Electron-phonon coupling in heterogeneous media is essential for defining the physical and chemical properties of material interfaces on the nanometer scale. We explore the mechanism for how electronic excitation drives the coherent nuclear motion for one atomic layer thick Na quantum well on a Cu(111) surface. Time-resolved second harmonic generation spectroscopy with $25\mathrm{fs}$ excitation pulses reveals how the charge fluctuations within the Cu substrate drive the 2.7 and $5.5\mathrm{THz}$ interface phonons of the Na-Cu interface.

• Received 28 May 2007

DOI:https://doi.org/10.1103/PhysRevB.76.115427