Scientists from Lucent Technologies’ Bell Labs have shown that soccer ball-shaped carbon molecules known as bucky balls can act as superconductors at relatively warm temperatures, raising hopes for inexpensive, power loss-free organic electronics and other practical applications such as quantum computers.
Superconductors are materials in which the resistance to the flow of electricity vanishes below a certain temperature.
The Bell Labs team was able to demonstrate that buckyballs acted as superconductors below 117 Kelvin (minus 249 degrees Fahrenheit), which is more than double the previous temperature record of 52 Kelvin (minus 366 degrees Fahrenheit) set last year.
Cold as the new temperature may sound, it is warm enough for the buckyball superconductors to function while cooled by liquid nitrogen instead of the much more expensive liquid helium.
‘This result makes bucky balls infinitely more interesting to study,’ said Federico Capasso, physical research vice president at Bell Labs. ‘This shows that bucky balls may live up to their initial promise of being a material that will be very important to technology.’
Bucky balls are named after American inventor R. Buckminster Fuller, since they resemble the geodesic domes that Fuller designed. They are large molecules made up of 60 carbon atoms. In 1991, a Bell Labs team first showed that bucky balls can act as superconductors at very low temperatures when mixed with potassium.
A Bell Labs team led by physicist Hendrik Schon inserted molecules of chloroform and bromoform (a chemical molecule similar to chloroform but with bromine atoms instead of chlorine atoms) in between bucky balls to create a ‘stretched’ bucky ball crystal where the bucky ball molecules were spaced further apart than usual since the chloroform and bromoform molecules were wedged amidst them.
This had the effect of lowering the electronic and molecular attraction between neighbouring bucky ball molecules in the crystal. By building a sensitive electronic device known as a field effect transistor and connecting it to the crystal, the Bell Labs scientists were able to produce superconductivity in the bucky ball crystal at a record-breaking temperature of minus 249 degrees Fahrenheit.
‘I’m surprised, I didn’t expect the temperature to go up so much,’ said Professor Peter Littlewood, head of theory of condensed matter physics research at the University of Cambridge, UK, and a former Bell Labs researcher. ‘It’s a very clean result.’
The only other known superconductors that work at this and higher temperatures are copper oxide superconductors. These, however, have other problems; the physics that governs copper oxide superconductors is non-conventional and not well understood, and they tend to be expensive.
Nonetheless, they have already been used commercially to make powerful magnets, microwave filters and superconducting wires for power transmission systems. The bucky ball superconductors, on the other hand, are potentially less expensive, and the physics is better understood, since bucky ball superconductors seem to act as conventional superconductors.
‘Our results show that high temperature superconductivity is not restricted to copper oxides,’ said Schon. ‘As research continues, we can expect other surprises in the form of new materials and so on in superconductivity.’
Other researchers involved in this work were Bell Labs scientists Christian Kloc and Bertram Batlogg (who is also affiliated with the Solid State Physics Laboratory in ETH-Zurich in Switzerland).