66,754 research outputs found
Systematic {\it ab initio} study of the magnetic and electronic properties of all 3d transition metal linear and zigzag nanowires
It is found that all the zigzag chains except the nonmagnetic (NM) Ni and
antiferromagnetic (AF) Fe chains which form a twisted two-legger ladder, look
like a corner-sharing triangle ribbon, and have a lower total energy than the
corresponding linear chains. All the 3d transition metals in both linear and
zigzag structures have a stable or metastable ferromagnetic (FM) state. The
electronic spin-polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co and
Ni linear chains is close to 90% or above. In the zigzag structure, the AF
state is more stable than the FM state only in the Cr chain. It is found that
the shape anisotropy energy may be comparable to the electronic one and always
prefers the axial magnetization in both the linear and zigzag structures. In
the zigzag chains, there is also a pronounced shape anisotropy in the plane
perpendicular to the chain axis. Remarkably, the axial magnetic anisotropy in
the FM Ni linear chain is gigantic, being ~12 meV/atom. Interestingly, there is
a spin-reorientation transition in the FM Fe and Co linear chains when the
chains are compressed or elongated. Large orbital magnetic moment is found in
the FM Fe, Co and Ni linear chains
A non-variational approach to nonlinear stability in stellar dynamics applied to the King model
In previous work by Y. Guo and G. Rein, nonlinear stability of equilibria in
stellar dynamics, i.e., of steady states of the Vlasov-Poisson system, was
accessed by variational techniques. Here we propose a different,
non-variational technique and use it to prove nonlinear stability of the King
model against a class of spherically symmetric, dynamically accessible
perturbations. This model is very important in astrophysics and was out of
reach of the previous techniques
An {\it ab initio} study of the magnetic and electronic properties of Fe, Co, and Ni nanowires on Cu(001) surface
Magnetism at the nanoscale has been a very active research area in the past
decades, because of its novel fundamental physics and exciting potential
applications. We have recently performed an {\it ab intio} study of the
structural, electronic and magnetic properties of all 3 transition metal
(TM) freestanding atomic chains and found that Fe and Ni nanowires have a giant
magnetic anisotropy energy (MAE), indicating that these nanowires would have
applications in high density magnetic data storages. In this paper, we perform
density functional calculations for the Fe, Co and Ni linear atomic chains on
Cu(001) surface within the generalized gradient approximation, in order to
investigate how the substrates would affect the magnetic properties of the
nanowires. We find that Fe, Co and Ni linear chains on Cu(001) surface still
have a stable or metastable ferromagnetic state. When spin-orbit coupling (SOC)
is included, the spin magnetic moments remain almost unchanged, due to the
weakness of SOC in 3 TM chains, whilst significant orbital magnetic moments
appear and also are direction-dependent. Finally, we find that the MAE for Fe,
and Co remains large, i.e., being not much affected by the presence of Cu
substrate.Comment: 4 pages, 2 figure
Band structure of honeycomb photonic crystal slabs
Two-dimensional (2D) honeycomb photonic crystals with cylinders and
connecting walls have the potential to have a large full band gap. In
experiments, 2D photonic crystals do not have an infinite height, and
therefore, we investigate the effects of the thickness of the walls, the height
of the slabs and the type of the substrates on the photonic bands and gap maps
of 2D honeycomb photonic crystal slabs. The band structures are calculated by
the plane wave expansion method and the supercell approach. We find that the
slab thickness is a key parameter affecting the band gap size while on the
other hand the wall thickness hardly affact the gap size. For symmetric
photonic crystal slabs with lower dielectric claddings, the height of the slabs
needs to be sufficiently large to maintain a band gap. For asymmetric
claddings, the projected band diagrams are similar to that of symmetric slabs
as long as the dielectric constants of the claddings do not differ greatly.Comment: Accepted for publication in Journal of Applied Physic
A sharp stability criterion for the Vlasov-Maxwell system
We consider the linear stability problem for a 3D cylindrically symmetric
equilibrium of the relativistic Vlasov-Maxwell system that describes a
collisionless plasma. For an equilibrium whose distribution function decreases
monotonically with the particle energy, we obtained a linear stability
criterion in our previous paper. Here we prove that this criterion is sharp;
that is, there would otherwise be an exponentially growing solution to the
linearized system. Therefore for the class of symmetric Vlasov-Maxwell
equilibria, we establish an energy principle for linear stability. We also
treat the considerably simpler periodic 1.5D case. The new formulation
introduced here is applicable as well to the nonrelativistic case, to other
symmetries, and to general equilibria
Measurement-induced nonlocality over two-sided projective measurements
Measurement-induced nonlocality (MiN), introduced by Luo and Fu [Phys. Rev.
