Until a few weeks ago, all so-called high temperature superconductors were layered copper oxides of the type discovered by Karl Muller and Georg Bednorz back in 1986. These are so-called because they become superconducting at temperatures above 30K, the theoretical limit predicted by the BCS theory (after Bardeen, Cooper and Schrieffer) of superconductivity that ruled supreme until then. The discovery won Muller and Bednorz the Nobel Prize in 1987.
But in February, Hideo Hosono at the Tokyo Institute of Technology announced that he had discovered a second family of high temperature superconductors based on iron arsenide. Initially these became superconducting at 26K. But within weeks, other groups had upped the temperature to 40K and then to 54K by make some subtle changes to the material’s composition.
Today two groups publish papers on the arXiv claiming versions of this material that superconduct at 41K and 54K. While another group claims to have made low cost wires out of iron arsenides (a considerable feat given that the annealing temperature of the new superconductors is some 1200C ).
These temperatures are s still nowhere near the record of 138K for copper oxides nor the 200K being claimed for aluminum nanoclusters. But its not bad for just 6 weeks work. Who knows what temperatures they might be possible with this material.
And therein lies the challenge. The question now is whether iron arsenides superconduct in the same way copper oxides do. If not, the theorists are going to have one helluva headache working this one out.
arxiv.org/abs/0804.3725: Superconductivity at 41.0 K in the F-doped LaFeAsO1-xFx
arxiv.org/abs/0804.3727: Superconductivity at 53.5 K in GdFeAsO1-δ
arxiv.org/abs/0804.3738: Superconductivity of powder-in-tube LaO0.9F0.1FeAs wires