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Abstract
This thesis deals with vortices in stacked long Josephson junctions and in twogap 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 T_{c} superconductors. Some of the wellknown and very important solutions to the nonlinear equations are discussed. A possible relationship between the linear and nonlinear modes is investigated numerically. The fluxonsolutions 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 fluxflow modes are investigated numerically. It is shown, that in some cases the fluxflow modes spontaneously jump from a triangular fluxonlattice to a square fluxonlattice, even in stacks with a strong inductive coupling. The second subject is vortices in twogap superconductors, such as MgB_{2}. These superconductors are investigated through the twocomponent GinzburgLandau theory. The usual Abrikosov vortex is investigated in the twocomponent version. The equations are solved in the farfield and the effect of a Josephsontype coupling is considered. The subject of vortexvortex 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 twocomponent theory for the case of zero magnetic field. The case of nonzero magnetic field is investigated numerically. The textured vortex seems to be unstable in even a small applied magnetic field.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  Danmarks Tekniske Universitet (DTU) 
Number of pages  108 
ISBN (Print)  8791184606 
Publication status  Published  Apr 2006 
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 1 Finished

Fluxdynamik i Højtemperatur Superleder
Madsen, S. P. (PhD Student), Pedersen, N. F. (Main Supervisor), Tønnesen, O. (Supervisor), Christiansen, P. L. (Supervisor), Sørensen, M. P. (Examiner), Ustinov, A. V. (Examiner) & Hedegård, P. (Examiner)
01/01/2003 → 28/04/2006
Project: PhD