Dr David Christen (Oak Ridge National Laboratory)
In this talk, I will provide a perspective on the fundamental properties of the cuprate high-temperature superconductors (HTS), and how early and ongoing fundamental research has identified the strengths and weaknesses, and has ultimately led to the development of superconducting wires for power applications--the so-called "coated conductors." Early work on the properties of various classes of cuprate HTS materials revealed their emergent behavior as type-II superconductors, even though it was apparent that the underlying pairing mechanism is likely quite different than for conventional, electron-phonon coupled materials. From the perspective of this talk, important findings documenting the level of electronic anisotropy, basic length scales, etc., and the effects of thermal energies on vortex matter are described, especially as they relate to the ability to carry loss-free currents. It became apparent that good supercurrent conduction was achieved only along well-aligned basal planes of the structure, and enhancement of those currents could be obtained by introduction of controlled nanostructures for flux pinning. From this work, the (RE)Ba_2 Cu_3 O_7-delta emerged as the best material class for potential high-current wires, mainly because it was the least anisotropic from among those with transition temperature exceeding the boiling point of liquid nitrogen. Ultimately, much effort has been devoted to the control and optimization of nanostructural modifications to the materials, at a size range and spacing that should be tailored to match the magnetic vortex array. The description, success, and consequences of these efforts will be presented.