Superconductivity of Lanthanum Superhydride Investigated Using the Standard Four-Probe Configuration under High Pressures

Recently, the theoretically predicted lanthanum superhydride, LaH_10 \pm \delta, with a clathrate-like structure was successfully synthesized and found to exhibit a record high superconducting transition temperature T_\rm c \approx 250 K at \sim 170 GPa, opening a new route for room-temperature superconductivity. However, since in situ experiments at megabar pressures are very challenging, few groups have reported the \sim 250 K superconducting transition in LaH_10 \pm \delta. Here, we establish a simpler sample-loading procedure that allows a relatively large sample size for synthesis and a standard four-probe configuration for resistance measurements. Following this procedure, we successfully synthesized LaH_10 \pm \delta with dimensions up to 10 \times 20 μm^2 by laser heating a thin La flake and ammonia borane at \sim 1700 K in a symmetric diamond anvil cell under the pressure of 165 GPa. The superconducting transition at T_\rm c \approx 250 K was confirmed through resistance measurements under various magnetic fields. Our method will facilitate explorations of near-room-temperature superconductors among metal superhydrides.