Ambient pressure high temperature superconductivity in RbPH3 facilitated by ionic anharmonicity

Recent predictions of metastable high-temperature hydride superconductors give hope that superconductivity at ambient conditions is within reach. In this work, we predict RbPH 3 as a new compound with a superconducting critical temperature of around 100 K at ambient pressure, dynamically stabilized thanks to ionic quantum anharmonic effects. RbPH 3 is thermodynamically stable at 30 GPa in a perovskite P m 3 ̄ m phase, allowing its experimental synthesis at moderate pressures far from the megabar regime. With lowering pressure it is expected to transform to a R 3 m phase that should stay dynamically stable thanks to ionic quantum fluctuations down to ambient pressures. Both phases are metallic, with the R 3 m phase having three distinct Fermi surfaces, composed mostly of states with phosphorus and hydrogen character. The structures are held together by strong P-H covalent bonds, resembling the pattern observed in the high-temperature superconducting H 3 S, with extra electrons donated by rubidium. These results demonstrate that ionic quantum fluctuations, neglected thus far in high-throughput calculations, can stabilize ambient pressure hydride superconductors with a high critical temperature.