Structure and magnetic property of potassium intercalated pentacene: Observation of superconducting phase in K_xC₂₂H₁₄

We report the results from systematic investigations on the structure and magnetic properties of potassium intercalated pentacene as a function of potassium content, K_xC₂₂H₁₄ (1 x 3). Synchrotron radiation powder x-ray diffraction technique revealed that there are two different stable phases can be obtained via potassium intercalation, namely, K₁C₂₂H₁₄ phase and K₃C₂₂H₁₄ phase. Structural phase transition was induced when the potassium content was increased to the nominal value x = 3. This phase transition is accompanied by drastic change in their magnetic property, where those samples with compositions K₁C₂₂H₁₄ shows ferromagnetic behavior and those with near K₃C₂₂H₁₄ lead to observation of superconductivity with transition temperature, T _c, of 4.5 K. It is first time that superconductivity was observed in linear oligoacenes. Both magnetization study and synchrotron radiation powder x-ray diffraction clearly indicates that the superconducting phase belong to K₃C₂₂H₁₄ as a result of phase transition from triclinic to monoclinic structure induced by chemical doping.