Lecture 2

The ordinary superconductors prior to the new revolution which began in 1986, had Tc < 25K and coherence lengths at zero temperature much larger (of the order of 500 Angstrom or more) than the interatomic or interelectronic distance. For this reason, it is quite accurate to use near Tc a mean field theory such as the Ginzburg-Landau (GL) macroscopic theory of superconductivity. In the new High Tc Systems, in contrast, the coherence length is small (of the order of 15 Angstrom in x-y plane and 2-3 Angstrom along z-axis) and the GL type scheme needs to be modified. This means that we must take account of the strong anisotropy of the new systems in developing the GL type scheme and here we shall mainly be interested in this aspect. This paper points out that the macroscopic phenomenology of GL has been given a microscopic basis by Gorkov by developing a spatially slowly varying theory of the Gorkov equations, which is usually known as the GLG scheme