Pronounced Isotope Effect in the Superconductivity of ${\mathrm{HfV}}_2$ Containing Hydrogen (Deuterium)

Superconducting transition temperatures of $\mathrm{Hf}{\mathrm{V}}_2{\mathrm{H}}_x$ and $\mathrm{Hf}{\mathrm{V}}_2{\mathrm{D}}_x$ have been measured in the composition ranges $x=0-1.5\mathrm{}$ and $x=0-1.0\mathrm{}$, respectively. Hydrogen or deuterium absorption is found to decrease $T_c$ of ${\mathrm{HfV}}_2$. Pronounced isotope effects have been observed. At $x=1\mathrm{}$, hydrogen absorption reduces $T_c$ by 4.8 K while deuterium absorption reduces $T_c$ by 6.9 K with respect to ${\mathrm{HfV}}_2$.