4 research outputs found
Vortices in superconducting strips: interplay between surface effects and the pinning landscape
Vortices in a narrow superconducting strip with a square array of pinning
sites are studied. The interactions of vortices with other vortices and with
external sources (applied magnetic field and transport current) are calculated
via a screened Coulomb model. The edge barrier is taken into account and shown
to have an important role on the system dynamics. Numerical simulations in this
approach show that the field dependent magnetic moment presents peaks
corresponding to history dependent configurations of the vortex lattice. Some
effects of the edge barrier on the I-V characteristics are also reported.Comment: 4 pages, 3 figure
Vortex configurations and metastability in mesoscopic superconductors
The vortex dynamics in mesoscopic superconducting cylinders with rectangular
cross section under an axially applied magnetic field is investigated in the
multivortex London regime. The rectangles considered range from a square up to
an infinite slab. The flux distribution and total flux carried by a vortex
placed in an arbitrary position of the sample is calculated analytically by
assuming Clem's solution for the vortex core. The Bean-Livingston energy
barrier is also analytically calculated in this framework. A Langevin algorithm
simulates the flux penetration and dynamical evolution of the vortices as the
external field is slowly cycled. The simulated magnetization process is
governed by metastable states. The magnetization curves are hysteretic, with
paramagnetic response in part of the downward branch, and present a series of
peaks corresponding to the entry or expulsion of a single vortex. For elongated
rectangles, the vortices arrange themselves into parallel vortex chains and an
additional modulation of the magnetization, corresponding to creation or
destruction of a vortex chain, comes out.Comment: 7 pages, 4 figures. Presented on the III European Conference on
Vortex Matter in Superconductors, Crete, 2003. To appear in Physica
Closer look at the low-frequency dynamics of vortex matter using scanning susceptibility microscopy
Using scanning susceptibility microscopy, we shed new light on the dynamics of individual superconducting vortices and examine the hypotheses of the phenomenological models traditionally used to explain the macroscopic ac electromagnetic properties of superconductors. The measurements, carried out on a 2H-NbSe2 single crystal at relatively high temperature T = 6.8 K, show a linear amplitude dependence of the global ac-susceptibility for excitation amplitudes between 0.3 and 2.6 Oe. We observe that the low amplitude response, typically attributed to the oscillation of vortices in a potential well defi ned by a single, relaxing, Labusch constant, actually corresponds to strongly non-uniform vortex shaking. This is particularly pronounced in the fi eld-cooled disordered phase, which undergoes a dynamic reorganization above 0.8 Oe as evidenced by the healing of lattice defects and a more uniform oscillation of vortices. These observations are corroborated by molecular dynamics simulations when choosing the microscopic input parameters from the experiments. The theoretical simulations allow us to reconstruct the vortex trajectories providing deeper insight in the thermally induced hopping dynamics and the vortex lattice reordering