Superconductivity at 3.5 K and/or 7.2 K in potassium-doped triphenylbismuth

We develop a two-step synthesis method - ultrasound treatment and low temperature annealing to explore superconductivity in potassium-doped triphenylbismuth, which is composed of one bismuth atom and three phenyl rings. The combination of dc and ac magnetic measurements reveals that one hundred percent of synthesized samples exhibit superconductivity at 3.5 K and/or 7.2 K at ambient pressure. The magnetization hysteresis loops provide a strong piece of evidence of type-II superconductors. It is found that the doped materials crystallize into the triclinic P1 structure, with a mole ratio of 4:1 between potassium and triphenylbismuth. Both the calculated electronic structure and measured Raman spectra indicate that superconductivity is realized by transferring electrons from the K-4s to C-2p orbital. Our study opens an encouraging window for the search of organic superconductors in organometallic molecules.