NATURE 

'Tantalizing' hints of room-temperature superconductivity

Doped graphite may superconduct at more than 100 ºC.

Researchers in Germany have claimed a breakthrough: a material that can act as a superconductor — transmit electricity with zero resistance — at room temperature and above. Superconductors offer huge potential energy savings, but until now have worked only at temperatures of lower than about -110 °C.

Now, Pablo Esquinazi and his colleagues at the University of Leipzig report that flakes of humble graphite soaked in water seem to continue superconducting at temperatures of greater than 100 °C¹. Even Esquinazi admits that the claim “sounds like science fiction”, but the work has been published in the peer-reviewed journal Advanced Materials, and other physicists contacted by Nature say that the results, although tentative, merit further scrutiny.

Graphite, which consists of layers of carbon atoms arranged in hexagonal lattices, can superconduct when doped with elements that provide it with additional free electrons. Calcium graphite, for example, superconducts at up to 11.5 kelvin (about -260 °C)², and theorists have predicted that temperatures of up to 60 kelvin could be reached if enough free electrons were available.

Esquinazi’s team speculates that high concentrations of electrons form at the interfaces between neighbouring thin segments of graphite. Having already observed superconductivity at more than 100 kelvin at the interfaces within an artificial type of bulk graphite known as pyrolytic graphite³, the researchers wondered whether they could reach even higher temperatures by doping flakes of graphite powder.

The first dopant they tried was ordinary water. They got lucky. They placed 100 milligrams of pure graphite powder made up of flakes a few hundredths of a millimetre long and tens of nanometres thick into 20 millilitres of distilled water. After stirring the mixture for around 23 hours, they filtered out the powder and then dried it overnight at 100 °C. They found that after being placed in a magnetic field, each sample would remain slightly magnetized after the field was removed.

Esquinazi says that this tiny residual magnetization is a sign of either superconductivity or ordinary ferromagnetism. To find out whether they were seeing the former, his team investigated how the magnetization varied with the strength of the applied field and with temperature. The resultant plots were very similar to those for the first high-temperature oxide superconductors, discovered in the 1980s.

Original Article