High-Temperature Superconductors

Chapter 8 covers the various properties of high-temperature superconductors. These superconductors show significant anisotropy due to the two-dimensional crystal structure composed of superconducting CuO2 layers and insulating block layers. This makes the states of flux lines extremely complicated. Various phase transitions of the flux line system to be pinned and the mechanisms responsible are reviewed. In particular, the transitions in which the pinning plays an important role, i.e., the order-disorder transition associated with the peak effect of critical current density and the glass-liquid transition associated with the irreversibility field, are discussed in detail. The influences on these transitions, not only of the flux pinning strength and the anisotropy of the superconductor, but also of the electric field and the specimen size are discussed. Y-123, Bi-2212, and Bi-2223, which have been developed for applications, are at the focus of the discussion, and their pinning properties and recent progress are introduced. In particular, the effect of nanorods introduced into Y-123 coated conductors as artificial pinning centers is reviewed.