Superconducting praseodymium superhydrides

Superhydrides have complex hydrogenic sublattices and are important prototypes for studying metallic hydrogen and high-temperature superconductors. Previous results for LaH₁₀ suggest that the Pr-H system may be especially worth studying because of the magnetism and valence-band f-electrons in the element Pr. Here, we successfully synthesized praseodymium superhydrides (PrH₉) in laser-heated diamond anvil cells. Synchrotron x-ray diffraction analysis demonstrated the presence of previously predicted F $$ 3m-PrH₉ and unexpected P6₃/mmc-PrH₉ phases. Experimental studies of electrical resistance in the PrH₉ sample showed the emergence of a possible superconducting transition (T _c) below 9 K and T _c dependent on the applied magnetic field. Theoretical calculations indicate that magnetic order and likely superconductivity coexist in a narrow range of pressures in the PrH₉ sample, which may contribute to its low superconducting temperature. Our results highlight the intimate connections between hydrogenic sublattices, density of states, magnetism, and superconductivity in Pr-based superhydrides.