Effect of argon and hydrogen coating on the superconducting transition temperature of granular aluminum

Superconducting transition temperatures of pure Al, Al-Ar, and Al-${\mathrm{H}}_2$ mixtures condensed on substrates at 4.2 °K are measured. A reduction in $T_c$ is observed for the Al-Ar mixture with respect to pure Al ($T_c=3.46\mathrm{}$ °K), and a significant increase in $T_c$ is measured for Al-${\mathrm{H}}_2$. These results are discussed following recent observation of (i) $T_c$ depression in films with noble-gas overlayers, and (ii) the formation of Pd-${\mathrm{H}}_2$ mixture superconductors.