in the
applied electric field $E$, that can result in a truly giant linear PMA. Also
possible is a Peierls mechanism, in which the magnetisation tilts from the
vertical, shifting these gaps to the Fermi level. As a consequence there are
low dissipation electric field driven dynamics, an alternative to the more
dissipative spin torque transfer (STT) effect. The theory requires the
introduction of an intrinsic spin Berry connection $\vec A_s$, an effective
vector potential, and is incompatible with current density functional theories
(DFT).",2206.07399v1
2022-06-30,Strain engineering of the magnetic anisotropy and magnetic moment in NdFeO3 epitaxial thin films,"Strain engineering is a powerful mean for tuning the various functionalities
of ABO3 perovskite oxide thin films. Rare-earth orthoferrite RFeO3 materials
such as NdFeO3 (NFO) are of prime interest because of their intriguing magnetic
properties as well as their technological potential applications especially as
thin films. Here, using a large set of complementary and advanced techniques,
we show that NFO epitaxial thin films, successfully grown by pulsed laser
deposition on (001)-SrTiO3, show a strong magnetic anisotropy below a critical
thickness tc of 54 nm, associated with the occurrence of structural
modifications related to symmetry and domain pattern changes. By varying the
tensile misfit strain through the decrease of film thickness below tc, the
amplitudes of in and out-of-plane magnetization can be continuously tuned while
their ratio stays constant. Furthermore, different low-temperature magnetic
behaviors are evidenced for strained and relaxed films, suggesting that the
strain-induced structural state impacts the magnetic phase stability.",2206.15071v1
2022-07-06,How fluid-mechanical erosion creates anisotropic porous media,"Using a Cauchy integral formulation of the boundary integral equations, we
simulate the erosion a porous medium comprised of up to 100 solid bodies
embedded in a Stokes flow. The grains of the medium are resolved individually
and erode under the action of surface shear stress. Through nonlinear feedback
with the surrounding flow fields, microscopic changes in grain morphology give
way to larger-scale features in the medium such as channelization. The
Cauchy-integral formulation and associated quadrature formulas enable us to
resolve dense configurations of nearly contacting bodies. We observe
substantial anisotropy to develop over the course of erosion; that is, the
configurations that result from erosion generally permit flow in the
longitudinal direction more easily than in the transverse direction by up to a
factor of six. These results suggest that the erosion of solid material from
groundwater flows may contribute to previously observed anisotropy of natural
porous media.",2207.02418v1
2022-07-06,Stress anisotropy in confined populations of growing rods,"Order and alignment are ubiquitous in growing colonies of rod-shaped bacteria
due to the nematic properties of the constituent particles. These effects are
the result of the active stresses generated by growth, passive mechanical
interactions between cells, and flow-induced effects due to the shape of the
confining container. However, how these contributing factors interact to give
rise to the observed global alignment patterns remains elusive. Here, we study,
in-silico, colonies of growing rod-shaped particles of different aspect ratios
confined in channel-like geometries. A spatially resolved analysis of the
stress tensor reveals a strong relationship between near-perfect alignment and
an inversion of stress anisotropy for particles with large length-to-width
ratios. We show that, in quantitative agreement with an asymptotic theory,
strong alignment can lead to a decoupling of active and passive stresses
parallel and perpendicular to the direction of growth, respectively. We
demonstrate the robustness of these effects in a geometry that provides less
restrictive confinement and introduces natural perturbations in alignment. Our
results illustrate the complexity arising from the inherent coupling between
nematic order and active stresses in growing active matter which is modulated
by geometric and configurational constraints due to confinement.",2207.02607v1
2022-07-08,2n-Stream Conservative Scattering,"We show how to use matrix methods of quantum mechanics to efficiently and
accurately calculate axially symmetric radiation transfer in clouds, with
conservative scattering of arbitrary anisotropy. Analyses of conservative
scattering, where the single scattering albedo is $\tilde\omega =1$ and no
energy is exchanged between the radiation and scatterers, began with work by
Schwarzschild, Milne, Eddington and others on radiative transfer in stars.
There the scattering is isotropic or nearly so. It has been difficult to extend
traditional methods to highly anisotropic scattering, like that of sunlight in
Earth's clouds. The $2n$-stream method described here is a practical way to
handle highly anisotropic, conservative scattering. The basic ideas of the
$2n$-stream method are an extension of Wick's seminal work on transport of
thermal neutrons by isotropic scattering to scattering with arbitrary
anisotropy. How to do this for finite absorption and $\tilde\omega<1$ was
described in our previous paper (arXiv:2205.09713v2). But those methods fail
for conservative scattering, when $\tilde \omega = 1$. Here we show that minor
modifications to the fundamental $2n$-scattering theory for $\tilde\omega <1$
make it suitable for $\tilde\omega = 1$.",2207.03978v1
2022-07-11,Bandwidth controlled quantum phase transition between an easy-plane quantum spin Hall state and an s-wave superconductor,"The quantum spin Hall state can be understood in terms of spontaneous O(3)
symmetry breaking. Topological skyrmion configurations of the O(3) order
parameter vector carry a charge 2e, and as shown previously, when they
condense, a superconducting state is generated. We show that this topological
route to superconductivity survives easy-plane anisotropy. Upon reducing the
O(3) symmetry to O(2)$\times$ Z$_2$, skyrmions give way to merons that carry a
unit charge. On the basis of large-scale auxiliary field quantum Monte Carlo
simulations, we show that at the particle-hole symmetric point, we can trigger
a continuous and direct transition between the quantum spin Hall state and
s-wave superconductor by condensing pairs of merons. This statement is valid in
both strong and weak anisotropy limits. Our results can be interpreted in terms
of an easy-plane deconfined quantum critical point. However, in contrast to the
previous studies in quantum spin models, our realization of this quantum
critical point conserves $U(1)$ charge, such that skyrmions are conserved.",2207.04803v3
2022-07-13,Experimental Determination of a Single Atom Ground State Orbital through Hyperfine Anisotropy,"Historically, electron spin resonance (ESR) has provided excellent insight
into the electronic, magnetic, and chemical structure of samples hosting spin
centers. In particular, the hyperfine interaction between the electron and the
nuclear spins yields valuable structural information of these centers. In
recent years, the combination of ESR and scanning tunneling microscopy
(ESR-STM) has allowed to acquire such information on individual spin centers of
magnetic atoms bound atop a surface, while additionally providing spatial
information about the binding site. Here, we conduct a full angle-dependent
investigation of the hyperfine splitting for individual titanium atoms on
MgO/Ag(001) by measurements in a vector magnetic field. We observe strong
anisotropy in both the g-factor and the hyperfine tensor. Combining the results
of the hyperfine splitting with the symmetry properties of the binding site
obtained from STM images and a basic point charge model allows us to predict
the shape of the electronic ground state configuration of the titanium atom.
Relying on experimental values only, this method paves the way for a new
protocol for electronic structure analysis for spin centers on surfaces.",2207.06037v2
2022-07-28,Holographic Study of Reflected Entropy in Anisotropic Theories,"We evaluate reflected entropy in certain anisotropic boundary theories dual
to nonrelativistic geometries using holography. It is proposed that this
quantity is proportional to the minimal area of the entanglement wedge cross
section. Using this prescription, we study in detail the effect of anisotropy
on reflected entropy and other holographic entanglement measures. In
particular, we study the discontinuous phase transition of this quantity for a
symmetric configuration consisting of two disjoint strips. We find that in the
specific regimes of the parameter space the critical separation is an
increasing function of the anisotropy parameter and hence the correlation
between the subregions becomes more pronounced. We carefully examine how these
results are consistent with the behavior of other correlation measures
including the mutual information. Finally, we show that the structure of the
universal terms of entanglement entropy is corrected depending on the
orientation of the entangling region with respect to the anisotropic direction.",2207.14169v1
2022-07-29,On the bending of rectangular atomic monolayers along different directions: an ab initio study,"We study the bending of rectangular atomic monolayers along different
directions from first principles. Specifically, choosing the phosphorene, GeS,
TiS$_3$, and As$_2$S$_3$ monolayers as representative examples, we perform
Kohn-Sham density functional theory calculations to determine the variation in
transverse flexoelectric coefficient and bending modulus with the direction of
bending. We find that while the flexoelectric coefficient is nearly isotropic,
there is significant and complex anisotropy in bending modulus that also
differs between the monolayers, with extremal values not necessarily occurring
along the principal directions. In particular, the commonly adopted orthotropic
continuum plate model with uniform thickness fails to describe the observed
variations in bending modulus for GeS, TiS$_3$, and As$_2$S$_3$. We determine
the direction-dependent effective thickness for use in such continuum models.
