Carbon-60 and the ultimate switch
Apr 28, 2000
NB: The publication on which this article is based has been retracted by its authors. The retraction followed an investigation into scientific misconduct by J Hendrik Schön. We are leaving this article here for archival purposes. Further information can be found at http://physicsweb.org/article/news/6/9/15
Physicists in the US have built a superconducting field-effect switch with carbon-60 molecules. The device switches from an insulating state to a superconducting state when a voltage is applied (Science 288 656). Jan Hendrik Schön and colleagues at Bell Laboratories in New Jersey claim that the work "opens up various opportunities to find superconductivity in new classes of materials." It might also, they write, open up new ways to "implement the longstanding idea of an ultimate field-induced switch."
Most materials only become superconducting when they are cooled to low temperatures. In this state the electrons inside the material overcome their natural repulsion and travel through the material in pairs. It has long been suspected that if the surface of a material was doped with enough electrons, the electrons would be pulled into the interface region, allowing a similar electron-pairing effect to occur.
Schön and colleagues used a field-effect transistor to induce three electrons per carbon-60 molecule into the top layer of their device. They discovered that when a positive voltage is applied to the crystal, the carbon switches into a superconducting state. This effect survives up to a temperature of 11 Kelvin.