Lett. 106(2011)120401], is a kind of quantum correlation that beyond
entanglement and even beyond quantum discord. Recently, we extended MiN to
infinite-dimensional bipartite system [arXiv:1107.0355]. MiN is defined over
one-sided projective measurements. In this letter we introduce a
measurement-induced nonlocality over two-sided projective measurements. The
nullity of this two-sided MiN is characterized, a formula for calculating
two-sided MiN for pure states is proposed, and a lower bound of (two-sided) MiN
for maximally entangled mixed states is given. In addition, we find that
(two-sided) MiN is not continuous. The two-sided geometric measure of quantum
discord (GMQD) is introduced in [Phys. Lett. A 376(2012)320--324]. We extend it
to infinite-dimensional system and then compare it with the two-sided MiN. Both
finite- and infinite-dimensional cases are considered.Comment: 12 page
Geometries for Possible Kinematics
The algebras for all possible Lorentzian and Euclidean kinematics with
isotropy except static ones are re-classified. The geometries
for algebras are presented by contraction approach. The relations among the
geometries are revealed. Almost all geometries fall into pairs. There exists correspondence in each pair. In the viewpoint of
differential geometry, there are only 9 geometries, which have right signature
and geometrical spatial isotropy. They are 3 relativistic geometries, 3
absolute-time geometries, and 3 absolute-space geometries.Comment: 40 pages, 7 figure
Anomalous Nernst and Hall effects in magnetized platinum and palladium
We study the anomalous Nernst effect (ANE) and anomalous Hall effect (AHE) in
proximity-induced ferromagnetic palladium and platinum which is widely used in
spintronics, within the Berry phase formalism based on the relativistic band
structure calculations. We find that both the anomalous Hall ()
and Nernst () conductivities can be related to the spin Hall
conductivity () and band exchange-splitting () by
relations and
,
respectively. In particular, these relations would predict that the
in the magnetized Pt (Pd) would be positive (negative) since
the is positive (negative). Furthermore, both
and are approximately proportional to the
induced spin magnetic moment () because the is a linear
function of . Using the reported in the magnetized Pt and Pd, we
predict that the intrinsic anomalous Nernst conductivity (ANC) in the magnetic
platinum and palladium would be gigantic, being up to ten times larger than,
e.g., iron, while the intrinsic anomalous Hall conductivity (AHC) would also be
significant.Comment: Accepted for publication in the Physical Review
Magnetic moment and magnetic anisotropy of linear and zigzag 4{\it d} and 5{\it d} transition metal nanowires: First-principles calculations
An extensive {\it ab initio} study of the physical properties of both linear
and zigzag atomic chains of all 4 and 5 transition metals (TM) within the
GGA by using the accurate PAW method, has been carried out. All the TM linear
chains are found to be unstable against the corresponding zigzag structures.
All the TM chains, except Nb, Ag and La, have a stable (or metastable) magnetic
state in either the linear or zigzag or both structures. Magnetic states appear
also in the sufficiently stretched Nb and La linear chains and in the largely
compressed Y and La chains. The spin magnetic moments in the Mo, Tc, Ru, Rh, W,
Re chains could be large (1.0 /atom). Structural transformation
from the linear to zigzag chains could suppress the magnetism already in the
linear chain, induce the magnetism in the zigzag structure, and also cause a
change of the magnetic state (ferromagnetic to antiferroamgetic or vice verse).
The calculations including the spin-orbit coupling reveal that the orbital
moments in the Zr, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir and Pt chains could be
rather large (0.1 /atom). Importantly, large magnetic anisotropy
energy (1.0 meV/atom) is found in most of the magnetic TM chains,
suggesting that these nanowires could have fascinating applications in
ultrahigh density magnetic memories and hard disks. In particular, giant
magnetic anisotropy energy (10.0 meV/atom) could appear in the Ru, Re,
Rh, and Ir chains. Furthermore, the magnetic anisotropy energy in several
elongated linear chains could be as large as 40.0 meV/atom. A
spin-reorientation transition occurs in the Ru, Ir, Ta, Zr, La and Zr, Ru, La,
Ta and Ir linear chains when they are elongated. Remarkably, all the 5 as
well as Tc and Pd chains show the colossal magnetic anisotropy (i.e., it is
impossible to rotate magnetization into certain directions). Finally, the
electronic band structure and density of states of the nanowires have also been
calculated in order to understand the electronic origin of the large magnetic
anisotropy and orbital magnetic moment as well as to estimate the conduction
electron spin polarization.Comment: To appear in Phys. Rev.
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