Putting the squeeze in superconductors.

Shrinking a crystal from the sides can make it bulge v upwards. Unexpectedly, in at least one case, such slimming also boosts the maximum temperature at which the material superconducts, letting electrons flow free of resistance.

Reducing the girth of a thin crystal of a low-temperature superconductor known as 214--a blend of lanthanum, strontium, copper, and oxygen with the formula [La.sub.19][Sr.sub.0.1]Cu[O.sub.4]--increased its maximum superconducting temperature from 25 to 49 kelvins, researchers report in the July 30 Nature. That unexpectedly steep jump may point the way to similar boosts among sister copper oxides, says the study's leader, Jean-Pierre Locquet of IBM's Zurich Research Laboratory in Ruschlikon, Switzerland. These oxides include the world's record holder for high temperature superconducting.

Earlier studies have shown that external pressure on that highest temperature superconductor raises its maximum from 133 kelvins to about 164 kelvins--but only as long as the pressure remains. Locquet's group has now caused a permanent increase in a crystal of 214 by making it pattern itself on a supporting material whose atoms are closer together than those of 214.

Whether the temperature jump results from the lateral squeeze or the accompanying vertical stretching--and whether it will work for other compounds--remains unknown, says team member Jean Fompeyrine. At a deeper level, "this experiment brings out a means to find out really what is the mechanism [underlying high-temperature superconductivity]," he says.