Credit: © 2009 AAAS

Fullerene-based superconductors have been studied since 1991, when it was discovered that samples of carbon-60 molecules doped with potassium lose their resistance to electric current when cooled below a transition temperature of 18 K. Since then it has been established that superconductivity in the alkali metal fullerides — compounds with the chemical composition A3C60, where A is an alkali metal such as potassium or sodium — is described by the Bardeen-Cooper-Schrieffer (BCS) theory that also explains the superconducting properties of simple metals and alloys at low temperatures. Now researchers in the UK, Slovenia and Japan have shown that Cs3C60 is also a superconductor but, unlike its alkali metal cousins, it is not described by the BCS theory1.

The alkali metal fullerides have a face-centred cubic structure and are superconducting at ambient pressures. On the other hand, Cs3C60 has a body-centred cubic structure and only becomes a superconductor under pressure. Moreover, it has a higher transition temperature (about 38 K at 7 kbar) than the alkali metal fullerides. Cs3C60 is also notable because it is free from the disorder that often hides the origins of superconductivity in other materials. The UK-Slovenia-Japan team show that superconductivity in Cs3C60 emerges from an antiferromagnetic parent state in a purely electronic transition as the pressure is increased.