Evolution of structural perfections in high Tc superconducting thin film.

摘要

In this dissertation work, I developed a forensic methodology to investigate the evolution of chemistry and superconductivity in a heteroepitaxial thin film system---YBa2Cu3O6+x (YBCO). Misfit lattice of a YBCO thin film and its substrate results in coherency strain that dictates the generation of oxygen deficiency and structural defects, which is eventually manifested in the superconductivity or normal state properties. To understand the dynamic process of such evolution, in my retrospective approach, a thicker film is stripped thinner step by step and then compared with an as-grown film of equal thickness. Through such one-to-one comparison, I succeeded in characterizing the effects of strain, partial strain-relaxation, and complete strain-relaxation on the chemistry and physics of thin film cuprate high temperature superconductors as probed by various analytical tools.