Electron-Phonon Interaction in the 4/3-Monolayer of Pb on Si(111): Theory Versus He-Atom Scattering Experiments

The electron-phonon coupling parameter for a dense phase of a 4/3-monolayer of Pb on Si(111) is derived from the temperature dependence of He-atom scattering (HAS) reflectivity upon cooling from the high-temperature (1 X 1) to the low-temperature (root 3 x root 3 R 30 degrees) phase. The obtained value and the phonon dispersion curves of the Pb nanofilm measured with HAS are in excellent agreement with the first-principles calculations when the influence of the substrate and the interface on the interaction of electrons and phonons is taken into account. Consideration of this effect is obviously very important for such small thicknesses as a single Pb wetting layer. An overall strong coupling constant, lambda = 0.84 +/- 0.07, is found.