The Empirical Approach to Superconductivity
It is interesting to consider some of the reasons why there is comparatively little discussion these days about new superconductors. First, superconductivity is a cooperative phenomenon for whose transition temperatures no quantitative answers exist. Cooperative phenomena, as you may know, are phenomena that occur only if there is a large number of individuals participating. Such phenomena are not confined to physics; they are a major occurrence in nature. Superconductivity is a cooperative phenomenon of electrical conductivity, but as long as one tries to explain superconductivity as some kind of pathological electrical conductivity, there is not much hope of predicting new superconducting materials or temperatures. Electrical conductivity is not dependent upon a cooperative phenomenon; it is abundant everywhere. Every metal has electrical conductivity, and even every insulator has some electrical conductivity. Yet superconductivity occurs only under certain conditions involving not only the conduction electrons but mostly the valence electrons.
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