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Buckyballs Offer Theory Link

The discovery of high-critical-temperature superconductivity in buckminsterfullerene, a carbon material called buckyballs because its molecular shape resembles Buckminster Fuller's geodesic domes, could provide a theory link between high-critical-temperature ceramic and organic superconductors, according to Professor Keith H. Johnson.

Professor Johnson of the Department of Materials Science and Engineering said that the search for the elusive mechanisms of superconductivity in both the high-critical-temperature ceramics and organics, discovered 5 and 10 years ago respectively, has preoccupied many condensed-matter theorists.

Neither the ceramic or organic superconductors fit the conventional "BCS" theory of superconductivity developed in the 1950s, he said. In BCS theory, superconducting electron pairs are induced by atomic harmonic vibrations in the material.

In a paper published recently in the journal Physica C (Superconductivity) with coauthors D.P. Clougherty and M.E. McHenry, and in a plenary talk in January at the International Superconductor Applications Convention in San Diego, Professor Johnson discussed the theory.

He suggests that superconducting buckminsterfullerene bears the signature of a mechanism for superconductivity he proposed in 1983 for organics and in 1987 for high-critical-temperature ceramics.

In this theory, superconducting electron pairs are induced by vibrations of the local molecular units that make up the superconductor. In the ceramics, these units are distorted oxygen octahedra; in the organics, they are the individual organic molecules; and in buckminsterfullerene, they are the individual buckyballs, he said.

Recent experiments confirm his theoretical predictions, Professor Johnson said.

Finally, Professor Johnson's theory suggests that the highest of high-critical-temperature superconductors tend to be unstable and room-temperature superconductivity is unlikely.

A version of this article appeared in the February 12, 1992 issue of MIT Tech Talk (Volume 36, Number 20).

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