Superconductivity-Basics and Applications (2 lectures)

As is well-known, field-effect transistor (FET) is the work-horse of today's semiconductor electronics. FET works so well in part because semiconductors have few carriers (or no carriers at all until the surface is inverted), so that the concentration of carriers can be managed by the readily accessible electric fields which are applied in the direction normal to the current flow. In metals (superconductors) the number of electrons is too large to be altered significantly by the accessible electric fields, even in monolayer films. There are, however, intermediate cases (semimetals like Bi, metallic oxides like doped SrTiO sub 3, degeneratly doped semiconductors) which hold some promise for field-effect in thin films and surface layers. High - T sub c oxide superconductors also have free-carrier (hole) concentrations which are lower than in typical metals, although these concentrations are presently not known with certainly, the best guess is that they are in the 10 sup (21) cm sup (-3) range.