Enhanced helium-atom scattering from longitudinal surface phonons in Cu(001)

Abstract

Inelastic helium-atom scattering from Cu(001) shows giant intensities for the longitudinal-surface-phonon resonance. This effect, most pronounced in the 〈100〉 direction and not visible with electron-energy-loss spectroscopy, indicates a very large anisotropic deformability of conduction electrons against the longitudinal modes of surface atoms. Its size and anisotropy are well accounted for by a pseudocharge model for surface dynamics.