We also show that the anisotropy in bending modulus is not associated with the
rehybridization of atomic orbitals.",2208.00091v2
2022-07-30,Skyrmion pinning by disk-shaped defects,"High precision skyrmion pinning by an intentionally created magnetic
structure is important in skyrmion manipulation. Here, we consider skyrmion
pinning by various types of disks. Among other findings, we clarify that, in
terms of pinning position and pinning potential landscape, one needs to
distinguish thin-wall skyrmions from thick-wall skyrmions because of
fundamental differences. A skyrmion wall prefers areas with a weaker exchange
stiffness, a larger DMI constant, or a smaller magnetic anisotropy while a
skyrmion core experiences only the magnetic anisotropy, not exchange stiffness
and DMI. Depending on disk type, skyrmion type, and the relative size of the
disk (to skyrmion), a skyrmion can be pinned at the symmetric (center) or
asymmetric (off-center) point of a disk. In case a skyrmion is pinned by a
local energy minimum, thermal agitation can depin the skyrmion, and the pinning
lifetime follows an Arrhenius law. Interestingly, when the disk size is
comparable to the skyrmion size, the skyrmion deforms greatly such that the
skyrmion will shrink or expand to fill the whole disk. These findings should be
important for skyrmion manipulations.",2208.00178v1
2022-07-24,Ion-Beam Radiation-Induced Eshelby Transformations: The Mean and Variance in Hydrostatic and Shear Residual Stresses,"Ion beam plays a pivotal role in ion implantations and the fabrication of
nanostructures. However, there lacks a quantitative model to describe the
residual stresses associated with the ion-beam radiation. Radiation-induced
residual stress/transformation strain have been mostly recognized in the
hydrostatic sub strain space. Here, we use molecular dynamics (MD) simulations
to show that the response of a material to irradiation is generally anisotropic
that depends on the ion-beam direction, and should be described using tensorial
quantities. We demonstrate that accelerator-based ion beam irradiation,
combined with the intrinsic lattice anisotropy and externally induced
anisotropy (such as anisotropic mechanical loadings), causes radiation-actuated
shear transformation strains in addition to hydrostatic expansion. We map out
these complex correlations for several materials. Radiation-induced defects are
shown to be responsible for residual shear stresses in the manner of Eshelby
inclusion transformation. We propose such tensorial response model should be
considered for accurate nanoscale fabrication using ion-beam irradiation.",2208.04147v1
2022-08-09,Momentum broadening of heavy quarks and jets in the Glasma from classical colored particle simulations,"We investigate the effects of the pre-equilibrium Glasma stage of heavy-ion
collisions on the broadening of momentum for heavy quarks and jets using
classical colored particle simulations based on Wong's equations. Confirming
previous studies, we find that these probes accumulate momentum on the order of
the saturation scale $Q_s$ and that the color field of the Glasma induces an
anisotropy with more broadening along the beam axis. For quark jets the
anisotropy is more pronounced at lower energies.",2208.04781v1
2022-08-09,Geometric-anisotropy induced high-order topological insulators in nonsymmorphic photonic crystals,"To a significant extent, the rich physical properties of photonic crystals
are determined by the underlying geometry, in which the composed symmetry
operators and their combinations contribute to the unique topological invariant
to characterize the topological phases. Particularly, the inter- and
intra-coupling modulation in the two-dimensional (2D) Su-Schrieffer-Heeger
model yields the topological phase transition, and exhibit first-order edge
localized states and second-order corner localized corner states. In this work,
we use the geometric anisotropy into the 2D square lattice composed of four
rectangle blocks. We show a variety of topological phase transitions in
designed nonsymmorphic photonic crystals (PCs) and these transitions shall be
understood in terms of the Zak phase and Chern number in synthetic space, as
well as the pseudospin-2 concept, combinationally. Furthermore, Zak phase
winding in the periodic synthetic parameter space yields high-order Chern
number and double interface states. Based on the extended Zak phase and
pseudo-spin Hall effect, higher-order topological insulator is constructed in
the PC system. The intriguing and abundant topological features are also
sustained in the corresponding three-dimensional PC slab, which makes it a very
interesting platform to control the flow of optical signals.",2208.04816v1
2022-08-11,Magnetic-field-induced ab-plane rotation of the Eu magnetic moments in trigonal EuMg2Bi2 and EuMg2Sb2 single crystals below their Neel temperatures,"The thermodynamic and electronic-transport properties of trigonal EuMg2Bi2 in
ab-plane magnetic fields Hx and the A-type antiferromagnetic structure have
recently been reported. At a temperature of 1.8 K < TN, the Eu magnetic moments
with spin S = 7/2 remain locked in the ab plane up to and above the ab-plane
critical field Hxc = 27.5 kOe at which the Eu moments become parallel to Hx.
Here additional measurements at low fields are reported that reveal a new
spin-reorientation transition at a field Hc1 = 465 Oe where the Eu moments
remain in the ab plane but become perpendicular to Hx. At higher fields, the
moments cant towards the field resulting in M proportional to Hx up to Hxc.
Similar results are reported from measurements of the magnetic properties of
EuMg2Sb2 single crystals, where Hc1 = 220 Oe is found. Theory is formulated
that models the low-field magnetic behavior of both materials, and the
associated anisotropies are calculated. The ab-plane trigonal anisotropy in
EuMg2Sb2 is found to be significantly smaller than in EuMg2Bi2.",2208.06020v1
2022-08-17,Thermoviscous Hydrodynamics in Non-Degenerate Dipolar Bose Gases,"We present a hydrodynamic model of ultracold, but not yet quantum condensed,
dipolar Bosonic gases. Such systems present both $s$-wave and dipolar
scattering, the latter of which results in anisotropic transport tensors of
thermal conductivity and viscosity. This work presents an analytic derivation
of the viscosity tensor coefficients, utilizing the methods established in
[Wang et al., arXiv:2205.10465], where the thermal conductivities were derived.
Taken together, these transport tensors then permit a comprehensive description
of hydrodynamics that is now embellished with dipolar anisotropy. An analysis
of attenuation in linear waves illustrates the effect of this anisotropy in
dipolar fluids, where we find a clear dependence on the dipole orientation
relative to the direction of wave propagation.",2208.08353v1
2022-08-18,Shear hardening in frictionless amorphous solids near the jamming transition,"The jamming transition, generally manifested by a rapid increase of rigidity
under compression (i.e., compression hardening), is ubiquitous in amorphous
materials. Here we study shear hardening in deeply annealed frictionless
packings generated by numerical simulations, reporting critical scalings absent
in compression hardening. We demonstrate that hardening is a natural
consequence of shear-induced memory destruction. Based on an elasticity theory,
we reveal two independent microscopic origins of shear hardening: (i) the
increase of the interaction bond number and (ii) the emergence of anisotropy
and long-range correlations in the orientations of bonds, the latter highlights
the essential difference between compression and shear hardening. Through the
establishment of physical laws specific to anisotropy, our work completes the
criticality and universality of jamming transition, and the elasticity theory
of amorphous solids.",2208.08793v2
2022-08-21,Enhanced magnetoresistance in perpendicular magnetic tunneling junctions with MgAl2O4 barrier,"Perpendicular magnetic tunnel junction with MgAl2O4 barrier is investigated.
It is found that reactive RF sputtering with O2 is essential to obtain strong
perpendicular magnetic anisotropy and large tunneling magnetoresistance in
MgAl2O4-based junctions. An interfacial perpendicular magnetic anisotropy
energy density of 2.25 mJ/m2 is obtained for the samples annealed at 400C. An
enhanced magnetoresistance of 60% has also been achieved. The Vhalf, bias
voltage at which tunneling magnetoresistance drops to half of the zero-bias
value, is found to be about 1V, which is substantially higher than that of
MgO-based junctions.",2208.09947v1
2022-08-22,"Current-induced magnetization reversal in (Ga,Mn)(Bi,As) epitaxial layer with perpendicular magnetic anisotropy","Pulsed current-induced magnetization reversal is investigated in the layer of
(Ga,Mn)(Bi,As) dilute ferromagnetic semiconductor (DFS) epitaxially grown under
tensile misfit strain causing perpendicular magnetic anisotropy in the layer.
The magnetization reversal, recorded through measurements of the anomalous Hall
effect, appearing under assistance of a static magnetic field parallel to the
current, is interpreted in terms of the spin-orbit torque mechanism. Our
results demonstrate that an addition of a small fraction of heavy Bi atoms,
substituting As atoms in the prototype DFS (Ga,Mn)As and increasing the
strength of spin-orbit coupling in the DFS valence band, significantly enhances
the efficiency of current-induced magnetization reversal thus reducing
considerably the threshold current density necessary for the reversal. Our
findings are of technological importance for applications to spin-orbit
torque-driven nonvolatile memory and logic elements.",2208.10318v1
2022-08-23,Anisotropic inflation in non-minimal kinetic coupling model,"We study anisotropic inflation in non-minimal derivative coupling model where
the scalar field non-minimally coupled to the $U(1)$ gauge fields and
derivative of the scalar field non-minimally coupled to the Einstein tensor.
Within the framework we find power-law anisotropic solutions in this model when
both the inflaton potential and the gauge kinetic function are power-law type
in the high friction regime. We show the ratio of anisotropy to the expansion
rate is nearly constant, small and proportional to the slow-roll parameters of
the theory. As a demonstration, we consider numerically calculation of the
model to show that the behavior of anisotropy by changing the parameters of the
model for quadratic inflationary potential. There is anisotropic attractor
solution for a wide range of values of the model parameters. We show both
numerically and analytically that there are two phases of inflation, similar to
those an anisotropic inflation in minimal coupling model, isotropic and
anisotropic phase. We can change the number of e-folds corresponding to each
phase of slow roll inflation by changing the gauge coupling constant or
non-minimal derivative coupling constant. There are the best agreement with the
numerically solutions and analytically solutions in this investigation.",2208.10757v2
2022-08-26,Geostatistics for large datasets on Riemannian manifolds: a matrix-free approach,"Large or very large spatial (and spatio-temporal) datasets have become common
place in many environmental and climate studies. These data are often collected
in non-Euclidean spaces (such as the planet Earth) and they often present
non-stationary anisotropies. This paper proposes a generic approach to model
Gaussian Random Fields (GRFs) on compact Riemannian manifolds that bridges the
gap between existing works on non-stationary GRFs and random fields on
manifolds. This approach can be applied to any smooth compact manifolds, and in
particular to any compact surface. By defining a Riemannian metric that
accounts for the preferential directions of correlation, our approach yields an
interpretation of the ''local anisotropies'' as resulting from ''local''
deformations of the domain. We provide scalable algorithms for the estimation
of the parameters and for optimal prediction by kriging and simulation able to
tackle very large grids. Stationary and non-stationary illustrations are
provided.",2208.12501v2
2022-08-28,Mechanical Anisotropy and Multiple Direction-Dependent Dirac States in the Synthesized Ag3C20 Monolayer,"Recently, a 2D orthorhombic silver-organic framework, Ag3C20 monolayer, was
synthesized by assembling organic molecules linked with multiple aryl-metal
bonds. Herein, via first-principles study, we demonstrate that owing to the
unique bonding feature, Ag3C20 monolayer not only exhibits strong mechanical
anisotropy, but also possesses various tunable direction-dependent Dirac
states. Around the Fermi level blow, the intrinsic Dirac points form two
antiparallel quasi type-III nodal lines protected by mirror symmetry, which can
further evolve into hybrid nodal loops under tiny strains. Intriguingly, near
the Fermi level above, a special semi-Dirac state can emerge under a critical
strain by merging two type-I Dirac cone, which harbors direction-dependent
strongly localized fermions, normal massive carries, and ultrafast Dirac
fermions at the same time. These findings suggest that the mechanically
sensitive Ag3C20 monolayer is a promising 2D material to realize the
interesting Dirac physics and highly anisotropic multiple carries transport.",2208.13202v1
2022-09-05,Generation and routing of nanoscale droplet solitons without compensation of magnetic damping,"Magnetic droplet soliton is a localized dynamic spin state which can serve as
a nanoscale information carrier and nonlinear oscillator. The present opinion
is that the formation of droplet solitons requires the compensation of magnetic
damping by a torque created by a spin-polarized electric current or pure spin
current. Here we demonstrate theoretically that nanoscale droplet solitons can
be generated and routed in ferromagnetic nanostructures with voltage-controlled
magnetic anisotropy in the presence of uncompensated magnetic damping.
