Electron-phonon coupling of the actinide metals

Abstract

We have estimated the strength of the electron-phonon coupling in Fr and Ra plus the light actinides Ac through Pu. The underlying self-consistent band-structure calculations were performed by the scalar relativistic linear-muffin-tin-orbital method including l quantum numbers s through g, and the electron-phonon parameters were obtained within the rigid-atomic-sphere approximation. The electron-phonon coupling in Fr through Th is found to be dominated by pd and df scattering and in Pa through Pu by pd and fg scattering. At the equilibrium volumes and as a function of atomic number, the electron-phonon parameter λ is found to attain its maximum value in Ac, and we predict a transition temperature of 9 K for this metal. In the light actinides Th through Pu, λ is found to be of order 0.4 and within a factor of 2 of experiments which is also the accuracy found in studies of the transition metals. The Hopfield parameter η is found to increase under compression in Th and U, as are the individual l,l+1 contributions to η, except the df contribution which is approximately pressure independent in Th and negligible in U. The calculations suggest that the unusual pressure dependence of $T_c$ in Th may be related to the changeover from an s-to-d to an s-to-f electronic transition and a related change in the topology of the Fermi surface.