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This thesis deals with vortices in stacked long Josephson junctions and in two-gap superconductors. The first part is about Josephson vortices, or fluxons, in stacked long Josephson junctions. The thesis introduces the model which is related to high Tc superconductors. Some of the well-known and very important solutions to the non-linear equations are discussed. A possible relationship between the linear and non-linear modes is investigated numerically. The fluxon-solutions can be made to shuttle back and forth in the junctions and they may emit radiation near the junction edge. This radiation is typically in the THz range. The main problem is, however, that the radiated power in a single junction is too small for applications. This is usually solved by stacking more junctions and getting the fluxons in the different junctions to bunch, radiate coherently, and thus increase the emitted power. The main problem is that the vortices repel each other and therefore prefer to be far apart, preventing coherent radiation. Some different ways of obtaining bunched solutions are discussed. A microwave field is shown to be able to introduce bunching in weakly coupled systems. This may also be done using a cavity instead of a microwave field. And finally, the very important flux-flow modes are investigated numerically. It is shown, that in some cases the flux-flow modes spontaneously jump from a triangular fluxon-lattice to a square fluxon-lattice, even in stacks with a strong inductive coupling. The second subject is vortices in two-gap superconductors, such as MgB2. These superconductors are investigated through the two-component Ginzburg-Landau theory. The usual Abrikosov vortex is investigated in the two-component version. The equations are solved in the far-field and the effect of a Josephson-type coupling is considered. The subject of vortex-vortex interaction is briefly discussed in the case of zero Josephson coupling. Due to the added complexity of having two order parameters, new features arise. A texture vortex solution is found analytically and numerically in the two-component theory for the case of zero magnetic field. The case of non-zero magnetic field is investigated numerically. The textured vortex seems to be unstable in even a small applied magnetic field.
|Place of Publication||Kgs. Lyngby|
|Publisher||Danmarks Tekniske Universitet (DTU)|
|Number of pages||108|
|Publication status||Published - Apr 2006|