Resonant vibrations of hydrogen isotopes in Pd: their contributions to the electron-defect scattering

The contribution of resonant modes (band modes) to the electron scattering in dilute interstitial Pd-hydrogen alloys is investigated computationally. The interaction of Bloch electrons with the vibrating defect is treated in the adiabatic approximation. Electron scattering from a frozen defect is described by a KKR-Green function method which accounts for all defect-induced multiple scattering effects. It appears that the combined oscillations of a hydrogen atom together with surrounding Pd atoms give rise to a considerable enhancement of the scattering quantities. It is conjectured that the measured isotope effects in the de Haas-van Alphen quantities of Pd(H), Pd(D) and Pd(T) can be attributed to differences in the resonant modes of the isotopes. The occurrence of a resonant mode depends critically on the Pd-hydrogen force constants, which are, due to anharmonicity, different for the three isotopes.