Steps up the ladder to superconductivity.

Ladder compounds--chains of atoms connected by atomic rungs--have a simplicity and symmetry that make them useful structures for studying how the spins of atoms in a material interact to produce an electric conductor or even a superconductor.

More often than not, however, such handy arrangements of atoms are just hypothetical structures created by theorists to clarify their ideas and make predictions. Now, researchers have synthesized a particular ladder structure made of copper, oxygen, and lanthanum atoms--key components of high-temperature superconductors--to check their theories.

Z. Hiroi and M. Takano of the Institute for Chemical Research at Kyoto University in Japan describe their findings in the Sept. 7 Nature.

The researchers produced a material consisting of two-leg ladders made of oxygen and copper atoms (see diagram). Lanthanum atoms occupy sites between adjacent ladders.

This lanthanum copper oxide compound is an electric insulator. Replacing some of the lanthanum atoms with strontium atoms modifies the spin interactions between copper atoms to turn the material into an electric conductor. But contrary to predictions by some theorists, the researchers observed no transition to superconductivity.

"In addition to the intrinsic interest in ladder compounds, there is also the more general hope that studies of such systems can provide new insights into the nature of the mechanism responsible for [superconductivity in high-temperature superconductors]," comments Douglas J. Scalapino of the University of California, Santa Barbara, in the same issue of Nature.