ABSTRACT
An outstanding feature of superconductivity is that the electrical resistivity is zero and a persistent current can continue to flow without diminishing. From their magnetic properties, superconductors are classified into two groups. In the mixed state, the magnetic flux in the superconductor is quantized. The quantized magnetic flux is called a fluxoid or fluxon. The chapter discusses the fundamental superconducting properties are in terms of Ginzburg-Landau theory, which, although phenomenological, is suitable for the description of phenomena in magnetic fields. The change from the normal conducting state to the superconducting state is a kind of phase transition, similar to the transition in ferromagnets from the paramagnetic state to the ferromagnetic state. The electromagnetic properties of superconductors are strongly associated with two characteristic lengths: the penetration depth and the coherence length. The chapter also discusses the reversible magnetic properties in the mixed state of type II superconductors are in the framework of Ginzburg-Landau theory.
