The term high-temperature superconductor
was initially employed to designate the new family of cuprate-perovskite ceramic
materials discovered by J.G. Bednorz and K.A. Mueller in 1986
. These materials are characterized by presenting superconductivity
at a higher temperature than conventional superconductors
(which require temperatures a few degrees above absolute zero), and by other unconventional
features. So-called high-temperature superconductors are generally considered to be those that demonstrate superconductivity at or above the temperature of liquid nitrogen
, or -196 degrees C.
Recently, other unconventional superconductors have been discovered. Some of them also have unusually high values of the critical temperature Tc, and hence they are sometimes also called high-temperature superconductors, although the record is still held by a cuprate perovskite material (Tc=133K, that is -140°C). Nevertheless it is widely believed that if room temperature superconductivity is ever achieved it will be in a different family of materials.