Researchers have combined two major surprises in 1980s physics--buckyballs (C60) and high-temperature superconductors--into one breakthrough. By placing a crystal of C60 spiked with other compounds in the heart of a transistor, they turned it into a superconductor, capable of conducting electricity without resistance at temperatures up to 117 kelvin (K).
crystals with other molecules nudged them toward
CREDIT: ILLUSTRATION: C. SLAYDEN
"This is huge," says Art Ramirez, a condensed matter physicist at Los Alamos National Laboratory in New Mexico. C60-based transistors spiked with new compounds might well superconduct at higher temperatures, perhaps even at room temperature, Ramirez says. Because superconducting electronics are extremely fast and are ideal for detecting minute magnetic fields, a new supply of C60-based superconducting devices could revolutionize fields as disparate as high-speed computing and medical imaging.
In 1991, Ramirez and others discovered that crystals made of C60 molecules would superconduct at 18 K if spiked with alkali metals. In the late 1990s, physicist Hendrik Schön of Lucent Technologies' Bell Laboratories in Murray Hill, New Jersey, and his colleagues began to suspect that they could raise the threshold temperature for superconducting if they could coax C60 to conduct positively charged "holes"--essentially electron vacancies in a material--instead of electrons. Doing so, they determined, would increase the material's "density of states," a property closely tied to the superconducting temperature.
Last year, Schön and other Bell Labs workers achieved this by building a transistor around the crystal to flood it with holes. As they reported last year, the C60 transistor could superconduct at temperatures as high as 52 K. Now, the team has found another way to increase the material's density of states: expanding the distance between individual C60 molecules in the crystal. After trying numerous additives, they found two, trichloromethane and tribromomethane, that more than doubled the superconducting temperature, the team reports in a paper published online today by Science.
The huge jump bodes well for researchers, Ramirez says. So far, nobody knows whether any additive will push C60 to room temperature without making the crystal fall apart. But several groups are sure to try their luck, says Ramirez.