<P> This temperature jump is particularly significant, since it allows liquid nitrogen as a refrigerant, replacing liquid helium . This can be important commercially because liquid nitrogen can be produced relatively cheaply, even on - site . Also, the higher temperatures help avoid some of the problems that arise at liquid helium temperatures, such as the formation of plugs of frozen air that can block cryogenic lines and cause unanticipated and potentially hazardous pressure buildup . </P> <P> Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics . There are currently two main hypotheses--the resonating - valence - bond theory, and spin fluctuation which has the most support in the research community . The second hypothesis proposed that electron pairing in high - temperature superconductors is mediated by short - range spin waves known as paramagnons . </P> <P> Since about 1993, the highest - temperature superconductor has been a ceramic material consisting of mercury, barium, calcium, copper and oxygen (HgBa Ca Cu O) with T = 133--138 K . The latter experiment (138 K) still awaits experimental confirmation, however . </P> <P> In February 2008, an iron - based family of high - temperature superconductors was discovered . Hideo Hosono, of the Tokyo Institute of Technology, and colleagues found lanthanum oxygen fluorine iron arsenide (LaO F FeAs), an oxypnictide that superconducts below 26 K. Replacing the lanthanum in LaO F FeAs with samarium leads to superconductors that work at 55 K . </P>

What are superconductors give one of their application