|Matsuhashi et al. describe superconductivity up to 17 Kelvin in picene doped with potassium (DOI). Organic superconductors are known for example the intercalated fullerene RbCs2C60 at 33 K and graphite intercalation compound KC6 at 11 K but not every alkali-metal/hydrocarbon mix is a winner. For comparison alkali-metal doped pentacene and Cs3C60 have thus far failed to produce the effect. |
A new synthetic method allowed the production of picene - closely related to pentacene - at gram scale and black K3picene was obtained by heating it with potassium at 400 K in a glass tube as a black powder. Not its conductivity was measured but rather the magnetic susceptibility which also shows a first order transition at the transition temperature. At the molecular orbital level superconductivity results from electron donation of the alkali metal HOMO to the picene LUMO forming the charge carriers with maximum effect at 50% capacity. The key property for picene appears to be the presence of a LUMO+1 very close to the energy of the LUMO itself creating an almost double degenerate state very similar to the triply degenerate LUMO found for fullerene.