Somayazulu et al. reported 'Evidence for Superconductivity above 260 K in Lanthanum Superhydride at Megabar Pressures' in Physical Review Letters in 2019.
Drozdov, Eremets and co-workers confirmed superconductivity at 250 K in lanthanum hydride in Nature the same year, at a pressure of 150 GPa.
The cubic Fm3m clathrate surrounds each lanthanum atom with 32 hydrogens; it was predicted in 2017 by Peng, Sun, Pickard et al. and first synthesized in 2018 by Geballe et al.