Molecular Hydride Superconductor BiH 4 with T c up to 91 K at 170 GPa

In pursuit of high- 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 2/ -BiH 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 up to 91 K at 170 GPa, as evidenced by a sharp drop of resistivity to zero and a characteristic downward shift of 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 , differentiating it from most high- superconducting hydrides. Our work not only places 2/ -BiH among the molecular hydride superconductors with the highest but also offers new directions for designing and synthesizing more high- hydride superconductors.