Current-limiting Factors in YBa2Cu3O7-x Studied with Single-Vortex Magentic Force Miscroscopy

摘要

The relevance of high-temperature superconductors (HTS) for the Air Force lies in their enormous potential for high-power microwave sources and high-energy magnet technology. HTS are complicated materials whose utility is limited by several factors, most fundamentally by the motion of quantum whirlpools of electrons, called vortices. Vortex motion is induced by current flow and causes dissipation, thereby destroying the utility of the superconductor. Understanding the microscopic mechanisms may enable improved current-carrying capability of HTS and achievement of Air Force objectives. The overarching objective of this research is to understand the dynamics of individual vortices,and to understand how vortex motion - and hence dissipation - is influenced by materials structure, by currents, and by other vortices. We used a Magnetic Force Microscope (MFM) to image and manipulate single vortices in YBCO thin films and crystals and quantitatively determine the local depinning force or single-vortex critical current. Thin films and thick single crystals show dramatically different behavior.