Enhancement of superconducting Tc in Pd-H like compounds by optical phonons

Abstract

We calculate the electron-phonon parameter λ for Pd-H like compounds using an isotropic phonon spectrum with nearest neighbour and next nearest neighbour interactions. We show 1) that λ can be decomposed into mass independent acoustic and optic contribution provided the two ion masses are very different, 2) that the acoustic contribution λac is enhanced above the value it would take with a stationary light ion, 3) that the optic contribution λop cannot be neglected and may even be larger than λac as is apparently the case for Pd-H. We finally discuss the possible sources for the increase of Tc in Pd-H when H is replaced by deuterium