PROPERTIES OF HIGH TEMPERATURE SUPERCONDUCTORS IN THE MIXED STATE

Abstract

The behavior of superconductors in the presence of a magnetic field has been the subject of much scientific as well as practical, interest over the past few decades. On the practical side, the design and performance of superconducting magnets are often limited by the suppression of superconductivity in large magnetic fields. The behavior observed in various experiments on superconductor in a magnetic field is quite diverse, and its full elucidation is a substantial scientific challenge. Discovery of high-temperature superconductors has spurred a significant reexamination of this subject. These materials exhibit phenomena that were not detected in previously studied superconductors. They also have the potential to remain superconducting at much higher magnetic fields than earlier materials and thus may eventually allow the construction of higher field magnets.

The thesis is organized as follows:

Chapter I is devoted for a survey on the historical background of superconductivity, the discovery of high temperature superconductors and the effect of their layered structure on their magnetic properties.

Many authors treated the problem of the creation of closed vortex by a transport current in isotropic superconductors. In chapter 2 we extend this work for anisotropic superconductor when the field lies along the crystal axis. The magnetic field, the supercurrent and the free energy for an isolated vortex are investigated in an infinite superconductor (unbounded • problem) and also for a superconductor of cylindrical shapeIbounded problem). Similarly, as in the isotropic case, the results show that the free • energy grows monotonicalJy with r5, the vortex radius, so the toroidal