Superconductivity above 70 K observed in lutetium polyhydrides

The binary polyhydrides of heavy rare earth lutetium that shares a similar valence electron configuration to lanthanum have been experimentally discovered to be superconductive. The lutetium polyhydrides were successfully synthesized at high pressure and high temperature conditions using a diamond anvil cell in combinations with the in-situ high pressure laser heating technique. The resistance measurements as a function of temperature were performed at the same pressure of synthesis in order to study the transitions of superconductivity (SC). The superconducting transition with a maximum onset temperature (T_c) 71 K was observed at pressure of 218 GPa in the experiments. The T_c decreased to 65 K when pressure was at 181 GPa. From the evolution of SC at applied magnetic fields, the upper critical field at zero temperature μH_c2(0 ) was obtained to be ∼36 T. The in-situ high pressure X-ray diffraction experiments imply that the high T_c SC should arise from the Lu₄H₂₃ phase with Pm3 ¯ n symmetry that forms a new type of hydrogen cage framework different from those reported for previous light rare earth polyhydride superconductors.