Superconducting praseodymium superhydrides.

Superhydrides have complex hydrogenic sublattices and are important prototypes for studying metallic hydrogen and high-temperature superconductors. Previous results for LaH suggest that the Pr-H system may be especially worth studying because of the magnetism and valence-band -electrons in the element Pr. Here, we successfully synthesized praseodymium superhydrides (PrH) in laser-heated diamond anvil cells. Synchrotron x-ray diffraction analysis demonstrated the presence of previously predicted 3-PrH and unexpected 6/-PrH phases. Experimental studies of electrical resistance in the PrH sample showed the emergence of a possible superconducting transition ( ) below 9 K and dependent on the applied magnetic field. Theoretical calculations indicate that magnetic order and likely superconductivity coexist in a narrow range of pressures in the PrH 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.