Superconductivity in alkali-metal-doped picene

Efforts to identify and develop new superconducting materials continue apace, motivated by both fundamental science and the prospects for application. For example, several new superconducting material systems have been developed in the recent past, including calcium-intercalated graphite compounds, boron-doped diamond and-most prominentlyg-iron arsenides such as LaO_{1-x F x} FeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (T_c) has been discovered in the past decade. Here we report that intercalating an alkali metal into picene, a wide-bandgap semiconducting solid hydrocarbon, produces metallic behaviour and superconductivity. Solid potassium-intercalated picene (K_x picene) shows T_c values of 7 K and 18 K, depending on the metal content. The drop of magnetization in K x picene solids at the transition temperature is sharp (<2 K), similar to the behaviour of Ca-intercalated graphite. The T_c of 18 K is comparable to that of K-intercalated C₆₀ (ref. 4). This discovery of superconductivity in K x picene shows that organic hydrocarbons are promising candidates for improved T_c values.