Aug 16, 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NB: The publication on which this article is based has been retracted by its authors.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
Superconductivity has been observed in a molecular crystal for the first time. Bertram Batlogg and co-workers at Bell Laboratories in the US have shown that thin films of the "acene" crystals - organic materials that contain linked rings of carbon - lose their electrical resistance and expel magnetic fields when they are cooled below a certain temperature (J H Schon, CH Kloc and B Batlogg 2000 Nature 406 702). Whereas many materials have to be "doped" before they lose their resistance, the acenes become superconducting when a current is passed through them.
Hendrik Schon, Christian Kloc and Batlogg investigated three different acenes: anthracene (which contains three linked rings), tetracene (four) and pentacene (five). The crystals are normally insulating, but when a thin layer of the material was included in a field-effect transistor, it became superconducting. The superconducting transition temperature ranged from 2 Kelvin for pentacene to 4 Kelvin for anthracene. This variation is in line with what is expected if the superconductivity is based on electron-phonon coupling - the mechanism that explains conventional low-temperature superconductivity.
The electrons in the acenes are confined to move in two dimensions, and Batlogg and co-workers recently observed the fractional quantum Hall effect - one of the most widely studied phenomena in two-dimensional electron gases - in pentacene. The Bell Labs team also demonstrated laser action in tetracene earlier this year - the first time that electrically-driven laser action has been achieved in an organic material.
Writing in Nature about the experiment, Philip Phillips of the University of Illinois states that "the achievements of Batlogg and colleagues offer a new avenue for tuning the magnitude of the electron interactions to study almost any aspect of two-dimensional solid-state physics."