Molecular Hydride Superconductor BiH4 with Tc up to 91 K at 170 GPa

In pursuit of high- T c hydride superconductors, the molecular hydrides have attracted less attention because the hydrogen quasimolecules are usually inactive for superconductivity. Here, we report on the successful synthesis of a novel bismuth hydride superconductor C 2/ c -BiH 4 at pressures around 170–180 GPa. Its structure comprises bismuth atoms and elongated hydrogen molecules with a H–H bond length of 0.81 Å at 170 GPa, characterizing it as a typical molecular hydride. Transport measurements revealed the occurrence of superconductivity with T c up to 91 K at 170 GPa, as evidenced by a sharp drop of resistivity to zero and a characteristic downward shift of T c under magnetic fields. Calculations by density functional theory elucidate that both midfrequency H-derived phonons and low-frequency vibrations from Bi atoms are important for the strong electron–phonon coupling in BiH 4, differentiating it from most high- T c superconducting hydrides. Our work not only places C 2/ c -BiH 4 among the molecular hydride superconductors with the highest T c but also offers new directions for designing and synthesizing more high- T c hydride superconductors.