A numerical study of steady-state vortex configurations and vortex pinning in type-II superconductors

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Title: A numerical study of steady-state vortex configurations and vortex pinning in type-II superconductors
Author: Kim, Sangbum
Abstract: In part I , a numerical study of the mixed states in a mesoscopic type -II superconducting cylinder is described . Steady -state configurations and transient behavior of the magnetic vortices for various values of the applied magnetic field H are presented . Transitions between different multi -vortex states as H is changed is demonstrated by abrupt changes in vortex configurations and jumps in the B vs H plot . An efficient scheme to determine the equilibrium vortex configuration in a mesoscopic system at any given applied field , not limited to the symmetry of the system , is devised and demonstrated . In part II , a superconducting thin film is subject to a non -uniform magnetic field from a vertical magnetic dipole , consisting of two magnetic monopoles of opposite charges . For a film with constant thickness and with no pins , it has been found that the film carries two pairs of vortex -antivortex in the steady state in the imposed flux range of 2 .15 < (Phi )+ < 2 .90 (in units of flux quantum ) and no vortex at all for (Phi )+ <= 2 .15 . Transitions from a superconducting state with 3 pairs of vortex -antivortex to one with 2 pairs , where a pair of vortex -antivortex annihilates , have been observed in the pseudo -time sequence . With a perturbation with antidots (holes ) , vortexantivortex pair has been created for lower magnetic fluxes down to (Phi )+ = 1 .3 . In the sample of size 16 (Xi ) x 16 (Xi ) , the attraction force between the vortex and antivortex always dominates over the pinning force , so that they eventually come out of pins , move toward each other , and annihilate each other . The annihilation rate , measured with time taken for the annihilation , is reduced noticeably by the increase of the distance between pins , or the increase in the pin size . A simulation of the magnetic vortex pinning in the sample of size 32 (Xi ) x 32 (Xi ) suggests we are likely to achieve pinning of the vortex -antivortex pair with the sample size around this and vortex -antivortex separation of 22 (Xi ) . Using this sample as a template , the maximum density of pinned vortices achievable is calculates to be about 7 .6 x 10^14 vortices /m2 for (Xi ) = ~ 1 .6A ? .
URI: http : / /hdl .handle .net /1969 .1 /3091
Date: 2006-04-12

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A numerical study of steady-state vortex configurations and vortex pinning in type-II superconductors. Available electronically from http : / /hdl .handle .net /1969 .1 /3091 .

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