Low temperature superconductors refer to materials with a critical temperature below 30 K, and are cooled mainly by liquid helium ( T c > 4.2 K). It may also reference materials that transition to superconductivity when cooled using liquid nitrogen – that is, at only T c > 77 K, although this is generally used only to emphasize that liquid nitrogen coolant is sufficient. Alternatively, a superconductor is called unconventional if the superconducting order parameter transforms according to a non-trivial irreducible representation of the point group or space group of the system.Ī superconductor is generally considered high-temperature if it reaches a superconducting state above a temperature of 30 K (−243.15 ☌) as in the initial discovery by Georg Bednorz and K. It is conventional if it can be explained by the BCS theory or its derivatives, or unconventional, otherwise. ![]() In that case the superconductor is of Type-1.5. Furthermore, in multicomponent superconductors it is possible to have a combination of the two behaviours. The most common are:Ī superconductor can be Type I, meaning it has a single critical field, above which all superconductivity is lost and below which the magnetic field is completely expelled from the superconductor or Type II, meaning it has two critical fields, between which it allows partial penetration of the magnetic field through isolated points. There are many criteria by which superconductors are classified. Main article: Superconductor classification The cheaply available coolant liquid nitrogen boils at 77 K (−196 ☌) and thus the existence of superconductivity at higher temperatures than this facilitates many experiments and applications that are less practical at lower temperatures. Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors. In 1986, it was discovered that some cuprate- perovskite ceramic materials have a critical temperature above 90 K (−183 ☌). The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. It is characterized by the Meissner effect, the complete cancelation of the magnetic field in the interior of the superconductor during its transitions into the superconducting state. ![]() Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon which can only be explained by quantum mechanics. The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. An electric current through a loop of superconducting wire can persist indefinitely with no power source. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. ![]() Any material exhibiting these properties is a superconductor. ![]() Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic fields are expelled from the material.
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