Talk:Superconductivity

Somewhere we need to mention the specific temperatures for some superconductors - and note that high temperature is not high in normal life. Probably need to use Celsius, not Kelvin scale for general readers. --rmhermen

---

I have re-written the article so that the distinction between conventional superconductors and unconventional superconductors is made clear. This is important, because although the field of unconventional superconductivity (including high-temperature superconductors) is very ebullient, conventional superconductivity on the other hand is a very well-established subfield of solid-tate physics (and particularly BCS theory is a fully-working theory, if you apply it to conventional superconductors). But the article seemed to have more about unconventional superconductors than conventional ones, which is odd. I have not deleted that material, but moved it to new articles (unconventional superconductors, high-temperature superconductors, technological applications of superconductivity). Hope this is all right.

By the way, I think keeping the Kelvin is all right, since it is the natural unit in superconductivity. It is important to have links to its definition, though. --quintanilla

---

I'm a bit in doubt about the first line. I'm not sure superconductivity is a "state of matter", but a characteristic of certain elements and substances in given conditions.

--

We know that superconductivity is not a property of metals, but a thermodynamic state of matter different from the metallic state, because of the Meissner effect. The argument is quite standard: a perfect metal (i.e. one with zero resistivity) would support resistanceless flow of an electric current and expel magnetic fields from its interior, just like a superconductor, but if at high temperatures, when the resistivity is finite, a magnetic field is applied, and then the temperature is lowered, the perfect metal does not expel the field, while the superconductor does. In contrast superconductivity is really a thermodynamic state which is characterised by zero field inside the sample however you got there (applying field first, cooling down afterwards, or the other way around). I know this is very sketchy. When I have time I will write it more carefully in the articler about the Meissner effect. Or if you have more time than me maybe you can look it up in "Superconductivity", J.B. Ketterson and S.N. Song, Cambridge University Press 1999, Section 1 - Introduction (pages 1 and 2) or in any other textbook on Superconductivity (e.g. the one by Tinkham, or the one by Schrieffer). Since this argument usually appears in the introduction of such textbooks, it is usually written in a way that is relatively easy to understand. Ciao, jqt