Highly reproducible superconductivity in K-doped triphenylbismuthine and tris(2/4-methylphenyl)bismuthine*

To search for new organic superconductors, we perform a systematic study on the magnetic and electrical properties of K-doped triphenylbismuthine and tris(2/4-methylphenyl)bismuthine, which are successfully synthesized by a two-step method - ultrasound treatment and low temperature annealing. The combination of dc and ac magnetic measurements show that one hundred percent of synthesized samples exhibit superconductivity at 3.5 K and/or 7.2 K for triphenylbismuthine, and at 3.6 K for tris(2/4-methylphenyl)bismuthine. The observed superconductivity is strongly supported by the resistivity measurements. Both calculated electronic structures 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.