Performing micromagnetic simulations for the MgO/Fe/MgO trilayer with almost
perpendicular-to-plane magnetization, we reveal the formation of the droplet
soliton under a nanoscale gate electrode subjected to a sub-nanosecond voltage
pulse. The soliton lives up to 50 ns at room temperature and can propagate over
micrometer distances in a ferromagnetic waveguide due to nonzero gradient of
the demagnetizing field. Furthermore, we show that an electrical routing of the
soliton to different outputs of a spintronic device can be realized with the
aid of an additional semiconducting nanostripe electrode creating controllable
gradient of the perpendicular magnetic anisotropy.",2209.01893v1
2022-09-08,Transport anisotropy and metal-insulator transition in striped Dirac fermion systems,"Using the determinant quantum Monte Carlo method, we investigate the
metal-insulator transitions induced by the stripe of charge density in an
interacting two-dimensional Dirac fermion system. The stripe will introduce the
transport anisotropy and insulating intermediate phase into the system,
accompanied by the change of band structure and a peak of density of states
around Fermi energy. In the case of strong correlation, stripe exhibits
competition with Coulomb repulsion through closing the energy gap and
disrupting the magnetic order, and finally drives the system in Mott insulating
phase back to the metallic state. Our results may provide a feasible way to
modify transport properties by setting charge stripes in experiments.",2209.03628v1
2022-09-11,Production yield and azimuthal anisotropy measurements of strange hadrons from BES at STAR,"We report the production and azimuthal anisotropy measurements of strange and
multi-strange hadrons at STAR BES energies. The $\Lambda/K^0_s$ ratio is
reported at 3 GeV and observed to increase faster with transverse momentum than
that at higher energies. The number-of-constituent quark (NCQ) scaling of $v_2$
has been studied at 19.6 GeV (BES-II). The NCQ scaling holds for particles and
anti-particles, which can be considered as an evidence of partonic
collectivity. The production of $K^{*0}$ resonance is also reported for 7.7-39
GeV (BES-I) and the $K^{*0}/K$ ratio suggests that hadronic re-scattering
dominates over regeneration in central A+A collisions. Using the $K^{*0}/K$
ratio, we also report the lower limit of hadronic phase lifetime $( t_{kin} -
t_{chem} )$.",2209.04863v1
2022-09-12,State Space Geometry of the Spin-1 Antiferromagnetic Heisenberg Chain,"We study the phase diagram of the spin-1 antiferromagnetic Heisenberg chain
with uniaxial anisotropy and applied magnetic field in terms of the genuine
multipartite entanglement as witnessed by the mean quantum Fisher information
density. By generalizing the manifold studied in [1, 2] to the many body case
for spin 1, we connect the state space curvature in the vicinity of the ground
state of the Heisenberg chain to the genuine multipartite entanglement. Our
analysis demonstrates that the quantum critical points and symmetry protected
topological (SPT) phase exhibit large state space curvature, while the
separable phases are completely flat, offering insight into the physical
interpretation of state space curvature. We further show that the entanglement
in the SPT phase is enhanced by the presence of uniaxial anisotropy, and
undiminished in the presence of uniform magnetic fields. The magnon condensate
phase induced by large fields is shown to emanate from the Gaussian critical
point, and exhibits massive multipartite entanglement over a robust region of
the parameter space.",2209.05005v4
2022-09-15,The Schönberg-Chandrasekhar limit in presence of small anisotropy and modified gravity,"The Sch\""{o}nberg-Chandrasekhar limit in post main sequence evolution for
stars of masses in the range $1.4\lesssim M/M_{\odot}\lesssim 6$ gives the
maximum pressure that the stellar core can withstand, once the central hydrogen
is exhausted. It is usually expressed as a quadratic function of $1/\alpha$,
with $\alpha$ being the ratio of the mean molecular weight of the core to that
of the envelope. Here, we revisit this limit in scenarios where the pressure
balance equation in the stellar interior may be modified, and in the presence
of small stellar pressure anisotropy, that might arise due to several physical
phenomena. Using numerical analysis, we derive a three parameter dependent
master formula for the limit, and discuss various physical consequences. As a
byproduct, in a limiting case of our formula, we find that in the standard
Newtonian framework, the Sch\""{o}nberg-Chandrasekhar limit is best fitted by a
polynomial that is linear, rather than quadratic, to lowest order in
$1/\alpha$.",2209.07389v2
2022-09-19,Emergent isotropy of a wave-turbulent cascade in the Gross-Pitaevskii model,"The restoration of symmetries is one of the most fascinating properties of
turbulence. We report a study of the emergence of isotropy in the
Gross-Pitaevskii model with anisotropic forcing. Inspired by recent
experiments, we study the dynamics of a Bose-Einstein condensate in a
cylindrical box driven along the symmetry axis of the trap by a spatially
uniform force. We introduce a measure of anisotropy $A(k,t)$ defined on the
momentum distributions $n(\boldsymbol{k},t)$, and study the evolution of
$A(k,t)$ and $n(\boldsymbol{k},t)$ as turbulence proceeds. As the system
reaches a steady state, the anisotropy, large at low momenta because of the
large-scale forcing, is greatly reduced at high momenta. While
$n(\boldsymbol{k},t)$ exhibits a self-similar cascade front propagation,
$A(k,t)$ decreases without such self-similar dynamics. Finally, our numerical
calculations show that the isotropy of the steady state is robust with respect
to the amplitude of the drive.",2209.08973v2
2022-09-19,Cavity-mediated superconductor$\unicode{x2013}$ferromagnetic insulator coupling,"A recent proof of concept showed that cavity photons can mediate
superconducting (SC) signatures to a ferromagnetic insulator (FI) over a
macroscopic distance [Phys. Rev. B, 102, 180506(R) (2020)]. In contrast with
conventional proximity systems, this facilitates long-distance
FI$\unicode{x2013}$SC coupling, local subjection to different drives and
temperatures, and studies of their mutual interactions without proximal
disruption of their orders. Here we derive a microscopic theory for these
interactions, with an emphasis on the leading effect on the FI, namely, an
induced anisotropy field. In an arbitrary practical example, we find an
anisotropy field of $14 \unicode{x2013} 16$ $\mu$T, which is expected to yield
an experimentally appreciable tilt of the FI spins for low-coercivity FIs such
as Bi-YIG. We discuss the implications and potential applications of such a
system in the context of superconducting spintronics.",2209.09308v2
2022-09-25,Ring-originated anisotropy of local structural ordering in amorphous and crystalline silicon dioxide,"Rings comprising chemically bonded atoms are essential topological motifs for
the structural ordering of network-forming materials. Quantification of such
larger motifs beyond short-range pair correlation is essential for
understanding the linkages between the orderings and macroscopic behaviors.
Here, we propose two quantitative analysis methods based on rings. The first
method quantifies rings by two geometric indicators: roundness and roughness.
These indicators reveal the linkages between highly symmetric rings and crystal
symmetry in silica and that the structure of amorphous silica mainly consists
of distorted rings. The second method quantifies a spatial correlation function
that describes three-dimensional atomic densities around rings. A comparative
analysis among the functions for different degrees of ring symmetries reveals
that symmetric rings contribute to the local structural order in amorphous
silica. Another analysis of amorphous models with different orderings reveals
anisotropy of the local structural ordering around rings; this contributes to
building the intermediate-range ordering.",2209.12116v2
2022-09-27,Leveraging Voltage-Controlled Magnetic Anisotropy to Solve Sneak Path Issues in Crossbar Arrays,"In crossbar array structures, which serves as an ""In-Memory"" compute engine
for Artificial Intelligence hardware, write sneak path problem causes undesired
switching of devices that degrades network accuracy. While custom crossbar
programming schemes have been proposed, device level innovations leveraging
non-linear switching characteristics of the cross-point devices are still under
exploration to improve the energy efficiency of the write process. In this
work, a spintronic device design based on Magnetic Tunnel Junction (MTJ)
exploiting the use of voltage-controlled magnetic anisotropy (VCMA) effect is
proposed as a solution to the write sneak path problem. Additionally, insights
are provided regarding appropriate operating voltage conditions to preserve the
robustness of the magnetization trajectory during switching which is critical
for proper switching probability manipulation.",2209.13677v4
2022-10-05,"Ln2(SeO3)2(SO4)(H2O)2 (Ln = Sm, Dy, Yb): A Mixed-Ligand Pathway to New Lathanide (III) Multifunctional Materials Featuring Nonlinear Optical and Magnetic Anisotropy Properties","Bottom-up assembly of optically nonlinear and magnetically anisotropic
lanthanide materials involving precisely placed spin carriers and optimized
metal-ligand coordination offers a potential route to developing electronic
architectures for coherent radiation generation and spin-based technologies,
but the chemical design historically has been extremely hard to achieve. To
address this, we developed a worthwhile avenue for creating new
noncentrosymmetric chiral Ln3+ materials Ln2(SeO3)2(SO4)(H2O)2 (Ln = Sm, Dy,
Yb) by mixed-ligand design. The materials exhibit phase-matching nonlinear
optical responses, elucidating the feasibility of the heteroanionic strategy.
Ln2(SeO3)2(SO4)(H2O)2 displays paramagnetic property with strong magnetic
anisotropy facilitated by large spin-orbit coupling. This study demonstrates a
new chemical pathway for creating previously unknown polar chiral magnets with
multiple functionalities.",2210.02342v1
2022-10-09,Direct visualization and control of antiferromagnetic domains and spin reorientation in a parent cuprate,"We report magnetic optical second-harmonic generation (SHG) polarimetry and
imaging on Sr$_2$Cu$_3$O$_4$Cl$_2$, which allows direct visualization of the
mesoscopic antiferromagnetic (AFM) structure of a parent cuprate. Temperature-
and magnetic-field-dependent SHG reveals large domains with 90$^{\circ}$
relative orientations that are stabilized by a combination of uniaxial magnetic
anisotropy and the Earth's magnetic field. Below a temperature $T_R$ $\sim$ 97
K, we observe an unusual 90$^{\circ}$ spin reorientation transition, possibly
driven by competing magnetic anisotropies of the two copper sublattices, which
swaps the AFM domain states while preserving the domain structure. This allows
deterministic switching of the AFM states by thermal or laser heating. Near
$T_R$, the domain walls become exceptionally responsive to an applied magnetic
field, with the Earth's field sufficient to completely expel them from the
crystal. Our findings unlock opportunities to study the mesoscopic AFM behavior
of parent cuprates and explore their potential for AFM technologies.",2210.04327v1
2022-10-17,"Constraining Anisotropic Cosmological Model in $f(\mathcal{R},\mathscr{L}_m)$ Gravity","The observational evidence regarding the present cosmological aspects tells
us about the presence of very little anisotropy in the universe on a large
scale. Here, in this paper, we attempt to study locally rotationally symmetric
(LRS) homogeneous Bianchi-I spacetime with the isotropic matter distribution.
