Theory of Type II Superconductors
This chapter presents the theory of bulk type II materials, based on Abrikosov's remarkable and complete analysis of the Ginzburg-Landau equations. Abrikosov showed that to the complete flux expulsion characteristic of the Meissner state, a type II superconductor can exhibit a mixed state, in which the magnetic flux penetrates the sample in the form of quantized flux lines. The main qualitative feature of the flux penetration in type II superconductors is a spatial variation of the superconducting order parameter. In contrast, type II superconductors, shows a partial Meissner effect, and the superconducting state persists even in high magnetic fields. The distinction between the two types of superconductors examines in detail on the basis of the Ginzburg-Landau theory. The Ginzburg–Landau theory is essentially a macroscopic theory of equilibrium phenomena and therefore cannot describe the details of the electronic states in the superconductor. The transport properties of type II superconductors are much less well understood than the equilibrium properties.