A superconducting smorgasbord.

A superconducting smorgasbord

Since the first observation of high-temperature superconductivity in lanthanum barium copper oxide in 1986, progress in understanding this phenomenon has been coupled with the discovery of new materials. Now, researchers at AT&T Bell Laboratories in Murray Hill, N.J., report the synthesis and crystal structure of a new family of layered copper-oxide superconductors with novel properties. Robert J. Cava and his colleagues describe their discovery--the fourth known family of high-temperature superconductors--in the Nov. 17 NATURE. Although the new materials set no records for the temperature at which they become superconducting, they possess unusual electron arrangements that may provide insights into the role of charge distribution in controlling superconductivity.

Difficult to synthesize, the new superconductors consist of copper and oxygen combined with lead, strontium and any one of a wide range of rare-earth metals. So far, the Bell Labs team has investigated only a small fraction of the many possible variations, achieving superconductivity at temperatures no higher than 70 kelvins, or -333[deg.]F. With the right combination of elements, higher temperatures may be attainable.

What is unique about the electronic configuration of the copper atoms in the new compounds is that their average valence, or net charge, is less than 2. In all previously known copper-oxide superconductors, the average valence is greater than 2. The difference seems related to how the atoms within the material are arranged.