In the 18 years since they were discovered, high-temperature superconductors have remained an enigma. These copper oxide ceramics conduct electricity without loss at temperatures far higher than those needed for conventional superconductors, albeit still far below room temperature. Physicists know that in both types of material, the superconductivity is caused by electrons pairing up and gathering en masse in a single collective quantum state. But they do not know what "glue" causes the pairing in the high-temperature ("high-Tc") superconductors. Numerous ideas have been proposed, but none has been proved. A recent experimental study suggests that two important theoretical possibilities can be eliminated.
In low-temperature superconductors, the crucial interaction among the electrons is mediated by vibrations of the metal's lattice of positive ions. One electron distorts the lattice as it passes by, and microseconds later the distortion influences the electron's partner when it arrives on the scene. The lattice vibrations are called phonons--they behave just like particles, and their emission and absorption by the electrons generate a weak attractive interaction. Physicists refer to this conventional model as the BCS theory, after the scientists who worked out the mathematics in 1957.
This article was originally published with the title High-Temp Knockout.