This is done within the framework of $f(\mathcal{R},\mathscr{L}_m)$ gravity.
Particularly, we consider a non-linear $f(\mathcal{R},\mathscr{L}_m)$ model,
$f(\mathcal{R},\mathscr{L}_m)=\dfrac{1}{2}\mathcal{R}+\mathscr{L}_m^{\,{\alpha}}$.
Furthermore, $\omega$, the equation of state parameter, which is vital stuff in
determining the present phase of the universe is constrained. To constrain the
model parameters and the equation of state parameter, we use 57 Hubble data
points and 1048 Pantheon supernovae type Ia data sample. And, for our
statistical analysis, we use Markoc Chain Monte Carlo (MCMC) simulation.
Moreover, with the help of obtained values of parameters, we measure the
anisotropy parameter for our model.",2210.09307v1
2022-10-22,Two-dimensional natural hyperbolic materials: From polaritons modulation to applications,"Natural hyperbolic materials (HMs) in two dimensions (2D) have an
extraordinarily high anisotropy and a hyperbolic dispersion relation. Some of
them can even sustain hyperbolic polaritons with great directional propagation
and light compression to deeply sub-wavelength scales due to their inherent
anisotropy. Herein, the anisotropic optical features of 2D natural HMs are
reviewed. Four hyperbolic polaritons (i.e., phonon polaritons, plasmon
polaritons, exciton-polaritons, and shear polaritons) as well as their
generation mechanism are discussed in detail. The natural merits of 2D HMs hold
promise for practical quantum photonic applications such as valley quantum
interference, mid-infrared polarizer, spontaneous emission enhancement,
near-field thermal radiation, and a new generation of optoelectronic
components, among others. These analyses' conclusion outlines existing issues
and potential interesting directions for 2D natural HMs. These findings could
spur more interest in anisotropic 2D atomic crystals in the future, as well as
the quick generation of natural HMs for new applications.",2210.12341v1
2022-10-24,Reduction of energy cost of magnetization switching in a biaxial nanoparticle by use of internal dynamics,"A solution to energy-efficient magnetization switching in a nanoparticle with
biaxial anisotropy is presented. Optimal control paths minimizing the energy
cost of magnetization reversal are calculated numerically as functions of the
switching time and materials properties, and used to derive energy-efficient
switching pulses of external magnetic field. Hard-axis anisotropy reduces the
minimum energy cost of magnetization switching due to the internal torque in
the desired switching direction. Analytical estimates quantifying this effect
are obtained based on the perturbation theory. The optimal switching time
providing a tradeoff between fast switching and energy efficiency is obtained.
The energy cost of switching and the energy barrier between the stable states
can be controlled independently in a biaxial nanomagnet. This provides a
solution to the dilemma between energy-efficient writability and good thermal
stability of magnetic memory elements.",2210.13514v2
2022-10-25,Radiant gravitational collapse with anisotropy in pressures and bulk viscosity,"We model a compact radiant star that undergoes gravitational collapse from a
certain initial static configuration until it becomes a black hole. The star
consists of a fluid with anisotropy in pressures, bulk viscosity, in addition
to the radial heat flow. A solution of Einstein's field equations with temporal
dependence was presented to study the dynamic evolution of physical quantities,
such as the mass-energy function, the luminosity seen by an observer at
infinity and the heat flow. We checked the acceptability conditions of the
initial static configuration to obtain a range of mass-to-radius ratio in which
the presented star model is physically reasonable. The energy conditions were
analyzed for the dynamic case, in order to guarantee that the model is composed
of a physically acceptable fluid within the range of the mass-to-radius ratio
obtained for the static configuration or if they will be modified during the
collapse",2210.14288v1
2022-10-26,"Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers","Nb and its compounds are widely used in quantum computing due to their high
superconducting transition temperatures and high critical fields. Devices that
combine superconducting performance and spintronic non-volatility could deliver
unique functionality. Here we report the study of magnetic tunnel junctions
with Nb as the heavy metal layers. An interfacial perpendicular magnetic
anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO
heterostructures. The tunneling magnetoresistance was evaluated in junctions
with different thickness combinations and different annealing conditions. An
optimized magnetoresistance of 120% was obtained at room temperature, with a
damping parameter of 0.011 determined by ferromagnetic resonance. In addition,
spin-transfer torque switching has also been successfully observed in these
junctions with a quasistatic switching current density of 7.3*10^5 A/cm2.",2210.14969v1
2022-10-28,"Pressure-dependent semiconductor-metal transition and elastic, electronic, optical, and thermophysical properties of SnS binary chalcogenide","Density functional theory based study of the pressure dependent physical
properties of binary SnS compound has been carried out. The computed elastic
constants reveal that SnS is mechanically stable and brittle under ambient
conditions. With increasing pressure, the compound becomes ductile. The
Poisson's ratio also indicates brittle-ductile transition with increasing
pressure. The hardness of SnS increases significantly with pressure. The
compound possesses elastic anisotropy. The ground state electronic band
structure is semiconducting with a small band gap which becomes metallic under
pressure. The band becomes more and more dispersive with the increase in
pressure while the electronic correlations decrease as pressure is raised. Both
the Debye temperature and the phonon thermal conductivity of SnS increase
sharply with pressure. The Melting temperature of the compound is low. Mixed
bonding characteristics are found with ionic and covalent contributions. SnS is
a good absorber of ultraviolet light. The reflectivity of the material
increases with the increase in pressure. The reflectivity is nonselective over
a wide spectral range. The low energy refractive index is high. All these
optical characteristics are useful for prospective optoelectronic device
applications. The optical anisotropy is low.",2210.16055v1
2022-10-28,The reconstructed CMB lensing bispectrum,"Weak gravitational lensing by the intervening large-scale structure (LSS) of
the Universe is the leading non-linear effect on the anisotropies of the cosmic
microwave background (CMB). The integrated line-of-sight mass that causes the
distortion -- known as lensing convergence -- can be reconstructed from the
lensed temperature and polarization anisotropies via estimators quadratic in
the CMB modes, and its power spectrum has been measured from multiple CMB
experiments. Sourced by the non-linear evolution of structure, the bispectrum
of the lensing convergence provides additional information on late-time
cosmological evolution complementary to the power spectrum. However, when
trying to estimate the summary statistics of the reconstructed lensing
convergence, a number of noise-biases are introduced, as previous studies have
shown for the power spectrum. Here, we explore for the first time the
noise-biases in measuring the bispectrum of the reconstructed lensing
convergence. We compute the leading noise-biases in the flat-sky limit and
compare our analytical results against simulations, finding excellent
agreement. Our results are critical for future attempts to reconstruct the
lensing convergence bispectrum with real CMB data.",2210.16203v1
2022-11-02,Spin wave excitations in a nanowire spin-torque oscillator with perpendicular magnetic anisotropy,"Spin torque oscillators (STOs) are emerging microwave devices that can
potentially be used in spin-logic devices and the next-generation high-speed
computing architecture. Thanks to their non-linear nature, STOs are easily
tunable by the magnetic field and the dc current. Spin Hall nano-oscillators
(SHNOs) are promising types of STOs and most of the current studies focus on
localized modes that can be easily excited. Here, we study using micromagnetic
simulations, the nature of the spin-torque-induced excitations in nanowire
devices made of perpendicular magnetic anisotropy (PMA) material. Our results
showed that upon including PMA the excitation of localized and propagating spin
wave modes is feasible. We study the nature of the mode excitations as a
function of the PMA strength (\text{K}$_u$), and the current. Indeed, we
estimate a critical value of \text{K}$_u$ to allow for the excitation of the
propagating spin wave. We attribute this mode selectivity between localized and
propagating modes to a switch in the sign of the nonlinearity of the system
from negative to positive at a non-zero \text{K}$_u$ which is supported by
analytical calculations. Our results provide deep insight into engineering
reconfigurable microwave devices for future magnonic and computational
applications.",2211.01078v1
2022-11-03,Harmonics of Parton Saturation in Lepton-Jet Correlations at the EIC,"Parton saturation is one of the most intriguing phenomena in the high energy
nuclear physics research frontier, especially in the upcoming era of the
Electron-Ion Collider (EIC). The lepton-jet correlation in deep inelastic
scattering provides us with a new gateway to the parton saturation at the EIC.
In particular, we demonstrate that azimuthal angle anisotropies of the
lepton-jet correlation are sensitive to the strength of the saturation momentum
in the EIC kinematic region. In contrast to the predictions based on the
collinear framework calculation, significant nuclear modification of the
anisotropies is observed when we compare the saturation physics results in e +
p and e + Au scatterings. By measuring these harmonic coefficients at the EIC,
one can conduct quantitative analysis in different collisional systems and
unveil compelling evidence for saturation effects.",2211.01647v4
2022-11-07,Determining Perpendicular Magnetic Anisotropy in Fe/MgO/Fe Magnetic Tunnel Junction: A DFT-Based Spin-Orbit Torque Method,"In our JunPy package, we have combined the first-principles calculated
self-consistent Hamiltonian with divide-and-conquer technique to successfully
determine the magnetic anisotropy (MA) in an Fe/MgO/Fe magnetic tunnel junction
(MTJ). We propose a comprehensive analytical derivation to clarify the crucial
roles of spin-orbit coupling that mediates the exchange and spin-orbit
components of spin torque, and the kinetic and spin-orbit components of spin
current accumulation. The angular dependence of cumulative spin-orbit torque
(SOT) indicates a uniaxial MA corresponding to the out-of-plane rotations of
magnetic moments of the free Fe layers. Different from the conventional MA
energy calculation and the phenomenological theory for a whole MTJ, our results
provide insight into the orbital-resolved SOT for atomistic spin dynamics
simulation in emergency complex magnetic heterojunctions.",2211.03603v3
2022-11-09,Activated vortex lattice transition in a superconductor with combined sixfold and twelvefold anisotropic interactions,"Numerical simulations are used to examine the transition dynamics between
metastable and ground state vortex lattice phases in a system with combined
sixfold and twelvefold contributions to the vortex-vortex interactions. The
system is initially annealed using a twelvefold anisotropy, yielding domains of
two different orientations and separated by grain boundaries. The vortex-vortex
interaction is then suddenly changed to a sixfold anisotropy, rendering the
twelvefold state metastable. Applying a drive that mimics an oscillating
magnetic field causes the metastable state to decay, indicated by the structure
factor that evolves from twelve to six peaks. The results fit the behavior seen
in recent small-angle neutron scattering studies of the vortex lattice in MgB2.
