Another family of superconducting materials has been found by researchers in Japan and China. The iron-and-arsenic compounds are being hailed as a great advance.
Some researchers hope the new materials will help solve the mystery of cuprate high temperature superconductors (discovered in 1986)
"It's possible that these materials will provide a cleaner system to work with, and suddenly [the physics of] the cuprates will become clearer," says Hai-Hu Wen, a physicist at the Institute of Physics (IoP) at the Chinese Academy of Sciences in Beijing. But Philip Anderson, a theorist at Princeton University and a Nobel Laureate, says that the new superconductors will be more important if they don't work like the old one. "If it's really a new mechanism, God knows where it will go," he says.
The new materials resemble the cuprates in some striking ways. They are also layered materials, but instead of copper and oxygen, they contain planes of iron and arsenic along which the electrons presumably glide. Between the planes lie elements such as lanthanum, cerium, or samarium mixed with oxygen and fluorine. On 23 February, Hideo Hosono of the Tokyo Institute of Technology and colleagues reported in the Journal of the American Chemical Society that lanthanum oxygen fluorine iron arsenide (LaO1-xFxFeAs) becomes a superconductor at 26 kelvin.
Then Chinese researchers took over. On 25 March, X.H. Chen of the University of Science and Technology of China in Hefei reported that samarium oxygen fluorine iron arsenide (SmO1-xFxFeAs) goes superconducting at 43 kelvin. Three days later, Zhong-Xian Zhao of the IoP reported that praseodymium oxygen fluorine iron arsenide (PrO1-xFxFeAs) has a "critical temperature" of 52 kelvin. On 13 April, Zhao and his team showed that the samarium compound becomes a superconductor at 55 kelvin if it is grown under pressure. All the materials have the same crystal structure, and calculations suggest that vibrations simply do not provide enough pull to account for such high critical temperatures.
All agree that the new materials will generate intense interest and that the next step is to synthesize higher quality samples consisting of a single pristine crystal.
The 55K superconductor charts.
Novel Superconductivity and Phase Diagram in the Iron-based Arsenicoxides
ReFeAsO1-δ (Re = rare earth metal) without F-Doping
A novel class of superconductors prepared by high pressure synthesis in the quaternary layered-structure ReFeAsO1-δ (Re = Sm, Nd, Pr, Ce, La) family without F doping. The onset superconducting critical temperature (Tc) in these compounds increases with substitution using smaller Re atoms, and the highest Tc that was obtained up to now is 55 K in SmFeAsO1-δ, which is the highest among all materials except for the multi-layered copper oxides. For the NdFeAsO1-δ system with different oxygen concentration that we studied, a dome-shaped phase diagram was found.
185K superconductor found
Signs of superconductance at 200K in aluminum nanoclusters