Superconducting Circuits with Π-shift Elements

Abstract

Although the two superconducting phase transitions manifest in the same manner, just one aspect of which is the abrupt disappearance of DC electrical resistance shown in Figure 1.1, scientists speculated they are probably a result of unlike physical processes. This claim is nowadays well accepted in the scientific community, there being much evidence about the different nature of the superconducting phase of high-T c and low-T c materials (even in the absence of an exact microscopic model for the former). Indeed, a few key characteristics differentiate the two groups of superconductors, the most prominent being the already mentioned unconventional order parameter symmetry. It is a feature superficially similar to anisotropy in crystals and results in a number of interesting effects distinctive to high-T c superconductors. The aspects of the unconventional order parameter symmetry relevant to superconducting circuits, which is the main focus of this thesis, are presented in Chapter 2.Chapter 4 describes the improvements to the hybrid YBCO-Nb fabrication process and discusses the results of the implemented changes that, together with the knowledge gained about particular procedures, show a positive trend in process robustness. Also presented are electromagnetic simulation techniques modelling electrical parameters of the superconducting thin films as well as comparison with experimentally obtained values. Subsequently, the same Chapter briefly addresses the experimental difficulties with magnetic shielding, where measurements were 2.2 Network aspects of current flow in superconductors