At higher drive amplitudes, the decay exhibits a two step process in which the
initial fast decrease is followed by a slower regime where avalanches or bursts
are correlated with dislocation annihilation events. The results are compared
to other types of metastable systems with quenched disorder that decay under a
periodic external drive.",2211.05045v4
2022-11-10,Giant magnetic anisotropy in the atomically thin van der Waals antiferromagnet FePS3,"Van der Waals (vdW) magnets are an ideal platform for tailoring
two-dimensional (2D) magnetism with immense potential for spintronics
applications and are intensively investigated. However, little is known about
the microscopic origin of magnetic order in these antiferromagnetic systems. We
used X-ray photoemission electron microscopy to address the electronic and
magnetic properties of the vdW antiferromagnet FePS3 down to the monolayer. Our
experiments reveal a giant out-of-plane magnetic anisotropy of 22 meV per Fe
ion, accompanied by unquenched magnetic orbital moments. Moreover, our
calculations suggest that the Ising magnetism in FePS3 is a visible
manifestation of spin-orbit entanglement of the Fe 3d electron system.",2211.05381v1
2022-11-12,Design of Spintronics-based Neuronal and Synaptic Devices for Spiking Neural Network Circuits,"Topologically stable magnetic skyrmion has a much lower depinning current
density that may be useful for memory as well as neuromorphic computing.
However, skyrmion-based devices suffer from the Magnus force originating from
the skyrmion Hall effect, which may result in unwanted skyrmion annihilation if
the magnitude of the driving current gets too large. A design of an artificial
neuron and a synapse using a synthetic antiferromagnetically coupled bilayer
device, which nullifies the Magnus force, is demonstrated in this work. The
leak term in the artificial leaky integrate-and-fire neuron is achieved by
engineering the uniaxial anisotropy profile of the neuronal device. The
synaptic device has a similar structure as the neuronal device but has a
constant uniaxial anisotropy. The synaptic device also has a linear and
symmetric weight update, which is a highly desirable trait of an artificial
synapse. Neuronal and synaptic devices based on magnetic domain-wall (DW)
motion are also studied and compared to skyrmionic devices. Our simulation
results show the energy required to perform such operation in DW or
skyrmion-based devices is on the order of a few fJ.",2211.06630v1
2022-11-16,Power-law decay of correlations after a global quench in the massive XXZ chain,"We investigate the relaxation dynamics of equal-time correlations in the
antiferromagnetic phase of the XXZ spin-1/2 chain following a global quantum
quench of the anisotropy parameter. We focus, in particular, on the relaxation
dynamics starting from an initial N\'eel state. Using state-of-the-art
density-matrix renormalization group simulations, the exact solution of an
effective free-fermion model, and the quench-action approach within the
thermodynamic Bethe ansatz, we show that the late-time relaxation is
characterized by a power-law decay $\sim t^{-3/2}$ independent of anisotropy.
This is in contrast to the previously studied exponential decay of the
antiferromagnetic order parameter. Remarkably, the effective model describes
the numerical data extremely well even on a quantitative level if higher order
corrections to the leading asymptotic behavior are taken into account.",2211.09204v2
2022-11-19,Silicon anisotropy in a bi-dimensional optomechanical cavity,"In this work, we study the effects of mechanical anisotropy in a 2D
optomechanical crystal geometry. We fabricate and measure devices with
different orientations, showing the dependence of the mechanical spectrum and
the optomechanical coupling with the relative angle of the device to the
crystallography directions of silicon. Our results show that the device
orientation strongly affects its mechanical band structure, which makes the
devices more susceptible to fabrication imperfections. Finally, we show that
our device is compatible with cryogenic measurements reaching ground state
occupancy of 0.2 phonons at mK temperature.",2211.10573v1
2022-11-21,A Continuous $hp-$Mesh Model for Discontinuous Petrov-Galerkin Finite Element Schemes with Optimal Test Functions,"We present an anisotropic $hp-$mesh adaptation strategy using a continuous
mesh model for discontinuous Petrov-Galerkin (DPG) finite element schemes with
optimal test functions, extending our previous work on $h-$adaptation. The
proposed strategy utilizes the inbuilt residual-based error estimator of the
DPG discretization to compute both the polynomial distribution and the
anisotropy of the mesh elements. In order to predict the optimal order of
approximation, we solve local problems on element patches, thus making these
computations highly parallelizable. The continuous mesh model is formulated
either with respect to the error in the solution, measured in a suitable norm,
or with respect to certain admissible target functionals. We demonstrate the
performance of the proposed strategy using several numerical examples on
triangular grids.
  Keywords: Discontinuous Petrov-Galerkin, Continuous mesh models, $hp-$
adaptations, Anisotropy",2211.11156v1
2022-11-23,Density jump for oblique collisionless shocks in pair plasmas: allowed solutions,"Shockwaves in plasma are usually dealt with using Magnetohydrodynamics (MHD).
Yet, MHD entails the assumption of a short mean free path, which is not
fulfilled in a collisionless plasma. Recently, for pair plasmas, we devised a
model allowing to account for kinetic effects within an MHD-like formalism. Its
relies on an estimate of the anisotropy generated when crossing the front, with
a subsequent assessment of the stability of this anisotropy in the downstream.
We solved our model for parallel, perpendicular and switch-on shocks. Here we
bridge between all these cases by treating the problem of an arbitrarily, but
coplanar, oriented magnetic field. Even though the formalism presented is valid
for anisotropic upstream temperatures, only the case of a cold upstream is
solved. We find extra solutions which are not part of the MHD catalog, and a
density jump that is notably less in the quasi parallel, highly magnetized,
regime. Given the complexity of the calculations, this work is mainly devoted
to the presentation of the mathematical aspect of our model. A forthcoming
article will be devoted to the physics of the shocks here defined.",2211.12876v1
2022-11-23,A study of the relativistic corrections to polarized tritium $β$-decay,"Forthcoming experiments like Project8 and Ptolemy aim at investigating with
high precision the end-point of the tritium $\beta$-decay spectrum sensitive to
the neutrino mass. In light of this, using the standard parametrization in
terms of nuclear polar form factors, we analyze the complete relativistic
expression for the spectrum of the $\beta$-electron emitted by a tritium
nucleus. Given the small parameters in the problem, we systematically discuss
the approximations that can be made, and present the first two corrections to
the standard lowest order formula. We particularly discuss the case of an
initially polarized target, and the consequences on the spectrum as a function
of the neutrino mass. We show that, while it induces an angular anisotropy that
can be measured by future experiments, such anisotropy cannot be used as an
additional handle to constrain the neutrino mass.",2211.13247v3
2022-11-25,Microscopic parameters of the van der Waals CrSBr antiferromagnet from microwave absorption experiments,"Microwave absorption experiments employing a phase-sensitive external
resistive detection are performed for a topical van der Waals antiferromagnet
CrSBr. The field dependence of two resonance modes is measured in an applied
field parallel to the three principal crystallographic directions, revealing
anisotropies and magnetic transitions in this material. To account for the
observed results, we formulate a microscopic spin model with a bi-axial
single-ion anisotropy and inter-plane exchange. Theoretical calculations give
an excellent description of full magnon spectra enabling us to precisely
determine microscopic interaction parameters for CrSBr.",2211.14117v1
2022-11-27,Holographic energy loss near critical temperature in an anisotropic background,"We study the energy loss of a quark moving in a strongly coupled QGP under
the influence of anisotropy. The heavy quark drag force, diffusion coefficient,
and jet quenching parameter are calculated using the Einstein-Maxwell-dilaton
model, where the anisotropic background is characterized by an arbitrary
dynamical parameter $A$.Our findings indicate that as the anisotropic factor
$A$ increases, the drag force and jet quenching parameter both increase, while
the diffusion coefficient decreases. Additionally, we observe that the energy
loss becomes more significant when the quark moves perpendicular to the
anisotropy direction in the transverse plane.The enhancement of the rescaled
jet quenching parameters near critical temperature $T_c$, as well as drag
forces for a fast-moving heavy quark is observed, which presents one of the
typical features of QCD phase transition.",2211.14792v3
2022-12-01,Invariant Data-Driven Subgrid Stress Modeling on Anisotropic Grids for Large Eddy Simulation,"We present a new approach for constructing data-driven subgrid stress models
for large eddy simulation of turbulent flows using anisotropic grids. The key
to our approach is a Galilean, rotationally, reflectionally and unit invariant
model form that also embeds filter anisotropy in such a way that an important
subgrid stress identity is satisfied. We use this model form to train a
data-driven subgrid stress model using only a small amount of anisotropically
filtered DNS data and a simple and inexpensive neural network architecture. A
priori and a posteriori tests indicate that the trained data-driven model
generalizes well to filter anisotropy ratios, Reynolds numbers and flow physics
outside the training dataset.",2212.00332v2
2022-12-01,Far-from-equilibrium slow modes and momentum anisotropy in expanding plasma,"The momentum distribution of particle production in heavy-ion collisions
encodes information about thermalization processes in the early-stage
quark-gluon plasma. We use kinetic theory to study the far-from-equilibrium
evolution of an expanding plasma with an anisotropic momentum-space
distribution. We identify slow and fast degrees of freedom in the
far-from-equilibrium plasma from the evolution of moments of this distribution.
