2 - Properties of high-temperature superconductors: New considerations in measurements

Abstract

This chapter intends to make measurements of properties of high-temperature superconductors, for the purpose of improving material quality or for a particular application. The properties of high-temperature superconductors have caused several changes to the techniques of superconducting measurements. The high transition temperatures and large anisotropies in these materials have provided many new insights into the dynamics of magnetic vortices. Dissipation at grain boundaries or other weak links in materials, in conventional superconductors, is correctly thought of as extrinsic. Conventional superconductors typically have larger volumes of superconducting coherence and, as a result, small imperfections in the material microstructure are nondetrimental. In high-temperature superconductors, this is not the case. Any defect in a unit cell can modify the structure over at least the range of coherence, causing a region of reduced superconductivity. For this reason, grain boundaries in these new superconductors are of great importance since very few applications exist for the materials in single crystalline form.