Isotope effects in the electronic structure ofPdHxandPdDxfrom de Haas—van Alphen measurements

The concentration dependence of extremal cross-sectional areas of the Fermi surface of dilute $\mathrm{Pd}{\mathrm{H}}_x$ and $\mathrm{Pd}{\mathrm{D}}_x$ alloys ($0\le x\le 0.005$) has been determined from de Haas—van Alphen measurements in fields up to 10.5 T. The data confirm the general features of the proton model: States at the Fermi level are lowered in energy and the electrons added to the metal by the dissolved hydrogen or deuterium are partially accommodated at the Fermi surface of the host. The de Haas—van Alphen measurements show for the first time that large isotope effects are present in the concentration dependence of some of the Fermi-surface sheets. The sheets that show the largest isotope effect are those that contain mostly states with a vanishing charge density at the hydrogen site. The experimental results are discussed in terms of a proton screening potential exhibiting a Thomas-Fermi behavior at short distance and Friedel-type oscillations at large distance.