Vortices and artificial defects in high-temperature superconducting thin films: Increasing the critical current densities via optimization of multilayer structures

Abstract

This dissertation studies the implications of vortex dynamics in high-temperature superconducting thin films. The combined use of both experimental and computational methods enabled one to draw otherwise unobtainable conclusions regarding the complex pinning mechanisms of the vortices. In particular, this enabled the study of zero field superconducting properties separately from the vortex dynamics governed highfield properties.

A particular interest was the study of vortex pinning within lattices of onedimensional self-assembled columnar defects, typically referred to as nanorods. Several distinct pinning mechanisms were identified for given configurations of nanorods under specific magnetic environments. The presence of the different pinning mechanisms is manifested as perturbations in the experimentally measured critical current anisotropies. In addition, the limits of vortex pinning within increasingly dense nanorod lattices were rigorously studied.

After obtaining the general knowledge of how the interplay between the vortices and the artificial defects affect the superconducting properties of studied films, the study was focused to superconducting multilayer structures. There are several previous studies where an arbitrary multilayer structure has been associated with increased superconducting properties with respect to corresponding single layer films. Here, such study was repeated and the underlying mechanisms of the critical current improvement for multilayer structures were rigorously studied.

Finally, the optimization of the multilayer structures for specific temperature and field ranges was considered. Firstly, the layer thicknesses within a simplistic bilayer film was optimized based on a theoretical model. After this, in order to efficiently address more broad-scale optimization of the multilayer structures, a new approach taking advantage of state-of-the-art artificial intelligence models is proposed. A set of rigorous experiments is suggested to reliably validate the presented theoretical predictions considering the properties of an optimal multilayer structure.