At late times, the slow modes correspond to hydrodynamic degrees of freedom and
are naturally gapped from the fast modes by the inverse of the relaxation time,
$\tau_R^{-1}$. At early times, however, there are an infinite number of slow
modes with a gap inversely proportional to time, $\tau^{-1}$. From the
evolution of the slow modes we generalize the paradigm of the
far-from-equilibrium attractor to vector and tensor components of the
energy-momentum tensor, and even to higher moments of the distribution function
that are not part of the hydrodynamic evolution. We predict that initial-state
momentum anisotropy decays slowly in the far-from-equilibrium phase and may
persist until the relaxation time.",2212.00820v1
2022-12-05,Current-induced nucleation and motion of zero field skyrmion,"We study the stabilization and electrical manipulation of skyrmions in
magnetic ultrathin films in the absence of an applied magnetic field. We show
that this requires an increased magnetic anisotropy, controlled by the sample
thickness, as compared to usual skyrmionic samples, so that the uniform state
corresponds to the zero field ground state and the skyrmions to metastable
excitations. Although skyrmion stabilization at zero field is demonstrated over
a broad range of thicknesses, electrical control appeared to be more demanding
to avoid skyrmion deformation. In the thinnest samples, the large magnetic
anisotropy prevents skyrmion deformations and we show that they can be
nucleated progressively by current pulses, which underlines that the only
possible transition occurs between uniform and skyrmion states. The solitonic
skyrmions in zero applied magnetic field have the same properties as compared
to field stabilized ones, with a long-term stability and high mobility when
excited by a spin-orbit torque.",2212.02351v1
2022-12-13,Spin wave spectra of single crystal CoPS$_3$,"The spin waves in single crystals of the layered van der Waals
antiferromagnet CoPS$_3$ have been measured using inelastic neutron scattering.
The data show four distinct spin wave branches with large ($\gtrsim 14$ meV)
energy gaps at the Brillouin zone center indicating significant anisotropy. The
data were modelled using linear spin wave theory derived from a Heisenberg
Hamiltonian. Exchange interactions up to the third nearest-neighbour in the
layered planes were required to fit the data with ferromagnetic $J_1 = -1.37$
meV between first neighbours, antiferromagnetic $J_3 = 3.0$ meV between third
neighbours, and a very small $J_2 = 0.09$ meV between second neighbours. A
biaxial single-ion anisotropy was required, with a collinear term $D^x = -0.77$
meV for the axis parallel to the aligned moment direction and a coplanar term
$D^z=6.07$ meV for an axis approximately normal to the layered crystal planes.",2212.06479v1
2022-12-17,Zero-field miniature skyrmion crystal and chiral domain state in breathing-kagome antiferromagnets,"The stability of a miniature skyrmion crystal (SkX) with only a small number
of spins in the magnetic unit cell has been theoretically investigated in
$J_1$-$J_3$ antiferromagnets on the breathing kagome lattice with a single-ion
anisotropy $D$ at zero field. It is found by means of Monte Carlo simulations
that due to the breathing bond-alternation, a zero-field triple-${\bf Q}$
miniature SkX can be stabilized not only in the specific case of $D=0$ [K.
Aoyama and H. Kawamura, Phys. Rev. B 105, L100407 (2022)] but also in more
general situations with easy-axis ($D<0$) and easy-plane ($D>0$) anisotropies
which favor triple-${\bf Q}$ collinear and noncoplanar states, respectively.
Since the SkX and anti-SkX each having positive or negative chirality are
energetically degenerate, the topological Hall effect of alternative sign is
possible at zero field. It is also found that reflecting the chiral degeneracy,
the collinear and coplanar phases preempting the SkX phase possess random
domain structures consisting of positive- and negative-chirality clusters.",2212.08778v2
2022-12-17,Densely packed skyrmions stabilized at zero magnetic field by indirect exchange coupling in multilayers,"Room-temperature stabilization of skyrmions in magnetic multilayered systems
is the result of a fine balance between different magnetic interactions namely
symmetric and antisymmetric exchange, dipolar, perpendicular magnetic
anisotropy as well as, in most cases, Zeeman through an applied external field.
Such field-driven stabilization approach is not compatible with most of the
anticipated skyrmion based applications, e.g. skyrmion memories, logic or
neuromorphic computing which motivates a reduction or a cancellation of field
requirements. Here we present a method to stabilize at room-temperature and
zero-field, a densely packed skyrmion phase in ferromagnetic multilayers with
moderate number of repetitions. To this aim, we finely tune the multilayer
parameters to stabilize a dense skyrmion phase. Then, relying on the interlayer
electronic coupling to an adjacent bias magnetic layer with strong
perpendicular magnetic anisotropy and uniform magnetization, we demonstrate the
stabilization of sub-60 nm diameter skyrmion at zero-field with adjustable
skyrmion density.",2212.08920v1
2022-12-19,Logarithmic negativity of the 1D antiferromagnetic spin-1 Heisenberg model with single-ion anisotropy,"We study the 1D antiferromagnetic spin-1 Heisenberg XXX model with external
magnetic field B and single-ion anisotropy D on finite chains. We determine the
nearest and non-nearest neighbor logarithmic entanglement LN. Our main result
is the disappearance of LN both for nearest and non-nearest neighbor
(next-nearest and next-next-nearest) sites at zero temperature and for low
temperature states. Such disappearance occurs at a critical value of B and D.
The resulting phase diagram for the behaviour of LN is discussed in the B - D
plane, including a separating line - ending in a triple point - where the
energy density is independent on the size. Finally, results for LN at finite
temperature as a function of B and D are presented and commented.",2212.09511v4
2022-12-19,Anisotropic fluctuations of angular momentum of heavy quarks in the Glasma,"We study the evolution of the angular momentum of the heavy quarks in the
very early stage of high energy nuclear collisions, in which the background is
made of evolving Glasma fields. Given the novelty of the problem, we limit
ourselves to the use of toy heavy quarks with a large, unphysical mass, in
order to implement the kinetic equations for the angular momentum in the
non-relativistic limit. We find that as a consequence of the anisotropy of the
background fields, angular momentum fluctuations are also anisotropic: we
understand this in simple terms relating the fluctuations of the angular
momentum, $L$, to those of linear momentum. While orbital angular momentum
diffuses and develops substantial fluctuations and anisotropies, the spin does
not. Hence, we can identify the fluctuations of $L$ with those of the total
angular momentum $J=L + S$. Therefore, our study suggests that the total
angular momentum of the heavy quarks in the early stage of high energy nuclear
collisions will present anisotropic fluctuations.",2212.09725v1
2022-12-19,"Anisotropic resistance with a 90-degree twist in a ferromagnetic Weyl semimetal, Co2MnGa","Co$_2$MnGa is a ferromagnetic semimetal with Weyl nodal lines identified by
ARPES. We studied electrical transport in thin Co$_2$MnGa lamellae (10 $\times$
10 $\times$ 0.4-5 microns) cut from single-crystals using a focused ion beam.
These crystals exhibit an unexpected and highly unusual planar resistance
anisotropy ($\sim$10 times) with principal axes that rotate by 90 degrees
between the upper and lower faces. Using symmetry arguments and simulations, we
find that the observed resistance anisotropy resembles that of an isotropic
conductor with anisotropic surface states that are impeded from hybridization
with bulk states. The origin of these states awaits further experiments that
can correlate the surface bands with the observed 90$^\circ$-twist geometry.",2212.09738v1
2022-12-20,Low $p_T$ direct photon production at RHIC measured with PHENIX,"PHENIX has used the versatility of RHIC to map out low $p_{T}$ direct photon
production as function of collision system size and beam energy. For systems
with a size corresponding to a $dN_{ch}/d\eta$ larger than 20-30, we observe a
large yield of direct photons, a large azimuthal anisotropy with respect to the
reaction plane, and a characteristic centrality dependence of $dN_{\gamma}/dy
\propto (dN_{ch}/d\eta)^{\alpha}$, with $\alpha \sim$ 1.2. \\ In this
proceeding, we will present new results from Au+Au collisions at
$\sqrt{s_{NN}}$ = 39, 62.4 and 200 GeV. After subtracting the prompt photon
component, the inverse slope for the $p_{T}$ range from 1-2 GeV/$c$ is 250
MeV/$c$, but increases to about 400 MeV/$c$ for the range from 2 to 4 GeV/$c$.
Within the experimental uncertainty, there is no indication of a system size
dependence of the inverse slope. Furthermore, the system size dependence of the
yield, expressed through the power $\alpha$, remains independent of $p_{T}$
over the entire observed range from 1 to 6 GeV/$c$. Like the large yield and
azimuthal anisotropy, these features, while qualitatively consistent with the
emission of thermal photons from the quark gluon plasma, elude a quantitative
description through theoretical model calculations.",2212.09953v1
2022-12-20,Anisotropy distorts the spreading of a fixed volume porous gravity current,"We consider the release and subsequent gravity-driven spreading of a finite
volume of fluid in an anisotropic porous medium bounded by an impermeable
substrate. When the permeability in the vertical direction is much smaller than
the horizontal direction, as is the case in many real geological reservoirs,
this restricts the spread of the current to a very thin layer near the
impermeable base. Using a combination of asymptotic analysis and finite
difference computations of Darcy flow, we show that there exist two distinct
flow regimes. At early times the bulk of the current descends slowly and
uniformly, injecting fluid into thin finger-like regions near the base. At much
later times the current transitions to the classical gravity-driven solution
and continues to spread with a self-similar shape. One interesting consequence
is that the swept volume of the current grows differently depending on the
anisotropy of the medium. This has important consequences for managing
contaminant spills, where it is important to minimise the contacted volume of
the aquifer, or during geological CO$_2$ sequestration where a larger contacted
volume results in more CO$_2$ being stored.",2212.10327v2
2022-12-23,Azimuthal anisotropy of jet particles in p-Pb and Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV,"The azimuthal anisotropy of particles associated with jets (jet particles) at
midrapidity is measured for the first time in p-Pb and Pb-Pb collisions at
$\sqrt{s_{\rm NN}}$ = 5.02 TeV down to transverse momentum ($p_{\rm T}$) of 0.5
GeV/$c$ and 2 GeV/$c$, respectively, with ALICE. The second-order Fourier
coefficient of the jet-particle azimuthal distribution ($v_2$) in
high-multiplicity p-Pb collisions is positive, with a significance reaching
6.8$\sigma$ at low $p_{\rm T}$. Comparisons with the inclusive charged-particle
$v_2$ and with AMPT calculations are discussed. The model describes
qualitatively the main features of the jet-particle $v_2$ in high-multiplicity
p-Pb collisions and indicates that the positive jet-particle $v_2$ is generated
by parton interactions.",2212.12609v1
2022-12-28,Intrinsic orbital and spin Hall effect in bismuth semimetal,"We investigate the intrinsic orbital Hall conductivity (OHC) and spin Hall
conductivity (SHC) in a bismuth semimetal, by employing an sp-orbital
tight-binding model. We report a notable difference between the anisotropy of
OHC and SHC whose orbital and spin polarizations lie within the basal plane. We
do not observe a substantial correlation between the orbital and spin Berry
curvatures with spin-orbit coupling (SOC) at the Fermi energy, disproving the
correlation between OHC and SHC in a strong SOC regime. We argue the huge SHC
in a Bi semimetal is attributed to its gigantic SOC which strongly affects the
hybridization of the p orbitals, despite its relatively small magnitude of OHC.
