CRYSTAL STRUCTURE, DEFECTS, PINNING AND MAGNETIC FLUX DYNAMICS IN HTNP COMPOUNDS OF THE 1-2-3 SYSTEM (brief review)

Abstract

A brief review of phenomena related to the dynamics of magnetic flux and its pinning in HTSС compounds of the 1-2-3 system is made on the basis of literature data and our own research. The review includes experimental studies of changes in the temperature dependences of electrical resistance and current-voltage characteristics of single crystals of YBa₂Cu₃O_7–δ under the influence of structural defects. Based on the features of the crystal structure of YBa₂Cu₃O_7–δ and typical structural defects of this compound, the dynamics of magnetic flux and the influence of thermal fluctuations on this dynamics, the phase state and dynamics of the vortex system in HTSC compounds of the 1-2-3 system, in particular, pinning of the vortex lattice on defects, intrinsic pinning in the compound YBa₂Cu₃O_7–δ, are considered. In high-temperature superconductors YBa₂Cu₃O_7–δ, the Peak-effect is associated with both the adaptation of the vortex lattice to the pinning potential and the phase transitions from one state of the vortex lattice to another. The Fishtail effect in YBa₂Cu₃O_7–δ can be due to phase transformations of the vortex lattice, the effect of bulk pinning, or the effect of Bean-Livingston surface barriers. The review contains a list of tasks that it is desirable to solve, in particular, the study of pinning and vortex dynamics in YBa₂Cu₃O_7–δ single crystals containing only controlled defects; establishing the role of intergranular bonds in increasing the critical current and effective pinning potential; studying the effect of oxygen vacancy clusters on the Peak-effect.