Unveiling mode‐selected electron‐phonon interaction in metal films by helium atom scattering
Giorgio Benedek
University Milano-Bicocca
17:15 - 18:15 Tuesday 14 December 2010 TUG P2 The quasi two‐dimensional electron gas of a metal film can transmit to the surface any tiny
mechanical disturbance occurring in the depth, thus allowing the gentlest of all surface
probes, helium atoms, to perceive the vibrations of the deepest atoms via the induced
surface‐charge density oscillations. Moreover this kind of quantum sonar driven by electron
density waves conveys direct information on the electron‐phonon coupling of individual
phonons of selected energy and momentum. A density functional perturbation theory
(DFPT) and a helium atom scattering study of the phonon dispersion curves in lead films of
up to 7 monolayers on Cu(111) show that: (a) the electron‐phonon interaction is responsible
for the coupling of He atoms to underground phonon modes; and (b) the inelastic HAS
intensity from a given phonon mode is proportional to its electron‐phonon coupling. The
direct determination of mode‐selected electron‐phonon coupling constants is believed to
have great relevance in the study of thin‐film superconductivity.
| 