We hope the distinct anisotropy of OHC and SHC provides a feasible means to
differentiate between the two effects in experiments.",2212.13891v2
2022-12-28,Imprint of galactic rotation curves and metric fluctuations on the recombination era anisotropy,"In applications of the conformal gravity theory it has been shown that a
scale of order 105 Mpc due to large scale inhomogeneities such as clusters of
galaxies is imprinted on the rotation curves of galaxies. Here we show that
this same scale is imprinted on recombination era anisotropies in the cosmic
microwave background. We revisit an analysis due to Mannheim and Horne, to show
that in the conformal gravity theory the length scale of metric signals that
originate in the primordial nucleosynthesis era at $10^{9\circ}$K can fill out
the entire recombination era sky. Similarly, the length scale of acoustic
signals that originate at $10^{13\circ}$K can also fill out the entire
recombination era sky. We show that the amplitudes of metric fluctuations that
originate in the nucleosynthesis era can grow by a factor of $10^{12}$ at
recombination, and by a factor of $10^{18}$ at the current time. In addition we
find that without any period of exponential expansion a length scale as small
as $10^{-33}$ cm can grow to the size of the recombination sky if it begins to
grow at a temperature of order $10^{33}$ degrees.",2212.13942v1
2022-12-31,Collective modes in the anisotropic collisional hot QCD medium at finite chemical potential,"We conducted a study on the collective modes within the hot QCD medium
generated in heavy-ion collision experiments. These modes, whether real or
imaginary, stable or unstable, play a crucial role in shaping the medium's
evolution. To gain a deeper understanding, we considered several factors
affecting the medium, including anisotropy, interactions among medium
particles, and finite baryonic chemical potential. While the first two aspects
have been thoroughly examined from various angles, the inclusion of finite
chemical potential was previously overlooked. To provide a comprehensive
analysis, we integrated these factors. The interactions among medium particles
were accounted for using the BGK collisional kernel, while anisotropy and
finite chemical potential were incorporated through the distribution functions
of quarks, anti-quarks, and gluons. Our findings suggest that the presence of
finite chemical potential amplifies the influence of unstable modes,
potentially affecting the rapid thermalization of the hot QCD medium.
Furthermore, exploring the implications of finite chemical potential in
conjunction with other aspects of the created medium is intriguing,
particularly in the context of low-energy heavy-ion collision experiments
conducted at low temperatures and finite baryon density.",2301.00187v2
2023-01-03,Spatially Varying Anisotropy for Gaussian Random Fields in Three-Dimensional Space,"Isotropic covariance structures can be unreasonable for phenomena in
three-dimensional spaces such as the ocean. In the ocean, the variability of
the response may vary with depth, and ocean currents may lead to spatially
varying anisotropy. We construct a class of non-stationary anisotropic Gaussian
random fields (GRFs) in three dimensions through stochastic partial
differential equations (SPDEs) where computations are done using Gaussian
Markov random field approximations.
  The approach is proven in a simulation study where the amount of data
required to estimate these models is explored. Then, the method is applied to
construct a GRF prior on an ocean mass outside Trondheim, Norway, based on
simulations from the complex numerical ocean model SINMOD. This GRF prior is
compared to a stationary anisotropic GRF using in-situ measurements collected
with an autonomous underwater vehicle where our approach outperforms the
stationary anisotropic GRF for real-time prediction of unobserved locations.",2301.01372v2
2023-01-05,Thomsen-type parameters and attenuation coefficients for constant-Q transverse isotropy,"Transversely isotropic (TI) media with the frequency-independent
quality-factor elements (also called ``constant-$Q$'' transverse isotropy) are
often used to describe attenuation anisotropy in sedimentary rocks. The
attenuation coefficients in constant-$Q$ TI models can be conveniently defined
in terms of the Thomsen-type attenuation-anisotropy parameters. Recent research
indicates that not all those parameters for such constant-$Q$ media are
frequency-independent. Here, we present concise analytic formulae for the
Thomsen-type attenuation parameters for Kjartansson's constant-$Q$ TI model and
show that one of them ($\delta_{Q}$) varies with frequency. The analytic
expression for $\delta_{Q}$ helps evaluate the frequency dependence of the
normalized attenuation coefficients of P- and SV-waves by introducing the newly
defined ``dispersion factors''. Viscoacoustic constant-$Q$ transverse isotropy
is also discussed as a special case, for which the elliptical condition and
simplified expressions for the parameters $\delta$ and $\delta_{Q}$ are
derived. Our results show that in the presence of significant absorption the
attenuation coefficients of the ``constant-$Q$'' model vary with frequency for
oblique propagation with respect to the symmetry axis. This variation needs to
be taken into account when applying the spectral-ratio method and other
attenuation-analysis techniques.",2301.01939v2
2023-01-07,Geometric quantum discord and coherence in a dipolar interacting magnetic system,"The study of low-dimensional metal complexes has revealed fascinating
characteristics regarding the ground-state crossover shown by spin-gaped
systems. In this context, this work explores the effect of the quantum-level
crossing, induced by the magnetic anisotropies of dipolar interacting systems,
on the quantum discord and coherence of the system. The analytical expressions
for the quantum discord, based on Schatten 1-norm, and the $l_1$ trace-norm
quantum coherence for dinuclear spin-1/2 systems, are provided in terms of the
magnetic anisotropies. The results show that, while the quantum discord has a
clear signature of the quantum level-crossing, the basis dependence of the
quantum coherence hides the crossover regarding the measured basis. In
addition, the global quantum coherence is wholly stored within the correlations
of the system, regardless of its reference basis.",2301.02891v1
2023-01-10,Force-free current sheets in the Jovian magnetodisk: the key role of electron field-aligned anisotropy,"Current sheets are an essential element of the planetary magnetotails, where
strong plasma currents self-consistently support magnetic field gradients. The
current sheet configuration is determined by plasma populations that contribute
to the current density. The most commonly investigated configuration is
supported by diamagnetic cross-field currents of hot ions, typical for the
magnetospheres of magnetized planets. In this study, we examine a new type of
the current sheet configuration supported by field-aligned currents from
electron streams in the Jovian magnetodisk. Such bi-directional streams
increase the electron thermal anisotropy close to the fire-hose instability
threshold and lead to strong magnetic field shear. The current sheet
configuration supported by electron streams is nearly force-free, with B=const
across the sheet. Using Juno plasma and magnetic field measurements, we
investigate the internal structure of such current sheets and discuss possible
mechanisms for their formation.",2301.03731v1
2023-01-12,Cryogenic temperature deposition of high-performance CoFeB/MgO/CoFeB magnetic tunnel junctions on 300 mm wafers,"We developed a cryogenic temperature deposition process for high-performance
CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) on 300 mm thermally oxidized
silicon wafers. The effect of the deposition temperature of the CoFeB layers on
the nanostructure, magnetic and magneto-transport properties of the MTJs were
investigated in detail. When CoFeB was deposited at 100 K, the MTJs exhibited a
perpendicular magnetic anisotropy (PMA) of 214 uJ/m2 and a voltage-controlled
magnetic anisotropy (VCMA) coefficient of -45 fJ/Vm, corresponding to 1.4- and
1.7-fold enhancements in PMA and VCMA, respectively, compared to the case of
room-temperature deposition of CoFeB. The improvement in the MTJ properties was
not simply due to the morphology of the MTJ films. The interface-sensitive
magneto-transport properties indicated that interfacial qualities such as
intermixing and oxidation states at the MgO/CoFeB interfaces were improved by
the cryogenic temperature deposition. Cryogenic-temperature sputtering
deposition is expected to be a standard manufacturing process for
next-generation magnetoresistive random-access memory.",2301.04823v1
2023-01-12,Investigating Dynamical Properties of Globular Clusters through a Family of Lowered Isothermal Models,"To investigate the dynamical properties of globular clusters, the surface
brightness and kinematic data were collected and fitted to a family of lowered
isothermal models called LIMEPY models. For 18 studied globular clusters, the
amounts of concentration, truncation, and anisotropy were determined. In
addition, the cluster mass, half-mass radius, distance, and mass-to-light ratio
were also obtained. In general, LIMEPY models could describe these clusters
well. Among these 18 clusters, NGC 5139, NGC 6388, and NGC 7078 were claimed to
be candidates to host intermediate-mass black holes in literature. The models
could not appropriately fit the central proper-motion velocity dispersion of
NGC 5139 and the slope of proper-motion velocity-dispersion profile of NGC
6388. Thus, more dedicated models with intermediate-mass black holes or a group
of stellar-mass black holes at cluster centers may need to be considered.
Considering NGC 7078, our model with some degree of anisotropy can fit the
data. Finally, the strong concentration-truncation anti-correlation and
truncation-semimajor-axis correlation were revealed, which could be the
observational imprint of the dynamical evolution of globular clusters.",2301.04868v1
2023-01-13,Multistep magnetization switching in orthogonally twisted ferromagnetic monolayers,"The advent of twist-engineering in two-dimensional (2D) crystals enables the
design of van der Waals (vdW) heterostructures exhibiting emergent properties.
