  Using a new two-step synthesis method - ultrasound treatment and low
temperature annealing, we 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
evidence of type-II superconductor, with the upper critical magnetic field up
to 1.0 Tesla. Both calculated electronic structure and measured Raman spectra
indicate that superconductivity is realized by transferring electron from
potassium to carbon atom. Our study opens an encouraging window for the search
of organic superconductors in organometallic molecules.
