751 research outputs found
Vortex patterns in a superconducting-ferromagnetic rod
A superconducting rod with a magnetic moment on top develops vortices
obtained here through 3D calculations of the Ginzburg-Landau theory. The
inhomogeneity of the applied field brings new properties to the vortex patterns
that vary according to the rod thickness. We find that for thin rods (disks)
the vortex patterns are similar to those obtained in presence of a homogeneous
magnetic field instead because they consist of giant vortex states. For thick
rods novel patterns are obtained as vortices are curve lines in space that exit
through the lateral surface.Comment: 4 pages, 4 figues, Proceeding of the Sixth International Conference
in School Format on Vortex Matter in Nanostructured Superconductors (VORTEX
VI
Energy dependence of a vortex line length near a zigzag of pinning centers
A vortex line, shaped by a zigzag of pinning centers, is described here
through a three-dimensional unit cell containing two pinning centers positioned
symmetrically with respect to its center. The unit cell is a cube of side
, the pinning centers are insulating spheres of radius , taken
within the range to , being the coherence length. We
calculate the free energy density of these systems in the framework of the
Ginzburg-Landau theory.Comment: Submitted to Braz. Jour. Phys. (http://www.sbfisica.org.br/bjp) 11
pages, 6 figures, 1 table, LaTex 2
Paramagnetic excited vortex states in superconductors
We consider excited vortex states, which are vortex states left inside a
superconductor once the external applied magnetic field is switched off and
whose energy is lower than of the normal state. We show that this state is
paramagnetic and develop here a general method to obtain its Gibbs free energy
through conformal mapping. The solution for any number of vortices in any cross
section geometry can be read off from the Schwarz - Christoffel mapping. The
method is based on the first order equations used by A. Abrikosov to discover
vortices.Comment: 14 pages, 7 figure
Vanishing of the upper critical field in Bi_2Sr_2CaCu_2O_{8+\delta} from Landau-Ott scaling
We apply Landau-Ott scaling to the reversible magnetization data of
BiSrCaCuO published by Y. Wang et al. [\emph{Phys.
Rev. Lett. \textbf{95} 247002 (2005)}] and find that the extrapolation of the
Landau-Ott upper critical field line vanishes at a critical temperature
parameter, T^*_c, a few degrees above the zero resistivity critical
temperature, T_c. Only isothermal curves below and near to T_c were used to
determine this transition temperature. This temperature is associated to the
disappearance of the mixed state instead of a complete suppression of
superconductivity in the sample.Comment: 3 figure
Transition to a Superconductor with Insulating Cavities
An extreme type II superconductor with internal insulating regions, namely
cavities, is studied here. We find that the cavity-bearing superconductor has
lower energy than the defect-free superconductor above a critical magnetic
induction for insulating cavities but not for metallic ones. Using a
numerical approach for the Ginzburg-Landau theory we compute and compare free
energy densities for several cavity radii and at least for two cavity
densities, assuming a cubic lattice of spherical cavities.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
Effects of boundaries in mesoscopic superconductors
A thin superconducting disk, with radius and height , is
studied in the presence of an applied magnetic field parallel to its major
axis. We study how the boundaries influence the decay of the order parameter
near the edges for three-dimensional vortex states.Comment: To appear in Physica C as a special issue of M2S-HTS
Effect of the boundary condition on the vortex patterns in mesoscopic three-dimensional superconductors - disk and sphere
The vortex state of mesoscopic three-dimensional superconductors is
determined using a minimization procedure of the Ginzburg-Landau free energy.
We obtain the vortex pattern for a mesoscopic superconducting sphere and find
that vortex lines are naturally bent and are closest to each other at the
equatorial plane. For a superconducting disk with finite height, and under an
applied magnetic field perpendicular to its major surface, we find that our
method gives results consistent with previous calculations. The matching
fields, the magnetization and , are obtained for models that differ
according to their boundary properties. A change of the Ginzburg-Landau
parameters near the surface can substantially enhance as shown here.Comment: 7 pages, 4 figures (low resolution
Inkjet Fabrication of Frame Dipole FSS
Digital fabrication techniques gives the possibility of producing elements with very thin and precise features which could allow the modification of UHF structures to reduce ink usage while still achieving similar performance. This paper investigates the case where dipole elements are modified into Frame Dipoles by removing areas where the surface current tends to be very low
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