18 research outputs found
Magnetic coupling between mesoscopic superconducting rings
Using the nonlinear Ginzburg-Landau theory we investigated the dependence of
the magnetic coupling between two concentric mesoscopic superconducting rings
on their thickness. The size of this magnetic coupling increases with the
thickness of the rings.Comment: 3 pages text, 3 ps figures, to be published in Physica C (Proceedings
of the 2nd European Conference in School Format "Vortex Matter in
Superconductors"
Distribution of the sheet current in a magnetically shielded superconducting filament
The distribution of the transport current in a superconducting filament
aligned parallel to the flat surface of a semi-infinite bulk magnet is studied
theoretically. An integral equation governing the current distribution in the
Meissner state of the filament is derived and solved numerically for various
filament-magnet distances and different relative permeabilities. This reveals
that the current is depressed on the side of the filament adjacent to the
surface of the magnet and enhanced on the averted side. Substantial current
redistributions in the filament can already occur for low values of the
relative permeability of the magnet, when the distance between the filament and
the magnet is short, with evidence of saturation at moderately high values of
this quantity, similar to the findings for magnetically shielded strips.Comment: 11 pages, 5 figures; submitted to Physica
Superconducting properties of mesoscopic cylinders with enhanced surface superconductivity
The superconducting state of an infinitely long superconducting cylinder
surrounded by a medium which enhances its superconductivity near the boundary
is studied within the nonlinear Ginzburg-Landau theory. This enhancement can be
due to the proximity of another superconductor or due to surface treatment.
Quantities like the free energy, the magnetization and the Cooper-pair density
are calculated. Phase diagrams are obtained to investigate how the critical
field and the critical temperature depend on this surface enhancement for
different values of the Ginzburg-Landau parameter \kappa. Increasing the
superconductivity near the surface leads to higher critical fields and critical
temperatures. For small cylinder diameters only giant vortex states nucleate,
while for larger cylinders multivortices can nucleate. The stability of these
multivortex states also depends on the surface enhancement. For type-I
superconductors we found the remarkable result that for a range of values of
the surface extrapolation length the superconductor can transit from the
Meissner state into superconducting states with vorticity L > 1. Such a
behaviour is not found for the case of large \kappa, i.e. type-II
superconductivity.Comment: submitted to Phys. Rev.
Bernoulli potential in type-I and weak type-II superconductors: I. Surface charge
The electrostatic potential close to the surface of superconductors in the
Meissner state is discussed. We show that beside the Bernoulli potential, the
quasiparticle screening, and the thermodynamic contribution due to Rickayzen,
there is a non-local contribution which is large for both type-I and weak
type-II superconductors.Comment: 7 pages, 4 figure
Dependence of the vortex configuration on the geometry of mesoscopic flat samples
The influence of the geometry of a thin superconducting sample on the
penetration of the magnetic field lines and the arrangement of vortices are
investigated theoretically. We compare superconducting disks, squares and
triangles with the same surface area having nonzero thickness. The coupled
nonlinear Ginzburg-Landau equations are solved self-consistently and the
important demagnetization effects are taken into account. We calculate and
compare quantities like the free energy, the magnetization, the Cooper-pair
density, the magnetic field distribution and the superconducting current
density for the three geometries. For given vorticity the vortex lattice is
different for the three geometries, i.e. it tries to adapt to the geometry of
the sample. This also influences the stability range of the different vortex
states. For certain magnetic field ranges we found a coexistence of a giant
vortex placed in the center and single vortices toward the corners of the
sample. Also the H-T phase diagram is obtained.Comment: 9 pages, 17 figures (submitted to Phys. Rev. B