Microcontacts to High-Tc Superconductors: A Study of the Crossover from an Andreev Reflection to a Tunnel-Junction Character

摘要

While the initial goal of the proposal was to concentrate on the study of point contact dots to HTSC, our initial measurements showed that surface preparation and impurities will be a major factor in determining the results, especially if we want to study the crossover from Andreev to tunneling behavior. We therefore launched a thorough study of the effects of single impurities and surface modifications on the tunneling spectra in HTSC. Our findings include the understanding of zero-bias anomalies as coming from point- impurities and the transition from spin-gap to superconducting-gap behavior as a function of strength of surface modification.