Superconducting Buckyballs Switch Allegiances

27 April 2000 6:30 pm

Buckyballs, those versatile, soccer-ball-shaped spheres of carbon, have a newly discovered ability. Under the right circumstances, they can transmit electricity without any resistance. What's more, the buckyballs can start and stop this superconducting with an electronic command--a trick that might let them one day serve as rapid electrical switches.

The spherical carbon molecules, also called fullerenes, were discovered in 1985. Lattices of 60, 70, or more carbon atoms form geodesic-dome shaped structures that have a range of unusual electronic properties and can encapsulate other molecules. Researchers already knew that crystals made of buckyballs could superconduct--but only if fortified with a few atoms of certain metals per sphere. The metal atoms donate electrons and allow the buckyballs to transmit an electric current much like metals do; at temperatures approaching absolute zero, the mix superconducts.

Now researchers have come up with a technique that induces buckyballs to switch in and out of superconductivity. Physicist Bertram Batlogg of Lucent Technologies in Murray Hill, New Jersey, and colleagues connected a tiny crystal slab of pure buckyballs a few millimeters long to two electrodes and passed a current through it. They found they could control the current by applying a voltage to a third electrode, separated from the buckyball solid by an insulating layer of aluminum oxide. If they cooled the contraption to within 11 degrees of absolute zero and applied 200 volts to the third electrode, called the gate, the buckyballs superconducted.

Apparently, the gate electrode temporarily injects electrons from the bulk of the buckyball solid into a thin layer of buckyballs adjacent to the aluminum oxide. The souped-up buckyballs act like a superconductor, says physicist George Sawatzky of Groningen University in the Netherlands. Team member Robert Haddon of the University of Kentucky, Lexington, speculates that such a switch might speed up electronic devices, if someone could figure out how to make the process work at higher temperatures.

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