Since their discovery in 1986, high critical temperature of cuprate oxide-based ceramics have intrigued physicists, particularly as the precise details of the superconducting mechanism are still not fully understood. Now, researchers from the Institute of Physics at the Chinese Academy of Sciences (CAS)1 describe an early investigation into iron-based oxide superconductors—an entirely new class of oxide superconductors.

The properties of iron-based superconductors were first reported at the end of February 2008 with the discovery of superconductivity at 26 K in LaO1-xFxFeAs. Although a number of other studies have appeared since, the present report by the CAS researchers is one of the first studies into this new class of superconductors (a preprint was made available online as early as March 3rd). “Our study is the first confirming the superconducting properties of the new iron-based superconductors,” says Nan Lin Wang, leader of the CAS group.

Fig. 1: Crystal structure of LaOFeAs compounds.

Since March, there has been a tremendous proliferation of research into this new class of superconductors. Particularly intriguing is their similarly to the cuprates, also showing a layered crystal structure (Fig. 1). However, as has also been shown recently in publications from CAS and others, there are important differences with the cuprates. Clearly, there is hope that further study of these properties may unravel important clues towards our understanding of high-temperature superconductivity.

One of the distinguishing properties of the new superconductors is their large critical field of 50 T. As there is a direct relation between the critical field and the maximum electrical current that can flow through the system, the high critical magnetic fields make these materials very interesting for possible use in superconducting power cables. However, for practical applications, operation above the boiling point of liquid nitrogen at 77 K is desired—beyond the highest critical temperatures of 55 K reported so far for iron-based compounds.

To achieve higher critical temperatures, the crystal structure may offer further clues. “The Fe2As2 tetrahedron layers appear to be the key unit for the new superconductors. As a large number of materials crystallize in such a structure, we are optimistic of the possibility of finding superconductivity in other systems, possibly with higher critical temperatures,” says Wang. Without doubt, this report marks only one of the first steps into an entirely new and intriguing class of superconductors.