2,774 research outputs found
Vortex-glass transition in superconducting Nb/Cu superlattices
Nb/Cu superconducting superlattices have been fabricated by dc magnetron
sputtering. This system shows a vortex glass transition with critical exponents
similar to high temperatures superconductors exponents. The transition
dymensionality is governed by the superconducting coupling regime. The vortex
glass transition shows a pure two dimensional behavior in decoupled
superlattices and a quasi-two dimensional behavior in the superlattice coupling
regime.Comment: 9 pages, 3 figure
Experimental ratchet effect in superconducting films with periodic arrays of asymmetric potentials
A vortex lattice ratchet effect has been investigated in Nb films grown on
arrays of nanometric Ni triangles, which induce periodic asymmetric pinning
potentials. The vortex lattice motion yields a net dc-voltage when an ac
driving current is applied to the sample and the vortex lattice moves through
the field of asymmetric potentials. This ratchet effect is studied taking into
account the array geometry, the temperature, the number of vortices per unit
cell of the array and the applied ac currents.Comment: 15 pages, figures include
Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning
We study the general problem of a manifold of interacting elastic lines whose
spatial correlations are strongly affected by the competition between random
and ordered pinning. This is done through magneto-transport experiments with
YBa2Cu3O7-d thin films that contain a periodic vortex pinning array created via
masked ion irradiation, in addition to the native random pinning. The strong
field-matching effects we observe suggest the prevalence of periodic pinning,
and indicate that at the matching field each vortex line is bound to an
artificial pinning site. However, the vortex-glass transition dimensionality,
quasi-2D instead of the usual 3D, evidences reduced vortex-glass correlations
along the vortex line. This is also supported by an unusual angular dependence
of the magneto-resistance, which greatly differs from that of Bose-glass
systems. A quantitative analysis of the angular magnetoresistance allows us to
link this behaviour to the enhancement of the system anisotropy, a collateral
effect of the ion irradiation
Mechanism for flux guidance by micrometric antidot arrays in superconducting films
A study of magnetic flux penetration in a superconducting film patterned with
arrays of micron sized antidots (microholes) is reported. Magneto-optical
imaging (MOI) of a YBCO film shaped as a long strip with perpendicular antidot
arrays revealed both strong guidance of flux, and at the same time large
perturbations of the overall flux penetration and flow of current. These
results are compared with a numerical flux creep simulation of a thin
superconductor with the same antidot pattern. To perform calculations on such a
complex geometry, an efficient numerical scheme for handling the boundary
conditions of the antidots and the nonlocal electrodynamics was developed. The
simulations reproduce essentially all features of the MOI results. In addition,
the numerical results give insight into all other key quantities, e.g., the
electrical field, which becomes extremely large in the narrow channels
connecting the antidots.Comment: 8 pages, 7 figure
Lattice effects and current reversal in superconducting ratchets
Competition between the vortex lattice and a lattice of asymmetric artificial
defects is shown to play a crucial role in ratchet experiments in
superconducting films. We present a novel and collective mechanism for current
reversal based on a reconfiguration of the vortex lattice. In contrast to
previous models of vortex current reversal, the mechanism is based on the
global response of the vortex lattice to external forces.Comment: 12 pages, 7 figure
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