  We synthesized lanthanum hydride (LaHx) by laser heating of lanthanum in
hydrogen atmosphere at pressure P = 170 GPa. The sample shows a superconducting
step at 209 K and 170 GPa and temperature dependence of resistance. By
releasing the pressure to 150 GPa, the superconducting transition temperature
Tc increases to 215 K - the record Tc. This finding supports a way of achieving
Tc higher than the one in H3S (203 K) in hydrides with sodalite-like
structures, first proposed for CaH6 (Tc=245 K) and later for yttrium and
lanthanum hydrides where higher, room temperature superconductivity is
expected.
