289 research outputs found
Conformal lattice of magnetic bubble domains in garnet film
We report experimental observations of magnetic bubble domain arrays with no
apparent translational symmetry. Additionally the results of comparative
numerical studies are discussed. Our goal is to present experimental evidence
for natural occurence of conformal structures.Comment: 7 pages, 2 figures, LaTeX2e, accepted as paper E090 at JEMS'01 (Joint
European Magnetic Symposia, formerly EMMA + MRM), August 28th to September
1st, 2001, Grenoble, Franc
Hysteresis in mesoscopic superconducting disks: the Bean-Livingston barrier
The magnetization behavior of mesoscopic superconducting disks can show
hysteretic behavior which we explain by using the Ginzburg-Landau (GL) theory
and properly taking into account the de-magnetization effects due to
geometrical form factors. In large disks the Bean-Livingston surface barrier is
responsible for the hysteresis. While in small disks a volume barrier is
responsible for this hysteresis. It is shown that although the sample
magnetization is diamagnetic (negative), the measured magnetization can be
positive at certain fields as observed experimentally, which is a consequence
of the de-magnetization effects and the experimental set up.Comment: Latex file, 4 ps file
Vortex phases in mesoscopic cylinders with suppressed surface superconductivity
Vortex structures in mesoscopic cylinder placed in external magnetic field
are studied under the general de Gennes boundary condition for the order
parameter corresponding to the suppression of surface superconductivity. The
Ginzburg-Landau equations are solved based on trial functions for the order
parameter for vortex-free, single-vortex, multivortex, and giant vortex phases.
The equilibrium vortex diagrams in the plane of external field and cylinder
radius and magnetization curves are calculated at different values of de Gennes
"extrapolation length" characterizing the boundary condition for the order
parameter. The comparison of the obtained variational results with some
available exact solutions shows good accuracy of our approach.Comment: RevTex, 11 pages, 10 figure
New combined PIC-MCC approach for fast simulation of a radio frequency discharge at low gas pressure
A new combined PIC-MCC approach is developed for accurate and fast simulation
of a radio frequency discharge at low gas pressure and high density of plasma.
Test calculations of transition between different modes of electron heating in
a ccrf discharge in helium and argon show a good agreement with experimental
data.
We demonstrate high efficiency of the combined PIC-MCC algorithm, especially
for the collisionless regime of electron heating.Comment: 6 paged, 8 figure
Structure and Melting of Two-Species Charged Clusters in a Parabolic Trap
We consider a system of charged particles interacting with an unscreened
Coulomb repulsion in a two-dimensional parabolic confining trap. The static
charge on a portion of the particles is twice as large as the charge on the
remaining particles. The particles separate into a shell structure with those
of greater charge situated farther from the center of the trap. As we vary the
ratio of the number of particles of the two species, we find that for certain
configurations, the symmetry of the arrangement of the inner cluster of
singly-charged particles matches the symmetry of the outer ring of
doubly-charged particles. These matching configurations have a higher melting
temperature and a higher thermal threshold for intershell rotation between the
species than the nonmatching configurations.Comment: 4 pages, 6 postscript figure
Perfectly Translating Lattices on a Cylinder
We perform molecular dynamics simulations on an interacting electron gas
confined to a cylindrical surface and subject to a radial magnetic field and
the field of the positive background. In order to study the system at lowest
energy states that still carry a current, initial configurations are obtained
by a special quenching procedure. We observe the formation of a steady state in
which the entire electron-lattice cycles with a common uniform velocity.
Certain runs show an intermediate instability leading to lattice
rearrangements. A Hall resistance can be defined and depends linearly on the
magnetic field with an anomalous coefficient reflecting the manybody
contributions peculiar to two dimensions.Comment: 13 pages, 5 figure
Influence of the confinement geometry on surface superconductivity
The nucleation field for surface superconductivity, , depends on the
geometrical shape of the mesoscopic superconducting sample and is substantially
enhanced with decreasing sample size. As an example we studied circular,
square, triangular and wedge shaped disks. For the wedge the nucleation field
diverges as with decreasing angle () of
the wedge, where is the bulk upper critical field.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev.
Classical Many-particle Clusters in Two Dimensions
We report on a study of a classical, finite system of confined particles in
two dimensions with a two-body repulsive interaction. We first develop a simple
analytical method to obtain equilibrium configurations and energies for few
particles. When the confinement is harmonic, we prove that the first transition
from a single shell occurs when the number of particles changes from five to
six. The shell structure in the case of an arbitrary number of particles is
shown to be independent of the strength of the interaction but dependent only
on its functional form. It is also independent of the magnetic field strength
when included. We further study the effect of the functional form of the
confinement potential on the shell structure. Finally we report some
interesting results when a three-body interaction is included, albeit in a
particular model.Comment: Minor corrections, a few references added. To appear in J. Phys:
Condensed Matte
Composite-fermion crystallites in quantum dots
The correlations in the ground state of interacting electrons in a
two-dimensional quantum dot in a high magnetic field are known to undergo a
qualitative change from liquid-like to crystal-like as the total angular
momentum becomes large. We show that the composite-fermion theory provides an
excellent account of the states in both regimes. The quantum mechanical
formation of composite fermions with a large number of attached vortices
automatically generates omposite fermion crystallites in finite quantum dots.Comment: 5 pages, 3 figure
Off center centers in a quantum well in the presence of a perpendicular magnetic field: angular momentum transition and magnetic evaporation
We investigate the effect of the position of the donor in the quantum well on
the energy spectrum and the oscillator strength of the D- system in the
presence of a perpendicular magnetic field. As a function of the magnetic field
we find that when the D- centers are placed sufficiently off-center they
undergo singlet-triplet transitions which are similar to those found in
many-electron parabolic quantum dots. The main difference is that the number of
such transitions depends on the position of the donor and only a finite number
of such singlet-triplet transitions are found as function of the strength of
the magnetic field. For sufficiently large magnetic fields the two electron
system becomes unbound. For the near center D- system no singlet-triplet and no
unbinding of the D- is found with increasing magnetic field. A magnetic field
vs. donor position phase diagram is presented that depends on the width of the
quantum well.Comment: 16 pages, 17 figures. Accepted for publication in Phys. Rev.
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