Superconducting lanthanum under pressure

We extend the recent hypothesis that the electron-phonon enhancement parameter lambda is of the order of 1.0 for lanthanum at zero pressure to the analysis of the tunneling experiments of Wuehl et al., under pressure. We find two models which are consistent with the available experimental data and calculations. In the first one, the changes in the thermodynamics under pressure obtained through the numerical solution of Eliashberg gap equations is almost solely due to a sharp decrease in the Coulomb repulsion pseudopotential μ(. In the second model, the softening of α2F(ω) plays a role as important as the decrease in μ(. The systems are experimentally distinguishable but there is not a sufficient amount of data available to decide which one is the dominant effect