  Room temperature superconductivity has been achieved under high pressure in
an organically derived carbonaceous sulfur hydride with a critical
superconducting transition temperature (Tc) of 288 kelvin. This development is
part of a new class of dense, hydrogen rich materials with remarkably high
critical temperatures. Metal superhydrides are a subclass of these materials
that provide a different and potentially more promising route to very high Tc
superconductivity. The most promising binary metal superhydrides contain
alkaline or rare earth elements, and recent experimental observations of LaH10
have shown them capable of Tc s up to 250 to 260 kelvin. Predictions have shown
yttrium superhydrides to be the most promising with an estimated Tc in excess
of 300 kelvin for YH10. Here we report the synthesis of an yttrium superhydride
that exhibits superconductivity at a critical temperature of 262 kelvin at 182
gigapascal. A palladium thin film assists the synthesis by protecting the
sputtered yttrium from oxidation and promoting subsequent hydrogenation. Phonon
mediated superconductivity is established by the observation of zero
resistance, an isotope effect and the reduction of Tc under an external
magnetic field. The upper critical magnetic field is 103 tesla at zero
temperature. We suggest YH9 is the synthesized product based on comparison of
the measured Raman spectra and Tc to calculated Raman results.