In the case of magnets, this approach can afford artificial antiferromagnets
with tailored spin arrangements. Here, we fabricate an orthogonally-twisted
bilayer by twisting 90 degrees two CrSBr ferromagnetic monolayers with an
easy-axis in-plane anisotropy. The magneto-transport properties reveal
multistep magnetization switching with a magnetic hysteresis opening, that is
absent in the pristine case. By tuning the magnetic field, we modulate the
remanent state and coercivity and select between hysteretic and non-hysteretic
magneto-resistance scenarios. This complexity pinpoints spin anisotropy as a
key aspect in twisted magnetic superlattices. Our results highlight the control
over the magnetic properties in vdW heterostructures, leading to a variety of
field-induced phenomena and opening a fruitful playground for creating desired
magnetic symmetries and manipulating non-collinear magnetic configurations.",2301.05647v2
2023-01-16,Optical conductivity of the threefold Hopf semimetal,"A multifold Hopf semimetal is a topological point node semimetal possessing
an anisotropy in the internal electronic structure, e.g., the dipole structure
of the Berry curvature. In this paper, the unique features of threefold Hopf
semimetals in terms of the optical conductivity are theoretically investigated
with a minimal theoretical model by using linear response theory for a linearly
polarized photon. The frequency spectrum of the optical conductivity shows an
anisotropic dependence on the polarization angle of the incident photon even if
the electronic band structure is completely isotropic. The longitudinal optical
conductivity linearly depends on the photon frequency and possesses step-like
changes in the frequency spectrum. The anisotropic electronic structure has a
varying the number of steps with the orientation of the photon polarization
axis. We reveal that the anisotropy is attributed to symmetries preserving the
point node in threefold Hopf semimetals. The linearly polarized photon also
induces a Hall current but it vanishes with the photon polarization axis
parallel to the Berry dipole axis. The numerical calculations show that these
characteristic features can be observed even with a non-zero temperature and
disorder.",2301.06254v1
2023-01-17,All-optical magneto-thermo-elastic skyrmion motion,"It is predicted magnetic skyrmions can be controllably moved on surfaces
using a focused laser beam. Here an absorbed power of the order 1 mW, focused
to a spot-size of the order 10 $\mu$m, results in a local temperature increase
of around 50 K, and a local perpendicular strain of the order 10$^{-3}$ due to
the thermo-elastic effect. For positive magneto-elastic coupling this generates
a strong attractive force on skyrmions due to the magneto-elastic effect. The
resultant motion is dependent on forces due to i) gradients in the local
strain-induced magnetic anisotropy, ii) gradients in the effective anisotropy
due to local temperature gradients, and magnetic parameters temperature
dependences, and iii) Magnus effect acting on objects with non-zero topological
number. Using dynamical magneto-thermo-elastic modelling, it is predicted
skyrmions can be moved with significant velocities (up to 80 m/s shown), both
for ferromagnetic and antiferromagnetic skyrmions, even in the presence of
surface roughness. This mechanism of controllably moving single skyrmions in
any direction, as well as addressing multiple skyrmions in a lattice, offers a
new approach to constructing and studying skyrmionic devices with all-optical
control.",2301.07034v2
2023-01-17,Resolving the emission transition dipole moments of single doubly-excited seeded nanorods via heralded defocused imaging,"Semiconductor nanocrystal emission polarization is a crucial probe of
nanocrystal physics and an essential factor for nanocrystal-based technologies.
While the transition dipole moment of the lowest excited state to ground state
transition is well characterized, the dipole moment of higher multiexcitonic
transitions is inaccessible via most spectroscopy techniques. Here, we realize
direct characterization of the doubly-excited state relaxation transition
dipole by heralded defocused imaging. Defocused imaging maps the dipole
emission pattern onto a fast single-photon avalanche diode detector array,
allowing the post-selection of photon pairs emitted from the biexciton-exciton
emission cascade and resolving the differences in transition dipole moments.
Type-I1/2 seeded nanorods exhibit higher anisotropy of the biexciton-to-exciton
transition compared to the exciton-to-ground state transition. In contrast,
type-II seeded nanorods display a reduction of biexciton emission anisotropy.
These findings are rationalized in terms of an interplay between transient
dynamics of the refractive index and the excitonic fine structure.",2301.07211v1
2023-01-25,AnisoTag: 3D Printed Tag on 2D Surface via Reflection Anisotropy,"In the past few years, the widespread use of 3D printing technology enables
the growth of the market of 3D printed products. On Esty, a website focused on
handmade items, hundreds of individual entrepreneurs are selling their 3D
printed products. Inspired by the positive effects of machine-readable tags,
like barcodes, on daily product marketing, we propose AnisoTag, a novel tagging
method to encode data on the 2D surface of 3D printed objects based on
reflection anisotropy. AnisoTag has an unobtrusive appearance and much lower
extraction computational complexity, contributing to a lightweight low-cost
tagging system for individual entrepreneurs. On AnisoTag, data are encoded by
the proposed tool as reflective anisotropic microstructures, which would
reflect distinct illumination patterns when irradiating by collimated laser.
Based on it, we implement a real-time detection prototype with inexpensive
hardware to determine the reflected illumination pattern and decode data
according to their mapping. We evaluate AnisoTag with various 3D printer
brands, filaments, and printing parameters, demonstrating its superior
usability, accessibility, and reliability for practical usage.",2301.10599v2
2023-02-03,Defect-induced magnetism in TiO$_2$: An example of quasi 2D magnetic order with perpendicular anisotropy,"Magnetic order at room temperature induced by atomic lattice defects, like
vacancies, interstitials or pairs of them, has been observed in a large number
of different nonmagnetic hosts, such as pure graphite, oxides and silicon-based
materials. High Curie temperatures and time independent magnetic response at
room temperature indicate the extraordinary robustness of this new phenomenon
in solid state magnetism. In this work, we review experimental and theoretical
results in pure TiO$_2$ (anatase), which magnetic order can be triggered by
low-energy ion irradiation. In particular, we discuss the systematic
observation of an ultrathin magnetic layer with perpendicular magnetic
anisotropy at the surface of this oxide.",2302.01803v1
2023-02-07,Sputtered terbium iron garnet films with perpendicular magnetic anisotropy for spintronic applications,"We report the structural, magnetic, and interfacial spin transport properties
of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron
sputtering. High crystallinity was achieved by growing the films on gadolinium
gallium garnet (GGG) substrates either at high temperature, or at room
temperature followed by thermal annealing, above 750 {\deg}C in both cases. The
films display large perpendicular magnetic anisotropy (PMA) induced by
compressive strain, and tunable structural and magnetic properties through
growth conditions or the substrate lattice parameter choice. The ferrimagnetic
compensation temperature (TM) of selected TbIG films was measured through
temperature-dependent anomalous Hall effect (AHE) in Pt/TbIG heterostructures.
In the studied films, TM was found to be between 190-225 K, i.e., approximately
25-60 K lower than the bulk value, which is attributed to the combined action
of Tb deficiency and oxygen vacancies in the garnet lattice evidenced by x-ray
photoelectron spectroscopy measurements. Sputtered TbIG ultrathin films with
large PMA and highly tunable properties reported here can provide a suitable
material platform for a wide range of spintronic experiments and device
applications.",2302.03758v1
2023-02-09,Intrinsic auxeticity and mechanical anisotropy of Si9C15 siligraphene,"The graphene-like two-dimensional (2D) silicon carbide or siligraphene has
attracted remarkable attentions, owing to its fascinating physical properties.
Nevertheless, the first high-quality siligraphene, i.e., monolayer Si9C15 was
synthesised very recently, which exhibits an excellent semiconducting
behaviour. In this work, we investigate the mechanical properties of Si9C15
siligraphene by using atomistic simulations including density functional theory
(DFT) calculations and molecular dynamics (MD) simulations. Both methods
confirm the existence of intrinsic negative Poisson's ratios in Si9C15
siligraphene, which, as illustrated by MD simulations, is attributed to the
tension-induced de-wrinkling behaviours of its intrinsic rippled configuration.
Different de-wrinkling behaviours are observed in different directions of
Si9C15 siligraphene, which result in the anisotropy of its auxetic property.
The fracture property of Si9C15 siligraphene is similarly anisotropic, but
relatively large fracture strains are observed in different orientations,
indicating the stretchability of Si9C15 siligraphene. The stretchability
together with the strain-sensitive bandgap of Si9C15 siligraphene observed in
DFT calculations indicates the effectiveness of strain engineering in
modulating its electronic property. The combination of unique auxetic property,
excellent mechanical property and tunable electronic property may render Si9C15
siligraphene a novel 2D material with multifunctional applications.",2302.04409v1
2023-02-10,Electrical characterization of the azimuthal anisotropy of $(\mathrm{Ni}_x\mathrm{Co}_{1-x})\mathrm{B}$-based ferromagnetic nanotubes,"We report on the structural, electric and magnetic properties of
$(\mathrm{Ni}_x\mathrm{Co}_{1-x})\mathrm{B}$ ferromagnetic nanotubes,
displaying azimuthal magnetization. The tubes are fabricated using electroless
plating in polycarbonate porous templates, with lengths several tens of
micrometers, diameters from 100nm to 500nm and wall thicknesses from 10nm to
80nm. The resistivity is $\sim 1.5\times10^{-6}\mathrm{\Omega/m}$, and the
anisotropic magnetoresistance~(AMR) of 0.2-0.3%, one order of magnitude
larger~(resp. smaller) than in the bulk material, which we attribute to the
resistance at grain boundaries. We determined the azimuthal anisotropy field
from M(H) AMR loops of single tubes contacted electrically. Its magnitude is
around 10mT, and tends to increase with the tube wall thickness, as well as the
Co content. However, surprisingly it does not dependent much on the diameter
nor on the curvature.",2302.05246v1
2023-02-15,A strain-controlled magnetostrictive pseudo spin valve,"Electric-field control of magnetism via inverse magnetostrictive effect is an
efficient path towards improving energy-efficient storage and sensing devices
based on giant magnetoresistance effect. In this letter, we report on lateral
electric-field driven strain-mediated modulation of magnetic properties in
Co$/$Cu$/$Py pseudo spin valve grown on ferroelectric PMN-PT substrate. We show
a decrease of the giant magnetoresistance ratio of the pseudo spin valve with
increasing electric field, which is attributed to the deviation of the Co layer
magnetization from the initial direction due to strain-induced magnetoelastic
anisotropy contribution. Additionally, we demonstrate that strain-induced
magnetic anisotropy effectively shifts the switching field of the
magnetostrictive Co layer, while keeping the switching field of the nearly
zero-magnetostrictive Py layer unaffected due to its negligible
magnetostriction constant. We argue that magnetostrictively optimized magnetic
films in properly engineered multilayered structures can offer a path to
enhancing the selective magnetic switching in spintronic devices.",2302.07620v1
2023-02-17,QCD Thermodynamics and Neutral Pion in a Uniform Magnetic Field: Finite Volume Effects,"We address finite volume effects of lattice QCD calculations in background
magnetic fields. Using chiral perturbation theory at next-to-leading order,
volume effects are calculated for thermodynamic quantities: the chiral
condensate, pressure anisotropy, and magnetization. The neutral pion effective
action in a finite volume is additionally derived. For these charge neutral
observables, volume and source averaging are shown to capitalize on magnetic
periodicity, which is the remnant translational invariance of the finite-volume
theory. For a fixed magnetic field strength, certain volume and source averaged
quantities are independent of the size of the lattice transverse to the
magnetic field. Despite this simplifying feature, finite volume corrections to
the magnetic field dependence of the chiral condensate and neutral pion
magnetic polarizability can be non-negligible. The pressure anisotropy at fixed
magnetic flux, moreover, appears acutely sensitive to the lattice volume.",2302.09179v1