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 compounds1, boron-doped diamond2 and—most prominently—iron arsenides such as LaO1–xF x FeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (Tc) 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 Tc 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 graphite1. The Tc 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 Tc values.
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The X-ray diffraction patterns were measured with synchrotron radiation at KEK-PF (proposal no. 2007G612), Tsukuba, Japan. This work was supported in part by Grants-in-Aid 20045012 and 18340104 from MEXT, Japan.
Author Contributions R.M., Y.S., Y.Y. and H.M. contributed equally to the preparation of superconducting picene materials and to the performance of magnetic susceptibility measurements with the assistance of T.K. and Y.K.; H.O. and M.Y. synthesized high-quality picene; N.K. and Y.M. provided assistance with X-ray diffraction measurements; N.I. and A.F. provided discussions and suggestions for the overall project, and discussed the experimental data with T.K. and Y.K.; Y.K. was responsible for the overall project direction, planning and integration among different research units.
The authors declare no competing financial interests.
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Mitsuhashi, R., Suzuki, Y., Yamanari, Y. et al. Superconductivity in alkali-metal-doped picene. Nature 464, 76–79 (2010). https://doi.org/10.1038/nature08859
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