Isotope effects and pressure dependence of theTcof superconducting stoichiometric PdH and PdD synthesized and measured in a diamond anvil cell

We have synthesized stoichiometric PdH and PdD in a diamond anvil cell and measured in situ the pressure dependence of the superconducting transition temperature. From an analysis of the results and band-structure calculations, we find that both the anharmonicity of the Pd-H potential and the effect of the large zero-point motion of the hydrogen isotopes are needed to explain the inverse isotope effect and the observed pressure dependence of $T_c$.