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Title: Time evolution of microstructure in complex systems : a computer simulation study
Author: Blackburn, J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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In superconductors, I set up the free energy of the system in terms of the macroscopic wavefunction and vector potential. I then computationally minimised the free energy to find the distribution of these quantities when the system is thermodynamically stable. This yielded the number density of superelectron distribution in space and the magnetic field distribution. The path that the system takes toward free energy minimisation gives its time evolution. I looked in particular at a force free case where both an external field and an external current are applied along the axis of a 3d superconducting cylinder. The current causes rings of magnetic field to form perpendicular to the applied field. I showed that, as expected, vortices tend to form along the local magnetic field direction. These vortices are tubes of normal material (with few superelectrons) surrounded by a whirlwind of supercurrent. The vortices repelled each other and formed a hexagonal lattice as expected. Normally, vortices will move under the influence of current causing a non-zero resistance, but I was able to show that the application of an additional magnetic field was enough to cause the vortices to be entangled and so pinned by each other. This effect could be useful in increasing Jc in superconductors in future. Various different currents and fields were tried including high currents which result in a complex, highly twisted vortex pattern. Two different ways of meshing the sample were tried in the computer simulation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available