986 research outputs found
A Circuit Model for Domain Walls in Ferromagnetic Nanowires: Application to Conductance and Spin Transfer Torques
We present a circuit model to describe the electron transport through a
domain wall in a ferromagnetic nanowire. The domain wall is treated as a
coherent 4-terminal device with incoming and outgoing channels of spin up and
down and the spin-dependent scattering in the vicinity of the wall is modelled
using classical resistances. We derive the conductance of the circuit in terms
of general conductance parameters for a domain wall. We then calculate these
conductance parameters for the case of ballistic transport through the domain
wall, and obtain a simple formula for the domain wall magnetoresistance which
gives a result consistent with recent experiments. The spin transfer torque
exerted on a domain wall by a spin-polarized current is calculated using the
circuit model and an estimate of the speed of the resulting wall motion is
made.Comment: 10 pages, 5 figures; submitted to Physical Review
Disorder-induced enhancement of the persistent current for strongly interacting electrons in one-dimensional rings
We show that disorder increases the persistent current of a half-filled
one-dimensional Hubbard-Anderson ring at strong interaction. This unexpected
effect results from a perturbative expansion starting from the strongly
interacting Mott insulator ground state. The analytical result is confirmed and
extended by numerical calculations.Comment: 7 pages, 2 figures, LaTeX, using epl.cls (included), considerably
revised final versio
Electron Transport through Disordered Domain Walls: Coherent and Incoherent Regimes
We study electron transport through a domain wall in a ferromagnetic nanowire
subject to spin-dependent scattering. A scattering matrix formalism is
developed to address both coherent and incoherent transport properties. The
coherent case corresponds to elastic scattering by static defects, which is
dominant at low temperatures, while the incoherent case provides a
phenomenological description of the inelastic scattering present in real
physical systems at room temperature. It is found that disorder scattering
increases the amount of spin-mixing of transmitted electrons, reducing the
adiabaticity. This leads, in the incoherent case, to a reduction of conductance
through the domain wall as compared to a uniformly magnetized region which is
similar to the giant magnetoresistance effect. In the coherent case, a
reduction of weak localization, together with a suppression of spin-reversing
scattering amplitudes, leads to an enhancement of conductance due to the domain
wall in the regime of strong disorder. The total effect of a domain wall on the
conductance of a nanowire is studied by incorporating the disordered regions on
either side of the wall. It is found that spin-dependent scattering in these
regions increases the domain wall magnetoconductance as compared to the effect
found by considering only the scattering inside the wall. This increase is most
dramatic in the narrow wall limit, but remains significant for wide walls.Comment: 23 pages, 12 figure
Transformation of Morphology and Luminosity Classes of the SDSS Galaxies
We present a unified picture on the evolution of galaxy luminosity and
morphology. Galaxy morphology is found to depend critically on the local
environment set up by the nearest neighbor galaxy in addition to luminosity and
the large scale density. When a galaxy is located farther than the virial
radius from its closest neighbor, the probability for the galaxy to have an
early morphological type is an increasing function only of luminosity and the
local density due to the nearest neighbor (). The tide produced by the
nearest neighbor is thought to be responsible for the morphology transformation
toward the early type at these separations. When the separation is less than
the virial radius, i.e. when , its morphology
depends also on the neighbor's morphology and the large-scale background
density over a few Mpc scales () in addition to luminosity and
. The early type probability keeps increasing as increases if
its neighbor is an early type. But the probability decreases as
increases when the neighbor is a late type. The cold gas streaming from the
late type neighbor can be the reason for the morphology transformation toward
late type. The overall early-type fraction increases as increases
when . This can be attributed to the hot halo gas
of the neighbor which is confined by the pressure of the ambient medium held by
the background mass. We have also found that galaxy luminosity depends on
, and that the isolated bright galaxies are more likely to be recent
merger products. We propose a scenario that a series of morphology and
luminosity transformation occur through distant interactions and mergers, which
results in the morphology--luminosity--local density relation.Comment: 14 pages, 7 figures, for higher resolution figures download PDF file
at http://astro.kias.re.kr/docs/trans.pdf ; references added and typos in
section 3.2 corrected; Final version accepted for publication in Ap
Lifetime of the first and second collective excitations in metallic nanoparticles
We determine the lifetime of the surface plasmon in metallic nanoparticles
under various conditions, concentrating on the Landau damping, which is the
dominant mechanism for intermediate-size particles. Besides the main
contribution to the lifetime, which smoothly increases with the size of the
