Enhancement of superconducting properties in the La-Ce-H system at moderate pressures

Ternary hydrides are regarded as an important platform for exploring high-temperature superconductivity at relatively low pressures. Here, we successfully synthesized the hcp-(La,Ce)H9-10 at 113GPa with the initial La/Ce ratio close to 3:1. The high-temperature superconductivity was strikingly observed at 176K and 100GPa with the extrapolated upper critical field H-c2(0) reaching 235T. We also studied the binary La-H system for comparison, which exhibited a T-c of 103K at 78GPa. The T-c and H-c2(0) of the La-Ce-H are respectively enhanced by over 80K and 100T with respect to the binary La-H and Ce-H components. The experimental results and theoretical calculations indicate that the formation of the solid solution contributes not only to enhanced stability but also to superior superconducting properties. These results show how better superconductors can be engineered in the new hydrides by large addition of alloy-forming elements. Recently, high-temperature superconductivity has been reported in LaH10 and CeH10. Here, the authors report superconductivity in the alloy (La,Ce)H9-10 with T-c=176K at 100GPa, providing an improved compromise between high transition temperature and low pressure requirements.