particle, our semiclassical evaluation yields an additional oscillating
component. For the case of noble metal particles embedded in a dielectric
medium, it is crucial to consider the details of the electronic confinement; we
show that in this case the lifetime is determined by the shape of the
self-consistent potential near the surface. Strong enough perturbations may
lead to the second collective excitation of the electronic system. We study its
lifetime, which is limited by two decay channels: Landau damping and
ionization. We determine the size dependence of both contributions and show
that the second collective excitation remains as a well defined resonance.Comment: 18 pages, 5 figures; few minor change
Embedding method for the scattering phase in strongly correlated quantum dots
The embedding method for the calculation of the conductance through
interacting systems connected to single channel leads is generalized to obtain
the full complex transmission amplitude that completely characterizes the
effective scattering matrix of the system at the Fermi energy. We calculate the
transmission amplitude as a function of the gate potential for simple
diamond-shaped lattice models of quantum dots with nearest neighbor
interactions. In our simple models we do not generally observe an interaction
dependent change in the number of zeroes or phase lapses that depend only on
the symmetry properties of the underlying lattice. Strong correlations separate
and reduce the widths of the resonant peaks while preserving the qualitative
properites of the scattering phase.Comment: 11 pages, 3 figures. Proceedings of the Workshop on Advanced
Many-Body and Statistical Methods in Mesoscopic Systems, Constanta, Romania,
June 27th - July 2nd 2011. To appear in Journal of Physics: Conference Serie
Critical spectral statistics in two-dimensional interacting disordered systems
The effect of Coulomb and short-range interactions on the spectral properties
of two-dimensional disordered systems with two spinless fermions is
investigated by numerical scaling techniques. The size independent universality
of the critical nearest level-spacing distribution allows one to find a
delocalization transition at a critical disorder for any non-zero
value of the interaction strength. At the critical point the spacings
distribution has a small- behavior , and a Poisson-like
decay at large spacings.Comment: 4 two-column pages, 3 eps figures, RevTeX, new results adde
A 4D Light-Field Dataset and CNN Architectures for Material Recognition
We introduce a new light-field dataset of materials, and take advantage of
the recent success of deep learning to perform material recognition on the 4D
light-field. Our dataset contains 12 material categories, each with 100 images
taken with a Lytro Illum, from which we extract about 30,000 patches in total.
To the best of our knowledge, this is the first mid-size dataset for
light-field images. Our main goal is to investigate whether the additional
information in a light-field (such as multiple sub-aperture views and
view-dependent reflectance effects) can aid material recognition. Since
recognition networks have not been trained on 4D images before, we propose and
compare several novel CNN architectures to train on light-field images. In our
experiments, the best performing CNN architecture achieves a 7% boost compared
with 2D image classification (70% to 77%). These results constitute important
baselines that can spur further research in the use of CNNs for light-field
applications. Upon publication, our dataset also enables other novel
applications of light-fields, including object detection, image segmentation
and view interpolation.Comment: European Conference on Computer Vision (ECCV) 201
Critical Spectral Statistics at the Metal-Insulator Transition in Interacting Fermionic Systems
The spectral properties of a disordered system with few interacting
three-dimensional spinless fermions are investigated. We show the existence of
a critical spacings distribution which is invariant upon increase of the system
size, but strongly depends on the number of particles. At the critical point,
we report a substantial decrease of the degree of level repulsion as the number
of particles increases indicating a decrease of nearest level correlations
associated with the sparsity of the Hamiltonian matrix.Comment: Revtex, 4 pages, 3 encapsulated postscript figures appended Final
version as accepted for publication in PR
Spin-dependent dipole excitation in alkali-metal nanoparticles
We study the spin-dependent electronic excitations in alkali-metal
nanoparticles. Using numerical and analytical approaches, we focus on the
resonances in the response to spin-dependent dipole fields. In the spin-dipole
absorption spectrum for closed-shell systems, we investigate in detail the
lowest-energy excitation, the "surface paramagnon" predicted by L. Serra et al.
[Phys. Rev. A 47, R1601 (1993)]. We estimate its frequency from simple
assumptions for the dynamical magnetization density. In addition, we
numerically determine the dynamical magnetization density for all low-energy
spin-dipole modes in the spectrum. Those many-body excitations can be traced
back to particle-hole excitations of the noninteracting system. Thus, we argue
that the spin-dipole modes are not of collective nature. In open-shell systems,
the spin-dipole response to an electrical dipole field is found to increase
proportionally with the ground-state spin polarization.Comment: 12 pages, 9 figure
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